Christophe Martayan
email: martayan@oma.be

Dietrich Baade
email: dbaade@eso.org

Juan Fabregat
email: juan.fabregat@uv.es

The WFI Halpha spectroscopic survey of the Magellanic Clouds: Be stars in SMC open clusters

Keywords: stars: emission-line, Be, Magellanic Clouds, galaxies: star clusters, techniques: spectroscopic, astronomical data bases:surveys

At low metallicity, B-type stars show lower loss of mass and, therefore, angular momentum so that it is expected that there are more Be stars in the Magellanic Clouds than in the Milky Way. However, till now, searches for Be stars were only performed in a very small number of open clusters in the Magellanic Clouds. Using the ESO/WFI in its slitless spectroscopic mode, we performed a Halpha survey of the Large and Small Magellanic Cloud. Eight million low-resolution spectra centered on Halpha were obtained. For their automatic analysis, we developed the ALBUM code. Here, we present the observations, the method to exploit the data and first results for 84 open clusters in the SMC. In particular, cross-correlating our catalogs with OGLE positional and photometric data, we classified more than 4000 stars and were able to find the B and Be stars in them. We show the evolution of the rates of Be stars as functions of area density, metallicity, spectral type, and age.

Introduction

Emission line stars (ELS) range from young to evolved stars (TTauri, Herbig Ae/Be, WR, Planetary Nebulae, etc), from hot to cool stars (Classical Be star, Oe, Supergiant star, Mira Ceti, Flare stars, etc). Among the ELS, here, we focus on the classical Be stars. They are non-supergiant B type stars, which have displayed at least once emission lines in their spectra, mainly in the Balmer series of the hydrogen. The emission lines come from a circumstellar decretion disk formed by episodic matter ejection of the central star. It appears that the Be phenomenon is related to fast rotation and probably additional properties such as non-radial pulsation or magnetic fields. For a comprehensive review of Be stars in the Milky Way we refer the reader to Porter & Rivinius (2003). It seems also that the low metallicity plays a role (Kudritzki et al. 1987): at low metallicity, typical of the Small Magellanic Cloud (SMC), the stellar radiatively driven winds are less efficient than at high metallicity (typical of the Milky Way [MW]), thus the mass loss is lower and the stars keep more angular momentum. As a consequence, B-type stars rotate faster in the SMC/LMC than in the MW (Martayan et al. 2007).

It is then expected that the metallicity has also an effect on the Be-phenomenon itself as reported by Maeder et al. (1999) or [START_REF] Wallace | User guide of ASTROM[END_REF], while the evolutionary phase could also play a role (Fabregat & Torrejón 2000). In most cases, the study of open clusters was done by using photometric observations, in the MW. The work by [START_REF] Mcswain | [END_REF] is a typical example. To test these issues and improve the comparisons between SMC and MW, spectroscopic observations of stars in open clusters have to be done. In the SMC, a survey of emission line objects was performed by Meyssonnier & Azzopardi (1993) using photographic plates. However, they were not able to study the stars in open clusters but mainly in the field. This paper deals with our slitless spectroscopic survey of ELS and Oe/Be/Ae stars in SMC open clusters, while in the whole SMC 3 million spectra were obtained.

Observations, data-reduction

To increase the number of open clusters studied in the SMC (1 to 6 in the previous photometric studies of Maeder et al. 1999[START_REF] Wallace | User guide of ASTROM[END_REF], to improve the statistics, and to quantify the evolution of the rates of Be stars to B stars with decreasing metallicity, we performed a slitless spectroscopic survey of the SMC. The observations were obtained on September 25, 2002 with the ESO Wide Field Imager (WFI, see Baade et al. 1999) at the 2.2m MPG Telescope located at La Silla in Chile. We used its slitless spectroscopic mode with the R50 grism and a narrow filter centered on Hα to reduce the crowding of observed areas. We recall that this kind of instrumentation is not sensitive to the diffuse ambient nebulosities and does not allow weak emission lines to be found. With 10-minutes exposures with WFI, it is possible to detect emission lines with EW 10 Å or with a relative intensity to the continuum equal to 2 down to V magnitudes around 17.5. For fainter stars, due to the noise in the spectra, it is only stronger emission lines are within reach. As an example of this kind of observations, see the study by Martayan et al. (2008a) in the MW NGC6611 open cluster and the Eagle Nebula.

The CCD image treatment was performed using IRAF tasks. The spectra extraction was done using the SExtractor code (Bertin & Arnouts 1996). The treatment of spectra and search for stars with emission were done by using the ALBUM code (see Martayan et al. 2008b).

Details about the samples used in this study are given in Table 1.

Results

After the data-reduction, the objects were sorted by categories (definite or candidate ELS, absorption stars), and the astrometry of the stars was performed with an accuracy of 0.5" with the ASTROM package of [START_REF] Wallace | User guide of ASTROM[END_REF] Classification of stars. We then cross-matched our catalogues with OGLE photometric catalogues in SMC open clusters from Udalski et al. (1998), Pietrzynski & Udalski (1999), and Udalski (2000), in order to obtain the B, V, I magnitudes of the stars, the reddening higher than in NGC330, an open cluster already known for its rich Be content. In order to abstract from the large variations from one open cluster to another in their frequency of Be stars, the stars were grouped in a global sample. We classified the 4300 stars in our sample by using the calibration provided by Lang (1992). Fig. 1 shows the corresponding global HR colour/magnitude diagrammes. From these results it seems that the SMC sample is complete for the ELS till spectral types B3-B4, while for absorption stars it is complete till B5. Notes:

1 No OGLE photometry available for these stars.

2 NGC346 is a complex young SMC open cluster, which contains both classical Be stars and Herbig Be/Ae stars but also other kinds of ELS (WR, TTauri). Because of the risk of possible confusions, the classical Be stars from this cluster are not included in the statistics of Be stars.

Ratios of Be to B stars vs. metallicity. To highlight and quantify a potential trend of the rates of Be stars to B stars with decreasing metallicity, we compared these ratios by spectral-type categories with the study of [START_REF] Mcswain | [END_REF] in the MW. The same calibration for the classification of the stars was used in the MW. The comparison of the rates is shown in Fig. 2. Down to the completness limit of our study of ELS, one can see that the ratios are several times higher in the SMC than in the MW. Thus, there is an impact of the metallicity on the number of Be stars probably corresponding to the increase of the rotational velocities in the SMC in comparison with the MW.

Distribution of Be stars with spectral types. The distribution of Be stars by spectral type categories in the SMC and MW was also studied. In the MW, the results from [START_REF] Mcswain | [END_REF] in open clusters, and from [START_REF] Zorec | SF2A-2005[END_REF] in the field, were used. The result is shown in Fig. 3. It appears that the maximum of Be stars is reached at the spectral type B2 in the SMC and MW. There is also another peak at B5-B6, which can be seen in the MW studies (complete for the whole B-main sequence). The first peak corresponds to the maximum of the emission intensity, the second one to the combined effects of the decrease of the emission intensity and the increase of the initial mass function of stars towards late type stars.

Distribution of open clusters with Be stars vs. age. From preliminary results it appears that predominantly young open clusters (age<100Myears) are found to contain classical Be (CBe) stars, but depending on the types of the stars, certain CBe stars could have reached the terminal-age main sequence (TAMS). For example in the case of B0e stars, the TAMS is reached in ∼10 Myears. Some other old open clusters (age>100Myears) host CBe stars. From these results, it seems that certain CBe could be born as CBe stars and some others appear during their evolution. This point needs more investigations star by star.

Conclusions

Preliminary studies have shown a trend of the increase of the fraction of Be stars with decreasing metallicity. However, up to now, the studies were only performed on a very limited sample of open clusters (less than 10 in the SMC) and with photometric data. could appear during the main sequence depending also probably on the metallicity and spectral types of stars.

Figure 1 .

 1 Figure1. Absolute V magnitude vs. dereddened colour (B-V)-top or (V-I)-bottom for SMC stars of our sample. Blue crosses correspond to definite ELS, blue diamonds correspond to candidate ELS, and red + to absorption stars.

Figure 2 .Figure 3 .

 23 Figure 2. Ratios of definite Be stars to B stars as a function of spectral type in the SMC (top), and in the MW (bottom, from McSwain & Gies 2005)

Table 1 .

 1 Details and comparison of samples used in this study

		SMC (this study) MW from McSwain & Gies (2005)
	N open clusters	84	54
	Definite Be stars	109	52
	Candidate Be stars	54	116
	Total calssical Be stars	163	168
	Ae stars	7	57
	Oe stars	6	3
	Other ELS (not MS)	90
	Unclassified ELS 1	49
	NGC346 2	54
	B stars	1384	1741
	other stars	2683	508

Acknowledgements C.M. acknowledges funding from the ESA/Belgian Federal Science Policy in the framework of the PRODEX program (C90290). C.M. thanks support from ESO's DGDF 2006, the IAUS SOC/LOC for the IAUS grant, and the FNRS for the travel grant.


Christophe Martayan
email: martayan@oma.be

Juan Zorec

Yves Frémat

ZAMS rotational velocities of Be/Oe stars and LGRBs progenitors in the Magellanic Clouds

Keywords: stars: emission-line, Be, Magellanic Clouds, stars: fundamental parameters, gamma rays: theory

The Large and Small Magellanic Clouds are priviledged environments to perform tests of theoretical predictions at low metallicity on rotational velocities and stellar evolution. According to theoretical predictions, the rotational velocities of B-type stars are expected to be higher in low metallicity (LMC/SMC) than in high metallicity (MW) environments. To verify the models, we observed with the VLT-FLAMES 523 B and Be stars, which form, at the moment, the largest observed sample of these kind of objects in the MCs. We first determined the stellar fundamental parameters and we found that B and Be stars rotate faster in the MCs than in the MW. We also determined the first distribution of the average ZAMS rotational velocities versus the mass of Be stars. These results indicate that the appearance of Be stars is mass-, metallicity-, stellar evolution-, and star-formation regions-dependant. Moreover, the recent models of Long Gamma Ray Bursts progenitors foresee possible LGRBs progenitors at the SMC's metallicity. We confront these models with the observed (ZAMS rotational velocities, masses) distributions of the fastest rotators (Be and Oe stars) in our sample. Furthermore, we compare the corresponding predicted rates from our study with observed rates of LGRBs.

Introduction, observations

This document deals with the determination of rotational velocities of B-type stars at different metallicities (MW, LMC, SMC) and their consequences on the stellar evolution in particular for the late stages. A comparison between the results from the observations and theory is also given. To perform this study, thanks to the VLT-FLAMES/GIRAFFE facilities in MEDUSA mode, a large sample of B and Be stars have been observed in the LMC-NGC2004 and SMC-NGC330 regions and their surroundings, 176 and 344 hot stars respectively. We used a medium resolution R= 6400 in the blue wavelength range around Hǫ, Hδ, Hγ (LR02) and R=8600 in the red one around Hα (LR06). Among this sample, 178 Be stars were observed.

Rotational velocities vs. metallicity: observations and theory

Using the GIRFIT code (Frémat et al. 2006) we determined the fundamental parameters for each star by fitting observed spectra with theoretical NLTE spectra. The 119 gravitational darkening effects for fast rotating stars such as Be stars were taken into account thanks to the FASTROT code (Frémat et al. 2005).

Statistically, Martayan et al. (2006Martayan et al. ( , 2007) ) found that B and Be stars with similar masses and ages rotate faster at low metallicity (in the SMC) than at high metallicity (in the MW). This result was the first confirmation, based on a significantly large star sample, of the theory from Maeder & Meynet (2001) about the behaviour of rotational velocities in respect of the metallicity for main sequence (SMC vs. MW) B and Be stars. Hunter et al. (2008) recently arrived at the same conclusions. Our results in the LMC are in agreement with those of Keller (2004).

More recently, Ekström et al. (2008) published new stellar evolutionary tracks at the SMC metallicity. In Fig. 1, we compare the independent results from Martayan et al. (2007), for which we add the values for the most massive SMC Be stars-late Oe stars, with the results from Ekström et al. (2008) for the Vsini distributions. As shown, there is a good agreement between the two studies and the theory seems to correctly reproduce the observations.

ZAMS rotational velocities

Using the observed values from Martayan et al. (2007) and evolutionary tracks from Schaller et al. (1992, SMC and MW metallicities) and Charbonnel et al. (1993, LMC metallicity), Martayan et al. (2007) also determined for the first time the ZAMS rotational velocities of Be stars in the SMC, LMC, and MW. The values for the linear rotational velocities in the MW come from Zorec et al. (2005).

In Fig. 2, we add the ZAMS rotational velocities for massive SMC Be and late Oe stars to the values from Martayan et al. (2007). We fitted 2nd order polynomials through these values. We compared our observational values to Ekström's et al. (2008)

Stellar evolution and Long Gamma Ray Bursts progenitors

The Gamma Ray Bursts are the most energetic events in the universe since the Big Bang. We distinguish two kinds of GRBs, the Short and Long soft GRBs. It is believed that Short LGRBs can be produced by the merging of two compact objects such as neutrons stars in a binary system.

Here we focus on the Long soft GRBs. Since the model of the collapsar from Woosley (1993), where LGRBs are produced by the collapse of massive fast rotating stars, the recent developments from Hirschi et al. (2005) or Yoon et al. (2006) predict the ranges of masses and rotational velocities of the LGRBs progenitors as a function of the metallicity. The distributions of ZAMS angular rotational velocities of Be stars in our SMC sample as a function of mass with the predicted area of LGRBs by Yoon et al. (2006) show that most of the massive Be stars and late Oe stars are located in the LGRBs progenitors' area.

However, Hirschi et al. (2005) foresee more LGRB progenitors from massive fast rotators stars than Yoon et al. (2006). As a consequence of these studies, we propose that the most probable LGRB progenitors are the low metallicity (Z of SMC or lower) early Be stars and late Oe stars. Moreover, after the main sequence, these stars must become fast rotating WR stars. To do that, it is necessary that the stars at the end of the main sequence be fast rotators and massive stars. The finding by Martayan et al. (2007) that massive Be stars at low metallicity are in the second part of the MS is an argument that favours this scenario.

Be/Oe stars as Long Gamma Ray Bursts progenitors: estimated rates

To test our scenario that takes massive Be stars and late Oe stars as progenitors of LGRBS, we determined the corresponding rates of LGRBs it implies. To do that, we use the proportions of SMC Be/Oe stars to B/O stars from Martayan et al. (2008, in preparation). We also use the number of B and O stars in the SMC estimated from OGLE catalogues for the whole SMC. We take into account the lifetime of the stars and the angle of γ-ray beams to infer the rates of LGRBs events. We obtain that they range as: 3. 10 -6 to 3. 10 -5 LGRB/year/galaxy. These rates must be compared with observed rates of LGRBs: from Hirschi et al. (2005, and references therein): 3. 10 -6 to 6. 10 -4 LGRB/year/galaxy, and from Fryer et al. (2007, and references therein) in the local universe (z<1), the values range from: 10 -6 to 10 -5 LGRB/year/galaxy.

The rates we estimated are in good agreement with the observed rates of LGRBs and as a consequence, massive Be stars and late Oe stars are then among the most probable candidates of the LGRBs progenitors.

Conclusions

The comparisons of rotational velocities distributions of Be stars from our VLT-GIRAFFE observations with theory show good agreements. The results are also similar for the ZAMS rotational velocities, while we added the most massive Be stars to the distributions. From the comparison of stellar evolution models to our observations of SMC Be stars we suggest that the most probable candidate of LGRB progenitors can be the more massive Be stars and late Oe stars. The rates of LGRBs we estimate with the distributions of Be stars at low metallicity are in good agreement with the observed rates of LGRBs in the local universe.

Figure 1 .

 1 Figure 1. Comparison of average Vsini distribution for observed Be/Oe stars in the SMC (black points from Martayan et al. 2007) with the theoretical tracks for stars, which display the Be-phenomenon at the SMC metallicity (pink and blue curves are from Ekström et al. 2008).

  theoretical ones. The comparison shows again a good agreement between the theory and observations. The distributions show an increase of V0 ZAMS for B stars and late O stars (due to low massloss) and a decrease of V0 ZAMS at the more massive O stars (in which the stellar winds Be/Oe stars and LGRBs progenitors 121 are strong enough to lead strong mass-loss and strong angular momentum-loss). However, we need observations of more massive stars, like O fast rotators stars to better constrain this trend. E08 W=0.99 from E08 from M2007

Figure 2 .

 2 Figure2. ZAMS rotational velocities distributions for observed Be/Oe stars in the SMC (black points and curve) compared with theoretical distributions fromEkström's et al. (2008).

Acknowledgements C.M. acknowledges funding from the ESA/Belgian Federal Science Policy in the framework of the PRODEX program (C90290). C.M. thanks the IAUS SOC/LOC for the IAUS grant and the FNRS for the travel grant.


Nanée Chahinian
email: nanee.chahinian@ird.fr

Thierry Bonnabaud

La Bruyère

Francesca Frontini

Carole Delenne

Marin Julien

Rachel Panckhurst

Mathieu Roche

Lucile Sautot

Laurent Deruelle

Maguelonne Teissiere

WEIR-P: An Information Extraction Pipeline for the Wastewater Domain

Keywords: Wastewater, Text mining, Information extraction, NLP, NER, Domain adapted systems

We present the MeDO project, aimed at developing resources for text mining and information extraction in the wastewater domain. We developed a specific Natural Language Processing (NLP) pipeline named WEIR-P (WastewatEr InfoRmation extraction Platform) which identifies the entities and relations to be extracted from texts, pertaining to network information, wastewater treatment, accidents and works, organizations, spatio-temporal information, measures and water quality. We present and evaluate the first version of the NLP system which was developed to automate the extraction of the aforementioned annotation from texts and its integration with existing domain knowledge. The preliminary results obtained on the Montpellier corpus are encouraging and show how a mix of supervised and rule-based techniques can be used to extract useful information and reconstruct the various phases of the extension of a given wastewater network. While the NLP and Information Extraction (IE) methods used are state of the art, the novelty of our work lies in their adaptation to the domain, and in particular in the wastewater management conceptual model, which defines the relations between entities. French resources are less developed in the NLP community than English ones. The datasets obtained in this project are another original aspect of this work.

Introduction

Water networks are part of the urban infrastructure and with increasing urbanization, city managers have had to constantly extend water access and sanitation Supported by the Occitanie-Pyrénées-Méditerrannée Region under grant 2017-006570/DF-000014.

services to new peripheral areas or to new incomers [START_REF] Araya | Understanding hosting communities as a stakeholder in the provision of water and wastewater services to displaced persons[END_REF]. Originally these networks were installed, operated, and repaired by their owners [START_REF] Rogers | Condition assessment of the surface and buried infrastructure/a proposal for integration[END_REF]. However, as concessions were increasingly granted to private companies and new tenders requested regularly by public authorities, archives were sometimes misplaced and event logs were lost. Thus, part of the networks' operational history was thought to be permanently erased. However, the advent of Web big data and text-mining techniques may offer the possibility of recovering some of this knowledge by crawling secondary information sources, i.e. documents available on the Web. Thus, insight might be gained on the wastewater collection scheme, the treatment processes, the network's geometry and events (accidents, shortages) which may have affected these facilities and amenities. This is the primary aim of the "Megadata, Linked Data and Data Mining for Wastewater Networks" (MeDo) project, funded by the Occitanie Region, in France, and carried out in collaboration between hydrologists, computational linguists and computer scientists.

Text mining is used in the field of water sciences but it is often implemented for perception analysis [START_REF] Hori | An exploratory analysis of the text mining of news articles about water and society[END_REF][START_REF] Altaweel | Applying content analysis for investigating the reporting of water issues[END_REF], indicator categorization [START_REF] Park | Text mining-based categorization and user perspective analysis of environmental sustainability indicators for manufacturing and service systems[END_REF] or ecosystem management [START_REF] Cookey | Text mining analysis of institutional fit of Lake Basin water governance[END_REF][START_REF] Ekstrom | Exploratory text mining of ocean law to measure overlapping agency and jurisdictional authority[END_REF]. To the best of our knowledge this work is the first attempt at using Natural Language Processing (NLP) and Text-Mining techniques for wastewater network management in cities.

The creation of domain adapted systems for Information Extraction (IE) has been an important area of research in NLP. The outcomes of many projects have led to creating systems capable of identifying relevant information from scientific literature as well as technical and non technical documents. A pioneering domain was that of biology; see [START_REF] Ananiadou | Event extraction for systems biology by text mining the literature[END_REF] for an overview of initial projects and [START_REF] Copara | Contextualized French Language Models for Biomedical Named Entity Recognition[END_REF] for a more recent contribution. More specifically, a fertile field of research has emerged at the intersection between NLP and Geographic Information Retrieval (GIR). Cf. [START_REF] Wang | Spatiotemporal and semantic information extraction from Web news reports about natural hazards[END_REF] and [START_REF] Kergosien | Automatic Identification of Research Fields in Scientific Papers[END_REF] for a domain overview and a list of relevant projects; [START_REF] Gregory | Visual GISting: bringing together corpus linguistics and Geographical Information Systems[END_REF] for Digital Humanities initiatives and [START_REF] Dominguès | Place and Sentiment-based Life story Analysis[END_REF] for the Matriciel project in French.

The NLP pipelines used to mine these specialised corpora are generally composed of a mix of supervised and unsupervised or rule-based NLP algorithms; crucially the collaboration with domain experts is essential since the state of the art tools need to be re-trained and tested using corpora with specific annotation and often require structured domain knowledge as input. Generally such systems are trained and tested on English; however in many cases multilingual pipelines, and therefore resources, have been created.

The use of general semantic resources e.g. EuroWordNet 8 or dedicated thesaurii Agrovoc 9 for the French language is not adapted to address the wastewater domain.Agrovoc is a terminology, where concepts are described and translated into various languages. In this sense it is used to standardize and control the use of domain vocabulary. WordNets are lexical resources, that can be used for NLP; EuroWordnet has been extended for specific domains. In both cases, to produce or adapt terminologies or computational lexicons for a new domain one would have to apply NLP techniques to extract and filter terms and lexemes from texts, and use a pre-processing pipeline along the lines of what we propose. The originality of our approach is based on the combination of well-known tools (e.g. spaCy, Heideltime) and the integration of expertise for highlighting semantic information related to the wastewater domain along with the selection of relevant documents using machine learning. Our global pipeline called WEIR-P combines Information Retrieval (IR) and Information Extraction (IE) techniques adapted for the French language and the wastewater domain.

Indeed, not only are there no domain specific terminological and lexical resources ready to use, but crucially also in terms of modelling, important work had to be done to identify which elements had to be annotated in the text, in order to extract the relevant information. In particular, two important contributions of this work are the implementation of NER methods for extracting original entities (Network element, Treatment, Network type, Accident, etc.) with new textual data manually labeled and the construction of relations based on spatial, temporal and thematic entities for discovering new knowledge is an original research direction. Finally French resources (i.e. corpora, specialized terminology, etc.) are less developed in the NLP community with many English datasets available. The datasets obtained in this project (i.e. labeled corpus, terminology dedicated to wastewater domain) are another original aspect of this work.

The research methodology we followed is quite similar to the DSRP model presented by [START_REF] Peffers | The design science research process: A model for producing and presenting information systems research[END_REF]. The problem identification and motivation is linked to previous research projects [START_REF] Chahinian | Automatic mapping of urban wastewater networks based on manhole cover locations[END_REF]. The Objectives of the solution are to develop a user-friendly tool that would help non-IT researchers and wastewater network managers transform unstructured text data from the Web into structured data and merge them with their business databases. The Design and Development step relied heavily on NLP, IR and IE literature. The new French data standard for drinking water and sewerage networks issued halfway into the project [START_REF] Covadis | Standard de données réseaux d'AEP & d'assainissement[END_REF] was used as a reference for the business data model. Two case studies were designed in two cities (Montpellier-France and Abidjan-Ivory Coast). Demonstrations were carried out during the meetings of the project's steering committee. The Evaluation is two fold. It was partly carried out during the bi-annual meetings of the steering committee. A restitution workshop is also planned with members of the Aqua-Valley French Competitiveness Water Cluster. As for the Communication, in addition to scholarly publications such as this one, a wastewater awareness workshop will be carried out in a primary school in March 2021.

In this paper we shall describe the general architecture of the system, as well as the linguistic resources used for domain adaptation and the evaluation of the various steps of the NLP pipeline. The structure of the paper is as follows: description of the data model ( §2), of the system's architecture ( §3) and its evaluation ( §4); finally the description of the resources produced ( §5) and some conclusions ( §6).

The Data model and the corpus

The MeDo project aims to use textual data -available on the Web or produced by institutions -for learning about the geometry and history of wastewater networks, by combining different data-mining techniques and multiplying analysed sources.

In order to achieve this, a system for document processing has been designed, which when in production will allow a hydrologist or a wastewater network manager to retrieve relevant documents for a given network, process them to extract potentially new information, assess this information by using interactive visualization and add it to a pre-existing knowledge base.

Although textual sources may be directly imported into the system, the default pipeline begins with a Web-scraping phase retrieving documents from the Internet. The system has been built within the context of a French regional project, and is currently developed and tested for French documents. However, its architecture allows for easy adaptation to other languages, including English.

Relevant information may come from technical documents, such as reports by municipalities or private companies, but also from the general public, for instance from newspaper articles and social media posts containing descriptions of accidents in the network, or announcements of works. The goal of the system is to allow for the identification and retrieval of relevant documents from the Web, their linguistic processing and the extraction of domain information.

The case study presented hereafter is on the city of Montpellier in France. Our corpus is composed of 1,557 HTML and PDF documents. The documents were collected in July 2018 using a set of Google queries with a combination of keywords. Given the absence of guidelines for the annotation and extraction of information for wastewater management we proceeded to create our own annotation model with the help of hydrologists [START_REF] Chahinian | Guide d'annotation du projet MeDo[END_REF]. As is generally the case, the MeDo domain specific annotation scheme has been created extending the commonly used Named Entities (NEs) tagsets, which are defined in the guidelines of well known annotation campaigns such as MUC-5 and following [START_REF] Chinchor | Muc-5 evaluation metrics[END_REF], with domain specific entities, or tags. Our current model contains a set of entities:

three of them are specific to the network: Network type, Network element and Network characteristics. Words such as "réseau pluvial" (stormwater network), "collecteur principal" (sewer main) or "gravitaire" (gravity fed) fall into these categories; one is related to the Wastewater treatment and may be used either for the plant and its components or the treatment process. This category includes for instance words like "station d'épuration" (wastewater treatment plant), "digestion anaérobie" (anaerobic digestion); two entities are used for the type of event reported in the document: Accident, Works i.e. "pollution", "inondation" (inundation/flooding), "raccordement au réseau" (connection to the network); one label describes the public or private Organizations such as "commune" (City council), "Entreprise" (company);

dates and locations are marked using two labels: Temporal, Spatial; all quantitative data of relevance are marked as Measurements; a category Indicator is used to annotate any information which specifies or adds to the information provided by other categories; finally, two more "generic" entities are used for all words related to Water quality i.e. "eau brute" (raw water supply), nitrates and the non-technical or legal aspects of wastewater management i.e. "délégation de service public" (Public service delegation), "directive cadre sur l'eau" (Water framework Directive).

The manual annotation of these entities is complex and requires expert knowledge to be carried out correctly. A test on inter-annotator agreement was carried out with two experts, who had in-depth knowledge of the annotations guidelines, and non experts -students who received one-hour training before annotating. The former were asked to annotate all categories, the latter were limited to the domain specific ones. Results (see Table 1) are encouraging, given the number and technical nature of categories. It is known that Fleiss' Kappa is not appropriate for multi-entity textual annotation [START_REF] Shardlow | A new corpus to support text mining for the curation of metabolites in the ChEBI database[END_REF]; we therefore evaluate agreement in terms of F-measure values, reporting the results for each typology of annotators. Non experts performed slightly more poorly, which is understandable; typically, they tended to miss more annotations; however, when they did annotate a portion of text, they tended to choose the right category, which seems to indicate that the chosen annotation model is sound. For two domain categories (Water Quality and Accident), which are quite rare in the corpus, agreement remains low. The annotation guide was modified following this experiment to further clarify the annotation guidelines. The documents annotated by the students were not used to train the NER modules.

Given these results, the Wastewater Domain Gold Standard Corpus was carefully checked and verified by hydrologists. It consists of 23 manually annotated documents: 3 calls for tenders, 6 announcements from the city's website and 12 newspaper articles, 1 technical document and 1 tweet. They amount to 1,387 sentences and 4,505 entities. The annotation was carried out using the BRAT system 10 . Figure 1 shows an example of an annotated sentence. An extended Gold Standard containing 80 documents with 649,593 words and 29,585 entities was later complied for further tests. It is available on DataSuds dataverse [START_REF] Chahinian | Gold Standard du projet MeDo[END_REF].

Once the entities have been identified, it is necessary to define the possible relations which may connect them. These are defined in the Wastewater Management Conceptual Model (see Figure 2) which was developed in collaboration with hydrologists.

Based on the possible abstract relations between the entity classes in the model, entity instances found in texts are thus linked with relations:an event of type Works is spatially and temporally localised and specified by the type of intervention (implementing a new wastewater network). English: On March 13, the road to Murviel will be closed to allow works to create a wastewater network

3 The WEIR-P system: Architecture

To automatically extract items of information such as the ones previously described, an information extraction system has been created. The NLP pipeline is similar to those generally used for this type of task (see references in §1), but had to be adapted for our specific needs. In particular it was necessary to create a system which is able to retrieve relevant sources within a specific geographical area, to manage different types of documents, to detect and correlate specific information in texts and finally to relate such information with existing knowledge on a given wastewater system. For this reason a pluri-disciplinary approach was required.

The global architecture of the WEIR-P system is depicted in Figure 3. The main steps of the proposed methodology are: In this article, we mainly focus on the text mining part of the MeDo project and on the domain adaptation of existing tools for the wastewater domain. It concerns the 1st, 2nd and 3rd steps of the global architecture of the WEIR-P tool (see Figure 3, Parts A andB).We also briefly present the visualization carried out at document level. The visualization of the network elements on a wastewater map after data fusion will not be presented in this paper.

Step One -document pre-processing and classification

This step is composed of different sub-steps. The document retrieval algorithm requires the user to specify a geographical area of interest (typically a city or a municipality) as input. The system scrapes documents from the Web using a set of Google queries which specify a combination of two domain-related keywords and a place name.

In the corpus creation phase the texts retrieved from the internet are transformed to plain text using various out-of-the-box Python libraries (such as Beau-tifulSoup or pdf2txt); some text cleaning is also necessary, in order to restore broken lines and remove boilerplate text using regular expressions. Finally, all the relevant metadata are recorded and the text collection is entered in the database. Once the corpus has been successfully created, a classification for relevance is carried out using Machine Learning techniques which are detailed in section §4.1. The pre-processing steps are similar to those followed for text classification using more complex learning methods [START_REF] Venkata Sailaja | Incremental learning for text categorization using rough set boundary based optimized Support Vector Neural Network[END_REF]. This is a necessary step since the crawling algorithm, which is carried out using a coarse filtering system, will retrieve many irrelevant documents which need to be excluded by using a finer-grain classification. For instance query for documents containing words such as "Montpellier", "eau" (water), "reseau" (network), may sometimes retrieve commercial sites for home plumbing repairs.

Step Two -Named-Entity Recognition and Classification (NERC)

The goal of the second step is the annotation of Named Entities (NE) in the texts corresponding to the 13 entities or tags defined in §2. The texts are first pre-processed by a basic NLP module which performs sentence splitting and tokenisation and PoS tagging, using the TreeTagger module for French [START_REF] Schmid | Treetagger, a language independent part-of-speech tagger[END_REF]. Subsequently, an ensemble NERC module is used, which combines the output of three systems: spaCy [15], CoreNLP [START_REF] Manning | The Stanford CoreNLP natural language processing toolkit[END_REF] and Heideltime [START_REF] Strötgen | Heideltime: High quality rule-based extraction and normalization of temporal expressions[END_REF], which is specifically used for temporal entities.

The system was benchmarked as follows:

1. first spaCy and CoreNLP were trained on a sub-set of the gold standard corpus in order to obtain domain adapted models; to improve the results for locations, gazetteers of place names (geographical features, locations, addresses) were extracted and used as additional training features from existing geographical bases. 2. then both spaCy and CoreNLP were tested to assess their performance on each class (except temporal entities). 3. Heideltime was tested without training on temporal entities without domain adaptation, and proved to be the best system for this type of entities.

Based on this, the final NERC algorithm runs as follows: first each text is separately annotated with all three systems and the results are compared. For all entities except temporal, in case of conflict between spaCy and CoreNLP, the best performing system for that category is given the priority. For temporal entities the Heideltime annotation is applied, if needed by overriding previous conflicting annotation by the other systems. Results of the evaluation for NERC, as well as the details of the benchmarking for each category are provided in section §4.2.

The NERC module is followed by an Entity Linking module, which is used to connect spatial entities such as addresses and locations to existing geographical knowledge bases, in order to produce a cartographic representation of the extracted information. The Geonames11 , BAN 12 and Nominatem13 geographical databases and corresponding APIs are currently used.

The Entity Linking algorithm is quite basic, since filtering on city or location greatly reduces ambiguity for place names, and will not be further discussed nor evaluated in this paper.

Step Three -Semantic relation extraction

The objective of the third step is to connect the spatial, temporal and thematic entities discovered in Step Two.

The relation extraction is applied to ensure that the spatial, temporal and network information is accurately linked to the type of event (Works, Accidents), and that network elements and characteristics are correctly linked to each other and the network type, so that they can be used to enrich the knowledge base.

The relation extraction is performed using basic rules. Generally, for this step, we use a more specific textual context (i.e. sentences or paragraphs) than the classification task related to the first step of the MeDo project. To resolve ambiguities in more complex cases we resort to semantics and use syntactic dependencies extracted using a spaCy out-of-the-box dependency parser for French. Preliminary evaluation results are provided in §4.3.

Step Four -Mapping and Visualization

Step four aims to offer the possibility of visualizing the results of the previous treatments. It consists of two sub-steps and only the first one which deals with visualization at document level will be presented in this paper. A graphical user interface was developed to enable users to run the annotation pipeline (Steps 1-2-3) on a selected location (e.g. a city), to inspect the extracted entities and relations, and to decide whether to inject the new knowledge in the system. The interface has been developed using FLASK 14 for the Web framework and celery15 to offset the calculations related to NERC and relation extraction. The d3js library 16 is used to represent the network as a graph where the nodes are coloured according to the NE category (e.g. Temporal, Spatial, Works) and the edges according to the type of relation (e.g. "Has Temporal", "Has Spatial"). The Leaflet library17 is used to map the extracted spatial entities.

The GUI is composed of a standard sign-in module, an administration panel, two monitoring menus to view the progression of tasks and the corresponding notifications and six menus that are more specifically related to the annotation platform. The Corpus menu allows registered users to compile corpora either directly from the , or by uploading a zipped file containing pdf documents. Users may also upload zipped files of previously annotated texts. The "Processing" menu allows users to run the classifications described in section §3.1 and the NE and relation extractions described in section §3.2 either simultaneously or sequentially.

Once these steps are completed, the user has the possibility of visualising the results for each individual document in the "Results" menu (Figure 4). The text and extracted NEs are displayed on the upper part of the screen using the set colour scheme presented in the legend. The semantic relations are displayed as a graph in the lower part of the screen. The export button allows users to create and download a zipped file containing: the document in original and text formats; a pdf of the annotated document and a text file containing the annotations in Brat format (.ann); the graph of relations in svg format; the metadata as a JSON file.

The statistics related to the entire corpus (e.g. number and types of documents, number of words, number and types of entities and relations, number of documents per website, etc.) are visualized in the "Corpus Statistics" menu and exported in pdf format and a map of the extracted spatial entities is displayed in the "Spatial rendering" menu. Finally, the export menu allows users to download a zipped file containing all the documents composing the corpus, the corresponding annotation files in Brat format and a JSON file of the metadata.

Evaluation

We describe the evaluation set-up and results of the domain adapted NERC and relation extraction modules. This project is part of the Wastewater Master Plan, which provides for the disconnection of the separate networks from the combined sewers in order to extend and rationalise wastewater collection up to the MAERA plant with a capacity of 470,000 equivalent inhabitants. Cf Map of the Eastern Interceptor. Given the importance of this operation in terms of cost and time, the planning of the installation works for this 12 km sewer main took into account the main constraints of the major urbanization projects and programmes in the Montpellier Méditerranée Métropole area: tramway, widening of

Text classification systems

In order to learn the classification model, a training corpus was produced using a subset of the Montpellier corpus. Relevant documents should contain information either about network configuration (location, flow type, design rules, material) or incidents (flooding, pollution, water intrusion).

The classifier has been trained using a multinomial Naive Bayes classification method, with a scikit-learn Python library. For each classification the features are bags-of-words, weighted by TF-IDF (term frequency-inverse document frequency [START_REF] Salton | Introduction to Modern Information Retrieval[END_REF]). One thousand stopwords were used with no lemmatization. The relevance training corpus has 441 elements (3,512 words), split into two classes ("Relevant Document/Keep" and "Not relevant document/Discard").

The evaluation of the relevance was carried out separately and is calculated in terms of precision, recall and F-score. The evaluation presented in Table 2 was obtained using 10-fold cross validation; "Macro" represents the average of the values calculated for each class; "Micro" represents the global score, regardless of classes. The precision, recall and F-score are high (>0.90): the proposed method is able to detect the relevant documents correctly.

NERC

Evaluation was carried out using the MUC-5 specification on the annotated corpus described in paragraph 2. We provide here the evaluation result of the best model for each entity type. As it can be seen in Table 3, we can achieve the best results for all of the classes except one (Network Type) by combination of two models, the first of which has precedence in case of conflict. The current results are encouraging for a subset of categories, however they still require improvement for other ones, for which the trained models seem to perform not as well. In some cases, the lower results are probably caused by the fact that some categories, such as Accident, are poorly represented in our corpus. In other cases, such as for Indicator, the problem may be linked to heterogeneity of this category, which includes modifiers such as adverbs and adjectives related to various types of information (temporal, spatial, domain specific...).

Relation extraction

As we have seen, the Relation Extraction (RE) module is rule based and adds semantic links between the various entities in order to identify units of knowledge. In order to eliminate any noise caused by possible NERC errors, and thus to evaluate RE performances in isolation, a sub-set of the gold standard was automatically annotated with relations; the output contains 2,913 relations. Seven documents corresponding to a sampling rate of 30% were randomly selected for expert evaluation. At this stage only precision was evaluated, and experts checked automatically extracted relations between entities, assessing and labelling them as correct or incorrect. Missing relations were not taken into account. The rate of correctly detected relations is relatively high (precision = 0.83). Errors mostly occur when Named Entities, i.e. spatial ones, are juxtaposed. Linkage results are also impacted by errors in Named Entity recognition and text conversion, i.e. missing punctuation marks which modify the sentence structure and impact dependency rules.

Use case and Discussion

The WEIR-P information extraction pipeline offers users the possibility of rapidly acquiring information on the wastewater network of a city. The pipeline is a timesaver namely because the automatic Web-scraping phase, using a pre-set list of keywords, enables the user to multi-task, while the relevance check reduces the number of documents the user has to go over. In addition, the entity recognition module improves visual foraging and reduces reading time as a highlighted text will be more likely to be attended to and remembered than a plain text [START_REF] Chi | Visual foraging of highlighted text: An eyetracking study[END_REF]. Note that it takes 5 hours to run 393 queries, under a minute to determine the relevance of a corpus containing 1,040 documents, and 5 hours and 17 minutes to extract 147,423 entities on 534 documents classified as relevant. In comparison, the average silent reading rate of an adult is 238 words per minute [START_REF] Brysbaert | How many words do we read per minute? a review and metaanalysis of reading rate[END_REF]. It would thus take an average adult 10 days, 8 hours and 9 minutes non stop to merely read the 1,040 documents.

The platform is an interesting aid as it can reconstruct events. Thus, hotspots can be identified through the "Accident" or "Works" labels or simply by analysing the frequency of occurrence of street or district names. A fully automated process is being implemented in the new version of the pipeline to carry out this task. Indeed, this type of information may also be useful to wastewater network managers who have just been granted concessions by public authorities in a new city and are not yet familiar with the network's history. Two representatives of the private sector leaders in Computer-aided Maintenance Management Systems (CMMS)/Enterprise Asset Management (EAM) and water and wastewater treatment services, are part of the project's steering committee and have been following the pipeline's development. Both expressed high interest in the pipeline's ability to recover dates and link them with network equipment as it would help plan maintenance operations. This feature was also highlighted by a representative of the public service in charge of wastewater management. We performed a test on the city of Montpellier and were able to recover 233 occurrences of the word "pose" (to lay, to place in French), 559 of "mise en place" (implementation), 512 of "extension" and 375 occurrences of "réhabilitation" in the "Works" category. This type of information may also be recovered using digital archives uploaded manually by the user into the pipeline in pdf or txt format. The implementation of the platform would not be costly to local stakeholders as small material and human resources are needed to run it. The day to day life of the institutions and their regular business practices would not be affected as it would be mostly used for asset management i.e. for decision making at mid-management level. However, as with any new tool, training and time will be necessary to take in the change in practice.

As with many emerging tools, there is of course room for improvement. The evaluation results show that the current version of the system still presents various shortcomings that will be addressed in an improved version of the pipeline. In terms of information content, quantitative data (geometry, hydraulic performance) is mentioned less than events (i.e. works or accidents) in our documents (3,333 occurrences vs. 11,936 in the Montpellier Corpus). Also, the granularity of the spatial data is based on the type of document: street or district names are often mentioned in both technical reports and newspaper articles, however real-world coordinates are seldom found in the latter. Thus the WEIR-P pipeline may be a good tool to complete existing network databases and GIS systems. This would imply using data fusion techniques to combine and merge sometimes conflicting information. In order to improve on the current system, a larger manually annotated corpus may be necessary. The genre adaptation of NERC, exploiting the results of the text classification, will also be implemented.

A Sample-based generalization strategy [START_REF] Wieringa | Six strategies for generalizing software engineering theories[END_REF] is implemented to ensure the genericity of the tool. Since WEIR-P relies heavily on Statistical learning, new samples from other French cities are currently being used for training. Validation is being carried out on other French speaking countries. The first tests on the city of Abidjan (Ivory Coast) are encouraging. The NER module is able to correctly label the network elements and the relation linking module will undergo further training in order to take into account local language uses.

Conclusions and perspectives

We have presented a global model of the information extraction from documents related to wastewater management and a platform which implements it. The preliminary results obtained on the Montpellier corpus are encouraging and show how a mix of supervised and rule-based techniques can be used to extract useful information and reconstruct the various phases of the extension of a given wastewater management network. The pipeline may also be used to recover the dates when given pieces of equipment were laid. This feature is deemed very useful by managers who need to plan ahead maintenance operations for old assets with missing implementation dates. The genericity of the tool we have developed is being assessed through tests on other cities in France and in French Speaking countries. Indeed, some countries in North and West Africa, namely Morocco and Ivory Coast use Special Technical Specifications (STS) guidelines that are strongly inspired by the French ones. A quick analysis of the guidelines used in Quebec [START_REF]'Envionnement et de la lutte contre les changements climatiques: Description des ouvrages municipaux d'assainissement des eaux usées (DOMAEU) -Guide de rédaction[END_REF] shows that the technical vocabulary used to designate the network elements are also similar to the French ones. However, local language uses may vary. For instance the expression "assainissement d'un quartier" (sanitation of a neighbourhood) refers to sanitation/wastewater network laying for the French media and to cleaning of illegal occupation of public space for the Abidjanese. Thus, some adaptation work might be necessary to remove ambiguities.

The system still requires slight improvements as the information extraction pipeline produces some noise. Manual inspection by an expert of the extracted results may therefore be necessary and could be carried out using the visualization and spatial representation modules which enable users to easily assess the extracted data and further improve the models. In order to improve on the current system, a larger manually annotated corpus may be necessary. We also plan to use alternative classification algorithms such as One-class SVM that has been successfully adapted for reduced training samples [START_REF] Guerbai | The effective use of the oneclass svm classifier for handwritten signature verification based on writerindependent parameters[END_REF] and perform semantic relation extraction based on document textual genre.

We believe that the domain modelling work carried out within MeDo will be useful to others working in the same domain, on French as well as on other languages. Since the NLP systems used in the NERC module of our pipeline support multiple languages, we assume that their adaptation should be a straightforward procedure.

Fig. 1 .

 1 Fig. 1. A portion of the corpus manually annotated for Named Entities.

1 .

 1 Collection of documents; 2. Named-Entity recognition; 3. Semantic relation extraction; 4. Mapping and data visualization.

Fig. 2 .

 2 Fig. 2. The wastewater conceptual model.

Fig. 3 .

 3 Fig. 3. The WEIR-P Architecture

Fig. 4 .

 4 Fig. 4. Screenshot of the results menu. English: WASTEWATER MASTER PLAN INFORMATION REGARDING WORKS ON AVENUE DE LA POMPIGNANE AND ACROSS THE LEZ RIVER. EASTERN INTERCEPTOR. 1. THE EASTERN INTERCEPTOR. In order to convey the wastewater of the inhabitants of the municipalities located north and east of Montpellier, Montpellier Méditerranée Métropole undertook the installation of a sewer main called "Eastern Interceptor". With a length of 12 km, this sewer main with diameters varying between 300 to 1200 mm serves the municipal areas of Prades-le-Lez, Montferrier-sur-Lez, Clapiers, Castelnau-le-Lez, Montpellier and Lattes.This project is part of the Wastewater Master Plan, which provides for the disconnection of the separate networks from the combined sewers in order to extend and rationalise wastewater collection up to the MAERA plant with a capacity of 470,000 equivalent inhabitants. Cf Map of the Eastern Interceptor. Given the importance of this operation in terms of cost and time, the planning of the installation works for this 12 km sewer main took into account the main constraints of the major urbanization projects and programmes in the Montpellier Méditerranée Métropole area: tramway, widening of

Table 1 .

 1 Agreement per category, calculated using F-Measure.

	Category	Expert Non Expert
	Network element	0.875	0.688
	Works	0.875	0.719
	Treatment	0.750	0.703
	Network type	0.750	0.719
	Indicator	0.875	0.484
	Network management 0.750	0.609
	Network characteristics 0.875	0.656
	Water quality	0.375	0.422
	Accident	0.250	0.328
	Measure	0.875	0.680
	Spatial	0.875	-
	Temporal	0.875	-
	Organization	0.875	-
	Overall	0.875	0.719

Table 2 .

 2 Evaluation of textual relevance.

	Precision Recall F-score
	Micro 0.925	0.925 0.925
	Macro 0.928	0.931 0.921

Table 3 .

 3 Results for each category of entities, using the best performing systems. [e] indicates the use of an ensemble model, where the first system has priority.

	Entity	Occurrences Precision Recall F-score Model
	Network type	360	70.41 68.54 69.46 corenlp
	Treatment	342	66.51 62.77 64.59 [e]corenlp-spaCy
	Network element	367	61.86 65.20 63.49 [e]spaCy-corenlp
	Works	310	59.74 67.29 63.29 [e]spaCy-corenlp
	Spatial	1001	58.05 67.75 62.52 [e]spaCy-corenlp
	Measure	882	59.07 65.42 62.08 [e]corenlp-spaCy
	Temporal	219	42.53 74.50 54.15 [e]heidel-corenlp
	Water quality	136	51.85 53.85 52.83 [e]corenlp-spaCy
	Network characteristics	196	55.00 47.06 50.72 [e]spaCy-corenlp
	Network management	255	40.47 42.83 41.61 [e]corenlp-spaCy
	Indicator	592	35.90 33.26 34.53 [e]corenlp-spaCy
	Organization	129	44.23 27.06 33.58 [e]corenlp-spaCy
	Accident	26	34.78 20.00 25.40 [e]corenlp-spaCy

https://brat.nlplab.org/

https://www.geonames.org

https://adresse.data.gouv.fr/

https://nominatim.org/

https://palletsprojects.com/p/flask/

http://www.celeryproject.org/

https ://d3js.org/

https://leafletjs.com/


Fabrice Sthal

Joël Imbaud

Xavier Vacheret

Patrice Salzenstein

Gilles Cibiel

Serge Galliou

Computation method for the short-term stability of quartz crystal resonators obtained from passive phase noise measures

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Since 1975, researchers have tried to discriminate the resonator's noise in crystal oscillators by means of passive systems [START_REF] Walls | Measurement of the short-term stability of quartz crystal resonators and the implications for crystal oscillator design and applications[END_REF]- [START_REF] Parker | 1/f frequency fluctuations in quartz acoustic resonators[END_REF]. The technique of carrier suppression to characterize the inherent phase stability about the ultrastable resonators was demonstrated at the beginning of the 21st century [START_REF] Rubiola | Flicker noise measurement of HF quartz resonators[END_REF], [START_REF] Sthal | Phase noise measurements of 10 MHz BVA quartz crystal resonator[END_REF]. Recently, a more advanced version of this instrument has been implemented [START_REF] Sthal | Advanced bridge instrument for the measurement of the phase noise and of the short-term frequency stability of ultra-stable quartz resonators[END_REF]- [START_REF] Sthal | New ultra stable crystal ovens and simple characterisation[END_REF]. The principle of this passive method, presented in Fig. 1, is to reduce the noise of the source as much as possible.

An oscillator is always noisier than the resonator alone because the random noises of the resonator and of the sustaining electronics are added in the output signal. Obviously, the noise of the best oscillator used as the source is always higher than the noise of the best resonator alone. Thus, the direct feeding of the driving source signal through only one resonator does not permit the extraction of information about the resonator noise from the total output noise. To perform the resonator noise measurement, the source signal can be subtracted when passing through two identical arms with two resonators considered to be quasi-identical. Then, the contribution of the source is reduced while the characteristic noise of both resonators is preserved. This is due to the noncorrelation of the intrinsic noise of each resonator. When the carrier suppression is achieved, the resulting signal is free of the source noise. Hence, the sum of both resonators noises is measured. First, this signal is then strongly amplified. Next, the signal is mixed with the source signal to be transposed to the low-frequency domain. Finally, it is processed by a fast Fourier spectrum analyzer (FFT). With this method, the measured noise for the two resonators is above the noise level of the driving source. Calibration of the measurement system is obtained by injecting a known sideband on one of the arms of the bridge. The result of the measurement bench is corrected using the calibration factor determined from this sideband.

Usually, the flicker floor of the short-term stability of a resonator is given by the Allan standard deviation σ y (τ) [START_REF] Rubiola | Flicker noise measurement of HF quartz resonators[END_REF], [START_REF] Sthal | Phase noise measurements of 10 MHz BVA quartz crystal resonator[END_REF], [START_REF]IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology-Random Instabilities[END_REF], which corresponds to an oscillator containing a tested resonator in which the only source of flicker frequency noise is the resonator inside the oscillator. In the case of flicker frequency noise (which is the resonator's noise), the relationship between the floor of the Allan standard deviation, σ y_floor , and the power spectral density (PSD) of relative frequency fluctuations S y ( f ), is given by [START_REF]IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology-Random Instabilities[END_REF]

σ yy S _floor 1 Hz =⋅ ⋅ 22 (ln) () , (1)
where ln is the natural logarithm function. S y ( f ) is given by the measurement of the PSD of the phase fluctuations, S ϕ (1 Hz), and the half bandwidth, also called the cut-off frequency F L [START_REF] Rubiola | Flicker noise measurement of HF quartz resonators[END_REF]:

S F f SF f Q y () () , 1 Hz 1 Hz with L res L res L = +         = 2 2 1 2 φ (2)
where f res is the resonant frequency of the resonator and Q L is the loaded quality factor of the resonator. The standard measure for characterizing frequency and phase instabilities in the frequency domain is L() .

f It is defined as one half of S ϕ ( f ) [START_REF]IEEE Standard Definitions of Physical Quantities for Fundamental Frequency and Time Metrology-Random Instabilities[END_REF]. The measured L() f of both 5-MHz resonators is shown in Fig. 2. Different drive level powers dissipated by the resonators are shown. The measured resonators are SC-cut quartz crystals. Drive power level P Xtal of the resonators varies from 20 to 200 µW. The resonator is considered as a low-pass filter. The cut-off frequency can be determined by the L() f curve at the intersection of the f -1 and f -3 asymptotes. A variation of F L is shown in Fig. 2 for both these extreme cases.

The L() f measurements are linked to Table I, in which the σ y_floor was obtained with the method previously described. The total noise measured is related to the two resonators. If the two resonators are considered to be iden- tical, then half of this noise is attributed to one resonator. In that case, it is equivalent to get S ϕ (1 Hz) equal to the L() 1 Hz measured.

The short-term stability of the resonator seems to be better at 200 µW than at 20 µW. Unfortunately, a simple calculation from the loaded Q shows that the result of σ y_ floor is not realistic. Typically, a 5-MHz ultra-stable resonator exhibits an unloaded quality factor, Q X , of about 2.5 • 10 6 . By means of (2), the loaded quality factor goes from 1.8 • 10 6 to 3.1 • 10 6 ; however, it is not possible to obtain a loaded quality factor higher than the unloaded quality factor. Moreover, identical results are obtained when F L is measured by injecting a white noise instead of the calibration source. In this case, we can directly observe the transfer function of the resonator inside the bench [START_REF] Rubiola | Flicker noise measurement of HF quartz resonators[END_REF].

To analyze the phenomenon, the transfer function of the resonator must be observed near the carrier frequency with a network analyzer. Resonators have been measured in their impedance matching (PI) network by means of a 4195A network analyzer (Agilent Technologies Inc., Santa Clara, CA). Fig. 3 shows the phase of the transfer function of the resonator inserted in the PI network for different values of power dissipations. It is given for three resonator's power dissipations. The amplitude-frequency effect of the quartz crystal is clearly shown. The low-pass filter behavior of the resonator can be characterized by the cutoff frequency defined by the ±45° bandwidth:

∆FFFF =-= -+ 2 L . (3)
F -and F + are the frequencies which correspond to a phase equal to ±45°.

In this kind of test setup, the measured noise or the transfer function of the resonator are obtained at the Fourier sideband frequencies. Thus, the noise spectrum is folded up around the carrier frequency. The spectrum folding implies that the asymmetry of the positive half bandwidth F + induced a reduction of F L measured in the curves of resonator's noise in a high-power situation. In this case, F L does not represent the actual value of the loaded quality factor. Thus, the great improvement of the short-term stability is not apparent. The classical calculus of the short-term stability must be done taking into account the resonator's drive level power and its amplitude-frequency effect. The previous method of computing the short-term stability using the filter behavior remains available for low-power drive levels. Therefore, Fig. 3 shows that the phase of the transfer function is not really affected by the drive power near the null phase. These curves are used in the conversion of the resonator's flicker frequency noise into the measured phase noise. F L can be defined by inverting the slope of the relationship between S y ( f ) and S ϕ ( f ) according to

S f f Sf F y f f () () =       = ±°1 1 2 1 res d d L then , φ φ φ ∆ ∆ (4)
where f res is the resonant frequency of the resonator and dϕ/df is the derivative of the phase according to the frequency near zero phase. We chose to compute the slope between ±1° (Fig. 3). The measurement of this slope should be done in the same framework as in the noise measurement. With this new method, the incorrect computation of the short-term sta- The resonators are 5-MHz SC-cut quartz crystals and are considered to be identical. bility and the loaded Q-factor is not possible. Table II shows a comparison of both methods. The noise source results are compared with the bandwidth methods of the first-order filter and with the slope method. Better results are obtained with the slope method. Moreover, the method can be easily applied inside the measurement bench when an OCXO is used as a source. F L can be obtained by small variations of the source frequency near the null phase instead of long measurements with a network analyzer.

Table III presents the resonator noise according to the dissipated power. In this kind of measurement, the error in the determination of L() f is usually ±2 dB because of the FFT analyzer precision. Error in the determination of F L can be reduced to 0.1 Hz with the proposed method. Even with the correcting computation, the noise of the resonator seems to be power dependent. Indeed, about half the difference in the calculated σ y (τ) values is from the difference in L() .

f In our case, the decrease of L() f is not due to a permanent change, as can be observed in [START_REF] Montress | Extremely low-phase-noise SAW resonators and oscillators: Design and performance[END_REF] after a burn-in process. Variation of the acoustic resonator noise according to the dissipated power has been already observed in BAW resonators (see [START_REF] Rubiola | Flicker noise measurement of HF quartz resonators[END_REF], [START_REF] Gufflet | Doubly rotated quartz resonators with a low amplitude-frequency effect: The LD-cut[END_REF]) and more recently in film bulk acoustic resonators (FBARs) [START_REF] Gribaldo | Experimental study of phase noise in FBAR resonators[END_REF].

A passive measurement system of a resonator's phase noise has been presented. Measurements have been correlated to the amplitude-frequency effect, a well-known phenomenon in quartz crystal resonators. These investigations have led to consideration of an alternative way of determining the loaded Q-factor for the resonator to obtain more reliable short-term stability of quartz crystal resonators. After correction of the measurements, we find that the short-term stability of the observed resonators evolves according to the dissipated power. A dependence of the noise on the dissipated power is now clearly shown. Resonators are considered to be identical. With slope method, F L = 1.55 ± 0.1 Hz. Errors in the measured L() 1 Hz are ±2 dB.

R

Fig. 1 .

 1 Fig. 1. Principle of the passive measurement bench. F. Sthal, J. Imbaud, X. Vacheret, P. Salzenstein, and S. Galliou are with the Franche-Comté Electronique Mécanique Thermique et Optique-Sciences et Technologies (FEMTO-ST) Institute, CNRS, École Nationale Supérieure de Mécanique et des Microtechniques (ENSMM), University of Franche-Comté, Université de Technologie Belfort-Montbéliard, Besançon, France (e-mail: fsthal@ens2m.fr). G. Cibiel is with the Microwave and Time-Frequency Department, Centre National d'Etudes Spatiales, Toulouse, France.

Fig. 2 .

 2 Fig. 2. The L() f of 5-MHz SC-cut resonators according to the dissipated power in the crystal. For P xtal = 20 µW, the cut-off frequency F L is 1.4 Hz. For P xtal = 200 µW, F L is 0.8 Hz.

Fig. 3 .

 3 Fig.3. Phase of 5-MHz SC-cut resonator, transfer functions obtained near its resonant frequency and according to P Xtal .

Computation Method for the Short-Term Stability of Quartz Crystal Resonators Obtained From Passive Phase Noise Measures

	Fabrice Sthal, Joel Imbaud, Member, IEEE,
	Xavier Vacheret, Patrice Salzenstein, Gilles Cibiel,
	and Serge Galliou

TABLE I .

 I σ   A   R' D P, P X .

	P Xtal (µW)	L() 1 Hz (dBc/Hz)	F L (Hz)	σ y floor	Q L (10 6 )
	20	-121.5	1.4	3.4 • 10 -13	1.8
	200	-130	0.8	9.5 • 10 -14	3.1

TABLE II .

 II C   S-T S C   W C W P X = 200 µW.

	L() 1 Hz (dBc/Hz)	Slope	Bandwidth
	-130	(±1°)	(±45°)	Noise curve
	F L (Hz) σ y floor Q L (10 6 ) Q L /Q X	1.55 1.37 • 10 -13 1.61 63%	1.5 1.34 • 10 -13 1.67 66%	0.8 9.5 • 10 -14 3.12 125%
	Resonators are considered to be identical.

TABLE III .

 III S-T S A   P D   R.

	P Xtal (µW)	L() 1 Hz (dBc/Hz)	σ y floor
	20	-121.5 ± 2	3.65 • 10 -13 ± 1.2 • 10 -13
	60	-126.7 ± 2	2.01 • 10 -13 ± 0.6 • 10 -13
	100	-128.5 ± 2	1.63 • 10 -13 ± 0.5 • 10 -13
	200	-130 ± 2	1.37 • 10 -13 ± 0.4 • 10 -13


Christophe Martayan
email: martayan@oma.be

Pascual Diago

Juan Gutiérrez-Soto

Juan Fabregat

Anne-Marie Hubert

Michèle Floquet

Coralie Neiner

Malek Mekkas

Variability of B and Be stars in the LMC/SMC: binaries and pulsations

Keywords: stars: early-type, stars: emission-line, Be, binaries: eclipsing, stars: oscillations (including pulsations), Magellanic Clouds

To study the variability of the 523 B and Be stars observed in the Magellanic clouds with the VLT-FLAMES, we cross-matched the stars of our sample with the photometric database MACHO, which provides for each star an 8 years lightcurve. We searched for long, medium, and short-term periodicity and found the eclipsing binaries in our sample. For these stars, combining, spectroscopy and photometry, we were able to provide information on several systems of stars (systemic velocities, ratios of masses, etc). We also present the ratios of Bbinaries to B-non binaries in the LMC/SMC in comparison with the MW. Note that this ratio is also an important issue to understand the mechanism of star-formation at low metallicity. We also found the first multiperiodic B and Be stars in the SMC, in particular the first SMC Beta Cep and SPB, while, according to the models, pulsations were not foreseen in low metallicity environments, i.e. typically in the SMC. Our results show that the instability strips are shifted towards higher temperatures in comparison with the Milky Way' strips of pulsating B-type stars. By the fact that we found more pulsating Be stars than pulsating B stars in the SMC, it seems that the fast rotation favours the presence of pulsations. However, the ratio of pulsating B-type stars to "non"-pulsating B-type stars at low metallicity is lower than at high metallicity.

Introduction, observations

To investigate the B-type star populations in the Magellanic Clouds, VLT-FLAMES observations of a large sample of B and Be stars were obtained in the LMC-NGC2004 (176 stars) and SMC-NGC330 (344 stars) regions and their surroundings. We used a medium resolution R=6400 in the blue wavelength range around Hγ (LR02) and R=8600 in the red one around Hα (LR06). Among this sample 178 Be stars were observed. We crosscorrelated the coordinates of observed stars with the MACHO photometric database. We obtained the lightcurves for the main part of stars of our sample in order to search their long-, medium-, and short-term variability/periodicity due to potential binarity or pulsations. The time span of MACHO lightcurves is large enough to provide a very high frequency resolution in the spectral analysis and allows us to distinguish between very close frequencies. 120 C. Martayan, P. Diago, J. Gutiérrez-Soto, et al.

Binaries

2.1. Spectroscopic and eclipsing binaries in the Magellanic Clouds Blue spectra of B and Be stars in the LMC were obtained 4 days before red ones and it was therefore possible to study the variation of the radial velocities and to detect spectroscopic binaries. Despite the small number of spectra for each object it was possible to estimate the mass ratio and the systemic velocity for some binaries (see Martayan et al. 2006a). By cross correlation with the MACHO and OGLE databases we detected 19 photometric binaries. Among them 14 are new photometric binaries (5 in the LMC, 9 in the SMC). Among the 19 photometric binaries, 6 are also spectroscopic binaries (5 in the LMC, 1 in the SMC) and 2 others are Be stars (2 in the SMC). For the eclipsing binaries, the orbital period was determined with an accuracy better than 0.001d.

Details about LMC and SMC binaries

Thanks to observations with the VLT-GIRAFFE spectrograph, we found 23 new binary systems among the B stars of our sample in the LMC (see Martayan et al 2006a). The orbital periods were found thanks to the MACHO data. In the SMC, contrary to the LMC, spectra in the blue and red wavelengths were obtained the same night and we cannot study the variation of radial velocity. We found 13 eclipsing binaries. Their periods range from 0.664d to 455d with most common values around 2d. All the periods and details are provided in Martayan et al. (2007b). Finally we found 5% of binaries among B-type stars in the SMC, 12% in the LMC, while in the MW, this ratio is 30% (Porter & Rivinius 2003). However, the detectability of binaries in the LMC/SMC is limited and then the ratios given here are certainly lower limits. Note that McSwain & Gies (2005) suggested that 75% of MW Be stars can be binaries. The identified binaries from our sample with more complete observations of the radial velocity variation should be used for testing/constraining the input parameters of stellar evolution models in low metallicity environments, in particular the stellar radii.

Pulsating B and Be stars

3.1. Pulsating B and Be stars in the LMC/SMC (low metallicity) A significant fraction of main-sequence B type stars are variable. The B main sequence is populated by 2 classes of pulsators: the Beta Cephei stars (Stankov & Handler 2005) and the Slowly Pulsating B stars (de Cat 2002). The pulsations are due to the κmechanism acting in the partial ionisation zones of the iron-group elements. Be stars are non-supergiant B stars whose spectrum has displayed at least once emission lines mainly in the Balmer series. Emission lines come from a circumstellar disk created by episodic matter ejections from the central star. Be stars are also known as fast rotator stars. In the MW, they display short-term variations like Beta Cep or SPB stars. The κ-mechanism depends on the abundance of iron-group elements, and hence the respective instability strips have a great dependence on the metallicity of the stellar environment. Pamyatnykh (1999) showed that the Beta Cep and SPB instability strips disappear at Z<0.01 and Z<0.006 respectively. The LMC metallicity is Z=0.007 and the SMC one is Z=0.002 (see Maeder et al. 1999, and references therein). Therefore it is expected to find a very low occurrence of Beta Cep and SPB pulsators in the LMC and no pulsator type in the SMC. Previous spectroscopic study of Baade et al. (2002) failed to find variability in two Be stars, while Balona (1992) found monoperiodic variable B-type stars in low metallicity environment. We downloaded MACHO lightcurves for LMC and SMC B and Be stars from the samples of Martayan et al. (2006aMartayan et al. ( , 2007b)). We searched then for Binaries and pulsating B and Be stars 121 pulsations with these lightcurves. The fundamental parameters based on VLT-FLAMES spectra provided by these authors and corrected from the fast rotation effects for Be stars (see Martayan et al. 2006bMartayan et al. , 2007a) ) are used. We found several B and Be stars with short-period variability. Many of the short-period variables were found multiperiodic and some of them show a beating due to close frequencies. We recall that this result was not expected at this low metallicity by the theory. We propose an observational instability strip in the SMC, which is shifted towards higher temperatures than in the MW. We also propose the hottest pulsating star in our sample as a Beta Cep variable. The results for the MW pulsating stars come from Gutiérrez-Soto et al. (2007). The results presented here are detailed in Diago et al. (2008).

3.2. Ratios of pulsating B and Be stars vs. the metallicity and rotational velocities In Table 1, for each galaxy, we provide the metallicity of the environment, the rates of pulsating B or Be stars, and also their ratios of angular velocities to breakup velocities (Ω/Ω c ), which come from Martayan et al. (2007a, LMC and SMC), for the MW: Frémat et al. (2005), Porter (1996), Chauville et al. (2001), andStepien (2002). When the metallicity decreases the radii of the stars decrease (see Maeder & Meynet 2001). At the opposite, the linear rotational velocities of stars increase (due to lower angular momentum loss due to lower mass-loss at low metallicity) and due to the combination of this increase with the decrease of the radii, the critical rotational velocities also increase. The evolution of the Ω/Ω c is due to the combination of these different effects. Finally, we note:

(a) a decrease of the rates of pulsating B stars with decreasing metallicity as expected by the theory.

(b) More pulsating Be stars than pulsating B stars at similar metallicity, which seems to indicate that the fast rotation in Be stars plays a role in the appearance of pulsations.

(c) A decrease of the rates of pulsating Be stars between the MW and the LMC, which corresponds to a metallicity effect.

(d) An increase of the rates of pulsating Be stars between the LMC and the SMC while the metallicity decreases. This may be explained by the fact that SMC Be stars rotate faster (Ω/Ω c ∼95%) than their counterparts in the LMC/MW (Ω/Ω c ∼85%).

(e) There is a similar trend in Ω/Ω c for B stars, but their ratios are always lower than the minimal ratio from which the fast rotation effects (Ω/Ω c ∼70%) on the stars are not negligeable (see for example Frémat et al. 2005). It explains why there is an effect of the fast rotation between the LMC and SMC for Be stars and not for B stars.

Conclusion

Our results provide new informations and constraints for the models about the pulsation theory at low metallicity. They seem to indicate an enhancement of the non-radial pulsations due to the high rotation rates. As a consequence, due to the rotational mixing, are the fast rotators (Be stars) enriched in metals? To confirm and enlarge our results, we need first to increase the samples by using WFI-spectroscopic samples of Be stars in the LMC/SMC, second to determine the chemical abundances of the stars by using high resolution spectra from VLT: UVES, X-Shooter, third to test the decrease of the stellar radii by using observations of binaries at differetn metallicities, fourth to analyse the COROT lightcurves of MW B and Be stars, which could help to understand the mechanisms at the origin of pulsations and the Be phenomenon.

Table 1 .

 1

		MW LMC SMC
	Metallicity Z	0.020	0.007 0.002
	Stellar radii	decrease with	Z
	Linear rotational velocities increase with	Z
	Critical rotational velocities increase with	Z
	Ω/Ωc (B stars) %	40	37	58
	Pulsating B stars %	16	7	5
	Ω/Ωc (Be stars) %	80-88	85	95
	Pulsating Be stars %	74	15	25

Acknowledgements

C.M. acknowledges funding from the ESA/Belgian Federal Science Policy in the framework of the PRODEX program (C90290). C.M. thanks the IAUS SOC/LOC for the IAUS grant and the FNRS for the travel grant.