R Avila
email: r.avila@astrosmo.unam.mx

E Carrasco

F Ibañez

J Vernin
email: jean.vernin@unice.fr

J.-L Prieur
email: prieur@ast.obs-mip.fr

D X Cruz

Generalized Scidar Measurements at San Pedro Mártir: II. Wind Profile Statistics

Keywords: site testing -atmospheric effects -turbulence -instrumentation, adaptive optics -instrumentation, high angular resolution

, where the results concerning the measurements of the optical turbulence strength obtained at the same site and time were presented. The principal results of the present article are as follows. (I) The wind profiles remain stable during each night. (II) No evident correlation is found between the turbulence intensity (C 2 N ) and the speed of the turbulent layers V . (III) The data only suggests a correlation between C 2 N values greater than 5 × 10 -17 m -2/3 and V values greater than 50 m s -1 approximately. (IV) Layers in the first 5 km and higher up than 16 km, above sea level, are similarly slow, with median speeds of 8.6 and 9.6 m s -1 . (V) Between 9 and 16 km, where the jet stream takes place in some of the nights, the median wind speed is 26.0 m s -1 , (VI) from the simultaneous measurements of C 2 N (h) and V (h), we compute the temporal coherence of the turbulence layer by layer. This is the first time that such data is published. In the hypothesis of Multi-Conjugate Adaptive Optics, our measurements show that the temporal responses of three deformable mirrors conjugated on the ground, at 6 and at 13 km, above sea level, would be 28, 25 and 15 ms respectively. (VII) The vertical variation of V dominates the vertical variation of the coherence time. (VIII) Also for the first time, we compare the wind velocity profiles obtained from three different techniques: generalized scidar, NCEP/NCAR (National Center for Enviromental Prediction/National Center for Atmospheric Research) Reanalysis data, and instrumented balloons. The comparison shows excellent agreement both in the modulus and the direction of the wind velocity.

Introduction

Optical-turbulence layers in the Earth atmosphere are responsible for the deformation of the incoming wavefronts in astronomical observations, which in turn degrade the angular resolution. Adaptive optical systems are aimed at fully or partially recovering of the angular resolution limited by the telescope. Current developments of such systems for existing or future telescopes involve several deformable mirrors, each optically conjugated at different altitudes. These systems are known as Multi-Conjugate Adaptive Optics (MCAO). Of particular importance is the application of MCAO for extremely large telescopes. The proper development of MCAO systems require increasingly detailed studies of the optical turbulence in the atmosphere. Apart from what concerns the turbulence outer scale, all the relevant parameters for the characterization of optical turbulence, in the context of astronomical observations, can be derived from the vertical profile of the refractive index structure constant C 2 N (h) (commonly referred as turbulence profile) and the vertical profile of the turbulence-layer velocity V(h)1 , where h denotes altitude. For example, the Fried parameter r 0 and the isoplanatic angle θ 0 can be calculated from the integral of C 2 N (h) with respect to h and the 5/3-order moment of h weighed by C 2 N (h), respectively, while the wavefront coherence time τ 0 is obtained from r 0 and the 5/3-order moment of V (h) weighed by C 2 N (h) (Vernin & Muñoz-Tuñón 1994) (V denotes the modulus of V). These are examples of parameters that refer to the wavefront located at the entrance pupil of the telescope. The development of MCAO needs, additionally, knowledge of the altitude and turbulence intensity of the predominant turbulencelayers and their displacement velocity, in order to determine the spatial and temporal requirements (retrieved from C 2 N (h) and V(h)) of each of the wavefront sensors and deformable mirrors in the system. Using predicting filters, like Kalman's, it is possible to configure the mirrors of a MCAO system for a given time, by (i) taking into account the corrections performed in the past and (ii) using information about the modulus and direction of the turbulent layers velocity. It would then be possible to anticipate most of the correction to be performed for a given time. This would improve the performances of MCAO, and decrease its response time. Hence wind speed and wind direction are two key parameters for operating future MCAO systems. Moreover, the selection of the sites where the next-generation ground-based telescopes are to be installed needs statistical studies of the C 2 N and V profiles at those sites. In this paper we present the results of monitoring V(h) at San Pedro Mártir, Baja California, Mexico, using a Generalized Scidar (GS). The instrument provides simultaneous measurements of V(h) and C 2 N (h). The results concerning the turbulence profiles have been presented by Avila et al. (2004) (hereafter referred to as Paper I). Paper I describes some generalities about the instrument and the measurement campaign. For completeness, in § 2.1 we give the relevant information about the measurement technique and in § 2.2, a résumé of the observing campaign. The results are grouped in § 3. § 3.1 gives a data overview. In § 3.2 we present the statistics of the layer velocities in several slabs of the atmosphere. A study of the vertical profile of the coherence time is given in § 3.3. A comparison of our measurements with wind profiles obtained using instrumented balloons is shown in § 3.4. In that Section we also compare our results with wind velocity profiles obtained at different elevations from a global circulation model of the NOAA (National Oceanic and Atmospheric Administration). Finally, § 4 gives a summary and conclusions.

Measurements of V profiles

The GS method

The method used to measure the velocity of the turbulent layers with the GS has been extensively explained by Avila et al. (2001) and Prieur et al. (2004). We give here a very succinct summary.

The GS concept consists in taking very short-exposure images of the scintillation produced by a double star, on a virtual plane located at a distance h gs , of the order of a few kilometers, below the pupil plane (h gs < 0 ). The C 2 N profile can be derived from the mean autocorrelation of those images, whereas wind-velocity profiles V(h) can be computed from the mean cross-correlation of images taken at times separated by a constant delay ∆t. Note that the mean autocorrelation and mean cross-correlation need to be normalized by the autocorrelation of the mean image. Hereafter, we will refer to this mean-normalized cross-correlation simply as cross-correlation. The method is based on the following principle:

We assume that the turbulent structures are carried by the mean wind without deformation. This assumption is known as Taylor hypothesis, and is valid for short enough time intervals. In this case, the scintillation pattern produced by a layer at altitude h, where the mean horizontal wind velocity is V(h), moves on the analysis plane a distance V(h) ∆t in a time ∆t. If the source was a single star, the cross-correlation of images separated by a lapse ∆t, would produce a correlation peak located at the point r = V(h) ∆t, on the correlation map. By determining this position, one can deduce V(h) for that layer. As we use a double star, the contribution of the layer at altitude h in the cross-correlation consists of three correlation peaks, which we call a triplet: a central peak located at r = V(h) ∆t and two lateral peaks separated from the central one by ±ρH, where H is the distance from the analysis plane to the given layer H = h -h gs and ρ is the angular separation of the double star. The cross-correlation can be written as:

C * * c (r, ∆t) = ∞ 0 dh C 2 N (h) { a C c (r -V(h)∆t, H) + b [ C c (r -V(h)∆t -ρH, H) +C c (r -V(h)∆t + ρH, H) ] }. ( 1
)
C c is the theoretical cross-correlation of the scintillation produced by a layer at an altitude h and unit C 2 N . It differs from the theoretical autocorrelation C (Prieur et al. 2004) only by an eventual temporal decorrelation of the scintillation (partial failure of Taylor hypothesis) and an eventual fluctuation of V(h) during the integration time. The decorrelation would make C c smaller than C, and the fluctuation of V(h) would make C c smaller and wider than C (Caccia et al. 1987). Those effects do not affect the determination of V(h), as the only information needed here is the position of each correlation peak. Note that C takes into account the spatial filtering introduced by the detector sampling. The factors a and b are given by the magnitude difference of the two stars ∆m through:

a = 1 + α 2 (1 + α) 2 and b = α (1 + α) 2 , with α = 10 -0.4∆m .
(2)

Observing Campaign

The data used in this work were obtained in May 2000, at the Observatorio Astronómico Nacional de San Pedro Mártir (OAN-SPM), Mexico, located at an altitude of 2850 m above sea level. We used the GS of the Laboratoire Universitaire d'Astrophysique de Nice, France. The instrument was installed on the 1.5-m and 2.1-m telescopes (1.5mT and 2.1mT, hereafter) during 9 and 7 nights (7-15 and 16-22 May UT), respectively.

Instrumental parameters

The concept of the GS method can be found in a number of papers (Rocca et al. 1974;Avila et al. 1997;Fuchs et al. 1998;Klückers et al. 1998;Avila et al. 2001;Prieur et al. 2001Prieur et al. , 2004)). In Paper I, the instrumental characteristics concerning the determination of C 2 N (h) were presented. Here we describe the relevant parameters for the determination of V(h).

The scintillation images used for the computation of the cross-correlations are the same as those used for the autocorrelations (see Paper I). The image plane is situated 3 or 4 km below the pupil plane. Images are recorded inside a 64x64 window of an intensified CCD. Each pixel covers a square area on the image plane of side ∆x equal to 3.1 and 4.1 cm, for the 1.5mT and 2.1mT, respectively. The spatial filtering introduced by such pixel sizes is taken into account in the inversion process by convolving the theoretical autocorrelation by the autocorrelation of the impulse response of the camera. The exposure time of each image is 1 or 2 ms, depending on the stars magnitudes and the prevailing observing conditions. One image is obtained every 20 ms. The wavelength is centered at 0.5 µm. Two 128×128 cross-autocorrelation maps -one for a time lapse of ∆t = 20 ms and another one for ∆t = 40 ms -are saved on disk at time intervals that depend on the number of images used to compute the cross-correlations. Most of the time, this number was equal to 2000, which gives a mean time lag between each registration of 1.32 min. The computation of the correlations are performed in quasi real time, so that only the correlations -and not the images -are stored on disk. Table 1 of Paper I lists the double stars used as light sources. Masciadri et al. (2002) presented an analysis of the C 2 N detectivity level for the same data as those used here. In their Fig. 12, it can be seen that ∆C 2N ∆h < 10 -15 m -1/3 for the 2.1mT and any of the stars used. Considering that the C 2 N profiles were resampled to an altitude resolution of ∆h = 500 m, we have ∆C 2 N < 2 × 10 -18 m -2/3 for the 2.1mT. From Eq. 1 of Masciadri et al. (2002), the C 2 N uncertainty is inversely proportional to the telescope diameter. Hence, for the 1.5mT, ∆C 2 N < 2.7 × 10 -18 m -2/3 .

The resolution ∆V of the wind velocity determination is set by ∆V = (∆x sec(z))/∆t, where z is the zenith angle. Table 1 gives the velocity resolution for each telescope, each ∆t value and z = 0.

Data reduction

The method used to obtain the velocity profiles out of the cross-correlation data is based on an interactive algorithm which is extensively explained by Avila et al. (2001). Prieur et al. (2004) presented an automatic version of that algorithm. For the reduction of the data presented here, we have used primarily the interactive algorithm. Part of the data were reduced twice using the automatic algorithm, finding an excellent agreement. Here we recall the basis of the interactive algorithm.

Figure 1 shows an example of a cross-correlation map. Three horizontally aligned tripletslabeled A, B and C -can be seen. As explained in § 2.1, for a given triplet, the distance from the map center to the central peak equals V∆t, which gives V, and the distance from the central peak to either of the lateral peaks equals ρH, which gives the layer altitude h through H = h -h gs . The interactive algorithm consists in clicking with the mouse on the triplet center and on either of the lateral peaks. The program computes the layer velocity V and altitude h, and determines the C 2 N value from the previously obtained C 2 N (h) profile. These data are used to compute a correlation triplet and subtract it from the cross-correlation map.

Sometimes, there are several layers apparently at the same altitude, with different velocities. Our interpretation is that they are actually situated at slightly different altitudes, which cannot be resolved in the C 2 N profile. In this case, the measured C 2 N at the altitude of these layers corresponds to the sum of the real C 2 N of each layer. To determine those individual C 2 N values, the measured C 2 N is distributed to the layers at the same altitude, with weights proportional to the peak amplitudes in each of the corresponding triplets.

The dome seeing is retrieved from the cross-correlation maps. When at least two triplets are detected at the observatory altitude and one of them has a velocity smaller than the velocity resolution, this triplet is interpreted as being generated inside the telescope dome, where the mean wind velocity is zero. The dome seeing is then retrieved as in the case of multiple layer at apparently the same altitude explained above.

Results and Discussions

V(h) Data Overview

We have been able to retrieve 3016 profiles from this observation campaign. Figure 2 shows a mosaic view of all the wind-speed profiles. It can be seen that at the observatory level, the wind is generally weak. As we have excluded the data corresponding to the dome seeing, wind values at ground level are associated to open-air turbulence.

In many cases, dots with different colors appear superimposed, which indicates the presence of several turbulent layers with altitude differences smaller than the vertical resolution of the C 2 N profiles, but with detectable velocity differences. This feature constitutes a strong advantage of the simultaneous measurement of C 2 N (h) and V(h) as opposed to the solely measurement of C 2 N (h). The velocity of the layers represents an additional dimension in the parameter space that characterizes each layer. Therefore, the determination of each layer velocity can help to identify individual turbulent layers.

The fastest turbulent layers are found between 9 and 16 km. In this altitude range, a slow modulation of the layer speed from night to night can be noticed: during the first four nights the speed was lower than 20 m s -1 , then it started to increase, reaching 55 m s -1 on May 17 UT, and then decreased to values lower than 10 m s -1 on the last was generally lower than 10 m s -1 .

The wind-direction profiles are shown in Fig. 3. It can be seen that the wind blows predominantly from West to East (i.e. around 270 • ) at every altitude. In general, the wind direction varies very little as a function of altitude. However, on May 21, there was a steep variation of the wind direction at 10 km approximately that lasted all night long. The following night, the same gradient in wind direction was still present, but less pronounced.

In Fig. 4 we reproduce Figure 1 of Paper I, which represents a mosaic view of the C 2 N profiles that were obtained using the same data as that used for the wind profiles. From a visual inspection of Figs. 2 and4, it can be seen that only the night on May 17 UT and in the jet stream layer, an evident correlation is present between C 2 N and speed values. This is confirmed by Fig. 5, where the C 2 N values are plotted against the layer speed, for each layer detected in the whole campaign. Each frame corresponds to a different altitude interval. No particular correlation between the V and C 2 N values is noticed, appart from the layers in the 9 to 16 km (Fig 5c) range having speeds higher than 50 m s -1 , which have particularly intense turbulence ( C 2 N 5 × 10 -17 m -2/3 ). Although this behavior is evident in our data set, further measurements would be required to draw a general conclusion. The observed general lack of correlation between C 2 N and V might be due to the fact that the optical turbulence is triggered by vertical instabilities that take place at scales much smaller than the altitude resolution of the C 2 N profiles obtained with the GS.

Wind Speed Profile Statistics

Using all the measured V profiles, we have computed the median, first and third quartiles values of the layer speed V as a function of height. We recall that the first quartile, median and third quartile, q 1 , q 2 and q 3 of a distribution are such that 25, 50 and 75% of the events have values lower than q 1 , q 2 and q 3 , respectively. The corresponding plots are shown in Fig. 6a. It can be seen that the wind speed has similar low values near the ground (within the first 4 km) and above 16 km. In between, which corresponds to the jet stream zone, the wind speed increases strongly. The significance of the statistical values for each altitude is indicated by the number of measurements used in the computation, i.e. the number of detected layers, shown in Fig. 6b.

A more complete statistical description of the wind speed values is obtained from their cumulative distribution function (CDF), which corresponds for each value of V , to the probability of occurrence of such a value or a lower one. We computed one CDF for the wind values grouped in each of four altitude intervals: 2-4, 4-9, 9-16 and 16-25 km above sea level, as shown in Fig. 7. We can see, for example, that 10% of the V values are lower than 3, 2, 10 and 5 m s -1 in the 2-4, 4-9, 9-16 and 16-25 km slabs, respectively, and 10% of the values are higher than 15, 28, 40 and 21 m s -1 . These numbers characterize the extreme wind conditions at each altitude interval.

Coherence Time Profiles

From the C 2 N and V values of each detected layer, the coherence time τ of the wavefront deformations produced by that layer can be calculated:

τ = 0.31 r 0 ind V , (3)
where r 0 ind corresponds to the Fried's parameter that would occur if only the given layer was present:

r 0 ind = 0.423 2π λ 2 C 2 N ∆h -3/5 , (4)
where the wavelength λ = 0.5 µm. The value of τ for a given layer constrains the temporal frequency at which a deformable mirror (DM) should operate if it had to completely compensate the wavefront deformations introduced by that layer. We have calculated τ (h) from each C 2 N and V profiles. The median, first and third quartiles of τ (h) are shown in Fig. 8. From the median C 2 N profile measured at SPM, shown in Fig. 3c of Paper I, one could envisage a MCAO system constituted of three deformable mirrors conjugated at ground level, 6 km and 13 km above sea level. For such conjugation altitudes, the median value of τ would be 38, 25 and 15 ms approximately.

It is interesting to note that the variation of τ with altitude, seems to be exclusively governed by the variation of V . This is shown by the outstanding agreement between the median of τ (h), and the median of the function τ * (h) = 0.31

r 0 med V (h) , (5)
where r 0 med = 0.91 m, is the median value of r 0 ind for all altitudes and all turbulence profiles. The median profiles of τ (h) and τ * (h) are shown in solid and dashed lines, respectively, in Fig. 8. This is the first time that a study on τ profiles is published. It is extremely useful for the development of the next generation of adaptive optics systems.

Comparison with other measurements and data sets

The goal here is to compare three different values of the wind velocity profiles: those obtained with the GS, the wind speed measured simultaneously from instrumented balloons and the values obtained, for the same nights, from the global circulation model NCEP/NCAR (National Center for Enviromental Prediction/National Center for Atmospheric Research) Reanalysis Project. This is the first published comparison between GS and NCEP/NCAR wind profiles.

The balloons used are described by Azouit & Vernin (2005). The wind values are retrieved from the temporal derivative of the balloon horizontal position.

The NCEP/NCAR Reanalysis database model uses a state-of-the-art analysis and forecasting system to perform data assimilation using data from 1948 to the present. It is considered as one of the most reliable analysed fields (Kisler et al. 2001) as it is constrained by observational information such as land, marine, balloon, satellite and aircraft data. The Derived NCEP Pressure Level Product provides the 6-hourly U-wind and V-wind components of wind velocity at 17 different pressure levels.

San Pedro Mártir (SPM) geographic coordinate are +31. • 05 latitude and -115. • 47 longitude while the grid points closest to SPM coordinates are +30. • 00 and -115. • 0 respectively. We assume a standard atmosphere to associate the 17 pressure levels to altitutes e.g. 200 mb corresponds to 12 km above sea level. For each altitute, we obtained the velocity module from the U and V wind components for the 4 daily forecasted values2 . For GS comparison purposes we average only the 6 and 12 UT wind velocity values.

Wind speed

The comparison of the wind speed profiles for 15 nights are shown in Fig. 9, where the date is indicated on top of each frame. The solid lines correspond to the mean speed profiles obtained each night with the GS, excluding dome turbulence. The dotted lines are the wind speeds measured with balloons when available. There was at most one balloon flight per night. The wind speed profiles obtained from the NCEP/NCAR Reanalysis model are shown in dashed lines. A visual comparison shows a very good agreement between the three data sets. The NCEP/NCAR Reanalysis profiles reproduce remarkably well the in situ measurements both, those from the instrumented balloons and also the GS values, excepting the features shown on 13, 14 and 15 May at about 5 km. The higher resolution of the balloon measurements shows the spatial wind speed fluctuations that could not be appreciated otherwise.

The wind direction profiles obtained with the three different methods are plotted in Fig. 10. The agreement below 20 km is generally remarkable. Above that level, the balloons measured virtually any direction. We believe that this is due to the extremely weak wind speed above 20 km.

This cross comparison brings confidence on either of the three methods for the determination of the wind speed profiles. Particularly, it indicates that for site prospection, it may suffice to determine the wind speed profile from the NCEP/NCAR Reanalysis rather than actually measure the profiles at a given site. However, for real time monitoring, the GS measurements appear to be the most adecuate method.

Summary and Conclusions

We presented the results of measurements of the speed and the intensity of optical turbulent layers above the Observatorio Astronómico Nacional de San Pedro Mártir, Mexico, performed with the GS, during 16 nights in May 2000. The analysis was performed on a data set where we could exclude the turbulence in the telescope dome.

The wind profiles remained fairly stable during each night. The wind speed variations occured in temporal scales of several nights.

Correlation between turbulence intensity and layer speed was only found during half a night, when very high values of both parameters were encoutered (C 2 N ≥ 5 × 10 -17 m -2/3 and V ≥ 50 m s -1 ). However, half a night of such events represents too few data to draw a definitive conclusion on the correlation of intense turbulence and fast wind.

The median wind profile shows wind velocities similarly low in the slabs that go from the ground up to 4 km and from 16 to 25 km. In between, the wind is much stronger due to the jet stream.

Using the wind and turbulence profiles, we presented the first published computation of layeroriented temporal coherence, which is particularly useful for the development of Multiconjugate Adaptive Optics systems. It shows that the temporal responses of three hypothetical deformable mirrors conjugated on the ground, at 6 and at 13 km, above sea level, would be 28, 25 and 15 ms respectively. The vertical variation of the coherence time seems to be governed by the vertical variations of the wind profile. Such a study on the coherence time can only be obtained from simultaneous C 2 N and V profiles. The results of this paper illustrate the usefulness of the wind velocity profile measurements performed with the GS. The consistency of those measurements with other means of wind profile determination, namely instrumented balloons and NCEP/NCAR Reanalysis, has been proved. For a virgin site, the GS is not a suitable method, as it requires a telescope of at least 1 m diameter. In that case, the NCEP/NCAR Reanalysis wind profiles are best suited. It has been shown here that NCEP/NCAR Reanalysis data can validly be used for determining both wind speed and wind direction profiles with a very good approximation. If C 2 N (h) models are required, one might employ a simulation code like Meso-NH (Masciadri et al. 1999a(Masciadri et al. ,b, 2004)). Should actual C 2 N (h) and V(h) measurements be needed at a virgin site, a possibility is to use a Single Star SCIDAR, which is being developed at Nice University (Habbib et al. 2005).

We are grateful to the OAN-SPM staff for their valuable support. This work was done in the framework of a collaboration between the Instituto de Astronomía of the Universidad Nacional Autónoma de México and the UMR 6525 Astrophysique, Université de Nice-Sophia Antipolis (France), supported by ECOS-ANUIES grant M97U01. Funding was also provided by the grants J32412E from CONACyT, IN118199 and IN111403 from DGAPA-UNAM, and the TIM project (IA-UNAM). NCEP Reanalysis data provided by the NOAA-CIRES Climate Diagnostics Center, Boulder, Colorado, USA, from their Web site at http://www.cdc.noaa.gov/. 2, but here each frame shows the mean speed profile as measured with the GS (solid lines), wind profiles obtained from the NCEP/NCAR Reanalysis project (dashed lines) and wind profiles measured with balloons (dotted lines). The GS profiles exclude dome turbulence. The NCEP/NCAR Reanalysis project profiles are the average of the 6 and 12 UT data. Each balloon profile corresponds to a single balloon launch. On some nights there was no balloon data. 2, but here each frame shows the wind direction profile as obtained with GS (solid lines), the NCEP/NCAR Reanalysis project (dashed lines) and those measured with the balloons (dotted lines). Wind blowing from the North, East, South and West correspond to 0, 90, 180 and 270 degrees, respectively. Like in Fig. 9, during some nights there was no balloon data.

Fig. 1 .

 1 Fig. 1.-Example of a mean cross-correlation. The data were obtained with 2000 scintillation images of the 6. 4 separation double star ζ Cbr, a lag between correlated images of ∆t = 20 ms and the analysis plane conjugated at h gs = -4 km. The observation was performed on 2000 May 9, 8h29 UT, at the 1.5mT. Three horizontally aligned correlation triplets can be seen -labeled A, B and C -each corresponding to a turbulent layer. The arrows point to the triplet centers. The color scale indicates normalized cross-correlation values.

Fig. 2 .

 2 Fig. 2.-Mosaic of the wind profiles measured during the whole campaign. Each box corresponds to one night. The vertical and horizontal axes represent the altitude above sea level (observatory altitude: 2850 m) and the Universal Time, respectively. The wind speed values are coded with the color scale shown at the bottom. The three upper rows and the two bottom rows contain the profiles obtained at the 1.5mT and 2.1-mT, respectively.

Fig. 3 .

 3 Fig. 3.-Similar to Fig. 2, but here colors represent the direction of the wind. 0 • , 90 • , 180 • and 270 • correspond to wind blowing from North, East, South and West.

  Fig. 5.-C 2N against V for all the turbulent layers detected. Each frame corresponds to a different altitude range above sea level, as indicated by the frame labels.

  Fig. 6.-(a). Profiles of median (solid line), first and third quartiles (dotted lines) of the wind speed. (b) Profile of the number of data used for the statistical calculations. The dome-seeing layer was excluded.

  Fig.10.-Similar to Fig.2, but here each frame shows the wind direction profile as obtained with GS (solid lines), the NCEP/NCAR Reanalysis project (dashed lines) and those measured with the balloons (dotted lines). Wind blowing from the North, East, South and West correspond to 0, 90, 180 and 270 degrees, respectively. Like in Fig.9, during some nights there was no balloon data.

Table 1

 1

	. Velocity Resolution
	∆t (ms)	∆V (m s -1 )
		1.5mT 2.1mT
	20	1.55	2.05
	40	0.77	1.02

All along the paper, symbols in bold face denote two-dimensional vectors and the same symbols in normal face correspond to the modulus of such vectors.

Wind blows to East and North for U > 0 and V > 0, respectively.


Marco Scardia

Jean-Louis Prieur

Luigi Pansecchi

Robert W Argyle

Marco Sala

J.-L Prieur

Speckle observations with PISCO

Keywords: binaries: close -binaries: visual -astrometry -techniques: interferometric -individual (ADS 11479, ADS 11584, ADS 16538

teaching and research institutions in France or abroad, or from public or private research centers.

Introduction

This paper is the sixth of a series (Scardia et al. 2005, 2006, 2007, 2008a, Prieur et al. 2008, herein: Papers I to V), whose purpose is to contribute to the determination of binary orbits, using speckle observations made in Merate (Italy) with the Pupil Interferometry Speckle camera and COronagraph (PISCO) on the 102 cm Zeiss telescope of INAF -Osservatorio Astronomico di Brera (OAB, Brera Astronomical Observatory). PISCO was developed at Observatoire Midi-Pyrénées and first used at Pic du Midi from 1993 to 1998. It was moved to Merate in 2004 and used there since. More information about the context and the purpose of this program can be found in Paper I.

This paper deals with the results of the observations performed during the second semester of 2006. In Sect. 2, we briefly describe our sample, the instrumental setup and the reduction procedure. The astrometric measurements are presented and discussed in Sect. 3. In Sect. 4 we propose new revised orbits for ADS 11479, 11584 and 16538, partly derived from those observations and derive estimates of the component masses.

Observations and data reduction

The purpose of our long term program is to monitor the relative motion of all visual binaries accessible with PISCO on the Zeiss telescope in Merate, for which new measurements are needed to improve their orbits. Our sample consists of visual binaries with the following characteristics, that are linked to instrumental or atmospheric limitations:

declination north of -5 • , -brighter than 10th magnitude in V , -magnitude difference less than 4, -angular separation smaller than ≈ 5 ′′ . The last limitation was chosen so that the binary systems fit inside the isoplanatic patch of the atmosphere, which is a theoretical necessary condition for speckle measurements. The distribution of the angular separations measured in this paper is displayed in Fig. 1 and shows a maximum for ρ ≈ 0 ′′ .7. The closest separation that can be measured with PISCO in Merate is of the order of the diffraction limit, which is λ/D ≈ 0 ′′ .13 with the R filter (i.e. λ = 650 nm) and the Zeiss telescope whose diameter is D = 1.02 m.

The observations were carried out with the PISCO speckle camera with the ICCD detector (CCD intensified with a micro-channel plate) belonging to Nice University (France). Details about the telescope and the instrumentation can be found in Paper I and in Prieur et al. (1998). For each observation, a series of about 10 000 short-exposure frames were digitized and processed in real-time with a Pentium III PC, to compute the mean auto-correlation with Worden's (1977) method (which subtracts most of the continuum), the mean power spectrum and the integration of the individual frames. Those frames were also recorded on a SVHS video tape for archiving and further processing such as the quadrant determination.

As the auto-correlation function is symmetric relative to the origin, it does not contain information about the location of the faintest companion. This is the origin of the well-known 180 • ambiguity of binary speckle measurements. This ambiguity can be resolved by using the mean triple-correlation function of the elementary frames (Weigelt, 1977) or a restricted version of this function as proposed by Aristidi et al. (1997), which is the method we use (see Paper III).

The positions of the secondary peaks of the mean auto-correlations were carefully measured with an interactive program that fitted and subtracted the residual background. The details of this procedure with an evaluation of the reliability of the determination of the errors can be found in Paper III. For the binaries with the smallest separations (i.e. ρ 0 ′′ .3) we also subtracted a model of the central background pattern to the auto-correlation images, as described in Paper IV.

Astrometric measurements

The astrometric measurements of the observations made during the second semester of 2006 are displayed in Table 1. The designation of the binary is reported in the first three columns: the WDS name (Washington Double Star Catalogue, Mason et al. 2007) in Col. 1, the official double star designation in Col. 2 (sequence is "discoverer-number"), and the ADS number in Col. 3 [START_REF] Aitken | New General Catalogue of Double Stars[END_REF]. For each observation, we then give the epoch in Besselian years (Col. 4), the filter (Col. 5), the focal length of the eyepiece used for magnifying the image (Col. 6), the angular separation ρ (Col. 7) with its error (Col. 8) in arcseconds, and the position angle θ (Col. 9) with its error (Col. 10) in degrees.

The characteristics of the PISCO R and V filters were given in Table 1 of Paper III. Some objects, like ADS 9426 and 10949, were observed without any filter because they were too faint. This is indicated with W (for "white" light) in the filter column (Col. 5). The corresponding bandpass is that of the ICCD detector, with a central wavelength of about 650 nm, close to that of the R filter.

The errors reported in Cols. 8 and 10 were computed by adding quadratically the calibration errors to the standard deviations of series of measurements obtained with the same data sets (see Paper III). As for the previous papers of this series, the minimum (onesigma) errors for the angular separation (Col. 8) were set to 0 ′′ .003 for close pairs and to 0.05% of ρ for wide pairs, on the basis of the uncertainties coming from the determination of the centres of the auto-correlation peaks (estimated at 0.1 pixel in the elementary frames) and those affecting the scale calibration (i.e., 0.05%), respectively. Similarly, the minimum (one-sigma) errors for the position angle (Col. 10) were estimated at 0 • .3. The average values of the errors of the 175 measurements reported in this table are 0 ′′ .012 ± 0 ′′ .005 and 0 • .56 ± 0 • .34 for ρ and θ, respectively. The validity of our error determination was studied in detail in Paper III.

The position angles presented in Col. 9 follow the standard convention with the North corresponding to θ = 0 • and the East to θ = 90 • . When the triple correlation files allowed us to resolve the 180 • ambiguity (see Sect. 2 and 3.1), an asterisk was added in Col. 9 to indicate that our determination is absolute. Otherwise, our angular measurements were reduced to the quadrant reported in the "Fourth Catalogue of Interferometric Measurements of Binary Stars" (Hartkopf et al. 2008, hereafter IC4).

In Col. 11, a flag is set to one for all the systems for which an orbit was found in the literature, e.g., mainly from the "Sixth Catalogue of Orbits of Visual Binary Stars" (Hartkopf & Mason, 2008), hereafter OC6. The residuals derived from the corresponding ephemerides will be discussed in Sect. 3.2.

In the note column (Col. 12), we give some comments about the secondary peaks of the autocorrelation files that have been measured (e.g., elongated, diffuse, faint, etc). An elongation of those peaks is generally a sign of an insufficient correction of the atmospheric dispersion by the Risley prisms (see Prieur et al., 1998). The auto-correlation files of ADS 13447 exhibited some spurious multiple peaks whose origin is unknown. Note that the case of ADS 11454 is noteworthy: it is a quadruple system that we detected as triple only because the two components A and B are presently too close (ρ < 0 ′′ .1) to be resolved with the 102 cm Zeiss telescope (see discussion in the next section). In order to provide the maximum accuracy, our measures of STF 2339 refer to the position of the components C and D relative to that of the unresolved couple AB. This is different from the convention adopted in the WDS Catalogue of reporting the mean position of C-D relative to AB.

Quadrant determination

As mentioned in Sect. 2, we have used the restricted triple-correlation technique of Aristidi et al. (1997) to try resolving the 180 • ambiguity in the θ measurements made from the auto-correlation files and determine the quadrant containing the companion. For each observation, we examined the location on the triple-correlation file of the faintest secondary spot, which corresponded to that of the companion. When the signal-to-noise ratio was good enough, we were able to unambiguously determine the location of this spot and thus resolve the 180 • ambiguity. For the couples with the largest separations, we could also see the location of the companion directly on the long integration files. As a result, in Table 1, we are able to give the non-ambiguous angular separation of 119 out of 176 measurements, i.e. 68% of the total (marked with an asterisk in Col 9).

Note that we used a different method for WAK 21CD. This pair belongs to the the quadruple system of ADS 11454 consisting of STF2339AB-CD = HU 322AB + WAK 21CD. With our observations we detected the three components AB, C and D (see Table 1), but we could not resolve the pair A-B (HU 322AB) that is presently too close (ρ < 0 ′′ .1) for the 102 cm Zeiss telescope. To determine the quadrant of WAK 21CD we computed the bispectrum from our data recorded on tape and managed to restore an image of the triple system AB, C and D, following the procedure described in Prieur et al. (2003). This image and the mean autocorrelation are displayed in Fig. 2. Our observations thus lead to a position angle of 265.5 • for WAK 21CD. This is in agreement both with the quadrant published in the last version of the WDS Catalogue, and with the speckle measurements of Scardia et al. (2000) and Balega et al. (2002), that are reported in IC4 (both were made in 1998).

When checking whether those "absolute" θ values were consistent with the values tabulated in IC4, we found a good agreement for all objects, except for ADS 12770, 15950, and 16037. We now discuss the cases of those three objects, using the usual convention of numbering the quadrants from 1 to 4 to indicate the North-East, South-East, South-West and North-West quadrants, respectively.

ADS 12770: our quadrant determination (Q=1) seems robust with a clear contrast between the two secondary peaks of the triple correlation. It is nevertheless in contradiction with the third quadrant reported in IC4, relative to observations made in the V band. Our quadrant determination was made without any filter (i.e. in W ), which results in a spectral band close to the R band (see Sect. 3). This may be the origin of the discrepancy, and a quadrant inversion could occur between V and R, since the two stars have a small magnitude difference: ∆m V = 0.1 mag. according to Germain et al. (1999).

ADS 15950: here also, our quadrant determination (Q=2) seems reliable and was made without any filter, whereas the quadrant of Q=4 reported in IC4 refers to the V band. The difference of magnitude is even smaller than for ADS 12770, with ∆m V = 0.06 mag. (WDS), Fig. 2 Triple system (AB, C, D) of ADS 11454: autocorrelation (top) and restored image with bispectral methods (bottom). To improve the clarity of this image, we have subtracted a circular halo that existed around the central component after deconvolution, and whose origin was due to an imperfect matching of the seeing between the object and the reference star.

which could naturally explain a quadrant inversion between V and R.

ADS 16037: in this case, our quadrant determination (Q=2) is not as clear as the others, but the signalto-noise ratio is still satisfactory. IC4 reports a quadrant Q=4 in disagreement with our determination that was also made without any filter (in W ) because of the low luminosity of this object. The magnitude difference is slightly larger in this case, with ∆m V ≈ 0.25 mag and an integrated spectral type F5. Hence a quadrant inversion is less likely, but cannot be excluded. We intend to re-observe this pair as soon as possible, as well as ADS 12770 and 15950, to check our quadrant determinations.

Finally, there is a quadrant discrepancy for ADS 12201 and 14839, when considering the quadrant convention adopted for the orbit computation by some authors (see next Section). Their convention seems doubtful since it is in contradiction with the last observations reported in IC4.

Comparison with published ephemerides

The (O -C) (Observed minus Computed) residuals of the measurements for the 58 systems with a known orbit of Table 1 are displayed in Table 2 in Cols. 6 and 7 for the separation ρ and position angle θ, respectively. The orbital elements used for computing the ephemerides were retrieved from OC6 and from our last publications (Scardia et al. 2006(Scardia et al. , 2008a(Scardia et al. , 2008b)). When extracted from OC6, the corresponding bibliographic references are indicated in Col. 3 as they appear in this catalogue, with an asterisk. The ρ values in Col. 5 are the relevant observed separations, taken from Col. 7 of Table 1. They are repeated here for the convenience of the reader, to be able to identify the cases when ρ is small. For ADS 11479, 11584 and 16538, we also give the residuals obtained with our new orbits presented in Sect. 4, for comparison.

We noted a 180 • discrepancy of the position angle between our measurements and the published ephemerides for ADS 12201 and 14839 (see Sect. 3.1). This is indicated with the superscript Q in Col. 7.

The residuals reported in Table 2 were computed with the most recent orbits found in OC6, but for some objects, we also give the O -C values relative to old orbits found in the previous issues of OC6, when they are still valid. This includes ADS 11635AB, 12889AB, 15115, 16373 for which the "old" and "new" orbits lead to comparable residuals. For ADS 11956, we used our last orbit published in Scardia et al. (2008b), that was computed using the PISCO measurement reported in Table 1.

Fig. 3 shows that the residuals are well centered around the origin, with a rather large scatter that can be explained by the (old) age of many orbits. The average values computed with the 63 residuals of Table 2 are < ∆ρ O-C >= 0 ′′ .00 ± 0 ′′ .09 and < ∆θ O-C >= -0 • .3 ± 1 • .8. The small values obtained for those offsets provide a new validation of our calibration made with a grating mask (see Paper III), which is thus in good agreement with the measurements made by the other observers.

A very large residual in separation was computed for ADS 13256 with Hopmann (1973)'s orbit: ∆ρ O-C = -0 ′′ .54. Unfortunately, the motion seems rectilinear for this object. The arc of orbit is very short and the derivation of valid orbital parameters is still impossible.

Concerning the position angles, the largest absolute values of the residuals were found for ADS 11584, with ∆θ = -6.1 • (Alzner 2006), and ADS 16538, with ∆θ = -5.3 • (Baize 1992). We propose new orbital elements for those objects in the next section.

Revised orbits for ADS 11479, 1158and 16538

In this section we present the new orbits we have computed for ADS 11584 and 16538, for which the previously published orbits resulted in large residuals from our measurements. We also computed new orbital elements for ADS 11479 since its orbit has not been revised for more than forty years although numerous observations have been done since.

Table 2

Residuals of the measurements of Table 1 with published orbits (begin.). In col. 3, an asterisk indicates that the references are reported as they appear in the Sixth Catalog of Orbits of Hartkopf & Mason (2008). The other references can be found in Sect. References, at the end of this paper. In col. 7, Q indicates discrepant quadrants between our measurements and those orbits. Fig. 3 Residuals of our measurements from the published orbits. The data point of the residual of ADS 13256, computed with Hopmann (1973)'s orbit, lies outside of this frame.

ADS

We have followed the same method for the three objects, using our last measurements with PISCO and the other available observations contained in the data base maintained by the United States Naval Observatory. We first computed the preliminary orbital elements with the analytical method of [START_REF] Kowalsky | Procès-verbaux de l'Université Imperiale de[END_REF], and then used them as initial values for the least-squares method of [START_REF] Hellerich | [END_REF].

The final orbital elements are presented in Table 3. In this table, Ω 2000 is the position angle of the ascending node, measured in the plane of the sky from north through east, taking the equinox of 2000 as a reference, ω is the longitude of the periastron in the plane of the true orbit, measured from the ascending node to the periastron, in the direction of motion of the companion, i is the inclination of the orbit relative to the plane of the sky, e the eccentricity, T the epoch of periastron passage, P the period, n the mean angular motion, and a is the semi-major axis. The four parameters A, B, F, and G are the Thiele-Innes constants (useful for an easier computation of the ephemerides).

The corresponding (O -C) residuals, restricted to the last observations for reasons of space, are given in Tables 4, 5 and 6 for ADS 11479, 11584 and 16538, respectively. For each measurement, the date in Besselian years is given in Col. 1, and the (O -C) residuals in ρ and θ in Cols. 2 and 3, respectively.

The apparent orbits are shown in Fig. 4 as solid lines and the observational data used for the calculation of the orbital elements are plotted as small crosses. The orientation of the graphs conforms to the convention adopted by the observers of visual binary stars. For each object, the big cross indicates the location of the primary component, and the straight line going through this point is the line of apsides. The sense of rotation of the companion is indicated with an arrow.

The ephemerides for 2008-2015 are presented in Table 7, with the date in Besselian years in Col. 1, the angular separations ρ in Cols. 2, 4 and 6, and the position angles θ in Cols. 3, 5 and 7.

We present some physical parameters derived for those systems from our orbital elements in Table 8. For each object whose name is given in Col. 1 we report its spectral type in Col. 2, the Hipparcos parallax π HIP in Col. 3, the apparent angular extent of the semi major axis a in arcseconds in Col. 4 (from Table 3), the linear size of a in AU in Col. 5, and the total mass of the system M total in Col. 6. Both the linear size of a and M total were computed from our orbital elements and using the Hipparcos parallax.

New orbit of ADS 11479 -STT 359

The revision of the orbit of ADS 11479 is mainly justified because the previous orbit is very old (Symms 1964) and we have taken advantage of the numerous measurements obtained by speckle interferometry. Indeed, out of the 257 measurements now available for this object, 132 were obtained since 1964, mostly with speckle techniques. The new orbital elements reported in Table 3 were computed with the analytical method of Kowalsky (1873) followed by the least-squares method of [START_REF] Hellerich | [END_REF]. During this computation, it appeared that 13 measurements had to be rejected because they were clearly aberrant. The standard deviations of the residuals are 0 ′′ .05 and 2 • .0 for ρ and θ, respectively.

The total mass of the system derived from our orbit is 5.3 ±3.3 M ⊙ (see Table 8), which is in good agreement with the value expected for a system of this spectral type (G9 III).

New orbit of ADS 11584 -STT 363

The orbital elements reported in Table 3 were derived from the 58 available measurements obtained since 1843. The standard deviations of the residuals are 0 ′′ .05 and 4 • .7 for ρ and θ, respectively. In the last 35 years, the best orbits have been calculated by Zulevic (1975), Baize (1989) and [START_REF] Alzner | [END_REF], with increasing values for the orbital period. Alzner (2006)'s orbit leads to a large residual with our last measurement: ∆θ O-C = -6 • .1. As the declination of ADS 11584 is high (close to 77 • ), all the measurements had to be carefully corrected for precession effects (which reached 4 • during the 160 year time-range of the observations). As the angular sepa- Convergence was difficult to obtain, and the weighting scheme appeared crucial in the process. This explains why our orbit is rather different from Alzner's, with a longer period (P = 642 yr instead of P = 405 yr for Alzner's orbit) and a larger eccentricity. The total mass derived from our elements of 4.2 M ⊙ (Table 8) is in agreement with the expected value for a system of this spectral type (F0 IV). Unfortunately this result is affected by a very large uncertainty (±7.3 M ⊙ !), that results from the large uncertainty of the period and of the major axis, due to an incomplete coverage of the orbit (see Fig. 4b). Using the formula that we have obtained for luminosity class IV in Scardia et al. (2008b), we find a dynamical parallax of π dyn = 8.50 mas, in good agreement with the Hipparcos measurement.

Even though we have obtained convergence on the orbital elements and thus derived their uncertainties, and although the systemic mass is in agreement which the expected mass for a system of this spectral type, the orbit of ADS 11584 should still be considered as badly determined, especially its period and its semimajor axis.

New orbit of ADS 16538 -STT 489 AB

π Cephei (HR 8819, HD 218658, ADS 16538) is a multiple system, whose main system A-B is constituted of a bright star with a faint companion. The resulting large magnitude difference makes measurements difficult to perform. It was first discovered as a visual binary by Otto Struve in 1843 (hence the name STT 489 AB for the visual binary), and later the primary star (G2 III according to SIMBAD whereas the WDS reports G0 IV) was found to be a spectroscopic binary with the Lick 0.91 m refractor by Campbell (1901). The first spectroscopic orbit of the Aa-Ab system was determined by Harper (1925) and recently improved by Scarfe et al. (1983).

The orbit of STT 489 AB could have been well constrained by the measurements made during the periastron passage of 1934. Unfortunately, the observations were difficult to perform at that time (with θ ≈ 0 ′′ .3) and perturbed by World War II, at least in Europe where very few astronomers could observe. The most recent orbit was computed by Baize (1992) with the measurements made until 1989. The last measurements lead now to negative residuals in ρ and θ. Note that Baize did not report any equinox value, because he probably did not perform any correction for precession effects.

From the 155 measurements obtained since 1846, we derived the orbital elements of STT 489 AB presented in Table 3. The standard deviations of the residuals are 0 ′′ .10 and 3 • .4 for ρ and θ, respectively. Those values are those expected for a sub-arcsecond couple. A few observations had to be discarded, but convergence was easy to achieve. As already mentioned by [START_REF] Muller | [END_REF] and Baize (1992) there is a systematic difference in separation for the measurements made before and after the periastron passage of 1934. In average, the former are larger and more scattered than the latter.

Using the Hipparcos parallax value revised by Gatewood et al. (2001) of π HIP = 13.8±0.41 mas, we obtain a total system mass of 7.6 ±1.6 M ⊙ . This value is in good agreement with the value of 8.8 ±0.9 M ⊙ derived by Gatewood et al. (2001), who performed a detailed study of this system that combined spectroscopic and visual data.

Conclusion

In the first semester of 2006, we performed 175 observations of 169 visual binaries with PISCO in Merate. When adding those made since 2004, the total reaches 1078 observations, which is more than twice the number of binary observations made with PISCO on the 2-meter Bernard Lyot telescope of Pic du Midi during the period 1993-1998. The new exploitation of PISCO in Merate has thus already provided a significant contribution to the measurements of close visual binary stars.

The measurements reported here have already been used to revise the orbits of ADS 11956 (Scardia et al., 2008b) and of ADS 11479, 11584 and 16538, whose elements are presented in this paper. We hope that our measurements will be useful to the astronomical community and help to improve the accuracy of many other orbits in the future.

  Fig. 1Histogram of the angular separations of the 175 measurements reported in this paper.

  Fig. 4New orbits of ADS 11479 (a), ADS 11584 (b) and ADS 16538 (c).

Table 1

 1 Measurements of visual binaries between July and December 2006 (begin.).

	WDS	Name	ADS Epoch Fil. Eyep.	ρ	σρ	θ	σ θ Orb. Notes
					(mm) (arcsec) (arcsec) (deg.) (deg.)
	01283+4247 AC 14	1161 2006.954 R	20	0.768	0.019	92.1 * 0.5
	14536-0028 BU 942	9426 2006.499 W	20	1.388	0.028	185.7 1.3
	15361+5531 A 1124	9720 2006.499 R	20	1.399	0.027	141.0 * 1.1
	16413+3136 STF 2084	10157 2006.642 R	10	1.019	0.005	208.7 * 0.5
	16442+2331 STF 2094AB	10184 2006.655 R	20	1.185	0.008	72.7 * 0.6
	16518+2840 STF 2107AB	10235 2006.680 R	20	1.452	0.008	99.6 * 0.3
	16541+0826 HEI 857	-	2006.680 R	20	0.563	0.008	142.2 * 0.5
	16564+6502 STF 2118AB	10279 2006.639 R	20	1.067	0.008	66.2 * 0.3
	17020+0827 STF 2114	10312 2006.674 R	20	1.343	0.008	193.8 * 0.3
	17053+5428 STF 2130AB	10345 2006.639 R	20	2.360	0.012	11.8 * 0.3
	17096+0356 HEI 894	-	2006.696 R	20	0.553	0.009	21.8 * 0.8
	17195+5832 KR 46	10487 2006.642 R	20	1.695	0.010	63.3 * 0.6
	17239+3627 STF 2162	10527 2006.674 R	20	1.355	0.010	282.2 0.7
	17240+3835 HU 1179	10531 2006.675 R	10	0.247	0.006	274.4 0.3
	17304-0104 STF 2173	10598 2006.680 R	10	0.451	0.003	166.2 * 0.3	Elongated
	17358+0100 STF 2186	10650 2006.639 R	20	3.022	0.015	78.2 * 0.3
	17386+5546 STF 2199	10699 2006.694 R	20	2.007	0.010	56.5 * 0.3
	17397+7256 H 1 41	10734 2006.639 R	20	1.036	0.008	336.0 * 0.4
	17399+0748 HDS2499	-	2006.639 R	20	0.680	0.008	239.3 * 0.9
	17436+2237 HU 1285	10743 2006.677 R	20	0.546	0.008	215.0 * 0.4
	17439+0551 STF 2200AB	10741 2006.677 R	20	1.594	0.008	162.8 * 0.3
	17457+1743 STF 2205	10769 2006.696 R	20	1.076	0.008	358.3 * 0.3
	17471+1742 STF 2215	10795 2006.677 R	10	0.505	0.003	254.8 * 0.3
	17533+3605 STF 2243	10874 2006.642 R	20	1.141	0.014	39.8 0.6
	17571+0004 STF 2244	10912 2006.680 R	10	0.611	0.003	97.8 * 0.4
	17571+4551 HU 235	10934 2006.680 R	20	1.608	0.008	282.9 * 0.3
	17590+0202 STF 2252AB	10945 2006.696 R	20	3.958	0.020	23.5 0.3
	17590+1226 STF 2254AB	10949 2006.675 W	20	3.502	0.018	265.6 * 0.3	Diffuse
	18003+5251 STF 2271AB	10988 2006.677 R	20	3.395	0.017	267.1 * 0.3
	18017+4011 STF 2267	11001 2006.642 R	20	0.567	0.008	269.9 0.5
	18025+4414 BU 1127Aa-B 11010 2006.639 R	20	0.775	0.008	55.2 * 0.7
	18065+4022 STF 2282	11074 2006.639 R	20	2.657	0.013	81.8 * 0.4
	18096+0400 STF 2281AB	11111 2006.718 W	10	0.602	0.010	291.0 * 0.7
	"	"	"	2006.721 R	20	0.588	0.008	290.8 * 1.0
	18097+5024 HU 674	11128 2006.677 R	20	0.753	0.008	216.1 * 0.7
	18101+1629 STF 2289	11123 2006.694 R	20	1.231	0.008	219.2 * 0.3
	18146+0011 STF 2294	11186 2006.696 R	20	1.295	0.014	92.6 0.6
	18208+7120 STT 353AB	11311 2006.699 R	10	0.480	0.004	267.6 * 0.3
	18238+5139 ES 187AB	11328 2006.642 R	20	2.561	0.014	206.0 0.3
	18250-0135 AC 11	11324 2006.696 R	20	0.873	0.008	354.7 * 0.3
	18250+2724 STF 2315AB	11334 2006.696 R	10	0.642	0.003	121.2 0.3
	18261+0047 BU 1203	11339 2006.726 R	20	0.459	0.009	153.9 * 0.5
	18272+0012 STF 2316Aa-B 11353 2006.726 R	20	3.681	0.018	319.8 * 0.3
	18320+0647 STT 354	11432 2006.699 R	20	0.610	0.008	210.8 1.3
	18338+1744 STF 2339AB-D 11454 2006.699 R	20	2.081	0.010	273.5 * 0.4	(outer autoc. peaks)
	"	"	"	2006.716 R	20	2.058	0.013	273.7 * 0.4
	18338+1744 STF 2339AB-C 11454 2006.699 R	20	1.632	0.014	276.4 * 0.4	(inner autoc. peaks)
	"	"	"	2006.715 W	20	1.640	0.008	275.3 * 0.5
	"	"	"	2006.716 R	20	1.627	0.008	275.8 * 0.4
	"	"	"	2006.715 W	10	-	-	-	-	Too diffuse
	18338+1744 WAK 21CD	11454 2006.699 R	20	0.441	0.018	265.5 * 0.5
	18339+5221 A 1377AB	11468 2006.677 R	10	0.251	0.005	120.7 * 0.6	Elongated
	18355+2336 STT 359	11479 2006.639 R	10	0.729	0.004	5.6 0.3
	18359+1659 STT 358AB	11483 2006.675 R	20	1.655	0.008	151.8 * 0.3
	18374+7741 STT 363	11584 2006.727 R	20	0.431	0.013	336.9 0.7
	18384+2842 STF 2356	11529 2006.642 R	20	1.125	0.010	62.8 0.5

Table 1

 1 Measurements of visual binaries between July and December 2006 (cont.).

	WDS	Name	ADS Epoch Fil. Eyep.	ρ	σρ	θ	σ θ Orb. Notes
					(mm) (arcsec) (arcsec) (deg.) (deg.)
	18387+0451 STT 360	11526 2006.743 R	20	1.672	0.008	281.4 * 0.3	0
	18393+2056 STF 2360	11546 2006.677 R	20	2.432	0.012	358.3 * 0.3	0
	18413+3018 STF 2367AB 11579 2006.743 R	10	0.378	0.003	75.4 0.5	1
	18443+3940 STF 2382AB 11635 2006.675 R	20	2.380	0.012	348.8 * 0.3	1
	18443+3940 STF 2383Cc-D 11635 2006.675 R	20	2.381	0.012	79.5 * 0.3	1
	18443+6103 STF 2403	11661 2006.680 R	20	1.091	0.008	277.2 * 0.3	0
	18477+4904 HEI 72	-	2006.724 R	20	0.618	0.008	231.4 * 0.6	0
	18490+2110 STF 2401AB 11715 2006.724 W	20	4.248	0.021	37.7 * 0.3	0
	18497+1041 STF 2402	11722 2006.784 R	20	1.455	0.008	208.8 * 0.6	0
	18502+1131 BU 265	11735 2006.784 R	20	1.390	0.013	228.4 * 0.3	0
	18508+1059 STF 2404	11750 2006.694 R	20	3.534	0.018	181.2 * 0.3	0
	18520+1047 STF 2408	11766 2006.784 W	20	2.286	0.011	90.7 * 0.3	0 Elongated
	18521+1148 HU 199	11769 2006.789 R	20	0.884	0.011	345.6 * 1.0	0
	18526+1400 STF 2412	11778 2006.694 R	20	1.449	0.008	55.9 0.3	0
	18555+2914 STF 2419	11847 2006.789 R	20	3.363	0.017	176.9 * 0.3	0
	18570+3254 BU 648AB	11871 2006.721 R	20	0.898	0.008	268.8 * 0.3	1
	18575+5814 STF 2438	11897 2006.716 R	10	0.867	0.008	359.6 * 0.3	1
	19019+1910 STF 2437	11956 2006.743 R	20	0.580	0.016	11.1 0.3	1
	19024+6927 STF 2478	12015 2006.680 W	20	0.953	0.008	313.6 * 0.5	0
	19030+5135 STF 2451	11997 2006.677 W	20	1.984	0.010	81.9 * 0.4	0
	19052+1050 BU 466	12021 2006.669 W	20	1.916	0.010	163.8 * 0.3	0
	19062+3026 STF 2454AB 12040 2006.822 W	20	1.326	0.019	288.6 * 0.5	1
	19070+1104 HEI 568	-	2006.724 R	10	0.304	0.004	274.9 * 0.4	0
	19071+7204 STT 369	12113 2006.721 R	20	0.695	0.011	11.3 * 0.5	0
	19083+5520 D 19AB	12104 2006.727 R	20	0.511	0.016	348.6 * 1.1	0
	19114+2116 A 151	12140 2006.819 R	20	0.574	0.011	156.2 0.7	0
	19143+1904 STF 2484	12201 2006.694 R	20	2.163	0.011	238.9 * 0.3	1
	19148+4756 A 706	12229 2006.789 R	20	1.600	0.014	73.4 0.5	0
	19220+2230 BU 141AB	12355 2006.694 R	20	0.895	0.008	82.1 0.9	0
	19251+1839 HU 339	12416 2006.792 W	20	0.834	0.008	243.5 0.7	0 Diffuse & elongated
	19261+3849 HO 450AB	12446 2006.697 R	20	1.000	0.013	264.1 0.8	0
	19266+2719 STF 2525	12447 2006.677 R	20	2.130	0.016	289.7 * 0.3	1
	19270+7322 STF 2550AB 12524 2006.680 R	20	1.942	0.010	250.8 0.3	0
	19299+4931 BU 143	12535 2006.697 W	20	2.188	0.017	192.3 * 0.3	0
	19307+2758 MCA 55Aac	12540 2006.721 R	10	0.359	0.012	105.5 * 1.3	1
	19311+0824 A 1184	12537 2006.743 W	20	0.901	0.024	108.4 * 0.4	0 Elongated
	19346+1808 STT 375	12623 2006.721 R	20	0.601	0.015	182.5 * 1.2	0
	19350+2947 A 368	12633 2006.699 R	20	0.507	0.011	153.2 * 0.8	0
	19357+7308 A 864	12729 2006.727 W	20	0.742	0.008	14.5 * 1.3	0
	19363+3540 STT 377AB	12667 2006.819 R	20	0.985	0.035	36.1 1.7	0
	19365+4101 STT 378AB	12687 2006.699 R	20	1.406	0.008	285.5 * 0.3	0
	19384+0021 BU 249AB	12708 2006.852 R	20	0.831	0.017	109.9 * 1.0	0
	19402+2331 A 166	12770 2006.830 R	20	0.821	0.015	241.2 1.2	0
	"	"	"	2006.830 W	20	0.805	0.017	62.4 * 0.7	0
	19413+3043 BU 145AB	12786 2006.852 R	20	0.825	0.011	269.5 * 0.8	0
	19448+1649 STF 2569	12861 2006.830 R	20	2.119	0.015	357.0 * 0.3	0
	19450+4508 STF 2579AB 12880 2006.721 R	20	2.666	0.013	220.4 * 0.3	1
	"	"	"	2006.762 R	20	2.647	0.013	220.5 * 0.3	1
	19453+3048 AG 237	12881 2006.762 W	20	2.375	0.018	140.2 * 0.5	0
	19456+3337 STF 2576AB 12889 2006.699 R	20	2.832	0.014	160.4 0.3	1
	19483+3710 STT 386	12965 2006.669 R	20	0.933	0.011	69.8 0.9	0
	19487+3519 STT 387	12972 2006.724 R	20	0.571	0.018	129.6 * 0.8	1
	19575+2018 BU 425AB	13165 2006.852 W	20	1.342	0.026	240.0 0.6	0 Elongated
	20011+4816 STF 2619AB 13269 2006.784 R	20	4.166	0.021	239.3 * 0.3	0
	20014+1045 STF 2613	13256 2006.727 R	20	3.637	0.018	354.2 * 0.3	1

Table 1

 1 Measurements of visual binaries between July and December 2006 (cont.).

	WDS	Name	ADS Epoch Fil. Eyep.	ρ	σρ	θ	σ θ Orb. Notes
					(mm) (arcsec) (arcsec) (deg.) (deg.)
	20042+1148 STF 2620AB 13320 2006.830 R	20	1.849	0.009	286.1 * 0.5
	20067+1256 BU 428	13384 2006.727 R	20	0.788	0.008	353.6 0.7
	20095+5140 STF 2645	13447 2006.789 R	20	1.594	0.010	138.5 0.8	Multiple peaks
	20102+4357 STT 400	13461 2006.699 R	20	0.593	0.008	337.4 0.7
	20187+3315 STT 405AB 13682 2006.819 R	20	0.799	0.017	150.6 0.7
	20200+3616 BU 431	13719 2006.820 R	20	0.530	0.008	29.8 * 1.8
	20229+4259 HO 128AB	13786 2006.820 R	20	1.361	0.021	358.8 * 0.6
	20244+2923 HO 457AB	13818 2006.830 W	20	2.021	0.010	60.4 * 0.3	Elongated
	20248+3545 BU 432	13830 2006.831 R	20	1.433	0.019	196.5 * 0.5
	20337+3835 A 1431	14007 2006.789 R	20	0.867	0.011	30.6 0.6
	20370+1203 STF 2701	14063 2006.697 R	20	2.057	0.020	221.1 * 0.5
	20375+1436 BU 151AB	14073 2006.790 R	10	0.532	0.003	5.5 * 0.3
	20445+2356 STF 2724	14227 2006.784 R	20	2.466	0.017	149.0 0.3
	20471+2525 BU 364	14286 2006.784 R	20	0.792	0.014	68.4 0.6
	20474+3629 STT 413Aa-B 14296 2006.784 R	20	0.876	0.008	5.7 * 0.5
	20531+2909 STT 417AB 14397 2006.790 R	20	0.880	0.015	28.2 0.7
	20553+4231 STT 423	14432 2006.918 R	20	2.766	0.014	76.1 * 0.3
	20557+0432 STF 2735	14430 2006.820 R	20	2.032	0.017	281.5 * 0.3
	20577+5849 A 756AB	14493 2006.918 R	20	0.565	0.018	209.3 2.1
	20591+0418 STF 2737AB 14499 2006.869 R	10	0.632	0.004	284.5 0.3
	20595+5013 BU 68	14520 2006.918 R	20	1.941	0.025	148.7 * 0.3
	20598+6152 BU 472	14540 2006.831 R	20	0.743	0.011	13.9 * 0.4
	21015+6643 HU 959	14578 2006.831 R	20	1.296	0.012	160.6 * 0.3
	21137+6424 H 1 48	14783 2006.727 R	10	0.229	0.004	235.7 1.6
	21186+1134 BU 163AB	14839 2006.727 R	20	0.757	0.008	257.8 0.8
	21237+5518 A 1892	14945 2006.727 R	20	0.747	0.009	348.7 0.7
	21289+1105 STF 2799AB 15007 2006.727 R	20	1.854	0.009	261.9 0.6
	21308+4752 A 769	15053 2006.943 R	20	0.704	0.014	292.9 1.0	Diffuse
	21355+2427 HU 371	15115 2006.953 R	10	0.255	0.003	314.6 0.7
	21441+2845 STF 2822AB 15270 2006.784 R	20	1.781	0.009	311.3 * 0.3
	21454+4356 HO 168AB	15295 2006.831 R	20	0.855	0.017	223.4 0.6
	21480+6920 STF 2835	15350 2006.918 W	20	1.904	0.012	270.1 * 0.6
	21555+1053 BU 75AB	15447 2006.784 R	20	0.906	0.008	19.9 1.0
	21557+0715 STT 452	15452 2006.915 R	20	0.744	0.014	178.2 0.4
	21565+0715 STT 453AB 15464 2006.915 R	20	0.717	0.012	268.1 0.5
	21581-0329 STF 2847	15494 2006.953 R	20	0.731	0.017	125.8 0.9
	22009+6250 HU 976	15558 2006.820 W	20	1.609	0.008	54.9 0.3
	22070+3605 STT 462AB 15645 2006.831 R	20	1.079	0.014	316.8 * 0.5
	22086+5917 STF 2872BC 15670 2006.790 R	20	0.829	0.022	298.4 0.3
	22094+2233 STF 2868	15673 2006.954 R	20	1.077	0.014	352.3 * 0.4
	22100+2308 COU 136	-	2006.954 R	20	0.485	0.012	27.7 * 0.6
	22122+6344 STF 2884	15742 2006.918 W	20	2.118	0.015	142.6 * 0.3
	22272+1509 STF 2905	15950 2006.915 W	20	3.326	0.017	104.5 * 0.4	Diffuse
	22312+5052 STF 2918	16020 2006.915 R	20	1.643	0.015	236.8 * 0.5	Diffuse
	22323+5512 AG 283	16032 2006.831 W	20	2.640	0.013	332.1 * 0.3
	22328+2625 HO 475AB	16037 2006.951 W	20	1.085	0.008	126.0 * 0.8
	22419+2126 STF 2934	16185 2006.951 W	20	1.337	0.008	57.9 * 0.4
	22426+4401 A 414AB	16204 2006.951 W	20	1.723	0.009	14.1 0.3	Diffuse
	22485+5409 AG 424	16280 2006.973 R	20	2.266	0.013	135.5 * 0.4
	22509+5303 BU 1332AB	16310 2006.918 W	20	1.509	0.013	128.3 * 0.4
	22514+6142 STF 2950AB 16317 2006.784 R	20	1.293	0.008	278.9 * 0.3
	22537+4445 BU 382AB	16345 2006.869 R	20	0.823	0.008	230.7 * 0.3
	22557+1547 HU 987	16373 2006.790 W	20	1.110	0.008	78.9 * 0.3
	22597+4149 HLD 56	16435 2006.790 W	20	1.158	0.008	93.1 * 0.6
	23072+6050 BU 180AB	16518 2006.869 R	20	0.548	0.013	136.1 * 0.6

Table 1

 1 Measurements of visual binaries between July and December 2006 (end).Note: In column 9, the exponent * indicates that the position angle θ could be determined without the 180 • ambiguity.

	WDS	Name	ADS Epoch Fil. Eyep.	ρ	σρ	θ	σ θ Orb. Notes
				(mm) (arcsec) (arcsec) (deg.) (deg.)
	23078+6338 HU 994	16530 2006.869 R	10	0.200	0.004	314.9 1.3	1
	23079+7523 STT 489AB 16538 2006.869 R	20	1.094	0.019	350.8 * 0.8	1
	23102+5727 STT 490AB 16560 2006.869 W	20	1.200	0.008	296.5 * 0.3	0
	23147+4116 A 200	16621 2006.954 R	20	0.652	0.014	74.7 2.2	0 Faint & diffuse
	23292+4042 A 1487	16785 2006.954 R	20	1.063	0.015	158.8 0.5	0
	23340+3120 BU 720	16836 2006.975 R	10	0.554	0.005	97.7 * 0.4	1
	23375+4426 STT 500AB 16877 2006.975 R	10	0.463	0.003	8.4 * 0.5	1
	23413+3234 BU 858AB 16928 2006.975 R	20	0.830	0.012	224.0 * 0.8	0
	23431+1150 A 1242	16951 2006.976 W	20	0.940	0.015	333.6 1.2	1
	23516+4205 STT 510AB 17050 2006.954 R	20	0.590	0.008	120.0 * 1.1	0
	23590+5315 HLD 59AB 17141 2006.954 R	20	1.155	0.013	12.5 0.7	0

Table 2

 2 Residuals of the measurements of Table1with published orbits (end).

		Name	Orbit	Epoch	ρ(O)	∆ρ(O-C) ∆θ(O-C)
					(arcsec)	(arcsec)	(deg.)
		STF 2084	Söderhjelm (1999) *	2006.642	1.019	-0.03	0.3
		STF 2107 AB	Scardia et al. (2003c) *	2006.680	1.452	0.07	-1.3
		STF 2118 AB	Scardia et al. (2002d) *	2006.639	1.067	-0.09	-1.3
		STF 2130 AB	Heintz (1981b) *	2006.639	2.360	0.05	1.9
		HU 1179	Hartkopf (2000b) *	2006.675	0.247	-0.01	1.7
		STF 2173	Heintz (1994a) *	2006.680	0.451	-0.01	0.5
		STF 2199	Popovic & Pavlovic (1995d) *	2006.694	2.007	0.09	1.4
		HU 1285	Seymour et al. (2002) *	2006.677	0.546	0.01	-0.2
		STF 2205	Cvetkovic (2007a) *	2006.696	1.076	-0.03	-0.4
		STF 2215	Cvetkovic & Novakovic (2006e) * 2006.677	0.505	0.02	1.2
		STF 2244	Heintz (1997) *	2006.680	0.611	0.08	-1.5
		BU 1127 Aa-B	Cvetkovic & Novakovic (2006e) * 2006.639	0.775	-0.05	-1.5
		STF 2281 AB	Söderhjelm (1999) *	2006.718	0.602	0.00	1.4
	"	"	"	2006.721	0.588	-0.01	1.2
		STF 2289	Hopmann (1964b) *	2006.694	1.231	-0.01	2.3
		HU 674	Seymour et al. (2002) *	2006.677	0.753	0.12	0.2
		STF 2294	Luyten (1934a) *	2006.696	1.295	0.10	-0.7
		STT 353 AB	Andrade (2005) *	2006.699	0.480	0.00	-0.9
		AC 11	Heintz (1995) *	2006.696	0.873	0.03	-0.1
		STF 2315 AB	Mason et al. (2004b) *	2006.696	0.642	0.01	0.7
		BU 1203	Popovic & Pavlovic (1996b) *	2006.726	0.459	-0.01	-0.6
		A 1377 AB	Scardia (1984e) *	2006.677	0.251	0.01	-4.1
		STT 359	Symms (1964)	2006.639	0.729	0.01	0.7
	"	"	This paper	"	"	-0.00	0.1
		STT 358 AB	Heintz (1995) *	2006.675	1.655	0.10	0.8
		STF 2367 AB	Pourbaix (2000b) *	2006.743	0.378	0.00	-0.2
		STT 363	Alzner (2006)	2006.727	0.431	0.01	-6.1
	"	"	This paper	"	"	0.02	-2.9
		STF 2382 AB	Mason et al. (2004b) *	2006.675	2.380	-0.03	0.3
	"	"	Novakovic & Todorovic (2006e) *	"	"	0.00	0.2
		STF 2383 Cc-D Docobo & Costa (1984b) *	2006.675	2.381	0.02	-0.1
		BU 648 AB	Heintz (1994a) *	2006.721	0.898	-0.03	1.5
		STF 2438	Hartkopf & Mason (2001a) *	2006.716	0.867	0.03	0.9
		STF 2437	Scardia et al. (2008b)	2006.743	0.580	0.00	0.1
		STF 2454 AB	Starikova (1982b) *	2006.822	1.326	0.00	0.5
		STF 2484	Hopmann (1973b) *	2006.694	2.163	-0.12	0.3 Q
		STF 2525	Heintz (1984b) *	2006.677	2.130	0.05	-0.5
		MCA 55 Aac	Scardia et al. (2008a)	2006.721	0.359	-0.02	-2.5
		STF 2579 AB	Scardia (1983a) *	2006.721	2.666	0.01	-1.0
	"	"	Scardia (1983a) *	2006.762	2.647	-0.01	-0.9
		STF 2576 AB	Scardia (1981) *	2006.699	2.832	-0.04	-0.9
	"	"	Söderhjelm (1999) *	"	"	-0.01	-0.3
		STT 387	Mason et al. (2006b) *	2006.724	0.571	0.00	0.1
		STF 2613	Hopmann (1973)	2006.727	3.637	-0.54	2.3
		STT 400	Heintz (1997) *	2006.699	0.593	0.01	0.1
		BU 151 AB	Alzner (1998a) *	2006.790	0.532	-0.01	-0.6
		STT 413 Aa-B	Rabe (1948b) *	2006.784	0.876	-0.03	2.7
		STF 2737 AB	Zeller (1965) *	2006.869	0.632	0.01	0.5
		H1 48	Scardia et al. (2008a)	2006.727	0.229	-0.06	-3.1
		BU 163 AB	Fekel et al. (1997) *	2006.727	0.757	0.02	-1.5 Q
		STF 2799 AB	Popovic (1987) *	2006.727	1.854	0.12	2.1
		HU 371	Scardia et al. (2006)	2006.953	0.255	-0.05	0.9
	"	"	Mason et al. (2006b) *	"	"	-0.03	-1.1
		STF 2822 AB	Heintz (1995) *	2006.784	1.781	0.06	-2.3
		BU 75 AB	Heintz (1996a) *	2006.784	0.906	-0.02	-0.8

Table 4

 4 ADS 11479: O-C residuals of our new orbit (after 1995). The symbol P indicates PISCO measurements.

	Epoch	∆ρ (O-C) ∆θ (O-C)
		(arcsec)	(deg.)
	1997.537	-0.023	0.6
	1997.537	-0.023	0.4
	1997.579	-0.013	0.1
	1997.601	-0.003	0.0
	1997.609	-0.023	-0.5
	1997.658	-0.033	-0.6
	1997.669	-0.003	0.0
	1998.673	0.004 P	0.7 P
	1999.512	-0.020	-1.7
	1999.512	-0.030	-1.3
	1999.550	0.030	0.2
	1999.728	0.001	1.0
	1999.745	-0.010	0.4
	2000.546	-0.023	0.2
	2001.417	-0.025	0.5
	2001.580	0.024	1.1
	2002.460	-0.059	0.4
	2002.510	0.011	1.7
	2003.598	-0.002	0.9
	2004.369	0.016	1.1
	2004.640	-0.003 P	0.5 P
	2004.694	0.015	0.2
	2006.389	-0.009	0.4
	2006.639	-0.001 P	0.1 P

Table 5

 5 ADS 11584: O-C residuals of our new orbit (after 1995). The symbol P indicates PISCO measurements.

	Epoch	∆ρ (O-C) ∆θ (O-C)
		(arcsec)	(deg.)
	1996.430	0.025	4.5
	1996.600	0.051	6.0
	1997.540	0.081	9.6
	1999.570	0.030	8.8
	2000.610	0.040	7.2
	2001.470	0.025	3.8
	2002.540	0.046	7.4
	2002.581	0.016	-0.8
	2003.560	0.019	2.1
	2004.510	0.014	3.6
	2005.630	0.007	0.6
	2006.727	0.022 P	-2.9 P

Table 3

 3 New orbital elements of ADS 11479, 11584 and 16538.

	ADS Ω2000	ω	i	e	T	P	n	a	A	B	F	G
	(deg.) (deg.) (deg.)		(yr)	(yr) (deg./yr) (arcsec) (arcsec) (arcsec) (arcsec) (arcsec)
	11479 10.0 197.7 119.9 0.8393 1929.081 219.3 1.64129	0.425 -0.40992 -0.00687 0.09220 0.22120
	±1.2 ±2.1 ±2.0 ±0.0066 ±0.54	±8.8	±0.066 ±0.014
	11584 159.7 55.9 78.3	0.890 1987.038 641.9 0.56083	0.950 -0.55487 0.03516 0.70033 -0.37422
	±1.5 ±4.8 ±1.7 ±0.057	±0.72 ±506.0 ±0.44	±0.244
	16538 90.3 90.0 30.0 0.5968 1934.573 162.8 2.21147	0.810 -0.70147 -0.00367 0.00424 -0.80999
	±4.9 ±4.4 ±3.0 ±0.0067 ±0.35	±2.8	±0.038 ±0.050

Table 6

 6 ADS 16538: O-C residuals of our new orbit (after 1995). The symbol P indicates PISCO measurements.

		Epoch		∆ρ (O-C) ∆θ (O-C)
				(arcsec)		(deg.)
		1996.760	-0.045		-0.4
		1996.940	0.075		4.2
		1997.660	-0.088		-1.6
		1998.770	-0.022		3.5
		1998.774	-0.011		-0.8
		1998.790	-0.002		-1.0
		1999.690	-0.095		0.4
		2000.690	0.022		-0.2
		2002.770	-0.034		0.2
		2004.974	-0.027 P		-0.9 P
		2005.750	0.020		-1.8
		2006.869	-0.018 P		-2.1 P
	Table 7	New ephemerides of ADS 11479, 11584 and
	16538.
		ADS 11479	ADS 11584	ADS 16538
	Epoch	ρ	θ	ρ	θ	ρ	θ
		(arcsec) (deg.) (arcsec) (deg.) (arcsec) (deg.)
	2008.0 0.733	5.3	0.427 340.1 1.114 353.9
	2009.0 0.735	5.2	0.441 340.4 1.116 354.7
	2010.0 0.737	5.0	0.454 340.6 1.117 355.5
	2011.0 0.739	4.9	0.467 340.8 1.118 356.3
	2012.0 0.741	4.7	0.480 340.9 1.119 357.1
	2013.0 0.743	4.6	0.492 341.1 1.119 357.9
	2014.0 0.744	4.5	0.504 341.3 1.120 358.7
	2015.0 0.746	4.3	0.516 341.4 1.120 359.5

Table 8

 8 Physical parameters (a and M total ) derived from the new orbital elements.

	Name	Sp. type πHIP	a		M total
			(mas)	( ′′ ) (AU)	M⊙
	ADS 11479 G9 III	6.70	0.425	63	5.3
			±1.38 ±0.014 ±13	±3.3
	ADS 11584	F0 IV	7.94	0.95	120	4.2
			±0.51 ±0.24 ±31	±7.3
	ADS 16538 G2 III	13.8	0.81	59	7.6
			±0.4 ±0.05	±4	±1.6
	ration is smaller than 1 ′′ , this couple is difficult to ob-
	serve and the measurements are very scattered. Some
	of them are clearly aberrant. Even the measurement of
	1991.25 made by Hipparcos (ρ = 0 ′′ .14, θ = 316 • .8) is
	doubtful. Nearly all the most recent observations are
	from Alzner, but the angular position measurements
	are rather scattered.

c 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.an-journal.orgc 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

c 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.an-journal.org

Acknowledgements. We thank the members of the United States Naval Observatory, Washington DC, for kindly sending on request some lists of measurements of visual binaries. This work has made use of the "Fourth Catalogue of Interferometric Measurements of Binary Stars" (http://ad.usno. navy.mil/wds/int4), the "Sixth Catalogue of Orbits of Visual Binary Stars" (http://ad.usno.navy.mil/wds/orb6), the Washington Double Star Catalogue maintained at the U.S. Naval Observatory (http://ad.usno.navy.mil/ wds/wds) and the SIMBAD data base operated by the Centre de Données Astronomiques de Strasbourg (France).