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The Astronomical Journal, 135:1803­1809, 2008 May c 2008. The American Astronomical Society. All rights reserved. Printed in

doi:10.1088/0004-6256/135/5/1803
the U.S.A.

FIRST RESULTS OF THE OPTICAL SPECKLE INTERFEROMETRY WITH THE 3.5 m TELESCOPE AT CALAR ALTO (SPAIN): MEASUREMENTS AND ORBITS OF VISUAL BINARIES
1

J. A. Docobo1 , V. S. Tamazian1 , M. Andrade1 ,J.F.Ling1 , Y. Y. Balega2 , J. F. Lahulla3 , and A. A. Maximov

2

´ ´ Observatorio Astronomico Ramon Mar´ Aller, Universidade de Santiago de Compostela, Avenida das Ciencias s/n, 15782 Santiago de Compostela, Spain; ia oadoco@usc.es, oatamaz@usc.es, oandrade@usc.es, and oafana@usc.es 2 Special Astrophysical Observatory, N. Arkhyz, Karachai-Cherkesia 369167, Russia; max@sao.ru, balega@sao.ru 3 Observatorio Astronomico Nacional, c./ Alfonso XII, Madrid; lahulla@oan.es Received 2008 February 13; accepted 2008 March 9; published 2008 April 7

ABSTRACT ´ First results of the optical speckle interferometry carried out with the 3.5 m telescope of the Centro Astronomico ´ Hispano-Aleman (CAHA, Almer´ Spain) in 2005 July for visual binaries are presented. Fifty stars with separations ia, between 0. 058 and 2. 1 were observed. Two new (COU 490 and A 2257) and six improved orbits along with their systemic masses are calculated. The obtained dynamical parallaxes in conjunction with the overview of spectral and photometric data allowed us to make the first rough distance estimates for COU 490 (145 pc) and A 2257 (210 pc). Total masses of pairs with both new and improved orbits are given, being generally concordant with their known spectral types and photometric data. We conclude that high-quality optical speckle data on binaries with separations close to its diffraction limit can routinely be obtained with the 3.5 m telescope. Key words: astrometry ­ binaries: visual ­ stars: fundamental parameters

1. INTRODUCTION It is well known that speckle interferometry is one of the most effective techniques for high-angular-resolution observations of binary stars. The high-quality astrometric information obtained at different wavelengths and close to the diffraction limit of the telescopes is of vital importance in the determination of orbits and dynamical parameters of binary and multiple stars. In turn, determination of accurate orbits in binary systems represents a direct and reliable method for obtaining dynamical masses of stars. The knowledge of masses provides insight into the binary formation mechanisms and improves our understanding of the astrophysics in these systems. Using our optical ICCD speckle camera, we have performed several runs with the 1.52 m telescope of the Observato´ ´ rio Astronomico Nacional located at the Centro Astronomico ´ Hispano-Aleman (CAHA, Almer´ Spain). Detailed reports on ia, these campaigns can be found in Docobo et al. (2001, 2004, 2007). Furthermore, observational time has been requested with the 3.5 m telescope of CAHA, which would provide a theoretical resolution on an order of 0. 04 in optical wavelengths. First speckle observations with the 3.5 m telescope in standard near-IR (NIR) photometric bands were performed more than 20 years ago (Leinert & Haas 1987). As regards binaries, important results on their studies have been obtained on the basis of NIR speckle data (Woitas et al. 2001, 2003 and references therein). On the other hand, due to a 2­4 times higher resolution at optical wavelengths, much closer pairs can be resolved with this telescope. Hence, optical speckle interferometry should provide data for closest pairs that cannot be resolved in the NIR bands. Besides this, a number of wider pairs at the critical points of the orbit such as periastron passage and/or minimal apparent separation can also be observed. In the paper, the results of our first campaign of speckle interferometric observations of 50 double stars are presented. New orbits for COU 490 and A 2257 as well as improved ones for six other binaries are reported. Systemic masses for all pairs and first distance estimates for COU 490 and A 2257 are presented. 1803

2. OBSERVATIONS The speckle camera, observation techniques, and reduction procedure are similar to those of previous runs at CAHA extensively described in Docobo et al. (2001, 2004, 2007) except for the scale of 5. 89 mm-1 at the F/10 Cassegrain focus of the 3.5 m telescope, to which the camera was attached. Correspondingly, the total field of view was about 2. 5 and the pixel scale was about 0. 0046 pix-1 . The scale and detector orientation angle used to convert separation and position angle to their final values were 4.084 ± 0.036 mas pix-1 and -1 16 ± . 0 41 respectively. The observations were routinely performed . using the 520/24 nm filter and 20â magnification of the microscope objective. In contrast with previous runs, data reduction was accomplished by taking advantage of the data storage and computing services of the Supercomputing Center of Galicia (CESGA). With this aim, we have extensively used the Galician Virtual Supercomputer (SVG) system which comprises 200 Intel Pentium III/4 processors with a peak performance of 528 Gflops running under Linux OS. A large amount of processing time was saved, and we hope it can be further shortened in the future. Calibration was done by observing binaries with high-quality orbits taken from the list of calibration stars (CS) catalog supplied with the 2005 version of the Sixth Catalog of Orbits of Visual Binary Stars (Hartkopf & Mason 2008). In addition, the detector orientation was checked by using star trails in right ascension. We could not use other calibration procedures because the telescope is not equipped with a slit mask. The use of an autocorrelation function introduces a 180 ambiguity in the position angle determination. As a rule, we overcame this by stipulating new measurements to be compatible with previously known data. We assigned relative weights to each astrometric observation based on the telescope aperture and observing technique. The weighting scheme described in Docobo & Ling (2003) and Mason et al. (1999) for visual and speckle data respectively was applied. In all, astrometric data for 50 stars were obtained under good seeing conditions between 1. 1 and 1. 5. They are presented in


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Table 1 Speckle Measurements WDS 13100+1732 14138+3059 14234+0827 15136+3453 15232+3017 15360+3948 15390+2545 15420+4203 16044-1122 16059+1041 16079+1425 16198+2647 16254+3724 16283-1613 16413+3136 16450+2928 16584+3943 17005+0635 17080+3556 17240-0921 17304-0104 17563+0259 18035+4032 18044+0337 18086+1838 18301+0404 18443+3940 19266+2719 19394+2215 19411+1349 19553-0644 20151+3742 20216+1930 20231+3342 20311+3333 20312+1116 20325-1637 20375+1436 20494+1124 21119+2524 21145+1000 21435+4448 21435+4448 21446+2539 21501+1717 21597+4907 22281+1215 22409+1433 23052-0742 23529-0309 ADS 8804 9247 9547 9617 9716 Name STF 1728 AB COU 606 BU 1111 BC HO 60 STF 1937 AB STT 298 AB COU 612 COU 1445 STF 1998 AB HDS 2273 Aa A 1798 A 225 CHR 55 RST 3950 STF 2084 COU 490 COU 1289 CHR 59 HU 1176 AB RST 3972 STF 2173 A 2189 COU 1785 A 2257 HU 314 CHR 72 Aa CHR 77 Cc STF 2525 STF 2556 KUI 93 STF 2597 AB COU 2416 COU 327 AB COU 1949 COU 1962 CHR 99 Aa SEE 512 BU 151 AB J 194 AB COU 643 STT 535 AB HO 167 AB LIN 1 Aa BU 989 AB COU 14 HU 774 BU 701 AB HO 296 AB A 417 AB FIN 359 2005.0+ 0.5232 0.5179 0.5232 0.5179 0.5178 0.5204 0.5233 0.5152 0.5205 0.5232 0.5180 0.5179 0.5152 0.5205 0.5151 0.5206 0.5153 0.5206 0.5206 0.5234 0.5180 0.5235 0.5154 0.5181 0.5235 0.5182 0.5155 0.5208 0.5154 0.5183 0.5209 0.5183 0.5156 0.5210 0.5184 0.5237 0.5238 0.5156 0.5212 0.5157 0.5184 0.5157 0.5157 0.5239 0.5159 0.5158 0.5240 0.5213 0.5213 0.5241 ( ) 13.0 346.7: 274.9 76.2 115.0 172.8 187.5 203.6 343.0 191.1 356.6 301.1 144.7 84.3 222.5 313.7 265.5 238.6 55.3 51.8: 175.7 250.7 348.6 27.6 81.0 42.5: 224.5: 291.0 358.0 313.9 102.8 100.0 237.7 76.6: 60.9 137.2 145.1 1.3 337.7 102.1 33.9 202.1 192.9: 240.4 327.8 174.6 186.3 117.1 315.9 45.4 ( ) 0.4 3.0 0.4 0.4 0.4 0.4 0.4 0.5 0.4 0.4 0.4 0.5 0.5 0.5 0.6 0.5 0.6 0.4 0.4 2.6 0.4 0.5 0.6 0.5 0.4 0.6 1.7 0.4 0.4 0.4 0.4 0.4 0.4 1.3 0.6 0.4 0.5 0.4 0.4 0.6 0.4 0.6 1.1 0.4 0.4 0.4 0.4 0.4 0.5 0.4 ( ) 0.465 0.162 0.186 0.146 0.507 0.888 0.286 0.084 0.725 0.451 0.179 0.068 0.096 0.204 0.919 0.140 0.087 0.162 0.078 0.064 0.314 0.074 0.069 0.148 0.276 0.103 0.058 2.100 0.370 0.187 0.526 0.214 0.103 0.209 0.085 0.397 0.120 0.573 0.645 0.222 0.179 1.135 0.183 0.105 0.148 0.198 0.948 0.141 0.086 0.091 : ( ) 0.004 0.020 0.002 0.001 0.005 0.008 0.003 0.001 0.006 0.004 0.002 0.001 0.001 0.002 0.008 0.002 0.002 0.002 0.001 0.012 0.003 0.001 0.001 0.002 0.003 0.002 0.001 0.019 0.003 0.002 0.005 0.003 0.001 0.002 0.002 0.004 0.001 0.005 0.006 0.003 0.002 0.015 0.011 0.001 0.001 0.002 0.008 0.001 0.001 0.001 CS c c c c
a

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9909 9931 10007

c

10157

c

10360 10598 10899 11033 11098 11399 11635 Cc 12447 12752 13104

:

c

: :

c c c

:

13946 13961 14073 14333 14773 15264 15281 15530 15962 16173 16497

c

c

:

c

c c

Note. a Calibration stars.

Table 1, where the first four columns list identifications from the Washington Double Star catalog (WDS; Mason et al. 2006), Aitken's catalog of double stars (ADS; Aitken & Doolittle 1932), the name of the couple and the epoch of observation in fractions of the Besselian year. The next columns give position angle and angular separation with their corresponding errors, and the last column indicates the CS. A colon stands for uncertain measurements coinciding with a relatively large magnitude difference between components ( 3 mag). An overview of the data presented in Table 1 shows that a wide range of separations between 0. 058 and 2. 100 has been covered. However, seeing conditions were not good enough to

reach diffraction-limited resolution, which we hope to achieve during further runs. In general, the observations confirm that high-quality optical speckle interferometry data can be obtained with the 3.5 m telescope of CAHA. In view of the successful results, we intend to use this telescope for follow-up observations of close binary and multiple systems of special astrophysical interest. 3. ORBITS AND SYSTEMIC MASSES For a number of stars, the measurements show a systematic departure of positions from those predicted by previous orbital


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MEASUREMENTS AND ORBITS OF VISUAL BINARIES
Table 2 Orbital Elements

1805

Star WDS 14138+3059 16198+2647 16450+2928 17563+0259 18035+4032 18044+0337 20151+3742 20216+1930 P (yr) 25.91 43.34 100.1 154.5 45.72 333. 52.26 42.46 ± ± ± ± ± ± ± ± 0.30 1.68 5.0 4.0 0.50 20. 5.00 1.00 T 2010.57 2005.90 2007.34 1976.35 1995.00 1988.73 1995.83 1986.60 ± ± ± ± ± ± ± ± 0.20 0.54 3.50 0.35 0.50 0.06 0.10 0.10 0.347 0.489 0.151 0.496 0.483 0.829 0.432 0.577 e ± ± ± ± ± ± ± ± 0.015 0.038 0.006 0.014 0.003 0.006 0.040 0.003

Orbital elements a( ) 0.183 0.129 0.218 0.218 0.135 0.324 0.211 0.147 ± ± ± ± ± ± ± ± 0.001 0.003 0.008 0.002 0.002 0.015 0.008 0.002 i ( ) 147.5 114.4 130.1 71.7 65.7 73.5 36.9 85.0 ± ± ± ± ± ± ± ± 1.5 1.0 1.5 1.0 1.0 1.0 3.0 0.5 ( ) 48.3 117.5 1.7 153.3 52.8 13.6 89.4 68.0 ± ± ± ± ± ± ± ± 3.0 1.0 2.0 1.0 1.0 1.0 1.0 0.5 ( ) 175.8 183.1 68.8 327.6 147.0 274.3 255.7 303.0 ± ± ± ± ± ± ± ± 4.0 2.3 11.2 2.0 3.0 2.0 1.0 1.0

Table 3 Systemic Masses WDS 14138+3059 16198+2647 16450+2928 17563+0259 18035+4032 18044+0337 20151+3742 20216+1930 m1 10.7 10.0 8.8 8.5 8.7 9.8 8.0 9.1 m2 11.3 9.8 8.8 8.8 8.9 10.0 8.5 9.1 Sp. type M0 G5 F2 * A5* F5 F2 * F0 F8 0 0 0 0 0 0 0 .01721 .00764 .00694 .00475 .00732 .00473 .01069 0.008 ( ) ± ± ± ± ± ± ± ± 0 0 0 0 0 0 0 0 .00163 .00126 .00010 .00015 .00010 .00020 .00030 .002c
a a b b b b b

Commission 26 Information Circular (CI) number, where they were announced, are given.
Systemic mass (M ) 1 2 3 4 3 2 2 3 .8 .6 .1 .1 .0 .9 .8 .0 ± ± ± ± ± ± ± ± 0 1 0 0 0 0 0 0 .5 .3 .5 .5 .6 .6 .7 .7

4.1. COU 606 (WDS 14138+3059), Docobo & Ling (2006), CI 160 According to our 2005.518 measurement, the orbit of this pair of red dwarfs has a slightly larger period than that reported by Docobo & Ling (2003). At present, speckle observations already cover 75% of orbit and show that a big part of visual observations located in the first quadrant have possibly too small separations. The dynamical parallax of 0. 0183 obtained by application of Baize­Romani's method (hereinafter BRM, Baize & Romani 1946; Heintz 1978, p. 62) lies within the 1 margin of the Hipparcos value. 4.2. A 225 (WDS 16198+2647), Andrade (2006), CI 160 This binary system, with apparent magnitudes of 10.04 and 9.79, was first resolved in 1901 by Aitken (1902). Although it has already completed about two revolutions since its discovery, until recently the set of available measurements from 1901 to 1991 covered an orbital arc of only 50 . During our observational run, we obtained a new measurement placed at the opposite side of orbit and very close to the periastron. The previous orbit was calculated by Heintz (1982), who obtained a period of 44.0 yr, a semi-major axis of 0. 113, and an eccentricity of 0.64. Our measurement gives residuals of -5 3 . and 0. 030 in position angle and angular separation, respectively. Using our near-periastron measurement, a new, less eccentric orbit (see Table 2), was calculated. Dynamical parallax of 0. 00787 and component masses of 1.14 M and 1.21 M are obtained by using BRM. In good agreement with these results, the parallax 0. 00764 ± 0. 00126 measured by Hipparcos leads to a semi-major axis of 16.9 ± 2.9 AU and a total mass of 2.6 ± 1.3 M (95.7% of uncertainty is caused by the large uncertainty of the Hipparcos parallax). According to Heintz (1982), who obtained the same mean value, the computed dynamical mass suggests an evolved pair. 4.3. COU 490 (WDS 16450+2928), Docobo & Tamazian (2007), CI 161 The apparent brightness of 8.8 mag and spectral type F5 for either component of this star in the catalog of Couteau (1999) is reported. While not included in the Hipparcos main catalog (ESA 1997), COU 490 appears in the Tycho-2 Spectral Type Catalog (Wright et al. 2003) with almost the same brightness V = 8.66 and B - V = 0.40 mag. At the same time, infrared colors J - H = 0.16 and H - K = 0.03 mag taken from the Two Micron All Sky Survey (2MASS Catalog; Cutri et al. 2003) suggest a somewhat earlier spectral type F0­F2V when

Notes. Apparent magnitudes and spectral types are taken from WDS except for spectral types (marked with an asterisk) taken from Wright et al. (2003)(see comments to individual objects in the text). a Hipparcos parallax. b Dynamical parallax. c Estimated parallax.

solutions. The method of Docobo (1985) was used in orbital calculations. With the aim of better adjusting the orbits to the observations, we improved them for six binaries. Besides this, the first orbits for COU 490 and A 2257 were calculated. Orbital elements for these eight stars are given in Table 2, and orbits are graphically represented in Figure 1 where our latest 3.5 m measurements are enclosed in a circle. All orbits were previously announced in the IAU Commission 26 Information Circulars No. 160, 161, and 162. It is worth noting that new measurements, used to calculate or to improve the orbits, are generally situated close to periastron, near the position of minimal apparent separation or scarcely observed parts of orbits. This shows that observations were carried out at critical points of their apparent orbit. Systemic masses for all pairs with newly calculated or improved orbits are presented in Table 3, which also contains data on apparent visual brightness of the components and combined spectral type of each star. For the six improved orbits, the obtained masses do not significantly differ from previously known values in spite of sometimes sensible changes both in the semi-major axis and the period of orbit for a given star. The weighted root mean squares (rms) and absolute means (AM) of (O ­C ) residuals in and are given in Table 4 both for the last known orbits and those reported in this paper in order to access numerically their characteristics. Finally, Table 5 contains ephemeris until 2018. 4. COMMENTS ON INDIVIDUAL STARS We now present brief comments on stars with either newly calculated or improved orbits. The authors of orbit and IAU


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WDS 16198+2647 A 225 0.2

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0.2

0.15

0.1

0.1

0
0.05

-0.1
0

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E N -0.2 -0.1 0 0.1 0.2
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E -0.05 N -0.15 -0.1 -0.05 0 0.05 0.1

0.2 WDS 16450+2928 COU 490 0.1

WDS17563+0259 A 2189 0.1

0.0

0.0

-0.1

-0.1

E
E

N -0.2 -0.2 -0.1 0.0 0.1 0.2

-0.2 N -0.1 0.0 0.1 0.2 0.3

Figure 1. Apparent orbits of stars (the scale on both axes is in arcseconds). Each measurement is connected to its predicted position by an O ­C line. The dashed line passing through the primary star is the line of nodes. The points and stars represent visual and speckle measurements respectively, and the arrow shows the direction of orbital motion. Latest measurements presented in this paper are enclosed in circles.

compared with standard colors of stars on the main sequence (Bessell & Brett 1988; Ducati et al. 2001). Adopting an F2V spectral type and hence a luminosity M = +3.0 (Gray 2005, p. 506), we obtain a rough estimate for its spectroscopic distance equal to 145 pc (or parallax = 0. 00692). By a direct application of Kepler's third law, a total mass of the system 3.12 M is then being obtained, in a good accordance with the standard mass of a F2 dwarf (1.56 M , Gray 2005, p. 506). Notably, the application of BRM to this pair leads to dynamical parallax of 0. 00694 (144 pc) and total mass of 3.1 M . Therefore, an approximate distance of 145 pc is a robust and reliable estimate for COU 490. Due to a large dispersion of visual observations, more speckle measurements are needed in order to obtain a more reliable orbit. Our measurement contributes to this objective, being separated from previous ones by a large arc of more than 40 .

4.4. A 2189 (WDS 17563+0259), Docobo & Tamazian (2006), CI 160 The combined spectral type of this star is A5 IV/V (Wright et al. 2003), and the component brightnesses are 8.5 and 8.8 mag (Mason et al. 2006). The Hipparcos parallax is poorly determined (0. 00367 ± 0. 00112), and its application to our orbit leads to a total mass of 8.8 ± 8.1 M . Apart from having a very large relative error, such a mass is unacceptably large for a couple of A dwarfs. By applying BRM, we obtain dynamical parallax 0. 00475 ± 0. 0005 and reasonable masses for its components of 2.1 M and 2.0 M , in good agreement with standard calibration (Gray 2005, p. 506). Thus, we suggest the use of dynamical parallax as a more reliable distance estimate for this star (220 pc). Note that six speckle measurements of this system allowed us to adjust the orbit after the periastron passage. Two visual measurements at epochs 1967.42 and 1967.47 were not taken into account in


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0.2 WDS 18035+4032 COU 1785 0.15

MEASUREMENTS AND ORBITS OF VISUAL BINARIES

1807

0.1

0.2 WDS 18044+0337 A 2257 0.15

0.05

0.1
0

0.05
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E -0.1 N -0.05 0 0.05 0.1 0.15

E N -0.2 -0.1
WDS 20216+1930 COU 327 AB 0.1

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WDS 20151+3742 COU 2416

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-0.15 E

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Figure 1. (Continued)

orbital or in rms and absolute means computation since they give residuals in of 0. 122 and 0. 117, respectively. The previous orbit of Docobo & Costa (1991) gives almost equal values. 4.5. COU 1785 (WDS 18035+4032), Docobo & Ling (2007a), CI 161 Our 2005.515 measurement and that obtained at 1995.611 by Hartkopf et al. (1997) comprise the part of orbit where no speckle measurements have yet been performed. Therefore, a much more reliable orbit can be computed due to these measurements. The rms of (O ­C ) residuals both in and are significantly improved (see Table 4) in comparison with the previous solution (Docobo & Ling 2003). There is no Hipparcos parallax for this star, and the systemic mass of 3.0 M obtained on the basis of its dynam-

ical parallax (0. 00732) is consistent with a pair of F5 type dwarfs. A parallax of 0. 01660 ± 0. 00569 is given in the catalog of Kharchenko (2001). This value leads to a total mass of 0.26 M , which is completely unrealistic for such spectral types. 4.6. A 2257 (WDS 18044+0337), Docobo & Tamazian (2007), CI 161 This star is not included in the Hipparcos main catalog. The WDS catalog gives brightness 9.8 mag and 10.0 mag for its main and secondary components respectively, and combined spectral type F5, whereas the Tycho-2 Spectral Type Catalog (Wright et al. 2003) assigns the F2/3 spectral type and B - V = 0.425 mag to this star. Infrared colors J - H = 0.19 and H - K = 0.02 mag taken from the 2MASS (Cutri et al. 2003)


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Table 4 Statistical Results WDS 14138+3059 Authors ( ) Docobo & Ling; this paper Docobo & Ling (2003) Ling (1992) Andrade; this paper Heintz (1982) Docobo & Tamazian; this paper Docobo & Tamazian; this paper Docobo & Costa (1991) Docobo & Ling; this paper Docobo & Ling (2003) Docobo & Ling (2002) Couteau (1999) Docobo & Tamazian; this paper Docobo & Ling; this paper Docobo & Ling (2003) Mante (1999) Couteau (1999) Docobo & Ling; this paper Docobo & Ling (2003) Docobo & Ling (2000) Tokovinin (1994) Table 5 Ephemerides Epoch/WDS 2008.0 2009.0 2010.0 2011.0 2012.0 2013.0 2014.0 2015.0 2016.0 2017.0 2018.0 14138+3059 298.7 273.1 246.7 220.8 195.4 170.7 148.3 129.3 113.9 101.4 91.1 0.123 0.118 0.119 0.120 0.121 0.124 0.133 0.147 0.163 0.181 0.197 16198+2647 266.0 240.9 208.4 181.1 164.0 153.4 146.6 141.4 137.5 134.4 131.8 0.050 0.041 0.039 0.048 0.062 0.077 0.092 0.107 0.120 0.133 0.144 16450+2928 298.4 291.5 284.2 276.7 269.2 261.8 254.6 247.9 241.5 235.7 230.3 0.127 0.124 0.121 0.120 0.121 0.122 0.125 0.129 0.134 0.139 0.145 17563+0259 264.4 268.9 273.0 276.7 280.1 283.1 285.9 288.4 290.7 292.8 294.7 0.080 0.084 0.088 0.092 0.097 0.102 0.107 0.112 0.118 0.123 0.128 18035+4032 18044+0337 8.5 13.8 18.2 21.9 25.0 27.8 30.2 32.4 34.5 36.3 38.1 0.094 0.104 0.114 0.123 0.133 0.141 0.149 0.157 0.163 0.169 0.174 27.7 28.4 29.1 29.8 30.5 31.1 31.8 32.4 33.0 33.7 34.3 0.157 0.159 0.161 0.163 0.165 0.166 0.168 0.169 0.171 0.172 0.173 20151+3742 110.8 114.9 118.8 122.6 126.3 129.9 133.5 137.0 140.5 144.0 147.5 0.230 0.235 0.240 0.243 0.246 0.248 0.250 0.251 0.251 0.251 0.251 20216+1930 240.5 241.2 241.9 242.5 243.0 243.5 244.0 244.4 244.8 245.3 245.7 0.129 0.138 0.146 0.153 0.159 0.165 0.169 0.172 0.174 0.175 0.174 3.0 8.2 8.1 3.0 8.2 3.7 4.8 5.6 3 18 14 13 .6 .1 .7 .3 rms ( ) 0.021 0.016 0.018 0.021 0.016 0.016 0.011 0.011 0 0 0 0 .012 .022 .015 .019 ( ) 1.4 3.8 3.9 1.4 3.8 1.9 2.9 3.7 2.7 8.1 7.4 9.3 2.0 1.6 6.7 10.5 17.8 4.3 4.6 4.4 4.9 AM ( ) 0.011 0.014 0.016 0.011 0.014 0.008 0.005 0.006 0 0 0 0 .008 .013 .012 .016

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2.8 2.6 10.7 14.4 31.6 6.0 6.2 5.8 6.0

0.029 0.013 0.016 0.046 0.024 0.023 0.021 0.030 0.032

0.021 0.008 0.011 0.033 0.017 0.017 0.015 0.025 0.025

20216+1930

Note. Position angles and angular separations are given in degrees and arcseconds respectively.

are fully concordant with standard values for F2 dwarfs (Bessell &Brett 1988; Ducati et al. 2001). The application of BRM (assuming combined spectral type F2V) leads to dynamical parallax dyn = 0. 00473 (distance 210 pc) and a dynamical mass of 2.9 M . Thus, by its physical characteristics the components of A 2257 are similar to those of COU 490 which is situated at somewhat lesser distance. More speckle measurements are needed in the future to better define the part of the orbit close to periastron. 4.7. COU 2416 (WDS 20151+3742), Docobo & Ling (2007b), CI 162 Our new 2005.518 observation demonstrates that, at this epoch, the secondary companion is situated at the position opposite to the first visual measurements. Along with the speckle measurement of Hartkopf et al. (2000) at 1996.699, this allowed us to improve significantly the previous solution (Docobo & Ling 2003).

4.8. COU 327 AB (WDS 20216+1930), Docobo & Ling (2007a), CI 161 Taking into account its spectral type, the most probable mass of this triple system is 3.3 ± 0.7 M (component A is itself a single-lined spectroscopic binary). Presented in this paper, the orbit based on our latest speckle measurement at epoch 2005.516 improves on the previous one (Docobo & Ling 2003). Yet it suggests that parallax of this star should be slightly larger (possibly about 0. 008) than that measured by Hipparcos (0. 00455), unless another star exists in this system. The authors thank the CAHA Administration and staff for technical assistance. The authors wish to thank the Administration of the Supercomputing Center of Galicia (CESGA) for providing access to its facilities. This paper was financed by research projects AYA2004-07003 and AYA2007-67324 of ´ Spanish Ministerio de Educacion y Ciencia and PGIDIT06


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MEASUREMENTS AND ORBITS OF VISUAL BINARIES

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PXIB243031PR of Xunta de Galicia. This research made use of the Washington Double Star Catalogs maintained at the U.S. Naval Observatory and SIDONIe Database maintained at the Nice-Cote d'Azur Observatory (France). ^ REFERENCES
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