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A&A 366, 868­872 (2001) DOI: 10.1051/0004-6361:20000298
c ESO 2001

Astronomy & Astrophysics

Binary star speckle measurements at Calar Alto. I.
J. A. Docob o1 , V. S. Tamazian1 , Yu. Yu. Balega2 , J. Blanco1 , A. F. Maximov2 , and V. A. Vasyuk
1

2

2

Astronomical Observatory Ramon Maria Aller, University of Santiago de Compostela. PO Box 197, Santiago de Compostela, Spain Special Astrophysical Observatory, Zelenchuk region, 369167, Russia

Received 24 May 2000 / Accepted 14 November 2000 Abstract. We present the first results of our speckle interferometric measurements of binary stars made with the ICCD speckle camera using the 1.52-m telescope of the Observatorio Astronomico Nacional at Calar Alto (Spain) in September, 1999. The data contain 123 observations of 83 systems. The measured angular separations range from 0. 153 to 6. 727. We have used there new speckle measurements to improve the orbital elements for the binaries COU 247 and BU 524 AB. Key words. binaries: visual ­ interferometry

1. Intro duction
At the present time, although the orbits for more than 1000 visual binaries are available, the study of orbital motion of visual and interferometric pairs remains an important astronomical discipline. Visual binaries are the key source of information about stellar masses and distances, while for the lower part of the main sequence they define practically our understanding of stellar physical properties. However, visual measurements of binaries with a filar micrometer are rarely performed today. In comparison with digital speckle interferometric methods, micrometric data show, in general, lower precision. They are also often associated with significant errors, which is especially true for small angular separations, 0. 1. By means of speckle interferometry, the Rayleigh resolution limit of 70 mas (0.07 arcsec) for a 1.5-m telescope can be routinely achieved. That is high enough to study the relative motion of the components of the most well known visual binary stars, in order to define the parameters of their orbits. Only for very close visual pairs are the larger apertures needed, but the lack of the observing time at large telescopes is the reason for rare and unsystematic binary star observations. Therefore, high quality speckle measurements, even with moderate size telescopes, can be an important source of data about the relative motion of the components in multiple star systems (Douglass et al. 1997). For these purposes a speckle interferometer with a photoncounting intensified CCD detector was developed in the Astronomical Observatory Ramon Maria Aller of the University of Santiago de Compostela, in cooperation with the Special Astrophysical Observatory (SAO) of the
Send offprint requests to : J. A. Docobo

Russian Academy of Sciences. The new instrument has been used for speckle observations of binary stars using the 1.52-m telescope at Calar Alto, in 1999. Below, we provide a brief description of the instrument and report on the first interferometric data obtained. Orbits of visual binaries Cou 247 and Bu 524 were improved using the new measurements.

2. Brief description of the sp eckle camera
The scheme of the instrument is essentially the same as for other speckle cameras in use today at several large telescopes. The main module contains a pair of interchangeable microscope ob jectives with magnifications 8в and 20в, which are necessary to sample the size of individual speckles (about 4 µ at 500 nm at the f/8 Cassegrain focus of the 1.52-m telescope) to a detector's pixel, with a size of 13.4 µ. The corresponding scale on the detector is 0.028 or 0.011 arcsec per pixel with total fields of view of 5.6 and 14.3 arcsec square. We normally use a 20в microscope objective; the 8в one is intended only for pointing at weak stars. In front of the microscope ob jective is the Uniblitz remote-controlled electronic shutter, which provides the exposure value in the range 5 to 40 ms. The shutter is synchronized with the CCD detector readout. An additional mirror, which can be installed in the beam in front of the shutter, sends light to the TV guidance camera for centering of an ob ject in the field of view. A combination of narrow-pass band interference filters and neutral density filters is used for wavelength selection. Data are routinely obtained through the 520/24-nm filter; however, a filter wheel assembly also includes 600/50-nm and 660/40-nm filters. A set of 4 zero mean deviation prisms, mounted on a rotation stage, is used for atmospheric dispersion compensation at different zenith angles. Each prism is


J. A. Docobo et al.: Calar Alto speckle interferometry

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designed to compensate for the atmospheric effect within a prescribed interval of zenith angle, while for the 20 radius from the zenith, the clear aperture is selected. The detector system consists of a PCO Computer Optics (Germany) Sensicam CCD camera with 1280(H ) в 1024(V ) pixels of 6.7 в 6.7 µm, optically coupled by means of a pair of f/1.5 transfer lenses to a 3-stage electrostatically focused image intensifier. The input 24-mm photocathode of the intensifier has an S-25 spectral response with a peak sensitivity of 12% at 510 nm, and about 2% sensitivity is still available at 800 nm. For faster readout we use the sampling of speckle images to 512 в 512 pixels. The dynamic range of the system is limited by the 12-bit digitization. Single photoelectron events are recorded by the system with a signal-to-noise ratio of about 30. Shorter exposures and narrower filters are utilized when bright stars are studied in an analogue readout mode. The data are transferred via optical fibers to a computer system and then onto Exabyte tapes. The system is capable of acquiring and storing 12-bit digitized data at a speed of 5 images per second.

Table 1. Orbital elements for COU 247 and BU 524 AB Star Author(s) P (years) T e a i masses COU 247 Blanco J. 280.00y 1990.21 0.426 0.846 124.9 21.3 47.1 2.9 M BU 524 AB Docobo­Vasyuk 31.528y ± 0.072y 1996.526 ± 0.014 0.753 ± 0.005 0.221 ± 0.003 121.0 ± 0.6 25.4 ± 0.6 265.0 ± 0.6 4.1 M ± 0.4 M

3. Observations and data reduction
The speckle camera has been primarily used for observations of binary stars at the Cassegrain focus of the 1.52-m telescope of the Observatorio Astronomico Nacional at Calar Alto, Spain. 83 pairs were observed between September 15 and 24, 1999, under a moderate seeing of 1 to 3 . For each binary, a typical observing procedure involved the accumulation of 1000 to 3000 short exposure images on Exabyte tapes. Calibration of our speckle data was accomplished only by observing wide binaries with very long orbital periods. A list of 10 pairs observed for calibration purpose on the 6-m telescope of SAO was used to define the orientation of the CCD with respect to the vertical. In addition, the detector orientation was checked by using star trails in right ascension with the magnification 8в. We could not use other calibration procedures because the telescope was not equipped with a slit mask and its focal length was not known to sufficient accuracy. The resulting value of the camera orientation error is less than 0.2 . Processing of speckle data is made in three steps. Firstly, for each speckle frame we make a flat-field photometric correction and geometric correction of field distortions caused by the image intensifier. Then, we compute the mean power spectrum of an ob ject following the standard Labeyrie procedure (1970). The average power spectrum is corrected for the photon noise bias. At the final stage, we compute a set of radial cross-sections through the power spectrum up to the diffraction cut-off frequency of the telescope and fit this with the model of a binary star spectrum to find the distance and position angle. From position measurements for pairs with at least 3 observations, we have found that the mean standard deviation in separation is 10 mas, while the error in position angle is 1 . With the present detector, we could observe binaries with

a secondary as faint as 10.5 magnitude. However, we expect that with an improved image intensifier and by using the cooling of the photocathode, the limiting magnitude will be near 13. Results of the measurements are given in Cols. (1) to (6) of Table 2. The first three columns list the Washington Double Star Catalogue coordinate (Worley & Douglass 1996), the name of the star or its catalogue number in common use and the discoverer designation. The fourth column gives the epoch of the observation in fractional Besselian year. The fifth and sixth columns contain the measured position angle in degrees and angular separation in arcseconds. The note "UR" denotes the cases when the binary was not resolved. This might indicate too close a companion (less than 70 mas), too large a magnitude difference (more than 3 magnitudes), very bad seeing, or any combination of these factors. Finally, the note "R" means the use of the red 660/40-nm filter.

4. New orbits
Using the measurements presented in this paper, the orbits of the systems COU 247 (WDS 00095+1907) and BU 524 AB (WDS 02537+3820) were revised, as announced previously in the IAU Commission 26 Information Circular Nos. 140 and 141, respectively. All available micrometric and speckle measurements, together with the analytical method of Docobo (1985), were used to compute the orbits shown in Figs. 1 and 2. Speckle data are indicated by dots, while O­C lines connect measures to their predicted locations on the orbit. For COU 247, visual measures are also included in the figure. The solid line connects the primary component, indicated by the cross, with the periastron position. In Table 1 the individual orbital parameters are given for each star: line 1 ­ star identification; line 2 ­ orbit author(s); lines 3 to 9 ­ new orbital elements; line 10 ­ total mass of the system obtained by combining new a and P values with the Hipparcos parallax (ESA 1997). Because the COU 247 orbit may be evaluated only as preliminary, no errors for the individual elements are given in the table. COU 247 The binarity of this star (V = 7.96, sp.type G3V) was discovered by P. Couteau in 1967. Jasinta (1996)


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J. A. Docobo et al.: Calar Alto speckle interferometry

Table 2. Speckle measurements on the 1.52-m telescope (also available at the CDS via anonymous ftp cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/366/868) Coord. 2000 00062+ 00095+ 00214+ 00318+ 00516+ 5826 1907 6700 5431 2237 Name/Catalog no. A DS +18 A DS A DS A DS 61 AB 0003 293 AB 434 AB 701 AB Discoverer designation STF 3062 COU 247 STT 6 STT 12 A 1808 STT 20 Epoch 1999.0+ 0.7259 0.7118 0.7232 0.7231 0.7119 0.7230 0.7229 0.7229 0.7254 0.7254 0.7280 0.7256 0.7285 0.7119 0.7230 0.7232 0.7259 0.7116 0.7116 0.7116 0.7119 0.7120 0.7228 0.7257 0.7094 0.7286 0.7230 0.7285 0.7121 0.7259 0.7285 0.7230 0.7228 0.7258 0.7286 0.7095 0.7121 0.7258 0.7229 0.7258 0.7096 0.7286 0.7286 0.7228 0.7258 0.7287 0.7095 0.7095 0.7095 0.7121 0.7121 0.7095 0.7123 0.7258 0.7124 ( ) 327.8 308.7 154.2 196.6 197.5 194.7 194.3 194.2 194.1 194.2 308.2 348.6 186.4 199.1 175.2 109.7 109.9 109.3 108.8 110.3 109.2 297.0 276.2 275.6 111.8 177.6 176.7 149.0 148.9 347.2 155.0 62.4 62.4 105.1 282.5 145.3 64.9 36.5 37.2 230.5 354.9 5.9 5.3 5.6 97.1 277.2 71.4 71.5 () 1.492 0.301 0.622 0.382 0.165 0.526 0.519 0.516 0.523 0.518 0.884 0.290 0.355 0.346 UR 1.148 0.301 0.290 0.301 0.302 0.303 0.310 0.229 UR 0.482 0.480 0.550 0.166 0.166 UR 0.288 0.282 0.726 0.331 1.037 1.033 UR 0.477 1.007 0.659 0.390 0.520 0.516 2.772 0.736 0.156 0.159 0.162 0.235 0.544 0.347 0.352 UR Note

UR

00546+1911

ADS 746 AB

00550+2338 00568+6022 00583+2124 00594-0040 01030+4723 01040+3528

A A A A A

D D D D D

S S S S S

755 784 805 819 862

A A A A A

B B B B B

STF 73 BU 1099 BU 302 A 1902 STT 21 HO 213

ADS 873 AB

R

R UR

01049+3649 01148+6056 01178+4901 01213+1132 01234+5809 01337-1213 01376-0924 01443+5732 01551+2847 01559+0151 01570+ 02039+ 02140+ 02231+ 02257+ 02280+ 3101 4220 4729 7021 6133 0158

ADS 883 AB ADS 999 AB ADS 1040 AB ADS 1097 AB ADS 1105 AB ADS 1223 AB -10 0343 ADS 1359 AB ADS 1522 AB ADS 1538 AB A DS A DS A DS +69 A DS +01 1548 1630 1709 0144 1833 0431 AB BC AB AB

A 1515 BU 1100 STF 102 BU 4 STF 115 HWE 4 KU I 7 BU 870 STF 183 STF 186 A 819 STT 38 STF 228 MLR 377 STF 257 KU I 8 STF 262 STT 43 STF 318

02290+6724 02407+2637 02537+3820

ADS 1860 AB ADS 2034 AB ADS 2200 AB

02586+2408 02589+2137 03054+2515 03096+0512

ADS 2246 AB ADS 2253 AB ADS 2336 AB ADS 2373 AB

BU 1173 BU 525 STF 346 A 2030


J. A. Docobo et al.: Calar Alto speckle interferometry Table 2. continued Coord. 2000 03280+2028 Name/Catalog no. ADS 2546 Aa Discoverer designation COU 260 Epoch 1999.0+ 0.7231 0.7231 0.7288 0.7230 0.7124 0.7124 0.7123 0.7261 0.7260 0.7234 0.7260 0.7260 0.7234 0.7260 0.7260 0.7277 0.7277 0.7251 0.7251 0.7251 0.7250 0.7250 0.7277 0.7277 0.7277 0.7278 0.7251 0.7114 0.7278 0.7250 0.7252 0.7252 0.7277 0.7277 0.7278 0.7280 0.7278 0.7252 0.7252 0.7279 0.7278 0.7279 0.7279 0.7115 0.7115 0.7279 0.7279 0.7280 0.7255 0.7256 0.7280 0.7116 0.7255 0.7255 0.7256 ( ) 24.9 24.2 24.9 163.8 353.1 351.8 211.9 210.8 328.7 77.4 78.4 79.1 150.9 150.5 149.9 104.9 318.6 () 0.245 0.252 0.247 6.727 0.349 0.344 0.156 0.155 0.220 0.236 0.237 0.228 0.362 0.359 0.357 4.844 0.537 Note

871

03280+2028 03284+6015 03503+2535 04263+3443 04512+1104

ADS 2546 AB ADS 2538 AB ADS 2799 ADS 3211 AB ADS 3475 AB

COU 260 A 980 STT 65 HU 609 BU 883

05056+2304

+22 0818

STT 97

R R

17146+1423 17239-0050 17563+0259 17575+1058 17584+0428 18031-0811 18055+0230 18339+5221 18355+2336 18386+1632 18594-1250 19110-0726 19159+2727

ADS 10418 AB ADS 10598 AB ADS 10899 AB ADS 10916 AB +04 3562 A DS A DS A DS A DS A DS -13 A DS A DS 11005 11046 11468 11479 11530 5172 12126 12239 A A A A A B B B B B

STF 2140 STF 2173 A 2189 BU 1299 KUI 84 STF 2262 STF 2272 A 1377 STT 359 HO 87 KUI 89 A 95 STT 371

UR UR 83.8 85.0 84.3 282.4 149.2 116.4 7.6 72.1 49.5 160.3 160.1 160.2 160.1 159.0 160.0 160.2 348.3 144.0 141.4 141.0 118.7 340.5 126.9 126.5 11.9 22.5 307.3 246.5 347.7 63.1 188.2 236.8 0.244 0.231 0.227 1.724 3.685 0.261 0.711 0.365 0.263 0.888 0.885 0.890 0.895 0.883 0.880 0.883 0.238 0.211 0.618 0.153 0.310 0.498 0.315 0.324 UR 0.346 2.348 1.915 0.338 0.192 0.288 1.919 0.490 UR

R

UR

AB AB

R R

19210+ 19459+ 19487+ 19487+ 19490+ 20203+ 20375+ 20396+

1909 5049 1504 3519 1909 3924 1436 0458

A DS A DS A DS A DS A DS A DS A DS +04 A DS +06 A DS A DS +16 A DS A DS A DS A DS +17

12336 13135 12961 12972 12973 13728 14073 4510 14412 4718 14889 15270 4612 15530 15902 15971 15992 4759

A A A A

B B B B

STF 2504 HU 687 A 1658 STT 387 AGC 11 A 1427 BU 151 KUI 99 A 751 KUI 102 STT 437 STF 2822 COU 14 HU 774 BU 172 STF 2909 HU 388 COU 234

UR

20537+5918 21001+0731 21208+3227 21441+2845 21501+1717 21597+4907 22241-0450 22288-0001 22302+2228 22307+1758

AB AB AB A A A A B B B B


872 Table 2. continued Coord. 2000 22402+ 23114+ 23126+ 23176+ 23340+ 3732 3813 0241 1818 3120

J. A. Docobo et al.: Calar Alto speckle interferometry

Name/Catalog no. A A A A A D D D D D S S S S S 16164 16576 16591 16650 16836 A A A A A B B B B B

Discoverer designation HO 188 HO 197 A 2298 HU 400 BU 720 A 643 AGC 14 BU 995 A 426 A 1498

23393+4543 23440+2922 23475+4650 23561+2520 23595+5441

ADS 16904 AB ADS 16957 AB ADS 17006 AB ADS 17105 AB ADS 17151 AB

Epoch 1999.0+ 0.7280 0.7282 0.7282 0.7120 0.7282 0.7255 0.7282 0.7117 0.7120 0.7118 0.7117 0.7117 0.7283

( ) 215.7 302.4 296.9 101.6 94.2 94.4 150.2 87.7 88.0 246.1 301.7 304.2 88.1

() 0.372 0.288 0.235 0.343 0.550 0.546 0.239 0.837 0.827 0.768 0.394 0.385 0.378

Note

Fig. 2. New visual orbit for BU 524 AB Acknow ledgements. The development of the speckle camera was entirely financed by the Secretaria Xeral de Investigacion e Desenvolvemento of the Xunta de Galicia (regional government of Galicia, Spain) on the basis of the Call for Proposals for Science Equipment in 1998. This work is a part of the Investigation Pro ject PGIDT99PXI24301B supported by the Xunta de Galicia. Authors thank Observatorio Astronomico Nacional for facilities made available at Calar Alto and Dr. V. Lanchares and P. Abelleira for their assistance with the observations.

Fig. 1. Preliminary orbit for COU 247

calculated the orbit with a period of 60.52 years. However, new speckle measurements indicate a longer period. Although the binary has completed only about 80 of orbital motion, the new orbital solution gives the dynamical parallax (15 mas), which is in agreement with the Hipparcos parallax value (13.8 mas). BU 524 AB Due to its short period, this bright binary star (V = 5.36, sp. type F4IV) has completed several revolutions since the discovery of its binary nature by S. W. Burnham in 1878. Nevertheless, the last orbit, calculated for the system by Aristidi et al. (1999), does not fit well with recent speckle measurements. We tried to adjust the orbital parameters to the latest speckle data, and with these improvements, the orbit seems to be almost definitive.

References
Aristidi, E., Prieur, J. L., Scardia, M., et al. 1999, A&AS, 545 Docobo, J. A. 1985, Celestial Mechan., 36, 143 Douglass, G. G., Hindsley, R. B., & Worley, C. E. 1997, 111, 289 ESA, 1997, The Hipparcos and Tycho catalogues (ESA 1200) Jasinta, D. M. D. 1996, A&AS, 118, 381 Labeyrie, A. 1970, A&A, 6, 85 Worley, C. E., & Douglass, G. G. 1996, The Washin Double Star Catalog (WDS), http://aries.usno.navy.mil/ad/wds/ 134,

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gton