Vol. 17 No. 1 January 1, 2021 Journal of Double Star Observations Page 27 Double Star Measurements at the Southern Sky with a 50 cm Reflector in 2019 Rainer Anton Altenholz/Kiel, Germany rainer.anton”at”ki.comcity.de Abstract: Recordings of 82 double and multiple systems, in total 92 pairs, were made with a fast CMOS camera attached to a 50 cm reflector, and were analyzed with “lucky imag- ing”. The scale was calibrated with reference systems, which were selected for the amount and precision of literature data, including from Gaia, so as to obtain trustworthy extrapolations to the epoch of own measurements. In particular, a number of binaries was found to fulfill this criterion, while other pairs exhibited more or less significant deviations from hitherto assumed orbits. A number of interesting systems are discussed in some detail, and a few images are also presented. Introduction measurements [4]), by data from Gaia DR2, and by the The telescope is of Ritchey-Chrétien type, and is recently revised ephemeris [Izm, 5]. Fourteen more maintained at the “Internationale Amateursternwarte” binaries were found, with separations between one and in Namibia, where I have already used it repeatedly in ten arcsec, with similarly trustworthy data, including the past [3]. The primary focal length of 4.1 m was from Gaia, so as to serve as reference. In two cases, extended by a 2x Barlow lens, resulting in an f-ratio of alpha Cen and gamma Vir, stars are too bright for about f/12. For any pair, series of up to 2000 images Gaia, but their orbits are well-known. The image scale each were recorded with a monochrome CMOS cam- was obtained in an iterative way by measuring all 15 era of type QHY5 III 178 M, with pixels of size 2.4 pairs and adjusting the calibration factor by minimiz- arcsec square. In some cases, the color version of the ing the mean value of the residuals, as well as their same type of camera was used instead. When using the standard deviation. The latter resulted in ±0.003 arcsec, monochrome version, a near infrared filter was insert- within a range of ±0.005 arcsec, which is then taken as ed, which reduces seeing effects, as well as chromatic standard error margin of the measurements. However, aberrations of the Barlow lens. Exposure times ranged in practice, it can actually be greater under bad seeing from less than a millisecond up to some tens of milli- conditions. seconds, depending on the star brightness, and on the The calibrated measurements of all 92 pairs are seeing. The resolution was 0.0665 arcsec/pixel, which listed in Table 1. Names, nominal coordinates, and was determined by calibration with reference systems, magnitudes are adopted from the WDS [6]. As many of as was mentioned above, and is described below. Be- the pairs are binaries, residuals mostly refer to actual fore stacking, the images were re-sampled 2x2 or 4x4, ephemeris data [5], or to trustworthy extrapolations of which resulted in smoothening of the intensity profiles literature data, if not otherwise noticed. In several cas- and better definition of the peak centroids. Position es, no reasonable residuals could be given, because of angles were measured by reference to star trails, which a dearth of data, and/or too large scatter. In figure 2, were recorded while the telescope drive was switched residuals of own measurements are plotted versus rho. off. Residuals of the 15 calibration systems are indicated with full symbols, see above. Residuals of other pairs Results either result from statistical errors of measurements, Figures 1 a and b illustrate the procedure of cali- own and/or in the literature, or from systematic devia- bration of the image scale. The binary STF2272 (70 tions from ephemeris data. Exceptionally large values Ophiuchi) was chosen because of the virtually unam- of the latter are marked with their RA numbers. Indi- biguous evolution with time of both the position angle vidual remarks are listed in the notes following table 1 PA and the separation rho. This is documented by in order of RA values for identification. many literature data with low scatter (mostly speckle Received December 2, 2020 Vol. 17 No. 1 January 1, 2021 Journal of Double Star Observations Page 28 Double Star Measurements at the Southern Sky with a 50 cm Reflector in 2019 Figure 1: Evolution with time of the position angle PA (a, left), and of the separation rho (b, right) of the binary STF 2272 (70 Oph). Blue rhombs: speckle data [4], black squares: data from the WDS catalog [6], green star: position from Gaia DR2, circles in magenta: own measurements (since 2007, each after calibration as described in the text), red curves: ephemeris from Izmailov 2019 [5]. Figure 2: Plots of the residuals of own measurements. Semi-logarithmic scaling. Left: delta rho versus rho. Right: delta PA versus rho. Residuals of the 15 calibration pairs are indicated with full symbols. Symbols with crosses mark pairs with systematic deviations from ephemeris data. Numbers refer to notes following table 1. PAIR RA + Dec MAGS AP rho Date N delta PA delta rho COP 1 09 30.7 -40 28 3.91 5.12 31.231 0.958 2019.405 1 0.16 -0.007 * AC 5 AB 09 52.5 -08 06 5.43 6.41 17273 0.494 2019.405 1 0.50 0.005 I 173 10 06.2 -47 22 5.32 7.10 33213 0.973 2019.405 1 0.20 -0.005 I 13 AB 10 09.5 -68 41 6.63 6.47 33.213 0.562 2019.405 1 -0.86 0.002 BU 411 10 36.1 -26 41 6.68 7.77 1312.3 1.327 2019.416 1 -0.10 -0.001 I 860 AB 10 42.0 -63 30 8.01 8.14 .93253 0.444 2019.405 1 -- -- I 294 10 45.3 -80 28 6.15 6.49 052.3 0.831 2019.433 1 -- -- R 155 10 46.8 -49 25 2.82 5.65 902.3 2.287 2019.405 1 -0.40 -0.025 BSO 5 11 24.7 -61 39 7.68 8.76 ..0203 7.737 2019.399 1 -0.10 -0.001 I 78 11 33.6 -40 35 6.13 6.16 331213 0.486 2019.405 1 -- -- I 422 7.10 7.42 3312.3 0.350 1 -4.40 0.021 AB 11 38.3 -63 22 2019.405 AC 7.10 9.91 9237 1.658 1 -- -- HLD 114 11 55.0 -56 06 7.60 7.81 310213 3.868 2019.438 1 0.20 -0.002 Vol. 17 No. 1 January 1, 2021 Journal of Double Star Observations Page 29 Double Star Measurements at the Southern Sky with a 50 cm Reflector in 2019 SEE 143 12 03.6 -39 01 7.05 7.65 1.72.3 0.343 2019.405 2 -0.36 0.012 HJ 4498 AB 12 06.4 -65 43 6.13 7.74 95233 8.769 2019.405 1 0.10 -0.002 BU 920 Crv 12 15.8 -23 21 6.86 8.22 1372.3 1.978 2019.438 1 0.10 0.010 BSO 8 12 24.9 -58 07 7.84 7.98 11.203 5.223 2019.405 1 0.15 -0.003 DUN 252 AB 1.25 1.55 333237 3.841 1 -- -- 12 26.6 -63 06 2019.405 A-C 1.25 4.80 .3.237 89.544 1 -- -- CPO 12 AB 12 28.3 -61 46 7.32 8.24 30.2.3 2.092 2019.438 1 0.30 0.009 HJ 4539 AB * 12 41.5 -48 58 2.82 2.88 11231 0.341 2019.42 3 0.61 0.003 STF 1670 AB 12 41.7 -01 27 3.48 3.53 1972.3 2.852 2019.405 1 -0.50 0.002 R 207 AB 12 46.3 -68 07 3.52 3.98 97259 0.956 2019.405 2 0.20 0.004 RST 2819 12 55.0 -85 07 5.94 6.86 ..32.3 0.662 2019.433 1 -0.10 -0.033 I 83 12 56.7 -47 41 7.39 7.68 .17213 0.838 2019.399 1 1.00 -0.003 R 213 13 07.4 -59 52 6.59 7.04 35213 0.643 2019.405 1 -- -- I 424 A-C 13 12.3 -59 55 4.8 8.4 3.2.3 1.911 2019.405 1 -0.40 6E-4 I 1227 13 13.4 -50 42 6.56 6.78 31123 0.365 2019.405 1 0.80 0.013 * I 298 13 32.5 -69 14 7.36 8.54 393233 0.507 2019.438 1 4.80 0.072 STF 1757 AB 13 34.3 -00 19 7.82 8.75 3..233 1.645 2019.405 1 0.30 0 BU 932 AB * 13 34.7 -13 13 6.30 7.29 11253 0.429 2019.405 1 0 0.004 HWE 95 13 43.8 -40 11 7.51 7.85 3092.3 0.899 2019.438 1 0.40 0.009 STF 1781 13 46.1 +05 07 7.89 8.10 357233 1.030 2019.405 1 -0.70 -0.005 HWE 28 AB 6.27 6.38 13123. 1.011 3 0.06 0.001 H V 124 AE 13 53.5 -35 40 6.27 8.65 72.. 68.22 2019.42 1 0.15 0.025 BE 6.38 8.65 7253 67.58 1 0.18 -0.014 STF 1788 13 55.0 -08 04 6.68 7.26 333253 3.740 2019.438 1 -0.20 0.080 SLR 19 14 07.7 -49 52 7.14 7.38 1132.3 1.029 2019.399 1 0.25 -0.011 STF 1819 AB 14 15.3 +03 08 7.73 7.92 390203 0.888 2019.405 1 -- -- RHD 1 14 39.6 -60 50 -0.01 1.33 1.32.3 5.150 2019.41 2 0.80 0.004 I 236 14 53.2 -73 11 5.87 7.59 3.0233 2.298 2019.416 1 -0.90 -0.002 HJ 4707 14 54.2 -66 25 7.53 8.09 .17273 1.248 2019.438 1 -0.30 -0.012 BU 239 14 58.7 -27 39 6.17 6.79 312.3 0.467 2019.438 1 -0.80 0.013 HJ 4728 15 05.1 -47 03 4.56 4.60 1129.