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Double Star Measurements at the Internationale Amateur Sternwarte (IAS) in Namibia in 2008 and 2009

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Double Star Measurements at the Internationale Amateur Sternwarte (IAS) in Namibia in 2008 and 2009 Vol. 6 No. 2 April 1, 2010 Journal of Double Star Observations Page 133 Double Star Measurements at the Internationale Amateur Sternwarte (IAS) in Namibia in 2008 and 2009 Rainer Anton Altenholz/Kiel, Germany rainer.anton“at“ki.comcity.de Abstract: A 40-cm-Cassegrain telescope in Namibia was used for observing double and multiple systems in the southern sky. Digital images were recorded with a CCD camera at high frame rates via a firewire interface directly in a computer. Measurements of 34 double and multiple systems are presented and compared with literature data. Some noteworthy objects are discussed in more detail. [2]. The nominal focal length is 6.3 m, which results in Introduction a resolution of about 0.19”/pixel with my b/w-CCD For several years I have been using the technique camera (DMK21AF04, The Imaging Source) with pixel of “lucky imaging” for recording and measuring double size 5.6 µm square. Several recordings were also made stars. In short, it means short exposure times to with a 2x-Barlow lens inserted, combined with a red “freeze” the moments of good seeing, and pick out the filter. A filter is necessary because of the chromatic best frames for superposition in a computer. In an ear- aberration of the lens. It also helps to reduce the at- lier article in this Journal, I have addressed the accu- mospheric spectrum. Exposure times were from 0.5 racy and reproducibility of measurements in images µsec up to 0.1 sec, depending on the star brightness thus obtained with telescopes of 40 cm and 50 cm ap- and the seeing. The stream of digital images is trans- erture and a fast CCD camera [1]. As a result, the ferred with rates up to 15/sec via a firewire interface resolution can be pushed to the theoretical limit, but into my notebook. To get the most out of the re- the accuracy of position measurements can even be cordings, I usually select the best frames by visual one order of magnitude better than this. Standard de- inspection. The typical yield is about 50 to 150 useful viations of separation measurements were typically frames out of a few thousand. These are one- or two- below +/-0.05". times re-sampled, and aligned with the program Reg- Among the 34 investigated systems, 18 are bina- istax, often with the option “manual”, and finally auto- ries. Most of the stars are brighter than 9 mag. Never- matically stacked. Resampling results in rather theless, for many cases there are only few data listed smooth intensity profiles, and in position measure- in the literature. For some systems, deviations from ments with sub-pixel accuracy. predicted movements could be manifested. Systems, for which trustworthy literature data exist, are used Calibration and Measurements for calibration of the image scale. As calculation of the image scale from the focal length and pixel size is not sufficiently accurate, espe- Instrumental cially when using the Barlow, I do the calibration in During two weeks in September 2008 and again in an iterative way by measuring a number of doubles September 2009, I used the 40-cm-Cassegrain at the with well known separation. All systems are suitable, Internationale Amateur Sternwarte (IAS) in Namibia for which literature data can unambiguously be ex- Vol. 6 No. 2 April 1, 2010 Journal of Double Star Observations Page 134 Double Star Measurements at the Internationale Amateur Sternwarte (IAS) in Namibia ... Table 1: List of measurements without Barlow. Systems used for calibration are marked by shaded lines. System names, posi- tions and magnitudes are taken from the WDS. The two columns before the last one show the differences D of measured position angles (P.A.) and separations (rho) minus reference data. N is the number of measurements at different nights, or with different camera settings. P.A. rho D D pair RA + DEC mags date N notes meas. meas. P.A. rho 168.2 27.01 2008.738 1 ~0 -0.03 LCL 119 AC 00315 -6257 4.28 4.51 1 168.4 27.05 2009.710 3 +0.2 +0.01 HDO 182 00427 -3828 6.60 7.01 21.0 0.69 2008.732 2 +1.0 -0.01 2 129.1 5.15 2008.740 1 +0.1 +0.05 HJ 3416 AB 01033 -6006 7.58 7.67 3 129.4 5.07 2009.718 1 +0.4 -0.03 117.4 0.39 2008.746 1 -0.3 -0.01 SLR 1 AB 01061 -4643 4.10 4.19 4 112.8 0.42 2009.693 1 +0.3 +0.01 318.2 4.80 2008.740 1 -0.8 -0.18 HJ 3423 AB 01158 -6853 5.00 7.74 5 318.9 4.75 2009.718 1 ~0 -0.28 I 27 CD 01158 -6853 7.84 8.44 308.7 1.00 2008.740 1 +0.2 -0.04 6 HJ 3447 01361 -2954 5.97 7.35 182.5 0.75 2008.732 2 +0.5 -0.03 7 STF 186 01559 +0151 6.79 6.84 66.7 0.83 2008.732 1 ~0 -0.03 8 BU 738 02232 -2952 7.60 7.97 212.3 1.79 2008.732 1 +0.5 -0.02 9 BU 739 02248 -2952 8.69 8.90 259.1 1.75 2008.732 1 -0.4 -0.02 10 245.1 10.63 2008.732 1 +0.1 -0.1 HJ 3506 02338 -2814 4.95 7.71 11 245.0 10.80 2009.718 1 ~0 +0.1 BU 741 AB 02572 -2458 8.06 8.20 342.9 0.91 2008.732 1 +1.3 -0.03 12 S 423 AC 02572 -2458 8.06 7.86 225.8 28.93 2008.732 1 -0.2 -0.05 12 HJ 3555 03121 -2859 3.98 7.19 300.6 5.17 2008.732 1 +0.8 -0.02 13 HJ 3596 03485 -3147 8.27 8.54 137.7 9.34 2008.732 1 -0.3 -0.01 14 DUN 16 03486 -3737 4.72 5.25 215.8 8.23 2008.732 1 -0.3 ~0 15 BU 1004 AB 04021 -3429 7.26 7.94 61.8 1.24 2008.732 1 +8.5 +0.43 16 I 152 AB 04049 -3527 8.37 8.65 79.6 1.03 2008.732 1 +0.4 +0.02 17 BU 311 04269 -2405 6.67 7.09 150.5 0.41 2008.732 1 +2.1 -0.03 18 I 154 04313 -3546 8.52 8.21 134.6 0.48 2008.732 1 -0.4 -0.01 19 95.1 8.73 2008.740 1 -0.4 +0.02 AGC 1 AB 06451 -1643 -1.46 8.5 20 89.8 8.78 2009.721 2 -0.2 -0.05 BU 332 AB 6.22 7.35 172.9 0.71 2008.740 1 +1.9 -0.01 STF1097 AC 6.0 8.5 313.3 20.07 2008.740 2 +0.3 +0.27 07279 -1133 21 BU 332 AD 6.0 9.5 156.8 22.86 2008.740 1 -0.2 +0.06 BU 332 AE 6.0 12.2 43.3 32.76 2008.740 1 +0.3 +0.56 HJ 608 AB 3.8 11.2 192.0 6.51 2008.732 2 - - HJ 608 AC 20181 -1233 3.8 11.5 199.1 7.39 2008.732 2 - - 22 AGC 12 BC 11.2 11.5 240.1 1.24 1959 2 +0.1 -0.06 HJ 5319 22120 -3818 7.65 7.66 314.5 2.08 2008.740 1 +0.5 -0.03 23 H N 56 AB 22143 -2104 5.63 6.72 112.1 5.25 2008.738 1 +0.4 +0.05 24 BU 172 AB 22241 -0450 6.45 6.63 42.5 0.41 2008.732 1 +0.9 +0.01 25 SHJ 345 AB 22266 -1645 6.29 6.39 34.7 1.35 2008.732 1 +0.7 +0.02 26 STF 2909 22288 -0001 4.34 4.49 171.3 2.04 2008.732 1 -1.6 -0.06 27 PZ 7 22315 -3221 4.28 7.12 172.4 30.35 2008.738 1 -0.1 +0.05 28 Vol. 6 No. 2 April 1, 2010 Journal of Double Star Observations Page 135 Double Star Measurements at the Internationale Amateur Sternwarte (IAS) in Namibia ... trapolated to the actual date. Main sources are the position. WDS [3], and the 4th Catalog of Interferometric Meas- For measuring the position angle, the east-west- urements of Binary Stars [4]. Results for binaries are direction was obtained by superposing series of images also compared with data from the Sixth Catalog of Or- recorded while the telescope drive was switched off. bits of Visual Binary Stars [5]. In the tables below, sys- The error margin is about +/-0.1o, but the total error is tems taken for reference are marked with shaded lines. greater, and depends on the separation, because of the The scale factors were adjusted such to obtain mini- limited lateral resolution of the camera. For pairs with mum mean values of the residuals, as well as of the separations close to the resolution limit of the tele- standard deviations (sd). The results were 0.187”/pix scope, deviations of the P.A. can be up to a few degrees. without Barlow, and 0.097”/pix with Barlow, with sd- Measurements are listed in two tables below, Table values of +/-0.05” and +/-0.04”, respectively, and total 1 for those obtained without Barlow lens, and Table 2 error margins of about +/-0.5%.
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