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Astrometric Measurement of WDS 03117

I am pleased to present this paper that I co-authored with two teachers and submitted to JDSO this year as part of the Boyce Astro program.

Hilde van den Bergh1, Chris Olivas2, Jerry Hilburn3

  1. Mentor, BEWiSE, Fleet Science Center, San Diego, California, USA.
  2. Chris Olivas, High Tech Middle School, San Marcos, California, USA.
  3. Epsilon Orion Observatory, San Diego, California, USA.

Abstract: We report CCD astrometric measurements of the components of the double star system WDS 03117+8128 STF327AB using the iTelescope network. We find the relative position to be r = 20.26± 0.12 arc-sec and q = 289.1±0.39 degrees at epoch 2016.84. When combined with the historical data over the last 114 years the trend suggests the decreasing of the distance between the AB pair.

We used the Washington Double Star Catalog (WDS) to identify a binary pair on which to conduct angle (Theta) and separation (Rho) measurements. The double star system was selected based on the following requirements:;


  • must be observable from the Northern hemisphere in the autumn
  • an angular separation greater than six arc seconds
  • a magnitude difference of no more than 5


The catalog star WDS 03117+8128 (STF 327 AB), satisfied these criteria

The A star in STF 327 is a spectroscopic binary (WDS Notes). The B star is not part of the spectroscopic pair. The primary has a spectral type of A7III-IV (Sordiglioni, G.). That means the star is a (A) white (IV) subgiant. The difference in magnitude between the A and B stars is 4.75 with the primary star having a magnitude of 5.914 in the visible and the secondary star having a magnitude of 10.7 in the visible, according to SIMBAD data. The first position angle and separation measurements taken in 1902 were 282o and 25 arc-seconds, respectively. The last measurements were 289o and 21.2 arc-seconds, respectively, in 2003.


Equipment, Observations and Data Reduction Procedures

CCD images were taken using the T7 and T18 telescopes, part of the iTelescope network. T7 is a Corrected Dall-Kirkham Astrograph with an aperture of 431mm, a focal length of 2929mm, and a F/Ratio of f/6.8. The CCD for the T7 is a SBIG STL-11000M (ABG) with a resolution of 0.63 arc-secs/pixel housing an array 4008 by 2672 (10.7 Mega pixels) with a FOV of 28.2 x 42.3 arc-mins and is located in Nerpio, Spain.

Additional images were taken using the T18 telescope located in Nerpio, Spain, using a Planewave 0.32-m f/8.0 reflector equipped with a 3072 by 2048 array imaging at a pixel scale of 1.69?. Both cameras can easily resolve separations above five arc-seconds.

A total of six images were acquired between epochs 2016.816 and 2016.854. Two images were taken with the T7 Telescope each with red (1-90sec, 1-120sec). Four images were taken with the T18 Telescope, two images each with the red (1-90sec,1-120sec), hydrogen alpha (1-120sec, 1-180sec). An additional 11 images were excluded due to tracking quality of the observations.

The remaining 6 images were preprocessed (dark and flatcorrection) by the iTelescope data reduction pipeline. MaximDL v6 was used to insert World Coordinate System (WCS) positions into the FITS headers through comparison of the image star field against the Fourth U.S. Naval Observatory CCD Astrograph Catalogue (UCAC4).

During this process MaximDL typically used approximately 400 stars out of a database of 3000 stars for this particular star field. Mirametrics Mira Pro x64 was used to compute accurate position angles and separations of the component stars. The A and B stars were identified, marked, and then measured using the algorithms of Mira Pro to find the centroids of each component. The telescopes and filters used for the 6 images measured gave consistent results so we calculated a master average of r and q.

 See full paper for results: WDS03117-8128 STF 327 AB