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.

Introduction
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

Astrometric Measurements of WDS 20210+1028

I am excited to report the submission of a double star research paper to the Journal of Double Star Observations. I co-authored the paper with a team of College professors in the local San Diego area. This research project was part of an Astronomy Research Seminar offered by Cuesta College, supported by the Institute for Student Astronomical Research (InStAR), and conducted by Boyce Research Initiatives and Education Foundation (BRIEF).

As a proof of concept of our data analysis process, we decided to observe a double star system listed in the Washington Double Star Catalog (WDS) as having a “known” orbital solution. The double star system we selected had to be observable from the Northern hemisphere in June, with an angular separation greater than six arc seconds, and with a listed maximum magnitude difference of 2.5 between the stars. WDS 20210+1028 J838 (hereafter referred to as J 838) satisfied these criteria. Motivations for these criteria are discussed in the telescope selection section below.

Observations of J 838 were first reported by Jonckheere (1912), who found a separation of only 2.9?. Robert Jonckheere (1888-1974) discovered and published measurements of over 3000 doubles in a career spanning circa 1908 to 1962, as described in detail by Knapp (2016a).  Among others studying J 838 in the twentieth century, Jonckheere published four more observations between 1948 and 1958, which showed the pair’s angular separation increasing to 3.5?. Jonckheere (1952) noted (translated from French):

“Rapid movement on the arc clearly confirmed. This couple is probably formed by stars of very small mass located about 8 parsecs.”

Another veteran observer, George van Biesbroeck, made micrometer measurements of J 838 in 1966, and published them with measurements of other doubles in van Biesbroeck (1974). From that paper’s Introduction:

“The present measures are a continuation of previous ones (Van Biesbroeck 1966). They will be the last ones that I made. My present physical condition precludes further work at the telescope. There has been no change in the method of observing or the telescopes used, except that on my 90th birthday in 1970 I was granted the use of the 90-inch (2.3-m) Steward Observatory telescope on Kitt Peak.”

Note: Dr. Van Biesbroeck observed last on the nights of 1974 January 1 and 2 with the 84-inch (2.1m) telescope. He wrote the above paragraph and compiled his last manuscript in the same month just before his 94th birthday. Immediately thereafter his health failed rapidly and he died on 1974 February 23.

This final paper, published posthumously, marked the end of a remarkable career in astronomy that began in 1904 (Tenn 2012).

The first calculated orbital elements for J 838 were published by Olevi? (2002) and give a period of 239.84 years, with periastron occurring at 1967.510. Eccentricity, semi major axis and inclination were given as 0.784, 7.451? and 77.6°, respectively. The Sixth Catalog of Orbits of Visual Binary Stars (Hartkopf et al. 2011) classifies this orbit as category 5, “poorly determined”. The fitted orbit suggests that the pair is currently (2016) nearing maximum angular separation, which warrants further observations to more accurately constrain its shape and size.

The first CCD measurements (in 2001) were reported by Hartkopf et al. (2013), and the first published results for the system using speckle interferometry were by Mason et al. 2004. Cvetkovi?, and collaborators in Eastern Europe, made seven measurements of J 838 with CCD astrometry between 2009 and 2013 (see Cvetkovi? et al. 2016, and references therein). They also provide relative photometry (B and V band) for the pair: ?B = 0.35±0.02 mag, and ?V=0.06±0.01 mag.

Three earlier papers in JDSO include measurements of this system. Muller et al. (2006, 2007) report CCD astrometry from 2005, while Knapp (2016b) reported V-band photometry for A and B members of the pair (12.54±0.01 mag and 12.58±0.01 mag, respectively) based on 3-second exposures using iTelescope in 2015.

Read More>> The completed paper is available by download: JDSO Double Star Paper