The Edward Corbould Research Fund (ECRF) is a research fund administered by the Astronomical Association of Queensland (AAQ). I was lucky enough to be awarded funds for a research project, and this part of my website is dedicated to recording the ongoing process of this research.
The project title is (in full) “Determining Optimum CCD Imaging & Reduction Methods for Measuring Double Stars”, but is more simply known as the AAQ Neglected Southern Doubles (AAQNDS) project.
This project seeks to compare various techniques for undertaking double star measurements, and then apply the selected technique to a range of previously neglected double stars in the southern hemisphere.
Binary star systems are currently the only direct method astronomers have for the calculation of stellar mass and other associated stellar parameters.[i] As a result, the study and measurement of double star systems is critical to distinguish between visual pairs and those doubles that are in fact gravitationally bound binary systems.
The Washington Double Star (WDS) catalogue, maintained by the United States Naval Observatory (USNO), is the world’s principal database of double star information, containing over 103,000 systems and over 750,000 observations. However, the WDS classifies more than 43% of these systems as being neglected, meaning they are unconfirmed or have not been observed in the last 20 years.
In his book Observing and Measuring Visual Double Stars, Editor Bob Argyle asked the question:
“… who is paying attention to the 90,000 plus pairs in the Washington Double Star (WDS) catalogue, the central repository for the subject? In particular, who is watching the southern binaries, many of which are being overlooked?”[ii]
Amateur astronomers have a long history in the observing of double stars, however there are still “too many binaries and too few observers” to quote the WDS home page.[iii] Amateurs need to optimise their techniques to provide increased efficiency whilst still providing results with low levels of error.
Tim Napier-Munn and Graeme Jenkinson, members of the Astronomical Association of Queensland (AAQ) have developed a method of measuring double stars using a Meade DSI CCD camera and the REDUC software that requires 10 images of a target system to be taken on each of 7 nights. In addition to this, various calibration images are required. This method has been based upon experimentation, as described in their as yet unpublished paper.[iv]
Ed Wiley, of the Remote Astronomical Society (RAS), has published a method using the Global-Rent-A-Scope (GRAS) [GRAS now operates under the name iTelescopes.net] network of robotic telescopes and the MPO Canopus software to undertake measurements requiring only three or four images on a single night.[v]
Both methods require downloading and calibration (in one form or other) of the images obtained, a process that adds to the amount of time required to reduce the data. It is the intention of this proposal to trial an alternative approach to determine whether it is more efficient than the methods described above, and to determine the optimum number of images/nights to reduce errors to acceptable levels.
The iTelescope.net network of robotic telescopes[vi] operate from dark sky sites in New Mexico and California (USA), Spain and in Australia. Paramount robotic mounts, large aperture telescopes and high-quality CCD cameras provide users with access to equipment and locations infrequently available to amateurs unable to make large financial commitments. Access to the equipment is available by a monthly subscription, and includes features such as unattended scripting of imaging runs.
In addition to the physical hardware, iTelescope has joint-ventured with a Norwegian software developer to develop a product called Photometrica[vii], which performs photometric and astrometric functions. When using Photometrica, images taken by the telescopes are automatically plate solved and calibrated with darks, flats and biases. The resulting calibrated image is then transferred to the Photometrica server, which hosts the web-based application. The user at no stage has to download images (unless they so desire), and all work is completed online.
- To image a set of thirty doubles of varying configurations selected from the WDS using the iTelescope telescopes.
- To conduct a comparison of the processes required to reduce the data using Photometrica, REDUC and MPO Canopus, with particular note of the time to complete the work and the number of images/sessions required to achieve acceptable levels of error.
- To classify, where possible, whether the target doubles have moved since their last observation, have remained static, or possibly where incorrectly identified originally.
- To publish the results of these trials and observations in a peer reviewed journal.
- Initial target systems will be requested from the United States Naval Observatory (UNSO), which meet the inclusion criteria described in the next section.
- Charts will be prepared for the initial target systems using the Aladin software system and a macro developed by the applicant that draws on the following resources:
- The charts will be examined to identify the targets from the initial target system list. If the target cannot be identified, then a single image will be taken at the target coordinates, and compared to the Aladin data. If the target system cannot be identified, then that target will be marked as a potential misidentification.
- Identifiable targets will be imaged ten times on each of ten nights using a photometric R filter. The R filter has been chosen to allow for tighter star images whilst maintaining minimum exposure times. Each imaging session or a particular target will be separated from the previous session by at least one week.
- The images will be processed in accordance with each of the three software systems, and the results analysed. Compounding error rates will be calculated for each of the ten evenings. Expended times will be records for each system.
- For each image, the following measurements will be recorded:
- Position angle (θ)
- Separation (ρ)
- Magnitude differential
- Coordinates of each component
- Estimates of errors for all measurements
- A comparative analysis based upon time and error rates will be prepared.
Professor Tim Napier-Munn, Double Star Section Director of the AAQ has kindly offered to provide support and guidance to the applicant during the reduction of the data obtained.
The following inclusion criteria have been defined to answer Bob Argyle’s question:
- Declination between -40° and -90°.
- Magnitude of both components in the range 10 to 14
- Separation of up to 6 arc seconds
- Most recent observation is earlier than 1990.
The Astronomia in Romania website[xii] has a beta version of a filtering tool[xiii] that can query the WDS. By using this tool to query for the above inclusion criteria, a total of 1,881 targets are identified, although a number of these return insufficient information to be identifiable.
It is the intention of the applicant to contact Brian Mason of the United States Naval Observatory (UNSO) who is responsible for managing the WDS to provide a target list matching the inclusion criteria. As the UNSO will be aware of other programmes of research being undertaken, having them provide the list will reduce the likelihood of duplication of effort, and also ensure that the targets selected are of value to the WDS.
[ii] p. xii, Observing and Measuring Double Stars, Bob Argyle, ed., London: Springer-Verlag, 2004, ISBN 1-85233-558-0.
[iv] Measurement of Some Neglected Southern Multiple Stars in Pavo, T. Napier-Munn, and G. Jenkinson. Webb Society Double Star Circulars, 17 (2009, in press)
[v] Try Your Hand at Double Stars, E. Wiley, http://ras.gras.wikispaces.net/file/view/Try+your+hand+at+Double+Stars_V2.pdf
[viii] The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166.
[ix] The Two Micron All Sky Survey (2MASS), M.F. Skrutskie, R.M. Cutri, R. Stiening, M.D. Weinberg, S. Schneider, J.M. Carpenter, C. Beichman, R. Capps, T. Chester, J. Elias, J. Huchra, J. Liebert, C. Lonsdale, D.G. Monet, S. Price, P. Seitzer, T. Jarrett, J.D. Kirkpatrick, J. Gizis, E. Howard, T. Evans, J. Fowler, L. Fullmer, R. Hurt, R. Light, E.L. Kopan, K.A. Marsh, H.L. McCallon, R. Tam, S. Van Dyk, and S. Wheelock, 2006, AJ, 131, 1163.
[x] The Guide Star Catalogue, Version 2.3.2, Lasker B., Lattanzi M.G., McLean B.J., et al., 2008, AJ, 136, 735
[xi] The Second U.S. Naval Observatory CCD Astrograph Catalog (UCAC2) Zacharias N., Urban S.E., Zacharias M.I., Wycoff G.L., Hall D.M., Germain M.E., Holdenried E.R., Winter L., 2004, AJ, 127, 3043
[xiii] WDS Filtering Tool, http://www.astroclubul.org/brasov/wdsfilter/wdsfilter.php