So why has this pair been listed? (1)
Although the most recent version of theWashington Double Star Catalog (WDS) available through the CDS Vizier service is more than ten years out of date (1996) the 2006.5 version can be found elsewhere. However many, if not most, of the new entries included since 1996 cannot be said with any degree of certainty to be binary systems and in a number of cases the available evidence points very strongly to the listed pair being a “line of sight” arrangement of no particular astronomical significance.
As an example consider the data for GRV 35. In the WDS it is listed as having a separation of 56.7 arc seconds at 175 degrees. So by no means are the two components particularly close together and the UCAC2 data does not suggest that the components are displaying common proper motion.
The image is 5 x 5 arc minutes
So on what basis has this pair been included in the standard catalog?
APPENDIX 1 - A crucial distinction: Binary Stars v's Double Stars
Two stars orbiting around their center of mass are called a binary star. Binary stars are important in astrophysics for a number of reasons - not least since orbital studies allows the mass of the stars to be determined. Various sub-types of binary star exist such as optical binaries, spectroscopic binaries and eclipsing binaries.
Optical double stars are just
Historically it was very difficult to distinguish between the wheat (binary stars) and the chaff (double stars). For this reason the Washington Double Star Catalog (WDS) is a mixture of three types of object:
- Binary stars
- Double stars
- Stars that, without further information, might fall into either class
