Journal of the British Astronomical Association, Vol. 115, No. 6, p.342
In July 2002 I contacted the United States Naval Observatory seeking advice as to what would qualify as a pair worth reporting. One section of the reply I received from Dr. William I. Hartkopf (July 2002) of the Astrometry Department is worth quoting in full.
"As for qualifications - what pairs are worth reporting - that's a more difficult question! The WDS contains a rather eclectic mix of physical and optical pairs - essentially any published double. Some are very wide and are only included because someone thought they were, for example, a common-proper motion pair, etc. and published a measurement! (In other words, they're included for historical interest or "completeness", but are otherwise of little use.) Physical pairs are most interesting from an astronomical standpoint, but it's very difficult to determine with any degree of certainty whether a pair is indeed physical. Several "rules of thumb" have been published, however. Robert Aitken used the following formula in one of his books: log p = 2.8 - 0.2 m, where p is the separation in arc-seconds and m is the apparent visual magnitude (probably combined magnitude, although it isn't mentioned). Binaries of a given magnitude closer than p are considered probably physical. Aitken (and others who came up with similar formula) would often include "borderline" cases if they found them interesting, so these rules weren't set in stone! For your purposes you might use this formula as a guideline, but also keep any systems fainter than 9th magnitude if their separations are 10" or less."
Brian D. Mason, Project Manager, Washington Double Star Program, subsequently contacted me (December 2002) asking:
What criteria did you use for identifying new doubles? When we have gone through astrometric catalogs (like the AC) looking for new doubles we've only selected ones meeting one of two possible parameter: a. Aitken's parameter : described in the introduction to the ADS, this relates apparent magnitude and separation, b. outer limit : we arbitrarily set this at ten arc seconds, i.e., if the two stars are at 10" and closer we call it a double and put it in the WDS, even if it is so faint that the likely physical separation probably rules out it being a real double. If you use criteria similar to this, it might reduce the number of doubles and increase the wheat to chaff ratio.
So what this means is that I asked for and was given very specific advice regarding what discoveries to report. I followed the advice given to the letter and so John Greaves is quite simply being disingenuous to suggest otherwise. Neither is it in dispute that staff at the United States Naval Observatory subsequently "moved the goalposts" once my many "discoveries" were made public. I imagine it was the sheer number of them that made them realise that they had set the criteria for inclusion incorrectly!
This page was last updated on July 29th 2009.
