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Tales of Cataloguing XIV -- the 0th finding chart
(This and the previous posting are because I've recently found & fixed
a few more mis-positioned legacy objects -- there's always more if you look hard enough, it seems. I give the more interesting ones here, for the record.) 20th century quasar discovery papers made liberal use of finding charts to display the precise location of new quasars, lest the listed co-ordinates weren't accurate enough. Astrometry had much improved by the 1990s but finding charts were still usually included, more as a tradition than a necessity. That was all fine so long as the listed astrometry and finding chart agreed. But sometimes they didn't. Sometimes they pointed to different objects. I've given examples of this in earlier postings in this series, notably #VIII "the log of jumping up & down" which is what you do when bad finding charts drive you crazy. But other times it is good finding charts which save the day when the listed co-ordinates are false, e.g., the quasar "TOL 1038.2-27.1" from Bohuski & Weedman 1979,ApJ 231,653, object #23 (last one in the list), 41 arcsec offset from the false listed co-ordinates (unsuitable photometry r=18.0 b=20.1) to the true finding chart object (r=19.2 b=19.5). Another example is the quasar "Q 0111-328" from Savage et al. 1984,MNRAS 207,393, which gave finding charts onto the original prism (grism) plates which are infallibly correct because the actual discovery spectrum is pointed at; the B1950 co-ordinates given in the microfiche were of a nearby object offset by 76 arcsec. Even big names like Schneider/Schmidt/Gunn did this for one object, "PC 0027+0515" in 1999, AJ 117,40, the Table 5 co-ordinates of which pointed near random objects whilst the true object was revealed on the finding chart at an offset of 17 arcsec. So there were bad finding charts and good finding charts. But then there's this, from Borra et al. 1996, AJ 111,1456, the quasar "Q 13034+2942" (called "130324+294245" in the paper) is the very first one on their list, and their first finding chart. They would make no error on the very first object, right? Of course not. Furthermore, on their Table 4a they lead right off with it as positioned at B1950 130324.21+294245.8, lest there be any mistake. That translates to J2000 130547.40+292643.0 which shows up on the SDSS finding chart as a flattish-spectrum 21-mag stellar-psf which my own data reports as a variable object which was 19th magnitude in the 1960's -- so very quasar-like and all good. So why did I previously have it catalogued as a reddish v=22 object 17 arcsec to the South-West? Let's have another look at that finding chart, the first finding chart of the paper. There it is, but wait, they are pointing to the reddish object (which is probably a red dwarf star). This is one of those finding charts where they don't use a photo, instead they re-create it with ink on paper. Looks like they used a plotter (remember those?) and optical data. Um, guys, your optical data did not include the true object. It's not there at all. They're pointing to the red dwarf because the quasar isn't on the chart. Their very first finding chart for quasar discoveries points to a red dwarf star. Looking at my archived catalogue versions, I originally had the right identification (inherited from VCV) but switched it to the red dwarf just before the publication of my Half-Million Quasars catalogue. Guess I'd looked at one finding chart too many. Well, that's no kind of first finding chart to have, is it? Maybe if the authors can "promote" it to the zero-eth finding chart, it will go away. And these are the kinds of Finding Chart Follies that I've encountered through the years. ------- On a separate note, the Soviet quasar "Q 0752+617" from Afanasiev/Lorenz/Nazarov 1989, SvAL 15,83 does not exist. I've looked for it for years. I've communicated with the lead author and he doesn't know where it is -- he knows only the old VCV location which is just the B1950 sky rectangle denoted by "0752+617". There is no radio, no X-ray, no WISE candidate, no suitable bluish optical. The paper stated narrow emission lines -- perhaps they measured a galaxy. I give up, it is removed from the Milliquas catalogue as of the next edition. I will gladly restore it if the authors provide its location. Eric Flesch 10-Jan-2019 |
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