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Tales of Cataloguing II
This is part 2 of anomalies I've encountered in cleaning QSO data.
99 44/100 % is fine. This is the story of the remaining 0.56%. The task in producing the "million quasars" catalog is to find the right optical object for each quasar. If the data positions a brightish quasar but I find no optical object there, then I must search for it. Any feedback welcome. Section A: When Veron 13th edition and NED disagree, Veron usually wins because of the careful attention of its authors. But not always, and following are 5 cases of mixed outcomes. 1) HE 0435-1223 (this old notation describes a B1950 tile of sky): a Cyril Hazard quasar -- he rarely published positions for these. Veron positions this at J043814.8-122314, NED has J043814.8-121715. NED is right -- Veron failed to convert the declination from B1950 to J2000. 2) IXO 40: Veron positions this at J115057.9-290043 but there is nothing there. NED has J115057.9-284402, which is right. Veron was off by exactly 1000 arcsec in declination, indicating a transcription error. 3) NGC 2859 U2, a Halton Arp quasar. Veron positions this at J092457.8+343952, in the middle of nowhere. NED has J092557.6+343950 which is correct. Veron has a transcription error of 1 time minute = about 900 arcsec. However, NED also has a "NGC 2859 U02" at the bogus location, so NED has a duplicate here. 4) NGC 2859 U3, much like (3), above. Veron has J092454.2+341648 which is off by 1 time minute. NED has J092554.0+341645 which is correct, but also has "NGC 2859 U03" at the bogus location, thus, again, a duplicate. 5) SBS 1014+565, a Soviet quasar: Veron correctly has this at J101724.4+562108. SDSS-DR7 re-surveyed this at the Veron location but erroneously called it "SBS 1014+566". NED has had SBS 1014+565 at the bogus location of J101715.0+561811 (not sure why), and has added the bogus-named "SBS 1014+566" at the true location given by SDSS-DR7, so NED has a duplicate here. Section B: bright Soviet quasars from Afanasjev et al,1979AN,300,31. This paper published 4 quasars, one of which, TB 0933+733, z=2.525, had a finding chart. A pity they didn't all have one, for 3 anomalies follow. (TB=Tautenburg objective prism survey, H. Lorenz) 1) TB 0748+611, z=2.492 v=17.5 is in NED as [HB89] 0747+613 at J075212.0+611223. However, that optical object is v=20.0 and at B074750.1+612006 is in 0747+613, not 0748+611. Investigation finds this object listed in Veron & NED as SBS 0747+611, z=2.487 v=17.2 at B074801.9+610537, ie J075222.6+605753. So the NED object [HB89] 0747+613 is duplicate. I will restore the original name TB 0748+611 in the next edition of the million quasars catalog. 2) TB 0948+722, v=17.5, z=0.529: Veron says J095224.6+715755 but this is only the centre of a 400-arcsec square tile of sky. I found this quasar at J095254.2+715803, 171 arcsec from the nominal location. It is an in-your-face v=17.2 quasar with X-ray 2RXP J095255.1+715758. 3) TB 0958+735, v=17.5, z=2.067: Veron says J100225.4+731532, but as with (2) this is only approximate. This is again an in-your-face v=17.1 quasar at J100317.6+731559 at 180 arcsec from the nominal location. It has X-ray 1RXS J100317.6+731558 and radio NVSS J100318.7+731558. More to come, Eric Flesch |
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Tales of Cataloguing II
In article , Eric Flesch
writes: This is part 2 of anomalies I've encountered in cleaning QSO data. 99 44/100 % is fine. This is the story of the remaining 0.56%. It looks like you have put some detailed work into this. The task in producing the "million quasars" catalog is to find the right optical object for each quasar. If the data positions a brightish quasar but I find no optical object there, then I must search for it. Any feedback welcome. What fraction of quasars are not detectable in the optical at all with current observations? Have you contacted the authors of the erroneous data? Especially if you have an obvious explanation for the mistake it might be worth writing this up as a short paper. One of the disadvantages of online data is that it is not obvious when something changes and one cannot continuously check it for updates. Worse, the authors might never update their data even when it has been shown to be wrong. Such a paper might be an important heads-up for folks working with such data. 1) HE 0435-1223 (this old notation describes a B1950 tile of sky): a Cyril Hazard quasar -- he rarely published positions for these. Veron positions this at J043814.8-122314, NED has J043814.8-121715. NED is right -- Veron failed to convert the declination from B1950 to J2000. HE is Hamburg-ESO, right? And the other objects have similar names denoting who discovered them etc. Have you checked the original literature, rather than compiled catalogues? |
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Tales of Cataloguing II
On Tue, 25 Oct 11, Phillip Helbig wrote:
writes: brightish quasar but I find no optical object there, then I must search for it. What fraction of quasars are not detectable in the optical at all with current observations? By "brightish" I mean quasars brighter than plate limit. My original quantification (of quasars not seen) of 0.56%, whilst tongue-in-cheek, is not far off the mark. Have you contacted the authors of the erroneous data? Yes, and sometimes I even get a reply. But many of the early investigators are retired and incommunicado. Especially if you have an obvious explanation for the mistake it might be worth writing this up as a short paper. ... Such a paper might be an important heads-up for folks working with such data. Indeed, but organizing my findings to present them here, is very useful. And corrections such as the following are valuable: 1) HE 0435-1223 (this old notation describes a B1950 tile of sky): a Cyril Hazard quasar -- he rarely published positions for these. HE is Hamburg-ESO, right? Ah yes, it isn't a Hazard quasar. So many early quasars beginning with H are Hazard that I fell into the trap of thinking this one was too. But this is actually a famous quadruple-image quasar surveyed in 2002. Why they gave it a B1950 monicker beats the heck outta me. Have you checked the original literature, rather than compiled catalogues? All the time, er, except this time. My next edition in this series will present ~20 duplicates in Veron, in tiresome detail -- well, it makes me tired to write it all out. Eric |
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Tales of Cataloguing II
In article , Eric Flesch
writes: On Tue, 25 Oct 11, Phillip Helbig wrote: writes: brightish quasar but I find no optical object there, then I must search for it. What fraction of quasars are not detectable in the optical at all with current observations? By "brightish" I mean quasars brighter than plate limit. My original quantification (of quasars not seen) of 0.56%, whilst tongue-in-cheek, is not far off the mark. So no objects detected in other bands? (If so, then I'm surprised that almost all have an optical ID.) Have you contacted the authors of the erroneous data? Yes, and sometimes I even get a reply. But many of the early investigators are retired and incommunicado. Or dead. :-( 1) HE 0435-1223 (this old notation describes a B1950 tile of sky): a Cyril Hazard quasar -- he rarely published positions for these. HE is Hamburg-ESO, right? Ah yes, it isn't a Hazard quasar. So many early quasars beginning with H are Hazard that I fell into the trap of thinking this one was too. But this is actually a famous quadruple-image quasar surveyed in 2002. Why they gave it a B1950 monicker beats the heck outta me. I don't know, but maybe the survey was started, or at least planned, before J2000 became common, so they decided to stick with a common system rather than risk conversion errors. |
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Tales of Cataloguing II
Phillip Helbig---undress to reply wrote
in : [...] I don't know, but maybe the survey was started, or at least planned, before J2000 became common, so they decided to stick with a common system rather than risk conversion errors. Keeping in mind that I am aware that stuff in the sky moves, is there finally a set way of cataloging things? The standard appears to change wildly every 20 years or so and personally I think it'd be nice if there we changed things in a set method in a specific period of time rather than how haphazard it looks right now. On that note, as a tech guy, I think it'd be more advantageous to have a cataloging system that was static in coordinates but could also include proper motion so that we could have coordinates and an area to look at using (if available) previously measured drift. OTOH this is all theory crafting and there's probably a way to do this now. |
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Tales of Cataloguing II
In article , eric gisse
writes: Keeping in mind that I am aware that stuff in the sky moves, is there finally a set way of cataloging things? The standard appears to change wildly every 20 years or so and personally I think it'd be nice if there we changed things in a set method in a specific period of time rather than how haphazard it looks right now. The difference between B1950 and J2000 is not due just to the precession of the equinoxes. On that note, as a tech guy, I think it'd be more advantageous to have a cataloging system that was static in coordinates but could also include proper motion so that we could have coordinates and an area to look at using (if available) previously measured drift. The standard methods mean that even without proper motion the position of the object moves away from the position it was named after. I don't know if there are better systems around now. The old systems, of course, were designed to be practical and back then were accurate enough. OTOH this is all theory crafting and there's probably a way to do this now. There is an iPad app where you just hold the iPad and it shows you a map of the sky with names of objects etc, including ones which move, getting its orientation from GPS or whatever. :-) |
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Tales of Cataloguing II
In article ,
eric gisse writes: Keeping in mind that I am aware that stuff in the sky moves, is there finally a set way of cataloging things? Making a catalog is separate from assigning source names. Which do you want to know about? Catalogs are maintained these days by data centers such as SIMBAD and NED. Each data center serves coordinates in a variety of formats, includng both B1950 and J2000 systems. How they store and update the data in their internal records is their problem, not mine. The IAU recommends how to assign source names. A short summary is at http://vizier.u-strasbg.fr/vizier/Dic/how.htx That URL has a link to the longer recommendations. The most important rule is that a source name, once assigned, never changes. This means, for example, that a name based on coordinates will not change even if the coordinates are later refined or found to be in error. Of course multiple names can be assigned to a single source and often are, but in principle any name should refer unambiguously to a single source. (This rule is, alas, sometimes violated by the careless or ignorant. "HR 10" is perhaps the most famous example, though it's usually clear in context which source is meant.) The standard appears to change wildly every 20 years or so That's news to me! There are minor updates from time to time, but I have never seen any changes I'd consider "wild." On that note, as a tech guy, I think it'd be more advantageous to have a cataloging system that was static in coordinates but could also include proper motion Data centers maintain proper motion information when it's relevant. How they store the information internally is their problem, but users can query the data in standardized formats. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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Tales of Cataloguing II
In article ,
Phillip Helbig---undress to reply writes: The difference between B1950 and J2000 is not due just to the precession of the equinoxes. There are some differences at the arcsecond level because of the updated reference frame (now based on quasars with VLBI positions), but is there anything else? -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
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Tales of Cataloguing II
Steve Willner wrote in
: In article , eric gisse writes: Keeping in mind that I am aware that stuff in the sky moves, is there finally a set way of cataloging things? Making a catalog is separate from assigning source names. Which do you want to know about? Catalogs are maintained these days by data centers such as SIMBAD and NED. Each data center serves coordinates in a variety of formats, includng both B1950 and J2000 systems. How they store and update the data in their internal records is their problem, not mine. Ah, this clears up what I've been wondering about but haven't thought of a good place to read it at. Its' nice to know that the designation is fixed, even if the coordinates change. [...good stuff...] |
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Tales of Cataloguing II
In article , Steve Willner
writes: In article , Phillip Helbig---undress to reply writes: The difference between B1950 and J2000 is not due just to the precession of the equinoxes. There are some differences at the arcsecond level because of the updated reference frame (now based on quasars with VLBI positions), but is there anything else? That's what I was thinking of. OK, I admit learning this from Christian de Vegt; maybe it was more important to him. :-) |
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