Known issues with the IGSL ============================= The IGSL was frozern in 9/2013 and subsequent use has revealed a number of problems. These would be relatively simple to fix but there was no provision made for updating the IGSL hence all downstream GAIA processing had to deal with these problems and we collect them here to have them in a central location. ========= DUPLICATE ENTRIES Duplicate HIPPARCOS/TYCHO2 entries: To avoid dropping HIPPARCOS stars those not matched were added as a "fake" Tycho-2 star with the Tycho-2 ID=9999999000000+HIP_Number. Some of these were repeat entries because of a bug in the matching procedures approximately 12000 Hipparcos stars were entered twice. These can be identified as the objects with auxHIP=1 and idTYCHO > 9999999000000. They should not be used for any purpose. ================ CLASSIFICATION PROBLEMS The 197921 non-stars in the GEPC were classified as 3 or 27 rather than 1 as in other catalogs. The classification of star is correctly listed as 0. The 167055567 SDSS objects have their classification inverted, that is stars are classed as 1 and non-stars as 0 or -1. When the sourceClassification is 0 it is because none of the catalogs with that object provided a Classification which should be set to null. =============== ECLIPTIC COORDINATE ERRORS (thanks to S. Roser) The ecliptic coordinates were calculated with a 1950B rather than J2000 transformation. ============== PROPER MOTION NULL VALUES The null value for proper motions is not consistent as it is derived from the null values original catalogs. Objects with proper motions and errors of 0 or "null" can be considered not provided except for the LQRF which is a defaulted value and except for the UCAC objects where the null erorrs are set to zero. ============= HEALPIX IN NAME For ~30000 entries from the GSC23 the name (sourceID) which is made up of the 12th level healpix of the first instance and the running number in the 6th level healpix has sometimes the incorrect 12th level healpix. As a name they are still valid but generally the user is encoruaged not to use the healpix part of the sourceID as an indication of the position in the sky. =============== GENERAL MAGNITUDE TRANSFORMATIONS The calculation of magnitudes from a transformation sometimes gives unreasonable numbers because of problems with the inputs or working outside the range of the transformations. Some examples: > IGSL sourceid = 2641188455049732224 (thanks to J. Sahlmann) has a bright Gs but is probably noise in the SDSS that has a large g-r and so this makes the G bright (http://skyserver.sdss3.org/dr10/en/tools/explore/obj.aspx?id=1237656906352361542) > IGSL sourceid = 1339762992985816960 (thanks to C. Fabricius) has a magBJ=27.5297, magRF= 13.35 and gives G=17.713, probably all magnitudes are unrealistic. The B is a transform from the SDSS so the problem is probably in the SDSS original data. > IGSL sourceid = 5283973366647424768 (thanks to M. Hauser) has a G=7.6 but no bright source is present. The magnitudes come from the PPMXL and has m_B=18.8 and m_R=13.0 transforming to G the error is very large. Approximately 80% of the G estimates comes from transforms of R,B and the distribution in B-R is: | Count | B-R | % | 5369038 | > -3 | 0.43 | 10500191 | -2 | 0.85 | 27462125 | -1 | 02.24 | 93452617 | 0 | 07.64 | 429794406 | 1 | 35.15 | 498277218 | 2 | 40.75 | 127782724 | 3 | 10.45 | 22512740 | 4 | 01.84 | 5610114 | 5 | 0.45 | 1309303 | 6 | 0.10 | 528054 | > 7 | 0.04 Most objects outside of -1 to 4 are probably unreal and the transform is only good from -1 to 2.5 so around 20% probably have large errors. > Very wrong G/Grvs (thanks to P. Sartoretti) Looking at 88000 HIP stars ~ 5% of them have have very wrong Grvs. A limit bad case HIP-112306 that has in IGSL Grvs = -0.885 and G = 5.57 and in litterature V=10.89 I=8.44 or HIP-114598 that has in IGSL Grvs=20.11 and G=16.299 and in litterature V= 8.1 and I=8.12. The error in IGSL (of ~0.5) are not indicative of these errors. For the objects with magnitudes coming from Tycho2, e.g. sourceGrvs=29, there is an error in the equation of the Grvs we used: GRVS = VT -.1313 - 1.3422(BT-VT) - 0.09316(BT-VT)^2 - 0.0663(BT-VT)^3 While starting with CJ-041-7 and the Tycho handbook it should be: GRVS = VT -.1313 - 1.3422(BT-VT) - 0.07918(BT-VT)^2 - 0.04790(BT-VT)^3 For large colors this becomes a problem at the 1-3 magnitude level, ========= MAGNITUDE ERRORS No check was made on the magnitude errors in the IGSL and they are usually just a simple function of the input catalog errors, so if they were high so the IGSL ones will be high. So for example the IGSL object 9698311034780416 has an unrealistic error in R RAJ2000 DEJ2000 magBJ emag magRF emag 051.794675 +06.859480 19.720 0.450 24.160 27.506 http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/324 that somes directly from the source of the Magnitudes in the SDSS: ra dec g r Err_g Err_r 51.794674912 6.859479824 19.90372 24.14491 0.4029701 27.50531 http://skyserver.sdss.org/dr12/en/tools/explore/Summary.aspx?id=1237673328683844256 ========= POSITION ERRORS No check was made on the error of the positions, if the catalog provides 0 or a number that is less than 0.5 mas so rounds to 0 when stored in mas then it's error is listed as 0. So for the Gaia EPC catalog (Altmann 2011) the object GEPCJ055642.10-665127.5 is in the EUCLIDRSC with error 0. # Cat_name RA_H RA_M RA_S error_RA DEC_D DEC_M DEC_S error_DEC GEPCJ055642.10-665127.5 5 56 42.0998 0.0176 -66 51 27.451 0.0 and in the SDSS a number of objects had errors less than 0.5mas and these got rounded to 0. ========= GRVS MAGNITUDES For the objects with magnitudes coming from Tycho2, e.g. sourceGrvs=29, there is an error in the equation of the Grvs, I had: GRVS = VT -.1313 - 1.3422(BT-VT) - 0.09316(BT-VT)^2 - 0.0663(BT-VT)^3 While starting with CJ-041-7 and the Tycho handbook it should be: GRVS = VT -.1313 - 1.3422(BT-VT) - 0.07918(BT-VT)^2 - 0.04790(BT-VT)^3 ======== OGLE Entries OGLE was considered on average to have better photometry than other catalogs so estimates of the G magnitude were taken from those values. We were provided with the deep catalogs of the OGLE surveys which did not have stars brighter than around 13. This means that sometimes a faint star was matched to the bright inputs and, because the OGLE magntiudes override others, these objects were sometimes dropped or have under estimated magnitudes. For example the 13th magnitude star at 91.9967388, -70.9623672 in the UCAC catalog was matched to a faint nearby star in the OGLE deep catalogs and assigned a G fainter than 21 so was dropped. This occured in the 5 OGLE regions which are small parts of the sky (a few square degrees in total). How many stars in this region that were mistakenly removed is not easy to estimate. ======== TYCHO Carbon Stars 17 BT-VT>4.9 Tycho2 sources are not found in IGSL, some ar flagged as Carbon stars in Simbad. "id_tycho","id_tmass","ra","dec" "1044008501","190215181014244",285.56326333,10.24018833 "1336013101","62614111904258",96.558845,19.07379889 "172026121","71538890503394",108.91204583,5.06102194 "282007531","122514390046109",186.30999389,0.76970611 "3243013631","233920644429365",354.83604417,44.4935625 "3325001041","34129575130115",55.37329972,51.50327778 "5144001961","-193014940050093",292.56222861,-0.835935 "6282000661","-185722341650327",284.34307806,-16.84240833 "6314006701","-200117211502425",300.32177528,-15.04517444 "6859003481","-184732752356559",281.88645389,-23.94894639 "7133040761","-80910993617070",122.29575889,-36.28527417 "741002701","63053541228455",97.72308611,12.47936083 "8191021641",,154.36662806,-50.09720278 "8659013941","-124724675941409",191.85285194,-59.69472833 "8957036081","-103843566049251",159.68146278,-60.82360944 "8961012191","-103417856242394",158.5743775,-62.71099417 "8988009611","-124932426146141",192.38507944,-61.77066194 These stars were not included because their G magnitudes did not come out to be < 21. This is because the color transformations from the BT/VT to G were not valid outside the range of BT-VT of 2.5. Obviously they are brighter than G=21. but being unable to calculate a magnitude the program rejected them. Many other stars that are this red have re-entered through the other catalogs but for these there was obviously no other entries that made the cuts. ========= Altitude Star Catalog II ====================== As this catalog was made in a significantly different way the object sourceIds were not consistent. I matched the ASC II to the the IGSL source database to try and obtain consistent sourceIds but sometimes these maybe wrong and for sure many will have different magnitudes because of the different starting set of catalogs - in particular I did not use the SDSS in the production of the ASC.