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The construction of the GSC2.2 Catalog

Seminars on formation and evolution of the Galaxy Feb 12, 2002. The construction of the GSC2.2 Catalog. Mario G. Lattanzi Osservatorio Astronomico di Torino.

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The construction of the GSC2.2 Catalog

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  1. Seminars on formation and evolution of the Galaxy Feb 12, 2002 The construction of the GSC2.2 Catalog Mario G. Lattanzi Osservatorio Astronomico di Torino

  2. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Basic Facts

  3. Seminars on formation and evolution of the Galaxy Feb 12, 2002

  4. RegionInfoContainer PlateInfoContainer PlateSource Page = Federated Database SourceIndex = Database ReferenceCatalogSource = Container = Class/Basic Object Plate Database Region Database (for each of 32768 regions) (for each plate) RegionCatalogContainers (for each plate defined area within region) (for each reference catalog) [ COMPASS Federated Database ] Seminars on formation and evolution of the Galaxy Feb 12, 2002 GSC2.2.01 exported from the COMPASS Data Base Approximately 1 Billion distinct objects found to date

  5. Seminars on formation and evolution of the Galaxy Feb 12, 2002

  6. Seminars on formation and evolution of the Galaxy Feb 12, 2002

  7. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Single-plate calibrations • Astrometry: polynomial fits + residual maps (mask) to TYCHO2 stars (onto the ICRS reference system) [>Smart] • Photometry: fits to a (B)VR CCD sequences to 18-19 mag (GSPC2) transformed to natural bandpasses (J and F) [GSPC2>Bucciarelli] • Classification: 30 ranked features + oblique decision trees • + voting [>Smart]

  8. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Single-plate photometric calibrations

  9. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Intensity Stellar PSF Photographic Density Density Saturation Sky background Intensity Sky background

  10. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Photographic Density Intensity Density Saturation Integrated density above threshold Stellar PSF Intensity Sky background Sky background GSC-II photometric parameter = Integrated photographic density above threshold (Dsky + 3sky )

  11. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Examples of saturated stellar PSF’s

  12. Seminars on formation and evolution of the Galaxy Feb 12, 2002

  13. Seminars on formation and evolution of the Galaxy Feb 12, 2002 GSPC2 stars Tycho stars

  14. Seminars on formation and evolution of the Galaxy Feb 12, 2002

  15. Seminars on formation and evolution of the Galaxy Feb 12, 2002 GSC2.2 Photographic photometry: bandpasses

  16. Seminars on formation and evolution of the Galaxy Feb 12, 2002 GSC2.2 Photographic photometry: transformation to platenatural bands

  17. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Photographic photometry

  18. Seminars on formation and evolution of the Galaxy Feb 12, 2002 The Catalog

  19. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Catalog extraction rules • Only plates included in the GSC2.2 plate list considered (POSS II: 897 XJxxx + 897 XFxxx fields; 606 SERC-J, Sxxx, 216 SERC-EJ, Erxxx, and the red material, XSxxx and GRxxx, short exp., plates) • Objects brighter than: J<19.5 OR F<18.5 • Objects classed as defect on only one plate discarded • Astrometry: export the position of that entry of a given object closest to the entry’s plate center (tolerance set to 0.25 deg). Brake ties by selecting entry with the most recent epoch • Photometry: for each bandpass, take the value of the entry closest to the plate center

  20. Seminars on formation and evolution of the Galaxy Feb 12, 2002 A view of the GSC2.2.01

  21. Seminars on formation and evolution of the Galaxy Feb 12, 2002

  22. Seminars on formation and evolution of the Galaxy Feb 12, 2002 The GSC2 Export Catalog: specifications • Positions: <0.”5 absolute (average across one plate); better than 0.”2 relative (over a 0.5 deg field); 0.”15 rms deviation from ICRS (average over all plates) • Magnitudes: precision to better than 0.2 mag for stars between 12 and 18 mag; accuracy <0.15 mag • Classification: 95% accuracy within 2 mag from plate limit • Completeness: V=18 minimum

  23. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Global Error Analysis

  24. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Astrometric errors Internal comparisons: on average relative error well within the 0.2 arcsec requirement. • External Comparisons to: • UCAC1 • Sky coverage: Southern hemisphere (-90 deg/-15 deg) • Mag limit = 16.0, precision: better than 0.1 arcsec per coordinate) • 2MASS • Approaching all-sky coverage. Mag limit close to that of GSC2.2; position to 0.2 arcsec (per coordinate)

  25. Seminars on formation and evolution of the Galaxy Feb 12, 2002 • Method: • Statistical tests on the residuals (also called catalog-to-catalog differences)>>> • d=(GSC2.2.01 - external catalog). • Ex.: a realization of the statistic d could be declination differences >> {di = DECi,gsc2 - DECi,ext.cat. } • The hypothesis put to test is that the residuals follow (within the chosen confidence level) the expected distribution: if the values from the two catalogs are Gaussian distributed >> d is also Gaussian distributed.

  26. Seminars on formation and evolution of the Galaxy Feb 12, 2002 TWO TESTS: Chi-square, Kolmogorov-Smirnov Sample mean and variance are computed before the application of the tests. Outliers are eliminated from the sample to avoid biased values. Chi-square: need to group data to form histogram >> depends on number of bins. Chi-sq statistic

  27. Seminars on formation and evolution of the Galaxy Feb 12, 2002 where ni is the number of differences in bin i-th, and the integral is evaluated using the error function.

  28. Seminars on formation and evolution of the Galaxy Feb 12, 2002 K-S Test: do not need to group data (> reliable even with small samples) K-S statistic where and

  29. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Confidence levels set to 95% for both tests: from the distributions of the Chi-square and K-S statistics we calculate the quantiles (the values) for which the probabilities of the two statistics to be above those values are 0.05. Finally, if the values of 2 and Dn calculated from the samples are smaller than the quantiles the tests are satisfied with the 95% confidence level.

  30. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Astrometric Error (external): UCAC1

  31. Astrometric Error (external): UCAC1, Chi2 and K-S tests Seminars on formation and evolution of the Galaxy Feb 12, 2002 (Large sample, no mag and no plate-based selection) Both tests fail!….But,…..

  32. Astrometric Error (external): UCAC1 , Chi2 and K-S tests Seminars on formation and evolution of the Galaxy Feb 12, 2002 (Selected sample, mag range 16-16.5, no plate-based selection) K-S tests passed, and Chi2 also well behaved!!

  33. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Astrometric Error (external): 2MASS

  34. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Astrometric Error (external): 2MASS , Chi2 and K-S tests (Large sample, no mag and no plate-based selection)

  35. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Astrometric Error (external): Conclusions Overall, the residuals appear well behaved, although simple statistical tests fail. As expected, this indicates the presence of magnitude and plate-based effects. Indeed, the same tests are consistently passed when limited to small magnitude bins or residuals from the same plate. This, in turn, is further proof that the single plate calibrations do obey gaussian statistics.

  36. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Photometric Errors • Internal Tests: J, F plate-to-plate, J-F=const • Semi-internal tests: J, F GSC2 vs. GSCPC2 • External tests: against photometric catalogs (M67, DMS, EIS, etc.) • Comparisons against starcounts from Galaxy models

  37. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Photometric Errors: internal test Residuals: JXJ443 - JXJ444 vs. J (red crosses)

  38. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Internal photometric errors:plate-to-plate comparison statistics RMS(m)=0.27 / 2 mag from the analysis of stellar objects from 67 GSC-II (CRA) plates by Pannunzio, Morbidelli et al. (2001, OATo Rept. 57/01). This is an upper limit for GSC 2.2 because it is based on all stars down to the plate limits.

  39. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Photometric Errors - Semi-Internal Test: GSC2.2 vs. GSPC2 GSCP2 vs. GSC2.2: >0°, b>30° (low crowding) GSCP2 vs. GSC2.2: >0°, -15 ° <b<+15° (galactic plane) (Spagna)

  40. Photometric Errors - Semi-Internal Test: GSC2.2 vs. GSPC2 Seminars on formation and evolution of the Galaxy Feb 12, 2002 GSCP2 vs. GSC2.2 (>0° b>30° ) - Stellar objects only

  41. Photometry. External Test: M67 (l=216°, b=+32°) Seminars on formation and evolution of the Galaxy Feb 12, 2002 All objects J = -0.07 RMS=0.11 F = -0.01 RMS=0.13 Stars only J = -0.06 RMS=0.10 F = 0.00 RMS=0.10 CCD data (0.5° x 0.5°) from Montgomery et al. (1993, AJ, 106, 181)

  42. Seminars on formation and evolution of the Galaxy Feb 12, 2002 External Test: GSC2.2 vs. DMS All objects J = -0.06 RMS=0.10 F = +0.01 RMS=0.17 Stars only J = -0.05 RMS=0.09 F = 0.02 RMS=0.15 (Spagna) Stellar objects CCD data (0.83 sq-deg in six fields) from DMS (Deep Multicolor Survey; Osmer et al, 1998, ApJS, 119, 189)

  43. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Classification Errors

  44. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Classification Errors

  45. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Classification Errors

  46. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Classification Errors

  47. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Classification Errors

  48. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Catalog Completeness (1/4) Toward the galactic center (l,b~0.5 deg) All stars, J mag Jcompl = 17.3

  49. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Catalog Completeness galactic center (l,b~0.5 deg) All stars, F mag Fcompl = 15.8

  50. Seminars on formation and evolution of the Galaxy Feb 12, 2002 Catalog Completeness galactic center (l,b~0.5 deg) All obj.s, J mag Jcompl = 18.4

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