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

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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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Seminars on formation and evolution of the Galaxy
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Basic Facts
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Seminars on formation and evolution of the Galaxy
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Seminars on formation and evolution of the Galaxy
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GSC2.2.01 exported from the COMPASS Data Base
Approximately 1 Billion distinct objects found to
date
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Seminars on formation and evolution of the Galaxy
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Seminars on formation and evolution of the Galaxy
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Single-plate calibrations

• Astrometry polynomial fits residual maps
  (mask) to TYCHO2 stars (onto the ICRS reference
  system) gtSmart
• Photometry fits to a (B)VR CCD sequences to
  18-19 mag (GSPC2) transformed to natural
  bandpasses (J and F) GSPC2gtBucciarelli
• Classification 30 ranked features oblique
  decision trees
• voting gtSmart

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Seminars on formation and evolution of the Galaxy
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Single-plate photometric calibrations
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Seminars on formation and evolution of the Galaxy
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Intensity
Stellar PSF
Photographic Density
Density
Saturation
Sky background
Intensity
Sky background
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Seminars on formation and evolution of the Galaxy
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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 )
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Examples of saturated stellar PSFs
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Seminars on formation and evolution of the Galaxy
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GSPC2 stars
Tycho stars
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Seminars on formation and evolution of the Galaxy
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GSC2.2 Photographic photometry bandpasses
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Seminars on formation and evolution of the Galaxy
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GSC2.2 Photographic photometry transformation to
plate natural bands
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Seminars on formation and evolution of the Galaxy
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Photographic photometry
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Seminars on formation and evolution of the Galaxy
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The Catalog
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Seminars on formation and evolution of the Galaxy
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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 Jlt19.5 OR Flt18.5
• Objects classed as defect on only one plate
  discarded
• Astrometry export the position of that entry of
  a given object closest to the entrys 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

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Seminars on formation and evolution of the Galaxy
Feb 12, 2002
A view of the GSC2.2.01
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Seminars on formation and evolution of the Galaxy
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Seminars on formation and evolution of the Galaxy
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The GSC2 Export Catalog specifications

• Positions lt0.5 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 lt0.15 mag
• Classification 95 accuracy within 2 mag from
  plate limit
• Completeness V18 minimum

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Seminars on formation and evolution of the Galaxy
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Global Error Analysis
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Seminars on formation and evolution of the Galaxy
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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)

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Seminars on formation and evolution of the Galaxy
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• Method
• Statistical tests on the residuals (also called
  catalog-to-catalog differences)gtgtgt
• d(GSC2.2.01 - external catalog).
• Ex. a realization of the statistic d could be
  declination differences gtgt 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 gtgt d is also
  Gaussian distributed.

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Seminars on formation and evolution of the Galaxy
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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
gtgt depends on number of bins. Chi-sq statistic

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Seminars on formation and evolution of the Galaxy
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where ni is the number of differences in bin
i-th, and
the integral is evaluated using the error
function.
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Seminars on formation and evolution of the Galaxy
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K-S Test do not need to group data (gt reliable
even with small samples)
K-S statistic
where
and
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Seminars on formation and evolution of the Galaxy
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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.
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Astrometric Error (external) UCAC1
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Seminars on formation and evolution of the Galaxy
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Astrometric Error (external) UCAC1, Chi2 and
K-S tests
(Large sample, no mag and no plate-based
selection)
Both tests fail!.But,..
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Astrometric Error (external) UCAC1 , Chi2 and
K-S tests
(Selected sample, mag range 16-16.5, no
plate-based selection)
K-S tests passed, and Chi2 also well behaved!!
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Seminars on formation and evolution of the Galaxy
Feb 12, 2002
Astrometric Error (external) 2MASS
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Seminars on formation and evolution of the Galaxy
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Astrometric Error (external) 2MASS , Chi2 and
K-S tests
(Large sample, no mag and no plate-based
selection)
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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.
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Photometric Errors

• Internal Tests ?J, ?F plate-to-plate, J-Fconst
• Semi-internal tests ?J, ?F GSC2 vs. GSCPC2
• External tests against photometric catalogs
  (M67, DMS, EIS, etc.)
• Comparisons against starcounts from Galaxy
  models

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Photometric Errors internal test
Residuals JXJ443 - JXJ444 vs. J (red crosses)
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Seminars on formation and evolution of the Galaxy
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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.
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Photometric Errors - Semi-Internal Test GSC2.2
vs. GSPC2
GSCP2 vs. GSC2.2 ?gt0, bgt30 (low crowding)
GSCP2 vs. GSC2.2 ?gt0, -15 ltblt15 (galactic
plane)
(Spagna)
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Seminars on formation and evolution of the Galaxy
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Photometric Errors - Semi-Internal Test GSC2.2
vs. GSPC2
GSCP2 vs. GSC2.2 (?gt0 bgt30 ) - Stellar objects
only
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Seminars on formation and evolution of the Galaxy
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Photometry. External Test M67 (l216,
b32)
All objects ??J? -0.07 RMS0.11 ??F? -0.01
RMS0.13 Stars only ??J? -0.06 RMS0.10 ??F?
0.00 RMS0.10
CCD data (0.5 x 0.5) from Montgomery et al.
(1993, AJ, 106, 181)
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Seminars on formation and evolution of the Galaxy
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External Test GSC2.2 vs. DMS
All objects ??J? -0.06 RMS0.10 ??F?
0.01 RMS0.17 Stars only ??J? -0.05
RMS0.09 ??F? 0.02 RMS0.15
(Spagna)
Stellar objects
CCD data (0.83 sq-deg in six fields) from DMS
(Deep Multicolor Survey Osmer et al, 1998, ApJS,
119, 189)
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Seminars on formation and evolution of the Galaxy
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Classification Errors
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Seminars on formation and evolution of the Galaxy
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Classification Errors
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Seminars on formation and evolution of the Galaxy
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Classification Errors
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Seminars on formation and evolution of the Galaxy
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Classification Errors
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Seminars on formation and evolution of the Galaxy
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Classification Errors
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Seminars on formation and evolution of the Galaxy
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Catalog Completeness (1/4)
Toward the galactic center (l,b0.5 deg)
All stars, J mag Jcompl 17.3
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Seminars on formation and evolution of the Galaxy
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Catalog Completeness
galactic center (l,b0.5 deg)
All stars, F mag Fcompl 15.8
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Seminars on formation and evolution of the Galaxy
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Catalog Completeness
galactic center (l,b0.5 deg)
All obj.s, J mag Jcompl 18.4
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Seminars on formation and evolution of the Galaxy
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Catalog Completeness
galactic center (l,b0.5 deg)
All obj.s, F mag Fcompl 18.0
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Comparison to SDSS
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Contributions for this presentation from
B. Bucciarelli R. Drimmel R. Smart A. Spagna
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THE END
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