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GSPC -II Program

GSPC -II Program. GOAL: extend GSPC-I photometry to B = V ˜ 20 add R band to calibrate red second-epoch surveys. HOW: take B,V,R CCD exposures centered at GSPC-I faintest star OR conveniently close to POSS-II centers (for POSS-II offset plates). The Data.

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GSPC -II Program

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  1. GSPC-II Program • GOAL: • extend GSPC-I photometry to B = V ˜ 20 • add R band to calibrate red second-epoch surveys • HOW: • take B,V,R CCD exposures centered at GSPC-I faintest star OR • conveniently close to POSS-II centers (for POSS-II offset plates)

  2. The Data • Given the long time span of this survey project, data come from different telescopes as well as different CCD cameras • Size of camera fields vary from ˜ 3.5 arc minutes to ˜20 arc minutes • Pixel scale ranges from ˜ 0.35 arc seconds/pixel to ˜ 0.7 arc seconds/pixel • When appropriate, both long and short exposures are acquired • Pre-selected sets of standard stars from the Landolt catalog are observed each night • Common fields are also regularly observed

  3. Example ofCCD frames taken at the 0.9m ESO Dutch poor Crowded medium

  4. Telescope usage and number of GSPC-II sequences collected (as of October 2001)

  5. Relevant Numbers • Target sequences are 1780 (1478 GSPC-I centers + 302 POSS-II new sequences) • Current in-house catalog contains 1619 sequences, of which 776 in the north and 856 in the south • data from one and a half runs performed in semester 01A still to be included in catalog • two more runs of 7 nights each, one at the ING/JKT and one at the CTIO 0.9m, to be performed in November/December

  6. Sky Coverage 1794 GSPCII targets - 1679 observed - 115 still remain

  7. Magnitude limit of current catalog sequences

  8. Number of stars/sequence in current catalog

  9. GSPC-II Reduction Pipeline • Photometry carried out with pipeline software (ARLO, Casalegno 1998) developed under IRAF 2.10.4 • Astrometry done within ARLO - fit to DSS positions • Catalog of all frame data is a flat ASCII file including photometric, astrometric and other relevant information about the original exposures • IRAF tables including additional statistical information are generated along with the frame catalogs • Object naming performed in IRAF/IDL (naming convention: S001-AAAA, S002-AAAB, etc…)

  10. Photometric Accuracy • Only fits to Landolt stars with rms better than 0.05 are accepted • Aperture photometry is carried out with fixed radius (2.3FWHM or < 4.5”) therefore not reliable in crowded fields • PSF photometry more stable, but need to be checked for systematic errors in case of bad choice of template stars for analytical PSF • Zero-point errors of transformation to standard system is also critical because it induces a photometric error of comparable magnitude

  11. Released Sequences • 622 GSPC-II fields ( Bucciarelli, Garcia, Casalegno et al. 2001, A&A 368, 335), 744 northern and 444 southern fields • data are from KPNO, CTIO and ESO, for a total of 153 observing nights • Aperture photometry only • selection criteria based on agreement between Aperture and PSF photometry: Linear regression M(apt) - M(psf) = Z + k M(apt) sequences for which |k| < 0.01 and rms < 0.3 mag were retained

  12. Zero-point errors Cumulative Distributions

  13. GSPC-I/GSPC-II Comparison 597 V objects rms 0.07 mag, mean 0.001 mag 380 B objects rms 0.06 mag, mean 0.003 mag

  14. Comparison of 10 common fields CTIO/KPNO

  15. Comparison of 47 common fields CTIO/ESO

  16. Summary • 95% of GSPC-II data secured and practically all reduced • Spin-off of observing activity • 622 photometric sequences made available to community • QA of new set of sequences for second release in progress • Plan to put images, along with photometric reduction files, on-line for easy retrieval

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