II. Contents of the Second 2MASS Incremental Data Release

1. General Properties of the Data Release

• Range of Dates Over Which Release Data Were Acquired:
  
  
  • North: 1997 June 7 - 1998 December 14 and 1999 February 2 - 1999 May 21 UT
  • South: 1998 March 19 - 1999 February 20 UT



• Total Number of Fully or Partially Photometric Nights in that Range:
  
  
  • North:     329
  • South:     239
  
  
  
• Number of Survey Tiles Included in Release (59,650 in full sky):     27,493



• Area of Release:
  
  
  • Nominal unique area covered by Tiles:                                       19,680.8 sq.degrees
  • Effective area of PSC (includes a 10´´ border for each Tile):     19,641.6 sq.degrees
  • Effective area of XSC (includes a 15´´ border for each Tile):     19,609.4 sq.degrees



• Sky Coverage Map for Second Incremental Release       (2MASS PSC JHK_s surface density map in galactic aitoff projection, with equatorial coordinate grid overlay; c.f. I.6a.)



• Criteria for Selection of Tiles to Include in Release (c.f. V.2 for more details):
  • Data Acquired in Photometric Conditions
    (residuals to a linear fit to photometric zero point offset < 0.04 mag in all 3 bands)
  
  
  
  • Photometric Sensitivity Meets Level 1 Requirements in all 3 Bands
    (based on Average Sky Background Levels and Seeing in Tile)
  
  
  
  • Average Seeing FWHM < 3.5´´ in all 3 Bands
    (for accurate photometry and star/galaxy separation)
  
  
  
  • H-Band Background Residual Noise Due to Atmospheric Airglow < 5x the Noise Value Predicted for Background Level and Source Density in >87% of a Tile Area (for accurate extended source photometry)
  
  
  
  • Tile Must Fall in Contiguous Block of >3 Acceptable Tiles (for accurate assessment of positional uncertainties)
  
  
  

• Basic Tile Information Available in the Scan Information Table Accessible via IRSA/GATOR
  • UT Observation Date and Time
  
  
  
  • Reconstructed Tile Corner Positions
  
  
  
  • Mean Photometric Parameters
  
  
  
  • Mean Point Source Noise Levels
  
  
  
  • Mean Extracted Source Densities
  
  
  

[Last Updated: 2000 April 10; by R. Cutri]