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J/A+A/390/961       VI photometry in NGC 188                 (Andreuzzi+, 2002)
The white dwarf cooling sequence in the old open cluster NGC 188.
    Andreuzzi G., Richer H.B., Limongi M., Bolte M.
   <Astron. Astrophys. 390, 961 (2002)>
   =2002A&A...390..961A
ADC_Keywords: Clusters, open ; Photometry, UBVRI

Keywords: open clusters and associations: individual: NGC 188 -
          stars: white dwarfs - stars: luminosity function

Abstract:
    We used HST-WFPC2 to study the white dwarf luminosity function of the
    old open cluster NGC 188 in order to determine a lower limit to the
    age of the cluster (∼5Gyr) by looking at the faint end of the
    cooling sequence (down to V∼26.5).

Description:
    HST-WFCs photometry in the F555W-F814W filters, is presented for 223
    objects belonging to 4 different fields located on the center of the
    cluster. By applying selection criteria to the catalog (stellarity
    index, c≥0.8), we identified 157 candidate stars of which 28 white
    dwarfs.
Objects:
    ----------------------------------------------------------
       RA   (2000)   DE      Designation(s)
    ----------------------------------------------------------
    00 48 26     +85 15 21   NGC 188 cluster center
    00 48 00     +85 13 30   Field f1
    00 48 00     +85 16 00   Field f2
    00 46 00     +85 16 00   Field f3
    00 46 00     +85 13 30   Field f4
    ----------------------------------------------------------

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
catalog.dat       70      223   V, V-I photometry for stars in NGC 188


See also:
 J/AJ/124/601 : Absolute positions & proper motions in NGC 188 (Platais+, 2002)


Byte-by-byte Description of file: catalog.dat

   Bytes Format Units   Label     Explanations

   3-  9  F7.3  pix     xpos      x coordinate (1)
  12- 18  F7.3  pix     ypos      y coordinate (1)
  22- 27  F6.3  mag     Imag      Johnson I magnitude (from F814W filter)
  32- 36  F5.3  mag     e_Imag    I photometric error
  40- 45  F6.3  mag     Vmag      Johnson V magnitude (from F555W filter)
  50- 54  F5.3  mag     e_Vmag    V photometric error
  59- 63  F5.3  ---     c         Stellarity index (2)
  65- 70  I6    ---     ID        Identification number (3)

Note (1): The observations consisted of four fields, f1, f2, f3 and f4,
    in such a way that WF4 of the field f4 overlaps WF2 of the field f1
    and WF4 of the field f3 overlaps WF2 of the field f2.
        1 pix = 0.1arcsec (HST-WFC).
    The coordinates in the catalogue are computed respect to different
    median images, obtained considering the single field and camera:
        4 x WF2
        4 x WF3
        4 x WF4
Note (2): The catalog includes only the objects for which stellarity
    index c is ≥0.2
Note (3): IDs in the catalog have been created to indicates the camera
    and the field in which each object has been identified: the first
    number in the ID indicate the field (f1, f2, f3, f4); the second one
    indicate the camera:
    WF2: ID<f30000; WF3: f30000≤ID<f40000; WF4: f40000≤ID<f50000


Acknowledgements: Gloria Andreuzzi 


History:
  * 14-Apr-2004: the original catalog contained a decimal fraction ".000" 
    attached to each ID number (last column of catalog), which has been
    removed.
(End)                                        Patricia Bauer [CDS]    30-Aug-2002