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J/AJ/124/601  Absolute positions and proper motions in NGC 188  (Platais+, 2002)
WIYN Open Cluster Study.
VIII. The geometry and stability of the NOAO CCD Mosaic Imager
    Platais I., Kozhurina-Platais V., Girard T.M., van Altena W.F.,
    Klemola A.R., Stauffer J.R., Armandroff T.E., Mighell K.J., Dell'Antonio I.,
    Falco E.E., Sarajedini A.
   <Astron. J. 124, 601 (2002)>
   =2002AJ....124..601P
ADC_Keywords: Clusters, open ; Proper motions ; Photometry, UBV

Keywords: astrometry - catalogs - instrumentation: detectors -
          open clusters and associations: individual (NGC 188)

Abstract:
    The field of direct imaging is experiencing a considerable growth in
    the number of available CCD mosaic imagers, especially on large
    telescopes. To fully exploit the astrometric potential of these
    imaging devices, we develop a technique, utilizing an astrometric
    standard, for precision transformation of pixel coordinates into a
    global coordinate system. We have constructed a new astrometric
    standard set of 1863 stars in the field of NGC 188 to derive the CCD
    chip constants for the NOAO CCD Mosaic Imager. The multiple-epoch data
    on the Mosaic's metrics indicate that this CCD mosaic device may have
    experienced a one-time nonelastic expansion. We also present a new
    determination of the pixel scale and the optical field angle
    distortion constants for the KPNO Mayall 4 m telescope prime focus
    field corrector. To establish a reliable history of the CCD mosaic
    imager metrics for current and potential future astrometric
    applications, we recommend obtaining astrometric calibrations for CCD
    mosaic imagers on a regular basis. Apart from mechanical positioning
    of the CCD mosaic camera on the telescope, noticeable changes in the
    thermal environment of CCD mosaic chips should also prompt new
    astrometric calibrations. It is shown that, following all precautions,
    the NOAO CCD Mosaic Imager can produce excellent astrometric results
    on the Mayall 4 m telescope.

Description:
    This file has not been included in the paper, although it was
    instrumental in deriving the NOAO Mosaic Imager CCD chip constants and
    distortion coefficients. The file contains an astrometric standard
    around the open cluster NGC 188. It can serve as a medium depth (V=17)
    astrometric standard and as a source of absolute proper motions. The
    typical accuracy of proper motions is 1.5 to 2.0mas/yr for stars
    brighter than V=14 and reaches 7.0mas/yr at the limiting magnitude.
    The mean internal precision of the equatorial coordinates is 60 mas or
    better. The precision of BV photographic photometry, calibrated using
    the available photoelectric BV photometry, is 0.07mag in each
    bandpass.

    The astrometric standard around NGC 188 is based on twenty five
    8x10 inch format plates taken with the Lick 51-cm double astrograph
    (scale 55.1"/mm) located on Mt. Hamilton, California. The basic data
    on this plate material are provided in Table 1, where the beginning
    and the end of exposures are given either in Universal Time (UT) or
    Local Siderial Time (LST) as listed on plate envelopes. In addition,
    the photographic emulsion, filter and observer are also indicated.

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
plates.dat        78       25   Plate material
ngc188.dat        64     1863   Catalog of positions, absolute proper motions and
                            BV photographic photometry in the region of
                            open cluster NGC 188


See also:
   J/AJ/122/1486 : NGC 2451A proper motions and membership  (Platais+, 2001)


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

   Bytes Format Units      Label     Explanations

   1-  7  A7    ---        Plate     Plate number (1)
   9- 18  A10 "YYYY/MM/DD" ObsDate   Observation date
  21- 28  A8    "HH:MM:SS" ObsTime1  Time of beginning of the observation
      29  A1    ---        ---       [-]
  30- 37  A8    "HH:MM:SS" ObsTime2  Time of end of the observation
  40- 42  A3    ---      n_ObsTime1  UT or LST time of observation
  45- 49  A5    ---        Emul      Emulsion
  52- 56  A5    ---        Filter    Filter
  59- 73  A15   ---        Obs       Observer's name

Note (1): Only a selected sample of stars was measured on the plates.
    All stars down to the plate limit have been measured within a circular
    area with a 30' radius centered on RA=0h 44m 20s, DE=+85°19'(J2000). 
    In addition, a sample of Hipparcos and Tycho-2 stars were measured in
    a larger 2x2° area having the same center. In the catalog the
    Hipparcos and Tycho-2 stars can be identified as those having
    identification numbers higher than 9800. (Some of them have duplicate
    entries among the stars in the main body of the catalog.) The details
    on plate measurements and reductions are given in the paper.


Byte-by-byte Description of file: ngc188.dat

   Bytes Format Units     Label   Explanations

   1-  4  I4    ---       ID      Object identifier
   6- 15  F10.8 rad       RArad   Right ascension for the epoch J2000 and in the
                                   ICRS reference system (i.e. equinox J2000.0)
  17- 26  F10.8 rad       DErad   Declination for the epoch J2000,
                                   equinox J2000.0
  28- 34  F7.1  mas/yr    pmRA    Absolute proper motion in right ascension
                                   multiplied by cos(DE)
  36- 42  F7.1  mas/yr    pmDE    Absolute proper motion in declination
  44- 48  F5.2  mag       Vmag    Photographic V-magnitude
  50- 54  F5.2  mag       B-V     Photographic B-V color
  56- 58  F3.1  mas/yr    e_pmRA  Estimated standard error of proper motion
                                   in one coordinate (mean of RA and DE)
  60- 61  I2    ---      n_RArad  Number of plates used for a solution in
                                   right ascension
  63- 64  I2    ---      n_DErad  Number of plates used for a solution in
                                   declination


History:
    Copied at http://www.astro.yale.edu/astrom

References:
 Von Hippel & Sarajedini,    Paper I   1998AJ....116.1789V
 Sarajedini et al.,          Paper II  1999AJ....118.2894S
 Sarajedini,                 Paper III 1999AJ....118.2321S
 Barrado y Navascues et al., Paper V   2001ApJ...549..452B
 Sills & Sarajedini,         Paper VI  2000ApJ...544..944S
 Platais et al.,             Paper VII 2001AJ....122.1486P, Cat. J/AJ/122/1486
 Grocholski & Sarajedini     Paper X   2002AJ....123.1603G
(End)                                          Patricia Bauer [CDS]  21-Jan-2002