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J/ApJ/602/264   Proper motions and radial velocities in M15    (Mcnamara+, 2004)
The dynamical distance to M15: estimates of the cluster's age and mass and
of the absolute magnitude of its RR Lyrae stars.
    Mcnamara B.J., Harrison T.E., Baumgardt H.
   <Astrophys. J., 602, 264-270 (2004)>
   =2004ApJ...602..264M
ADC_Keywords: Clusters, globular ; Proper motions ; Radial velocities

Keywords: distance scale - globular clusters: individual (M15)


Abstract:
    Newly determined high-precision relative proper motions determined
    from the Hubble Space Telescope Wide Field Planetary Camera 2 are used
    along with radial velocity measurements to determine the dynamical
    distance to the globular cluster M15. A comparison of the proper
    motion and radial velocity dispersions from a sample of 237 stars,
    located at an average radial distance of about 10" from the cluster
    center, yields a cluster distance of 9.98±0.47kpc. This distance
    agrees to within the stated errors to other distance estimates but
    places this object about 5% closer than the currently adopted value of
    10.4kpc. Using this new distance, we estimate that RR Lyrae stars
    having [Fe/H]=-2.15 have a value of Mv(RR)=0.51±0.11. We also
    estimate that M15 has an age of about 13.2Gyr, which places it among
    the oldest of the Galactic globular clusters. From a comparison of the
    observed velocity dispersion with results from recent N-body
    calculations, we derive a total cluster mass for M15 of
    MC=4.5x105M☉.

Description:
    The proper motion and radial velocity measurements employed in this
    study are those published by McNamara et al. (2003, Cat.
    J/ApJ/595/187) and Gebhardt et al. (2000, Cat. J/AJ/119/1268),
    respectively. The former investigation relied on Hubble Space
    Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) images taken in
    1995 and 2003.
Objects:
    -----------------------------------------
       RA   (2000)   DE      Designation(s)
    -----------------------------------------
    21 29 58.4   +12 10 01   M15 = NGC 7078
    -----------------------------------------

File Summary:

       FileName      Lrecl  Records   Explanations

ReadMe            80        .   This file
table1.dat        55      242   Proper motion and radial velocity data


See also:
  J/A+AS/119/307 : Position in M15 (Le Campion+, 1996)
    J/AJ/106/154 : HST Observations in inner region of M15 (Ferraro+ 1993)
   J/AJ/107/1745 : HST UVI photometry of M15. II. (Yanny+, 1994)
    J/AJ/110/704 : RR Lyrae Variables in M15 (Silbermann+ 1995)
    J/AJ/115/708 : Radial Velocities in the Field of M15 (Drukier+ 1998)
   J/AJ/119/1268 : CFHT adaptive optics observations of M15 (Gebhardt+, 2000)
   J/AJ/124/3255 : UBV photometry in M15 (van der Marel+, 2002)
   J/ApJ/595/187 : Proper motions in M15 (McNamara+, 2003)


Byte-by-byte Description of file: table1.dat

   Bytes Format Units     Label   Explanations

   1-  5  F5.1  pix       Xpos    X pixel location (1)
   7- 11  F5.1  pix       Ypos    Y pixel location (1)
  13- 18  F6.3  10mas/yr  pmX     Proper motion in X direction
  20- 25  F6.3  10mas/yr  pmY     Proper motion in Y direction
  27- 31  F5.3  10mas/yr  e_pmX   X proper motion error
  33- 37  F5.3  10mas/yr  e_pmY   Y proper motion error
  39- 43  I5    ---       VGG     ID given in Gebhardt et al. (2000,
                                   Cat. J/AJ/119/1268), Cl* NGC 7078 VGG NNNNN
  45- 50  F6.1  km/s      RV      Radial velocity in Gebhardt et al. (2000,
                                   Cat. J/AJ/119/1268)
  52- 55  F4.1  km/s      e_RV    Error in RV

Note (1): On HST Image WFPC2 U2AS0201T.
      The scale of these images is 0.0455"/pix and they cover an area of
      36"x36" approximately centered on the cluster core.


History:
    From electronic version of the journal
(End)                  Greg Schwarz [AAS], Patricia Vannier [CDS]    06-Apr-2004