J/AJ/159/272 Orion Nebula Cluster PMs with HST Treasury Program (Platais+, 2020)
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Hubble Space Telescope astrometry in the Orion Nebula Cluster: census of
low-mass runaways.
    Platais I., Robberto M., Bellini A., Kozhurina-Platais V., Gennaro M.,
    Strampelli G., Hillenbrand L.A., de Mink S.E., Soderblom D.R.
   <Astron. J., 159, 272 (2020)>
   =2020AJ....159..272P
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ADC_Keywords: Clusters, open; Photometry, HST; Proper motions; Optical
Keywords: Hubble Space Telescope ; Space astrometry ; Proper motions ;
          Young star clusters ; Low mass stars ; Stellar dynamics ;
          Runaway stars

Abstract:
    We present a catalog of high-precision proper motions in the Orion
    Nebula Cluster (ONC), based on Treasury Program observations with the
    Hubble Space Telescope's (HST) ACS/WFC camera. Our catalog contains
    2454 objects in the magnitude range of 14.2<m_F775W_<24.7, thus
    probing the stellar masses of the ONC from ~0.4M{sun} down to
    ~0.02M{sun} over an area of ~550arcmin^2^. We provide a number of
    internal velocity dispersion estimates for the ONC that indicate a
    weak dependence on stellar location and mass. There is good agreement
    with the published velocity dispersion estimates, although nearly all
    of them (including ours at {sigma }_{v,x}_=0.94 and
    {sigma}_{v,y}_=1.25mas/yr) might be biased by the overlapping young
    stellar populations of Orion A. We identified four new ONC candidate
    runaways based on HST and the Gaia DR 2 data, all with masses less
    than ~1M{sun}. The total census of known candidate runaway sources is
    10-one of the largest samples ever found in any Milky Way open star
    cluster. Surprisingly, none of them have tangential velocities
    exceeding 20km/s. If most of them indeed originated in the ONC, it may
    compel the re-examination of dynamical processes in very young star
    clusters. It appears that the mass function of the ONC is not
    significantly affected by the lost runaways.

Description:
    The Treasury Program on the Orion Nebula Cluster (ONC) (GO-10246;
    PI: M. Robberto) produced a large number of observations with three
    different Hubble Space Telescope (HST) cameras through 10 different
    filters.

    This first HST Treasury Program on the ONC was done over two sets of
    epochs, 2004-October-11 November-7 and 2005-March-3 April-26, with
    a ~180{deg} change of the HST orientation between these periods. These
    two sets of observations constitute our first epoch.

    We designed a second HST Treasury Program on the ONC (GO-13826;
    PI: M. Robberto). For the purpose of deriving proper motions, the
    ACS/WFC observations were designed to reproduce-to the extent
    possible-the same pointings and exposure time, telescope orientation,
    guide stars, and the Earth-orbit position as in our first survey. Only
    the broadband filter F775W was used for these observations over two
    time periods in 2015-February-8 April-28 and 2015-August-1 October-29,
    thus establishing our second epoch.

File Summary:
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 FileName    Lrecl  Records  Explanations
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ReadMe          80        .  This file
table1.dat     122     2454  Proper Motion Catalog
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See also:
 J/A+AS/118/503 : Proper motions of stars in Ori Nebula (Tian+ 1996)
 J/AJ/113/1733  : Orion Nebula Cluster population (Hillenbrand 1997)
 J/AJ/125/277   : High proper motions in central Orion nebula (O'dell+, 2003)
 J/A+A/446/949  : Open clusters proper motions based on UCAC2 (Dias+, 2006)
 J/ApJ/676/1109 : Velocities of stars in the Orion Nebula Cluster (Furesz+,2008)
 J/ApJ/697/1103 : Kinematics of Orion Nebula Cluster (Tobin+, 2009)
 J/ApJ/722/1092 : Optical photometry of the ONC. II. (Da Rio+, 2010)
 J/ApJ/748/14   : ONC population data from WFI observations (Da Rio+, 2012)
 J/AJ/144/192   : Spitzer survey of Orion A & B. I. YSO catalog (Megeath+, 2012)
 J/ApJS/207/10  : HST Treasury Program on the ONC (Robberto+, 2013)
 J/A+A/587/A153 : VISION I. VISTA Orion A Survey (Meingast+, 2016)
 J/A+A/608/A148 : Stellar populations towards Orion with Gaia DR1 (Zari+, 2017)
 J/A+A/619/A106 : 3D shape of Orion A from Gaia DR2 (Grossschedl+, 2018)
 J/AJ/156/84    : APOGEE-2 survey of Orion Complex. II. (Kounkel+, 2018)
 J/AJ/156/98    : Runaway stars in 30 Doradus region of the LMC (Platais+, 2018)
 J/AJ/157/109   : Stellar proper motions in the Orion Nebula Cluster (Kim+,2019)
 J/ApJ/870/32   : Kinematics in young star clusters & associations (Kuhn+, 2019)

Byte-by-byte Description of file: table1.dat
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   Bytes Format Units    Label Explanations
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  1-  4 I4     ---      ID     [1/8185] Entry number (1)
  6- 11 F6.2   mas/yr   pmx    [-46.3/38.6] Weighed relative proper motion in X
 13- 18 F6.2   mas/yr   pmy    [-46/38.3] Weighed relative proper motion in Y
 20- 23 F4.2   mas/yr e_pmx    [0/2.5] Error in pmx
 25- 28 F4.2   mas/yr e_pmy    [0/2.5] Error in pmy
 30- 34 F5.2   ---      chi2-x [0/96.6]?=99.99 Normalized {chi}^2^ for proper
                                motion in X
 36- 40 F5.2   ---      chi2-y [0.0/99.9]?=99.99 Normalized {chi}^2^ for proper
                                motion in Y
 42- 45 F4.2   ---      qx     [0/1] Goodness-of-fit probability Q in X
 47- 50 F4.2   ---      qy     [0/1] Goodness-of-fit probability Q in Y
 52- 57 F6.3   mag      imag   [13.9/24.8] Sloan i-band magnitude; ACS/WFC+F775W
 59- 63 F5.2   yr       Tspan  [9.85/11.05] Time span of observations
     65 I1     ---      n1     [1/9] Number of first epoch observations (2)
 67- 68 I2     ---      n2     [1/13] Number of second epoch observations (2)
     70 I1     ---      nDel   [0/5] Number of deleted observations (2)
 72- 76 F5.3   pix      resid  [0.003/1.4] Largest residual in least-squares
                                fitting
 78- 86 F9.2   pix      Xpix   [-10810/20132] X-coordinate in ACS/WFC pixels (3)
 88- 96 F9.2   pix      Ypix   [-21337/13554] Y-coordinate in ACS/WFC pixels (3)
 98-108 F11.8  deg      RAdeg  [83.54/83.98] Right Ascension (J2000)
110-120 F11.8  deg      DEdeg  [-5.69/-5.2] Declination (J2000)
    122 I1     ---      flag   [0/9] Proper motion flag (4)
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Note (1): From Table 5 of Robberto+, 2013, J/ApJS/207/10
Note (2): Total number of available observations=n1+n2+nDel.
Note (3): X and Y are aligned with RA and Dec accordingly.
          The X-coordinate has a flipped sign.
Note (4): Flags as follows:
    0 = proper motion discrepant wrt other sources (34 occurrences)
    1 = likely reliable proper motion (2274 occurrences)
    2 = confirmed larger proper motion from other source(s) (64 occurrences)
    3 = larger proper motion uncertain from comparison with other source
        (15 occurrences)
    4 = possibly incorrect large proper motion (26 occurrences)
    9 = detected discrepant proper motion in the other source (9 occurrences)
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History:
    From electronic version of the journal

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(End)                          Prepared by [AAS], Coralie Fix [CDS], 27-Aug-2020