J/ApJ/595/187 Proper motions in M15 (McNamara+, 2003)
Does M15 possess an intermediate-mass black hole in its core?
McNamara B.J., Harrison T.E., Anderson J.
<Astrophys. J. 595, 187 (2003)>
=2003ApJ...595..187M 2003ApJ...595..187M
ADC_Keywords: Clusters, globular ; Proper motions ; Photometry, UBV
Keywords: astrometry - black hole physics - globular clusters: individual: M15 -
methods: N-body simulations - stellar dynamics
Abstract:
We present the results of an internal proper motion analysis of the
inner region of M15 using Hubble Space Telescope Wide Field Planetary
Camera 2 images. The motions of 704 stars with brightnesses above that
of the cluster turnoff (V<18.3) are analyzed to determine the
velocity dispersion profile within about 15" of the cluster center.
The average signal-to-noise ratio of these motions is about 3, and
stars in the innermost radial bin have an average core distance of
only 0.7". Assuming a distance to M15 of 10kpc, we estimate that the
velocity dispersion within this innermost bin is 14.5±2.5km/s and
that it slowly decreases outward, reaching a value of 9.8±0.8km/s at
R=15.6". We find that the proper-motion dispersion profile is in good
agreement with the predictions of recent N-body simulations that do
not require the presence of a central intermediate-mass black hole
(IMBH). The agreement between the observed profile and the N-body
simulations is marginally improved if one assumes that when a neutron
star is created as a result of stellar evolution, it escapes from the
cluster. Based on the results of this study and a review of other
investigations, it is concluded that there is little direct evidence
that M15 possesses an intermediate-mass black hole.
Description:
M15 HST WFPC2 images were employed. These images consist of four
first-epoch exposures obtained on 1994 April 7 and 12 additional
exposures obtained on 2002 April 5 as part of our HST project
GO-09039. Both sets of images were acquired with the WFPC2 filter
F555W. Longer exposure times were used for the 2002 April images to
increase the accuracy of the measured stellar positions.
Objects:
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RA (2000) DE Designation(s)
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21 29 58.4 +12 10 01 M15 = NGC 7078
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 57 1764 M15 Proper Motion Data
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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/113/1026 : Fabry-Perot Observations of M15 (Gebhardt+ 1997)
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/ApJ/602/264 : Proper motions and radial velocities in M15
(Mcnamara+, 2004)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 F5.1 pix Xpix The x position on HST image U2AS0201T (1)
7- 11 F5.1 pix Ypix The y position on HST image U2AS0201T (1)
13- 18 F6.3 0.125pix/yr Xpm The X pixel displacement relative proper
motion over 8 years (in pix/8yr)
20- 25 F6.3 0.125pix/yr Ypm The Y pixel displacement relative proper
motion over 8 years (in pix/8yr)
27- 31 F5.3 0.125pix/yr e_Xpm Error in Xpm
33- 37 F5.3 0.125pix/yr e_Ypm Error in Ypm
39- 44 F6.2 mag Vmag Uncalibrated instrumental V magnitude
46- 49 F4.2 mag B-V Uncalibrated instrumental (B-V) magnitude
51- 55 I5 --- GID Guhathakurta et al. (1996AJ....111..267G 1996AJ....111..267G)
identification number
57 I1 --- IM [0/1] Internal proper motion analysis (2)
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Note (1): The (x,y)-positions are in units of pixels and correspond to
the position on HST image U2AS0201T, This image is accessible from the
HST archive (http://archive.stsci.edu/hst/index.html). In Simbad,
objects are identified as [MHA2003] XXX.x-YYY.y
Note (2): Internal proper motion analysis:
1 = used to compute internal motion dispersions;
0 = not used for this purpose.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Bauer [CDS] 17-Nov-2003