CDROM/AJ/V113/P1026
Fabry-Perot Observations of M15 (Gebhardt+ 1997)
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Fabry-Perot Observations of Globular Clusters. III. M15
Karl Gebhardt, Carlton Pryor, T. B. Williams, James E. Hesser
and Peter B. Stetson
<1997, AJ, 113, 1026>
=1997AJ....113.1026G
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Abstract:
We have used an Imaging Fabry-Perot Spectrophotometer with the
Sub-arcsecond Imaging Spectrograph on the Canada-France-Hawaii
Telescope to measure velocities for 1534 stars in the globular cluster
M15 (NGC 7078) with uncertainties between 0.5 and 10 km/s. Combined
with previous velocity samples, the total number of stars with measured
velocities in M15 is 1597. An average seeing of 0.8" allowed us to
obtain velocities for 144 stars within 10" of the center of M15,
including 12 stars within 2". The velocity dispersion profile for M15
remains flat at a value of 11 km/s from a radius of 0.4 into our
innermost reliable point at 0.02 (0.06 pc). Assuming an isotropic
velocity dispersion tensor, this profile and the previously-published
surface brightness profile can be equally well represented either by a
stellar population whose M/L varies with radius from 1.7 in solar units
at large radii to 3 in the central region, or by a population with a
constant M/L of 1.7 and a central black hole of 1000 Msun. A
non-parametric mass model that assumes no black hole, no rotation, and
isotropy constrains the mass density of M15 to better than 30% at a
radius of 0.07 parsecs. The mass-density profile of this model is well
represented by a power law with an exponent of -2.2, the value
predicted by models of cluster core-collapse. Using the assumption of
local thermodynamic equilibrium, we estimate the present-day mass
function and infer a significant number of 0.6-0.7 Msun objects in the
central few parsecs, 85% of which may be in the form of stellar
remnants. Not only do we detect rotation; we find that the position
angle of the projected rotation axis in the central 10" is 100 deg
different from that of the whole sample. We also detect an increase in
the amplitude of the rotation at small radii. Although this increase
needs to be confirmed with better-seeing data, it may be the result of
a central mass concentration. (Copyright) 1997 American Astronomical
Society.
File Summary:
------------------------------------------------------------------------------File Name
Lrecl
Records
Explanations
------------------------------------------------------------------------------table1.dat
52
1601
Velocity data
table1.tex
70
1621
AASTeX version of table1.dat
table2.dat
70
512
Repeat measurements
table2.tex
108
537
AASTeX version of table2.dat
------------------------------------------------------------------------------Byte-by-byte Description of file: table1.dat
------------------------------------------------------------------------------Bytes Format Units
Label
Explanations
------------------------------------------------------------------------------1- 5
A5
--ID
Star identification
6-13
F8.1
arcsec X
*X offset from cluster center (E thru
N)
14-21
F8.1
arcsec Y
*Y offset from cluster center (E thru
N)
22-29
F8.1
km/s
Vel
Mean velocity
30-35
F6.1
km/s
e_Vel
Uncertainty in Vel
36-41
F6.1
mag
V_FP
*Fabry-Perot magnitude
42-43
2X
----Blank
44-52
A9
--Prob
*Probability of the chi-square
------------------------------------------------------------------------------Notes for file: table1.dat
------------------------------------------------------------------------------X, Y:
The cluster center coordinates are given in Guhathakutra et al.
1996, AJ, 111, 267.
V_FP:
Fabry-Perot magnitude, estimated from the fitted continuum of the
authors' 3 Angstrom spectrum.
Prob:
The probability of the chi-square from the multiple measurements
exceeding the observed value -- a low probability suggests a
variable velocity -- or a note. A note of 'bias' indicates the
star is beyond the unbiased radius and is not used in the
dynamical analysis. A note of 'non' indicates the star was
determined to be a non-member based on its radial velocity.
------------------------------------------------------------------------------Byte-by-byte Description of file: table2.dat
------------------------------------------------------------------------------Bytes Format Units
Label
Explanations
------------------------------------------------------------------------------1- 5
A5
--ID
Star identification
6-13
F8.1
km/s
CFHT95
[]? Velocity from the 1995 CFHT data
14-18
F5.1
km/s
e_CFHT95
[]? Uncertainty in CFHT95
19-26
F8.1
km/s
CFHT94
[]? Velocity from the 1994 CFHT data
27-31
F5.1
km/s
e_CFHT94
[]? Uncertainty in CFHT94
32-39
F8.1
km/s
FP92
[]? Velocity from 1992 CTIO data
(paper I)
40-44
F5.1
km/s
e_FP92
[]? Uncertainty in FP92
45-52
F8.1
km/s
FP91
[]? Velocity from 1991 CTIO data
(paper I)
53-57
F5.1
km/s
e_FP91
[]? Uncertainty in FP91
58-65
F8.1
km/s
PSC
[]? Velocity from the PSC
66-70
F5.1
km/s
e_PSC
[]? Uncertainty in PSC
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(End)
Lee Brotzman [ADS] 09Apr-1997