CDROM/AJ/V107/P2067 Dynamics of M15 (Gebhardt+ 1994)
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Fabry-Perot Measurements of the Dynamics of Globular Cluster Cores: M15
(NGC 7078)
K. Gebhardt, C. Pryor, T.B. Williams, & James E. Hesser
<1994, AJ, 107, 2067>
=1994AJ....107.2067G
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Abstract:
We report the first use of the Rutgers Imaging Fabry-Perot
Spectrophotometer to study the dynamics of the cores of globular
clusters. We have obtained velocities for cluster stars by tuning the
Fabry-Perot to take a series of narrowband (0.8 A FWHM at 5890 A)
images at different wavelengths across one of the Na D (5890 A)
absorption lines. Measuring the flux in every frame yields a short
portion of the spectrum for each star simultaneously. This proves to
be a very efficient method for obtaining accurate stellar velocities;
in crowded regions we are able to measure hundreds of velocities in 3-4
h of observing time. We have measured velocities with uncertainties of
less than 5 km/s for 216 stars within 1.5' of the center of the
globular cluster M15 (NGC 7078). The velocity dispersion profile shows
a sharp rise from 7 to 12 km/s at 0.6' (1.8 parsec), and then appears
to flatten into our innermost point at 0.1'. A rotation amplitude of
1.4 +/- 0.8 km/s is detected. The rotation has been measured at a
radius of 0.6' using stellar velocities and at 0.2' using the
integrated light profile. The amplitude and position angle are the
same at both radii, indicating a constant rotation profile in this
region. Combining our two epochs of Fabry-Perot observation with
published measurements, we have repeat velocity measurements for 67
stars. We calculate a binary fraction of about 7% for binary periods
between 0.2 and 20 years and mass ratios larger than 0.22, which is in
agreement with measurements for other globular clusters.
File Summary:
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File Name Lrecl Records Explanations
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------- table1.dat 62 480 M15 stars table1.tex 93 507 LaTeX planotable version of Table 1
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- ID *Star ID, blank indicates continuations
7-13 F7.1 arcsec X *[]? X offset from cluster center
14-21 F8.1 arcsec Y *[]? Y offset from cluster center
22-27 F6.1 mag VFP []? Fabry-Perot V magnitude
28-35 F8.1 km/s Vel *Velocity
36-40 F5.1 km/s e_Vel Error in velocity

41-42 2X --- --- Blank
43-46 A4 --- r_Vel *Source for velocity
47-52 F6.2 --- ChiSq *[]? Chi-square for multiple measurements
53-62 A10 --- Note *Notes, explained in comments
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Notes for file: table1.dat
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ID:
If the ID field is blank, then Vel, e_Vel, and r_Vel are continued from
the previous record. ID is taken from Kuestner, F. 1921, Veroeff.
Sternw.
Bonn., No. 15, or Auriere, M., & Cordoni, J.P. 1981, A&AS, 46, 347 if the
star has been previously studied, or an FP number if it has not.
X, Y:
The center of the cluster was taken to be 21h27m33.3s, +11d56m49s
(1950),
as measured by HST (Lauer, T.R. et al. 1991, ApJ, 369, L45).
Vel:
When there are multiple velocity measurements for the same star, the first
line for that star lists the average velocity calculated from all of the
measurements weighted by their uncertainties and the following lines are
the individual measurements. r_Vel:
Source of velocity measurement. All the measurements from Peterson, R.
C.,
Seitzer, P., & Cudworth, K. M. 1989, ApJ, 347, 251 (PSC) are included.
Other
sources are listed as FP91 or FP92 for the authors 1991 or 1992 Fabry-
Perot
observations.
ChiSq:
Probability of chi-square for multiple measurements being drawn from the
same velocity.
Note:
Notes include code numbers, as follows:
1: Binary star candidates
2: Not used in dynamics due to radical FP bias
3: Not used in dynamics due to severe contamination
4: PSC has 33 measurements for this star
Other notes include additional ID's for stars, as follows:
V: Variable star number (Sawyer-Hogg, H. 1973, Publ. David
Dunlap Obs., 3, No. 6)
S: Sandage, A. 1970, ApJ, 162, 841
I-V: Roman numerals from Arp, H. C. 1955, AJ, 60, 317
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(End) Lee Brotzman [ADS] 16-
Aug-1994