J/AJ/106/1508 Dynamics of globular cluster NGC 362 (Fischer+ 1993)
Dynamics of the globular cluster NGC 362
FISCHER P., WELCH D.L., MATEO M., COTE P.
<Astron. J. 106, 1508 (1993)>
=1993AJ....106.1508F 1993AJ....106.1508F
ADC_Keywords: Clusters, globular; Radial velocities
Abstract:
In this paper we have examined the internal dynamics of the globular
cluster NGC 362 using a combination of V-band CCD images and echelle
spectra of the member red giants. A V-band surface brightness profile
(SBP) was constructed from the CCD images, and, after it was determined
that the cluster is not post core-collapse, fit with single- and
multi-pass King-Michie (KM) models. We found that for small values of
the mass function slope, x, anisotropic models were favored while for
steeper mass functions isotropic orbits provided superior fits. The
total cluster luminosity is 1.70 ± 0.1 x 10^5 L(Vsun) [assumes
(m-M)0 = 14.77]. A total of 285 stellar spectra were obtained of 215
stars for radial velocity determinations. Three stars were obvious
nonmembers and four showed strong evidence for radial velocity
variations; these latter stars are probably members of binary systems
with periods less than a few years. The true cluster binary fraction
was determined from simulations to be 0.15 for circular orbits or 0.27
for orbits with a distribution function f(e) = e (e is eccentricity).
This relatively high binary detection frequency may indicate that NGC
362 is overabundant in binaries compared to other clusters. The 208
remaining stellar velocities showed no sign of rotation and had
kinematics which were incompatible with KM models having isotropic
orbits and luminosity profiles consistent with the SBP. Therefore,
the best agreement with both the kinematic data and the SBP were for
shallow mass functions x = 0.0-0.5 and intermediate amounts of
anisotropy in the velocity dispersion tensor. In this best-fit range,
the derived cluster mass is M = 2.5-3.5x10^5 Msun for a global
mass-to-light ratio of M/L(V) = 1.5-2.0 Msun/L(Vsun). This low value
for x is in disagreement with the correlation between x and the height
above the Galactic disk seen for a sample of other clusters. The
results are also different from the sharp turnup in the low mass end of
mass functions derived from the deep luminosity functions of three
other globular clusters.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 112 284 Radial velocities
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Star name
7- 8 I2 h RAh Right ascension J2000.0
10- 11 I2 min RAm Right ascension J2000.0
13- 17 F5.2 s RAs Right ascension J2000.0
19 A1 --- DE- Declination sign
20- 21 I2 deg DEd Declination J2000.0
23- 24 I2 arcmin DEm Declination J2000.0
26- 29 F4.1 arcsec DEs Declination J2000.0
31- 36 F6.2 arcsec Radius Derived projected radius
38- 43 F6.2 deg PA Position angle
44- 56 F13.4 d HJD Heliocentric Julian Date
58- 63 F6.2 km/s VR Observed radial velocity
67- 70 F4.2 km/s u_VR rms uncertainty on VR
71- 77 F7.2 km/s ? Mean radial velocity for stars with
multiple observations
83- 86 F4.2 km/s e_ ? rms uncertainty on
87- 93 F7.2 --- Chi2 ? Chi squared for stars with multiple
observations
94- 96 I3 --- d_Chi2 ? Number of degrees of freedom of Chi2
98-112 A15 --- Comment Comments
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Courtesy: Phil Fischer.
(End) Patricia Bauer [CDS] 28-Jun-1994