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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
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:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 112 284 Radial velocities
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
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 <VR> ? Mean radial velocity for stars with multiple observations 83- 86 F4.2 km/s e_<VR> ? rms uncertainty on <VR> 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
Courtesy: Phil Fischer.
(End) Patricia Bauer [CDS] 28-Jun-1994
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