Computer Science – Numerical Analysis
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...426..192d&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 426, no. 1, p. 192-203
Computer Science
Numerical Analysis
18
Celestial Mechanics, Computerized Simulation, Cross Correlation, Error Analysis, Globular Clusters, Numerical Analysis, Velocity Distribution, Astronomical Observatories, Charge Coupled Devices, Hubble Space Telescope, Spectrographs
Scientific paper
A projected velocity dispersion sigmap of 0 = 14.0 km/s is derived from an integrated light spectrum obtained at the European Southern Observatory (ESO) at La Silla, Chile, over a central 6 sec x 6 sec area in the core of the globular cluster M15. Extensive numerical simulations of velocity dispersion determinations from integrated light spectra show that all the velocity dispersions obtained from integrated light measurements over small central areas suffer from large statistical errors due to the small numbers of bright stars present in the integration area. These simulations, over our area of integration of 6 sec x 6 sec, give sigmap = 15(+6/-4) km/s as the most probable values for the central velocity dispersion and its statistical error. The observational result differs from the challenging high central velocity dispersion sigmap of 0 = 25 km/s derived by Peterson, Seitzer, & Cudworth (1989) are consistent with ours. In a similar way, all the above velocity dispersion values obtained from integrated light measurements are consistent with the velocity dispersion sigmap = 14.2 +/- 1.9 km/s obtained by Peterson et al. (1989) from the radial velocities of 27 stars within 20 sec of the center. Given the large statistical errors on the integrated light measurements, there is no significant observational evidence that the central value of the velocity dispersion is much larger than about 15 km/s. All observed values are consistent with the predictions from various theoretical dynamical models of M15: sigmap of 0 = 12-17 km/s from Illingworth & King (1977), sigma p of 0 = 13-15 km/s from Phinney & Sigurdsson (1991) and Phinney (1993), and sigmap of 0 = 14 km/s from Grabhorn et al. (1992). Although it cannot be ruled out, the presence of a massive black hole or some nonthermal dynamics in the core of M15 is not required by the present observations.
Dubath Pierre
Mayor Marcel
Meylan George
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