The global mass function of M 15

Free access article

Issue		A&A Volume 428, Number 2, December III 2004


Page(s)		469 - 478
Section		Galactic structure, stellar clusters and populations
DOI		http://dx.doi.org/10.1051/0004-6361:20034192

A&A 428, 469-478 (2004)
DOI: 10.1051/0004-6361:20034192

The global mass function of M 15

A. Pasquali¹, G. De Marchi², L. Pulone³ and M. S. Brigas^{1, 4}

¹ ESO/ST-ECF, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
    e-mail: apasqual@eso.org
² ESA, Space Telescope Operations Division, 3700 San Martin Drive, Baltimore, MD 21218, USA
    e-mail: gdemarchi@rssd.esa.int
³ INAF, Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone (RM), Italy
    e-mail: pulone@coma.mporzio.astro.it
⁴ Osservatorio Astronomico di Cagliari, Strada 54, Poggio dei Pini, 09012 Capoterra, Cagliari, Italy
    e-mail: sbrigas@eso.org

(Received 14 August 2003 / Accepted 21 July 2004 )

Abstract
Data obtained with the NICMOS instrument on board the Hubble Space Telescope (HST) have been used to determine the H-band luminosity function (LF) and mass function (MF) of three stellar fields in the globular cluster M 15, located ~ $7^\prime$ from the cluster centre. The data confirm that the cluster MF has a characteristic mass of ~ 0.3 $M_{\odot}$ , as obtained by Paresce & De Marchi (2000) for a stellar field at $4\farcm6$ from the centre. By combining the present data with those published by other authors for various radial distances (near the centre, at $20^{\prime\prime}$ and at $4\farcm6$ ), we have studied the radial variation of the LF due to the effects of mass segregation and derived the global mass function (GMF) using the Michie-King approach. The model that simultaneously best fits the LF at various locations, the surface brightness profile and the velocity dispersion profile suggest that the GMF should resemble a segmented power-law with the following indices: $x \simeq 0.8$ for stars more massive than 0.8 $M_{\odot}$ , $x \simeq 0.9$ for $0.3{-}0.8\,M_\odot$ and $x \simeq -2.2$ at smaller masses (Salpeter's IMF would have x=1.35). The best fitting model also suggests that the cluster mass is ~ $5.4 \times 10^5\,M_\odot$ and that the mass-to-light ratio is on average $M/L_V \simeq 2.1$ , with $M/L_V \simeq 3.7$ in the core. A large amount of mass (~ $44\%$ ) is found in the cluster core in the form of stellar heavy remnants, which may be sufficient to explain the mass segregation in M 15 without invoking the presence of an intermediate-mass black hole.

Key words: globular clusters: general -- globular clusters: individual: M 15

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.