AN INITIAL MASS FUNCTION FOR INDIVIDUAL STARS IN GALACTIC DISKS. I. CONSTRAINING THE SHAPE OF THE INITIAL MASS FUNCTION

Journal Article · Sat Jan 01 00:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/726/1/27· OSTI ID:21567725

Parravano, Antonio ^[1]; McKee, Christopher F ^[2]; Hollenbach, David J ^[3]

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1. Universidad de Los Andes, Centro de Fisica Fundamental, Merida 5101a (Venezuela, Bolivarian Republic of)
2. Physics Department and Astronomy Department, University of California at Berkeley, Berkeley, CA 94720 (United States)
3. NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035 (United States)

We derive a semi-empirical galactic initial mass function (IMF) from observational constraints. We assume that the IMF, {psi}(m), is a smooth function of the stellar mass m. The mass dependence of the proposed IMF is determined by five parameters: the low-mass slope {gamma}, the high-mass slope -{Gamma} (taken to be -1.35), the characteristic mass m{sub ch} ({approx} the peak mass of the IMF), and the lower and upper limits on the mass, m{sub l} and m{sub u} (taken to be 0.004 and 120 M{sub sun}, respectively): {psi}(m)dln m {proportional_to} m{sup -}{Gamma}{l_brace}1 - exp [- (m/m{sub ch}){sup {gamma}}+{Gamma}]{r_brace}dln m. The values of {gamma} and m{sub ch} are derived from two integral constraints: (1) the ratio of the number density of stars in the range m = 0.1-0.6 M{sub sun} to that in the range m = 0.6-0.8 M{sub sun} as inferred from the mass distribution of field stars in the local neighborhood and (2) the ratio of the number of stars in the range m = 0.08-1 M{sub sun} to the number of brown dwarfs in the range m = 0.03-0.08 M{sub sun} in young clusters. The IMF satisfying the above constraints is characterized by the parameters {gamma} = 0.51 and m{sub ch} = 0.35 M{sub sun} (which corresponds to a peak mass of 0.27 M{sub sun} ). This IMF agrees quite well with the Chabrier IMF for the entire mass range over which we have compared with data, but predicts significantly more stars with masses <0.03 M{sub sun}; we also compare with other IMFs in current use and give a number of important parameters implied by the IMFs.

• OSTI ID: 21567725
• Journal Information: Astrophysical Journal, Vol. 726, Issue 1; Other Information: DOI: 10.1088/0004-637X/726/1/27; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
FUNCTIONS
MASS
STAR EVOLUTION
STARS
EVOLUTION