The substellar mass function: A Bayesian approach

Allen, Peter R. and Koerner, David W. and Reid, I. Neill and Trilling, David E. (2005) The substellar mass function: A Bayesian approach. Astrophysical Journal, 625 (1). pp. 385-397. ISSN 1538-4357

Preview

Text Allen_PR_et_al_2005_Substellar_mass_function_Bayesian_approach(1).pdf Download (755kB) | Preview

Abstract

We report our efforts to constrain the form of the low-mass star and brown dwarf mass function via Bayesian inference. Recent surveys of M, L, and T dwarfs in the local solar neighborhood are an essential component of our study. Uncertainties in the age distribution of local field stars make reliable inference complicated. We adopt a wide range of plausible assumptions about the rate of Galactic star formation and show that their deviations from a uniform rate produce little effect on the resulting luminosity function for a given mass function. As an ancillary result, we calculate the age distribution for M, L, and T spectral types. We demonstrate that late L dwarfs, in particular, are systematically younger than objects with earlier or later spectral types, with a mean age of 3 Gyr. Finally, we use a Bayesian statistical formalism to evaluate the probability of commonly used mass functions in the light of recent discoveries. We consider three functional forms of the mass function, including a two-segment power law, a single power law with a low-mass cutoff, and a lognormal distribution. Our results show that at a 60% confidence level the power-law index α for the low-mass arm of a two-segment power law has a value between -0.6 and 0.6 for objects with masses between 0.04 and 0.10 M-circle dot;. The best-fit index is alpha = 0.3 plus or minus; 0.6 at the 60% confidence level for a single-segment mass function. Current data require this function to extend to at least 0.05 M-circle dot with no restrictions placed on a lower mass cutoff. Inferences of the parameter values for a lognormal mass function are virtually unaffected by recent estimates of the local space density of L and T dwarfs. We find that we have no preference among these three forms using this method. We discuss current and future capabilities that may eventually discriminate between mass function models and refine estimates of their associated parameter values.

Item Type:	Article
ID number or DOI:	10.1086/429548
Keywords:	brown dwarfs; dynamical interactions; extrasolar giant planets; formation history; infrared photometry; luminosity functions; solar neighborhood; stars : evolution; stars : low-mass, brown dwarfs; stars : luminosity function, mass function; star spectroscopic survey; t-dwarfs; ultracool dwarfs
Subjects:	Q Science > QB Astronomy
NAU Depositing Author Academic Status:	Faculty/Staff
Department/Unit:	College of Engineering, Forestry, and Natural Science > Physics and Astronomy
Date Deposited:	29 Sep 2015 22:00
URI:	http://openknowledge.nau.edu/id/eprint/87

Actions (login required)

IR Staff Record View

Downloads