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A Large-Area Search for Low-Mass Objects in Upper Scorpius. II. Age and Mass Distributions

Slesnick, Catherine L. and Hillenbrand, Lynne A. and Carpenter, John M. (2008) A Large-Area Search for Low-Mass Objects in Upper Scorpius. II. Age and Mass Distributions. Astrophysical Journal, 688 (1). pp. 377-397. ISSN 0004-637X. doi:10.1086/592265.

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We present continued results from a wide-field, ~150deg^2, optical photometric and spectroscopic survey of the northern part of the ~5 Myr old Upper Scorpius OB association. Photometry and spectral types were used to derive effective temperatures and luminosities and place newly identified association members onto a theoretical Hertz-sprung-Russell diagram. From our survey, we have discovered 145 new low-mass members of the association and determined ~10% of these objects to be actively accreting material from a surrounding circumstellar disk. Based on comparison of the spatial distributions of low- and high-mass association members, we find no evidence for spatial segregation by mass within the northern portion of the association. Measured data are combined with pre-main-sequence evolutionary models to derive a mass and age for each star. Using Monte Carlo simulations, we show that, taking into account known observational uncertainties, the observed age dispersion for the low-mass population in USco is consistent with all stars forming in a single burst ~5 Myr ago, and we place an upper limit of ±3 Myr on the age spread if the star formation rate has been constant in time. We derive the first spectroscopic mass function for USco that extends into the substellar regime and compare these results to those for three other young clusters and associations.

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Carpenter, John M.0000-0003-2251-0602
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Additional Information:© 2008. The American Astronomical Society. Received 2008 April 21, accepted for publication 2008 August 4. Print publication: Issue 1 (2008 November 20). Facilities: PO:1.2m (Quest-2), Hale (Double Spectrograph), Blanco (Hydra)
Subject Keywords:open clusters and associations; individual (Upper Scorpius) -- stars; fundamental parameters -- star; low-mass, brown dwarfs -- stars; luminosity function, mass function -- stars; pre-main-sequence
Issue or Number:1
Record Number:CaltechAUTHORS:SLEapj08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:13291
Deposited By: Arun Sannuti
Deposited On:06 Feb 2009 00:21
Last Modified:08 Nov 2021 22:36

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