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NICMOS2 hubble space telescope observations of the embedded cluster associated with Mon R2: Constraining the substellar initial mass function

Andersen, M. and Meyer, M. R. and Oppenheimer, B. and Dougados, C. and Carpenter, J. (2006) NICMOS2 hubble space telescope observations of the embedded cluster associated with Mon R2: Constraining the substellar initial mass function. Astronomical Journal, 132 (6). pp. 2296-2308. ISSN 0004-6256. doi:10.1086/508485.

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We have analyzed Hubble Space Telescope NICMOS2 F110W-, F160W-, F165M-, and F207M-band images covering the central 1' × 1' region of the cluster associated with Mon R2 in order to constrain the initial mass function (IMF) down to 20M_J. The flux ratio between the F165M and F160W bands was used to measure the strength of the water-band absorption feature and select a sample of 12 out of the total sample of 181 objects that have effective temperatures between 2700 and 3300 K. These objects are placed in the H-R diagram together with sources observed by Carpenter et al. to estimate an age of ~1 Myr for the low-mass cluster population. By constructing extinction-limited samples, we are able to constrain the IMF and the fraction of stars with a circumstellar disk in a sample that is 90% complete for both high- and low-mass objects. For stars with estimated masses between 0.1 and 1.0 M_☉ for a 1 Myr population with A_V ≤ 19 mag, we find that 27% ± 9% have a near-infrared excess indicative of a circumstellar disk. The derived fraction is similar to or slightly lower than the fraction found in other star-forming regions of comparable age. We constrain the number of stars in the mass interval 0.08-1.0 M_☉ to the number of objects in the mass interval 0.02-0.08 M_☉ by forming the ratio R^(**) = N(0.08-1 M_☉)/N(0.02-0.08 M_☉) for objects in an extinction-limited sample complete for A_V ≤ 7 mag. The ratio is found to be R^(**) = 2.2 ± 1.3, assuming an age of 1 Myr, consistent with the similar ratio predicted by the system IMF proposed by Chabrier. The ratio is similar to the ratios observed toward the Orion Nebula Cluster and IC 348, as well as the ratio derived in the 28 deg^2 survey of Taurus by Guieu et al.

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Meyer, M. R.0000-0003-1227-3084
Oppenheimer, B.0000-0001-7130-7681
Additional Information:© 2006 The American Astronomical Society. Received 2006 March 3; accepted 2006 July 30. This paper is based on observations made with the NASA/ESA Hubble Space Telescope, operated by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. This work was supported by a Cottrell Scholar’s Award to M. R. M. from the Research Corporation and NASA grant HST13-9846. We would like to thank Catherine Slesnick and Lynne Hillenbrand for providing the data from their spectroscopic survey of the ONC. We thank Steve Strom for discussions during the early stages of the project, France Allard for assistance with the models, Erick Young and Hua Chen for help in preparations of the observations, Angela Cotera for advice concerning the image processing, and Kevin Luhman for assistance in calculating the mass ratios for IC 348 and Taurus. We also thank the referee, August Muench, for comments and suggestions that improved and clarified the paper.
Funding AgencyGrant Number
Cottrell Scholar Award from the Research CorporationUNSPECIFIED
Subject Keywords:open clusters and associations: individual (Mon R2); stars: formation; stars: low-mass, brown dwarfs; stars: luminosity function, mass function; stars: pre-main sequence
Issue or Number:6
Record Number:CaltechAUTHORS:20120124-070253847
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Official Citation:NICMOS2 Hubble Space Telescope Observations of the Embedded Cluster Associated with Mon R2: Constraining the Substellar Initial Mass Function M. Andersen et al. 2006 The Astronomical Journal 132 2296
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:28927
Deposited By: Ruth Sustaita
Deposited On:24 Jan 2012 15:36
Last Modified:09 Nov 2021 17:02

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