NICMOS/HST Observations of the Embedded Cluster Associated with Mon R2: Constraining the sub-stellar Initial Mass Function

Abstract

We have analyzed HST/NICMOS2 F110W, F160W, F165M, and F207M band images covering the central 1'x1' of the cluster associated with Mon R2 in order to constrain the Initial Mass Function (IMF) down to 20 Mjup. 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 K and 3300 K. These objects are placed in the HR diagram together with sources observed by Carpenter et al. (1997) 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 Msun and 1.0 Msun for a 1 Myr population with Av < 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 0.08-1.0Msun to the number of objects in the mass interval 0.02-0.08 Msun by forming the ratio, R**=N(0.08-1Msun)/N(0.02-0.08Msun) for objects in an extinction limited sample complete for Av < 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 (2003). The ratio is similar to the ratios observed towards the Orion Nebula Cluster and IC 348 as well as the ratio derived in the 28 square degree survey of Taurus by Guieu et al. (2006).

arXiv commentAccepted in AJ, Full version with Figure 1 in color can be found at http://matisse.as.arizona.edu/mortena/download/monr2.ps

References in corpus (22)

• Galactic Stellar and Substellar Initial Mass Function
• The Initial Mass Function of Stars: Evidence for Uniformity in Variable Systems
• The NextGen Model Atmosphere grid for $3000\le \Teff \le 10000\K$
• Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
• A Census of the Young Cluster IC 348
• The Formation of Brown Dwarfs as Ejected Stellar Embryos
• The Luminosity & Mass Function of the Trapezium Cluster: From B stars to the Deuterium Burning Limit
• Constraints on the Stellar/Sub-stellar Mass Function in the Inner Orion Nebula Cluster
• New Brown Dwarfs and an Updated Initial Mass Function in Taurus
• The Spectroscopically Determined Substellar Mass Function of the Orion Nebula Cluster
• Infrared L Band Observations of the Trapezium Cluster: A Census of Circumstellar Disks and Candidate Protostars
• HST Observations of 10 Two-Image Gravitational Lenses
• Gravity Indicators in the Near-Infrared Spectra of Brown Dwarfs
• A High Angular Resolution Multiplicity Survey of the Open Clusters alpha Persei and Praesepe
• Simulating star formation in molecular cores II. The effects of different levels of turbulence
• Circumstellar Disks in the IC 348 Cluster
• 17 new very low-mass members in Taurus. The brown dwarf deficit revisited
• From Stars to Super-planets: the Low-Mass IMF in the Young Cluster IC348
• The Substellar Mass Function: A Bayesian Approach
• Spherically symmetric model atmospheres for low mass pre-Main Sequence stars with effective temperatures between 2000 and 6800 K
• Low Mass Stars and Substellar Objects in the NGC 1333 Molecular Cloud
• An explanation for the unusual IMF in Taurus

Cited by in corpus (26)

• The Spitzer c2d Legacy Results: Star Formation Rates and Efficiencies; Evolution and Lifetimes
• A Universal Stellar Initial Mass Function? A Critical Look at Variations
• The Effects of Radiative Transfer on Low-Mass Star Formation
• The Formation and Early Evolution of Low-mass Stars and Brown Dwarfs
• Driven and Decaying Turbulence Simulations of Low-Mass Star Formation: From Clumps to Cores to Protostars
• Evidence for a Turnover in the IMF of Low Mass Stars and Sub-stellar Objects: Analysis from an Ensemble of Young Clusters
• The formation and dynamical evolution of young star clusters
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: I The Pleiades
• An Initial Mass Function for Individual Stars in Galactic Disks: I. Constraining the Shape of the IMF
• The very low-mass stellar content of the young supermassive Galactic star cluster Westerlund 1
• The IMF and multiplicity of stars from gravity, turbulence, magnetic fields, radiation and outflow feedback
• Can magnetized turbulence set the mass scale of stars?
• Far-infrared observations of a massive cluster forming in the Monoceros R2 filament hub
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: II The Alpha Persei open cluster
• HST/NICMOS Observations of NGC 1333: The Ratio of Stars to Sub-Stellar Objects
• The low-mass Initial Mass Function in the Orion Nebula cluster based on HST/NICMOS III imaging
• The role of the turbulence driving mode for the Initial Mass Function
• Submillimeter Array High-angular Resolution Observations of the Monoceros R2 Star Forming Cluster
• Detection of brown dwarf-like objects in the core of NGC3603
• Substellar and low-mass dwarf identification with near-infrared imaging space observatories
• New H2 Jets in Monoceros R2
• Evolutionary status of isolated B[e] stars
• Which young clusters/associations are we missing today?
• Aligned grains and inferred toroidal magnetic fields in the envelopes of massive young stellar objects
• The influence of the cloud virial parameter on the initial mass function
• Time series photometry and multi-wavelength characterisation of the young stellar cluster Mon R2