The first spectroscopically confirmed brown dwarfs in NGC 2264

Abstract

We present spectroscopic follow-up observations of 68 red, faint candidates from our multi-epoch, multi-wavelength, previously published survey of NGC 2264. Using near-infrared spectra from VLT/KMOS, we measure spectral types and extinction for 32 young low-mass sources. We confirm 13 as brown dwarfs in NGC 2264, with spectral types between M6 and M8, corresponding to masses between 0.02 and 0.08$M_{\odot }$. These are the first spectroscopically confirmed brown dwarfs in this benchmark cluster. 19 more objects are found to be young M-type stars of NGC 2264 with masses of 0.08 to 0.3$M_{\odot }$. 7 of the confirmed brown dwarfs as well as 15 of the M-stars have IR excess caused by a disc. Comparing with isochrones, the typical age of the confirmed brown dwarfs is $<$0.5 to 5Myr. More than half of the newly identified brown dwarfs and very low mass stars have ages $<$0.5Myr, significantly younger than the bulk of the known cluster population. Based on the success rate of our spectroscopic follow-up, we estimate that NGC 2264 hosts 200-600 brown dwarfs in total (in the given mass range). This would correspond to a star-to-brown dwarf ratio between 2.5:1 and 7.5:1. We determine the slope of the substellar mass function as $\alpha =0.43_{-0.56}^{+0.41}$, these values are consistent with those measured for other young clusters. This points to a uniform substellar mass function across all star forming environments.

arXiv commentAccepted for publication in MNRAS; 12 pages, 13 figures

References in corpus (38)

• Astropy: A Community Python Package for Astronomy
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Automated data reduction workflows for astronomy
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• Observations of IC348: The Disk Population at 2-3 Million Years
• A Near-Infrared Spectroscopic Study of Young Field Ultracool Dwarfs
• Infrared Spectroscopy of Substellar Objects in Orion
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• Identifying Young Brown Dwarfs Using Gravity-Sensitive Spectral Features
• A rotational and variability study of a large sample of PMS stars in NGC 2264
• X-Shooter spectroscopy of young stellar objects: II. Impact of chromospheric emission on accretion rate estimates
• Gravity Indicators in the Near-Infrared Spectra of Brown Dwarfs
• A Census of Young Stars and Brown Dwarfs in IC 348 and NGC 1333
• The Software Package for Astronomical Reductions with KMOS: SPARK
• A Survey for New Members of the Taurus Star-Forming Region with the Sloan Digital Sky Survey
• Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses
• Spectroscopy of new brown dwarf members of rho Ophiuchi and an updated initial mass function
• Infrared Spectroscopy and Analysis of Brown Dwarf and Planetary Mass Objects in the Orion Nebula Cluster
• Substellar Objects in Nearby Young Clusters (SONYC) IV: A census of very low mass objects in NGC1333
• Substellar Objects in Nearby Young Clusters (SONYC) V: New brown dwarfs in rho Ophiuchi
• Spitzer observations of NGC2264: The nature of the disk population
• The low-mass content of the massive young star cluster RCW 38
• Astrometric and photometric initial mass functions from the UKIDSS Galactic Clusters Survey: IV Upper Sco
• Characterizing the Cool KOIs. VI. H- and K-band Spectra of Kepler M Dwarf Planet-Candidate Hosts
• The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264
• Substellar Objects in Nearby Young Clusters (SONYC) IX: The planetary-mass domain of Chamaeleon-I and updated mass function in Lupus-3
• The Initial Mass Function and Young Brown Dwarf Candidates in NGC 2264. IV. The Initial Mass Function and Star Formation History
• Gaia-ESO Survey: The analysis of pre-main sequence stellar spectra
• Mass segregation and sequential star formation in NGC 2264 revealed by Herschel
• Looking deep into the Rosette Nebula's heart: the (sub)stellar content of the massive young cluster NGC 2244
• A Spitzer View of Mon OB1 East/NGC 2264
• Undetected Binary Stars Cause an Observed Mass Dependent Age Gradient in Upper Scorpius
• Spatially resolved spectroscopy of close massive visual binaries with HST/STIS: I. Seven O-type systems
• A deep, wide-field search for substellar members in NGC 2264
• The brown dwarf population in the star forming region NGC2264

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• Search for Brown Dwarfs in IC 1396 with Subaru HSC: Interpreting the Impact of Environmental Factors on Sub-stellar Population