Confirmation of the binary status of Cha Halpha 2 - a very young low-mass binary in Chamaeleon

Abstract

Neuhaeuser & Comeron (1998, 1999) presented direct imaging evidence, as well as first spectra, of several young stellar and sub-stellar M6- to M8-type objects in the Cha I dark cloud. One of these objects is Cha Halpha 2, classified as brown dwarf candidate in several publications and suggested as possible binary in Neuhaeuser et al. (2002). We have searched around Cha Halpha 2 for close and faint companions with adaptive optics imaging. Two epochs of direct imaging data were taken with the Very Large Telescope (VLT) Adaptive Optics instrument NACO in February 2006 and March 2007 in Ks-band. We retrieved an earlier image from 2005 from the European Southern Observatory (ESO) Science Archive Facility, increasing the available time coverage. After confirmation of common proper motion, we deduce physical parameters of the objects by spectroscopy, like temperature and mass. We find Cha Halpha 2 to be a very close binary of ~0.16 arcsec separation, having a flux ratio of ~0.91, thus having almost equal brightness and indistinguishable spectral types within the errors. We show that the two tentative components of Cha Halpha 2 form a common proper motion pair, and that neither component is a non-moving background object. We even find evidence for orbital motion. A combined spectrum of both stars spanning optical and near-infrared parts of the spectral energy distribution yields a temperature of 3000+/-100 K, corresponding to a spectral type of M6+/-1 and a surface gravity of log g= 4.0 +0.75-0.5, both from a comparison with GAIA model atmospheres. We derive masses of ~0.110 Msun (>0.070 Msun) and ~0.124 Msun (>0.077 Msun) for the two components of Cha Halpha 2, i.e., probably low-mass stars, but one component could possibly be a brown dwarf.

6 pages, 8 figures, accepted for publication in A&A

References in corpus (14)

• The USNO-B Catalog
• L' and M' Photometry of Ultracool Dwarfs
• Accretion in Brown Dwarfs: an Infrared View
• Young Low-Mass Stars and Brown Dwarfs in IC 348
• The T Tauri Phase Down to Nearly Planetary Masses: Echelle Spectra of 82 Very Low Mass Stars and Brown Dwarfs
• The Onset of Planet Formation in Brown Dwarf Disks
• Exploring Brown Dwarf Disks
• Rotational periods of very young brown dwarfs and very low-mass stars in ChaI
• UVES spectra of young brown dwarfs in Cha I: radial and rotational velocities
• A Survey for Low-Mass Stars and Brown Dwarfs in the Eta Cha and Eps Cha Young Associations
• HST, VLT, and NTT imaging search for wide companions to bona-fide and candidate brown dwarfs in the Cha I dark cloud
• Probing Dust around Brown Dwarfs: The naked LP 944-20 and the Disk of Cha Ha2
• The ratio of N(C18O) and Av in Chamaeleon I and III-B using 2MASS and SEST
• XMM-Newton probes the stellar population in Cha I South

Cited by in corpus (3)

• Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions
• New companions in the stellar systems of DI Cha, Sz 22, CHXR 32, and Cha Halpha 5 in the Cha I star-forming region
• A direct imaging search for close stellar and sub-stellar companions to young nearby stars