Confirmation of the binary status of Chamaeleon Hα 2 – a very young low-mass binary in Chamaeleon

Abstract

Context. Neuhäuser & Comerón (1998, Science, 282, 83; 1999, A&A, 350, 612) 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 Hα 2, classified as brown dwarf candidate in several publications and suggested as possible binary in Neuhäuser et al. (2002, A&A, 384, 999 After confirmation of common proper motion, we deduce physical parameters of the objects by spectroscopy, like temperature and mass. Results. We find Cha Hα 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 Hα 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. Furthermore, we obtained an optical extinction of A V 4.3 mag from this comparison. Conclusions. We derive masses of ∼0.110 M (≥0.070 M ) and ∼0.124 M (≥0.077 M ) for the two components of Cha Hα 2, i.e., probably low-mass stars, but one component could possibly be a brown dwarf.

Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions

“…(13) supposed by Neuhäuser et al (2002). (14) confirmed by Ahmic et al (2007), Lafrenière et al (2008) and Schmidt et al (2008b). (15) Schmidt et al (2008b).…”

“…We used either the newest values combining most of the previous data with new measurements, in this case of UCAC3 (Zacharias et al 2010) combining data from about 140 catalogues, or the weighted mean proper motion of several independent measurements, as for Cha Hα 2 (see e.g. Schmidt et al 2008b), which was previously supposed to be a faint brown dwarf candidate and whose data were in part derived by us from SuperCOSMOS Sky Survey (SSS) data (Hambly et al 2001) and NTT/SofI and VLT/FORS measurements (see Table 4), to check whether the objects have a common PM, as we describe in the following sections. For comparison, we give in addition the median proper motion value of the Chamaeleon I association derived from the UCAC2 (Zacharias et al 2004) data by Luhman et al (2008) in Table 4.…”

“…(5) Ducourant et al (2005). (6) Schmidt et al (2008b); Hambly et al (2001). (7) Camargo et al (2003).…”

“…(14) confirmed by Ahmic et al (2007), Lafrenière et al (2008) and Schmidt et al (2008b). (15) Schmidt et al (2008b). (16) wide companion candidate: Reipurth & Zinnecker (1993), close binary: Brandner (1992), close triple: Brandeker et al (2001).…”

“…We obtained direct imaging of a total of 51 Cha association member stars with the European Southern Observatory (ESO) Very Large Telescope (VLT) instrument Naos-Conica (NACO, Lenzen et al 2003;Rousset et al 2003), in the near-infrared (J, H, and Ks) to carry out high precision astrometry and photometry of them and their nearby candidate companions. In some cases, follow-up spectroscopic observations could be obtained, as for Cha Hα 2 (Schmidt et al 2008b) and CT Cha (Schmidt et al 2008a). The A&A 546, A63 (2012) Notes.…”