New companions in the stellar systems of DI Cha, Sz 22, CHXR 32, and Cha Hα5 in the Chamaeleon I star-forming region

Abstract

Context. The star-forming regions in Chamaeleon (Cha) are among the nearest (distance ∼165 pc) and youngest (age ∼2 Myr) conglomerates of recently formed stars and among the ideal targets for studies of star formation. Aims. We search for new, hitherto unknown binary or multiple-star components and investigate their membership in Cha and their gravitationally bound nature. Methods. We used the Naos-Conica (NACO) instrument at the Very Large Telescope Unit 4/YEPUN of the Paranal Observatory, at 2 or 3 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and Ks band. On the basis of known proper motions and these observations, we analysed the astrometric results in our proper motion diagrams (PMD: angular separation/position angle versus time) to eliminate possible (non-moving) background stars and establish co-moving binaries and multiples. Results. DI Cha turns out to be a quadruple system with a hierachical structure, consisting of two binaries: a G2/M6 pair and a co-moving pair of two M5.5 dwarfs. For both pairs we detected orbital motion (P ∼ 130 and ∼65 years respectively), although in opposite directions. Sz 22 is a binary whose main component is embedded in a circumstellar disc or reflection nebula, accompanied by a co-moving M4.5 dwarf. CHXR 32 is a triple system, consisting of a single G5 star, weakened by an edge-on disc and a co-moving pair of M1/M3.5 dwarfs whose components show significant variations in their angular separation. Finally, Cha Hα 5 is a binary consisting of two unresolved M6.5 dwarfs whose strong variations in position angle at its projected separation of only 8 AU imply an orbital period of ∼46 years. DI Cha D and Cha Hα 5 A and B are right at the stellar mass limit and could possibly be brown dwarfs. Conclusions. In spite of various previously published studies of the star-forming regions in Cha we still found four hitherto unknown components in young low-mass binaries and multiple systems. All are gravitationally bound, and at least the case Cha Hα 5 presents a link between our high-resolution astrometry and the radial velocity method, avoiding a blind gap of detection possibility.

The Curious Case of Glass I: High Ionization and Variability of Different Types

“…To test the characterization of Glass Ib as a young star, we investigated the proper motions and modeled the SEDs of Glass Ia and Ib and found that the system is most likely associated with the Chameleon I star-forming region. Our models fit well with the SEDs using a G-type star for Glass Ib and a combined K-type and M-type to simulate a binary in Glass Ia (Schmidt et al 2013). Glass Ib also shows HCN, CO 2 , and H 2 O emission, which are commonly found in young stars (Pontoppidan et al 2010).…”

“…This in turn is inconsistent with the CO overtone absorption features at 2300 nm, which resemble a late K or early M dwarf. Schmidt et al (2013) do in fact resolve Glass Ia as a close double star in recent epochs of VLT/NACO AO images. Hence, Glass Ia could consist of an early to mid-K dwarf and an early M dwarf component, which would explain the spectral features we see.…”

“…To estimate the extinction in Glass Ib, we used Kurucz (1993) models to model the ratio of Glass Ib/Ia. We used a 5250 K spectrum to estimate the G-type star in Glass Ib and divided by a combined 4500 K and 3750 K spectrum to simulate the K-type (Feigelson & Kriss 1989;Koresko et al 1997) and M-type (Schmidt et al 2013) components in Glass Ia. We then found a good fit with Glass Ib showing only 1.3 mag of visual extinction more than that toward Glass Ia (shown in Figure 7).…”

X-Shooter study of accretion in Chamaeleon I

“…This object is a confirmed member of Chamaeleon I by Lopez Martí et al (2013) from proper motion studies. The best fit was obtained by including all the additional points listed above and with a value of A V much lower than the one reported in the literature (Luhman 2007;Schmidt et al 2013). No signs of the companion were found in the overall shape of the spectrum.…”

“…Only the close binary at the center (Schmidt et al 2013) is included in the slit. This object is a confirmed member of Chamaeleon I by Lopez Martí et al (2013) from proper motion studies.…”