A lunar occultation and direct imaging survey of multiplicity in the Ophiuchus and Taurus star-forming regions

Abstract

We present an IR lunar occultation and direct imaging search for companions in the Ophiuchus starforming region and update a similar search of the Taurus region. The search is sensitive to companions in the angular separation range 0.005-10". In Ophiuchus we surveyed 35 young star targets; this sample contains at least 10 binaries, two triples, and one quadruple. Ten of the companion stars are newly discovered. In Taurus, the survey now includes 47 systems among which there are at least 22 binaries and four triples. Only two companion stars are newly identified because there is strong overlap with prior work. All the triples and quadruple are hierarchical. The observed binary frequency in Ophiuchus, in the 3-1400 AU range of separations, is at least 1.1 ± 0.3 that of the nearby solar-like stars. This value is a lower bound because we make no corrections for incompleteness. In Taurus, in the same range of separations, the observed binary frequency is at least 1.6 ± 0.3 that of the nearby solar-like stars. This value extends Ghez et al.'s (1993) and Leinert's et al.'s (1993) determination of an excess binary frequency to 3 AU separation. We used the WT/TT type and the K-L color index to distinguish between systems with and without inner disks. We find no convincing difference in the binary frequency or distribution of separations of the systems with and without inner disks. The 1.3 mm continuum emission of the single systems exceeds that of the multiples suggesting that their extensive outer disks are more massive. The specific angular momenta of the binaries overlap those of molecular cloud cores measured by Goodman et al. (1993). Subject headings: binaries: visual-occultations-open clusters and associations: generalstars: pre-main-sequence a coauthor. David Allen died on 1994 July 26. We dedicate the paper to his memory.

Fragmentation of a Protostellar Core: The Case of CB 230

“…The specific angular momentum of the double core is J/M ∼ 5×10 −17 pc 2 s −1 , which is at the lower end of values for dense cores in dark clouds (e.g., Goodman et al 1993), but still at the upper end of the range for pre-main sequence binary star systems (Simon et al 1995). In this sense, the CB 230 system closes the gap between pre-star-forming molecular cloud cores and young binary star systems.…”

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

“…The binary fraction is thus ≈ 49 percent over this separation range. Simon et al (1995) find 22 binaries and 4 triples among 47 systems. The binary frequency in the range 3 − 1400 AU is at least 1.6 ± 0.3 times the value of the canonical Galactic field sample (Duquennoy & Mayor 1991;Raghavan et al 2010).…”

Periodic variability in the emission spectrum of T Tauri

“…Binary and multiple systems are common among T Tauri stars (Duguennoy & Mayor 1991;Mathieu et al 2000), many having been discovered by the techniques of speckle interferometry, lunar occultation and adaptive optics in the infrared (Dyck et al 1982;Simon et al 1995;Kohler & Leinert 1998). For the prototype of T Tauri stars, T Tau itself, one finds three components, labeled T TauN, T TauSa and T TauSb, with angular separations of 0.68 between N and S and 0.12 between Sa and Sb (Koresco 2000;Duchene et al 2002).…”