The Taurus Boundary of Stellar/Substellar (TBOSS) Survey

Abstract

With the PACS instrument on Herschel, 134 low mass members of the Taurus star-forming region spanning the M4-L0 spectral type range and covering the transition from low mass stars to brown dwarfs were observed. Combining the new Herschel results with other Herschel programs, a total of 150 of the 154 M4-L0 Taurus members have observations, and we have added an additional 3 targets from Spitzer to form the 153-object TBOSS (Taurus Boundary of Stellar/Substellar) sample, a 99% complete study. Among the 150 targets, 70 µm flux densities were measured for 7 of the 7 Class I objects, 48 of the 67 Class II objects, and 3 of the 76 Class III objects. For the detected Class II objects, the median 70 µm flux density level declines with spectral type; however, the distribution of excess relative to central object flux density does not change across the stellar/substellar boundary in the M4-L0 range. Connecting the 70 µm TBOSS values with the results from K0-M3 Class II members results in the first comprehensive census of far-IR emission across the full mass spectrum of the stellar and substellar population of a star-forming region, and the median flux density declines with spectral type in a trend analogous to the flux density decline expected for the central objects. Spectral energy distributions (SEDs) were constructed for all TBOSS targets covering the optical to far-IR range and extending to the submm/mm for a subset of sources with longer wavelength data. Based on an initial exploration of the impact of different physical parameters on the Herschel flux densities, geometrical factors such as inclination and structural parameters such as scale height and flaring have the largest influence on the flux densities in the PACS bands. From the 24 µm to 70 µm spectral index of the SEDs, 5 new candidate transition disks were identified. Considering the previously known and new candidate transition disks, the spectral indices over longer wavelengths (≥70 µm) are not distinct from those of the full Class II population, suggesting that the outer regions of the transition disks are similar to Class II disks. The steep 24 µm to 70 µm slope for a subset of 8 TBOSS targets may be an indication of truncated disks in these systems, however additional measurements are required to establish the outer radii of these disks conclusively. From existing high angular resolution companion search observations, two examples of mixed pair systems that include secondaries with disks were measured in the Herschel data. Finally, comparing the TBOSS results with a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks around the Taurus substellar population with flux densities comparable to the Ophiuchus disks.

NEAR-INFRARED SPECTROSCOPY OF 2M0441+2301 AabBab: A QUADRUPLE SYSTEM SPANNING THE STELLAR TO PLANETARY MASS REGIMES

“…The hierarchical arrangement of orbits between the compact binaries and much larger binary-binary pair suggests the system is dynamically stable. Both pairs are well-established members of Taurus (Luhman et al 2009), have little or no reddening (A V ∼ 0.2 mag; Bulger et al 2014), and are confirmed to be physical binaries rather than chance alignments based on multi-epoch astrometry (Todorov et al 2014). An excess of mid-infrared emission was previously identified from both unresolved pairs, indicating that at least one component of each subsystem harbors a circum-(sub)stellar disk (Adame et al 2010;Bulger et al 2014).…”

“…Both pairs are well-established members of Taurus (Luhman et al 2009), have little or no reddening (A V ∼ 0.2 mag; Bulger et al 2014), and are confirmed to be physical binaries rather than chance alignments based on multi-epoch astrometry (Todorov et al 2014). An excess of mid-infrared emission was previously identified from both unresolved pairs, indicating that at least one component of each subsystem harbors a circum-(sub)stellar disk (Adame et al 2010;Bulger et al 2014). Spectroscopic validation is essential to confirm the low temperatures, luminosities, and masses of candidate planets at these very young ages when edge-on disks around brown dwarfs or low-mass stars can cause extinction and mimic the photometric properties of faint protoplanets (Bowler et al 2014;Kraus et al 2014;Wu et al 2015).…”

Hints for Small Disks around Very Low Mass Stars and Brown Dwarfs∗

“…FUTauA has a known molecular outflow (Monin et al 2013), and it is possible that the outflow contributes to the [O I] 63 μm line, in which case the flux we report in Table 3 <´--). All of the eight Taurus sources were also observed with the PACS photometer by Bulger et al (2014). Literature 70 μm flux densities are reported in the last column of Table 3.…”

A homogeneous analysis of disks around brown dwarfs

“…All the targets have been observed by the Photodetector Array Camera and Spectrograph (PACS; Poglitsch et al 2010) on board Herschel with various programs (André et al 2010;Harvey et al 2012a;Alves de Oliveira et al 2013;Bulger et al 2014). The ObsIDs for all the observations are listed in Table 1.…”

“…The systematically lower flux density at far-IR wavelengths of the LTBDs implies that disks around lower mass stars are generally less flared. Bulger et al (2014) investigated the effect of individual disk parameter on the appearance of the SED, and their results indicate that the flaring index and scale height work together to determine the emission level at Herschel/PACS bands. Moreover, the observational trends of far-IR flux densities may also help us to consider whether there is any evidence for differences in disk mass with different stellar masses, since the Herschel/PACS photometry can provide a rough mass estimation of BD disks (e.g., Harvey et al 2012a;Spezzi et al 2013;Liu et al 2015).…”