Susan Terebey

The Taurus Spitzer Survey: New Candidate Taurus Members Selected Using Sensitive Mid-Infrared Photometry

We report on the properties of pre-main-sequence objects in the Taurus molecular clouds as observed in seven mid- and far-infrared bands with the Spitzer Space Telescope. There are 215 previously identified members of the Taurus star-forming region in our ~44 deg^2 map; these members exhibit a range of Spitzer colors that we take to define young stars still surrounded by circumstellar dust (noting that ~20% of the bona fide Taurus members exhibit no detectable dust excesses). We looked for new objects in the survey field with similar Spitzer properties, aided by extensive optical, X-ray, and ultraviolet imaging, and found 148 new candidate members of Taurus. We have obtained follow-up spectroscopy for about half the candidate sample, thus far confirming 34 new members, three probable new members, and 10 possible new members, an increase of 15%–20% in Taurus members. Of the objects for which we have spectroscopy, seven are now confirmed extragalactic objects, and one is a background Be star. The remaining 93 candidate objects await additional analysis and/or data to be confirmed or rejected as Taurus members. Most of the new members are Class II M stars and are located along the same cloud filaments as the previously identified Taurus members. Among non-members with Spitzer colors similar to young, dusty stars are evolved Be stars, planetary nebulae, carbon stars, galaxies, and active galactic nuclei.

A Candidate Protoplanet in the Taurus Star-forming Region

Hubble Space Telescope/Near-Infrared Camera and Multiobject Spectrometer images of the class I protostar TMR-1 (IRAS 04361+2547) reveal a faint companion with 100=1400 AU projected separation. The central protostar is itself resolved as a close binary with 031=42 AU separation, surrounded by circumstellar reflection nebulosity. A long narrow filament seems to connect the protobinary to the faint companion TMR-1C, suggesting a physical association. If the sources are physically related, then we hypothesize that TMR-1C has been ejected by the protobinary. If TMR-1C has the same age and distance as the protobinary, then current models indicate that its flux is consistent with a young giant planet of several Jovian masses.

Shocked molecular gas around the extremely young source IRAS 03282+3035

We present observations of the shock tracers H2 and SiO around the young stellar object IRAS 03282+3035. This unusual low-luminosity (L approximately = 2 solar luminosity) source drives a strong highly collimated CO outflow, and it is one of the youngest stellar objects known so far. The near-infrared H2 emission, tracing 2000 K gas, comes from extremely high velocity CO bullets along the axis of the blueshifted lobe of the outflow. The millimeter SiO emission, tracing roughly 100 K gas, arises from lower velocity material at the end of the outflow lobe. The lack of high-temperature and high-velocity gas at the end of the outflow lobe indicates there is no not bow shock at the outflow termination. In the context of current jet models this appears to rule out a bow shock driven by a steady state jet. Possible explanations for the structure include a time-dependent jet or a jet dominated by turbulent entrainment.

The Circumstellar Structure of the Class I Protostar TMC-1 (IRAS 04381+2540) from Hubble Space Telescope NICMOS Data

The class I protostar TMC-1 (IRAS 04381+2540) is oriented favorably for determining the properties of its circumstellar envelope and outflow cavity. Deep, high spatial resolution Hubble Space Telescope (HST) NICMOS images at 1.6 μm exhibit both a narrow jet and a wide-angle conical outflow cavity. Model images of the scattered-light distribution fit the data well, reproducing the intensity level, cavity width, and observed limb brightening. The best-fit geometry for TMC-1 has a 45° ± 5° source inclination and an 80° ± 5° deprojected wind opening angle (full width). The age, normally a poorly known quantity, is well constrained; the protostar age, i.e., time since the onset of cloud collapse, is 1 × 105 yr to within a factor of 2. We offer a possible resolution to the well-known luminosity problem. By considering the efficiency of infall onto the protostar, we find that plausible parameters can give an efficiency, and hence accretion luminosity, as low as 10% of the value derived from the collapsing cloud core. The efficiency, together with a luminosity constraint, leads to a mass estimate that ranges from about 0.1 M☉ for high efficiency to 0.2 M☉ for low accretion efficiency onto the protostar. Similarly, the estimated mass accretion rate onto the protostar ranges over roughly (0.9-1.4) × 10-6 M☉ yr-1, which is smaller than the (1.6-3.5) × 10-6 M☉ yr-1 infall rate of the cloud. If low efficiency rates are prevalent for protostars, one important consequence is that it will take longer to assemble the central star than the time t = Min/in, a time that assumes all of the infalling material lands on the protostar.

The Spectrum of TMR-1C Is Consistent with a Background Star

In a previous paper we proposed that there may be a population of runaway planets and brown dwarfs that formed via ejection from multiple-star systems. We further suggested TMR-1C as a candidate runaway protoplanet. Hubble Space Telescope NICMOS images of the Class I protostar TMR-1 (IRAS 04361+2547) reveal TMR-1C as a faint near-infrared companion with 100 = 1400 AU projected separation. The central protostar is itself resolved as a close binary with 031 = 42 AU separation, surrounded by circumstellar reflection nebulosity. A long, narrow filament seems to connect the protobinary to the faint companion TMR-1C, suggesting a physical association, which can plausibly be explained if TMR-1C was ejected by the protobinary. This paper presents near-infrared grism spectroscopy to constrain the effective temperature of TMR-1C, obtained with the Near-Infrared Camera (NIRC) at Keck Observatory. To interpret the data, we construct a grid of extincted M dwarf spectra to compare with the low-resolution (R ~ 120) NIRC spectrum. The assumed extinction corresponds to standard interstellar dust. With the additional assumption that no near-infrared dust excess contributes to the spectrum, then M4.5 is the latest spectral type TMR-1C can have within the uncertainties. Adopting 2 σ error bars, this translates to Teff > 2700 K effective temperature and AK = 2.5 ± 0.75 extinction at K band (AV = 22 ± 6.6 for standard dust). We compare the luminosity and effective temperature of TMR-1C with evolutionary tracks of young giant planets and brown dwarfs in a theoretical H-R diagram. Given a relatively low inferred luminosity of ~10-3 L⊙, then TMR-1C is hotter than predicted by available theoretical models. However, the models are very uncertain at such young ages, less than 300,000 yr, so that it is unclear whether the theoretical tracks by themselves provide a suitably strong test. Given the quality of the observed spectrum, only a partial answer is possible. The new data do not lend weight to the protoplanet interpretation, and the results remain consistent with the explanation that TMR-1C may be a background star. We discuss additional observational tests that may be useful.

Wide-Field Infrared Survey Explorer Observations of Young Stellar Objects in the Lynds 1509 Dark Cloud in Auriga

The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4 μm, 4.6 μm, 12 μm, and 22 μm, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

A Deep Optical Search for Substellar Candidates in the Nearby ρ Ophiuchi Star-Forming Region

We report preliminary results from a deep I-band optical search for substellar candidates in the p Oph star-forming region. The dusty molecular cloud provides an opaque screen at optical wavelengths, making the survey sensitive to faint substellar candidates near the cloud surface. Of the 89 objects detected in the oph A and oph C molecular cores, one third are substellar candidates.