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تسجيل مستخدم جديدThe Taurus Boundary of Stellar/Substellar (TBOSS) Survey I: far-IR disk emission measured with Herschel
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With Herschel/PACS 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 programs, a total of 150 of the 154 M4-L0 Taurus members members have observations with Herschel. Among the 150 targets, 70um flux densities were measured for 7 of the 7 ClassI objects, 48 of the 67 ClassII members, and 3 of the 76 ClassIII targets. For the detected ClassII objects, the median 70um 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 70um TBOSS values with the results from K0-M3 ClassII 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. 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. Based on an initial exploration of the impact of different physical parameters; inclination, scale height and flaring have the largest influence on the PACS flux densities. From the 24um to 70um spectral index of the SEDs, 5 new candidate transition disks were identified. The steep 24um to 70um slope for a subset of 8 TBOSS targets may be an indication of truncated disks in these systems.Two examples of mixed pair systems that include secondaries with disks were measured. Finally, comparing the TBOSS results with a Herschel study of Ophiuchus brown dwarfs reveals a lower fraction of disks around the Taurus substellar population.
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We report 885$mu$m ALMA continuum flux densities for 24 Taurus members spanning the stellar/substellar boundary, with spectral types from M4 to M7.75. Of the 24 systems, 22 are detected at levels ranging from 1.0-55.6 mJy. The two non-detections are
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he chemical composition of protoplanetary disks. The six Taurus sources in the program (DM Tau, AA Tau, LkCa 15, GM Aur, CQ Tau and MWC 480) range in stellar spectral type from M1 to A4 and offer an opportunity to test the effects of stellar luminosity on the disk chemistry. The disks were observed in 10 different lines at ~3 resolution and an rms of ~100 mJy beam-1 at ~0.5 km s-1. The four brightest lines are CO 2-1, HCO+ 3-2, CN 2_3-1_2 and HCN 3-2 and these are detected toward all sources (except for HCN toward CQ Tau). The weaker lines of CN 2_2-1_1, DCO+ 3-2, N2H+ 3-2, H2CO 3_03-2_02 and 4_14-3_13 are detected toward two to three disks each, and DCN 3-2 only toward LkCa 15. CH3OH 4_21-3_12 and c-C3H2 are not detected. There is no obvious difference between the T Tauri and Herbig Ae sources with regard to CN and HCN intensities. In contrast, DCO+, DCN, N2H+ and H2CO are detected only toward the T Tauri stars, suggesting that the disks around Herbig Ae stars lack cold regions for long enough timescales to allow for efficient deuterium chemistry, CO freeze-out, and grain chemistry.
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er a large angular region in the Taurus cloud. In addition, we examine the spatial distribution of stars and BD relative to the underlying molecular gas Methods. In this paper, we present new and updated photometry data from the Infrared Array Camera (IRAC) aboard the Spitzer Space Telescope on 43 BDs in the Taurus cloud, and recalculate of the BD disk fraction in this region. We also useed recently available CO mm data to study the spatial distribution of stars and BDs relative to the clouds molecular gas. Results. We find that the disk fraction among BDs in the Taurus cloud is 41 pm 12%, a value statistically consistent with the one among TTS (58 pm 9%). We find that BDs in transition from a state where they have a disk to a diskless state are rare, and we study one isolated example of a transitional disk with an inner radius of approx 0.1 AU (CFHT BD Tau 12, found via its relatively small mid-IR excess compared to most members of Taurus that have disks. We find that BDs are statistically found in regions of similar molecular gas surface density to those associated with stars. Furthermore, we find that the gas column density distribution is almost identical for stellar and substellar objects with and without disks.
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We present fundamental parameters for 110 canonical K- & M-type (1.3$-$0.13$M_odot$) Taurus-Auriga young stellar objects (YSOs). The analysis produces a simultaneous determination of effective temperature ($T_{rm eff}$), surface gravity ($log$ g), ma
gnetic field strength (B), and projected rotational velocity ($v sin i$). Our method employed synthetic spectra and high-resolution (R$sim$45,000) near-infrared spectra taken with the Immersion GRating INfrared Spectrometer (IGRINS) to fit specific K-band spectral regions most sensitive to those parameters. The use of these high-resolution spectra reduces the influence of distance uncertainties, reddening, and non-photospheric continuum emission on the parameter determinations. The median total (fit + systematic) uncertainties were 170 K, 0.28 dex, 0.60 kG, 2.5 km s$^{-1}$ for $T_{rm eff}$, $log$ g, B, and $v sin i$, respectively. We determined B for 41 Taurus YSOs (upper limits for the remainder) and find systematic offsets (lower $T_{rm eff}$, higher $log$ g and $v sin i$) in parameters when B is measurable but not considered in the fit. The average $log$ g for the Class II and Class III objects differs by 0.23$pm$0.05dex, which is consistent with Class III objects being the more evolved members of the star-forming region. However, the dispersion in $log$ g is greater than the uncertainties, which highlights how the YSO classification correlates with age ($log$ g), yet there are exceptionally young (lower $log$ g) Class III YSOs and relatively old (higher $log$ g) Class II YSOs with unexplained evolutionary histories. The spectra from this work are provided in an online repository along with TW Hydrae Association (TWA) comparison objects and the model grid used in our analysis.
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