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Title: Residual Gas and Dust around Transition Objects and Weak T Tauri Stars

Abstract

Residual gas in disks around young stars can spin down stars, circularize the orbits of terrestrial planets, and whisk away the dusty debris that is expected to serve as a signpost of terrestrial planet formation. We have carried out a sensitive search for residual gas and dust in the terrestrial planet region surrounding young stars ranging in age from a few to ∼10 Myr. Using high-resolution 4.7 μ m spectra of transition objects (TOs) and weak T Tauri stars, we searched for weak continuum excesses and CO fundamental emission, after making a careful correction for the stellar contribution to the observed spectrum. We find that the CO emission from TOs is weaker and located farther from the star than CO emission from nontransition T Tauri stars with similar stellar accretion rates. The difference is possibly the result of chemical and/or dynamical effects (i.e., a low CO abundance or close-in low-mass planets). The weak T Tauri stars show no CO fundamental emission down to low flux levels (5 × 10{sup −20} to 10{sup −18} W m{sup −2}). We illustrate how our results can be used to constrain the residual disk gas content in these systems and discuss their potential implications formore » star and planet formation.« less

Authors:
 [1];  [2];  [3]
  1. W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743 (United States)
  2. National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)
  3. Naval Research Laboratory, Code 7213, Washington, DC 20375 (United States)
Publication Date:
OSTI Identifier:
22663752
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 836; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; CARBON; CARBON MONOXIDE; CORRECTIONS; DUSTS; EMISSION; GASES; INTERSTELLAR SPACE; MASS; PLANETS; PROTOPLANETS; RESOLUTION; SPECTRA; SPIN; T TAURI STARS

Citation Formats

Doppmann, Greg W., Najita, Joan R., and Carr, John S., E-mail: gdoppmann@keck.hawaii.edu, E-mail: najita@noao.edu, E-mail: carr@nrl.navy.mil. Residual Gas and Dust around Transition Objects and Weak T Tauri Stars. United States: N. p., 2017. Web. doi:10.3847/1538-4357/AA5C3C.
Doppmann, Greg W., Najita, Joan R., & Carr, John S., E-mail: gdoppmann@keck.hawaii.edu, E-mail: najita@noao.edu, E-mail: carr@nrl.navy.mil. Residual Gas and Dust around Transition Objects and Weak T Tauri Stars. United States. doi:10.3847/1538-4357/AA5C3C.
Doppmann, Greg W., Najita, Joan R., and Carr, John S., E-mail: gdoppmann@keck.hawaii.edu, E-mail: najita@noao.edu, E-mail: carr@nrl.navy.mil. Mon . "Residual Gas and Dust around Transition Objects and Weak T Tauri Stars". United States. doi:10.3847/1538-4357/AA5C3C.
@article{osti_22663752,
title = {Residual Gas and Dust around Transition Objects and Weak T Tauri Stars},
author = {Doppmann, Greg W. and Najita, Joan R. and Carr, John S., E-mail: gdoppmann@keck.hawaii.edu, E-mail: najita@noao.edu, E-mail: carr@nrl.navy.mil},
abstractNote = {Residual gas in disks around young stars can spin down stars, circularize the orbits of terrestrial planets, and whisk away the dusty debris that is expected to serve as a signpost of terrestrial planet formation. We have carried out a sensitive search for residual gas and dust in the terrestrial planet region surrounding young stars ranging in age from a few to ∼10 Myr. Using high-resolution 4.7 μ m spectra of transition objects (TOs) and weak T Tauri stars, we searched for weak continuum excesses and CO fundamental emission, after making a careful correction for the stellar contribution to the observed spectrum. We find that the CO emission from TOs is weaker and located farther from the star than CO emission from nontransition T Tauri stars with similar stellar accretion rates. The difference is possibly the result of chemical and/or dynamical effects (i.e., a low CO abundance or close-in low-mass planets). The weak T Tauri stars show no CO fundamental emission down to low flux levels (5 × 10{sup −20} to 10{sup −18} W m{sup −2}). We illustrate how our results can be used to constrain the residual disk gas content in these systems and discuss their potential implications for star and planet formation.},
doi = {10.3847/1538-4357/AA5C3C},
journal = {Astrophysical Journal},
number = 2,
volume = 836,
place = {United States},
year = {Mon Feb 20 00:00:00 EST 2017},
month = {Mon Feb 20 00:00:00 EST 2017}
}
  • We present 3.6 to 70 {mu}m Spitzer photometry of 154 weak-line T Tauri stars (WTTSs) in the Chamaeleon, Lupus, Ophiuchus, and Taurus star formation regions, all of which are within 200 pc of the Sun. For a comparative study, we also include 33 classical T Tauri stars which are located in the same star-forming regions. Spitzer sensitivities allow us to robustly detect the photosphere in the IRAC bands (3.6 to 8 {mu}m) and the 24 {mu}m MIPS band. In the 70 {mu}m MIPS band, we are able to detect dust emission brighter than roughly 40 times the photosphere. These observationsmore » represent the most sensitive WTTSs survey in the mid- to far-infrared to date and reveal the frequency of outer disks (r = 3-50 AU) around WTTSs. The 70 {mu}m photometry for half the c2d WTTSs sample (the on-cloud objects), which were not included in the earlier papers in this series, those of Padgett et al. and Cieza et al., are presented here for the first time. We find a disk frequency of 19% for on-cloud WTTSs, but just 5% for off-cloud WTTSs, similar to the value reported in the earlier works. WTTSs exhibit spectral energy distributions that are quite diverse, spanning the range from optically thick to optically thin disks. Most disks become more tenuous than L{sub disk}/L{sub *} = 2 x 10{sup -3} in 2 Myr and more tenuous than L{sub disk}/L{sub *} = 5 x 10{sup -4} in 4 Myr.« less
  • A search for high-velocity moleular gas in the /sup 12/CO J = 1-0 transition around 28 T Tauri and three Herbig Ae/Be stars reveals high-velocity CO emission towrd T Tau, AS 353 A, and HL Tau. Maps of the spatially extended, high-velocity gas around T Tau and AS 353 A yield mass-loss rates of greater than 1 x 10/sup -7/ M/sub sun/ yr/sup -1/, respectively. These values are in excess of the 3 x 10/sup -8/ M/sub sun/ yr/sup -1/ theoretical limit set by DeCampli for mass-loss rates from T Tauri stars. The association of high-velocity CO wings with themore » presence of Herbig-Haro objects and the impact of T Tauri winds on molecular cloud dynamics are discussed.« less
  • A general mechanism is presented for generating pressure-driven winds that are intrinsically bipolar from objects undergoing disk accretion. The energy librated in a boundary layer shock as the disk matter impacts the central object is shown to be sufficient to eject a fraction ..beta..approx.10/sup -2/ to 10/sup -3/ of the accreted mass. These winds are driven by a mechanism that accelerates the flow perpendicular to the plane of the disk and can therefore account for the bipolar geometry of the mass loss observed near young stars. The mass loss contained in these winds is comparable to that inferred for youngmore » stars. Thus, disk accretion-driven winds may constitute the T Tauri phase of stellar evolution. This mechanism is generally applicable, and thus massive pre-main-sequence objects as well as cataclysmic variables at times of enhanced accretion are predicted to eject bipolar outflows as well. Unmagnetized accreting neutron stas are also expected to eject bipolar flows. Since this mechanism requires stellar surfaces, however, it will not operate in disk accretion onto black holes.« less
  • We present the discovery of a cold massive dust disk around the T Tauri star V1094 Sco in the Lupus molecular cloud from the 1.1 mm continuum observations with AzTEC on ASTE. A compact (r{approx}< 320 AU) continuum emission coincides with the stellar position having a flux density of 272 mJy, which is the largest among T Tauri stars in Lupus. We also present the detection of molecular gas associated with the star in the five-point observations in {sup 12}CO J = 3-2 and {sup 13}CO J = 3-2. Since our {sup 12}CO and {sup 13}CO observations did not showmore » any signature of a large-scale outflow or a massive envelope, the compact dust emission is likely to come from a disk around the star. The observed spectral energy distribution (SED) of V1094 Sco shows no distinct turnover from near-infrared to millimeter wavelengths, can be well described by a flattened disk for the dust component, and no clear dip feature around 10 {mu}m suggestive of the absence of an inner hole in the disk. We fit a simple power-law disk model to the observed SED. The estimated disk mass ranges from 0.03 M{sub sun} to {approx}>0.12 M{sub sun}, which is one or two orders of magnitude larger than the median disk mass of T Tauri stars in Taurus. The resultant temperature is lower than that of a flared disk with well-mixed dust in hydrostatic equilibrium and is probably attributed to the flattened disk geometry for the dust which the central star cannot illuminate efficiently. From these results, together with the fact that there is no signature of an inner hole in the SED, we suggest that the dust grains in the disk around V1094 Sco sank into the midplane with grain growth by coalescence and are in the evolutional stage just prior to or at the formation of planetesimals.« less