53 research outputs found
A high resolution mid-infrared survey of water emission from protoplanetary disks
We present the largest survey of spectrally resolved mid-infrared water
emission to date, with spectra for 11 disks obtained with the Michelle and
TEXES spectrographs on Gemini North. Water emission is detected in 6 of 8 disks
around classical T Tauri stars. Water emission is not detected in the
transitional disks SR 24 N and SR 24 S, in spite of SR 24 S having
pre-transitional disk properties like DoAr 44, which does show water emission
(Salyk et al. 2015). With R~100,000, the TEXES water spectra have the highest
spectral resolution possible at this time, and allow for detailed lineshape
analysis. We find that the mid-IR water emission lines are similar to the
"narrow component" in CO rovibrational emission (Banzatti & Pontoppidan 2015),
consistent with disk radii of a few AU. The emission lines are either single
peaked, or consistent with a double peak. Single-peaked emission lines cannot
be produced with a Keplerian disk model, and may suggest that water
participates in the disk winds proposed to explain single-peaked CO emission
lines (Bast et al. 2011, Pontoppidan et al. 2011). Double-peaked emission lines
can be used to determine the radius at which the line emission luminosity drops
off. For HL Tau, the lower limit on this measured dropoff radius is consistent
with the 13 AU dark ring (ALMA partnership et al. 2015). We also report
variable line/continuum ratios from the disks around DR Tau and RW Aur, which
we attribute to continuum changes and line flux changes, respectively. The
reduction in RW Aur line flux corresponds with an observed dimming at visible
wavelengths (Rodriguez et al. 2013).Comment: To appear in the Astrophysical Journa
Non-detection of L-band Line Emission from the Exoplanet HD189733b
We attempt to confirm bright non-local thermodynamic equilibrium (non-LTE) emission from the exoplanet HD 189733b at 3.25 μm, as recently reported by Swain et al. based on observations at low spectral resolving power (λ/δλ ≈ 30). Non-LTE emission lines from gas in an exoplanet atmosphere will not be significantly broadened by collisions, so the measured emission intensity per resolution element must be substantially brighter when observed at high spectral resolving power. We observed the planet before, during, and after a secondary eclipse event at a resolving power λ/δλ = 27, 000 using the NIRSPEC spectrometer on the Keck II telescope. Our spectra cover a spectral window near the peak found by Swain et al., and we compare emission cases that could account for the magnitude and wavelength dependence of the Swain et al. result with our final spectral residuals. To model the expected line emission, we use a general non-equilibrium formulation to synthesize emission features from all plausible molecules that emit in this spectral region. In every case, we detect no line emission to a high degree of confidence. After considering possible explanations for the Swain et al. results and the disparity with our own data, we conclude that an astrophysical source for the putative non-LTE emission is unlikely. We note that the wavelength dependence of the signal seen by Swain et al. closely matches the 2ν_2 band of water vapor at 300 K, and we suggest that an imperfect correction for telluric water is the source of the feature claimed by Swain et al
H2O and OH gas in the terrestrial planet-forming zones of protoplanetary disks
We present detections of numerous 10-20 micron H2O emission lines from two
protoplanetary disks around the T Tauri stars AS 205A and DR Tau, obtained
using the InfraRed Spectrograph on the Spitzer Space Telescope. Follow-up 3-5
micron Keck-NIRSPEC data confirm the presence of abundant water and spectrally
resolve the lines. We also detect the P4.5 (2.934 micron) and P9.5 (3.179
micron) doublets of OH and 12CO/13CO v=1-0 emission in both sources. Line
shapes and LTE models suggest that the emission from all three molecules
originates between ~0.5 and 5 AU, and so will provide a new window for
understanding the chemical environment during terrestrial planet formation. LTE
models also imply significant columns of H2O and OH in the inner disk
atmospheres, suggesting physical transport of volatile ices either vertically
or radially; while the significant radial extent of the emission stresses the
importance of a more complete understanding of non-thermal excitation
processes.Comment: 9 pages, 3 figures, 1 table, aastex, to appear in the Astrophysical
Journa
A Spitzer survey of mid-infrared molecular emission from protoplanetary disks I: Detection rates
We present a Spitzer InfraRed Spectrometer search for 10-36 micron molecular
emission from a large sample of protoplanetary disks, including lines from H2O,
OH, C2H2, HCN and CO2. This paper describes the sample and data processing and
derives the detection rate of mid-infrared molecular emission as a function of
stellar mass. The sample covers a range of spectral type from early M to A, and
is supplemented by archival spectra of disks around A and B stars. It is drawn
from a variety of nearby star forming regions, including Ophiuchus, Lupus and
Chamaeleon. In total, we identify 22 T Tauri stars with strong mid-infrared H2O
emission. Integrated water line luminosities, where water vapor is detected,
range from 5x10^-4 to 9x10^-3 Lsun, likely making water the dominant line
coolant of inner disk surfaces in classical T Tauri stars. None of the 5
transitional disks in the sample show detectable gaseous molecular emission
with Spitzer upper limits at the 1% level in terms of line-to-continuum ratios
(apart from H2). We find a strong dependence on detection rate with spectral
type; no disks around our sample of 25 A and B stars were found to exhibit
water emission, down to 1-2% line-to-continuum ratios, in the mid-infrared,
while almost 2/3 of the disks around K stars show sufficiently intense water
emission to be detected by Spitzer. Some Herbig Ae/Be stars show tentative
H2O/OH emission features beyond 20 micron at the 1-2 level, however, and one of
them shows CO2 in emission. We argue that the observed differences between T
Tauri disks and Herbig Ae/Be disks is due to a difference in excitation and/or
chemistry depending on spectral type and suggest that photochemistry may be
playing an important role in the observable characteristics of mid-infrared
molecular line emission from protoplanetary disks.Comment: 19 pages, accepted for publication in Ap
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