366 research outputs found
Spectrally resolved pure rotational lines of water in protoplanetary disks
We present ground-based high resolution N-band spectra (\Delta v = 15 km/s)
of pure rotational lines of water vapor in two protoplanetary disks surrounding
the pre-main sequence stars AS 205N and RNO 90, selected based on detections of
rotational water lines by the Spitzer IRS. Using VISIR on the Very Large
Telescope, we spectrally resolve individual lines and show that they have
widths of 30-60 km/s, consistent with an origin in Keplerian disks at radii of
~1 AU. The water lines have similar widths to those of the CO at 4.67 micron,
indicating that the mid-infrared water lines trace similar radii. The
rotational temperatures of the water are 540 and 600K in the two disks,
respectively. However, the lines ratios show evidence of non-LTE excitation,
with low-excitation line fluxes being over-predicted by 2-dimensional disk LTE
models. Due to the limited number of observed lines and the non-LTE line
ratios, an accurate measure of the water ortho/para ratio is not available, but
a best estimate for AS 205N is ortho/para = 4.5 +/- 1.0, apparently ruling out
a low-temperature origin of the water. The spectra demonstrate that high
resolution spectroscopy of rotational water lines is feasible from the ground,
and further that ground-based high resolution spectroscopy is likely to
significantly improve our understanding of the inner disk chemistry recently
revealed by recent Spitzer observations.Comment: Accepted for publication in ApJ
The narrow, inner CO ring around the magnetic Herbig Ae star, HD 101412
We describe and model emission lines in the first overtone band of CO in the
magnetic Herbig Ae star HD 101412. High-resolution CRIRES spectra reveal
unusually sharp features which suggest the emission is formed in a thin disk
centered at 1 AU with a width 0.32 AU or less. A wider disk will not fit the
observations. Previous observations have reached similar conclusions, but the
crispness of the new material brings the emitting region into sharp focus.Comment: Accepted as Astronomy and Astrophysics Letter; 4 pages, 5 figure
Characterizing CO Fourth Positive Emission in Young Circumstellar Disks
Carbon Monoxide is a commonly used IR/sub-mm tracer of gas in protoplanetary
disks. We present an analysis of ultraviolet CO emission in {HST}-COS spectra
for 12 Classical T Tauri stars. Several ro-vibrational bands of the CO A^1\Pi -
X^1\Sigma^+ (Fourth Positive) electronic transition system are spectrally
resolved from emission of other atoms and H_2. The CO A^1\Pi v'=14 state is
populated by absorption of Ly\alpha photons, created at the accretion column on
the stellar surface. For targets with strong CO emission, we model the Ly\alpha
radiation field as an input for a simple fluorescence model to estimate CO
rotational excitation temperatures and column densities. Typical column
densities range from N_{CO} = 10^{18} - 10^{19} cm^{-2}. Our measured
excitation temperatures are mostly below T_{CO} = 600 K, cooler than typical
M-band CO emission. These temperatures and the emission line widths imply that
the UV emission originates in a different population of CO than that which is
IR-emitting. We also find a significant correlation between CO emission and the
disk accretion rate M_{acc} and age. Our analysis shows that ultraviolet CO
emission can be a useful diagnostic of CTTS disk gas
CO Rovibrational Emission as a Probe of Inner Disk Structure
We present an analysis of CO emission lines from a sample of T Tauri, Herbig Ae/Be, and transitional disks with known inclinations in order to study the structure of inner disk molecular gas. We calculate CO inner radii by fitting line profiles with a simple parameterized model. We find that, for optically thick disks, CO inner radii are strongly correlated with the total system luminosity (stellar plus accretion) and consistent with the dust sublimation radius. Transitional disk inner radii show the same trend with luminosity, but are systematically larger. Using rotation diagram fits, we derive, for classical T Tauri disks, emitting areas consistent with a ring of width ~0.15 AU located at the CO inner radius; emitting areas for transitional disks are systematically smaller. We also measure lower rotational temperatures for transitional disks, and disks around Herbig Ae/Be stars, than for those around T Tauri stars. Finally, we find that rotational temperatures are similar to, or slightly lower than, the expected temperature of blackbody grains located at the CO inner radius, in contrast to expectations of thermal decoupling between gas and dust
ALMA Observations of the T Tauri Binary System AS 205: Evidence for Molecular Winds and/or Binary Interactions
In this study, we present high-resolution millimeter observations of the dust
and gas disk of the T Tauri star AS 205 N and its companion, AS 205 S, obtained
with the Atacama Large Millimeter Array. The gas disk around AS 205 N, for
which infrared emission spectroscopy demonstrates significant deviations from
Keplerian motion that has been interpreted as evidence for a disk wind
(Pontoppidan et al. 2011; Bast et al. 2011), also displays significant
deviations from Keplerian disk emission in the observations presented here.
Detections near both AS 205 N and S are obtained in 1.3 mm continuum, 12CO 2-1,
13CO 2-1 and C18O 2-1. The 12CO emission is extended up to 2 arcsec from AS
205N, and both 12CO and 13CO display deviations from Keplerian rotation at all
angular scales. Two possible explanations for these observations hold up best
to close scrutiny - tidal interaction with AS 205 S or disk winds (or a
combination of the two), and we discuss these possibilities in some detail.Comment: accepted by The Astrophysical Journa
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