66 research outputs found
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
Detection of water vapor in the terrestrial planet forming region of a transition disk
We report a detection of water vapor in the protoplanetary disk around DoAr
44 with the Texas Echelon Cross Echelle Spectrograph --- a visitor instrument
on the Gemini north telescope. The DoAr 44 disk consists of an optically thick
inner ring and outer disk, separated by a dust-cleared 36 AU gap, and has
therefore been termed "pre-transitional". To date, this is the only disk with a
large inner gap known to harbor detectable quantities of warm (T=450 K) water
vapor. In this work, we detect and spectrally resolve three mid-infrared pure
rotational emission lines of water vapor from this source, and use the shapes
of the emission lines to constrain the location of the water vapor. We find
that the emission originates near 0.3 AU --- the inner disk region. This
characteristic region coincides with that inferred for both optically thick and
thin thermal infrared dust emission, as well as rovibrational CO emission. The
presence of water in the dust-depleted region implies substantial columns of
hydrogen (>10^{22} cm-2) as the water vapor would otherwise be destroyed by
photodissociation. Combined with the dust modeling, this column implies a
gas/small-dust ratio in the optically thin dusty region of >1000. These results
demonstrate that DoAr 44 has maintained similar physical and chemical
conditions to classical protoplanetary disks in its terrestrial-planet forming
regions, in spite of having formed a large gap.Comment: Paper accepted to the Astrophysical Journal Letter
Volatiles in protoplanetary disks
Volatiles are compounds with low sublimation temperatures, and they make up
most of the condensible mass in typical planet-forming environments. They
consist of relatively small, often hydrogenated, molecules based on the
abundant elements carbon, nitrogen and oxygen. Volatiles are central to the
process of planet formation, forming the backbone of a rich chemistry that sets
the initial conditions for the formation of planetary atmospheres, and act as a
solid mass reservoir catalyzing the formation of planets and planetesimals.
This growth has been driven by rapid advances in observations and models of
protoplanetary disks, and by a deepening understanding of the cosmochemistry of
the solar system. Indeed, it is only in the past few years that representative
samples of molecules have been discovered in great abundance throughout
protoplanetary disks - enough to begin building a complete budget for the most
abundant elements after hydrogen and helium. The spatial distributions of key
volatiles are being mapped, snow lines are directly seen and quantified, and
distinct chemical regions within protoplanetary disks are being identified,
characterized and modeled. Theoretical processes invoked to explain the solar
system record are now being observationally constrained in protoplanetary
disks, including transport of icy bodies and concentration of bulk
condensibles. The balance between chemical reset - processing of inner disk
material strong enough to destroy its memory of past chemistry, and inheritance
- the chemically gentle accretion of pristine material from the interstellar
medium in the outer disk, ultimately determines the final composition of
pre-planetary matter. This chapter focuses on making the first steps toward
understanding whether the planet formation processes that led to our solar
system are universal.Comment: Accepted for publication as a chapter in Protostars and Planets VI,
University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C.
Dullemond, Th. Hennin
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
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