52 research outputs found
2D disc modelling of the JWST line spectrum of EX Lupi
We introduce a number of new theoretical approaches and improvements to the
thermo-chemical disc modelling code ProDiMo to better predict and analyse the
JWST line spectra of protoplanetary discs. We develop a new line escape
probability method for disc geometries, a new scheme for dust settling, and
discuss how to apply UV molecular shielding factors to photorates in 2D disc
geometry. We show that these assumptions are crucial for the determination of
the gas heating/cooling rates and discuss how they affect the predicted
molecular concentrations and line emissions. We apply our revised 2D models to
the protoplanetary disc around the T Tauri star EX Lupi in quiescent state. We
calculate infrared line emission spectra between 5 and 20 mic by CO, H2O, OH,
CO2, HCN, C2H2 and H2, including lines of atoms and ions, using our full 2D
predictions of molecular abundances, dust opacities, gas and dust temperatures.
We develop a disc model with a slowly increasing surface density structure
around the inner rim that can simultaneously fit the spectral energy
distribution, the overall shape of the JWST spectrum of EX Lupi, and the main
observed molecular characteristics in terms of column densities, emitting areas
and molecular emission temperatures, which all result from one consistent disc
model. The spatial structure of the line emitting regions of the different
molecules is discussed. High abundances of HCN and C2H2 are caused in the model
by stellar X-ray irradiation of the gas around the inner rim.Comment: accepted by A&A, 25 pages, 15 figures, 7 table
Radial Surface Density Profiles of Gas and Dust in the Debris Disk around 49 Ceti
We present ~0.4 resolution images of CO(3-2) and associated continuum
emission from the gas-bearing debris disk around the nearby A star 49 Ceti,
observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We
analyze the ALMA visibilities in tandem with the broad-band spectral energy
distribution to measure the radial surface density profiles of dust and gas
emission from the system. The dust surface density decreases with radius
between ~100 and 310 au, with a marginally significant enhancement of surface
density at a radius of ~110 au. The SED requires an inner disk of small grains
in addition to the outer disk of larger grains resolved by ALMA. The gas disk
exhibits a surface density profile that increases with radius, contrary to most
previous spatially resolved observations of circumstellar gas disks. While ~80%
of the CO flux is well described by an axisymmetric power-law disk in Keplerian
rotation about the central star, residuals at ~20% of the peak flux exhibit a
departure from axisymmetry suggestive of spiral arms or a warp in the gas disk.
The radial extent of the gas disk (~220 au) is smaller than that of the dust
disk (~300 au), consistent with recent observations of other gas-bearing debris
disks. While there are so far only three broad debris disks with well
characterized radial dust profiles at millimeter wavelengths, 49 Ceti's disk
shows a markedly different structure from two radially resolved gas-poor debris
disks, implying that the physical processes generating and sculpting the gas
and dust are fundamentally different.Comment: 20 pages, 8 figures, accepted for publication in ApJ March 31, 2017
(submitted Nov 2016
A Resolved Debris Disk Around the Candidate Planet-hosting Star HD 95086
Recently, a new planet candidate was discovered on direct images around the young (10-17 Myr) A-type star HD 95086. The strong infrared excess of the system indicates that, similar to HR8799, Beta Pic, and Fomalhaut, the star harbors a circumstellar disk. Aiming to study the structure and gas content of the HD 95086 disk, and to investigate its possible interaction with the newly discovered planet, here we present new optical, infrared, and millimeter observations. We detected no CO emission, excluding the possibility of an evolved gaseous primordial disk. Simple blackbody modeling of the spectral energy distribution suggests the presence of two spatially separate dust belts at radial distances of 6 and 64 AU. Our resolved images obtained with the Herschel Space Observatory reveal a characteristic disk size of approx. 6.0 5.4 (540 490 AU) and disk inclination of approx 25 deg. Assuming the same inclination for the planet candidate's orbit, its reprojected radial distance from the star is 62 AU, very close to the blackbody radius of the outer cold dust ring. The structure of the planetary system at HD 95086 resembles the one around HR8799. Both systems harbor a warm inner dust belt and a broad colder outer disk and giant planet(s) between the two dusty regions. Modeling implies that the candidate planet can dynamically excite the motion of planetesimals even out to 270 AU via their secular perturbation if its orbital eccentricity is larger than about 0.4. Our analysis adds a new example to the three known systems where directly imaged planet(s) and debris disks coexist
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