Cs. Kiss

ALMA OBSERVATIONS OF THE MOLECULAR GAS IN THE DEBRIS DISK OF THE 30 Myr OLD STAR HD 21997

The 30?Myr old A3-type star HD?21997 is one of the two known debris dust disks having a measurable amount of cold molecular gas. With the goal of understanding the physical state, origin, and evolution of the gas in young debris disks, we obtained CO line observations with the Atacama Large Millimeter/submillimeter Array (ALMA). Here, we report on the detection of 12CO and 13CO in the J = 2-1 and J = 3-2 transitions and C18O in the J = 2-1 line. The gas exhibits a Keplerian velocity curve, one of the few direct measurements of Keplerian rotation in young debris disks. The measured CO brightness distribution could be reproduced by a simple star+disk system, whose parameters are r in < 26?AU, r out = 138 ? 20?AU, ?M ?, and i = 32.?6 ? 3.?1. The total CO mass, as calculated from the optically thin C18O line, is about (4-8) ? 10?2?M ?, while the CO line ratios suggest a radiation temperature on the order of 6-9?K. Comparing our results with those obtained for the dust component of the HD?21997 disk from ALMA continuum observations by Mo?r et?al., we conclude that comparable amounts of CO gas and dust are present in the disk. Interestingly, the gas and dust in the HD?21997 system are not colocated, indicating a dust-free inner gas disk within 55?AU of the star. We explore two possible scenarios for the origin of the gas. A secondary origin, which involves gas production from colliding or active planetesimals, would require unreasonably high gas production rates and would not explain why the gas and dust are not colocated. We propose that HD?21997 is a hybrid system where secondary debris dust and primordial gas coexist. HD?21997, whose age exceeds both the model predictions for disk clearing and the ages of the oldest T?Tauri-like or transitional gas disks in the literature, may be a key object linking the primordial and the debris phases of disk evolution.

“TNOs are Cool”: A survey of the trans-Neptunian region - IX. Thermal properties of Kuiper belt objects and Centaurs from combined Herschel and Spitzer observations

Aims. The goal of this work is to characterize the ensemble thermal properties of the Centaurs/trans-Neptunian population. Methods. Thermal flux measurements obtained with Herschel/PACS and Spitzer/MIPS provide size, albedo, and beaming factors for 85 objects (13 of which are presented here for the first time) by means of standard radiometric techniques. The measured beaming factors are influenced by the combination of surface roughness and thermal inertia effects. They are interpreted within a thermophysical model to constrain, in a statistical sense, the thermal inertia in the population and to study its dependence on several parameters. We use in particular a Monte-Carlo modeling approach to the data whereby synthetic datasets of beaming factors are created using random distributions of spin orientation and surface roughness. Results. Beaming factors eta range fromvalues \textless1 to similar to 2.5, but high eta values (\textgreater2) are lacking at low heliocentric distances (r(h) \textless 30 AU). Beaming factors lower than 1 occur frequently (39% of the objects), indicating that surface roughness effects are important. We determine a mean thermal inertia for Centaurs/TNO of Gamma = (2.5 +/- 0.5) J m(-2) s(-1/2) K-1, with evidence of a trend toward decreasing Gamma with increasing heliocentric (by a factor similar to 2.5 from 8-25 AU to 41-53 AU). These thermal inertias are 2-3 orders of magnitude lower than expected for compact ices, and generally lower than on Saturns satellites or in the Pluto/Charon system. Most high-albedo objects are found to have unusually low thermal inertias. Our results suggest highly porous surfaces, in which the heat transfer is affected by radiative conductivity within pores and increases with depth in the subsurface.

Discovery of Molecular Gas around HD 131835 in an APEX Molecular Line Survey of Bright Debris Disks

Debris disks are considered to be gas-poor, but recent observations revealed molecular or atomic gas in several 10-40 Myr old systems. We used the APEX and IRAM 30m radiotelescopes to search for CO gas in 20 bright debris disks. In one case, around the 16 Myr old A-type star HD 131835, we discovered a new gas-bearing debris disk, where the CO 3-2 transition was successfully detected. No other individual system exhibited a measurable CO signal. Our Herschel Space Observatory far-infrared images of HD 131835 marginally resolved the disk both at 70 and 100

A Resolved Debris Disk around the Candidate Planet-hosting Star HD 95086

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The discovery of new warm debris disks around F-type stars

m, with a characteristic radius of ~170 au. While in stellar properties HD 131835 resembles

Sky confusion noise in the far-infrared: Cirrus, galaxies and the cosmic far{infrared background ?

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Stirring in massive, young debris discs from spatially resolved Herschel images

Pic, its dust disk properties are similar to those of the most massive young debris disks. With the detection of gas in HD 131835 the number of known debris disks with CO content has increased to four, all of them encircling young (

The European Large Area ISO Survey – VIII. 90-μm final analysis and source counts

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Far-infrared loops in the 2nd Galactic Quadrant

40 Myr) A-type stars. Based on statistics within 125 pc, we suggest that the presence of detectable amount of gas in the most massive debris disks around young A-type stars is a common phenomenon. Our current data cannot conclude on the origin of gas in HD 131835. If the gas is secondary, arising from the disruption of planetesimals, then HD 131835 is a comparably young and in terms of its disk more massive analogue of the

Unveiling new members in five nearby young moving groups

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