Young stars inϵChamaleontis and their disks: disk evolution in sparse associations

Abstract

Context. The nearby young stellar association Cha has an estimated age of 3-5 Myr, making it an ideal laboratory to study the disk dissipation process and provide empirical constraints on the timescale of planet formation. Aims. We wish to complement existing optical and near-infrared data of the Cha association, which provide the stellar properties of its members, with mid-infrared data that probe the presence, geometry, and mineralogical composition of protoplanetary disks around individual stars. Methods. We combine the available literature data with our Spitzer/IRS spectroscopy and VLT/VISIR imaging data. We use proper motions to refine the membership of Cha. Masses and ages of individual stars are estimated by fitting model atmospheres to the optical and near-infrared photometry, followed by placement in the Hertzsprung-Russell diagram. The Spitzer/IRS spectra are analyzed using the two-layer temperature distribution spectral decomposition method. Results. Two stars previously identified as members, CXOU J120152.8 and 2MASS J12074597, have proper motions that are very different from those of the other stars. But other observations suggest that the two stars are still young and thus might still be related to Cha. HD 104237C is the lowest mass member of Cha with an estimated mass of ∼13-15 Jupiter masses. The very low mass stars USNO-B120144.7 and 2MASS J12005517 show globally depleted spectral energy distributions, pointing at strong dust settling. 2MASS J12014343 may have a disk with a very specific inclination, where the central star is effectively screened by the cold outer parts of a flared disk, but the 10 μm radiation of the warm inner disk can still reach us. We find that the disks in sparse stellar associations are dissipated more slowly than those in denser (cluster) environments. We detect C 2 H 2 rovibrational band around 13.7 μm on the IRS spectrum of USNO-B120144.7. We find strong signatures of grain growth and crystallization in all Cha members with 10 μm features detected in their IRS spectra. We combine the dust properties derived in the Cha sample with those found using identical or similar methods in the MBM 12, Coronet, η Cha associations, and in the cores-to-disks legacy program. We find that disks around low-mass young stars show a negative radial gradient in the mass-averaged grain size and mass fraction of crystalline silicates. A positive correlation exists between the mass-averaged grain sizes of amorphous silicates and the accretion rates if the latter is above ∼10 −9 M yr −1 , possibly indicating that those disks are sufficiently turbulent to prevent grains of several microns in size to sink into the disk interior.

NGC 1980 Is Not a Foreground Population of Orion: Spectroscopic Survey of Young Stars with Low Extinction in Orion A

“…Its SED shows the strong infrared excess emission (see the right panel in Figure 12), suggesting that it is surrounded by a disk. Similar young stars have been discovered in our previous spectroscopic surveys in Orion (Fang et al 2009(Fang et al , 2013a, and also found in other regions, e.g., the Lupus 3 dark cloud, Taurus, and òCha White & Hillenbrand 2004;Fang et al 2013b). One promising hypothesis for these exotic objects is that they are harboring disks with high inclinations, and the light seen mainly comes from photons scattered off the disk surfaceand is therefore much reduced.…”

Precession and accretion in circumbinary discs: the case of HD 104237

“…Since we are well below the self-gravitating limit the mass effectively becomes a scaling factor and does not affect the hydrodynamics. SED models of HD 104237 are consistent with a nonflaring disc (Fang et al 2013;Hales et al 2014), while our equation of state enforces a flared disc. The flaring is not strong, and H/R only goes from 0.03 at the inner edge to 0.07 at the outer edge of our disc, so we do not expect this to affect the results of our simulations.…”

GW Orionis: Inner disk readjustments in a triple system

“…Therefore, the interaction between disks and companions has been proposed as an efficient mechanism to dissipate disks (Lin & Papaloizou 1993). Observationally, this mechanism can be very efficient in disk disperal at very early stages (<1 Myr, Cieza et al 2009;) and may play a key role in dissipating the Table 4 is available in electronic form at http://www.aanda.org disks in sparse stellar associations (Bouwman et al 2006;Fang et al 2013b).…”