Browsing by Subject "brown dwarf disks"
Now showing 1 - 3 of 3
- Results Per Page
- Sort Options
Item An Alma Disk Mass for the Candidate Protoplanetary Companion to FW Tau(2015-01) Kraus, Adam L.; Andrews, Sean M.; Bowler, Brendan P.; Herczeg, Gregory; Ireland, Michael J.; Liu, Michael C.; Metchev, Stanimir; Cruz, Kelle L.; Kraus, Adam L.We present ALMA observations of the FW Tau system, a close binary pair of M5 stars with a wide-orbit (300 AU projected separation) substellar companion. The companion is extremely faint and red in the optical and near-infrared, but boasts a weak far-infrared excess and optical/near-infrared emission lines indicative of a primordial accretion disk of gas and dust. The component-resolved 1.3mm continuum emission is found to be associated only with the companion, with a flux (1.78 +/- 0.03 mJy) that indicates a dust mass of 1-2M(circle plus). While this mass reservoir is insufficient to form a giant planet, it is more than sufficient to produce an analog of the Kepler-42 exoplanetary system or the Galilean satellites. The mass and geometry of the disk-bearing FW Tau companion remains unclear. Near-infrared spectroscopy shows deep water bands that indicate a spectral type later than M5, but substantial veiling prevents a more accurate determination of the effective temperature (and hence mass). Both a disk-bearing "planetary-mass" companion seen in direct light or a brown dwarf tertiary viewed in light scattered by an edge-on disk or envelope remain possibilities.Item The Spitzer Infrared Spectrograph Survey of T Tauri Stars in Taurus(2011-07) Furlan, E.; Luhman, K. L.; Espaillat, C.; D'Alessio, P.; Adame, L.; Manoj, P.; Kim, K. H.; Watson, D. M.; Forrest, W. J.; McClure, M. K.; Calvet, N.; Sargent, B. A.; Green, Joel D.; Fischer, W. J.; Green, Joel D.We present 161 Spitzer Infrared Spectrograph (IRS) spectra of T Tauri stars and young brown dwarfs in the Taurus star-forming region. All of the targets were selected based on their infrared excess and are therefore surrounded by protoplanetary disks; they form the complete sample of all available IRS spectra of T Tauri stars with infrared excesses in Taurus. We also present the IRS spectra of seven Class 0/I objects in Taurus to complete the sample of available IRS spectra of protostars in Taurus. We use spectral indices that are not significantly affected by extinction to distinguish between envelope-and disk-dominated objects. Together with data from the literature, we construct spectral energy distributions for all objects in our sample. With spectral indices derived from the IRS spectra we infer disk properties such as dust settling and the presence of inner disk holes and gaps. We find a transitional disk frequency, which is based on objects with unusually large 13-31 mu m spectral indices indicative of a wall surrounding an inner disk hole, of about 3%, and a frequency of about 20% for objects with unusually large 10 mu m features, which could indicate disk gaps. The shape and strength of the 10 mu m silicate emission feature suggests weaker 10 mu m emission and more processed dust for very low mass objects and brown dwarfs (spectral types M6-M9). These objects also display weaker infrared excess emission from their disks, but do not appear to have more settled disks than their higher-mass counterparts. We find no difference for the spectral indices and properties of the dust between single and multiple systems.Item Spitzer Infrared Spectrograph Survey of Young Stars in the Chamaeleon I Star-forming Region(2011-03) Manoj, P.; Kim, K. H.; Furlan, E.; McClure, M. K.; Luhman, K. L.; Watson, D. M.; Espaillat, C.; Calvet, N.; Najita, J. R.; D'Alessio, P.; Adame, L.; Sargent, B. A.; Forrest, W. J.; Bohac, C.; Green, Joel D.; Arnold, L. A.; Green, Joel D.We present 5-36 mu m mid-infrared spectra of 82 young stars in the similar to 2 Myr old Chamaeleon I star-forming region, obtained with the Spitzer Infrared Spectrograph (IRS). We have classified these objects into various evolutionary classes based on their spectral energy distributions and the spectral features seen in the IRS spectra. We have analyzed the mid-IR spectra of Class II objects in Chamaeleon I in detail, in order to study the vertical and radial structure of the protoplanetary disks surrounding these stars. We find evidence for substantial dust settling in most protoplanetary disks in Chamaeleon I. We have identified several disks with altered radial structures in Chamaeleon I, among them transitional disk candidates which have holes or gaps in their disks. Analysis of the silicate emission features in the IRS spectra of Class II objects in Cha I shows that the dust grains in these disks have undergone significant processing (grain growth and crystallization). However, disks with radial holes/gaps appear to have relatively unprocessed grains. We further find the crystalline dust content in the inner (less than or similar to 1-2 AU) and the intermediate (less than or similar to 10 AU) regions of the protoplanetary disks to be tightly correlated. We also investigate the effects of accretion and stellar multiplicity on the disk structure and dust properties. Finally, we compare the observed properties of protoplanetary disks in Cha I with those in slightly younger Taurus and Ophiuchus regions and discuss the effects of disk evolution in the first 1-2 Myr.