119236401
THE TW Hya DISK AT 870 μm: COMPARISON OF CO AND DUST RADIAL STRUCTURES
We present high-resolution (0.''3 = 16 AU), high signal-to-noise ratio Submillimeter Array observations of the 870 {mu}m (345 GHz) continuum and CO J = 3 - 2 line emission from the protoplanetary disk around TW Hya. Using continuum and line radiative transfer calculations, these data and the multiwavelength spectral energy distribution are analyzed together in the context of simple two-dimensional parametric disk structure models. Under the assumptions of a radially invariant dust population and gas-to-dust mass ratio, we are unable to simultaneously reproduce the CO and dust observations with model structures that employ either a single, distinct outer boundary or a smooth (exponential) taper at large radii. Instead, we find that the distribution of millimeter-sized dust grains in the TW Hya disk has a relatively sharp edge near 60 AU, contrary to the CO emission (and optical/infrared scattered light) that extends to a much larger radius of at least 215 AU. We discuss some possible explanations for the observed radial distribution of millimeter-sized dust grains and the apparent CO-dust size discrepancy, and suggest that they may be hallmarks of substructure in the dust disk or natural signatures of the growth and radial drift of solids that might be expected for more » disks around older pre-main-sequence stars like TW Hya. « less
119195257
Spitzer, Near-Infrared, and Submillimeter Imaging of the Relatively Sparse Young Cluster, Lynds 988e
We present Spitzer images of the relatively sparse, low-luminosity young cluster L988e, as well as complementary near-infrared (NIR) and submillimeter images of the region. The cluster is asymmetric, with the western region of the cluster embedded within the molecular cloud, and the slightly less dense eastern region to the east of, and on the edge of, the molecular cloud. With these data, as well as with extant Hα data of stars primarily found in the eastern region of the cluster, and a molecular 13CO gas emission map of the entire region, we investigate the distribution of forming young stars with respect to the cloud material, concentrating particularly on the differences and similarities between the exposed and embedded regions of the cluster. We also compare star formation in this region to that in denser, more luminous and more massive clusters already investigated in our comprehensive multiwavelength study of young clusters within 1 kpc of the Sun.
119110413
RESOLVED SUBMILLIMETER OBSERVATIONS OF THE HR 8799 AND HD 107146 DEBRIS DISKS
We present 880 {mu}m Submillimeter Array observations of the debris disks around the young solar analog HD 107146 and the multiple-planet host star HR 8799, at an angular resolution of 3'' and 6'', respectively. We spatially resolve the inner edge of the disk around HR 8799 for the first time. While the data are not sensitive enough (with rms noise of 1 mJy) to constrain the system geometry, we demonstrate that a model by Su et al. based on the spectral energy distribution (SED) with an inner radius of 150 AU predicts the spatially resolved data well. Furthermore, by modeling simultaneously the SED and visibilities, we demonstrate that the dust is distributed in a broad (of order 100 AU) annulus rather than a narrow ring. We also model the observed SED and visibilities for the HD 107146 debris disk and generate a model of the dust emission that extends in a broad band between 50 and 170 AU from the star. We perform an a posteriori comparison with existing 1.3 mm CARMA observations and demonstrate that a smooth, axisymmetric model reproduces all of the available millimeter-wavelength data well.
15020665
ON THE EVOLUTION OF THE DENSE CORE MASS FUNCTION
The mass distributions of dense cores in star-forming regions are measured to have a shape similar to the initial mass function of stars. This has been generally interpreted to mean that the constituent cores will form individual stars or stellar systems at a nearly constant star formation efficiency. This article presents a series of numerical experiments evolving distributions of dense cores into stars to quantify the effects of stellar multiplicity, global core fragmentation, and a varying star formation efficiency. We find that the different evolutionary schemes have an overall small effect on the shape of the resulting distribution of stars. Our results imply that at the current level of observational accuracy, the comparison between the mass functions of dense cores and stars alone is insufficient to discern between different evolutionary models. Observations over a wide range of mass scales including the high- or low-mass tails of these distributions have the largest potential for discerning between different core evolutionary schemes.
18815074
Massive Protoplanetary Disks in Orion Beyond the Trapezium Cluster
We present Submillimeter Array1The Submillimeter Array is a joint project between the Submillimeter Astrophysical Observatory and the Academica Sinica Institute of Astronomy and Astrophysics and is funded by the Smithsonian Institution and the Academica Sinica. observations of the 880 μm continuum emission from three circumstellar disks around young stars in Orion that lie several arcminutes ( 1 pc) north of the Trapezium cluster. Two of the three disks are in the binary system 253-1536. Silhouette disks 216-0939 and 253-1536a are found to be more massive than any previously observed Orion disks, with dust masses derived from their submillimeter emission of 0.045 M ☉ and 0.066 M ☉, respectively. The existence of these massive disks reveals that the disk mass distribution in Orion does extend to high masses, and that the truncation observed in the central Trapezium cluster is a result of photoevaporation due to the proximity of O-stars. 253-1536b has a disk mass of 0.018 M ☉, making the 253-1536 system the first optical binary in which each protoplanetary disk is massive enough to potentially form solar systems.
16521702
Hot corinos in NGC 1333-IRAS 4 B and IRAS 2 A
Context. Complex organic molecules have been detected in massive hot cores for over two decades, and only recently in three hot corinos (the inner regions surrounding Sun-like protostars, where the dust temperature exceeds 100 K). Since hot corinos have sizes of ∼100 AU (i.e., of the order of the extent of the Solar System), it is particularly relevant to understand whether they are common and to identify the formation route(s) of complex organic molecules. Much has yet to be learned on this topic, since even recent models predicted it was not possible to form these molecules in low-mass protostars. Aims. We aim to enlarge the number of known hot corinos and carry out a first comparative study with hot cores. The ultimate goal is to understand whether complex organic molecules form in the gas phase or on grain surfaces, and what the possible key parameters are. Methods. We observed millimeter rotational transitions of HCOOH, HCOOCH3 CH3OCH3 CH3CN and C2H5CN in a sample of low-mass protostars with the IRAM-30m. Using the rotational diagram method coupled with the information about the sources’ structure, we calculate the abundances of the observed molecules. To interpret these abundances, we review the proposed formation processes of the above molecules. Results. We report the detection of HCOOCH3 and/or CH3CN towards NGC1333-IRAS4B and NGC1333-IRAS2A. We find that abundance ratios of O-bearing molecules to methanol or formaldehyde in hot corinos are comparable and about unity, and are relatively (depending on how the ratios are determined) higher than those in hot cores and in Galactic center clouds. Conclusions. So far, complex organic molecules were detected in all the hot corinos where they were searched for, suggesting that it is a common phase for low-mass protostars. While some evidence points to grain-surface synthesis (either in the cold or warm-up phase) of these molecules (in particular for HCOOH and HCOOCH3), the present data do not allow us to disregard gas-phase formation. More observational, laboratory, and theoretical studies are required to improve our understanding of hot corinos.
115237596
Calculations of charge-symmetry breaking in n-p elastic scattering