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Register a new userA rotating disk around the very young massive star AFGL 490
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Added by
Katharina Schreyer Dr.
Publication date
2006
fields
Physics
and research's language is
English
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We observed the embedded, young 8--10 Msun star AFGL 490 at subarcsecond resolution with the Plateau de Bure Interferometer in the C17O (2--1) transition and found convincing evidence that AFGL 490 is surrounded by a rotating disk. Using two-dimensional modeling of the physical and chemical disk structure coupled to line radiative transfer, we constrain its basic parameters. We obtain a relatively high disk mass of 1 Msun and a radius of ~ 1500 AU. A plausible explanation for the apparent asymmetry of the disk morphology is given.
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We present Spitzer IRAC and MIPS observations of the star-forming region containing intermediate-mass young stellar object (YSO) AFGL 490. We supplement these data with near-IR 2MASS photometry and with deep SQIID observations off the central high extinction region. We have more than doubled the known membership of this region to 57 Class I and 303 Class II YSOs via the combined 1-24 um photometric catalog derived from these data. We construct and analyze the minimum spanning tree of their projected positions, isolating one locally over-dense cluster core containing 219 YSOs (60.8% of the regions members). We find this cluster core to be larger yet less dense than similarly analyzed clusters. Although the structure of this cluster core appears irregular, we demonstrate that the parsec-scale surface densities of both YSOs and gas are correlated with a power law slope of 2.8, as found for other similarly analyzed nearby molecular clouds. We also explore the mass segregation implications of AFGL 490s offset from the center of its core, finding that it has no apparent preferential central position relative to the low-mass members.
We present Atacama Large Millimeter/submillimeter Array (ALMA) line and continuum observations at 1.2mm with ~0.3 resolution that uncover a Keplerian-like disk around the forming O-type star AFGL 4176. The continuum emission from the disk at 1.21 mm (source mm1) has a deconvolved size of 870+/-110 AU x 330+/-300 AU and arises from a structure ~8 M_sun in mass, calculated assuming a dust temperature of 190 K. The first-moment maps, pixel-to-pixel line modeling, assuming local thermodynamic equilibrium (LTE), and position-velocity diagrams of the CH3CN J=13-12 K-line emission all show a velocity gradient along the major axis of the source, coupled with an increase in velocity at small radii, consistent with Keplerian-like rotation. The LTE line modeling shows that where CH3CN J=13-12 is excited, the temperatures in the disk range from ~70 to at least 300 K and that the H2 column density peaks at 2.8x10^24 cm^-2. In addition, we present Atacama Pathfinder Experiment (APEX) 12CO observations which show a large-scale outflow from AFGL 4176 perpendicular to the major axis of mm1, supporting the disk interpretation. Finally, we present a radiative transfer model of a Keplerian disk surrounding an O7 star, with a disk mass and radius of 12 M_sun and 2000 AU, that reproduces the line and continuum data, further supporting our conclusion that our observations have uncovered a Keplerian disk around an O-type star.
Protoplanetary disks are known to posses a stunning variety of substructure in the distribution of their mm~sized grains, predominantly seen as rings and gaps (Andrews et al. 2018), which are frequently interpreted as due to the shepherding of large grains by either hidden, still-forming planets within the disk (Zhang et al. 2018) or (magneto-)hydrodynamic instabilities (Flock et al. 2015). The velocity structure of the gas offers a unique probe of both the underlying mechanisms driving the evolution of the disk, the presence of embedded planets and characterising the transportation of material within the disk, such as following planet-building material from volatile-rich regions to the chemically-inert midplane, or detailing the required removal of angular momentum. Here we present the radial profiles of the three velocity components of gas in upper disk layers in the disk of HD 163296 as traced by 12CO molecular emission. These velocities reveal significant flows from the disk surface towards the midplane of disk at the radial locations of gaps argued to be opened by embedded planets (Isella et al. 2016, 2018, Teague et al. 2018, Pinte et al. 2018), bearing striking resemblance to meridional flows, long predicted to occur during the early stages of planet formation (Szulagyi et al. 2014, Morbidelli et al. 2014, Fung & Chiang 2016, Dong et al. 2019). In addition, a persistent radial outflow is seen at the outer edge of the disk, potentially the base of a wind associated with previously detected extended emission (Klaassen et al. 2013).
Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk. Such fallback is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar. The disk does not power the pulsars X-ray emission but is passively illuminated by these X-rays. The estimated mass of the disk is of order 10 Earth masses, and its lifetime (at least a million years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.
Observations of protoplanetary disks around very low-mass stars and brown dwarfs remain challenging and little is known about their properties. The disk around CIDA1 ($sim$0.1-0.2$M_odot$) is one of the very few known disks that host a large cavity (20au radius in size) around a very low-mass star. We present new ALMA observations at Band7 (0.9mm) and Band4 (2.1mm) of CIDA1 with a resolution of $sim 0.05times 0.034$. These new ALMA observations reveal a very bright and unresolved inner disk, a shallow spectral index of the dust emission ($sim2$), and a complex morphology of a ring located at 20au. We also present X-Shooter (VLT) observations that confirm the high accretion rate of CIDA1 of $dot{M}_{rm acc}$=1.4 $times~10^{-8}M_odot$/yr. This high value of $dot{M}_{rm acc}$, the observed inner disk, and the large cavity of 20au exclude models of photo-evaporation to explain the observed cavity. When comparing these observations with models that combine planet-disk interaction, dust evolution, and radiative transfer, we exclude planets more massive than 0.5$M_{rm{Jup}}$ as the potential origin of the large cavity because with these it is difficult to maintain a long-lived and bright inner disk. Even in this planet mass regime, an additional physical process may be needed to stop the particles from migrating inwards and to maintain a bright inner disk on timescales of millions of years. Such mechanisms include a trap formed by a very close-in extra planet or the inner edge of a dead zone. The low spectral index of the disk around CIDA1 is difficult to explain and challenges our current dust evolution models, in particular processes like fragmentation, growth, and diffusion of particles inside pressure bumps.
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