139 research outputs found
Unifying low and high mass star formation through density amplified hubs of filaments
Context: Star formation takes place in giant molecular clouds, resulting in
mass-segregated young stellar clusters composed of Sun-like stars, brown
dwarves, and massive O-type(50-100\msun) stars. Aims: To identify candidate
hub-filament systems (HFS) in the Milky-Way and examine their role in the
formation of the highest mass stars and star clusters. Methods: Filaments
around ~35000 HiGAL clumps that are detected using the DisPerSE algorithm. Hub
is defined as a junction of three or more filaments. Column density maps were
masked by the filament skeletons and averaged for HFS and non-HFS samples to
compute the radial profile along the filaments into the clumps. Results:
~3700~(11\%) are candidate HFS of which, ~2150~(60\%) are pre-stellar,
~1400~(40\%) are proto-stellar. All clumps with L>10^4 Lsun and L>10^5 Lsun at
distances respectively within 2kpc and 5kpc are located in the hubs of HFS. The
column-densities of hubs are found to be enhanced by a factor of ~2
(pre-stellar sources) up to ~10 (proto-stellar sources). Conclusions: All
high-mass stars preferentially form in the density enhanced hubs of HFS. This
amplification can drive the observed longitudinal flows along filaments
providing further mass accretion. Radiation pressure and feedback can escape
into the inter-filamentary voids. We propose a "filaments to clusters" unified
paradigm for star formation, with the following salient features: a)
low-intermediate mass stars form in the filaments slowly (10^6yr) and massive
stars quickly (10^5yr) in the hub, b) the initial mass function is the sum of
stars continuously created in the HFS with all massive stars formed in the hub,
c) Feedback dissiption and mass segregation arise naturally due to HFS
properties, and c) explain age spreads within bound clusters and formation of
isolated OB associations.Comment: 20 pages, 17 figures, Accepted by Astronomy and Astrophysic
Recommended from our members
Current Advances in the Computational Simulation of the Formation of Low-Mass Stars
Developing a theory of low-mass star formation ({approx} 0.1 to 3 M{sub {circle_dot}}) remains one of the most elusive and important goals of theoretical astrophysics. The star-formation process is the outcome of the complex dynamics of interstellar gas involving non-linear interactions of turbulence, gravity, magnetic field and radiation. The evolution of protostellar condensations, from the moment they are assembled by turbulent flows to the time they reach stellar densities, spans an enormous range of scales, resulting in a major computational challenge for simulations. Since the previous Protostars and Planets conference, dramatic advances in the development of new numerical algorithmic techniques have been successfully implemented on large scale parallel supercomputers. Among such techniques, Adaptive Mesh Refinement and Smooth Particle Hydrodynamics have provided frameworks to simulate the process of low-mass star formation with a very large dynamic range. It is now feasible to explore the turbulent fragmentation of molecular clouds and the gravitational collapse of cores into stars self-consistently within the same calculation. The increased sophistication of these powerful methods comes with substantial caveats associated with the use of the techniques and the interpretation of the numerical results. In this review, we examine what has been accomplished in the field and present a critique of both numerical methods and scientific results. We stress that computational simulations should obey the available observational constraints and demonstrate numerical convergence. Failing this, results of large scale simulations do not advance our understanding of low-mass star formation
Direct Imaging of Fine Structures in Giant Planet Forming Regions of the Protoplanetary Disk around AB Aurigae
We report high-resolution 1.6 \micron polarized intensity () images of
the circumstellar disk around the Herbig Ae star AB Aur at a radial distance of
22 AU () up to 554 AU (3.85), which have been obtained by the
high-contrast instrument HiCIAO with the dual-beam polarimetry. We revealed
complicated and asymmetrical structures in the inner part (140 AU) of
the disk, while confirming the previously reported outer ( 200 AU)
spiral structure. We have imaged a double ring structure at 40 and
100 AU and a ring-like gap between the two. We found a significant
discrepancy of inclination angles between two rings, which may indicate that
the disk of AB Aur is warped. Furthermore, we found seven dips (the typical
size is 45 AU or less) within two rings as well as three prominent
peaks at 40 AU. The observed structures, including a bumpy double ring, a
ring-like gap, and a warped disk in the innermost regions, provide essential
information for understanding the formation mechanism of recently detected
wide-orbit ( 20 AU) planets.Comment: 12 pages, 3 figure
High-Resolution Near-Infrared Polarimetry of a Circumstellar Disk around UX Tau A
We present H-band polarimetric imagery of UX Tau A taken with HiCIAO/AO188 on
the Subaru Telescope. UX Tau A has been classified as a pre-transitional disk
object, with a gap structure separating its inner and outer disks. Our imagery
taken with the 0.15 (21 AU) radius coronagraphic mask has revealed a strongly
polarized circumstellar disk surrounding UX Tau A which extends to 120 AU, at a
spatial resolution of 0.1 (14 AU). It is inclined by 46 \pm 2 degree as the
west side is nearest. Although SED modeling and sub-millimeter imagery
suggested the presence of a gap in the disk, with the inner edge of the outer
disk estimated to be located at 25 - 30 AU, we detect no evidence of a gap at
the limit of our inner working angle (23 AU) at the near-infrared wavelength.
We attribute the observed strong polarization (up to 66 %) to light scattering
by dust grains in the disk. However, neither polarization models of the
circumstellar disk based on Rayleigh scattering nor Mie scattering
approximations were consistent with the observed azimuthal profile of the
polarization degrees of the disk. Instead, a geometric optics model of the disk
with nonspherical grains with the radii of 30 micron meter is consistent with
the observed profile. We suggest that the dust grains have experienced frequent
collisional coagulations and have grown in the circumstellar disk of UX Tau A.Comment: 20 pages, 8 figures, and 1 table. accepted to PAS
Discovery of Small-Scale Spiral Structures in the Disk of SAO 206462 (HD 135344B): Implications for the Physical State of the Disk from Spiral Density Wave Theory
We present high-resolution, H-band, imaging observations, collected with
Subaru/HiCIAO, of the scattered light from the transitional disk around SAO
206462 (HD 135344B). Although previous sub-mm imagery suggested the existence
of the dust-depleted cavity at r~46AU, our observations reveal the presence of
scattered light components as close as 0.2" (~28AU) from the star. Moreover, we
have discovered two small-scale spiral structures lying within 0.5" (~70AU). We
present models for the spiral structures using the spiral density wave theory,
and derive a disk aspect ratio of h~0.1, which is consistent with previous
sub-mm observations. This model can potentially give estimates of the
temperature and rotation profiles of the disk based on dynamical processes,
independently from sub-mm observations. It also predicts the evolution of the
spiral structures, which can be observable on timescales of 10-20 years,
providing conclusive tests of the model. While we cannot uniquely identify the
origin of these spirals, planets embedded in the disk may be capable of
exciting the observed morphology. Assuming that this is the case, we can make
predictions on the locations and, possibly, the masses of the unseen planets.
Such planets may be detected by future multi-wavelengths observations.Comment: 8 pages, 5 figures, ApJL in press, typo correcte
Associated molecular and atomic clouds with X-ray shell of superbubble 30 Doradus C in the LMC
30 Doradus C is a superbubble which emits the brightest nonthermal X- and TeV
gamma-rays in the Local Group. In order to explore detailed connection between
the high energy radiation and the interstellar medium, we have carried out new
CO and HI observations using the Atacama Large MillimeterSubmillimeter Array
(ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope
Compact Array with resolutions of up to 3 pc. The ALMA data of CO( =
1-0) emission revealed 23 molecular clouds with the typical diameters of
6-12 pc and masses of 600-10000 . The comparison with
the X-rays of - at 3 pc resolution shows that X-rays are
enhanced toward these clouds. The CO data were combined with the HI to estimate
the total interstellar protons. Comparison of the interstellar proton column
density and the X-rays revealed that the X-rays are enhanced with the total
proton. These are most likely due to the shock-cloud interaction modeled by the
magnetohydrodynamical simulations (Inoue et al. 2012, ApJ, 744, 71). Further,
we note a trend that the X-ray photon index varies with distance from the
center of the high-mass star cluster, suggesting that the cosmic-ray electrons
are accelerated by one or multiple supernovae in the cluster. Based on these
results we discuss the role of the interstellar medium in cosmic-ray particle
acceleration.Comment: 20 pages, 14 figures, 3 tables, accepted for publication in The
Astrophysical Journa
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