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Zhu M.,National Astronomical Observatory of China | Davis C.J.,Joint Astronomy Center | Wu Y.,Peking University | Whitney B.A.,Space Science Institute | And 2 more authors.
Astrophysical Journal | Year: 2011

We report the discovery of an extremely red object embedded in the massive SCUBA core JCMT 18354-0649S. This object is not associated with any known radio or far-IR source, though it appears in Spitzer IRAC data obtained as part of the GLIMPSE survey. At shorter wavelengths, this embedded source exhibits an extreme color, K - L′ = 6.7. At an assumed distance of 5.7 kpc, this source has a near-IR luminosity of ∼1000 L⊙. Its spectral energy distribution (SED) rises sharply from 2.1 μm to 8 μm, similar to that of a Class0 young stellar object. Theoretical modeling of the SED indicates that the central star has a mass of 6-12 M⊙, with an optical extinction of more than 30. As both inflow and outflow motions are present in JCMT 18354-0649S, we suggest that this deeply embedded source is (1) a massive protostar in the early stages of accretion, and (2) the driving source of a massive molecular outflow evident in HCN J = 3-2 profiles observed toward this region. © 2011. The American Astronomical Society. All rights reserved.. Source


Liu J.,National Astronomical Observatory of China | Liu J.,Harvard - Smithsonian Center for Astrophysics | Di Stefano R.,Harvard - Smithsonian Center for Astrophysics | Wang T.,Harvard - Smithsonian Center for Astrophysics | And 2 more authors.
Astrophysical Journal | Year: 2012

The explosion of a Type Ia supernova, SN2011fe, in the nearby Pinwheel galaxy (M101 at 6.4 Mpc) provides an opportunity to study pre-explosion images and search for the progenitor, which should consist of a white dwarf (WD), possibly surrounded by an accretion disk, in orbit with another star. We report on our use of deep Chandra observations and Hubble Space Telescope observations to limit the luminosity and temperature of the pre-explosion WD. It is found that if the spectrum was a blackbody, then pre-SN WDs with steady nuclear burning of the highest possible temperatures and luminosities are excluded assuming moderate n H values, but values of kT between roughly 10eV and 60eV are permitted even if the WD was emitting at the Eddington luminosity. This allows the progenitor to be an accreting nuclear-burning WD with an expanded photosphere 4-100 times the WD itself, or a super-critically accreting WD blowing off an optically thick strong wind, or possibly a recurrent nova with luminosities an order of magnitude lower than Eddington. The observations are also consistent with a double degenerate scenario, or a spinning down WD that has been spun up by accretion from the donor. © 2012. The American Astronomical Society. All rights reserved. Source


Liu J.,National Astronomical Observatory of China | Liu J.,Harvard - Smithsonian Center for Astrophysics | Orosz J.,San Diego State University | Bregman J.N.,University of Michigan
Astrophysical Journal | Year: 2012

Dynamical mass measurements hold the key to answering whether ultraluminous X-ray sources (ULXs) are intermediate-mass black holes (IMBHs) or stellar-mass black holes with special radiation mechanisms. NGC 1313 X-2 is so far the only ULX with Hubble Space Telescope light curves, the orbital period, and the black hole's radial velocity amplitude based on the He II λ4686 disk emission line shift of ∼ 200kms-1. We constrain its black hole mass and other parameters by fitting observations to a binary light curve code with accommodations for X-ray heating of the accretion disk and the secondary. Given the dynamical constraints from the observed light curves and the black hole radial motion and the observed stellar environment age, the only acceptable models are those with 40-50Myr old intermediate-mass secondaries in their helium core and hydrogen shell burning phase filling 40%-80% of their Roche lobes. The black hole can be a massive black hole of a few tens of M⊙ that can be produced from stellar evolution of low-metallicity stars, or an IMBH of a few hundred to above 1000 M⊙ if its true radial velocity 2K′ < 40kms-1. Further observations are required to better measure the black hole radial motion and the light curves in order to determine whether NGC 1313 X-2 is a stellar-mass black hole or an IMBH. © 2012. The American Astronomical Society. All rights reserved. Source


Yu Q.,Peking University | Lu Y.,National Astronomical Observatory of China | Mohayaee R.,CNRS Paris Institute of Astrophysics | Colin J.,CNRS Paris Institute of Astrophysics
Astrophysical Journal | Year: 2011

Dual active galactic nuclei (AGNs) are natural byproducts of hierarchical mergers of galaxies in the ΛCDM cosmogony. Recent observations have shown that only a small fraction (0.1%-2.5%) of AGNs at redshift z ≲ 0.3 are dual with kpc-scale separations, which is rather low compared to the high merger rate of galaxies. Here we construct a phenomenological model to estimate the number density of dual AGNs and its evolution according to the observationally estimated major merger rates of galaxies and various scaling relations on the properties of galaxies and their central massive black holes. We show that our model reproduces the observed frequency and separation distribution of dual AGNs provided that significant nuclear activities are triggered only in gas-rich progenitor galaxies with central massive black holes and only when the nuclei of these galaxies are roughly within the half-light radii of their companion galaxies. Under these constraints, the observed low dual AGN frequency is consistent with the relatively high merger rate of galaxies and supports the hypothesis that major mergers lead to AGN/QSO activities. We also predict that the number of kpc-scale dual AGNs decreases with increasing redshift and only about 0.02%-0.06% of AGNs are dual AGNs with double-peaked narrow line features at redshifts of z 0.5-1.2. Future observations of high-redshift dual AGNs would provide a solid test for this prediction. © 2011. The American Astronomical Society. All rights reserved. Source


Rumble D.,University of Exeter | Hatchell J.,University of Exeter | Gutermuth R.A.,University of Massachusetts Amherst | Kirk H.,National Research Council Canada | And 75 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

We present SCUBA-2 450 and 850 μm observations of the Serpens MWC 297 region, part of the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey of nearby star-forming regions. Simulations suggest that radiative feedback influences the star formation process and we investigate observational evidence for this by constructing temperature maps. Maps are derived from the ratio of SCUBA-2 fluxes and a two-component model of the JCMTbeam for a fixed dust opacity spectral index of β = 1.8.Within 40 arcsec of the B1.5Ve Herbig star MWC 297, the submillimetre fluxes are contaminated by free-free emission with a spectral index of 1.03 ± 0.02, consistent with an ultracompact HII region and polar winds/jets. Contamination accounts for 73 ± 5 per cent and 82 ± 4 per cent of peak flux at 450 μm and 850 μm, respectively. The residual thermal disc of the star is almost undetectable at these wavelengths. Young stellar objects (YSOs) are confirmed where SCUBA-2 850 μm clumps identified by the FELLWALKER algorithm coincide with Spitzer Gould Belt Survey detections. We identify 23 objects and use Tbol to classify nine YSOs with masses 0.09 to 5.1M⊙. We find two Class 0, one Class 0/I, three Class I and three Class II sources. The mean temperature is 15 ± 2 K for the nine YSOs and 32 ± 4 K for the 14 starless clumps. We observe a starless clump with an abnormally high mean temperature of 46 ± 2 K and conclude that it is radiatively heated by the star MWC 297. Jeans stability provides evidence that radiative heating by the star MWC 297 may be suppressing clump collapse. © 2015 The Authors. Source

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