arXiv subjects

Yuwei Wang

Publications and source records attributed to Yuwei Wang.

78 records · Page 5Linked to original sources

arXiv2019

Surveys of Clumps, Cores, and Condensations in Cygnus X: I. a New Catalog of ~0.1 pc Massive Dense Cores

Using infrared to (sub)millimeter data from Spitzer, Herschel, the James Clerk Maxwell Telescope, and the IRAM 30-m telescope, we conducted an unbiased survey of the massive dense cores (MDCs) in the Cygnus X molecular cloud complex, aimed at characterizing the physical conditions of high-mass star formation (HMSF) at ~0.1 pc scales. We created 5 deg times 6 deg images of the 70-1200 um dust continuum, gas column density, and dust temperature of Cygnus X. A spatial relation between the dense regions (Av > 15) and the developed HII regions was found, indicating the impact of the latter on the global structures of Cygnus X. With a 35-Msun mass threshold implied by HMSF signposts, we identified 151 MDCs with sizes of ~0.1 pc, masses of 35-1762 Msun, and temperatures of 8-35 K. Our MDC sample is statistically complete in Cygnus X and is three times larger than that in Motte et al. (2007). The MDCs were classified into IR-bright/IR-quiet ones based on their mid-infrared fluxes and a large "IR-quiet" proportion (90%) was found in our sample. Two possible scenarios were proposed to interpret this: accelerated HMSF and the incapability of HMSF of the IR-quiet MDCs. We also found 26 starless MDCs by their lack of compact emissions at 21-70 um wavelengths, of which the most massive ones are probably the best candidates of initial HMSF sites in Cygnus X.

astro-ph.GA↗

arXiv2018

Differences in water vapor radiative transfer among 1D models can significantly affect the inner edge of the habitable zone

An accurate estimate of the inner edge of the habitable zone is critical for determining which exoplanets are potentially habitable and for designing future telescopes to observe them. Here, we explore differences in estimating the inner edge among seven one-dimensional (1D) radiative transfer models: two line-by-line codes (SMART and LBLRTM) as well as five band codes (CAM3, CAM4_Wolf, LMDG, SBDART, and AM2) that are currently being used in global climate models. We compare radiative fluxes and spectra in clear-sky conditions around G- and M-stars, with fixed moist adiabatic profiles for surface temperatures from 250 to 360 K. We find that divergences among the models arise mainly from large uncertainties in water vapor absorption in the window region (10 um) and in the region between 0.2 and 1.5 um. Differences in outgoing longwave radiation increase with surface temperature and reach 10-20 Wm^-2; differences in shortwave reach up to 60 Wm^-2, especially at the surface and in the troposphere, and are larger for an M-dwarf spectrum than a solar spectrum. Differences between the two line-by-line models are significant, although smaller than among the band models. Our results imply that the uncertainty in estimating the insolation threshold of the inner edge (the runaway greenhouse limit) due only to clear-sky radiative transfer is ~10% of modern Earth's solar constant (i.e., ~34 Wm^-2 in global mean) among band models and ~3% between the two line-by-line models. These comparisons show that future work is needed focusing on improving water vapor absorption coefficients in both shortwave and longwave, as well as on increasing the resolution of stellar spectra in broadband models.

astro-ph.EP↗

arXiv2018

An Isothermal Outflow in High-mass Star-forming Region G240.31+0.07

We present Atacama Pathfinder EXperiment (APEX) observations toward the massive star-forming region G240.31+0.07 in the CO J = 3--2, 6--5, and 7--6 lines. We detect a parsec-sized, bipolar, and high velocity outflow in all the lines, which allow us, in combination with the existing CO J = 2--1 data, to perform a multi-line analysis of physical conditions of the outflowing gas. The CO 7--6/6--5, 6--5/3--2, and 6--5/2--1 ratios are found to be nearly constant over a velocity range of $\sim$5--25 km s$^{-1}$ for both blueshifted and redshifted lobes. We carry out rotation diagram and large velocity gradient (LVG) calculations of the four lines, and find that the outflow is approximately isothermal with a gas temperature of $\sim$50 K, and that the the CO column density clearly decreases with the outflow velocity. If the CO abundance and the velocity gradient do not vary much, the decreasing CO column density indicates a decline in the outflow gas density with velocity. By comparing with theoretical models of outflow driving mechanisms, our observations and calculations suggest that the massive outflow in G240.31+0.07 is being driven by a wide-angle wind and further support a disk mediated accretion at play for the formation of the central high-mass star.

astro-ph.GA↗

arXiv2018

First Data Release of the ESO-ARO Public Survey SAMPLING --- SMT "All-sky" Mapping of PLanck Interstellar Nebulae in the Galaxy

We make the first data release (DR1) of the ongoing ESO Public Survey SAMPLING (http://dx.doi.org/10.7910/DVN/0L8NHX). DR1 comprises of 124 fields distributed in $70^\circ < l < 216^\circ$, $-35^\circ < b < 25^\circ$. The 12CO and 13CO (2-1) cubes are gridded in $8"$ pixels, with an effective resolution of $36"$. The channel width is 0.33 km/s and the RMS noise is $T_{\rm mb}<0.2$ K. Once completed, SAMPLING and complementary surveys will initiate the first major step forward to characterize molecular clouds and star formation on truly Galactic scales.

astro-ph.GA↗

arXiv2017

Effects of eccentricity on climates and habitability of terrestrial exoplanets around M dwarfs

Eccentricity is an important orbital parameter. Understanding its effect on planetary climate and habitability is critical for us to search for a habitable world beyond our solar system. The orbital configurations of M-dwarf planets are always tidally-locked at resonance states, which are quite different from those around Sun-like stars. M-dwarf planets need to be investigated separately. Here we use a comprehensive three-dimensional atmospheric general circulation model to systematically investigate how eccentricity influences climate and habitability of M-dwarf exoplanets. The simulation results show that (1) the seasonal climatic cycles of such planets are very weak even for e = 0.4. It is unlikely that an aqua planet falls out of a habitable zone during its orbit. (2) The annual global mean surface temperature significantly increases with increased eccentricity, due to the decrease of the cloud albedo. Both the runaway greenhouse inner edge and moist greenhouse inner edge shift outward. (3) Planets in an eccentric orbit can be captured in other spin-orbit resonance states which lead to different climate patterns, namely eyeball pattern and striped-ball pattern.The striped-ball pattern has evidently higher surface temperatures due to the reduced planetary albedo. Near the outer edge, planets with p = 1.0 and 2.0 are more resistant to the snowball state due to more locally-concentrated stellar fluxes. Thus, planets with integer spin-orbit resonance numbers have wider habitable zones than those with half-integer spin-orbit resonance states. Above all, as a comparison to circular orbit, eccentricity shrinks the width of the habitable zone.

astro-ph.EP↗

arXiv2015

The jets-accretion relation, mass-luminosity relation in Fermi blazars

A sample of 111 Fermi blazars each with a well-established radio core luminosity, broad-line luminosity, bolometric luminosity and black hole mass has been compiled from the literatures.We present a significant correlation between radio core and broad-line emission luminosities that supports a close link between accretion processes and relativistic jets. Analysis reveals a relationship of $\rm{LogL_{BLR}\sim(0.81\pm0.06)LogL_{R}^{C}}$ which is consistant with theoretical predicted coefficient and supports that blazar jets are powered by energy extraction from a rapidly spinning Kerr black hole through the magnetic field provided by the accretion disk. Through studying the correlation between the intrinsic bolometric luminosity and the black hole mass, we find a relationship of $\rm{{Log}\frac{L_{in}}{L_{\odot}}=(0.95\pm0.26){Log}\frac{M}{M_{\odot}}+(3.53\pm2.24)}$ which supports mass-luminosity relation for Fermi blazars derived in this work is a powerlaw relation similar to that for main-sequence stars. Finally, evolutionary sequence of blazars is discussed.

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