分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ruben Fedriani
Jonathan C. Tan
Zoie Telkamp
Yichen Zhang
Yao-Lun Yang
Mengyao Liu
Chi-Yan Law
Maria T. Beltran
Viviana Rosero
Kei E. I. Tanaka
Giuliana Cosentino
Prasanta Gorai
Juan Farias
Jan E. Staff
James M. De Buizer
Barbara Whitney
摘要： We present $\sim10-40\,\mu$m SOFIA-FORCAST images of 11 isolated protostars as part of the SOFIA Massive (SOMA) Star Formation Survey, with this morphological classification based on 37 $\mu$m imaging. We develop an automated method to define source aperture size using the gradient of its background-subtracted enclosed flux and apply this to build spectral energy distributions (SEDs). We fit the SEDs with radiative transfer models, developed within the framework of turbulent core accretion (TCA) theory, to estimate key protostellar properties. Here, we release the sedcreator python package that carries out these methods. The SEDs are generally well fitted by the TCA models, from which we infer initial core masses $M_c$ ranging from $20-430\:M_\odot$, clump mass surface densities $\Sigma_{\rm cl}\sim0.3-1.7\:{\rm{g\:cm}}^{-2}$ and current protostellar masses $m_*\sim3-50\:M_\odot$. From a uniform analysis of the 40 sources in the full SOMA survey to date, we find that massive protostars form across a wide range of clump mass surface density environments, placing constraints on theories that predict a minimum threshold $\Sigma_{\rm cl}$ for massive star formation. However, the upper end of the $m_*-\Sigma_{\rm cl}$ distribution follows trends predicted by models of internal protostellar feedback that find greater star formation efficiency in higher $\Sigma_{\rm cl}$ conditions. We also investigate protostellar far-IR variability by comparison with IRAS data, finding no significant variation over an $\sim$40 year baseline.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Prasanta Gorai
Chi-Yan Law
Jonathan C. Tan
Yichen Zhang
Ruben Fedriani
Kei E. I. Tanaka
Melisse Bonfand
Giuliana Cosentino
Diego Mardones
Maria T. Beltran
Guido Garay
摘要： We study the astrochemical diagnostics of the isolated massive protostar G28.20-0.05. We analyze data from ALMA 1.3~mm observations with resolution of 0.2 arcsec ($\sim$1,000 au). We detect emission from a wealth of species, including oxygen-bearing (e.g., $\rm{H_2CO}$, $\rm{CH_3OH}$, $\rm{CH_3OCH_3}$), sulfur-bearing (SO$_2$, H$_2$S) and nitrogen-bearing (e.g., HNCO, NH$_2$CHO, C$_2$H$_3$CN, C$_2$H$_5$CN) molecules. We discuss their spatial distributions, physical conditions, correlation between different species and possible chemical origins. In the central region near the protostar, we identify three hot molecular cores (HMCs). HMC1 is part of a mm continuum ring-like structure, is closest in projection to the protostar, has the highest temperature of $\sim300\:$K, and shows the most line-rich spectra. HMC2 is on the other side of the ring, has a temperature of $\sim250\:$K, and is of intermediate chemical complexity. HMC3 is further away, $\sim3,000\:$au in projection, cooler ($\sim70\:$K) and is the least line-rich. The three HMCs have similar mass surface densities ($\sim10\:{\rm{g\:cm}}^{-2}$), number densities ($n_{\rm H}\sim10^9\:{\rm{cm}}^{-3}$) and masses of a few $M_\odot$. The total gas mass in the cores and in the region out to $3,000\:$au is $\sim 25\:M_\odot$, which is comparable to that of the central protostar. Based on spatial distributions of peak line intensities as a function of excitation energy, we infer that the HMCs are externally heated by the protostar. We estimate column densities and abundances of the detected species and discuss the implications for hot core astrochemistry.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The unprecedented angular resolution and sensitivity of ALMA makes it possible to unveil disk populations in distant ($>$2 kpc), embedded young cluster environments. We have conducted an observation towards the central region of the massive protocluster G286.21+0.16 at 1.3 mm. With a spatial resolution of 23 mas and a sensitivity of 15 $\rm \mu Jy~beam^{-1}$, we detect a total of 38 protostellar disks. These disks have dust masses ranging from about 53 to 1825 $M_\oplus$, assuming a dust temperature of 20 K. This sample is not closely associated with previously identified dense cores, as would be expected for disks around Class 0 protostars. Thus, we expect our sample, being flux limited, to be mainly composed of Class I/flat-spectrum source disks, since these are typically more massive than Class II disks. Furthermore, we find that the distributions of disk masses and radii are statistically indistinguishable with those of the Class I/flat-spectrum objects in the Orion molecular cloud, indicating similar processes are operating in G286.21+0.16 to regulate disk formation and evolution. The cluster center appears to host a massive protostellar system composed of three sources within 1200 au, including a potential binary with 600 au projected separation. Relative to this center, there is no evidence for widespread mass segregation in the disk population. We do find a tentative trend of increasing disk radius versus distance from the cluster center, which may point to the influence of dynamical interactions being stronger in the central regions.
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