Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userA massive star-forming region in a very early stage of evolution
78
0
0.0
(
0
)
Authors
K. J. Brooks
Ask ChatGPT about the research
No Arabic abstract
We present results from a study of two luminous IRAS sources thought to be young massive star-forming regions and which have no previously detected radio continuum emission: IRAS 15596-5301 and IRAS 16272-4837. Our study incorporates sensitive ATCA radio continuum data, SEST 1.2-mm continuum (using the new SIMBA bolometer) and line data, as well as data taken from the MSX database. The results show that both sources are associated with dense molecular cores which appear to host recently formed massive stars. We argue that IRAS16272 is in a very early stage of evolution, prior to the formation of an ultra compact HII region and that IRAS15596 is in a more advanced stage and hosts a cluster of B-type stars.
rate research
Read More
We report molecular line observations, made with ASTE and SEST, and dust continuum observations at 0.87 mm, made with APEX, towards the cold dust core G305.136+0.068. The molecular observations show that the core is isolated and roughly circularly symmetric and imply that it has a mass of $1.1times10^3~M_odot$. A simultaneous model fitting of the spectra observed in four transitions of CS, using a non-LTE radiative transfer code, indicates that the core is centrally condensed, with the density decreasing with radius as $r^{-1.8}$, and that the turbulent velocity increases towards the center. The dust observations also indicate that the core is highly centrally condensed and that the average column density is 1.1 g cm$^{-2}$, value slightly above the theoretical threshold required for the formation of high mass stars. A fit to the spectral energy distribution of the emission from the core indicates a dust temperature of $17pm2$ K, confirming that the core is cold. Spitzer images show that the core is seen in silhouette from 3.6 to 24.0 $mu$m and that is surrounded by an envelope of emission, presumably tracing an externally excited photo-dissociated region. We found two embedded sources within a region of 20 centered at the peak of the core, one of which is young, has a luminosity of $66~L_odot$ and is accreting mass with a high accretion rate, of $sim1times10^{-4}~M_odot$ yr$^{-1}$. We suggest that this object corresponds to the seed of a high mass protostar still in the process of formation. The present observations support the hypothesis that G305.136+0.068 is a massive and dense cold core in an early stage of evolution, in which the formation of a high mass star has just started.
This article presents a multi-wavelength study towards S87, based on a dataset of submillimeter/far-/mid-infrared (sub-mm/FIR/MIR) images and molecular line maps. The sub-mm continuum emission measured with JCMT/SCUBA reveals three individual clumps, namely, SMM1, SMM2, and SMM3. The MIR/FIR images obtained by the Spitzer Space Telescope indicate that both SMM1 and SMM3 harbor point sources. The J=1-0 transitions of CO, 13CO, C18O, and HCO+, measured with the 13.7m telescope of the Purple Mountain Observatory, exhibit asymmetric line profiles. Our analysis of spectral energy distributions (SEDs) shows that all of the three sub-mm clumps are massive (110--210 $M_{odot}$), with average dust temperatures in the range ~20--40K. A multi-wavelength comparison convinces us that the asymmetric profiles of molecular lines should result from two clouds at slightly different velocities, and it further confirms that the star-forming activity in SMM1 is stimulated by a cloud-cloud collision. The stellar contents and SEDs suggest that SMM1 and SMM3 are high-mass and intermediate-mass star-forming sites respectively. However, SMM2 has no counterpart downwards 70 micron, which is likely to be a cold high-mass starless core. These results, as mentioned above, expose multiple phases of star formation in S87.
We present a multi-wavelength study of the star forming region ISOSS J 20298+3559, which was identified by a cross-correlation of cold compact sources from the 170 micron ISOPHOT Serendipity Survey (ISOSS) database coinciding with objects detected by the MSX, 2MASS and IRAS infrared surveys. ISOSS J 20298+3559 is associated with a massive dark cloud complex (M ~ 760 M$_{odot}$) and located in the Cygnus X giant molecular cloud. We derive a distance of 1800 pc on the basis of optical extinction data. The low average dust temperature (T ~ 16 K) and large mass (M ~ 120 M$_{odot}$) of the dense inner part of the cloud, which has not been dispersed, indicates a recent begin of star formation. The youth of the region is supported by the early evolutionary stage of several pre- and protostellar objects discovered across the regio n: I) Two candidate Class 0 objects with masses of 8 and 3.5 M$_{odot}$, II) a gravitationally bound, cold (T ~ 12 K) and dense (n(H$_{2}$) ~ 2 x 10$^{5}$ cm$^{-3}$) cloud core with a mass of 50 M$_{odot}$ and III) a Herbig B2 star with a mass of 6.5 M$_{odot}$ and a bolometric luminosity of 2200 L$_{odot}$, showing evidence for ongoing accretion and a stellar age of less than 40000 years. The dereddened SED of the Herbig star is well reproduced by an accretion disc + star model. The externally heated cold cloud core is a good candidate for a massive pre-protostellar object. The star formation efficiency in the central cloud region is about 14 %.
Aims: To investigate properties of [CII]158 $mu$m emission of RCW36 in a dense filamentary cloud. Methods: [CII] observations of RCW36 covering an area of ~30 arcmin$times$30 arcmin were carried out with a Fabry-P{e}rot spectrometer aboard a 100-cm balloon-borne far-infrared (IR) telescope with an angular resolution of 90 arcsec. By using AKARI and Herschel images, the spatial distribution of the [CII] intensity was compared with those of emission from the large grains and PAH. Results: The [CII] emission is spatially in good agreement with shell-like structures of a bipolar lobe observed in IR images, which extend along the direction perpendicular to the direction of a cold dense filament. We found that the [CII]--160 $mu$m relation for RCW36 shows higher brightness ratio of [CII]/160 $mu$m than that for RCW 38, while the [CII]--9 $mu$m relation for RCW36 is in good agreement with that for RCW38. Conclusions: The [CII] emission spatially well correlates with PAH and cold dust emissions. This means that the observed [CII] emission dominantly comes from PDRs. Moreover, the L_[CII]/L_FIR ratio shows large variation compared with the L_[CII]/L_PAH ratio. In view of the observed tight correlation between L_[CII]/L_FIR and the optical depth at $lambda$=160 $mu$m, the large variation in L_[CII]/L_FIR can be simply explained by the geometrical effect, viz., L_FIR has contributions from the entire dust-cloud column along the line of sight, while L_[CII] has contributions from far-UV illuminated cloud surfaces. Based on the picture of the geometry effect, the enhanced brightness ratio of [CII]/160 $mu$m is attributed to the difference in gas structures where massive stars are formed: filamentary (RCW36) and clumpy (RCW38) molecular clouds and thus suggests that RCW36 is dominated by far-UV illuminated cloud surfaces compared with RCW38.
We present the first physical characterization of the young open cluster VVV CL041. We spectroscopically observed the cluster main-sequence stellar population and a very-massive star candidate: WR62-2. CMFGEN modeling to our near-infrared spectra indicates that WR62-2 is a very luminous (10$^{6.4pm0.2} L_{odot}$) and massive ($sim80 M_{odot}$) star.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
