arXiv subjects

S. Paron

Publications and source records attributed to S. Paron.

61 records · Page 4Linked to original sources

arXiv2009

A multiwavelength study of the star forming region IRAS 18544+0112

This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90" x 90" region around l = 34.69, b = -0.65, using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS J=7-6 lines with an angular resolution of 22". The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. From the molecular analysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The 12CO J=3-2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin in size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um emission. The non-detection of ionized gas related to IRAS 18544+0112, together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112, has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propos that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8-0.7, might be related to the formation of IRAS 18544+0112.

astro-ph.GA↗

arXiv2009

Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1

We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and G352.7-0.1, to understand the causes of such morphology. The research was carried out based on new and reprocessed archival VLA observations and XMM-Newton archival data. The surrounding was investigated based on data extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring Survey and the HI Southern Galactic Plane Survey. The present study revealed that the overall morphology of both SNRs is the result of the mass-loss history of their respective progenitor stars. Kes79 would be the product of the gravitational collapse of a massive O9 star evolving near a molecular cloud and within the precursor's wind-driven bubble, while G352.7-0.1 would be the result of interactions of the SNR with an asymmetric wind from the progenitor together with projection effects. No radio point source or pulsar wind nebula was found associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray radiation completely fills in the interior of the remnant and originates in heated ejecta. Characteristic parameters, like radio flux, radio spectral index, age, distance, shock velocity, initial energy and luminosity, were estimated for both SNRs.

astro-ph.GA↗

arXiv2009

The environs of the ultracompact HII region G45.45+0.06

G45.45+0.06 is an ultra-compact HII (UCHII) region extensively studied. It is known that G45.45+0.06 is embedded in a complex of UCHII regions, but up the date, the surrounding ISM in a larger spatial scale has not been analyzed. Using data from large-scale surveys: Two Micron All Sky Survey, GLIMPSE, MIPSGAL, MAGPIS and GRS, we performed a multiwavelength study of a region about 7' x 7'in the vicinity of G45.45+0.06. We found that the UCHII complex lies in a border of a larger (diameter of ~ 3') and fainter HII region, which is located at the same distance as G45.45+0.06, ~ 8 kpc. In this work, this larger HII region was called G45L. A good morphological correlation is observed between the PDRs and the molecular gas mapped in the 13CO J=1--0 and CS J=2--1 lines, suggesting that G45L may be collecting the molecular material. From a near- and mid-IR photometric study, we found three sources, likely O-type stars, that are possibly responsible for the creation of G45L. Additionally we found several YSO candidates lying preferently in the molecular shell that surrounds G45L. Our results confirm that the region southeastern the UCHII complex where G45.45+0.06 is embedded and eastern G45L is active in star formation. We suggest that G45L has been expanding during about 2 x 10^6 yr and could have triggered the formation of the zero-age main sequence stars that are ionizing the UCHII region G45.45+0.06. However we can not discard that both HII regions are coeval.

astro-ph.GA↗

arXiv2009

Discovery of a dense molecular cloud towards a young massive embedded star in 30 Doradus

The 30 Doradus region in the Large Magellanic Cloud is one of the most outstanding star forming regions of the Local Group and a primary target to study star formation in an environment of low metallicity. In order to obtain a more complete picture of the not yet consumed or dispersed cool gas, we searched for line emission from molecular clouds that could be associated with molecular hydrogen emission detected in the region. We obtained a high sensitivity 12CO J=2-1 map with the 15-m SEST telescope, complemented by pointed observations of 13CO J=2-1 and CS J=2-1. We report the discovery of a dense molecular cloud towards an embedded young massive star at ~ 20" (~5 pc, at the distance of 50 kpc) northwest of R136, the compact massive central stellar cluster powering 30 Doradus in the LMC, that could be triggering star formation in the surrounding molecular clouds. We derived a molecular mass of $\lesssim 10^4$ \msol, a linear radius of 3 pc, as an upper limit, and a mean density of $\gtrsim 10^{3}$ cm$^{-3}$ for the cloud. The detection of CS J=2-1 emission line indicates larger densities, $\sim 10^{6}$ cm$^{-3}$. The dense molecular cloud is associated with molecular 2.12 um H2 emission. We suggest that the observed molecular gas could be the remains of dense molecular material surviving the action of strong UV fields and winds in which the young massive star has formed.

astro-ph.CO↗

arXiv2009

A molecular outflow evidencing star formation activity in the vicinity of the HII region G034.8-0.7 and the SNR W44

This work aims at investigating the molecular gas component in the vicinity of two young stellar object (YSO) candidates identified at the border of the HII region G034.8-0.7 that is evolving within a molecular cloud shocked by the SNR W44. The purpose is to explore signatures of star forming activity in this complex region. We performed a near and mid infrared study towards the border of the HII region G034.8-0.7 and observed a 90" X 90" region near 18h 56m 48s, +01d 18' 45" (J2000) using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3--2, 13CO J=3--2, HCO+ J=4--3 and CS J=7--6 lines with an angular resolution of 22". Based on the infrared study we propose that the source 2MASS 18564827+0118471 (IR1 in this work) is a YSO candidate. We discovered a bipolar 12CO outflow in the direction of the line of sight and a HCO+ clump towards IR1, confirming that it is a YSO. From the detection of the CS J=7--6 line we infer the presence of high density (>10^7 cm^-3) and warm (>60 K) gas towards IR1, probably belonging to the protostellar envelope where the YSO is forming. We investigated the possible genetic connection of IR1 with the SNR and the HII region. By comparing the dynamical time of the outflows and the age of the SNR W44, we conclude that the possibility of the SNR has triggered the formation of IR1 is unlikely. On the other hand, we suggest that the expansion of the HII region G034.8-0.7 is responsible for the formation of IR1 through the "collect and collapse" process.

astro-ph.GA↗

arXiv2008

High resolution CO observations towards the Bright Eastern Knot of the SNR Puppis A

This paper reports molecular observations towards the Bright Eastern Knot (BEK) in the SNR Puppis A, a feature where radio and X-ray studies suggest that the shock front is interacting with a dense molecular clump. We performed high-resolution millimetric observations towards the BEK of Puppis A using the SEST telescope in the 12CO J=1-0 and 2-1 lines (beams of 45" and 23" respectively). More extended, lower angular resolution 12CO J=1-0 observations taken from NANTEN archival data were also analyzed to obtain a complete picture. In the velocity range near 16 km/s, the Puppis A systemic velocity, our study revealed two important properties: (i) no dense molecular gas is detected immediately adjacent to the eastern border of the BEK and (ii) the molecular clump detected very close to the radiocontinuum maximum is probably located in the foreground along the line of sight and has not yet been reached by the SNR shock front. We propose two possible scenarios to explain the absence of molecular emission eastwards of the BEK border of Puppis A. Either the shock front has completely engulfed and destroyed a molecular clump or the shock front is interacting with part of a larger cloud and we do not detect CO emission immediately beyond it because the molecules have been dissociated by photodissociation and by reactions with photoionized material due to the radiative precursor.

astro-ph↗

arXiv2005

G0.57-0.018: A young supernova remnant? INTEGRAL and VLA observations

We report INTEGRAL/IBIS gamma-ray and VLA radio observations of G0.570-0.018, a diffuse X-ray source recently discovered by ASCA and Chandra in the Galactic center region. Based on its spectrum and morphology, G0.570-0.018 has been proposed to be a very young supernova remnant. In this scenario, the presence of gamma-ray lines coming from the short-lived radioactive nucleus 44Ti as well as synchrotron radio continuum emission are expected. The first could provide informations on nucleosynthesis environments in the interior of exploding stars, the latter could probe the interaction between the supernova blast wave and the circumstellar/interstellar matter. We have not detected 44Ti lines nor any conspicuous radio feature associated with this source down to the achieved sensitivities. From the derived upper limits we set constraints on the nature of G0.570-0.018.

astro-ph↗