Masers in star forming regions

Bartkiewicz, A.; Langevelde, H. J. van

doi:10.1017/s1743921312006771

Cited by 4 publications

(1 citation statement)

References 82 publications

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“…Methanol (CH 3 OH) masers have been widely established as good tracers for the early stages of high-mass star formation regions (Pandian et al 2011;Ellingsen 2007;Caswell 1996). Hydroxyl and water masers have also been observed to be associated with the early stages of massive star formation regions (Bartkiewicz & Langevelde 2012), but they can also be found in the later stages of a star's life (Xu et al 2003;Ellingsen et al 2007), making methanol masers unique indicators for the early stages of massive star-formation. Methanol maser emissions have been observed in several transitions (Fontani et al 2010;Goddi et al 2007), the strongest being the 5 1 -6 0 A + line at 6.7 GHz which also happens to be the second strongest Galactic maser of any known molecule (Xu et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Formaldehyde and H110α observations towards 6.7 GHz methanol maser sources

Okoh

Esimbek

Zhou

et al. 2014

Astrophys Space Sci

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Intriguing work on observations of 4.83 GHz formaldehyde (H 2 CO) absorptions and 4.87 GHz H110α radio recombination lines (RRLs) towards 6.7 GHz methanol (CH 3 OH) maser sources is presented. Methanol masers provide ideal sites to probe the earliest stages of massive star formation, while 4.8 GHz formaldehyde absorptions are accurate probes of physical conditions in dense (10 3 -10 5 cm −3 ) and low temperature molecular clouds towards massive star forming regions. The work is aimed at studying feature similarities between the formaldehyde absorptions and the methanol masers so as to expand knowledge of events and physical conditions in massive star forming regions. A total of 176 methanol maser sources were observed for formaldehyde absorptions, and formaldehyde absorptions were detected 138 of them. 53 of the formaldehyde absorptions were newly detected. We noted a poor correlation between the methanol and formaldehyde intensities, an indication that the signals (though arise from about the same regions) are enhanced by different mechanisms. Our results show higher detection rates of the formaldehyde lines for sources with stronger methanol signals. The strongest formaldehyde absorptions were associated with IRAS sources and IRDCs that have developed HII regions, and that do not have EGOs.

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Section: Introductionmentioning

confidence: 99%

Formaldehyde and H110α observations towards 6.7 GHz methanol maser sources

Okoh

Esimbek

Zhou

et al. 2014

Astrophys Space Sci

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Evolution of the Water Maser Expanding Shell in W75n Vla 2

Kim

Kurayama

et al. 2013

ApJ

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We present Very Long Baseline Interferometry (VLBI) observations of 22GHz H 2 O masers in the high-mass star-forming region of W75N, carried out with VLBI Exploration of Radio Astrometry (VERA) for three-epochs in 2007 with an angular resolution of ∼ 1 mas. We detected H 2 O maser emission toward the radio jet in VLA 1 and the expanding shell-like structure in VLA 2. The spatial distribution of the H 2 O masers detected with VERA and measured proper motions around VLA 1 and VLA 2 are similar to those found with previous VLBI observations in epochs 1999 and 2005, with the masers in VLA 1 mainly distributed along a linear structure parallel to the radio jet and, on the other hand, forming a shell-like structure around VLA 2. We have made elliptical fits to the VLA 2 H 2 O maser shell-like structure observed in the different epochs (1999, 2005, and 2007), and found that the shell is still expanding eight years after its discovery. From the difference in the size of the semi-major axes of the fitted ellipses in the epochs 1999 (≃ 71±1 mas), 2005 (≃ 97±3 mas), and 2007 (≃ 111±1 mas), we estimate an average expanding velocity of ∼ 5 mas yr −1 , similar to the proper motions measured in the individual H 2 O maser features. A kinematic age of ∼ 20 yr is derived for this structure. In addition, our VERA observations indicate an increase in the ellipticity of the expanding shell around VLA 2 from epochs 1999 to 2007. In fact, the elliptical fit of the VERA data shows a ratio between the minor and major axes of ∼ 0.6, in contrast with a most circular shape for the shell detected in 1999 and 2005 (b/a ∼ 0.9). This suggests that we are probably observing the formation of a jet-driven H 2 O maser structure in VLA2, evolving from a non-collimated pulsed-outflow event during the first stages of evolution of a massive young stellar object (YSO). This may support predictions made earlier by other authors on this issue, consistent with -3recent magnetohydrodynamical simulations. We discuss possible implications of our results in the study of the first stages of evolution of massive YSOs.

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Physical Characteristics of G331.5-0.1: The Luminous Central Region of a Giant Molecular Cloud

Merello

Bronfman

Garay

et al. 2013

ApJ

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We report molecular line and dust continuum observations toward the high-mass star-forming region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO(J = 1 → 0) and C 18 O(J = 1 → 0) lines with NANTEN, while its central region was mapped in CS(J = 2 → 1 and J = 5 → 4) with SEST, and in CS(J = 7 → 6) and 13 CO(J = 3 → 2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2 × 10 3 M , molecular hydrogen density of 3.7 × 10 4 cm −3 , dust temperature of 32 K, and integrated luminosity of 5.7 × 10 5 L , consistent with values found toward other massive star-forming dust clumps. The CS and 13 CO spectra show the presence of two velocity components: a high-velocity component at ∼−89 km s −1 , seen toward four of the clumps, and a low-velocity component at ∼−101 km s −1 seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8 ± 0.2 and 1.2 ± 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s −1 (FWHM) in CS(J = 7 → 6). Observations of SiO(J = 7 → 6 and J = 8 → 7), and SO(J K = 8 8 → 7 7 and J K = 8 7 → 7 6 ) lines provide estimates of the gas rotational temperature toward this outflow >120 K and >75 K, respectively.

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Masers in star forming regions

Cited by 4 publications

References 82 publications

Formaldehyde and H110α observations towards 6.7 GHz methanol maser sources

Formaldehyde and H110α observations towards 6.7 GHz methanol maser sources

Evolution of the Water Maser Expanding Shell in W75n Vla 2

Physical Characteristics of G331.5-0.1: The Luminous Central Region of a Giant Molecular Cloud

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