European VLBI Network imaging of 6.7 GHz methanol masers

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dc.contributor.author Bartkiewicz, Anna
dc.contributor.author Szymczak, Marian
dc.contributor.author van Langevelde, Huib Jan
dc.date.accessioned 2017-05-07T10:58:53Z
dc.date.available 2017-05-07T10:58:53Z
dc.date.issued 2016
dc.identifier.citation Astronomy and Astrophysics
dc.identifier.other 10.1051/0004-6361/201527541
dc.identifier.uri http://repozytorium.umk.pl/handle/item/4323
dc.description.abstract Context. Methanol masers at 6.7 GHz are well known tracers of high-mass star-forming regions. However, their origin is still not clearly understood. Aims. We aimed to determine the morphology and velocity structure for a large sample of the maser emission with generally lower peak flux densities than those in previous surveys. Methods. Using the European VLBI Network (EVN) we imaged the remaining sources from a sample of sources that were selected from the unbiased survey using the Torun 32 m dish. In this paper we report the results for 17 targets. Together they form a database of a total of 63 source images with high sensitivity (3σ rms = 15−30 mJy/beam ), milliarcsecond angular resolution (6−10 mas) and very good spectral resolution (0.09 km/s or 0.18 km/s ) for detailed studies. Results. We studied in detail the properties of the maser clouds and calculated the mean and median values of the projected size (17.4 ± 1.2 au and 5.5 au, respectively) as well as the FWHM of the line (0.373 ± 0.011 km/s and 0.315 km/s for the mean and median values, respectively), testing whether it was consistent with Gaussian profile. We also found maser clouds with velocity gradients (71%) that ranged from 0.005 km/s/au to 0.210 km/s/au. We tested the kinematic models to explain the observed structures of the 6.7 GHz emission. There were targets where the morphology supported the scenario of a rotating and expanding disk or a bipolar outflow. Comparing the interferometric and single-dish spectra we found that, typically, 50–70% of the flux was missing. This phenomena is not strongly related to the distance of the source. Conclusions. The EVN imaging reveals that in the complete sample of 63 sources the ring-like morphology appeared in 17% of sources, arcs were seen in a further 8%, and the structures were complex in 46% cases. The ultra-compact (UC) H II regions coincide in position in the sky for 13% of the sources. They are related both to extremely high and low luminosity masers from the sample.
dc.description.sponsorship National Science Centre Poland (NCN) grant 2011/03/B/ST9/00627
dc.language.iso eng
dc.publisher EDP Sciences
dc.relation.ispartofseries 587;A104
dc.rights Attribution-NoDerivs 3.0 Poland
dc.rights info:eu-repo/semantics/openAccess
dc.rights.uri http://creativecommons.org/licenses/by-nd/3.0/pl/
dc.subject masers
dc.subject stars: massive
dc.subject instrumentation: interferometers
dc.subject stars: formation
dc.title European VLBI Network imaging of 6.7 GHz methanol masers
dc.type info:eu-repo/semantics/article

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