2,061 research outputs found
RadioAstron space-VLBI project: studies of masers in star forming regions of our Galaxy and megamasers in external galaxies
Observations of the masers in the course of RadioAstron mission yielded
detections of fringes for a number of sources in both water and hydroxyl maser
transitions. Several sources display numerous ultra-compact details. This
proves that implementation of the space VLBI technique for maser studies is
possible technically and is not always prevented by the interstellar
scattering, maser beaming and other effects related to formation, transfer, and
detection of the cosmic maser emission. For the first time, cosmic water maser
emission was detected with projected baselines exceeding Earth Diameter. It was
detected in a number of star-forming regions in the Galaxy and megamaser
galaxies NGC 4258 and NGC 3079. RadioAstron observations provided the absolute
record of the angular resolution in astronomy. Fringes from the NGC 4258
megamaser were detected on baseline exceeding 25 Earth Diameters. This means
that the angular resolution sufficient to measure the parallax of the water
maser source in the nearby galaxy LMC was directly achieved in the cosmic maser
observations. Very compact features with angular sizes about 20 microarcsec
have been detected in star-forming regions of our Galaxy. Corresponding linear
sizes are about 5-10 million kilometers. So, the major step from milli- to
micro-arcsecond resolution in maser studies is done in the RadioAstron mission.
The existence of the features with extremely small angular sizes is
established. Further implementations of the space-VLBI maser instrument for
studies of the nature of cosmic objects, studies of the interaction of
extremely high radiation field with molecular material and studies of the
matter on the line of sight are planned.Comment: To be published in Astrophysical Masers: Unlocking the Mysteries of
the Universe, IAU Symposium 336, 201
Detection of a new methanol maser line with ALMA
Aims. We aimed at investigating the structure and kinematics of the gaseous
disk and outflows around the massive YSO S255 NIRS3 in the S255IR-SMA1 dense
clump. Methods. Observations of the S255IR region were carried out with ALMA at
two epochs in the compact and extended configurations. Results. We
serendipitously detected a new, never predicted, bright maser line at about
349.1 GHz, which most probably represents the CHOH A transition. The emission covers most of the 6.7 GHz methanol maser emission
area of almost 1 in size and shows a velocity gradient in the
same sense as the disk rotation. No variability was found on the time interval
of several months. It is classified as Class II maser and probably originates
in a ring at a distance of several hundreds AU from the central star.Comment: 4 pages, 4 figures, accepted by Astronomy and Astrophysic
RadioAstron probes the ultra-fine spatial structure in the HO maser emission in the star forming region W49N
HO maser emission associated with the massive star formation region W49N
were observed with the Space-VLBI mission RadioAstron. The procedure for
processing of the maser spectral line data obtained in the RadioAstron
observations is described. Ultra-fine spatial structures in the maser emission
were detected on space-ground baselines of up to 9.6 Earth diameters. The
correlated flux densities of these features range from 0.1% to 0.6% of the
total flux density. These low values of correlated flux density are probably
due to turbulence either in the maser itself or in the interstellar medium.Comment: Accepted for publication in Advances in Space Researc
How do methanol masers manage to appear in the youngest star vicinities and isolated molecular clumps?
General characteristics of methanol (CH3OH) maser emission are summarized. It
is shown that methanol maser sources are concentrated in the spiral arms. Most
of the methanol maser sources from the Perseus arm are associated with embedded
stellar clusters and a considerable portion is situated close to compact HII
regions. Almost 1/3 of the Perseus Arm sources lie at the edges of optically
identified HII regions which means that massive star formation in the Perseus
Arm is to a great extent triggered by local phenomena. A multiline analysis of
the methanol masers allows us to determine the physical parameters in the
regions of maser formation. Maser modelling shows that class II methanol masers
can be pumped by the radiation of the warm dust as well as by free-free
emission of a hypercompact region hcHII with a turnover frequency exceeding 100
GHz. Methanol masers of both classes can reside in the vicinity of hcHIIs.
Modelling shows that periodic changes of maser fluxes can be reproduced by
variations of the dust temperature by a few percent which may be caused by
variations in the brightness of the central young stellar object reflecting the
character of the accretion process. Sensitive observations have shown that the
masers with low flux densities can still have considerable amplification
factors. The analysis of class I maser surveys allows us to identify four
distinct regimes that differ by the series of their brightest lines.Comment: 8 pages, 4 figures, invited presentation at IAU242 "Astrophysical
Masers and their environments
- …