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Register a new userAstrometry of H$_{2}$O Masers in Nearby Star-Forming Regions with VERA. III. IRAS 22198+6336 in L1204G
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We present results of multi-epoch VLBI observations with VERA (VLBI Exploration of Radio Astrometry) of the 22 GHz H$_{2}$O masers associated with a young stellar object (YSO) IRAS 22198+6336 in a dark cloud L1204G. Based on the phase-referencing VLBI astrometry, we derive an annual parallax of IRAS 22198+6336 to be 1.309$pm$0.047 mas, corresponding to the distance of 764$pm$27 pc from the Sun. Although the most principal error source of our astrometry is attributed to the internal structure of the maser spots, we successfully reduce the errors in the derived annual parallax by employing the position measurements for all of the 26 detected maser spots. Based on this result, we reanalyze the spectral energy distribution (SED) of IRAS 22198+6336 and find that the bolometric luminosity and total mass of IRAS 22198+6336 are 450$L_{odot}$ and 7$M_{odot}$, respectively. These values are consistent with an intermediate-mass YSO deeply embedded in the dense dust core, which has been proposed to be an intermediate-mass counterpart of a low-mass Class 0 source. In addition, we obtain absolute proper motions of the H$_{2}$O masers for the most blue-shifted components. We propose that the collimated jets aligned along the east-west direction are the most plausible explanation for the origin of the detected maser features.
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We measured the trigonometric annual parallax of H$_2$O maser source associated with the massive star-forming regions IRAS 06061+2151 with VERA. The annual parallax of $0.496pm0.031$ mas corresponding to a distance of $2.02^{+0.13}_{-0.12}$ kpc was obtained by 10 epochs of observations from 2007 October to 2009 September. This distance was obtained with a higher accuracy than the photometric distance previously measured, and places IRAS 06061+2151 in the Perseus spiral arm. We found that IRAS 06061+2151 also has a peculiar motion of larger than 15 km s$^{-1}$ counter to the Galactic rotation. That is similar to five sources in the Perseus spiral arm, whose parallaxes and proper motions have already been measured with higher accuracy. Moreover, these sources move at on average 27 km s$^{-1}$ toward the Galactic center and counter to the Galactic rotation.
Maser emission plays an important role as a tool in star formation studies. It is widely used for deriving kinematics, as well as the physical conditions of different structures, hidden in the dense environment very close to the young stars, for example associated with the onset of jets and outflows. We will summarize the recent observational and theoretical progress on this topic since the last maser symposium: the IAU Symposium 242 in Alice Springs.
We present results of a multi-epoch monitoring program on variability of 6$,$cm formaldehyde (H$_2$CO) masers in the massive star forming region NGC$,$7538$,$IRS$,$1 from 2008 to 2015 conducted with the GBT, WSRT, and VLA. We found that the similar variability behaviors of the two formaldehyde maser velocity components in NGC$,$7538$,$IRS$,$1 (which was pointed out by Araya and collaborators in 2007) have continued. The possibility that the variability is caused by changes in the maser amplification path in regions with similar morphology and kinematics is discussed. We also observed 12.2$,$GHz methanol and 22.2$,$GHz water masers toward NGC$,$7538$,$IRS$,$1. The brightest maser components of CH$_3$OH and H$_2$O species show a decrease in flux density as a function of time. The brightest H$_2$CO maser component also shows a decrease in flux density and has a similar LSR velocity to the brightest H$_2$O and 12.2$,$GHz CH$_3$OH masers. The line parameters of radio recombination lines and the 20.17 and 20.97$,$GHz CH$_3$OH transitions in NGC$,$7538$,$IRS$,$1 are also reported. In addition, we observed five other 6$,$cm formaldehyde maser regions. We found no evidence of significant variability of the 6$,$cm masers in these regions with respect to previous observations, the only possible exception being the maser in G29.96$-$0.02. All six sources were also observed in the H$_2^{13}$CO isotopologue transition of the 6$,$cm H$_2$CO line; H$_2^{13}$CO absorption was detected in five of the sources. Estimated column density ratios [H$_2^{12}$CO]/[H$_2^{13}$CO] are reported.
An overview is given of the analysis of more than a decade of H2O maser data from our monitoring program. We find the maser emission to generally depend on the luminosity of the YSO as well as on the geometry of the SFR. There appears to be a threshold luminosity of a few times 10**4 Lsol above and below which we find different maser characteristics.
We report the detection of water maser emission from four nearby galaxies hosting ultradense HII (UDHII) regions, He 2-10, the Antennae galaxies (NGC 4038/4039), NGC 4214, and NGC 5253, with the Green Bank Telescope. Our detection rate is 100%, and all of these H2O kilomasers (L(H2O) < 10 L_sun) are located toward regions of known star formation as traced by UDHII regions and bright 24 micron emission. Some of the newly discovered H2O masers have luminosities 1-2 orders of magnitude less than previous extragalactic studies and the same order of magnitude as those typical of Galactic massive star-forming regions. The unusual success of this minisurvey suggests that H2O maser emission may be very common in starburst galaxies, and the paucity of detections to date is due to a lack of sufficient sensitivity. While the galaxy sample was selected by the presence of UDHII regions, and the UDHII regions lie within the telescope beam, in the absence of H2O spectral line maps the connection between H2O masers and UDHII regions has not yet been demonstrated.
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