Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMonitoring water masers in star-forming regions
286
0
0.0
(
0
)
Authors
J. Brand
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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 here a mid-infrared imaging survey of 26 sites of water maser emission. Observations were obtained at the InfraRed Telescope Facility 3-m telescope with the University of Florida mid-infrared imager/spectrometer OSCIR, and the JPL mid-infrared camera MIRLIN. The main purpose of the survey was to explore the relationship between water masers and the massive star formation process. It is generally believed that water masers predominantly trace outflows and embedded massive stellar objects, but may also exist in circumstellar disks around young stars. We investigate each of these possibilities in light of our mid-infrared imaging. We find that mid-infrared emission seems to be more closely associated with water and OH maser emission than cm radio continuum emission from UC HII regions. We also find from the sample of sources in our survey that, like groups of methanol masers, both water and OH masers have a proclivity for grouping into linear or elongated distributions. We conclude that the vast majority of linearly distributed masers are not tracing circumstellar disks, but outflows and shocks instead.
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.
Using the Very Long Baseline Array (VLBA) we performed a high resolution OH maser survey in Galactic star-forming regions (SFRs). We observed all the ground state spectral lines: the main lines at 1665 and 1667 MHz and the satellite lines at 1612 and 1720 MHz. Due to the exceptionality of finding satellite lines in SFRs, we will focus our discussion on those lines. In our sample of 41 OH maser sources, five (12%) showed the 1612 MHz line and ten (24%) showed the 1720 MHz line, with only one source showing both lines. We find that 1720 MHz emission is correlated with the presence of HII regions, suggesting that this emission could be used to diagnose or trace high-mass star formation. We include an analysis of the possible mechanisms that could be causing this correlation as well as assessing the possible relationships between lines in our sample. In particular, the presence of magnetic fields seems to play an important role, as we found Zeeman splitting in four of our sources (W75 N, W3(OH), W51 and NGC 7538). Our results have implications for current understanding of the formation of high-mass stars as well as on the masing processes present in SFRs.
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.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
