- ID:
- ivo://CDS.VizieR/J/A+A/291/261
- Title:
- H2O masers in HII regions
- Short Name:
- J/A+A/291/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of 22.2GHz H2O maser emission towards a large sample of HII regions (427) detected in hydrogen recombination lines (Lockman) are presented. The sample favours classical HII regions with large excitation parameter. We found 68 water maser sources, 17 of which are new detections. Adding the detections found in the literature, the total number of masers associated with the sample is 80. The overall maser percentage is low (19%), much less than what found in samples of ultracompact (UC) HII regions. The percentage changes if we divide our sample into two sub-classes: HII regions known to have ultracompact components (i.e. where a younger generation of star formation is also present) and the rest. In the first sub-class the maser percentage is 28%, in the second 15%. The total number of masers in HII regions where no UC component has been (so far) reported is 43. This value is greater than that expected from the ratio between the lifetime of the HII region (10^6^yr) and that of the maser phase, even assuming a maser lifetime as long as 10^5^yr. This implies that maser excitation (and star formation) occurs several times in the lifetime of the same star forming complex. From 410 positions observed, 230 can be associated with a high degree of confidence to an IRAS Point Source. We expect that most of the HII regions not associated with IRAS PS are diffuse regions in the last phases of their evolution. The percentage of water masers in this sub-class is very low: 8%. The number of masers with no counterpart in the Lockman sample (and above Dec=-30{deg}) is very large: 334. This number most probably reflects the extreme high density conditions known to exist in the earliest phases of an HII region, which strongly reduce its radio continuum and line emission. The analysis of a homogeneous sample of classical HII regions allows to confirm in a quantitative fashion the well known result that the maser phenomenon occurs during the earliest phase of the evolution of a massive star and that it fades away as the HII region evolves into the diffuse stage.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/805/53
- Title:
- H2O masers in W43A monitored with VLBA
- Short Name:
- J/ApJ/805/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the distribution patterns of H_2_O maser features in the "water fountain" source (WF) W43A and show that they are closely related to the early morphological changes in a planetary nebula (PN). Using the Very Long Baseline Array, we have detected detected H_2_O maser features in W43A in 13 epochs across >10yr. W43A is the only WF that has been observed for over a decade. We introduce a new cavity model scenario --a halo with a bipolar evacuated volume that has a partially enhanced wall-- and compare it with the "traditional" precessing jet model particularly in terms of explaining the bow-shaped distribution patterns of H_2_O maser features in the most recent epochs and their temporal evolution. Long-term observations show that the distribution patterns require more than a single jet to form. Moreover, we have identified six groups of H_2_O maser features at both the redshifted and blueshifted sides with point symmetry. The six groups are believed to correspond to periodic mass profiles in the envelope and have recorded the mass-loss history. Together with a geometric similarity to the mid-infrared morphology of W43A, the results suggest that H_2_O masers can be used to trace the inner morphology and rapid temporal changes in evolved stars, especially where the PN shaping has just started.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/577
- Title:
- H2O masers in W49 North and Sagittarius B2
- Short Name:
- J/ApJS/155/577
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using the Very Large Array (VLA) of the National Radio Astronomy Observatory in the A and B configurations, we have obtained simultaneous high-resolution observations of both the 22GHz H2O maser lines as well as the 22GHz continuum for the H II regions W49N and Sagittarius B2.
- ID:
- ivo://CDS.VizieR/J/A+AS/127/181
- Title:
- H2O maser sources new detections
- Short Name:
- J/A+AS/127/181
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations of H_2_O maser sources on the 13.7m radio telescope of Purple Mountain Observatory from 1990 Aug. to 1994 Jan. are summarized. For searching new water masers, the total number of search candidates is about 360, with 110 objects detected. Among them are 96 new detections. A list of the new detections and their spectra are presented.
- ID:
- ivo://CDS.VizieR/J/A+A/624/A42
- Title:
- H2O megamaser galaxies radio continuum 5GHz data
- Short Name:
- J/A+A/624/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An essential part of the paradigm describing active galactic nuclei is the alignment between the radio jet and the associated rotation axis of the sub-pc accretion disks. Because of the small linear and angular scales involved, this alignment has not yet been checked in a sufficient number of low luminosity active galactic nuclei (LLAGNs). The project examines the validity of this paradigm by measuring the radio continuum on the same physical scale as the accretion disks to investigate any possible connection between these disks and the radio continuum. We observed a sample of 18 LLAGNs in the 4.8GHz (6cm) radio continuum using the Very Long Baseline Array (VLBA) with 3.3-6.5ms resolution. The sources were selected to show both an edge-on accretion disk revealed by 22GHz H_2_O megamaser emission and signatures of a radio jet. Furthermore, the sources were previously detected in 33GHz radio continuum observations made with the Very Large Array. Five out of 18 galaxies observed were detected at 8{sigma} or higher levels (Mrk 0001, Mrk 1210, Mrk 1419, NGC 2273, and UGC 3193). While these five sources are known to have maser disks, four of them exhibit a maser disk with known orientation. For all four of these sources, the radio continuum is misaligned relative to the rotation axis of the maser disk, but with a 99.1% confidence level, the orientations are not random and are confined to a cone within 32{deg} of the maser disk's normal. Among the four sources the misalignment of the radio continuum with respect to the normal vector to the maser disk is smaller when the inner radius of the maser disk is larger. Furthermore, a correlation is observed between the 5GHz VLBA radio continuum and the [OIII] luminosity and also with the H_2_O maser disk's inner radius.
- ID:
- ivo://CDS.VizieR/J/MNRAS/470/1462
- Title:
- HOPS. III. Dense molecular gas properties
- Short Name:
- J/MNRAS/470/1462
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H_2_O Southern Galactic Plane Survey (HOPS) has mapped 100deg^2^ of the Galactic plane for water masers and thermal molecular line emission using the 22m Mopra telescope. We describe the automated spectral-line fitting pipelines used to determine the properties of emission detected in HOPS data cubes, and use these to derive the physical and kinematic properties of gas in the survey. A combination of the angular resolution, sensitivity, velocity resolution and high critical density of lines targeted make the HOPS data cubes ideally suited to finding precursor clouds to the most massive and dense stellar clusters in the Galaxy. We compile a list of the most massive HOPS ammonia regions and investigate whether any may be young massive cluster progenitor gas clouds. HOPS is also ideally suited to trace the flows of dense gas in the Galactic Centre. We find the kinematic structure of gas within the inner 500pc of the Galaxy is consistent with recent predictions for the dynamical evolution of gas flows in the centre of the Milky Way. We confirm a recent finding that the dense gas in the inner 100pc has an oscillatory kinematic structure with characteristic length-scale of 20pc, and also identify similar oscillatory kinematic structure in the gas at radii larger than 100pc. Finally, we make all of the above fits and the remaining HOPS data cubes across the 100deg^2^ of the survey available to the community.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A73
- Title:
- Horsehead H2CO and CH3OH 30m and PdBI maps
- Short Name:
- J/A+A/560/A73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical models and laboratory experiments show that CH_3_OH is efficiently formed on cold grain surfaces through the successive hydrogenation of CO, forming HCO and H_2_CO as intermediate species. In cold cores and low UV-field illumination photo-dissociation regions (PDRs) the ices can be released into the gas-phase through nonthermal processes such as photodesorption, which considerably increases their gas-phase abundances. We investigate the dominant formation mechanism of H_2_CO and CH_3_OH in the Horsehead PDR and its associated dense core.
- ID:
- ivo://CDS.VizieR/J/MNRAS/416/1764
- Title:
- H_2_O Southern Galactic Plane Survey (HOPS)
- Short Name:
- J/MNRAS/416/1764
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results of the H_2_O Southern Galactic Plane Survey (HOPS), using the Mopra Radio Telescope with a broad-band backend and a beam size of about 2arcmin. We have observed 100deg^2^ of the southern Galactic plane at 12mm (19.5-27.5GHz), including spectral line emission from H_2_O masers, multiple metastable transitions of ammonia, cyanoacetylene, methanol and radio recombination lines. In this paper, we report on the characteristics of the survey and H2O maser emission. We find 540 H_2_O masers, of which 334 are new detections.
- ID:
- ivo://CDS.VizieR/J/MNRAS/426/1972
- Title:
- H_2_O Southern Galactic Plane Survey, HOPS. II
- Short Name:
- J/MNRAS/426/1972
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The H2O Southern Galactic Plane Survey (HOPS) has mapped a 100{deg} strip of the Galactic plane (-70{deg}>l>30{deg}, |b|<0.5{deg}) using the 22m Mopra antenna at 12mm wavelengths. Observations were conducted in on-the-fly mode using the Mopra spectrometer (MOPS), targeting water masers, thermal molecular emission and radio-recombination lines. Foremost among the thermal lines are the 23GHz transitions of NH3 J,K=(1,1) and (2,2), which trace the densest parts of molecular clouds (n>10^4^cm^-3^). In this paper, we present the NH_3_(1,1) and (2,2) data, which have a resolution of 2arcmin and cover a velocity range of +/-200km/s.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A49
- Title:
- H_2_O spectra of W33B in 1981-1985
- Short Name:
- J/A+A/575/A49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The active star-forming region W33B is a source of OH and H_2_O maser emission located in distinct zones around the central object. The aim was to obtain the complete Stokes pattern of polarised OH maser emission and to trace its variability and to investigate flares and long-term variability of the H_2_O maser and evolution of individual emission features. Observations in the OH lines at a wavelength of 18cm were carried out on the Nancay radio telescope (France) at a number of epochs in 2008-2014; H_2_O line observations (long-term monitoring) at {lambda}=1.35cm were performed on the 22m radio telescope of the Pushchino Radio Astronomy Observatory (Russia) between 1981 and 2014.
