- 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/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/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/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+AS/132/211
- Title:
- Interstellar SiO sources
- Short Name:
- J/A+AS/132/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of SiO emission using the 15-m SEST and the 20-m Onsala telescope are presented in two tables. The sample contains altogether 369 objects including 270 H2O masers, 19 OH masers and 62 IRAS sources with colours typical for ultracompact HII regions. The remaining target sources consist of dust continuum peaks a CS emission peak near H2O masers (12) and Herbig-Haro objects (6). The entries are arranged according to increasing right ascension.
- ID:
- ivo://CDS.VizieR/J/A+AS/129/363
- Title:
- IRAS flux densities of S stars
- Short Name:
- J/A+AS/129/363
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- It is the purpose of this paper to rediscuss the circumstellar properties of S stars and to put these properties in perspective with our current understanding of the evolutionary status of S stars, in particular the intrinsic/extrinsic dichotomy. This dichotomy states that only Tc-rich ("intrinsic") S stars are genuine thermally-pulsing asymptotic giant branch stars, possibly involved in the M-S-C evolutionary sequence. Tc-poor S stars are referred to as "extrinsic" S stars, because they are the cooler analogs of barium stars, and like them, owe their chemical peculiarities to mass transfer across their binary system. Accordingly, an extensive data set probing the circumstellar environment of S stars (IRAS flux densities, maser emission, CO rotational lines) has been collected and critically evaluated. This data set combines new observations (9 stars have been observed in the CO J=2-1 line and 3 in the CO J=3-2 line, with four new detections) with existing material (all CO and maser observations of S stars published in the literature). The IRAS flux densities of S stars have been re-evaluated by co-adding the individual scans, in order to better handle the intrinsic variability of these stars in the IRAS bands, and possible contamination by Galactic cirrus.
- ID:
- ivo://CDS.VizieR/J/MNRAS/276/57
- Title:
- IRAS Galactic star-forming regions. II.
- Short Name:
- J/MNRAS/276/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of the analysis of the occurrence of 22.2-GHz H_2_O maser emission in a sample of 1409 IRAS sources north of declination -30deg associated with star-forming regions are presented. Our sample contains all the IRAS sources that satisfy Emerson criteria for selecting molecular cores associated with the earliest evolutionary stages of the star-forming process. In a previous paper (Paper I, 1994MNRAS.266..123P), we have reported the results of the observations of about one third of the sample. In the present paper the observations of the remaining IRAS sources are presented: 18 of them are newly detected maser sources. The results show that 20 per cent of all IRAS sources that satisfy the Wood & Churchwell criteria have H2O water masers. This is in agreement with the assumption that these criteria select objects that are connected with the early phases of the evolution of high-mass star-forming regions. Moreover, about one third of the whole sample selected according to Emerson criteria contains IRAS sources that are not associated with massive star-forming processes, but probably with molecular cores in low-mass star-forming regions.
- ID:
- ivo://CDS.VizieR/J/PASJ/54/719
- Title:
- IRAS/SiO sources in the Galactic bulge
- Short Name:
- J/PASJ/54/719
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Near-infrared imaging observations of IRAS sources with SiO masers were made with the 2.3-m telescope of the Australian National University at Siding Spring Observatory, Australia, on 1997 June 18-23, 1998 June 9-12, and 2000 July 16-19, using the infrared array camera CASPIR. These infrared observations were made in parallel with long-term (1997-1999) SiO maser surveys at Nobeyama. The near-infrared observations were made within a year or so of the SiO detections. The details of the observations, data reduction, and method of identification were described in Deguchi et al. (1998PASJ...50..597D, 2001, Cat. <J/PASJ/53/293>), so they are not repeated here. All of the sources discussed in this paper are IRAS sources with detected SiO masers in the sky region of -10{deg}<l<15{deg} and |b|<3{deg} (Deguchi et al., 2000ApJS..130..351D).
