H2O Maser Sources Research Articles

Formation of OB clusters - CO, NH3, and H2O observations of the distant H II region complex in S128

The spectral line emission from the (C-12)O, (C-13)O, C(0-18), and NH3 molecular species was mapped for the molecular cloud surrounding the S128 H II region. The (C-12)O map shows an elongated cloud (about 9 x 3 arcmin) having at least two cloud components at -74 and -72.8 km/s. The extent of the CO cloud was searched for H2O maser emission. A further H2O maser was detected close to the compact H II region S128N. All the signposts of star formation, the H II regions, and the H2O maser sources are found to lie along the transition between the -75 km/s and -72.8 km/s clouds, suggesting that the interaction of these two clouds may have initiated the observed star formation. 27 references.

A very bright water vapour maser source in the galaxy NGC3079

The 616–523 transition of water vapour at 22.235080 GHz has been found in our Galaxy to be associated with regions of young star formation1,2. H2O maser emission was detected initially in an external galaxy by Churchwell et al.3. To extend the range of detected properties of ‘star burst’ galaxies (galaxies showing an enhanced star formation from their optical spectra) we undertook an initial survey for H2O maser emission in this type of galaxy, but with negative results. Here we report on the subsequent extension of this survey to spiral galaxies displaying continuum radio emission, which is also an indication of star formation activity. We have detected the most luminous H2O maser source yet reported, ∼500 L0, in the galaxy NGC3079. OH absorption was also detected in this galaxy and we suggest that maser amplification of the nuclear radio source causes the observable H2O emission.

New radio sources at AFGL 2591 - Young cluster or single star?

view Abstract Citations (43) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New radio sources at AFGL 2591 : young cluster or single star ? Campbell, B. Abstract New sensitive VLA observations in the region about the galactic infrared source AFGL 2591 are reported. In addition to the two sources already known, two new sources at S(5 GHz) less than 1 mJy are identified. None of the four sources is coincident with the infrared position or the nearby H2O maser source. Two broad explanations for this disparity are discussed: that the radio sources are 'leaks' from an otherwise highly obscured ionizing source at the infrared position, or that AFGL 2591 is a cluster of at least five (four radio and one infrared) B0 or earlier stars powering individual H II regions. Publication: The Astrophysical Journal Pub Date: December 1984 DOI: 10.1086/162692 Bibcode: 1984ApJ...287..334C Keywords: Infrared Astronomy; Radio Sources (Astronomy); Star Clusters; Stellar Evolution; Astronomical Maps; Nebulae; Water Masers; Astronomy full text sources ADS | data products SIMBAD (8) NED (1)

Search for maser emission by water vapor in the nu-2 excited vibrational state

view Abstract Citations (5) References (5) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for maser emission by water vapor in the nu2 excited vibrational state. Myers, P. C. ; Barrett, A. H. Abstract A search was conducted for the 42,3 → 33,0 transition of water vapor in the ν2 excited vibrational state at 12,008.80 MHz. Sixteen known H2O maser sources were searched to °T*A rms levels ranging from 0.014 K to 0.026 K without detecting any emission. Publication: The Astrophysical Journal Pub Date: December 1982 DOI: 10.1086/160542 Bibcode: 1982ApJ...263..716M Keywords: Interstellar Masers; Interstellar Matter; Water Masers; Water Vapor; Molecular Excitation; Vibrational Spectra; Astrophysics full text sources ADS | data products SIMBAD (10)

Far-infrared mapping of the double-lobed H II region S106

Photometry of S106 at 50 and 100 microns, as well as its mapping with 35 arcsec resolution and a search for a nearby H2O maser source at 2 and 10 microns, have yielded data that are consistent with a 900 pc distance and an O9 (ZAMS) spectral type for a single, central exciting star. The correlation of dust temperature with optical emission, and anticorrelation of dust optical depth with optical emission, support models of S106 which envision an exciting star surrounded by a dusty disk having very low optical extinction along its approximately north-south axis. A local maximum in the dust column density was found to the west of the optical nebula, near the position of an H2O maser, although no local near- or far-IR flux maximum was detected.

The location of the hot molecular core in Orion

view Abstract Citations (15) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The location of the hot molecular core in Orion Zuckerman, B. ; Morris, M. ; Palmer, P. Abstract The hot molecular core in the Kleinmann-Low (KL) infrared nebula in Orion in the (7, 6) ammonia inversion transition was mapped. The source is small (less than about 20 arcsec), and the position of its centroid agrees best with the compact infrared source IRc4 and the strong H2O maser Source A. Profiles of the (4, 3) and (6, 5) inversion transitions with high signal-to-noise ratios were also obtained. A comparison of the temperatures of the hot molecular core and IRc4 suggests that the latter is a protostar that is very heavily reddened by obscuration local to itself. Publication: The Astrophysical Journal Pub Date: November 1981 DOI: 10.1086/183670 Bibcode: 1981ApJ...250L..39Z Keywords: Ammonia; Infrared Astronomy; Interstellar Gas; Molecular Gases; Orion Nebula; Position (Location); Astrometry; Brightness Temperature; Cosmic Dust; Gas Temperature; Interstellar Masers; Water Masers; Astrophysics full text sources ADS |

Proper motions and distances of H2O maser sources. III - W51NORTH

Accurate relative positions of the W51NORTH masers, determined by VLBI observations of the water vapor maser emission at 22 GHz, show changes of a few milli-arcsec over a two-year period. These displacements are interpreted as the result of transverse motions of about 50 km/sec, comparable with the radial velocity dispersion for this source, which are not random and show that clusters of maser features travel as a unit. The members of the maser cluster seem to be embedded in cloudlets of molecular gas having a scale size of 5 x 10 to the 14th cm. B-alpha observations made to establish the ambient velocity of the W51 region show that the ambient LSR velocity of the H II region is consistent with the molecular cloud velocity of about 56 km/sec. The distance to W51NORTH is estimated to be 8.3 + or - 2.5 kpc.

Proper motions and distances of H2O maser sources. II - W51 MAIN

view Abstract Citations (164) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Proper motions and distances of H2O maser sources. II. W51 MAIN. Genzel, R. ; Downes, D. ; Schneps, M. H. ; Reid, M. J. ; Moran, J. M. ; Kogan, L. R. ; Kostenko, V. I. ; Matveenko, L. I. ; Ronnang, B. Abstract VLBI measurements of relative proper motions of H2O maser features in W51 MAIN are presented, and relative positional accuracies of approximately 100 microarcsec from the analysis of the fringe phases and from the aperture synthesis maps are reported. A detailed description of the observation procedure and the data reduction are given. The observed proper motions are typically 1 milliarcsec/yr, and it is thought that they represent the kinematic motions of maser cloudlets. The transverse motions of most features appear to be random and are interpreted as turbulent motions created when strong stellar wind interacts with density inhomogeneities in the surrounding molecular cloud. The transverse and the radial velocity dispersions are compared, and the distance of W51 is calculated to be 7 + or - 1.5 kpc. Data are also presented on maser spot sizes, and maser cloud physical sizes. A large spread in the brightness temperatures of the maser features is reported, and the line widths of individual maser features are correlated with the local velocity dispersion. Publication: The Astrophysical Journal Pub Date: August 1981 DOI: 10.1086/159113 Bibcode: 1981ApJ...247.1039G Keywords: Interstellar Masers; Molecular Clouds; Radial Velocity; Very Long Base Interferometry; Water Masers; Brightness Temperature; Maser Outputs; Spectral Line Width; Velocity Distribution; Astronomy full text sources ADS | data products SIMBAD (2) Related Materials (1) Part 1: 1981ApJ...244..884G

Proper motions and distances of H2O maser sources. I - The outflow in Orion-KL

view Abstract Citations (450) References (59) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Proper motions and distances of H2O maser sources. I. The outflow in Orion-KL. Genzel, R. ; Reid, M. J. ; Moran, J. M. ; Downes, D. Abstract The measurement of relative proper motions of H2O maser features at 22 GHz with VLBI methods is reported. In the H2O source in Orion-KL, the transverse motions are typically a few milli-arcsec per year; these motions are interpreted as kinematic motions of compact cloudlets of masing gas. The data from Orion show a large-scale outflow of maser features at 18 km/s from a common origin located within 5 arcsec of the compact infrared source IRc2. It is suggested that all outflow phenomena observed in molecular lines with a velocity spread of about plus or minus 20 km/s are associated with the luminuous heavily obscured infrared source IRc2 and not with the BN object. Publication: The Astrophysical Journal Pub Date: March 1981 DOI: 10.1086/158764 Bibcode: 1981ApJ...244..884G Keywords: Interstellar Gas; Interstellar Masers; Molecular Clouds; Orion Nebula; Very Long Base Interferometry; Water Masers; Distance; Infrared Radiation; Spectrum Analysis; Stellar Evolution; Stellar Mass Ejection; Astronomy full text sources ADS | data products SIMBAD (3) Related Materials (1) Part 2: 1981ApJ...247.1039G

Redox reactions and the optical properties of interstellar grains

view Abstract Citations (22) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Redox reactions and the optical properties of interstellar grains. Duley, W. W. Abstract The role of surface and photochemical reactions on the oxidation state of interstellar grain material is examined. The equilibrium in the Fe oxide series (Fe, FeO, Fe3O4, Fe2O3) as a function of ambient conditions is investigated showing primarily that pure Fe grains are unlikely to exist in H I regions because of low temperature oxidation to Fe oxides by O atoms. In addition, it is found that several optical effects usually ascribed to size changes in interstellar grains can be interpreted in terms of chemically induced modifications in the optical properties of the grains. The optical properties of a silicon oxide series SiO(x) is used to study a possible relationship between refractive index variations and variations in the wavelength of maximum linear polarization, suggesting that reduction of silicate or oxide grains in H II regions may be related to OH and H2O maser sources in these regions. Publication: The Astrophysical Journal Pub Date: September 1980 DOI: 10.1086/158308 Bibcode: 1980ApJ...240..950D Keywords: Granular Materials; Interstellar Matter; Optical Properties; Photochemical Reactions; Surface Reactions; H I Regions; H Ii Regions; Interstellar Masers; Iron Oxides; Refractivity; Silicon Oxides; Water Masers; Astrophysics; Interstellar Grains:Chemical Composition full text sources ADS |

Observations of a compact H II region and water vapor maser sources in the vicinity of the Herbig-Haro objects 7-11

The H2O maser source near the Herbig-Haro objects H-H 7-11, which has velocity components between -10 and -30 km/s, was monitored at approximately monthly intervals over a period of three years. Two additional sites of maser emission were discovered at velocities close to the ambient cloud velocity of 8.3 km/s but separated from the original maser source by 0.5 and 2.5 arcmin, respectively. The time variations both in velocity and intensity of all three sources are characterized by periods of rapid activity lasting about 1 year, followed by a period of months to years in which the maser is unobservable within our sensitivity limits. Two of the maser sources abruptly turned on within 10 days of each other after an 18 month period of quiescence. These masers may have a common maser pump. A compact H II region coincident in angle with one of the masers was discovered. A VLBI measurement showed that the maser had an unusually small apparent size of about 3 x 10 to the 12th cm.

Disk structure in protostellar H2O maser sources

view Abstract Citations (61) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Disk structure in protostellar H2O maser sources. Elmegreen, B. G. ; Morris, M. Abstract Protostellar maser sources are modeled as orbiting gaseous disks surrounding massive windy stars. According to the model, parts of the disk may be H2O masers. The high-velocity features seen in several H2O sources may be due to the material ejected from the inner regions of the disk by pressure from the wind. Radial intervals in which the gas density is suitable for a maser determine the velocity and distance range of these features. Maser spot size, the temperatures and densities in the maser region, and the duration of the maser phase can all be accounted for through reference to the model. Publication: The Astrophysical Journal Pub Date: April 1979 DOI: 10.1086/156994 Bibcode: 1979ApJ...229..593E Keywords: Interstellar Masers; Protostars; Stellar Models; Stellar Structure; Stellar Winds; Water Masers; Infrared Astronomy; Kelvin-Helmholtz Instability; Kepler Laws; Stellar Atmospheres; Stellar Envelopes; Stellar Evolution; Stellar Radiation; Astrophysics; Star Formation:Water Masers full text sources ADS |

Strong far-infrared emission from a compact source in sharpless 140

High-spatial-resolution observations of S140 are presented at wavelengths from 35 to 175 microns. A single strong far-infrared source has been found coincident with a compact near-infrared and H2O maser source and the center of a molecular cloud. The far-infrared spectrum suggests either significant absorption in the 20-micron region or a two-temperature dust structure. The infrared luminosity of approximately 20,000 suns is comparable to that of a late O or early B star, although no radio continuum flux has been seen from this object. The source is quite likely a dust-embedded protostar.

Evolution of Maser Sources

H2O and OH maser sources are observed in the direction of compact regions of HII and IR stars and molecular complexes. Besides, the maser sources are observed in the direction of star formation regions and are associated with Herbiga-Aro objects and T-Tau stars.

Detailed observations of the M17 molecular cloud complex.

view Abstract Citations (127) References (47) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detailed observations of the M17 molecular cloud complex. Lada, C. J. Abstract Detailed molecular line observations of CO, CS, H2CO, NH5, and some of their isotopes toward the giant molecular cloud complex near M17 are presented and discussed. Extensive 12CO and 13CO observations are made of two separate clouds characterized by velocities of 20 km s ' and 23 km 1, respectively. The cloud at 20 km 1 is found to be approximately 15' x 30' (10 x 20 pc) in extent and to contain a mass in excess of 3 x 10 M0. Within the 20 km 1 cloud are three bright spots of 12CO emission, two of which are mapped in CS and H2CO emission and shown to be localized high-density fragments ( > 1 0 cm-3) a few parsecs in size. Subsequent identification of infrared sources and H2O maser sources within their boundaries is interpreted as an indication that star formation has recently taken place within those two fragments. Observations of millimeter-wave CO, CS, HCN, H2CO, and SO and centimeter-wave NH emission and H2CO absorption are combined with model cloud calculations in a self-consistent manner to determine the physical and chemical conditions in M17 SW, the largest of the CO bright spots. Integrated intensity ratios of 13CO to C18O are found to be significantly greater than the terrestrial value, suggesting an overabundance of 13CO relative to C18O. Line widths of 12CO and 13CO are found to increase near M17 SW. Careful examination and comparison of 12CO and 13CO line intensities across M17 and within individual profiles show that the entire cloud cannot be in uniform spherical collapse of any form. Collapse, however, could be in progress in a small region around M17 SW, but lack of sufficient angular resolution prohibits direct observational tests of this possibility. It is concluded that line widths of 3 km s ' must be maintained by some mechanism other than systematic collapse or expansion motions. Comparison of the molecular line observations with optical, infrared, and radio continuum data is made. Consideration of all these observations suggests that the 20 km s ' molecular cloud, the M 17 H ii region, and the star cluster NGC 6618 are related in a geometrical evolutionary sequence. Cloud evolution (dissipation) seems to have proceeded from the outer edge of a once more extensive proto-molecular cloud inward to the location of the high-density fragments in the present molecular cloud. The 23 km 1 cloud is found to be about 9' x 15' in extent and to have a 12CO emission peak coincident with the bright northern component of the M 17 H ii region. The mass of this cloud is crudely estimated to be 2 x 10 M0. Subject headings: interstellar: molecules - nebulae: abundances - nebulae: individual - radio sources: general - star clusters - star formation 603 Publication: The Astrophysical Journal Supplement Series Pub Date: October 1976 DOI: 10.1086/190409 Bibcode: 1976ApJS...32..603L full text sources ADS | data products SIMBAD (2)

The unusual H2O maser source near Herbig-Haro object number 11

Abstract : H2O emission spectra of an unusual source near Herbig-Haro (HH) 11 have been monitored over a 14-month period. Variations of the intensity and the radial velocity of the emission are noticeable on time scales as short as one day. At any given time, only one or two velocity components are present in the spectrum. The variations are such that each component appears and disappears at a fixed radial velocity, and new components appear at seemingly random velocities within a 40 km/s range. It is suggested that the exciting source is losing mass via a stellar wind, and that the H2O emission arises in the transition region between the cavity created by the stellar wind and the surrounding molecular medium. The proposed model can be tested by VLBI observations; an accurate position for the H2O maser source is required to determine the physical relationship between the maser source and the IR or HH objects. (Author)

Accurate positions of OH sources.

The Owens Valley interferometer was used at 1665, 1667, and 1720 MHz to measure the positions of eleven OH emission sources. The 1720-MHz OH source in W3 (continuum) was found to be 40 seconds away from the H2O maser source and was found not to coincide with any radio or infrared feature. Two OH emission sources were found in NGC 7538; one is identifiable with a very compact radio infrared source, while the other, 80 seconds to the south, is as yet unidentified. The OH sources 0739-14 and Sharpless 269 also coincide with infrared sources.