H2O Maser Sources Research Articles

Stellar molecular jets traced by maser emission

AbstractHighly collimated jets found in AGB and post-AGB stars are expected to play an important role for shaping planetary nebulae. Recent VLBI observations of H2o maser sources have revealed that some of the spatio-kinematical structures of H2o maser sources exhibit stellar jets with extremely spatially and kinematically high collimation. Such stellar H2o maser jets, so-called “water fountains”, have been identified in about 10 sources to date. Here we review recent VLBI observations and relevant observational results of the water fountain sources. They have revealed a typical dynamical age and the detailed kinematical structures of the water fountains, the possibility of the existence of “equatorial flows”, and the evolutionary status of the host stars. The location and kinematics of one of the water fountain sources in the Galaxy is also revealed and shown here.

The λ0 = 1.35 cm H2O maser line: The hyperfine structure and profile asymmetry

The spectra of several H2O maser sources exhibit single λ0 = 1.35 cm maser lines with narrow asymmetric profiles. We consider the hyperfine structure of the line that corresponds to the transition between the rotational 616 → 523 levels of ortho-H2O molecules to account for the line asymmetry. Our numerical simulations of the maser line profile agree well with the observations if the hyperfine structure is taken into account.

First Detection of Millimeter/Submillimeter Extragalactic H 2 O Maser Emission

We report the first detection of an extragalactic millimeter wavelength H2O maser at 183 GHz towards NGC 3079 using the Submillimeter Array (SMA), and a tentative submillimeter wave detection of the 439 GHz maser towards the same source using the James Clerk Maxwell Telescope (JCMT). These H2O transitions are known to exhibit maser emission in star-forming regions and evolved stars. NGC 3079 is a well-studied nuclear H2O maser source at 22 GHz with a time-variable peak flux density in the range 3 -- 12 Jy. The 183 GHz H2O maser emission, with peak flux density $\sim$0.5 Jy (7$\sigma$ detection), also originates from the nuclear region of NGC 3079 and is spatially coincident with the dust continuum peak at 193 GHz (53 mJy integrated). Peak emission at both 183 and 439 GHz occurs in the same range of velocity as that covered by the 22 GHz spectrum. We estimate the gas to dust ratio of the nucleus of NGC 3079 to be $\approx$150, comparable to the Galactic value of 160. Discovery of maser emission in an active galactic nucleus beyond the long-known 22 GHz transition opens the possibility of future position-resolved radiative transfer modeling of accretion disks and outflows $<1$ pc from massive black holes.

Evidence of Evolution in the Dense Cores in Massive Star Forming Regions

The excitation of H2O masers usually needs very high density gas, hence it can serve as a marker of dense gas in HII region. We selected a sample of H2O maser sources from Plume et al. (four with, and four without detected CS(J = 7 - 6) emission), and observed them ill (CO)-C-13(j = 1-0) and (CO)-O-18 (j = 1-0). (CO)-O-18 (J = 1-0) emission was detected only in three of the sources with detected CS(J = 7-6) emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.

The IC 133 Water Vapor Maser in the Galaxy M33: A Geometric Distance

We report on the results of a 14 yr long VLBI study of proper motions in the IC 133 H2O maser source in the galaxy M33. The method of ordered motion parallax was used to model the three-dimensional structure and dynamics of IC 133 and to obtain a distance estimate, 800 ± 180 kpc. Our technique for determining the distance to M33 is independent of calibrations common to other distance indicators, such as Cepheid period-luminosity relations, and therefore provides an important check for previous distance determinations.

CLC][ITAL]BeppoSAX[/ITAL][/CLC] Observation of NGC 3079

Using the BeppoSAX observatory, we have observed a nearby LINER/Seyfert 2 galaxy, NGC 3079, which is known as an outflow galaxy and a bright H2O maser source. Using the Phoswich Detection System, we have revealed that the NGC 3079 nucleus suffers from a Compton-thick absorption, with a hydrogen column density ~1025 cm-2. After corrected the absorption, the 2-10 keV luminosity becomes 1042-1043 ergs s-1 at a distance of 16 Mpc. It is 2-3 orders of magnitude higher than that observed in the Medium Energy Concentrator Spectrometer band (below 10 keV). We also detected a strong Fe K line at 6.4 keV with an equivalent width of 2.4 keV, which is consistent with the heavy absorption.

Ring structures in Orion KL

We present the results of studies of the superfine structure of H2O maser sources in the Orion Nebula. Powerful, low-velocity, compact maser sources are distributed in eight active zones. Highly organized structures in the form of chains of compact components were revealed in two of these, in the molecular cloud OMC-1. The component sizes are ∼0.1 AU and their brightness temperatures are T b =1012−1016 K. The structures correspond to tangential sections of concentric rings viewed edge-on. The ring emission is concentrated in the azimuthal plane, decreasing the probability of their discovery. The formation of protostars is accompanied by the development of accretion disks and bipolar flows, with associated H2O maser emission. The accretion disks are in the stage of fragmentation into protoplanetary rings. In a Keplerian approximation, the protostars have low masses, possibly evidence for instability of the systems. Supermaser emission of the rings is probably triggered by precession of the accretion disk. The molecular cloud’s radial velocity is V LSR=7.74 km/s and its optical depth is τ≈5. The emission from components with velocities within the maser window is additionally amplified. The components’ emission is linearly polarized via anisotropic pumping.

A model for the molecular accretion disk and H2O maser in the nucleus of the galaxy NGC 4258

A model is developed for the H2O maser source observed in the circumnuclear region of the galaxy NGC 4258. The maser emission originates at distances of 0.15–0.29 pc from the center in a thin, cold accretion disk (gas-dust torus) rotating around a supermassive black hole of mass 4 × 107M⊙. The conditions for the emergence of an inverse population of the signal 616−523 levels in ortho-H2O working molecules are simulated numerically. The complex line profile, which includes both central and high-velocity components, is calculated. A comparison of the calculations with radiointerferometric and spectrophotometric observations allowed the physical conditions in the emitting region to be determined.

Near-infrared images of star forming regions containing masers

We present sensitive high resolution near infrared (NIR) broad band (J, H, and K) observations of a sample of 31 Star Forming Regions (SFRs) which contain H2O and OH maser sources. The observations are aimed at the detection and characterization of Young Stellar Objects (YSOs) which may be the source of excitation of the maser emission. In spite of the large number of sources detected in the regions, using positional coincidence and NIR colours we are able to reliably identify K-band sources related to the masing gas in a large fraction of the observed regions. The NIR infrared sources selected from close positional coincidence with the maser show strong NIR excesses and most probably represent the YSOs still embedded in their parental cocoon where the maser emission occurs.

Spatially Resolved H2O Masers as Probes of Supersonic Turbulence

AbstractVLBI of the H2O maser sources associated with outflows from young stars reveals, besides the regular velocity component (expansion and rotation), a random component suggestive of highly supersonic turbulence generated by the interaction of the star’s jets with the quiescent ambient gas. Our analysis of the geometry and velocity statistics in Sgr B2(M)–H2O demonstrates low fractal dimension of the turbulence and strong deviations of the velocity increments from Gaussian statistics—both indicating strong intermittency of the turbulent energy dissipation. These properties are discussed, along with the two-point velocity scaling law, and compared with the related properties of incompressible turbulence.

New detections of H2O maser sources on the 13.7 m radio telescope of Purple Mountain Observatory

Observations of H2O maser sources on the 13.7 m 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.

Water Masers Associated with Circumstellar Shells

view Abstract Citations (46) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Water Masers Associated with Circumstellar Shells Benson, Priscilla J. ; Little-Marenin, Irene R. Abstract We report observational parameters for 62 H2O maser sources, 23 not previously reported, and upper limits of H2O maser emission for 223 nondetected sources. The detected long-period variables (LPVs) are at D < 1.8 kpc for a detection limit of about 1 Jy. The distance adjusted detection rate varies from 18% for Miras variables with P < 200 days to over 50% for stars with P> 300 days and seems to be determined primarily by the amount of material in their associated circumstellar shells, since detected stars have infrared to photospheric flux ratios [flux(12 μm flux(2.2 μm)] > 0.2, whereas nondetected stars have ratios less than 0.3. Stars in the overlap region, 0.2 < r <0.3, may have been observed at the wrong phase. The minimum mass-loss rate needed to sustain detectable H2O maser emission from stars in this program is 0.5 × 10-7 Msun yr-1. The mass-loss rate increases with period. Mira variables with H2O masers have more asymmetric light curves (f = 43) compared to nondetected Miras variables (f = 46). The average H2O maser flux (normalized to 1 kpc) for Mira variables in our observing program with P < 300 days is about 15 Jy km s-1, corresponding to L(H2O)/L(star) ≍ 1 × 10-10 or L(H20)/Lsun 3 x 10-7 and to a photon luminosity 1043-1044 s-1. The low detection rates for Mira variables with P < 200 days is primarily due to the smaller amount of material in their circumstellar shells as compared to the longer period Mira variables and does not appear to be a strong function of their lower metallicities. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1996 DOI: 10.1086/192349 Bibcode: 1996ApJS..106..579B Keywords: STARS: CIRCUMSTELLAR MATTER; MASERS; STARS: MASS LOSS; STARS: VARIABLES: OTHER LONG-PERIOD VARIABLES full text sources ADS | data products SIMBAD (281)

The Thermal Radio Jet of Cepheus A HW2 and the Water Maser Distribution at 0[farcs]08 Scale (60 AU)

We report observations of the thermal radio jet in Cepheus A HW2, and the associated water masers, carried out with the highest (008) angular resolution available to date at the VLA (A configuration at λ = 1.3 cm). To calibrate the 1.3 cm continuum emission, we used the strong (~1000 Jy) H2O maser source as the reference, thus correcting the amplitude and phase instabilities introduced by the atmosphere. This powerful technique, first applied here to a star-forming region, allowed us to achieve a dynamic range of 15,000:1 for the strongest maser feature, a signal-to-noise ratio (S/N) of 70:1 for the radio jet and an accuracy of the order of 1 mas in the relative positions between the radio-continuum jet and the H2O masers in the region. We resolved the 1.3 cm jet into two maxima plus a fainter tail to the southwest. The separation between these two maxima (014) and the total size of the jet (039) are both consistent with models for a biconical ionized jet. The observed flux density (39 mJy) is, however, higher than expected. We detected 39 H2O maser spots toward the Cepheus A region, 28 of which are associated with the HW2 object, most of them distributed on either sides of the radio jet. We suggest that these latter maser features might be tracing a circumstellar molecular disk of radius ~300 AU, nearly perpendicular to the radio jet. The velocity gradient of 30 ± 10 km s-1 observed in the H2O spots over 600 AU along the axis perpendicular to the radio jet could be gravitationally bound by a central mass of 70 ± 40 M☉.

Synchrotron emission from the H2O maser source in W3(OH)

view Abstract Citations (93) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Synchrotron Emission from the H 2O Maser Source in W3(OH) Reid, M. J. ; Argon, A. L. ; Masson, C. R. ; Menten, K. M. ; Moran, J. M. Abstract We present a study of the radio continuum source found near the position of the H2O masers and the Turner-Welch (TW) source in the W3(OH) region. The source spectrum from 1.6 to 15 GHz exhibits a power law with spectral index -0.6. The continuum source is elongated in the east-west direction and its size decreases linearly with increasing frequency. These observations provide strong evidence for synchrotron emission from an inhomogeneous source. The elongated continuum source is coincident within 0.1 arcsec of the center of expansion of the H2O masers and is aligned with the dominant H2O outflow pattern. A possible model for the system includes an early-type star with a fast collimated wind that drives a jetlike outflow. Fast shocks in the wind or jet accelerate electrons, via a first-order Fermi process, to relativistic speeds necessary for synchrotron emission. The jet impinges on the surrounding molecular material and shocks and accelerates this material, leading to the microns observed in the H2O masers. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175518 Bibcode: 1995ApJ...443..238R Keywords: Continuous Spectra; Hydroxyl Emission; Radio Astronomy; Radio Emission; Synchrotron Radiation; Water Masers; Continuum Modeling; Gas Jets; Interstellar Matter; Jet Flow; Radio Spectra; Astrophysics; ISM: INDIVIDUAL ALPHANUMERIC: W3; ISM: JETS AND OUTFLOWS; MASERS; RADIATION MECHANISMS: NONTHERMAL; RADIO CONTINUUM: ISM full text sources ADS | data products SIMBAD (8)

Powerful jets and weak outflows: HH 1-2 and HH 34

view Abstract Citations (48) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Powerful Jets and Weak Outflows: HH 1--2 and HH 34 Chernin, Lawrence M. ; Masson, Colin R. Abstract We have mapped the molecular outflows in the regions surrounding the Herbig-Haro (HH) 1-2 and HH 34 jets. The molecular outflows associated with the jets are predominantly redshifted, as expected for outflows that originate near the front surfaces of clouds. The HH 1-2 region contains a 0.3 solar masses outflow originating near the very large array (VLA) continuum and H2O maser source 1.3 min to the northwest of the driving source of the HH 1-2 optical flow. We can put a rough upper limit of 0.03 solar masses on the amount of molecular outflow associated with the HH 1-2 jet. The HH 34 molecular outflow is well aligned with the jet axis but amounts only to a mass of 0.003 solar masses, making it one of the weakest outflows measured. Since these outflows are so weak, we estimate that the jets must have deposited more than two orders of magnitude more momentum in the intercloud medium (ICM) than the ambient cloud. This suggests that shocks generated by the jet may exist far outside the cloud boundaries, and have a significant effect on the ICM. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175512 Bibcode: 1995ApJ...443..181C Keywords: Herbig-Haro Objects; Interstellar Matter; Jet Flow; Mapping; Molecular Clouds; Red Shift; Pre-Main Sequence Stars; Star Formation; Stellar Winds; Very Large Array (Vla); Water Masers; Astrophysics; ISM: JETS AND OUTFLOWS; STARS: FORMATION; STARS: MASS LOSS; STARS: PRE--MAIN-SEQUENCE full text sources ADS | data products SIMBAD (11)

G305.8 - 0.2: A Young Object with a Dust and Gas Envelope

The H2O maser source in G305.8 - 0.2 was first detected by Haynes et al. (1984). Inspection of the Southern Hemisphere radio surveys did not show any strong compact HII region or water maser placed nearby this source. The IRAS point source catalog (2.0) shows a strong source in the direction of the maser. We analysed the temporal variation and line profile of the H2O maser emission and discussed the nature of its associated IRAS source. These source characteristics seem compatible with the hypothesis that the maser is associated with a protostellar disk around an early-type star of spectral type 07 to 09 surrounded by a spherical shell of gas and dust.

First images of water vapor masers in the galaxy M33

The first successful VLBI observations of 10 extragalactic H2O masers in the M33 galaxy are reported. A spectral-line VLBI synthesis map is constructed, the first of any extragalactic H2O maser sources. The map has the lowest noise of any K-band spectral line VLBI map yet produced. The maser emission extends over about 300 milliarcseconds and is divided into 14 distinct spatial components, the strongest of which has a correlated flux density of about 0.7 Jy. The relative positions of some of these components are determined accurately enough to provide first-epoch measurements for proper motion studies. The characteristics of the maser are similar to those of the most powerful maser in the Galaxy, W49N. A compact H II region is found close to the maser which is 1 pc in diameter and whose emission measure is about 6 x 10 to the 7th pc/cm exp 6. This region is the compact component of a more extended H II complex that extends over about 100 pc.

Flares of radio line emission H2O in Ori A and W49N

The results of observations of H2O maser sources Ori A and W49N at 1.35cm made the RATAN-600 radio telescope from June 1981 till December 1988 are presented. The light curves of these sources showed several outbursts. Duration of the strongest outbursts for the Ori A and W49N are approximately 1 and 1.5yr respectively. The maximum of the total luminosity (assuming isotropic emission) of these sources for the velocity range ±8km.s-1 is egual to 1×1047 ph.s-1 and 2×1049 ph.s-1 respectively. The time behaviour of the water maser source in W49N during more than 7yr is monitored for the first time.

Distribution of the H2O Masers in the Sagittarius B2 Core

The distribution of H2O masers in the Sgr B2 core was observed with a 2.5′×2.5′ wide field and with 540 km s−1 total velocity coverage by the Nobeyama Millimeter Array. Thirty-nine resolved maser spots were detected with a relative positional accuracy of 0.3″, which are clustered into four separate regions. In Sgr B2 north, the cluster lies at the edge of the continuum ridge. One of the maser spots shows strong and wide velocity-spread emission, suggesting it may correspond to a center of star forming activity. In Sgr B2 main, the strong maser spots are projected just on the face of a compact HII region, and are red-shifted relative to the central velocity of the HII region. There are two possibilities to interpret our results in Sgr B2 (M). One is that the H2O maser spots are distributed around the HII region and are infailing to the HII region. The other is that the H2O maser sources are associated with the cloud in the foreground of the HII region.

Star formation in the southern complex region NGC 3576

NGC 3576 (RCW 57) is a very bright optically visible nebula (~10' in size) located near the galactic plane at a distance of 3.6kpc. The region is associated with the HII region G291.28–0.71 (Retallack &amp; Goss), and with a giant molecular cloud of M≃9×104 M⊙ (Cheung et al.1980) The source is reported in the IRAS Small Scale Structure Catalog. From the observed far-IR fluxes we derive a total luminosity of L(FIR)≃7×105 L⊙, suggesting that at least seven possible 07–09 stars could ionize the entire observed region. A cluster of five IR sources and extended 10μm emission were found by Frogel &amp; Persson (1974). IRS 1 is a very compact object (&lt;3'), while IRS 2–5 show diffuse infrared emission. In addition IRS 2, very close to IRS 1, is coincident with the radio emission peak. An H2O maser source and NH3 emission are present in the complex region.We present multidiaphragm photometry from 1 to 20μm of 1RS 1, IRS 3 and IRS 4 and CVF observations between 2-μm and 8–13μm of IRS 1, collected at the 1m and 3.6m ESO telescopes.