MHz OH Research Articles

The Linear Shell Diameter of IRC+10011

view Abstract Citations (46) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The linear shell diameter of IRC +10011. Jewell, P. R. ; Webber, J. C. ; Snyder, L. E. Abstract The line-of-sight diameter of the circumstellar OH shell about IRC +10011 has been measured at (6.6+-1.4)E16 cm. This size was determined from the phase relation between variations in the 1612 MHz OH maser emission originating from opposite sides of the shell. The measurement is hence independent of any assumptions about the distance to the source and constitutes the first direct evaluation of the size of such an object. The linear extent of the maser region extrapolated from this measurement provides an independent check to VLBI results. Publication: The Astrophysical Journal Pub Date: November 1980 DOI: 10.1086/183395 Bibcode: 1980ApJ...242L..29J Keywords: masers; stars: circumstellar shells full text sources ADS | data products SIMBAD (14)

VLBI observations of main-line OH emission from U Orionis

Compact structure in the 1665 MHz OH emission from the long-period variable star U Orionis was detected using a five-telescope VLBI array. The U Orionis spectrum contains many compact, highly circularly polarized features which are spread over an area about 0''.5 in size. The polarization of the 1665 MHz emission from U Orionis cannot be understood by a simple Zeeman model. The extent of the main-line emission from U Orionis is significantly larger than that of previously measured 1612 MHz emission. This result is at odds with current models of circumstellar maser emission which predict that the main-line masers should lie closer to the central star than do the 1612 MHz masers.

A radio molecular maser line study of symbiotic stars

view Abstract Citations (29) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A radio molecular maser line study of symbiotic stars. Cohen, N. L. ; Ghigo, F. D. Abstract A sample of symbiotic stars has been searched for maser emission from the 1665 and 1667 MHz OH mainlines, the 22-GHz H2O line, and the 43-GHz SiO line. R Aqr remains the sole symbiotic for which maser emission has been detected. Its SiO spectrum reveals a pedestal of emission with a narrow superposed peak at V(LSR) -26.4 plus or minus 0.7 km/s. The line's existence and the pedestal feature are both characteristic of SiO lines found in late-type variables by Snyder et al. (1978). For the other symbiotic stars, it is possible that conditions favorable for maser emission have been suppressed by the presence of a hot companion. Alternatively these findings may argue against the presence of late-type variables in symbiotic stars. In either case, R Aqr seems to be in a class by itself. The suggestion that R Aqr is a binary cannot be confirmed, since the spectral feature has not shifted noticeably in the two years since the observations by Lepine, LeSqueren, and Scalise (1978). Publication: The Astronomical Journal Pub Date: April 1980 DOI: 10.1086/112695 Bibcode: 1980AJ.....85..451C Keywords: Companion Stars; Hot Stars; Interstellar Masers; Line Spectra; Molecular Spectra; Radio Emission; Stellar Spectra; Water Masers; Absorption Spectra; Emission Spectra; Oxygen Spectra; Spectrum Analysis; Variable Stars; Astronomy full text sources ADS | data products SIMBAD (32)

A SURVEY OF SYMBIOTIC STARS AT 1612 MHZ.

ABSTRACT Twelve symbiotic stars and related objects were observed at the 1612 MHz OH line with negative results. The infrared pumping rate is calculated and upper limits are given for the 1612 MHz line. A probable value for the least amount of infrared photons per second necessary for an OH maser is also suggested.

OH emission from early-type emission-line stars with large infrared excesses

We present the results of a search for ground-state OH emission from 23 early-type emission-line stars with large infrared excesses. The objects were searched at 1612, 1665, and 1667 MHz with the 300 m Arecibo telescope. We detected one new object, Vy 2--2, and confirmed the results of Fix and Mutel for the peculiar OH source M 1--92. The 1612 MHz profile for Vy 2--2 displays a single, strong, asymmetric feature about 10 km s/sup -1/ wide. Vy 2--2 is also an infrared source and a thermal radio continuum source, and has been classified as a planetary nebula of stellar appearance . If the latter classification is correct, it is the first planetary nebula detected in OH. The association of 1612 MHz OH emission and the infrared spectrum suggest that the pump mechanism for Vy 2--2 is far-infrared radiation. Vy 2--2 may represent a planetary nebula in the process of formation. The bipolar nebula M 1--92 has remained unchanged in intensity since 1973. Its evolutionary state is not known. The stars HK Ori and LkH..cap alpha.. 208, suggested as possible weak OH emitters by Lepine and Nguyen-Quang-Rieu, were not detected.

The structure of stellar hydroxyl masers

This paper presents the results of two spectral-line very long baseline (VLB) interferometric experiments on stellar OH masers. These masers are usually associated with long-period variable stars, and exhibit a characteristic double-peaked 1612 MHz OH spectrum. The sources IRC +10011, R Aql, and U Ori were carefully studied in order to determine the spatial structure of their masers. Maser components in these sources exhibited a complex structure which can be interpreted in terms of ''core-halo'' models. For these sources, the emission at any velocity appears to originate from a small (approximately-less-than0.''03) region of brightness approximately-greater-than10/sup 9/ K, and from a large (approximately-greater-than0.''5) region of brightness approximately-less-than10/sup 8/ K. In IRC+10011, ''core'' components in the two OH peaks probably are separated by less than the apparent size of the ''halos.'' A map of the low-velocity emission of U Ori with a resolution of 0.''01 indicates that the ''cores'' are distributed over a region of only 0.''2. This region is smaller than the apparent sizes of the ''halos.'' Other sources surveyed to determine apparent maser sizes include IRC+50137, OH 1821--12, OH 1837--05, OH 26.5+0.6, W43 A, and VX Sgr at 1612 MHz; and W Hya, R Aql, and IRC--10529 at 1667 MHz.more » The results of all VLB observations of 1612 MHz stellar OH masers are summarized.The apparent sizes of the strongest components (''halos'') of stellar OH masers typically are approximately-greater-than0.''5, corresponding to linear dimensions of approximately-greater-than3 x 10/sup 15/ cm. These surprisingly large sizes imply brightness temperatures much lower than those observed in most other types of astronomical masers. The large sizes rule out models of the 1612 MHz OH masers that require contracting or rotating circumstellar envelopes to explain the double-peaked OH spectra, or that try to explain the apparent maser sizes by interstellar or interplanetary scattering.« less

IRC +10 420 - A hot supergiant maser

view Abstract Citations (49) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS IRC +10420: a hot supergiant maser. Giguere, P. T. ; Woolf, N. J. ; Webber, J. C. Abstract IRC +10 420, of spectral type F8 Ia, is a maser in the OH molecule's ground-state lines at 1612, 1665, and 1667 MHz. Two 1612-MHz components are separated by 58 km/s, with peak fluxes of 47 and 7 Jy. Upper limits are given for the 1720-MHz OH line and the 22,235-MHz H2O line. New infrared data are also presented. Publication: The Astrophysical Journal Pub Date: August 1976 DOI: 10.1086/182211 Bibcode: 1976ApJ...207L.195G Keywords: Hydroxyl Emission; Masers; Stellar Spectra; Supergiant Stars; Ground State; Infrared Spectra; Molecular Spectra; Water Masers; Astrophysics full text sources ADS | data products SIMBAD (12)

OH-ir stars. II. A model for the 1612 MHz masers.

A model is presented for the 1612 MHz OH masers associated with infrared stars. Its principal conclusions are as follows. The central stars are losing approx.3 x 10/sup -5/ M/sub sun/yr/sup -1/, and the masers operate in the outer regions (r>10/sup 16/ cm) of the circumstellar envelopes. The maser radiation is narrowly beamed in the radial direction, both inward and outward. Thus the two maser emission features originate in the near and the far sides of the expanding circumstellar gas. The 1612 MHz maser is powered by the absorption of 35 ..mu.. photons which excite the OH molecules from the /sup 2/Pi/sub 3///sub 2/,J=3/2 ground state to the /sup 2/Pi/sub 1///sub 2/,J=5/2 state. The excited OH molecules return to the ground state by a series of radiative decays. In most cases, the radiative cascade proceeds directly down the /sup 2/Pi/sub 1///sub 2/ ladder. The final and the most important step in the pump cycle is the radiative decay from the /sup 2/Pi/sub 1///sub 2/,J=1/2 state to the /sup 2/Pi/sub 3///sub 2/,J= =3/2 state. If the transitions which link these two states are optically thick, a strong inversion of the F=1..-->..F=2 1612 MHz transition is produced. (AIP)

Comparison of Radio and Optical Studies in a Region of the Southern Coalsack

Detailed observations of the 4830 MHz formaldehyde absorption and the 1667 MHz OH emission have been made in the direction of a region in the Southern Coalsack. These are compared with an optical study of the same region, which contains several dark globules for which the interstellar extinction is estimated to be high ( > 10 mag). The formaldehyde distribution is found to agree quite well with that of the dense globules, whilst the OH distribution although more widespread still agrees closely with the formaldehyde and dust distribution. Assuming a simple model for the globule complex, we have determined transition temperatures and optical depths for each species. From these parameters, estimates of the column density for both the formaldehyde and OH clouds are made.

Evidence for Zeeman splitting in 1720-MHz OH line emission.

A number of 1720-MHz OH maser sources have relatively simple spectra consisting of doublets with opposite senses of circular polarization. Such doublets could be due to the Zeeman splitting of the $sup 2$Pi$sub 3$/$sub 2$ F=2$Yields$1 transition. A three-station VLBU experiment was conducted to measure the spatial separation of the emitting regions of the components of opposite sense polarization. The doublets in the 1720-MHz OH spectra of W3(OH), W51, NGC 6334 (N), and NGC 7538 (N) are found to be spatially coincident to within a linear dimension of approx.10$sup 15$ cm (10$sup 2$ AU), suggesting that they originate from the same region in space. This is taken to be strong evidence for identifying the doublets as Zeeman components. The magnetic field within the OH maser sources responsible for the observed splitting is typically a few times 10$sup -3$ gauss. (AIP)

The Galactic Distribution and Kinematics of OH Stars (A Preliminary Discussion)

The majority of OH/IR stars have been identified as M-type Mira variables, but there are a few cases where the stars have been identified as M supergiants or late-type semi-regular variables. A large number of OH sources have also been discovered with the 1612 MHz OH characteristics of OH/IR stars but no apparent optical or infrared counterparts. In several cases the velocities of these unidentified sources (OH stars) have been outside the velocity range of the neutral hydrogen distribution, suggesting that some of these sources may represent a population with a higher velocity dispersion than Population I objects (Kerr and Bowers 1974a, b). The lack of infrared and optical counterparts may indicate that the sources are quite distant, since identified OH/IR stars are often bright infrared objects. A large-scale 1612 MHz sky survey has therefore been initiated to study the galactic distribution and kinematics of the OH stars and to investigate the possibility that they may represent an older population of stars (Bowers et al. 1974).

The Structure of Four 1612 MHz OH Emission Sources

Three M-type supergiant infra-red/OH objects, NML Cyg, VY CMa and VX Sag, and the W43A source have been studied with the Mark II–Mark III interferometer in the 1612 MHz OH satellite line. Detailed structure has been determined for the NML Cyg and VY CMa sources. The blue-shifted emission was found at the centre of the objects while the zero velocity emission (relative to the star) was found at the periphery. Both objects were elongated in a direction perpendicular to their apparent rotation axis. A model of these objects has been constructed from the observations which indicates an efflux of 5 × 10 −3 solar masses per year from the vicinity of the central star. The implications of the results for theories of circumstellar clouds is discussed.

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.

Radio Observations of IR/OH/H2O Stars

A small percentage of infrared stars, selected on the basis of their IR brightness at 2.2 µm and their redness (I–K colour index), show 18 cm OH emission, and some exhibit 1.35 cm H2O emission; further investigations identify some of these objects as M-type supergiants and the remainder as M-type giant long-period variable stars.For the strongest 1612 MHz OH emitters, long-baseline interferometry shows that the emission arises from a large number of small-diameter features distributed over a much larger, approximately elliptical region corresponding to a circumstellar cloud. Models for the geometry of the emitting regions are discussed.The OH characteristics with respect to the ratios of line intensities for different transitions and the velocity structure are distinctive, not being found in other types of OH source; consequently a large number of new OH emitters can be recognized as probably IR/OH objects despite the absence of IR or optical data; the precise classification of these sources is considered together with their relevance in understanding the identified sources.

Some High-Velocity Sources of 1612 MHz OH Emission

A pilot survey was made to study the feasibility of using radio observations of OH/IR stars to investigate the galactic distribution and kinematics of these presumably intermediate-population objects. Seven new sources were found, four near the center, two near l = 30°, and one at l = 128°.

18 cm Observations of 19 New Southern OH Emission Sources

In a search for 1665 MHz OH emission in the southern Milky Way, 19 new sources have been discovered. Line profiles of all four 18 cm transitions are presented for all but one of the sources, and we discuss the general properties of the sources and their distribution in relation to the positions searched.

Anomalous 1720-MHz OH Emission from V1057 Cygni

view Abstract Citations (26) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Anomalous 1720-MHz OH Emission from V1057 Cygni Lo, K. Y. ; Bechis, Kenneth P. Abstract We detected a new type of OH ermssion source from the V1057 Cyg star position. Only the 1 720-MHz line is observable in emission. The line can be decomposed into two Gaussian cornponents, each with a line width at half-power of about 0.3 km s-i, separated by about 0.3 km -i Both components are elliptically polarized. Subject headings:spectra, radio - star formation - stars, individual Publication: The Astrophysical Journal Pub Date: October 1973 DOI: 10.1086/181323 Bibcode: 1973ApJ...185L..71L full text sources ADS | data products SIMBAD (2)

The Relative Density of H, OH and H2CO in Interstellar Clouds

I have attempted to obtain an answer to the question “In which gas (neutral hydrogen) clouds do we find molecules?” By limiting the investigation to those clouds which might be considered normal (i.e. specifically excluding the class of clouds which emit by maser action) it is possible to obtain a definitive answer to the question namely, those clouds which have the highest gas concentration. Further data on the correlation between the distribution of neutral hydrogen and of different molecules can be found.The clouds which are seen in absorption against background radio sources are most ideally suited for this purpose and I have used the absorption spectra of neutral hydrogen (21 cm wavelength), of the OH radical (18 cm, the 1667 MHz line) and the formaldehyde molecule (6 cm). Only the absorption spectra of the three strongest non-thermal sources (Cas A, Cyg A, and Tau A) were used because only these have unambiguous neutral hydrogen absorption spectra and also because they, unlike the HII regions, do not have 1667 MHz OH spectra which may be confused by anomalous emission. In the absorption spectra of these three sources individual clouds at specific velocities can be recognized on the H, OH and H2CO spectra. We can then investigate the OH and H2CO content of each cloud relative to its neutral hydrogen content.

A Thermal Source with Strong 1612 MHz OH Emission

During 1968 we have found at Parkes several types of emission in the lines of the 18 cm quadruplet of the ground-state OH molecule. This note describes a strong source of 1612 MHz emission near galactic longitude 331°.OH emission was originally detected in the vicinity of HII regions, and a search of a large number of HII regions showed that about a third had associated OH emission. This type of emission is usually strongest at 1665 MHz, and is also seen at 1667 MHz and weakly on one of the satellite lines.