Radio Observations of Magnetic Stars

Altenhoff, W. J.; Pfleiderer, J.; Weiss, W. W.

doi:10.1017/s0252921100080799

Cited by 3 publications

(4 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…All experiments were negative in that no emission was observed. It is interesting to note here that Altenhoff et al (1983) detected 1.3 cm emission from Comet Iras-Araki-Alcock, while VLA observations at 2 and 6 cm did not show a detection. The 3<r upper limit at 2 cm was 4 times less (750 ^Jy) than that expected from a blackbody with a flux density of 9 mjy at 1.3 cm as observed.…”

Section: Continuum Observationsmentioning

confidence: 51%

See 1 more Smart Citation

A Review of Radio Interferometric Imaging of Comets

Pater¹,

Palmer²,

Snyder³

1989

International Astronomical Union Colloquium

View full text Add to dashboard Cite

ABSTRACT. We present an overview of cometary observations carried out with the VLA. These include OH imaging observations, studies of other molecules and searches for continuum emission. Primarily, we discuss the OH observations obtained of Comet Halley, a periodic comet, and Comet Wilson, a "new" comet. The emission from Comet Halley is confined to a region a few times 10 km. The emission from Comet Wilson shows sporadic blobs at large distances (~ 10 km from the center), which vary abruptly in both position and velocity. The generally accepted picture of excitation by UV pumping in a spherical outflow of cometary gas explains the coarse phenomenology, but other effects seem to cause significant modulations of the OH emission. We suggest that for Comet Halley, collisional effects near the edge of the quenching region, which is coincidently the approximate distance to the cometopause, may be important, and that for Comet Wilson, outgassing from cometesimals ejected from the nucleus may be significant. We further show that asymmetric line profiles are more common than previously thought. Lengthening integration times and lowering the velocity resolution results in a smooth, round shape for the comet's brightness distribution. In addition, spectral profiles become broader and more symmetric after long integration times and after integration over larger spatial regions. In addition to the OH observations we summarize the HoCO detection experiments for comets Halley and Machholz. I n t r o d u c t i o nIt is generally accepted t h a t water ice is the primary constituent of a cometary nucleus and sublimated H 2 0 flows radially away as the comet approaches the sun. It is very difficult to observe H 2 0 directly from the ground. T w o probable detections have been m a d e at 22 GHz (Jackson, Clark and Donn, 1976;Altenhoff et al, 1983). Snyder (1982) has summarized a *Alfred P. Sloan Fellow.

show abstract

Section: Continuum Observationsmentioning

confidence: 51%

“…It is very difficult to observe H 2 0 directly from the ground. T w o probable detections have been m a d e at 22 GHz (Jackson, Clark and Donn, 1976;Altenhoff et al, 1983). Snyder (1982) has summarized a *Alfred P. Sloan Fellow.…”

mentioning

confidence: 99%

A Review of Radio Interferometric Imaging of Comets

Pater¹,

Palmer²,

Snyder³

1989

International Astronomical Union Colloquium

View full text Add to dashboard Cite

show abstract

“…The distribution of nitrogen between ammonia and molecular nitrogen is indicative of the environment where comets formed (see, e.g., Prinn and Fegley 1989). Ammonia was marginally detected by direct observation at radio wavelengths in Comet IRAS-ArakiAlcock (1983 VII) (Altenhoff et al 1983). From the NMS experiment on Giotto, an upper limit of 10% for the volume mixing relative to H2O has been reported (Krankowsky et al 1986).…”

Section: Ammoniamentioning

confidence: 98%

“…The tentative identification of water in Comet Bradfield (1974 III) by its 1.35-cm line at radio wavelengths by Jackson et al (1976) was challenged by Crovisier et al (1981) and by Hollis et al (1981). Searches for the 1.35-cm line in other comets gave negative results, except for Comet IRAS-Araki-Alcock (1983 VII), where apparently this line was detected by Altenhoff et al (1983). Similarly, efforts to identify water ice were not conclusive.…”

Section: Water Vapormentioning

confidence: 99%

The Composition of Comets

Krankowsky

1991

International Astronomical Union Colloquium

View full text Add to dashboard Cite

ABSTRACT. The chemical composition of gases in the coma of Comet Halley obtained from in situ and remote observations is reviewed. Water vapor with an abundance of approximately 80% by number is the dominant parent gas. Carbon monoxide is the second most abundant molecule, with about one-seventh of the water abundance. The other expected parent gasescarbon dioxide, methane, and ammonia-contributed with at most a few percent to the coma gas. Molecular nitrogen is found to be a minor species, with an abundance of less than one percent. Formaldehyde is relatively abundant, with a few percent relative to water. Gas-phase isotope ratios of nitrogen, oxygen, and sulfur are found to agree with solar system values within experimental errors. Halley's hydrogen isotope ratio is comparable t o t h e values found in other solar system objects poor in hydrogen, but distinctly different from t h e protosolar nebula and objects that accreted hydrogen in gaseous form. Carbon in the cyanide radical is enriched by 35% in 1 3 C compared to the bulk solar system value that indicates the presence of non-homogenized interstellar carbon in Halley. Volatiles released from grains contribute noticeably to the coma gas. Complex organic molecules, inferred from various observations as constituents of the dust grains, are believed to be the origin of the distributed C O source, CN, and other jet structures in the coma.

show abstract

Stellar radio emission (review)

Zheleznyakov¹

1983

Radiophys Quantum Electron

View full text Add to dashboard Cite

Radio Observations of Magnetic Stars

Abstract: SummaryThirteen Ap stars have been observed with the Effelsberg 100-m-telescope, at a wavelength of 2 cm. No star was detected. The detection limits ranged from 3 to 8 mJy.

Cited by 3 publications

References 1 publication

A Review of Radio Interferometric Imaging of Comets

A Review of Radio Interferometric Imaging of Comets

The Composition of Comets

Stellar radio emission (review)

Contact Info

Product

Resources

About