scholarly journals VLBI Observations of WR Stars

1991 ◽  
Vol 143 ◽  
pp. 87-94
Author(s):  
M. Felli ◽  
M. Massi
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Small Region ◽  
Early Type ◽  
Radio Observations ◽  
Thermal Component ◽  
Vlbi Observations ◽  
Early Type Stars

We present the first VLBI radio observations of two WR stars (WR140 and WR146) and of two early type stars (HD167971 and θ1 ORI A). The derived size and brightness temperature suggest that in all cases the radio emission originates from two distinct components: a steady weak emission due to the ionized wind of the primary and a smaller diameter brighter non-thermal component, probably associated to a small region within the ionized envelope of the star.

scholarly journals The auroral radio emission of the magnetic B-type star ρ OphC

2020 ◽  
Vol 499 (1) ◽  
pp. L72-L76
Author(s):  
P Leto ◽  
C Trigilio ◽  
C S Buemi ◽  
F Leone ◽  
I Pillitteri ◽  
...  
Keyword(s):  
Radio Emission ◽  
Indirect Evidence ◽  
Magnetic Star ◽  
Early Type ◽  
Radiation Beam ◽  
Polar Caps ◽  
Thermal Radio ◽  
Thermal Radio Emission ◽  
Early Type Stars ◽  
Rotational Phase

ABSTRACT The non-thermal radio emission of main-sequence early-type stars is a signature of stellar magnetism. We present multiwavelength (1.6–16.7 GHz) ATCA measurements of the early-type magnetic star ρ OphC, which is a flat-spectrum non-thermal radio source. The ρ OphC radio emission is partially circularly polarized with a steep spectral dependence: the fraction of polarized emission is about $60{{\ \rm per\ cent}}$ at the lowest frequency sub-band (1.6 GHz) while is undetected at 16.7 GHz. This is clear evidence of coherent Auroral Radio Emission (ARE) from the ρ OphC magnetosphere. Interestingly, the detection of the ρ OphC’s ARE is not related to a peculiar rotational phase. This is a consequence of the stellar geometry, which makes the strongly anisotropic radiation beam of the amplified radiation always pointed towards Earth. The circular polarization sign evidences mainly amplification of the ordinary mode of the electromagnetic wave, consistent with a maser amplification occurring within dense regions. This is indirect evidence of the plasma evaporation from the polar caps, a phenomenon responsible for the thermal X-ray aurorae. ρ OphC is not the first early-type magnetic star showing the O-mode dominated ARE but is the first star with the ARE always on view.

scholarly journals Radio Observations of Flare Stars

1971 ◽  
Vol 15 ◽  
pp. 114-115
Author(s):  
A. J. Wilson
Keyword(s):  
Radio Emission ◽  
Solar Neighbourhood ◽  
Early Type ◽  
Radio Observations ◽  
Flare Stars

Observations of the radio emission from the red dwarf flare stars in the solar neighbourhood have been made at Jodrell Bank since 1958. In Australia, observations have been made both of these flare stars and of the early type flare stars in stellar aggregates. Observations in both Britain and Australia have been hampered by the difficulties involved in obtaining radio and optical coverage at the same time.In the initial Jodrell Bank programme, at a frequency of 240 mhz, between 1958 and 1960, 474 hours of observations were obtained, mostly on UV Ceti, and 13 events compatible with bursts of radio emission from the star were seen, but due to poor seeing conditions at the Cambridge Observatories the correlation between radio and optical flares could not be established, although the rate of occurence of radio events was similar to the reported rate for optical events of a few magnitudes.

Kinematic studies of early-type stars. I. Photometric survey, space motions, and comparison with radio observations.

1962 ◽  
Vol 67 ◽  
pp. 491 ◽  
Author(s):  
V. C. Rubin ◽  
J. Burtley ◽  
A. Kiasatpoor ◽  
B. Klock ◽  
G. Pease ◽  
...  
Keyword(s):  
Early Type ◽  
Radio Observations ◽  
Kinematic Studies ◽  
Early Type Stars

scholarly journals Planetary Nebulae as a Part of the Galaxy

1968 ◽  
Vol 34 ◽  
pp. 7-22 ◽  
Author(s):  
L. Perek
Keyword(s):  
Total Mass ◽  
Neutral Hydrogen ◽  
Planetary Nebulae ◽  
Galactic Structure ◽  
Solar Neighbourhood ◽  
Early Type ◽  
Radio Observations ◽  
The Galaxy ◽  
Early Type Stars

Planetary nebulae form one of the most important subsystems of the Galaxy. If we knew more about this subsystem, an important gap in our ideas about the galactic structure would be filled. Very briefly, we are facing the following situation:Population I, which contributes to the total mass of the Galaxy by hardly more than 7 %, can be tracked almost over the entire Galaxy thanks to the radio observations of neutral hydrogen at 21 cm wavelength. Other data, for a wide solar neighbourhood, follow from observations of Cepheids and early-type stars.

Some results of the Barbier-Chalonge-Divan system of stellar classification

1966 ◽  
Vol 24 ◽  
pp. 77-90 ◽  
Author(s):  
D. Chalonge
Keyword(s):  
Early Type ◽  
Parameter System ◽  
Early Type Stars ◽  
Two Parameter

Several years ago a three-parameter system of stellar classification has been proposed (1, 2), for the early-type stars (O-G): it was an improvement on the two-parameter system described by Barbier and Chalonge (3).

Radio Continuum Measurements of Southern Early‐Type Stars. III. Nonthermal Emission from Wolf‐Rayet Stars

1999 ◽  
Vol 518 (2) ◽  
pp. 890-900 ◽  
Author(s):  
Jessica M. Chapman ◽  
Claus Leitherer ◽  
Barbel Koribalski ◽  
Roderick Bouter ◽  
Michelle Storey
Keyword(s):  
Radio Continuum ◽  
Early Type ◽  
Nonthermal Emission ◽  
Early Type Stars

Preliminary Observations of Interstellar Sodium D-Line Absorption towards the Carina Nebula

1980 ◽  
Vol 4 (1) ◽  
pp. 95-97 ◽  
Author(s):  
J. B. Whiteoak ◽  
F. F. Gardner
Keyword(s):  
High Resolution ◽  
Hii Regions ◽  
Early Type ◽  
Interstellar Clouds ◽  
Carina Nebula ◽  
Line Absorption ◽  
General Investigation ◽  
Early Type Stars ◽  
Resolution Study

As part of a general investigation of interstellar clouds associated with southern HII regions we have begun a high-resolution study of the sodium D-line absorption in the directions of early-type stars that are likely to be associated with or located behind the clouds.

scholarly journals A circular polarization survey for radio stars with the Australian SKA Pathfinder

2021 ◽  
Vol 502 (4) ◽  
pp. 5438-5454
Author(s):  
Joshua Pritchard ◽  
Tara Murphy ◽  
Andrew Zic ◽  
Christene Lynch ◽  
George Heald ◽  
...  
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Circular Polarization ◽  
Flux Density ◽  
Wide Band ◽  
M Dwarfs ◽  
Square Kilometre Array ◽  
Population Statistics ◽  
Chemically Peculiar ◽  
Radio Stars

ABSTRACT We present results from a circular polarization survey for radio stars in the Rapid ASKAP Continuum Survey (RACS). RACS is a survey of the entire sky south of δ = +41○ being conducted with the Australian Square Kilometre Array Pathfinder telescope (ASKAP) over a 288 MHz wide band centred on 887.5 MHz. The data we analyse include Stokes I and V polarization products to an RMS sensitivity of 250 μJy PSF−1. We searched RACS for sources with fractional circular polarization above 6 per cent, and after excluding imaging artefacts, polarization leakage, and known pulsars we identified radio emission coincident with 33 known stars. These range from M-dwarfs through to magnetic, chemically peculiar A- and B-type stars. Some of these are well-known radio stars such as YZ CMi and CU Vir, but 23 have no previous radio detections. We report the flux density and derived brightness temperature of these detections and discuss the nature of the radio emission. We also discuss the implications of our results for the population statistics of radio stars in the context of future ASKAP and Square Kilometre Array surveys.

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