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1

Digitale Medien

First dynamic spectra of stellar microwave flares (1987)

Bastian, T. S. ; Bookbinder, J. A.

[s.l.] : Nature Publishing Group

Nature 326 (1987), S. 678-680

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ISSN: 1476-4687

Quelle: Nature Archives 1869 - 2009

Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik

Notizen: [Auszug] We used the Very Large Array (VLA) on 28 June 1986 in 16 channel spectral line mode centred at 1,415 MHz. The 50-MHz bandwidth was divided into 15 channels of 3.125-MHz width; the sixteenth channel was reserved for recording the integral flux over the inner 37.5 MHz of the bandwidth. The array was ...

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1038/326678a0

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2

Digitale Medien

Stellar flares (1994)

Bastian, T. S.

Springer

Space science reviews 68 (1994), S. 261-274

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ISSN: 1572-9672

Schlagwort(e): Stars: Activity ; Stars: Flare ; Radio Continuum: Stars ; X-Rays: Stars

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract Radio and X-ray observations of stellar flares provide the most direct probes of energy relaase particle acceleration, and energy transport on stars other than the Sun. In this review, the observational basis for our understanding of the flare phenomenon on other stars is briefly described and outstanding interpretive and theoretical issues are discussed. I shall confine my attention to objects which are “solar-like”, to the extent that they possess deep convective envelopes and display activity which is presumed to be magnetic in origin. These include pre-main sequence objects, classical flare stars, and close binaries. Future directions are briefly discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00749152

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3

Digitale Medien

First millimetric detections of AE Aquarii (1994)

Abada-Simon, M. ; Lecacheux, A. ; Bastian, T. S. ; [weitere]

Springer

Space science reviews 68 (1994), S. 291-292

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ISSN: 1572-9672

Schlagwort(e): accretion, accretion disks ; binaries ; novae, cataclysmic variables ; radio continuum: stars ; stars: individual (AE Aquarii)

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract We report the first millimetric detections of the magnetic cataclysmic variable AE Aquarii, accompanied by contemporaneous microwave observations. These data show that the time-averaged spectrum is well fit by a power-law which extends to mm wavelengths. We suggest that the spectrum is consistent with that expected from a superposition of flare-like events.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00749154

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4

Digitale Medien

Radio observations of the M8.1 solar flare of 23 June, 1988: Evidence for energy transport by thermal processes (1992)

Bastian, T. S. ; Gary, D. E.

Springer

Solar physics 139 (1992), S. 357-385

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The Very Large Array (VLA) and the frequency agile interferometer at the Owens Valley Radio Observatory (OVRO) were used to observe the M8.1 flare of 23 June, 1988. The VLA obtained images prior to and during the flare at 333 MHz, and at 1.5 and 4.7 GHz. The frequency agile interferometer at Owens Valley obtained interferometer amplitude and total power spectra of the flare at 45 frequencies between 1 and 18 GHz. The observations were supplemented by radiometer measurements made by the USAF RSTN network site at Palehua, HI, by GOES soft X-ray observations, by USAF SOON Hα filtergrams, and by a KPNO photospheric magnetogram. The radio data reveal a wide variety of phenomena, including: (i) a multiply impulsive microwave burst that is essentially thermal in character; (ii) stationary discrete components at 1.5 GHz, associated temporally and spatially with distant brightenings in Ha; (iii) a dynamical component at 1.5 GHz associated with hot plasma moving subsonically into the corona; (iv) the appearance of intense, short-lived, decimetric burst activity near the lead sunspot in the active region at 1.5 GHz, indicative of a high degree of inhomogeneity in the source. The unusually complete radio coverage allows us to investigate the transport of energy from the initial site to sites of distant Hα brightenings. The transport of energy appears to be most consistent with slow, thermal processes, rather than rapid transport by nonthermal electron beams.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00159159

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5

Digitale Medien

Radio emission from flare stars (1990)

Bastian, T. S.

Springer

Solar physics 130 (1990), S. 265-294

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract Observations of radio emission from flare stars are reviewed, including surveys of flare stars in the solar neighborhood and in stellar associations, studies of quiescent emission, and continuum and spectral studies of radio burst emission. The radio observations are placed in an observational context provided by soft X-ray, UV, and optical observations. It is stressed that, as is the case for the latter wavelength regimes, observations of rado bursts on flare stars are qualitatively similar to those on the Sun, albeit in a dramatically scaled-up fashion.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00156794

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6

Digitale Medien

Stellar dynamic spectroscopy (1982)

Bastian, T. S. ; Dulk, G. A. ; Bookbinder, J. A.

Springer

Solar physics 113 (1982), S. 289-290

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The dynamic spectrum, a three dimensional record of the radio intensity as a function both of time and frequency, has long been used as a probe of plasma processes in the solar corona. Beginning with the work of Wild and McCready (1950) dynamic spectroscopy has been used to distinguish between the multitude of radio wave emitting phenomena which occur in the solar corona and to infer the physical mechanisms responsible. Stellar dynamic spectroscopy has always been a tantalizing prospect. The vast body of experience with solar dynamic spectroscopy would prove invaluable in interpreting stellar dynamic spectra. Further, the new parameter regimes presented by stellar coronas would allow further insight to be gained in the physical processes at work in stellar coronas. Recently, Bastian and Bookbinder (1987) used the Very Large Array The National Radio Astronomy Observatory is operated by Associated Universities, Inc. under contract with the National Science Foundation. in spectral line mode at 1.4 GHz with a bandwidth of 50 MHz to obtain the first dynamic spectra of nearby flare stars. The spectral resolution was 3.125 MHz and the temporal resolution was 5 s. While the relative bandwidth was less than ideal (δν/ν ∼ 5%), the spectra so obtained were sufficient to show the presence of narrowband structure in a radio outburst from the well-known dMe flare star UV Ceti. Several efforts are now underway to obtain stellar dynamic spectra, of both RS CVn binaries and dMe flare stars, with higher degrees of spectral and temporal resolution. Among these are use of a 1024 channel correlator with the 1000' telescope at Arecibo and use of the Berkeley Fast Pulsar Search Machine (Kulkarni et al. 1984) with the Green Bank 140' telescope.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00147709

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7

Digitale Medien

Location of type I radio continuum and bursts on Yohkoh soft X-ray maps (1995)

Krucker, S. ; Benz, A. O. ; Aschwanden, M. J. ; [weitere]

Springer

Solar physics 160 (1995), S. 151-169

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract A solar type I noise storm was observed on 30 July, 1992 with the radio spectrometer Phoenix of ETH Zürich, the Very Large Array (VLA) and the soft X-ray (SXR) telescope on board theYohkoh satellite. The spectrogram was used to identify the type I noise storm. In the VLA images at 333 MHz a fully left circular polarized (100% LCP) continuum source and several highly polarized (70% to 100% LCP) burst sources have been located. The continuum and the bursts are spatially separated by about 100″ and apparently lie on different loops as outlined by the SXR. Continuum and bursts are separated in the perpendicular direction to the magnetic field configuration. Between the periods of strong burst activities, burst-like emissions are also superimposed on the continuum source. There is no obvious correlation between the flux density of the continuum and the bursts. The burst sources have no systematic motion, whereas the the continuum source shows a small drift of ≈ 0.2″ min−1 along the X-ray loop in the long-time evolution. The VLA maps at higher frequency (1446 MHz) show no source corresponding to the type I event. The soft X-ray emission measure and temperature were calculated. The type I continuum source is located (in projection) in a region with enhanced SXR emission, a loop having a mean density of 〈n e〉 = (1.5 ± 0.4) × 109 cm−3 and a temperature ofT = (2.1 ± 0.1) × 106 K. The centroid positions of the left and right circularly polarized components of the burst sources are separated by 15″–50″ and seem to be on different loops. These observations contradict the predictions of existing type I theories.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00679102

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8

Digitale Medien

Joint radio and soft x-ray imaging of an ‘anemone’ active region (1996)

Vourlidas, A. ; Bastian, T. S. ; Nitta, N. ; [weitere]

Springer

Solar physics 163 (1996), S. 99-120

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ISSN: 1573-093X

Quelle: Springer Online Journal Archives 1860-2000

Thema: Physik

Notizen: Abstract The Very Large Array and the Soft X-ray Telescope (SXT) aboard the Yohkoh satellite jointly observed the rapid growth and decay of a so-called ‘anemone’ active region on 3–6 April, 1992 (AR 7124). The VLA obtained maps of the AR 7124 at 1.5, 4.7, and 8.4 GHz. In general, discrete coronal loop systems are rarely resolved at 1.5 GHz wavelengths because of limited brightness contrast due to optical depth effects and wave scattering. Due to its unusual anemone-like morphology, however, several discrete loops or loop systems are resolved by both the VLA at 1.5 GHz and the SXT in AR 7124. Using extrapolations of the photospheric field and the radio observations at 4.7 and 8.4 GHz, we find that the microwave emission is the result of gyroresonance emission from a hot, rarefied plasma, at the second and/or third harmonic. The decimetric source is complex -1.5 GHz emission from the leading part of AR 7124 is due to free-free emission, while that in the trailing part of the active region is dominated by gyroresonance emission. We also examine an interesting case of a discrete radio loop with no soft X-ray (SXR) emission adjacent to a hot SXR loop. This observation clearly shows the multithermal nature of the solar corona.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00165459

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