Search Publications

EXOSAT Detection of a Very Large Flare on EQ Peg

Pallavicini, R.; Kundu, M. R.; Jackson, P. D.

Stellar chromospheres, coronae, and winds (invited review)

Simon, T.

Within the last few years there have been important advances in our understanding of the chromospheres, coronae, and winds of late-type stars. This progress has been the result of ultraviolet and X-ray observations obtained from space with theInternational Ultraviolet Explorer andEinstein satellites. In addition, ground-based astronomy has contrib…

Far-Ultraviolet and Optical Spectrophotometry of X-Ray Selected Seyfert Galaxies

Grewing, M.; Bowyer, S.; Clarke, J. T.

Five X-ray selected Seyfert galaxies were examined via near-simultaneous far-ultraviolet and optical spectrophotometry in an effort to test models for excitation of emission lines by X-ray and ultraviolet continuum photoionization. The observed Ly-alpha/H-beta ratio in the present sample averages 22, with an increase found toward the high-velocity…

Magnetic reconnection and energy release in a long-duration stellar flare

Pallavicini, R.; Poletto, G.; Kopp, R. A.

A dynamical model of magnetic reconnection in solar two-ribbon flares is applied to EXOSAT observations of a long-decay flare from the star EQ Peg. We show that the model is able of reproducing correctly the energy release rate and temporal evolution of the decay phase of the observed flare. We conclude that the flare was the stellar counterpart o…

X-ray and optical observations of a dMe flare star in the T Tauri field.

Charles, P. A.; Jordan, C.; Walter, F. +3 more

The authors present observations of a newly discovered dMe flare star within 20 pc of the Sun. An EXOSAT observation of this source shows an almost complete X-ray flare light curve with rise time ≡600 s, decay time ≡1500 s, and peak luminosity L_x = 6.1×10²⁹erg s^-1, a 40-fold increase in brightness over the quiescen…

IUE observations of the highly luminous Seyfert galaxy ESO 113-IG45 (Fairall 9).

Penston, M. V.; Moles, M.; Masegosa, J.

Ultraviolet variations of the continuum in ESO 113-IG45 with a doubling time of 50 days indicate a maximum size of 1×10¹⁷cm to the emitting region. Power law and blackbody fits to the continuum are both possible. The power-law fit is preferred because of the observed correlation between flux and spectral index which is similar to that f…

X-ray, UV, and optical observations of the dwarf nova BV Puppis.

Szkody, Paula; Howell, Steve B.; Kennicutt, Robert

The authors present quiescent state optical-to-IR photometry and IUE and optical spectroscopy as well as midstate EXOSAT and optical spectroscopy which indicate some unusual properties of this little-studied dwarf nova. The observed 2 - 6 keV X-ray flux of 4 - 5×10^-12ergs cm^-2sec^-1 is high for a system at outburst.…

Coronae of Late-Type Stars Observed with EXOSAT

Monsignori-Fossi, B. C.; Landini, M.; Pallavicini, R.

Distribution and kinematics of MgII in the LISM

Molaro, P.; Beckman, J. E.; Vladilo, G. +1 more

We have analyzed MgII emissions in the IUE spectra of 91 cool stars in a systematic search for interstellar components. 60% of the stars show evidence of interstellar contamination. The radial velocities of the IS features show that even at short distances (d < 30 pc) the motion of the LISM agrees with that derived from the analysis of optical …

Search for transition zone lines in early dwarf A stars.

Freire Ferrero, R.

The presence of hot external atmospheric layers in some A stars, demonstrated by the X-ray detections with the Einstein satellite, stimulated the search for optical counterparts, in particular, the search for the UV transition zone indicators like Si IV, C IV and He II lines. The observations of a sample of early dwarf A stars with IUE allows one …