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Rotational modulation and flares on RS Canum Venaticorum and BY Draconis-type stars. XIV. Phasen eclipse and flare observations of YY Geminorum by EXOSAT and IUE.

Schmitt, J. H. M. M.; Rodono, M.; Haisch, B. M. +1 more

The eclipsing spectroscopic binary YY Geminorum has been observed at optical, ultraviolet, and X-ray wavelengths for rotational modulation, eclipse variability, and flaring. The epoch T(phi = 0) = JD 2425698.3561, and the phase P = 0.81428224 d. The quiescent level of Mg II emission is remarkably steady during the three-year observing interval, wi…

An X-ray flare observed from van Biesbroeck 8.

Tagliaferri, G.; Doyle, J. G.; Giommi, P.

An X-ray flare was detected on the previously unknown flare-star van Biesbroeck 8 ( = Gl 644 C). The total energy of the event in the 0.05-2 keV energy range was 8 x 10 to the 31st erg/s with a mean luminosity of 1.8 x 10 to 28th erg/s. This implies an emission measure of about 6 x 10 to the 50th/cu cm, and adopting a simple loop model an electron…

Interpretation of the inner coma observations of comet P/Halley by the Halley Multicolour Camera.

Keller, H. U.; Thomas, N.

The brightness dependence with distance of the inner coma of comet P/Halley, as observed by the Halley Multicolour Camera on board Giotto, shows 3 distinct regions. From about 400 - 2000 km from the nucleus, deviations from a z^-1 law are evident where z is the distance from the nucleus centre. Fountain model calculations indicate that s…

Coronal X-ray emission from the short-period eclipsing binary XY UMa.

Jeffries, R. D.; Bedford, D. K.; Vilhu, O. +1 more

XY UMa, a close binary showing photospheric and chromospheric activity, has been observed with Exosat through 1.26 orbital cycles, with supporting optical photometry. The G2-5 V primary star is found to be responsible for the observed soft X-ray flux, which shows a clear primary eclipse. The X-ray-emitting coronal plasma is modeled to have two com…

Coordinated Optical and Ultraviolet Observations of IM Pegasi

Huenemoerder, David P.; Buzasi, Derek L.; Ramsey, Lawrence W.

IUE spectra and optical observations of IM Peg obtained during the summers of 1985 and 1986 are analyzed. The modulations of the UV emission lines and the H-alpha, H-beta, and the CaII IR triplet (IRT) optical lines are examined. It is observed that: the UV emissin-line modulation increases as a function of height, H-alpha variability is related t…

Photospheric absorption lines in the UV spectra of O and B type stars.

Prinja, R. K.

Measurements of the equivalent widths of ultraviolet photo spheric lines of He II λ1640, C III λ1247, N III λλ1748, 1752, O IV λ1339, Si II λ1265, Si III λ1299, Si III λ1417, Si IV λλ1394, 1403 and Fe IV λ1765 in O3 to B5 stars are presented, using high-resolution IUE spectra of 300 supergiant, giant and dwarf stars.

All the ions exhibit a we…

H1722+119: A Highly Polarized X-Ray--selected BL Lacertae Object

Schwartz, D. A.; Tuohy, I. R.; Remillard, R. A. +2 more

We report the discovery of a 15th magnitude X-ray-selected BL Lacertae object as part of a program to identify X-ray sources observed by the Scanning Modulation Collimator experiment during the HEAO I all-sky survey. The BL Lac object, H1722+119, is a strong and persistent X-ray source originally discovered by Uhuru and located by the HRI instrume…

A newly discovered carbon-poor planetary nebula : PN 242-37.1

Pena, M.; Torres-Peimbert, S.; Ruiz, M. T. +1 more

An emission line object with galactic coordinates l = 242.17 deg and b = - 37.11 deg corresponding to a previously unreported very high-excitation planetary nebula is described. The spectrophotometric data obtained in October 1988 is detailed, as well as the UV observations from a satellite in November 1988. Reddening and physical conditions are o…

Rotational modulation and flares on RS Canum Venaticorum and BY Draconis-type stars. XV. Observations of Proxima Centauri and solar calibration data.

Foing, B.; Rodono, M.; Butler, C. J. +2 more

Results are reported from simultaneous Exosat and IUE observations of flaring in Proxima Cen on March 2, 1985. The data are presented in extensive tables and sample spectra and discussed in detail. The peak emission of the soft-X-ray flare is found to be about 3 x 10 to the 27th erg/sec, with energy about 3 x 10 to the 30th erg and an associated i…

Flaring and quiescent X-rays from Castor.

Schmitt, J. H. M. M.; Tagliaferri, G.; Pallavicini, R. +2 more

Using data obtained with the Low Energy (LE) and Medium Energy instruments aboard Exosat, the first detection of both flaring and quiescent X-ray emission from the A-type visual binary Castor (alpha Gem) is reported. In the LE, Castor was clearly resolved from the nearby star YY Gem, which was also observed to flare some hours after Castor. After …