Robert Joseph Patterer

Extreme Ultraviolet Explorer Bright Source List

Initial results from the analysis of the Extreme Ultraviolet Explorer (EUVE) all-sky survey (58-740 A) and deep survey (67-364 A) are presented through the EUVE Bright Source List (BSL). The BSL contains 356 confirmed extreme ultraviolet (EUV) point sources with supporting information, including positions, observed EUV count rates, and the identification of possible optical counterparts. One-hundred twenty-six sources have been detected longward of 200 A.

Detection of rotational modulation in the coronal extreme-ultraviolet emission from V711 Tauri?

The RS CVn binary V711 Tauri was observed by the Extreme Ultraviolet Explorer satellite (EUVE) twice during the latter half of 1992, for periods lasting several days. Light curves for the waveband 60-180 angstroms derived from the all-sky survey scanning in August and from a pointed calibration observation made in October both exhibit a modulation of about 40%. The modulation in both data sets is very similar, with minimum flux occurring near orbital phase phi=0.5. Analysis using a two-temperature optically thin plasma emission model reveals that most of the detected extreme ultraviolet (EUV) flux emanates from hot (approximately 10(7) K) coronal plasma. The modulation is probably mostly due to either flare-like activity or to rotational occultation of a long-lived, compact, and especially bright coronal structure on the more active star of the system. The phased data support the latter hypothesis. This coronal structure is then likely to be associated with the persistent spot patterns seen on V711 Tau when using Doppler and photometric surface imaging techniques. Comparison with contemporaneous Stromgren b-band photometry indicates that the optical minimum light leads the EUV maximum light by 90 degrees in phase.

EUVE Photometric Eclipse Observations of AR Lacertae

We report on observations of the eclipsing RS CVn system AR Lac with the Extreme Ultraviolet Explorer (EUVE) scanning and deep survey (DS) telescopes. This system consists of a G2 IV star and a KO IV star separated by 9.2R0 with an orbital period of about 1.98 days. The scanner observations consisted of a single pointing over a period of 25 hours, providing some coverage of both primary and secondary eclipses, and subsequent scanning during the all-sky survey. During the pointed observation AR Lac was detected in the EUVE Lexan/boron (Lexan/B, 50-180 Â) and Al/Ti/C (160-240 Â) bands at average count rates of 0.12 and 0.016 count s, respectively. During primary eclipse, the Lexan/B count rate was at about one-third of its subsequent value at quadrature, suggesting that, in the case of a compact and relatively homogeneous corona, a minimum of 60%-70% of the extreme ultraviolet (EUV) emission originates on the G star. There was no detectable modulation corresponding to secondary eclipse in either Lexan/B or Al/Ti/C bands. Data taken several months later during the EUVE all-sky survey yield the same Lexan/B count rate as the pointed data but only an upper limit in the Al/Ti/C bandpass. AR Lac was observed again with the DS as part of a Guest Observer pointed observation. This single pointing lasted slightly more than three days and included both primary and secondary eclipses. AR Lac was detected in the DS Lexan/B band with an average count rate of 0.31 count s. The primary eclipse is easily visible as a —40% decrease in intensity. A dip in the light curve is present at the time of secondary eclipse, but is not readily discernible from the average level of variability. A flare corresponding to a factor of 2 increase over the quiescent emission count rate was observed during the next expected secondary eclipse. We have performed an elementary emission measure analysis and compared isothermal models that fit the EUVE data to earlier Einstein, EXOSAT, ASCA, and ROSAT two-temperature models culled from the literature. In general, the EUVE data indicate very similar emission measures to those derived in previous work, indicating that the corona of AR Lac does not vary in average x-ray or EUV luminosity over periods of years up to a decade. Assuming an isothermal model with r~10 K, as indicated by the emission measure analysis, the total Lexan/B count rate at quadrature implies an EUV luminosity of 1.1 X10 ergs in the 50-180 Â bandpass.

Lithium line variations in weak-lined T Tauri stars

We have observed seven weak-lined T Tauri stars to examine the effects of magnetic activity on the Li I 6707 A equivalent width and line profile. Six of the seven program stars were observed at least twice per evening on four consecutive nights. Variable Li I equivalent width is certainly present in two targets, which are the only known binaries (single-lined spectroscopic) in our sample, and likely in three others. The amplitude of the variability is consistent with previous estimates of activity effects. The variability itself supports hypotheses that observed spread in Li I equivalent widths may be explained by magnetic activity. It is unclear whether or not the binary nature of our two detections is significant. We find no indication that similarity to RS CVn systems, other than rapid rotation, is responsible for the variable activity detected

Extreme ultraviolet emission from late-type stars - Initial results from Extreme Ultraviolet Explorer

We present initial measurements of the extreme ultraviolet (EUV) emission from two nearby late-type dwarfs, α Cen (G2 V+K1 V) and HR 6094 (G5 V), obtained with the Extreme Ultraviolet Explorer (EUVE) satellite. Both objects were observed for extended periods during the in-orbit calibration pointings of EUVE. Alpha Cen was detected in four bandpasses spanning the entire EUV, between 100 and 700 A, while HR 6094 was detected for the first time as an EUV source in two bandpasses. Neither source exhibited any variability or flaring. An emission measure analysis of the EUVE data for α Cen combined with previously published Einstein X-ray and IUE measurements indicates two distinct temperature components for the combined α Cen binary system

Extreme Ultraviolet Explorer observations of the RS Canum Venaticorum systems AR Lacertae and II Pegasi

We report observations of two RS CVn systems, II Peg and AR Lac, which were calibration targets during the in-orbit checkout phase of the Extreme Ultraviolet Explorer (EUVE). We have determined count rates, and, based on these count rates, preliminary emission measure analyses have been done. The Lexan/boron band count rates were 0.0849 +/- 0.0023 counts/s for AR Lac and 0.218 +/- 0.031 counts/s for II Peg during its quiescent state. Temperatures and emission measures derived from the EUVE data are consistent with previously published values. We also report a flare seen during the II Peg observations which has characteristics similar to previously observed flares on II Peg. During the flare the Lexan/boron count rate increased by at least a factor of 2.5, and the minimum total duration was about 34,000 s (about 9.4 hr).