ALBERT

Description: The ROSAT mission made the first x ray survey of the entire sky using an imaging detector. Although ROSAT is a joint NASA/German project and involves direct American participation during its second phase of pointed observations, the all-sky survey remains the sole property of the German investigators. NASA grant represented the first use of ROSAT data analysis funds to support direct American participation in the ROSAT all-sky survey. The project involved a collaborative agreement between the Joint Institute for Laboratory Astrophysics (JILA) and the Max-Planck-Institut fur Extraterrestrische Physik (MPE) where JILA supplied MPE with a post-doctoral research associate with experience in the field of stellar (coronal) x ray emission to work within their ROSAT group. In return, members of the cool star research group at JILA were given the opportunity to collaborate on projects involving ROSAT all-sky survey data. Both sides have benefitted (and still benefit) from this arrangement since MPE suffers from a shortage of researchers who are interested in x ray emission from 'normal' stars and white dwarfs. MPE has also drawn upon experience in optical identification of x ray sources from the Einstein Extended Medium Sensitivity Survey in planning their own identification strategies for the ROSAT all-sky survey. The JILA cool stars group has benefitted since access to all-sky survey data has expanded the scope of their already extensive research programs involving multiwavelength observations of late-type stars. ROSAT was successfully launched on 1 June 1990 and conducted the bulk of the survey from 30 July 1990 to 25 January 1991. Data gaps in the survey have subsequently been made up. At the time of this writing (February 1992), the survey data have been processed once with the Standard Analysis Software System (SASS). A second processing will soon begin with improvements made to the SASS to correct errors and bugs found while carrying out scientific projects with data from the first processing. We outline the major research activities of Dr. Fleming over the past year (detailed accounts of his activities during the first two years of this grant can be found in the first-year and second-year status reports on this grant). Regarding the three specific projects which were proposed in the original proposal, two of them (White Dwarfs and Late M Dwarfs) are near completion. The results are described in two conference proceedings which are appended.

Description: This NASA grant covers our ADP research program, which involved detailed radiative transfer calculations of hydrodynamic models of pulsating asymptotic giant branch stars. Synthetic spectra resulting from these calculations are compared with International Ultraviolet Explorer (IUE) observations of these stars to test the validity of the models.

Description: As part of a coordinated program of multi-wavelength observations of RS CVn close binary systems, we observed 15 systems with the Very Large Array (VLA) and 10 systems with IUE, simultaneously or nearly simultaneously with the ROSAT All Sky Survey observations of these stars. Of the 22 systems observed with ROSAT, three were observed both by IUE and the VLA. Radio observations were made at 3.6, 6 and 20 cm. Of the 15 observed RS CVn systems, we detected 11 with greater than 4 sigma confidence at one or more wavelengths. The IUE observations were made within the RIASS (ROSAT-IUE All Sky Survey) program. We present the results of the VLA observations, along with the corresponding subsets of the ROSAT Position Sensitive Proportional Counter (PSPC) X-ray and Wide Field Camera (WFC) XUV survey, and RIASS IUE observations. We obtained an extended VLA/IUE/ROSAT simultaneous coverage of one system, TY Pyx, covering more than one orbital period. These observations reveal that the quiescent radio flux of TY Pyx is relatively constant over time scales of up to 7 hours, but that it did change by a factor of 3 over 24 hours, probably due to a flare on 1990 Nov. 12. The UV, XUV and X-ray fluxes do not show large day-to-day or phase-related variability. The observation of the decay phase of a radio flare on EI Eri, with no accompanying X-ray or XUV flare, suggests that the lack of a strong correlation between X-ray and radio flares previously noted for dMe flare stars holds for RS CVn systems as well. We suggest that the radio flare may have been due to a coherent emission process such as electron cyclotron emission. The simultaneous measurements presented here provide a unique test of the general correlation between radio and soft X-ray luminosities, L(sub radio) approximately L(sub x exp m) (Drake et al. 1989) with a power-law slope close to unity, which was previously derived using data obtained years apart. Our derived slopes are consistent with and thus support the general correlations between coronal and chromospheric/transition region emissions previously derived from nonsimultaneous measurements of a much larger sample of these variable sources. However, the importance of simultaneous measurements for accurate energy balance calculations is stressed.

Description: We analyze high-resolution HST spectra of the dMOe flare star AU Mic, including the profiles of the C IV 1548.2 A, 1550.8 A and Si IV 1393.8 A, 1402.8 A lines obtained with the G160M grating of the Goddard High-Resolution Spectrograph. The quiescent profiles of the C IV and Si IV lines are broad, and not simple Gaussians in shape. Flux in the C IV and Si IV lines, for example, can be measured reliably out to about +/- 200 km/s from line center. Each of the C IV and Si IV profiles can be fitted accurately by two Gaussians (one narrow and the other broad) centered on nearly the same wavelength, with the narrower component accounting for roughly 60% ofthe total integrated flux. The narrow components have similar line widths to those observed in solar active and quiet regions. The broad Gaussian components of the AU Mic line profiles are reminiscent of the broad C IV profiles observed in solar transition region explosive events, which are thought to be associated with emerging magnetic flux regions where field reconnection occurs.

Description: One hundred and thirty-six RS CV(n) active binary systems were observed with the ROSAT Position Sensitive Proportional Counter (PSPC) during the All-Sky Survey component of the mission. The entire sky was surveyed, which represents the largest sample of RS CV(n) systems observed to date at any wavelength, including X-rays. X-ray surface fluxes for the RS CV(n) systems are found to lie in the range 10 exp 4 to 10 exp 8 ergs/sq cm seconds. Surface flux as a function of (B - V) color is reported. A decrease in surface flux with increasing rotation period for the entire sample is observed. The rotation period provides the best stellar or orbital parameter to predict the X-ray surface flux level. The absence of correlation of F(x) or L(x) with Gamma is noted due to the fact that the coronal heating mechanism for these active stars must be magnetic in character, and the magnetic field depends on the interaction between convection and differential rotation inside the star. X-ray properties of the RS CV(n) systems with 6 cm radio and C IV UV emission systems is compared.