ALBERT

Description: We report on our ongoing program to measure the deuterium/hydrogen (D/H) ratio and interstellar gas properties along many lines of sight through the local interstellar medium using the HST Goddard High-Resolution Spectrograph. For the line of sight towards Capella (12.5 pc) we had previously found D/H = 1.65(+0.07, -0.18) x 10(exp -5), T = 7000 K, and turbulent velocity 1.66 km/s. These quantities were determined by modeling the interstellar hydrogen and deuterium Lyman alpha lines and the resonance lines of Fe II and Mg II against the background stellar emission-line profiles. We now report on our preliminary analysis of these spectral lines for the line of sight toward Procyon (3.5 pc). We find that D/H = 1.40 +/- 0.05 x 10(exp -5) (+/- 3 sigma) photometric random errors only), which is lower than but perhaps consistent with the value of D/H derived for the Capella line of sight when the systematic errors associated with the uncertain intrinsic Procyon emission line are included. Further analysis of this and other lines of sight are planned to determine whether the D/H ratio varies within the local interstellar medium. We infer the primordial value of D/H from Galactic evolution models and comment on the derived baryon density of the Universe.

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: Observations from IUE were used to study the structure of the lower chromosphere of AR Lacertae in the light of Mg II k. Sequences of LWR/P-HI images distributed around the binary period at three epochs were obtained. Discrete plage-like regions of enhanced Mg II surface flux in this system are identified. There are temporal variations in the Mg II flux on timescales of hours as well as substantial changes in chromospheric morphology on timescales of years. Even with the limited S/N attainable with the IUE, one can map the gross structures of active stellar atmospheres. With such information, one can begin to study the true 3-D structure of the atmospheres of late-type stars.

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: The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. Ultraviolet photons influence the atmospheric temperature profiles and production of potential biomarkers on Earth-like planets around these stars. At present, little observational or theoretical basis exists for understanding the ultraviolet spectra of M dwarfs, despite their critical importance to predicting and interpreting the spectra of potentially habitable planets as they are obtained in the coming decades. Using observations from the Hubble Space Telescope, we present a study of the UV radiation fields around nearby M dwarf planet hosts that covers both far-UV (FUV) and near-UV (NUV) wavelengths. The combined FUV+NUV spectra are publicly available in machine-readable format. We find that all six exoplanet host stars in our sample (GJ 581, GJ 876, GJ 436, GJ 832, GJ 667C, and GJ 1214) exhibit some level of chromospheric and transition region UV emission. No "UV-quiet" M dwarfs are observed. The bright stellar Lyman-alpha emission lines are reconstructed, and we find that the Lyman-alpha line fluxes comprise approximately 37%-75% of the total 1150-3100 A flux from most M dwarfs; approximately greater than 10(exp3) times the solar value. We develop an empirical scaling relation between Lyman-alpha and Mg II emission, to be used when interstellar H I attenuation precludes the direct observation of Lyman-alpha. The intrinsic unreddened flux ratio is F(Lyman-alpha)/F(Mg II) = 10(exp3). The F(FUV)/F(NUV) flux ratio, a driver for abiotic production of the suggested biomarkers O2 and O3, is shown to be approximately 0.5-3 for all M dwarfs in our sample, greather than 10(exp3) times the solar ratio. For the four stars with moderate signal-to-noise Cosmic Origins Spectrograph time-resolved spectra, we find UV emission line variability with amplitudes of 50%.500% on 10(exp2)-10(exp3) s timescales. This effect should be taken into account in future UV transiting planet studies, including searches for O3 on Earth-like planets. Finally, we observe relatively bright H2 fluorescent emission from four of the M dwarf exoplanetary systems (GJ 581, GJ 876, GJ 436, and GJ 832). Additional modeling work is needed to differentiate between a stellar photospheric or possible exoplanetary origin for the hot (T(H2) approximately equal to 2000-4000 K) molecular gas observed in these objects.

Description: Extrasolar planets orbiting M-stars may represent our best chance to discover habitable worlds in the coming decade. The ultraviolet spectrum incident upon both Earth-like and Jovian planets is critically important for proper modeling of their atmospheric heating and chemistry. In order to provide more realistic inputs for atmospheric models of planets orbiting low-mass stars, we present new near- and far-ultraviolet (NUV and FUV) spectroscopy of the M-dwarf exoplanet host GJ 876 (M4V). Using the COS and STIS spectrographs on board the Hubble Space Telescope, we have measured the 1150-3140 A spectrum of GJ 876. We have reconstructed the stellar H1 Ly alpha emission line profile, and find that the integrated Ly alpha flux is roughly equal to the rest of the integrated flux (1150-1210 A + 1220-3140 A) in the entire ultraviolet bandpass (F(Ly alpha)/F(FUV+NUV) equals approximately 0.7). This ratio is approximately 2500x greater than the solar value. We describe the ultraviolet line spectrum and report surprisingly strong fluorescent emission from hot H2 (T(H2) greater than 2000 K). We show the light curve of a chromospheric + transition region flare observed in several far-UV emission lines, with flare/quiescent flux ratios greater than or equal to 10. The strong FUV radiation field of an M-star (and specifically Ly alpha) is important for determining the abundance of O2--and the formation of biomarkers-in the lower atmospheres of Earth-like planets in the habitable zones of low-mass stars.

Description: We have used the Goddard High Resolution Spectrometer (GHRS) to observe the spectoscopic binary system Capella (G8 III + G1 III). Exposures with the G140L, G140M, G160M, G200M, and echelle gratings provide emission line profiles with unprecedented signal-to-noise and spectral resolving power (lambda/Delta-lambda) up to 92,000. Multi-Gaussin fits to the line profiles show that the hotter star contributes 60%-70% of the total flux in the chromospheric O I and Mg II resonance lines, but about 90% of the flux in the Si III, Si IV, and C IV lines formed in the transition region at T less than or = 10(exp 5) K. We find clear evidence that the emission lines from the hotter star are systemtically redshifted relative to the photosphere with Doppler shifts of 5 +/- 1 km/s for the +9 +/- 3 km/s in the chromospheric Mg II and O I lines, respectively, increasing to +24 +/- 5 km/s for the transition region Si IV 1393.8A line. The multi-Gaussian fits to permitted transition region lines of SI III, Si IV, C IV, and N V indicate the presence of three components: moderately broad lines formed in the transition region of the hotter star (component H), narrow lines formed in the transition region of the cooler star (component C), and very broad lines that we think are formed in microflares on the hotter star (component B). The He II 1640.4 A feature has an broad profile, which indicates that it is formed by collisional excitation primarily from the hotter star, and a weak narrow component that we interpret as due to radiative recombination on the cooler star. We observed spin-forbidden emission lines of C III), O III), Si III), O IV), O V), and S IV) that are sensitive to electron density. Fainter members of the O IV) multiplet and all of the S IV) lines have never before been seen in any star than the Sun. We determine electron densities in the transition regions of the Capella stars using lines ratios of O IV) lines and emission measure analysis. The emission measures are self-consistent only when the fluxes from each emitting component are considered separately. In particular, the transition region abundance distributions appear to be different on the two stars, and the spin-forbidden lines were not detected in the B component. The emission measures for component H (the G1 star) are consistent with a constant electron pressure (or hydrostatic equilibrium) transition region with P(sub e) = 10(exp 15 + 0.1)/cu cm K and possibly solar 'coronal' abundances.

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: Our analysis of high-resolution Goddard High-Resolution Spectrograph (GHRS) spectra of late-type stars shows that the Si IV and C IV lines formed near 10(exp 5) K can be decomposed into the sum of two Gaussians, a broad component and a narrow component. We find that the flux contribution of the broad components is correlated with both the C IV and X-ray surface fluxes. For main-sequence stars, the widths of the narrow components suggest subsonic nonthermal velocities, and there appears to be a tight correlation between these nonthermal velocities and stellar surface gravity [xi(sub nc) varies as g(sup (-.68 +/-.07))]. For evolved stars with lower surface gravities, the nonthermal velocities suggested by the narrow components are at or just above the sound speed. Nonthermal velocities computed from the widths of the broad components are always highly supersonic. We propose that the broad components are diagnostics for microflare heating. Turbulent dissipation and Alfven waves are both viable candidates for the narrow component heating mechanism. A solar analog for the broad components might be the 'explosive events' detected by the High-Resolution Telescope and Spectrograph (HRTS) experiment. The broad component we observe for the Si IV lambda 1394 line of alpha Cen A, a star that is nearly identical to the Sun, has a FWHM of 109 +/- 10 km/s and is blueshifted by 9 +/- 3 km/s relative to the narrow component. Both of these properties are consistent with the properties of the solar explosive events. However, the alpha Cen A broad component accounts for 25% +/- 4% of the total Si IV line flux, while solar explosive events are currently thought to account for no more than 5% of the Sun's total transition region emission. This discrepancy must be resolved before the connection between broad components and explosive events can be positively established. In addition to our analysis of the Si IV and C IV lines of many stars, we also provide a more thorough analysis of all of the available GHRS data for alpha Cen A (G2 V) and alpha Cen B (K1 V). We find that the transition region lines of both stars have redshifts almost identical to those observed on the Sun: showing an increase with line formation temperature up to about log T = 5.2 and then a rapid decrease. Using the O IV] lines as density diagnostics, we compute electron densities of log n(sub e) = 9.65 +/- 0.20 and log n(sub e) = 9.50 +/- 0.30 for alpha Cen A and alpha Cen B, respectively.