Space Telescope Goddard High Resolution Research Articles

FUSEOBSERVATIONS OF A FULL ORBIT OF SCORPIUS X-1

We obtained UV spectra of X-ray binary Scorpius X-1 in the 900-1200 A range with the Far Ultraviolet Spectroscopic Explorer over the full 0.79 day binary orbit. The strongest emission lines are the doublet of O VI at 1032,1038 A and the C III complex at 1175 A. The spectrum is affected by a multitude of narrow interstellar absorption lines, both atomic and molecular. Examination of line variability and Doppler tomograms suggests emission from both the neighborhood of the donor star and the accretion disk. Models of turbulence and Doppler broadened Keplerian disk lines Doppler shifted with the orbit of the neutron star added to narrow Gaussian emission lines with undetermined Doppler shift fit the data with consistent values of disk radius, inclination, and radial line brightness profile. The Doppler shift of the narrow component with the orbit suggests an association with the donor star. We test our line models with previously analyzed near UV spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph and archival spectra obtained with the HST Cosmic Origins Spectrograph.

VLA Observations of ζ Aurigae: Confirmation of the Slow Acceleration Wind Density Structure

Studies of the winds from single K and early M evolved stars indicate that these flows typically reach a significant fraction of their terminal velocity within the first couple of stellar radii. The most detailed spatially resolved information of the extended atmospheres of these spectral types comes from the ζ Aur eclipsing binaries. However, the wind acceleration inferred for the evolved primaries in these systems appears significantly slower than for stars of similar spectral type. Since there are no successful theories for mass loss from K and early M evolved stars, it is important to place strong empirical constraints on potential models and determine whether this difference in acceleration is real or an artifact of the analyses. We have undertaken a radio continuum monitoring study of ζ Aurigae (K4 Ib + B5 V) using the Very Large Array to test the wind density model of Baade et al. that is based on Hubble Space Telescope (HST) Goddard High Resolution Spectrograph ultraviolet spectra. ζ Aur was monitored at centimeter wavelengths over a complete orbital cycle, and flux variations during the orbit are found to be of similar magnitude to variations at similar orbital phases in the adjacent orbit. During eclipse, the flux does not decrease, showing that the radio emission originates from a volume substantially larger than R ~ (150 R⊙)3 surrounding the B star. Using the one-dimensional density model of the K4 Ib primary's wind derived from HST spectral line profile modeling and electron temperature estimates from previous optical and new HST studies, we find that the predicted radio fluxes are consistent with those observed. Three-dimensional hydrodynamic simulations indicate that the accretion flow perturbations near the B star do not contribute significantly to the total radio flux from the system, consistent with the radio eclipse observations. Our radio observations confirm the slow wind acceleration for the evolved K4 Ib component. ζ Aur's velocity structure does not appear to be typical of single stars with similar spectral types. This highlights the need for more comprehensive multiwavelength studies for both single stars, which have been sadly neglected, and other ζ Aur systems to determine if its wind properties are typical.

The Nature and Origin of the Nonvoid Lyα Cloud Population

I continue my study of the low-redshift Lyα cloud population. Previous work showed how galaxy catalogs could be used to attribute relative degrees of isolation to low-redshift Lyα clouds found in Hubble Space Telescope-Goddard High Resolution Spectrograph spectra. This enabled the separation of clouds into two distinct populations corresponding to two distinct environments, variously characterized as void/unshocked and nonvoid/shocked. Void clouds have a steep equivalent width distribution (i.e., many smaller absorbers), while nonvoid clouds have a flat distribution. I show that N-body/hydro simulations of Lyα clouds are inconsistent with observations of the clouds as a function of their environments. Simulations fail to predict the existence of significant numbers of detectable void clouds and incorrectly predict the characteristics of nonvoid clouds. Implicated in this failure is the so-called fluctuating Gunn-Peterson approximation (FGPA), which envisions that Lyα absorbers are formed in the large-scale structures of coalescing matter. A recent paper (of mine) has modeled the void cloud population as subgalactic perturbations that have expanded in response to reionization. It is notable that success in this modeling was contingent on using the more massive isothermal halo in place of the standard Navarro, Frenk, & White halo, for it was found that gravitational restraint on evaporation of baryons is key to producing detectable void absorbers. In this paper I extend my modeling of Lyα clouds to nonvoid clouds, using the same basic cloud model. In the case of voids, clouds are in a quiescent environment, while nonvoid clouds are thought of as void clouds that have accreted to the denser, turbulent intergalactic medium surrounding galaxies and are thus subjected to bow shock stripping. Model void clouds are analytically shock-stripped, and a column density spectrum (CDS) is derived, based on the same halo velocity distribution function as that used to explain the void CDS. The nonvoid CDS produced by shocked subgalactic clouds are found to be capable of producing an excellent fit to the observed nonvoid CDS without recourse to the FGPA mechanism.

Variable Na i Absorption toward Leonis: Biased Neutral Formation in the Diffuse Interstellar Medium?

We present multiepoch KPNO coude feed telescope observations of interstellar Na I and Ca II absorption toward the bright star ρ Leo. Comparisons of the Na I profiles observed over a period of 8 yr reveal significant temporal variations in the Na I column in at least one component, implying that there is structure at scales on the order of the proper motion (~12 AU). Archival Hubble Space Telescope (HST) Goddard High Resolution Spectrograph observations of the C I fine-structure excitation in the variable component suggest that the density is 20 cm-3, significantly lower than the densities inferred in past H I 21 cm and Na I studies. We suggest that the bulk of the trace neutral species are in the density peaks within an interstellar cloud. The patchy distribution of these species naturally gives rise to the large fluctuations seen on scales of 10-1000 AU in past temporal and binary studies. This picture predicts that the scales over which fluctuations will be observed vary as a function of the ionization rate of a species.

FUSE and HST ultraviolet observations of the disc wind of RWSextantis

We present Far Ultraviolet Spectroscopic Explorer (FUSE) satellite time-series data of the low-inclination, nova-like cataclysmic variable RW Sex. The data span the wavelength range between ∼905 and 1188 A, which contains the resonance lines of C iii, N iii, S iv, P v, S vi and O vi. All these spectral lines are present in the form of blueshifted absorption components, with no evidence for the lines redward of rest velocity; the FUSE data probe the fast disc-wind of RW Sex. The time-variable nature of these features is established. Substantial line profile variability is observed, confined between ∼−1000 and 0 km s−1 , and modulated on the orbital period of the system (∼0.245 d) . The fundamental characteristics of the temporal behaviour are very similar between the low and high ionization lines. The wind-dominated lines exhibit a cyclic increase in absorption optical depth which is accompanied by a shift in the maximum absorption velocity from ∼−1000 km s−1 to near zero velocity. We argue that the empirical evidence from the FUSE analysis supports an interpretation of blueshifted absorptive changes as opposed to the action of a variable (in velocity) blueshifted (perhaps disc-formed) emission component. This conclusion is further bolstered by an analysis of archival Hubble Space Telescope (HST) Goddard High Resolution Spectrograph (GHRS) data of RW Sex. We discuss a phenomenological picture of the ultraviolet (UV) line profile variability where the symmetry of a confined bipolar wind in RW Sex is broken by assuming that the outflow is oblique, perhaps because it is seated on a warped or tilted disc. The temporal UV absorption properties of non-eclipsing nova-like systems are compared.

Hubble Space TelescopeSpectroscopy of the Dwarf Nova RX Andromedae. I. The Underlying White Dwarf

We obtained Hubble Space Telescope Goddard High Resolution Spectrograph phase-resolved spectroscopic observations of the dwarf nova RX Andromedae at three times in its outburst cycle: (1) near the end of an extraordinarily deep and long dwarf nova quiescence, 3 months after the last outburst; (2) during the rise to outburst; and (3) near the end of a decline from outburst. The spectral wavelength range covered was 1149-1435 A. All of the spectra are dominated by absorption lines with weak to moderately strong emission wings due to the continued presence of disk material. Uncertainties in line velocities preclude a K1 determination or mass information. Our best-fitting model yielded Twd/1000 = 34.0 ± 0.1 K, log g = 8.0 ± 0.1, and Vrot= 600 km s-1. The Teff value is very similar to the Teff of the white dwarf in U Geminorum, but the rotational velocity appears to be higher than U Gem's value. We report approximate subsolar chemical abundances of carbon and silicon for RX And with C being 0.05 times solar and Si being 0.1 times solar while other elements are at essentially their solar values. However, accurate abundances are complicated by line emission, and we cannot exclude the possibility that the abundances of all species are essentially at the solar values. We see no evidence of thermonuclear-processed abundance ratios. If the white dwarf mass is 0.8 M☉, then the corresponding white dwarf cooling age, 4 × 106 years, is a lower limit to the age of this cataclysmic variable (CV). If the peculiar line features seen in the spectrum on the late decline from outburst are inverse P Cygni in nature, then infall velocities of ~ 2000 km s-1 are indicated during the decline from outburst. We compare the surface properties of the RX And white dwarf with the properties of other CV degenerates studied to date with the Hubble Space Telescope, the Hopkins Ultraviolet Telescope, and the International Ultraviolet Explorer.

STIS and GHRS Observations of Warm and Hot Gas Overlying the Scutum Supershell (GS 018−04+44)

We present Space Telescope Imaging Spectrograph (STIS) and Goddard High Resolution Spectrograph (GHRS) observations of interstellar UV absorption toward HD 177989, a B0 III star at 4.9 kpc in the direction l = 178, b = -119. The line of sight passes through the high-latitude ejecta of the Scutum supershell (GS 018-06+44), which is ~5° in diameter extending ~7° below the Galactic plane at a kinematic distance of ~3.5 kpc in the Scutum spiral arm. The observations with the STIS E140H and GHRS echelle B gratings provide far- and middle-UV spectra at resolutions (FWHM) of ~3 km s-1 and a signal-to-noise ratio (S/N) of ~20:1 to 50:1. The observations reveal strong and broad absorption in the lines of Si IV and C IV centered on LSR velocities of +18 and +42 km s-1 and weaker absorption from these ions near -50 and -13 km s-1. Weak absorption by N V extends over the full velocity range traced by Si IV and C IV. The +18 km s-1 high-ionization absorption likely occurs in gas ~400 pc below the Sagittarius spiral arm, while the extremely strong +42 km s-1 absorption occurs in highly ionized gas in the Scutum supershell at a distance of ~700 pc below the Galactic plane. The properties of the highly ionized gas associated with the Scutum supershell are similar to the gas found in radio loops I and IV; in both cases there is a strong enhancement in the column density of C IV without a corresponding increase in the column density of N V, which causes N(C IV)/N(N V) to be among the largest measured in the interstellar medium. The low-ionization absorption lines of N I, S II, Si II, and Fe II produce narrow absorption features at +37, +40 km s-1 and +55, +60 km s-1. The strength and kinematic properties of these absorption features bear no resemblance to those expected for the high-latitude neutral cloud seen in the H I 21 cm line. This may be due to the relatively low angular resolution (FWHM ~21') of the 21 cm observations. The kinematic relationships among the high-ionization and low-ionization absorption lines observed in the UV suggest a related origin in a hot-warm gas interface region. We are possibly seeing the warm gas in the swept-up shell surrounding a region where hot gas is being vented into the halo. In the warm gas, N(N I)/N(S II) ~0.01 solar, which implies a similar value for N(H0)/[N(H0) + N(H+)]. The warm neutral and ionized gas in the matter overlying the Scutum supershell has values of Si /S and Fe /S roughly similar to those found in the warm neutral medium of the Galactic disk in the vicinity of the Sun. While there has been grain processing in the ejecta of the Scutum supershell, the processing has not been complete. Based on observations of interstellar C IV and Si IV at high S/N and high resolution toward four very distant stars, we determine that highly ionized gas absorption components occur at a frequency of ~1 component kpc-1. The strongest components are associated with lines of sight that pass over or under spiral arms or that pass though Galactic supershells.

Episodic absorption in the outflow of the old nova V603 Aquilae

We report on the time-dependent behaviour of ultraviolet spectral lines in Hubble Space Telescope Goddard High-Resolution Spectrograph data of the classical nova V603 Aql. In particular, episodic blueshifted absorption (extending to ∼-2500 km s−1) is present, with a variability time-scale down to ∼1 min. The data provide a rare opportunity to study the rapid evolution of absorption structures that may be associated with accretion-disc winds in cataclysmic variables. At least three absorption events are recorded (at blueward velocities only) over ∼5 h, each lasting ∼10–15 min. The derived velocity, acceleration and optical depth properties provide an empirical picture of stochastically variable structures in the outflow, with no evidence for short-term (less than ∼1 h) cyclic or modulated behaviour in the overall absorption properties. In contrast, the emission components of the ultraviolet resonance lines are very stable in velocity and strength in this low-inclination system. On at least two occasions there is an intriguing short-term ‘flare’ in the ultraviolet continuum flux (of up to ∼40 per cent). Though there is no clear one-to-one relation in these data between the continuum fluctuations and the occurrence of the absorption events, the time-scales for the two variable phenomena are essentially the same. The irregular absorption episodes in the ultraviolet data of V603 Aql presently defy a clear physical interpretation. Their overall characteristics are discussed in the context of instabilities in radiation-pressure-driven disc winds.

Episodic absorption in the outflow of the old nova V603 Aquilae

We report on the time-dependent behaviour of ultraviolet spectral lines in Hubble Space Telescope Goddard High-Resolution Spectrograph data of the classical nova V603 Aql. In particular, episodic blueshifted absorption (extending to similar to -2500 km s(-1)) is present, with a variability time-scale down to similar to1 min. The data provide a rare opportunity to study the rapid evolution of absorption structures that may be associated with accretion-disc winds in cataclysmic variables. At least three absorption events are recorded (at blueward velocities only) over similar to5 h, each lasting similar to 10-15 min. The derived velocity, acceleration and optical depth properties provide an empirical picture of stochastically variable structures in the outflow, with no evidence for short-term (less than similar to 1h) cyclic or modulated behaviour in the overall absorption properties. In contrast, the emission components of the ultraviolet resonance lines are very stable in velocity and strength in this low-inclination system. On at least two occasions there is an intriguing short-term 'flare' in the ultraviolet continuum flux (of up to similar to 40 per cent). Though there is no clear one-to-one relation in these data between the continuum fluctuations and the occurrence of the absorption events, the time-scales for the two variable phenomena are essentially the same. The irregular absorption episodes in the ultraviolet data of V603 Aql presently defy a clear physical interpretation. Their overall characteristics are discussed in the context of instabilities in radiation-pressure-driven disc winds.

An Optical Region Elemental Abundance Analysis of the HgMn Type Star HR 7775

Optical region spectra of the chemically peculiar HgMn type star HR 7775 have been analyzed for the determination of elemental abundances and spectral line identification as a complementary study to the analysis of Hubble Space Telescope Goddard High Resolution Spectrograph spectra. The spectra were obtained with the SOFIN echelle spectrograph on the Nordic Optical Telescope at nominal resolving powers of R = 25,000, 80,000, and 170,000 and signal-to-noise ratios typically in excess of 100 : 1. The overall nature of the elemental abundance distribution is similar to other cool, HgMn stars; somewhat enhanced abundances for the iron-group elements, with progressively stronger enhancements for heavier elements. Of particular note are the presence of lines from the rare-earth spectra Nd III and Pr III, and the heavy elements Pt, Au, Hg, Tl, and Bi. The isotopic mixture for several lines of mercury and platinum has been investigated. For mercury a possible difference is found between the mixtures as derived from lines of Hg I and Hg II. Three lines of Pt II display the same mixture, which is different from that found from lower excitation lines at ultraviolet wavelengths. We present new laboratory Fourier Transform spectrometer measurements for isotopic and hyperfine structure components of Hg I λ4046 and 4358 and Hg II λ3984 A.

Search for Proton Aurora and Ambient Hydrogen on Io

A search was conducted using the Hubble Space Telescope (HST) Goddard High Resolution Spectrograph (GHRS) in 1994 August for Iogenic H Lyα emission predicted from electron capture by precipitating trapped magnetospheric protons. The Doppler-shifted diffusely reflected solar Lyα component was detected in the combined high-resolution spectra, partly resolved from the geocoronal emission. This component had a disk-averaged intensity of 2.5 ± 0.7 kR. Io's corresponding geometric albedo in this line, which must include the effects of atmospheric SO2 absorption, was 0.055 ± 0.015. Iogenic emission from ambient H atoms was probably also detected, with a disk-averaged intensity greater than 280 R, most likely ≈485 R, which suggests a significant column of atmospheric or coronal H. The dominant brightness of the reflected solar line in our GHRS data supports the proposed hypothesis that the primary source of Io's H Lyα emission observed more recently (1997–1998) by the HST Space Telescope Imaging Spectrograph at low spectral resolution is diffusely reflected sunlight, rather than Iogenic H. The consequence is a significant increase in the absorbing SO2 column of Io's trailing atmosphere as Jupiter moved 0.37–0.44 AU closer to the Sun; this could result from the higher SO2 equilibrium vapor pressure over the 4–5 K warmer ice. Averaging low-resolution HST GHRS archival far-ultraviolet spectra of Io obtained during 1994–1996 provided a 2 σ upper limit of 5.2 R A-1 for the disk-averaged intensity of Lyα emission from energetic (27–223 keV) precipitating protons. This corresponds to an estimated upper limit of 47 R, integrated over the red Doppler wing of the thermal distribution for protons of mean energy 30–60 keV. This is close to estimates for a proton aurora generated in the SO2 column of Io's trailing atmosphere, indicating that SO2 may be Io's dominant atmospheric gas. A 2 σ upper limit of 123 R per line is derived for nearby fluorescence of extreme-UV radiation by ambient atmospheric sulfur.

A Uniform Analysis of Boron in F and G Disk Dwarfs fromHubble Space TelescopeArchival Spectra

The boron abundance is derived for 14 near-solar metallicity F and G dwarfs from the archived data set of spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph in the region of the B I resonance line near 2497 A. These abundances are derived in a uniform way with respect to recent work on solar boron. The synthetic spectra of the B I region were calculated by means of an improved linelist to fit the spectra of the stars spanning a range in Teff between 5650 and 6700 K and metallicity between [Fe/H] = -0.75 and +0.15. The synthetic spectra were computed considering all major sources of metal opacities and, in particular, an updated lower value of Mg I b-f opacity at 2500 A was used in the calculations. Adopting Li and Be abundances from the literature, significant B depletions (~0.3-0.5 dex) are found only for the two stars with the most extreme Li depletions (≥2.5 dex) and Be depletions (≥1.5 dex), although the trend of B versus Be indicates that mild B depletions may exist in many of the stars. These results are in concordance with the Boesgaard et al. conclusion that a slow mixing in the outer envelope is responsible for depletions of Li, Be, and B. Stars with less severe Li and Be depletions exhibit roughly solar [B/Fe] ratios. A comparison of the boron abundances from the disk stars (with undepleted boron) with metal-poor halo dwarfs reveals that B is linearly related to Fe over the entire range of metallicities from [Fe/H] ~ -2.5 to 0.1. The B/Be ratio found for stars with near-solar metallicities and no Li depletion is B/Be = 27 ± 5, equal to the solar ratio (B/Be = 23).

Hercules X‐1: Empirical Models of Ultraviolet Emission Lines

The UV emission lines of Hercules X-1, resolved with the Hubble Space Telescope (HST) Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph, can be divided into broad (FWHM ? 750 km s-1) and narrow (FWHM ? 150 km s-1) components. The broad lines can be unambiguously identified with emission from an accretion disk which rotates prograde with the orbit. The narrow lines, previously identified with the X-ray-illuminated atmosphere of the companion star, are blueshifted at both = 0.2 and = 0.8, and the line flux at = 0.2 is ?0.2 of the flux at = 0.8. Line ratio diagnostics show that the density of the narrow-line region is log ne = 13.4 ? 0.2, and Te = 1.0 ? 0.2 ? 105 K. The symmetry of the eclipse ingress suggests that the line emission on the surface of the disk is left-right symmetric relative to the orbit. Model fits to the O V, Si IV, and He II line profiles agree with this result, but fits to the N V lines suggest that the receding side of the disk is brighter. We note that there are narrow absorption components in the N V lines with blueshifts of ?500 km s-1.

Digging Deeper in the Coronal Graveyard: Postscript

An X-ray upper limit—from the ROSAT High Resolution Imager—is presented for Corvi (HD 105707), a K2 giant that lies in the noncoronal zone of the Hertzsprung-Russell diagram, but which previously was detected by the Hubble Space Telescope Goddard High Resolution Spectrograph in far-ultraviolet coronal proxies. The new measurement strengthens the anticorrelation between coronal X-rays and λ1380 carbon monoxide emission among the red giants.

Sleuthing the Dynamo. II.Hubble Space TelescopeGoddard High Resolution Spectrograph Observations of Solar‐Type Dwarfs in Young Galactic Clusters

Far-ultraviolet (1150-1670 A) spectra of three solar-type dwarfs in the young galactic clusters α Persei and the Pleiades were obtained with the Hubble Space Telescope Goddard High-Resolution Spectrograph (G140L mode). Time series of Si IV λ1393 show erratic variability on timescales of tens of minutes. An X-ray/C IV flux-flux diagram displays a power-law slope of ~2, up to the level of the most active cluster stars. These fall systematically below the extrapolation owing to X-ray saturation. In rotation-activity diagrams, the X-rays plateau above ~15 km s-1 (P ~ 3 days), while C IV continues to rise until ~35-50 km s-1 (P ~ 1-1.5 days). Such behavior is significant for understanding the magnetic dynamo at high rotational velocities and is relevant for predicting the ionizing environment bathing newly formed planets around low-mass main-sequence stars.

The Diffuse Interstellar Clouds toward 23 Orionis

Spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph are combined with high-resolution optical spectra and UV spectra from Copernicus to study the abundances and physical conditions in the diffuse interstellar clouds seen along the line of sight to the star 23 Ori. Multiple absorption components are present for each of several distinct types of gas, which are characterized by different relative abundance and depletion patterns and physical conditions.?????Strong low-velocity (SLV) absorption, due to cool, moderately dense neutral gas and representing about 92% of the total N(H I), is seen for various neutral and singly ionized species at +20 km s-1 v? +26 km s-1. Most typically severely depleted species are less depleted by factors of 2-4, compared to the cold, dense cloud pattern found, for example, in the main components toward ? Oph.For the two strongest SLV components, T ~ 100 K and the thermal pressure log (nHT) ~ 3.1 cm-3 K; we thus have nH ~ 10-15 cm-3 and a total thickness of 12-16 pc. The adopted average SLV electron density, ne = 0.15 ? 0.05 cm-3, implies a relatively large ne/nH ~ 0.01 and thus some ionization of hydrogen in these predominantly neutral components.?????Weaker low-velocity (WLV) absorption, probably largely due to warmer neutral gas, is seen primarily for various singly ionized species at 0 km s-1 v? +30 km s-1. The depletions in the WLV gas are typically less severe by a factor of 2-3 than in the SLV gas and are somewhat similar to the warm cloud pattern seen in lines of sight with low reddening, low mean density, and/or low molecular fraction. If T ~ 3000 K for the WLV components, then we have log(nHT) ~ 4.7-4.8 cm-3 K, nH ~ 15-20 cm-3, ne ~ 0.2 cm-3, ne/nH ~ 0.01, and a total thickness of 0.7-0.9 pc.?????Absorption from a number of singly and doubly ionized species, perhaps due to a radiative shock, is seen at -108 km s-1 v? -83 km s-1. While the depletions in these ionized components are uncertain owing to unobserved ionization stages, aluminum (typically severely depleted) is probably depleted there by only a factor ~3, even at cloud velocities in excess of 100 km s-1. The individual high-velocity components typically have T ~ 8000 ? 2000 K, ne = nH ~ 0.4-0.5 cm-3, thermal pressure log(2neT) ~ 3.7-4.0 cm-3 K, and thicknesses of order 0.1 pc.?????Weak absorption components from ionized (H II) gas are seen in C II, Mg II, and Si III at intermediate velocities (-43 km s-1 v? -4 km s-1). Broad, weak absorption from the higher ions S III, C IV, Si IV, and N V is centered at -5 km s-1 v? +6 km s-1. No obvious absorption is discerned from a circumstellar H II region around 23 Ori itself.?????The large range in ne (from 0.04 to 0.95 cm-3) derived independently from nine pairs of neutral and singly ionized species in the SLV gas suggests that additional processes besides simple photoionization and radiative recombination affect the ionization balance. Charge exchange with protons may reduce the abundances of S I, Mn I, and Fe I; dissociative recombination of CH+ may help to enhance C I. The large apparent fractional ionization in the SLV and WLV gas may be due to an enhanced flux of X-rays in the Orion region, to mixing of neutral and ionized gas at the boundary of the Orion-Eridanus bubble, or perhaps (in part) to charge exchange between singly ionized atomic species and large molecules (in which case the true ne would be somewhat smaller). Comparisons of the SLV depletions and nH with those found for the strong component B (v? ~ -14 km s-1) blend toward ? Oph hint at a possible relationship between depletion and local density for relatively cold interstellar clouds. Calcium appears to be more severely depleted in warm, low density gas than has generally been assumed.?????An appendix summarizes the most reliable oscillator strengths currently available for a number of the interstellar absorption lines analyzed in this work.

Stellar Masses, Kinematics, and White Dwarf Composition for Three Close DA+dMe Binaries

We determine the mass functions and mass ratios for three close white dwarf plus red dwarf binaries (EUVE J0720-317, 1016-053, and 2013+400). Hubble Space Telescope Goddard High-Resolution Spectrograph spectra of the He II ?1640 and C IV ?1550 spectral lines trace the white dwarf orbital motion, and Hamilton Spectrograph echelle spectra (Lick Observatory) and lower dispersion spectra trace the red dwarf orbital motion. The data sets allow us to measure orbital periods and velocities, as well as the white dwarf gravitational redshifts. The red dwarf and white dwarf mass estimates obtained from a combination of independent mass measurements for the white dwarf stars and our new orbital elements help constrain probable evolutionary outcomes. We find that EUVE J0720-317 will probably come into contact within a Hubble time and that the mass transfer will be unstable on a dynamical time. We also conclude that the much lower secondary masses in EUVE J1016-053 and EUVE J2013+400 exclude the possibility of significant interaction in these systems. We also present new helium and carbon photospheric abundance measurements in the three white dwarfs. The white dwarf atmospheric composition may show the effects of accretion of red dwarf mass-loss material onto its surface. Finally, we study the kinematics of the systems, and we also show that the white dwarf in EUVE?J1016-053 is part of a quadruple system.

The Boron Abundance of the Orion G‐Dwarf Member BD −05o1317

The boron abundance is derived for the young Orion solar-type member BD -05°1317 from Hubble Space Telescope Goddard High Resolution Spectrograph spectra of the B I resonance lines near 2497 A. The abundance of log (B) = 2.1 ± 0.2 is ~0.6-0.7 dex below solar. As this young pre-main-sequence star has an undepleted lithium abundance, such a low boron abundance in a near-solar metallicity star is unexpected. No simple explanation apparently accounts for the low boron abundance observed for this star. A comparison of the boron and oxygen abundances in BD -05°1317 with those of other near-solar metallicity disk stars suggests that there might be a large scatter (~0.8 dex) in the boron abundance at a given oxygen abundance. Such a scatter also has been reported in the literature for beryllium at a given metallicity.

Masses and Other Parameters of the Post–Common Envelope Binary BE Ursae Majoris

The binary star BE Ursae Majoris is recently emerged from the common envelope phase; indeed, the hot sdO/DAO component is the central star of the associated planetary nebula. As such, BE UMa represents an important test case of stellar evolution theory. Using the Hubble Space Telescope (HST) Goddard High Resolution Spectrograph (GHRS), we measured the radial velocity amplitude of the He II λ1640 absorption line from the sdO/DAO component of this eclipsing system. Combining our results with those of Crampton, Cowley, & Hutchings, we determine stellar masses in units of solar mass as follows: for the sdO, the mass is 0.70 ± 0.07, and that of the secondary star is 0.36 ± 0.07, where we report the 1 σ value for all errors. The separation between the component stars is 7.5 R☉ ± 0.5 R☉ and is insensitive to small changes in inclination angle due to the near edge-on viewing angle of 84° ± 1°. Using these values, we modeled the eclipse light curve. Our results matched observed UBVR light curves of Wood and coworkers only if the modeled secondary star radius of 0.72 R☉ ± 0.05 R☉ has nearly double the radius expected from the main-sequence mass-radius relation. The secondary star has thus not yet relaxed to thermal equilibrium since the common envelope phase ended ~104 yr ago. Using the λ1640 absorption-line profile and the surrounding continuum, we also were able to constrain the sdO helium abundance as log nHe=-1.1 ± 0.2 and log nFe < 1. Our results support the sdO/DAO log g ~6.5 surface gravity and Teff~100,000 K values of Liebert et al. and are consistent with the post-AGB evolutionary track. Our best estimate of the distance to the BE UMa system is 2000 pc.

Goddard High‐Resolution Spectrograph Observations of the BiiiResonance Doublet in Early B Stars: Abundances and Isotope Ratios

Boron abundances and isotope ratios in two early B stars have been measured by using the Hubble Space Telescope's Goddard High-Resolution Spectrograph (GHRS) in order to observe the B III resonance doublet near 2066 A. We also report new experimental and theoretical results for the wavelengths, isotope shift, and hyperfine structure of these boron lines. In HD 886 (γ Pegasi; B2 IV), and HD 35299 (B1 V) the abundance of boron is about a factor of 2 lower than that inferred from solar system meteorites. The 11B/10B isotope ratio in HD 886 is determined to be 4.7, and for HD 35299 a value of 3.7 is found. These values are consistent with the solar system isotope ratio. In a third star, HD 3360 (ζ Cassiopeiae; B2 IV), our GHRS observations show that the boron abundance is a factor of 40 below the solar system abundance. Our results for HD 886 and HD 35299 appear to be consistent with little dispersion in the initial boron-to-oxygen ratio among Population I stars and a universal 11B/10B isotope ratio. However, the abundance measured for HD 3360 shows that either some stars suffer significant boron depletion while still in the core-hydrogen burning phase of their evolution, or there is indeed a very wide variation in initial Population I boron abundances. A much-improved understanding of boron astration in early B stars will be required before this question can be resolved.