IUE Absorption-Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early-Type Stars
We present measurements of Galactic interstellar Al III, Si IV, and C IVabsorption recorded in high-resolution archival ultraviolet spectra of164 hot early-type stars observed by the International UltravioletExplorer (IUE) satellite. The objects studied were drawn from the listof hot stars scheduled to be observed with the Far UltravioletSpectroscopic Explorer (FUSE) satellite as part of observing programsdesigned to investigate absorption by O VI in the Galactic disk andhalo. Multiple IUE echelle-mode integrations have been combined toproduce a single ultraviolet (1150-1900 Å) spectrum of each starwith a spectral resolution of ~25 km s-1 (FWHM). Selectedabsorption-line profiles are presented for each star along with plots ofthe apparent column density per unit velocity for each line of the AlIII, Si IV, and C IV doublets. We report absorption-line equivalentwidths, absorption velocities, and integrated column densities based onthe apparent optical depth method of examining interstellar absorptionlines. We also determine column densities and Doppler parameters fromsingle-component curve-of-growth analyses. The scientific analysis ofthese observations will be undertaken after the FUSE satellite producessimilar measurements for absorption by interstellar O IV, Fe III, S III,and other ions. Based on archival data from observations obtained withthe International Ultraviolet Explorer (IUE) satellite sponsored byNASA, SERC, and ESA.
|
An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
|
Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
|
Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
|
Element depletions in interstellar gas. II - The density-dependence of calcium and sodium depletions
The behavior of Ca and Na depletions in interstellar gas is studied inview of complementary, high resolution optical and UV spectra for ninestars in the same region of sky. The optical absorption lines of Ca IIand Na I are analyzed to determine their column densities in eachline-of-sight, and the UV data are used to estimate H column densitiesand to perform ionization balance calculations from which thecontributions to Ca and Na abundances from unobserved ion stages can bededuced. The resultant element depletions relative to solar abundancesare compared with estimates of the average interstellar gas density indifferent lines-of-sight. The depletion of Ca is a strong function ofpresent interstellar medium densities, while Na appears to be depletedby a constant factor of about 4 over the range of densities sampled.Shock sputtering of grains plays an important role in determiningelement depletions, even in low velocity interstellar gas.
|
A study of element depletions in interstellar gas
Optical and ultraviolet studies have shown that most elements in the gasphase of the interstellar medium are underabundant relative to the solarcomposition. The missing gas atoms are assumed to be contained ininterstellar grains. The study of the depletion of interstellar elementsin the gas phase provides, in this connection, a means for studying thecomposition of interstellar dust and possibly its formation/destructionmechanisms. The present investigation is concerned with ultravioletobservations of interstellar gas in the lines-of-sight toward sevenstars. The high resolution ultraviolet spectra of the seven stars wereobtained with the International Ultraviolet Explorer (IUE) satellite.The results of the investigation indicate that, at least for certainelements, the level of depletion depends on present densities in theinterstellar medium. The implications of this conclusion are examined.
|
Element depletions in interstellar gas
High resolution IUE observations were analyzed to derive elementdepletions in low velocity interstellar gas toward several stars in thesame region of sky. The results were combined with previous observationsto determine how the level of depletion of a given element depends onpresent densities in the interstellar medium. The density dependence ofdepletions is found to vary from element to element; this variation isdiscussed in light of depletion models. Results indicate that sputteringof grains in interstellar shocks is important in determining elementdepletions.
|
Infrared photometry of southern early-type stars
The paper presents infrared photometry tied to the JHKL (1.2-3.5microns) broadband photometric system for 229 southern early-type stars.To determine data for stars of low reddening intrinsic visual-IR colorindices were used; the E(V-K)/E(B-V) diagram was applied to evaluate theratio of total selective extinction. A mean value of R = 3.12 plus orminus 0.05 was found for stars close to the galactic plane, but a highervalue of R (about 4.0) applies to the Orion and Sco-Oph regions.Infrared two-color diagrams were used to investigate the occurrence ofinfrared excess emission in different classes of shell star; no excesseswere found for supergiants or Of stars. It is concluded that theanomalous position HD 164740 in the two-color diagrams is produced bystrong infrared excess and not by a peculiar extinction law.
|
Spectral classification from the ultraviolet line features of S2/68 spectra. V - Supplement series
The paper presents the ultraviolet classification of more than 450 B-Aand F spectra obtained with the sky survey telescope mounted on the TD1satellite. Concerning abnormal objects, attention is given to the Bestars, the binary stars, the helium weak stars, and the lambda Booobjects. With regard to Be stars, it is concluded that the 1930 Awavelength feature is linked to the existence of either shell structuresor Fe II emission lines in the visual spectral range. In addition, it issuggested that stellar spectra at wavelengths of 1410, 1610-20 and 2400A are equivalent to the He-weak group in the classical range.
|
H-beta photometry of southern early-type stars and galactic structure away from the plane
H-beta photoelectric photometry is reported for 165 early-type stars atintermediate and high galactic latitudes. The data are combined withearlier UBV and spectroscopic results to determine the stellar spacedistribution. Stars of type B2 and earlier, at distances of up to 1 kpcfrom the galactic plane, appear to follow spiral structure in the plane.The available material, particularly the derived color excesses, is usedto select a number of blue stars which may be subluminous.
|
UBV photometry of southern early-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974MNRAS.168..451H&db_key=AST
|
UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]
Not Available
|
INHABITED SKY
