New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
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The standard theory of extinction and the spectrum of stars with very little reddening
This paper examines the relationship between spectra of stars of samespectral type with extremely low reddenings. According to the standardtheory, the relationship between the spectrum of stars with samespectral type and small, but different reddenings should be different inthe optical and in the UV. This difference is not observed: the ratio ofthe spectra of two stars in directions where the reddening is largeenough to be detected and low enough not to give a noticeable2200Å bump is an exponential of /1/λ from the near-infraredto the far-UV. This result is in conformity with the ideas introduced inpreceding papers: the exponential optical extinction extends to the UV,and the spectrum of stars with enough reddening is contaminated by lightscattered at close angular distance from the stars. An application willbe the determination of the spectrum of a non-reddened star from thespectrum of a star of same spectral type with little reddening.
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Rotational velocities of B-type stars from the Edinburgh-Cape survey
The projected rotational velocity distribution for a sample of 34 highGalactic latitude B-type stars from the Edinburgh-Cape Faint Blue ObjectSurvey is presented to investigate the evolutionary status of the groupas a whole. Statistical analyses of the distribution show it to besimilar to that expected if the sample contained mainly normalPopulation i early B-type stars, although a contamination of up to 20 %by evolved stars cannot be ruled out. This implies that a large fractionof the sample consists of normal Population i B-type stars similar tothose found in the Galactic disk. Possible mechanisms explaining thepresence of these stars in the halo are briefly discussed.
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Supplementary southern standards for UBV(RI)c photometry
We present UBV(RI)c photometry for 80 southern red and blue stars foruse as additional standards. The data are tied to the Johnson UBV andCousins (RI)c systems and extend the range of the available stars forcolor equation determination, especially in (U-B) for blue stars and(V-R) and (V-I) for red stars. Comparisons with published data are madeand particularly good agreement is found with Bessell for the red(Gliese) stars.
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High-resolution spectroscopic observations of B-type stars from the Edinburgh-Cape survey
High-resolution spectroscopy has been obtained for 25 high-latitudestars identified from the Edinburgh-Cape faint blue object survey ashaving B-type spectra. Five objects are found to be subluminous(subdwarf or horizontal branch), chemically peculiar, or later thanB-type. We present model atmosphere analyses for the other 20 objects,and conclude that 17 stars exhibit stellar properties typical of youngB-type dwarfs. Photospheric abundances determined for a subset of starswere also found to be consistent with a Population I composition.Furthermore, we believe EC 05229-6058 to be an evolved object currentlyon the post-asymptotic giant branch phase, whilst EC 20411-2704 and11074-2912 are consistent with being zero-age horizontal branch andpost-blue horizontal branch objects respectively. A kinematic analysisof the normal stars implies that all could have formed in, and have beensubsequently ejected from, the Galactic disc.
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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.
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Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
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A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
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Highly-evolved stars
The ways in which the IUE has proved useful in studying highly evolvedstars are reviewed. The importance of high dispersion spectra forabundance analyses of the sd0 stars and for studies of the wind from thecentral star of NGC 6543 and the wind from the 0 type component of VelaX-1 is shown. Low dispersion spectra are used for absolutespectrophotometry of the dwarf nova, Ex Hya. Angular resolution isimportant for detecting and locating UV sources in globular clusters.
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Some optical observations of HD 192273 - A proposed identification for a possible EUV source
Spectroscopic and photometric observations have been made of thehigh-latitude B2 V star HD 192273, which had been proposed as in(uncertain) identification for an (uncertain) EUV detection. The opticalobservations do not establish any peculiarities or variability.Furthermore, a preexisting, null proper-motion determination does notsupport a suggestion that the star is a nearby, hot subdwarf. Theavailable data are most consistent with an interpretation of HD 192273as a normal main-sequence star rather far from the galactic plane, andthere is no compelling reason to associate it with an EUV source at thepresent time.
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An upper limit on the EUV flux from HD192273
Observations placing an upper limit on the EUV flux from the proposedEUV source HD 192273 are reported. The region of the sky correspondingto the position of the star was observed by the Voyager 1 UVspectrometer to have a strong signal in the 912-1707 A range, however nostatistically significant signal was detected in the range 534-776 A. Atwo-standard-deviation upper limit to the stellar flux in this region of0.008 photons/sq cm per sec per A, corresponding to 10% of the 500-780 Aflux reported by Cash et al. (1978) for the EUV source in theconstellation Pavo, is thus placed on the flux from HD 192273 and it isconcluded that the star is probably not the source detected by Cash etal. The observed flux of the object at 1565 A is also observed to beconsistent with its effective temperature and gravity.
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The ultraviolet spectrum of the anomalous EUV-source halo star HD 192273
The proposed EUV source HD 192273 was observed with InternationalUltraviolet Explorer at both low and high resolution. Results of ananalysis of the stellar and interstellar spectrum are presented.Strengths of interstellar absorption lines give a value for the columndensity of neutral hydrogen atoms, NH = 2.0 + or - 0.5 x 10to the 20th power cm sq, making the proposed EUV identificationuntenable. The star appears to be a normal B2 V star witheB-V = 0.04 but an approximate distance of 0.5 kpc wasderived from the IUE data and this leaves the star 4 magnitudes toofaint for Be V.
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The distribution of interstellar C IV in the galaxy
Some high dispersion spectra of 13 halo and disc stars were reduced andcolumn densities of C IV presented. The galactic distribution of C IV isdiscussed and, combining the data with other published measurements, amean exponential scale height of 3 + 2 -1 kpc and disk space densityno = 8.5 x 10 to the minus 9th power cu cm are derived. Theresults were compared with Copernicus O VI data. Strengths and profilesof Si IV, C IV and N V from International Ultraviolet Explorer data werealso compared for a few representative lines of sight. N V/O VI ratiosimply log T 5.5, while SI IV/C IV (including the value for the wholehalo towards 3C 273) require 4.80 less than Log T less than 4.95.
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The Ultraviolet Spectrum of the Anomalous Extreme Ultraviolet Source Halo Star HD192273
Not Available
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The high-latitude EUV source HD192273 as a low-mass binary
Not Available
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Visual wavelength observations of the proposed extreme ultraviolet source, HD 192273
Results are reported for visual spectroscopy (3500 - 5000 A) and UBV,BVRI, and Stromgren photoelectric photometry of the eighth-magnitudestar HD 192273, which has been suggested as a UV source at 500 A. It isshown that HD 192273 cannot be degenerate, but more likely appears to bea B-type horizontal-branch subdwarf or a slightly reddened main-sequencestar. The data indicate atmospheric parameters in the neighborhood of aneffective temperature of 27,000 K and log g 4.8, as well as anear-normal helium abundance. It is suggested that such a model couldexplain the UV observations if the intervening hydrogen density is verylow (hydrogen column density less than 5 x 10 to the 17th power per sqcm).
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INHABITED SKY
