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Scorpius the Winter-Bug.
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| Discovery of magnetic fields in the βCephei star ξ1 CMa and in several slowly pulsating B stars*
We present the results of a magnetic survey of a sample of eightβCephei stars and 26 slowly pulsating B (SPBs) stars with the FOcalReducer low dispersion Spectrograph at the Very Large Telescope. A weakmean longitudinal magnetic field of the order of a few hundred Gauss isdetected in the βCephei star ξ1CMa and in 13 SPBstars. The star ξ1CMa becomes the third magnetic staramong the βCephei stars. Before our study, the star ζCas wasthe only known magnetic SPB star. All magnetic SPB stars for which wegathered several magnetic field measurements show a field that varies intime. We do not find a relation between the evolution of the magneticfield with stellar age in our small sample. Our observations imply thatβCephei and SPB stars can no longer be considered as classes ofnon-magnetic pulsators, but the effect of the fields on the oscillationproperties remains to be studied.
| A high-resolution spectroscopy survey of β Cephei pulsations in bright stars
We present a study of absorption line-profile variations in early-B typenear-main-sequence stars without emission lines. We have surveyed atotal of 171 bright stars using the Nordic Optical Telescope (NOTSA),William Herschel Telescope (ING) and Coudé Auxiliary Telescope(ESO). Our sample contains 75% of all O9.5-B2.5 III-V non-emission-linestars brighter than 5.5 mag. We obtained high signal-to-noise,high-resolution spectra of the SiIII λ4560 triplet - for 125stars of our sample we obtained more than one spectrum - and examinedthese for pulsational-like line-profile variations and/or structure. Weconclude that about half of our sample stars show evidence forline-profile variations (LPV). We find evidence for LPV in about 65% ofour sample stars brighter than V=5.5. For stars with rotationalbroadening V sin i 100 km s-1, we find evidence for LPVin about 75% of the cases. We argue that it is likely that these LPV areof pulsational origin, and that hence more than half of thesolar-neighbourhood O9.5-B2.5 III-V stars is pulsating in modes that canbe detected with high-resolution spectroscopy. We detected LPV in 64stars previously unknown to be pulsators, and label these stars as newβ Cep candidates. We conclude that there is no obvious differencein incidence of (pulsational) LPV for early-B type near-main-sequencestars in binaries or in OB associations, with respect to single fieldstars.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Catalog of Galactic β Cephei Stars
We present an extensive and up-to-date catalog of Galactic β Cepheistars. This catalog is intended to give a comprehensive overview ofobservational characteristics of all known β Cephei stars, coveringinformation until 2004 June. Ninety-three stars could be confirmed to beβ Cephei stars. We use data from more than 250 papers publishedover the last nearly 100 years, and we provide over 45 notes onindividual stars. For some stars we reanalyzed published data orconducted our own analyses. Sixty-one stars were rejected from the finalβ Cephei list, and 77 stars are suspected to be β Cepheistars. A list of critically selected pulsation frequencies for confirmedβ Cephei stars is also presented.We analyze the β Cephei stars as a group, such as the distributionsof their spectral types, projected rotational velocities, radialvelocities, pulsation periods, and Galactic coordinates. We confirm thatthe majority of the β Cephei stars are multiperiodic pulsators. Weshow that, besides two exceptions, the β Cephei stars with highpulsation amplitudes are slow rotators. Those higher amplitude starshave angular rotational velocities in the same range as thehigh-amplitude δ Scuti stars (Prot>~3 days).We construct a theoretical HR diagram that suggests that almost all 93β Cephei stars are main-sequence objects. We discuss theobservational boundaries of β Cephei pulsation and the physicalparameters of the stars. We corroborate that the excited pulsation modesare near to the radial fundamental mode in frequency and we show thatthe mass distribution of the stars peaks at 12 Msolar. Wepoint out that the theoretical instability strip of the β Cepheistars is filled neither at the cool nor at the hot end and attempt toexplain this observation.
| The orbit of the close spectroscopic binary \varepsilon Lup and the intrinsic variability of its early B-type components
We subjected 106 new high-resolution spectra of the double-linedspectroscopic close binary \varepsilon Lup, obtained in a time-span of17 days from two different observatories, to a detailed study of orbitaland intrinsic variations. We derived accurate values of the orbitalparameters. We refined the sidereal orbital period to 4.55970d days andthe eccentricity to e=0.277. By adding old radial velocities, wediscovered the presence of apsidal motion with a period of the rotationof apses of about 430 years. Such a value agrees with theoreticalexpectations. Additional data is needed to confirm and refine thisvalue. Our dataset did not allow us to derive the orbit of the thirdbody, which is known to orbit the close system in 64 years. We presentthe secondary of \varepsilon Lup as a new β Cephei variable, whilethe primary is a β Cephei suspect. A first detailed analysis ofline-profile variations of both primary and secondary led to detectionof one pulsation frequency near 10.36 c d-1 in thevariability of the secondary, while no clear periodicity was found inthe primary, although low-amplitude periodicities are still suspected.The limited accuracy and extent of our dataset did not allow any furtheranalysis, such as mode-identification.
| Metallicity of mono- and multiperiodic β Cephei stars
Analyzing IUE ultraviolet spectra of β Cep pulsating stars wenoticed that multiperiodic variables have a larger mean metal abundancein the photosphere, [ m/H] , than monoperiodic ones. We applystatistical tests to verify this dichotomy. We obtain that, with a largeprobability, the multiperiodic β Cep stars have greater values of [m/H] . This result is consistent with the linear non-adiabatic theory ofpulsation of early B-type stars.
| Metallicities of the β Cephei stars from low-resolution ultraviolet spectra
We derive basic stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddening for all βCephei stars observed during the IUE satellite mission, including thosebelonging to three open clusters. The parameters are derived by means ofan algorithmic procedure of fitting theoretical flux distributions tothe low-resolution IUE spectra and ground-based spectrophotometricobservations. Since the metallicity has a special importance forpulsating B-type stars, we focus our attention in particular on thisparameter.Tables 1, 2, 4 and 5 are only available in electronic form athttp://www.edpsciences.org
| Disentangling component spectra of κ Scorpii, a spectroscopic binary with a pulsating primary. II. Interpretation of the line-profile variability
We analyse the complex short-term SiIII line-profile variability of the spectroscopic binary β Cep star κ Scorpii after orbit subtraction, before and after spectral disentangling. We refine the known oscillation frequency of the star: f1=4.99922 c d-1 and detect2f1. Variability is also found at frequencies nearf2≃ 4.85 c d-1 and f3≃ 5.69c d-1 or their aliases. These frequencies are not significantif we consider the spectra alone, but they survive our selection afterthe consideration that they were derived previously from independentground-based and space photometry by different teams. Moreover, we finddominant variability in the equivalent width with a frequency in theinterval [0.22,0.30] c d-1 which we interpret as therotational frequency frot of the star. The complex windowfunction does not allow us to determine definite values forf2, f3, frot. The variability withf1 is interpreted as a prograde non-radial oscillation modewith spherical wavenumbers (ℓ,m)=(2,-1) or (1,-1). The additionalfrequencies are explained in terms of rotational modulation superposedto the main oscillation. We also point out that we cannot disprove thevariability in κ Scorpii to originate from co-rotating structures. KOREL disentangling preserves the large-amplitude line-profile variability but its performance for complex low-amplitude variability remains to bestudied in detail.Based on observations obtained with the Coudé ÉchelleSpectrograph on the ESO CAT telescope and with the CORALIEéchelle spectrograph on the 1.2-m Euler Swiss telescope, bothsituated at La Silla, Chile.
| Disentangling component spectra of κ Sco, a spectroscopic binary with a pulsating primary. I. Improved physical elements and analysis of periodic rapid variations of scalar quantities
A new reduction and a new analysis of a rich series of high-S/N spectraof the bright star κ Sco is carried out to test the technique ofspectral disentangling in the case when one of the components is anon-radial oscillator. We improve the orbital elements of the system andfind the basic physical properties of the binary to be Teff =24 500 K, masses of 10.7-11.9 Mȯ and 9.6-10.7Mȯ and the primary radius and rotational period of 7-8Rȯ and 3d.56-3d.68, respectively.This also implies log g ,= 3.70-3.78 [cgs]. KOREL disentangling isapplied and we find that it worked properly and was not misled by thecomplex line-profile variability of the pulsating primary. Moreover, thepulsational frequencies are detected via the period search in the lineintensities and radial-velocity residuals of the primary derived byKOREL and in the time series of residual spectra in the rest frame ofthe primary after KOREL disentangling. This constitutes a much betterstarting point to interpret the complex pixel-by-pixel variations of thedisentangled profiles of the primary in terms of stellar oscillationsand/or additional rotational modulation than the original spectra beforedisentangling.Based on spectral observations obtained at ESO with the CAT/CES, LaSilla, Chile.
| β Cep stars from a spectroscopic point of view
In this review we present the current status of line-profile-variationstudies of β Cep stars. Such studies have been performed for 26bright members of this class of pulsating stars in the past 25 years. Wedescribe all these currently available data and summarize theinterpretations based on them in terms of the excited pulsation modes.We emphasize that line-profile variations offer a much more detailedpicture of the pulsational behaviour of pulsating stars compared toground-based photometric data. The latter, however, remain necessary tounravel the often complex frequency pattern and to achieve unambiguousmode identification for multiperiodic β Cep stars and also toderive the pulsational properties of the faint members of the class. Wehighlight the statistical properties of the sample of 26 stars for whichaccurate spectroscopic studies are available and point out some futureprospects.
| Statistics of the Instability Strip of β Cephei Stars
We present a study of the β Cephei instability strip based on asample of 49 stars of this type. After deriving their effectivetemperatures and luminosities from their observed (B-V), (U-B) colorsand parallaxes we find their positions in the HR diagram to be mostlyconfined to the main sequence, and their masses to lie between 7Mȯ and 30 Mȯ. Their distribution on theHR diagram matches well with our previous theoretical instability stripwhich has an upper bound in the luminosity and rather tight boundariesin the effective temperature.
| Potential Variations in the Interstellar N I Abundance
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and SpaceTelescope Imaging Spectrograph observations of the weak interstellar N Iλ1160 doublet toward 17 high-density sight lines[N(Htot)>=1021 cm-2]. When combinedwith published data, our results reveal variations in the fractional N Iabundance showing a systematic deficiency at large N(Htot).At the FUSE resolution (~20 km s-1), the effects ofunresolved saturation cannot be conclusively ruled out, although O Iλ1356 shows little evidence of saturation. We investigated thepossibility that the N I variability is due to the formation ofN2 in our mostly dense regions. The 0-0 band of thec'41Σ+u-X1Σ+gtransition of N2 at 958 Å should be easily detected inour FUSE data; for 10 of the denser sight lines, N2 is notobserved at a sensitivity level of a few times 1014cm-2. The observed N I variations are suggestive of anincomplete understanding of nitrogen chemistry.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer, which is operated for NASA by the Johns HopkinsUniversity under NASA contract NAS 5-32985, and the NASA/ESA HubbleSpace Telescope, obtained from the Multimission Archive at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under the NASA contractNAS 5-26555.
| Interstellar Silicon Abundance
We present 34 measurements of silicon gas phase column densities in theinterstellar medium. We have used spectra containing the SiII 1808 Angline which were obtained with the Goddard High Resolution Spectrograph(GHRS) aboard the Hubble Space Telescope (HST). Extinction curveparameters are determined for analyzed lines of sight and relationbetween Si/H ratio and extinction parameters is discussed. We find theabundance of gas phase silicon in diffuse clouds to be lower than thesolar value by a factor of four.
| Quantitative Stellar Spectral Classification. II. Early Type Stars
The method developed by Stock & Stock (1999) for stars of spectraltypes A to K to derive absolute magnitudes and intrinsic colors from theequivalent widths of absorption lines in stellar spectra is extended toB-type stars. Spectra of this type of stars for which the Hipparcoscatalogue gives parallaxes with an error of less than 20% were observedwith the CIDA one-meter reflector equipped with a Richardsonspectrograph with a Thompson 576×384 CCD detector. The dispersionis 1.753 Å/pixel using a 600 lines/mm grating in the first order.In order to cover the spectral range 3850 Å to 5750 Å thegrating had to be used in two different positions, with an overlap inthe region from 4800 Å to 4900 Å . A total of 116 stars wasobserved, but not all with both grating positions. A total of 12measurable absorption lines were identified in the spectra and theirequivalent widths were measured. These were related to the absolutemagnitudes derived from the Hipparcos catalogue and to the intrinsiccolors (deduced from the MK spectral types) using linear and secondorder polynomials and two or three lines as independent variables. Thebest solutions were obtained with polynomials of three lines,reproducing the absolute magnitudes with an average residual of about0.40 magnitudes and the intrinsic colors with an average residual of0.016 magnitudes.
| Line-profile variations of the double-lined spectroscopic binary kappa Scorpii
We present a total time series of high signal-to-noise, high-resolutionspectra of the SiIII lambda 4552.6, lambda 4567.8 and lambda 4574.8Å lines of the fast-rotating, spectroscopic binary and beta Cepheistar kappa Scorpii. Among this data set is a sample of 422 spectra ofintensive monitoring during eight subsequent nights in July 1997. Wefind variability of the line profiles on two time-scales: a variation ofseveral months as a result of the orbital motion and rapid variations ofa few hours, which are explained in terms of non-radial pulsation modes.From the total dataset, covering a time span of 9 years, we derive forthe first time the orbital parameters of kappa Scorpii and find anorbital period of 195 days. The complex patterns on the grayscalerepresentations of the residual SiIII lambda 4552.6 Å profileswith respect to the average profile point towards more than one(non-axisymmetric) pulsation mode. A frequency analysis of the threenormalised velocity moments confirms the main period of 4.80 hours andthe second period of 4.93 hours, which were previously derived fromphotometric data. We attempt an identification of the pulsation modes bymeans of the moment method and line-profile fitting and find that kappaScorpii pulsates in a main prograde sectoral mode of degree 1 or 2 andin an additional tesseral mode for which l = 5, m = 1 are the mostlikely wavenumbers. In the variations of the line profiles we findindications for the presence of additional pulsation modes. Based onobservations obtained at ESO with the CAT/CES, La Silla, Chile.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Infrared spectral classification of OB stars with ISO-SWS
We present observations of the Bralpha , Brbeta and Pfalpha lines of 16dwarf and (sub)giant stars in the spectral range O9-B3. The observationswere done using the Short Wavelength Spectrometer on board the InfraredSpace Observatory, and have a signal-to-noise of ~ 20 to > 150 and aresolving power varying from ~ 1400 to 2100. We compare the equivalentwidths of these lines with predictions using non-LTE model atmospheresto investigate to what extent these infrared lines can be used to deriveeffective temperatures. We find that Pfalpha is a sensitive T_effdiagnostic for the range of spectral types investigated, and Bralpha fortypes O9-B2, yielding agreement with optical results to within 1-4 kK orone-three spectral sub-types. We find evidence for a gradient in theturbulent velocity, increasing from la 5 km s-1 for theatmospheric region in which Bralpha is formed to ~ 15 km s-1for the regime where Pfalpha originates. When this gradient in turbulentvelocity is taken into account, the accuracy of the spectral typecalibration is improved to ~ 1 kK or one spectral sub-type. The gravitydependence of the strengths of the investigated infrared lines isrelatively weak, and could not be used to constrain luminosity class.This failure is in part a result of the modest S/N and resolution and inpart a result of a cancelation of gravity effects in the line core andline wing. Our line predictions show that Hei lambda 2.058 is relativelyunsuited for spectral classification of O9-B3 stars. Hualpha , however,is expected to be an even better diagnostic as are Pfalpha and Bralpha .This line may be observed with the VLT Imager and Spectrometer for midInfraRed when it is installed on the Very Large Telescope.
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| Interstellar Carbon Abundance
We present 10 new measurements of carbon gas phase column density in theinterstellar medium. We have used spectra made with the Goddard HighResolution Spectrograph aboard the Hubble Space Telescope containing theCII 1334.5 Ang and CII* 1335.7 Ang lines. The continuum reconstructionmethod has been used to obtain the carbon column density from theLorentzian damped lines. Extinction curve parameters are determined inselected directions and relation between C/H ratio and extinctionparameters is discussed. A correlation has been found between C/H andthe strength of the 2175 Ang bump. Unlike previous results, we noticethat C/H changes with fractional abundance of molecular hydrogen,f(H_2). The average value of C/H=3.55*10^{-4} for lines of sight withf(H_2)<1*10^{-3} is the same as solar photospheric abundance fromGrevese and Noels (1993) and may represent the real cosmic carbonabundance.
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,199 of the stars in Part I are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives in addition to the SI mode the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| Long-term spectroscopic monitoring of pulsating B stars : a tribute to the CAT.
Not Available
| An improved method for the determination of the orbital parameters of a binary system that contains a pulsating component
In this paper we present a method to assign statistical weights toradial-velocity measurements of a binary system of which one of thecomponents is a variable star. The basic idea of the method is toseparate the radial-velocity changes due to the intrinsic variabilityfrom those due to the orbital motion. This can be achieved if part ofthe data set consists of good coverages of the intrinsic variabilitycycle. These full coverages are used to estimate the variability for thenights on which only one or a few spectra were obtained. Our techniqueis applicable when the intrinsic variability has a period that isconsiderably shorter than the orbital period. Once weights have beenassigned, existing methods to derive the orbital parameters can be usedwith better accuracy compared to the case where all data points aretreated as if no intrinsic variability were present (equal weights). Weillustrate our method and compare the orbital solution obtained with andwithout assigning weights for three pulsating stars in a binary system:beta Cru, varepsilon Per, and kappa Sco.
| HD 42927 and HD 126341: two pulsating B stars surrounded by circumstellar dust
We have performed an infrared study of pulsating B stars. The mainconclusion is that none of the 163 (non-)radial pulsators shows an IRexcess flux due to free-free emission, despite the fact that the samplecontains several rapid rotators. Two beta Cep stars and two slowlypulsating B stars do exhibit an unexpected infrared colour excess at 12mu m. The small IR excess of the B 2 IV beta Cep star HD 126341 (tau (1) Lup) is not accompanied by H alpha emission nor by a near-IR excess.It follows an energy distribution described by a power-law that pointsto dust emission. An optically thin dust model is fitted to the IR dataand leads to the presence of circumstellar dust which is situated veryfar from the star. The infrared data of the star HD 42927 also pointtowards the presence of (hotter) dust which is situated close to thestar. We have gathered follow-up photometry and high-resolutionspectroscopy that confirm the Hipparcos classification of the star as anew slowly pulsating B star. We briefly discuss the connection betweenthese two pulsating stars and the occurrence of circumstellar dustaround main-sequence stars. Based on observations collected with the CATand the ESO-MPI 2.2m Telescopes of the European Southern Observatory andwith the Swiss Photometric Telescope of the Geneva Observatory, allsituated at La Silla in Chile
| Evidence for binarity and multiperiodicity in the beta Cephei star beta Crucis
We present numerous high signal-to-noise spectroscopic data of the betaCep star beta Crucis that were gathered during a total time span of 13years. Although only one pulsation period was up to now known for betaCrucis, our data clearly point out that the star is multiperiodic. Wefind evidence for the presence of at least two new frequencies, besidesthe one already detected in photometric observations. Different modesare dominant in each of the observing seasons. We attempted anidentification of the pulsation modes by means of the moment method andfind that none of them is radial. The newly detected frequencies belongto modes that have l>=3, explaining why they were not detectedphotometrically. We also find that the star is seen at a low inclinationangle. The average radial velocity varies for different seasons; itspeak-to-peak amplitude amounts to 12km/s and confirms the binary natureof beta Crucis. We have determined the orbital parameters of the systemand find an eccentric orbit (e=0.38) with a period of 5 years. Fromspectroscopic arguments we infer a B2V companion. Based on observationsobtained at the European Southern Observatory, Chile
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Performance of the Extreme Ultraviolet Explorer Imaging Telescopes
The Extreme Ultraviolet Explorer (EUVE) observatory, successfullylaunched on 1992 June 7, provided astronomers with the first observatorydedicated to observation in the extreme ultraviolet. The scientificobjectives of EUVE include an all-sky survey in four spectral bands, adeep survey in two spectral bands, and a spectroscopic survey carriedout through a NASA guest observer program. We describe here the hardwarecomponents of the four telescopes used to carry out both the all-skysurvey and the deep survey, and we present the imaging and photometricperformance characteristics of the instruments as determined from groundcalibration and in-orbit data.
| An All-Sky Catalog of Faint Extreme Ultraviolet Sources
We present a list of 534 objects detected jointly in the ExtremeUltraviolet Explorer (EUVE) 100 Angstroms all-sky survey and in theROSAT X-Ray Telescope 0.25 keV band. The joint selection criterionpermits use of a low count rate threshold in each survey. This lowthreshold is roughly 60% of the threshold used in the previous EUVEall-sky surveys, and 166 of the objects listed here are new EUV sources,appearing in neither the Second EUVE Source Catalog nor the ROSAT WideField Camera Second Catalog. The spatial distribution of this all-skycatalog shows three features: an enhanced concentration of objects inUrsa Major, where the Galactic integrated H I column reaches its globalminimum; an enhanced concentration in the third quadrant of the Galaxy(lII from 180 deg to 270 deg) including the Canis Major tunnel, whereparticularly low H I columns are found to distances beyond 200 pc; and aparticularly low number of faint objects in the direction of the fourthquadrant of the Galaxy, where nearby intervening H I columns areappreciable. Of particular interest is the composition of the 166detections not previously reported in any EUV catalog. We offerpreliminary identifications for 105 of these sources. By far the mostnumerous (81) of the identifications are late-type stars (F, G, K, M),while 18 are other stellar types, only five are white dwarfs (WDs), andnone are extragalactic. The paucity of WDs and extragalactic objects maybe explained by a strong horizon effect wherein interstellar absorptionstrongly limits the effective new-source search volume and, thereby,selectively favors low-luminosity nearby sources over more luminous butdistant objects.
| The Abundance of Interstellar Nitrogen
Using the Hubble Space Telescope Goddard High Resolution Spectrograph(GHRS), we have obtained high S/N echelle observations of the weakinterstellar N I lambda lambda 1160, 1161 absorption doublet toward thestars gamma Cas, lambda Ori, iota Ori, kappa Ori, delta Sco, and kappaSco. In combination with a previous GHRS measurement of N I toward zetaOph, these new observations yield a mean interstellar gas-phase nitrogenabundance (per 10 6 H atoms) of 10 6 N/H = 75 +/-4 (+/-1 sigma ). There are no statistically significant variations inthe measured N abundances from sight line to sight line and no evidenceof density-dependent nitrogen depletion from the gas phase. Since N isnot expected to be depleted much into dust grains in these diffuse sightlines, its gas-phase abundance should reflect the total interstellarabundance. Consequently, the GHRS observations imply that the abundanceof interstellar nitrogen (gas plus grains) in the local Milky Way isabout 80% of the solar system value of 10 6 N/H = 93 +/- 16.Although this interstellar abundance deficit is somewhat less than thatrecently found for oxygen and krypton with GHRS, the solar N abundanceand the N I oscillator strengths are too uncertain to rule outdefinitively either a solar ISM N abundance or a \frac {2}{3} solar ISMN abundance similar to that of O and Kr.
| The line-profile variable λ Scorpii is a spectroscopic triple system.
An analysis of 278 spectra of the line-profile variable λ Scorpiileads to the following conclusions. λ Sco is the primary of abinary system. The radial-velocity variations have a peak-to-peakamplitude of ~60km/s and an orbital period of 5.959 days. The orbit isnot circular but has an eccentricity of 0.29. The 5.959^d^-binary systemprobably moves in orbit with another distant, as yet unknown third star.By means of three five-hour time series of high-resolution spectra, theoscillations of the rapidly rotating β Cephei-type main componentare investigated. Line-profile variations, which reveal travellingsubfeatures across the lines, are discovered. λ Sco is so far oneof the very few βCephei stars in which such a moving-bumpphenomenon is detected. Radial-velocity variations are derived from thedata and analysed to reveal a main oscillation frequency near4.66cycles/day, and some more candidate frequencies. λ Sco is anon-radially pulsating β Cephei star which rotatessupersynchronously. The characteristics of λ Sco and the ζOph stars are briefly addressed. Despite the common line-profilebehaviour, spectral type, and vsin(i), we find no evidence ofcircumstellar material around λ Sco.
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