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Scorpius the Winter-Bug.
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| Orbital elements, masses and distance of λ Scorpii A and B determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy
The triple system HD158926 (λSco) has been observedinterferometrically with the Sydney University Stellar Interferometer,and the elements of the wide orbit have been determined. These aresignificantly more accurate than the previous elements foundspectroscopically. The inclination of the wide orbit is consistent withthe inclination previously found for the orbit of the close companion.The wide orbit also has low eccentricity, suggesting that the threestars were formed at the same time.The brightness ratio between the two B stars was also measured atλ = 442 and 700nm. The brightness ratio and colour index areconsistent with the previous classification of λ Sco A as B1.5and λ Sco B as B2. Evolutionary models show that the two starslie on the main sequence. Since they have the same age and luminosityclass (IV), the mass-luminosity relation can be used to determine themass ratio of the two stars: MB/MA = 0.76 +/-0.04.The spectroscopic data have been reanalyzed using the interferometricvalues for P, T, e and ω, leading to revised values fora1 sin i and the mass function. The individual masses can befound from the mass ratio, the mass function, spectrum synthesis and therequirement that the age of both components must be the same:MA = 10.4 +/- 1.3 and MB = 8.1 +/- 1.0Msolar.The masses, angular semimajor axis and the period of the system can beused to determine the dynamical parallax. We find the distance toλSco to be 112 +/- 5pc, which is approximately a factor of 2closer than the Hipparcos value of 216 +/- 42pc.
| High-precision photometry with the WIRE satellite .
Around 200 bright stars (V<6) have been monitored with the two-inchstar tracker on the WIRE satellite since observations started in 1999.Here we present new results for the solar-like star Procyon A, the twodelta Scuti stars Altair and epsilon Cephei, and the triple systemlambda Scorpii which consist of two B-type stars - one of which we findto be an eclipsing binary.
| Variations in D/H and D/O from New Far Ultraviolet Spectroscopic Explorer Observations
We use data obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) to determine the interstellar abundances of D I, N I, O I, Fe II,and H2 along the sight lines to WD 1034+001, BD +39 3226, andTD1 32709. Our main focus is on determining the D/H, N/H, O/H, and D/Oratios along these sight lines, with logN(H)>20.0, that probe gaswell outside of the Local Bubble. Hubble Space Telescope (HST) andInternational Ultraviolet Explorer (IUE) archival data are used todetermine the H I column densities along the WD 1034+001 and TD1 32709sight lines, respectively. For BD +39 3226, a previously published N(HI) is used. We find(D/H)×105=2.14+0.53-0.45,1.17+0.31-0.25, and1.86+0.53-0.43 and(D/O)×102=6.31+1.79-1.38,5.62+1.61-1.31, and7.59+2.17-1.76 for the WD 1034+001, BD +39 3226,and TD1 32709 sight lines, respectively (all 1 σ). The scatter inthese three D/H ratios exemplifies the scatter that has been found byother authors for sight lines with column densities in the range19.2
| 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.
| The epoch of the constellations on the Farnese Atlas and their origin in Hipparchus's lost catalogue
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| 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 D/H Ratio toward PG 0038+199
We determine the D/H ratio in the interstellar medium toward the DOwhite dwarf PG 0038+199 using spectra from the Far UltravioletSpectroscopic Explorer (FUSE), with ground-based support from KeckHIRES. We employ curve-of-growth, apparent optical depth, andprofile-fitting techniques to measure the column densities and limits ofmany other species (H2, Na I, C I, C II, C III, N I, N II, OI, Si II, P II, S III, Ar I, and Fe II), which allows us to determinerelated ratios such as D/O, D/N, and the H2 fraction. Ourefforts are concentrated on measuring gas-phase D/H, which is key tounderstanding Galactic chemical evolution, and comparing it topredictions from big bang nucleosynthesis. We find column densitieslogN(HI)=20.41+/-0.08, logN(DI)=15.75+/-0.08, andlogN(H2)=19.33+/-0.04, yielding a molecular hydrogen fractionof 0.14+/-0.02 (2 σ errors), with an excitation temperature of143+/-5 K. The high H I column density implies that PG 0038+199 liesoutside of the Local Bubble; we estimate its distance to be297+164-104 pc (1 σ).[DI+HD]/[HI+2H2] toward PG 0038+199 is1.91+0.52-0.42×10-5 (2 σ).There is no evidence of component structure on the scale ofΔv>8 km s-1, based on Na I, but there is marginalevidence for structure on smaller scales. The D/H value is high comparedto the majority of recent D/H measurements but consistent with thevalues for two other measurements at similar distances. D/O is inagreement with other distant measurements. The scatter in D/H valuesbeyond ~100 pc remains a challenge for Galactic chemical evolution.This paper is dedicated in memory of Ervin J. Williger, father of thefirst author, who passed away on 2003 September 13. His enthusiasticsupport and encouragement were essential to its successful completion.Based on data from the Far Ultraviolet Spectroscopic Explorer and the W.M. Keck Observatory.
| Deuterium Depletion and Magnesium Enhancement in the Local Disk
The local disk deuterium is known to be depleted in comparison to thelocal bubble. We used Hubble Space Telescope (HST) spectra to obtaincolumn densities of Si, Mg and Fe. We compared normalized columndensities of these elements in the directions with high and lowdeuterium abundances.We show, that the lines of sight that are depleted in deuterium, areenhanced in magnesium. This observation implicates that astration isresponsible for both deuterium depletion and magnesium enhancement.
| Star formation in Sandqvist 187 and 188
We present 1.2 mm continuum data of the filamentary dark cloud Sandqvist187/188 - also known as the Norma cloud - taken with SIMBA (SEST ImagingBolometer Array). The data are complemented by measurements from the2MASS, MSX and IRAS surveys. The extended 1.2 mm emission traces theoptical dark cloud down to a visual extinction of AV = 3.7mag. We derive a mean column density of N(H_2) = 1.4 ×1022 cm-2, equivalent to a visual extinction ofAV = 7.6 mag and a total mass of the cloud of 340 M_ȯ.We also find six compact millimetre sources, labelled MMS 1 to 6, fiveof which coincide with known stellar objects. MMS 6, however, only has avery weak MSX counterpart at 14.56 μm and an absorption feature at8.28 μm consistent with a visual extinction of AV > 145mag. Dust temperatures, luminosities and gas masses for all compactmillimetre sources are given. In an effort to further constrain theuncertain distance to Sandqvist 187/188, we analyse its stellar contentbased on 2MASS colours and find an improved lower limit of 440 ±50 pc.
| 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
| Two New Low Galactic D/H Measurements from the Far Ultraviolet Spectroscopic Explorer
We analyze interstellar absorption observed toward two subdwarf O stars,JL 9 and LS 1274, using spectra taken by the Far UltravioletSpectroscopic Explorer (FUSE). Column densities are measured for manyatomic and molecular species (H I, D I, C I, N I, O I, P II, Ar I, FeII, and H2), but our main focus is on measuring the D/Hratios for these extended lines of sight, as D/H is an importantdiagnostic for both cosmology and Galactic chemical evolution. We findD/H=(1.00+/-0.37)×10-5 toward JL 9 andD/H=(0.76+/-0.36)×10-5 toward LS 1274 (2 σuncertainties). With distances of 590+/-160 and 580+/-100 pc,respectively, these two lines of sight are currently among the longestGalactic lines of sight with measured D/H. With the addition of thesemeasurements, we see a significant tendency for longer Galactic lines ofsight to yield low D/H values, consistent with previous inferences aboutthe deuterium abundance from D/O and D/N measurements. Short lines ofsight with H I column densities of logN(HI)<19.2 suggest that thegas-phase D/H value within the Local Bubble is(D/H)LBg=(1.56+/-0.04)×10-5. However, thefour longest Galactic lines of sight with measured D/H, which haved>500 pc and logN(HI)>20.5, suggest a significantly lower valuefor the true local disk gas-phase D/H value,(D/H)LDg=(0.85+/-0.09)×10-5. Oneinterpretation of these results is that D is preferentially depletedonto dust grains relative to H and that longer lines of sight thatextend beyond the Local Bubble sample more depleted material. In thisscenario, the higher Local Bubble D/H ratio is actually a betterestimate than (D/H)LDg for the true local disk D/H,(D/H)LD. However, if (D/H)LDg is different from(D/H)LBg simply because of variable astration and incompleteinterstellar medium mixing, then (D/H)LD=(D/H)LDg.Based on observations made with the NASA-CNES-CSA Far UltravioletSpectroscopic Explorer (FUSE), which is operated for NASA by JohnsHopkins University under NASA contract NAS5-32985.
| High Precision Photometry with WIRE: Converting Spectroscopic Binaries to Eclipsing Systems
In February - March 2004, the WIRE satellite observed Lambda Sco and 57Eri, two early B subgiant stars. Lambda Sco is a known β Cepheidand spectroscopic binary (Uytterhoeven et al. 2004), while 57 Eri hasbeen previously reported only as a spectroscopic binary. The WIRE lightcurves, which are characterized by white noise levels more than an orderof magnitude less than those obtained from ground-based sources, showclearly that both stars are multimodal β Cepheids. In this paper,we present data and preliminary analysis of the modal structure of theoscillations for both stars.In addition, for each star we detect 3 eclipses, which have never beforebeen seen in these (previously) spectroscopic binaries. We use data fromthe eclipses to refine fundamental orbital parameters for these systems.
| Interpretation of the variability of the β Cephei star λ Scorpii. II. The line-profile diagnostics
We present the results of our analysis of a time series ofhigh-resolution spectra of the multiple β Cephei star λScorpii. The data set has a total time-span of more than 5000 days andincludes an intensive monitoring campaign during 8 consecutive nights.We confirm the presence of a dominant frequency f1 = 4.679410c d-1 in the data. We show that the amplitude is variable intime according to the light-time effect in the multiple system. Thedominant frequency is identified as a prograde dipole pulsation mode.From modelling of the amplitudes and phases across the profiles wederive pulsational parameters, the inclination angle 70°≤ i ≤ 90° and v sin i 125 kms-1. From a comparison between theoretically calculatedforcing eigenfrequencies induced by the close companion and theeigenfrequencies of the observed oscillation mode we find no tidalenhancement or excitation of the pulsation mode of λ Scorpii. Wefind indications for the presence of additional frequencies with lowamplitudes.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, Chile.
| Interpretation of the variability of the β Cephei star λ Scorpii. I. The multiple character
We derive accurate values of the orbital parameters of the close binaryβ Cephei star λ Scorpii. Moreover, we present the firstdetermination of the properties of the triple system to which λScorpii belongs. Our analysis is based on a time series of 815high-resolution spectra, covering a timespan of 14 years. We find aclose orbit of 5.9525 d days (e=0.26) and a wide orbit of approximately1082d days (e=0.23). The orbital parameters of the triplestar and a spectrum synthesis lead us to conclude that the system iscomposed of two early-type B stars and a low-mass pre-main-sequence starrather than containing an ultra-massive white dwarf as claimed before.Our proposed configuration is compatible with population synthesis. Theradial velocity variations of the primary allow us to confirm thepresence of at least one pulsation mode with frequency 4.679410 cd-1 which is subject to the light-time effect in the triplesystem. A detailed analysis of the complex line-profile variations isdescribed in a subsequent paper.Based on observations obtained with the Coudé EchelleSpectrograph on the ESO CAT telescope and with the CORALIE EchelleSpectrograph on the 1.2-m Euler Swiss telescope, both situated at LaSilla, ChileTable \ref{observations} is only available in electronic form athttp://www.edpsciences.org
| Atomic Deuterium/Hydrogen in the Galaxy
An accurate value of the D/H ratio in the local interstellar medium(LISM) and a better understanding of the D/H variations with position inthe Galactic disk and halo are vitally important questions as theyprovide information on the primordial D/H ratio in the Galaxy at thetime of the protosolar nebula, and the amount of astration and mixing inthe Galaxy over time. Recent measurements have been obtained with UVspectrographs on FUSE, HST, and IMAPS using hot white dwarfs, OB stars,and late-type stars as background light sources against which to measureabsorption by D and H in the interstellar medium along the lines ofsight. Recent analyses of FUSE observations of seven white dwarfs andsubdwarfs provide a weighted mean value of D/H = (1.52±0.08)× 10‑5 (15.2 ± 0.8 ppm), consistent withthe value of (1.50 ± 0.10) × 10‑5 (15.0± 1.0 ppm) obtained from analysis of lines of sight toward nearbylate-type stars. Both numbers refer to the ISM within about 100 pc ofthe Sun, which samples warm clouds located within the Local Bubble.Outside of the Local Bubble at distances of 200 to 500 pc, analyses offar-UV spectra obtained with the IMAPS instrument indicate a much widerrange of D/H ratios between 0.8 to 2.2 ppm. This portion of the Galacticdisk provides information on inhomogeneous astration in the Galaxy.
| 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.
| The Deuterium-to-Oxygen Ratio in the Interstellar Medium
Because the ionization balances for H I, O I, and D I are lockedtogether by charge exchange, the deuterium-to-oxygen ratio, D/O, is animportant tracer for the value of the D/H ratio and for potentialspatial variations in the ratio. As the D I and O I column densities areof similar orders of magnitude for a given sight line, comparisons ofthe two values will generally be less subject to systematic errors thancomparisons of D I and H I, which differ by about 5 orders of magnitude.Moreover, D/O is additionally sensitive to astration, because as starsdestroy deuterium, they should produce oxygen. We report here theresults of a survey of D/O in the interstellar medium performed with theFar Ultraviolet Spectroscopic Explorer. We also compare these resultswith those for D/N. Together with a few results from previous missions,the sample totals 24 lines of sight. The distances range from a few to~2000 pc and logN(D I) from ~13 to ~16 cm-2. The D/O ratio isconstant in the local interstellar medium out to distances of ~150 pcand N(DI)~=1×1015 cm-2, i.e., within theLocal Bubble. In this region of the interstellar space, we findD/O=(3.84+/-0.16)×10-2 (1 σ in the mean). Thehomogeneity of the local D/O measurements shows that the spatialvariations in the local D/H and O/H must be extremely few, if any. Acomparison of the Local Bubble mean value with the few D/O measurementsavailable for low-metallicity quasar sight lines shows that the D/Oratio decreases with cosmic evolution, as expected. Beyond the LocalBubble, we detected significant spatial variations in the value of D/O.This likely implies a variation in D/H, as O/H is known to not varysignificantly over the distances covered in this study. Our data setsuggests a present-epoch deuterium abundance below1×10-5, i.e., lower than the value usually assumed,around 1.5×10-5.
| The Chemical Composition and Gas-to-Dust Mass Ratio of Nearby Interstellar Matter
We use recent results on interstellar gas toward nearby stars andinterstellar by-products within the solar system to select among theequilibrium radiative transfer models of the nearest interstellarmaterial presented in Slavin & Frisch. For the assumption thatO/H~400 parts per million, models 2 and 8 are found to yield good fitsto available data on interstellar material inside and outside of theheliosphere, with the exception of the Ne abundance in the pickup ionand anomalous cosmic-ray populations. For these models, the interstellarmedium (ISM) at the entry point to the heliosphere hasn(H0)=0.202-0.208 cm-3,n(He0)=0.0137-0.0152 cm-3, and ionizationsχ(H)=0.29-0.30, χ(He)=0.47-0.51. These best models suggest thatthe chemical composition of the nearby ISM is ~60%-70% subsolar if S isundepleted. Both H0 and H+ need to be includedwhen evaluating abundances of ions found in warm diffuse clouds. Models2 and 8 yield an H filtration factor of ~0.46. Gas-to-dust mass ratiosfor the ISM toward ɛ CMa are Rgd=178-183 for solarabundances of Holweger or Rgd=611-657 for an interstellarabundance standard 70% solar. Direct observations of dust grains in thesolar system by Ulysses and Galileo yield Rgd~=115 for models2 and 8, supporting earlier results (Frisch and coworkers). If the localISM abundances are subsolar, then gas and dust are decoupled over smallspatial scales. The inferred variation in Rgd over parseclength scales is consistent with the fact that the ISM near the Sun ispart of a dynamically active cluster of cloudlets flowing away from theSco-Cen association. Observations toward stars within ~500 pc show thatRgd correlates with the percentage of the dust mass that iscarried by iron, suggesting that an Fe-rich grain core (by mass) remainsafter grain destruction. Evidently large dust grains (>10-13g) and small dust grains (<10-13 g) are not well mixedover parsec length spatial scales in the ISM. It also appears that verysmall C-dominated dust grains have been destroyed in the ISM withinseveral parsecs of the Sun, since C appears to be essentiallyundepleted. However, if gas-dust coupling breaks down over the cloudlifetime, the missing mass arguments applied here to determineRgd and dust grain mineralogy are not appropriate.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| 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.
| delta Scorpii: Visual Photometric Variability in 2000-2002
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| Abundances of Deuterium, Nitrogen, and Oxygen in the Local Interstellar Medium: Overview of First Results from the FUSE Mission
Observations obtained with the Far Ultraviolet Spectroscopic Explorer(FUSE) have been used to determine the column densities of D I, N I, andO I along seven sight lines that probe the local interstellar medium(LISM) at distances from 37 to 179 pc. Five of the sight lines arewithin the Local Bubble, and two penetrate the surrounding H I wall.Reliable values of N(H I) were determined for five of the sight linesfrom Hubble Space Telescope (HST) data, International UltravioletExplorer (IUE) data, and published Extreme Ultraviolet Explorer (EUVE)measurements. The weighted mean of D I/H I for these five sight lines is(1.52+/-0.08)×10-5 (1 σ uncertainty in the mean).It is likely that the D I/H I ratio in the Local Bubble has a singlevalue. The D I/O I ratio for the five sight lines within the LocalBubble is (3.76+/-0.20)×10-2. It is likely that O Icolumn densities can serve as a proxy for H I in the Local Bubble. Theweighted mean for O I/H I for the seven FUSE sight lines is(3.03+/-0.21)×10-4, comparable to the weighted mean(3.43+/-0.15)×10-4 reported for 13 sight lines probinglarger distances and higher column densities. The FUSE weighted mean ofN I/H I for five sight lines is half that reported by Meyer andcolleagues for seven sight lines with larger distances and higher columndensities. This result combined with the variability of O I/N I (sixsight lines) indicates that at the low column densities found in theLISM, nitrogen ionization balance is important. Thus, unlike O I, N Icannot be used as a proxy for H I or as a metallicity indicator in theLISM.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
| An atlas of 2.4 to 4.1 mu m ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with theShort Wavelength Spectrometer (SWS) during the Post-Helium program ofthe Infrared Space Observatory (ISO). This program is aimed at extendingthe Morgan & Keenan classification scheme into the near-infrared.Later type stars will be discussed in a separate publication. Theobservations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 μm, supplemented with 10 spectra acquired during the nominal mission witha similar observational setting. For B-type stars, this sample providesample spectral coverage in terms of subtype and luminosity class. ForO-type stars, the ISO sample is coarse and therefore is complementedwith 8 UKIRT Larcmin -band observations. In terms of the presence ofdiagnostic lines, the Larcmin -band is likely the most promising of thenear-infrared atmospheric windows for the study of the physicalproperties of B stars. Specifically, this wavelength interval containsthe Bralpha , Pfgamma , and other Pfund lines which are probes ofspectral type, luminosity class and mass loss. Here, we present simpleempirical methods based on the lines present in the 2.4 to 4.1 mu minterval that allow the determination of i) the spectral type of Bdwarfs and giants to within two subtypes; ii) the luminosity class of Bstars to within two classes; iii) the mass-loss rate of O stars and Bsupergiants to within 0.25 dex. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA. The appendix is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin.qcat?J/A+A/384/473
| The accretion/diffusion theory for lambda Bootis stars in the light of spectroscopic data
Most of the current theories suggest the lambda Bootis phenomenon tooriginate from an interaction between the stellar surface and its localenvironment. In this paper, we compare the abundance pattern of thelambda Bootis stars to that of the interstellar medium and find largerdeficiencies for Mg, Si, Mn and Zn than in the interstellar medium. Acomparison with metal poor post-AGB stars showing evidence forcircumstellar material indicates a similar physical process possiblybeing at work for some of the lambda Bootis stars, but not for all ofthem. Despite the fact that the number of spectroscopically analysedlambda Bootis stars has considerably increased in the past, a test ofpredicted effects with observations shows current abundance andtemperature data to be still controversial.
| Apsidal motion and non-radial pulsations in psi 2 Ori
We present a time series of high-resolution echelle spectra of thedouble-lined close binary psi 2 Ori. The spectra sample thewavelength region of 3800-6800 Å. In the absorption lines of theearly-B type primary we find clear evidence for non-radial pulsationswith intermediate values of the modal degree l. Using across-correlation technique we derive the radial velocity of bothcomponents. We compare our orbital solution with those reported in theliterature to derive the apsidal motion period in this system: 47.5 +/-0.7 year. We analyse the absorption line profiles of the primary usingFourier techniques to derive apparent pulsation periods and l values oftwo detected modes with apparent frequencies f_1=10.48 c/d and f_2=10.73c/d. We discuss whether the non-radial pulsations in this star areinternally excited or due to tidal forcing. Comparing the pulsationfrequencies with those expected for tidal forcing and for internallyexcited modes, we tentatively conclude that these modes are probably dueto internally excited beta Cephei pulsations. Based on observations madewith the Isaac Newton Telescope operated on the island of La Palma bythe Isaac Newton Group in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofisica de Canarias.
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