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Ultraviolet spectroscopy of the extended solar corona
The first observations of ultraviolet spectral line profiles andintensities from the extended solar corona (i.e., more than 1.5 solarradii from Sun-center) were obtained on 13 April 1979 when arocket-borne ultraviolet coronagraph spectrometer of theHarvard-Smithsonian Center for Astrophysics made direct measurements ofproton kinetic temperatures, and obtained upper limits on outflowvelocities in a quiet coronal region and a polar coronal hole. Followingthose observations, ultraviolet coronagraphic spectroscopy has expandedto include observations of over 60 spectral lines in coronal holes,streamers, coronal jets, and solar flare/coronal mass ejection (CME)events. Spectroscopic diagnostic techniques have been developed todetermine proton, electron and ion kinetic temperatures and velocitydistributions, proton and ion bulk flow speeds and chemical abundances.The observations have been made during three sounding rocket flights,four Shuttle deployed and retrieved Spartan 201 flights, and the Solarand Heliospheric Observatory (SOHO) mission. Ultraviolet spectroscopy ofthe extended solar corona has led to fundamentally new views of theacceleration regions of the solar wind and CMEs. Observations with theUltraviolet Coronagraph Spectrometer (UVCS) on SOHO revealedsurprisingly large temperatures, outflow speeds, and velocitydistribution anisotropies in coronal holes, especially for minor ions.Those measurements have guided theorists to discard some candidatephysical processes of solar wind acceleration and to increase and expandinvestigations of ion cyclotron resonance and related processes.Analyses of UVCS observations of CME plasma properties and the evolutionof CMEs have provided the following: temperatures, inflow velocities andderived values of resistivity and reconnection rates in CME currentsheets, compression ratios and extremely high ion temperatures behindCME shocks, and three dimensional flow velocities and magnetic fieldchirality in CMEs. Ultraviolet spectroscopy has been used to determinethe thermal energy content of CMEs allowing the total energy budget tobe known for the first time. Such spectroscopic observations are capableof providing detailed empirical descriptions of solar energetic particle(SEP) source regions that allow theoretical models of SEP accelerationto be tailored to specific events, thereby enabling in situ measurementsof freshly emitted SEPs to be used for testing and guiding the evolutionof SEP acceleration theory. Here we review the history of ultravioletcoronagraph spectroscopy, summarize the physics of spectral lineformation in the extended corona, describe the spectroscopic diagnostictechniques, review the advances in our understanding of solar windsource regions and flare/CME events provided by ultraviolet spectroscopyand discuss the scientific potential of next generation ultravioletcoronagraph spectrometers.
| 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.
| Radial velocity measurements of B stars in the Scorpius-Centaurus association
We derive single-epoch radial velocities for a sample of 56 B-type starsmembers of the subgroups Upper Scorpius, Upper Centaurus Lupus and LowerCentaurus Crux of the nearby Sco-Cen OB association. The radial velocitymeasurements were obtained by means of high-resolution echelle spectravia analysis of individual lines. The internal accuracy obtained in themeasurements is estimated to be typically 2-3 km s-1, butdepends on the projected rotational velocity of the target. Radialvelocity measurements taken for 2-3 epochs for the targets HD 120307, HD142990 and HD 139365 are variable and confirm that they arespectroscopic binaries, as previously identified in the literature.Spectral lines from two stellar components are resolved in the observedspectra of target stars HD 133242, HD 133955 and HD 143018, identifyingthem as spectroscopic binaries.
| Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction
We relate the equivalent widths of 11 diffuse interstellar bands,measured in the spectra of 49 stars, to different colour excesses in theultraviolet. We find that most of the observed bands correlatepositively with the extinction in the neighbourhood of the2175-Åbump. Correlation with colour excesses in other parts of theextinction curve is more variable from one diffuse interstellar band toanother; we find that some diffuse bands (5797, 5850 and 6376 Å)correlate positively with the overall slope of the extinction curve,while others (5780 and 6284 Å) exhibit negative correlation. Wediscuss the implications of these results on the links between thediffuse interstellar band carriers and the properties of theinterstellar grains.
| Dust Properties in the Far-Ultraviolet in Ophiuchus
We have derived the albedo (a) and phase function asymmetry factor (g)of interstellar dust grains at 1100 Å using archival Voyagerobservations of diffuse radiation in Ophiuchus. We have found that thegrains are highly forward-scattering, with g=0.55+/-0.25 anda=0.40+/-0.10. Even though most of the gas in this direction is in theOphiuchus molecular cloud, the diffuse FUV radiation is almost entirelydue to scattering in a relatively thin foreground cloud. This suggeststhat one cannot assume that the UV background is directly correlatedwith the total amount of gas in any direction.
| A Study of Far-Ultraviolet Extinction in the Upper Scorpius Cloud Using the SPINR Sounding Rocket Experiment
In this study, six new interstellar extinction curves in thefar-ultraviolet are presented using data from a sounding rocketexperiment. The sounding rocket data were combined with IUE data for sixlines of sight in the Upper Scorpius group to cover the wavelength rangeof 912-3030 Å. The extinction curves were produced using the paircomparison method with B stars of similar spectral types.Parameterizations from Fitzpatrick & Massa, Cardelli et al., andFitzpatrick were then fitted to the derived extinction curves. From thederived extinction curves, their corresponding fits, and the dust modelof Weingartner & Draine, it is concluded that the dust population inthe Upper Scorpius region exhibits a larger than average grainpopulation with a depletion of smaller grains.
| 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.
| A multiplicity survey of the ρ Ophiuchi molecular clouds
We present a volume-limited multiplicity survey with magnitude cutoff({m}K≤ 10.5 mag) of 158 young stellar objects locatedwithin or in the vicinity of the ρ Ophiuchi Dark Cloud. Withexception of eleven already well observed objects, all sources have beenobserved by us in the K-band with 3.5 m telescopes by using speckletechniques. The separation range covered by our survey is0.13''≤θ≤ 6.4'', where the lower limit is given by thediffraction limit of the telescopes and the upper limit by confusionwith background stars. The multiplicity survey is complete for fluxratios ≥ 0.1 (Δ{m}K≤ 2.5) at the diffractionlimit. After taking the background density into account the degree ofmultiplicity is 29.1%± 4.3% and thus only marginally higher thanthe value 23.5%± 4.8 % derived for the given separation range forthe main-sequence solar-like stars in the solar neighbourhood (Duquennoy& Mayor 1991). We discuss the implications of these findings.
| 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.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Classification of Spectra from the Infrared Space Observatory PHT-S Database
We have classified over 1500 infrared spectra obtained with the PHT-Sspectrometer aboard the Infrared Space Observatory according to thesystem developed for the Short Wavelength Spectrometer (SWS) spectra byKraemer et al. The majority of these spectra contribute to subclassesthat are either underrepresented in the SWS spectral database or containsources that are too faint, such as M dwarfs, to have been observed byeither the SWS or the Infrared Astronomical Satellite Low ResolutionSpectrometer. There is strong overall agreement about the chemistry ofobjects observed with both instruments. Discrepancies can usually betraced to the different wavelength ranges and sensitivities of theinstruments. Finally, a large subset of the observations (~=250 spectra)exhibit a featureless, red continuum that is consistent with emissionfrom zodiacal dust and suggest directions for further analysis of thisserendipitous measurement of the zodiacal background.Based on observations with the Infrared Space Observatory (ISO), aEuropean Space Agency (ESA) project with instruments funded by ESAMember States (especially the Principle Investigator countries: France,Germany, Netherlands, and United Kingdom) and with the participation ofthe Institute of Space and Astronautical Science (ISAS) and the NationalAeronautics and Space Administration (NASA).
| Reanalysis of Copernicus Measurements of Interstellar Carbon Monoxide
We used archival data acquired with Copernicus to reexamine CO columndensities, as self-consistent oscillator strengths are now available.Our focus is on lines of sight containing modest amounts of molecularspecies. Our resulting column densities are small enough thatself-shielding from photodissociation does not occur in the cloudsprobed by the observations. While our sample shows that the columndensities of CO and H2 are related, no correspondence withthe CH column density is evident. The case for the CH+ columndensity is less clear. Recent chemical models for these sight linessuggest that CH is mainly a by-product of CH+ synthesis inlow-density gas. The models are most successful in reproducing theamounts of CO in the densest sight lines. Thus, much of the COabsorption must arise from denser clumps along the line of sight toaccount for the trend with H2.
| Tomography of stellar non-radial pulsations
The stellar surface imaging technique is used for studying stellarnon-radial pulsations on the basis of inversions of time series ofvariable line profiles without making assumptions on the specific shapeof the pulsations. The inversion results in an image of the stellarsurface in which sectoral and tesseral modes can be distinguished inmany cases and the pulsational degree and the azimuthal order can bedetermined. The capability of the technique is studied with simulateddata. Then, the surface imaging technique is applied to high-resolutionspectra of the rapidly rotating Beta Cep-type star ω1Sco, which shows strong line-profile variations. Stellar surface imagingis concluded to be a useful technique for pulsation-mode identification.
| On the relation between diffuse bands and column densities of H2, CH and CO molecules
Mutual relations between column densities of H2, CH and COmolecules as well as between the latter and strengths of the major 5780and 5797 diffuse bands are presented and discussed. The CH radical seemsto be a good H2 tracer, possibly better than CO. It is alsodemonstrated that the molecular fraction of the H2 moleculeis correlated with an intensity ratio of 5797 and 5780 DIBs, suggestingthe possible formation of narrow DIB carriers in denser clouds,dominated by molecular hydrogen and reasonably shielded from ionizing UVradiation by small dust grains.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/414/949
| J - K DENIS photometry of a VLTI-selected sample of bright southern stars
We present a photometric survey of bright southern stars carried outusing the DENIS instrument equipped with attenuating filters. Theobservations were carried out not using the survey mode of DENIS, butwith individual target pointings. This project was stimulated by theneed to obtain near-infrared photometry of stars to be used in earlycommissioning observations of the ESO Very Large TelescopeInterferometer, and in particular to establish a network of brightcalibrator sources.We stress that near-infrared photometry is peculiarly lacking for manybright stars. These stars are saturated in 2MASS as well as in regularDENIS observations. The only other observations available for brightinfrared stars are those of the Two Micron Sky Survey dating from overthirty years ago. These were restricted to declinations above≈-30°, and thus cover only about half of the sky accessible fromthe VLTI site.We note that the final 2MASS data release includes photometry of brightstars, obtained by means of point-spread function fitting. However, thismethod only achieves about 30% accuracy, which is not sufficient formost applications.In this work, we present photometry for over 600 stars, each with atleast one and up to eight measurements, in the J and K filters. Typicalaccuracy is at the level of 0\fm05 and 0\fm04 in the J and K_s bands,respectively.Based on observations collected at the European Southern Observatory, LaSilla.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/413/1037
| 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.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| The Asiago Database on Photometric Systems
The Asiago Database on Photometric Systems (ADPS) is a compilation ofbasic information and reference data on 215 photometric systems (1386bands in all), both from the ground and space, and covering the UV,optical and IR wavelength ranges. Paper I is available in book format\citep{moro}. It censed only the information available from theliterature. Paper II \citep{fiorucci} presents an homogeneous derivationand calibration of band and reddening parameters for all systems withknown band transmission profiles (178 systems for a total of 1251bands). Following papers in the ADPS project will include calibration ofrelations sensitive to physical quantities (like Teff, lg g,[Fe/H], EB-V, etc.) and homogeneous transformation equationsfor all systems with known band transmission profiles. The ADPS projectweb page is http://ulisse.pd.astro.it/ADPS/
| High-Resolution Observations of Interstellar Ca I Absorption-Implications for Depletions and Electron Densities in Diffuse Clouds
We present high-resolution (FWHM~0.3-1.5 km s-1) spectra,obtained with the AAT UHRF, the McDonald Observatory 2.7 m coudéspectrograph, and/or the KPNO coudé feed, of interstellar Ca Iabsorption toward 30 Galactic stars. Comparisons of the column densitiesof Ca I, Ca II, K I, and other species-for individual componentsidentified in the line profiles and also when integrated over entirelines of sight-yield information on relative electron densities anddepletions (dependent on assumptions regarding the ionizationequilibrium). There is no obvious relationship between the ratio N(CaI)/N(Ca II) [equal to ne/(Γ/αr) forphotoionization equilibrium] and the fraction of hydrogen in molecularform f(H2) (often taken to be indicative of the local densitynH). For a smaller sample of sight lines for which thethermal pressure (nHT) and local density can be estimated viaanalysis of the C I fine-structure excitation, the average electrondensity inferred from C, Na, and K (assuming photoionizationequilibrium) seems to be independent of nH andnHT. While the electron density (ne) obtained fromthe ratio N(Ca I)/N(Ca II) is often significantly higher than the valuesderived from other elements, the patterns of relative nederived from different elements show both similarities and differencesfor different lines of sight-suggesting that additional processesbesides photoionization and radiative recombination commonly andsignificantly affect the ionization balance of heavy elements in diffuseinterstellar clouds. Such additional processes may also contribute tothe (apparently) larger than expected fractional ionizations(ne/nH) found for some lines of sight withindependent determinations of nH. In general, inclusion of``grain-assisted'' recombination does reduce the inferred ne,but it does not reconcile the ne estimated from differentelements; it may, however, suggest some dependence of ne onnH. The depletion of calcium may have a much weakerdependence on density than was suggested by earlier comparisons with CHand CN. Two appendices present similar high-resolution spectra of Fe Ifor a few stars and give a compilation of column density data for Ca I,Ca II, Fe I, and S I.
| The Homogeneity of Interstellar Krypton in the Galactic Disk
We present an analysis of high-resolution Hubble Space Telescope SpaceTelescope Imaging Spectrograph (STIS) observations of Kr I λ1236absorption in seven sight lines that probe a variety of interstellarenvironments. In combination with krypton and hydrogen column densitiesderived from current and archival STIS and Far-Ultraviolet SpectroscopicExplorer data, the number of sight lines with reliable Kr/H ISMabundance ratios has been increased by 50% to 26-including paths thatsample a range of nearly 5 orders of magnitude in f(H2) andover 2 orders of magnitude in , and extend up to4.8 kpc in length. For sight lines contained entirely within the localspiral arm (the Orion spur), the spread of Kr/H ratios about the mean oflog10[N(Kr)/N(H)]ISM=-9.02+/-0.02is remarkably tight (0.06 dex), less than the typical data-pointuncertainty. Intriguingly, the only two sight lines that extend throughneighboring structures, in particular gas associated with theCarina/Sagittarius arm, exhibit relatively large, near-solar kryptonabundances (log10[N(Kr)/N(H)]combined=-8.75+0.09-0.11).Although these deviations are only measured at the 2 σ level, theysuggest the possibility that krypton abundances beyond the Orion spurmay differ from the local value.Based on observations with the NASA/ESA Hubble Space Telescope (HST) andthe NASA-CNES-CSA Far-Ultraviolet Spectroscopic Explorer (FUSE). HSTspectra were obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc. under NASA contract NAS5-26555 FUSE is operated for NASA by theJohns Hopkins University under NASA contract NAS-32985.
| Nonthermal Chemistry in Diffuse Clouds with Low Molecular Abundances
High-quality archival spectra of interstellar absorption from C I towardnine stars, taken with the Goddard High Resolution Spectrograph on theHubble Space Telescope, were analyzed. Our sample was supplemented bytwo sight lines, 23 Ori and β1 Sco, for which the C Imeasurements of Federman, Welty, & Cardelli were used. Directionswith known CH+ absorption, but only upper limits onabsorption from C2 and CN, were considered for our study.This restriction allows us to focus on regions where CH+chemistry dominates the production of carbon-bearing molecules. Profilesynthesis of several multiplets yielded column densities and Dopplerparameters for the C I fine-structure levels. Equilibrium excitationanalyses, using the measured column densities as well as the temperaturefrom H2 excitation, led to values for gas density. Thesedensities, in conjunction with measurements of CH, CH+,C2, and CN column densities, provided estimates for theamount of CH associated with CH+ production, which in turnset up constraints on the present theories for CH+ formationin this environment. We found for our sample of interstellar clouds thaton average 30%-40% of the CH originates from CH+ chemistry,and in some cases it can be as high as 90%. A simple chemical model forgas containing nonequilibrium production of CH+ was developedfor the purpose of predicting column densities for CH, CO,HCO+, CH+2, andCH+3 generated from large abundances ofCH+. Again, our results suggest that nonthermal chemistry isnecessary to account for the observed abundance of CH and probably thatof CO in these clouds.Based on observations obtained with the NASA/ESA Hubble Space Telescopethrough the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
| Grey extinction in the solar neighbourhood?
Some of the close O and B dwarfs appear to be fainter than indicated bytheir Hipparcos distances, intrinsic absolute magnitudes attributed totheir spectral types, and estimated selective interstellar extinction.This discrepancy is explained in the paper by the grey (neutral)interstellar extinction in the visual range of spectrum. The measure ofsuch an effect is related to discrete features of the interstellarmatter.
| 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
| Surface imaging of stellar non-radial pulsations. II. The β Cephei star ω1 Sco
We apply the surface imaging technique to high-resolution spectra of therapidly rotating beta Cep-type star omega 1 Sco which showsstrong line-profile variations in the Si Iii lambda 4552, 4567, 4574Å triplet. These variations have been interpreted in terms ofnon-radial pulsations by Telting & Schrijvers (1998). Their analysisof the spectral time series with traditional Fourier transforms resultedin one significant frequency, suggesting that the profile variations aredue to only one dominant pulsation mode. Here we apply a spectralinversion technique to the same time series of the profiles. Assumingonly temperature fluctuations due to pulsations, we obtain an image ofthe dominant pulsation mode. We estimate the pulsation degree from theimage, put constraints on the azimuthal number of the mode, and studythe latitudinal distribution of the pulsation pattern. In addition tothe known dominant mode we find traces of a second pulsation mode.Based on observations collected at ESO, La Silla.
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/913
| Spectroscopic mode identification for the beta Cephei star EN (16) Lacertae
We perform for the first time spectroscopic mode identification in theeclipsing binary beta Cephei star EN (16) Lac. This mode identificationis based upon a time series of 942 line profiles of the He I lambdalambda 6678 Åline in its spectrum. All three known frequenciesf1, f,SUB>2,/SUB>, f3 of the star arepresent in the line-profile variations, but we failed to find additionalmodes. Using different identification methods we find conclusiveevidence for the radial nature of the main mode and for the l=2, m=0identification of the mode with frequency f2. A uniqueidentification of the third mode is not possible from the spectra, butwe do derive that l3<3. Fits to the amplitude and phasevariability of the modes imply a rotation frequency between 0.1 and 0.4c d-1. The star's rotation axis is not aligned with theorbital axis.Based on observations gathered with the coudé spectrographattached to the 2.0 m reflector telescope at Tautenburg Observatory.
| delta Scorpii: Visual Photometric Variability in 2000-2002
Not Available
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다음 그룹에 속해있음:
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관측 및 측정 데이터
천체목록:
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