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Early-type stars observed in the ESO UVES Paranal Observatory Project - I. Interstellar NaI UV, TiII and CaII K observations*
We present an analysis of interstellar NaI (λair=3302.37 and 3302.98 Å), TiII(λair= 3383.76Å) and CaII K (λair= 3933.66 Å) absorptionfeatures for 74 sightlines towards O- and B-type stars in the Galacticdisc. The data were obtained from the Ultraviolet and Visual EchelleSpectrograph Paranal Observatory Project, at a spectral resolution of3.75 km s-1 and with mean signal-to-noise ratios per pixel of260, 300 and 430 for the NaI, TiII and CaII observations, respectively.Interstellar features were detected in all but one of the TiIIsightlines and all of the CaII sightlines. The dependence of the columndensity of these three species with distance, height relative to theGalactic plane, HI column density, reddening and depletion relative tothe solar abundance has been investigated. We also examine the accuracyof using the NaI column density as an indicator of that for HI. Ingeneral, we find similar strong correlations for both Ti and Ca, andweaker correlations for Na. Our results confirm the general belief thatTi and Ca occur in the same regions of the interstellar medium (ISM) andalso that the TiII/CaII ratio is constant over all parameters. We henceconclude that the absorption properties of Ti and Ca are essentiallyconstant under the general ISM conditions of the Galactic disc.
| A multiwavelength investigation of the temperature of the cold neutral medium
We present measurements of the HI spin temperatures (Ts) ofthe cold neutral medium (CNM) towards radio sources that are closelyaligned with stars for which published H2 ortho-paratemperatures (T01) are available from ultraviolet (UV)observations. Our sample consists of 18 radio sources close to 16 nearbystars. The transverse separation of the lines of sight of thecorresponding UV and radio observations varies from 0.1 to 12.0 pc atthe distance of the star. The UV measurements do not have velocityinformation, so we use the velocities of low ionization species (e.g.NaI/KI/CI) observed towards these same stars to make a plausibleidentification of the CNM corresponding to the H2 absorption.We then find that T01 and Ts match withinobservational uncertainties for lines of sight with H2 columndensity above 1015.8cm-2, but deviate from eachother below this threshold. This is consistent with the expectation thatin the CNM Ts tracks the kinetic temperature due tocollisions and that T01 is driven towards the kinetictemperature by proton exchange reactions.
| Circumstellar Disk around HD 143275 and Interstellar Absorption
This paper presents a collection of spectra of the star HD 143275(δ Sco), acquired during the last 11 years. During this period,stellar absorption lines turned into emission features possiblyoriginating in the circumstellar disk. We demonstrate that thecircumstellar shell does not produce any components of interstellarabsorption features (atomic lines, molecular features, and diffuseinterstellar bands), which remain of the same equivalent widths duringthe whole period covered by our observations.
| Investigating Disk Evolution: A High Spatial Resolution Mid-Infrared Survey of T Tauri Stars
We present a high spatial resolution, 10-20 μm survey of 65 T Tauribinary stars in Taurus, Ophiuchus, and Corona Australis using the Keck10 m telescopes. Designed to probe the inner ~1 AU region of thecircumstellar disks around the individual stellar components in thesebinary systems, this study increases the number of binaries withspatially resolved measurements at 10 μm by a factor of ~5. Combinedwith resolved near-infrared photometry and spectroscopic accretiondiagnostics, we find that ~10% of stars with a mid-infrared excess donot appear to be accreting. In contrast to an actively accreting disksystem, these passive disks have significantly lower near-infraredcolors that are, in most cases, consistent with photospheric emission,suggesting the presence of an inner disk hole. In addition, thereappears to be a spectral type/mass dependence associated with thepresence of a passive disk, with all passive disks occurring aroundM-type stars. The presence of a passive disk does not appear to berelated to the fact that these objects are in visual binary systems; thepassive disk systems span the entire range of binary separations presentin the sample, and a similar fraction of passive disks is observed in asample of single stars. The possibility that the passive disks arecaused by the presence of an as yet undetected companion at a smallseparation (0.3-3 AU) is possible for any individual system; however, itcannot account for the spectral type dependence of the passive disksample as a whole. We propose that these passive disks represent asubset of T Tauri stars that are undergoing significant disk evolution.The fraction of observed passive disks and the observed spectral typedependence can both be explained by models of disk evolution thatinclude disk photoevaporation from the central star.
| 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.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| Orbital parameters, masses and distance to β Centauri determined with the Sydney University Stellar Interferometer and high-resolution spectroscopy
The bright southern binary star β Centauri (HR5267) has beenobserved with the Sydney University Stellar Interferometer (SUSI) andspectroscopically with the European Southern Observatory Coude AuxiliaryTelescope and Swiss Euler telescope at La Silla. The interferometricobservations have confirmed the binary nature of the primary componentand have enabled the determination of the orbital parameters of thesystem. At the observing wavelength of 442nm the two components of theprimary system have a magnitude difference of 0.15 +/- 0.02. Thecombination of interferometric and spectroscopic data gives thefollowing results: orbital period 357.00 +/- 0.07d, semimajor axis 25.30+/- 0.19mas, inclination 67.4 +/-0.3, eccentricity0.821 +/- 0.003, distance 102.3 +/- 1.7pc, primary and secondary massesM1=M2= 9.1 +/- 0.3 Msolar and absolutevisual magnitudes of the primary and secondary M1V=-3.85 +/-0.05 and M2V=-3.70 +/- 0.05, respectively. The high degree ofaccuracy of the results offers a fruitful starting point for futureasteroseismic modelling of the pulsating binary components.
| Estimating the Porosity of the Interstellar Medium from Three-dimensional Photoionization Modeling of H II Regions
We apply our three-dimensional photoionization code to model WisconsinHα Mapper observations of the H II region surrounding the O9.5 Vstar ζ Oph. Our models investigate the porosity of the interstellarmedium around ζ Oph and the effects of three-dimensional densitieson the Hα surface brightness and variation in the [N II]λ6583/Hα line ratio. The ζ Oph H II region has awell-characterized ionizing source, so it is an excellent starting pointfor three-dimensional models of diffuse ionized gas. We investigatevarious hierarchically clumped density structures, varying the overallsmoothness within the clumping algorithm. By simulating theobservations, we estimate the porosity of the medium in the vicinity ofζ Oph and find that within the context of our hierarchicallyclumped models, around 50%-80% of the volume is occupied by clumpssurrounded by a low-density smooth medium. We also conclude that inorder for O stars to ionize the diffuse warm ionized medium, the O starenvironment must be more porous than that surrounding ζ Oph, withclumps occupying less than one-half of the interstellar volume. Ourclumpy models have irregular boundaries, similar to observed H IIregions. However, in observed H II regions, it is difficult to identifythe precise location of the boundary because of the foreground and/orbackground emission from the widespread warm ionized medium. Thiscomplicates the interpretation of the predicted rapid rise of someemission-line ratios near the edge of uniform density H II regions and,combined with the three-dimensional clumpy nature of the interstellarmedium, may explain the apparent lack of distinctive emission-lineratios near H I-H II interfaces.
| 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.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| The Chemistry of Fluorine-bearing Molecules in Diffuse and Dense Interstellar Gas Clouds
We present a theoretical investigation of the chemistry offluorine-bearing molecules in diffuse and dense interstellar gas clouds,combining recent estimates for the rates of relevant chemical reactionswith a self-consistent model for the physical and chemical conditionswithin gas clouds that are exposed to the interstellar ultravioletradiation field. The chemistry of interstellar fluorine is qualitativelydifferent from that of any other element, because unlike the neutralatoms of any other element found in diffuse or dense molecular clouds,atomic fluorine undergoes an exothermic reaction with molecularhydrogen. Over a wide range of conditions attained within interstellargas clouds, the product of that reaction, hydrogen fluoride, ispredicted to be the dominant gas-phase reservoir of interstellarfluorine nuclei. Fluorine is the heavy element that shows the greatesttendency toward molecule formation; in diffuse clouds of smallextinction, the predicted HF abundance can even exceed that of CO, eventhough the gas-phase fluorine abundance is 4 orders of magnitude smallerthan that of carbon. Our model predicts HF column densities of~1013 cm-2 in dark clouds and column densities aslarge as 1011 cm-2 in diffuse interstellar gasclouds with total visual extinctions as small as 0.1 mag. Such diffuseclouds will be detectable by means of absorption-line spectroscopy ofthe J=1-0 transition at 243.2 μm using the Stratospheric Observatoryfor Infrared Astronomy (SOFIA) and the Herschel Space Observatory (HSO).The CF+ ion is predicted to be the second most abundantfluorine-bearing molecule, with typical column densities a factor of~102 below those of HF; with its lowest two rotationaltransitions in the millimeter-wave spectral region, CF+ maybe detectable from ground-based observatories. HF absorption in quasarspectra is a potential probe of molecular gas at high redshift,providing a possible bridge between the UV/optical observations capableof probing H2 in low column density systems and theradio/millimeter-wavelength observations that probe interveningmolecular clouds of high extinction and large molecular fraction; atredshifts beyond ~0.3, HF is potentially detectable from ground-basedsubmillimeter observatories in several atmospheric transmission windows.
| Far Ultraviolet Spectroscopic Explorer Measurements of Interstellar Fluorine
The source of fluorine is not well understood, although core-collapsesupernovae, Wolf-Rayet stars, and asymptotic giant branch stars havebeen suggested. A search for evidence of the ν-process during Type IIsupernovae is presented. Absorption from interstellar F I is seen inspectra of HD 208440 and HD 209339A acquired with the Far UltravioletSpectroscopic Explorer. In order to extract the column density for F Ifrom the line at 954 Å, absorption from H2 has to bemodeled and then removed. Our analysis indicates that for H2column densities less than about 3×1020cm-2, the amount of F I can be determined from λ954.For these two sight lines, there is no clear indication for enhanced Fabundances resulting from the ν-process in a region shaped by pastsupernovae.Based on observations made with the NASA/CNES/CSA Far UltravioletSpectroscopic Explorer (FUSE), which is operated for NASA by the JohnsHopkins University under NASA contract NAS 5-32985.
| 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.
| 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
| Amateur Spectroscopy of Hot Stars: Long Term Tracking of Circumstellar Emission
Not Available
| Variable Star Network: World Center for Transient Object Astronomy and Variable Stars
Variable Star Network (VSNET) is a global professional-amateur networkof researchers in variable stars and related objects, particularly intransient objects, such as cataclysmic variables, black-hole binaries,supernovae, and gamma-ray bursts. The VSNET has been playing apioneering role in establishing the field of transient object astronomy,by effectively incorporating modern advances in observational astronomyand global electronic networks, as well as collaborative progress intheoretical astronomy and astronomical computing. The VSNET is now oneof the best-featured global networks in this field of astronomy. Wereview the historical progress, design concept, associated technology,and a wealth of scientific achievements powered by VSNET.
| Correlations between diffuse interstellar bands and atomic lines
We present and discuss correlations between strengths of the well-known,strong interstellar atomic lines of KI and CaII, and four selected,strong unidentified diffuse interstellar bands (DIBs): 5780, 5797, 5850and 6614. In order to analyse a homogeneous sample of echellehigh-resolution spectra it has been chosen to use measurements fromTerskol Observatory in Northern Caucasus plus a selected number ofhigher resolution observations performed using other instruments. Wedemonstrate that the strength of certain DIBs correlate well withneutral potassium lines and to a much lower degree with ionized calciumlines. This fact suggests that the degree of irradiation of a cloud withUV photons, capable to ionize interstellar atoms, plays a crucial rolein the formation/maintenance of certain molecular species: possiblecarriers of DIBs.
| 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).
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| 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.
| Interstellar Carbon in Translucent Sight Lines
We report interstellar C II column densities or upper limits determinedfrom weak absorption of the 2325.4029 Å intersystem transitionobserved in six translucent sight lines (AV>~1) with theSpace Telescope Imaging Spectrograph (STIS). The sight lines sample awide range of interstellar characteristics, including total to selectiveextinction, RV=2.6-5.1 average hydrogen density along thesight line, =3-14 cm-3 and fraction of H inmolecular form, 0-~40%. Four of the sight lines, those toward HD 37021,HD 37061, HD 147888, and HD 207198, have interstellar gas-phaseabundances that are consistent with the diffuse sight line ratio of161+/-17 carbon atoms in the gas per million hydrogen nuclei. We notethat while it has a gas-phase carbon abundance that is consistent withthe other sight lines, a large fraction of the C II toward HD 37061 isin an excited state. The sight line toward HD 152590 has a measuredinterstellar gas-phase carbon abundance that is well above the diffusesight line average; the column density of C in this sight line may beoverestimated because of noise structure in the data. Toward HD 27778 wefind a 3 σ abundance upper limit of <=108 C atoms in the gasper million H, a substantially enhanced depletion of C as compared tothe diffuse sight line value. The interstellar characteristics toward HD27778 are otherwise not extreme among the sample, except for anunusually large abundance of CO molecules in the gas.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555.
| Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential Photometry
Five hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory.
| The Abundance of Interstellar Fluorine
Despite the importance of measuring the interstellar fluorine abundanceonly three previous detection has been made due to the low relativeabundance of fluorine, the lack of lines outside the far-ultraviolet,and blending of the available transitions with lines of molecularhydrogen. The nucleosynthetic source(s) of fluorine are still a matterof debate, and the present day abundance of fluorine can potentiallyconstrain models for its production. Furthermore, due to its extremereactivity, measurement of the gas-phase interstellar fluorine abundanceis important for models of gas and grain chemistry.We report on the results of high S/N-ratio (50-100) FUSE observations ofthe interstellar absorption lines of neutral fluorine at 951 and 954Angstroms toward two distant Galactic stars (HD 103779 and HD 164816).The sightline toward HD 103779 lies near the edge of the North PolarSpur and Radio Loop 1. HD 164816 is associated with the Lagoon nebula (M8) at a distance of about 1.5 kpc, and also probes both distant andlocal gas. Modeling of both interstellar and stellar absorption lineshas been used to determine the abundance from the (blended) strongfluorine line at 954.83 Angstroms. We have also made a sensitive searchfor the weaker line at 951.87 Angstroms to provide a consistency checkfor our models, and have made a tentative detection toward HD 103779.While preliminary analysis of these data suggests that the observedfluorine gas-phase abundances (and hence inferred depletions) areroughly consistent with previous measures toward delta Sco (Copernicus)and two stars in Cep OB2 (FUSE), there may be a slight enhancement inthe gas-phase abundance toward HD 103779.This research was supported by NASA grant NAG5-13005.
| Be Star Hα Line Profile Variability
The monitoring of the spectroscopic variability of Be stars is crucialfor testing Be star models. Motivated by this, a Be star monitoringproject was developed for undergraduate student research involvement. Wehave been obtaining 0.8 Angstrom/pixel resolution Hα line profilesfor several bright Be stars since 2003 June. These spectra were acquiredusing the UCA Fiber Fed Spectrograph used at the UCA Observatory and theNubbin Ridge Observatory in Royal, AR. H-α line profiles,velocities, and variability are shown for Delta Sco, Chi Oph, Eta PsA,48 Lib, and Upsilon Sgr (HD181615).Funding has been provided by the UCA University Research Council and theArkansas Space Grant Consortium.
| On the Hipparcos parallaxes of O stars
We compare the absolute visual magnitude of the majority of bright Ostars in the sky as predicted from their spectral type with the absolutemagnitude calculated from their apparent magnitude and the Hipparcosparallax. We find that many stars appear to be much fainter thanexpected, up to five magnitudes. We find no evidence for a correlationbetween magnitude differences and the stellar rotational velocity assuggested for OB stars by Lamers et al. (1997, A&A, 325, L25), whosesmall sample of stars is partly included in ours. Instead, by means of asimulation we show how these differences arise naturally from the largedistances at which O stars are located, and the level of precision ofthe parallax measurements achieved by Hipparcos. Straightforwardlyderiving a distance from the Hipparcos parallax yields reliable resultsfor one or two O stars only. We discuss several types of bias reportedin the literature in connection with parallax samples (Lutz-Kelker,Malmquist) and investigate how they affect the O star sample. Inaddition, we test three absolute magnitude calibrations from theliterature (Schmidt-Kaler et al. 1982, Landolt-Börnstein; Howarth& Prinja 1989, ApJS, 69, 527; Vacca et al. 1996, ApJ, 460, 914) andfind that they are consistent with the Hipparcos measurements. AlthoughO stars conform nicely to the simulation, we notice that some B stars inthe sample of \citeauthor{La97} have a magnitude difference larger thanexpected.
| Properties of galactic B[e] supergiants. III. MWC 300
We present the results of optical and near-IR spectroscopic and mid-IRimaging observations of the emission-line star MWC 300. Its propertiesand evolutionary state are still under debate (a B[e] supergiant or aHerbig Be star). For the first time we detected radial velocityvariations of the photospheric lines and found a correlation betweenthem and those of the He I λ5876 Åline. Most of the pureemission lines had stable positions for nearly 20 years. New estimatesof the object's luminosity (log L/Lȯ=5.1±0.1),distance (D=1.8±0.2 kpc), and systemic velocity (+26±2 kms-1) were derived. We found that both the circumstellarextinction in the disk-like dusty envelope and the interstellarextinction play a significant role in the attenuation of the stellarbrightness. Our 2D modeling of the observed spectral energy distributionin the wavelength range from 0.3 μm to 1.3 mm suggests that the staris viewed through a gaseous-and-dusty flared disk with an opening angleof 30 °, an inclination angle of 10 °, an equatorial opticaldepth τV=3.0, and a total mass of 0.08Mȯ. We argue that MWC 300 is most likely a binarysystem, because of the similarities of its observed parameters withthose of recognized B[e] binaries.Partially based on observations collected at the Canada-France-Hawaiitelescope (CFHT), operated by the National Research Council of Canada,the Centre National de la Recherche Scientifique, and Univeristy ofHawaii.
| Survey of long-term variability of stars. I. Reliability of magnitudes in old star catalogues
The comparison of visual magnitudes of stars compiled in old cataloguesis expected to yield information about their long-term magnitudevariations. In seven old catalogues whose historical data have beenintensively compared, 2123 sampled stars have been studied, disregardingstars that we could not identify, double stars which could bemisidentified, or stars observed under poor conditions, and knownvariable stars with large amplitude discrepancies. The independence ofstellar magnitude catalogues is demonstrated by comparing seven oldstudies to each other, suggesting that the magnitude estimates in eachcatalogue reflect the brightness at each observational period.Furthermore, by comparing them with a modern star catalogue, themagnitude differences show a Gaussian distribution. Therefore, if theyare sufficiently larger than the deduced standard deviations, themagnitude variations between the catalogues can be considered real.Thus, the stellar magnitudes compiled in old studies can be used asscientific data within the average intrinsic uncertainty. These sevenold catalogues can be used as data for the survey of the long-termvariability of stars.
| 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
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