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Optical spectroscopy of the dwarf nova U Geminorum
The dwarf nova U Gem is unique in having a direct measurement of the Kvelocity of its white dwarf from Hubble Space Telescope (HST) spectra(K1 = 107 +/- 2kms-1 from Long et al.). We presenthigh-resolution optical spectra of U Gem in quiescence taken to test theaccuracy to which the HST value can be recovered from optical data. Wefind that, even with data of very high signal-to-noise ratio on thisarchetypal system, we cannot recover Long et al.'s value to better thanabout 20 per cent by any method. Contamination by neighbouring emissionlines seems a likely culprit. Our data reveal a number of new features:Doppler tomograms show emission at low velocity, close to the centre ofmass, and a transient, narrow absorption feature is seen in the Balmerlines near the line centres at the time of eclipse. We suggest thatstellar prominences, as previously invoked for the dwarf novae IP Pegand SS Cyg in outburst, may explain both of these features. The HeII4686.75 Å line emission is dominated by the gas stream/disc impactregion. Two distinct spots are seen in Doppler maps, the first beingvery narrow and showing a velocity close to that of the accretion discin the impact region, and the second much broader and located betweenthe velocities of the (ballistic) stream and the (Keplerian) disc. Wepresent tentative evidence of weak spiral structure, which may supportexplanations for `spiral shocks' based upon three-body effects. We findno evidence of stream-disc overflow in the system. Our data suggest aninclination angle >70°, favouring a mass <1.1Msolarfor the white dwarf, in disagreement with measurements of itsgravitational redshift. The mass donor is clearly seen in the Dopplermaps, with emission concentrated towards its poles, and mainly on theside facing the white dwarf. This suggests irradiation with shielding bythe disc from which we estimate a height-to-radius ratio (H/R) between0.15 and 0.25.
| Caroline Herschel's catalogue of nebulae
Not Available
| Rotational and Cyclical Variability in γ Cassiopeia
γ Cas is an unusual classical Be star for which the optical-bandand hard X-ray fluxes vary on a variety of timescales. We report resultsof a 9 yr monitoring effort on this star with a robotic ground-based(APT) telescope in the B, V filter system, as well as simultaneousobservations in 2004 November with this instrument and the RXTE. Ourobservations disclosed no correlated optical response to the rapid X-rayflares in this star, nor did the star show any sustained flux changesany time during two monitored nights in either wavelength regime.Consistent with an earlier study by Robinson et al., optical lightcurves obtained in our new APT program revealed that γ Casundergoes ~3% amplitude cycles with lengths of 50-91 days. Ourobservations in 2004 showed a similar optical cycle. Over the 9 days wemonitored the star with the RXTE, the X-ray flux varied in phase withits optical cycle and with an amplitude predicted from the data inRobinson et al. In general, the amplitude of the V magnitude cycles are30%-40% larger than the corresponding B amplitude, suggesting that theproduction site of the cycles is circumstellar. The cycle lengthsconstantly change and can damp or grow on timescales as short as 13days. We have also discovered a coherent period of 1.21581+/-0.00004days in all our data, which appears consistent only with rotation. Thefull amplitude of this variation is 0.0060 in both filters, and,surprisingly, its waveform is almost sawtooth in shape. This variationis likely to originate on the star's surface. This circumstance hints atthe existence of a strong magnetic field with a complex topology and apossible heterogeneous surface distribution of metals.
| A Comprehensive Search for Gamma-Ray Lines in the First Year of Data from the INTEGRAL Spectrometer
We have carried out an extensive search for gamma-ray lines in the firstyear of public data from the spectrometer (SPI) on the INTEGRAL mission.INTEGRAL has spent a large fraction of its observing time in theGalactic plane with particular concentration in the Galactic center (GC)region (~3 Ms in the first year). Hence the most sensitive searchregions are in the Galactic plane and center. The phase space of thesearch spans the energy range 20-8000 keV and line widths from 0 to 1000keV (FWHM). It includes both diffuse and pointlike emission. We havesearched for variable emission on timescales down to ~1000 s. Diffuseemission has been searched for on a range of different spatial scalesfrom ~20° (the approximate field of view of the spectrometer) up tothe entire Galactic plane. Our search procedures were verified by therecovery of the known gamma-ray lines at 511 and 1809 keV at theappropriate intensities and significances. We find no evidence for anypreviously unknown gamma-ray lines. The upper limits range from afew×10-5 to a few×10-2 cm-2s-1 depending on line width, energy, and exposure; regions ofstrong instrumental background lines were excluded from the search.Comparison is made between our results and various prior predictions ofastrophysical lines.
| 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
| The Homogeneity of Interstellar Elemental Abundances in the Galactic Disk
We present interstellar elemental abundance measurements derived fromSpace Telescope Imaging Spectrograph echelle observations of 47 sightlines extending up to 6.5 kpc through the Galactic disk. These pathsprobe a variety of interstellar environments, covering ranges of nearly4 orders of magnitude in molecular hydrogen fraction f(H2)and more than 2 in mean hydrogen sight-line density. Coupling the current data with Goddard HighResolution Spectrograph data from 17 additional sight lines and thecorresponding Far Ultraviolet Spectroscopic Explorer and Copernicusobservations of H2 absorption features, we explore magnesium,phosphorus, manganese, nickel, copper, and germanium gas-phase abundancevariations as a function of : density-dependentdepletion is noted for each element, consistent with a smooth transitionbetween two abundance plateaus identified with warm and cold neutralinterstellar medium depletion levels. The observed scatter with respectto an analytic description of these transitions implies that totalelemental abundances are homogeneous on length scales of hundreds ofparsecs, to the limits of abundance measurement uncertainty. Theprobable upper limit we determine for intrinsic variability at any is 0.04 dex, aside from an apparent 0.10 dexdeficit in copper (and oxygen) abundances within 800 pc of the Sun.Magnesium dust abundances are shown to scale with the amount of siliconin dust, and in combination with a similar relationship between iron andsilicon, these data appear to favor the young F and G star values ofSofia & Meyer as an elemental abundance standard for the Galaxy.Based on observations with the NASA/ESA.
| The Remarkable Be Star HD 110432 (BZ Crucis)
HD 110432 (B1e) has gained considerable recent attention because it is ahard, variable X-ray source with local absorption and also because itsoptical spectrum is affected by an extensive Be disk. From time-serialechelle data obtained over 2 weeks during 2005 January and February, wehave discovered several remarkable characteristics in the star's opticalspectrum. The line profiles show rapid variations on some nights, whichcan most likely be attributed to irregularly occurring and short-livedmigrating subfeatures. Such features have been found in spectra ofγ Cas and AB Dor, two stars for which it is believed magneticfields force circumstellar clouds to corotate over the star's surface.The star's optical spectrum also exhibits a number of mainly Fe II andHe I emission features with double-lobed profiles typical of anoptically thin circumstellar disk viewed nearly edge-on. Using spectralsynthesis techniques for the January data, we find that its temperatureand column density are close to 9800 K and roughly3×1022 cm-2, respectively. Its projecteddisk size covers remarkably large 100 stellar areas, and the emittingvolume resides at a surprisingly large distance of 1 AU from the star.Surprisingly, we also find that the absorption wings of the strongestoptical and UV lines in the spectrum extend to at least +/-1000 kms-1, even though the rotational velocity is 300-400 kms-1. We are unable to find a satisfactory explanation forthese extreme line broadenings. Otherwise, HD 110432 and γ Casshare similarly peculiar X-ray and optical characteristics. Theseinclude a high X-ray temperature, erratic X-ray variability ontimescales of a few hours, optical metallic emission lines, andsubmigrating features in optical line profiles. Because of thesesimilarities, we suggest that HD 110432 is a member of a select newclass of ``γ Cas analogs.''
| Constraining Disk Parameters of Be Stars using Narrowband Hα Interferometry with the Navy Prototype Optical Interferometer
Interferometric observations of two well-known Be stars, γ Cas andφ Per, were collected and analyzed to determine the spatialcharacteristics of their circumstellar regions. The observations wereobtained using the Navy Prototype Optical Interferometer equipped withcustom-made narrowband filters. The filters isolate the Hαemission line from the nearby continuum radiation, which results in anincreased contrast between the interferometric signature due to theHα-emitting circumstellar region and the central star. Because thenarrowband filters do not significantly attenuate the continuumradiation at wavelengths 50 nm or more away from the line, theinterferometric signal in the Hα channel is calibrated withrespect to the continuum channels. The observations used in this studyrepresent the highest spatial resolution measurements of theHα-emitting regions of Be stars obtained to date. Theseobservations allow us to demonstrate for the first time that theintensity distribution in the circumstellar region of a Be star cannotbe represented by uniform disk or ringlike structures, whereas aGaussian intensity distribution appears to be fully consistent with ourobservations.
| Properties and nature of Be stars. 24. Better data and model for the Be+F binary V360 Lacertae
Aims.We include existing photometric and spectroscopic material with newobservations in a detailed study of the Be+F binary V360Lac. Methods: .We used the programs FOTEL and KOREL toderive an improved linear ephemeris and to disentangle the line profilesof both binary components and telluric lines. The BINSYN software suite(described in the paper) is used to calculate synthetic light curves andspectra to fit the {UBV} photometry, an {IUE} spectrum, blue and redground-based spectra, and observed radial-velocity curves.Results: .The observations provide evidence of circumstellar matter inthe system. The system model shows that the Be primary star iscritically rotating, and that the synchronously rotating secondary starfills its Roche lobe. The primary star has a mass of7.45ȯ. Radial-velocity observations establish a massratio of 0.163. Light curve synthesis demonstrates that the observedlight curves are controlled largely by tidal distortion and irradiationof the massive primary by the less massive secondary. Synthetic spectrafit both blue and red observed spectra with the exception of spectrallines affected by circumstellar matter in the system. The syntheticspectra allow for gravity darkening and are consistent with criticalrotation of the primary. Synthetic spectrum fits to a dereddened {IUE}spectrum produce a calculated system distance of 512 pc. This distanceis 2σ beyond the Hipparcos distance.
| New γ Cassiopeiae-like objects: X-ray and optical observations of SAO 49725 and HD 161103
A growing number of early Be stars exhibit X-ray luminosities that areintermediate between those typical of early type stars and those emittedby most Be/X-ray binaries in quiescence. We report on XMM-Newtonobservations of two such Be stars, SAO 49725 andHD 161103, which were originally discovered in asystematic cross-correlation between the ROSAT all-sky survey andSIMBAD. The new observations confirm the X-ray luminosity excess(LX ~ 1032-33 erg s-1) and the hardnessof their X-ray spectra, which are both unusual for normal early typestars. An iron Kα complex is clearly detected in HD161103 in which the H-like, He-like, and fluorescentcomponents are resolved, while strong evidences also exist for thepresence of similar features in SAO 49725. X-rayspectra can be equally well-fitted by a thermal plasma (mekal) with T ~108 K and solar abundances or by a power law + iron linemodel with photon index ~1.5-1.8, both with a soft thermal componentwith T ~ 107 K. The intensity of the fluorescence 6.4 keVline reflects the presence of large amounts of cold material close tothe X-ray sources and strongly argues against accretion onto a companionneutron star in a large orbit. On the other hand, the probable thermalorigin of the X-ray emission, as supported by the ionised iron lines,disagrees with those observed in all known Be/X-ray binaries, in which anon-thermal component is always required. Remarkably, the X-ray featuresare similar to those of white dwarves in several cataclysmic variables.There is no evidence of high frequency pulsations in neither of the twosystems. However, a large oscillation in the light curve of HD161103 with P ~ 3200 s is readily detected. The X-ray lightcurve of SAO 49725 exhibits clear variability by ~80%on time scales as short as ~1000 s. New optical observations provideupdated spectral types (B0.5 III-Ve) and disclose a dense, large, andapparently stable circumstellar disc for both stars. The nature of theexcess X-ray emission is discussed in light of the models proposed forγ Cas, magnetic disc-star interaction, oraccretion onto a compact companion object - whether neutron star orwhite dwarf. These two new objects, added to similar cases discovered inXMM-Newton surveys, point to the emergence of a new class ofγ Cas analogs.
| The polar wind of the fast rotating Be star Achernar. VINCI/VLTI interferometric observations of an elongated polar envelope
Context: .Be stars show evidence of mass loss and circumstellarenvelopes (CSE) from UV resonance lines, near-IR excesses, and thepresence of episodic hydrogen emission lines. The geometry of theseenvelopes is still uncertain, although it is often assumed that they areformed by a disk around the stellar equator and a hot polar wind.Aims: .We probe the close environment of the fast rotating Be starAchernar at angular scales of a few milliarcseconds (mas) in theinfrared, in order to constrain the geometry of a possible polar CSE. Methods: .We obtained long-baseline interferometric observations ofAchernar with the VINCI/VLTI beam combiner in the H and K bands, usingvarious telescope configurations and baseline lengths with a wideazimuthal coverage. Results: .The observed visibility measurementsalong the polar direction are significantly lower than the visibilityfunction of the photosphere of the star alone, in particular at lowspatial frequencies. This points to the presence of an asymmetricdiffuse CSE elongated along the polar direction of the star. To ourdata, we fit a simple model consisting of two components: a 2Delliptical Gaussian superimposed on a uniform ellipse representing thedistorted photosphere of the fast rotating star. Conclusions: .Weclearly detected a CSE elongated along the polar axis of the star, aswell as rotational flattening of the stellar photosphere. For theuniform-ellipse photosphere we derive a major axis of θ_eq = 2.13± 0.05 mas and a minor axis of θ_pol = 1.51 ± 0.02mas. The relative near-IR flux measured for the CSE compared to thestellar photosphere is f = 4.7 ± 0.3%. Its angular dimensions areloosely constrained by the available data at ρ_eq = 2.7 ± 1.3mas and ρ_pol = 17.6 ± 4.9 mas. This CSE could be linked tofree-free emission from the radiative pressure driven wind originatingfrom the hot polar caps of the star.
| 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.
| First sky validation of an optical polarimetric interferometer
Aims.We present the first lab and sky validation of spectro-polarimetricequipment put at the combined focus of an optical long-baselineinterferometer. We tested the polarimetric mode designed for the visibleGI2T Interferometer to offer spectropolarimetric diagnosis at themilliarcsecond scale. Methods.We first checked the wholeinstrumental polarization in the lab with a fringe simulator, and thenwe observed α Cep and α Lyr as stellar calibrators ofdifferent declinations to tabulate the polarization effects throughoutthe GI2T declination range. Results.The difference between bothlinear polarizations is within the error bars and the visibilitiesrecorded in natural light (i.e. without the polarimeter) for calibrationpurposes are the same order of magnitude as the polarized ones. Wefollowed the α Cep visibility for 2 h after the transit andα Lyr for 1.5 h and detected no decrease with hour angle due tothe fringe pattern smearing by instrumental polarization. Conclusions.Differential celestial rotation due to the dissymetricCoudé trains of the GI2T is well-compensated by the fieldrotators, so the instrumental polarization is controlled over arelatively wide hour angle range (±2 h around the transit atleast). Such a polarimetric mode opens new opportunities especially forstudies of circumstellar environments and significantly enhances boththe potential of an optical array and its ability for accuratecalibration.
| INTEGRAL survey of the Cassiopeia region in hard X rays
We report on the results of a deep 1.6 Ms INTEGRAL observation of theCassiopeia region performed from December 2003 to February 2004. Elevensources were detected with the imager IBIS-ISGRI at energies above 20keV, including three new hard X-ray sources. Most remarkable is thediscovery of hard X-ray emission from the anomalous X-ray pulsar 4U0142+61, which shows emission up to ~150 keV with a very hard power-lawspectrum with photon index Γ = 0.73 ± 0.17. We derived fluxupper limits for energies between 0.75 MeV and 30 MeV using archivaldata from the Compton telescope COMPTEL. In order to reconcile the veryhard spectrum of 4U 0142+61 measured by INTEGRAL with the COMPTEL upperlimits, the spectrum has to bend or break between ~75 keV and ~750 keV.1E 2259+586, another anomalous X-ray pulsar in this region, was notdetected. INTEGRAL and COMPTEL upper limits are provided. The newINTEGRAL sources are IGR J00370+6122 and IGR J00234+6144. IGRJ00370+6122 is a new supergiant X-ray binary with an orbital period of15.665 ± 0.006 days, derived from RXTE All-Sky Monitor data.Archival BeppoSAX Wide-Field Camera data yielded four more detections.IGR J00234+6144 still requires a proper identification. Other sourcesfor which INTEGRAL results are presented are high-mass X-ray binaries 2S0114+650, γ Cas, RX J0146.9+6121 and 4U 2206+54, intermediatepolar V709 Cas and 1ES 0033+595, an AGN of the BL-Lac type. For each ofthese sources the hard X-ray spectra are fitted with different modelsand compared with earlier published results.
| Observations of Hα, iron, and oxygen lines in B, Be, and shell stars
We carried out a spectroscopic survey of several B, Be, and shell starsin optical and near-infrared regions. Line profiles of the Hα lineand of selected Fe II and O I lines are presented.
| Is the model of one-armed oscillations able to explain the long-term V/R changes of Be stars?
Context: .Many scientists studying Be stars currently adopt the model ofone-armed oscillations as the correct explanation of the cycliclong-term {V/R} variations observed for a number of Be stars. We testthe ability of this model to be used for the predictions of V/Rvariations in real observed Be stars. Aims: .The behavior of theone-armed oscillations can be described as a solution of linearizedhydrodynamical equations with the presence of "distorted" gravitationalpotential and a radiation force. Methods: .We developed a newcomputer program to model one-armed oscillations in Be star disks, whichincludes both the pressure force and the quadrupole term in thegravitational potential, related to the obliquity of a rapidly rotatingstar inside the disk. Moreover, we slightly improved the model in aneffort to decrease the number of input parameters with the help of NLTEstellar atmosphere models. Results: .We carried out detailed testsof the dependence of V/R "periods" predicted by the model on allindividual input parameters. We arrived at the following results: (1)the model has great potential to explain not only the cause of thecyclic long-term V/R changes but also some of the observed statisticalproperties of the phenomenon. (2) The model in its present linear formcannot be considered as proven. Its ability to predict the duration ofV/R cycles for individual well observed Be stars is insufficient.Changing some of the input parameters of the model, which are stillloosely constrained by observations and/on current understanding of thedisks, like the radial density distribution in the disk, one can easilyarrive at any desired cycle length from, say, 1 to 20 years.Conclusions: . Clearly, a much more sophisticated non-linear andself-consistent model of disk structure and its oscillations will beneeded before a truly quantitative test of a one-armed model vs.observations will be possible.
| 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.
| Non-LTE Line-Formation and Abundances of Sulfur and Zinc in F, G, and K Stars
Extensive statistical-equilibrium calculations on S I and Zn I were carried out, in orderto investigate how the non-LTE effect plays a role in the determinationof their abundances in F-K stars. Having checked on the spectra ofrepresentative F-type stars (Polaris, Procyon, α Per) and the Sunthat our non-LTE corrections yield a reasonable consistency between theabundances derived from different lines, we tried an extensive non-LTEreanalysis of published equivalent-width data of S I and Zn I lines for metal-poorhalo/disk stars. According to our calculations, S I 9212/9228/9237 lines suffer significant negative non-LTEcorrections (lesssim 0.2‑0.3 dex), while LTE is practically validfor S I 8683/8694 lines. As far as the verymetal-poor regime is concerned, a marked discordance is observed betweenthe [S/Fe] values from these two abundance indicators, in the sense thatthe former attains a nearly flat plateau (or even a slight downwardbending) while the latter shows an ever-increasing trend with a furtherlowering of metallicity. The characteristics of [Zn/Fe] reported fromrecent LTE studies (i.e., an evident/slight increase of [Zn/Fe] with adecrease of [Fe/H] for very metal-poor/disk stars) were almostconfirmed, since the non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be positive andgradually increasing toward lower [Fe/H]) are quantitatively of lesssignificance (lesssim 0.1 dex).
| Sulfur Abundances in Metal-Poor Stars Based on OAO-1.88m/HIDES Spectra
The LTE abundances of sulfur (S) of 21 metal-poor stars and one normalstar were explored in the metallicity range of -3 < [Fe/H] ≤ 0,based on the equivalent widths of the S I (1) 9212, 9237Å and S I(6) 8693, 9894Å lines measured on high-resolution spectra, whichwere observed by the OAO 1.88-m telescope equipped with HIDES. Our mainresults are: (1) The abundances derived from the S I (6) lines areconsistent with those from the S I (1) lines among our sample stars inthe range of [Fe/H] > -2 with an average difference of +0.03 ±0.05 dex, whereas a significant discrepancy is observed in the range of[Fe/H] ≤ -2. (2) The behavior of [S(6)/Fe], versus [Fe/H] of ourhalo sample stars exhibits a nearly flat trend with an average of +0.62± 0.09 dex in the range of -3 < [Fe/H] < -1.25, and shows adistribution around +0.29 dex in -1.25 ≤ [Fe/H] ≤ -0.7. Oursample stars with -1.25 ≤ [Fe/H] ≤ -0.5 follow an increasingtrend with decreasing [Fe/H]. The behavior of [S(1)/Fe] of our samplestars also shows essentially the same trend as [S(6)/Fe], though it isquantitatively different. (3) The S behavior in the range of -3 <[Fe/H] ≤ 0 inferred from the abundances of multiplets 6 and 1 arequalitatively consistent with each other, and may be represented by acombination of a nearly flat trend and a linearly increasing trend withdecreasing [Fe/H]. A transition of the trend is likely to occur at[Fe/H] -1.5 dex.
| Forty Years of Spectroscopic Stellar Astrophysics in Japan
The development of Japanese spectroscopic stellar astrophysics in therecent 40 years is reviewed from an observational point of view. In thisarticle, the research activities are provisionally divided into fourfields: hot stars, hot emission-line (Be) stars, cool stars, and otherstars. Historical developments of the observational facilities atOkayama Astrophysical Observatory (spectrographs and detectors) are alsosummarized in connection with the progress in scientific researchactivities.
| On the feasibility of detection of neutron star companions to OB runaways using Gaia astrometry
For an illustrative sample of classical OB runaway stars, we examine thecapability of the upcoming Gaia satellite to detect compact companionsby the use of astrometric techniques. For the OB runaway stars in oursample, we estimate initial system parameters and consider the modifyingevolutionary effects of mass transfer and supernova explosion of theprimary. The possible system configurations that follow from this, andthe expected Gaia accuracy, determine the likelihood of detecting amovement of the photocentre due to an unseen companion. As the size ofthe natal kick imparted to the core of the exploding star is increasedthe overall probability of detecting a neutron star companion decreasesas more systems become disrupted. The overall detection probabilitiesfor our illustrative sample range from 2% to 27%, which imply thatwithin a distance of approximately 5 kpc from the Sun around 48detections of compact companions to runaway stars can be expected. Forcomparison, around 15% of High Mass X-ray Binaries would exhibit wobblesdetectable with Gaia.
| La supernova de 1572, une diversite d'interpretations.
Not Available
| FUSE Determination of a Low Deuterium Abundance along an Extended Sight Line in the Galactic Disk
We present a study of the deuterium abundance along the extended sightline toward HD 90087 with the Far Ultraviolet Spectroscopic Explorer(FUSE). HD 90087 is a O9.5 III star located in the Galactic disk at adistance of ~2.7 kpc away from the Sun. Both in terms of distance andcolumn densities, HD 90087 has the longest and densest sight lineobserved in the Galactic disk for which a deuterium abundance has beenmeasured from ultraviolet absorption lines so far. Because manyinterstellar clouds are probed along this sight line, possiblevariations in the properties of individual clouds should be averagedout. This would yield a deuterium abundance that is characteristic ofthe interstellar medium on scales larger than the Local Bubble. The FUSEspectra of HD 90087 show numerous blended interstellar and stellarfeatures. We have measured interstellar column densities of neutralatoms, ions, and molecules by simultaneously fitting the interstellarabsorption lines detected in the different FUSE channels. As far aspossible, saturated lines were excluded from the fits in order tominimize possible systematic errors. IUE (International UltravioletExplorer) archival data are also used to measure neutral hydrogen. Wereport D/O=(1.7+/-0.7)×10-2 andD/H=(9.8+/-3.8)×10-6 (2 σ). Our new resultsconfirm that the gas-phase deuterium abundance in the distantinterstellar medium is significantly lower than the one measured withinthe Local Bubble. We supplement our study with a revision of the oxygenabundance toward Feige 110, a moderately distant (~200 pc) sdOB star,located ~150 pc below the Galactic plane. Excluding saturated lines fromthe fits of the FUSE spectra is critical; this led us to derive an O Icolumn density about 2 times larger than the one previously reported forFeige 110. The corresponding updated D/O ratio on this sight line isD/O=(2.6+/-1.0)×10-2 (2 σ), which is lower thanthe one measured within the Local Bubble. The data set available nowoutside the Local Bubble, which is based primarily on FUSE measurements,shows a contrast between the constancy of D/O and the variability ofD/H. As oxygen is considered to be a good proxy for hydrogen within theinterstellar medium, this discrepancy is puzzling.
| Chandra HETGS Multiphase Spectroscopy of the Young Magnetic O Star θ1 Orionis C
We report on four Chandra grating observations of the oblique magneticrotator θ1 Ori C (O5.5 V), covering a wide range ofviewing angles with respect to the star's 1060 G dipole magnetic field.We employ line-width and centroid analyses to study the dynamics of theX-ray-emitting plasma in the circumstellar environment, as well asline-ratio diagnostics to constrain the spatial location, and globalspectral modeling to constrain the temperature distribution andabundances of the very hot plasma. We investigate these diagnostics as afunction of viewing angle and analyze them in conjunction with new MHDsimulations of the magnetically channeled wind shock mechanism onθ1 Ori C. This model fits all the data surprisinglywell, predicting the temperature, luminosity, and occultation of theX-ray-emitting plasma with rotation phase.
| Fluorescent Molecular Hydrogen Emission in IC 63: FUSE, Hopkins Ultraviolet Telescope, and Rocket Observations
We present far-ultraviolet observations of IC 63, an emission/reflectionnebula illuminated by the B0.5 IV star γ Cas, located 1.3 pc fromthe nebula. Molecular hydrogen fluorescence was detected first in IC 63by IUE and later at shorter wavelengths by ORFEUS. Here we present FarUltraviolet Spectroscopic Explorer (FUSE) observations toward threelocations in the nebula, complemented by Hopkins Ultraviolet Telescope(HUT) data on the central nebular position. In addition, we present asounding rocket calibration of a FUSE spectrum of γ Cas. Molecularhydrogen fluorescence is detected in all three FUSE pointings. Theintensity of this emission, as well as the contributions from otherspecies, are seen to vary with position. The absolute flux calibrationof the sounding rocket data allows us to reliably predict the radiationfield incident on IC 63. We use these data to test models of thefluorescent process. Our modeling resolves the perceived discrepancybetween the existing ultraviolet observations and achieves asatisfactory agreement with the H2 rotational structureobserved with FUSE.
| Properties of the Hα-emitting Circumstellar Regions of Be Stars
Long-baseline interferometric observations obtained with the NavyPrototype Optical Interferometer of the Hα-emitting envelopes ofthe Be stars η Tau and β CMi are presented. For compatibilitywith the previously published interferometric results in the literatureof other Be stars, circularly symmetric and elliptical Gaussian modelswere fitted to the calibrated Hα observations. The models areadequate for characterizing the angular distribution of theHα-emitting circumstellar material associated with these Be stars.To study the correlations between the various model parameters and thestellar properties, the model parameters for η Tau and β CMiwere combined with data for other Be stars from the literature. Afteraccounting for the different distances to the sources and stellarcontinuum flux levels, it was possible to study the relationship betweenthe net Hα emission and the physical extent of theHα-emitting circumstellar region. A clear dependence of the netHα emission on the linear size of the emitting region isdemonstrated, and these results are consistent with an optically thickline emission that is directly proportional to the effective area of theemitting disk. Within the small sample of stars considered in thisanalysis, no clear dependence on the spectral type or stellar rotationis found, although the results do suggest that hotter stars might havemore extended Hα-emitting regions.
| A Multiwavelength Study of IC 63 and IC 59
IC 63 and IC 59 are two nearby arc-shaped nebulae with relatively simplegeometries and minimal obscuring material. The two regions, in spite ofa similar projected distance from their ionizing star, have verydifferent observational properties, both in continuum emission and inthe presence and strength of line emission from molecular species. Thispaper conducts a multiwavelength study of the two regions using archiveddata from a variety of sources, including the Canadian Galactic PlaneSurvey and the Infrared Space Observatory. The multiwavelengthmorphology and structure of the two nebulae are studied in detail,particularly the ionization fronts in IC 63. The possibility oftriggered star formation in IC 63 is investigated and determined to bespurious. H2 and polycyclic aromatic hydrocarbon emission isdetected in both IC 63 and IC 59, confirming the presence of molecularhydrogen in IC 59. The averaged line ratios are similar in the tworegions, but variations are seen within each region. Temperatures anddensities were calculated from the S(3) and S(5) pure rotational linesof molecular hydrogen. We derived a temperature of 630 K in IC 63,comparable to previous results, and a column density of5.8×1017 cm-2, somewhat lower than previousvalues. New results for IC 59 show values of 590 K and3.4×1017 cm-2, slightly cooler and withlower column density than IC 63. The contrast in appearance between IC63 and IC 59 is consistent with a difference in actual (rather thanprojected) distances and a small variation in temperature and columndensity.
| On the evolutionary status of Be stars. I. Field Be stars near the Sun
A sample of 97 galactic field Be stars were studied by taking intoaccount the effects induced by the fast rotation on their fundamentalparameters. All program stars were observed in the BCDspectrophotometric system in order to minimize the perturbationsproduced by the circumstellar environment on the spectral photosphericsignatures. This is one of the first attempts at determining stellarmasses and ages by simultaneously using model atmospheres andevolutionary tracks, both calculated for rotating objects. The stellarages (τ) normalized to the respective inferred time that eachrotating star can spend in the main sequence phase (τ_MS) reveal amass-dependent trend. This trend shows that: a) there are Be starsspread over the whole interval 0 τ/τ_MS 1 of themain sequence evolutionary phase; b) the distribution of points in the(τ/τMS,M/Mȯ) diagram indicates thatin massive stars (M 12~Mȯ) the Be phenomenon ispresent at smaller τ/τ_MS age ratios than for less massive stars(M 12~Mȯ). This distribution can be due to: i)higher mass-loss rates in massive objets, which can act to reduce thesurface fast rotation; ii) circulation time scales to transport angularmomentum from the core to the surface, which are longer the lower thestellar mass.
| First VLTI/MIDI observations of a Be star: Alpha Arae
We present the first VLTI/MIDI observations of the Be star alpha Ara (HD158 427), showing a nearly unresolved circumstellar disk in the N band.The interferometric measurements made use of the UT1 and UT3 telescopes.The projected baselines were 102 and 74 meters with position angles of 7° and 55°, respectively. These measurements put an upper limiton the envelope size in the N band under the uniform disk approximationof φmax= 4±1.5 mas, corresponding to 14R*, assuming R*=4.8 Rȯ and theHipparcos distance of 74 pc. On the other hand the disk density must belarge enough to produce the observed strong Balmer line emission. Inorder to estimate the possible circumstellar and stellar parameters wehave used the SIMECA code developed by Stee et al. (1995, A&A, 300,219) and Stee & Bittar (2001, A&A, 367, 532). Optical spectrataken with the échelle instrument Heros and the ESO-50 cmtelescope, as well as infrared ones from the 1.6m Brazilian telescopewere used together with the MIDI spectra and visibilities. Theseobservations place complementary constraints on the density and geometryof the alpha Ara circumstellar disk. We discuss the potential truncationof the disk by a companion and we present spectroscopic indications of aperiodic perturbation of some Balmer lines.
| 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
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