SKY-MAP.ORG
 Home Getting Started To Survive in the Universe News@Sky Astro Photo The Collection Forum Blog New! FAQ Press Login

ζ Aql (Okab)

Contents

Images

DSS Images   Other Images

Related articles

 Reliability Checks on the Indo-US Stellar Spectral Library Using Artificial Neural Networks and Principal Component AnalysisThe Indo-US coudé feed stellar spectral library (CFLIB) madeavailable to the astronomical community recently by Valdes et al. (2004,ApJS, 152, 251) contains spectra of 1273 stars in the spectral region3460 to 9464Å at a high resolution of 1Å (FWHM) and a widerange of spectral types. Cross-checking the reliability of this databaseis an important and desirable exercise since a number of stars in thisdatabase have no known spectral types and a considerable fraction ofstars has not so complete coverage in the full wavelength region of3460-9464Å resulting in gaps ranging from a few Å to severaltens of Å. We use an automated classification scheme based onArtificial Neural Networks (ANN) to classify all 1273 stars in thedatabase. In addition, principal component analysis (PCA) is carried outto reduce the dimensionality of the data set before the spectra areclassified by the ANN. Most importantly, we have successfullydemonstrated employment of a variation of the PCA technique to restorethe missing data in a sample of 300 stars out of the CFLIB. Near-Ultraviolet Observations of HD 221170: New Insights into the Nature of r-Process-rich StarsEmploying high-resolution spectra obtained with the near-UV-sensitivedetector on the Keck I HIRES, supplemented by data obtained with theMcDonald Observatory 2d-coudé, we have performed a comprehensivechemical composition analysis of the bright r-process-rich metal-poorred giant star HD 221170. Analysis of 57 individual neutral and ionizedspecies yielded abundances for a total of 46 elements and significantupper limits for an additional five. Model stellar atmosphere parameterswere derived with the aid of ~200 Fe peak transitions. From more than350 transitions of 35 neutron-capture (Z>30) species, abundances for30 neutron-capture elements and upper limits for three others werederived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, wederive ratios of logε(Th/La)=-0.73 (σ=0.06) andlogε(Th/Eu)=-0.60 (σ=0.05), values in excellent agreementwith those previously derived for other r-process-rich metal-poor starssuch as CS 22892-052, BD +17 3248, and HD 115444. Based on the Th/Euchronometer, the inferred age is 11.7+/-2.8 Gyr. The abundancedistribution of the heavier neutron-capture elements (Z>=56) isfitted well by the predicted scaled solar system r-process abundances,as also seen in other r-process-rich stars. Unlike other r-process-richstars, however, we find that the abundances of the lighterneutron-capture elements (37 Resolving the Effects of Rotation in Altair with Long-Baseline InterferometryWe report the successful fitting of a Roche model, with a surfacetemperature gradient following the von Zeipel gravity darkening law, toobservations of Altair made with the Navy Prototype OpticalInterferometer. We confirm the claim by Ohishi et al. that Altairdisplays an asymmetric intensity distribution due to rotation, the firstsuch detection in an isolated star. Instrumental effects due to the highvisible flux of this first magnitude star appear to be the limitingfactor in the accuracy of this fit, which nevertheless indicates thatAltair is rotating at 0.90+/-0.02 of its breakup (angular) velocity. Ourresults are consistent with the apparent oblateness found by van Belleet al. and show that the true oblateness is significantly larger owingto an inclination of the rotational axis of ~64° to the line ofsight. Of particular interest, we conclude that instead of beingsubstantially evolved as indicated by its classification, A7 IV-V,Altair is only barely off the zero-age main sequence and represents agood example of the difficulties rotation can introduce in theinterpretation of this part of the HR diagram. Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey IWe 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. New clues on outburst mechanisms and improved spectroscopic elements of the black hole binary V4641 Sagittarii*We present spectroscopic observations of the black hole binary V4641Sagittarii, obtained between 2004 July 4 and 2005 March 28, which coverthe minor outburst of the star in early 2004 July and quiescencevariations on 19 nights scattered over six months. During the outburst,the star peaked approximately 3 mag brighter than usual, and our spectrawere dominated by broad hydrogen, helium and iron emission lines. Thevery first spectra showed P Cygni profiles, which disappeared within afew hours, indicating rapid changes in matter ejection. The Hαline had multiple components, one being a broad blueshifted wingexceeding 5000 km s-1. During a simultaneously observed10-min photometric flare up, the equivalent width of the Hα linetemporarily decreased, implying that it was a flare of the continuum.The overall spectral appearance was similar to that observed in the 1999September active phase, which suggests that similar mass-ejectionprocesses were associated with both eruptions. In quiescence, thespectra were those of the early-type secondary star showing its orbitalmotion around the primary. By measuring cross-correlation radialvelocities, we give an improved set of spectroscopic elements. Whereaswe measure the same velocity amplitude (K2= 211.3 +/- 1.0 kms-1), within errors, as Orosz et al., our centre-of-massvelocity (γ= 72.7 +/- 3.3 km s-1) differs significantlyfrom the previously published value (107.4 +/- 2.9 km s-1).However, we find evidence that the difference is caused by a systematicerror in data reduction in the previous study, rather than bygravitational effects of an invisible third component. A Spitzer Study of Dusty Disks around Nearby, Young StarsWe have obtained Spitzer Space Telescope MIPS (Multiband ImagingPhotometer for Spitzer) observations of 39 A- through M-type dwarfs,with estimated ages between 12 and 600 Myr; IRAC observations for asubset of 11 stars; and follow-up CSO SHARC II 350 μm observationsfor a subset of two stars. None of the objects observed with IRACpossess infrared excesses at 3.6-8.0 μm however, seven objectsobserved with MIPS possess 24 and/or 70 μm excesses. Four objects(κ Phe, HD 92945, HD 119124, and AU Mic), with estimated ages12-200 Myr, possess strong 70 μm excesses, >=100% larger thantheir predicted photospheres, and no 24 μm excesses, suggesting thatthe dust grains in these systems are cold. One object (HD 112429)possesses moderate 24 and 70 μm excesses with a color temperature,Tgr=100 K. Two objects (α1 Lib and HD177724) possess such strong 24 μm excesses that their 12, 24, and 70μm fluxes cannot be self-consistently modeled using a modifiedblackbody despite a 70 μm excess >2 times greater than thephotosphere around α1 Lib. The strong 24 μm excessesmay be the result of emission in spectral features, as observed towardthe Hale-Bopp star HD 69830. The Massive Runaway Stars HD 14633 and HD 15137We present results from a radial velocity study of two runaway O-typestars, HD 14633 (ON8.5 V) and HD 15137 [O9.5 III(n)]. We find that HD14633 is a single-lined spectroscopic binary with an orbital period of15.4083 days. The second target, HD 15137, is a radial velocity variableand a possible single-lined spectroscopic binary with a period close to1 month. Both binaries have large eccentricity, small semiamplitude, anda small mass function. We show the trajectories of the stars in the skybased on an integration of motion in the Galactic potential, and wesuggest that both stars were ejected from the vicinity of the opencluster NGC 654 in the Perseus spiral arm. The binary orbital parametersand runaway velocities are consistent with the idea that both thesestars were ejected by supernova explosions in binaries and that theyhost neutron star companions. We find that the time of flight sinceejection is longer than the predicted evolutionary timescales for thestars. This discrepancy may indicate that the stars have a lower massthan normally associated with their spectral classifications, that theywere rejuvenated by mass transfer prior to the supernova, or that theirlives have been extended through rapid rotation.Based in part on observations made at the Observatoire de Haute Provence(CNRS), France. Determining the Physical Properties of the B Stars. II. Calibration of Synthetic PhotometryWe present a new calibration of optical (UBV, Strömgren uvbyβ,and Geneva) and near-IR (Johnson RIJHK and Two Micron All Sky Survey)photometry for B and early A stars derived from Kurucz ATLAS9 modelatmospheres. Our sample of stars consists of 45 normal nearby B andearly A stars that have high-quality, low-resolution IUE spectra andaccurate Hipparcos parallaxes. The calibration is unique because itrelies only on the UV spectral energy distributions, the absolute fluxcalibration of the V filter, and the Hipparcos distances to determinethe appropriate model atmospheres for the program stars. These modelsare then used to calibrate the synthetic photometry. We compare ourresults with previous well-accepted results and provide a thoroughdiscussion of the random errors and systematic effects affecting thecalibration. In particular, we demonstrate the influence of vsini onsurface gravities derived from fitting model atmospheres. Finally, wediscuss some of our intended applications of this new calibration. The Indo-US Library of Coudé Feed Stellar SpectraWe have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http. Asymmetric Surface Brightness Distribution of Altair Observed with the Navy Prototype Optical InterferometerAn asymmetric surface brightness distribution of the rapidly rotating A7IV-V star Altair has been measured by the Navy Prototype OpticalInterferometer (NPOI). The observations were recorded simultaneouslyusing a triangle with long baselines of 30, 37, and 64 m, on 19 spectralchannels, covering the wavelength range of 520-850 nm. The outstandingcharacteristics of these observations are (1) high resolution with theminimum fringe spacing of 1.7 mas, easily resolving the 3 mas stellardisk, and (2) the measurement of the closure phase, which is a sensitiveindicator of the asymmetry of the brightness distribution of the source.Uniform-disk diameters fitted to the measured squared visibilityamplitudes confirm Altair's oblate shape due to its rapid rotation. Themeasured observables of Altair showed two features that are inconsistentwith both the uniform-disk and limb-darkened-disk models, while themeasured observables of the comparison star, Vega, are consistent withthe limb-darkened-disk model. The first feature is that measured squaredvisibility amplitudes at the first minimum do not reach zero but ratherremain at ~0.002, indicating the existence of a small bright region onthe stellar disk. The other is that the measured closure phases areneither 0° nor 180° at all spectral channels, which requires anasymmetric surface brightness distribution. We fitted the measuredobservables to a model with a bright spot on a limb-darkened disk andfound that the observations are well reproduced by a bright spot, whichhas relative intensity of 4.7%, on a 3.38 mas limb-darkened stellardisk. Rapid rotation of Altair indicates that this bright region is apole, which is brighter than other part of the star owing to gravitydarkening. Mass and Angular Momentum Transfer in the Massive Algol Binary RY PerseiWe present an investigation of the Hα emission-line variationsobserved in the massive Algol binary RY Per. We give new radial velocitydata for the secondary based on our optical spectra and for the primarybased on high-dispersion UV spectra. We present revised orbital elementsand an estimate of the primary's projected rotational velocity (whichindicates that the primary is rotating 7 times faster than thesynchronous rate). We use a Doppler tomography algorithm to reconstructthe individual primary and secondary spectra in the region of Hα,and we subtract the latter from each of our observations to obtainprofiles of the primary and its disk alone. Our Hα observations ofRY Per show that the mass-gaining primary is surrounded by a persistentbut time-variable accretion disk. The profile that is observed outsideeclipse has weak double-peaked emission flanking a deep centralabsorption, and we find that these properties can be reproduced by adisk model that includes the absorption of photospheric light by theband of the disk seen in projection against the face of the star. Wedeveloped a new method to reconstruct the disk surface densitydistribution from the ensemble of Hα profiles observed around theorbit, and this method accounts for the effects of disk occultation bythe stellar components, the obscuration of the primary by the disk, andflux contributions from optically thick disk elements. The resultingsurface density distribution is elongated along the axis joining thestars in the same way as seen in hydrodynamical simulations of gas flowsthat strike the mass gainer near the trailing edge of the star. Thistype of gas stream configuration is optimal for the transfer of angularmomentum, and we show that rapid rotation is found in other Algolsystems that have passed through a similar stage. The Massive Triple Star System HD 16429 AHD 16429 A is a triple star system consisting of a single-linedspectroscopic binary and a widely separated third component, previouslyidentified via speckle interferometry. Here I present the first orbitalelements for the unblended spectroscopic binary as well as estimates ofthe spectral types and relative flux contributions for each visiblecomponent based on a Doppler tomographic reconstruction of theirspectra. There are several stars around HD 16429 A, including the nearbyBe X-ray binary and microquasar LS I +61deg303, which allprobably belong to a subcluster within the Cas OB6 association. Local Interstellar Matter: The Apex CloudSeveral nearby individual low column density interstellar cloudlets havebeen identified previously on the basis of kinematical features evidentin high-resolution Ca+ observations near the Sun. One ofthese cloudlets, the Apex Cloud'' (AC), is within 5 pc of the Sun inthe solar apex direction. The question of which interstellar cloud willconstitute the next Galactic environment of the Sun can, in principle,be determined from cloudlet velocities. The interstellar absorptionlines toward α Cen (the nearest star) are consistent withinmeasurement uncertainties with the projected G'' cloud (GC) and ACvelocities, and also with the velocity of the cloud inside of the solarsystem (the local interstellar cloud [LIC]), provided a small velocitygradient is present in the LIC. The high GC column density towardα Oph compared to α Aql suggests that α Aql may beembedded in the GC so that the AC would be closer to the Sun than theGC. This scenario favors the AC as the next cloud to be encountered bythe Sun, and the AC would have a supersonic velocity with respect to theLIC. The weak feature at the AC velocity toward 36 Oph suggests that theAC cloud is either patchy or does not extend to this direction.Alternatively, if the GC is the cloud that is foreground to α Cen,the similar values for N(H0) in the GC components towardα Cen and 36 Oph indicate this cloud is entirely contained withinthe nearest ~1.3 pc, and the Ca+ GC data toward α Ophwould then imply a cloud volume density of ~5 cm-3, withdramatic consequences for the heliosphere in the near future. Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.We have embarked on a project, under the aegis of the Nearby Stars(NStars)/Space Interferometry Mission Preparatory Science Program, toobtain spectra, spectral types, and, where feasible, basic physicalparameters for the 3600 dwarf and giant stars earlier than M0 within 40pc of the Sun. In this paper, we report on the results of this projectfor the first 664 stars in the northern hemisphere. These resultsinclude precise, homogeneous spectral types, basic physical parameters(including the effective temperature, surface gravity, and overallmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. Observed and derived data presented in this paper arealso available on the project's Web site. The DDO IVC Distance Project: Survey Description and the Distance to G139.6+47.6We present a detailed analysis of the distance determination for oneintermediate-velocity cloud (IVC, G139.6+47.6) from the ongoing DDO IVCDistance Project. Stars along the line of sight to G139.6+47.6 areexamined for the presence of sodium absorption attributable to thecloud, and the distance bracket is established by astrometric andspectroscopic parallax measurements of demonstrated foreground andbackground stars. We detail our strategy regarding target selection,observational setup, and analysis of the data, including a discussion ofwavelength calibration and sky subtraction uncertainties. We find adistance estimate of 129+/-10 pc for the lower limit and257+211-33 pc for the upper limit. Given the highnumber of stars showing absorption due to this IVC, we also discuss thesmall-scale covering factor of the cloud and the likely significance ofnondetections for subsequent observations of this and other similarIVCs. Distance measurements of the remaining targets in the DDO IVCproject will be detailed in a companion paper. Phase-referenced Stellar Interferometry at the Palomar Testbed InterferometerWe discuss implementation and testing of phase referencing at thePalomar Testbed Interferometer. A new instrument configuration providesa coherent integration of 10 or 20 ms on a bright star while stabilizingthe fringe phase of a nearby (20") and faint visual companion, allowingcoherent integration times of at least 250 ms. Observations have beenmade of several visual binaries, including 16 Cyg AB (mK=4.5and mK=4.6) and HD 173648/49 (mK=4.3 andmK~5) to test the performance of the technique. Thesemeasurements also demonstrate that phase-referenced visibilitymeasurements can be calibrated at the level of 3%-7%. Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type starsThis 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 The Velocity Distribution of the Nearest Interstellar GasThe bulk flow velocity for the cluster of interstellar cloudlets within~30 pc of the Sun is determined from optical and ultraviolet absorptionline data, after omitting from the sample stars with circumstellar disksor variable emission lines and the active variable HR 1099. A total of96 velocity components toward the remaining 60 stars yield a streamingvelocity through the local standard of rest of -17.0+/-4.6 kms-1, with an upstream direction of l=2.3d, b=-5.2d (usingHipparcos values for the solar apex motion). The velocity dispersion ofthe interstellar matter (ISM) within 30 pc is consistent with that ofnearby diffuse clouds, but present statistics are inadequate todistinguish between a Gaussian or exponential distribution about thebulk flow velocity. The upstream direction of the bulk flow vectorsuggests an origin associated with the Loop I supernova remnant.Groupings of component velocities by region are seen, indicatingregional departures from the bulk flow velocity or possibly separateclouds. The absorption components from the cloudlet feeding ISM into thesolar system form one of the regional features. The nominal gradientbetween the velocities of upstream and downstream gas may be an artifactof the Sun's location near the edge of the local cloud complex. The Sunmay emerge from the surrounding gas patch within several thousand years. The Spectral Components of SS 433We present results from new optical and UV spectroscopy of the unusualbinary system SS 433, and we discuss the relationship of the particularspectral components that we observe to the properties of the binary.These spectral components include1. The continuum spectrum, which weassociate with flux from the super-Eddington accretion disk and thedense part of its wind. A far-UV spectrum from the Hubble SpaceTelescope Space Telescope Imaging Spectrograph made during the edge-onorientation of the disk places an upper limit on the temperature of anequivalent blackbody source (T<21,000 K for AV=7.8) whencombined with near-UV and optical fluxes. The continuum source has aneffective projected radius of approximately half the binary separation,so that the source may be larger than the Roche radius of the compactstar.2. Hα moving components, whichare formed far from the binary orbital plane in the relativistic jets.We confirm that these emission features appear as bullets'' at a fixedwavelength and may last for a few days. We present a contemporary radialvelocity curve for the precessional motion of the jets that includes thenodding motion caused by tidal interaction with the opticalstar.3. Hα and He I stationary''emission lines, which we suggest are formed in the disk wind in a volumelarger than the dimensions of the binary. These lines vary on alltimescales and sometimes appear as P Cygni lines. We suggest that theirradial velocity curves (which show greatest redshift at inferiorconjunction of the optical star) result from an evacuation of the diskwind surrounding the optical star (caused by physical blockage, heating,or colliding winds). We argue that the wake of this interaction regioncauses an extended eclipse of the X-ray source (as seen in Rossi X-RayTiming Explorer All-Sky Monitor light curves).4.A weak stationary'' emission feature, which we identify as a CII λλ7231, 7236 blend that attains maximum radial velocityat the orbital quadrature of disk recession (like the velocity curve ofHe II λ4686). This is probably formed in outflow from the centralregion of the disk near the compact star.5.Absorption and emission features from outflowing clumps in thedisk wind (seen most clearly in an episode of blueshifted Na Iemission).6. We found no clear evidence ofthe absorption-line spectrum of the optical star, although we point outthe presence of He I absorption features (blended with the stationaryemission) with the expected radial velocity trend at the orbital andprecessional phases when the star might best beseen.7. A rich interstellar absorptionspectrum of diffuse interstellar bands.The resultssuggest that the binary is embedded in an expanding thick disk (detectedin recent radio observations) that is fed by the wind from thesuper-Eddington accretion disk. Magnetic survey of bright northern main sequence starsThe first results of a systematic search for magnetic fields in thebrightest upper main sequence (MS) stars are presented. The main goal isto survey the stars with about the same detection limit and to improveexisting statistics of their magnetism. The target list contains 57upper MS stars and represents well B0.5-F9 stars. High-resolution Zeemanspectra were obtained for 30 stars of the list. The accuracy of themagnetic field measurements ranges from 20 to 300 G depending mainly onspectral class. In the majority of studied stars we did not detectmagnetic fields. In some stars we suspect the presence of a weakmagnetic field. These are the best candidates for more extensivestudies. A particular case is the star chi Dra where we probablydetected the global magnetic field. The longitudinal field strength isB_l= -54+/-12 G. Further observations of this star are needed to confirmthe detection and to ascertain if the magnetic field is variable withthe period of rotation. Based on observations collected at the 1 mtelescope of the Special Astrophysical Observatory (Nizhnij Arkhyz,Russia). Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin iThis work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897 On the effective temperatures and surface gravities of superficially normal main sequence band B and A starsEffective temperatures and surface gravities for 48 main sequence band Band A stars were found by matching optical region spectrophotometry andHγ profiles with the predictions of ATLAS9 solar composition modelatmospheres. When these values were compared with those found usingStrömgren uvbybeta photometry based on ATLAS6 model atmospheres, wefound a difference (photometry-spectrophotometry) of 25+/- 118 K for 29stars with 8000 K le Teff <= 10 050 K compared to 76 +/-105 K for 14 stars with 10 050 K <= Teff <= 17 000 K.The surface gravity scales are in agreement. These stars aresufficiently hot that their effective temperatures and surface gravitydeterminations are unaffected by discrepancies due to the choice ofMixing-Length or Canuto-Mazzitelli convection theories. Hipparcos, IUE, and the Stellar Content of the Solar NeighbourhoodThe spectroscopic parallaxes in the Hipparcos catalogue can be used totranslate absolute stellar fluxes observed at Earth to the fluxesemerging at the stellar surface for nearby stars. The comparison ofthese fluxes with the predictions of theoretical model atmospheresallows us to determine the effective temperature and the metallicity ofthe stars. It is suggested that it is possible to study the stellarcontent of the solar neighbourhood making use of the large number ofultraviolet spectra in the archive of the IUE satellite. The Orbit of the Massive X-Ray Binary LS 5039We present the first spectroscopic orbit for the massive X-ray binary LS5039, which we find to be a short-period (P=4.117+/-0.011 days) andhighly eccentric (e=0.41+/-0.05) system. The low-mass function for theorbit appears to be most consistent with a neutron star companion,although a black hole remains a possibility if the system has a lowinclination. The spectrum of the O7 V optical star appears to be normalfor its type (suggesting that there is little flux in the red from anaccretion disk) except that the C IV λλ5801, 5812 linesare very weak, perhaps indicating the presence of CNO-processed gas inthe O star. There is no evidence of Hα emission, so the system isprobably not currently undergoing Roche lobe overflow. The projectedrotational velocity, Vsini=131+/-6 km s-1, suggests that theoptical star is rotating faster than synchronously with the orbit. Thepeculiar component of the systemic radial velocity is -17+/-3 kms-1, so the system is not a runaway star (at least not inthis dimension). A search for the cause of cyclical wind variability in O stars. Simultaneous UV and optical observations including magnetic field measurements of the O7.5III star xi PerseiWe present the results of an extensive observing campaign on the O7.5III star xi Persei. The UV observations were obtainedwith the International Ultraviolet Explorer. xi Perwas monitored continuously in October 1994 during 10 days at ultravioletand visual wavelengths. The ground-based optical observations includemagnetic field measurements, Hα and He I lambda 6678 spectra, andwere partially covered by photometry and polarimetry. We describe amethod to automatically remove the variable contamination of telluriclines in the groundbased spectra. The aim of this campaign was to searchfor the origin of the cyclical wind variability in this star. Wedetermined a very accurate period of 2.086(2) d in the resonance linesof Si Iv and in the subordinate N Iv and Hα line profiles. Theepochs of maximum absorption in the UV resonance lines due to discreteabsorption components (DACs) coincide in phase with the maxima inblue-shifted Hα absorption. This implies that the periodicvariability originates close to the stellar surface. The phase-velocityrelation shows a maximum at -1400 km s-1. The general trendof these observations can be well explained by the corotatinginteraction region (CIR) model. In this model the wind is perturbed byone or more fixed patches on the stellar surface, which are mostprobably due to small magnetic field structures. Our magnetic fieldmeasurements gave, however, only a null-detection with a 1sigma errorbarof 70 G in the longitudinal component. Some observations are moredifficult to fit into this picture. The 2-day period is not detected inthe photospheric/transition region line He I lambda 6678. The dynamicspectrum of this line shows a pattern indicating the presence ofnon-radial pulsation, consistent with the previously reported period of3.5 h. The edge variability around -2300 km s-1 in thesaturated wind lines of C Iv and N V is nearly identical to the edgevariability in the unsaturated Si Iv line, supporting the view that thistype of variability is also due to the moving DACs. A detailed analysisusing Fourier reconstructions reveals that each DAC actually consists of2 different components: a fast'' and a slow'' one which merge athigher velocities. Based on observations obtained using theInternational Ultraviolet Explorer, collected at NASA Goddard SpaceFlight Center and Villafranca Satellite Tracking Station of the EuropeanSpace Agency. Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521 The 2000 outburst of the recurrent nova CI Aquilae: Optical spectroscopyWe present low- and medium resolution spectra of the recurrent nova CIAquilae taken at 14 epochs in May and June, 2000. The overall appearanceis similar to other U Sco-type recurrent novae (U Sco, V394 CrA). Mediumresolution (lambda /Delta lambda ~7000-10 000) hydrogen and ironprofiles suggest an early expansion velocity of 2000-2500 kms-1. The Hα evolution is followed from Delta t = -0.6 dto +53 d, starting from a nearly Gaussian shape to a double peakedprofile through strong P-Cyg profiles. The interstellar component of thesodium D line and two diffuse interstellar bands put constraints on theinterstellar reddening which is estimated to be E(B-V)=0fm85 +/-0fm3 .The available visual and CCD-V observations are used to determine t_0,t_2 and t_3. The resulting parameters are: t_0=2451669.5 +/- 0.1,t_2=30+/-1 d, t_3=36+/-1 d. The recent lightcurve is found to begenerally similar to that observed in 1917 with departures as large as1-2 mag in certain phases. This behaviour is also typical for the U Scosubclass. Based on the data obtained at the David Dunlap Observatory,University of Toronto, Canada. The spectral variability of HD 192639 and its implications for the star's wind structureWe report the analysis of an extensive set of spectroscopic data of theO(f) supergiant HD 192639. A Fourier analysis of our time-series revealsa recurrent variability with a period'' of roughly 4.8 days which ismost prominent in the absorption components of the He {ii}\ lambda 4686and Hα P-Cygni profiles. The same periodicity is also detected inthe blue wing of several absorption lines (e.g. Hβ ). Thevariations of the absorption components correspond most probably to acyclical modulation of the amount of stellar wind material along theline of sight towards the star. The 4.8-day period affects also themorphology of the double-peaked He {ii}\ lambda 4686 and Hαemission components, although these emission components display alsovariations on other (mainly longer) time scales. The most likelyexplanation for the 4.8-day modulation is that this cycle reflects thestellar rotational period (or half this period). We find that the mostimportant observational properties can be explained - at leastqualitatively - by a corotating interaction region or a tilted confinedcorotating wind. Based on observations collected at the Observatoire deHaute Provence, France and the Ritter Observatory, Toledo, USA. The proper motions of fundamental stars. I. 1535 stars from the Basic FK5A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222 On the identification of the C60+ interstellar featuresThe identity of the carriers of the diffuse interstellar bands (DIBs) isone of the most fascinating puzzles of modern spectroscopy. Over thelast few years the number of known DIBs has grown substantially. In thispaper we discuss the two recently discovered near-infrared weakinterstellar features which have already been proposed as fingerprintsof the buckminsterfullerene [formmu2] We present and discussmeasurements of the two related DIBs within a larger sample of reddenedtargets, observed with different spectrometers, telescopes and siteconditions. We provide additional arguments in favour of theinterstellar origin of the two bands. We find evidence around the9577-Å DIB of far-wing structures, which may affect broad-bandmeasurements. We estimate corrections and errors for telluric andstellar blends, and show that the cores of the two DIBs are wellcorrelated with a ratio near unity within 20per cent. Finally, wediscuss their relation to the laboratory spectra of [formmu3] and thesearch for two expected weaker [formmu4] transitions.
Submit a new article

• - No Links Found -