Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
Evolution of X-ray emission from young massive star clusters
The evolution of X-ray emission from young massive star clusters ismodelled, taking into account the emission from the stars as well asfrom the cluster wind. It is shown that the level and character of thesoft (0.2-10 keV) X-ray emission change drastically with cluster age andare tightly linked with stellar evolution. Using the modern X-rayobservations of massive stars, we show that the correlation betweenbolometric and X-ray luminosity known for single O stars also holds forO+O and (Wolf-Rayet) WR+O binaries. The diffuse emission originates fromthe cluster wind heated by the kinetic energy of stellar winds andsupernova explosions. To model the evolution of the cluster wind, themass and energy yields from a population synthesis are used as input toa hydrodynamic model. It is shown that in a very young cluster theemission from the cluster wind is low. When the cluster evolves, WRstars are formed. Their strong stellar winds power an increasing X-rayemission of the cluster wind. Subsequent supernova explosions pump thelevel of diffuse emission even higher. Clusters at this evolutionarystage may have no X-ray-bright stellar point sources, but a relativelyhigh level of diffuse emission. A supernova remnant may become adominant X-ray source, but only for a short time interval of a fewthousand years. We retrieve and analyse Chandra and XMM-Newtonobservations of six massive star clusters located in the LargeMagellanic Cloud (LMC). Our model reproduces the observed diffuse andpoint-source emission from these LMC clusters, as well as from theGalactic clusters Arches, Quintuplet and NGC 3603.
| Correlation patterns between 11 diffuse interstellar bands and ultraviolet extinction
We relate the equivalent widths of 11 diffuse interstellar bands,measured in the spectra of 49 stars, to different colour excesses in theultraviolet. We find that most of the observed bands correlatepositively with the extinction in the neighbourhood of the2175-Åbump. Correlation with colour excesses in other parts of theextinction curve is more variable from one diffuse interstellar band toanother; we find that some diffuse bands (5797, 5850 and 6376 Å)correlate positively with the overall slope of the extinction curve,while others (5780 and 6284 Å) exhibit negative correlation. Wediscuss the implications of these results on the links between thediffuse interstellar band carriers and the properties of theinterstellar grains.
| Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. II. Analysis
To complement the optical absorption line survey of diffuse moleculargas in Paper I, we obtained and analyzed far-ultraviolet H2and CO data on lines of sight toward stars in Cep OB2 and Cep OB3.Possible correlations between column densities of different species forindividual velocity components, not total columns along a line of sightas in the past, were examined and were interpreted in terms of cloudstructure. The analysis reveals that there are two kinds of CH indiffuse molecular gas: CN-like CH and CH+-like CH. Evidenceis provided that CO is also associated with CN in diffuse molecularclouds. Different species are distributed according to gas density inthe diffuse molecular gas. Both calcium and potassium may be depletedonto grains in high-density gas, but with different dependencies onlocal gas density. Gas densities for components where CN was detectedwere inferred from a chemical model. Analysis of cloud structureindicates that our data are generally consistent with the large-scalestructure suggested by maps of CO millimeter-wave emission. On smallscales, the gas density is seen to vary by factors greater than 5.0 overscales of ~10,000 AU. The relationships between column densities of COand CH with that of H2 along a line of sight show similarslopes for the gas toward Cep OB2 and Cep OB3, but the CO/H2and CH/H2 ratios tend to differ, which we ascribe tovariation in average density along the line of sight.
| Close binary stars in ob-association regions i. preliminary investigation
We performed a sample of O- and B-eclipsing binary stars inOB-association regions and obtained the preliminary list of 147 binariesin 45 OB-association regions. We tried to elucidate the question whether(or not) the close binaries belong to corresponding OB-associations,from the commonness of their proper motions, radial velocities anddistances. Based on the completeness of the data,the binaries aredevided into three groups and the scheme for calculation of degree ofbelonging of stars to OB-associations is developed. Necessary data arenot available for nine systems and they are given in a specific table.For 12 cases, the binaries project onto the regions of two associations.We show that 33 (22.3%) close binary stars are members, 65 (43.9%) areprobable members and 39 (26.4%) are less probable members of theOB-associations. We find that 11 binaries belong to the Galaxybackground. The comparison of the distributions of orbital periods forthe binaries in OB-associations and for O-, B-binaries of the Galaxybackground shows their considerable differences in the vicinity of thetwo-day period.
| 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.
| Cloud Structure and Physical Conditions in Star-forming Regions from Optical Observations. I. Data and Component Structure
We present high-resolution optical spectra (at ~0.6-1.8 kms-1) of interstellar CN, CH, CH+, Ca I, K I, andCa II absorption toward 29 lines of sight in three star-forming regions,ρ Oph, Cep OB2, and Cep OB3. The observations and data reduction aredescribed. The agreement between earlier measurements of the totalequivalent widths and our results is quite good. However, our higherresolution spectra reveal complex structure and closely blendedcomponents in most lines of sight. The velocity component structure ofeach species is obtained by analyzing the spectra of the six species fora given sight line together. The tabulated column densities and Dopplerparameters of individual components are determined by using the methodof profile fitting. Total column densities along lines of sight arecomputed by summing results from profile fitting for individualcomponents and are compared with column densities from the apparentoptical depth method. A more detailed analysis of these data and theirimplications will be presented in a companion paper.
| 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).
| A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
| Stars with ISM Polarization Observed with HPOL. II
Polarization data are given for stars whose polarizations are mostlyinterstellar which were observed with the University of Wisconsinspectropolarimeter (HPOL) during 1995-2003. Several cases are found forwhich K in the Serkowski Law for ISM polarization is higher than allowedby published formulas.
| 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.
| Toward an adequate method to isolate spectroscopic families of diffuse interstellar bands
We divide some of the observed diffuse interstellar bands (DIBs) intofamilies that appear to have the spectral structure of single species.Three different methods are applied to separate such families, exploringthe best approach for future investigations of this type. Starting witha statistical treatment of the data, we found that statistical methodsby themselves give insufficient results. Two other methods of dataanalysis (`averaging equivalent widths' and `investigating the figureswith arranged spectrograms') were found to be more useful as tools forfinding the spectroscopic families of DIBs. On the basis of thesemethods, we suggest some candidates as `relatives' of 5780- and5797-Å bands.
| Masses and other parameters of massive binaries
Binary stars provide us with the means to measure stellar mass. Here Ipresent several lists of known O-type stars with reliable mass estimatesthat are members of eclipsing, double-lined spectroscopic binaries. Themasses of young, unevolved stars in binaries are suitable for testingthe predictions of evolutionary codes, and there is good agreementbetween the observed and predicted masses (based upon temperature andluminosity) if the lower temperature scale from line-blanketed modelatmospheres is adopted. A final table lists masses for systems in awide variety of advanced evolutionary stages.
| Apsidal Motion in Binaries: Rotation of the Components
A sample of 51 separated binary systems with measured apsidal periodsand rotational velocities of the components is examined. The ranges ofthe angles of inclination of the equatorial planes of the components tothe orbital plane are estimated for these systems. The observed apsidalvelocities can be explained by assuming that the axes of rotation of thestars are nonorthogonal to the orbital plane in roughly 47% of thesystems (24 of the 51) and the rotation of the components is notsynchronized with the orbital motion in roughly 59% of the systems (30of 51). Nonorthogonality and nonsynchrony are defined as deviations from90° and a synchronized angular velocity, respectively, at levels of1 or more.
| The Lack of Blue Supergiants in NGC 7419, a Red Supergiant-rich Galactic Open Cluster with Rapidly Rotating Stars
According to previous studies based on photometry alone, NGC 7419reveals a surprisingly low ratio of blue to red supergiants: only oneblue supergiant (BSG) along with a record number of five red supergiants(RSGs). However, for a cluster like NGC 7419 with solar metallicity, oneexpects twice as many BSGs as RSGs. To verify the small ratio of BSGs toRSGs, we have obtained spectroscopic observations of the seven mostluminous blue member stars using the 1.6 m telescope of the MountMégantic Observatory. (The RSGs have already been studiedspectroscopically.) To classify the stars, we have developed a systemespecially adapted for these heavily reddened stars in a spectral regionfrom 8400 to 8920 Å, near the hydrogen Paschen series limit. Thisclassification system is based on standard stars of known MK spectraltype extending over O9-B5 and all luminosity classes and is linkedthrough a grid of synthetic spectra to the atmospheric physicalparameters Teff and logg. We also include Be stars. Among theseven blue stars observed in NGC 7419, four have red spectra that aredominated by absorption lines and three by emission lines. The spectraltypes for the former are B2.5 II-III, B2.5 III, B0 III, and B4 III (e),while those for the latter are Be, B1 III-Ve, and Be, respectively. Theaverage heliocentric radial velocity of these stars is -66+/-6 kms-1, compatible with the value of -74+/-9 km s-1measured for the five RSG members. A distance of 1.7+/-0.4 kpc for thiscluster was estimated using the blue-star spectral types, in agreementwith the value of 2.3+/-0.3 kpc found by Beauchamp and coworkers, basedon isochrone fitting in the color-magnitude diagram. With no BSG starsdetected spectroscopically, we confirm the low number, in this caseabsence, of BSGs in this cluster. The high fraction of Be stars detectedby us and others among the bright blue member stars could be explainedby an average rotational velocity for the stars in NGC 7419, which issignificantly higher than in other clusters of similar age andmetallicity. Since higher stellar rotation rates shorten the BSG phase,we suggest that this explains why the evolved stars in NGC 7419 havebecome RSGs. Thus, NGC 7419 is an exceptional case, since high stellarrotation normally tends to occur at lower metallicity.
| Tomographic Separation of Composite Spectra. IX. The Massive Close Binary HD 115071
We present the first orbital elements for the massive close binary HD115071, a double-lined spectroscopic binary in a circular orbit with aperiod of 2.73135+/-0.00003 days. The orbital semiamplitudes indicate amass ratio of M2/M1=0.58+/-0.02, and yet the starshave similar luminosities. We used a Doppler tomography algorithm toreconstruct the individual component optical spectra, and we appliedwell-known criteria to arrive at classifications of O9.5 V and B0.2 IIIfor the primary and secondary, respectively. We present models of theHipparcos light curve of the ellipsoidal variations caused by the tidaldistortion of the secondary, and the best-fit model for a Roche-fillingsecondary occurs for an inclination of i=48.7d+/-2.1d. The resultingmasses are 11.6+/-1.1 and 6.7+/-0.7Msolar for the primary andsecondary, respectively, so both stars are very overluminous for theirmass. The system is one of only a few known semidetached, Algol-typebinaries that contain O stars. We suggest that the binary has recentlyemerged from extensive mass transfer (possibly through a delayed contactand common-envelope process).
| Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (δ Orionis A)
We present the first double-lined spectroscopic orbital elements for thecentral binary in the massive triple δ Orionis A. The solutionsare based on fits of cross-correlation functions of IUE high-dispersionUV spectra and He I λ6678 profiles. The orbital elements for theprimary agree well with previous results, and in particular, we confirmthe apsidal advance with a period of 224.5+/-4.5 yr. We also presenttomographic reconstructions of the primary and secondary stars' spectrathat confirm the O9.5 II classification of the primary and indicate aB0.5 III type for the secondary. The relative line strengths between thereconstructed spectra suggest magnitude differences ofΔm=-2.5log(Fs/Fp)=2.6+/-0.2 in the UV andΔm=2.5+/-0.3 at 6678 Å. The widths of the UVcross-correlation functions are used to estimate the projectedrotational velocities, Vsini=157+/-6 and 138+/-16 km s-1 forthe primary and secondary, respectively (which implies that both theprimary and the secondary rotate faster than the orbital motion). Weused the spectroscopic results to make a constrained fit of theHipparcos light curve of this eclipsing binary, and the model fits limitthe inclination to the range i=67deg-77deg. Thelower limit corresponds to a near Roche-filling configuration that hasan absolute magnitude that is consistent with the photometricallydetermined distance to Ori OB1b, the Orion Belt cluster in which δOri resides. The i=67deg solution results in masses ofMp=11.2 and Ms=5.6 Msolar, both ofwhich are substantially below the expected masses for stars of theirluminosity. The binary may have experienced a mass ratio reversal causedby case A Roche lobe overflow or the system may have suffered extensivemass loss through a binary interaction (perhaps during a common envelopephase) in which most of the primary's mass was lost from the systemrather than transferred to the secondary. We also made three-componentreconstructions to search for the presumed stationary spectrum of theclose visual companion δ Ori Ab (Hei 42 Ab). There is noindication of the spectral lines of this tertiary in the UV spectrum,but a broad and shallow feature is apparent in the reconstruction of HeI λ6678 indicative of an early B-type star. The tertiary may be arapid rotator (Vsini~300 km s-1) or a spectroscopic binary.
| On the Absolute Magnitudes of the O Stars
The conclusion published in 1992 by Garmany & Stencel from a studyof northern OB associations, that the absolute magnitudes of the O starsshow ``a large scatter ... intrinsic to the classification system,'' iscritically examined. It is found that the differences between theirderived absolute magnitudes of O stars and this author's 1973calibration exhibit large systematic effects in several associations,ranging from -0.74 to +1.02 mag with substantially smaller dispersions.Of course, when these results are combined, the scatter equals the fullrange of the systematic effects. To investigate the possibility ofdistance errors, the Garmany & Stencel B0-B2.5 stars in the sameassociations are subjected to the same analysis. The results for the Bstars show no significant systematic differences, eliminating errors inthe association distances derived by Garmany & Stencel from the Bstars as the source of the differences found for the O stars. It isnoteworthy that the dispersions in the absolute magnitudes of the Bstars within a given association are similar to or larger than those ofthe O stars. An examination of the distribution on the sky of the starsshows that the O and B stars in the discrepant associations aregenerally not colocated; such was already known to be the case for theimportant Perseus OB1 association. It is suggested that despite theirefforts to improve them, significant problems remain with theassociation memberships adopted by Garmany & Stencel; the relativelysmall dispersions of the O star absolute magnitudes even in thediscrepant cases indicate that they belong to different, usually moredistant associations near the lines of sight to the B associations withwhich they have been mistakenly connected. Several individual cases ofunrecognized multiple systems and classification errors are also foundin the Garmany & Stencel sample. It is concluded that the scatter inthe absolute magnitudes of the O stars is not as large as found byGarmany & Stencel, and not larger than that of the B stars.
| The ISO-SWS post-helium atlas of near-infrared stellar spectra
We present an atlas of near-infrared spectra (2.36 mu m-4.1 mu m) of ~300 stars at moderate resolution (lambda /delta lambda ~ 1500-2000). Thespectra were recorded using the Short-Wavelength Spectrometer aboard theInfrared Space Observatory (ISO-SWS). The bulk of the observations wereperformed during a dedicated observation campaign after the liquidhelium depletion of the ISO satellite, the so-called post-heliumprogramme. This programme was aimed at extending the MK-classificationto the near-infrared. Therefore the programme covers a large range ofspectral types and luminosity classes. The 2.36 mu m-4.05 mu m region isa valuable spectral probe for both hot and cool stars. H I lines(Bracket, Pfund and Humphreys series), He I and He II lines, atomiclines and molecular lines (CO, H2O, NH, OH, SiO, HCN,C2H2, ...) are sensitive to temperature, gravityand/or the nature of the outer layers of the stellar atmosphere(outflows, hot circumstellar discs, etc.). Another objective of theprogramme was to construct a homogeneous dataset of near-infraredstellar spectra that can be used for population synthesis studies ofgalaxies. At near-infrared wavelengths these objects emit the integratedlight of all stars in the system. In this paper we present the datasetof post-helium spectra completed with observations obtained during thenominal operations of the ISO-SWS. We discuss the calibration of the SWSdata obtained after the liquid helium boil-off and the data reduction.We also give a first qualitative overview of how the spectral featuresin this wavelength range change with spectral type. The dataset isscrutinised in two papers on the quantitative classification ofnear-infrared spectra of early-type stars ({Lenorzer} et al.\cite{lenorzer:2002a}) and late-type stars (Vandenbussche et al., inprep). Based on observations with ISO, an ESA project with instrumentsfunded by ESA Members States (especially the PI countries France,Germany, the Netherlands and the United Kingdom) and with theparticipation of ISAS and NASA. The full atlas is available inelectronic form at www.edpsciences.org Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?/A+A/390/1033
| An atlas of 2.4 to 4.1 mu m ISO/SWS spectra of early-type stars
We present an atlas of spectra of O- and B-type stars, obtained with theShort Wavelength Spectrometer (SWS) during the Post-Helium program ofthe Infrared Space Observatory (ISO). This program is aimed at extendingthe Morgan & Keenan classification scheme into the near-infrared.Later type stars will be discussed in a separate publication. Theobservations consist of 57 SWS Post-Helium spectra from 2.4 to 4.1 μm, supplemented with 10 spectra acquired during the nominal mission witha similar observational setting. For B-type stars, this sample providesample spectral coverage in terms of subtype and luminosity class. ForO-type stars, the ISO sample is coarse and therefore is complementedwith 8 UKIRT Larcmin -band observations. In terms of the presence ofdiagnostic lines, the Larcmin -band is likely the most promising of thenear-infrared atmospheric windows for the study of the physicalproperties of B stars. Specifically, this wavelength interval containsthe Bralpha , Pfgamma , and other Pfund lines which are probes ofspectral type, luminosity class and mass loss. Here, we present simpleempirical methods based on the lines present in the 2.4 to 4.1 mu minterval that allow the determination of i) the spectral type of Bdwarfs and giants to within two subtypes; ii) the luminosity class of Bstars to within two classes; iii) the mass-loss rate of O stars and Bsupergiants to within 0.25 dex. Based on observations with ISO, an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, The Netherlands and the UK) and with theparticipation of ISAS and NASA. The appendix is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin.qcat?J/A+A/384/473
| Far-ultraviolet extinction and diffuse interstellar bands
We relate the equivalent widths of the major diffuse interstellar bands(DIBs) near 5797 and 5780Å with different colour excesses,normalized by E(B-V), which characterize the growth of interstellarextinction in different wavelength ranges. It is demonstrated that thetwo DIBs correlate best with different parts of the extinction curve,and the ratio of these diffuse bands is best correlated with thefar-ultraviolet (UV) rise. A number of peculiar lines of sight are alsofound, indicating that the carriers of some DIBs and the far-UVextinction can be separated in certain environments, e.g. towards thePer OB2 association.
| Fundamental parameters and new variables of the galactic open cluster NGC 7128
CCD photometry in Johnson UBV and Strömgren uvby systems andmedium-resolution spectroscopy of the galactic open cluster NGC 7128 arepresented. Spectral types of the brightest 12 stars in the cluster fieldwere determined based on equivalent widths of the Hα and the Hei6678-Å line. The spectroscopic observations also revealed twoobvious and one probable Be-type stars showing Hα emission. Theanalysis of the photometric diagrams gave a colour excess ofE(B-V)=1.03+/-0.06mag, a distance modulus DM=13.0+/-0.2mag and an ageabove 10Myr. Time-resolved photometric observations obtained on onenight resulted in the detection of short time-scale light variations ofseven new and three already known variable stars in the cluster field.
| Profiles of blue and infrared diffuse interstellar bands
The paper presents a survey of profiles of reasonably strong diffuseinterstellar bands (DIBs) based on the extensive set of high-resolutionspectra acquired with the aid of echelle spectrographs installed at the2-m Terskol, 2-m Pic du Midi and 1-m SAO telescopes. The surveyeddiffuse interstellar bands cover the spectral ranges of blue andnear-infrared, i.e the DIBs not surveyed by Krełowski &Schmidt. The possible modifications caused by stellar and telluric linesare discussed. The very broad features such as 4430 are not discussedbecause the shapes of their profiles, extracted from echelle spectra,are very uncertain. The signal-to-noise (S/N) ratios of the spectra arenot high enough to enable discussion of the profiles of numerous weakinterstellar features discovered recently.
| Variations of Polarization in the Emission of ≀ Andromedae and LZ Cephei
The results of observations of polarization for the Be star And that aregiven are in fully satisfactory agreement with the results obtained byArsenijevic, Vince, and Kubicela in 1974-1977. All these observationstogether support Harmanec's hypothesis that strengthening of thecircumstellar envelope of And occurs during periastron passage of itscompanion, moving in an elongated orbit with a period of 8.5 years. Theresults of polarimetric observations of LZ Cep indicate that its slight,variable intrinsic polarization may originate, as in most semidetachedsystems, in the scattering of radiation of these stars from particles ofmatter escaping from the component that is filling its Roche lobe.
| A possible sets of diffuse bands originating at the same carrier
This paper discusses measurements of eight selected diffuse interstellarbands (DIBs): lambda lambda 5793, 5809, 5819, 5828, 6196, 6397, 6614 and6660 performed in high resolution, high S/N spectra of 41 reddenedstars. Central depths, considered less error-prone than equivalentwidths, are measured and mutual correlations between the selected DIBsare analyzed. Tight correlations between the DIBs: 5809, 6196, 6614 and6660 may suggest their common origin despite their widths differing by afactor of up to 2. The performed simulations prove that this fact doesnot preclude a common, molecular carrier of such features.
| Apsidal Motion in Double Stars. I. Catalog
A catalog of 128 double stars with measured periods of apsidal motion iscompiled. Besides the apsidal periods, the orbital elements of binariesand physical parameters of components (masses, radii, effectivetemperatures, surface gravities) are given. The agreement of the apsidalperiods found by various authors is discussed.
| Discovery of the variable phase-locked polarization in LZ Cephei
The early-type non-eclipsing binary LZ Cep has been observed with theUBVRI polarimeter during 25 nights in 1996-1997. A variable phase-lockedlinear polarization has been found. The principal Fourier components ofthe observed variations are the second harmonics of the orbital period.The most probable explanation of this variability is reflection of theradiation from each component of the binary off the facing hemisphere ofits companion. We have constructed a simple numerical model of thereflection process which is capable of reproducing the amplitude andphase dependence of the polarized light-curve.
| On correlations between diffuse interstellar bands
One way to better apprehend the problem of diffuse interstellar bands(DIBs) is to search for correlations between the bands in a large sampleof spectra towards various lines of sight: a strict correlation mayimply that a common carrier is at the origin of the bands, whereas anon-correlation means that different species are involved. We proposethis observational test for 10 DIBs collected in up to 62 Galactic linesof sight. Strong DIBs do not strictly correlate, and sometimes thecorrelation is very poor. Only one example of a strict correlation hasbeen found in our sample between the DIBs at 6614 and 6196 Ä, thatcould signify a single carrier for those two bands. The general absenceof strict correlations is discussed in the context of molecular carriersfor the DIBs.
| V606 Centauri: an early-type eclipsing contact binary
We present a spectroscopic and photometric analysis of the early-typeeclipsing binary V606 Cen. Based on new high-resolution CCD spectra thefirst radial velocity curve of this system is given, which allows for anaccurate determination of radial velocity amplitudes (K_1=181.8 km s(-1), K_2=345.2 km s(-1) ) and the spectroscopic mass ratio q_spec=0.527.Moreover, equivalent widths are listed. The line strengths of He i 4922show strong variations with the orbital phase, related to the so-called(and hitherto unexplained) ``Struve-Sahade effect". In this context,some aspects concerning the determination of equivalent widths in closebinary systems are discussed, with special reference to the influence ofthe ellipsoidal light variations. For the first time, photoelectric UBVlight curves of V606 Cen are presented, which were solved with the MOROcode, based on the Wilson-Devinney model. The first set of solutions wasachieved with effective temperatures according to the previous spectralclassification B1-2 Ib/IIb, but the derived absolute dimensions, surfacegravities, as well as an investigation of the equivalent widths led to arevision of the spectral type. We now suggest B0-0.5 V for the primary,and B2-3 V for the secondary component, respectively. Using thecorresponding effective temperatures, another light curve analysis wasperformed, yielding the following absolute dimensions: M_1=14.7 M_sun,M_2=8.0 M_sun, R_1=6.8 R_sun, R_2=5.2 R_sun, log L_1/L_sun=4.48, and logL_2/L_sun=3.74. In all cases, a contact configuration is found. Theevolutionary state of V606 Cen is discussed in the light of modernevolutionary grids. It turns out that this contact system was formedduring the slow phase of case A mass transfer after reversal of its massratio. In this respect it is similar to other early-type contactbinaries such as V382 Cyg, V701 Sco or RZ Pyx. Based on observationscollected at the European Southern Observatory, La Silla, Chile
| Interacting OB star binaries: LZ Cep, SZ Cam and IU AUR
New spectroscopic observations of three O+O binary stars (LZ Cep, SZ Camand IU Aur), obtained over a number of years at the DominionAstrophysical Observatory, are analysed using state-of-the-artcross-correlation techniques to produce radial velocity curves. Theseresults are combined with new (LZ Cep) and published (SZ Cam and IU Aur)photometry to yield masses, temperatures, radii and luminosities. Wefind that LZ Cep is a semi-detached system, in agreement with theresults of Howarth et al., with the secondary star filling its Rochelobe. We find a distance modulus of 9.6+/-0.2, which is slightly smallerthan the distance modulus to Cep OB2 (=9.9).The reddening of LZ Cep isalso at the lower end of the cluster range, suggesting that the binaryis located on the near side of the cluster. SZ Cam is a triple system,and we are able to measure the radial velocities of the three componentsthat are observed in the absorption lines. A light-curve solutionemploying our new mass ratio shows that the short-period binary isdetached. The third body emits about 40 per cent of the radiation fromthe system, and is probably a binary itself. The distance modulus for SZCam (=9.88) is in good agreement with that of its parent cluster NGC1502 (=9.71). IU Aur is another triple system, although we are unable tofind spectroscopic evidence for the tertiary. The close binary issemi-detached, with the secondary filling its Roche lobe. The distancemodulus of the system is 11.0, which is in approximate agreement withthat of the Aur OB1 association (=10.6+/-0.2). We note that the currentmodels for interacting massive binaries all assume case B mass transfer,in which the mass-loser becomes a Wolf-Rayet star. Case A mass-transfermodels (in which the mass-loser fills its Roche lobe while still on themain sequence) are required in order to see whether or not they canexplain the observed properties of these interacting systems.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Cefeo |
| Ascensión Recta: | 22h02m04.60s |
| Declinación: | +58°00'02.0" |
| Magnitud Aparente: | 5.56 |
| Distancia: | 1428.571 parsecs |
| Movimiento Propio en Ascensión Recta: | 0 |
| Movimiento Propio en Declinación: | 0 |
| B-T magnitude: | 5.558 |
| V-T magnitude: | 5.543 |
Catálogos y designaciones:
|
INHABITED SKY
