Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
The SPEAR Instrument and On-Orbit Performance
The SPEAR (or ``FIMS'') instrumentation has been used to conduct thefirst large-scale spectral mapping of diffuse cosmic far-ultraviolet(FUV; 900-1750 Å) emission, including important diagnostics ofinterstellar hot (104-106 K) and photoionizedplasmas, H2, and dust-scattered starlight. Theinstrumentation's performance has allowed for the unprecedenteddetection of astrophysical diffuse FUV emission lines. A spectralresolution of λ/Δλ~550 and an imaging resolution of5' is achieved on-orbit in the Short (900-1150 Å) and Long(1350-1750 Å) bandpass channels within their respective4.0d×4.6 arcmin and 7.4d×4.3 arcmin fields of view. Wedescribe the SPEAR imaging spectrographs, their performance, and thenature and handling of their data.
| Looking for Discrete UV Absorption Features in the Early-Type Eclipsing Binaries μ1 Scorpii and AO Cassiopeiae
A search for discrete absorption components in the ultraviolet spectraof the early-type binaries μ1 Scorpii and AO Cassiopeiaehas been undertaken by analyzing material secured with the InternationalUltraviolet Explorer satellite during an exclusively assigned intervalof nearly 50 hr. While the spectra of μ1 Sco definitely donot show the presence of such lines, the spectra of AO Cas do confirmthem and permit us to draw some conclusions about where they may beformed.
| To see or not to see a bow shock. Identifying bow shocks with Hα allsky surveys
OB-stars have the highest luminosities and strongest stellar winds ofall stars, which enables them to interact strongly with theirsurrounding ISM, thus creating bow shocks. These offer us an idealopportunity to learn more about the ISM. They were first detected andanalysed around runaway OB-stars using the IRAS allsky survey by vanBuren et al. (1995, AJ, 110, 2614). Using the geometry of such bowshocks information concerning the ISM density and its fluctuations canbe gained from such infrared observations. As to help to improve the bowshock models, additional observations at other wavelengths, e.g.Hα, are most welcome. However due to their low velocity these bowshocks have a size of 1°, and could only be observed as awhole with great difficulties. In the light of the new Hα allskysurveys (SHASSA/VTSS) this is no problem any more. We developeddifferent methods to detect bow shocks, e.g. the improved determinationof their symmetry axis with radial distance profiles. Using twoHα-allsky surveys (SHASSA/VTSS), we searched for bow shocks andcompared the different methods. From our sample we conclude, that thecorrelation between the direction of both proper motion and the symmetryaxis determined with radial distance profile is the most promisingdetection method. We found eight bow shocks around HD17505, HD 24430, HD48099, HD 57061, HD92206, HD 135240, HD149757, and HD 158186 from 37 candidatestaken from van Buren et al. (1995, AJ, 110, 2614). Additionally to thetraditional determination of ISM parameters using the standoff distanceof the bow shock, another approach was chosen, using the thickness ofthe bow-shock layer. Both methods lead to the same results, yieldingdensities ( 1 cm-3) and the maximal temperatures (104 K), that fit well to the up-to-date picture of the WarmIonised Medium.
| The origin of massive O-type field stars: II. Field O stars as runaways
In two papers we try to confirm that all Galactic high-mass stars areformed in a cluster environment, by excluding that O-type stars found inthe Galactic field actually formed there. In de Wit et al. (2004) wepresented deep K-band imaging of 5 arcmin fields centred on 43 massiveO-type field stars that revealed that the large majority of theseobjects are single objects. In this contribution we explore thepossibility that the field O stars are dynamically ejected from youngclusters, by investigating their peculiar space velocity distribution,their distance from the Galactic plane, and their spatial vicinity toknown young stellar clusters. We (re-)identify 22 field O-type stars ascandidate runaway OB-stars. The statistics show that 4 ± 2% ofall O-type stars with V<8m can be considered as formedoutside a cluster environment. Most are spectroscopically singleobjects, some are visual binaries. The derived percentage for O-typestars that form isolated in the field based on our statistical analysesis in agreement with what is expected from calculations adopting auniversal cluster richness distribution with power index of β= 1.7,assuming that the cluster richness distribution is continuous down tothe smallest clusters containing one single star.
| NSV 15852 is likely an Elliptical Variable akin in type to AO Cas
Variability of NSV 15852 is confirmed by NSVS data. It is likely anelliptical variable similar to AO Cas with a period of 1.175 days.
| 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.
| The Nebular Environment and Enigmatic Hard X-Ray Emission of the Hot DO White Dwarf KPD 0005+5106
We have detected an ionized nebula around the hot DO white dwarf KPD0005+5106 and used the [O III]/Hα ratios and nebular velocities toseparate this nebula from the background H II region of AO Cas. Theangular size of the [O III] nebula of KPD 0005+5106 is ~3°. Thevelocity of this nebula is similar to those of the local interstellar HI gas and the interstellar/circumstellar absorption lines in the UVspectra of KPD 0005+5106 but has a large offset from those of thestellar photospheric lines. The mass of the ionized nebula, ~70Msolar, indicates that it consists of interstellar materialand that the velocity offset between the star and the ambient mediumshould not be interpreted as a wind outflow. We have also analyzed theROSAT PSPC observation of KPD 0005+5106 to determine its hard X-rayluminosity. Using the LX/Lbol relation forlate-type stars and the lack of obvious near-IR excess of KPD 0005+5106,we exclude the possible existence of a binary companion with coronalactivity. Without a wind outflow, the presence of stellar O VIIIemission requires that X-rays at energies greater than 0.871 keV arepresent in the vicinity of KPD 0005+5106. This hard X-ray emission ismost puzzling, since neither photospheric emission at such high energiesnor a high-temperature corona is expected from current stellaratmospheric models of KPD 0005+5106. X-ray observations with highangular resolution and sensitivity are needed to confirm the positionalcoincidence and to enable X-ray spectral analyses for constraining thephysical origin of the hard X-ray emission from KPD 0005+5106.
| 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.
| On the properties of contact binary stars
We have compiled a catalogue of light curve solutions of contact binarystars. It contains the results of 159 light curve solutions. Theproperties of contact binary stars were studied using the cataloguedata. As is well known since Lucy's (\cite{Lucy68a},b) and Mochnacki's(\cite{Mochnacki81}) studies, primary components transfer their ownenergy to the secondary star via the common envelope around the twostars. This transfer was parameterized by a transfer parameter (ratio ofthe observed and intrinsic luminosities of the primary star). We provethat this transfer parameter is a simple function of the mass andluminosity ratios. We introduced a new type of contact binary stars: Hsubtype systems which have a large mass ratio (q>0.72). These systemsshow behaviour in the luminosity ratio- transfer parameter diagram thatis very different from that of other systems and according to ourresults the energy transfer rate is less efficient in them than in othertypes of contact binary stars. We also show that different types ofcontact binaries have well defined locations on the mass ratio -luminosity ratio diagram. Several contact binary systems do not followLucy's relation (L2/L1 =(M2/M1)0.92). No strict mass ratio -luminosity ratio relation of contact binary stars exists.Tables 2 and 3 are available in electronic form athttp://www.edpsciences.org
| The origin of massive O-type field stars. I. A search for clusters
We present a study aimed at clarifying the birthplace for 43 massiveO-type field stars. In this first paper we present the observationalpart: a search for stellar clusters near the target stars. We derivestellar density maps at two different resolving scales, viz. 0.25pc and 1.0 pc from NTT and TNG imaging and the 2MASS catalogue.These scales are typical for cluster sizes. The main result is that thelarge majority of the O-type field population are isolated stars: only12% (5 out of 43) of the O-type field stars is found to harbour asmall-scale stellar cluster. We review the literature and aim atcharacterizing the stellar field of each O-type field star with theemphasis on star formation and the presence of known young stellarclusters. An analysis of the result of this paper and a discussion ofthe O-type field population as products of a dynamical ejection event ispresented in an accompanying paper.Based on observations collected at the European Southern Observatory,Chile, and at the Italian Telescopio Nazionale Galileo (TNG) operated onthe island of La Palma by the Centro Galileo Galilei of the CNAA(Consorzio Nazionale per l'Astronomia e l'Astrofisica) at the SpanishObservatorio del Roque de los Muchachos of the Instituto de Astrofisicade Canarias.Table 2 and Figs. 4 to 17 are available in electronic form athttp://www.edpsciences.org
| 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.
| Evolution of Wolf-Rayet Stars in Binary Systems: An Analysis of the Mass and Orbital-Eccentricity Distributions
We have undertaken a statistical study of the component mass ratios andthe orbital eccentricities of WR + O close binary, detachedmain-sequence (DMS), contact early-type (CE), and semidetached (SD)systems. A comparison of the characteristics of WR + O systems and ofDMS, CE, and SD systems has enabled us to draw certain conclusions aboutthe evolutionary paths of WR + O binaries and to demonstrate that up to90% of all known WR + O binaries formed as a result of mass transfer inmassive close O + O binary systems. Since there is a clear correlationbetween the component masses in SD systems with subgiants, the absenceof an anticorrelation between the masses of the WR stars and O stars inWR + O binaries cannot be considered evidence against the formation ofWR + O binaries via mass transfer. The spectroscopic transitionalorbital period P tr sp corresponding to the transition from nearlycircular orbits (e sp<0.1) to elliptical orbits (e sp≥0.1) is14d for WR + O systems and 2d 3d for OB + OB systems. Theperiod range in which all WR + O orbits are circular &$(1mathop dlimits_. 6 ≤slant P ≤slant 14(d) ); is close to the range for SD systems with subgiants, &0mathop dlimits_. 7 ≤slant P ≤slant 15(d); . The large difference between the P tr sp values for WR + O and OB +OB systems suggests that a mechanism of orbit circularization additionalto that for OB + OB systems at the DMS stage (tidal dissipation of theorbital energy due to radiative damping of the dynamical tides) acts inWR + O binaries. It is natural to suggest mass transfer in the parent O+ O binaries as this supplementary orbit-circularization mechanism.Since the transitional period between circular and elliptical orbits forclose binaries with convective envelopes and ages of 5×109 yearsis &P_{tr} = 12mathop dlimits_. 4$; , the orbits of most known SD systems with subgiants had enough timeto circularize during the DMS stage, prior to the mass transfer. Thus,for most SD systems, mass transfer plays a secondary role incircularization of their orbits. In many cases, the initial orbitaleccentricities of the O + O binary progenitors of WR + O systems arepreserved, due to the low viscosity of the O-star envelopes and theshort timescale for their nuclear evolution until the primary O starfills its Roche lobe and the mass transfer begins. The mass transfer inthe parent O + O systems is short-lived, and the number of orbitalcycles during the early mass-transfer stage is relatively low (lowerthan for the progenitors of SD systems by three or four orders ofmagnitude). The continued transfer of mass from the less massive to themore massive star after the component masses have become equal leads tothe formation of a WR + O system, and the orbit's residual eccentricityincreases to the observed value. The increase of the orbitaleccentricity is also facilitated by variable radial mass loss via thewind from the WR star in the WR + O system during its motion in theelliptical orbit. The result is that WR + O binaries can haveconsiderable orbital eccentricities, despite their intense masstransfer. For this reason, the presence of appreciable eccentricitiesamong WR + O binaries with large orbital periods cannot be consideredfirm evidence against mass transfer in the parent O + O binary systems.Only for the WR + O binaries with the longest orbital periods (4 of 35known systems, or 11 %) can the evolution of the parent O + O binariesoccur without filling of the Roche lobe by the primary O star, beinggoverned by radial outflow in the form of the stellar wind and possiblyby the LBV phenomenon, as in the case of HD 5980.
| 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.
| A study of RV in Galactic O stars from the 2MASS catalogue
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 185 O stars, using J, H,Ks photometry from the 2MASS project. The results arecombined with data from the literature of 95 stars where RVhas been derived with the same technique, 22 of which in common with ourpresent sample from the 2MASS project catalogue. The averageRV from these 258 O stars is of 3.19 +/- 0.50. All objectswhose RV departs from this value by more than 2 sigma havebeen recognized. Ten objects have RV higher than this valueand two lower. It is found that anomalous RV can scarcely beassociated with anomalies in the general interstellar medium, e.g. withdifferent behaviour in different spiral arms. They are clearly linked tolocal cloud effect. In the Cygnus region RV values follow thebehaviour of the general interstellar medium, while in the Carina arm,in spite of the relatively larger distance, local cloud effects prevail.An explanation for this is suggested. The relatively few stars of oursample whose Hipparcos parallaxes are reliable, are found to havedistances systematically smaller than the distances derived by thespectroscopic parallaxes. We argue that this effect is consistent withthe recently claimed discovery of grey extinction towards OB stars.This publication makes use of data products from the Two Micron All SkySurvey (2MASS), which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center/CaliforniaInstitute of Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/905
| Einige interessante Bedeckungsveraenderliche.
Not Available
| A Dozen Colliding-Wind X-Ray Binaries in the Star Cluster R136 in the 30 Doradus Region
We analyzed archival Chandra X-ray observations of the central portionof the 30 Doradus region in the Large Magellanic Cloud. The imagecontains 20 X-ray point sources with luminosities between5×1032 and 2×1035 ergs s-1(0.2-3.5 keV). A dozen sources have bright WN Wolf-Rayet or spectraltype O stars as optical counterparts. Nine of these are within ~3.4 pcof R136, the central star cluster of NGC 2070. We derive an empiricalrelation between the X-ray luminosity and the parameters for the stellarwind of the optical counterpart. The relation gives good agreement forknown colliding-wind binaries in the Milky Way Galaxy and for theidentified X-ray sources in NGC 2070. We conclude that probably allidentified X-ray sources in NGC 2070 are colliding-wind binaries andthat they are not associated with compact objects. This conclusioncontradicts earlier studies where it was argued, using ROSAT data, thattwo earlier discovered X-ray sources are accreting black hole binaries.Five of the 18 brightest stars in R136 are not visible in our X-rayobservations. These stars either are single, have low-mass companions,or have very wide orbits. The resulting binary fraction among early-typestars is then unusually high (at least 70%).
| Optical spectroscopy of X-Mega targets - II. The massive double-lined O-type binary HD 93205
A new high-quality set of orbital parameters for the O-typespectroscopic binary HD 93205 has been obtained combining échelleand coudé CCD observations. The radial velocity orbits derivedfrom the Heii λ4686Å (primary component) and Heiλ4471Å (secondary component) absorption lines yieldsemi-amplitudes of 133+/-2 and 314+/-2kms-1 for each binarycomponent, resulting in minimum masses of 31 and 13Msolar(q=0.42). We also confirm for the binary components the spectralclassification of O3V+O8V previously assigned. Assuming for the O8Vcomponent a `normal' mass of 22-25Msolar we would derive forthe primary O3V a mass of `only' 52-60Msolar and aninclination of about 55° for the orbital plane. We have alsodetermined for the first time a period of apsidal motion for thissystem, namely 185+/-16yr using all available radial velocity data setsof HD 93205 (from 1975 to 1999). Phase-locked variations of the X-rayemission of HD 93205 consisting of a rise of the observed X-ray fluxnear periastron passage are also discussed.
| Roche-Lobe Overflow in the Vicinity of the Inner Lagrangian Point in Close Binary Systems
The formation of flows in the vicinity of the inner Lagrangian point hasbeen computed for various close binary systems (from short-period U Gemto long-period β Lyr systems). The dependence of the masstransferrate through the inner Lagrangian point on the degree of Roche-lobeoverflow is derived. One new aspect of this work is the use of Kuruczstellar model atmospheres when constructing the initial configuration ofthe outer layers of the mass-losing star and also the use of the“large particles” numerical method of Belotserkovski andDavydov. The application of these stellar model atmospheres provides amore realistic description of the stream than do polytropic models. Thecomputations show that the influence of the Coriolis and centrifugalforces on the rate of mass transfer is negligible and does not exceed afew percent. In certain specific cases (β Per and W UMa), thestream models differ strongly from those of Lubow and Shu. The degree ofRoche-lobe overflow and the rate of mass transfer indicated byobservations are such that the atmospheric layers of the mass-losingstar are nearly always located at the inner Lagrangian point. The onlyexceptions are compact binary systems and U Gem stars, in which theinner Lagrangian point resides in layers of the mass-losing star thatare denser than its atmospheric layers, and the β Per system, inwhich the mass-losing atmosphere is located inside its Roche lobe. Thenumerical dependences of the mass-transfer rate on the degree ofRoche-lobe overflow differ from the analytical dependences for bothlarge and small overflows. This is due to differences between the Kuruczmodel stellar atmospheres and the polytropic models used in previousanalytical calculations and also to the presence of dynamical effectsconnected with the mass transfer in the computations. The polytropicindices corresponding to the best agreement between the numerical andanalytical dependences are 4.5 for β Lyr, 2.4 2.6 for thecataclysmic binaries, and 3.1 3.3 for the remaining stars. Thesepolytropic indices indicate that the Roche lobes of the mass-losingstars in close binary systems are usually overflowing.
| Tomographic Separation of Composite Spectra. VII. The Physical Properties of the Massive Triple System HD 135240 (δ Circini)
We present the results of a radial velocity study of the massive,double-lined, O binary HD 135240 based primarily on UV spectroscopy fromthe International Ultraviolet Explorer. Cross-correlation methodsindicate the presence of a third stationary spectral line componentwhich indicates that the system is a triple consisting of a central 3.9day close binary with a distant companion. We measured radial velocitiesfrom the cross-correlation functions after removal of the thirdcomponent, and we combined these with velocities obtained from Hαspectroscopy to reassess the orbital elements. We applied a Dopplertomography algorithm to reconstruct the individual UV spectra of allthree stars, and we determine spectral classifications of O7 III-V, O9.5V, and B0.5 V for the primary, secondary, and tertiary, respectively,using UV criteria defined by Penny, Gies, & Bagnuolo. We comparethese reconstructed spectra to standard single-star spectra to find theUV flux ratios of the components(F2/F1=0.239+/-0.022, andF3/F1=0.179+/-0.021). Hipparcos photometry revealsthat the central pair is an eclipsing binary, and we present the firstmodel fit of the light curve from which we derive an orbitalinclination, i=74deg+/-3deg. This analysisindicates that neither star is currently experiencing Roche lobeoverflow. We place the individual components in the theoretical H-Rdiagram, and we show that the masses derived from the combinedspectroscopic and photometric analysis(Mp/Msolar=21.6+/-2.0 andMs/Msolar=12.4+/-1.0) are significantly lower thanthose computed from evolutionary tracks for single stars.
| O Iiject{HD 152248}: Evidence for a colliding wind interaction
We present the results of a four year spectroscopic campaign on theearly-type binary system HD 152248. Our analysis yields a newclassification as O7.5III(f) + O7III(f), in contradiction with previousclassifications of the components as supergiants. We derive improvedorbital elements and the corresponding masses (M_1=29.6 Msunand M_2=29.9 Msun) are somewhat larger than previouslyreported in the literature, although they are still significantly lowerthan the ones expected from evolutionary tracks. Both components of thesystem are close to filling their Roche lobe at periastron passage. Wealso investigate the equivalent width variations of the lines of the twocomponents and we discuss their relation to the Struve-Sahade effect.Finally, we show that the line profile variability of the He Iil4686 andHα lines is consistent with a strong wind interaction between thetwo stars, quite as predicted by current colliding wind models. Based ondata collected at the European Southern Observatory (La Silla, Chile)and at the Cerro Tololo Inter-American Observatory (Cerro Tololo,Chile).
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The 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
| Classification and properties of UV extinction curves
The catalog of Savage et al. (\cite{ref27}) reporting colour excesses of1415 stars from ANS photometry offers the opportunity to deeplyinvestigate the characteristics of UV extinction curves which differfrom the standard extinction of the diffuse interstellar medium. To thisaim we have selected a sample of 252 curves, which have been comparedwith the relations derived by Cardelli et al. (\cite{ref4}; CCM in thefollowing) for a variety of R_V values in the range 2.4-5 and have beenclassified as normal if they fit at least one of the CCM curves oranomalous otherwise. We find that normal curves with small R_V are justas numerous as those with large R_V. The anomalous objects are arrangedinto two groups according to the strength of the bump at 0.217 mu . Fora given value of c_2 this increases along the sequence: type Aanomalous, normals and type B anomalous, suggesting that this sequenceshould correspond to an increase of the amount of small grains along thesightline. Considerations concerning the environmental characteristicsindicate that the anomalous behaviour is not necessarily tied to theexistence of dense gas clouds along the line of sight.
| On the Variability of O4-B5 Luminosity Class III-V Stars
We investigate the Hipparcos Satellite photometry of O4-B5 luminosityclass III-V stars. Some for which further study is desirable areidentified. These stars in general are more variable than cooler stars
| The Struve-Sahade Effect: A Tale of Three Stars
The ``Struve-Sahade effect'' (S-S effect) is the apparent weakness oflines of the secondary in massive binaries when the secondary isreceding. This effect poses problems for the accurate reconstruction ofthe separated primary and secondary spectra. We have reexamined IUEspectra of three classical, hot binaries studied by D. Stickland in1997. From various cross-correlation and tomographic techniques we finddifferent results for each of the three systems. For HD 1337 (AO Cas),we find a slight S-S effect which can be explained by a mechanism oflocalized heating by the colliding stellar winds, as proposed by Gies,Bagnuolo, & Penny in 1997. For HD 47129 (Plaskett's star), noconsistent S-S effect was found, and none is expected based on the windheating model because the secondary has a slightly stronger wind.Finally, for HD 57060 (29 UW CMa), a strong S-S effect was found duringthe receding phases (0.13-0.63). In addition, we find a strong featurenear phase 0.2, similar to the secondary in spectral type but shifted by~-400 km s-1. We explain this by absorption and reemission bystrong winds wrapping around the secondary. Thus, in general, we findthat the S-S effect may arise from several distinct mechanisms.
| The Interacting Early-Type Binary BD +40 deg4220 (V729 Cyg): Modeling the Colliding Winds Region
We present an analysis of an extensive set of spectroscopic observationsof the mysterious early-type binary BD +40 deg4220. A new orbitalsolution is derived from the radial velocities of the absorption lines.We confirm that the secondary star is highly overluminous for its mass.The absorption lines of both components display phase-locked profilevariations, with some of the secondary's lines going into emissionbetween phi=0.20 and phi=0.55. A detailed investigation of the profilevariability of the He II lambda4686 emission line reveals that thepattern of variability of this line is very stable. We show that part ofthe He II lambda4686 emission is produced in the wind interaction regionbetween the stars. Most of the emission lines in the visual spectrum ofBD +40 deg4220 display variations that are reminiscent of those observedon the He II lambda4686 line, pointing toward a similar origin. Wepresent numerical simulations of emission-line profiles in a collidingwinds binary, showing that an important part of the variability observedin BD +40 deg4220 can be explained by a colliding winds phenomenon. Theproperties of the wind interaction region can be accounted for if weassume that the secondary star is an evolved object, most probably somekind of Ofpe/WN9 transition star, with a mass loss rate of ~5.5x10^-6M_solar yr^-1. We finally discuss the fundamental parameters of thebinary, concluding that mass transfer must have played a crucial role inthe evolution of this system.
| 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.
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. I. Mapping the MKK classification system
We present an Echelle+CCD high resolution spectroscopic atlas (0.25Ä/pix dispersion, 0.43 Ä FWHM resolution and 20 000 resolvingpower) mapping the MKK classification system over the interval lambdalambda 8500-8750 Ä. The wavelength interval is remarkably free fromtelluric lines and it is centered on the near-IR triplet of Ca II, thehead of hydrogen Paschen series and several strong metallic lines. Thespectra of 131 stars of types between O4 and M8 and luminosity classes Ithrough V are included in the atlas. Special care was put in maintainingthe highest instrumental homogeneity over the whole set of data. Thecapability to derive accurate MKK spectral types from high resolutionobservations over the interval lambda lambda 8500-8750 Ä isdiscussed. The observations have been performed as part of an evaluationstudy of possible spectroscopic performances for the astrometric missionGAIA planned by ESA. Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/ Abstract.html}\fnmsep\thanks{ Thespectra of the stars listed in Table~2 are also available in electronicform at the CDS or via the personal HomePagehttp://ulisse.pd.astro.it/Astro/Atlases/}\fnmsep\thanks{ Figures 3--28are only available in electronic form at http://www.edpsciences.com
| 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
| A common resonance of delta SCT stars and ellipsoidal binaries.
Not Available
| ICCD speckle observations of binary stars. XIX - an astrometric/spectroscopic survey of O stars
We present the results of a speckle interferometric survey made with theCHARA speckle camera and 4 m class telescopes of Galactic O-type starswith V less than 8. We can detect with the speckle camera binaries inthe angular separation range 0.035-1.5 arcsec with delta M less than 3,and we have discovered 15 binaries among 227 O-type systems. We combinedour results on visual binaries with measurements of wider pairs from theWashington Double Star Catalog and fainter pairs from the HipparcosCatalog, and we made a literature survey of the spectroscopic binariesamong the sample. We then investigated the overall binary frequency ofthe sample and the orbital characteristics of the known binaries.Binaries are common among O stars in clusters and associations but lessso among field and especially runaway stars. There are many triplesystems among the speckle binaries, and we discuss their possible rolein the ejection of stars from clusters. The period distribution of thebinaries is bimodal in log P, but we suggest that binaries with periodsof years and decades may eventually be found to fill the gap. The massratio distribution of the visual binaries increases toward lower massratios, but low mass ratio companions are rare among close,spectroscopic binaries. We present distributions of the eccentricity andlongitude of periastron for spectroscopic binaries with ellipticalorbits, and we find strong evidence of a bias in the longitude ofperiastron distribution.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
| Csillagkép: | Kassziopeia |
| Rektaszcenzió: | 00h17m43.00s |
| Deklináció: | +51°25'59.0" |
| Vizuális fényesség: | 6.14 |
| Távolság: | 1754.386 parszek |
| RA sajátmozgás: | -5.9 |
| Dec sajátmozgás: | -1.5 |
| B-T magnitude: | 5.914 |
| V-T magnitude: | 6.082 |
Katalógusok és elnevezések:
|
INHABITED SKY
