Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Interacting Binary Stars Environments and the W Ser-DPV-Algol Connection
Recent work on some kinds of interacting binaries is summarized, withemphasis on Cataclysmic Variables, Algol-like variables and the recentlydiscovered Double Periodic Variables (DPVs). The sequence W Serpentids(very massive with irregular variability and large mass loss) ?DPVs (less massive with regular variability and ciclic mass loss) ?Algols (even less massive with small mass loss) could correspond to anevolutionary sequence, and illustrate the importance of the masstransfer rate in shaping observable and mass loss properties for thesesystems.
| Radio emission from the massive stars in the galactic super star cluster Westerlund 1
Aims: Current mass-loss rate estimates imply that main sequenceline-driven winds are not sufficient to strip away the H-rich envelopeto yield Wolf-Rayet (WR) stars. The rich transitional population of theyoung massive cluster Westerlund 1 (Wd 1) provides an ideal laboratoryto observe and constrain mass-loss processes throughout the transitionalphase of stellar evolution. Methods: We present an analysis ofdeep radio continuum observations of Wd 1 obtained with the AustraliaTelescope Compact Array at four frequency bands that permitinvestigation of the intrinsic characteristics of the radio emission. Results: We detect 18 cluster members, a sample dominated by thecool hypergiants, with additional detections amongst the hotter OBsupergiants and WR stars. The radio properties of the sample arediverse, with thermal, non-thermal and composite thermal/non-thermalsources present. Mass-loss rates determined for stars with partiallyoptically thick stellar winds are ~10-5 M?yr-1 across all spectral types, insufficient to enable theformation of WRs during a massive star lifetime, and the stars mustundergo a period of greatly enhanced mass loss. The sgB[e] star W9, thebrightest radio source in Wd 1, may provide an example, with a currentmass-loss rate an order of magnitude higher than the other clustermembers, and an extended nebula interpreted as a wind from an earlierepoch with a density ~3× the current wind. Such an envelopestructure in W9 is reminiscent of luminous blue variables, and one thatshows evidence of two eras of high, possibly eruptive mass loss.Surprisingly, three of the OB supergiants are detected, implyingunusually dense winds, though they are embedded in more extendedemission regions that may influence the derived parameters. They alsomay have composite spectra, suggesting binarity, which can lead to ahigher flux than expected from a stellar wind. Spatially resolvednebulae are associated with three of the four RSGs and three of the sixYHGs in the cluster, which are due to quiescent mass loss rather thanoutbursts. The extended nebulae of W20 and W26 have a cometarymorphology, implying significant interaction with either theintracluster medium or cluster wind. For some of the cool star winds,the ionizing source may be a companion star though the cluster radiationdensity is sufficiently high to provide the necessary ionizingradiation. Five WR stars are detected with composite spectra,interpreted as arising in colliding-wind binaries.
| Massive binaries as the source of abundance anomalies in globular clusters
Abundance anomalies observed in globular cluster stars indicatepollution with material processed by hydrogen burning. Two main sourceshave been suggested: asymptotic giant branch (AGB) stars and massivestars rotating near the break-up limit (spin stars). We propose massivebinaries as an alternative source of processed material. We compute theevolution of a 20 {M}? star in a close binaryconsidering the effects of non conservative mass and angular momentumtransfer and of rotation and tidal interaction to demonstrate theprinciple. We find that this system sheds about 10 {M}?of material, nearly the entire envelope of the primary star. The ejectaare enriched in He, N, Na, and Al and depleted in C and O, similar tothe abundance patterns observed in gobular cluster stars. However, Mg isnot significantly depleted in the ejecta of this model. In contrast tothe fast, radiatively driven winds of massive stars, this material istypically ejected with low velocity. We expect that it remains insidethe potential well of a globular cluster and becomes available for theformation or pollution of a second generation of stars. We estimate thatthe amount of processed low-velocity material ejected by massivebinaries is greater than the contribution of AGB stars and spin starscombined, assuming that the majority of massive stars in aproto-globular cluster interact with a companion and return theirenvelope to the interstellar medium. If we take the possiblecontribution of intermediate mass stars in binaries into account andassume that the ejecta are diluted with an equal amount of unprocessedmaterial, we find that this scenario can potentially provide enoughmaterial to form a second generation of low-mass stars, which is asnumerous as the first generation of low-mass stars, without the need tomake commonly adopted assumptions, such as preferential loss of thefirst generation of stars, external pollution of the cluster, or ananomalous initial mass function.
| A binary merger model for the formation of the Supernova 1987A triple-ring nebula
We examine a binary merger model for the formation of the mysterioustriple-ring nebula surrounding Supernova 1987A, which still has not beenconvincingly explained in detailed hydrodynamical calculations. Duringthe merger of 15 and 5Msolar binary systems, mass is ejectedprimarily at mid-latitudes for a sufficiently evolved primary, asdemonstrated by Morris & Podsiadlowski. This material is swept up bythe fast wind of the central star during its post-merger blue supergiantphase, leading to a density contrast of ~150 in the outer rings at thetime of the supernova. The equatorial ring probably formed later whenthe star contracted to become a blue supergiant. The asymmetry betweenthe northern and southern outer rings can be explained by a 10 per centasymmetry during the merger, perhaps due to a pulsational instability inthe common envelope.We present a parameter study from which we determine a mass-loss rate inthe blue supergiant wind in the range 1.5-3 ×10-7Msolaryr-1 in agreement withprevious estimates. The morphology of the best model is consistent withthe well-known Hubble Space Telescope image at better than 5 per centand is also in broad agreement with light-echo observations. Thecircumstellar environment on larger scales (up to 3pc) is alsoinvestigated. We conclude with a brief discussion of the bipolar nebulaesurrounding the Galactic stars, Sheridan 25, HD 168625 and ?Carinae.
| Description of the ``Scenario Machine''
We present an updated description of the “Scenario Machine”code, which is used to carry out population-synthesis analyzes of theevolution of close binary stars.
| The Evolutionary State of the Massive Interacting Binary BD+36°4063
We present a spectroscopic and photometric analysis of the remarkablemassive binary system, BD+36°4063. We argue that the visible ON staris undergoing a rapid mass transfer episode that results in a thick andopaque disk that surrounds and renders invisible its massive companion.A comparison of the projected rotational velocity and the orbitalsemiamplitude of the visible star indicates a mass ratio near unity.Models for conservative mass transfer show that the equal mass stateoccurs at the point of minimum separation, and we argue thatBD+36°4063 may represent the first system identified at this rapidand rare stage of massive binary evolution.
| A Point-Source Survey of M31 with the Spitzer Space Telescope
We explore the stellar population of M31 in a Spitzer Space Telescopesurvey utilizing IRAC and MIPS observations. Red supergiants are thebrightest objects seen in the infrared; they are a prominentevolutionary phase. Due to their circumstellar envelopes, many of theseradiate the bulk of their luminosity at IRAC wavelengths and do notstand out in the near-infrared or optically. Going fainter, we see largenumbers of luminous asymptotic giant branch stars (AGB), many of whichare known long-period variables. Relative to M33 the AGB carbon starpopulation of M31 appears sparse, but this needs to be spectroscopicallyconfirmed.
| On the origin of field O-type stars
Aims. We aim to identify the origins of field O-stars in the nearest 2to 3 kpc around the Sun using the best presently available kinematicdata on O-stars and on young open clusters. We investigate the questionof whether the present-day data are consistent with the assumption thatO-stars have formed in groups (clusters, associations), or in isolation. Methods: We apply the epicycle theory to back-trace the orbits ofO-type stars and of candidate parent open clusters. Results: From the370 O-stars in the “Galactic O star catalog v 2.0” (GOSV2)we have investigated 93 stars classified as field, and found the originfor 73 of them in 48 open clusters younger than 30 Myr. Only for 32stars or about 9% of all O-stars from this catalogue is the question oftheir origin in groups not solved; some of them may have originated inisolation or may have disintegrated the group in which they formed.Fifty percent of the young open clusters (age < 30 Myr) in the“Catalogue of Open Cluster Data” (COCD) have O-stars asmembers, or have ejected at least one O-star in the first 10 Myr oftheir life, or both. During this period the average mass loss from openclusters by ejecting O-stars is found to be 3 to 5 M_ȯ per Myr. Weprove that ζ Pup had its origin in the open cluster Trumpler 10which it left about 2.5 Myr ago, and that its present-day distance is300 pc (compared to 440 pc before). The revised distance implies asignificant revision of the stellar parameters (a radius of 14 R_ȯ,a mass of 22.5 M_ȯ, and a luminosity of log L/L_ȯ of 5.74)i.e., ζ Pup is closer, less massive, and less luminous thanpreviously thought. Our findings provide independent estimates of thepresent-day distances and absolute magnitudes of field O-stars.
| Accretion Disk in the Massive Binary RY Scuti
The UBVR light curves of the massive eclipsing binary RY Sct, obtainedat the Maidanak Observatory from 1979 to 1992, have been re-analyzed inorder to prove the hypothesis of the presence of an accretion disk inthe system. This hypothesis is supported by a new spectroscopic study ofGrundstrom et al., and by a specific light-curve shape exhibiting aslight asymmetry around the secondary minima and a small difference inthe height of the successive maxima. The light-curve analysis wasperformed using a Roche model of a binary containing a geometrically andoptically thick accretion disk around the more massive primary star. Bysolving the inverse problem, the orbital elements and the physicalparameters of the system components and of the accretion disk wereestimated for all the individual UBVR light curves. The model gives aconsistent solution for the RY Sct binary system and supports thehypothesis of the existence of an optically thick disk around themassive component. Our results suggest a mass exchange between thecomponents and a mass loss from the system. This could be considered asa possible mechanism of the formation of the accretion disk around themore massive component and of the circumbinary envelope of toroidal formin the orbital plane of the system.
| Silicate Dust in the Environment of RS Ophiuchi following the 2006 Eruption
We present further Spitzer Space Telescope observations of the recurrentnova RS Ophiuchi, obtained over the period 208-430 days after the 2006eruption. The later Spitzer IRS data show that the line emission andfree-free continuum emission reported earlier is declining, revealingincontrovertible evidence for the presence of silicate emission featuresat 9.7 and 18 ?m. We conclude that the silicate dust survives thehard radiation impulse and shock blast wave from the eruption. Theexistence of the extant dust may have significant implications forunderstanding the propagation of shocks through the red giant wind andlikely wind geometry.
| Detection of 6-cm radio-continuum emission from an EB (?-Lyrae type) variable star - HIP 68718
We report the 6-cm radio-continuum detection of a previously unknownradio star, HIP 68718, identified by the Hipparcos satellite as an EB or?-Lyrae type optical variable. Only five prior radio detections ofthis type are reported in the literature. The radio source (VLAJ140402-002145) was detected at the 6? level, with an associated<1arcsec position error. The radio-optical separation is 0.2arcsecand is well within the position errors. A ROSAT X-ray source (RXJ1404.0-0021) is located 4.5 arcsec from the radio position. Based on thecomponent spectral types (F5V + G5V), 1.52 d period, variations in thepeak of the light curve and the X-ray and 6-cm radio luminosities, weconclude the star is a candidate RS CVn. The binary is in a near-contactphase based on the asymmetric light curve (O'Connell effect). Evidenceof two faint possible companion objects was also found in the J- andK-band Two-Micron All-Sky Survey images.
| On the circumstellar environment of SS433
We present new 8200-8900 Å high-resolution spectroscopicobservations of the unusual accreting source SS433. The spectra arehighly variable on a night-to-night basis, and are dominated by emissionfrom the Paschen series and OI emission. Differences in line profilesbetween the two species suggest that they arise in kinematicallydistinct and highly variable circumstellar regions. Moreover, thestrength of OI emission argues against identifying the mass donor as aWolf-Rayet star since we might expect oxygen to be depleted by the CNOcycle in such a star. Weak NI absorption lines are present, which, ifarising in the photosphere of the mass donor would imply a spectral typeof B5 or later. However, no evidence was found for orbital modulation intheir radial velocity curves suggesting that they too arise in theaccretion-driven outflow. Finally, by analogy to the massive closebinary RY Scuti, we suggest that the recent detection of a mid-infraredexcess attributed to warm dust may arise in a circumbinary disc,implying that SS433 hosts a rich, highly structured circumstellarenvironment driven by the high mass-transfer rate from the mass donor.
| A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representativeof an active mass-transferring system that is changing before our eyesand which may be an example of the formation of a Wolf-Rayet starthrough tidal stripping. Utilizing new and previously published spectra,we present examples of how a number of illustrative absorption andemission features vary during the binary orbit. We identify spectralfeatures associated with each component, calculate a new, double-linedspectroscopic binary orbit, and find masses of 7.1+/-1.2Msolar for the bright supergiant and 30.0+/-2.1Msolar for the hidden massive companion. Through tomographicreconstruction of the component spectra from the composite spectra, weconfirm the O9.7 Ibpe spectral class of the bright supergiant anddiscover a B0.5 I spectrum associated with the hidden massive companion;however, we suggest that the latter is actually the spectrum of thephotosphere of the accretion torus immediately surrounding the massivecompanion. We describe the complex nature of the mass-loss flows fromthe system in the context of recent hydrodynamical models for ?Lyr, leading us to conclude RY Scuti has matter leaving the system intwo ways: (1) a bipolar outflow from winds generated by the hiddenmassive companion, and (2) an outflow from the bright O9.7 Ibpesupergiant in the region near the L2 point to fill out a large, densecircumbinary disk. This circumbinary disk (radius ~1 AU) may feed thesurrounding double-toroidal nebula (radius ~2000 AU).
| Toward Understanding the B[e] Phenomenon. I. Definition of the Galactic FS CMa Stars
The B[e] phenomenon is defined as the simultaneous presence oflow-excitation forbidden line emission and strong infrared excess in thespectra of early-type stars. It was discovered in our Galaxy 30 yearsago in the course of the early exploration of the infrared sky andinitially identified in 65 Galactic objects, of which nearly halfremained unclassified. The phenomenon is associated with objects atdifferent evolutionary stages, ranging from the pre-main-sequence to theplanetary nebula stage. We review the studies of both the original 65and subsequently identified Galactic stars with the B[e] phenomenon. Anew classification is proposed for stars with the B[e] phenomenon basedon the time of dust formation in their environments. Properties of theunclassified Galactic B[e] stars are analyzed. We propose that theseobjects are binary systems that are currently undergoing or haverecently undergone a phase of rapid mass exchange, associated with astrong mass loss and dust formation. A new name, FS CMa stars, andclassification criteria are proposed for the unclassified B[e] stars.
| And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae
We report the discovery of two new circumstellar ring nebulae in thewestern Carina Nebula, and we discuss their significance in stellarevolution. The brighter of the two new objects, SBW 1, resembles alidless staring eye and encircles a B1.5 Iab supergiant. Although seenin Carina, its luminosity class and radial velocity imply a largerdistance of ~7 kpc in the far Carina arm. At that distance its size andshape are nearly identical to the equatorial ring around SN 1987A, butSBW 1's low N abundance indicates that the ring was excreted without itsstar passing through a red supergiant phase. The fainter object, SBW 2,is a more distorted ring, is N-rich, and is peculiar in that its centralstar seems to be invisible. We discuss the implications of these two newnebulae in context with other circumstellar rings such as those aroundSN 1987A, Sher 25, HD 168625, RY Scuti, WeBo 1, SuWt 2, and others. Thering bearers fall into two groups: Five rings surround hot supergiants,and it is striking that all except for the one known binary are carboncopies of the ring around SN 1987A. We propose a link between these Bsupergiant rings and B[e] supergiants, where the large spatiallyresolved rings derive from the same material that would have given riseto emission lines during the earlier B[e] phase, when it was much closerto the star. The remaining four rings surround evolved intermediate-massstars; all members of this ring fellowship are close binaries, hintingthat binary interactions govern the forging of such rings. Two-thirds ofour sample are found in or near giant H II regions. We estimate thatthere may be several thousand more dark rings in the Galaxy, but we arescarcely aware of their existence-either because they are onlyilluminated in precious few circumstances or because of selectioneffects. For intermediate-mass stars, these rings might be thepreexisting equatorial density enhancements invoked to bind the waistsof bipolar nebulae.Based in part on observations made at the Clay Telescope of the MagellanObservatory, a joint facility of the Carnegie Observatories, HarvardUniversity, the Massachusetts Institute of Technology, the University ofArizona, and the University of Michigan.
| Discovery of a Nearby Twin of SN 1987A's Nebula around the Luminous Blue Variable HD 168625: Was Sk -69 202 an LBV?
Spitzer Space Telescope images of the luminous blue variable (LBV)candidate HD 168625 reveal the existence of a bipolar nebula severaltimes larger than its previously known equatorial dust torus. The outernebula of HD 168625 has a full extent of ~80" or 0.85 pc, and one of thelobes has a well-defined polar ring. The nebula is a near twin of thetriple-ring system around SN 1987A. Because of these polar rings, andaccounting for stellar/progenitor luminosity, HD 168625 is an evencloser twin of SN 1987A than the B supergiant Sher 25 in NGC 3603. HD168625's nebula was probably ejected during a giant LBV eruption and notduring a red supergiant phase, so its similarity to the nebula around SN1987A may open new possibilities for the creation of SN 1987A's rings.Namely, the hypothesis that Sk -69 202 suffered an LBV-like eruptionwould avert the complete surrender of single-star models for its bipolarnebula by offering an alternative to an unlikely binary merger scenario.It also hints that LBVs are the likely progenitors of some Type IIsupernovae, and that HD 168625's nebula is a good example of apre-explosion environment.Based on observations made with the Spitzer Space Telescope, which isoperated by the Jet Propulsion Laboratory, California Institute ofTechnology, under NASA contract 1407.
| Spitzer Spectroscopy of Dusty Disks around B[e] Hypergiants in the Large Magellanic Cloud
We used the Spitzer Space Telescope Infrared Spectrograph (IRS) toobtain mid-infrared (5-35 μm) spectra of two highly luminous B[e]stars in the Large Magellanic Cloud (LMC), R126 (HD 37974) and R66 (HD268835). Both stars display flat spectra with silicate emissionfeatures; R66 displays, in addition, spectral evidence of crystallinegrains and PAHs. Given the similarity of the IRS spectra of R126 and R66to those of pre-main-sequence stars, we interpret these spectra as beingdue to thermal emission from circumstellar dust disks. Comparison with amodel of thermal emission from a passive, irradiated dust disk suggeststhat the disks around R126 and R66 are quite massive, with~3×10-3 Msolar of dust contained between 120and 2500 AU from the star in the case of R126. Episodic mass ejectionsand/or debris disks (perhaps surrounding as-yet undetected companionstars) represent potential sources for the thermal dust emission fromthese and other B[e] hypergiants in the LMC.
| Infrared [Fe II] Emission from P Cygni's Nebula: Atomic Data, Mass, Kinematics, and the 1600 AD Outburst
We present moderate- and high-dispersion 1-2.5 μm spectra of the ~10"radius nebula around P Cygni, dominated by bright emission lines of [FeII]. Observed [Fe II] line ratios disagree with theoretical transitionrates in the literature, so we use the spectrum of P Cyg's nebula toconstrain the atomic data for low-lying levels of [Fe II]. Of particularinterest is the ratio [Fe II] λ12567/λ16435, often used asa reddening indicator, for which we empirically derive an intrinsicvalue of 1.49, which is 10%-40% higher than previous estimates.High-dispersion spectra of [Fe II] λ16435 constrain the geometry,detailed structure, and kinematics of P Cyg's nebula, which is the majorproduct of P Cyg's outburst in 1600 AD. We use the [N II]/[N I] lineratio to conclude that the nebula is mostly ionized, with a total massof ~0.1 Msolar, more than the mass lost by the stellar windsince the eruption. For this mass, we would expect a larger infraredexcess than observed. We propose that the dust that obscured the starafter the outburst has since been largely destroyed, releasing Fe intothe gas phase to produce the bright [Fe II] emission. The kinetic energyof this shell is ~1046.3 ergs, far less than the kineticenergy released during the giant eruption of η Car in the 1840s, butclose to the value for η Car's smaller 1890 outburst. In thisrespect, it is interesting that the infrared spectrum of P Cyg's nebularesembles that of the ``Little Homunculus'' around η Car, ejected inthat star's 1890 eruption. The mass and kinetic energy in the nebulae ofη Car and P Cyg give insight into the range of parameters expectedfor extragalactic η Car-like eruptions.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| Anisotropic mass ejection in binary mergers
We investigate the mass loss from a rotationally distorted envelopefollowing the early, rapid in-spiral of a companion star inside a commonenvelope. For initially wide, massive binaries(M1+M2= 20Msolar, P~10yr), the primaryhas a convective envelope at the onset of mass transfer and is able tostore much of the available orbital angular momentum in its expandedenvelope. Three-dimensional smoothed particle hydrodynamics calculationsshow that mass loss is enhanced at mid-latitudes due to shock reflectionfrom a torus-shaped outer envelope. Mass ejection in the equatorialplane is completely suppressed if the shock wave is too weak topenetrate the outer envelope in the equatorial direction (typically whenthe energy deposited in the star is less than about one-third of thebinding energy of the envelope). We present a parameter study to showhow the geometry of the ejecta depends on the angular momentum and theenergy deposited in the envelope during a merging event. Applications tothe nearly axisymmetric, but very non-spherical nebulae around SN1987Aand Sheridan 25 are discussed, as well as possible links to RY Scuti andthe Small Magellanic Cloud object R4.
| MWC 930 - a new luminous blue variable candidate
We present the results of optical high-resolution and near-infraredlow-resolution spectroscopy and multicolour optical and near-infraredphotometry of the emission-line star MWC 930. The spectrum is rich withFeII emissions, most of which have P Cyg-type profiles. The emissionlines are strong and narrow, indicating a powerful stellar wind with alow terminal velocity (v&infy;~ 140kms-1). Thephotospheric absorption lines are broad and show splitting, which mightbe due to the object's binarity. MWC 930 is most probably located in theNorma spiral arm at a distance of D= 3-4kpc. This strong and slow windas well as the star's luminosity (logL/Lsolar~ 5.5) and theinfrared excess shape suggest that MWC 930 is an unusual B-typesupergiant, most likely undergoing the luminous blue variableevolutionary phase.
| Properties of galactic B[e] supergiants. V. Two-dimensional radiative transfer model of RY Sct and its dusty disc
We present results of the first two-dimensional radiative transfermodelling of the eclipsing binary RY Sct and itsdusty disc. Assuming an effective temperature Tstar = 27 000K for both components and the distance D = 1.8 kpc, we derive the totalluminosity Lstar = 4.2 × 105Lȯ. The optically thin dusty disc (τV≈ 0.04 in the equatorial plane) extends from its inner boundary atR1 = 60 AU to the distances of R2 ≈105 AU, where it blends into the interstellar medium. Thevery high energy output of the supergiants heats up the interstellardust, well beyond the outer boundary, to temperatures of 100 K. It isthe large interstellar extinction towards RY Sct(AV = 4.5 mag) that defines its spectral energy distributionin the ultraviolet, optical and near infrared. The disc has a fullopening angle {ψ} = 26° and we observe it at a viewing angleθv = 14° from its midplane (inclination i =76°). There is a strong density enhancement in the disc within anarrow ring at r = 1500 AU, that emits most of the infrared flux and isprominent in Keck telescope images (Gehrz et al. 2001, ApJ, 559, 395).The dust mass contained in the disc within 1´´ from the star(r < 1800 AU) is md = 3.2 × 10-7Mȯ, by a factor of 3 lower than in previous estimates.However, in our model there is 30 times more mass in the surroundingsof the binary system than within the dense ring. As much as 95% of thetotal dust mass Md = 9 × 10-6Mȯ and gas mass M = 0.017 Mȯ of thecircumbinary material is contained in the outer, old wind at 1800 < r< 105 AU. Presumably the dense ring has been created by afast wind that swept out and compressed the previously lost material inthe older and slower stellar wind. Based on the new Keck data, our modelpredicts that presently there is a relatively large number of small, hotdust grains in the dust formation zone, whose emission substantiallychanges the shape of the SED of RY Sct in the nearinfrared. This suggests a higher mass-loss rate or dust-to-gas massratio or lower wind velocity, or a combination of these factors.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Modelling Dusty Circumbinary Disk around B[e] Supergiant RY Sct
The supergiant RY Sct is an eclipsing binary system with a fairly largeinfrared (IR) excess caused by the presence of circumbinary dust. Manystrong forbidden lines ([O i], [N ii], [S iii], [Fe ii]), in combinationwith the near-IR excess, put it in the list of peculiar Be or B[e]stars. Although RY Sct is one of the best-studied systems, even itsbasic physical parameters remain unreliable. Recent IR images of thesystem, obtained with a 0.3 arcsec resolution at the 10-m Kecktelescope, showed the dusty disk at the wavelengths 3-20 ?m andstimulated us to perform its detailed modelling using our 2-D radiativetransfer code. Our model reproduces all available observations of RY Sctobtained during the last few decades. The modelling demonstrated thatthe observations cannot be described by a single model at one moment intime, implying rapid changes in the dusty disk during the last 20 years.Assuming that a temperature of 27,000 K describes both components of thebinary and that its distance is 1.8 kpc, its total luminosity is 4.2 - 105 solar luminosity. The model disk has the optical depth of 0.04 andthe opening angle of 26° (between the boundaries). Dust in the diskexists between 60 AU and 105 AU, where it blends into the interstellarmedium. We observe the disk almost edge-on, at an angle of 14° toits midplane. The total mass of the disk is 0.017 solar mass. There is astrong density enhancement at 1800 AU from the binary, which emits mostof the IR radiation and is prominent in the Keck telescope images.Presumably, the dense ring has been created by a fast wind that sweptout and compressed the previously lost material in the older and slowerstellar wind. Our model predicts that presently there is a large amountof small, hot dust grains in the dust formation zone, whose emissionchanged the shape of the SED of RY Sct in the near IR. The dust densitymust now be significantly greater in the dust formation zone, suggestinga much higher massloss rate or dust-to-gas mass ratio or much lower windvelocities than before, or a combination of these factors.
| 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.
| Properties of galactic B[e] supergiants. IV. Hen 3-298 and Hen 3-303
We present the results of optical and near-IR spectroscopic and near-IRphotometric observations of the emission-line stars Hen 3-298 and Hen3-303. Strong emission in the H? line is found in both objects.The presence of Fe ii and [O i] emission lines in the spectrum of Hen3-298 indicates that it is a B[e] star. The double-peaked CO lineprofiles, found in the infrared spectrum of Hen 3-298, along with theoptical line profiles suggest that the star is surrounded by a rotatingcircumstellar disc. Both objects also show infrared excesses, similar tothose of B[e] stars. The radial velocities of the absorption andemission lines as well as a high reddening level suggest that theobjects are located in the Norma spiral arm at a distance of 3-4.5 kpc.We estimated a luminosity of log L/L? ˜ 5.1 and aspectral type of no earlier than B3 for Hen 3-298. Hen 3-303 seems to bea less luminous B-type object (log L/L? ˜ 4.3),located in the same spiral arm.
| Bipolar Symbiotic Planetary Nebulae in the Thermal Infrared: M2-9, Mz 3, and He 2-104
We present thermal-infrared images of three extreme bipolar objects,M2-9, Mz 3, and He 2-104. They are bipolar planetary nebulae with brightcentral stars and are thought to be powered by symbiotic binary systems.The mid-infrared images spatially resolve the spectral energydistributions of the central engines from the surrounding nebulae. Awarm dust component of several hundred degrees can account for the coreemission, while a cooler component of ~100 K produces the more extendedemission from the bipolar lobes. In every case, the dust mass for theunresolved core region is orders of magnitude less than that in theextended lobes, raising doubts that the hypothetical disks in the corecould have been responsible for pinching the waists of the nebulae. Wefind total masses of roughly 0.5-1 Msolar in the nebulae ofM2-9 and Mz 3, requiring that this material was donated byintermediate-mass progenitor stars. The mass of He 2-104's nebula ismuch lower, and any extended emission is too faint to detect in ourimages. Extended dust emission is detected around both M2-9 and Mz 3, inboth cases resembling the distribution of ionized gas. Our images of Mz3 have the highest signal-to-noise ratio in the extended polar lobes,and we show that the fairly uniform color temperature derived from ourimages can explain the 110 K dust component that dominates thefar-infrared spectral energy distribution. In the case of Mz 3, most ofthe mass traced by dust is concentrated at high latitudes, and we notepossible evidence for grain destruction in shocks indicated by ananticorrelation between [Fe II] and dust emission. Except for theseregions with enhanced [Fe II] emission, the dust continuum closelyresembles the distribution of ionized gas.
| 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
| 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.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Щит |
| Прямое восхождение: | 18h25m31.48s |
| Склонение: | -12°41'24.2" |
| Видимая звёздная величина: | 9.216 |
| Собственное движение RA: | -0.4 |
| Собственное движение Dec: | -1.1 |
| B-T magnitude: | 10.409 |
| V-T magnitude: | 9.315 |
Каталоги и обозначения:
|
