目录
图像
上传图像
DSS Images Other Images
相关文章
Constraining Disk Parameters of Be Stars using Narrowband Hα Interferometry with the Navy Prototype Optical Interferometer
Interferometric observations of two well-known Be stars, γ Cas andφ Per, were collected and analyzed to determine the spatialcharacteristics of their circumstellar regions. The observations wereobtained using the Navy Prototype Optical Interferometer equipped withcustom-made narrowband filters. The filters isolate the Hαemission line from the nearby continuum radiation, which results in anincreased contrast between the interferometric signature due to theHα-emitting circumstellar region and the central star. Because thenarrowband filters do not significantly attenuate the continuumradiation at wavelengths 50 nm or more away from the line, theinterferometric signal in the Hα channel is calibrated withrespect to the continuum channels. The observations used in this studyrepresent the highest spatial resolution measurements of theHα-emitting regions of Be stars obtained to date. Theseobservations allow us to demonstrate for the first time that theintensity distribution in the circumstellar region of a Be star cannotbe represented by uniform disk or ringlike structures, whereas aGaussian intensity distribution appears to be fully consistent with ourobservations.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| On the evolutionary status of Be stars. I. Field Be stars near the Sun
A sample of 97 galactic field Be stars were studied by taking intoaccount the effects induced by the fast rotation on their fundamentalparameters. All program stars were observed in the BCDspectrophotometric system in order to minimize the perturbationsproduced by the circumstellar environment on the spectral photosphericsignatures. This is one of the first attempts at determining stellarmasses and ages by simultaneously using model atmospheres andevolutionary tracks, both calculated for rotating objects. The stellarages (τ) normalized to the respective inferred time that eachrotating star can spend in the main sequence phase (τ_MS) reveal amass-dependent trend. This trend shows that: a) there are Be starsspread over the whole interval 0 τ/τ_MS 1 of themain sequence evolutionary phase; b) the distribution of points in the(τ/τMS,M/Mȯ) diagram indicates thatin massive stars (M 12~Mȯ) the Be phenomenon ispresent at smaller τ/τ_MS age ratios than for less massive stars(M 12~Mȯ). This distribution can be due to: i)higher mass-loss rates in massive objets, which can act to reduce thesurface fast rotation; ii) circulation time scales to transport angularmomentum from the core to the surface, which are longer the lower thestellar mass.
| Amateur Spectroscopy of Hot Stars: Long Term Tracking of Circumstellar Emission
Not Available
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Speckle Observations of Binary Stars with the WIYN Telescope. IV. Differential Photometry
Five hundred seventy-six magnitude difference measures are presented for260 binary stars. These measures are derived from CCD-based speckleobservations taken at the WIYN 3.5 m telescope at Kitt Peak NationalObservatory during the period 1997-2000. Separations of the systemsrange from over 1" down to near the diffraction limit of the telescope.A study of multiple measures of the same targets indicates that themeasures have a typical uncertainty of better than 0.13 mag per 2 minuteobservation, and that multiple observations can be averaged to arrive atsmaller uncertainties. Results presented here are also compared, insofaras it is possible, with measures in the Hipparcos Catalogue and toprevious studies using adaptive optics. No major systematic errors wereidentified.The WIYN Observatory is a joint facility of the University ofWisconsin-Madison, Indiana University, Yale University, and the NationalOptical Astronomy Observatory.
| A potential φ Per-type (Be+sdO) binary: FY CMa
The spectrum of the Be star FY CMa is shown to vary periodically withP=37.26±0.03 d. The types of variation, exhibiting transientstrong shell phases and a radial-velocity variable He I emissioncomponent, suggest the star to be of the same type as φ Per, i.e.having an evolved hot companion ionizing the outer parts of theprimary's circumstellar disc where it faces the hot companion. Afterφ Per and the candidates 59 Cyg and HR 2142, this is only thefourth promising candidate, although such systems should be relativelyabundant. The similarities found between φ Per, 59 Cyg, and FY CMainclude a radial velocity-variable He I emission feature and aphase-locked V/R cycle. An ephemeris is given that allows a test of theproposed recurrent nature of a strong shell feature observed only in asingle spectrum at present.Based on observations collected at the South African AstronomicalObservatory.
| Autocorrelation Analysis of Hipparcos Photometry of Short-Period Be Stars
We have used Hipparcos epoch photometry and a form of autocorrelationanalysis to investigate the amplitude and timescale of the short-periodvariability of 82 Be stars, including 46 Be stars that were analyzed byHubert & Floquet using Fourier and CLEAN analysis and 36 other Bestars that were suspected of short-period variability. Our method hasgiven useful information for about 84% of these stars; for the rest, thetime distribution of the Hipparcos epoch photometry limits thecapability of our technique.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Population Synthesis of Binary Be Stars with Degenerate Companions in the Galaxy
Using the numerical code (`Scenario Machine') we study of number andphysical properties of binary Be stars. Evolutionary tracks leading to aformation of the observational binary systems are presented. We concludethat synchronization must be taken into account when calculating binaryBe star evolution and calculate the minimal orbital period forBe/evolved companion binary. The obtained distributions over orbitalparameters are in good agreement with the observational lack ofshort-period Be/X-ray binaries. According to our calculations 70% of allBe stars must have a white dwarf. The white dwarfs in these systemsshould be hot enough with the surface temperature distribution peakingat 10000-20000 K. Their detection is possible during the period of thelack of Be star envelope by the detection of white dwarf extremely UVand soft X-ray emission. This method of registration appears to beparticularly promising for `single' early-type Be stars because in thesesystems the white dwarfs must have a very high surface temperature.However, the loss of the Be disc-like envelope does not often occur andit is a rather rare event for many Be stars. The best possibility ofwhite dwarf detection is given by the study of helium spectral linesfound in emission from several Be stars. The ultraviolet continuumenergy of these Be stars is found to be not enough to produce theobserved helium emission. Besides, we also discuss the orbitalproperties of binary Be star systems with other evolved companions suchas helium stars and neutron stars and give a possible explanation forthe lack of Be/black hole binaries.
| Speckle Observations of Binary Stars with the WIYN Telescope. II. Relative Astrometry Measures during 1998-2000
Five hundred twelve relative astrometry measures are presented for 253double stars, including 53 double stars discovered by Hipparcos. In 15cases, relative astrometry is reported for the first time for newlyconfirmed pairs. In addition, 20 high-quality nondetections ofcompanions are reported for stars suspected of being nonsingle byHipparcos. Observations were taken using a fast-readout CCD camerasystem at the WIYN 3.5 m telescope at Kitt Peak, Arizona. In comparingthese measures with ephemeris predictions for binary stars with verywell known orbits, we find that the measurement precision is better than3 mas in separation and 1° in position angle per individualobservation. Measurement precision and detection capabilities are fullydiscussed, and confirmed orbital motion is reported in four cases of theHipparcos double star discoveries. The WIYN Observatory is a jointfacility of the University of Wisconsin-Madison, Indiana University,Yale University, and the National Optical Astronomy Observatory.
| Search for duplicity in periodic variable Be stars
Four Be stars, HR 1960, HR 2968,HR 3237 and HR 3642, selectedaccording to their periodic variations in HIPPARCOS and GENEVAphotometries, were monitored from 1998 until 2001 with the CORALIEspectrograph. Among these stars, two are new spectroscopic binaries andone is a new lambda Eri short period variable. HR 1960 is a lowamplitude (K = 3.4 km s-1) SB1 with a period of 395.48 d inagreement with the photometric prediction. HR 3237 is a short period SB1(P = 5.1526 d). HR 3642 presents some interesting variations inphotometry and spectroscopy: indeed, a mid- and a short-term variationis present with periods of 137.99 d (Hp magnitude) and 1.13028 d (radialvelocity) respectively. The short-term variation, characteristic of thelambda Eri stars, probably implies non-radial pulsations orinhomogeneities in the corotating disc. The last star, HR 2968, is anexcellent photometric binary candidate, but no spectroscopic obviousnessof a companion has been found. Based on observations collected at theSwiss 40 cm, 70 cm and 120 cm telescopes at the European SouthernObservatory (La Silla, Chile) and on data from the ESA HIPPARCOSsatellite. The photometric and radial velocity data are only availablein electronic 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/385/488 Table 3 is onlyavailable in electronic form at http://www.edpsciences.org
| Ultraviolet Spectrophotometry of Variable Early-Type Be and B Stars Derived from High-Resolution IUE Data
High-dispersion IUE data encode significant information about aggregateline absorptions that cannot be conveniently extracted from individualstellar spectra. Here we apply a new technique in which fluxes from eachechelle order of a short-wavelength IUE spectrum are binned together toconstruct low-resolution spectra of a rapidly varying B or Be star. Thedivision of binned spectra obtained during a ``bright-star'' phase byspectra from a ``faint-star'' phase leads to a ratioed spectrum thatcontains information about the mechanism responsible for a star'svariability. The most likely candidate mechanisms are either theperiodic or episodic occultations of the star by ejected matter or achange in photospheric structure, e.g., from pulsation. We model thevariations caused by these mechanism by means of model atmosphere andabsorbing-slab codes. Line absorptions strength changes are rathersensitive to physical conditions in circumstellar shells and ``clouds''at temperatures of 8000-13,000 K, which is the regime expected forcircumstellar structures of early B stars. To demonstrate proofs of thisconcept, we construct spectral ratios for circumstellar structuresassociated with flux variability in various Be stars: (1) Vela X-1 has abow-shock wind trailing its neutron star companion; at successive phasesand hence in different sectors, the wind exhibits spectrophotometricsignatures of a 13,000 or 26,000 K medium; (2) 88 Her undergoes episodic``outbursts'' during which its UV flux fades, followed a year later by adimming at visible wavelengths as well; the ratioed spectrum indicatesthe ``phase lag'' is a result of a nearly gray opacity that dominatesall wavelengths as the shell expands from the star and cools, permittingthe absorptions in the visible to ``catch up'' to those in the UV; and(3) ζ Tau and 60 Cyg exhibit periodic spectrum and flux changes,which match model absorptions for occulting clouds but are actually mosteasily seen from selective variations of various resonance lines. Inaddition, ratioed UV spectra of radial and large-amplitude nonradialpulsating stars show unique spectrophotometric signatures, which can besimulated with model atmospheres. An analysis of ratioed spectraobtained for a representative sample of 18 classical Be stars known tohave rapid periodic flux variations indicates that 13 of them haveratioed spectra that are relatively featureless or have signatures ofpulsation. Ratioed spectra of three others in the sample exhibitsignatures that are consistent with the presence of corotating clouds.
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| High and intermediate-resolution spectroscopy of Be stars 4481 lines
We present an atlas of Hγ , He i lambda 4471 and Mg ii lambda 4481line profiles obtained in a 10 year observation period of 116 Be stars,which enabled many of them to be observed at quite different emissionepochs. From the best fit of the observed He i lambda 4471 line profileswith non-LTE, uniform (Teff,log g) and full limb-darkenedmodel line profiles, we determined the V sin i of the program stars. Toaccount, to some degree, for the line formation peculiarities related tothe rapid rotation-induced non-uniform distributions of temperature andgravity on the stellar surface, the fit was achieved by considering(Teff,log g) as free parameters. This method produced V sin iestimations that correlate with the rotational velocities determined bySlettebak (1982) within a dispersion sigma <= 30 km s-1and without any systematic deviation. They can be considered as given inthe new Slettebak's et al. (1975) system. Only 13 program stars havediscrepant V sin i values. In some objects, this discrepancy could beattributed to binary effects. Using the newly determined V sin iparameters, we found that the ratio of true rotational velocitiesV/Vc of the program Be stars has a very low dispersion aroundthe mean value. Assuming then that all the stars are rigid rotators withthe same ratio V(/lineω)/Vc, we looked for the value of/line ω that better represents the distribution of V sini/Vc for randomly oriented rotational axes. We obtained/lineω = 0.795. This value enabled us to determine the probableinclination angle of the stellar rotation axis of the program stars. Inthe observed line profiles of Hγ , He i lambda 4471, Mg ii lambda4481 and Fe ii lambda 4351 we measured several parameters related to theabsorption and/or emission components, such as: equivalent width,residual emission and/or absorption intensity, FWHM, emission peakseparations, etc. The parameters related to the Hγ line emissionprofiles were used to investigate the structure of the nearbyenvironment of the central star. From the characteristics of thecorrelations between these quantities and the inferred inclinationangle, we concluded that in most of cases the Hγ line emissionforming regions may not be strongly flattened. Using a simplerepresentation of the radiation flux emitted by the star+envelopesystem, we derived first order estimates of physical parameterscharacterizing the Hγ line emission formation region. Thus, weobtained that the total extent of the Hγ region is Rf=~ 2.5 +/- 1.0 R* and that the density distribution in theselayers can be mimicked with a power law rho ~ R-alpha , wherealpha =2.5+2.2-0.6. The same approach enabled usto estimate the optical depth of the Hγ line emission formationregion. From its dependence with the aspect angle, we concluded thatthese regions are caracterized by a modest flattening and that the rho(equator)/rho (pole) density contrast of the circumstellar envelope nearthe star should be two orders of magnitude lower than predicted bymodels based on a priori disc-shaped circumstellar envelopes. We foundthat the separation between the emission peaks, Deltap, andthe full width at half maximum, Delta 1/2, of the Hγline emission are not only sensitive to kinematic effects, but to lineoptical depth as well. This finding agrees with previous theoreticalpredictions and confirms that Huang's (1972) relation overestimates theextent of the Hγ line emission formation region. Data obtained atCASLEO operated under agreement between the CONICET and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina, at ESOLa Silla, Chile and at OHP, France.}\fnmsep\thanks{Tables 2 to 7 andFigs. 1 and 2 are only available in full in electronic form at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/378/861}} \subtitle{Anatlas of Hγ , He {\fontsize {10pt}{12pt}\selectfont I} 4471 and Mg{\fontsize {10pt}{12pt}\selectfont II
| Hα emission line spectroscopy in NGC 330. On the hybrid model for global oscillations in Be star circumstellar disks
We perform an observational test on global oscillations in Be starcircumstellar disks in the metal deficient environment of the SMC.According to the hybrid model of disk oscillations early-type Be starsrequire an optically thin line force to establish a density wave. Thelow metallicity in the SMC should therefore diminish or prevent theformation of disk oscillations in early-type Be stars. We present shortwavelength range spectra around Hα of 48 Be stars in the youngopen cluster NGC 330 in the SMC. We find that the fraction of early-typeBe stars in NGC 330 which host a global disk oscillation does not differfrom the known fraction of Galactic field Be stars. This observationalresult is in contradiction to the theoretical prediction. We discussseveral interpretations and propose a further observational test. Basedon observations collected with VLT-Kueyen-FORS2-MXU during thecommissioning~1 of FORS2 and the mechanical commissioning of the MXU,operated on Cerro Paranal (Chile) by the European Southern Observatoryand the VLT instrument consortium (FORS2).
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| Population synthesis of Be/white dwarf binaries in the Galaxy
Using the ``Scenario Machine'' (a numerical co-de that models theevolution of large ensembles of binary systems) we study the number andphysical properties of binary Be stars with white dwarfs taking accountof the compact object cooling and we discuss the ways of theirformation. In our calculations we take into account the influence oftidal synchronization on the evolution of stars in a close binary. Thesynchronization time scale may be less than the life-time of a Be staron the main sequence after the first mass transfer. It has strongeffects on the resulting number distribution of binary Be stars overorbital periods. In particular, it can explain the lack of short periodBe binaries. According to our calculations the number of binary systemscontaining a Be star paired with a white dwarf in the Galaxy is verylarge - 70% of all Be stars formed as a result of binary evolution musthave a white dwarf as a companion. Based on our calculations we concludethat the compact companion in these systems must have a high surfacetemperature. The number distribution over the surface temperature peaksat 2 104 K for all white dwarfs and at 4 104 K forwhite dwarfs paired with early-type Be stars (between B0 and B2). Theregistration of white dwarfs in such systems is hampered by the factthat the entire orbit of a white dwarf is embedded in the densecircumstellar envelope of the primary star (our calculations show thatthe majority of Be/WD systems have orbital periods less than one year)and all extreme-UV and soft X-ray photons of a compact companion areabsorbed by the Be star envelope. The detection of a white dwarf ispossible during the period when the Be star disc-like envelope islacking by the detection of white dwarf extreme-UV and soft X-rayemission. This method of registration appears to be particularlypromising for ``single'' early-type Be stars because in these systemsthe white dwarfs must have a very high surface temperature. However, theloss of the Be disc-like envelope does not often occur and it is arather rare event for many Be stars. The best possibility of white dwarfdetection is given by the study of helium spectral lines found inemission from several late-type Be stars. The ultraviolet continuumenergy of these Be stars is found to be not enough to produce theobserved helium emission. Besides, we also discuss the orbitalproperties of binary Be star systems with other evolved companions suchas helium stars and neutron stars and give a possible explanation forthe lack of Be/black hole binaries.
| 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
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Be star binary systems with non-compact secondaries
Not Available
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Near-simultaneous Spectroscopic and Broadband Polarimetric Observations ofBE Stars
Near simultaneous optical spectroscopic (on four nights) and broadbandlinear continuum (B, V, R,and I bands) polarimetric (on seven nights)observations of 29 Be stars were carried out during1993November-December. The program Be stars displayed wavelengthdependence of intrinsic polarizations with no frequency dependence ofpolarimetric position angles. Some of the Be stars displayed long-termpolarization variability. The Be and Be-shell stars could not bedistinguished from one another solely on the basis of their polarizationvalues. Full widths at half-maximum of the Hα profiles and theintrinsic linear continuum polarizations are closely correlated with theprojected rotational velocities of the program stars.Photospheric-absorption-corrected equivalent widths of Hα profiles[W(alpha)] and the radii of Hα-emitting or -absorbing envelopes(R_e or R_a) are nonlinearly correlated with the intrinsic continuumpolarizations of these stars. However, W(alpha) and R_e are linearlycorrelated. With large uncertainties, there is a trend of spectraldependence of polarization. Detailed discussion of these results ispresented in this paper.
| 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.
| Towards understanding rapid line-profile and light variations of early-type stars. 3. Some thoughts and reflections
The current situation in the research of rapid line-profile and lightvariations of early-type stars is critically reviewed. It is suggestedthat the ultimate understanding of the physical processes causing thesevariations can only come from an open-minded and complex approach to theproblem and from systematic observational effort. It is argued that theresults of the search for periodicities in the complicated variations ofthese objects depend critically on whether the method used isappropriate to the real physical situation. The danger of detection of afalse multiperiodicity is pointed out for two particular situations: (i)a single-periodic signal which undergoes slow periodic change, e.g., dueto the light time effect in a binary system, and (ii) a single-periodicsignal with a complicated phase curve (a model of not exactlyequidistant corotating spokes). It is argued that the observed rapidvariations need not be due to classical non-radial pulsations but mayarise from more complicated velocity fields in the stellar atmospheresand/or mantles. Two early-type stars, ěp and zeta Oph, arediscussed in detail. It is argued that both may be the cases where thevariations are caused by corotating structures slightly above thestellar photosphere. For ěn, the pattern of the variations canalso be affected by the motion of the star in a binary orbit. For zetaOph, a double-wave light curve with the corotation period of 0. (v {r) md}64 (suggested by the author earlier for the line-profile variations)was found from Hipparcos V photometry and its presence can also besuspected in other existing photometric data and in the recurrence timesof the narrow features seen in the UV spectra.
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - II.
Not Available
| The interstellar clouds of ADAMS and Blaauw revisited: an HI absorption study - I.
Not Available
| ORFEUS-SPAS II Observations of Algol-type Interacting Binaries
The first results from ORFEUS-SPAS II observations of five Algol-typebinary systems obtained during the shuttle mission STS-80 in 1996November/December are reported. Single spectra covering 900-1220 A of AUMon, Z Vul, U CrB, and TX UMa were acquired with the Berkeleyspectrograph. TT Hya was observed at three phases (0.19, 0.63, and 0.95)to study mass flow and to investigate asymmetry in the circumstellarmaterial in the system. O VI was not detected in any of the binaries,which allows us to place an upper limit on Tion in the high-temperatureplasma seen in Algol-type binaries. Circumstellar material, presumablyassociated with the accretion disk, was detected in Fe III (UV1) in AUMon. We estimate a particle density in the range 108-109 cm-3 for theregion of the disk sampled during the observations. Evidence for massinfall was found in the phase 0.95 spectrum of TT Hya. From theadditional (redshifted) absorption in N II (1085 A) and N I (1135 A), wefind evidence for superionization in this plasma and estimate a lowerlimit of 10-12 Msolar yr-1 for the current infall rate.
| Hubble Space Telescope Goddard High Resolution Spectrograph Observations of the Be + sdO Binary phi Persei
Mass transfer during the evolution of intermediate-mass stars in a closebinary system can result in a rejuvenated and spun-up secondary star(which may appear as a rapidly rotating Be star) orbiting an unseen,stripped-down, remnant companion. One of the best candidates for such asystem is the long-period (127 days) binary phi Per. Here we present newHubble Space Telescope Goddard High Resolution Spectrograph spectra ofphi Per in several UV regions that show clearly for the first time thespectral signature of the faint remnant companion. We derive adouble-lined solution for the radial velocity curve that yields massesof 9.3 +/- 0.3 Mȯ and 1.14 +/- 0.04 Mȯ for the Be star andcompanion, respectively. A Doppler tomographic reconstruction of thesecondary spectrum shows a rich spectrum dominated by sharp Fe IV and FeV lines, similar to those observed in hot sdO stars. Non-LTE spectrumsynthesis indicates that the subdwarf has temperature Teff = 53 +/- 3 kKand gravity log g = 4.2 +/- 0.1 and that the subdwarf-to-Be star fluxratio is 0.165 +/- 0.006 and 0.154 +/- 0.009 for the 1374 and 1647Angstroms regions, respectively. The spectrum of the Be primary appearsnormal for a very rapidly rotating early B-type star, but we argue thatthe star is overluminous for its mass (perhaps owing toaccretion-induced mixing). Additional sharp lines of Fe IV appear whenthe companion is in the foreground, and we show that these form in aheated region of the Be star's disk that faces the hot subdwarf.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
