A Minimum in the Light Curve of the Classical Symbiotic Star YY Her in 2001
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The secondary minimum in YY Herculis: Evidence for a tidally distorted giant
We present and analyze quiescent UBVRI light curves of the classicalsymbiotic binary YY Her. We show that the secondary minimum, which isclearly visible only in the quiescent VRI light curves, is due toellipsoidal variability of the red giant component. Our simple lightcurve analysis, by fitting of the Fourier cosine series, resulted in aself-consistent phenomenological model of YY Her, in which the periodicchanges can be described by a combination of the ellipsoidal changes anda sinusoidal changes of the nebular continuum and line emission.
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Photometric and Spectrophotometric Observations of the Classical Symbiotic Star YY Her during Its Return to Quiescence
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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.
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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
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Photometric and Spectrophotometric Observations of the Evolution of a Strong Outburst of the Classical Symbiotic Star YY Herculis
We present spectrophotometric (3400 7500 Å) observations of theevolution of a strong outburst of the classical symbiotic star YY Her in1993 and photoelectric UBV observations of the star’s eclipse in1997. The duration of the phase of lowest brightness, when the Ubrightness had decreased by 1.3m, was 0.17 P orb (P orb is theorbital period). If this phase is due to the total eclipse of 70%of the radiation of the circumstellar envelope, this duration impliesthat the cool component of YY Her fills its Roche lobe, the bulk of theenvelope’s volume emission measure is concentrated around the hotcomponent in a region with rather sharp boundaries r&MediaObjects/Figure1.jpg;
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UV spectrophotometry and UBVJHKL photometry of the symbiotic nova V443 Her.
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Rotational Velocity Determinations for 164 Be and B Stars
Rotational velocities, v sin i, have been obtained for 96 Be and 68normal B stars by measurements of the FWHM of the He I lambda-4471 line(for spectral types B0-B4.5) and Mg II lambda-4481 (for types B5-B9.5).The consistency of various published sources is examined. (SECTION:Stars)
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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UBV photometric properties of the symbiotic star V443 Herculis.
We present extensive UBV photoelectric photometry of the symbiotic starV443 Her covering the period 1979-1993. It is found that the meanbrightness of V443 Her has remained constant at a level of 2-3% in anyof the UBV bands over the last 40 years . This suggests that both theradiation output of the white dwarf and the mass loss of the M5 IIIcompanion have remained constant over the last 40 years. No flickeringassociated with accretion processes has been observed. Two shortduration, {DELTA}U~0.5mag phases and an irregular {DELTA}V~0.1magintrinsic variability of the cool giant have been discovered. V443 Herpresents a marked modulation of the brightness along the orbital cyclewhich is ascribed to the heating effect frequently observed in symbioticstars. The orbital period is found to be 594(+/-3) days and theamplitude of the heating effect {DELTA}U=0.9, {DELTA}B=0.4 and{DELTA}V=0.1mag. No evidence for an eclipse scenario of the WD or acompact nebular region surrounding the latter is found in the opticalphotometry. The V band lightcurve along the orbital period indicatesthat the M5 III star is well inside its Roche Lobe and thus V443 Her isa detached system. The color evolution of V443 Her along the orbitalperiod is very similar to that exhibited by the yellow symbiotic starHe2-467. Given the large differences between the wind outflow regimes ofthe cool giants of these two systems, this similarity suggests that thebasic characteristics of the heating effect in symbiotic stars are notstrongly affected by the details of the cool giant mass loss. A lowerlimit to the amount of energy deposited by the WD radiation field ontothe LTG facing side for impacting photons with energies >=0.01keV isobtained in a direct, assumption-free way.
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The behavior of the O I line 7772 in Be and related stars
We describe the spectra of more than sixty stars in the 7570-7980region. We find that O I 7772 is always in emission in Be stars: in theearliest types it is seen in clear emission whereas in the later typesit fills in the observed absorption line. We find a good correlation ofthe line intensity of O I 8446 with O I 7772, the former being aboutfour times stronger than the latter. We confirm the correlation with FeII 7712. We also derive the outer radii of the line emission formingregions and find that O I 7772 is formed very close to the starssurface, whereas Fe II is formed farther away. We also provide criteriato distinguish, at this wavelength range, the classical Be, Herbig Ae-Beand B(e) stars.
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Spectral reclassification of some Be stars using Delta-Q method
The way in which the new defined value Delta-Q can play a role in thespectral reclassification of Be stars is shown by means of aninvestigation of 56 Be stars. A general survey carried out in order toobtain spectral subclasses or U, B, V values for these stars ispresented. The suggested Delta-Q method was found to be very helpful inchoosing the correct spectral subclass from among many subclassesassigned for the same star, and hence, the reclassification for thisstar.
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Ultraviolet observations of Be stars. II - Superionization in Be stars of different spectral types
The results of an investigation of the dependence of thestrength/presence of lines from superionized species (N V, C IV, Si IV)on spectral type and v sin i in the ultraviolet spectra of Be stars arepresented. No evidence is found for N V in stars later than B2; thisapparent absence may, however, simply reflect problems with the IUEreduction procedure. The C IV and Si IV lines pervade the ultravioletspectra of all B subtypes, with a trend toward increasing strength withincreasing effective temperature. A similar trend in the 'edge velocity'of the feature with spectral type is found. The data also suggest apossible trend toward the presence of stronger C IV and a higher edgevelocity in stars with larger values of v sin i. The observed temporalvariability in N V, C IV, and Si IV in some Be stars is discussed.
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Rotational velocity of Be stars correlated with emission characteristics
A sample of shell and nonshell B0e-B5e stars with weak and strongemission, and shell and nonshell B6e-B9e stars with weak emission, arestudied to seek a correlation between the rotational velocity of Bestars and the emissive strength. These results and the distributions ofV sin i indicate that the hottest Be stars, B0e-B5e, with rotationalvelocities of about 345 km/s can develop the characteristics of strongemission. For stars which are slightly less hot, or stars with slightlysmaller rotational velocities, only characteristics of weak emission canbe developed, and the shell characteristics only develop when the staris viewed at a greater-than-33-deg inclination to the pole. It is alsonoted that stars with large rotational velocities, the strong-emissionB0e-B5e and weak-emission B6e-B9e stars, can show metallic shellcharacteristics when seen near the equatorial plane.
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Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
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Far ultraviolet colors of B and Be stars
A far-UV color index, G, which is free of interstellar reddening effectsis applied to TD-1 satellite observations of B and Be stars listed inthe catalogs of Jamar et al. (1976) and Macau-Hercot et al. (1978). Theexpressions defining G(in terms of the wavelengths 146, 235, and 274 nm)and the S70 index of spectral type are set forth. Tables of mean andindividual-star G and S70 indices and plots of G versus S70, Delta-Gversus spectral type, Delta-G versus H-alpha and H-beta intensity, and Gversus V(sin i) are presented and discussed. The Be stars are classifiedas strong if they show strong Balmer emission, some Paschen and Fe IIemission, and IR excess; otherwise they are 'weak'. Weak Be stars arefound to have G similar to that of B stars, while G in strong Be starsis either much more negative or much less negative than in the B stars.No correlation is found between G and V(sin i) for either B or Be stars.
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The interstellar 2200 A band - A catalogue of equivalent widths
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The influence of the envelope in the variations of transitory type Be stars
The contribution of the stellar envelope to variations oftransitory-type Be stars, which are alternately of types B and Be, isinvestigated. The Rojas-Herman classification is applied to thequantification of long-term stellar variation for a sample of Be starsbrighter than magnitude 7, and compared with the spectral properties ofthese stars. A relation is derived between the equivalent widths of theH-alpha and H-beta lines and the stellar U-B index. The U-B index isthen calibrated as a function of the Balmer discontinuity in order toseparate the contributions of the star and its envelope to the emission.The separate U-B indices derived for the star, which are characterizedby long-term variations, and the envelope, which is sensitive toshort-term variations, are observed to be additive, implying that theobserved flux is a convolution of the fluxes emitted by the star and itsenvelope.
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A classification of Be stars
Based upon a sample of 140 stars observed over 20 years for which about5,000 spectrograms are available, a classification scheme of Be stars ispresented. This is the first attempt to subdivide the Be star group intophysically significant subgroups, from which typical objects can beselected for further study. The four groups proposed are based upon adiscussion of spectrum characteristics, multicolor photometry,polarization, rotational velocities, UV spectral types and timevariability. Starting with the group membership of a Be star,predictions can be made of the future behavior of it.
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Photoelektrische Photometrie von Shell-Sternen
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974A&AS...15..311H&db_key=AST
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Etude photometrique a bande etroite de l'emission dans les etoiles Be
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Be stars and galactic rotation.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..338C&db_key=AST
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Spectral Classifications of 239 Early-Type Stars
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Observations spectroscopiques d'etoiles Be.
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Spectral Classifications of some Emission B Stars
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Enveloppes d'étoiles Be : variations spectrales et caractéristiques physiques
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Troisième catalogue de l'Observatoire de Besançon comprenant 764 étoiles réduites à 1950, 0 sans mouvement propre et 326 étoiles FK3 pour l'époque moyenne d'observation
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Die galaktischen Emissions-B-Sterne : (Spectralklassifikation, Photometrie, Entwicklung und Verteilung in der Milchstraszenebene)
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Photoelectric distances of 461 Northern OB-stars and galactic structure from Hγ- luminosities Author: Beer, A.
Abstract image available at:http://adsabs.harvard.edu/abs/1964MNRAS.128..261B
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Spectroscopic studies of 60 Be stars over a period of 24 years
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INHABITED SKY
