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Pulsation-decline relationships in R Coronae Borealis stars
Decline onset times were measured in long-term visual light curves forfive R Coronae Borealis (RCB) variable stars. These included RYSgr andV854Cen, the two RCB stars previously reported to have a relationshipbetween dust formation events and pulsational variations. Analysis ofthe decline epochs showed that all decline onsets for a given star obeya linear ephemeris tied to the object's dominant radial pulsationperiod. Thus, in addition to confirming the pulsation-declinecorrelation for RYSgr and V854Cen, this same behaviour was demonstratedin UWCen, RCrB and SAps for the first time. This general result firmlyestablishes the connection between radial pulsation and mass loss in theRCB stars. The dominant pulsation period of ~40d for all of theseobjects therefore represents the characteristic time-scale on whichthese stars produce dust.
| RCoronae Borealis at the 2003 light minimum.
Not Available
| Discovery of Five New R Coronae Borealis Stars in the MACHO Galactic Bulge Database
We have identified five new R Coronae Borealis (RCB) stars in theGalactic bulge using the MACHO Project photometry database, raising thetotal number of known Galactic RCB stars to about 40. We have obtainedspectra to confirm the identifications. The fact that four out of thefive newly identified RCB stars are ``cool'' (Teff<6000 K)rather than ``warm'' (Teff>6000 K) suggests that thepreponderance of warm RCB stars among the existing sample is a selectionbias. These cool RCB stars are redder and fainter than their warmcounterparts and may have been missed in surveys done with blue plates.Based on the number of new RCB stars discovered in the MACHO bulgefields, there may be ~250 RCB stars in the reddened ``exclusion'' zonetoward the bulge.
| RCoronae Borealis stars at minimum light - UW Cen
Two high-resolution optical spectra of the R Coronae Borealis (R CrB)star UW Cen in decline are discussed. A spectrum from mid-1992 when thestar had faded by 3mag shows just a few differences with the spectrum atmaximum light. The ubiquitous sharp emission lines seen in R CrB at asimilar drop below maximum light are absent. In contrast, a spectrumfrom mid-2002 when the star was 5mag below maximum light shows an arrayof sharp emission lines and a collection of broad emission lines.Comparisons are made with spectra of R CrB obtained during the deep1995-1996 minimum. The many common features are discussed in terms of atorus-jet geometry.
| Self-Correlation Analysis of R Coronae Borealis Stars: A Pilot Project
R. Coronae Borealis (RCB) stars are peculiar yellow supergiant starswhich suddenly and unpredictably decrease in brightness by up to severalmagnitudes, then slowly return to normal. Most (perhaps all) RCB starsalso pulsate, and the pulsations may be related to the ejection of thedust clouds which produce the fadings. As a pilot project, we haveapplied self-correlation analysis to two datasets: long-term photometryof R CrB itself by J. D. Fernie, and long-term photometry of severalsouthern RCB stars by P. L. Cottrell, L. Skuljan, and their colleagues.Self-correlation is a simple form of time series analysis which displaysthe cycle-to-cycle behavior of a variable star, averaged over a dataset.It is especially useful for semi-regular variables. Generally, theseasonal pulsation time scales and amplitudes which we derive are inagreement with Fourier analysis of the same datasets. In the case of RCrB, we confirm that there is apparent mode-switching from season toseason.
| Possible RCB-star DY Per: the Current Decline Will be Deep and Needs Observations
The light curve of a decline phase of deep decline event of DY Per isfirstly obtained. Blueing of the starlight during the minimum isconfirmed, at least two months time interval for the present low lightlevel is predicted, and importance of observations of the star at thisphase is expressed.
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable 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/qcat?J/A+A/397/997
| Photometry of R Coronae Borealis Stars during the Recovery Phase of their Declines
The photometric observations (UBVRI) of nine cool R Coronae Borealis(RCB) stars have been collected at Mt John University Observatory, NewZealand, over a period of twelve years. The analysis of themagnitude-colour and colour-colour diagrams for the recovery phasedemonstrates that all declines exhibit a similar asymptotic approach totheir normal brightness. Declines return to maximum brightness along aline with essentially the same slope that does not depend on the star orthe depth of the decline. Assuming a uniform obscuration of thephotosphere by the dust cloud during the recovery phase, the extinctionproperties of the material were determined. The ratio of total toselective extinction (RV) for the RCB stars in our sample isin the range 2.5 to 4.6, indicating that the obscuring dust hasextinction properties similar to that of the interstellar dust.Observations have been compared with the theoretical extinction curvesfor different sorts of grains.
| Relation Between Light Weakening and Equivalent Widths of Circumstellar Na I D-Lines in Stars with R CRB-Type Variability
High-resolution spectra in the Na I D-line region for target stars withR Coronae Borealis type variability are analyzed. Two types of relationsbetween light weakening and equivalent widths of circumstellar lines arefound, one of them being considerably different from a similar relationfor the interstellar medium.
| Recent declines of RS Telescopii, UW Centauri, and V Coronae Australis
Not Available
| Carbon-rich giants in the HR diagram and their luminosity function
The luminosity function (LF) of nearly 300 Galactic carbon giants isderived. Adding BaII giants and various related objects, about 370objects are located in the RGB and AGB portions of the theoretical HRdiagram. As intermediate steps, (1) bolometric corrections arecalibrated against selected intrinsic color indices; (2) the diagram ofphotometric coefficients 1/2 vs. astrometric trueparallaxes varpi are interpreted in terms of ranges of photosphericradii for every photometric group; (3) coefficients CR andCL for bias-free evaluation of mean photospheric radii andmean luminosities are computed. The LF of Galactic carbon giantsexhibits two maxima corresponding to the HC-stars of the thick disk andto the CV-stars of the old thin disk respectively. It is discussed andcompared to those of carbon stars in the Magellanic Clouds and Galacticbulge. The HC-part is similar to the LF of the Galactic bulge,reinforcing the idea that the Bulge and the thick disk are part of thesame dynamical component. The CV-part looks similar to the LF of theLarge Magellanic Cloud (LMC), but the former is wider due to thesubstantial errors on HIPPARCOS parallaxes. The obtained meanluminosities increase with increasing radii and decreasing effectivetemperatures, along the HC-CV sequence of photometric groups, except forHC0, the earliest one. This trend illustrates the RGB- and AGB-tracks oflow- and intermediate-mass stars for a range in metallicities. From acomparison with theoretical tracks in the HR diagram, the initial massesMi range from about 0.8 to 4.0 Msun for carbongiants, with possibly larger masses for a few extreme objects. A largerange of metallicities is likely, from metal-poor HC-stars classified asCH stars on the grounds of their spectra (a spheroidal component), tonear-solar compositions of many CV-stars. Technetium-rich carbon giantsare brighter than the lower limit Mbol =~ -3.6+/- 0.4 andcentered at =~-4.7+0.6-0.9 at about =~(2935+/-200) K or CV3-CV4 in our classification. Much like the resultsof Van Eck et al. (\cite{vaneck98}) for S stars, this confirms theTDU-model of those TP-AGB stars. This is not the case of the HC-stars inthe thick disk, with >~ 3400 K and>~ -3.4. The faint HC1 and HC2-stars( =~ -1.1+0.7-1.0) arefound slightly brighter than the BaII giants ( =~-0.3+/-1.3) on average. Most RCB variables and HdC stars range fromMbol =~ -1 to -4 against -0.2 to -2.4 for those of the threepopulation II Cepheids in the sample. The former stars show the largestluminosities ( <~ -4 at the highest effectivetemperatures (6500-7500 K), close to the Mbol =~ -5 value forthe hot LMC RCB-stars (W Men and HV 5637). A full discussion of theresults is postponed to a companion paper on pulsation modes andpulsation masses of carbon-rich long period variables (LPVs; Paper IV,present issue). This research has made use of the Simbad databaseoperated at CDS, Strasbourg, France. Partially based on data from theESA HIPPARCOS astrometry satellite. Table 2 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/390/967
| Multicolor Variability of the Carbon Star DY Per
Photographic monitoring in the I(0.81), R(0.63), v, b and u passbandswith the Baldone Schmidt telescope in 1975--2002, the infrared J, H, K,L and M photometry carried out in 1995--2002 with the 0.7 m telescope ofthe Crimean Astrophysical Observatory and with the 1.25 m telescope ofthe Crimean Station of the Sternberg Astronomical Institute, as well asphotovisual magnitude estimates on the Sonneberg Observatory Patrolplate archive of 1963--1980 are used to study the photometric behaviorof DY Per, an unusual carbon star. The characteristics of lightvariations of DY Per are compared with those of long period variables,RCB stars and LMC DY Per-like stars.
| The MACHO Project LMC Variable Star Inventory. X. The R Coronae Borealis Stars
We report the discovery of eight new R Coronae Borealis (RCB) stars inthe Large Magellanic Cloud (LMC) using the MACHO project photometrydatabase. The discovery of these new stars increases the number of knownRCB stars in the LMC to thirteen. We have also discovered four starssimilar to the Galactic variable DY Per. These stars decline much moreslowly and are cooler than the RCB stars. The absolute luminosities ofthe Galactic RCB stars are unknown since there is no direct measurementof the distance to any Galactic RCB star. Hence, the importance of theLMC RCB stars. We find a much larger range of absolute magnitudes(MV=-2.5 to -5 mag) than inferred from the small pre-MACHOsample of LMC RCB stars. It is likely that there is atemperature-MV relationship with the cooler stars beingintrinsically fainter. Cool (~5000 K) RCB stars are much more commonthan previously thought based on the Galactic RCB star sample. Using thefairly complete sample of RCB stars discovered in the MACHO fields, wehave estimated the likely number of RCB stars in the Galaxy to be ~3200.The SMC MACHO fields were also searched for RCB stars, but none werefound.
| Reprocessing the Hipparcos data for evolved giant stars II. Absolute magnitudes for the R-type carbon stars
The Hipparcos Intermediate Astrometric Data for carbon stars have beenreprocessed using an algorithm which provides an objective criterion forrejecting anomalous data points and constrains the parallax to bepositive. New parallax solutions have been derived for 317 cool carbonstars, mostly of types R and N. In this paper we discuss the results forthe R stars. The most important result is that the early R stars (i.e.,R0 - R3) have absolute magnitudes and V-K colors locating them among redclump giants in the Hertzsprung-Russell diagram. The average absolutemagnitude MK for early R-type stars (with V - K < 4) hasbeen derived from a Monte-Carlo simulation implicitly incorporating allpossible biases. It appears that the simulated magnitude distributionfor a population with a true Gaussian distribution of mean MK= -2.0 and intrinsic standard deviation 1.0 mag provides a satisfactorymatch to the observed distribution. These values are consistent with theaverage absolute magnitude MK = -1.6 for clump red giants inthe solar neighborhood (Alves 2000). Further, early R-type stars arenon-variable, and their infrared photometric properties show that theyare not undergoing mass loss, properties similar to those of the redclump giants. Stars with subtypes R4 - R9 tend to be cooler and havesimilar luminosity to the N-type carbon stars, as confirmed by theirposition in the (J-H, H-K) color-color diagram. The sample of earlyR-type stars selected from the Hipparcos Catalogue appears to beapproximately complete to magnitude K0 ~ 7, translating intoa completeness distance of 600 pc if all R stars had MK= -2(400 pc if MK= -1). With about 30 early R-type stars in thatvolume, they comprise about 0.04% (0.14% for MK= -1) of thered clump stars in the solar neighborhood. Identification with the redclump locates these stars at the helium core burning stage of stellarevolution, while the N stars are on the asymptotic giant branch, wherehelium shell burning occurs. The present analysis suggests that for asmall fraction of the helium core burning stars (far lower than thefraction of helium shell-burning stars), carbon produced in the interioris mixed to the atmosphere in sufficient quantities to form a carbonstar. Based on observations from the Hipparcos astrometric satelliteoperated by the European Space Agency (ESA 1997).
| The effective temperatures of carbon-rich stars
We evaluate effective temperatures of 390 carbon-rich stars. Theinterstellar extinction on their lines of sights was determined andcircumstellar contributions derived. The intrinsic (dereddened) spectralenergy distributions (SEDs) are classified into 14 photometric groups(HCi, CVj and SCV with i=0,5 and j=1,7). The newscale of effective temperatures proposed here is calibrated on the 54angular diameters (measured on 52 stars) available at present from lunaroccultations and interferometry. The brightness distribution on stellardiscs and its influence on diameter evaluations are discussed. Theeffective temperatures directly deduced from those diameters correlatewith the classification into photometric groups, despite the large errorbars on diameters. The main parameter of our photometric classificationis thus effective temperature. Our photometric < k right >1/2 coefficients are shown to be angular diameters on arelative scale for a given photometric group, (more precisely for agiven effective temperature). The angular diameters are consistent withthe photometric data previously shown to be consistent with the trueparallaxes from HIPPARCOS observations (Knapik, et al. \cite{knapik98},Sect. 6). Provisional effective temperatures, as constrained by asuccessful comparison of dereddened SEDs from observations to modelatmosphere predictions, are in good agreement with the values directlycalculated from the observed angular diameters and with those deducedfrom five selected intrinsic color indices. These three approaches wereused to calibrate a reference angular diameter Phi 0 and theassociated coefficient CT_eff. The effective temperatureproposed for each star is the arithmetic mean of two estimates, one(``bolometric'') from a reference integrated flux F0, theother (``spectral'') from calibrated color indices which arerepresentative of SED shapes. Effective temperatures for about 390carbon stars are provided on this new homogeneous scale, together withvalues for some stars classified with oxygen-type SEDs with a total of438 SEDs (410 stars) studied. Apparent bolometric magnitudes are given.Objects with strong infrared excesses and optically thick circumstellardust shells are discussed separately. The new effective temperaturescale is shown to be compatible and (statistically) consistent with thesample of direct values from the observed angular diameters. Theeffective temperatures are confirmed to be higher than the mean colortemperatures (from 140 to 440 K). They are in good agreement with thepublished estimates from the infrared flux method forTeff>= 3170 K, while an increasing discrepancy is observedtoward lower temperatures. As an illustration of the efficiency of thephotometric classification and effective temperature scale, the C/Oratios and the Merrill-Sanford (M-S) band intensities are investigated.It is shown that the maximum value, mean value and dispersion of C/Oincrease along the photometric CV-sequence, i.e. with decreasingeffective temperature. The M-S bands of SiC2 are shown tohave a transition from ``none'' to ``strong'' at Teff =~(2800+/- 150right ) K. Simultaneously, with decreasing effectivetemperature, the mean C/O ratio increases from 1.04 to 1.36, thetransition in SiC2 strength occurring while 1.07<= C/O<= 1.18. This research has made use of the Simbad database operatedat CDS, Strasbourg, France. Table 10 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)}or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/178
| Behavior of the Line Profiles of the Sodium Doublet and the Calcium Triplet in the Spectrum of R CrB in the Shallow Minima of 1998-1999
The behavior of profiles of the Na I D line and of the infrared Ca IItriplet for the star R Coronae Borealis (R CrB) during shallow lightminima of 1998-1999 is traced using high-resolution spectra. During alight maximum, the sodium lines had an absorption profile with a shiftof —(2-4) km/sec. During a light minimum, a narrow emissionfeature, which has an almost constant absolute intensity and a shift of—(8-10) km/sec, and an intense circumstellar absorption feature,which has a variable profile and a variable relative shift correspondingto an increase to 220 km/sec in the velocity of mass ejection, appearedin the cores of absorption lines. For several days before the onset of alight minimum, all three calcium lines exhibited a narrow emissionfeature in the line core with a shift of —(1-5) km/sec. All thesubsequent changes in a line involved mainly the shape of the absorptionline profile. The narrow emission feature's absolute intensity andrelative position were maintained during all our observations. Thebehavior of the Na I D line profiles can be described qualitativelywithin the framework of the model of a spherical dust shell.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| General Catalog of Galactic Carbon Stars by C. B. Stephenson. Third Edition
The catalog is an updated and revised version of Stephenson's Catalogueof Galactic Cool Carbon Stars (2nd edition). It includes 6891 entries.For each star the following information is given: equatorial (2000.0)and galactic coordinates, blue, visual and infrared magnitudes, spectralclassification, references, designations in the most significantcatalogs and coordinate precision classes. The main catalog issupplemented by remarks containing information for which there was noplace in entries of the main part, as well as some occasional notesabout the peculiarities of specific stars.
| Some Characteristics of the Circumstellar Shells of Stars with Variability of the R Coronae Borealis Type
The transformation of the line and molecular spectra of R CrB fromabsorption to emission at the 1985 minimum is traced from spectroscopicobservations, and it is concluded for the first time, from a comparisonwith light curves and color indices, that the rapid variation of thecolor index U - B by -0m.6 during fading is due exclusively to thistransformation. The transformation of the spectrum can result in anincrease in the star's brightness in the UBV photometric bands by about1m.4, 0m.75, and up to 0m.75, respectively. This removes one of the mainobjections to using the concept of a homogeneous spherical shell tointerpret the R Coronae Borealis phenomenon. High-resolutionspectroscopic observations of SV Sge, a star with variability of the RCoronae Borealis type, showed the presence of an intense circumstellarcomponent in Na I D lines with a violet shift corresponding to 240km/sec, which is unrelated to visible brightness minima. It is suggestedthat a stream of matter with such a velocity through the star's vicinityis the cause of the excitation not only of the broad emission featuresobserved during brightness minima upon fading of the photosphericemission but also of the narrow ones. Assuming that a brightness minimumis associated with the temporary formation of another sphericalscreening shell, some characteristics of the permanent shell aredetermined. Its optical depth and geometrical thickness are 0.2-0.7 andat least 0.4 of its radius, respectively.
| Post-AGB Variables and Stellar Mass-Loss
Not Available
| The 1995-96 decline of R Coronae Borealis: high-resolution optical spectroscopy
A set of high-resolution optical spectra of R CrB acquired before,during and after its 1995-96 decline is discussed. All of the componentsreported from earlier declines are seen. This novel data set providesnew information on these components including several aspects notpreviously seen in declines of R CrB and other R Coronae Borealis stars.In the latter category is the discovery that the onset of the decline ismarked by distortions of absorption lines of high-excitation lines, andquickly followed by emission in these and in low-excitation lines. This`photospheric trigger' implies that dust causing the decline is formedclose to the star. These emission lines fade quickly. After 1995November 2, low-excitation narrow (FWHM ~12kms-1) emissionlines remain. These appear to be a permanent feature, slightlyblueshifted from the systemic velocity, and unaffected by the declineexcept for a late and slight decrease of flux at minimum light. Thelocation of the warm dense gas providing these lines is uncertain.Absorption lines unaffected by overlying sharp emission are greatlybroadened, weakened and redshifted at the faintest magnitudes whenscattered light from the star is a greater contributor than direct lighttransmitted through the fresh soot cloud. A few broad lines (FWHM~=300kms-1) are seen at and near minimum light withapproximately constant flux: prominent among these are the Hei tripletseries, Nai D and [Nii] lines. These lines are blueshifted by about30kms-1 relative to the systemic velocity, with no change invelocity over the several months for which the lines were seen. It issuggested that these lines, especially the Hei lines, arise from anaccretion disc around an unseen compact companion which may be alow-mass white dwarf. If so, R CrB is similar to the unusualpost-asymptotic giant branch star 89 Her.
| The spectrum of the cool R Coronae Borealis variable Z Ursae Minoris at minimum
Not Available
| Dust extinction and intrinsic SEDs of carbon-rich stars. II. The hot carbon stars
The present work is an extension of a recent study by Knapik &Bergeat (\cite{knapik}, henceforth called Paper I) of the spectralenergy distributions (SEDs) of about 300 cool carbon-rich variables andof the interstellar extinction observed on their line of sights. Themethods were originally developed for Semi-Regular (SR) and Irregular(L)-variables. Shortly, this is a kind of a pair method making usesimultaneously of the whole SED from UV to IR. Our approach is appliedhere to the galactic carbon-rich giants with bluer SEDs, namely the hotcarbon (HC) stars, including many ``constant'' stars and a minority ofvariables: AC Her a RV Tau star, the R Coronae Borealis (RCB) stars andothers. Some HdC (i.e. carbon-rich hydrogen deficient stars) and Ba IIstars are also considered. The total number of studied HC stars amountsto about 140. With few exceptions, the colour excesses for interstellarextinction are found in good agreement with the field values from mapspublished in the literature, taking into account the approximatedistances to our stars from HIPPARCOS data (\cite{esa}, henceforthcalled ESA) or binarity. We propose a classification scheme with sixphotometric groups (or boxes: HC0 to HC5) from the bluest to the reddestSEDs. Oxygen-rich SEDs earlier than HC0, are attributed to the hotteststars (AC Her, most RCB-variables and a few others). Previous findingsare confirmed of a junction between oxygen-rich and carbon-rich SEDs atspectral type G. The latest (HC5) group is immediately close to theearliest one in Paper I, namely CV1. The sequence of groups then goesregularly from HC0 to CV6. Substantial infrared excesses with respect toour solutions are found in HD 100764 a HC1 carbon star, AC Her a G0g RVTau star, and the RCB stars classified in either HC or oxygen-groups.The colour excesses at maximum light can usually be attributed tointerstellar reddening, with neutral circumstellar (CS) reddening (largegrains) or no CS extinction at all on the line of sight (non sphericalgeometry) as possible explanations. The latter model (disc or patchydistribution through successive puffs) is favoured. Two RCB variablesfor which we exploit SEDs on a rising branch (V CrA) or minimum light(RS Tel), show CS laws, respectively a selective extinction compatiblewith small grains and an extinction partly neutral indicative of largegrains on the line of sight. This research has made use of the Simbaddatabase operated at CDS, Strasbourg, France.}\fnmsep\thanks{Partiallybased on data from the ESA HIPPARCOS astrometrysatellite}\fnmsep\thanks{Tables~3 and 4 are only available in electronicform at the CDS via anonymous ftp 130.79.128.5
| Spectroscopic and photometric observations of the R Coronae Borealis stars S Apodis and RZ Normae throughout their recent declines
Spectroscopic and photometric observations of two R Coronae Borealis(RCB) stars, S Apodis and RZ Normae, have been obtained during thedecline phase of each of these stars. Although the declines have verydifferent global characteristics -- the depth of the decline inbrightness is respectively 6 and 2 mag in S Aps and RZ Nor -- there aresome strong similarities in the spectroscopic and photometriccharacteristics. The photometry shows strong reddening during theinitial phase of these declines. The spectroscopy indicates that similarcharacteristics are observed in the Na I D region, with very few otherspectroscopic changes. In both declines Na I D lines show strongemission components and high-velocity (blueshifted by up to 300 km s^-1)absorption lines. The centre of the absorption features appears to beshifted gradually during the declines, indicating the acceleration ofthe dust cloud.
| HIPPARCOS observations of hydrogen-deficient carbon stars
Parallax measurements for 21 hydrogen-deficient carbon stars have beenmade by the Hipparcos satellite. These stars include most of thebrighter R Coronae Borealis (RCB) variables, other coolhydrogen-deficient carbon (HdC) stars, and several higher-temperatureextreme helium (eHe) stars. Most of these stars have either negative orstatistically insignificant parallaxes, indicating that they lie beyondthe detection capability of Hipparcos. Although the distances to thegalactic hydrogen-deficient carbon stars remain unknown, at least theHipparcos observations do confirm that these objects must have highluminosity like the LMC RCB stars, for which M_bol = -4 to -5. Basedupon Hipparcos proper motions, we derive UVW velocities for the RCB andHdC stars, assuming M_bol = -3 and -5. The UW-velocity dispersion of theRCB/HdC stars is similar to that already reported for the eHe stars,further supporting that these groups of stars have predominantly bulgedistributions. However, UW Cen may be a second example of a halo RCBstar currently seen transitting the galactic plane.
| On anticorrelation in changes of visual and infrared brightness of stars with the R Coronae Borealis type variability.
Not Available
| The Evolution of the Final Helium Shell Flash Star V605 Aquilae From 1917 to 1997
Abstract image available at:http://adsabs.harvard.edu/abs/1997AJ....114.2679C
| Parallaxes and Proper Motions of Prototypes of Astrophysically Interesting Classes of Stars. I. R Coronae Borealis Variables
Hipparcos data were obtained under the 1982 announcement of opportunityfor the seven brightest R CrB stars then known. None of the parallaxmeasurements is different from zero in a statistically significant way,though most of the proper motions are. The body of the data neverthelesssuggest that the stars belong to two rather different populations ineither luminosity, kinematics, or both. The best-known stars (R. CrBitself, RY Sgr, and perhaps others) probably are the very luminous, Msubscript v = -4 to -5, objects they are generally accused of being, butothers may belong to a fainter class for which there is some independentevidence among stars in the Large Magellanic Cloud. Alternatively, or inaddition, the apparently fainter stars may belong to a higher-velocitypopulation that we have had rather bad luck in sampling. Of two rashassumptions, the one that all seven stars are at the same distance of1200 pc leads to a velocity ellipsoid U superscript 2 superscript 1/2, Vsuperscript 2 superscript 1/2, W superscript 2> superscript 1/2 = 41,30, 35 km sec superscript -1, which is "not inconsistent" with valuestypical of (other) old disk populations, like carbon stars, long periodvariables, and planetary nebulae. The seemingly less rash assumptionthat all stars have M subscript v = -4.5 leads to U superscript 2superscript 1/2, V superscript 2 superscript 1/2, W superscript 2superscript 1/2, = 52, 60, and 104 km sec supercript -1, resembles noknown stellar population, at least not in our galaxy. (SECTION: Stars)
| The Spectrum Near Maximum Light of the Unusual R Coronae Borealis Variable DY Persei
DY Per was confirmed photometrically as an R CrB variable by Alksnis in1994. Spectra near maximum light show the high-speed ejection of matter(sodium at -174 km/sec in DY Per) characteristic of many of thesevariable stars. Moderate hydrogen deficiency may also be present. DY Peris remarkable in having a temperature many hundreds of degrees lowerthan most of the R CrB variables. It is unusual also in not showingclear spectroscopic evidence of high luminosit. (SECTION: Stars)
| The Spectrum of the Cool R Coronae Borealis Variable S Apodis in a Deep Decline
A high resolution spectrum (5575 - 8875\AA) of the cool R CoronaeBorealis variable S Apodis in its 1993 deep decline is discussed. Narrowor chromospheric emission lines of Na I, K I, Ca II, and Ba II and broademission lines of He I 7065\AA and Na I D are seen, as expected frompublished reports of warmer RCBs in decline. The surprise of the S Apsspectrum is the considerable blue shift of the broad emissions componentto the Na D lines. The blue shift may result from lines formed in abipolar flow which is obscured asymmetrically by soot clouds along theline of sight. (SECTION: Stars)
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