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A photometric survey of stars with circumstellar material
We present the result of a follow-up Strömgren photometric surveyof sixteen southern bright stars with circumstellar material, in orderto detect possible weak photometric variations. We found new variationsof the β~ Pictoris brightness from 1999 to 2002 with a weaklong-term variation of ~-0.8× 10-3 mag per year, overabout 3 years. These variations look similar to those seen from 1975 to1981 and from 1995 to 1998 (Nitschelm et al. 2000, A&AS, 145, 275).They can be due to differential occultation by dust inhomogeneitiestransiting the star through the years. We detected new periodicvariations for HD 256 (HR 10) with periods ranging from 0.35 day to 6.69days during several months. These variations may also be interpreted interms of variable obscuration due to structures in the circumstellardisk suspected to be surrounding this star.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| EXPORT: Optical photometry and polarimetry of Vega-type and pre-main sequence stars
This paper presents optical UBVRI broadband photo-polarimetry of theEXPORT sample obtained at the 2.5 m Nordic Optical Telescope. Thedatabase consists of multi-epoch photo-polarimetry of 68pre-main-sequence and main-sequence stars. An investigation of thepolarization variability indicates that 22 objects are variable at the3sigma level in our data. All these objects are pre-main sequence stars,consisting of both T Tauri and Herbig Ae/Be objects while the mainsequence, Vega type and post-T Tauri type objects are not variable. Thepolarization properties of the variable sources are mostly indicative ofthe UXOR-type behaviour; the objects show highest polarization when thebrightness is at minimum. We add seven new objects to the class of UXORvariables (BH Cep, VX Cas, DK Tau, HK Ori, LkHα 234, KK Oph and RYOri). The main reason for their discovery is the fact that our data-setis the largest in its kind, indicating that many more young UXOR-typepre-main sequence stars remain to be discovered. The set of Vega-likesystems has been investigated for the presence of intrinsicpolarization. As they lack variability, this was done using indirectmethods, and apart from the known case of BD+31o643, thefollowing stars were found to be strong candidates to exhibitpolarization due to the presence of circumstellar disks: 51 Oph,BD+31o643C, HD 58647 and HD 233517. Table A1 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/379/564
| EXPORT: Spectral classification and projected rotational velocities of Vega-type and pre-main sequence stars
In this paper we present the first comprehensive results extracted fromthe spectroscopic campaigns carried out by the EXPORT (EXoPlanetaryObservational Research Team) consortium. During 1998-1999, EXPORTcarried out an intensive observational effort in the framework of theorigin and evolution of protoplanetary systems in order to obtain clueson the evolutionary path from the early stages of the pre-main sequenceto stars with planets already formed. The spectral types of 70 stars,and the projected rotational velocities, v sin i, of 45 stars, mainlyVega-type and pre-main sequence, have been determined from intermediate-and high-resolution spectroscopy, respectively. The first part of thework is of fundamental importance in order to accurately place the starsin the HR diagram and determine the evolutionary sequences; the secondpart provides information on the kinematics and dynamics of the starsand the evolution of their angular momentum. The advantage of using thesame observational configuration and methodology for all the stars isthe homogeneity of the set of parameters obtained. Results from previouswork are revised, leading in some cases to completely new determinationsof spectral types and projected rotational velocities; for some stars noprevious studies were available. Tables 1 and 2 are only, and Table 6also, available 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/378/116 Based onobservations made with the Isaac Newton and the William Herscheltelescopes operated on the island of La Palma by the Isaac Newton Groupin the Spanish Observatorio del Roque de los Muchachos of the Institutode Astrofísica de Canarias.
| 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
| Falling Evaporating Bodies around Herbig stars. A theoretical study
Transient spectral absorption events monitored now for years towards thestar beta Pictoris have been interpreted as resultingfrom the transit across the line of sight of evaporating star-grazingkilometer-sized bodies (Falling Evaporating Bodies, or FEBs). SeveralHerbig Ae/Be stars of various ages have been observed to exhibit somehowsimilar absorption events that have been attributed to similar FEBevents. We investigate here this question from a modeling point of view.Adapting the FEB simulation code we had developed earlier specificallyfor beta Pic, to the case of typical Herbig Ae/Bestars, we try to derive in which conditions FEB-like objects maygenerate detectable transient absorption events. We compare theseconditions with those found in the case of beta Pic.A major difference with beta Pic is that Herbig Ae/Bestars have strong stellar winds (10-9-10-7 M_sunyr-1). Those winds appear to have a drastic interaction withthe gaseous material escaped from the FEBs. With the presence of suchstellar winds, the spectral signatures of FEBs are not detectable,unless their mass loss rate is huge. This translates into very largebodies (~100 km size), instead of ~15 km for beta PicFEBs. This appears unrealistic in terms of amount of planetesimal massneeded in the disks surrounding these stars. We discuss then thevalidity of the FEB hypothesis for specific example stars. It turns outthat for the younger (a few 106 yr old) Herbig Ae/Be starslike AB Aur, with well identified winds gtrsim10-8 M_sun yr-1, the variable features sometimesobserved are not likely to be due to FEBs, unless produced in wind freecavities. For older (gtrsim 107 yr old) stars Herbig Ae/Belike HD 100546, the FEB scenario could still explainthe spectral events observed, but either the wind must to be weaker than~m10-10 M_sun yr-1 (which cannot be excluded sofar), or the FEBs approach the star in wind free cavities.
| EXPORT: Near-IR observations of Vega-type and pre-main sequence stars
We present near-IR JHK photometric data of a sample of 58 main-sequence,mainly Vega-type, and pre-main sequence stars. The data were takenduring four observing runs in the period May 1998 to January 1999 andform part of a coordinated effort with simultaneous optical spectroscopyand photo-polarimetry. The near-IR colors of the MS stars correspond inmost cases to photospheric colors, although noticeable reddening ispresent towards a few objects, and these stars show no brightnessvariability within the observational errors. On the other hand, the PMSstars show near-IR excesses and variability consistent with previousdata. Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/110
| A three-year Strömgren photometric survey of suspected beta Pictoris-like stars
We carried out a Strömgren photometric survey of thirteen southernbright stars, including beta Pictoris itself, during three years,d'Astrophysique de Paris, in order to detect possible weak photometricvariations. beta Pictoris presents a small long-term variation with achange of brightness by -2.1 10-3 mag per year, over abouttwo years from beginning of 1996, a situation relatively similar to theone about 18 years ago. Among the other stars, only HD 38392 presentsweak photometric variations with a period of 21.4 days, probably relatedto the star rotation period. The negative result concerning photometricvariations of all other stars suggests that those stars are actuallyreally stable and strengthens the reality of the variations discoveredin the case of beta Pictoris and HD 38392. Based on observationsobtained at the Danish 50 cm telescope (SAT) at ESO, La Silla, Chile.
| A-shell stars in the Geneva system
Among the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| β Pictoris, a young planetary system? A review
β Pictoris is a bright southern hemisphere star observed in 1983 bythe IRAS satellite as presenting a large and unexpected IR excess. Thisexcess was called the Vega-like phenomenon and quickly identified as dueto circumstellar dust. Subsequently in 1984, using stellar coronography,dust was also directly seen as an edge-on disk extended to severalhundreds of AUs. Since then, β Pictoris has been continuouslyobserved. We present here a review of our present understanding of theβ Pictoris circumstellar environment which still appears unique inthe solar neighborhood. The circumstellar dust disk is predominantlymade of relatively large particles (one micron or more) extendingoutward to more than 1000 AU and presenting a clearer (dust free)central region away to about 35 AU from the star. The gas is detectedthrough stable and variable spectroscopic signatures revealing apermanent gas disk with sporadic inflows and also a few outflows. Theseare partially interpreted in terms of evaporation of kilometer-sizedbodies very close to the star. Evaporation or destruction throughcollisions of kilometer-sized bodies seems to be needed also to explainboth the dust as well as the very presence of the CO molecule detectedin the circumstellar gas. Several indirect arguments along with theobservation of a very peculiar photometric variation of the starsuggests that even giant planets may have already formed in the βPictoris system. β Pictoris is thus possibly the missing linkbetween young stellar objects presenting proto-planetary circumstellardisks and much more evolved systems in which planets (at least giantones) are already formed. β Pictoris is probably a unique placewhere we may now observe planetary formation as well as other phenomenathat have taken place in the first 108 years of a youngstellar system.
| Infrared Photometry of beta Pictoris Type Systems
We obtained small-aperture (4"-5" diameter) infrared (2-20 μm)photometry of 10 early-type main-sequence stars with infrared excessesfrom circumstellar dust. These systems possibly exemplify the betaPictoris phenomenon. We observed them with either the NASA MarshallSpace Flight Center bolometer array camera (``Big Mac'') or the InfraredTelescope Facility 2-30 μm single-channel bolometer system.Measurements were obtained in the KLMNQ filters and the narrowband(Deltalambda ~ 1 μm) 10 μm ``silicate'' filters. We fitted Kuruczphotospheric models to the photometric data to determine excess-emissionspectra. We report the nondetection of small-aperture circumstellar dustemission from HR 10 and 21 LMi. We confirmed previous nondetections ofnear-infrared or 10 μm excess emission from 68 Oph, alpha PsA, and HR4796A. We did not detect prominent silicate emission from any of thesources. The spectra of gamma Oph, sigma Her, HR 2174A, beta UMa, andzeta Lep show weak 10 μm excesses. We fitted simple models to thesedata, together with IRAS excess fluxes, to determine plausibledistributions of temperature and density of circumstellar dust grains.Significant quantities of these grains around HR 2174A, zeta Lep, andbeta UMa are at temperatures similar to terrestrial material in thesolar system.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Beta Pic-like circumstellar disk gas surrounding HR 10 and HD 85905
We present high spectral resolution observations of the absorption linesof Ca II and Na I associated with the circumstellar gas disk surroundingthe two A-type shell stars HR 10 and HD85905. Data taken over two four-night periods in January andNovember 1997 reveal substantial changes in the circumstellar absorptionline profiles between successive observations of both stars. Suchvariable features have both blue and red-shifted velocities up to 50 kms(-1) away from the central absorbing component, and are similar tothose routinely observed in the beta Pictoris system. The sporadicpresence of the circumstellar absorption components observed towardsboth HR 10 and HD 85905 may be explained by the infalling evaporatingcomet model developed for the beta Pictoris system by Beust {et al./}(\cite{beust90}). We note that variable circumstellar absorptionfeatures have also been detected in rapidly rotating A-type stars, suchthat they may be suffering irregular mass-loss that could give rise tosimilar circumstellar disks and shells.
| Les disques autour des etoiles de la sequence principale.
Not Available
| HST-GHRS observations of candidate β Pictoris-like circumstellar gaseous disks.
We present HST-GHRS observations of four stars in search of βPictoris-like circumstellar gaseous disks. We detected gas around HR 10,HR 2174 and 51 Oph at large distances from the stars; this gas iscircumstellar since the absorption lines from very excited levelsrequire densities incompatible with those found in the diffuseinterstellar medium. The shape of the lines and the Mgii doublet ratiogive evidence that clumpy gas is continuously falling onto these stars.Possible interpretations are discussed.
| The beta Pictoris Phenomenon in A-Shell Stars: Detection of Accreting Gas
We present the results of an expanded survey of A-shell stars using IUEhigh-dispersion spectra and find accreting, circumstellar gas in theline of sight to nine stars, in addition to the previously identifiedbeta Pic, HR 10, and 131 Tau, which can be followed to between +70 and100 km s-1 relative to the star. Two of the program stars, HD 88195 andHD 148283, show variable high-velocity gas. Given the small number ofIUE spectra for our program stars, detection of high-velocity, accretinggas in 2/3 of the A-shell stars sampled indicates that accretion is anintrinsic part of the A-shell phenomenon and that beta Pic is not uniqueamong main-sequence A stars in exhibiting such activity. Our programstars, as a group, have smaller column densities of high-velocity gasand smaller near-IR excesses compared with beta Pic. These features areconsistent with greater central clearing of a remnant debris disk,compared with beta Pic, and suggest that the majority of field A-shellstars are older than beta Pic.
| Polarisation in A-type stars with circumstellar shells.
We present the results of optical linear polarisation measurements ofabout 30 A-type stars that are known to be either Ae/A shell stars orhave shown anomalous emission in the infrared. Compared with the generalpopulation of A-type stars, stars of this group are found to havepolarisation that is also anomalous and is suggested to be circumstellarin origin.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| UvbyHbeta_ photometry of main sequence A type stars.
We present Stroemgren uvby and Hbeta_ photometry for a set of575 northern main sequence A type stars, most of them belonging to theHipparcos Input Catalogue, with V from 5mag to 10mag and with knownradial velocities. These observations enlarge the catalogue we began tocompile some years ago to more than 1500 stars. Our catalogue includeskinematic and astrophysical data for each star. Our future goal is toperform an accurate analysis of the kinematical behaviour of these starsin the solar neighbourhood.
| HST WFPC2 IDT Observations of Circumstellar Material
The HST WFPC2 camera has been used to search for circumstellar materialaround T Tauri and main sequence stars. Young stellar objects(protostars and T Tauri stars) are often surrounded by optically thickdisks. HH30 is a protostar which has a slightly inclined disk ( 7degrees) appearing as two reflection nebulae separated by a dark lane.Collimated, bipolar jets extend from very close to the obscuredprotostar. Proper motions of knots in the jets have been determined fromimages taken about one year apart. GM Aurigae (K. Stapelfeldt et al,this conference) is surrounded by a moderately inclined ( 20 degrees),flattened disk. DG Tau B is embedded in a thick envelope with twin jetsemerging at about 25 degrees to the plane of the sky. HL Tau iscompletely obscured by nebulosity, with no visible disk. Light from thestar is visible as reflection from a compact, C-shaped nebula. The twoclassical T Tauri stars observed, DG Tau and T Tau, are surrounded bycavities illuminated by starlight. In each case, the star appears offsetfrom the cavity apex, indicating that the star has begun to clear thecircumstellar environment. DG Tau also has a wide jet. No material wasdetected around the naked T Tauri stars SAO 76411A and HDE 283572.Images of Beta Pic show details in the disk to within 1.5 arcsec of thestar (C. Burrows et al, this conference). They reveal a thin, almostperfectly edge-on disk with an exponential vertical profile, densitypower law changeover at 100 AU, and an asymmetry in the inner disk. Mainsequence stars with IRAS infrared excesses and shell-star absorption,properties shared with Beta Pic, were also observed. No disk wasdetected around Vega, though it is expected to be nearly face on. Also,no disks were seen around the shell stars HR 2174 and HR 4368.Experiments indicate that if a slightly inclined Beta Pic-type disk waspresent in any of these objects, it should have been detected.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Observations of Disks around Main Sequence Stars (\beta Pictoris)
Not Available
| 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| β Pictoris: evidence of light variations.
We have analyzed β Pictoris photometric measurements obtained fromLa Silla by the Geneva Observatory from 1975 to 1992. These data showevidence of variations in the brightness of the star, with no colordependency. Here, we demonstrate that the light variations are presenton long as well as on short time scales. On a long time scale, we showthat the apparent magnitude of β Pictoris decreased by0.011+/-0.004mag from 1979 to 1982. Moreover, when we consider all themeasurements, the chance that there is no variation at all can beestimated to be less than 10^-4^. On short time scales there is apeculiar feature observed during about 30 days; the variations may be ashigh as 0.04mag magnitude. A maximum entropy reconstruction of thephotometric data is tentatively proposed and some physicalinterpretations are presented.
| Radial velocity studies of A-type shell stars.
We have measured radial velocities for a sample of A-type shell stars.We examine the results for the H I, Ti II and Ca II shell lines andcompared them with the radial velocities derived for the underlyingstars. We found that the A-type shell stars reproduce on a smaller scalethe phenomena observed in B-type shell stars.
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