A photometric pilot study on Sonneberg archival patrol plates. How many ``constant'' stars are in fact long-term variables?
The light curves of 216 arbitrarly chosen field stars and of 23 knownvariables in the Aur/Tau/Ori region were derived (7.8 m ≤ B ≤12.2 m) from scanned, blue-sensitive archival patrol plates, covering atotal of 34 years (1961-1995). We achieved a photometric accuracy of0.07 ... 0.12 mag in spite of rather unfavourable locations of moststars near the plate borders. 17 field stars turned out to be variables,most of them with time scales of 1000-8000 days in the form of slowwaves with amplitudes between 0.1 and 0.3 mag, i.e. below the thresholdof traditional variable searches on photographic plates. About 50% ofthese new long-term variables exhibit drifts indicating periodic orerratic variability at much longer time scales than covered here. Forthe 23 known variables we achieved improvements in their periods andamplitudes and detected long-term variations (drifts, waves) in about50% of them. The above fraction of low-amplitude long-term variablesamong field stars implies that a total of about 45 000 new variablesshould be detectable in the Sonneberg patrol plate archive. They willrepresent a new, hitherto not investigated population of variable starswith a possibly significant impact on our understanding of the stellarinterior and evolution.Tables 2 and 3 are only available in electronic form athttp://www.edpsciences.org
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Optical Properties of the Circumstellar Dust around Stars with Aperiodic Fadings
Multicolor observations of 21 rapid, irregular variable stars withAlgol-like fadings and of R Coronae Borealis are used to derive theoptical extinction coefficients of the circumstellar dust associatedwith these objects, θ(λ). We used more than 3600 uniformmulti-color brightness measurements obtained in a rigorous U BV R systemat the Terskol High-altitude Observing Station. The mean extinctioncoefficient θ for the circumstellar dust for this sample of starscoincides almost exactly with the interstellar extinction coefficient,θis, but is somewhat higher in the ultraviolet. We suggest anexplanation for this difference.
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A Photometric Catalog of Herbig AE/BE Stars and Discussion of the Nature and Cause of the Variations of UX Orionis Stars
UBVR photometric monitoring of Herbig Ae/Be stars and some relatedobjects has been carried out at Maidanak Observatory in Uzbekistan since1983. More than 71,000 observations of about 230 stars have beenobtained and are made available for anonymous ftp. Virtually all HerbigAe/Be stars observed are irregular variables (called ``UXors'' after UXOri), but there is a wide range of amplitudes from barely detectable tomore than 4 mag in V. Our data confirm the results of previous studies,which indicate that large-amplitude variability is confined to starswith spectral types later than B8. The distribution of variabilityranges is quite similar to what is seen in classical T Tauri stars. Acareful search has failed to reveal any evidence for periodic variationsup to 30 days, which can be interpreted as rotation periods. This is aclear distinction between the light variations of low-mass and high-masspre-main-sequence stars. The Herbig Ae/Be stars evidently do not possesseither the large, stable cool spots or persistent hot spots associatedwith strong surface magnetic fields and magnetically funneled accretionin classical T Tauri stars. A wide variety of shapes, timescales, andamplitudes exists, but the most common behavior is well illustrated bythe light curve of LkHα 234. There are two principal components:(1) irregular variations on timescales of days around a mean brightnesslevel that changes on a much longer timescale (typically years),sometimes in a quasi-cyclic fashion, and (2) occasional episodes of deepminima, occurring at irregular intervals but more frequently near thelow points of the brightness cycles. Our data suggest that many T Tauristars of K0 and earlier spectral type share the same variabilitycharacteristics as Herbig Ae/Be stars and should be regarded as UXors.Two FU Orionis stars (``FUors''), FU Ori and V1515 Cyg, also have recentlight curves that are similar, in some respects, to UXors. The mostdeveloped model to account for the variations of some large-amplitudeUXors involves variable obscuration by circumstellar dust clumpsorbiting the star in a disk viewed nearly edge-on. However, there areproblems in extending this model to the entire class, which lead us topropose an alternative mechanism, i.e., unsteady accretion. Evidencefavoring the accretion model over the obscuration model is presented. Itis suggested that the thermal instability mechanism responsible foroutbursts in interacting binary system disks, and possibly FUors, may bethe cause of the deep minima in UXors.
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The luminosity of the Halpha_-emission envelopes of variable Is(A)-type stars.
We present the results of the analysis of the emission spectra ofvariable Is(A)-type stars. Sixteen stars have been observed in 1988-1992at the 6-m telescope of Special Astrophysical Observaroty, RussianAcademy of Sciences (SAO RAS) with the middle-resolution (R=~3000)echelle spectrograph ``Zebra". Equivalent widths of theHalpha_ and Hbeta_ (if available) emissioncomponents were obtained, the underlying profile of the correspondingabsorption lines were taken into account. The luminosities of theemission envelopes in the Halpha_ and Hbeta_ lineswere then calculated. The main result of the investigation is that theluminosity of the emission envelope appears to depend on the effectivetemperature of the star.
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Determination of lg G of several variable Herbig Ae/Be stars.
Echelle spectrogrammes of 19 variable Herbig Ae/Be stars were obtainedin 1988-1992 in the wavelength interval 4000-7000Å with thespectral complex ``Zebra" at the 6-m telescope of Special AstrophysicalObservatory, Russian Academy of Sciences (SAO RAS). Kurucz's models wereemployed for the analysis of the hydrogen absorption line profiles. Forall programme and standard stars lg(g) gravity parameters were obtained.The location of the stars on the "lg(g)-T_eff_" diagram does not agreewith the hypothesis that the studied objects are pre-main sequencestars.
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A study of the candidates for Herbig Ae/Be stars HD 35929 and HD 203024.
Not Available
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Periodic phenomena in Ae/Be Herbig stars light curves. I - Light curves classification and digital analysis methods. II - Results and probable interpretation for selected stars
Digital analysis methods are used to study the light curves of 78 HerbigAe/Be stars. The mean epoch for a star is 5 yr. A morphologicalclassification of the light curves is proposed. The digital analysismethod is briefly described. To estimate the reliability of the cyclicphenomena discovered in the present study, a large number of them areexamined. Three types of cyclic phenomena are identified and discussed.These phenomena are interpreted in terms of Keplerian rotation ofvarious structures in accretion disks and formations. The hypothesis ofgiant protocomets is suggested to explain P(0) periods. Short-periodcyclicity is associated with the variation of hot compact shell shapesmodulated by rotation.
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The SVS Numbering Series Discontinued
Not Available
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The prophology of Is(A) irregular variables. II. The location on the H-R diagram.
Not Available
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The morphology of Is(A) irregular variables. I. The multicolour photometry of the stars in Orion and Taurus.
Not Available
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Star formation in the Lambda Orionis region. I - The distribution of young objects
The results are presented of the first thoroughly sampled survey of theentire Lambda Orionis region for alpha hydrogen emission objects, andphotographic photometry is presented of the entire list of previouslyknown and newly discovered such objects. The majority of the objects arenot projected against dark cloud material, and many appear to be withinthe central regions of the extended low density H II region excited byLambda Orionis. The vast majority of the objects form an elongated,barlike structure two by eight degrees in extent. It is concluded thatLambda Orionis is an important region for studies of star formation. Thecomplex is in an intermediate stage of disruption; the expanding H IIregion has displaced most of the gaseous mass. The young stars haveapparently not moved very far from their original locations and thusprovide a fossil record of the original cloud structure.
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An infrared survey of RW Aurigae stars
An infrared photometric survey of 89 RW Aur type variables in bothhemispheres has been made. JHKL magnitudes and colors are listed. The RWAur variables include a small number of highly reddened late-type stars.All T Tauri and hot Orion population stars show infrared excesses andthe infrared properties mark certain field stars as being young. Thegreatest infrared excesses are found for A and F stars while youngvariable B stars usually show no excesses. The location of the RW Aurstars in the two-color H-K, K-L diagram favor dust re-radiation overfree-free emission as the mechanism responsible for the infrared excess.A weak correlation of H-K with emission class links the occurrence ofcircumstellar dust and gas shells.
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Einige Beziehungen der RW-Aurigae-Sterne zur interstellaren Materie.
Not Available
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New Emission Stars in the Constellation Orion.
Not Available
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Second Supplement to the Mount Wilson Catalogue and Bibliography of Stars of Classes B and a whose Spectra have Bright Hydrogen Lines.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1949ApJ...110..387M&db_key=AST
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