Starspot activity in late stars: Methods and results
Three types of methods for studying the surface inhomogeneities of coolstars and the results of their use on type BY Dra, RS CVn, FK Com, and TTau variables are discussed. The current relevance of traditionalphotometric methods and the advantages of the zonal spottedness modelare pointed out. Dependences of the maximum total areas, averagelatitudes, and temperatures of spots on the global parameters of thestars are given. Analogs of the solar cycle in the variations of theareas and latitudes of starspots are examined, as well as the effects ofdifferential rotation and active longitudes.
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Archival light curves from the Bamberg Sky Patrol: CF Octantis, 1964-76
We use the archive of the Bamberg Sky Patrol to obtain light curves ofthe active K subgiant CF Octantis (HD 196818) for the interval 1964-76.Digitized images of the field near CF Oct were obtained with a flat-bedscanner. Aperture photometry was performed of photo-positives of theseimages. Using a transformation to second order in plate magnitude, andfirst order in B-V, for nine field stars for each plate, the Bmagnitudes of CF Oct were obtained for just over 350 plates. Theestimated precision of an individual determination of the B magnitude ofCF Oct is 0.05 mag. Analysis of the resulting data reveals the known 20d rotational variation of this star, and shows the evolution of thelight curves from year to year. We obtain light curves with good phasecoverage for 1964 to 1969 inclusive, partial light curves for 1970 and1976, and a few data points from 1971. The amplitude of variation rangesfrom ~0.2 to ~0.4 mag. There is evidence that the characteristicrotation period of the star in the 1960s was slightly less than thatmeasured from photoelectric photometry in the 1980s.
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Variability of the Photospheric Radiation of Active K-M Dwarfs and Their X-ray Luminosities
Variability of the photospheric radiation of 40 (dKe-dMe) dwarfs in thesolar neighborhood due to variations in the spottedness of theirsurfaces is analyzed based on the behavior of their mean annualbrightnesses over long time intervals. The amplitudes and characteristictime scales of the variations of the mean annual brightness are taken tobe indicators of photospheric activity and were used to infer the levelsof photospheric activity in the stars studied. The influence of axialrotation on the development of cyclic activity in young red dwarfs andF-M main-sequence stars is analyzed. The durations and amplitudes of thephotospheric variability of rapidly rotating (dK0e-dK5e) stars testifiesto a higher level of photospheric activity among red dwarfs andsolar-type stars. The X-ray luminosities of these stars grow with theamplitude of the variations of the mean annual brightness. However, thisis not typical of rapidly rotating M dwarfs, for which the X-rayemission varies by more than two orders of magnitude, although theirdegrees of spottedness are all virtually the same. A linear relationshipbetween the X-ray and bolometric luminosities is observed for young(dKe-dMe) stars, with their ratios log(L x/L bol) being about -3. Theseproperties can be used to determine whether a red dwarf is a young staror is already on the main sequence.
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Statistics of BY Draconis Variables
A statistical survey of 113 spotted red dwarf stars that are known orsuspected BY Draconis variables is presented. Typical indicators ofstellar photometric activity—the amplitudes of the rotationalmodulation and seasonal mean brightness variations ΔV andΔ〈V〉—are compared to the global parameters of thestars. First, photometric variability shows a weak dependence onspectral type; second, ΔV and Δ〈V〉 grow withincreasing stellar rotational velocity and decreasing Rossby number,with the dependences saturating at the critical values V crit15 20km/s and Rocrit0.2 0.3; and third, the Sun as a star fits well intothe derived relations. Thus, the spottedness of stars, like otherindicators of stellar activity, depends on their global parameters.
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Identifications for Wachmann's Variables in SA 98
Not Available
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Catalogue and bibliography of the UV Cet-type flare stars and related objects in the solar vicinity
This new catalogue of flare stars includes 463 objects. It containsastrometric, spectral and photometric data as well as information on theinfrared, radio and X-ray properties and general stellar parameters.From the total reference list of about 3400 articles, partial listsselected by objects, authors, key words and by any pairs of thesecriteria can be obtained Tables 1, 2 and 3 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html.
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PZ Mon - An Active Evolved Star
An Hipparcos parallax and new high-resolution spectra show that PZ Mon,long considered a spotted UV Ceti flare star, is actually a distantactive giant (K1III+?), probably an RS CVn, with km s
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EUV activity in late-type stars during the ROSAT WFC All-Sky Survey - I. Techniques and initial results
We study 127 active late-type stars, including the well-known flarestars, in the extreme ultraviolet (EUV) region of the electromagneticspectrum, using the ROSAT Wide Field Camera (WFC) survey observations.Our analysis includes photometry for all the stars in the sample, timinganalysis of the observed photon events, and a statistical analysis forpossible small-scale, low-level variability. 49 stars in our sample weredetected in one or both EUV wavebands. A total of 35 flares were seen,from 23 stars, not all of them well-known flare stars. In addition,about half of the detections exhibited low-level variability. Furtheranalysis reveals that the observed low-level variability was not due torotational or orbital modulation, but rather was related to small-scaleactivity on the stars, possibly in the form of small-amplitude,flare-like events which were too faint to be recognized as individualflares at the sensitivity of the WFC. We call this low-level activity`milliflaring'. We also give estimated upper-limit count rates for thenon-detections.
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Search for long-term variations of dKe-dMe stars.
Not Available
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The long-term variability in active red dwarfs.
Photographic magnitudes of 29 red dwarf stars have been measured on timescales of 5-90 years using the archival plate collections of theSternberg State Astronomical Institute (Russia), AstronomicalObservatory of Odessa State University (Ukraine) and SonnebergObservatory (Germany). Long-term changes in yearly mean magnitudes weredetected or suspected for 10 objects. Two stars, V833 Tau and PZ Mon,showed remarkable amplitudes of variability up to 0.6mag and 1.0magrespectively. Eight stars have long-term changes in the range from 0.2to 0.5mag. Variations of other programme stars were less than 0.2mag,which is comparable to the scatter in the mean light of check stars.Typical time scale of the long-term variability is 20-60years.
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The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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PZ Mon - the Flare Star with the Largest Amplitude of the Long-Term Light Variability
Not Available
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The nearby flare stars
A review of the observed properties of solar neighborhood flare stars ispresented and a catalog of such stars is provided. The role of duplicityis discussed in relation to stellar rotation and age. It appears thatstellar rotation determines stellar activity levels in slowly rotatingstars. It is seen that for rotation rates above five km per sec theactivity levels saturate, making active flare stars into deviators fromrotation-activity relationships established for other types of stars.
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A spectroscopic survey of red dwarf flare stars
Low resolution CCD spectra of dKe and dMe stars, many of which areactive flare stars and spotted stars are presented. Most objects arecovered from 3500 A to 7500 A; some have coverage extending to 9000 A.The strength of various chromospheric emission lines and photosphericmolecular features is measured, and the run of these quantities withstellar intrinsic brightness is investigated.
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X-ray emission and structure of coronas of active late-type dwarfs
A method for the determination of the density in stellar coronas fromX-ray data is suggested. Its application to 45 G, K, and M main-sequencestars shows that the density at the corona base increases by thetransition from G stars to MO-M3 stars, and drops thereafter. Therising-density branch is connected with the intensification ofsolar-type activity processes on G-K stars. The properties of the X-rayemission of active M3-M6 stars, its rapid variability, and itsassociation with flare activity and with nonthermal radio emission areapparently evidence that heating of the coronas of these stars is due tonumerous processes of the subflare type.
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Study of quiescent state X-ray emission from flare stars
Quiescent-state X-ray emission of seven flare stars was studied as wellas the relationship between the emissions of the chromosphere,transition region and corona. These X-ray emission characteristics werethen compared with those of nonflaring dMe and dM stars and RS CVnbinaries. The dependency of quiescent state X-ray luminosity L(x) onflare-star rotation period is discussed, as well as the similaritiesfound between the spectra of the flare stars and the RS CVn binaries.Results indicate that the mean value of L(x) is about 2 X 10 to the28th/ergs; energy spectra analysis of three of the stars gives the valueof the corona temperature as three million K. The L(x)/bolometricluminosity distribution of the flare stars was found to be similar tothat of the regular period RS CVn binaries but dissimilar to that of thenonflaring dwarf M stars. A strong correlation was found between L(x)and bolometric luminosity L(Bol), for the flare stars and regular periodRS CVn binaries which is described by L(x) = 10 to the -3.23 + or - 22L(Bol).
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HEAO 1 observations of quiescent X-ray emission from flare stars
The HEAO A-2 data were searched at the positions of the 70 known flarestars for evidence of X-ray emission. Thirteen of them appear to bedetected at the equal to or greater than 3 sigma level. Their X-rayluminosities in the 2-20 keV energy band are in the range 5 x 10 to the28th - 6 x 10 to the 29th ergs/s and L(x)/L(bal) approximately 0.0001 to0.01. There were no detectable X-ray flare events during the time ofHEAO 1 observations. This detection, therefore, refers to the quiescentstate X-ray emission from the coronae of these stars. It appears thatintense coronae belonging to fairly active flare stars are beingobserved. X-ray variability over periods of 6 months was observed forseveral of them.
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On 'negative flares' and 'dips' of UV Cet-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&A....76..242R&db_key=AST
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Discussion of infrared measurements of T Tauri stars and related objects
It is pointed out that in comparison with main-sequence stars of thesame spectral type, all irregular variable stars in thepre-main-sequence stage (briefly called T Tauri stars), show an infraredexcess. Infrared observations provide information concerning thephysical characteristics of stars, including the total energy output.The reported investigation considers infrared observations of T Tauristars conducted during the last ten years. The exclusion of some starsnot belonging to the group of the T Tauri stars is considered along withaspects related to a subdivision of the T Tauri stars. The various typesof T Tauri stars with their characteristics are represented in graphs.It is found that in some cases the infrared excess may be caused by thethermal radiation of the circumstellar particles which are heated by thestar. In other stars, thermal bremsstrahlung and dust radiation areresponsible for the infrared excess.
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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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Infra-red observations of young stars. II. T Tau stars and the ORI population.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.161...97C&db_key=AST
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Photoelectric observations of flare stars. II
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS...10...47C&db_key=AST
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Photoelectric observations of some flare stars.
Not Available
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Flare activity of BY DRA (HDE 234677).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....12..152C&db_key=AST
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Photoelectric observations of flare stars. I
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....2..223C&db_key=AST
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Research on flare stars at the Catania Astrophysical Observatory
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Flares Observed at the Catania Astrophysical Observatory
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Beobachtungen von 71 bekannten Veraenderlichen in der Umgebung des Kapteynschen Eichfeldes SA 98 (Monoceros).
Not Available
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The Abundance of Lithium in T Tauri Stars and Related Objects.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1960ApJ...131...83B&db_key=AST
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Absolute Proper Motions of 21 Variables of the RW Aur Type.
Not Available
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