Contents
Images
Upload your image
DSS Images Other Images
Related articles
Long-term magnetic activity in close binary systems. I. Patterns of color variations
Aims.This is the first of a series of papers in which we present theresults of a long-term photometric monitoring project carried out atCatania Astrophysical Observatory aimed at studying magnetic activity inlate-type components of close binary systems, its dependence on globalstellar parameters, and its evolution on different time scales from daysto years. In this first paper, we present the complete observationdataset and new results of an investigation into the origin ofbrightness and color variations observed in the well-known magneticallyactive close binary stars: AR Psc, VYAri, UX Ari, V711 Tau,EI Eri, V1149 Ori, DHLeo, HU Vir, RS CVn,V775 Her, AR Lac, SZPsc, II Peg and BY Dra Methods: About 38 000 high-precision photoelectric nightly observationsin the U, B and V filters are analysed. Correlation and regressionanalyses of the V magnitude vs. U-B and B-V color variations are carriedout and a comparison with model variations for a grid of active regiontemperature and filling factor values is also performed. Results: Wefind the existence of two different patterns of color variation. Eightstars in our sample: BY Dra, VYAri, V775 Her, II Peg,V1149 Ori, HU Vir, EIEri and DH Leo become redder when theybecome fainter, as is expected from the presence of active regionsconsisting of cool spots. The other six stars show the oppositebehaviour, i.e. they become bluer when they become fainter. ForV711 Tau this behaviour could be explained by theincreased relative U- and B-flux contribution by the earlier-typecomponent of the binary system when the cooler component becomesfainter. On the other hand, for AR Psc, UXAri, RS CVn, SZ Psc andAR Lac the existence of hot photospheric faculae mustbe invoked. We also found that in single-lined and double-lined binarystars in which the fainter component is inactive or much less active theV magnitude is correlated to B-V and U-B color variations in more than60% of observation seasons. The correlation is found in less than 40% ofobservation seasons when the fainter component has a non-negligiblelevel of activity and/or hot faculae are present but they are eitherspatially or temporally uncorrelated to spots.I dedicate this paper to the memory of the P.I. of this project, Prof.Marcello Rodonò, who suddenly passed away on October 23, 2005. Tohim my sincere estimation and deepest gratitude.Based onobservations collected at INAF-Catania Astrophysical Observatory, Italy.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| RS CVN Stars in the AAVSO Photoelectric Photometry Program
We report V Photometry of three RS CVn stars--HK Lac, SZ Psc, and LambdaAnd--from the AAVSO photoelectric photometry program, and fromtransformed Hipparcos photometry, over 3500 days. Eighteen photoelectricphotometry observers contributed to this project. The stars vary onperiods of days to weeks, due to rotation of a spotted photosphere. Therotational light curves vary on time scales of months to years, due tochanges in the area and/or distribution of the spots.
| Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Long-term starspot evolution, activity cycle and orbital period variation of AR Lacertae
A sequence of AR Lac seasonal light curves covering the period 1967-1992is analysed in the framework of the starspot hypothesis to derive thespot distribution and evolution on the component stars. The adoptedapproach makes use of the Maximum Entropy and Tikhonov principles tocompute maps of the stellar photospheres exploiting also the eclipsescanning technique. Reliable results on the distribution of the spottedareas can be derived through a critical comparison of the maps obtainedby the above quoted regularizing criteria. Satisfactory fits arecomputed assuming that spots are located on the photospheres of bothcomponents and that their unspotted luminosity ratio in the V band is:frac {L_{1 }}{L_{2 }} =3D0.59 +/- 0.03. The derived yearly spotdistributions are analysed to infer general activity characteristics.The spot patterns appear to consist of two components, one uniformly andthe other non-uniformly distributed in longitude, the latter suggestingthe presence of preferential longitudes. Starspots at latitudes higherthan ~ 50(deg) are not needed to reproduce the photometric modulation.On the less luminous primary we find evidence for quite compact spottedareas ( ~ 30(deg}-40({deg)) in diameter) which are occulted duringprimary eclipses. On the more luminous and larger secondary, spotscluster preferentially around longitudes ~ 60(deg) , ~ 180(deg) (i.e.,around the substellar point) and ~ 300(deg) without showing evidence fora regular migration. The variation of the spotted area does not give asignificant evidence for an activity cycle on the primary, whereas apossible modulation on a time scale of about 17 yr may be present on thesecondary. The spatial association among photospheric spots andchromospheric and coronal plages (as detected in the UV and X-rayspectral domains) is significant for the large active region around thesubstellar point on the secondary and is suggested also for the smallerstarspots on the secondary and primary components. A possiblerelationship between the orbital period modulation with a period of ~ 35yr and an activity cycle on the secondary component is tentativelysuggested and, if confirmed by future observations, can provide furthersupport to recently proposed models for the connection between magneticactivity and orbital period variations.
| Classification of Population II Stars in the Vilnius Photometric System. II. Results
The results of photometric classification of 848 true and suspectedPopulation II stars, some of which were found to belong to Population I,are presented. The stars were classified using a new calibrationdescribed in Paper I (Bartkevicius & Lazauskaite 1996). We combinethese results with our results from Paper I and discuss in greaterdetail the following groups of stars: UU Herculis-type stars and otherhigh-galactic-latitude supergiants, field red horizontal-branch stars,metal-deficient visual binaries, metal-deficient subgiants, stars fromthe Catalogue of Metal-deficient F--M Stars Classified Photometrically(MDPH; Bartkevicius 1993) and stars from one of the HIPPARCOS programs(Bartkevicius 1994a). It is confirmed that high galactic latitudesupergiants from the Bartaya (1979) catalog are giants or even dwarfs.Some stars, identified by Rose (1985) and Tautvaisiene (1996a) as fieldRHB stars, appear to be ordinary giants according to our classification.Some of the visual binaries studied can be considered as physical pairs.Quite a large fraction of stars from the MDPH catalog are found to havesolar metallicity. A number of new possible UU Herculis-type stars, RHBstars and metal-deficient subgiants are identified.
| Time-series photometric SPOT modeling. III. Thirty years in the life of HK Lacertae.
We present a spot modeling analysis of the active late-type giant HK Lacusing 30 years of photometry, including 600 new data points from thelast six years. We have analyzed folded light curves and, when we hadlong continuous data sets, applied a new computer code for time-seriesmodeling. The validity of the modeling results was tested as a functionof the photometric noise. We have determined the unspotted brightness ofHK Lac in the BV(RI)_C_ bandpasses and obtained a spot temperature of{DELTA}T=1200+/-100K. Polar active regions were recovered throughout themodeling because no other scenario was able to describe both the meanlight variability of over 0.25mag accompanied by rotational modulationof similar amplitude. This result has gotten strong theoretical supportrecently (see Schuessler). The active regions preferably cluster aroundtwo orbital phases separated by =~110°. New spot appearances withinactive regions and, possibly, their interactions with the old ones couldbe the cause of rapid changes in the light curves.
| 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.
| UVB photometry of the RS CVn-type binary HK Lacertae
The new UBV photometry presented for the long-period RS CVn-type binaryHK Lac, obtained in 1981 and 1982 and covering six complete cycles foreach of the two years, shows strong variations in the shape, maximum andminimum levels, amplitude, mean brightness, asymmetry, and period of thelight curve. The rotation of the visible KO giant component of HK Lacmay be thought of as synchronized with the orbital motion. Thecolor-independent complex light variation observed is interpretable interms of a rearrangement of two magnetically active regions withoutsignificant variation of the activity level on the surface of thevisible component.
| MK classification and photometry of stars used for time and latitude observations at Mizusawa and Washington
MK spectral classifications are given for 591 stars which are used fortime and latitude observations at Mizusawa and Washington. Theclassifications in the MK system were made by slit spectrograms ofdispersion 73 A/mm at H-gamma which were taken with the 91 cm reflectorat the Okayama Astrophysical Observatory. Photometric observations in UBV were made with the 1-meter reflector at the Flagstaff Station of U.S.Naval Observatory. The spectrum of HD 139216 was found to show a strongabsorption line of H-beta. The following new Am stars were found:HD9550, 25271, 32784, 57245, 71494, and 219109. The following new Apstars were found: HD6116, 143806, 166894, 185171, and 209260. The threestars, HD80492, 116204, and 211376, were found to show the emission inCaII H and K lines.
| Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.
Not Available
| UBV Observations of the RS CVn Binary HK Lacertae between 1978-1985
We report 524 UBV observations of the RS CVn binary HK Lac made between1978-1985. Our starspot modelling results published previously for 12light curves (using V colour) are summarized. Three additional modelledlight curves are presented which have not been published before. NineUBV light and colour curves obtained between 1982-85 in 16 American and2 Hungarian observatories, are given. Light curve modelling made for theV and B light curves separately show that the resulting model parametersagree well within the error of the modelling procedure.
| E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
| Starspots on HK Lacertae
Using altogether 500 nightly mean magnitudes of HK Lac (200 of themnew), previous conclusions (Olah et al., 1985) about its lightvariations are supplemented. With new data from the last 3 years, itbecomes clear that the median brightness of the star undergoescomplicated but possibly about 7-year cyclic variations. The corotatinglatitude is determined by two techniques: 32 + or - 2 deg from theperiod vs average latitude diagram, and 28 + or - 15 deg from the phasedrift of the two spots (one situated above and one under the corotatinglatitude). The presence of a 4-sector Active Longitude Belt, which haskept its place over the last 17 years, is indicated.
| Three-dimensional calssification of F-M type halo stars in the Vilnius photometric system
Not Available
| Photometric observations of RS Canum Venaticorum stars
Photometric observations of the following RS CVn stars are presented anddiscussed: HR 3 (33 Psc), HR 373 (39 Cet), LX Per, HR 4374 (53 UMa), HR4665, HR 7275, HK Lac, HR 8448 (AR Lac), HR 8575, HR 8703 and SZ Psc.Observations of HR 3 and HR 8448 are fragmentary. HR 4374 is notphotometrically variable. For the other stars, the range, phase andshape of the photometric distortion wave have been determined.
| Two-colour photoelectric investigation of AR Lacertae
The eclipsing binary AR Lac was observed on 70 nights in 1978 and 1979with a 48 cm Cassegrain reflector using standard B and V filters.Several times of minima have been obtained and the new light elementshave been calculated. The orbital period of the system is found todecrease by 14.6 s/century.
| Variable stars among CA II emission binaries.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&A....26..137H&db_key=AST
| Light-variation of HD 209813.
Abstract image available at:http://adsabs.harvard.edu/abs/1970A&A.....4..482B
| A Catalog of Magnetic Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1958ApJS....3..141B&db_key=AST
| A List of Newly Discovered Peculiar Objects.
Not Available
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Cygnus |
| Right ascension: | 21h57m04.91s |
| Declination: | +46°35'32.8" |
| Apparent magnitude: | 6.794 |
| Distance: | 497.512 parsecs |
| Proper motion RA: | 6.5 |
| Proper motion Dec: | 0.3 |
| B-T magnitude: | 8.287 |
| V-T magnitude: | 6.918 |
Catalogs and designations:
|
INHABITED SKY
