Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Mass loss and orbital period decrease in detached chromospherically active binaries
The secular evolution of the orbital angular momentum (OAM), thesystemic mass (M=M1+M2) and the orbital period of114 chromospherically active binaries (CABs) were investigated afterdetermining the kinematical ages of the subsamples which were setaccording to OAM bins. OAMs, systemic masses and orbital periods wereshown to be decreasing by the kinematical ages. The first-orderdecreasing rates of OAM, systemic mass and orbital period have beendetermined as per systemic OAM, per systemic mass and per orbitalperiod, respectively, from the kinematical ages. The ratio of d logJ/dlogM= 2.68, which were derived from the kinematics of the presentsample, implies that there must be a mechanism which amplifies theangular momentum loss (AML) times in comparison to isotropic AML ofhypothetical isotropic wind from the components. It has been shown thatsimple isotropic mass loss from the surface of a component or bothcomponents would increase the orbital period.
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| Kinematics of chromospherically active binaries and evidence of an orbital period decrease in binary evolution
The kinematics of 237 chromospherically active binaries (CABs) werestudied. The sample is heterogeneous with different orbits andphysically different components from F to M spectral-type main-sequencestars to G and K giants and supergiants. The computed U, V, W spacevelocities indicate that the sample is also heterogeneous in velocityspace. That is, both kinematically younger and older systems exist amongthe non-evolved main sequence and the evolved binaries containing giantsand subgiants. The kinematically young (0.95 Gyr) subsample (N= 95),which is formed according to the kinematical criteria of moving groups,was compared with the rest (N= 142) of the sample (3.86 Gyr) toinvestigate any observational clues of binary evolution. Comparing theorbital period histograms between the younger and older subsamples,evidence was found supporting the finding of Demircan that the CABs losemass (and angular momentum) and evolve towards shorter orbital periods.The evidence of mass loss is noticeable on the histograms of the totalmass (Mh+Mc), which is compared between theyounger (only N= 53 systems available) and older subsamples (only N= 66systems available). The orbital period decrease during binary evolutionis found to be clearly indicated by the kinematical ages of 6.69, 5.19and 3.02 Gyr which were found in the subsamples according to the periodranges of logP<= 0.8, 0.8 < logP<= 1.7 and 1.7 < logP<=3, respectively, among the binaries in the older subsample.
| VLA Radio Positions of Stars: 1978-1995
VLA astrometric positions of the radio emission from 52 stars arereported, from observations obtained between 1978 and 1995. Thepositions of these stars have been obtained and reduced in a uniformmanner. Based on our measurements, the offset of the optical (Hipparcos)frame from the radio reference frame is in agreement with the Hipparcosextragalactic link results, within their mean errors. Comparison of theVLA measurements with the Hipparcos optical positions confirms earlierestimates of the accuracy of these positions as 30 mas. Long-termmeasurements of UX Ari have improved its proper motion.
| WW Dra - ein heller BAV-Programmstern mit vielen Problemen.
Not Available
| Determination of the Ages of Close Binary Stars on the Main Sequence from Evolutionary Model Stars of Claret and Gimenez
A grid of isochrones, covering a wide range of stellar ages from thezero-age main sequence to 10 billion years, is calculated in the presentwork on the basis of the model stars of Claret and Gimenez withallowance for convective overshoot and mass loss by the components. Theages of 88 eclipsing variables on the main sequence from Andersen'scatalog and 100 chromospherically active stars from Strassmeier'scatalog are calculated with a description of the method of optimuminterpolation. Comparisons with age determinations by other authors aregiven and good agreement is established.
| Optical positions of 55 radio stars from astrolabe observations from the Yunnan Observatory
The observations by the photoelectric astrolabe at Yunnan Observatoryrelative to the Hipparcos Catalogue and the optical positions of 55radio stars were obtained from observations between 1991 and 2000. Theyall resulted from processing the photon counts obtained by means of theastrolabe after the automation of the instrument. There are 46 stars incommon with the Hipparcos Catalogue. Tables \ref{t1} and \ref{t2} arealso available in electronic form at the CDS via anonymous ftpcdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/383/1062.
| 149 Bedeckungssterne der BAV-Programme. Eine Analyse der Beobachtungstatigkeit seit den Angangen.
Not Available
| Einige interessante Bedeckungsveraenderliche.
Not Available
| The Catania Automatic Photoelectric Telescope on Mt. Etna: a systematic study of magnetically active stars
A photometric monitoring of about 50 magnetically active stars, that arespread almost all over the H-R diagram, was initiated at the mountainstation of Catania Observatory on Mt. Etna (1750-m a.s.l.) in 1992 withan 80-cm robotic telescope (APT-80) built by AutoScope Co. (USA). Thissystematic survey is now approaching its 10th year anniversary. For mostof the stars, quite well defined solar-like spot maps have been derivedfrom UBV data obtained in different epochs. These data have allowed usto investigate some relevant characteristics of spot activity andvariability on stars, and to obtain clear evidence of long-term activitycycles, in the range from a few to about 10 years, on some of theobserved targets. Starspot maps are constructed by using advanced tools,such as massive parallel computing and are based on Maximum Entropy andTikhonov regularization criteria. Selected results are here presented.Our systematic observation program is still underway and a secondAPT80/2, equipped with a CCD camera, will pair the APT80/1 on the samesite. Its operation is foreseen for mid 2002.
| S 10947 Aquilae == RX J2009.8+1557: a probable RS CVn star which sometimes stops its eclipses
We report the discovery of a new variable star, called S 10947 Aql, asthe likely optical counterpart of RX J2009.8+1557. The opticalvariability pattern as well as the detected X-ray emission suggest thatit is a chromospherically active binary of the RS Canum Venaticorum(equiv RS CVn) type. We discovered an occasional disappearance of theeclipsing minima as well as large variations in the eclipse amplitude.We discuss possible causes of this peculiarity. The complete Table 1 isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| On X-Ray Variability in Active Binary Stars
We have compared the X-ray emissions of active binary stars observed atvarious epochs by the Einstein and ROSAT satellites in order toinvestigate the nature of their X-ray variability. The primary aim ofthis work is to determine whether or not active binaries exhibitlong-term variations in X-ray emission, perhaps analogous to theobserved cyclic behavior of solar magnetic activity. We find that, whilethe mean level of emission of the sample remains steady, comparison ofdifferent ROSAT observations of the same stars shows significantvariation on timescales <~2 yr, with an ``effective variability''ΔI/I=0.32+/-0.04, where I and ΔI represent the mean emissionand variation from the mean emission, respectively. A comparison of theROSAT All-Sky Survey and later pointed observations with earlierobservations of the same stars carried out with Einstein yields onlymarginal evidence for a larger variation (ΔI/I=0.38+/-0.04 forEinstein vs. ROSAT All-Sky Survey and 0.46+/-0.05 for Einstein vs. ROSATpointed) at these longer timescales (~10 yr), thus indicating thepossible presence of a long-term component to the variability. Whetheror not this long-term component is due to the presence of cyclicvariability cannot be decided on the basis of existing data. However,assuming that this component is analogous to the observed cyclicvariability of the Sun, we find that the relative magnitude of thecyclic component in the ROSAT passband can, at most, be a factor of 4,i.e., I_cyc/I_min<4. This is to be compared with the correspondingbut significantly higher solar value of ~10-10^2 derived from GOES,Yohkoh, and Solrad data. These results are consistent with thesuggestions of earlier studies that a turbulent or distributive dynamomight be responsible for the observed magnetic activity on the mostactive, rapidly rotating stars.
| Time Evolution of the Magnetic Activity Cycle Period. II. Results for an Expanded Stellar Sample
We further explore nondimensional relationships between the magneticdynamo cycle period P_cyc, the rotational period P_rot, the activitylevel (as observed in Ca II HK), and other stellar properties byexpanding the stellar sample studied in the first paper in this series.We do this by adding photometric and other cycles seen in active starsand the secondaries of CV systems and by selectively adding less certaincycles from the Mount Wilson HK survey; evolved stars, long-term HKtrends and secondary P_cyc are also considered. We confirm that moststars with age t>~0.1 Gyr occupy two roughly parallel branches,separated by a factor of ~6 in P_cyc, with the ratio of cycle androtational frequencies ω_cyc/Ω~Ro^-0.5, where Ro is theRossby number. Using the model of the first paper in this series, thisresult implies that the α effect increases with mean magneticfield (contrary to the traditional α-quenching concept) and thatα and ω_cyc decrease with t. Stars are not strictlysegregated onto one or the other branch by activity level, though thehigh-ω_cyc/Ω branch is primarily composed of inactive stars.The expanded data set suggests that for t>~1 Gyr, stars can havecycles on one or both branches, though among older stars, those withhigher (lower) mass tend to have their primary P_cyc on the lower(upper) ω_cyc/Ω branch. The Sun's ~80 yr Gleissberg cycleagrees with this scenario, suggesting that long-term activity ``trends''in many stars may be segments of long (P_cyc~50-100 yr) cycles not yetresolved by the data. Most very active stars (P_rot<3 days) appear tooccupy a new, third branch with ω_cyc/Ω~Ro^0.4. Many RS CVnvariables lie in a transition region between the two most activebranches. We compare our results with various models, discuss theirimplications for dynamo theory and evolution, and use them to predictP_cyc for three groups: stars with long-term HK trends, stars in youngopen clusters, and stars that may be in Maunder-like magnetic minima.
| Mutual irradiation and absorption and surface temperature variation in detached binary systems
In the paper, we calculate the absorbed flux of the mutual irradiationof the components in detached binary systems, and obtain the surfacetemperature distribution on the components. The maximum temperaturedifference over the surface is a measure of the deviation betweenisothermal and equipotential surfaces. For 33 late-type binary systemswith known elements, we evaluate this maximum difference. The resultshows that the isothermal-equipotential deviation is always larger inthe cooler than in the hotter components. This result supports Zhou andLeung's idea that the large difference between ``star-spots'' andsunspots is due to cyclones and anticyclones. The effect of limbdarkening (amounting to over 18% and always larger in the hottercomponent) is included in the consideration.
| Mutual irradiation and absorption in detached binary systems and surface temperature variation.
Not Available
| Accurate Positions for Radio Stars as Determined from CCD Observations in the Extragalactic Reference Frame.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1679S&db_key=AST
| Radio stars for linking celestial reference frames
Radio stars play a key role in establishing the link between opticalreference frames and the conventional celestial reference frame based onextragalactic radio sources. The relevant astrometric, astrophysical andradio quantities are compiled of 66 cardinal radio stars currentlysuited to frame connection and maintenance of the link. The catalogueentries are supplied with ample bibliographical codes and annotationsfor easy data retrieval. The catalogue is available electronically atthe CDS via anonymous ftp 130.79.128.5 and viahttp://cdsweb.u-strasbg.fr/Abstract.html
| EUV Emission from RS Canum Venaticorum binaries.
We performed a study of 104 RS CVn systems in the extreme ultraviolet(EUV) using the all-sky survey data obtained by the Extreme UltravioletExplorer (EUVE). The present sample includes several new RS CVndetections; 11 more than in the published EUVE catalogs, and 8 more thanin the ROSAT Wide Field Camera catalog. The ratio of detections tonon-detections remained constant throughout the sky, implying that ourdetections are not limited by the exposure time but are most likelylimited by absorption from the interstellar medium. A general trend ofincreasing Lex/B (50-180Å) flux with decreasing rotational periodis clear. The dwarf systems exhibit a leveling-off for the fasterrotators. In contrast, the evolved systems exhibit no such effect. Forthe RS CVn systems the losses in the EUV represent a smaller fraction ofthe coronal radiative losses, as compared to active late-type dwarfs.
| The behaviour of the excess CA II H and K and Hɛ emissions in chromospherically active binaries.
In this work we analyze the behaviour of the excess Ca II H and K andHɛ emissions in a sample of 73 chromospherically active binarysystems (RS CVn and BY Dra classes), of different activity levels andluminosity classes. This sample includes the 53 stars analyzed byFernandez-Figueroa et al. (1994) and the observations of 28 systemsdescribed by Montes et al. (1995c). By using the spectral subtractiontechnique (subtraction of a synthesized stellar spectrum constructedfrom reference stars of spectral type and luminosity class similar tothose of the binary star components) we obtain the active-chromospherecontribution to the Ca II H and K lines in these 73 systems. We havedetermined the excess Ca II H and K emission equivalent widths andconverted them into surface fluxes. The emissions arising from eachcomponent were obtained when it was possible to deblend bothcontributions. We have found that the components of active binaries aregenerally stronger emitters than single active stars for a giveneffective temperature and rotation rate. A slight decline of the excessCa II H and K emissions towards longer rotation periods, P_rot_, andlarger Rossby numbers, R_0_, is found. When we use R_0_ instead ofP_rot_ the scatter is reduced and a saturation at R_0_=~0.3 is observed.A good correlation between the excess Ca II K and Hɛchromospheric emission fluxes has been found. The correlations obtainedbetween the excess Ca II K emission and other activity indicators, (C IVin the transition region, and X-rays in the corona) indicate that theexponents of the power-law relations increase with the formationtemperature of the spectral features.
| RS CVn Versus Algol-Type Binaries: A Comparative Study of Their X-Ray Emission
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.2415S&db_key=AST
| Optical positions of radio stars. I.
The optical positions of 31 radio stars obtained from the observationswith the photoelectric astrolabe at Yunnan Observatory are presented inthis paper. These are all the stars in the astrometric catalogue ofradio stars observable by our astrolabe.
| The emission of the RS CVn binaries in the IRAS passbands.
In the literature, there is an ambiguity pertaining to the existence ofa far-IR excess in RS CVn systems. In the current paper we undertook astudy of the behaviour of 103 such systems in the IRAS passbands. Wefound 72 acceptable detections in the 12μm band, and 40 in the25μm band (50% more than the IRAS Point Source Catalog). Although ourfindings may be interpreted as indicating towards the existence of anexcess beyond 12μm for some systems, the evidence is not conclusivein all but two cases. These are systems GX Lib and HR 7428, with Capellabeing the only system where the IRAS fluxes in all four bands originatefrom the stellar photosphere. Given the accuracy of the data we did notfind 12μm excess for any system. We argue that the IRAS data alonecannot settle the issue, as their uncertainty is, in many cases, higherthan what the Signal-to-Noise ratio of each observation implies.Furthermore, at the higher wavelength bands the IRAS angular resolutiondrops from 0.5' at 12μm to 2' at 100μm and the background becomesvery complex, so one cannot be certain about the origin of the observedflux. The existence of IR excess in the RS CVn stars is important as faras the evolutionary scenarios for these systems are concerned. Futuremissions such as the Infrared Space Observatory will return moresensitive and accurate measurements and the ambiguity can be removed.The fluxes we quote will be helpful when planning these futureobservations, as we provide more accurate photometry and for a largerselection of sources than the IRAS Point Source Catalog.
| On the Role of Mass Transfer in X-Ray Emission of RS CVN Systems
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....109.2187W
| Excess Hα emission in chromospherically active binaries.
We study the behaviour of the excess Hα emission in a sample of 51chromospherically active binary systems (RS CVn and BY Dra classes), ofdifferent activity levels. This sample include the 27 stars analysed byFernandez-Figueroa et al. (1994) and the new observations of 24 systemsdescribed by Montes et al. (1994b). By using the spectral subtractiontechnique (subtraction of a synthesized stellar spectrum constructedfrom reference stars of similar spectral type and luminosity class) weobtain the active-chromosphere contribution to the Hα line inthese 51 systems. We have determined the excess Hα emissionequivalent widths and converted it to surface fluxes. The Hαemissions arising from each component star were obtained when it waspossible to deblend both contributions. The comparison of the excessHα emission, obtained with the spectral subtraction technique,with other Hα activity indices allows us to conclude that this isthe preferable activity indicator for binaries. The behaviour of theexcess Hα emission as a function of the rotation has beenanalyzed. A slight decline toward longer rotational periods, P_rot_, andlarger Rossby numbers, R_0_, is present in agreement with previousresults using others activity indicators. We have compared the derivedexcess Hα emission fluxes with those obtained in the Ca II K andHɛ lines finding that a good correlation exits between thesethree chromospheric activity indicators. The Hα losses seem to bemore important than Ca II K losses for cooler stars, in fact all thesystem with Hα emission above the continuum are cooler than 5000K.Correlations with other activity indicators, (C IV in the transitionregion, and X-rays in the corona) indicate that the exponents of thepower-law relations increase with the formation temperature of thespectral features.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
| Are the Rotational Axes Perpendicular to the Orbital Planes in the Binary Systems? II. Synchronous Long-Period RS CVn Stars
Inclinations of the rotational axes, irot, are determined for37 synchronous long-period RS CVn binaries by combining v sin imeasurements with rotational period information. These inclinations arethen compared with the orbital inclinations of the systems,iorb, to test the alignment between the equatorial andorbital planes. Contrary to the asynchronous RS CVn systems (see PaperI), in all 37 cases irot is equal or nearly equal toiorb, and the assumption about coplanarity of theirequatorial and orbital planes is justified.
| The age-mass relation for chromospherically active binaries. I. The evolutionary status
In this paper we present a study of the evolutionary status of a sampleof chromospherically active binary systems for which accuratedeterminations of their stellar parameters are available. Stellar ageshave been obtained by using evolutionary tracks. The agreement betweenthe estimates of ages for the two components of a given system is verygood, which proves the reliability of our method. It has been possibleto separate the chromospherically active binaries in three groups,according to the mass of the primary component: evolved stars withmasses in the range 2.5-5Msun_, evolved stars (subgiants)with M=~1.4Msun_ and main-sequence stars withM=~1.1Msun_. We have found a relationship between stellarmasses and ages of the formLog(Age)=9.883(+/-0.022)-2.965(+/-0.122)Log(Mass/Msun_). Thisrelationship is very close to that for stars on the TAMS. The relationcan be understood, in the framework of the evolution of the componentsand orbital elements of binary systems, as an effect of the increase ofthe stellar radius as the components evolve off the main sequence, andthe decrease of the rotation period due to tidal effects which leads toenhanced chromospheric emission levels, several times higher than thatof the Sun. The relationship has a dependence on rotation, due to thefact that for a given range of masses, younger stars rotate faster. Wehave also found that the more evolved stars are the more active, for agiven interval of rotation periods.
| Rotational modulation and flares on RS Canum Venaticorum and BY Draconis stars. 18: Coordinated VLA, ROSAT, and IUE observations of RS CVn binaries
As part of a coordinated program of multi-wavelength observations of RSCVn close binary systems, we observed 15 systems with the Very LargeArray (VLA) and 10 systems with IUE, simultaneously or nearlysimultaneously with the ROSAT All Sky Survey observations of thesestars. Of the 22 systems observed with ROSAT, three were observed bothby IUE and the VLA. Radio observations were made at 3.6, 6 and 20 cm. Ofthe 15 observed RS CVn systems, we detected 11 with greater than 4 sigmaconfidence at one or more wavelengths. The IUE observations were madewithin the RIASS (ROSAT-IUE All Sky Survey) program. We present theresults of the VLA observations, along with the corresponding subsets ofthe ROSAT Position Sensitive Proportional Counter (PSPC) X-ray and WideField Camera (WFC) XUV survey, and RIASS IUE observations. We obtainedan extended VLA/IUE/ROSAT simultaneous coverage of one system, TY Pyx,covering more than one orbital period. These observations reveal thatthe quiescent radio flux of TY Pyx is relatively constant over timescales of up to 7 hours, but that it did change by a factor of 3 over 24hours, probably due to a flare on 1990 Nov. 12. The UV, XUV and X-rayfluxes do not show large day-to-day or phase-related variability. Theobservation of the decay phase of a radio flare on EI Eri, with noaccompanying X-ray or XUV flare, suggests that the lack of a strongcorrelation between X-ray and radio flares previously noted for dMeflare stars holds for RS CVn systems as well. We suggest that the radioflare may have been due to a coherent emission process such as electroncyclotron emission. The simultaneous measurements presented here providea unique test of the general correlation between radio and soft X-rayluminosities, Lradio approximately Lx exp m (Drakeet al. 1989) with a power-law slope close to unity, which was previouslyderived using data obtained years apart. Our derived slopes areconsistent with and thus support the general correlations betweencoronal and chromospheric/transition region emissions previously derivedfrom nonsimultaneous measurements of a much larger sample of thesevariable sources. However, the importance of simultaneous measurementsfor accurate energy balance calculations is stressed.
| Eclipse observations of RS CVn binaries. 2: A parametric model of extended matter
We have surveyed ten RS CVn binary systems and have detected largeregions of extended, prominencelike material which we have shown to be acommon feature in these systems. These extended regions are apparent asanomalous absorption features in the spectra when they obscure the diskof the eclipsed star and as weak emission features when they appear withno disk behind. We have constructed a first-generation model to verifythe general prominencelike nature of the material and to estimate itsextent and its most basic physical characteristics. In this paper wepresent our results of our modeling on four of the systems in our surveythat showed clear signatures of extended material: AW Her, MM Her, SSBoo, and UV Psc. We find that these stellar prominencelike structuresare very much larger than their solar counterparts, though their grossphysical characteristics (i.e., their electron density and temperatureand their general appearance as tenuous, vertically oriented,magnetically confined structures) are similar to those seen in solarprominences. These features appear to evolve fairly rapidly, sincemoderate- to high-velocity flows ranging from several tens of km/s to170 km/s are apparent. However, in at least one case (SS Boo) they arerecurrent over a time scale of at least a year. We conclude bydiscussing the implications of this work regarding the nature of closebinary star active structures and their evolution.
| CA II H and K and H alpha emissions in chromospherically active binary systems (RS Canum Venaticorum and BY Draconis)
We report high-resolution observations of the Ca II H and K and Balmer Halpha lines in 53 chromospherically active binary systems including theRS Canum Venaticorum binaries (RS CVn) and BY Draconis (BY Dra) classes.The rotational periods of the sample cover a range from 0.8 to 83.2days. H and K emission-line surface fluxes have been calculated for allthe stars in the sample. In spectra where the H eta line appears inemission, absolute surface fluxes were also determined. The Ca II lineprofiles corresponding to different seasons and orbital phases areanalyzed in order to determine the contribution of each component and tostudy the chromospheric activity variations. We have measured the Halpha equivalent width of the program stars and the H alpha coreemission was determined by subtraction of the equivalent width of apresumably inactive star of the same spectral type and luminosity class.Three different types of H alpha line profiles have been found: strongemission line, weak emission line with strong superposed absorptionprofile, and filled-in absorption line profile.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Auriga |
| Ascensió Recta: | 06h03m53.65s |
| Declinació: | +31°19'41.2" |
| Magnitud Aparent: | 9 |
| Moviment propi RA: | -0.4 |
| Moviment propi Dec: | -4.5 |
| B-T magnitude: | 10.08 |
| V-T magnitude: | 9.09 |
Catàlegs i designacions:
|
INHABITED SKY
