Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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.
| Reprocessing the Hipparcos Intermediate Astrometric Data of spectroscopic binaries. II. Systems with a giant component
By reanalyzing the Hipparcos Intermediate Astrometric Data of a largesample of spectroscopic binaries containing a giant, we obtain a sampleof 29 systems fulfilling a carefully derived set of constraints andhence for which we can derive an accurate orbital solution. Of these,one is a double-lined spectroscopic binary and six were not listed inthe DMSA/O section of the catalogue. Using our solutions, we derive themasses of the components in these systems and statistically analyzethem. We also briefly discuss each system individually.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997) and on data collected with theSimbad database.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| 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.
| The age-mass relation for chromospherically active binaries. III. Lithium depletion in giant components
We present a study of the lithium abundances of a sample of evolvedcomponents of Chromospherically Active Binary Systems. We show that asignificant part of them have lithium excesses, independently of theirmass and evolutionary stage. Therefore, it can be concluded that Liabundance does not depend on age for giant components of CABS. Theseoverabundances appear to be closely related to the stellar rotation, andwe interpret them as a consequence of the transfer of angular momentumfrom the orbit to the rotation as the stars evolve in and off the MainSequence, in a similar way as it happens in the dwarf components of thesame systems and in the Tidally Locked Binaries belonging to the Hyadesand M67. Based on observations collected with the 2.2\,m telescope ofthe German-Spanish Observatorio de Calar Alto (Almeria, Spain), and withthe 2.56\,m Nordic Optical Telescope in the Spanish Observatorio delRoque de los Muchachos of the Instituto de Astrof\'\i sica de Canarias(La Palma, Spain)
| On the rotation-activity correlation for active binary stars
We present an investigation of rotation-activity correlations usingInternational Ultraviolet Explorer (IUE) SWP measurements of the Civemission line at 1550Angstroms for 72 active binary systems. We use astandard stellar evolution code to derive non-empirical Rossby numbers,R_0, for each star in our sample and compare the resulting Civrotation-activity correlation to that found for empirically derivedvalues of the Rossby number and that based on rotation alone. For dwarfstars our values of R_0 do not differ greatly from empirical ones and wefind a corresponding lack of improvement in correlation. Only a marginalimprovement in correlation is found for evolved components in oursample. We discuss possible additional factors, other than rotation orconvection, that may influence the activity levels in active binaries.Our observational data imply, in contrast to the theoretical predictionsof convective motions, that activity is only weakly related to mass inevolved stars. We conclude that current dynamo theory is limited in itsapplication to the study of active stars because of the uncertainty inthe angular velocity-depth profile in stellar interiors and the unknowneffects of binarity and surface gravity.
| Alignment of rotational axes in asynchronous late type binaries
41 RS CVn and BY Dra type binaries with reliable orbital and physicalparameters have been found to rotate asynchronously with the orbitalrevolution. For this sample inclinations of the rotational axes, i_r, ofthe primaries and the orbital inclinations, i_o, are independentlydetermined to test the alignment between the equatorial and the orbitalplanes. The observed difference Delta i=| {i_o} - {i_r}| measures adeviation from coplanarity of these planes. It turns out that mostasynchronous systems prove to be misaligned, especially when theinfluence of the position angle is taken into account. Thus, thegenerally accepted assumption that rotational axes are perpendicular toorbital planes is not valid for asynchronous RS CVn and BY Dra typebinaries. The influence of the position angle of the observer on thederived values of Delta i can be studied only by statistical methods.The distribution of the observed Delta i is compared wih the expectedvalues of Delta i() e for two cases: a) the rotational axes are randomlyinclined to the orbital planes, and b) the rotational axes areperpendicular to the orbital planes. The best fit to our observed sampleof asynchronous binaries is obtained for the case a), while for thesynchronous RS CVn and BY Dra type binaries the rotational axes areperpendicular to their orbital planes. The appendix is available onlyelectronically with the on-line publication athttp://link.springer.de/link/service/journals/00230
| The ROSAT All-Sky Survey of Active Binary Coronae. III. Quiescent Coronal Properties for the BY Draconis--Type Binaries
We present X-ray observations of 35 active late-type BY Draconis dwarfbinary systems and 28 evolved binary systems, similar in nature to theRS Canum Venaticorum systems, obtained with the Position SensitiveProportional Counter (PSPC) during the ROSAT All-Sky Survey phase of themission. Of this sample, 52 targets were detected in exposures ofroughly 600 s or less. When these new data are combined with the earlierresults from Dempsey et al. (1993b), this survey represents the largestsample of active binary systems observed to date at any wavelength,including X-rays. We expand our investigation of how coronal properties(e.g., surface flux, luminosity, etc.) correlate with stellar parameters(e.g., rotation period, color, etc.) and confirm the conclusions ofDempsey et al. (1993b). Rotation period provides the best correlationwith X-ray surface flux with F_{{X}}~P^{-0.59+/-0.10}_{{rot}} for theentire sample. We find no evidence for a "basal" or nonmagnetic X-rayflux component. We model the low-resolution pulse-height spectra for 12systems with two-temperature thermal plasmas. The derived temperaturesfor the BY Dra systems are identical to those previously derived foractive evolved giants and subgiants in close binaries (Dempsey et al.1993c). We also show that the dependence of temperature and emissionmeasures on rotation period is the same for the dwarf, subgiant, andgiant binaries.
| 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. I. Asynchronous Long-Period RS CVn Stars
We show that only 12 out of 27 analyzed binaries have data good enoughfor reliable determination of iorb and irot. In 4systems (out of these 12) assumption about coplanarity of rotationalequatorial plane and orbital plane is justified. In the remaining casesrotational axes are not perpendicular to the orbital planes(non-coplanar case). The commonly accepted assumption about thecoplanarity of rotational and orbital planes should be revised.
| The active dynamo stars: RS CVn, BY Dra, FK Com, Algol, W UMa, and T Tau
Not Available
| A catalog of chromospherically active binary stars (second edition)
The catalog contains 206 spectroscopic binary systems with at least onelate-type component that shows Ca II H and K emission in its spectrum.These systems include the classical RS CVn binaries and BY Dra binaries.The catalog summarizes information on the photometric, spectroscopic,orbital, and physical properties of the systems as well as space motionsand positions. Up to 42 'parameters' for each stellar system are listedfollowed by the appropriate reference to direct interested colleagues tothe original papers. A comprehensive selection of further informationfor each star is given in the individual notes. In addition, the catalogcontains a candidate list of 138 stars that have similar characteristicsbut are not definitely known binaries or have not had Ca II H and Kemission observed.
| Lithium in Rs-Canum Binaries and Related Chromospherically Active Stars - Part Two - Spectrum Synthesis Analysis
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...273..194R&db_key=AST
| Statistical Analysis of a Sample of Spectroscopic Binaries Containing Late Type Giants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&A...271..125B&db_key=AST
| Kinematics and age of RS Canum Venaticorum and by Draconis stars
Space velocities of 146 chromospherically active binary stars have beencalculated. Containing F-M spectral types on the main sequence togetherwith G and K giants and subgiants, this very heterogeneous sample hasbeen divided into groups in order to segregate stars which have similarkinematics and ages. After many trials for different criteria, thesample was divided into five groups - two groups for giants, two groupsfor main-sequence systems, and one group for main-sequence systems.Kinematics of subgiants implies a stellar age of about 2-3 Gyr. Youngand old groups of giants and main-sequence systems could becharacterized by a kinematical age of about 1 Gyr and more than 5 Gyr,respectively. These ages are estimated approximately according to spacevelocity distributions and dispersions in velocity space in each group.Inferred ages for the groups above agrees with circulation, rotationactivity relation, and stellar evolution theories.
| Lithium in RS CVn binaries and related chromospherically active stars. I - Observational results
The present survey of the Li I 6708 A line in a sample of spectral typeG and K stars with luminosity classes III, IV, and V shows that manyK-type stars in the sample, including a large number of RS CVn binaries,show an anomalously high Li abundance relative to typical inactive starsof the same spectral type. Only a few stars in the sample are likely tobe premain sequence objects of stars which have recently arrived on themain sequence. Mechanisms that could lead to the enhanced Li absorptionin chromospherically active stars are discussed; these encompass largecool spots on the stellar surface, the production of Li in stellarflares by spallation reactions, and the evolution from main-sequenceprogenitors without, or with very shallow, outer convective zones.
| The 69th Name-List of Variable Stars
Not Available
| Chromospherically active stars. VII - 39 Ceti = AY Ceti, HD 185151 = V1764 Cygni, and binary synchronization
Improved orbital elements have been determined for 39 Ceti and HD185151.39 Cet has a circular orbit with an orbital period of 56.82 days,which differs substantially from its rotational period of 75-78 days. Anobservation of the lithium region of 39 Cet shows that the G5 IIIcomponent has almost no lithium in its outer atmosphere. HD 185151 has acircular orbit with an orbital period of 40.142 days and has a nearlyidentical rotational period. The large mass function suggests that thesecondary is a late A to mid F type star whose continuum should bevisible at ultraviolet wavelengths. The orbital inclination is estimatedto be 62 + or - 12, while the distance is about 390 pc. Orbital androtational periods are compared for 114 chromospherically activebinaries.
| A catalog of chromospherically active binary stars
A catalog of 168 chromospherically active binary stars is presented,including the class of RS CVn, BY Dra binaries, and other binaries whichshow strong Ca II H and K emission in their spectra. The catalogcontains information on the photometric, spectroscopic, orbital, andphysical properties of the systems as well as the space motions andpositions. Summarized in a candidate list are in additional 37 starshaving similar characteristics but which are not definitely knownbinaries or have not had H and K emission observed. The catalog containsstars in both the northern and the southern sky.
| A microwave survey of southern active stars
The results of a survey of 153 active-chromosphere stars made with theParkes 64-m telescope at 5.0/8.4 GHz from 1981 to 1987 are reported.Microwave emission was detected from 70 stars on at least one occasion,with the highest detection rate of 68 percent from the RS CVn group. TheCa II stars and Algol-type binaries yielded detection rates of 44 and 30percent, respectively. The maximum powers emitted by the stars at5.0/8.4 GHz ranged over five orders of magnitude, with a median of 2.5 x10 to the 10th W/Hz. The maximum brightness temperatures had a smallerrange of three orders of magnitude, with a median of 3.6 x 10 to the 9thK.
| Infrared properties of CP stars
Seventeen chemically peculiar stars of type CP2 and CP4 have beenobserved in the infrared bands J, H, K, L and M. Flux excesses in theM-band, previously reported by Groote and Kaufmann (1983) could not beconfirmed. A detector nonlinearity may be responsible for contradictingobservational results. No indications for dust shells or othercircumstellar matter around CP stars could be found. The photometricvariability in the IR - if present - is smaller than about 0.05magnitudes for the observed stars.
| UBV(RI)c photometry for CaII emission stars. I - Observations at Sutherland
Extensive photometry in the UBV(RI)c system is given for 55 stars withstrong Ca II H and K emission. The UBV observations were made relativeto the standard stars of Lloyd Evans et al. (1983) while the (RI)cobservations were made relative to E-region standards over greaterangular distances. The data are plotted in phase diagrams.
| Radial velocities of calcium emission stars. II - Observations at Mt. Stromlo and Siding Spring Observatories and at Mt. John University Observatory
Radial velocities are presented for 17 bright late-type stars withstrong emission cores in the Ca II H and K lines. Most of the stars arespectroscopic binaries.
| Radial velocities of calcium emission stars. I - Observations at Sutherland
Radial velocities are presented for 53 bright late-type stars withemission in the H and K lines of Ca II, which is indicative of a highlevel of chromospheric activity. Most of the stars are spectroscopicbinaries, for which orbital elements are presented.
| Observations of active stars at 843 MHz
The Molonglo Observatory Synthesis Telescope is being used in ancontinuing program of observation of known Southern active stars. By May1987, a total of 41 stars had been observed, and 843-MHz quiescentemission, presumably associated with the star, had been detected in nineinstances. The emission from five of these stars has shown markedvariation on a time scale over 1 day.
| Local photometric standards for CaII emission stars
UBV data are given for 108 stars which are suitable local standards for52 stars with strong Ca2 emissions. An additional eight stars wererejected as possible standards because of suspected variability.
|
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: | Pictor |
| Ascensió Recta: | 06h07m56.94s |
| Declinació: | -54°26'21.3" |
| Magnitud Aparent: | 7.702 |
| Distancia: | 286.533 parsecs |
| Moviment propi RA: | 6.5 |
| Moviment propi Dec: | 18.4 |
| B-T magnitude: | 8.956 |
| V-T magnitude: | 7.806 |
Catàlegs i designacions:
|
