내용
사진
사진 업로드
DSS Images Other Images
관련 글
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.
| 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.
| 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.
| Ten CORAVEL spectroscopic binary orbits of evolved stars
On the basis of Coravel observations, we present orbital parameters for10 spectroscopic-binary systems including an evolved star, namely HD13530, HD 28591, HD 47415, HD 78414, HD 123999, HD 153751, HD 174881, HD179094, HD 212280 and HD 217188. The most significant result is relatedto HD 13530, for which we have found an orbital period of 1575.48+/-1.63days and an eccentricity of 0.8815. Such an eccentricity value is thelargest one known up to date for a single-lined spectroscopic binarywith a giant component. The other spectroscopic orbits described in thispaper principally confirm with independent data previously obtainedorbital solutions except HD 179094 for which the double-lined status wasstill unknown. Based on observations collected at the Haute-ProvenceObservatory, Saint-Michel, France and at ESO, La Silla, Chile.
| 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
| Observations of active-chromosphere stars - IV. Photometry and spectroscopy of CF Octantis (HD 196818)
We present photometry and spectroscopy of the single, K-type,active-chromosphere star CF Octantis (=HD 196818), from 1982 to 1986.The photometric data show the 20-d rotation period seen previously, andalso demonstrate that the light curve is variable on time-scales of afew months, which we ascribe to variations in the properties ofstarspots. We postulate that a temporary dimming of minimum light seenin mid-1983 was a result of the appearance and later disappearance of arelatively small spot or spot group, which had a lifetime between 10 and24 months. The main spot appeared relatively stable during the intervalof our observations, with a lifetime of at least 3 years. Our radialvelocity data are consistent with the results of other work in that novariations above observational scatter are seen. Both the Ca K andHα emission are variable, with tentative evidence for the latterthat a lower emission level occurred near the phase of photometricmaximum, although the spectroscopic and photometric data were notcontemporaneous. The lithium abundance is found to be logN(Li)=0.45+/-0.15. The star may have evolved from a rapidly rotating A-Fmain-sequence star.
| 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.
| HD 12545, A Study in Spottedness
We have solved two sets of light curves of HD 12545 at its epoch ofextreme spottedness in 1990-91, one of which coincides with anindependent set analyzed recently by Strassmeier and Olah. Even for thehuge amplitudes observed, these light-curve solutions did not givereliable determinations of several important spot properties.Specifically, we find that we could obtain acceptable solutions for awide range of inclination; that spot temperature depends on inclinationassumed, falling in the range Delta-T = T_star - T_spot = 650-1200 K forinclinations of 70-30 deg; that spot latitudes derived from the lightcurves are unreliable; and that our independent spot solutions disagreewith Strassmeier and Olah's. On a more positive note, changes in thelight curve over the past five years seem to have been caused primarilyby rearrangement of persisting spot groups, and we note that the highlevel of activity implied by its H-alpha emission, makes HD 12545 aprime candidate for a white-light flare star. (SECTION: Stars)
| Starspot evolution, differential rotation, and magnetic cycles in the chromospherically active binaries lambda andromedae, sigma Geminorum, II Pegasi, and V711 Tauri
We have analyzed 15-19 yr of photoelectric photometry, obtained manuallyand with automated telescopes, of the chromospherically active binarieslambda And, sigma Gem, II Peg, and V711 Tau. These observations let usidentify individual dark starspots on the stellar surfaces from periodicdimming of the starlight, follow the evolution of these spots, andsearch for long-term cyclic changes in the properties of these starspotsthat might reveal magnetic cycles analogous to the Sun's 11 yr sunspotcycle. We developed a computer code to fit a simple two-spot model toour observed light curves that allows us to extract the most easilydeterminable and most reliable spot parameters from the light curves,i.e., spot longitudes and radii. We then used these measured propertiesto identify individual spots and to chart their life histories byconstructing migration and amplitude curves. We identified and followed11 spots in lambda And, 16 in sigma Gem, 12 in II Peg, and 15 in V711Tau. Lifetimes of individual spots ranged from a few months to longerthan 6 yr. Differential rotation coefficients, estimated from theobserved range of spot rotation periods for each star and defined byequation (2), were 0.04 for lambda And, 0.038 for sigma Gem, 0.005 forII Peg, and 0.006 for V711 Tau, versus 0.19 for the Sun. We searched forcyclic changes in mean brightness, B-V color index, and spot rotationperiod as evidence for long-term cycles. Of these, long-term variabilityin mean brightness appears to offer the best evidence for such cycles inthese four stars. Cycles of 11.1 yr for lambda And, 8.5 yr for sigmaGem, 11 yr for II Peg, and 16 yr V711 Tau are implied by these meanbrightness changes. Cyclic changes in spot rotation period were found inlambda And and possibly II Peg. Errors in B-V were too large for anylong-term changes to be detectable.
| 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.
| Chromospherically active stars. X - Spectroscopy and photometry of HD 212280
The system HD 212280 is a chromospherically active double linedspectroscopic binary with an orbital period of 45.284 days and aneccentricity of 0.50. The spectrum is composite with spectral types ofG8 IV and F5-8 V for the components. An estimated inclination of 78 +/-8 deg results in masses of 1.7 and 1.4 solar mass for the G subgiant andmid-F star, respectively. The distance to the system is estimated to be112 pc. Photometric observations obtained between 1987 November and 1992June reveal that HD 212280 is a newly identified variable star with a Vamplitude of about 0.15 mag and a mean period of 29.46 days. Our V datawere divided into 11 sets and in all but one case two spots wererequired to fit the data. Lifetimes of 650 days and a minimum of 1350days have been determined for two of the four spots. The differentialrotation coefficient of 0.05 is relatively small. The age of the systemis about 1.9 X 10 exp 9 yrs. The G subgiant is rotating slower thanpseudosynchronously while the F-type star is rotating faster.
| The 71st Name-List of Variable Stars
Not Available
| 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.
| 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 survey of chromospherically active stars
Photometric and/or spectroscopic observations have been obtained of 52late-type stars which are suspected or known to be chromosphericallyactive. Although not all types of observations were obtained for eachstar, these observations include all-sky BVRI Johnson photometry,ultraviolet spectrograms, low-dispersion blue-wavelength spectrograms,and high-dispersion red-wavelength spectrograms. From the spectroscopicobservations v sin i's, radial velocities, and the appearance of the CaII H and K emission lines have been determined as well as the H-alphaline. The photometric observations indicate that chromosphericallyactive stars have V - R and V - I color excesses. Such excesses willaffect the surface fluxes determined with the surface brightness-colorrelationship. On the other hand all-sky BVRI photometry appears to be anexcellent way to identify chromospherically active stars. A small groupof moderately rapidly rotating, possibly single G8-K2 giants has beenfound. These stars have very modest chromospheric activity and so arenot FK comae stars. A number of other unusual chromospherically activestars are identified.
| Automatic Photoelectric Telescope: Second and Third Quarter 1984 Observations
Not Available
| Objective-prism discoveries in the northern sky. I
Attention is given to 175 northern hemisphere stars whose newlyrecognized peculiar, or otherwise prepossessing characteristics havebeen noted in a preliminary inspection of moderate dispersion objectiveprism plates. The plates were obtained with a 10-deg prism. The starlist gives HD or BD, alpha and delta values, magnitude, and type.
| Photoelectric photometry of selected AG stars in the 25D to 30D zone.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968AJ.....73..187B&db_key=AST
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
