Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The CCD photometric study of the newly identified RS CVn binary star DV Piscium
This paper presents new CCD BVRI light curves of the newly discovered RSCVn eclipsing binary star DV Psc. From the asymmetric light curvesoutside the eclipse, we find there are two depressions in the phaseranges 0.3-0.45 and 0.6-0.9, respectively. By analyzing thelight curves using the Wilson-Devinney program, the fourphotometric solutions of the system are obtained and the starspotparameters are also derived. It turns out that the case of two spotsbeing on the primary is most successful in reproducing the light curvedistortion of DV Psc. Moreover, analysis the longitudes of spotssuggests that there are two active longitude belts (one is about90°, the other is about 270°). At the same time, on 22 November2008, the first flare-like event was detected on DV Psc at phase 0.35whose duration was about 13.5 min. These findings reveal that DV Psc hasa high degree of magnetic activity.
| Cyclic Variations of Orbital Period and Long-Term Luminosity in Close Binary RT Andromedae
Solutions of standard VR light curves for the eclipsing binary RT Andwere obtained using the PHOEBE program (ver. 0.3a). Absolute parametersof the stellar components were then determined, enabling them to bepositioned on the mass-luminosity diagram. Times of minima data ("O- C curve") were analyzed using the method of Kalimeris et al. Acyclic variation in the orbital period and brightness, with timescalesof about 11.89 and 12.50 yr were found, respectively. This is associatedwith a magnetic activity cycle modulating the orbital period of RT Andvia the Applegate mechanism. To check the consistency of the Applegatemodel, we have estimated some related parameters of the RT And system.The calculated parameters were in accordance with those estimated byApplegate for other similar systems, except B, the subsurface magneticfield of which shows a rather high value for RT And.
| Starspots
Starspots are created by local magnetic fields on the surfaces of stars,just as sunspots. Their fields are strong enough to suppress theoverturning convective motion and thus block or redirect the flow ofenergy from the stellar interior outwards to the surface andconsequently appear as locally cool and therefore dark regions againstan otherwise bright photosphere (Biermann in Astronomische Nachrichten264:361, 1938; Z Astrophysik 25:135, 1948). As such, starspots areobservable tracers of the yet unknown internal dynamo activity and allowa glimpse into the complex internal stellar magnetic field structure.Starspots also enable the precise measurement of stellar rotation whichis among the key ingredients for the expected internal magnetictopology. But whether starspots are just blown-up sunspot analogs, we donot know yet. This article is an attempt to review our current knowledgeof starspots. A comparison of a white-light image of the Sun (G2V, 5Gyr) with a Doppler image of a young solar-like star (EK Draconis;G1.5V, age 100 Myr, rotation 10 × ? Sun) and witha mean-field dynamo simulation suggests that starspots can be ofsignificantly different appearance and cannot be explained with ascaling of the solar model, even for a star of same mass and effectivetemperature. Starspots, their surface location and migration pattern,and their link with the stellar dynamo and its internal energytransport, may have far reaching impact also for our understanding oflow-mass stellar evolution and formation. Emphasis is given in thisreview to their importance as activity tracers in particular in thelight of more and more precise exoplanet detections around solar-like,and therefore likely spotted, host stars.
| SV Gem, ein circumpolares EA-system, gut fur ueberraschungen.
Not Available
| B.R.N.O. Times of minima
Not Available
| High levels of surface differential rotation on the young G0 dwarf HD171488
We present high-resolution images of the young, rapidly rotating G0dwarf HD171488, using both Stokes I and Stokes V data. The observationswere secured with the MuSiCoS spectropolarimeter at Telescope BernardLyot from 2005 May 31 to June 10. The photospheric surface brightnessdistributions show a strong and slightly decentred polar cap thatdominates over weak high- and low-latitude spot features. Thelarge-scale magnetic field topology shows a strong ring of anticlockwiseazimuthal field with a latitudinal dependence on polarity and largeregions of radial field with negative polarity at all latitudes. Usingthe good phase coverage of our data, we measure the differentialrotation on HD171488. The results indicate that the equator laps thepole every 12 days for brightness data and 13 days for magnetic data,which is the highest measurement of differential rotation obtained usingZeeman-Doppler imaging techniques.Spectropolarimetric observations were obtained, from 2005 May 31 to June10, with the MuSiCoS echelle spectropolarimeter at the Telescope BernardLyot (Observatoire du Pic du Midi, France).E-mail: s.v.jeffers@uu.nl
| A catalogue of chromospherically active binary stars (third edition)
The catalogue of chromospherically active binaries (CABs) has beenrevised and updated. With 203 new identifications, the number of CABstars is increased to 409. The catalogue is available in electronicformat where each system has a number of lines (suborders) with a uniqueorder number. The columns contain data of limited numbers of selectedcross references, comments to explain peculiarities and the position ofthe binarity in case it belongs to a multiple system, classicalidentifications (RS Canum Venaticorum, BY Draconis), brightness andcolours, photometric and spectroscopic data, a description of emissionfeatures (CaII H and K, Hα, ultraviolet, infrared),X-ray luminosity, radio flux, physical quantities and orbitalinformation, where each basic entry is referenced so users can go to theoriginal sources.
| Comparative statistics and origin of triple and quadruple stars
The statistics of catalogued quadruple stars consisting of two binaries(hierarchy 2 + 2), is studied in comparison with triple stars, withrespective sample sizes of 81 and 724. Seven representative quadruplesystems are discussed in greater detail. The main conclusions are asfollows. (i) Quadruple systems of ? Lyr type with similar massesand inner periods are common, in 42 per cent of the sample the outermass ratio is above 0.5 and the inner periods differ by less than 10times. (ii) The distributions of the inner periods in triple andquadruple stars are similar and bimodal. The inner mass ratios do notcorrelate with the inner periods. (iii) The statistics of outer periodsand mass ratios in triples and quadruples are different. The medianouter mass ratio in triples is 0.39 independently of the outer period,which has a smooth distribution. In contrast, the outer periods of 25per cent quadruples concentrate in the narrow range from 10 to 100yr,the outer mass ratios of these tight quadruples are above 0.6 and theirtwo inner periods are similar to each other. (iv) The outer and innermass ratios in triple and quadruple stars are not mutually correlated.In 13 per cent of quadruples both inner mass ratios are above 0.85(double twins). (v) The inner and outer orbital angular momenta andperiods in triple and quadruple systems with inner periods above 30dshow some correlation, the ratio of outer-to-inner periods is mostlycomprised between 5 and 104. In the systems with small periodratios the directions of the orbital spins are correlated, while in thesystems with large ratios they are not. The properties of multiple starsdo not correspond to the products of dynamical decay of small clusters,hence the N-body dynamics is not the dominant process of theirformation. On the other hand, rotationally driven (cascade)fragmentation possibly followed by migration of inner and/or outerorbits to shorter periods is a promising scenario to explain the originof triple and quadruple stars.
| On the Period Variations of BH Virginis
In the present work, 17 new times of the light minimum for BHVir werederived from observations by Kjurkchieva etal. (2004, A&A, 424,993). Combining the new determined eclipse times with others compiledfrom the literature, the behavior of their O-C variation wasinvestigated. It has been found that the orbital period of BHVir showssome cyclic variations with three different periods: a long-periodvariation of 51.7years, and two short-period variations of 9.2years and11.8years, respectively. The mechanisms that could explain the periodchanges of the system are discussed.
| Coronae of Young Fast Rotators
AB Dor, Speedy Mic, and Rst 137B are in their early post-T Taurievolutionary phase (<100 Myr), at the age of fastest rotation in thelife of late-type stars. They straddle the coronalsaturation-supersaturation boundary first defined by young stars in openclusters. High-resolution Chandra X-ray spectra have been analyzed tostudy their coronal properties as a function of coronal activityparameters Rossby number, LX/Lbol, and a coronaltemperature index. Differences between stars suggest that assupersaturation is reached the DEM slope below the temperature of peakDEM becomes shallower, while the DEM drop-off above this temperaturebecomes more pronounced. A larger sample comprising our three targetsand 22 active stars studied in the recent literature reveals a generalincrease of plasma at T>~107 K toward thesaturated-supersaturated boundary but a decline beyond this amongsupersaturated stars. The coronal Fe abundances of the stellar sampleare inversely correlated with LX/Lbol, decliningslowly with rising LX/Lbol, but with a much moresharp decline atLX/Lbol>~3×10-4. For dwarfsthe Fe abundance is also well correlated with Rossby number. The coronalO/Fe ratios for dwarfs show a clear increase with decreasing Rossbynumber, apparently reaching saturation at [O/Fe]=0.5 at the coronalsupersaturation boundary.
| New absolute magnitude calibrations for detached binaries
Lutz-Kelker bias corrected absolute magnitude calibrations for thedetached binary systems with main-sequence components are presented. Theabsolute magnitudes of the calibrator stars were derived at intrinsiccolours of Johnson-Cousins and 2MASS (Two Micron All Sky Survey)photometric systems. As for the calibrator stars, 44 detached binarieswere selected from the Hipparcos catalogue, which have relative observedparallax errors smaller than 15% (σπ/π≤0.15).The calibration equations which provide the corrected absolute magnitudefor optical and near-infrared pass bands are valid for wide ranges ofcolours and absolute magnitudes: -0.18<(B-V)0<0.91,-1.6
| Light-curve inversions with truncated least-squares principal components: Tests and application to HD 291095 = V1355 Orionis
We present a new inversion code that reconstructs the stellar surfacespot configuration from the light curve of a rotating star. Our codeemploys a method that uses the truncated least-squares estimation of theinverse problem's objects principal components. We use spot fillingfactors as the unknown objects. Various test cases that represent arapidly-rotating K subgiant are used for the forward problem. Tests arethen performed to recover the artificial input map and include dataerrors and input-parameter errors. We demonstrate the robustness of thesolution to false input parameters like photospheric temperature, spottemperature, gravity, inclination, unspotted brightness and differentspot distributions and we also demonstrate the insensitivity of thesolution to spot latitude. Tests with spots peppered over the entirestellar surface or with phase gaps do not produce fake activelongitudes. The code is then applied to ten years of V and I-band lightcurve data of the spotted sub-giant HD 291095. A total of 22 lightcurves is presented. We find that for most of the time its spots weregrouped around two active longitudes separated on average by 180°.Switches of the dominant active region between these two longitudeslikely occurred about every 3.15±0.23 years while the amplitudemodulation of the brightness occurred with a possible period of3.0±0.15 years. For the first time, we found evidence that thetimes of the activity flips coincide with times of minimum light as wellas minimum photometric amplitude, i.e. maximum spottedness. From acomparison with simultaneous Doppler images we conclude that theactivity flips likely take place near the rotational pole of the star.
| A Mechanism for Orbital Period Modulation and Irregular Orbital Period Variations in Close Binaries
Orbital period modulation is observed in many magnetically active closebinaries. It can be explained by magnetic connection between two stars.Magnetic connection produces weak force between the two stars. As themagnetic field varies periodically, the orbital period also showscyclical variations. The mechanism can also be used to explain irregularorbital period variations and orbital period jumps. The mean surfacemagnetic strength is calculated by using the Radia package, which isdedicated to 3D magnetostatics computation. On the basis of the results,a practical equation is given to calculate surface magnetic strength.
| B.R.N.O. Contributions #34
Not Available
| Spectroscopic and photometric observations of the eclipsing star UV Leo
High-resolution spectroscopic observations around the H? line andBVRI photometry of the eclipsing short-period RS CVn star UV Leo arepresented. The simultaneous light-curve solution and radialvelocity-curve solution led to the following values of the globalparameters of the binary: temperatures T1 = 6000 +/- 100 Kand T2 = 5970 +/- 20 K; masses M1 = 0.976 +/-0.067Msolar and M2 = 0.931 +/-0.052Msolar separation a = 3.716 +/- 0.048Rsolarorbital inclination ; radii R1 = 1.115 +/-0.052Rsolar and R2 = 1.078 +/-0.051Rsolar equatorial velocities V1 = 98.8 +/-2.3kms-1 and V2 = 89.6 +/- 2.7kms-1.These results lead to the conclusion that the two components of UV Leoare slightly oversized for their masses and lie within the main-sequenceband on the mass-radius diagram, close to the isochrone 9 ×1010yr.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Eclipsed X-ray flares in binary stars: geometrical constraints on the flare's location and size
Aims: The observation of eclipses during X-ray flares taking place inactive cool stars binaries allows us to calculate the position and sizeof the flares. This information cannot be derived by analyzing the decayof the flares, a frequently used approach in the literature thatrequires the assumption of a physical model. We make use of theeclipsing light curve to constrain the set of possible solutions, fromthe geometrical point of view, in two flares of Algol, and one flare inVW Cep. Methods: We make use of a technique developed with the systemSV Cam (i˜ 90°) and generalize it to binary systems witharbitrary inclination. The method simulates all possible geometricalsituations that can produce the times of the four contacts of theeclipse. As an approximation we assume that the emitting region has aspherical shape that remains unchanged during the eclipse. We show,however, that this is a good approximation for the problem. Results:The solutions observed indicate that in two of the three cases the flarecannot be polar (|θ| < 55°) and in a third one the flarecan be placed either near the pole or at other latitudes. The emittingregions must have a small size (0.002-0.5 R*), but ifinterpreted as the apex of coronal loops, their length could actually beup to 3.1 R* for one of the Algol flares. These measurementsimply a lower limit to the electron density in the emitting regionbetween log ne (cm-3) 10.4 and 14.0, and amagnetic field between 70 and 3500 G. Similar results are found if theemitting region is assumed to be loop-shaped.Figures 8-12 and 15-18 are only available in electronic form viahttp://www.aanda.org
| The Distribution of Activity on the RS CVn-Type Star SZ Piscium
We use contemporaneous spectra and BV light curves to derive a model ofthe distribution of spots and active regions on the cooler component ofSZ Psc for the 1993-1994 season. For that epoch, both spots and activeregions were visible at all rotational phases of this chromosphericallyactive star. The lack of large distortions of Doppler profiles ofoptical lines argues for >~15 spots with angular radii of<~8°-10°. Transition region emission was constant to within+/-12% over the orbit, nor was it eclipsed appreciably. This leads us toestimate that there are at least 20 active regions, perhaps severalhundred. Chromospheric Mg II emission seems to have been proportional tothe unspotted area of the star, not to the area of spots visible. Wedetected one strong flare in transition region lines during thisprogram. We also present new light-curve and radial velocity solutions.These solutions find the more massive, cool star very close to its Rochelobe, and the hot star rotating more slowly than synchronously, makingSZ Psc an important system for tecent he structure and evolution ofbinary stars. Changes in the radial velocities over 2 years ofsubsequent monitoring show that SZ Psc is a triple system. Hαemission seems independent of phase on the average, but it can increasemarkedly for periods of a few orbital cycles.
| Visual Minima Timings of Eclipsing Binaries Observed in the Years 1992 - 1996
The paper contains a list of 283 new times of minima and 77 revisedtimes of minima for 63 eclipsing binaries derived by the author fromhis visual observations.
| Very Large Array Plus Pie Town Astrometry of 46 Radio Stars
We have used the Very Large Array, linked with the Pie Town Very LongBaseline Array antenna, to determine astrometric positions of 46 radiostars in the International Celestial Reference Frame (ICRF). Positionswere obtained in the ICRF directly through phase referencing of thestars to nearby ICRF quasars whose positions are accurate at the 0.25mas level. Radio star positions are estimated to be accurate at the 10mas level, with position errors approaching a few milliarcseconds forsome of the stars observed. Our measured positions were combined withprevious measurements taken from as early as 1978 to obtainproper-motion estimates for all 46 stars with average uncertainties of~1.7 mas yr-1. We compared our radio star positions andproper motions with the Hipparcos Catalogue data and found consistencyin the reference frames produced by each data set on the 1 σlevel, with errors of ~2.7 mas per axis for the reference frameorientation angles at our mean epoch of 2003.78. No significant spin isfound between our radio data frame and the Hipparcos Celestial ReferenceFrame, with the largest rotation rates of +0.55 and -0.41 masyr-1 around the x- and z-axes, respectively, with 1 σerrors of 0.36 mas yr-1. Thus, our results are consistentwith a nonrotating Hipparcos frame with respect to the ICRF.
| Magnetic activity on AB Doradus: temporal evolution of star-spots and differential rotation from 1988 to 1994.
Surface brightness maps for the young K0 dwarf AB Doradus arereconstructed from archival data sets for epochs spanning 1988 to 1994.By using the signal-to-noise enhancement technique of Least-SquaresDeconvolution, our results show a greatly increased resolution of spotfeatures than obtained in previously published surface brightnessreconstructions. These images show that for the exception of epoch1988.96, the starspot distributions are dominated by a long-lived polarcap, and short-lived low to high latitude features. The fragmented polarcap at epoch 1988.96 could indicate a change in the nature of the dynamoin the star. For the first time we measure differential rotation forepochs with sufficient phase coverage (1992.05, 1993.89, 1994.87). Thesemeasurements show variations on a timescale of at least one year, withthe strongest surface differential rotation ever measured for AB Doroccurring in 1994.86. In conjunction with previous investigations, ourresults represent the first long-term analysis of the temporal evolutionof differential rotation on active stars.
| Aus den IBVS 5721, 5722, 5723, 5724, 5726, 5728, 5729, 5731, 5732 und 5735.
Not Available
| Dynamical evolution of active detached binaries on the logJo-logM diagram and contact binary formation
Orbital angular momentum (OAM, Jo), systemic mass (M) andorbital period (P) distributions of chromospherically active binaries(CAB) and W Ursae Majoris (W UMa) systems were investigated. Thediagrams of and logJo-logM were formed from 119 CAB and 102 WUMa stars. The logJo-logM diagram is found to be mostmeaningful in demonstrating dynamical evolution of binary star orbits. Aslightly curved borderline (contact border) separating the detached andthe contact systems was discovered on the logJo-logM diagram.Since the orbital size (a) and period (P) of binaries are determined bytheir current Jo, M and mass ratio, q, the rates of OAM loss(dlogJo/dt) and mass loss (dlogM/dt) are primary parametersto determine the direction and the speed of the dynamical evolution. Adetached system becomes a contact system if its own dynamical evolutionenables it to pass the contact border on the logJo-logMdiagram. The evolution of q for a mass-losing detached system is unknownunless the mass-loss rate for each component is known. Assuming q isconstant in the first approximation and using the mean decreasing ratesof Jo and M from the kinematical ages of CAB stars, it hasbeen predicted that 11, 23 and 39 per cent of current CAB stars wouldtransform to W UMa systems if their nuclear evolution permits them tolive 2, 4 and 6 Gyr, respectively.
| Active binary stars
Not Available
| The Case for Third Bodies as the Cause of Period Changes in Selected Algol Systems
Many eclipsing binary star systems show long-term variations in theirorbital periods, evident in their O-C (observed minus calculated period)diagrams. With data from the Robotic Optical Transient Search Experiment(ROTSE-I) compiled in the SkyDOT database, New Mexico State University 1m data, and recent American Association of Variable Star Observers(AAVSO) data, we revisit Borkovits and Hegedüs's best-casecandidates for third-body effects in eclipsing binaries: AB And, TV Cas,XX Cep, and AK Her. We also examine the possibility of a third bodyorbiting Y Cam. Our new data support their suggestion that a third bodyis present in all systems except AK Her, as is revealed by thesinusoidal variations of the O-C residuals. Our new data suggest that athird body alone cannot explain the variations seen in the O-C residualsof AK Her. We also provide a table of 143 eclipsing binary systems thathave historical AAVSO O-C data with new values computed from the SkyDOTdatabase.
| New Times of Minima of Some Eclipsing Binary Systems
We present 42 photoelectric minima observations of 24 eclipsingbinaries.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Contact Binaries with Additional Components. II. A Spectroscopic Search for Faint Tertiaries
It is unclear how very close binary stars form, given that during thepre-main-sequence phase the component stars would have been inside eachother. One hypothesis is that they formed farther apart but were broughtin closer after formation by gravitational interaction with a thirdmember of the system. If so, all close binaries should be members oftriple (or higher order) systems. As a test of this prediction, wepresent a search for the signature of third components in archivalspectra of close binaries. In our sample of 75 objects, 23 show evidencefor the presence of a third component, down to a detection limit oftertiary flux contributions of about 0.8% at 5200 Å (consideringonly contact and semidetached binaries, we find 20 out of 66). In ahomogeneous subset of 59 contact binaries, we are fairly confident thatthe 15 tertiaries we have detected are all tertiaries present with massratios 0.28<~M3/M12<~0.75 and implied outerperiods P<~106 days. We find that if the frequency oftertiaries were the same as that of binary companions to solar-typestars, one would expect to detect about 12 tertiaries. In contrast, ifall contact binaries were in triple systems, one would expect about 20.Thus, our results are not conclusive but are sufficiently suggestive towarrant further studies.
| Activity-induced variability in SV Cam, RZ Tau and II Peg in winter 2004/2005
We report on a search for activity-induced variability in two eclipsingsystems SV Cam, RZ Tau and a single lined spectroscopic binary II Peg inthe winter season 2004/2005. The SV Cam system was modelled with twoactivity centers-spots on the primary cooler than the surroundingphotosphere with total spot coverage 20%. On the contrary, the RZTau system (its Roche lobe filling factor of order 0.42) displayssymmetric light curves and no O'Connell effect is detected. The shape ofthe II Peg light curve can not be matched easily with a single spotmodel. Instead, a two spot model (alternatively a non-uniform highlatitude spot complex) cooler than the photosphere can model theobserved light curves with spot coverage 10%.
| Photometric study of the active binary star V1430 Aquilae
New BVR light curves and a photometric analysis of the eclipsing binarystar V1430 Aql are presented. The light curves were obtained at theÇanakkale Onsekiz Mart University Observatory in 2004. The lightcurves are generally those of detached eclipsing binaries, but there arelarge asymmetries between maxima. New BVR light curves were analysedwith an ILOT procedure. Light curve asymmetries of the system wereexplained in terms of large dark starspots on the primary component. Theprimary star shows a long-lived and quasi-poloidal spot distributionwith active longitudes in opposite hemispheres. Absolute parameters ofthe system were derived. We also discuss the evolution of the system:the components are likely to be pre-main sequence stars, but a post-mainsequence stage cannot be ruled out. More observations are needed todecide this point.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Жираф |
| Прямое восхождение: | 06h41m19.08s |
| Склонение: | +82°16'02.4" |
| Видимая звёздная величина: | 9.375 |
| Собственное движение RA: | 41.5 |
| Собственное движение Dec: | -150.9 |
| B-T magnitude: | 10.17 |
| V-T magnitude: | 9.441 |
Каталоги и обозначения:
|
