Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Modelling eclipsing binaries with pulsating components: Phase dependence of observed pulsation amplitudes
We investigate the phase dependence of the light variations due topulsations, as modulated with light variations due to the eclipses. Thestudy is based, both on a simplified model and on the rigorous lightcurve (LC) synthesis software of Wilson and Devinney. We model AB Cas asa prototype, using both of these approaches. The phase dependence of thedifferential light variations for total systems is also discussed .
| 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.
| Veraenderliche fuer den kleinen Feldstecher.
Not Available
| Strichspuraufnahmen zur Veraenderlichenbeobachtung.
Not Available
| Beta Lyr - eigentlich ein ideales Objekt auch fuer CCD.
Not Available
| MERLIN Astrometry of 11 Radio Stars
We report accurate positions in the International Celestial ReferenceFrame (ICRF) for 11 radio stars. Observations were made using theMulti-Element Radio Linked Interferometer Network at a radio frequencyof 5 GHz. The positions are estimated to be accurate at the 5 mas level.Positions were obtained directly in the ICRF by phase referencing theradio stars to ICRF quasars whose positions are estimated to be accurateat the 0.25 mas level. We use our results together with results ofprevious observations to obtain proper-motion estimates for these stars.The average proper-motion uncertainties are 1.1 mas yr-1 inμαcosδ and 1.2 mas yr-1 inμδ, comparable to the Hipparcos values.
| Indirect imaging of an accretion disk rim in the long-period interacting binary W Crucis
Context: .Light curves of the long-period Algols are known for theircomplex shape (asymmetry in the eclipse, light variations outside theeclipse, changes from cycle-to-cycle), but their interpretation is notpossible in the standard model of binary stars. Aims: . Wedetermined that complex structures present in these active Algol systemscould be studied with the eclipse-mapping method that was successfullyapplied to the new 7-color photometric observations in the Geneva systemof W Cru, belonging to the isolated group of these active Algols.Methods: . Several cycles of this long-period (198.5 days) eclipsingbinary were covered by observations. We used a modified Rutten'sapproach to the eclipse-mapping. The optimization of the system'sparameters and the recovery of the disk intensity distribution areperformed using a genetic algorithm (GA). Results: .The finding ofa primary (hot) component is hidden in thick accretion disk confirmsprevious solutions. The mass of the primary component, M1 =8.2 Mȯ, indicates that it is a mid-B type star. Themass-losing component fills its critical lobe, which, for the system'sparameters, means it is a G-type supergiant with a mass M2 =1.6 Mȯ. The disk is very extended geometrically, and itsouter radius is about 80% of the primary's critical lobe. Areconstructed image reveals the rather clumpy and nonuniform brightnessdistribution of an accretion disk rim in this system that is seen almostedge-on. This clumpiness accounts for light curve distortions andasymmetries, as well as for secular changes.
| Antoine Darquier et la decouverte de la nebuleuse de la Lyre.
Not Available
| Caroline Herschel as observer
Not Available
| Zur Beobachtung und Auswertung von Cepheiden-Lichtkurven.
Not Available
| Bericht uber die Veranderlichen-Beobachtungswoche an der VdS-Sternwarte in Kirchheim.
Not Available
| Infrared Photometry for Five Close Binary Systems
We present the JHKLM photometry for five close (W Ser) binary systemsobtained in the period 1996 2004. Positive phase shifts (with respect ofthe adopted ephemerides) have been found in the orbital infrared lightcurves for three binaries, RX Cas, KX And, and β Lyr; the rates ofincrease in their periods are 3.5 × 10-4, 1.6 ×10-3, and 1.4 × 10-4 days yr-1, respectively. We haveperformed the spectral classification of the components of the binariesunder study and estimated their parameters.
| Polarimetric Study of the Massive Interacting Binary W Serpentis: Discovery of High-Latitude Scattering Spot/Jet
We present multicolor (UBVRI) polarimetry and additional B-band CCDpolarimetry of the peculiar, strongly interacting binary W Ser, withgood coverage over the 14.16 day orbital period in the three observingseasons 2001-2003. An interesting finding is that the first harmonicdominates in polarization variations over the binary cycle in eachseason, indicating that the main contribution to the polarized flux iscoming from a localized region away from the orbital plane. We apply ournew model codes for electron scattering in circumstellar matter tointerpret the data and find that a ``spot or jet'' like region atlatitude φ~65deg has clearly the best signal-to-noiseratio (>30) among the detected scattering components. Significantshell and stream components are also found, but no disk is seen in thepolarized light. The upper limits for the total number of free electronsin an optically thin scattering disk are an order of magnitude lowerthan in the spherical shell around the primary star. A possible reasonis that the accretion disk is optically thick and has a clearly definedand visible pseudophotosphere. Multiple scattering and absorptioneffects in an optically thick regime reduce the polarization of theobserved light to small levels. Scattering from optically thin parts ofthe circumstellar matter, the shell, the stream, and the high-latitudespot/jet, possibly associated with optically thin polar regions of theaccretion disk, dominates in the observed polarization of W Ser.
| Evolution of Close Binary Systems
We collect data on the masses, radii, etc., of three classes of closebinary stars: low-temperature contact binaries (LTCBs), near-contactbinaries (NCBs), and detached close binaries (DCBs). We restrictourselves to systems in which (1) both components are, at leastarguably, near the main sequence, (2) the periods are less than a day,and (3) there is both spectroscopic and photometric analysis leading toreasonably reliable data. We discuss the possible evolutionaryconnections between these three classes, emphasizing the roles played bymass loss and angular momentum loss in rapidly rotating cool stars. Wedescribe a new mechanism, differential rotation as observed in the Sun,which can explain the remarkable efficiency of heat transport in theouter envelopes of contact binaries.
| Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| On the detection of chemically peculiar stars using Δa photometry
We have summarized all Δ a measurements for galactic field stars(1474 objects) from the literature published over more than two decades.These measurements were, for the first time, compiled and homogeneouslyanalyzed. The Δ a intermediate band photometric system samples thedepth of the 5200 Å flux depression by comparing the flux at thecenter with the adjacent regions with bandwidths of 110 Å to 230Å. Because it was slightly modified over the last three decades,we checked for systematic trends for the different measurements butfound no correlations whatsoever. The Δ a photometric system ismost suitable to detecting magnetic chemically peculiar (CP) stars withhigh efficiency, but is also capable of detecting a small percentage ofnon-magnetic CP objects. Furthermore, the groups of (metal-weak)λ Bootis, as well as classical Be/shell stars, can besuccessfully investigated. In addition, we also analyzed the behaviourof supergiants (luminosity class I and II). On the basis of apparentnormal type objects, the correlation of the 3σ significance limitand the percentage of positive detection for all groups was derived. Wecompared the capability of the Δ a photometric system with theΔ (V1 - G) and Z indices of the Geneva 7-color system to detectpeculiar objects. Both photometric systems show the same efficiency forthe detection of CP and λ Bootis stars, while the indices in theGeneva system are even more efficient at detecting Be/shell objects. Onthe basis of this statistical analysis it is possible to derive theincidence of CP stars in galactic open cluster and extragalactic systemsincluding the former unknown bias of undetected objects. This isespecially important in order to make a sound statistical analysis ofthe correlation between the occurrence of these objects andastrophysical parameters such as the age, metallicity, and strength ofglobal, as well as local, magnetic fields.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| A catalog of stellar magnetic rotational phase curves
Magnetized stars usually exhibit periodic variations of the effective(longitudinal) magnetic field Be caused by their rotation. Wepresent a catalog of magnetic rotational phase curves, Be vs.the rotational phase φ, and tables of their parameters for 136stars on the main sequence and above it. Phase curves were obtained bythe least squares fitting of sine wave or double wave functions to theavailable Be measurements, which were compiled from theexisting literature. Most of the catalogued objects are chemicallypeculiar A and B type stars (127 stars). For some stars we also improvedor determined periods of their rotation. We discuss the distribution ofparameters describing magnetic rotational phase curves in our sample.All tables and Appendix A are only available in electronic form athttp://www.edpsciences.org
| The Impact of Space Experiments on our Knowledge of the Physics of the Universe
With the advent of space experiments it was demonstrated that cosmicsources emit energy practically across all the electromagnetic spectrumvia different physical processes. Several physical quantities givewitness to these processes which usually are not stationary; thosephysical observable quantities are then generally variable. Thereforesimultaneous multifrequency observations are strictly necessary in orderto understand the actual behaviour of cosmic sources. Space experimentshave opened practically all the electromagnetic windows on the Universe.A discussion of the most important results coming from multifrequencyphotonic astrophysics experiments will provide new inputs for theadvance of the knowledge of the physics, very often in its more extremeconditions. A multitude of high quality data across practically thewhole electromagnetic spectrum came at the scientific community'sdisposal a few years after the beginning of the Space Era. With thesedata we are attempting to explain the physics governing the Universeand, moreover, its origin, which has been and still is a matter of thegreatest curiosity for humanity. In this paper we will try to describethe last steps of the investigation born with the advent of spaceexperiments, to note upon the most important results and open problemsstill existing, and to comment upon the perspectives we can reasonablyexpect. Once the idea of this paper was well accepted by ourselves, wehad the problem of how to plan the exposition. Indeed, the exposition ofthe results can be made in different ways, following several points ofview, according to: - a division in diffuse and discrete sources; -different classes of cosmic sources; - different spectral ranges, whichimplies in turn a sub-classification in accordance with differenttechniques of observations; - different physical emission mechanisms ofelectromagnetic radiation; - different vehicles used for launching theexperiments (aircraft, balloons, rockets, satellites, observatories). Inorder to exhaustively present The Impact of Space Experiments on ourKnowledge of the Physics of the Universe it would then have beennecessary to write a kind of Encyclopaedia of the Astronomical SpaceResearch, which is not our desire. On the contrary, since our goal is toprovide an useful tool for the reader who has not specialized in spaceastrophysics and for the students, we decided to write this paper in theform of a review, the length of which can be still consideredreasonable, taking into account the complexity of the argumentsdiscussed. Because of the impossibility of realizing a complete pictureof the physics governing the Universe, we were obliged to select how toproceed, the subjects to be discussed the more or the less, or those tobe rejected. Because this work was born in the Ph.D. thesis of one of us(LSG) (Sabau-Graziati, 1990) we decided to follow the `astronomicaltradition' used there, namely: the spectral energy ranges. Although suchenergy ranges do not determine physical objects (even if in many casessuch ranges are used to define the sources as: radio, infrared, optical,ultraviolet, X-ray, γ-ray emitters), they do determine themethods of study, and from the technical point of view they define thetechnology employed in the relative experiments. However, since then wehave decided to avoid a deep description of the experiments, satellites,and observatories, simply to grant a preference to the physical results,rather than to technologies, however fundamental for obtaining thoseresults. The exposition, after an introduction (Section 1) and somecrucial results from space astronomy (Section 2), has been focussed intothree parts: the physics of the diffuse cosmic sources deduced fromspace experiments (Section 3), the physics of cosmic rays from ground-and space-based experiments (Section 4), and the physics of discretecosmic sources deduced from space experiments (Section 5). In this firstpart of the paper we have used the logic of describing the main resultsobtained in different energy ranges, which in turn characterize theexperiments on board space vehicles. Within each energy range we havediscussed the contributions to the knowledge of various kind of cosmicsources coming from different experiments. And this part is mainlyderived by the bulk of the introductory part of LSG's Ph.D. thesis. Inthe second part of the paper, starting from Section 6, we have preferredto discuss several classes of cosmic sources independently of the energyranges, mainly focussing the results from a multifrequency point ofview, making a preference for the knowledge of the physics governing thewhole class. This was decided also because of the multitude of new spaceexperiments launched in the last fifteen years, which would haverendered almost impossible a discussion of the results divided intoenergy ranges without weakening the construction of the entire puzzle.We do not pretend to cover every aspect of every subject consideredunder the heading of the physics of the universe. Instead a crosssection of essays on historical, modern, and philosophical topics areoffered and combined with personal views into tricks of the spaceastrophysics trade. The reader is, then, invited to accept this papereven though it obviously lacks completeness and the arguments discussedare certainly biased by a selection effect owed essentially to ourknowledge, and to it being of a reasonable length. Some parts of itcould seem, in certain sense, to belong to an older paper, in which the`news' is not reported. But this is owed to our own choice, just in fullaccord with the goals of the text: we want to present those resultswhich have, in our opinion, been really important, in the development ofthe science. These impacting results do not necessarily constitute thelast news. This text was formally closed just on the day of the launchof the INTEGRAL satellite: October 17, 2002. After that date onlyfinishing touches have been added.
| Photometric Studies of the Near-Contact Binary AX Draconis
We have obtained CCD photometric observations of the near-contact binaryAX Dra during two observing seasons from 2001 March through May and from2003 April and May. From these measurements, the seasonal light curvesof AX Dra for 2001 and 2003 were compiled, and a total of 13 new timingsof minimum light were calculated. An analysis of the resulting O-Cdiagram reveals evidence for a periodic change with a semiamplitude of0.0061 days and a period of 56.1 yr, but this conclusion dependsentirely on the photographic plate estimates around 1960. Our lightcurves display the conventional O'Connell effect and small-scaleyear-to-year light variability. If these light variations are producedby a stellar spot, a cool-model spot on the secondary star satisfiesboth seasonal light curves quite well. The same representation appliesto the only other published photoelectric light curves.
| Astrophysics in 2003
Five coherent sections appear this year, addressing solar physics,cosmology (with WMAP highlights), gamma-ray bursters (and theirassociation with Type Ia supernovae), extra-solar-system planets, andthe formation and evolution of galaxies (from reionization to assemblageof Local Group galaxies). There are also eight incoherent sections thatdeal with other topics in stellar, galactic, and planetary astronomy andthe people who study them.
| A new method for probing the atmospheres of transiting exoplanets
Although atmospheric transmission spectroscopy of HD 209458b with theHubble Space Telescope has been very successful, so far no atmosphericabsorption features have been detected from the ground. Here we presenta new method for probing the atmospheres of transiting exoplanets whichmay be more suitable for ground-based observations, making use of theRossiter effect. During a transit, an exoplanet sequentially blocks offlight from the approaching and receding parts of the rotating star,causing an artificial radial velocity wobble. The amplitude of thissignal is directly proportional to the effective size of the transitingobject, and the wavelength dependence of this effect can revealatmospheric absorption features, in a similar way as with transmissionspectroscopy. The advantage of this method over conventional atmospherictransmission spectroscopy is that it does not rely on accuratephotometric comparisons of observations on and off transit, but insteaddepends on the relative velocity shifts of individual stellar absorptionlines within the same on-transit spectra. We used an archival data setfrom the UV-Visual Echelle Spectrograph on the Very Large Telescope toapply this method to HD 209458. The amplitude of the Rossiter effect isshown to be 1.7+1.1-1.2 m s-1 higher inthe Sodium D lines than in the weighted average of all other absorptionlines in the observed wavelength range, corresponding to an increment of4.3 +/- 3 per cent (1.4σ). The uncertainty in this measurementcompares to a photometric accuracy of 5 × 10-4 forconventional atmospheric transmission spectroscopy, more than an orderof magnitude higher than previous attempts using ground-basedtelescopes. Observations specifically designed for this method couldincrease the accuracy further by a factor of 2-3.
| The BAA Observers' Workshops: Observing eclipsing variables: a beginners' guide
The General Catalogue of Variable Stars (GCVS)1 lists many differentclasses of variable star. Some of these are well known and contain manymembers; others are more obscure and contain only a few examples.However, it is also possible to split variable stars into just two basiccategories: the intrinsic variables ? stars like Mira variables, Cepheidvariables, novae and supernovae ? in which the stars themselves arevarying in brightness, and the extrinsic variables, in which theindividual stars themselves do not actually vary, and prominent amongthese are the eclipsing variables.
| The physical properties of normal A stars
Designating a star as of A-type is a result of spectral classification.After separating the peculiar stars from those deemed to be normal usingthe results of a century of stellar astrophysical wisdom, I define thephysical properties of the "normal" stars. The hotter A stars haveatmospheres almost in radiative equilibrium. In the A stars convectivemotions can be found which increase in strength as the temperaturedecreases.
| RR Lyrae Sterne und ihre Bahnen in der Galaxis.
Not Available
| Wer beobachtet mit: AH Virginis.
Not Available
| Beobachtungsergebnisse Bundesdeutsche Arbeitsgemeinschaft fur Veranderlichen Serne e.V.
Not Available
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| Catalogue of Algol type binary stars
A catalogue of (411) Algol-type (semi-detached) binary stars ispresented in the form of five separate tables of information. Thecatalogue has developed from an earlier version by including more recentinformation and an improved layout. A sixth table lists (1872) candidateAlgols, about which fewer details are known at present. Some issuesrelating to the classification and interpretation of Algol-like binariesare also discussed.Catalogue is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/417/263
| WWW Database of Variable Star Fourier Coefficients
Fourier coefficients are a valuable tool in the study of a wide varietyof pulsating stars. In the case of RR Lyrae stars they, can be used toestimate various physical parameters, such as mass, luminosity,metallicity, and effective temperature. They are frequently used todiscriminate between different pulsation modes for both RR Lyrae starsand Cepheids. Fourier coefficients have been published for stars basedon many different photometric systems as well as for radial velocitymeasurements. With the release of coefficients from large-scale surveysand the availability of these data on the Internet, the number ofFourier coefficients available for study has significantly increased,and it is difficult to obtain all available data for individual stars ora given subset of stars. To assist researchers in obtaining and makinguse of Fourier coefficients, an on-line archive of published values ofFourier coefficients has been established. Users can search the databaseusing a variety of tools, and the data sets extend beyond the Milky Wayto include extragalactic variables. The archive is located at the Website http://nitro9.earth.uni.edu/fourier/.
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Calgi |
| Sað Açýklýk: | 18h50m04.80s |
| Yükselim: | +33°21'46.0" |
| Görünürdeki Parlaklýk: | 3.45 |
| Uzaklýk: | 270.27 parsek |
| özdevim Sað Açýklýk: | 1 |
| özdevim Yükselim: | -4.1 |
| B-T magnitude: | 3.682 |
| V-T magnitude: | 3.631 |
Kataloglar ve belirtme:
|
