Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
Random forest automated supervised classification of Hipparcos periodic variable stars
We present an evaluation of the performance of an automatedclassification of the Hipparcos periodic variable stars into 26 types.The sub-sample with the most reliable variability types available in theliterature is used to train supervised algorithms to characterize thetype dependencies on a number of attributes. The most useful attributesevaluated with the random forest methodology include, in decreasingorder of importance, the period, the amplitude, the V-I colour index,the absolute magnitude, the residual around the folded light-curvemodel, the magnitude distribution skewness and the amplitude of thesecond harmonic of the Fourier series model relative to that of thefundamental frequency. Random forests and a multi-stage scheme involvingBayesian network and Gaussian mixture methods lead to statisticallyequivalent results. In standard 10-fold cross-validation (CV)experiments, the rate of correct classification is between 90 and 100per cent, depending on the variability type. The main mis-classificationcases, up to a rate of about 10 per cent, arise due to confusion betweenSPB and ACV blue variables and between eclipsing binaries, ellipsoidalvariables and other variability types. Our training set and thepredicted types for the other Hipparcos periodic stars are availableonline.
| A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun
Traditionally, runaway stars are O- and B-type stars with large peculiarvelocities. We would like to extend this definition to young stars (upto ?50 Myr) of any spectral type and to identify those present in theHipparcos catalogue by applying different selection criteria, such aspeculiar space velocities or peculiar one-dimensional velocities.Runaway stars are important for studying the evolution of multiple starsystems or star clusters, as well as for identifying the origins ofneutron stars. We compile the distances, proper motions, spectral types,luminosity classes, V magnitudes and B-V colours, and we utilizeevolutionary models from different authors to obtain star ages. We studya sample of 7663 young Hipparcos stars within 3 kpc from the Sun. Theradial velocities are obtained from the literature. We investigate thedistributions of the peculiar spatial velocity and the peculiar radialvelocity as well as the peculiar tangential velocity and itsone-dimensional components and we obtain runaway star probabilities foreach star in the sample. In addition, we look for stars that aresituated outside any OB association or OB cluster and the Galactic planeas well as stars for which the velocity vector points away from themedian velocity vector of neighbouring stars or the surrounding local OBassociation/cluster (although the absolute velocity might be small). Wefind a total of 2547 runaway star candidates (with a contamination ofnormal Population I stars of 20 per cent at most). Thus, aftersubtracting these 20 per cent, the runaway frequency among young starsis about 27 per cent. We compile a catalogue of runaway stars, which isavailable via VizieR.
| BAV-Results of observations - Photoelectric minima of selected eclipsing binaries and maxima of pulsating stars.
Not Available
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Masses and luminosities of O- and B-type stars and red supergiants
Massive stars are of interest as progenitors of supernovae, i.e.neutron stars and black holes, which can be sources of gravitationalwaves. Recent population synthesis models can predict neutron star andgravitational wave observations but deal with a fixed supernova rate oran assumed initial mass function for the population of massive stars. Here we investigate those massive stars, which are supernovaprogenitors, i.e. with O- and early B-type stars, and also allsupergiants within 3 kpc. We restrict our sample to those massive starsdetected both in 2MASS and observed by Hipparcos, i.e. only those starswith parallax and precise photometry. To determine the luminositieswe calculated the extinctions from published multi-colour photometry,spectral types, luminosity class, all corrected for multiplicity andrecently revised Hipparcos distances. We use luminosities andtemperatures to estimate the masses and ages of these stars usingdifferent models from different authors. Having estimated theluminosities of all our stars within 3 kpc, in particular for all O- andearly B-type stars, we have determined the median and mean luminositiesfor all spectral types for luminosity classes I, III, and V. Ourluminosity values for supergiants deviate from earlier results: Previouswork generally overestimates distances and luminosities compared to ourdata, this is likely due to Hipparcos parallaxes (generally moreaccurate and larger than previous ground-based data) and the fact thatmany massive stars have recently been resolved into multiples of lowermasses and luminosities. From luminosities and effective temperatureswe derived masses and ages using mass tracks and isochrones fromdifferent authors. From masses and ages we estimated lifetimes andderived a lower limit for the supernova rate of ?20 events/Myraveraged over the next 10 Myr within 600 pc from the sun. These data arethen used to search for areas in the sky with higher likelihood for asupernova or gravitational wave event (like OB associations).
| Synchronization and circularization in early-type binaries on main sequence
We showed in a preceding paper based on an analysis of the observedrates of apsidal motion that synchronization in early-type eclipsingbinaries continues on the main sequence, and the observedsynchronization times, tsyn, agree with the Zahn's theory andare inconsistent with the shorter time-scale proposed by Tassoul. Itfollows from this that circularization in early-type binaries must alsoproceed in accordance with the Zahn's theory because the circularizationtimes, tcirc, in both theories are rather tightly related totsyn via relation tcirc ~?tsyn,where ? is the orbital-to-axial momentum ratio.To further investigate this problem, we compile a catalogue of 101eclipsing binaries with early-type main-sequence components(M1,2 > 1.6Msolar). We determine the ages, t,and circularization time-scales, tcirc, for all these systemsin terms of the two competing theories by comparing observational datawith modern models of stellar evolution of Claret and atmospheric modelsof Kurucz. We compute tcirc with the allowance for theevolutionary variations of the physical parameters of the componentsand, for the first time in such studies, also take into account thevariations of the orbital parameters (P, a, e) in the process ofcircularization subject to the conservation of the total angularmomentum.The results of these computations show that the mechanism of orbitalcircularization in early-type close binary systems (CBSs) suggested byTassoul is, like in the case of synchronization, inconsistent withobservational data. At the same time, the Zahn's mechanism, which isbased on the dissipation of the energy of dynamic tides in the upperlayers of the envelopes of CBSs components due to non-adiabaticity ofthese layers, agrees satisfactorily with observations.
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| BAV-Results of Observations - Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| Recent Minima of 155 Eclipsing Binary Stars
The AAVSO's publication of times of minima for eclipsing binary stars has shifted from the recent publication series, Observed Minima Timings of Eclipsing Binaries, Number 1-12, back to the JAAVSO. Times of minima fromobservations made in the past eight months are presented. New lightelements for AC CMi have been calculated from recent AAVSO observations:Min(JD) = 2451978.7504 + 0.867216691 E± 0.0004 ± 0.00000024
| B.R.N.O. Times of minima
Not Available
| Rapid apsidal motion in eccentric eclipsing binaries: OX Cassiopeia, PV Cassiopeia, and CO Lacertae
Aims.Double-lined eclipsing binaries are a traditional tool to test thecapability of the stellar evolutionary models. If such binaries showapsidal motion, it is also possible to check, in addition to theirabsolute dimensions, some aspects of their internal structure. In orderto perform this additional test, we monitored the times of a minimum ofthree eclipsing binaries with accurate absolute dimensions. Methods:Approximately thirty new precise times of minimum light recorded withCCD photometers were obtained for three early-type eccentric-orbiteclipsing binaries OX Cas (P = 2.49°, e = 0.041), PV Cas (1.75°,0.032), and CO Lac (1.54°, 0.029). O-C diagrams were analyzed by theLacy's method using all reliable timings found in the literature, andthe elements of apsidal motion were improved. On the other hand, stellarmodels computed for the precise observed masses of the three systemswere used as theoretical tools to compare with the observed shift in theperiastron position. Results: We confirm very short periods of apsidalmotion of approximately 38.2, 91.0, and 43.4 years for OX Cas, PV Cas,and CO Lac, respectively. The relativistic effects are negligible, beingup to 6% of the total apsidal motion rate in all systems. Thecorresponding observed apsidal motion rates are in good agreement withthe theoretical predictions, except for the case of PV Cas, whosecomponents seem to be more mass concentrated than the models predict.
| Programmsterne: Beobachtungen erwuenscht.
Not Available
| Spectroscopic solution of the star QX Cas
High-resolution spectroscopic observations around the H? line ofthe binary star QX Cas covering the whole orbital period are presented.Our radial velocity solution, the first ever determined, requires aneccentric orbit with the following orbital parameters: eccentricity, e =0.22 +/- 0.01; longitude of periastron, ? = 45° +/- 5°semi-amplitudes of the radial velocity curves of the primary andsecondary stars, K1 sini = 125.8 +/- 0.9kms-1 andK2 sini = 144.8 +/- 1.1kms-1 gamma velocity,V0 = 65.1 +/- 0.5kms-1 and mass ratio, q = 0.869+/- 0.013. The corresponding lower limits of the masses of thecomponents and their separation are , and a sini = 31.34 +/-0.48Rsolar.
| Determination of the axial rotation rate using apsidal motion for early-type eclipsing binaries
Because the modern theory of stellar structure and evolution has a soundobservational basis, we can consider that the apsidal parametersk2 computed in terms of this theory correctly reflect theradial density distribution in stars of different masses and spectraltypes. This allows us to address the problem of apsidal motion in closebinary systems in a new way. Unlike the traditional approach, in thispaper we use the observed apsidal periods Uobs to estimatethe angular axial velocities of components, ωr, atfixed model values of k2. We use this approach to analyse theobservational data for 28 eclipsing systems with known Uobsand early-type primaries (M >= 1.6 Msolar or Te>= 6000 K). We measure the age of the system in units of thesynchronization time, t/tsyn.Our analysis yielded the following results. (i) There is a clearcorrelation between ωr/ωsyn andt/tsyn: the younger a star, the higher the angular velocityof its axial rotation in units of ωsyn, the angularvelocity at pseudo-synchronization. This correlation is more significantand obvious if the synchronization time, tsyn, is computed interms of the Zahn theory. (ii) This observational fact implies that thesynchronization of early-type components in close binary systemscontinues on the main sequence. The synchronization times for the innerlayers of the components (i.e. those that are responsible for apsidalmotion) are about 1.6 and 3.1 dex longer than those predicted by thetheories of Zahn and Tassoul, respectively. The average initial angularvelocities (for the zero-age main sequence) are equal toω0/ωsyn ~ 2.0. The dependence of theparameter E2 on stellar mass probably needs to be refined inthe Zahn theory. (iii) Some components of the eclipsing systems of thesample studied show radially differential axial rotation. This isconsistent with the Zahn theory, which predicts that the synchronizationstarts at the surface, where radiative damping of dynamical tidesoccurs, and develops toward the interior. Therefore, one would expectthe inner parts of young double early-type stars to rotate faster thanthe outer parts.
| B.R.N.O. Contributions #34
Not Available
| A new catalogue of eclipsing binary stars with eccentric orbits
A new catalogue of eclipsing binary stars with eccentric orbits ispresented. The catalogue lists the physical parameters (includingapsidal motion parameters) of 124 eclipsing binaries with eccentricorbits. In addition, the catalogue also contains a list of 150 candidatesystems, about which not much is known at present.Full version of the catalogue is available online (see the SupplementaryMaterial section at the end of this paper) and in electronic form at theCDS via http://cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/MNRAS/(vol)/ (page)E-mail: ibulut@comu.edu.tr
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| New Times of Minima of Eclipsing Binary Systems and of Maximum of SXPHE Type Stars
We present 64 photoelectric minima observations of 31 eclipsingbinaries. We also report three new times of maxima of three SXPHE typepulsating stars.
| 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.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| X-Ray Counterparts of Runaway Stars
An X-ray search for possible compact companions of runaway OB stars hasbeen conducted using pointed ROSAT observations. Of a list of 71 runawaystars, ROSAT exposures were available for 24, of which 13 are detected.These numbers are nearly 3 times larger than for a previously studiedEinstein sample, and spectral information is exploited as well.Luminosities, hardness ratios, and long-term variability are as fornormal OB stars and do not suggest the presence of collapsed companions.A result like this is often interpreted as support for dynamicalejection from a dense group rather than a supernova event in a binary asa production process for runaway stars. There are, however, severalcircumstances that may adversely affect the observability of a compactcompanion, or after a supernova explosion systems may be disruptedbecause of the large natal kick velocity imparted to the neutron star asa result of asymmetries in the explosions. It is noted that there isactually evidence for both of these production routes and that they maybe expected to occur sequentially in the evolution of OB associations.
| Photoelectric Minima of Selected Eclipsing Binaries
Not Available
| Photoelectric Minimum Times of Some Eclipsing Binary Stars
We present 20 minima times of 8 eclipsing binaries.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| CCD Minima for Selected Eclipsing Binaries in 2002
Not Available
| Zur qualitat der visuellen Beobachtung kurzperiodisch Veranderlicher.
Not Available
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
Kataloglar ve belirtme:
|
INHABITED SKY
