Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| A comprehensive study of the SX Phoenicis star BL Camelopardalis
Context.BL Cam is an extreme field multiperiodic short-periodlow-metallicity high-amplitude SX Phe-type variable where its probablycomplex pulsational content is subject of controversies. Aims.Acomprehensive study has been carried out to investigate the nature andpulsational properties of this object. Methods.The analysis isbased on new photometric data collected during the last few years atdifferent sites, as well as on all available previously published data.Frequency analyses have been performed on a number of reliable data setsto analyse the pulsational content. In addition, the classical O-Cmethod was used to study the behaviour of the main period. Results.Our frequency analysis confirms some aspects on themultiperiodicity of BL Cam, previously found by other authors, showing anumber of secondary modes close to the main frequency f_0=25.5769cd-1. The secondary modes present eventual amplitudevariations. However, the main frequency exhibits no significant changesin its amplitude and seems to correspond to the fundamental mode ofradial pulsation. Abrupt changes sometimes observed in the light curvescould be due to spurious activity on or close to the star's photosphere.We confirm the existence of a secondary frequency at 31.6 or 32.6cd-1, with variable amplitude, and with the possibility ofboth frequencies being intrinsic to the star. More than one hundred ofnew times of light maxima have been determined in the present work.These together with those available in the literature allow us a morediscriminating analysis of the O-C diagram. This shows that the observedvariations of the main period can be described by two terms: (i) asecular increase of the main period at a rate ofdP/Pdt=117(±3)×10-9 yr-1; and (ii) aperturbation from a companion star in a rather eccentric orbit with aperiod of 10.5(±0.2) yr causing a light time semi-amplitude of148(±12) s.
| 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.
| Pulsational behaviour of the SX Phe variable BL Cam.
The pulsational behaviour of the field high-amplitude SX Phe variable BLCam is investigated here on the basis of new photometric data collectedduring the last few years at different sites together with a revision ofall the available photometric data sets in the literature. Our resultsconfirm the existence of multiperiodicity in this star previously foundby other authors. In addition to the main frequency f_0=25.5769 c/d andits harmonics 2f_0 and 3f_0, with stable amplitude, a secondaryfrequency f_1 exists in the region 31-32 c/d with variable amplitude.Microvariability takes also place in this star, in the region close tof_0, with some additional secondary peaks shown as significant togetherwith some frequency combinations of these modes with f_0.Concerning f_1,it is shown that there is a possibility of the existence of twoindependent peaks (around 31.6 c/d and 32.6 c/d), nonradial and withvariable amplitudes.
| Binarity and multiperiodicity in high-amplitude delta Scuti stars .
We present our first results for a sample of southern high-amplitudedelta Scuti stars (HADS), based on a spectrophotometric survey startedin 2003. For CY Aqr and AD CMi, we found very stable light and radialvelocity (RV) curves; we confirmed the double-mode nature of ZZ Mic, BQInd and RY Lep. Finally, we detected gamma -velocity changes in RS Gruand RY Lep.
| Pulsational behaviour of the HADS RY Lep
RY Lep is a long-period High Amplitude Delta Sct-type pulsator (V=8.21,DeltaV=0.35) with a main period of 0.2254d (Diethelm 1985). This starwas assumed to be monoperiodic with stable light curves for a long time.However, some disturbances have recently been discovered by Laney et al.(2002). New observations were collected at Sierra Nevada Observatory(SNO), Spain, with simultaneous uvby photometry, from 1998 to 2002, butonly the two data sets collected in 1998 and 2002 are good enough toperform individual Fourier analyses. Additional VJHK data were collectedat South African Astronomical Observatory (SAAO), South Africa, duringthe same epoch.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| delta Sct-type nature of the variable V2109 Cyg
We present the results of simultaneous uvbybeta photometry carried outfrom 1999 to 2001 of the variable V2109 Cyg together with aspectroscopic analysis based on one high resolution spectrum obtained in2000. From this study, the star is definitively classified as an evolveddelta Sct-type variable with solar metal abundances. This conclusion isalso supported by the detected multiperiodic pulsational behaviour andthe observed variation of the m1 index over the pulsationcycle. This variation is slightly reversed relative to the V lightcurve, in very good agreement with the m1 variation expectedfrom the photometric calibrations. Besides the main frequencyf1=5.3745 cd-1 and its first harmonic2f1, a secondary peak is found at f2=5.8332cd-1 (f1/f2=0.92) with f1identified as a radial mode and f2 as non-radial. Whereas nosignificant variations are found in the amplitude of f1 fromseason to season, the amplitude of f2 changes strongly.Moreover, the main period has remained constant since 1990, within theobservational uncertainties. Additional secondary frequencies may alsobe excited in this variable.Based on observations collected at the Sierra Nevada, San PedroMártir and Haute-Provence observatories.Tables 2, 5 and 7 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi -bin/qcat?J/A+A/407/1059
| A search for period changes in delta Scuti stars with the super-LOTIS sky patrol system
We have observed a sample of delta Scuti stars discovered by the ROTSEcollaboration in 1999 with Super-LOTIS in order to characterize changesin their pulsation periods over a time baseline of roughly three years.Achieving these goals required the creation of an automated astrometricand photometric data reduction pipeline for the Super-LOTIS camera.Applying this pipeline to data from a June 2002 observing campaign, wedetect pulsations in 18 objects, and find that in two cases the periodshave changed significantly over the three years between the ROTSE andSuper-LOTIS observations. Since theory predicts that evolutionary periodchanges should be quite small, sources of non-evolutionary periodchanges due to the interactions of pulsations modes are discussed.
| Variable stars in the Tycho photometric observations. I. Detection
We present an original way to detect variable stars in the Tychophotometric observations. A modified Kolmogorov-Smirnov statistical testhas been constructed, based on a model of most of the satellite'sparameters, leading to the dispersion in the measurements. This allowsus to build a treatment taking into account truncated detections andcensored measurements, and to search for variability in the faint partof the catalogue. The selection threshold of variable stars has beencalibrated to minimize false alarm rate. Reliable results were thusobtained for stars as faint as 11 mag. One thousand and ninety-onesuspected variable stars have been listed, 407 of which are alreadyknown in Hipparcos, GCVS or NSV, and 684 of which are suspected variablestars to be identified soon.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Preliminary Baade-Wesselink Radii Solutions for Several Dwarf Cepheids
It has been shown (Laney 1995) that VJHK photometry when combined withradial velocities leads to improved Baade-Wesselink radii solutions forCepheids. Preliminary results indicate the same method can be applied todwarf Cepheids (also known as High-Amplitude Delta Scuti stars). Ourobservations obtained at the South African Astrophysical Observatoryinclude echelle spectroscopy with simultaneous visual and infraredphotometry. This procedure helps remove phase discrepancies andstrengthen the radius solution. Initial results for BS Aqr, AD CMi, RYLep, and EH Lib are presented. Special thanks to SAAO for the observingtime, support from the American Astronomical Society through a smallresearch grant, and continued funding from the Department of Physics andAstronomy at Brigham Young University.
| A revised catalogue of delta Sct stars
An extensive and up-dated list of delta Sct stars is presented here.More than 500 papers, published during the last few years, have beenrevised and 341 new variables have been added to our last list, sixyears ago. This catalogue is intended to be a comprehensive review onthe observational characteristics of all the delta Sct stars known untilnow, including stars contained in earlier catalogues together with othernew discovered variables, covering information published until January2000. In summary, 636 variables, 1149 references and 182 individualnotes are presented in this new list. Tables 1 and 2 will be accessibleonly in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Luminosities of SX Phoenicis, Large-Amplitude Delta Scuti, and RR Lyrae Stars
Strömgren _uvbyβ photometry of SX Phoenicis andlarge-amplitude δ Scuti variables is analyzed to determine themean temperatures, metal abundances, and surface gravities of the stars.The mean temperatures and fundamental periods are used in conjunctionwith the pulsation equation and stellar models to derive masses, radii,surface gravities, and M_bol of the variables. The stars exhibit aperiod-luminosity relation. With the aid of Hipparcos trigonometricparallaxes the zero-point of the M_v, p is set. We find M_v = -3.725 logP - 1.933. This P-L relation is utilized to find the M-v values of RRLyrae stars or horizontal-branch stars in globular clusters and theCarina galaxy-objects that contain both SX Phe, and RR Lyrae variables,or horizontal-branch stars. The M_v values of the metal-poor RR Lyraestars are found to be consistent with M_v [Fe/H] calibrations derived bySandage (1993) and by McNamara (1997) from revised Baade- Wesselink M_vvalues. At [Fe/H] = -1.9 M_v is 0.42. Feast and Catchpole (1997)suggestion that M_v = 0.25 at [Fe/H] = -1.9 for RR Lyrae is discussed.This M_v value is too luminous because it makes the (T_eff) of RR Lyraestoo high-well off any (T_eff) = _f (color index) calibration. (SECTION:Stars)
| Structural Properties of Pulsating Star Light Curves Through Fuzzy Divisive Hierarchical Clustering
Not Available
| Pulsation in high amplitude delta Scuti stars.
It has been pointed out by earlier authors that radial pulsation seemsto be the only type present in high amplitude δ Sct stars, atleast for monoperiodic stars. In order to confirm this or not, we havecollected all the multicolor data available for these stars in theStroemgren and Johnson photometric systems. Then, the type of pulsationhas been analysed on the basis of the phase shifts and amplitude ratiosbetween observed light and colour variations. The results indicate thatall the stars analysed, including both high amplitude δ Sct(Population I) and SX Phe (Population II) stars, are radial pulsators.This is also true for the monoperiodic medium amplitude δ Sctstars analysed.
| Photometric study of RS Gru and RY Lep
Simultaneous uv bybeta photometric observations of the high-amplitudedelta Sct-type stars RS Gru and RY Lep have been collected and new timesof light maxima have been obtained. Using the classical O-C method, itis found that the pulsation of RS Gru can be well described by means ofa quadratic ephemeris with the period decreasing at a rate ofdP/Pdt=-10.6(+/-0.8)10^-8 yr^-1 over more than 30 yr. Intrinsic b-y, m_1and c_1 values are derived and the physical parameters of these twostars are determined.
| Period-Finding Methods, Techniques and Applications to Variable Stars Observations
The problem of finding periods of variable stars is considered and it'smain methods are generally reviewed. Special attention has been devotedto three methods based on Fourier transform. These methods have beencoded in Fortran and have been applied to data of three eclipsingbinaries (AD Cnc, UZ Pup and? Per), three? Scuti stars (HR1170, HR 1223 and RY Lep) and one spectroscopic binary (RS Sag). Themethods have been tested, compared and evaluated concerning their speed,resolution and sensitivity. It has been found that data exhibitingirregular variations lead to erroneous periods. To save computing timeand to avoid any spurious period a practical procedure for periodfinding is proposed with an effective approach for period refinement.The revised and refined periods for the above stated variables have beendiscussed with comparison to the ones given in literatures and they canbe adopted for future work. Some of these variables have been found toshow variations in both their periods and amplitudes.
| A catalogue of variable stars in the lower instability strip.
Identifications, positions, photometry, spectra, some pulsationalfeatures, other astrophysical parameters and literature for 302pulsating variable stars in the lower instability strip, near the ZAMS,are given. About 185 stars have near homogeneous photometric informationin the Stroemgren's uvby-β photometric system. Thiscatalogue/database covers information published until November 1993.
| δ Scuti stars: a new revised list
An extensive and up to date list of δ Sct stars is presented. Thiscatalogue is intended to be a comprehensive review of observationalcharacteristics of all the δ Sct stars known until now, includingstars contained in earlier catalogues together with other new discoveredvariables, covering information published until November 1993. Globalinformation in the form of histograms and diagrams are also shown.
| The m(1)-index curve in pulsating stars
We have carried out a systematic study of the behavior of the Delta-m(1)metallicity parameter for SX Phe and high amplitude Delta Sct(pop. I)stars. It is shown that it has a different behavior for the two samplesof stars. The Delta-m(1) parameter increases (SX Phe) or decreases(Delta Sct) towards minimum light for these two types of variables.Moreover, the m(1)-index variation is larger when the metal abundance ofthe star is smaller. An analogous effect is found in, other photometricindices.
| Comparison between standard evolution models for high amplitude ? Sct stars.
Recent ubvy? observations of high amplitude ? Sct starsobtained at Sierra Nevada (Spain) and La Silla (Chile) observatories arecompared with standard evolution models. The authors find very goodagreement between Claret et al. model's (1989) and those from VandenBerg (1985). However, a systematic effect on the derived masses is foundif one uses the Hejlesen's results as indicated by previous work byAndersen et al. (1984). The results derived from the evolution modelsare compared with those derived from pulsation theory. A good agreementis found.
| Internal consistency test about ?m1 metallicity index for SX Phe and high amplitude ? Sct stars.
The authors have carried out a systematic study of the behaviour of the?m1 metallicity index for SX Phe and high amplitude? Sct stars. It is shown to be different for the two samples ofstars. The ?m1 parameter increases or decreases towardsthe minimum light for the first or second sample, respectively. Them1 index variation is larger when the metal abundance of thestar is smaller.
| Modal discrimination of pulsating stars by using Stromgren photometry
New observations of Delta Scuti pulsating stars in the Stromgrenphotometric system are used for model identification of theiroscillation periods. It is found that all the observed stars are radialpulsators. A new technique is outlined to calculate both the phasedifference between temperature and radius variations together with theiramplitude variation ratio.
| Phase shifts between colours in pulsating stars
Observational evidence is presented showing that the time of maximumlight for pulsating stars depends on observed wavelength. This fact iswell explained by assuming that starlight variations comets from bothtemperature and gravity variations. Conversely, from the time shiftsbetween two colors, temperature and gravity variations can be derived,together with the phase lag between them.
| The SX Phe stars
A systematic photometry study of SX Phe stars together with highamplitude Delta Sct stars has been carried out. The uvby-beta indicesare obtained and the physical parameters are determined. The resultsobtained by using the pulsation and evolution theories independently arecompared. A good agreement is found.
| Empirical P-L-C relation for Delta Scuti stars - A catalogue
An extensive and up-to-date list of 192 Delta Scuti stars is presented.Empirical period - luminosity - color (P-L-C) relations are obtained forthe four lowest modes corresponding to radial pulsations. Agreement withpredicted values indicates that, in general, both Stroemgren photometriccalibration and pulsation theory work well for these stars.
| Quasi-160-minute oscillation period of Delta Scuti stars
The resonance power spectrum (or commensurability spectrum) computed for217 Delta Scuti stars indicates that the dominant (most commensurate)period for the total set of oscillation periods of these stars is 162.2+ or - 2.8 min. Within the error limits, this period coincidesapproximately with the 160-min period of global oscillations of the sun.
| Fourier decomposition of the light curves of high amplitude Delta Scuti and SX Phe stars
The light curves of monoperiodic, high amplitude ? Scuti and SXPhe stars have been Fourier decomposed in order to study theirstructural properties. The computed phase differences show a trend toincrease with the period similar to the trend observed in short periodCepheids and RR Lyrae stars. There is some evidence of a separation ofthe light curves in two groups, which indicates the presence of twotypes of pulsation. The proposed separation is discussed taking alsointo account the amplitude-amplitude diagrams, and some comparisons withRR Lyrae star light curves are made. For the present there are noevident physical differences between the stars in the two groups whichcan explain the separation.
| RY Leporis - A bright, high-amplitude delta Scuti star
Walraven VBLUW photometry is reported for the variable RY Leporis (alsoknown as HD 38882, BV 425, and 0545-200 from its Epoch 1950coordinates). It is shown that this star - until now considered to be aneclipsing binary - is actually a relatively bright high-amplitude deltaScuti star with a period of 0.2254 day and an amplitude of delta V-sub-J= 0.35 magnitude in the Johnson system. After an evaluation of thereddening suffered by Ry Leporis (0.038 plus or minus 0.01), the basicphysical parameters of this variable are determined from asemi-theoretical calibration of the colors of the Walraven system. Acomparison is made of the physical characteristics of RY Leporis withobservational parameters of similar variables and with theoreticalcalculations. The results support the 'high-mass' interpretation oflarge-amplitude delta Scuti stars.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Заяц |
| Прямое восхождение: | 05h48m10.26s |
| Склонение: | -20°01'25.0" |
| Видимая звёздная величина: | 8.262 |
| Расстояние: | 159.49 парсек |
| Собственное движение RA: | 0.6 |
| Собственное движение Dec: | 22.9 |
| B-T magnitude: | 8.67 |
| V-T magnitude: | 8.296 |
Каталоги и обозначения:
|
