Contents
Images
Upload your image
DSS Images Other Images
Related articles
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
| Binarity and multiperiodicity in high-amplitude ? Scuti stars
We have carried out a photometric and spectroscopic survey of brighthigh-amplitude ? Scuti (HADS) stars. The aim was to detectbinarity and multiperiodicity (or both) in order to explore thepossibility of combining binary star astrophysics with stellaroscillations. Here, we present the first results for 10, predominantlysouthern, HADS variables. We detected the orbital motion of RS Gru witha semi-amplitude of ~6.5 kms-1 and 11.5 d period. Thecompanion is inferred to be a low-mass dwarf star in a close orbitaround RS Gru. We found multiperiodicity in RY Lep from both photometricand radial velocity data and detected orbital motion in the radialvelocities with hints of a possible period of 500-700 d. The data alsorevealed that the amplitude of the secondary frequency is variable onthe time-scale of a few years, whereas the dominant mode is stable.Radial velocities of AD CMi revealed cycle-to-cycle variations, whichmight be due to non-radial pulsations. We confirmed the multiperiodicnature of BQ Ind, while we obtained the first radial velocity curves ofZZ Mic and BE Lyn. The radial velocity curve and the O-C diagram of CYAqr are consistent with the long-period binary hypothesis. We took newtime series photometry on XX Cyg, DY Her and DY Peg, with which weupdated their O-C diagrams.
| The first high-amplitude ? Scuti star in an eclipsing binary system
We report the discovery of the first high-amplitude ? Scuti starin an eclipsing binary, which we have designated UNSW-V-500. The systemis an Algol-type semi-detached eclipsing binary of maximum brightness V= 12.52 mag. A best-fitting solution to the binary light curve and tworadial velocity curves is derived using the Wilson-Devinney code. Weidentify a late-A spectral-type primary component of mass 1.49 +/-0.02Msolar and a late-K spectral-type secondary of mass 0.33+/- 0.02Msolar, with an inclination of , and a period of5.3504751 +/- 0.0000006 d. A Fourier analysis of the residuals from thissolution is performed using PERIOD04 to investigate the ? Scutipulsations. We detect a single pulsation frequency of f1 =13.621 +/- 0.015 cd-1, and it appears that this is the firstovertone radial mode frequency. This system provides the firstopportunity to measure the dynamical mass for a star of this variabletype; previously, masses have been derived from stellar evolution andpulsation models.
| 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.
| The Radius and Absolute Magnitude of the Dwarf Cepheid RS Gruis
The dwarf Cepheid RS Gruis is shown to be a monoperiodic, high amplitudeDelta Scuti variable star. We present high quality radial velocityobservations that conclusively demonstrate that RS Gru is aspectroscopic binary with an orbital period of approximately two weeks.These radial velocities have been combined with visual and IR photometryto produce a reasonable Baade-Wesselink solution. The radius andabsolute magnitude that we determine are consistent with the previouswork we have done in establishing observational PR and PL relations forthis class of variable stars.
| 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 photometric monitoring of bright high-amplitude delta Scuti stars. I. The double-mode pulsation of V567 Ophiuchi
We present the first results of an observational project, whichaddresses the period changing behaviour of a sample of high-amplitudedelta Scuti stars. In this paper we discuss the double-mode nature ofV567 Ophiuchi. It was observed on 15 nights in two consecutive years inorder to resolve the long-standing ambiguity related to its secondaryperiod. A frequency analysis of almost 5000 individual single-filteredCCD V measurements resulted in two independent frequencies(f1=6.6879 d-1 and f2=11.8266d-1) with a ratio of f1/f2=0.565.Earlier data taken from the literature were used to refine the dominantperiod, and the re-analysis supports the existence of the secondaryperiod. Possible asteroseismological implications are briefly 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.
| Linear Nonadiabatic Properties of SX Phoenicis Variables
We present a detailed linear, nonadiabatic pulsational scenario foroscillating blue stragglers (BSs)/SX Phe variables in Galactic globularclusters (GGCs) and in Local Group (LG) dwarf galaxies. The sequences ofmodels were constructed by adopting a wide range of input parameters andproperly cover the region of the H-R diagram in which these objects areexpected to be pulsationally unstable. Current calculations togetherwith more metal-rich models already presented by Gilliland et al.suggest that the pulsation properties of SX Phe variables are partiallyaffected by metal content. In fact, the pulsation periods for the firstthree modes are marginally affected when moving from Z=0.0001 to 0.006,whereas the hot edges of the instability region move toward coolereffective temperatures by approximately 300-500 K. The inclusion of ametallicity term in the period-luminosity-color (P-L-C) relations causesa substantial decrease in the intrinsic scatter and in the individualerror of the coefficients. This supports the result recently brought outby Petersen & Christensen-Dalsgaard for δ Scuti stars.Moreover, we find that the discrepancy between our relation and similartheoretical and empirical relations available in the literature istypically smaller than 5%. The comparison between theory andobservations in the MV-logP plane as well as in theluminosity amplitude-logP plane does not help to disentangle thelong-standing problem of mode identification among SX Phe stars.However, our calculations suggest that the secular period change seemsto be a good observable to identify the pulsation mode of cooler SX Phevariables. Together with the previous models we also constructed newsequences of models by adopting selected effective temperatures andluminosities along two evolutionary tracks characterized by the samemass value and metal content (M/Msolar=1.2, Z=0.001) butdifferent He contents in the envelope, namely, Y=0.23 and 0.30. The Hecontent in the latter track was artificially enhanced soon after thecentral H exhaustion to mimic, with a crude approximation, thecollisional merging between two stars. Interestingly enough, we findthat the He-enhanced models present an increase in the pulsation periodand a decrease in the total kinetic energy of the order of 20% whencompared with the canonical ones. At the same time, the blue edge of thefundamental mode for the He-enhanced models is approximately 1000 Kcooler than for canonical ones. Moreover, we find that the secularperiod change for He-enhanced models is approximately a factor of 2larger than for canonical ones. According to this evidence, we suggestthat the pulsation properties of SX Phe variables can be soundly adoptedto constrain the evolutionary history of BSs and in turn to single outthe physical mechanisms that trigger their formation.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| 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.
| 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
| Identification of Variable Stars in Grus
Not Available
| Mode identification and asteroseismology of delta Scuti stars
The use of multicolour photometry for mode identification in pulsatingstars is discussed. We present a new, statistically based, algorithm forfinding the best estimate of the spherical harmonic degree, and aconfidence level from which the uniqueness can be ascertained. Themethod is applied to some well-observed delta Sct stars with multicolourphotometry. We also propose an algorithm to deduce the effectivetemperature, luminosity and equatorial velocity from the observedfrequencies. We find that fixing the modes of at least some frequenciesis essential for a unique solution. The method is applied to a subset ofthe delta Sct stars which have a suitable number of frequencies and modeidentifications.
| Mode and period changes in pulsating stars near the main sequence : delta Scuti stars.
Not Available
| The delta Scuti Star GSC 2985-01044
GSC 2985-01044 is a delta Scuti star with a period of 0.0933584 days anda V-magnitude range of 11.85-12.05 its light curve is slightly variable.The location, space motion, and other properties of this star indicatethat it is a higher amplitude delta Scuti star (or ``dwarf Cepheid'')that is a member of the old disk population. The problem of determiningthe local space densities of the various populations of the higheramplitude delta Scuti stars is discussed.
| Period changes of delta Scuti stars and stellar evolution
Period changes of delta Scuti stars have been collected or redeterminedfrom the available observations and are compared with values computedfrom evolutionary models with and without convective core overshooting.For the radial pulsators of Pop. I, the observations indicate (1/P)dP/dt values around 10(-7) year(-1) with equal distribution betweenperiod increases and decreases. The evolutionary models, on the otherhand, predict that the vast majority should show increasing periods.This increase should be a factor of about ten times smaller thanobserved. For nonradial delta Scuti pulsators of Pop. I, thediscrepancies are even larger. The behavior suggests that for theserelatively unevolved stars the rate of evolution cannot be deduced fromthe period changes. The period changes of most Pop. II delta Scuti (SXPhe) stars are characterized by sudden jumps of the order of Delta P/P ~10(-6) . However, at least one star, BL Cam, shows a large, continuousperiod increase. The variety of observed behavior also seems to excludean evolutionary origin of the changes. Model calculations show that theevolutionary period changes of pre-MS delta Scuti stars are a factor of10 to 100 larger than those of MS stars. Detailed studies of selectedpre-MS delta Scuti stars are suggested.
| HIPPARCOS parallaxes and period-luminosity relations of high-amplitude delta Scuti stars
Hipparcos parallaxes of high-amplitude delta Scuti stars are used toderive a period-luminosity relation with a scatter of about +/-0.1 mag,which is independent from photometric calibrations to absoluteluminosities. Comparisons with several P-L relations from the literatureshow satisfactory agreement, and all deviations from the Hipparcos meanrelation can be explained by uncertainties in the data available beforeHipparcos. Hipparcos data for a few stars of relatively small anduncertain parallaxes indicate that they may have systematically very lowluminosity. However, briefly discussing Lutz-Kelker corrections andconsidering the full sample of high-amplitude delta Scuti stars, it isconcluded that this sample is homogeneous and has similar basic physicalproperties as the ``normal'' low-amplitude delta Scuti stars. It isemphasized that the Hipparcos P-L relation defines a new distance scalewhich is independent from those of the classical Cepheids and RR Lyraestars. Therefore, observations of high-amplitude delta Scuti stars canbe used to check fundamental distance determinations to e.g. globularclusters, the Galactic bulge and the Magellanic Clouds.
| HIPPARCOS Parallaxes and Distances of High-Amplitude δ Scuti Stars
Not Available
| 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)
| Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.
The absolute magnitudes of δ Scuti stars derived from parallaxesmeasured by the Hipparcos astrometric satellite are discussed andcompared with the previous estimates based on photometric uvbyβindices. There are significant differences which are related tophotometric effects of metallicity and rotational velocity, but thepossible effect of a close companion on the measured apparent magnitudeshould be also taken into account. The possibility of differentgroupings of δ Scuti stars based on the absolute magnitudes isbriefly discussed. Some high amplitude δ Scuti stars withintermediate or normal metallicity and small and uncertain parallax haveapparently a very low luminosity; this could be a systematic effectrelated to the observational errors.
| The HIPPARCOS Mission
Not Available
| HIPPARCOS parallaxes and the nature of δ Scuti stars.
Hipparcos parallaxes give new tests of the nature of δ Sctvariables. For many individual stars accurate distances are nowavailable, i.e. directly determined luminosities and radii can be usedto test theoretical models. Of particular interest are the at presentvery unclear relations between high-amplitude δ Sct stars and themuch more abundant low-amplitude δ Sct variables, and therelations between field variables and the SX Phe stars in globularclusters. Only a few high-amplitude variables have Hipparcos parallaxessufficiently accurate to provide precise model tests. Here we give adiscussion of this group, considering SX Phoenicis and AI Velorum, whichhave the best parallaxes among the high-amplitude stars, in some detail.It is shown that two new tests based on the improved parallaxes are ingood agreement with the (generally accepted) assumption that thehigh-amplitude variables are normal stars following standard evolution.AD Canis Minoris may be an interesting exception with strongly deviatingproperties. We briefly comment on globular cluster variables andperiod-luminosity relations.
| 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 changes and evolution in the lower part of the Instability Strip.
Observed period changes in SX Phe and Population I high amplitude deltaSct stars have been collected and compared with those expected fromdifferent stellar evolutionary tracks inside the Lower Instability Stripincluding modern evolution models using the new opacities by Rogers& Iglesias (???) and Kurucz (???).
| 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.
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Kranich |
| Right ascension: | 21h43m04.22s |
| Declination: | -48°11'22.2" |
| Apparent magnitude: | 8.265 |
| Distance: | 226.244 parsecs |
| Proper motion RA: | -70.3 |
| Proper motion Dec: | -20.4 |
| B-T magnitude: | 8.587 |
| V-T magnitude: | 8.292 |
Catalogs and designations:
|
