Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Photoelectric Minima of Selected Eclipsing Binaries and Maxima of Pulsating Stars
Not Available
| The double-mode nature of the HADS star GSC 00144-03031 and the Petersen diagram of the class
The double-mode pulsation of GSC 00144-03031 has been detected whensearching for COROT targets. A very large dataset composed of 4722photometric measurements was collected at six observatories in Europeand America. There is no hint of the excitation of additional modes(down to 0.6 mmag) and therefore GSC 00144-03031 seems to be a puredouble-mode pulsator, with a very short fundamental radial mode (P = 84min). From uvbyβ photometry and evolutionary tracks it appears tobe a Pop. I star with M = 1.75 Mȯ, located in the middleof the instability strip, close to the Zero-Age Main Sequence. We alsodiscovered other new double-mode pulsators in the databases oflarge-scale projects: OGLE BW2_V142, OGLE BW1_V207, ASAS3 094303-1707.3,ASAS3 000116-6037.0, NSVS 3234596 and NSVS 3324715. An observationalPetersen diagram is presented and explained by means of new models. Acommon sequence connecting Pop. I stars from the shortest to the longestperiods is proposed and the spreads in the period ratios are ascribed todifferent metallicities (at the shortest periods) and to differentmasses (at the longest ones).
| 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
| New H-alpha emission stars towards the galactic bulg
This paper is dealing with the investigation of H-alpha emission starstowards the galactic bulge. In this important region 533 H-alphaemission stars have already been discovered. We add 98 new and 9possible new (perhaps identical with known objects) H-alpha emissionstars found in the objective-prism survey of planetary nebulae and wegive the identification charts, the accurate coordinates as well as arough description. The distribution in l, b of all objects shows theexpected concentration towards the galactic equator with the maximumnear l=0o and b=0o distorted probably due tostrong interstellar extinction.Based on observations collected at the European Southern Observatory atLa Silla (Chile).
| TOPS Telescope Projects on Variable Stars and Other Objects
Teachers and high school students who attended the University ofHawaii's "Toward Other Planetary Systems" workshop in June 2002 gavepresentations on introductory telescope projects on lunar photography,variable stars, and Messier Objects at the AAVSO 91st Spring meeting inJuly 2002. Other participants discussed advanced projects on photometry,CCDs, and spectroscopy. Former student participants presented thediscovery of a new variable star and an on-going remote observingproject utilizing the Lowell Observatory 31-inch telescope. Thesevarious projects are described and/or summarized.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| 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 spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| V802 Aquilae and V854 Scorpii : Two Neglected High Amplitude delta Scuti Stars
To test the observational limits of the David Derrick Telescope in theOrson Pratt Observatory at Brigham Young University a number of faint,southern, high amplitude δ Scuti stars were observed. These starsranged in declination from -03 to -32 and in V magnitude from 7.5 to14.5. The stars used for this test were HY Librae, V976 Scorpii, V703Scorpii, V802 Aquilae, and V854 Scorpii. Results from two of thesestars, V802 Aql and V854 Sco, will be presented. Early reductions seemto indicate that V802 Aql is not a member of the HADS group.
| 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
| 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.
| HIPPARCOS Parallaxes and Distances of High-Amplitude δ Scuti Stars
Not Available
| 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.
| The HIPPARCOS Mission
Not Available
| Time-Series Ensemble Photometry of SX Phoenicis Stars. I. BL Camelopardalis
We present an analysis of the multiperiodic SX Phoenicis star BLCamelopardalis (GD 428). Along with 24 times of maximum light fromarchival data, six previously unpublished times of maximum light fromphotomultiplier observations and 39 new CCD observations of maximumlight are reported. The new CCD observations indicate that BL Cam is adouble-mode variable with a primary period of 0.0391 day, a secondaryperiod of 0.0306 day, and a $\pi1$/ $\pi0$ ratioof 0.783. The relation between metallicity and period ratio for largeamplitude $\delta$ Scuti variables is examined in detail. Finally,evidence is presented that the fundamental period $\pi0$ hasincreased by 0.009 seconds in the last 20 years. (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.
| 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.
| Pulsation models of δ Scuti variables. I. The high-amplitude double-mode stars.
The relations between high-amplitude δ Scuti stars and the muchmore abundant low-amplitude δ Sct variables are not clear. Bothgroups have similar periods and seem to have almost the same basicphysical properties, although their light-curve characteristics are verydifferent. In the last few years much improved observational data havebeen published, and improved theoretical physics - in particular the newOPAL/OP opacities - now allows much more accurate calculations oftheoretical evolution models including the normal-mode pulsationfrequencies. We here use new series of stellar envelope models to givecalibrations of the first overtone-to-fundamental mode and thesecond-to-first overtone period ratios in terms of the primary modelparameters: metal content and mass-luminosity relation. Effects of thesecondary model parameters: hydrogen content, position within theinstability strip and assumed efficiency of convection are also studiedin detail, and shown to be small. These results combined with pulsationanalysis of new stellar evolution models are applied to discuss theavailable information for double-mode high-amplitude δ Sct stars.We conclude that observed period ratios and positions in the HR-diagramare in agreement with the assumption that these variables are normalstars following standard evolution. Observational data for SX Phoenicisand AI Velorum are compared with theoretical evolution sequences. It isshown that the photometry and the observed two periods of SX Pheconstrain the metal content to Z=0.001, the mass to 1.0 solar masses andthe bolometric magnitude to about 2.70mag. The inferred distance of SXPhe gives a parallax of 0.012+/-0.002arcsec compared with that of theHIPPARCOS Input Catalogue of 0.023+/-0.008arcsec. For AI Vel theavailable photometry and the two primary observed periods do not providea unique solution. Models based on OPAL opacities allow Z=0.01-0.02 withcorresponding masses 1.6-2.0 solar masses. This can be understood by thecompensating effects from Z and the mass-luminosity relation in thecalibration of the period ratio. It is suggested that the surprisinglynarrow interval in the first overtone-to-fundamental mode period ratioobserved in the double-mode δ Sct stars may be due to thesecompensating effects. Attempting to fit low-amplitude modes observed inAI Vel in addition to the primary oscillations, it is concluded that thepresent models cannot explain these oscillations in terms of radialmodes. The little understood relations between high- and low-amplitudeδ Sct stars are briefly discussed, and the problem of modeidentification is emphasized.
| 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.
| Post-main-sequence and POST red giant branch variables with pulsation periods less than one day
Post-main-sequence (mass 1 to 3 solar masses) and post-giant branch (0.5to 1 solar mass) pulsators are discussed on the basis of four color andH beta light curves published elsewhere. The post-main-sequencevariables, called ultrashort period cepheid (USPC) (delta Sct), pulsatein the fundamental and first harmonic modes of radial pulsation and, inmany cases, in nonradial modes. The variables for which photometryallows accurate, luminosity estimates and are known to pulsatesimultaneously in the fundamental and first harmonic or in thefundamental mode alone, define a PL relation (MV = -2.80 logP - 0.60, fundamental). It is notable that the slope of this relation isin the range of slopes found for classical cepheids. Accurate Vphotometry is lacking for many of the variables known as 'anomalouscepheids', but the available data divide them into low mass,pseudocepheids (BL Her and W Vir stars) and post-main-sequence USPC(delta Sct) variables. Four USPC in NGC 5053 and six in NGC 6466, forwhich accurate photometry is available, give remarkably consistentmoduli of 16.06 +/- 0.05 and 15.98 +/- 0.08 mag, respectively, for theclusters, in which they are blue stragglers similar to SX Phe inKapteyn's star group. The assumption that the four post-giant branchvariables, called VSPC (RR Lyr), S Ari, SU Dra, and ST Leo in Kapteyn'sstar group and RR Lyr in the Groombridge 1830 group, are physicalmembers of these groups and share their V-velocities, leads to acalibration of the photometry for the derivation of reddening,luminosity, and heavy element abundance of 45 field variables. Theresulting reddenings are consistent with values obtained by othermethods and the metallicities are consistent with the most accuratelyavailable spectroscopic determinations of delta S and of Ca II K. Theluminosities of the bulk of the variables confirm Sandage's (1993)relation between MV and (Fe/H). Four or five of the fieldvariables are probably binary, including BB Vir which Kinman &Carreta (1992) have independently noted as double. The PL relation forUSPC (delta Sct) variables intersects the horizontal branch (HB) near P= 0.3d and at least two field very short period cepheid (VSPC) (RR Lyr)star, FW Lup (0.484 d) and ST Pic (0.486 d) may be first overtonepulsators of the USPC (delta Sct) variety. A dozen field VSPC (RR Lyr)stars populate a (Fe/H), MV relation with the same slope asthe other stars but displaced 0.7 mag toward higher luminosities. Theonly cluster variable found to populate this diplaced relation is No. 9in 47 Tuc, although ST Vir, which may be a member of the Arcturus group,should also be considered. The elevated luminosities are unlikely to becaused by either evolution or errors in the photometric indices. Apossible source of these apparently young VSPC(RR Lyr) variables withhalo metallicity is in second (or third) generation globular clustersformed during an episodic collapse of the galaxy that produced metalpoor stars but in a dynamical situation that hastened the disruption ofthe clusters, currently formed, before the still older globularclusters, created under conditions that have kept them in a moredisruptive free environment.
| 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 visual surface brightness method and the radii of dwarf Cepheids
In order to determine the radii of dwarf Cepheids by applying the visualsurface brightness method, the empirical relationship between F(v) and(b - y) was derived. Seventeen stars of spectral type A to F, where bothangular diameters and uvby beta photometric data are available, wereselected from the literature. A theoretical F(v), (b-y) relation wasderived by using the Kurucz model atmospheres. It was found that thetheoretical relation is strongly dependent upon metallicity and surfacegravity. To demonstrate that the visual surface brightness method is aneffective way to determine the radii of dwarf Cepheids, both theoreticaland empirical relations were applied to seven dwarf Cepheids. The mostreliable result was obtained for AD CMi where the quality of the radialvelocity data is superior.
| 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.
| The rotational velocities of the dwarf Cepheids and related stars
The rotational velocities of the dwarf Cepheids are discussed, and someapparent differences between the dwarf Cepheids and the delta Scutivariables (other than light amplitude) are noted. For dwarf Cepheids,the rotational velocities are very small compared with the typicalrotational velocity of delta Scuti variables. The dwarf Cepheids,moreover, are restricted to a much more confined region in the H-Rdiagram. Unlike many typical delta Scuti variables, no dwarf Cepheidsare found near the ZAMS.
| Revised list of pulsating stars with ultra-short periods
A comprehensive list of 178 known Delta Scuti and RR Lyrae-stars ispresented. Using this revised list a HR diagram for these ultra shortperiod pulsating stars is plotted and the blue and red edges of theresultant instability strip are determined. Selection effects arediscussed, and the PLC relationship of Breger (1979) is tested usingdata from this list. Stars lying outside the defined instability regionare discussed.
| Delta Scuti variables. II - Comparison of theoretical evolution sequences with observational data
Delta Scuti variable observational data concerning periods, periodratios, effective temperatures, gravities, radii, and metal abundancesare compared with novel theoretical stellar evolution sequences,including a pulsation analysis for models in the lower Cepheidinstability strip, in order to consider such physical properties asmasses, ages, composition parameters, and the occurrence ofhelium-depleted outer zones. It is established that the metal-rich, highamplitude Delta Scuti variables are shell hydrogen-burning stars, andthat the observed period ratios of double mode Delta Scuti variables canbe explained by means of homogeneous standard models (although somehelium depletion in surface zones is also possible). It is concludedthat all evidence is in agreement with the assumption that Delta Scutistars are evolving in accordance with standard stellar evolutionarytheory.
| The nature of dwarf Cepheids. V - Analysis and conclusions
The various observational arguments that can be or have been used todetermine the nature of dwarf Cepheids are examined. Three evolutionaryhypotheses are outlined and shown to lead to different expected periodchanges. Despite careful analysis, the derived period changes do notprovide definite information on the evolutionary stage of most of thestars examined. Evidence for the Population I nature of most dwarfCepheids (which are normal delta Scuti stars with large amplitudes) ispresented.
| Delta Scuti and related stars
An extensive review is given of the current status of our knowledge ofthe stars in the lower instability strip. Current problems areemphasized. Particular attention is given to the following areas: theconfusion concerning naming and the implied astrophysical properties(often erroneous), single and multiple periods, the effect of rotationand metallicism on pulsation, the nature of the so-called dwarfcepheids, and pulsation in Ap stars. Various reports of unusal andstrange effects are also discussed with personal, possibly biasedjudgment on their reality.
| The classification of intrinsic variables. VIII - Ultrashort period Cepheids
The photometric and astrometric data for ultrashort-period Cepheids withmaximum visual magnitudes brighter than 11.5 are collected anddiscussed. Most of these variables are high-mass, little-evolved starswhich, in the halo and disk populations, are blue stragglers. Theluminosities are calibrated from membership in disk and halo populationgroups; the visual magnitude equals 8(1-/c1/sub c) for disk stars, where(C1)sub c is a reddening- and temperature-free parameter.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Scorpione |
| Ascensione retta: | 17h42m16.80s |
| Declinazione: | -32°31'23.6" |
| Magnitudine apparente: | 7.853 |
| Distanza: | 255.754 parsec |
| Moto proprio RA: | 1.4 |
| Moto proprio Dec: | 16.2 |
| B-T magnitude: | 8.285 |
| V-T magnitude: | 7.889 |
Cataloghi e designazioni:
|
