내용
사진
사진 업로드
DSS Images Other Images
관련 글
The Pulsation Spectrum of VX Hydrae
We present the results of a two-year, multisite observing campaigninvestigating the high-amplitude ? Scuti star VX Hydrae during the2006 and 2007 observing seasons. The final data set consists of nearly8500 V-band observations spanning HJD 2453763.6 to 2454212.7 (2006January 28 to 2007 April 22). Separate analyses of the two individualseasons of data yield 25 confidently detected frequencies common to bothdata sets, of which two are pulsation modes, and the remaining 23 areFourier harmonics or beat frequencies of these two modes. The 2006 dataset had five additional frequencies with amplitudes less than 1.5 mmag,and the 2007 data had one additional frequency. Analysis of the full2006-2007 data set yields 22 of the 25 frequencies found in theindividual seasons of data. There are no significant peaks in thespectrum other than these between 0 and 60 cycles day. The frequenciesof the two main pulsation modes derived from the 2006 and 2007 observingseasons individually do not differ at the level of 3?, and thus wefind no conclusive evidence for period change over the span of theseobservations. However, the amplitude of f=5.7898 cycles day-1changed significantly between the two seasons, while the amplitude off=4.4765 cycles day-1 remained constant; amplitudes of theFourier harmonics and beat frequencies of f also changed. Similarbehavior was seen in the 1950s, and it is clear that VX Hydrae undergoessignificant amplitude changes over time.
| Photometry of GSC 762-110, a new triple-mode radially pulsating star
Context: Stars pulsating in three radial modes are very rare; only threeexamples are known in the Galaxy. These stars are very useful sincetheir periods may be measured very precisely, and this will constrainthe global stellar parameters and the models of the star's interior. Aims: The purpose of this paper is to present a new example of theclass of triple-mode radial pulsators. Methods: A search forcandidate multi-mode pulsators was carried out in public survey data.Time-series photometry of one of the candidates, GSC762-110, was performed. Results: GSC 762-110 was foundto be a triple-mode radial pulsator, with a fundamental period of 0.1945d and period ratios of 0.7641 and 0.8012. In addition two non-radialmodes were found, for which the amplitude has diminished considerablyover the last few years.Tables 2-4 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/478/865
| Times of Maxima for Selected Delta Scuti 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).
| 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
| 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)
| A Photometric Study of V798 Cygni
New photometric $(uvby\beta)$ observations of the intrinsic variablestar V798 Cyg have been secured and used to derive values of foregroundreddening, E($b - y$) = 0\fm117, and metallicity, [Fe/H] = 0.64.Intrinsic ($b - y$) and $c1$ values indicate a mean effectivetemperature, $< Teff >$ = 7150 K, and a mean surfacegravity, $< \log g >$ = 3.39. Pulsation theory and theoreticalevolutionary tracks yield a mass of 2.3$M_{\odot}$ and an age of 0.63Gyrs. Although V798 Cyg has been described as being multi-periodic, thisconclusion is not confirmed by our observations. V798 Cyg in mostrespects resembles a typical population I dwarf Cepheid. (SECTION:Stars)
| 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)
| 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.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| 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.
| 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.
| CCD Observations of Short-Period Variables at Middlebury College
The Middlebury College Observatory is equipped with a 0.41-m reflectingtelescope and a CCD imaging camera. Among the observational programs wehave undertaken is the photometric study of short-period variable stars,especially delta Sct variables. There are many short-period (P < 6h)variables with amplitudes of several hundredths of a magnitude orgreater, which are ideal objects for study with CCDs on smalltelescopes, especially in educational settings.
| A new approach to the Cepheid period-luminosity law - Delta Scuti stars as small Cepheids
It is argued that the apparent separation of Delta Scuti stars andclassical Cepheids into two classes is due to a simple selection effect,and that Delta Sct stars and Cepheids are really a single class ofvariable star. The precision with which the P-L and other relations areknown can be greatly improved by combining the two classes.
| 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.
| 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.
| The radii and masses of dwarf Cepheids
A radial velocity curve for CY Aqr, and VJK photometry for CY Aqr, YZBoo, and VZ Cnc, are used to derive absolute magnitudes and masses forthese three dwarf Cepheids. If dwarf Cepheids are earlypost-main-sequence stars, a pulsation mass of 1.2 + or - 0.3 solarmasses is found, and the pulsation mass to evolutionary mass ratio isabout 0.75. A mean value of -8.6 x 10 to the -11th days/day for theperiod changes is derived which is an order of magnitude larger thanpredicted by early post-main-sequence evolutionary tracks. Problems inmodeling these stars at a more advanced evolutionary state are noted.Comparison is made between the properties of fundamental and possibleovertone pulsators. The possible relationship between Delta Scutibehavior and the small cycle-to-cycle variations found in dwarf Cepheidlight curves is also considered.
| 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.
| Revised photometric properties for the multiperiodic variable HD 200925
The spectroscopic data collected on the HD 200925 variable star in theuvby and beta systems have been analyzed. The results indicate that thisvariable is multiperiodic, with a reddening value, E(b-y), equal to0.029 mag. The reddening-corrected normals for y, (b-y), and c(1)yielded a mean effective temperature of 7020 K, mean log surface gravityof 3.44, and a mean bolometric magnitude of 0.8 mag. A preliminary meanradius of 4.1 solar radii has been determined. The m(1) data show thatthe blanketing is high, but this index varied in an anomalous way whichprecluded a definitive determination of Fe/H. Two possible explanationsare considered for the behavior of the m(1) index: (1) a highmicroturbulence excited by the secondary pulsation mode, and (2) theAm/Fm phenomenon.
| 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.
| 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.
| L O,1,2, and 3 Pulsation Constants for Evolutionary Models of Delta-Scuti Stars
Abstract image available at:http://adsabs.harvard.edu/abs/1981ApJ...249..218F
| 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.
| 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.
| Double mode pulsation as a resonance phenomenon
It is proposed that the maintenance of stable double-mode pulsationinvolves a resonant interaction between the two excited modes. Thishypothesis yields a simple explanation of the narrow range of periodratio observed in both the double-mode Cepheids and the double-mode AIVelorum stars. The resonance idea is consistent with the under-massivemodels previously invoked to match the double-mode Cepheids, but seemsto rule out normal Population I masses for the AI Velorum stars. It isargued that observational evidence regarding the pulsations of the AIVel objects does not at present preclude the latter result.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
