Contents
Images
Upload your image
DSS Images Other Images
Related articles
δ Scuti stars and their related objects
δ Scuti stars are a group of stars located on or a little abovethe main sequence of H-R diagram with spectral type from A3 to F5. Theyare low amplitude single or multi period pulsators with period shorterthan 0.3 d. Within the same area there are several groups of variablesor special stars correlated with them, e.g., Dwarf Cepheids, γ Dorvariables, Blue Stragglers, Am stars, Ap stars, ROAp variables, λBoo variables and δ Del variables. In this paper a general reviewin this field, including the number of new variables discovered after1995, is presented. The most reliable period variation rates for all thehigh amplitude variables and several low amplitude variables are listed.Statistic shows the higher the rotation rate v sin i is, the lower thelight variation amplitude is. Thus within young open clusters highamplitude variables cannot be found. The amplitudes-periods distributionhave 3 peaks with the highest of 1.0 mag in V at 0.17 d in period. Forδ Scuti variables in stellar systems the shorter the averageperiod is, the lower the metallicity and the older the age of thestellar system are.
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Time-resolved spectroscopy of the roAp star gamma Equ
We report results of the spectroscopic monitoring of the roAp star gammaEqu/ with the ESO 3.6-m telescope. During 1.5 hours of observations aseries of very high-resolution and high S/N spectra was obtained forthis star in the 6138-6165 Å/ spectral region. Short exposuretimes allowed us to resolve changes of gamma Equ/ line profiles due tothe rapid pulsations and to follow profile variations over 5 oscillationcycles. From this unique observational material information onamplitudes and phase shifts of radial velocity (RV) variations wasextracted for 29 lines of 17 individual ions. We confirmed that spectrallines of rare-earth elements (REE) have the largest pulsationamplitudes, reaching up to 0.8 km s-1. Moreover, we detecteda phase shift between RV variations of singly and doubly ionized REE,discovered significant RV shifts of weak Na I lines and analysed lineprofile variations of Pr Iii/ and Nd Iii/ spectral features. This richobservational material opens a possibility to obtain a detailed pictureof the vertical stratification of chemical elements and extract the maincharacteristics of the pulsational mode(s). In our observations we didnot find support for the existence of the unique dependence of RVamplitude on line strength suggested in earlier spectroscopic studies ofroAp stars. Instead, we argue that the individuality of the variationsof all ions is a result of the complex interplay between inhomogeneousvertical and horizontal distributions of chemical elements andindividual pulsation modes of gamma Equ. We show that the extra linebroadening observed in gamma Equ/ spectrum is most likely caused bypulsations. A detailed analysis of Pr Iii/ and Nd Iii/ line profilevariations resulted in the estimate of l=2 or 3, m=-l or -l+1 andvp,~10 km s-1/ for the p-mode of the mainpulsation frequency. Based on observations obtained at the EuropeanSouthern Observatory, La Silla, Chile.
| Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. V. The high-degree modes in the pulsational content of BV Circini
We discuss here the pulsation properties of the delta Scuti star BVCircini on the basis of data obtained during a simultaneous photometricand spectroscopic campaign in 1996 and a spectroscopic one in 1998, andtaking also advantage of the previous photometric observations by Kurtz(\cite{kur81}). Nine pulsation modes were detected from photometry andthirteen from spectroscopy; five of them are in common to bothtechniques. The spectroscopic data give ample evidence of dramaticamplitude variations in some modes, in particular the strongestspectroscopic mode in 1998 was not detectable in 1996 data. The twodominant photometric modes (6.33 and 7.89 cd-1) are observedon both seasons. The typing of the modes was performed by means of asimultaneous model fit of line profile and light variations. The 6.33cd-1 photometric term is probably the fundamental radialmode, while the 7.89 cd-1 is a nonradial mode with m!=q 0.There are six high-degree prograde modes with an azimuthal order mranging from -12 to -14, and also a retrograde mode with m ~ 7. Thesemodes combined with the identification of the 6.33 cd-1 modeallowed us to estimate i ~ 60o for the value of theinclination of the rotation axis. An accurate evaluation of the mainstellar physical parameters is also proposed as a result of thepulsational analysis. Based on observations collected at ESO-La Silla(Proposals 57.E-0162, 61.E-0120).}
| On the Variability of F1-F9 Luminosity Class III-V Stars
Hipparcos Satellite photometry of F1-F9 luminosity class III-V starsindicates that most are not particularly variable. A few stars for whichfurther study is desirable are identified.
| Asteroseismology of Delta Scuti Stars
This paper presents recent results for delta Scuti stars based onmeasurements obtained by WET/Delta Scuti Network as well as theoreticalmodeling of the pulsation modes. In particular, the two stars indifferent stages of evolution, FG Vir and 4 CVn, are discussed. For 4CVn, the XCOV13 campaign has revealed 34 frequencies, which sets a newrecord for delta Scuti stars. Preliminary mode identifications arepresented, indicating pulsation in low radial order and low degree (l =0 to 2). The star shows strong amplitude variability with timescales often years or longer, although for neighbouring years the amplitudesusually are similar. The cyclic behavior of the amplitude variationsexcludes an evolutionary origin. The pulsation mode at 7.375 c/dexhibits the most rapid decrease found so far: the V amplitude droppedfrom the highest known value of 15 mmag in 1974 to 4 mmag in 1976 and 1mmag in 1977. After that the mode has been increasing in amplitude.There exists a phase jump between 1976 and 1977, suggesting the growthof a new mode.
| 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
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Line profile analysis of the delta Scuti star HD 2724 = BB Phe: mode identification and amplitude variations
The line profile variations of the delta Scuti star HD 2724equiv BB Phewere studied on the basis of new 189 high-resolution spectrogramscovering 52 hours of observations on a baseline of 8.3 days. Bycombining these results with those of a previous campaign 13 pulsationmodes were identified: 5 of them are both photometric and spectroscopic,3 are purely spectroscopic and 5 purely photometric. For the first timeit was possible to compare spectroscopic data taken in two differentseasons: 6 modes were found to be common to both datasets andfurthermore strong amplitude variations of the excited modes weredetected. The fit of the line profile variations with a model ofnon-radial pulsating star allowed us to obtain a reasonable estimate ofthe inclination of the rotational axis and to propose the l,m typing ofthe spectroscopic modes. The frequency content resembles that of 4 CVn,a delta Sct star with similar physical parameters. Based on observationscollected at the Coudé Auxiliary Telescope of the EuropeanSouthern Observatory -- La Silla, Chile (Proposal 60.E-0113)
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Are metallic A-F giants evolved AM stars? Rotation and rate of binaries among giant F stars
We test the hypothesis of Berthet (1992) {be91} which foresees that Amstars become giant metallic A and F stars (defined by an enhanced valueof the blanketing parameter Delta m_2 of the Geneva photometry) whenthey evolve. If this hypothesis is right, Am and metallic A-FIII starsneed to have the same rate of binaries and a similar distribution ofvsin i. From our new spectroscopic data and from vsin i and radialvelocities in the literature, we show that it is not the case. Themetallic giant stars are often fast rotators with vsin i larger than 100kms(-1) , while the maximum rotational velocity for Am stars is about100 kms(-1) . The rate of tight binaries with periods less than 1000days is less than 30% among metallic giants, which is incompatible withthe value of 75% for Am stars - [Abt & Levy 1985] {ab85}).Therefore, the simplest way to explain the existence of giant metallic Fstars is to suggest that all normal A and early F stars might go througha short ``metallic" phase when they are finishing their life on the mainsequence. Besides, it is shown that only giant stars with spectral typecomprised between F0 and F6 may have a really enhanced Delta m_2 value,while all A-type giants seem to be normal. Based on observationscollected at Observatoire de Haute Provence (OHP), France.
| Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. III. Mode identifications and physical calibrations in HD 2724
On the basis of our new simultaneous photometry and spectroscopy (885 \(uvby \) differential measurements in 11 nights and 154 spectrograms ofthe FeII\( \lambda \)4508 region in 5 nights), we can detect 12 probableperiodicities in the variability pattern of this star, determining thefrequencies of 7 without any ambiguity. Through a direct fit ofpulsational models to our data, we estimate the inclination ofrotational axis to be about 50\( ^{\circ} \) and get a reliableidentification of 4 modes as well as useful bits of information aboutthe others: no retrograde mode is visible, whereas the star seems toshow a certain preference for purely sectorial prograde oscillations.Finally, the attribution of our lowest frequency to the radialfundamental pulsation allows a new calibration of physical parameters.In particular, the gravity can be determined with unusual accuracy andthe luminosity evaluation becomes more consistent with the Hipparcosastrometry. This work is based on observations performed at the EuropeanSouthern Observatory (ESO), La Silla, Chile.
| Amplitude variations of the multimode nonradial δ Scuti pulsator 4 CVn
New photoelectric photometry of the δ Scuti variable 4 CVn revealslong-term slow variations of multimode pulsational frequencies and theiramplitudes. We have confirmed 5(f1, f2,f3, f5, f7) of the 7 frequenciesidentified in the literature. Besides presenting the long-termvariations of the different amplitudes, we have found three newsuspected frequencies in the new data. Although Blazhko effect and moderesonance along with its coupling between different nonradial modesthrough interaction can be reasonably used to explain the observedchanges of periods and amplitudes, it should be carefully checked andanalyzed before RR Lyr-like light curve shape and new pulsation modescan be established with certainty.
| Amplitude variations of the multimode nonradial delta Scuti pulsator 4 CVn.
Not Available
| The Complex Pulsational Pattern of the delta-SCUTI Star HD 2724
Not Available
| The stability of the frequency content in the light curves of the δ Scuti stars HD16439=V663 Cassiopeiae, AZ Canis Minoris, HD 223480=BF Phoenicis.
Within the frame of the study of the pulsational behaviour of δSct stars, multicolour photometry of (previously) consideredmonoperiodic or double mode pulsators was undertaken. The frequencycontent of the light variation of SAO 4710=HD 16439=V663 Cas is clearlychanging as a new frequency, not present in 1989, was observed in 1995;a slight decrease is also observed in the amplitude of the dominantterm. The light curve of V663 Cas is now explained by three frequencies,but the residual noise probably masks other terms. SAO 231800=HD223480=BF Phe is confirmed to be a monoperiodic δ Sct star, butcomparing the 1989 and 1993 photometric measurements a strong reductionin the b amplitude is observed; on the other hand, the V amplituderemained stable in 1991 and 1993. The monoperiodic light curve of HR2989=AZ CMi seems more stable, giving only slight hints that smallchanges occurred. The different photometric behaviours of these starsare discussed, also by comparing them with other monoperiodic pulsators(β Cas, 28 And, τ Peg).
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| 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.
| Long-term amplitude and period variations of delta Scuti stars: A sign of chaos?
On short time-scales of under a year, the vast majority of delta Scutistars studied in detail show completely regular multiperiodic pulsation.Nonradial pulsation is characterized by the excitation of a large numberof modes with small amplitudes. Reports of short-term irregularity ornon-periodicity in the literature need to be examined carefully, sinceinsufficient observational data can lead to an incorrect impression ofirregularity. Some interesting cases of reported irregularities areexamined. A few delta Scuti stars, such as 21 Mon, have shown stablevariations with sudden mode switching to a new frequency spectrum. Thissituation might be an indication of deterministic chaos. However, theobservational evidence for mode switching is still weak. One the otherhand, the case for the existence of long-term amplitude and periodchanges is becoming quite convincing. Recently found examples ofnonradial pulsators with long-term changes are 4 CVn, 44 Tau, tau Pegand HD 2724. Neither the amplitude nor the period changes are periodic,although irregular cycles with time scales between a few and twentyyears can be seen. While the amplitude changes can be very large, theperiod changes are quite small. The nonperiodic long-term changes areinterpreted in terms of resonances between different nonradial modes. Itis shown that a large number of the nonradial acoustic modes can be inresonance with other modes once the mode interaction terms, differentradial orders and rotational m-mode splitting are considered. Theseresonances are illustrated numerically by the use of pulsation model.Observational evidence is presented that these interaction modes existin the low-frequency domain.
| Study of Delta Scuti stars in the Geneva photometric system. II - The complex case of HD 2724 (= HR 119)
The results of the frequency analyses for the complex case of HD 2724are presented. Although based on a large and accurate data set coveringmore than one year, we were unable to derive a common frequency solutionfor the data of different years. Two frequencies can be unambiguouslyidentified in the proposed multiperiodic solution, with sufficient proofof their reliability. The possible modal content of HD 2724 is discussedin view of its physical parameters derived in the Geneva PhotometricSystem. HD 2724 is a plausible candidate for amplitude modulation inmultimode Delta Scuti stars.
| 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.
| Metallicism among A and F giant stars
132 stars considered as A and F giants have been studied for theirproperties in the Geneva photometric system. It is shown that thissystem to derive the temperature, absolute magnitude and Fe/H value forstars in this part of the HR diagram. 36 percent of the stars of oursample exhibit an enhanced value Delta m2 that can be interpreted interms of Fe/H. The red limit of stars having an enhanced Fe/H value is0.225 in B2-V1 or 6500 K in Teff. This corresponds to the limit definedby Vauclair and Vauclair (1982) where the diffusion timescale is equalto the stellar lifetime and permits the assumption that the diffusion isthe process responsible for the metallicism observed in the A and Fgiants.
| The 67th Name-List of Variable Stars
Not Available
| Cepheids and nonvariable supergiants
Photometric parameters for Cepheids in a previous paper are adapted foruse with nonvariable supergiants of similar temperature. The closecorrelation between the abundance and luminosity parameters forclassical, short-period Cepheids (SPC) confirms the nearlydispersionless luminosity temperature relation for these variables. Theassumptions that (1) the C-type variables are transiting the Cepheidtemperature for the first time, (2) the classical SPC are mostlytransiting for the second time, and (3) the long-period Cepheids (LPC)are a mixture of stars transiting for the first to third or fourth timesare found to be consistent with the various correlations of temperatureand luminosity parameters. The nonvariable supergiants with photometricparameters similar to those for the Cepheids are found to haveluminosities consistent with their spectroscopic luminosity class. Few,if any, nonvariable supergiants have temperatures and luminositiessimilar to the LPC.
| The South Galactic Pole - Results from uvby-beta photometry of 572 O-F stars
Photometric observations on the uvby-beta system are presented for 572O-F stars within about 20 deg of the South Galactic Pole. Theinterstellar extinction near the pole is found to be zero out to 400 pcfrom the sun, in agreement with the H I maps of Burstein and Heiles(1982). Several evolved and Population II objects are identified.
| 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.
| Two New Variable Stars in the Bright Star Catalogue
Not Available
| Study of the F-type 1 MK spectral types.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..637M&db_key=AST
| A finding list of early-type stars near the south galactic pole.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76..338S&db_key=AST
|
Submit a new article
Related links
Submit a new link
Member of following groups:
|
Observation and Astrometry data
| Constellation: | Φοίνιξ |
| Right ascension: | 00h30m27.80s |
| Declination: | -40°56'22.0" |
| Apparent magnitude: | 6.19 |
| Distance: | 128.7 parsecs |
| Proper motion RA: | -3.6 |
| Proper motion Dec: | 17 |
| B-T magnitude: | 6.554 |
| V-T magnitude: | 6.211 |
Catalogs and designations:
|
INHABITED SKY
