Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
Amplitude ratios as mode characterizors in delta Scuti stars .
Seismology of delta Scuti star s holds great potential for testingtheories of stellar structure and evolution. The ratio of modeamplitudes in light and in equivalent width of spectral lines can beused for mode identification. However, the amplitude ratios (AR)predicted from theory are usually inconsistent with observations. Wehere present the first results from a campaign aimed at calibratingobservationally the absolute values of the AR.
| Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars
We obtained high-resolution spectroscopic observations of 34 γDoradus candidates. From the red-wavelength spectra, we determinedspectral classes, radial velocities, and projected rotationalvelocities. The spectra of seven late A or early F stars show metalliclines that have composite profiles consisting of a narrow component nearthe center of a broad line, indicating that they may be shell stars orbinaries. Several stars, including HD 152896, HD 173977, HD 175337, andHD 195068/9, show large line profile asymmetries. Two stars, HD 11443(=α Trianguli) and HD 149420, are ellipsoidal variables and notγ Doradus stars. The percentage of binary systems in our samplemay be as high as 74%.
| On the Period-Luminosity-Colour-Metallicity relation and the pulsational characteristics of lambda Bootis type stars
Generally, chemical peculiarity found for stars on the upper mainsequence excludes delta Scuti type pulsation (e.g. Ap and Am stars), butfor the group of lambda Bootis stars it is just the opposite. This makesthem very interesting for asteroseismological investigations. The groupof lambda Bootis type stars comprises late B- to early F-type,Population I objects which are basically metal weak, in particular theFe group elements, but with the clear exception of C, N, O and S. Thepresent work is a continuation of the studies by Paunzen et al.(\cite{Pau97}, \cite{Pau98}), who presented first results on thepulsational characteristics of the lambda Bootis stars. Since then, wehave observed 22 additional objects; we found eight new pulsators andconfirmed another one. Furthermore, new spectroscopic data (Paunzen\cite{Pau01}) allowed us to sort out misidentified candidates and to addtrue members to the group. From 67 members of this group, only two arenot photometrically investigated yet which makes our analysis highlyrepresentative. We have compared our results on the pulsationalbehaviour of the lambda Bootis stars with those of a sample of deltaScuti type objects. We find that at least 70% of all lambda Bootis typestars inside the classical instability strip pulsate, and they do sowith high overtone modes (Q < 0.020 d). Only a few stars, if any,pulsate in the fundamental mode. Our photometric results are inexcellent agreement with the spectroscopic work on high-degree nonradialpulsations by Bohlender et al. (\cite{Boh99}). Compared to the deltaScuti stars, the cool and hot borders of the instability strip of thelambda Bootis stars are shifted by about 25 mmag, towards smaller(b-y)_0. Using published abundances and the metallicity sensitiveindices of the Geneva 7-colour and Strömgren uvbybeta systems, wehave derived [Z] values which describe the surface abundance of theheavier elements for the group members. We find that thePeriod-Luminosity-Colour relation for the group of lambda Bootis starsis within the errors identical with that of the normal delta Scutistars. No clear evidence for a statistically significant metallicityterm was detected. Based on observations from the Austrian AutomaticPhotoelectric Telescope (Fairborn Observatory), SAAO and Siding SpringObservatory.
| 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.
| 10 New γ Doradus and δ Scuti Stars
We present high-resolution spectroscopy and precision photometry of fivenew γ Doradus and five new δ Scuti variables. The five newγ Doradus variables substantially increase the number of confirmedstars of this class. All 10 stars fall in the spectral class rangeF0-F2, but they are cleanly separated into two groups by theirluminosity and photometric periods. However, the period gap between theγ Doradus and δ Scuti stars is becoming very narrow since weconfirm that HD 155154 is a γ Doradus star with the shortestperiods reported to date (the shortest of its four periods is ~0.312days). We do not find any evidence in our sample for stars exhibitingboth δ Scuti- and γ Doradus-type pulsations.
| CCD Speckle Observations of Binary Stars from the Southern Hemisphere. III. Differential Photometry
Two hundred seventy-two magnitude difference measures of 135 double starsystems are presented. The results are derived from speckle observationsusing the Bessel V and R passbands and a fast readout CCD camera.Observations were taken at two 60 cm telescopes, namely the Helen SawyerHogg Telescope, formerly at Las Campanas, Chile, and the Lowell-TololoTelescope at the Cerro Tololo Inter-American Observatory, Chile. Thedata analysis method is presented and, in comparing the results to thoseof Hipparcos as well as to recent results using adaptive optics, we findvery good agreement. Overall, the measurement precision appears to bedependent on seeing and other factors but is generally in the range of0.10-0.15 mag for single observations under favorable observingconditions. In four cases, multiple observations in both V and R allowedfor the derivation of component V-R colors with uncertainties of 0.11mag or less. Spectral types are assigned and preliminary effectivetemperatures are estimated in these cases.
| 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).
| 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.
| CCD Speckle Observations of Binary Stars from the Southern Hemisphere. II. Measures from the Lowell-Tololo Telescope during 1999
Speckle observations of 145 double stars and suspected double stars arepresented and discussed. On the basis of multiple observations, a totalof 280 position angle and separation measures are determined, as well as23 high-quality nondetections. All observations were taken with the(unintensified) Rochester Institute of Technology fast-readout CCDcamera mounted on the Lowell-Tololo 61 cm telescope at the Cerro TololoInter-American Observatory during 1999 October. We find that themeasures, when judged as a whole against ephemeris positions of binarieswith very well-known orbits, have root mean square deviations of1.8d+/-0.3d in position angle and 13+/-2 mas in separation. Elevendouble stars discovered by Hipparcos were also successfully observed,and the change in position angle and/or separation since the Hipparcosobservations was substantial in three cases.
| 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
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Simultaneous intensive photometry and high resolution spectroscopy of delta Scuti stars. IV. An improved picture of the pulsational behaviour of X Caeli
The delta Scuti star X Caeli has been the target of a simultaneousphotometric (14 consecutive nights) and spectroscopic campaign (8consecutive nights). From the analysis of light curves we were able topick up 17 frequency components, most of which were already detected intwo previous campaigns. The comparison with the results of the previouscampaigns shows that while some terms are rather stable (in particularthe dominant mode at 7.39 cd-1 ) others have conspicuousamplitude variations. 14 photometric terms have been also detected inthe radial velocity curve or in the analysis of the line profilevariations. There are no spectroscopic terms without photometriccounterparts, and this means that there are no high-degree modes asobserved in other delta Scuti stars. The simultaneous fit of light andline profile variations has allowed the estimation of the inclination ofrotational axis (about 70o) and the l,m identification formany modes. In particular there is clear evidence that the two shortestperiod modes are retrograde. Rather reliable results were found for thedominant mode which has l=1, m=-1. The resulting physical parameters ofits pulsation are in good agreement with the prediction of theoreticalmodels and suggest for this star a mixing length parameter of about 0.5.Finally the fundamental stellar physical parameters and their refinementare discussed in the light of the identification of the 7.47cd-1 term as a radial mode. Based on observations collectedat European Southern Observatory(Proposal 58.E-0278)
| The Oscillations of Tau Pegasi
We present extensive spectroscopic time series observations of themultiperiodic, rapidly rotating, delta Scuti star tau Pegasi.Information about the oscillations is contained within the patterns ofline-profile variation of the star's blended absorption-line spectrum.We introduce the new technique of Doppler deconvolution with which toextract these patterns by modeling the intrinsic stellar spectrum andthe broadening functions for each spectrum in the time series.Frequencies and modes of oscillation are identified from the variationsusing the technique of Fourier-Doppler imaging and a two-dimensionalleast-squares cleaning algorithm. We find a rich mode spectrum withdegrees up to l = 20 and with frequencies below about 35 cycles day-1.Those modes with the largest amplitudes have frequencies that lie withina narrow band. We conclude that the observed spectrum can be explainedif the modes of tau Peg propagate in the prograde direction with l ~=|m| and with frequencies that are about equal in the corotating frame ofthe star. We discuss the implications of these results for the prospectof delta Scuti seismology.
| 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
| 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
| 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.
| High azimuthal number pulsation modes in fast rotating δ Scuti stars: the case of HD 101158 = V837 Cen.
The frequency analysis of the line profile variations of the fastrotating (vsini=132km/s) δ Scuti star HD 101158, observed forthree consecutive nights, shows the presence of two high azimuthalnumber non radial pulsation modes. The star is probably seen almostequator-on and both modes (ν_i_=12.9c/d and ν_2_=18.5 c/d) areprograde with m=-10 and m=-14 or -15 respectively; their frequencies aredifferent with respect to the three frequencies identified inphotometric data (Poretti 1991), which probably owe due to low l modes.Indications of the presence of these photometric modes have been foundfrom the frequency analysis of the first two line moments. The lineprofile variations also show the possible presence of further modes withfrequencies of 16.2, 20.3 and 21.1c/d and small amplitudes.
| 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).
| Simultaneous intensive photometry and high resolution spectroscopy of δ Scuti stars. II. X Caeli: a star with unusual spectral features.
Simultaneous photometric B, V (14 consecutive nights; 100 hours ofobservations) and high resolution spectroscopic observations (4consecutive nights; 27 hours) were performed on the δ Scuti star XCaeli at La Silla Observatory in 1992. The photometric data allow thedetection of 14 pulsation terms, some of which coincide in frequencywith the second harmonics or the non-linear coupling terms of the lowerfrequency components. Possible excitation by resonance is suggested. Thecomparison with our previous observations of 1989 shows that while theamplitude of the strongest term (ν=7.39c/d) is very stable, a fewother terms have changed their amplitudes. From the study of lineprofiles and their variations we derive vsin i=70km/s,65deg<=i<=90deg, and that the dominant photometric term is aprograde mode with m=-1 and l=1 or 2. The other terms are probably nonradial p modes with l=2+/-1. There is no evidence of the presence ofhigh-degree sectorial modes with l=|m|. The stellar spectral lines havea narrow absorption core which could be due to the presence of acircumstellar shell.
| 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.
| Spectroscopy and photometry as a synergetic approach to the study of stellar pulsations.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994RMxAA..29..158B&db_key=AST
| Insight into the Pulsational Behaviour of δ Scuti Stars
Not Available
| 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.
| Doing research with small telescopes : frequency analysis of multiperiodic delta Scuti stars.
Not Available
| Pulsational behaviour of the Delta Scuti star X Caeli
1013 V observations of the Delta Sct star X Caeli obtained at La SillaObservatory on 10 consecutive nights have been analyzed in the frequencydomain. Five independent pulsational modes have been detected, and froma comparison with theoretical models we suggest that two of them arenonradial modes and one of them is the first overtone radial mode. Thetwo strongest modes are nonlinearly coupled and their light curves areslightly nonsinusoidal. Finally, the highest frequency mode could be ahigh-order nonradial mode excited by resonance with a low-order one. Acomparison with the former data set of Smyth et al. (1975) shows noevidence of variations of the mode amplitudes.
| 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.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Caelum |
| Ascensió Recta: | 05h04m26.10s |
| Declinació: | -35°42'19.0" |
| Magnitud Aparent: | 6.34 |
| Distancia: | 102.354 parsecs |
| Moviment propi RA: | 26.8 |
| Moviment propi Dec: | 42.2 |
| B-T magnitude: | 6.669 |
| V-T magnitude: | 6.351 |
Catàlegs i designacions:
|
