תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| 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.
| 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
| Mode and period changes in pulsating stars near the main sequence : delta Scuti stars.
Not Available
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| XCOV13 and Asteroseismology of Delta Scuti Stars
The Whole Earth Telescope XCOV13 campaign, which was carried out from atemporary command center in Vienna, included two main-sequencepulsators: the delta Scuti star 4 CVn and the new gamma Dor variable, HD108100. The astronomical results for these stars are summarized. Thepaper also discusses the progress as well as further potential of deltaScuti stars for asteroseismology. Extensive multi-site campaigns ofindividual delta Scuti stars show that 24 or more pulsation modes with lvalues of 0, 1 and 2 can be detected photometrically. Spectroscopically,also about 30 modes have been detected, and these can be identified withmodes of l values up to 20. Since each technique favors the detection ofspecific types of modes, hundreds or thousands of modes must be excitedin delta Scuti stars. We examine the quantities which can be matchedbetween observations and theoretical models specifically computed foreach star. Recent progress in the mode identification of multiplepulsation modes is illustrated by presenting an application of the phaseshift method for the two stars, FG Vir and 4 CVn, recently measured byDSN (Delta Scuti Network) and WET. The XCOV13 results on 4 CVn can beused to illustrate why less extensive studies of delta Scuti could leadto erroneous conclusions of unstable pulsation modes.
| Spectroscopic survey of delta Scuti stars. I. Rotation velocities and effective temperatures
Projected rotational velocities and effective temperatures for 68 deltaSct stars as well as 41 non-variable stars of similar spectral type andluminosity are presented here. The rotational velocities have beencalculated following the method developed in \cite[Gray (1992)]{ref38}and effective temperatures have been derived using the Balmer lineprofiles. The temperatures obtained from this method are shown to be inreasonable agreement with those calculated using the Infrared FluxMethod (IRFM) or spectrophotometric methods. This result has allowed usto use our temperatures to compare different uvby beta photometriccalibrations. We find that the calibration given by \cite[Moon \&Dworetsky (1985)]{ref72} is the most consistent. In the second part ofthis paper we have studied the relation between the pulsationalproperties (periods and amplitudes) and the physical parameters (v sin iand Teff). Where pulsation modes have been determined, thelow amplitude $\delta$ Scutis tend to be multimode (radial andnon-radial) pulsators, consistent with the theory that non-linearcoupling between modes acts to limit the amplitude in these stars. Wehave compared the distribution of v sin i for low amplitude $\delta$Scutis and non-variable stars. This shows the $\delta$ Scutis have abroader distribution in v sin i suggesting that a high rotation velocitymay favour pulsation. We find that the large amplitude delta Scuti starstend to have longer periods, cooler temperatures and lower rotationvelocities. Given that the large amplitude stars are also relativelyrare all the above are consistent with the hypothesis that these starsare more evolved (sub-giants) than the low amplitude delta Scutis (mainsequence or early post-main sequence).
| Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.
The absolute magnitudes of δ Scuti stars derived from parallaxesmeasured by the Hipparcos astrometric satellite are discussed andcompared with the previous estimates based on photometric uvbyβindices. There are significant differences which are related tophotometric effects of metallicity and rotational velocity, but thepossible effect of a close companion on the measured apparent magnitudeshould be also taken into account. The possibility of differentgroupings of δ Scuti stars based on the absolute magnitudes isbriefly discussed. Some high amplitude δ Scuti stars withintermediate or normal metallicity and small and uncertain parallax haveapparently a very low luminosity; this could be a systematic effectrelated to the observational errors.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&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.
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| Photometric observations of short period variable stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990RMxAA..21..401G&db_key=AST
| 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 early F-type stars - Refined classification, confrontation with Stromgren photometry, and the effects of rotation
The classification for early F-type stars in the MK spectralclassification system presented by Gray and Garrison (1987) is refined.The effect of rotation on spectral classification and ubvy-betaphotometry of early F-type stars is examined. It is found that theclassical luminosity criterion, the 4417 A/4481 A ratio givesinconsistent results. It is shown that most of the stars in the DeltaDelphini class of metallic-line stars are either normal or areindistinguishable from proto-Am stars. It is suggested that thedesignation Delta Delphini should be dropped. The classifications arecompared with Stromgren photometry. The effects of rotation on thedelta-c1 index in the early-F field dwarfs is demonstrated.
| The extension of the MK spectral classification system to the intermediate population II F type stars
A grid of metal-weak spectral-classification standards is used tosystematically extend the MK spectral-classification system to F-typestars of the intermediate population II. The present method allowsmetal-weak program stars to be compared with standards of similarmetallicity and effective temperature. The results demonstrate that theintermediate population II is very homogeneous. Excellent agreement isobtained between the classifications of the present extended system anduvby-beta photometric results.
| 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.
| ICCD speckle observations of binary stars. I - A survey for duplicity among the bright stars
A survey of a sample of 672 stars from the Yale Bright Star Catalog(Hoffleit, 1982) has been carried out using speckle interferometry onthe 3.6-cm Canada-France-Hawaii Telescope in order to establish thebinary star frequency within the sample. This effort was motivated bythe need for a more observationally determined basis for predicting thefrequency of failure of the Hubble Space Telescope (HST) fine-guidancesensors to achieve guide-star lock due to duplicity. This survey of 426dwarfs and 246 evolved stars yielded measurements of 52 newly discoveredbinaries and 60 previously known binary systems. It is shown that thefrequency of close visual binaries in the separation range 0.04-0.25arcsec is 11 percent, or nearly 3.5 times that previously known.
| Population I pulsating stars. III - Period-Evolutionary mass(-colour) relations
Evolutionary masses of Population I pulsating stars (89 Delta Scutivariables and 155 classical Cepheids are investigated in Iben's andPaczynski's systems of tracks. The evolutionary masses are larger in thelatter system than in the former. The uncertainty of the evolutionarymass of a star is estimated, when various evolutionary phases arepossible for this star (a smaller evolutionary mass corresponds to alater phase). Semi-empirical period-evolutionary mass-color (P-Me-C) andperiod-evolutionary mass (P-Me) relations are derived for various modes,groups of stars, color indices (and effective temperature), andevolutionary phases. For Delta Scuti stars, the uncertainty ofevolutionary masses calculated from the P-Me relations for differentmodes, is estimated. The improvement of the evolutionary mass accuracyis estimated, when a P-Me-C relation is used instead of thecorresponding P-Me relation. The theoretical and semi-empirical periodratios of radial pulsations derived from the P-Me relations for DeltaScuti stars, are compared. There is relatively good agreement betweenthe P-Me relations for the two types of Population I pulsating stars,but a 'gap' exists between them.
| Population I pulsating stars. II - Period-age (-colour) relations
Ages corresponding to various evolutionary phases of population Ipulsating stars (89 Delta Scuti variables and 155 classical cepheids)are interpolated in the evolutionary track systems of Iben (1967) andPaczynski (1970). The stellar ages are considerably less in the lattersystem than in the former one. The undertainty of the age of a star isestimated when various evolutionary phases are possible for this star (agreater age corresponds to a later phase). Semiempiricalperiod-age-color (P-t-C) and period-age (P-1) relations are derived forvarious modes, groups of stars, color indices (and effectivetemperature), and evolutionary phases. For Delta Scuti stars, theuncertainty of ages calculated from the P-t relations for differentmodes, is estimated. Theoretical P-t-C and P-t relations for Delta Scutistars are obtained and compared with semiempirical relations (such acomparison of P-t relations is performed for classical cepheids too).The improvement of the age accuracy is estimated when a P-t-C relationis used instead of the corresponding P-t relation. The theoretical andsemiempirical period ratios of radial pulsations, derived from the P-trelations for Delta Scuti stars, are compared. There is relatively goodagreement between the P-t relations for the two types of population Ipulsating stars, but a 'gap' exists between them.
| Radial pulsation modes as a possible cause for the heterogeneity of the Delta Scuti stars
On the basis of observational data (Breger, 1979), a radial pulsationmode of 83 Delta Scuti stars is estimated in two ways. These stars canpulsate in four lowest modes - F, 1H, 2H, 3H - and, perhaps, in 4H and5H. An earlier suggestion that the apparent heterogeneity of theseobjects in both the period luminosity plane and the period-frequencydistribution may be explained by means of pulsations in various modes -is confirmed. Semiempirical period-luminosity relations for the fourlowest modes are derived and the semiempirical period ratios arecompared with the theoretical ones.
| Photoelectric H-beta photometry for A and F stars brighter than V = 14 M in four areas in directions towards the South Galactic Pole
Data from photoelectric H-beta observations of 145 mainly A and F starswith V = 14 mag or brighter in four regions totalling 60 sq deg andlocated near galactic latitude b(II) = -60 deg, obtained using atwo-channel H-beta photometer on the 1.5-m Danish reflecting telescopeat ESO on two nights in 1981 and four nights in 1982, are presented intables along with the Stromgren b magnitudes calculated from thewide-channel H-beta counts. These observations are undertaken in theframework of a uvby photometric search for A-F stars of Population IIbrighter than V = 15.5 mag. The mean error per observation is given as +or - 0.020 mag in b and + or - 0.009 mag in H-beta.
| 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.
| Properties of Am, Delta Del and Delta SCT stars in the VBLUW system
The spread with respect to the main sequence in the two-color diagramsfor 115 Am, Delta Del and Delta Sct, for which VBLUW photometricobservations have been obtained, is primarily attributed to gravityeffects. Exceptions to this rule can be recognized from a comparison oftheir positions in these diagrams and in the reddening-independentdiagram L-U/B-L, where some Delta Sct stars have experienced relativelyhigh reddenings, while others are presumably metal-poor. It is notedthat gravities and temperatures compare satisfactorily with those ofDavis Philip et al. (1976), which were based on uvby-beta photometry.
| The radial pulsation modes of the Delta Scuti stars, and their nonuniform period distribution
From Breger's 1979 survey of the observational data for the Delta Sctvariables, radial pulsation modes are assigned to 83 of these stars.They can pulsate in the four lowest modes: F, 1H, 2H, 3H, and perhapsalso in 4H and even 5H. Confirming the author's earlier suggestion, theapparent nonuniformity in the distribution of Delta Sct stars both withrespect to period and in the period-luminosity diagram may naturally beattributed to pulsation in differing modes. Semiempirical (P, L)relations are derived for the four lowest modes, and the semiempiricaland theoretical period ratios are compared. Several statisticalrelationships are obtained, and in certain cases criteria are proposedfor determining the radial-pulsation mode.
| Photometric properties of AP stars in the Geneva system
An examination of the properties in some photometric diagrams of morethan 600 Ap stars measured in the Geneva photometric system confirm thatthe Balmer discontinuity is smaller than for normal stars, along withthe link between a proposed peculiarity parameter and both rotationalvelocity and effective magnetic field. It is shown that the peculiarityparameter is sensitive to interstellar reddening, and it is foundthrough examination of the standard deviations for visual magnitudesthat cool CP 2 stars without Eu peculiarity have the greatestamplitudes. Rapid rotators have a mild peculiarity, while positivecorrelation exists for Si and SrCr stars.
| On the stability of observed frequencies in Delta Scuti stars - A reanalysis of Theta TUC
The claim that some Delta Scuti stars change their frequencies on timescales as short as 24 hr is examined. It is suggested that thehypothesis that these Delta Scuti stars have stable frequencies isviable. Stobie and Shobbrook's (1976) data on Theta Tuc is reanalyzedalong with 954 new observations obtained during 70 hr on 21 nights in1979. The frequency of highest amplitude is shown to be present at aconstant amplitude over the 7-yr time span of the entire data set. Apossible set of frequencies is fitted to the Theta Tuc data. Other DeltaScuti stars which have been claimed to have variable frequencies arediscussed. Some of these stars are now known to have stable frequencies.A reanalysis of Stobie, Pickup and Shobbrook's data (1977) and Gupta'sdata (1973) on 21 Mon gives the same result found by Stobie, Pickup, andShobbrook: 21 Mon appears to have changed frequencies in the 2-yrinterval between the data sets. It is pointed out that claims ofchanging frequencies for Delta Scuti stars should only be made withcaution and a large amount of data.
| 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.
| Possible Heterogeneity of the delta Sct Complex
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | דלי |
| התרוממות ימנית: | 20h55m08.10s |
| סירוב: | -01°22'24.0" |
| גודל גלוי: | 6.55 |
| מרחק: | 79.428 פארסק |
| תנועה נכונה: | 14.7 |
| תנועה נכונה: | 25.6 |
| B-T magnitude: | 6.871 |
| V-T magnitude: | 6.568 |
קטלוגים וכינוים:
|
