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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.
| 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.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| The δ Scuti Star DK Virginis (HR 5005) Revisited
An analysis of Hp photometry of DK Virginis is carried out. The analysisreveals two frequencies, f1=9.2095 and f2=7.5764cycles day-1. These values turn out to be good enough tobridge the gap between the two available series of ground-based data,obtained in 1973 and 1980, so that the frequencies can be refined. Therefined values are equal to 9.20945 and 7.57641 cycles day-1.The corresponding V amplitudes amount to 8.6+/-0.4 and 11.1+/-0.4 mmag,and the epochs of maximum light are equal to JDsolar2,441,715.0294+/-0.0008 and 2,441,715.1205+/-0.0007. The synthetic lightcurve, computed with these parameters, correctly reproduces the largelight range on JD 2,439,177, the night in 1966 when the star wasdiscovered to be variable, and the small range on JD 2,440,682, when thelight variation was not detected. In this way, all photometricobservations of DK Vir are accounted for, indicating that the twofrequencies have not changed appreciably since 1965, and that the Vamplitudes were constant over the interval from 1965 to 1980. Using aphotometric effective temperature and Hipparcos parallax, we plot thestar in the H-R diagram. Comparison with evolutionary tracks then showsthat DK Vir is at the end of the main-sequence stage of its evolution orslightly beyond, with a mass of 2.1 Msolar or somewhatsmaller. Finally, an examination of linear nonadiabatic pulsationfrequencies of modes with l<=2 indicates that the two observed modescannot both be radial, and that the f1 mode must be nonradialif the star is still on the main sequence. The properties of theHipparcos spectral window are examined in the Appendix. Based in part ondata from the ESA Hipparcos astrometry satellite.
| 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.
| 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. 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
| The Angular Momentum of Main Sequence Stars and Its Relation to Stellar Activity
Rotational velocities are reported for intermediate-mass main sequencestars it the field. The measurements are based on new, high S/N CCDspectra from the Coudé Feed Telescope of the Kitt Peak NationalObservatory. We analyze these rotation rates for a dependence on bothmass and age. We compare the average rotation speeds of the field starswith mean velocities for young stars in Orion, the Alpha Persei cluster,the Pleiades, and the Hyades. The average rotation speeds of stars moremassive than $\sim1.6$ \msun\experience little or no change during theevolutionary lifetimes of these stars on the zero age main sequence orwithin the main sequence band. Less massive stars in the range betwee n1.6\msun\ and 1.3\msun\ also show little decline in mean rotation ratewhile they are on the main sequence, and at most a factor of 2 decreasein velocity as they evolve off the main sequence. The {\it e}-foldingtime for the loss of angular momentum b y the latter group of stars isat least 1--2 billion years. This inferred characteristic time scale forspindown is far longer than the established rotational braking time forsolar-type stars with masses below $\sim1.3$ \msun. We conclude from acomparison of the trends in rotation with trends in chromospheric andcoronal activity that the overall decline in mean rotation speed alongthe main sequence, from $\sim2$ \msun\ down to $\sim1.3$ \msun, isimposed during the pre-main sequence phase of evolution, and that thispattern changes little thereafter while the star resides on the mainsequence. The magnetic activity implicated in the rotational spindown ofthe Sun and of similar stars during their main sequence lifetimes mus ttherefore play only a minor role in determining the rotation rates ofthe intermediate mass stars, either because a solar-like dynamo is weakor absent, or else the geometry of the magnetic field is appreciablyless effective in removing angular momentu m from these stars. (SECTION:Stars)
| Luminosity and related parameters of δ Scuti stars from HIPPARCOS parallaxes. General properties of luminosity.
The absolute magnitudes of δ Scuti stars derived from parallaxesmeasured by the Hipparcos astrometric satellite are discussed andcompared with the previous estimates based on photometric uvbyβindices. There are significant differences which are related tophotometric effects of metallicity and rotational velocity, but thepossible effect of a close companion on the measured apparent magnitudeshould be also taken into account. The possibility of differentgroupings of δ Scuti stars based on the absolute magnitudes isbriefly discussed. Some high amplitude δ Scuti stars withintermediate or normal metallicity and small and uncertain parallax haveapparently a very low luminosity; this could be a systematic effectrelated to the observational errors.
| 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
| Lithium Abundances in delta Scuti Stars and Their Relationship with the Lithium Dip
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...451..747R&db_key=AST
| 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.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| 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.
| 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.
| Magnetic structure in cool stars. XV - The evolution of rotation rates and chromospheric activity of giants
For cool giants and subgiants the observed dependence of rotationalvelocity and Ca II H and K line-core emission on color B-V isinterpreted in terms of changes in the moment of inertia by stellarevolution. Modeling of the rotational velocity during the evolution ofcool giants with masses between 2.0 and 3.0 solar masses, by taking intoaccount the change in the moment of inertia and assuming rigid-bodyrotation and conservation of angular momentum, describes the observeddecrease of v sin i with B-V. The computed evolution of the rotationalvelocity, together with the empirical relation between the Ca IIline-core emission and the rotation rate, explain the observed drop inthe Ca II line-core emission for giants at B-V = about 0.95. Forsubgiants with masses of about 1.5 solar mass, the change in the momentof inertia by itself cannot explain the observed v sin i distribution:there are indications of loss of angular momentum, presumably bymagnetic braking.
| 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.
| 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.
| 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.
| Period determination of the Delta Scuti star HR 5005
A periodogram analysis and least square fitting to periodic functions ofthe results of differential photoelectric photometry for the Delta Scutistar HR 5005 have yielded pulsation frequencies of 8.606 and 9.208 c/d.The ratio of these frequencies is inconsistent with the radial mode ofpulsation. If this star is pulsating at such close frequencies,destructive interference must occur.
| 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.
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| Takýmyýldýz: | Basakci |
| Sað Açýklýk: | 13h16m25.50s |
| Yükselim: | -01°23'26.0" |
| Görünürdeki Parlaklýk: | 6.68 |
| Uzaklýk: | 121.803 parsek |
| özdevim Sað Açýklýk: | -33.7 |
| özdevim Yükselim: | -31.3 |
| B-T magnitude: | 7.064 |
| V-T magnitude: | 6.72 |
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