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The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| Analysing the Hipparcos epoch photometry of λ Bootis stars
We performed a homogeneous analysis of the available Hipparcos epochphotometry for all members of the LB group. Besides the known δScuti like pulsation frequencies, we searched for eclipses due tobinarity or rotational induced variability. The already knownfrequencies of HD 15165 are confirmed with an additional lower singlefrequency, which might be caused by an accretion episode. But we are notable to rule out a possible aliasing due to the temporal sampling of thedata set. Furthermore, three candidates (HD 15759, HD 120500, and HD149130) for a possible eclipse were detected. Otherwise, the frequencyanalysis reveals a null result within our strict detection limits.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| C, N, O in λ Boo stars and in composite spectra
The selective abundance of C, N, O (almost solar) with respect to thatof other elements (underabundant) in λ Boo stars has beeninterpreted as a characteristic peculiarity of these objects, whenconsidered as single stars. We show here that a similar selectiveabundance is predicted from the composite spectra resulting from twounresolved stars in the same temperature range as the λ Boostars.
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| The heterogeneous class of lambda Bootis stars
We demonstrate that it is arduous to define the lambda Boo stars as aclass of objects exhibiting uniform abundance peculiarities which wouldbe generated by a mechanism altering the structure of their atmosphericlayers. We collected the stars classified as lambda Boo up to now anddiscuss their properties, in particular the important percentage ofconfirmed binaries producing composite spectra (including our adaptiveoptics observations) and of misclassified objects. The unexplained RVvariables (and thus suspected binaries), the known SB for which we lackinformation on the companion, the stars with an UV flux inconsistentwith their classification, and the fast rotating stars for which noaccurate abundance analysis can be performed, are also reviewed.Partly based on observations collected at the CFH Telescope (Hawaii) andat TBL of the Pic du Midi Observatory (France).Table \ref{tab5} is only available in electronic form athttp://www.edpsciences.org
| The status of Galactic field λ Bootis stars in the post-Hipparcos era
The λ Bootis stars are Population I, late B- to early F-typestars, with moderate to extreme (up to a factor 100) surfaceunderabundances of most Fe-peak elements and solar abundances of lighterelements (C, N, O and S). To put constraints on the various existingtheories that try to explain these peculiar stars, we investigate theobservational properties of λ Bootis stars compared with areference sample of normal stars. Using various photometric systems andHipparcos data, we analyse the validity of standard photometriccalibrations, elemental abundances, and Galactic space motions. Therecrystallizes a clear picture of a homogeneous group of Population Iobjects found at all stages of their main-sequence evolution, with apeak at about 1 Gyr. No correlation of astrophysical parameters such asthe projected rotational velocities or elemental abundances with age isfound, suggesting that the a priori unknown mechanism, which createsλ Bootis stars, works continuously for late B- to early F-typestars in all stages of main-sequence evolution. Surprisingly, the sodiumabundances seem to indicate an interaction between the stars and theirlocal environment.
| 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.
| The accretion/diffusion theory for lambda Bootis stars in the light of spectroscopic data
Most of the current theories suggest the lambda Bootis phenomenon tooriginate from an interaction between the stellar surface and its localenvironment. In this paper, we compare the abundance pattern of thelambda Bootis stars to that of the interstellar medium and find largerdeficiencies for Mg, Si, Mn and Zn than in the interstellar medium. Acomparison with metal poor post-AGB stars showing evidence forcircumstellar material indicates a similar physical process possiblybeing at work for some of the lambda Bootis stars, but not for all ofthem. Despite the fact that the number of spectroscopically analysedlambda Bootis stars has considerably increased in the past, a test ofpredicted effects with observations shows current abundance andtemperature data to be still controversial.
| The abundance pattern of lambda Bootis stars
Within a project to investigate the properties of lambda Bootis stars,we report on their abundance pattern. High resolution spectra have beenobtained for a total of twelve candidate lambda Bootis stars, four ofthem being contained in spectroscopic binary systems, and detailedabundance analyses have been performed. All program stars show acharacteristic lambda Bootis abundance pattern (deficient heavy elementsand solar abundant light elements) and an enhanced abundance of Na. Thiswork raises the fraction of lambda Bootis stars with known abundances to50%. The resulting abundances complemented by literature data are usedto construct a ``mean lambda Bootis abundance pattern'', which exhibits,apart from general underabundances of heavy elements (~-1 dex) and solarabundances of C, N, O, Na and S, a star-to-star scatter which is up totwice as large as for a comparable sample of normal stars. Based onobservations obtained at the Osservatorio Astronomico di Padua-Asiago,OPD/LNA, KPNO and DSO.
| Physical parameters of lambda Bootis stars
This is the first of two papers whose main goal is to update and improvethe information available on the physical properties of the lambdaBootis stars. The determination of the stellar parameters is offundamental importance to shed light into the different theoriesproposed to explain the lambda Bootis phenomenon. With this aim,projected rotational velocities, effective temperatures, surfacegravities and chemical abundances of a sample of suspected lambda Bootisstars have been calculated. Five objects showing composite spectratypical of binary systems were found in our analysis. The abundancedistribution of the program stars does not resemble the chemicalcomposition of the class prototype, lambda Boo, which poses someconcerns regarding the idea of a well-defined, chemically homogeneousgroup of stars. A possible relation between rotational velocities andthe lambda Bootis phenomenon has been found. This result would be inagreement with the accretion scenario proposed by Turcotte &Charbonneau (\cite{Turcotte93}). Figure 3 is only available inelectronic form at http://www.edpsciences.org
| A spectroscopic survey for lambda Bootis stars. III. Final results
In the third paper of a series dedicated to the spectroscopic survey fornew lambda Bootis stars, we present all new and confirmed members of thegroup as well as a detailed analysis of the observed sample. The natureof this small group of chemically peculiar stars of the upper mainsequence still challenges our understanding of processes like diffusion,mass-loss and accretion. The typical abundances pattern (nearly solarvalues for C, N, O and S whereas the Fe-peak elements are moderate tostrong underabundant) can still not be explained by any proposed theory.Hence, the significant increase of new members gives the opportunity toinvestigate the group properties in more detail. We report the discoveryof 26 new members of the group and the confirmation of 18 candidatesfrom the literature. This almost triples the number of known lambdaBootis stars. The existence of one member in the young open cluster NGC2264 and four members in the Orion OB1 association proves that thelambda Bootis phenomenon already works at very early stages of stellarevolution. Recent results from the Hipparcos mission have shown that thewell established lambda Bootis stars of the Galactic field comprise thewhole area from the Zero Age Main Sequence to the Terminal Age MainSequence (~ 109 yr for an A-type star). There is a continuoustransition between very young and rather evolved evolutionary stages. Wefind that the overall percentage of lambda Bootis type among all normaltype stars in the spectral range from B8 to F4 is 2% in the Galacticfield as well as in open clusters. Furthermore, 44 metal-weak objectsare listed which might be connected with the lambda Bootis phenomenon.Our biased sample (chosen by photometric boxes) is not distinguishedfrom all A-type stars in the corresponding spectral region by therotational velocity distribution. Only for the luminosity classes IV andIII (especially for the cooler program stars) the determined mean v sini values are very high compared to those of the literature. 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).
| 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).
| Kinematics of Metal-poor Stars in the Galaxy. II. Proper Motions for a Large Nonkinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected withoutkinematic bias and with available radial velocities, distance estimates,and metal abundances in the range -4.0<=[Fe/H]<=0.0. This updateof the 1995 Beers & Sommer-Larsen catalog includes newly derivedhomogeneous photometric distance estimates, revised radial velocitiesfor a number of stars with recently obtained high-resolution spectra,and refined metallicities for stars originally identified in the HKobjective-prism survey (which account for nearly half of the catalog)based on a recent recalibration. A subset of 1258 stars in this cataloghave available proper motions based on measurements obtained with theHipparcos astrometry satellite or taken from the updated AstrographicCatalogue (second epoch positions from either the Hubble Space TelescopeGuide Star Catalog or the Tycho Catalogue), the Yale/San Juan SouthernProper Motion Catalog 2.0, and the Lick Northern Proper Motion Catalog.Our present catalog includes 388 RR Lyrae variables (182 of which arenewly added), 38 variables of other types, and 1680 nonvariables, withdistances in the range 0.1 to 40 kpc.
| How many lambda Bootis stars are binaries?
In the attempt to shed new light on the lambda Boo phenomenon weanalyzed the astrometric, photometric and spectroscopic characteristicsof stars out of a list of recently selected lambda Boo candidates. Weshow that the class is still ill-defined and discuss the possibilitythat some, if not most stars presently classified as lambda Boo, are infact binary pairs and that peculiar abundances may not correspond toactual values if the average values of the atmospheric parameters{Teff} and log g are assumed and the effect of veiling is nottaken into account. Partly based on data from the ESA Hipparcosastrometry satellite.
| Pulsation in lambda Bootis stars
In this paper we present a further step in applying asteroseismictechniques to the group of lambda Bootis stars which can becharacterized as nonmagnetic A to F-type Population I dwarfs withsignificant (surface) underabundances of Fe-peak elements. Since noconclusive theory explaining the origin of the observed abundanceanomalies exists, an extensive photometric survey for pulsation in thisgroup has been initiated. Knowledge about the pulsational properties(most members are located within the classical instability strip) couldhelp to establish constrains about the overall abundance of these starsas well as on the evolutionary status. New photometric observations werecarried out for eleven stars. Variability was detected in four stars(e.g. lambda Bootis itself) whereas the remaining seven objects areprobably constant. In total, 52 members of this group have beenphotometrically investigated so far. With 22 pulsating and 30``constant'' stars, we derive a ratio of at least 50 % for variable tononvariable members inside the classical instability strip. This resultis based on high quality Hipparcos and new photometric data. Theobserved log /lineρ//lineρ_ȯ and log P values for thepulsating members are compatible with standard (solar abundant) deltaScuti models supporting the hypothesis that the found abundanceanomalies are restricted to the surface only. Otherwise the pulsationalproperties of this group are not outstanding compared to ``normal''delta Scuti stars, indicating that the mechanism driving the pulsationsis very similar. Based on observations obtained at ESO-La\,Silla, CTIO,SAAO, McDonald Observatory, Instituto Astrofisica Andalucia Observatoryand with the Hipparcos satellite
| On the evolutionary status of λ Bootis stars using HIPPARCOS data.
We have used the Hipparcos data to derive absolute magnitudes and thusthe evolutionary status for the group of λ Bootis stars. Theorigin for this small group of nonmagnetic, chemically peculiar stars,still remains a matter of debate. Using new evolutionary tracks, we areable to provide an age determination to distinguish between the twoproposed theories - the diffusion/mass-loss and the accretion theory.Our results establish the member of this group as objects which are veryclose to the Main Sequence. This is also supported by Pre-Main Sequenceevolutionary tracks as well as by observational results. We thereforecontradict prior conclusions that most of these stars are in the middleof their Main Sequence lifetime. The new results strongly support thepredictions of the accretion theory.
| Nonvariability among lambda Bootis stars
With asteroseismic techniques it is possible to investigate the interiorand the evolutionary status of stars via their frequency spectrum. Bothinformation would be very much needed for lambda Bootis stars, a groupof metal-poor Population I, A-type stars, since no conclusive theoryexists explaining the observed abundance anomalies. Geneva and Stromgrenphotometry place these stars inside the classical instability strip orat least very close to it. We therefore have started an extensivephotometric survey for pulsation in lambda Bootis stars and havediscovered so far 13 new variables. In this paper we present results forstars which presumably are constant, because we are able to establishonly an upper level for possible variability. A typical noise level of 3mmag for Stromgren b was achieved in the relevant frequency domain up to100 d^{-1}. Considering the given noise level of our survey, we concludethat at least 50% of all investigated lambda Bootis stars inside theinstability strip are pulsating, making this group remarkable comparedto stars with similar spectral types. This may suggest that a low(surface) metallicity has an influence on the pulsation Based onobservations obtained at ESO-La Silla, CTIO, SAAO, McDonald Observatory,Instituto Astrofisica Andalucia Observatory.
| A consolidated catalogue of lambda Bootis stars
lambda Bootis stars challenge our understanding of diffusion andaccretion processes related to stars and their circumstellarenvironment, and they are interesting components of the classicalinstability strip. Attempts to derive group properties with statisticalmethods are severely limited by the small number of unambiguouslyidentified lambda Bootis stars. In general, the subject appears to beobscured by incorrect memberships and it is therefore essential toprovide a sufficiently large catalogue of definitive group membersbefore modeling the lambda Bootis phenomenon. This paper describes thefirst steps towards this goal, based on our current knowledge of wellinvestigated members, leading to a concise definition of lambda Bootisstars: {Pop I hydrogen burning metal poor (except of C,N,O and S) A-typestars.} The definition does not depend on phenomenological features,like flux depressions, colour excesses, v sin i values, etc. Based on anew homogeneous catalogue with 45 lambda Bootis stars, we discussclassification criteria which can be used for a spectroscopic andphotometric all-sky survey for lambda Bootis stars in the field and inclusters of different ages. Based on observations obtained atESO-La,Silla, CTIO, Observatoire de Haute-Provence, OsservatorioAstronomico di Padua-Asiago, Univ. Toronto Southern Observatory,Observatorio do Pico dos Dias-LNA/CNPq/MCT (Brazil). Table 1 is alsoavailable 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.
| Interstellar Reddening in the Southern Hemisphere. II. Analysis of the uvby-Beta Observations
Photometric color excesses and distances plus heliocentric coordinatesare calculated for 3,762 southern A and early F stars. The presentresults, combined with those previously published for the northernhemisphere, complete the coverage of the spatial distribution ofinterstellar reddening in the entire solar neighborhood. The newreddening maps show that the interstellar matter within 300 pc of theSun forms a single very large cloud complex that is somewhatasymmetrical with respect to both the galactic center and the galacticplane. This complex is characterized by pronounced local irregularitiesin both density and spatial extent. The observations further indicatethat (1) the cloud complex is not associated with Gould's belt; (2)there exist large regions of the sky devoid of dust; (3) interstellarreddening is negligible at the galactic poles; (4) the role ofintercloud dust in the southern hemisphere; (5) the Sun is not locatedin a dust-free, spherically symmetric bubble as previously thought; and(6) the Sun is, however, located in an elongated dust-free region knownas the "local trough.". (SECTION: Interstellar Medium and Nebulae)
| Nonvariability among lambda Bootis Stars III.: CTIO (1995) and McDonald (1995) Data
Not Available
| uvby beta Photometry of Stars of "Astrophysical Interest"
Not Available
| Kinematics of metal-poor stars in the galaxy
We discuss the kinematic properties of a sample of 1936 Galactic stars,selected without kinematic bias, and with abundances (Fe/H) is less thanor equal to -0.6. The stars selected for this study all have measuredradial velocities, and the majority have abundances determined fromspectroscopic or narrow-/intermediate-band photometric techniques. Incontrast to previous examinations of the kinematics of the metal-poorstars in the Galaxy, our sample contains large numbers of stars that arelocated at distances in excess of 1 kpc from the Galactic plane. Thus, amuch clearer picture of the nature of the metal-deficient populations inthe Galaxy can now be drawn.
| Catalogue of Lambda Bootis Candidates
Not Available
| Astrometric and astrophysical discontinuities between the galactic old disk and halo stellar populations
Intermediate band, RI, and DDO photometry of the weak-lined stars in thefirst three volumes of the Michigan catalogs of spectral type arediscussed on the basis of luminosity and heavy element abundance. Theinterface between the old disk (Fe/H greater than -0.8 dex) and halo(Fe/H less than -1.2 dex) populations represents discontinuities in boththe stellar motions and the stellar physics. The CN strengths of bothevolved and unevolved halo stars decrease with decreasing temperature,in a mirror image of the increase with decreasing temperature for thedisk objects. The result for the halo giants has been attributed to deepmixing in the stellar atmospheres but the similar result for unevolveddwarfs indicates a difference in formation rather than in evolutionaryprocess of the two populations.
| Further DA Photometry of I-Bootis Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989A&AS...81..335M&db_key=AST
| Search for Lambda Bootis type candidates
An extensive search for Lambda Bootis candidates has been madethroughout the whole Geneva photometric catalogue and 17 stars have beenfound, matching the photometric conditions to be Lambda Bootis stars.Thirteen stars proposed by Abt (1984) as Lambda Bootis candidates, onthe basis of the weakness of the 4481 Mg II line, also match theseconditions.
| Population studies. I - The Bidelman-MacConnell 'weak-metal' stars
BRVI and DDO photometry are presented for 309 Bidelman-MacConnell'weak-metal' stars. Radial velocities are calculated for most of thestars having Fe/H abundances of no more than -0.8. The photometricobservations were carried out using the 0.6-meter and 1.0-metertelescopes of the Siding Spring Observatory. Photometric taxonomy wasused to classify the stars as dwarfs, giants, red-horizontal branchstars, and ultraviolet-bright stars, respectively. It is found that 35percent of the stars are giants; 50 percent are dwarfs; and 5 percentbelong to the red-horizontal branch group. The role of selection effectsin investigations of the formation of the Galaxy is discussed on thebasis of the photometric observations and the observational constraintsproposed by Eggen et al. (1962).
| Weak-lined stars in the Michigan spectral survey. I - A-, F-, and G-type stars
Data from intermediate-band and H-beta photometric observations of 89early-type stars classified as weak-lined by Bidelman and MacConnell(1973), Houk and Cowley (1975), or Houk (1978 and 1982) are presented intables and graphs and analyzed. The group is found to comprise 55 diskstars and 34 halo stars (Fe/H less than -0.65), including 21 near themain-sequence turnoff, seven red horizontal-branch stars, one bluehorizontal-branch star, one suprahorizontal-branch object, and four bluestragglers; five of the newly identified halo stars are shown to haveradial velocities in excess of 100 km/s. Special consideration is givento the 17 early-type members of Kapetyn's star group (Eggen, 1977), andthe mean luminosity and Fe/H ratio of the four very-short-periodCepheids of this group are determined as 0.75 mag and -1.7.
| Metal-Deficient Giants in the Galactic Field - Catalogue and Some Physical Parameters
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | מפרש |
| התרוממות ימנית: | 09h23m02.06s |
| סירוב: | -49°03'30.8" |
| גודל גלוי: | 8.889 |
| מרחק: | 265.252 פארסק |
| תנועה נכונה: | -10.3 |
| תנועה נכונה: | -12.4 |
| B-T magnitude: | 9.227 |
| V-T magnitude: | 8.917 |
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