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The S-Type Asymptotic Giant Branch Stars RS Cnc, ST Her, OP Her And HR Peg
We present FCAPT differential Johnson l BV and Cousins l RI photometryand radial velocities of the S-type AGB stars RS Cnc, ST Her, OP Her andHR Peg. We performed multiperiodic analyses of this photometry to learnabout the frequencies of variability. The l B, V, R, and l I lightcurves are generally in phase. RS Cnc has periods of order 122 and 248days. Repeating the analyses using our data with the extensive l V and lR photometry of Percy et al. (2001) shows several periods near 248 daysand a period near 135 days. The primary period of ST Her appears to beabout 144 days although it is manifested most readily by its 103 dayalias. OP Her and HR Peg exhibit periods, respectively, of about 416 and116 days and of 54 and 74 days. The differences between our data set andthe larger one of Percy et al. (2001) for RS Cnc raises importantquestions about multiperiodic analyses for AGB stars.Tables 2, 4 and 6 are 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/Abstract.html.
| 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
| Long-Term VRI Photometry of Small-Amplitude Red Variables. I. Light Curves and Periods
We report up to 5000 days of VRI photometry, from a robotic photometrictelescope, of 34 pulsating red giants, namely, TV Psc, EG And, Z Psc, RZAnd, 4 Ori, RX Lep, UW Lyn, η Gem, μ Gem, ψ1 Aur,V523 Mon, V614 Mon, HD 52690, Y Lyn, BC CMi, X Cnc, UX Lyn, RS Cnc, VYUMa, ST UMa, TU CVn, FS Com, SW Vir, 30 Her, α1 Her,V642 Her, R Lyr, V450 Aql, V1293 Aql, δ Sge, EU Del, V1070 Cyg, WCyg, and μ Cep, as well as a few variable comparison stars. V, R, andI variations are generally in phase. The length and density of the dataenable us to look for variations on timescales ranging from days toyears. We use both power-spectrum (Fourier) analysis and autocorrelationanalysis, as well as light-curve analysis; these three approaches arecomplementary. The variations range from regular to irregular, but inmost of the stars, we find a period in the range of 20-200 days, whichis probably due to low-order radial pulsation. In many of the stars, wealso find a period which is an order of magnitude longer. It may be dueto rotation, or it may be due to a new kind of convectively inducedoscillatory thermal mode, recently proposed by P. Wood.
| Levels of coronal and chromospheric activity in late-type stars and various types of dynamo waves
We analyze the X-ray emission and chromospheric activity of late-type F,G, and K stars studied in the framework of the HK project. More powerfulcoronas are possessed by stars displaying irregular variations of theirchromospheric emission, while stars with cyclic activity arecharacterized by comparatively modest X-ray luminosities and ratios ofthe X-ray to bolometric luminosity L X/L bol. This indicates that thenature of processes associated with magnetic-field amplification in theconvective envelope changes appreciably in the transition from small tolarge dynamo numbers, directly affecting the character of the(α-Ω) dynamo. Due to the strong dependence of both thedynamo number and the Rossby number on the speed of axial rotation,earlier correlations found between various activity parameters and theRossby number are consistent with our conclusions. Our analysis makes itpossible to draw the first firm conclusions about the place of solaractivity among analogous processes developing in active late-type stars.
| Photometric and Ca II H and K Spectroscopic Variations in Nearby Sun-like Stars with Planets. III.
We present the results of an analysis of time-series photometry, Ca II Hand K spectrophotometry, and high-dispersion visible spectra of ninenearby Sun-like stars recently identified as having planets. For the sixstars whose presumed planets have orbital periods of less than 4 months(τ Boo, 51 Peg, υ And, ρ1 Cnc, ρ CrB, and70 Vir), sine-curve fits to the photometric data show no variations withsemiamplitude greater than 1 or 2 parts in 104. Photometricvariations in 47 UMa are similarly small, although our photometric dataof this star are slightly affected by variability of the comparisonstar. Nonvariability at this level of precision is sufficient to ruleout surface magnetic activity as the cause of the observedradial-velocity variations in these seven stars and makes nonradialpulsations unlikely as well. Thus, our photometry provides indirect butstrong support for true reflex motions-planets-in these seven stars, butcannot yet so support the planetary hypothesis for the two additionalstars, 16 Cyg B and Gl 411. Continued photometric monitoring of theshort-period systems may soon result in the direct detection of theseplanets in reflected light. We have used our photometric fluxes tosearch for possible transits of the extrasolar planets. Transitsdefinitely do not occur in τ Boo, 51 Peg, υ And, andρ1 Cnc, and probably do not occur in ρ CrB and 70Vir. Our transit-search results are inconclusive for 47 UMa, and wecannot address the issue for 16 Cyg B and Gl 411. The precision of ourphotometry is sufficient to detect transits of planets even if they arenot gas giants, as currently assumed, but much smaller objects withrocky compositions. The chance of finding at least one transit in thesix stars is ~40%. We find significant year-to-year photometricvariability only in τ Boo, which is not only the youngest star inthe sample but also the star with the shallowest convective zone. Theinterseasonal range in its yearly mean photometric flux is ~0.002 mag,roughly twice the 0.0008 mag decadal variation in the Sun's totalirradiance. Monitoring of the relative Ca II H and K fluxes beganbetween 1966 and 1968 for 51 Peg, τ Boo, ρ CrB, and Gl 411,between 1990 and 1993 for 47 UMa, 70 Vir, 16 Cyg B, andρ1 Cnc, and in 1996 for υ And. The data have beennewly recalibrated for improved long-term instrumental stability,resulting in better precision of the Ca II records. Five of the ninestars in this study have little or no detectable year-to-year variationin Ca II flux. The remaining four show moderate or pronouncedvariability: τ Boo, whose radial-velocity and photometric variationshave comparatively high amplitudes; Gl 411, whose planetary companionwas inferred astrometrically, not spectroscopically; ρ1Cnc, which may undergo decadal cyclic activity; and υ And, whichshows moderate year-to-year variability. Except for 47 UMa,intraseasonal variability consistent with rotation was detected in theCa II records of all stars. However, the rotation periods determined forυ And, 70 Vir, and 16 Cyg B are of low confidence. Anexamination of the recalibrated Ca II records for 51 Peg finds arotation period of 22 days, in contrast to our previous result of 37days. Ages have been estimated from the mean Ca II flux and, wherepossible, the rotation period. We find general consistency with the agesdetermined by others comparing properties determined fromhigh-resolution spectroscopy to evolutionary models, although theuncertainties are, in general, large. Based on observations made atMount Wilson Observatory, operated by the Mount Wilson Institute, underan agreement with the Carnegie Institution of Washington and theautomatic photoelectric telescope at Fairborn Observatory in thePatagonia Mountains of southern Arizona.
| Library of Medium-Resolution Fiber Optic Echelle Spectra of F, G, K, and M Field Dwarfs to Giant Stars
We present a library of Penn State Fiber Optic Echelle (FOE)observations of a sample of field stars with spectral types F to M andluminosity classes V to I. The spectral coverage is from 3800 to 10000Å with a nominal resolving power of 12,000. These spectra includemany of the spectral lines most widely used as optical and near-infraredindicators of chromospheric activity such as the Balmer lines (Hαto Hepsilon), Ca II H & K, the Mg I b triplet, Na I D_1, D_2, He ID_3, and Ca II IRT lines. There are also a large number of photosphericlines, which can also be affected by chromospheric activity, andtemperature-sensitive photospheric features such as TiO bands. Thespectra have been compiled with the goal of providing a set of standardsobserved at medium resolution. We have extensively used such data forthe study of active chromosphere stars by applying a spectralsubtraction technique. However, the data set presented here can also beutilized in a wide variety of ways ranging from radial velocitytemplates to study of variable stars and stellar population synthesis.This library can also be used for spectral classification purposes anddetermination of atmospheric parameters (T_eff, logg, [Fe/H]). A digitalversion of all the fully reduced spectra is available via ftp and theWorld Wide Web (WWW) in FITS format.
| Patterns of Variation among Sun-like Stars
We examine the patterns of variation among a sample of 35 stars thatincludes the Sun, particularly on the timescale of the 11 yr solaractivity cycle. Our investigation uses contemporaneous photometric andchromospheric HK emission time series measurements from the Lowell andMount Wilson Observatories, and comparable solar data. We find that thephotometric and HK variability of the stars in our sample can be relatedto their average level of chromospheric activity by power laws. Thephotometric variability of the Sun may be somewhat subdued for itsaverage activity level. We find that the younger, more active stars inour sample tend to become fainter as their HK emission increases,whereas the older, less active stars tend to become brighter as their HKemission increases, as the Sun does during its activity cycle.
| The Photometric Variability of Sun-like Stars: Observations and Results, 1984--1995
Using differential Stromgren b, y photometry, we monitored thebrightness variations of 41 program stars and their 73 comparison starsfrom 1984 through 1995. The predominantly main-sequence program starsspanned ranges of temperature and mean chromospheric activity centeredon solar values. About 40% of all the stars showed measurablevariability, typically at levels below 0.01 mag (~1%), on bothnight-to-night and year-to-year timescales. The variability correlatedwith mean chromospheric activity and advancing spectral type. We presentdifferential light curves and statistical descriptions of ourobservations.
| Magnetic Field and Rotation in Lower Main-Sequence Stars: an Empirical Time-dependent Magnetic Bode's Relation?
We find a significant correlation between the magnetic and rotationalmoments for a sample of 112 lower main-sequence stars. The rotationalmoment is calculated from measurements of the rotation period in most ofthe stars (not from the projected rotational velocity inferred fromDoppler broadening). The magnetic moment is computed from a database ofhomogeneous measurements of the mean level of Ca II H and K emissionfluxes sampled for most of the stars over an interval of 25 yr. Theslope connecting the logarithm of the magnetic moment and the logarithmof the rotational moment is about +0.5--0.6, with a Pearson correlationcoefficient of about +0.9. The scatter of points from the mean relationhas a component that is natural and caused by decade-long surfacevariability.
| Coronal X-ray emission of cool stars in relation to chromospheric activity and magnetic cycles.
We study the relationship between the coronal X-ray emission of single,main-sequence F-K stars and the characteristics of their magneticcycles. We use X-ray data primarily from the ROSAT all-sky survey (RASS)as well as data acquired by us in the ROSAT pointed program, and thepublished data of the Mt. Wilson CaII H+K monitoring program. Accordingto their CaII H+K long-term variability characteristics, we divide thestars into three groups: non-variable, regular variable and irregular(chaotic) variable stars. We show that the regular and the irregularstars differ mainly in their Rossby-numbers (Ro): regular stars havealmost always Ro<1 whereas the irregular group is characterized byRo>1 further, the X-ray surface flux distributions differsignificantly between these three groups. We discuss to what extentstars exhibiting constant Ca II fluxes can be considered "Maunderminimum" stars, and demonstrate - in a statistical sense - that cyclicchromospheric activity also implies cyclic coronal activity. From areanalysis of the flux-flux relation between the calcium excess fluxdensity ({DELTA}F_Ca_) and F_X_, we find different relations between theregular and the constant stars on one hand and the irregular stars onthe other hand. Performing regression analysis in the form of a powerlaw, the coefficient κ is derived to be κ=~1 for constantand regular stars whereas κ=~2 for the more active irregularstars. We discuss our findings in the context of a transition from anonlinear to a linear dynamo regime when going from irregular to regularstars.
| Chromospheric variations in main-sequence stars
The fluxes in passbands 0.1 nm wide and centered on the Ca II H and Kemission cores have been monitored in 111 stars of spectral type F2-M2on or near the main sequence in a continuation of an observing programstarted by O. C. Wilson. Most of the measurements began in 1966, withobservations scheduled monthly until 1980, when observations werescheduled sevral times per week. The records, with a long-term precisionof about 1.5%, display fluctuations that can be identified withvariations on timescales similar to the 11 yr cycle of solar activity aswell as axial rotation, and the growth and decay of emitting regions. Wepresent the records of chromospheric emission and general conclusionsabout variations in surface magnetic activity on timescales greater than1 yr but less than a few decades. The results for stars of spectral typeG0-K5 V indicate a pattern of change in rotation and chromosphericactivity on an evolutionary timescale, in which (1) young stars exhibithigh average levels of activity, rapid rotation rates, no Maunderminimum phase and rarely display a smooth, cyclic variation; (2) starsof intermediate age (approximately 1-2 Gyr for 1 solar mass) havemoderate levels of activity and rotation rates, and occasional smoothcycles; and (3) stars as old as the Sun and older have slower rotationrates, lower activity levels and smooth cycles with occasional Maunderminimum-phases.
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| All-sky Stromgren photometry of speckle binary stars
All-sky Stromgren photometric observations were obtained for 303 specklebinaries. Most stars were in the range of V = 5-8. These data, whencombined with ratios of intensities from the CHARA speckle photometryprogram, will allow the determination of photometric indices for theindividual components of binary stars with separations as small as 0.05arcsec. These photometric indices will complement the stellar massesfrom the speckle interferometry observations to provide a much improvedmass-luminosity relationship.
| CA II H and K measurements made at Mount Wilson Observatory, 1966-1983
Summaries are presented of the photoelectric measurements of stellar CaII H and K line intensity made at Mount Wilson Observatory during theyears 1966-1983. These results are derived from 65,263 individualobservations of 1296 stars. For each star, for each observing season,the maximum, minimum, mean, and variation of the instrumental H and Kindex 'S' are given, as well as a measurement of the accuracy ofobservation. A total of 3110 seasonal summaries are reported. Factorswhich affect the ability to detect stellar activity variations andaccurately measure their amplitudes, such as the accuracy of the H and Kmeasurements and scattered light contamination, are discussed. Relationsare given which facilitate intercomparison of 'S' values with residualintensities derived from ordinary spectrophotometry, and for convertingmeasurements to absolute fluxes.
| A first catalogue of speckle-interferometric measurements of binary stars made with 6-m telescope of the USSR AS.
Not Available
| A uvby-beta survey of CaII emission stars. I - The observations
Homogeneous uvby-beta photometry has been obtained for 73 Ca II emissionstars. The standard colors and V magnitudes are presented, with adetailed discussion of atmospheric extinction and transformationcoefficients. A study of reddening is also included.
| Interferometric Observations of Double Stars in 1985 and 1986
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988A&AS...72..563T&db_key=AST
| Spectral classification of weak-lined stars discovered photometrically
A random sample of 140 stars of the 800+ members in Olsen's (1984)sample of stars believed to be weak-lined has been observed andclassified independently of knowledge of the stars' photometriccharacteristics. It is found that 97 percent of the proposed weak-lineddwarfs are indeed such; the remainder are composites or normal, moreluminous stars. Deficiencies in the metallic-line types are comparedwith (Fe/H) values and metallic strength indices. These comparisons showthat a metal deficiency of at least a factor of two is needed before thespectra look weak-lined.
| Digital speckle interferometry of 72 binary stars
Position angles and separations have successfully been measured for 72double stars with a digital speckle interferometer on the 6-m telescope.In both Theta and rho the internal measurement error is about 0.003 ofarc mins. The small residuals from published orbits indicate thatappreciable systematic effects are abent. In addition, 43 other starswere unresolved at the epochs specified.
| Rotation, convection, and magnetic activity in lower main-sequence stars
Rotation periods are reported for 14 main-sequence stars, bringing thetotal number of such stars with well determined rotation periods to 41.It is found that the mean level of their Ca II H and K emission(averaged over 15 years) is correlated with rotation period, asexpected. However, there is a further dependence of the emission onspectral type. When expressed as the ratio of chromospheric flux tototal bolometric flux, the emission is well correlated with theparameter P(obs)/tau(c), where P(obs) is the observed rotation periodand tau(c)(B - V) is a theoretically-derived convective overturn time,calculated assuming a mixing length to scale height ratio alpha of about2. This finding is consonant with general predictions of dynamo theory,if the relation between chromospheric emission and dynamo-generatedmagnetic fields is essentially independent of rotation rate and spectraltype for the stars considered. The dependence of mean chromosphericemission on rotation and spectral type is essentially the same for starsabove and below the Vaughan-Preston (1980) 'gap', thus casting doubt onexplanations of the gap in terms of a discontinuity in dynamocharacteristics.
| The photometric variability of solar-type stars. II - Stars selected from Wilson's chromospheric activity survey
Eleven solar-type main-sequence stars have been observed to search forcontinuum variability. Stars were selected from Wilson's chromosphericactivity survey, and were observed for periods of three to six monthswith intermediate-band Stroemgren uvby photometry. Evidence is foundthat two of these eleven stars are variable and that one other may be.Comparison with contemporaneous Ca II H + K emission flux measurementsshows that the amplitude of photometric variability correlates stronglywith both the mean emission flux and the amplitude of its variation.Variations in continuum light and emission flux tend to correlate intime, as well, with continuum minima coinciding with emission maxima andvice-versa. It is inferred that the surface activity of these starstends to be confined to localized activity centers that include bothemission plages and dark spots, similar to the active regions observedon the sun.
| Binary Stars Unresolved by Speckle Interferometry - Part Two
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981PASP...93..221M&db_key=AST
| Short time-scale variability of chromospheric CA II in late-type stars
The short time-scale variability of singly ionized calcium chromosphericemission has been investigated in a few late-type stars. Emission-linevariations with time scales of a few minutes to hours are seen in AlphaTau (K5 III), Lambda And (G8 III-IV), and Epsilon Eri (K2 V). Theexistence of substantial chromospheric flux changes (10 to the 30th to10 to the 32nd ergs) over short periods of time suggests that thecalcium emission arises from a few small, coherent regions. Frequenciespresent in the data are discussed in the context of acoustic wavepredictions and estimated acoustic cutoff frequencies for giants anddwarfs.
| MK spectral types for some F and G stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979PASP...91...83C&db_key=AST
| Binary stars unresolved by speckle interferometry
The epochs of 372 speckle observations obtained with the 4-m Mayalltelescope at KPNO during 1975-77 are given for 156 unresolved visual,astrometric, spectrum, occultation, and spectroscopic binary stars.Specified thresholds are set for detectible angular separations andmagnitude differences so that the negative observations presented herecan be used to place constraints on orbital parameters.
| Flux measurements of CA II H and K emission
A four-channel photon-counting spectrophotometer (designated HKP-2) isdescribed which is designed for measuring stellar chromospheric calciumemission. The HKP-2 is calibrated, and its performance and accuracyevaluated, by observing 63 of Wilson's (1968) program stars on the samenights with both the HKP-2 and a coude scanner designated HKP-1. Theresults of the observations are discussed in terms of the calibration ofmean H-K flux indices, variations in individual stellar fluxes, the fluxratio for H and K, and the instrument color index. It is shown that theHKP-2 provides satisfactory performance in the measurement of stellarchromospheric emission in a manner closely analogous to the method ofWilson and that a single observation yields a color index as well asflux indices for H and K that can be calibrated and transferredunambiguously to Wilson's system of measurement.
| Chromospheric variations in main-sequence stars
An analysis is given of fluxes measured in 1-A bands centered on the CaII H and K lines for a sample of 91 main-sequence stars, extending fromabout F5 to M2, over time intervals of nine to 11 years. The results arediscussed separately for a set of 18 stars with minimal chromosphericfluxes used as standards, the program stars of spectral types F7 to G3,the program stars of types G5 and later, as well as the sun. K/H ratiosare determined and compared for the different groups of stars. It istentatively concluded that: (1) no stellar chromospheres are likely tobe constant in time; (2) short-term fluctuations tend to increase insize with average flux; (3) cyclical variations occur with periodsranging from about 7 years to probably at least twice as long; (4) thestellar cycles observed in H and K flux should be regarded as evidencefor analogs of the solar cycle; and (5) the incidence of complete orprobable partial cycles increases toward later spectral types.
| Absolute luminosity calibration of F stars
Luminosity calibrations are performed for a restricted sample of 706F-type field stars of all luminosity classes and a similarly restrictedsample of 251 main-sequence F stars. The samples are restricted withrespect to values of photometric and metallicity indices, propermotions, radial velocities, and apparent magnitudes. Both linear andsecond-order relations between absolute magnitude and the photometricindices beta, /c1/ or (b-y), /c1/ are considered.These relations are calibrated by the statistical parallax method basedon the principle of maximum likelihood. The possible effect ofinterstellar absorption on the calibration results is investigated alongwith an effect of a photometric correction to the absolute magnitudes.The results obtained are compared with those of Crawford (1975) as wellas with the trigonometric parallaxes. The coefficients of thecalibration relations are derived from the trigonometric parallaxes, andpoor agreement is indicated. It is concluded that the trigonometricparallaxes must be used very carefully and only for nearby stars.
| Spectral classification of the bright F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88...95C&db_key=AST
| A Spectroscopic Orbit for the AM Eclipsing System AN Andromedae
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974PASP...86...63Y&db_key=AST
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