On metal-deficient barium stars and their link with yellow symbiotic stars
This paper addresses the question of why metal-deficient barium starsare not yellow symbiotic stars (YSyS). Samples of (suspected)metal-deficient barium (mdBa) stars and YSyS have been collected fromthe literature, and their properties reviewed. It appears in particularthat the barium nature of the suspected mdBa stars needs to beascertained by detailed abundance analyses. Abundances are thereforederived for two of them, HD 139409 and HD 148897, which reveal that HD148897 should not be considered a barium star. HD 139409 is a mildbarium star, with overabundances observed only for elements belonging tothe first s-process peak (Y and Zr). It is only moderately metal-poor([Fe/H] = -0.4). The evidence for binarity among mdBa stars is thenreviewed, using three different methods: (i) radial-velocity variations(from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii)a method based on the comparison between the Hipparcos and Tycho-2proper motions. An orbit is obtained for HIP 55852, whereas evidence forthe (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874and HIP 107478 is presented. No conclusion regarding the binary natureof HIP 11595, HIP 25161 could be reached. Two stars with no evidence forbinarity whatsoever (HIP 58596 and BD +3°2688) are candidateslow-metallicity thermally-pulsing asymptotic giant branch stars, asinferred from their large luminosities. The reason why mdBa stars arenot YSyS is suggested to lie in their different orbital perioddistributions: mdBa stars have on average longer orbital periods thanYSyS, and hence their companion accretes matter at a lower rate, for agiven mass loss rate of the giant star. The definite validation of thisexplanation should nevertheless await the determination of the orbitalperiods for the many mdBa stars still lacking periods, in order to makethe comparison more significant.
|
Analysis of the Na, Mg, Al, and Si Abundances in the Atmospheres of Red Giants of Different Spectral Subgroups
We analyze the Na, Mg, Al, and Si abundances in the atmospheres of morethan 40 stars, includingred giants of different spectral subgroups(normal red giants, mild and classical barium stars) and severalsupergiants. All these elements exhibit abundance excesses, with theoverabundance increasing with the star’s luminosity. Thedependence of the overabundances for each of these elements on theluminosity (or log g) is the same for all the spectral subgroups,testifying to a common origin: they are all products of hydrogen burningin the NeNa and MgAl cycles that have been dredged up from the stellarinteriors to the outer atmospheric layers by convection that graduallydevelops during the star’s evolution from the main sequence to thered-giant stage. The sodium abundances derived for several stars arelower than for other stars with similar atmospheric parameters. The agesand kinematic characteristics of these two groups of stars suggest thatthey probably belong to different stellar generations.
|
The Structure of Pluto's Atmosphere from the 2002 August 21 Stellar Occultation
We have observed the 2002 August 21 occultation by Pluto of the R=15.7mag star P131.1, using 0.5 s cadence observations in integrated whitelight with the Williams College frame-transfer, rapid-readout CCD at the2.24 m University of Hawaii telescope. We detected an occultation thatlasted 5 minutes, 9.1+/-0.7 s between half-light points. The ``kinks''in the ingress and egress parts of the curve that were apparent in 1988had become much less pronounced by the time of the two 2002 occultationsthat were observed, indicating a major change in the structure ofPluto's atmosphere. Analysis of our light curves shows that the pressurein Pluto's atmosphere has increased at all the altitudes that we probed.Essentially, the entire pressure scale has moved up in altitude,increasing by a factor of 2 since 1988. Spikes in our light curve revealvertical structure in Pluto's atmosphere at unprecedentedly highresolution. We have confirmation of our spikes at lower time resolutionas part of observations of the emersion made at 1.4 s and 2.4 s cadencewith the 3.67 m AEOS telescope on Maui.
|
Analysis of Atmospheric Abundances in Classical Barium Stars
We present our analysis of elemental abundances in the atmospheres of 16classical barium stars derived from high-resolution spectra and modelatmospheres. Comparison of the results with analogous data for moderatebarium stars and normal red giants shows that the abundance patterns forelements before the iron peak are the same for all three groups of redgiants, testifying to a similar origin. For binary systems, we confirmthe influence of the orbital period and, hence, the componentseparation, on the overabundance of s-process elements. The amount ofenrichment in s-process elements is also influenced by mass,metallicity, and evolutionary phase. Any of these parameters can beimportant in individual objects.
|
Catalogs of temperatures and [Fe/H] averages for evolved G and K stars
A catalog of mean values of [Fe/H] for evolved G and K stars isdescribed. The zero point for the catalog entries has been establishedby using differential analyses. Literature sources for those entries areincluded in the catalog. The mean values are given with rms errors andnumbers of degrees of freedom, and a simple example of the use of thesestatistical data is given. For a number of the stars with entries in thecatalog, temperatures have been determined. A separate catalogcontaining those data is briefly described. Catalog only available atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|
Neptune's Stratospheric Winds from Three Central Flash Occultations
We present observations of three Neptune central flash events: the 20August 1985 occultation of n39 from the European Southern Observatory(ESO), the 12 September 1988 occultation of N51 from Pic du Midi, andthe 8 July 1989 occultation of N55 from ESO. From simultaneous fits tothe three central flash lightcurves, we determine the shape of Neptune'slimb, and show that winds near the 0.38-mbar level have decayed to about~=0.6 +/- 0.2 times their strength at 100 mbar, assuming that thelatitude-dependence of the stratospheric winds follows the zonal windprofile of L. A. Sromovsky et al. (1993, Icarus 105, 110-141). From themeasured decay of winds with height, we find that the average verticalshear in the zonal wind between 100 and 0.38 mbar is very close to theVoyager IRIS results for the 30- to 120-mbar region (B. J. Conrath etal., 1989, Science 246, 1454-1459), at the latitudes to which thecentral flashes are most sensitive. We also determine the shape of thelimb at the 0.7-mubar level from the ``half-light'' points of theatmospheric immersion and emersion light curves of five stellaroccultations by Neptune. The winds in this pressure regime have decayedto ~=0.17 times their strength at the 100-mbar level, and the verticalshear in the zonal wind as determined from the thermal wind equation andVoyager IRIS measurements extends essentially unchanged all the way upto the microbar level of the stratosphere. Alternatively, a simpleoblate model fit to the planetary limb gives an oblateness of epsilon =0.0180 +/- 0.0010 and an equatorial radius of r_e = 25262.7 +/- 3.5 km.The corresponding rotation period is 16.59 +/- 0.92 h, quite similar tothat of Neptune's deep interior (16.11 h). This near corotation suggeststhat there is some coupling between Neptune's interior and the upperstratosphere, even though the intervening atmosphere between the clouddeck and the stratosphere has strong retrograde flow.
|
Barium stars, galactic populations and evolution.
In this paper HIPPARCOS astrometric and kinematical data together withradial velocities from other sources are used to calibrate bothluminosity and kinematics parameters of Ba stars and to classify them.We confirm the results of our previous paper (where we used data fromthe HIPPARCOS Input Catalogue), and show that Ba stars are aninhomogeneous group. Five distinct classes have been found i.e. somehalo stars and four groups belonging to disk population: roughlysuper-giants, two groups of giants (one on the giant branch, the otherat the clump location) and dwarfs, with a few subgiants mixed with them.The confirmed or suspected duplicity, the variability and the range ofknown orbital periods found in each group give coherent resultssupporting the scenario for Ba stars that are not too highly massivebinary stars in any evolutionary stages but that all were previouslyenriched with Ba from a more evolved companion. The presence in thesample of a certain number of ``false'' Ba stars is confirmed. Theestimates of age and mass are compatible with models for stars with astrong Ba anomaly. The mild Ba stars with an estimated mass higher than3Msun_ may be either stars Ba enriched by themselves or``true'' Ba stars, which imposes new constraints on models.
|
Absolute magnitudes and kinematics of barium stars.
The absolute magnitude of barium stars has been obtained fromkinematical data using a new algorithm based on the maximum-likelihoodprinciple. The method allows to separate a sample into groupscharacterized by different mean absolute magnitudes, kinematics andz-scale heights. It also takes into account, simultaneously, thecensorship in the sample and the errors on the observables. The methodhas been applied to a sample of 318 barium stars. Four groups have beendetected. Three of them show a kinematical behaviour corresponding todisk population stars. The fourth group contains stars with halokinematics. The luminosities of the disk population groups spread alarge range. The intrinsically brightest one (M_v_=-1.5mag,σ_M_=0.5mag) seems to be an inhomogeneous group containing bariumbinaries as well as AGB single stars. The most numerous group (about 150stars) has a mean absolute magnitude corresponding to stars in the redgiant branch (M_v_=0.9mag, σ_M_=0.8mag). The third group containsbarium dwarfs, the obtained mean absolute magnitude is characteristic ofstars on the main sequence or on the subgiant branch (M_v_=3.3mag,σ_M_=0.5mag). The obtained mean luminosities as well as thekinematical results are compatible with an evolutionary link betweenbarium dwarfs and classical barium giants. The highly luminous group isnot linked with these last two groups. More high-resolutionspectroscopic data will be necessary in order to better discriminatebetween barium and non-barium stars.
|
The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
|
S-process element overabundances of BA stars through wind accretion.
Not Available
|
Examination of the wind accretion scenario for barium stars
In this note, we confront the results of a spectroscopic analysis givings-process element abundances in a sample of barium stars withtheoretical predictions from the wind accretion scenario of Boffin &Jorissen (1988). This comparison is done in the overabundance-orbitaqlperiod plane.
|
A Spectroscopic Analysis of Barium Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994A&A...283..937Z&db_key=AST
|
Lithium in the barium stars
Analysis of high-resolution spectra of classical barium giants revealsthat an unidentified line is a major contributor to thestellar-absorption feature at 6707.8 A attributed previously to a blendof CN lines and the Li I resonance doublet. The strength of theunidentified line is well correlated with the strength of a Ce II line.In contrast to published reports of positive identifications ofabsorption due to the Li I doublet, an acceptable fit of a syntheticspectrum to the observed spectrum of a barium giant is obtainablewithout a significant contribution from the Li I doublet. Upper limitsto the Li abundance of classical barium giants are now consistent withthose expeeted if CH subgiants evolve into barium giants.
|
The southern Vilnius photometric system. I - Transformation to the standard system
This paper is the first in a series on the extension of the Vilniusphotometric system to the southern hemisphere. Observations of a commonset of 73 stars measured in both hemispheres are described and ananalysis of the differences is given.
|
UBV photometry of barium stars
Magnitudes in V and B-V and U-B colors observed by the 91-cm telescopeat Okayama are presented for 109 stars including both classical andmarginal barium stars. The two-color diagram shows a fair amount ofspread. This can be interpreted by interstellar reddening and variableamounts of line blocking effect. Both classical and marginal bariumstars form a fairly homogeneous group.
|
Taxonomy of barium stars
Spectral classification, barium intensity, radial velocity, luminosity,and kinematical properties are determined for 389 barium stars byanalyzing image-tube spectra and photometric observation data. Diskkinematics for the stars are based on whether they are Ba weak or Bastrong. Weak barium stars in general have smaller velocity dispersions,brighter apparent magnitude, and lower luminosity than strong bariumstars. These characteristics are confirmed by solving for meanspectroscopic distances, z-scale height distances, and reduced propermotions.
|
Spectroscopical study of barium stars. IV. Chemical composition of HD 77247, 130386, 131670, 139409, 202109, 218356.
Not Available
|
Spectroscopic Study of Barium Stars - Part Two - Chemical Composition of HD16458 HD204075 HD199394 HD199939 and HD196678
Not Available
|
Photoelectric photometry of carbon and barium stars in the Vilnius seven-color system and their color excesses
Not Available
|
E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
|
Lithium in the barium stars
New high-resolution spectra of the lithium resonance doublet haveprovided lithium abundances or upper limits for 26 classical and mildbarium stars. The lithium lines always are present in the classicalbarium stars. Lithium abundances in these stars obey a trend withstellar masses consistent with that previously derived for ordinary Kgiants. This supports the notion that classical barium stars arepost-core-He-flash or core-He-burning stars. Lithium contents in themild barium stars, however, often are much smaller than those of theclassical barium stars; sometimes only upper limits may be determined.The cause for this difference is not easily understood, but may berelated to more extensive mass loss by the mild barium stars.
|
DDO Observations of Southern Stars
Not Available
|
The occultation of beta Scorpii by Jupiter. VII - The angular diameters of beta Scorpii A1 and A2
A new technique for measuring angular diameters of stars, which makesuse of stellar images formed by planetary atmospheres duringoccultations, is described. This method has been applied to light curvesof the 1971 May 13 occultation of beta Sco by Jupiter, yielding theangular diameters of the two early B stars comprising the spectroscopicbinary beta Sco A. An angular diameter of about .000422 arcsec for betaSco A1 and about .000264 arcsec is found for beta Sco A2. These angulardiameters are in good agreement with that obtained with the intensityinterferometer for beta Sco, a star of nearly the same magnitude andspectral type as beta Sco A1. If the distance to beta Sco A wereprecisely known, beta Sco A1 and A2 would become fundamental standardsof mass, luminosity, and radius for early B stars. Present constraintson the distance and methods by which it could be accurately determinedare discussed.
|
Absolute magnitudes of barium stars based on the width of H alpha in absorption.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975PASP...87..537K&db_key=AST
|
On the 1968 occultation of BD-17 deg 4388 by Neptune
The 1968 occultation light curves are reanalyzed, and the uncertainty ofresults obtained with the inversion technique is emphasized.Refractivity profiles are used for this analysis, and the influence ofray crossing on light curves is described. The scale height defining thegross variation of refractivity is determined to be about 49 km with anuncertainty of at least 2 km. It is shown that detailed temperatureprofiles derived from the light curves exhibit considerably greateruncertainty.
|
On the upper atmosphere of Neptune.
Abstract image available at:http://adsabs.harvard.edu/abs/1974ApJ...189..569V
|
The absolute magnitudes of the barium stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..384M&db_key=AST
|
Photographic observations of Neptune and BD -17 4388 near the time of the occultation in April 1968.
Abstract image available at:http://adsabs.harvard.edu/abs/1969AJ.....74..958D
|
Diameter, flattening and optical properties of the upper atmosphere of Neptune as derived from the occultation of BD -17 4388.
Abstract image available at:http://adsabs.harvard.edu/abs/1969A&A.....2..398K
|
