WIKISKY.ORG
 Home Getting Started To Survive in the Universe News@Sky Astro Photo The Collection Forum Blog New! FAQ Press Login

20 Peg

Contents

Images

DSS Images   Other Images

Related articles

 Lithium abundances for early F stars: new observational constraints for the Li dilutionAims.To investigate any correlation between Li abundances and rotationalvelocities among F-G evolved stars, we study a large sample of early Fstars from the Bright Star Catalogue (BSC), most of them classified inthe literature as giant stars.Methods.Physical parameters and Liabundances are estimated for each star, often for the first time, bycomparing observed and synthetic spectra. We analyse the position of thestars in the H-R Diagram based on Hipparcos data using stellarevolutionary tracks and we discuss their Li abundances and projectedrotational velocities.Results.Observed stars are mostly on theturnoff, with masses between 1.5 and 2.0 Mȯ. The starswith measured A(Li) abundance show high Li content, most of them withabundance near the cosmic value. The A(Li) versus V sin i diagram showsthe same trend as reported in previous studies: fast rotators (V sinigse 30 km s-1) are also stars with high Li content, whereasslow rotators present a wide range of values of A(Li), ranging from nodetected Li to the cosmic value. Abundances of Carbon, Nitrogen, Oxygen, and Other Elements in the Atmospheres of the Giants 25 Mon and HR 7389An analysis of high-resolution CCD spectra of the giant 25 Mon, whichshows signs of metallicity, and the normal giant HR 7389 is presented.The derived effective temperatures, gravitational accelerations, andmicroturbulence velocities are T eff = 6700 K, log g = 3.24, and ξ t= 3.1 km/s for 25 Mon and T eff = 6630 K, log g = 3.71, and ξ t = 2.6km/s for HR 7389. The abundances (log ε) of nine elements aredetermined: carbon, nitrogen, oxygen, sodium, silicon, calcium, iron,nickel, and barium. The derived excess carbon abundances are 0.23 dexfor 25 Mon and 0.16 dex for HR 7389. 25 Mon displays a modest (0.08 dex)oxygen excess, with the oxygen excess for HR 7389 being somewhat higher(0.15 dex). The nitrogen abundance is probably no lower than the solarvalue for both stars. The abundances of iron, sodium, calcium (for HR7389), barium, and nickel exceed the solar values by 0.22 0.40 dex forboth stars. The highest excess (0.62 dex) is exhibited by the calciumabundance for 25 Mon. Silicon displays a nearly solar abundance in bothstarssmall deficits of -0.03 dex and -0.07 dex for 25 Mon and HR7389, respectively. No fundamental differences in the elementalabundances were found in the atmospheres of 25 Mon and HR 7389. Based ontheir T eff and log g values, as well as theoretical calculations, A.Claret estimated the masses, radii, luminosities, and ages of 25 Mon(M/M ȯ = 2.45, log(R/R ȯ) = 0.79, log(L/L ȯ) = 1.85, t =5.3 × 108 yr) and HR 7389 (M/M ȯ = 2.36, log(R/R ȯ) =0.50, log(L/L ȯ) = 1.24, t = 4.6 × 108 yr), and also of thestars 20 Peg (M/M ȯ = 2.36, log(R/R ȯ) = 0.73, log(L/L ȯ)= 1.79, t = 4.9 × 108 yr) and 30 LMi (M/M ȯ = 2.47, log(R/Rȯ) = 0.73, log(L/L ȯ) = 1.88, t = 4.8 × 108 yr) studiedby the author earlier. Photometric periods of HN Peg from multichannel analysisWe applied the method of three-stage weighted multichannel periodanalysis (MPA) to photometric observations of HN Peg obtained in1992-99. We detected two periods: the longer one stayed almost constantnear 5.5 d but appeared only during the observing seasons in 1993-98,while the shorter one was present for all observing seasons, havingfluctuations within . If the two periods are interpreted as caused bydifferential rotation, we may have detected two distinct latitude zonesof spot activity, one where spots were confined to within a very narrowrange of latitude, and another where the latitude range may be somewhatbroader. The existence of two latitude zones of activity in this youngsolar analogue closely matches what is seen in the Sun. However, thepresence of two periods may also be caused by long-lived active areasmoving in longitude. We use HN Peg as a test case for our new MPAstatistical method. Because of the limited quality of the data and thecomplexity of stellar activity our results are tentative, leaving spacealso for other interpretations.Based on observations collected at the Mt. Maidanak (Uzbekistan) andFairborn (USA) observatories. The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfsWe 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. Our63 000 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 Abundances of Carbon, Nitrogen, Oxygen, and Other Elements in the Atmosphere of the Giant 20 PegWe have studied the giant 20 Peg using high-resolution spectra. Wederive the star’s effective temperature, T eff=6970 K, gravity,logg=3.35, and microturbulence velocity from FeI lines, ξt=2.70 km/s,and from NiI lines, ξt=2.45 km/s. The abundances of carbon,logɛ(C)=8.78, nitrogen, logɛ(N)=8.28, and silicon,logɛ(Si)=7.85, are enhanced compared to the solar values by0.23, 0.31, and 0.30 dex, respectively. The abundances of oxygen,logɛ(O)=8.83, sodium, logɛ(Na)=6.37, and sulfur,logɛ(S)=7.33, are nearly solar. Calcium and nickel show normalabundances, logɛ(Ca)=6.44 and logɛ(Ni)=6.32. Ironlogɛ(Fe)=7.63 and yttrium logɛ(Y)=2.41 are only slightlyoverabundant compared to the solar values (by 0.13 and 0.17 dex). Wefind a rather large (0.95 dex) overabundance of bariumlogɛ(Ba)=3.08. Pre-discovery Photometry of the gamma Doradus-type Pulsating Star HR 8330 (= HD 207223)Not Available Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statisticsThe Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521 The proper motions of fundamental stars. I. 1535 stars from the Basic FK5A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222 Simultaneous photometry and spectroscopy of the newly discovered γ Doradus variable HR 8330=HD 207223We present BV photometry and simultaneous high-resolution, highsignal-to-noise ratio spectroscopy of the newly-discovered γDoradus variable HR 8330 taken during the 1997 and 1998 observingseasons. We calculate power spectra for the B- and V-band data sets andfor the time series defined throughout the observing season at eachpoint across the Feii λ4508.289 and the Tiii λ4501.278line profiles to search for periodic variability. Period analysisreveals a single, 2.6-d period in both the photometric and thespectroscopic data, with a 237 deg phase lag between them. Based on thelocation of HR 8330 in the HR diagram and the characteristics of itsphotometric and spectroscopic variations, we conclude that HR8330 is abona fide γ Doradus-type pulsating variable. Are metallic A-F giants evolved AM stars? Rotation and rate of binaries among giant F starsWe test the hypothesis of Berthet (1992) {be91} which foresees that Amstars become giant metallic A and F stars (defined by an enhanced valueof the blanketing parameter Delta m_2 of the Geneva photometry) whenthey evolve. If this hypothesis is right, Am and metallic A-FIII starsneed to have the same rate of binaries and a similar distribution ofvsin i. From our new spectroscopic data and from vsin i and radialvelocities in the literature, we show that it is not the case. Themetallic giant stars are often fast rotators with vsin i larger than 100kms(-1) , while the maximum rotational velocity for Am stars is about100 kms(-1) . The rate of tight binaries with periods less than 1000days is less than 30% among metallic giants, which is incompatible withthe value of 75% for Am stars - [Abt & Levy 1985] {ab85}).Therefore, the simplest way to explain the existence of giant metallic Fstars is to suggest that all normal A and early F stars might go througha short metallic" phase when they are finishing their life on the mainsequence. Besides, it is shown that only giant stars with spectral typecomprised between F0 and F6 may have a really enhanced Delta m_2 value,while all A-type giants seem to be normal. Based on observationscollected at Observatoire de Haute Provence (OHP), France. The Angular Momentum of Main Sequence Stars and Its Relation to Stellar ActivityRotational 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) A catalogue of [Fe/H] determinations: 1996 editionA fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html 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. SANTIAGO 91, a right ascension catalogue of 3387 stars (equinox J2000).The positions in right ascension of 3387 stars belonging to the Santiago67 Catalogue, observed with the Repsold Meridian Circle at Cerro Calan,National Astronomical Observatory, during the period 1989 to 1994, aregiven. The average mean square error of a position, for the wholeCatalogue, is +/-0.009 s. The mean epoch of the catalogue is 1991.84. Corrections to the right ascension to be applied to the apparent places of 1217 stars given in "The Chinese Astronomical Almanach" for the year 1984 to 1992.Not Available Carbon and nitrogen abundances determined from transition layer linesThe possibility of determining relative carbon, nitrogen, and siliconabundances from the emission-line fluxes in the lower transition layersbetween stellar chromospheres and coronae is explored. Observations formain-sequence and luminosity class IV stars with presumably solarelement abundances show that for the lower transition layers Em =BT-gamma. For a given carbon abundance the constants gammaand B in this relation can be determined from the C II and C IVemission-line fluxes. From the N V and S IV lines, the abundances ofthese elements relative to carbon can be determined from their surfaceemission-line fluxes. Ratios of N/C abundances determined in this wayfor some giants and supergiants agree within the limits of errors withthose determined from molecular bands. For giants, an increase in theratio of N/C at B-V of about 0.8 is found, as expected theoretically. Santiago Fundamental Catalogue - A catalogue of 1105 FK5 stars (equinox J2000.0)The positions in right ascension and declination of 1105 FK5 stars,observed with a Meridian Circle during the period 1979 to 1991, aregiven. The average mean square error of a position, for the wholecatalog, is +/- 0.009 s in right ascension and +/- 0.10 arcsec indeclination. The mean epoch of the catalog is 1983.148. The correction in right ascension of 508 stars determinated with PMO photoelectric transit instrument.Not Available Abundance distribution of A-F giant starsThe detailed spectroscopic analysis of A-F giant stars is presentedwhich show photometric characteristics of the classical Am stars. Theresults of the three newly studied stars (HR 6492, HR 8222, and HR 8392)reveal that these stars exhibit the same behavior as the previous ones,with abundance distributions similar to those of delta Delphini stars.It is pointed out that in HR 8222 the distribution abundance of rareearth and associated elements follows without ambiguity the odd-eveneffect. A general enhancement by a factor of about four with respect tothe solar abundance pattern is observed. Physical data of the fundamental stars.Not Available The evolution of chromospheric activity of cool giant and subgiant starsIUE spectra for a large sample of cool subgiant stars are examined, andevidence is found that subgiants in the mass range 1.2-1.6 solar massesundergo a sudden decline in UV transition region emission near B - V =0.6, which corresponds to spectral type G0 IV. The decline in UVemission coincides with a sharp decrease in stellar rotation rates, andit is suggested that this decay in activity and rotation marks atransformation from acoustic heating in the early F stars to magneticdynamo-driven activity in the cooler stars, resulting in a strongrotational braking action by stellar wind. For more massive giant stars,there is a similar transformation in the nature of chromosphericactivity near B - V = 0.7, or spectral type G0 III, from acousticheating in the F-type giants to a solarlike dynamo mechanism in thecooler giants. No sign of an abrupt drop in activity near spectral typeG5 III at the location of Gray's proposed rotational boundary line isseen. The granulation boundary in the H-R diagramA granulation boundary in the H-R diagram is found. The boundary runssmoothly from spectral type G1 Ib to near F0 on the main sequence. Onthe cool side of the boundary, the spectral line bisectors are of theclassical type associated with granulation. On the hot side thebisectors show a reversed slope and curvature indicative of some othertype of photospheric velocity field, possibly having velocitiessubstantially larger than typical granulation velocities. Santiago declination catalogue - A declination catalogue of 412 FK4 stars (equinox 1950.0)This catalog contains the positions in declination, of 412 FK4 stars.The observations were carried out with the Repsold Meridian Circle atCerro Calan National Astronomical Observatory, during the period1963-1968. The average mean square error of one observation (for thewhole catalog) is + or - 0.13 arcsec. The mean epoch of observation ofthe catalog is 1965.75. Metallicism among A and F giant stars132 stars considered as A and F giants have been studied for theirproperties in the Geneva photometric system. It is shown that thissystem to derive the temperature, absolute magnitude and Fe/H value forstars in this part of the HR diagram. 36 percent of the stars of oursample exhibit an enhanced value Delta m2 that can be interpreted interms of Fe/H. The red limit of stars having an enhanced Fe/H value is0.225 in B2-V1 or 6500 K in Teff. This corresponds to the limit definedby Vauclair and Vauclair (1982) where the diffusion timescale is equalto the stellar lifetime and permits the assumption that the diffusion isthe process responsible for the metallicism observed in the A and Fgiants. Observed and computed spectral flux distribution of non-supergiant O9-G8 stars. III - Determination of T(eff) for the stars in the Breger CatalogueThe effective temperatures and angular diameters of nonsupergiant O9-G8stars are determined from visible spectrophotometry. The results, whichrefer to 302 stars included in the Breger Catalogue, are derived fromthe comparison between the observed flux distributions and thepredictions of Kurucz's models (1979). The uncertainties to be expectedin individual results are discussed; their sizes are of the order of 5percent in effective temperature and 10 percent in angular diameter. On the dispersion in brightness of far-ultraviolet emission lines of cool giant starsLow-resolution spectra have been obtained with the short-wavelengthcamera of IUE for late-type giant stars of spectral type F5 III-G8 III.These stars are believed to be in their first crossing of the H-Rdiagram, as inferred from their location along the blue edge of theHertzsprung gap or their high abundance of lithium. From the earliestspectral type observed along the blue edge of the gap, the normalized CIV flux, which is indicative of 100,000 K plasma, increases to a maximumat G0 and then falls with advancing spectral type. The total range inemission measure of 100,000 K gas is an order of magnitude or more amongstars making their first appearance as yellow giants and averages about25 times higher in these stars than in other G8-K0 yellow giants, themajority of which are probably He-burning post-red giants. Theobservations tentatively show that transition region emission, and byinference coronal emission, increases in intensity with the growth ofconvection zones in late-type giants and then declines at lower surfacetemperatures, perhaps because of rotational spin-down and a weakening ofdynamo action. The fourth meridian catalog of Besancon ObservatoryThe catalog presented gives differential meridian positions for 670F-type stars between plus 15 and plus 45 deg declination. The positionsare reduced to the equinox of 1950.0 without proper motions; 333 FK4stars were used as reference stars. A minimum of three and an average offive transits of each program star were observed photoelectrically usinga Gautier transit circle and a Hog grid. The internal accuracy ofindividual measurements is shown to range from 0.013 sec in rightascension and 0.30 arcsec in declination for brighter stars under betterobserving conditions to 0.020 sec in right ascension and 0.38 arcsec indeclination for fainter stars under worse conditions. The standarderrors were applied to compute weighted mean positions, mean epochs, andunweighted means for the program stars. Mean corrections for 283 FK4stars are also provided. Magnetic structure in cool stars. VI - CA II H and K fluxes from evolved starsQuantitative measurements of the Ca II H and K flux of 335 evolved starsare presented and discussed. The results show that there is a largespread in the fluxes from stars with (B-V) less than 0.95 while the CaII H and K flux of single stars with (B-V) greater than 0.95 correlateswith color with little spread. Short-period binaries show a relativelyhigh Ca II H and K flux indicating that high fluxes result from rapidrotation independent of spectral type. The data are consistent with thehypothesis that the emission depends on dynamo action in the convectiveenvelope, the dynamo efficiency decreasing with decreasing rotationrate. The evolution of the emission is discussed as a function ofstellar mass. It is shown that stars which leave the main sequence withrelatively low or high rotational velocities show relatively low or highemission values, respectively. The flux lasts up to higher (B-V) valuesfor progressively higher masses. Prediction of spectral classification from photometric observations - Application of the UVBY beta photometry and the MK spectra classification. II - General caseAbstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85...93M&db_key=AST Prediction of spectral classification from photometric observations-application to the UVBY beta photometry and the MK spectral classification. I - Prediction assuming a luminosity classAn algorithm based on multiple stepwise and isotonic regressions isdeveloped for the prediction of spectral classification from photometricdata. The prediction assumes a luminosity class with reference touvbybeta photometry and the MK spectral classification. The precisionattained is about 90 percent and 80 percent probability of being withinone spectral subtype respectively for luminosity groups I and V and forluminosity groups III and IV. A list of stars for which discrepanciesappear between photometry and spectral classification is given.
Submit a new article

• - No Links Found -