Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
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
| Statistical cataloging of archival data for luminosity class IV-V stars. II. The epoch 2001 [Fe/H] catalog
This paper describes the derivation of an updated statistical catalog ofmetallicities. The stars for which those metallicities apply are ofspectral types F, G, and K, and are on or near the main sequence. Theinput data for the catalog are values of [Fe/H] published before 2002February and derived from lines of weak and moderate strength. Theanalyses used to derive the data have been based on one-dimensional LTEmodel atmospheres. Initial adjustments which are applied to the datainclude corrections to a uniform temperature scale which is given in acompanion paper (see Taylor \cite{t02}). After correction, the data aresubjected to a statistical analysis. For each of 941 stars considered,the results of that analysis include a mean value of [Fe/H], an rmserror, an associated number of degrees of freedom, and one or moreidentification numbers for source papers. The catalog of these resultssupersedes an earlier version given by Taylor (\cite{t94b}).Catalog is only available in electronic form at the CDS via anonymousftp cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/731
| Statistical cataloging of archival data for luminosity class IV-V stars. I. The epoch 2001 temperature catalog
This paper is one of a pair in which temperatures and metallicitycatalogs for class IV-V stars are considered. The temperature catalogdescribed here is derived from a calibration based on stellar angulardiameters. If published calibrations of this kind are compared by usingcolor-index transformations, temperature-dependent differences among thecalibrations are commonly found. However, such differences are minimizedif attention is restricted to calibrations based on Johnson V-K. Acalibration of this sort from Di Benedetto (\cite{dib98}) is thereforetested and adopted. That calibration is then applied to spectroscopicand photometric data, with the latter predominating. Cousins R-Iphotometry receives special attention because of its high precision andlow metallicity sensitivity. Testing of temperatures derived from thecalibration suggests that their accuracy and precision are satisfactory,though further testing will be warranted as new results appear. Thesetemperatures appear in the catalog as values of theta equiv5040/T(effective). Most of these entries are accompanied by measured orderived values of Cousins R-I. Entries are given for 951 stars.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/721
| Kinematics of Hipparcos Visual Binaries. II. Stars with Ground-Based Orbital Solutions
This paper continues kinematical investigations of the Hipparcos visualbinaries with known orbits. A sample, consisting of 804 binary systemswith orbital elements determined from ground-based observations, isselected. The mean relative error of their parallaxes is about 12% andthe mean relative error of proper motions is about 4%. However, even 41%of the sample stars lack radial velocity measurements. The computedGalactic velocity components and other kinematical parameters are usedto divide the stars with known radial velocities into kinematical agegroups. The majority (92%) of binaries from the sample are thin diskstars, 7.6% have thick disk kinematics and only two binaries have halokinematics. Among them, the long-period variable Mira Ceti has a verydiscordant {Hipparcos} and ground-based parallax values. From the wholesample, 60 stars are ascribed to the thick disk and halo population.There is an urgent need to increase the number of the identified halobinaries with known orbits and substantially improve the situation withradial velocity data for stars with known orbits.
| Speckle Interferometry of Southern Double Stars. II. Measures from the CASLEO 2.15 Meter Telescope, 1995-1996
Relative astrometry is presented for 198 observations of 160 doublestars. The data were obtained at the 2.15 m telescope at the ComplejoAstronómico El Leoncito (Argentina) with a multianodemicrochannel array (MAMA) detector system. Five high-qualitynondetections are also reported. When judged against ephemeris positionsfor binaries with very well determined orbits, the separation residualsexhibit a root mean square deviation of13.2+3.4-1.9 mas and the position angle residualsexhibit rms deviation of 2.9d+0.8d-0.5d. Factorsaffecting the measurement precision are discussed.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The 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
| CCD Speckle Observations of Binary Stars from the Southern Hemisphere. II. Measures from the Lowell-Tololo Telescope during 1999
Speckle observations of 145 double stars and suspected double stars arepresented and discussed. On the basis of multiple observations, a totalof 280 position angle and separation measures are determined, as well as23 high-quality nondetections. All observations were taken with the(unintensified) Rochester Institute of Technology fast-readout CCDcamera mounted on the Lowell-Tololo 61 cm telescope at the Cerro TololoInter-American Observatory during 1999 October. We find that themeasures, when judged as a whole against ephemeris positions of binarieswith very well-known orbits, have root mean square deviations of1.8d+/-0.3d in position angle and 13+/-2 mas in separation. Elevendouble stars discovered by Hipparcos were also successfully observed,and the change in position angle and/or separation since the Hipparcosobservations was substantial in three cases.
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| A Multiplicity Survey of Chromospherically Active and Inactive Stars
Surveys of three samples of solar-type stars, segregated bychromospheric emission level, were made to determine their multiplicityfractions and to investigate the evolution of multiplicity with age. Intotal, 245 stars were searched for companions with DeltaV <= 3.0 andseparations of 0.035" to 1.08" using optical speckle interferometry. Byincorporating the visual micrometer survey for duplicity of theLamontHussey Observatory, the angular coverage was extended to 5.0" withno change in the DeltaV limit. This magnitude difference allows massratios of 0.63 and larger to be detected throughout a search region of2-127 AU for the stars observed. The 84 primaries observed in thechromospherically active sample are presumably part of a youngpopulation and are found to have a multiplicity fraction of 17.9% +/-4.6%. The sample of 118 inactive, presumably older, primaries wereselected and observed using identical methods and are found to have amultiplicity fraction of only 8.5% +/- 2.7%. Given the known linkbetween chromospheric activity and age, these results tentatively implya decreasing stellar multiplicity fraction from 1 to 4 Gyr, theapproximate ages of the two samples. Finally, only two of the 14 veryactive primaries observed were found to have a companion meeting thesurvey detection parameters. In this case, many of the systems areeither very young, or close, RS CVn type multiples that are unresolvableusing the techniques employed here.
| Kinematics and Metallicity of Stars in the Solar Region
Several samples of nearby stars with the most accurate astrometric andphotometric parameters are searched for clues to their evolutionaryhistory. The main samples are (1) the main-sequence stars with b - ybetween 0.29 and 0.59 mag (F3 to K1) in the Yale parallax catalog, (2) agroup of high-velocity subgiants studied spectroscopically by Ryan &Lambert, and (3) high-velocity main-sequence stars in the extensiveinvestigation by Norris, Bessel, & Pickles. The major conclusionsare as follows: (1) The oldest stars (halo), t >= 10-12 Gyr, haveV-velocities (in the direction of Galactic rotation and referred to theSun) in the range from about -50 to -800 km s^-1 and have aheavy-element abundance [Fe/H] of less than about -0.8 dex. The agerange of these objects depends on our knowledge of globular clusterages, but if age is correlated with V-velocity, the youngest may be M22and M28 (V ~ -50 km s^-1) and the oldest NGC 3201 (V ~ -500 km s^-1) andassorted field stars. (2) The old disk population covers the large agerange from about 2 Gyr (Hyades, NGC 752) to 10 or 12 Gyr (Arcturusgroup, 47 Tuc), but the lag (V) velocity is restricted to less thanabout 120 km s^-1 and [Fe/H] >= -0.8 or -0.9 dex. The [Fe/H] ~ -0.8dex division between halo and old disk, near t ~ 10-12 Gyr, is marked bya change in the character of the CN index (C_m) and of the blanketingparameter K of the DDO photometry. (3) The young disk population, t <2 Gyr, is confined exclusively to a well-defined area of the (U, V)velocity plane. The age separating young and old disk stars is also thatseparating giant evolution of the Hyades (near main-sequence luminosity)and M67 (degenerate helium cores and a large luminosity rise) kinds. Thetwo disk populations are also separated by such indexes as the g-indexof Geveva photometry. There appears to be no obvious need to invokeexogeneous influences to understand the motion and heavy-elementabundance distributions of the best-observed stars near the Sun.Individual stars of special interest include the parallax star HD 55575,which may be an equal-component binary, and the high-velocity star HD220127, with a well-determined space velocity near 1000 km s^-1.
| CCD and micrometric observations of visual double stars
Relative positions and separations for 65 visual binaries are given. CCDframes were taken at the 1-m coudetelescope and micrometric observationswere carried out at the 65-cm refractor, both at the Venezuelan NationalObservatory. The visual double stars observed were selected from theRamon Maria Aller Observatory program list. In addition, we alsoobserved several long period double stars with poorly determined orbitalelements.
| F, G and K stars in the ROSAT all-sky survey. I. Photometry
We present accurate BV(RI)_c photometry for a sample of F, G and K starsdetected in selected areas of the ROSAT all-sky survey (RASS). We haveused the photometry, in addition to low-resolution spectroscopy, toestimate spectral classifications, distances and X-ray luminosities. Thelog (L_X / L_V) in the sample lies below -2. Although the samplecontains also nearby, inactive stars, it is dominated by active objects.The median X-ray luminosity in our sample is < L_X > = 29.88 andthe mean value of the hardness ratios = 0.13 +/- 0.35. Wecompare the derived X-ray luminosity function with similar functionsobtained from the serendipitous samples of the Einstein Observatorymedium sensitivity survey (EMSS) and EXOSAT. Our sample is completelyconsistent with the EMSS sample of solar type stars, indicating thatboth our sources and the EMSS sources are representative of the highgalactic latitude X-ray stellar population. We do not find extremelyactive stars (log (L_X) >= 32), as are found in the EMSS sample, andwe argue that these objects are rare. Table 3 is also available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| CCD Speckle Observations of Binary Stars From the Southern Hemisphere
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2117H&db_key=AST
| A catalogue of [Fe/H] determinations: 1996 edition
A 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
| Micrometer measurements of southern double stars made at The Observatory of Llano del Hato at Merida (Venezuela)
We present 93 micrometer measurements of 46 double stars observed withthe 65 cm refractor at the Llano del Hato Observatory (Merida,Venezuela).
| A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars
More than 800 southern stars within 50 pc have been observed forchromospheric emission in the cores of the Ca II H and K lines. Most ofthe sample targets were chosen to be G dwarfs on the basis of colors andspectral types. The bimodal distribution in stellar activity first notedin a sample of northern stars by Vaughan and Preston in 1980 isconfirmed, and the percentage of active stars, about 30%, is remarkablyconsistent between the northern and southern surveys. This is especiallycompelling given that we have used an entirely different instrumentalsetup and stellar sample than used in the previous study. Comparisons tothe Sun, a relatively inactive star, show that most nearby solar-typestars have a similar activity level, and presumably a similar age. Weidentify two additional subsamples of stars -- a very active group, anda very inactive group. The very active group may be made up of youngstars near the Sun, accounting for only a few percent of the sample, andappears to be less than ~0.1 Gyr old. Included in this high-activitytail of the distribution, however, is a subset of very close binaries ofthe RS CVn or W UMa types. The remaining members of this population maybe undetected close binaries or very young single stars. The veryinactive group of stars, contributting ~5%--10% to the total sample, maybe those caught in a Maunder Minimum type phase. If the observations ofthe survey stars are considered to be a sequence of snapshots of the Sunduring its life, we might expect that the Sun will spend about 10% ofthe remainder of its main sequence life in a Maunder Minimum phase.
| Stars resembling the Sun
This review is primarily directed to the question whether photometricsolar analogues remain such when subjected to detailed spectroscopicanalyses and interpreted with the help of internal stucture models. Inother words, whether the physical parameters: mass, chemicalcomposition, age (determining effective temperature and luminosity),chromospheric activity, equatorial rotation, lithium abundance, velocityfields etc., we derive from the spectral analysis of a photometric solaranalogue, are really close to those of the Sun. We start from 109photometric solar analogues extracted from different authors. The starsselected had to satisfy three conditions: i) their colour index (B-V)must be contained in the interval: Δ (B-V) = 0.59-0.69, ii) theymust possess a trigonometric parallax, iii) they must have undergone ahigh resolution detailed spectroscopic analysis. First, this reviewpresents photometric and spectrophotometric researches on solaranalogues and recalls the pionneering work on these stars by the lateJohannes Hardorp. After a brief discussion on low and high resolutionspectroscopic researches, a comparison is made between effectivetemperatures as obtained, directly, from detailed spectral analyses andthose obtained, indirectly, from different photometric relations. Aninteresting point in this review is the discussion on the tantalilizingvalue of the (B-V)solar of the Sun, and the presentation of anew reliable value of this index. A short restatement of the kinematicproperties of the sample of solar analogues is also made. And, finally,the observational ( T eff, M bol) diagram,obtained with 99 of the initially presented 109 analogues, is comparedto a theoretical ( T eff, M bol) diagram. Thislatter has been constructed with a grid of internal structure models forwhich, (very important for this investigation), the Sun was used asgauge. In analysing the position, with respect to the Sun, of each starwe hoped to find a certain number of stars tightly neighbouring the Sunin mass, chemical composition and state of evolution. The surprisingresult is that the stars occupy in this HR Diagram a rather extendedregion around the Sun, many of them seem more evolved and older than theSun, and only 4 of the evolved stars seem younger. The age of some starsin the sample is also discussed in terms of chromospheric activity andLi-content. Our conclusion is much the same as that contained inprevious papers we have written on the subject: in spite of a muchlarger number of stars, we have not been able to nominate a single starof the sample for a ``perfect good solar twin''. Another aim inbeginning, 25 years ago, this search for solar analogues, was to haveready a bunch of stars resembling the Sun and analysed spectroscopicallyin detail, in order that, when planets hunters of solar type stars,finally would have found such a specimen, we would have been able toimmediately compare the physical parameters of this star to those of theSun. We have been lucky enough: one of the good solar analogues wepresent herewith, is 51 Pegasi (HD 217014) which, according to the veryrecent observations by Mayor and Queloz (1995), has a planet orbitingaround it. And what is more: two other stars possessing planets: 47Ursae Majoris (HD 95128) and 70 Virginis (HD 117176), have just beendiscovered by Marcy and Butler (187th Meeting of the AAS,January 1996). One of them, 47 Ursae Majoris, is also included in thelist of photometric solar analogues. The other star, 70 Virginis, hasonly been included after the ``Planets News'', because the colour index(B-V) of this star is slightly higher than the prescribted limit of theselection, (B-V = 0.71, instead, 0.69). It would have been a pity toleave the third '' planet star out of the competition.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&db_key=AST
| Photographic observations of visual double stars.
We present the results of photographic observations of 399 visual doublestars of the Hipparcos Input Catalogue (HIC), observed in the years 1980and 1990-1991 with the 60-cm double-refractor of the Bosscha Observatoryat Lembang, Java.
| 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.
| CCD measurements of visual binaries.
We report CCD measurements of 33 visual double stars observed at the1-meter coude reflector of the Observatorio de Llano del Hato located atMerida, Venezuela. We also present an algorithm to determine the stars'centroids for superimposed images as well as a brief comparison ofaccuracies attained by the algorithm and the program CENTER of the IRAFpackage.
| Photographic observations of visual double stars.
We present the analysis result of photographic observations of 221visual double stars, observed in the years 1987-1989 with the 60cmdouble-refractor at the Bosscha Observatory at Lembang, Java.
| Stroemgren photometry of F- and G-type stars brighter than V = 9.6. I. UVBY photometry
Within the framework of a large photometric observing program, designedto investigate the Galaxy's structure and evolution, Hβ photometryis being made for about 9000 stars. As a by-product, supplementary uvbyphotometry has been made. The results are presented in a cataloguecontaining 6924 uvby observations of 6190 stars, all south ofδ=+38deg. The overall internal rms errors of one observation(transformed to the standard system) of a program star in the interval6.5
| Lithium abundances of nearby solar-like stars
We discuss Li abundances in a well defined sample of nearby (GO-G5)solar-like stars. High resolution (R = 100,000), high S/N (greater thanor equal to 150) data have been analyzed using state-of-the-arttechniques and up-to-date atmospheric models. We have investigatedwhether the abundance of Li in solar-type stars can be described interms of stellar physical parameters like Teff, age andmetallicity. We confirm the presence of a group of stars with high Licontent, but apparently old age, finding that this group is ratherconspicuous and not restricted to a few exceptional cases. The analysisof our data, together with published observations of G dwarfs in openclusters, strongly suggests that for stars older than approximately 1Gyr another parameter in addition to the above mentioned ones plays arelevant role in Li depletion. When this additional mechanism iseffective, it depletes Li by a factor 10-100, but in some stars it maynot act at all during a large part of their main sequence lifetimes. Wemake some suggestions as to the nature of this additional parameter butnone of them can be difinitely proven. When compared to the other starsin or sample, the Sun appears to be representative of the low-Li stars,which comprise about one half of the G dwarfs having stellar parametersand ages similar to the Sun. We confirm that Li is not a good tracer ofage for solar-type stars, but we show that a high Li content coupled tohigh chromospheric activity can be used to identify stars significantlyyounger than the Hyades.
| The CA II K line in solar type stars
High resolution, high S/N ratio Ca II data are presented for an unbiasedsample of stars that have overall characteristics similar to the sun.The observed behavior of Ca II K line features over the solar cycle iscompared with similar quantities observed in solar-type stars. It isshown that all trends observed for the sun are true for the observedstars, and the claim that the solar paradigm can be extended to other Gdwarfs is confirmed. Accurate Wilson Bappu (W-B) widths were measuredfor sample stars; the G stars as a group were found to be consistentwith the W-B relationships proposed by Lutz (1970). Within themeasurement errors, no dependence of the W-B width on activity wasfound. A comparison with solar plages shows significant similaritybetween solar plage spectra and active star spectra. It is suggestedthat activity in solar-type stars is most likely due to the presence ofplages similar to those observed on the sun.
| Photographic observations of visual double stars
Results are presented of photographic observations of 186 pairs ofvisual double stars, carried out with the 60-cm visual refractor of theBosscha Observatory at Lembang (Java) between 1984 and 1986. Theprocedures used in observations, measurements, and reducing wereidentical to those described by van Albada-van Dien (1983).
| BVRI photometry of the Gliese Catalogue stars
Photoelectri BVRI photometry on the Cousins (Kron-Cape) system has beenobtained for many of the southern faint stars in the Gliese Catalog(1969). This extends the work of Cousins (1980) and provides a uniformset of data for the nearby stars. Several red dwarfs are noted, whichwere used to define the red end of the Cousins system.
| Micrometric measurements of visual double stars (IV list)
The results of 301 micrometric measurements of 88 double stars aregiven. The measurements were made at Brera-Merate, Collurania (Teramo),and La Silla Observatories during the period 1986.000-1986.999.
| Fermi paradox and alternative strategies for SETI programs - The anthropic principle and the search for close solar analogs
The anthropic principle, a new trend of modern cosmology, claims thatthe origin of life and the development of intelligent beings on theearth is the result of highly selective biological processes, strictlytuned in the fundamental physical characteristics of the universe. Thisprinciple could account for the failure of some programs of search forextraterrestrial intelligences (SETI) and suggests that the search forstrict solar analogs should be a primary target for SETI strategies. Inthis connection, 22 solar analogs are selected and their choice isdiscussed.
| Large and kinematically unbiased samples of G and K type stars. I - The dwarfs
Four-color, H-beta, and (R,I) photometry for the little-evolvedmain-sequence stars from the Bright Star Catalogue, South Galactic Pole,Griffin (1971), and Moore-Paddock-Wayman (Moore and Paddock 1950, andWayman 1960) samples are analyzed. The luminosity and heavy-elementabundances for these stars are calculated in terms of the Hyadessupercluster, the Wolf 630 group, the Sirius supercluster, and theKapteyn star group. The data reveal the presence of a metal-abundancedependent discontinuity near M(v) = +7 mag in the photometric parametersof dwarfs. The distributions of the abundances and the space motions ofthe sample stars are discussed.
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
Catálogos y designaciones:
|
INHABITED SKY
