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51 Eridani and GJ 3305: A 10-15 Myr old Binary Star System at 30 Parsecs
Following the suggestion of Zuckerman and coworkers, we consider theevidence that 51 Eri (spectral type F0) and GJ 3305 (M0), historicallyclassified as unrelated main-sequence stars in the solar neighborhood,are instead a wide physical binary system and members of the youngβ Pic moving group (BPMG). The BPMG is the nearest (d<~50 pc) ofseveral groups of young stars with ages around 10 Myr that arekinematically convergent with the Oph-Sco-Cen association (OSCA), thenearest OB star association. Combining South African AstronomicalObservatory optical photometry, Hobby-Eberly Telescope high-resolutionspectroscopy, Chandra X-Ray Observatory data, and Second US NavalObservatory CCD Astrograph Catalog kinematics, we confirm with highconfidence that the system is indeed extremely young. GJ 3305 itselfexhibits very strong magnetic activity but has rapidly depleted most ofits lithium. The 51 Eri/GJ 3305 system is the westernmost known memberof the OSCA, lying 110 pc from the main subgroups. The system is similarto the BPMG wide binary HD 172555/CD -64 1208 and the HD 104237 quintet,suggesting that dynamically fragile multiple systems can survive theturbulent environments of their natal giant molecular cloud complexes,while still having high dispersion velocities imparted. Nearby youngsystems such as these are excellent targets for evolved circumstellardisk and planetary studies, having stellar ages comparable to that ofthe late phases of planet formation.
| Young Stars Near the Sun
Until the late 1990s the rich Hyades and the sparse UMa clusters werethe only coeval, comoving concentrations of stars known within 60 pc ofEarth. Both are hundreds of millions of years old. Then beginning in thelate 1990s the TW Hydrae Association, the Tucana/Horologium Association,the Pictoris Moving Group, and the AB Doradus Moving Group wereidentified within 60 pc of Earth, and the Chamaeleontis cluster wasfound at 97 pc. These young groups (ages 8 50 Myr), along with othernearby, young stars, will enable imaging and spectroscopic studies ofthe origin and early evolution of planetary systems.
| Differential rotation in rapidly rotating F-stars
We obtained high quality spectra of 135 stars of spectral types F andlater and derived ``overall'' broadening functions in selectedwavelength regions utilizing a Least Squares Deconvolution (LSD)procedure. Precision values of the projected rotational velocity v \siniwere derived from the first zero of the Fourier transformed profiles andthe shapes of the profiles were analyzed for effects of differentialrotation. The broadening profiles of 70 stars rotating faster than v\sini = 45 km s-1 show no indications of multiplicity nor ofspottedness. In those profiles we used the ratio of the first two zerosof the Fourier transform q_2/q_1 to search for deviations from rigidrotation. In the vast majority the profiles were found to be consistentwith rigid rotation. Five stars were found to have flat profilesprobably due to cool polar caps, in three stars cuspy profiles werefound. Two out of those three cases may be due to extremely rapidrotation seen pole on, only in one case (v \sini = 52 km s-1)is solar-like differential rotation the most plausible explanation forthe observed profile. These results indicate that the strength ofdifferential rotation diminishes in stars rotating as rapidly as v \sini>~ 50 km s-1.Table A.1 is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/813Based on observations collected at the European Southern Observatory, LaSilla, 69.D-0015(B).
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| The β Pictoris Moving Group
Following the 1983 IRAS detection and subsequent imaging of itsextensive dusty circumstellar disk, β Pictoris became theprototypical and most studied example of a potential forming planetarysystem. Here we report the identification of 17 star systems, each withone or more characteristics indicative of extreme youth, that are movingthrough space together with β Pic. This diverse set of ~12 millionyr old star systems, which includes a ~35 Jupiter mass brown dwarf, anda wide assortment of dusty circumstellar disks, is the comoving,youthful group closest to Earth. Their unique combination of youth andproximity to Earth makes group members-many of which have masses similarto that of the Sun-prime candidates for imaging of warm planets anddusty circumstellar disks with ground- and space-based telescopes.
| Fundamental properties of the open cluster NGC 2355
NGC 2355 is an old open cluster in the outer part of the galactic disk(l=203fdg4 , b=+11fdg8 ) which has been little studied until now. Thispaper presents the first astrometric and spectroscopic investigation ofthis cluster. We have measured precise absolute proper motions from oldCarte du Ciel plates, POSS-I plates and recent CCD observations obtainedwith the Bordeaux meridian circle. The proper motion data reveal 38highly probable cluster members down to Blim = 15 mag within7' of the cluster center. We have also obtained ELODIE high resolutionspectra for 24 stars. Seventeen of them are confirmed to be members ofthe cluster on the basis of radial velocity. Eight of them are fastrotating turnoff stars for which the projected rotational velocity hasbeen determined. The spectroscopic observations have also providedestimates of the physical parameters Teff, log g, {[Fe/H]},MV of the 24 target stars. Two stragglers have beenidentified in the cluster. Combining our astrometric and spectroscopicresults with previous UBV photometry and recent JHK_s photometry fromthe 2MASS survey we have derived the fundamental properties of thecluster: metallicity, age, distance, size, spatial velocity and orbit.Based on observations made on the 193cm telescope at the Haute-ProvenceObservatory, France, and on plate digitisation at the Centre d'Analysedes Images, Paris. This publication makes use of data products from theTwo Micron All Sky Survey, which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center, funded bythe National Aeronautics and Space Administration and the NationalScience Foundation.
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| GPM - compiled catalogue of absolute proper motions of stars in selected areas of sky with galaxies.
Not Available
| DDO photometry of E-region stars and equatorial standards - II
This paper deals with the observations of 72 of McClure's equatorialstandard stars, made with the same photometer and DDO filters as wereused for the E-region stars in Cousins' Paper I in order to standardizethe observations. These observations were reduced in the natural systemand later transformed into McClure's system. Zero-point ties between theequatorial and E-region stars were also needed to standardize the lattersystem. With the exception of C(38-41), our photometry agrees as wellwith McClure's standard system as his own observations do, but both showsome small, apparently systematic, differences which are almostinevitable with a system like the DDO unless the response functions arevery well matched. Comparisons with 17 of Dean's measurements ofE-region stars show good agreement (~2 mmag) for the averagedzero-points, but there are small colour differences affecting C(35-38)and C(38-41) because of differences between the filters and thereduction procedures. This paper also deals with several problems in theDDO photometry that have implications for precision photometry ingeneral.
| The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources - II. The 2RE Source Catalogue
During 1990-1991 the Wide Field Camera (WFC) on the ROSAT satelliteperformed the first all-sky survey at EUV wavelengths. The survey wasconducted in two `colours' using broad-band filters to define wavebandscovering the ranges 60-140 A and 112-200 A. It was fully imaging, witheffective spatial resolution of about 3 arcmin FWHM, and point sourcelocation accuracy of typically better than 1 arcmin. From an initialanalysis, Pounds et al. published the WFC Bright Source Catalogue (BSC)of 383 sources. In this paper we report results from reprocessing of thecomplete survey database; the resulting list of sources is the `2RE'Catalogue. It contains 479 sources, of which 387 are detected in bothsurvey wavebands, a significant advance on the BSC (80 per cent versus60 per cent). Improvements over the original BSC include: (i) betterrejection of poor aspect periods, and smaller random errors in theaspect reconstruction; (ii) improved background screening; (iii)improved methods for source detection; (iv) inclusion of atime-variability test for each source; (v) more extensive investigationof the survey sensitivity. We define the catalogue selection criteria,and present the catalogue contents in terms of tables and sky maps. Wealso discuss the sky coverage, source number-flux relations, opticalidentifications and source variability.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| 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.
| Photographic Observations of NSV 1671
Not Available
| A catalog of stellar Lyman-alpha fluxes
We present a catalog of stellar Ly-alpha emission fluxes, based on newand archival images obtained with the IUE spacecraft. The catalogincludes 227 stars with detectable Ly-alpha emission fluxes, and upperlimits on the Ly-alpha emission flux for another 48 stars. Multiple fluxmeasurements are given for 52 stars. We present a model for correctingthe observed Ly-alpha flux for attenuation by the local interstellarmedium, and we apply this model to derive intrinsic Ly-alpha fluxes for149 catalog stars which are located in low H I column density directionsof the local interstellar medium. In our catalog, there are 14 late-Aand early-F stars at B-V = 0.29 or less that show detectable emission atLy-alpha. We find a linear correlation between the intrinsic Ly-alphaflux and C II 1335 A flux for stars with B-V greater than 0.60, but theA and F stars deviate from this relation in the sense that theirLy-alpha flux is too low. We also find a good correlation betweenLy-alpha strength and coronal X-ray emission. This correlation holdsover most of the H-R diagram, even for the F stars, where an X-raydeficit has previously been found relative to the transition regionlines of C II and C IV.
| Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..551L&db_key=AST
| The extension of the MK spectral classification system to the intermediate population II F type stars
A grid of metal-weak spectral-classification standards is used tosystematically extend the MK spectral-classification system to F-typestars of the intermediate population II. The present method allowsmetal-weak program stars to be compared with standards of similarmetallicity and effective temperature. The results demonstrate that theintermediate population II is very homogeneous. Excellent agreement isobtained between the classifications of the present extended system anduvby-beta photometric results.
| UBV Photometry of Equatorial Stars
Not Available
| The Boehm-Vitense gap in the Geneva photometric system
A gap among A-F stars is searched on the main sequence of differentstellar samples in the photometric space M defined by the four colorindexes U-B1, B1-B2, B2-V1 and V1-G of the Geneva photometric system. Agap is noticed for the field and the eight young open clustersinvestigated when selected stars are not visual or spectroscopicbinaries, and not chemically peculiar. It is shown that this gap isinduced by the existence of two differently oriented star branches in M,the so-called radiative and convective branches. The gap is suggestednot to be only a mere artefact of having previously excluded Am and Apstars but partly due to an abrupt onset of convection in late A stars asproposed by Boehm-Vitense (1970). The locus of the gap's red edgeaccording to B2-V1 with regard to the diffusion region, the lowerinstability strip and the low rotational velocities domain supports theidea that the onset of convection lowers the metallicity, stabilizes thepulsations and brakes the rotation. The locus of the gap's blue edgeseems to be connected with age.
| A photoelectric measurement of magnesium for late-type stars
A photoelectric index of MgH + Mg b for late-type stars has been createdby the addition of one filter bandpass to the DDO system. Measurementsshow that this index has good sensitivity to surface gravity for Kstars, and suggest that it can differentiate metal-poor halo giants fromdisk stars. From this index, involving measurement through two filtersalone, it appears that membership can be determined for stars on thegiant branch of globular clusters. It is possible that the index couldbe used, after calibration with cluster giants, to determine ages ofgiant stars in the field.
| Spectral classification and UBV H BET photometry.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977ApJ...213..105D&db_key=AST
| K-Line Photometry of Southern a Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJS...23..421H&db_key=AST
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
| Photovisual differences in magnitudes of 331 mainly southern double stars
Not Available
| Spectroscopic magnitudes of A-type stars.
Not Available
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| קבוצת-כוכבים: | ארידנוס |
| התרוממות ימנית: | 04h37m36.10s |
| סירוב: | -02°28'24.0" |
| גודל גלוי: | 5.23 |
| מרחק: | 29.762 פארסק |
| תנועה נכונה: | 43.6 |
| תנועה נכונה: | -64.1 |
| B-T magnitude: | 5.546 |
| V-T magnitude: | 5.244 |
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