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

# HD 116160

Contents

### Images

DSS Images   Other Images

### Related articles

 Statistical Constraints for Astrometric Binaries with Nonlinear MotionUseful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr). The Hamburg/RASS Catalogue of optical identifications. Northern high-galactic latitude ROSAT Bright Source Catalogue X-ray sourcesWe present the Hamburg/RASS Catalogue (HRC) of optical identificationsof X-ray sources at high-galactic latitude. The HRC includes all X-raysources from the ROSAT Bright Source Catalogue (RASS-BSC) with galacticlatitude |b| >=30degr and declination delta >=0degr . In thispart of the sky covering ~ 10 000 deg2 the RASS-BSC contains5341 X-ray sources. For the optical identification we used blue Schmidtprism and direct plates taken for the northern hemisphere Hamburg QuasarSurvey (HQS) which are now available in digitized form. The limitingmagnitudes are 18.5 and 20, respectively. For 82% of the selectedRASS-BSC an identification could be given. For the rest either nocounterpart was visible in the error circle or a plausibleidentification was not possible. With ~ 42% AGN represent the largestgroup of X-ray emitters, ~ 31% have a stellar counterpart, whereasgalaxies and cluster of galaxies comprise only ~ 4% and ~ 5%,respectively. In ~ 3% of the RASS-BSC sources no object was visible onour blue direct plates within 40\arcsec around the X-ray sourceposition. The catalogue is used as a source for the selection of(nearly) complete samples of the various classes of X-ray emitters. A systematic study of X-ray variability in the ROSAT all-sky surveyWe present a systematic search for variability among the ROSAT All-SkySurvey (RASS) X-ray sources. We generated lightcurves for about 30 000X-ray point sources detected sufficiently high above background. For ourvariability study different search algorithms were developed in order torecognize flares, periods and trends, respectively. The variable X-raysources were optically identified with counterparts in the SIMBAD, theUSNO-A2.0 and NED data bases, but a significant part of the X-raysources remains without cataloged optical counterparts. Out of the 1207sources classified as variable 767 (63.5%) were identified with stars,118 (9.8%) are of extragalactic origin, 10 (0.8%) are identified withother sources and 312 (25.8%) could not uniquely be identified withentries in optical catalogs. We give a statistical analysis of thevariable X-ray population and present some outstanding examples of X-rayvariability detected in the ROSAT all-sky survey. Most prominent amongthese sources are white dwarfs, apparently single, yet neverthelessshowing periodic variability. Many flares from hitherto unrecognisedflare stars have been detected as well as long term variability in theBL Lac 1E1757.7+7034.The complete version of Table 7 is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/403/247 Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin iThis 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 HV Virginis and WZ Sge-Type Dwarf NovaeA dwarf nova HV Vir was observed photometrically for eight nights duringan outburst in 1992 April--May. The star showed two distinct types ofperiodic variation: (1) 82.20-min (0.05708 d) double-humped variationwith decaying amplitudes during the early stage of the outburst, and (2)83.80-min (0.05820 d) superhumps in later stages. We attributed theformer to early superhumps'', which are only seen in the earlieststage of WZ Sge-type outbursts. The superhump period and evolution ofthe superhumps, together with general characteristics of the lightcurve, make HV Vir a typical WZ Sge-type dwarf nova. HV Vir also showeda large increase of the superhump period during the superoutburst. Uponrecognizing the WZ Sge-type nature of an object previously considered asa nova, we present a comprehensive list of candidates for WZ Sge-typedwarf novae and related systems. Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald ObservatoryThe Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission. A spectroscopic survey for lambda Bootis stars. II. The observational datalambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas). 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 Coronal X-Ray Emission from the Stellar Companions to Transiently Accreting Black HolesMany neutron stars and black holes are in binaries where the masstransfer rate onto the compact object is highly variable. X-rayobservations of these transients in quiescence(LX<1034 ergs s-1) have found thatthe binaries harboring black holes are much fainter than those thatcontain a neutron star. Narayan and collaborators postulated that thefaint X-ray emission from black hole binaries was powered by anadvection- dominated accretion flow (ADAF). The subsequent ADAF modelingrequires that an appreciable fraction of the constant Roche-lobeoverflow into the outer disk proceeds into the black hole duringquiescence''. A robust and nearly uniform quenching mechanism mustthen be hypothesized for the neutron star binaries, as comparably largeaccretion rates would lead to luminosities in excess of 1036ergs s-1 in quiescence. We explore an alternative explanationfor the quiescent X-ray emission from the black hole systems: coronalemission from the rapidly rotating optical companion. This is commonlyobserved and well studied in other tidally locked binaries, such as theRS CVn, Algol, and By Dra systems. We show that two of the three X-raydetected black hole binaries (A0620-00 and GRO J1655-40) exhibit X-rayfluxes entirely consistent with coronal emission. The X-ray spectra ofthese objects should be best fitted with thermal Raymond-Smith modelsrich in lines when coronal emission predominates, a prediction that willbe tested with Chandra and XMM-Newton observations. One black holesystem (V404 Cyg) is too X-ray bright to be explained as coronalemission and remains a candidate for ADAFs in quiescence. The quiescentX-ray emission from all the neutron star binaries is far too bright forcoronal emission. It might be that all soft X-ray transients havevariable accretion rates in quiescence and that the basal quiescentX-ray flux is set by either coronal emission from the companion or-whenpresent-by thermal emission from the neutron star. We have also searchedfor other indicators of coronal activity in these companion stars. Forexample, we show that the lithium abundances in the black hole systemsare comparable to those in the RS CVns. Indeed, both the X-ray flux andlithium abundance from the K star in the binary V471 Tau match that ofA0620-00. Though the production mechanisms for lithium in active coronaeis still under debate, our work makes it clear that there is no longer aneed for mechanisms that involve the compact object. The ROSAT Bright Survey: II. Catalogue of all high-galactic latitude RASS sources with PSPC countrate CR > 0.2 s-1We present a summary of an identification program of the more than 2000X-ray sources detected during the ROSAT All-Sky Survey (Voges et al.1999) at high galactic latitude, |b| > 30degr , with countrate above0.2 s-1. This program, termed the ROSAT Bright Survey RBS, isto more than 99.5% complete. A sub-sample of 931 sources with countrateabove 0.2 s-1 in the hard spectral band between 0.5 and 2.0keV is to 100% identified. The total survey area comprises 20391deg2 at a flux limit of 2.4 x 10-12 ergcm-2 s-1 in the 0.5 - 2.0 keV band. About 1500sources of the complete sample could be identified by correlating theRBS with SIMBAD and the NED. The remaining ~ 500 sources were identifiedby low-resolution optical spectroscopy and CCD imaging utilizingtelescopes at La Silla, Calar Alto, Zelenchukskaya and Mauna Kea. Apartfrom completely untouched sources, catalogued clusters and galaxieswithout published redshift as well as catalogued galaxies with unusualhigh X-ray luminosity were included in the spectroscopic identificationprogram. Details of the observations with an on-line presentation of thefinding charts and the optical spectra will be published separately.Here we summarize our identifications in a table which contains opticaland X-ray information for each source. As a result we present the mostmassive complete sample of X-ray selected AGNs with a total of 669members and a well populated X-ray selected sample of 302 clusters ofgalaxies with redshifts up to 0.70. Three fields studied by us remainwithout optical counterpart (RBS0378, RBS1223, RBS1556). While the firstis a possible X-ray transient, the two latter are isolated neutron starcandidates (Motch et al. 1999, Schwope et al. 1999). Speckle Interferometry of New and Problem HIPPARCOS BinariesThe ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged G,''O,'' V,'' or X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as suspected nonsingle'' (flag S'' in field H61), thusyielding a total of 11,687 problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras. X-ray emission from A0-F6 spectral type starsWe use the ROSAT public data archive to study the X-ray emission of asample of supposedly single A0-F6 spectral type stars from the BrightStar Catalogue. We detected X-ray emission from 19 A- and 33 F-typestars. However, our results are not sufficient to associate withcertainty the X-ray emission to the A-type stars themselves, since theusual argument that it may originate from a binary companion cannot beexcluded. A spectral analysis was conducted for 14 sources (3 A and 11F), finding that for 12 of them a two temperature thermal plasma modelis needed to reproduce the observed spectra. The two temperatures arecentered at 0.13 and 0.54 keV, respectively. The values found for thehigher temperature are lower than that ones of X-ray selected singlelate-type stars. The X-ray luminosities are in the range LX ~10(28}-10({30)) erg s(-1) , with a distribution similar to that ofactive late-type stars. No correlation is found between LXand B-V color, V sin i and Lbol, while a positive correlationis found between the X-ray luminosity and the hardness ratio. The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant starsWe 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 The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circleThe 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. Photometric survey near the main Galactic meridian: 2.1. Finding charts and photoelectric U,B,V,R stellar magnitudes in 26 fields. Photometric properties of the night sky at Mount Terskol observatoryFinding charts and photoelectric magnitudes of stars in the \ubvr\system in 26 fields of the MEGA programme are presented. This part ofthe photometric survey near the Main Galactic Meridian includes thefields with right ascentions 8(h) < alpha < 16(h) 30(m) anddeclinations -2(deg) < delta < 58(deg) . Together with the findingcharts of 2.5(deg) x2.5(deg) the equatorial coordinates of the stars aregiven for epoch and equinox 1950. Photometric properties of the nightsky at the Mount Terskol observatory near Mount Elbrus are derived fromthe photoelectric observations. 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 X-Ray Emission of A-Type StarsFrom X-ray images in the ROSAT public archives, we determine soft X-rayfluxes, or flux upper limits, for 74 A-type stars, which have beenobserved during deep integrations with the PSPC. Nine supposedly single,late A stars (0.20 < B-V < 0.35) are found to coincide with X-raysources. The X-ray luminosities we infer for these stars range fromlevels comparable to the Active Sun, at log L_x ~27.6, to much brighteremission levels similar to those observed for active late-type binarysystems, near log L_x ~30.1. Another 10 sources are identified withearly A stars (0.0 < B-V < 0.2). Five of these are confirmeddouble stars, the rest are ostensibly single. The maximum luminosity wedetect in the early A stars, log L_x = 30.1, is 3.5 orders of magnitudebrighter than the X-ray upper limits for the nondetected stars.Additional study, including radial velocity monitoring and/or opticalinterferometry, will be needed to determine whether the putativelysingle X-ray emitting stars are in fact single, or whether theiremission is produced entirely or in part by unknown or unresolved binarycompanions. The level of X-ray emission associated with chemicallynormal, single A stars thus far appears to be uncorrelated with anyobvious stellar property, including the rotation rate, which is known togreatly influence the dynamo activity and the X-ray emission levels oflower mass stars. (SECTION: Stars) The Relation between Rotational Velocities and Spectral Peculiarities among A-Type StarsAbstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST Photometric Survey Near the Main Galactic Meridian - Part One - Photoelectric Stellar Magnitudes and Colours in the UBVR SystemNot Available 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. The second Quito astrolabe catalogueThe paper contains 515 individual corrections {DELTA}α and 235corrections {DELTA}δ to FK5 and FK5Supp. stars and 50 correctionsto their proper motions computed from observations made with theclassical Danjon astrolabe OPL-13 at Quito Astronomical Observatory ofEcuador National Polytechnical School during a period from 1964 to 1983.These corrections cover the declination zone from -30deg to +30deg. Meanprobable errors of catalogue positions are 0.047" in αcosδand 0.054" in δ. The systematic trends of the catalogue{DELTA}αalpha_cosδ,{DELTA}αdelta_cosδ,{DELTA}δalpha_, {DELTA}δdelta_ arepresented for the observed zone. Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 ExtensionNot Available New Photoelectric Observations of the Eclipsing Binary FO VirNot Available Vacuum ultraviolet imagery of the Virgo cluster regionThe results are reported of an experiment using the UV imager aboard anattitude-controlled S520 type sounding rocket. The total UV fluxes ofgalaxies in the Virgo Cluster as well as the flux level of the diffuseUV background around the cluster were measured. The data on NGC 4486 andNGC 4472 confirm the variation in the degree of the 'turnup' below 200nm in the energy spectrum of the total light of elliptical galaxies. Attwo-color diagram of galaxies of visual/near-UV/vacuum UV indicates thatcolors of spiral galaxies are distributed within a strip andwell-correlated with the morphological type, while elliptical galaxiesare located differently from spiral galaxies. Photometry and elements of the pre-contact system FO VIRAn analysis of the measures carried out at Merate Observatory has shownthat FO Vir is an eclipsing binary. It has been possible to determinethe geometric and photometric elements from the V light curve usingKopal's method. The comparison with the results of Mochnacki et al.(1986) is quite satisfactory and FO Vir is confirmed to be asemidetached system. FO Virginis - A pre-contact binaryThe star FO Vir, a recently discovered eclipsing binary with a period of0.776 days, has been observed photometrically and spectroscopically.Light-curve and line-profile synthesis shows that FO Vir is semidetachedwith a mass ratio of 0.15 + or - 0.02. The A7 V primary component verynearly fills its Roche lobe. Radial velocities from the observed andsynthesized profiles have been measured by cross correlation. Thetheoretical radial-velocity curve fits the observations well, to yield amass of 1.9 + 0.9 or - 0.6 solar mass for the primary and 0.29 + 0.08 or- 0.06 solar mass for the secondary. The mean density is 0.17 + or -0.02 g/cu cm for the primary, 0.33 + or - 0.03 g/cu cm for thesecondary, with log g about 3.9 and Mv about 1.7 for the primary. Thissuggests the primary has evolved off the zero-age main sequence, whilethe secondary has a density that shows that for its mass it is highlyevolved. The period and mass ratio are typical of the more extreme'A-type' W UMa systems, which suggests that FO Vir will evolve into acontact binary of this type. Short-period semidetached binaries may bethe progenitors of at least some W UMa systems. The local system of early type stars - Spatial extent and kinematicsPublished uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter. The first astrolabe catalogue at ValinhosIndividual corrections to the ascensions and declinations of 199 starsof the FK4 and FK4 Supplement, derived from the Danjon astrolabeobservations at Valinhos and covering the zone from +5 to -51 deg ofdeclination, are presented. The chain method of differences was used tomake the corrections. The observational station formulas used to obtainthe catalogue are cited and discussed and the systematic errors for thezone of the catalogue are given. The results are compared with those ofthe General Catalogue of Astrolabes. First astrolabe catalogue of Rio de JaneiroA catalogue of right ascensions and declinations of FK4 and FK4Supplement stars, obtained from astrolabe observations at Rio deJaneiro, is presented. The quantity and accuracy of the observations,the systematic errors of the catalogue, the group corrections, and theascension and declination corrections are considered. Spectral classification from the ultraviolet line features of S2/68 spectra. III - Early A-type starsAbstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...33...15C&db_key=AST
Submit a new article