תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
New homogeneous iron abundances of double-mode Cepheids from high-resolution echelle spectroscopy
Aims.We define the relationship between the double-mode pulsation ofCepheids and metallicity in a more accurate way, determine the empiricalmetallicities of double-mode Cepheids from homogeneous, high-resolutionspectroscopic data, and study of the period-ratio - metallicitydependence. Methods: The high S/N echelle spectra obtained with theFEROS spectrograph were analyzed using a self-developed IRAF script, andthe iron abundances were determined by comparing with synthetic spectraassuming LTE. Results: Accurate [Fe/H] values of 17 galactic beatCepheids were determined. All these stars have solar or slightlysubsolar metallicity. Their period ratio (P1 / P_0) showsstrong correlation with their derived [Fe/H] values. The correspondingperiod ratio - metallicity relation has been evaluated.Based on observations taken with the ESO 2.2-m telescope at La Silla,Chile (Proposal 073.D-0072) and the 1.82 m telescope at David DunlapObservatory, Canada.
| Cepheid parallaxes and the Hubble constant
Revised Hipparcos parallaxes for classical Cepheids are analysedtogether with 10 Hubble Space Telescope (HST)-based parallaxes. In areddening-free V, I relation we find that the coefficient of logP is thesame within the uncertainties in our Galaxy as in the Large MagellanicCloud (LMC), contrary to some previous suggestions. Cepheids in theinner region of NGC4258 with near solar metallicities confirm thisresult. We obtain a zero-point for the reddening-free relation and applyit to the Cepheids in galaxies used by Sandage et al. to calibrate theabsolute magnitudes of Type Ia supernova (SNIa) and to derive the Hubbleconstant. We revise their result for H0 from 62 to 70 +/-5kms-1Mpc-1. The Freedman et al. value is revisedfrom 72 to 76 +/- 8kms-1Mpc-1. These results areinsensitive to Cepheid metallicity corrections. The Cepheids in theinner region of NGC4258 yield a modulus of 29.22 +/- 0.03 (int.)compared with a maser-based modulus of 29.29 +/- 0.15. Distance modulifor the LMC, uncorrected for any metallicity effects, are 18.52 +/- 0.03from a reddening-free relation in V, I; 18.47 +/- 0.03 from aperiod-luminosity relation at K; 18.45 +/- 0.04 from aperiod-luminosity-colour relation in J, K. Adopting a metallicitycorrection in V, I from Macri et al. leads to a true LMC modulus of18.39 +/- 0.05.
| High-Mass Triple Systems: The Classical Cepheid Y Carinae
We have obtained a Hubble Space Telescope STIS ultraviolethigh-dispersion echelle-mode spectrum of the binary companion of thedouble-mode classical Cepheid Y Car. The velocity measured for the hotcompanion from this spectrum is very different from reasonablepredictions for binary motion, implying that the companion is itself ashort-period binary. The measured velocity changed by 7 kms-1 during the 4 days between two segments of theobservation, confirming this interpretation. We summarize ``binary''Cepheids that are in fact members of a triple system and find that atleast 44% are triples. The summary of information on Cepheids withorbits makes it likely that the fraction is underestimated.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc.
| SB9: The ninth catalogue of spectroscopic binary orbits
The Ninth Catalogue of Spectroscopic Binary Orbits(http://sb9.astro.ulb.ac.be) continues the series of compilations ofspectroscopic orbits carried out over the past 35 years by Batten andcollaborators. As of 2004 May 1st, the new Catalogue holds orbits for2386 systems. Some essential differences between this catalogue and itspredecessors are outlined and three straightforward applications arepresented: (1) completeness assessment: period distribution of SB1s andSB2s; (2) shortest periods across the H-R diagram; (3)period-eccentricity relation.
| The orbits of southern binary Cepheids
High-resolution spectroscopic observations have been made of a number ofsouthern Cepheids. The stars studied were part of a long-term programmeto observe southern variable stars and to complete a data base of radialvelocities over a long time interval. The radial velocities have aprecision of ~300 m s-1, allowing the detection of velocitydifferences of ~1 km s-1 with confidence. Our new dataprovide a consistent set of data against which other sources of data canbe compared.Masses were determined for two systems, the 9-d Cepheid S Mus (6.2 +/-0.2 Msolar) and the 5-d Cepheid V350 Sgr (6.0 +/- 0.9Msolar). For another seven Cepheids (Y Car, YZ Car, AX Cir,BP Cir, V636 Sco, W Sgr and T Mon), new or improved orbital solutionswere found.New results presented here include the first orbital solution for AXCir, a completely revised orbital solution for YZ Car, which establishedits eccentricity and orbital motion, and a new pulsation period (2.39819 d) for BP Cir. The pulsational mass determinations provide furtherconfirmation of the convergence of mass determinations between dynamicaland evolutionary methods.
| The Beat Cepheids NSV 6728, GSC 8607-0608, EY Car and BE Pup
Analysis of the publicly available ASAS3 data has lead to the discoveryof four new Galactic beat Cepheids: NSV 6728, GSC 8607-0608, EY Car andBE Pup are pulsating in the fundamental and first overtone modes.
| Polaris: Amplitude, Period Change, and Companions
Polaris has presented us with the rare phenomenon of a Cepheid with apulsation amplitude that has decreased over the last 50 yr. In thisstudy we have used this property to see whether the amplitude decreaseduring the last 15 yr has had any effect on upper atmosphere heating. Weobtained IUE high- and low-resolution spectra but found no change ineither the Mg II chromospheric emission or the flux at 1800 Åbetween 1978 and 1993 when the pulsation amplitude dropped by 50% (from2.8 to 1.6 km s-1). The energy distribution from 1700 Åthrough V, B, R(KC), and I(KC) is like that of a nonvariable supergiantof the same color rather than a full amplitude Cepheid in that it hasmore flux at 1800 Å than the full amplitude Cepheid δ Cep.Polaris also has a rapidly changing period (3.2 s yr-1), incommon with other overtone pulsators. We argue that this is a naturalconsequence of the different envelope locations that dominate pulsationgrowth rates in fundamental and overtone pulsation. In fundamental modepulsators, the deeper envelope is more important in determining growthrates than for overtone pulsators. For fundamental mode pulsators,evolutionary changes in the radius produce approximately linear changesin period. In overtone pulsators, pulsation reacts to small evolutionarychanges in a more unstable way because the modes are more sensitive tohigh envelope features such as opacity bumps, and the growth rates forthe many closely spaced overtone modes change easily. Finally, the upperlimit to the X-ray flux from an Einstein observation implies that thecompanion in the astrometric orbit is earlier than F4 V. The combinationof upper and lower limits on the companion from IUE and Einsteinrespectively catch the companion mass between 1.7 and 1.4Msolar. The X-ray limit is consistent with the more distantcompanion α UMi B being a physical companion in a hierarchaltriple system. However the X-ray limits require that the even moredistant companions α UMi C and D are too old to be physicallyassociated with Polaris.
| Photoelectric Observations of Southern Cepheids in 2001
A total of 2097 photometric observations in the BVIc systemare presented for 117 Cepheids located in the southern hemisphere. Themain purpose of the photometry is to provide new epochs of maximumbrightness for studying Cepheid period changes, as well as to establishcurrent light elements for the Cepheids.
| Multiperiodicities from the Hipparcos epoch photometry and possible pulsation in early A-type stars
A selection criterion based on the relative strength of the largestpeaks in the amplitude spectra, and an information criterion are used incombination to search for multiperiodicities in Hipparcos epochphotometry. The method is applied to all stars which have beenclassified as variable in the Hipparcos catalogue: periodic, unsolvedand microvariables. Results are assessed critically: although there aremany problems arising from aliasing, there are also a number ofinteresting frequency combinations which deserve further investigation.One such result is the possible occurrence of multiple periods of theorder of a day in a few early A-type stars. The Hipparcos catalogue alsocontains a number of these stars with single periodicities: such starswith no obvious variability classifications are listed, and informationabout their properties (e.g., radial velocity variations) discussed.These stars may constitute a new class of pulsators.
| 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
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Astrophysical Quantities of Cepheid Variables Measured with the Navy Prototype Optical Interferometer
We present mean angular diameters for two Cepheid variables, α UMiand ζ Gem, determined with the Navy Prototype OpticalInterferometer (NPOI). We present linear radii for these Cepheids andtwo additional Cepheids, δ Cep and η Aql, previously observedat the NPOI. We find the limb-darkened angular diameters of α UMiand of ζ Gem to be 3.28+/-0.02 and 1.55+/-0.09 mas, respectively.Using trigonometric parallaxes, we find the linear radii of α UMi,ζ Gem, δ Cep, and η Aql to be 46+/-3,60+25-14, 45+8-6, and69+28-15 Rsolar, respectively. Wecompare the pulsation periods and linear radii of this sample ofCepheids, which range in period from 3 to 11 days, to theoretical andempirical period-radius and period-radius-mass relations found in theliterature. We find that the observed diameter of α UMi is inexcellent agreement with the predicted diameter as determined from bothsurface brightness techniques and theory only if α UMi is afirst-overtone pulsator.
| Masses for Galactic Beat Cepheids
Accurate mass determinations for Cepheids may be used to determine thedegree of excess mixing in the interiors of their main-sequenceprogenitors: the larger the excess mixing, the larger the luminosity ofthe Cepheid of a given mass, or the smaller the mass of a Cepheid withgiven luminosity. Dynamical masses determined recently for a few Cepheidbinaries indicate excess mixing somewhat stronger than thatcorresponding to the convective overshoot models by Schaller et al. BeatCepheids can be used similarly to test main-sequence mixing in stellarinteriors. The period ratios for beat Cepheids depend on luminosity,Teff, heavy element abundance, and mass. By comparingpulsational models and the observationally derived luminosity,Teff, metallicities, and period ratios it is possible toobtain masses for these stars, the so-called beat masses. With the oldopacities masses much smaller than the evolutionary masses wereobtained. With the new OPAL opacities a beat mass close to the dynamicalmass was obtained for the binary beat Cepheid Y Carinae, showing that itis now possible to obtain reliable beat masses. In this paper, wedetermine beat masses for seven Galactic beat Cepheids for whichphotometric and spectroscopic data are available. We find an averagemass around 4.2+/-0.3 Msolar for these stars, though theactual error limits for each star may be larger mainly because ofuncertainties in E(B-V) and the heavy element abundances. (As derivedspectroscopically, beat Cepheids are in general metal-poor, with-0.4<~[Fe/H]<~0.0). The relation between the derived beat massesand the luminosities again indicates excess mixing that is somewhatlarger than that corresponding to the models by Schaller et al.
| Toward an Orbit for the High-Luminosity Cepheid T Monocerotis
We have obtained new velocities of the long-period Cepheid T Mon fromthe ground and velocities of its hot companion with the Hubble SpaceTelescope (HST) and the International Ultraviolet Explorer (IUE).Although observations do not cover a full orbit, both the maximum andminimum orbital velocities have now been obtained. We present apreliminary orbit and discuss the uncertainties in the orbitalparameters. The velocities for the companion appear to be inconsistentwith binary orbital motion, and it is likely that the companion isitself a binary in a short-period orbit. The HST spectrum of thecompanion shows that it is a chemically peculiar star, probablymagnetic. Because it is coupled with the more massive Cepheid, it mustbe very close to the zero-age main sequence. The well-determined massfunction from the preliminary orbit implies that the inclination of thelong-period system is close to 90 deg.
| I- and JHK-band photometry of classical Cepheids in the HIPPARCOS catalog
By correlating the \cite[Fernie et al. (1995)]{F95} electronic databaseon Cepheids with the ``resolved variable catalog'' of the hipparcosmission and the simbad catalog one finds that there are 280 Cepheids inthe hipparcos catalog. By removing W Vir stars (Type ii Cepheids),double-mode Cepheids, Cepheids with an unreliable solution in thehipparcos catalog, and stars without photometry, it turns out that thereare 248 classical Cepheids left, of which 32 are classified asfirst-overtone pulsators. For these stars the literature was searchedfor I-band and near-infrared data. Intensity-mean I-band photometry onthe Cousins system is derived for 189 stars, and intensity-mean JHK dataon the Carter system is presented for 69 stars.
| The Mass of the Cepheid Binary V636 Scorpii
The mass-luminosity relation for Cepheids depends on the degree ofmixing in their main-sequence progenitors. Masses of Cepheids can beinferred by using different aspects of pulsation theory. These methodshave in the past led to diverging results, showing that something waswrong in either evolution theory or pulsation theory or both. For somebinary Cepheids dynamical masses, which are independent of pulsation andevolution theories, can be determined. V636 Sco is one of a handful ofCepheid binaries whose companions are bright enough in the ultravioletthat orbital radial velocities can be measured. We have here attemptedto determine the radial velocity of the companion V636 Sco B to theCepheid V636 Sco A by means of two Hubble Space Telescope (HST) spectrataken at phases of minimum and maximum Cepheid orbital velocities. Theratio of the orbital velocity of the companion and the Cepheid (which isthe inverse of their mass ratio) came out to be 1.25 +/- 0.17. V636 ScoB has a spectral type B9.5 V, for which we expect a stellar mass of 2.5M_ȯ. For the Cepheid we thus determine a mass of 3.1 +/- 0.4M_ȯ, which is surprisingly low. If true, such a low mass wouldindicate an extremely large amount of excess mixing, which is veryunlikely. We discuss the likely possibility that V636 Sco B may itselfbe a binary with an unseen secondary, in which case the mass derivedfrom the two measurements discussed above is not correct. Although theerror limits for the mass of each Cepheid are rather large, the combinedmass-luminosity relation for all Cepheids studied by us so far by meansof HST spectra indicates excess mixing corresponding to core convectiveovershoot by 0.25 to about 0.5 pressure scale height in themain-sequence progenitors of the Cepheids. Based on observations madewith the NASA/ESA Hubble Space Telescope, obtained at the SpaceTelescope Science Institute, which is operated by the Association ofUniversities for Research in Astronomy, Inc., under NASA contractNASS-26555.
| A HgMn companion to the Cepheid SU Cyg.
We report here the discovery of a chemically peculiar star of the HgMntype as a companion to the classical Cepheid variable SU Cyg. This isthe first investigation of a HgMn star in a binary system in which astar of a more advanced evolutionary stage is the primary. The age ofthe Cepheid provides an estimate to the age of the chemicalpeculiarities which is independent of the photometric calibration ofHgMn field stars. From a synthetic spectrum analysis it is determinedthat the HgMn star, SU Cyg B, displays the abundance deficiency fornitrogen and enhancements for manganese (+1.5\,dex) and the very heavyelements mercury (+5.8\,dex) and platinum (+5.0\,dex). Absorption fromthe strong transitions Au Ii lambda1740 and Tl Ii lambda1908 eachimplies abundance enhancements of 3.0\,dex. A search through the IUE andHST/GHRS spectral archives reveals several binary-Cepheid companionswhich are candidates for chemically peculiar stars.
| Classical Cepheid Masses: U Aquilae
We have obtained medium-resolution spectra ( lambda / Delta lambda ~20,000) of the hot binary companion to the classical Cepheid U Aql withthe Goddard High Resolution Spectrograph on the Hubble Space Telescope(HST). These have been used to determine the orbital velocity amplitude.Combining this with the orbital velocity amplitude of the Cepheid fromthe ground-based orbit and the mass of the companion inferred from itsspectral type, we measure a mass of the Cepheid of 5.1 +/- 0.7 Mȯ.We discuss the full sample of Cepheids for which we have determinedmasses with HST (S Mus, V350 Sgr, Y Car, and U Aql) and also SU Cyg(mass from IUE). The HST masses are in agreement with the luminositiespredicted by recent evolutionary tracks with moderate overshoot. Thiscomparison, however, may be altered by reassessment of Cepheid distancesbased on Hipparcos parallaxes.
| The shape and scale of Galactic rotation from Cepheid kinematics
A catalog of Cepheid variables is used to probe the kinematics of theGalactic disk. Radial velocities are measured for eight distant Cepheidstoward l = 300 deg; these new Cepheids provide a particularly goodconstraint on the distance to the Galactic center, R0. We model the diskwith both an axisymmetric rotation curve and one with a weak ellipticalcomponent, and find evidence for an ellipticity of 0.043 +/- 0.016 nearthe sun. Using these models, we derive R0 = 7.66 +/- 0.32 kpc andv(circ) = 237 +/- 12 km/s. The distance to the Galactic center agreeswell with recent determinations from the distribution of RR Lyraevariables and disfavors most models with large ellipticities at thesolar orbit.
| Galactic kinematics of Cepheids from HIPPARCOS proper motions
The Hipparcos proper motions of 220 Galactic Cepheids, together withrelevant ground-based photometry, have been analyzed. The effects ofGalactic rotation are very clearly seen. Mean values of the Oortconstants, A = 14.82 +/- 0.84 km/s kpc, and B = -12.37 +/- 0.64 km/skpc, and of the angular velocity of circular rotation at the sun, 27.19+/- 0.87 km/s kpc, are derived. A comparison of the value of A withvalues derived from recent radial velocity solutions confirms, withinthe errors, the zero-points of the period-luminosity andperiod-luminosity-color relations derived directly from the Hipparcostrigonometrical parallaxes of the same stars. The proper motion resultssuggest that the Galactic rotation curve is declining slowly at thesolar distance from the Galactic Center (-2.4 +/- 1.2 km/s kpc). Thecomponent of the solar motion towards the North Galactic Pole is foundto be +7.61 +/- 0.64 km/s. Based on the increased distance scale deducedin the present paper, the distance to the Galactic Center derived in aprevious radial velocity study is increased to 8.5 +/- 0.5 kpc.
| The dynamical mass of the beat cepheid Y carinae and stellar opacities.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1176B&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
| The galactic double-mode Cepheids. II. Properties of the generalized phase differences.
By considering the least-squares fits of the double-mode Cepheid lightcurves discussed in Paper I we defined their properties by their Fourierparameters and generalized phase differences G_i,j_. When plotting thelatter quantities as a function of the order, the second order terms areconfined in the region just below 3π/2; the third order terms haveπ/2
| The galactic double-mode Cepheids. I. Frequency analysis of the light curves and comparison with single-mode Cepheids.
We submitted the available photometric V data of all the known galacticDouble Mode Cepheids (DMCs) to a careful frequency analysis with the aimof detecting in each case the importance of the harmonics and of thecross coupling terms. For each object, starting from different datasubsets, we progressively built a homogenous set of data, checking theconsistency of the results step by step. It was demonstrated that eachstar displays a different content, showing that no a priori fit can beapplied. Up to 4 harmonics were found for the fundamental radial mode(F); in every case, 2 harmonics were found for the first overtone radialmode (1O). We also proceeded to a preliminar analysis of the Fourierparameters of the DMC light curves and we found a very close similaritybetween i) the light curves of the classical Cepheids and those of theF-mode of the DMCs; ii) the light curves of the s-Cepheids and those ofthe 1O-mode of the DMCs. The analysis of DMC light curves offers thepossibility of unifying the light curves of classical and s-Cepheids.The case of the unique DMC CO Aur is also discussed.
| The Mass of the Classical Cepheid V350 SGR
Two medium resolution spectra of the hot companion of the Cepheid V350Sgr have been obtained with the Goddard High Resolution Spectrographaboard the Hubble Space Telescope. Comparison of these spectra (in thewavelength range 1840 to 1880 \AA) with the spectrum of $\alpha$ Lyrshows that V350 Sgr B has a projected rotation velocity which may be ashigh as 150 km sec$^{-1}$. The velocity difference between the spectraof V350 Sgr B at two orbital phases is measured to be -23.1 $\pm$ 3.8 kmsec$^{-1}$. The error is dominated by the aperture centering. Whencombined with the orbital velocity variation of the Cepheid derived fromthe ground-based orbit and the mass of the companion deduced from IUEspectra, the mass of the Cepheid is found to be 5.2 $\pm$ 0.9 M$\sun$.The observed mass--luminosity combination of V350 Sgr A is a good matchto recent evolutionary calculations which use moderate convectiveovershoot near the main sequence, however, the blue loops do not extendto temperatures as hot as the Cepheid. (SECTION: Stars)
| Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
| Photometric Parameters for Short-Period Cepheids
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1313E&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.
| The mass ratios of Cepheid binaries
The distribution of mass ratios in binary systems is important forcomparison with star formation calculations but has been difficult toobtain observationally. This study uses IUE spectra of the hotcompanions of classical Cepheids with observed orbital motion todetermine the companion types and hence their masses. Combining thesewith Cepheid masses inferred from an appropriate mass-luminosityrelation produces a distribution of mass ratios q =M2/M1 (where M1 is the mass of theCepheid). This is a distribution of spectroscopic (as opposed todynamic) mass ratios for intermediate-mass stars with orbital periodslonger than a year. The distribution is strongly peaked to low-masscompanions. The IUE spectra can detect companions in systems with massratios as small as 0.26. Incompleteness in detecting low-amplitudeorbital motion means the concentration to low masses is even larger thanthat in the observed distribution. The fact that the orbital periods arelonger than one year, and only one eccentricity is zero, implies that itis unlikely that there has been mass transfer between the components inthe systems, except possibly in one case.
| Photoelectric Observations of Southern Cepheids in 1995
Not Available
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | שדרית |
| התרוממות ימנית: | 10h33m10.85s |
| סירוב: | -58°29'55.1" |
| גודל גלוי: | 8.148 |
| מרחק: | 436.681 פארסק |
| תנועה נכונה: | -9.4 |
| תנועה נכונה: | 3.5 |
| B-T magnitude: | 8.879 |
| V-T magnitude: | 8.209 |
קטלוגים וכינוים:
|
