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Observed Orbital Eccentricities
For 391 spectroscopic and visual binaries with known orbital elementsand having B0-F0 IV or V primaries, we collected the derivedeccentricities. As has been found by others, those binaries with periodsof a few days have been circularized. However, those with periods up toabout 1000 or more days show reduced eccentricities that asymptoticallyapproach a mean value of 0.5 for the longest periods. For those binarieswith periods greater than 1000 days their distribution of eccentricitiesis flat from 0 to nearly 1, indicating that in the formation of binariesthere is no preferential eccentricity. The binaries with intermediateperiods (10-100 days) lack highly eccentric orbits.
| Mid-IR observations of circumstellar disks. II. Vega-type stars and a post-main sequence object
We present spectral energy distributions and new N-band photometry andspectroscopy for a sample of six main sequence stars and one post-MSobject using the ESO TIMMI2 camera at La Silla observatory (Chile). Allobjects are thought to possess circumstellar material and for themajority of the targets this is their first N-band spectroscopicobservation. The emission spectra (observed in three cases), modelledwith a mixture of silicates consisting of different grain sizes andcomposition, confirm the suspected presence of disks around thesetargets. The most important discovery is that HD 113766, a youngVega-type star, is host to highly processed dust which is probablysecond generation. It is the first time a Vega-type star with suchhighly evolved dust has been observed. Silicate emission of basicallyunevolved dust is seen in case of the post-MS object HD 41511 and theVega-type star HD 172555. In addition, to study the cold dust, weobserved a subsample at 1200 μm with the bolometer array SIMBA at theSEST in La Silla but we only got upper limits for those five objects.This shows that these Vega-type stars have a smaller amount of dust thantheir precursors, the T Tauri and Herbig Ae/Be stars.Based on observations collected at the European Southern Observatory, LaSilla, Chile (70.C-0468, 71.C-0001).
| Tidal Effects in Binaries of Various Periods
We found in the published literature the rotational velocities for 162B0-B9.5, 152 A0-A5, and 86 A6-F0 stars, all of luminosity classes V orIV, that are in spectroscopic or visual binaries with known orbitalelements. The data show that stars in binaries with periods of less thanabout 4 days have synchronized rotational and orbital motions. Stars inbinaries with periods of more than about 500 days have the samerotational velocities as single stars. However, the primaries inbinaries with periods of between 4 and 500 days have substantiallysmaller rotational velocities than single stars, implying that they havelost one-third to two-thirds of their angular momentum, presumablybecause of tidal interactions. The angular momentum losses increase withdecreasing binary separations or periods and increase with increasingage or decreasing mass.
| On the Flux of Extrasolar Dust in Earth's Atmosphere
Micron-size extrasolar dust particles have been convincingly detected bysatellites. Larger extrasolar meteoroids (5-35 μm) have most likelybeen detected by ground-based radar at Arecibo and New Zealand. Wepresent estimates of the minimum detectable particle sizes and thecollecting areas for both radar systems. We show that particles largerthan ~10 μm can propagate for tens of parsecs through theinterstellar medium, opening up the possibility that ground-based radarsystems can detect AGB stars, young stellar objects such as T Tauristars, and debris disks around Vega-like stars. We provide analyticaland numerical estimates of the ejection velocity in the case of a debrisdisk interacting with a Jupiter-mass planet. We give rough estimates ofthe flux of large micrometeoroids from all three classes of sources.Current radar systems are unlikely to detect significant numbers ofmeteors from debris disks such as β Pictoris. However, we suggestimprovements to radar systems that should allow for the detection ofmultiple examples of all three classes.
| A Spectroscopic Program to Monitor and Discover A-type Classical Shell Stars
We have embarked on a spectroscopic program to monitor and discover"classical" A-type shell stars. These are late-B, A and early F-typestars which show Fe II and Ti II lines similar in strength to A-typebright giants or supergiants, but their hydrogen lines indicate giant oreven dwarf luminosities. Well known members of the class include 17Leporis and HD 195325. We are particularly interested in stars whichexhibit static shells. We will present preliminary results for thisprogram, including our strategy for discovering new A-type shell stars.
| Spectroscopy of Early F Stars: γ Doradus Candidates and Possible Metallic Shell Stars
We obtained high-resolution spectroscopic observations of 34 γDoradus candidates. From the red-wavelength spectra, we determinedspectral classes, radial velocities, and projected rotationalvelocities. The spectra of seven late A or early F stars show metalliclines that have composite profiles consisting of a narrow component nearthe center of a broad line, indicating that they may be shell stars orbinaries. Several stars, including HD 152896, HD 173977, HD 175337, andHD 195068/9, show large line profile asymmetries. Two stars, HD 11443(=α Trianguli) and HD 149420, are ellipsoidal variables and notγ Doradus stars. The percentage of binary systems in our samplemay be as high as 74%.
| 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
| Large Circumbinary Dust Grains around Evolved Giants?
We have detected continuum emission at 450 μm, 850 μm, and 1.35 mmfrom SS Lep (or 17 Lep), 3 Pup, and probably BM Gem, respectively, whichare likely or confirmed binary systems consisting of at least oneevolved giant. The observed submillimeter fluxes are probably emitted bygrains rather than ionized gas. The fluxes are larger than thoseexpected from a ``normal'' dusty wind; the dust temperature is <=70 Kwithin 6" of the stars. To explain why grains are so cold near the star,we suggest that the emission at λ>=450 μm is produced byparticles as large as 0.1 mm in radius and that these large particlesprobably have grown by coagulation in circumbinary orbiting disks withmasses >=5×1028 g.
| Four Years of Extreme Ultraviolet Observations of Markarian 421. II. Temporal Analysis
The Extreme Ultraviolet Explorer (EUVE) satellite accumulated ~1,000,000s of public data between 1994 and 1997 for the BL Lacertae objectMarkarian 421. This is the second of two papers in which we present theresults of spectral and temporal analysis of this EUVE data set. Weanalyze in the present paper the imaging data by means of power spectrumand structure function techniques, while the spectral analysis ispresented in a companion paper. We find for Mrk 421 a power spectrumwith slope -2.14+/-0.28 with a break at ~3 days. This is the first timethat a break in the power spectrum of a BL Lacertae object has beenfound. We also find evidence of nonstationarity for Mrk 421 EUVemission.
| A photometric catalogue of southern emission-line stars
We present a catalogue of previously unpublished optical and infraredphotometry for a sample of 162 emission-line objects and shell starsvisible from the southern hemisphere. The data were obtained between1978 and 1997 in the Walraven (WULBV), Johnson/Cousins(UBV(RI)c) and ESO and SAAO near-infrared (JHKLM) photometricsystems. Most of the observed objects are Herbig Ae/Be (HAeBe) stars orHAeBe candidates appearing in the list of HAeBe candidates of Théet al. (1994), although several B[e] stars, LBVs and T Tauri stars arealso included in our sample. For many of the stars the data presentedhere are the first photo-electric measurements in the literature. Theresulting catalogue consists of 1809 photometric measurements. Opticalvariability was detected in 66 out of the 116 sources that were observedmore than once. 15 out of the 50 stars observed multiple times in theinfrared showed variability at 2.2 mu m (K band). Based on observationscollected at the European Southern Observatory, La Silla, Chile and onobservations collected at the South African Astronomical Observatory.Tables 2-4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/380/609
| 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
| Analysis of correlations between polarimetric and photometric characteristics of young stars. A new approach to the problem after eleven years' study
We present the results of the investigation of correlations between thepolarimetric and photometric characteristics of a sample (496 objects)of young Herbig Ae/Be (HAEBE) stars and T Tauri (TT) stars. It is shownthat, for 85% of the sample stars there is a general relation betweenthe degree of optical polarization and the infrared colour index(V-L)_obs and the colour excess E(V-L) due to the contribution of acircumstellar dust shell. Polarimetric data were also compared with thevalue of vsin i to search for a possible correlation between thepolarization and an inclination of circumstellar disks. Polarimetricdata as well as IR excesses are considered and compared for differentsubgroups of young stars namely: HAEBE and TT stars with Algol-likeminima of brightness (26 objects), Vega-type stars and post HAEBE stars(114 objects) and young solar-type stars (58 objects). For statisticalpurposes the data for young stars were compared with those collected fordifferent groups of evolved objects such as: classical Be stars (~300objects), Mira Ceti stars (39 objects), early-type supergiants from theSerkowski et al. (\cite{serk}) catalogue (120 objects) and main sequence(MS) stars within 50 pc from the Sun from the Leroy (\cite{leroy})catalogue (68 objects). The value of polarization is discussed incontext with the stages of evolution of circumstellar shells which wereestablished by comparison of spectral energy distribution in the far IR(using the IRAS data). It is shown that most young stars havestatistically larger value of polarization in comparison with the starswhich are on a stage of evolution close to MS. We are able to contendthat the changes in polarimetric behaviour of young stars are connectedwith evolution of their circumstellar shells. Appendices 1 to 5 are onlyavailable in electronic form at http://www.edpsciences.org
| A-shell stars in the Geneva system
Among the various kinds of A stars having a peculiar spectrum, we findthe A-shell stars. Many questions are still open concerning these stars,including their evolutionary status. In the present study we have useddata from the Hipparcos catalogue to examine this point. We have foundthat the majority of A-shell stars are well above the main sequence. Nodifferences could be established between A-shell stars in luminosityclasses III and I and those in luminosity class V as regardsvariability, duplicity, or the importance of the shell feature.
| Be star binary systems with non-compact secondaries
Not Available
| Orbiting Molecular Reservoirs around Evolved Red Giant Stars
We report molecular emission from the circumstellar envelopes of twocarbon-rich stars with oxygen-rich envelopes, EU And and BM Gem. We finda narrow (FWHM~5 km s^-1) CO (2-1) emission line from EU And and an evennarrower (FWHM ~ 1 km s^-1) ^13CO emission line from BM Gem. We alsoplace upper limits to the emission of HCN, SiO, SO, HCO^+, and CS fromBM Gem. We argue that the narrow CO emission lines are signatures oflong-lived reservoirs of orbiting gas and that standard models for COemission from red giant winds are not appropriate for these two stars.By including the Red Rectangle and AC Her, narrow CO emissioncharacteristic of gravitationally bound gas has been detected from fourpost-main-sequence systems, and we can begin to characterize theseapparently similar environments. Some common characteristics are thefollowing: (1) Their diameters are typically between ~100 and ~1000 AU.(2) The masses of CO are near 10^27 g. (3) Unlike the envelopes aroundmass-losing carbon stars where M_CO/M_dust~ 2, the circumstellarorbiting reservoirs often appear to have M_CO
| 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.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The 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.
| Radial velocities of HIPPARCOS southern B8-F2 type stars
Radial velocities have been determined for a sample of B8-F2 type starsobserved by the Hipparcos satellite. Observations were obtained withinthe framework of an ESO key-program. Radial velocities have beenmeasured using a cross-correlation method, the templates being a grid ofsynthetic spectra. The obtained precision depends on effectivetemperature and projected rotational velocity of the star as well as ona possible asymmetry of the correlation peak generally due to secondarycomponents. New spectroscopic binaries have been detected from theseasymmetries and the variability of the measured radial velocity.Simulations of binary and triple systems have been performed. Forbinaries our results have been compared with Hipparcos binary data.Adding the variable radial velocities, the minimum binary fraction hasbeen found 60% for physical systems. Radial velocities have beendetermined for 581 B8-F2 stars, 159 being new. Taking into accountpublished radial velocities, 39% south A-type stars with V magnitudelower than 7.5 have a radial velocity. Based on observations obtained atthe European Southern Observatory (ESO, La Silla, Chile) and on datafrom the ESA Hipparcos astrometry satellite.}\fnmsep \thanks{Tables 7, 8and 9 are only available in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| JHK photometry of symbiotic stars
We present the results of multi-epoch JHK photometry of a sample of 30known or suspected symbiotics and related objects. These are the firstresults of an ongoing programme of near-IR monitoring of symbiotic starsfrom the Mt. Abu IR Observatory of Physical Research Laboratory (PRL).
| Dust shells around certain early-type stars with emission lines.
Not Available
| An ultraviolet, optical and infrared study of Herbig Ae/Be stars
We have selected a list of 45 Herbig Ae/Be-type candidates on the baseof their IRAS colors and their spectral types. We propose the presenceof a broad infrared excess as a defining criterion for these stars,rather than the detection of circumstellar nebulosity. In this way, ourselection also includes more evolved young stars, that are no longerembedded in their star-forming region. A few objects in our sample arewell-known Herbig Ae/Be stars, others are new. New optical andnear-infrared photometric observations, as well as ultraviolet ones, arepresented. The position of the objects in several color-color diagrams,as well as their de-reddened energy distributions, permit a reliableclassification. Three objects probably are binaries with a coolsecondary, 9 appear to be related to the Vega-type stars and 33 objectscan be classified as genuine Herbig Ae/Be stars. The majority of theHerbig Ae/Be stars have a dusty environment consisting of a distinct hotand cool component. These isolated Herbig Ae/Be stars suggest anevolution from embedded Herbig Ae/Be stars to beta Pictoris-likemain-sequence stars, an evolution in which planet formation may play animportant role. Based on observations obtained at the European SouthernObservatory, La Silla, Chile; and at the Swiss Telescope, La Silla,Chile; and at the Swiss Telescope, Hochalpine ForschungsstationJungfraujoch, Switzerland, and with the International UltravioletExplorer (IUE)
| HIPPARCOS photometry of Herbig Ae/Be stars
The photometric behaviour of a sample of 44 Herbig Ae/Be (HAeBe)candidate stars was studied using a uniform set of optical photometryobtained by the Hipparcos mission. Astrophysical parameters (distance,temperature, luminosity, mass, age) of this sample of stars were derivedas well by combining the astrometric data provided by Hipparcos withdata from literature. Our main conclusions can be summarized as follows:(1) More than 65% of all HAeBe stars show photometric variations with anamplitude larger than 0\fm05; (2) HAeBes with a spectral type earlierthan A0 only show moderate (amplitude < 0\fm5) variations, whereasthose of later spectral type can (but not necessarily have to) showvariations of more than 2\fm5. We explain this behaviour as being due tothe fact that stars with lower masses become optically visible, andhence recognizable as Herbig Ae stars, while still contracting towardsthe zero-age main sequence (ZAMS), whereas their more massivecounterparts only become optically visible after having reached theZAMS; (3) The Herbig stars with the smallest infrared excesses do notshow large photometric variations. This can be understood by identifyingthe stars with lower infrared excesses with the more evolved objects inour sample; (4) No correlation between the level of photometricvariability and the stellar v sin i could be found. If the largephotometric variations are due to variable amounts of extinction by dustclouds in the equatorial plane of the system, the evolutionary effectsprobably disturb the expected correlation between the two. Based on datafrom the Hipparcos astrometry satellite.
| Observational Overview of Young Intermediate-Mass Objects: Herbig Ae/Be Stars
Not Available
| Classification and Identification of IRAS Sources with Low-Resolution Spectra
IRAS low-resolution spectra were extracted for 11,224 IRAS sources.These spectra were classified into astrophysical classes, based on thepresence of emission and absorption features and on the shape of thecontinuum. Counterparts of these IRAS sources in existing optical andinfrared catalogs are identified, and their optical spectral types arelisted if they are known. The correlations between thephotospheric/optical and circumstellar/infrared classification arediscussed.
| A Renewed Search for Water Maser Emission from Mira Variables.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.1602L&db_key=AST
| The Spectrum of Wakuda's Eruptive Star near the Time of Outburst
We have made complete wavelength measurements and line identificationsfor the star discovered by Wakuda to have risen to magnitude 10.5 aboutone year before our observation on 3 April 1994. Wavelength coverage wasfrom 4900 to 8800A. The spectrum is that of a "shell" with many emissionlines of singly ionized metals. The systemic velocity is near +63.5 kms^-1, which transforms to +76 km s^-1 with respect to the local standardof rest indicating that Wakuda's star is a disk object, as are mostsymbiotic objects. If classified as a nova its distance indicates thatit belongs to the Galactic bulge population. (SECTION: Stars)
| ST Pup: a binary Type II Cepheid with a peculiar chemical composition
Analysis of recent photometric observations of the W Vir star ST Pupreveals that it has experienced one sudden period change in the last 35years. This is in sharp contrast to its erratic behaviour in the firsthalf of this century when the period changed much more frequently.Application of the surface brightness version of the Baade-Wesselinkmethod to the observations yields M_v=-3.86+/-0.2. Using spectroscopicobservations spanning almost 7yr, we have discovered that ST Pup is asingle-lined spectroscopic binary. The orbital period, 410.4+/-2.9d, isconsiderably longer than that of the other three known binary Type IICepheids, which average about 100d. It has a very low orbitaleccentricity, implying that orbital circularization and mass transferhave already taken place in this system. We estimate that[Fe/H]=-1.47+/-0.13 from a local thermodynamic equilibrium (LTE) fineanalysis of high-resolution spectra obtained near minimum light. Thevalue of C/O is 0.3, demonstrating that ST Pup is not a carbon star eventhough it displays strong CH and CN bands near minimum light. Most ofthe elements show an abundance pattern that correlates with condensationtemperature similar to that of diffuse interstellar clouds and peculiarhigh-latitude A-F supergiants, which have been interpreted as low-masspost-AGB stars that have undergone selective mass-loss via grainformation. However, the Ca/Ti abundance ratio in the atmosphere of STPup is too high to be consistent with this interpretation. The Caanomaly may have been caused by overionization of Ca^+ by Lyalphaphotons when the star was losing mass. An infrared excess is seen at theJHKL and IRAS bands, indicating the presence of dust spanning a largerange in distance from ST Pup.
| Polarisation in A-type stars with circumstellar shells.
We present the results of optical linear polarisation measurements ofabout 30 A-type stars that are known to be either Ae/A shell stars orhave shown anomalous emission in the infrared. Compared with the generalpopulation of A-type stars, stars of this group are found to havepolarisation that is also anomalous and is suggested to be circumstellarin origin.
| On the nature of 17 Leporis
We have obtained many optical spectra of 17 Lepris during its 1991-1992,1992-1993, and 1993-1994 observing seasons. We determined that thesecondary's spectral type is about M4, later than the M1 type commonlyassumed. We measured the M star secondary's radial velocity for eachobservation from lines in the far red and determined orbital elementsfrom those data. In particular, we find that the eccentricity issignificantly smaller (e = 0.024) than the previously published value (e= 0.132), on which the classical interpretation of the system has beenbased. We have measured radial velocities for the Mg II 4481 A line ofthe A star primary, and have determined the mass ratio to be 3.5 +/-0.6. Based on the small eccentricity we determined we find no evidencefor the classical model of post-periastron mass transfer, although thefour shell outbursts we observed did all occur within 0.6 orbit afterperiastron. A small upper limit on Li I 6707 A equivalent width arguesagainst the recent suggestion that 17 Lep is a pre-main-sequence binarysystem, as does its apparent HR diagram location, although otherspectroscopic considerations support its pre-main-sequence status.
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| קבוצת-כוכבים: | ארנבת |
| התרוממות ימנית: | 06h04m59.10s |
| סירוב: | -16°29'04.0" |
| גודל גלוי: | 4.93 |
| מרחק: | 327.869 פארסק |
| תנועה נכונה: | -6.3 |
| תנועה נכונה: | -3.3 |
| B-T magnitude: | 5.191 |
| V-T magnitude: | 4.988 |
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