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The Unusual Silicate Dust around HV 2310, an Evolved Star in the Large Magellanic Cloud
The spectrum of HV 2310, an evolved star in the Large Magellanic Cloud,taken with the Infrared Spectrograph (IRS) on the Spitzer SpaceTelescope, reveals the presence of an optically thin shell of silicatedust with unusual spectral structure in the 10 μm feature: anemission peak at 9.7 μm, a saddle at 10.4 μm, and an extendedshoulder to 11.2 μm. This structure is similar to spectra fromcrystalline silicate grains, and of the available optical constants,forsterite provides the best fit. The spectrum also shows structure at14 μm that may arise from an unidentified dust feature.
| Testing the companion hypothesis for the origin of the X-ray emission from intermediate-mass main-sequence stars
Context: .The X-ray emission from B-type main-sequence stars is alongstanding mystery in stellar coronal research. Since there is notheory at hand that explains intrinsic X-ray emission fromintermediate-mass main-sequence stars, the observations have often beeninterpreted in terms of (unknown) late-type magnetically activecompanion stars. Aims: .Resolving the hypothesized companionsrequires high spatial resolution observations in the infrared and inX-rays. We use Chandra imaging observations to spatially resolve asample of main-sequence B-type stars with recently discovered companionsat arcsecond separation. Methods: .Our strategy is to search forX-ray emission at the position of both the B-type primary and the faintcompanion. Results: .We find that all spatially resolvedcompanions are X-ray emitters, but seven out of eleven intermediate-massstars are also X-ray sources. If this emission is interpreted in termsof additional sub-arcsecond or spectroscopic companions, this implies ahigh multiplicity of B-type stars. Firm results on B star multiplicitypending, the alternative, that B stars produce intrinsic X-rays, cannotbe discarded. An appropriate scenario would be a magnetically confinedwind, as suggested for the X-ray emission of the magnetic Ap star IQAur. However, the only Ap star in the Chandra sample is not detected inX-rays, and therefore does not support this picture.
| Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| A study of bright southern slowly pulsating B stars. III. Mode identification for singly-periodic targets in spectroscopy
We present the results of the mode identification for a sample of 7bright southern slowly pulsating B stars showing one pulsation frequencyin the λλ 413 nm Si II profiles. We combined the resultsfrom (1) the method of photometric amplitudes; (2) the moment method;and (3) the amplitude and phase variation across the profile to searchfor the ℓ and m values of the modes best fitting the data. It is thefirst time that the applicability of these techniques is tested to asample of main-sequence g-mode pulsators. Combining the moment methodwith the amplitude and phase variations across the observed line profilegives an improvement in spectroscopic identification of low degree ℓg-mode pulsations. Using the variations of the higher order even moments< v4> and < v6> of the moment methodsolutions can also help. For HD 181558, HD 24587, HD 140873 and HD177863, the photometric and spectroscopic results are compatible andpoint towards (ℓ,m) = (1, +1) sectoral modes. For HD 215573, HD53921 and HD 92287, the results are inconclusive. Our proposedmethodology for mode identification is also applicable to γDoradus stars.Based on observations collected with the CAT Telescope of the EuropeanSouthern Observatory and with the Swiss Photometric Telescope of theGeneva Observatory, both situated at La Silla in Chile.
| Empirical Absolute Magnitudes, Luminosities and Effective Temperatures of SPB Variables and the Problem of Variability Classification of Monoperiodic Stars
We derive semi--empirical log L/Lodot for 27 stars classifiedas SPB on the basis of Hipparcos photometry and we plot these stars onthe log Teff-log L/Lodot diagram. We confirmpulsations of HIP 63210 and HIP 108348 and show that luminosities andmasses derived from photometry are of limited use for asteroseismology.For HIP 69174 and 77227, two SB2 systems with an SPB primary, we computethe age of the systems, the orbital inclination - i, the large semi-axis- a, and the masses, radii, log Teff, log g and logL/Lodot of the components.We discover five new multiperiodic stars classified in the literature asSPB, namely, HIP 5161, 20963, 26243, 26464 and 44996. One of thesestars, HIP 26243, shows periods on the time-scales of days and hours.Finally, we discuss classification of monoperiodic SPBs and show thatphotometry combined with evolutionary models can be helpful inpreselecting tentative pulsators.
| A Photometric and Spectroscopic Study of 3 Vulpeculae: An Observer's Nightmare
We describe photometry of 3 Vulpeculae obtained with the Four CollegeAutomated Photoelectric Telescope and spectroscopy obtained with the1.22 m telescope of the Dominion Astrophysical Observatory. We haveanalyzed differential uvby photometric observations obtained over 7 yr.Three main frequencies (f1=0.9719, f2=0.7923, andf3=0.8553 cycles day-1) were found, as well as asum frequency (f1+f2=1.76420 cyclesday-1). A study of the photographic region usinghigh-dispersion spectrograms obtained with a Reticon detector at thecoudé spectrograph confirms the variable nature of 3 Vul as a 53Persei star and indicates that the star's abundances are normal formain-sequence band B stars. The new spectra were combined with thosepreviously published to confirm an orbital period very close to 1 yr.Finally, comparison with models yielded both a mass (4.16Msolar) and an age (25 Myr), and a mass range for thecompanion (0.6-1.1 Msolar). With an orbital period of almost1 yr and a pulsation period of almost 1 day, this star is indeed anobserver's nightmare.
| ``Thermal'' SiO radio line emission towards M-type AGB stars: A probe of circumstellar dust formation and dynamics
An extensive radiative transfer analysis of circumstellar SiO``thermal'' radio line emission from a large sample of M-type AGB starshas been performed. The sample contains 18 irregulars of type Lb (IRV),7 and 34 semiregulars of type SRa and SRb (SRV), respectively, and 12Miras. New observational data, which contain spectra of several groundvibrational state SiO rotational lines, are presented. The detectionrate was about 60% (44% for the IRVs, and 68% for the SRVs). SiOfractional abundances have been determined through radiative transfermodelling. The abundance distribution of the IRV/SRV sample has a medianvalue of 6*E-6, and a minimum of 2*E-6 and amaximum of 5*E-5. The high mass-loss rate Miras have a muchlower median abundance, la 10-6. The derived SiO abundancesare in all cases well below the abundance expected from stellaratmosphere equilibrium chemistry, on average by a factor of ten. Inaddition, there is a trend of decreasing SiO abundance with increasingmass-loss rate. This is interpreted in terms of depletion of SiOmolecules by the formation of silicate grains in the circumstellarenvelopes, with an efficiency which is high already at low mass-lossrates and which increases with the mass-loss rate. The high mass-lossrate Miras appear to have a bimodal SiO abundance distribution, a lowabundance group (on average 4*E-7) and a high abundance group(on average 5*E-6). The estimated SiO envelope sizes agreewell with the estimated SiO photodissociation radii using an unshieldedphotodissociation rate of 2.5*E-10 s-1. The SiOand CO radio line profiles differ in shape. In general, the SiO lineprofiles are narrower than the CO line profiles, but they havelow-intensity wings which cover the full velocity range of the CO lineprofile. This is interpreted as partly an effect of selfabsorption inthe SiO lines, and partly (as has been done also by others) as due tothe influence of gas acceleration in the region which produces asignificant fraction of the SiO line emission. Finally, a number ofsources which have peculiar CO line profiles are discussed from thepoint of view of their SiO line properties.Based on observations using the SEST at La Silla, Chile, the 20 mtelescope at Onsala Space Observatory, Sweden, the JCMT on Hawaii, andthe IRAM 30 m telescope at Pico Veleta, Spain.
| Late B-type stars and their candidate companions resolved with Chandra
We present the first results from a series of Chandra observationscarried out with the aim to examine the origin of X-ray emission inmain-sequence late B-type stars. X-ray detections of late-B and earlyA-type stars have remained a mystery as none of the two major theoriesfor stellar X-ray emission applies in this spectral range: while O- andearly B-type stars drive strong winds that are subject to instabilities,late-type stars produce X-rays as a result of magnetic dynamo action.Since any dynamo works only in the presence of a convective zone,early-type stars are not magnetically active. We use high spatialresolution X-ray observations to enlighten the prevalent speculationthat previously unknown late-type or low-mass companion stars are thesites of the X-ray emission, instead of the B-type primaries. Here wepresent the results for HD 1685, HD 113703, HD 123445, HD 133880, and HD169978. Adaptive optics observations have recently revealed at least onefaint object near each of these B-type stars (at separation of1-6''). Four of the new infrared objects show infrared colorsand magnitudes typical for low-mass pre-main sequence stars, and arelikely true companions to the ~ 10-50 Myr old B-type stars. Thesemultiple systems are now resolved for the first time in X-ray light. Weuncover that four of the new companions are X-ray emitters, and thefifth one is likely to be a weak X-ray source below the detection limit.Three of the B-type primaries are X-ray dark down to the detection limitof Lx ~ 1028 erg/s. But we do detect X-rayemission from the position of HD 1685 A and HD 169978 A. The latter oneindeed is a spectroscopic binary. The characteristics of all X-raysources are compatible with those of typical young late-type stars: hardX-ray spectrum (kT > 0.5 keV) and high X-ray luminosity (logLx ~ 29...30 erg/s). Spectroscopic observations in theinfrared will solve the question whether the one remaining X-raydetected B-star in our sample, HD 1685 A, also has an even closercompanion or whether this is an intrinsic X-ray emitter.This work made use of observations obtained at the European SouthernObservatory, La Silla, Chile (ESO program No. 67.C-0261(B)).
| Infrared spectral classification of normal stars.
Moderate resolution (~400) 2.38-45.2 mu m infrared spectra of starswithout dust features were obtained with the Short WavelengthSpectrometer (SWS) on board the Infrared Space Observatory (ISO). Theobservations are part of a larger program with the objective to extendand refine the current infrared classification schemes. In particular,our data provide the basis for a more detailed classification of the1.N-1.NO sources (ordinary and oxygen rich naked stars) as defined byKraemer et al. (\cite{kraemer}) in a comprehensive classification of theISO-SWS spectra. For our analysis, the continuum was determined byfitting Engelke's function (Engelke \cite{engelke}) to the SWS data. Thestellar angular diameters derived from these estimates of the continuumare in good agreement with values obtained by other methods. Analysis ofthe equivalent widths of the CO fundamental and first overtone molecularbands, the SiO fundamental and first overtone, as well as theH2O bending mode band as a function of MK class, reveals thatthere is sufficient information in the SWS spectra to distinguishbetween hot (B, A, F) and cool stars. Furthermore, it is possible todetermine the spectral type for the G, K and M giants, and subtyperanges in a sequence of K and M giants. The equivalent widths of the COand SiO bands are found to be well correlated in K and M stars, suchthat the equivalent widths of the CO fundamental, the SiO first overtoneand the SiO fundamental can be reasonably well extrapolated from thedepth of the CO first overtone. We have identified two stars,HR 365 and V Nor, whosemid-infrared spectrum does not correspond to their respective opticalclassification. HR 365 may have a late M companion,which dominates the observed infrared spectrum while VNor is a late type giant that was included because itsspectrum was classified as featureless under the IRAS LRS scheme.According to Kraemer et al. (\cite{kraemer}), V Norhas a thin dust shell, which distorts the analysis of its mid-infraredabsorption bands. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, The Netherlands and the UK) and with the participationof ISAS and NASA.
| A study of bright southern slowly pulsating B stars. II. The intrinsic frequencies
We present the results of detailed frequency analyses of a sample ofthirteen confirmed slowly pulsating B stars. Our analysis is based on acombination of elaborate photometric and spectroscopic data-sets. Theoriginal sample consists of a mixture of five confirmed slowly pulsatingB stars and twelve candidate slowly pulsating B stars discovered thanksto the photometric measurements of the HIPPARCOS satellite. HD 55522 andHD 131120 turn out to be chemically peculiar stars. HD 169978 and HD69144 are two ellipsoidal variables for which no intrinsic variabilityis found. At least nine of the thirteen studied slowly pulsating B starsare multi-periodic. For HD 74195, HD 85953, HD 123515 and HD 215573, theobserved frequency spacings suggest that we are dealing with frequencymultiplets. For the apparent mono-periodic binary HD 24587, it is notclear if the observed variations are induced by stellar pulsation and/orby rotation modulation. We highlight the statistical character of theobserved pulsational properties of our sample. Based on observationscollected with the CAT Telescope of the European Southern Observatoryand with the Swiss Photometric Telescope of the Geneva Observatory, bothsituated at La Silla in Chile Full Tables 2-4, 6-15 are only availablein electronic form at the CDS via anounymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/965
| Search for low-mass PMS companions around X-ray selected late B stars
We have observed 49 X-ray-detected bright late B-type dwarfs to searchfor close low-mass pre-main sequence (PMS) companions using the EuropeanSouthern Observatory's ADONIS (Adaptive Optics Near Infrared System)instrument. We announce the discovery of 21 new companions in 9binaries, 5 triple, 4 quadruple system and 1 system consisting of fivestars. The detected new companions have K magnitudes between 6.5m and17.3m and angular separations ranging from 0.12 arcsec to 14.1 arcsec(18-2358 AU). Based on observations obtained at the European SouthernObservatory, La Silla, Chile (ESO programme No.~62.I-0477, and Swiss70~cm photometric telescope).
| 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
| A study of bright southern slowly pulsating B stars. I. Determination of the orbital parameters and of the main frequency of the spectroscopic binaries
In 1996, we started a long-term spectroscopic and photometric study of17 southern Slowly Pulsating B-stars. In this paper, we report ourfinding that at least 8 of them turn out to be spectroscopic binaries.We present the results of the determination of the orbits from thespectroscopic data. There is a great variety in the derived orbits.HD123515 and HD140873 were known as single-lined spectroscopic binaries,but both turn out to be double-lined. All the others binaries aresingle-lined. For HD140873 and HD177863, we find orbits with a largeeccentricity of respectively e=0.731 +/- 0.006 and e=0.603 +/- 0.007.HD69144, HD92287 and HD169978 are three circular binaries with a veryshort orbital period (a few days). Since their photometric measurementsare dominated by a (close to) sinusoidal variation with twice theorbital frequency, these stars are ellipsoidal variables. Their orbitalperiods are of the same order of magnitude as the periods of pulsation.After removing the orbit, we find the same first frequency in theresidual radial velocities as in the gathered photometric measurementsfor 6 stars. For HD69144 and HD169978 we did not yet succeed in derivingan intrinsic period, although HD69144 has prominent line profilevariations. HD169978 was misclassified as an SPB. Based on observationscollected with the CAT Telescope of the European Southern Observatoryand with the Swiss Photometric Telescope of the Geneva Observatory, bothsituated at La Silla in Chile
| The 74th Special Name-list of Variable Stars
We present the Name-list introducing GCVS names for 3153 variable starsdiscovered by the Hipparcos mission.
| Selection of a sample of bright southern Slowly Pulsating B Stars for long-term photometric and spectroscopic monitoring
The photometric experiment on Hipparcos has led to the discovery of,among other types of variables, a large amount of new Slowly Pulsating BStars. We have selected twelve bright southern stars of this sample,together with five previously known Slowly Pulsating B Stars, forspectroscopic and photometric monitoring. These seventeen stars havespectral types ranging from B 2 up to B 9 and thus fully cover theinstability strip. We here present the results of a preliminary analysisof our data and show that our sample is an extremely important one toperform seismology of intermediate-massive stars. In particular, we findthat all but one of the selected stars exhibit clear line-profilevariability. The broader-lined Slowly Pulsating B Stars tend to havemore complex line-profile variations. One of the previously known SlowlyPulsating B stars was known to be a binary. Besides this star, anothersix of the selected Slowly Pulsating B stars turn out to be multiplesystems. Five of these seven binaries have large rotational velocitiesand complicated line-profile variations with moving subfeatures. It isnot yet clear whether or not the binarity results in a particularspectrum of excited modes. Based on observations collected with the CATTelescope of the European Southern Observatory and with the SwissPhotometric Telescope of the Geneva Observatory, both situated at LaSilla in Chile
| Study of an unbiased sample of B stars observed with Hipparcos: the discovery of a large amount of new slowly pulsating B stars
We present a classification of 267 new variable B-type stars discoveredby Hipparcos. We have used two different classification schemes and theyboth result in only a few new beta Cephei stars, a huge number of newslowly pulsating B stars, quite some supergiants with alpha Cyg-typevariations and variable CP stars, and further some new periodic Be starsand eclipsing binaries. Our results clearly point out the biased naturetowards short-period variables of earlier, ground-based surveys ofvariable stars. The position of the new beta Cephei stars and slowlypulsating B stars in the HR diagram is determined by means of Genevaphotometry and is confronted with the most recent calculations of theinstability strips for both groups of variables. We find that the newbeta Cephei stars are situated in the blue part of the instability stripand that the new slowly pulsating B stars almost fully cover thetheoretical instability domain determined for such stars. Thesupergiants with alpha Cyg-type variations are situated between theinstability strips of the beta Cephei and the slowly pulsating B starson the one hand and previously known supergiants that exhibitmicrovariations on the other hand. This suggests some connection betweenthe variability caused by the kappa mechanism acting in a zone ofpartially ionised metals and the unknown cause of the variations insupergiants.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| Semiregular variables of types SRa and SRb. Circumstellar CO emission of an oxygen-rich sample.
O-rich Semiregular Variables (SRVs) of types SRa and SRb have beenobserved in the ^12^CO(J=1-0) and (J=2-1) lines using the SEST, LaSilla, Chile, and the 20-m telescope at Onsala, Sweden. In total 22detections (13 are new ones) and 1 tentative detection can be reportedamong the 48 stars observed. In 7 cases detections are precluded becauseof strong interference from interstellar CO emission. The majority ofthe detected objects, covering both small and longer periods, are weakin CO, i.e. they are low mass-loss rate objects(<=10^-7^Msun_/yr), and have, with only a few exceptions,envelopes with small expansion velocities (the mean value is =~8km/s).However, in this respect their properties are very similar to those ofbright O-rich Mira variables, whose pulsational periods are on theaverage 2-3 times higher. A comparison between stellar and circumstellarproperties shows that the gas expansion velocity does not depend on thestellar effective temperature, nor on the period. Likewise, we find nocorrelation between mass-loss rate and period, but there might be a weakdependence of the former on the stellar effective temperature.
| A catalog of far-ultraviolet point sources detected with the fast FAUST Telescope on ATLAS-1
We list the photometric measurements of point sources made by the FarUltraviolet Space Telescope (FAUST) when it flew on the ATLAS-1 spaceshuttle mission. The list contains 4698 Galactic and extragalacticobjects detected in 22 wide-field images of the sky. At the locationssurveyed, this catalog reaches a limiting magnitude approximately afactor of 10 fainter than the previous UV all-sky survey, TDl. Thecatalog limit is approximately 1 x 10-14 ergs A sq cm/s,although it is not complete to this level. We list for each object theposition, FUV flux, the error in flux, and where possible anidentification from catalogs of nearby stars and galaxies. Thesecatalogs include the Michigan HD (MHD) and HD, SAO, the HIPPARCOS InputCatalog, the Position and Proper Motion Catalog, the TD1 Catalog, theMcCook and Sion Catalog of white dwarfs, and the RC3 Catalog ofGalaxies. We identify 2239 FAUST sources with objects in the stellarcatalogs and 172 with galaxies in the RC3 catalog. We estimate thenumber of sources with incorrect identifications to be less than 2%.
| Silicate Emission at 10 Microns in Variables on the Asymptotic Giant Branch
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...451..758S&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 local distribution of NA I interstellar gas
We present high-resolution absorption measurements (lambda/Delta lambdaapproximately 75,000) of the interstellar Na I D lines at 5890 A toward80 southern hemisphere early-type stars located in the localinterstellar medium (LISM). Combining these results with other sodiummeasurements taken from the literature, we produce galactic maps of thedistribution of neutral sodium column density for a total of 293 starsgenerally lying within approximately 250 pc of the Sun. These mapsreveal the approximate shape of the mid-plane contours of the rarefiedregion of interstellar space termed the Local Bubble. Its shape is seenas highly asymmetric, with a radius ranging from 30 to 300 pc, and withan average radius of 60 pc. Similar plots of the Galactic mid-planedistribution of sources emitting extreme ultraviolet radiation show thatthey also trace out similar contours of the Local Bubble derived from NaI absorption measurements. We conclude that the Local Bubble absorptioninterface can be represented by a hydrogen column density,NuETA = 2 x 1019 cm-2, which explainsboth the local distribution of Na I absorption and the observed galacticdistribution of extreme ultraviolet sources. The derived mid-planecontours of the Bubble generally reproduce the large-scale featurescarved out in the interstellar medium by several nearby galactic shellstructures.
| B stars - A new dimension
JHKL photometry is reported for three normal B stars and three Be starsin the direction of the south galactic cap with FIR excesses evidentfrom their IRAS fluxes. For the Be stars this excess is alreadyunderstood as originating from plasma emission in their extendedatmospheres. The FIR emission from the other three objects originates invery extended (2-6 arcmin) dust shells surrounding otherwise normal Bstars. These shells are larger and more luminous than the well knownBeta Pic-type shells found around A stars. Their temperatures are of theorder of 60 K, diameters about 50,000 AU and luminosities in the rangeof 0.05-1 solar luminosity.
| The Wolf 630 moving group of stars
An analysis is made of the probability of collective membership of thestars assigned by Eggen to the Wolf 630 moving group. This probabilityis estimated from the scatter of points in the color-absolute magnitudediagram when compared to the intrinsic scatter observed for M67.Particular attention is paid to the random errors for all the observedand deduced stellar parameters. Results show that either theobservational errors must be about 2.4 times larger than given in theproper motion and radial velocity source catalogues, or the intrinsicscatter in the color-magnitude diagram for the Wolf 630 group must bemuch larger than for M67, or many of the stars considered cannot bemembers.
| Standard Stars for Hα Photometry
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981A&AS...44..337S&db_key=AST
| Infrared photometry of southern early-type stars
The paper presents infrared photometry tied to the JHKL (1.2-3.5microns) broadband photometric system for 229 southern early-type stars.To determine data for stars of low reddening intrinsic visual-IR colorindices were used; the E(V-K)/E(B-V) diagram was applied to evaluate theratio of total selective extinction. A mean value of R = 3.12 plus orminus 0.05 was found for stars close to the galactic plane, but a highervalue of R (about 4.0) applies to the Orion and Sco-Oph regions.Infrared two-color diagrams were used to investigate the occurrence ofinfrared excess emission in different classes of shell star; no excesseswere found for supergiants or Of stars. It is concluded that theanomalous position HD 164740 in the two-color diagrams is produced bystrong infrared excess and not by a peculiar extinction law.
| Prediction of spectral classification from photometric observations - Application of the UVBY beta photometry and the MK spectra classification. II - General case
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85...93M&db_key=AST
| Prediction of spectral classification from photometric observations-application to the UVBY beta photometry and the MK spectral classification. I - Prediction assuming a luminosity class
An algorithm based on multiple stepwise and isotonic regressions isdeveloped for the prediction of spectral classification from photometricdata. The prediction assumes a luminosity class with reference touvbybeta photometry and the MK spectral classification. The precisionattained is about 90 percent and 80 percent probability of being withinone spectral subtype respectively for luminosity groups I and V and forluminosity groups III and IV. A list of stars for which discrepanciesappear between photometry and spectral classification is given.
| Spectral classification from the ultraviolet line features of S2/68 spectra. II - Late B-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...30...71C&db_key=AST
| Structure and age of the local association /Pleiades group/
Intermediate-band indices are used to derive luminosities for some 500early-type stars with well-determined proper motions and radialvelocities. Space motion vectors and galactic coordinates are computedfor the stars considered. It is found that the local association membersare mainly concentrated in the Sco-Cen region in the Southern Hemisphereand the Cas-Tau region in the north.
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הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | טווס |
| התרוממות ימנית: | 18h31m22.40s |
| סירוב: | -62°16'42.0" |
| גודל גלוי: | 4.64 |
| מרחק: | 146.843 פארסק |
| תנועה נכונה: | -0.8 |
| תנועה נכונה: | -47.2 |
| B-T magnitude: | 4.478 |
| V-T magnitude: | 4.593 |
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