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Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful 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).
| A study of the behaviour of the NaI/KI column density ratio in the interstellar medium using the Na ultraviolet doublet
Here we make a new study of the behaviour of the NaI/KI column densityratio in the interstellar medium, using a sample of new observations of28 stars obtained at the Nordic Optical Telescope (NOT) in 1996 and1997, and previously published observations (obtained by some of theauthors) of 21 stars. The sightlines cover a range of distances anddirections, including into the Galactic halo. We make use of newobservations of the NaI ultraviolet (UV) doublet for some 18 stars. Thisdoublet is much weaker than the NaI D doublet and so is less susceptibleto saturation effects, and it is well known that it can be used toobtain more accurate NaI column densities with a smaller error range. Wefind an average N(NaI)/N(KI) ratio from the NaI UV data of about 90,which is rather higher than that found previously by Hobbs and Lequeux.The Na UV-KI ratio shows a small increase in value with increasingcolumn density, while we also find a sample of low N(NaI)/N(KI) ratioclouds generally seen towards distant objects on high-latitudesightlines that reach into the halo, so that the ratio decreases moresharply at lower column densities. As the values of the ratio for thesehalo clouds (10-20) bracket the cosmic Na/K abundance ratio, we suggestthat these ratios result from a harder radiation field in the lowerhalo, such that the ionized fractions of NaI and KI become similar.Clearly caution needs to be applied in using any kind of `standardvalue' for the NaI/KI column density ratio.
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| CO 1st overtone spectra of cool evolved stars: Diagnostics for hydrodynamic atmosphere models
We present spectra covering the wavelength range 2.28 to 2.36 mu m at aresolution of Delta lambda = 0.0007 mu m (or R = 3500) for a sample of24 cool evolved stars. The sample comprises 8 M supergiants, 5 M giants,3 S stars, 6 carbon stars, and 2 RV Tauri variables. The wavelengthscovered include the main parts of the 12C16O v =2-0 and 3-1 overtone bands, as well as the v = 4-2 and 13CO v= 2-0 bandhead regions. CO lines dominate the spectrum for all the starsobserved, and at this resolution most of the observed features can beidentified with individual CO R- or P-branch lines or blends. Theobserved transitions arise from a wide range of energy levels extendingfrom the ground state to E/k > 20 000 K. We looked for correlationsbetween the intensities of various CO absorption line features and otherstellar properties, including IR colors and mass loss rates. Two usefulCO line features are the v = 2-0 R14 line, and the CO v = 2-0 bandhead.The intensity of the 2-0 bandhead shows a trend with K-[12] color suchthat the reddest stars (K-[12] > 3 mag) exhibit a wide range in 2-0bandhead depth, while the least reddened have the deepest 2-0 bandheads,with a small range of variation from star to star. Gas mass loss ratesfor both the AGB stars and the red supergiants in our sample correlatewith the K-[12] color, consistent with other studies. The data implythat stars with dot M_gas < 5x 10-7 Msuny-1 exhibit a much narrower range in the relative strengthsof CO 2-0 band features than stars with higher mass loss rates. Therange in observed spectral properties implies that there are significantdifferences in atmospheric structure among the stars in this sample.Figures 4-9, 11-14, 16, 17, 19-21, 23, 24 are only avalaible inelectronic form at http://www.edpsciences.org
| A Search for High-Velocity Be Stars
We present an analysis of the kinematics of Be stars based uponHipparcos proper motions and published radial velocities. We findapproximately 23 of the 344 stars in our sample have peculiar spacemotions greater than 40 km s-1 and up to 102 kms-1. We argue that these high-velocity stars are the resultof either a supernova that disrupted a binary or ejection by closeencounters of binaries in young clusters. Be stars spun up by binarymass transfer will appear as high-velocity objects if there wassignificant mass loss during the supernova explosion of the initiallymore massive star, but the generally moderate peculiar velocities of BeX-ray binaries indicate that the progenitors lose most of their massprior to the supernova (in accordance with model predictions). Binaryformation models for Be stars predict that most systems bypass thesupernova stage (and do not receive runaway velocities) to createultimately Be+white dwarf binaries. The fraction of Be stars spun up bybinary mass transfer remains unknown, since the post-mass transfercompanions are difficult to detect.
| High and intermediate-resolution spectroscopy of Be stars 4481 lines
We present an atlas of Hγ , He i lambda 4471 and Mg ii lambda 4481line profiles obtained in a 10 year observation period of 116 Be stars,which enabled many of them to be observed at quite different emissionepochs. From the best fit of the observed He i lambda 4471 line profileswith non-LTE, uniform (Teff,log g) and full limb-darkenedmodel line profiles, we determined the V sin i of the program stars. Toaccount, to some degree, for the line formation peculiarities related tothe rapid rotation-induced non-uniform distributions of temperature andgravity on the stellar surface, the fit was achieved by considering(Teff,log g) as free parameters. This method produced V sin iestimations that correlate with the rotational velocities determined bySlettebak (1982) within a dispersion sigma <= 30 km s-1and without any systematic deviation. They can be considered as given inthe new Slettebak's et al. (1975) system. Only 13 program stars havediscrepant V sin i values. In some objects, this discrepancy could beattributed to binary effects. Using the newly determined V sin iparameters, we found that the ratio of true rotational velocitiesV/Vc of the program Be stars has a very low dispersion aroundthe mean value. Assuming then that all the stars are rigid rotators withthe same ratio V(/lineω)/Vc, we looked for the value of/line ω that better represents the distribution of V sini/Vc for randomly oriented rotational axes. We obtained/lineω = 0.795. This value enabled us to determine the probableinclination angle of the stellar rotation axis of the program stars. Inthe observed line profiles of Hγ , He i lambda 4471, Mg ii lambda4481 and Fe ii lambda 4351 we measured several parameters related to theabsorption and/or emission components, such as: equivalent width,residual emission and/or absorption intensity, FWHM, emission peakseparations, etc. The parameters related to the Hγ line emissionprofiles were used to investigate the structure of the nearbyenvironment of the central star. From the characteristics of thecorrelations between these quantities and the inferred inclinationangle, we concluded that in most of cases the Hγ line emissionforming regions may not be strongly flattened. Using a simplerepresentation of the radiation flux emitted by the star+envelopesystem, we derived first order estimates of physical parameterscharacterizing the Hγ line emission formation region. Thus, weobtained that the total extent of the Hγ region is Rf=~ 2.5 +/- 1.0 R* and that the density distribution in theselayers can be mimicked with a power law rho ~ R-alpha , wherealpha =2.5+2.2-0.6. The same approach enabled usto estimate the optical depth of the Hγ line emission formationregion. From its dependence with the aspect angle, we concluded thatthese regions are caracterized by a modest flattening and that the rho(equator)/rho (pole) density contrast of the circumstellar envelope nearthe star should be two orders of magnitude lower than predicted bymodels based on a priori disc-shaped circumstellar envelopes. We foundthat the separation between the emission peaks, Deltap, andthe full width at half maximum, Delta 1/2, of the Hγline emission are not only sensitive to kinematic effects, but to lineoptical depth as well. This finding agrees with previous theoreticalpredictions and confirms that Huang's (1972) relation overestimates theextent of the Hγ line emission formation region. Data obtained atCASLEO operated under agreement between the CONICET and the NationalUniversities of La Plata, Córdoba and San Juan, Argentina, at ESOLa Silla, Chile and at OHP, France.}\fnmsep\thanks{Tables 2 to 7 andFigs. 1 and 2 are only available in full in electronic form at 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/378/861}} \subtitle{Anatlas of Hγ , He {\fontsize {10pt}{12pt}\selectfont I} 4471 and Mg{\fontsize {10pt}{12pt}\selectfont II
| A representative sample of Be stars III: H band spectroscopy
We present H band (1.53 mu m-1.69 mu m) spectra of 57 isolated Be starsof spectral types O9-B9 and luminosity classes III, IV & V. The H iBrackett (n-4) series is seen in emission from Br-11-18, and Fe iiemission is also apparent for a subset of those stars with H i emission.No emission from species with a higher excitation temperature, such asHe ii or C iii is seen, and no forbidden line emission is present. Asubset of 12 stars show no evidence for emission from any species; thesestars appear indistinguishable from normal B stars of a comparablespectral type. In general the line ratios constructed from thetransitions in the range Br-11-18 do not fit case B recombination theoryparticularly well. Strong correlations between the line ratios withBr-gamma and spectral type are found. These results most likelyrepresent systematic variations in the temperature and ionization of thecircumstellar disc with spectral type. Weak correlations between theline widths and projected rotational velocity of the stars are observed;however no systematic trend for increasing line width through theBrackett series is observed.
| A representative sample of Be stars. IV. Infrared photometry and the continuum excess
We present infra-red (JHK) photometry of 52 isolated Be\ stars ofspectral types O9-B9 and luminosity classes III-V. We describe a newmethod of reduction, enabling separation of interstellar reddening andcircumstellar excess. Using this technique we find that the discemission makes a maximum contribution to the optical (B-V) colour of afew tenths of a magnitude. We find strong correlations between a rangeof emission lines (Hα , Brgamma , Br11, and Br18) from the Bestars' discs, and the circumstellar continuum excesses. We also findthat stellar rotation and disc excess are correlated.
| Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars
We present the results of statistical analyses of a sample of 627 Bestars. The parameters of intrinsic polarization (p*),projected rotational velocity (v sin i), and near IR excesses have beeninvestigated. The values of p* have been estimated for a muchlarger and more representative sample of Be stars (~490 objects) thanpreviously. We have confirmed that most Be stars of early spectral typehave statistically larger values of polarization and IR excesses incomparison with the late spectral type stars. It is found that thedistributions of p* diverge considerably for the differentspectral subgroups. In contrast to late spectral types (B5-B9.5), thedistribution of p* for B0-B2 stars does not peak at the valuep*=0%. Statistically significant differences in the meanprojected rotational velocities (/line{vsin i}) are found for differentspectral subgroups of Be stars in the sense that late spectral typestars (V luminosity class) generally rotate faster than early types, inagreement with previously published results. This behaviour is, however,not obvious for the III-IV luminosity class stars. Nevertheless, thecalculated values of the ratio vt/vc of the truerotational velocity, vt, to the critical velocity forbreak-up, vc, is larger for late spectral type stars of allluminosity classes. Thus, late spectral type stars appear to rotatecloser to their break-up rotational velocity. The distribution of nearIR excesses for early spectral subgroups is bi-modal, the position ofthe second peak displaying a maximum value E(V-L)~ 1 . m 3for O-B1.5 stars, decreasing to E(V-L)~0. m8 for intermediatespectral types (B3-B5). It is shown that bi-modality disappears for latespectral types (B6-B9.5). No correlations were found betweenp* and near IR excesses and between E(V-L) and vsin i for thedifferent subgroups of Be stars. In contrast to near IR excesses, arelation between p* and far IR excesses at 12 mu m is clearlyseen. A clear relation between p* and vsin i (as well asbetween p* and /line{vsin i}/vc) is found by thefact that plots of these parameters are bounded by a ``triangular"distribution of p*: vsin i, with a decrease of p*towards very small and very large vsin i (and /line{vsini}/vc) values. The latter behaviour can be understood in thecontext of a larger oblateness of circumstellar disks for the stars witha rapid rotation. From the analysis of correlations between differentobservational parameters we conclude that circumstellar envelopes forthe majority of Be stars are optically thin disks with the range of thehalf-opening angle of 10degr
| 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 representative sample of Be stars. II. K band spectroscopy
We present K band (2.05 mu m - 2.22 mu m) spectra of 66 isolated Bestars of spectral types O9-B9 and luminosity classes III, IV & V. Wefind that objects with He i features either in emission or absorptionare B3 or earlier. Objects with Mg ii emission but no He i are B2 to B4,while objects with Brgamma emission but no evidence of He i or Mg ii areB5 or later. Na i emission in the spectra of 4 objects appears toindicate that regions of the circumstellar envelopes of these stars mustbe shielded from direct stellar radiation. Systematic trends in the linestrength and profile of Brgamma are seen from early to late spectraltypes which can be understood in terms of differences in the disctemperature and density. 30 percent of the stars do not currently showevidence for line emission. Compared to the emission line stars theseobjects have a significantly lower mean rotational velocity and adistribution of spectral types that is significantly earlier. This canbe explained either as the original misidentification of these objectsas Be stars (i.e. they never had line emission), or as evidence thatstars with lower rotational velocities may be more prone to changesbetween the Be and B phases.
| A representative sample of Be stars . I. Sample selection, spectral classification and rotational velocities
We present a sample of 58 Be stars containing objects of spectral typesO9 to B8.5 and luminosity classes III to V. We have obtained 3670 - 5070Angstroms spectra of the sample which are used to derive spectral typesand rotational velocities. We discuss the distribution of spectral typesand rotational velocities obtained and conclude that there are nosignificant selection effects in our sample.
| Catalogue of H-alpha emission stars in the Northern Milky Way
The ``Catalogue of Stars in the Northern Milky Way Having H-alpha inEmission" appears in Abhandlungen aus der Hamburger Sternwarte, Band XIin the year 1997. It contains 4174 stars, range {32degr <= l() II< 214degr , -10degr < b() II < +10degr } having the Hαline in emission. HBH stars and stars of further 99 lists taken from theliterature till the end of 1994 were included in the catalogue. We givethe cross-identification of stars from all lists used. The catalogue isalso available in the Centre de Données, Strasbourg ftp130.79.128.5 or http://cdsweb.u-strasbg.fr and at the HamburgObservatory via internet.
| Catalogue of stars in the northern Milky Way having H-alpha in emission
Not Available
| UBV photometry of Be stars at Hvar: 1972--1990
A summary of results of the systematic UBV photoelectric monitoring ofbright northern Be stars carried out at the Hvar Observatory between1972 and 1990 is presented. Altogether, 76 Be stars of all luminosityclasses were observed and 13,848 UBV measurements secured.Simultaneously, 9,648 UBV measurements of 48 check stars (most of themof early spectral types) were obtained. A careful transformation of allobservations into the standard Johnson system allowed detection andmonitoring of even very mild long-term light and colour variations ofthese objects. Almost all early-type Be stars in the sample turned outto be variable. For several stars phase-locked light variations relatedto their binary nature were established. Sudden brightenings, on a timescale of a few days, were detected for o Cas and QR Vul. Tables 2 and 3are only available in electronic form at CDS via ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Molecular Cloudlets Embedded in a Diffuse H i Cloud within 120 Parsecs of the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...457..731T&db_key=AST
| 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.
| On the structure of Be star disks.
We investigate the geometrical structure of the emitting part ofcircumstellar envelopes around Be stars from an empirical point of view.We use new high-resolution, high-S/N spectroscopic data of the FeIIλ5317 and some other faint FeII emission lines in 27 Be starsshowing symmetrical emission lines (class 1). We find a clearcorrelation between its total width (measuring the maximum velocities ofcircumstellar matter) and the stellar rotational velocity. Thiscorrelation means that a typical Be envelope (or, more precisely, thatpart of it which is visible in optical emission lines) is anaxisymmetric, rotationally supported disk. For empirical investigationof the vertical structure, we use the occurrence of shell lines. Wedefine, as shell criterion based on FeII lines, a Be shell star as onewith FeII central intensity F_cd_/F_*_(FeII)<1. Using this forcalibrating an appropriate parameter for the much more frequentlyobserved Hα line, we find that shell stars are those withF_p_/F_cd_(Hα)>=1.5 where F_p_ is the mean peak intensity atHα. In a sample of 114 programme stars, we find a shell starfraction of 22.8%. This number is readily transformed into a halfopening angle of Be star disks, φ=13deg. We furthermore show thatBe disks must be thin at the inner edge, and may become fairly thick atthe outer rim. This, together with the small value of φ, isevidence for a conical or concave shape, the latter typical of ahydrostatically balanced disk. Finally we provide evidence that thefamous "shell-Be" phase transitions can naturally occur in such disks asa geometrical effect if they are seen under inclination i=~70deg and iftheir outer radius is variable with time.
| A cold massive interstellar cloud within 120 parsecs of the Sun: K I optical and H I radio observations
We first discovered the presence of a particularly massive cloud in theneighborhood of the Sun, close to the Galactic plane in the direction ofPerseus, toward l = 150 deg, b = -10 deg, using interstellar absorptionby the 7699 A resonance line of K I (Trapero et al. 1992). In thepresent investigation we show the results of mapping the cloud in the 21cm line of H I, supplemented by further K I observations. Thiscombination is particularly effective, since the K I observations giveus distances, within close limits, and accurate velocities of the singlestrong interstellar component detected along each line of sight, whichenables us to identify the cloud as seen in absorption in the H Ispectra, from among many emission components due to more distant cloudsin the plane. The absorption spectra in H I at 21 cm can then be used tofind temperatures and to carry out more comprehensive mapping than usingK I. We find that the cloud has kinetic temperatures going down to 30 K,densitites in the range up to 70/cu cm, a diameter of approximately 15pc, and a mass of some 1300 solar mass. The cloud is a good candidate tocontain a molecular core.
| 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.
| Chemical transitions for interstellar C2 and CN in cloud envelopes
Observations were made of absorption from CH, C2, and CN towardmoderately reddened stars in Sco, OB2, Ceo OB3, and Taurus/Auriga. Forthese directions, most of the reddening is associated with a singlecloud complex, for example, the rho Ophiuchus molecular cloud, and as aresult, the observations probe moderately dense material. When combinedwith avaliable data for nearby directions, the survey provides the basisfor a comprehensive analysis of the chemistry for these species. Thechemical transitions affecting C2 and CN in cloud envelopes wereanalyzed. The depth into a cloud at which a transition takes place wascharacterized by tauuv, the grain optical depth at 1000 A.One transition at tauuv approx. = 2, which arises from, theconversion of C(+) into CO, affects the chemistries for both moleculesbecause of the key role this ion plays. A second one involvingproduction terms in the CN chemistry occurs at tauuv ofapprox. = 3; neutral reactions which C2 and CH is more important atlarger values for tauuv. The transition fromphotodissociation to chemical destruction takes place attauuv approx. = 4.5 for C2 and CN. The observational data forstars in Sco OB2, Cep OB3, and Taurus/Auriga were studied with chemicalrate equations containing the most important production and destructionmechanisms. Because the sample of stars in Sco OB2 includes sight lineswith Av ranging from 1-4 mag, sight lines dominated byphotochemistry could be analyzed separately from those controlled bygas-phase destruction. The analysis yielded values for two poorly knownrate constants for reactions involved in the production of CN; thereactions are C2 + N yields CN + C and C(+) + NH yields all products.The other directions were analyzed with the inferred values. Thepredicted column densities for C2 and CN agree with the observed valuesto better than 50%, and in most instances 20%. When combining theestimates for density and temperature derived from chemical modeling andmolecular excitation for a specific cloud, such as the rho Ophiuchusmolecular cloud, the portion of the cloud envelope probed by C2 and CNabsorption was found to be in pressure equilibrium.
| A catalogue of radii of Be star line emitting regions
A bibliographic catalog of the radii of the line-emitting regions aroundBe stars is presented. The table also provides the separation of theemission peaks, the wavelength of the line used, observing date, and theV sin i value given by the author.
| The behavior of the O I line 7772 in Be and related stars
We describe the spectra of more than sixty stars in the 7570-7980region. We find that O I 7772 is always in emission in Be stars: in theearliest types it is seen in clear emission whereas in the later typesit fills in the observed absorption line. We find a good correlation ofthe line intensity of O I 8446 with O I 7772, the former being aboutfour times stronger than the latter. We confirm the correlation with FeII 7712. We also derive the outer radii of the line emission formingregions and find that O I 7772 is formed very close to the starssurface, whereas Fe II is formed farther away. We also provide criteriato distinguish, at this wavelength range, the classical Be, Herbig Ae-Beand B(e) stars.
| Observation of fine structure in the cold phase of the local interstellar medium using K I absorption
The K I 7699-A resonance absorption line was used to observe a group of18 early-type stars within a 200-pc radius of the sun with asignal-to-noise ratio of 50-250. The interstellar absorptions provide away to 'tag' a cloud via its radial velocity to within +/-1.5 km/s.Based on the hypothesis of pressure confinement, the temperatures of theclouds are estimated at 100 K or less. The mass fraction of the localinterstellar medium (LISM) is found to be high in these clouds, at least80 percent of the total, whereas the filling factor is low, well below10 percent of the total LISM volume. One cloud with high densities andlower temperatures was detected which is thought to be on the edge ofatomic-molecular equilibrium.
| Near-IR observations of 101 Be stars
Observations of 101 Be stars taken over a two year period in the near-IRbetween 1 and 5 microns are presented and discussed. The near-IR colorexcess of all program stars is derived, and found to increase withwavelength for all these stars. The fraction of stars with color excessdoubles between 1.25 and 3.6 microns. There appears to be an upper limitto the magnitude of the color excess as a function of stellar type, withearly-type stars having a higher upper limit than later spectral types.No correlation of the presence or magnitude of color excess withprojected rotational velocity is evident. The spectral index of theexcess emission spectra is calculated for stars having color excess. Onaverage, the spectral index through the near-IR and far-IR IRASwavelength regimes is constant. There is evidence that some stars haveexcess emission with spectral index values outside the range expectedfor free-free and bound-free emission. This is attributed to either dustemission or the effect of absorption of photospheric emission by coolcircumstellar material along the line of sight to the star.
| The Paschen P7 line in Be, AE and shell type stars
Observations of 36 Be, Ae, and shell stars in the region 984-1020 nm arepresented. P7 is seen in emission until AO and not afterwards. Fe II999.7 nm is seen in emission in about the same types; both emissionshave similar structures, and a good correlation exists between theequivalent widths of both lines. Also detected in nine Be stars is1.0173-micron emission and in four stars 995.6-nm emission. Both linesbelong to Fe II and appear when 999.7 nm is strong in emission.
| IRAS observations of Be stars. I - Statistical study of the IR excess of 101 Be stars
IRAS observations at 12, 25, and 60 microns are reported for 101 Bestars from the Bright Star Catalog of Hoffleit (1982). The data arepresented in extensive tables and graphs and analyzed. Normal-starcolor-color relations are used to derive the IR excesses, and theposition of the Be stars on the (12-60) versus (12-25) diagram is shownto correspond to free-free emission from a star surrounded by ionizedgas with density inversely proportional to r exp 2.5-3. An apparentupper limit on the degree of optical polarization and a link betweenlarge polarization and large IR excess are found.
| The NASA infrared telescope facility Comet Halley monitoring program. I - Preperihelion results
The 1-20 microns IR monitoring program for Comet Halley whose resultsare presented covered January 1985 to January 1986, using a 7-arcsecaperture. It is noted that the comet's dust production was about 6million g/s at a heliocentric distance of 1 AU; the albedo of the dustin the coma was 3-4 percent. These results are compared with those forpreviously observed comets.
| Rotational velocity of Be stars correlated with emission characteristics
A sample of shell and nonshell B0e-B5e stars with weak and strongemission, and shell and nonshell B6e-B9e stars with weak emission, arestudied to seek a correlation between the rotational velocity of Bestars and the emissive strength. These results and the distributions ofV sin i indicate that the hottest Be stars, B0e-B5e, with rotationalvelocities of about 345 km/s can develop the characteristics of strongemission. For stars which are slightly less hot, or stars with slightlysmaller rotational velocities, only characteristics of weak emission canbe developed, and the shell characteristics only develop when the staris viewed at a greater-than-33-deg inclination to the pole. It is alsonoted that stars with large rotational velocities, the strong-emissionB0e-B5e and weak-emission B6e-B9e stars, can show metallic shellcharacteristics when seen near the equatorial plane.
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Osservazione e dati astrometrici
| Costellazione: | Perseo |
| Ascensione retta: | 03h48m18.30s |
| Declinazione: | +50°44'12.0" |
| Magnitudine apparente: | 6.14 |
| Distanza: | 182.149 parsec |
| Moto proprio RA: | -7.3 |
| Moto proprio Dec: | -3.9 |
| B-T magnitude: | 6.224 |
| V-T magnitude: | 6.191 |
Cataloghi e designazioni:
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INHABITED SKY
