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3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| 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
| Dusty Circumstellar Disks
Dusty circumstellar disks in orbit around main-sequence stars werediscovered in 1983 by the infrared astronomical satellite. It was thefirst time material that was not another star had been seen in orbitaround a main-sequence star other than our Sun. Since that time,analyses of data from the infrared astronomical satellite, the infraredspace observatory, and ground-based telescopes have enabled astronomersto paint a picture of dusty disks around numerous main-sequence andpost-main-sequence stars. This review describes, primarily in anevolutionary framework, the properties of some dusty disks orbiting,first, pre-main-sequence stars, then main-sequence andpost-main-sequence stars, and ending with white dwarfs.
| A spectroscopic survey for lambda Bootis stars. II. The observational data
lambda Bootis stars comprise only a small number of all A-type stars andare characterized as nonmagnetic, Population i, late B to early F-typedwarfs which show significant underabundances of metals whereas thelight elements (C, N, O and S) are almost normal abundant compared tothe Sun. In the second paper on a spectroscopic survey for lambda Bootisstars, we present the spectral classifications of all program starsobserved. These stars were selected on the basis of their Strömgrenuvbybeta colors as lambda Bootis candidates. In total, 708 objects insix open clusters, the Orion OB1 association and the Galactic field wereclassified. In addition, 9 serendipity non-candidates in the vicinity ofour program stars as well as 15 Guide Star Catalogue stars were observedresulting in a total of 732 classified stars. The 15 objects from theGuide Star Catalogue are part of a program for the classification ofapparent variable stars from the Fine Guidance Sensors of the HubbleSpace Telescope. A grid of 105 MK standard as well as ``pathological''stars guarantees a precise classification. A comparison of our spectralclassification with the extensive work of Abt & Morrell(\cite{Abt95}) shows no significant differences. The derived types are0.23 +/- 0.09 (rms error per measurement) subclasses later and 0.30 +/-0.08 luminosity classes more luminous than those of Abt & Morrell(\cite{Abt95}) based on a sample of 160 objects in common. The estimatederrors of the means are +/- 0.1 subclasses. The characteristics of oursample are discussed in respect to the distribution on the sky, apparentvisual magnitudes and Strömgren uvbybeta colors. Based onobservations from the Observatoire de Haute-Provence, OsservatorioAstronomico di Padova-Asiago, Observatório do Pico dosDias-LNA/CNPq/MCT, Chews Ridge Observatory (MIRA) and University ofToronto Southern Observatory (Las Campanas).
| 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.
| Beta Pic-like circumstellar disk gas surrounding HR 10 and HD 85905
We present high spectral resolution observations of the absorption linesof Ca II and Na I associated with the circumstellar gas disk surroundingthe two A-type shell stars HR 10 and HD85905. Data taken over two four-night periods in January andNovember 1997 reveal substantial changes in the circumstellar absorptionline profiles between successive observations of both stars. Suchvariable features have both blue and red-shifted velocities up to 50 kms(-1) away from the central absorbing component, and are similar tothose routinely observed in the beta Pictoris system. The sporadicpresence of the circumstellar absorption components observed towardsboth HR 10 and HD 85905 may be explained by the infalling evaporatingcomet model developed for the beta Pictoris system by Beust {et al./}(\cite{beust90}). We note that variable circumstellar absorptionfeatures have also been detected in rapidly rotating A-type stars, suchthat they may be suffering irregular mass-loss that could give rise tosimilar circumstellar disks and shells.
| 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.
| The Gronbech-Olsen photometry: Transformations to a Hyades-Coma system
In this paper, we consider the zero points of six sets of Stromgren-betaphotometry. The color-index system to which our results are referred isa 'Hyades-Coma' system composed of photometry by Crawford and Perry(1966) and Crawford and Barnes (1969). For V magnitudes, we usemeasurements by Taylor and Joner (1992). Our results are as follows. (1)The zero points of photometry by Gronbech and Olsen (1976, 1977) areoffset from those of the Hyades-Coma system. The offsets can amount toseveral mmag; they appear for V and all color indices except beta, anddepend on right ascension and (usually) declination. (2) These offsetscan be applied to photometry by Stetson (1991), who reduced his resultsto the Gronbech-Olsen system. After correction, Stetson's results for aset of 'transfer stars' differ from comparable data published byCrawford and Barnes (1970). (3) A direct comparison of the transferstars to the Hyades yields consistency between the Hyades-Coma andCrawford-Barnes zero points (for the transfer stars specifically). Thisresult supports a conclusion drawn by Taylor and Joner, and suggeststhat here is some problem with the zero points of Stetson'stransfer-star data. (4) From Stetson's corrected data, one finds thatthe Crawford-Perry zero points for the Hyades are consistent with theCrawford-Barnes zero points for Coma. This result agrees with aconclusion drawn by Taylor and Joner from their own data, and suggeststhat the problem postulated for Stetson's transfer-star data does notextend to his results for the Hyades and Coma.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Early type high-velocity stars in the solar neighborhood. IV - Four-color and H-beta photometry
Results are presented from photometric obaservations in the Stromgrenuvby four-color and H-beta systems of early-type high-velocity stars inthe solar neighborhood. Several types of photometrically peculiar starsare selected on the basis of their Stromgren indices and areprovisionally identified as peculiar A stars, field horizontal-branchstars, metal-poor stars near the Population II and old-disk turnoffs,metal-poor blue stragglers, or metallic-line A stars. Numerousphotometrically normal stars were also found.
| Anomalous infrared emitters among A-type stars
Spectroscopic observations of a sample of 26 stars have been analyzed inthe blue and near-IR to find out if anomalous IR emitters (AIEs) have aspectral signature. It is found that many, but not all, such starsexhibit shell characteristics. Analysis of available IRAS photometricobservations of A-type stars shows that the detection of circumstellarfeatures depends strongly on the number of IR bands at which the objectwas observed. Out of the 707 stars observed by IRAS, 41 AIEs, or 5.7percent, are found. Among nonsupergiant AIEs, 23 percent show shellfeatures. The true percentage of AIEs among A-type stars is estimated tobe 1.5 percent in a volume-corrected sample. A list of 24 stars whichwere apparently not previously detected as AIEs is given.
| Search for Beta Pictoris-like star
The results are reported of a systematic search for Beta Pic-like stars,undertaken at ESO, CFHT and OHP. The candidate stars, either IRAS excessstars or shell stars, are investigated by means of high resolutionspectroscopy in the Ca II and Na I lines, which in the case of Beta Pic,are very peculiar. The observations are presented and it is shown thatamong the selected stars, few do show spectral similarities with BetaPic. Some interesting cases, HR10, HR2174, HR9043 and HR6519 arediscussed.
| The H-alpha line in AE and A shell stars
The H-alpha profiles of a sample of 20 Ae and A shell stars areanalyzed. In the earlier types, emission features are present; in themiddle A-types only absorption cores are seen; and in the late A-typesthe H-alpha profiles are normal both in the profiles and the equivalentwidths. In this latter group the shell features visible in the360-480-nm region are unrelated to H-alpha. Because of the short timeinterval covered, some few cases of variability are found.
| Bright southern stars of astrophysical interest
The paper lists a number of bright peculiar stars in the SouthernHemisphere discovered on 20-A/mm spectrograms. Recent information isalso given for a few known peculiar objects. The lists include: oneLambda Boo star, 4 Hg and other Bp stars, 7 Am stars, 17 shell oremission-line stars, and 37 double-lined spectroscopic binaries, amongwhich are two triple-lined, four composite, eight variable or eclipsing,and three peculiar shell and/or emission-line systems.
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| Takýmyýldýz: | Su Yilani |
| Sað Açýklýk: | 09h54m31.70s |
| Yükselim: | -22°29'18.0" |
| Görünürdeki Parlaklýk: | 6.24 |
| Uzaklýk: | 140.252 parsek |
| özdevim Sað Açýklýk: | -24.9 |
| özdevim Yükselim: | -0.8 |
| B-T magnitude: | 6.291 |
| V-T magnitude: | 6.221 |
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