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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
| Towards understanding rapid line-profile and light variations of early-type stars. 3. Some thoughts and reflections
The current situation in the research of rapid line-profile and lightvariations of early-type stars is critically reviewed. It is suggestedthat the ultimate understanding of the physical processes causing thesevariations can only come from an open-minded and complex approach to theproblem and from systematic observational effort. It is argued that theresults of the search for periodicities in the complicated variations ofthese objects depend critically on whether the method used isappropriate to the real physical situation. The danger of detection of afalse multiperiodicity is pointed out for two particular situations: (i)a single-periodic signal which undergoes slow periodic change, e.g., dueto the light time effect in a binary system, and (ii) a single-periodicsignal with a complicated phase curve (a model of not exactlyequidistant corotating spokes). It is argued that the observed rapidvariations need not be due to classical non-radial pulsations but mayarise from more complicated velocity fields in the stellar atmospheresand/or mantles. Two early-type stars, ěp and zeta Oph, arediscussed in detail. It is argued that both may be the cases where thevariations are caused by corotating structures slightly above thestellar photosphere. For ěn, the pattern of the variations canalso be affected by the motion of the star in a binary orbit. For zetaOph, a double-wave light curve with the corotation period of 0. (v {r) md}64 (suggested by the author earlier for the line-profile variations)was found from Hipparcos V photometry and its presence can also besuspected in other existing photometric data and in the recurrence timesof the narrow features seen in the UV spectra.
| On the HIPPARCOS photometry of chemically peculiar B, A, and F stars
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Multiperiodicity of zeta Ophiuchi from Multisite Observations
We present results from simultaneous multisite high-resolutionspectroscopic and photometric observations of zeta Oph (HD 149757) takenin 1993 May. Our spectroscopic data include about 100 hr of continuousmonitoring of the star. The line-profile variations of He I lambda 6678,which are characterized by features traveling from blue to red, are wellreproduced by two large-amplitude sinusoids and other sinusoids withsmaller amplitudes. The period of the sinusoid with the largestamplitude is 2.018 hr (f1), which differs from the 2.43 hr of previouspublications, although it is possible that 2.43 hr is an alias of 2.018hr. The period of the second largest amplitude is, in agreement withprevious studies, 3.337 hr (f2). Periods of smaller amplitude sinusoidsare 2.432 hr (f3), 1.257 hr (f1 + f2), 1.008 hr (2f1), 2.107 hr (f4),1.293 hr (f2 + f4), and 1.668 hr (2f2), all of which have some relationto the two main periods. The two principal periods have closesuperperiods of about 10.05 hr. We discuss the commensurability andother features of the periodicity. Our photometric observations,although limited, confirm again the very small amplitude of the lightvariations that are close to their detection limit. No counterpart ofthe 2.018 hr and 3.337 hr periods can be detected.
| 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
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&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.
| Radial velocities in selected B-G stars
Spectroscopic observations of a sample of nearby B-G stars are reported.The observations were obtained at resolution 19 km/s in the spectralregion near the 448.1228-nm line of Mg II using a CCD-detectorspectrograph on the coude-feed telescope at KPNO on April 16-20, 1986.The data are presented in extensive tables and briefly characterized.
| ICCD speckle observations of binary stars. I - A survey for duplicity among the bright stars
A survey of a sample of 672 stars from the Yale Bright Star Catalog(Hoffleit, 1982) has been carried out using speckle interferometry onthe 3.6-cm Canada-France-Hawaii Telescope in order to establish thebinary star frequency within the sample. This effort was motivated bythe need for a more observationally determined basis for predicting thefrequency of failure of the Hubble Space Telescope (HST) fine-guidancesensors to achieve guide-star lock due to duplicity. This survey of 426dwarfs and 246 evolved stars yielded measurements of 52 newly discoveredbinaries and 60 previously known binary systems. It is shown that thefrequency of close visual binaries in the separation range 0.04-0.25arcsec is 11 percent, or nearly 3.5 times that previously known.
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| קבוצת-כוכבים: | נושא הנחש |
| התרוממות ימנית: | 16h54m40.30s |
| סירוב: | -11°47'33.0" |
| גודל גלוי: | 6.57 |
| מרחק: | 90.662 פארסק |
| תנועה נכונה: | 16.3 |
| תנועה נכונה: | -12.5 |
| B-T magnitude: | 6.762 |
| V-T magnitude: | 6.585 |
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