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NaI and CaII absorption components observed towards the Orion-Eridanus Superbubble
We present medium-resolution spectra (R ~ 7.5 km s-1) of theinterstellar NaI and CaII interstellar absorption lines observed towards16 early-type stars with distances of 160-1 kpc in the line-of-sighttowards the Orion-Eridanus Superbubble (OE-S). These data have beensupplemented with measurements of NaI absorption towards a further 13stars with similar sight-lines taken from the literature. We detect twomajor absorption components with velocities of Vlsr ~ +7.0and -8.0 km s-1. The former component, seen in 70% of thesight-lines is associated with the boundary to the Local Bubble cavitylocated at a distance of 140-150 pc. The other absorption component isonly detected towards a limited region of the sky bounded by (190°< l < 215°) and (-50° < b < -30°). If gas withthis velocity is associated with an outer expansion shell of the OE-S,then we can place its distance at 163-180 pc in agreement with theestimate by Guo et al. (1995, ApJ, 453, 256). Several other negativevelocity components at Vlsr ~ -20.4, -28.5 and -33.5 kms-1 have also been detected for sight-line distances > 220pc within an area coincident with that of the 0.75 keV X-ray enhancementof the OE-S. Column density ratios, N(NaI)/N(CaII), for the mostnegative velocity components have values < 1.0, suggesting that thisgas has been disrupted by a possible shock event. Our data do notsupport a simple model for the OE-S that involves a single stellarbubble cavity that stretches from the Orion Nebula to high galacticlatitudes. Instead, our detection of multiple positive and negativevelocity components suggests the presence of several gas shells producedby supernovae and/or stellar wind-driven shocks. We also confirm thatthe prominent "hook-like" feature of H-α emission thatcharacterizes the OE-S, in in fact composed of two physically separateemission arcs, with the brighter Arc A being at a distance > 500 pc.Finally, we place a similar distance limit for any coherently structuredrear shell of neutral gas associated with expansion of the OE-S towardsthe galactic halo.
| The 2MASS Wide-Field T Dwarf Search. II. Discovery of Three T Dwarfs in the Southern Hemisphere
We present the discovery of three new southern hemisphere T dwarfsidentified in the Two Micron All Sky Survey. These objects, 2MASS0348-6022, 2MASS 0516-0445, and 2MASS 2228-4310, have classificationsT7, T5.5, and T6.5, respectively. Using linear absolutemagnitude/spectral type relations derived from T dwarfs with measuredparallaxes, we estimate spectrophotometric distances for thesediscoveries; the closest, 2MASS 0348-6022, is likely within 10 pc of theSun. Proper motions and estimated tangential velocities are consistentwith membership in the Galactic disk population. We also list southernhemisphere T dwarf candidates that were either not found in subsequentnear-infrared imaging observations and are most likely uncataloged minorplanets, or have near-infrared spectra consistent with background stars.
| 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
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| 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).
| 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
| The distance to the nearest star-forming clouds: MBM12 and MBM20
We present high-resolution spectra (R ~ 49,000) of stars that haveparallax measurements from the Hipparcos satellite and are projectedalong the line of sight to the two nearest known star forming clouds tothe Sun: MBM12 and MBM20. The spectra were obtained with the FOCESEchelle Spectrograph at the 2.2 meter telescope in Calar Alto, Spain andthe wavelength range was chosen to include the interstellar Na I D linesat lambda 5889.950 Ä and lambda 5895.924 Ä. Since the starsare at a range of distances, we use their spectra along with theirparallaxes from Hipparcos to determine the distance to the moleculargas. The stars in front of the cloud do not show interstellar Na I Dabsorption features while the stars behind the cloud do showinterstellar absorption features. We find that both clouds are somewhatmore distant than previously estimated. The revised distance to MBM12 is58+/-5 pc < d < 90+/-12 pc and the distance to MBM20 is 112+/-15pc < d < 161+/-21 pc.
| 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
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Dust Extinction in Starburst Galaxies - NGC1614 and NGC7714
We present high signal-to-noise ratio observations of the near- infraredhydrogen recombination fines Paβ, Brβ and Brα in thegalaxies NGC 1614 and 7714. The data are used in conjunction withexisting optical line fluxes to examine the dust extinction towards thestar-forming nuclei of these galaxies. In the case of NGC 1614, atleast, the conventional model of a foreground absorbing screen is foundto be incorrect, resulting in an underestimate of the true extinction.
| Photometric and spectroscopic analysis of high galactic latitude molecular clouds. II - High-resolution spectroscopic observations of NA I, CA II, CA I, CH, and CH(+1)
High-resolution spectroscopic observations in the wavelengths of thespecies Na I, Ca II, and Ca I and the molecular species CH and CH(+)have been performed toward stars behind a variety of high galacticlatitude molecular clouds (HLCs). Seventeen new detections of molecularabsorption are reported. The sizes, densities, and molecular contentfound for the HLCs are consistent with an interpretation of HLCmolecular cores as extremely compact structures of enhanced molecularcontent which may have evolved from larger H I shells.
| Ca II H and K filter photometry on the UVBY system. I - The standard system
A fifth filter (fwhm = 90 A) centered on Ca II H and K has beendeveloped for use with the standard uvby system. The filter, called Ca,is designed primarily for applications to metal-poor dwarfs and redgiants, regions where the uvby metallicity index, m(l), loses somesensitivity. An index, hk, is defined by replacing v in m(l) by Ca. Theeffects of interstellar extinction on the index are modeled anddemonstrated to be modest and relatively insensitive to spectral type.Observations of V, (b-y), and hk for 163 primary standards are detailedand transformed to the standard V and (b-y) system. A qualitativeanalysis using only the primary standards indicates that hk is moresensitive than m(l) over the regions of interest by about a factor of 3.
| Stromgren and H-beta photometry of stars earlier than G0 in 5 areas containing high latitude molecular clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1989A&AS...80..127F&db_key=AST
| Visual multiples. VIII - 1000 MK types
A total of 1000 new classifications are given for stars brighter than B= 8.0 mag in the Aitken double star catalog. The classificationssupplement 865 classifications obtained in 1981 and 1984. Among thenewly discovered stars are 12 new Ap stars, eight Lambda Bootis stars,one Ba II star, and 60 Am stars. A detailed list of the newclassifications is given.
| A sample of solar-type stars of known age
A sample of field F and G dwarfs of known ages is presented. All thedwarfs are secondaries of visual binaries in which the temperature andgravity of the hotter primary has been estimated from Stromgrenphotometry, and its age derived from reference to isochrones. This ageis taken to apply to the secondary. Even in the case of F-typesecondaries, which themselves have measured Stromgren indices, it ismuch better to estimate ages from the primaries as it is demonstratedthat use of isochrones to determine age of stars not far evolved fromthe main sequence can lead to significant systematic overestimates ofages when the photometric measurements have typical random errors. Anumber of systems in which photometry is available for both componentshave primaries which appear much younger than the secondaries,suggesting a need for further investigation.
| Ages and uvbybeta photometry of wide visual binaries. II
Visual magnitudes and color indices b-y, m1, c1 and beta have beenobtained for the members of 39 double or multiple systems containingstars with magnitudes greater than 4m. Relationships between stellarages, spectral types and photometric indices are given from a sample ofabout 3,500 stars. Data is presented with regard to MK spectral types,the separation, and absolute magnitudes; also tabulated are the meanvalues of photometric unreddened indices with their standard deviationfor intervals of 0.2 in log age. From calculations for each binary ofthe relative difference in the ages of the components and the differencein the effective temperatures, an increase in the relative differencesin ages with the differences in temperatures is noted.
| About the Consistency of Absolute Luminosity Calibrations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....82..370H&db_key=AST
| UVBY photometry of wide visual double stars with B, A and F spectral type- I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..453O&db_key=AST
| The proper motions of Struve double stars
The proper motions of the components of 103 Struve double stars fromMuller's list of neglected stars and of 15 other systems were measuredrelative to sets of reference stars, for the primary purpose ofdistinguishing physical from optical pairs. A by-product of thisinvestigation is a list of measured position angles and distances ofthese objects, at two epochs each.
| Infrared radiation of planetary nebulae. II. New and revised observations at 1.0-2.5 μ
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