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The Distribution of Thermal Pressures in the Diffuse, Cold Neutral Medium of Our Galaxy. II. An Expanded Survey of Interstellar C I Fine-structure Excitations
We analyzed absorption features arising from interstellar neutral carbonthat appeared in the UV spectra of 89 stars recorded in the highestresolution echelle modes of the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope so that we could determine the relativepopulations of collisionally excited fine-structure levels in the atom'selectronic ground state. From this information, in combination withmolecular hydrogen rotation temperatures, we derive the distribution ofthermal pressures in the diffuse, cold neutral medium (CNM). We find alognormal pressure distribution (weighted by mass) with a mean in log(p/k) equal to 3.58 and an rms dispersion of at least 0.175 dex thatplausibly arises from turbulence with a characteristic Mach number inthe range 1 < M < 4. The extreme tails in the distribution are,however, above the lognormal function. Overall, pressures are wellcorrelated with local starlight intensities and extreme kinematics, andthey show some anticorrelation with kinetic temperatures. A subsamplerestricted to low ambient UV intensities reveals a mode in thedistribution of log (p/k) that is nearly the same as the completesample, but with a strong negative skewness created by a near absence ofa tail at high pressures. Approximately 23% of this gas is at a pressurethat is below that which is allowed for a static CNM. Accompanyingnearly all of the gas is a small fraction (~0.05%) that has anextraordinarily large pressure, log (p/k) > 5.5, and this conditionis more prevalent at high velocities or for regions with enhancedstarlight densities. This survey suggests that the dispersion of thermalpressures in the CNM is predominantly governed by microscopic turbulencedriven by star-forming regions, with some additional effects frommacroscopic events (e.g., supernova explosions), and these measurementsprovide constraints for future studies of the broader impact ofturbulence on the ISM and star formation.
| StarCAT: A Catalog of Space Telescope Imaging Spectrograph Ultraviolet Echelle Spectra of Stars
StarCAT is a catalog of high resolution ultraviolet spectra of objectsclassified as "stars," recorded by Space Telescope Imaging Spectrograph(STIS) during its initial seven years of operations (1997-2004). StarCATis based on 3184 echelle observations of 545 distinct targets, with atotal exposure duration of 5.2 Ms. For many of the objects, broadultraviolet coverage has been achieved by splicing echellegrams taken intwo or more FUV (1150-1700 Å) and/or NUV (1600-3100 Å)settings. In cases of multiple pointings on conspicuously variablesources, spectra were separated into independent epochs. Otherwise,different epochs were combined to enhance the signal-to-noise ratio(S/N). A post-facto correction to the {\sf calstis} pipeline data setscompensated for subtle wavelength distortions identified in a previousstudy of the STIS calibration lamps. An internal "fluxing" procedureyielded coherent spectral energy distributions (SEDs) for objects withbroadly overlapping wavelength coverage. The best StarCAT materialachieves 300 m s-1 internal velocity precision;absolute accuracy at the 1 km s-1 level; photometricaccuracy of order 4%; and relative flux precision several times better(limited mainly by knowledge of SEDs of UV standard stars). WhileStarCAT represents a milestone in the large-scale post-processing ofSTIS echellegrams, a number of potential improvements in the underlying"final" pipeline are identified.
| Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data
Context: .This paper is the last in a series devoted to the analysis ofthe binary content of the Hipparcos Catalogue. Aims: .Thecomparison of the proper motions constructed from positions spanning ashort (Hipparcos) or long time (Tycho-2) makes it possible to uncoverbinaries with periods of the order of or somewhat larger than the shorttime span (in this case, the 3 yr duration of the Hipparcos mission),since the unrecognised orbital motion will then add to the propermotion. Methods: .A list of candidate proper motion binaries isconstructed from a carefully designed χ2 test evaluatingthe statistical significance of the difference between the Tycho-2 andHipparcos proper motions for 103 134 stars in common between the twocatalogues (excluding components of visual systems). Since similar listsof proper-motion binaries have already been constructed, the presentpaper focuses on the evaluation of the detection efficiency ofproper-motion binaries, using different kinds of control data (mostlyradial velocities). The detection rate for entries from the NinthCatalogue of Spectroscopic Binary Orbits (S_B^9) is evaluated, as wellas for stars like barium stars, which are known to be all binaries, andfinally for spectroscopic binaries identified from radial velocity datain the Geneva-Copenhagen survey of F and G dwarfs in the solarneighbourhood. Results: .Proper motion binaries are efficientlydetected for systems with parallaxes in excess of ~20 mas, and periodsin the range 1000-30 000 d. The shortest periods in this range(1000-2000 d, i.e., once to twice the duration of the Hipparcos mission)may appear only as DMSA/G binaries (accelerated proper motion in theHipparcos Double and Multiple System Annex). Proper motion binariesdetected among S_B9 systems having periods shorter than about400 d hint at triple systems, the proper-motion binary involving acomponent with a longer orbital period. A list of 19 candidate triplesystems is provided. Binaries suspected of having low-mass(brown-dwarf-like) companions are listed as well. Among the 37 bariumstars with parallaxes larger than 5 mas, only 7 exhibit no evidence forduplicity whatsoever (be it spectroscopic or astrometric). Finally, thefraction of proper-motion binaries shows no significant variation amongthe various (regular) spectral classes, when due account is taken forthe detection biases.Full Table [see full textsee full text] is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/464/377
| The Subdwarf Database: Released
The work on the Subdwarf Database, presented at the previous meeting,has been completed, and the tool is now publicly available. The firstrelease contains data from close to 240 different literature sources,but more still awaits entry. The database interface includes advancedsearch capabilities in coordinate, magnitude and color space. Outputtables can be generated in HTML with hyperlinks to automaticallygenerated finding charts, the Aladin viewer and a detailed data sheetthat displays all registered data for each target, including physicaldata such as temperature, gravity and helium abundance, together with afinding chart. Search results can be visualized automatically asinteractive position, magnitude or color diagrams.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| 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).
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Spectrophotometry: Revised Standards and Techniques
The telluric features redward of 6700 Å have been removed from theaccurate spectrophotometric standards of Hamuy et al. to permit morereliable relative and absolute spectrophotometry to be obtained from CCDspectra. Smooth fluxes from 3300 to 10500 Å are best determined bydividing the raw spectra of all objects taken in a night by the rawspectrum of a ``smooth'' spectrum star before deriving the instrumentalresponse function using the revised standard star fluxes. In this waythe telluric features and any large instrumental variation withwavelength are removed from the raw data, leaving smooth spectra thatneed only small corrections to place them on an absolute flux scale.These small corrections with wavelength are well described by alow-order polynomial and result in very smooth flux-calibrated spectra.
| A study of optically featureless objects from the EC Survey: searching for new southern BL Lac objects
In an attempt to discover new southern BL Lac objects, 14 opticallyfeatureless objects from the Edinburgh-Cape Survey were selected.Optical polarimetry and spectroscopy, radio and IR observations werecarried out in order to improve their classifications. The 14 objectswere examined according to special criteria that are described. TheirUBV and JHK colour-colour distributions, spectrograms, radioobservations and visible-region polarimetry were utilized to concludethat the selected objects are not BL Lacs. Most of them are apparentlynot extragalactic objects. It is suggested that four of the 14candidates are DC white dwarfs, one is a QSO, three are DA white dwarfsor sdB subdwarfs, one is a cataclysmic variable, one is a DAO/sdO andanother is possibly a DA+dM binary (composite system with a `primary'hot white dwarf and a `secondary' M-type main-sequence dwarf) or acataclysmic variable. One object is likely to be a subdwarf, while tworemain unclassifiable.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Infrared flux excesses from hot subdwarfs.
Observations of 27 hot subdwarf stars and white dwarfs have beenperformed with an IR photometer in a search for excess fluxes in the JHKbands. 22 of the objects are observed for the first time in theinfrared. In 11 of the stars a significant excess flux was found, 2 ofwhich are new discoveries: GD 274 and GD 299. We confirm the suspicionof Moehler et al. (1990) that PG0232+095 is a composite system, and wereinforce the suggestion of Thejll et al. (1991, 1994a) that Feige 34 isa composite system. The excesses are most likely due to companion stars,mainly of spectral types A - K. We estimate the subdwarf gravities,assuming zero-age main sequence companions, and thus find upper limitson log(g). For the hot sdO Feige 34 we estimate from the publishedtrigonometric parallaxes an absolute magnitude M_v_^F34^=5.6^+0.9^_-1.6_and surface gravity log(gpi_)=6.8^+0.3^_-0.7_.
| Search for EUV emission from hot subdwarfs in the ROSAT wide-field camera survey
A search for positional coincidences of catalogued hot subdwarfs withsources detected in the ROSAT wide-field camera (WFC) EUV survey isconducted. Six such coincidences are found. Optical follow-upobservations reveal four of these stars to be hot DA white dwarfs (plusone other, less certain DA), previously misclassified as subdwarfs.These five are all within the 90 percent confidence levels of the WFCsource positions, and are therefore reliable identifications with aclass of sources known to be detectable EUV emitters. The remaining staris confirmed to be a hot, helium-rich subdwarf. This star lies justoutside the 90 percent confidence level of the weak WFC source position.The possibility that this could be the first detection of EUV emissionfrom a hot subdwarf is discussed. Upper limits are derived for severalwell-known, brighter hot subdwarfs which were not detected in the WFCsurvey.
| Broad-band photometry of selected southern ultraviolet-bright stars.
Not Available
| A catalogue of spectroscopically identified hot subdwarf stars.
Not Available
| NLTE Analysis and Chemical Composition of Hot Low-Mass Stars
Spectroscopic analyses of hot pre-white dwarfs, i.e. subluminous O and Bstars, are presented. In the B-type stars, the resulting abundancepatterns are indicative of atmospheric diffusion. Amongst the O-typesubdwarfs, a new group of comparatively luminous stars is identified.Their position in the HR-diagram suggests that, unlike the "classical"sdOs, they are in a post-AGB stage of evolution. Spectroscopic evidenceis presented showing that the born-again post-AGB star scenario of Ibenet al. (1983) can explain their origin.
| Photometry of faint blue stars. VII - More southern stars
Photoelectric uvby photometry is presented for 103 southern stars,mostly from the LB and PB catalogs. Using photometric criteria, thestars appear to be a mixture of hot subdwarfs, horizontal-branch andpopulation II objects. Four high-latitude hot stars which are too redfor their c1 indices are suggested to be possible binary systems.Observations of metal-weak secondary standards indicate that the uvbyphotometry of the population II stars is close to the standard system.
| UBV photoelectric catalogue (1986). II - Analysis
The UBV photoelectric data of the stars presenting several entries inthe 1986 edition of the UBV catalog have been systematicallyintercompared, and this paper presents a discussion of the stars forwhich discrepancies larger than 0.2 mag were found. Thirty-six probablyvariable stars have been detected, among which 18 are Be stars. Sixtyfurther stars present differences in the V magnitude larger than 0.2mag. Sixteen stars already appear in the NSV catalog. Although manyproblems are probably due to poor observations, new (eclipsing) variablestars may be found in this sample. Complete disagreement is foundbetween the values published from two independent sources in 34 cases. Afirst analysis of the quality of the UBV data shows that 65 percent ofthe differences in the V magnitude and in U-B color, for respectively11,500 and 7200 stars with two sources of data, are smaller than 0.04.The scatter on the B-V index appears to be smaller, since the samepercentage reaches 79 percent.
| CASPEC observations of sdO stars - Are some sdOs lazy remnants from the AGB?
Eight newly discovered subdwarf O stars which were observed in the bluespectral range (3900-4800 A) are analyzed. Strong lines of ionizedhelium are present in all eight stars whereas He I is very weak or evenabsent. This indicates very high effective temperatures (greater than55,000 K). The NLTE analyses revealed the existence of a new group ofsdO stars that were once CSPNs but were born again just before theyreached the hot end of the cooling sequence of white stars; a lastthermal pulse brought them back to life as a post-AGB star.
| Non-thermal phenomena in the atmosphere of hot subdwarfs X-ray upper limit for BD-3deg2179
The investigation of the nonthermal phenomena in the atmosphere of hotsublimunous stars (sdO) provides information for the study of thesubatmospheric structure in evolved stars. It is noted that large massoutflows have been measured from extensive ultraviolet (IUE)observations in a number of sdO stars, which also seem to exhibit alarge microturbulent activity. An upper limit of about 10 to the 31sterg/sec is found for the X-ray luminosity of the mass losing sdO starBD3deg2179 observed with the Einstein satellite. These results arecompared with the X-ray fluxes of early type stars and of othersubluminous stars. It is determined that the observed upper limit forthe X-ray luminosity of this star is in agreement with the f(x)/f(bol)flux ratio of the O stars.
| A survey of ultraviolet objects
An all-sky survey of ultraviolet objects is presented together with astatistical analysis that leads to the conclusion that there is asignificantly higher population of hot subdwarfs lying below themain-sequence than hitherto thought. The distribution of all ultravioletobjects, main sequence ultraviolet objects, and MK unclassifiedultraviolet objects are shown in galactic coordinates, and the absolutemagnitudes and color-color diagrams for these groups are presented.Scale heights are derived, giving values similar to planetary nebulaefor the hottest groups.
| Spectroscopy of four subdwarf O stars
Four stars which, from their photometry, would appear to be O subdwarfsare discussed. These stars (II + 18009, II + 22021, IV + 10009, and VI -03019), having colors much bluer than other OB+ stars brighter thanphotographic magnitude 12, lie at the very tip of the locus forunreddened main sequence stars in the U-B, B-V diagram. The four starshave visual magnitudes between 10 and 13 and, since any main sequence ormore luminous stars as faint as that would be noticeably reddened, theyare expected to be O subdwarfs. Two of the stars, 18009, and 22021, liein the galactic plane where distance can be estimated with reasonableaccuracy from interstellar dust absorption.
| A sample of new hot subluminous stars taken from the list of ultraviolet objects detected by the S2/68 Sky Survey Experiment
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....85..367B&db_key=AST
| Photometry of faint blue stars. V - A third list of southern stars
Stromgren photometry is presented for 37 faint blue stars, six of whichhave been identified by ultraviolet observations made with the ESRO TD-1satellite. The stars are classified using their observed photometricindices.
| Galactic structure in monoceros : a photometric study of luminous stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&A....53....9V&db_key=AST
| UBV photometry of OB+ stars north of 1950.0 declinaison -15.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..128D&db_key=AST
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