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β Cephei stars in the ASAS-3 data. II. 103 new β Cephei stars and a discussion of low-frequency modes
Context: The β Cephei stars have been studied for over a hundredyears. Despite this, many interesting problems related to this class ofvariable stars remain unsolved. Fortunately, these stars seem to bewell-suited to asteroseismology. Hence, the results of seismic analysisof β Cephei stars should help us to better understand pulsationsand the main sequence evolution of massive stars, particularly theeffect of rotation on mode excitation and internal structure. It istherefore extremely important to increase the sample of known βCephei stars and select targets that are useful for asteroseismology. Aims: We analysed ASAS-3 photometry of bright early-type stars with thegoal of finding new β Cephei stars. We were particularly interestedin β Cephei stars that would be good for seismic analysis, i.e.,stars that (i) have a large number of excited modes; (ii) showrotationally split modes; (iii) are components of eclipsing binarysystems; (iv) have low-frequency modes, that is, are hybrid βCephei/SPB stars. Methods: Our study was made with a homogeneous sampleof over 4100 stars having MK spectral type B5 or earlier. For thesestars, the ASAS-3 photometry was analysed by means of a Fourierperiodogram. Results: We have discovered 103 β Cephei stars,nearly doubling the number of previously known stars of this type. Amongthese stars, four are components of eclipsing binaries, seven have modesequidistant or nearly equidistant in frequency. In addition, we foundfive β Cephei stars that show low-frequency periodic variations,very likely due to pulsations. We therefore regard them as candidatehybrid β Cephei/SPB pulsators. All these stars are potentially veryuseful for seismic modeling. Moreover, we found β Cephei-typepulsations in three late O-type stars and fast period changes in one, HD168050.Table 2 and Figs. 2-14 are only available in electronic form athttp://www.aanda.org The V photometry for all 103 stars is available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/477/917
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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.
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| High-Velocity Clouds
High-velocity clouds (HVCs) consist of neutral hydrogen (\HI) atvelocities incompatible with a simple model of differential galacticrotation; in practice one uses {the absolue value of} VLSR {greater orequal to} 90 km/s to define HVCs. This review describes the mainfeatures of the sky and velocity distributions, as well as the availableinformation on cloud properties, small-scale structure, velocitystructure, and observations other than in 21-cm emission. We show thatHVCs contain heavy elements and that the more prominent ones are morethan 2 kpc from the Galactic plane. We evaluate the hypotheses proposedfor their origin and reject those that account for only one or a fewHVCs. At least three different hypotheses are needed: one for theMagellanic Stream and possibly related clouds, one for the Outer ArmExtension, and one (or more) for the other HVCs. We discuss the evidencefor the accretion and the fountain model but cannot rule out either one.
| Dust emission as a quantitative probe of star-forming regions.
This article discusses thermal emission from interstellar dust as aquantitative probe of gas in star-forming regions, with particularemphasis on the interpretation of observations made at millimeter andsubmillimeter wavelengths. Expressions relating dust opacity to thecolumn density of hydrogen are derived. Examination of the uncertaintiesassociated with the observations and with intepretation shows thatbeam-averaged hydrogen column densities in these regions can bedetermined within factors of 5-20. The largest source of uncertaintylies in the conversion of derived dust opacities into gas columndensities. Within the wavelength range 100<λ<3000μm, wesuggest the relationshipN(H)/τ_dust_=~1.1x10^20lambda^2.0^cm^-2^ for dense dustclouds until the nature of the dust grains within these clouds becomesbetter known.
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Optical studies of interstellar material in low density regions of the Galaxy. I - A survey of interstellar NA I and CA II absorption toward 57 distant stars
We present high-resolution spectra of the Na I D and Ca II K linestoward 57 late-O and early-B stars along extended (d greater than 1 kpc)low-density paths through the Milky Way disk and halo. The sight linespreferentially sample diffuse gas in the interstellar medium (ISM) alonginterarm, Galactic center, and high latitude directions. We measureequivalent widths, apparent column densities, and absorption componentstructure. The Ca II to Na I ratios presented as a function of velocityfor each sight line exhibit variations due to elemental depletion,ionization, and density enhancements. Absorption along high latitudesight lines is kinematically simpler than it is along interarm andGalactic center sight lines. Galactic rotation noticeably broadens theabsorption profiles of distant stars located in these latter directions.Along several sight lines, we see Ca II absorption at velocitiescorresponding to large distances (/z/ about 1 kpc) from the Galacticplane. The effects of differences in the Ca II and Na I scale heightsand nonzero velocity dispersions are readily apparent in the data. Briefnotes are given for several sight lines with interesting absorptionproperties.
| Ultraviolet and radio observations of Milky Way halo gas
Interstellar-absorption-line and 21-cm emission-line data for sightlines to 56 stars are combined in order to study the kinematics andspatial distribution of the gas that is at great distances from theGalactic plane. Measurements of the interstellar velocities and H Icolumn densities from the 21-cm emission and Ly-alpha absorption areincluded. The problem of contamination of the interstellar Ly-alphaabsorption line by stellar Ly-alpha absorption is analyzed, and thisinformation is used to reevaluate the vertical distribution of H I. Anew method for determining lower limits on the vertical distribution ofgas by including information on the velocity structure in the gas ispresented. The data for individual sight lines are discussed.
| Selection of standard stars for photometric observations with the 91-cm reflector at Okayama
Not Available
| A catalog of ultraviolet interstellar extinction excesses for 1415 stars
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
| The galactic reddening law - The evidence from uvby-beta photometry of B stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1985A&A...142..189T&db_key=AST
| On the nature of early-type stars in the galactic halo
Effective temperatures and surface gravities of 46 intermediate and highgalactic latitude OB stars have been estimated from Stromgren /C1/ andH-beta photometry. In addition, helium, calcium and magnesium abundancesrelative to hydrogen have been derived for eleven stars. The typicalOB-type stellar parameters indicate that they are normal Population Istars, several of which require ejection velocities of more than 100km/s from the plane in order to reach their present z-distances duringtheir lifetimes. The observed correlation between peculiar velocity andmass for stars with /z/ not less than 400 pc is compatible with theBlaauw runaway hypothesis as the acceleration mechanism. A plot of logN(Na I) versus E(B-V) implies that the gas-to-dust ratio in the halo isprobably similar to that found for material in the galactic disc. Thisimplies that the sputtering of calcium from grain surfaces is probablyresponsible for the observed velocity dependence of the N(Na I)/N(Ca II)ratio.
| A study of interstellar absorption at high galactic latitudes. I - Highly ionized gas
IUE interstellar absorption line data for C IV, Si IV, N V and Fe II, ina sample of 24 distant, early-type stars at high galactic latitudes, areanalyzed with other published results in order to study the distributionand physical conditions of highly ionized gas in the halo of the Galaxy.The C IV and Si IV lines, which are detected in front of approximatelytwo-thirds of the stars observed, are significantly stronger that thoseobserved in the spectra of disk stars of similar spectral types, andtheir velocities show no correlation with the velocities of thebackground stars. The observed variation of the column densities of C(3+) and Si (3+) with distance z from the plane is consistent with thesuggested existence of a Galactic transition layer between cool gas inthe disk and outer halo regions at temperatures greater than thoseobservable with IUE. Attention is drawn to the fact that the observed C(3+)/Si (3+) ratio may be a characteristic signature of hot gas ingalactic halos.
| H-beta photometry of southern early-type stars
H-beta photoelectric photometry is presented for 209 southern hemisphereearly-type stars from the HD catalog with galactic latitudes /b/ greaterthan 6 deg. Four-color photometry exists for all these stars and MKtypes for most of them. Absolute magnitudes have been estimated for allbut the emission-line stars and distances from the sun and the galacticplane determined.
| Four colour photometry of southern early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978MNRAS.182..629K&db_key=AST
| Photometry and spectral classification of early-type stars away from the galactic plane.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970MNRAS.150...23H&db_key=AST
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| Takýmyýldýz: | Pompa |
| Sað Açýklýk: | 09h56m33.25s |
| Yükselim: | -31°26'31.0" |
| Görünürdeki Parlaklýk: | 9.55 |
| özdevim Sað Açýklýk: | -7.9 |
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| B-T magnitude: | 9.377 |
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