A Photometric Method to Search for Be Stars in Open Clusters
We describe a technique to identify Be stars in open clusters usingStrömgren b, y, and narrowband Hα photometry. We firstidentify the B-type stars of the cluster using a theoretical isochronefit to the (b-y, y) color-magnitude diagram. The strongest Be stars areeasily identified in a (b-y, y-Hα) color-color diagram, but thosewith weaker Hα emission (classified as possible Be stardetections) may be confused with evolved or foreground stars. Here wepresent such photometry plus Hα spectroscopy of members of thecluster NGC 3766 to demonstrate the accuracy of our technique.Statistical results on the relative numbers of Be and B-type stars inadditional clusters will be presented in a future paper.
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The N Enrichment and Supernova Ejection of the Runaway Microquasar LS 5039
We present an investigation of new optical and ultraviolet spectra ofthe mass donor star in the massive X-ray binary LS 5039. The opticalband spectral line strengths indicate that the atmosphere is N-rich andC-poor, and we classify the stellar spectrum as type ON6.5 V((f)). TheN-strong and C-weak pattern is also found in the stellar wind P Cygnilines of N V λ1240 and C IV λ1550 (narrow absorptioncomponents in the former indicate that the wind terminal velocity isV&infy;=2440+/-190 km s-1). We suggest that the Nenrichment may result from internal mixing if the O star was born as arapid rotator or the O star may have accreted N-rich gas prior to acommon envelope interaction with the progenitor of the supernova. Wereevaluated the orbital elements to find an orbital period ofP=4.4267+/-0.0005 days. We compared the spectral line profiles with newnon-LTE line-blanketed model spectra from Lanz and Hubeny, from which wederive an effective temperature Teff=37.5+/-1.7 kK, gravitylogg=4.0+/-0.1, and projected rotational velocity Vsini=140+/-8 kms-1. We fitted the UV, optical, and IR flux distribution byusing a model spectrum and extinction law with parametersE(B-V)=1.28+/-0.02 and R=3.18+/-0.07. We confirm the covariability ofthe observed X-ray flux and stellar wind mass-loss rate derived from theHα profile, which supports the wind accretion scenario for theX-ray production in LS 5039. Wind accretion models indicate that thecompact companion has mass MX/Msolar=1.4+/-0.4,consistent with its identification as a neutron star. We argue that theO star has mass in the range 20-35 Msolar (based on a lowerlimit for the distance and the lack of eclipses). The observedeccentricity and runaway velocity of the binary can be reconciled onlyif the neutron star received a modest kick velocity due to a slightasymmetry in the supernova explosion (during which more than 5Msolar was ejected).Based on observations with the NASA/ESA Hubble Space Telescope obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS5-26555.
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A homogeneous catalog of new UBV and H-beta photometry of B- and A-type stars in and around the Scorpius-Centaurus OB association
B- and A-type stars in and near the Sco-Cen OB association areinvestigated with UBV and H-beta photometry to acquire data relevant tothe luminosity function of Sco-Cen. The measurements generally consistof two 10-s integrations of U, B, V, (W, N) filters, and theobservations are corrected iteratively for atmospheric extinction andinstrumental response. The data presented give the mean V magnitude,mean B-V, mean U-B, and the estimated uncertainties for these values.The catalog provides a homogeneous catalog of data for a large fieldwith stellar objects delineating membership to the association Sco-Cenand that affect the luminosity function of the aggregate.
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Secondary UVBY standards in the Harvard E-regions
Photoelectric uvby photometry for 201 stars which are already UBV (RI)cstandards is presented. The photoelectric data are closely tied to theCousins uvby standards and the stars should be suitable for use asfainter (7-11 mag) secondary standards.
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Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
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The distance and structure of the Coalsack. I - Photometric data
The results of UBV and H-beta photometry for 284 stars of spectral typesB to F located in the area of the dark cloud Coalsack are presented.Most of the present stars are brighter than 10.0 mag and are classifiedin the MK system of Houk and Cowley (1975). For each star, the bestvalues for the extinction and distance modulus are provided, withtypical estimated errors of + or - 0.08 mag for the extinction and + or- 0.32 mag for the distance modulus. Possible misclassifications andspectral peculiarities are noted for several of the stars.
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UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
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A photoelectric BVRI sequence in the field of the globular cluster NGC 6121 (M4)
A photoelectric BVRI sequence of eleven stars homogeneously covering thefield of the Galactic globular cluster NGC 6121 (M4) is presented usingdata acquired in the Cousins BVRI photometric system. Three of the starsin the sequence are also on the list of Alcaino and Liller (1984), and acomparison is made with their data. This photometric sequence can beused in the calibration of future observations of NGC 6121 with otherdetectors.
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Secondary standards for the Stromgren UVBY system
Observations of 158 E region stars have been made in the Stromgrensystem, using the 46-cm reflector at Cape Town. They are mostly brighterthan eighth magnitude and are intended for use as secondary standardsfor the four-color system. The E region relative zero points are definedwith a precision of + or - 0.001 mag, and the internal standard errorsof the colors life between + or - 0.001 and + or - 0.002 mag.
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Atmospheric extinction in the /U-B/ color index
Various methods for obtaining the atmospheric extinction in the (U-B)color index taking into account the dependence of extinction coefficienton the intrinsic color index of the star are examined. Numericalintegrations are performed to determine synthetic color indices for 32stars of spectral classes O9 to M0 and luminosity classes I, III and Vthrough 0, 1 and 2 air masses, resulting in three (u-b) color indicesfor each star. Photometric reduction of the color indices to the (U-B)color index was then performed by the classical method, by the methodproposed by Gutierrez-Moreno et al. (1966) and various modifications ofit, and by the method proposed by Moffat and Vogt (1977). Comparisonwith observations of 71 stars in the standard region E5, nine extinctionstandard stars and 25 Johnson standard stars in the UBV reveals that thereduction of (U-B) by the classical method gives internal errors betweentwo and three times larger than those obtained for (B-V) and V, whilethe methods of Gutierrez-Moreno et al. and Moffat and Vogt providegreatly improved accuracy.
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DDO Observations of Southern Stars
Not Available
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Photometric standard stars for the UBV and (RI)KC systems.
Not Available
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VRI standards in the E regions
Not Available
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Standard Stars for VRI Photometry with S25 Response Photocathodes [Errata: 1974MNSSA..33....1C]
Not Available
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Lichtelektrische UBV-Photometrie von Standardsternen und in vier Sternfeldern am Äquator
Not Available
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Standard magnitudes in the E regions.
Not Available
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INHABITED SKY
