The field of IC 2602: Strömgren-Hβ photometry approach
A homogeneous data-base collating all uvbyβ photometry available atpresent for O-B9 stars in the field of IC 2602 is presented. Thecharacteristics of the field are studied. Four spatially coherent groupscan be distinguished. A low reddened compact group located at156±6 pc is identified with IC 2602, followed by backgroundlayers at 546±33 pc, 1117±61 pc, and possibly at2626±163 pc. The apparent depth of the first three layers isabout 1 kpc, which is consistent with the thickness of a spiral arm.There is an indication for the existence of a region free of massiveluminous stars between 1.2 and 2.6 kpc, which could be associated withinterarm space between the Local Association and the distant spiralstructures toward Carina. A comparison between the photometric andHipparcos parallaxes is presented.
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Strömgren and Hβ photometry of O and B type stars in star-forming regions. III. Carina Spiral Feature
Strömgren and Hβ photometry of O and B type stars, generallybrighter than 9.5 mag is reported for the field of the Carina SpiralFeature. The observations are based on the PPM catalogue identificationsand are designed to improve the completeness of the existing uvbybetadata for the bright early-type stars in the field. We present new uvbyphotometry for 283 stars and Hβ photometry for 225 of them. Theseobservations are part of an ongoing effort to study the structure ofselected star-forming regions in the Milky Way by means of uvbybetaphotometry. A comparison of the new data to other uvbybeta data sets forthis field is presented. Based on data from the Strömgren AutomaticTelescope of the Copenhagen University Observatory, La Silla. Tables 1and 2 are only available in electronic form at the CDS via anonymous ftpto 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
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Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
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The broad lambda-5200 continuum depression in the CP star HD 126515
Delta-a photometry of HD 126515 shows the extraordinary variability ofits continuum depression around 5200 A. The Delta-a peculiarity is about0.06 m over most of the rotation cycle, but drops to about half thatvalue at phase of minimum surface field strength Hs and minimum lineblocking. It is argued that the surface region which produces the highpeculiarity values is associated with the regions of enhanced spectralline strength, rather than with local field strength.
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Metallicities and distances of galactic clusters as determined from UBV-data. II - The metallicities and distances of 38 open clusters. III - Ages and abundance gradients of open clusters
After presenting a novel method for the simultaneous calculation of UVexcess and reddening in open clusters, the former is transformed into anFe/H abundance ratio value on the basis of the relation due to Cameron(1985), and the reddening is used to determine the distances of theclusters, incorporating a ratio of total-to-selective absorption that isboth a function of interstellar extinction and dependent on spectraltype. Metallicities and distances for 38 open clusters are therebyobtained and used to estimate the variation of metal abundance along thegalactic disk. The ages of the clusters are determined using the turnoffpoint method in the H-R diagram, and noted to cover a span of 5.1billion years. No firm relationship between cluster ages and theirmetallicity can be deduced; it is instead shown that, at a given age,there is a metallicity spread of up to + or - 0.3 dex.
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Investigation of the initial mass spectrum of open star clusters
The mass spectra of 228 open star clusters were derived by comparison ofcolor-magnitude diagrams with evolutionary tracks. The application tobinary stars showed the reliability of the mass determination. Thederived mass spectra were fitted by power laws as well as exponentiallaws. It could be shown that both approximate the mass spectra of openstar clusters on the same average significance level. The presentinvestigation revealed a correlation of the slope of the mass spectrawith the cluster age, whereas a detected correlation of the slope withgalactocentric distance is slight. The results suggest that the slope ofthe mass spectrum increases with increasing cluster and galactocentricdistance. These findings are discussed with respect to their reasons andprevious results concerning open clusters and field stars.
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The Boehm-Vitense gap in the Geneva photometric system
A gap among A-F stars is searched on the main sequence of differentstellar samples in the photometric space M defined by the four colorindexes U-B1, B1-B2, B2-V1 and V1-G of the Geneva photometric system. Agap is noticed for the field and the eight young open clustersinvestigated when selected stars are not visual or spectroscopicbinaries, and not chemically peculiar. It is shown that this gap isinduced by the existence of two differently oriented star branches in M,the so-called radiative and convective branches. The gap is suggestednot to be only a mere artefact of having previously excluded Am and Apstars but partly due to an abrupt onset of convection in late A stars asproposed by Boehm-Vitense (1970). The locus of the gap's red edgeaccording to B2-V1 with regard to the diffusion region, the lowerinstability strip and the low rotational velocities domain supports theidea that the onset of convection lowers the metallicity, stabilizes thepulsations and brakes the rotation. The locus of the gap's blue edgeseems to be connected with age.
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A re-calibration of the luminosities of early-type stars - Its effect on the Cepheid luminosity scale
The most recently published data on 421 stars in 13 open clusters isused to recalibrate the Stromgren beta index as a luminosity indicatorfor early type stars. Since all the clusters independently tie up withthe Pleiades, previous problems involving the use of associations areavoided. The final calibration is presented as an analytical expressionin (beta c0). Analysis of evolutionary diagrams for the calibratingclusters show small trends which are best explained as due todifferences in zero-point of the beta index. A calibration for thezero-age main sequence is presented and compared with results by variousauthors. The effect of the calibration on the zero point of the Cepheidluminosity scale is investigated in an appendix.
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RGU photometry of a field in the Carina region near the cluster IC 2581
A field of 0.21 sq deg containing 2099 stars in the Carina region nearthe cluster IC 2581, has been measured on 14 plates in the RGU system.The reddening is caused by a thin absorbing cloud at 770 pc with E(G-R)= 0.23 mag, as well as an interstellar absorption free zone followed bya moderate gradient which increases with distance. The density gradientscorresponding to late-type giants and main sequence stars of the sameabsolute magnitude do not display the same behavior. Assuming that theouter edge of the arm of Carina is being observed, the present resultsseem to corroborate the existence of external spiral features between 12and 13 kpc. The distribution of F0-F5 stars seems to confirm predictionsof the theory of density waves.
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The nature of the visual companions of AP and AM stars
The stars in 43 visual multiples with Ap or Am primaries have beenclassified, and the fraction of systems that have Ap or Am secondariesis counted. The numbers of Ap secondaries are too few to be informative,but an apparent excess of Am secondaries is found. That result isunderstandable in terms of the (published) moderate correlation inrotational velocities between components in visual multiples. But invarious open clusters, the variations in frequencies of Ap and Am starscan be explained probably as statistical fluctuations in small numbersof stars, indicating no tendency for abnormal stars to group togetherfor dimensions larger than those of visual multiples.
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Concentrations in the Local Association - Part Two - the Northern Concentrations Including the Alpha-Persei Pleiades M34 and Delta-Lyrae Clusters
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983MNRAS.204..391E&db_key=AST
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Concentrations in the local association. I - The southern concentrations NGC 2516, IC 2602, Centaurus-Lupus and upper Scorpius
Abstract image available at:http://adsabs.harvard.edu/abs/1983MNRAS.204..377E
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Photoelectric Photometry of Ap Stars in IC 2602, NGC 6281 and in the Scorpio-Centaurus Group: Preliminary Results
Not Available
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Analysis of UBV Data in Open Clusters
Not Available
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Catalogue of Masses and Ages of Stars in 68 Open Clusters
Not Available
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The galactic cluster IC 2602 (Errata: 17 310)
Not Available
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