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Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Coupled Line-Profile and Continuum Variations in EZ Canis Majoris: Implications for the Driving Mechanism of Global Wind Structures in Wolf-Rayet Winds
EZ CMa is an apparently unusual Wolf-Rayet star of the nitrogen sequencethat exhibits strong variations on a period of 3.77 days with coherencylasting typically about 10 cycles. We have used an extensive set ofoptical spectroscopic observations to investigate a possible linkbetween its line-profile and photometric continuum variability. Despitethe strong epoch dependency of the variations, a persistent correlationis found between changes in the wind line profiles (N V lambda lambda4604, 4620 in particular) and in continuum flux emanating near thestellar core. We suggest that these observations give further support tothe idea that the physical conditions prevailing in the vicinity of thestar's photosphere have a significant impact on the wind structure andthat a spatial dependence of these conditions at the base of the outflowinduces the formation of azimuthal wind structures in EZ CMa. Theepoch-dependent nature of the variability could be related to long-termbehavior of corotating magnetic structures, although pulsationalinstabilities constitute a viable alternative.
| Optical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind
We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMaduring 20 consecutive nights in 1995 January in support of the IUEMega-project. In parallel with this optical spectroscopy, we alsomonitored EZ CMa using narrowband photometry. The light curve was foundto be remarkably stable when folded with the P=3.77 day period, and ithad a peak-to-valley amplitude of 0.1 mag. The P Cygni absorptioncomponents of He I lambda 3889 and He I lambda 5876 display a similarglobal pattern of variability as was found for the simultaneouslyacquired UV profiles. The strengthening of the P Cygni absorptioncomponent of these transitions is associated with the maximum of thecontinuum flux. Conversely, the absorption trough of N V lambda 4604gradually disappears as the star brightens. Although the emission partsof the lines are variable at different levels, they all show the samepattern of variability, which consists of phase-dependent shifts ofextra emission components superposed on the profiles. A strongcorrelation is found between the continuum-light level and theequivalent width of most transitions. The line skewness and thefull-width at half-maximum show a daily recurrence timescale, reflectingthe light curve changes. We have addressed in a rigorous statistical waythe significance of the variations by calculating the "temporal variancespectrum." For any given line, we found enhanced variability at somevelocities, although the whole profile displays a statisticallysignificant level of variability. Arguments against a compact companionas the cause of the observed periodic variability are presented.Instead, our observations strongly support the suggestion in the IUEMega analysis that the atypical level of variability results from therotation of a structured wind. We propose that the wind variability ofEZ CMa is triggered by photospheric activity, or that the wind iscontrolled by a large-scale magnetic field.
| Multi-colour photometric and spectroscopic monitoring of the WN5 star EZ Canis Majoris.
We present and analyse photometric and spectroscopic observations of theWN5 star EZ Canis Majoris obtained over a period of 7years. We discussthe changing light curve, the shift in phase of the maxima and point toflare type variability seen in one night. Small amplitude variations arereported in another night. We have investigated the change of theaverage visual magnitude over a time span of 18years and found atentative cyclic variation with a time scale of 2425d (6.6yr) with arange of ~0.07mag. This, of course, should be verified. If true, aprecession phenomenon may offer an explanation. The trend of the maximumlight amplitude of the 3.766d cycle is also investigated and it shows asaw-tooth character with a timescale of ~400d. A possible relation withthe magnetic activity of the star is discussed. We conclude that theline emission variability can be caused by both a single star model withan ever-changing wind and a binary (WN+NS) model.
| A unique period for the WN5 star EZ CMa
We have obtained three months (mid Feb.-mid May 1993) of uninterrupted,precision, narrowband visual, continuum photometry of EZ CMa whichallows a viable search for periodicities at unprecedented highresolution in the frequency domain. We find only one independentsignificant period, P = 3.76d, as first claimed in 1980. The phasedlight curve shows complex structure (3peaks) but a high levelof coherency during the first approximately 8 weeks. A sudden changeleads to a different, but still coherent, light curve during the lastapproximately 4 weeks. Since only one period persists, it must have itsorigin either in rotation as a single WR star (e.g., oblique rotator) orin a binary (e.g., with a compact companion).
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| 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.
| Photometry and polarimetry of the unusual WN5 star EZ Canis Majoris
New high-precision polarimetric data (based on four observing runsspanning 16 months and a nearly contiguous 62-night photometric run) arepresented for the unique Wolf-Rayet star of type WN5, EZ CMa. Eventhough the shape of the polarization curve changes from one run to thenext, the previously known 3.77-d period is always present in each runof data; no significant circular polarization variation is detected. Thedata are interpreted in terms of a binary system with a low-mass(probably compact) companion or rotating spots on a single star. Theformer is preferred; if correct, EZ CMa would fill the heretoforemissing link in the evolution of massive binaries.
| The region of NGC 2287 and CR 121
Intermediate band and H-beta observations of 135 stars in the regions ofthe clusters NGC 2287 and Cr 121 are discussed, and a luminositycalibration of photometric parameters for late G- to early K-type brightgiants and supergiants is introduced. Results indicate that NGC 2287 isat a distance of 740 pc, very little reddened, 100-million years old,and contains three or four G8-K2 bright giants and supergiants and ablue straggler. Cr 121 is 1.17 kpc distant, very little reddened, 1.5million years old and an extension of CMa OB1. Cr 121 contains a nearerconcentration of stars at the same distance as NGC 2287, and theassociation appears to be the same age as CMa OB1, although presequencestars may exist. Intermingling of stars in CMa OB2 and NGC 2287 is alsoconsidered possible, and a test of the calibration of two methods ofluminosity determination of early A-type stars using photometricparameters shows them to be entirely consistent.
| Collinder 121: a Young Southern Open Cluster Similar to H and χ Persei
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1967ApJ...149..107F&db_key=AST
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