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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).
| Light variations of massive stars (alpha Cyg variables). XVIII. The B[e] supergiants S 18 in the SMC and R 66 = HDE 268835 and R 126 = HD 37974 in the LMC
We discuss photometric monitoring (VBLUW system) of three B[e]supergiants. All three objects appear to be variable. They are subjectto two (R 66 and R 126 in the LMC) and three (S 18 in the SMC) types oflight oscillations which range from a few days to years, and areprobably due to pulsations. We argue that a classification as alpha Cygvariables is justified. Their classification as mixed B[e]/S Dorvariables is less certain, though not impossible. Also based on othercases, a strong B[e]-S Dor variable connection seems to be present.Based on observations obtained at the European Southern Observatory atLa Silla, Chile.
| Speckle Interferometry of New and Problem HIPPARCOS Binaries
The ESA Hipparcos satellite made measurements of over 12,000 doublestars and discovered 3406 new systems. In addition to these, 4706entries in the Hipparcos Catalogue correspond to double star solutionsthat did not provide the classical parameters of separation and positionangle (rho,theta) but were the so-called problem stars, flagged ``G,''``O,'' ``V,'' or ``X'' (field H59 of the main catalog). An additionalsubset of 6981 entries were treated as single objects but classified byHipparcos as ``suspected nonsingle'' (flag ``S'' in field H61), thusyielding a total of 11,687 ``problem stars.'' Of the many ground-basedtechniques for the study of double stars, probably the one with thegreatest potential for exploration of these new and problem Hipparcosbinaries is speckle interferometry. Results are presented from aninspection of 848 new and problem Hipparcos binaries, using botharchival and new speckle observations obtained with the USNO and CHARAspeckle cameras.
| The Luminous Eclipsing SMC OB + WN Binary HD 5980 before and during the Recent LBV-like Outburst: an Extreme Case of Colliding Winds
The 1994 LBV-(luminous blue variable)like outburst of one of theluminous, hot components of the binary HD 5980 made it the brighteststar in the Small Magellanic Cloud for an interval of 5 months. The mostintriguing question to arise from this event is the following: Why didthe HD 5980 spectrum change from an H-poor WN3 with veiled OB absorptionlines about 20 yr ago to an H-rich WN11 without central absorption linesduring the outburst? In an attempt to answer this apparent enigma, wepresent and analyze new phase-dependent spectroscopic, polarimetric, andlight-curve observations. Together with other published data, these newobservations allow us to improve the orbital parameters considerably,except for the radial velocity amplitudes and hence the masses, whichare only roughly constrained. Especially important in HD 5980 is thestrong collision of the two nearly equal pre-outburst winds. Theemission-line spectrum generated by the collision tends to mask theunderlying line spectra of both components when the system is relativelyquiescent. We argue that the pre-erupting system consists of a veryluminous but moderately massive H-rich O type supergiant, possibly withemission lines, and a low-mass, H-poor, relatively faint WN companion,whose lines are mostly drowned out by wind collision emission, thespectrum of which largely imitates that of a WNE star. It was the Osupergiant that erupted in a normal way as an H-rich, visually brightWN11 star. In this way, the need for peculiar evolutionary scenarios(e.g., rapid evolution from a faint, low-mass, H-poor WNE star to aluminous, H-rich WNL star) is avoided.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Obscured AGB stars in the Magellanic Clouds. I. IRAS candidates
We have selected 198 IRAS sources in the Large Magellanic Cloud, and 11in the Small Magellanic Cloud, which are the best candidates to bemass--loosing AGB stars (or possibly post--AGB stars). We used thecatalogues of \cite[Schwering \& Israel (1990)]{ref42} and\cite[Reid et al. (1990)]{ref36}. They are based on the IRAS pointedobservations and have lower detection limits than the Point SourceCatalogue. We also made cross-identifications between IRAS sources andoptical catalogues. Our resulting catalogue is divided in 7 tables.Table \ref{tab1} lists optically known red supergiants and AGB stars forwhich we found an IRAS counterpart (7 and 52 stars in the SMC and LMC,respectively). Table \ref{tab2} lists ``obscured'' (or ``cocoon'') AGBstars or late-type supergiants which have been identified as such inprevious works through their IRAS counterpart and JHKLM photometry (2SMC and 34 LMC sources; no optical counterparts). Table \ref{tab3} listsknown planetary nebulae with an IRAS counterpart (4 SMC and 19 LMC PNe).Table \ref{tab4} lists unidentified IRAS sources that we believe to begood AGB or post--AGB or PNe candidates (11 SMC and 198 LMC sources).Table~\ref{tab5} lists unidentified IRAS sources which could be any typeof object (23 SMC and 121 LMC sources). Table \ref{tab6} lists IRASsources associated with foreground stars (29 SMC and 135 LMC stars).Table \ref{tab7} lists ruled out IRAS sources associated with HIIregions, hot stars, etc... We show that the sample of IRAS AGB stars inthe Magellanic Clouds is very incomplete. Only AGB stars more luminousthan typically 10^4 L_\odot and with a mass-loss rate larger thantypically 5 10^{-6} M_\odot/yr could be detected by the IRAS satellite.As a consequence, one expects to find very few carbon stars in the IRASsample. We also expect that most AGB stars with intermediate mass--lossrates have not been discovered yet, neither in optical surveys, nor inthe IRAS survey. Tables 1 to 8 are also available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The δ Scuti star θ Tucanae. II. UVBY colour variations and pulsational/orbital properties.
On the basis of almost 1500 uvby photometric observations of θTucanae collected in 1993, we discuss the colour variation of thismulti-periodic δ Scuti star and debate some of its binary andpulsational properties. The frequencies f_1_=0.281 and f_2_=0.142c/dembody orbital motion in a 7.04d day ellipsoidal configurationcharacterised by a light curve with unequal maxima and minima and acolour index that becomes bluer during the minimum phases. The firstresults of an analysis of the light curve points towards a mass ratio qof the order of 0.10-0.15. We present dependable numerical values forcolour phase differences and amplitude ratios A_b-y_/A_y_,φ_b-y_-φ_y_, A_v-y_/A_y_, φ_v-y_-φ_y_ andA_u-y_/A_y_, φ_u-y_-φ_y_ which can be used for pulsation-modeidentification. The principal pulsation frequency f_7_=20.28c/d isreconcilable with a radial mode.
| Complex behaviour of the δ Scuti star θ Tucanae. I. Frequencies in the light variation.
On the basis of more than 2300 new Stroemgren y and Johnson Vphotometric observations collected during 246 hours spread over 42nights at three sites in 1993, we present a frequency analysis of thelight variation of θ Tuc. 10 frequencies were found in the rangeof 15.8 to 20.28cycles/day displaying an extreme regularity. Frequenciesare situated in groups and these groups are equally spaced. Some kind ofsplitting is definitely involved. The frequencies are constant inamplitude on a short time scale. Two frequencies, 0.282 and0.142cycles/day (3.56 and 7.04days period) were found to be responsiblefor the mean light level variation of θ Tuc. Although θTuc is known as a single star, the length and shape of the mean lightlevel variation and the unusual behaviour of θ Tuc in ultravioletand infrared suggest that the δ Scuti star θ Tuc is aprimary in a binary system with a late F type companion.
| Positional reference stars in the Magellanic Clouds
The equatorial coordinates are determined of 926 stars (mainly ofgalactic origin) in the direction of the Magellanic Clouds at the meanepoch T = 1978.4 with an overall accuracy characterized by the meanvalues of the O-C coordinates, Sa = 0.35 arcsec and Sd = 0.38 arcsec,calculated from the coordinates of the Perth reference stars. Thesevalues are larger than the accuracy expected for primary standard stars.They allow the new positions to be considered as those of reliablesecondary standard stars. The published positions correspond to anunquestionable improvement of the quality of the coordinates provided inthe current catalogs. This study represents an 'astrometric step' in thestarting of a 'Durchmusterung' of the Magellanic Clouds organized by deBoer (1988, 1989).
| Secondary standards for H-beta photometry in the Southern Hemisphere (second series).
Not Available
| UBV (RI)c standard stars in the E- and F-regions and in the Magellanic Clouds - a revised catalogue.
Not Available
| Infrared observations of the Magellanic Clouds. I - The Small Magellanic Cloud
Results of IRAS pointed observations in four infrared wavelength bands(12, 25, 60, and 100 microns) for the SMC are presented. Maps withorthogonal scan directions are shown, and a source list containing 219infrared sources is extracted from the data. Comparison with the IRASPoint Source Catalog (PSC) shows that only three entries in this catalogare spurious. All 13 entries in the IRAS Small Scale Structure Catalog(SSS) in the SMC are confirmed. Seventy-two new infrared sources, notincluded in either the PSC or in the SSS are found. The present SMCinfrared source list is compared to other object lists. Two blueglobular clusters, 28 SAO stars, and seven planetary nebulae areidentified. No SMC stars are found. In general there is a goodcorrelation of infrared emission with the distributiion of H II regionsand dark clouds.
| Zero-Point Checks of Magellanic Cloud Sequences
Not Available
| UBV(RI)c photometry of some standard sequences in the Harvard F regions and in the Magellanic Clouds
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1988MNRAS.231.1047M&db_key=AST
| Revised UBV photometry of Magellanic Cloud sequences
The old photometry of UBV secondary standards in the Magellanic Clouds(Cousins 1970) has been revised. New measurements made at Sutherland arepresented and analyzed.
| Local photometric standards for CaII emission stars
UBV data are given for 108 stars which are suitable local standards for52 stars with strong Ca2 emissions. An additional eight stars wererejected as possible standards because of suspected variability.
| Einstein Observations of X-ray emission from A stars
Results are reported from the combined CfA Stellar Survey of selectedbright A stars and an Einstein Guest Observer program for Ap and Amstars. In an initial report of results from the CfA Stellar Surveys byVaiana et al. (1981) it was noted that the spread in observed X-rayluminosities among the few A stars observed was quite large. The reasonsfor this large spread was studied by Pallavicini et al. (1981). It wasfound that the X-ray emission from normal stars is related very stronglyto bolometric luminosity for early-type stars and to rotation rate forlate-type stars. However, an exception to this rule has been theapparently anomalous behavior of A star X-ray emission, for which thelarge spread in luminosity showed no apparent correlation with eitherbolometric luminosity or stellar rotation rate. In the present study, itis shown that the level of emission from normal A stars agrees with thecorrelation observed for O and B stars.
| Lists of photometric AM candidates
The Geneva photometric m parameter (Nicolet and Cramer, 1982) is used inorder to select Am photometric candidates from the Rufener (1981)catalogue. Two lists are given, the first containing field stars and thesecond cluster stars. According to the photometric criteria thediffusion process probably responsible for the Am phenomenon takes placerather quickly as Am candidates are present in young clusters. It isconfirmed that the phenomenon is enhanced by low rotational velocity andhigh metallicity. The age seems to slightly affect the Am phenomenon.
| A magnitude limited stellar X-ray survey and the F star X-ray luminosity function
An X-ray survey has been conducted of stars brighter than visualmagnitude 8.5 that have serendipitously fallen into the fields of viewof the Imaging Proportional Counter of the Einstein Observatory. Thesurvey includes 227 separate 1 x 1 deg fields, containing 274 stars witha visual magnitude of no more than 8.5 and covering a wide range ofspectral types and luminosity classes. X-ray emission was detected from33 stars, and upper limits have been determined for the remainder of thesample. F type stars dominate the detected sample, and most of these areshown to be dwarfs. An X-ray luminosity function for dF stars has beendeduced, and reveals that the average 0.2-4.0 keV luminosity of thesestars is around 10 to the 29th erg/sec. Constraints have been placed onthe high luminosity tails and medians of the X-ray luminosity functionsfor other types of stars.
| Five-colour photometry of blue stars in the Magellanic-Cloud region
The results of photoelectric observations of about 500 stars in andbetween the Magellanic Clouds are given. The observations were made inthe Walraven VBLUW-system. Within the limits of the study, no cloudmembers are found to be associated with the neutral hydrogen between theclouds. Seventy-five stars, previously reported to be cloud members byothers, were found independently. A large number of new members of thewing system of the SMC are identified. The great eastward extension ofthe wing system is clearly illustrated by the results
| On the stability of observed frequencies in Delta Scuti stars - A reanalysis of Theta TUC
The claim that some Delta Scuti stars change their frequencies on timescales as short as 24 hr is examined. It is suggested that thehypothesis that these Delta Scuti stars have stable frequencies isviable. Stobie and Shobbrook's (1976) data on Theta Tuc is reanalyzedalong with 954 new observations obtained during 70 hr on 21 nights in1979. The frequency of highest amplitude is shown to be present at aconstant amplitude over the 7-yr time span of the entire data set. Apossible set of frequencies is fitted to the Theta Tuc data. Other DeltaScuti stars which have been claimed to have variable frequencies arediscussed. Some of these stars are now known to have stable frequencies.A reanalysis of Stobie, Pickup and Shobbrook's data (1977) and Gupta'sdata (1973) on 21 Mon gives the same result found by Stobie, Pickup, andShobbrook: 21 Mon appears to have changed frequencies in the 2-yrinterval between the data sets. It is pointed out that claims ofchanging frequencies for Delta Scuti stars should only be made withcaution and a large amount of data.
| The globular cluster system of the Galaxy. I - The metal abundances and reddenings of 70 globular clusters from integrated light measurements
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980ApJS...42...19Z&db_key=AST
| A classification of star clusters in the Magellanic Clouds
Four-color photometry of the integrated light from 61 star clusters inthe Magellanic Clouds, together with a rediscussion of Danziger'smultivariate spectrophotometric data for some of these same clusters,have made possible for the first time an intelligible classificationscheme for their integrated spectra. It is found that the integratedspectra of populous star clusters in the Magellanic Clouds may bearranged in a one-dimensional sequence in such a way, that on traversingthe sequence, all spectral features behave regularly - not necessarilymonotonically, but as smoothly as can be expected from the magnitude ofobservational error. The character of the spectral variations along thesequence suggests that both cluster age and chemical composition varysmoothly as the sequence is traversed. The newly discovered sequence isdistinctly different from the analogous one for star clusters of theGalaxy, and this fact is interpreted as indicating that the relationbetween epoch and average chemical composition of the interstellarmedium is qualitatively different in different stellar systems.
| Sir John Herschel's Observations of Stars in the Small Magellanic Cloud
Not Available
| Intermediate band photometry of early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..205E&db_key=AST
| Properties of the Walraven VBLUW photometric system
The Walraven five-channel (VBLUW) photometer has been used primarily tostudy Cepheids and RR Lyrae variables. Those properties of the VBLUWphotometric system are discussed which are important for analyzing andinterpreting data on such stars. The standard stars that define thesystem are examined, the long-term stability of these stars is examined,and the responses of the photometric passbands are analyzed. Correctionsfor atmospheric extinction and interstellar reddening are reviewed,noting that color terms in the extinction corrections are sufficientlysmall to be neglected and that nonlinear terms in reddening correctionscan also be neglected provided the reddening is not higher than about1.25 magnitudes. Application of the VBLUW system to the classificationof A, F, and G stars, Hyades main-sequence stars, bright field stars,and subdwarfs is demonstrated, and observed two-color diagrams arecompared with theoretical diagrams based on model atmospheres. It isconcluded that a three-dimensional classification based on effectivetemperature, surface gravity, and heavy-element abundance is possiblefor A, F, and G spectral types and that VBLUW photometry is more thantwice as sensitive as Stroemgren uvby photometry to differences inheavy-element abundances below 8000 K.
| Standard Stars for VRI Photometry with S25 Response Photocathodes
Not Available
| UBV Magnitude Sequences in the Magellanic Clouds
Not Available
| Polarization measurements of stars in the Magellanic Clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..778M&db_key=AST
| Polarization measurements and magnetic field structure within the magellanic clouds.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&A.....6..294S&db_key=AST
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