Tomographic separation of composite spectra. The components of Plaskett's Star

The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correlation analysis, which showed that the secondary produces significant lines in the UV, indicates that the mass ratio is q = 1.18 + or - 0.12 (secondary slightly more massive). A tomography algorithm was used to produce the separate spectra of the two stars in six spectral regions. The interpolated spectral classifications of the primary and secondary, 07.3 I and 06.2 I, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. The intensity ratio of the stars in the UV is 0.53 + or - 0.05 (primary brighter). The secondary lines appear rotationally broadened, and the projected rotational velocity V sin i for this star is estimated to be 310 + or - 20 km/s. The possible evolutionary history of this system is discussed through a comparison of the positions of the components and evolutionary tracks in the H-R diagram

HD 62454 and HD 68192: Two New γ Doradus Variables

We present multilongitude, multicolor photometry and simultaneous high-resolution, high signal-to-noise spectroscopy of the newly discovered γ Doradus variables HD 62454 and HD 68192. From combined Johnson and Strömgren data, we are able to identify five independent periods in HD 62454 and two stable periods in HD 68192. The data presented are sufficient to rule out all physically meaningful types of variations, with the one exception of the high-order, low-degree, nonradial gravity-mode pulsations that are believed to be at work in γ Doradus stars. We also find that HD 62454 is a double-lined spectroscopic binary and we present an orbital solution

Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (delta Orionis A)

Double-lined spectroscopic orbital elements have recently been found for the central binary in the massive triple, delta Orionis A based on radial velocities from cross-correlation techniques applied to IUE high dispersion spectra and He I 6678 spectra obtained at Kitt Peak. The primary and secondary velocity amplitudes were found to be 94.9 +/- 0.6 km/s and 186 +/- 9 km/s respectively. Tomographic reconstructions of the primary and secondary stars' spectra confirm the O9.5 II classification of the primary and indicate a B0.5 III type for the secondary. The widths of the UV cross-correlation functions are used to estimate the projected rotational velocities, Vsin i = 157 +/- 6 km/s and 138 +/- 16 km/s for the primary and secondary, respectively implying that both stars rotate faster than their orbital motion. We used the spectroscopic results to make a constrained fit of the Hipparcos light curve of this eclipsing binary, and the model fits limit the inclination to the range between 67 and 77 degrees. The i = 67 degrees solution, which corresponds to a near Roche-filling configuration, results in a primary mass of 11.2 solar masses and a secondary mass of 5.6 solar masses, both of which are substantially below the expected masses for stars of their luminosity. This binary may have experienced a mass ratio reversal caused by Case A Roche lobe overflow, or the system may have suffered extensive mass loss through a binary interaction, perhaps during a common envelope phase, in which most of the primary's mass was lost from the system rather than transferred to the secondary.Comment: 27 pages, 15 figures in press, the Astrophysical Journal, February 1, 200

Binary and Multiple O-Type Stars in the Cas OB6 Association

We present the results of time-resolved spectroscopy of 13 O-type stars in the Cas OB6 stellar association. We conducted a survey for radial velocity variability in search of binary systems, which are expected to be plentiful in young OB associations. Here we report the discovery of two new single-lined binaries, and we present new orbital elements for three double-lined binaries (including one in the multiple star system HD 17505). One of the double-lined systems is the eclipsing binary system DN Cas, and we present a preliminary light curve analysis that yields the system inclination, masses, and radii. We compare the spectra of the single stars and the individual components of the binary stars with model synthetic spectra to estimate the stellar effective temperatures, gravities, and projected rotational velocities. We also make fits of the spectral energy distributions to derive E(B-V), R=A_V/E(B-V), and angular diameter. A distance of 1.9 kpc yields radii that are consistent with evolutionary models. We find that 7 of 14 systems with spectroscopic data are probable binaries, consistent with the high binary frequency found for other massive stars in clusters and associations.Comment: 40 pages, ApJ, in pres

The stellar composition and evolution of irregular and other late-type galaxies

The stellar content and history of star formation of a number of Irregular and other late-type galaxies have been analyzed by means of 10-color photometery of the galaxies and a comparison of their colors to the calculated colors of a set of three-parameter models. The galaxy models are assumed to be composed of various amounts of "clusters" from 10[superscript 6] to 10[superscript 10] years old, the colors of which were calculated from stellar-evolutionary tracks and observations of 102 stars of all spectral types. The colors of the model clusters were checked by comparison to the colors of 46 clusters in the Magellanic Clouds. The first chapter of the thesis gives the principal results of the work, the analysis of the galaxies; the second gives a description of the cluster models and comparison to the cluster observations; the third presents the colors of the 102 calibrating stars. In the first chapter the colors from 79 observations of 46 different Irregular and other late-type galaxies (mostly Sc's) are given first. The construction of model cluster colors and their behavior as a function of time, t, are briefly discussed. A principal component analysis of the galaxy colors indicates that only three parameters could explain most of the variation in galaxy colors. Accordingly, a set of three-parameter models is adopted to explain their colors. The three parameters chosen govern the star formation history of the galaxies. The Limber initial mass formation function is assumed. Various two-color plots of some of the galaxy models were made. It is found that the loci of the models agree well with observations. Finally, fits to individual galaxies in the three parameters are made, as well as estimates of the "uniqueness" of the fits. The average difference between the best-fitting parameters of Irregulars and Sc's is interpreted to mean that Irregulars have both relatively more star formation in the recent past and an initial mass formation function enriched in massive stars compared to the Sc's. An irregular rate of star formation in the recent past (t <10[superscript 8] yr) is also indicated. The second chapter describes the construction of cluster models and a comparison between the model colors and the colors of 46 clusters in the Magellanic Clouds. Cluster models are found to fit observations well in general. Furthermore, the observations permit estimates of n[subscript b]/n[subscript r], the ratio of blue to red supergiants, to be obtained for stars of 3 to 20 solar masses. The third chapter gives a description of the observation of 102 stars of all luminosity classes and spectral types from O5 to M6. The behavior of the colors of stars of different luminosity classes as functions of assumed log T[subscript e] and spectral type are discussed

CHARA recent technology and science

International audienc

CHARA recent technology and science

International audienc