5 research outputs found
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
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