Paper: astro-ph/0512254
Date: Fri, 9 Dec 2005 17:06:04 GMT (370kb)

Title: The Multiple System HD 27638

Authors: Guillermo Torres (Harvard-Smithsonian Center for Astrophysics)

Comments: 16 pages in 2-column format, including tables and figures. To appear
in The Astronomical Journal
\\
We report spectroscopic observations of HD 27638B, the secondary in a visual
binary in which the physically associated primary (separation approximately 19
arcsec) is a B9V star. The secondary shows strong Li 6708 absorption suggesting
youth, and has attracted attention in the past as a candidate post-T Tauri star
although this has subsequently been ruled out. It was previously known to be a
double-lined spectroscopic binary (F8+G6) with a period of 17.6 days, and to
show velocity residuals indicating a more distant massive third companion with
a period of at least 8 years. Based on our radial velocity measurements
covering more than two cycles of the outer orbit, along with other
measurements, we derive an accurate triple orbital solution giving an outer
period of 9.447 +/- 0.017 yr. The third object is more massive than either of
the other two components of HD 27638B, but is not apparent in the spectra. We
derive absolute visual magnitudes and effective temperatures for the three
visible stars in HD 27638. Isochrone fitting based on those properties gives an
age of 200 +/- 50 Myr for the system. We infer also an inclination angle of
about 53.3 degrees for the inner orbit of HD 27638B. We detect a near-infrared
excess in HD 27638B which we attribute to the third star being a close binary
composed of late-type stars. This explains its large mass and lack of a visible
signature. Modeling of this excess allows us to infer not only the masses of
the components of the unseen companion, but also the inclination angle of the
outer orbit (approximately 73 deg). The HD 27638 system is thus at least
quintuple.

\\ ( http://arXiv.org/abs/astro-ph/0512254 , 370kb)