19 research outputs found
The pre-main sequence spectroscopic binary AK Scorpii revisited
We present an analysis of 32 high-resolution echelle spectra of the pre-main
sequence spectroscopic binary AK Sco obtained during 1998 and 2000, as well as a
total of 72 photoelectric radial-velocity observations from the period
1986–1994. These data allow considerable improvement of the period and other
orbital parameters of AK Sco. Our analysis also includes eight series of photometric
observations in the uvby and Geneva seven-color systems from 1987, 1989,
1990, 1992, 1994 and 1997. No eclipses or other periodic variations are seen in
the photometry, but the well-determined HIPPARCOS parallax allows us to
constrain the orbital inclination of the system to the range 65°°, leading to the following physical parameters for the two
near-identical stars: , , and
km s-1.
Disk models have been fit to the spectral energy distribution of AK Sco from 350 nm to 1100 μm. The above stellar parameters permit a consistent solution with
an inner rim temperature of 1250 K, instead of the usual 1500 K corresponding to
the dust evaporation temperature. Dynamical effects due to tidal interaction of
the binary system are supposed to be responsible for pushing the inner disk
radius outwards. Combining simultaneous photometric and spectroscopic data sets
allows us to compute the dust obscuration in front of each star at several points
over the orbit. The results demonstrate the existence of substructure at scales
of just a single stellar diameter, and also that one side of the orbit is more
heavily obscured than the other.
The spectrum of AK Sco exhibits emission and absorption lines that show
substantial variety and variability in shape. The accretion-related lines may
show both outflow and infall signatures. The system displays variations at the
binary orbital period in both the photospheric and accretion-related line
intensities and equivalent widths, although with appreciable scatter. The
periodic variations in the blue and red wing of Hβ are almost 180° out
of phase.
We find no evidence of enhanced accretion near the periastron passage in AK Sco
as expected theoretically and observed previously in DQ Tau, a similarly young
binary system with a mass ratio near unity and an eccentric orbit. The Hα
equivalent width displays rather smooth variations at the stellar period,
peaking around phases 0.6–0.7, far away from periastron where theory expects the
maximum accretion rate to occur