Multiwavelength optical observations of chromospherically active binary systems*
IV. The X-ray/EUV selected binary BK Psc (2RE J0039+103)
Departamento de Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain e-mail: dmg@astrax.fis.ucm.es
Corresponding author: D. Montes, dmg@astrax.fis.ucm.es
Received:
11
February
2002
Accepted:
16
April
2002
We present high resolution echelle spectra taken during
four observing runs from 1999 to 2001 of the recently
X-ray/EUV selected chromospherically active binary
BK Psc (2RE J0039+103).
Our observations confirm the single-lined spectroscopic binary (SB1) nature
of this system and allow us to obtain, for the first time,
the orbital solution of the system as in the case of a SB2 system.
We have determined precise radial velocities of both components:
for the primary by using the cross correlation technique,
and for the secondary by using its chromospheric emission lines.
We have obtained a circular orbit with an orbital period
of 2.1663 days, very close to its photometric period of 2.24 days
(indicating synchronous rotation).
The spectral type (K5V) we determined for our spectra and the mass ratio
(1.8) and minimum masses (
) resulting from the orbital
solution are compatible with the observed K5V primary
and an unseen M3V secondary.
Using this spectral classification, the projected rotational
velocity (
, of 17.1 km s-1)
obtained from the width of the cross-correlation function
and the data provided by Hipparcos, we have derived other
fundamental stellar parameters.
The kinematics and the non-detection of the Li i line indicate
that it is an old star.
The analysis of the optical chromospheric activity indicators
from the Ca ii H & K to Ca ii IRT lines,
by using the spectral subtraction technique, indicates that
both components of the binary system show
high levels of chromospheric activity.
Hα emission above the continuum from both components is a
persistent feature of this system during
the period 1999 to 2001 of our observations as well as in previous
observations.
The Hα and Hβ emission seems
to arise from prominence-like material, and the Ca ii IRT emission
from plage-like regions.
Key words: stars: individual: BK Psc / stars: activity / stars: binaries: spectroscopic / stars: chromospheres / stars: late-type / stars: rotation
Based on observations made with the 2.2 m telescope of the German-Spanish Astronomical Centre, Calar Alto (Almería, Spain), operated by the Max-Planck-Institute for Astronomy, Heidelberg, jointly with the Spanish National Commission for Astronomy, with the Nordic Optical Telescope (NOT), operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias, and with the Isaac Newton Telescope (INT) operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias.
© ESO, 2002