X-ray emission from young stars in Taurus-Auriga-Perseus: Luminosity functions and the rotation -activity -age -relation*
Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
Corresponding author: B. Stelzer, stelzer@xray.mpe.mpg.de
Received:
4
September
2000
Accepted:
26
July
2001
We report on a systematic search for X-ray emission from pre-main sequence
and young main sequence stars in the Taurus-Auriga-Perseus region.
Our stellar sample consists of all T Tauri stars from the
Taurus-Auriga region, and all late-type stars from the Pleiades and
Hyades clusters which have been observed by the ROSAT PSPC in pointed
observations.
We present the X-ray parameters for all observed stars
in tables. Next to the basic results of the data analysis
(such as count rates,
exposure time, and off-axis angle) we give X-ray luminosities and
hardness ratios for all detected stars. Upper limits are given for
non-detections. Detection rates for different spectral types are compiled.
We use these results to
study the connection between coronal X-ray activity and stellar parameters
for different subgroups of our sample. In particular we
compile X-ray luminosity functions (XLF),
and discuss the relations between X-ray emission and
spectral type, age, and rotation, which have been disputed extensively in
the past. Here, we study these questions with the largest sample so far.
The XLF for classical and weak-line T Tauri stars are different, with
weak-lines being the stronger X-ray emitters. Proceeding towards the
main-sequence (Pleiades, Hyades) the X-ray luminosity declines for all
spectral types examined (G, K, and M stars).
Within an age group Lx decreases towards later spectral types,
while 
remains constant or even increases,
reflecting the opposed influence of stellar radius, i.e. emitting area, and
convection zone depth. For
a given spectral type the fastest rotators show the highest X-ray luminosity.
Rotation rate and X-ray emission are clearly correlated for all groups of
stars with power law indices for 
versus 
of
~-0.7 to -1.5. The study of XLF for binary stars shows that
the known unresolved secondaries likely contribute a significant amount
to the X-ray emission.
Key words: X-rays: stars / stars: late-type / stars: pre-main sequence / stars: coronae / stars: activity
© ESO, 2001