Konkoly Observatory Budapest 17 June 2003 HU ISSN 0374 - 0676 (print) HU ISSN 1587 - 2440 (on-line) |
SIMBAD object(s):
Type(s):
ZAMS
Keyword(s):
stars: variability
Abstract:
We present evidence of X-ray rotational modulation on VXR45,
a young very fast rotator star member of IC2391 open cluster,
observed with XMM-Newton observatory.
VXR45 is a young very fast rotator star (RA (J2000) = 8h42m
14s.8, Dec (J2000) = -52°56'01", V=10.70, B-V=0.81,
photometric period =0.223 days (Patten & Simon, 1996)), member of IC2391
open cluster.
The observation has been performed in November 20, 2001
with EPIC/PN on XMM-Newton satellite and covers, almost continuously,
two photometric periods of VXR45.
We extracted photon counts from a circular region centered on the VXR45
and selected in order to include 80% of the source photons
(Ghizzardi, 2001; Saxon, 2002), corresponding to a radius of 37".
The total number of photon counts in the 0.3-7.8 keV band
amounts to 7431; the local background has been determined from a source-free
region near VXR45 for a total of 506 counts.
Fig. 1 shows the light-curve of VXR45 obtained in the 0.3-7.8 keV band
(top) and that of the corresponding background (bottom).
The X-ray rotational modulation, with a period very similar to the
photometric one, is clearly evident. Note that other short-term
variability not due to rotational modulation may also be present
in the light-curve.
Fig. 2 shows the X-ray light-curve folded with the photometric rotational
period. Phase-related variability is clearly evident; the amplitude of the
variations in the X-ray light-curve is ~30% of the average count-rate.
We find, for the first time, unambiguous evidence of rotational modulation
of X-ray stellar coronal emission in a very fast rotating star in the
``supersaturated'' regime.
The detection of X-ray rotational modulation implies the presence
of not uniformly distributed active regions on the star.
Furthermore we do not find evidence of spectral changes
as function of the phase, consistently with the hypothesis that the
modulation we observe is mainly due to a coverage
effect, and that at all times the emission is largely due to the same
mixture of emitting structures, probably composed by active regions hosting
several flares.
References:
Patten, B. M., & Simone, T., 1996, ApJS, 106, 489
(1996ApJS..106..489P)
Ghizzardi, S., 2001, ``EPIC-MCT-TN-011'', Tech. rep., EPIC Milano Calibration Team
Saxon, R. D., 2002, ``XMM-CCF-REL-116'', Tech. rep., XMM-SOC
X-ray light-curve of VXR45 (top) and
background (bottom) as seen with EPIC/PN in the 0.3-7.8 keV band,
time bins are 700 sec long. The photometric rotational period of
~ 19.3 ksec is well visible.
Folding of the X-ray data with the rotational
period versus photometric period phase. Circles are points observed at
t<0.223 days (the photometric period) and triangles those observed at
t>0.223 days.