Chandra HETGS and VLA Radio Observations of the Active Coronae
on the Short-Period Binary ER Vul (G0 V + G5 V)
Alexander Brown(CASA, University of Colorado) Rachel A. Osten, Thomas R. Ayres, Graham Harper (CASA, University of Colorado), Edward Guinan (Villanova University),
Abstract
We present results from a long (114 ksec) Chandra HETGS observation of
the short period (P
= 0.69 d)
active binary ER Vul, which consists of two solar-like dwarfs with
rotation rates
40 times that of the Sun. X-ray spectra were
obtained on 2001 March 29-30 along with 12 hours of simultaneous
VLA monitoring at 3.6 and 20 cm. The Chandra Medium Energy Grating
(MEG)
covers the wavelength range 1.8 - 25 Å in first order,
while the High Energy Grating (HEG) covers 1.8-18 Å.
ER Vul showed continuous low-level variability throughout the
observation with the largest flare peaking at slightly more than twice
the ``quiescent'' level. Contrary to the behaviour of most longer
period active binaries, no large, long-duration flares were detected,
consistent with previous X-ray observations of this binary.
The largest flare detected has a duration of only
30 minutes,
and appears to be very ``solar-like''.
Unfortunately this flare was not observed in the radio. The 20 cm radio
emission does show a highly polarized (LCP) flare that has at best only
a weak X-ray resonse. We characterise the flare-related
variability seen in the coronal line and continuum emission, place
limits on any orbital phase-related variability,
and quantify the quiescent coronal temperature and density
distributions.
CATEGORY: NORMAL STARS AND WHITE DWARFS