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 $_{\rm orb}$ = 0.69 d) active binary ER Vul, which consists of two solar-like dwarfs with rotation rates $\sim$ 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 $\sim$ 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