STELLAR CORONAE, SOLAR FLARES: A DETAILED COMPARISON OF Σ GEM, HR 1099, AND THE SUN IN HIGH-RESOLUTION X-Rays

Abstract

The Chandra High Energy Transmission Grating Spectrometer (HETG) spectra of the coronally active binary stars σ Gem and HR 1099 are among the highest fluence observations for such systems taken at high spectral resolution in x-rays with this instrument. This allows us to compare their properties in detail to solar flare spectra obtained with the Russian CORONAS-F spacecraft's RESIK instrument at similar resolution in an overlapping bandpass. Here we emphasize the detailed comparisons of the 3.3-6.1Å region (including emission from highly ionized S, Si, Ar, and K) from solar flare spectra to the corresponding σ Gem and HR 1099 spectra. We also model the the larger wavelength range of the HETG, from 1.7-25Å-having emission lines from Fe, Ca, Ar, Si, Al, Mg, Ne, O, and N-to determine coronal temperatures and abundances. σ Gem is a single-lined coronally active long-period binary which has a very hot corona. HR 1099 is a similar, but shorter period, double-lined system. With very deep HETG exposures we can even study emission from some of the weaker species, such as K, Na, and Al, which are important since they have the lowest first ionization potentials, a parameter well known to be correlated with elemental fractionation in the solar corona. The solar flare temperatures reach ≈ 20 MK, comparable to the σ Gem and HR 1099 coronae. During the Chandra exposures, σ Gem was slowly decaying from a flare and its spectrum is well characterized by a collisional ionization equilibrium plasma with a broad temperature distribution ranging from 2-60 MK, peaking near 25 MK, but with substantial emission from 50 MK plasma. We have detected K XVIII and Na XI emission which allow us to set limits on their abundances. HR 1099 was also quite variable in x-rays, also in a flare state, but had no detectable K XVIII. These measurements provide new comparisons of solar and stellar coronal abundances, especially at the lowest FIP values. The low FIP elements do not show enhancement in the stellar coronae as they do in the Sun, except perhaps for K in σ Gem. While σ Gem and HR 1099 differ in their emission measure distributions, they have very similar elemental abundances.

Chandra X-ray study confirms that the magnetic standard Ap star KQ Vel hosts a neutron star companion

“…In this latter scenario, the unusually hard and luminous X-rays might be coronal in nature, arising from either one or both of the companions. However, the KQ Vel X-ray luminosity is 3-5 times greater than that of the stars II Peg (Testa et al 2004) or σ Gem (Huenemoerder et al 2013), which are considered strong coronal sources (D. Huenemoerder, priv. comm.…”

Laboratory Measurements of the K-Shell Transition Energies in L-Shell Ions of Si and S

“…Prominent absorption and emission X-ray features from highly charged silicon and sulfur ions have been detected and measured in a medley of celestial sources, including solar flares (Neupert 1971), other stellar coronae (e.g., Kastner et al 2002;Huenemoerder et al 2013), various types of active galactic nuclei (e.g., Lee et al 2001;Kaspi et al 2002;Kinkhabwala et al 2002;Holczer et al 2007;Holczer & Behar 2012;Reeves et al 2013), and high-mass X-ray binaries (HMXBs; e.g., Sako et al 2002;Boroson et al 2003;Watanabe et al 2006;Chang & Cui 2007;Hanke et al 2008;Miškovičová et al 2016). HMXBs, although well studied and cataloged, are not yet fully understood.…”

THE X-RAY LINE FEATURE AT 3.5 KeV IN GALAXY CLUSTER SPECTRA

“…Unfortunately, these authors have neglected the fact that this region has been seen with high spectral resolution in numerous solar flare spectra with temperatures up to 22 MK (1.9 keV) using the RESIK crystal spectrometer (Sylwester et al 2005(Sylwester et al , 2010b and in the spectra of a binary star system with an active corona (σ Gem) using the Chandra HETG spectrometer (Huenemoerder et al 2013a(Huenemoerder et al , 2013b. The RESIK observations have a spectral resolution of 11 eV (11.5 mÅ), and the Chandra HETG spectra a spectral resolution of 12 eV (12 mÅ).…”