Helium-like triplet density diagnostics

Abstract

Abstract. Electron density diagnostics based on the triplets of helium-like C v, N vi, and O vii are applied to the X-ray spectra of Capella and Procyon measured with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. New theoretical models for the calculation of the line ratios between the forbidden (f ), intercombination (i), and the resonance (r) lines of the helium-like triplets are used. The (logarithmic) electron densities (in cgs units) derived from the f/i ratios for Capella are < 9.38 cm −3 for O vii (2σ upper limit) (f/i = 4.0 ± 0.25), 9.86 ± 0.12 cm −3 for N vi (f/i = 1.78 ± 0.25), and 9.42 ± 0.21 cm −3 for C v (f/i = 1.48 ± 0.34), while for Procyon we obtain 9.28for N vi (f/i = 1.33 ± 0.28), and < 8.92 cm −3 for C v (f/i = 0.48 ± 0.12). These densities are quite typical of densities found in the solar active regions, and also pressures and temperatures in Procyon's and Capella's corona at a level of T ∼ 10 6 K are quite similar. We find no evidence for densities as high as measured in solar flares. Comparison of our Capella and Procyon measurements with the Sun shows little difference in the physical properties of the layers producing the C v, N vi, and O vii emission. Assuming the X-ray emitting plasma to be confined in magnetic loops, we obtain typical loop length scales of L Capella ≥ 8 LProcyon from the loop scaling laws, implying that the magnetic structures in Procyon and Capella are quite different. The total mean surface fluxes emitted in the helium-and hydrogen-like ions are quite similar for Capella and Procyon, but exceed typical solar values by one order of magnitude. We thus conclude that Procyon's and Capella's coronal filling factors are larger than corresponding solar values.

The weak-line T Tauri star V410 Tau

“…Other techniques, such as e.g. the comparison between the decay of X-ray light curves and hydrodynamic flare models (Stelzer et al 2002), or X-ray line analysis (Ness et al 2001), have also yielded loop sizes which are much smaller than the stellar radius.…”

X-ray spectroscopy of the W UMa-type binary 44 Bootis

“…The X-ray emission would originate from low-lying magnetic loops similar in size to those found in the solar corona, suggesting that 44 Boo corona has an apparence similar to the Sun's. Ness et al (2001) plotted a G vs. R diagram using solar observations of the OVII triplet in the quiescent corona (Freeman & Jones 1970;McKenzie et al 1978), in active regions (Parkinson 1975) and in flares (McKenzie et al 1982;Brown et al 1986). These authors found that most of the solar measurements yield R value between 3 and 4.…”

The corona of V390 Aurigae (HD 33798)

“…The emitting volume of the different plasma components could be constrained if their electron densities were known. These can be measured using density sensitive spectral lines originating from metastable levels, such as the forbidden (f) 2 3 S−1 1 S line in helium like ions (Ness et al 2001. This line and the associated resonance (r) 2 1 P−1 1 S and inter-combination (i) 2 3 P−1 1 S lines make up the so-called helium like triplet lines (Gabriel & Jordan 1969;Pradhan 1982).…”