No first ionization potential fractionation in the active stars AR Piscium and AY Ceti

Abstract

Context. The comparison of coronal and photospheric abundances in cool stars is an essential question to resolve. In the Sun an enhancement of the elements with low first ionization potential (FIP) is observed in the corona with respect to the photosphere. Stars with high levels of activity seem to show a depletion of elements with low FIP when compared to solar standard values; however, the few cases of active stars in which photospheric values are available for comparison lead to confusing results, and an enlargement of the sample is mandatory for solving this longstanding problem. Aims. We calculate in this paper the photospheric and coronal abundances of two well known active binary systems, AR Psc and AY Cet, to get further insight into the complications of coronal abundances. Methods. Coronal abundances of 9 elements were calculated by means of the reconstruction of a detailed emission measure distribution, using a line-based method that considers the lines from different elements separately. Photospheric abundances of 8 elements were calculated using high-resolution optical spectra of the stars. Results. The results once again show a lack of any FIP-related effect in the coronal abundances of the stars. The presence of metal abundance depletion (MAD) or inverse FIP effects in some stars could stem from a mistaken comparison to solar photospheric values or from a deficient calculation of photospheric abundances in fast-rotating stars. Conclusions. The lack of FIP fractionation seems to confirm that Alfvén waves combined with pondermotive forces are dominant in the corona of active stars.

A Chandra/LETGS Survey of Main-sequence Stars

“…As for the abundance diagnostic, the solar corona and wind exhibit an abundance pattern where elements with low first ionization potential (FIP) have abundances that are enhanced relative to elements with high FIP (von Steiger et al 1995;Feldman & Laming 2000;Laming 2015). Similar "FIP effects" have been observed for some stellar coronae (Drake et al 1997;Laming & Drake 1999), but in other cases coronal abundances appear to be close to photospheric (Drake et al 1995;Audard et al 2001;Sanz-Forcada et al 2009). Finally, there are a number of cases where an "inverse FIP effect" is observed, where low-FIP elements are depleted relative to high-FIP elements Huenemoerder et al 2001;Audard et al 2003;Robrade & Schmitt 2005).…”

The Coronal Abundance Anomalies of M Dwarfs

“…One purpose of this figure is to demonstrate that even with a simpler FIP bias quantifier, with no attempt whatsoever to normalize to photospheric abundances, you can still see the same correlation in Figure 4b as in 4a, demonstrating that the FBST correlation is not a product of assumptions about photospheric abundances. Sanz-Forcada et al (2009) hypothesized that inverse FIP effects reported in the literature might be an artifact of assuming solar photospheric abundances for these stars, as none of these stars have measured photospheric abundances. However, the consistency the M dwarfs show with the overall spectral type dependence in Figure 4 would argue against this interpretation, as do observations of flares in such stars (e.g., EV Lac; Laming & Hwang 2009), where composition changes during the event, interpreted as the result of chromospheric evaporation, suggest a photospheric composition similar to that of the Sun.…”

Photospheric and coronal abundances in solar-type stars: the peculiar case ofτ Bootis

“…An intermediate activity star with an EMD similar to those of τ Boo, Eri, and κ 1 Cet, should display Ne/Fe ∼ 1. However, this scenario was constructed assuming stellar photospheric abundances similar to the solar ones -a common practice for many years -which has recently been challenged by studies where coronal abundances are compared to accurate measurements of stellar photospheric abundances: in most cases, this properly consistent comparison has shown little if any significant difference between photospheric and coronal compositions (Sanz-Forcada et al 2004;Maggio et al 2007;Sanz-Forcada et al 2009). …”