Detection of stellar-like abundance anomalies in the slow solar wind

TL;DR

This paper reports the discovery of rare inverse abundance anomalies in the slow solar wind, linking in-situ measurements to solar sources and supporting models of chromospheric wave-driven abundance variations, with implications for stellar winds.

Contribution

It introduces in-situ detection of inverse abundance anomalies in the slow solar wind, connecting these to solar sources and theoretical models, a novel approach in stellar wind studies.

Findings

Inverse events occur during high solar activity periods.

Detected anomalies support models of chromospheric wave-driven abundance variations.

Results suggest M-dwarf winds are plasma depleted in easily ionized elements.

Abstract

The elemental composition of the Sun's hot atmosphere, the corona, shows a distinctive pattern that is different than the underlying surface, or photosphere (Pottasch 1963). Elements that are easy to ionize in the chromosphere are enhanced in abundance in the corona compared to their photospheric values. A similar pattern of behavior is often observed in the slow speed (< 500 km/s) solar wind (Meyer 1985), and in solar-like stellar coronae (Drake et al. 1997), while a reversed effect is seen in M-dwarfs (Liefke et al. 2008). Studies of the inverse effect have been hampered in the past because only unresolved (point source) spectroscopic data were available for these stellar targets. Here we report the discovery of several inverse events observed in-situ in the slow solar wind using particle counting techniques. These very rare events all occur during periods of high solar activity that mimic conditions more widespread on M-dwarfs. The detections allow a new way of connecting the slow wind to its solar source, and are broadly consistent with theoretical models of abundance variations due to chromospheric fast mode waves with amplitudes of 8-10 km/s; sufficient to accelerate the solar wind. The results imply that M-dwarf winds are dominated by plasma depleted in easily ionized elements, and lend credence to previous spectroscopic measurements.