SIMBAD references

2016ApJ...829...74W - Astrophys. J., 829, 74-74 (2016/October-1)

Hubble Space Telescope constraints on the winds and astrospheres of red giant stars.


Abstract (from CDS):

We report on an ultraviolet spectroscopic survey of red giants observed by the Hubble Space Telescope, focusing on spectra of the Mg ii h and k lines near 2800 Å in order to study stellar chromospheric emission, winds, and astrospheric absorption. We focus on spectral types between K2 III and M5 III, a spectral type range with stars that are noncoronal, but possessing strong, chromospheric winds. We find a very tight relation between Mg ii surface flux and photospheric temperature, supporting the notion that all K2-M5 III stars are emitting at a basal flux level. Wind velocities (Vw) are generally found to decrease with spectral type, with Vw decreasing from ∼40 km/s at K2 III to ∼20 km/s at M5 III. We find two new detections of astrospheric absorption, for σ Pup (K5 III) and γ Eri (M1 III). This absorption signature had previously only been detected for α Tau (K5 III). For the three astrospheric detections, the temperature of the wind after the termination shock (TS) correlates with Vw, but is lower than predicted by the Rankine-Hugoniot shock jump conditions, consistent with the idea that red giant TSs are radiative shocks rather than simple hydrodynamic shocks. A full hydrodynamic simulation of the γ Eri astrosphere is provided to explore this further.

Abstract Copyright: © 2016. The American Astronomical Society. All rights reserved.

Journal keyword(s): stars: chromospheres - stars: late-type - stars: winds, outflows - ultraviolet: stars - ultraviolet: stars

Simbad objects: 24

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