Judge, Philip

Contact Email: judge@ucar.edu
Institute: High Altitude Observatory
National Center for Atmospheric Research
First Coauthor: Steven Saar
Institute: Harvard Smithsonian Center for Astrophysics
Second Coauthor: Mats Carlsson
Institute: Institute for Theoretical Astrophyics, University of Oslo
Subject Area: Other (Please Specify Below)
Waveband: Ultraviolet
Technique: Spectroscopy
Other: Solar-stellar connection
Presentation: Poster Display
Title: Atmospheric Heating in a Very Inactive Star: $\tau$ Ceti Up Close
Abstract: To better understand the role of acoustic versus magnetic mechanisms in heating the chromospheres of solar-like stars, we observed the extremely inactive dwarf star $\tau$ Ceti (G8 V) with the STIS on HST. $\tau$ Ceti shows no cycling activity, and may be in a phase analogous to the solar Maunder minimum (making the STIS spectrum a proxy for the solar spectrum in this state). We analyze the $\tau$ Ceti spectrum, comparing line profiles with those of solar disk spectra from SUMER, and with synthetic data from time-dependent radiation hydrodynamic models. Accurate chromospheric line profiles can in principle reveal whether the stellar surface is dominated by upward propagating acoustic shocks (blue shifted emission) or by magnetic effects (red shifted emission, origin unknown). We also compare an emission measure analysis of the $\tau$Ceti spectra with results for solar data and more active G stars. We hope to clarify the source of the ``basal'' heating component. For example, lack of a significant acoustic signature in the spectra of $\tau$ Ceti would indicate that a small-scale local dynamo is largely responsible for the basal component of chromospheric heating.