Short-Term Chromospheric Variability in alpha Tauri (K5 III): Results from IUE Time Series Observations

Details Short-Term Chromospheric Variability in alpha Tauri (K5 III): Results from IUE Time Series Observations Short-Term Chromospheric Variability in alpha Tauri (K5 III): Results from IUE Time Series Observations

Jun 1996

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996apj...464..426c&link_type=abstract

Astrophysical Journal v.464, p.426

Astronomy and Astrophysics

Astronomy

4

Stars: Chromospheres, Stars: Activity, Stars: Individual Constellation Name: Alpha Tauri, Stars: Late-Type, Ultraviolet: Stars

Scientific paper

We evaluate time series observations of chromospheric lines (Mg II, Mg I, and C II) for the K giant α Tau obtained using the IUE LWP camera at high dispersion. These observations cover a time span of about 2 weeks in 1994 February-March and were designed to resolve variations occurring within hours, days, and weeks. We consider the observational results in relation to theoretical acoustic heating models, motivated by the fact that αTau may exhibit a basal (i.e., minimum) level of chromospheric activity. The data reveal flux variations between the extremes of 8% in Mg II h + k and 15% in each emission component. These variations occur on timescales as short as 8 hr but not on timescales longer than ˜3 days. For the h and k components, flux variations occurring on a timescale as short as 1.5 hr are also found. These changes are often not correlated (and are sometimes even anticorrelated), leading to remarkable differences in the h/k ratios. We argue that these results are consistent with the presence of strong acoustic shocks, which can lead to variable Mg II line emission when only a small number of strong shocks are propagating through the atmosphere. We deduce the electron density in the C II] λ2325 line formation region to be log Ne ≃ 9.0, in agreement with previous studies. Our data provide evidence that the Mg II basal flux limit for K giants might be a factor of 4 higher than suggested by Rutten et al.

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