FUSE Observations of alpha Centauri B

Over the last several decades we have been carrying out a study of stellar magnetic activity, dynamos, atmospheric physics, and spectral irradiances from a sample of G0-5 V stars with different ages. One of the major goals of this program is to study the evolution of the Sun's X-ray through UV spectral irradiances with age. Of particular interest is the determination of the young Sun's high levels of high energy fluxes because of the critical roles that X-ray and FUV coronal through chromospheric emissions play on the photochemical and photoionization evolution (and possible erosion) of early young planetary atmospheres and ionospheres. Motivated by the upcoming exoplanetary search missions (Kepler, Eddington, SIM, Darwin/TPF) that will search for earth-size planets in the habitable zones of nearby G-M stars, we are extending this program to cooler, less luminous (but much more numerous) early K-type stars, such as alpha Centauri B. This program parallels our ``Sun in Time'’ program, but extends the study to stars with deeper convective zone depths.

Presented here are FUSE Cycle 7/8 observations of the K1 V star alpha Cen B (HD128621; V = 1.33; (B-V) = 0.88; tau = 5.5 Gyr). These recent observations are combined with the pre-existing Cycle 2 spectra to analyze temporal changes in its FUV emissions. We find that in this short span of five years alpha Cen B has exhibited significant variability in the key FUV fluxes, which may indicate an activity cycle. Examination of other high energy measures, such as X-ray (coronal; ROSAT, and XMM), UV (transition region; IUE), and NUV (chromospheric; IUE) emissions are also presented in order to obtain a more complete look into the nature of alpha Cen B's magnetic activity.

We gratefully acknowledge support by NASA Grants NNX06AC45G, NNX08AG95G, and the Villanova University Research for Undergraduates Award Program.