Long-Term Variability of Magnetic Structures on BD +26 730
Abstract
BD +26 730 , a rapidly rotating, BY Dra variable, is one of the most magnetically active K dwarfs known, and is the most active of the few stars with a known magnetic cycle period. The star is viewed nearly poleon; thus, almost all variability results from the evolution of activity in time, rather than rotational modulation. Direct measurement of the magnetic field strength and area coverage of plages on the star is possible. BD +26*730 thus presents a unique opportunity for observing long-term, purely temporal variability due to a magnetic cycle. IUE observations at two epochs already exist. We propose to continue monitoring the longterm variability of this star, now nearing starspot (and magnetic activity) maximum, with IUE in order to study the time-variability of the chromospheric and transition-region activity on long time-scales. Contemporaneous photometry, optical spectra, linear polarization, and magnetic line broadening measurements will be combined with the IUE data to explore the connections between photospheric magnetic fields, and the structure and energy balance of the hot, upper-atmospheric layers of the star. Comparison of the UV fluxes with earlier epoch IUE spectra, some taken near activity minimum, will allow us to investigate differences in stellar activity over the magnetic cycle of the star, yielding fundamental data on the behavior of stellar dynamos at high activity levels. Our study will be the first investigation of strictly temporal evolution of magnetic fields and related activity over the activity cycle on a star other than the Sun.
- Publication:
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IUE Proposal
- Pub Date:
- 1991
- Bibcode:
- 1991iue..prop.4028S