Magnetic Activity in Very Late M Dwarfs: Enhanced or Reduced?
Abstract
The degree of magnetic activity on very late M dwarfs (roughly dM5 and later) is currently very uncertain. This is because there is very little data, and because the few observations that do exist are contradictory. Optical observations suggest both enhanced and reduced levels of chromospheric activity. An apparent drop-off in coronal heating for stars cooler than B-V - 1.7 (spectral type M4-M5) largely disappears if the quantity Lx/Lbol is considered, rather than Lx. Since stars this late are believed to be fully convective, and since many theoretical solar and stellar dynamo models postulate magnetic flux generation or amplification at the base of the convective zone, a reduction in all magnetically induced phenomena might be expected. Low dispersion, short wavelength IUE observations of the transition region lines of eight nearby, very late, single M dwarfs represents perhaps the most efficient way to resolve this uncertainty. This study extends previous survey work on M dwarfs to the coolest spectral types. Except for the particularly active late M stars Prox Cen and UV Cet, there are no short wavelength IUE observations in this part of the HR diagram.
- Publication:
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IUE Proposal
- Pub Date:
- 1985
- Bibcode:
- 1985iue..prop.2173L