The m-type STARS are becoming dominant targets in searches for earth-like planets that could occupy their habitable zones. The low masses and luminosities of m-dwarf central STARS make them very…

This federal contract award to The Regents of the University of Colorado, doing business as the University of Colorado Office of Contracts and Grants Division, is a $596,836.50 grant for research on the magnetic behavior and dynamo processes of M-type stars. The research aims to understand how these stars, which are becoming primary targets in the search for Earth-like exoplanets, can exhibit intense magnetic activity and flaring despite their modest luminosities. The award is funded by the National Aeronautics and Space Administration (NASA) and does not have a set-aside designation. As a leading public research university, the University of Colorado has extensive expertise in space physics, climate science, and other STEM disciplines that are relevant to this fundamental astrophysics study. The findings could provide important insights to support NASA's ongoing exoplanet detection and characterization efforts.

The m-type STARS are becoming dominant targets in searches for earth-like planets that could occupy their habitable zones. The low masses and luminosities of m-dwarf central STARS make them very attractive for such exoplanetary hunts. The habitable zone of m dwarfs is close to the star due to their low luminosity. Thus possibly habitable planets will have short orbital periods, making their detection feasible both with the transit method (used by kepler, K2 and soon with tess) and with the radial velocity approaches. Yet habitability on a planet likely requires both solid surfaces and atmospheres, but also a favorable radiation environment. IT is here that the m-dwarf central STARS raise major theoretical puzzles, for many of them exhibit remarkably intense and frequent flaring, despite their modest intrinsic luminosities. The super-flares release their energy both in white light and in x-rays, and can be thousands of times brighter than the strongest solar flares. Such striking events must have magnetic origins, likely from fields built by convective dynamos operating in their interiors. Further, recent observations suggest that the surface of some m STARS is carpeted with magnetic fields of 3 KG or more. Such field strengths are reminiscent of a sunspot, but here instead cover much of the stellar surface. With m STARS now taking center stage in the search for earth-like planets, IT is crucial to begin to understand how convective dynamos may be able to build intense magnetic fields involved with super-flares and vast star spots, and how they depend upon the mass and rotation rate of these STARS. We propose to use major 3-d MHD simulations with our anelastic spherical harmonic (ASH) code to study the coupling of turbulent convection, rotation, and magnetism within full spherical domains such as the interior of an m dwarf. This permits the exploration of the magnetic dynamos that must be responsible for the evolving magnetism and intense activity of many m dwarfs. We bring to this our prior experience with studying dynamo processes in the outer convective envelopes of g- (the sun) and f-type STARS, briefly of m dwarfs, and in full convective cores within more massive a- and b-type STARS. Our previous work suggests that m dwarfs could display a broad range of dynamo behavior, from cyclic reversals to more chaotic variations, and further to both weak and strong dynamo states. We will focus on the latter, exploring how super-equipartition magnetic fields could be achieved by dynamo action in m dwarfs, as are likely needed to energize super-flares and huge active regions, and what limits the peak field strengths. M-type STARS are distinctive in becoming fully convective with decreasing mass at about M3.5 in spectral type (or about 0.35 solar masses). At this transition, a steep rise in the fraction of magnetically active STARS is observed that is accompanied by an increasing rotational velocity. Clearly how mass-loss and spin-down can lead to this is of interest in itself. However, here we propose to study the manner in which dynamos operating in fully convective m dwarf interiors beyond the transition may be able to achieve very strong magnetic fields, and how field strengths and apparent magnetic activity increases with rotation rate as suggested by observations. We believe that global connectivity of flows and fields across the core center will admit new classes of strong behavior, as revealed by our b star core dynamos, not realized when a convective envelope is bounded below by a tachocline. These ideas need to be tested in a selfconsistent manner with global ASH simulations to gain theoretical insights into what is the origin of the fierce magnetic activity in some of m dwarfs that may be potential hosts to earth-like planets. Such 3-d MHD simulations, though challenging, are now feasible and would complement the intensive observational searches under way.