On an Emerging Paradigm of Tepid Stars: Assessing the Magnetic Desert and the Magnetic Origin of Surprisingly Common Star Spots

Abstract

The past decade has seen several significant shifts in the field of stellar magnetism, particularly on the observational front. A new generation of dramatically more efficient, high-resolution spectropolarimetric instruments have enabled measurements of magnetic fields hosted by intermediate mass stars to be obtained with unprecedented precision. Moreover, the Kepler and TESS spacecraft have yielded optical light curves that are sensitive to flux variations on the order of parts per million. Both of these advancements have facilitated potentially paradigm shifting discoveries including (1) the emerging picture of a "magnetic dichotomy" in which the magnetic fields hosted by a small fraction of intermediate mass stars are either very prominent (B > 200 G) or ultra-weak (B < 1 G); and (2) that a large fraction of these tepid stars may not be as quiescent as previously believed, as demonstrated by the surprising detection of variability that is consistent with rotational modulation, which is interpreted to be a consequence of magnetic activity. In this thesis, I will present the results obtained from three related studies that have expanded upon these recent discoveries. The first study was designed to test the validity of the magnetic dichotomy and elaborate on properties of the "strong field" population of stars by carrying out a volume-limited survey of magnetic intermediate mass stars within 100 pc. The second study focuses on the unexpected result obtained using Kepler -- the widespread detection of rotationally modulated light curves of A- and B-type stars -- which suggests that a much larger fraction of intermediate mass stars than has previously been believed may be magnetic. The third study consists of a search for A-type stars that exhibit similar rotational modulation in their light curves obtained with the recently launched TESS spacecraft.