Earth and Planetary Astrophysics (astro-ph.EP)

Abstract: The term `$\alpha$-meteoroid' was introduced to describe a group of micrometeoroids with certain dynamical properties, which -- alongside the group of the $\beta$-meteoroids -- had been identified by the first generation of reliable in-situ dust detectors in interplanetary space. In recent years, use of the term $\alpha$-meteoroid has become more frequent again, under a subtly but crucially altered definition. This work shall bring attention to the discrepancy between the term's original and newly established meaning, and spotlight the now-overlooked group of particles that the term used to describe. We review past and present pertinent literature around the term $\alpha$-meteoroid, and assess the dynamics of the originally referred-to particles with respect to possible sources, showing that their formation is the expected consequence of collisional grinding of the zodiacal cloud at short heliocentric distances. The abundance of the original $\alpha$-meteoroids, which are essentially `bound $\beta$-meteoroids', makes them relevant to all in-situ dust experiments in the inner solar system. Due to the change of the term's meaning, however, they are not considered by contemporary studies. The characterization of this particle population could elucidate the processing of the innermost zodiacal cloud, and should thus be objective of upcoming in-situ dust experiments. The attained ambiguity of the term $\alpha$-meteoroid is not easily resolved, warranting great care and clarity going forward.

Abstract: We combine Hubble Space Telescope (HST) Fine Guidance Sensor, Hipparcos, and Gaia DR3 astrometric observations of the K0 V star 14 Her with the results of an analysis of extensive ground-based radial velocity data to determine perturbation orbits and masses for two previously known companions, 14 Her b and c. Radial velocities obtained with the Hobby-Eberly Telescope and from the literature now span over twenty five years. With these data we obtain improved RV orbital elements for both the inner companion, 14 Her b and the long-period outer companion, 14 Her c. We also find evidence of an additional RV signal with P $/sim$ 3789d. We then model astrometry from Hipparcos, HST, and Gaia with RV results to obtain system parallax and proper motion, perturbation periods, inclinations, and sizes due to 14 Her b and c. We find P_b = 1767.6 +/- 0.2 d, perturbation semi-major axis {\alpha}_b = 1.3 +/- 0.1 mas, and inclination i_b = 36 +/- 3 degrees, P_c = 52160 +/- 1028 d, perturbation semi-major axis {\alpha}_c = 10.3 +/- 0.7 mas, and inclination i_c = 82 +/- 14 degrees. In agreement with a past investigation, the 14 Her b, c orbits exhibit significant mutual inclination. Assuming a primary mass M = 0.98 +/- 0.04Msun, we obtain companion masses M_b = 8.5 +/- 1.0Mjup and M_c = 7.1 +/- 1.0Mjup.