2021AJ....162..120G

HST UV spectra were obtained to study whether the φ Leo system has one or more stellar companions, as shown for the A-star dwarf, HR10, stellar pulsation, or transiting exocomets. During five partial HST observation sets spread over 13 months, redshifted gas with radial velocities up to +245 km s^–1 was observed on one occasion, with lower velocity infalling material seen twice. Blueshifted gas features with velocities as high as -150 km s^–1 with up to three features in two spectra were also seen. Low-mass stellar companions to late A stars are coronal sources. Assuming an age of 450 Myr, G-K companions to φ Leo, and multiple M-star companions would have been detected in the ROSAT All-Sky Survey data, but are not seen. Further, the star shows only 1 major pulsation component, suggesting it is single, excluding an A- or early F-star companion. Low covering factor absorption features with |v| <= 200 km s^–1 have been reported in optical spectra with variation on timescales consistent with nonradial pulsation. However, the highest velocity infall feature has a broader, continuous absorption profile extending from the stellar velocity to +245 km s^–1, with a covering factor of ∼25% which is more consistent with a transit by a body on a star-grazing orbit.