arXiv subjects

Julia Sheffler

Publications and source records attributed to Julia Sheffler.

2 recordsLinked to original sources

arXiv2026

A Multi-Method Age Determination for the Ursa Major Moving Group

The Ursa Major Moving Group (UMa) is one of the closest stellar associations, yet its age has remained controversial, with published estimates ranging from 200 Myr to 1 Gyr. We present a comprehensive age analysis using the largest sample of candidate UMa members to date. Using Gaia DR3, we identify 1172 stars within 100 pc of the Sun with 3D kinematic motions consistent with group membership. We determine the age of UMa's dominant population using three independent methods: lithium equivalent widths $(393.6^{+85.1}_{-80.9}\,\mathrm{Myr})$, gyrochronology $(428 \pm 93\,\mathrm{Myr})$, and photometric variability indicators $(449^{+114}_{-79}\,\mathrm{Myr})$. The three methods converge on a consistent age of $418^{+32}_{-34}\,\mathrm{Myr}$. While our kinematic selection includes field stars that share UMa's space motion but are not coeval members, the convergent age determinations clearly identify a dominant population that formed together approximately 400 Myr ago. These stars are important benchmarks for studies of stellar rotation, magnetic activity evolution, and lithium depletion. The presence of systems such as HD~63433, a young multiplanet host within the group, further illustrates the value of UMa as a laboratory for early planetary system evolution. Our expanded catalog of kinematic candidates lays the groundwork for spectroscopic membership confirmation, refined mapping of the group's structure and chemistry, and future investigations of both stellar and planetary evolution at this key epoch.

astro-ph.SR↗

arXiv2022

Combining Photometry and Astrometry to Improve Orbit Retrieval of Directly Imaged Exoplanets

Future missions like Roman, HabEx, and LUVOIR will directly image exoplanets in reflected light. While current near infrared direct imaging searches are only sensitive to young, self-luminous planets whose brightness is independent of their orbital phase, reflected light imaging will reveal changes in planet brightness over the course of an orbit due to phase variations. One of the first objectives will be determining the planet's orbit via astrometry, the projected position of the planet with respect to its host star in the sky plane. We show that phase variations can significantly improve the accuracy and precision of orbital retrieval with two or three direct images. This would speed up the classification of exoplanets and improve the efficiency of subsequent spectroscopic characterization. We develop a forward model to generate synthetic observations of the two dimensional position of the planet with respect to its host star on the sky plane, and the planet/star flux ratio. Synthetic data are fitted with Keplerian orbits and Henyey-Greenstein phase variations to retrieve orbital and phase parameters. For astrometric uncertainties of 0.01 AU in projected separation and flux ratio uncertainties of 10^-12, using photometry in orbit retrieval improves the accuracy of semi-major axis by 47% for two epochs and 61% for three epochs if the phase curves have a known shape, but unknown amplitude. In the more realistic scenario where the shape and amplitude of the phase curve are a priori unknown, photometry still improves accuracy by 16% for two epochs and 50% for three.

astro-ph.EP↗