arXiv subjects

Isabelle Winnick

Publications and source records attributed to Isabelle Winnick.

3 recordsLinked to original sources

arXiv2025

Giant Planets and Eccentric Orbits Are Common Around Galactic Thick Disc Stars

Planet formation in the Galactic thick disc is expected to be inefficient---low solid reservoirs, short disc lifetimes, and harsh irradiation environments should conspire to inhibit the assembly of planetary bodies---yet, planets are there, and they are stranger than we expected. Here, we present a homogeneous characterisation of 32 exoplanetary systems orbiting chemically and kinematically confirmed thick disc stars, combining new detections with a systematic reassessment of archival systems, increasing the total number of exoplanets orbiting thick disc stars to 66. When planets form in the thick disc, a notable fraction are giants and move on more eccentric orbits than their thin disc counterparts---two results that challenge standard disc-evolution models. However, this should be interpreted with caution given detection biases and sample size. We also report TOI-1927 b and TOI-2643 b, the first puffy, low-density giant planets known to orbit thick disc stars, unexpected in old, metal-poor environments where planets should cool and contract efficiently. Together, these findings reveal an early Milky Way far more hospitable to planetary diversity than its harsh conditions would initially suggest.

astro-ph.EP↗

arXiv2025

Extreme Lithium Depletion in Solar Twins: Challenging Non-Standard Mixing Models

Lithium (Li) is a powerful tracer of stellar mixing, gradually depleted in solar twins by non-standard transport below the convective zone. Here, we identify six new solar twins with exceptionally low Li levels that are not explained by current non-standard mixing models and, together with our previously reported anomalous solar twin HIP 8522, suggest a distinct population marked by a violent evolutionary past. Employing high-resolution spectra ($R=60,000 - 165,000$), we infer precise stellar parameters and chemical compositions, including Li abundances. We consider possible scenarios generating enhanced mixing, including planetary engulfment, blue straggler stars (BSSs), and early episodic accretion. Our planet engulfment simulations indicate that only one star may have engulfed an exoplanet, rapidly depleting Li via thermohaline convection. In the BSS scenario, radial velocity data rule out binary mass transfer, revealing no stellar companions but instead two new exoplanets. If these stars are field BSSs, a binary merger is likely though uncertain given that current BSS models focus mostly on stars in open clusters. Using pre-main-sequence episodic accretion models, we find that solar-mass stars can experience enhanced Li depletion without significant beryllium (Be) depletion. This is consistent with the Be abundances measured in two of our stars and represents the most plausible scenario, pending Be measurements for the remaining stars. These unique stars, together with HIP 8522, represent exceptional cases for testing stellar evolution models and probing internal mixing processes in Sun-like stars.

astro-ph.SR↗

arXiv2024

Searching for GEMS: TOI-5688 A b, a low-density giant orbiting a high-metallicity early M-dwarf

We present the discovery of a low-density planet orbiting the high-metallicity early M-dwarf TOI-5688 A b. This planet was characterized as part of the search for transiting giant planets ($R \gtrsim8$ M${}_\oplus$) through the Searching for GEMS (Giant Exoplanets around M-dwarf Stars) survey. The planet was discovered with the Transiting Exoplanet Survey Satellite (TESS), and characterized with ground-based transits from Red Buttes Observatory (RBO), the Table Mountain Observatory of Pomona College, and radial velocity (RV) measurements with the Habitable-Zone Planet Finder (HPF) on the 10 m Hobby Eberly Telescope (HET) and NEID on the WIYN 3.5 m telescope. From the joint fit of transit and RV data, we measure a planetary mass and radius of $124\pm24$ M$_\oplus$ ($0.39\pm0.07$ M${}_J$) and $10.4\pm0.7$ R$_\oplus$ ($0.92\pm0.06$ R${}_J$) respectively. The spectroscopic and photometric analysis of the host star TOI-5688 A shows that it is a metal-rich ([Fe/H] $ = 0.47\pm0.16$ dex) M2V star, favoring the core-accretion formation pathway as the likely formation scenario for this planet. Additionally, Gaia astrometry suggests the presence of a wide-separation binary companion, TOI-5688 B, which has a projected separation of $\sim5"$ (1110 AU) and is an M4V, making TOI-5688 A b part of the growing number of GEMS in wide-separation binary systems.

astro-ph.EP↗