Search

We study transits of several ``hot Jupiter'' systems - including WASP-12 b, WASP-43 b, WASP-103 b, HAT-P-23 b, KELT-16 b, WD 1856+534 b, and WTS-2 b - with the goal of detecting tidal orbital decay and extending the baselines of transit times. We find no evidence of orbital decay in any of the observed systems except for that of the extensively studied WASP-12 b. Although the orbit of WASP-12 b is unequivocally decaying, we find no evidence for acceleration of said orbital decay, with measured $\ddot{P} = (-7 \pm 8) \times 10^{-14} \rm ~s^{-1}$, against the expected acceleration decay of $\ddot{P} \approx -10^{-23} \rm ~s^{-1}$. In the case of WD 1856+534 b, there is a tentative detection of orbital growth with $\dot{P} = (5.0 \pm 1.5) \times 10^{-10}$. While statistically significant, we err on the side of caution and wait for longer follow-up observations to consider the measured $\dot{P}$ real. For most systems, we provide a 95\%-confidence lower limit on the tidal quality factor, $Q_\star'$. The possibility of detecting orbital decay in hot Jupiters via long-term radial velocity (RV) measurements is also explored. We find that $\sim 1 \rm ~m~s^{-1}$ precision in RVs will be required to detect orbital decay of WASP-12 b with only 3 yr of observations. Currently available RV measurements and precision are unable to detect orbital decay in any of the systems studied here., Comment: 14 pages, 11 figures; Accepted in MNRAS on 2024 August 30. Received 2024 August 29; in original form 2024 February 13

We report the discovery of a high velocity, very low-mass star or brown dwarf whose kinematics suggest it is unbound to the Milky Way. CWISE J124909.08+362116.0 was identified by citizen scientists in the Backyard Worlds: Planet 9 program as a high proper motion ($\mu$ $=$ 0''9/yr) faint red source. Moderate resolution spectroscopy with Keck/NIRES reveals it to be a metal-poor early L subdwarf with a large radial velocity ($-$103$\pm$10 km/s), and its estimated distance of 125$\pm$8 pc yields a speed of 456$\pm$27 km/s in the Galactic rest frame, near the local escape velocity for the Milky Way. We explore several potential scenarios for the origin of this source, including ejection from the Galactic center $\gtrsim$3 Gyr in the past, survival as the mass donor companion to an exploded white dwarf. acceleration through a three-body interaction with a black hole binary in a globular cluster, and accretion from a Milky Way satellite system. CWISE J1249+3621 is the first hypervelocity very low mass star or brown dwarf to be found, and the nearest of all such systems. It may represent a broader population of very high velocity, low-mass objects that have undergone extreme accelerations., Comment: 17 pages, 3 figures, accepted for publication in Astrophysical Journal Letters

Globular clusters contain vast repositories of metal-poor stars that represent some of the oldest stellar generations in the Universe. The archaeological footprint of early Galactic evolution may be retained in the measurable properties of globular clusters, such as their ages, mass functions and chemical abundances. Until recently, all photometric studies of globular clusters were restricted to stellar members. Now, the sensitivity of JWST can extend this analysis to the substellar regime. If detected in sufficient numbers, brown dwarf members can provide tight constraints on the properties of their parent population. We present SANDee - a new grid of stellar models that accurately represent the color-magnitude diagrams of globular clusters across the hydrogen-burning limit at a wide range of metallicities. Using JWST NIRCam photometry and the new models, we identify three brown dwarfs in the globular cluster NGC 6397 with effective temperatures of 1300-1800 K, confirmed by both proper motion and model fitting. We use the observed luminosities of discovered brown dwarfs to obtain the first age estimate of a globular cluster from its substellar cooling sequence: 13.4 +/- 3.3 Gyr. We also derive the local mass function of the cluster across the hydrogen-burning limit and find it to be top-heavy, suggesting extensive dynamical evolution. We expect that the constraints on both age and mass function of NGC 6397 derived in this work can be greatly improved by a second epoch of NIRCam imaging in the same field., Comment: Accepted for publication in the Astrophysical Journal on 05/31/2024