Abstract

As binarity is a direct outcome of formation and evolution, studying multiplicity across all ranges of masses and separations is key to fully understand stellar formation mechanisms. In this talk, I will present results from campaigns compiled to investigate substellar binary statistics as a function of mass and age for the extreme low-mass end of the Initial Mass Function, and discuss the implications of the observed disparities for brown dwarf formation and evolution processes.

Abstract

NGC 6302, also known as "The Butterfly Nebula," is the dramatic creation of an intermediate-mass star (about 5 solar masses) in the throes of expelling its outer layers and producing a remarkable bi-lobe, narrow-waisted planetary nebula (PN). It is unique among PNe in displaying a dark lane cutting through its center, as discovered by UT's own David Evans. It possesses an extremely hot central star (T > 200,000 K), absorption in the H I 21 cm line, a luminous infrared torus, and an obscured central star. Currently, it is copiously spewing  both (O-rich) crystalline silicate dust and (C-rich) PAHs. I will show a few images from work in progress based on data from program JWST-GO-01742, as well as excerpts from a recent IGRINS-2 spectrum obtained during Science Verification on Gemini North that reveal the excitation and kinematics of H2 in the central regions.

Abstract

The Milky Way has a significant gradient in the abundance of metals, making the outer Galaxy an excellent laboratory to study the effects of lower metallicity. Values of Z (normalized to unity for the solar neighborhood) as low as 0.3 are known in HII regions in the outer Galaxy. Metallicity in the Galactic Center may be twice the local value. We are using this variation to study the effects of metallicity on disk fraction in clusters and on factors used to convert observations into mass. While gas to dust ratios and conversion factors from CO to mass and HCN to dense gas mass are usually taken to be constant, we find evidence for strong variations with Z and thus galactocentric radius. These variations affect estimates of masses of molecular and dense gas and predictions of star formation rates across the Galaxy. Studies in the Milky Way can inform analysis of other galaxies.

Abstract

Protostellar disks are expected to form early during the star formation process due to conservation of angular momentum throughout the collapse. While recent surveys by the Very Large Array (VLA) and the Atacama Large Millimeter/submillimeter Array (ALMA) have resolved disks around hundreds of nearby protostars, numerical simulations assuming ideal magnetohydrodynamics (MHD) have historically struggled to achieve disk formation – the “magnetic braking catastrophe.” Non-ideal MHD effects, which become relevant at the low ionization fractions typical of molecular clouds, have been shown to reduce the effectiveness of magnetic braking. However, most numerical studies of disk formation also adopt highly-idealized initial conditions of isolated, uniform-density spherical cores collapsing to form individual protostars. This setup may exaggerate the influence of magnetic braking. Furthermore, most stars are born as members of bound systems, and dynamical interactions between stellar neighbors likely affect subsequent disk evolution. It is therefore clear that a comprehensive study of disk formation and evolution must incorporate both external dynamics as well as increasingly sophisticated physics. In this talk, I will present the results from a suite of numerical calculations following the collapse of a turbulent, magnetized 50 solar-mass core down to the formation of stellar clusters and disks using the 3D radiation+gravity MHD code GIZMO, with additional modules for protostellar feedback developed within the STARFORGE numerical framework. These simulations aim to investigate the effects of including non-ideal MHD and realistic protostellar feedback on disk formation and evolution within the context of star cluster (rather than single-star) formation.

Abstract

Abstract

NASA's Kepler mission taught us that small close-in planets occur at a rate of ~1 per Sun-like star. Meanwhile, ground-based RV surveys have shown that long-period gas giants are rarer, with an occurrence rate of ~0.15 per Sun-like star. In January of 2024 I completed the Distant Giants Survey, a 3-year radial velocity (RV) survey to estimate the conditional occurrence of long-period Jupiter analogs in systems hosting small transiting planets. By searching for giant planets in systems with known close-in small planets, I found that giant planets are more common (~0.3 per star) when a close-in small planet is present. This finding will help to refine exoplanet formation models and determine whether the solar system's architecture is a common outcome of exosystem evolution.

Abstract

Stellar obliquity---the angle between a star's rotation axis and the orbital angular momentum vector of its planets---provides valuable insight into the formation and evolutionary history of planetary systems. However, it is unclear whether the origin of observed stellar obliquities is primordial (i.e., inherited from the protoplanetary disk) or generated by dynamical processes after the epoch of planet formation. We present the first comprehensive analysis of primordial stellar obliquities from an exhaustive compilation of young disk-bearing stars with resolved submillimeter imaging from ALMA together with new stellar inclination constraints using projected rotational velocities and stellar rotation periods. We find that modest levels of misalignment are common, which is consistent with a scenario of late anisotropic infall and delivery of a distinct source of angular momentum to the outer disk, perhaps along accretion streamers. These results contextualize the observed spin-orbit orientations of planetary systems, including the Solar System.