Colloquia

Olivia Mostow:  The Core-Cusp Problem in Low-Mass Galaxies: Is One Burst Enough? (15 minutes)

We present a novel method for assessing the ability of a single burst of star formation to transform dark matter cusps into cores in low-mass galaxies. Following the approach of Rose et al. 2022, we manually add a contribution to the potential that accounts for a centrally concentrated baryon component within an otherwise dark matter only simulation. This approach allows us to maintain control over how and when these bursts occur. We demonstrate that this method can reproduce the established result of core formation for systems that undergo multiple episodes of bursty outflows. In contrast, we find that equivalent models that undergo only a single (or small number) of burst episodes do not form cores with the same efficacy. This is important because many low-mass galaxies in the local universe are observed to have tightly constrained star formation histories that are best described by a single, early burst of star formation. Using a suite of cosmological, zoom-in simulations, we identify the regimes in which single bursts can and cannot form a cored density profile, and therefore, can or cannot resolve the core-cusp problem.

Sam Crowe:  Unveiling Massive Star Formation: Near-Infrared Observations of Protostellar Jets (15 Minutes)

Massive stars are significant throughout the universe, as they impact their surroundings from the early stages of their formation until they die in the form of supernova. Observations in the near-infrared (NIR) of the bright and large-scale (~parsec) jets that young stars ubiquitously produce during their formation process can place important constraints on the phenomenon of massive star formation. Here, I present a detailed NIR view of two massive star-forming complexes at opposite ends of the sky, AFGL 5180 and Sagittarius C, utilizing extremely high-resolution imaging from the Large Binocular Telescope, Hubble Space Telescope, and James Webb Space Telescope. In AFGL 5180, the data reveal several multidirectional outflows indicative of highly clustered star formation, confirmed by the detection of over a dozen compact sub-millimeter sources using data from the Atacama Large Millimeter/Submillimeter Array (ALMA). By sampling the number density of young stellar objects in the vicinity of the central massive (~12 Msun) protostar, and comparing with recent numerical simulations, we present a novel method for directly distinguishing between theories of massive star formation in situ. Conversely, in Sagittarius C, located in the turbulent and chaotic center of our Milky Way, we find relatively ordered and isolated massive star formation, evidenced by collimated and undisturbed NIR jets. We report the discovery of a new star-forming region ~1 arcminute to the west of Sagittarius C, hosting two prominent bow shocks visible in the NIR imaging, and characterize the most luminous protostar in each neighboring complex via ancillary ALMA data and Spectral Energy Distribution fitting, shedding light on how the process of massive star formation is unfolding in this extreme region.

Alex Rosenthal:  Mass-Loss Rates for Massive Stars from Stellar Bowshocks (15 Minutes)

Massive stars lose a significant portion of their mass through stellar winds over the course of their lifetime, and understanding the rate of mass-loss is critical for understanding stellar evolution and compact object genesis. Traditional methods of determining mass-loss rates rely on UV observations and parameterizing a “clumping” factor, which varies significantly and results in a two-order-of-magnitude difference between prediction and observation for stars with weak winds. We intend to address this “weak-wind problem” using a novel method to measure mass-loss rates of massive stars powering stellar bowshocks using optical spectroscopy of the central stars, far infrared measurements of the bowshock nebulae, and space velocities calculated from GAIA DR3 proper motions. This method utilizes the geometry of the bowshock and the principle of balancing the momentum flux between stellar winds and ambient interstellar material to make a mass-loss rate determination. We observed late-O and early-B type stars with bowshocks with the Apache Point Observatory 3.5m telescope with the KOSMOS long-slit spectrograph and the Wyoming Infrared Observatory’s 2.3m telescope with an optical spectrograph. We used the emcee package in Python and interpolated between models from the PoWR OB-I grid to fit their spectra to find temperatures and surface gravities. We found that our sample spanned a range of stellar parameters, with temperatures varying from 16,000-38,000 K and the log of surface gravity ranging from 2.8-4.1 dex. Using these parameters and photometric data, we calculated predicted mass-loss rates. This work is supported by the National Science Foundation under REU grant AST 1852289