Department of Astronomy and Astrophysics

We describe the design and first-light early science performance of the Shane Adaptive optics infraRed Camera- Spectrograph (ShARCS) on Lick Observatory’s 3-m Shane telescope. Designed to work with the new ShaneAO adaptive optics system, ShARCS is capable of high-efficiency, diffraction-limited imaging and low-dispersion grism spectroscopy in J, H, and K-bands. ShARCS uses a HAWAII-2RG infrared detector, giving high quantum efficiency (>80%) and Nyquist sampling the diffraction limit in all three wavelength bands. The ShARCS instrument is also equipped for linear polarimetry and is sensitive down to 650 nm to support future visible-light adaptive optics capability. We report on the early science data taken during commissioning.

Using the Dark Energy Spectroscopic Instrument (DESI) Milky Way Survey, we examine the six-dimensional space of the anticenter region of the Milky Way stellar disk (150° < Galactic longitude < 220°) using 61,883 main-sequence turnoff stars. We focus on two well-known stellar overdensities in the anticenter: the Monoceros Ring (MRi) and Anticenter Stream (ACS). We find that the MRi overdensity has kinematic signatures consistent with a tidally induced spiral arm, a type of dynamic spiral arm created by an interaction with a satellite galaxy, most likely the Sagittarius dwarf spheroidal galaxy (Sgr). We use the kinematics of the MRi to calculate the two most recent passage times of Sgr, finding 0.25 ± 0.09 Gyr and 1.10 ± 0.23 Gyr from the present day. We validate that the ACS is kinematically decoupled from the MRi because they are moving in opposite radial and vertical directions. We find that the kinematics associated with the ACS extends beyond our defined overdensity. The features we see in the ACS region are likely part of a broader distribution of stars with the same kinematic signature as detected in other places, like the vertical wave in the outer disk and phase spiral.

The climate crisis and its attendant difficulties present more challenges than any single government, institution or individual can fix. From one perspective, universities and campus-community members have responded actively, creating new schools and centers, refocusing research, and doing their best to tackle the challenges of a warming world. More practically, however, current efforts are often a siloed mosaic of individual strategies. Time is of the essence – we must face the reality of almost certainly exceeding a 1.5° global temperature rise and potentially a 2.0° rise, if not more. This paper is a call for a more comprehensive, strategic, and coordinated response to the threat of climate change. This white paper presents a bird's-eye view of how a campus’s many components – administrators, faculty, staff, students, academic departments, interdisciplinary groups, operations units, and outreach services – can work together. Compiling the perspectives of United States and Canadian higher-education faculty and administrators from two workshops in 2024 and 2025, it highlights effective strategies and suggestions for expanded implementation, many without significant additional investment. This paper encourages a refocus of normal academic procedures like updating research goals and course curricula and an expansion into additional efforts. This conference synthesis and collection of current examples and opinions attempts to provide inspiring ideas, encouragement, and potential benefits to sustain readers as they work to create real-world change.

There are millions of undetected black holes wandering through our galaxy. Observatories like Chandra, LIGO, and more recently, Gaia, have provided valuable insights into the configurations of these elusive objects when residing in binary systems. Motivated by these advances, we study, for the first time, the enhanced accretion of metals from the interstellar medium (ISM) onto low-mass companions in binary systems with highly unequal mass ratios, utilizing a series of hydrodynamical simulations. Our study demonstrates that a stellar companion’s metal accretion history from the ISM alone, from its formation to the present, can significantly influence its surface abundance, especially when enhanced by a massive black hole companion. However, this effect is likely only measurable in stars that are still on the main sequence. Once a stellar companion evolves off the main sequence, similar to what has been observed with the Gaia BH3 companion, the initial dredge-up process is likely to erase any excess surface abundance resulting from the metals that were accreted. As we discover more unequal mass ratio binary systems, it is crucial to understand how the observed metallicity of Sun-like companions may differ from their birth metallicity, especially if they are not yet evolved.

We model the optical and infrared transient ZTF SLRN-2020, previously associated with a star-planet merger. We consider the scenario in which orbital decay via tidal dissipation led to the merger, and we find that tidal heating within the star was likely unobservable in the archival image of the system taken 12 yr before the merger. The observed dust formation months before the merger is consistent with a planet of mass Mp ≳ 5MJ ejecting material as it skims the stellar surface. This interaction gradually intensifies, leading to significant mass ejection on a dynamical timescale (≈hours) as the planet plunges into the stellar interior. Part of the recombination transient associated with this dynamical mass ejection might be inaccessible to the optical observations because its duration (≈hours) is comparable to the cadence. Correspondingly, the observed duration of the transient (≈100 days) is inconsistent with a single episode of dynamical mass ejection. Instead, the transient could be powered by the recombination of 3.4 × 10−5M⊙ of hydrogen in an outflow, or the contraction of an inflated envelope of mass ≈10−6M⊙ that formed during the merger. The observed ejecta mass 320 days after the peak of the optical transient is ≈1.3 × 10−4M⊙, consistent with the idea that a fraction of the ejecta might be unobservable in the light curve. Energetically, this post-merger ejecta mass suggests a planet at least as massive as Jupiter. Our results suggest that ZTF SLRN-2020 was the result of a merger between a star close to the main sequence and a planet with mass at least several times that of Jupiter.

Abstract The 2020 killing of George Floyd by officer Derek Chauvin sparked one of the largest protest movements in the United States. Chauvin was ultimately convicted of murder—a rare but necessary step to police officer accountability for wrongdoing. The media play an important role in framing the public's attitudes surrounding high‐profile cases involving police killings of unarmed civilians. The current study investigates media narratives surrounding the Floyd case for evidence of cultural violence, which occurs when direct, physical violence becomes institutionalized, accepted as normative, and legitimized. We looked for evidence of cultural violence across 300 articles from three U.S. newspapers (i.e., New York Times, Wall Street Journal, and The Star Tribune). We coded for cultural violence themes, which we operationalized as the seven mechanisms of moral disengagement, that is, the process of convincing oneself that ethical standards do not apply. Cultural violence was prevalent across all news outlets (i.e., it occurred in 88.9% of articles in the overall sample). These findings have implications for how media framing influences attitudes surrounding high‐profile police brutality cases involving Black victims, and psychological theory related to violence, morality, and racism. Public Significance Statement Media coverage of the killing of Black people by police shapes narratives of this violence. When media coverage engages in cultural violence—which occurs when direct violence becomes institutionalized, accepted as normative, and legitimized—it normalizes narratives of moral disengagement from the direct violence of the state killing Black people. Media interventions are needed to prevent this distancing, disengagement, and victim‐blaming.

We investigate the spatial distribution, kinematics, and metallicity of stars in the Draco dwarf spheroidal galaxy using data from the Dark Energy Spectroscopic Instrument (DESI). We identify 155 high-probability members of Draco using line-of-sight velocity and metallicity information derived from DESI spectroscopy along with Gaia Data Release 3 proper motions. We find a mean line-of-sight velocity of −290.62 ± 0.80 km s−1 with dispersion = 9.57−0.62+0.66 km s−1 and mean metallicity [Fe/H] = −2.10 ± 0.04, consistent with previous results. We also find that Draco has a steep metallicity gradient within the half-light radius, and a metallicity gradient that flattens beyond the half-light radius. We identify eight high-probability members outside the King tidal radius, four of which we identify for the first time. These extratidal stars are not preferentially aligned along the orbit of Draco. We compute an average surface brightness of 34.02 mag arcsec−2 within an elliptical annulus from the King tidal radius of 48 .′ 1–81′.

Once per ≈104–105 yr, an unlucky star may experience a close encounter with a supermassive black hole (SMBH), partially or fully tearing apart the star in an exceedingly brief, bright interaction called a tidal disruption event (TDE). Remnants of partial TDEs are expected to be plentiful in our Galactic center, where at least six unexplained, diffuse, star-like “G objects” have already been detected, which may have formed via interactions between stars and the SMBH. Using numerical simulations, this work aims to identify the characteristics of TDE remnants. We take 3D hydrodynamic FLASH models of partially disrupted stars and map them into the 1D stellar evolution code MESA to examine the properties of these remnants from tens to billions of years after the TDE. The remnants initially exhibit a brief, highly luminous phase, followed by an extended cooling period as they return to stable hydrogen burning. During the initial stage (≲105 yr) their luminosities increase by orders of magnitude, making them intriguing candidates to explain a fraction of the mysterious G objects. Notably, mild TDEs are the most common, and result in the brightest remnants during this initial phase. However, most remnants exist in a long-lived stage where they are only modestly offset in temperature and luminosity compared to main-sequence stars of equivalent mass. Nonetheless, our results indicate remnants will sustain abnormal, metal-enriched envelopes that may be discernible through spectroscopic analysis. Identifying TDE survivors within the Milky Way could further illuminate some of the most gravitationally intense encounters in the Universe.

We present a simulation of the time-domain catalog for the Nancy Grace Roman Space Telescope’s High-Latitude Time-Domain Core Community Survey. This simulation, called the Hourglass simulation, uses the most up-to-date spectral energy distribution models and rate measurements for 10 extragalactic time-domain sources. We simulate these models through the design reference Roman Space Telescope survey: four filters per tier, a five-day cadence, over 2 yr, a wide tier of 19 deg², and a deep tier of 4.2 deg², with ∼20% of those areas also covered with prism observations. We find that a science-independent Roman time-domain catalog, assuming a signal-to-noise ratio at a max of >5, would have approximately 21,000 Type Ia supernovae, 40,000 core-collapse supernovae, around 70 superluminous supernovae, ∼35 tidal disruption events, three kilonovae, and possibly pair-instability supernovae. In total, Hourglass has over 64,000 transient objects, 11,000,000 photometric observations, and 500,000 spectra. Additionally, Hourglass is a useful data set to train machine learning classification algorithms. We show that SCONE is able to photometrically classify Type Ia supernovae with high precision (∼95%) to a z > 2. Finally, we present the first realistic simulations of non-Type Ia supernovae spectral time series data from Roman’s prism.

Systems hosting multiple giant planets are important laboratories for understanding planetary formation and migration processes. We present a nearly decade-long Doppler spectroscopy campaign from the HIRES instrument on the Keck-I telescope to characterize the two transiting giant planets orbiting Kepler-511 on orbits of 27 days and 297 days. The radial velocity measurements yield precise masses for both planets: 0.10 0 − 0.039 + 0.036 (2.6σ) and 0.4 4 − 0.12 + 0.11 (4σ) Jupiter masses, respectively. We use these masses to infer their bulk metallicities (i.e., metal mass fraction 0.87 ± 0.03 and 0.22 ± 0.04, respectively). Strikingly, both planets contain approximately 25-30 Earth masses of heavy elements but have very different amounts of hydrogen and helium. Envelope mass loss cannot account for this difference due to the relatively large orbital distance and mass of the inner planet. We conclude that the outer planet underwent runaway gas accretion while the inner planet did not. This bifurcation in accretion histories is likely a result of the accretion of gas with very different metallicities by the two planets or the late formation of the inner planet from a merger of sub-Neptunes. Kepler-511 uniquely demonstrates how giant planet formation can produce dramatically different outcomes even for planets in the same system.