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   Horch, Elliott P.; Broderick, Kyle G.; Casetti-Dinescu, Dana I.; Henry, Todd J.; Fekel, Francis C.; Muterspaugh, Matthew W.; Willmarth, Daryl W.; Winters, Jennifer G.; van Belle, Gerard T.; Clark, Catherine A.; et al (June 2021, The Astronomical Journal)

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2. Confronting Strange Stars with Compact-Star Observations and New Physics

   https://doi.org/10.3390/universe9050202  

   Yang, Shuhua; Pi, Chunmei; Zheng, Xiaoping; Weber, Fridolin (May 2023, Universe)

   Strange stars ought to exist in the universe according to the strange quark matter hypothesis, which states that matter made of roughly equal numbers of up, down, and strange quarks could be the true ground state of baryonic matter rather than ordinary atomic nuclei. Theoretical models of strange quark matter, such as the standard MIT bag model, the density-dependent quark mass model, or the quasi-particle model, however, appear to be unable to reproduce some of the properties (masses, radii, and tidal deformabilities) of recently observed compact stars. This is different if alternative gravity theory (e.g., non-Newtonian gravity) or dark matter (e.g., mirror dark matter) are considered, which resolve these issues. The possible existence of strange stars could thus provide a clue to new physics, as discussed in this review. 

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3. The Stars of the HETDEX Survey. I. Radial Velocities and Metal-poor Stars from Low-resolution Stellar Spectra

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   Hawkins, Keith; Zeimann, Greg; Sneden, Chris; Cooper, Erin Mentuch; Gebhardt, Karl; Bond, Howard E.; Carrillo, Andreia; Casey, Caitlin M.; Castanheira, Barbara G.; Ciardullo, Robin; et al (April 2021, The Astrophysical Journal)

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4. Observations of R-Process Stars in the Milky Way and Dwarf Galaxies

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5. The Galactic Distribution of Phosphorus: A Survey of 163 Disk and Halo Stars*

   https://doi.org/10.3847/1538-3881/ac77f8  

   Maas, Zachary G.; Hawkins, Keith; Hinkel, Natalie R.; Cargile, Phillip; Janowiecki, Steven; Nelson, Tyler (July 2022, The Astronomical Journal)

   Abstract Phosphorus (P) is a critical element for life on Earth, yet the cosmic production sites of P are relatively uncertain. To understand how P has evolved in the solar neighborhood, we measured abundances for 163 FGK stars over a range of –1.09 < [Fe/H] < 0.47 using observations from the Habitable-zone Planet Finder instrument on the Hobby–Eberly Telescope. Atmospheric parameters were calculated by fitting a combination of astrometry, photometry, and Fe I line equivalent widths. Phosphorus abundances were measured by matching synthetic spectra to a P I feature at 10529.52 Å. Our [P/Fe] ratios show that chemical evolution models generally underpredict P over the observed metallicity range. Additionally, we find that the [P/Fe] differs by ∼0.1 dex between thin disk and thick disk stars that were identified with kinematics. The P abundances were compared withα-elements, iron-peak, odd-Z, and s-process elements, and we found that the evolution of P in the disk most strongly resembles that of theα-elements. We also find that molar P/C and N/C ratios for our sample match the scatter seen from other abundance studies. Finally, we measure a [P/Fe] = 0.09 ± 0.1 ratio in one low-αhalo star and probable Gaia–Sausage–Enceladus member, an abundance ratio ∼0.3–0.5 dex lower than the other Milky Way disk and halo stars at similar metallicities. Overall, we find that P is likely most significantly produced by massive stars in core-collapse supernovae, based on the largest P abundance survey to date. 

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