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1. Spectroscopic Observations of Obscured Populations in the Inner Galaxy: 2MASS-GC02, Terzan 4, and the 200 km s ⁻¹ stellar peak*

   https://doi.org/10.3847/1538-3881/ac0888  

   Kunder, Andrea ; Crabb, Riley E. ; Debattista, Victor P. ; Koch-Hansen, Andreas J. ; Huhmann, Brianna M. ( August 2021 , The Astronomical Journal)
2. Measuring the Mass of the Large Magellanic Cloud with Stellar Streams Observed by S ⁵

   https://doi.org/10.3847/1538-4357/ac2e93  

   Shipp, Nora ; Erkal, Denis ; Drlica-Wagner, Alex ; Li, Ting S. ; Pace, Andrew B. ; Koposov, Sergey E. ; Cullinane, Lara R. ; Da Costa, Gary S. ; Ji, Alexander P. ; Kuehn, Kyler ; et al ( December 2021 , The Astrophysical Journal)

   Abstract Stellar streams are excellent probes of the underlying gravitational potential in which they evolve. In this work, we fit dynamical models to five streams in the Southern Galactic hemisphere, combining observations from the Southern Stellar Stream Spectroscopic Survey ( S 5 ), Gaia EDR3, and the Dark Energy Survey, to measure the mass of the Large Magellanic Cloud (LMC). With an ensemble of streams, we find a mass of the LMC ranging from ∼14–19 × 10 10 M ⊙ , probed over a range of closest approach times and distances. With the most constraining stream (Orphan–Chenab), we measure an LMC mass of 18.8 − 4.0 + 3.5 × 10 10 M ⊙ , probed at a closest approach time of 310 Myr and a closest approach distance of 25.4 kpc. This mass is compatible with previous measurements, showing that a consistent picture is emerging of the LMC’s influence on structures in the Milky Way. Using this sample of streams, we find that the LMC’s effect depends on the relative orientation of the stream and LMC at their point of closest approach. To better understand this, we present a simple model based on the impulse approximation and we show thatmore »the LMC’s effect depends both on the magnitude of the velocity kick imparted to the stream and the direction of this kick.« less
3. S ⁵ : The Orbital and Chemical Properties of One Dozen Stellar Streams

   https://doi.org/10.3847/1538-4357/ac46d3  

   Li, Ting S. ; Ji, Alexander P. ; Pace, Andrew B. ; Erkal, Denis ; Koposov, Sergey E. ; Shipp, Nora ; Da Costa, Gary S. ; Cullinane, Lara R. ; Kuehn, Kyler ; Lewis, Geraint F. ; et al ( March 2022 , The Astrophysical Journal)

   Abstract We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey ( S 5 ), proper motions from Gaia EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ∼10 and 50 kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwarf galaxies (DGs), while the other half originated from disrupted globular clusters (GCs), hereafter referred to as DG and GC streams. Based on the mean metallicities of the streams and the mass–metallicity relation, the luminosities of the progenitors of the DG streams range between those of Carina and Ursa Major I (−9.5 ≲ M V ≲ −5.5). Four of the six GC streams have mean metallicities of [Fe/H] < −2, more metal poor than typical Milky Way (MW) GCs at similar distances. Interestingly, the 300S and Jet GC streams are the only streams on retrograde orbits in our dozen-stream sample. Finally, we compare the orbital properties of the streams with known DGsmore »and GCs in the MW, finding several possible associations. Some streams appear to have been accreted with the recently discovered Gaia–Enceladus–Sausage system, and others suggest that GCs were formed in and accreted together with the progenitors of DG streams whose stellar masses are similar to those of Draco to Carina (∼10 5 –10 6 M ⊙ ).« less
4. Kinematics of Antlia 2 and Crater 2 from the Southern Stellar Stream Spectroscopic Survey (S ⁵ )

   https://doi.org/10.3847/1538-4357/ac1869  

   Ji, Alexander P. ; Koposov, Sergey E. ; Li, Ting S. ; Erkal, Denis ; Pace, Andrew B. ; Simon, Joshua D. ; Belokurov, Vasily ; Cullinane, Lara R. ; Da Costa, Gary S. ; Kuehn, Kyler ; et al ( October 2021 , The Astrophysical Journal)
5. Progress on nuclear reaction rates affecting the stellar production of ²⁶ Al

   https://doi.org/10.1088/1361-6471/ac9cf8  

   Laird, A M ; Lugaro, M ; Kankainen, A ; Adsley, P ; Bardayan, D W ; Brinkman, H E ; Côté, B ; Deibel, C M ; Diehl, R ; Hammache, F ; et al ( January 2023 , Journal of Physics G: Nuclear and Particle Physics)

   Abstract The radioisotope 26 Al is a key observable for nucleosynthesis in the Galaxy and the environment of the early Solar System. To properly interpret the large variety of astronomical and meteoritic data, it is crucial to understand both the nuclear reactions involved in the production of 26 Al in the relevant stellar sites and the physics of such sites. These range from the winds of low- and intermediate-mass asymptotic giant branch stars; to massive and very massive stars, both their Wolf–Rayet winds and their final core-collapse supernovae (CCSN); and the ejecta from novae, the explosions that occur on the surface of a white dwarf accreting material from a stellar companion. Several reactions affect the production of 26 Al in these astrophysical objects, including (but not limited to) 25 Mg( p , γ ) 26 Al, 26 Al( p , γ ) 27 Si, and 26 Al( n , p / α ). Extensive experimental effort has been spent during recent years to improve our understanding of such key reactions. Here we present a summary of the astrophysical motivation for the study of 26 Al, a review of its production in the different stellar sites, and a timely evaluation ofmore »the currently available nuclear data. We also provide recommendations for the nuclear input into stellar models and suggest relevant, future experimental work.« less