This study presents a comprehensive chemodynamical analysis of LAMOST J1109+0754, a bright (V = 12.8), extremely metal-poor ([Fe/H] = −3.17) star, with a strong r-process enhancement ([Eu/Fe] = +0.94 ± 0.12). Our results are based on the 7D measurements supplied by Gaia and the chemical composition derived from a high-resolution (R ∼ 110,000), high signal-to-noise ratio ( optical spectrum obtained by the 2.4 m Automated Planet Finder Telescope at Lick Observatory. We obtain chemical abundances of 31 elements (from lithium to thorium). The abundance ratios ([X/Fe]) of the light elements (Z ≤ 30) suggest a massive Population III progenitor in the 13.4–29.5 M _⊙ mass range. The heavy-element (30 < Z ≤ 90) abundance pattern of J1109+075 agrees extremely well with the scaled-solar r-process signature. We have developed a novel approach to trace the kinematic history and orbital evolution of J1109+0754 with a cOsmologically deRIved timE-varyiNg Galactic poTential (the ORIENT) constructed from snapshots of a simulated Milky Way analog taken from the Illustris-TNG simulation. The orbital evolution within this Milky Way–like galaxy, along with the chemical abundance pattern, implies that J1109+0754 likely originated in a low-mass dwarf galaxy located ∼60 kpc from the center of the Galaxy, which was accreted ∼6–7 Gyr ago, and that the star now belongs to the outer-halo population.

We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of −3.3 < [Fe/H] < −2.4. These stars were selected from the LAMOST DR3 low-resolution (R ∼ 2000) spectroscopic database as metal-poor candidates and followed up with high-resolution spectroscopy (R ∼ 110,000) with the Lick/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114−0616, shows high enhancement in carbon ([C/Fe] = 1.37), nitrogen ([N/Fe] = 1.88), barium ([Ba/Fe] = 1.00), and europium ([Eu/Fe] = 0.84). Such chemical abundance pattern suggests that J2114−0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe] = 0.44 and [Ba/Fe] = −0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars show that J2114−0616 is member of the outer-halo population, while the remaining stars belong to the inner-halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.

We consider the existence of a neutron star magnetic field by the detected cyclotron lines. We collected data on nine sources of high-mass X-ray binaries with supergiant companions as a test case for our model, to demonstrate their distribution and evolution. The wind velocity, spin period and magnetic field strength are studied under different mass loss rates. In our model, correlations between mass-loss rate and wind velocity are found and can be tested in further observations. We examine the parameter space where wind accretion is allowed, avoiding the barrier of rotating magnetic fields, with robust data on the magnetic field of neutron stars. Our model shows that most sources (six of nine systems) can be fed by the wind with relatively slow velocity, and this result is consistent with previous predictions. In a few sources, our model cannot fit the standard wind accretion scenario. In these peculiar cases, other scenarios (disk formation, partial Roche lobe overflow) should be considered. This would provide information about the evolutionary tracks of various types of binaries, and thus exhibit a clear dichotomy behavior in wind-fed X-ray binary systems.