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1. Light elements Na and Al in 58 bulge spheroid stars from APOGEE

   https://doi.org/10.1093/mnras/stad2888  

   Barbuy, B; Friaça, A_C S; Ernandes, H; Moura, T; Masseron, T; Cunha, K; Smith, V V; Souto, D; Pérez-Villegas, A; Souza, S O; et al (September 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We identified a sample of 58 candidate stars with metallicity [Fe/H] ≲ −0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20 per cent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H] ≲ −1.0. For the lower-metallicity end ([Fe/H < −2.5), hypernovae are assumed to be the main contributor to yields. 

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2. CAPOS: the bulge Cluster APOgee Survey IV elemental abundances of the bulge globular cluster NGC 6558

   https://doi.org/10.1093/mnras/stad3178  

   González-Díaz, Danilo; Fernández-Trincado, José G; Villanova, Sandro; Geisler, Doug; Barbuy, Beatriz; Minniti, Dante; Beers, Timothy C; Moni Bidin, Christian; Mauro, Francesco; Muñoz, Cesar; et al (October 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT This study presents the results concerning six red giant stars members of the globular cluster NGC 6558. Our analysis utilized high-resolution near-infrared spectra obtained through the CAPOS initiative (the APOgee Survey of Clusters in the Galactic Bulge), which focuses on surveying clusters within the Galactic Bulge, as a component of the Apache Point Observatory Galactic Evolution Experiment II survey (APOGEE-2). We employ the Brussels Automatic Code for Characterizing High accUracy Spectra (BACCHUS) code to provide line-by-line elemental-abundances for Fe-peak (Fe, Ni), α-(O, Mg, Si, Ca, Ti), light-(C, N), odd-Z (Al), and the s-process element (Ce) for the four stars with high-signal-to-noise ratios. This is the first reliable measure of the CNO abundances for NGC 6558. Our analysis yields a mean metallicity for NGC 6558 of 〈[Fe/H]〉 = −1.15 ± 0.08, with no evidence for a metallicity spread. We find a Solar Ni abundance, 〈[Ni/Fe]〉 ∼ +0.01, and a moderate enhancement of α-elements, ranging between +0.16 and <+0.42, and a slight enhancement of the s-process element 〈[Ce/Fe]〉 ∼ +0.19. We also found low levels of 〈[Al/Fe]〉 ∼ +0.09, but with a strong enrichment of nitrogen, [N/Fe] > +0.99, along with a low level of carbon, [C/Fe] < −0.12. This behaviour of Nitrogen-Carbon is a typical chemical signature for the presence of multiple stellar populations in virtually all GCs; this is the first time that it is reported in NGC 6558. We also observed a remarkable consistency in the behaviour of all the chemical species compared to the other CAPOS bulge GCs of the same metallicity. 

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3. Cool stars in the Galactic center as seen by APOGEE: M giants, AGB stars, and supergiant stars and candidates

   https://doi.org/10.1051/0004-6361/202038327  

   Schultheis, M.; Rojas-Arriagada, A.; Cunha, K.; Zoccali, M.; Chiappini, C.; Zasowski, G.; Queiroz, A. B.; Minniti, D.; Fritz, T.; García-Hernández, D. A.; et al (October 2020, Astronomy & Astrophysics)

   The Galactic center region, including the nuclear disk, has until recently been largely avoided in chemical census studies because of extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), allow the measurement of metallicities in the inner region of our Galaxy. Making use of the latest APOGEE data release (DR16), we are able for the first time to study cool Asymptotic Giant branch (AGB) stars and supergiants in this region. The stellar parameters of five known AGB stars and one supergiant star (VR 5-7) show that their location is well above the tip of the red giant branch. We studied metallicities of 157 M giants situated within 150 pc of the Galactic center from observations obtained by the APOGEE survey with reliable stellar parameters from the APOGEE pipeline making use of the cool star grid down to 3200 K. Distances, interstellar extinction values, and radial velocities were checked to confirm that these stars are indeed situated in the Galactic center region. We detect a clear bimodal structure in the metallicity distribution function, with a dominant metal-rich peak of [Fe/H] ∼ +0.3 dex and a metal-poor peak around {Fe/H] = −0.5 dex, which is 0.2 dex poorer than Baade’s Window. The α -elements Mg, Si, Ca, and O show a similar trend to the Galactic bulge. The metal-poor component is enhanced in the α -elements, suggesting that this population could be associated with the classical bulge and a fast formation scenario. We find a clear signature of a rotating nuclear stellar disk and a significant fraction of high-velocity stars with v gal  >  300 km s −1 ; the metal-rich stars show a much higher rotation velocity (∼200 km s −1 ) with respect to the metal-poor stars (∼140 km s −1 ). The chemical abundances as well as the metallicity distribution function suggest that the nuclear stellar disk and the nuclear star cluster show distinct chemical signatures and might be formed differently. 

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4. The Chemodynamics of the Stellar Populations in M31 from APOGEE Integrated-light Spectroscopy

   https://doi.org/10.3847/1538-4357/acd9a9  

   Gibson, Benjamin J.; Zasowski, Gail; Seth, Anil; Ashok, Aishwarya; Goold, Kameron; Wainer, Tobin; Hasselquist, Sten; Holtzman, Jon; Imig, Julie; Bizyaev, Dmitry; et al (July 2023, The Astrophysical Journal)

   Abstract We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ∼7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [ α /M]. With this, we determine the mean kinematics, metallicities, α abundances, and ages of the stellar populations of M31's bar, bulge, and inner disk (∼4–7 kpc). We find a nonaxisymmetric velocity field in M31 resulting from the presence of a bar. The bulge of M31 is less metal-rich (mean [M/H] = − 0.149 − 0.081 + 0.067 dex) than the disk, features minima in metallicity on either side of the bar ([M/H] ∼ −0.2), and is enhanced in α abundance (mean [ α /M] = 0.281 − 0.038 + 0.035 ). The disk of M31 within ∼7 kpc is enhanced in both metallicity ([M/H] = − 0.023 − 0.052 + 0.050 ) and α abundance ([ α /M] = 0.274 − 0.025 + 0.020 ). Both of these structural components are uniformly old at ≃12 Gyr. We find the mean metallicity increases with distance from the center of M31, with the steepest gradient along the disk major axis (0.043 ± 0.021 dex kpc −1 ). This gradient is the result of changing light contributions from the bulge and disk. The chemodynamics of stellar populations encodes information about a galaxy’s chemical enrichment, star formation history, and merger history, allowing us to discuss new constraints on M31's formation. Our results provide a stepping stone between our understanding of the Milky Way and other external galaxies. 

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5. The Blanco DECam Bulge Survey (BDBS): VIII. Chemo-kinematics in the southern Galactic bulge from 2.3 million red clump stars with Gaia DR3 proper motions

   https://doi.org/10.1051/0004-6361/202347570  

   Marchetti, Tommaso; Joyce, Meridith; Johnson, Christian I; Rich, R Michael; Clarkson, William; Kunder, Andrea; Simion, Iulia T; Pilachowski, Catherine A (February 2024, Astronomy & Astrophysics)

   Context.The inner Galaxy is a complex environment, and the relative contributions of different formation scenarios to its observed morphology and stellar properties are still debated. The different components are expected to have different spatial, kinematic, and metallicity distributions, and a combination of photometric, spectroscopic, and astrometric large-scale surveys is needed to study the formation and evolution of the Galactic bulge. Aims.The Blanco DECam Bulge Survey (BDBS) provides near-ultraviolet to near-infrared photometry for approximately 250 million unique stars over more than 200 square degrees of the southern Galactic bulge. By combining BDBS photometry with the latestGaiaastrometry, we aim to characterize the chemodynamics of red clump stars across the BDBS footprint using an unprecedented sample size and sky coverage. Methods.Our field of view of interest is |ℓ| ≤ 10°, −10° ≤b ≤ −3°. We constructed a sample of approximately 2.3 million red clump giants in the bulge with photometric metallicities, BDBS photometric distances, and proper motions. Photometric metallicities are derived from a (u − i)₀versus [Fe/H] relation; astrometry, including precise proper motions, is from the third data release (DR3) of the ESA satelliteGaia. We studied the kinematics of the red clump stars as a function of sky position and metallicity by investigating proper-motion rotation curves, velocity dispersions, and proper-motion correlations across the southern Galactic bulge. Results.By binning our sample into eight metallicity bins in the range of −1.5 dex < [Fe/H] < +1 dex, we find that metal-poor red clump stars exhibit lower rotation amplitudes, at ∼29 km s⁻¹kpc⁻¹. The peak of the angular velocity is ∼39 km s⁻¹kpc⁻¹for [Fe/H] ∼ −0.2 dex, exhibiting declining rotation at higher [Fe/H]. The velocity dispersion is higher for metal-poor stars, while metal-rich stars show a steeper gradient with Galactic latitude, with a maximum dispersion at low latitudes along the bulge minor axis. Only metal-rich stars ([Fe/H] ≳ −0.5 dex) show clear signatures of the bar in their kinematics, while the metal-poor population exhibits isotropic motions with an axisymmetric pattern around Galactic longitudeℓ = 0. Conclusions.This work describes the largest sample of bulge stars with distance, metallicity, and astrometry reported to date, and shows clear kinematic differences with metallicity. The global kinematics over the bulge agrees with earlier studies. However, we see striking changes with increasing metallicity, and, for the first time, kinematic differences for stars with [Fe/H]>  − 0.5, suggesting that the bar itself may have kinematics that depends on metallicity. 

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