More Like this

1. Many Elements Matter: Detailed Abundance Patterns Reveal Star Formation and Enrichment Differences among Milky Way Structural Components

   https://doi.org/10.3847/1538-3881/adc07f  

   Griffith, Emily J; Hogg, David W; Hasselquist, Sten; Johnson, James W; Price-Whelan, Adrian; Sit, Tawny; Stone-Martinez, Alexander; Weinberg, David H (April 2025, The Astronomical Journal)

   Abstract Many nucleosynthetic channels create the elements, but two-parameter models characterized byαand Fe nonetheless predict stellar abundances in the Galactic disk to accuracies of 0.02–0.05 dex for most measured elements, near the level of current abundance uncertainties. It is difficult to make individual measurements more precise than this to investigate lower-amplitude nucleosynthetic effects, but population studies of mean abundance patterns can reveal more subtle abundance differences. Here, we look at the detailed abundances for 67,315 stars from the Apache Point Observatory Galactic Evolution Experiment (or APOGEE) Data Release 17, but in abundance residuals away from a best-fit two-parameter, data-driven nucleosynthetic model. We find that these residuals show complex structures with respect to age, guiding radius, and vertical action that are not random and are also not strongly correlated with sources of systematic error such as $\log \left(g\right)$ ,T_eff, and radial velocity. The residual patterns, especially in Na, C+N, Mn, and Ce, trace kinematic structures in the Milky Way, such as the inner disk, thick disk, and flared outer disk. A principal component analysis suggests that most of the observed structure is low-dimensional and can be explained by a few eigenvectors. We find that some, but not all, of the effects in the low-αdisk can be explained by dilution with fresh gas, so that the abundance ratios resemble those of stars with higher metallicity. The patterns and maps we provide can be combined with accurate forward models of nucleosynthesis, star formation, and gas infall to provide a more detailed picture of star and element formation in different Milky Way components. 

   more » « less
2. Extending the [C/N]–Age Calibration: Using Globular Clusters to Explore Older and Metal-poor Populations

   https://doi.org/10.3847/1538-3881/ae14ec  

   Spoo, Taylor; Thomas, Katelyn; Toguchi-Tani, Ellie Kaleo; Otto, Jonah; Myers, Natalie; Tayar, Jamie; Schonhut-Stasik, Jessica S; Shetrone, Matthew; Wiggins, Alessa Ibrahim; Donor, John; et al (November 2025, The Astronomical Journal)

   Abstract In the coming years, detailed chemical abundances from large-scale high-resolution spectroscopic surveys will become available for vast numbers of stars across the Milky Way. Previous work has suggested that abundance ratios from these spectra can allow us to estimate ages from a large number of stars. These data will be leveraged to calibrate chemical clocks to age-date field stars, as reliable stellar ages remain elusive. In this work, we extended our empirical relationship between stellar age and their carbon-to-nitrogen ([C/N]) abundance ratio for evolved stars to older and more metal-poor stars by combining the original open cluster calibration sample and four globular clusters: 47 Tuc, M 71, M 4, and M 5. With this extension, [C/N] can be used as a chemical clock for evolved field stars to investigate not only regions within the metal-rich disk but also more metal-poor regions of our Galaxy. We have established the [C/N]–age relationship for Apache Point Observatory Galactic Evolution Experiment (APOGEE) DR17 red giant stars, which have experienced the first dredge-up but have not yet undergone any extramixing, in clusters usable for ages between $8.62\le \log \left(\mathrm{Age}\right[\mathrm{yr}\left]\right)\le 10.13$ and for metallicities of −1.2 ≤ [Fe/H] ≤ +0.3. This relationship can be uniformly applied to these stars within the APOGEE DR17 sample. This measured [C/N]–age APOGEE DR17 relationship is also shown to be consistent with stellar ages derived from asteroseismic results of APOKASC and APO-K2. 

   more » « less
3. A Galactic Self-portrait: Density Structure and Integrated Properties of the Milky Way Disk

   https://doi.org/10.3847/1538-4357/adf723  

   Imig, Julie; Holtzman, Jon A; Zasowski, Gail; Lian, Jianhui; Boardman, Nicholas F; Stone-Martinez, Alexander; Mackereth, J Ted; Prescott, Moire_K M; Beaton, Rachael L; Beers, Timothy C; et al (September 2025, The Astrophysical Journal)

   Abstract The evolutionary history of the Milky Way disk is imprinted in the ages, positions, and chemical compositions of individual stars. In this study, we derive the intrinsic density distribution of different stellar populations using the final data release of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. A total of 203,197 red giant branch stars are used to sort the stellar disk (R≤ 20 kpc) into subpopulations of metallicity (Δ[M/H]  = 0.1 dex), age ( $\mathrm{\Delta }\log \left(\frac{\mathrm{age}}{\mathrm{yr}}\right)=0.1$ ), andα-element abundances ([α/M]). We fit the present-day structural parameters and density distribution of each stellar subpopulation after correcting for the survey selection function. The low-αdisk is characterized by longer scale lengths and shorter scale heights, and is best fit by a broken exponential radial profile for each population. The high-αdisk is characterized by shorter scale lengths and larger scale heights, and is generally well-approximated by a single exponential radial profile. These results are applied to produce new estimates of the integrated properties of the Milky Way from early times to the present day. We measure the total stellar mass of the disk to be $5.27_{-1.5}^{+0.2}\times 10^{10}$ M_⊙, and the average mass-weighted scale length isR_d = 2.37 ± 0.2 kpc. The Milky Way’s present-day color of (g − r) = 0.72 ± 0.02 is consistent with the classification of a red spiral galaxy, although it has only been in the “green valley” region of the galaxy color–mass diagram for the last ∼3 Gyr. 

   more » « less
4. κ Andromedae b Is a Fast Rotator from KPIC High-resolution Spectroscopy

   https://doi.org/10.3847/1538-3881/ad4ecf  

   Morris, Evan C; Wang_王, Jason_J 劲飞; Hsu, Chih-Chun; Ruffio, Jean-Baptiste; Xuan, Jerry W; Delorme, Jacques-Robert; Hood, Callie; Bryan, Marta L; Martin, Emily C; Pezzato, Jacklyn; et al (September 2024, The Astronomical Journal)

   Abstract We used the Keck Planet Imager and Characterizer to obtain high-resolution (R∼ 35,000)K-band spectra ofκAndromedae b, a planetary-mass companion orbiting the B9V star,κAndromedae A. We characterized its spin, radial velocity, and bulk atmospheric parameters through use of a forward-modeling framework to jointly fit planetary spectra and residual starlight speckles, obtaining likelihood-based posterior probabilities. We also detected H₂O and CO in its atmosphere via cross correlation. We measured a $v\sin \left(i\right)$ value forκAndromedae b of 38.42 ± 0.05 km s⁻¹, allowing us to extend our understanding of the population of close-in bound companions at higher rotation rates. This rotation rate is one of the highest spins relative to breakup velocity measured to date, at close to 50% of breakup velocity. We identify a radial velocity $-{17.35}_{-0.09}^{+0.05}$ km s⁻¹, which we use with existing astrometry and radial velocity measurements to update the orbital fit. We also measure an effective temperature of 1700 ± 100 K and a $\log \left(g\right)$ of 4.7 ± 0.5 cgs dex. 

   more » « less
5. ELemental abundances of Planets and brown dwarfs Imaged around Stars (ELPIS). I. Potential Metal Enrichment of the Exoplanet AF Lep b and a Novel Retrieval Approach for Cloudy Self-luminous Atmospheres

   https://doi.org/10.3847/1538-3881/acf768  

   Zhang 张, Zhoujian 周健; Mollière, Paul; Hawkins, Keith; Manea, Catherine; Fortney, Jonathan J.; Morley, Caroline V.; Skemer, Andrew; Marley, Mark S.; Bowler, Brendan P.; Carter, Aarynn L.; et al (October 2023, The Astronomical Journal)

   Abstract AF Lep A+b is a remarkable planetary system hosting a gas-giant planet that has the lowest dynamical mass among directly imaged exoplanets. We present an in-depth analysis of the atmospheric composition of the star and planet to probe the planet’s formation pathway. Based on new high-resolution spectroscopy of AF Lep A, we measure a uniform set of stellar parameters and elemental abundances (e.g., [Fe/H] = −0.27 ± 0.31 dex). The planet’s dynamical mass ( ${2.8}_{-0.5}^{+0.6}$ M_Jup) and orbit are also refined using published radial velocities, relative astrometry, and absolute astrometry. We usepetitRADTRANSto perform chemically consistent atmospheric retrievals for AF Lep b. The radiative–convective equilibrium temperature profiles are incorporated as parameterized priors on the planet’s thermal structure, leading to a robust characterization for cloudy self-luminous atmospheres. This novel approach is enabled by constraining the temperature–pressure profiles via the temperature gradient $\left(d\ln T/d\ln P\right)$ , a departure from previous studies that solely modeled the temperature. Through multiple retrievals performed on different portions of the 0.9–4.2μm spectrophotometry, along with different priors on the planet’s mass and radius, we infer that AF Lep b likely possesses a metal-enriched atmosphere ([Fe/H] > 1.0 dex). AF Lep b’s potential metal enrichment may be due to planetesimal accretion, giant impacts, and/or core erosion. The first process coincides with the debris disk in the system, which could be dynamically excited by AF Lep b and lead to planetesimal bombardment. Our analysis also determinesT_eff≈ 800 K, $\log \left(g\right)\approx 3.7$ dex, and the presence of silicate clouds and disequilibrium chemistry in the atmosphere. Straddling the L/T transition, AF Lep b is thus far the coldest exoplanet with suggested evidence of silicate clouds. 

   more » « less