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ABSTRACT Previous results in the literature have found the young inner-disc open cluster NGC 6705 to be mildly α-enhanced. We examined this possibility via an independent chemical abundance analysis for 11 red-giant members of NGC 6705. The analysis is based on near-infrared APOGEE spectra and relies on LTE calculations using spherical model atmospheres and radiative transfer. We find a mean cluster metallicity of $$\rm [Fe/H] = +0.13 \pm 0.04$$, indicating that NGC 6705 is metal-rich, as may be expected for a young inner-disc cluster. The mean α-element abundance relative to iron is $$\rm \langle [\alpha /Fe]\rangle =-0.03 \pm 0.05$$, which is not at odds with expectations from general Galactic abundance trends. NGC 6705 also provides important probes for studying stellar mixing, given its turn-off mass of M ∼ 3.3 M⊙. Its red giants have low 12C abundances ([12C/Fe] = −0.16) and enhanced 14N abundances ([14N/Fe] = +0.51), which are key signatures of the first dredge-up on the red giant branch. An additional signature of dredge-up was found in the Na abundances, which are enhanced by [Na/Fe] = +0.29, with a very small non-LTE correction. The 16O and Al abundances are found to be near-solar. All of the derived mixing-sensitive abundances are in agreement with stellar models of approximately 3.3 M⊙ evolving along the red giant branch and onto the red clump. As found in young open clusters with similar metallicities, NGC 6705 exhibits a mild excess in the s-process element cerium with $$\rm [Ce/Fe] = +0.13\pm 0.07$$.
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ACACIAS I: element abundance labels for 192 stars in the dwarf galaxy NGC 6822
ABSTRACT The element abundances of local group galaxies connect enrichment mechanisms to galactic properties and serve to contextualize the Milky Way’s abundance distributions. Individual stellar spectra in nearby galaxies can be extracted from integral field unit (IFU) data, and provide a means to take an abundance census of the local group. We introduce a programme that leverages $R=1800$, $$\mathrm{SNR}=15$$, IFU resolved spectra from the multi unit spectroscopic explorer . We deploy the data-driven modelling approach for labelling stellar spectra with stellar parameters and abundances, of The Cannon, on resolved stars in NGC 6822. We construct our model for The Cannon using $$\approx$$19 000 Milky Way lamost spectra with apogee labels. We report six inferred abundance labels (denoted $$\ell _\mathrm{X}$$), for 192 NGC 6822 disc stars, precise to $$\approx$$0.15 dex. We validate our generated spectral models provide a good fit to the data, including at individual atomic line features. We infer mean abundances of $$\ell _\mathrm{[Fe/H]} = -0.90 \pm 0.03$$, $$\ell _\mathrm{[Mg/Fe]} = -0.01 \pm 0.01$$, $$\ell _\mathrm{[Mn/Fe]} = -0.22 \pm 0.02$$, $$\ell _\mathrm{[Al/Fe]} = -0.33 \pm 0.03$$, $$\ell _\mathrm{[C/Fe]} =-0.43 \pm 0.03$$, $$\ell _\mathrm{[N/Fe]} =0.18 \pm 0.03$$. These abundance labels are similar to those of dwarf galaxies observed by apogee, and the lower enhancements for NGC 6822 compared to the Milky Way are consistent with expectations. This approach supports a new era in extragalactic archaeology of characterizing the local group enrichment diversity using low-resolution, low signal to noise ratio IFU resolved spectra. Furthermore, we conclude that it is feasible to build a model based on spectra observed with one instrument and apply it to spectra obtained with another.
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- Award ID(s):
- 2206264
- PAR ID:
- 10571959
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 537
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 2798-2818
- Size(s):
- p. 2798-2818
- Sponsoring Org:
- National Science Foundation
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