Nicole's second paper calibrates [C/N] as an age clock for giant stars. It works well for lower RGB stars with [Fe/H] > -1 between 2-10 Gyr, but breaks down at young and old extremes and for upper RGB and RC stars where extra mixing scrambles the signal. arxiv.org/abs/2609.21928 ☄️🔭
![Comparison between the predicted and observed trends of [C/N] as a function of the logarithm of stellar age. The data consist of Kepler stars (LRGB, URGB,RC) divided into three bins of [Fe/H]. Filled circles represent stars within ±0.1 dex of the corresponding model [Fe/H]. Theoretical models from Lagarde et al. (2012) are shown for three metallicity Z values. The curves represent models with standard prescription (S, solid line) and rotation-induced mixing and thermohaline instability (R, dot-dashed line). Black points on the model curves indicate the values corresponding to stellar masses of 1, 1.5, 2, 2.5𝑀⊙.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreibdqbo554cpjksymrfjr4inyxbrjugqhd6l36clioo2eb2nvdbnby)
![P abundances as a function of metallicity for our sample compared to literature measurements. Literature data from multiple studies are shown in blue, while the re-analyzed Z.G. Maas et al. (2022) sample is shown in gray, and results from this work are shown in black. For the abundances derived in this study, filled circles denote abundance detections, while inverted triangles indicate upper limits. The scaled Galactic chemical evolution model of G. Cescutti et al. (2012), multiplied by a factor of 2.75 in [P/Fe], is shown as a dashed red curve. The distribution of literature sources is indicated in the legend. Representative median uncertainties for this work and the literature are shown in the lower-left corner.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreigvxizmt2yuzmbqjmiuqjdyhljkja7rb2ybgf6yrj4xmjdkbamfwe)
![Fig 2 (left) and 5 (right) : Fig. 2 : Toomre diagram for the MSTO sample colour-coded by metallicity. The candidate star is highlighted with a star symbol. The dashed curves indicate the kinematic loci commonly used to distinguish thin-disc, thick-disc, and halo populations based on total velocity with respect to the LSR. Fig. 5: Distribution of the MSTO sample in the [Al/Fe]-[Mg/Mn] plane, colour-coded by metallicity. The black solid lines indicate the empirical separation between Galactic components proposed by Alinder et al. (2026). The candidate is marked with a star symbol.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreih7rxafw72ko5t7tjfvzslwc4radgnzxpp5hcnaszjttv3the2yoq)
![Variations in the decoded rest-frame SED when varying one latent eight times with all the others fixed. A different latent is traversed in each panel from top to bottom. The left panel displays the full SED while the right panel zooms into the [O ii], [O iii], H β, and H α regions. The first two and last two columns share a 𝑦-axis range. The different latents are ranked by their relative effect on the spectrum.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreie5ro252vsifrt4ix3vla3vso6c43wycgctfyrz6kzgpubarsx5xm)
![Images of W2246f and its companion galaxy to the North-West, extracted from the MUSE datacube. On the left is the white light image showing the stellar continuum. In the middle is an RGB image with the Hα emission in red, the [O iii] emission in green and the stellar continuum in blue. In this image the Hα and [O iii] maps have not been continuum subtracted. And on the right is a continuum-subtracted image showing the [N ii] λ6584 emission in red, the Hα emission in green and the [O iii] emission in blue. The images are orientated with North up and East to the left, and a scale bar is shown in the stellar continuum image for reference, where 5′′ corresponds to ∼ 9.15 kpc.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreifvkpdbhbw742ws7ie45lztdo4fmvdjxwmcvcnsr2pzte5klul4ii)
![Top panel surface evolution of [Fe/H], horizontal dotted gray line
is the observed [Fe/H], the vertical line is the expected age for the inferred best model. bottom panel surface evolution of [Li/H], horizontal dotted gray line is the observed [Li/H], the vertical line is the expected age for the inferred best model. Models described in tables 3.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreiasdniavon5hmjw4osrl47ssbtip2gy3dyu3cgi2laubowndgzm3u)
![Illustration of our chemical evolution modeling framework applied to the highest (top) and lowest (bottom) velocity dispersion bins of the SDSS sample. Left: Best-fit SFHs and (in black) the cumulative number of SNe Ia. The high-dispersion galaxy has a shorter SFH and therefore experiences fewer SNe Ia, consistent with its higher [Mg/Fe]. Middle: The best-fit light-weighted [Mg/Fe] vs. [Mg/H] tracks color-coded by time, for all seven SDSS bins (lines). Observed values are shown as stars. Right: Light-weighted multi-element abundance patterns as a function of time, color-coded from early (blue) to late (red). The final time step (red) represents the predicted observable stellar abundances. We also show the predicted abundance pattern from the basic application of our empirically-derived yields (Section 3.3; gray lines), which anchors the abundances to the observed [Mg/H] and [Mg/Fe] without modeling the full enrichment history.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreiedzowezawhb7jok5rsprvasw3rh2odi2mhh5uqfh6mnix3ixkvki)
![Energy-metallicity relation of the identified substructures. Each point represents the MDF peak ([Fe/H]) and the median orbital energy of a given substructure. Circles and triangles denote substructures in the low-e and intermediate-e ranges, respectively, while symbols of the same color indicate groups associated with the same progenitor. The cyan line shows the best-fit relation defined by low-e LRS 3, intermediate-e LRS 3L, low-e LRS 4, low-e LRS 5, and intermediate-e LRS 5, which are interpreted as debris from a primary progenitor (Primary Retrograde Progenitor; black symbols). To account for their different energy distributions, intermediate-e LRS 3 and intermediatee LRS 2 are subdivided into low- and high-energy components (3L/3H and 2L/2H). Substructures that deviate from this relation indicate independent progenitors. Excluding the red symbols associated with Thamnos 2, the distribution reveals at least four distinct dwarf galaxy progenitors, indicated by the black, blue, purple, and orange groups. This relation illustrates a coherent metallicity-energy sequence for the dominant progenitor, as well as the presence of multiple independent accretion events, highlighting the complex assembly history of the MW’s retrograde halo.](https://cdn.bsky.app/img/feed_thumbnail/plain/did:plc:cugc4wn2mruqtvx7lm2kztiy/bafkreicbnajncjvultujym2feyapgs645l2nxtt7il5nauwf34jis6tq2i)
