arXiv subjects

Sven Buder

Publications and source records attributed to Sven Buder.

At least 55 records · Page 3Linked to original sources

arXiv2024

3D NLTE Lithium abundances for late-type stars in GALAH DR3

Lithium's susceptibility to burning in stellar interiors makes it an invaluable tracer for delineating the evolutionary pathways of stars, offering insights into the processes governing their development. Observationally, the complex Li production and depletion mechanisms in stars manifest themselves as Li plateaus, and as Li-enhanced and Li-depleted regions of the HR diagram. The Li-dip represents a narrow range in effective temperature close to the main-sequence turn-off, where stars have slightly super-solar masses and strongly depleted Li. To study the modification of Li through stellar evolution, we measure 3D non-local thermodynamic equilibrium (NLTE) Li abundance for 581 149 stars released in GALAH DR3. We describe a novel method that fits the observed spectra using a combination of 3D NLTE Li line profiles with blending metal line strength that are optimized on a star-by-star basis. Furthermore, realistic errors are determined by a Monte Carlo nested sampling algorithm which samples the posterior distribution of the fitted spectral parameters. The method is validated by recovering parameters from a synthetic spectrum and comparing to 26 stars in the Hypatia catalogue. We find 228 613 Li detections, and 352 536 Li upper limits. Our abundance measurements are generally lower than GALAH DR3, with a mean difference of 0.23 dex. For the first time, we trace the evolution of Li-dip stars beyond the main sequence turn-off and up the subgiant branch. This is the first 3D NLTE analysis of Li applied to a large spectroscopic survey, and opens up a new era of precision analysis of abundances for large surveys.

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arXiv2024

Assembling a high-precision abundance catalogue of solar twins in GALAH for phylogenetic studies

Stellar chemical abundances have proved themselves a key source of information for understanding the evolution of the Milky Way, and the scale of major stellar surveys such as GALAH have massively increased the amount of chemical data available. However, progress is hampered by the level of precision in chemical abundance data as well as the visualization methods for comparing the multidimensional outputs of chemical evolution models to stellar abundance data. Machine learning methods have greatly improved the former; while the application of tree-building or phylogenetic methods borrowed from biology are beginning to show promise with the latter. Here we analyse a sample of GALAH solar twins to address these issues. We apply The Cannon algorithm to generate a catalogue of about 40,000 solar twins with 14 high precision abundances which we use to perform a phylogenetic analysis on a selection of stars that have two different ranges of eccentricities. From our analyses we are able to find a group with mostly stars on circular orbits and some old stars with eccentric orbits whose age-[Y/Mg] relation agrees remarkably well with the chemical clocks published by previous high precision abundance studies. Our results show the power of combining survey data with machine learning and phylogenetics to reconstruct the history of the Milky Way.

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arXiv2023

Chemical Doppelgangers in GALAH DR3: the Distinguishing Power of Neutron-Capture Elements Among Milky Way Disk Stars

The observed chemical diversity of Milky Way stars places important constraints on Galactic chemical evolution and the mixing processes that operate within the interstellar medium. Recent works have found that the chemical diversity of disk stars is low. For example, the APOGEE "chemical doppelganger rate," or the rate at which random pairs of field stars appear as chemically similar as stars born together, is high, and the chemical distributions of APOGEE stars in some Galactic populations are well-described by two-dimensional models. However, limited attention has been paid to the heavy elements (Z > 30) in this context. In this work, we probe the potential for neutron-capture elements to enhance the chemical diversity of stars by determining their effect on the chemical doppelganger rate. We measure the doppelganger rate in GALAH DR3, with abundances rederived using The Cannon, and find that considering the neutron-capture elements decreases the doppelganger rate from 2.2% to 0.4%, nearly a factor of 6, for stars with -0.1 < [Fe/H] < 0.1. While chemical similarity correlates with similarity in age and dynamics, including neutron-capture elements does not appear to select stars that are more similar in these characteristics. Our results highlight that the neutron-capture elements contain information that is distinct from that of the lighter elements and thus add at least one dimension to Milky Way abundance space. This work illustrates the importance of considering the neutron-capture elements when chemically characterizing stars and motivates ongoing work to improve their atomic data and measurements in spectroscopic surveys.

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arXiv2023

Roman Early-Definition Astrophysics Survey Opportunity: Galactic Roman Infrared Plane Survey (GRIPS)

A wide-field near-infrared survey of the Galactic disk and bulge/bar(s) is supported by a large representation of the community of Galactic astronomers. The combination of sensitivity, angular resolution and large field of view make Roman uniquely able to study the crowded and highly extincted lines of sight in the Galactic plane. A ~1000 deg2 survey of the bulge and inner Galactic disk would yield an impressive dataset of ~120 billion sources and map the structure of our Galaxy. The effort would foster subsequent expansions in numerous dimensions (spatial, depth, wavelengths, epochs). Importantly, the survey would benefit from early defintion by the community, namely because the Galactic disk is a complex environment, and different science goals will require trade offs.

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arXiv2023

CN and CO Features: Key Indicators of Red Giant Evolutionary Phase in Moderate-Resolution X-Shooter Spectra

Data-driven analysis methods can help to infer physical properties of red giant stars where "gold-standard" asteroseismic data are not available. The study of optical and infrared spectra of red giant stars with data-driven analyses has revealed that differences in oscillation frequencies and their separations are imprinted in said spectra. This makes it possible to confidently differentiate core-helium burning red clump stars (RC) from those that are still on their first ascent of the red giant branch (RGB). We extend these studies to a tenfold larger wavelength range of 0.33 to 2.5 microns with the moderate-resolution VLT/X-shooter spectrograph. Our analysis of 49 stars with asteroseismic data from the K2 mission confirms that CN, CO and CH features are indeed the primary carriers of spectroscopic information on the evolutionary stages of red giant stars. We report 215 informative features for differentiating the RC from the RGB within the range of 0.33 to 2.5 microns. This makes it possible for existing and future spectroscopic surveys to optimize their wavelength regions to deliver both a large variety of elemental abundances and reliable age estimates of luminous red giant stars.

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arXiv2023

Peeking beneath the precision floor -- II. Probing the chemo-dynamical histories of the potential globular cluster siblings, NGC 288 and NGC 362

The assembly history of the Milky Way (MW) is a rapidly evolving subject, with numerous small accretion events and at least one major merger proposed in the MW's history. Accreted alongside these dwarf galaxies are globular clusters (GCs), which act as spatially coherent remnants of these past events. Using high precision differential abundance measurements from our recently published study, we investigate the likelihood that the MW clusters NGC 362 and NGC 288 are galactic siblings, accreted as part of the Gaia-Sausage-Enceladus (GSE) merger. To do this, we compare the two GCs at the 0.01 dex level for 20+ elements for the first time. Strong similarities are found, with the two showing chemical similarity on the same order as those seen between the three LMC GCs, NGC 1786, NGC 2210 and NGC 2257. However, when comparing GC abundances directly to GSE stars, marked differences are observed. NGC 362 shows good agreement with GSE stars in the ratio of Eu to Mg and Si, as well as a clear dominance in the r- compared to the s-process, while NGC 288 exhibits only a slight r-process dominance. When fitting the two GC abundances with a GSE-like galactic chemical evolution model, NGC 362 shows agreement with both the model predictions and GSE abundance ratios (considering Si, Ni, Ba and Eu) at the same metallicity. This is not the case for NGC 288. We propose that the two are either not galactic siblings, or GSE was chemically inhomogeneous enough to birth two similar, but not identical clusters with distinct chemistry relative to constituent stars.

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arXiv2023

The GALAH survey: New diffuse interstellar bands found in residuals of 872,000 stellar spectra

We use more than 872,000 mid-to-high resolution (R $\sim$ 20,000) spectra of stars from the GALAH survey to discern the spectra of diffuse interstellar bands (DIBs). We use four windows with the wavelength range from 4718 to 4903, 5649 to 5873, 6481 to 6739, and 7590 to 7890 Å, giving a total coverage of 967 Å. We produce $\sim$400,000 spectra of interstellar medium (ISM) absorption features and correct them for radial velocities of the DIB clouds. Ultimately, we combine the 33,115 best ISM spectra into six reddening bins with a range of $0.1 \,\mathrm{mag} < E\mathrm{(B-V)} < 0.7\, \mathrm{mag}$. A total of 183 absorption features in these spectra qualify as DIBs, their fitted model parameters are summarized in a detailed catalogue. From these, 64 are not reported in the literature, among these 17 are certain, 14 are probable and 33 are possible. We find that the broad DIBs can be fitted with a multitude of narrower DIBs. Finally, we create a synthetic DIB spectrum at unit reddening which should allow us to narrow down the possible carriers of DIBs and explore the composition of the ISM and ultimately better model dust and star formation as well as to correct Galactic and extragalactic observations. The majority of certain DIBs show a significant excess of equivalent width when compared to reddening. We explain this with observed lines of sight penetrating more uniform DIB clouds compared to clumpy dust clouds.

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arXiv2023

Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc

We employ our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy) to obtain high-quality stellar age estimates for 68,360 red giant and red clump stars present in the 17th data release of the Sloan Digital Sky Survey, the APOGEE-2 high-resolution spectroscopic survey. By examining the denoised age-metallicity relationship of the Galactic disc stars, we identify a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a chemical enrichment episode with increasing [Fe/H] and decreasing [Mg/Fe]. This result is congruent with the chemical evolution induced by an early-epoch gas-rich merger identified in the Milky Way-like zoom-in cosmological simulation Auriga. In the initial phase of the merger of Auriga 18 there is a drop in metallicity due to the merger diluting the metal content and an increase in the [Mg/Fe] of the primary galaxy. Our findings suggest that the last massive merger of our Galaxy, the Gaia-Sausage-Enceladus, was likely a significant gas-rich merger and induced a starburst, contributing to the chemical enrichment and building of the metal-rich part of the thick disc at an early epoch.

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arXiv2023

Spectroscopic follow-up of statistically selected extremely metal-poor star candidates from GALAH DR3

The advent of large-scale stellar spectroscopic surveys naturally leads to the implementation of machine learning techniques to isolate, for example, small sub-samples of potentially interesting stars from the full data set. A recent example is the application of the t-SNE statistical method to $\sim$600,000 stellar spectra from the GALAH survey in order to identify a sample of candidate extremely metal-poor (EMP, [Fe/H] $\leq$ -3) stars. We report the outcome of low-resolution spectroscopic follow-up of 83 GALAH EMP candidates that lack any previous metallicity estimates. Overall, the statistical selection is found to be efficient ($\sim$one-third of the candidates have [Fe/H] $\leq$ -2.75) with low contamination ($<$10% have [Fe/H] $>$ -2), and with a metallicity distribution function that is consistent with previous work. Five stars are found to have [Fe/H] $\leq$ -3.0, one of which is a main sequence turnoff star. Two other stars are revealed as likely carbon-enhanced metal-poor (CEMP) stars of type CEMP-$s$, and a known carbon star is re-identified. The results indicate that the statistical selection approach employed was successful, and therefore it can be applied to forthcoming even larger stellar spectroscopic surveys with the expectation of similar positive outcomes.

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arXiv2022

The Pristine Inner Galaxy Survey (PIGS) IV: A photometric metallicity analysis of the Sagittarius dwarf spheroidal galaxy

We present a comprehensive metallicity analysis of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using $Pristine\,CaHK$ photometry. We base our member selection on $Gaia$ EDR3 astrometry applying a magnitude limit at $G_{0} = 17.3$, and our population study on the metallicity-sensitive photometry from the $Pristine$ Inner Galaxy Survey (PIGS). Working with photometric metallicities instead of spectroscopic metallicities allows us to cover an unprecedented large area ($\sim 100$ square degrees) of the dwarf galaxy, and to study the spatial distribution of its members as function of metallicity with little selection effects. Our study compares the spatial distributions of a metal-poor population of 9719 stars with [Fe/H] $< -1.3$ and a metal rich one of 30115 stars with [Fe/H] $> -1.0$. The photometric Sgr sample also allows us to assemble the largest sample of 1150 very metal-poor Sgr candidates ([Fe/H] $< -2.0$). By investigating and fitting the spatial properties of the metal-rich and metal-poor population, we find a negative metallicity gradient which extends up to 12 degrees from the Sgr center (or $\sim 5.5$ kpc at the distance of Sgr), the limit of our footprint. We conclude that the relative number of metal-poor stars increases in the outer areas of the galaxy, while the central region is dominated by metal-rich stars. These finding suggest an outside-in formation process and are an indication of the extended formation history of Sgr, which has been affected by the tidal interaction between Sgr and the Milky Way.

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arXiv2022

The GALAH Survey: A New Sample of Extremely Metal-Poor Stars Using A Machine Learning Classification Algorithm

Extremely Metal-Poor (EMP) stars provide a valuable probe of early chemical enrichment in the Milky Way. Here we leverage a large sample of $\sim600,000$ high-resolution stellar spectra from the GALAH survey plus a machine learning algorithm to find 54 candidates with estimated [Fe/H]~$\leq$~-3.0, 6 of which have [Fe/H]~$\leq$~-3.5. Our sample includes $\sim 20 \%$ main sequence EMP candidates, unusually high for \emp surveys. We find the magnitude-limited metallicity distribution function of our sample is consistent with previous work that used more complex selection criteria. The method we present has significant potential for application to the next generation of massive stellar spectroscopic surveys, which will expand the available spectroscopic data well into the millions of stars.

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arXiv2022

Neutron-capture elements record the ordered chemical evolution of the disc over time

An ensemble of chemical abundances probing different nucleosynthetic channels can be leveraged to build a comprehensive understanding of the chemical and structural evolution of the Galaxy. Using GALAH DR3 data, we seek to trace the enrichment by the supernovae Ia, supernovae II, asymptotic giant branch stars, and neutron-star mergers and/or collapsars nucleosynthetic sources by studying the [Fe/H], [$α$/Fe], [Ba/Fe], and [Eu/Fe] chemical compositions of $\sim$50,000 red giant stars, respectively. Employing small [Fe/H]-[$α$/Fe] cells, which serve as an effective reference-frame of supernovae contributions, we characterise the abundance-age profiles for [Ba/Fe] and [Eu/Fe]. Our results disclose that these age-abundance relations vary across the [Fe/H]-[$α$/Fe] plane. Within cells, we find negative age-[Ba/Fe] relations and flat age-[Eu/Fe] relations. Across cells, we see the slope of the age-[Ba/Fe] relations evolve smoothly and the [Eu/Fe] relations vary in amplitude. We subsequently model our empirical findings in a theoretical setting using the flexible Chempy Galactic chemical evolution (GCE) code, using the mean [Fe/H], [Mg/Fe], [Ba/Fe], and age values for stellar populations binned in [Fe/H], [Mg/Fe], and age space. We find that within a one-zone framework, an ensemble of GCE model parameters vary to explain the data. Using present day orbits from \textit{Gaia} EDR3 measurements we infer that the GCE model parameters, which set the observed chemical abundance distributions, vary systematically across mean orbital radii. Under our modelling assumptions, the observed chemical abundances are consistent with a small gradient in the high mass end of the initial mass function (IMF) across the disc, where the IMF is more top heavy towards the inner disc and more bottom heavy in the outer disc.

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arXiv2022

Combined APOGEE-GALAH stellar catalogues using the Cannon

APOGEE and GALAH are two high resolution multi-object spectroscopic surveys that provide fundamental stellar parameters and multiple elemental abundance estimates for about half a million stars in the Milky Way. Both surveys observe in different wavelength regimes and use different data reduction pipelines leading to significant offsets and trends in stellar parameters and abundances for the common stars observed in both surveys. Such systematic differences/offsets in stellar parameters and abundances make it difficult to effectively utilise them to investigate Galactic abundance trends in spite of the unique advantage provided by their complementary sky coverage and different Milky Way components they observe. Hence, we use the \textit{Cannon} data-driven method selecting a training set of 4418 common stars observed by both surveys. This enables the construction of two catalogues, one with the APOGEE scaled and the other with the GALAH scaled stellar parameters. Using repeat observations in APOGEE and GALAH, we find high precision in metallicity (~ 0.02-0.4 dex) and alpha abundances (~ 0.02-0.03 dex) for spectra with good signal-to-noise ratio (SNR > 80 for APOGEE, SNR > 40 for GALAH). We use open and globular clusters to validate our parameter estimates and find small scatter in metallicity (0.06 dex) and alpha abundances (0.03 dex) in APOGEE scaled case. The final catalogues have been cross matched with the Gaia EDR3 catalogue to enable their use to carry out detailed chemo-dynamic studies of the Milky Way from perspectives of APOGEE and GALAH.

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arXiv2022

The K2 Galactic Archaeology Program Data Release 3: Age-abundance patterns in C1-C8 and C10-C18

We present the third and final data release of the K2 Galactic Archaeology Program (K2 GAP) for Campaigns C1-C8 and C10-C18. We provide asteroseismic radius and mass coefficients, $κ_R$ and $κ_M$, for $\sim 19,000$ red giant stars, which translate directly to radius and mass given a temperature. As such, K2 GAP DR3 represents the largest asteroseismic sample in the literature to date. K2 GAP DR3 stellar parameters are calibrated to be on an absolute parallactic scale based on Gaia DR2, with red giant branch and red clump evolutionary state classifications provided via a machine-learning approach. Combining these stellar parameters with GALAH DR3 spectroscopy, we determine asteroseismic ages with precisions of $\sim 20-30\%$ and compare age-abundance relations to Galactic chemical evolution models among both low- and high-$α$ populations for $α$, light, iron-peak, and neutron-capture elements. We confirm recent indications in the literature of both increased Ba production at late Galactic times, as well as significant contribution to r-process enrichment from prompt sources associated with, e.g., core-collapse supernovae. With an eye toward other Galactic archaeology applications, we characterize K2 GAP DR3 uncertainties and completeness using injection tests, suggesting K2 GAP DR3 is largely unbiased in mass/age and with uncertainties of $2.9\%\,(\rm{stat.})\,\pm0.1\%\,(\rm{syst.})$ & $6.7\%\,(\rm{stat.})\,\pm0.3\%\,(\rm{syst.})$ in $κ_R$ & $κ_M$ for red giant branch stars and $4.7\%\,(\rm{stat.})\,\pm0.3\%\,(\rm{syst.})$ & $11\%\,(\rm{stat.})\,\pm0.9\%\,(\rm{syst.})$ for red clump stars. We also identify percent-level asteroseismic systematics, which are likely related to the time baseline of the underlying data, and which therefore should be considered in TESS asteroseismic analysis.

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arXiv2022

The GALAH Survey: Chemical tagging and chrono-chemodynamics of accreted halo stars with GALAH+ DR3 and $Gaia$ eDR3

Since the advent of $Gaia$ astrometry, it is possible to identify massive accreted systems within the Galaxy through their unique dynamical signatures. One such system, $Gaia$-Sausage-Enceladus (GSE), appears to be an early "building block" given its virial mass $> 10^{10}\,\mathrm{M_\odot}$ at infall ($z\sim1-3$). In order to separate the progenitor population from the background stars, we investigate its chemical properties with up to 30 element abundances from the GALAH+ Survey Data Release 3 (DR3). To inform our choice of elements for purely chemically selecting accreted stars, we analyse 4164 stars with low-$α$ abundances and halo kinematics. These are most different to the Milky Way stars for abundances of Mg, Si, Na, Al, Mn, Fe, Ni, and Cu. Based on the significance of abundance differences and detection rates, we apply Gaussian mixture models to various element abundance combinations. We find the most populated and least contaminated component, which we confirm to represent GSE, contains 1049 stars selected via [Na/Fe] vs. [Mg/Mn] in GALAH+ DR3. We provide tables of our selections and report the chrono-chemodynamical properties (age, chemistry, and dynamics). Through a previously reported clean dynamical selection of GSE stars, including $30 < \sqrt{J_R~/~\mathrm{kpc\,km\,s^{-1}}} < 55$, we can characterise an unprecedented 24 abundances of this structure with GALAH+ DR3. Our chemical selection allows us to prevent circular reasoning and characterise the dynamical properties of the GSE, for example mean $\sqrt{J_R~/~\mathrm{kpc\,km\,s^{-1}}} = 26_{-14}^{+9}$. We find only $(29\pm1)\%$ of the GSE stars within the clean dynamical selection region. Our methodology will improve future studies of accreted structures and their importance for the formation of the Milky Way.

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arXiv2021

The GALAH Survey: Improving our understanding of confirmed and candidate planetary systems with large stellar surveys

Pioneering photometric, astrometric, and spectroscopic surveys are helping exoplanetary scientists better constrain the fundamental properties of stars within our galaxy, and the planets these stars host. In this study, we use the third data release from the stellar spectroscopic GALAH Survey, coupled with astrometric data of eDR3 from the \textit{Gaia} satellite, and other data from NASA's Exoplanet Archive, to refine our understanding of 279 confirmed and candidate exoplanet host stars and their exoplanets. This homogenously analysed data set comprises 105 confirmed exoplanets, along with 146 K2 candidates, 95 TESS Objects of Interest (TOIs) and 52 Community TOIs (CTOIs). Our analysis significantly shifts several previously (unknown) planet parameters while decreasing the uncertainties for others; Our radius estimates suggest that 35 planet candidates are more likely brown dwarfs or stellar companions due to their new radius values. We are able to refine the radii and masses of WASP-47 e, K2-106 b, and CoRoT-7 b to their most precise values yet, to less than 2.3\% and 8.5\% respectively. We also use stellar rotational values from GALAH to show that most planet candidates will have mass measurements that will be tough to obtain with current ground-based spectrographs. With GALAH's chemical abundances, we show through chemo-kinematics that there are five planet-hosts that are associated with the galaxy's thick disc, including NGTS-4, K2-183 and K2-337. Finally, we show there is no statistical difference between the chemical properties of hot Neptune and hot rocky exoplanet hosts, with the possibility that short-period rocky worlds might be the remnant cores of hotter, gaseous worlds.

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arXiv2021

The GALAH survey: Chemical homogeneity of the Orion complex

Due to its proximity, the Orion star forming region is often used as a proxy to study processes related to star formation and to observe young stars in the environment they were born in. With the release of Gaia DR2, the distance measurements to the Orion complex are now good enough that the three dimensional structure of the complex can be explored. Here we test the hypothesis that, due to non-trivial structure and dynamics, and age spread in the Orion complex, the chemical enrichment of youngest stars by early core-collapse supernovae can be observed. We obtained spectra of 794 stars of the Orion complex with the HERMES spectrograph at the Anglo Australian telescope as a part of the GALAH and GALAH-related surveys. We use the spectra of $\sim300$ stars to derive precise atmospheric parameters and chemical abundances of 25 elements for 15 stellar clusters in the Orion complex. We demonstrate that the Orion complex is chemically homogeneous and that there was no self-pollution of young clusters by core-collapse supernovae from older clusters; with a precision of 0.02 dex in relative alpha-elements abundance and 0.06 dex in oxygen abundance we would have been able to detect pollution from a single supernova, given a fortunate location of the SN and favourable conditions for ISM mixing. We estimate that the supernova rate in the Orion complex was very low, possibly producing no supernova by the time the youngest stars of the observed population formed (from around 21 to 8 Myr ago).

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arXiv2021

Residual Abundances in GALAH DR3: Implications for Nucleosynthesis and Identification of Unique Stellar Populations

We investigate the [X/Mg] abundances of 16 elements for 82,910 Galactic disk stars from GALAH+ DR3. We fit the median trends of low-Ia and high-Ia populations with a two-process model, which describes stellar abundances in terms of a prompt core-collapse and delayed Type-Ia supernova component. For each sample star, we fit the amplitudes of these two components and compute the residual $Δ$[X/H] abundances from this two-parameter fit. We find RMS residuals $\lesssim 0.07$ dex for well-measured elements and correlated residuals among some elements (such as Ba, Y, and Zn) that indicate common enrichment sources. From a detailed investigation of stars with large residuals, we infer that roughly $40\%$ of the large deviations are physical and $60\%$ are caused by problematic data such as unflagged binarity, poor wavelength solutions, and poor telluric subtraction. As one example of a population with distinctive abundance patterns, we identify 15 stars that have 0.3-0.6 dex enhancements of Na but normal abundances of other elements from O to Ni and positive average residuals of Cu, Zn, Y, and Ba. We measure the median elemental residuals of 14 open clusters, finding systematic $\sim0.1-0.4$ dex enhancements of O, Ca, K, Y, and Ba and $\sim0.2$ dex depletion of Cu in young clusters. Finally, we present a restricted three-process model where we add an asymptotic giant branch star (AGB) component to better fit Ba and Y. With the addition of the third process, we identify a population of stars, preferentially young, that have much higher AGB enrichment than expected from their SNIa enrichment.

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