arXiv subjects

Giada Pastorelli

Publications and source records attributed to Giada Pastorelli.

At least 19 recordsLinked to original sources

arXiv2026

A homogeneous view of asymptotic giant branch carbon stars as seen by Gaia

Carbon stars on the asymptotic giant branch are major contributors to galactic dust enrichment, with gas mass-loss rates up to 1e-4 Msun/yr. We present a homogeneous spectral energy distribution analysis of the Gaia DR3 Golden Sample of carbon stars in the Milky Way and Magellanic Clouds. Our dataset includes 14,747 sources with multi-band photometry from Gaia, 2MASS, and WISE, combined with recent distance and extinction estimates. For a subsample of 2,494 Mira variables, we model multi-band light curves to derive accurate mean magnitudes. Stellar and circumstellar parameters are obtained by fitting observations with a large grid of synthetic spectra computed with the DUSTY radiative transfer code using COMARCS atmospheres. We derive effective temperature, optical depth, and gas mass-loss rate for each source. The distributions peak around Teff = 3150 K, with mass-loss rates spanning 1e-11 to 1e-4 Msun/yr and inner dust temperatures near 1000 K. We find a correlation between variability amplitude and mass-loss rate. This framework provides a statistically robust view of carbon stars across environments with different metallicities. Apparent environmental dependencies are influenced by luminosity distributions and selection effects rather than purely intrinsic metallicity differences. The combined Gaia and WISE selection limits the detection of both highly obscured and faint Magellanic Cloud sources, but the observed trends remain significant within the sampled populations.

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arXiv2025

Strikingly high fraction of fast rotators in Magellanic Cloud star clusters

There has been growing evidence that the rich star clusters in the Magellanic Clouds contain significant fractions of rapidly rotating stars. In this work, we aim to constrain these fractions by studying the colour-magnitude diagrams of four star clusters, selected among those with the most striking signatures of fast rotators. Using isochrones derived from PARSEC v2.0 stellar tracks, we generate distinct stellar populations, each covering a limited interval of initial rotation rates $\omega_\mathrm{i}$, referred to as 'Partial Models' (PMs). Using optimization algorithms and Monte Carlo Markov Chains, PMs are combined to create the final best-fitting model. In our analysis, we adopt two key assumptions: a uniform age and an isotropic distribution of stellar spin axes within each cluster. The solutions are allowed to explore the entire range of $\omega_\mathrm{i}$, and different values of age, metallicity, distance and foreground extinction. We find that the rotational velocity distributions in all four clusters reveal a high fraction of stars with $\omega_\mathrm{i}$ close to the break-up value, in all cases. Specifically, the fraction of stars with $\omega_\mathrm{i}>0.7$ exceeds $80\%$ in the clusters NGC 419 of the Small Magellanic Cloud (SMC) and NGC 1831 and NGC 1866 of the Large Magellanic Cloud (LMC). For NGC 2203 of the LMC, this fraction is smaller, although it still exceeds $50\%$, confirming that also this cluster is mainly populated by fast-rotating stars.

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arXiv2025

The Local Ultraviolet to Infrared Treasury II. Refining Star Formation Histories of Ten Metal-Poor Dwarf Galaxies with Simultaneous UV-Optical Two-CMD Fitting

We present the star formation histories (SFHs) of ten metal-poor (<12% Zsun), star-forming dwarf galaxies from the Local Ultraviolet to Infrared Treasury (LUVIT) survey. The derived SFHs exhibit significant variability, consistent with the irregular star formation expected for dwarf galaxies. Using synthetic near ultraviolet (UV) and optical CMDs with various yet targeted configurations for dust and input SFHs, we quantitatively demonstrate that simultaneous modeling of the UV and optical CMDs ("UVopt" case) improves the precision of SFH measurements in recent time bins up to ~1 Gyr, compared to the classical single optical CMD modeling ("Opt-only" case). The UVopt case reduces uncertainties relative to the Opt-only case by ~4-8% over the past 10 Myr, ~8-20% over 100 Myr, and ~8-14% over 1 Gyr, across various dust configurations and input SFHs. Additionally, we demonstrate discrepancies in stellar models for blue core helium-burning (BHeB) stars at the low metallicity regime. This discrepancy can artificially inflate star formation rate (SFR) estimates in younger age bins by misinterpreting the evolved BHeB stars as reddened upper main-sequence (MS) stars. Incorporating UV data improves BHeB-MS separation and mitigates the limitations of current low metallicity stellar models. Comparisons of the UVopt SFHs with Ha and FUV-based SFRs reconfirm that Ha is an unreliable tracer over its nominal 10 Myr timescale for low-SFR galaxies, while FUV provides a more reliable tracer but yields SFR_FUV values up to twice those of CMD-based _100Myr. Our findings underscore the importance of UV data in refining recent SFHs in low-metallicity environments.

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arXiv2024

Self-Excited Pulsations and the Instability Strip of Long-Period Variables: the Transition from Small-Amplitude Red Giants to Semi-Regular Variables

We use one-dimensional hydrodynamic calculations combined with synthetic stellar population models of the Magellanic Clouds to study the onset of self-excited pulsation in luminous red giants. By comparing the results with OGLE observations in the period-luminosity diagram we are able to link the transition from small-amplitude red giants to semi-regular variables with a shift from stochastic driving to self-excited pulsations. This is consistent with previous studies relating this transition with an increase in mass-loss rate, dust formation, and the appearance of long secondary periods. The luminosity and effective temperature at the onset of pulsation are found to depend on metallicity, hydrogen content, and the adopted mixing length parameter. This confirms the role of partial hydrogen ionization in driving the pulsation, supporting the idea of a heat mechanism similar to that of classical pulsators. We examine the impact of turbulent viscosity, and find clear evidence that it must be adjusted according to the stellar chemical and physical parameters to fully match observations. In order to improve the predictive power of pulsation models, the turbulent viscosity and the temperature scale of pulsating red giants must be jointly calibrated. This is critical for model-based studies of the period-luminosity relations of evolved stars and to exploit their potential as distance and age indicators, in particular given the sensitivity of the onset of pulsation to the envelope composition. The grid of models is made publicly available with a companion interpolation routine.

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arXiv2024

The Local Ultraviolet to Infrared Treasury I. Survey Overview of the Broadband Imaging

The Local Ultraviolet to Infrared Treasury (LUVIT) is a Hubble Space Telescope program that combines newly acquired data in the near ultraviolet (NUV), optical, and near infrared (NIR) with archival optical and NIR imaging to produce multiband panchromatic resolved stellar catalogs for 23 pointings in 22 low-mass, star-forming galaxies ranging in distance from the outskirts of the Local Group to ~3.8 Mpc. We describe the survey design, detail the LUVIT broadband filter observations and the archival datasets included in the LUVIT reductions, and summarize the simultaneous multiband data reduction steps. The spatial distributions and color-magnitude diagrams (CMDs) from the resulting stellar catalogs are presented for each target, from the NUV to the NIR. We demonstrate in which regions of the CMDs stars with NUV and optical, optical and NIR, and NUV through NIR detections reside. For each target, we use the results from artificial star tests to measure representative completeness, bias, and total photometric uncertainty as a function of magnitude in each broadband filter. We also assess which LUVIT targets have significant spatial variation in the fraction of stars recovered at a given magnitude. The panchromatic LUVIT stellar catalogs will provide a rich legacy dataset for a host of resolved stellar population studies.

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arXiv2024

Calibration of the JAGB method for the Magellanic Clouds and Milky Way from Gaia DR3, considering the role of oxygen-rich AGB stars

The JAGB method is a new way of measuring distances with use of AGB stars that are situated in a selected region in a J versus J-Ks CMD, using the fact that the absolute J magnitude is (nearly) constant. It is implicitly assumed in the method that the selected stars are carbon-rich AGB stars. However, as the sample selected to determine M_J is purely colour based there can also be contamination by oxygen-rich AGB stars. As the ratio of C to O-rich stars is known to depend on metallicity and initial mass, the star formation history and age-metallicity relation in a galaxy should influence the value of M_J. The aim of this paper is to look at mixed samples of O- and C-rich stars for the LMC, the SMC and Milky Way (MW), using the Gaia catalogue of long period variables as basis. We report the mean and median magnitudes and the results of fitting Gaussian and Lorentzian profiles to the luminosity function (LF) using different colour and magnitudes cuts. For the SMC and LMC we confirm the previous results in the literature. The LFs of the SMC and LMC JAGB stars are clearly different, yet the mean magnitude inside a selection box can be argued to agree at the 0.02~mag level. The analysis of the MW sample is less straightforward. The contamination by O-rich stars is substantial for a classical lower limit of (J-Ks)0= 1.3, and becomes less than 10% only for (J-Ks)0= 1.5. The sample of AGB stars is much smaller than for the MCs for two reasons. Nearby AGB stars tend to be absent as they saturate in the 2MASS catalogue, and the parallax errors of AGB stars tend to be larger compared to non-AGB stars. The mean and median magnitudes are fainter than for the MC samples by about 0.4~mag which is not predicted by theory. We do not confirm the claim in the literature that the absolute calibration of the JAGB method is independent of metallicity up to solar metallicity.

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arXiv2024

The JWST Resolved Stellar Populations Early Release Science Program VI. Identifying Evolved Stars in Nearby Galaxies

We present an investigation of evolved stars in the nearby star-forming galaxy WLM, using NIRCam imaging from the JWST resolved stellar populations early-release science (ERS) program. We find that various combinations of the F090W, F150W, F250M, and F430M filters can effectively isolate red supergiants (RSGs) and thermally-pulsing asymptotic giant branch (TP-AGB) stars from one another, while also providing a reasonable separation of the primary TP-AGB subtypes: carbon-rich C-type stars and oxygen-rich M-type stars. The classification scheme we present here agrees very well with the well-established Hubble Space Telescope (HST) medium-band filter technique. The ratio of C to M-type stars (C/M) is 0.8$\pm$0.1 for both the new JWST and the HST classifications, which is within one sigma of empirical predictions from optical narrow-band CN and TiO filters. The evolved star colors show good agreement with the predictions from the PARSEC$+$COLIBRI stellar evolutionary models, and the models indicate a strong metallicity dependence that makes stellar identification even more effective at higher metallicity. However, the models also indicate that evolved star identification with NIRCam may be more difficult at lower metallicies. We test every combination of NIRCam filters using the models and present additional filters that are also useful for evolved star studies. We also find that $\approx$90\% of the dusty evolved stars are carbon-rich, suggesting that carbonaceous dust dominates the present-day dust production in WLM, similar to the findings in the Magellanic Clouds. These results demonstrate the usefulness of NIRCam in identifying and classifying dust-producing stars without the need for mid-infrared data.

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arXiv2023

The JWST Resolved Stellar Populations Early Release Science Program IV: The Star Formation History of the Local Group Galaxy WLM

We present the first star formation history (SFH) and age-metallicity relation (AMR) derived from resolved stellar populations imaged with the JWST NIRCam instrument. The target is the Local Group star-forming galaxy WLM at 970 kpc. The depth of the color-magnitude diagram (CMD) reaches below the oldest main sequence turn-off with a SNR=10 at M_F090W=+4.6 mag; this is the deepest CMD for any galaxy that is not a satellite of the Milky Way. We use Hubble Space Telescope (HST) optical imaging that overlaps with the NIRCam observations to directly evaluate the SFHs derived based on data from the two great observatories. The JWST and HST-based SFHs are in excellent agreement. We use the metallicity distribution function measured from stellar spectra to confirm the trends in the AMRs based on the JWST data. Together, these results confirm the efficacy of recovering a SFH and AMR with the NIRCam F090W-F150W filter combination and provide validation of the sensitivity and accuracy of stellar evolution libraries in the near-infrared relative to the optical for SFH recovery work. From the JWST data, WLM shows an early onset to star formation, followed by an extended pause post-reionization before star formation re-ignites, which is qualitatively similar to what has been observed in the isolated galaxies Leo~A and Aquarius. Quantitatively, 15% of the stellar mass formed in the first Gyr, while only 10% formed over the next ~5 Gyr; the stellar mass then rapidly doubled in ~2.5 Gyr, followed by constant star formation over the last ~5 Gyr.

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arXiv2023

Dissecting the Gaia HR diagram II. The vertical structure of the star formation history across the Solar Cylinder

Starting from the Gaia DR3 HR diagram, we derive the star formation history (SFH) as a function of distance from the Galactic Plane within a cylinder centred on the Sun with a 200~pc radius and spanning 1.3~kpc above and below the Galaxy's midplane. We quantify both the concentration of the more recent star formation in the Galactic Plane, and the age-related increase in the scale height of the Galactic Disc stellar component, which is well-described by power-laws with indices ranging from $1/2$ to $2/3$. The vertically-integrated star formation rate falls from $(1.147 \pm 0.039)\times10^{-8}\, \text{M}_{\odot} \text{yr}^{-1} \text{pc}^{-2}$ at earlier times down to $(6.2 \pm 3.0) \times10^{-9}\, \text{M}_{\odot} \text{yr}^{-1} \text{pc}^{-2}$ at present times, but we find a significant peak of star formation in the 2 to 3 Gyr age bin. The total mass of stars formed per unit area over time is $118.7 \pm 6.2\, \text{M}_{\odot} \text{pc}^{-2}$, which is nearly twice the present stellar mass derived from kinematics within 1~kpc from the Galactic Plane, implying a high degree of matter recycling in successive generations of stars. The method is then modified by adopting an age-dependent correlation between the SFH across the different slices, which results in less noisy and more symmetrical results without significantly changing the previously mentioned quantities. This appears to be a promising way to improve SFH recovery in external galaxies.

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arXiv2023

The first comprehensive Milky Way stellar mock catalogue for the Chinese Space Station Telescope Survey Camera

The Chinese Space Station Telescope (CSST) is a cutting-edge two-meter astronomical space telescope currently under construction. Its primary Survey Camera (SC) is designed to conduct large-area imaging sky surveys using a sophisticated seven-band photometric system. The resulting data will provide unprecedented data for studying the structure and stellar populations of the Milky Way. To support the CSST development and scientific projects related to its survey data, we generate the first comprehensive Milky Way stellar mock catalogue for the CSST SC photometric system using the TRILEGAL stellar population synthesis tool. The catalogue includes approximately 12.6 billion stars, covering a wide range of stellar parameters, photometry, astrometry, and kinematics, with magnitude reaching down to $g\,=\,27.5$ mag in the AB magnitude system. The catalogue represents our benchmark understanding of the stellar populations in the Milky Way, enabling a direct comparison with the future CSST survey data. Particularly, it sheds light on faint stars that are hidden from current sky surveys. Our crowding limit analysis based on this catalogue provides compelling evidence for the extension of the CSST Optical Survey (OS) to cover low Galactic latitude regions. The strategic extension of the CSST-OS coverage, combined with this comprehensive mock catalogue, will enable transformative science with the CSST.

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arXiv2022

A Panchromatic Study of Massive Stars in the Extremely Metal-Poor Local Group Dwarf Galaxy Leo A

We characterize massive stars (M>8 M_sun) in the nearby (D~0.8 Mpc) extremely metal-poor (Z~5% Z_sun) galaxy Leo A using Hubble Space Telescope ultra-violet (UV), optical, and near-infrared (NIR) imaging along with Keck/LRIS and MMT/Binospec optical spectroscopy for 18 main sequence OB stars. We find that: (a) 12 of our 18 stars show emission lines, despite not being associated with an H II region, suggestive of stellar activity (e.g., mass loss, accretion, binary star interaction), which is consistent with previous predictions of enhanced activity at low metallicity; (b) 6 are Be stars, which are the first to be spectroscopically studied at such low metallicity -- these Be stars have unusual panchromatic SEDs; (c) for stars well-fit by the TLUSTY non-local thermodynamic equilibrium (non-LTE) models, the photometric and spectroscopic values of T_eff and log(g) agree to within ~0.01 dex and ~0.18 dex, respectively, indicating that NUV/optical/NIR imaging can be used to reliably characterize massive (M ~ 8-30 M_sun) main sequence star properties relative to optical spectroscopy; (d) the properties of the most massive stars in H II regions are consistent with constraints from previous nebular emission line studies; and (e) 13 stars with M>8 M_sun are >40 pc from a known star cluster or H II region. Our sample comprises ~50% of all known massive stars at Z < 10% Z_sun with derived stellar parameters, high-quality optical spectra, and panchromatic photometry.

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arXiv2022

Simulating the Legacy Survey of Space and Time stellar content with TRILEGAL

We describe a large simulation of the stars to be observed by the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). The simulation is based on the TRILEGAL code, which resorts to large databases of stellar evolutionary tracks, synthetic spectra, and pulsation models, added to simple prescriptions for the stellar density and star formation histories of the main structures of the Galaxy, to generate mock stellar samples through a population synthesis approach. The main bodies of the Magellanic Clouds are also included. A complete simulation is provided for single stars, down to the $r=27.5$ mag depth of the co-added wide-fast-deep survey images. A second simulation is provided for a fraction of the binaries, including the interacting ones, as derived with the BinaPSE module of TRILEGAL. We illustrate the main properties and numbers derived from these simulations, including: comparisons with real star counts; the expected numbers of Cepheids, long-period variables and eclipsing binaries; the crowding limits as a function of seeing and filter; the star-to-galaxy ratios, etc. Complete catalogs are accessible through the NOIRLab Astro Data Lab, while the stellar density maps are incorporated in the LSST metrics analysis framework (MAF).

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arXiv2021

A Fresh Look at AGB stars in Galactic Open Clusters with Gaia: Impact on Stellar Models and the Initial-Final Mass Relation

Benefiting from the GAIA second and early third releases of photometric and astrometric data we examine the population of asymptotic giant branch (AGB) stars that appear in the fields of intermediate-age and young open star clusters. We identify 49 AGB star candidates, brighter than the tip of the red giant branch, with a good-to-high cluster membership probability. Among them we find 19 TP-AGB stars with known spectral type: 4 M stars, 3 MS/S stars and 12 C stars. By combining observations, stellar models, and radiative transfer calculations that include the effect of circumstellar dust, we characterize each star in terms of initial mass, luminosity, mass-loss rate, core mass, period and mode of pulsation. The information collected helps us shed light on the TP-AGB evolution at solar-like metallicity, placing constraints on the third dredge-up process, the initial masses of carbon stars, stellar winds, and the initial-final mass relation (IFMR). In particular, we find that two bright carbon stars, MSB 75 and BM IV 90, members of the clusters NGC 7789 and NGC 2660 (with similar ages of $\simeq 1.2-1.6$ Gyr and initial masses $ 2.1 \ge M_{\rm i}/M_{\odot} \ge 1.9$), have unusually high core masses, $M_{\rm c} \approx 0.67-0.7\,M_{\odot}$. These results support the findings of a recent work (Marigo et al. 2020) that identified a kink in the IFMR, which interrupts its monotonic trend just at the same initial masses. Finally, we investigate two competing scenarios to explain the $M_{\rm c}$ data: the role of stellar winds in single-star evolution, and binary interactions through the blue-straggler channel.

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arXiv2021

The VMC survey -- XLIII. The spatially resolved star formation history across the Large Magellanic Cloud

We derive the spatially-resolved star formation history (SFH) for a $96$ deg$^2$ area across the main body of the Large Magellanic Cloud (LMC), using the near-infrared photometry from the VISTA survey of the Magellanic Clouds (VMC). The data and analyses are characterised by a great degree of homogeneity and a low sensitivity to the interstellar extinction. 756 subregions of size $0.125$ deg$^2$ -- corresponding to projected sizes of about $296\times322\,\mathrm{pc}^{2}$ in the LMC -- are analysed. The resulting SFH maps, with typical resolution of $0.2$--$0.3$ dex in logarithm of age, reveal main features in the LMC disc at different ages: the patchy star formation at recent ages, the concentration of star formation on three spiral arms and on the Bar up to ages of $\sim\!1.6$ Gyr, and the wider and smoother distribution of older populations. The period of most intense star formation occurred roughly between 4 and 0.5 Gyr ago, at rates of $\sim\!0.3\,\mathrm{M}_{\odot}\mathrm{yr}^{-1}$. We compare young and old star formation rates with the observed numbers of RR Lyrae and Cepheids. We also derive a mean extinction and mean distance for every subregion, and the plane that best describes the spatial distribution of the mean distances. Our results cover an area about 50 per cent larger than the classical SFH maps derived from optical data by Harris & Zaritsky (2009). Main differences with respect to those maps are lower star formation rates at young ages, and a main peak of star formation being identified at ages slightly younger than $1$ Gyr.

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arXiv2020

Modelling Long-Period Variables -- II. Fundamental mode pulsation in the nonlinear regime

Long-period variability in luminous red giants has several promising applications, all of which require models able to accurately predict pulsation periods. Linear pulsation models have proven successful in reproducing the observed periods of overtone modes in evolved red giants, but they fail to accurately predict their fundamental mode periods. Here, we use a 1D hydrodynamic code to investigate the long-period variability of M-type asymptotic giant branch stars in the nonlinear regime. We examine the period and stability of low-order radial pulsation modes as a function of mass and radius, and find overtone mode periods in complete agreement with predictions from linear pulsation models. In contrast, nonlinear models predict an earlier onset of dominant fundamental mode pulsation, and shorter periods at large radii. Both features lead to a substantially better agreement with observations, that we verify against OGLE and Gaia data for the Magellanic Clouds. We provide simple analytic relations describing the nonlinear fundamental mode period-mass-radius relation. Differences with respect to linear predictions originate from the readjustment of the envelope structure induced by large-amplitude pulsation. We investigate the impact of turbulent viscosity on linear and nonlinear pulsation, and probe possible effects of varying metallicity and carbon abundance.

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arXiv2020

Constraining the thermally pulsing asymptotic giant branch phase with resolved stellar populations in the Large Magellanic Cloud

Reliable models of the thermally pulsing asymptotic giant branch (TP-AGB) phase are of critical importance across astrophysics, including our interpretation of the spectral energy distribution of galaxies, cosmic dust production, and enrichment of the interstellar medium. With the aim of improving sets of stellar isochrones that include a detailed description of the TP-AGB phase, we extend our recent calibration of the AGB population in the Small Magellanic Cloud (SMC) to the more metal rich Large Magellanic Cloud (LMC). We model the LMC stellar populations with the TRILEGAL code, using the spatially-resolved star formation history derived from the VISTA survey. We characterize the efficiency of the third dredge-up by matching the star counts and the $K_{\rm s}$-band luminosity functions of the AGB stars identified in the LMC. In line with previous findings, we confirm that, compared to the SMC, the third dredge-up in AGB stars of the LMC is somewhat less efficient, as a consequence of the higher metallicity. The predicted range of initial mass of C-rich stars is between $M_{\rm i} \approx 1.7 - 3~\mathrm{M}_{\odot}$ at $Z_{\rm i} = 0.008$. We show how the inclusion of new opacity data in the carbon star spectra will improve the performance of our models. We discuss the predicted lifetimes, integrated luminosities and mass-loss rate distributions of the calibrated models. The results of our calibration are included in updated stellar isochrones publicly available.

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arXiv2020

PHAT XX. AGB stars and other cool giants in M31 star clusters

The presence of AGB stars in clusters provides key constraints for stellar models, as has been demonstrated with historical data from the Magellanic Clouds. In this work, we look for candidate AGB stars in M31 star clusters from the Panchromatic Hubble Andromeda Treasury (PHAT) survey. Our photometric criteria selects stars brighter than the tip of the red giant branch, which includes the bulk of the thermally-pulsing AGB stars as well as early-AGB stars and other luminous cool giants expected in young stellar populations (e.g. massive red supergiants, and intermediate-mass red helium-burning stars). The AGB stars can be differentiated, a posteriori, using the ages already estimated for our cluster sample. 937 candidates are found within the cluster aperture radii, half (450) of which are very likely cluster members. Cross-matching with additional databases reveals two carbon stars and ten secure variables among them. The field-corrected age distribution reveals the presence of young supergiants peaking at ages smaller than 100 Myr, followed by a long tail of AGB stars extending up to the oldest possible ages. This long tail reveals the general decrease in the numbers of AGB stars from initial values of 50e-6/Msun at 100 Myr down to 5e-6/Msun at 10 Gyr. Theoretical models of near-solar metallicity reproduce this general trend, although with localized discrepancies over some age intervals, whose origin is not yet identified. The entire catalogue is released together with finding charts to facilitate follow-up studies.

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arXiv2020

Carbon star formation as seen through the non-monotonic initial-final mass relation

The initial-final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved. A new analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR, located over a range of initial masses, $1.65 \lesssim M_{\rm i}/M_{\odot} \lesssim 2.10$. The kink's peak in WD mass of $\approx 0.70-0.75 \, M_{\odot}$ is produced by stars with $M_{\rm i} \simeq 1.8 - 1.9 \, M_{\odot}$, corresponding to ages of about $1.8 - 1.7 $ Gyr. Interestingly, this peak coincides with the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their impact on the spectrophotometric properties of galaxies.

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