PARSEC V2.0: Rotating tracks and isochrones for seven addtional metallicities in the range Z=0.0001-0.03

TL;DR

The paper extends PARSEC v2.0 by adding seven metallicities (from $Z=0.0001$ to $0.03$) and seven initial rotation rates $\omega_i$, delivering about 3,040 new rotating tracks and corresponding isochrones, and enabling interpolation for intermediate $\omega_i$ values. Using diffusive angular momentum transport, rotation-enhanced mass loss, and a calibrated overshoot framework, the work analyzes rotation’s impact on structure and surface abundances, and contrasts PARSEC v2.0 with GENEC and MIST to highlight differences in input physics. Validation against the open cluster NGC 6067 demonstrates that rotating models are essential to reproduce observed broadening velocities and CMD features, though metallicity and abundance measurements carry significant uncertainties. All models are publicly accessible via dedicated web interfaces, with improved isochrone interpolation and inclination-dependent bolometric corrections enhancing applicability to Gaia and other photometric systems. The results underscore the importance of rotation in stellar evolution modeling and provide a richer, more flexible toolset for interpreting stellar populations and clusters.

Abstract

PARSEC v2.0 rotating stellar tracks were previously presented for six values of metallicity from subsolar to solar values, with initial rotation rates ($ω_\mathrm{i}$, defined as the ratio of angular velocity and its critical value) spanning from the non-rotating case to very near the critical velocity (i.e. $ω_\mathrm{i}=0.99$), and for initial masses covering the $\sim 0.7 M_\odot$ to $14 M_\odot$ interval. Furthermore, we provided the corresponding isochrones converted into several photometric systems, for different inclination angles between the line-of-sight and the rotation axes, from $0^\circ$ (pole-on) to $90^\circ$ (equator-on). In this work, we expand this database with seven other sets of metallicity, including five sets of low metallicity ($Z=0.0001-0.002$) and two sets of super-solar values (up to $Z=0.03$). Here, we present the new stellar tracks, comprising $\sim$3\,040 tracks in total ($\sim$5\,500 including previous sets), along with the new corresponding rotating isochrones. We also introduce the possibility of creating isochrones, by interpolation, for values of rotating rates not available in the initial set of tracks. We compare a selection of our new models with rotating stellar tracks from the Geneva Stellar Evolution Code, and we assess the quality of our new tracks by fitting the colour-magnitude diagram of the open cluster NGC6067. We take advantage of the projected rotational velocity of member stars measured by Gaia to validate our results and examine the surface oxygen abundances in comparison with the observed data. All newly computed stellar tracks and isochrones are retrievable via our dedicated web databases and interfaces.

Figures (11)

• Figure 1: Hertzsprung–Russell diagram of stellar mass models in three sets of initial rotation rates: $\omega_\mathrm{i}=0.00,0.60$, and $0.90$ for a given metallicity $Z=0.001$, $Y=0.250$. The colour bar indicates the evolution of the rotation rate ($\omega$) of each single model. For the sake of clarity, the PMS evolution is cut off in this plot.
• Figure 2: Difference between rotating models and their non-rotating counterparts in He-core mass (top panel), He-core radius (middle panel) at the TAMS ($X_\mathrm{c}\sim 10^{-7}$), and the MS lifetime ratios (bottom panel). Models from low- to intermediate-mass are shown here with an initial metallicity $Z=0.02$.
• Figure 3: Impact of rotation on the HRD and several surface abundances normalised to their initial values. Models with a mass of $1.5~\hbox{$\mathrm{M}_{\odot}$}$ are shown in the top row (panels a-e), and models with a mass of $6~\hbox{$\mathrm{M}_{\odot}$}$ are shown in the second row (panels f-j). Different initial rotation rates are shown by different colours. The first column shows the HRD of the selected models. The second and third columns show the C-isotope ratio and the C/N ratio, respectively, with respect to the initial values. That is, we plot the quantity $(X/Y)-(X/Y)_\mathrm{ini}$, where $X/Y= n_X/n_Y$ is number density ratio of species $X$ and $Y$, and the $(X/Y)_\mathrm{ini}$ value is specified in the plot. The abundances of $^{16}$O and $^7$Li are shown in the fourth and fifth columns, respectively. In the latter cases, we plot the quantity $A(X)-A(X)_\mathrm{ini}$, where $A(X)=\log(n_X/n_\mathrm{H})+12$ is the abundance of element $X$, and $A(X)_\mathrm{ini}$ is its initial value, as specified in each panel. $n_\mathrm{H}$ is the hydrogen density number. The models are shown from the ZAMS to the RGB tip for the $1.5~\hbox{$\mathrm{M}_{\odot}$}$ model, and at the end of the He-burning phase for the $6~\hbox{$\mathrm{M}_{\odot}$}$. The black dot marks the TAMS.
• Figure 4: Upper panel: Difference of the surface CNO abundances between the TAMS and initial value for $6~\hbox{$\mathrm{M}_{\odot}$}$ stellar tracks with different metallicities and various initial rotation rates. Bottom panel: Initial values of the CNO abundances. The grey star indicates the initial abundances at solar metallicity.
• Figure 5: Same as Fig. \ref{['DX_CNO']}, but for lithium. The upper panel shows the abundance difference for $6~\hbox{$\mathrm{M}_{\odot}$}$ stars, the middle panel shows it for $1.5~\hbox{$\mathrm{M}_{\odot}$}$ stars, and the bottom panel is the initial $^7$Li-abundance at a given metallicity.