Toward a Comprehensive Grid of Cepheid Models with MESA. III. Evolutionary and Pulsation Relations for Models with Core and Envelope Overshooting

Abstract

Evolutionary tracks for 2-8M$_\odot$ models, covering a [Fe/H]=$-$1.0 ($Z=0.0014$) to [Fe/H]=+0.2 ($Z=0.02$) metallicity range are computed with Modules for Experiments in Stellar Astrophysics, MESA, to investigate evolutionary and pulsation properties of classical, fundamental mode Cepheids. We examine in detail the effects of convective overshooting from the Main Sequence core, as well as from the convective envelope on the Red Giant Branch. Mass loss is also included in a few model sets. Linear pulsation properties are derived consistently with a module of MESA, Radial Stellar Pulsation, RSP. We provide edges of the classical Instability Strip, as well as ages, crossing times through the Instability Strip and period change rates. Period-Luminosity, Mass-Luminosity, Period-Radius and Period-Age relations are provided, both in analytical and tabular form. Their dependence on metallicity, crossing number and overshooting parameters are investigated. Qualitative comparisons with classical Cepheids in the Milky Way and Magellanic Clouds as well as other theoretical relations are presented. We find satisfactory agreement for most of the observables and good match with other theoretical work, however reproducing short-period Cepheids in the Small Magellanic Cloud as well as Cepheid mass discrepancy pose a challenge for the presented models. Considering metallicity effect of the Period-Luminosity relation, we find $γ\approx -0.20$ mag dex$^{-1}$, nearly independent on photometric pass band and in good agreement with recent observational studies. The magnitude of this effect depends on the underlying mass-luminosity relation, being stronger for relations that predict higher luminosities at a given mass.

Figures (19)

• Figure 1: Location of the F-mode IS determined for: panel a) different crossing numbers, panel b) different metallicities, panel c) different parameter sets describing convection-pulsation coupling and, panel d), models with and without convective core overshoot. In all panels evolutionary tracks of O24 set and 2, 3, 4, 6 and 8 M⊙$_{\odot}$ are plotted for a reference.
• Figure 2: Fiducial hot (upper panel) and cool (lower panel) IS edges on the HRD along with the midline (green curve). Data used to determine the edges (O24, $Z=0.004$) are plotted with filled symbols of different shapes corresponding to crossing number. Over-plotted are data for F-mode classical Cepheids from sources indicated in the top panel.
• Figure 3: The effects of core (top row) and envelope (bottom row) overshooting on evolutionary tracks of $2-8\,{\rm M}_$_⊙$$ models of high ($Z=0.014$, left column), intermediate ($Z=0.004$, middle column) and low ($Z=0.0014$, right column) metallicity. Fiducial hot IS strip is over-plotted for a reference.
• Figure 4: Temperature extent of the blue loop across mass (vertical axis in each panel), metallicity (horizontal axis in each panel) and overshooting scenarios (rows and columns). The extent of MS core overshooting increases in rows, while the extent of envelope overshooting increases in columns. In a single panel, overshooting parameters are fixed and color of each square codes the effective temperature of the tip of the blue loop for models of different $M$/$Z$. In case the loop enters the hot IS, a black frame is drawn around square.
• Figure 5: The effects of mass-loss ($\eta=0.6$) on evolutionary tracks of high ($Z=0.014$, left panel) intermediate ($Z=0.004$, middle panel) and low metallicity ($Z=0.0014$, right panel). The models include overshooting both from the MS core and envelope (O24_ML6 models). Tracks are color codded according to a fraction of mass lost, $\Delta M$. Tracks without mass loss (O24) are plotted with dashed black lines for a reference.