The brightness of the red giant branch tip

Abstract

Context. The brightness of the tip of the Red Giant Branch is a useful reference quantity for several fields of astrophysics. An accurate theoretical prediction is needed for such purposes. Aims. We intend to provide a solid theoretical prediction for it, valid for a reference set of standard physical assumptions, and mostly independent of numerical details. Methods. We examine the dependence on physical assumptions and numerical details, for a wide range of metallicities and masses, and based on two different stellar evolution codes. We adjust differences between the codes to treat the physics as identical as possible. After we have succeeded in reproducing the tip brightness between the codes, we present a reference set of models based on the most up to date physical inputs, but neglecting microscopic diffusion, and convert theoretical luminosities to observed infrared colours suitable for observations of resolved populations of stars and include analytic fits to facilitate their use. Results. We find that consistent use of updated nuclear reactions, including an appropriate treatment of the electron screening effects, and careful time-stepping on the upper red giant branch are the most important aspects to bring initially discrepant theoretical values into agreement. Small, but visible differences remain unexplained for very low metallicities and mass values at and above 1.2 M ⊙ , corresponding to ages younger than 4 Gyr. The colour transformations introduce larger uncertainties than the differences between the two stellar evolution codes. Conclusions. We demonstrate that careful stellar modeling allows an accurate prediction for the luminosity of the Red Giant Branch tip. Differences to empirically determined brightnesses may result either from insufficient colour transformations or from deficits in the constitutional physics. We present the best-tested theoretical reference values to date.

Constraining dark photon properties with Asteroseismology

“…Our theoretical model with m V = 900 and χ = 9 × 10 −15 gives a log L/L 0 increase of ≈ 0.1. This variation correspond to a magnitude variation ≈ 0.3, which is more than twice the observational uncertainties (0.12 mag) reported by Serenelli et al (2017) and Viaux et al (2013).…”

On Stellar Evolution in a Neutrino Hertzsprung–Russell Diagram

“…The He core flash phase, which occurs in M ZAMS 2 M stars, is characterized by a series of subflashes that propagate toward the stellar center (Thomas 1967;Serenelli & Weiss 2005;Bildsten et al 2012;Gautschy 2012;Serenelli et al 2017). For example, the 1 M model in Figure 2 undergoes five subflashes with the first subflash occurring at 0.18 M and reaching L ν 10 4 L ν, .…”

The Updated BaSTI Stellar Evolution Models and Isochrones. I. Solar-scaled Calculations

“…As shown by Cassisi et al (2007), these opacity calculations affect only slightly (small decrease) the He-core mass at He ignition for low-mass models, and the luminosity of the following horizontal branch (HB) phase (small decrease), compared to the BaSTI calculations that were based on the Potekhin (1999) conductive opacities. For more details on this issue, we refer the reader to the quoted reference as well as to Serenelli et al (2017).…”

“…However, we have repeated the analysis here to verify the expected variation with Serenelli et al (2017).…”