Confronting uncertainties in stellar physics

Abstract

We assess the systematic uncertainties in stellar evolutionary calculations for low-to intermediate-mass, main-sequence stars. We compare published stellar tracks from several different evolution codes with our own tracks computed using the stellar codes stars and mesa. In particular, we focus on tracks of 1 and 3 M at solar metallicity. We find that the spread in the available 1 M tracks (computed before the recent solar composition revision) can be covered by tracks between 0.97−1.01 M computed with the stars code. We assess some possible causes of the origin of this uncertainty, including how the choice of input physics and the solar constraints used to perform the solar calibration affect the tracks. We find that for a 1 M track, uncertainties of around 10% in the initial hydrogen abundance and initial metallicity produce around a 2% error in mass. For the 3 M tracks, there is very little difference between the tracks from the various different stellar codes. The main difference comes in the extent of the main sequence, which we believe results from the different choices of the implementation of convective overshooting in the core. Uncertainties in the initial abundances lead to a 1−2% error in the mass determination. These uncertainties cover only part of the total error budget, which should also include uncertainties in the input physics (e.g., reaction rates, opacities, convective models) and any missing physics (e.g., radiative levitation, rotation, magnetic fields). Uncertainties in stellar surface properties such as luminosity and effective temperature will further reduce the accuracy of any potential mass determinations.

The effects of diffusion in hot subdwarf progenitors from the common envelope channel

“…MESA was chosen because it is a robust code capable of approximating the evolution through helium flashes, a key step in the evolution of hot subdwarfs which populate the extreme hor- izontal branch (EHB) and in which helium core burning has started. Input physics parameters were chosen to be similar to that of other recent work with MESA on hot subdwarfs (Xiong et al 2017;Schindler et al 2015), that is starting with a Population I atomic composition (Z = 0.02 and X = 0.7) with other important parameters listed in Table 1, including recent calibrations of the mixing length parameter in MESA (Stancliffe et al 2016). Because the phase of evolution examined during this work was the transition from the red giant branch (RGB) to the extreme horizontal branch (EHB) at the onset of core helium burning, type I opacity tables were used.…”

Pulsation in faint blue stars

“…Evolution models were computed using mesa (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015(Paxton et al , 2018(Paxton et al , 2019. Physics options were similar to those used in , namely the Schwarzchild convection criterion, a convective overshoot parameter α M LT = 1.9 following Stancliffe et al (2016), no mass loss (aside from the initial stripping of the red giant progenitor) and an initial metallicity of Z = 0.02 with the mixture of Grevesse & Sauval (1998). Atomic diffusion in mesa uses the Burgers equations (Burgers 1969), following the approach of Thoul et al (1994), with radiative accelerations computed using the methods outlined by Hu et al (2011).…”

Star Masses and Star-Planet Distances for Earth-like Habitability

“…Other stellar evolution models could be used ( e.g. , Spada et al , 2013; Valle et al , 2014; Stancliffe et al 2016), but the resulting changes are not significant, as uncertainties in stellar evolution are small compared to issues such as the uncertainty in n discussed above.…”