Astrophysical Axion Bounds

Axion emission by hot and dense plasmas is a new energy-loss channel for stars. Observational consequences include a modification of the solar sound-speed profile, an increase of the solar neutrino flux, a reduction of the helium-burning lifetime of globular-cluster stars, accelerated white-dwarf cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We review and update these arguments and summarize the resulting axion constraints.Comment: Contribution to Axion volume of Lecture Notes in Physics, 20 pages, 3 figure

Comparing the asteroseismic properties of pulsating extremely low-mass pre-white dwarf stars and

We present the first results of a detailed comparison between the pulsation properties of pulsating Extremely Low-Mass pre-white dwarf stars (the pre-ELMV variable stars) and δ Scuti stars. The instability domains of these very different kinds of stars nearly overlap in the log Teff vs. log g diagram, leading to a degeneracy in the classification of the stars. Our aim is to provide asteroseismic tools for their correct classification

First axion bounds from a pulsating helium-rich white dwarf star

The Peccei-Quinn mechanism proposed to solve the CP problem of Quantum Chromodynamics has as consequence the existence of axions, hypothetical weakly interacting particles whose mass is constrained to be on the sub-eV range. If these particles exist and interact with electrons, they would be emitted from the dense interior of white dwarfs, becoming an important energy sink for the star. Due to their well known physics, white dwarfs are good laboratories to study the properties of fundamental particles such as the axions. We study the general effect of axion emission on the evolution of helium-rich white dwarfs and on their pulsational properties. To this aim, we calculate evolutionary helium-rich white dwarf models with axion emission, and asses the pulsational properties of this models. Our results indicate that the rates of change of pulsation periods are significantly affected by the existence of axions. We are able for the first time to independently constrain the mass of the axion from the study of pulsating helium-rich white dwarfs. To do this, we use an estimation of the rate of change of period of the pulsating white dwarf PG 1351+489 corresponding to the dominant pulsation period. From an asteroseismological model of PG 1351+489 we obtain $g_{ae}<3.3\times10^{-13}$ for the axion-electron coupling constant, or $m_a\cos^2{\beta}\lesssim$ 11.5 meV for the axion mass. This constraint is relaxed to $g_{ae}<5.5\times10^{-13}$ ($m_a\cos^2{\beta}\lesssim$ 19.5 meV), when no detailed asteroseismological model is adopted for the comparison with observations.Comment: 17 pages, 6 figures, 2 tables, prepared for submission to JCA

Asteroseismology of pulsating DA white dwarfs with fully evolutionary models

We present a new approach for asteroseismology of DA white dwarfs that consists in the employment of a large set of non-static, physically sound, fully evolutionary models representative of these stars. We already have applied this approach with success to pulsating PG1159 stars (GW Vir variables). Our white dwarf models, which cover a wide range of stellar masses, effective temperatures, and envelope thicknesses, are the result of fully evolutionary computations that take into account the complete history of the progenitor stars from the ZAMS. In particular, the models are characterized by self-consistent chemical structures from the centre to the surface, a crucial aspect of white dwarf asteroseismology. We apply this approach to an ensemble of 44 bright DAV (ZZ Ceti) stars

Discovery, TESS Characterization, and Modeling of Pulsations in the Extremely Low-mass White Dwarf GD 278

Contains fulltext : 240947pub.pdf (Publisher’s version ) (Closed access) Contains fulltext : 240947.pdf (Author’s version preprint ) (Open Access

A consistency test of white dwarf and main sequence ages: NGC 6791

NGC 6791 is an open cluster that it is so close to us that can be imaged down to very faint luminosities. The main sequence turn-off age (∼8 Gyr) and the age derived from the cut-off of the white dwarf luminosity function (∼6 Gyr) were found to be significantly different. Here we demonstrate that the origin of this age discrepancy lies in an incorrect evaluation of the white dwarf cooling ages, and we show that when the relevant physical separation processes are included in the calculation of white dwarf sequences both ages are coincident