White dwarfs as physics laboratories: the case of axions (original) (raw)
Related papers
Axions and the Cooling of White Dwarf Stars
Astrophysical Journal, 2008
White dwarfs are the end product of the lifes of intermediate-and low-mass stars and their evolution is described as a simple cooling process. Recently, it has been possible to determine with an unprecedented precision their luminosity function, that is, the number of stars per unit volume and luminosity interval. We show here that the shape of the bright branch of this function is only sensitive to the averaged cooling rate of white dwarfs and we propose to use this property to check the possible existence of axions, a proposed but not yet detected weakly interacting particle. Our results indicate that the inclusion of the emission of axions in the evolutionary models of white dwarfs noticeably improves the agreement between the theoretical calculations and the observational white dwarf luminosity function. The best fit is obtained for m a cos 2 β ≈ 5 meV, where m a is the mass of the axion and cos 2 β is a free parameter. We also show that values larger than 10 meV are clearly excluded. The existing theoretical and observational uncertainties do not yet allow the confirmation of the existence of axions, but our results clearly show that if their mass is of the order of few meV, the white dwarf luminosity function is sensitive enough to detect their existence.
Axions and the white dwarf luminosity function
Journal of Physics: Conference Series, 2009
The evolution of white dwarfs can be described as a simple cooling process. Recently, it has been possible to determine with an unprecedented precision their luminosity function, that is, the number of stars per unit volume and luminosity interval. Since the shape of the bright branch of this function is only sensitive to the average cooling rate, we use this property to check the possible existence of axions, a proposed but not yet detected weakly interacting particle. We show here that the inclusion of the axion emissivity in the evolutionary models of white dwarfs noticeably improves the agreement between the theoretical calculations and the observational white dwarf luminosity function, thus providing the first positive indication that axions could exist. Our results indicate that the best fit is obtained for macos 2 β ≃ 2 − 6 meV, where ma is the mass of the axion and cos 2 β is a free parameter, and that values larger than 10 meV are clearly excluded.
White dwarfs are almost completely degenerate objects that cannot obtain energy from the thermonuclear sources and their evolution is just a gravothermal process of cooling. The simplicity of these objects, the fact that the physical inputs necessary to understand them are well identified, although not always well understood, and the impressive observational background about white dwarfs make them the most well studied Galactic population. These characteristics allow to use them as laboratories to test new ideas of physics. In this contribution we discuss the robustness of the method and its application to the axion case. Comment: 4 pages, 1 figure, to appear in the Proceedings for the 6th Patras meeting on Axions, WIMPs and WISPs
Axions and the pulsation periods of variable white dwarfs revisited
Astronomy and Astrophysics, 2010
Context. Axions are the natural consequence of the introduction of the Peccei-Quinn symmetry to solve the strong CP problem. All the efforts to detect such elusive particles have failed up to now. Nevertheless, it has been recently shown that the luminosity function of white dwarfs is best fitted if axions with a mass of a few meV are included in the evolutionary calculations. Aims. Our aim is to show that variable white dwarfs can provide additional and independent evidence about the existence of axions. Methods. The evolution of a white dwarf is a slow cooling process that translates into a secular increase of the pulsation periods of some variable white dwarfs, the so-called DAV and DBV types. Since axions can freely escape from such stars, their existence would increase the cooling rate and, consequently, the rate of change of the periods as compared with the standard ones. Results. The present values of the rate of change of the pulsation period of G117-B15A are compatible with the existence of axions with the masses suggested by the luminosity function of white dwarfs, in contrast with previous estimations. Furthermore, it is shown that if such axions indeed exist, the drift of the periods of pulsation of DBV stars would be noticeably perturbed.
Monthly Notices of the Royal Astronomical Society, 2012
We employ a state-of-the-art asteroseismological model of G117−B15A, the archetype of the H-rich atmosphere (DA) white dwarf pulsators (also known as DAV or ZZ Ceti variables), and use the most recently measured value of the rate of period change for the dominant mode of this pulsating star to derive a new constraint on the mass of axion, the still conjectural non-barionic particle considered as candidate for dark matter of the Universe. Assuming that G117−B15A is truly represented by our asteroseismological model, and in particular, that the period of the dominant mode is associated to a pulsation g-mode trapped in the H envelope, we find strong indications of the existence of extra cooling in this star, compatible with emission of axions of mass m a cos 2 β = 17.4 +2.3 −2.7 meV.
An independent limit on the axion mass from the variable white dwarf star R548
Journal of Cosmology and Astroparticle Physics, 2012
Pulsating white dwarfs with hydrogen-rich atmospheres, also known as DAV stars, can be used as astrophysical laboratories to constrain the properties of fundamental particles like axions. Comparing the measured cooling rates of these stars with the expected values from theoretical models allows us to search for sources of additional cooling due to the emission of weakly interacting particles. In this paper, we present an independent inference of the mass of the axion using the recent determination of the evolutionary cooling rate of R548, the DAV class prototype. We employ a state-of-the-art code which allows us to perform a detailed asteroseismological fit based on fully evolutionary sequences. Stellar cooling is the solely responsible of the rates of change of period with time (Π) for the DAV class. Thus, the inclusion of axion emission in these sequences notably influences the evolutionary timescales, and also the expected pulsational properties of the DAV stars. This allows us to compare the theoreticalΠ values to the corresponding empirical rate of change of period with time of R548 to discern the presence of axion cooling. We found that if the dominant period at 213.13 s in R548 is associated with a pulsation mode trapped in the hydrogen envelope, our models indicate the existence of additional cooling in this pulsating white dwarf, consistent with axions of mass m a cos 2 β ∼ 17.1 meV at a 2σ confidence level. This determination is in agreement with the value inferred from another well-studied DAV, G117−B15A. We now have two independent and consistent estimates of the mass of the axion obtained from DAVs, although additional studies of other pulsating white dwarfs are needed to confirm this value of the axion mass.
Journal of Cosmology and Astroparticle Physics, 2016
We employ an asteroseismic model of L19−2, a relatively massive (M ⋆ ∼ 0.75M ⊙) and hot (T eff ∼ 12 100 K) pulsating DA (H-rich atmosphere) white dwarf star (DAV or ZZ Ceti variable), and use the observed values of the temporal rates of period change of its dominant pulsation modes (Π ∼ 113 s and Π ∼ 192 s), to derive a new constraint on the mass of the axion, the hypothetical non-barionic particle considered as a possible component of the dark matter of the Universe. If the asteroseismic model employed is an accurate representation of L19−2, then our results indicate hints of extra cooling in this star, compatible with emission of axions of mass m a cos 2 β 25 meV or an axion-electron coupling constant of g ae 7 × 10 −13 .
Exploring uncharted territory in particles physics using pulsating white dwarfs: Prospects
Arxiv preprint astro-ph/0510103, 2005
Pulsating white dwarfs, especially DBVs, can be used as laboratories to study elusive particles such as plasmon neutrinos and axions. In the degenerate interiors of DBVs, plasmon decay is the dominant neutrino producing process. We can measure the neutrino luminosity using asteroseismology and constrain plasmon neutrino rates. In the same way, we can measure any additional loss of energy due to other weakly interacting particles, such as axions. Depending upon their (theoretically largely unconstrained) mass, axions could be a significant source of energy loss for DAVs as well. We are looking at what the uncertainties in the observables are, and what mass and temperature range minimizes them.
White Dwarfs as Astroparticle Physics Laboratories
EAS Publications Series, 2007
White dwarfs are well studied objects. The relative simplicity of their physics allows to obtain very detailed models which can be ultimately compared with their observed properties. Among them there is a specific class of stars, the ZZ-Ceti stars that are characterized by the extreme stability of their periods of pulsation. The rate of change of the period is closely related to the characteristic cooling time of the star, which can be accurately computed. This property not only allows to directly test the evolution of white dwarfs but also to constrain parameters of any new physical theory able to perturb the cooling regime. This technique has been successfuly aplied to the case of axions and can be used to constrain the properties of other theoretical particles. The program we propose here consists in using the ability of the Antartic plateau to perform long time and non-interrupted observations to establish the seismological properties of a well defined set of variable white dwarfs (and other stable pulsators).