M. A. Corti

An independent limit on the axion mass from the variable white dwarf star R548

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 () 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 theoretical 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 macos 2? ~ 17.1 meV at a 2? 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.

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences : III. The pre-ELM white dwarf instability strip

Two low-mass pre-white dwarfs, which could be precursors of ELM white dwarfs, have been observed to show multiperiodic photometric variations. They could constitute a new class of pulsating low-mass pre-white dwarf stars. We present a detailed nonadiabatic pulsation study of such stars, employing full evolutionary sequences of low-mass He-core pre-white dwarf models. We have considered models in which element diffusion is accounted for and also models in which it is neglected. We confirm and explore in detail a new instability strip in the domain of low gravities and low effective temperatures of the

GS263-02+45 : a new H I supershell with evidence of having triggered star formation?

T_{\rm eff}-\log g

Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

diagram, where low-mass pre-white dwarfs are currently found. The destabilized modes are radial and nonradial

Members of Centaurus OB1 and NGC 4755: new spectroscopic and astrometric studies

p

LSS 1135: An O-type spectroscopic binary in the galactic OB association Bochum 7

and

GS305+04-26: revisiting the interstellar medium around the Centaurus OB1 stellar association

g

A deep and wide-field view at the IC 2944/2948 complex in Centaurus

modes excited by the

A New Feature in the Spectrum of the Large Magellanic Cloud Hypergiant HDE 269896

\kappa-\gamma

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

mechanism acting mainly at the zone of the second partial ionization of He, with non-negligible contributions from the region of the first partial ionization of He and the partial ionization of H. The computations with element diffusion are unable to explain the pulsations observed in the two known pulsating pre-white dwarfs, suggesting that element diffusion might be inhibited at these stages of the pre-white dwarf evolution. Our nonadiabatic models without diffusion, on the other hand, naturally explain the existence and range of periods of the pulsating pre-white dwarf star WASP J1628