Effect of neutrino magnetic moment on solar neutrino observations

Neutrino spin precession effects in the magnetic field of the Sun are considered as an explanation of the outcome of Davis' solar neutrino experiments. Theoretically, it is possible to account for a neutrino magnetic moment only as the result of the interaction of the electromagnetic field with charged particles into which the neutrino can transform virtually. The currently accepted theory of weak interactions (the two component neutrino andV-A interactions) forbids a resulting magnetic moment interaction with the electromagnetic field for all such virtual processes. Modifications of this theory are considered to find out whether an appreciable precession effect is permitted within the experimentally established limits. It is found that the value for the neutrino magnetic moment evaluated under these theoretically anomalous circumstances is still so small that only the largest possible estimate for the magnetic field strength in the Sun's interior would cause the required effect.The author has received scholarship support from the Latin American Scholarship Program of American Universities during the preparation of this work.     

Dirac neutrino magnetic moment and possible time evolution of the neutrino signal from a supernova

We analyze the influence of neutrino helicity conversion, ν _L → ν _R, on the neutrino flux from a supernova attributable to the interaction of the Dirac neutrino magnetic moment with a magnetic field.We show that if the neutrino has a magnetic moment in the interval 10⁻¹³μ_B < μ_ν < 10⁻¹²μ_B and provided that a magnetic field of ∼10¹³–10¹⁴ G exists in the supernova envelope, a peculiar kind of time evolution of the neutrino signal from the supernova attributable to the resonance transition ν _L → ν _R in the magnetic field of the envelope can appear.     

Dynamical determination of the quadrupole mass moment of a white dwarf

In this paper we dynamically determine the quadrupole mass moment Q of the magnetic white dwarf WD 0137-349 by looking for deviations from the third Kepler law induced by Q in the orbital period of the recently discovered brown dwarf moving around it in a close 2-hr orbit. It turns out that a purely Newtonian model for the orbit of WD 0137-349B, assumed circular and equatorial, is adequate, given the present-day accuracy in knowing the orbital parameters of such a binary system. Our result is Q=(−1.5±0.9)×10⁴⁷ kg m² for i=35 deg. It is able to accommodate the 3-sigma significant discrepancy of (1.0±0.3)×10⁻⁸ s⁻² between the inverse square of the phenomenologically determined orbital period and the inverse square of the calculated Keplerian one. The impact of i, for which an interval Δ i of possible values close to 35 deg is considered, is investigated as well.     

Theoretical model of a magnetic white dwarf

In this paper a theoretical model of a magnetic white dwarf is studied. All numerical calculations are performed under the assumption of a spherically symmetric star. The obtained equation of state is stiffer with the increase of value of the magnetic field (B). Numerical values of the maximum mass and radius are presented. The influence of the magnetic field on the results is evident. Finally the departure from the condition of isothermality of a degenerate electron gas in the gravitational field is discussed.     

Photometry of the magnetic white dwarf SDSS 121209.31+013627.7

The results of 27 h of time series photometry of SDSS 121209.31+013627.7 are presented. The binary period established from spectroscopy is confirmed and refined to 0.061 412 d (88.43 min). The photometric variations are dominated by a brightening of about 16 mmag, lasting a little less than half a binary cycle. The amplitude is approximately the same in V ,  R and white light. A secondary small brightness increase during each cycle may also be present. We speculate that SDSS 121209.31+013627.7 may be a polar in a low state.     

A new magnetic white dwarf: PG 2329+267

We have discovered that the white dwarf PG 2329+267 is magnetic, and, assuming a centred dipole structure, has a dipole magnetic field strength of approximately 2.3 MG. This makes it one of only approximately 4 per cent of isolated white dwarfs with a detectable magnetic field. Linear Zeeman splitting, as well as quadratic Zeeman shifts, is evident in the hydrogen Balmer sequence and circular spectropolarimetry reveals ∼10 per cent circular polarization in the two displaced σ components of Hα. We suggest from comparison with spectra of white dwarfs of known mass that PG 2329+267 is more massive than typical isolated white dwarfs, in agreement with the hypothesis that magnetic white dwarfs evolve from magnetic chemically peculiar Ap and Bp type main-sequence stars.     

Lessons for asteroseismology from white dwarf stars

The interpretation of pulsation data for sun-like stars is currently facing challenges quite similar to those faced by white dwarf modelers ten years ago. The observational requirements for uninterrupted long-term monitoring are beginning to be satisfied by successful multi-site campaigns and dedicated satellite missions. But exploration of the most important physical parameters in theoretical models has been fairly limited, making it difficult to establish a detailed best-fit model for a particular set of oscillation frequencies. I review the past development and the current state of white dwarf asteroseismology, with an emphasis on what this can tell us about the road to success for asteroseismology of other types of stars.     

The Cr and Sr sources in BOREXINO as tools for neutrino magnetic moment searches

We calculate the event rates induced by a ⁵¹Cr ν_e source and by a ⁹⁰Sr---⁹⁰Y source in BOREXINO through elastic scattering on electrons, assuming a nonzero neutrino magnetic moment μ_ν. We consider a source activity of about 2 MCi and estimate the solar ν (“source-off”) background for various oscillation scenarios. It is shown that values of μ_ν as low as 0.5 × 10⁻¹⁰μ_B ( 0.2 × 10⁻¹⁰μ_B) can be proved with the ⁵¹Cr source (⁹⁰Sr source) in about 100 days of data taking.     

Determining the mass of the accreting white dwarf in magnetic cataclysmic variables using RXTE data

We have extracted spectra of 20 magnetic cataclysmic variables (mCVs) from the RXTE archive and best fitted them using the X-ray continuum method of Cropper et al. to determine the mass of the accreting white dwarf in each system. We find evidence that the mass distribution of these mCVs is significantly different from that of non-magnetic isolated white dwarfs, with the white dwarfs in mCVs being biased towards higher masses. It is unclear if this effect is a result of selection or whether this reflects a real difference in the parent populations.     

On the interpretation of white dwarf spectra

Following the line of research outlined by Strittmatter and Wickramasinghe (1971) and recently by Shipman (1972), attention was drawn to the study of convective zones in white dwarfs for various masses and chemical compositions, in order to understand some observational features of their spectra. According to the results, convection strongly depends on the mass of the star, forM<0.5 M_⊙, and low hydrogen abundancesX?0.2) are sufficient to decrease the extension of the He-convection zones with respect to pure-He models. It is shown that the existence of DB white dwarfs seems not in agreement with the accretion rates predicted by Bondi (1952), and that DB's must evolve into H-lacking white dwarfs.     

Constraints on the gravitational constant from the observations of white dwarfs

Recently some authors have questioned whether Newton's law of gravitation is actually true on scales less than 1 km. The available constraints on the gravitational constant show that is laboratory valueG ₀ may differ from the value at infinityG by 40%. Long (1976) reported experimental evidence for departures from Newton's law. In this note it is shown that the difference betweenG ₀ andG modifies the mass-radius relation of degenerate stars. The observations of white dwarfs are consistent with the theory of stellar evolution only ifG ₀ differs fromG by not more than 10%. This estimate may be improved by a higher accuracy of observations.     

Constraints on ultracompact minihalos using neutrino signals from gravitino dark matter decay

Ultracompact dark matter minihalos(UCMHs) would be formed during the early universe if there were large density perturbations.If dark matter can decay into particles described by the standard model,such as neutrinos,these objects would become potential astrophysical sources of emission which could be detected by instruments such as IceCube.In this paper,we investigate neutrino signals from nearby UCMHs due to gravitino dark matter decay and compare these signals with the background neutrino flux which is mainly from the atmosphere to obtain constraints on the abundance of UCMHs.     

Capture radius and synchronization of the white dwarf in the unique magnetic cataclysmic system V1432 Aql

Results from two-color VR photometry of the unique cataclysmic magnetic variable star V1432 Aql and a theoretical model of these data are presented. The accuracy is improved by using the “mean-weighted comparison star” method. The derivative of the rotational period is dP/dt = −1.11(±0.016)·10⁻⁸. The characteristic synchronization time for the rotational and orbital motions of the white dwarf is 96.7±1.5 years, in good agreement with theory for the acceleration of an asynchronous propeller owing to the angular momentum of accreting matter. A third type of minimum detected in the light curve is interpreted in terms of the presence of an arc, or ring, rather than an accretion disk. A theoretical model is developed for determining the capture radius of accreted matter by the magnetic field of the white dwarf using the phase difference between the two types of minima associated with the axial rotation. This parameter is estimated to be 16–28 times the radius of the white dwarf for an inclined column model. A dependence of the main characteristics of the system on the mass of the white dwarf is derived which yields better values for the range of this quantity than those determined by indirect methods. For the assumed masses (M₁ = 0.9 M_⊙ and M₂ = 0.3 M_⊙) the estimated accretion rate is ∼7×10⁻¹⁰ M_⊙. It is shown that in a synchronizing polar the contribution to the change in the period by the variation in the angular momentum of the white dwarf is negligible compared to the accretion torque. In the future multicolor monitoring is needed for studying the spin-orbital synchronization and periodic changes in the accretion structure caused by “spinning” of the white dwarf. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 135–159 (February 2007).     

Magnetic deformation of the white dwarf surface structure

The influence of strong, large‐scale magnetic fields on the structure and temperature distribution in white dwarf atmospheres is investigated. Magnetic fields may provide an additional component of pressure support, thus possibly inflating the atmosphere compared to the non‐magnetic case. Since the magnetic forces are not isotropic, atmospheric properties may significantly deviate from spherical symmetry. In this paper the magnetohydrostatic equilibrium is calculated numerically in the radial direction for either for small deviations from different assumptions for the poloidal current distribution. We generally find indication that the scale height of the magnetic white dwarf atmosphere enlarges with magnetic field strength and/or poloidal current strength. This is in qualitative agreement with recent spectropolarimetric observations of Grw+10°8247. Quantitatively, we .nd for e.g. a mean surface poloidal field strength of 100 MG and a toroidal field strength of 2‐10 MG an increase of scale height by a factor of 10. This is indicating that already a small deviation from the initial force‐free dipolar magnetic field may lead to observable effects. We further propose the method of finite elements for the solution of the two‐dimensional magnetohydrostatic equilibrium including radiation transport in the diffusive approximation. We present and discuss preliminary solutions, again indicating on an expansion of the magnetized atmosphere.     

The neutrino emission due to plasmon decay and neutrino luminosity of white dwarfs

One of the effective mechanisms of neutrino energy losses in red giants, pre-supernovae and in the cores of white dwarfs is the emission of neutrino–antineutrino pairs in the process of plasmon decay. In this paper, we numerically calculate the emissivity due to plasmon decay in a wide range of temperatures 10⁷–10¹¹ K and densities (2 × 10²–10¹⁴) g cm⁻³. Numerical results are approximated by convenient analytical expressions. We also calculate and approximate by analytical expressions the neutrino luminosity of white dwarfs due to plasmon decay, as a function of their mass and internal temperature. This neutrino luminosity depends on the chemical composition of white dwarfs only through the parameter μ_e (the net number of baryons per electron) and is the dominant neutrino luminosity in all white dwarfs at the neutrino cooling stage.     

The neutrino in the primordial magnetic field

We discuss the evolution of the massive Dirac particle in the cosmic magnetic field. The magnetic field makes the space metric anisotropic. By solving the Dirac equation we obtain the apparent magnetic moment of the neutrino in the cosmic magnetic field.