Electromagnetic transitions of the helium atom in superstrong magnetic fields

Al-Hujaj, Omar-Alexander; Schmelcher, Peter

doi:10.1103/physreva.68.053403

Cited by 30 publications

(20 citation statements)

References 43 publications

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“…We note that younger NSs may possess atmospheres composed of helium rather than hydrogen; however, the opacities of bound states of helium in strong magnetic fields are still largely unknown (see e.g. Bezchastnov, Pavlov & Ventura 1998; Al‐Hujaj & Schmelcher 2003a,b; Pavlov & Bezchastnov 2005).…”

Section: Discussionmentioning

confidence: 98%

Magnetic hydrogen atmosphere models and the neutron star RX J1856.5-3754

Kaplan

Chang

et al. 2007

Monthly Notices of the Royal Astronomical Society

138

151

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RX J1856.5−3754 is one of the brightest nearby isolated neutron stars, and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5−3754, within the uncertainties. In our simplest model, the best-fit parameters are an interstellar column density N H ≈ 1 × 10 20 cm −2 and an emitting area with R ∞ ≈ 17 km (assuming a distance to RX J1856.5−3754 of 140 pc), temperature T ∞ ≈ 4.3 × 10 5 K, gravitational redshift z g ∼ 0.22, atmospheric hydrogen column y H ≈ 1 g cm −2 , and magnetic field B ≈ (3 − 4) × 10 12 G; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the neutron star surface as well as general relativistic effects, to determine pulsations; we find there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5−3754.

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Section: Discussionmentioning

confidence: 98%

Magnetic hydrogen atmosphere models and the neutron star RX J1856.5-3754

Kaplan

Chang

et al. 2007

Monthly Notices of the Royal Astronomical Society

138

151

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“…At temperatures above ∼ 10000 K, MWDs can also exhibit Zeeman split HeI lines in their spectra (DBp WDs). The two electron problem is much more difficult to treat and calculations for n ≤ 5 singlet and triplet states for m = 0, ±1, ±2, ±3 only became available in the late 90s (Jordan et al 1998;Jones et al 1999;Becken et al 1999;Schmelcher 2000b,a, 2001;Al-Hujaj and Schmelcher 2003). We show in Fig.…”

Section: Beyond Hydrogenmentioning

confidence: 95%

Magnetic White Dwarfs

2015

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In this paper we review the current status of research on the observational and theoretical characteristics of isolated and binary magnetic white dwarfs (MWDs). Magnetic fields of isolated MWDs are observed to lie in the range 10^3-10^9G. While the upper limit cutoff appears to be real, the lower limit is more difficult to investigate. The incidence of magnetism below a few 10^3G still needs to be established by sensitive spectropolarimetric surveys conducted on 8m class telescopes. Highly magnetic WDs tend to exhibit a complex and non-dipolar field structure with some objects showing the presence of higher order multipoles. There is no evidence that fields of highly magnetic WDs decay over time, which is consistent with the estimated Ohmic decay times scales of ~10^11 yrs. MWDs, as a class, also appear to be more massive than their weakly or non-magnetic counterparts. MWDs are also found in binary systems where they accrete matter from a low-mass donor star. These binaries, called magnetic Cataclysmic Variables (MCVs) and comprise about 20-25\% of all known CVs. Zeeman and cyclotron spectroscopy of MCVs have revealed the presence of fields in the range $\sim 7-230$\,MG. Complex field geometries have been inferred in the high field MCVs (the polars) whilst magnetic field strength and structure in the lower field group (intermediate polars, IPs) are much harder to establish. The origin of fields in MWDs is still being debated. While the fossil field hypothesis remains an attractive possibility, field generation within the common envelope of a binary system has been gaining momentum, since it would explain the absence of MWDs paired with non-degenerate companions and also the lack of relatively wide pre-MCVs.Comment: 73 pages, 22 figures, 2 large tables. Invited review chapter on Magnetic White Dwarfs to appear in Space Science Reviews, Springe

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“…The stronger B is, the more important the effects of finite nuclear mass are. Apart from the H atom, these effects have been calculated only for the He atom which rests as a whole , but has a moving nucleus (Al‐Hujaj & Schmelcher 2003a,b), and for the He + ion (Bezchastnov, Pavlov & Ventura 1998; Pavlov & Bezchastnov 2005).…”

Section: Introductionmentioning

confidence: 99%

“…There were relatively few publications devoted to radiative transitions of non‐hydrogenic atoms in strong magnetic fields. Several authors (Miller & Neuhauser 1991; Thurner et al 1993; Jones et al 1999; Mori & Hailey 2002; Al‐Hujaj & Schmelcher 2003b) calculated oscillator strengths for bound–bound transitions; Miller & Neuhauser (1991) also presented a few integrated bound–free oscillator strengths. Rajagopal et al (1997) calculated opacities of strongly magnetized iron, using photoionization cross‐sections obtained by M. C. Miller (unpublished).…”

Section: Introductionmentioning

confidence: 99%

Radiative transitions of the helium atom in highly magnetized neutron star atmospheres

Medin¹,

Lai²,

Potekhin³

2008

Monthly Notices of the Royal Astronomical Society

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Recent observations of thermally emitting isolated neutron stars revealed spectral features that could be interpreted as radiative transitions of He in a magnetized neutron star atmosphere. We present Hartree–Fock calculations of the polarization‐dependent photoionization cross‐sections of the He atom in strong magnetic fields ranging from 1012 to 1014 G. Convenient fitting formulae for the cross‐sections are given along with the related oscillator strengths for various bound–bound transitions. The effects of finite nucleus mass on the radiative absorption cross‐sections are examined using perturbation theory.

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Electromagnetic transitions of the helium atom in superstrong magnetic fields

Cited by 30 publications

References 43 publications

Magnetic hydrogen atmosphere models and the neutron star RX J1856.5-3754

Magnetic hydrogen atmosphere models and the neutron star RX J1856.5-3754

Magnetic White Dwarfs

Radiative transitions of the helium atom in highly magnetized neutron star atmospheres

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