EDP Sciences
Free access
Volume 409, Number 2, October II 2003
Page(s) 737 - 744
Section Formation and evolution of planetary systems
DOI http://dx.doi.org/10.1051/0004-6361:20031175

A&A 409, 737-744 (2003)
DOI: 10.1051/0004-6361:20031175

The formation of helium lines in the spectrum of COM J1740-5340

L. B. Lucy

Astrophysics Group, Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK
(Received 7 May 2003 / Accepted 29 July 2003 )

The He $\:$I $\lambda$5876 Å absorption line recently discovered in the spectrum of the companion to the millisecond pulsar PSR J1740-5340 is tentatively attributed to electron impact excitations due to the irradiation of its atmosphere by $\gamma$-rays emitted by the pulsar's magnetosphere. Numerical calculations, similar to those carried out previously for type Ib SNe, indicate that a pulsar beam with photon energies ~1 MeV gives rise to a $\lambda$5876 Å line of the observed strength if the beam's spin-down conversion efficiency approaches 1%. However, a significant difficulty for the proposed mechanism is the strength of the singlet line at $\lambda$6678 Å. Compared to the corresponding triplets, singlet lines are weak because of the loss of excitation when photons emitted in the series $ n^{1}{\rm P}^{0} \rightarrow 1^{1}{\rm S}$ ionize hydrogen atoms, an effect absent in the hydrogen-free atmospheres of type Ib SNe.

Key words: stars: pulsars: individual: PSR J1740-5340 -- radiative transfer -- stars: atmospheres -- line: formation

SIMBAD Objects

© ESO 2003