The Conversion of St. John: A Case Study on the Interplay of Theory and Experiment

The ArgumentGravitational redshift of spectral lines as one of the three early-known experimental implications of Einstein's general theory of relativity and gravitation was intensively searched for by researchers all over the world, but around 1920 most of the contemporary evidence in the sun's Fraunhofer-spectrum conflicted with the predictions of relativity theory.In 1923 the American astrophysicist Charles Edward St. John announced that his own solar spectroscopic data would force him to retreat from his former skepticism concerning the existence of gravitational redshift. This statement was at the time widely interpreted by scientists and journalists alike as the open confession of a rapid conversion of one of the few remaining serious scientific opponents of Einstein's theory.This paper demonstrates that this illusion of a sudden “Gestalt switch” in St. John's evaluation of data can be dissolved by a careful step-by-step account of St. John's research practice between 1917 and 1923. After a fine-grained diachronic report of the development of St. John's interpretation of his and others' data, the second part of the paper consists in a systematic analysis of the heuristics and arguments used by St. John pro and contra gravitational redshift.

On X-ray Pulsar Radiation Mechanisms

In this report we shall discuss the origin of radiation from the neutron star component of X-ray binary systems whose spectra contain cyclotron lines (Her X-1 and 4U0115+63). A relevant model of the polar region of a neutron star is presented in Figure 1. According to this model the observed X-rays (continuum + cyclotron lines) are generated in the dense plasma atmosphere of a star (in its hot spot heated by accreting matter). The problem of heating the neutron star atmosphere due to accretion has been earlier investigated by Zeldovich and Shakura (1969). Cyclotron lines are formed similarly to the Fraunhofer spectrum of ordinary stars and are absorption lines. For objects such as Her X-1 and 4U0115+63 the cyclotron emission and absorption in the extended accreting column with an inhomogeneous magnetic field should be unessential. Otherwise the accreting column will produce an X-ray continuum devoid of any line type features.