The Role of Radioactivities in Astrophysics

I present both a history of radioactivity in astrophysics and an introduction to the major applications of radioactive abundances to astronomy

Extensive optical and near-infrared observations of the nearby, narrow-lined type Ic SN 2007gr: days 5 to 415

We present photometric and spectroscopic observations at optical and near-infrared wavelengths of the nearby type Ic SN 2007gr. These represent the most extensive data-set to date of any supernova of this sub-type, with frequent coverage from shortly after discovery to more than one year post-explosion. We deduce a rise time to B-band maximum of 11.5 \pm 2.7 days. We find a peak B-band magnitude of M_B=-16.8, and light curves which are remarkably similar to the so-called 'hypernova' SN 2002ap. In contrast, the spectra of SNe 2007gr and 2002ap show marked differences, not least in their respective expansion velocities. We attribute these differences primarily to the density profiles of their progenitor stars at the time of explosion i.e. a more compact star for SN 2007gr compared to SN 2002ap. From the quasi-bolometric light curve of SN 2007gr, we estimate that 0.076 $\pm$ 0.010 Msun of 56Ni was produced in the explosion. Our near-infrared (IR) spectra clearly show the onset and disappearance of the first overtone of carbon monoxide (CO) between ~70 to 175 days relative to B-band maximum. The detection of the CO molecule implies that ionised He was not microscopically mixed within the carbon/oxygen layers. From the optical spectra, near-IR light curves, and colour evolution, we find no evidence for dust condensation in the ejecta out to about 400 days. Given the combination of unprecedented temporal coverage, and high signal-to-noise data, we suggest that SN 2007gr could be used as a template object for supernovae of this sub-class.Comment: A&A accepted; 26 pages & 16 figure

James Franck, the Ionization Potential of Helium, and the Experimental Discovery of Metastable States

In 1920, James Franck together with Fritz Reiche and Paul Knipping found strong experimental evidence that the lowest lying triplet state in helium is metastable—an atom in this state cannot make a spontaneous transition to the ground state. Even though their evidence was entirely experimental, they tied their results almost inextricably to Alfred Landé’s 1919 model of the helium atom, and in the process, misunderstood the new theoretical selection rules of Adalbert Rubinowicz and Niels Bohr. In an additional complication, experiments of the English physicists Frank Horton and Ann Catherine Davies contradicted Franck’s. Although Franck’s result has held up, the reasons for the discrepancies remain unclear

Epicycles, eccentrics, and ellipses: The predictive capabilities of Copernican planetary models

A theoretical analysis of the potential accuracy of early modern planetary models employing compound circles suggests that fairly simple extensions of those models can be sufficiently accurate to meet the demands of TYCHO BRAHE’s observations in both ecliptic longitude and latitude. Some of these extensions, such as the substitution of the true sun for the mean sun, had already been taken by KEPLER before he abandoned circular models. Other extensions, involving one or two extra epicycles, were well within the mathematical capabilities of sixteenth-century and seventeenth-century astronomers. Hence neither the failure of astronomers before KEPLER to correct errors in planetary positions nor KEPLER’s decision to abandon circular models was a consequence of inherent limitations in those models

The Franck-Hertz experiments, 1911-1914: Experimentalists in search of a theory. With an appendix, “On the history of our experiments on the energy exchange between slow electrons and atoms” by Gustav Hertz

In 1911, James Franck and Gustav Hertz began a collaboration to investigate the nature of collisions of slow electrons with gas molecules that led to a series of carefully planned and executed experiments, culminating in their discovery of inelastic collisions of electrons with mercury vapor atoms in 1914. This paper tells the story of their collaboration and the eventual reinterpretation of their results as a confirmation of Niels Bohr’s new atomic theory, largely as a result of experiments done in North America during the Great War

Specific heats and the equipartition law in introductory textbooks

A majority of introductory calculus‐based physics textbooks, including many widely used ones, give misleading or incorrect explanations for the failure of the equipartition law to describe correctly the classically expected rotational degrees of freedom in monatomic and diatomic gases. This article outlines typical textbook treatments and reviews the quantum mechanical explanation

Einstein before 1905: The early papers on statistical mechanics

Albert Einstein’s work on the quantum and Brownian motion, which he began to publish in 1905, was preceded by three papers on kinetic theory and statistical mechanics published between 1902 and 1904. In these early papers, which give us considerable insight into Einstein’s early education and development, Einstein independently derived many of Boltzmann’s and Gibbs’ results, including the canonical ensemble, an analysis of fluctuations, and the relation between entropy and probability. This article discusses those papers and their background in 19th‐century physics

Planck, the quantum, and the historians

In late 1900, the German theoretical physicist Max Planck derived an expression for the spectrum of black-body radiation. That derivation was the first step in the introduction of quantum concepts into physics. But how did Planck think about his result in the early years of the twentieth century? Did he assume that his derivation was consistent with the continuous energies inherent in Maxwellian electrodynamics and Newtonian mechanics? Or did he see the beginnings, however tentative and uncertain, of the quantum revolution to come? Historians of physics have debated this question for over twenty years. In this article, I review that debate and, at the same time, present Planck\u27s achievement in its historical context