Teaching is like engineering: my living educational theory

The traditional view of scientific progress is that human understanding of the world is contiguous and cumulative, with both theories and concepts ‘improving’ incrementally through gradational change. Thomas Kuhn’s (1962) The Structure of Scientific Revolutions challenged this traditional view by arguing, on the contrary, that scientific progress is made through leaps and bounds, when “the earlier results of science [are] rejected, replaced, and reinterpreted by new theories and conceptual frameworks” (“Scientific Progress.”, 2020). Stated simply, scientific progress is revolutionary, not evolutionary. History is seemingly no different. Indeed, although it is often said that history is written by the victors, human understanding of the past is always under threat, as new data are revealed, for example, ideologies and cultural hegemonies change, or scientific developments in other academic disciplines emerge. [...] This context statement documents my historical journey through the Doctor of Professional Studies by Public Works process. The logic is largely chronological in nature, but doubtless some historical revisionism has crept into my narrative. [...

Studying the small scale ISM structure with supernovae

AIMS. In this work we explore the possibility of using the fast expansion of a Type Ia supernova photosphere to detect extra-galactic ISM column density variations on spatial scales of ~100 AU on time scales of a few months. METHODS. We constructed a simple model which describes the expansion of the photodisk and the effects of a patchy interstellar cloud on the observed equivalent width of Na I D lines. Using this model we derived the behavior of the equivalent width as a function of time, spatial scale and amplitude of the column density fluctuations. RESULTS. The calculations show that isolated, small (<100 AU) clouds with Na I column densities exceeding a few 10^11 cm^-2 would be easily detected. In contrast, the effects of a more realistic, patchy ISM become measurable in a fraction of cases, and for peak-to-peak variations larger than ~10^12 cm^-2 on a scale of 1000 AU. CONCLUSIONS. The proposed technique provides a unique way to probe the extra-galactic small scale structure, which is out of reach for any of the methods used so far. The same tool can also be applied to study the sub-AU Galactic ISM structure.Comment: 6 pages, 3 figures. Accepted for publication in Astronomy & Astrophysic

Determination of the Hubble Constant Using a Two-Parameter Luminosity Correction for Type Ia Supernovae

In this paper, we make a comprehensive determination of the Hubble constant $H_0$ by using two parameters - the B-V color and the rate of decline $\Delta m_{15}$ - to simultaneously standardize the luminosities of all nearby Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more distant sample of 29 SNe Ia. Each group is treated in as similar a manner as possible in order to avoid systematic effects. A simultaneous $\chi ^2$ minimization yields a standardized absolute luminosity of the Cepheid-calibrated supernovae as well as the Hubble constant obtained from the more distant sample. We find $H_0 = 62 km/s Mpc^{-1}$ and a standardized absolute magnitude of -19.46. The sensitivity of $H_0$ to a metallicity dependence of the Cepheid-determined distances is investigated. The total uncertainty $\delta H_0$, dominated by uncertainties in the primary Cepheid distance indicator, is estimated to be 5 km/s Mpc^{-1}.Comment: To appear in Ap

Supernova Resonance-Scattering Profiles in the Presence of External Illumination

We discuss a simple model for the formation of a supernova spectral line by resonance scattering in the presence of external illumination of the line-forming region by light from circumstellar interaction (toplighting). The simple model provides a clear understanding of the most conspicuous toplighting effect: a rescaling or, as we prefer, a ``muting'' of the line profile relative to the continuum. This effect would be present in more realistic models, but would be harder to isolate. An analytic expression for a muting factor for a P-Cygni line is derived that depends on the ratio E of the toplighting specific intensity to the specific intensity from the supernova photosphere. If E<1, the line profile is reduced in scale or ``muted''. If E=1, the line profile vanishes altogether. If E>1, the line profile flips vertically: then having an absorption component near the observer-frame line center wavelength and a blueshifted emission component.Comment: accepted for publication in PAS

Hydrogen in Type Ic Supernovae?

By definition, a Type Ic supernova (SN Ic) does not have conspicuous lines of hydrogen or helium in its optical spectrum. SNe Ic usually are modelled in terms of the gravitational collapse of bare carbon-oxygen cores. We consider the possibility that the spectra of ordinary (SN 1994I-like) SNe Ic have been misinterpreted, and that SNe Ic eject hydrogen. An absorption feature usually attributed to a blend of Si II 6355 and C II 6580 may be produced by H-alpha. If SN 1994I-like SNe Ic eject hydrogen, the possibility that hypernova (SN 1998bw-like) SNe Ic, some of which are associated with gamma-ray bursts, also eject hydrogen should be considered. The implications of hydrogen for SN Ic progenitors and explosion models are briefly discussed.Comment: Accepted by PASP. Several significant changes including one additional figur