DAO Astronomy Colloquium

DAO Astronomy Colloquium Schedule

In person talks will take place in the LCR and will be streamed live online via Zoom.

Tuesdays at 11am unless otherwise indicated with (***)

Archive of previous seminar schedules (2010-)


Winter/Spring 2023

Tues January 17, 11am, Norm Murray (CITA), in person Recording

Why the day is 24 hours long
The length of the day and the month are seen to be increasing, due to gravitational tidal torques. Geologic data suggests, however, that between about 2,000 million years ago (Ma) and 1,000 Ma, the length of day (LOD) was fixed at about 19.5 hours, while the length of the month was increasing. Following a suggestion by Zahnle and Walker in the 1980’s, I and my co-workers explore the hypothesis that the fixed LOD results from the Solar thermal atmospheric tide, which was stronger in the past, due in part to a resonance in Earth’s atmosphere. Absent this resonance, the LOD today would be around 60 hours. We use two global circulation models (or GCMs), PlaSim and LMD, to estimate the frequencies of normal modes (or free oscilliations) in Earth’s atmosphere, finding excellent agreement with recent measurements. Using the GCMs, we show that an atmospheric resonant period of 19.5 hours corresponds to a mean global surface temperature T in the range 40-50 C; the GCMs show that T could have been that high despite the lower Solar flux 2,000 Ma, if the partial pressure of CO2 was of order a tenth of a bar, compared to the present day value of 0.0004 bar. This is at the upper range of estimates 1,500 Ma based on geochemical and paleosoil evidence. Thermal tides are likely to have affected the length of day of many exoplanets.

Tues January 24, 11am, Kevin Casteels (HAA), in person Recording

Complex Spacetime and Luminosity Driven Expansion
The two pillars of modern physics, Quantum Mechanics and General Relativity, interpret reality in very different ways, the former as purely statistical, and latter purely geometrical. This apparent incompatibility can be reconciled through the use of complex math to describe spacetime. We will explore previous work done on Complex Spacetime including recent studies which show imaginary numbers aren’t merely a mathematical convenience, but essential to describe observation. A new model will be described which treats real spacetime as composed of two imaginary parts, or layers, which mix to create real space. One of the predictions of this model is that when mass is converted to energy, the real space metric expands by an amount proportional to the photon’s half wavelength. We will explore the consequences of this prediction, and calculate expansion rates for various objects. It is found that the Local Group of Galaxies produces a luminosity driven expansion rate of ~70 km/s, which is comparable to measurements of the Hubble flow. When considering galaxy clusters, the luminosity driven real space expansion would act to increase the observed velocity dispersions, giving virial mass estimates several times greater than the observed baryonic mass, potentially removing the need for large dark matter components in these systems.

Tues January 31, 11am, Melissa Graham (UWash), in person Recording

Supernova Science with Large Sky Surveys
As the endpoints of stellar evolution, sources of dust, and cosmological standard candles, supernovae are a useful and important astrophysical phenomenon to understand. In this talk I will describe how I use large sky surveys and targeted follow-up to constrain the physical nature of Type Ia supernovae (SN Ia), the thermonuclear explosions of carbon-oxygen white dwarf stars. I will also provide a look towards the future with the Rubin Observatory, which will detect millions of supernovae over its 10-year Legacy Survey of Space and Time (LSST). I am currently a research staff scientist at the University of Washington in Seattle, and I hold the roles of Data Management Science Analyst and Lead Community Scientist for the Rubin Observatory. This talk will also cover how individuals without Rubin data rights can participate in LSST science, and provide an inside look at how Rubin staff are preparing themselves — and the science community — for the data revolution of the LSST.


Tues February 7, 11am, Joan Najita (NOIRLab), on zoom

Clues to Our History from Debris Disks and the Dynamics of Andromeda’s Halo

Abstract: The patterns we notice in astronomical data can provide simple but valuable clues to how systems evolve and to our own origins. I’ll share two examples. (1) The similar sizes of the spectacular rings observed in protoplanetary disks and debris disks suggest that they share a common origin. New calculations of the evolution of rings of pebbles and planetesimals lead us to a simple picture in which large protoplanetary disks evolve into the known bright debris disks, with our Solar System following a distinct evolutionary path that originates in compact disks. (2) Data recently obtained by DESI, the highly multiplexed multi-object spectrograph on the 4m Mayall Telescope on Kitt Peak, reveal delicate structures—streams, wedges, and chevrons—in the positions and velocities of individual stars:

evidence of a recent galactic immigration event in exquisite detail. The observations may open a window onto our past, offering a view of what our own galaxy may have looked like billions of years ago. 

Tues February 14, 11am, Jessie Christiansen  (Caltech), in person

Tues February 21, 11am, Ryan Jackson (UVic), in person

Tues February 28, 11am, Iris Dillmann (TRIUMF), in person

Thursday March 9, 11am, Mark Voit (MSU), in person

Tues March 14, 11am, Melissa Amenouche (HAA), in person

Tues March 21, 11am, Hao He (McMaster), on zoom

Wednesday March 29, 11am, Tarraneh Eftekhari (Northwestern), in person

Tues April 4, 11am, Kartheik Iyer (Columbia), on zoom