Magellan Telescopes

The twin 6.5-m Magellan Telescopes at Las Campanas Observatory, Chile.

There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable.  There is another theory which states that this has already happened.  — Douglas Adams

I like that quote from The Hitchhiker’s Guide to the Galaxy because in some sense, it really did happen that way.  I remember being a graduate student at the University of Toronto, around the time when cosmologists were confident that they had figured out the Universe.  The Hubble constant was well measured, giving a scale to the Universe.  The matter content was the other important quantity to know.  There was Dark Matter, sure, but it was detectable and still amounted to less than 30% of the energy content needed for the Universe to re-collapse.  The Universe was believed to be open and would expand forever at an ever-slowing pace.

Then it happened:  precise measurements of type Ia supernovae showed that the Universe was not slowing down, but speeding up!  It was as if Adams’ notion of a new, bizarre Universe taking the place of our well-understood one actually happened.  But, of course, it made for opportunities to research this new exotic beast:  Dark Energy.  That’s what I’m embroiled in right now, but I also have other interests as well…

The Carnegie Supernova Project

The Carnegie Supernova Project is attempting to provide independent constraints on the nature of Dark Energy by both improving the low-redshift sample of supernovae and constructing an I-band Hubble diagram for higher-redshift supernovae.

  1. Hamuy, M. et al., (2006), The Carnegie Supernova Project:  The Low-Redshift Survey (ADS,PASParXiv)
  2. Freedman et al., (2009), “The Carnegie Supernova Project:  First Near-Infrared Hubble Diagram to z~0.7”,  (ADSApJarXiv)
  3. Burns et al. (2018) “The Carnegie Supernova Project:  Absolute Calibration and the Hubble Constat”,  (ADS,ApJarXiv)

Distances in Astronomy

This is one of the big problems faced by astronomers.  We are presented with a 2-dimensional view of a 3-dimensional universe (4 if you count time).  Inferring that 3rd dimension is tricky.  Here are some projects I’m (or have been) involved with this problem:

  • CARRS (Carnegie RR-Lyra Survey).  A survey of RR-Lyra variables which, like Cepheid variables, can be used as standard candles.
  • CHP (The Carnegie Hubble Program).  A follow-up survey of Cepheid Variables conducted in the Near Infra Red, where these standard candles are more standard.
    • Freedman et al., 2012, Carnegie Hubble Program:  A Mid-Infrared Calibration of the Hubble Constant (ADS, arXiv)
  • Probing HI clouds.  A group of graduate students (including yours truly) used the David Dunlap Observatory (DDO) to observe stars along the line of sight toward some Intermediate Velocity Clouds (IVCs).  If the spectra of these stars showed sodium absorption blueshifted to the velocity of the cloud, we determined the star was behind the cloud.  Lack of this absorption feature told us it was in front.  Using spectroscopic parallax, we could bracket the distance to the IVC.
    • Burns, C.R. et al., 2003, The DDO IVC Distance Project:  Survey Description and the Distance to G139.6+47.6 (ADS,AJ,astro-ph)
    • Gladders, M. et al, 1998, The Distance to the Draco Intermediate Velocity Cloud (ADSApJ)

Gravitation Lensing of Polarized Objects

My thesis work involved using the fact that the polarization angle of background sources is not changed by an intervening gravitational lens.  If the polarization is aligned with the morphology of the background source, observed departures from this alignment directly measures the shear of the lens.

  • Burns, C.R. et. al, 2004, Theoretical Modeling of Weakly Lensed Polarized Radio Sources (ADSApJastro-ph)
  • Kronberg, P.P et al., 1996, Estimates of the Global Masses of Two Distant Galaxies Using a New Type of Astrophysical Mass “Laboratory” (ADS)

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