lowest scatter Hubble diagrams ever published (Bailey et al)

[marcus]

"...lowest scatter Hubble diagrams ever published" (Bailey et al)

This is big news for cosmology. More accurate determination of distances and therefore of the Hubble parameter---a key proportion basic to the whole field.

http://arxiv.org/abs/0905.0340
Using Spectral Flux Ratios to Standardize SN Ia Luminosities

S. Bailey, G. Aldering, P. Antilogus, C. Aragon, C. Baltay, S. Bongard, C. Buton, M. Childress, N. Chotard, Y. Copin, E. Gangler, S. Loken, P. Nugent, R. Pain, E. Pecontal, R. Pereira, S. Perlmutter, D. Rabinowitz, G. Rigaudier, K. Runge, R. Scalzo, G. Smadja, H. Swift, C. Tao, R. C. Thomas, C. Wu (The Nearby Supernova Factory)
6 pages, 3 figures, 2 tables; accepted by A&A Letters
(Submitted on 4 May 2009)

"We present a new method to standardize Type Ia supernova (SN Ia) luminosities to ~<0.13 magnitudes ... When combined with broad-band color measurements, spectral flux ratios can standardize SN Ia magnitudes to ~0.12 mag. These are the first spectral metrics that improve over the standard normalization methods based upon light curve shape and color and they provide among the lowest scatter Hubble diagrams ever published."

The SciAm has a news item about this:
http://www.scientificamerican.com/blog/60-second-science/post.cfm?id=a-better-way-to-size-up-distant-gal-2009-05-22

===sample excerpt==
the new method can be used to measure a supernova's luminosity, and hence distance, much more quickly, and with a level of accuracy the study's authors say surpasses the traditional approach.

The researchers found that the ratio of the brightness of two colors in the supernova's light spectrum strongly correlate with the explosion's magnitude. Specifically, the ratio of 642-nanometer-wavelength (orange-red) light to that of light with a wavelength of 443 nanometers (indigo) gives an accurate estimate of the supernova's brightness, in concert with other observed characteristics.

Type Ia supernovae are useful as markers because of their fairly standard brightness, which facilitates gauging their distance across the universe. Their uniformity derives from unusual birth circumstances: they are believed to arise from white dwarfs that have swollen to 1.4 times the mass of the sun by drawing material from a nearby companion star. At that point, says study co-author Greg Aldering, a cosmologist at Lawrence Berkeley National Laboratory, "a white dwarf star cannot support itself against gravity," exploding in a thermonuclear blast that is visible even in distant galaxies. "The conversion of a fixed mass—1.4 solar masses—into energy," Aldering says, "sets a reasonably narrow range to the resulting brightness."...
==endquote==

 

[Evan Fox]

It is exciting to see the progress being made in our understanding of SN Ia and their use as standard candles. Bailey et al's work on spectral flux ratios could provide a major breakthrough in the accuracy of measuring distances with SN Ia, and ultimately the determination of the Hubble parameter. This could lead to a better understanding of the universe and of cosmology.