Analyzing SNe Ia

Identification, m-M, WM , WL , & q0

 

Before any analysis can begin, SNe must be identified.  This is done by taking current observations of a SNe (such as the HST ACS images shown in the top two panels), and subtracting from it either observations from before the SN occured (such as the HST WFPC2 in the lower left) or else an image from after the SN has dimmed beyond being detectable.  The result (like that shown in the lower right) not only makes the SN clearly stand out, but also isolates it for photometric measurements.

 

 ACS 775nm

Blakeslee et al (HZT), 2003

 ACS 850nm
WFPC2 814nm Before SN Host Galax Subtracted

 

Once the SN has been identified, it is observed over many nights to get a light curve.  Models are then fit to the data in order to determine the peak brightness.  Spectra of the host galaxy are then used to find the redshift of the host galaxy.

Riess et al (HZT), 1998

Once distances and redshifts have been found, a Hubble diagram is produced.  Using WM, WL, and H0 as free parameters, a c2 fitting is used to compare various models.  Also, based on the goodness of fit for many combinations of WM and WL, probabilities ellipses are computed like those shown below.  The deceleration parameter, q0, is then found from the most likely combination of those parameters.

Riess et al (HZT), 1998

Riess et al (HZT), 1998