CfA3: 185 Type Ia Supernova Light Curves from the CfA

TL;DR

This paper presents a large, high-precision, homogeneously-observed sample of 185 Type Ia supernova light curves, significantly enhancing data quality and quantity for cosmological studies and improving distance measurement accuracy.

Contribution

It provides the largest homogeneous SN Ia dataset to date, with detailed photometry and systematic uncertainty analysis, aiding the development of better light-curve fitters and reducing distance measurement errors.

Findings

SN Ia light curves have a precision of 0.02 mag in BVRIr'i' bands.

Systematic uncertainties are estimated at 0.03 mag in BVRIr'i' and 0.07 mag in U.

1991bg-like SN Ia are distinct and should be treated separately in analyses.

Abstract

We present multi-band photometry of 185 type-Ia supernovae (SN Ia), with over 11500 observations. These were acquired between 2001 and 2008 at the F. L. Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics (CfA). This sample contains the largest number of homogeneously-observed and reduced nearby SN Ia (z < 0.08) published to date. It more than doubles the nearby sample, bringing SN Ia cosmology to the point where systematic uncertainties dominate. Our natural system photometry has a precision of 0.02 mag or better in BVRIr'i' and roughly 0.04 mag in U for points brighter than 17.5 mag. We also estimate a systematic uncertainty of 0.03 mag in our SN Ia standard system BVRIr'i' photometry and 0.07 mag for U. Comparisons of our standard system photometry with published SN Ia light curves and comparison stars, where available for the same SN, reveal agreement at the level of a few hundredths mag in most cases. We find that 1991bg-like SN Ia are sufficiently distinct from other SN Ia in their color and light-curve-shape/luminosity relation that they should be treated separately in light-curve/distance fitter training samples. The CfA3 sample will contribute to the development of better light-curve/distance fitters, particularly in the few dozen cases where near-infrared photometry has been obtained and, together, can help disentangle host-galaxy reddening from intrinsic supernova color, reducing the systematic uncertainty in SN Ia distances due to dust.