printable versionKavli researchers join supernova search
BY MASAO SAKO
Masao Sako, a postdoctoral researcher at the Kavli Institute, explains type Ia supernovae, such as our Milky Way’s SN1006, shown below.
Several members of the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC)—Masao Sako, Roger Romani, Chen Zheng, Roger Blandford and Steve Kahn—have joined the Sloan Digital Sky Survey II (SDSS-II) collaboration to participate in a massive search for supernova explosions from the distant universe. The survey uses the SDSS 2.5-meter telescope at Apache Point Observatory in New Mexico to obtain repeated multi-color images of the same 300 square-degree patch of the sky approximately every other night. A unique large-format charge-coupled-device camera array with a total of 120 million pixels is capable of recording 200 gigabytes of imaging data in a single night, allowing efficient discoveries of supernova explosions out to redshift z~0.4, or about one-third of the way back to the Big Bang.
The search consists of three campaigns each lasting from Sept. 1 through Nov. 30 of 2005, 2006 and 2007. During the first season, which ended just a few months ago, the primary focus was to study type Ia supernovae, a class associated with thermonuclear explosions of white dwarfs. The 2005 campaign was a remarkable success. A total of 130 type Ia supernovae in the redshift interval of 0.01 < z < 0.42 (called the "redshift desert" since other surveys have not found many supernovae in this range) were spectroscopically confirmed, producing the best rookie year of any previous supernova searches. This unique set of supernovae will help scientists understand and quantify the systematics of type Ia supernovae as distance indicators, and will provide independent constraints on dark matter, dark energy and the expansion history of the universe. Interestingly, the redshift range of the SDSS-II supernova search covers most of the period where recent work suggests that dark energy is the dominant constituent of the cosmos.</P>
Stanford's partnership in the 9.2-meter Hobby-Eberly Telescope at the McDonald Observatory in Texas has allowed KIPAC members to follow up and obtain optical spectra of about 50 type Ia high-redshift supernovae, which make up a large chunk of the "distant" sample most useful for cosmological studies. The KIPAC group also has targeted different types of supernovae including the peculiar Ib/c hypernovae that are believed to be associated with cosmic gamma-ray bursts and other rare types of supernovae that are poorly sampled in other surveys.
Masao Sako is a postdoctoral research fellow at KIPAC. This article first appeared in SLAC Today (http://today.slac.stanford.edu).