Supernovae

• Historically: “new stars” in sky

• Seen in 1006, 1054, 1181, 1572, 1604, 1680

• SN 1054 visible in daytime sky for many months (Chinese records)

• SN 1572 – Tycho, SN 1604 – Kepler

• SN 1987A is the only SN visible to the naked eye since the development of telescopes. It is in the Large Magellanic Cloud (50 kpc distant)

Tycho’s report on his observations of the SN of 1572

Supernovae

• Historically: “new stars” in sky

• Seen in 1006, 1054, 1181, 1572, 1604, 1680

• SN 1054 visible in daytime sky for many months (Chinese records)

• SN 1572 – Tycho, SN 1604 – Kepler

• SN 1987A is the only SN visible to the naked eye since the development of telescopes. It is in the Large Magellanic Cloud (50 kpc distant)

Most of what we know today about SN comes from studying them in other galaxies.

Why are SNe important?

• The source of most heavy (> He) in the universe.

• Input a lot of mechanical energy into the interstellar medium (1051 erg).

• A laboratory for studying physics under extreme conditions.

• Associated with useful/interesting phenomena: neutron stars and pulsars; SN Ia used in cosmology; SN II associated with gamma ray bursts.

Supernovae are energetic explosions

• Rapid rise (10 days) to peak luminosities of about 1010 solar luminosities.

• Spectra show broad, blue-shifted absorption lines with velocities of about 104 km/s.

• Luminous stellar progenitor seen in a few cases.

SNe Types

• Type Ia: no hydrogen in spectrum, brightest peak luminosity, seen only in both elliptical and spiral galaxies.

• Type Ib/Ic: no hydrogen in spectrum, fainter peak L, seen only in spiral galaxies.

• Type II: hydrogen seen in spectrum, fainter than Ia’s, seen only in spiral galaxies. Light curve (brightness vs time) comes in two broad types – linear (II L) and plateau (II P); though there is a wide diversity in this class.

SN spectra at early times: broad absorption lines, some with PCygni profiles.

SNe spectra at late times become dominated by emission lines (hot, low-density gas) of Fe/Co (Type Ia) or light and intermediate elements (Type II and Ib/c)

SNe Types

• Type Ia: no hydrogen in spectrum, brightest peak luminosity, seen only in both elliptical and spiral galaxies.

• Type Ib/Ic: no hydrogen in spectrum, fainter peak L, seen only in spiral galaxies.

• Type II: hydrogen seen in spectrum, fainter than Ia’s, seen only in spiral galaxies. Light curve (brightness vs time) comes in two broad types – linear (II L) and plateau (II P); though there is a wide diversity in this class.

Sne Light Curves

Supernovae searches & rates• Used to be found by dedicated amateurs, today

mostly found by automated surveys (of nearby galaxies) and scheduled discovery campaigns (for distant galaxies).

• Type Ia: one every 300 years in the Milky Way Galaxy (a typical big galaxy).

• Type Ib/c, II: one every 30-50 years in the Milky Way.

Berkeley Automated Telescopes

• KAIT: 0.76m automated telescope

• Images about 1000 galaxies a night out to a distance of about 200 Mpc

• Discovers about 80 SNe a year.

SN 2008I

SN Ia Phillips relation

• Peak brightness is related to the initial rate of decline of the light curve (faster decline goes with a fainter peak).

• More generally, the peak brightness correlates with the shape and color of the light curve.

• Reduces the scatter from 0.4 – 0.5 magnitude to 0.12 – 0.15 mag.