credit: o. krause (steward obs.) et al., ssc, jpl, caltech, nasa south africa and the sdss-ii...
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Credit: O. Krause (Steward Obs.) et al., SSC, JPL, Caltech, NASA
South Africa and the SDSS-II Supernova Survey
Ed Elson (SAAO/NASSP)Bruce Bassett (SAAO/ICG)Kurt van der Heyden (SAAO)Zebalon Vilakazi (UCT)
Dark energyDark energy
What constitutes our What constitutes our Universe?Universe?
Simply radiation and Simply radiation and baryonic matter?baryonic matter?
Is there more than Is there more than meets the eye?meets the eye?
Up to 95% of its Up to 95% of its energy content is energy content is thought to be exotic. thought to be exotic.
Dark energyDark energy
2 leading DE models: cosmological constant (2 leading DE models: cosmological constant () ) and quintessence.and quintessence.
has constant negative pressure, causing has constant negative pressure, causing expansion of the Universe to accelerate.expansion of the Universe to accelerate.
Quintessence is a dynamical field in which Quintessence is a dynamical field in which negative pressure DE varies in space and time.negative pressure DE varies in space and time.
is the most economical solution to cosmic is the most economical solution to cosmic expansion.expansion.
Dark energy and the UniverseDark energy and the Universe
DE has many DE has many implications for the implications for the history and fate of history and fate of the Universe.the Universe.
The more DE, the The more DE, the older the Universe older the Universe and the expansion and the expansion increases with time.increases with time.
Type Ia SupernovaeType Ia Supernovae
SNIa are semi-detachedSNIa are semi-detached
binary systems.binary systems. When the ChandrasekharWhen the Chandrasekhar
mass limit is reached, mass limit is reached,
the white dwarf explodes violently.the white dwarf explodes violently. SNIa have a characteristic light curve.SNIa have a characteristic light curve. Important feature: decay rate is related to peak Important feature: decay rate is related to peak
intrinsic luminosity of SN.intrinsic luminosity of SN.
Credit: High-Z Supernova Search Team, HST, NASA (Riess et al. 1996a, 1998a)
Supernova 1994d, type Ia.
Supernova 1987A, thought to be type II.
Evidence from SNIa of Evidence from SNIa of accelerationacceleration
A SNIa survey in the late A SNIa survey in the late 1990’s provided some of 1990’s provided some of the 1the 1stst evidence of cosmic evidence of cosmic acceleration.acceleration.
SNIa were used as SNIa were used as standard candles to standard candles to measure the expansion measure the expansion history of the Universe.history of the Universe.
Results indicated Results indicated acceleration , i.e. large DE acceleration , i.e. large DE content.content.
SDSS-IISDSS-II
Aim: Study structure of Milky WayAim: Study structure of Milky Way
and nature of dark energy.and nature of dark energy. Expected to discover ~200 new SNIa by 2008.Expected to discover ~200 new SNIa by 2008. Already over 100 new confirmed SNIa have been Already over 100 new confirmed SNIa have been
announced.announced. After each night’s observing, hand scanners work After each night’s observing, hand scanners work
through ~5000 objects to try identify SNIa through ~5000 objects to try identify SNIa candidates.candidates.
SDSS-IISDSS-II
Performance of the scanners is continuously Performance of the scanners is continuously monitored.monitored.
Spectroscopic follow up observations and Spectroscopic follow up observations and multi-band light curve fitting are carried out multi-band light curve fitting are carried out on SNIa candidates.on SNIa candidates.
South Africa’s InvolvementSouth Africa’s Involvement SALT will study the Universe at SALT will study the Universe at
very early times.very early times.
The high res. Spectrograph The high res. Spectrograph
could be used to obtain SNIa could be used to obtain SNIa
spectra.spectra.
Multi-wavelength observations Multi-wavelength observations
of SNIa will help determine of SNIa will help determine
extinction effects of galaxies.extinction effects of galaxies.
Significant results would yet Significant results would yet
again change out view of the again change out view of the
Universe!Universe!
The end.The end.
Email: [email protected] (Ed Elson) [email protected] (Bruce Bassett) [email protected] (Kurt van der Heyden) [email protected] (Zebalon Vilakazi)