1. The Absolute Luminosities of Type Ia Supernovae
Pskovski and Phillips had previously proposed that the luminosities
of Type Ia supernovae were correlated with their post maximum decline rates.
Thanks to the high quality data of the survey that I carried out between
1990-1993 (the Calan/Tololo project) I confirmed these results and provided
the most precesie tool to measure extragalactic distances. This
method was later on adopted by Brian Schmidt and Saul Perlmutter to
determine distances to very distant supernovae. Combining the distances
to the distant and nearby supernovae discovered in the course of the
Calan/Tololo survey, Schmidt and Perlmutter demonstrated in 1998
that the Universe is undergoing an accelerated expansion, an unexpected
result which implies that we need to review the understanding of
gravity formulated by Einstein in 1916 or that there is a new type of force
in Nature.
2. Environmental Effects on Type Ia Supernovae on Galaxy Type
By comparing the luminosities of the Calan/Tololo supernovae to the
properties of their host galaxies, in 1993 I discovered that the most luminous
supernovae occur in spiral galaxies. This implies that either
young progenitors or metal-poorer progenitors lead to brighter
supernovae. Other people (eg. Garnavich) have shown that the role
of metallicity is not the primary source of scatter, implying that
younger progenitors lead to more luminous Type Ia supernovae.
3. Type II Supernovae as Standardized Candles
Toward the end of my PhD thesis in 2001, I discovered a correlation between
the luminosities of Type II plateau supernovae and their expansion velocities,
which established a new method to determine precise extragalactic distances.
This technique will allow us to obtain an independent measurement
of the acceleration of the Universe. Other people (Nugent, Olivares, Poznanski)
have confirmed this finding from independent data sets.
4. First detection of Hydrogen in a Type Ia Supernova
In 2002 I took a spectrum of a Type Ia supernova. The object, SN 2002cx,
was remarkable due to the presence of Hydrogen in the spectrum. This
was the first long-awaited detection of hydrogen around a Type Ia supernova.
The observations imply high density circumstellar gas around the supernova,
possibly arising from a donor having undergone a high mass loss rate (eg. AGB star).
5. Last but not least: Spectrophotometric Standards
Between 1989-1992 I obtained CCD multiple-epoch spectrophotometry for 20+ stars
which provided the most accurate and precise set of standard stars for
flux measurements in the southern hemisphere. This set of stars
still constitutes a fundamental reference for observers.
With Stritzinger and Suntzeff we followed
up on this work and extended the grid to a new set of 100+ stars.