Nicholas B. Suntzeff
CTIO Scientific Staff
Areas of Interest
tellar Populations, Globular Clusters, Stellar Chemical Abundances,
Galactic Structure, Magellanic Clouds, Supernovae, Large-Scale Structure,
Astronomical Site Characteristics
Recent Research Results
Suntzeff, in collaboration with Phillips, Schommer, and the rest of the
Calan/Tololo supernovae project, has continued his long-term study of
supernovae. The first phase of the Calan/Tololo project has been
finished, and over 50 supernovae (SNe) were discovered out to z=0.12.
We have used the Type Ia subsample of these SNe to measure the local
structure of the universe. The Tololo group has shown that a Type Ia
event can be used to measure relative distances accurate to about 6%.
Of particular interest is the measurement of the local rate of
universal expansion (the Hubble constant) with respect to the SNe
reference frame. The distant SNe overcome the problem associated with
local, non-cosmological flows affecting the perceived expansion rate of
the universe. The SNe results, coupled with HST-based distance
calibrations to nearby galaxies that have hosted SNe (published by
Saha, Sandage, and collaborators), show that the Hubble constant is
near 65 km/sec/Mpc with an error dominated by the distance to the local
calibrators, not the SNe reference frame. The Calan/Tololo group also
finds that the reference frame for the universal expansion is directed
towards the dipole defined by the microwave signal measured by the COBE
satellite. In stellar astronomy, Suntzeff is working with T.D. Kinman
at KPNO to measure the spatial and kinematical structure of the
Galactic halo. This study will provide clues as to the origin of the
halo, and ultimately, the origin of the Milky Way Galaxy. Suntzeff, in
collaboration with Schommer, Walker, and others, is also pursuing a
similar project in the Large and Small Magellanic Clouds. They seek to
find the original population of the stars in the Clouds to study the
age and kinematics of the oldest stars, in order to compare the
galaxian formation of these close satellite galaxies with the formation
of our Galaxy.
Future Research Plans
The future research for Suntzeff will concentrate on using new samples
of supernovae to measure physical properties of supernovae explosions
and to measure the local geometry of the universe. In collaboration
with Phillips, Schommer, and others, he will start a new search for
supernovae at CTIO, concentrating on galaxy clusters out to z=0.1. This
search will attempt to find up to 100 SNe to establish the natural
population of supernova explosions. These data will be a key to
understanding the explosion mechanism for Type Ia events (which is
still unknown) and estimating the intrinsic luminosity spread in the
range of Type Ia explosions. This latter property is extremely
important to tie down, since many modern studies of the local rate of
expansion and the geometry of the universe rely on a detailed knowledge
of the range of SNe luminosities.
Another CTIO collaboration seeks to measure q0, the local geometry of
the universe. One of the outstanding questions of cosmology is the
local curvature of the universe. The Calan/Tololo team has shown that
the Type Ia SNe are such good standard candles that a simple comparison
of SNe events at z=0.5 with local events can be used to measure the q0
geometry factor to better than 20% if roughly 25 SNe can be discovered.
The CTIO group is spearheading an international campaign of astronomers
at CfA, University of Washington, the MSSSO in Australia, and in Chile
to discover a distant sample of supernovae to measure q0. A by-product
of this survey will be a list of variable stars, which Suntzeff will
use to continue his Galactic structure studies with Kinman, Cook
(LLNL), and Schmidt (MSSSO), with the goal of measuring Galactic
structure based on field stars out to 100 kpc.
Service
Suntzeff will continue in a multi-faceted program of service to CTIO.
He is in charge of the Argus and bench-mounted echelle instruments. He
is actively participating in the upgrade of the Argus fiber system to a
Hydra system similar to that at the WIYN telescope, which will increase
the number of objects that can be observed by a factor of six. He will
work with John Filhaber to try to bring significant improvements in
image quality to the smaller telescopes, using the knowledge gained
during the 4-m telescope image improvement campaign. Suntzeff will
continue to be in charge of the basic site monitoring at CTIO,
including the seeing telescope that is now routinely measuring the CTIO
site seeing. He will also work with Gemini to begin a permanent
monitoring for the Pachon site, in order to build up environmental and
seeing data prior to the inauguration of the Gemini South telescope.
Suntzeff will continue to serve on the CTIO TAC and ACTR committees.
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Posted: 06Dec1996