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NED Abstract
Copyright by American Astronomical Society.
Reproduced by permission
1996AJ....112.2398H
THE HUBBLE DIAGRAM OF THE CALAN/TOLOLO TYPE Ia SUPERNOVAE
AND THE VALUE OF H_0_
MARIO HAMUY, M. M. PHILLIPS, NICHOLAS B. SUNTZEFF,
AND ROBERT A. SCHOMMER
National Optical Astronomy Observatories, Cerro Tololo InterAmerican
Observatory, Casilla 603, La Serena, Chile
Electronic mail: mhamuy@as.arizona.edu, mphillips@noao.edu,
nsuntzeff@noao.edu, rschommer@noao.edu
JOSE MAZA
Departamento de Astronomia, Universidad de Chile, Casilla 36D, Santiago,
Chile
Electronic mail: jmaza@das.uchile.cl
R. AVILES
National Optical Astronomy Observatories, Cerro Tololo InterAmerican
Observatory, Casilla 603, La Serena, Chile
Received 1996 June 17; revised 1996 September 5
ABSTRACT
The Calan/Tololo supernova survey has discovered ~30 type Ia supernovae
at redshifts out to z 0.1. Using BV(I)_KC_ data for these objects and
nearby SNe Ia, we have shown that there exists a significant dispersion
in the intrinsic luminosities of these objects. We have devised a robust
X^2^ minimization technique simultaneously fitting the BVI light curves
to parametrize the SN event as a function of
[t_B_,m_i_,{DELTA}m_15_(B)], where t_B_ is the time of B maximum, m is
the peak BVI magnitude corrected for luminosity variations, and
{DELTA}m_15_(B) is a single parameter describing the whole light curve
morphology. When properly corrected for {DELTA}_m_15_(B), SNe Ia prove to
be high precision distance indicators, yielding relative distances with
errors ~7%10%. The corrected peak magnitudes are used to construct BVI
Hubble diagrams, and with Cepheid distances recently measured with the
Hubble Space Telescope to four nearby SNe Ia (1937C, 1972E, 1981B, and
1990H) we derive a value of the Hubble constant of H_0_ = 63.1+/3.4
(internal) +/2.9 (external) km s^1^ Mpc^1^. This value is ~10%15%
larger than the value obtained by assuming that SNe Ia are perfect
standard candles. As we have shown in Paper V, there is now strong
evidence that galaxies with younger stellar population (spirals and
irregulars) appear to host the slowest declining, and therefore most
luminous SNe Ia. Hence, the use of Pop I objects such as Cepheids to
calibrate the zero point of the SNe Ia Hubble diagram can easily bias the
results toward luminous SNe Ia, unless the absolute magnitudedecline
relation is taken into account. Using the inertial reference frame of the
distant SNe Ia, and the "corrected" apparent magnitudes of the best
observed SNe Ia in the Virgo and Fornax clusters, we have evaluated the
recession velocities of these two clusters based on the Calan/Tololo
Hubble diagrams. We find a cosmic recession velocity for Virgo of
1223+/115 km s^1^ and for Fornax of 1342+/70 km s^1^, and a relative
distance modulus of {DELTA}_{mu}_(FornaxVirgo) = 0.19^m^+/0.23^m^.
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