An HST Program for the Luminosity Calibration of Type Ia Supernovae

In summary: The other one from a couple of astronomers at UCSC strikes me more as a first attempt to get something out before the 2006 deadline and probably isn't the final word from them. Both are interesting though.In summary, the paper "The Hubble Constant: A Summary of the HST Program for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids" by Sandage et al. discusses the challenges and methods for determining the Hubble constant (H0). They argue that a lower value for H0, around 62.3, is more consistent with various distance indicators and the age of the universe. This lower value also allows for better explanations of early structure formation. They also mention another
  • #1
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Here is an interesting [and important] paper, IMO:

The Hubble Constant: A Summary of the HST Program for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids
Authors: A. Sandage (1), G.A. Tammann (2), A. Saha (3), B. Reindl (2), F.D. Macchetto (4), N. Panagia (4)
http://www.arxiv.org/abs/astro-ph/0603643

P25
. . . To obtain H0 some assumptions on Omega[M] and Omega[lambda] necessary. The disadvantage of long look-back times for the deermination of H0 becomes most pronounced in case of the Fourier spectrum of the CMB acoustic waves, where a number of free parameters must simultaneously be solved for. The solution for H0 depends therefore on the number of free parameters allowed for and on some priors forced on the data as well as on the observations used. A six-parameter solution of the WMAP data with some priors and additional observational constraints has yielded H0 = 71+4−3 Spergel et al. (2003). This has often been taken as a confirmation of H0 = 72± 8 as obtained from various distance indicators by Freedman et al. (2001), and has led to the opinion that the problem
of H0 has been solved. We disagree. The actual situation has been illustrated by Rebolo et al. (2004) who have used the Very Small Array and WMAP data to derive H0 = 66 ± 7 allowing for twelve free parameters and no priors. Clearly a strong motive to further reduce the systematic error of H0 by conventional means comes from the desire to use the Hubble constant itself as a reliable prior for the interpretation of the CMB spectrum.

A value of H0 = 62.3 corresponds in an Omega[M] = 0.3 and Omega[lambda] = 0.7 universe to an expansion age of 15.1 Gyr, which may be compared with the age of M92 of 13.5 Gyr (VandenBerg et al. 2002) and the Th/Eu age of the Galactic halo of ~15 Gyr (Pagel 2001). Ultra-metal-poor giants yield radioactive ages between 14.2±3.0 to 15.6±4.0 Gyr (Cowan et al. 1999; Westin et al. 2000; Truran et al. 2001; Sneden et al. 2003). A high-weight determination of the U/Th age of the Milky Way gives 14.5 ± 2.5 Gyr (Dauphas 2005). All these values must, of course, still to be increased by the gestation time of the chemical elements.

P26
. . . 7. CONCLUSIONS
(1) The final result of our HST collaboration, ranging over 15 years, is that
H0(cosmic) = 62.3 ± 1.3 (random) ± 5.0 (systematic) (8)
based on 62 SNe Ia with 3000 < vCMB < 20 000 kms−1 and on 10 luminosity-calibrated SNe Ia. All SNe Ia have been corrected for Galactic and internal absorption and are normalized to decline rate #m15 and color (Paper III). The weighted mean luminosities of the 10 calibrators of MB = −19.49, MV = −19.46, and MI = −19.22 (Table 4) are based on metallicity-corrected Cepheid distances (Paper IV) from the new P-L relations of the Galaxy and LMC (Paper I & II). (2) The local value of H0 (300 ∼< v220 < 2000 kms−1) is H0(local) = 60.9 ± 1.3 (random) ± 5.0 (systematic) (9)
from 25 Cepheid and 16 SNe Ia distances, involving a total of 34 di#erent galaxies. Their distances are related to the barycenter of the Local Group and their observed velocities are corrected for a self-consistent Virgocentric infall model with a local infall vector of 220 kms−1.
The local value of H0 is supported by the mean distances and mean velocities hv220i of the Virgo and Fornax cluster (Table 7).
 
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  • #2
"Cosmologists are often in error and never in doubt"

Its always wise to be uncertain of one's certainty.

Garth
 
  • #3
Garth said:
"Cosmologists are often in error and never in doubt"

Its always wise to be uncertain of one's certainty.

:biggrin: :approve:
 
  • #4
:rofl:

Wow, Sandage is still sticking to those guns, I see.

BTW, I think you meant to link this paper:

http://www.arxiv.org/abs/astro-ph/0603647" [Broken]
 
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  • #5
Indeed he is, ST. In this particular case, I think he has made one of his stronger arguments. The lower value for H0 gives more wiggle room for early structure formation that is difficult to explain under modern theory. I also agree the latest WMAP release relies upon some apparently unnecessary [IMO] a priori's. It seems to be a well reasoned paper.
 
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1. What is the purpose of the HST Program for the Luminosity Calibration of Type Ia Supernovae?

The purpose of this program is to accurately measure the luminosity of Type Ia supernovae, which can then be used to calculate distances to these objects and ultimately improve our understanding of the expansion rate of the universe.

2. How does the HST Program for the Luminosity Calibration of Type Ia Supernovae work?

The program uses the Hubble Space Telescope (HST) to observe and collect data on Type Ia supernovae, specifically focusing on a specific type called "standardizable" supernovae. These objects have a consistent luminosity that can be used as a standard candle to measure distances. The program also uses ground-based telescopes and spectroscopy to gather additional data.

3. What is the significance of calibrating the luminosity of Type Ia supernovae?

By accurately calibrating the luminosity of Type Ia supernovae, we can use these objects as standard candles to measure distances to faraway galaxies. This allows us to better understand the expansion rate of the universe and the effects of dark energy.

4. What are the expected outcomes of the HST Program for the Luminosity Calibration of Type Ia Supernovae?

The program is expected to improve our understanding of the expansion rate of the universe and provide more accurate measurements of distances to galaxies. It may also help to refine existing theories about dark energy and the evolution of the universe.

5. How will the data collected from the HST Program for the Luminosity Calibration of Type Ia Supernovae be shared with the scientific community?

The data will be shared through various channels, including scientific publications and online databases. The program also has a public data archive where anyone can access and analyze the data collected by the HST. This allows for collaboration and further research by the wider scientific community.

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