At z = 1.7, m = 26.58, thus SN1997ff is 10^{(26.58 - 25.85)/2.5} = 1.96,

i.e. about twice as bright, as expected.

Riess and Nugent claimed not so long ago: "SN1997ff is more

than twice as bright as predicted by theories that the universe

is not accelerating, because it's closer than it would be if

it were moving away at the rate the universe is expanding now.

This means that the universe was expanding less quickly

10 billion years ago and has since accelerated."

In fact, such excess brightness is an artefact due to the

hypothesis of an expanding universe.

At a theoretical redshift of 5, a SN would be considered as

20.5 times too bright!

But with the non-relativistic relation, no such excess brightness

is found.

Marcel Luttgens, November 28, 2003

mluttgens@spamorange.fr

APPENDIX : EXCERPTS FROM SNe Ia LITERATURE

__________________________________________

(I) Supernovae and Cosmology (astro- ph/ 0010634 v1 31 Oct 2000)

Monique Signore, Denis Puy

From 5 Conclusions:

"After a brief review of type Ia supernovae properties (Section 2)

and of cosmological background (section 3), we presented the work

done by two separate research teams on observations of high-z SNIa

(Section 4) and their interpretation (Section 5) that the expansion

of the Universe is accelerating. If verified, this will proved

to be a remarkable discovery.

However, many questions without definitive answers remain.

What are SNIa and SNIa progenitors ?

Are they single or double degenerate stars ?

Do they fit Chandrasekhar or sub-Chandrasekhar mass models at

explosion ?

Is the mass of radioactive 56 Ni produced in the explosion really

the main parameter underlying the Phillips relation ?

If so, how important are SNIa evolutionary corrections ?

Can systematic errors be negligible and can they be converted

into statistical errors ?

Can a satellite, like SNAP, provide large homogeneous samples

of very distant SNIa and help determine several key cosmological

parameters with an accuracy exceeding that of planned CMB

observations ?

Meanwhile, cosmologists are inclined to believe the SNIa results,

because of the preexisting evidence for dark energy that led to

the prediction of accelerated expansion."

II. Verifying the use of supernovae as probes of the cosmic

expansion (astro- ph/ 0011369 v1 20 Nov 2000)

Richard Ellis and Mark Sullivan

From Introduction:

<..>

"In combination with the results of recent microwave background

measurements (de Bernardis et al. 2000; Jaffe et al. 2000)

which indicate a spatially flat infationary universe, the SNe Ia

results suggest a significant non-zero cosmological constant

(Omega = 0.28, Lambda = 0.72).

Conclusions of this importance require excellent supporting

evidence. In particular, it is appropriate to question the

homogeneity, environmental trends and evolutionary behaviour

of the SNe found at all redshifts.

Systematic differences between high and low redshift samples

might change the derived cosmological parameters without

destroying the small dispersion seen in the SNe Ia Hubble diagrams.

Evolutionary differences between low and high-redshift SNe Ia

might arise via the progenitor composition (Höflich 1999),

a differential dust extinction with greater amounts of dust

in high-redshift environments, either in the host galaxy

(Totani & Kobayashi 1999) or `grey' dust in the IGM (Aguirre 1999),

or a dependence of the SNe properties on host galaxy environments.

Addressing this last possibility forms the basis of this

present study."

III. The Farthest Known Supernova: Support for an Accelerating

Universe and a Glimpse of the Epoch of Deceleration

(astro- ph/ 0104455 v1 27 Apr 2001)

Adam G. Riess et al.

From 1. Introduction:

The unexpected faintness of Type Ia supernovae (SNe Ia) at

z ~ 0.5 provides the most direct evidence that the expansion

of the Universe is accelerating, propelled by "dark energy"

(Riess et al. 1998; Perlmutter et al. 1999).

From Abstract, p.2

"The apparent SN brightness is consistent with that expected

in the decelerating phase of the preferred cosmological model,

Omega M ~ 1/3; Omega lambda ~ 2/3.

It is inconsistent with grey dust or simple luminosity evolution,

candidate astrophysical effects which could mimic previous

evidence for an accelerating Universe from SNe Ia at z ~ 0.5.

We consider several sources of potential systematic error

including gravitational lensing, supernova misclassification,

sample selection bias, and luminosity calibration errors."

From 5. Conclusions:

"1. SN 1997ff is the highest-redshift SN Ia observed to date,

and we estimate its redshift to be ~ 1.7. <...>

2. The derived constraints for the redshift and distance of

SN 1997ff are consistent with the early decelerating phase

of a currently accelerating Universe and thus are a valuable

test of a Universe with dark energy. The results are inconsistent

with simple evolution or grey dust, the two most favored

astrophysical effects which could mimic previous evidence for

an accelerating Universe from SNe Ia at z ~ 0.5.

3. We consider several sources of potential systematic error

including gravitational lensing, supernova misclassification,

sample selection bias, and luminosity calibration errors.

Currently, none of these effects alone appears likely

to challenge our conclusions. However, observations of more

SNe Ia at z > 1 are needed to test more complex challenges

to the accelerating Universe hypothesis and to probe the

nature of dark energy."

IV. Do SNe Ia Provide Direct Evidence for Past Deceleration

of the Universe? (astro- ph/ 0106051 v1 4 Jun 2001)

Michael S. Turner and Adam G. Riess

From ABSTRACT:

"Observations of SN 1997ff at z ~ 1.7 favor the accelerating

Universe interpretation of the high-redshift type Ia supernova

data over simple models of intergalactic dust or SN luminosity

evolution. Taken at face-value, they provide direct lines of

evidence that the Universe was decelerating in the past,

an expected but untested feature of the current cosmological model.

We show that the strength of this conclusion depends upon

the nature of the dark energy causing the present acceleration.

Only for a cosmological constant is the SNe evidence definitive.

Using a new test which is independent of the contents of the

Universe, we show that the SN data favor recent acceleration

(z < 0.5) and past deceleration (z > 0.5)."

From Concluding remarks:

"The absence of an early, decelerating phase would be a much

bigger surprise than the discovery that the Universe is

accelerating today. It would be essentially impossible to

reconcile with the standard hot big-bang cosmology.

In addition to providing strong support for the accelerating

Universe interpretation of high-redshift SNe Ia, SN 1997ff

at z ~ 1.7 provides direct evidence for an early phase of

slowing expansion if the dark energy is a cosmological constant

(Riess et al. 2001).

However, because supernova observations do not directly measure

changes in the expansion rate, a model for H(z) or q(z)

is needed to perform a more robust test for past deceleration.

The former requires assumptions (or a deeper understanding)

about the nature of dark energy responsible for the recent

speed up while the latter requires more SNe Ia at z > 1.

<...>

In summary, we have shown that for a flat Universe the current

supernova data:

1. provide strong, direct evidence of past deceleration if

it is assumed that the dark energy is vacuum energy (cosmological

constant).

2. alone do not provide direct evidence of past deceleration

unless the dark-energy equation-of-state wX is close to -1.

However, using dynamical measurements of the amount of matter,

deceleration can be indirectly inferred for the redshift range

of the SN sample (if omegaM > 0.12).

3. without recourse to a specific model of the contents of

the Universe, favor deceleration at z > 0.5 with ~ 90% confidence.

An even stronger statement is that the SN data favor increasing

q(z) with increasing redshift, a sign of the assertion of

attractive gravity in the past."

V. Cosmological Results from High-z Supernovae

(astro- ph/ 0305008 v1 1 May 2003)

by John L. Tonry et al.

"Supernovae provide the only qualitative signature of the

acceleration itself, through the relation of luminosity distance

with redshift, and most of that effect is produced in the recent

past, from z = 1 to the present, and not at redshift 1100 where

the imprint on the CMB is formed.

This is why more supernova data, better supernova data, and

supernova data over a wider redshift range are needed to confirm

cosmic acceleration."

From p. 39:

"Evidently there is a tendency for the SN Ia to be brighter

at z > 0.9 (although the uncertainties are still large), suggesting

that we are truly seeing a change in the deceleration of the universe

and the effects of dark energy."

"Nevertheless, we are apparently starting to see SN Ia become

brighter at z ~ 0.9, rather than becoming ever dimmer because

of a systematic effect."