Nearby Supernova Factory: Étalonnage des données de SNIFS et ...
Nearby Supernova Factory: Étalonnage des données de SNIFS et ...
Nearby Supernova Factory: Étalonnage des données de SNIFS et ...
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tel-00372504, version 1 - 1 Apr 2009<br />
CHAPTER 2. OBSERVATIONAL COSMOLOGY<br />
Magnitu<strong>de</strong> + const<br />
8<br />
10<br />
12<br />
14<br />
16<br />
18<br />
K-7<br />
H-6<br />
J-5<br />
U+1<br />
I-3<br />
R-2<br />
V-1<br />
0 50 100<br />
Days from B max<br />
(a)<br />
B<br />
M max − 5log(H o /65)<br />
−20<br />
−19<br />
−18<br />
−17<br />
−20<br />
−19<br />
−18<br />
−17<br />
−20<br />
−19<br />
−18<br />
−17<br />
B<br />
V<br />
I<br />
1.0 1.5 2.0<br />
Δm 15 (B) obs<br />
Figure 2.6: (a) Light curve in several bands (Johnson-Cousins UBVRI and near-infrared) from a typical<br />
SN Ia (SN2003du). Phase is with relation to B maximum. Adapted from Stanishev <strong>et</strong> al. (2007); (b)<br />
Brigther-slower correlation for SNe Ia light curves. Adapted from Phillips <strong>et</strong> al. (1999).<br />
On the other hand, if one wants to know their absolute magnitu<strong>de</strong> (to test our standard<br />
candle assumption), the case is somewhat different, since we need to have a measure of its<br />
distance. Hamuy <strong>et</strong> al. (1996) observed a number of nearby supernovæ in the smooth Hubble<br />
flow 7 , for which the distance can be estimated via the host galaxy redshift and Hubble’s law.<br />
The found (uncorrected - see next paragraph) values present some dispersion (Fig. 2.7a): scatters<br />
of 0.38 and 0.26 magnitu<strong><strong>de</strong>s</strong> for MB and MV (the absolute magnitu<strong>de</strong> in the B and V bands<br />
respectively) were found. These scatters are compatible with results from several teams, which<br />
have been using observations of SNe Ia on galaxies with distances known through different<br />
techniques, like Cepheids measurements, for the <strong>de</strong>termination of the Hubble constant: Sandage<br />
<strong>et</strong> al. (2006) observes mean absolute magnitu<strong><strong>de</strong>s</strong> MBV b<strong>et</strong>ween -19.3 and -19.55, compatible with<br />
the 0.3 magnitu<strong><strong>de</strong>s</strong> range span of the MB measured by other teams, <strong>de</strong>pending on calibration<br />
techniques and observational m<strong>et</strong>hods (see Table 2 in Gibson <strong>et</strong> al. (2000)).<br />
Despite the existence of this scatter (thought to be mainly due to the amount of 56 Ni produced<br />
during the explosion (Timmes <strong>et</strong> al. 2003)), it is remarkably small: SNe Ia seem in<strong>de</strong>ed<br />
to be good standard candles.<br />
The first step in the SNe Ia standardization was ma<strong>de</strong> when, as new supernovæ started<br />
7 Where they are far enough (z > 0.02) so that intrinsic velocities are negligible, and near enough (z < 0.08) so<br />
that the cosmological expansion acceleration effects are negligible and Hubble’s law is valid in first approximation.<br />
28<br />
(b)