From: Isobel Hook (imh@astro.ox.ac.uk)
Date: Sun Mar 09 2003 - 06:31:09 PST
Hi,
Here is an updated summary of systematics following the telecon last
Friday. Note that we all generally agree with Ariel's comment that we
should concentrate on effects new to this paper, especially effects on
colours. The expectation is that most of the list below will generate a
few sentences in the paper saying that the effect is similar to that in
P99 - but we do need to check that is correct for each item below. Also it
would be good to advertise our other recent papers such as the rise-time
paper and the work on host galaxy types (Sullivan et al).
Isobel.
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Summary of systematic effects v2. Updated with comments from telecon
on 07/03/03.
4.1 Extragalactic extinction
- thouroughly covered in HST paper
4.2 Malmquist bias
- What matters is the difference in Malmquist bias between low and
high-z sets. HST paper uses new data for both low- and high-z SNe.
High-z: P99 estimated size of effect by considering completeness
and associating this with SN number counts as a fn of mag
(actually it's not clear how this was done!). Also took
into account non-perfect correlation between discovery mag
and peak mag.
07/03/03: Greg will recalculate correlation, and will look
into method from last time. Need to check how we used the
efficiency measurements in P99 and whether we need to redo
that. [Greg]
Low-z: P99 assumed similar effect but correlation between peak and
discovery mags is stronger.
07/03/03 Greg: Reiss sample probably less malmquist biased
because included heavily reddened ones. Sullivan et al
paper claimed Riess sample are fainter than Hamuy sample.
Other malmquist-bias related checks
Include comparison of stretch distributions as in P99 [Rob]
Redo cosmology fits with and without new R99 [Rob]
4.3 Gravitational Lensing
07/03/03: Greg states that uncertainties in the details of the
model for the form of lensing (machos, empty beam etc) dominates
over the small change in z range of HST SNe compared to P99.
Need a sentence in the text saying this [Greg?]
4.4 SN evolution
- Spectra consistent at low & high-z (same argument as P99)
- lightcurve rise-time & shape similar (same argument as P99 but
update based on Gerson's paper) > constraint on changes in
width-luminosity relation. [Gerson/Peter/Greg?]
07/03/03: simplest test is to check the current HST ones are
consistent with template from recent paper [Don?]
Also, can we state that the current set does not constrain
rise-times compared to previous paper?? CHECK [who???].
- Small evolutionary effects on rest-frame U-band (cf Hofflich's
paper) could affect colour & k-correction. P99 argument needs
updating since more of the HST data sample the
U-band. [Greg/Rob/Peter?]
07/03/03: Metallicity effect on selection: cf Hamuy et al (host
paper from 2001). Also cite Nomoto paper limit on metallicity.
[Greg].
- Mention constraints from Sullivan et al. paper: e.g. constraints
on variation of width-luminosity relation with environment
[Mark?] Note we don't have host types for these ones
(yet). Someone needs to work out what we can say about
this. [Mark?]
4.5 Further checks
- Sensitivity to width-luminosity relation. Could redo fit without
using stretch correction? (cf fit D in P99) or at least show
stretch distribution. [Rob]
- Sensitivity to non-Ia contamination.
07/03/03 There is one SN from P99 that we now think is not a Ia and
4(5?) more we don't have good enough info. Throw these out now
for main result, and do cross check keeping them in [Rob]. Need a
sentence explaining more conservative strategy compared to P99 now
that we have enough data to do this [Saul?]
- sensitivity to galactic extinction model: P99 re-did fits using
Burstein & Heiles extinction model. Not necessary now? (or just
re-quote numbers from P99?)
07/03/03: Greg says that if anything, HST ones have lower galactic
extinction because better field selection (higher resolution maps
were available). Need a sentence about this in the paper [Greg]
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