From: clidman@eso.org
Date: Sun Jan 11 2004 - 22:03:41 PST
Hi Gaston,
Thanks for the new version of the EW paper. I have read it and I attach some
suggestions on how the paper could be improved. I also have some questions
concerning parts of the paper that are not clear to me. I have not checked the
grammar and I will not comment on the style at any great length. This can be
corrected later.
Cheers, Chris.
General
=======
It may be clearer to use a single phrase to describe these quantities.
In the title, you call them indices; in the abstract, you call them
quantities, features, and indicators.
In some cases you use the term "Branch normal SNe Ia and in other cases
you use "normal SNe Ia". Please use the former term throughout the paper.
Sometimes you use the term "fast decliner" or "91bg-like SNe" to describe
91bg-like SNe. Use one term, ie, use 91bg-like SNe.
Abstract
========
The abstract is much better, but it could still be improved. Generally, it
lacks precision. The abstract is the most important part of the paper so it
is worth the effort in writing a good one.
The first two sentences could be written as
"We define and use a new set of eight empirical spectral quantities - similar
to equivalent widths (EW) - to characterise the spectra of type Ia
supernovae (SNe Ia). We analyse how these quantities evolve with
phase and we search for correlations between these quantities and
the peak B-band luminosity."
In the next section, homogeneous is too strong here, I prefer the word
similar. Note that, on average, 91bg- and 91T-like SNe have different EWs to
Branch normal SNe. Their evolution with phase is similar. Hence, the next
sentence, and the ones that follow it, could be written as ...
"The evolution of the quantities we label as "Fe II 4800", "Mg II
4300" and "Ca II IR" show a remarkably similar behaviour for
all SNe Ia - including 91bg- and 91T-like SNe, while the behaviour
of the Si II based quantities ("Si II 4000", "Si II 5800" and "Si II 6150")
can be used to differentiate between Branch normal and 91bg-
and 91T-like SNe"
"appears ... calibrator" can be rewritten as "correlates strongly with
peak B-band luminosity.
The word promising implies that
a) it correlates and
b) it is useful.
The former is clear, the latter less so.
The last sentence leaves the reader hanging. A better sentence might be.
"We discuss the applicability of these correlations in the analysis of SNe Ia
up to z~1."
Introduction
============
The first paragraph is difficult to follow; there are two many ideas
in it. As a general rule, each new idea or concept should have its own
paragraph. The second sentence does not make sense.
Data Description
================
What does "mean Poisson errors" mean? Perhaps, it would be clearer to
write, "the errors were estimated from the point-to-point dispersion."
What does "integer number of days since maximum" mean? Were the real numbers
rounded to the nearest integer.
Feature Definitions
===================
What does "The spectrum is normalised by the continuum" mean? This should be
defined or removed, since the EW should be independent of any normalisation.
Systematic Effects
==================
I do not like the way the systematic error is computed. If I have
understood the text correctly, you shift the region by 1/4 of the
region size and you recompute the EW. Why 1/4. Why not 1/10th? This
is arbitrary and I do not think it is a valid method in estimating the
systematic error.
Remove ", given by the point-to-point ratio ... wavelength range,"
Table 5 and other tables like it
================================
What is the error (1 sigma uncertainty) for columns 3,6 and 8. Is
it related to delta? Saul asked this question, but I have not seen this
issue addressed in your reply to him.
Table 9.
========
Perhaps the footnote "e" should label the Delta m15 values and not Delta
M_B.
EW^{max}_{(2+3)} (I've used Latex notation here) should be EW_{(2+3)} at
B band maximum.
Section 5.1.2
=============
"We here do not ..." should be "We do not..."
In paragraph six, you state that we should expect to see a correlation between
t_br and absolute magnitude. Why? They are measuring different quantities.
The fact that they measure these quantities over a similar wavelength region
is not sufficient for me.
Section 4.1.3
=============
Paragraph 3.
The distance uncertainties may be overestimated, but what evidence is there to
suggest that the uncertainties are dominated by systematic effects.
Where does the 0.3 magnitude systematic uncertainty come from? It cannot be
because of the different distance estimates given by Saha and Freedman, as you
have used the one distance measurement throughout the paper, i.e. the distance
estimates of Freedman et al.
I'd suggest that you delete the clause "especially ... 0.3 mag."
Paragraph 7.
This paragraph is not clear. I do not understand how you have computed
the affect of contamination on alpha(2+3).
"no further attempts". Was there an initial attempt to remove the
contamination?
I do not understand figure 13. If half the B band flux is host, then,
according to figure 13, alpha changes by 30%. If alpha was initially 10, then
alpha becomes 7. This is a change of 3, i.e 30%. According to equation 6,
the estimate of the peak magnitude would then change by 0.103 * 3, which
is 0.3 magnitudes and not 0.1 magnitudes as one would infer from the
lower panel in figure 13.
Quoting Gaston Folatelli <gaston@physto.se>:
> Hi Tony,
>
> Could you make this an announcement to the whole SCP? Thank you very
> much,
>
> -Gastón
>
> Dear collaborators,
>
> I have posted a new version of the paper draft on EW's. This version is
> 7.1 and can be retrieved (with the usual SCP access) from:
> http://www.physto.se/~snova/private/internal.html
>
> This version accounts for Saul's and Isobel's comments to v 7.0.
>
> I have a few comments on Saul's thorough review:
>
> - In section 3.3: The estimated error from the definition of the
> pseudo-continuum can be added to the statistical error without
> double-counting the errors, since the former is just a measure of the
> scatter of the EW's as one varies the points defining the continuum.
>
> - Sections 4 and 4.4: The concept that the Si II features serve to
> separate the SN Ia subtypes is correct. The text was wrong by saying the
> the scatter of EW is greater in these features than in the others. This is
> only true in relative terms. The text has been corrected.
>
> - Fig. 7: An average curve for Branch normal SNe was added in this plot.
> As a consequence, a new table (Table 8) was added to quantify the
> differences between normal and 1991T-like SNe.
>
> - Sections 5 and 5.1.3: The other correlations found are mentioned now,
> though no further analysis is shown. This choice of \alpha(2+3)
> is justified in the text.
> The comment on other correlations tried has simply been taken away from
> the beginning of section 5 and is left in section 5.1.3 exclusively.
>
> - Section 5: Host galaxy extinction estimates. A reference saying that SN
> 1999aa is believed to be unreddened in the host has been added. This
> reduces the number of SNe with unknown host galaxy extinction to two (SN
> 1999ac and SN 1999bp). The magnitude error of the former of these two is
> big enough to account for anything. This is what we've got...
>
> - Section 5.1.3: When comparing the residuals of Phillip's relation (after
> Eqn. 7), I don't attempt to stick to the same range of Delta_m15 as the
> authors because our sample would be very much reduced and because we'd
> like to find a parameter that works for all Ia's.
>
> - Sections 4 and 6: The comments of the kind "individual SNe follow
> parallel paths to the average curves" were changed to "SN Ia subtypes
> follow parallel..." because this is what the analysis and the plots show.
> This is why we changed the plots to divide the measurements in the three
> SN Ia subtypes instead of showing the SNe individually.
>
> About Isobel's comments I'd like to say:
>
> - Including the actual EW measurements in the paper would be too much, I
> think. A table with that information would be several pages long. I think
> the best would be to publish these data in the web.
>
> - I added the information necessary to reproduce the average curves shown
> in Figures 2, 3, 4 and 7.
>
> - Yes, I have tried to plot the Delta_EW vs M_B for individual SNe. The
> very first versions of the paper, before Section 5 appeared, included this
> analysis. But again, the correlation was not as strong as the ones finally
> presented.
>
> - In my opinion, a plot of EW_(2+3) as a function of epoch wouldn't add
> really that much substance to the analysis.
>
> - Section 4.6 (S II "W"): Thanks for the comment. Now the text makes more
> sense in this somewhat forgotten (by me) section.
>
> - Section 5.1.2: Now the text explains why we don't use Phillip's relation
> to go from delta_m15 vs t_br to M_B vs t_br.
>
> I also would like to say that I haven't forgotten to switch to the AAS
> LaTex macro. I just decided to do it once and at the end, right before
> submission.
>
> Thanks for the reviews. I hope we all enjoy this new version.
>
> -Gastón
>
>
>
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