From: Chris Lidman (clidman@eso.org)
Date: Fri Nov 07 2003 - 12:03:28 PST
Hi Gaston,
This took me a day or two longer than I expected. Sorry for the
delay.
It will be important for others to comment on the paper as well. I
will send them a reminder.
Abstract
========
SNe -> supernovae (Although obvious to the expert reader, this acronym
has
not yet been defined. In the abstract, I think you should spell it out.)
I have the overall impression that the abstract does not accurately
reflect what you have found. The abstract needs to be precise.
You highlight the fact that one of the indicators can be used as a
secondary indicator. I think you should highlight the fact that it can
be used as a primary indicator, and, as I mentioned in my previous
e-mail, the trend between Delta-m15 corrected magnitude and alpha(2+3)
(bottom of figure 12) is marginal. It becomes even less marginal if
one removes 91T. I think you should show this plot, but I do not think
we can make a strong claim.
We have not demonstrated the fact that we no longer need to do
time-consuming photometry. You have to ask your self the following
questions,
Can we use just the spectra without photometry? The answer is obviously
no.
Can we use the spectra and one photometric point in one filter? The
answer
is "We don't know". In principle this might work in the following way
i) use the spectra to work out the epoch and hence the date of maximum
ii) use the spectra to measure alpha(2+3) to determine the light curve
shape.
iii) use i) and ii) to determine the peak magnitude
Even if this might work, it has not been shown to work, so I do not
think we can state in the abstract that time-consuming photometry is
no longer needed. Additionally, we usually like an additional
photometric
point in a second filter to check for reddening.
Perhaps you could consider the following.
"We define a new set of empirical quantities to characterize the time
evolution of type Ia supernovae spectra and we search for correlations
between these quantities and the magnitude at maximum B-band
light. We present several of the best correlations and we show that
they are dominated by the uncertainties in the distances to the host
galaxies. Future upcoming surveys for large numbers of type Ia
supernovae
in the Hubble flow have the potential to reduce these uncertainties and,
thus, to sharpen the standard candle nature of type Ia supernovae."
Or something similar.
Introduction
============
Paragraph 1.
"the tool" -> "a tool" (the "the" give the impression that spectra are
the
"best" tool.
Paragraph 2.
"attempts" - You should choose another word. The work of Peter and
David were more than "attempts". A better word is "pioneering."
Paragraph 3.
I think that you should mention some of the "weirdos" which do not fall
into
the Branch normal, 91bg and 91T subclasses. Some of the wierdos include
00cx,
02cx and 02ic.
Paragraph 4.
The order of the list should be changed and the contents revised.
a) Provide empirically derived quantities of SN Ia spectra as a
function of epoch.
b) As written
c) As written
The next sentence "This work ..." is superfluous and can be removed.
Data Description
================
2nd paragraph
redshift values (z) -> redshifts
Presumably the tilting of the spectra occurred before the SN spectra
were shifted to the rest frame. In the text the tilting is mentioned
after
the shifting. These two sentences should be swapped.
3rd paragraph
'value of z from" -> redshifts in
Table 1
=======
I don't think I've heard of a heliocentric redshift. Usually, there is
z - in which case, it is "Earth" centric.
z_CMB - which is corrected for our motion relative to the CMB
You would use the former to shift spectra to the rest frame and
you would use the latter when estimating the distance from the linear
Hubble relation.
S: - does this means spiral? Is this a standard astronomical
classification.
NED - an undefined acronym. If you used NED, you probably need to
acknowledge that you used it.
Section 3.2 Equivalent Widths
=============================
Last paragraph. EW -> the EW
Section 3.3 Systematic effects.
===============================
First sentence. The phrase "on sliding windows" is not precise. How much
were
the windows allowed to slide?
Section 4. Spectral Evolution
=============================
2nd paragraph
Drop "even including peculiar SNe". Peculiar is a relative term.
Last paragraph
I do not understand the sentence that starts with "Epochs were
considered ..."
Section 4.1 FeII
================
1st paragraph.
"The overall increase ..." can be rewritten to read "The overall
increase in
the EW is mainly due to the rise of the emission peaks relative to the
toughs between them.
It might be worth to have a paragraph explaining the physical reasons
why 91T like SNe have smaller EWs that Branch normal SNe. Perhaps Peter
Nugent can help you here.
3rd paragraph
"is fewer data" -> "are fewer data"
Table 4 and 5
=============
Why can't Delta EW (last column) be estimates when n =1 (second last
column),
i.e. when you have one object.
Section 5.1.2 "MgII 4300" Break
===============================
Paragraph 1
In the cases -> For
given -> Used
Section 5.1.3 EW around maximum light
====================================
1st paragraph
You have probably done this, but did you try to correlate Delta EW as
is listed in table 4 with absolute magnitude over the interval -5 to
+5 days around maximum light for individual SNe and for the following
combination of features
4 alone
4+8
4+8+6+7
4+8+2+6+7
The paper does not explicitly mention which correlations you tried. This
does
not need to be written in the paper, but it would certainly be worth
including
this in your thesis or a some other report. I think that the
collaboration
would be very interested in knowing which correlations you tried.
4th paragraph
Total exposure time of 4 hours => 2 hours each? You could try this on
Beethoven directly. The spectrum of Beethoven was two hours. What is the
uncertainty of EW(2+3) for the Beethoven spectrum. There are not going
to be
many type Ias at z=0.5 that have a spectrum as good as the one of
Beethoven.
Is an uncertainty of 0.25 magnitudes acceptable? Probably not. The
uncertainty in using the light curve method is ~0.17 magnitudes.
Section 6. Conclusion
=====================
This is much better. It still lacks a bit of punch, but this can be
improved later.
Paragraph 2.
"including peculiar" -> including both 91T-like and 91bg-like.
Peculiar is a relative term. It may be that we discover that 91T and
91bg are just at the extremes of a continuous range.
Paragraph 4.
"to luminosity" -> with luminosity
Although t_br can be used in principle with SNe as far as z=1, the
observations are not feasible with current the generation of
large telescopes.
Paragraph 5.
Drop "... and with the use of a lower amount of observing time."
Paragraph 6.
I don't like the last sentence. To assess evolutionary effects one
needs very large, well controlled samples at both low and high redshifts
I'd suggest that you drop the last sentence and join the first
sentence to the end of paragraph 5.
Other General Comments
======================
In figures 2,3,4,5,6,7,8,9, it would be useful to list the feature
numbers as well as the mnemonic names.
Comments sent on Monday (part 1)
================================
I have modified the last point.
Distance indicators.
====================
Page 9.
Patat et al. I think that this reference is outdated. Please check the
more recent work of Freedman et al. You will find that SBF and Cephied
distances are in much better agreement.
Averaging the distance estimates of Saha et al. and Freedman et al for
1981B, 1989B and 1990N is bad. You should use one or the other, and I
would suggest that you use just the Freedman et al. estimates for
these 3 SNe. For 91T, you have no choice, you have to use Saha et
al. It is important to stress, as you do in the text, that the Saha et
al. derive larger distances and hence infer SNe Ia to be brighter than
Freedman et al. This is very interesting, because 91T sticks above
the best fits in figures 11 and 12.
Primary versus Secondary Calibrators
====================================
The argument that alpha(2+3) can be use as a second parameter is not
convincing. If you remove 91T, whose absolute luminosity may have been
over-estimated, then a straight line fit is probably equally
plausible. Even with 91T, the error on the slope in equation 7 is
0.03. The slope is a 2 sigma result. However, I think that you should
still show this plot, but I do not think that the result is
significant enough to stake a claim.
The probability argument in the sentence that follows equation 7
should be removed. I do not think that you understand the errors
(mostly from the distance) to make this sort of comparison.
The correlation between alpha(2+3) and absolute magnitude is better
than the correlation between Delta_m15 and absolute magnitude. Hence
we should be arguing that alpha(2+3) is a better primary calibrator.
Why is the scatter in Delta_m15 and absolute magnitude (0.33
magnitudes) so much worse that what has been derived before. This
needs to be understood. If it is due to distance errors, then that is
OK,
but why is the alpha(2+3) correlation so good.
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