From: clidman@eso.org
Date: Wed Jan 14 2004 - 19:31:12 PST
Hi Gaston,
Thanks for the most recent version (version 7.2). Here are some
additional comments.
Before I go into the comments in detail, I wanted to add an additional
reason to support Isobel's suggestion of including plots showing the
correlation between EW of one or more quantities versus absolute magnitude.
Both alpha(2+3) and t_br require 2 or more spectra. This is expensive in
terms of telescope time. An EW requires only one spectrum. I suggest that you
include the plot that shows the best correlation between EW and magnitude.
EW(3+4) looks promising. It can be measured out to relatively high redshift,
there is a good correlation and it only requires a single spectrum
around maximum light.
General
=======
I've asked Lifan to review the paper before the teleconference. I hope
that the teleconference (whenever it may be) will clear up any remaining
issues. The next step will be to get someone to help you with the
expression.
There are a few points we should discuss during the teleconference. These
points are hi-lighted below.
Abstract
========
Looks good.
Second last sentence.
"This small ... to those SNe." can be re-written as "Uncertainties in the
distances to these SNe dominate the scatter."
Introduction
============
I'd suggest the following changes to the first paragraph to make it
easier for the reader.
- Drop the second sentence and attach all the references to the first
sentence.
- "affect the present measurements" -> "rule out the need for dark energy,"
3rd paragraph
"three subtypes" -> "three main subtypes", since it is becoming clearer
that some SNe, such as 99ac, 02cx, etc., do not fit into this scheme.
Section 2 - Data Description
============================
Paragraph 2.
I think the reference to Cardalli and Schlegel is unnecessary here. This sort
of detail can be left in the Folatelli et al. paper concerning the method used
to reduce the nearby SNe data.
Paragraph 4.
For set B, you write that the the spectra of these SNe were moved to
the rest frame (presumably you mean the zero redshift rest frame) and
then were adjusted with the available broadband colours. Should this not
be the other way around. I.e, you correct the spectra according to the
photometry and then shift them to the zero redshift restframe?.
This point had been brought up in an earlier review. See
http://panisse.lbl.gov/collab/archive/eqwidths/0019.html
Table 1.
========
Is "S:" standard nomenclature?
Sometimes you have Scd and SAB. Is there a reason for capitalising "AB" and
not "cd".
Table 2
=======
SO pec should be S0 pec ie S zero pec and not S "oh" pec.
Section 3.2 - Equivalent Widths
===============================
4th paragraph
The statement about dividing by the pseudo-continuum before determining the
equivalent width may confuse people. I suggest that you rephrase the
beginning of the paragraph to
"Once the pseudo-continuum is traced, the EW with is computed for each
feature according to:"
Then include equation 1 and the rest of the paragraph.
Section 3.3 - Systematic effects
================================
The explanation why l/4 was chosen is now clearer, but it is not clear to me
if this is a valid way of estimating the systematic error. Has this
method been used before? I'd like to bring this point up during the
teleconference.
"defined in a limited wavelength range" -> "defined over a limited wavelength
range"
Table 5
=======
Thanks for explaining what the one sigma errors in table 5, etc. are. I guess
the problem here is one of presentation. The reader could assume that the
error is the error of the mean equivalent width. However, this is not
precisely true as you have first computed the RMS in a particular bin and then
you have divided it by the sqrt(n), where n is the number of points in that
bin. If we assume that the underlying distribution of equivalent widths
is Gaussian, then this is true. However, we are making an assumption.
I think that the 1 sigma errors are unnecessary. Instead, use delta. It
is clearly defined and it lets the reader see what the spread in EW are.
Hence table 5 should have the following columns.
Branch normal 1991T-like 1991bg-like
Epoch n <EW> delta(1) n Delta_EW(2) delta(2) n Delta_EW(3) delta(3)
Where, delta(1) is delta in your table, delta(2) is the RMS of Delta_EW(2)
and delta(3) is the RMS of Delta_EW(3).
Table 9.
========
"G. Clusters" -> "Globular Clusters"
>> Section 5.1.2
>> =============
>>
>> 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.
>
>The location of that statement in the text was wrong. It was meant to
>refer to the correlation between t_br and Delta m_15 (and not M_B). This
>is fixed now and an additional sentence was added to explain what I mean.
We need to be careful here. The strengthening is partly artificial,
because the wavelength interval over which the feature is measured has
a large discontinuous increase. I think that we need to discuss this
point during the teleconference.
Section 5.1.3
=============
6th paragraph - I still do not follow this argument. We need to discuss this
at the teleconference.
7th paragraph
"can be done using a minimum of" -> "requires at least"
Conclusion
==========
5th paragraph
You might want to mention the problem with host galaxy contamination in
determining the alpha(2+3) parameter.
I think we should mention that the SN ratio in spectra of z~1 SNe
will not be high enough to determine the alpha(2+3) and t_br parameters.
Probably z~0.6 is the limit. This could be added as a single paragraph after
paragraph 5 in the conclusion.
You can add the following paragraph.
"Although the wavelength interval over which alpha(2+3) and t_br are
determined is accessible to optical spectrographs for SNe Ia up to $z~1$, the
quality of z~1 SNe Ia spectra is generally too poor for these parameters to be
determined with sufficient accuracy, even with several hours of integration on
an 8~m class telescope. A more reasonable limit is z~0.6. Additionally, these
parameters need 2 or more spectra. Hence, the lightcurve width brightness
correlation remains as a key tool in calibrating the luminosity of SNe Ia."
Cheers, Chris.
Quoting Gaston Folatelli <gaston@physto.se>:
> Dear all,
> I found a couple of typos and I changed the title of Section 3 and other
> details.
> The updated version 7.2 is available from the usual place (usual SCP
> access):
> http://www.physto.se/~snova/private/internal.html
>
> Cheers,
> -Gastón
>
>
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