From: Chris Lidman (clidman@eso.org)
Date: Fri Jul 16 2004 - 17:06:41 PDT
Hi Serena,
Thank you for the new version of the paper. I am sorry that it has
taken so long for me to get back to you, but I went to Paranal the day
after the new version arrived and I just got back yesterday.
I understand that you are not coming to the SCP meeting. That is
a pity. It would have good to share a few beers with you, Gabriele and
Gaston.
Before I go into the paper, are the new spectral templates available.
I'd like to use it for computing k-corrections for some z>1 SNe that
we have observed with ISAAC.
Now, to the paper.
One thing that I'd like to avoid a bit in the paper is the tendency
to highlight inadequacies in the research of the "other" group. I know
that they often criticize aspects of our work, but I do not want to
see us sink to the same level. I'll try to point out the parts of
the text where I think we have been too negative.
Introduction
------------
- There is some more recent work on using low-z clusters to constrain
Omega_M. See Schuecker et al. A\&A, 398, 867.
Caption to Table 1
------------------
- Although it is generally true that I_1 = I_max, it might not
always be true. If t_2-t_1 is less that the rise time of the template,
then part of the second template will contribute to the light curve
at maximum light. You should qualify the last sentence.
Section 2.1
-----------
In the last sentence of this section, it is not clear who thinks the
uncertainty of the Leibundgut is 0.06 magnitudes. Perhaps this sentence
can be stated more clearly.
We take this as an estimate of the measurement uncertainty in data
of Liebundgut et al. (1993) as no errors are reported in that work.
Section 2.2
-----------
In the second last paragraph
"The uncertainties for this supernova may be underestimated."
I find this to be too vague. It might be true, but do you have any
evidence other than the poor fit that this is true. Otherwise, it
would be better to leave this sentence out. It might be that the
template is a poor description for the light curve of this
supernova. Indeed, the latter is more likely to be true because the
fit to the early and late parts of the light curve (figure 1.)
clearly show a systematic trend. Compare the rising part of 94D with
the rising part in 94ae, 95bd, 92bo, 92bc, etc. Compare the tail 94D
with the tail of 94M.
Figure 5.
--------
Just a comment. In this plot I would argue that we see a break. For SNe
with s_B < 0.9, there is a clear relationship between M_sec and s_B.
For SNe with larger stretch, there is no relationship. I think that it
would worth pointing this out in the paper.
Section 3.
---------
For my own benefit, geometrically means
(sigma_intrinsic)^2 = (sigma_total)^2 - (sigma_measured),
correct?
Section 4.1.
-----------
I think we can improve the discussion on the cross filter k-corrections.
There has been quite a bit of work on trying to relate the IR and
optical photometric systems and we can say that the we know the
relationship
to 2%. I attach an e-mail which I had sent out on May 16th. The
most important part of the e-mail is that we need to add an extra term
to the IR to optical k-correction which accounts for the small
difference
in IR and optical systems. The text should be changed to reflect this.
Section 4.2
-----------
How different are the J to I k corrections for 99ff between the Serena
mark I and Serena mark II templates?
For 99ff and 99Q, I'd like us to come up with a more diplomatic
way of stating that the other group are wrong.
For 99ff, simply drop the sentences starting with "We found differences
..." and ending with "...communication." You can also drop the section
saying that the I-band magnitudes have been adjusted, since I presume
that
this will now be absorbed in the k-correction as described below.
For 99Q, say that "The mean difference was found to be xx magnitudes
rather
than quoting the maximum magnitude difference."
Fit to the high z SNe.
---------------------
The following is not in the paper and it is something that we do not
have to add, but it is something that should be done at some stage.
The high redshift SNe are poorly sampled in time. We have explored the
systematics of how photometric errors might affect the
fits for both the high and low z SNe, but we have explored the
systematics caused by poor sampling.
Section 5.
---------
Second last paragraph. I do not believe this to be true any longer. The
entire paragraph should be removed.
Section 6
---------
For the R_V = 4.5, you mention that the ellipses would only move by 0.03
and
0,04 magnitudes in E(B-V) and E(B-I). Can you please check this.
In the next paragraph you mention that R_V=4.5 is disfavored at the 90%
confidence level and that something, presumably R_V=9.5 is disfavored
at the 97% level.
Figure 13
---------
Could you also double check figure 13. It surprises me that there
is so little difference between the R_V=4.5 and R_V=9.5 models.
I would have expected the R_V models (dotted line) to be much closer
to the solid line. Have you used the formulas in Cardelli, Clayton and
Mathis ApJ 345, 245? The formulas are very involved (see table 3 and
equations 2a to 3b). I imagine that the calculation for SNe at z~0.5
must be very complex because one has to take into account the redshift.
Dust at low redshift will have a relatively low effect when compared
to the same dust at high redshift because the spectra are already
redshifted.
Figure 14.
----------
I think that you should avoid using E(B-V) as the vertical axis as the
reader might take it that dust is the cause for the spread in
SNe colours. I think \Delta(B-V) = (B-V)_SN - (B-V)_local may be
clearer.
Conclusion
----------
In the last sentence, remove the sentence
SN 99ff and SN 99Q
------------------
In the revised version, 99Q is even more of an outlier? 99ff is less
problematic, but there are only two data points in the light
curve. Since these SNe were not observed with by the SCP, do we want
to keep them in the paper, or do we keep just 99ff.
I am not advocating that we remove them, but I think it is something
we should openly discuss. From might point of view, here are the
negatives
The negatives of 99Q and 99ff
- We are relying on the photometry of the other group.
- We find significant differences in the k-correction
- We've already excluded one their SNe because we it was probably
heavily reddened.
- For 99ff, there are only two points in the light curve.
- I have not see a spectrum of 99Q. It is faint and the second maximum
is not convincing. If it were not for the B-band stretch, one could
argue that it is an sub-luminous SNe, both from the I-band maximum and
the
lack of a second maximum.
The positives about Beethoven
- The Beethoven observations are more precise as we know the Js filter
curve very precisely (I measured it myself).
- We measured all aspects of this SNe.
Overall, I do not think we should put these two SNe in the paper
unless we are comfortable with the work that has been done by the
other group, and, quite frankly, I do not feel at ease with their
work. I do not think that we would weaken the paper if these 2 SNe
were excluded; however, the last couple of sections in the paper
would be considerably shorter.
Cheers, Chris.
IR to Optical k-corrections
===========================
The cross filter k-correction is defined in Kim, Goobar and Perlmutter
(1996) and is applied to apparent magnitudes according to
m_y = m_x + K_xy(z)
where x and y are different filters.
Let's assume that z=0 and that Z=F. Let's further assume that we are
using
the Kurucz model for Vega. In this case K_xy(0) = 0 and, hence,
m_y = m_x
However this is not true for Vega for all x and y (i.e. all filters)
m_V=0.026 +/- 0.008 (Bohlin and Gilliland, 2004)
m_I=0.031 +/- 0.009 (Bessell, Castelli and Plez, 1998)
m_J=-0.001 +/ -0.005 (Cohen, Wheaton and Megeath, 2003)
where J is on the 2MASS system.
If we set x to I and y to J
Hence m_J=m_I-0.032.
or m_I - m_J = 0.032 = -K_IJ
I propose that we add an extra term to the cross filter k-correction as
defined by Alex which reflects the colours of Vega. Note that Alex's
definition is completely correct for an object in which all colours are
zero.
The new k correction is then
K'_xy(z) = K_xy(z) - (x-y),
where (x-y) is the colour of Vega and K_xy(z) is the k-correction
defined by Alex.
For the I band paper, we added this correction to the J band
photometry. I think we should change this by changing the way we do
the k-correction, as I have described above.
Apart from the uncertainties described here, there is a systematic
uncertainty in how well the Kurucz spectrum represents Vega. Bohlin
and Gilliland quote an uncertainty of 2% from optical to IR
wavelengths. We should add this systematic uncertainty to all IR to
optical K corrections.
Bessell, M. S., Castelli, F. and Plez, B. 1998, AA, 333, 231
Bohlin, R. C. and Gilliland R. L. 2004, astro-ph/0403712
Cohen, M., Wheaton, WM. A. and Megeath, AJ, 2003, 126,1090
Kim, A, Goobar, A, and Perlmutter, S. 1996, PASP, 108, 190
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