Comments on the current version

From: Chris Lidman (clidman@eso.org)
Date: Wed Dec 08 2004 - 12:18:58 PST

  • Next message: Gabriele Garavini: "Re: Comments on the current version"

    Hi Gabriel,
      Here are some comments to the November 23 version.

    General Comments
    ================

    I think that the paper can be sent out to the collaboration for review
    as it is. However, I have some additional suggestions you might want
    to think about before you send it out.

    Isobel's article will be submitted in the coming weeks. Since it is
    probable
    that Isobel's paper will be submitted before yours, I think there are
    a couple of places where we should explicitly refer to it.

    Introduction
    ============

    The first paragraph could still be improved. The first (and last)
    paragraphs in a paper are important, so it is worth spending time
    getting them right. I don't have any specific suggestions but you
    might want to think of the following.

    Before launching into the assumptions we make about low and high
    redshift SNe, perhaps you can start differently.

    - First, mention that the accelerating universe and dark energy were
    discovered through high-z SNe (with all the standard references),

    - then mention that there are now even more ambitious programs that aim
    to try to constrain the nature of the dark energy and that a good
    control of the systemmatic errors in these new surveys is critical
    to their success. 

    ----

    In paragraph 3, change 

    "As of now few attempts have been made to quantitatively compare
supernovae properties at different redshifts and only based on light
curve parameters ..."

    to

    "However, the number of studies that quantitativrly compare the
obsereved propoerties low and high redshift SNe~Ia are still very few
..."

    and then add a reference to Isobel's work as she makes a comparison
between
the CaII velocities oif low and high z SNe as you do in figure 4.

    ----

    Add a reference to Isobel's work in paragraph 5.

    ----

    Remove the double quote at the end of the last paragraph.

    Section 2.1
===========

    In the first paragraoh, replace

    "Since SN2001go was observed at three epochs, there ..."

    with

    One SNe, SN 2001go, was observed at three epochs, so there ..."

    In the second paragraph, drop the clause "and scaled to the width in the
trace of the supernova.

    In the fourth paragraph, refer to Isobel's paper when quoting the
accuracy of the dating with spectroscopy.

    Figure 1
========

    Have a look at how Isobel has done figure 18 in her paper. This figure
in
Isobel's paper looks really nice and is very informative.

    Figure 2
========

    The lower axis has only one number.

    Section 2.3
===========

    In the last paragraph, change "is on of" to "is one of"

    Section 2.4
===========

    I think that this section and the figure can be removed. It does not
add much to the paper. However, you can leave it in for others to see
and
you can wait until you have had comments by others before deciding if it
should go.

    Figure 3
========

    Is the spectrum of 92A at +30 days too red. How do other
nearby SNe at this date look? Perhaps, there is a problem with the
extraction of the 92A spectrum and not the extraction of 01go.

    Figure 3. The red edge of the CaII feature looks well defined. It is the
blue edge that is more uncertain. Did you try a fit? The epochs of the 
92A spectrum should be identified. I presume that the epochs will differ
slightly.

    Table 3.
=======

    The CaII velocity of 02gi has a typo.

    Figure 4
========

    You might think about adding Isobel's points to this diagram.

    Section 3.2
===========

    In the first paragraph, change "accordingly" to "according"

    Section 4
=========

    I think that you should remove the last paragraph. 

    Cheers, Chris.

    On Wed, 2004-12-08 at 09:03, Gabriele Garavini wrote:
> Dear Tony, Dear All,
> 
> I think we can  discuss the Evolution paper on the 21th.
> You now find the latest version in the usual link in  the Stockholm
> web page : http://www.physto.se/~snova/private/internal.html
> 
> Since is not known to everybody I'm going to briefly resume the discussion
> Eric, Rob and myself had on the  possible systematics related with the
> measurements of the EW on high redshift SNe. The bottom line was that Eric 
> was finding a systematic difference in between the measurements of EW he 
> was doing on the 97 SCP dataset (I believe) and those Gaston did (and 
> that I report in my paper) on the VLT data presented in Chris's paper.
> 
> The issue was solved (at least that's the way I understood it) saying that
> Gaston did not rebin the data for finding the maxima around the features,
> while Eric did. The problem is of course related with the S/N ratio of the 
> measured spectra and the ability to recognize the features. 
> This is why these measurements should be done on decently
> high signal to noise SNe spectra.
> 
> There is also an other possible source of systematics
>  in the amount of galaxy removed and the technique used to do
> that. We did not use the same techniques (I used Gregory's code, Eric used
> Andy's) and Me and Gaston estimated (based on a work that Gregory Sainton
> did ) that a possible uncertainty of 10% should be allowed in this
> process. The effect of this uncertainties on the EW was added  in 
> quadrature to the EW measurements errors.
> 
> I find peculiar that Eric was reporting a systematic difference only in
> the measurements of EW of MgII but not in FeII. This might be more due to
> the galaxy subtraction than to the way the EW was measured. I personally
> believe there is not much of a difference between Gaston's method and
> Eric's method if one takes into account the error bars and the identified
> systematics.
>  
> Cheers
> 
> Gabriele
>

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