From: Gabriele Garavini (gabri@physto.se)
Date: Mon Jan 05 2004 - 06:56:37 PST
Hi Rollin, and co.
in what follow I try to explain my point of view on the comments Rollin
sent on the paper of 99ac. I will not make any change until I get
comments from the rest of the people that were supposed to sent some. I
did not receive comments, nor news, from Peter and Lifan so far. The dead
line was last year :-).
I would be glad if we could converge on this paper in a matter of few
days. I need to finish my thesis in less than a month.
Thank you very much.
> [1] Why is this SN important? I can see two things, maybe three.
> First of all, this set of spectroscopy adds to the growing set of
> those events with good time coverage, not just after maximum light
> but before maximum too.
This is exactly why I think showing the data is interesting even if the
analysis is only partial.
> Second, this premaximum spectroscopy shows
> pretty convincing signs of C II, and the C II ejection velocities
> measured are roughly consistent with the unburned layers of W7.
> There is also (perhaps) evidence of C III at lower velocities. I am
> not completely convinced yet that the C III is there
The evidence for CIII is definitely less strong than in 99aa but still it
helps in the fit maybe I should make that more clear.
>
> [2] What previous work does this SN have relevance to? Well, it's
> pretty much contingent upon that really being C III there. If you
> have only C II above the W7 cutoff only, then you've got evidence in
> support of W7. But if you've got C III below that velocity, then
> you've got something supporting the 3D deflagration results with the
> ashes and fuel mixed at all ejection velocities. So if the result
> that this is C III is only circumstantial, then you can only suggest
> that 3D models are pretty good. If that is the case, then you need to
> address some of the diversity issues that David has brought up with
> respect to the 3D models. How do we reconcile the crenellated results
> from Khokhlov and Hillebrant with the required upper limit on
> asphericity? What new observations are needed to help us out here?
> I've suggested surveys of absolute depths of Si II features, or
> something similar that constrains covering factor. Perhaps these
> ideas should be developed further?
I'm not sure what you mean here. I do not think we can say much about
limits on asphericity on the basis of these Synow models, or rather I
can't. I do not have any 3D modeling tool to work with. This might be in
my plan for the future, maybe learning to use Brute if that is possible or
Dan's code, but it is not something I can do right now. I can of course
put a general comments on 3D problems/concerns/hints but. As it is now the
paper does not leave much room for a deep discussion about 3D I think,
though. Concrete ideas are always welcome anyway.
> [3] Implications for the future. Well, since these C II features are
> rather small (I always want to see the 7000-ish feature along with the
> Si II-imposed feature, too), you should estimate the required signal
> to noise for looking for C in the future.
I think that any estimate of the required S/N depends of what we need the
detection for. I mean, I do not know of any particular parameter of the
models that would be constrained by the presence of C (if not the min vel
of CII for W7 or DDT for example) and that needs to be constrained with a
certain uncertainty that would mirror in a uncertainties on the C
detection and thus on the S/N of the spectrum. If you see what I mean.
But again I'm more on the observer side here, you might have a different
point of you.
>
> In your presentation of the fits in section 3, I think you might want
> to restructure. Clearly you want to focus on C, and I set a bad
> example of this in 2000cx by only caring about three ions, but make
> each ion a separate paragraph, and end each paragraph by saying
> ``evidence for such-and-such is (definitive|probable|possible|
> inconclusive).'' This is the clearest way to do it. With each ion,
> you can address anything weird you had to do with the ion, like put
> it at some velocity where there is no evidence for other ions.
>
Yes, I'm implementing this right now.
> Now about those other spectra after max. Why don't you do something
> with them? Isn't there at least one that might show evidence of the C
> II there? Maybe day +11, or +16, or +24? What was the rationale
> behind only paying attention to the early time? State it clearly I
> think, in the paper. Of course, I think you ought to look at these
> spectra with this kind of eye on C II and C III. You don't have to
> present it in the paper, but you might want to address it.
Ok here is the story. I actually originally (1 year ago) was planning to
write a 99aa-like kind of paper. So I started producing Synow spectra for
after max epochs too. But then I realized that there was nothing that
outstanding there and that would have made the paper just longer,
without gaining much. Thus, I decided to cut it short only showing the
most interesting spectra, where I could see C. I do agree with you that
this 'story' should probably find some space in the paper addressing why I
picked only those two spectra. And I'm putting that in now.
>
> And since you only analyze those first two spectra, (and I admit I am
> getting into this game pretty late), why do you need to present the
> others in this paper?
I think is better to present the whole data set especially since there is
not much to say after max more than they are normal looking. I do agree
that it looks strange presenting them all and then forget about all the
spectra but -15 and -9. I think the best is to put in a couple of more
comparison plots of later epochs. This actually would then copy the
organization of Branch's paper on 98aq. I'd like to ear what the rest of
the collab has to say about it though.
> About that figure of the ``radial composition.'' PLEASE BE CAREFUL. You
> are on thin ice with a plot like this I think. I realize that someone
> suggested that you do this for 1999aa, but I have to reiterate that
> you must make it unequivocally clear in the paper that this is *not* a
> definitive plot of the composition. The reason is because with
> Sobolev optical depths you really have no good sense of densities and
> temperatures without further analysis and without either doing full
> NLTE or LTE calculations at least. If you look carefully, for
> example, your optical depths for C II show C going all the way up to
> 40000. This is misleading; the optical depth and e-folding velocities
> show that the optical depths goes practically to zero well before
> v_max, and if you were to move v_max down to 30000 kmps the difference
> between the two spectra would probably be minimal at most. So I say,
> remember the results of direct analysis: (1) line identifications and
> (2) constraining ejection velocities for various species. This is not
> the same as deriving a composition! :)
I know, I'll state it clear and I'll make some example. e.g. tau for CII
goes below 0.001 after 34000km/s
> With respect to the case for C III, I think it's hard to say from your
> paper whether or not it is there in the fits. Recall that before I
> left for vacation, I supported the idea of showing full fits to the
> spectrum turning one ion on and off. This is good because often those
> without a spectroscopic background will want to see what it does
> overall. So I suggest that when you are making a case for C III, you
> do one fit with solid lines, and another fit with dashed ones (the one
> without the C III could be the dashed one) and then you overplot them.
> This can get kind of busy, so I also advocate putting an inset plot
> which retains the aspect ratio of the larger diagram, but focuses on
> and enlarges the C III region of interest. The referee on my 2000cx
> paper complained about this, and it's pretty important that if you are
> making a claim for an ion to be there, you do everything you can to
> demonstrate it both to yourself and to the reader.
Don't you think figs 6,7 and 8 show which is the effect of CII and CIII.
This ions do not effect at all the rest of the spectrum. I should probably
spell that out more clearly, but I do not see how the whole spectrum only
without CII for example would make it clearer, I would end up putting a
inner graph, as you do in 00cx that would be exactly as my figure 6,7,8
now.
> Also, you might have noticed that David has begun to experiment with
> plotting wavelength axes in log space, and sometimes plotting weird
> combinations of flux and wavelength on the flux axis. Once you show
> plots of all the spectra in straight flux, it is perfectly okay (for
> the purposes of analysis) to flatten the spectrum out and rescale the
> wavelength axes in this way. Since we are asking our readers to
> evaluate the goodness of fit basically by eye, we need to make it easy
> for them to do so. By taking the log of the wavelength axis, we make
> the blue features and red features have the same intrinsic width (you
> can demonstrate to yourself that this kind of operation is kind of a
> plot in velocity space for a given feature). So if you have two lines
> that have identical optical depth profiles (regardless of what their
> parent ion is), they will have the same shape no matter what
> wavelength they have at rest. By plotting, say, lambda * f_lambda you
> flatten out the spectrum and bring up the red end of the spectrum.
> I think David goes even further. This reduces the flux contrast, and
> you know that we can't ever get the flux right, we can only hope to
> get the overall shapes of line profiles correct. This makes it easier
> to do plots where you fit rather shallow infrared features, like the
> Ca IR triplet.
I tried this for 99aa and I did not see much improvement. I'll try again
for this guy.
> Finally, I'd like to suggest a more descriptive title for the paper.
> I'm not sure the C you refer to in the title qualifies as ``high
> velocity'' especially since the optical depths go below 0.01 before
> the v_max you set was reached. How about ``Direct Analysis of the
> Type Ia Supernova 1999ac before Maximum Light: Further Evidence for
> Carbon.'' This puts your work into context with the papers on 1990N,
> 1998aq, 1999aa and doubtless the others which will come along as
> higher S/N spectra are obtained. And most importantly, it contains
> the phrase ``direct analysis.'' Some people in SCP are confused by
> this, but we will change that. :)
>
> Happy holidays,
>
> Rollin
The titles.... at the very end was changed even for 99aa, without the
``direct analysis'' in it. I'll see what the collab says.
Thank you very much. I hope we'll converge soon with this paper, I really
need to finish my thesis. I have only one month to go.
Cheers
Gabriele
-- _____________________________________________________________________________ Gabriele Garavini (gabri@physto.se) FYSIKUM-Stockholm University Roslagstullsbacken 21 S-106 91 Stockholm SWEDEN Phone:+46 8 55378661 Fax:+46 8 553 78 601
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