From: Chris Lidman (clidman@eso.org)
Date: Thu Apr 29 2004 - 10:44:17 PDT
Hi Andy,
OK, we'll leave it as unclassified.
I do not want to use photometric information to help in the
classification because the photometric data is very heterogeneous
and the current analysis of the data is even more so.
The classification scheme you use for the legacy survey has merit. I
like it. However, I do not propose that we adopt it for the VLT paper.
If I was to map what we have used for the VLT paper then
a VLT Ia is somewhere between 1 and 2 on the legacy scheme of
classification
a VLT Ia? is somewhere between 2 and 3 on the legacy scheme
a VLT - (unclassified) is not on the legacy scheme.
Would you agree with this assessment?
Cheers, Chris.
On Thu, 2004-04-29 at 10:02, Andy Howell wrote:
> Chris,
>
> >From the spectrum alone I just would not say it reaches the level I would
> call a "Ia?". So if these classifications are from spectra alone, I would
> say no. I am just imagining someone from the other team, looking at that
> figure with skeptical eyes, thinking (and saying loudly at every possible
> collection of astronomer) that we have no idea what we are doing. However,
> if you are willing to let other factors slip in, then that might change
> the classification as long as we are very up front about that.
>
> For the Legacy survey, I have a 5 level classification scheme:
> 5: Certain Ia
> 4: Probable Ia (Ia?)
> 3: Possible Ia, but no strong evidence
> 2: Probably not a Ia
> 1: Certainly not a Ia
>
> In this scheme, C02-028 is a "3".
>
> Do you have the light curve? I could fit it with our software here and
> see how closely it matches a Ia. If the light curve fits a Ia, and we
> can't rule it out as being a Ia from the spectrum, then I am willing to
> classify it as something like Ia?* where the "*" means we used the
> lightcurve and the fact that the spectrum was heavily contaminated by
> galaxy light. Or Rob or Alex C. could probably run a quick SNMinuit fit
> if you want to keep everything done with SCP tools.
>
> We should be very clear and well defined about what our classifications mean.
> Because I have seen in the past that as soon as someone calls something a
> "Ia?" for any reason it is lumped in with the "Ia"'s and used in every
> plot imaginable. Then the reason it was classified that way gets
> forgotten.
>
> -Andy
>
> On 28 Apr 2004, Chris Lidman wrote:
>
> > Hi Andy,
> > Thanks for re-doing the fit. Do you think it is reasonable if we
> > classify C02-028 as Ia?
> >
> > Cheers, Chris.
> >
> > On Wed, 2004-04-28 at 18:25, Andy Howell wrote:
> > > Chris,
> > > I re-ran C02-028 as you suggested, with no color mangling allowed.
> > > You do have to subtract about half Sa galaxy to get the color to
> > > match though. See attached comparison to a Ia at +5d.
> > > I am still not convinced it is a Ia. It is not out of the question
> > > though.
> > >
> > > -Andy
> > >
> > > On 26 Apr 2004, Chris Lidman wrote:
> > >
> > > > Hi Andy,
> > > > I've been having a closer look at C02-028. This one is currently
> > > > classified as "?".
> > > >
> > > > Could I ask you to try this one again, but with the extinction turned
> > > > off. It will be difficult because it is dominated by the host. The
> > > > reason why this could be a SN~Ia is that:
> > > >
> > > > i) The H and K absorption from the galaxy do not form a clean
> > > > 4000 Angstrom break. There might be some light from the blue
> > > > emission wing of the CaII feature of the SN.
> > > >
> > > > ii) A bump at 6600 Angstroms.
> > > >
> > > > iii) A reasonable looking light curve. See the attached plot. (You will
> > > > see from the tiles why this was a difficult one to do spectrally.)
> > > >
> > > > The spectrum was taken on May 18th, about 4 days past Maximum light.
> > > >
> > > > Perhaps we can get a better match with these constraints.
> > > >
> > > > Cheers, Chris.
> > > >
> > > > On Mon, 2004-03-08 at 17:53, Andy Howell wrote:
> > > > > Chris,
> > > > >
> > > > > I have mande several improvements to my program recently, most notably
> > > > > better outlier rejection and better handling of error spectra, so it
> > > > > certainly is worth rerunning objects for which we have questions. In these
> > > > > plots, blue is the rebinned spectrum after host galaxy subtraction
> > > > > (usually 5 A binning for these plots), black is the low-z template, and
> > > > > green is the original data.
> > > > >
> > > > > I have attached 5 postscript plots of the best fits to the 4 SNe you sent.
> > > > > > S01-004 - currently classified as ?
> > > > >
> > > > > Rerun with no host. The fit here shows a comparison to SN 1993J at +17d
> > > > > at z=0.41 (z is not known from the host). The fit isn't that bad. Do we
> > > > > know the date our spectrum was taken with respect to maximum light? I'm
> > > > > sure +17d is too late, but these IIb's have different features come in at
> > > > > different times depending on the relative thicknesses of the H and He
> > > > > envelopes. I wouldn't say that it is either a II or Ib for certain, but I
> > > > > think it is unlikely that it is a Ia. How about (IIb?) for the
> > > > > classification?
> > > > >
> > > > > > S01-028 - currently classified as ?
> > > > > > Significant host contamination. The percentage increase is only 27%.
> > > > > > Previously, we had this one as Ia?
> > > > >
> > > > > As you say, the host contamination is pretty bad. Here I show a
> > > > > comparison to SN 1999ee (Ia) at -8d after subtraction of an SB6 host
> > > > > galaxy. I find it very unconvincing. CaII should be obvious but is
> > > > > not. Still "?" as far as I'm concerned.
> > > > >
> > > > > > C02-028 - currently classified as ?
> > > > > > Another one with significant host contamination. The percentage increase
> > > > > > is only 13%.
> > > > >
> > > > > C02-028_spec.1.ps shows the comparison to SN 1999aa at -1d.
> > > > > The blue side looks ok, and it is possible that the feature at 9000A is Si
> > > > > 6150. The problem with this interpretation is that the SII "W" at rest
> > > > > 5400A should be there, but it isn't! Neither is the "emission" (really
> > > > > lack of absorption) just blueward of it at rest 5100A.
> > > > >
> > > > > C02-028_spec.18.ps shows a comparison to SN 1987K (II) at +7d after some
> > > > > serious host galaxy subtraction and mangling of the color. I don't
> > > > > believe it either, but it shows the difficulty in narrowing down the type.
> > > > >
> > > > > > SuF02-002 - currently classified as ?
> > > > > > This one has some host contamination. Previously we had Ia?
> > > > >
> > > > > Ugh. This one is disgusting. About the only thing I can say is that it
> > > > > is not inconsistent with a Ia. But on the other hand, there isn't
> > > > > anything to make me believe it is a Ia either!
> > > > >
> > > > > -Andy
> > > >
> >
>
>
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