From: Greg Aldering (aldering@panisse.lbl.gov)
Date: Wed May 14 2003 - 10:02:05 PDT
>On Tue, May 13, 2003 at 11:15:03AM -0700, Greg Aldering wrote:
>> a) Follow Phillips 1999 in throwing out very red objects even though
>> you are going to extinction correct. I believe that Phillips
>> threw-out objects with Bmax-Vmax > 0.2 mag. (Talk about dirty
>> laundry!)
>
>It's not clear to me that he did this when finding his RB values. He
>did do that for a bunch of the analysis, but for the RB stuff
>specifically he only talks about throwing out the SNe without a point
>near max. I believe that his value *is* with the most reddened SNe (he
>certainly plots those), and as such throwing out the most reddened SNe
>from our set isn't a matter of saying "just as Phillips"....
Correct. Ok, then just throw out the red ones, as Phillips did in his
analysis and use the regular R_B. From my fitting, I find that when the
reddest objects (E(B-V) > 0.2) are thrown out, our SNe like R_B =
3.3+/-0.5. The chi^2 is only worse by 2.5 when R_B = 4.1 is used. This
means that we should get a good fit using the canonical R_B if we
exclude the red objects. In this case, I believe we can simply cite
Phillips 1999. (By the way, you can see in figure 10 of Phillips that
his red objects systematically prefer a smaller R_B.)
Note that there is an old and ugly history of low R_B's having been
suggested for SNe, prior to the advent of width-luminosity relations.
So using the canonical R_B is definitely the safest thing to do,
otherwise older reviewers could really light into us. Challenging the
canonical R_B requires a very high level of proof that all the other
steps (like determination of the fiducical color) are unassailable. On
a related note, Lifan says that the CMAGIC analysis likes R_B = 4.1.
>The expression I'm using is:
>
> B-V = -0.076 + 0.0446 * (1/s - 1)
>
>I think the numbers you used in P99 were -0.11 and 0.243 respectively.
>This is a redder central color and a milder slope, but looking at the
>fits I couldn't justify the bluer color, and the slope wasn't as clear
>as all that. (Indeed, the uncertainty on the slope is 0.037, nearly the
>full size of the slope.)
Concerning your shallow color-versus stretch relation, have you compared
it to equation 23 of Phillips 1999? He finds:
(Bmax-Vmax)_0 = (Bmax-Vmax) - 0.114*(dm15 - 1.1)
Using equation 5 of P97 (dm15 = -1.96*(1/s-1) + 1.07), this becomes:
(Bmax-Vmax)_0 = (Bmax-Vmax) - 0.114*(1.96*(1/s-1) + 1.07 - 1.1)
(Bmax-Vmax) - 0.114*(1.96*(1/s-1) + 1.96*0.114*1.07 - 0.114*1.1)
(Bmax-Vmax) - 0.223*(1/s - 1) - 0.11
That is, Phillips 99 gets a relation almost identical to what we used
in P99. I know that you are using (B-V)@Bmax and not Bmax-Vmax, but
still, I'm surprised that the dependence of color on stretch basically
vanishes in your analysis.
To make some progress here, can't you plot your measured B-V vs stretch
for SNe in E/S0 hosts, and overlay your color-stretch relation to look for
consistency? I think that would settle this issue.
- Greg
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