Spring VLT 2001 Spectra

At Chris' request I have taken a look at the spring 2001 VLT data, and I agree with his preliminary assessments, but I also have some comments of my own. The major new information is:

• I think Sibelius/Vilaine (previously unknown) is probably a Ib/c.
• Lalo was identified as a Ia, and it probably is, but judging from the specrum alone, I don't think we can say for certain.
• Chopin was previously unknown. It might be a Ic at z=0.22, but the spectrum really is too noisy / contaminated to tell.
• S01-031 Bach was listed as SN? I think it is a Ic at z=0.32, similar to SN 1991A.
• S01-035 Mussorgsky and S01-037 Gershwin were listed as FBTs (Featureless blue things). Mussorgsky may be an AGN. It appears to be at the center of what might be an E galaxy. Then again it could always be an early Type II if the galaxy is a spiral. Gershwin is slightly more likeley to be an early Type II, because it doesn't appear the be at the center of its host, though it is somewhat hard to tell from the discovery image.

This is a very interesting SN. I normal Type Ia spectrum doesn't fit too well: S01-004.92a.p05.ps The observed data has been Savitzky-Golay smoothed and an E galaxy spectrum has been subtracted. SN 1991T at +10 days isn't much better: S01-004.91T.p10.ps. In general, the fact that there are no features in the blue part of the spectrum means that it is unlikely to be a Ia.

A much better fit is to the very strange SN 1991L. There is only one spectrum of this SN available, and the epoch is not known. The type is thought to be a SN Ib/c, but even that is not certain. See my comparison at S01-004.91L.ps and also Matheson et al. 2001, ApJ, 121, 1648 The observed data has been Savitzky-Golay smoothed.

I think we can upgrade its status to SN I, probably SN Ib/c

It looks like SN 1992A at +6 days. S01-005.92a.p05.ps was S-G smoothed. However, in a normal SN Ia there are 2 peaks in the 4000 A (rest) region, which is 6000 A in the observed Bizet spectrum. Bizet has 3 peaks. The third peak, at 6200 A (observed) usually gets strong a few days later, at around 10 days, but when that happens, the second peak decreases. Here, all 3 peaks are about the same intensity. I have never seen this.   It is possible that this is due to some artifact from night sky lines or galaxy subtraction, but this three peak structure is also seen in Bruch, at a different redshift.

I agree, beautiful, roughly s=1 SN near max. See the comparison to 94D at +5 days at: S01-007.92a.p05.ps These data have been S-G smoothed. It is interesting that Bruch also has 3 peaks like Bizet from 6000 to 6500 A observed.

Decent fit to 94D at +2 days, except that there is no Si at ~6000 observed (4000 rest). See S01-017.94d.p02.ps, where the data have been S-G smoothed, and 10% Sb galaxy has been subtracted.

Without Si, it is hard to say that this is a Ia. It is possible that this SN is on the hot side of normal SNe Ia, and there is weakish Si, like 90n, and what is left is buried in the noise.

It possible that this is a Ib/c. See the comparison to the Ib SN 1999dn at +10 days: S01-017.99dn.z56.ps These data have not been smoothed, nor has any galaxy light been subtracted. Note that this redshift is 0.02 off in redshift from what Chris reported. The data also fits at z=0.54, but not as well.

While the data are not a perfect match, all of the lines are there. I also cannot stress enough the diversity of Ib/c. There is no earlier spectrum of 99dn, so it is hard to say what it would have looked like at peak.

You can also fit the same SN Ib (SN 1999dn at +10 days) at z=0.34: S01-017.99dn.p10.ps. The high redshift data is on top and has been S-G smoothed. In this case all of the features identified would be different than if the match was at z=0.56! This "match" is probably not correct, if Chris' determination of the redshift from the OII line is right, but it goes to show that we have to be very thorough when we are matching up spectra. Just matching wiggles can be very misleading, unless we have an unambiguous detection of Si of some kind.

And just to drive home this point even more, compare the spectrum to the peculiar SN Ia 91T at z=0.75: S01-017.91t.z75.ps As above, I don't think this is the correct "match," I am just making the point that without a redshift is is easy to match many things.

I would suggest downgrading this one to Type Ia? It is best fit as a Ia, but without the Si II it is hard to say for certain. It is possible that when we factor in light curve data it will seem more solidly like a Ia.

Doesn't seem to fit anything at z=0.658. Could be a Ic at z=0.22, like SN 1991A. You can see this comparison to the S-G smoothed data at S01-028.91A.ps. Note that the feature at 8000 A (observed) is a trace of H-alpha in the template, which Chopin doesn't have. See comments on Bach below.

This is by no means definitive! I have no confidence in this one at all. I am not even sure it is a SN.

Chris made a heroic effort to separate the SN from the galaxy, but I think it is just too noisy to make an ID.

This is a Ic. It is similar to SN 1991A, which was classified as a Ic, however there are is a trace of He in 91A, (which would make it a Ib), and there is even some weak H-alpha, which would make it a II. In S01-031.91A.ps I compare Bach to the spectrum of 91A at 1-17-91, though it also fits well to the spectrum taken at 1-6-91. Bach is unsmoothed. You can see that Bach doesn't have H-alpha (the feature on the right hand side of the spectrum). Of the double absorption at ~7500 A in 91A, the blue one is probably He I, and the red one is probably Na I D. Note that Bach doesn't appear to have He. The line near 7800 A in Bach is from the Earth's atmosphere. The phase of 91A is unknown, but note that it was discovered by Pennypacker et al. (!) on January 1. 

This is certainly a Ia see the comparison to SN 1981b at: S01-033.81b.max.ps

You can tell it is a Ia from the Si II absorption at 5500 A, but note that you can't really see the main Si II feature at 8500 A. I don't think this is a problem, though because you can't really trust any of the spectra in the red (this spectrum has been S-G smoothed). The Keck data shows some hint of what might be Si II there, but it is hard to say without the final reduction.

The SN is at the center of what looks like an E galaxy from the discovery image, so it is probably an AGN. Then again, it could be an early type II if the host is not an E galaxy. See, e.g. SN 1979C at +7 days, SN 1993J at +3, etc. 

Certainly a Ia due to the 6000 A (observed) Si feature. The best match is to 94d at +2 days for z=0.49. This is 0.02 off of the OII feature observed by Chris, and it isn't because of the redshift of the template -- 94d was at z=0.0015. Possibly it is due to unusual velocities. See S01-035.94d.p02.ps, where the data have been S-G smoothed. Note that 94D was a normal SN Ia, but it was very blue (Patat et al. 1996, MNRAS, 278, 111). Even though, SN 1994D was similar to SN 1992A, SN 1992A is not a great fit because the "emission" feature at 6800 A observed is lower in Massenet than in 92A.

This Ca feature is somewhat similar to the depth and width of the feature in SN 1981b, but if you match up these features using 81b as a template, then none of the other features match. The Ca II absorption at ~5500 A observed, 3700 A rest, seems to be deeper, broader, and more blueshifted than in 94d. (Note that this absorption is not due to TiII as in SN 1991bg and SN 86G.) This indicates that Massenet may have had unusually high velocity Ca, perhaps like 84A (though I don't have the 84A spectra).

Another reasonable match is SN 1990n at -7 days, though again if you match up Ca, then the other lines are off. Note that strong, high velocity Ca is a signature of certain types of SNe Ia, like 84A, but it can also be a sign that this spectrum was taken at an early epoch. See, e.g. Hatano et al. 2000, ApJ, 543, L49

More likeley to be an SN II than Mussorgsky, because it doesn't appear to be at the center of its host, though it is somewhat hard to tell based on the discovery image.

We can say with complete metaphysical certitude that this is a Ia. It looks like SN 1981b at max at z=0.58, though the Ca absorption at 6000 A at 3700 A rest is somewhat bluer and broader in Junk 15 (we really have to give this a real name). See S01-054.81b.max.ps, which has been S-G smoothed.

Another one that we can nail with complete metaphysical certitude, and even more so here because you can see Si 6355! See the S-G smoothed S01-065.81b.max.ps

Again the best fit is to SN 1981b at maximum. This is a very good fit, though Joe Strauss looks to be somewhat bluer. This could be due to the standard star calibration rather than any intrinsic property though.

Page written by Andy Howell (DAHowell@lbl.gov)