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Date: Tue, 13 Apr 93 15:11:56 PDT
From: alex%bkyim.hepnet@Lbl.Gov (ALEX FILIPPENKO, UC BERKELEY, 510-642-1813)
Subject: SN 93J: some potentially useful info.
4-13-93
SN 1993J Cult Members:
A few notes:
(1) There are disturbing discrepancies (at the few percent level,
but sometimes much larger) between early-time optical spectra I have
received thus far. While some of these might be due to intrinsic
changes in SN 1993J, I think most of them are more likely to be
subtle calibration errors. The very early-time spectrum was quite
featureless; thus, even minor inaccuracies with the relative flux
calibration at different wavelengths can lead to false wiggles.
To minimize such problems with future spectra, it is important
that spectroscopists observe Star B (defined in previous messages)
in the same way as SN 1993J (that is, through 2" and 8" slits), and
that they calibrate both of these stars relative to the same global
flux standards. Through comparison with an adopted "final spectrum,"
the individual spectra of Star B will allow us to determine small
nightly correction factors as a function of wavelength that will be
applied to the spectra of SN 1993J.
I would appreciate receiving, as soon as convenient, any spectra
of SN 1993J that you might want to contribute to the collaboration.
Spectra from the first week are particularly important at this stage,
as I am trying to assess the reality of subtle features before the
theorists spend too much more time trying to reproduce them in their
spectral syntheses! Remember to also e-mail me reduced spectra of
Star B if you took them.
Again, my preferred format is 2-column ASCII (Ang vs. f_nu or
f_lambda); e.g.,
3200 2.6444e-26
3202 2.6483e-26
3204 2.6277e-26
etc.
My e-mail address is alex@bkyast.berkeley.edu
***
(2) From George Wallerstein (wall@laban.uu.se , temporarily):
Some of the early obs showed sharp H-alpha and possible other sharp
lines. This reminds me of Nova RS Oph in 1958 that showed a lot of sharp
lines on its first night and then progressively fewer. See PASP 70,537,
1958. This was evidently due to the outburst "lighting up" the envelope
that had been contributed by the red giant. The lines weakened as the
envelope was swept up by the expanding shell. Since your estimate of the
pre SN star is KO Ia it is likely to have had an envelope, as several have
suggested. The similarity is quite interesting.
The excitation of the coronal lines by an expanding shock was
suggested in PASP 73,153,1961.
(3) From Michael Richmond (richmond@spiff.Princeton.EDU):
Hear ye, hear ye! Through a combination of laziness and
circumstance, the fair name of the UC Berkeley Supernova Team
has been unintentionally besmirched! Several compilations of
SN 1993J photometry have included measurements labelled
"Berkeley" which are completely inaccurate. I wish to
explain the affair and clear our name by giving better, but
NOT FINAL and NOT CALIBRATED measurements.
The numbers you have seen have simply been the raw instrumental
difference between the SN and my star "B" (Corwin's star 4), plus a
constant of 11.90. Yes, that's right, in all colors.
I didn't mean such values to be distributed, but ... they
were. Now, please understand that a "correct" value for
the SN's magntiude cannot be found until we derive the
transformation coefficients that turn raw, instrumental
magnitudes into standard ones on the Landolt system. We haven't
managed to find those coefficients, so the numbers you see
below are RAW and UNCALIBRATED. Please keep that in mind.
What I've done below is to take Corwin's values for the
magnitudes of star "B" (his star 4):
U B V R I
12.32 12.40 11.90 11.60 11.30
and add to them the raw, instrumental difference in magnitudes
between star "B" and the SN. No color corrections have been
made! I list the measurements on two telescopes: a 30-inch
and a 20-inch (both completely automated, of course :-) )
Uncalibrated, raw measurements on 30-inch
MJD U B V R I
(0.03) (0.01) (<0.01) (0.01) (0.01) (typical scatter)
------------------------------------------------
9076.7 10.70 10.61 10.66
9077.7 9.85 10.95 10.82 10.69 10.58
9079.7 10.79 11.77 11.39 11.13 11.12
9080.7 11.55 12.03 11.68 11.35 11.08
9083.7 11.83 11.35 11.21
9084.72 11.96 12.15 11.74 11.36 11.15
9084.80 11.94 12.15 11.72 11.24 11.15
9085.74 11.90 12.06 11.62 11.10 11.07
9085.82 11.92 12.05 11.61 11.18 11.06
9087.73 11.79 11.85 11.35 10.95 10.88 bad weather
9087.90 11.82 11.83 11.33 10.97 10.87 bad weather
9088.71 11.24 10.82 10.78
I suspect the R filter of having some surface defects
that can cause "glitches" in differential measurements
if the pointing changes slightly so that stars fall in
a different area of the field.
Uncalibrated, raw measurements on 20-inch
MJD U B V R I
(0.04) (0.02) (0.01) (0.01) (0.01) (typical scatter)
------------------------------------------------
9080.72 11.52 12.02 11.67 11.36 11.08
9083.72 11.89 12.24 11.84 11.47 11.24
9084.74 11.90 12.17 11.73 11.37 11.16
9085.71 11.86 12.05 11.62 11.26 11.07
9087.71 11.69 11.86 11.37 11.04 10.90 bad weather
9088.67 11.56 11.72 11.27 10.94 10.79
9088.72 11.57 11.71 11.26 10.93 10.78
9089.71 11.46 11.61 11.14 10.83 10.70
I hope that this will clear up some of the confusion
in people's lists. Please forgive me for troubles
I've caused.
On behalf of the Berkeley SN Team (Alex Filippenko,
Bruno Leibundgut, Dick Treffers and Young Paik),
Michael Richmond
*****
(4) From Bill Herbst (bill@elysium.astro.wesleyan.edu):
Calibrating SN 1993J Photometry
Just to let you guys know that the KNAC consortium is getting lots of
data on [SN 1993J] and I just sent the following message to people about
calibration standards:
I mentioned in an earlier note that we are using the field with PG 0918 +029
(Landolt, AJ 104, 340) and the M67 dipper asterism field (Schild PASP 95, 1021)
as calibrators. The M67 field is superior in the sense that it has more stars
that are brighter, but if we go with it, we should decide whose standard
magnitudes to adopt (there are several). I suggest that we use those given
by Joner and Taylor (PASP 102, 1004, Table 6). These agree well with
Chevalier and Ilovaisky (A&AS 90, 225) and with the UBVI photometry by
Montgomery, Marschal and Janes (preprint: AJ 1993).
PS:
Messages from Priscilla [Benson] and Michael Richmond prompt me to add that
since Joner and Taylor don't give B-V values and since there seems to
be a pretty good linear relation between Schild's B-V's and
both Montgomery, Marschall and Janes' (b-v)0 and Chevalier and Ilovaisky's
(b-v)0, I think we should adopt the Schild values of B-V for calibration.
For U-B, I guess the best bet would be Montgomery, Marschall and Janes'
Table 7; the rather poor blue sensitivity of the Keck [Consortium] CCDs
precludes U-B in most cases.
As we continue to gather data on SN1993J, it is not too early to reduce
M67 or the Landolt field data and derive the transformation coefficient slopes.
I would be most interested in seeing how these agree from place to place.
The most useful form for compariosn with what we do here would be to send the
T values in the following expressions:
(B-V) = T(BV)(b-v) + c(bv)
(V-R) = T(VR)(v-r) + c(vr)
(R-I) = T(RI)(r-i) + c(ri)
(R-r) = T(R)(R-I) + c(r)
In case anybody wants more detail on the method we use here for reduction,
I can send it --- the Keck [Consortium] people already have it.
*****
(5) From G. de Vaucouleurs (gav@astro.as.utexas.edu):
Foreground (Galactic) color excess in the M81 field.
To assist in the interpretation of the photometry/spectrophotometry
of SN1993J, I have estimated - by comparison with the standard main
sequence of Johnson and Morgan (ApJ 117, 313, 1953) - the color excess
of 10 field stars for which UBV magnitudes are available.
Sources: J. Neff, McDonald (ApJS 24, 421, 1972), 3 stars (N);
A. Sandage, Palomar (AJ 89, 621, 1984), 4 stars (S);
H. Corwin, McDonald (IAUC 5742), 3 stars (C).
The range of individual values of E(B-V) is from 0.00 to +0.26, with
means 0.065 (S), 0.077 (C), and 0.167 (N). For the total sample the
unweighted mean is <E(B-V)> = 0.099 +/- 0.025 (n = 10, s.d. = 0.080)
or, after rejection of two largest values, 0.069 +/- 0.017.
With the standard Av/E = 3.3, this implies Av = 0.30 or 0.23, and
A(B) = 0.43 or 0.30.
For comparison, published values for the reddening in the M81 field
range from A(B) = 0.43 (Jacoby et al. ApJ 344, 704, 1988) to
0.30 (RC2, 1976), 0.17 (Tonry, ApJ 373, L1, 1991), 0.16 (RC3, 1991
after Burstein and Heiles), and 0.07 (Sandage, loc.cit), for an
unweighted average of <A(B)> = 0.23 +/- 0.06.
These figures may be compared with the much higher total extinction
quoted by R. Humphreys for the suspected precursor star.
****
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