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Date: Sat, 3 Apr 93 08:29:36 PST
From: alex%bkyim.hepnet@Lbl.Gov (ALEX FILIPPENKO, UC BERKELEY, 510-642-1813)
Subject: Optical news on SN 1993J
4-3-93
Dear SN 1993J observers:
It is very important to continue observations of SN 1993J as
frequently as possible. There is substantial evidence that this is
a peculiar supernova: the spectrum is unusual, as is the light curve.
The object is fading rapidly, but it might brighten again (as did
SN 1987A). Or, it might plummet (as did S And). We can't be sure of
what it will do --- observations are needed! I know that there are
several observers who are trying to get IR photometry and spectroscopy,
as well as high-resolution spectra to study the ISM in the Galaxy and
in M81. It is also crucial that we obtain the necessary optical
photometry and low-dispersion spectroscopy during the next week,
around full moon. If possible, please try to use the observing
guidelines (including observations of local standards, etc.) that
I outlined in previous messages to the nova/supernova network.
I would appreciate receiving calibrated low-to-moderate dispersion
optical spectra and broad-band optical photometry over e-mail as soon
as possible (from those who wish to contribute to this collaboration).
Be sure to include a note concerning details of observations and
reduction procedures.
Below I include some comments from other observers. Some of
you have undoubtely received this directly from their sources, but
many others haven't. Just ignore them if they are not new to you.
Based on Richmond's note, the following ACTION ITEM is called for:
REALLY GOOD ANALYSIS IS NEEDED OF THE COMPARISON STARS, OVER MANY
NIGHTS, BEFORE WE USE THEM FOR FINAL PHOTOMETRIC CALIBRATION OF SN 1993J.
Good luck!
Alex Filippenko
*******
From Michael Richmond (richmond@astro.Princeton.edu):
It looks like the max light in UBVRI has DEFINITELY
been reached. The SN is still blue, but reddening
pretty quickly.
One disquieting note: stars A and B are showing quite
a difference in relative brightness night-to-night,
with a trend of A getting fainter relative to B.
We'd better watch this carefully! star C seems
to be pretty constant relative to A, but it's much
fainter (about 3 mag), so the photometry isn't as
good.
****
From Gerard de Vaucouleurs:
(1) Hi!
I thought the appended notes that I am circulating in our Dept
might be of some interest to you and your team. Please feel free
to use them in any way you want. I would appreciate receiving
photometric observations which are NOT in the IAU circulars. Thanks.
Regards and best wishes.
G. de Vaucouleurs (gav@astro.as.utexas.edu)
Notes on M 81 and SN1993J
G. de Vaucouleurs
Department of Astronomy, University of Texas, Austin, TX 78712
1. The mean extinction-corrected distance modulus of M 81 is
(m-M)$_{\circ}$ = 27.75 $\pm$ 0.1 (mean and median of 11 estimates
by seven different authors or teams using ten different methods, 1978-1991).
Extinction corrections are uncertain, however, with A$_{B}$ varying from
0.1 to 0.4.
2. The V-band magnitudes (ranging from 8.9 to 15.3) of two dozen comparison
stars in the M 81 field are given in the Thompson \& Bryan 'Atlas of SN
Search Charts' (Cambridge U. Press, 1988) which observers are urged to use.
In particular stars B and C mentioned in the IAU Circulars are shown at
V(B) = 11.9 and V(C) = 14.0.
3. If V $\simeq$ 10.3 observed on March 30-31 is the maximum, SN1993J is
$\sim$ 0.8 mag brighter than the Type II SN 1970 in M101 (neglecting color
and extinction corrections). Assume that it was a good match to SN1993J, then,
if the distance modulus of M 101 is
(m-M)$_{o}$ = 28.6 $\pm$ 0.1 (mean and median of 20 estimates by a dozen
sources, 1973-1986), the distance modulus of SN1993J and M 81 is
(m-M) $\simeq$ 28.6 - 0.8 = 27.8 (consistent with mean above) and
the absolute magnitude of SN1993J at maximum is M$_{V} \simeq - 17.5$,
somewhat more luminous that the average type II SNae on the short
distance scale (de Vaucouleurs, ApJ, 227, 753, 1979).
4. If the post-maximum light curve of SN1993J follows the average for
`plateau-type' Type II SNae, the plateau phase will begin 40-50 days past
maximum and at a level $\simeq$ 2.0 mag below maximum (de Vaucouleurs, in
`SNae and Supernova Remnants', Reidel, 1974, p. 203), or about m $\sim$ 12.3
(again neglecting as yet unknown color and extinction corrections).
5. The plateau phase should end $\sim$ 100 days after the initial
outburst or $\sim$ 90 days past maximum, at the end of June 1993.
It will be important to closely monitor (photometry, spectroscopy) the
onset of the rapid decline phase following to see if the break is as sudden
and sharp as in, e.g. SN1923 in M83, or is a more progressive transition.
The differences between SNIIae at the end of the plateau phase are not yet
understood.
6. For comparisons with SN1987A (light echo, etc) remember that the distance
of M 81 is about 75 times that of the LMC (1" = 17 pc).
(2) Hi!
I tried to send you this memo yesterday, but the e-mail address in the
AAS directory must be wrong. [Yes, it is wrong. The correct address
is alex@bkyast.berkeley.edu --- Alex.] I hope this will reach you.
Please feel free to use it in any way you want.
I am concerned that many observers
do not seem to be aware of the M81 comparison stars in the Thompson-Bryan
Atlas and waste their efforts by adopting bad magnitudes from other
sources (including the GSC). Harold Corwin has sent me some unpublished
UBVRI McDonald observations of some of these stars, from which we can
cook up approximate JHK magnitudes to help the IR and spectrophotometric
observers. Best regards.
G. de Vaucouleurs (gav@astro.as.utexas.edu)
Here are Harold Corwin's UBVRI observations:
Star V B-V U-B V-R V-I n RA (B1950.0) Dec Chart ID
1 12.45 0.63 0.11 0.39 0.76 3 09 50 25.6 +69 15 38 12.4 overline
2 11.78 0.69 0.16 0.40 0.80 3 09 50 35.9 +69 20 04 11.8 overline
3 11.62 0.53 -0.04 0.33 0.69 3 09 51 21.2 +69 05 34 11.6 (near 14.1)
4 11.90 0.50 -0.08 0.30 0.60 2 09 51 36.1 +69 14 44 11.9 overline
5 13.65 0.57 -0.09: 0.34 0.69 3 09 52 11.1 +69 09 41 13.6 overline
6 11.85 1.30 1.29 0.68 1.29 3 09 52 39.7 +69 24 18 11.8 underline
7 14.73 0.46 0.12: 0.36 0.60: 3 09 53 17.7 +69 24 54 14.7 overline
The V-R and V-I are on Cousins's system. All the observations
were made in 1982 Nov, 1983 Feb, and 1983 Apr, with the 76-cm
reflector at McDonald Obs. There is no evidence of variability
for any of the stars. The three values marked with a colon have
each had a discordant measure rejected (the means with no
rejections are -0.04, 0.09, and 0.66, respectively). The mean
internal standard deviations for these seven stars only are
V: +-0.015
B-V: +-0.011
U-B: +-0.032 (no rejections)
+-0.014 (two rejections)
V-R: +-0.019
R-I: +-0.029 (no rejections)
+-0.018 (one rejection)
These are about the values that I expected based on error analyses
of my other McDonald data.
The positions are from the GSC (mean errors about 1 arcsec), and
the "Chart ID" refers to the label on the Thompson/Bryan N3031
chart.
******
From Alain Porter:
Dear supernova colleagues: here are 2 news items about SN 1993J I have
just submitted to the IAU Circulars. The situation with the light curve
is especially urgent. Observe it even several times per night if you can.
It has been some time since I updated this distribution list. If I
should use a different address for you, if you know anyone I should add,
or you want to be dropped from the list, please let me know.
I have heard relatively little news today. Is the spectrum still
featureless?
Alain Porter
APORTER@NOAO.EDU
* * * * * * * * * *
SN 1993J ALREADY FADING
* * * * * * * * * *
A. C. Porter, KPNO, reports: unfiltered and Harris VRI band photometry of
SN 1993J by A. W. Neely, NF/ Observatory, reveals that the supernova
has already started to fade. V magnitudes on three post-discovery
nights are: UT March 31.21, V = 10.33, April 1.18, 10.60; April 2.15, 10.97.
Rms errors are about 0.03 magnitudes for each night. The V magnitudes
are measured relative to the V = 11.42 GSC star 87" east and 43"
south of the supernova [Mike Richmond's star B]. The R and I band
photometry, not yet calibrated, indicate that the supernova is
reddening, with the maximum occurring progressively later in redder
bands: the R magnitude dropped by 0.07 and 0.25 between Mar 31-Apr 1
and Apr 1-2, respectively. The I magnitude dropped by 0.04 and 0.16
during the same intervals. Unfiltered photometry, including 2 prediscovery
frames, confirm that maximum occurred on about March 31: UT March 28.30,
13.8; March 29.18, 11.2; March 31.21, 9.9; April 1.18, 10.5; April 2.15, 11.0.
The unfiltered magnitude on UT March 28 is measured relative to the GSC V
magnitude of the [14.6 magnitude] star 8" west and 24" south of the supernova.
The unfiltered magnitudes on the remaining 4 nights are measured
relative to the 11.42 star mentioned above. All
images were taken with the 0.445m f/4.5 reflector of NF/ Observatory using
a Craf-Cassini Ford-JPL 1024 x 1024 CCD at a prime focus scale of 1.2"
per pixel. Seeing averaged about 4". The V exposure times were 100
seconds, the R and I exposure times 60 seconds, and the unfiltered exposure
times 30 seconds.
This unexpected rapid fading from an initial V absolute magnitude of -15.4
(assuming the distance modulus of 25.7 from the Tully Nearby Galaxies
Catalog, with no reddening correction) suggests that SN 1993J may
develop a light curve resembling that of SN1987A, in which an initial
sharp but optically faint spike is followed by an extended plateau.
Frequent photometry in as many bands as possible becomes especially
urgent under these circumstances.
* * * * * * * * * *
SN 1993J PROGENITOR COLOR
* * * * * * * * * *
A. C. Porter, KPNO, reports: Images of M81 taken on UT January
21, 1985, by J. G. Cohen, CIT, show the progenitor of SN 1993J
as a red stellar object. The images were taken on the 1.5m Palomar
reflector, with an RCA CCD, at an image scale of 1.2"/pixel.
The night was photometric and the seeing was 3". Preliminary photometry
of two images each in the Thuan-Gunn g and r passbands gives r = 21.0,
g-r = 0.9. The measurements were made with a 5" aperture and 5" wide
sky annulus to minimize background contamination. The uncertainty in
the color may be as large as +- 0.25 due to the galaxy background, but
the redness of the progenitor is certain, and the value derived suggests
a spectral type of about M0.
Archival images of M81, plates as well as CCDs, offer an unprecedented
opportunity to observe a well sampled light curve of a massive Type
II supernova progenitor in the last few years before its explosion.
The likely interest of such data is demonstrated not only by already
emerging reports of the variation of SN 1993J's progenitor,
but by the fact that the peculiar Type II SN 1984E apparently
ejected a shell sometime between 2 and 23 years before its explosion
(Gaskell and Keel 1988, in Kafatos and Michalitsianos, "SN 1987A in the LMC",
p. 13). Such a light curve could significantly constrain models of the
endpoints of the evolution of massive stars.
*****
From Thomas J. Balonek (tbalonek@colgateu.bitnet):
(1) For IAU Circulars:
T.J. Balonek, C.A. Tremonti, Colgate University; and J. Koch, St. Lawrence
University report: "V-band CCD photometry with the Burrell Schmidt
telescope of the Warner and Swasey Observatory, Case Western Reserve
University, on Kitt Peak indicates a near-linear
0.30 magnitude per day decrease in brightness during the two day
interval 1993 March 31.2 to April 2.4. Adopting a V magnitude of 11.42
(from the Hubble Guide Star Catalog) for the comparison star located
approximately 0.7' S and 1.5' E of the supernova (at R.A. = 09h 55m 41.5s;
Decl. = 69D 00' 30", equinox 2000.0) we obtain approximate V photometry:
March 31.17 UT, 10.31; 31.26, 10.34; April 1.21, 10.59; 1.40, 10.65;
2.13, 10.89; 2.22, 10.91; 2.37, 10.97. Each value is the average of three
to five consecutive exposures. A different detector was used for
the April 1 observations; color corrections have not yet been applied to
these measurements."
(2) Additional note for optical observers:
There are major discrepencies in the V magnitudes of potential
comparision stars for SN 1993J in the Hubble Guide Star Catalog.
Our observations on three nights with the Burrell Schmidt telescope
(CWRU) on Kitt Peak indicate that relative to comparison star B
(labels from Michael Richmond's March 30 email "finder map")
comparison stars C, F, and G may each be approximately 0.6 magnitudes
brighter than indicated in the memo (that is, 0.6 magnitudes brighter
than given in the Guide Star Catalog), and star A may be 1.4 magnitudes
brighter. Comparsion stars D and E agree to within 0.05 magnitude
with star B, consistent with magnitude errors typical of the GSC.
Observers should thus be careful to specify which comparision
stars are being used, at least until well determined magnitudes
are available for these stars.
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