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[vsnet-history 548] SN 1993J in M81 (from nova net)




Date:    Tue, 30 Mar 93 11:21:29 PST
From: alex%avf.hepnet@Lbl.Gov (ALEX FILIPPENKO, UC BERKELEY, 510-642-1813)
Subject: SN 1993J in M81

   3-30-93
Dear Nova and Supernova Observers:
   SN 1993J is the brightest supernova in the northern hemisphere since
SN 1937C. This is an unprecedented opportunity for us to really observe
it well. It is almost certainly a Type II caught extremely early in its
development.

   As I mentioned last night, we need to get really good data on it
throughout the electromagnetic spectrum. I am willing to coordinate
ground-based photometry and spectroscopy. IUE is already on it, thanks
to George Sonneborn and gang. Bob Kirshner is looking into HST. I think
James Graham (Berkeley) will try to coordinate IR efforts. GRO has
been notified. Rob Petre is looking into X-ray observations. We will
see what EUVE can do here.
   
   Regarding optical (and near-UV and near-IR) ground-based observations:
Low- or moderate-resolution spectroscopy and UVBRI photometry during the 
next few months is important to do. The next two weeks (bright run) are
especially crucial, and will be difficult because most of the larger 
telescopes will be equipped with IR equipment or high-dispersion 
spectrographs (also very useful, of course!). Some details:

    Spectroscopy: Please try to get nightly spectra (even a few times 
per night might be good during the next week) over as broad a wavelength 
range as possible. Use a roughly 2" slit for good resolution, and a 8-10" 
slit for good spectrophotometry. The wide slit should be used even on 
non-photometric nights, to be sure that you are not suffering 
differential light losses due to atmospheric dispersion. Aligning
the slit along the parallactic angle also helps (see Filippenko
1982, PASP, 94, 715). Take spectra of standard stars through the same
slit widths (roughly 2" and 8-10" slits). I suggest Feige 34 for the
UV part (since it does not contain strong Balmer lines and is therefore
easier to calibrate).

   Photometry: Be sure to get as many bands (primarily UBVRI) as possible.
Do standard stars, especially if the nights are photometric. Even if they
are not photometric, differential photometry will be useful from stars
on the same field.

   Nick Suntzeff of CTIO has contacted me, and offers very valuable advice
(based on their experience with SN 1987A). To implement it, we will need
some help, as outlined below.

   (1) We should consider defining a local star of neutral color as the 
standard star for use, especially by people with photoelectric photometers. 
Since the SN might reach mag 8-9, we should probably find an A star or F 
star in this mag range as our standard. Also, let's pick another star 
2-3 mag fainter.  As the SN fades these two stars will allow a uniform 
set of photometric calibrations.

   This will reduce the errror in the photometry due to the extinction, 
which can easily dominate the overall errors. Observers with photoelectric
photometers on small telescopes can often get really good phtometry even 
in non-photometic conditions if we provide a local standard.

   ACTION ITEM: WE NEED THE COLORS OF STARS NEAR SN 1993J TO CHOOSE GOOD
LOCAL STANDARDS. Can anyone get this? OTHERWISE, LET'S USE THE STARS
CLOSEST TO THE SUPERNOVA (SEE BELOW).

   (2) Much more importantly, we need to define a local spectrophotometric 
standard. EVERYONE reduces spectrophotometry differently, and if there are 
no stars in common, we will have a hell of a time getting out the 5% 
wiggles in the data, which I am sure will turn out to be interesting to 
a large number of theorists. (The "Bochum" event comes to mind for SN 1987A.)
With the local standard, we will not have to worry about extinction and a 
host of other problems. ANY star will do, but if we choose an early-type
star, we can at least see the errors in the continuum (away from the 
H-lines at least). We need to verify that both the spectroscopic and
photometric standards are not variable.

   It is extremeley important to always observe this local 
spectrophotometric standard! Observe it in the same way that you observe
the supernova. Also observe one of the normal KPNO standards, of course.
(I recommend Feige 34

    UNTIL FURTHER INFORMATION ABOUT THE COLORS AND NON-VARIABILITY OF NEARBY 
STARS BECOMES AVAILABLE, I SUGGEST THAT WE CHOOSE THE 11.4 MAG (HST GSC "V")
STAR SOMEWHAT TO THE SOUTHEAST OF THE SUPERNOVA AS OUR "BRIGHT" STANDARD STAR
(CALL IS "STAR B"), AND THE 14.6 MAG (HST GSC "V") STAR IMMEDIATELY TO THE 
SOUTH OF THE SUPERNOVA AS OUR "FAINT" STANDARD STAR (CALL IT "STAR C").

  THE BRIGHT STAR'S J2000 POSITION IS (STAR B):
                ALPHA = 09 55 41.5, DELTA = 69 00 30.
  THE FAINT STAR'S J2000 POSITION IS (STAR C):
                ALPHA = 09 55 23.6, DELTA = 69 00 49.
  THE SUPERNOVA'S J2000 POSITION IS APPROXIMATELY 
                ALPHA = 09 55 25.0, DELTA = 69 01 13.

  NOTE THAT THE BRIGHT STAR (HST GSC "V" = 12.3) TO THE NORTHEAST OF THE
SN (CALL IT "STAR A") IS SURROUNDED BY A BRIGHTER BACKGROUND. THUS, ALL 
OTHER THINGS BEING EQUAL, IT IS NOT AS FAVORABLE. HOWEVER, IF IT TURNS OUT 
TO HAVE MORE NEUTRAL COLORS THAN STAR B MENTIONED ABOVE, WE MIGHT WANT TO 
USE IT.

   (Note that the above naming convention follows that established by
Michael Richmond a few hours ago. His e-mail address is 
richmond@astro.princeton.edu, in case you want an e-mail version
of a finder chart for the SN.)

    Stay tuned for more information.....

    Cheers,

    Alex Filippenko


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