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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