Visual Discovery of SN 1996bk in NGC 5308.
Last October 12, Piero Mazza and myself found visually our second supernova
in edge-on spiral NGC 5308 located in Ursa Major. The star was found right
after twilight and at the begining of our search and it was the climax of a
very intense day at our observing site Passo del GiovÁ (it was "partial
eclipse day" here in Europe).
It may look odd but the night had began badly, meteorologically speaking. The winds were blowing from south and in northern Italy this means moist laden air and subsequent rainy days. At sunset a thick layer of mid air fog formed at our elevation (some 1500 meters). With telescopes dripping water everywhere and visibility reduced to a few meters we were thinking of going back home (we had observed the night before and we had seen the eclipse, we were satisfied). But as the temperature began to drop the fog drifted lower. Stars came out of the haze and a poorly trasnparent sky but with excellent seeing greeted us. And that's when the supernova popped into our view, less then 10 degrees above the horizon.
You may wonder that we may be a pair of fanatics, desperately seeking clear holes in the sky where to point our telescopes and search for supernovae. In fact, quite the contrary is true. Of course we are pleased when we make a discovery, but visually observing galaxies is our real pleasure; supernovae may be the "rational" motive to look at a galaxy. But we would still be observing galaxies even if supernovae didn't exist.
Nothing beats the mental joys of a clear night spent nesting tens of galaxies across the cosmos, in peaceful darkness, listening to soft background music... A friend of ours compares us to bees, buzzing from flower to flower on a vast praire, inspecting each of them; there would be no bees without flowers and probably no flowers without bees.
Back to science... For those who love statistics here are some numbers to ponder. Some 30,000 observations in four years on a programme of 600 to 800 galaxies (priority is given to the northern ones) have produced two official supernovae, one in 1995 and this one. We missed two in 1994 (remember M51 and NGC 4526?), the first by 20 hours the second by three days (we didn't have the Net, yet). We "overlooked" M81 back in 1993 at the right time... (let's be honest: 1993J was right there, still waiting official discovery notice, we were sleeping at the eyepiece...). We check one galaxy every 2/3 minutes, using exit pupils of 1.5-2mm, with home made telescopes 40 or 51 cm in diameter. Our target galaxies are usually closer than 40 megaparsecs, and should produce supernovae brighter than magnitude 15.5. Last year we did some 10,000 observations, this year we'll finish at 6,000 (bad weather is the culprit). Each year we observe on 20 to 30 nights in three sites north or south of Milan, that can be reached in a two hours drive.
We would like to thank the amateurs directly involved in confirming 1996bk. They are: Michael Schwartz, Guy Hurst, John McKay. A big thank you also to Harvard astronomer Peter Garnavich who confirmed spectroscopically the supernova.
Good galaxy observing (...and good hunting)!
See the SN Atlas
Imaging by Nick James of The Astronomer
Spectrogram by P. Garnavich of Harvard CfA - (see IAUC 6491, Oct. 15, 1996)
See the light curve of SN 1996bk by Pedro Re'