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Thu, 25 Aug 2011

Supernova in M101 – use our new finder chart

Discovery image of the supernova (right). Credit: Peter Nugent and the PTF collaboration.

British astronomers have announced the discovery of a supernova in galaxy M101, which they claim is the nearest supernova of its type for more than 40 years. The object was discovered at magnitude 17, but as it appears to be rising in magnitude, the team say that it could become as bright as magnitude 10 within the next few days. This would bring it well within the reach of small telescopes and even large binoculars. But the SPA warning is – don't expect to spot it yourself unless you have really dark skies and know how to find faint galaxies! See below for a finder chart.

The galaxy M101 is currently well placed for observation in Ursa Major, not far from the well-known stars Mizar and Alkaid in the Plough. But it is notoriously hard to find in average skies, and books on binocular astronomy often don't even mention it.

The supernova was first seen on 24 August at around 8 pm BST, within the spiral arms of M101. An image taken the previous night had shown no such object in this position. The discovery was made using the venerable 48-inch Schmidt telescope at Mt Palomar, which is now operated robotically by a team of British and American astronomers known as the Palomar Transient Factory.

A spectrum shows that it appears to be a Type 1a supernova, which occurs when a white dwarf star in a binary system explodes. The famous supernova of 1572, in our own galaxy, was of this type. Though closer, the supernova 1987a in the Large Magellanic Cloud was of the rarer Type II-P.

Amateur astronomers with suitable instruments should be able to photograph the supernova, which has the discovery name PTF11kly. Its position is RA: 14:03:05.81 , Dec: +54:16:25.4.

Update 30 August

The supernova now has the official designation SN2011FE. Observations submitted to the American Association of Variable Star Observers show it to be at about magnitude 11.5

The photo below was taken by Phil Benson on 29 August using a 115 mm refractor with ST8300M CCD camera, 4 x 10 minute exposures.


Update 7 September

Th supernova is now about magnitude 10, so should be just within the reach of good binoculars in a dark sky to anyone who is accustomed to locating such things. But from typical suburban skies, and if you are not used to finding celestial objects, it will be a struggle! News stories suggesting that you can just go out and spot it are way off the mark, and were written by people with little or no experience of actually finding such objects in the sky. A medium-sized telescope, particularly with Go To finding facility, will give you a better chance, but even then for many people it will be a tricky observation.

The problem is that there are many stars of this brightness in that part of the sky, so you need to be able to see the galaxy M101 itself to be sure you're seeing the right one. You also need to look as soon as it gets fully dark, as this part of the heavens gets quite low in the sky after about 9.30 pm, which makes it even more difficult to find the object. A waning Moon adds to the sky brightness, drowning out the galaxy.

M101 is a tricky galaxy to locate at the best of times, as it has a low surface brightness. Use the chart below to find the right part of the sky, using the Plough (in the north east) as your guide. From the star Mizar, use a little chain of stars to find M101, which is a faint fuzzy area. The larger and higher magnification your binoculars, the better.

If you can see M101, use the chart linked here, covering the area shown by the white square below, to pick out the supernova, shown by the white circle. Bear in mind that you might not see the galaxy covering the full area shown by the green circle, so the supernova may appear to be outside the galaxy. Stars are shown to magnitude 11.


Added by: Robin Scagell