new star: nova delphinus 2013

Thanks to one of the other astronomy guides I work with, I've now been on the trail of the newest nova in the Milky Way galaxy: Nova Delphinus 2013! Yes, we astronomers are excellently creative with names - Nova means 'new star' and refers to stars that brighten rapidly several magnitudes (usually a white-dwarf/companion star system where the dwarf accretes material from its nearby neighbour and then detonates when it gets too much), Delphinus is the lucky constellation it is in, and the year incidentally is 2013. But it makes sense, at least.

Here's my iPhone snapshot of it, through a 16" Meade:

Some very nice photos already coming out of this nova, including this one by Anthony Ayiomamitis, some cool spectroscopy by Gianluca Masi and this way awesome animated gif by E. Guido and N. Howes.

I was curious which star exactly it was that went 'nova' - kind of a mini-SN1987A investigation. Someone posted that they thought it might be TYC 1643-2104-1 which is a pretty good guess - it's a magnitude 12 star, and the closest catalogued for that position in the sky. However, I went digging a bit in the Aladin archived images, and I think it might be a different (uncatalogued) star.

Here is the photo by Ayiomamitis:

Now here is the region of sky from Aladin, centred on TYC 1643-2104-1 (circled in orange):

If we play the geometric matching game, then we can highlight some key stars (again in orange) on the Ayiomamitis image, and pick out the same stars on the image from Aladin:

I've circled the two stars that I think could be responsible for the nova in red. I don't think either of them are catalogued? Or if they are, they don't seem to be listed in Simbad because the default entry for the closest position is TYC 1643-2104-1. Not too sure about binary system angular resolution, maybe it is possible that we are seeing the dwarf and companion? Someone can correct me on this!

In any case, this is pretty cool and hopefully we will see a bit more brightening of this 'new star' over the next days :) It's no supernova (I'm still hanging out for a nearby Galactic supernova…) but it's the next best thing and maybe even will become a Type Ia supernova sometime in the future!

Update! (16/08/2013)
So a couple of things. One: those two stars are pretty definitely not the binary system. I had no idea, but the usual nova separation between white dwarf and companion star is ~0.01 AU! That's 1/100th of the distance from Earth to the Sun! This does kind of make sense if you think about it - the dwarf needs to be close enough to the companion star so that it can steal its mass, and gravitational attraction drops off pretty quickly with distance. So unless the system was super close to us (like, waaaaay close), we would not resolve the separation.

Also, those two stars are in fact catalogued. Perhaps not in Simbad, but in Vizier you can put in the closest position (20:23:30.59 +20:46:03.8, for the brighter star on the right) and it gives 1-3 stars from different catalogues, with measured magnitudes of about +16 to +18. That's really super faint. Click here to see the Vizier search results (based on taking the brighter star position within 10").

For fun, if we take the red magnitudes listed by the various catalogues (USNO, CMC, GSC), we can plot the change in magnitude over time for the two stars nearest where the nova went off (where the red point is the current nova magnitude of +5.1, which may not be the red magnitude but is probably fairly close):

Caveat: I'm a radio astronomer! I'm not sure how much of the change in magnitude on these plots could be systematics in the magnitude determination, or whether we are seeing actual variability in the sources. I think I've gotten the right epochs. I'm not sure about that 2006 CMC values for the first plot, maybe it is an outlier since I think nova brightening happens on very short timescales (hours, days), not over years. Still, interesting!

Looking forward to seeing more developments. For now I will put my money on the inspiringly-named 1050-17497951 from the USNO catalogue as the source of Nova Delphinus 2013 :)

Update (17/08/2013)
Have a look at this way cool light curve generator for the nova, based on the contributed observations of people all over the world!

Keeping everyone excited, Nova Delphinus 2013 is continuing to climb in brightness and has now reached a magnitude of around +4.5. This is easy to see in a dark sky, and possible in a suburban sky if you know where to look. Maybe it will get even brighter over the weekend… so much for my predicted +5 peak!

Update (25/08/2013)
Nova Delphinus has come and gone, slowly fading away into dimness again (check the light curve). It will be bright in the sky for a while though! According to this telegram, the update (2013 08 14.826) states that the star has been identified as "the blue star USNO-B1.0 1107-0509795". Well, that happens to be the SAME star as the one I predicted (USNO-A2.0 1050-17497951), but from a newer catalogue… yeah. I still was right. I probably should have realised that B1 was newer than A2, haha, but there you go.

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