IC4901 supernova discovered by Greg Bock

[kinetic (Steve)]

Originally Posted by gregbradley

Good one Steve.

I managed a short image last night before clouds spoiled the party and it still seems about the same brightness.

Greg.

I finally got a decent night of seeing tonight Greg.
I'm pretty happy with this one.
The seeing allowed me to upsample, process, apply a bit more sharpening
and then downscale 0.75x to a good viewing size.
Seeing is king at this FL
Apologies for the moon gradient and dust bunnies though

Steve

[gregbradley]

Good one Steve.
Its still amazingly bright. It must be close to the brightness of the entire galaxy. What a phenomenol concept. I suppose we are looking at a massive star that is throwing up in months what normal stars would over huge periods of time.

Greg.

[DavidTrap (David)]

I managed to setup the scope last night (actually first light for my VC200L) and did some imaging on the SN in IC4901.

Here are my offerings - a stack of 5 x 10min subs through an 8 inch scope beside a quarter moon looking south towards Brisbane. I have run a DBE on these in PixInsight which revealed just how many dust bunnies I have on my CCD - look closely at the thumbnail of the inverted image below . My next post will be to Exfso about a light box!

The reference star that Terry indicated in a previous post had blown out completely in these 10min images, however, I had a one 5 min sub taken at Bin 1 in which that star was ~90% saturated. While this is pushing the friendship of linearity with an ABG chip, I followed a tutorial for Maxim DL Photometry and calculated a magnitude of the SN at ~15.2. (This was taken through a luminance filter) I'd be interested to know how this compares to measurements taken by those who actually know what they're doing!

As for the VC200L - very impressed with the field flatness - the results from CCD inspector were <10% curvature and this was with collimation done on the bench only as I didn't have time to fiddle with a star test. This yields a small round star without elongation visible in the OAG prism of the QSI. I am sure this helps the guide software track an accurate centroid. The guiding graph was almost flat.

Cheers
DT

[Terry B]

Dear all
I took a few images of this last night after the clouds had disappeared also using a VC200L
I took images of 120 sec binned 2x2 with my ST10XME through BVRI filters.
Using the loneos star I mentioned before as the comp star I measured mags of
B= 14.8
V= 14.54 (error range 0.045)
R= 14.21
I= 13.92
The attached image is of 3 x V images averaged.
All of these mags include the flux of the galaxy in the measurement annulus of the star. To make a more accurate estimate I would need to subtract an image of just the galaxy without the SN but this would have to wait until the SN is gone as I don't have an image of the galaxy without the SN.

[Greg Bock (Greg Bock)]

Hi guys
its great to see some images coming back now, wish I had the honour too, but the only clear night when I had any chance without clouds was last night, but the wind blew everything around and the seeing was terrible...
When will we get a break here in SE Qld ( or SE Cloudland)??

[gregbradley]

Just think of all the supernovas you may have missed over the years due to clouds. By the time you imaged them they may have faded!

Greg

[DavidTrap (David)]

Thanks for posting the numbers Terry - I'm happy to be at least in the ball-park. I was experiencing the same problem with the annulus of the aperture overlapping the galaxy - was wondering what you did about that This photometry stuff seems quite clever - something to fiddle with in due course.

DT

[Terry B]

Originally Posted by DavidTrap

Thanks for posting the numbers Terry - I'm happy to be at least in the ball-park. I was experiencing the same problem with the annulus of the aperture overlapping the galaxy - was wondering what you did about that This photometry stuff seems quite clever - something to fiddle with in due course.

DT

I used a 5 pixel (radius) central annulus with about 30 and 40 pixel outer annulus. (the actual numbers are a home). This isolated the rest of the galaxy. The comp star was Ok with the same settings.
These settings will vary depending on the sampling size ie arcsec/ pixel and the seeing on the night.

[DavidTrap (David)]

The FMHW of the comp star was ~4, so I set the aperture in Maxim to 8 (the tutorial I read said 1.5-2x the FMHW).

How valid is it to subtract a galaxy from a previous night - I would guess that variations in seeing could affect magnitude, or do you "scale" the amount of subtraction in some way using the known value of the comparison star?

DT