Long subs with trial datasets.

[ollypenrice]

This is the deepest dataset I've ever processed on M31 but it is by no means the longest in exposure time. It had just 3.5 hours plus 14 minutes for the core. The image above is just stretched and combined with the shorts. No other processing. Here's the detail;

Tak FSQ106N at F5 with Atik 11000 mono at -20C on Tak EM200 mount. Baader Luminance filter. 3.5 arcseconds per pixel unbinned.

Main subs 7x30 minutes. Core subs 7x2 minutes.

Calibration and stacking in AstroArt 5. Master bias used as a dark. Defect Map applied. (Made by clipping 2000 ADU off a 15 minute Master Dark.) Hot pixel filter applied for both singles and pixel groups and set to 50%. Flats (x30) were all through the green filter, exposed to peak at 13000 counts and calibrated by bias subtraction. The filters are clean so there is no point in taking separate ones and the use of the green puts them mid spectrum and eliminates the risk of IR reflection. ( https://www.sbig.com/about-us/blog/flat-fields-the-ugly-truth/ )

The value or otherwise of long subs like these at a dark site is much discussed, so rather than invite more theorising I simply invite you to download the stacks and have a play with them. I won't be changing from this approach since I feel it has given me a remarkable dataset extremely quickly and painlessly. The Kodak 11 meg chip is not famously quiet but I'd call this stack clean.

Please feel free to use the data and post images which use some or all of it, but a credit would be appreciated if you do so.

https://dl.dropboxusercontent.com/u/63721631/M31%207X1800%20L.tif

https://dl.dropboxusercontent.com/u/63721631/M31%207X1800%20L.tif

Cheers,

Olly

[narrowbandpaul]

Hi Olly.

Cracking image there. I'm pleased to see agreement between theory and experiment. I too am convinced that long is better.

Paul

[opticalpath]

Hi Olly.  Your Dropbox links are both to the same file.  I think we're missing the 2 min set.

Adrian

[Russe]

Love it - gonna download the data later to have a play!!

[ollypenrice]

Hi Olly.  Your Dropbox links are both to the same file.  I think we're missing the 2 min set.

Adrian

Apologies! The short subs stack is here. If the mods spot this they could put it in the OP, perhaps. These short subs were only caibrated with flats and by subtracting a bias with the hot pixel filter running. The data is so bright (and the faint stuff not destined to appear in the final image) that this was OK.

https://dl.dropboxusercontent.com/u/63721631/L%207X120.tif

I'll be interested to see if folks are persuaded by the long sub principle!

Olly

[opticalpath]

..... I'll be interested to see if folks are persuaded by the long sub principle!

The results are very convincing, Olly. Definitely looks like the way to go at a dark site.

 

Here in L-P land, it has to be more like 42 x 5m rather than 7 x 30m ,  but the fewer-longer principle should apply with ultra NB even here. 

 

Adrian

[Steve Ward]

Amazing result for such a short , by your standards , run ... 

Do you plan to go on a larger run of 30 minute subs to see how much further it can be pushed or am I just being greedy ... ?

[ollypenrice]

Amazing result for such a short , by your standards , run ... 

Do you plan to go on a larger run of 30 minute subs to see how much further it can be pushed or am I just being greedy ... ?

I suspect that this is about worked out, quite honestly. Given the lack of noise, and the fact that there was a fairly clean cutoff between background and halo, I think I'll leave it as is, at least at this resolution. Even if I found more halo I'm not sure that I'd know how to present it while respecting the fairly important idea that the core is brighter than the halo!

However, the TEC140 tells me that it is itching to add resolution to the main galaxy in a two panel mosaic...   It won't be just now though.

Olly