M51 in visible and near-IR

5th May 2006
Object name: M51 Whirlpool galaxy
Object type: Galaxy
Magnitude: 8.9
Size: 11.2 6.9
Position angle: 0
Classification: Sbc
Apparent RA: 13 29 52.6 Apparent Dec: +47 11 44
Constellation: Canes Venatici

I have recent aquired an Astronomik Planet IR Pro 807 filter from Modern Astronomy. These filters are designed to image planets in the IR, to negate the effects of seeing. I have got one to try and see what some of the brighter DSOs look like in the very near infra red. This filter blocks all visible light - it only starts transmitting around 800nm. The frequency response of the ICX285 ccd chip in my Artemis camera is around 30-40% at 800nm, and deceases as the wavelength increases. Therefore we do not have much light to go around. I was taking 6 minute exposures at 2x2 binning. Compare this with the visible light image, which was 3 minute frames at 1x1 binning, for a much better result.

On the left is the Near IR image of M51. On the right is a resized version of my visible light M51 from last month.

Compare with the 2 micron image of M51 (near infra-red 2MASS). One of the most striking features of M51 in my visible image are the dust lanes in the spiral arms. In the IR image, (allowing for the poor image quality) these lanes are much less distinct. Although the IR image appears more "blurry" - note that the stars in the IR image are still quite crisply defined.

This IR image was taken in poor conditions for such work, Half moon, and LOTS of misty moisture in the atmosphere. However, we are approaching mid May, and darkness is now a rare commodity are my latitude. This first experimental image shows that it is worth tryng this filter on other deep sky objects in more favourable conditions. Due to various factors, I have difficulty flattening the field, mainly because the signal is very small.

Captured in Artemis Capture. Calibrated, aligned and combined in Maxim. DDP applied.

This image was autoguided using my 400mm focal length refractor and my black and white SC1 webcam.

Current Imaging equipment configuration

Exposure Details :

Planet IR Pro 807 MPCC 16x360s on 200mm @ F5 with ART285

Curdridge Observatory, Southampton,UK