After several months of bad weather, the Sun finally made its return on the morning of the 22nd, and the seeing was not bad
It was an opportunity to compare the G-band Altair filter which was just released (430.3 nm FWHM = 2 nm) to the Antlia 393-3 nm which was released last year. These two filters show the photosphere.
First Antlia 393-3 nm (which is not a Ca K contrary to what Antlia claims) :
http://astrosurf.com/viladrich/astro/so ... 93-3nm.jpg
The new G-band Altair :
http://astrosurf.com/viladrich/astro/so ... 30-2nm.jpg
To see the differences, you have to put the images side by side:
- if we look at the full disk, the Antlia brings some more contrast: the facular areas are a little brighter, and they are detectable closer to the center of the solar disk. That being said, the difference is still quite subtle,
- if we zoom to 100%, we can see the Antlia is more affected by turbulence. Sharp areas are small patches separated by blurry areas, whereas with G-band the resolution is fairly uniform. On the other hand, on the sharp areas, the granulation is a little more resolved with the Antlia.
As the seeing conditions were good, I tested the effect of increasingly narrower bandpass in Ca K
- Alluxa Ca K 0.37 nm:
http://astrosurf.com/viladrich/astro/so ... K037nm.jpg
- Barr Ca K 0.24 nn :
http://astrosurf.com/viladrich/astro/so ... r026nm.jpg
- Alluxa Ca K 0.14 nm:
http://astrosurf.com/viladrich/astro/so ... luxa1A.jpg
- double stack Alluxa 0.37 nm + 0.14 nm:
http://astrosurf.com/viladrich/astro/so ... 7nm-1A.jpg
Again, you have to put the images side by side to see the differences:
- the Alluxa 0.37 nm obviously shows the (lower) chromosphere unlike the Antlia 393-3 nm which only shows the photosphere. It is clear that the facular areas of the photospheres match the bright plages visible in Ca K,
- the Barr 0.24 nm gives an image very close to that of the Alluxa 0.37 nm. In fact, some small differences are visibles if we zoom in at 100% and observe the edge of the solar disk. The difference is more evident in high resolution,
- the difference between the Alluxa 0.37 nm and the Alluxa 0.14 nm is a little greater. The plages are a little more contrasted (especially towards the center of the solar disk), and the borders of the plages seem a little more blurred. This is because they are located at a greater height in the chromosphere.
- the double stack 0.37 nm + 0.14 nm combination brings a significant increase in contrast. The disk becomes darker and the plages brighter This is not the level of contrast achieved with a SHG (e.g. Sol'Ex), but it is a bit like this. As we sample a greater height of the chromosphere, the sunspots take on a different appearance. Here too, the difference is greater than when observed with a longerfocal length.
And finally, some Ca K double stack images of the different groups visble. The conditions had unfortunately deteriorated a little:
http://astrosurf.com/viladrich/astro/so ... -014nm.jpg
http://astrosurf.com/viladrich/astro/so ... -014nm.jpg
http://astrosurf.com/viladrich/astro/so ... -014nm.jpg
Then, the weather turned bad again ...
Christian
