Astroart Forum

Hi,

The other night I caught 10 lights each of 30 seconds of IRAS 19597+2258 in order to measure it's V mag.

I have tried the following in AstroArt:

1) Open a single RAW: IMG_0042.CR2 (http://b-rasmussen.dk/astro/2016/0824/IMG_0042.CR2)
2) Press "Find coordinates" button in order to platesolve, write M27 to guide AstroArt in the right direction.
3) Open "Star Atlas" in AstroArt.
4) Press Find button, again, write M27.
5) Press "Astrometry - reference start: Automatic".

...and voila!, when I open the "Stars", after having added IRAS 19597+2258 (ra=20 01 52,07 dec=+23 07 04.6), see that the IRAS 19597+2258 has a V mag og 10.399.

To improve accuracy I have used DeepSkyStacker to stack the 10 raws and made a FITS file from the result in AstroArt:
http://b-rasmussen.dk/astro/2016/0824/stacked.fit

However, if I try the same procedure as above on the fits file, AstroArt star atlas says: No Match!!!

I have also tried stacking the images in AstroArt with the same result, No Match.

I've noticed that AstroArt only finds stars in the left half of the image...

PS: focus is not perfect in the images, could that cause the problems?

Can anyone give hints? Do You need more information? FOV, FWHM, etc settings?

Hope someone can assist, cause this is a little frustrating since the Photometry function in one of the main motivations to why I purchased AstroArt.

PS: I have only used AstroArt a few times under the stars, but I am already extremely pleased with it's camera control and plate solve capabilities. I have written a script so that I can take an image,plate solve and then sync the telescope - thus homing in on a target very precisely!

Hi,
the severe asymmetric coma/focus could be the cause, but I see that you can solve using the UCAC4 catalog, instead of the default GSC, (which cannot be used for good photometry anyway).
FindCoordinate uses a pattern database while "Photometry/Astrometric automatic stars" uses the catalog that is currently opened in the Star Atlas, so they may not give the same result if the image is critical.

In any case, please check if the "interpolation photometry" is what you really need (see the Manual about it), usually it's better to use aperture photometry and work in ADU, and, with DSLRs, photometry is usually made on a single channel.
Clear skies,
Fabio.

Hi Fabio,

Thanks for the reply. And sorry for my late reply.

I found another way to do accurate photometry by using only the green channel, something like this:

My setup gives a FOV of approximately 2° by 1°3.
The magnitude of the variable is asumed to be in the range 13-15, therefore AAVSO Chart X16665FD is chosen.

1) Open the DeepSkyStacker TIFF file with AstroArt.
2) Split into RGB.
3) Close R and B, use G.
4) Platesolve and rotate to bring north approximately up, then it is easier to locate stars moving mouse cursor arround.
5) Lokalize IRAS 19597+2258, ref#137 and ref#139 and add them to the Stars window by clicking them - in the given order.
6) Select Tools->Photometry.
7) Press the small camera icon (Instrumental magnitude).
8) Press [OK] in the Photometry window.
9) Click in the cell for ref#137, the cell should now show REF.
10) Select the row with ref#137, rightclick and choose edit.
11) Type 13.725 in the bottom of the ADU, Magnitude, and press [OK].
12) Choose Tools->Photometry again and press [OK].

Now the magnitude is calculated for the variable IRAS 19597+2258 and for the reference star ref#139.

20160906 22:30
IRAS 14,387
137 13,725*
139 14,021 (13,907) fejl ca 0,8%

20160906 21:30
IRAS 14,058
137 13,725*
139 13,865 (13,907) fejl ca -0,3%

20160925 20:50
IRAS 13,982
137 13,725*
139 13,904 (13,907) fejl ca 0,0%

So, I am only using one star as reference and one star to check.

The above method was carried out on a DeepSkyStacker TIFF and not the raw canon file mentioned above.

/Rudi

Thank you for the interesting tutorial.
In the next Service Pack 2 there will be a command to that more quickly.
Meanwhile, the Service Pack 1 contains a partial support for quick one-star photometry:

1) Open the image and click the reference star.
2) Open the Stars Window and click Edit from the context menu: write the magnitude of the star and click OK.
3) In the Stars Window click the "P" field to make the star a REF (photometric reference).
4) Click Tool/Photometry : it's now possible to calibrate the image using just that star.

Great Fabio, looking forward to seeing that