Friday, 12 November 2010

2010-11-05: A night of Planetary Nebulae

As mentioned in the previous post, last Friday Miguel Sánchez and me expent few hours at SATAN Hill in ESAC to test few imaging and tracking topics of our equipment. The observing conditions, on spite of the New Moon, were pretty bad but still allowed to do some imaging tests. In particular, Miguel wanted to test the "Polar Align" option of the CG5 mount of his 15 cm Newtonian and I tried to do a manual Polar aligment refinement using as a reference the AR of an equatorial star to improve the orientation of the equatorial fork mount of my SCT C8. As the night conditions were not good enough to image low surface brightness objects like galaxies we selected as targets two planetary nebulae.

The following image shows the M27 Dumbbell Nebula. It was captured with the Miguel equipment and the Meade DSI CCD with 2 minutes of exposure without any additional guiding. The shape of the stars is very circular showing the good polar aligment achieved with the CG5 Mount. The image was obtained by means of only a histogram stretching using SAO Image SW. The central star can be identified without any doubt.

The Dumbbell Nebula (M27)

The next image shows the M57 Ring Nebula. It was captured with my telescope and a Canon 400D camera in the prime focus with ISO 1600. The picture was produced stacking four images of M57 with 2 minutes of exposure and stretching the histogram with AstroArt SW. As the shape of the stars is not circular, it means that something was wrong with the station of the telescope Maybe because it was very fast due to that the SMOS pass was comming.

The Ring Nebula (M57)

I cannot resist the oportunity show an image never posted here of M57 produced four years ago (2006-07-13) with the Leo's telescope (a 60 cm Dobsonian) and the Meade DSI CCD. The picture was produced stacking 24 images of 1 second of exposure. The result as you see is quite impressive. The central star of the planetary nebula is clearly visible.

The Ring Nebula (M57)

Wednesday, 10 November 2010

2010-11-05: SMOS track

Last Friday, Miguel and me were at ESAC to perform some imaging& tracking test with our equipment in a new edition of the Friday's experiment "program". Between the targets that we selected, we tried to image the track of SMOS. Predictions can be done easily by everybody using the heavens-above website to forecast the passes of LEO satellites. Thus we detected pass over Valencia suitable to capture an image of the track: satellite-to-ESAC range around 1000 km and eastern pass, i.e. illuminated over dark sky. Finally, we tried and the following image was captured by us using a 500 mm. SCT Vivitar Telelens and a Canon 400D Rebel at ISO 1600 and 30 seconds of exposure.

I have been working with the image to try to estimate the SMOS intrinsic magnitude (not reported yet). It can be very useful for SSA and other operational events, specially in the case when a satellite must be localized to have an independent orbit assessment (e.g. a satellite radio black out... like in the case of XMM recovery. But, I must recognize that the capture was not a well planned experiment. As at that moment I was not sure about the effective field of view of the telelens, the imaged area didn't covered enough good stars to localize easily reference star brightness. In this case, it is very difficult... even with the Mount Palomar Survey plates... ;) ... Apart from the field distortions introduced by the SCT Telelens (no field correction, vigneting, etc), the main difficult was that not all the star-like features are real stars... With the fast changes of arrangement... I forgot to take some flats and darks and now I cannot discriminate these features... sometimes they can be well identified with the colour but in this case the image was taken in gray! In consequence and resuming, I'm afraid that by now I can forget to use these images to derive the intrinsic SMOS magnitude. However, some lessons can be learned from this experience for the next trials that for sure, we will perform very soon...

To avoid tracking problems:
  • Select the equipment: field of view (FOV) is very important!
  • The equipment must be stationed carefully... not in 15 minutes!
  • Analyse and Plan carefully the areas crossed by the track to be able to change from one area to another. In this case, I tried first with a well prepared area close to Cassiopea but the capture failed due to a FOV problem (not well known for the used SCT Telelens). After the fail I moved very fast to Pegasus without enough time to assure the pass and identify the area. Fortunatelly, it was catched up!
To reference the images: The FOV should be wide enough to capture bright starts easy to identify in the catalogues: preferably tracing constellation stars.

To correct the images: some darks and flats must be taken just after or/and before the imaging.