Planetary Nebula NGC 6210 (PLN 43+37.1)

This planetary nebula in Hercules is claimed to have a distance of about 6500 light years. Its central star has designation HD 151121, and according to the Tycho catalog, its distance is 136.7 light years, which doesn't add up.

A SIMBAD search reveals the central star is of type O7, the radial velocity is -35.6 Km/s (moving away from our solar system) and the parallax is an unreliable -4.0±11.00 mas (!), which corresponds to 250pc, or 815 light years.

2003-03-06: 1 minute exposure (1x60s). Camera cooled to -20°C.

Planetary Nebula NGC 6058

2003-03-06: 3 minute exposure (3x60s). Camera cooled to -20°C.

Seyfert's Sextet (NGC 6027)

Flat field subtracted using a flat that was constructed from all the session's images as described here.

2003-03-06: 3 minute exposure (3x60s). Camera cooled to -20°C.

Galaxy NGC 5474

Obviously in need for a much longer exposure.

2003-03-06: 1 minute exposure (1x60s). Camera cooled to -20°C.

Galaxy M101

2003-03-06: 4 minute exposure (4x60s). Camera cooled to -20°C.

Globular Cluster M92

2003-03-06: 1 minute exposure (1x60s). Camera cooled to -20°C.

Planetary Nebula M57

The famous Ring Nebula, imaged using the horribly bad .33 focal reducer. I had to reduce the size of the image just to cover up the extended coma. The field of view with this focal reducer is great, but because the vignetting and coma is so severe, if not resizing it I would have to crop the image so extensively that I could as well just use the .63 focal reducer!

2003-03-06: 3 minute exposure (3x60s). Camera cooled to -20°C.

Spiral Galaxy M51 (NGC 5194) Revisited

A second attempt of this galaxy, this time using the .33 focal reducer. Only a two minute exposure (the previous one was 25 minutes), but the increased field of view is rather nice. The low quality of the reducer spoils it though (notice the strong coma at the bottom half of this image).

2003-03-06: 2 minute exposure (2x60s). Camera cooled to -20°C.

Globular Cluster M13

Coma is noticeable at the bottom left of the image.

2003-03-06: 2 minute exposure (2x60s). Camera cooled to -20°C.

Galaxies MCG +9-23-50, +9-23-51, +9-23-52, +9-23-56 and CGCG 272-40, 272-42 in Ursa Major

2003-03-06: 3 minute exposure (3x60s). Camera cooled to -20°C.

Creating a flat field from light exposures

On the 2003-03-06 imaging session, I used my newly obtained FR/0.33 focal reducer for the first time. The images obtained using it show severe vignetting. For example, the following image is of Seyfert's Sextet (50% of original size):

At the lower left, the average ADU is 24% less than in the center of the image. Also, the vignetting is off-center.

By combining 49 images from different fields that night, all with the same camera orientation, and applying a dust and scratches filter with radius 30 and blurring with radius 30, the result is:

Applying this flat field to the above image, the image now looks like this:



Here the black and white points remained the same. There is still some residu of the vignetting, but it is not very severe.
The difference of the average ADU is now much smaller. There is now only a difference of 1.4% between the center and the border. I don't know why this central area is overcorrected by this amount. It is not a replacement for a real flat field of course, as the noise is much higher (not half full-well limit).

I returned this focal reducer, because the 24% vignetting is unacceptable. In addition it also created severe coma. Not only in the corners of the main CCD, but especially in the tracking CCD all stars had a V shape. The replacement only exhibits a 7% vignetting and much less coma.

Minor Planet (1951) Lick

On March 7, 2003 I took 14 successive 60 second images of an area the size of about one quarter of the full moon in Hercules, near the borders of Draco and Bootes. Each image was taken with a delay of 60 seconds, except for the second image, which was taken after a delay of about 4 minutes. The movie below depicts this sequence, in reality lasting a little more than 30 minutes, accelerated 480 times.

Look closely, and you'll find asteroid (1951) Lick moving in front of the background stars. This asteroid was discovered on July 26, 1949, by Carl A. Wirtanen (Lick Observatory, CA, USA, I guess that's why it was named Lick). He also discovered comet 46P/Wirtanen, that originally would be visited by the European Rosetta spacecraft, before it was delayed and a different target was chosen. Unlike many other asteroids, it does not move around the Sun in an orbit that lies between those of planets Mars and Jupiter, but one that is a little closer to the Sun and one that does not lie in the ecliptic plane, but is inclined 39° [1]. It has an eccentricity of 0.0615. The distance of Mars to the Sun is about 1.52 AU (228 million kilometers), whereas that of the asteroid is up to 1.39 AU (209 million kilometers) [1]. Because the Earth moves around the Sun too (at a distance of 1 AU, or 150 million kilometers), the distance between the asteroid and Earth varies a lot, and at the time of these images, it was about 0.74 AU (111 million kilometers). The positions of the planets and the asteroid at the time of imaging, is depicted in the following graph. The planets and asteroid (the square) move clockwise in this orientation.

The bright star in the images is the V magnitude 8.5 HIP 78421, which has a distance of 492.68 light-years (4661 trillion kilometers) [2]. The star below the center of the image is magnitude 14.43 GSC 3497:1453. Using the latter star for unfiltered differential photometry, I determined that the magnitude of the asteroid was about 16.4 at the time. I estimate the accuracy of this to be only about 0.5 magnitude, as a result of a combination of severe vignetting (this was before I exchanged the poor focal reducer), and field rotation (ALT-AZ mount). Nonetheless the measured magnitude matches the computed magnitude 16.5 well.

This inaccuracy did also not allow me to determine a light curve for the asteroid. It is known to have a rotational period of 5.3016 hours [3;4;5;6] (secure result with no ambiguity, full lightcurve coverage), and a V magnitude variation of 0.17-0.27. Using GSC 3497:1453 (mag 14.43) and GSC 3497:1319 (mag 14.09) as C and K stars, I found the variation of C-K to be of the order of 0.4 magnitude, which is larger than the expected variation of the asteroid. Of course, half an hour of imaging would be too short for confirming this rotational period anyway.

The asteroid moved 57.02 arcseconds between the first and last image, which corresponds to an apparent speed of 0.0313 arcsecs/sec (taking half exposure as the time of an image, the first and last image were 1824 seconds apart). This is slightly less than the computed 0.0382 arcsecs/sec (computed RA rate of 0.0294 and dec rate of 0.0244). This difference is likely caused by the small change in image scale during imaging (clearly visible in the above movie).

Using my measured value of 0.0313 arcsecs/sec, and the computed distance of 111 million kilometers, this means the asteroid was moving at a speed of at least 16.8 Km/sec relative to the Earth.

The parallactic angle (angle between the top of the image and true North) of the aligned images is 273.43°. Combined with the positional differences between the first and last images, I found the angle of the asteroid move to be 329.67°.

The last image is an averaged combination of all 14 images. It shows fainter stars, up to about magnitude 17.5, and a trail for the asteroid (in case you still didn't find it). The uneven background is a result of vignetting and processing.

2003-03-06: 14 minute exposure (14x60s). Camera cooled to -20°C.

Bibliography

[1] Minor Planet Center Orbit Database (MPCORB); 2003.
[2] Hipparcos Catalog.
[3] IAU Minor Planet lightcurve parameters list; 2003-12-15.
[4] Velichko, F.P., Krugly, Yu.N., Lupishko, D.F., Mohamed, R.A.; 1989, Astron. Tsirk. 1546, 39-40.
[5] Wisniewski, W.Z., Michalowski, T.M., Harris, A.W., McMillan, R. S.; 1997, Icarus 126, 395-449; 1995, Lunar & Planetary Science XXVI, 1511-1512.
[6] Pravec, P., Wolf, M., Sarounova, L.: 2003, posted on WWW; http://sunkl.asu.cas.cz/~ppravec/neo.htm.