MPL 2860 Pasacenten

A preliminary light curve spanning 4 hours for Minor Planet 2860 Pasacenten. Determined from 81 frames obtained on 2003-11-01. Each 3 minute frame was binned 2x2. The camera was cooled to -20°C. The telescope used was the 254mm SCT in a f/12 configuration (focuser/AO-7/CFW-8/ST-7XE). No focal reducer was used to minimize vignetting. The image scale is 1.23 arc seconds per binned pixel.

As can be seen from the light curve, the rotational period of this minor planet is around 2.5 hours. I used GSC3674:761 (mag 14.1) and GSC3674:3 (mag 13.5) as K,C stars for the photometry.

I also determined from these Pasacenten frames that I can go until magnitude 18.5 in 3 minutes when binning 2x2 at F/12 from my San Jose patio, and possibly a bit deeper. By combining all 81 images (243 minutes = 4 hours), I determined that I can go until magnitude 20 in that period. Possibly even deeper if during the last hour the frames were not out of focus due to the dropping temperature.

Moon

A combination of 4 of the best images, automatically selected using CCDOps. Partially overexposed. Click on the image to see the full version.

2003-10-16:

The Bubble Nebula NGC 7635

My first true LRGB image.

2003-10-11:

Uranus, Umbriel, Oberon and Titania

The following image of Uranus and three of its moons was taken on the night of October 11, 2003 in front of my apartement in San Jose, CA. In this image, North is down, and East is left. Uranus has a computed magnitude of 5.75, and an apparent angular diameter of 3.62 arc seconds. Known stars of the GSC catalog are marked with their GSC magnitudes (decimal dot before last digit removed).

Using AIP4WIN (star aperture 4, inner sky annulus 6, outer sky annulus 10) and the magnitude 11.2 GSC 5805:40 star at the top left of the image (chosen because it is the faintest one mentioned in the Tycho catalog, and therefore assumed to have a more reliable magnitude: Vt=11.265), it was determined that the three moons had the following magnitude:

Object	Magnitude
Umbriel	-
Oberon	13.9
Titania	13.8

Umbriel is too close to Uranus in the image for an accurate magnitude determination. These values are close to the values calculated using the NASA Ephiremide generator:

Object	Magnitude
Umbriel	15.0
Oberon	14.2
Titania	14.0

The difference is caused by the fact that the image was obtained through a RGB red filter, while the comparisment star magnitude is a V magnitude. Another reason is that the difference in brightness between the moons and the comparisent star is almost 3 magnitudes, which reduces the accuracy.

2003-10-10: 8 minute exposure (50x10s). Camera cooled to -20°C.

Using the known positions of the GSC stars, it was determined that the center of the image is located at 22h 06m 18.67s -12d 29m 56.55s. Similary, the locations of Uranus and its moons were determined as:

Object	RA             Dec
Uranus	22h 06m 17.00s -12d 29m 39.79s
Umbriel	22h 06m 16.79s -12d 28m 20.68s*
Oberon	22h 06m 17.10s -12d 29m 06.70s
Titania	22h 06m 16.24s -12d 29m 19.85s

*The position of Umbriel is only an approximation, as it could not be determined accurately.
The apparent angular distance between the objects in arc seconds and their position angle is:

Object   Uranus     Umbriel Oberon    Titania
Uranus   -          ?       33.1 2.6  22.9 330.8
Umbriel  ?          -       ?         ?
Oberon   33.1 357.4 ?       -         18.2 316.1
Titania  22.9 29.2  ?       18.2 43.9 -

Miranda & Ariel are too close to Uranus (8 arc seconds from center) and could not be imaged. The star left under of Uranus can be found in the USNO-SA2.0 database as a mag 15.3 star. The object right of Uranus doesn't exist in this database (in other words, I do not know yet what it is).

Galaxy NGC 891

A clear improvement of my first attempt, 9 months earlier on my third imaging session.

2003-10-10: 15 minute exposure (3x300s). Camera cooled to -20°C.

Planetary Nebula NGC 246

This planetary nebula was discovered in 1785 by William Herschel. It is of relatively low surface brightness. As can be seen in this image, the central star of this nebula is actually two stars close in angular separation. The central star is of magnitude 11.9. Its companion at 3.8 arcseconds distance is of magnitude 14.

The planetary nebula has an apparent diameter of 4 arcminutes. Compare this to the moon, which has an apparent diameter of 30 arcminutes. Several stars are superimposed on this nebula.

2003-10-10: 30 minute exposure through a red, green and blue filter each (3x3x600s). Camera cooled to -20°C.

Galaxy M77 (NGC 1068)

M77 is a magnitude 9.6 (8.9?), type Sb spiral galaxy in the constellation Cetus. It is over 170,000 light years across (bright part measuring about 120,000 light years,) and over 49 million light years away (60000 (kly)?).

It is the nearest and brightest example of a type II Seyfert galaxy, showing broad and strong emission lines due to high velocity gas in the galaxy's inner regions. A strong radio source (probably a supermassive blackhole) known as Cetus A sits in the nucleus.

The foreground star to the left of M77 is the magnitude 10.81 HIP 12668, on a distance of 982.40 light years and spectral type G0. Using this image, I determined the angular separation between this star and the galaxy core is 88.1 arcseconds (PA 295°).

2003-10-10: 30 minute exposure through a red, green and blue filter each (3x3x600s). Camera cooled to -20°C.

Galaxy M31

Last night I did my first attempts to color imaging with my ST-7XE. This LRGB image depicts the central region of M31. The dust is clearly visible, but the coma in the source images made it impossible for me to properly line up the individual images.

2003-10-10: Camera cooled to -20°C.

Mars Revisited

2003-08-26:

AO-7 Wiggle

TODO

Setting up for CCD imaging

1. Setup the tripod, attach the wedge and roughly level it.
   
2. Table south of telescope
   
3. Attach te telescope. Make sure the locks are disengaged. The OTA is kept in place by a piece of velcro that's wrapped around it.
   
4. Attach the finder, microfocuser, diagonal and 19mm eyepiece.
   
5. Attach all the cables to the camera, telescope and laptop. I always put the bulky camera power supply on the wedge.
   
6. Level the combination more accurately (using the wedge level).
   
7. Attach the dew shield and camera. Dynamically balance the telescope, disengaging the locks whenever necessary.
   
8. If necessary, cover the telescope and let it cool down for one hour.
   
9. Turn on the laptop, camera and telescope, in that order.
   
10. Make sure Autostar is set to Polar mode. I have told Autostar to do a GPS sync on startup.
    
11. Point the telescope to a bright star, align the finder and focus.
    
12. If necessary, remote the dew shield, collimate the telescope using the camera and attach the dew shield.
    
13. Usually, the camera equipment will not fit through the forks, so the Autostar polar alignment functions cannot be used. But, as an Autostar SYNC resets both the RA and DEC values to the ones of the currently selected object, a SYNC is all that needs to be done when the telescope is properly aligned. Not using any Autostar alignment function, move the telescope to a known star and do an Autostar sync.
    
14. Using the camera, do an accurate alignment.
    
15. Do the Autostar sync afterwards.
    
16. When I turn off the equipment, I first turn off the telescope.
    
17. Determine the seeing condition by taking a well focused 0.01s exposure of a bright star and determine its FWHM.
    
18. If possible, I modify the setup such that the FWHM on this short exposure is between 2 and 2.5 pixels. I find a larger (e.g. 3 pixels) FWHM visually much less pleasing, and smaller would result in undersampling. As the typical rms stellar wander is about half of the FWHM, I reduce the system further to a FWHM of at most 2 pixels when I am not using the AO-7.
    

Techniques

1. Do a PEC before each long exposure, overwriting previous one. This will compensate RA drift caused by imperfect polar alignment. Also gives most accurate PEC I believe.
   
2. Disable X/Y corrections of drive while autoguiding. All corrections should be done by AO-7 only. With proper alignment and PEC, this should be all that's necessary.
   

Mars

2003-07-13: 12 second exposure (300x1/25s) using ToUCam Pro webcam at f/20.

Uranus

2003-07-13: 4 second exposure (100x1/25s) using ToUCam Pro webcam at f/20.

Globular Cluster NGC 6229

2003-05-11: 50 minute exposure (5x600s). Camera cooled to -20°C. Image scale 1.03 arc secs/pixel.

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.

Spiral Galaxy M51 (NGC 5194)

2003-02-03: 25 minute exposure (5x300s). Camera cooled to -25°C.

Planetary Nebula M97

2003-02-03: 15 minute exposure (3x300s). Camera cooled to -25°C.

Spiral Galaxy M108 (NGC 3556) Revisited

This image was taken just two days after the previous one. The effects of much improved tracking and a longer exposure (40 minutes instead of 10) are clearly visible. Notice the difference in details of the dust in the galaxy.

2003-02-03: 40 minute exposure (4x600s). Camera cooled to -25°C.

Spiral Galaxy M108 (NGC 3556)

I am obviously having trouble with tracking.

2003-02-01: 10 minute exposure (5x120s). Camera cooled to -25°C.

SAO 24929 (7 Camelopardalis)

While I was looking for galaxy UGC3217 on the 2003-01-25 imaging session (which I didn't find), I took this overexposed image of SAO 24929. Nothing interesting to see here, but the only result of that session.

Galaxy NGC3631

Another binning test.

2003-01-18: 4 minute 2x2 binned exposure (4x60s). Camera cooled to -29°C.

Galaxy NGC 891

On my third imaging session I have been experimenting with binning. This image was made with 2x2 binning. Because the ST-7XE main CCD doesn't have many pixels to begin with, then resulting image is rather small. However, the sensitivity for each pixel is increased fourfold, and the well depth twofold. For LRGB imaging and photometry this will certainly have its uses. In this case, with normal binning I would only have reached the depth of this image after 42 minutes, instead of the 10.5 minutes used here.

2003-01-18: 630s 2x2 binned exposure (21x30s). Camera cooled to -30°C.

Mirach (β Andromeda)

I found this overexposed image of Mirach between my images of the 2003-01-18 imaging session. Nothing interesting to see here, except for the faint star at 11h relative to and close by Mirach, which is the magnitude 14.2 GSC 2286:693. After all, this is only a one second exposure.

Galaxy M63

2003-01-18: 150s exposure (5x30s). Camera cooled to -30°C.

Globular Cluster M3 (NGC5272)

2003-01-18: 150s exposure (15x10s). Camera cooled to -30°C.

Galaxy M81

While experimenting with automatic tracking and stacking, I took this image of galaxy M81. The polar alignment of the telescope was poor, hence the common part of all sub-images was relatively small. So I ended up with a galaxy not even fitting in the final image.

Anyway, the spiral arms and dust in this galaxy are obvious.

30x30s exposures combined (total 15 minutes). Camera cooled to -25°C.

Planetary Nebula M76 (NGC 650) in Perseus

For the second imaging night with the ST-7XE, I mounted the telescope in Polar Mode. This is the first time I used the tracking CCD of the camera for automatic guiding of the telescope and I experimented with automatic tracking and stacking. The striping in this final image is the result of poor polar alignment and the sub-exposures being too short.

In this image of M76, commonly known as the Little Dumbbell Nebula, the bright expanding elliptical ring seen almost edge-on is quite obvious. The dim "wings" along the axis perpendicular to this ring are visible as well, although barely in this image. Both of these structures are expanding.

20x15s exposures combined (total 5 minutes). Camera cooled to -25°C.

Galaxy M82

That same night I pointed the telescope towards the irregular Galaxy M82 (NGC 3034), in Ursa Major (Big Dipper). Its visual brightness is magnitude 8.4 and apparent dimension 11.2' x 4.3' (Uranometria 2000 2nd ed.).

For this object I enabled the telescope tracking and used a focal reducer. With the ALT-AZ mounted telescope, the longest exposure I can take in this area of the sky at this focal length (about f/6.9), without the effects of field rotation causing the stars to streak too much, is about 30 seconds. This single unguided 60 second automatically dark subtracted image is the best result of this night. The camera was cooled to -25°C.

The amorphous galaxy M82 contains a starbursting nucleus. Images in the light of ionized Hydrogen and Sulfur show vast filaments of ionized gas streaming away from the galaxy. In the image below, this ionized gas is not visible, but dark dust lanes and patches in the central part of M82 are. The central dark dust lane can be observed visually as well with the same telescope. The stars in this image are all part of our own galaxy. Their distances are up to a few hundred light years. M82 itself lies far beyond the borders of our galaxy, at a distance of about 12 million light years.

One minute exposure. Camera cooled to -25°C.

Polaris (North Star)

This is the first image of an astronomical object I ever took with my ST-7XE camera. Last night, I mounted the telescope in ALT-AZ mode, attached the camera, pointed the telescope to Polaris, roughly focused it, and shot this 10 second exposed image. The camera was cooled to -10°C.

As this was just a simple camera check, even the telescope tracking was completely turned off.
Polaris itself is completely overexposed in this image, and the raw image contains blooming streaks above and below the star, proving that this camera indeed has a NABG sensor. You see, Astronomics initially sent me an ABG version, which I returned immediately after discovering this using a pin-hole test.

I manually cleaned the blooming streaks (some artifacts are still visible), and used non-linear histogram stretching to improve the visibility of the companion.

Polaris is a binary star at a distance of 431 light years, consisting of a bright magnitude 2 supergiant and a much dimmer magnitude 9 main sequence star, separated by about 18 arcsecs. Even though this 7 magnitude difference makes it a bit harder, I found on 2005-03-25 that I could easily resolve the binary with my 80mm refractor at a magnification of 31x.

From the original (bloomed) image, I determined that the apparent distance between the two components is 26.7 pixels. Attaching the camera directly to the focuser therefore results in a system with a focal ratio close to f/11.

The same night, I also took my first image of galaxy M82.