2008-04-10

The Fan on Leo I Revealed

The unidentified fan on bottom edge of the image of Leo I has really simple explanation! Rays are diffraction patterns of Regulus lying twenty arc minutes bellow Leo I. The connection has been revealed by readers of IAN.cz. Thank you very much! It is a very good example how Internet can help expand of a knowledge. I have no explanation how I had ignored this fact. I inspected the position of Leo I with Xephem and I miss the critical proximity and I had in mind that the Leo I falls to the head of Leo. So don't forget look under legs when you are watching of the sky...

When I play with raw images, I inspect ones by an animation. The animation (warning 36M!) shows "a shut of the fan" near of its end so I gather from the investigation that the light pollution is due of a Earth's source. The animation shows a relative motion of the telescope (corrected by pointing), an airplane, cosmic-ray event and inner lights of our dome.


A last step to full explanation of the secret has been done by exebece. It take note that all stars are fainter at the end of the observation run. The instrumental magnitudes of the star UCAC2 36118678 shows rapid fall of its light fluxes. An explanation of the fainting is direct. The aperture of the telescope, controlled by the siderical motion, has been occult by our dome. A creativity of all possible mistakes by me is unbelievable...;)

2008-04-06

The Zodiacal Light

A mysterious zodiacal light can be sight at the season of the spring equinox. The weather and the sky prepared for us an absolutely excellent spectacle during last weekend and we was able to view the zodiacal light for the first time!

We made three journeys to Rojetin's airport. At first evening, we did sight some lights above west's horizont, but we did understand that we did sight the zodiacal light after that it disappeared. Also, we made some photos but with ISO 600 only so all images are underexposed and noisily. Our second journey was the most successful. Horrible clouds has dissolved and we sight clearly the zodiacal light with help of our fresh experience. Our last journey started really optimistically because the sky has no clouds for whole day. Unfortunately, an atmospheric front moved to west's horizont and it did scatter a light over the zodiacal light. We did not sight anything.

The first image shows the zodiacal light during our second journey. The zodiacal light is a white difuse part of sky below Pleyades (rightly). A head of Taurus is at center of the image, Orion is on the left. Do you know where a white dwarf can be found? The image was acquired at 2008-03-30, 18:05 UT, EOS 30D, f/2.8 fish-eye, ISO 1600, 32 sec and processed by Ufraw+dcraw (histogram equalisation, wavelet denoising) and Gimp (unsharp, resize). The camera configuration and processing is common to all related images (larger).
Next two images recorded a passage of the ISS and Jules Verne spacecrafts during evening of 2008-03-31, 17:39 UT (the same camera configuration). I prepared two versions of the image in a large format (I believe) useful for wallpapers.

I dedicated, inspired by Paulie, the 31's evening to made a sequence of horizont-centered exposures. Unfortunately, clouds has been brighter than the zodiacal light.

Thx to all peoples of my team: Janis, Petoš, Barča, Ushas, Maceška, Jarda, Janapka, Kočka, Fantom, Ondratik and Paulie.

2008-04-04

Color transformation

This record is just for future references.

Some time ago, I got profiles of transmissivity of our new set of photometric UBRVI filters (thx to K.Navrátil). The filters are offered as a part of the official SBIG's accessories. Profiles of trasmissivity of the filter set and Landolt's (Astron. J. 104, 340 (1992)) filter set is displayed on the image:(in PDF). All filter profiles together with various useful files are included in archive newfilters.tar.gz.

A knowledge of the profiles enable us to create a transformation between our and Landolt's filters set. The transformation is constructed only on base of the filter's transmissivity. That means that another one made as a product of a real measurement will perhaps different due to any different spectral sensitivities of others parts of our optical equipment (mainly telescope, detector and atmosphere). We are use the transformation between our set {|u>,|b>,|v>,|r>,|i>} and Landolt's {|U>,|B>,|V>,|R>,|I>} as the matrix equation

|u> = U><U|u> + |B><B|u> + |V> <V|u> + |R><R|u> + |I><I|u>
|b> = U><U|b> + |B><B|b> + |V> <V|b> + |R><R|b> + |I><I|b>
|v> = U><U|v> + |B><B|v> + |V> <V|v> + |R><R|v> + |I><I|v>
|r> = U><U|r> + |B><B|r> + |V> <V|r> + |R><R|r> + |I><I|r>
|i> = U><U|i> + |B><B|i> + |V> <V|i> + |R><R|i> + |I><I|i>

where the matrix elements are defined as area determined by the product of the transmissivity of the filters. For example

<U|u> = ʃ U(λ)u(λ) dλ
<B|u> = ʃ B(λ)u(λ) dλ

...

for all wavelengths λ = 0 to ∞. The results of the integration and solution of the matrix equation are in the table:

0.5051 -0.0131 -0.0008 -0.0001 -0.0000
0.1680 2.5373 0.0233 0.0028 0.0008
-0.0010 0.0587 1.4170 -0.1299 -0.0381
0.0003 -0.0104 -0.0828 0.9252 0.0747
-0.0000 0.0009 0.0073 -0.0460 1.0063

The filter based transformation between our instrumental magnitudes mi for i = U,B,V,R,I and Landolt's Mi is described by the term

m_u - M_U =
-2.5( log10 <U|u> + log e (<B|u> + <V|u>+<R|u>+<I|u>)/<U|u>)
+ <B|u>/<B|b> (MB - MU)
+ <V|u>/<B|b> (MV - MU)
+ <R|u>/<B|b> (MR - MU)
+ <I|u>/<B|b> (MI - MU)
...

(analogically for other filters). The numerical results are:

mu - mU = 0.8110 - 0.0260 (mB - mU) - 0.0016 (mV - mU) - 0.0002 (mR - mU)

mb - mB = -1.203 + 0.0662 (mU - mB) + 0.0092 (mV - mB) + 0.0011 (mR - mB) + 0.0003 (mI - mB)

mv - mV = -0.1838 - 0.0007 (mU - mV) + 0.0415 (mB - mV) - 0.0917 (mR - mV) - 0.0269 (mI - mV)

mr - mR = 0.1338 + 0.0003 (mU - mR) -0.0113 (mB - mR) - 0.0895 (mV - mR) + 0.0807 (mI - mR)

mi - mI = 0.0870 + 0.0009 (mB - mI) + 0.0073 (mV - mI) - 0.0457 (mR - mI)

Detailed description of the used method and an application to our old
filters can be found in Janis's bachelor work (in Czech).

(The old school typhographics rules! A "modern" graphics technologies doesn't supports a little bit complicated typesetting as (La)TeX did twenty years ago.)