We installed a “flat panel” for the second pier (Pier 2). “Flat field correction” is another facet of image calibration in astrophotography and attempts to remove artifacts and other aberrations that occur as light travels though your specific optical train. These could be anything from dust to stray light or shadows occurring due to various equipment components and set-ups. The goal is to achieve a uniform field across the target image. The “flat field” is itself an image of a uniformly lit area which when exposure is adjusted properly, yields a “flat image” showing the artifacts present in your set up. When you subtract this image from the actual astronomical image, the result will be (hopefully) a clean image of your galaxy, nebula etc. Several options exist for a uniformly lit target to produce adequate flat frames. For pier 1 up here at the observatory I use what are called ‘sky flats’. At dusk or dawn if it is clear there is a region of sky where brightness is uniform. The 16″ scope routinely takes these sky flats before and after the imaging session. They work very well- when it’s clear. The other potential issue is that you have to keep changing exposure times as the sky continues to darken or brighten during dusk or dawn in order to maintain the same peak intensity of your flat, typically 40-70% of the saturation point of your sensor. While this exposure adjustment happens automatically with the control software for Pier 1, at some point it either becomes too dark or too light in the sky to continue so you will always be limited with the numbers of flats you can acquire using the sky flat method.
Flat panel which is placed in this case in front of the FSQ106 refractor for obtaining flat frames
Enter the “flat panel”! This is a really neat device which is a uniformly lit artificial light panel where you can adjust the brightness until you have reached the desired level for your equipment. Then you can fire away and take as many flats as you like whenever you want! I decided to try this out for pier 2 and I have to say it works very nicely. Now it may be difficult to automate this feature because the flats in this case are obtained when the telescope is in the parked position and the imaging session is completed. However it is easily carried out through a PC software interface and thus can be obtained remotely!
“Spika flat fielder” is available through a company called All Pro Software and is very easy to set up and use. I purchased their standard panel which is about 15″ and can be used for scopes up to 12″ in diameter. Larger ones can be purchased for bigger scopes if needed. I modified an artists easel to accommodate the panel and this enables me to move the panel around if needed. A standard AC power converter enables a usb connection to your PC and also powers the panel. The software control is quite simple. An example of a flat frame is shown below.
The flat panel is mounted onto an easel. The entire assembly is fairly light weight and can be easily positioned in front of your telescope
This is all there is in the control panel! Just click up or down on the panel brightness.
An example of a flat frame. The round spheres are dust particles in the optical train. Notice also the darker “shadows” in the corners. This frame is subtracted from the target image to arrive at a uniform result without the artifacts present in your system
Happy Flat Fielding!
Thanks for reading!
It’s been about a year and a half now since the 16” scope up at Orion’s Belt saw first light. Now, finally, the very first imaging project with that telescope is completed! The “Bubble” nebula, or NGC 7635, it’s official designation in the “New General Catalog” of deep space objects, is a true bubble in space, about 7000 light years from us in the constellation Cassiopeia! Not science fiction! The bubble is created by “stellar wind” or gas ejected from the upper atmosphere of a very hot centrally located star in the nebula. Surrounding the bubble is a huge cloud of hydrogen gas. Since all of you who have been reading these posts are now experts in spectroscopy 😊 you know that hydrogen gas after it absorbs radiation can then emit that radiation back into space in the “hydrogen alpha” wavelength of light which is the visible red portion of the spectrum.
This data was a total bear to process and I almost bailed on the whole thing when I realized that the bubble was hidden in a dense star field! (see below). We forget how many stars are out there. 250 billion in our galaxy alone! It really seemed to me that they were all congregated right there in one frame. The processing challenge was to somehow remove the stars to bring out the nebulosity. Folks, if you are going to image a nebula in a dense star field my suggestion is to use narrow band filters all the way. I felt I could get the natural color of the nebula using just the hydrogen alpha filter, which is narrow band ( in other words just allows the light in the H alpha region to pass through), but only one channel, combined with the regular band width red-green-blue filters. Problem is the regular band width filters do not filter out the stars! The details of the processing are beyond the scope of this one post but I tried to show the essence of what was done in the images shown here. Star removal is still not a perfect “science”. I have yet to see one method that does a complete job with no artifacts, but the method I used seemed to work pretty well. The software Pixinsight has a number of processes that in combination can achieve the desired result. The “star mask process” can be applied repeatedly to “mask” different sized stars which can then be removed by applying the mask back to the image as a “defect map” (another process) to do the actual removal. Anyway it took weeks of trial and error to get it right enough where the residual artifacts were manageable!
If you click on the thumbnail under “My Astro images” on the right side of this blog (scroll down a bit) you will go to the full resolution version.
This is the Hydrogen alpha version. Notice it is black and white. You have to combine this with one or more other channels for color. The detail in the nebula is able to be detected with this filter since it is only letting the narrow 3nm width of light through in the H alpha region of the spectrum. Most of the star field is filtered out however to achieve the red color you have to combine this with another channel, typically red ,but in my case it was the regular band width red channel which is full of stars!
This is the standard “tricolor” RGB image! This is how we obtain color images in general with astroimaging, combining individual red, green and blue filtered images. Amazing to see how the nebula is really hidden in this image behind all of these stars! Also notice the slightly pink color of the nebula which is from the blue channel
Going through the star removal process for the RGB image above, then combining that with the Hydrogen alpha image (first one above) I was able to get to this workable solution which then had to be tweaked some to arrive at the final result many hours later. I did look at trying to sharpen things up a bit as it does get a little soft at full res, but that wasn’t possible due to the processing artifact in the background. Overall I think this was a decent salvage effort!
Thanks for reading!
This was my second spectrum accepted into the BeSS database. It is a high resolution spectrum I just obtained of the H alpha region of the Be star (B emission) HD43544. This is a 6th magnitude star in the well known Winter constellation Canis Major. Captured with the Lhires III spectrograph, C14, Atik 460EX, Paramount ME from Las Cruces, NM. Many B spectral type stars exhibit emission lines rather than absorption (meaning they spike upward , not downward ). These are actively researched now because it is believed that several, possibly most B stars, are actually part of close binary systems with a small “type O subdwarf” ,or white dwarf ( or in some cases neutron star or even black hole!) accounting for mass transfer between the 2 stars which gives rise to the rapid rotation of the B star and formation of a gaseous disc surrounding the star. This is the reason for the emission feature. Close analysis of the emission profile changes over time in the HA region or other regions can yield a solution for orbital parameters of a binary system, thus proving they exist! The peaked nature of the Ha emission is dependent on line of sight from earth as shown in this schematic:
Position ‘A’ viewed from Earth would be looking directly ‘above’ the star where we see only an emission peak. Position ‘B’ is an oblique view where we would see 2 peaks with central dip depending on degree of obliquity but this “dip” gradually increases in depth toward the “C” position where we see the full absorption component (peak pointing down) at the H alpha 6563 angstrom point when we are looking at the star edge on!
I think one of the compelling things about amateur spectroscopy is that this kind of data that I have shown here, despite being obtained with amateur equipment, is still highly sought after by professional researchers. Once these spectra are “validated” by the BeSS administrators then they are considered accurate enough to be used in astrophysical research. Remember that most astronomers do not have daily access to equipment like we do! They have to vie for telescope time with many others and perhaps they will get a day or a few days once every year or more, if they are lucky, on one of the big telescopes either on Earth or in space but this resource that we provide enables researchers to acquire data any time anywhere at will! Spectroscopy or the analysis of light from stars and other objects in space is the way that we have figured out how stars work and evolve over time as well as the large scale structure of the universe. It is also a very viable way that we amateurs, you and me , can still participate and be relevant in new discoveries out there in our universe! For more information on astronomical spectroscopy you can read my primer that I wrote for ‘Reflector” magazine in this post
Thanks for reading!
Haven’t had a chance to report on the last 2 days of the conference, now 3 weeks ago, which was really a ground breaking event all around. I met a lot of great people from literally all over the world! Many were inspired to hopefully get started in this fascinating “subspecialty” of amateur astronomy. For myself, I learned a ton and was able to get started on a couple of research projects with the professional astronomers in attendance. Probably as a direct result of the information presented at this event, I was able to have my first spectrum accepted into the Be star global database (called BeSS) which is a resource used by astronomers worldwide.
Attendees at the recent workshop. I am in the back (arrow) . People came from as far away as Australia and New Zealand!
Francois Cochard, one of the co-owners of Shelyak Instruments discussed the challenge of finding dimmer stars when doing spectroscopy observations.
Dr Katie Devine from the College of Idaho gave a presentation on her focus of interest which is the study of massive star forming regions and spectroscopic observations of these areas in the radio frequencies
My favorite talk was by Drew Chojnowski, graduate student from New Mexico State University ,on the spectroscopy of giant emission binary systems or those with a type B emission star (B star with a surrounding disk of gas) and also containing a small type O star orbiting, called an O “subdwarf”. These are much dimmer than regular type O stars but still have a brightness 10-100 times that of the Sun!
Drew presented spectroscopy data he obtained using the Apogee 3.5m scope and Echelle spectrograph (not far from here!) from another exotic binary star consisting of a Be star and a probable OB subdwarf. Using emission lines in the spectra he was able to resolve the orbital parameters of the binary system!
Olivier Garde, also from Shelyak Instruments in France presented a fascinating talk on how to identify new planetary nebulae with spectroscopy!
Inspired by the fascinating talks at the event, I obtained this spectrum of HD51354 the second night, when the weather was good. It is a magnitude 7.2 Be star with suspected O companion which is not readily detectable with any of the usual absorption or emission lines but apparently it was directly observed in the ultraviolet region. This is just showing the H alpha peak emission which is split because of the orbiting disc component. My future task is to observe Silicon emission a little more to the blue side of this so that the orbital parameters of the binary can be calculated! I was pretty excited that this spectrum was accepted into the BeSS database (see above) because it kind of confirms that you “probably” know what you are doing and can now focus on the science!
And here is my very first entry into the database. Many more to come!
Thanks for reading!
The much anticipated “SMSW 2” has arrived! Attendees from 20 or so US states and several countries around the world convened for the 3 day spectroscopy workshop featuring the world renowned experts in the field (scroll to bottom of program for bios on the featured speakers)
Unfortunately the one day we needed to have good weather it did not pan out. Rain and clouds blew in for the evening’s observing session so my big event was cancelled! However all the preparation I did do only made the event more useful for me since I had many questions to ask the experts! I figure I will be better than I was before and ready to do more challenging projects.
Some of the highlights from Day 1:
The second annual astronomical spectroscopy workshop has a record number of attendees, close to 80. Last year it was 21!
Dr David Whelan, a professional astronomer from Austin College in Texas gave a fascinating talk about Be stars and explained how the different emission line patterns we see have to do with our line of sight to the star
Dr Stella Kafka gave a very inspirational talk about how we all can participate in research by contributing spectra to the newly configured AAVSO spectral database. This is also a great way to see if your spectra is “on the level” as they will reject the spectrum if certain acquisition criteria are not met. Dr Kafka is the president of the American Association of Variable Star Observers (AAVSO) which until recently was focused primarily on visual and photometric observations of variable stars but now they have a newly developed “spectroscopy arm”
Other great sessions included talks by Francois Cochard, founder of Shelyak Instruments, addressing spectroscopy basics and instrumentation, processing software for spectra and other aspects of spectroscopy science and set up.
Yes it was quite disappointing the observing session didn’t happen but a great conference day #1 nonetheless! My wife also had a great time as one of the tour guides for the “spectroscopy wives”. They toured Las Cruces and saw many interesting aspects of New Mexico life.
Thanks for reading!
Only 12 days until the spectroscopy conference! Apparently they have sold out. About 80 attendees have registered from all over the world!
In the last spectroscopy post I discovered that my camera was oriented upside down and since then I have corrected that. I have also oriented my spectrum horizontally. The results are shown here. Notice in the previous spectrum of Alhena, a strong type A star, the H-alpha absorption line is “blue shifted” which is not the result of some bizarre physical phenomenon of this star but a disoriented camera! After reorienting the camera the absorption line occurs at the 6563 Angstrom point- which is correct! Remember this star is the calibration star meaning that is what I am using to correct for aberrations in my optical set up and seeing conditions. The target star is shown below which is a Be star and has emission lines as well as absorption lines. So it would appear that I am now essentially prepared to do the demonstration on acquiring a spectrum with the Lhires III!
Thanks for reading!
This was the first spectrum taken of Alhena. Note the absorption line is “shifted” left from the expected point of 6563 (arrow)
This is the corrected spectrum taken with a new data set and the camera properly oriented . Absorption line is properly located at the H alpha point of 6563 Angstroms
This is a single raw spectrum showing the proper horizontal alignment, at roughly the center of the ccd with the H-alpha absorption line also in the center
The final fully processed result from the target star Nu Geminorum. This is a Be star showing emission lines as well as absorption
What’s happening this month at Orion’s Belt Remote Observatory?
A new project is started on the 16″! The “Needle Galaxy” NGC 4565. This is a fantastic edge-on fairly bright galaxy in the constellation Coma Berenices. It is well positioned, now visible almost the entire night so we should be able to complete the project in the next month or 2.
Single raw red filtered image of NGC 4565 , the “Needle Galaxy” viewed edge-on from Earth. 15 minute image taken with the RiDK 400 telescope, SBIG 16803 camera. Note the galaxies visible to the lower left, NGC 4562 and lower right IC 3546. The image is annotated with some of the Tycho catalogued stars labeled as well in yellow
Work continues on M77 galaxy in Cetus. Luminance is completed and red channel almost done. The recent supernova in the galaxy discovered in Nov. continues to fade. M77 is getting pretty low in the sky and is only a suitable target until around 10pm or so. This will likely have to wait until next year to complete. Weather in Mayhill has generally been poor this Winter, uncharacteristically.
M77 galaxy in the constellation Cetus. Single raw luminance image, 15 minutes, also obtained with the RiDK 400mm and SBIG 16803 camera
No major operational issues to report except 2 of the mirror shutters on the 16″, which we have been struggling with since the initial installation, have basically failed. We had to manually open them at a recent observatory visit and leave all of them full open. This does not affect the imaging operations at all. It’s a very cool feature but so far I think more of a hassle than perhaps it’s worth. You have to accept gradual accumulation of dust on the mirrors regardless! An upgraded shutter system is supposed to be available soon.
That’s it for now! Thanks for reading.