Day 12

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!

Dr Dave

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 new at Orion’s Belt- Feb 2019

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.

Dr Dave

Day 27

Just under 4 weeks to go until the world’s spectroscopy experts convene right here at the Talavera Space Hut (my backyard!). Progress is being made. I was able to identify a suitable target for the session. The program organizers suggested I use a “Be” star as my target. That is a star with a B spectral type that has a hydrogen emission line in its spectrum, not necessarily just an absorption line although they can have both. That is a unique subset of the spectral type and an active area of research. These stars are not that difficult to find. There is a handy online catalog I found several years ago. Unfortunately the physics of this I have to defer to perhaps another post and is beyond the scope of this for now. My job here is to demonstrate how to capture a high resolution spectra with the Lhires III spectrograph. We will leave the analysis of the spectra for later.

The target star is located in Gemini. Gemini is pretty high in the sky currently so that makes it a good candidate. Nu Geminorum (white arrow and circle) is a binary star which is pretty bright, 4th magnitude and located about 450 light years from us. The “calibration star” is Alhena which is a spectral type A (blue arrow). (Reproduced from the application “Stellarium”)

The strategy is as follows:

1. Capture your “calibration star” spectra. This is typically a bright type A spectral class star which has a very strong H alpha absorption line. Later you compare that spectrum with one from a professional database and adjust your spectrum to match that. This will eliminate errors due to for example water molecules in the atmosphere etc
2. Capture your target star. We need to figure out what exposure time will yield about 80% saturation of the camera sensor. We take around 15 or so images
3. Do all the calibration frames. The difference here with regular imaging is that all of the calibration can be done with the telescope parked and the cover on. Flat frames are done inside the spectrograph with a tungsten lamp you simply turn on. You do have to take a calibration lamp image which is an image of 3 neon lamp emission lines also done inside the instrument simply turning on a switch.

That’s basically it! Both the target star and calibration star are pretty bright so I found that exposure times were extremely short. The first run was with 40 sec exposures. The entire project takes about an hour! Compare that to a typical 30 hour regular imaging project! Probably as I get further into this I might do something that takes a lot longer but for the purposes of demonstration, this is ideal.

This is the field seen by the telescope through the “eye” of the guider. Since the main camera cannot see the stars, this is how you set up your image. The guide camera is in a sense also your main camera. The blue arrow shows the center of the field indicated by the crosshair. The black arrow points to the spectrograph slit at the center of the slit. You can see the thin black line going through the center of the field. This is in fact the slit of the spectrograph. The white arrow points to the edge of the illuminated field

I was very confused about this guide field shown above. Apparently the center of the field shown by the reticle is NOT the center of the spectrograph slit. That is fairly common and I was told not a major issue. In order to center the spectrum on the sensor after exposing the main camera, I have to move the star to the location shown by the black arrow. I discovered this pretty much by trial and error. That isn’t that hard to do using the mount’s joystick. Centering the star on the slit is fairly easily done as well. Once the star is centered on the slit, I click on a small star in the same guide field and start the guiding. You could make the argument that guiding for such bright stars is not really necessary however you are taking multiple exposures and during the course of the 10 minutes or so that is happening the star could move off the slit center. The other issue is this weird field illumination that I mentioned in an earlier post. That is not actually the edge of the spectrograph slit (white arrow) but could very possibly be a shadow from the internal lamp as I was told. So again, not anything to worry about. Focusing is also interesting since I am just using the knob of the primary mirror on the Celestron. That is not particularly fine focusing! After several sessions though you learn how to improve it and even with a fine focuser I can assure you there wouldn’t be a huge difference with this optical system.

And now, the results from our first run:

Spectrum from the calibration star Alhena. Note the strong h-alpha absorption line! I was thrilled to capture a spectrum at all but as I found out it does matter if it’s not horizontal!

 

Target star spectrum! This is a spectrum from the Be star Nu Geminorum. The white arrows point to 2 emission zones, not just one! The blue arrow points to the H alpha absorption in between. The reticle shown is inside the processing software for the spectrum. There is some loss of resolution if the spectrum is not oriented horizontally as in this case

 

This is the calibration lamp showing the 3 neon emission lines.

 

Flats and darks were also obtained. We took the images at -10C and a series of 40 sec darks to be used for all of the images. The software can extrapolate for shorter exposures but not longer. The flat images are easy to take because all you do is turn on a tungsten lamp in the spectrograph and use that.

I did a rough processing of the spectra to see if we’re on the right track:

Kewl!! A high resolution absorption spectrum! However there is a problem. See the text below

Awesome! A high resolution absorption spectrum! Unfortunately something is wrong. The H alpha absorption line is well known and occurs exactly at 6563 A. NOT where it is shown here.

 

This is the spectrum from the Be target star Nu geminorum. This really is fantastic! In contrast to the single absorption line seen in Alhena above, which is a drop in relative intensity, you can see 2 emission spikes (increased intensity) bordering an absorption area! This is a characteristic of several Be star systems.

 

Ok so what now? I reviewed everything we did and looked at the calibration lamp lines again. I compared the ones I took to a reference I found on Christian Buil’s website and began to realize something!

These are the same calibration lamp emission lines but they appear to be oriented differently from the ones I took!

The longest wavelength line 6599 which is off by itself is supposed to be on the far right. You can see here it is reversed. Doh! My camera was upside down!! To confirm that I went back to the telescope during the day, took the cover off and pointed to a random region of sky. Doing that you should be able to see absorption lines from the Sun.

Here is what you see exposing the main camera during daylight! Multiple absorption lines. Dense black line is HA absorption line from the Sun

 

This is the micrometer on the spectrograph

Now if you turn the micrometer counterclockwise increasing the numerical values, you should be moving the spectrograph’s “window” toward longer wavelengths which means the absorption lines should be moving to the left. By convention a spectrum has blue or shorter wavelength on the LEFT and the longer wavelengths are to the RIGHT. This is in fact the exact opposite of what I observed! My suspicions were correct. The camera needs to be flipped 180 degrees!

Back to round 2. We need to reorient the camera correctly and adjust the spectrum as it is recorded so that the spectral line is horizontal. Stay tuned….and thanks for reading.

Dr Dave

 

 

 

What’s happening at Orion’s Belt!

We begin the New Year with what will be hopefully a monthly regular update of events at Orion’s Belt Remote Observatory. Several visitors stopped by during the Holiday week, including a bunch with 4 legs! I had installed a “critter cam” on the observatory’s west wall a couple of months ago and this location apparently paid off when after the first significant snowfall occurred, a herd of elk appeared exiting the National Forest to the West! (see images below). The first major snow event of the winter occurred, causing observatory operations to temporarily shut down. Installation of imaging equipment on the second pier was completed and this will add a wide field platform to our imaging options!

“Critter cam” installed on the observatory’s west wall which faces a long trail into the Lincoln National Forest

 

Four-legged visitors stop by during the first significant snowfall of the winter!

They appear to be disappointed the observatory is closed!

 

Imaging equipment installed on the second pier. This includes a Takahashi Epsilon 180ED astrograph (orange tube) and FSQ106N refractor (white tube). Cameras include an SBIG STXL 6303E on the refractor and a Canon 60Da on the astrograph. There is a powered usb hub on the back of the 180 and a 12 volt power strip mounted on the side of a Tak guider (see below). The entire load sits on a Paramount MX+ mount

 

Another view showing the 12 volt power strip mounted on a small guide scope with a Moonlite focuser rotator connected. The focuser is the red object right behind the white refractor to the right of the orange tube 180 astrograph. 

 

We spent the Christmas weekend up at the Mayhill house. My 3 wonderful kids (Ben, Samantha, Max left to right) paid a visit to the observatory to see the final equipment install!

 

Here is the final set up at least for now. The 16″ RiDK sits on the east pier and the smaller scopes on the west. So we have east for deep field and west for wide field!

Thanks for reading!
Dr Dave

 

 

Day 62- First Spectrum!

Success! I went back to the telescope and tried to get the guider to plate solve. (See last entry). Unfortunately the peripheral stars in the field I think are too distorted and probably not enough of them to get a consistent solution. I did get it to work sporadically but this was not going to be sufficient to get the job done. Went to plan B which was to remove the spectrograph and put the regular focuser back on, then proceeded with the mount pointing model and polar alignment with the imager, the Atik 460EX. In other words, I did the mount calibration the usual way with the main camera like we do in the case for regular imaging. After we got a decent pointing model and more accurate polar alignment, I reattached the spectrograph. Moving around the sky confirmed satisfactory pointing accuracy. The star shows up in the guider field consistently. Although not centered, it was a simple matter to center the star using the cross hair in the software program. Interestingly, the spectrograph slit in the guider field is easy to see now due to the waxing gibbous moonlight! Thank you Moon! I found it was very easy to place the star onto the slit even if it was slightly off center! Next step was to test the guiding capability . I calibrated the guider on the target star because that is typically the brightest star in the field and the software will default to that if you select a dimmer star. Great! I see the calibration is successful. I select a star in the field other than the target star and start guiding! So the target star starts on the slit and lets see if we can keep it there after 10 minutes. Looks like we can! Now the guiding accuracy is OK. Generally we are staying under a pixel error but because of the moonlight probably there is a lot of noise that perhaps fools the guider thinking those pixels are part of the star (see image below). Looks like we are ready to take our first test spectrum! I slew to a nearby medium bright star, 4th magnitude. I’m not sure about the spectral type but this is a test. The star is centered manually. Guide star is selected and we start the guiding. I start a 10 minute exposure on the imager and wait…………..Image download……….A stellar spectrum is seen on the screen!!! I have never been so excited to see a thin streak of light across a computer screen. It actually works!

So this is a star in the constellation Cygnus which has a Hipparcos catalog number HIP106481 (see below). Turns out it is a “G” type star and as you can see there are lots of absorption lines. For now we won’t worry about what it means but we celebrate a successful spectrum acquisition! Next we slewed to the star Alhena in Gemini which I know from my early spectroscopy experience with a simple grating called a “star analyser” that it is an A0 star with a strong H alpha absorption line. After a 5 minute exposure there I was able to recognize a distinct absorption line which must be what we’re looking for. Won’t know for sure until we process it but I would say we are moving along pretty well now! Looks like we are ready to do a full project including calibrating and processing. Onward and upward!

Thanks for reading!

Dr Dave

Live spectroscopy set up! The Lhires is connected directly to the C14. No intervening focuser. We are using the knob on the primary to focus.

 

This is the guide field. You can see the target star is centered on the spectrograph slit (dark oblique line running from upper left to lower right through the center). Notice as you go out from the center the stars are distorted. I am thinking this is due to the lens in the guide port. Doesn’t matter though as we can find several stars near the center that are suitable for guiding!

 

Active guiding session! The guide star is pretty well centered. Guider exposure here is 4 sec. Guide errors probably average less than a pixel although in this image you can see it’s a little more than that (left side guide set up window) . Notice the noise in the guide star live image (right) which is likely affecting guide accuracy. The Moon is 2 days before full on this night!

 

Very first spectrum captured! G type star, HIP106481. You can see multiple absorption lines. The broadest line (arrow) is probably H alpha

 

Spectrum from a known A0 star. Very strong H alpha absorption line! (arrow)

Day 71

Time is flying by. I confirmed with Shelyak that we are good with the spacing on the imaging camera. Next was the guider set up. For the Lhires spectrograph, the guider is really the critical sensor for acquisition because as we discussed in an earlier post the camera that is recording the spectrum is totally blind to anything beyond the slit. It only can deal with the light coming through the slit. That’s why focusing the lens inside of the spectrograph is so key because the resolution of the spectrum really depends on that more than anything. The guider I am using is a ZWO ASI 174. It has a 1936 x 1216 pixel CMOS chip, field of view 6 x 10 arc min. The chip size is a little bigger than other options for the guider on this setup. The QE (quantum efficiency) is pretty high, 78%, so this should make things easier for plate solving and finding guide stars, at least theoretically. The camera is light weight and there is no cooler because all we are doing is plate solving, finding stars and guiding. Nothing else. Plate solving, by the way, is a frequent function of astronomical optical platforms. What happens is your system takes an image of the field of view and tries to match what it is seeing with known stellar databases. It is one of the most remarkable technological accomplishments of the early part of the 21st century in my opinion because now amateurs can do what the professionals do! Once the image is “matched” to the known stellar database by the software, the image is considered “solved” and the system now “knows” where it is in the sky! Many software programs are capable of doing this now.

The guide port on the spectrograph is tiny! 1/2 inch and not much more. The thread on it is called a “C” mount. I’ve heard of T-threads, M42 and several others but not this one. It just so happened that ZWO had this exact adaptor for the camera so I was in luck there!

I screwed the camera onto the port and it looks like everything is good in terms of focusing the slit, which is the dark straight line. The backfocus on the camera is 6.5mm and the distance from the spectrograph to the camera face was measured with the caliper at around 45mm so it appears that the total distance is correct within a mm or 2 if you look at the diagram below. Now the illuminated field looks weird. I get that, but I’m thinking it may be vignetting or internal reflection or something, maybe in part due to the larger chip size. Bottom line is we have a slit line of a few pixels in width that is centered on the chip shown by the cross hairs below!

What we have so far is a focused spectrograph doublet lens which we accomplished by using the internal calbration lamp Day 89. ,and now (hopefully) a centered slit in the guide camera. We are now ready to go to the telescope!

This is the guide port on the Lhires spectrograph. The opening is maybe 1/2-3/4 inch. The threads are male “C-mount” threads and actually are at the end of a small lens which is used to bring the spectrograph slit into focus

This is the lens which fits into the guide port sleeve and serves to focus the slit onto the guider chip

 

Technical drawing for Lhires showing the optimal distance to the guider ccd is 53mm. Subtract backfocus of ASI 174 camera which is 6.5 and that leaves 46.5mm distance between the spectrograph base and the camera face. I am at about 45mm for that so I think we’re good!

 

Recall the guider is seeing reflected light from the slit. It is the only camera that can actually see the optical field of view so in essence it is the eye of the spectrograph!

 

This is a 0.2 sec unbinned exposure in a room with what I thought was pretty dim lighting! I rotated the guider until the slit (black line) was dead center in the cross hair. Orientation of the slit is not critical as long as it is centered. The illumination is strange and not sure why it appears asymmetric like this but we will soon find out if this is correct or not!

 

2 camera configuration with guider on top, imager on the bottom

 

A Star Explodes!

On November 24 a supernova was discovered in the galaxy M77. Named “SN 2018 ivc” it is the only supernova to date discovered in the brightest Seyfert galaxy we know! M77 is an active galaxy with a quasar-like nucleus. It is pretty bright for a galaxy, about 9th magnitude, and is located in the constellation Cetus. A supernova discovery in a Messier object is pretty rare, and as it just so happened I had started an imaging project at Orion’s Belt Remote Observatory on the galaxy when one of the Astronomical Society members alerted us to the discovery! The supernova is a “Type II” which is distinguished by the presence of hydrogen in the spectrum. (Perhaps a spectroscopy project for a future event!) I was able to locate the star in one of the 15 minute frames I had taken of the galaxy (see below). Initially it was around 14-15 magnitude, located pretty close to the core . In the image I obtained nearly 2 weeks later it does not appear to have changed significantly in brightness.

Single raw uncalibrated 15 minute image, unfiltered, of SN 2018 ivc. Dec 5 at 5:20 UT. From Orion’s Belt Remote Observatory, Mayhill NM. The supernova is located at the intersection of the 2 black tic marks