Difference between revisions of "Astronomical Spectroscopy"

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The overall goal of the Astronomical Spectroscopy Project is to be able to collect and reduce data gathered from astronomical objects. This will be done using a Celestron CPC 800 GPS (XLT) telescope and a fiber-fed Ocean Optics USB2000+ spectrometer. The initial setup at the beginning of Fall term consisted of the telescope with a beam splitter and lens tube system attached to the back. The beam splitter attached to an eye piece on top and a lens tube at the back with a converging lens and the fiber attached at the end of the lens tube. The fiber was attached using a fiber adapter with thumb screws which gave three degrees of freedom for the fiber: 1 along the z axis where the length of the lens tube can be changed on the outside, and 2 and 3 along the x and y axis where the position of the fiber can be adjusted using the two thumb screws.
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== Astronomical Spectroscopy Project ==
  
At the end of the 2012-2013 school year, the student group working on the project was able to collect a spectra of vega, however, the minimum integration time required to get a spectra that resembled Vega was 600 seconds. The group (Annika Gustafsson, Gerald Buxton, and Zach Small) concluded that the large integration time was necessary for multiple reasons: 1.) the fiber was not perfectly aligned on the back of the telescope which allowed for loss of light 2.) the use of a 50:50 beam splitter in the fiber adapter, which allowed for 50% light loss, was too much loss, and 3.) the Ocean Optics spectrometer might not be suitable (i.e. not sensitive enough) for gathering spectra of astronomical objects.  
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[http://hank.uoregon.edu/experiments/Astronomical-Spectroscopy/astro.html Astronomical Spectroscopy Web Page]
  
This term, the current students on the project, which include Annika Gustafsson, Justin Stockwell, and Gerald Buxton, are going to work on improving the spectrometer-telescope setup to rule out some of these factors. In the 2 weeks, the group ordered a flip mirror, machined an adapter for the lens tube to connect to the flip mirror, and began initial lab table setup.
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The overall goal of the Astronomical Spectroscopy Project is to be able to collect and reduce data gathered from astronomical objects. Before spectra can be collected, the system needs to be prepared. This preparation involves aligning the telescope-fiber system and calculating the efficiency of the ratio to determine that the project is feasible with the current setup.  
  
The flip mirror replaces the beam splitter in the fiber adapter. This allows us to retain all of the light coming through the back of the telescope instead of dividing it 50:50 between the fiber and the eyepiece. With the fiber adapter assembled using the newly machined adapter between the lens tube and flip mirror, the group was able to begin designing the lab table setup. The goal is to have the simplest setup possible to eliminate excess opportunities for light loss.
 
  
Initially, the group used a red laser with known power and wavelength and aligned it directly into a fiber using a converging lens where the fiber was attached directly into the spectrometer. The idea was to gather a baseline sensitivity measurement which we can compare to the expected 61 photons/count at 600nm given by Ocean Optics. Then, we could have the laser go through our telescope system to gather another sensitivity measurement. Thus, allowing us to calculate the ratio of efficiency of our telescope system.
 
  
However, data measurements revealed a loss of light that was about a factor of 10,000 less than that emitted by the laser. The group used a hand held power meter in front of laser and found that there should be the expected 1mW of power from the laser going down the fiber. We also checked the numerical aperture of our setup to rule out loss of light due to that reason, however, our focal distance was large enough that it would not have played any effect. The group concluded that the lab table setup had too many places for light loss and there were not enough ways to do fine alignment on the fiber.
+
The current setup for the project involves a Celestron CPC 800 GPS (XLT) telescope and a fiber-fed Ocean Optics USB2000+ spectrometer.
  
With the guidance of Bryan Boggs, the group changed the setup to allow for the possibility of doing fine alignment on the fiber. The setup consisted of the laser emitted through an iris to a converging lens, and directed into the fiber using two square mirrors with thumb screws for alignment. The focal distance of the lens was greater was consistent with the numerical aperture of our fiber. We were able to track power loss through the system using the hand held power meter and found that the power of laser light at the fiber was about 0.7mW. We took spectra of our data and gathered a bias frame which we would later subtract off of our data.  
+
[[File:TelescopeSystem.png]]  [[File:TAdapter.png]]
  
Moving forward, in Week 7, the group will first work on fine alignment of the fiber by first aligning the eyepiece to the finderscope, done in the atrium, and then the fiber to the eyepiece, done on the lab table. This needs to be done first before we can gather any data of the laser through our telescope system. Once we have our fiber perfectly aligned, we will use the same procedure as in the lab to gather data which we can then use to create an efficiency ratio of our telescope system.
 
  
Finally, we want to characterize the Ocean Optics Spectrometer. The overall goal for this term is to be able to calculate a sensitivity measurement for the spectrometer to determine if it is feasible to use this spectrometer for astronomical purposes.
+
Efficiency of the more basic system is calculated using a lab table procedure. An efficiency of the entire telescope system can be used in comparison to create an efficiency ratio of the system.
 +
 
 +
[[File:LabTableSetup.png]]
 +
 
 +
 
 +
All of the telescope alignment takes place at long distances greater than the focal distance of the telescope, like the Willamette Basement Hallways. Here, the finderscope is being aligned to the eyepiece.
 +
 
 +
[[File:AligningTelescope.png]]
 +
 
 +
 
 +
The fiber alignment process, which involves aligning the fiber to the eyepiece, is the most difficult part of the preparation. This is done in large areas as well, including the Willamette Basement Hallways, but dark rooms like Willamette 100 have given the best results.
 +
 
 +
[[File:AligningFiber.png]]
 +
 
 +
 
 +
Data is collected during the alignment process to track the max number of counts read by the spectrometer.
 +
 
 +
[[File:AlignmentData.png]]
 +
 
 +
 
 +
 
 +
The furthest progress that has been made on the project is successfully getting a spectra of Vega using the SpectraSuite software. However, the integration time used to get the spectra was 60 seconds with a scans to average of 10, and box car smoothing of 10.
 +
 
 +
[[File:Vega.png]]
 +
 
 +
 
 +
'''Winter 2014'''
 +
During the winter term of 2014 the Astronomical Spectroscopy group, comprised of Gerald Buxton, William McNichols, and Justin Stockwell, made some good headway in determining how best to rebuild the fiber setup.  To do so we focused on precisely determining the visual spot size of a calibrated beam coming out of the telescope.  This was done through the use of a calibrated light source placed across the room and a beam profiler. Our results form this test are shown below.
 +
 
 +
              [[File:Beam Profile Winter 2014.jpg|750px]]
 +
 
 +
The key measurement needed to determine the feasibility of our setup is the Effective Beam Diameter.  This measurement measures the number of pixels above a Clip Level of 1%.  This effectively means that 99% of the light is focused into a spot with a precise diameter of 656nm.  Our fiber size is 600nm so we are able to capture almost the entire amount of light from a calibrated light source. 
 +
 
 +
We also were able to effectively determine the focal distance of our telescope.  This will allow us to build a new fiber adapter to place the fiber mount at the focal distance of the telescope. With this information we no longer need a focusing mirror, instead we can use the telescope itself to focus the light into our fiber/spectrometer setup
 +
 
 +
Next term we plan on using the information gleaned from the beam profiler to rebuild our fiber adapter setup.  This should allow us to couple at least 80% of the incoming light into our fiber, which is far better than the 1.1% we were coupling during the Fall term.  We need to machine a new adapter that directly attaches the flip mirror to the telescope, as well adapter that couples the fiber with the flip mirror at an approximate distance of 11.88cm from the back of the telescope.  With these adapters built, we should be able to take advantage of the nicer weather and get some better spectra of some astronomical objects.
 +
 
 +
'''Spring 2014'''
 +
This term we focused once again on using the beam profiler to determine minimum spot size coming through our telescope.  But this time we wanted to see how the back focus knob affected the the focal distance of our telescope.  We set up the profiler setup exactly as we had done it during Winter term with a calibrated L.E.D light source across the room, and the beam profiler set on the stands behind the telescope.  This time, however, we placed the profiler on a sliding base that way we could see how the spot size changed as we adjusted the focus knob. Using this setup we discovered that our minimum spot size was 177um which is far better than the 656um we were able to achieve last term, and is well within the 600um core size of our fiber.  Therefore with proper alignment we should be able to couple 100% of the incoming light through our telescope.  We also discovered that were able to change the back focal distance substantially by turning the focus knob.  Just 12 full turns increased the back focal distance to 48.5cm. 
 +
                                          [[File:Beam Profile Near Screenshot Spring 2014.png|750px]]   
 +
 
 +
We also wanted to determine the overall efficiency our our spectrometer.  That is, we wanted to determine a photons/count number at a particular wavelength.  To do this we used a laser setup that consisted of a laser, a converging lens, two focusing aluminum plates, three neutral density filters and then our fiber fed spectrometer. This set up looks like this.
 +
                                          [[File:Laser Setup 2 Fall 2013.jpg|350px]]
 +
Through the use of a power meter we were able to a power meter we were able to accurately determine the laser thruput coming out of our fiber.  Then by converting that power into number of photons/second we were able to compare that with the number of counts recorded by our spectrometer.  The math for this is shown below.
 +
                                          [[File:20140612_161231.jpg|350px]]
 +
This showed that it was taking nearly 1850 photons at 634nm to record one count.  This poor result may be an indication that the spectrometer we're using is not suitable for the high signal=to=noise, low signal that we get from observing stars.
 +
 
 +
The last thing we did was actually take the telescope out to observe. This allowed us to get a functional understanding of observation, and allowed us to figure out how to couple our telescope with the computer program Stellarium. This process is fully detailed in the new Observational Astronomy wiki under the advanced Projects tab.  A couple of our results are shown below.
 +
                        [[File:20140612_000609.jpg|350px]][[File:Saturn Spring 2014.jpg|350px]]
 +
 
 +
'''Presentations:'''
 +
 
 +
[https://docs.google.com/presentation/d/12X-PH-YWL5QNGBpAwOIU7EYMS1AtcNG7aff_62sN-rE/edit#slide=id.p Spring2013]
 +
 
 +
[https://docs.google.com/presentation/d/1IBA_8ghSto6H9ivADDnq0qd3YHWw_VMEhpLkqUiVbXs/edit#slide=id.p9 Fall2013]
 +
 
 +
 
 +
 
 +
 
 +
'''Links:'''
 +
 
 +
[http://www.oceanoptics.com/products/usb2000+.asp Ocean Optics Spectrometer]
 +
 
 +
[http://www.celestron.com/astronomy/celestron-cpc-800-gps-xlt.html Celestron Telescope]
 +
 
 +
[http://en.wikipedia.org/wiki/Spectrometer Wiki- Spectrometer]
 +
 
 +
[http://en.wikipedia.org/wiki/Astronomical_spectroscopy Wiki-Astronomical Spectroscopy]

Latest revision as of 09:27, 24 November 2014

Astronomical Spectroscopy Project

Astronomical Spectroscopy Web Page

The overall goal of the Astronomical Spectroscopy Project is to be able to collect and reduce data gathered from astronomical objects. Before spectra can be collected, the system needs to be prepared. This preparation involves aligning the telescope-fiber system and calculating the efficiency of the ratio to determine that the project is feasible with the current setup.


The current setup for the project involves a Celestron CPC 800 GPS (XLT) telescope and a fiber-fed Ocean Optics USB2000+ spectrometer.

TelescopeSystem.png TAdapter.png


Efficiency of the more basic system is calculated using a lab table procedure. An efficiency of the entire telescope system can be used in comparison to create an efficiency ratio of the system.

LabTableSetup.png


All of the telescope alignment takes place at long distances greater than the focal distance of the telescope, like the Willamette Basement Hallways. Here, the finderscope is being aligned to the eyepiece.

AligningTelescope.png


The fiber alignment process, which involves aligning the fiber to the eyepiece, is the most difficult part of the preparation. This is done in large areas as well, including the Willamette Basement Hallways, but dark rooms like Willamette 100 have given the best results.

AligningFiber.png


Data is collected during the alignment process to track the max number of counts read by the spectrometer.

AlignmentData.png


The furthest progress that has been made on the project is successfully getting a spectra of Vega using the SpectraSuite software. However, the integration time used to get the spectra was 60 seconds with a scans to average of 10, and box car smoothing of 10.

Vega.png


Winter 2014 During the winter term of 2014 the Astronomical Spectroscopy group, comprised of Gerald Buxton, William McNichols, and Justin Stockwell, made some good headway in determining how best to rebuild the fiber setup. To do so we focused on precisely determining the visual spot size of a calibrated beam coming out of the telescope. This was done through the use of a calibrated light source placed across the room and a beam profiler. Our results form this test are shown below.

              Beam Profile Winter 2014.jpg

The key measurement needed to determine the feasibility of our setup is the Effective Beam Diameter. This measurement measures the number of pixels above a Clip Level of 1%. This effectively means that 99% of the light is focused into a spot with a precise diameter of 656nm. Our fiber size is 600nm so we are able to capture almost the entire amount of light from a calibrated light source.

We also were able to effectively determine the focal distance of our telescope. This will allow us to build a new fiber adapter to place the fiber mount at the focal distance of the telescope. With this information we no longer need a focusing mirror, instead we can use the telescope itself to focus the light into our fiber/spectrometer setup

Next term we plan on using the information gleaned from the beam profiler to rebuild our fiber adapter setup. This should allow us to couple at least 80% of the incoming light into our fiber, which is far better than the 1.1% we were coupling during the Fall term. We need to machine a new adapter that directly attaches the flip mirror to the telescope, as well adapter that couples the fiber with the flip mirror at an approximate distance of 11.88cm from the back of the telescope. With these adapters built, we should be able to take advantage of the nicer weather and get some better spectra of some astronomical objects.

Spring 2014 This term we focused once again on using the beam profiler to determine minimum spot size coming through our telescope. But this time we wanted to see how the back focus knob affected the the focal distance of our telescope. We set up the profiler setup exactly as we had done it during Winter term with a calibrated L.E.D light source across the room, and the beam profiler set on the stands behind the telescope. This time, however, we placed the profiler on a sliding base that way we could see how the spot size changed as we adjusted the focus knob. Using this setup we discovered that our minimum spot size was 177um which is far better than the 656um we were able to achieve last term, and is well within the 600um core size of our fiber. Therefore with proper alignment we should be able to couple 100% of the incoming light through our telescope. We also discovered that were able to change the back focal distance substantially by turning the focus knob. Just 12 full turns increased the back focal distance to 48.5cm.

                                         Beam Profile Near Screenshot Spring 2014.png    

We also wanted to determine the overall efficiency our our spectrometer. That is, we wanted to determine a photons/count number at a particular wavelength. To do this we used a laser setup that consisted of a laser, a converging lens, two focusing aluminum plates, three neutral density filters and then our fiber fed spectrometer. This set up looks like this.

                                         Laser Setup 2 Fall 2013.jpg

Through the use of a power meter we were able to a power meter we were able to accurately determine the laser thruput coming out of our fiber. Then by converting that power into number of photons/second we were able to compare that with the number of counts recorded by our spectrometer. The math for this is shown below.

                                         20140612 161231.jpg

This showed that it was taking nearly 1850 photons at 634nm to record one count. This poor result may be an indication that the spectrometer we're using is not suitable for the high signal=to=noise, low signal that we get from observing stars.

The last thing we did was actually take the telescope out to observe. This allowed us to get a functional understanding of observation, and allowed us to figure out how to couple our telescope with the computer program Stellarium. This process is fully detailed in the new Observational Astronomy wiki under the advanced Projects tab. A couple of our results are shown below.

                        20140612 000609.jpgSaturn Spring 2014.jpg

Presentations:

Spring2013

Fall2013



Links:

Ocean Optics Spectrometer

Celestron Telescope

Wiki- Spectrometer

Wiki-Astronomical Spectroscopy