A new fibre-based spectrometer was commissioned from 2017 May 8 to May 26. The system was initially commissioned using the light feed from the secondary cœlostat on the lower-level platform in the main observing room of the solar pyramid building. Limited operational time was achieved in this phase due to bad weather. At the end of the site visit the whole system was moved into the apex of the pyramid sharing light from the primary cœlostat with the Mark-I spectrometer, and remains running in this configuration. Data from the spectrometer suffers from poor low- and high-frequency noise that are thought to be caused by the size of the solar image formed on the end of the fibre.



The guiding performance of the Skywatcher mount was tested when operating via a Raspberry Pi single-board computer, and results are consistent with earlier tests at Mount Wilson. No issues are expected with the use of the low-power system

Hale, Steven J.

University of Birmingham Research Archive, E-papers Repository

BiSONBirminghamSolar-OscillationsNetworkTECHNICAL REPORT NO. 384Fibre-feed tests at Izaña in 2017 MaySteven J. HaleThe University of Birmingham, Edgbaston, Birmingham B15 2TT2017 September 29This technical report series is published by:SLHigh-Resolution Optical-Spectroscopy GroupSchool of Physics and AstronomyThe University of BirminghamEdgbaston, Birmingham B15 2TT, United KingdomTelephone: +44-121-414-4551Fibre-feed tests at Izaña in 2017 MaySteven J. HaleThe University of Birmingham, Edgbaston, Birmingham B15 2TT2017 September 29AbstractA new fibre-based spectrometer was commissioned from 2017 May 8 to May 26. Thesystem was initially commissioned using the light feed from the secondary cœlostat on thelower-level platform in the main observing room of the solar pyramid building. Limitedoperational time was achieved in this phase due to bad weather. At the end of the site visitthe whole system was moved into the apex of the pyramid sharing light from the primarycœlostat with the Mark-I spectrometer, and remains running in this configuration. Datafrom the spectrometer suffers from poor low- and high-frequency noise that are thought tobe caused by the size of the solar image formed on the end of the fibre.The guiding performance of the Skywatcher mount was tested when operating via aRaspberry Pi single-board computer, and results are consistent with earlier tests at MountWilson. No issues are expected with the use of the low-power system.Contents1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 12 Trip Log and Data Quality . . . . . . . . . . . . . . . . . 23 Skywatcher Mount . . . . . . . . . . . . . . . . . . . . . 71 IntroductionThis is the first of a two-part report on a two-stage visit to Izaña. Steven Hale visited Izañafrom 2017 May 8 to May 26. The second-stage visit was completed in 2017 September and isreported in BTR385 [1]. Prior to this site visit, the last visit to Izaña was in 2012 October toreplace a failed data acquisition computer for Mark-I [2].The purpose of this visit was to begin the initial testing of a prototype optical-fibre basedspectrometer. Some fibre testing was carried out at Mount Wilson during 2016 September,where spectrometer-K (“Klaus”) was temporarily modified to accept a fibre input and run withfibre collection optics fitted on a consumer-grade Skywatcher HEQ5-Pro motorised mount [3].On this visit the testing included the commissioning of a new spectrometer designed specificallyfor use with fibre-feed input, in addition to the use of the inexpensive Skywatcher mount.Much of the first half of the site visit was spent on hardware commissioning, and marredby bad weather. Initial setup of the spectrometer was in the main observing room of the solar1pyramid building, making use of the light feed from the secondary cœlostat on the lower-levelplatform. The Skywatcher mount and control electronics arrived at the end of the first week, andwere set up outside whilst continuing to run via the cœlostat. Due to delays in manufacturinga weather-proof housing for the mount, at the end of the visit the new spectrometer was movedup to the pyramid apex and continues to operate sharing light from the Mark-I cœlostat.It is not intended that this technical report provide significant detail on the hardware designor the software controlling the new data acquisition system — this will be published in laterreports. The intention of this trip report is only to log the work completed and to present theinitial results of the performance tests. Section 2 provides a log of events and configurationinformation, and discusses performance problems. Section 3 discusses performance of the Sky-watcher mount when running on the Raspberry Pi including comparison with expectations fromprevious tests.2 Trip Log and Data QualityThe spectrometer and mount were sent out to Izaña via DHL in two separate shipments, ap-proximately one week apart. The first shipment was on site at arrival, and the mount arrivedabout a week later as expected. The spectrometer was initially setup in the main observingroom of the solar pyramid building, making use of the light feed from the secondary cœlostaton the lower-level platform, whilst waiting for the dedicated mount to arrive. Whilst setup tookonly a few days, cloud and strong wind prevented observing until May 13.The cœlostat on the lower platform sometimes has trouble guiding and requires the systemto be aligned and reset. The primary mirror also vibrates in strong wind with approximatelyan arcminute of oscillation which is large in comparison to our typical guiding accuracy of a fewarcseconds [3, 4]. Since the fibre-feed makes use of an 80mm focal length lens to focus a 1mmimage of the Sun onto the end of the 1mm fibre, it was considered that the wind-inducedoscillation was causing some noise issues experienced in the data. The fibre-feed was movedfrom the cœlostat onto the more-stable Skywatcher mount on May 19.The first few days of observation were taken at high-cadence in an attempt to measureatmospheric scintillation noise. The data acquisition system is based on a Raspberry Pi single-board computer and three Texas Instruments ADS1210 24-bit ADCs. These were configured torun at a 1 kHz sampling rate and used our normal 4-second period for logging, which resultedin 3000 samples taken over 3-seconds followed by almost 1 second to write out to disk. Thepolarisation state is switched using an LCD retarder at 5Hz. Unfortunately the polarisationswitching and dead time proved to add complications to the scintillation noise measurementmaking it unreliable. A second more successful attempt at measuring scintillation noise isdescribed in BTR385 [1]. The data acquisition was re-configured and finalised to the normal4-second cadence on May 20, and only May 20 onward is presented here. The following is a logof the key events during the last third of the site visit.2.1 2017 May 20Shown in Figure 1. At 09:00UT the hot-to-cold ratio was measured to be 7.7 for scatteringdetector-1 and 8.5 for scattering detector-2. This is very good. At approximately 12:00UT thetransmission monitor was covered up and so removed from the optical path. The scatteringcounts dropped a little, indicating that some back reflections are making it into the cell, andthe ratio changed significantly. Unfortunately neither the low frequency or high frequency noiseimproved, and so while back reflection is clearly an issue it is not causing the noise problems.22.2 2017 May 21Shown in Figure 2. At the beginning of the day an attempt was made to improve the focus ofthe objective lens onto the end of the fibre, and also to improve the alignment onto the fibre.The high frequency noise appears to have improved a little but the low frequency issues are stillpresent. The image appears very slightly larger than the 1mm diameter fibre, and this is causingvignetting of the solar disc which is almost certainly the cause of the low frequency problems.2.3 2017 May 22Shown in Figure 3. Pere visited and discussed the design and the noise problems. The mountwas operating for only a hour in the afternoon.2.4 2017 May 23Shown in Figure 4. No data due to clouds.2.5 2017 May 24Shown in Figure 5. All the hardware was moved up into the apex of the pyramid. Due to delaysin manufacturing a weather-proof housing for the Skywatcher mount, the option of sharing lightfrom the Mark-I cœlostat is the only way to allow the system to continue operating past the endof this site visit. The Mark-I cœlostat is smaller than the cœlostat on the lower platform whichmeans that it has better mirror stability in windy conditions. The guider system is also better,and due to being positioned at the top of the pyramid has a wider field of view than the lowercœlostat.2.6 2017 May 25Shown in Figure 6. At approximately 09:30UT the isolation of the transmission monitor wasimproved by pushing some blackout material into the exit aperture of the oven/magnet. Thismade things worse and appeared to increase the back reflections into the cell.2.7 2017 May 26Shown in Figure 7. At approximately 07:30UT the material was removed from the oven/magnetand the transmission monitor covered separately with a strip of blackout material.2.8 SummaryThe measured velocity ratios appear to be slightly lower than measured by Mark-I, and this lowersensitivity is expected due to using a 0.3T magnet rather than the ideal 0.18T normally usedfor the scattering cells. The system remained operating after the site visit in the configurationas of May 26. The low and high frequency noise problems are almost certainly due to issueswith the solar image size on the end of the fibre, and this was addressed in the second stage sitevisit in 2017 September reported in BTR385 [1].3Izana/Mini - 2017 May 20-505101520253005e+061e+071.5e+072e+076 8 10 12 14 16 18 2005001,0001,5002,0002,5003,0003,5000 2 4 6 8 10FOM high: 7.9, FOM low: 0.8InvSens: 5189 m/s  Oﬀset: 700 m/s-8-6-4-202468108 9 10 11 12 13 14 15 16Figure 1: 2017 May 20 running on the Skywatcher mount. The step-change at approximately12:00UT was due to the transmission monitor being covered up and removed from the opticalpath.Izana/Mini - 2017 May 21-20-15-10-5051015202505e+061e+071.5e+072e+076 8 10 12 14 16 18 2001,0002,0003,0004,0000 2 4 6 8 10FOM high: 15.5, FOM low: 3.0InvSens: 4968 m/s  Oﬀset: 548 m/s-8-6-4-2024689 10 11 12 13 14 15 16Figure 2: 2017 May 21. Data from the Skywatcher mount.4Izana/Mini - 2017 May 22-2002040608010005e+061e+071.5e+072e+076 8 10 12 14 16 18 2001,0002,0003,0004,0005,0006,0000 2 4 6 8 10FOM high: 8.3, FOM low: 3.7InvSens: 4779 m/s  Oﬀset: 524 m/s-8-6-4-2024614.5 15 15.5 16 16.5 17 17.5Figure 3: 2017 May 22. Data from the Skywatcher mount.Izana/Mini - 2017 May 23-0.1-0.0500.050.10.15195,000200,000205,000210,000215,000220,000225,000230,000235,0006 8 10 12 14 16 18 20No spectrum.No residuals.Figure 4: 2017 May 23. Cloudy.5Izana/Mini - 2017 May 24-2002040608010005e+061e+071.5e+072e+076 8 10 12 14 16 18 2005001,0001,5002,0002,5003,0000 2 4 6 8 10FOM high: 11.9, FOM low: 1.4InvSens: 4879 m/s  Oﬀset: 532 m/s-8-6-4-2024681012 13 14 15 16 17 18 19Figure 5: 2017 May 24. The spectrometer was moved to the apex of the pyramid, sharing thebeam with Mark-I.Izana/Mini - 2017 May 25-505101520253002e+064e+066e+068e+061e+071.2e+076 8 10 12 14 16 18 2001,0002,0003,0004,0005,0000 2 4 6 8 10FOM high: 17.1, FOM low: 2.3InvSens: 5518 m/s  Oﬀset: 526 m/s-8-6-4-2024686 8 10 12 14 16 18 20Figure 6: 2017 May 25. Data from the primary cœlostat. The step-change at approximately09:30UT is due to trying to improve the isolation of the transmission monitor, but actuallymaking the back reflections into the cell worse.6Izana/Mini - 2017 May 26-80-60-40-2002040608002e+064e+066e+068e+061e+071.2e+076 8 10 12 14 16 18 2005001,0001,5002,0002,5003,0003,5000 2 4 6 8 10FOM high: 9.8, FOM low: 1.4InvSens: 4992 m/s  Oﬀset: 545 m/s-10-505106 8 10 12 14 16 18 20Figure 7: 2017 May 26. Data from the primary cœlostat. The step-change at approximately07:30UT is where the isolation of the transmission monitor was improved with some blackoutmaterial covering the lens at the exit aperture of the oven/magnet.3 Skywatcher MountThe Skywatcher HEQ5-Pro has already been tested at Mount Wilson running from a laptop [3].The aim is to condense all control systems down to a small number of Raspberry Pi single-board computers. Since these are of somewhat limited power compared to full-size systems, itis important to test the image processing and guiding performance.Images are captured from a CCD camera using the Instrument Neutral Distributed In-terface library (INDIlib [5]), and processed using the Open Source Computer Vision library(OpenCV [6]). Both of these projects had to be compiled from source on the Raspberry Pi inorder to obtain the most recent versions. Once installed, the mount control and guiding perfor-mance was as expected based on the tests at Mount Wilson. There appear to be no issues andthe Raspberry Pi is more than capable of powering our control systems.Some minor issues were experienced. Although the fibre-collection optics are small, at certaintimes of year it is possible for the optics to hit the telescope pier. This is a known problem withequatorial mounts, and requires a meridian-flip at local-noon in order to keep the telescope opticson the top of the mount. This makes an equatorial mount more difficult to fully automate. Itwould be easier to automate an altaz mount, although this may create problems due to imagerotation on the end of the fibre, and would also involve a slightly more complicate guidingalgorithm. Alternative mounts should be considered before going forward with the currentdesign. Also, a solid-state DC relay was included in the mount controller chassis in order tocontrol power to the mount. However, this does not appear to switch off properly under controlof the Raspberry Pi. It is not clear if the relay is faulty or if a different component is required.7References[1] Hale, S. J. Fibre-feed tests at Izaña in 2017 September. BiSON Technical Report Series,Number 385, High-Resolution Optical-Spectroscopy Group, University of Birmingham, UK,2017. URL http://epapers.bham.ac.uk/3136/. [page 1, 2, 3][2] Hale, S. J. PC replaced in Izana in 2012 October. BiSON Technical Report Series,Number 359, High-Resolution Optical-Spectroscopy Group, University of Birmingham, UK,2012. URL http://epapers.bham.ac.uk/2054/. [page 1][3] Hale, S. J. Fibre-feed tests at Mount Wilson in 2016 September. BiSON Technical ReportSeries, Number 382, High-Resolution Optical-Spectroscopy Group, University of Birming-ham, UK, 2016. URL http://epapers.bham.ac.uk/3134/. [page 1, 2, 7][4] Hale, S. J. Repairs to Jabba at Carnarvon in 2016 August. BiSON Technical Report Series,Number 381, High-Resolution Optical-Spectroscopy Group, University of Birmingham, UK,2016. URL http://epapers.bham.ac.uk/3133/. [page 2][5] INDIlib. Instrument Neutral Distributed Interface. URL http://indilib.org. [page 7][6] Itseez. Open Source Computer Vision Library. URL http://opencv.org/. [page 7]8

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