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MARK SLADE REMOTE OBSERVATORY (MSRO) EXOPLANET HUNTERS
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Remote Observatory (MSRO) Exoplanet Hunters
by William Paolini, 10/3/2018
In 1992 the face of our cosmos changed. What had been hoped for, dreamed of, was finally confirmed. Our solar system was indeed not unique in the galaxy and there were other planets orbiting distant stars! Using the Arecibo Observatory in Puerto Rico, Polish astronomer Aleksander Wolszczan and American astronomer Dale Frail announced the first confirmed exoplanets on January 9th, 1992. Discovered with the massive 305 meter radio telescope, the two exoplanets were calculated to have at least 2.8 and 3.4 Earth masses, orbiting their very inhospitable host star pulsar PSR B1257+12. Their almost circular orbits were at a distance of 0.47 AU and 0.36 AU from the pulsar with very short periods of only 98 and 67 days.
Seventeen years later exoplanet discoveries abounded with the launch of the dedicated exoplanet hunting Kepler Space Observatory in 2009. As of 2018, Kepler had confirmed over 2,600 exoplanets and cataloged an additional 2,700 suspected exoplanets awaiting data confirmation. Of all the confirmed exoplanets, only 30 are thought to be potentially habitable, having less than twice the size of the Earth and within the habitable zone of their host stars. This “habitable zone” is defined as the region in a planetary system where liquid water might pool on the surface of an orbiting planet. While we know that these 30 exoplanet planets could potentially sustain water, more advanced telescopes and technologies are needed to determine the suitability of the atmospheres and geologies of these distant worlds.
Fig. 1. An artist’s impression of some of the thousands of exoplanets discovered by NASA’s Kepler Space Telescope.
The fundamental process used by Kepler to determine candidate exoplanets around a star is fundamentally simple. Light from the star is precision measured for an extended period to determine if there is a dimming in the brightness that could be due to the transiting of an orbiting exoplanet. This process requires that the exoplanet’s orbit be oriented in such a way as it causes an occultation of the star as viewed from Earth. Once a detection is made, the data from the observed transit is used to calculate the planet's size based on how much the light dimmed, then orbital size, star size, and planetary mass can be further calculated. From the orbital data and the temperature of the star, the likely temperature at the planet is calculated and this determines whether or not the planet is in the human-habitable zone from of its host star.
Fig. 2. These light curves of Kepler's first five planet discoveries show not only drop in star brightness as the planet transits the star, but an indication of the planet's inclination--how far from the center the planet is passing across the star.
Credit: NASA/Kepler Mission
While Kepler has discovered many exoplanets, its search zone was very limited, scanning only in a very narrow part of the sky looking outward along the Orion Spur Arm of the Milky Way Galaxy (in the direction of the constellation Cygnus as viewed from Earth). Although Kepler’s search zone was so small, it still gathered an enormous amount of data -- as of 2015 gathering 12.5 billion brightness measurements on over 300,000 stars! With a volume this high the professional community has more data than people or computer time can fully assess in reasonable time frames. As a result of the massive amount of data, the public at large is assisting in the exoplanet hunting through the analysis of Kepler mission data on several websites, including www.planethunters.org, www.zooniverse.org/projects/ianc2/exoplanet-explorers, www.projectpanoptes.org, and www.diskdetective.org.
For the non-professional astronomy community however, is there any way outside of just data analysis to participate in the exiting realm of exoplanet measurement and discovery? While many amateur astronomers may think detecting transiting exoplanets around distant stars is only the stuff of professionals using state-of-the-art ground-based and space-based telescopes, the fact of the matter is that for those amateurs adept at imaging with their telescopes, detecting exoplanets is actually doable, and even with small aperture telescopes!
One such group of Virginia amateur astronomers have done just that by helping establish the exoplanet detection capable Mark Slade Remote Observatory (MSRO) in Wilderness, Virginia (readers can search @remotetelescope on Facebook to find the MRSO’s Facebook page). MSRO is now fully operational and open for use by local astronomers and members of the Rappahannock Astronomy Club (). Equipment for the observatory was donated by the estate of Mark Slade, Explore Scientific, LLC, the Rappahannock Astronomy Club, and donations from private individuals in the Fredericksburg, VA, region. The local astronomers responsible for establishing the observatory formed the MSRO Commission to oversee the building out of the observatory’s capabilities. These local astronomers include: Dr. Myron Wasiuta (Director MSRO; Optometrist), Jerry Hubbell (Assistant Director MSRO; Director Electrical Engineering, Explore Scientific, LLC), Dr. Bart Billard (Physicist), Linda Billard, Lauren Lennon (MSRO Staff Astronomer; Astrophysicist; Investment Analyst), and Scott Landsdale (President Rappahannock Astronomy Club).
The MSRO Commission began the design and construction for the observatory in November 2015. Just a few months later, in February 2016, the observatory completed commissioning and declared operational. While all the equipment was in place and operational, this by no means meant exoplanet detection could proceed. Instead, observatory users who wanted to do exoplanet transit imaging needed to take the time necessary to get their individual imaging skills honed for the process.
Fig. 3. The Mark Slade Remote Observatory (MSRO) in Wilderness, Virginia. Credit: William Paolini © 2018.
Generally, the process used for exoplanet detection at MSRO is very similar to any amateur astronomical imaging process:
· Acquire the raw frames
· Calibrate the frames by applying bias, dark and flat frames
· Perform aperture photometry procedure on each target and reference object in each frame (i.e., measure of star brightness subtracted from the brightness of the sky background around the star, then adjust that based on several reference stars in the frame).
Where special attention is needed however, is in the level of precision for the imaging. As these exoplanet hunters explained, after the equipment is in place and operational, the next step is to get it calibrated to perform transit imaging. It is further important that each person using the equipment hones their own individual knowledge and skills with the equipment. As MSRO’s Jerry Hubbell explains,
“The goal is understanding the impacts of each piece of equipment used, how it operates, and how it either adds to or detracts from the quality of your raw data. To get the best exoplanet transit data one really needs to maximize the performance of the mount system in tracking the object so that it keeps the light from the objects measured on the same pixels of the CCD for hours on end. The main factor in getting the appropriate precision for exoplanet measurements is to maximize the signal-to-noise-ratio. A signal-to-noise-ratio of at least 1000 to 2000 is required to get the shot or Poisson Noise precision (a statistical noise present in all radiation measurements that is independent of environmental errors) down to the milli-mag (1/1000 magnitude) level. Once that is done, then it’s time to deal with the scintillation precision and get that to the level you desire. Overall, the biggest challenge is to minimize the error in the measurement system while maximizing the signal to noise ratio. Key items for obtaining the best transit data include: consistently tracking the object, keeping the camera temperature stable to minimize the need for data corrections due to small temperature changes, and observing when the skies are cloud free and the seeing is as good as possible to minimize the need for de-trending the data for air mass changes.”
MSRO astronomers further explain that there are multiple levels of calibration one must perform when tuning any imaging system for exoplanet transits. There are of course the typical more “static” aspects of calibrating the system that are needed such as precise pointing and tracking accuracy. Further than that for successful exoplanet detection there are also critical “dynamic” data corrections necessary with every observing session. Some of these more dynamic corrections include: de-trending the data from the effects of air mass changes during each transit observation, and also correcting the data from each observing session for slight changes in the CCD temperature to name a few. Then during twilight, prior to the session, flat frame calibration must be done. Flat calibration is important because every pixel of your CCD has slightly different sensitivity. In addition to pixel sensitivity variation one also needs to account for current dust on the optics or on the CCD, vignetting, and any optical defects in the system. All this is done by normalizing the individual pixel response differences across a test frame. Less often one also needs to acquire calibration frames for the Dark and Bias correction. This is the digital “noise” from the amplifier circuits and noise from thermal increase of the CCD as it operate. These issues though are not typically impacted day to day since they are intrinsic to the camera and are fairly constant at a given temperature.
While all this sounds complicated, with practice they explain it really only takes about 15 minutes during twilight to gather these session-level calibrations, another 10 minutes or so slewing to and identifying the target, then the imaging schedule can be established and started. The imaging process typically runs for a few hours for an exoplanet transit conformation. During this time a meridian flip of the telescope may also be needed. If it is needed, the imaging stops during the flip, then it typically takes only about 5-10 minutes to get back on target to complete the transit imaging.
Fig. 4. Jerry Hubbell (left) and Dr. Myron Wasiuta inside the Mark Slade Remote Observatory (MSRO).
Credit: William Paolini © 2018.
As far as what equipment the MSRO Commission chose for exoplanet transit imaging, it is nothing exotic or prohibitively expensive, and typical equipment common to the amateur astronomy community. The MSRO is equipped with the following for exoplanet detection:
· 165 mm f/7 ED Apochromatic Explore Scientific carbon-fiber refractor with a 0.7x focal reducer/field flattener (effective f/4.9, 809 mm focal length),
· Losmandy G11 mount with the Explore Scientific PMC-Eight mount control system and an Explore Scientific Telescope Drive Master (TDM) drive correction system to provide precision tracking to less than 1 arc-second RMS,
· A GPS receiver and NMEATime software for precision time reference accurate to 10 ms when imaging minor planets,
· SBIG ST2000XM Monochrome CCD camera (1600×1200 7.4 micron pixels) with a plate scale of 1.88 arc-seconds/pixel and field of view of 50.2×37.7 arc-minutes,
· Newly Installed QHY174M-GPS Monochome CMOS camera (1920x1200 5.86 micron pixels) with a plate scale of 1.48 arc-seconds/pixel and field of view of 48 x 30 arc-minutes (this has replaced the SBIG camera as the primary camera),
· An integrated filter wheel with red, V-band, blue, and luminance filters for imaging and photometric measurements,
· A 200 line-per-millimeter spectroscopic grating with an effective resolution of about 13 angstroms/pixels,
· MaximDL software (to calibrate the images) and AstroImageJ software (to measure and plot the resulting photometric measurements)
With this equipment, the observatory can detect minor planets and stars as dim as magnitude 18, and their astrometric measurements are possible with a typical error of 0.15 arc-seconds. Their first observation and detection using the MSRO was exoplanet HAT-P-30/WASP-51 b. They imaged the exoplanet transit on January 6, 2018 and submitted their data to the Exoplanet Transit Database (ETD) the following week. Their data is now available to all exoplanet researchers, both professional and amateur. Their final light curve data is shown in Figure 5.
Fig. 5. MSRO transit curve data on exoplanet HAT-P-30/WASP-51 b. Credit: Barton Billard and Jerry Hubbell.
For anyone interested in tuning their existing imaging system for exoplanet transit research, or building a system from scratch, there are several good resources available. Bruce L. Gary produced a wonderfully detailed 162 page PDF resource called “EXOPLANET OBSERVING FOR AMATEURS”. It is free for download at: . As Bruce Gary explains, exoplanet transits have been observed even with small 4” telescopes. However, he recommends a minimum beginner setup be more along the lines of a 10” or 11” SCT with polar mounting, a monochrome 16-bit CCD with color filters, and a good CCD with Maxim DL astronomical imaging software suite. For as little as around $5000 and the dedication to honing one’s skills at precision imaging, the amateur astronomer can contribute to the exciting realm of exoplanet research.
A second excellent resource to the community is the internet portal of Czech Variable Star advanced amateur and professional astronomers founded in 1924 - (note - each page of the site conveniently has a British flag to have it displayed in English). Their Project TRESCA (TRansiting ExoplanetS and CAndidates) section is devoted to exoplanet transits and there they maintain the transit data for more than 300 known transiting exoplanets. The first exoplanet transit light curve at MSRO by Barton Billard and Jerry Hubbell can be found here as well: .
Fig. 6. Jerry Hubbell in the MSRO reviewing transit curve data they detected
and published on exoplanet HAT-P-30/WASP-51 b. Credit: William Paolini © 2018.
Future transit plans by the group at MSRO include collaborating with Denis Conti, Exoplanet Coordinator for the American Association of Variable Star Observers’ (AAVSO). They are working on new instruments and techniques to obtain higher resolution photometry with smaller instruments. Why is this important? So amateurs can provide critical follow-up observations for the professional observations from the new Transiting Exoplanet Survey Satellite (TESS), launched April 18, 2018. TESS’s two-year all-sky survey will focus on nearby G, K, and M type stars, including the 1,000 closest red dwarfs in an area 400 times larger than that covered by the Kepler mission. TESS will also provide prime targets for more detailed investigation with the James Webb Space Telescope (JWST) and other large ground-based and space-based telescopes. TESS’s system has a 20 arcsec/pixel resolution whereas ground instruments like MSRO have a 1.4 arcsec/pixel resolution. Follow-up readings for TESS from ground-based instrumentation like MSRO is therefore vital to increase confidence that any light curve changes in TESS’s data are not due to background stars in its resolution field. Exoplanet research has therefore opened a new area where professional-amateur collaboration is not only desired, but can be critically supportive.
For those amateurs that want to venture out into the exciting realm of exoplanet transit imaging, some of the rewards the MRSO exoplanet hunters tell us you will encounter are:
· The thrill of being able to verify what other professional astronomers have been observing
· Being able to develop and build a system that can operate at a professional level even though it is modest instrumentation
· Becoming skilled in using the same techniques to the same precision level that professionals are using today with much more expensive equipment
· Knowing that you have a verified system that can put to effective operational use in doing both science and in training amateur astronomers.
· As an individual being able to "see" for yourself there is scientific evidence of planets orbiting other stars and being able to continue to make and contribute scientific measurements without needing sponsorship or as some part of a “job”.
When I asked the Rappahannock exoplanet hunters what’s the one thing they would most want to communicate to the other amateur astronomers who have an interest in exoplanet transit observing, Jerry Hubbell responded eloquently saying,
“I want everyone to understand that this work can and is being done by dedicated amateur astronomers across the globe and that you can do it also if you task yourself with obtaining the skills and knowledge about the equipment available and needed to do this work. You can do real, valuable science that even the professional astronomers do not have the opportunity to do on a day-to-day basis. I would not call ourselves amateurs even though we pursue this love of ours, we are all astronomers, so that is what you should refer to yourself as... an astronomer.”
For those readers interested in learning more about how to get started in exoplanet transit imaging and research contribution, please don’t hesitate to contact Jerry Hubbell at . To discover more about the Mark Slade Remote Observatory, search @remotetelescope on Facebook to find the MRSO’s Facebook page.
This article is placed into the Public Domain by William Paolini 2018.
Author images © William Paolini 2018. Contact firstname.lastname@example.org.
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