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Observing Double Stars – Genet Et Al Observing Double Stars – Genet et al. Observing Double Stars Russell M. Genet California Polytechnic State University and Cuesta College 4995 Santa Margarita Lake Road, Santa Margarita, CA 93453 [email protected] B.J. Fulton, Federica B. Bianco, John Martinez Las Cumbres Observatory Global Telescope 6740B Cortona Drive, Ste. 102, Goleta, CA 93177 [email protected], [email protected], [email protected] John Baxter, Mark Brewer, Joseph Carro, Sarah Collins, Chris Estrada, Jolyon Johnson, Akash Salam, Vera Wallen, Naomi Warren Cuesta Community College, Highway 1, San Luis Obispo, CA 93403 [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected], [email protected] Thomas C. Smith Dark Ridge Observatory, 701 NM Highway 24, Weed, NM 88354 [email protected] James D. Armstrong University of Hawaii, Institute for Astronomy, and Las Cumbres Observatory Global Telescope 34 Ohiaku Street, Makawao, Maui, Hawaii 96768 [email protected] Steve McGaughey Haleakala Amateur Astronomers, 5 Kamauhalii Way, #3-A, Wailuku, Maui, HI 96793 [email protected] John Pye University of Hawaii Maui College, 310 W. Ka’ahamanu Ave., Kahului, HI 96732 [email protected] Kakkala Mohanan, Rebecca Church University of Hawaii, Leeward Community College, 96-045 Ala Ike St., Pearl City, HI 96782 [email protected], [email protected] Abstract Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitation- ally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determina- tion of stellar masses. Double star observations have been a prolific field, with observations and discoveries— often made by students and amateurs—routinely published in a number of specialized journals such as the Jour- nal of Double Star Observations. All published double star observations from Herschel’s to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published “hands-on” student science education, and CCD observations of both bright and very faint doubles. The other two are recent tech- nologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read 147 Observing Double Stars – Genet et al. out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limi- tations to be overcome so very close doubles can be accurately measured. 1. Introduction 2. Early Double Star Observations Observing double stars has engaged generations Galileo thought that the sun was the center of the of student, amateur, and professional astronomers for universe and stars were just points of light on a the better part of three centuries. Over 100,000 dou- nearby sphere. For those, contrary to Galileo, who ble stars have been discovered. As each year goes by, thought stars were distant suns, he suggested they new doubles are discovered and the observations of should look for and observe close double stars—one already known doubles continue to accumulate. bright and one faint that happened, by chance, to ap- A wide range of telescopes, instruments, and pear close together along the line-of-sight from Earth. techniques are currently used to measure the separa- If the bright star was nearby and the faint one far tions and position angles of double stars. Telescopes away, then the nearby bright star should shift its posi- range from a 3-inch Tasco refractor equipped with a tion with respect to the faint star over a six month $150 astrometric eyepiece observing relatively wide period due to the rotation of the Earth around the sun optical doubles (Grisham et al., 2008) to a 10-meter (parallax). Keck reflector with adaptive optics/laser guide star Following up on Galileo’s suggestion, William observing very close late-M binaries (Dupuy et al., Herschel began measurements of the separation of 2012). Instruments include visual eyepieces and filar position angles and separation of double stars in ear- micrometers, regular CCD cameras, and fast, low nest in 1779. Three years later he reported his obser- noise EMCCD frame transfer cameras. Advanced vations of 269 binaries to the Royal Society techniques include blind or other deconvolution (Herschel 1782). Continued observations led, a cou- strategies, lucky imaging, and speckle interferometry. ple of decades later, to the somewhat unexpected Although beyond the scope of this paper, the ab- conclusion by Herschel (1803) that many double stars solute cutting edge with respect to close separation were gravitationally bound binaries. Interestingly, (and hence short binary periods) is amplitude inter- John Michel (1767) had earlier reported to the Royal ferometry arrays such as the Center for High Angular Society that, based on a statistical analysis of a few Resolution Array (CHARA) on Mt. Wilson (McAl- bright visual double stars, he had concluded they ister 1999). Six 1-meter telescopes in a “Y” configu- occurred at a higher frequency than one would expect ration interferometer provide milli-arcsecond resolu- due to chance alignment alone and hence were tion allowing binaries with orbital periods of just a probably truly gravitationally bound stars. It is day to be observed. In this paper we will, after a brief probably a good thing that Herschel was unaware of history of double star observations, describe two Michel’s paper or he might not have initiated his spreadsheets we have developed to aid us in selecting search for and a measurement of double stars, as his doubles for observation. We will then describe both goal was determining parallaxes. visual and CCD observations we make with students that have both scientific and educational goals. Fi- nally, we will describe two advanced techniques we are exploring—lucky imaging and speckle interfer- ometry—to aid us in observing close double stars. Our observations were made on 8- to 32-inch tele- scopes in California, and 9-inch to 2- meter tele- scopes in Hawaii. Most of the coauthors of this paper will be giv- ing talks at the Maui International Double Star Con- ference in February 2013. In many cases they will be meeting each other for the first time, and will also be meeting other double star observers from around the planet. For details on this conference see www.AltAzInitiative.org. Figure 1. William Herschel’s 20-foot telescope was relo- cated to Table Mountain near Cape Town, South Africa, where his son John observed double stars in the south- ern skies. 148 Observing Double Stars – Genet et al. In the mid 1800’s, while he was director of the SAO and other identifiers, number of past observa- Dorpat Observatory in what was then Livonia, Frie- tions, etc., was not included. Increasingly sophisti- drich Georg Wilhelm von Struve made micrometric cated students would prefer to use their laptops to measurements of 2,714 double stars from 1824 to help them sort and select potential doubles for obser- 1837 and published these in his work Stellarum du- vation, while SAO or other identifiers are handy for plicium et multiplicium mensurae micrometricae. entry into today’s computerized telescopes. F.G.F. von Struve’s son, Otto Wilhelm von Struve, Joseph Carro has prepared a spreadsheet catalog (1897-1963), continued his father’s work using a 15- of 3,950 double stars that is ideal for student use. inch refractor at the Pulkovo Observatory near St. Carro incorporated information from SIMBAD—the Petersburg, cataloging several thousand double stars. astronomical data base operated at the CDS in Stras- Another notable double star observer was Robert bourg, France—into a series of Microsoft Excel Innes at the Meteorological Observatory in Johan- spread sheets that facilitate sorting and selecting dou- nesburg, South Africa. He compiled in 1927 The bles for study. The spreadsheets are arranged by con- Southern Double Star Catalog consisting of 1,600 stellation, and include star names, common identifi- entries. Robert Aitken, with the help of collaborator ers, and details on each double star. Summary tables W.J. Hussey, published in 1932 the New General of all 3,950 stars are sorted in various ways as a con- Catalogue of Double Stars within 120° of the North venience for the user. A diagram showing the major Pole consisting of 17,180 doubles. The Lick Obser- stars of each constellation is provided. Using the star vatory at Mount Hamilton near San Jose, CA, pub- name as the key, a hyperlink to SIMBAD allows ad- lished the 1963 Index Catalog of Visual Double ditional information, such as parallax, to be conven- Stars, containing 64,250 objects covering the entire iently obtained. Carro’s catalog can be accessed at sky. In 1965 it was transferred to the United States www.AltAzInitiative.org, or you can contact him at Naval Observatory as the Washington Double Star [email protected]. Carro is expanding his catalog to Catalog (WDS) which now contains over 100,000 include additional double stars and further informa- double stars. tion. Observations of the double star Zeta Ursae Ma- To select doubles for advanced projects, such as joris were indirectly used by Savary (1827) to obtain multiple stars across many constellations, faint dou- an orbital solution, while a solution directly using all ble stars, etc., it is helpful to have a way to choose the observations was provided shortly thereafter by them quickly and easily.
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