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Spectroscopic Analysis of Algol During Eclipse Cycle

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Spectroscopic Analysis of Algol During Eclipse Cycle Algol Spectroscopy – Boyd et al. Spectroscopic Analysis of Algol during Eclipse Cycle Jonathan Boyd, Kodiak Darling, Elise Sparks, Lajeana West Students Estrella Mountain Community College, Phoenix, Arizona Douglas Walker Adjunct Faculty Estrella Mountain Community College, Phoenix, Arizona [email protected] Abstract Algol, within the Perseus constellation, is referred to as the Winking Demon Star due to its varying apparent magnitude and its representation of the Gorgon Medusa. Every 68.75 hours its light dims suddenly, and bright- ens again over a ten-hour period. Further observation shows a small dip in light output halfway in between the large dips, indicating that Algol is an eclipsing binary star system. Detailed inspection of the spectrum indicates that Algol is also a spectroscopic binary. Algol consists of a 3 solar diameter B8V star and a 3.5 solar diameter K0IV in very close orbit around each other. This project investigated the spectral characteristics of Algol A and B during the primary eclipse cycle. Low-resolution spectroscopy of the eclipse cycle was imaged over several nights in order to investigate any changes in the emission line profile of the star system. This work lays the foun- dation for future studies in low-resolution spectroscopy of the Algol and Algol-type systems. 1. Introduction 1.2 Special Projects Course Structure 1.1 Background Estrella Mountain Community College is part of the Maricopa County Community College System. Since the fall of 2010, Estrella Mountain Com- This system consists of ten colleges, two skill cen- munity College (EMCC) has offered a series of spe- ters. and numerous education centers, all dedicated to cial mathematics project courses focused on applied educational excellence, and to meeting the needs of research for the undergraduate student. The first se- businesses and the citizens of Maricopa County. Each ries of courses, offered in the fall 2010 and spring college is individually accredited, yet part of a larger 2011 semesters, engaged the students in observing system – the Maricopa County Community College and recording visual measurements of double stars, District, which is one of the largest providers of selected from the US Naval Observatory maintained higher education in the United States. Washington Double Star Catalog. This research ori- EMCC’s special mathematics course, designated ented course was extended in the fall 2011 semester, MAT298AC, is a student driven research course fo- in a learning community which combined an intro- cused on the application of learned techniques in the ductory astronomy course with the special mathemat- fields of astronomy, applied mathematics, and statis- ics projects course. This approach was intended to tics. Students study with a large array of goals in extend the student’s exposure to observational as- mind; a common goal amongst the student body is to tronomy and data collection and analysis. The suc- gain the knowledge necessary for work in a gamut of cess of this sequence resulted in a special astronomy fields and professions. MAT298AC offered a unique projects course being offered for spring 2012, focus- opportunity within this environment to gain a particu- ing on spectroscopy. The objective of this course was larly advantageous amount of experience in primary to introduce the student to spectroscopy and its appli- research and data analysis. The class, having been cations to stellar observation and analysis. The intent reclassified as AST298A, now has a greater focus on of this course offering was to give students the oppor- the techniques and skills needed for astronomy spe- tunity to conduct original astronomical research with cific activities. At the start of the semester the class the application of mathematics to data collections and had a wide variety of possible research projects to analysis. choose from, each with its own unique obstacles and avenues of experience. The field of study chosen, spectroscopic analysis of the Algol system during its primary eclipse, was both within the capabilities of EMCC equipment and the classes' experience in the 121 Algol Spectroscopy – Boyd et al. astronomical sciences. This study resumes work in difficulty of resolving Algol C as an individual star, it the field of binary star research, further augmenting is often overlooked and incorporated with light emit- EMCC's fledgling contributions to this field. With ted from Algol B. this in mind, the students of AST298A began their research project with the following objectives: • to gain further knowledge of the nature of the in- dividual stars within the Algol system • to use the knowledge gained to make inferences about the Algol system • to provide data for more accurate models of bi- nary stars Figure 1. Diagram of Algol’s eclipse cycle. • to establish a foundation for further Algol re- search 2. Equipment & Resources • to expand upon individual knowledge of research processes and analysis 2.1 Telescope • to provide an avenue for the students to attempt Equipment for observing sessions consisted of a publication of their work in a recognized journal Celestron 11-inch Schmidt-Cassegrain telescope with a 2800mm focal length. The telescope was used in 1.3 Algol System conjunction with a Meade DSIPro CCD camera fitted with a diffraction grating to image the Algol system. Algol, also known as Beta Persei, is the most The telescope was kept on target through the use of a famous eclipsing binary star system, because it can heavy-duty (CG-5GT) computerized German Equato- be distinguished with the naked eye. It is found in the rial Mount. constellation of Perseus, named for the ancient hero The Celestron 11-inch Schmidt-Cassegrain tele- who killed the gorgon Medusa. Because of the stars’ scope is equipped on a mobile tripod base which dramatic eclipse cycle and the star's position on the made transport to and from a remote location observ- disembodied “head” of Medusa, it has been nick- ing site relatively quick and easy. named the Winking Demon star. Algol is an eclipsing trinary star system, deter- mined to be 93 light years from Sol. It is one of the first eclipsing variable stars to ever be discovered. The main star (Algol A) is a spectral class B8V main sequence star with a mass 3.5 times greater, a diame- ter 3 times greater, and an absolute brightness 100 times brighter than our Sun. The secondary star (Al- gol B) is a spectral class K2IV type subgiant that measures about 0.8 solar masses, 3.5 solar diameters, and an absolute brightness 3 times brighter than our Sun. Algol A and B are a close binary pair, about 8 solar diameters apart, with a period of 2.87 days. The primary eclipse happens when the less massive Algol B passes in front of the more massive Algol A. The Figure 2. Celestron Schmidt-Cassegrain telescope and eclipse cycle lasts for a period of about 10 hours. At student, Jonathan Boyd. the eclipse's minima, the luminosity changes from an apparent magnitude of 2.1 to an apparent magnitude 2.2 Star Analyzer of 3.4. There is a faint third star (Algol C) in the Al- gol system, which is a spectral class F1 main se- The Paton Hawksley Star Analyser 100 was used quence star. Algol C measures 1.7 solar masses, with to provide the spectra of the Algol system. The Star a diameter slightly smaller than our Sun and an abso- Analyser 100 was designed specifically for amateur lute brightness of about 4 times that of our Sun. Algol astronomical spectroscopy. It can be mounted on the C orbits the inner two stars at a distance of about 2.69 telescope similarly to other 1.25-inch filters and will AU with a period of about 1.86 years. Due to the 122 Algol Spectroscopy – Boyd et al. work with most cameras. It can image dim objects line profiles, for identifying the compounds that cor- and display the zero-order (star) along with the spec- respond to the spectral features within the calibrated trum. This makes it easy for spectra to be calculated. graph. The Star Analyser was mounted on the end of the CCD camera. Figure 5. Screenshot of RSpec software in use. 2.5 Observing Site Figure 3 Hawksley Star Analyser 100 2.3 Meade DSIpro CCD Camera The Meade DSIpro CCD camera is designed to help novice and amateur astronomers capture the images of a variety of objects throughout the night sky. By attaching the Star Analyser to the camera, the spectral images created were captured for later analy- sis. Figure 6. Student Jonathan Boyd, guest Melissa Boyd, and instructor Doug Walker at Litchfield Park location. Figure 4. Meade DSIpro CCD Camera 2.4 RSpec Real-Time Spectroscopy Software RSpec is a new form of software that allows as- Figure 7. Students Elise Sparks, Lajeana West, and Ko- tronomers to take raw spectrum images and create a diak Darling at Buckeye location. calibrated profile in real time. The software allows the user to analyze the composition of various stellar Observations were taken at two separate coordi- objects ranging from stars, to nebula emission lines, nates. The first quarter of the eclipse cycle was im- to detecting the red shift of a receding quasar. It also aged at 33.503049° N, 112.363466° W, in Litchfield provides a library of reference series including pro- Park, Arizona, with medium levels of light pollution. files for all star spectral types and a small variety of The other part of the eclipse cycle was imaged at 123 Algol Spectroscopy – Boyd et al. 33.365849° N, 112.577612° W in Buckeye Arizona, 3.2 Observing Session 1 with low levels of light pollution. Ambient tempera- ture at ground level was between 14-25 degrees Cel- The first night of observation encompassed the sius.
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