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 , is referred to as the Winking Demon due to its varying 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 , 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 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 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 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. evening February 28 to the morning of February 29. Reduction and analysis of raw images was ac- The minimum of the eclipse was scheduled for 01:46 complished through the use of RSpec v1.5. The li- on February 29, which meant the eclipse would begin brary of reference spectra for B8V and K0IV stars at 20:46. The first image was taken at 20:00 then included in Rspec 1.5 was used as a calibration and further images were taken at 15 minute intervals. analysis tool throughout the research process. Adobe This allowed for a couple images outside of the Photoshop CS5 was used as an aid in the analysis of eclipse to be considered as a baseline image. changing spectral features as the eclipse cycle pro- February 28-29 had been chosen for its ideal gressed. time frame. The eclipse would begin shortly after sunset and finish approximately at sunrise. However, 3. Observations at the beginning of the eclipse cycle, the star was almost directly overhead. Therefore, due to the star’s 3.1 Observation Procedure movement across the sky, the images became unclear as the star approached the horizon. Images were cap- Imaging of the eclipse cycle was broken into two tured until 23:30, approximately 30% completion of segments due to the Algol system setting on the hori- the eclipse. The star was no longer within view after zon during the latter portion of the eclipse cycle. The 23:37. first imaging session took place on 2012 February 28. The second imaging session took place on 2012 3.3 Observing Session 2 March 2 with the third and final imaging session tak- ing place on 2012 March 3. To continue with the eclipse cycle, another night of observation would be required. The evening of March 2 to the morning of March 3 was chosen be- cause the minimum would be at 22:36. The eclipse would begin at 17:36, but by the time images could be captured, beginning at 19:30, the star would be at approximately 25% completion. This allowed for overlap with the previous session of observation. In the hopes of keeping view of the star system for a longer time frame, the location had been changed from Litchfield Park to Buckeye, in order to lower light pollution and the number of ground level obstructions. Images were collected through the minimum and until 00:30, approximately 70% com- Figure 8. Laptop image of spectrum of Algol pletion of the eclipse cycle.

The telescope was set to track on the Algol sys- 3.4 Observing Session 3 tem, and the CCD camera mounted on the view- piece; the CCD camera was connected to its accom- Observation 3 was conducted outside of the pri- panying computer software, which was used to set mary eclipse, in order to establish a set of data image parameters and capture images. Images were against which spectra changes during the primary taken at 15 minute intervals, beginning immediately eclipse could be compared to. Observations were before Algol B began its eclipse of Algol A, and end- undertaken at the original Litchfield Park location, ing directly after the conclusion of the eclipse cycle. initiating at 19:45 on March 3rd and ending at 22:15 Images were taken through the use of the CCD cam- the same night. era and diffraction filter described above. The Images were saved as FTS files and analyzed in their raw format with the RSpec computer program. 4. Data Collection and Reduction

4.1 Measurement Data

During observing sessions, imagery was cap- tured at 15 minute intervals on the quarter hour. Each

124 Algol Spectroscopy – Boyd et al. set of observation data was archived in separate fold- ers that were organized according to date of observa- tion. The raw profile line image is shown in Figure 12. During the early part of the observing run, the line profile was relatively clean, but as Algol began to approach the horizon, atmospheric extinction be- gan to take its toll: the line profile became very noisy, as shown in Figure 10. Figure 11. Instrumented corrected profile on February 28 at 22:00, includes Hydrogen Balmer lines.

5.2 Analysis Observing Session 2 (Mar 2)

Data from observing session 2 consists of 49 in- dividual profiles spanning the time from 20:00 until 00:15. In order to validate the quality of the data be- ing collected, the response curve during the same portion of the eclipse cycle for observing session 1 and 2 were compared. As shown in Figure

5.3 Analysis Observing Session 3 (Mar 3)

Data from observing session 3 consists of 11 in-

Figure 9. Algol line profile during early part of observing dividual profiles spanning the time from 19:45 until session. 22:15. This observing run was conducted to obtain additional baseline data outside of the eclipse cycle.

5.4 Summary Analysis of Eclipse

To establish a baseline of instrumentation stabil- ity throughout the eclipse, two profiles were taken at the same time within the eclipse cycle. The first pro- file was from February 28 and the second one was from March 2 at 25% completion within the eclipse cycle. As shown in Figure 12, the profiles from both lines align, establishing stability within the data col- lection between the two separate nights

Figure 10. Algol profile during latter part of observing session. The data reduction process consisted of review- ing the quality of the line profiles and producing in- strument response curves for all good profiles. Figure 12. Line profiles from March 2 at 20:00 and Feb- 5. Data Analysis ruary 28 at 11:15: 25% completion of the eclipse cycle.

5.1 Analysis of Observing Session 1 A comparison of line profiles covering the pre- (Feb 28) eclipse from observing session 1 with line profiles during the first quarter, last quarter from sessions 1 and 2, and from outside the eclipse from session 3 Data from observing session 1 consists of 17 in- shows the changes in the Hydrogen Alpha, Beta, dividual profiles spanning the time from 20:00 until Gamma and Delta absorption lines as shown in Table 23:30. The Hydrogen Balmer absorption lines were I and Figures 13, 14, 15, and 16 respectively. the primary focus of the analysis.

125 Algol Spectroscopy – Boyd et al.

Table I. Measurement Data Spreadsheet.

Figure 16. Hydrogen Delta.

6. Conclusion

Variations in spectral features at this point may be attributed to several possible factors, which are currently under further investigation. Additional data and updated conclusions are available upon request. Throughout the data analysis process, student Figure 13. Hydrogen Alpha. familiarity with the RSpec program and associated equipment has increased to a point which will allow for more thorough and complex research initiatives in the future. Using the data of this paper as a launching point for future lines of inquiry, EMCC special pro- jects courses may be able to contribute to the current available body of data on the Algol system in a sig- nificant way.

7. Acknowledgments

The authors thank Tom Fields for his guidance and assistance with the use and acquisition of the RSpec program; to Doug Walker for the use of his equip-

ment, expertise, and guidance. A very special thanks Figure 14. Hydrogen Beta. goes to Jeff Hopkins of the Hopkins Phoenix Obser- vatory for his guidance and assistance at every step of the way. Finally, we thank the Estrella Mountain Community College administration for their enthusi- astic support.

8. References

Rspec reference libraries

NASA.gov

The SAO/NASA Astrophysics Data System

Figure 15. Hydrogen Gamma. Sky and Telescope Magazine star charts

126