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Astrometric Study of Binary Systems and Photometric ASTROMETRIC STUDY OF BINARY SYSTEMS AND PHOTOMETRIC STUDY OF A VARIABLE STAR by Tyce Olaveson A senior thesis submitted to the faculty of Brigham Young University - Idaho in partial fulfillment of the requirements for the degree of Bachelor of Science Department of Physics Brigham Young University - Idaho April 2021 Copyright c 2021 Tyce Olaveson All Rights Reserved BRIGHAM YOUNG UNIVERSITY - IDAHO DEPARTMENT APPROVAL of a senior thesis submitted by Tyce Olaveson This thesis has been reviewed by the research advisor, research coordinator, and department chair and has been found to be satisfactory. Date Stephen McNeil, Advisor Date Lance Nelson, Committee Member Date Brian Tonks, Committee Member Date R. Todd Lines, Chair ABSTRACT ASTROMETRIC STUDY OF BINARY SYSTEMS AND PHOTOMETRIC STUDY OF A VARIABLE STAR Tyce Olaveson Department of Physics and Astronomy Bachelor of Science My senior research gave me opportunities to complete two astronomy based projects. During each of these I proposed an object of study and presented my findings. The first of these projects is focused on binary stars and studies the separation distance and position angle of two star systems. The system with a primary star at RA 11 : 06 : 30:6 DEC −46 : 10 : 28:97 is determined to have position angle of 154o and separation distance of 7:00 arcsec. This system is possibly a binary star and a minimum orbit is calculated. The second system has primary star at RA 11 : 06 : 34:7 DEC −46 : 11 : 55:3, its position angle is measured as 72:67o and separation distance is 11:08 arcsec. GAIA data suggests that this system is likely not a physical binary. The second project is devoted to the variable star V0893 Her. The star is observed in the B, v i and z filters and light curves are generated for each filter. From these curves, we calculate period information and used these to determine the theoretical absolute magnitude in each filter. The period is calculated as 0:495 ± 0:036 days. The distance to the star is calculated as 501 ± 24 parsecs, which is significantly different from the GAIA spacecraft mission. We conclude that our data was not as clean as we would have hoped, possibly due to the binary nature of the system or some other factors at play. ACKNOWLEDGMENTS I would like to thank Dr. McNeil for giving me direction and helping me complete this research. I would also like to thank Rachel Freed at InStAR for providing the resources and opportunity to complete the binary star project as well as Michael Fitzgerald at Our Solar Siblings for help working through the variable star project. I would also like to acknowledge my group members: Roberta Bonnell, Jakob Bergstedt and Dallin Fisher all made considerate con- tributions to the binary star project. My group members for the variable star project were Amber Mistry, Dr. McNeil and Rachel Freed and they helped complete the project. Lastly I would like to thank my wife Rebecca for sup- porting and encouraging me through this entire processes. Contents Table of Contents vii List of Figures viii 1 An Overview1 1.1 Binary Stars................................1 1.2 Variable Stars...............................3 2 Binary Stars5 2.1 Introduction................................5 2.2 Methods and Procedure.........................6 2.3 Results and Analysis...........................9 2.4 Discussion................................. 14 3 Variable Stars 15 3.1 Introduction................................ 15 3.2 Methods and Procedures......................... 17 3.3 Results and Analysis........................... 20 3.4 Discussion................................. 22 4 Conclusion 25 4.1 Challenges is all things.......................... 25 4.2 Future Rewards.............................. 26 Bibliography 27 vii List of Figures 2.1 Image of Double 1 taken from the Siding Spring Observatory on May 28 2020, boxed in red. The Siding Spring Observatory is located in Australia and is part of the LCO global telescope network.......8 2.2 Image of Double 2 taken from the Siding Spring Observatory on May 28 2020, boxed in red...........................9 2.3 An example of using AstroImageJ to take measurements of Double 1. 10 2.4 The HR diagram we plotted on. We can see that the stars in Double 1 are both main sequence, whereas those of Double 2 are more likely on the giant branch............................ 10 3.1 An example of a light curve for an RRab vairable star [1]........ 16 3.2 An image of V0893 Her taken from the Aladin stargazing software.. 18 3.3 An image of V0893 Her taken in the z filter from our cadence..... 18 3.4 Light curve in the i filter using the String Test to calculate the period and sex photometry............................ 22 3.5 Light curve in the V filter using String Test to calculate the period and apt photometry.............................. 22 3.6 Light curve in the z filter using String Test to calculate the period and apt photometry.............................. 22 3.7 Light curve generated with information from data collected by Hipparcos 23 3.8 An image of the V0893 Her system exhibiting its binary nature.... 23 viii Chapter 1 An Overview During the summer of 2020 and amid the swing of Covid-19, I participated in two research projects. In each of these projects I experienced the entire research process, from proposing a project to writing a paper and presenting my results at a conference. This thesis will go through the details of each project including the conclusions and future prospects for each. 1.1 Binary Stars The first project is devoted to Binary Stars and is part of the larger effort designed to provide research opportunities for undergraduate students. This program is provided through InStAR [2] and was overseen by Rachel Freed who currently runs the orga- nization. A Binary star system consists of two or more stars that are gravitationally bound together into an orbit and have long been of interest to astronomers. Because we cannot go visit these stars personally (for obvious reasons) we must observe them through our earthly telescopes and make due with what light can tell us. We can learn a lot from light; however, our two dimensional images can lead to some incorrect 1 1.1 Binary Stars 2 conclusions at times. As astronomers, we are only able to see stars in a two dimensional plane. The fact that not all stars have the same luminosity can make it challenging to determine dis- tance just by looking at an image of a star field. To compensate for this, astronomers define two categories of binary stars: optical doubles and physical binaries. Optical doubles are binary stars that appear to be in close proximity, but are not in reality. We often see optical doubles within constellations, where stars appear to be next to each other but are in fact separated by millions of light years of empty space. Quick identification of these types of stars are done through parallax angles. The parallax angle of a star is determined by its change in angular position when seen from differ- ent positions and can be used to calculate the distances to nearby stars. When the parallax angle of stars are similar, it is indicative of stars in close proximity, when the parallax angles are significantly different we can know that the stars are not near each other. Systems without similar parallax angles are not true binary stars since they are not in close physical proximity. Of the two, physical binaries are the most interesting. These are stars that are gravitationally bound together and what is most commonly known as a binary star. From these stars, astronomers can use Keplers equations of orbits to determine masses of stars. Sometimes, there are binary stars that fall into neither category and are thus, undetermined. In these cases we begin to calculate potential orbits of the two stars by measuring their positions over hundreds of years. To keep track of all of these stars, the Washington Double Star Catalog (WDS) keeps a database of millions of documented double stars as well as relevant information about their positions. In my research, I find two double star systems that are not included in the WDS and take observations of them to find their classification. The first of these systems is likely an optical double since the parallaxes of the two stars 1.2 Variable Stars 3 do not show significant overlap. The second of these systems shows more promise. I measure the positions of these stars and calculate a minimum orbit for the star using Keplers laws. In the end, this research will most likely benefit future generations of astronomers. Since we can neither prove nor disprove something with a single measurement, future observers will be able to draw upon my contribution and use this data to make a definite decision. 1.2 Variable Stars The second of these projects involves Variable Stars. This research is also part of a larger project organized and directed by Michael Fitzgerald at Our Solar Siblings [3]. Variables are stars that vary in magnitude (relative brightness of a star) in a predictable and oscillatory fashion. For some types of variable stars (like Cepheid and RR Lyrae variables) astronomers have created empirical and theoretical formulas that can relate the period of a star's oscillation to its absolute magnitude, making some variable stars reliable standards for measuring distances. Of course, we can't expect these equations to be exact or perfect, and for this reason the organization Our Solar Siblings has designed this research project to improve these derived formulas by taking into account other stellar properties such as metallicity. Unlike binary stars, variable stars require much more attention to get decent information. Since the star oscillates in magnitude, we must observe it over a period of time.
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