Delora Chere’ Tanner and Dr. Benjamin Taylor, Physics and Astronomy
Unlike research in many other disciplines, astronomical research is highly dependent upon the weather. My original proposed research was to further the task of calibrating standard stars in the M67 open cluster. Unfortunately the weather was unfavorable during the window of time that this cluster was available for viewing, therefore, I could not secure the amount of data needed to conduct my proposed research. I decided to change the focus of my research to an individual star located in M67, AH Cancri. I was able to use raw archive data of the M67 star field to study this star.
AH Cancri is a faint eclipsing binary star of the WUma type located in the M67 open cluster amongst hundreds of other stars. The purpose of this study is to gain information about and obtain new light curves for AH Cancri. Known data was collected from published journal articles. The archive data used was originally obtained for use in the calibration of standard stars in the M67 cluster. It is three nights of data that were obtained by Professor M. Joner using the Burrell Smidt telescope at the Kitt Peak National observatory in February 1992. Although U, B, V, and R filter exposures were taken, this study has only made use of the V filter exposures.
Due to the fact that the majority of stars are in binary systems, the study of binary systems is crucial to gaining an understanding of the dynamics, evolution and formation of all stars. How stars were formed and how they are evolving is of great interest in astronomy. The large time scale of the lifetime of a star in relation to the lifetime of mankind makes it difficult for mankind to study the lives of stars. Most stars will remain in about the same stage throughout one’s lifetime. The study of the lives of stars then must be extended to the many different stars in different stages of life. Stars that appear to be in similar stages are grouped into types. For example AH Cancri is a W UMa type eclipsing binary. The study of these types of stars is used to understand the physical processes involved in their particular stage of life. In addition, various approximations can be made about the stages preceding and following this stage. The results can then be added to the many studies of other types of stars in different stages. The combination of all these studies provides valuable information about the formation and evolution of all kinds of stars.
Eclipsing binaries are of great interest because they are aligned such that we can see the changes caused by their mutual revolution. These changes can be illustrated on and analyzed from a light curve of the binary system. A light curve is a plot of the binary system’s magnitude as a function of time. A great amount of information can be gained from these studies, such as, the masses, radii and velocities of stars. In fact there is no practical, direct way to measure the mass of a single star so binary systems must be studied in order to gain information about the masses of stars. 1 An important aspect of a light curve used to determine this information is the period of the curve.
Determining an accurate period is crucial and, in the case of AH Cancri, is also difficult. This difficulty arises due to the faintness and location of this system. The known data for this system was obtained when the techniques used to reduce and analyze data were not as advanced as what is available today. Thus, the accuracy of the data obtained and the results are questionable. This study used modern IRAF reduction software to obtain a new light curve for AH Cancri and compared it to one from an article published in 1979. 2 The purpose being to find if a more accurate light curve, period and general information could be obtained for this star.
The old and new light curves are shown below. Due to the small amount of data available, the new light curve is of the same quality as the old. Yet, the advanced technology used to produce the new light curve definitely made data reduction and presentation easier and faster. The data was easily fitted to the period and could be tested and changed with only a few keystrokes. The period could not be obtained to a greater accuracy with this limited amount of data but I conclude that it can be when more data is obtained and added to the study. I recommend that further observations be made and reduced using the advanced methods available in order to further the study of AH Cancri and add pieces to the puzzle of stellar formation and evolution.
References
- Kaufmann, W., and R. Freedman. ed. 1998. Universe, 5th ed. New York, NY: W.H. Freeman and Company: 478-9, 484, 532-4.
- Whetlan et. al. 1979. AH CANCRI – A contact binary in M67. Royal Astronomical Society, Monthly Notices, 186:729-41.