The Mid-Infrared Light Curve Structure of LMC Cepheids

1. The Mid-Infrared Light Curve Structure of LMC Cepheids Kunal Datta1, Chow-ChoongNgeow2, Shashi Kanbur3 1:SUNY Geneseo, Geneseo, NY 2:National Central University, Jhongli, Taiwan 3:SUNY Oswego, Oswego, NY Plots of Parameter Relations vs. LogP Purpose Compare Theoretical Models of Cepheid Variable Stars with Observational data to Assess the validity of those models. Cepheids Stars with a variable pulsation period that shows a defined relationship between luminosity and pulsation period. They are useful in creating extragalactic distance scales due to their special properties and relationships. Why Mid-Infrared? Mid- Infrared radiation is a subdivision of Infrared radiation that has longer wavelengths and has the ability to resist the effects of stellar extinction. This extinction is a process in which light travelling through space is absorbed by interstellar dust and particles and re-emitted at different wavelengths, thus it doesn’t accurately represent the original light. This lack of extinction allows more accurate light curve analysis to be made. Conclusions From the limited theoretical sample size, an agreement is visible. A larger sample size is needed to be able to draw conclusions from the results. The resonance dip present at LogP of 1.05 or 1.1 days may be a conclusion that can be supported by further research on the topic. • Fourier Decomposition • Fourier analysis is the process of recreating a curve by adding together sines and/or cosines. • The Coefficients are used to then find certain parameters: • Parameter Relations: Phi21, Phi31, R21, R31 • Lc_Fourierfit2.c code by Dr. Ngeow was used to carry out this Fourier analysis. Full Spectrum Theoretical Model Marcella Marconi created different theoretical models for Cepheid systems (Kanbur et al 2013). They are 1D, spherically symmetric, time dependent full amplitude Cepheid pulsation models with a non-local mixing length theory of convection. Each model has an xyz metallicity composition of x=.742, y=..25, z=.008. Where x= hydrogen content, y= helium content, and z= all other metals and their total equals 1. We were given 10 different temperature models of systems of 7 solar masses, 7.15 solar masses, and 7.3 solar masses, analysis was run on each system of models. Observational Data Danielle Citro ran Fourier Analysis on 85 Large Magellanic Cloud Cepheid stars. . (Data from Scowcroft et al., 2012) Used Lc_Fourierfit2.c to output fitted light curves to make sure the fits were accurate. The separate resonance dips for the OGLE visible light data and the Mid-Infrared light could be a topic for further exploration. Results Acknowledgements National Science Foundation's Office of International Science and Engineering award number 1065093, NCU, the Department of Physics and Astronomy at NCU, Dr. Shashi Kanbur, the International Office at NCU Bono, G., M. Marconi, and R. F. Stellingverf. "Classical Cepheid Pulsation Models." Astronomy and Astrophysics (2000): 245+. Print. Kanbur et al 2013 Ngeow, Chow-Choong, and Shashi M. Kanbur. "Nonlinear Period‐Luminosity Relation for the Large Magellanic Cloud Cepheids: Myths and Truths." The Astrophysical Journal 650.1 (2006): 180-88. Print. Scowcroft, Victoria, Wendy L. Freedman, Barry F. Madore, Andy Monson, S. E. Persson, Jane R. Rigby, and Mark Seibert. "The Carnegie Hubble Program: The Leavitt Law at 3.6µm and 4.5µm in the Large Magellanic Cloud." (2012): n. pag. Xxx.lanl.gov. Los Alamos National Laboratory, 22 Sept. 2012. Web. <http://lanl.arxiv.org/abs/1209.4946v1>. Smale, Alan. "Cepheid Variables as Cosmic Yardsticks." Cepheid Variables. HEASARC, n.d. Web. 11 July 2013.