The Cepheid Period-Luminosity Relation and Astronomy Education in Rural Upstate New York Shashi M. Kanbur SUNY Oswego, February 28 2007.
Collaborators • Chow Choong Ngeow (University of Illinois) • Douglas Leonard (San Diego State University), Lucas Macri (NOAO),Nial Tanvir (University of Hertfordshire, UK) Alan Ominisky (SCC High School) • Daniel Crain, Greg Feiden, Richard Stevens, Christina Phelps, Sean Scott, Jim Young, Dylan Wallace.
WHY? • Precision comsology: affects H0 to the level of 1-2%. • Zero Point errors are being reduced – NGC 4258. • Theory of Stellar Pulsation/Evolution. • Constrain Mass-Luminosity relations and Cepheid atmospheric/pulsation/evolutionary effects. • Nature of convection in stellar interiors.
Statistical/Physical Tests • F tests, Least Absolute Deviation. • Testimators (estimation plus smooting), Schwarz Information Criteria – likelihood based methods. • Robust Estimation, non-parametric LOESS, least absolute deviation. • Adding data: OGLE plus SEBO, MACHO plus SEBO, CALDWELL and LANEY etc.
Statistical/Physical Tests • So far, LMC data is consistent with two lines of significantly differing slope with the “break” at a period of 10 days. • Break is present for U,B,V,R,I,J, marginal at K. • SMC/Galactic PL relations do not show the break. • 2 weeks of time on NOAO/SMARTS facilities in Chile yielded over 100Gb of data for SUNY Oswego undergraduates to analyze.
Period-Color and Amplitude-Color Relations in Cepheids. • Stefan Boltzmann law: • logL(max) – logL(min) =4logT(max) – 4logT(min). • Period-Color relation flat at maximum/minimum then Amplitude-Color relation flat at minimum/maximum. • Properties at mean light are really an average of properties at all phases. • PC/AC relations change abruptly at a period of 10 days in the LMC. • PL relation changes strongly related to PC relation changes due to PLC.
The Photosphere/HIF Interaction • Hydrogen Ionization front (HIF): region of rapid spatial change in temperature. Photosphere (optical depth 2/3) are NOT comoving as the star pulsates. • When the photosphere is located at the base of the HIF, photospheric temperature and hence color is related to the temperature at which hydrogen ionizes. • At low densities, this temperature is almost independent of global stellar parameters, leading to a rapid change in the PC and hence PL relation. • This interaction may affect observational properties of other variable stars eg. RR Lyraes and other parts of the HR diagram.
Undergraduate Involvement • Need to study PC/AC relations as a function of phase. • Usually only studied at mean light. • Download data, Fourier decomposition with simulated annealing, Principal Component Analysis. • Construct PC/AC relations. Perform statistical tests on these and PL relations as a function of phase. • Unix, numerical methods, statistical methods, stellar evolution/pulsation, cosmology.
Current Undergraduate Projects • Analysis of M31 RR Lyrae light curves taken by HST: Dylan Wallace. • Analysis of SDSS RR Lyrae light curves: Christina Phelps. • Analysis of M31/M33/IC 1613 Cepheid data: Dan Crain/Jim Young/Sean Scott • Hydrodynamic modeling of Cepheids/RR Lyraes: Greg Feiden. • Development of generalized bootstrap methods to estimate confidence intervals for “break” period: Dan Crain, Richard Stevens.
JHK Observations of LMC Cepheids • Using NOAO/SMARTS facilities and CPAPIR intsruments. • 100Gb of new data taken in Nov 2006/Jan 2007. • Addition to exisiting data. • PL relations, light curve structure, modeling, data reduction methods. • Statistical methods.
Southern Caygua School Observatory Involvement • SCCS has a 14” GOTO telescope on a reasonably dark site – Alan Ominisky. • SUNY Oswego purchased a ST9XE CCD camera from SBIG with some filters (UBVRI). • Galactic Cepheid data needs to be enhanced. • Such Cepheids are pretty bright – about 6-8th magnitude. Easily observable. • Primarily educational, but could result in some new publishable data points, especially for longer period Cepheids.
References • Kanbur and Ngeow, MNRAS, 2004 • Ngeow and Kanbur 2005, 2006a 2006b • Kanbur and Ngeow 2006a • Kanbur, Ngeow, Nanthakumar and Stevens, 2006b (submitted) • Kanbur and Mariani 2004, MNRAS • Kanbur and Fernando 2005, MNRAS