The Cepheid Period-Luminosity Relation and Astronomy Education in Rural Upstate New York Shashi M. Kanbur SUNY Oswego, February

Collaborators Chow Choong Ngeow (University of Illinois) 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) 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. 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%. Precision comsology: affects H0 to the level of 1-2%. Zero Point errors are being reduced – NGC Zero Point errors are being reduced – NGC Theory of Stellar Pulsation/Evolution. Theory of Stellar Pulsation/Evolution. Constrain Mass-Luminosity relations and Cepheid atmospheric/pulsation/evolutionary effects. Constrain Mass-Luminosity relations and Cepheid atmospheric/pulsation/evolutionary effects. Nature of convection in stellar interiors. Nature of convection in stellar interiors.

Statistical/Physical Tests F tests, Least Absolute Deviation. F tests, Least Absolute Deviation. Testimators (estimation plus smooting), Schwarz Information Criteria – likelihood based methods. Testimators (estimation plus smooting), Schwarz Information Criteria – likelihood based methods. Robust Estimation, non-parametric LOESS, least absolute deviation. Robust Estimation, non-parametric LOESS, least absolute deviation. Adding data: OGLE plus SEBO, MACHO plus SEBO, CALDWELL and LANEY etc. 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. 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. Break is present for U,B,V,R,I,J, marginal at K. SMC/Galactic PL relations do not show the break. 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. 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: Stefan Boltzmann law: logL(max) – logL(min) =4logT(max) – 4logT(min). logL(max) – logL(min) =4logT(max) – 4logT(min). Period-Color relation flat at maximum/minimum then Amplitude-Color relation flat at minimum/maximum. 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. 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. 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. 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. 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. 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. 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. 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. Need to study PC/AC relations as a function of phase. Usually only studied at mean light. Usually only studied at mean light. Download data, Fourier decomposition with simulated annealing, Principal Component Analysis. 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. 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. 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 M31 RR Lyrae light curves taken by HST: Dylan Wallace. Analysis of SDSS RR Lyrae light curves: Christina Phelps. Analysis of SDSS RR Lyrae light curves: Christina Phelps. Analysis of M31/M33/IC 1613 Cepheid data: Dan Crain/Jim Young/Sean Scott Analysis of M31/M33/IC 1613 Cepheid data: Dan Crain/Jim Young/Sean Scott Hydrodynamic modeling of Cepheids/RR Lyraes: Greg Feiden. Hydrodynamic modeling of Cepheids/RR Lyraes: Greg Feiden. Development of generalized bootstrap methods to estimate confidence intervals for “break” period: Dan Crain, Richard Stevens. 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. Using NOAO/SMARTS facilities and CPAPIR intsruments. 100Gb of new data taken in Nov 2006/Jan Gb of new data taken in Nov 2006/Jan Addition to exisiting data. Addition to exisiting data. PL relations, light curve structure, modeling, data reduction methods. PL relations, light curve structure, modeling, data reduction methods. Statistical methods. Statistical methods.

Southern Caygua School Observatory Involvement SCCS has a 14” GOTO telescope on a reasonably dark site – Alan Ominisky. 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). SUNY Oswego purchased a ST9XE CCD camera from SBIG with some filters (UBVRI). Galactic Cepheid data needs to be enhanced. Galactic Cepheid data needs to be enhanced. Such Cepheids are pretty bright – about 6-8 th magnitude. Easily observable. Such Cepheids are pretty bright – about 6-8 th magnitude. Easily observable. Primarily educational, but could result in some new publishable data points, especially for longer period Cepheids. Primarily educational, but could result in some new publishable data points, especially for longer period Cepheids.

References Kanbur and Ngeow, MNRAS, 2004 Kanbur and Ngeow, MNRAS, 2004 Ngeow and Kanbur 2005, 2006a 2006b Ngeow and Kanbur 2005, 2006a 2006b Kanbur and Ngeow 2006a Kanbur and Ngeow 2006a Kanbur, Ngeow, Nanthakumar and Stevens, 2006b (submitted) Kanbur, Ngeow, Nanthakumar and Stevens, 2006b (submitted) Kanbur and Mariani 2004, MNRAS Kanbur and Mariani 2004, MNRAS Kanbur and Fernando 2005, MNRAS Kanbur and Fernando 2005, MNRAS