Hubble’s Constant, the Oosterhoff Dichotomy and Hydrogen Ionization Fronts. Shashi M. Kanbur University of Florida, September 2009

Acknowledgments  Chow Choong Ngeow, Douglas Leonard, Lucas Macri, Robert Szabo, Robert Buchler, Marcella Marconi.  SUNY Oswego undergrads: Dylan Wallace, Dan Crain, Greg Feiden, Richard Stevens, Robin Dienhoffer, Frank Ripple, Sean Scott, Earl Bellinger, Lillie Ghobrial, Mike Evans, Martin Berke.  Isaac Richter, Tim De Haas, Andy Missert, Matthew Turner, Alex James, Eamonn Moyer, Jillian Neeley.  NSF, AAS, HST.

The Cepheid PL Relation  This relation is not linear – at least in the LMC: change of slope between short (log P 1) period Cepheids.  OGLE II/III data using OGLE determined reddenings and the Zaritsky reddening map.  Need detailed statistical tests for this.  It is NOT sufficient just to look at the slopes plus or minus some standard deviations.

Multiphase PL/PC relations  9/Vphase.mov 9/Vphase.mov 9/Vphase.mov  9/Iphase.mov 9/Iphase.mov 9/Iphase.mov  9/Cphase.mov 9/Cphase.mov 9/Cphase.mov  9/Wphase.mov 9/Wphase.mov 9/Wphase.mov

LMC tests  F test.  Schwarz Information Criterion.  Testimator plus others.  OGLE II/OGLE III plus long period Cepheids.  MACHO, Sebo et al, Perrson et al.  OGLE II reddenings plus Zaritsky reddenings.  BVIJH non-linear.  K marginally nonlinear. OGLE II Wessenheit linear, OGLE III Wessenheit marginally nonlinear.  PL/PC cancel each other out – that is the Wessenheit is linear.

JHK Data  3 years observing campaign using 1.5m NOAO telescope plus CPAPIR and OGLE LMC pointings.  2 years of Sloan filter data again using LMC OGLE pointings.  Analyzing this data currently.

M33 DIRECT data

Impact on H0  Calibrate SNIa diagram with Cepheids.  μ 0 = μ V – 2.45(μ V – μ I ).  W = V – 2.45(V-I).  There is a difference when used with OGLE III with these data.  W is less sensitive to possible changes of slope in V and I.  9/H0impact.pdf 9/H0impact.pdf 9/H0impact.pdf

Mid-InfraRed PL relations

Physics  PL/PC relation connected through the PLC relation.  PC relation affected through the interaction of the stellar photosphere and hydrogen ionization front (HIF).  Engaged: Color of star which is related to the Temperature of photosphere = temperature of HIF.  Engaged at low densities: Color of Star is related to temperature of photosphere which is less dependent on period.  Engaged at high densities: more sensitive to period.  Sudden: - either engaged or not.  ML relation affects phase/period of interaction.  Flat PC relation at maximum light for Galactic Cepheids, and for logP > 1 for LMC Cepheids.

PC/AC Relations  L max ~ R 2 max T 4 max, L min ~ R 2 min T 4 min  Amplitude ~ 4log(T max – T min ).  PC relation flat at maximum light – AC relation at minimum light and vice versa.  See this in LMC OGLE II/III Cepheids.  s/paper1.pdf s/paper1.pdf s/paper1.pdf

RR Lyraes  PC relation at minimum light is flat.  Higher amplitude RR Lyraes are driven to hotter/bluer temperatures/colors at maximum light.  PC relation is flat at minimum light because the HIF is further out in the mass distribution.  HIF always engaged with stellar photosphere for RR Lyraes.  But density changes as pulsation proceeds from minimum light. 

The Oosterhoff Dichotomy The Oosterhoff Dichotomy  OoI: ~ 0.65 days, Z =  OoII: ~ 0.55 days, Z =  Period-Amplitude (PA) relation different in the two groups.  Evolved RRab stars in OoI clusters follow a similar PA relation to that in OoII clusters  M3: OoI, M15: OoII.  V = a + blog P  V = a + c(B-V) – c(B-V) + blogP  Related to PC/AC relations as a function of phase

M3/M15 analysis  M3 data from Benko et al (2007)  M15 data from Corwin et al (2008)  Fourier decomposition to smooth out observed data.  Use decomposition to estimate max/min.  BVI light curves.  Concentrate on RRab stars.  Possible evidence of a difference in PC/AC relations as a function of phase.

PC/AC relations in RR Lyraes  Sloan RR Lyraes and M31 data usign HST.  Theoretical models computed by Robert Szabo.  M,L,T,X,Z. Two values of Z=0.001, Z=  Range of M/L. Strong possibilities to constrain models and estimate reddening.  Kurucz atmosphere parametrized by effective gravity and photospheric temperature.  Comparing models with observations and understanding possible implications.

Model Results