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Hubble’s Constant, the Oosterhoff Dichotomy and Hydrogen Ionization Fronts.

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Hubble’s Constant, the Oosterhoff Dichotomy and Hydrogen Ionization Fronts.

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### 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) and long (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

- http://www.oswego.edu/~kanbur/IRES2009/Vphase.mov
- http://www.oswego.edu/~kanbur/IRES2009/Iphase.mov
- http://www.oswego.edu/~kanbur/IRES2009/Cphase.mov
- http://www.oswego.edu/~kanbur/IRES2009/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.

Impact on H0

- Calibrate SNIa diagram with Cepheids.
- μ0 = μV – 2.45(μV – μI).
- 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.
- http://www.oswego.edu/~kanbur/IRES2009/H0impact.pdf

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

- Lmax ~ R2max T4max, Lmin ~ R2min T4min
- Amplitude ~ 4log(Tmax – Tmin).
- PC relation flat at maximum light – AC relation at minimum light and vice versa.
- See this in LMC OGLE II/III Cepheids.
- http://www.astro.umass.edu/~shashi/papers/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.
- http://www.astro.umass.edu/~shashi/papers/paper9.pdf

The Oosterhoff Dichotomy

- OoI:
~ 0.65 days, Z = 0.001

- OoII:
~ 0.55 days, Z = 0.0001

- 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=0.0001
- 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.

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