The MidInfrared PeriodLuminosity Relations for Classical Cepheids
Chow-Choong Ngeow (IANCU)
withMarcella Marconi, Ilaria Musella, Michele Cignoni (INAF),
Shashi M. Kanbur (SUNY-Oswego) & Hilding Neilson (Argelander Institute for Astronomy)
Graduate Institute of Astronomy, National Central UniversityGraduate Institute of Astronomy, National Central University
The Need of Accurate & Independent Measurement of H
o in Cosmology
Macri et al (2006)
Freedman & Madore (2010)
The MIR P-L Relation: LMC
● Ngeow & Kanbur (2008):
– SAGE single epoch data
– OGLEII Cepheids (N~600)
● Ngeow et al. (2009):
– SAGE two epoch data
– OGLEIII Cepheids (N ~ 1800)
● Open squares: rejected outliers using sigmaclipping method
A Note on SMC MIR P-L Relations
● SMC PL relation is known to exhibit break at log(P)=0.4 in optical
● Confirmed the break in MIR PL relation
● Due to evolutionary effect (Baraffe et al 1998)
Ngeow & Kanbur (2010)
The AKARI P-L Relation
Slope for N3 P-L Relation: -3.25 ± 0.05 Ngeow et al. (2010)
In contrast to SAGE data, AKARI data include MJD information →apply randomphase correction for singlephase epoch data
Summary of Empirical MIR P-L Slopes for MC Cepheids
● LMC:– N3: 3.25 ± 0.05
– 3.6 micron: 3.25 ± 0.01
– 4.5 micron: 3.21 ± 0.01
– 5.8 micron: 3.18 ± 0.02
– 8.0 micron: 3.20 ± 0.04
● SMC:– 3.6 micron: 3.23 ± 0.02
– 4.5 micron: 3.18 ± 0.02
– 5.8 micron: 3.23 ± 0.04
– 8.0 micron: 3.25 ± 0.05
Expected MIR P-L Slopes
● L=4 Rπ 2Bλ(T); for B
λ(T) ~ T (RayleighJean approx.)
● Then, MIRAC
= 5aRlog(P) + a
Tlog(P) + const., adopt a
R=0.68
(Gieren et al (1999)
● Beaulieu et al (2001): log(T) – (VI) conversion
– LMC (VI) PC relation from Sandage et al (2004)
– SMC (VI) PC relation from Sandage et al (2009)
● Slope of IRAC band PL:
– LMC: 5 x 0.68 + 0.18 = 3.22
– SMC: 5 x 0.68 + 0.19 = 3.21
See Neilson et al (2010) for more details
The Theoretical Slopes
Synthetic P-L relations from pulsation models with different input Y and Z (models from Marcella Marconi,Ilaria Musella & Michele Cignoni)
Non-linear pulsations models include time-dependent treatment of pulsation and convection
Evolution M-L relation
~1000 pulsators with 5 -11 Solar mass populated the instability strip according to a given mass law
Convert to IRAC mag using stellar atmosphere models
Theoretical Vs. Empirical: GAL
GAL1: ''Old'' IRSB; GAL2: ''New'' IRSB; GAL3: HST parallaxes; From Marengo et al (2010)
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