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AGB variables;Distance Indicators; Bolometric Magnitudes;

Pulsation Modes.

Michael Feast

University of Cape Townand

South African Astronomical Observatory

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Topics

1. How good are Mira variables as distance indicators?

2. Problems in Bolometric Corrections and distances for C-Miras

3. Problems in determiningpulsation modes and evolution for low amplitude

AGB variables in theintermediate age cluster NGC419 (SMC)

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Comparison of the Mira distance scale

with other distance indicatorsincluding RR Lyrae variables.

New HST trigonometrical parallaxesof 5 RR Lyrae variables

gives RR Lyrae calibrationto ±0.03 mag.

Important also for absolute magnitudes of Miras

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MK – Log P relations for LMC Miras

Whitelock et al. (2008)

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Zero Point Calibration for O-MirasM

K = -3.51(Log P -2.38) + β

β Trig. Parallaxes (Hipparcos) -7.32 ± 0.10

OH Phase Lag VLBI OH -7.08 ± 0.17

VLBI H2O (T Lep) -7.17± 0.28

Globular Clusters -7.34± 0.13

Adopted (Whitelock et al. 2008) -7.25 ± 0.07

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Distance Modulus of the LMC

O-Miras (K) 18.49±0.07 RR Lyraes (K) 18.53±0.04

Cepheids (K&VI) 18.50±0.03

Eclipsers (OB) ~18.4 Eclipser (G) 18.50± (0.06)

SN Ring 18.55± (0.05) Clump 18.47±0.02

δ Sct 18.48±0.1

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Distance to the Galactic Centre (kpc)

O-Miras (JHK) 8.39±0.54 Central orbits 8.28±0.33

Cepheids (JHK) 7.9±0.2 RR Lyraes (K) 8.32±0.62

Sgr B2 7.9±0.8 Clump 7.87±0.34

CephII (K) 7.63±0.21 Kinematics 7.6±0.5

RR Lyraes (V) with non-standard reddening law9.3±(0.4)

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Distance Modulus of NGC185O-Miras (24 stars) (K) 24.16±0.08 (1)

HB (V) 24.22±0.07 (2) RR Lyraes (V) 24.14±0.05 (3)

(1) Lorenz et al. 2011, Iamp

≥1.0mag,

(2) Butler & Martinez-Delgado 2005 (3) Saha et al. 1990

O-Mira Zero point Whitelock et al. (2008)HB and RR Lyrae zero-point (Benedict et al. 2011)

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NGC 147O-Miras (11 stars)(K) 24.32±0.09 HB(V) 24.49±(0.02)

RR Lyraes(V) 24.18±0.10

Apparent Mags (V)HB 25.57 (Butler et al.)

RR Lyraes 25.29 (Saha et al.)

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Bolometric Correction for Carbon Stars(Whitelock et al. 2006)

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Mbol

– Log P relation for LMC C-Miras

Whitelock et al. (2006)

PL Relations for C-Miras in Local GroupFornax, LeoI, Phoenix, Sculptor, LeoII, WLM

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Distance modulus of the Fornax Dwarf Spheroidal

C-Miras (Mbol

) 20.80

RR Lyraes (clusters)(V) 20.93

Clump (K) (20.75) Clump(I) 20.72

δ Sct ([Fe/H] = –1.4) 20.69 δ Sct ([Fe/H] = –1.0) 20.76

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Distance Modulus of the LeoI Dwarf Spheroidal

C-Miras (Mbol

) 21.91±0.12

RR Lyraes ([Fe/H]=−1.82)(V) 22.09±0.14 ([Fe/H]=−1.4)(V) 22.00±0.14

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Bolometric Correction for Carbon Stars(Whitelock et al. 2006)

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Examples of Dust obscuration eventsWhitelock et al. (2006)

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Reddening in Circumstellar shellsΔK/Δ(J−K)

R For ~ 1.0EV Eri ~1.0

DY Per ~1.3 09164-5349 ~ 1.6 10136-5743 ~1.4

and some suggestions of non-uniform absorption

over surface.Apparent mbol from BCK – (J-K) falls

in obscuration phases.e.g.

09164-5349 ΔK= 2.1, Δ(J-K)= 1.3, Δmbol = 0.90

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Wood Sequences in the LMC (Ita et al. 2004)

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NGC419 K – Log PData from Kamath et al.

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Mbol

– Log P for NGC419 (SMC) variablesKamath et al. (2010)

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Distance Modulus of NGC419 (SMC)(LMC Mod = 18.50)

Miras (2) (Mbol) 18.87±0.20Oxygen SR (2nd overtone)(K) 18.89± <0.01

Carbon SR (1st overtone)(K) 18.81±0.05

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Conclusions1. Miras variables are robust distance indicators.

However care must be taken with C-Miraswith significant circumstellar shells,

especially those of intermediate periods.

2. There is an apparent conflict between theinterpretation of AGB variables in NGC419depending on whether one uses K or m

bol

suggesting uncertainties in the derivationof the latter