Alistair Walker Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory

May 3 2011 Naples, Distance Scale meeting 2

May 3 2011 Naples, Distance Scale meeting 3

•  It’s important to know the LMC distance itself for study of the LMC!

•  The LMC is THE place to compare multiple distance indicators and compare for consistency. But it’s not the only place.

•  We need to do this sort of comparison since distance determinations in general have been dominated by systematic errors.

•  The insidious problem of large systematic errors developing from the multi-step approach can to some extent be circumvented by making the steps bigger.

•  But our requirements have become more stringent! Thirty years ago we were worried about a factor two, now we are concerned with a (very) few percent.

–  e.g. Rowan-Robinson (1985): 18.91 (Cepheids), 18.42 (RR Lyrae), 18.86 (Novae)

•  There has been a great deal of progress in the last decade.

Benedict et al. 2002

Catelan & Cortés (2008), synthetic evolutionary models -> MV = 0.60 ± 0.13 for RR Lyrae

May 3 2011 4 Naples, Distance Scale meeting

Benedict et al. 2002

80 estimators, ~35 do not include a modulus of 18.50 in their range…

This is an unbiased look at the data, but uncritical.

Is bias a significant factor – see Schaefer (2008)

May 3 2011 5 Naples, Distance Scale meeting

•  “Distances to Local Group Galaxies” by ARW, in Stellar Candles for the Extragalactic Distance Scale, Lecture Notes in Physics, ed. D. Alloin & W. Gieren, 2003

INDICATOR VALUE

CEPHEIDS 18.55±0.06

RRLYRAES 18.44±0.05

RGCLUMP 18.49±0.06

TRGB 18.59±0.09

ECLIPSINGBINARIES 18.46±0.1

MIRAS 18.59±0.2

SN1987A 18.55±0.17

MEAN 18.52±0.10

May 3 2011 6 Naples, Distance Scale meeting

Pulsating Variable Stars in the Magellanic Clouds, by Gisella Clementini, IAU Symp. 256, 2008

•  Period – metallicity – K band relation for RR Lyraes •  HST parallaxes for Cepheids •  Some addition refinements (e.g. delta Scuti stars, “agree”, but with

calibration errors typically estimated to be ± 0.1 mag) •  Various new observations (OGLE III, other targeted optical and IR

surveys etc)

May 3 2011 7 Naples, Distance Scale meeting

METHOD MODULUS REFERENCE PL, Delta Scuti stars 18.50 ± 0.22 McNamara et al. 2007

Model fitting, Delta Scuti 18.48 ± 0.15 McNamara et al. 2007

Model fitting, bump Cepheids 18.54 ± 0.02 Keller & Wood 2006

Model fitting, RR Lyraes 18.54 ± 0.02 Marconi & Clementini 2005

MV-[Fe/H], field RRL 18.46 ± 0.07 Clementini et al. 2003

PLKZ field RRL 18.48 ± 0.08 Borissova et al. 2004

PLKZ field RRL 18.58 ± 0.12 Szewczyk et al. 2008 Various PL, PLC, Cepheids 18.4-18.5 Van Leeuwen et al.2007

PLKZ Reticulum RRL 18.52 ± 0.12 Dall’Ora et al. 2004

May 3 2011 Naples, Distance Scale meeting 8

•  Can anchor to the 10 Cepheids with HST parallaxes (Benedict et al. 2007). They calculate a Wesenheit WVI distance for the LMC.

•  A theoretical investigation by Bono et al (2010) plus observational evidence (e.g. Petrzynski et al (2006) and others) show that the PL Wesenheit V-I relation is independent of metallicity.

•  But Storm et al. (2011) find from IR SPF technique that γ(WVI) = -0.23 ± 0.10 mag/dex plus an effect on the slope. Recommend PL (K), with a -0.10 ± 0.10 mag/dex metallicity effect.

•  Independently we can use the multi-wavelength approach – (e.g. Freedman & Madore 2010). No metallicity corrections.

May 3 2011 9 Naples, Distance Scale meeting

Method Modulus

VI Wesenheit PL (Benedict, no Z correction)

18.50±0.03

VI Wesenheit PL (Benedict, with Z correction)

18.40±0.05

VIWesenheitPL(noZcorr.) 18.44±0.03

VIWesenheitPL(Stormetal.) 18.45±0.04(int)

Std.ext.curvefittoBVIJHK(FM)

18.40±0.01&E(B‐V)=0.10

May 3 2011 10 Naples, Distance Scale meeting

•  The parallax for RR Lyrae is just a foretaste of what we expect for many RR Lyraes from Gaia – n.b. reddening, and fundamental parameters will be needed for all stars, e.g. as provided for RR Lyrae by Kolenberg et al. 2010).

•  There has been a move to the IR for the usual reasons. Great technical advances in the last decade have helped.

•  Samples are large enough that systematic (calibration) errors dominate

MV-[Fe/H], field RRL 18.46 ± 0.07 Clementini et al. 2003 PLKZ field RRL 18.48 ± 0.08 Borissova et al. 2004

PLKZ field RRL 18.58 ± 0.12 Szewczyk et al. 2008

May 3 2011 11 Naples, Distance Scale meeting

May 3 2011 12 Naples, Distance Scale meeting

•  There are several discussions of the Period-Metallicity-K band relation (Sollima et al., Dall’Ora et al., Szewczyk et al., Borissova et al.)

•  All show consistency with the metallicity-V band relation and indicate an LMC modulus of ~ 18.55 ± 0.1 mag.

•  These discussions anchor their zeropoints to RR Lyrae (K magnitude) or calibrations such as Gratton et al (1997) GC calibration from Hipparcos subdwarfs MV(RR) = 0.61 ± 0.07 at [Fe/H] = -1.5 and various empirical and/or theoretical relations.

May 3 2011 13 Naples, Distance Scale meeting

•  Double-lined, detached systems •  One step, you get the fractional radii from the light curves and the

masses and orbital parameters from the radial velocities – inherently direct and geometric.

•  Need the effective temperature to get the luminosity, which can be done via SB-color relations calibrated from angular diameters or by matching to models.

•  Surface-brightness to color (preferably V-K) relations are only well-established for spectral types later than ~ A5

•  Later spectral types are fainter, need very large telescopes for spectroscopy

•  4 B type systems (3 in the LMC bar), 1 G type, 1 O type. •  Many more (OGLE discoveries) to come!!

May 3 2011 Naples, Distance Scale meeting 14

May 3 2011 Naples, Distance Scale meeting 15

Pietrzyński et al. 2009

May 3 2011 Naples, Distance Scale meeting 16

Spectral Type Modulus Reference O + O 18.52 ± 0.07 Bonanos et al 2011 B + B 18.30 ± 0.07 Guinan et al. 1998 B2IV-V + B2III-IV 18.38 ± 0.08 Ribas et al. 2002 B0.5V + B2III 18.18 ± 0.08 Fitzpatrick et al. 2003 B1IV-V + B1IV-V 18.53 ± 0.05 Fitzpatrick et al. 2003 G4III + G 4III 18.50 ± 0.06 Pietrzyński et al. 2009

May 3 2011 17 Naples, Distance Scale meeting

•  RGB clump calibration – from SAAO IR survey, Koerwer et al, (2009), calibrating from stellar evolution libraries, LMC modulus = 18.54 ± 0.06. Earlier, Alves (2002) = 18.46 ± 0.07.

•  K band luminosity of the red clump in 17 intermediate-age LMC clusters, by Grocholski et al 2007 = 18.40 ± 0.04 (random) ± 0.08 (systematic).

•  Mid IR (Spitzer) PL relation - Spitzer SAGE 3.6, 4.5, 5.8, 8.0 microns for 70 Cepheids, Freedman et al 2008. More observations needed to fill In the light curves. Also Marengo et al 2010 Galactic Cepheids with Spitzer

May 3 2011 18 Naples, Distance Scale meeting

•  VMC = VISTA near-IR survey of the MC, YJK of the whole MC system, including K time-series

•  The Dark Energy Camera on the CTIO Blanco 4m telescope (2.2 deg diam FOV), in early 2012. Available filters g,r,i,z,Y, plus we hope, u

•  The VST plus OmegaCam

•  GAIA 2012-2017. Will directly measure parallaxes for the brighter stars in the LMC (σπ ~ 15-25 µarcsec at V ~ 15, a star in the LMC has a parallax around 200 µarcsec).

May 3 2011 Naples, Distance Scale meeting 19

•  Sample sizes have grown such that systematic, calibration effects dominate in most cases

•  We are close to the stage where fundamental photometric calibration errors (~ 0.02 mag) are important… –  IR Persson, Elias, Carter, 2MASS systems –  Move to surveys only with SDSS (u),g,r,i, z

•  We need to nail down the metallicity dependency of Cepheid luminosities

•  Parallaxes for fundamental calibrators such as Cepheids and RR Lyraes will be provided by Gaia

•  RELIABLE Eclipsing Binaries are new! •  There is no short-long dichotomy anymore, nor indeed a large

spread in estimates. •  Just careful work is needed…

May 3 2011 20 Naples, Distance Scale meeting

Knownsystema9cs

Keyproject(2001)

Revisions(2007/2009)

An9cipatedSpitzer/JWST

Basis

Cepheidzp ±0.12mag ±0.06mag ±0.03mag Galac^cparallaxes

Metallicity ±0.10mag ±0.05mag ±0.02mag IR+models

Reddening ±0.05mag ±0.03mag ±0.01mag IR20‐30xreduc^on

Transforma^ons ±0.05mag ±0.03mag ±0.02mag Flightmagnitudes

FinalUncertainty ±0.20mag ±0.09mag ±0.04mag AddedinQuadrature

%erroronH0 ±10% ±5% ±2% Distamces

May 3 2011 21 Naples, Distance Scale meeting

May 3 2011 Naples, Distance Scale meeting 22