The Cepheid distance to the LMC from the first results of ...

The Cepheid distance to the LMC from the first results of the VISTA Magellanic Cloud (VMC) Survey.

Vincenzo Ripepi INAF-Osservatorio Astronomico Capodimonte - ItalyMarcella Marconi INAF-Osservatorio Astronomico Capodimonte - ItalyMaria Ida Moretti INAF-Osservatorio Astronomico di Bologna - ItalyGisella Clementini INAF-Osservatorio Astronomico di Bologna - ItalyMaria Rosa Cioni Univ. of Hertfordshire, UK & Univ. Observatory Munich, Germany & the VMC team

venerdì 6 maggio 2011

The VMC Survey• VMC is an ESO public survey (P.I. M.R. Cioni, see Cioni et al. 2011, A&A, 527, 116)• The most sensitive near-infrared survey of the Magellanic Cloud (MC) system • Total surveyed area ~ 180 deg2 (LMC = 116 deg2; SMC = 45 deg2 ; Bridge = 20 deg2)• Specifically designed to have a good sampling of RR Lyrae and Cepheid light curves • Started on October 2010 (present completion ~ 11%)


VMC Survey: observations•Observa)onsinYJKswithVIRCAM@VISTA4m(Paranal,Chile)

•Datareduc)onwiththeVISTA Data Flow System (VDFS) pipeline at CASU(Cambridge

AstronomicalSurveyUnit)

•CatalogueshandlingthroughtheVistaScienceArchive(VSA)

1 Tile = 1.017 º x 1.475 º ∼ 1.5 ☐

Cioni et al. (2011) Cioni et al. (2011)


I. Spa)allyresolvedSFH

II. 3Dstructure(variablestars,redclump,…)

III. ThedistancetotheLMC

IV. Stellarsub‐‐‐structures(clusters,streams…)

V. PNe,SNRsandotherextendedsources(galaxies)

VI. Differen)alpropermo)on

VII.Starforma)on

VIII.Tes)ngmodelsoftheMagellanicClouds

evolu)on

IX. Ex)nc)onmaps

X. …

The VMC Survey: Science


Cepheids in the NIR

• Low-amplitude light curves

• Low dependence on reddening

• PL in J and K linear

• Low dependence on metallicity

• Low dispersion (< 0.1 mag)

Madore & Freedman (1991)

Caputo, Marconi, Musella 2000 A&A Persson et al. (2004)


Wesenheit relations

✓ Reddening independent

✓ Low metallicity dependence

✓ Very low dispersion

✓ Ideal for tracing the 3D structure of the MCs

Caputo et al. 2000

Persson et al. 2004

W(K,VK)=K-0.13(V-K)=αlogP+β


VMC Survey: RR Lyrae stars and Cepheids

• Optical data from EROS II B,R (⇒V,I) light curves for (≈16000) RR Lyrae stars and(∼5800) Cepheids in the LMC (kindly made available to us by J.B. Marquette)

• OGLE III V,I light-curves and accurate variable star classification in the LMC (3375 Classical Cepheids and ∼ 24900 RR Lyrae) and SMC (4630 Classical Cepheids and 2475 RR Lyrae)

• Only two fields completed so far:

✓ Gaia field (South Ecliptic Pole test field) 12 Cepheids; 111 RR Lyrae stars ( see Moretti et al. Poster, this conference)

✓ 30 Dor region ∼ 320 Cepheids and ∼ 700 RR Lyrae stars


Gaia Field

EROS 2 RR Lyrae distribution in LMC; courtesy J.B. Marquette and M.I. Moretti


30 Dor Field

VMC three color imageEROS 2 Cepheid distribution in LMC; courtesy J.B. Marquette and M.I. Moretti


Cepheid Light Curves

• GAIA Field: 4 F

8 FO

• 30 Dor Field: 161 F

8 F/FO 139 FO15 FO/SO


Results: PLK in 30 Dor


Results: PLK and W(K,VK) in 30 Dor

Strong differential reddening makes the use of the W(V,K) relation more appropriate.


Results: W(V,K) in 30 Dor

W(K,VK)F=(-3.260±0.028)logP+(15.830±0.019) rms=0.070 mag

W(K,VK)FO=(-3.530±0.025)logP+(15.400±0.008) rms=0.071 mag


W(V,K) in 30 Dor: comparison with the literature

Persson et al. (2004) sample


30 Dor sample


Caputo et al. 2000


W(V,K) in 30 Dor and LMC sample



30 Dor sample



W(V,K) in 30 Dor and LMC sample



30 Dor sample


Joint samples:



W(V,K) in 30 Dor and Gaia fields

Perhaps we are observing stars located at different distances from the LMC center


W(V,K): Galactic Cepheids with Trig. Parallaxes

Trigonometric parallaxes by Benedict et al.(2007) and van Leeuwen et al. (2007)

Lutz-Kelker correction by Benedict et al. (2002).

LSQ:W(K,VK)F=(-3.28±0.14)logP-(2.61±0.12) rms=0.10 mag

LMC slope imposed:W(K,VK)F=-3.325logP-(2.57±0.03)

⇓(m-M)0=18.44±0.08 mag


W(K,VK) in NCG 1866

Using:

• Ks-band photometry for NGC 1866 by Storm et al. (2004), Testa et al. (2007);

• UBVI proprietary data

Molinaro et al. (Poster this conference) applied a modified version of the CORS Baade-Wesselink method to 9 cepheids in NGC 1866, deriving (m-M)0=18.56±0.03 mag (random error).

⇓

(m-M)0=18.54±0.08±sist. mag

HV12204


Distance to the 30 Dor Field (LMC) from the W(K,VK)

Calibrators Method (m-M)0 Dispersion

Caputo et al. (2000) Theory 18,69 0,10

Benedict et al. (2007)van Leeuwen et al. (2007)

Trigonometric parallaxes

18,44 0,08

Fouque’ et al. (2007) Various Galactic 18,42 0,08

Gieren et al. (2005) LMC Cep. ISBM 18,43 0,09

Molinaro et al. B-W NGC 1866 18,54 0,08

AVERAGE 18,46 0,06


Distance to 30 Dor Field (LMC) from W(K,VK)

After Clementini et al. (2003)


Conclusions

✓ VMC survey is going on

✓ First results on the Gaia and 30 Dor fields

✓ Nice light curves for all pulsating variables, in particular Classical Cepheids and RR Lyrae stars

✓ W(K,VK) low dispersion ➱ good 3D tracer

✓ Using different calibrations we find:

(m-M)0[30 Dor]=18.46±0.06

✓ waiting for GAIA ⇒ direct distance measure of LMC Cepheids


The Cepheid distance to the LMC from the first results of ...

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