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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%)
venerdì 6 maggio 2011
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)
venerdì 6 maggio 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
venerdì 6 maggio 2011
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)
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011
Gaia Field
EROS 2 RR Lyrae distribution in LMC; courtesy J.B. Marquette and M.I. Moretti
venerdì 6 maggio 2011
30 Dor Field
VMC three color imageEROS 2 Cepheid distribution in LMC; courtesy J.B. Marquette and M.I. Moretti
venerdì 6 maggio 2011
Cepheid Light Curves
• GAIA Field: 4 F
8 FO
• 30 Dor Field: 161 F
8 F/FO 139 FO15 FO/SO
venerdì 6 maggio 2011
Results: PLK and W(K,VK) in 30 Dor
Strong differential reddening makes the use of the W(V,K) relation more appropriate.
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011
W(V,K) in 30 Dor: comparison with the literature
Persson et al. (2004) sample
W(K,VK)F=(-3.359±0.034)logP+(15.91±0.043) rms=0.088 mag
30 Dor sample
W(K,VK)F=(-3.260±0.028)logP+(15.830±0.019) rms=0.070 mag
Caputo et al. 2000
venerdì 6 maggio 2011
W(V,K) in 30 Dor and LMC sample
Persson et al. (2004) sample
W(K,VK)F=(-3.359±0.034)logP+(15.91±0.043) rms=0.088 mag
30 Dor sample
W(K,VK)F=(-3.260±0.028)logP+(15.830±0.019) rms=0.070 mag
venerdì 6 maggio 2011
W(V,K) in 30 Dor and LMC sample
Persson et al. (2004) sample
W(K,VK)F=(-3.359±0.034)logP+(15.91±0.043) rms=0.088 mag
30 Dor sample
W(K,VK)F=(-3.260±0.028)logP+(15.830±0.019) rms=0.070 mag
Joint samples:
W(K,VK)F=(-3.325±0.014)logP+(15.87±0.013) rms=0.078 mag
venerdì 6 maggio 2011
W(V,K) in 30 Dor and Gaia fields
Perhaps we are observing stars located at different distances from the LMC center
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011
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
venerdì 6 maggio 2011