the distance scale in the gaia era · the lmc pl is used to measure the distance to extragalactic...
TRANSCRIPT
The Distance Scale in the Gaia Era
G. Clementini INAF - Osservatorio Astronomico, Bologna
Acknowledgements: A. Brown, C. Cacciari, M. Marconi, V. Ripepi, DPAC, ESA, EADS Astrium
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 1
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 2
Layout of the lecture
- The astronomical distance scale: - basic concepts - typical distances
- Direct measure: trigonometric parallax
- Indirect measure: Distance Indicators - Primary indicators
- Secondary indicators - Tertiary indicators
- Primary Indicators - The distance to the Large Magellanic Cloud - Gaia
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
The Hubble Law
“ In standard big bang cosmology the universe expands uniformly; and locally, according to the Hubble law,
v = Ho x d
where v is the recession velocity of a galaxy at a distance d, and Ho is the Hubble constant, the
expansion rate at the current epoch.”
Freedman et al. 2001, Ap.J. 533, 47
Typical astronomical distances in time
Earth - Sun ~ 8 m ~ 1 A.U. Earth - Pluto ~ 660 m ~ 39.4 A.U.
Sun - Alpha Centauri ~ 4.2 l.y. ~ 1.3 pc Sun - Iades ~ 150 l.y. ~ 50 pc Sun - Galactic Center ~ 25.000 l.y. ~ 8 kpc
Sun -LMC ~ 50 kpc
Sun - Andromeda ~ 2.5 x 106 l.y. ~ 770 kpc Sun - Locale Group ~ 3.3 x 106 l.y. ~ 1 Mpc Sun - M81 and Sculptor clusters ~ 6-10 x 106 l.y . ~ 2.5 Mpc Sun - M101 cluster ~ 15-20 x 106 l.y. ~ 5.4 Mpc Sun - Virgo cluster ~ 40 x 106 l.y. ~ 12 Mpc Sun - Coma cluster ~ 300 x 106 l.y. ~ 92 Mpc
p
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__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
m - M = - 5 + 5logdpc distance modulus
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Distance Ladder
”Given the range spanned
by the astronomical distances, the
astronomical distance ladder
is made by overlapping techniques and
distance indicators, starting from the most
closeby that we can calibrate
directly."
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Gaia
TRGB
Direct methods: trigonometric parallax 0<d<100 pc
Indirect methods::
Distance indicators primary 500 -3×107pc
tertiary
- Proper motions + statistical parallax 0-500 pc
- Main Sequence Fitting open clusters 40- 7000 pc
Milky Way
globular clusters 3000-10000 pc
Spectroscopic and photometric parallax > 10000 pc Beyond the
Milky Way
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2×105 - 109 pc and beyond
secondary
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
Hipparcos
Gaia
Trigonometric Parallax
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Direct method: trigonometric parallax
p = tang U.A./d ~ U.A./d
dpc = 1/p"
p « 1"
pα Cen = 0.76"
0 < d < 100 pc
p = 1" d = 1 pc
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HIPPARCOS
Satellite astrometrico lanciato dall'ESA nel
1989 e operativo fino al 1993. Ha
misurato la parallasse di
118.000 stelle con magnitudine apparente V fino alla 9 e precisione di 0.001”
Catalogo finale nel 1997.
"Come vedere un astronauta in piedi
sulla Luna" 9
Satellite astrometrico che verra'
lanciato dall'ESA nel 2012. Misurera' le parallassi
di 1000 milioni di stelle della nostra Galassia
con magnitudine apparente V fino alla 20-22 e
precisione di 0.000001" a V=15.
GAIA
"Come vedere l'unghia di un astronauta sulla Luna”
http://www.rssd.esa.int/Gaia http://yoda.bo.astro.it 10
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Gaia in a nutshell ESA mission for launch in mid 2012, expected 5 (+1?) yr lifetime
all sky (i.e. ~ 40,000 deg2) survey complete to Vlim = 20-22 ~ one billion sources
high accuracy astrometry (parallaxes, positions, proper motions)
optical spectrophotometry (luminosities, astrophysical parameters)
spectroscopy (radial velocities, rotation, chemistry) to V = 16-17
5D (some 6D … up to 9D) phase space survey over a large fraction of the Galaxy volume
Data distribution policy: final catalogue ~ 2019–20 intermediate data release (TBD) science alerts data released immediately no proprietary data rights
11 __________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
Astrometric accuracy: the Pleiades
π = 7.59 ± 0.14 mas - 132 pc, MS fitting (Pinsonneault et al. 1998) π = 7.69 mas - 130 pc, various methods (Kharchenko et al. 2005 ) π = 7.49 ± 0.07 mas - 133 pc, from 3 HST-FGS parallaxes in inner halo (Soderblom et al. 2005) π = 8.18 ± 0.13 mas - 122 pc, new reduction Hipparcos data (Van Leeuwen 2007) faintest MS stars have V < 15 Gaia individual parallaxes with σ(π)/π < 0.1 %
12 __________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
2010 updated performance for
B1V-G2V
M6V
Sky-averaged end-of-mission parallax standard error, in units of µas, as function of Johnson V magnitude for 3 reference stellar types Estimates include a 20% margin for unmodelled errors (e.g. radiation damage effect on CCDs not fully taken into account) Nominal max density for GAIA N20 ~ 0.25 stars arcsec-2 (likely smaller)
Astrometric performance: summer 2009 status
Courtesy A. Brown (J. De Bruijne , GAIA-CA-TN-ESA-JDB-055)
σω ≤ 0.3 mas
Vlim = 20-22
σpos = 0.74 σω
σµ = 0.53 σω
13 __________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
I metodi indiretti: gli indicatori di distanza
La distanza degli oggetti al di fuori della nostra Galassia viene stimata attraverso "tecniche indirette" che si basano sulla
identificazione di oggetti celesti di luminosita' nota, che costituiscono delle
”standard candles". Queste ”standard candles" devono, pero', essere accuratamente "calibrate".
Indicatori Primari Indicatori Secondari Indicatori Terziari
100 Watt
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Primary Indicators Variable Stars
Cepheids ~ 3×107 pc P/L
RR Lyrae < 106 pc MV ~ const.
Novae 106 - 107 pc L/td
Eclipsing binaries
Miras ~ 107 pc P/L
Stars and evolutionary phases with constant luminosity
RGB Tip ~ 107 pc Red Clump
MS Fitting of open and globular clusters
HB stars
40 < d < 7000 pc 3000 < d < 10000 pc __________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 15
Main Secondary Indicators Brightest stars in galaxies ~ 8×106 pc
Brightest HII regions ~ 2×107 pc
Globular clusters luminosity function ~ 10-20×106 pc
Main Tertiary Indicators
Luminosity class of spiral galaxies Dimensions of galaxies Total luminosity of the brightest galaxies
Surface brightness fluctuations ~ 7×107 pc
Colour-luminosity relation in ellipticals ~ 108 pc
3×108 pc
> 109 pc
Supernovae ~ 108 pc
Tully-Fischer relation ~ 15×107 pc
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Primary Indicators Pulsating variable stars
Cepheids ~ 3×107 pc P/L
RR Lyrae < 106 pc MV ~ const.
Stars and evolutionary phases at constant luminosity
RGB Tip ~ 107 pc
MS Fitting of open and globular clusters 40 < d < 7000 pc 3000 < d < 10000 pc
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 17
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 17
Pulsating Variable Stars
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Class Period (days) MV Pop Evo. Phase δ Cephei (CC) 1 – 100(?) -7(-8) ÷ -2 I Blue Loop δ Scuti (δSc) < 0.5 2 ÷ 3 I MS-PMS β Cephei < 0.3 -4.5 ÷ -3.5 I MS RV Tauri 30 – 100 -2 ÷ -1 I, II post-AGB Miras > 100 -2 ÷ 1 I, II AGB Semiregulars (SR) > 50 -3 ÷ 1 I, II AGB RR Lyrae (RRL) 0.2 – 1 ~0.5 ÷ 0.6 II HB W Virginis (Type2C) 10 – 50 -3 ÷ -1 II post-HB BL Herculis (Type2C) < 10 -1 ÷ 0 II post-HB SX Phoenicis (SXPhe) < 0.1 2 ÷ 3 II MS ACs 0.3 - 2.5 -2 ÷ 0 ? HB-turnover SP Cepheids (SPC) < 2 ≤ 0.0 I Blue Loop LL Cepheids (LLC) 0.55 – 0.65 ≤ 0.4 ? ?
Pulsating Stars
adapted from Marconi 2001 19
Soszynski et al. 2009
CCs ACs
Type2C RRL δSc
LMC pulsating variables from OGLE III
Red Variables
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OGLE II LMC
OGLE III
Soszynski et al. 2006 Soszynski et al. 2009
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__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
Classical Cepheids
P = 1 – 100(?) days Av ≤ 1.5 mag Sp Type: F6 – K2 Pop I Evo. Phase: Blue Loop Young stars, tracing star forming regions, spiral arms
Characteristics
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Classical Cepheid P/L relation
B-W of MW Cepheids
universal ?
metallicity dependent ?
if yes
if yes
-0.2 ± 0.2 mag/dex in V, I
HST Key Project 31 galaxies 700 Kpc < d < 20 Mpc
H0 = 72 ± 8 km s-1 Mpc -1 (*)
Madore & Freedman 1991, 1992 MCs Cepheid P/L relation at varius wavelengths
Cepheids in the LMC α
Trig. Parall. of MW Cepheids β
Freedman et al. 2001
(*) but see e.g. Saha et al. (2001), Tamman et al (2008, and references therein) for different conclusions about the value of H0.
Cepheid PL relation
L = αLog P + β
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Classical Cepheid P/L relation
B-W of MW Cepheids
universal ?
metallicity dependent ?
if yes
if yes
-0.2 ± 0.2 mag/dex in V, I
HST Key Project 31 galaxies 700 Kpc < d < 20 Mpc
H0 = 72 ± 8 km s-1 Mpc -1 (*) Madore & Freedman 1991, 1992 MCs Cepheid P/L relation at varius wavelengths
Cepheids in the LMC α
Trig. Parall. of MW Cepheids β
MCs Cepheid VIW(Ogle2)JHK P/L relations Fouque et al . 2003 Freedman et al. 2001
(*) but see e.g. Saha et al. (2001), Tamman et al (2008, and references therein) for different conclusions about the value of H0.
Cepheid PL relation
L = αLog P + β
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Cepheid P/L relations in the MCs
Udalski et al. 1999
V0(LMC)=-2.760 logP-17.042 σ=0.159 mag (649 FU CCs)
Theoretical P/L: Mv=-2.75 logP -1.37 σ= 0.18 mag
V0(SMC)=-2.760 logP-17.611 σ=0.258 mag (466 FU CCs)
Caputo, Marconi, Musella 2000 24
Classical Cepheids: open issues
2) Linearity of the PL over the whole observed period range
1) Dependence of the Cepheid properties and PL relation on the chemical composition
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Dependence of the Cepheid PL on chemical composition
The Cepheid PL relation is often assumed to be universal: the LMC PL is used to measure the distance to extragalactic Cepheids independently of their chemical composition (see e.g. the HST Key Project).
Dependence on chemical composition ⇒ systematic effects on the extragalactic distance scale (and H0)!!
A general consensus on the “universality” of the P-L relations for Cepheids has not been reached yet !
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__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
- Is the Cepheid P/L relation metallicity dependent?
Romaniello et al. 2008
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__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
Non-linear LMC P/L relations: the 10 days break
Marconi, Musella & Fiorentino 2005
Ngeow et al. 2005
see also: Fouque et al. 2003 Sandage et al. 2004
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Ultra Long Period Cepheids
Bird et al. 2009 29
Ultra Long Period Cepheids
Bird et al. 2009 30
Ultra Long Period Cepheids
Bird et al. 2009 31
RR Lyrae stars Characteristics
Mv (RR) = α[Fe/H] +β PLZ in the K band
Pop II Evo. Phase: HB (He-core burning) t > 10 Gyr
Smith 1995 32
- Trig. Parallax πRRLyr
Hipparcos π = 4.36 ± 0.59 mas
HST π = 3.82 ± 0.2 mas
Luminosity – metallicity relation of RR Lyrae stars
Mv(RR) = α [Fe/H] + β 0.13 < α < 0.30 0.5 < β < 1.0
- Baade-Wesselink
- HB (non variable stars)
- Statistical Parallaxes
Trig. Parallaxes
HB models
MSF
β from :
33 __________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
RR Lyrae stars
α from:
LMC α = 0.214 ± 0.047
HB Models
α ∼ 0.23
MW α = 0.20 ± 0.04
M31 α = 0.22 ± 0.06
Pulsation Models α ∼ 0.23
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RR Lyrae stars in the near-IR
Smaller amplitudes (AK~ 0.2-0.3 mag)
Tight PLZK relation (σ~0.05 mag)
MK=-2.101 logP+0.231[Fe/H] – 0.77 (Bono et al. 2003) MK=-2.353 logP+0.175logZ – 0.597 (Catelan et al. 2004) MK=-2.38 logP+0.08[Fe/H] – 1.07 (Sollima et al. 2008)
Szewczyk et al. 2008 Dall’Ora et al. 2004
Reticulum
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RR Lyrae PLK in the Gaia SEP calibra4on field
Blue=Bono et al. (2003); Red=Sollima et al. (2006)
RR Lyrae PLK in the Gaia SEP calibra4on field
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__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
Stars and evolutionary phases with constant luminosity
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RGB Tip The I luminosity of the RGB Tip is constant with metallicity: -2.2< [Fe/H] <-0.7 and age: 7< t < 17 Gyr
The RGB Tip luminosity in the I band is about 4 mag brighter than the HB: d ~ 3 ×106 - 107 pc
Calibration: a) via a theoretical model
providing the absolute luminosity of the RGB Tip
b) from the absolute magnitude of the RGB Tip of a cluster at known distance (e.g. ωCen)
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RGB Tip
Calibration: a) from the absolute
magnitude of the RGB Tip of a cluster at known distance (e.g. ωCen)
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 43
MS Fitting of open clusters
Ammasso Aperto M11 ~ 920 pc
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MS Fitting: Open Clusters
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MS Fitting: Open Clusters
ΔV = 3 mag
(m-M)Iades = 3.3 mag
(m-M)Praesepe = 3.3 + 3 = 6.3 mag
dPraesepe = 182 pc
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
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MS Fitting: Globular Clusters
Ammasso globulare M80 ~ 10 kpc
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MS Fitting: Globular Clusters
Fitting the Main Sequence of a globular cluster to a reference sequence formed by field subdwarfs of the same metallicity with known distance via trigonometric parallax.
(m - M )0 = - 5 + 5 log dpc
globular cluster MS
subdwarf reference sequence
globular cluster distance
Carretta et al. 2000, Ap. J. 533, 215
MS Fitting: Globular Clusters
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MS Fitting: Globular Clusters
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The distance to the LMC: short or long scale ?
Freedman et al. 2001
Benedict et al. 2002
The distance to the LMC: short or long scale ?
short scale Red Clump Eclipsing Binaries White Dwarfs
long scale GCs MSF Miras SN1987A RGB tip double mode RR Lyrae
Trig. Parallax Baade – Wesselink PL relation MS fitting
Mv(RR) = 0.70 at [Fe/H] = -1.5 Age(GCs) = 16 x 109 yrs μLMC = 18.25 mag D = 45 kpc Ho = 65-80 km s-1 Mpc
Mv(RR) = 0.50 at [Fe/H] = -1.5 Age(GCs) = 13 x 109 yrs μLMC = 18.50 mag D = 50 kpc Ho = 55-75 km s-1 Mpc
RR Lyrae statistical parallaxes Baade - Wesselink
Cepheids
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Distanza della Grande Nube di Magellano
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The promise of Gaia Gaia is planned for launch in mid 2012. During its lifetime of nominally 5(+1?) years, Gaia will scan the entire sky (i.e. ~ 40,000 deg2) repeatedly, observing all the sources brighter than Vlim = 20-22 mag (109 stars), with 80 measurements/object on average over the 5 year span.
According to current estimates, from 2000 to 8000 Classical Cepheids and about 70000 RR Lyrae stars will be observed by Gaia. Also, about 2000 Population II Cepheids are likely to be observed by the satellite.
Complete census of the MW Classical Cepheids. ~2000/1000 Classical Cepheids are know in the Magellanic Clouds and
observable by Gaia
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 54
The distance scale: local standard candles
RR Lyrae Mv= 0.5-0.6: Presently, 126 RR Lyraes with < V > = 10 to 12.5 (750 - 2500 pc) σπ/π ≥ 30 % (Hipparcos) (Fernley et al. 1998)
RR Lyr (<V>=7.8): only RRL star with good parallax estimate
π = 3.46 ± 0.64 mas mod = 7.30 mag (new Hipparcos, van Leeuwen 2007) π = 3.82 ± 0.20 mas mod = 7.09 mag (HST, Benedict et al. 2002) ΔMv ~ 0.2 mag distance to 10% !
Gaia: within 1.5 kpc to σπ/π < 1% (≤ 2.5% within 3 kpc, 25-30% at 10 kpc) RR Lyraes in globular clusters with mean σπ/π < 1%
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 55
The distance scale: local standard candles
Metal-poor subdwarfs Mv= 5.0 to 7.5:
Gaia: within 1 kpc distance to σπ/π < 2–6 % a factor 10 (1000) in distance (volume) several thousands expected
Presently, ~ 30 subdwarfs available (Hipparcos) within 100 pc
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The distance scale: MW Cepheids
Only ~ 800 Galactic Cepheids are known – most are located in the Solar neighbourhood
400 Galactic Cepheids from David Dunlap DB distance and magnitude Gaia predicted accuracy for parallax 15 @ d < 0.5 kpc 65 @ d < 1 kpc 165 @ d < 2 kpc
Presently, ~ 250 Cepheids with parallax & photometry (10 with HST parallax) only ~ 100 with σπ ≤ 1 mas (Hipparcos)
Figure courtesy A. Brown
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Most (~ 3/4) Galactic Cepheids will have Gaia individual parallaxes to < 3%
__________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
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The distance scale: MC Cepheids
The bulk of the distribution for fundamental LMC pulsators lies at Period = 3 – 5 days Mv ~ -3 V ~ 15.8 – 16 individual distances to ~ 150% mean of 400 to ~ 7-8 %
Cepheids with P ≥ 10 d Mv ≤ ~ - 4.2 V ~ 14.5 individual distances to ~ 80%
Ultra-long period (> 100 d) Cepheids Mv ≤ ~ - 7 V ~ 12 4 in LMC, 3 in SMC (Bird et al. 2009) individual distances to ~ 45% (LMC) - 55% (SMC)
600 Cepheids in the LMC (OGLE, Udalski et al. 1999)
direct (trigonometric) calibration of the cosmological distance scale
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~ 2000/1000 Cepheids are known (and observable by Gaia) in the LMC/SMC
__________________________________________________________________________________ G. Clementini – School ofAstrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010
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GAIA Concept and Technology Study Report, 2000, ESA-SCI(2000)4 The Three-Dimensional Universe with GAIA, 2005, ESA-SP 576
more information on
http://www.rssd.esa.int/Gaia
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The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective
Naples, May 3-6, 2011
more information on: http://www.oacn.inaf.it/ESFdistance
see also: WGA8 Distance scale, at: http://camd08.ast.cam.ac.uk/Greatwiki/WGA8DistanceScales
Thank you !
59 __________________________________________________________________________________ G. Clementini – School of Astrophysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010