The Distance Scale in the Gaia Era

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1 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, October

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, October

3 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 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

4 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 ~ l.y. ~ 8 kpc p Sun -LMC ~ 50 kpc Sun - Andromeda ~ 2.5 x 10 6 l.y. ~ 770 kpc Sun - Locale Group ~ 3.3 x 10 6 l.y. ~ 1 Mpc Sun - M81 and Sculptor clusters ~ 6-10 x 10 6 l.y. ~ 2.5 Mpc Sun - M101 cluster ~ x 10 6 l.y. ~ 5.4 Mpc Sun - Virgo cluster ~ 40 x 10 6 l.y. ~ 12 Mpc Sun - Coma cluster ~ 300 x 10 6 l.y. ~ 92 Mpc I m - M = logd pc distance modulus 3 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

5 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." Gaia TRGB 4

6 Milky Way Direct methods: trigonometric parallax 0<d<100 pc Indirect methods:: - Proper motions + statistical parallax pc - Main Sequence Fitting open clusters pc globular clusters pc Beyond the Milky Way Spectroscopic and photometric parallax > pc Distance indicators primary secondary tertiary pc pc and beyond 5

7 Trigonometric Parallax Gaia Hipparcos 7 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

8 Direct method: trigonometric parallax p = tang U.A./d ~ U.A./d p = 1" d = 1 pc d pc = 1/p" p «1" p α Cen = 0.76" 0 < d < 100 pc 8

HIPPARCOS Satellite astrometrico lanciato dall'esa nel 1989 e operativo fino al 1993. Ha misurato la parallasse di 118.

9 HIPPARCOS Satellite astrometrico lanciato dall'esa nel 1989 e operativo fino al Ha misurato la parallasse di stelle con magnitudine apparente V fino alla 9 e precisione di Catalogo finale nel "Come vedere un astronauta in piedi sulla Luna" 9

GAIA Satellite astrometrico che verra' lanciato dall'esa nel 2012.

10 GAIA Satellite astrometrico che verra' lanciato dall'esa nel Misurera' le parallassi di 1000 milioni di stelle della nostra Galassia con magnitudine apparente V fino alla e precisione di " a V=15. "Come vedere l'unghia di un astronauta sulla Luna

11 Gaia in a nutshell ESA mission for launch in mid 2012, expected 5 (+1?) yr lifetime all sky (i.e. ~ 40,000 deg 2 ) survey complete to V lim = ~ one billion sources high accuracy astrometry (parallaxes, positions, proper motions) optical spectrophotometry (luminosities, astrophysical parameters) spectroscopy (radial velocities, rotation, chemistry) to V = D (some 6D up to 9D) phase space survey over a large fraction of the Galaxy volume Data distribution policy: final catalogue ~ 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, October 2010

Astrometric accuracy: the Pleiades π = 7.59 ± 0.14 mas - 132 pc, MS fitting (Pinsonneault et al. 1998) π = 7.

07 mas - 133 pc, from 3 HST-FGS parallaxes in inner halo (Soderblom et al. 2005) π = 8.18 ± 0.

12 Astrometric accuracy: the Pleiades π = 7.59 ± 0.14 mas pc, MS fitting (Pinsonneault et al. 1998) π = 7.69 mas pc, various methods (Kharchenko et al ) π = 7.49 ± 0.07 mas pc, from 3 HST-FGS parallaxes in inner halo (Soderblom et al. 2005) π = 8.18 ± 0.13 mas pc, new reduction Hipparcos data (Van Leeuwen 2007) faintest MS stars have V < 15 Gaia individual parallaxes with σ(π)/π < 0.1 % G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

13 Astrometric performance: summer 2009 status 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 N 20 ~ 0.25 stars arcsec -2 (likely smaller) σ ω 0.3 mas V lim = σ pos = 0.74 σ ω σ µ = 0.53 σ ω 2010 updated performance for B1V-G2V M6V Courtesy A. Brown (J. De Bruijne, GAIA-CA-TN-ESA-JDB-055) G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

14 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". 100 Watt Indicatori Primari Indicatori Secondari Indicatori Terziari G. Clementini School of Astorphysics F. Lucchin II Cycle 2010, Asiago, October

15 Primary Indicators Variable Stars Cepheids ~ pc P/L RR Lyrae < 10 6 pc M V ~ const. Novae pc L/t d Eclipsing binaries Miras ~ 10 7 pc P/L Stars and evolutionary phases with constant luminosity RGB Tip ~ 10 7 pc Red Clump HB stars MS Fitting of open and globular clusters 40 < d < 7000 pc 3000 < d < pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

16 Main Secondary Indicators Brightest stars in galaxies Brightest H II regions Globular clusters luminosity function Surface brightness fluctuations Tully-Fischer relation Colour-luminosity relation in ellipticals Supernovae ~ pc ~ pc ~ pc ~ pc ~ pc ~ 10 8 pc ~ 10 8 pc Main Tertiary Indicators Luminosity class of spiral galaxies Dimensions of galaxies Total luminosity of the brightest galaxies pc > 10 9 pc 16

17 Primary Indicators Pulsating variable stars Cepheids ~ pc P/L RR Lyrae < 10 6 pc M V ~ const. Stars and evolutionary phases at constant luminosity RGB Tip ~ 10 7 pc MS Fitting of open and globular clusters 40 < d < 7000 pc 3000 < d < pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

18 Pulsating Variable Stars G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

19 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

20 Pulsating Stars Class Period (days) M V Pop Evo. Phase δ Cephei (CC) 1 100(?) -7(-8) -2 I Blue Loop δ Scuti (δsc) < I MS-PMS β Cephei < I MS RV Tauri I, II post-agb Miras > I, II AGB Semiregulars (SR) > I, II AGB RR Lyrae (RRL) ~ II HB W Virginis (Type2C) II post-hb BL Herculis (Type2C) < II post-hb SX Phoenicis (SXPhe) < II MS ACs ? HB-turnover SP Cepheids (SPC) < I Blue Loop LL Cepheids (LLC) ?? adapted from Marconi

21 LMC pulsating variables from OGLE III Red Variables CCs ACs Type2C RRL δsc Soszynski et al

OGLE II LMC OGLE III Soszynski et al. 2006 Soszynski et al. 2009 G.

22 OGLE II LMC OGLE III Soszynski et al Soszynski et al G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

23 Characteristics Classical Cepheids P = 1 100(?) days A v 1.5 mag Sp Type: F6 K2 Pop I Evo. Phase: Blue Loop Young stars, tracing star forming regions, spiral arms 22

24 Classical Cepheid P/L relation Cepheid PL relation L = αlog P + β Cepheids in the LMC α Trig. Parall. of MW Cepheids B-W of MW Cepheids β universal? metallicity dependent? if yes if yes MCs Cepheid P/L relation at varius wavelengths Madore & Freedman 1991, 1992 (*) but see e.g. Saha et al. (2001), Tamman et al (2008, and references therein) for different conclusions about the value of H 0. HST Key Project 31 galaxies 700 Kpc < d < 20 Mpc H 0 = 72 ± 8 km s -1 Mpc Freedman et al ± 0.2 mag/dex in V, I -1 (*) 23

25 Classical Cepheid P/L relation Cepheid PL relation L = αlog P + β Cepheids in the LMC α Trig. Parall. of MW Cepheids B-W of MW Cepheids β universal? metallicity dependent? if yes if yes MCs Cepheid P/L relation at varius wavelengths Madore & Freedman 1991, 1992 MCs Cepheid VIW(Ogle2)JHK P/L relations Fouque et al HST (*) but Key see Project e.g. Saha -0.2 et ± 0.2 al. mag/dex (2001), 31 Tamman galaxies et al (2008, and in V, references I 700 therein) Kpc < for d < different 20 Mpc conclusions about H 0 = 72 ± 8 km s -1 Mpc -1 (*) the value of H 0. Freedman et al

26 Cepheid P/L relations in the MCs V 0 (LMC)= logp σ=0.159 mag (649 FU CCs) V 0 (SMC)= logp σ=0.258 mag (466 FU CCs) Theoretical P/L: Udalski et al Mv=-2.75 logp σ= 0.18 mag Caputo, Marconi, Musella

27 Classical Cepheids: open issues 1) Dependence of the Cepheid properties and PL relation on the chemical composition 2) Linearity of the PL over the whole observed period range G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

28 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 H 0 )!! A general consensus on the universality of the P-L relations for Cepheids has not been reached yet! G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

- Is the Cepheid P/L relation metallicity dependent? Romaniello et al. 2008 G.

29 - Is the Cepheid P/L relation metallicity dependent? Romaniello et al G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

30 Non-linear LMC P/L relations: the 10 days break Marconi, Musella & Fiorentino 2005 see also: Fouque et al Sandage et al Ngeow et al

31 Ultra Long Period Cepheids Bird et al

32 Ultra Long Period Cepheids Bird et al

33 Ultra Long Period Cepheids Bird et al

34 Characteristics RR Lyrae stars Pop II Evo. Phase: HB (He-core burning) t > 10 Gyr M v (RR) = α[fe/h] +β PLZ in the K band Smith

35 Luminosity metallicity relation of RR Lyrae stars M v (RR) = α [Fe/H] + β 0.13 < α < < β < 1.0 β from : - Trig. Parallax π RRLyr Hipparcos HST π = 4.36 ± 0.59 mas π = 3.82 ± 0.2 mas - Baade-Wesselink - HB (non variable stars) - Statistical Parallaxes Trig. Parallaxes MSF HB models 33 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

36 RR Lyrae stars α from: MW α = 0.20 ± 0.04 LMC α = ± M31 α = 0.22 ± 0.06 HB Models α 0.23 Pulsation Models α

37 RR Lyrae stars in the near-ir Smaller amplitudes (A K ~ mag) Tight PLZ K relation (σ~0.05 mag) M K = logp+0.231[fe/h] 0.77 (Bono et al. 2003) M K = logp+0.175logz (Catelan et al. 2004) M K =-2.38 logp+0.08[fe/h] 1.07 (Sollima et al. 2008) Reticulum Dall Ora et al Szewczyk et al

38 RR Lyrae PLK in the Gaia SEP calibra4on field G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

39 RR Lyrae PLK in the Gaia SEP calibra4on field Blue=Bono et al. (2003); Red=Sollima et al. (2006) 37

40 Stars and evolutionary phases with constant luminosity G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

41 The I luminosity of the RGB Tip is constant with metallicity: -2.2< [Fe/H] <-0.7 and age: 7< t < 17 Gyr RGB Tip The RGB Tip luminosity in the I band is about 4 mag brighter than the HB: d ~ 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) G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

42 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, October

43 MS Fitting of open clusters Ammasso Aperto M11 ~ 920 pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

44 MS Fitting: Open Clusters G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

MS Fitting: Open Clusters ΔV = 3 mag (m-m) Iades = 3.3 mag (m-m) Praesepe = 3.3 + 3 = 6.

45 MS Fitting: Open Clusters ΔV = 3 mag (m-m) Iades = 3.3 mag (m-m) Praesepe = = 6.3 mag d Praesepe = 182 pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

46 MS Fitting: Globular Clusters Ammasso globulare M80 ~ 10 kpc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

47 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 = log d pc globular cluster MS subdwarf reference sequence globular cluster distance G. Clementini School ofastrphysics F. Lucchin II Cycle 2010, Asiago, October

48 MS Fitting: Globular Clusters Carretta et al. 2000, Ap. J. 533,

49 MS Fitting: Globular Clusters G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

50 The distance to the LMC: short or long scale? Freedman et al Benedict et al

51 The distance to the LMC: short or long scale? short scale RR Lyrae Red Clump Eclipsing Binaries White Dwarfs statistical parallaxes Baade - Wesselink M v (RR) = 0.70 at [Fe/H] = -1.5 Age(GCs) = 16 x 10 9 yrs μ LMC = mag D = 45 kpc Ho = km s -1 Mpc long scale Cepheids GCs MSF Miras SN1987A RGB tip double mode RR Lyrae Trig. Parallax Baade Wesselink PL relation MS fitting M v (RR) = 0.50 at [Fe/H] = -1.5 Age(GCs) = 13 x 10 9 yrs μ LMC = mag D = 50 kpc Ho = km s -1 Mpc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

52 Distanza della Grande Nube di Magellano 52

53 The promise of Gaia Gaia is planned for launch in mid During its lifetime of nominally 5(+1?) years, Gaia will scan the entire sky (i.e. ~ 40,000 deg 2 ) repeatedly, observing all the sources brighter than V lim = mag (10 9 stars), with 80 measurements/ object on average over the 5 year span. According to current estimates, from 2000 to 8000 Classical Cepheids and about 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, October 2010

54 The distance scale: local standard candles RR Lyrae Mv= : Presently, 126 RR Lyraes with < V > = 10 to 12.5 ( pc) σ π /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, October

55 The distance scale: local standard candles Metal-poor subdwarfs Mv= 5.0 to 7.5: Presently, ~ 30 subdwarfs available (Hipparcos) within 100 pc Gaia: within 1 kpc distance to σπ/π < 2 6 % a factor 10 (1000) in distance (volume) several thousands expected G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

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

56 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 d < 0.5 kpc d < 1 kpc d < 2 kpc Presently, ~ 250 Cepheids with parallax & photometry (10 with HST parallax) only ~ 100 with σ π 1 mas (Hipparcos) Figure courtesy A. Brown Most (~ 3/4) Galactic Cepheids will have Gaia individual parallaxes to < 3% 56 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

57 The distance scale: MC Cepheids ~ 2000/1000 Cepheids are known (and observable by Gaia) in the LMC/SMC The bulk of the distribution for fundamental LMC pulsators lies at Period = 3 5 days Mv ~ -3 V ~ individual distances to ~ 150% mean of 400 to ~ 7-8 % Cepheids with P 10 d Mv ~ 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 57 G. Clementini School ofastrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

58 GAIA Concept and Technology Study Report, 2000, ESA-SCI(2000)4 The Three-Dimensional Universe with GAIA, 2005, ESA-SP 576 more information on 58 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October 2010

59 The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective Naples, May 3-6, 2011 more information on: see also: WGA8 Distance scale, at: Thank you! G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, October

Building the cosmic distance scale: from Hipparcos to Gaia

The Fundamental Distance Scale: state of the art and the Gaia perspectives 3-6 May 2011 Building the cosmic distance scale: from Hipparcos to Gaia Catherine TURON and Xavier LURI 1 ESA / ESO-H. Heyer Fundamental