The Distance Scale in the Gaia Era · the LMC PL is used to measure the distance to extragalactic Cepheids independently of their chemical composition (see e.g. the HST Key Project)

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


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

I


m - M = - 5 + 5logdpc distance modulus

3

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."

4

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

5

2×105 - 109 pc and beyond

secondary


Hipparcos

Gaia

Trigonometric Parallax

7

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

8

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

11

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 %


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


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

14

__________________________________________________________________________________ G. Clementini – School of Astorphysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010

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

16

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



Pulsating Variable Stars


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

21


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

23

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


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 !

26


- Is the Cepheid P/L relation metallicity dependent?

Romaniello et al. 2008

27


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


Bird et al. 2009 30


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 :


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

35


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

37


Stars and evolutionary phases with constant luminosity

40


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)


RGB Tip

Calibration: a)  from the absolute

magnitude of the RGB Tip of a cluster at known distance (e.g. ωCen)


MS Fitting of open clusters

Ammasso Aperto M11 ~ 920 pc


MS Fitting: Open Clusters

45

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



MS Fitting: Globular Clusters

Ammasso globulare M80 ~ 10 kpc

__________________________________________________________________________________ G. Clementini – School ofAstrphysics “F. Lucchin” II Cycle 2010, Asiago, 24-30 October 2010 47


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


48



48

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


Distanza della Grande Nube di Magellano

52

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



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%


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

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 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

56

Most (~ 3/4) Galactic Cepheids will have Gaia individual parallaxes to < 3%


57

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

57

~ 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

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

http://www.rssd.esa.int/Gaia


59

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 !


Documents

The Distance Scale in the Gaia Era · the LMC PL is used to measure the distance to extragalactic Cepheids independently of their chemical composition (see e.g. the HST Key Project)