Galactic Disk Gradients & Kinematics: Classical Cepheids as Tracers

1. Classical Cepheids as tracers of disk gradients & kinematics G. Bono: Univ. of Rome Tor Vergata F. Caputo + romans + P.B. Stetson (DAO) V.I.M.M.A (napoletans) M. Romaniello, F. Primas (ESO) P. Francois (IAP) J. Lub, J.W. Pel, B. Lemasle, G. Fiorentino (NL)

2. Summary • Cepheids as distance indicators • Cepheids as chemical tracers • Galactic Abundance Gradient • Recent Findings • VST Survey [outer disk] • Why and Where • Conclusions

3. Classical Cepheids • Masses: 3 – 11 Mo • Age: young (Pop I) • Magnitude: Mv ≈ -2, -7 • Period: 1 – a few 100 days Walraven-NIR (Pel 1979) GRAPES (Marconi et a. 2008) BaSTI (Cassisi et al. 2008)

4. V-band PL relation is affected by metal abundance (95% c.l.) And this finding is minimally affected by the adopted LMC distance 2σ 9σ Metal-poor bin Metal-rich bin The metallicity effect on the PL relation PLV Freedman et al. (2001) δMV > 0  Cepheid is fainter than the one obtained with the standard PL relation Metal-rich Cepheids in the V band are, at a fixed period, fainter than metal-poor ones

5. Calibration of chemical evolution models of the Galactic Disk Andrievsky et al. 2004; Luck et al.2006; Lemasle et al. 2007; Romaniello et al. 2008: (-0.02, -0.05) dex/kpc Neese & Yoss 1998; Kilian-Montenbruck et al. 1994: (-0.017, 0.003) dex/kpc Galactic abundance gradient Photometric abundances: Walraven VBLUW: (B-L), (V-B), (L-U) Spectral type: F – G Stroemgren: m1 = (v-b) – (b-y) Spectral type: A – G

6. Linear/Bi-Linear Metallicity Gradient Steeper in the inner disk Shallower in the outer disk Large spread at fixed Galactocentric distance Pedicelli et al. (2009)

7. Radial distribution across the Galactic plane Lack of a clear radial trend, when moving from the innermost to the outermost regions

8. Cepheid radial distribution and spiral arms The chemical composition across the Galactic disk is clumpy

9. Conclusions: The Disk Abundance Gradient • We investigated the Galactic abundance gradient using 265 Cepheids • Current data indicate a global slope of –0.051 ± 0.004 dex kpc−1 in the 5–17 kpc range • Inner disk: RG ≤ 8.0 kpc  -0.130 ± 0.015 dex kpc−1 • Outer disk: RG > 8.0 kpc  -0.042 ± 0.005 dex kpc−1 • The spread in iron abundance, at fixed Galactocentrinc distance, is real • The metallicity distribution across the disk is clumpy • Relevant constraints for Galactic chemical evolution models

10. RADIO MEASUREMENTS VLBI + VERA Accurate trigonometric parallaxes and proper motion of masers of a Handful (18) of High-Mass-Star-Forming Regions by Reid et al. (2009) New estimates: Galactic center  Ro=8.4±0.6 kpc Circ.Rot.speed  Θo=254±16 km/s The HMSFRs are orbiting the MW 15 km/s slower than expected for circular orbits!!!

11. RADIO MEASUREMENTS The Galaxy and M31 have similar masses Drift in the rotation curve between HMSFR and the rotation curve of the Galaxy

12. Limits of current surveys •  OUTER DISK DESERT • Only a few known Cepheids are located at Galactocentric distances larger than 12-15 kpc • Survey on selected disk regions  VST •  INNER DISK DESERT • Only a few known Cepheids are located at Galactocentric distances smaller than 3-6 kpc [where is the edge between the bulge and the inner disk?] • Highly Reddened regions  VISTA

13. VST FILLER SURVEY • Two selected regions 50 degree squared each • Located across the I and the II quadrant • Located in the III quadrant TWO STEPS: Identification Characterization Limiting magnitude B=22, S/N=20 Seeing 1” 2” ETC by A.R. 2+1(over) 6+1(over) Tot (100 pointings) 60h 140h TWO-THREE nights of good seeing conditions for accurate --u,v,B,V,I-- magnitudes and periods

14. REWARD-1 Current survey indicate a density of almost 1 Cepheid per degree squared with a limiting magnitude of V~15 (Caldwell et al. 1991) • A decrease of 7 magnitudes implies the detection of Cepheids with a lifetime that is on average one order of magnitude longer Conservative estimates indicate that with this survey we can double the number of known Galactic Cepheids

15. REWARD-2 At least three magnitudes deeper than GAIA PAN-STAR is the real competitor, but We know what we are looking for ... Synergies with other proposed surveys (talk by K. Kuijken): Detection of variable stars (RR Lyrae) up to the edge of the Galaxy (DM=20) Galactic disk white dwarfs

16. Scientific Drivers • Metallicity estimates (u,v,B,V,I)  • Calamida et al. 2008,2009) • Metallicity distribution in the outer disk • Spectroscopic follow-up  Bright  FLAMES@GIRAFFE •  faint  FORS2 • Galactic Rotation Curve •  Mass distribution across the Galactic disk

17. TEAM WE CAN COPE WITH THE REDUCTION AND the ANALYSIS OF THE IMAGES WE PLAN TO COLLECT IN THIS PROJECT iff The pre-reduced images are eitherMEGACAM@CFHT or SUPRIME@SUBARU like [zero-points within 0.02 mag across the entire field] NO WAY IF THEY ARE WFI@2.2m like

18. CREDITS • S. Pedicelli (Rome-ESO PhD) looking for a post-doc • M. Dall’ORA Ricercatore astronomo idoneo • A. Calamida, post-doc at ESO Garching • M. Monelli, post-doc at IAC • G. Fiorentino, post-doc in Groeningen • M. Dicriscienzo, post-doc in Rome