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Mid-IR excess of evolved and MS stars in 47 Tuc

Mid-IR excess of evolved and MS stars in 47 Tuc. Pier Giorgio Prada Moroni Dipartimento di Fisica “E. Fermi” Università di Pisa. Collaborators. Giuseppe Bono (INAF-OAR) Pauline Barmby (Harvard-Smithsonian CfA) Ivan Ferraro (INAF-OAR) Massimo Marengo (Harvard-Smithsonian CfA)

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Mid-IR excess of evolved and MS stars in 47 Tuc

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  1. Mid-IR excess of evolved and MS stars in 47 Tuc Pier Giorgio Prada Moroni Dipartimento di Fisica “E. Fermi” Università di Pisa

  2. Collaborators • Giuseppe Bono (INAF-OAR) • Pauline Barmby (Harvard-Smithsonian CfA) • Ivan Ferraro (INAF-OAR) • Massimo Marengo(Harvard-Smithsonian CfA) • Roberto Buonanno (Univ. Roma Tor Vergata) • Carlo Corsi (INAF-OAR)

  3. DATA SET • IRAC-Spitzer: 3.6, 4.5, 5.8, 8 μm (GTO Prog. 623 Nov. 14 2004; Cycle 2 GOP 20298 Sept. 21 2005) • MIPS-Spitzer: 24 μm (Cycle 3 GTO 30031 June 12 2006) • U,B,V,I: ground based telescopes

  4. DATA SET • Mid-IR Catalogue: 42000 stars • Optical Catalogue: 173000 stars

  5. Theretical isochrones • FRANEC (Cariulo et al. 2004) • Z=0.004 Y=0.24 • BCs and color index for the optical bands by Bessell et al. 1998

  6. IRAC/MIPS color transformation • Kurucz’s atmospheric models: ATLAS 9(Castelli et al. 2003) IRAC/MIPS transmission curves

  7. IRAC/MIPS: extinction coefficients • IRAC bands: • MIPS 24 μm: table 1 by Mathis 1990

  8. 47 Tuc • DM0= 13.35±0.15 • E(B-V)=0.03±0.02 (Zoccali et al. 2001, Percival et al. 2002, Gratton et al. 2003, Salaris et al. 2008) • Age= 11 Gyr

  9. Spitzer-IRAC 3.6 - 4.5

  10. Spitzer-IRAC 5.4 - 8

  11. Spitzer-IRAC 3.6 • Large spread in optical-MIR colors Δ (B-3.6) ~ 2 mag • Observed color excess » photometric error

  12. IR-excess sources • Red extragalactic sources • Binaries or photometric blends • Circumstellar dusty envelopes • Circumstellar dusty disk

  13. Working hypothesis:debris disk • Chiang & Goldreich 1997 • Jura 2003

  14. Spitzer-IRAC 3.6 - 4.5

  15. Spitzer-IRAC 5.4 - 8

  16. Spitzer-IRAC

  17. SED

  18. CONCLUSIONS • Mid-IR excess for evolved and MS stars • Dusty disks

  19. FIR/Ftot • MS star: ~0.016 • RGB star: ~0.02-0.03 • HB star: ~0.0036

  20. Mass estimate • Silicate grains: χ= 1000 – 0.05 cm2/g • M≥ Aring/ χ • MS: 1021-1025 g • RGB: 1022-1026 g • HB: 1023-1027 g

  21. Circumstellar envelope

  22. AGB Stars

  23. AGB Stars

  24. AGB Stars

  25. Binary/photometric blend: BD Burrows et al. 1997

  26. Binary/photometric blend: VLM VLM MS (Brocato et al. 1998)

  27. Binary/photometric blend: RGB

  28. HB M=0.65 Mo

  29. RGB M=0.9 Mo

  30. MS M=0.86 Mo

  31. Photometric error MIR-bands

  32. RGB Bump Stars

  33. RGB Stars

  34. Metallicity • [Fe/H]=-0.67±0.05 (Carretta et al. 2004) • [α /Fe]=0.3(Gratton et al. 2003) Salaris et al. 1993; Degl’Innocenti, Prada Moroni & Ricci 2006 • Z=0.04

  35. DATA SET • IRAC-Spitzer: 3.6, 4.5, 5.8, 8 μm 1.GTO Prog. 623 Nov. 14 2004: tot. int. time 135 sec, 22’x26’ 2. Cycle 2 GOP 20298 Sept. 21 2005: tot. int. time 940 sec, 5’x15’ • MIPS-Spitzer: 24 μm Cycle 3 GTO 30031 June 12 2006: tot. int. Time 100 sec, 5.4’x10.6’ • U,B,V,I: ground based telescopes 20’x18’

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