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ASTROBIOLOGICALLY INTERESTING STARS: SELECTION CRITERIA

2nd Brazilian COROT Workshop 2005. ASTROBIOLOGICALLY INTERESTING STARS: SELECTION CRITERIA. Observatório do Valongo Universidade Federal do Rio de Janeiro. Gustavo Porto de Mello Eduardo del Peloso Luan Ghezzi. Darwin (ESA). COROT (CNES+Brazil+others). Terrestrial Planet Finder (NASA).

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ASTROBIOLOGICALLY INTERESTING STARS: SELECTION CRITERIA

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  1. 2nd Brazilian COROT Workshop 2005 ASTROBIOLOGICALLYINTERESTINGSTARS:SELECTIONCRITERIA Observatório do Valongo Universidade Federal do Rio de Janeiro Gustavo Porto de Mello Eduardo del Peloso Luan Ghezzi Darwin (ESA) COROT (CNES+Brazil+others) Terrestrial Planet Finder (NASA)

  2. Scientific Motivation 2nd Brazilian COROT Workshop 2005 To establish state of the art criteria for characterizing stars which might be hosts to biospheres detectable remotely COROT will probably detect the first ever Earthlike planet Final goal: to remotely detect the presence of life, able to thermodynamically alter a planetary atmosphere to a non-equilibrium state THE PRESENT BACKGROUND: New constraints on the concept of Habitable Zone in Astrobiology: Kasting et al. 1993, Franck et al. 2000, Gonzalez et al. 2001, Lineweaver et al. 2004 Long term climate stability, bioproductivity, oxygenation time scale, Galactic chemical evolution, stability agains catastrophes RECENT APPROACHES:Habitability catalogue:Turnbull & Tarter 2003Nearby Biostar catalogue: Porto de Mello et al. 2004, 2005 (d < 15 pc)

  3. Remote Detection of Life 2nd Brazilian COROT Workshop 2005 Star/Planet contrats in the thermal infrared Des Marais et al 2002 Segura et al 2003 THE KEY: SIMULTANEOUS DETECTION O3 + CO2 + H2O CO2 15 m, O3 9.6 m, H2O 6.3 m, CH4 7.7 m 8-12 m window: surface temperature, radius

  4. The Habitable Zone Concept 2nd Brazilian COROT Workshop 2005 Planetary and stellar assumptions: Surface H2O for a few Gyr, geologic activity, CO2-H2O-N2 atmosphere magnetic field, climate stability, threshold metallicity, stellar ages > 3 Gyr O3 observable during Proterozoic ~ 2 Gyr ago (Segura et al 2003) CH4 observable only up to 10-1 PAL of O2 (Proterozoic) Oxygenation timescale (Blair-Hedges et al 2004, Catling et al 2005) ~ 3 Gyr Climate Models: J. Kasting et al (Univ. Penn.), S. Franck et al (Potsdam Climate Research) Negative feedback: pCO2 if T  (greenhouse effect by the carbonate-silicate cycle) Destabilizing effects: pH2O  if T  and albedo  if T 

  5. The Habitable Zone Concept 2nd Brazilian COROT Workshop 2005 Arrenhius equation: (1-a) Seff = 4 Tb4 Surface temperature: TS = Tb + T OUTER EDGE INNER EDGE Water Loss Seff = 1.10 Runaway Greenhouse Seff = 1.41 First Condensation Seff = 0.53 Maximum Greenhouse Seff = 0.36

  6. The Habitable Zone Concept 2nd Brazilian COROT Workshop 2005 Assumption: main sequence lifetime > oxygenation timescale Upper mass limit: F9V-F7V stars, M ~ 1.2 M Upper mass limit: K2V-K3V stars, M ~ 0.7 M

  7. The Habitable Zone Concept 2nd Brazilian COROT Workshop 2005 Tidal Lock Radius Questions:  Orbital resonances  Magnetic moment  Quick climate damage  Initial long lived phase of extremely high XUV flux and mass loss rate

  8. 2nd Brazilian COROT Workshop 2005 Continuously Habitable Zone and Timescales

  9. 2nd Brazilian COROT Workshop 2005 Continuously Habitable Zone and Timescales Franck et al 1999, 2000 Bioprodutivity (biomass/time/area): pCO2 > 150 ppm Grasses and other lower species: pCO2 > 10 ppm Age of highly diversified biosphere (animals and plants) is less than 20% of total biosphere lifetime Too advanced an age is a liability

  10. 2nd Brazilian COROT Workshop 2005 The Candidates: selection in (B-V) and MV Hipparcos HR diagram for d < 10 pc: 182 stars 27% = 50 pre-selected candidates

  11. 2nd Brazilian COROT Workshop 2005 Candidates: age & metallicity

  12. 2nd Brazilian COROT Workshop 2005 Candidates: isochronal ages HR222, 4458 and 4523

  13. 2nd Brazilian COROT Workshop 2005 Candidates: isochronal ages HR5019 61 Vir

  14. 2nd Brazilian COROT Workshop 2005 Candidates: isochronal ages HR7665 Delta Pavonis

  15. 2nd Brazilian COROT Workshop 2005 The “biostars” within 10 parsecs HD Name mass age [Fe/H] orbit rank d(pc) 1581  Tuc ~ ~ ~ >   8.6 4628 < ? < ~  7.5 10476 107 Psc < ? < > 7.5 16160 < ? ~ >  7.2 32147 < ~ > >  8.8 100623 < > < > 9.5 102365 < > < > 9.2 109358  CVn > ~ < ~  8.4 115617 61 Vir ~ ~ ~ >   8.5 185144  Dra < > < > 5.8 190248  Pav > ~ > ~  6.1 192310 < > ~ >  8.8 219134 < ? ~ >  6.5

  16. 2nd Brazilian COROT Workshop 2005 Conclusions & Perspectives • We can strongly constrain stars in the astrobiological sense, wit present • data: [Fe/H] and Teff, chromospheric activity, evolutionary state, age, mass • 2) In all neighborhood stars: ~7% are interesting • <2% if we take galactic orbits as relevant • <1% is actually similar to the Sun • 3) Data completeness: only up to ~15 parsecs for [Fe/H] and activity • 4) We should better constrain the stellar [Fe/H] and Teff: better ages and • masses • 5) Theoreticians should explore habitability criteria for planets appreciably • different from the Earth

  17. THANK YOU

  18. 3 - O Conceito de Zona Habitável 6 Ciclo carbonato-silicato: atua em escalas ~ 106 anos Pode remover todo o carbono: oceanos + atmosfera em ~ 400 Mano

  19. 3a – Massas Estelares 11 Limite inferior de massa: fase inicial de vento denso + excesso de XUV Remoção de ~ 10% a 100% de voláteis em escalas de ~ 1-2 Gano Tipo GK: fase saturada for ~ 100 Mano a níveis 100 vezes maiores Tipo M: fase saturada de ~ 1 Gano ou mais Güdel et al 1997 Wood et al 2002

  20. 12 3b – Massas Planetárias ocean planets 3 M < M < 10 M  (Léger et al 2004) Marte < 0,5 M Terra 0,5 M  < M < 3 M Urano M > 10 M  Robustez: estabilidade climática (fatores internos e externos) Planetas de maior massa podem ter ZCH maiores Atividade geológica Campos magnéticos

  21. 13 3c – Metalicidade: formação planetária Forte relação entre metalicidade e presença de planetas gigantes Composição planetária: Massa  101.5[Fe/H] (Lissauer 1995) Razão [Si/Fe] e [Mg/Fe] Razão litosfera/núcleo Convecção no núcleo (magnetismo) Também Fisher & Valenti (2005)

  22. 14 3d – Ainda a metalicidade Aquecimento radiogênico: fonte preponderante de calor interno terrestre 40K meia-vida = 1.3 Gano 235U meia-vida = 0.7 Gano 238U meia-vida = 4.6 Gano 232Th meia-vida = 14.1 Gano produção nucleossintética vs. diluição [X/Fe] vs. decaimento Incertezas na razão 40K/K da Terra

  23. 15 3e – Órbitas Galácticas Balázs 2000, Lépine et al 2001, 2003: co-rotação na posição do Sol Leitch & Vasisht 1998: extinções Riscos: SN, explosões de raios-, nuvens moleculares gigantes, glaciações (Elis & Schramm 1993, Gehrels et al. 2003, Gies & Helsel 2005)

  24. 16 4 – Zona Continuamente Habitável e Escalas de Tempo Paleozóico Mesozóico Cenozóico Arqueozóica Proterozóica 0 1 2 3 4 Metazoários Explosão Cambriana Fotossíntese Aeróbica RNA Origem? Procariotas Eucariotas Inteligência Cognitiva O3 observável no Proterozóico ~ 2 Gano atrás (Segura et al 2003) CH4 observável apenas a 10-1 PAL de O2 (Proterozóico) Eventos de oxigenação (Blair-Hedges et al 2004): ~ 2.3 e 3.0 Gano de idade

  25. 21 5b – Candidatas: multiplicidade Dois problemas: Possibilidade de formação de planetas: Barbieri et al 2002 (planetesimais em Eps Eri e 47 UMa) Thébault et al 2002 (planetesimais em Alfa Centauri) Estabilidade em binárias: Pendleton & Black 1993 Holman & Wiegert 1997,1999 limitações, erosão zonas de estabilidade (104 órbitas), problema da coplanaridade 34% da amostra de 50 estrelas é binária ou múltipla Metade é eliminada apenas por ser binária/múltipla Casos interessantes: Alfa Centauri, massas 1.16 e 0.97, P = 80 anos, a = 23.6, e = 0.52 (1999) Eta Cas, massas 0.95 e 0.62, P = 480 anos, e = ?, a = 71 UA Mu Cas, SB1, P = 22 anos, e = 0.61 HR753, K3V e M7V, P ~ 60 anos, a ~ 15 UA, e ~ 0.75 41 Ara, G8V e e anã M, P ~ 690 – 2.200 anos

  26. 22 5c – Candidatas: idade e metalicidade Porto de Mello & Lyra 2005: atividade cromosférica Forte queda exponencial em ~1 Gano Período inicial de bombardeio ~ 0.5 a 1.0 Gano (Hartmann 2004) Mesmo comportamento: Ca II HK Raios-X Perda de massa

  27. 24 5d – Candidatas: idade e metalicidade Eliminamos estrelas com indicadores cromosféricos sugerindo ~ 1 Gano de idade

  28. 25 5e – Candidatas: órbitas galácticas 12 estrelas sobrevivem a todos os critérios: nenhuma possui planeta

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