Stability of Planets in Binary Star Systems
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StabilityStability ofof PlanetsPlanets inin BinaryBinary StarStar SystemsSystems Ákos Bazsó in collaboration with: E. Pilat-Lohinger, D. Bancelin, B. Funk ADG Group Outline Exoplanets in multiple star systems Secular perturbation theory Application: tight binary systems Summary + Outlook About NFN sub-project SP8 “Binary Star Systems and Habitability” Stand-alone project “Exoplanets: Architecture, Evolution and Habitability” Basic dynamical types S-type motion (“satellite”) around one star P-type motion (“planetary”) around both stars Image: R. Schwarz Exoplanets in multiple star systems Observations: (Schwarz 2014, Binary Catalogue) ● 55 binary star systems with 81 planets ● 43 S-type + 12 P-type systems ● 10 multiple star systems with 10 planets Example: γ Cep (Hatzes et al. 2003) ● RV measurements since 1981 ● Indication for a “planet” (Campbell et al. 1988) ● Binary period ~57 yrs, planet period ~2.5 yrs Multiplicity of stars ~45% of solar like stars (F6 – K3) with d < 25 pc in multiple star systems (Raghavan et al. 2010) Known exoplanet host stars: single double triple+ source 77% 20% 3% Raghavan et al. (2006) 83% 15% 2% Mugrauer & Neuhäuser (2009) 88% 10% 2% Roell et al. (2012) Exoplanet catalogues The Extrasolar Planets Encyclopaedia http://exoplanet.eu Exoplanet Orbit Database http://exoplanets.org Open Exoplanet Catalogue http://www.openexoplanetcatalogue.com The Planetary Habitability Laboratory http://phl.upr.edu/home NASA Exoplanet Archive http://exoplanetarchive.ipac.caltech.edu Binary Catalogue of Exoplanets http://www.univie.ac.at/adg/schwarz/multiple.html Habitable Zone Gallery http://www.hzgallery.org Binary Catalogue Binary Catalogue of Exoplanets http://www.univie.ac.at/adg/schwarz/multiple.html Dynamical stability Stability limit for S-type planets Rabl & Dvorak (1988), Holman & Wiegert (1999), Pilat-Lohinger & Dvorak (2002) Parameters (a , e , μ) bin bin Outer limit at roughly max. ¼ of stellar separation (for μ = 0.5) Implications for planet formation → truncation of protoplanetary disk Secular perturbation theory in a nutshell Secular perturbation theory “secular” = long time-scales: T sec ≫T rev min. 3 interacting massive bodies (m , m , m ) 0 1 2 gravitational perturbations lead to ... ● mean motion resonances (MMR) ● secular resonances (SR) resonance = integer ratio of 2 frequencies f 1/f 2=p/q∈ℚ Single star – single planet two-body problem = indefinitely stable Basic parameters ● Semi-major axis a ● Eccentricity e 0 < e < 1 ● Solar system planets: e ≤ 0.2 pericenter apocenter Binary star system precession of pericenter (and line of nodes) with time Laplace-Lagrange linear theory Developed for solar system (low mass-ratio) Limits = low eccentricity / inclination Objects = host star + 2 perturbers + massless test planet Simple analytical formula (Murray & Dermott 1999) h(t)=e sin(g t+ϕ)+ A (g , g ,e )sin(g t+ϕ ) free ∑ j j j j j g = free (proper) secular frequency of test planet g = fundamental Eigenfrequencies of system j Free/forced eccentricity Example 1: frequencies for planets Example 2: asteroid main-belt Image: Tsiganis (2008) Application Binary star systems with separation a < 100 AU Typical setting: ● host star (“primary”) ● companion star (“secondary”) ● giant planet (Jupiter like) around primary ● stability of additional (terrestrial) planets ? Explanation for numerical results Semi-analytical method ● Determine secular frequency of giant planet ● Find intersection with analytical curve of free frequency Aim of study Investigated systems Star 1 Star 2 Planet name Mass Spectral Mass Distance Ecc. Mass Distance Ecc. M Type M AU M AU sun sun jup GJ 3021 0.90 G6V 0.15 (?) 68 0.20 (?) 3.37 0.49 0.51 Gliese 86 0.83 K0V 0.49 19 0.40 4.01 0.11 0.05 94 Cet 1.34 F8V 0.20 (?) ≥ 100 (?) 0.20 (?) 1.68 1.42 0.30 HD 41004 0.70 K2V 0.15 (?) 23 0.20 (?) 2.54 1.64 0.20 (?) τ Boo 1.30 F6IV 0.40 (?) 45 0.20 (?) 5.90 0.046 0.02 HD 177830 1.47 K0IV 0.23 97 0.20 (?) 1.49 1.22 ≈ 0.00 HD 196885 1.33 F8V 0.45 21 0.42 2.98 2.60 0.48 γ Cep 1.40 K1III 0.41 19 0.41 1.85 2.05 0.05 (?) = estimated values; minimum masses M sin(i) Selected systems Star 1 Star 2 Planet name Mass Spectral Mass Distance Ecc. Mass Distance Ecc. M Type M AU M AU sun sun jup GJ 3021 0.90 G6V 0.15 68 0.20 3.37 0.49 0.51 Gliese 86 0.83 K0V 0.49 19 0.40 4.01 0.11 0.05 94 Cet 1.34 F8V 0.20 ≥ 100 0.20 1.68 1.42 0.30 HD 41004 0.70 K2V 0.15 23 0.20 2.54 1.64 0.20 τ Boo 1.30 F6IV 0.40 45 0.20 5.90 0.046 0.02 HD 177830 1.47 K0IV 0.23 97 0.20 1.49 1.22 ≈ 0.00 HD 196885 1.33 F8V 0.45 21 0.42 2.98 2.60 0.48 γ Cep 1.40 K1III 0.41 19 0.41 1.85 2.05 0.05 Numerical results for HD 41004 Image: E. Pilat-Lohinger Why not the other systems ? HD 1237 HD 41004 Dependence on secondary star 1 increasing a 2 Dependence on secondary star 2 increasing m 2 HD 196885 Outlook Ongoing work Determine width of perturbation – dependence on parameters (mass, distance, eccentricity, …) Goals: ● Catalogue for observers ● Binary star systems allowing “unperturbed” habitable zone (small eccentricity) That'sThat's allall folksfolks ...... References Campbell, Walker & Yang (1988), ApJ 331, 902 Hatzes, Cochran, Endl et al. (2003), ApJ 599, 1383 Holman & Wiegert (1999), AJ 117, 621 Mugrauer & Neuhäuser (2009), A&A 494, 373 Murray & Dermott (1999), Solar System Dynamics, Cambridge Univ. Press Pilat-Lohinger & Dvorak (2002), CMDA 82, 143 Rabl & Dvorak (1988), A&A 191, 385 Raghavan, Henry, Mason et al. (2006), ApJ 646, 523 Raghavan, McAlister, Henry et al. (2010), ApJS 190, 1 Roell, Neuhäuser, Seifahrt & Mugrauer (2012), A&A 542, 92 Tsiganis (2008), Lecture Notes in Physics 729, 111, Springer .