Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
arXiv: 1604.01086 ADS: 2016arXiv160401086M DOI: 10.1007/s11084-016-9493-2 Reflected Light from Giant Planets in Habitable Zones 1,2,3 2,3 2 1 J. H. C. Martins , N. C. Santos , P. Figueira and C. Melo 1 - European Southern Observatory 2 - Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal 3 - Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal Motivation Why detect reflected light in the visible? FPlanet = FStar ? At optical wavelengths, an exoplanet’s signal is essentially a reflected copy of the star’s spectrum; ? To probe exoplanet atmospheres as different elements and/or molecules absorb/reflect light differently (e.g. Garcia-Muñoz & Isaac, 2015). The problem: ? ? ? Ag g(α) 2 RP a e.g, for Jupiter at 1 AU and opposition: Planets are small and HZ are far from the planet’s host stars (RP << a); Planets only reflect a fraction of their incident light (albedo - usually Ag < 1); Only the portion of the planet facing the star is visible (phase function - gα < 1). FPlanet FStar ∼ 10 −7 The Method To surpass the problem, we apply the technique proposed in Martins et al 2013 (MNRAS, Vol. 436-2, p.1215) and summarized in the diagram below. Star + Planet Observations Star + Planet CCFs 1 Individual Planet CCFs 2 Star removal Cross-Correlation Function Planet Signal 3 RV Correction and CCF stack 1 The Cross Correlation Function (CCF) of a spectrum with a binary mask enhances its S/N by a factor proportional to the square root of lines in the mask. It can be seen as an average spectral line as it stacks together the information of all lines in the mask. 2 The removal of the star signal is done by normalizing the CCF of the observations by a star template. We constructed this template by co-adding the CCFs of all available observations: this will dilute the planet’s signal and enhance the star’s. 3 Stacking the planet CCFs after correcting them for the planet RV will increase the signal of the planet by a factor corresponding to the square root of the number of stacked CCFs. As a proof of concept, we applied this technique to HARPS observations of 51 Peg b and recovered the planet spectroscopic signal with a 3-σ significance: 51Peg b should be an inflated hot-Jupiter with a high albedo - Martins et al 2015 (A&A, Vol. 576, A134). Giant Planets in Habitable Zones For our study, we selected all planets in the habitable zone of their host stars available in the exoplanet.eu database (Fig. 1). For each one of them we computed the flux ratio and the minimum integration time required for a 3-σ detection with ESO’s E-ELT (Fig. 2). It can be seen that 5 targets 55Cnc f, Gl687 b, Gliese876 b, Gliese876 c and HIP57050 b - have total exposure times under 100h (Tab. 1), making them ideal test candidates for the detection of their spectrographic reflected signals in the optical. Figure 1: Table 1: Planets in sample that require less than 100h for a 3-σ detection with the E-ELT. Planets orbiting stars with 2000K < Teff < 8000K ; Planets orbiting in the HZ of their hosts. Host Planet Type magV Figure 2: Minimum time required for a 3-3-σ detection with the E-ELT of the planets in Fig. 1 SNPlanet at 3-σ SN after 30s Exposure Time [hours] 55Cnc f K0IV-V 6.0 2.68x107 4031 89.5 Gl687 b M3.5V 9.2 3.05x106 923 22.1 Gliese876 b M4V 10.2 3.54x106 577 76.0 Gliese876 c M4V 10.2 1.05x106 577 6.7 HIP57050 b M4V 11.9 5.28x105 260 8.3 The final sample we present consists only of giant planets, unsuitable for life as we know it. Nonetheless, those might be orbited by satellites with conditions to have liquid water on their surface and to support life, yielding good prospects towards the detection of a habitable planet similar to our own. Of great interest is the case of the planets orbiting M dwarfs: despite the host’s low brightness, the habitable zone is close enough to the star to make these planets detectable with the E-ELT. In particular, Gliese876 c and HIP57050 b are close enough to their host to be detected with under 10h of total integration time, which extrapolating to a VLT sized telescope yields a 3-σ detection under 40h. This is a promising prospect, meaning that even current generation facilities can start to be used to detect these targets. Of great importance towards these studies are surveys missions like PLATO (4 < magV < 16) who will greatly increase the amount of suitable targets. Acknowledgments This work was supported by the COST Action TD 1308 «ORIGINS» and by Fundação para a Ciência e a Tecnologia (FCT) through research grants UID/FIS/04434/2013 (POCI-01-0145-FEDER-007672) and project PTDC/FIS-AST/1526/2014 and by FEDER through COMPETE2020 (ref. POCI-01-0145-FEDER-016886). PF and NCS acknowledge support by Fundação para a Ciência e a Tecnologia (FCT) through Investigador FCT contracts of reference IF/01037/2013 and IF/00169/2012, respectively, and POPH/FSE (EC) by FEDER funding through the program “Programa Operacional de Factores de Competitividade - COMPETE”. PF further acknowledges support from Fundação para a Ciência e a Tecnologia (FCT) in the form of an exploratory project of reference IF/01037/2013CP1191/CT0001. arXiv: 1604.01086 ADS: 2016arXiv160401086M DOI: 10.1007/s11084-016-9493-2