Characterisation of detected planets Radial velocity

Darwin 2.0: Detecting & Characterising Hundreds of Exoplanets

Jens Kammerer & Sascha P. Quanz

The National Centres of Competence in Research (NCCR)

are a research instrument of the Swiss National Science Foundation

We present the first study to quantify the planet yield of a Darwin-like space telescope based on planet occurrence rates from Kepler. We simulate 2000 exoplanet systems around nearby main-sequence stars to show that such an instrument could detect >300 planets. Our baseline scenario consists of a formation flying space telescope having specifications similar to Darwin (proposed to ESA in 2007) equipped with the sensitivity of the MIRI instrument of the James Webb Space Telescope.

Expected number of observable exoplanets in the radius-temperature plane using filters with λeff = 5.6μm (F560W, left), 10μm (F1000W, center) and 15μm (F1500W, right)

Relative amount (number in percent) of exoplanets which would be detectable via radial velocity (vrv ≥0.1m/s) for all planets with radii below 2 Earth radii (mean density = 5000kg/m³)

Assumptions for our MC simulation

Artist’s concept of Darwin4

1 from Darwin mission proposal, Cockell et al. 2007 2 from Glasse et al. 2015 3 from Burke et al. 2015, Dressing et al. 2015, Fressin et al. 2013 4 from Liège University

How many planets can we detect?

500m imaging baseline1

5mas @ 10μm resolution1

4 x 2.82m diameter formation flying mirrors1

Original MIRI filter curves

Original MIRI faint source detection limits2

• 0.16μJy @ 5.6μm, 0.54μJy @ 10μm, 1.39μJy @ 15μm

• 10σ in 10000s

Complete sky coverage1 (> 99%)

Instrument parameters

326 nearby main-sequence stars

8 A stars, 54 F stars, 72 G stars, 71 K stars, 121 M stars

Distance ≤ 20pc

Culled for binaries closer than 5’’

Apparent brightness <7mag out to 10pc and <5mag out to 20pc

Stellar sample

Planet occurrence rates from Kepler3

• Planet radius in [0.5, 22] Rearth, orbital period in [0.5, 418] d

Randomly distributed circular planet orbits

Randomly drawn wavelength-independent planet albedos

• Bond albedo distributed linearly in [0, 0.8]

• Geometric albedo distributed linearly in [0, 0.1]

Planets & host stars are spherical blackbodies

Planet effective temperature = planet equilibrium temperature

Planet population

Stellar type

Expected number of observable planets

Completeness

total per star

A 6.79 0.85 96%

F 43.31 0.80 92%

G 69.79 0.97 67%

K 58.75 0.83 58%

M 150.46 1.24 39%

Expected number of observable exoplanets for each individual star (histogram)

• The list shows the 15 host stars with the highest planet yield and their completeness (number in brackets)

Completeness = expected number of observable planets divided by total number of simulated planets

The blue histogram shows the radial velocity (RV) of all simulated planets with radii R ≤ 2Rearth

• The vertical red line indicates our baseline RV sensitivity limit of vRV ≥ 0.1m/s

The green histogram shows the RV of only these planets which are detectable via direct imaging, too

171 rocky planets RV + dir. imaging

3.22 around A stars 22.53 around F stars 55.13 around G stars 58.36 around K stars

243.68 around M stars

383 rocky planets detectable via RV

3.02 around A stars 19.99 around F stars 34.88 around G stars 29.42 around K stars 83.35 around M stars

Expected number of exoplanets which are detectable in only one, two or all three filters

• The numbers in the legend state the effective wavelengths of the filters in μm

Roughly half of all detectable planets can be observed in all filters and therefore be analysed spectroscopically