Characterizing ultracool dwarfs on the search for exoplanets : the SPECULOOS project & the Trappist-1 system

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Characterizing ultra-cool dwarfs on the search for exoplanets

the SPECULOOS project & the Trappist-1 system

F F = ✓ R_p R_⇤ ◆2

c.fernandes@ulg.ac.be | speculoos@astro.ulg.ac.be & trappist@astro.ulg.ac.be

Catarina S. Fernandes with the SPECULOOS and the TRAPPIST teams

• 3 planets in the Habitable Zone

• Assuming Earth-like atmospheres these could

harbour liquid water oceans on their surface

• Ultra-cool dwarf stars (UCDs) (M6-M9) are the smallest,

dimmest, coolest and most abundant stars in our galaxy

M_*=0.07 — 0.10 M , R_*=0.09 — 0.15 R  

Teff=2,000 — 2,600 K, logg = 5.0 — 5.5 

• High probability of detecting small planets

• Studying the host star sets the physical constraints for

exoplanets and for the potential to sparkle life

Trappist-1 system

Ultra-cool dwarfs & transiting exoplanets

Seven earth-sized planets orbiting a M8 dwarf at 12 pc

2MASS J23062928 − 0502285

Trappist-1e transit. Combined light-curve observed with “Europa” and “Io” telescopes

Stellar evolution code developed at the University of Liege

Planets

Host star

7-planet resonant chain

• Trappist-1 h period confirmed: 18.77 days

• No additional planets detected • 3-body orbital-resonance

3

NATURE ASTRONOMY 1, 0129 (2017) | DOI: 10.1038/s41550-017-0129 | www.nature.com/nastronomy

LETTERS

NATURE ASTRONOMY

less frequent than active M6–M9 dwarfs29) are consistent with a

low-activity M8 star, also arguing in favour of a relatively old system. An energetic flare erupted near the end of the K2 Campaign and was observed by Kepler. Full modelling of flares will be presented in a forthcoming p.

m

aper.

The K2 observations of the TRAPPIST-1 star have enabled the detection of the orbital period of TRAPPIST-1 h, continuing the pattern of Laplace resonance among adjacent triplets of planets. We search for, but do not detect, additional planets in the system. Compared with previous ground-based and Spitzer observations, the continuous coverage, high precision and shorter wavelength of the K2 observations enable a robust estimate of the rotational period and flare activity of the star, motivating further study of the atmospheres and dynamical evolution of the planetary system.

Q6

Although the long spin-down times of ultra-cool dwarfs pre-vent the derivation of a robust gyrochronology relation25, the

rota-tional period of TRAPPIST-1 can be used to derive a provisional age estimate for the system. Fourier analysis of the detrended K2 data (Fig. 2), which is visibly modulated by star spots, leads to the determination of a rotational period of ~3.3 days for the host star (see Methods). This rotation corresponds to an angular momentum of ~1% of that of the Sun. It is roughly in the middle of the period distribution of nearby late M dwarfs26, suggesting an age in the range

3–8 Gyr based on a star formation history that decreases slightly over time27_{. Such an age is consistent with the star’s solar}

metallic-ity1 and borderline thin disk–thick disk kinematics28. The amplitude

of the modulation due to star spots and infrequent weak optical flares (0.26 day−1_{for peak fluxes}> 1% of the continuum, 40 times

70 60 50 40 0.985 0.990 0.995 1.000 1.005 a b c d 101 100 90 80 0.985 0.990 0.995 1.000 1.005 –0.05 0.00 0.05 0.90 0.92 0.94 0.96 0.98 1.00 –0.06 –0.04 –0.02 0.00 0.02 0.04 0.06 –0.06 –0.04 –0.02 0.00 0.02 0.04 0.06

K2 long cadence data

Barycentric julian date 2,457,700 (day)

Relative brightness

K2 in safe mode

1b 1c 1d 1e 1f 1g 1h

Time from mid–transit (day)

Relative brightness Transit 1 Transit 2 Transit 3 Transit 4 Folded lightcurve

Orbital separation (au)

Figure 1 | Long cadence K2 light curve of TRAPPIST-1 detrended with EVEREST. a, b, Full detrended K2 light curve with stellar variability removed. m

via LOESS regression (order _{= 1; width = 0.15 day). Data points are in black and our highest likelihood transit model for all seven planets is plotted in thin grey.} Coloured diamonds indicate which transit belongs to which planet. Four transits of TRAPPIST-1 h are observed (light blue diamonds). c, Top four curves

show the detrended and whitened short cadence in light blue, with a transit model based on the Spitzer parameters in dark blue. Binned data is over-plotted in white for clarity. The folded light curve is displayed at the bottom. d, View from above (observer to the right) of the TRAPPIST-1 system at the

date when the first transit was obtained for this system. The grey region is the surface liquid water habitable zone.

Q22

Gillon et al. 2016 Nature 533, 221

Illustration: NASA

K2 data. Long cadence (texp = 30 min) _{one in 78 days (K2 data length)}Super flare  

Low-activity, middle-aged, late M-dwarf

• Flare rate above 1% of the continuum: 0.26 events/day • Stellar rotational period: 3.3 days

• Stellar age: 3 — 8 Gyr

Luger et al. 2017 Nat. Astron, 1, 0129

• The SPECULOOS project will search for transiting

exoplanets

• This is a survey targeting the nearest UCDs with

four 1-m robotic telescopes at Paranal, Chile

• This concept has been tested with the

Trappist-South and North telescopes

Stellar models for UCDs and the Trappist-1 star

Conclusion and what is next

Gillon et al. 2017 Nature 542, 456

CLES

Scuflaire et al. 2008 Astrophys. Space. Sci.316, 83

Code Liégeois d’Évolution Stellaire Van Grootel et al.

in prep.

• UCDs are excellent targets for searching transiting earth-sized planets • Trappist-1 system was discovered while surveying UCDs

• CLES stellar evolution code is ready to carry-on studies with UCDs

• To account for an age > 7Gyr for Trappist-1, the stellar models suggest a

revision of the stellar mass which has an affect on planetary-star relations

• New discoveries made with the SPECULOOS project are potential targets for

the Extremely Large Telescopes and the JWST/NASA with further studies on atmospheric characterisation and searching biosignatures

• Continuing working on improving stellar evolution models for low-mass stars

Fernandes et al. in prep.

Recently adapted to account for low-mass stars

• Include meaningful equation of state _{[1], [2]}

• Adapt public atmosphere model grid: BT-Settl _[3]

• Able to choose different metallicities, other than solar

• Compared with low-mass stellar evolution code (BHAC15)_[4]  

with the same input physics (differences less than 1%)

• Testing with M7 binary [5]: M (dynamical [5]) = 0.088 ± 0.001 M

Updated CLES

• Stellar parameters from observations and from combining

observations and stellar models

L_*=(0.000524 ± 0.000034)L , ρ_*= ρ  

[Fe/H]= 0.04 ± 0.08, Age > 500 Myr

M_*=(0.082 ± 0.011)M , R_*=(0.116 ± 0.006)R , Teff= 2,555 ± 85 K

data-analysis from the K2 campaign 12

Testing new age

Stellar luminosity and density for CLES and BHAC15 evolution models for 0.08 M⊙ and 0.09 M⊙ with various metallicities, compared to luminosity and density measured for Trappist-1. If Trappist-1 star was ‘young’: M_*= 0.08 M would agree with observations

Trappist-1 is not a young-star

• Indications of a middle-aged star has recently been constrained in _[7] to 7.6 ± 2.2 Gyr

References

• [1] Saumon, D., Chabrier, G., & van Horn, H. M. 1995, ApJS, 99, 713

• [2] Fontaine, G., Graboske, Jr., H. C., & van Horn, H. M. 1977, ApJS, 35, 293

• [3] Allard, F., Homeier, D., & Freytag, B. 2012a, Philosophical Transactions of the Royal

Society of London Series A, 370, 2765

Kepler-2 mission

View from above at the date when the first transit was obtained. The grey region is the surface liquid water HZ

New-mass from stellar models

•

M

_*

=0.09 M , with CLES and also confirmed by BHAC15 for measured luminosity

•

Need to increase the metallicity to further account for the stellar density derived

from transits

• [4] Baraffe, I., Homeier, D., Allard, F., & Chabrier, G. 2015, A&A, 577, A42 • [5] Dupuy, T. J., Forbrich, J., Rizzuto, A., et al. 2016, ApJ, 827, 23

• [6] Press, W. H., Teukolsky, S. A., Vetterling, W. T., & Flannery, B. P. 1992, Numerical recipes in FORTRAN • [7] Burgasser & Mamajek 2017, arxiv: 1706.02018

{

Search for Planets EClipsing ULtra-cOOl Stars

PI: Michaël Gillon, Uni. Liège, michael.gillon@ulg.ac.be

{

The SPECULOOS project is an international collaboration

project

Time

• M (CLES & [6]) = 0.078 ± 0.03 M (with [Fe/H] (1σ) = 0.12) • M (BHAC15) = M