Brown Dwarfs and Planets - Brown Dwarfs come of Age · Brown Dwarfs come of Age - Fuerteventura Mickaël Bonnefoy 16/2612/121/11 Direct imaging A - Combinaison of technics & new strategies

Brown Dwarfs

Mickaël Bonnefoy1 & Gaël Chauvin21Max Planck Institute for Astronomy (Germany)

2Institut de Planétologie et d’Astrophysique de Grenoble (France)

and Planets

Contributions from J. Sahlmann, E. Vorobyov, P. Delorme, B. Biller, A-M. Lagrange

Brown Dwarfs come of age - Fuerteventura - May 21, 2013

(Very low mass stars)

Outline1/ Brief Introduction: • Planet/Brown Dwarf Definition• Formation processes• Planetary formation around BDs

2/ Search for Planetary Mass Companions• Radial velocity surveys• Direct Imaging • µlensing• Astrometry

3/ ConclusionsMickaël Bonnefoy 1/1112/121/11Brown Dwarfs come of Age - Fuerteventura

Planet/BD definition

Mass (IAU): “Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) that orbit stars or stellar remnants are "planets" (no matter how they formed). The minimum mass/size required for an extrasolar object to be considered a planet should be the same as that used in our Solar System.” (IAU, WGESP, 2003)

Core/Gas Accretion (alternative): “planet form dominantly from planetesimal and gas accretion in a disk and thus should be significantly enriched in heavy elements compared to their parent star.” Chabrier et al. 2005, PPV,

Fusion (alternative): “planets are just planemos, objects without the ability for fusion,

orbiting fusors, objects that have this ability”. Basri et al. 2006, AREPS

“Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located.“ (IAU, WGESP, 2003)

1/11Mickaël Bonnefoy 1/1112/121/11Brown Dwarfs come of Age - Fuerteventura 1/26

Brown Dwarfs

Exoplanets

Brown dwarf formation • Collapse/Fragmentation

• Disk fragmentation

• Premature Ejection

• Photo-erosion Withworth et al., PPV, 2005

> F. Palla, E. Vorobyov’s Talks

Bates (2002)


Planetary formation

Formation of giant planets proceeds in a two step

way:

1/ A solid core accretes first.

2/ Once this core reaches a critical mass (∼10 M⊕) the gaseous envelope is accreted in a runaway process.

Pollack et al. (1996) Mordasini et al. (2012)


Core Accretion

Planetary formation

Disk fragmentation / Gravitational instability 1/ Dense disk to trigger instabilities

2/ Cool disk to favor fragmentation

> Stellar-like mechanism

Cameron 1976Boss 1997Rafikov 2005

Mayer et al. 2002


Very active research field !

Core Accretion

• No reason to stop planetary formation at the BD boarder.

• BDs show similar (downsized) properties compared to TTstars

• BDs show Accretion/Outflows, disk & Grain Growth

Discovery of a Bipolar Outflow from 2M1207, young 8 Myr BD of TWA

Continuum-subtracted PV diagram of the [OI] 6300A line.

Outflow with velocities of -8 and +4 km/s

Whelan et al. (2007)

Planetary formation & BDs


> V. Joergen’s, and B. Riaz’s Talks

Planetary formation & BDs • No reason to stop planetary formation at the BD boarder.



2MASSJ04442713+251, a young BD of the Taurus association

A compact accreting disk

Optical-to-mm SED Analysis. Disk geometry similar to TTauri. Disk mass in large grains. Crystallization processes?

Bouy et al. (2008)





ALMA observations of the young BD ρ-Oph 102

CO molecular gas observedDusty disk R < 40 AUEvidence for mm-sized grains

> L. Ricci’s Talk

Ricci et al. 2012

Planetary formation & BDs





• BUT, Core Accretion for BDs?• Disks are cooler and lighter than for TTauri stars • Inward drift of dust more rapid, (drift timescale

Outline

1/11Mickaël Bonnefoy 1/1112/121/11Brown Dwarfs come of Age - Fuerteventura

1/ Brief Introduction: • Planet/Brown Dwarf Definition• Formation processes• Planetary formation around BDs


3/ Conclusions

Hunting Techniques


• Radial velocity

• Transit

• µ-lensing

• Direct Imaging

• Astrometry

Radial Velocity1/ RV survey around brown dwarfs

Sensitive to a < 1 AU and a < 10 AU for the field and clusters

A 16–20 MJup RV companion around the very young (~3 Myr) BD/VLM candidate Cha Hα 8 (M5.75–M6.5)

q = 0.2 – 0.3a = 0.97 – 1.1 AU

Joergens et al. 2008a


Radial Velocity1/ RV survey around brown dwarfs*UVES/VLT spectroscopy the binary frequency of brown dwarfs

and (very) low-mass stars (M4.25-M8) in Chamaeleon I Most detected spectroscopic BD binaries confirmed have q ~ 1.0

Do not miss a significant fraction of BD binaries at < 3AUOverall binary frequency of BDs and VLMS: 10–30%

Evidence of a continuous formation mechanism fromlow-mass stars to brown dwarfs.

BUT: Planet population around BDs probably not reached?Limitations: Target faintness, variability and activity

Joergens et al. 2008b


Blake et al. 2007, 2010

*NIRSPEC survey: 59 VLMS and field Brown dwarfs: Can detect tight PMCs (1

Radial Velocity2/ HARPS RV survey around M dwarfs (102 objects)

Giant planets, 100-1000 M⊕ f =< 1% (1-10days)

f = 0.02% (10-100days)

Super-Earths, 1-10 M⊕f=0.36% (1-10 days)

F = 0.52% (10-100 days)

> likely very abundant

Bonfils et al. 2011


Bonfils et al. 2013

Direct imaging

2M1207: First planetary mass companion imaged around a young BD

Chauvin et al. 2004

•Core-accretion: too slow•Gravitational instability?

(Lodato et al. 2006)

Among the 30 planetary mass companions (PMC) detected:•6 around low mass stars (M < 0.5 MSun)•6 around brown-dwarfs


Surveys and statistics:1/ AO imaging: high mass ratio binaries and planet/BD companions

•Keck survey / BDs in Upper Sco (Biller et al. 2011):★ Binary fraction of

Surveys and statistics:2/ Looking for PMC formed by disk-instability: > P. Delorme’s Talk


Direct imaging

A - Combinaison of technics & new strategies.

B - New young late-type objects < 100 pc identified

•L-band imaging (3.8 µm)•NIR wavefront sensors, efficient AO systems (ex: LBT), Laser guide stars•Angular differential imaging (Marois et al. 2006)•Sparse aperture masking

> J. Gagné’s Talk

Surveys and statistics:A&A 539, A72 (2012)

Fig. 7. Summary of the detection probabilities of the survey for a rangeof companion masses, obtained by averaging the detection probabilitiesof the 14 targets with an accurate age determination. The semi-majoraxis values are therefore in real AU, not projected AU.

combination of excentricity and angle of sight. Using the full52-star sample, these limits could be used to derive constraintson the existence of giant planets around late-type stars and con-sequently on planetary formation models around low-mass stars.However, the sub-sample of 16 stars we present here is too smallto derive meaningful statistics, so more observations are neededto bring it to a more statistically robust size.

5. Conclusion

We presented the results of the deepest imaging survey ofyoung M dwarfs to date, using L′ imaging with NACO at VLT.After developing a dedicated reduction and analysis pipeline,we achieved detections limits in average down to 1.5 MJup be-yond 20 AU and up to 100–200 AU, and 3 MJup at 10 AU. Onthe closest and latest targets, we achieved detection limits wellbelow the mass of Jupiter beyond 10 AU, therefore actually start-ing to probe (on 5 objects) the mass/separation range whereplanets around M dwarfs are supposed to be be more frequent(Gould et al. 2010; Bonfils et al. 2011), but found none. Wealso probed the high planetary mass range (M < 13 MJup) atclose separations, reaching planetary sensitivity at 5 AU or lesson nine out of our 16 targets. In spite of these deep observations,we found only one planetary companion, 2M1207B, discoveredby Chauvin et al. (2004), in this sample of young M dwarfs.Unfortunately, our sample is currently too small to derive mean-ingful constraints on the existence of giant planets around latetype stars, beyond the simple statement that giant planets moremassive than 1 MJup are not common. With the same statisti-cal limitations, our data also support the “brown dwarfs desert”hypothesis (Halbwachs et al. 2000) down to the lowest browndwarf masses, since we find no brown dwarfs companions, whileour survey had on average more than 95% de-projected sensitiv-ity to brown dwarfs beyond 15 AU and could discover a fractionof them as close as 5 AU from the central star. Further deep ob-servations in L′ of such targets are needed to increase our sta-tistical significance and to put stronger constraints on formationmodels around low-mass stars.

Acknowledgements. We acknowledge financial support from the FrenchProgramme National de Planétologie (PNP, INSU) and from the FrenchNational Research Agency (ANR) through the GuEPARD project grant ANR10-BLANC0504-01. P.D. was financed by a grant from the Del Duca foundation. Wethank David Lafrenière for his precious help with the LOCI code. This researchhas made use of the VizieR catalogue access tool, of the SIMBAD database,and of Aladin, operated at the CDS, Strasbourg. We thank the referee for her/hisaccurate comments.

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Nearby Loose Associations, ed. B. Reipurth, 757

A72, page 10 of 10

2/ Looking for PMC formed by disk-instability:

•NaCo/VLT (P.I. Delorme):

•PALMS (P.I. Bowler):

Delorme et al. 2012

•Others: SEEDS (HiCIAO, Subaru, P.I. Tamura), NICI, GDPS

★ 106 dwarfs observed★ 2-4 MJup at 20 AU★ 2 companions detected (Bowler et al. 2012a,b)

★ 16 targets observed (~56 planed in total)★ 3 MJup at 10 AU, 1.5 MJup > 20 AU ★ One 12-14 MJup companion around a pair of M5 dwarfs (Delorme et al. 2013)

> P. Delorme’s Talk


Direct imaging

Strange new worlds:

Chauvin et al. 2004

A PMC at 15 AU around a BD in Taurus

Todorov et al. 2010

2M044144

A PMC at 84 AU around a pair of low-mass stars

Delorme et al. 2013


Direct imaging

Characterization: detached (?) disks around planetary mass companions

1/ Paschen β lines:•GQ Lup b (Seifahrt et al. 2007)•CT Cha b (Schmidt et al. 2008)•GSC 06214-00210 b (Bowler et al. 2010)

2/ Excesses:

Bowler et al. 2010

•GSC 06214-00210 b (Bowler et al. 2010)


Direct imaging22

1 10! (µm)

10−16

10−15

10−14

10−13

10−12

!f! (

W m

−2)

GSC 06214−00210

GSC 06214−00210 b

Phoenix−Gaia4200/4.0

BT−Settl−20102200/4.0

BT−Settl−20102700/4.0

CMC−14DENIS

2MASSWISE

Ireland et al. 2011

Fig. 10.— Spectral energy distributions of GSC 06214-00210 and its companion. The Teff=4200 K/log g=4.0 Phoenix-Gaia model matchthe 0.6–12 µm photometry of the primary. For the companion the Teff=2700 K/log g=4.0 and Teff=2200 K/log g=4.0 BT-Settl-2010models are plotted. The warmer temperature is from fitting atmospheric models and the cooler temperature is the evolutionary modelprediction. Both models are flux calibrated to the J band photometry of the companion. The excess flux in L′, and perhaps also in K arelikely caused by thermal emission from a circumplanetary disk. Uncertainties in the photometry are smaller than the symbol sizes exceptfor the WISE 22 µm point. The slight excess at 22 µm seen in the primary may be caused by a circumstellar disk.

•FU Tau B(Luhman et al. 2009)+ system outflow(Monin et al. 2013)

Characterization: atmospheric properties

> J. Faherty, Y. Pavlenko, F. Allard, K. Allers ’s talks

Faherty et al. 2013

NIR spectra: similarities with young BDs(Bonnefoy et al. 2010, Faherty et al. 2013, Allers et al. 2013, Cruz et al. in prep)

Low surface gravity:✦ Formation of thick clouds ✦ Non-equilibrium chemistry

(Skemer et al. 2011, Barman et al. 2011)


Direct imaging12 Faherty et al.

1.4 1.5 1.6 1.7 1.8 1.9Wavelength (µm)

0.6

0.8

1.0

1.2

1.4

Nor

mal

ized

Flu

x (f !

)

2M0835 (> 1 Gyr)

2M1207b (~10 Myr)

2M0355

Fig. 4.— SpeX cross-dispersed H-band spectra of 2M0355 (black solid line) compared to the field L5 near-infrared standard (blue dashedline) 2M0835 (defined in Kirkpatrick et al. 2010) and the young planetary mass companion (red dashed line) 2M1207b (from Patience et al.2012). The strong triangular shape seen in 2M1207b and 2M0355 is interpreted as a hallmark of low surface gravity.

> F. Marocco’s poster


µ lensing

First 2 brown dwarfs with tight PMCs!(Choi et al. 2013)OGLE-2009-BLG-151 OGLE-2011-BLG-0420

MA=18 MJupMB=7.5 MJup

@ 0.31 AU

MA=25 MJupMB=9.4 MJup

@ 0.19 AU

6 MICROLENSING BINARY BROWN DWARFS

FIG. 4.— Projected separation versus total system mass for a compilationof binaries. Grey circles indicate old field binaries, whereas blue squaresindicate young (< 500 Myr) systems. The size of the symbols is proportionalto the square root of the mass ratio. The red stars are the two tight, low-massbinary BDs discussed here, which have mass ratios of∼ 0.4. The dashed lineshows a binding energy of 2× 1042 erg, assuming a mass ratio of 1.

FIG. 5.— Binding energy (Gm1m2/a) versus total system mass for the samebinaries as shown in Fig. 4. Symbols and line are the same.

even an estimate of their frequency relative to more massivestellar binaries, the discovery of two systems among the rela-tively small sample of binary lensing events with precise massestimates strongly suggests that very low-mass, very tight BDbinaries are not rare. Thus these detections herald a muchlarger population of such systems. We can therefore concludethat BD binaries can robustly form at least down to systemmasses of ∼ 0.02 M!, providing a strong constraint for for-mation models.

5. DISCUSSIONThe discoveries of the binary BDs reported in this paper

demonstrate the importance of microlensing in BD studies.The microlensing method has various advantages. First, it en-ables to detect faint old populations of BDs that could notbe studied by the conventional method of imaging surveysand the sensitivity extends down to planetary mass objects(Sumi et al. 2011). It also allows one to detect BDs distributedthroughout the Galaxy. Therefore, microlensing enables tostudy BDs based on a sample that is not biased by the bright-ness and distance. Second, in many cases of microlensingBDs, it is possible to precisely measure the mass, which isnot only the most fundamental physical parameter but alsoa quantity enabling to unambiguously distinguish BDs fromother low mass populations such as low mass stars. Whilemass measurements by the conventionalmethod require long-term and multiple stage observation of imaging, astrometry,and spectroscopy by using space-borne or very large ground-based telescopes, microlensing requires simple photometry byusing 1 m class telescopes. Despite the observational sim-plicity, the mass can be measured with uncertainties equiva-lent to or smaller than those of the measurement by conven-tional methods. Finally, microlensing can expand the rangesof masses and separations in the binary BD sample that isincomplete below ∼ 0.1 M! in mass and ∼ 3 AU in separa-tion. Microlensing sensitivity to binary objects peaks whenthe separation is of order the Einstein radius. Consideringthat the Einstein radius corresponding to a typical binary BDis< 1 AU, microlensing method will make it possible to studybinary BDs with small separations.The number of microlensing BDs is expected to increase in

the future with the upgrade of instruments in the existing sur-vey experiments and the advent of new surveys. The OGLEgroup recently upgraded its camera with a wider field of viewto significantly increase the observational cadence. The KoreaMicrolensing Telescope Network (KMTNet), now being con-structed, will achieve 10 minute sampling of all lensing eventsby using a network of 1.6 m telescopes on three different con-tinents in the Southern hemisphere with wide-field cameras.Furthermore, there are planned lensing surveys in space in-cluding EUCLID and WFIRST. With the increase of the mi-crolensing event rate combined with the improved precisionof observation, microlensing will become a major method tostudy BDs.

Work by C.Han was supported by the research grant ofChungbuk National University in 2011. The OGLE projecthas received funding from the European Research Coun-cil under the European Communityąŕs Seventh FrameworkProgramme (FP7/2007-2013) / ERC grant agreement no.246678. The MOA experiment was supported by grantsJSPS22403003 and JSPS23340064. This work is based inpart on data collected by MiNDSTEp with the Danish 1.54mtelescope at the ESO La Silla Observatory, which is operatedbased on a grant from the Danish Natural Science Founda-tion (FNU). The MiNDSTEp monitoring campaign is pow-ered by ARTEMiS (Dominik et al. 2008, AN 329, 248). MHacknowledges support by the German Research Foundation(DFG). DR (boursier FRIA), FF (boursier ARC) and JSur-dej acknowledge support from the Communauté française deBelgique – Actions de recherche concertées – Académie uni-versitaire Wallonie-Europe. KA, DMB, MD, KH, MH, CL,CS, RAS, and YT are thankful to Qatar National Research

Choi et al. 2013

Similar total masses as directly imaged systems ( Oph 16225-240515, 2M1207) but much higher binding energy!

1/ Can detect faint old BDs / imaging surveys2/ Sensitivity extends down to planetary mass objects (Sumi et al. 2011).

> J.P. Beaulieu’s Talk

Astrometry• PALTA, Planets Around M and L dwarfs with

Astrometry 20 late-M and early-L dwarfs close to the Gal. plane within 30 pc

2-years programme, 2010 – 2012

10 epochs per target

15 nights of FORS2 . FORS2 pixel size (0.126”). FoV of 4’

Sahlmann et al. 2013, subm.; Lazorenko et al., in prep


Ultimate Performances

• PALTA, Planets Around M and L dwarfs with Astrometry

20 late-M and early-L dwarfs close to the Gal. plane within 30 pc 2-years programme, 2010 - 2012 10 epochs per target15 nights of FORS2. FORS2 pixel size (0.126”). FoV of 4’

1/ Parallax & proper motion2/ Milli-pixel accuracy . average epoch uncertainty: 110 µas. residual dispersion: 140 µas



Astrometry


1/ Evaluate 5-parameter Astrometric model for simulated orbits

2/ Maximum companion mass compatible with measurement noise (rms-based)



Astrometry

Planet exclusion limit


1/ The long-term accuracy is < 130 µas per epoch.

2/ Exclude planets more massive than Jupiter in intermediate periods (~50-400 days) for several targets.

3/ Follow up of several candidates!! (Stay tuned)



Astrometry

Preliminary results

Outline

1/11Mickaël Bonnefoy 1/1112/121/11Brown Dwarfs come of Age - Fuerteventura

1/ Brief Introduction: • Planet/Brown Dwarf Definition• Formation processes• Planetary formation around BDs


3/ Conclusions


Conclusions1/ How can we distinguish planets from brown dwarfs?

2/ Several indices of planetary formation processes around brown-dwarfs3/ Only some surveys are targeting brown-dwarfs

• goes down to Saturn or even Neptune-mass planets !• exclude planets more massive than Jupiter in intermediate periods (~50-400 days) for several targets

• 2 MJup > 20 AU• 100-150 sources within the next two years

★ RV: Studies mostly sensitive to high mass ratio objects

★ Imaging:

★ Astrometry:

★ µ-lensing: 2 discoveries! ok for ∼0.1M⊙ binaries < 3 AU


Conclusions4/ Prospects:

a - New stable high resolution/sensitivity spectrographs:

e.g. Carmenes (2014), SPIRrou (2017)

b - Direct imaging on new instruments:

e.g. LBT/LMIRCam, possibly SPHERE and GPI, HiCIAO+LGS, ERIS, E-ELT-CAM

c - Astrometry: increasing the sample, new instrumentse.g. GAIA, ELT-CAM

Documents

Brown Dwarfs and Planets - Brown Dwarfs come of Age · Brown Dwarfs come of Age - Fuerteventura Mickaël Bonnefoy 16/2612/121/11 Direct imaging A - Combinaison of technics & new strategies