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Exploring the Giant Planet - Brown Dwarf Connection with Astrometry

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Exploring the Giant Planet - Brown Dwarf Connection with Astrometry Exploring the giant planet - brown dwarf connection with astrometry Johannes Sahlmann ESA Research Fellow at ESAC Who’s Who, Paris - 2 July 2015 IS MASS A GOOD DEMOGRAPHIC INDICATOR ? L30 G. Chauvin et al.: A giant planet candidate near a young brown dwarf 2MASSWJ1207334−393254 Editor “first image of a planetary mass companion in a different the system than our own” (Chauvin et al., A&A, 2005) to M1 ~ 25 MJup M2 ~ 5 MJup mass ratio q ≃ 0.2 778 mas N 55 AU at 70 pc Letter E Fig. 2. Detection limits at 3σ achieved during our observations in lar planets. vealed the signature of a Jupiter-mass planet around a star J-band (dotted black line), H-band (dashed blue line), Ks-band in an unresolved binary (Muterspaugh et al., 2010), which, Fig. 1. Composite image of brown dwarf 2M1207 and its GPCC in H 8.3. Results from Astrometry (dashed-dotted green line)andL!-band (solid red line). The contrasts if confirmed independently, represents the first planet dis- (blue), K (green)andL (red). The companion appears clearly distin- 8.3.1. Combination with radial velocities covered by astrometry. Recent improvements of imaging s ! between 2M1207 and its GPCC are reported for H (filled triangle), astrometry techniques towards 0.1 mas precision made the For a planet detected with radial velocities (RV), five out guishable in comparison to the color of the brown dwarf 2M1207. discovery of a 28 M companion to an early L dwarf pos- Ks (filled box)andL! (filled circle)(theGPCCwasnotdetectedin of seven orbital parameters are constrained. The two re- J sible (Fig. 15) and demonstrated that such performance can maining parameters, the inclination i and ⌦, can be deter- J band). be realised with a single-dish telescope from the ground. mined by measuring the astrometric orbit. The knowledge Planet masses and radii are difficultTable to 1. Nightmeasure Log of the observations. (in non- S27 and L27 correspond re- of the RV parameters (or the high weight of RV measure- ments) leads to a significant reduction of the required S/N spectively to a platescale of 27.03 and 27.12 mas. DIT and NDIT cor- for a robust astrometric detection. Second, even an astro- respond respectively to an individual integration time and the number 3. Discussion metric non-detection carries valuable information, e.g., an transiting systems) upper limit to the companion mass. Therefore, this type of of integrations. Sr and FWHM correspond to the strehl ratio and the combined analysis is so far the most successful application full width at half maximum intensity. 3.1. Membership in the TW Hydrae association of astrometry in the exoplanet domain. Hipparcos astrom- etry yielded mass upper limits of RV planets (Perryman Gizis (2002) undertooka 2MASS-based search for isolated low et al., 1996; Torres, 2007; Reffert and Quirrenbach, 2011) Filt. Obj. DIT NDIT Seeing Airm. Sr FWHM and revealed that, in rare cases, brown dwarf (Sahlmann mass brown dwarfs in the area covered by stellar members et al., 2011a) or stellar companions (Zucker and Mazeh, (s) (!!)(%)(mas) 2001) are mistaken for RV planets because their orbital Astrometry gives a good handle on companion masses of TWA and found two late M-type objects which he identi- planes are seen with small inclinations. Similarly, the Hub- Imaging fied as brown dwarfs. The one of interest in the present paper, ble fine guidance sensor was used to determine the orbits N and masses of brown dwarf companions to Sun-like stars J S27 30 8 0.59 1.07 6 122 2M1207, showed impressively strong Hα emission in addition initially detected with RV (Martioli et al., 2010; Benedict et al., 2010) and ground-based imaging astrometry yielded H S27 30 16 0.46 1.10 15 91 to signs of low surface gravity, which both are characteristic a mass upper limit of 3.6 M to the planet around GJ317 ⇠ J (Anglada-Escude´ et al., 2012). Sahlmann et al. (2011b) E Ks S27 30 16 0.52 1.08 23 89 of very young objects. Gizis (2002) noted also that the proper (Fig. 14) used Hipparcos data to eliminate low-inclination L! L27 0.175 1300 0.43 1.14 30 107 motion of 2M1207 is consistent with membership in the TWA. binary systems mimicking brown dwarf companions de- tected in a large RV survey, revealing a mass range where Spectroscopy Subsequently, Mohanty et al. (2003) obtained echelle spec- giant planets and close brown dwarf companions around tra of 2M1207. The radial velocity is also consistent with Sun-like stars are extremely rare. Fig. 15.— The barycentric orbit of the L1.5 dwarf DENIS- SH S54 300 6 0.45 1.15 P J082303.1-491201 caused by a 28 Jupiter mass compan- TWA membership. They detected a narrow Na I (8200 Å) ab- 1 ion in a 246 day orbit discovered through ground-based astrometry with an optical camera on an 8 m telescope Planets and brown dwarfs with astrometry sorption line indicating low surface gravity. Finally, the spec- 0.8 Johannes Sahlmann 2 Giant Planets Void (Sahlmann et al., 2013a). trum displays various He I and H I emission lines (Mohanty 0.6 close vicinity a faint and red object at 778 mas and a position Brown dwarf angle of 125.8 in H, K and L .Thefaintobjectwasnotde- et al. 2003; Gizis 2002) and the Hα line is asymmetric and 0.4 companions 8.4. The Future ◦ ! broad. Taken together, these characteristics led Mohanty et al. 0.2 Without a doubt, our expectations are high for the Gaia tected down to 3σ of 18.5 in J-band. In Figs. 1 and 2, we dis- Cumulative distribution mission which was launched on 19 December 2013. Gaia is (2003) to suggest the occurrence of ongoing accretion onto 0 a cornerstone mission of the European Space Agency that play an H, Ks and L! composite image and the detection limits 13 26 39 52 65 78 M sin i (Jupiter mass) 2 will implement an all-sky survey of an estimated billion obtained in each band during our observations. After cosmetic (a young) brown dwarf. Although L!-band observations of stellar objects with visible magnitudes of 6–20 (Perryman Fig. 14.— The minimum mass distribution of substellar et al., 2001; de Bruijne, 2012). On average, the astrometry reductions using eclipse (Devillar 1997), we used the myopic Jayawardhana et al. (2003) did not reveal significant IR excess companions within 10 AU of Sun-like stars from the Coralie of a star will be measured 70 times over the mission life- deconvolution algorithm MISTRAL (Conan et al. 2000) to ob- at 3.8 µm, recent mid-IR observations of Sterzik et al. (2004, RV survey after constraining the orbital inclinations with time of five years with a single measurement precision of 0.02-0.05 mas for stars brighter than 14th magnitude. Hipparcos astrometry. ⇠ ⇠ tain H, K and L! photometry and astrometry of the GPCC. The accepted) found excess emission at 8.7 µmand10.4µmand Another look at Fig. 13 shows that hundreds of known ex- oplanet systems will be detectable and it is expected that results are reported in Table 2. The transformations between the confirm disk accretion as the likely cause of the strong activ- 8.3.2. Independent discoveries Gaia will discover thousands of new exoplanets (Casertano filters Ks and K were found to be smaller than the measuring ity. New Chandra observations of Gizis & Bharat (2004) cor- Working towards the goal of exoplanet detection, optical et al., 2008), yielding a complete census of giant exoplan- imaging surveys have succeeded in measuring the orbits of ets in intermediate-period orbits around nearby stars. The errors. roborates this disk-accretion scenario as they suggest that less low-mass binaries and substellar companions to M dwarfs sight of astrometric orbits caused by planets around stars (Pravdo et al., 2005; Dahn et al., 2008), relying on astro- will then become just as common as radial velocity curves On 19 June 2004, 2M1207 and its GPCC were simultane- than 20% of the Hα emission can be due to chromospheric ac- metric measurements only. Interferometric observations re- and dips in light-curves are today. Assuming that it will ously observed using the NACO spectroscopic mode. The low tivity. All in all, multiple lines of evidence point toward mem- bership of 2M1207 in the TWA. 17 resolution (Rλ = 700) grism was used with the 86 mas slit, the S54 camera (54 mas/pixel) and the SH filter (1.37 1.84 µm). − The spectra of 2M1207 and its GPCC were extracted and cali- 3.2. Age and distance of the system brated in wavelength with IRAF/DOSLIT.Tocalibratetherel- ative throughput of the atmosphere and the instrument, we di- The age of the TWA can be established by comparison with vided the extracted spectra by the spectra of a standard star the somewhat older β Pictoris moving group’s space motions (HIP 062522, B9III) and then multiplied by a blackbody to re- (UVW; Zuckerman et al. 2001) and HR diagrams. Ortega et al. store the shape of the continuum. (2002) and Song et al. (2003) have traced members back to HIGH-MASS TAIL OF PLANET MASSES OVERLAPS WITH SUBSTELLAR COMPANIONS IN BINARY SYSTEMS J. Sahlmann et al.: Search for brown-dwarf companions of stars 15 J. Sahlmann et al.: Search for brown-dwarf companions of stars HD17289 20 10 HD43848 M2 = 0.52 ± 0.05 M⊙ HD30501 . HD3277 CORALIE . HD17289 CORALIE . 2000 10 5 4000 1500 M2 sin i = 49 ± 2 MJup 15 CORALIE radial velocity survey of 1647 GK dwarfs: 5 1000 0 2000 0 ➔ 20 companions with M2 sin i = 13 - 80 MJup 500 10 −5 (mas) (mas) (mas) RV [m/s] 0 RV [m/s] 0 Δδ Δδ ➔ 10 discarded as M-dwarfs by Hipparcos −5 Δδ −500 −10 −2000 5 −10 N −1000 astrometry (Sahlmann et al., 2011,−0.1 0.0 0.1 A&A, 0.2 0.3 0.4 525 0.5 0.6) 0.7 0.8 0.9 1.0 1.1 −0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 −15 φ φ −15 E 0 .
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