abstract arxiv:1912.02565v2 [astro-ph.ep] 9 dec …(2016) reported a potential brown dwarf companion...

Astronomy amp Astrophysics manuscript no ms ccopyESO 2019December 10 2019

Letter to the Editor

A dusty benchmark brown dwarf near the ice line of HD 72946

A-L Maire1 J-L Baudino2 S Desidera3 S Messina4 W Brandner5 N Godoy6 7 F Cantalloube5 R Galicher8M Bonnefoy9 J Hagelberg10 J Olofsson6 7 O Absil1

G Chauvin9 11 T Henning5 and M Langlois12

(Affiliations can be found after the references)

Received 18 November 2019 Accepted 4 December 2019

ABSTRACT

Context HD 72946 is a bright and nearby solar-type star hosting a low-mass companion at long period (Psim 16 yr) detected with the radial velocity(RV) method The companion has a minimum mass of 604plusmn22 MJ and might be a brown dwarf Its expected semi-major axis of sim243 mas makesit a suitable target for further characterization with high-contrast imaging in particular to measure its inclination mass and spectrum and thusdefinitely establish its substellar natureAims We aim to further characterize the orbit atmosphere and physical nature of HD 72946BMethods We present high-contrast imaging data in the near-infrared with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE)instrument We also use proper motion measurements of the star from Hipparcos and GaiaResults The SPHERE data reveal a point source with a contrast of sim9 mag at a projected separation of sim235 mas No other point sources aredetected in the field of view By jointly fitting the RV imaging and proper motion data we constrain all the orbital parameters of HD 72946Band assess a dynamical mass of 724plusmn16 MJ and a semi-major axis of 645+008

minus007 au Empirical comparison of its SPHERE spectrum to templatedwarfs indicates a spectral type of L50plusmn15 The J-H3 color is close to the expectations of the DUSTY models and suggests a cloudy atmo-sphere Comparison with atmospheric models of the spectrophotometry suggests an effective temperature of sim1700 K The bolometric luminosity(log(LL) = -411plusmn010 dex) and dynamical mass of HD 72946B are more compatible with evolutionary models for an age range of sim09ndash3 GyrThe formation mechanism of the companion is currently unclear as the object appears slightly away from the bulk of model predictions HD 72946Bis currently the closest benchmark brown dwarf companion to a solar-type star with imaging RV and proper motion measurements

Key words brown dwarfs ndash methods data analysis ndash stars individual HD 72946 ndash planet and satellites dynamical evolution and stability ndashtechniques high angular resolution ndash techniques image processing

1 Introduction

Dynamical mass measurements of brown dwarfs are a powerfultest of their formation and evolution models Most studies ex-ploit brown dwarf binaries (eg Konopacky et al 2010 Dupuyamp Liu 2017 Dieterich et al 2018) which have likely formed byfragmentation of a collapsing cloud (eg Bate 2009) Howeverit is still unclear whether brown dwarfs found at close-in sepa-rations to stars form like stellar binaries or by disk gravitationalinstabilities (Boss 1997) In the past years a few radial velocity(RV) surveys started to target stars with slow drifts to constrainthe orbit and minimum mass of the suspected long-period com-panions (eg Bouchy et al 2016 Sahlmann et al 2011 Ferozet al 2011) These surveys have shown a paucity of brown dwarfcompanions within 5 au from the host stars with respect to plane-tary and stellar companions (the so-called ldquobrown dwarf desertrdquosee eg Grether amp Lineweaver 2006 Sahlmann et al 2011 Maamp Ge 2014) Nevertheless Ma amp Ge (2014) found that their oc-currence increases at larger separations when brown dwarf de-tections from various techniques are combined

Using the ELODIE and SOPHIE instruments Bouchy et al(2016) reported a potential brown dwarf companion to the G5Vstar HD 72946 located at 2587plusmn008 pc (Gaia Collaborationet al 2016 2018) The RV data cover a full orbit of HD 72946B

Based on observations collected at the European Organisation forAstronomical Research in the Southern Hemisphere under ESO pro-gramme 0102C-0781 FRS-FNRS Postdoctoral Researcher

FRS-FNRS Research Associate

which allowed the authors to place good constraints on its orbit(period P = 1593+015

minus013 yr eccentricity e = 0495plusmn0006 and peri-astron T0 [HJD] = 2455958plusmn10) They derived a minimum dy-namical mass of 604plusmn22 MJ and an upper mass limit of 02 Mfrom the analysis of the cross-correlation function of the star

We present in this paper the confirmation and charac-terization of the brown dwarf companion to HD 72946 withthe Spectro-Polarimetric High-contrast Exoplanet REsearch(SPHERE) instrument and Hipparcos-Gaia proper motion mea-surements We present an updated analysis of the properties ofthe host star in Sect 2 and the SPHERE imaging observationsin Sect 3 We perform a joint orbital fit of the imaging RV andastrometric data and derive a dynamical mass for HD 72946B inSect 4 Section 5 discusses the spectral properties of the com-panion Finally we compare the physical and spectral propertiesof HD 72946B to model predictions in Sect 6

2 Properties of the host star

Bouchy et al (2016) inferred from spectroscopic observationsan effective temperature Teff = 5686plusmn 40 K a surface gravitylog g = 450plusmn006 dex and a metallicity [FeH] = 011plusmn003 dexThe supersolar metallicity has been confirmed by other studies(Aguilera-Goacutemez et al 2018 Luck amp Heiter 2006 Casagrandeet al 2011 015plusmn006 016plusmn004 and 012 dex respectively)

We derived the stellar age and mass from isochrones usingthe PARAM web interface1 (da Silva et al 2006) We adopted

1 httpstevoapdinafitcgi-binparam_13

Article number page 1 of 10

arX

iv1

912

0256

5v2

[as

tro-

phE

P] 9

Dec

201

9

AampA proofs manuscript no ms

Table 1 Relative photometry and astrometry of HD 72946B

Filter λ0 ∆λ ∆mag Abs mag Flux Separation PA(microm) (microm) (mag) (mag) (times10minus15 W mminus2 micromminus1) (mas) ()

H2 1593 0052 897plusmn007 1251plusmn007 3027plusmn0188 2357plusmn20 3365plusmn031H3 1667 0054 881plusmn007 1235plusmn007 3236plusmn0204 2356plusmn20 3368plusmn031

Notes The photometric error bars were derived assuming an error budget including the measurement uncertainties (image post-processing) andsystematic uncertainties (temporal variability of the flux calibration and of the science sequence)

the spectroscopic Teff and [FeH] in Bouchy et al (2016) withenlarged uncertainties to account for systematic errors We alsoadopted the Gaia parallax and the V-band magnitude from Hip-parcos (708plusmn002 mag) This results in an age 1712plusmn1684 Gyra mass 0986plusmn0027 M and a radius 0908plusmn0018 R Tighterconstraints on the age from isochrones can be derived from theF8 comoving companion HD 72945 (16plusmn10 Gyr Appendix A)

Lithium data (A(Li) = 141 123 122plusmn015 dex Luck 2017Luck amp Heiter 2006 Ramiacuterez et al 2012) indicate an age olderthan that of the Hyades and similar to the open cluster NGC 752(Sestito et al 2004) The stellar kinematics suggest an ageyounger than the Sun the UVW velocities being at the boundaryof the kinematic space of young stars in Montes et al (2001)Comparisons with stars with similar kinematics in Casagrandeet al (2011) indicated that it is unlikely that the star is older thansim3 Gyr and much younger than 05 Gyr

We searched for archival photometric data to derive an agewith gyrochronology but we did not find suitable data (sam-pling accuracy blending with HD 72945 andor calibration is-sues) Using the relations in Mamajek amp Hillenbrand (2008) andan averaged measured chromospheric activity of -460 dex (in-dividual values -454 -474plusmn005 -466 and -447 dex Rocha-Pinto et al 2004 Bouchy et al 2016 Gray et al 2003 BoroSaikia et al 2018) we derive a rotation period of sim15 d whichimplies a gyrochronological age of sim1 Gyr This is in betweenthe loci of the Hyades (625ndash700 Myr) and NGC 752 (2000 Myr)The star has X-ray data from ROSAT but is blended withHD 72945 However X-ray activity is expected to correlate withchromospheric activity so that it does not provide a fully inde-pendent age estimate Assuming our derived stellar radius and anaveraged measured projected rotational activity of 414 km sminus1

(individual values 323 39plusmn1 and 53 km sminus1 Martiacutenez-Arnaacuteizet al 2010 Bouchy et al 2016 Luck 2017) we derive an up-per limit for the rotation period of 12 d which implies a gy-rochronological age younger than 1 Gyr considering a B minus Vcolor of 071 mag Considering the large uncertainties in vsin ithe upper limit for the gyrochronological age could be as old as15 Gyr This means that our various age estimates agree overallIn the following we choose to adopt an age range of 08ndash3 Gyrwith a most probable value of 1ndash2 Gyr

3 Observations and data analysis

We observed HD 72946 on 2019 March 21 UT with the standardIRDIFS mode of SPHERE (Beuzit et al 2019) which allows forsimultaneous near-IR observations with IRDIS with the H23 fil-ter pair (Dohlen et al 2008 Vigan et al 2010) and the integralfield spectrograph IFS in the Y J bands (Claudi et al 2008) Theseeing and coherence time measured by the differential imagemotion monitor at 05 microm were 05ndash07primeprime and 6-8 ms respec-

H2+H3

E

N

027

7 au

+

YJ

E

N

027

7 au

+

Fig 1 SPHERE contrast images of HD 72946 The central regions ofthe images are numerically masked out to hide bright stellar residualsThe white crosses indicate the location of the primary star

tively The detector integration time was set to 16 s and 128frames were recorded amounting to a field rotation of 155

An apodized pupil Lyot coronagraph (Carbillet et al 2011Martinez et al 2009) was used We acquired data before and afterthe sequence to calibrate the flux of the images and the locationof the star behind the coronagraph (Langlois et al 2013) Night-time sky background frames were taken and additional daytimecalibration performed following the standard procedure at ESO

The data were reduced with the SPHERE Data Reductionand Handling software (v0150 Pavlov et al 2008) and customroutines for IFS data adapted from Mesa et al (2015) and Viganet al (2015) This corrected for the cosmetics and instrument dis-tortion registered the frames and normalized their flux For IFSit also performed the wavelength calibration and extracted theimage cubes Then the data were analyzed with angular differ-ential imaging (Marois et al 2006) using three algorithms (Ap-pendix B) ANDROMEDA TLOCI and PCA Figure 1 showsthe ANDROMEDA images

The photometry and astrometry were extracted using threealgorithms but we chose to retain the TLOCI values (Ta-ble 1) The astrometry was calibrated following Maire et al(2016) with pixel scales of 12255plusmn0009 maspix (H2) and12251plusmn0009 maspix (H3) and a North correction angle ofminus175plusmn008 The absolute magnitudes were computed using the2MASS values (Cutri et al 2003) for the stellar magnitudes

4 Orbital analysis

We retrieved the RV measurements in Bouchy et al (2016)through the VizieR interface With only one imaging datapoint there is still an ambiguity in the inclination and lon-gitude of the ascending node To solve for this we alsosearched for an astrometric signature of the companion inthe Hipparcos-Gaia catalog of accelerations (Brandt 20182019) pmra_g_hg = minus2837plusmn0140 mas yrminus1 and pmdec_g_hg


A-L Maire et al A dusty benchmark brown dwarf near the ice line of HD 72946

1000 2000 3000 4000 5000 6000BJD-2450000

1000

750

500

250

0

250

500

750

1000

RV (m

s)

ELODIESOPHIE

020100010203RA (as)

02

01

00

01

02

03

Dec

(as)

2015

2020

2025

2030

SPHERE

0

5

10

RA (m

asy

r)

GaiaHipparcos

0 2000 4000 6000 8000BJD-2450000

10

5

0

5

DEC

(mas

yr)

Fig 2 Sample of 50 model orbits fitted on the HD 72946B data (colored points) from RV (left) imaging (middle) and astrometry (right) In themiddle panel the yellow star marks the location of the primary star and the black dots show the median predicted position for given epochs

= minus0515plusmn0082 mas yrminus1 for Gaia (Gaia Collaboration et al2018) pmra_h_hg = 9411plusmn4245 mas yrminus1 and pmdec_h_hg =4734plusmn2839 mas yrminus1 for Hipparcos (Perryman et al 1997 vanLeeuwen 2007) These values imply an astrometric detection at(203 63)σ with Gaia and (21 17)σ with Hipparcos We veri-fied that the Gaia DR2 record is well behaved with a renormal-ized unit weight error below 14 (Lindegren et al 2018)

We performed a joint fit of the RV imaging and proper mo-tion data with the parallel-tempered Markov chain Monte Carlo(MCMC) algorithm provided in the emcee package (Foreman-Mackey et al 2013) which is based on the algorithm describedby Earl amp Deem (2005) Our implementation follows Brandtet al (2019a) in the broad lines We sampled the parameter spaceof our 13-parameter model assuming 15 temperatures for thechains and 100 walkers The first 8 parameters are the semi-major axis a the eccentricity e and argument of periastron pas-sageω (parameterized as

radice cosω and

radice sinω) the inclination

i the longitude of the ascending node Ω the time at periastronpassage T0 the RV semi-amplitude of the star κA and the sys-temic velocity γ We present the results for Ω and ω as relativeto the companion To fit the imaging and proper motion data weused the equations in Appendix A of Makarov amp Kaplan (2005)

The initial state of the sampler was set assuming uniform pri-ors in log a

radice cosω

radice sinω Ω T0 and κA as well as a sin i

prior for i The width of the priors were selected from the re-sults in Bouchy et al (2016) and a fit to the RV and imaging datawith a least-squares Monte Carlo approach (Maire et al 2015Schlieder et al 2016) to derive first ranges for i and Ω We disen-tangled the two (iΩ) solutions by comparing the predictions forthe instantaneous stellar proper motions to the measurements

The next two parameters in our model are the parallax andthe semi-major axis of the orbit of the host star around the cen-ter of mass of the system For the parallax we drew the initialguesses around the nominal value measured by Gaia assuminga combination of a Gaussian distribution for the measurementuncertainties and a uniform distribution for potential system-atics (lt01 mas httpswwwcosmosesaintwebgaiadr2) We drew the semi-major axis of the star around a guessvalue computed from its mass (099 M) the companion mass(007 M) and the total semi-major axis assuming a uniformdistribution with a half-width of 15 mas The last free modelparameters are one RV offset and two RV jitters using the re-sults in Bouchy et al (2016) as first guesses

We ran the MCMC for 125 000 iterations and verified theconvergence of the chains using the integrated autocorrelationtime (Foreman-Mackey et al 2013 Goodman amp Weare 2010)

Table 2 Orbital parameters and dynamical mass of HD 72946B

Parameter Unit Median plusmn 1σ Best fitFitted parameters

Semi-major axis a mas 2491+31minus30 2504

radice cosω 0231+0019

minus0020 0230radic

e sinω 0662+0008minus0009 0663

Inclination i 593+23minus20 596

PA of asc node Ω -120+43minus39 -118

Time periastron T0 BJD 24559567+107minus101 24559551

RV semi-ampl κA m sminus1 7787+105minus94 7741

Syst velocity γ m sminus1 -2032+84minus86 -2074

Parallax π mas 3865plusmn012 3866SMA primary a1 mas 1628+029

minus026 1612RV offset ZPSOPHIE m sminus1 906+156

minus169 962RV jitter σELODIE m sminus1 244+41

minus33 229RV jitter σSOPHIE m sminus1 161+50

minus35 1267Computed parameters

M1 M 099plusmn003 101M2 MJ 724plusmn16 725Mass ratio M2M1 0070plusmn0002 0069Period P yr 1591+016

minus013 1590Semi-major axis a au 645+008

minus007 648Eccentricity e 0493+0007

minus0008 0493Arg periastron ω 2507plusmn17 2509

The posterior distributions in Appendix C were obtained afterthinning the chains by a factor 100 to mitigate the correlationsand discarding the first 75 of the chains as the burn-in phaseThe median values with 1σ uncertainties and the best-fit valuesof the parameters are given in Table 2 The uncertainties in theparameters in common with Bouchy et al (2016) are slightlylarger or similar A sample of model orbits is shown in Fig 2

We note that the proper motion anomaly measured by Hip-parcos in RA is different by sim2σ from the orbital predictionswhereas the measurement in DEC is well reproduced within theuncertainties The Hipparcos and Gaia data affect the derived



M8 M9 L0 L1 L2 L3 L4 L5 L6 L7 L8 L9 T0 T1 T2SpT

0

5

10

15

20

25

30

35

40Re

duce

d 2

Fig 3 Reduced χ2 as a function of the spectral type of the comparisonof the IFS spectrum of HD 72946B to SpeX template dwarfs

orbital parameters and dynamical mass within the uncertaintieswith respect to a fit that only uses the RV and imaging data ex-cept for breaking the ambiguity in the inclination and longitudeof ascending node

5 Spectral analysis

We used the IRDIS dual-band photometry of the companionto compute the color-magnitude diagram in Appendix D (de-tails from Appendix C of Bonnefoy et al 2018) We note thatHD 72946B is located near mid-L template dwarfs and is closeto HIP 65426b (Chauvin et al 2017)

We compared the IFS spectrum to spectra of template dwarfsof the SpeX spectral library using the SPLAT toolkit (Burgasser2014) Figure 3 shows the reduced χ2 as a function of the spectraltype We include the uncertainties of the template spectra in theχ2 computation The best-fit object is the red L dwarf 2MASSJ03552337+1133437 (Bardalez Gagliuffi et al 2014) (reducedχ2 = 089 assuming 38 degrees of freedom) which is classifiedas L5γ by Cruz et al (2009) From a parabolic fit to the χ2 valueswe estimate a spectral type of L50plusmn15 considering all spectraltypes that satisfy χ2ltχ2

min+1To fit the spectrophotometry of HD 72946B with at-

mospheric models we converted the contrast measurementsinto physical fluxes using a model spectrum for the star(Teff = 5600 K log g = 45 dex and [FeH] = 00 dex) from theBT-NextGen library (Allard et al 2012) and the SPHERE filtertransmission curves The BT-NextGen spectrum is fit to the stel-lar spectral energy distribution (SED) over the range 03ndash12 micromusing the Virtual Observatory SED Analyzer (Bayo et al 2008)The stellar SED is built using data from Tycho (Hoslashg et al 2000)2MASS (Cutri et al 2003) WISE (Cutri amp et al 2013) andIRAS (Helou amp Walker 1988) as well as Johnson photometry(Mermilliod 2006) and Stroumlmgren photometry (Paunzen 2015)

We show in Fig 4 the resulting SED of HD 72946B We per-formed a grid search for best-fit models in the BT-Settl spec-tral library (Allard et al 2011) The characteristics of the gridare Teff = 700ndash2500 K by steps of 100 K log g = 35ndash55 dexby steps of 05 dex and [FeH] = 00 dex We allowed the ra-dius to vary and kept solutions with radii in the range 07-11 RJWe show the four best-match model spectra in Fig 4 An effec-tive temperature of sim1700 K provides a good match to the datawhich is in the range expected from evolutionary models for anage of sim1ndash3 Gyr given the dynamical mass It also agrees witha spectral type of L5 from the relation for field dwarfs in Filip-pazzo et al (2015) (left panel of their Fig 15)

Fig 4 Spectral energy distribution of HD 72946B (black) The fourbest-match BT-Settl spectra are shown for comparison (colors)

Fig 5 Bolometric luminosity vs age of HD 72946B (gray area) com-pared to evolutionary tracks from the models COND (Baraffe et al2003) Saumon amp Marley (2008) (for two treatments of the clouds)Burrows et al (1997) and Baraffe et al (2015) assuming the mass rangefor the companion from the orbital fit (data points) Small horizontaloffsets are applied to all models except for COND for clarity

6 Discussion

HD 72946B joins the short list of benchmark brown dwarf com-panions to stars with RV and imaging measurements HR 7672B(Liu et al 2002 Crepp et al 2012) HD 19467B (Crepp et al2014) HD 4747B (Sahlmann et al 2011 Crepp et al 2016Peretti et al 2018) GJ 758B (Thalmann et al 2009 Bowleret al 2018) HD 4113C (Cheetham et al 2018b) and GJ 229B(Nakajima et al 1995 Brandt et al 2019b) HD 72946B standsout among these objects because a complete orbit is covered byRV and it has the smallest physical separation to the star sim64-65 au This is slightly outside the ice line for a Sun-like star

To evaluate a possible formation mechanism for HD 72946Bwe compared its mass (or mass ratio to the star) and separationto model objects formed by fragmentation of a collapsing cloudin Bate (2009) (Fig 21) or by disk gravitational instabilities inForgan amp Rice (2013) and Vigan et al (2017) (left panel of Fig8 in the latter paper) The semi-major axes of most of the modelobjects with mass ratios similar to HD 72946B formed in the for-mer process are in the range 20ndash5000 au The semi-major axesof most of the model objects with masses similar to HD 72946Bformed in the latter process are in the range sim10ndash50 au Thismeans that the semi-major axis of HD 72946B is smaller thanthose of model objects from both formation mechanisms andwe cannot exclude any of them



Figure 5 shows the estimated bolometric luminosity andage of HD 72946B with the predictions from the modelsCOND (Baraffe et al 2003) Saumon amp Marley (2008) (fortwo treatments of the clouds hybrid and no clouds) Bur-rows et al (1997) and Baraffe et al (2015) assuming the954 confidence interval for the companion mass from theorbital fit (724plusmn32 MJ) We estimate the bolometric lumi-nosity to be log(LL) = -411plusmn010 dex using the magnitude-bolometric luminosity relation in Filippazzo et al (2015) forfield dwarfs and the Js magnitude computed from the IFS spec-trum (1544plusmn013 mag) with a correction of 005 dex betweenthe Js and J bands estimated using SpeX spectra of the threebest-fit template dwarfs The J-H3 color of the companion(108plusmn008 mag) is consistent with expectations from mid-Lfield dwarfs (Cheetham et al 2019) and is closer to the color pre-dicted given the mass and age of the companion by the DUSTYmodel (cloudy atmosphere Chabrier et al 2000 J-H3gt1 mag)than to the color predicted by the COND model (cloudless at-mosphere J-H3lt08 mag)2 This suggests a cloudy atmosphereFor ages younger than 800 Myr HD 72946B is fainter than thepredictions of all evolutionary models At 1 Gyr the compan-ion properties are best reproduced by the hybrid cloud model ofSaumon amp Marley (2008) and Burrows et al (1997) At 2 Gyrthe best-match models are COND and the cloudless model ofSaumon amp Marley (2008) and Baraffe et al (2015) At 3 Gyrthe models of Baraffe et al (2015) account better for the com-panion properties Observations to better constrain the stellar agewith gyrochronology may allow a better distinction between themodels

The characterization of HD 72946B clearly illustrates theimprovements in the high-contrast imaging instrumentation to-ward bridging the gap in separation to the star with RV and as-trometry The combination of these data provides stronger con-straints on the properties of substellar companions than can bereached with one technique alone This allows testing their mass-luminosity models The SPHERE data are sensitive to low-massbrown dwarfs down to sim30 MJ at separations as close as 02primeprime(Appendix E) The next generation of high-contrast imaging in-struments on extremely large telescopes will enable extendinganalyses like this to the bulk of substellar companions that aredetected with RV at closer separations and at lower masses downto the planetary regime and building empirical mass-luminosityrelations for exoplanets The future release of the Gaia epochastrometry will permit more accurate measurements of propermotion anomalies This will improve dynamical mass estimatesand provide new targets for this purpose

Acknowledgements The authors thank the referee for a constructive report thathelped to clarify the manuscript The authors thank the ESO Paranal Stafffor support in conducting the observations N G and J O acknowledge fi-nancial support from the ICM (Iniciativa Cientiacutefica Milenio) via the NuacutecleoMilenio de Formacioacuten Planetaria grant from the Universidad de Valparaiacutesoand from Fondecyt (grant 1180395) N G acknowledges grant support fromproject CONICYT-PFCHADoctorado Nacional2017 folio 21170650 We ac-knowledge financial support from the Programme National de Planeacutetologie(PNP) the Programme National de Physique Stellaire (PNPS) of CNRS-INSUin France and the Agence Nationale de la Recherche (GIPSE project grantANR-14-CE33-0018) TH acknowledges support from the European ResearchCouncil under the Horizon 2020 Framework Program via the ERC AdvancedGrant Origins 83 24 28 This work made use of recipes from the IDL li-braries IDL Astronomy Usersrsquos Library (Landsman 1993) Coyote (httpwwwidlcoyotecomindexhtml) EXOFAST (Eastman et al 2013) JBIU(httpwwwsimulated-galaxiesuaedujbiu) and the s3drs pack-age (httpwwwheliodocscomxdocindexhtml) It also made use ofthe Python packages NumPy (Oliphant 2006) emcee (Foreman-Mackey et al

2 Tables available at httppersoens-lyonfrfranceallard

2013) corner (Foreman-Mackey 2016) Matplotlib (Hunter 2007) Astropy(Astropy Collaboration et al 2013 2018) and dateutil (httpdateutilreadthedocsio) This publication makes use of VOSA developed under theSpanish Virtual Observatory project supported by the Spanish MINECO throughgrant AyA2017-84089 VOSA has been partially updated by using funding fromthe European Unionrsquos Horizon 2020 Research and Innovation Programme un-der Grant Agreement no 776403 (EXOPLANETS-A) This research has bene-fitted from the SpeX Prism Spectral Libraries maintained by Adam Burgasserat httpponoucsdedu~adambrowndwarfsspexprism This researchmade use of the SIMBAD database and the VizieR Catalogue access tool bothoperated at the CDS Strasbourg France The original descriptions of the SIM-BAD and VizieR services were published in Wenger et al (2000) and Ochsen-bein et al (2000) This research has made use of NASArsquos Astrophysics DataSystem Bibliographic Services

ReferencesAguilera-Goacutemez C Ramiacuterez I amp Chanameacute J 2018 AampA 614 A55Allard F Homeier D amp Freytag B 2011 in Astronomical Society of the

Pacific (ASP) Conf Ser ed C Johns-Krull M K Browning amp A A WestVol 448 91

Allard F Homeier D Freytag B amp Sharp C M 2012 in EAS PublicationsSer ed C Reyleacute C Charbonnel amp M Schultheis Vol 57 3ndash43

Astropy Collaboration Price-Whelan A M Sipocz B M et al 2018 AJ 156123

Astropy Collaboration Robitaille T P Tollerud E J et al 2013 AampA 558A33

Bailey V Meshkat T Reiter M et al 2014 ApJL 780 L4Baraffe I Chabrier G Barman T S Allard F amp Hauschildt P H 2003

AampA 402 701Baraffe I Homeier D Allard F amp Chabrier G 2015 AampA 577 A42Bardalez Gagliuffi D C Burgasser A J Gelino C R et al 2014 ApJ 794

143Bate M R 2009 MNRAS 392 590Bayo A Rodrigo C Barrado Y Navascueacutes D et al 2008 AampA 492 277Beichman C Gelino C R Kirkpatrick J D et al 2014 ApJ 783 68Beuzit J L Vigan A Mouillet D et al 2019 AampA 631 A155Boccaletti A Sezestre E Lagrange A-M et al 2018 AampA 614 A52Bonnefoy M Chauvin G Lagrange A-M et al 2014 AampA 562 A127Bonnefoy M Perraut K Lagrange A M et al 2018 AampA 618 A63Boro Saikia S Marvin C J Jeffers S V et al 2018 AampA 616 A108Boss A P 1997 Science 276 1836Bouchy F Seacutegransan D Diacuteaz R F et al 2016 AampA 585 A46Bowler B P Dupuy T J Endl M et al 2018 AJ 155 159Brandt T D 2018 ApJS 239 31Brandt T D 2019 ApJS 241 39Brandt T D Dupuy T J amp Bowler B P 2019a AJ 158 140Brandt T D Dupuy T J Bowler B P et al 2019b arXiv e-prints

arXiv191001652Burgasser A J 2014 in Astronomical Society of India Conf Ser Vol 11 7Burningham B Pinfield D J Leggett S K et al 2008 MNRAS 391 320Burrows A Marley M Hubbard W B et al 1997 ApJ 491 856Cantalloube F Mouillet D Mugnier L M et al 2015 AampA 582 A89Carbillet M Bendjoya P Abe L et al 2011 Exp Astron 30 39Casagrande L Schoumlnrich R Asplund M et al 2011 AampA 530 A138Chabrier G Baraffe I Allard F amp Hauschildt P 2000 ApJ 542 464Chauvin G Desidera S Lagrange A-M et al 2017 AampA 605 L9Cheetham A Bonnefoy M Desidera S et al 2018a AampA 615 A160Cheetham A Seacutegransan D Peretti S et al 2018b AampA 614 A16Cheetham A C Samland M Brems S S et al 2019 AampA 622 A80Claudi R U Turatto M Gratton R G et al 2008 in SPIE Conf Ser Vol

7014 70143ECrepp J R Gonzales E J Bechter E B et al 2016 ApJ 831 136Crepp J R Johnson J A Fischer D A et al 2012 ApJ 751 97Crepp J R Johnson J A Howard A W et al 2014 ApJ 781 29Cruz K L Kirkpatrick J D amp Burgasser A J 2009 AJ 137 3345Cutri R M amp et al 2013 VizieR Online Data Catalog 2328 0Cutri R M Skrutskie M F van Dyk S et al 2003 VizieR Online Data

Catalog 2246 0da Silva L Girardi L Pasquini L et al 2006 AampA 458 609De Rosa R J Patience J Ward-Duong K et al 2014 MNRAS 445 3694Delorme P Delfosse X Albert L et al 2008 AampA 482 961Delorme P Schmidt T Bonnefoy M et al 2017 AampA 608 A79Dieterich S B Weinberger A J Boss A P et al 2018 ApJ 865 28Dohlen K Langlois M Saisse M et al 2008 in SPIE Conf Ser Vol 7014

70143LDommanget J amp Nys O 2002 VizieR Online Data Catalog I274Ducourant C Teixeira R Galli P A B et al 2014 AampA 563 A121



Dupuy T J amp Kraus A L 2013 Science 341 1492Dupuy T J amp Liu M C 2017 ApJS 231 15Duquennoy A amp Mayor M 1991 AampA 500 337Earl D J amp Deem M W 2005 Physical Chemistry Chemical Physics (Incor-

porating Faraday Transactions) 7 3910Eastman J Gaudi B S amp Agol E 2013 PASP 125 83Faherty J K Burgasser A J Walter F M et al 2012 ApJ 752 56Feroz F Balan S T amp Hobson M P 2011 Monthly Notices of the Royal

Astronomical Society 416 L104Filippazzo J C Rice E L Faherty J et al 2015 ApJ 810 158Foreman-Mackey D 2016 The Journal of Open Source Software 1 24Foreman-Mackey D Hogg D W Lang D amp Goodman J 2013 PASP 125

306Forgan D amp Rice K 2013 MNRAS 432 3168Gaia Collaboration Brown A G A Vallenari A et al 2018 AampA 616 A1Gaia Collaboration Prusti T de Bruijne J H J et al 2016 AampA 595 A1Galicher R Boccaletti A Mesa D et al 2018 AampA 615 A92Gauza B Beacutejar V J S Peacuterez-Garrido A et al 2015 ApJ 804 96Gizis J E Allers K N Liu M C et al 2015 ApJ 799 203Goodman J amp Weare J 2010 Communications in Applied Mathematics and

Computational Science 5 65Gray R O Corbally C J Garrison R F McFadden M T amp Robinson P E

2003 AJ 126 2048Grether D amp Lineweaver C H 2006 The Astrophysical Journal 640 1051Hayes D S 1985 in IAU Symposium Vol 111 Calibration of Fundamental

Stellar Quantities ed D S Hayes L E Pasinetti amp A G D Philip 225ndash252

Helou G amp Walker D W eds 1988 Infrared astronomical satellite (IRAS)catalogs and atlases Volume 7 The small scale structure catalog Vol 7

Hoslashg E Fabricius C Makarov V V et al 2000 AampA 355 L27Hunter J D 2007 Computing in Science amp Engineering 9 90Kirkpatrick J D Cushing M C Gelino C R et al 2011 ApJS 197 19Kirkpatrick J D Gelino C R Cushing M C et al 2012 ApJ 753 156Kirkpatrick J D Reid I N Liebert J et al 2000 AJ 120 447Konopacky Q M Ghez A M Barman T S et al 2010 ApJ 711 1087Konopacky Q M Thomas S J Macintosh B A et al 2014 in Society

of Photo-Optical Instrumentation Engineers (SPIE) Conference Series Vol9147 Ground-based and Airborne Instrumentation for Astronomy V 914784

Lachapelle F-R Lafreniegravere D Gagneacute J et al 2015 ApJ 802 61Lafreniegravere D Jayawardhana R amp van Kerkwijk M H 2010 ApJ 719 497Landsman W B 1993 in Astronomical Society of the Pacific Conference Se-

ries Vol 52 Astronomical Data Analysis Software and Systems II ed R JHanisch R J V Brissenden amp J Barnes 246

Langlois M Vigan A Moutou C et al 2013 in Proceedings of the ThirdAO4ELT Conference ed S Esposito amp L Fini 63

Leggett S K Allard F Dahn C et al 2000 ApJ 535 965Lindegren L Hernaacutendez J Bombrun A et al 2018 AampA 616 A2Liu M C Dupuy T J amp Allers K N 2016 ApJ 833 96Liu M C Fischer D A Graham J R et al 2002 ApJ 571 519Liu M C Magnier E A Deacon N R et al 2013 ApJ 777 L20Lucas P W Tinney C G Burningham B et al 2010 MNRAS 408 L56Luck R E 2017 AJ 153 21Luck R E amp Heiter U 2006 AJ 131 3069Luhman K L amp Esplin T L 2016 AJ 152 78Ma B amp Ge J 2014 Monthly Notices of the Royal Astronomical Society 439

2781Mace G N Kirkpatrick J D Cushing M C et al 2013 ApJS 205 6Macintosh B Graham J R Ingraham P et al 2014 PNAS 111 12661Maire A-L Langlois M Dohlen K et al 2016 in SPIE Conf Ser Vol

9908 990834Maire A-L Skemer A J Hinz P M et al 2015 AampA 576 A133Makarov V V amp Kaplan G H 2005 AJ 129 2420Mamajek E E amp Hillenbrand L A 2008 ApJ 687 1264Marois C Correia C Galicher R et al 2014 in SPIE Conf Ser Vol 9148

91480UMarois C Lafreniegravere D Doyon R Macintosh B amp Nadeau D 2006 ApJ

641 556Martinez P Dorrer C Aller Carpentier E et al 2009 AampA 495 363Martiacutenez-Arnaacuteiz R Maldonado J Montes D Eiroa C amp Montesinos B

2010 AampA 520 A79Mawet D Milli J Wahhaj Z et al 2014 ApJ 792 97Mermilliod J C 2006 VizieR Online Data Catalog II168Mesa D Gratton R Zurlo A et al 2015 AampA 576 A121Montes D Loacutepez-Santiago J Gaacutelvez M C et al 2001 MNRAS 328 45Mountain C M Leggett S K Selby M J Blackwell D E amp Petford A D

1985 AampA 151 399Mugnier L M Cornia A Sauvage J-F et al 2009 Journal of the Optical

Society of America A 26 1326Nakajima T Oppenheimer B R Kulkarni S R et al 1995 Nature 378 463Nielsen E L De Rosa R J Macintosh B et al 2019 AJ 158 13

Ochsenbein F Bauer P amp Marcout J 2000 AampAS 143 23Oh S Price-Whelan A M Hogg D W Morton T D amp Spergel D N 2017

AJ 153 257Oliphant T E 2006 A guide to NumPy Vol 1 (Trelgol Publishing USA)Patience J King R R de Rosa R J amp Marois C 2010 AampA 517 A76Paunzen E 2015 AampA 580 A23Pavlov A Moumlller-Nilsson O Feldt M et al 2008 in SPIE Conf Ser Vol

7019 701939Peretti S Seacutegransan D Lavie B et al 2018 AampA in press

arXiv180505645Perrin M D Ingraham P Follette K B et al 2016 in Society of Photo-

Optical Instrumentation Engineers (SPIE) Conference Series Vol 9908Ground-based and Airborne Instrumentation for Astronomy VI 990837

Perrin M D Maire J Ingraham P et al 2014 in SPIE Conf Ser Vol 91473

Perryman M A C Lindegren L Kovalevsky J et al 1997 AampA 500 501Pourbaix D Tokovinin A A Batten A H et al 2004 AampA 424 727Rajan A Rameau J De Rosa R J et al 2017 AJ 154 10Ramiacuterez I Fish J R Lambert D L amp Allende Prieto C 2012 ApJ 756 46Rocha-Pinto H J Flynn C Scalo J et al 2004 AampA 423 517Sahlmann J Seacutegransan D Queloz D et al 2011 Astronomy and Astro-

physics 525 A95Saumon D amp Marley M S 2008 ApJ 689 1327Schlieder J E Skemer A J Maire A-L et al 2016 ApJ 818 1Schneider A C Cushing M C Kirkpatrick J D et al 2015 ApJ 804 92Sestito P Randich S amp Pallavicini R 2004 AampA 426 809Soummer R Pueyo L amp Larkin J 2012 ApJL 755 L28Stone J M Skemer A J Kratter K M et al 2016 ApJ 818 L12Thalmann C Carson J Janson M et al 2009 ApJL 707 123Tinney C G Faherty J K Kirkpatrick J D et al 2014 ApJ 796 39van Leeuwen F 2007 AampA 474 653Vigan A Bonavita M Biller B et al 2017 AampA 603 A3Vigan A Gry C Salter G et al 2015 MNRAS 454 129Vigan A Moutou C Langlois M et al 2010 MNRAS 407 71Wahhaj Z Liu M C Biller B A et al 2011 ApJ 729 139Warren S J Mortlock D J Leggett S K et al 2007 MNRAS 381 1400Wenger M Ochsenbein F Egret D et al 2000 AampAS 143 9Zapatero Osorio M R Beacutejar V J S Miles-Paacuteez P A et al 2014 AampA 568

A6

1 STAR Institute Universiteacute de Liegravege Alleacutee du Six Aoucirct 19c B-4000Liegravege Belgiume-mail almaireuliegebe

2 Department of Physics University of Oxford Oxford UK3 INAFndashOsservatorio Astronomico di Padova Vicolo

dellrsquoOsservatorio 5 I-35122 Padova Italy4 INAF Catania Astrophysical Observatory via S Sofia 78 95123

Catania Italy5 Max-Planck-Institut fuumlr Astronomie Koumlnigstuhl 17 D-69117 Hei-

delberg Germany6 Instituto de Fiacutesica y Astronomiacutea Facultad de Ciencias Univ de Val-

paraiacuteso Av Gran Bretantildea 1111 Playa Ancha Valparaiacuteso Chile7 Nuacutecleo Milenio Formacioacuten Planetaria - NPF Univ de Valparaiacuteso

Av Gran Bretantildea 1111 Playa Ancha Valparaiacuteso Chile8 LESIA Observatoire de Paris PSL Research University CNRS

Sorbonne Universiteacutes UPMC Univ Paris 06 Univ Paris DiderotSorbonne Paris Citeacute 5 place Jules Janssen F-92195 Meudon France

9 Univ Grenoble Alpes CNRS IPAG F-38000 Grenoble France10 Geneva Observatory University of Geneva Chemin des Maillettes

51 1290 Versoix Switzerland11 Unidad Mixta Internacional Franco-Chilena de Astronomiacutea

CNRSINSU UMI 3386 and Departamento de AstronomiacuteaUniversidad de Chile Casilla 36-D Santiago Chile

12 CRAL UMR 5574 CNRSENS-LyonUniversiteacute Lyon 1 9 av ChAndreacute F-69561 Saint-Genis-Laval France



Appendix A Stellar multiplicity

Bouchy et al (2016) noted that HD 72946 is part of a multiplesystem HD 72945 is a comoving F8 star located at a projectedseparation of 230 au Duquennoy amp Mayor (1991) identified itas a spectroscopic binary SB1 with a period of 143 d

The Gaia parallaxes of HD 72945 and HD 72946 differ at the42σ level indicating a distance difference along the line of sightof about 041plusmn010 pc The similar proper motion and systematicvelocities of the two stars argue in favor of a physical associa-tion (see also Oh et al 2017) We speculate that the separationalong the line of sight could be significantly larger than the oneprojected on the plane of the sky Alternatively the parallaxes ofone or both components can be altered above the formal errorsby the presence of the companions

In addition Dommanget amp Nys (2002) reported three stellarcompanions with angular separations of 93primeprime 117primeprime and 122primeprime

Using the Gaia parallaxes we find that the three compo-nents identified by Dommanget amp Nys (2002) (πlt 12 mas)do not form a system with HD 72945 and HD 72946 (πsim 38ndash39 mas) Instead we note in the Gaia catalog a star (2MASSID 08354678+0635294) at sim130primeprime (sim3400 au) from HD 72946with a parallax of 388196plusmn00584 mas (distance along the lineof sight sim011plusmn005 pc) and similar proper motion but withouta measured RV Therefore we argue that the system is formedby four stellar and one substellar components For the orbitalanalysis we assumed that the acceleration seen in the propermotion of HD 72946 is entirely due to the substellar companionHD 72946B

The other components may provide additional constraints onthe age of the system In particular we derive for HD 72945an age and a mass using the PARAM web interface the Teff

derived by Casagrande et al (2011) from Stroumlmgren pho-tometry the Gaia parallax the V magnitude from Hipparcos(592plusmn001 mag) and the metallicity measured by Bouchy et al(2016) for HD 72946 (001-dex difference only with the metal-licity of HD 72945 measured by Casagrande et al 2011) Wefind an age of 1584plusmn0952 Gyr and a mass of 1245plusmn0030 MFor this computation we assumed that the spectroscopic com-panion of HD 72945 does not contribute significantly to the in-tegrated photometry This should be the case if its mass is notmuch higher than the expected minimum mass from the RV or-bit Using the SB9 orbit (Pourbaix et al 2004) and the isochronalmass above we derive a minimum mass for the secondary of034 M In any case a significant contribution to the photome-try would shift the measured isochronal age toward higher valuesthan expected We report archival GPI data of HD 72945 in Ap-pendix F

Appendix B Comparison of extractedspectrophotometry

We show in Fig B1 the comparison of the spectrophotometryextracted with the ANgular DiffeRential Optimal Method Ex-oplanet Detection Algorithm (ANDROMEDA Mugnier et al2009 Cantalloube et al 2015) and with the Template LocallyOptimized Combination of Images (TLOCI Marois et al 2014)and Principal Component Analysis (PCA Soummer et al 2012)algorithms provided by the SpeCal pipeline (Galicher et al2018) For the TLOCI extraction we used the fitting of a modelplanet image whereas for PCA we employed the negative syn-thetic planet injection The fitting uncertainties are given at 3 σWe note the good agreement between the TLOCI and PCA re-sults within the TLOCI uncertainties The IFS spectra between

Fig B1 Comparison of the TLOCI ANDROMEDA and PCA spec-trophotometry The measurement uncertainties are shown at 3 σ for allalgorithms

TLOCI and ANDROMEDA did not formerly agree for wave-lengths longer than sim12 microm with the ANDROMEDA spectrumshowing a steeper slope than the TLOCI spectrum The IRDISphotometry for ANDROMEDA looks fainter than the TLOCIphotometry by sim15 although the uncertainties are large Thisresults in an IRDIFS spectrum that is redder for TLOCI than forANDROMEDA

We tested both ANDROMEDA and TLOCI SED for the at-mospheric fitting We experienced convergence problems whenfitting the ANDROMEDA SED and we chose the TLOCI SEDfor the analysis shown in this paper We did not notice any sig-nificant discrepancies in the extracted astrometry but we choseto use the TLOCI astrometry for consistency

Appendix C Corner plot of the orbital fit

We provide here the corner plot of the orbital parameters derivedin Sect 4

Appendix D Color-magnitude diagram

To build the diagram in Fig D1 we used spectra of M Land T dwarfs from the SpeX-Prism library (Burgasser 2014)and from Leggett et al (2000) and Schneider et al (2015) togenerate synthetic photometry in the SPHERE filter passbandsThe zero-points were computed using a flux-calibrated spectrumof Vega (Hayes 1985 Mountain et al 1985) We also consid-ered the spectra of young andor dusty free-floating objects fromLiu et al (2013) Mace et al (2013) Gizis et al (2015) andof young companions (Wahhaj et al 2011 Gauza et al 2015Stone et al 2016 De Rosa et al 2014 Lachapelle et al 2015Bailey et al 2014 Rajan et al 2017 Bonnefoy et al 2014 Pa-tience et al 2010 Lafreniegravere et al 2010 Chauvin et al 2017Delorme et al 2017 Cheetham et al 2018a) The colors and ab-solute fluxes of the benchmark companions and isolated T-typeobjects were generated from the distance and spectra of theseobjects in Appendix B in Bonnefoy et al (2018) To concludewe used the spectra of Y dwarfs published in Schneider et al(2015) Warren et al (2007) Delorme et al (2008) Burninghamet al (2008) Lucas et al (2010) Kirkpatrick et al (2012) andMace et al (2013) to extend the diagrams in the late-T and early-Y dwarf domain We used the distances of the field dwarfs re-ported in Kirkpatrick et al (2000) Faherty et al (2012) Dupuyamp Kraus (2013) Tinney et al (2014) Beichman et al (2014)



Fig C1 MCMC posteriors of the orbital parameters (left) and of the masses of HD 72946 A and B (top right) The diagrams displayed on thediagonals represent the 1D histogram distributions for the parameters The off-diagonal diagrams show the correlations In the histograms thedashed vertical lines indicate the 16 50 and 84 quantiles

and Luhman amp Esplin (2016) We considered those reported inKirkpatrick et al (2011) Faherty et al (2012) Zapatero Oso-rio et al (2014) and Liu et al (2016) for the dusty dwarfs Thecompanion distances were taken from van Leeuwen (2007) andDucourant et al (2014)

Appendix E SPHERE detection limits

Figure E1 shows the SPHERE detection limits in contrast tothe star and the planet mass obtained with ANDROMEDA Forthe IFS detection limits we assumed a T5 dwarf template spec-trum (Cantalloube et al in preparation) retrieved from the SpeXlibrary The detection limits account for the coronagraphic trans-mission (Boccaletti et al 2018) and the small sample statistics

correction (Mawet et al 2014) The contrast to planet mass con-version was derived assuming the ldquohot-startrdquo evolutionary andatmospheric models of Baraffe et al (2003 2015) and an age of2 Gyr for the system (table from Vigan et al 2015) The H3 curveis sensitive to more massive objects than the H2 curve becausethe probed mass regime corresponds to cold objects with strongmethane absorption features and the H3 filter matches a strongmethane band We excluded additional brown dwarf companionsmore massive than sim20 MJ at separations beyond 8 au

Appendix F GPI archival data of HD 72945

The stellar SB companion HD 72945 was observed with theGemini Planet Imager (GPI Macintosh et al 2014) on 2015



-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

M0-M5M6-M9L0-L5L6-L9T0-T5T6-T95

youngdusty dwarfs

WISE1647+56

HR8799bHR8799cHR8799dHR8799e

1RXS1609b

2M1207b

GU Psc B

HN Peg Bβ Pic b

UScoCTIO 108B

HIP 64892B

HIP 78530B

GSC0621-0021B

VHS 1256ABb (127171pc)

ζ Del B

HIP 43620B

51 Eri b

HD 106906 b

GJ 758b

GJ 504b

HIP 65426b

HD 72946B

Y0-Y2

-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

Fig D1 Color-magnitude diagram of HD 72946B (orange) using theIRDIS photometry Template dwarfs (colored points) and a few younglow-mass companions (black labels) are also shown for comparison

April 4 UT in the H band The data were presented in the firststatistical analysis of the GPIES survey (Nielsen et al 2019 tar-get name HR 3395) The target was observed for an integrationtime of 328 min which amounts to a field rotation of 195

We retrieved the data from the Gemini archive and reducedthem with the GPI data reduction pipeline v140 (Perrin et al2014 2016) which applies an automatic correction for the Northoffset of minus100plusmn003 measured by Konopacky et al (2014)Then we post-processed them using ANDROMEDA No pointsource is detected above 5σ We show in Fig F1 the detectionlimits obtained for a T5 dwarf template spectrum We assumedan age of 2 Gyr a distance of 263 pc from the Gaia DR2 paral-lax and the models of Baraffe et al (2003 2015) For the stellarmagnitude we used the 2MASS value although we note that itis affected by saturation We included the small sample statis-tics correction We cut the curves to separation larger than 015primeprimebecause we were unable to find GPI coronagraphic transmissioncurves

Fig E1 SPHERE 5σ detection limits in contrast with respect to thestar (top) and the planet mass (bottom) We also indicate the location ofHD 72946B for comparison



Fig F1 GPI 5σ detection limits of HD 72945 in contrast with respectto the star (top) and the planet mass (bottom)


1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion

A Stellar multiplicity

B Comparison of extracted spectrophotometry

C Corner plot of the orbital fit

D Color-magnitude diagram

E SPHERE detection limits

F GPI archival data of HD72945


Table 1 Relative photometry and astrometry of HD 72946B

Filter λ0 ∆λ ∆mag Abs mag Flux Separation PA(microm) (microm) (mag) (mag) (times10minus15 W mminus2 micromminus1) (mas) ()

H2 1593 0052 897plusmn007 1251plusmn007 3027plusmn0188 2357plusmn20 3365plusmn031H3 1667 0054 881plusmn007 1235plusmn007 3236plusmn0204 2356plusmn20 3368plusmn031

Notes The photometric error bars were derived assuming an error budget including the measurement uncertainties (image post-processing) andsystematic uncertainties (temporal variability of the flux calibration and of the science sequence)

the spectroscopic Teff and [FeH] in Bouchy et al (2016) withenlarged uncertainties to account for systematic errors We alsoadopted the Gaia parallax and the V-band magnitude from Hip-parcos (708plusmn002 mag) This results in an age 1712plusmn1684 Gyra mass 0986plusmn0027 M and a radius 0908plusmn0018 R Tighterconstraints on the age from isochrones can be derived from theF8 comoving companion HD 72945 (16plusmn10 Gyr Appendix A)

Lithium data (A(Li) = 141 123 122plusmn015 dex Luck 2017Luck amp Heiter 2006 Ramiacuterez et al 2012) indicate an age olderthan that of the Hyades and similar to the open cluster NGC 752(Sestito et al 2004) The stellar kinematics suggest an ageyounger than the Sun the UVW velocities being at the boundaryof the kinematic space of young stars in Montes et al (2001)Comparisons with stars with similar kinematics in Casagrandeet al (2011) indicated that it is unlikely that the star is older thansim3 Gyr and much younger than 05 Gyr

We searched for archival photometric data to derive an agewith gyrochronology but we did not find suitable data (sam-pling accuracy blending with HD 72945 andor calibration is-sues) Using the relations in Mamajek amp Hillenbrand (2008) andan averaged measured chromospheric activity of -460 dex (in-dividual values -454 -474plusmn005 -466 and -447 dex Rocha-Pinto et al 2004 Bouchy et al 2016 Gray et al 2003 BoroSaikia et al 2018) we derive a rotation period of sim15 d whichimplies a gyrochronological age of sim1 Gyr This is in betweenthe loci of the Hyades (625ndash700 Myr) and NGC 752 (2000 Myr)The star has X-ray data from ROSAT but is blended withHD 72945 However X-ray activity is expected to correlate withchromospheric activity so that it does not provide a fully inde-pendent age estimate Assuming our derived stellar radius and anaveraged measured projected rotational activity of 414 km sminus1

(individual values 323 39plusmn1 and 53 km sminus1 Martiacutenez-Arnaacuteizet al 2010 Bouchy et al 2016 Luck 2017) we derive an up-per limit for the rotation period of 12 d which implies a gy-rochronological age younger than 1 Gyr considering a B minus Vcolor of 071 mag Considering the large uncertainties in vsin ithe upper limit for the gyrochronological age could be as old as15 Gyr This means that our various age estimates agree overallIn the following we choose to adopt an age range of 08ndash3 Gyrwith a most probable value of 1ndash2 Gyr


We observed HD 72946 on 2019 March 21 UT with the standardIRDIFS mode of SPHERE (Beuzit et al 2019) which allows forsimultaneous near-IR observations with IRDIS with the H23 fil-ter pair (Dohlen et al 2008 Vigan et al 2010) and the integralfield spectrograph IFS in the Y J bands (Claudi et al 2008) Theseeing and coherence time measured by the differential imagemotion monitor at 05 microm were 05ndash07primeprime and 6-8 ms respec-

H2+H3

E

N

027

7 au

+

YJ

E

N

027

7 au

+

Fig 1 SPHERE contrast images of HD 72946 The central regions ofthe images are numerically masked out to hide bright stellar residualsThe white crosses indicate the location of the primary star

tively The detector integration time was set to 16 s and 128frames were recorded amounting to a field rotation of 155

An apodized pupil Lyot coronagraph (Carbillet et al 2011Martinez et al 2009) was used We acquired data before and afterthe sequence to calibrate the flux of the images and the locationof the star behind the coronagraph (Langlois et al 2013) Night-time sky background frames were taken and additional daytimecalibration performed following the standard procedure at ESO

The data were reduced with the SPHERE Data Reductionand Handling software (v0150 Pavlov et al 2008) and customroutines for IFS data adapted from Mesa et al (2015) and Viganet al (2015) This corrected for the cosmetics and instrument dis-tortion registered the frames and normalized their flux For IFSit also performed the wavelength calibration and extracted theimage cubes Then the data were analyzed with angular differ-ential imaging (Marois et al 2006) using three algorithms (Ap-pendix B) ANDROMEDA TLOCI and PCA Figure 1 showsthe ANDROMEDA images

The photometry and astrometry were extracted using threealgorithms but we chose to retain the TLOCI values (Ta-ble 1) The astrometry was calibrated following Maire et al(2016) with pixel scales of 12255plusmn0009 maspix (H2) and12251plusmn0009 maspix (H3) and a North correction angle ofminus175plusmn008 The absolute magnitudes were computed using the2MASS values (Cutri et al 2003) for the stellar magnitudes

4 Orbital analysis

We retrieved the RV measurements in Bouchy et al (2016)through the VizieR interface With only one imaging datapoint there is still an ambiguity in the inclination and lon-gitude of the ascending node To solve for this we alsosearched for an astrometric signature of the companion inthe Hipparcos-Gaia catalog of accelerations (Brandt 20182019) pmra_g_hg = minus2837plusmn0140 mas yrminus1 and pmdec_g_hg



1000 2000 3000 4000 5000 6000BJD-2450000

1000

750

500

250

0

250

500

750

1000

RV (m

s)

ELODIESOPHIE

020100010203RA (as)

02

01

00

01

02

03

Dec

(as)

2015

2020

2025

2030

SPHERE

0

5

10

RA (m

asy

r)

GaiaHipparcos

0 2000 4000 6000 8000BJD-2450000

10

5

0

5

DEC

(mas

yr)




radice cosω and




radice cosω









minus0020 0230radic

e sinω 0662+0008minus0009 0663




















0

5

10

15

20

25

30

35

40Re

duce

d 2



5 Spectral analysis








6 Discussion





















































A6










































-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

M0-M5M6-M9L0-L5L6-L9T0-T5T6-T95

youngdusty dwarfs

WISE1647+56


1RXS1609b

2M1207b

GU Psc B

HN Peg Bβ Pic b

UScoCTIO 108B

HIP 64892B

HIP 78530B

GSC0621-0021B

VHS 1256ABb (127171pc)

ζ Del B

HIP 43620B

51 Eri b

HD 106906 b

GJ 758b

GJ 504b

HIP 65426b

HD 72946B

Y0-Y2

-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2









1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion








1000 2000 3000 4000 5000 6000BJD-2450000

1000

750

500

250

0

250

500

750

1000

RV (m

s)

ELODIESOPHIE

020100010203RA (as)

02

01

00

01

02

03

Dec

(as)

2015

2020

2025

2030

SPHERE

0

5

10

RA (m

asy

r)

GaiaHipparcos

0 2000 4000 6000 8000BJD-2450000

10

5

0

5

DEC

(mas

yr)




radice cosω and




radice cosω









minus0020 0230radic

e sinω 0662+0008minus0009 0663




















0

5

10

15

20

25

30

35

40Re

duce

d 2



5 Spectral analysis








6 Discussion





















































A6










































-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

M0-M5M6-M9L0-L5L6-L9T0-T5T6-T95

youngdusty dwarfs

WISE1647+56


1RXS1609b

2M1207b

GU Psc B

HN Peg Bβ Pic b

UScoCTIO 108B

HIP 64892B

HIP 78530B

GSC0621-0021B

VHS 1256ABb (127171pc)

ζ Del B

HIP 43620B

51 Eri b

HD 106906 b

GJ 758b

GJ 504b

HIP 65426b

HD 72946B

Y0-Y2

-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2









1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion









0

5

10

15

20

25

30

35

40Re

duce

d 2



5 Spectral analysis








6 Discussion





















































A6










































-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

M0-M5M6-M9L0-L5L6-L9T0-T5T6-T95

youngdusty dwarfs

WISE1647+56


1RXS1609b

2M1207b

GU Psc B

HN Peg Bβ Pic b

UScoCTIO 108B

HIP 64892B

HIP 78530B

GSC0621-0021B

VHS 1256ABb (127171pc)

ζ Del B

HIP 43620B

51 Eri b

HD 106906 b

GJ 758b

GJ 504b

HIP 65426b

HD 72946B

Y0-Y2

-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2









1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion
























































A6










































-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

M0-M5M6-M9L0-L5L6-L9T0-T5T6-T95

youngdusty dwarfs

WISE1647+56


1RXS1609b

2M1207b

GU Psc B

HN Peg Bβ Pic b

UScoCTIO 108B

HIP 64892B

HIP 78530B

GSC0621-0021B

VHS 1256ABb (127171pc)

ζ Del B

HIP 43620B

51 Eri b

HD 106906 b

GJ 758b

GJ 504b

HIP 65426b

HD 72946B

Y0-Y2

-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2









1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion



































-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2

M0-M5M6-M9L0-L5L6-L9T0-T5T6-T95

youngdusty dwarfs

WISE1647+56


1RXS1609b

2M1207b

GU Psc B

HN Peg Bβ Pic b

UScoCTIO 108B

HIP 64892B

HIP 78530B

GSC0621-0021B

VHS 1256ABb (127171pc)

ζ Del B

HIP 43620B

51 Eri b

HD 106906 b

GJ 758b

GJ 504b

HIP 65426b

HD 72946B

Y0-Y2

-4 -2 0 2H2-H3

20

18

16

14

12

10

8

6

MH

2









1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion










1 Introduction



4 Orbital analysis

5 Spectral analysis

6 Discussion







abstract arxiv:1912.02565v2 [astro-ph.ep] 9 dec …(2016) reported a potential brown dwarf companion...

Documents