Discovery of a Brown Dwarf Companion to the Star HIP 64892? A

A&A 615, A160 (2018) Astronomy https://doi.org/10.1051/0004-6361/201832650 & © ESO 2018 Astrophysics

Discovery of a brown dwarf companion to the star HIP 64892? A. Cheetham1, M. Bonnefoy2, S. Desidera3, M. Langlois4,5, A. Vigan5, T. Schmidt6, J. Olofsson7,8,9, G. Chauvin2,8, H. Klahr7, R. Gratton3, V. D’Orazi3, T. Henning7, M. Janson7,10, B. Biller7,11, S. Peretti1, J. Hagelberg1,2, D. Ségransan1, S. Udry1, D. Mesa3,12, E. Sissa3, Q. Kral6,13, J. Schlieder7,14, A.-L. Maire7, C. Mordasini7,15, F. Menard2, A. Zurlo5,16, J.-L. Beuzit2, M. Feldt7, D. Mouillet2, M. Meyer17,18, A.-M. Lagrange2, A. Boccaletti6, M. Keppler7, T. Kopytova7,19,20, R. Ligi5, D. Rouan6, H. Le Coroller5, C. Dominik21, E. Lagadec22, M. Turatto3, L. Abe22, J. Antichi23, A. Baruffolo3, P. Baudoz6, P. Blanchard5, T. Buey6, M. Carbillet22, M. Carle5, E. Cascone24, R. Claudi3, A. Costille5, A. Delboulbé2, V. De Caprio24, K. Dohlen5, D. Fantinel3, P. Feautrier2, T. Fusco25, E. Giro3, L. Gluck2, N. Hubin26, E. Hugot5, M. Jaquet5, M. Kasper26, M. Llored5, F. Madec5, Y. Magnard2, P. Martinez22, D. Maurel2, D. Le Mignant5, O. Möller-Nilsson7, T. Moulin2, A. Origné5, A. Pavlov7, D. Perret6, C. Petit25, J. Pragt27, P. Puget2, P. Rabou2, J. Ramos7, F. Rigal21, S. Rochat2, R. Roelfsema27, G. Rousset6, A. Roux2, B. Salasnich3, J.-F. Sauvage25, A. Sevin6, C. Soenke26, E. Stadler2, M. Suarez28, L. Weber1, and F. Wildi1 (Afﬁliations can be found after the references)

Received 16 January 2018 / Accepted 6 March 2018

ABSTRACT

We report the discovery of a bright, brown dwarf companion to the star HIP 64892, imaged with VLT/SPHERE during the SHINE exoplanet survey. The host is a B9.5V member of the Lower-Centaurus-Crux subgroup of the Scorpius Centaurus OB association. The measured angular separation of the companion (1.2705 0.0023”) corresponds to a projected distance of 159 12 AU. We observed the target with the dual-band imaging and long-slit spectroscopy± modes of the IRDIS imager to obtain its spectral± energy distribution (SED) and astrometry. In addition, we reprocessed archival NACO L-band data, from which we also recover the companion. Its SED is consistent with a young (<30 Myr), low surface gravity object with a spectral type of M9 1. From comparison with the BT-Settl γ ± atmospheric models we estimate an effective temperature of Teff = 2600 100 K, and comparison of the companion photometry to the ± +15 COND evolutionary models yields a mass of 29 37 MJ at the estimated age of 16 7 Myr for the system. The star HIP 64892 is a rare example of an extreme-mass ratio system∼ (q −0.01) and will be useful for testing− models relating to the formation and evolution of such low-mass objects. ∼ Key words. brown dwarfs – stars: individual: HIP 64892 – techniques: high angular resolution – planets and satellites: detection – planets and satellites: atmospheres

1. Introduction knowledge of such companions is limited by the small number of objects detected to date, covering a wide range of parameter While evidence suggests that the frequency of short period space in terms of companion mass, primary mass, age, and stellar and planetary-mass companions to main sequence stars orbital semi-major axis. Only a few wide-separation objects is high, there appears to be a relative lack of companions in have been detected around stars with masses >2 M , such as the brown dwarf regime (Grether & Lineweaver 2006). These HIP 78530B (Lafrenière et al. 2011), κ And b (Carson et al. objects appear to exist in an overlap region of formation pro- 2013), HR 3549B (Mawet et al. 2015), and HIP 77900B (Aller cesses, as the low-mass tail of stellar binary formation and as et al. 2013). the high-mass end of the planetary distribution. Observations of A new generation of dedicated planet-finding instru- brown dwarf companions to young stars then present an impor- ments such as the Spectro-Polarimetric High-contrast Exoplanet tant opportunity to study these different formation pathways. REsearch (SPHERE) instrument (Beuzit et al. 2008) and the The processes that form companions of all masses appear to Gemini Planet Imager (Macintosh et al. 2008) offer significant have a sensitive dependence on the host star mass, with evidence improvements in the detection capability for substellar compan- suggesting that high and intermediate mass stars have more ions, as well as for spectroscopic and astrometric follow-up. of such companions than their lower mass counterparts (e.g. The SHINE (SpHere INfrared survey for Exoplanets) survey Bowler et al. 2010; Johnson et al. 2010; Janson et al. 2013; Jones (Chauvin et al. 2017) utilises the SPHERE instrument at the et al. 2014; Bowler et al. 2015; Lannier et al. 2016). However, our Very Large Telescope (VLT) to search the close environments of ? Based on observations collected at the European Organisation 600 young, nearby stars for substellar and planetary companions. for Astronomical Research in the Southern Hemisphere under ESO In this paper, we present the imaging discovery and follow- programmes 096.C-0241 and 198.C-0209 (PI: J.-L. Beuzit), 098.A- up spectroscopy of a young, low-mass brown dwarf companion 9007(A) (PI: P. Sarkis), and 087.C-0790(A) (PI: M. Ireland). identified during the course of this survey.

Article published by EDP Sciences A160, page 1 of 10 A&AA&A proofs: 615,manuscript A160 (2018) no. output

TableGagné 1. Stellar et al. (2018) parameters gives of HIP a membership 64892. probability of 64% to the LCC subgroup, 33% to the younger Upper Centaurus Lupus subgroup,Parameter and a 3% probability Value of HIP Ref. 64892 being a field star. Since the star is not included in GAIA Data Release 1, we adopt V (mag) 6.799 0.008 Slawson et al.(1992) the trigonometric parallax± by van Leeuwen (2007), yielding a distanceU B (mag) of 125 9 –0.094 pc. Photometry0.011 ofSlawson the system et al.( is1992 collected) B−V (mag)± –0.018 ±0.006 Slawson et al.(1992) in Table− 1. No significant± variability is reported by Hipparcos (photometricV I (mag) scatter 0.007 0.00 mag). HIPPARCOS J (mag)− 6.809 0.023 Cutri et al.(2003) To further characterise the± system, the star was observed with theH FEROS (mag) spectrograph 6.879 at the0.034 2.2m Cutri MPG et telescope al.(2003) operated K (mag) 6.832 ± 0.018 Cutri et al.(2003) by the Max Planck Institute±+0 for.02 Astronomy. Data were obtained E(B-V) 0.01 0.01 This paper on 2017-Mar-30 and were−− reduced with the CERES package (BrahmParallax et al. (mas) 2017).1 7.98A summary0.55 ofvan the Leeuwenstellar properties(2007) de- Distance (pc) 125 ± 9 pc From parallax rived from this1 analysis, and± those compiled from the literature, is givenµα (mas in yrTable− ) 1. From –30.83 the FEROS0.50 spectrum,van Leeuwen we(2007 measured) a 1 ± radialµδ (mas velocity yr− (RV)) of–20.22 14.9 km0.43/s and van a projected Leeuwen rotational(2007) ve- 1 ± locityRV of(km 178 s− km)/s, using 14.9 the cross-correlation This paper function (CCF) procedureSpT described in Chauvin B9.5V et al. (2017).Houk(1993 This) latter value is notT unusualeff (K) among stars 10400 of similar spectral SpT+Pecaut type, unless calib. signifi- 1 cantv sin projectioni (km s− e)ffects are 178at work. This paper +15 AgeThe (Myr) FEROS CCF does16 not7 show anyThis indication paper of additional − components.Mstar(M ) This agrees2.35 with0.09 the conclusions This paper of Chini et al. ± (2012),Rstar(R who) found no1.79 evidence0.10 R of, binarity This paper from five RV mea- ± surements. The observed RV values from that study were not published, preventing an assessment of possible long-term RV Fig.Fig. 1. TheThe V-bandV-band absolute absolute magnitude magnitude and and effective effective temperature temperature of HIP of variability.2 The SPHERE data also do not provide any indica- HIP64892 64892 compared compared to predictions to predictions from thefrom 5, the 12, 5,20, 12, 30, 20, 70 30,and70, 200Myr and 2. Stellar properties 200isochrones Myr isochrones of Bressan of etBressan al. (2012). et al. The(2012 placement). The placement of HIP 64892 of HIP is tion of the presence of bright stellar companions, ruling out an consistent with the estimated local age of 16 Myr within the measured The star HIP 64892 was assigned a B9.5 spectral type by Houk 64892 is consistent with the estimated local age of 16 Myr within the equal-luminosity binary down to a separation of about 40 mas. measureduncertainties. uncertainties. (1993By) and comparing classified theobserved as a member colours of of the HIP Lower 64892 Centaurus with those Crux (hereafter LCC) association by de Zeeuw et al.(1999) and expected from the tables by Pecaut & Mamajek (2013), we find out an equal-luminosity binary down to a separation of about Rizzuto et al.(2011), with membership probabilities of 99% tation period 4.66d, Kiraga 2012). Given this value, we think they are consistent with the B9.5 spectral classification, and find 40 mas. and 74%, respectively. A recent update to the BANYAN tool by it unlikely that HIP 64892 is older than 30 Myr. We adopt an a low reddening value of E(B-V)=0.01 consistent with the lack By comparing the observed colours of∼ HIP 64892 with+15 those Gagné et al.(2018) gives a membership probability of 64% to uncertainty of 15 Myr, leading to an age estimate of 16 7 . The of V-band extinction found by Chen et al. (2012). In addition, expected from the tables by Pecaut & Mamajek(2013), we− find the LCC subgroup, 33% to the younger Upper Centaurus Lupus stellar mass and radius from the Bressan et al. (2012) models are the Chen et al. (2012) analysis showed no signs of an infrared they are consistent with the B9.5 spectral classification, and find subgroup, and a 3% probability of HIP 64892 being a field star. 2.35 0.09 M and 1.79 0.10 R , respectively. excess. We explore the implications of this on the presence of a low± reddening value of± E(B–V) = 0.01 consistent with the lack Since the star is not included in Gaia Data Release 1, we adopt Due to its unknown rotational inclination and large mea- dust in the system in Appendix A. of V-band extinction found by Chen et al.(2012). In addition, the the trigonometric parallax by van Leeuwen(2007), yielding a sured v sin i, HIP 64892 is expected to show significant oblate- The Pecaut & Mamajek (2013) tables predict an effective Chen et al.(2012) analysis showed no signs of an infrared excess. distance of 125 9 pc. Photometry of the system is collected ness. For this reason, any measurements of the stellar parameters temperature of 10400± K for a B9.5 star. For such a hot star, the We explore the implications of this on the presence of dust in the in Table1. No significant variability is reported by H IPPARCOS may be influenced by its orientation. While a similar degeneracy pre-main sequence isochrones collapse on the zero-age main se- system in AppendixA. (photometric scatter 0.007 mag). between inclination and age caused issues for studies of other quence (ZAMS) in less than 10 Myr, and significant post-main The Pecaut & Mamajek(2013) tables predict an effective To further characterise the system, the star was observed rapidly rotating stars such as κ And (e.g. Hinkley et al. 2013; sequence evolution is not expected for tens of Myr following temperature of 10 400 K for a B9.5 star. For such a hot star, with the FEROS spectrograph at the 2.2 m MPG telescope oper- Jones et al. 2016), our age estimate relies on the firm Sco-Cen this. When combined with the large uncertainty on the paral- the pre-main sequence isochrones collapse on the zero-age main ated by the Max Planck Institute for Astronomy. Data were membership of HIP 64892, which is independent of these con- lax of HIP 64892, this makes prediction of its age based on sequence (ZAMS) in less than 10 Myr, and significant post-main obtained on 2017-Mar-30 and were reduced with the CERES cerns. However, the effective temperature and mass in particular isochronal analysis difficult. The V magnitude and effective tem- sequence evolution is not expected for tens of Myr following this. package (Brahm et al. 2017)1. A summary of the stellar prop- may be affected by the inclination of HIP 64892. perature of HIP 64892 are shown in Figure 1, relative to the Bres- When combined with the large uncertainty on the parallax of erties derived from this analysis, and those compiled from the san et al. (2012) isochrones at various ages between 5-200 Myr. HIP 64892, this makes prediction of its age based on isochronal literature, is given in Table1. From the FEROS spectrum, we Within the uncertainties, the placement of HIP 64892 is close to analysis difficult. The V magnitude and effective temperature of measured a radial velocity (RV) of 14.9 km s 1 and a projected the ZAMS, and therefore consistent with LCC− membership. HIP 64892 are shown in Fig.1, relative to the Bressan et al. rotational velocity of 178 km s 1, using the cross-correlation 3. Observations and data reduction The Sco-Cen subgroups are− known to show significant age (2012) isochrones at various ages between 5 and 200 Myr. Within function (CCF) procedure described in Chauvin et al.(2017). spread. The recent age map by Pecaut & Mamajek (2016) yields the3.1. uncertainties, SPHERE imaging the placement of HIP 64892 is close to the This latter value is not unusual among stars of similar spectral a value of 16 Myr at the location of our target, equal to the com- ZAMS, and therefore consistent with LCC membership. type, unless significant projection effects are at work. monly adopted age for the group. We adopt this value as the TheThe star Sco-Cen HIP 64892 subgroups was observed are known with toSPHERE show significant on 2016-Apr- age The FEROS CCF does not show any indication of addi- most likely age of HIP 64892, with the approximate ZAMS time spread.01 as part The of recent the SHINE age map exoplanet by Pecaut survey. & Mamajek These data(2016 were) yields taken tional components. This agrees with the conclusions of Chini as a lower limit. While an upper limit from comparison with the awith value the of IRDIFS 16 Myr mode. at the locationAfter a bright of our companion target, equal candidate to the com- was et al.(2012), who found no evidence of binarity from five RV isochrones would be 100 Myr, we instead use the nearby star monlydiscovered adopted in these age for data, the group.follow-up We observationsadopt this value were as the taken most on measurements. The observed∼ RV values from that study were TYC 7780-1467-1 to place a more precise bound on the age. likely2017-Feb-08 age of HIP using 64892, the IRDIFS_EXT with the approximate mode to ZAMS confirm time its co- as not published, preventing an assessment of possible long-term This star has a well-determined age of 20 Myr calculated from amoving lower limit. status While and extend an upper the spectral limit from coverage. comparison with the RV variability2. The SPHERE data also do not provide any comparison with isochrones and supported by its lithium abun- isochronesThesemodes would be allow100 the Myr, Integral we instead Field useSpectrograph the nearby (IFS; star indication of the presence of bright stellar companions, ruling dance (EW Li=360 mÅ, Torres et al. 2006) and fast rotation (ro- TYCClaudi 7780-1467-1 et al. 2008) to and∼ place Infra-Red a more Dual-band precise bound Imager on and the Spec- age. trograph (IRDIS; Dohlen et al. 2008) modules to be used si- 1 This star has a well-determined age of 20 Myr calculated from 1 https://github.com/rabrahm/ceres multaneously through the use of a dichroic. In these configu- 2 https://github.com/rabrahm/ceres. comparison with isochrones and supported by its lithium abun- 2 The RV provided by SIMBAD originates from the study of Madsen rations, IFS provides a low-resolution spectrum (R 55 across The RV provided by SIMBAD originates from the study of Madsen dance (EW Li = 360 mÅ; Torres et al. 2006) and fast rotation et al.(2002) and was not derived from spectroscopic measurements but Y-J bands or R 35 across Y-H bands) while IRDIS∼ operates in ratheret al. (2002)from the and velocity was not expected derived from from kinematics. spectroscopic measurements but (rotation period 4.66 d; Kiraga 2012). Given this value, we think rather from the velocity expected from kinematics. dual-band imaging∼ mode (Vigan et al. 2010). A160, page 2 of 10 Article number, page 2 of 12 A. Cheetham et al.: Discovery of a brown dwarf companion to the star HIP 64892

Table 2. Observing log.

a a a UT Date Instrument Filter DIT Nexp ∆π True North correction Plate scale 1 [s] [◦][◦] [mas pixel− ]

2011-Jun-08 NACO L0 0.2 8000 130.4 0.5 0.1 27.1 0.05 2016-Apr-01 IRDIS H2/H3 64 64 45 −1.73 ± 0.06 12.255± 0.009 2016-Apr-01 IFS YJ 64 64 45 −102.21± 0.06 7.46 ±0.02 2017-Feb-08 IRDIS K1/K2 64 72 61 − 1.71 ±0.06 12.249± 0.009 2017-Feb-08 IFS YH 64 72 61 −102.19± 0.06 7.46 ±0.02 − ± ± (a) Notes. DIT refers to the integration time of each image, Nexp to the total number of images obtained, and ∆π to the parallactic angle range during the sequence. it unlikely that HIP 64892 is older than 30 Myr. We adopt an basic image cleaning steps (background subtraction, flat fielding, ∼ +15 uncertainty of 15 Myr, leading to an age estimate of 16 7 . The removal of bad pixels, calculation of the star’s position behind stellar mass and radius from the Bressan et al.(2012) models− are the coronagraph, as well as extraction of the spectral data cubes 2.35 0.09 M and 1.79 0.10 R , respectively. for IFS). To process the IFS data, the DRH routines were aug- Due± to its unknown rotational± inclination and large measured mented with additional routines from the SPHERE Data Centre v sin i, HIP 64892 is expected to show significant oblateness. to reduce the spectral cross-talk and improve the wavelength cal- For this reason, any measurements of the stellar parameters may ibration and bad pixel correction (Mesa et al. 2015). Both IFS be influenced by its orientation. While a similar degeneracy and IRDIS data were corrected using the astrometric calibration between inclination and age caused issues for studies of other procedures described in Maire et al.(2016b). rapidly rotating stars such as κ And (e.g. Hinkley et al. 2013; A bright companion candidate is clearly visible in the raw Jones et al. 2016), our age estimate relies on the firm Sco-Cen coronagraphic frames, at a separation of 1.270 0.00200 in the membership of HIP 64892, which is independent of these con- 2016 dataset (159 12 AU in projected physical± separation). cerns. However, the effective temperature and mass in particular This separation places± it outside of the field of view of the may be affected by the inclination of HIP 64892. IFS module, and so we report the results from IRDIS only. To extract the astrometry and photometry of this object, a classical 3. Observations and data reduction angular differential imaging procedure (ADI; Marois et al. 2006) was applied to remove the contribution from the primary star 3.1. SPHERE imaging while minimising self-subtraction and other systematic effects The star HIP 64892 was observed with SPHERE on 2016-Apr-01 that may be introduced by more aggressive PSF subtraction as part of the SHINE exoplanet survey. These data were taken techniques. The ADI procedure and calculation of the relative with the IRDIFS mode, and are summarised in Table2. After astrometry and photometry of the companion were accomplished a bright companion candidate was discovered in these data, using the Specal pipeline developed for the SHINE survey follow-up observations were taken on 2017-Feb-08 using the (R. Galicher, 2018, in prep.). The final reduced images from this IRDIFS_EXT mode to confirm its co-moving status and extend approach are shown in Fig.2. the spectral coverage. The astrometry was measured using the negative compan- These modes allow the Integral Field Spectrograph (IFS; ion injection technique (Lagrange et al. 2010), where the mean Claudi et al. 2008) and Infra-Red Dual-band Imager and Spec- unsaturated PSF of the primary star was subtracted from the trograph (IRDIS; Dohlen et al. 2008) modules to be used raw frames. The position and flux of the injected PSF was var- simultaneously through the use of a dichroic. In these config- ied to minimise the standard deviation inside a 3 FWHM (full urations, IFS provides a low-resolution spectrum (R 55 across width at half maximum) diameter region around the compan- Y–J bands or R 35 across Y–H bands) while IRDIS∼ operates ion in the final ADI processed image. Once the best-fit values in dual-band imaging∼ mode (Vigan et al. 2010). were found, each parameter was varied until the standard devi- For each observing sequence, several calibration frames were ation increased by a factor of 1.15. This value was empirically taken at the beginning and end of the sequence. These consisted calculated to correspond to 1σ uncertainties across a range of of unsaturated short exposure images to estimate the flux of the potential companion and observational parameters. A system- primary star and as a point spread function (PSF) reference, fol- atic uncertainty of 2 mas on the star position was adopted for the lowed by a sequence of images with a sinusoidal modulation 2016 dataset, which dominates the astrometric uncertainty bud- introduced to the deformable mirror to generate satellite spots get. The resulting astrometric and photometric measurements are used to calculate the position of the star behind the corona- given in Table3. graph. The majority of the observing sequence consisted of long A second reduction of each dataset was performed with the exposure (64 s) coronagraphic imaging. aim of searching for companions at higher contrasts. For the For the 2017 data, the satellite spots were used for the IRDIS datasets, the TLOCI algorithm was used (Marois et al. entirety of the coronagraphic imaging sequence rather than a 2014), while for the IFS datasets we used the PCA-based angular separate set of frames at the beginning and end. This allowed us and spectral differential imaging algorithm described in Mesa to correct for changes in flux and the star’s position during the et al.(2015). The resulting detection limits are shown in Fig.3. observations, at the cost of a small contrast loss at the separation Apart from the bright companion at 1.2700, we find no evidence of the satellite spots. of companions at smaller separations. Three additional objects The data were reduced using the SPHERE data reduction were detected at much larger separations, and are discussed in and handling (DRH) pipeline (Pavlov et al. 2008) to perform the Sect. 4.1.

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Fig.Fig. 2. ADI-processed 2. ADI-processed images images from from the thetwo two SPHERE-IRDIS SPHERE-IRDIS datasets datasets taken taken with with the theK1 K1and and H2 H2filters, filters, and and the theNACO NACO data data taken taken with with the theL0 filter. L’ filter. TheThe companion companion is detected is detected with withS/N SNR> 1000> 1000 in the in two the SPHEREtwo SPHERE epochs, epochs, and S and/N SNR> 8 in> the8 in NACO the NACO data. data.

Table 3. Observed astrometry and photometry of HIP 64892 B. Projected Separation (AU) ies on potential systematic biases introduced into the companion 0 50 100 150 200 250 astrometry by applying this technique to SAM data, we conser- 4 UT10 date Instrument Filter ρ (00) 10 θ (◦vatively) added Contrast an (mag)additional Abs. uncertainty mag to Mass the companion(COND) posi- 2016 IRDIS H2 tion of one pixel (27.1 mas). Of particular concern is the way in 2011-Jun-08 NACO L 20171.272 IRDIS 0K1.029 310.0 1.3 6.10 0.08 7.61 0.17 37 9 11 0 2016-Apr-01 IRDIS H2 12016.2703 IFS ±YJ 0.0023 311.68 ±which0.15 the time-varying 7.23 ± 0.08 ﬁne 8 structure.73 ± 0.17 of the large 29 ± SAM4 PSF may )

g 2017 IFS ±YH ±inﬂuence the calculation± of the star’s± position. ±

2016-Apr-01a IRDIS H3 1.2704 0.0022 311.69 0.15 6.99 0.08 8.46 0.17 29 5 12

Fig. 2. m ADI-processed images from the two SPHERE-IRDIS± datasets taken with± the K1 and H2± ﬁlters, and the NACO± data taken with± the L’ ﬁlter.

2017-Feb-08( IRDIS K1 1.2753 0.00105 311.74 0.12 6.80 0.08 8.29 0.17 34 7

The companiont is detected with SNR > 1000 in the two± SPHERE10 epochs, and± SNR > 8 in the± NACO data. ± ± 2017-Feb-08s IRDIS K2 1.2734 0.0010 311.77 0.12 6.49 0.12 7.97 0.19 35 8 a 13 r ± ± ± ± ± t 4. Results n o C

14 ies on potential systematic biases introduced into the companion Projected Separation (AU) Contrast Ratio Additional4.1. Astrometry sky backgrounds were also obtained at the end of the

5 0 50 100 150 200 250 astrometry by applying this technique to SAM data, we conser- 4 sequence along with an unsaturated spectrum of the star to serve 10 6 15 1010 asvatively referenceTo conﬁrm added for the anthe co-movingadditional contrast. uncertainty status of HIP to the64892B, companion we compared posi- 2016 IRDIS H2 tionits of position one pixel relative (27.1 mas). to HIP Of 64892A particular between concern the is thedatasets. way in We 2017 IRDIS K1 The data were reduced using the SILSS pipeline (Vigan 11 16 2016 IFS YJ 2016whichused). Thisthe the time-varying pipelineastrometry combines ﬁnefrom structure the recipes 2016 of fromSPHERE the large the SAM standard dataset PSF with ESO may the ) 0.0 0.5 1.0 1.5 2.0

g 2017 IFS YH inﬂuenceparallax the and calculation proper motion of the of star’s HIP position. 64892 to predict the position

a pipeline with custom IDL routines. Brieﬂy, data are background 12 Angular Separation (arcsec)

m expected for a background object at the 2011 and 2017 epochs.

( 5 subtracted, ﬂat ﬁelded, and corrected for bad pixels. The wave-

t 10 The result is shown in Figure 4. s length calibration is performed and the data are corrected for the a 13 Fig.r 3. Detection limits for the two SPHERE datasets, after process- t slight4. Results tiltFor of HIP the 64892B, grism, which the observed causes positionsa change in 2011 the position and 2017 ingn using the TLOCI algorithm. The grey shaded region indicates the o of thediﬀer PSF from with the wavelength. prediction for Finally, a background the speckles object are by subtracted 4σ and 8σ C

separations 14 partially or fully blocked by the coronagraph. Contrast Ratio using4.1.respectively. Astrometry principal component Instead we analysis, find a lack with of the significant modes constructed relative mo- 5 tion. This clearly shows that the object is co-moving with HIP 6 from the spectra obtained with the companion outside of the slit. 15 10 To64892A. confirm the co-moving status of HIP 64892B, we compared its position relative to HIP 64892A between the datasets. We exposures of 0.2s each. Each of the five blocks was interspersed3.3. ArchivalThe angular NACO separation sparse aperture of HIP 64892B masking corresponds data to a pro- amongst16 observations of other targets. used the astrometry from the 2016 SPHERE dataset with the 0.0 0.5 1.0 1.5 2.0 parallaxjected and separation proper motion of 159 of12 HIP AU. 64892 With to the predict primary the position star mass Rather than process the data in an interferometric frame-In addition to the SPHERE± data, we utilised archival sparse Angular Separation (arcsec) expectedof 2.35 for M awe background would expect object an at orbital the 2011 period and 2017 of the epochs. order of work, we treated it as a traditional ADI dataset to focus onaperture3 masking (SAM) data from the VLT-NACO instrument, The result10 yr. is This shown is consistent in Figure with4. the lack of significant motion in Fig.larger 3. Detection separations. limits The for the data two were SPHERE processed datasets, using after the GRAPHICprocess- takenthe∼ on measured 2011-Jun-08 astrometry, (Program and suggests 087.C–0790(A), that an additional PI: Ireland). epoch Fig. 3. Detection limits for the two SPHERE datasets, after process- ingpipeline using the (Hagelberg TLOCI algorithm. et al. 2016). The grey The shaded data region were sky indicates subtracted, the WhileinFor 2018 the HIP main or 64892B, later purpose may the show of observed the clear SAM orbital positions mode motion is to in detect 2011 and helpand compan- 2017 to con- separationsing using the partially TLOCI or algorithm. fully blocked The by grey the coronagraph. shaded region indicates the ionsdiffer and from resolve the prediction structuresfor at small a background angular separations object by 4 (typicallyσ and 8σ separationsflat fielded, partially cleaned or fully of blockedbad pixels, by the centred coronagraph. on the primary star, strain the orbital parameters of the companion. and stacked by binning 200 frames at a time. A Gaussian fit was

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Table 3. Observed Astrometry and Photometry of HIP 64892 B

UT Date Instrument Filter ρ (") θ (◦) Contrast (mag) Abs. mag Mass (COND) 2011-Jun-08 NACO L’ 1.272 0.029 310.0 1.3 6.10 0.08 7.61 0.17 37 9 2016-Apr-01 IRDIS H2 1.2703 ± 0.0023 311.68 ± 0.15 7.23 ± 0.08 8.73 ± 0.17 29 ± 4 2016-Apr-01 IRDIS H3 1.2704 ± 0.0022 311.69 ± 0.15 6.99 ± 0.08 8.46 ± 0.17 29 ± 5 2017-Feb-08 IRDIS K1 1.2753 ± 0.0010 311.74 ± 0.12 6.80 ± 0.08 8.29 ± 0.17 34 ± 7 2017-Feb-08 IRDIS K2 1.2734 ± 0.0010 311.77 ± 0.12 6.49 ± 0.12 7.97 ± 0.19 35 ± 8 ± ± ± ± ± Table 4. Additional objects detected by SPHERE-IRDIS

Candidate UT Date Filter ρ (mas) θ (deg) ∆RA (mas) ∆Dec (mas) Contrast (mag) 1 2016-Apr-01 H2 6000 3 201.86 0.12 2234 12 5568 5 10.5 0.1 1 2017-Feb-08 K1 5978 ± 4 201.60 ± 0.07 − 2201± 7 −5558 ± 5 10.7 ± 0.1 2 2016-Apr-01 H2 5865 ± 5 202.86 ± 0.12 −2278 ±12 −5404 ± 7 13.7 ± 0.1 3 2016-Apr-01 H2 7003 ± 6 186.89 ± 0.12 − 840 ±14 −6952 ± 6 10.2 ± 0.1 A. Cheetham et al.: Discovery± of a brown dwarf± companion− to the± star HIP− 64892± ±

920 860 HIP 64892B HIP 64892B 940 840 960

980 ) 820 ) s s a a 1000 m m ( (

800 c A 1020 e R D 1040 780

1060 760 1080

1100 740 2456000 2456500 2457000 2457500 2456000 2456500 2457000 2457500 Date (JD) Date (JD)

Fig. 4. Measured position of HIP 64892B relative to HIP 64892A. The 2011 NACO L0, 2016 IRDIS H2, and 2017 IRDIS K1 positions are shown Measured position of HIP 64892B relative to HIP 64892A. The 2011 NACO L’, 2016 IRDIS H2, and 2017 IRDIS K1 positions are shown withFig. blue 4. triangles. The predicted motion for a stationary background object relative to the 2016 position is marked by the black line, with its with blue triangles. The predicted motion for a stationary background object relative to the 2016 position is marked by the black line, with its uncertainty represented by the grey shaded region. The observed positions of HIP 64892B strongly conﬂict with the predictions for a background uncertainty represented by the grey shaded region. The observed positions of HIP 64892B strongly conﬂict with the predictions for a background object, suggesting that it is co-moving. object, suggesting that it is co-moving. Table 4. Additional objects detected by SPHERE-IRDIS. 5545 Candidate 1 Candidate 1 Candidate UT Date Filter ρ (mas) θ (deg) ∆RA (mas) ∆Dec. (mas) Contrast (mag) 2200 1 2016-Apr-01 H2 6000 3 201.86 0.1255502234 12 5568 5 10.5 0.1 1 2017-Feb-08 K1 5978 ± 4 201.60 ± 0.07 − 2201± 7 −5558 ± 5 10.7 ± 0.1 2210 ± ± − ± − ± ± ) 5555

) 2 2016-Apr-01 H2 5865 5 202.86 0.12 2278 12 5404 7 13.7 0.1 s s

± ± a − ± − ± ± a 3 2016-Apr-01 H2 7003 6 186.89 0.12 840 14 6952 6 10.2 0.1 m m ± ± ( − ± − ± ± ( 5560

2220 c A e R D resulting in the redetection of the SPHERE companion. The final The5565 angular separation of HIP 64892B corresponds to a pro- reduced image2230 is shown in the right panel of Fig.2. jected separation of 159 12 AU. With the primary star mass To calculate the position and flux of the companion, we used of 2.35 M we would expect± an orbital period of the order of 35570 the negative2240 companion injection technique applied to the data 10 yr. This is consistent with the lack of significant motion in cube after binning. We chose to minimise the square of the ∼the measured astrometry, and suggests that an additional epoch residuals within a circle of radius λ/D centred on the compan- in 20185575 or later may show clear orbital motion and help to ion peak calculated2457500 from the2457600 first reduced2457700 image. To2457800 explore constrain the2457500 orbital parameters2457600 of the2457700 companion.2457800 the likelihood function, we used emceeDate ((JD)Foreman-Mackey et al. In addition to HIP 64892B,Date three (JD) objects were detected at 2013), a python implementation of the affine-invariant Markov larger separations in the IRDIS field of view. Their astrometry chainFig. Monte 5. Same Carlo as Fig. ensemble 4, showing sampler. the measured Due to position the lack of of companion detailed candidateand photometry 1 with respect are to given HIP 64892A. in Table This4. Candidate object agrees 1 waswith thedetected prediction studiesfor a on background potential object. systematic biases introduced into the com- at high significance in both epochs, while the other two were not panion astrometry by applying this technique to SAM data, we detected in the 2017-Feb-08 K-band data. The relative motion of conservatively added an additional uncertainty to the companion candidate 1 between the two epochs is shown in Fig.5 and is position of one pixel (27.1 mas). Of particular concern is the way similar to that expected from a background star. Its position dif- Article number, page 6 of 12 in which the time-varying fine structure of the large SAM PSF fers from the prediction by 1.3σ, while it is inconsistent with may influence the calculation of the star’s position. a co-moving object at 2.8σ, showing that it is likely to be a background star. The IRDIS H2 and H3 photometry of the remaining two 4. Results objects indicates that they are also likely to be background stars. 4.1. Astrometry If located at the same distance as HIP 64892, their H2 magnitudes and H2–H3 colours would be inconsistent with those To confirm the co-moving status of HIP 64892B, we compared of other known objects. Their H2 magnitudes would be con- its position relative to HIP 64892A between the datasets. We sistent with those of T dwarfs, but without significant methane used the astrometry from the 2016 SPHERE dataset with the absorption that would be measurable in their H2–H3 colours. parallax and proper motion of HIP 64892 to predict the position expected for a background object at the 2011 and 2017 epochs. 4.2. Mass The result is shown in Fig.4. For HIP 64892B, the observed positions in 2011 and 2017 To estimate the mass of HIP 64892B, we first converted each differ from the prediction for a background object by 4σ and of the apparent photometric fluxes for the companion (IRDIS 8σ respectively. Instead, we find a lack of significant relative H2, H3, K1, K2, and NACO L0) into absolute magnitudes motion. This clearly shows that the object is co-moving with HIP using the distance of 125 9 pc. To calculate the photometric 64892A. zeropoint of each filter, we± used the spectrum of Vega from

A160, page 5 of 10 A&A proofs: manuscript no. output

Table 3. Observed Astrometry and Photometry of HIP 64892 B

920 860 HIP 64892B HIP 64892B 940 840 960

980 ) 820 ) s s a a 1000 m m ( (

800 c A 1020 e R D 1040 780

1060 760 1080

1100 740 2456000 2456500 2457000 2457500 2456000 2456500 2457000 2457500 Date (JD) Date (JD)

Fig. 4. Measured position of HIP 64892B relative to HIP 64892A. The 2011 NACO L’, 2016 IRDIS H2, and 2017 IRDIS K1 positions are shown with blue triangles. The predicted motion for a stationary background object relative to the 2016 position is marked by the black line, with its uncertainty represented by the grey shaded region. The observed positions of HIP 64892B strongly conﬂict with the predictions for a background object, suggesting that it is co-moving. A&A 615, A160 (2018)

5545 Candidate 1 Candidate 1 2200 5550

2210

) 5555 ) s s a a m m ( ( 5560

2220 c A e R D 5565 2230

5570 2240 5575 2457500 2457600 2457700 2457800 2457500 2457600 2457700 2457800 Date (JD) Date (JD)

Same as Fig.4, showing the measured position of companion candidate 1 with respect to HIP 64892A. This object agrees with the prediction Fig. 5. Same as Fig. 4, showingA. the Cheetham measured positionet al.: Discovery of companion of a brown candidate dwarf 1 with companion respect to to theHIP star 64892A. HIP 64892 This object agrees with the prediction for aFig. background 5. object. for a background object.

Article number, page 6 of 12

Observed spectrum of HIP 64892B. SPHERE IRDIS LSS data are shown in blue, while the SPHERE IRDIS and NACO photometric Fig.Fig. 6. 6. Observed spectrum of HIP 64892B. SPHERE IRDIS LSS data are shown in blue, while the SPHERE IRDIS and NACO photometric measurementsmeasurements are in are red. in red.The Theerrorbars errorbars on the onx the-axis x-axis of the of photometric the photometric measurements measurements represent represent the theFWHM FWHM of the of the ﬁlter ﬁlter used. used.

Bohlin(2007) along with the filter transmission profiles from subgroup (Lodieu et al. 2008) as well as companions of Upper each instrument.10000 We then interpolated the COND evolutionary Scorpiusrare (the stars so-called (Lafrenière “brown et al. dwarf 2008 desert”;; Lachapelle Grether et al. & 2015 Lineweaver). We models (BaraffeField etdwarfs al. 2003) using the age and absolute mag- also2006; compared Kraus the et companional. 2008; Metchev spectrum & to Hillenbrand those of young 2009), free evi- nitudes to yieldUpper estimates Sco. objects (Lodieu+08) of the mass of HIP 64892B. The floatingdence objects suggests from that the the Montreal occurrence3 (Robert rates of et companions al. 2016; Gagné around VL-G and INT-G objects (Allers+13) measurements,1000 Young listed objects in - Montreal Table lib.3, are consistent with masses of et al.intermediate 2014a,b, 2015a mass) stars and mayAllers be & substantially Liu(2013) libraries,higher (Vigan and to et al. Companions to Upper Sco stars 29–37 MJ. This implies a mass ratio between the brown dwarf libraries2012). of This medium-resolution trend is seen for spectra companions of old with M, masses L, and Tspanning field and the primary of q 0.014. dwarfsthe planetary (Burgasser to et stellar al. 2002 regimes; McLean (e.g. et Johnson al. 2003 et; al.Cushing 2010; et Janson al. ∼ et al. 2013).

G 100 2005; Rayner et al. 2009). The result is plotted in Fig.7 for a 4.3. Spectral properties range ofDespite objects this, covering HIP 64892 different is one ages, of masses, the highest and mass spectral stars types.around Wewhich find the a bestsubstellar matches companion are given has by been young, detected, low sur- due We produced a spectral model for the primary by scaling a to the challenges associated with observing such stars and the 10 face gravity objects with spectral types close to M9. From this, BT-Settl spectrum with Teff = 10400 K, log g = 4,[M/H] = tendency for large surveys to focus on solar-like or low-mass GSC 06214 B (M9γ) we adopt a spectral type of M9 1 for HIP 64892B. 0.5 using photometric measurementsUScoJ1606-23 compiled (M9) from 2MASS, stars. Only HIP 78530B (Lafrenière± et al. 2011), κ And b (Car- − 2M2000-75 (M9γ) In Fig.8, we show the comparison of the observed spectrum Tycho-2, and WISE (Høg et al.TWA28 2000 (M9 VL-G) ; Skrutskie et al. 2006; 1 of HIPson et64892B al. 2013), to those andof HIP young 77900B and (Allerold field et dwarfs al. 2013) at the orbit M/L stars Wright et al.M0 2010).M5 This wasL0 then usedL5 to convertT0 theT5 contrastY0 with a larger mass. Spectral type transition. Several features in the spectrum are indicative of a measurements from IRDIS and NACO to apparent fluxes. The youngThe object. large The mass doublets of the of primary gravity-sensitive leads to a potassium mass ratio bands for HIP resulting spectrum is shown in Fig.6. at 1.169/1.17764892B thatµm is and particularly 1.243/1.253 smallµm ( areq reduced.0.014). The ForH low-mass-band ToFig. estimate 7. Goodness-of-fit the spectral statistic type andG plotted effective as a functiontemperature of spectral of the type and solar-like stars, such a value would∼ correspond to objects for a number of objects in the range M0-T8. A clear G minimum is seenhas a triangular shape characteristic of low gravity atmospheres. companion, we compared the observed spectrum and photom- at or below the deuterium burning limit, making HIP 64892B at late M spectral types and the best matches are given by young, lowVisually, the spectrum agrees well with those of M9γ candidate etrysurface of HIP gravity 64892B objects with with a range spectral of types spectra of M9. compiled from the a valuable object for studying the overlapping processes of bi- literature, using the goodness-of-fit statistic G (e.g. Cushing et al. 3 https://jgagneastro.wordpress.com/the-montreal-nary star and planet formation in the brown dwarf regime. In- 2008). We considered young L dwarfs from the Upper-Scorpius spectral-library/deed, the properties of HIP 64892B raise the possibility that it ing the SPHERE filter bandpasses. In addition, we also show formed via gravitational instability, either through a binary-star A160,a pagerange 6 of 10 young companions with SPHERE K1K2 photome- mechanism or through disk instability in the circumstellar disk try or K-band spectra from the literature (Luhman et al. 2007; of the primary (Boss 1997). We investigate the latter idea further Lafrenière et al. 2008; Patience et al. 2010; Bonnefoy et al. in Appendix B, finding that the observed mass and separation of 2014a; Lachapelle et al. 2015; Lagrange et al. 2016; Maire et al. HIP 64892B are compatible with in-situ formation via disk in- 2016a; Zurlo et al. 2016; Chauvin et al. 2017, 2018). stability. This process is one of the proposed pathways for giant The position of HIP 64892B is similar to PZ Tel B and HIP planet formation, making HIP 64892B an important object for 78530B, both young companions with late-M spectral types. All understanding this mechanism. three lie close to the mid-M sequence of field dwarfs, showing The brown dwarf HIP 64892B also stands to be an impor- a slight over-luminosity compared to late-M field objects that tant object for calibrating substellar formation and evolutionary match their spectral types. This trend is also seen in young field models, with a well-known age tied to that of the LCC associa- brown dwarfs (Faherty et al. 2012; Liu et al. 2013). tion, and its brightness allowing high SNR (signal-to-noise ratio) spectroscopic and photometric measurements. While the spec- 5. Discussion and conclusion troscopic and photometric measurements presented here have high SNR, the uncertainty on the distance is relatively large, and The star HIP 64892 joins a growing number of high or intermedi- dominates the uncertainties on the absolute magnitudes, lumi- ate mass stars with extreme mass ratio companions at large sep- nosity, and isochronal mass for HIP 64892B. A much more pre- arations (< 10%, > 10 AU). While brown dwarf companions to cise distance measurement will come from the GAIA parallax, solar-type stars from both RV and imaging surveys are inherently which should be included in the second data release.

Article number, page 7 of 12 A. Cheetham et al.: Discovery of a brown dwarf companion to the star HIP 64892

Fig. 6. Observed spectrum of HIP 64892B. SPHERE IRDIS LSS data are shown in blue, while the SPHERE IRDIS and NACO photometric measurements are in red. The errorbars on the x-axis ofA& theA photometric proofs: manuscript measurements no. output represent the FWHM of the ﬁlter used. A. Cheetham et al.: Discovery of a brown dwarf companion to the star HIP 64892

10000 rare (the6 so-called “brown dwarf desert”; Grether & Lineweaver Na FeH Field dwarfs H O VO 2 2006; KrausM0-M5 et al. 2008; Metchev & Hillenbrand 2009), evi- UpperFeH Sco. objects (Lodieu+08) dence suggestsM6-M9 that the occurrence rates of companions2M1610-1913B around 5 H2O VL-G and INT-G objects (Allers+13) CO L0-L5 1000 Young objects - Montreal lib. intermediate8 mass stars may beHIP substantially 64892B higherPZ Tel B (Vigan et al. K I K I L6-L9 HIP 78530B Companions to Upper Sco stars USCOCTIO 108B (M9.5) 2012). This trend is seen for companions with masses spanning T0-T5 GSC0621-0021B the planetaryT6-T8 to stellar regimes (e.g. Johnson etUScoCTIO al. 2010; 108B Janson >T8 H2O et al. 2013).

G 100 2M2000-75 (M9γ) 10 1RXS1609b 4 Despite this, HIP 64892 is one of the highest mass stars around which a substellar companion has beenHD 106906 detected, b due HIP 65426b TWA 27 (M8) to the challenges12 associated with observing2M1207b such stars and the 10 K1 young/dusty dwarfs

tendencyM for large surveys to focus on solar-like or low-mass GSC 06214 B (M9γ) UScoJ1606-23 (M9) stars. Only HIP 78530B (Lafrenière et al. 2011), κ And b (Car- 2M2000-75 (M9γ) HIP 78530B (M7) TWA28 (M9 VL-G) 14 HN Peg B 13 son et al. 2013), and HIP 77900B (Aller et al. 2013)HD 95086b orbit stars M0 M5 L0 L5 T0 T5 Y0 with a larger mass. WISE1647+56 Spectral type PZ Tel B (M7) The large mass of the primary leads to a mass ratio for HIP 64892B16 that is particularly small (q 0.014). For low-mass Fig. 7. Goodness-of-fit statistic G plotted as a function of spectral type Fig. 7. Goodness-of-fit statistic G plotted as a function of spectral type and solar-like stars, such a value would∼ correspond to objects forfor a a number number of of objects objects in in the the range range M0-T8. M0-T8. A A clear clearFieldGGminimum L1minimum (2M1439+19) is is seen seen HR8799b HR8799c atat late late MNormalized flux (+constant) M2 spectral spectral types types and and the the best best matches matches are are given givenA& byA by proofs: young, young,manuscript low low at or no. below output the deuterium burning limit, making HIP 64892B 18 HR8799d surfacesurface gravity gravity objects objects with with spectral spectral types types of of M9. M9. a valuable object for studying the overlapping processesHR8799e of bi- Field L0 (2M1731+27) nary star and planet formation in the brown dwarf regime. In- -3 -2 -1 0 1 deed, the6 properties of HIP 64892B raise the possibility that it ing the SPHERENa filterFeH bandpasses. In addition, we also show K1-K2 VO H2O Field M9 (LHS2065) formed via gravitational instability, either through a binary-star FeH M0-M5 a range1 of young companions with SPHEREH O K1K2 photome- mechanismM6-M9 or through disk instability in the2M1610-1913B circumstellar disk 5 2 CO Fig. 9. Colour-magnitude diagram comparing K1 absolute magnitudes try or K-band spectra from the literature (Luhman et al. 2007; Fig.of the 9. Colour-magnitude primaryL0-L5 (Boss 1997). diagram We comparing investigate K1 the absolute latter idea magnitudes further K I and K1–K28 coloursL6-L9 of a range ofHIP low-mass 64892B stellar andPZ Tel B substellar objects K I Field M8 (VB10) and K1-K2 colours of a range of low-mass stellarHIP 78530B and substellar ob- Lafrenière et al. 2008; Patience et al. 2010;USCOCTIO Bonnefoy 108B (M9.5) et al. fromin Appendix the literature.T0-T5 B, finding Synthetic that K1 the and observed K2 fluxes mass were andcomputed separation for each of jects from the literature. SyntheticGSC0621-0021B K1 and K2 fluxes were computed 2014a; Lachapelle et al. 2015; Lagrange et al. 2016; Maire et al. targetHIP 64892B from publishedT6-T8 are compatible spectra. A with number in-situ of young formationUScoCTIO and dusty 108B via compan- disk in- for each target>T8 from published spectra. A number of young and dusty 2016a; Zurlo etH al.O 2016; Chauvin et al. 2017, 2018). 2 ionsstability. observed10 This with process SPHERE is one or of with the published proposedK pathways-band spectra for giantwere 2M2000-75 (M9γ) companions observed with SPHERE or with published1RXS1609b K-band spectra The0 position of HIP 64892B is similar to PZ Tel B and HIP added to the diagram. HIP 64892B falls in a similar location to PZ Tel B 4 wereplanet added formation, to the diagram. making HIP HIP 64892B 64892B falls inan a important similar location object to PZ for 78530B,0.94 both1.03 young1.13 companions1.24 1.37 1.50 with1.65 late-M1.81 spectral1.99 2.18 types.2.40 All andunderstanding HIP 78530B, this both mechanism. young brown dwarfs with late-MHD 106906 spectral b types. λ [µm] Tel B and HIP 78530B, both young brown dwarfs withHIP late-M 65426b spectral three lie close to the mid-M sequence of fieldTWA 27 dwarfs, (M8) showing types.The12 brown dwarf HIP 64892B2M1207b also stands to be an impor- K1 young/dusty dwarfs

a slight over-luminosity compared to late-M field objects that tantM object for calibrating substellar formation and evolutionary Fig. 8. Comparison of the observed spectrum (in black) with field compared to the SPHERE-LSS data of the M7 companion PZ match their spectral types. This trend is also seen in young field models, with a well-known age tied to that of the LCC associa- dwarfs and similar young low-mass brown dwarf companionsHIP 78530B (M7) (coloured Tel B (Maire et al. 2016a), we can see a clear difference in brown dwarfs (Faherty et al. 2012; Liu et al. 2013). work for Astronomy (OPTICON) underHN grant Peg B number RII3-Ct-2004-001566 for lines).3 The measured photometric points from the IRDIS filters are tion, and14 its brightness allowing high SNR (signal-to-noiseHD 95086b ratio) FP6slope (2004-2008), indicating grant a number later spectral226604 for type FP7 (2009-2012), for HIP 64892B. and grant number Also shown with grey circles. The M9 object 2MASS J20004841–7523070 shownspectroscopic are the and objects photometric UScoCTIO measurements.WISE1647+56 108B (Béjar While et al. the 2008 spec-), PZ Tel B (M7) 312430 for FP7 (2013-2016). (2M2000-75)5. Discussion provides and the conclusion best match to the measured spectrum of HIP ThisHIPtroscopic work 78530B has and made (Lafrenière photometric use of the et SPHERE al.measurements 2011 Data), and Centre, several presented jointly field operated here dwarfs. have by 64892B. OSUGUsinghigh/ SNR,IPAG16 the (Grenoble), empirical the uncertainty PYTHEAS relation on/LAM thebetween distance/CeSAM spectral (Marseille), is relatively type OCA and large,/Lagrange effec- and The star HIP 64892 joins a growing number of high or intermedi- (Nice),dominates and Observatoire the uncertainties de Paris/LESIA on the (Paris) absolute and supported magnitudes, by a grant lumi- from Field L1 (2M1439+19) tive temperature for young objects with low surfaceHR8799b gravity from Labex OSUG@2020 (Investissements d’avenir – ANR10 LABX56).HR8799c This publi- ate massNormalized flux (+constant) 2 stars with extreme mass ratio companions at large sep- Filippazzonosity, and et isochronal al.(2015), mass our spectral for HIP type 64892B. constraints A much correspond more pre- arationsMany ( of< 10%, the derived> 10 AU). properties While of brown the newly dwarf discovered companions com- to cationcise distancemakes18 use ofmeasurement data products from will the come Two Micronfrom the AllHR8799d SkyGAIA Survey, parallax, which isto a an joint effective project of temperature the University of of MassachusettsTeff = 2600 and300 theHR8799e InfraredK. Processing panionsolar-type match stars those from of both the RVplanet-hosting and imaging brown surveysField L0 dwarf (2M1731+27) are inherentlyTWA 27, which should be included in the second data± release. with an excellent match found between their spectra. This object and AnalysisFrom the Center flux-calibrated/California Institute LSS of spectrum,Technology, funded we derived by the National a syn- Aeronauticsthetic absolute-3 and Space magnitude-2 Administration of -1M and the National=0 9.37 Science0.115 Foundation.mag. Com- may prove to be a useful analogue and a point of direct compari- This publication makes use of VOSA,K1-K2 developedJ,2MASS Article under the number,± Spanish page Virtual 7 of Ob- 12 Field M9 (LHS2065) bining this with the spectral type of M9 1, we can use the son between young brown dwarfs in single and multiple systems. servatory project supported from the Spanish MICINN± through grant AyA2011- 1 24052.bolometric correction relations from Filippazzo et al.(2015) to The HIP 64892 system as a whole has many parallels to that Colour-magnitude diagram comparing K1 absolute magnitudes Fig.R.derive G., 9. R. a C., bolometric S. D. acknowledge luminosity support of fromlog(L the/L “Progetti) = 2 Premiali”.66 0.10 fundingdex. of κ And. While the stellar hosts have a similarField mass M8 (VB10) and spectral and K1-K2 colours of a range of low-mass stellar and substellar ob- schemeIn addition, of the Italian we converted Ministry of Education, the K1 fluxUniversity, measurement and− Research.± to a pre- type, the companion HIP 64892B appears to be a hotter, younger, jectsJ. O. from acknowledges the literature. financial Synthetic support from K1 and ICM K2 Núcleo fluxes Milenio were de computed Formación and higher-mass analogue of κ And B (Hinkley et al. 2013; Bon- forPlanetaria,dicted each targetKS,2MASS NPF. fromabsolute published magnitude spectra. A number using the of young SpeX and spectrum dusty companionsQ.of K. TWA acknowledges 27A observed as funding an with analog. SPHERE from STFCThe or resulting via with the published Institute value of ofK-band Astronomy,MKs,2MASS spectra Cam-= nefoy0 et al. 2014b; Jones et al. 2016). When combined with HIP werebridge8.02 added Consolidated0. to17 themag diagram. Grant. corresponds HIP 64892B to a falls luminosity in a similar of locationlog(L/ toL PZ) = 78530B0.94 (Lafrenière1.03 1.13 et1.24 al. 2011),1.37 1.50 HR1.65 3549B1.81 (Mawet1.99 2.18 et al.2.40 2015), ± λ [µm] Tel2 B.51 and HIP0.11 78530B,dex using both the young same brown method. dwarfs with late-M spectral HD 1160 (Nielsen et al. 2012), and η Tel B (Lowrance et al. − ± 2000), they form a useful sample to explore the properties of types.We also compared the observed spectrum to the BT-Settl Fig.Fig.low 8. and8.ComparisonComparison intermediate-mass of of the the observed observed brown spectrum dwarf spectrum companions (in (in black) black) with to with young, field field model grid (Baraffe et al. 2015) as a function of Teff, log g, and dwarfs and similar young low-mass brown dwarf companions (coloured References dwarfs2-3 M andstars. similar young low-mass brown dwarf companions (coloured radius R. We find a best-fit temperature and radius of Teff = lines).lines). The The measured measured photometric photometric points points from from the the IRDIS IRDIS filters filters are are workAller, for K. Astronomy M., Kraus, (OPTICON) A. L., Liu,. M.under C., grant. et al. number2013, ApJ, RII3-Ct-2004-001566 773, 63 for FP62600 (2004-2008),100 K grant and numberR = 2 2266043 0 for14 FP7RJ, (2009-2012), similar to and those grant predicted number shownshownAcknowledgements. with with grey grey circles. circles.This work The The hasM9 M9 been object object carried 2MASS 2MASS out within J20004841–7523070 J20004841–7523070 the frame of the Na- Allers,by the± K. COND N. & Liu, models M. C. 2013, for a ApJ,±33 M 772,object 79 with an age of 16 Myr. (2M2000-75)tional Centre for provides Competence thebest in Research match “PlanetS” to the measured supported spectrum by the Swiss of HIP Na- 312430Baehr, for H., FP7 Klahr, (2013-2016). H., & Kratter, K. M. 2017,J ApJ, 848, 40 (2M2000-75) provides the best match to the measured spectrum of HIP ThisWe work find has that made the log useg ofvalue the SPHERE is poorly Data constrained, Centre, jointly with operated a best-fit by 64892B.64892B.tional Science Foundation (SNSF). Baraffe, I., Chabrier, G., Barman, T. S., Allard, F., & Hauschildt, P. H. 2003, SPHERE is an instrument designed and built by a consortium consisting of OSUGvalueA&A,/IPAGlog 402, (Grenoble),g = 7015.5. When PYTHEAS combined/LAM/CeSAM with the (Marseille), radius, OCA this/ predictsLagrange a IPAG (Grenoble, France), MPIA (Heidelberg, Germany), LAM (Marseille, (Nice),Baraff ande, I., Observatoire Homeier, D., de Allard, Paris/LESIA F., & Chabrier, (Paris) and G. 2015, supported A&A, by 577, a grant A42 from Labexmuch OSUG@2020 larger mass (Investissements than expected. d’avenir However, – ANR10 gravity-sensitive LABX56). This publi- fea- membersFrance), LESIA of (Paris,the β France),Pictoris Laboratoire and Argus Lagrange moving (Nice, France), groups INAF (20– - Bayo,tures A., are Rodrigo, generally C., Barrado narrow Y Navascués, and fitting D., to et al.the 2008, entire A&A, spectrum 492, 277 at OsservatorioMany of dithe Padova derived (Italy), properties Observatoire of the Astronomique newly discovered de l’Université com- de cationBéjar, makes V. J. S.,use Zapatero of data products Osorio, M. from R., the Pérez-Garrido, Two Micron A., All et Sky al. Survey, 2008, ApJ, which 673, panion50Genève Myr; match (Switzerland), Gagné those et al. of ETH the2015b Zurich planet-hosting), with (Switzerland), 2MASS brown NOVA J20004841?7523070 dwarf (Netherlands), TWA 27, ON- isonce a jointL185may project complicate of the University this of measurement. Massachusetts and To the investigate Infrared Processing this, we withgivingERA an (France), excellent the best and fit.ASTRON match found (Netherlands) between in collaboration their spectra. with This ESO. object SPHERE andBeuzit,performed Analysis J.-L., Center Feldt, the/ sameCalifornia M., Dohlen, fit to Institute K.,the et two al.of Technology,2008, sections in Proc. of funded SPIE, the byLSS Vol. the 7014 spectrum National wasAs funded seen by ESO, in Fig. with8 additional, the spectrum contributions of from HIP CNRS 64892B (France), is also MPIA AeronauticsBohlin,either sideR. and C. of2007, Space the in Administration1 Astronomical.4 µm telluric and Society the feature National of the individually. Pacific Science Conference Foundation. The Series,Y–J- may prove to be a useful analogue and a point of direct compari- This publication makes use of VOSA, developed under the Spanish Virtual Ob- well(Germany), reproduced INAF (Italy), by the FINES spectrum (Switzerland), of the and8 Myr-old NOVA (Netherlands). M8 dwarf bandVol. spectrum 364, The Future gives of an Photometric, estimate of Spectrophotometriclog g = 4.0 0 and.5, Polarimetric while the sonSPHERE between also young received brown funding dwarfs from the in European single and Commission multiple Sixth systems. and Sev- servatoryStandardization, project supported ed. C. from Sterken, the Spanish 315 MICINN through± grant AyA2011- 2M1207A (TWA27) from the TW Hydrae association, which 24052.H-band spectrum yields log g = 3.5 1.0, indicating that a lower enthThe Framework HIP 64892 Programmes system as as part a whole of the Optical has many Infrared parallels Coordination to that Net- Bonnefoy, M., Chauvin, G., Lagrange, A.-M.,± et al. 2014a, A&A, 562, A127 showsκ many of the same features seen in our data. When R.value G., R. C.,is likely. S. D. acknowledge support from the “Progetti Premiali” funding of And. While the stellar hosts have a similar mass and spectral scheme of the Italian Ministry of Education, University, and Research. type,Article the number, companion page HIP 8 of 64892B12 appears to be a hotter, younger, J. O. acknowledges financial support from ICM Núcleo MilenioA160, de page Formación 7 of 10 and higher-mass analogue of κ And B (Hinkley et al. 2013; Bon- Planetaria, NPF. nefoy et al. 2014b; Jones et al. 2016). When combined with HIP Q. K. acknowledges funding from STFC via the Institute of Astronomy, Cam- 78530B (Lafrenière et al. 2011), HR 3549B (Mawet et al. 2015), bridge Consolidated Grant. HD 1160 (Nielsen et al. 2012), and η Tel B (Lowrance et al. 2000), they form a useful sample to explore the properties of low and intermediate-mass brown dwarf companions to young, References 2-3 M stars. Aller, K. M., Kraus, A. L., Liu, M. C., et al. 2013, ApJ, 773, 63 Acknowledgements. This work has been carried out within the frame of the Na- Allers, K. N. & Liu, M. C. 2013, ApJ, 772, 79 tional Centre for Competence in Research “PlanetS” supported by the Swiss Na- Baehr, H., Klahr, H., & Kratter, K. M. 2017, ApJ, 848, 40 tional Science Foundation (SNSF). Baraffe, I., Chabrier, G., Barman, T. S., Allard, F., & Hauschildt, P. H. 2003, SPHERE is an instrument designed and built by a consortium consisting of A&A, 402, 701 IPAG (Grenoble, France), MPIA (Heidelberg, Germany), LAM (Marseille, Baraffe, I., Homeier, D., Allard, F., & Chabrier, G. 2015, A&A, 577, A42 France), LESIA (Paris, France), Laboratoire Lagrange (Nice, France), INAF - Bayo, A., Rodrigo, C., Barrado Y Navascués, D., et al. 2008, A&A, 492, 277 Osservatorio di Padova (Italy), Observatoire Astronomique de l’Université de Béjar, V. J. S., Zapatero Osorio, M. R., Pérez-Garrido, A., et al. 2008, ApJ, 673, Genève (Switzerland), ETH Zurich (Switzerland), NOVA (Netherlands), ON- L185 ERA (France), and ASTRON (Netherlands) in collaboration with ESO. SPHERE Beuzit, J.-L., Feldt, M., Dohlen, K., et al. 2008, in Proc. SPIE, Vol. 7014 was funded by ESO, with additional contributions from CNRS (France), MPIA Bohlin, R. C. 2007, in Astronomical Society of the Pacific Conference Series, (Germany), INAF (Italy), FINES (Switzerland), and NOVA (Netherlands). Vol. 364, The Future of Photometric, Spectrophotometric and Polarimetric SPHERE also received funding from the European Commission Sixth and Sev- Standardization, ed. C. Sterken, 315 enth Framework Programmes as part of the Optical Infrared Coordination Net- Bonnefoy, M., Chauvin, G., Lagrange, A.-M., et al. 2014a, A&A, 562, A127

Article number, page 8 of 12 A&A 615, A160 (2018)

The spectral type estimate and low surface gravity are also precise distance measurement will come from the Gaia parallax, supported by the position of HIP 64892B on colour-magnitude which should be included in the second data release. diagrams. In Fig.9 we show its K1 magnitude and K1–K2 colour Many of the derived properties of the newly discovered com- compared to a range of field objects assembled from the SpeX panion match those of the planet-hosting brown dwarf TWA 27, Prism Library (Burgasser 2014) and from Leggett et al.(2000). with an excellent match found between their spectra. This object For these objects we generated synthetic photometry using the may prove to be a useful analogue and a point of direct com- SPHERE filter bandpasses. In addition, we also show a range of parison between young brown dwarfs in single and multiple young companions with SPHERE K1K2 photometry or K-band systems. spectra from the literature (Luhman et al. 2007; Lafrenière et al. The HIP 64892 system as a whole has many parallels to that 2008; Patience et al. 2010; Bonnefoy et al. 2014a; Lachapelle of κ And. While the stellar hosts have a similar mass and spectral et al. 2015; Lagrange et al. 2016; Maire et al. 2016a; Zurlo et al. type, the companion HIP 64892B appears to be a hotter, younger, 2016; Chauvin et al. 2017, 2018). and higher-mass analogue of κ And B (Hinkley et al. 2013; The position of HIP 64892B is similar to PZ Tel B and HIP Bonnefoy et al. 2014b; Jones et al. 2016). When combined 78530B, both young companions with late-M spectral types. All with HIP 78530B (Lafrenière et al. 2011), HR 3549B (Mawet three lie close to the mid-M sequence of field dwarfs, showing et al. 2015), HD 1160 (Nielsen et al. 2012), and η Tel B a slight over-luminosity compared to late-M field objects that (Lowrance et al. 2000), they form a useful sample to explore match their spectral types. This trend is also seen in young field the properties of low and intermediate-mass brown dwarf brown dwarfs (Faherty et al. 2012; Liu et al. 2013). companions to young, 2–3 M stars.

Acknowledgements. This work has been carried out within the frame of the National Centre for Competence in Research “PlanetS” supported by the Swiss 5. Discussion and conclusion National Science Foundation (SNSF). SPHERE is an instrument designed and built by a consortium consisting of IPAG (Grenoble, France), MPIA The star HIP 64892 joins a growing number of high or inter- (Heidelberg, Germany), LAM (Marseille, France), LESIA (Paris, France), Lab- mediate mass stars with extreme mass ratio companions at large oratoire Lagrange (Nice, France), INAF – Osservatorio di Padova (Italy), Obser- separations (<10%, >10 AU). While brown dwarf companions vatoire Astronomique de l’Université de Genève (Switzerland), ETH Zurich to solar-type stars from both RV and imaging surveys are (Switzerland), NOVA (The Netherlands), ONERA (France), and ASTRON (The Netherlands) in collaboration with ESO. SPHERE was funded by ESO, inherently rare (the so-called “brown dwarf desert”; Grether & with additional contributions from CNRS (France), MPIA (Germany), INAF Lineweaver 2006; Kraus et al. 2008; Metchev & Hillenbrand (Italy), FINES (Switzerland), and NOVA (The Netherlands). SPHERE also 2009), evidence suggests that the occurrence rates of compan- received funding from the European Commission Sixth and Seventh Frame- ions around intermediate mass stars may be substantially higher work Programmes as part of the Optical Infrared Coordination Network for (Vigan et al. 2012). This trend is seen for companions with Astronomy (OPTICON) under grant number RII3-Ct-2004-001566 for FP6 (2004-2008), grant number 226604 for FP7 (2009-2012), and grant number masses spanning the planetary to stellar regimes (e.g. Johnson 312430 for FP7 (2013-2016). This work has made use of the SPHERE Data et al. 2010; Janson et al. 2013). Centre, jointly operated by OSUG/IPAG (Grenoble), PYTHEAS/LAM/CeSAM Despite this, HIP 64892 is one of the highest mass stars (Marseille), OCA/Lagrange (Nice), and Observatoire de Paris/LESIA (Paris) around which a substellar companion has been detected, due and supported by a grant from Labex OSUG@2020 (Investissements d’avenir – ANR10 LABX56). This publication makes use of data products from to the challenges associated with observing such stars and the the Two Micron All Sky Survey, which is a joint project of the University of tendency for large surveys to focus on solar-like or low-mass Massachusetts and the Infrared Processing and Analysis Center/California Insti- stars. Only HIP 78530B (Lafrenière et al. 2011), κ And b tute of Technology, funded by the National Aeronautics and Space Administra- (Carson et al. 2013), and HIP 77900B (Aller et al. 2013) orbit tion and the National Science Foundation. This publication makes use of VOSA, stars with a larger mass. developed under the Spanish Virtual Observatory project supported from the Spanish MICINN through grant AyA2011-24052. R.G., R.C., S.D. acknowledge The large mass of the primary leads to a mass ratio for HIP support from the “Progetti Premiali” funding scheme of the Italian Ministry of 64892B that is particularly small (q 0.014). For low-mass and Education, University, and Research. J.O. acknowledges ﬁnancial support from solar-like stars, such a value would∼ correspond to objects at or ICM Núcleo Milenio de Formación Planetaria, NPF. Q.K. acknowledges funding below the deuterium burning limit, making HIP 64892B a valu- from STFC via the Institute of Astronomy, Cambridge Consolidated Grant. able object for studying the overlapping processes of binary star and planet formation in the brown dwarf regime. Indeed, the properties of HIP 64892B raise the possibility that it formed References via gravitational instability, either through a binary-star mech- Aller, K. M., Kraus, A. L., Liu, M. C., et al. 2013, ApJ, 773, 63 anism or through disk instability in the circumstellar disk of the Allers, K. N., & Liu, M. C. 2013, ApJ, 772, 79 primary (Boss 1997). We investigate the latter idea further in Baehr, H., Klahr, H., & Kratter, K. M. 2017, ApJ, 848, 40 AppendixB, ﬁnding that the observed mass and separation of Baraffe, I., Chabrier, G., Barman, T. S., Allard, F., & Hauschildt, P. H. 2003, HIP 64892B are compatible with in situ formation via disk insta- A&A, 402, 701 Baraffe, I., Homeier, D., Allard, F., & Chabrier, G. 2015, A&A, 577, A42 bility. This process is one of the proposed pathways for giant Bayo, A., Rodrigo, C., Barrado Y Navascués, D., et al. 2008, A&A, 492, 277 planet formation, making HIP 64892B an important object for Béjar, V. J. S., Zapatero Osorio, M. R., Pérez-Garrido, A., et al. 2008, ApJ, 673, understanding this mechanism. L185 The brown dwarf HIP 64892B also stands to be an impor- Beuzit, J.-L., Feldt, M., Dohlen, K., et al. 2008, Proc. SPIE, 7014, 701418 tant object for calibrating substellar formation and evolutionary Bohlin, R. C. 2007, ASP Conf. Ser., 364, 315 Bonnefoy, M., Chauvin, G., Lagrange, A.-M., et al. 2014a, A&A, 562, A127 models, with a well-known age tied to that of the LCC associa- Bonnefoy, M., Currie, T., Marleau, G.-D., et al. 2014b, A&A, 562, A111 tion, and its brightness allowing high signal-to-noise ratio (S/N) Boss, A. P. 1997, Science, 276, 1836 spectroscopic and photometric measurements. While the spec- Bowler, B. P., Johnson, J. A., Marcy, G. W., et al. 2010, ApJ, 709, 396 troscopic and photometric measurements presented here have Bowler, B. P., Liu, M. C., Shkolnik, E. L., & Tamura, M. 2015, ApJS, 216, 7 Brahm, R., Jordán, A., & Espinoza, N. 2017, PASP, 129, 034002 high S/N, the uncertainty on the distance is relatively large, and Bressan, A., Marigo, P., Girardi, L., et al. 2012, MNRAS, 427, 127 dominates the uncertainties on the absolute magnitudes, lumi- Burgasser, A. J. 2014, Astron. Soc. India Conf. Ser., 11, 7 nosity, and isochronal mass for HIP 64892B. A much more Burgasser, A. J., Kirkpatrick, J. D., Brown, M. E., et al. 2002, ApJ, 564, 421

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A160, page 9 of 10 A. Cheetham et al.: Discovery of a brown dwarf companion to the star HIP 64892 A&A 615, A160 (2018) A&A proofs: manuscript no. output Appendix B: Disk instability models for HIP 64892B 2 3 10 10 To investigate the possibility that HIP 64892BG.I. formed allowed via disk instability, we estimate the range of fragment masses that could be produced as a function of semi-major axis using a set of frag- mentation criteria as recently conﬁrmed in local high resolution 10 3 three-dimensional simulations (Baehr et al. 2017). These mod- ] )

J 2 10 els areM described in detail in Janson et al. (2012) and Bonnefoy ( M Cooling parameter

[

* s

t M s et al. (2014b).s 50 Brieﬂy,% fragments must satisfy the Toomre crite- u a d

rion form self-gravitating clumps (Toomre 1964) and be able to M

t * 10 4 cool fastern than% the M local Keplerian timescale. These models re- e 20

quire them star’s initial luminosity andToomre metallicity. parameter The former was g M * a 1 0% estimatedr 10 for1 HIP 64892 from the isochrones of Bressan et al. (2012),F while for the latter we assumed a solar metallicity. The result is plotted in Fig. B.1. We also compared the primordial 10 5 101 102 disk mass required to support fragments of a given mass for disks r [au] with 10%, 20%, and 50% of the mass of the host star.

We found0 that if the currently observed projected separation 10 Fig. A.1. Blue-shaded area shows the region in the r-Mdust plane, in 1 2 3 Blue-shaded area shows the region in the r-M plane, in of HIP 64892B10 is close to its semi-major10 axis, then its predicted10 Fig.which A.1. a debris disk could be present and remain compatibledust with the which a debris disk could be present and remain compatible with the mass and location are closeSemi-major to the Toomre axis (AU) limit. This opens the mid- and far-IR observations. mid- and far-IR observations. possibility that the companion may have formed in-situ via grav- itationalFig.Fig. A.2. B.1. instability.PredictionsPredictions for for the the fragment fragment masses masses compatible with with produc- produc- tiontionThe via via gravitational same gravitational models instability instability were applied for for HIP HIP by 64892. 64892. Bonnefoy Fragments Fragments et with al. with (2014b) masses masses above the orange dashed line cannot cool efficiently enough, while those Appendix A: Upper limits on the dust mass to theabove companions the orange dashedκ And line B, cannot HR cool 7329B, efficiently HD enough, 1160B, while and those HIP Appendix A: Upper limits on the dust mass 78530B.belowbelow the the These blue blue solid objectssolid line line do are do not not all satisfy satisfy young the the substellar Toomre criterion. criterion. companions The The mass mass to 2-2.5andand projected M projectedstars. separation separation The brown of of HIP HIP dwarf 64892B 64892B HIP are 64892B marked. falls We We find infind a that that similar HIP HIP Chen et al.( (2012)2012) reported reported a a non-detection non-detection of of a a mid-IR mid-IR excess excess 64892B is compatible with in-situ formation via gravitational instabil- region64892B of is the compatible diagram with to κ inAnd situ formation B, HR 7329B, via gravitational and HD 1160B. instabil- around HIP 64892, with a Spitzer//MIPSMIPS upper limit at 70µm ity,ity, although although further further constraints constraints on on the the semi-major semi-major axis axis are are needed needed to to These four objects are compatible with in-situ formation via disk of 15..8 mJy. Using a similar approach to that of Chauvin et al. confirmconfirm this this idea. idea. The The initial initial disk disk masses masses required to to form form fragments fragments of of instabilitya given size and are require shown only with black modest dotted disk lines. masses of 10-20% of the (2017)(2017) for for HIP HIP 65426, 65426, we we can can convert convert this this value value to an to upper an upper limit a given size are shown with black dotted lines. mass of the primary star to form. The brown dwarf HIP 78530B onlimit the on dust the mass dust around mass HIP around 64892. HIP Similar 64892. to HIPSimilar 65426, to HIP this is a clear outlier at a much larger separation that puts it below the upper65426, limit this does upper not limit reach does the photospheric not reach the flux photospheric ( 1.4 mJy). flux ∼ ToomreAppendix limit, B: indicating Disk instability that its formation models proceeded for through a ( 1.4 mJy). We gather the optical to mid-IR photometry of the star using diffHIPerent 64892B pathway, or that it underwent significant outward or- ∼ We gather4 the optical to mid-IR photometry of the star using the VOSA tool (Bayo et al. 2008). For the given stellar luminos- bital migration following its formation epoch. itythe and VOSA mass4 tool (33 (LBayoand et 2. al.35 2008M , respectively)). For the given we stellarestimate lumi- the To investigate the possibility that HIP 64892B formed via disk sizenosity of anddust mass grains (33 that L wouldand 2 still.35 M be on, respectively) bound orbits we around estimate the instability, we estimate the range of fragment masses that could star.the size We of use dust the grains optical that constant would of still astro-silicates be on bound (Draine orbits around 2003) be produced as a function of semi-major axis using a set of frag- andthe star.we compute We use the the radiation optical constant pressure of to astro-silicates gravitational forces (Draineβ mentation criteria as recently confirmed in local high-resolution ratio2003) as and in Burns we compute et al. (1979). the radiation We find that pressure for this to composition, gravitational three-dimensional simulations (Baehr et al. 2017). These mod- grainsforces largerβ ratio than as ins Burns4 et.8 al.µm(1979 should). We remain findon that bound for this or- els are described in detail in Janson et al.(2012) and Bonnefoy blow ∼ bitscomposition, around the grains star. To larger estimate than s theblow possible4.8 µm configurations should remain for on a et al.(2014b). Briefly, fragments must satisfy the Toomre cri- ∼ debrisbound disk orbits to around remain the compatible star. To estimate with the the mid- possible and far-IR configura- obser- terion for self-gravitating clumps (Toomre 1964) and be able vations,tions for we a debris compute disk a series to remain of disk compatible models (similar with the to Olofssonmid- and to cool faster than the local Keplerian timescale. These models etfar-IR al. 2016). observations, We consider we compute a grain a seriessize distribution of disk models of the (similar form require the star’s initial luminosity and metallicity. The former 3.5 dton (Olofssons) s− etd al.s, between2016). Wesmin consider= sblow a grainand sizesmax distribution= 1 mm. We of was estimated for HIP 64892 from the isochrones of Bressan ∝ 3.5 samplethe form 100 dn(rs)valuess− fords,the between radialsmin distance= sblow ofand thes beltmax between= 1 mm. et al.(2012), while for the latter we assumed a solar metallicity. i ∝ 10We and sample 200 au.100 Forri eachvaluesri, for we theconsider radial adistance disk model of between the belt The result is plotted in Fig. A.2. We also compared the primor- 0between.9 r 10r and1.1200rau.. We For then each slowlyri, we increase consider the a mass disk model of the dial disk mass required to support fragments of a given mass for × i ≤ i ≤ × i diskbetween until0 the.9 thermalri ri emission1.1 r (plusi. We the then stellar slowly contribution) increase the is disks with 10%, 20%, and 50% of the mass of the host star. × ≤ ≤ × largermass of than the either disk until the WISE the thermal/W4 22 emissionµm point (plus or the theSpitzer stellar/MIPS con- We found that if the currently observed projected separation 70tribution)µm point. is larger We therefore than either delimit the WISE a region/W4 in22 theµmr- pointMdust orplane the of HIP 64892B is close to its semi-major axis, then its predicted whereSpitzer debris/MIPS disks 70 µm could point. exist We therefore and remain delimit undetected a region with in the ther- mass and location are close to the Toomre limit. This opens currentMdust plane observations where debris (see disks Fig. couldA.1).exist Overall, and remainwith our undetected assump- the possibility that the companion may have formed in situ via tionswith onthe the current radial observations extent of the debris (see Fig. disk, A.1 we). findOverall, the dust with mass our gravitational instability. 3 mustassumptions be less onthan the radial2 10 extent− M ofat the about debris 100 disk,au from we the find star. the The same models were applied by Bonnefoy et al.(2014b) ∼ × ⊕ 3 Whendust mass compared must be to less the than well-known2 10−β MPictorisat about debris100 disk,au from we to the companions κ And B, HR 7329B, HD 1160B, and HIP ∼ × ⊕ findthe star. that any When potential compared belts to around the well-known HIP 64892β mustPictoris be substan- debris 78530B. These objects are all young substellar companions to tiallydisk, weless find massive. that any The potential total dust belts mass around of the HIPβ Pictoris 64892 debris must 2–2.5 M stars. The brown dwarf HIP 64892B falls in a similar 2 diskbe substantially was measured less at massive.8 10 The− M total(Dent dust et mass al. 2014) of the betweenβ Pic- region of the diagram to κ And B, HR 7329B, and HD 1160B. ∼ × ⊕ 2 2 50-120AU,toris debris diskimplying was measured a value of at 83 1010− −MM(Dentfor an et al. annulus 2014) These four objects are compatible with in situ formation via disk ∼ ×× ⊕ ⊕ 2 atbetween 100AU 50 that and can 120 be AU, compared implying with a value our simulation of 3 10 (assuming− M for instability and require only modest disk masses of 10–20% of the ∼ × ⊕ constantan annulus density). at 100 AU that can be compared with our simulation mass of the primary star to form. The brown dwarf HIP 78530B (assuming constant density). is aArticle clear outliernumber, at page a much 12 of 12 larger separation that puts it below the Toomre limit, indicating that its formation proceeded through a 4 http://svo2.cab.inta-csic.es/theory/vosa/. different pathway, or that it underwent significant outward orbital 4 http://svo2.cab.inta-csic.es/theory/vosa/ migration following its formation epoch. Article number, page 11 of 12 A160, page 10 of 10