arXiv:1901.03687v1 [astro-ph.SR] 11 Jan 2019 [email protected] orsodn uhr hrot .Wood M. Charlotte author: Corresponding htrslsi ihywvlnt-eedn opacities molecules wavelength-dependent of highly presence ( the in and results formation, that cloud possibil- of the ity zones, convection multiple including cated, h anfco ndtriighwabondwarf brown a how determining in factor main the aly&Rbno 2015 Robinson & Marley h topee fbondaf r ut compli- quite are dwarfs brown of atmospheres The yee sn L using 2019 Typeset 14, January version Draft 7 tla srpyisCnr,Dprmn fPyisadAst and Physics of Department Centre, Astrophysics Stellar ecmrigSbtla vltoayMdl sn e g Estimate Age New Using Models Evolutionary Substellar Benchmarking hrot .Wood M. 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E X ihaglrrslto ehius interferometric techniques: – resolution angular high rw wrs–sas vlto tr:idvda H 77 D19 HD 4747, (HD individual stars: – evolution stars: – dwarfs brown INTRODUCTION twocolumn 4 aeUiest,Dprmn fAtooy ..Bx208101, Box P.O. Astronomy, of Department University, Yale 6 .Amshrceet r also are effects Atmospheric ). h HR ra fGogaSaeUiest,MutWlo,C Wilson, Mount University, State Georgia of Array CHARA The , 1 alSchaefer Gail aeh Boyajian Tabetha 3 Rcie etme 0 08 cetdJnay1,2019) 10, January Accepted 2018; 10, September (Received oelOsraoy 40WMr ilR,Fasa,A 86001 AZ Flagstaff, Rd, Hill Mars W 1400 Observatory, Lowell tl nAASTeX62 in style ∼ 0 . e o D147B h iceace nlmnst orsodto correspond luminosity in discrepancies The B. 19467 HD for dex 5 ∼ , 6 2 o D44 and B 4747 HD for 12% rhrAdams Arthur , 2 umte oApJ to Submitted aprvnBraun von Kaspar ABSTRACT Denmark ooy ahsUiest,N ukgd 2,D-00Aarhu DK-8000 120, Munkegade Ny University, Aarhus ronomy, ∼ . 74 %frH 77B nLTtasto betthat object transition L/T an B, 4747 HD for 8% − +6 , 6 4 nm,22NcosnHl,BtnRue A70803 LA Rouge, Baton Hall, Nicholson 202 onomy, l r tl arylmtddet eeeaisbetween degeneracies to due limited fairly still predeces- are their els than objects match- ( and sors older dwarfs for brown observations of ing color optical predicting at atmosphere. the from cannot than other properties determined whose be dwarfs, brown free- com- studying “field” Having when models floating important effects. especially need these is of models we all plete account objects, into take substellar brown understand that other fully to and hope we dwarfs If cools. and evolves . . 75 87 and eetsbtla vltoaymdl oabte job better a do models evolutionary substellar Recent 6 5 et10hSre,NwYr,N 10027 NY York, New Street, 120th West 550 46, y o D44 n 10 and A 4747 HD for Gyr aaee l 2015 al. et Baraffe ioh .White R. Timothy n cec al or ae N46556 IN Dame, Notre Hall, Science and , ∼ 3 onM Brewer M. John 0 o D147B eas show also We B. 19467 HD for 30% ooerclmnste by luminosities bolometric t ne-rdcino uioiyto luminosity of under-prediction tla rcs n Yonsei-Yale and Tracks, Stellar d e ae,C 06520 CT Haven, New t ouet ecmr SSEMs. benchmark to use to cts eeabondafi on sa as found is dwarf brown a here o D44 n D147B 19467 HD and B 4747 HD for s aue h nua diameters angular the easured s,ae n uioiyo the of luminosity and age, ass, ermiigdsrpnisis discrepancies remaining he fe tigterparameters their fitting After . ffiutdet degeneracy a to due ifficult 47Bhv h aeages same the have B 9467 91023 A .Hwvr et fteemod- these of tests However, ). 7 , ,5 4, 6)–techniques: – 467) . utnR Crepp R. Justin 06 − +1 0 . . 16 82 y for Gyr ∼ 0.75 , C, s 1 2 Wood et al. mass, age, and luminosity for brown dwarfs; a young, ranging from ∼ 30 − 330 meters (ten Brummelaar et al. less massive brown dwarf can appear to have the same 2005). The predicted angular sizes of HD 4747 A and luminosity as an old, more massive brown dwarf. These HD 19467 A, based on the surface brightness relations in degeneracies are the main source of uncertainty in age Boyajian et al. (2014), are on the order of a few tenths of estimates for field brown dwarfs, inhibiting the accuracy a milli-arcsecond (mas). Thus, we conducted our obser- of model tests. To properly constrain the models, we vations using the PAVO beam combiner (Ireland et al. need benchmark brown dwarfs – objects whose masses, 2008) in the R-band with the baseline configurations ages, and luminosities can be determined independently. listed in Table 1 in order to adequately resolve the The mass of a benchmark brown dwarf can be cal- stars. culated using the orbital mechanics of the system in HD 4747 A was observed during the nights of 14 Au- which it is found (Liu et al. 2008; Dupuy et al. 2009a; gust 2015 UT, 1 August 2016 UT, and 11 November Crepp & Johnson 2011; Dupuy & Liu 2017). Other 2016 UT. HD 19467 A was observed during the nights properties of a benchmark brown dwarf – such as age of 6 and 7 September 2014 UT, 17 August 2015 UT, and metallicity – can be more readily inferred by study- and 11 November 2016 UT. The observations of our ing the host star rather than the brown dwarf itself. targets are bracketed in time with several calibrator Using isochronal models, a more accurate age esti- stars, the selection of which is based on the JMMC mate of the host star can be determined by measuring Stellar Diameters Catalog (JSDC; Duvert 2016)1. In the precise stellar radius, which places additional con- order to identify and thus avoid unknown systematic straints on the location of the star on the HR-diagram errors in our interferometry data, we require the use (Crepp et al. 2012). For nearby stars (d ≤ 50 parsecs), of at least two calibrator stars per target, the use of it is possible to determine the stellar radius precisely at least two combinations of telescopes (baselines), and using interferometry (Boyajian et al. 2012a,b). data from at least two nights. Calibrator stars for In this paper, we present angular diameter measure- HD 4747 A are HD 2696 (θUD,R = 0.34 ± 0.03 mas) ments from the Center for High Angular Resolution As- and HD 4622 (θUD,R =0.219 ± 0.006 mas). Calibrators tronomy (CHARA) Array and calculate the radius (§2) for HD 19467 A are HD 16141 (θUD,R = 0.366 ± 0.010 of two Sun-like stars, HD 4747 A and HD 19467 A, mas), HD 17943 (θUD,R = 0.234 ± 0.007 mas), and known to host benchmark brown dwarf companions HD 22243 (θUD,R = 0.185 ± 0.005 mas) (Duvert 2016; (Crepp et al. 2014, 2016, 2018). We also present new age Chelli et al. 2016). These calibrators are selected based estimates for these systems (§4) using the Dartmouth upon their physical attributes: no known multiplicity, Stellar Evolution Database, MESA Isochrones and Stel- low projected rotational velocity, similar brightness as lar Tracks (MIST), and Yonsei-Yale (YY) isochrone the respective target in R, close angular proximity (max models (Dotter et al. 2007, 2008; Paxton et al. 2011, 10 degrees) to the respective science target, and to be 2013, 2015; Dotter 2016; Choi et al. 2016; Spada et al. unresolved sources based on their estimated angular 2013). Assuming the directly imaged brown dwarf com- sizes (van Belle & van Belle 2005; Boyajian et al. 2013; panions HD 4747 B and HD 19467 B have the same ages von Braun et al. 2014). A summary of our observations as their respective host stars, we use the isochronal age is shown in Table 1. estimates to test and constrain several substellar evolu- Our data reduction procedure to extract calibrated tionary models (§6) (Chabrier et al. 2000; Baraffe et al. squared-visibility measurements (V 2, Figure 1) is de- 2002, 2003, 2015; Saumon & Marley 2008). Both bench- scribed in section 2.1 in Boyajian et al. (2015) and mark brown dwarfs have precisely measured dynamical is based on the methods outlined in Maestro et al. masses and metallicities, making them ideal objects to (2013) and White et al. (2013). We measure uniform calibrate models. disk angular diameters of θUD = 0.367 ± 0.006 mas for HD 4747 A and θUD = 0.355 ± 0.011 mas for 2. INTERFEROMETRIC OBSERVATIONS AND HD 19467 A. We determine limb-darkened angular di- STELLAR RADII ameters of θLD =0.390 ± 0.007 mas for HD 4747 A and θLD =0.376±0.014mas for HD 19467 A using respective In order to obtain direct estimates for the stel- limb-darkening coefficients of µR =0.63 and µR =0.60 lar diameters, we performed interferometric observa- (Claret & Bloemen 2011). Combined with parallaxes tions with Georgia State University’s CHARA Ar- from Gaia DR2 (Gaia Collaboration et al. 2018), we ob- ray, a long-baseline optical/infrared interferometer lo- cated within the Mount Wilson Observatory in Cal- ifornia. The CHARA Array consists of six 1-m di- 1 http://www.jmmc.fr/jsdc. ameter telescopes with distances between telescopes Benchmarking Substellar Evolutionary Models 3
Table 1. Observation Log
Object UTDate CHARABaseline Calibrator HD 4747 2015/08/14 W1-E1 (313.53 m) HD 4622 2016/08/01 W2-E2 (156.27 m) HD 4622 2016/11/11 W1-E2 (251.34 m) HD 2696, HD 4622
HD 19467 2014/09/06 E1-S1 (330.66 m) HD 17943, HD 22243 2014/09/07 W1-E1 (313.53 m) HD 17943, HD 22243 2015/08/17 E2-S1 (278.76 m) HD 17943, HD 22243 2016/11/11 W1-E2 (251.34 m) HD 16141, HD 17943, HD 22243 Note—Refer to §2 for details.
tain stellar radii of R = 0.789±0.014 R⊙ for HD 4747 A 3. BOLOMETRIC FLUXES, STELLAR EFFECTIVE and R = 1.295 ± 0.048 R⊙ for HD 19467 A (Table 2). TEMPERATURES, AND STELLAR Our new radius measurements are consistent with litera- LUMINOSITIES ture values within 1σ for HD 4747 A (Crepp et al. 2018) Coupled with stellar angular diameter, the knowledge and within 3σ for HD 19467 A (Crepp et al. 2014). of stellar bolometric flux (FBOL) provides a direct esti- mate of stellar temperature, which, when combined with physical stellar radius, yields stellar luminosity via a re- Table 2. Properties of the Host Stars formulation of the Stefan-Boltzmann Law,
1 2 4 Property HD 4747 A HD 19467 A Teff (K) = 2341(FBOL/θLD) , (1) RA (J2000) 00 49 26.77 03 07 18.57 where F has units of 10−8 erg/cm2/s and θ has Dec (J2000) -23 12 44.93 -13 45 42.42 BOL LD units of milliarcseconds. F can be obtained by spec- Spectral Type G9Va G3Vb BOL tral energy distribution (SED) fitting by scaling spectral Parallax (mas)c 53.184 ± 0.126 31.225 ± 0.041 templates to literature photometry values. For the SED Distance (pc) 18.80 ± 0.04 32.02 ± 0.04 a b fitting of our targets (Figure 2), we follow the approach Mass (M⊙) 0.82 ± 0.04 0.95 ± 0.02 a b used in Mann et al. (2013) and von Braun et al. (2014). [Fe/H ] −0.22 ± 0.04 −0.15 ± 0.02 Interstellar extinction is set to zero for both targets due −2 a b log(g) (cm s ) 4.65 ± 0.06 4.40 ± 0.06 to the small distances to our targets (less than 70 pc)2 d θUD (mas) 0.367 ± 0.006 0.355 ± 0.011 and we use the updated broad-band filter profiles pre- d θLD (mas) 0.390 ± 0.007 0.376 ± 0.014 sented in Mann & von Braun (2015). In the calculation d Radius (R⊙) 0.789 ± 0.014 1.295 ± 0.048 of the errors in effective temperature and stellar lumi- −8 −1 −2 d FBOL (10 erg s cm ) 4.02 ± 0.03 4.54 ± 0.03 nosity, we inflate the calculated uncertainty in our FBOL d Luminosity (L⊙) 0.444 ± 0.004 1.456 ± 0.010 (as given below) by adding 2% of the error in quadra- d Teff, interferometric (K) 5308 ± 48 5572 ± 104 ture, thereby compensating for unknown systematic er- d,e Teff, spectroscopic (K) 5305 ± 25 5748 ± 25 rors in the literature photometry (Bohlin et al. 2014). Based on fitting a G8V spectral template from the a Crepp et al. (2016) Pickles (1998)3 library to literature photometry from b Crepp et al. (2014) Irwin (1961), Stoy (1963), Wild (1969), Mermilliod c Gaia Collaboration et al. (2018) (1986), Rufener (1988), Mermilliod & Nitschelm (1989), Olsen (1993), Hauck & Mermilliod (1998), Cutri et al. d This paper (§2, 3, 4) (2003), and Koen et al. (2010), we measure HD 4747 A’s e −8 −1 −2 Statistical uncertainty only, does not include model uncertainty. FBOL to be (4.02 ± 0.03) × 10 erg s cm , which,
2 See Aumer & Binney (2009) for more details. 3 See also https://lco.global/∼apickles/INGS/ for updated spectral templates. 4 Wood et al.
Figure 1. Calibrated interferometric V 2 values (points) and the R-band, limb-darkened fits to those measurements (line) for HD 4747 (left) and HD 19467 (right). The units of the x-axis correspond to the baseline length in unit of operational wavelength. For more details, see §2.
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