Evidence of a substellar companion around a very young T Tauri star

0.18 MB·

by  P. Viana Almeida

Astronomy&Astrophysicsmanuscriptno.As205a (cid:13)cESO2017
January11,2017
Evidence of a substellar companion around a very young T Tauri
⋆
star
P.VianaAlmeida1,3,J.F.Gameiro2,3 P.P.Petrov5,C.Melo4,N.C.Santos2,3,P.Figueira2,3,andS.H.P.Alencar1
1 UniversidadeFederaldeMinasGerais,31270-901Pampulha,BeloHorizonte-MG,Brasil
e-mail:[email protected]
2 DepartamentodeFísicaeAstronomia,FaculdadedeCiências,UniversidadedoPorto,RuaCampoAlegre,4169-007Porto,Portugal
7 3 InstitutodeAstrofísicaeCiênciasdoEspaço,UniversidadedoPorto,CAUP,RuadasEstrelas,4150-762Porto,Portugal
1 4 ESO,AlonsodeCordova3107,Casilla19001,Vitacura,Santiago,Chile
0 5 CrimeanAstrophysicalObservatory,RussianAcademyofSciences,298409,Nauchny,RepublicofCrimea
2
January11,2017
n
a
J
ABSTRACT

0
1 Wepresent resultsfromaNear Infrared multi-epochspectroscopic campaign todetect ayoung low-masscompanion toaT Tauri
star.AS205Aisalate-typedwarf(≈K5)of∼1M⊙thatbelongstoatriplesystem.Independentphotometricsurveysdiscoveredthat
]
AS205Ahastwodistinctperiods(P =6.78andP =24.78days)detectedinthelightcurvethatpersistoverseveralyears.PeriodP
R 1 2 1
seemstobelinkedtotheaxial-rotationofthestarandiscausedbythepresenceofcoolsurfacespots.PeriodP iscorrelatedwiththe
S 2
modulationinAS205Abrightness(V)andredcolor(V-R),consistentwithagravitatingobjectwithintheaccretiondisk.
.
h We here derive precise Near Infrared radial velocities to investigate the origin of period P which is predicted to correspond to a
2
p coolsourceinaKeplerianorbitwithasemi-majoraxisof∼0.17AUpositionedclosetotheinnerdiskradiusof0.14AU.Theradial
- velocityvariationsofAS205AwerefoundtohaveaperiodofP≈24.84daysandasemi-amplitudeof1.529kms−1.Thisresultclosely
o
resemblestheP periodinpastphotometricobservations(P≈24.78days).Theanalysisofthecross-correlationfunctionbisector
r 2
t hasshownnocorrelationwiththeradialvelocitymodulations,stronglysuggestingthattheperiodisnotcontrolledbystellarrotation.
s
a Additionalactivityindicatorsshouldhoweverbeexploredinfuturesurveys.Takingthisintoaccountwefoundthatthepresenceofa
[ substellarcompanionistheexplanationthatbestfitstheresults.WederivedanorbitalsolutionforAS205Aandfoundevidenceofa

m sini≃19.25M objectinanorbitwithmoderateeccentricityofe≃0.34.Ifconfirmedwithfutureobservations,preferablyusing
1 2 Jup
amultiwavelengthsurveyapproach, thiscompanion couldprovideinterestingconstraintsonbrowndwarfandplanetaryformation
v
models.
3
1
Keywords. infrared:spectroscopy–stars:pre-mainsequence–planetarysystems:stars–stars:individual–AS205A
7
2
0
.1. Introduction Johns-Krull 2007; Melo 2003), and to intense stellar activity
1
which causes RV variability of PMS objects. These effects in-
0
Tobestaddresstheplanetaryformationprocessweshouldstudy
7 troduce high uncertainties to the RV measurements as well as
pre-main-sequence objects (PMS) that are still enshrouded in
1 relevant modulations of spectral line profiles that can mimic
:theiroriginalenvironmentalconditions.Theagerangebetween the presence of substellar companions (e.g., Saar&Donahue
v∼1-5x106 yrsinPMSsisparticularlyinterestingsinceitisthe
i 1997; Hatzes 2002; Figueiraetal. 2010a). While spectral dis-
Xexpected moment when the physicalconditions in the disk en-
tortionsproducedbycoolspotsarewavelengthdependent(e.g.,
rableplanetesimalgrowthanddiskmigration. Vrbaetal. 1986; Huélamoetal. 1998; Figueiraetal. 2010a),
a
In the last few years, several young planet detection sur-
RV variations caused by the presence of a low-mass compan-
veys have been conducted in PMS stars using different tech-
ionaffectallwavelengthsequally.TodiagnosewhetherRVvari-
niques, such as direct imaging (e.g., Lafrenièreetal. 2010;
abilityiscompanion-orspot-induced,RVsandcross-correlation
Kraus&Ireland2012)orradialvelocity(RV)monitoring(e.g.,
functionbisector(BIS)measurementsarecorrelatedasaremea-
Martínetal. 2006; Setiawanetal. 2007; Crockettetal. 2012).
suresofotheractivityindices(e.g.,Figueiraetal.2013)inorder
TodeployRVsurveysonyounglow-massstars(whicharecon-
tosearchforactivityinducedtrends(seeSect4.2).
siderably faint, distant and affected by extinction) is, in most
In the Near Infrared(NIR), the effect of stellar spots is ex-
of cases, an arduous task. This is partly due to the presence
pectedtobeconsiderablyweakenedwhencomparedtotheopti-
of cool spots produced by strong stellar magnetic fields (e.g.,
caldomain(however,seeReinersetal.2013).Furthermore,ex-
tinction of PMS stars is also significantly reduced in the NIR.
⋆ BasedonobservationscollectedwiththeCRIRESspectrographat
Forthesereasons,RVstudiesonlow-massPMSstarscanbede-
theVLT/UT18.2-mAntuTelescope(ESOrunsID385.C-0706(A)and
093.C-0400(A))attheParanalObservatory,Chile. liveredwithanenhancedprecisionandahighersignal-to-noise
Articlenumber,page1of6
A&Aproofs:manuscriptno.As205a
ratio (S/N) in the NIR. Observations in the NIR also favor the high-resolutionspectrographmounted on the UT1 telescope at
detectionofsubstellarcompanionstoT Tauristars(TTS).TTS Paranal Observatory (ESO). AS 205A was visited eight times
areyoungsolaranalogs(∼1-10x106yrs)thathavespectralen- duringthisperiod.Spectrawerecollectedusingthe4096×512
ergydistribution(SED)emissionthatpeaksat1-2µm.Classical pixel Aladdin III detectors and a 0.2” slit which delivered a
TTSs (CTTS)sare a subclass thatfurtherdisplay observational R∼100000around1598.0nm (CRIRES setup 36). This partic-
evidenceofthepresenceofanaccretingcircumstellardisk(e.g., ularsettingwaschosenbecausewecouldbenefitfromtheCO
2
Bouvieretal. 2007). It is in the rich circumstellar environment telluric atmospheric lines as simultaneous wavelength calibra-
of CTTSs that protoplanets are thought to coalesce and grow tors (Huélamoetal. 2008; Figueiraetal. 2010c) to derive pre-
in size (e.g., Pollacketal. 1996). More recently, this idea has ciseRVs.Previousstudieshaveindeedshownthattelluriclines
beenexplicitlyreinforcedbythefindingsofDonatietal.(2016); aresteadyRVzero-pointtracers(Figueiraetal.2010b)thatdis-
Johns-Krulletal. (2016) and Mannetal. (2016), who reported play a long-term stability and, for this reason, can deliver RVs
robust evidence of the existence of Jupiter- and Neptune-sized withaprecisiondownto5-10ms−1.Finaldatawereacquiredin
objectsaroundyoungTTS(2Myrsand5-10Myrs,respectively). 2ABnoddingcycleswithanaverageS/N∼20perpixelandan
One of the the most promising CTTS for protoplanetary expectedfinalprecisionofaround30ms−1,sufficient,according
searches is AS 205A (≈V866 Sco). It is a young(∼ 0.5 Myrs) to our simulations,to spotan objectof a few to severalJupiter
late-type dwarf (≈K5) with mean V=12.4 mag that belongs to massesattheestimatedphotometricperiodof24.78days.
a hierarchical triple system. At an angular separation of 1.3′′ In addition to the AS 205A data, we also collected spec-
(≈180 AU at 140 pc) from AS 205A lies a very low-mass tra of telluric standardstars (featurelessearly-typeB stars) ob-
(K7/M0) spectroscopic binary (Ghezetal. 1993; Pratoetal. tainedwithsimilarairmassandinstrumentalsetuptoAS205A.
2003; Eisneretal. 2005). An extensive photometric survey by All observations were taken back-to-back with a RV standard
Artemenkoetal.(2010)revealedtwodistinctandstableperiods HD192310(K2V)ofsimilarspectraltypetoexaminethepreci-
(P =6.78andP =24.78days)inthepowerspectrumofthelight sionofourRVmeasurementsalongthetimespanofoursurvey.
1 2
variationsofAS205A.The24-dayphotometricperiodwasalso Reduction was performed using an optimized IRAF-based
confirmedby Percyetal. (2010). The value of P is typicalfor pipeline (see VianaAlmeidaetal. 2012, for more details). In
1
a rotationalperiodof a CTTS andis causedbythe presenceof summary, all spectra were nonlinearity-corrected, dark-current
cool surface spots. In this context, the anti-phase variations of subtracted, flat-fielded, sky-subtracted (through subtraction of
the(U-B)colorcanbeexplainedaschromosphericemissionre- opposing nodded spectra) and optimally extracted using the
lated to the cool spots. The phase diagram for P , on the other Horne (1986) algorithm. Owing to the blendingof telluric and
2
hand,showsmodulationinbrightnessandredcolors,whichin- stellar lines in the final spectra, we also performed telluric re-
dicatesthepresenceofacoolsource.SinceAS205Aisabout2 movalby dividing each extracted spectrum by the spectrum of
magbrighterthanAS205B(Herbig&Bell1988)intheVband telluricstandardsstars.
itwas concludedthattheobservedmodulatedsignal(V = 0.25 Wavelength calibration was performed using telluric ab-
mag) belongs to the primary or to its circumstellar environ- sorption lines (see e.g., Figueiraetal. 2010c; Baileyetal.
ment.ThemassofAS205A,asderivedfromitsstellartempera- 2012). Laboratory wavelength zero-points of each telluric
tureandbolometricluminosity(Andrewsetal.2009),andusing spectral line were collected from the HITRAN database
the recentlyreleasedpre-evolutionarytracksfromBaraffeetal. (Rothman&Gordon2009).TheRVsinthisstudywerederived
(2015), is expectedto be close to solar (∼ 0.9 M⊙). According using the Figueiraetal. (2010c) pipeline and its adapted ver-
to Artemenkoetal. (2010), the period P should correspondto sion to young stars developed by VianaAlmeidaetal. (2012).
2
the Keplerian location of an unknown close companion of AS Both versions of the pipeline are based on a two-dimensional
205A which perturbed the accretion disk with density waves. (2D) cross-correlation function (CCF) inspired by TODCOR
The orbit was predicted to have semimajor axis of ∼0.18 AU, (Mazeh&Zucker 1992). They were specifically built to derive
which is close to the inner disk radius R =0.14 AU, measured theRVofanobjectrelativetothezero-pointestablishedbythe
in
by IR-interferometry (Eisneretal. 2005; Andrewsetal. 2009). telluriclines.
Artemenkoetal. (2010) further interpret the light variations of To determine the barycentric RVs we cross-correlatedeach
P as the effect of scattering or extinctionin the disturbeddisk nodded spectrum against the spectra supplied by the NIR
2
nearthedustsublimationradius. PHOENIX synthetic database (Husseretal. 2013) and against
Inthisworkwederivedprecisemulti-epochNIRRVstoin- the spectra of HD192310 observed on the same date. Two-
vestigate the origin of period P and searched for the presence dimensionalCCFs werefittedusingGaussianfunctionprofiles.
2
ofalow-masscompanion.Wereporthereourresultsandbriefly Wavelength solutions, barycentric Julian dates and RVs were
discusstheimplicationsofthestudy. then adjusted to the center of mass of the solar system using
theBretagnon&Francou(1988)ephemerids.
3. Analysis
2. Observationalmethodanddatareduction
3.1.Rotationandstellarmodels
High-resolution observations of AS 205A were conducted in
the NIR, most specifically in the H-band where CTTS pho- To obtainthe best-fittingtemplate forcross-correlationand de-
tospheric information can be accessed. Spectroscopic observa- termine the projected equatorial velocity (v sin i) of the target
tions were carried out in good seeing conditions (∼0.8”) be- we used the effective temperature/SpT scales of Luhmanetal.
tweenApr22,2010,andMay1,2014,usingCRIRES,theNIR (1998)toselectasubsetofPHOENIXmodelscompatiblewith
Articlenumber,page2of6
P.VianaAlmeida etal.:EvidenceofasubstellarcompanionaroundaveryyoungTTauristar
the photospheric properties of AS 205A. From the PHOENIX
databasewecollectedmodelswitheffectivetemperatures(T )
eff
rangingfrom4100to4700K,surfacegravities(logg)between
3.5 and 4.0 (typical values found in TTS), and metallicities
([Fe/H])rangingfrom-0.5to0.5dex.Theabundancesofαele-
mentswereconsideredsolar.
WethenusedthegausstaskfromtheIRAFpackagetode-
1.02
1
0.98
m
uu 0.96
n
nti
o
d c 0.94
e
aliz
orm 0.92
N
0.9
0.88
0.86
15730.0 15740.0 15750.0 15760.0 15770.0 Fig.2.Upperpanel:RVmeasurementsofAS205Avs.orbitalphasein
Wavelength (Å) JulianDays withan orbital period of 24.84 days. Lower panel: Same
butusinganorbitalperiodof24.78days.Overlayedarethebest-fitting
Fig.1.Overplotofastellarsyntheticspectra(solidline)convolvedwith
Kepleriancurvesforeachperiod.Blackcrossesclosetothex-axisrep-
avsiniof11kms−1onaspectrumofAS205A(dots).Datashownwere
resentRVdatafromHD192310.
smoothed for clarity,continuum normalized andDoppler corrected to
therestwavelength.
lected CRIRES setup (containing ∼ 15 absorption lines). Final
gradetheresolutionofthe syntheticmodels(R∼500000)in or- RV uncertainties were calculated dividing the rms of each RV
der to match that of our observations. Using a stellar rotation measurementby the square root of the number of independent
broadening kernel, we applied v sin i, which ranged from 6 to exposures acquired in each date. The average error bar of the
20 kms−1, to the models creating a wider grid of models. We data is ∼85ms−1. The reason for this large value is essentially
finally used a routine to interpolate through the models to find duetotheincreasedlevelofblendingofstellarandtelluriclines
themodelthatminimizedthechi-square(χ2)statisticsandbest insomeofthespectra.Telluricremovalinthesecasesislesseffi-
adjusted the spectrum of AS 205A. Figure 1 shows one of the cientandisknowntodecreasetheS/Nofthefinalspectra,hence
best-fit models. The final stellar parameters of our best model thefinalprecisionofthemeasurements.
were Teff = 4300K, logg = 3.5cms−2, [Fe/H]= 0.0dex,and As mentioned before, in order to check for possible drifts
vsini=11kms−1.
Keepingthese parametersin mind, if we assume a TTS ra-
diusof3.7R (asprovidedinAndrewsetal.2010)andasystem
⊙ MJD vrad[kms−1] <σ>
inclinationof∼23.6◦(givenbyArtemenkoetal.2012)wecalcu-
2455308.8595 -1.518 0.059
latearotationalperiodofP∼6.81days,whichisincloseagree-
mentwithpreviousresultsforP fromArtemenkoetal.(2012). 2455403.6020 1.144 0.073
1
Curiously, the v sin i found by iteratively fitting the models is 2455455.5253 -0.170 0.212
also close to the estimates used in Artemenko’s publication. It 2455463.5396 -0.714 0.066
can be seen that the rotational period is clearly not of the or- 2455467.4938 0.004 0.070
der of the period P of 24.78 days encountered in the studies 2455470.5179 0.628 0.064
2
ofArtemenkoetal.(2010)andPercyetal.(2010).Theapparent 2456767.9046 1.510 0.062
disparitybetweenthetwoperiodsmayseemtoreinforcetheidea 2456778.7772 -1.046 0.070
that P is of companion origin and not rotationally driven, but
2
a possible relation between P and 4xP cannot be completely
1 2 Table1.Barycentricjuliandatesofeachnoddedimage,derivedradial
ruledoutandshouldbeinvestigatedfurtherinthefuturewitha velocitiesandfinaldispersionforeachdateAS205Awasobserved.
largerdataset.
inthelong-termRV measurementsobtainedusingourmethod-
3.2.Radialvelocities
ology,we retrievedRVs of a controlstar (HD192310)overthe
The RV measurementsfor each date are shown in Table 1 and time span of the study. In order to keep the same intrumental
plotted in Fig. 2. They are the result of the correlation of the profileandreproducethesameobservationconditionsasinour
spectralinformationsampledinDetectors1,2,and4ofthese- scientific target, spectra of HD192310 were observed back-to-
Articlenumber,page3of6
A&Aproofs:manuscriptno.As205a
back with AS 205A. Pepeetal. (2011), using high-resolution
spectroscopy,publishedtheKepleriansolutionsoftwoorbiting 400
planetsaroundHD192310.ThedispersionoftheirRVmeasure-
200
ments, however, had a rms of only 2.6 ms−1 over a 6.5-year
interval. Our own study detected variations in the HD192310 0
RV profile with a standard deviation of ≤11 ms−1 over 4 years
-200
ofobservations.Althoughitwasbeyondourdetectionlimitwe
triedneverthelesstoadjusttheKepleriansolutionsofPepeetal.
-400
(2011)tothevariationsobserved.Thelackofconsistentfitsim-
-2 -1 0 1 2
plied that the dispersion in our RV data was instead associated
RV [km/s]
withtheinternaluncertaintyofourmethod.
For the sake of clarity, we plot the RV measurements of Fig.3.BISplottedagainstRVsofAS205A.Aswecanseenocorrela-
HD192310along with those of AS 205A in Fig. 2. As we can tionwasdetected.
seeinthisfigure,theRVvariationsofHD192310overtheentire
studyarecomparativelysmall,providingsolidevidencethatob-
and the period that best-fitted our RV data. The overall rms
servationaluncertaintiesarenotattheoriginoftheRVvariations and the reduced chi-quare (χ2 ) of the solution using a period
observed in the classical T Tauri stars. The RVs of HD192310 of 24.78 days were of 421 mresd−1 and 66.1, respectively. Con-
seem therefore to confirm the stability and precision of the re-
versely, when minimizing the rms of the fit, after some itera-
sultsobtainedforAS205A.
tions,we obtaina periodof24.84dayswith a muchlowerrms
of 73.4 ms−1 and a χ2 of 1.07. This χ2 of the P∼24.84 day
red red
4. Discussion solution found for the RV data suggests a good fit to the data.
Therefore,itseemsthatthisperiodbetterexplainstheresults.In
4.1.Preliminaryorbitalparameters
Table2wedisplaytheorbitalelementsforthe24.84dayperiod
Using the RVs from Table 1 we found preliminary Keplerian finalfit.Theuncertaintiesdepictedareconfidenceintervalspro-
orbitalsolutionsfor the suggestedcompanion.For these calcu- videdbythe bootstrapmethod.We resampledthe originaldata
lationsweconsideredaprimarymassasestimatedfromthere- set100000timesandfittedaKepleriansolutiontoeachresam-
cently released pre-evolutionary tracks of Baraffeetal. (2015) pledsettherebyproducingdistributionsforeachorbitalparam-
which presentsignificantimprovementsoveroldertrackscom- eter.Wenotethatthedegreesoffreedomoftheorbitalsolution
monlyemployedinpreviousstudiesonAS205A,suchasthose almost equals the number of data points. This implies that we
fromSiessetal.(2000).WeusedtheSystemiccode2tofitaKe- mustbecautiouswheninterpretingoftheresults.
pleriansolutiontotheRVmeasurements.Tofindthebestorbital
parameters, first we fixed the Period at 24.78 days and the ec-
4.2.Stellaractivity
centricity e at null value while letting all the other parameters
converge. To determine whether variability was driven by surface cool
Assoonasweobtainedpreliminaryapproximationsforthe spots, we probed the correlation of the BIS and the RVs in
the CCFs obtained in each date. A clear correlation between
these two quantitiesis expectedwhen CCF profiles are subject
Orbitalparameters Value
to asymmetries caused by stellar spots (Quelozetal. 2001).
P (days) 24.84±0.03
orb Since young active stars are likely to have BIS that vary with
m (M ) 0.9
1 ⊙ time, their study can provide useful hints on the activity of
m2sini(MJup) 19.25±1.96 AS 205A at the time of the observations. Furthermore, high
K (kms−1) 1.529±0.16 stellar v sin i (11kms−1 in the AS 205A case) are expected to
e 0.34±0.06 favorthesensitivenessoftheBISmethodasanactivity-induced
indicator (see e.g., Santosetal. 2003). We note, however, that
ω(deg) 94.14±7.67
in the wavelength interval of our observations this correlation
Semi-majoraxis(AU) 0.162±0.04
is expected to decrease by a factor of ∼ 2-3 (see, e.g., models
V -10.25±0.07
sys from Desortetal. 2007; Reinersetal. 2010; Ma&Ge 2012).
χ2 1.07 We show in Fig. 3 the BIS plotted against the RVs obtained
red
O-C(ms−1) 73.4 for AS 205A. Despite the small sample size we performed a
preliminary examination of the correlation between RV and
Table2.Orbitalparametersforthesubstellarcompanion. BIS in our data set using different statistical diagnostics. We
used a Bayesian analysis tool from Figueiraetal. (2016) to
compute Pearson’s correlation coefficient ε and Spearman’s
systemicvelocityV ,longitudeofperiastronωandm sini,we
sys 2 rankcorrelationcoefficientρandassociatedp-values(formore
fine-tuned the results by letting all the orbital parameters con-
detailsonthemethodseetheabovepublication).ThePearson’s
verge simultaneously. In Fig. 2 we present the best Keplerian
coefficient,whichmeasuresthestrengthofthelinearassociation
curvesfor photometricperiod P from Artemenkoetal. (2010)
2 betweenthetwovariables,wasfoundtobe-0.171witha0.686
2 www.oklo.org two-sided p-value and the Spearman’s rank coefficient, which
Articlenumber,page4of6
P.VianaAlmeida etal.:EvidenceofasubstellarcompanionaroundaveryyoungTTauristar
characterizes their monotonic relationship, was found to be (Cushingetal. 2006; Sarroetal. 2013), its SED could thus be
approximately -0.071 with a 0.867 two-sided p-value. Both masked by the strong circumstellar IR emission of AS 205A
results seem to suggest that there is no statistical correlation (see,e.g.,Andrewsetal.2010).Ideally,newdedicatedspectro-
betweenthedistributionsofthetwoquantities.Theseresultsled scopic observations,both high-resolutionand high S/N, should
ustoconcludethat,atleastintheNIR,thederivedRVsarenot bepreparedinthethenearfuturewiththeaimofidentifyingno-
correlated with BIS, hence, most probably they are not driven tablespectralfeaturesofbrowndwarfsorverylate-typeMstars
bystellaractivity. thatcouldbeimprintedintheAS205Aspectrum.Giventhevery
Intheopticaldomain,however,pastRVmeasurementsmay distinctnatureoflate-typeMstarsandbrowndwarfs(see,e.g.,
imply the influence of cool spots in the shape of the CCFs. McLeanetal.2007;Riceetal.2010),thisstrategycouldleadto
Melo (2003) derived six optical RVs (<σ>∼450ms−1) for AS asuccessfulidentificationofthespectraltypeandmassregime
205A using the CORALIE spectograph and reported clear RV ofthesubstellarcompanion.
variationsontheorderof4.34kms−1.Strikingly,thisvariability Recent sensitive high-resolution mm observations of AS
is comparablein orderofmagnitudeto ourownRV variations. 205AwiththeALMAfacility(Salyketal.2014)revealedanin-
Wenote,however,thatoneofitsAS205ACCFs(showninFig. triguingextendedasymmetricprofileofthe12CO(2-1)emission.
5 ofMelo2003) displayedan abnormaldeformationwhichthe Despitetheirbestefforts,theauthorscouldnotexplainthisemis-
authorinterpretedasapossiblespectroscopicstellarcompanion. sionmerelyonthebasisofaKepleriangas-diskmodelsand/or
WesuspectthatthisCCFdeformationmayhavebeencaused,in stellarwindparametrization.Indeed,whencomparedwithtypi-
part,bystellaractivityeventhoughvisualinspectionofitsCCF caloutflowsproducedinprotostars(e.g.,Jørgensenetal.2007),
seemstoruleoutthisexplanation. the12COemissionofAS205Apresentsquitedistinctandunique
Future studies should consider further testing of the effects characteristics (see, e.g., Salyketal. 2014). While some of the
ofstellaractivityand,morespecifically,ofrotationalharmonics emission can be associated with tidal stripping from the close
intheRVmeasurements.HarmonicsareexpectedtoaffectRVs binaryAS205Batjust1.3′′,itisunlikelythatthisphenomenon
whenrotationalmodulationoflightbystellarspotsoccurs(see, alone could explain the observations. Arguably, the discrepan-
e.g., Boisseetal. 2011). We made a preliminary test of the cies observed may suggestthe unaccountedpresence of an ad-
presence of such rotational harmonics in our data (using the ditionalcompanionto AS 205A.This possibilityshouldbe ex-
rotational period calculated in Sect. 3.1.) by fitting sinusoidal ploredinthefutureiffollow-upstudiesconfirmtheexistenceof
functions to the residuals of the Keplerian fits shown in Fig 2. aclosesubstellarobject.
We were unable, however, to find any coherent signs of the
first three rotational harmonics (P /2, P /3, P /4) which
rot rot rot
could be imprinted in the RV jittering amplitudes. This result 5. Conclusion
and the goodness of the fit of the adjusted Keplerian solution
It is interesting to note the close agreement between the esti-
using P = 24.84 days increases our confidence that the results
matedphotometricperiodP (∼24.78days)ofArtemenkoetal.
presented do not depend on stellar spot modulation. But to 2
(2010) and the Keplerian period obtained with our NIR
further explore these effects we need a better sampling of the
spectroscopy (P∼24.84 days). Period P , to the best of our
RV curve with a higher number of data points. This kind of 2
knowledge, does not seem to be a rotational modulation pro-
studywouldcertainlyimprovetheorbitalcharaterizationofthe
duced by spots in the stellar surface. More RV measurements,
reportedsubstellarcompanion.
however, are necessary in order to confirm these results. Even
though unacounted phenomena such as stellar activity and/ or
accretion (e.g., Bouvieretal. 2007) could have influenced the
4.3.NewperspectiveontheAS205Asystem spectralprofile,thehigh-precisionattainedinthisstudy(below
70ms−1 inmostofthecases)andthelackofcorrelationofBIS
Following the results presented here and the results from and RVs variations provide strong support for our companion
Artemenkoetal.(2010),wesuggesttheexistenceofalow-mass interpretation. The substellar companion hypothesis is, to the
companiontoAS205A.Weproposethatobservationalevidence best of our knowledge, the most robust explanation for the
of this low-masscompanionin previouscampaignscouldhave resultsobtained.
beenhinderedbytheprolificIRemissionobservedinAS205A. Theconfirmationofasubstellarcompanionattheborderof
Assuming that the orbit of the planet is aligned with the inner gap of the protoplanetary disk at such an early time
the stellar rotation and that the inclination of the system is (∼0.5- 1 Myrs) couldprovideinterestingconstraintsonbrown
between ∼25 ◦ (Andrewsetal. 2010; Artemenkoetal. 2012; dwarfandplanetformationtheoriesandontheprocessinwhich
Pontoppidanetal.2011)and∼15◦,asthestudyof(Salyketal. planets migrate within the circumstellar disk. The AS 205A
2014) suggests, then the absolute mass range of the proposed systemremainsanimportanttargettoengagenewobservations
substellar companion would be between ∼45.6 and 74.3 M . inthenearfuture.
Jup
This mass range suggests an upper and lower limit in T
eff
of around ∼2200 K and 1500K (see, e.g., Kirkpatrick 2005;
Acknowledgements. PVAacknowledgesthesupportfromComissãoNacionalde
Riceetal. 2010), respectively. In this temperature range the Pesquisa(CNPq)andtheBrazilianNationalCouncilofScientificandTechno-
object would fall into the temperature-mass domain of ultra- logic Development, in the form of a grant PDJ with reference 160111/2012-
9. This work was supported by Fundação para a Ciência e a Tecnologia
cool dwarfs or very late-type M stars. Since the peak emission
(FCT) within projects reference PTDC/FIS-AST/1526/2014 (POCI-01-0145-
of such objects is located in the NIR range, close to 1.0 µm FEDER-016886) and UID/FIS/04434/2013 (POCI-01-0145-FEDER-007672).
Articlenumber,page5of6
A&Aproofs:manuscriptno.As205a
PF and NCS acknowledge support by Fundação para a Ciência e a Tecnolo- Reiners,A.,Shulyak,D.,Anglada-Escudé,G.,etal.2013,A&A,552,A103
gia (FCT) through Investigador FCT contracts of reference IF/01037/2013 Rice,E.L.,Barman,T.,Mclean,I.S.,Prato,L.,&Kirkpatrick,J.D.2010,ApJS,
and IF/00169/2012, respectively, and POPH/FSE (EC) by FEDER funding 186,63
through the program “Programa Operacional de Factores de Competitividade Rothman, L. S. & Gordon, I. E. 2009, in 64th International Symposium On
- COMPETE”. PF also acknowledges support from Fundação para a Ciên-
MolecularSpectroscopy,1
cia e a Tecnologia (FCT) in the form of an exploratory project of reference
Saar,S.H.&Donahue,R.A.1997,ApJ,485,319
IF/01037/2013CP1191/CT0001.
Salyk,C.,Pontoppidan,K.,Corder,S.,etal.2014,ApJ,792,68
Santos,N.C.,Udry,S.,Mayor,M.,etal.2003,A&A,406,373
Sarro,L.M.,Berihuete,A.,Carrión,C.,etal.2013,A&A,550,A44
References Setiawan,J.,Weise,P.,Henning,T.,etal.2007,ApJ,660,L145
Siess,L.,Dufour,E.,&Forestini,M.2000,A&A,358,593
Andrews,S.M.,Wilner,D.J.,Hughes,A.M.,Qi,C.,&Dullemond,C.P.2009, VianaAlmeida,P.,Melo,C.,Santos,N.C.,etal.2012,A&A,539,A62
ApJ,700,1502 Vrba,F.J.,Rydgren,A.E.,Chugainov,P.F.,Shakovskaia,N.I.,&Zak,D.S.
Andrews,S.M.,Wilner,D.J.,Hughes,A.M.,Qi,C.,&Dullemond,C.P.2010, 1986,ApJ,306,199
ApJ,723,1241
Artemenko,S.A.,Grankin,K.N.,&Petrov,P.P.2010,AstronomyReports,54,
163
Artemenko,S.A.,Grankin,K.N.,&Petrov,P.P.2012,AstronomyLetters,38,
783
Bailey,III,J.I.,White,R.J.,Blake,C.H.,etal.2012,ApJ,749,16
Baraffe,I.,Homeier,D.,Allard,F.,&Chabrier,G.2015,A&A,577,A42
Boisse,I.,Bouchy,F.,Hébrard,G.,etal.2011,A&A,528,A4
Bouvier,J.,Alencar,S.H.P.,Harries,T.J.,Johns-Krull,C.M.,&Romanova,
M.M.2007,ProtostarsandPlanetsV,479
Bretagnon,P.&Francou,G.1988,A&A,202,309
Crockett,C.J.,Mahmud,N.I.,Prato,L.,etal.2012,ApJ,761,164
Cushing,M.C.,Roellig,T.L.,Marley,M.S.,etal.2006,ApJ,648,614
Desort,M.,Lagrange,A.-M.,Galland,F.,Udry,S.,&Mayor,M.2007,A&A,
473,983
Donati,J.F.,Moutou,C.,Malo,L.,etal.2016,Nature,534,662
Eisner,J.A.,Hillenbrand,L.A.,White,R.J.,Akeson,R.L.,&Sargent,A.I.
2005,ApJ,623,952
Figueira,P.,Faria,J.P.,Adibekyan,V.Z.,Oshagh,M.,&Santos,N.C.2016,
OriginsofLifeandEvolutionoftheBiosphere
Figueira,P.,Marmier,M.,Bonfils,X.,etal.2010a,A&A,513,L8
Figueira,P.,Pepe,F.,Lovis,C.,&Mayor,M.2010b,A&A,515,A106
Figueira,P.,Pepe,F.,Melo,C.H.F.,etal.2010c,A&A,511,A55
Figueira,P.,Santos,N.C.,Pepe,F.,Lovis,C.,&Nardetto,N.2013,A&A,557,
A93
Ghez,A.M.,Neugebauer,G.,&Matthews,K.1993,AJ,106,2005
Hatzes,A.P.2002,AstronomischeNachrichten,323,392
Herbig,G.H.&Bell,K.R.1988,ThirdCatalogofEmission-LineStarsofthe
OrionPopulation:3:1988
Horne,K.1986,PASP,98,609
Huélamo,N.,Figueira,P.,Bonfils,X.,etal.2008,A&A,489,L9
Huélamo, N., Gómez de Castro, A. I., & Franqueira, M. 1998, in ESA Spe-
cial Publication, Vol. 413, Ultraviolet Astrophysics Beyond the IUE Final
Archive,ed.W.Wamsteker,R.GonzalezRiestra,&B.Harris,121
Husser,T.-O.,Wende-vonBerg,S.,Dreizler,S.,etal.2013,A&A,553,A6
Johns-Krull,C.M.2007,ApJ,664,975
Johns-Krull,C.M.,McLane,J.N.,Prato,L.,etal.2016,ApJ,826,206
Jørgensen,J.K.,Bourke,T.L.,Myers,P.C.,etal.2007,ApJ,659,479
Kirkpatrick,J.D.2005,ARA&A,43,195
Kraus,A.L.&Ireland,M.J.2012,ApJ,745,5
Lafrenière,D.,Jayawardhana,R.,&vanKerkwijk,M.H.2010,ApJ,719,497
Luhman,K.L.,Rieke,G.H.,Lada,C.J.,&Lada,E.A.1998,ApJ,508,347
Ma,B.&Ge,J.2012,ApJ,750,172
Mann,A.W.,Newton,E.R.,Rizzuto,A.C.,etal.2016,AJ,152,61
Martín,E.L.,Guenther,E.,ZapateroOsorio,M.R.,Bouy,H.,&Wainscoat,R.
2006,ApJ,644,L75
Mazeh,T.&Zucker,S.1992,inAstronomicalSocietyofthePacificConference
Series,Vol.32,IAUColloq.135:ComplementaryApproachestoDoubleand
MultipleStarResearch,ed.H.A.McAlister&W.I.Hartkopf,164–+
McLean,I.S.,Prato,L.,McGovern,M.R.,etal.2007,ApJ,658,1217
Melo,C.H.F.2003,A&A,410,269
Pepe,F.,Lovis,C.,Ségransan,D.,etal.2011,A&A,534,A58
Percy,J.R.,Grynko,S.,Seneviratne,R.,&Herbst,W.2010,PASP,122,753
Pollack,J.B.,Hubickyj,O.,Bodenheimer,P.,etal.1996,Icarus,124,62
Pontoppidan,K.M.,Blake,G.A.,&Smette,A.2011,ApJ,733,84
Prato,L.,Greene,T.P.,&Simon,M.2003,ApJ,584,853
Queloz,D.,Henry,G.W.,Sivan,J.P.,etal.2001,A&A,379,279
Reiners,A.,Bean,J.L.,Huber,K.F.,etal.2010,ApJ,710,432
Articlenumber,page6of6