First light of the VLT planet finder SPHERE

24 Pages·2016·4.62 MB·English

A&A587,A56(2016) Astronomy
DOI:10.1051/0004-6361/201526594 &
(cid:13)c ESO2016 Astrophysics
First light of the VLT planet finder SPHERE
II. The physical properties and the architecture of the young systems
PZ Telescopii and HD 1160 revisited(cid:63)
A.-L.Maire1,M.Bonnefoy2,3,C.Ginski4,A.Vigan5,6,S.Messina7,D.Mesa1,R.Galicher8,R.Gratton1,S.Desidera1,
T.G.Kopytova9,10,M.Millward11,C.Thalmann12,R.U.Claudi1,D.Ehrenreich13,A.Zurlo5,1,14,15,G.Chauvin2,3,
J.Antichi16,A.Baruffolo1,A.Bazzon12,J.-L.Beuzit2,3,P.Blanchard5,A.Boccaletti8,J.deBoer6,M.Carle5,
E.Cascone17,A.Costille5,V.DeCaprio17,A.Delboulbé2,3,K.Dohlen5,C.Dominik18,M.Feldt9,T.Fusco19,5,
J.H.Girard6,2,3,E.Giro1,D.Gisler20,L.Gluck2,3,C.Gry5,T.Henning9,N.Hubin21,E.Hugot5,M.Jaquet5,
M.Kasper21,2,3,A.-M.Lagrange2,3,M.Langlois22,5,D.LeMignant5,M.Llored5,F.Madec5,P.Martinez23,
D.Mawet24,J.Milli6,2,3,O.Möller-Nilsson9,D.Mouillet2,3,T.Moulin2,3,C.Moutou5,25,A.Origné5,A.Pavlov9,
C.Petit19,J.Pragt26,P.Puget2,3,J.Ramos9,S.Rochat2,3,R.Roelfsema26,B.Salasnich1,J.-F.Sauvage19,5,
H.M.Schmid12,M.Turatto1,S.Udry13,F.Vakili23,Z.Wahhaj6,5,L.Weber13,andF.Wildi13
(Affiliationscanbefoundafterthereferences)
Received25May2015/Accepted13October2015
ABSTRACT
Context.TheyoungsystemsPZTelandHD1160,hostingknownlow-masscompanions,wereobservedduringthecommissioningofthenew
planetfinderoftheVeryLargeTelescope(VLT)SPHEREwithseveralimagingandspectroscopicmodes.
Aims.Weaimtorefinethephysicalpropertiesandarchitectureofbothsystems.
Methods.WeuseSPHEREcommissioningdataanddedicatedRapidEyeMount(REM)observations,aswellasliteratureandunpublisheddata
fromVLT/SINFONI,VLT/NaCo,Gemini/NICI,andKeck/NIRC2.
Results.Wederivenewphotometryandconfirmtheshort-term(P=0.94d)photometricvariabilityofthestarPZTelAwithvaluesof0.14and
0.06magatopticalandnear-infraredwavelengths,respectively.Wenotefromthecomparisontoliteraturedataspanning38yrthatthestaralsoex-
hibitsalong-termvariabilitytrendwithabrighteningof∼0.25mag.The0.63−3.8µmspectralenergydistributionofPZTelB(separation∼25AU)
allowsustoreviseitsphysicalcharacteristics:spectraltypeM7±1,Teff=2700±100K,log(g)<4.5dex,luminositylog(L/L(cid:12))=−2.51±0.10dex,
andmass38−72M from“hot-start”evolutionarymodelscombiningtherangesofthetemperatureandluminosityestimates.The1−3.8µmSED
J
[oMfH/HD]=11−600.5B−(0∼.085deaxu,)lsuumgigneosstistyalmoga(sLsi/vLeb)r=ow−n2.d8w1±arf0.o1r0adleoxw,-amndasmsasstasr3w9−it1h6s6peMctr.aTlhtyeppehMys6ic.a0l−+01p..50ro,pTeeffrti=es3d0e0r0iv±ed10f0orKH,Dsu1b1s6o0larCm(∼et5a6ll0icaiuty)
(cid:12) J
fromK L(cid:48)-bandphotometryareconsistentwiththediscoverystudy.TheorbitalstudyofPZTelBconfirmsitsdecelerationandthehigheccen-
s
tricityofitsorbit(e > 0.66).Foreccentricitiesbelow0.9,theinclination,longitudeoftheascendingnode,andtimeofperiastronpassageare
wellconstrained.Inparticular,bothstarandcompanioninclinationsarecompatiblewithasystemseenedge-on.Basedon“hot-start”evolutionary
models,werejectotherbrowndwarfcandidatesoutside0.25(cid:48)(cid:48)forbothsystems,andgiantplanetcompanionsoutside0.5(cid:48)(cid:48)thataremoremassive
than3M forthePZTelsystem.WealsoshowthatK1−K2colorcanbeusedalongwithYJHlow-resolutionspectratoidentifyyoungL-type
J
companions,providedhighphotometricaccuracy(≤0.05mag)isachieved.
Conclusions.SPHEREopensnewhorizonsinthestudyofyoungbrowndwarfsandgiantexoplanetsusingdirectimagingthankstohigh-contrast
imagingcapabilitiesatoptical(0.5−0.9µm)andnear-infrared(0.95−2.3µm)wavelengths,aswellashighsignal-to-noisespectroscopyinthe
near-infrareddomain(0.95−2.3µm)fromlowresolutions(R∼30−50)tomediumresolutions(R∼350).
Keywords.browndwarfs–stars:individual:PZTelescopii–stars:individual:HD1160–techniques:highangularresolution–
techniques:imageprocessing–techniques:spectroscopic
1. Introduction Several formation mechanisms have been proposed to account
for the diversity of these objects: core accretion (Pollack et al.
Direct imaging of young ((cid:46)300 Myr) stars has revealed a pop-
1996),gravitationalinstability(Boss1997),andbinary-likefor-
ulation of giant planet and brown dwarf companions at wide
mation. Direct imaging surveys attempted to place first con-
(>5 au) separations (e.g., Chauvin et al. 2005a,b; Itoh et al. straints on the occurrence of giant planets (∼10−20%) and/or
2005; Luhman et al. 2006, 2007; Marois et al. 2008, 2010b;
brown dwarfs (∼1−3%) and their formation mechanisms for
Thalmann et al. 2009; Lagrange et al. 2010; Biller et al. 2010;
separations beyond ∼10−20 au (e.g., Lafrenière et al. 2007;
Mugraueretal.2010;Lafrenièreetal.2010;Carsonetal.2013;
Chauvin et al. 2010, 2015; Ehrenreich et al. 2010; Vigan et al.
Kuzuharaetal.2013;Rameauetal.2013a;Baileyetal.2014).
2012b;Rameauetal.2013b;Wahhajetal.2013;Nielsenetal.
(cid:63) Based on data collected at the European Southern Observatory, 2013; Biller et al. 2013; Brandt et al. 2014). A new genera-
Chile,duringthecommissioningoftheSPHEREinstrumentandESO tion of high-contrast imaging instruments designed to search
programs085.C-0277,087.C-0109,087.C-0535,and060.A-9026. for and characterize giant exoplanets at separations as close as
ArticlepublishedbyEDPSciences A56,page1of24
A&A587,A56(2016)
the snow line (∼5 au), such as the Spectro-Polarimetric High- (Nielsen et al. 2012) discovered as part of the Gemini NICI
contrastExoplanetREsearch(SPHERE,Beuzitetal.2008)and Planet-Finding Campaign (Liu et al. 2010b). Nielsen et al.
the Gemini Planet Imager (GPI, Macintosh et al. 2014), have (2012)showthatbothcompanionsaregravitationallyboundus-
recentlystartedoperations. ing archival data from VLT/NaCo and VLT/ISAAC spanning
WepresentinthispaperSPHEREfirstlightobservationsof almostadecade(2002−2011)andobtainedforpurposesofpho-
the young systems PZ Tel (Biller et al. 2010; Mugrauer et al. tometric calibration. They also present Gemini/NICI photome-
2010) and HD 1160 (Nielsen et al. 2012). This includes near- try in the J, H, and K bands and Keck/NIRC2 photometry in
s
infrared images and integral field spectroscopy at low resolu- the L(cid:48) and M bandsforbothcompanionsandNIRIRTF/SpeX
s
tion (R ∼ 30) for the brown dwarf companions PZ Tel B and spectraforthefarthestcompanion.UsingtheNICIphotometry,
HD1160B,aswellasopticalimagesandnear-infraredlong-slit theseauthorsfindthatbothcompanionshavecolorsatoddswith
spectroscopy at low and medium resolutions (R ∼ 50 and 350) field M dwarfs but consistent with colors of giant M stars, al-
forPZTelB. thoughthecompanionscannotbegiantstarsbasedontheirab-
PZ Tel is a G9IV star (Torres et al. 2006) member of the solute magnitude. Nielsen et al. (2012) are not able to explain
young (21±4 Myr, Binks & Jeffries 2014) stellar association this discrepancy, but note that an error in the calibration of the
β Pictoris (Zuckerman et al. 2001; Torres et al. 2008) and lo- NICIphotometrycouldaccountforit.ForHD1160C,thespec-
cated at a distance d=51.5±2.6 pc (van Leeuwen 2007). The trumindicatesalow-massstarofspectraltypeM3.5±0.5and
hoststarwasfirstknowntobesingle(Balona1987;Innisetal. massM =0.22+0.03solarmasses(M ).ForHD1160B,thepho-
−0.04 (cid:12)
1988)andtoshowactivity-relatedtostarspotswitharotational tometrysuggestsabrowndwarfofspectraltypeL0±2andmass
period of 0.94486 d (Coates et al. 1980) and lightcurve ampli- M = 33+12 M .Bonnefoy etal.(2014b) arguethatHD 1160B
−9 J
tudevariationsupto∆V=0.22mag(Innisetal.1990).Alate- may have formed according to the gravitational instability sce-
M brown dwarf companion to PZ Tel was discovered indepen- nario(Boss1997)inamassivedisk(∼20%ofthehoststarmass).
dently by two teams (Biller et al. 2010; Mugrauer et al. 2010). We describe the observations and the data reduction in
Using Gemini/NICI photometry in the J, H, and K bands, Sects. 2 and 3. Then we present new analyses of the physical
s
Billeretal.(2010)estimateaspectraltypeofM5−M9,aneffec- propertiesofPZTelA(Sect.4),thespectralenergydistribution
tive temperature of Teff=2700±84 K, and a surface gravity of (SED) of the companions for both systems (Sect. 5), the orbit
log(g)=4.20±0.11dex.Mugraueretal.(2010)derivephotom- of PZ Tel B (Sect. 6), as well as further constraints on putative
etryinthesamebandsfromVLT/NaCodataandfindaspectral additionalcompanionsineachsystem(Sect.7).
type and an effective temperature consistent with the results of
Billeretal.(2010):M6−M8and2500−2700K,respectively.
Astrometric follow-up of the companion shows significant 2. Observations
orbital motion (separation increase of ∼35 mas/yr) and sug-
gests that its orbit is highly eccentric (>0.6, Biller et al. 2010; The SPHERE planet-finder instrument installed at the VLT
Mugraueretal.2012;Ginskietal.2014).Mugraueretal.(2012) (Beuzitetal.2008)isahighlyspecializedinstrumentdedicated
detectadecelerationofthecompanionusingNaCodatatakenin tohigh-contrastimagingandthespectroscopyofyounggiantex-
2007and2009,suggestingthatthecompaniongetsclosertoits oplanet.ItwasbuiltbyalargeconsortiumofEuropeaninstitutes
apoastron. Ginski et al. (2014) note a similar trend using 2012 andisbasedontheSAXOsystem(SphereAdaptiveOpticsfor
NaCo data, although at low significance (∼2σ), and advocate eXoplanetObservation,Fuscoetal.2006,2014;Petitetal.2014;
forfurtherastrometricmonitoring.Near-infrared(NIR)spectro- Sauvage et al. 2014), which includes a 41×41-actuator wave-
scopic observations with VLT/SINFONI in the H + K bands front control, pupil stabilization, differential tip tilt control and
at medium resolution (R=1500) of the host star and the com- stresspolishedtoricmirrors(Hugotetal.2012)forbeamtrans-
panionindicatespectraltypesofG6.5andM6−L0,respectively portation to the coronagraphs and science subsystems. Several
(Schmidt et al. 2014). Schmidt et al. (2014) also derive for the coronagraphsforstellardiffractionsuppressionareprovided,in-
companionTeff = 2500+−113185 K,log(g)=3.5+−00..5310 dex,ametallic- cludingapodizedpupilLyotcoronagraphs(Soummer2005)and
ityenhancement[M/H]=0.30+0.00dex,aradiusR=2.42+0.28R achromatic four-quadrant phase masks (Boccaletti et al. 2008).
(Jupiter radii), and a range −f0o.3r0the mass M=3.2−24−.04.34MJ The instrument is equipped with three science channels: an in-
J
frareddual-bandimagerandspectrograph(IRDIS,Dohlenetal.
(Jupitermasses)withamostlikelyvalueof21M .Schmidtetal.
J
2008), an integral field spectrometer (IFS, Claudi et al. 2008),
(2014)stresstheneedforspectraofPZTelBwithbetterquality
andarapid-switchingimagingpolarimeter(ZIMPOL,Thalmann
and wider coverage to further constrain its physical properties.
et al. 2008). We refer to Beuzit et al. (in prep.) for detailed de-
Using HARPS, Lagrange et al. (2013) measure for PZ Tel A a
projected rotational velocity v sin(i)=80 kms−1, but the short scriptionsofthesubsystemsandobservingmodes.
We observed PZ Tel and HD 1160 during six nights of the
timebaselineandthesmallamplitudeoftheradialvelocityvari-
SPHERE commissioning runs (Table 1). The observations of
ationspreventatrendduetoPZTelB.Rebulletal.(2008)find
anexcessat70µmusingSpitzer/MIPSbutnotat24µm.Rebull PZ Tel include all the three science subsystems: IRDIS in both
etal.(2008)attributethe70-µmexcesstoalow-mass(∼0.3lunar dual-bandimagingmode(Viganetal.2010)andlong-slitspec-
masses)andcold(Teff ∼ 41K)debrisdiskspanningarangeof troscopy mode (Vigan et al. 2008), IFS, and ZIMPOL in dual-
separations35−165au.However,thishypothesisisrejectedby bandimagingmode.HD1160wasobservedwithIRDISindual-
bandimagingmodeandIFSinparallel.
Billeretal.(2013),becauseofalikelywrongstaridentification
in the Spitzer data, and Riviere-Marichalar et al. (2014), who
findnoIRexcesseswithHerschel/PACSat70,100,and160µm.
2.1. SimultaneousIRDISandIFSobservations
HD 1160 is a moderately young (50+50 Myr) A0V star
−40
located at a distance d=108.5±5.0 pc (van Leeuwen 2007), The observations with IRDIS in dual-band imaging mode and
whichisnotclassifiedasamemberofanyoftheknownyoung IFS are simultaneous (IRDIFS and IRDIFS_EXT modes in
stellar associations (Nielsen et al. 2012). This star hosts two Table 1). In the IRDIFS mode, IRDIS is operated in the filter
low-masscompanionsatprojectedseparations∼85and∼560au pair H23 (Table 2) and IFS in the bands YJ (0.95−1.35 µm,
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A.-L.Maireetal.:PhysicalpropertiesandarchitectureofthePZTelandHD1160systemsrevisitedwithVLT/SPHERE
Table1.LogoftheSPHEREobservations.
Object UTdate Seeing((cid:48)(cid:48)) Mode Bands DIT(s)×NDIT N ∆PA(◦)
exp
IRDISorZIMPOL IFS
PZTel 2014/07/15 0.88−1.11 IRDIFS H2H3+YJ 20×6 60×2 16 7.6
PZTel 2014/08/06 0.5−0.7 IRDIS-LRS YJHK 20×10 − 6 −
s
PZTel 2014/08/06 0.6−0.7 IRDIS-MRS YJH 30×5 − 6 −
PZTel 2014/08/08 0.78−1.05 IRDIFS_EXT K1K2+YJH 12×5 30×2 16 9.0
PZTel 2014/08/16 1.12−1.58 ZIMPOL R(cid:48)I(cid:48) 50×12 − 3 14.1
PZTel 2014/10/11 1.12−1.97 IRDIFS H2H3+YJ 8×1a 32×20a 1 3.7b
HD1160 2014/08/13 0.54−0.84 IRDIFS_EXT K1K2+YJH 4×20 8×15 16 18.4
Notes.Theseeingisthevaluemeasuredbythedifferentialimagemotionmonitor(DIMM)at0.5µm.DIT(detectorintegrationtime)referstothe
singleexposuretime,NDIT(NumberofDetectorInTegrations)tothenumberofframesinasingledatacube,N tothenumberofdatacubes,
exp
and∆PAtotheamplitudeoftheparallacticrotation.(a) Thissequencewasatestandweonlyusedthecoronagraphicimageswiththesatellite
spotsformeasuringtheastrometryofthecompanion.(b)FortheIFSdata.
Table2.PhotometricmeasurementsofPZTelBandHD1160BCrelativetothehoststar.
Filter λ(µm) ∆λa(µm) PZTelB HD1160B HD1160C
SPHERE
R(cid:48) 0.6263 0.1486 9.76+0.22 − −
−0.30
I(cid:48) 0.7897 0.1525 7.529±0.108 − −
H2 1.5888 0.0531 5.34±0.18 − −
H3 1.6671 0.0556 5.28±0.18 − −
K1 2.1025 0.1020 5.29±0.08 7.03±0.05 5.35±0.06
K2 2.2550 0.1090 5.02±0.09 6.77±0.04 5.16±0.04
Otherinstruments
L(cid:48) 3.8000 0.6200 5.15±0.15b 6.54±0.10c 4.69±0.05c
Notes.(a)Fullwidthathalfmaximum.(b)NaCo;Beustetal.(2016).(c)NaCo;thiswork.
R∼54).IntheIRDIFS_EXTmode,IRDISisoperatedinthefil- SPHERE(socommontoIRDISandIFS)isinsertedintothe
terpairK12(Table2)andIFSinthebandsYJH(0.95−1.65µm, lightbeam(averagetransmission∼1/100)1.
R∼33). – The science coronagraphic images are acquired in pupil-
PZTelwasobservedtwiceintheIRDIFSmodeandoncein stabilized mode to take advantage of the ADI technique
theIRDIFS_EXTmode. TheIRDIFSsequenceswere obtained (Maroisetal.2006a).ForIRDIS,aditherpatternof4×4po-
inpoorobservingconditions(July2014)orforpurposesoftech- sitionswithshiftsofonepixelisappliedtohandlethedetec-
nicaltests(October2014).TheIRDIFS_EXTsequencewasac- torbadpixels.ForIFS,noditherpatternisused.
quiredinbetterobservingconditions.HD1160wasobservedin – A second set of a PSF and coronagraphic images with four
theIRDIFS_EXTmodeingoodobservingconditions. satellitespotsisrecorded.Thissecondsetofcalibrationsal-
Thesequencesareobtainedusingthefollowingstrategy: lows us to evaluate the photometric error due to the stellar
fluxvariationsandthestabilityofthestarcentering.
– The star is centered on the coronagraphic mask. The coro-
nagraph used for all the sequences is an apodized pupil Aftereachsequence,sixskybackgroundsareacquired,withthe
Lyot coronagraph (Soummer 2005) with inner working an- sameexposuretimesusedforthecoronagraphicimagesandthe
gleIWA∼0.09(cid:48)(cid:48),exceptfortheJuly2014IRDIFSsequence PSF. All the other calibration data used in the data reduction
forwhichIWA∼0.07(cid:48)(cid:48). (Sect.3)areobtainedthefollowingday.
– Acoronagraphicimagewithfourcrosswisefaintreplicasof Forcalibratingthedistortion,platescale,andorientationof
the star is acquired for estimating the star location, based theIRDISimages,afieldintheouterregionsofthe47Tucglob-
on the original concept proposed by Marois et al. (2006b) ularclusterwasobservedduringeachoftheobservingrunswith
andSivaramakrishnan&Oppenheimer(2006).Theserepli- the same instrument setup (filter and coronagraph), except for
cas are produced by applying a 2D periodic modulation on theK12filterpair.Forthelatterconfiguration,weusedthecal-
the deformable mirror of SPHERE. This calibration is crit- ibration in the H23 filter pair. The 47 Tuc field is selected be-
icalforaccurateregistrationoftheframesbeforethe appli- causeithasabrightstarforadaptiveopticsguidingandaccurate
cation of the angular differential imaging processing (ADI, HubbleSpaceTelescope(HST)astrometry(Bellini&Anderson,
Marois et al. 2006a) and for precise relative astrometry of privatecomm.;datacollectedaspartoftheprogramGO-10775:
thedetectedcompanions. P.I.Sarajedini).NoIFSdataofastrometriccalibratorswereob-
– Anunsaturatedimageofthestar(point-spreadfunction,PSF tainedduringthecommissioningruns.
hereafter) is recorded for purposes of photometric calibra-
tion. This image is obtained by shifting the star out of the 1 Thetransmissioncurvesoftheneutraldensityfilterscanbefound
coronagraphic mask using a tip-tilt mirror. A neutral den- in the User Manual available at www.eso.org/sci/facilities/
sity filter located in the common path and infrastructure of paranal/instruments/sphere/doc.html
A56,page3of24
A&A587,A56(2016)
K1 K2
C C
N
E
1"
109 AU
B B
Fig.1.IRDISimagesofPZTelBintheH23andK12filterpairs(left)andHD1160BCintheK12filterpair(right).Theintensityscaleisthe
sameforagiventargetandissquareroot.
2.2. IRDISlong-slitspectroscopy domeflats with the coronagraph in place were taken right after
theobservations.Inaddition,biasframesweretakenduringthe
PZ Tel B was observed with the long-slit spectroscopy (LSS)
followingday.
mode of IRDIS with two setups (Table 1). The LSS mode
includes a low-resolution mode (LRS), which covers the
YJHK bands at resolutions of 35−50 in one shot, and a 2.4. SINFONIintegralfieldspectroscopy
s
medium-resolution mode (MRS), which covers the YJH bands
For comparison purposes, we compare the SPHERE IFS and
at a resolution of ∼350 (Vigan et al. 2012a). The LSS obser-
LSS spectra of PZ Tel B to archival SINFONI data. SINFONI
vations are always performed in field-stabilized mode to keep
(Eisenhauer et al. 2003; Bonnet et al. 2004) was operated with
theobjectwithintheslitduringthecompleteintegration.Ase-
theadaptiveopticssystemoftheinstrumentlockedonthestar.
quenceconsistsofimageswiththestarbehindthecoronagraph,
ThesystemwasobservedonSeptember5,9,and13,2011with
anoff-axisreferencePSF,inwhichthestarisshiftedoutofthe the J-bandandH+K bandgratingandthepreopticsleadingto
coronagraph within the slit, and finally a series of sky back-
a 25×50 mas sampling of the 0.8(cid:48)(cid:48) ×0.8(cid:48)(cid:48) field of view (ESO
grounds. The sky backgrounds are particularly important for
program087.C-0535,P.I.Tecza).Additionalobservationswere
the LRS mode that covers the Ks band, for which the thermal obtainedinthe H+K bandonSeptember8,2011.Wealsore-
backgroundoftheinstrumentandskyaremuchhigher.These-
analyzedtheobservationsmadeonAugust22,2011(ESOpro-
quencesdonotdifferbetweentheLRSandMRSmodesexcept gram 087.C-0109, P.I. Mugrauer) with the H +K band grating
for the change of the dispersive element. For the observations
andthepreopticsleadingto25×50masspaxelsandpresented
reported in this paper, we used the configuration Wide slit and
by Schmidt et al. (2014). With respect to the spectra presented
Largemask(WL),wherethewidthoftheslitis120masandthe
in Schmidt et al. (2014), the combined SINFONI observations
radiusofthecoronagraphicmaskis0.2(cid:48)(cid:48).Nospectrophotometric
enabledustoextendthewavelengthcoveragetothe J bandand
calibrator was observed after the sequences. Other calibrations toimprovethesignal-to-noiseratio(S/N)inthe H bandfrom5
(darks, flat fields) were acquired during the morning following to10(noS/NimprovementintheK band,S/N =11).
theobservations.
3. Datareductionandanalysis
2.3. ZIMPOLimaging
3.1. IRDISimaging
PZ Tel B was observed simultaneously in the R(cid:48) and I(cid:48) broad-
bandfilterswiththetwocamerachannelsofZIMPOL(Table1). All the data reported in Table 1 were preprocessed in the same
ToimplementADI(Maroisetal.2006a),thesequenceofscience way: subtraction of the sky background, correction of the flat
observationswasobtainedinpupil-stabilizedmode.Aclassical field,processingofthebadpixels,andregistrationoftheframes
Lyotcoronagraph(Lyot1932)ofdiameter155masandthesatel- using the coronagraphic images with the satellite spots. Then
litespotswerealsoused.Thesequencewasstartedabout30min the data were processed using derotation and median-stacking
after the meridian passage of PZ Tel. For photometric calibra- of the temporal frames in each filter separately in the case of
tion,theunsaturatedPSFoftheprimarystarwasacquiredonce thePZTeldatasets(Fig.1,left)anddifferentialimagingforthe
afterthesciencesequence.Forthispurpose,atip-tiltmirrorwas HD1160dataset.ForthePZTeldatasets,wecheckedthatthe
used to move the star away from the coronagraph. No neutral derivedphotometricvaluesagreewiththephotometryextracted
density filter was inserted into the light beam. To avoid satura- usingtheTLOCIdifferentialimagingalgorithm(seebelow).
tion, the exposure time for the PSF was set to 2 s. A total of In the second case, two independent algorithms were con-
twentysubintegrationsinonedatacubeweretakeninthiscase. sideredforcalibratingthestellarresiduals.Themainalgorithm
The companion is well detected in the raw (without any pre- wasanupgradeoftheTemplateLocallyOptimizedCombination
processing)individualI(cid:48)-bandscienceimagesandintheprepro- ofImagesalgorithm(TLOCI,Maroisetal.2014).Asecondal-
cessedI(cid:48)-bandPSF(aftercosmeticcorrection,frameregistering, gorithm, which was used for checks for the photometry of the
and median combination). For data reduction purposes, special companionsandprovidedconsistentresultswithintheerrorbars
A56,page4of24
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Table3.AstrometricmeasurementsofPZTelBandHD1160BCrelativetothehoststar.
Object Instrument Epoch Band Separation(mas) Parallacticangle(◦)
PZTelB IFS 2014.53 YJ 478.22±0.70 59.71±0.19
PZTelB IFS 2014.60 YJH 479.53±0.69 59.62±0.14
PZTelB IFS 2014.78 YJ 482.60±0.93 59.44±0.15
PZTelB IRDIS 2014.53 H2 478.48±2.10 59.58±0.48
PZTelB IRDIS 2014.53 H3 476.44±2.09 60.06±0.49
PZTelB IRDIS 2014.60 K1 479.69±0.34 59.71±0.47
PZTelB IRDIS 2014.60 K2 479.61±0.34 60.17±0.47
PZTelB IRDIS 2014.78 H2 483.87±0.34 59.49±0.16
PZTelB IRDIS 2014.78 H3 483.87±0.29 59.51±0.16
HD1160B IFS 2014.62 YJH 780.87±1.06 244.25±0.13
HD1160B IRDIS 2014.62 K1 780.97±0.47 243.89±0.21
HD1160C IRDIS 2014.62 K1 5149.75±2.69 349.17±0.10
Notes.TheIFSandIRDISmeasurementswereobtainedfromthecoronagraphicimageswiththesatellitespots(Sect.2).
withrespecttotheTLOCIpipeline,consistedinderotatingand TheS/NmapwasestimatedusingtheTLOCIpipeline.Each
median-combining the frames followed by a spatial filtering in pixelvaluewasdividedbythestandarddeviationofthefluxin-
boxesofsize5λ/D×5λ/D.FortheTLOCIalgorithm,wecon- side the annulus of same angular separation with a 1 FWHM
sidered the dual-band data set in each filter separately and per- width.Thealgorithmthroughputwasaccountedforbyinjecting
formedADI(Maroisetal.2006a)inordertoavoidambiguities syntheticcompanionsinthepreprocesseddataatregularsepara-
inthephotometriccalibration(Maireetal.2014).Thedatawere tionsbetween0.15(cid:48)(cid:48)and6(cid:48)(cid:48)andperformingtheTLOCIanalysis.
also binned temporally to reduce the number of frames, hence Theprocesswasrepeatedseveraltimesusingdifferentposition
the computing time. The TLOCI pipeline selected the 80 most anglesinordertoaveragetheeffectsofrandomspeckleresidu-
correlatedframesforwhichthetotalself-subtraction,estimated alsintheestimationofthealgorithmthroughput.TheS/Nmaps
using the measured PSF, was at maximum 70% (Marois et al. wereusedtoderivethedetectioncurves(Sect.7).
2014).Thenitfoundthebestlinearcombinationforsubtracting
the speckles in annuli of width ∼1 full width at half maximum
3.2. IRDISLSS
(FWHM).Finally,wederotatedtheframestoalignnorthupand
median-combinedthem(Fig.1,right). The LRS and MRS data of PZ Tel were reduced in a similar
TherelativephotometryofHD1160BCwasderivedusing way. The reduction and analysis procedures are very similar to
themethodofthe“negativesyntheticcompanions”(Maroisetal. thosepresentedinHinkleyetal.(2015a).Astandardsetofcal-
2010a; Bonnefoy et al. 2011). We subtracted a synthetic com- ibrationdata(dark,flatfield,badpixelmaps)wasproducedus-
panioninthepreprocesseddataatthemeasuredlocationofthe ing the preliminary release (v0.14.0−2) of the Data Reduction
companionsbasedonthemedianoftheobservedPSF(Sect.2). and Handling software (DRH, Pavlov et al. 2008), the official
We then processed the data assuming the TLOCI coefficients pipeline of the SPHERE instrument. Then the science frames
computed on the data without the synthetic companions to ac- were dark-subtracted and divided by the flat field. Bad pixels
countfortheADIbiases.Thesubpixelpositionandthefluxof werereplacedwiththemedianofneighboringgoodpixels.The
themodeledimageswereadjustedtooptimizethesubtractionof remainingbadpixelswerefilteredusingasigma-clippingalgo-
themodeltotherealimagewithinadiskofradius1.5FWHM rithm. Each of the science frames were combined using a me-
centeredontherealimage.Forthephotometry,the1σerrorbar dian,producinga2Dspectrumfromwhichthecompanionsignal
ofthefittingwastheexcursionthatincreasedtheresidualsinthe wasextracted.
√
1.5-FWHMareabyafactorof 2.Thisfactorwasempirically Forthesubtractionofthestellarhaloandspecklesatthepo-
determinedinGalicher&Marois(2011).Theerrorbarsinclude sitionofthecompanion,wecomparedtwoapproachesthatgave
thevariationsinthePSF,thevariationsinthestellarfluxduring similarresults.Thefirstmethodwasbasedonspectraldifferen-
the sequence (estimated from the intensity fluctuations of the tial imaging (Racine et al. 1999; Sparks & Ford 2002) adapted
stellarresiduals),andthefittingaccuracyofthemodelcompan- for LSS data, as presented in Vigan et al. (2008) and demon-
ionimagestotheirmeasuredimages.Fortherelativephotometry stratedon-skyinViganetal.(2012a).Thesecondtechniquewas
ofPZTelB,thesamesourcesoferrorareincludedintheerror much simpler and consisted of subtracting the symmetric part
bars,exceptforthefittingerror. ofthehaloatthepositionofthecompanionwithrespecttothe
star. Given that the level of the halo and speckles was a fac-
Theastrometryofthecompanionswasmeasuredinthecoro-
tor ∼18 fainter than the peak signal of the companion, this ap-
nagraphic images with the satellite spots. These images were
proach gave good results and introduced a negligible bias after
corrected for the distortion of the telescope and the instrument
thesubtraction.
(Sect.3.6).TheastrometriccalibrationisdescribedinSect.3.6. The1Dspectrumofthecompanionandtheoff-axisprimary
Wereportthemeasuredrelativephotometryandastrometry were extracted in the following way: for each spectral channel,
inTables2and3.ForthephotometryofPZTelBintheH23fil- thesignalwassummedinanaperturecenteredontheobjectpo-
terpair,weonlyconsideredtheJuly2014dataset,becausethe sition with a width of (cid:15) λ/D. When (cid:15) was varied from 0.5 to
October2014observationwasashorttechnicaltestsothedata 1.0, there were only very small variations in the output spec-
qualitywaspoorer.FortheupdatedorbitalanalysisofPZTelB trum. The local noise was estimated by summing the residual
(Sect. 6), we only considered the IRDIS H2 measurement ob- specklenoiseinanapertureatthesameseparationasthecom-
tainedinJuly2014. panion, but on the other side of the primary. We checked that
A56,page5of24
A&A587,A56(2016)
the spectra extracted with the two subtraction schemes and the YJH YJH
differentaperturesizeslaywithintheseerrorbars. N N
The flux spectrum of the companion was converted into a
E E
contrast spectrum by dividing by the flux spectrum of the pri-
mary extracted in an aperture of the same width. To properly B
measure the contrast, we took the transmission of the neutral
density filter used for acquiring the off-axis PSF data into ac-
count.TheneutraldensityfilterusedfortheLRSandMRSob-
B
servationshadanaveragetransmissionof1/3160and1/100,re-
0.25" 0.25"
spectively(seenote1).
13 AU 27 AU
ThecomparisonoftheLSSspectraofPZTelBtothoseof
late-Mobjects(Sect.5.2)andthoseobtainedwiththeSINFONI
instrument (Sect. 3.3.2) revealed a residual error in wavelength Fig.2.IFSmedian-collapsedimagesofPZTelB(left)andHD1160B
dispersion relation of the SPHERE spectra. For the MRS spec- (right) after derotation and stack of the temporal frames. The square
rootintensityscaleshavedifferentranges.
trum, we fitted a new dispersion relation matching ten telluric
featureswiththosefoundintoasyntheticspectrumoftheEarth
atmosphere transmission curve (Noll et al. 2012; Jones et al.
2013).FortheLRSspectrum,weappliedalinearcorrectionfac- each angular separation. We estimated the PCA subtraction of
tor to the wavelengths derived by the DRH pipeline. The fac- off-axis point sources using synthetic companions injected into
tors were found by comparing the PZ Tel B LRS spectrum to thepreprocesseddataatseveralseparationsandpositionangles.
theSINFONIspectrumandtothespectrumoftheM8standard WeoptimizedthenumberofPCAmodestomaximizethedetec-
VB10(vanBiesbroeck1961;Burgasseretal.2004). tionperformance.
3.3. IFSspectroscopy 3.3.2. SINFONIspectraofPZTelB
WereducedthedatacorrespondingtotheSINFONIobservations
3.3.1. SPHEREIFS
of PZ Tel B (Sect. 2.4) with the ESO data reduction pipeline
TherawdatawerepreprocessedusingtheSPHEREDRHsoft- (Modiglianietal.2007)version2.5.2.Thepipelinebuiltthebad
ware (Pavlov et al. 2008) up to the extraction of the calibrated pixelmaskandflatfieldassociatedtoeachobservationdateand
data cubes. The design of the SPHERE IFS differs in two setup.Itcorrectedeachrawframefortheinstrumentdistortion,
mainpointsfromtheIFSofthehigh-contrastexoplanetimagers derived a map of wavelength associated to each detector pixel,
P1640 and GPI. First, the cross talk between adjacent pixels is and found the position of the spectra (slitlets) on the detector.
minimized (Antichi et al. 2009). Then, the spectra are aligned After these steps, we obtained the final data cube from the raw
with the detector columns (see Fig. 2 in Mesa et al. 2015). 2Dscienceframes.FortheAugust2011data,theskyemission
These differences allow for a simpler reduction procedure for was evaluated and removed using exposures of an empty field
the SPHERE IFS data, which does not rely on determining the obtainedduringtheobservationsequence.Noskyexposurewas
instrumentPSF(Zimmermanetal.2011;Perrinetal.2014). obtained for the remaining observations. Therefore, we instead
The raw data were first corrected for the dark and the de- subtracted a dark frame from the raw science images in order
tector flat. Then the positions of the spectra were defined from toremovethebiasandthedetectorrampeffect,andappliedthe
an image in which the whole integral field unit (IFU) was uni- algorithms of Davies (2007) implemented into the pipeline to
formlyilluminatedwithawhitecalibrationlamp.Eachpixelof removetheskycontribution(thermalbackgroundandemission
the detector was assigned a first-guess wavelength. In a second lines).
step, the wavelength was further refined based on the illumina- PZ Tel A was located inside the field of view of the instru-
tionoftheIFUwiththree(resp.four)monochromaticlaserswith ment for the September 2011 observations. This was not the
knownwavelengthfortheYJ(resp.YJH)data.Finally,thedata casefortheAugust2011observations(Schmidtetal.2014),for
cubes(science,PSF,andsatellitespots)wereextractedandcor- which the PSF core of PZ Tel A was located a few pixels out-
rectedforthevariationsintheresponseoftheIFUlenslets.Each sidethefieldofview.Weremovedthestellarhalousingaradial
data cube had 39 monochromatic images. Right before the ex- profile for both cases. For the August 2011 data, we chose the
tractionofthespectraldatacubes,anadditionalstepexploiting approximatestarpositionthatminimizedthehaloresiduals.The
customIDLroutines(Mesaetal.2015)wasperformedforim- companionwasalwaysmasked(circularmaskofradius7pixels)
provingthecorrectionofthebadpixelsandspectralcross-talk. whilecomputingtheradialprofile.
We used the coronagraphic images with the satellite spots ThefluxofPZTelBwasmeasuredinthehalo-removeddata
(Sect.2)ofthedatasetslistedinTable1toobtaintheastrometry cubes using aperture photometry (circular aperture of radius 5
ofPZTelBandHD1160B(Table3). or 6 pixels). The aperture radius was determined by eye with
For extracting the spectrum of the companions, we consid- respect to the encircled energy of a given observation and the
eredeachspectralchannelseparatelyandperformedderotation levelofresidualsfromthehalosubtractionclosetothecompan-
and median-stacking of the frames (Fig. 2). For the purpose of ion.Allextractedspectrawerecorrectedfortelluricabsorptions
searchingforadditionalcompanionsinthesystem,wealsocon- usingthoseofB-typestandardstarsobservedafterPZTel(here-
sideredeachspectralchannelseparatelybutsubtractedthestellar after Method 1). For the case of the data acquired on Sept. 11,
residuals with a principal component analysis approach (PCA, 2014,wealsousedthespectrumofPZTelAextractedwithcir-
Soummer et al. 2012; Amara & Quanz 2012), as illustrated in cularaperturesofsimilarsizeasanalternativecorrection(here-
Maireetal.(2014). after Method 2). This enabled the estimation of a companion-
The 1D detection limits (Sect. 7) were derived as the stan- to-star contrast ratio at each wavelength that can be compared
dard deviation of the residual flux in annuli of 1 λ/D width at directly to the SPHERE spectra and that was less sensitive to
A56,page6of24
A.-L.Maireetal.:PhysicalpropertiesandarchitectureofthePZTelandHD1160systemsrevisitedwithVLT/SPHERE
(cid:49)(cid:46)(cid:50)
(cid:76)(cid:83)(cid:83)(cid:32)(cid:45)(cid:32)(cid:76)(cid:82) (cid:76)(cid:83)(cid:83)(cid:32)(cid:45)(cid:32)(cid:77)(cid:82)
(cid:83)(cid:73)(cid:78)(cid:70)(cid:79)(cid:78)(cid:73) (cid:49)(cid:46)(cid:50) (cid:83)(cid:73)(cid:78)(cid:70)(cid:79)(cid:78)(cid:73)
(cid:49)(cid:46)(cid:48)
(cid:110)(cid:116)(cid:41) (cid:110)(cid:116)(cid:41)
(cid:97) (cid:97)
(cid:115)(cid:116) (cid:115)(cid:116)
(cid:111)(cid:110) (cid:111)(cid:110) (cid:49)(cid:46)(cid:48)
(cid:99) (cid:99)
(cid:43)(cid:32) (cid:48)(cid:46)(cid:56) (cid:43)(cid:32)
(cid:120)(cid:32)(cid:40) (cid:120)(cid:32)(cid:40)
(cid:117) (cid:117)
(cid:100)(cid:32)(cid:102)(cid:108) (cid:100)(cid:32)(cid:102)(cid:108)
(cid:101) (cid:101)
(cid:109)(cid:97)(cid:108)(cid:105)(cid:122) (cid:48)(cid:46)(cid:54) (cid:109)(cid:97)(cid:108)(cid:105)(cid:122) (cid:48)(cid:46)(cid:56)
(cid:111)(cid:114) (cid:111)(cid:114)
(cid:78) (cid:78)
(cid:48)(cid:46)(cid:52) (cid:48)(cid:46)(cid:54)
Fig.3. Comparison of the SINFONI
H+K band spectrum and the SPHERE
(cid:49)(cid:46)(cid:54) (cid:49)(cid:46)(cid:56) (cid:50)(cid:46)(cid:48) (cid:50)(cid:46)(cid:50) (cid:49)(cid:46)(cid:53)(cid:48) (cid:49)(cid:46)(cid:53)(cid:53) (cid:49)(cid:46)(cid:54)(cid:48) (cid:49)(cid:46)(cid:54)(cid:53) (cid:49)(cid:46)(cid:55)(cid:48) (cid:49)(cid:46)(cid:55)(cid:53) long-slit spectra of PZ Tel B at compa-
(cid:108)(cid:32)(cid:40)(cid:109)(cid:109)(cid:41) (cid:108)(cid:32)(cid:40)(cid:109)(cid:109)(cid:41)
rableresolutions.
(cid:50)(cid:46)(cid:48) (cid:50)(cid:46)(cid:48)
(cid:76)(cid:83)(cid:83)(cid:32)(cid:45)(cid:32)(cid:76)(cid:82) (cid:76)(cid:83)(cid:83)(cid:32)(cid:45)(cid:32)(cid:77)(cid:82)
(cid:83)(cid:73)(cid:78)(cid:70)(cid:79)(cid:78)(cid:73) (cid:83)(cid:73)(cid:78)(cid:70)(cid:79)(cid:78)(cid:73)
(cid:110)(cid:116)(cid:41) (cid:49)(cid:46)(cid:53) (cid:110)(cid:116)(cid:41) (cid:49)(cid:46)(cid:53)
(cid:97) (cid:97)
(cid:115)(cid:116) (cid:115)(cid:116)
(cid:110) (cid:110)
(cid:111) (cid:111)
(cid:99) (cid:99)
(cid:43)(cid:32) (cid:43)(cid:32)
(cid:117)(cid:120)(cid:32)(cid:40) (cid:49)(cid:46)(cid:48) (cid:117)(cid:120)(cid:32)(cid:40) (cid:49)(cid:46)(cid:48)
(cid:100)(cid:32)(cid:102)(cid:108) (cid:100)(cid:32)(cid:102)(cid:108)
(cid:101) (cid:101)
(cid:122) (cid:122)
(cid:97)(cid:108)(cid:105) (cid:97)(cid:108)(cid:105)
(cid:109) (cid:109)
(cid:78)(cid:111)(cid:114) (cid:48)(cid:46)(cid:53) (cid:78)(cid:111)(cid:114) (cid:48)(cid:46)(cid:53)
(cid:48)(cid:46)(cid:48) (cid:48)(cid:46)(cid:48) Fig.4. Comparison of the SINFONI
(cid:49)(cid:46)(cid:49)(cid:48) (cid:49)(cid:46)(cid:49)(cid:53) (cid:49)(cid:46)(cid:50)(cid:48) (cid:49)(cid:46)(cid:50)(cid:53) (cid:49)(cid:46)(cid:51)(cid:48) (cid:49)(cid:46)(cid:51)(cid:53) (cid:49)(cid:46)(cid:49)(cid:48) (cid:49)(cid:46)(cid:49)(cid:53) (cid:49)(cid:46)(cid:50)(cid:48) (cid:49)(cid:46)(cid:50)(cid:53) (cid:49)(cid:46)(cid:51)(cid:48) (cid:49)(cid:46)(cid:51)(cid:53) and the SPHERE long-slit spectra of
(cid:108)(cid:32)(cid:40)(cid:109)(cid:109)(cid:41) (cid:108)(cid:32)(cid:40)(cid:109)(cid:109)(cid:41)
PZTelBintheJband.
differential flux losses due to the limited size of the apertures. 3.4. ZIMPOLimaging
WeconvertedthecontrastobtainedfollowingMethod2toaflux-
TherawdatawerepreprocessedusingtheSPHEREDRHsoft-
calibratedspectrumfollowingthemethoddescribedinSect.5.1.
ware (Pavlov et al. 2008). This included bias subtraction and
Both methods give results that agree within error bars esti- flat-fielding with coronagraphic flats taken after the science se-
matedfromthestandarddeviationofthefluxateachwavelength quences,aswellasZIMPOLspecifictasks,suchasthecropping
obtainedfromthedifferentepochs.TheHK-bandspectrumob- oftheimageandtheinterpolationofpixelsintheimageydirec-
tainedwithMethod1benefitsfromtheincreasedexposuretime tioninordertoproduceasquareimage.Usingthetimestampsin
from all combined data sets. It looks identical to the spectrum theimageheader,foreachindividualexposuretheparallactican-
obtained by Schmidt et al. (2014) except for the 1.45−1.6 µm glewascomputedandtheimagescombinedusingasimpleADI
range, where it has less pronounced H2O absorptions. It nev- approach (Marois et al. 2006a). A reference image of the stel-
ertheless reproduces all the features of the low-resolution LSS lar signature was generated by median combination of all pre-
spectraofthesourceobtainedwithSPHEREwell(Fig.3). processed images. Owing to the field rotation during the pupil-
The J-band SINFONI spectrum and low-resolution stabilizedobservations,thelargemajorityofthefluxofthecom-
LSS spectrum of PZ Tel B have an identical slope from 1.2 to panionwasrejectedinthisprocess.Thisreferenceimageofthe
1.3µm(Fig.4).TheLSSspectrumis,however,notaffectedby stellarsignaturewasthensubtractedfromallindividualframes,
strong telluric residuals shortward of 1.2 µm, which probably which were subsequently derotated to align north up and com-
arise from an improper subtraction of the stellar halo in the bined.ThetruenorthwasestimatedusingtheIRDISastrometry
SINFONI data at these wavelengths. The medium-resolution ofthecompanionmeasuredduringthesamerun.Sincethecoor-
LSS spectrum has a bluer slope than the SINFONI spectrum. dinatesysteminZIMPOLcamera1isflippedintheydirection
The origin of this slope is unclear. The preprocessed data were with respect to the sky, all R(cid:48)-band images were first flipped in
checked for saturation and contamination by the star signal. the y direction before derotation and image combination. The
We are still analyzing the data, as well as other LSS data resultingimagesareshowninFig.5.
sets from the commissioning runs, to determine the science We used relative aperture photometry to measure the flux
performanceandlimitationsofthisobservingmode.Theresults of PZ Tel B in both bands. For all measurements, the Aperture
willbepresentedinaforthcomingpaper.TheSPHEREspectra Photometry Tool (Laher et al. 2012) was utilized. The aperture
supersede the SINFONI spectrum inside this wavelength range sizewassettoaradiusoffivepixelsforallmeasurements.This
becauseoftheirhigherS/Natacomparablespectralresolution. was chosen to exclude the bright diffraction-related features in
A56,page7of24
A&A587,A56(2016)
Fig.5. ADI-reduced R(cid:48)-band and I(cid:48)-band
coronagraphicZIMPOLimagesofPZTelB
obtained simultaneously in the imaging
mode(seetext).Thecompanionismarked
inbothimageswithadashedcircle.Thear-
tifactseenaroundthecompanionsignalin
bothimagesisduetoanintermittentinstru-
mental effect currently under study, possi-
blyrelatedtothetelescope.
the companion PSF. The companion flux was measured in the HD 1160 B and C, respectively. The values were consistent
ADI-reduced images, while the star flux was measured in the with those derived from the four other epochs within the error
reference images and then rescaled to the longer observation bars. The NaCo photometry also agrees within the error bars
time of the science images. Care was taken to choose regions (3σ)withtheKeck/NIRC2photometryreportedinNielsenetal.
for background subtraction that were not contaminated by the (2012).Nevertheless,wepreferredtousetheNaCophotometry
stellarhalotoavoidoversubtraction.SinceADIimagingsuffers below,sinceitenabledadirectcomparisontothephotometryof
from self-subtraction of the companion flux, we corrected for PZTelB.TheNaCoL(cid:48)photometrybringstheK −L(cid:48)bandcolor
s
thiseffectaswell.Forthispurpose,weusedtheunsaturatedim- ofHD1160B(K −L(cid:48)=0.53±0.12mag)intobetteragreement
s
ages of PZ Tel A to generate fake companion PSF, which we withthoseofmid-tolate-Mfielddwarfs.UsingtheL-bandmag-
injectedinthepreprocesseddata.Wethenmeasuredtheamount nitudeofHD1160AreportedinvanderBlieketal.(1996),we
of self-subtraction of these fake planets. Care was taken to in- foundL(cid:48) =13.60±0.10magandL(cid:48) =11.76±0.05mag.
B C
ject the fake companions at the same angular separation as the Wenotethat,independentlyofournewphotometry,theL(cid:48)−
realcompanionPZTelBandvariouspositionangles,toensure M colorofHD1160B(Nielsenetal.2012)appearstobemuch
s
similar self-subtraction effects during ADI processing. The re- redder with respect to M or early-L dwarf companions (Fig. 5,
sulting photometric measurements are summarized in Table 2. Bonnefoy et al. 2014b). Therefore, we decided not to use the
The uncertainties include the statistical uncertainties from the Keck/NIRC2photometryofthesystembelow.
aperturephotometry,theuncertaintiesfromthecalibrationofthe
ADI self-subtraction, and the temporal variations of the stellar
3.6. IRDISandIFSastrometriccalibration
fluxduringthesequence(measuredusingoneofthesimultane-
ous satellite spots). The self-subtraction uncertainties were es- The IRDIS astrometric measurements reported in Table 3 were
timated according to the range of correction factors calculated derivedusingtheplatescaleandthetruenorthorientationmea-
fromseveralfakecompanions.Thephotometricerrorduetothe sured for the 47 Tuc data (Table 4). We recall that no rele-
PSF variations could not be estimated since only one PSF was vant observations of astrometric calibrators were obtained for
recorded.Theastrometryofthecompanionwasnotconsidered IFS (Sect. 2). For the IFS data we estimated a plate scale
forthispaper,becauseoftheavailabilityofIRDISandIFSdata of 7.46±0.01 mas/pix and a relative orientation to IRDIS data
close in time. The ZIMPOL astrometry will be discussed in a of−100.46±0.13◦fromsimultaneousdataofdistortiongridsof
forthcomingpaper. both instruments. Using this calibration and correcting for the
instrument distortion (see below), we estimated the astrometry
ofthecompanionsinIFSdatalistedinTable3.
3.5. NaCoL(cid:48)-bandimagesofHD1160 The 47 Tuc IRDIS data were reduced and analyzed using
the SPHERE DRH software (Pavlov et al. 2008) and custom
The Keck/NIRC2 L(cid:48)-band images reported in Nielsen et al. IDL routines. The star positions were measured using the cen-
(2012) appear to have poorer quality than the NaCo (Nasmyth troid IDL routine cntrd2 derived from the DAOphot software
Adaptive Optics System and Near-Infrared Imager and (Stetson1987).Themeasuredpositionswerethencomparedto
Spectrograph, Rousset et al. 2003; Lenzen et al. 2003) L(cid:48)-band HST positions corrected for the differential proper motions of
images obtained at multiple epochs and available in the ESO the individual stars between the HST observations (March 13,
public archive (ESO program 60.A-9026). We made use of 2006)andtheSPHEREobservations(Bellini&Anderson,priv.
theseNaCoimagestochecktheconsistencyoftheKeck/NIRC2 comm.; see Bellini et al. 2014, for the description of the meth-
L(cid:48)-band photometry. We reduced five epochs of observations ods used for deriving the catalog positions and the individual
(Dec. 23, 2005; Sept. 17, 2010; Jul. 11, 2011; Sept. 2, 2011; stellarpropermotions).Thetypicalaccuracyofthecatalogpo-
Nov.8,2011)withtheESOEclipsesoftware(Devillard1997). sitionsis∼0.3masandtakesthetimebaselinebetweentheHST
HD 1160 B was resolved at each epoch, but the strehl and and SPHERE observations into account. Typically, more than
residual background close to the star appeared to have better 50 stars were cross-identified and used for the analysis. The
quality in the images obtained in November 2011. We chose distortion measured on-sky is dominated by an anamorphism
to perform aperture photometry (circular apertures of radius (0.60±0.02%)betweenthehorizontalandtheverticaldirections
160 mas) on the star and its companion on these images and
found∆L(cid:48) =6.54±0.10magand∆L(cid:48) =4.69±0.05magfor 2 http://idlastro.gsfc.nasa.gov/ftp/pro/idlphot/
B/A C/A
A56,page8of24
A.-L.Maireetal.:PhysicalpropertiesandarchitectureofthePZTelandHD1160systemsrevisitedwithVLT/SPHERE
Table4.MeanplatescaleandtruenorthorientationfortheSPHEREcommissioningrunsmeasuredonthe47Tucfield-stabilizedobservationsin
theIRDISimagesintheH23filterpairobtainedwiththeAPLCcoronagraph(Sect.2).
H2 H3
Com.date Platescale(mas/pix) Truenorth(◦) Platescale(mas/pix) Truenorth(◦)
July2014 12.252±0.006 −1.636±0.013 12.247±0.006 −1.653±0.005
August2014 12.263±0.006 −1.636±0.013 12.258±0.006 −1.653±0.005
October2014 12.259±0.006 −1.788±0.008 12.254±0.005 −1.795±0.008
Notes. To align the IRDIS science images so that north is oriented up and east left, an offset accounting for the zeropoint of the derotator in
pupil-stabilizedmodeof135.87±0.03◦ hastobeaddedtotheparallacticanglesindicatedinthefitsheader.Thisoffsetismeasuredondataof
47TucacquiredinJuly2014inbothstabilizationmodesandassumedtobeconstantbetweentheruns.FortheastrometriccalibrationoftheIFS
scienceimages,anadditionaloffsetaccountingfortherelativeorientationbetweentheIFSandIRDISfieldsof−100.46±0.13◦ alsohastobe
added.Thisvalueismeasuredonsimultaneousdataofdistortiongridsofbothinstruments.
Table5. ComparisonstarsusedfortheREMphotometry.
Name RA(J2000.0) Dec(J2000.0) V
(hhmmss) (◦(cid:48)(cid:48)(cid:48)) (mag)
C1 TYC8381-2548-1 185255.39 −500913.26 10.487±0.016
C2 CD-5012193 185328.02 −501308.26 10.173±0.015
C3 2MASSJ18531926-5014042 185319.26 −501404.20 12.233±0.060
ofthedetector.Theon-skydistortionissimilartothedistortion October29,2014untilDecember5,2014foratotalof30nights.
measured in laboratory, suggesting that the distortion from the Afterdiscardingframescollectedinverypoorseeingconditions
telescopeisnegligiblewithrespecttothedistortionofSPHERE. andframesmissingoneormorecomparisonstars(duetoinac-
Theanamorphismisproducedbycylindricalmirrorsinthecom- curatetelescopepointing),wewereleftwithatotalof173,131,
monpathandinfrastructureoftheinstrument,hencecommonto and133framesinthe J,H,andK filters,respectively,and205,
IRDIS and IFS, except that the anamorphism is rotated for the 166,and219framesintheg,r,andifilters.Theexposuretime
IFSdata.Theplatescaleandthetruenorthorientationgivenin was fixed to 1 s in the ROS2 camera, whereas five consecutive
Table4werecorrectedfortheanamorphism. ditherframesof1seachwerecollectedwiththeREMIRcamera
oneachtelescopepointing.Allframeswerefirstbias-subtracted
and then flat-fielded. Aperture photometry was used to extract
4. UpdatedphotometryofPZTelA
themagnitudesofPZTelAandotherstarsinthefieldtobeused
Young,late-typestarsareknowntoshowphotometricvariabil- as comparison stars. All reduction steps were performed using
ityonseveraltimescales,hourlyduetoflares,dailyduetorota- thetaskswithinIRAF3.Afterremovingafewoutliersfromthe
tionalmodulationsofactiveregionsonthestellarsurface,andon magnitude time series, using a 3σ filtering, we averaged con-
longertimescalesdueto,forinstance,reconfigurationofactive secutivedatacollectedwithinonehour,andfinallywewereleft
regions and activity cycles. Long-term variations of these stars with24,18,and19averagedmagnitudesinthe J,H,andK fil-
were studied less intensively than short-term variations due to ters,respectively,and38,26,and34averagedmagnitudesinthe
thelongtimebaselineneededfortheanalysis. g,r,andifilters,respectively.
The characterization of substellar objects like those pre- The mean standard deviations associated to the average
sentedinthispaperaretypicallyobtaineddifferentiallywithre- magnitudeswereσ =0.017,σ =0.018,σ =0.013mag,and
J H K
spect to the host stars. Ideally, the magnitude of the host star σ =0.035, σ =0.021, σ =0.018 mag. Analyzing the All Sky
g r i
should be derived simultaneously to the high-angular resolu- AutomatedSurvey(ASAS,Pojmanski1997)photometrictime-
tion observations, but this is difficult to achieve in practice. seriesofthebrighterstarsinthefieldofPZTelA,weidentified
Photometric monitoring in the same observing season as the three stars (Table5) whose light curves were very stable, and
high-contrastobservationsinsuresthatthelatterareproperlycal- theywerethereforesuitableascomparisonstars.Theirdifferen-
ibrated.Fromtheanalysisofliteraturedata(Sect.4.4),PZTelA tialmagnitudesalsoduringourobservingrunwerefoundtobe
is shown to have photometric variations of up to 0.2 mag over constantwithinourphotometricprecisioninbothopticalandthe
several decades. We present below new photometric observa- NIRphotometricbands(Table6).
tions of the star taken in the same season as the SPHERE data Wecomparedtheaveragedifferentialvaluesofthecompari-
andthestudyofitsphotometricvariabilityonvarioustimescales. sonstars(C1−C2,C1−C3,andC2−C3)withrespecttothedif-
ferential values derived from the Two Micron All Sky Survey
(2MASS, Cutri et al. 2003) listed in Table 7. Table 6 lists the
4.1. REMobservations
differentialvalues.Wenotethattheyareallconsistentwitheach
WeobservedPZTelAwiththe60-cmRapidEyeMount(REM, other within the uncertainties, verifying that these stars do not
Chincarinietal.2003)telescope(LaSilla,ESO,Chile)withboth vary also in the NIR. Only the comparison star C3 exhibits
the NIR REMIR and the optical ROS2 cameras. The REMIR
camerahostsa512pix×512pixCCDandhasafieldofviewof 3 IRAFisdistributedbytheNationalOpticalAstronomyObservatory,
10(cid:48)×10(cid:48) andaplatescaleof1.2(cid:48)(cid:48)/pix.TheROS2camerahosts whichisoperatedbytheAssociationoftheUniversitiesforResearch
a 2048 pix×2048 pix CCD and has a field of view of 8(cid:48) ×8(cid:48) in Astronomy, Inc. (AURA) under cooperative agreement with the
and a plate scale of 0.58(cid:48)(cid:48)/pix. We could observe the star from NationalScienceFoundation.
A56,page9of24
A&A587,A56(2016)
Table 6. Average differential magnitudes from 2MASS catalog and
REMobservations.
2MASS REM Filter
(mag) (mag)
C1−C2 1.00±0.04 1.01±0.03 J
C1−C3 −0.24±0.04 −0.26±0.04 J
C2−C3 −1.24±0.03 −1.26±0.02 J
C1−C2 1.12±0.06 1.17±0.03 H
C1−C3 −0.01±0.05 −0.02±0.04 H
C2−C3 −1.13±0.04 −1.17±0.04 H
C1−C2 1.28±0.03 1.25±0.02 K
C1−C3 0.13±0.04 0.11±0.03 K
C2−C3 −1.14±0.03 −1.12±0.02 K
Table7.2MASSmagnitudesofcomparisonstarsadoptedtocalibrate
theREMmagnitudes.
J(mag) H(mag) K(mag)
C1 8.493±0.035 7.904±0.044 7.801±0.029
C2 7.495±0.023 6.781±0.036 6.525±0.020
C3 8.734±0.023 7.915±0.020 7.667±0.023
slightlylargermagnitudevariationswithrespecttothe2MASS
values.Moreprecisely,itremainedconstantduringtheobserva-
tion run, but probably has a long-term (on the order of years)
smallamplitudevariation.
Once we checked that the comparison stars were not
variable, we could use the C1 and C2 2MASS magnitudes
(Table 7) to transform the PZ Tel A differential magni- Fig.6. LS and CLEAN periodograms of the H+K timeseries (top
tudes into absolute values. We finally obtained the aver- panels)andoftheg+r+itimeseries(bottompanels)(seetext).
age magnitudes: J=6.84±0.04 mag, H=6.430±0.045 mag,
and K=6.27±0.03 mag in the NIR, g=8.51±0.04 mag,
r=8.11±0.04mag,andi=7.70±0.04magintheoptical.
exhibiting a higher degree of correlation) and also among all
g+r +i bands (r = 0.87, r = 0.53, r = 0.46 mag) with
gr gi ri
significancelevelof>95%(withtherandimagnitudesexhibit-
4.2. YorkCreekObservatoryobservations
ingasmallerdegreeofcorrelation).ToimprovetheS/Nofour
PZTelAwasobservedfromNovember18,2014toDecember2, time series, we built a new light curve by averaging the H and
2014, for a total of six nights at the York Creek Observatory Klightcurves(whichisjustifiedbythehighcorrelationbetween
(41◦06(cid:48)06(cid:48)(cid:48)S; 146◦50(cid:48)33(cid:48)(cid:48)E, Georgetown, Tasmania) using a thelightcurves)andbyaveragingtheg,r,andilightcurves.
f/10 25-cm Takahashi Mewlon reflector, equipped with a QSI Both LS and CLEAN periodograms showed that the
683ws-8camera,andB,V,andRstandardJohnson-Cousinsfil- major power peak in the averaged NIR light curve is at
ters.Thetelescopehasafieldofviewof24.5(cid:48)×18.5(cid:48).Theplate P=0.943±0.002dandwithfalsealarmprobabilityFAP<1%.
scale is 0.44(cid:48)(cid:48)/pix. A total of 48 frames in each filter were col- The FAP, which is the probability that a power peak of that
lectedusinganintegrationtimeof30s.Datareductionwasper- height simply arises from Gaussian noise in the data, was es-
formed as described in the previous section for the REM data. timated using a Monte-Carlo method, i.e., by generating 1000
The photometric accuracies we could achieve are σB = 0.009, artificial light curves obtained from the real one, keeping the
σV = 0.007,andσR = 0.006mag.Wederivednewphotometry datebutscramblingthemagnitudevalues.Theresultsaresum-
for PZ Tel A using the differential B, V, and R light curves of marized in Fig. 6, where in the top panels we plot the LS
thestar,aswellasliteratureBandVmagnitudesofthecompari- periodograms and the CLEAN periodograms in the lower pan-
sonstarsC1andC2(seeSect.4.1).Theaveragemagnitudesare els.IntheLSperiodogramwealsonoteanumberofsecondary
B=9.05±0.05magandV=8.30±0.05mag. powerpeaksatahighsignificancelevel.Thesepeaksarebeats
of the rotation period according to the relation B=(1/P)±n,
where B is the beat period and n an integer. They arise from
4.3. Rotationperiodsearch
aone-daysamplingintervalimposedbytherotationoftheEarth
WeusedtheLomb-Scargle(Scargle1982)andCLEAN(Roberts and the fixed longitude of the observation site. It can be noted
et al. 1987) periodogram analyses on our own observations to that in the CLEAN periodograms, the power peak arising from
searchfortherotationperiodofPZTelA.Asexpected,wefound thelightrotationalmodulationdominates,whereasallsecondary
thatthestarexhibitsvariabilityinallbands.Acorrelationstudy peaks areeffectively removed.The horizontal dashed lineindi-
showedthatthemagnitudevariationsamongallJ+H+Kbands catesthepowerlevelassociatedtoaFAP=1%,whereasthered
are correlated (r = 0.70, r = 0.42, r = 0.84 mag) dottedlineshowsthespectralwindowarisingfromthedatatime
JH JK HK
with significance level >99% (with the H and K magnitudes sampling.
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