Accretion and outflow activity on the late phases of pre-main-sequence evolution. The case of RZ Piscium

0.48 MB·

by  I. S. Potravnov

Astronomy&Astrophysicsmanuscriptno.RZ_Psc_art7 (cid:13)cESO2017
January13,2017
Accretion and outflow activity on the late phases of
pre-main-sequence evolution. The case of RZ Piscium.
I.S.Potravnov1,D.E Mkrtichian2,V.P. Grinin1,3,I.V.Ilyin4,andD.N. Shakhovskoy5
1 PulkovoAstronomicalObservatory,RussianAcademyofSciences,196140,Pulkovo,St.Petersburg,Russia
e-mail:[email protected]
2 NationalAstronomicalResearchInstituteofThailand,ChiangMai50200,Thailand
3 Saint-PetersburgStateUniversity,Universitetskipr.28,198504St.Petersburg,Russia
7 4 Leibniz-InstitutfürAstrophysikPotsdam(AIP),AnderSternwarte16,14882Potsdam,Germany
1 5 CrimeanAstrophysicalObservatory,P.Nauchny,298409RepublicofCrimea
0
2
Received13May2016/accepted02December2016
n
a
J ABSTRACT

2
1 RZPscisanisolatedhigh-latitudepost-TTauristarthatdemonstratesaUXOri-typephotometricactivity.Thestarshowsveryweak
spectroscopicsignaturesofaccretion,butatthesametimepossessestheunusualfootprintsofthewindinNaiDlines.Inthepresent
] work we investigate new spectroscopic observations of RZ Psc obtained in 2014 during two observation runs. We found variable
R blueshifted absorption components (BACs) in lines of the other alcali metals, Ki 7699 Å and Caii IR triplet. We also confirmed
S the presence of a weak emission component in the Hα line, which allowed us to estimate the mass accretion rate on the star as
. M˙ ≤7·10−12M⊙yr−1.WecouldnotrevealanyclearperiodicityintheappearanceofBACsinsodiumlines.Nevertheless,theexact
h coincidenceofthestructureandvelocitiesoftheNaiDabsorptionsobservedwiththeintervalofaboutoneyearsuggeststhatsucha
p periodicityshouldexist.
-
o Keywords. stars:individual:RZPsc–stars:pre-mainsequence–stars:lowmass–accretion,accretiondisks
r
t
s
a
[1. Introduction exceptions.Afewyearsagowefoundaninterestingexception:
theunusualvariablestarRZPsc.

1
RZ Psc is classified as a UX Ori-type star on the basis of
Itiswellknownfromobservationsthatmanyyoungstarsaresur-
v
photo-polarimetricobservations:most of the time the star is in
2roundedbythecircumstellardisks.Duringtheirevolutiondisks
a brightstate (V ∼ 11m.5), but it occasionally falls into a deep
1dissipatepartlyowingtogasaccretionontothestar,partlyinthe
(up to ∆V ∼ 2m) and very short (up to 2d) Algol-like min-
3course of the photoevaporation and planets formation (see re-
ima (Zajtseva 1985). The "blueing effect" and the anticorrela-
3viewsbyWilliams&Cieza2011;Alexanderetal.2014).Inthe
0case of low-mass T Tauri stars (TTS), these processesare well tion between the stellar brightness and linear polarization de-
1.studied both from observational and theoretical points of view greearealso observedinthedeepminima(Kiselevetal.1991;
Shakhovskoietal.2003).
0(see Bouvieretal. (2007) and references therein). The interac-
RZ Psc is a relatively young star: we found the prominent
7tion between the stellar magnetosphere and circumstellar disk
Lii λ6708 line in its spectrum (Grininetal. 2010) and our age
1playsacrucialroleintheaccretionprocess.Thebulkoftheac-
:creting gas infalls onto the star and only a minor part(∼ 10%) estimation, based on a kinematical approach, is 25 ± 5 Myr
v
(Potravnov&Grinin2013).RZPscshowsstrongmid-IRexcess
leaves the stellar vicinity via magnetospheric conical and X-
i
Xwinds(seereviewbyFerreira2013andreferencestherein).The (λ&3µm)andabsenceofanexcessofemissionatshorterwave-
lengths (deWitetal. 2013). This means that the circumstellar
robservationalsignaturesof this processare well known:strong
aemissionintheBalmerandsomemetalliclines,andtheirtypical diskofRZPschasaninnergapwiththeradiusofseveraltenths
ofAU.Theblackbodyradiationwithatemperatureofabout500
PCygprofiles.
Kfitstheobservedexcesswell,andthefractionalluminosityof
Through the evolution of protoplanetary disks and the dis- the dust in this case is ∼ 8%. The large amount of warm dust
sipation of gaseous matter in their inner parts, the accretion, was interpretedby deWitetal. (2013) in the frameworkof the
and hence outflow, gradually decays. The characteristic time debrisdiskmodelasaresultofpossiblerecentcollisionalevents
of this decay is several millions years (Myr). On the timescale intheplanetesimalbelt.
of about 10 Myr accretion becomes vanishingly small (less Commonly, the debris disks are considered gas-poor disks
than 10−11M yr−1) (Fedeleetal. 2010). However, such a short (seereviewsbyMatthewsetal.2014;Wyatt2008andreferences
⊙
timescaleprobablyarisesasaresultofselectioneffects.Insome therein). Only small amounts of cold gas are observed in CO
young objects the time of disk dissipation is prolonged above linesorviaweakspectroscopicsignaturesofevaporatingcomets
thislimit(Pfalzneretal.2014).Nevertheless,thesimpleruleis asinthe caseof23Myrold(Mamajek&Bell2014) βPic and
thattherearenosignsofoutflowifthereisnoactiveaccretionin fewotherA-typestarswithdebrisdisks(Welsh&Montgomery
the system. Untilrecently,thisrule was applicablewithoutany 2013).
Articlenumber,page1of10
A&Aproofs:manuscriptno.RZ_Psc_art7
Table1.ParametersofRZPsc
11111111........55555555
Parameter Value Reference 11111111 MMMMMMMMyyyyyyyyrrrrrrrr 11111111........55555555 11111111........00000000
11111111........00000000 1111111100000000 MMMMMMMMyyyyyyyyrrrrrrrr
T 5350±150K 1
eff
lgg 4.2±0.2 1 00000000........33333333
00000000........55555555
[M/H] -0.3±0.05 1 3333333300000000 MMMMMMMMyyyyyyyyrrrrrrrr
Vsini 12.0±0.5km/s 1 ) ) ) ) ) ) ) )unununununununun
SSSSSSSS
R⋆/R⊙ 0.9 2 L/LL/LL/LL/LL/LL/LL/LL/L 00000000........00000000
M /M 1.0 2 g(g(g(g(g(g(g(g(
⋆ ⊙ oooooooo
L⋆/L⊙ 0.7 2 llllllll −−−−−−−−00000000........55555555
EW(Lii) 0.202Å 3
EW(Hαemission) 0.5Å 2,4 −−−−−−−−11111111........00000000
M˙ ≤7·10−12M yr−1 2
⊙
Galacticlatitude -35◦ 3 −−−−−−−−11111111........55555555
RV -1.2±0.33km/s 5 33333333........88888888 33333333........7777777755555555 33333333........77777777 33333333........6666666655555555 33333333........66666666 33333333........5555555555555555 33333333........55555555
lllllllloooooooogggggggg TTTTTTTT
eeeeeeeeffffffff
Notes. References: 1- Potravnovetal. (2014b); 2- this work, 3 -
Grininetal.(2010);4-Grininetal.(2015);5-Potravnovetal.(2014a)
Fig.1. RZPsc(filledsquare)ontheHRdiagram.Theerrorsindicate
the precision of the determination of the T and lgg. The light gray
eff
Incontrast,RZPscshowsperceptiblecircumstellaractivity. solidlineistheZAMS.Thinsolidlinesaretheevolutionarytracksfrom
At a first glance, the spectrum of the star looks like the spec- Siessetal.(2000)models,thesetracksarelabeledwiththecorrespond-
trumofalate-typemain-sequence(MS)star.Thespectrumdoes ingvaluesofthestellarmasses.Thedashedlinesaretheisochronesfor
theages1,10,and30Myrs.
not show any emission abovethe continuum,and there is only
very weak emission (EW ∼ 0.5 Å) in the core of the Hα line.
At the same time the star possesses the prominent and vari- beresultofthechromosphericactivity,weakaccretion,oracom-
ablesignaturesofthe matteroutflowin NaiD resonancelines binationofbothoftheseeffects(seeSection5).Thespectrumof
(Potravnovetal. 2013). Such outflow activity is nottypical for thestarindicatesthatRZPschasalreadypassedthestageofan
stars with debris disks, but this activity can be expected in the activelyaccretingclassicalTTSandnowappearsspectroscopi-
lateevolutionaryphasesofstarswithprimordialdisks. callytobeaveryweak-lineTTSorpost-TTS.
We suppose that the unusual spectral variability of RZ Psc InourpreviouspaperweestimatedtheageofRZPsc(25±5
is caused bythe interactionbetweenan inclined stellar magne- Myr) using the calculations of its space motion under the as-
tosphereandremnantsoftheaccretinggasinthemagneticpro- sumptionoftheGalaxyplaneasthestartingpoint.However,one
pellerregime(Grininetal.2015).Inthisinstanceonecanexpect should take this estimate with some caution because the exact
the modulationof variabledetails in Nai D lineswith a period birthplaceofRZPscintheGalaxyispresentlyunknownandthe
thatisclosetotherotationalperiodofthestar.Theidentification precisionofthecalculationsislimitedbytheuncertaintiesofthe
of the recurrentdetails in Nai D lines, on the basis of the new inputdata,inparticular,thedistance.
spectroscopicobservationsof RZ Psc, isthe aim of thepresent Inthepresentworkweadoptthedistancevalue D ∼160pc
work. fromPickles&Depagne(2010).Theextinctioninthedirection
onRZ Psc is A = 0.3±0.05(G.Gontcharov,privatecommu-
v
nication). Hence, the luminosity of RZ Psc is about of 0.7L .
⊙
2. Stellarparameters
WiththisluminosityandtemperatureT =5350Ktheevolution-
eff
Inthissectionwe describeandupdatesomeofthebasicstellar arymodelsof Siessetal. (2000) providethe value∼ 0.9R⊙ for
parameters.TheparametersofRZPscatmospherewerederived thestellarradiusandcorrespondingmass∼1.0M⊙.Theposition
usinghigh-resolutionspectroscopyobtainedwiththeNordicOp- ofthestarontheHRdiagramisshownintheFigure 1.RZPsc
ticalTelescope(Potravnovetal.2014b).Thesedataaresumma- liesattheendofitspre-main-sequence(PMS)track,however,it
rized,alongwithotherdata,inTable 1. isstilllocatedabovetheMS.
Figure2comparestheRZPscspectruminthevicinityofthe Taking the stellar radius R⋆ = 0.9R⊙ and the projected ro-
HαlinewiththatoftheK0VstandardσDra(Keenan&McNeil tation velocity Vsin i = 12.0 km s−1 into account, we can es-
1989).WeusedσDrasinceitsatmosphericparameters,includ- timate the rotational period of the star. Since RZ Psc belongs
ing its metallicity (Misheninaetal. 2013), were close to those toUX Ori-typestars, theorientationofits circumstellardiskis
determinedforRZPsc.Takingintoaccounttheslowrotationof closetoedge-on.Wethereforeassumethattheinclinationangle
σ Dra, which is Vsini = 1.4km s−1 (Marsdenetal. 2014), we isi = 70◦,asinUXOriitself(Kreplinetal.2016).Inthiscase
convolveditsspectrumwiththecorrespondingrotationalkernel therotationalperiodisaboutP∼3.6d.
to adjust the rotational broadeningof the lines observed in the
RZ Psc spectrum (Vsini = 12 km s−1). One can see the good
3. Observationaldata
coincidence of the photospheric Fei, Sii, and Nii lines in the
bothspectrawhich,ingeneral,extendsoverthewholeavailable The new spectra of RZ Psc were obtained during the two
wavelengthrange (exceptthe lines of the alkali metals, see the observational runs. The first was carried out by I. Potravnov
nextsection).Ontheotherhand,theHαlineintheRZPscspec- and D. Shakhovskoy in September 2014 at the 2.6 m Shajn
trumlooksdifferentfromthestandardspectrum.Whiletheouter telescopeofCrimeanAstrophysicalObservatorywiththeESPL
partsofthelinewingscoincidewellwiththestandardones,the echelle spectrograph. The ESPL was equipped with a Andor
linecoreisshallowerthanthatinthestandardspectrum.Thiscan iKon-L 936 CCD detector of 2048 × 2048 pixels (pixel size
Articlenumber,page2of10
Potravnovetal.:
11..22
FFee II ll 66554466..22 SSii II ll 66555555..55 FFee II ll 66556699..22 CCaa II ll 66557722..88 FFee II ll 66557755..00 NNii II ll 66558866..33
11
00..88
yy
sitsit
nn 00..66
ee
ntnt
II
00..44
00..22
00
66554400 66555500 66556600 66557700 66558800 66559900
WWaavveelleennggtthh ((ÅÅ))
Fig.2. Comparison oftheregion around HαlineinRZPscspectrum(solidlightgray lineor redintheelectronicversion of thepaper) with
the same line in the σ Dra spectrum (dotted line). The spectrum of RZ Psc was obtained on 2013 November 21 with the FIES spectrograph
ontheNordicOpticalTelescope(R∼46000).ThespectrumofσDra(R∼42000)wasretrievedfromtheELODIEarchiveatObservatoirede
Haute-Provence(Moultakaetal.2004).
13.5µm).A4×4binningwasused.Aslitwidthwas2.0arcsec the MRES observations have worse time coverage, the quality
projected on the sky, which corresponds to a resolving power of these spectra allows us to measure the radialvelocity of RZ
of R ∼ 22000or about13.5km s−1. The exposurecoveredthe Pscandinvestigateitsspectralvariabilityinthewidewavelength
spectral region from about 4400 to 7800 Å in 48 orders but range.Thevariablelinesofalkalimetals,Na,K,Ca,aswellas
with substantial interorder gaps across the whole wavelength theHαline,weresimultaneouslycoveredbyasingleexposure.
range.ThesegapsaretheresultofthefactthatthecurrentCCD In terms of understandingthe unusual variability in the Nai D
is smaller than detector for which spectrograph was designed. linesthesedataalsoplayanimportantroleintherecognitionthe
The typical S/N ratio for this observationalmaterial was about typicalpatternsof the additionalcomponentsand in increasing
50-60perresolutionelement.BecauseoftherelativelylowS/N thestatisticsoftheirvelocitiesdistribution.
ratio, interorder gaps, and the impossibility of constructing an Thequasi-simultaneousphotometricobservationswerecar-
accurate global dispersion curve for further cross-correlation ried out by D.N. Shakhovskoy and S.P. Belan using the 1.25
radial velocities measurements, we only analyzed orders that mAZT-11telescopeoftheCrimeanAstrophysicalObservatory.
containanNaiDdoublet. TheseobservationshaveshownthatRZPscwasinabrightstate
duringthetimeofspectralobservations,i.e.,V∼11m.5.
The second portion of the observationshave been obtained
Table2.ObservationallogandradialvelocitiesofRZPsc.
by D. Mkrtichian in December 2014 at the 2.4 m telescope of
Thai National Observatory with MRES echelle spectrograph.
Thecoveredregionwasfrom4400to8800Åin41orderswith Date JD2450000+ Instrument RV[kms−1]
thegoodoverlapping.Themeasurementsofseveralunsaturated
telluriclinesintheregionaround5900Åprovideameanvalue 2014Sept13 6914.42 ESPL —
of FWHM = 0.35 Å, which corresponds to resolving power 2014Sept14 6915.43 ESPL —
R∼17000orabout18kms−1onthevelocityscale.Inthesame 2014Sept15 6916.43 ESPL —
region, S/N was about 95 per resolution element. A full set of 2014Sept16 6917.41 ESPL —
calibration frames was obtained each night. Also the spectrum 2014Sept17 6918.43 ESPL —
of the hot fast rotating A2V star θ And was observed for the 2014Sept18 6919.45 ESPL —
furthertelluriccorrectionofsciencedata.
The spectra from both sets were processed in the same 2014Dec13 7005.02 MRES -2.22±0.53
manner using the standard IRAF reduction tools. The telluric 2014Dec15 7007.12 MRES -1.40±0.44
correctionofsciencedatawasperformedusingthetellurictask 2014Dec19 7011.12 MRES -1.96±0.53
inIRAF.Eachspectrumwascorrectedfortheinstrumentalshift 2014Dec24 7016.06 MRES -1.54±0.60
of zero point velocity. The values of correction were obtained 2014Dec25 7017.05 MRES -1.93±0.45
bymeasuringthepositionoftheatmosphericlines. 2014Dec27 7019.07 MRES -1.22±0.60
ItisimportanttonotethattheESPLexposureshaveagreat
advantage in their extension over six successive nights, which
covered the whole suspected rotational period of the star. The
3.1.Radialvelocities
total duration of the MRES observations was 15 days but the
spectraobtainedweresparselydistributedoverthisinterval.The Heliocentric radial velocity (RV) of RZ Psc were measured on
completeobservationallogispresentedintheTable 2.Although MRESdatausingthecross-correlationtechniquerealizedinthe
Articlenumber,page3of10
A&Aproofs:manuscriptno.RZ_Psc_art7
IRAF fxcor task. The linearized observed spectrum was corre-
latedwiththesyntheticspectruminthewavelengthrange5000-
6500Å,withtheexceptionofvariableNaiDdoublet.Thepo- 1
sitionofCCFpeakwasobtanedbyfittingtoaGaussianprofile. 0.8
ThesemeasurementsarepresentedinTable 2.Thetypicalerror, sity 0.6 −68
ascanbeseenfromTable 2,wasabout±0.5kms−1.Themean en −55
valueofRZPscradialvelocityfromthesespectrawas–1.7km Int 0.4 −34
s−1.PreviouslyweobtainedtwoveryclosevaluesofRV(about 0.2
2014 Sep. 13 2014 Dec. 13 −26
–1.2kms−1)usinghigh-resolutionFIESspectraseparatedbyan 0
intervalofaboutthreemonths(Potravnovetal.2014a).Actually 1
thesetwovaluesarewithintheerrorlimitsandthedifferenceis
0.8
possibly the result of the offset MRES zero point with respect y −78
totheFIESsystem.Nevertheless,thesituationwithRZPscRV ensit 0.6 −61
remains unclear because in the paper cited above we reported Int 0.4 −30. −25
aboutRVfluctuationsuptoseveralkms−1 observedonthedif- 0.2
2014 Sep. 14 2014 Dec. 15
ferentinstruments. Subsequenthomogeneousobservationswill
0
possiblyclarifytherealityofthesefluctuations.
1
Since we investigatethe circumstellar gasmotions with re-
specttothestar,hereafterweconsiderthevelocitiesofthespec- 0.8
y −62
tral features in the rest frame of the star using the RV values sit 0.6 −63
n
e
obtainedabove. Int 0.4
0.2
2014 Sep. 15 2014 Dec. 19
4. Results 0
1
4.1.PreviousspectroscopyofRZPsc
0.8
The spectral variability of RZ Psc and its generalbehaviorhas sity 0.6
been found in the moderate resolution spectra from Terskol en
Observatory (Potravnovetal. 2013). The photospheric Nai D Int 0.4 −108
−35
lines were usually flanked by the variable blueshifted absorp- 0.2
2014 Sep. 17 2014 Dec. 24
tioncomponents(BACs). These componentscompletelydisap- 0
pearedsomenights.Itisimportanttostressthatonlyblueshifted
1
components have been observed; there were no signs of ab-
0.8
sorptions displaced to the red or any signatures of emission in
y
sodium lines. Valuable information about the fine structure of nsit 0.6
these BACs was obtained from the two FIES (Nordic Optical Inte 0.4 −89
Telescope)exposures.Theseobservationswerepartlydiscussed 0.2 −110
in Potravnovetal. (2013) and Grininetal. (2015). It was clear 2014 Sep. 18 2014 Dec. 25 −36
0
from these high-resolution(R ∼ 46000) spectra that the BACs −300 −100 0 100
that were practically unresolvedin the Terskol shots consisted,
in reality, of one or two narrow discrete components. The ve-
locitiesofthesecomponentsvariedalongwith theirintensities.
Thisvariabilityclearlyindicatesthecircumstellaroriginofthese
−113
discretecomponents.Afterdeconvolutionwiththeinstrumental
profile(6.5kms−1)theFWHMofthenarrowestcomponentwas 2014 Dec. 27
about12.7km s−1. Thisvalueindicatesthe verysmallvelocity
−300 −100 0 100
dispersion in the stream where this absorption componentwas v (km s−1)
formed.TheratiooftheinternalvelocityofthestreamtoitsRV
wasabout1/10.
The FIES spectra also showed the existence of a very Fig.3. Naiλ5889linesintheRZPscspectraobservedwithESPL(left
weakvariableemissioncomponentinthe centerofthe Hαline column) andMRES(rightcolumn). Thevelocitiesof thevariableab-
(Potravnovetal. 2013, 2014b). The residual emission, which sorptioncomponentsarelabeledinkms−1.Theweakabsorptionsnear
wasobtainedaftersyntheticprofilesubstraction,hadEW∼0.5 therededgeofλ5889lineintheESPLspectraaretheresidualatmo-
sphericcontaminationafterimperfecttelluriccorrection
Åandconsistedofanarrowpeakcenteredonzerovelocityand
weakemissionwingsthatextendedupto±200kms−1
first component increased up to −61 km s−1 on the following
night. The second appeared closer to the photospheric profile.
4.2.NaiDlines The tenativemeasurementof its velocitygave a value of about
Figure 3showsthesuccessiveevolutionoftheNaiλ5889pro- −30kms−1.
file in the ESPL and MRES spectra. We describe these spectra In the following spectrum obtained on September 15, the
below starting from the earliest ESPL data. The first spectrum −30 km s−1 component completely disappeared, while the
(ofSeptember13)clearlydemonstratedtwoseparateBACswith second component stayed near the same position as on the
velocities of about −55 and −34 km s−1. The velocity of the previousnight. However the central intensity and width of this
Articlenumber,page4of10
Potravnovetal.:
absorption were somewhat reduced. The spectrum obtained 6
on September 16 is not shown in Fig. 3 because of its poor
quality. However, as on the following plot (September 17), we
5
lacked additional components. Only the slight asymmetry of
the blue wing of the photosphericprofiles can be noticed. The
lastspectrumobservedonSeptember18demonstratedthesud- 4
denappearanceofstrongBACatavelocityofabout−89kms−1.
N 3
The profilesof the Nai λ5889 line fromthe MRES run are
presentedintherightcolumnofFig.3andintheleftcollumnof 2
Fig.5.ItisreasonabletosupposethatinthespectrumthatbyDe-
cember27,wedealwiththepurephotosphericprofile(plusthe
1
possibleunresolvedinterstellarcontribution).Weusedthisasthe
referenceprofileandsubtracteditfromtheotherobservedpro-
files.Thevelocitiesandequivalentwidthsoftheabsorptioncom- 0
-120 -100 -80 -60 -40 -20 0
ponentsintheresidualspectraweremeasuredwiththeGaussian RV (km/s)
fittinginIRAFsplotroutine.Thesemeasurementsarepresented
Fig.4. DistributionofvelocitiesoftheadditionalNaiDcomponents
intheTable 3.TheEWerrorswereestimatedusingtheformu-
inthespectraobservedwithFIES,ESPL,andMRES.
laefromCayrel(1988).Errorswerebetterthan5%forthestrong
lines(EW&100mÅ)andabout10-15%forweakerlines.
The first two exposures obtained on December 13 and 15 Thelineof Kiat7665Åisseverelyblendedbythetelluric O
2
showedthedeepblueshiftedprofiles,whichweretheunresolved absorption,whiletheKiλ7699componentismoresuitablefor
blends of the photospheric and intense circumstellar compo- investigation.Nevertheless,thetelluriccorrectioninthisspectral
nents. On the night of December 19, we observed the zero- rangewasalsoperformed.
velocityphotosphericprofileandoneadditionalcomponentdis- One can see in the third columnofFig. 5 thatthe first four
placedbyabout−62kms−1. Itishardto foreseethefollowing spectrademonstratedthesingleprofilesbuttheirdepthwasvari-
evolutionofthiscomponentbecauseofthemissingfourobser- able.Subtractionofthereferenceprofile(Dec.27),asinthecase
vational nights and rapid variability in the Nai D lines. In the of sodium lines, allowed us to obtain the residual low-velocity
spectrum obtained on December 24 one can see a complicated circumstellarcomponentobservedatDecember13,15,and25.
pictureinwhichthephotosphericprofileappearedwiththeblue The values of its RV and EW are also presented in the Table
wing distorted by the unresolved absorption and another sep- 3. On the nightsof December13 and15 these componentsap-
arate component was displaced at −108 km s−1. On the suc- pearedslightlyshiftedshortwardastheNaiDlines.Inthespec-
cessive night the low-velocity (−36 km s−1) component grew trum obtained on December 25 the two additional BACs were
significantly and almost reached the saturation. Another com- clearly observed. At the same time the intensity of shortward
ponent stayed almost at the same velocity, although it also be- NaiDcomponentsalsoreachedtheirmaximum.
camedeeper.Afteronenight,onDecember27theintenselow-
velocitycomponentcompletelydisappearedbut the second ab-
4.4.CaiiIRtriplet
sorptiononlyslightlyreducedinintensityandshiftedafewkm
s−1 to the blue. The mean FWHM of this componentfor three ThelinesoftheinfraredCaiitripletat8498,8542,and8662Å
dates(December24,25,and27)wasabout25.5kms−1.There
areclearlyobservedontheourMRESspectra.Sincethelinesof
isthestrongreasontosuggestthat,despitethemissingthenight
thePaschenseriescompletelydisappearinthespectraofdwarfs
of December 26, we are dealing with a slowly evolved high-
withspectraltypelaterthanG0(Gray&Corbally2009),theef-
velocitycomponentforminginthesameportionofthegas.On fectsofblendingCaiitripletbythehydrogenlinesinthecaseof
the other hand the low-velocitycomponentshowed sufficiently
RZPscareneglible.Nevertheless,weobservedthecomplicated
fasterevolutiononthetimescaleofaboutoneday.
picture in the calcium lines. For a detailed analysis we choose
The velocity distribution of the Nai D BACs is shown in Caii8542Å,sinceitspositionontheechelleorderprovidesthe
Fig. 4. From the histogram one can see that there are three mostreliablecontinuumtracinginthevicinityoftheline.
intervalsof radialvelocitiesin whichthese componentsappear ThevariabilityoftheCaii8542Ålineisshownintheright
mostfrequently.Possiblythismeansthattheabsorptioncompo-
columnofFig.5.Theouterpartsofthelinewingscoincidewith
nents are formed in different coils of the same gaseous stream
the synthetic profile, while the line core shows significant de-
withtherelativelystableparameters.Hereafter,basedonFig.3
viationsfromit. On December19 and27 the observedprofiles
and this histogram, we define the intense and rapidly evolving
appearalmostsymmetricalbutwiththecorefilledbyemission.
BACs, fromthe rightbin, as low-velocityBACs. We callother
OntheotherdatestheBACbecomedeeperandarecenteredon
components,fromthemiddleandleftbins,high-velocityBACs. different velocities, from −17 km s−1 up to −27 km s−1. The
presenceoftheCaiivariableBACcorrelateswellwiththelow-
velocitycomponentintheNai5889Åline,whichindicatestheir
4.3.Ki7699Åline commonorigin.Subtractionofthesyntheticprofilefromtheob-
servedprofilesrevealsthestructureofemissioncoreoftheCaii
Theresonancedoubletoftheneutralpotassiumat7665and7699 8542Åline.InFig.6onecanseethenarrowpeakclosetozero
Åhaslowionizationpotential(4.3eV)andformsundersimilar velocity,broad(upto±100kms−1)wings,andsuperimposedab-
conditionsassodiumDlines.Therebyweexpectthatvariability sorptioncomponent.Whilethenarrowvariablepeakmostlikely
inthepotassiumlinesshouldresembletheobservedvariationsin arisesinthestellarchromosphere,thevelocitiesoftheemission
NaiDlines,butscaledaccordingtolowerpotassiumabundance. wingsarenottypicalforchromosphericdetailsandpossiblycan
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A&Aproofs:manuscriptno.RZ_Psc_art7
Table3.StructureofthealkalimetalsBACsinRZPscspectra.Thelabel"a"correspondstolow-velocityBACs,"b"correspondstohigh-velocity
BACs. Since there is no possibility of determining the true continuum for the shell component of Caii λ8542, there are no equivalent width
measurementsforthisline.
Date Line Component RV(kms−1) W(mÅ) Line RV(kms−1) W(mÅ) Line RV(kms−1)
2014Dec13 D λ5889 a –26 343 Kiλ7699 –13 88 Caiiλ8542 –17
2
b –68 202 – – –
2014Dec15 D λ5889 a –25 384 Kiλ7699 –3 114 Caiiλ8542 –13
2
b –78 133 – – –
2014Dec19 D λ5889 a – 17 Kiλ7699 – – Caiiλ8542 –
2
b –62 169 – – –
2014Dec24 D λ5889 a –35 383 Kiλ7699 – – Caiiλ8542 –26
2
b –108 299 – – –
2014Dec25 D λ5889 a –36 569 Kiλ7699 –40 125 Caiiλ8542 –27
2
b –110 340 –112 46 –
2014Dec27 D λ5889 a – – Kiλ7699 – – Caiiλ8542 –
2
b –113 277 – – –
beattributedtoaccretionflow.ThesameistruefortheHαline
(seebelow).
1,4
Na I D12
4.5.TheHαline 1,2 Fe I Ti I
5883.8 Fe I 5899.3
5892.8
Figure 6 also shows the behavior of the emission component
1,0
ofHαlineinRZPscspectra.Toincreasethestatistics,thedata
y
from MRES run were complementedby the two FIES spectra, sit 0,8
n
which are convolvedwith a correspondinginstrumentalprofile nte
foradjustmentof thespectralresolution,andone spectrumob- I 0,6 -114
tainedonOctober23,2012withtheMSSspectrographofthe6 -110
m BTA telescope by I. Yakunin and I. Potravnov (R∼ 13500). 0,4
The most notable feature of the Fig. 6 is the contrast between 21.11.2013
0,2
the variability of the red and blue emission wings. While the -30 25.12.2014
blue emission feature at a velocity of about −70 km s−1 is al- -25
0,0
mostconstant,theredemissionfeaturevariesconsiderably.This 5880 5885 5890 5895 5900 5905
featurecompletelydisappearedonseveraldatesandappearedon Wavelength
anotherdate.Theequivalentwidthofthemeanemissionprofile
was about 0.5 Å . We discuss the possible interpretation of its Fig.7. ComparisonoftheMRESspectrumobtainedon2014December
shapeinthelastsectionofthearticle. 25(dottedline,redintheelectronicversion)withthepreviousspectrum
observedon2013November21withtheFIESspectrograph(solidline).
5. Discussionandconclusions
Bothofourobservationalruns(withtheESPLandMRESspec- thedifferentactivitylevelsduringtheseruns.The ESPL obser-
trographs) completely covered the suspected ∼ 3.6d rotational vationsshowedthelocationofadditionalcomponentsmostlyin
period of RZ Psc (see Section 2). While the first observational theintermediatevelocitybininthehistogramandtheabsenceof
setcoveredsuccessivenights,thesecondsethadsomegaps.In strongabsorptionin thevelocitiesofabout–20- 30kms−1.In
bothcasesweobservedtheprominentevolutionoftheBACsin contrast the MRES spectra demonstrated high-velocityabsorp-
the Nai D lines, but we did not find any clear signs of period- tionat∼–110kms−1 andaprominentlow-velocitycomponent
icityintheirappearance.Fromtheothersidethecomparisonof infourofoursixspectra.
thetwospectrafromthetwodifferentobservationalsetsshowed The theoretical calculations for the magnetospheric accre-
analmostexactcoincidenceofradialvelocitiesoftheBACsob- tion model (e.g., Muzerolleetal. 2001) show that if the accre-
servedonDecember25,2014andNovember21,2013(Fig.7). tionrateishigherthan10−8M yr−1 thetypicalformoftheNai
⊙
Apparently,weobservedthesamegaseousstructurewherethese D profiles is an assymetricalsingle profileor an inverseP Cyg
BACswereformedonthesetwodates.Thisfindingsupportsour profilewithablueshiftedemissioncomponent.Theemissional-
assumption that the variability of the BACs in sodium lines is mostcompletelydisappearsinthecaseofloweraccretionrates.
periodicbutcomplicatedbyrandomfluctuations. Butthesignsofthematterinfallarestillpreserved.Inthecase
The histogram presented in the Fig. 4 confirms the issue of RZ Psc we deal with a completely inverse picture. In all of
mentionedabove.FromthecomparisonoftheESPLandMRES our spectra we observed only signatures of the matter outflow
observations(Fig.3)itisalsoevidentthatthestardemonstrates andneverobservedany tracesof infallor emission in the lines
Articlenumber,page6of10
Potravnovetal.:
ofthe sodiumdoublet.Theabsenceofthe NaiD emission can 2010; Potravnov&Grinin 2013) and with the very low
beexplainedbythelowaccretionrate(seebelow).Intheframe- accretionrate.
workofthemodel,whichincludesboththemagnetosphericac-
cretionand magnetospheric(or disk) wind,it is possible to ex- – RZ Psc is surrounded by remnants of the protoplanetary
plaintheformationofthePCyg-typeprofile.However,noneof disk. The spectroscopic signatures of circumstellar gas
theexistingwindmodelscanexplaintheappearanceofthedis- are very weak in comparison with the actively accreting
creteblueshiftedabsorptioncomponents.Inourpreviouspaper classical T Tauristars, but exceedthe circumstellar activity
(Grininetal. 2015) we explainedthe existenceof suchcompo- footprints in more evolved systems with debris disks. The
nentsastheresultoftheinteractionofthecircumstellargaswith structure and kinematics of the BACs observed in RZ Psc
the inclined magnetosphere in the magnetic propeller regime. spectrastronglyresemblesuchBACsinthespectraofsome
The low mass-accretion rate is favorable to realize this mech- activelyaccretingPMSstars(Grininetal.2015).
anism. It arises when the angular velocity of the star (and the
magnetosphere) exceeds the angular velocity of the Keplerian – The IR data show that the circumstellar disk around RZ
diskatthetruncationradius(R ).Underthiscondition,spiral Psc is in a more advanced evolutionary stage, than young
trunk
structuresintheoutflowingmatterareformed(Romanovaetal. protoplanetarydisks.Ithasaninnergapandalargeamount
2009) and most of the accreting gas is scattered into the sur- ofwarmdust(deWitetal.2013).
roundingspace. This issue can explain the total absence of the
spectroscopicsignaturesofmatterinfallinNaiDlines.
The careful consideration of the Hα and the IR Caii lines We deduce that RZ Psc is a high-latitude isolated post-T
intheRZPscspectra(Sections4.4,4.5)showsthattheresidual Tauri and post-UX Ori-type star whose disk is in the transi-
emission in these lines cannot be completely explained by the tional evolutionary stage between primordial and debris disks.
chromosphericactivity.Whilethenarrowpeakcanbeattributed TheevolutionarystatusandobservationalcharacteristicsofRZ
tothechromosphericemission,thebroademissionwings(upto Psc make this object a point of a great interest in studying the
±200kms−1)possibleariseduetothemicroflares(Montesetal. very late phases of accretion and outflow processes in the cir-
1998)oraccretion(Murphyetal.2011). cumstellardiskaroundyoungstarsnearthemainsequence.
The knowledge of the stellar distance and radius allows us
Acknowledgements. ThisworkwassupportedbygrantRFBR15-02-09191(V.
toestimatetheupperlimitofthemassaccretionrateonthestar, Grinin,I.Potravnov,D.Shakhovskoy) andinpartbytheRFBR15-02-05399
usingtheempiricalrelationshipbetweentheobservedemission (I.PotravnovandD.Shakhovskoy).V.GrininandI.Potravnovwerealsosup-
line luminosity and total accretion luminosity. The equivalent portedbytheProgrammeofFundamentalResearchoftheRussianAcademyof
Sciences7P“ExperimentalandtheoreticalresearchoftheobjectsofSolarsys-
width of the mean Hα emission in RZ Psc spectra is about0.5
temandplanetarysystemsofstars”.WearegratefultoP.P.Petrovfortheuseful
Å(seeGrininetal.2015andSection4.5).Usingtheparameters discussionsandtothereferee,whosecommentshavehelpedtoimprovethepa-
obtainedaboveandthe continuumfluxfromthecorresponding persignificantly.TheassistanceofS.P.Belaninphotometricobservationsisalso
model of the MARCS grid (Gustafssonetal. 2008), we obtain gratefullyacknowledged.
theHαluminosity L /L ∼ 3·10−5. Theextrapolationofthe
Hα ⊙
relationshipsfromRigliacoetal.(2012)givesthetotalaccretion
luminosityforRZPscaslog(Lacc/L⊙)=−3.74andthemassac- References
cretionrateofM˙ ∼7·10−12M yr−1.Thisvalueistheupperlimit
⊙
of the realaccretionrate, since thereis no certaintythatall the Alexander,R.,Pascucci,I.,Andrews,S.,Armitage,P.,&Cieza,L.2014,Proto-
starsandPlanetsVI,475
HαemissioninRZPscspectrumiscausedbyaccretion(seethe
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rate (Table 1), we recalculated the corotation and truncation
Fedele,D.,vandenAncker,M.E.,Henning,T.,Jayawardhana,R.,&Oliveira,
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accretionrate candisturbthe expectedperiodicityofthe BACs
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variations expected in our model. Therefore, the observed pic- Marsden,S.C.,Petit,P.,Jeffers,S.V.,etal.2014,MNRAS,444,3517
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Articlenumber,page8of10
Potravnovetal.:
NNaa II DD22 HHaa KK II ll 77669999 CCaa IIII ll 88554422
11
00..88
sitysity 00..66 −−6688
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−−2266 22001144 DDeecc.. 1133
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IntInt 00..44 −−110088
−−3355 −−−222666
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−−2277
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vv ((kkmm ss−−11)) vv ((kkmm ss−−11)) vv ((kkmm ss−−11)) vv ((kkmm ss−−11))
Fig.5. ProfilesofthevariablelinesobservedintheRZPscspectraduringtheMRESrun.Thevelocitiesinkms−1ofthecircumstellarabsorptions
arelabeled.ThereferencephotosphericprofilesoftheNaiλ5889andKiλ7699areplottedwithadashed(redintheelectronicversion)line(see
thetextfordetails).InthecaseoftheHαline,thespectrumoftheσDraconvolvedwiththecorrespondinginstrumentalandrotationalkernels
wasusedasreference.FortheCaiiλ8542,thedashedlineindicatesthesyntheticprofile.
Articlenumber,page9of10
A&Aproofs:manuscriptno.RZ_Psc_art7
CCCCCCaaaaaaIIIIIIIIIIII llllll 888888555555444444222222 HHHHHHHHHH aaaaaaaaaa
000000......444444 0000000000..........4444444444
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−−−−−−000000......111111 −−−−−−−−−−0000000000..........1111111111
−−−−−−000000......222222 −−−−−−−−−−0000000000..........2222222222
−−−−−−333333000000000000 −−−−−−111111000000000000 000000 111111000000000000 333333000000000000−−−−−−−−−−333333333300000000000000000000 −−−−−−−−−−111111111100000000000000000000 0000000000 111111111100000000000000000000 333333333300000000000000000000
vvvvvv ((((((kkkkkkmmmmmm ssssss−−−−−−111111)))))) vvvvvvvvvv ((((((((((kkkkkkkkkkmmmmmmmmmm ssssssssss−−−−−−−−−−1111111111))))))))))
Fig.6. ResidualprofilesofCaii8542ÅandHαlines.ThemeanHαemissionprofileisshownwithathickgrayline(redintheelectronicversion)
Articlenumber,page10of10