Search for systemic mass loss in Algols with bow shocks

9.5 MB·

by  Andreas Mayer

Astronomy&Astrophysicsmanuscriptno.be_stars_Language_Corrected (cid:13)cESO2016
January15,2016
Search for systemic mass loss in Algols with bow shocks
A.Mayer1,R.Deschamps2,3,andA.Jorissen2
1 UniversityofVienna,DepartmentofAstrophysics,Sternwartestraße77,1180Wien,Austria
e-mail:[email protected]
2 Institutd’Astronomieetd’Astrophysique,UniversitéLibredeBruxellesCP226,Av.F.Roosevelt50,B-1050Brussels,Belgium
3 EuropeanSouthernObservatory,AlonsodeCordova3107,Casilla19001,Santiago,Chile
Received28May2015;accepted24December2015
6
1
ABSTRACT
0
2
Aims.Variousstudies indicate that interactingbinary starsof Algol type evolvenon-conservatively. However, direct detections of

n systemic mass loss in Algols have been scarce so far. We study the systemic mass loss in Algols by looking for the presence of
a infraredexcessesoriginatingfromthethermalemissionofdustgrains,whichislinkedtothepresenceofastellarwind.
J Methods.Incontrasttopreviousstudies,wemakeuseofthefactthatstellarandinterstellarmaterialispiledupattheedgeofthe
4 astrospherewherethestellarwindinteractswiththeinterstellarmedium.WeanalyseWISEW312µmandWISEW422µmdataof
1 Algol-typebinaryBeandB[e]starsandthepropertiesoftheirbowshocks.Fromthestand-offdistanceofthebowshockweareable
todeterminethemass-lossrateofthebinarysystem.
] Results.Althoughthevelocitiesofthestarswithrespecttotheinterstellarmediumarequitelow,wefindbowshockspresentintwo
R systems, namely πAqr, and ϕPer;athirdsystem, CXDra, shows amoreirregular circumstellar environment morphology which
S mightsomehowberelatedtosystemicmassloss.Thepropertiesofthetwobowshockspointtomass-lossratesandwindvelocities
typicalofsingleBstars,whichdonotsupportanenhancedsystemicmassloss.
.
h
p Keywords. Binaries:close–Circumstellarmatter–Infrared:stars–Stars:winds,outflows
-
o
r
t1. Introduction We take advantage of the fact that some of these stars
s
are not at rest, but move with a certain speed with respect
a
[The group of Algols host stars with many different observed to their surrounding medium. Assuming that mass is expelled
properties, like W Ser stars, β Lyræ stars, binary B[e] and Be supersonically from the binary system, it is decelerated by
2stars, and symbiotic Algols, which all have in common the the oncoming interstellar medium (ISM) and forms a bow
vparadox that the donor star is more evolved but less massive shock (Baranovetal. 1971; Weaveretal. 1977). Bow shocks
8than the accretor. This is achieved by mass transfer when at a have been observed at all kinds of wavelengths around many
1
certain point the mass ratio reverses. Non-conservative evolu- stellar types, covering runaway O stars to AGB stars (e.g.
2
0tionin Algol-typebinarysystemshasbeenknownfor60years vanBuren&McCray 1988; Coxetal. 2012). In the mid-IR,
0(Crawford 1955). For example Chaubey (1979), Sarna (1993), theseshocksarevisiblethroughthermaldustemission,whenthe
.andvanRensbergenetal. (2011)notedthatAlgolmodelsmust shockfrontheatsupdustgrainsattheinterfacebetweenthestel-
1lose a significant fraction of their mass to reproduce observed larwindandtheISM(Uetaetal.2006).Abowshockdetection
0properties.Oneofthemostefficientscenariosthatremovesmass around an Algol is therefore direct evidence of stellar material
6
1from the system is via a hotspot on the surface of the gainer1. aroundthebinarysystem.Inthiscase,thedistanceofthesystem
:However, no direct detection of systemic mass loss during the totheapexofthebowshockcanbeusedtoderivethesystemic
vmasstransferprocessinclosebinarieshasbeenreportedforAl- mass-lossrateifthewindvelocity,stellarvelocity,andISMden-
Xigolssofar. sityareknown(Baranovetal.1971).
Inthiswork,wefocusonBeandB[e]starsforwhichbina- This research note is a complementary study to the work
r
arityhasbeenconfirmedandthepropertiesofthesystemsarewell done by Deschampsetal. (2015, hereafter D15), but with em-
constrained.ABestarisanon-supergiantBstarwhosespectrum phasis on the observational aspects of the systemic mass loss.
has, or had at some time, one or more Balmer lines in emis- Basedonradiativetransfercalculations,Deschampsetal.(2015,
sion, and might also show infrared (IR) excess (Collins 1987). their Fig. 13) predicted the IR colour excesses expected in the
The origin of these spectral features in these binary Be stars case of systemic mass loss. In additionto the WISE detections
isprobablylinkedtothemass-transferevent(Porter&Rivinius of extended material around CZ Vel and SX Aur presented in
2003). The IR excess is most likely caused by hot circumstel- D15,we discussthepropertiesofthecircumstellaremissionof
lardust(Lamersetal.1998),whichispresentinthecase ofan threeotherobjects,namelyCXDra,πAqr,andϕPer.
evolvedbinarysystemassociatedwithmasstransferevents(e.g.
Dunstalletal.2012).B[e]starsalsohavestrongforbidden(Fe)
2. WISEobservations
emissionlines.
InD15,weperformedasystematicsearchforextendedIRemis-
1 for an extensive explanation of the hotspot mechanism, see sionaroundAlgols(collectedfromthecataloguesofBrancewicz
vanRensbergenetal.(2011)andDeschampsetal.(2013,2015). &Dworak1980andBuddingetal.2004) andAlgol-relatedBe
Articlenumber,page1of8
A&Aproofs:manuscriptno.be_stars_Language_Corrected

-3
2.40x10
-4
3.00x10
CX Dra W3, PA: 30(cid:176)-65(cid:176)
-3 CX Dra W4, PA: 45(cid:176)-135(cid:176)
2.39x10 CX Dra W3, PA: 210(cid:176)-245(cid:176)
c†] ec†]
nsity [Jy/arcse 22..3378xx1100--33 ensity [Jy/arcs 22..9968xx1100--44
nte 2.36x10-3 Int
I
2.35x10-3 2.94x10-4
-3
2.34x10 200 150 100 50 0
200 150 100 50 0
Distance [arcsec]
Distance [arcsec]
Fig. 2. Upper panel: WISE W3 images of CX Dra at 12µm. Lower
Fig.1. Upperpanel:WISEW4imageofCXDraat22µm.Thecon-
panel:IntegratedintensitycutsthroughawedgecoveringP.A.:30◦–65◦
tinuous blackarrow gives theuncorrected proper motionfromthere-
(black line) where emission is visible and P.A.: 210◦–245◦ (red line)
processedHipparcoscatalogue(vanLeeuwen2007),whilethedashed
withoutextendedemission.Wehadtochoosesmallerwedgestoavoid
arrowpointstothedirectionofthespacemotioncorrectedfromtheso-
thefluxbeingdominatedbythediffractionspikesofthePSF.
larmotion(Cos¸kunogˇluetal.2011).Thevaluesofthemotionaregiven
in Tab. 1. The values of the colour bar are given in Jypix−1. Lower
panel: Integrated intensity cut through a wedge covering position an-
gles(P.A.):45◦–135◦. tionofthepolarisationwithorbitalphase,andfromthefactthat
the less massive, moreevolvedF5IIIcompanionfills its Roche
lobe (Berdyugin&Piirola 2002). In π Aqr photometric, spec-
andB[e]systems(Harmanec2001),usingarchivedatafromthe troscopic (broad and complex Hα line profile), and polarimet-
Wide-field Infrared Survey Explorer (WISE)2. WISE is an all- ric variations observed during the second half of the 20th cen-
skysurvey,whichmappedtheskyinfourbandsat3.4,4.6,12, turyare tentativelyattributedto variablemasstransferbetween
and22µmwithangularresolutionsof6′.′1,6′.′4,6′.′5,and12′.′0, the binary components (Bjorkmanetal. 2002; Hanuschiketal.
respectively(Wrightetal.2010).Basedonthelistof70objects 1996).
(Algols and Algol-like Be stars with a WISE-source counter- The extended emission around the stars was detected in
part) providedby D153, we foundthat three systems, CX Dra, Band 3 (W3) at 12µm (CX Dra, π Aqr) and Band 4 (W4) at
πAqr,andϕPer,haveunambiguouscircumstellaremissionand 22µm (CX Dra, π Aqr, ϕ Per). For the two objects with cir-
thereforedeservea specific analysis(in additiontoCZ Veland cumstellar emission (CSE) detected in both bands, WISE W4
SXAur,alreadydiscussedinD15). offersgreaterdetails, most likely becausethe thermalemission
AllthreeobjectsareinthelistofbinaryBestarscompiledby of the shock-heated dust grains peaks at longer wavelengths
Harmanec(2001).TheyexhibitpeculiaritiesthatflagthemasAl- (Draine 1981). In the following, the CSM morphology of the
golcandidates,oratleastassystemswithon-goingmasstrans- threeobjectsisdescribed.Figures1–5depicttheWISEimages
fer. With its sdO companion,ϕ Per has obviouslyundergonea ofCXDra,πAqr,andϕPer,whileTab.1providestheirstellar
severemasstransfer,theprimaryandmoreluminousB2[e]com- properties.
ponentbeingthemostmassivebuttheleastevolved.InCXDra,
mass transfer in the binary has been inferred from the varia-
2.1.CXDra
2 The IRSA:WISE archive can be found at
http://irsa.ipac.caltech.edu/applications/wise/ CX Dra (HIP 92133) is a 6.696d period Algol B2.5Ve+F5III
3 ThelistofobjectscanbefoundinAppendixA system at a distance of 396pc (vanLeeuwen 2007); one of
Articlenumber,page2of8
A.Mayer etal.:SearchforsystemicmasslossinAlgolswithbowshocks

-3 -4
6.36x10 6.96x10
-3 Aqr W4, PA: 45(cid:176)-135(cid:176) Aqr W3, PA: 30(cid:176)-65(cid:176)
6.34x10
arcsec†]6.32x10-3 y/arcsec†] 6.92x10-4 Aqr W3, PA: 210(cid:176)-245(cid:176)
ensity [Jy/66..2380xx1100--33 ntensity [J 6.88x10-4
nt I -4
I 6.84x10
-3
6.26x10
-4
-3 6.80x10
6.24x10 300 250 200 150 100 50 0
300 250 200 150 100 50 0
Distance [arcsec]
Distance [arcsec]
Fig.4.SameasFig.2forπAqrat12µm.Theintegratedintensitycuts
Fig.3.SameasFig.1forπAqr.Theintegratedintensitycutinthelower
inthelower panel cover P.A.:30◦–65◦ (black line)whereemission is
panelcoversPA:45◦–135◦.
visibleandP.A.:210◦–245◦(redline)withoutextendedemission.
the components rotates rapidly. Although it is not eclipsing, fortheB2.5Vestarandanorbitalperiodof6.696dfortheF5III
Berdyugin&Piirola (2002) estimate the mass of the two com- companion,theresultingspiralspacingis3.87au,whichissev-
ponentstobe3.9M⊙ and0.9M⊙ ati = 70◦.Theauthors,how- eralordersofmagnitudesmallerthanwhatisseenontheWISE
ever,correctlynotethatthesemassesaretoosmalltomatchthe image. For comparison, the pixel size of the image is 1′.′375,
spectraltypesofthetwostars. which is 545au at 396pc. This implies that a spiral formed by
ThecircumstellarenvironmentofthestarisshowninFigs.1 the B2.5Ve+F5IIIsystem wouldshow 140 windingsper WISE
and2.TheemissionintheWISEW422µmbandisconcentrated W4pixel.Theobservedarcisthereforenotrelatedtothisshap-
totheeastofthestarandistraceabletoadistanceofabout120′′ ingmechanism.
(47500auat396pc).Themorphologyofthecircumstellarma- In the colour-colourdiagram shown in Fig. 13 of D15 that
terial is somewhat puzzling because several aspects are not in depicts the WISE W4/W1 against 2MASS J/K flux ratios,
s
favour of an ISM interaction. First, the direction of the proper CX Dra is located only slightly above the black-body curve
motion is S-E, but the shape of the emission is not symmetric (F /F =1.678, F /F =0.047). Many other objects fall into
J Ks W4 W1
andismoreconcentratedN-Eofthestar. Second,the emission thisregionofthediagramandnopeculiaritycanbedrawnfrom
isnotdetachedfromthestarandthefluxseemstodecreasewith it.Still,thereisnodoubtthatextendedemissionispresentinthe
distance,whichisnotexpectedforabowshockwherethebright- WISEW4image.
estregionisatthepositionoftheshockfront. IntheshorterWISEW3bandat12µm(seeFig.2),CXDra
Furthermore, the circumstellar material of CX Dra on also shows extendedemission east of the star but in much less
the WISE image describes an arc emerging east of the star detail than in the W4 image. The detection of emission in W3
and curved towards the north. Similar arcs are found to be and W4, however,allows us to estimate the temperatureof the
part of an Archimedean spiral which is caused by a semi- dustemissionaroundCXDra.Weperformedaperturephotome-
detachedcompanioninteractingwiththewindofaprimary(e.g. tryonacircleofradius15′′inbothbands.Theregionwechose
Mastrodemos&Morris1999;Mayeretal.2011;Maerckeretal. is centred at a distance of 56′′ from the star at PA = 48◦ and
2012). Thespacingof the spiralarmsis therebydefinedby the falls between the diffraction spikes of the PSF which is domi-
windvelocityofthemasslosingstarandtheorbitalperiodofthe natingthe W3 image. The resultingfluxesare F = 0.207Jy
ν,12
companion.However,assumingawindvelocityof1000kms−1 andF =1.650Jyat12µmand22µm,respectively.Adopting
ν,22
Articlenumber,page3of8
A&Aproofs:manuscriptno.be_stars_Language_Corrected
The WISE W4 image of π Aqr is depicted in Fig. 3. The
emission shows a morphology that is typical for a wind-ISM
interaction with a bow shock in the direction of the space mo-
tion.Thebowshockconeisquitesymmetriconthenorthernand
southernhalf, extendingto about220′′ (52800au at 240pc) in
thosedirections.Inthedirectionofmotion,thematerialcanbe
traced to about 150′′ (36000au) from the binary system. The
emission peak, however, is closer to the system at about 52′′
(12480au).
InWISEW3at12µm(seeFig.4),theCSEisconcentrated
totheeastofthestaratthesamepositionwherethebowshock
inW4isvisible,butnotasextendedinthenorth-southdirection.
ThelowerpanelofFig. 4 showscutsthroughregionswith and
withoutextendedemission.
InthesamemannerasforCXDra,wealsoperformedaper-
ture photometry(r = 15′′) for π Aqr in both bands at a region
centredatadistanceof61′′fromthestaratPA=46◦.Theresult-
ingfluxesareF =0.481JyandF =4.411Jyat12µmand
ν,12 ν,22
-3 22µm, respectively. Adopting the same absorption coefficients
3.72x10
of astronomical silicates as for CX Dra, the 12µm and 22µm
Per W4, PA: 80(cid:176)-165(cid:176) fluxescorrespondtoatemperatureof120K.
c†] 3.71x10-3
e
s 2.3.ϕPer
c
ar
Jy/ -3 PhiPersei(HIP8068)isalongperiodAlgolB2[e]+sdOsystem
y [ 3.70x10 (P = 127d)atadistanceof220pc(vanLeeuwen2007).The
sit orb
n systemislikelyattheendofitsmass-transferphase(Giesetal.
e
nt 1998)andthematerialtransferredfromthedonorstarhaslargely
I -3
3.69x10 spun up the gainer star (primary) to the rotation rate now ob-
served.Basedondouble-linespectroscopicorbitalelements,the
massesofthecomponentshavebeenestimatedtobe9.3±0.3M
⊙
-3 fortheB[e]primaryand1.14±0.04M forthesdOsecondary
3.68x10 ⊙
300 250 200 150 100 50 0 (donorstar). A hotspotregion detected on the edge of the disc
Distance [arcsec] producesstrongFeivlines.Theenvelopeofthecompanionhas
Fig.5.SameasFig.1forϕPer.Theintegratedintensitycutinthelower mostly been stripped off by the Roche-lobe overflow (RLOF)
panelcoversP.A.:80◦–165◦.Thepeaksatdistancesofabout223′′ and
event and the secondary, now a hot sdO star, is only visible in
283′′ inthelowerpanelcorrespondtothestarsvisibleintheimageat
theUV.
positionanglesof99◦and164◦,respectively.
TheWISEW422µmemissionofϕPerisshowninFig.5.
The CSM is elliptically shaped with the major axis approxi-
the corresponding absorption coefficients of astronomical sili- mately in the N-S direction. The extent of the emission to the
cates Q = 5.60×10−2 and Q = 3.39×10−2 (Draine southisabout290′′(63800auat220pc),whiletheframeiscut
abs,12 abs,22
1985),the12µmand22µmfluxescorrespondtoatemperature off in the north 250′′ from the star. East of the star at ≈ 100′′
of124K(fordetailsseeJorissenetal.2011). (22000au),abrightenedbarisvisiblewiththesameN-Sorien-
Since no other archival observations are available for tationasthewholeellipticalemissionandalengthofabout240′′
CX Dra, we cannot conclude on the shaping mechanism of its (52800au).Thebarisbenttowardsthestaratthesameposition
circumstellarmaterial.Wenote,however,thatthestarmightbe angleasthedirectionofthespacemotion,whichindicatesthat
a possible candidate for showing systemic mass loss in its cir- thisistheinterfacewheretheISMinteractswiththestellarmate-
cumstellarenvironment,butfurtherobservationsareneeded. rial.Thesebendingsarevisibleinhydrodynamicsimulationsof
bowshockswheretheshockedstellarandambientmaterialcool
efficiently (see Fig. 15 in Comeron&Kaper 1998). A beauti-
2.2.πAqr
fulexampleofa bentbowshockisfoundaroundtheAGBstar
PiAquarii(HIP110672)isa84.1dperiodbinarylocated240pc XHer(Jorissenetal.2011).Incontrasttotheothertwoobjects,
from the sun (vanLeeuwen 2007). The system comprises a ϕPerdoesnotshowextendedemissioninWISEW3.
rapidly rotating B1Ve star at the origin of the Be phenomenon
and an A-F type companion. Bjorkmanetal. (2002) estimate
the mass of the components to be M1sin3i = 12.4M⊙ and 3. Bowshockpropertiesandsystemicmassloss
M sin3i = 2.0M with an orbital inclination i = (50− 75)◦.
2 ⊙
The stellar wind is one of the fastest among the Be stars with Forastarthatmoveswithrespecttoitssurroundingmedium,the
a terminalvelocityof 1450kms−1; the mass-loss rate is one of stellar motion adds an asymmetry to the wind velocity profile,
the highest with M˙ = 2.61×10−9M yr−1 estimated from the sincedifferentpartsofthewindfacetheISMwithdifferentrela-
⊙
Siivprofile(Snow1981).WenotethattheSiivlineslikelyform tivevelocities.Ifthemotionissupersonic,abowshockarisesat
insidetheRochelobeofthegainerstarandmightthereforenot the interfacewherethe rampressure of the ISM and the stellar
tracethesystemicmass-lossrate. windbalance.Thestand-offdistance,i.e.thedistanceofthestar
Articlenumber,page4of8
A.Mayer etal.:SearchforsystemicmasslossinAlgolswithbowshocks
Table1.Stellarproperties.Thespacevelocitieswerecalculatedfollow-
5.´106
ing Johnson&Soderblom (1987) using the Hipparcos proper motion
and parallax (vanLeeuwen 2007) and radial velocities from the cata- 1500
loguebydeBruijne&Eilers(2012).Thesolarmotionadoptedtocon-
vertheliocentricmotionintoLSRmotionis(U,V,W) = (8.50±0.29,
13.38±0.43,6.49±0.26)kms−1(Cos¸kunogˇluetal.2011).
CXDra πAqr ϕPer 1000 5.´105
Spec.type B2.5Ve+F5III B1Ve+[A-F] B2[e]+sdO Ds
M [M ] 3.9 14.0±1.0 9.3±0.3 (cid:144)m
1 ⊙ k
M [M ] 0.9 2.3 1.1±0.1 @
2 ⊙ w
v
P [d] 6.696 84.1 127
orb
D[pc] 396±35 240±15 220±9 500
z[pc] 149 169 43 5.´104
n [cm−3] 0.45 0.37 1.30
H
RV[km/s] −2.1±2.3 −4.9±0.1 −4.0±2.1
v [km/s] 21.1±2.0 21.0±1.1 29.8±1.6
∗
P.A.[◦] 107.6±1.2 82.3±0.6 119.7±0.2 0
i[◦] −5.7±63.1 −13.5±1.2 −7.7±30.3 -11 -10 -9 -8 -7 -6 -5

v∗,LSR[km/s] 25.5±2.1 13.5±1.0 13.1±1.7 logHML@Msun(cid:144)yrD 5.´103
P.A. [◦] 125.7±1.0 31.5±0.5 109.4±0.6
LSR
i [◦] 32.4±11.4 6.6±3.7 −4.4±90
LSR
Fig. 6. Density plot relating the mass-loss rate and wind velocity of
Ref. 1 2,3,4 5
πAqrtothebow-shockstand-offdistanceR .Thecoloursindicatethe
0
differenceinautothemeasuredR =36000au.
References. (1) Berdyugin&Piirola (2002); (2) Zharikovetal. 0
(2013); (3) Linnelletal. (1988); (4) Bjorkmanetal. (2002);
(5)Hummel&Štefl(2001)
(10.00±0.36,5.25±0.62,7.17±0.38)kms−1 determinedfrom
the Hipparcos data by Dehnen&Binney (1998) leads to v
LSR
totheapexoftheshockfront,isgivenby velocitieswhichareslightlyclosertothebettermatchinghelio-
centricvalues.Asimilardiscrepancybetweenbow-shockorien-
M˙v tationandLSRmotion(andlesssowithheliocentricmotion)is
R = w , (1) foundby Perietal. (2012, 2015) for a large number of O- and
0 s4πρ0v2∗ B-typestarswithbowshocks,ascollectedintheWISEE-BOSS
survey.Forthisreason,weoverplottedboththeheliocentricand
where v is the terminal wind velocity, v the stellar veloc-
w ∗ LSRmotionsontheWISEimagesinFigs.1,3,and5.
ity with respect to the ISM, M˙ the mass-loss rate, and ρ the
0
Sarna (1993), vanRensbergenetal. (2011), and more re-
density of the surrounding medium (Baranovetal. 1971). The
centlyDeschampsetal.(2013,2015)havesuggestedthatAlgols
densitycan beexpressedin numberdensityofhydrogenatoms
(m =1.6727×10−27kg),whichfollowsroughly lose a significantfractionof their initialmass duringthe mass-
H
transferphase.vanRensbergenetal.(2011)statethatahotspot
nH =2.0e−10|0z|pc, (2) msyesctehmaniinsimtiamlmayasbse.Iinnvtohkisedscteonarerimo,otvheousepptoar1ts5o%ftohfetshteelblainrasruyr--
wherez isthe galacticheight(Mihalas&Binney1981) andn facehitbytheRLOFstream(thehotspot)emitradiationwhose
H
is given in atoms per cm3. Wilkin (1996) demonstrated that pressuretriggersmasslossatarateofupto10−5M⊙yr−1.Sucha
the shape of the bow shock only depends on the stand-off dis- highmass-lossratewouldchangethesizeofthebowshockcon-
tance, while Coxetal. (2012) showed that this assumption re- siderably.Moreover,astreamwindingaroundthebinarysystem
mainsvalidforviewinganglesupto70◦.Abovethisvalue,the forms(seeFig.1ofD15),possiblyalteringtheshapeofthebow
bow shock cone becomes broader. Therefore, we were able to shockaswell.
useEq.1toestimatethemass-lossratefromthebinarysystem In order to identify the origin of the mass causing the ob-
by measuring the stand-off distance. Generally, the ISM den- servedbowshocks,onehastoevaluatethedynamicalageofthe
sity andstellar velocitycan be determinedfollowingEq.2 and bowshock.Thedistanceofthebowshockstothecentralsystem
Johnson&Soderblom (1987), respectively. While the error of is 22000au and 36000au for ϕ Per and π Aqr, respectively.If
the space motion is negligible, the ISM density value is only the bow shocks are caused by systemic mass loss triggered by
an estimate since the star could move through a dense cloud, ahotspot,thewindvelocityisabout1000kms−1 (seeFig.3of
whichisnotconsideredbyEq.2.Therespectivevaluesofthese D15)andtheresultingkinematicagesofthebowshocksareof
quantitiesforthethreeobjectsaregiveninTab.1.Toobtainthe theorderof100yr,muchshorterthanthedurationofthemass-
space motion (v ) with respectto the local standard of rest, transferphaseinAlgolsystems(105yr;Deschampsetal.2013).
∗,LSR
wecorrectedtheheliocentricmotionsfromthesolarmotionvec- Therefore,forAlgolscurrentlyintherapidmass-transferphase,
tor(U,V,W) = (8.50±0.29,13.38±0.43,6.49±0.26)kms−1 if a bow shock is present it will stay for the whole durationof
⊙
(Cos¸kunogˇluetal.2011).However,sincethepropermotionsare themasstransfer.
quite small (a few masyr−1), the correction for the solar mo- SincethewindvelocitiesofπAqrandϕPerarenotknown,
tion has a large impact, especially on the P.A. of the motion. we cannot directly use Eq. 1 to relate the bow-shock stand-off
Interestingly, the P.A. of the corrected LSR motion is a worse distance to the mass-loss rate causing the bow shock and then
match to the bow-shock orientation than the P.A. of the un- compare the latter with the predictions of systemic mass-loss
corrected motion (see Figs. 1, 3, and 5). Using (U,V,W) = rates from the hotspot scenario of D15. Nevertheless, the rela-
⊙
Articlenumber,page5of8
A&Aproofs:manuscriptno.be_stars_Language_Corrected

10 10
Algols
Algols
8 Algols with high W4/W1 flux ratio
Algols with high W4/W1 flux ratio
8 Algols with W4 extended emission
Algols with W4 extended emission
6
s
ol s]
Alg 6 ma 4
ber of allax [ 2
m 4 ar
u P
N
0
2
-2
0 -4
O9B0B1B2B3B4B5B6B7B8B9A0A1A2A3A4A5A6A7A8A9 O9 B0 B1 B2 B3 B4 B5 B6 B7 B8 B9
Spectral type Spectral type
Fig.7.DistributionofAlgolsamongearlyspectraltypes(orangebars), Fig.8.DistancedistributionofAlgolsearlierthanspectraltypeA.Or-
alongwiththosewithdetectedextendedemissionintheWISEW4band ange squares are Algols without detection of circumstellar material,
(cyan bars) and withW4/W1flux ratios fallingabove the black-body cyansquaresshowthosewithdetectedextendedemissionintheWISE
line(blackbars). W4band,andblacksquaresthosewithW4/W1fluxratiosfallingabove
theblack-bodyline(accordingtoFig.13ofD15).
tionbetweenthemass-lossrateandthewindvelocitymayhelp
ustoevaluatethelikelihoodofsystemicmasslosstriggeredby onlyextendupto15′′ fromthestar,andwouldnotberesolved
thehotspotscenario.Inthesecalculations,weusedtheISMden- byWISE.ThisconclusionissupportedbyFig.8,whichreveals
sities ρ0 = nH × mH and space velocities v∗,LSR listed in Ta- thatthe Be stars witha detectedbowshockare thenearestand
ble 1 with stand-off distancesof R = 36000au for π Aqr and thewarmestinthesample.
0
R = 22000au for ϕ Per, as measured on the WISE images. The secondBe star with extendedemission thatwe didnot
0
Fig.6depictstherelationshipbetweenmass-lossrateandwind includeinthisstudyistheB2VnestarV696Mon.TheWISEW4
velocityforπAqr.Thecoloursshowthedifferencesinthe cal- imageisdepictedintheupperpanelofFig.9andshowsapecu-
culatedR totheobservedvalueof36000au. liarmorphologyaroundthestar.Theextendedemissionreaches
0
Foranexpectedwindvelocitybetween700and1500kms−1, north of V696 Mon and seems to engulf the star BD-06◦1393
only a small range of mass-loss rates from 4 × 10−10M⊙yr−1 located 148′′ from V696 Mon at PA = 8◦. This association is
to 4×10−9M⊙yr−1 can match the observed stand-off distance probablynotreal,since the Tycho-1parallaxesofthe twostars
(±5000au)ofthebowshockaroundπAqr.Thisrangeofmass- are quite different. Although the space velocity of V696 Mon
loss rates is well below the systemic mass-loss rate inferred [v = (15.8± 6.2)kms−1] is comparable to the three stars
∗,LSR
from the hotspot scenario (of the order of 10−5M⊙yr−1). Such studied here and the IR emission seems to be aligned with the
a high mass-loss rate in combination with a wind velocity of direction of the space motion, the upstream structure does not
≈1000kms−1wouldcauseastand-offdistancethatisafactorof resembleabowshock.
100largerthanobserved.Tobringthewindvelocityinlinewith We also notethatthesurroundingISMofV696Monisex-
theproposedM˙ fromthehotspotscenarioandwiththeobserved tremelyrich(thestar-formingregionMonocerosR2is56′away)
R , it has to decrease almost to 0. In other words, it is highly asseenintheIRAS100µmimage(lowerpanelofFig.9),andit
0
unlikelythat a systemic massloss of the orderof10−5M⊙yr−1 isdifficulttoconcludewhethertheWISE22µmemissionorigi-
iscurrentlypresentinπAqr.Ifsystemicmasslossisongoing,it natesfromCSMorISM.
doesnotexceed10−8M yr−1.Weemphasise,however,thatthe
⊙
mass-lossrateofπAqrinferredfromthebow-shockproperties
fitswellthevalueobservedfortheBestar(2.61×10−9M yr−1; 4. Conclusion
⊙
Snow1981).WeobtainsimilarresultsForϕPer:M˙ =2×10−10
We studied a sample of 70 Algol and Algol-like Be systems
–6×10−9M yr−1 forv =700–1500kms−1 forameasuredR
⊙ w 0 with entries in the WISE catalogue4 with the aim of identify-
of22000±5000au.
ing those Algol systems surrounded by dust left over by sys-
The Be star wind as the origin of the bow shock is further
temic mass loss. In D15, the two objects, CZ Vel and SX Aur,
demonstratedbythe factthatthe bow shocksdiscoveredin the
werediscussed,andherewefindthatthreenewobjects,CXDra,
presentstudyarerestrictedtoearly-typeBstars(Figs.7–8).Our
πAqr,andϕPer,showcircumstellarmaterialin theWISE W4
samplealsoincludesaO9.7Ibestar,RYSct,whichshowsahigh
bandat22µm;πAqrandCX Draalso showmaterialin WISE
WISEW4/W1fluxratio.However,RYSctismuchfartheraway
W3 at 12µm. The two objectsπ Aqr and ϕ Per show clear ev-
than the three B stars discussed in the present paper since it
idenceofaninteractionofcircumstellarmaterialwiththeISM.
hasaparallaxnotsignificantlydifferentfromzero(vanLeeuwen
For these events, we used the distance of the star to the bow
2007);hence,ifpresent,theextendedemissionwouldbehardly
shocktoderivethemass-lossrateofthematterthatescapesfrom
detectable. Given that the V magnitude of RY Sct (O9.7Ibe)
amountsto9.1,comparedtoV =4.6forπAqr(B1Ve),RYSctis 4 WecheckedtheHerschelScienceArchiveaswell,butonly2ofthe
locatedatleastafactorof10fartherawaythanπAqr.Allother 70targetshadbeenobservedbytheHerschelSpaceObservatory,nei-
parameters being equal, the bow shock of RY Sct would thus therofwhichshowedcircumstellaremission.
Articlenumber,page6of8
A.Mayer etal.:SearchforsystemicmasslossinAlgolswithbowshocks
(seeFigs.1–5andFigs.13-14ofD15).Itisconceivablethatthe
simulationsofD15overestimatetheamountofdustthatsurvives
thehotspotmechanism.Forthetwostarsthatshowthepresence
ofcircumstellarmaterialexpressedbya bowshock(π Aqrand
ϕPer),neithershockappearstobetiedtosystemicmassloss.
In the case of CX Dra, we were not able to identify the
shapingmechanismresponsibleforthe asymmetriccircumstel-
lar emission. Both common triggers for asymmetries, ISM in-
teraction forming a bow shock and binary interaction forming
anArchimedeanspiral,canbeexcludedforvariousreasons.We
notethereforethatthis system is an interestingcase for further
observations since it may be a case where mass lost from the
systemisvisibleinthecircumstellarenvironment.
Acknowledgements. Wewanttothanktheanonymousrefereefortheconstruc-
tiveandhelpfulremarks.ThisresearchissupportedbytheBelgianFederalSci-
encePolicyofficeviathePRODEXProgramofESA.AMacknowledgesfunding
bytheAustrianScienceFundFWFunderprojectnumbersP23586andP23006-
N16andbytheAustrianResearchPromotionAgencyFFGunderprojectnumber
FA538019.RDacknowledgessupportfromtheCommunautéfrançaisedeBel-
gique–ActionsdeRechercheConcertéesandbenefitsfromaEuropeanSouth-
ernObservatorystudentship.WemadeuseoftheNASA/IPACInfraredScience
Archive,whichisoperatedbytheJetPropulsionLaboratory,CaliforniaInstitute
ofTechnology,undercontractwiththeNationalAeronauticsandSpaceAdmin-
istrationandoftheSIMBADdatabase,operatedatCDS,Strasbourg,France.
References
Baranov,V.B.,Krasnobaev,K.V.,&Kulikovskii,A.G.1971,SovietPhysics
Doklady,15,791
Berdyugin,A.&Piirola,V.2002,A&A,394,181
Bjorkman, K.S.,Miroshnichenko, A.S.,McDavid, D.,& Pogrosheva, T.M.
2002,ApJ,573,812
Brancewicz,H.K.&Dworak,T.Z.1980,ActaAstron.,30,501
Budding,E.,Erdem,A.,Çiçek,C.,etal.2004,A&A,417,263
Chaubey,U.S.1979,Ap&SS,64,177
Cos¸kunogˇlu,B.,Ak,S.,Bilir,S.,etal.2011,MNRAS,412,1237
Collins,II,G.W.1987,inIAUColloq.92:PhysicsofBeStars,ed.A.Slettebak
&T.P.Snow,3–19
Comeron,F.&Kaper,L.1998,A&A,338,273
Fig.9.Upperpanel:WISEW4imageofV696Monat22µm.Thecon- Cox,N.L.J.,Kerschbaum,F.,vanMarle,A.-J.,etal.2012,A&A,537,A35
Crawford,J.A.1955,ApJ,121,71
tinuous blackarrow gives theuncorrected proper motionfromthere-
deBruijne,J.H.J.&Eilers,A.-C.2012,A&A,546,A61
processedHipparcoscatalogue(vanLeeuwen2007),whilethedashed
Dehnen,W.&Binney,J.J.1998,MNRAS,298,387
arrowpointstothedirectionofthespacemotioncorrectedfromtheso- Deschamps,R.,Braun,K.,Jorissen,A.,etal.2015,A&A,577,A55
lar motion (Cos¸kunogˇluetal. 2011). The colour bar values are given Deschamps,R.,Siess,L.,Davis,P.J.,&Jorissen,A.2013,A&A,557,A40
in Jypix−1. Lower panel: IRAS 100µm image of the surroundings Draine,B.T.1981,ApJ,245,880
of V696 Mon (marked as an X). The colour bar values are given in Draine,B.T.1985,ApJS,57,587
MJysr−1. Dunstall,P.R.,Fraser,M.,Clark,J.S.,etal.2012,A&A,542,A50
Gies,D.R.,Bagnuolo,Jr.,W.G.,Ferrara,E.C.,etal.1998,ApJ,493,440
Hanuschik, R.W.,Hummel,W.,Sutorius, E.,Dietle, O.,&Thimm,G.1996,
A&AS,116,309
the system. For both systems we estimate a mass-loss rate of Harmanec,P.2001,PublicationsoftheAstronomicalInstituteoftheCzechoslo-
≈10−9M yr−1,whichiscomparabletothemass-lossratefound vakAcademyofSciences,89,9
⊙ Hummel,W.&Štefl,S.2001,A&A,368,471
for single B-type stars and much lower than the predicted sys- Johnson,D.R.H.&Soderblom,D.R.1987,AJ,93,864
temicmass-lossratefromthehotspotscenario(∼10−5M yr−1, Jorissen,A.,Mayer,A.,vanEck,S.,etal.2011,A&A,532,A135
⊙
vanRensbergenetal. 2011; Deschampsetal. 2013, 2015). In- Kobulnicky,H.A.,Lundquist,M.J.,Bhattacharjee, A.,&Kerton,C.R.2012,
AJ,143,71
cidentally, several bow shocks have been reported around sin-
Lamers,H.J.G.L.M.,Zickgraf,F.-J.,deWinter,D.,Houziaux,L.,&Zorec,J.
gle Be stars by e.g. Kobulnickyetal. (2012), Perietal. (2012, 1998,A&A,340,117
2015), and Noriega-Crespoetal. (1997). It seems most likely, Linnell,A.P.,Peters,G.J.,&Polidan,R.S.1988,ApJ,327,265
therefore,thatthebowshocksreportedhereareunrelatedtothe Maercker,M.,Mohamed,S.,Vlemmings,W.H.T.,etal.2012,Nature,490,232
Mastrodemos,N.&Morris,M.1999,ApJ,523,357
binary nature of the considered Be stars, and are of the same
Mayer,A.,Jorissen,A.,Kerschbaum,F.,etal.2011,A&A,531,L4
origin as those observedamongnon-binaryBe stars. However, Mihalas,D.&Binney, J.1981,Galactic astronomy:Structure andkinematics
thisdoesnotentirelyexcludetheexistenceofsystemicmassloss /2ndedition/
inthesesystems.Itcouldwellbethatthemasstransferepisode Noriega-Crespo,A.,vanBuren,D.,&Dgani,R.1997,AJ,113,780
Peri,C.S.,Benaglia,P.,Brookes,D.P.,Stevens,I.R.,&Isequilla,N.L.2012,
hasalreadycometoanendandthesystemicmass-lossratehas
A&A,538,A108
dropped. Peri,C.S.,Benaglia,P.,&Isequilla,N.L.2015,A&A,578,A45
Therefore,theprospectsoffindingobservationalsupportfor Porter,J.M.&Rivinius,T.2003,PASP,115,1153
Sarna,M.J.1993,MNRAS,262,534
systemicmasslossinAlgolsseemdark.Oftheinitialsampleof
Snow,Jr.,T.P.1981,ApJ,251,139
70targets,onlyahandfulofstarsappeartoexhibitIRexcesses Ueta,T.,Speck,A.K.,Stencel,R.E.,etal.2006,ApJ,648,L39
Articlenumber,page7of8
A&Aproofs:manuscriptno.be_stars_Language_Corrected
Continuedfrompreviouscolumn
vanBuren,D.&McCray,R.1988,ApJ,329,L93
vanLeeuwen,F.2007,A&A,474,653 V*Name 2MASS HD/BD Spec.type Ref.
vanRensbergen,W.,deGreve,J.P.,Mennekens,N.,Jansen,K.,&deLoore,C.
CGCyg J20581343+3510298 G9.5V 2,3
2011,A&A,528,A16
V367Cyg+ J20475958+3917156 HD198288 A3Ibep 1,2
Weaver,R.,McCray,R.,Castor,J.,Shapiro,P.,&Moore,R.1977,ApJ,218,
ABPer J03374520+4045494 HD275604 A5 2,3
377
SXAur*+ J05114292+4209553 HD33357 B1Vne 1,2,3
Wilkin,F.P.1996,ApJ,459,L31
RWPer J04201676+4218517 HD276247 A2 1,2,3
Wright,E.L.,Eisenhardt,P.R.M.,Mainzer,A.K.,etal.2010,AJ,140,1868
TXUMa J10452050+4533586 HD93033 B8V 1,2,3
Zharikov,S.V.,Miroshnichenko, A.S.,Pollmann,E.,etal.2013,A&A,560,
GKAnd J23534719+4534458 3
A30
V995Cyg J19483443+4613424 B8 3
SWCyg J20065793+4617581 HD191240 A2 1,2,3
IMAur J05152973+4624214 HD33853 B9 2,3
AppendixA: Listofobjects
RYPer J02454210+4808379 HD17034 B8V 1,2,3
KXAnd J23070621+5011324 HD218393 B3pe 1
TableA.1.SeventyAlgolsandAlgol-likeBestarswithaWISEsource ϕPer*+ J01433964+5041192 HD10516 B1.5Ve 1
counterpartsortedbydeclination.Objectsmarkedwithanasterisk(*) AYPer J03102513+5055543 HD232756 B9 2,3
show extended emission in WISEW4, while the plus sign (+)marks CXDra*+ J18464309+5259166 HD174237 B2.5Ve 1,3
objects with a WISE W4/W1 flux ratio which is above the black- V442Cas+ J23401479+5357339 A0 3
SXCas J00104207+5453293 HD232121 B5 1,2,3
bodylaw(seeTab.6inD15).References:(1):Harmanec(2001);(2):
DMPer J02255800+5606099 HD14871 B5V 2,3
Brancewicz&Dworak(1980);(3):Buddingetal.(2004).
GGCas BD+55274 B5 2,3
RXCas J03074573+6734387 A5III 2,3
XYCep J23523291+6856015 B8 2,3
SSCam J07162474+7319570 G1III 2,3
V*Name 2MASS HD/BD Spec.type Ref.
XZCam J05171266+7550053 A0 2,3
BPMus J12503772-7146186 3 RSCep J05060320+8014524 A5III 1,2,3
DWAps J17233003-6755448 HD156545 B6III 2,3 TYUMi J15175751+8351340 HD138818 F0 3
EPTrA J15492615-6415574 HD140809 A0 2,3
ANTuc J23302225-5825346 HD221184 A5III 2,3
RAra HD149730 B9IV 1,2,3
UZNor+ J16281156-5319215 B? 3
V646Cen J11365877-5312354 HD100987 B8IV 2,3
RVPic J04572970-5208458 HD32011 A1V 2,3
CZVel*+ J09104446-5042405 B3 3
KVPup J07471912-4832122 HD63562 A0IV 2,3
TTHor J03270438-4552566 3
DNVel J09193768-4540477 HD80692 A0III 2,3
VYMic J20490707-3343543 HD198103 A4III 2,3
DMPup J08070409-2531522 A2.5 3
AAPup J08013612-2443034 HD66226 F3IV 2,3
YYCMa J07005186-1914315 A2V 3
AOEri J04320093-1744475 A2 2,3
SSLep+ J06045913-1629039 HD41511 A1V 1
WSer+ J18095070-1533009 HD166126 F5III 1,2,3
RYSct+ J18253147-1241241 HD169515 O9.7Ibep 1,2,3
XYPup HD67862 A3 1,2,3
V644Mon J06570938-1049281 HD51480 Ape 1
AWMon BD-102233 A2 2,3
RZSct J18263352-0912060 HD169753 B3Ib 1,2,3
XZAql J20221335-0721034 HD193740 A2 2,3
V696Mon*+ J06041349-0642321 HD41335 B2Vne 1
ARMon J07204845-0515357 HD57364 K0II 2,3
AUMon J06545471-0122328 HD50846 B4IV 1,2,3
V509Mon+ J06471071-0102147 G4IV 3
πAqr*+ J22251662+0122389 HD212571 B1Ve 1
ACTau J04370635+0141311 A8 2,3
SSCet HD17513 A2 2,3
AXMon J06303293+0552012 HD45910 B2III 1
DNOri J06002835+1013049 HD40632 A2e 1,2,3
FMOri J05085439+1033341 HD241071 A5 3
V930Oph J18414565+1202111 3
BIDel J20273862+1420091 G0 2,3
ALLeo J09581290+1817282 F5 2,3
USge J19184840+1936377 HD181182 B7.5V 1,2,3
ALGem J06573855+2053325 HD266913 F6V 2,3
RSVul J19174000+2226284 HD180939 B5V 2,3
DHHer+ J18473455+2250458 HD343047 A5 2,3
RWTau J04035432+2807334 HD25487 B8Ve 1,2,3
UCrB J15181133+3138492 HD136175 B6V 1,2,3
BCAur J05461654+3250500 3
RXGem J06501154+3314207 HD49521 A0 1,2,3
Continuedinnextcolumn
Articlenumber,page8of8