Thisisthesameeventdataasbox2butsampledathighspa5alresolu5on.The cross‐shapedChandra PSF is elongated and bluer (harder) in theNW,unlikeanyothersourceintheCOUPdata.Theposi5onsofθ2OriA1+A2andθ2 Ori A3 are superposed. Image reconstruc5on confirms this result: thehardx‐raysareproducedbythe~5MA3companion,notthehigh‐massSBA1+A2. During the flare, A3 accounts for ⅔ of the total x‐ray luminosity.ThoughhighLXisnottypicallyseeninintermediate‐massstars,wenotethatthesecondbrightestx‐raysourceinOrion,θ1OriE,isalate‐B+earlyGSB.

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Chandra Orion Ultra‐deep Project (COUP) image of the central 2’ of the3×105year‐oldOrionNebulacluster.Northisup,eastistothele^.θ1OriC(O5.5 V) is the bright saturated source at center. θ2Ori A (O9.5 V) is thebrightorangesourcenearthesoutheastcorner.Inthisfalse‐colorimage,redrepresentsso^0.3‐1.5keVcounts,green1.5‐2.5keVcounts,andbluehard2.5‐8keVcounts.Thedata,obtainedoverthecourseof10daysinJanuary,2003, show strong x‐ray flares from the blue low‐mass T Tauri stars andlower‐amplitude,periodicvaria5onsfromtheso^erOstars.

X‐raysandMagne-cFieldsonYoungOBStarsMarcGagné1,DavidCohen2,StanOwocki3,LeisaTownsley4andPatBroos4

1WestChesterUniversity,2SwarthmoreCollege,3BartolIns5tute,4PennStateUniversity

Isothermal3DMHDsimula5onofmagne5callyconfinedwindshocksonthecentral star of theOrionNebula, θ1Ori C (O5.5 V). This snapshot ofwindspeed(incms‐1)showsthatshocksnearthemagne5cequatorialplanearefast enough to produce hard x‐rays. The 3D simula5ons provide theazimuthalextentoftheshocks,neededtoes5matethetotalx‐rayemissionmeasure. In the simula5ons the field is Ini5ally dipolar withBp = 1100 G.Mass loss distorts the field lines (in black), channeling plasma from highmagne5cla5tudestotheequatorialplane.CourtesyAsifud‐Doula.

PeterCon5(1972)notedthevariablespectraltypeofθ1OrionisC(O5.5V),thecentral starof theOrionNebula.NolanWalborn (1972 ,1973)definedtheOf?pstarsandsuggestedin1981thatθ1OriC’sspectralvaria5onsweremagne5c in nature, like those of the magne5c star σ Ori E (B2 Vp). Inaddi5on to theHe‐strongBp stars, a dozenor soOand very earlyB starsnowhavemeasuredmagne5cfields:τSco(B0.2V),ζOri(O9.7I),HD191612(O8f?p),HD36879(O7V),HD148937(O6.5f?p),HD152408(O8Iafpe),HD155806(O7.5V[n]e)andtheyoungO4V((f))star9Sgr,thoughnofieldsareasstrongasθ1OriC’s.Le0panel:θ1OriC’slongitudinalfieldstrengthversusphasefromHubrigetal. (2008).Rightpanel:Chandra0.3‐8keVcountrateversusphase (datapointswitherrorbars).Alsoshown is itsHαequivalentwidth versus phase (solid line). Maximum field strength, Hα and x‐rayemissionare seenatphase0.0when theobliquemagne5c rotator is seenpole‐on.Atphase0.5,themagne5cequatorisseenedge‐on.

ChandraHETGspectrumofthemagne5cB0.2dwarfτScorpii,amemberofthe 5 Myr old Sco OB2 associa5on. Bp ≈ 500 G, its magne5c topology iscomplexandit’sanultra‐slowrotatorwithProt=41days(Dona5etal.2006).τSco’sx‐raylines(blacklineinlowerle^panel)arenarrowerthanθ1OriC‘s,butbroaderthancoronallines(grayline).τSco’srichX‐rayspectrumarisesfromhardershocksthanthoseinolderB0starslikeβCrucis.

theta 2 Ori A3 (0.383")theta 2 Ori A1+A2

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Toppanel:Raw(red)andpileupcorrected(black)countratesofCEN1A in2002 and 2006. CEN 1B shows a similar range of count rates, but not theramp seen on CEN 1A in 2006August. Lower panels: the pileup correctedCCDspectraofCEN1B(le^)andCEN1A(right)showveryhightemperaturesof100MKand35MK.CEN1Ashowsa6.5keVFeKαlineaswell.Thistypeofhardvariableemission is reminiscentofηCarandHR5980. In LBVandWRbinaries,thex‐raysariseinthewindinterac5onzonebetweentwoverymassivestars.ThusCEN1maybeahierarchicalquadruplesystem.

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ThisChandra0.3‐8keVhigh‐resolu5onimageofthecoreofM17,revealsapair of hard, variable x‐ray sources separated by 1.8” (> 3000 AU at thedistanceofM17).TheO4pairCEN1Aand1B(a^erChini,Elsaesser&Neckel1980) is the ionizing source of the Omega Nebula. So^er, diffuse x‐rayspervadethecavitytotheeast.Theclustercontainsatleast2000x‐raypointsources(bluecircles).All14OstarsinM17aredetectedwithChandra.MostlikeCEN1Aand1Bshowanomalouslyhardx‐rays.ChandraHETGspectratobeobtainedin2009onCEN1A+1Bwillmeasuref/ira5osandlinewidths.

TheMg XI resonance, intercombina5on and forbidden of θ1 Ori C (solidhistogram and error bars). The three panels show the expected linestrengthsatthreeradii(reddo�edlines).Notetheforbiddenlinestrengthat4R★.Lower le0:2Dnon‐isothermalMHDsimula5onofMCWSonθ1OriC.Thesesimula5onsincludeadetailedtreatmentofthewindenergybalance,accoun5ngforbothshockhea5ngandradia5vecooling.Theblackcontourcontains 1‐40 MK plasma. The MCWS model predicts the right amount,temperatureandloca5onofthex‐rayemi�ngplasma.

Chandrahigh‐energy transmissiongra5ngspectraof themagne5cOdwarfθ1OriCandthenon‐magne5cOsupergiantζPuppis.Thex‐raylinesofζPuparebroad,asymmetric,andformedthroughoutthewindstar5ngataradiusofjust1.5R*.ζPup’s4MKshocksproducearela5velyweakbremsstrahlungcon5nuum.Theforbidden linesofHe‐likeSi,MgandNeareweakbecauseelectrons in theupper level of the forbidden line arephoto‐excited to theupper level of the intercombina5on line. θ1Ori C‘s lines are resolved butnarrowerandsymmetric.Thestrongcon5nuumemission,andstronglinesofFeXXV,SXVIandSiXIVindicateveryhighshocktemperatures.

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θ1OriC:T≈33MK,Rshock≈2R⋆,vturb≈350kms‐1

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Thethirdbrightestx‐raysourceinOrionandtheonlyotherOstar,θ2OriA,isahierarchicaltriple:aspectroscopicbinaryA1(O9.5V,25M)+A2(8M)in anellip5cal orbitwitha = 0.47AUandA3 (5M) at 0.4” (160AUat adistanceof400pc).Long‐andshort‐termvariability,includingastrong,hardflare,wereseenintheCOUPlightcurve.Schulzetal.(2006)proposedthatboth A1 and A2 are magne5c stars (lower‐mass analogs of θ1Ori C) andfurther suggested that the flares reported by Stelzer et al. (2005) andFeigelsonetal. (2002)weremanifesta5onsofbinary‐inducedreconnec5onwhereinthemagnetospheresofA1andA2interactatperiastron.

Stelzeretal.(2005)

MCWS:θ2OriA1primary(O9.5,so^)

COUPflare:θ2OriA3(hard)

X‐rayProper+esofMagne+cO4‐B0Dwarfs

1.  Polarfieldstrengthsof50‐1100G,fossilfields2.  Young(lessthan5Myr)3.  Strongfieldsslowrotators4.  X‐raysfrommagne5callyconfinedwindshocks5.  Moderate‐amplitude,periodicx‐rayemission6.  Symmetriclines,smallredshi^s7.  Variabilitycausedbyrota5onandocculta5on8.  200‐1000 km s‐1 x‐ray line widths, depending

onconfinement9.  8‐40MKshocks,dependingonconfinement10.  1.5‐3.0R⋆x‐rayforma5onradius11.  Nox‐rayflaresobservedonmagne5cOBstars,

thoughflaresseenonσOriE(B2Vp)12.  Long‐term,large‐amplitudevariabilityandvery

hardx‐raysmayindicatecollidingwindshocks,notmagne5cconfinement

StrategiesforFindingMagne+cOBStars

Thoughmagne5cfieldshavebeendetectedonOBdwarfs, He‐strong Bp stars, He‐weak Bp stars,slowly pulsa5ng B stars, β Cephei stars, δ Scu5stars,andHerbigBestars(e.g.,Hubrigetal.2006,Briquet et al. 2007,Bouret et al. 2007 and2008,Alecianetal.2008aand2008b,Wadeetal.2006,Dona5 et al. 2006, Dona5 et al. 2002), fields onmostOBstarsareweakorabsent.

Thoughhardandvariablex‐rays fromθ1OriC,θ2Ori A and τ Sco strongly suggest magne5c windshocks,inbroad‐bandsurveysmostotherOBstars(magne5candnon‐magne5c)haverela5velyso^,constantx‐rays.High‐resolu5onx‐rayspectroscopyisneeded.

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