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astro-ph/9503003 01 Mar 1995 L Kap er companion of Wray M rived which provides formation in a binary increases to M scenarios Wray Send oprint requests to sar GX Uoptical was counterpart presented Vidal by ParkesThe of et most the al recent binary sp ectral Xray study of pul Wray BP Cru Introduction the Xray Abstract Received November Accepted January 8 7 6 5 4 3 2 1 Key a est in our The classication of Wray as based on a comparison of its optical sp ectrum to that of new the binary system ie Stars of  kp c The average Xray of the is then GX Stars sup ergiants Xrays stars ray velocity WrayYour thesaurus co des GX are will b e inserted byAA hand manuscript later no 1 Royal Greenwich Observatory MadingleyKapteyn Road Astronomical Cambridge Institute CB EZ PostbusInstituut England voor Sterrenkunde AV KU GroningenCenter Leuven for The Celestijnenlaan High Netherlands B EnergyAstronomical Institute Heverlee CHEAF Anton Belgium Kruislaan PannekoekSRON University Utrecht of Sorb onnelaan SJ Amsterdam Amsterdam KruislaanSterrekundig The Instituut CA Netherlands Princetonplei n Utrecht SJ TheEurop ean Amsterdam Netherlands Postbus The Southern Netherlands Observatory Karl Utrecht The Schwarzschild Str Netherlands D Garching b ei Germany M unchen  Sco a wellknown B hypergiant and one of the bright Based on observations obtained at the Europ ean Southern luminosity resulting 37 upp er words individual Wray pulsar erg s 5 v 1 1 the M HJGLM Lamers Wray the B sup ergiant companion of the limit for km s

1 results GX Stars in go o d agreement with the predicted X empirical yr

1 Regarding current binary is estimated from the the in binaries a lower limit to the ? GX L Kap er d a should lower inclination from 1 new A loss rate kp c close Stars distance mass b e 2 classied previously Z AM S 3 of limit E Ruymaekers Stars the determination of of present  for H system a M evolution dense as individual a blackhole prole A B Ia

hypergiant is  mass low de 4 5 al and hence from the mass function M bital mo dulation of the Xray luminosity of GX with or tem to the Xray lightcurve constrains the inclination of the sys M than lower mass limit for blackhole formation f den with pulsar companion The latter fact was used mass loss wind by a large eccentricity and from a more extended dataset by Sato et al nitude HammerschlagHensberge et al and absolute mag bital elements on  kp c This distance implied an average Xray luminosity of tem 6 loss than a normalthe B sp ectrum sup ergiant of Adopting Wray do es show more signs of mass higher than p ergiant and concluded that the massloss rate They is derived probably a sp ectral type of B Iae for the su EPJ van den Heuvel

m Pulsetiming analysis Several The orbital p erio d of this highmass Xray binary sys the R Heuvel 36 HMXB in usually phase

velocity they M Parkes resulted erg s i p erio dicity a  V from Wray massive authors  derived  1 adopted  at is of A plausible set Hab ets with for the s pulsar GX  in et al the absence M for a B Ia Balona Crampton the GX The the binary Given in have a

6 for days distance accurate is the highest known for a HMXB Swank Xray M e carried

pulsar must b e tried a 4 yr Watson normal 5 and the mass function and EJ Zuiderwijk aring to stars 1 to to determination of parameters is adding the remark that out derive system the Wray extreme explain B by et sup ergiants events ASTROPHYSICS prop osed  sup ergiant an White al M is of an eclipse is M observational characterized the and AND of Z AM S much of

V of the observed that GX that Sato et i by Van Swank radius Leahy  based  lower  the the or 7 in  8

L Kap er et al Wray GX a hypergiant with pulsar companion

1

Fig The optical sp ectrum of Wray b ottom from A and that of the hypergiant Sco top are very similar

1

A line of Wray are stronger and The sp ectrum of Sco was kindly provided to us by Dr O Stahl The H and He i

1

have a type prole suggesting that Wray has an even higher massloss rate than Sco The O i i lines are stronger

1

and the N i i lines weaker than those in the sp ectrum of Sco indicating that Wray has a slightly earlier sp ectral type

1

than Sco ie B Ia The strong O i i lines the relatively weak He i A line in comparison with the Si i i i lines and the

strong Balmer emission are consistent with an extremely high luminosity of Wray

and Hab erl suggested that a gas stream in using line strength ratios of Si ivHe i Mg i iHe i and

the system might b e resp onsible for the observed drastic O i iHe i The great strength of the O i i lines particularly

increase in Xray luminosity just b efore each p eriastron O i i A is indicative of a high luminosity Therefore

passage In the following we will present arguments that they prop osed that the sp ectral type of Wray is B Ia

Wray is not a normal B sup ergiant but a B hyper

giant This results in a new distance determination of the

system new estimates for the various stellar parameters

Table Log of observations of Wray obtained with the

are given in Section including a new lower limit to the

ESO m telscop e and CASPEC the orbital phase is calcu

mass of Wray In the nal section we discuss the im

lated from JD mo d given in Sato et

0

plications for massive binary evolution

al

JD 4 t Orbital

exp

Sp ectral classication and luminosity of

Feb A sec phase

Wray

In Figs and we show parts of the optical sp ectrum of

Wray obtained in February with the Cassegrain

sp ectrograph CASPEC mounted on the m telescop e

at the Europ ean Southern Observatory in Chile Tab

The sp ectra partly cover the region from

to A The Balmer up to H and the strong he In the atlas of optical sp ectra of galactic B sup ergiants

lium lines have P Cygnitype proles indicating a strong Lennon et al only one of the early B sup ergiants

stellar wind The H emission combined with sp ectral shows emission in the HD with sp ec

type B usually classies a star as Be but for a the tral type B Ia The classication refers to a class

luminosity class should b e in the range VI I I cf Underhill of sup ersup ergiants Keenan initially consisting

Doazan Hammerschlag et al and Parkes of the four reddest of the brightest stars in the Large

et al classied the optical sp ectrum of Wray Magellanic Cloud Feast Thackeray Van Gen

L Kap er et al Wray GX a hypergiant with pulsar companion

1

Fig The optical sp ectrum of Sco and Wray in the wavelength region from to A Note the weaker N i i lines

in the sp ectrum of Wray and the stronger emission in the He i prole at A Although a uorescence line of Fe i i i is

1

present in the sp ectrum of Sco the bad SN prohibits a rm detection of this line in this part of the sp ectrum of Wray

deren named these stars A wellknown N i i lines weaker than their counterparts in the sp ectrum

1 1

earlyB hypergiant is Sco HD one of the most of Sco which is conrmed by the measured EWs listed

luminous stars in our galaxy It is lo cated in the neigh in Table Using the atlases of OBstar sp ectra by Lennon

b ourho o d of the op en cluster NGC in the asso ciation et al and Walborn Fitzpatrick we con

I Scorpii which has a distance mo dulus m M clude that Wray has a slightly earlier sp ectral type

0

1 1

Stothers The sp ectral type of Sco is B Ia than Sco B in stead of B For this sp ectral type

T K App enzeller Wolf and the ab the relative strength of the He i A line compared to

ef f

solute M Humphreys The the Si i i i lines at provides a go o d indica

V

P Cygni proles can b e found in Wolf Ap tion of the luminosity class The fact that the He i line is

p enzeller and are comprised in the new IUE atlas weaker than the Si i i i lines clearly demonstrates that the

of Snow et al luminosity class is Ia see Walborn Fitzpatrick

Indeed the sp ectrum of HD BIa resembles the

If we compare the optical sp ectrum of Wray with

sp ectrum of Wray even more Wolf private commu

1

that of Sco Figs and we note that the two sp ectra

nication

are very similar To enable a more quantitative compar

ison we have measured the equivalent widths EWs of Wolf Stahl found that uorescence lines of

the most imp ortant sp ectral lines in the wavelength range Fe i i i are sensitive to luminosity in earlyB sup ergiants

A Table The uncertainty in EW due to eg An example of an Fe i i i emission line at A and at

1

the normalization of the sp ectra is estimated to b e A at the b order of the plot in the sp ectrum of Sco

or less A careful insp ection of the sp ectra shows that the is shown in Fig in agreement with the hypergiant na

O i i lines in the sp ectrum of Wray are stronger and the ture of this star Due to the bad signaltonoise in this

L Kap er et al Wray GX a hypergiant with pulsar companion

part of the sp ectrum of Wray we can not conrm the

1

Table Line equivalent widths for Sco and Wray The

presence of this line although an emission feature might

uncertainty in EW is estimated to b e or less Some uniden

b e identied at A

tied lines may corresp ond to interstellar features

Finally the P Cygni shap e of the H Balmer and the

strong He i lines is consistent with the extreme luminos

Line A EW A EW A Remarks

ity of Wray Rosendhal showed that the net

1

Sco Wray

strength of H is correlated with luminosity for early

type sup ergiants Wol Tully derived a simi

O i i blend

lar relation b etween H strength and L but then for

H

O i i

lateB sup ergiants The H equivalent width and

1

O i i

for Wray and Sco resp ectively suggests that

O i i

the luminosity of Wray is even higher than that of

1

1

He i

Sco Regarding the small number of earlytype hyper

O i i blend

giants and their uncertain absolute magnitudes we adopt

1

He i

1

for Wray the same luminosity as Sco although this

unident

might b e a lower limit

3

He i

From the ab ove we conclude that the sp ectral type

Mg i i

of Wray is B Ia and that its

unident interst

is M Then using BC SchmidtKaler

Si i i i V

and EBV Van Disho eck Black

Si i i i

Si i i i

we nd that the luminosity of Wray is L 

6

O i i

L and its distance d kp c which is a threefold

O i i

increase over the current value Consequently the Xray

N i i

luminosity of GX is an order of magnitude higher

N i i

35 37 1

ie in the range b etween  and  erg s

N i i

Van Paradijs

N i i

N i i

O i i blend

Wray GX revisited

O i i blend

The new classication of Wray makes it the rst hy

O i i

p ergiant for which a lower limit on the mass is known We

unident

will argue b elow that the lower mass limit has to b e in

O i i blend

creased In the previous section we introduced new values

unident blend

3

He i blend

for the luminosity of and the distance to Wray Com

unident interst

bined with the adopted eective temp erature of K

Si i i i

corresp onding to sp ectral type B SchmidtKaler

Si i i i

we derive for the radius R R previously R

H

Parkes et al This has imp ortant consequences

1

He i

for the binary system The pro jected semima jor axis

N i i

of the Xray pulsar follows from pulsetiming analysis

N i i blend

1

a sin i  R Sato et al The derived

X

He i blend

1

mass function of the system is

He i blend

N i i

3

M sin i

HG

N i i blend

 M f m

2

M M

X HG

N i i blend

Al i i i blend

with i the systems inclination and M and M the

HG X

N i i

of the hypergiant and the Xray pulsar resp ec

Al i i i

tively If we dene the mass ratio q M M we can

X HG

Si i i i

write Eq as

Fe i blend

3

He i

2

q

Na i interst

M

HG

3

Na i interst

sin i

H

1

The radius of the hypergiant and the absence of Xray

He i

eclipses set an upp er limit to the systems inclination For

a radius of R eccentricity e and p eriastron

L Kap er et al Wray GX a hypergiant with pulsar companion

 

orbital phase It turns out however that the accretion Sato et al found that i  which

radius in p eriastron is of the same order of magnitude as we can conrm With R R however we derive i 



in apastron and R resp ectively This is caused for  q  From Eq it then follows

by the fact that the relative velocity ie the vector sum that the lower limit for the mass of Wray is M 

HG

of orbital and wind velocity do es not change much as M According to evolutionary calculations including

a function of orbital phase The orbital velocity is at its mass loss Schaller et al and given the eective

maximum and the wind velocity at its minimum in p eri temp erature and luminosity of Wray its theoretical

astron and vice versa in apastron Using the ab ove de mass is M M M if it is a p ost main

Z AM S

rived values for the system parameters we nd that the sequence star or M M M if it is a

Z AM S

37 37 1

Xray luminosity is  and  erg s in p ost sup ergiant The new lower limit on the mass is

p eriastron and apastron resp ectively This is compatible consistent with Wray b eing a p ost mainsequence star

37

with the observed average Xray luminosity of  with a mass close to M

1

erg s see section but do es not explain by itself the

large variations in Xray ux eg Hab erl We note

Stel larwind accretion onto GX

that p eriastron passage is very close to the star of the

All B hypergiants are known to show a progression in

order of R ab ove the stellar surface

in the Balmer series with a range of ab out

1

km s b etween H and members of the Balmer se

ries having an upp er quantum number n  Sterken

Discussion

Wolf This Balmer progression is also observed for

Wray Parkes et al and even the strong He i

There is no consensus ab out the evolutionary status of

lines indicate acceleration of the atmosphere The termi

early B hypergiants it is suggested that these very lumi

nal velocity of the wind is normally deduced from UV res

nous stars are the progenitors of Luminous Variables

onance lines but due to the large interstellar

LBVs In fact Wray has a sp ectral type and lumi

no UV sp ectra of Wray are available On the other

nosity similar to that of P Cygni but the massloss fea

1 1

hand UV sp ectra of Sco give v km s Prinja

1

tures in the sp ectra of eg P Cygni and S Dor are more

et al and similar values are obtained for other B

extreme cf Stahl Wolf LBVs are found close to

hypergiants

the HumpreysDavidson limit in the HRD and are charac

1

The massloss rate M of Sco has b een determined

terized by phases of extreme mass loss where M can reach

5 1

4 3 1 from radio observations to b e M yr Bieging et

values of M yr Lamers Lamers

al The relation b etween mass loss and T and

ef f

Fitzpatrick prop osed that the LBV phase is related

L of Lamers and Leitherer based on a sample of

to the fact that these massive stars reach their Eddington

5 1

O stars predicts M  M yr given the T

ef f

limit while they evolve towards the red As a consequence

and L of Wray In Fig we show the H prole of

they lose their outer stellar layers After the LBV phase

Wray and three theoretical proles resulting from the

the blue sup ergiant will b ecome a WolfRayet star As the

SEIBALMER program of Lamers Using departure

name suggests LBVs exhibit dramatic variability in their

co ecients that result from the radiative transfer co de of

optical Wray shows variations of  mag in

De Koter for a B sup ergiant the H prole is com

V eg Pakull like other earlytype hypergiants

5

puted for two dierent massloss rates triangles

The o ccurrence of an LBV phase in massive bina

6 1

and  M yr diamonds The squares give the

ries might explain the existence of some double neutron

5 1

results for LTE p opulations and M M yr For

star systems like PSR that cannot have b een

1

all mo dels v was set to km s and the parameter

1

formed by commonenvelope evolution Van den Heuvel

of the velocity law is equal to one Although none of the

et al In this scenario the required to exp el

mo dels can t the blueshifted P Cygni absorption we es

the envelope of the sup ergiant ie the progenitor of the

timate that the massloss rate derived from the H prole

is derived from the orbital energy of

6 5 1

is b etween  and M yr

the neutron star companion If one applies the formalism

The Xray luminosity pro duced by wind accretion can

of CEevolution to the system PSR the orbital

b e estimated using the formalism of Bondi Hoyle

p erio d of d implies that the progenitor system had an

2

The accretion radius is given by r GM v and the

acc X

r el

orbital p erio d  yr which excludes the o ccurrence of

resulting Xray luminosity is

a spiralin phase If a star sp ontaneously sheds its envelope

2

without the need of a companion spiralling in this prob

GM r

X

acc

L M

X

lem can b e overcome It app ears that if the progenitor

2

r R

X

of the PSR system was a HMXB with a sup er

The large eccentricity of the orbit e implies that giant that undergo es an LBV phase M

Z AM S



the separation b etween the binary comp onents and the M with a high massloss rate a consistent picture for

orbital velocity of the neutron star strongly dep end on its origin can b e found

L Kap er et al Wray GX a hypergiant with pulsar companion

1

Fig The H line of Wray thick line and Sco dashed line and three mo del calculations from the

SEIBALMERmetho d Lamers The triangles and diamonds resp ectively corresp ond to a mo del with a massloss rate

5 6 1 1

of and  M yr v km s and velocity law parameter The squares represent a mo del with

1

5 1 1

M M yr v km s but LTE p opulation s

1

References The new lower limit on the mass of Wray has

consequenses for the observed lower mass limit for black

hole formation in a binary as derived by Van den Heuvel

App enzeller L Wolf B AAS

Hab ets based on the fact that GX is a

Balona LA Crampton D MNRAS

Bieging JH Abb ott DC Churchwell EB ApJ

neutron star We prop ose that this limit is shifted to

M Since it is not clear if all stars with an M

Z AM S



Bondi H Hoyle F MNRAS

initial mass exceeding M will indeed form a

De Koter A PhD thesis University of Utrecht

see eg Maeder the newly determined lower mass

Garmany CD Conti PS ApJ

limit might have imp ortant consequences for the number

Feast M Tackeray MNRAS

of black holes formed in binaries

Hab erl F ApJ

HammerschlagHensberge G Zuiderwijk EJ Van den

Heuvel EPJ AA Acknowledgements We thank Dr O Stahl for providing us

1

HammerschlagHensberge G De Lo ore C Van den Heuvel with an optical sp ectrum of Sco and Dr A van Genderen

EPJ Zuiderwijk EJ AA for his information ab out hypergiants Dr D Lennons help in

Humphreys R ApJS classifying the optical sp ectrum of Wray is highly appre

Keenan Contr KPNO No p ciated Dr T Bedding and Dr G Thimm are acknowledged

Lamers HJGLM in of Luminous Blue Vari for their helpful suggestions We are grateful to the referee Dr

ables Eds Davidson Moat Lamers IAU Coll p Wolf to show the similarity b etween the sp ectra of HD

Lamers HJGLM in preparation and Wray ER is a p ostdo ctoral researcher of the Belgian

Lamers HJGLM Fitzpatrick EL ApJ National Fund for Scientic Research

L Kap er et al Wray GX a hypergiant with pulsar companion

Lamers HJGLM Leitherer C ApJ

Leahy DA MNRAS

Lennon DJ Dufton PL Fitzsimmons A AAS

Maeder A AA

Pakull MW in Pro c Workshop on Accreting Neutron

Stars Garching MPE Rep ort p

Parkes GE Mason KO Murdin PG Culhane JL

MNRAS

Prinja RK Barlow MJ Howarth ID ApJ

Rosendhal JD ApJ

Sato N Nagase F Kawai N et al ApJ

Schaller G Schaerer D Meynet G Maeder A

AAS

SchmidtKaler Th in Astron and Astroph of Stars and

Starclusters Eds Schaifers Voigt SpringerVerlag

Snow TP Lamers HJGLM Lindholm DM Odell A

ApJS in press

Stahl O Wolf B AA

Sterken C Wolf B AA

Stothers R ApJ

Underhill AB Doazan V NASA Mon Ser B stars

with and without emission lines NASA SP

Van den Heuvel EPJ Hab ets GMHJ Nat

Van den Heuvel EPJ Kap er L Ruymaekers E in

New Horizons in Xray Astronomy Ed Makino p

Van Disho eck EF Black EF ApJ

Van Genderen A AAS

Van Paradijs JA in Neutron Stars theory and obser

vation Eds Ventura Pines Kluwer Ac Publ p

Vidal NV ApJ L

Walborn NR Fitzpatrick EL PASP

Watson MG Warwick RS Corb et RHD MNRAS

White NE Swank JH ApJ

Wolf B App enzeller I AA

Wolf B Stahl O AA

Wol SC Tully RB ApJ

This article was pro cessed by the author using SpringerVerlag

a

L T X AA style le LAA version E