HD 108 and the Other Peculiar Of?p Stars: Still Puzzling Peter, Jean-Marie, and the

Massive Star Community

Yaël Nazé (Liège University), Nolan R. Walborn (STScI),

and Maxime Spano (Geneva Observatory)

Conti Vreux

Outline of the talk

Of?p, a long story…

• HD108

• HD191612

• HD148937

• Others…

• Conclusions

Of?p, what is that for a spectral type ?

• The Of?p zoo : – introduced by N.R. Walborn in 1972,1973

– principal defining Of?p characteristic :

C III 4650 comparable to N III 4640+ narrow emission/PCyg in Balmer lines+ asymmetric/PCyg HeI lines+ peculiar wind lines in UV

– Rare : 3 Galactic objects

HD108• My first job :

– Jean-Marie : “I have a bunch of spectra”– CIII, H lines, HeI lines variable (+ HeII4686)– 4542 cst

apparent ST changes : O4f?p O8.5fp (Nazé et al. 2001,2004)

– Not so new :• Andrillat, Fehrenbach, Swings & Vreux 1973

“Observations recentes du spectre de HD108 (Of)”• Vreux & Conti 1979 “Spectral variations in the Of

star HD108: are they periodic?”

HD108

• What is it ?– Binary ? (Hutchings 1975, Aslanov & Barranikov 1989)

– Expanding atmosphere ? (Andrillat et al. 1973)

– Disc & jets ? (Underhill 1994)

– Wind variations ? (Vreux & Conti 1979)

– Disc & oscillations ? (Nazé et al. 2001)

– Magnetically confined wind ? (Nazé et al. 2001)

– XRB ? (Nazé et al. 2001)

Prob. not

No

No

?

?

?

?

HD108

XMM observations from Jean-Marie :• A soft X-ray spectrum (T1=0.2-0.3 keV – dominates!, T2=1-3keV) • Luminous, but log(Lx/Lbol)= –6.1

(Nazé et al. 2004)

Not an XRB !

HD191612• Just as HD 108…

– Spectral type : O6.5f?p O8fp – LPV with P=538d– Photometric variations too !– Binary with P=1540d(Walborn et al. 2003,2004, Nazé et al. 2007,

Howarth et al. 2007 )

HD108 too !

HD191612

XMM, again…

Nearly identical high-E spectra !• Soft X-ray spectrum, with only ~30% of flux

(0.5-10keV) in the high T

• Broad lines (FWHM~1800km/s), overluminosity log(Lx/Lbol)= –6.1 to –6.2

• Variations! less X-rays when less visible

emissions & star fainter (Nazé et al. 2007)

is it phase-locked ? YES !

40%

New XMM observation taken at the same phase in the LPV cycle, but at +1.6 in orbital phase

HD148937• Not just the same…

– Spectral type : O6f?p – Not a binary : Indeed… see Conti et al. 1977– LPV for HeII4686, H & H– Possible period : ~7d but sampling inadequate

(Nazé et al. 2008a,b)

– Additional monitoring with Coralie– Amplitude of variations from H to H– HeI5876 also variable !– Period of ~7d confirmed !

– What about the photometry ?

- May 8

- May 12

- May 15

- May 20

An answer ?• HD 191612 : detection of a magnetic field !

– Zeeman signature in metallic & HeI lines – line-of-sight component : -220 +/- 38 G (Donati et al. 2006)

• HD148937 : – Line-of-sight component : -276 +/- 88 G (Hubrig et al. 2008)

• What about HD 108 ?

HD191612

Others…

• In the MCs :a few ones were detected (Heydari-Malayeri & Melnick 1992, Walborn et al. 2000, Massey & Duffy 2001)

but are they similar to the Galactic ones ?

• In the Galaxy : ONE MORE !CPD-28°2561 (Barba & OWN survey team, 2008, in prep.)

– Spectral variations similar to HD191612

– Period not yet identified due to lack of spectra

Of?p, unsolved mysteriesQuestions to be answered• Observationally :

– Are they all magnetic ? Test HD108 & the new ones !– What is the magnetic field geometry ? Monitor it !– Are small-scale variations periodic too ?

Make short-term monitoring of HD108 & HD191612 !

• Theoretically :– If LPV period = rotation period, is it possible to brake

rotation up to 55yrs, as for HD108 ?– Where does the soft X-ray emission come from ?– Why is HD148937 the only one to have a nebula ?– Where does the strong CIII emission come from ?

Liege Colloquium

1996

President of the colloquium : « Andre, I am no longer sure my scenario is correct, what should I do ? »

A. Maeder : « It’s too late to cancel everything… most of the participants are seated… some of them look agressive »

Concluding remarks by the president : « you did convince me, I temporarily maintain my scenario »

Astronomy is a serious affair…

but doing it in Belgium has advantages…

Rendez-vous in 2010 !