HD 148937: A MULTIWAVELENGTH STUDY OF THE THIRD GALACTIC MEMBER OF THE Of?p CLASS

Nazé, Yaël; Walborn, N. R.; Rauw, Grégor; Martins, F.; Pollock, A. M. T.; Bond, Howard E.

doi:10.1088/0004-6256/135/5/1946

Cited by 56 publications

(127 citation statements)

References 62 publications

(80 reference statements)

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“…In the past, stars displaying this feature were classified by Walborn (1972) in a separate category, dubbed Of?p. In recent years, this category has attracted a lot of attention, as one can see from the numerous publications (Walborn et al 2003(Walborn et al , 2004Donati et al 2006;Howarth et al 2007;Hubrig et al 2008;Nazé et al 2001Nazé et al , 2004Nazé et al , 2007Nazé et al , 2008a. They dealt with the peculiar properties of these stars (for a summary see Nazé et al 2008b) and led to a modification of the definition of these stars.…”

Section: Introductionmentioning

confidence: 99%

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New findings on the prototypical Of?p stars

Nazé¹,

ud‐Doula

Spano

et al. 2010

A&A

111

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Aims. In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken. These multiwavelength studies revealed the peculiar properties of these objects (in the X-rays as well as in the optical): magnetic fields, periodic line profile variations, recurrent photometric changes. However, many questions remain unsolved.Methods. To clarify some of the properties of the Of?p stars, we have continued their monitoring. A new xmm-Newton observation and two new optical datasets were obtained. Results. Additional information about the prototypical Of?p trio has been found. HD 108 has now reached its quiescent, minimumemission state for the first time in 50-60 yr. The échelle spectra of HD 148937 confirm the presence of the 7d variations in the Balmer lines and reveal similar periodic variations (though of lower amplitudes) in the He i λ 5876 and He ii λ 4686 lines, underlining its similarities with the other two prototypical Of?p stars. The new xmm-Newton observation of HD 191612 was taken at the same phase in the line modulation cycle, but at a different orbital phase from previous data. It clearly shows that the X-ray emission of HD 191612 is modulated by the 538d period and not by the orbital period of 1542d -it is thus not of colliding-wind origin. The phenomenon responsible for the optical changes appears also at work in the high-energy domain. There are problems however: our MHD simulations of the wind magnetic confinement predict both a harder X-ray flux of a much larger strength than what is observed (the modelled differential emission measure peaks at 30-40 MK, whereas the observed one peaks at 2 MK) and narrow lines (hot gas moving with velocities of 100-200 km s −1 , whereas the observed full width at half maximum is ∼2000 km s −1 ).

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Section: Introductionmentioning

confidence: 99%

“…lines weaker than for typical Of supergiants (Nazé et al 2008a;Walborn et al 2010). Stars that appear otherwise normal but display strong C iii λ 4650 emission are now called "Ofc" stars (Walborn et al 2010).…”

Section: Introductionmentioning

confidence: 99%

New findings on the prototypical Of?p stars

Nazé¹,

ud‐Doula

Spano

et al. 2010

A&A

111

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“…A previous 3-yrs spectral monitoring revealed small-amplitude (a few percent of the peak's amplitude) variations of the Hα line, with a potential period of 7d (Nazé et al 2008b). While the X-ray data were undistinguishable from those of HD 108 and HD 191612, the optical properties thus appeared quite different from those of the other two "prototypical" Of?p stars (which display large variations of many lines, occurring with a long period and correlated with rather large photometric changes).…”

Section: Hd 148937mentioning

confidence: 85%

“…These objects were then known to display strong C III 4650 emission lines but recent studies showed that this is not their sole peculiar characteristics (in fact, at the present time, stars displaying "only" strong C III 4650 emission should be classified as Ofc, see Walborn et al 2010). Of?p stars also possess: narrow P Cygni/emission features in Balmer, HeI,... lines which vary in a recurrent manner; correlated photometric variations; strong magnetic fields; and large X-ray overluminosities (for a review, see Nazé et al 2008a). Five Galactic Of?p stars are known, but only the first three stars which were identified as such in the 1970s (the so-called "prototypical" objects HD 108, HD 148937, HD 191612) have been extensively studied, though some questions remained open about their physical properties.…”

Section: Introductionmentioning

confidence: 85%

The latest developments on Of?p stars

Nazé¹,

ud‐Doula

Spano

et al. 2010

Proc. IAU

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Abstract. In recent years several in-depth investigations of the three prototypical Of?p stars were undertaken, revealing their peculiar properties. To clarify some of the remaining questions, we have continued our monitoring of the prototypical Of?p trio. HD 108 has now reached its quiescent, minimum-emission state, for the first time in 50-60yrs, while new echelle spectra of HD 148937 confirm the presence in several H and He lines of the 7d variations detected previously only in the Hα line. A new XMM observation of HD 191612 clearly shows that its Xray emission is not modulated by the orbital period of 1542d, but the high-energy variations are rather compatible with the 538d period of the optical changes -it is thus not of colliding-wind origin but linked to the phenomena responsible for the spectral/photometric variations, though our current MHD simulations remain at odds with the observational properties.

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“…Likewise, the peak X-ray luminosity of VFTS 399 is two orders of magnitude greater than that found for Of?p stars and the subset of strongly magnetic O-type stars which, in turn, are X-ray over-luminous with respect to the wider population of massive stars (cf. Nazé et al 2008;Clark et al 2009, and refs. therein).…”

Section: Understanding the X-ray Emissionmentioning

confidence: 99%

The VLT-FLAMES Tarantula survey

Clark

Bartlett

Broos

et al. 2015

A&A

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Context. The stellar population of the 30 Doradus star-forming region in the Large Magellanic Cloud contains a subset of apparently single, rapidly rotating O-type stars. The physical processes leading to the formation of this cohort are currently uncertain. Aims. One member of this group, the late O-type star VFTS 399, is found to be unexpectedly X-ray bright for its bolometric luminosity − in this study we aim to determine its physical nature and the cause of this behaviour. Methods. To accomplish this we performed a time-resolved analysis of optical, infrared and X-ray observations. Results. We found VFTS 399 to be an aperiodic photometric variable with an apparent near-IR excess. Its optical spectrum demonstrates complex emission profiles in the lower Balmer series and select He i lines − taken together these suggest an OeBe classification.The highly variable X-ray luminosity is too great to be produced by a single star, while the hard, non-thermal nature suggests the presence of an accreting relativistic companion. Finally, the detection of periodic modulation of the X-ray lightcurve is most naturally explained under the assumption that the accretor is a neutron star. Conclusions. VFTS 399 appears to be the first high-mass X-ray binary identified within 30 Dor, sharing many observational characteristics with classical Be X-ray binaries. Comparison of the current properties of VFTS 399 to binary-evolution models suggests a progenitor mass 25 M for the putative neutron star, which may host a magnetic field comparable in strength to those of magnetars. VFTS 399 is now the second member of the cohort of rapidly rotating "single" O-type stars in 30 Dor to show evidence of binary interaction resulting in spin-up, suggesting that this may be a viable evolutionary pathway for the formation of a subset of this stellar population.

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HD 148937: A MULTIWAVELENGTH STUDY OF THE THIRD GALACTIC MEMBER OF THE Of?p CLASS

Cited by 56 publications

References 62 publications

New findings on the prototypical Of?p stars

New findings on the prototypical Of?p stars

The latest developments on Of?p stars

The VLT-FLAMES Tarantula survey

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