On the class of Oe stars'

Negueruela, I.; Steele, I. A.; Bernabeu, Guillermo

doi:10.1002/asna.200310258

Cited by 71 publications

(99 citation statements)

References 44 publications

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“…Oe stars were first introduced by Conti & Leep (1974), and usually fall inside the range O9-B0. However, Negueruela et al (2004) mention that some published spectral types are too early most likely due to filling in of HeI lines. That is why we also included spectral types earlier than O9.…”

Section: Obe Starsmentioning

confidence: 99%

“…HIP32947, HIP35933, HIP74147, HIP88149). There are 3 studied Oe stars in the sample (HIP27941, HIP37074 and HIP30722) and their spectral types have been estimated to be too early (Negueruela et al 2004), they are rather O8.5Ve, B0IVe and O9.5IVe, respectively. Rauw et al (2007) find long term spectroscopic variations for HIP30722 (HD45314) and HIP37074 (HD60848), and our study points toward a new shorter period of 2.983 days for HIP37074, that remains to be studied in more detail.…”

Section: Special Casesmentioning

confidence: 99%

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A systematic study of variability among OB-stars based on HIPPARCOS photometry

Lefèvre

Марченко²,

Moffat

et al. 2009

A&A

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Context. Variability is a key factor for understanding the nature of the most massive stars, the OB stars. Such stars lie closest to the unstable upper limit of star formation. Aims. In terms of statistics, the data from the HIPPARCOS satellite are unique because of time coverage and uniformity. They are ideal to study variability in this large, uniform sample of OB stars. Methods. We used statistical techniques to determine an independant threshold of variability corresponding to our sample of OB stars, and then applied an automatic algorithm to search for periods in the data of stars that are located above this threshold. We separated the sample stars into 4 main categories of variability: 3 intrinsic and 1 extrinsic. The intrinsic categories are: OB main sequence stars (∼2/3 of the sample), OBe stars (∼10%) and OB Supergiant stars (∼1/4).The extrinsic category refers to eclipsing binaries. Results. We classified about 30% of the whole sample as variable, although the fraction depends on magnitude level due to instrumental limitations. OBe stars tend to be much more variable (≈80%) than the average sample star, while OBMS stars are below average and OBSG stars are average. Types of variables include α Cyg, β Cep, slowly pulsating stars and other types from the general catalog of variable stars. As for eclipsing binaries, there are relatively more contact than detached systems among the OBMS and OBe stars, and about equal numbers among OBSG stars.

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Section: Obe Starsmentioning

confidence: 99%

Section: Special Casesmentioning

confidence: 99%

A systematic study of variability among OB-stars based on HIPPARCOS photometry

Lefèvre

Марченко²,

Moffat

et al. 2009

A&A

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show abstract

“…Simultaneously, He ii and other high-ionization lines, such as N iii and Si iv, are observed in absorption. Since the Be phenomenon tends to become very rare for spectral types earlier than O9.5 (Negueruela et al 2004), the few known Oe stars deserve detailed investigation, as they could provide important constraints on the physical mechanism generating the emission lines of these stars.…”

Section: Introductionmentioning

confidence: 99%

The discovery of a shell-like event in the O-type star HD 120678

Gamen

Arias

Barbá

et al. 2012

A&A

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Aims. We report the detection of a shell-like event in the Oe-type star HD 120678. Methods. HD 120678 has been intensively observed as part of a high-resolution spectroscopic monitoring program of southern Galactic O stars and Wolf-Rayet stars of the nitrogen sequence.Results. An optical spectrogram of HD 120678 obtained in June 2008 shows strong H and He i absorption lines instead of the double-peaked emission profiles observed both previously and subsequently, as well as a variety of previously undetected absorption features, mainly of O ii, Si iii and Fe iii. Photometric data reveal that the development of the absorption spectrum coincided with a remarkable dip in the V-band lightcurve. The "shell phase" of HD 120678 did not persist for very long: the V magnitude recovered its previous average value in fewer than 120 days, whereas H and He emission lines became detectable one year later. Similar spectral variations have been observed in a few Be stars, and they are usually interpreted as changes in the circumstellar disk.

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“…Of these, 15 stars are of spectral type O8-O9.5 III-V 11 and hence might be expected to exhibit the OeBe phenomenon (Negueruela et al 2004). However, at the time of our spectral observations, only VFTS 102 and 399 were found to support the gaseous circumstellar discs from which a putative neutron star/black hole might accrete.…”

Section: The O-type Star Mass Donormentioning

confidence: 86%

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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On the class of Oe stars'

Cited by 71 publications

References 44 publications

A systematic study of variability among OB-stars based on HIPPARCOS photometry

A systematic study of variability among OB-stars based on HIPPARCOS photometry

The discovery of a shell-like event in the O-type star HD 120678

The VLT-FLAMES Tarantula survey

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