On the Hipparcos parallaxes of O stars

Context. Early B-type stars are ideal indicators for present-day cosmic abundances since they preserve their pristine abundances and typically do not migrate far beyond their birth environments over their short lifetimes, in contrast to older stars like the Sun. They are also unaffected by depletion onto dust grains, unlike the cold/warm interstellar medium (ISM) or H ii regions. Aims. A carefully selected sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Quantitative spectroscopy is used to characterise their atmospheric properties in a self-consistent way. Present-day abundances for the astrophysically most interesting chemical elements are derived in order to investigate whether a present-day cosmic abundance standard can be established. Methods. High-resolution and high-S/N FOCES, FEROS and ELODIE spectra of well-studied sharp-lined early B-type stars are analysed in non-LTE. Line-profile fits based on extensive model grids and an iterative analysis methodology are used to constrain stellar parameters and elemental abundances at high accuracy and precision. Atmospheric parameters are derived from the simultaneous establishment of independent indicators, from multiple ionization equilibria and the Stark-broadened hydrogen Balmer lines, and they are confirmed by reproduction of the stars' global spectral energy distributions. Results. Effective temperatures are constrained to 1-2% and surface gravities to less than 15% uncertainty, along with accurate rotational, micro-and macroturbulence velocities. Good agreement of the resulting spectroscopic parallaxes with those from the new reduction of the Hipparcos catalogue is obtained. Absolute values for abundances of He, C, N, O, Ne, Mg, Si and Fe are determined to better than 25% uncertainty. The synthetic spectra match the observations reliably over almost the entire visual spectral range. Three sample stars, γ Ori, o Per and θ 1 Ori D, are identified as double-lined, indicating the presence of an early/mid B-type companion. Conclusions. A present-day cosmic abundance standard is established from a sample of 29 early B-type stars, indicating abundance fluctuations of less than 10% around the mean. Our results (i) resolve the long-standing discrepancy between a chemical homogeneous gas-phase ISM and a chemically inhomogeneous young stellar component out to several hundred parsec from the Sun, (ii) facilitate the amount of heavy elements locked up in the interstellar dust to be constrained precisely -the results imply that carbonaceous dust is largely destroyed inside the Orion H ii region, unlike the silicates, and that graphite is only a minority species in interstellar dust -, (iii) show that the mixing of CNO-burning products in the course of massive star evolution follows tightly the predicted nuclear path, (iv) provide reliable present-day reference points for anchoring Galactic chemical evolution models to observation, and (v) imply that the Sun has migrated outwards from the inne...

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“…2. This resolves the apparent overluminosity of the star found by Schröder et al (2004) from an evaluation of its Hipparcos parallax.…”

Section: Stars Excluded From the Analysissupporting

confidence: 65%

Present-day cosmic abundances

Nieva

Przybilla²

2012

A&A

432

506

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“…The new SFXT presented here, IGR J08408Ϫ4503, was discovered in the Vela region on 2006 May 15 with INTE-GRAL during a bright outburst lasting about 15 minutes (Götz et al 2006). The candidate optical counterpart was first tentatively identified as the supergiant, Ob5Ib(f), HD 74194 star Masetti et al 2006) located at 3 kpc in the Vela region (e.g., Walborn 1973;Humphreys 1978;Schröder et al 2004 with an uncertainty of 5.4Љ) was derived, strengthening the association with HD 74194 (Kennea & Campana 2006). Optical spectra of HD 74194 measured a few days after the outburst (Barba et al 2006) strongly resemble the ones of the companion star of another SFXT, IGR J17544Ϫ2619 (Pellizza et al 2006).…”

Section: Introductionmentioning

confidence: 93%

IGR J08408-4503: A New Recurrent Supergiant Fast X-Ray Transient

Götz

Falanga

Senziani

et al. 2007

ApJ

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The supergiant fast X-ray transient IGR J08408Ϫ4503 was discovered by INTEGRAL on 2006 May 15 during a bright flare. The source shows sporadic recurrent short bright flares, reaching a peak luminosity of 10 36 ergs s Ϫ1 within less than 1 hr. The companion star is HD 74194, an Ob5Ib(f) supergiant star located at 3 kpc in the Vela region. We report the light curves and broadband spectra (0.1-200 keV) of all the three flares of IGR J08408Ϫ4503 detected up to now, based on INTEGRAL and Swift data. The flare spectra are well described by a power-law model with a highenergy cutoff at ∼15 keV. The absorption column density during the flares was found to be ∼10 21 cm Ϫ2 , indicating a very low matter density around the compact object. Using the supergiant donor star parameters, the wind accretion conditions imply an orbital period of the order of 1 yr, a spin period of the order of hours, and a magnetic field of the order of 10 13 G.

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“…Our measurement here of ζ Ori comes in low and would indicate a location on the near side of the association. Apart from the more general criticism of Hipparcos distances of O-stars expressed by Schröder et al (2004), there are reasons particular to the ζ Ori system to be careful. As an astrometric binary with a period of less than a decade, and Hipparcos measuring over three years, a five-parameter solution, i.e.…”

Section: Orbital Elements and Distancementioning

confidence: 99%

Dynamical mass of the O-type supergiant inζOrionis A

Hummel

Rivinius

Nieva

et al. 2013

A&A

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Aims. A close companion of ζ Orionis A was found in 2000 with the Navy Precision Optical Interferometer (NPOI), and shown to be a physical companion. Because the primary is a supergiant of type O, for which dynamical mass measurements are very rare, the companion was observed with NPOI over the full 7-year orbit. Our aim was to determine the dynamical mass of a supergiant that, due to the physical separation of more than 10 AU between the components, cannot have undergone mass exchange with the companion. Methods. The interferometric observations allow measuring the relative positions of the binary components and their relative brightness. The data collected over the full orbital period allows all seven orbital elements to be determined. In addition to the interferometric observations, we analyzed archival spectra obtained at the Calar Alto, Haute Provence, Cerro Armazones, and La Silla observatories, as well as new spectra obtained at the VLT on Cerro Paranal. In the high-resolution spectra we identified a few lines that can be associated exclusively to one or the other component for the measurement of the radial velocities of both. The combination of astrometry and spectroscopy then yields the stellar masses and the distance to the binary star. Results. The resulting masses for components Aa of 14.0 ± 2.2 M and Ab of 7.4 ± 1.1 M are low compared to theoretical expectations, with a distance of 294 ± 21 pc which is smaller than a photometric distance estimate of 387 ± 54 pc based on the spectral type B0III of the B component. If the latter (because it is also consistent with the distance to the Orion OB1 association) is adopted, the mass of the secondary component Ab of 14 ± 3 M would agree with classifying a star of type B0.5IV. It is fainter than the primary by about 2.2 ± 0.1 magnitudes in the visual. The primary mass is then determined to be 33 ± 10 M . The possible reasons for the distance discrepancy are most likely related to physical effects, such as small systematic errors in the radial velocities due to stellar winds.

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On the Hipparcos parallaxes of O stars

Cited by 32 publications

References 29 publications

Present-day cosmic abundances

Present-day cosmic abundances

IGR J08408-4503: A New Recurrent Supergiant Fast X-Ray Transient

Dynamical mass of the O-type supergiant inζOrionis A

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