The spectroscopic Hertzsprung-Russell diagram of Galactic massive stars

Castro, N.; Fossati, L.; Langer, N.; Simón‐Díaz, S.; Schneider, F. R. N.; Izzard, Robert G.

doi:10.1051/0004-6361/201425028

Cited by 136 publications

(210 citation statements)

References 86 publications

(164 reference statements)

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“…We note that Castro et al (2014) recently came to a similar conclusion for Galactic B-type supergiants, based on their distribution in the spectroscopic HertzsprungRussell diagram.…”

Section: Hertzsprung-russell Diagramsupporting

confidence: 67%

The VLT-FLAMES Tarantula Survey

McEvoy

Dufton

Evans

et al. 2015

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Context. Model atmosphere analyses have been previously undertaken for both Galactic and extragalactic B-type supergiants. By contrast, little attention has been given to a comparison of the properties of single supergiants and those that are members of multiple systems. Aims. Atmospheric parameters and nitrogen abundances have been estimated for all the B-type supergiants identified in the VLT-FLAMES Tarantula survey. These include both single targets and binary candidates. The results have been analysed to investigate the role of binarity in the evolutionary history of supergiants.Methods.  non-local thermodynamic equilibrium (LTE) model atmosphere calculations have been used to determine atmospheric parameters and nitrogen abundances for 34 single and 18 binary supergiants. Effective temperatures were deduced using the silicon balance technique, complemented by the helium ionisation in the hotter spectra. Surface gravities were estimated using Balmer line profiles and microturbulent velocities deduced using the silicon spectrum. Nitrogen abundances or upper limits were estimated from the N  spectrum. The effects of a flux contribution from an unseen secondary were considered for the binary sample. Results. We present the first systematic study of the incidence of binarity for a sample of B-type supergiants across the theoretical terminal age main sequence (TAMS). To account for the distribution of effective temperatures of the B-type supergiants it may be necessary to extend the TAMS to lower temperatures. This is also consistent with the derived distribution of mass discrepancies, projected rotational velocities and nitrogen abundances, provided that stars cooler than this temperature are post-red supergiant objects. For all the supergiants in the Tarantula and in a previous FLAMES survey, the majority have small projected rotational velocities. The distribution peaks at about 50 km s −1 with 65% in the range 30 km s −1 ≤ v e sin i ≤ 60 km s −1 . About ten per cent have larger v e sin i (≥100 km s −1 ), but surprisingly these show little or no nitrogen enhancement. All the cooler supergiants have low projected rotational velocities of ≤70 km s −1 and high nitrogen abundance estimates, implying that either bi-stability braking or evolution on a blue loop may be important. Additionally, there is a lack of cooler binaries, possibly reflecting the small sample sizes. Single-star evolutionary models, which include rotation, can account for all of the nitrogen enhancement in both the single and binary samples. The detailed distribution of nitrogen abundances in the single and binary samples may be different, possibly reflecting differences in their evolutionary history. Conclusions. The first comparative study of single and binary B-type supergiants has revealed that the main sequence may be significantly wider than previously assumed, extending to T eff = 20 000 K. Some marginal differences in single and binary atmospheric parameters and abundances have been identified, possibly implying non-stand...

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“…We note that Castro et al (2014) recently came to a similar conclusion for Galactic B-type supergiants, based on their distribution in the spectroscopic HertzsprungRussell diagram.…”

Section: Hertzsprung-russell Diagramsupporting

confidence: 67%

The VLT-FLAMES Tarantula Survey

McEvoy

Dufton

Evans

et al. 2015

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“…L ≡ T 4 eff /g c is proportional to L/M, thus to Γ e /κ, where κ is the flux-mean opacity (see Langer & Kudritzki 2014). For a fixed κ, the vertical axis of this diagram thus sorts the stars according to their proximity to the Eddington limit: the higher up in the diagram the closer their atmospheres are to zero effective gravity (see also Castro et al 2014). Figure 6 shows both diagrams for our stars.…”

Section: Gravities and Luminosity Classificationmentioning

confidence: 95%

The VLT-FLAMES Tarantula Survey

Grin

Ramírez-Agudelo

Koter

et al. 2017

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Context. The Tarantula region in the Large Magellanic Cloud contains the richest population of spatially resolved massive O-type stars known so far. This unmatched sample offers an opportunity to test models describing their main-sequence evolution and massloss properties. Aims. Using ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS), we aim to determine stellar, photospheric and wind properties of 72 presumably single O-type giants, bright giants and supergiants and to confront them with predictions of stellar evolution and of line-driven mass-loss theories. Methods. We apply an automated method for quantitative spectroscopic analysis of O stars combining the non-LTE stellar atmosphere model fastwind with the genetic fitting algorithm pikaia to determine the following stellar properties: effective temperature, surface gravity, mass-loss rate, helium abundance, and projected rotational velocity. The latter has been constrained without taking into account the contribution from macro-turbulent motions to the line broadening.Results. We present empirical effective temperature versus spectral subtype calibrations at LMC-metallicity for giants and supergiants. The calibration for giants shows a +1kK offset compared to similar Galactic calibrations; a shift of the same magnitude has been reported for dwarfs. The supergiant calibrations, though only based on a handful of stars, do not seem to indicate such an offset. The presence of a strong upturn at spectral type O3 and earlier can also not be confirmed by our data. In the spectroscopic and classical Hertzsprung-Russell diagrams, our sample O stars are found to occupy the region predicted to be the core hydrogen-burning phase by Brott et al. (2011) andKöhler et al. (2015). For stars initially more massive than approximately 60 M ⊙ , the giant phase already appears relatively early on in the evolution; the supergiant phase develops later. Bright giants, however, are not systematically positioned between giants and supergiants at M init ∼ > 25 M ⊙ . At masses below 60 M ⊙ , the dwarf phase clearly precedes the giant and supergiant phases; however this behavior seems to break down at M init ∼ < 18 M ⊙ . Here, stars classified as late O III and II stars occupy the region where O9.5-9.7 V stars are expected, but where few such late O V stars are actually seen. Though we can not exclude that these stars represent a physically distinct group, this behaviour may reflect an intricacy in the luminosity classification at late O spectral subtype. Indeed, on the basis of a secondary classification criterion, the relative strength of Si iv to He i absorption lines, these stars would have been assigned a luminosity class IV or V. Except for five stars, the helium abundance of our sample stars is in agreement with the initial LMC composition. This outcome is independent of their projected spin rates. The aforementioned five stars present moderate projected rotational velocities (i.e., e sin i < 200 km s −1 ) and hence do no...

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“…Therefore these stars hold the key to a precise calibration of stellar structure and evolution models of massive stars. Such calibrations are much needed because the observed distribution of massive stars does not agree with theoretical predictions, as shown by Castro et al (2014), and internal mixing is likely to be one of the possible solutions. Before the space revolution of asteroseismology began with the launch of the MOST (Microvariablity and Oscillations of STars; Walker et al 2003) and CoRoT (Convection Rotation and planetary Transits; Auvergne et al 2009) missions, it was very difficult to collect sufficient photometric data of SPB stars, mainly because their dominant oscillation modes have typical periods of 0.5-3 days (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Signatures of internal rotation discovered in theKeplerdata of five slowly pulsating B stars

Pápics

Tkachenko

Reeth

et al. 2017

A&A

159

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Context. Massive stars are important building blocks of the Universe, and their stellar structure and evolution models are fundamental cornerstones of various fields in modern astrophysics. The precision of these models is strongly limited by our lack of understanding of various internal mixing processes that significantly influence the lifetime of these objects, such as core overshoot, chemical mixing, or the internal differential rotation. Aims. Our goal is to calibrate models by extending the sample of available seismic studies of slowly pulsating B (SPB) stars, providing input for theoretical modelling efforts that will deliver precise constraints on the parameters describing the internal mixing processes in these objects. Methods. We used spectral synthesis and disentangling techniques to derive fundamental parameters and to determine precise orbital parameters from high-resolution spectra. We employed custom masks to construct light curves from the virtually uninterrupted four year long Kepler pixel data and used standard time-series analysis tools to construct a set of significant frequencies for each target. These sets were first filtered from combination frequencies, and then screened for period spacing patterns. Results. We detect gravity mode period series of modes, of the same degree with consecutive radial order n, in four new and one revisited SPB star. These series (covering typically 10 to 40 radial orders) are clearly influenced by moderate to fast rotation and carry signatures of chemical mixing processes. Furthermore, they are predominantly prograde dipole series. Our spectroscopic analysis, in addition to placing each object inside the SPB instability strip and identifying KIC 4930889 as an SB2 binary, reveals that KIC 11971405 is a fast rotator that shows very weak Be signatures. Together with the observed photometric outbursts this illustrates that this Be star is a fast rotating SPB star. We hypothesise that the outbursts might be connected to its very densely compressed oscillation spectrum.

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The spectroscopic Hertzsprung-Russell diagram of Galactic massive stars

Cited by 136 publications

References 86 publications

The VLT-FLAMES Tarantula Survey

The VLT-FLAMES Tarantula Survey

The VLT-FLAMES Tarantula Survey

Signatures of internal rotation discovered in theKeplerdata of five slowly pulsating B stars

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