The IACOB project

Godart, M.; Simón‐Díaz, S.; Herrero, A.; Dupret, M.-A.; Grötsch-Noels, A.; Salmon, Sébastien; Ventura, P.

doi:10.1051/0004-6361/201628856

Cited by 23 publications

(32 citation statements)

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“…Aside from this, the quasi-stable frequency ∼ 0.37 d −1 seems to point towards a phenomenon of coherent variability as it persists over years in both the spectroscopy and the space photometry. A combination of stable heat-driven gravity modes (Godart et al, 2017) with convectively-driven stochastic gravity waves excited in the stellar interior -either in the convective core (Aerts & Rogers, 2015) or in the convection zone in the stellar envelope due to the iron opacity bump (Grassitelli et al, 2015) -seems to offer the best explanation for the complex variability detected in the spectroscopy of HD 2905.…”

Section: Discussionmentioning

confidence: 99%

Low-frequency photospheric and wind variability in the early-B supergiant HD 2905

Diaz

Aerts

Urbaneja

et al. 2018

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Context. Despite the important advances in space asteroseismology during the last decade, the early phases of evolution of stars with masses above ∼15 M (including the O stars and their evolved descendants, the B supergiants) have been only vaguely explored up to now. This is due to the lack of adequate observations for a proper characterization of the complex spectroscopic and photometric variability occurring in these stars. Aims. Our goal is to detect, analyze and interpret variability in the early-B type supergiant HD 2905 (κ Cas, B1 Ia) using long-term, ground based, high resolution spectroscopy. Methods. We gather a total of 1141 high-resolution spectra covering some 2900 days with three different high-performance spectrographs attached to 1 -2.6m telescopes at the Canary Islands observatories. We complement these observations with the Hipparcos light curve, which includes 160 data points obtained during a time span of ∼1200 days. We investigate spectroscopic variability of up to 12 diagnostic lines by using the zero and first moments of the line profiles. We perform a frequency analysis of both the spectroscopic and photometric dataset using Scargle periodograms. We obtain single snapshot and time-dependent information about the stellar parameters and abundances by means of the fastwind stellar atmosphere code. Results. HD 2905 is a spectroscopic variable with peak-to-peak amplitudes in the zero and first moments of the photospheric lines of up to 15% and 30 km s −1 , respectively. The amplitude of the line-profile variability is correlated with the line formation depth in the photosphere and wind. All investigated lines present complex temporal behavior indicative of multi-periodic variability with timescales of a few days to several weeks. No short-period (hourly) variations are detected. The Scargle periodograms of the Hipparcos light curve and the first moment of purely photospheric lines reveal a low-frequency amplitude excess and a clear dominant frequency at ∼0.37 d −1 . In the spectroscopy, several additional frequencies are present in the range 0.1 -0.4 d −1 . These may be associated with heat-driven gravity modes, convectively-driven gravity waves, or sub-surface convective motions. Additional frequencies are detected below 0.1 d −1 . In the particular case of Hα, these are produced by rotational modulation of a non-spherically symmetric stellar wind. Conclusions. Combined long-term uninterrupted space photometry with high-precision spectroscopy is the best strategy to unravel the complex low-frequency photospheric and wind variability of B supergiants. 3D simulations of waves and of convective motions in the sub-surface layers can shed light on a unique interpretation of the variability.

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Section: Discussionmentioning

confidence: 99%

Low-frequency photospheric and wind variability in the early-B supergiant HD 2905

Diaz

Aerts

Urbaneja

et al. 2018

A&A

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“…In Simón-Díaz (2015) we used part of the observational sample presented here to investigate possible correlations between the location of stars with a remarkable macroturbulent broadening contribution and the high-order g-mode instability strips from Miglio et al (2007a) and Godart (2011). Later on, the same observations were included in the work by Grassitelli et al (2015a) to assess the proposed connection between turbulent pressure fluctuations initiated in inefficient (in transporting energy) sub-surface convection zones and the occurrence of macroturbulent broadening in OB stars.…”

Section: Distribution Of Macroturbulent Broadening In the Shrd And Drmentioning

confidence: 99%

“…7 is an updated version of Fig. 2 from Simón-Díaz (2015) in which we present results in the sHR diagram (instead of the log g-logT eff diagram), and include the instability strips for heat-driven p-and g-modes with ℓ=1 resulting from a new homogeneous set of adiabatic and non-adiabatic computations by Godart et al (2016) in the whole 3 -70 M ⊙ range 12 . As already commented in Simón-Díaz (2015), the presence of large red circles in the upper part of the sHR diagram outside the predicted instability domains implies a strong empirical challenge to non-radial modes excited by a heat mechanism being the main physical driver of the non-rotational broadening affecting O stars and B Sgs (except maybe for the early-B Sgs, located inside the post-TAMS g-mode strip for stars with M 10 M ⊙ , see also notes in Aerts et al 2009).…”

Section: Distribution Of Macroturbulent Broadening In the Shrd And Drmentioning

confidence: 99%

“…The situation may improve when accounting for 11 For comparative purposes with the observational dataset used in Simón-Díaz (2015) and Grassitelli et al (2015a), the sample considered here includes ≈150 stars more and excludes ≈20 stars afterwards detected to be spectroscopic binaries using new multi-epoch observations compiled since then. 12 Although we concentrate here on ℓ=1, Godart et al (2016) actually include and discuss results for ℓ=1 -20.…”

Section: 22 and 523)mentioning

confidence: 99%

“…Last, not to forget the predicted occurrence of adiabatic strange modes for logL /L ⊙ > 3.7 (these refer to modes for which the excitation in the iron opacity bump due to the κ-mechanism is enhanced by the large amplitude of the mode trapped into a superficial cavity; see, e.g, Saio et al 1998, and references therein; Aerts et al 2010a). Some of these points are explored and discussed in more detail in the parallel work by Godart et al (2016).…”

Section: 22 and 523)mentioning

confidence: 99%

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Simón‐Díaz

Godart

Castro

et al. 2016

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Context. The term 'macroturbulence' of O-and B-type stars is commonly used to refer to a source of non-rotational broadening affecting their spectral line-profiles. It has been proposed to be a spectroscopic signature of the presence of stellar oscillations; however, we still lack a definitive confirmation of this hypothesis. Aims. We aim to provide new empirical clues about macroturbulent spectral line broadening in O-and B-type stars to evaluate its physical origin. Methods. We use high-resolution spectra of ≈430 stars with spectral types in the range O4 -B9 (all luminosity classes) compiled in the framework of the IACOB project. We characterize the line-broadening of adequate diagnostic metal lines using a combined Fourier transform and goodness-of-fit technique. We perform a quantitative spectroscopic analysis of the whole sample using automatic tools coupled with a huge grid of fastwind models to determine their effective temperatures and gravities. We also incorporate quantitative information about line asymmetries to our observational description of the characteristics of the line-profiles, and present a comparison of the shape and type of line-profile variability found in a small sample of O stars and B supergiants with still undefined pulsational properties and B main sequence stars with variable line-profiles (due to a well identified type of stellar oscillations or to the presence of spots in the stellar surface).Results. We present a homogeneous and statistically significant overview of the (single snapshot) line-broadening properties of stars in the whole O and B star domain. We find empirical evidence of the existence of various types of non-rotational broadening agents acting in the realm of massive stars. Even though all of them could be quoted and quantified as a macroturbulent broadening from a practical point of view, their physical origin can be different. Contrarily to the early-to late-B dwarfs/giants, which present a mixture of cases in terms of line-profile shape and variability, the whole O-type and B supergiant domain (or, roughly speaking, stars with M ZAMS 15 M ⊙ ) is fully dominated by stars with a remarkable non-rotational broadening component and very similar profiles (including type of variability). We provide some examples illustrating how this observational dataset can be used to evaluate scenarios aimed at explaining the existence of sources of non-rotational broadening in massive stars.

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