TY - JOUR A1 - Ramiaramanantsoa, Tahina A1 - Ratnasingam, Rathish A1 - Shenar, Tomer A1 - Moffat, Anthony F. J. A1 - Rogers, Tamara M. A1 - Popowicz, Adam A1 - Kuschnig, Rainer A1 - Pigulski, Andrzej A1 - Handler, Gerald A1 - Wade, Gregg A. A1 - Zwintz, Konstanze A1 - Weiss, Werner W. T1 - A BRITE view on the massive O-type supergiant V973 Scorpii BT - hints towards internal gravity waves or sub-surface convection zones JF - Monthly notices of the Royal Astronomical Society N2 - Stochastically triggered photospheric light variations reaching similar to 40 mmag peak-to-valley amplitudes have been detected in the O8 Iaf supergiant V973 Scorpii as the outcome of 2 months of high-precision time-resolved photometric observations with the BRIght Target Explorer (BRITE) nanosatellites. The amplitude spectrum of the time series photometry exhibits a pronounced broad bump in the low-frequency regime (less than or similar to 0.9 d(-1)) where several prominent frequencies are detected. A time-frequency analysis of the observations reveals typical mode lifetimes of the order of 5-10 d. The overall features of the observed brightness amplitude spectrum of V973 Sco match well with those extrapolated from two-dimensional hydrodynamical simulations of convectively driven internal gravity waves randomly excited from deep in the convective cores of massive stars. An alternative or additional possible source of excitation from a sub-surface convection zone needs to be explored in future theoretical investigations. KW - convection KW - waves KW - techniques: photometric KW - stars: massive KW - supergiants Y1 - 2018 U6 - https://doi.org/10.1093/mnras/sty1897 SN - 0035-8711 SN - 1365-2966 VL - 480 IS - 1 SP - 972 EP - 986 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Ramiaramanantsoa, Tahina A1 - Moffat, Anthony F. J. A1 - Harmon, Robert A1 - Ignace, R. A1 - St-Louis, Nicole A1 - Vanbeveren, Dany A1 - Shenar, Tomer A1 - Pablo, Herbert A1 - Richardson, Noel D. A1 - Howarth, Ian D. A1 - Stevens, Ian R. A1 - Piaulet, Caroline A1 - St-Jean, Lucas A1 - Eversberg, Thomas A1 - Pigulski, Andrzej A1 - Popowicz, Adam A1 - Kuschnig, Rainer A1 - Zoclonska, Elzbieta A1 - Buysschaert, Bram A1 - Handler, Gerald A1 - Weiss, Werner W. A1 - Wade, Gregg A. A1 - Rucinski, Slavek M. A1 - Zwintz, Konstanze A1 - Luckas, Paul A1 - Heathcote, Bernard A1 - Cacella, Paulo A1 - Powles, Jonathan A1 - Locke, Malcolm A1 - Bohlsen, Terry A1 - Chené, André-Nicolas A1 - Miszalski, Brent A1 - Waldron, Wayne L. A1 - Kotze, Marissa M. A1 - Kotze, Enrico J. A1 - Böhm, Torsten T1 - BRITE-Constellation high-precision time-dependent photometry of the early O-type supergiant zeta Puppis unveils the photospheric drivers of its small- and large-scale wind structures JF - Monthly notices of the Royal Astronomical Society N2 - From 5.5 months of dual-band optical photometric monitoring at the 1 mmag level, BRITE-Constellation has revealed two simultaneous types of variability in the O4I(n)fp star ζ Puppis: one single periodic non-sinusoidal component superimposed on a stochastic component. The monoperiodic component is the 1.78-d signal previously detected by Coriolis/Solar Mass Ejection Imager, but this time along with a prominent first harmonic. The shape of this signal changes over time, a behaviour that is incompatible with stellar oscillations but consistent with rotational modulation arising from evolving bright surface inhomogeneities. By means of a constrained non-linear light-curve inversion algorithm, we mapped the locations of the bright surface spots and traced their evolution. Our simultaneous ground-based multisite spectroscopic monitoring of the star unveiled cyclical modulation of its He ii λ4686 wind emission line with the 1.78-d rotation period, showing signatures of corotating interaction regions that turn out to be driven by the bright photospheric spots observed by BRITE. Traces of wind clumps are also observed in the He ii λ4686 line and are correlated with the amplitudes of the stochastic component of the light variations probed by BRITE at the photosphere, suggesting that the BRITE observations additionally unveiled the photospheric drivers of wind clumps in ζ Pup and that the clumping phenomenon starts at the very base of the wind. The origins of both the bright surface inhomogeneities and the stochastic light variations remain unknown, but a subsurface convective zone might play an important role in the generation of these two types of photospheric variability. KW - techniques: photometric KW - techniques: spectroscopic KW - stars: massive KW - stars: rotation KW - starspots KW - supergiants KW - stars: winds, outflows Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx2671 SN - 0035-8711 SN - 1365-2966 VL - 473 IS - 4 SP - 5532 EP - 5569 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Richardson, Noel D. A1 - Russell, Christopher M. P. A1 - St-Jean, Lucas A1 - Moffat, Anthony F. J. A1 - St-Louis, Nicole A1 - Shenar, Tomer A1 - Pablo, Herbert A1 - Hill, Grant M. A1 - Ramiaramanantsoa, Tahina A1 - Corcoran, Michael A1 - Hamuguchi, Kenji A1 - Eversberg, Thomas A1 - Miszalski, Brent A1 - Chene, Andre-Nicolas A1 - Waldron, Wayne A1 - Kotze, Enrico J. A1 - Kotze, Marissa M. A1 - Luckas, Paul A1 - Cacella, Paulo A1 - Heathcote, Bernard A1 - Powles, Jonathan A1 - Bohlsen, Terry A1 - Locke, Malcolm A1 - Handler, Gerald A1 - Kuschnig, Rainer A1 - Pigulski, Andrzej A1 - Popowicz, Adam A1 - Wade, Gregg A. A1 - Weiss, Werner W. T1 - The variability of the BRITE-est Wolf-Rayet binary, gamma(2) Velorum-I. Photometric and spectroscopic evidence for colliding winds JF - Monthly notices of the Royal Astronomical Society N2 - We report on the first multi-colour precision light curve of the bright Wolf-Rayet binary gamma(2) Velorum, obtained over six months with the nanosatellites in the BRITE-Constellation fleet. In parallel, we obtained 488 high-resolution optical spectra of the system. In this first report on the data sets, we revise the spectroscopic orbit and report on the bulk properties of the colliding winds. We find a dependence of both the light curve and excess emission properties that scales with the inverse of the binary separation. When analysing the spectroscopic properties in combination with the photometry, we find that the phase dependence is caused only by excess emission in the lines, and not from a changing continuum. We also detect a narrow, high-velocity absorption component from the He perpendicular to lambda 5876 transition, which appears twice in the orbit. We calculate smoothed-particle hydrodynamical simulations of the colliding winds and can accurately associate the absorption from He perpendicular to to the leading and trailing arms of the wind shock cone passing tangentially through our line of sight. The simulations also explain the general strength and kinematics of the emission excess observed in wind lines such as C III lambda 5696 of the system. These results represent the first in a series of investigations into the winds and properties of gamma(2) Velorum through multi-technique and multi-wavelength observational campaigns. KW - stars: early type KW - stars: individual: gamma(2) Vel KW - stars: mass loss KW - stars: winds KW - outflows KW - stars: Wolf-Rayet Y1 - 2017 U6 - https://doi.org/10.1093/mnras/stx1731 SN - 0035-8711 SN - 1365-2966 VL - 471 SP - 2715 EP - 2729 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Boehm, Thorsten A1 - Holschneider, Matthias A1 - Lignieres, Frederic A1 - Petit, Pascal A1 - Rainer, Monica A1 - Paletou, Francois A1 - Wade, Gregg A1 - Alecian, Evelyne A1 - Carfantan, Herve A1 - Blazere, Aurore A1 - Mirouh, Giovanni M. T1 - Discovery of starspots on Vega First spectroscopic detection of surface structures on a normal A-type star JF - Astronomy and astrophysics : an international weekly journal N2 - Context. The theoretically studied impact of rapid rotation on stellar evolution needs to be compared with these results of high-resolution spectroscopy-velocimetry observations. Early-type stars present a perfect laboratory for these studies. The prototype A0 star Vega has been extensively monitored in recent years in spectropolarimetry. A weak surface magnetic field was detected, implying that there might be a (still undetected) structured surface. First indications of the presence of small amplitude stellar radial velocity variations have been reported recently, but the confirmation and in-depth study with the highly stabilized spectrograph SOPHIE/OHP was required. Aims. The goal of this article is to present a thorough analysis of the line profile variations and associated estimators in the early-type standard star Vega (A0) in order to reveal potential activity tracers, exoplanet companions, and stellar oscillations. Methods. Vega was monitored in quasi-continuous high-resolution echelle spectroscopy with the highly stabilized velocimeter SOPHIE/OHP. A total of 2588 high signal-to-noise spectra was obtained during 34.7 h on five nights (2 to 6 of August 2012) in high-resolution mode at R = 75 000 and covering the visible domain from 3895 6270 angstrom. For each reduced spectrum, least square deconvolved equivalent photospheric profiles were calculated with a T-eff = 9500 and log g = 4.0 spectral line mask. Several methods were applied to study the dynamic behaviour of the profile variations (evolution of radial velocity, bisectors, vspan, 2D profiles, amongst others). Results. We present the discovery of a spotted stellar surface on an A-type standard star (Vega) with very faint spot amplitudes Delta F/Fc similar to 5 x 10(-4). A rotational modulation of spectral lines with a period of rotation P = 0.68 d has clearly been exhibited, unambiguously confirming the results of previous spectropolarimetric studies. Most of these brightness inhomogeneities seem to be located in lower equatorial latitudes. Either a very thin convective layer can be responsible for magnetic field generation at small amplitudes, or a new mechanism has to be invoked to explain the existence of activity tracing starspots. At this stage it is difficult to disentangle a rotational from a stellar pulsational origin for the existing higher frequency periodic variations. Conclusions. This first strong evidence that standard A-type stars can show surface structures opens a new field of research and ask about a potential link with the recently discovered weak magnetic field discoveries in this category of stars. KW - starspots KW - stars: early-type KW - stars: rotation KW - stars: oscillations KW - stars: individual: Vega KW - asteroseismology Y1 - 2015 U6 - https://doi.org/10.1051/0004-6361/201425425 SN - 0004-6361 SN - 1432-0746 VL - 577 PB - EDP Sciences CY - Les Ulis ER -