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$\delta$ Orionis is the closest massive multiple stellar system and one of the brightest members of the Orion OB association. The primary (Aa1) is a unique evolved O star. In this work, we applied a two-step disentangling method to a series of spectra in the blue region (430 to 450 nm), and we detected spectral lines of the secondary (Aa2). For the first time, we were able to constrain the orbit of the tertiary (Ab) - to 55 450 d or 152 yr - using variable $\gamma$ velocities and new speckle interferometric measurements, which have been published in the Washington Double Star Catalogue. In addition, the Gaia DR3 parallax of the faint component (Ca+Cb) constrains the distance of the system to (381 $\pm$ 8) pc, which is just in the centre of the Orion OB1b association, at (382 $\pm$ 1) pc. Consequently, we found that the component masses according to the three-body model are 17.8, 8.5, and 8.7 M$_{\odot}$, for Aa1, Aa2, and Ab, respectively, with the uncertainties of the order of $1$ M$_{\odot}$. We used new photometry from the BRITE satellites together with astrometry, radial velocities, eclipse timings, eclipse duration, spectral line profiles, and spectral energy distribution to refine radiative properties. The components, classified as O9.5 II + B2 V + B0 IV, have radii of 13.1, 4.1, and 12.0 R$_{\odot}$, which means that $\delta$ Ori A is a pre-mass-transfer object. The frequency of 0.478 cycles per day, known from the Fourier analysis of the residual light curve and X-ray observations, was identified as the rotation frequency of the tertiary. $\delta$ Ori could be related to other bright stars in Orion, in particular, $\zeta$ Ori, which has a similar architecture, or $\varepsilon$ Ori, which is a single supergiant, and possibly a post-mass-transfer object., Comment: 22 pages, 22 figures

The effects of an accretion disk are crucial to understanding the evolution of young stars. During the combined evolution, stellar and disk parameters influence each other, motivating a combined stellar and disk model. This makes a combined numerical model, evolving the disk alongside the star, the next logical step in the progress of studying early stellar evolution. We aim to understand the effects of metallicity on the accretion disk and the stellar spin evolution during the T~Tauri phase. We combine the numerical treatment of a hydrodynamic disk with stellar evolution, including a stellar spin model, allowing a self-consistent calculation of the back-reactions between the individual components. We present the self-consistent theoretical evolution of T-Tauri stars coupled to a stellar disk. We find that disks in low metallicity environments are heated differently and have shorter lifetimes, compared to their solar metallicity counterparts. Differences in stellar radii, the contraction rate of the stellar radius, and the shorter disk lifetimes result in faster rotation of low metallicity stars. We present an additional explanation for the observed short disk lifetimes in low metallicity clusters. A combination of our model with previous studies (e.g., a metallicity-based photo-evaporation) could help to understand disk evolution and dispersal at different metallicities. Furthermore, the stellar spin evolution model includes several important effects, previously ignored (e.g., the stellar magnetic field strength and a realistic calculation of the disk lifetime) and we motivate to include our results as initial or input parameters for further spin evolution models, covering the stellar evolution towards and during the main sequence., Comment: accepted for publication in A&A

The physics of early stellar evolution (e.g. accretion processes) is often not properly included in the calculations of pre-main-sequence models, leading to insufficient model grids and hence systematic errors in the results. We aim to investigate current and improved approaches for the asteroseismic modelling of pre-main-sequence delta Scuti stars. We calculated an extensive grid of pre-main-sequence models including the early accretion phase and used the resulting equilibrium models as input to calculate theoretical frequency spectra. These spectra were used to investigate different approaches in modelling echelle diagrams to find the most reliable methods. By applying Petersen diagrams, we present a simple algorithm to extract echelle diagrams from observed pulsation frequencies. We show that model grids with insufficient input physics and imperfect modelling approaches lead to underestimated uncertainties and systematic errors in the extracted stellar parameters. Our re-discussion of HD 139614 leads to different stellar parameters than the ones derived by Murphy et al. (2021). We performed a model comparison between this previous investigation and our results by applying the Akaike and Bayesian information criteria. While the results with regard to our 10-d model are inconclusive, they show (very) strong evidence of a 6-d model with fixed accretion parameters (leading to almost identical stellar parameters to those of the 10-d model) to be preferred over the model applied by Murphy et al. (2021). In general, our modelling approach can provide narrow constraints on the stellar parameters (\Delta R ~ 0.05 R_\odot, \Delta log g <~ 0.01, and \Delta M_\star ~ 0.1 M_\odot). The extensively tested modelling approaches and automatic extraction of echelle diagrams should allow us to study many more pre-main-sequence delta Scuti stars in the future and lead to reliable stellar parameters., Comment: 18 pages, 13 figures, accepted for publication in Astronomy & Astrophysics

Context: The pre-main sequence evolution is often simplified by choosing classical initial models. These have large initial radii and sufficient uniform contraction to make them fully convective. Contrary to that, real stars are born as small protostellar seeds in collapsing molecular clouds and obtain their final mass by means of accretion. Aims: We aim to constrain the input physics of accretion on protostellar seeds with observed spectroscopic parameters and stellar pulsations of young stellar objects and pre-main sequence stars. Methods: We conducted a literature search for spectroscopic samples of young stellar objects and pre-main sequence stars including all previously known pulsators. The sample size of pulsating pre-main sequence stars is increased by analysing TESS observations and presenting discoveries in CoRoT data. We employ MESA and GYRE to calculate evolutionary tracks of accreting protostellar seeds in a constant accretion scenario, the subsequent pre-main sequence evolution, and their pulsation properties. The results are then compared with observations to constrain the input physics. Results: We discuss 16 formerly unknown pulsating pre-main sequence stars and candidates that are either of SPB, $\delta$ Scuti,$\gamma$ Doradus or $\delta$ Scuti - $\gamma$ Doradus hybrid type. We find that evolutionary tracks with a mass accretion rate of $5\times10^{-6} M_\odot/{\rm yr}$ and fraction of injected accretion energy of $\beta=0.1$ provide the best results in enveloping the spectroscopic parameters of pre-main sequence stars in a constant accretion scenario. The calculated instability regions constrain the atmospheric boundary conditions to Eddington Gray atmospheres; we discuss the future potential for additional constraints by instability regions that are dependent on radial order. We present a possible candidate for pulsations in M-type young stellar objects., Comment: 21 pages plus 12 for the appendix, 17 figures plus 27 for the appendix, accepted for publication in Astronomy & Astrophysics

Results of an analysis of the BRITE-Constellation and SMEI photometry and radial-velocity observations, archival and new, of two single-lined spectroscopic binary systems $\nu$ Centauri and $\gamma$ Lupi are reported. In the case of $\gamma$ Lup AB, a visual binary, an examination of the light-time effect shows that component A is the spectroscopic binary. Both $\nu$ Cen and $\gamma$ Lup exhibit light variations with the orbital period. The variations are caused by the reflection effect, i.e. heating of the secondary's hemisphere by the early-B main sequence (MS) primary component's light. The modelling of the light curves augmented with the fundamental parameters of the primary components obtained from the literature photometric data and Hipparcos parallaxes, shows that the secondary components are pre-MS stars, in the process of contracting onto the MS. $\nu$ Cen and $\gamma$ Lup A are thus found to be non-eclipsing counterparts of the B2 IV eclipsing binary (and a $\beta$ Cephei variable) 16 (EN) Lac, the B5 IV eclipsing binary (and an SPB variable) $\mu$ Eri, and the recently discovered LMC nascent eclipsing binaries., Comment: 15 pages, 15 figures, published in MNRAS

Photometric monitoring of Beta Pictoris in 1981 showed anomalous fluctuations of up to 4% over several days, consistent with foreground material transiting the stellar disk. The subsequent discovery of the gas giant planet Beta Pictoris b and the predicted transit of its Hill sphere to within 0.1 au projected distance of the planet provided an opportunity to search for the transit of a circumplanetary disk in this $21\pm 4$ Myr-old planetary system. Continuous broadband photometric monitoring of Beta Pictoris requires ground-based observatories at multiple longitudes to provide redundancy and to provide triggers for rapid spectroscopic followup. These observatories include the dedicated Beta Pictoris monitoring observatory bRing at Sutherland and Siding Springs, the ASTEP400 telescope at Concordia, and observations from the space observatories BRITE and Hubble Space Telescope. We search the combined light curves for evidence of short period transient events caused by rings and for longer term photometric variability due to diffuse circumplanetary material. We find no photometric event that matches with the event seen in November 1981, and there is no systematic photometric dimming of the star as a function of the Hill sphere radius. We conclude that the 1981 event was not caused by the transit of a circumplanetary disk around Beta Pictoris b. The upper limit on the long term variability of Beta Pictoris places an upper limit of $1.8\times 10^{22}$ g of dust within the Hill sphere. Circumplanetary material is either condensed into a non-transiting disk, is condensed into a disk with moons that has a small obliquity, or is below our detection threshold. This is the first time that a dedicated international campaign has mapped the Hill sphere transit of a gas giant extrasolar planet at 10 au., Comment: 12 pages, 9 figures, 1 table, accepted for publication in A&A. Reduced data and reduction scripts on GitHub at https://github.com/mkenworthy/beta_pic_b_hill_sphere_transit

In recent years, our understanding of solar-like oscillations from main sequence to red giant stars has improved dramatically thanks to pristine data collected from space telescopes. One of the remaining open questions focuses around the observational identification of solar-like oscillations in pre-main sequence stars. We aim to develop an improved method to search for solar-like oscillations in pre-main sequence stars and apply it to data collected by the Kepler K2 mission. Our software APOLLO includes a novel way to detect low signal-to-noise ratio solar like oscillations in the presence of a high background level. By calibrating our method using known solar-like oscillators from the main Kepler mission, we apply it to T Tauri stars observed by Kepler K2 and identify several candidate pre-main sequence solar-like oscillators. We find that our method is robust even when applied to time-series of observational lengths as short as those obtained with the TESS satellite in one sector. We identify EPIC 205375290 as a possible candidate for solar-like oscillations in a pre-main sequence star with $\nu_\mathrm{max} \simeq 242\,\mu$Hz. We also derive EPIC 205375290's fundamental parameters to be $T_\mathrm{eff}$ = 3670$\pm$180 K, log $g$ = 3.85$\pm$0.3, $v$sin$i$ = 8 $\pm$ 1 km s$^{-1}$, and about solar metallicity from a high-resolution spectrum obtained from the Keck archive., Comment: 14 pages, 13 figures

Chemically peculiar (CP) stars with a measurable magnetic field comprise the group of mCP stars. The pulsating members define the subgroup of rapidly oscillating Ap (roAp) stars, of which Alpha Circini is the brightest member. Hence, Alpha Circini allows the application of challenging techniques, such as interferometry, very high temporal and spectral resolution photometry, and spectroscopy in a wide wavelength range, that have the potential to provide unique information about the structure and evolution of a star. Based on new photometry from BRITE-Constellation, obtained with blue and red filters, and on photometry from WIRE, SMEI, and TESS we attempt to determine the surface spot structure of Alpha Circini and investigate pulsation frequencies. We used photometric surface imaging and frequency analyses and Bayesian techniques in order to quantitatively compare the probability of different models. BRITE-Constellation photometry obtained from 2014 to 2016 is put in the context of space photometry obtained by WIRE, SMEI, and TESS. This provides improvements in the determination of the rotation period and surface features (three spots detected and a fourth one indicated). The main pulsation frequencies indicate two consecutive radial modes and one intermediate dipolar mode. Advantages and problems of the applied Bayesian technique are discussed., Comment: 11 pages, 8 figures, 5 tables

Stellar components in binaries are subject to tidal forces which influence asteroseismic properties. Tidally pertubed pulsations have been reported for different objects but none of these are in their pre-main sequence phase of evolution. This makes RS Cha, consisting of two $\delta$ Scuti stars and with pulsational characteristics influenced by tidal effects , the first such object observed. We aim to investigate the pulsational properties of the eclipsing binary RS Cha in terms of the theory of tidally perturbed pulsations. Based on photometric time series obtained from the TESS satellite, we performed binary modelling using PHOEBE to interpret the binary light curve and to allow the investigation of the pulsations of both components in RS Cha. We modelled the detrended light curve with the superposition of linear modes. The frequencies were then interpreted as self excited modes perturbed by tidal forces. We find evidence for tidally perturbed modes, which enables the identification of pulsation modes. RS Cha mainly exhibits dipole modes, while one prominent $l=2$ or $l=3$ mode is also inferred. The latter verifies previous results from spectroscopic time series. This work shows that RS Cha is an ideal candidate to test the theory of tidally perturbed pulsations within the framework of asteroseismic modelling. The identification of multiple pulsation modes using this theory is unprecedented and will be a keystone in the future of pre-main sequence asteroseismology. However, amplitude modulation caused by the changing light ratio during the orbital phase in an eclipsing binary also plays a significant role, which can complicate mode identification., Comment: 11 pages plus 7 for the appendix, 8 pages plus 8 for the appendix, accepted for publication in Astronomy & Astrophysics

Continuous photometry with up to three BRITE satellites was obtained for 12 targets and subjected to a period search. Contemporaneous high-resolution optical spectroscopy with STELLA was used to obtain radial velocities through cross correlation with template spectra as well as to determine astrophysical parameters through a comparison with model spectra. The Capella red light curve was found to be constant over 176 days with a root mean square of 1 mmag, but the blue light curve showed a period of 10.1$\pm$0.6 d, which we interpret to be the rotation period of the G0 component. The BRITE light curve of the F0 supergiant $\varepsilon$Aur suggests 152 d as its main pulsation period, while the STELLA radial velocities reveal a clear 68 d period. An ingress of an eclipse of the $\zeta$Aur binary system was covered with BRITE and a precise timing for its eclipse onset derived. $\eta$Aur is identified as a slowly pulsating B (SPB) star with a main period of 1.29 d and is among the brightest SPB stars discovered so far. The rotation period of the magnetic Ap star $\theta$Aur is detected from photometry and spectroscopy with a period of 3.6189 d and 3.6177 d, respectively, likely the same within the errors. Photometric rotation periods are also confirmed for the magnetic Ap star $\tau$Aur of 2.463 d and for the solar-type star $\kappa^1$Cet of 9.065 d, and also for the B7 HgMn giant $\beta$Tau of 2.74 d. Revised orbital solutions are derived for the eclipsing SB2 binary $\beta$Aur, for the 27 year eclipsing SB1 $\varepsilon$Aur, and for the RS CVn binary HR 1099. The two stars $\nu$ Aur and $\iota$Aur are found to be long-term, low-amplitude RV and brightness variables, but provisional orbital elements based on a period of 20 yr and an eccentricity of 0.7 could only be extracted for $\nu$Aur. The variations of $\iota$Aur are due to oscillations with a period of $\approx$4 yr.

F type stars are characterised by several physical processes such as different pulsation mechanisms, rotation, convection, diffusion, and magnetic fields. The rapidly rotating delta Scuti star beta Cas can be considered as a benchmark star to study the interaction of several of these effects. We investigate the pulsational and magnetic field properties of beta Cas. We also determine the star's apparent fundamental parameters and chemical abundances. Based on photometric time series obtained from three different space missions (BRITE-Constellation, SMEI, and TESS), we conduct a frequency analysis and investigate the stability of the pulsation amplitudes over four years of observations. We investigate the presence of a magnetic field and its properties using spectropolarimetric observations taken with the Narval instrument by applying the Least Square Deconvolution and Zeeman Doppler Imaging techniques. beta Cas shows only three independent p-mode frequencies down to the few ppm-level; its highest amplitude frequency is suggested to be a $n=3$, $\ell = 2$, $m=0$ mode. Its magnetic field structure is quite complex and almost certainly of a dynamo origin. beta Cas' atmosphere is slightly deficient in iron peak elements and slightly overabundant in C, O, and heavier elements. Atypically for delta Scuti stars, we can only detect three pulsation modes down to exceptionally low noise levels for beta Cas. The star is also one of very few delta Scuti pulsators known to date to show a measurable magnetic field, and the first delta Scuti star with a dynamo magnetic field. These characteristics make beta Cas an interesting target for future studies of dynamo processes in the thin convective envelopes of F-type stars, of the transition region between fossil and dynamo fields, and the interaction between pulsations and magnetic field., Comment: 16 pages plus 9 for the appendix, accepted for publication in Astronomy & Astrophysics

Results of an analysis of the BRITE-Constellation photometry of the SB1 system and ellipsoidal variable $\pi^5$ Ori (B2\,III) are presented. In addition to the orbital light-variation, which can be represented as a five-term Fourier cosine series with the frequencies $f_{\rm orb}$, $2f_{\rm orb}$, $3f_{\rm orb}$, $4f_{\rm orb}$ and $6f_{\rm orb}$, where $f_{\rm orb}$ is the system's orbital frequency, the star shows five low-amplitude but highly-significant sinusoidal variations with frequencies $f_i$ ($i ={}$2,..,5,7) in the range from 0.16 to 0.92~d$^{-1}$. With an accuracy better than 1$\sigma$, the latter frequencies obey the following relations: $f_2-f_4 = 2f_{\rm orb}$, $f_7 - f_3 = 2f_{\rm orb}$, $f_5 = f_3 - f_4 = f_7 - f_2$. We interpret the first two relations as evidence that two high-order $\ell = 1, m = 0$ gravity modes are self-excited in the system's tidally distorted primary component. The star is thus an ellipsoidal SPB variable. The last relations arise from the existence of the first-order differential combination term between the two modes. Fundamental parameters, derived from photometric data in the literature and the {\em Hipparcos\/} parallax, indicate that the primary component is close to the terminal stages of its main sequence (MS) evolution. Extensive Wilson-Devinney modeling leads to the conclusion that best fits of the theoretical to observed light-curves are obtained for the effective temperature and mass consistent with the primary's position in the HR diagram and suggests that the secondary is in an early MS evolutionary stage.

Solar-like oscillations in red-giant stars are now commonly detected in thousands of stars with space telescopes such as the NASA Kepler mission. Parallel radial velocity and photometric measurements would help to better understand the physics governing the amplitudes of solar-like oscillators. Yet, most target stars for space photometry are too faint for light-demanding ground-based spectroscopy. The BRITE Constellation satellites provide a unique opportunity of two-color monitoring of the flux variations of bright luminous red giants. Those targets are also bright enough to be monitored with high-resolution spectrographs on small telescopes, such as the SONG Network. In these proceedings, we provide a first overview of our comprehensive, multi-year campaign utilizing both BRITE and SONG to seismically characterize Aldebaran, one of the brightest red giants in the sky. Because luminous red giants can be seen at large distances, such well-characterized objects will serve as benchmark stars for galactic archeology., Comment: Proceedings paper for an oral contribution at the 'Stars and their Variability' conference in August 2019, in Vienna Austria. Five pages, two colored figures

Recent BRITE-Constellation space photometry of the slowly rotating, magnetic $\beta$ Cep pulsator $\xi^1$ CMa permits a new analysis of its pulsation properties. Analysis of the two-colour BRITE data reveals the well-known single pulsation period of $0.209$ d, along with its first and second harmonics. A similar analysis of SMEI and TESS observations yields compatible results, with the higher precision TESS observations also revealing several low-amplitude modes with frequencies below 5 d$^{-1}$; some of these are likely $g$ modes. The phase lag between photometric and radial velocity maxima - equal to 0.334 cycles - is significantly larger than the typical value of $1/4$ observed in other large-amplitude $\beta$ Cep stars. The phase lag, as well as the strong dependence of phase of maximum light on wavelength, can be reconciled with seismic models only if the dominant mode is the fundamental radial mode. We employ all published photometric and radial velocity measurements, spanning over a century, to evaluate the stability of the pulsation period. The $O-C$ diagram exhibits a clear parabolic shape consistent with a mean rate of period change $\dot P=0.34\pm 0.02$ s/cen. The residuals from the best-fit parabola exhibit scatter that is substantially larger than the uncertainties. In particular, dense sampling obtained during the past $\sim$20 years suggests more complex and rapid period variations. Those data cannot be coherently phased with the mean rate of period change, and instead require $\dot P\sim0.9$ s/cen. We examine the potential contributions of binarity, stellar evolution, and stellar rotation and magnetism to understand the apparent period evolution., Comment: 14 pages, accepted by MNRAS

We present the first asteroseismic results for $\delta$ Scuti and $\gamma$ Doradus stars observed in Sectors 1 and 2 of the TESS mission. We utilise the 2-min cadence TESS data for a sample of 117 stars to classify their behaviour regarding variability and place them in the Hertzsprung-Russell diagram using Gaia DR2 data. Included within our sample are the eponymous members of two pulsator classes, $\gamma$ Doradus and SX Phoenicis. Our sample of pulsating intermediate-mass stars observed by TESS also allows us to confront theoretical models of pulsation driving in the classical instability strip for the first time and show that mixing processes in the outer envelope play an important role. We derive an empirical estimate of 74% for the relative amplitude suppression factor as a result of the redder TESS passband compared to the Kepler mission using a pulsating eclipsing binary system. Furthermore, our sample contains many high-frequency pulsators, allowing us to probe the frequency variability of hot young $\delta$ Scuti stars, which were lacking in the Kepler mission data set, and identify promising targets for future asteroseismic modelling. The TESS data also allow us to refine the stellar parameters of SX Phoenicis, which is believed to be a blue straggler., Comment: 33 pages (incl. appendix), accepted for publications in MNRAS

$\varepsilon$ Lupi A is a binary system consisting of two main sequence early B-type stars Aa and Ab in a short period, moderately eccentric orbit. The close binary pair is the only doubly-magnetic massive binary currently known. Using photometric data from the BRITE-Constellation we identify a modest heartbeat variation. Combining the photometry with radial velocities of both components we determine a full orbital solution including empirical masses and radii. These results are compared with stellar evolution models as well as interferometry and the differences discussed. We also find additional photometric variability at several frequencies, finding it unlikely these frequencies can be caused by tidally excited oscillations. We do, however, determine that these signals are consistent with gravity mode pulsations typical for slowly pulsating B stars. Finally we discuss how the evolution of this system will be affected by magnetism, determining that tidal interactions will still be dominant., Comment: 18 pages, 7 figures

Exoplanet properties crucially depend on their host stars' parameters. In case the exoplanet host star shows pulsations, asteroseismology can be used for an improved description of the stellar parameters. We aim to revisit the pulsational properties of beta Pic and identify its pulsation modes from normalised amplitudes in five different passbands. We also investigate the potential presence of a magnetic field. We conduct a frequency analysis using three seasons of BRITE-Constellation observations in the BRITE blue and red filters, the ~620-day long bRing light curve and the nearly 8-year long SMEI photometric time series. We calculate normalised amplitudes using all passbands including previously published values obtained from ASTEP observations. We investigate the magnetic properties of beta Pic using spectropolarimetric observations conducted with the HARPSpol instrument. Using 2D rotating models, we fit the normalised amplitudes and frequencies through Monte Carlo Markov Chains. We identify 15 pulsation frequencies in the range from 34 to 55c/d, where two display clear amplitude variability. We use the normalised amplitudes in up to five passbands to identify the modes as three l = 1, six l = 2 and six l = 3 modes. beta Pic is shown to be non-magnetic with an upper limit of the possible undetected dipolar field of 300G. Multiple fits to the frequencies and normalised amplitudes are obtained including one with a near equator-on inclination for beta Pic, which corresponds to our expectations based on the orbital inclination of beta Pic b and the orientation of the circumstellar disk. This solution leads to a rotation rate of 27% of the Keplerian break-up velocity, a radius of 1.497+-0.025Rsun, and a mass of 1.797+-0.035Msun. The ~2% errors in radius and mass do not account for uncertainties in the models and a potentially erroneous mode-identification., Comment: 26 pages, 19 figures, accepted in Astronomy & Astrophysics

Context: The study of stellar structure and evolution depends crucially on accurate stellar parameters. The photometry from space telescopes has provided superb data that allowed asteroseismic characterisation of thousands of stars. However, typical targets of space telescopes are rather faint and complementary measurements are difficult to obtain. On the other hand, the brightest, otherwise well-studied stars, are lacking seismic characterization. Aims: Our goal is to use the granulation and/or oscillation time scales measured from photometric time series of bright red giants (1.6$\leq$Vmag$\leq$5.3) observed with BRITE to determine stellar surface gravities and masses. Methods: We use probabilistic methods to characterize the granulation and/or oscillation signal in the power density spectra and the autocorrelation function of the BRITE time series. Results: We detect a clear granulation and/or oscillation signal in 23 red giant stars and extract the corresponding time scales from the power density spectra as well as the autocorrelation function of the BRITE time series. To account for the recently discovered non-linearity of the classical seismic scaling relations, we use parameters from a large sample of Kepler stars to re-calibrate the scalings of the high- and low-frequency components of the granulation signal. We develop a method to identify which component is measured if only one granulation component is statistically significant in the data. We then use the new scalings to determine the surface gravity of our sample stars, finding them to be consistent with those determined from the autocorrelation signal of the time series. We further use radius estimates from the literature to determine the stellar masses of our sample stars from the measured surface gravities. We also define a statistical measure for the evolutionary stage of the stars., Comment: 17 pager, 12 figures, accepted for publication in A&A

HD149404 is an evolved non-eclipsing O-star binary that has previously undergone a Roche lobe overflow interaction. Understanding some key properties of the system requires a determination of the orbital inclination and of the dimensions of the components. The BRITE-Heweliusz satellite was used to collect photometric data of HD149404. Additional photometry was retrieved from the SMEI archive. These data were analysed using a suite of period search tools. The orbital part of the lightcurve was modelled with the nightfall binary star code. The Gaia-DR2 parallax of HD149404 was used to provide additional constraints. The periodograms reveal a clear orbital modulation of the lightcurve with a peak-to-peak amplitude near 0.04 mag. The remaining non-orbital part of the variability is consistent with red noise. The lightcurve folded with the orbital period reveals ellipsoidal variations, but no eclipses. The minimum when the secondary star is in inferior conjunction is deeper than the other minimum due to mutual reflection effects between the stars. Combined with the Gaia-DR2 parallaxes, the photometric data indicate an orbital inclination in the range of 23{\deg} to 31{\deg} and a Roche lobe filling factor of the secondary larger than or equal to 0.96. The luminosity of the primary star is consistent with its present-day mass, whereas the more evolved secondary appears overluminous for its mass. We confirm that the primary's rotation period is about half the orbital period. Both features most probably stem from the past Roche lobe overflow episode., Comment: Accepted for publication in Astronomy & Astrophysics

In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups. The goal of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8\,IIIe shell star $\nu$ Pup. Time-series analyses are performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003--011), and Hipparcos (1989-1993). Two IUE SWP and 27 optical echelle spectra spanning 20 years were retrieved from various archives. The optical spectra exhibit no anomalies or well-defined variabilities. A magnetic field was not detected. All three photometry satellites recorded variability near 0.656 c/d which is resolved into three features separated by ~0.0021 c/d. First harmonics form a second frequency group, also spaced by ~0.0021 c/d. The frequency spacing is very nearly but not exactly equidistant. Variability near 0.0021 c/d was not detected. The long-term frequency stability could be used to derive meaningful constraints on the properties of a putative companion star. The IUE spectra do not reveal the presence of a hot subluminous secondary. $\nu$\,Pup is another Be star exhibiting an NRP variability pattern with long-term constancy and underlining the importance of combination frequencies and frequency groups. The star is a good target for efforts to identify an effectively single Be star., Comment: 16 pages, 12 figures, 5 tables, submitted to Astronomy & Astrophysics

The bright $(V=3.86)$ star $\beta$ Pictoris is a nearby young star with a debris disk and gas giant exoplanet, $\beta$ Pictoris b, in a multi-decade orbit around it. Both the planet's orbit and disk are almost edge-on to our line of sight. We carry out a search for any transiting planets in the $\beta$ Pictoris system with orbits of less than 30 days that are coplanar with the planet $\beta$ Pictoris b. We search for a planetary transit using data from the BRITE-Constellation nanosatellite BRITE-Heweliusz, analyzing the photometry using the Box-Fitting Least Squares Algorithm (BLS). The sensitivity of the method is verified by injection of artificial planetary transit signals using the Bad-Ass Transit Model cAlculatioN (BATMAN) code. No planet was found in the BRITE-Constellation data set. We rule out planets larger than 0.6 $\mathrm{R_J}$ for periods of less than 5 days, larger than 0.75 $\mathrm{R_J}$ for periods of less than 10 days, and larger than 1.05 $\mathrm{R_J}$ for periods of less than 20 days., Comment: 6 pages, 6 figures, 3 tables. Accepted for publication in A&A

The Antartica Search for Transiting Extrasolar Planets (ASTEP), an automatized 400 mm telescope located at Concordia station in Antarctica, monitored beta Pictoris continuously to detect any variability linked to the transit of the Hill sphere of its planet beta Pictoris b. The long observation sequence, from March to September 2017, combined with the quality and high level duty cycle of our data, enables us to detect and analyse the delta Scuti pulsations of the star. Time series photometric data were obtained using aperture photometry by telescope defocussing. The 66 418 data points were analysed using the software package Period04. We only selected frequencies with amplitudes that exceed four times the local noise level in the amplitude spectrum. We detect 31 delta Scuti pulsation frequencies, 28 of which are new detections. All the frequencies detected are in the interval 34.76-75.68 d-1 . We also find that beta Pictoris exhibits at least one pulsation mode that varies in amplitude over our monitoring duration of seven months., Comment: 4 pages, 4 figures

Observations of 25 Ori much expand the picture derived of other early-type Be stars with BRITE and SMEI. Two instead of one difference frequencies rule the variability: (a) The lower one, 0.0129 c/d, is the frequency of events with full amplitudes of 100-200 mmag which may signal mass loss possibly driven by the higher one, 0.1777 c/d. (b) Much of the entire power spectrum is a tightly woven network of combination frequencies: (i) Below 0.25\,c/d, numerous frequencies are difference frequencies. (ii) Many frequencies above 2.5 c/d can be represented as sum frequencies and in a few cases as harmonics. (iii) Many frequencies between 1.1 and 1.75\,c/d can be portrayed as parents of combination frequencies. The number and fraction of combination frequencies increases steeply with decreasing amplitude and and accuracy of the frequency matching., Comment: 8 pages, 0 figures, to appear in Proc. 3rd BRITE Science Conference, Lac Taureau, Quebec, Aug. 7-10, 2017 (eds. G.A. Wade et al.); the page footer is wrong (bug in template)

The BRITE Constellation of nanosatellites obtained mmag photometry of 28 Cygni for 11 months in 2014-2016. Observations with the Solar Mass Ejection Imager in 2003-2010 and 118 H$\alpha$ line profiles were added. For decades, 28 Cyg has exhibited four large-amplitude frequencies: two closely spaced frequencies of spectroscopically confirmed $g$ modes near 1.5 c/d, one slightly lower exophotospheric (Stefl) frequency, and at 0.05 c/d the difference frequency between the two g modes. This top-level framework is indistinguishable from eta Cen (Paper I), which is also very similar in spectral type, rotation rate, and viewing angle. The Stefl frequency is the only one that does not seem to be affected by the difference frequency. The amplitude of the latter undergoes large variations; around maximum the amount of near-circumstellar matter is increased, and the amplitude of the Stefl frequency grows by some factor. During such brightenings dozens of transient spikes appear in the frequency spectrum, concentrated in three groups. Only eleven frequencies were common to all years of BRITE observations. Be stars seem to be controlled by several coupled clocks, most of which are not very regular on timescales of weeks to months but function for decades. The combination of g modes to the low difference frequency and/or the atmospheric response to it appears significantly nonlinear. Like in eta Cen, the difference-frequency variability seems the main responsible for the modulation of the star-to-disc mass transfer in 28 Cyg. A hierarchical set of difference frequencies may reach the longest timescales known of the Be phenomenon., Comment: 17 pages, 21 figures, submitted to Astronomy & Astrophysics

Stellar rotation affects the transport of chemical elements and angular momentum and is therefore a key process during stellar evolution, which is still not fully understood. This is especially true for massive stars, which are important for the chemical enrichment of the universe. It is therefore important to constrain their physical parameters and internal angular momentum distribution to calibrate stellar structure and evolution models. Stellar internal rotation can be probed through asteroseismic studies of rotationally split oscillations but such results are still quite rare, especially for stars more massive than the Sun. The SPB star HD201433 is known to be part of a single-lined spectroscopic triple system, with two low-mass companions orbiting with periods of about 3.3 and 154 d. Our results are based on photometric observations made by BRITE - Constellation and the SMEI on board the Coriolis satellite, high-resolution spectroscopy, and more than 96 years of radial velocity measurements. We identify a sequence of 9 rotationally split dipole modes in the photometric time series and establish that HD201433 is in principle a solid-body rotator with a very slow rotation period of 297+/-76 d. Tidal interaction with the inner companion has, however, significantly accelerated the spin of the surface layers by a factor of approximately one hundred. The angular momentum transfer onto the surface of HD201433 is also reflected by the statistically significant decrease of the orbital period of about 0.9 s during the last 96 years. Combining the asteroseismic inferences with the spectroscopic measurements and the orbital analysis of the inner binary system, we conclude that tidal interactions between the central SPB star and its inner companion have almost circularised the orbit but not yet aligned all spins of the system and have just begun to synchronise rotation., Comment: 21 pages, 19 figures, accepted for publication in A&A

Space photometric time series of the most massive members of the young open cluster NGC 2264 allow us to study their different sources of variability down to the millimagnitude level and permits a search for Slowly Pulsating B (SPB) type pulsation among objects that are only a few million years old. Our goal is to conduct a homogeneous study of young B type stars in the cluster NGC 2264 using photometric time series from space in combination with high-resolution spectroscopy and spectropolarimetry obtained from the ground. The latter will be presented in a separate follow-up article. We performed frequency analyses for eleven B stars in the field of the young cluster NGC 2264 using photometric time series from the MOST, CoRoT and Spitzer space telescopes and the routines Period04 and SigSpec. We employ the MESA stellar evolution code in combination with the oscillation code GYRE to identify the pulsation modes for two SPB stars which exhibit short period spacing series. From our analysis we identify four objects that show SPB pulsations, five stars that show rotational modulation of their light curves caused by spots, one star that is identified to be a binary, and one object in the field of the cluster that is found to be a non-member Be star. In two SPB stars we detect a number of regularly spaced pulsation modes that are compatible with being members of a g mode period series. Despite NGC 2264's young age, our analysis illustrates that its B type members have already arrived on the zero-age main sequence (ZAMS). Our asteroseismic analysis yields masses between 4 and 6 Msun and ages between 1 and 6 million years, which agree well to the overall cluster age., Comment: 19 pages, 20 figures, accepted for publication in Astronomy & Astrophysics

The BRIght Target Explorer (BRITE) Constellation is the first nanosatellite mission applied to astrophysical research. Five satellites in low-Earth orbits perform precise optical two-colour photometry of the brightest stars in the night sky. BRITE is naturally well suited for variability studies of hot stars. This contribution describes the basic outline of the mission and some initial problems that needed to be overcome. Some information on BRITE data products, how to access them, and how to join their scientific exploration is provided. Finally, a brief summary of the first scientific results obtained by BRITE is given., Comment: 5 pages, 1 figure, to appear in the proceedings of "Seismology of the Sun and the Distant Stars 2016. Using Today's Successes to Prepare the Future. Joint TASC2/KASC9 Workshop - SPACEINN/HELAS8 Conference", ed. M. J. P. F. G. Monteiro

New high-cadence observations with BRITE covering many months confirm that coupled pairs of nonradial pulsation modes are widespread among early-type Be stars. With the difference frequency between the parental variations they may form a roughly sinusoidal variability or the amplitude may cyclicly vary. A first - amplified - beat pattern is also found. In all three cases the amplitudes of difference frequencies can exceed the amplitude sum of the base frequencies, and modulations of the star-to-circumstellar-disk mass-transfer rate may be associated with these slow variations. This suggests more strongly than any earlier observations that significant dissipation of pulsational energy in the atmosphere may be a cause of mass ejections from Be stars. A unifying interpretative concept is presented., Comment: 10 pages, 3 figures, preliminary formatting. To appear in Proc. 2nd BRITE-Constellation Science Conference: 'small satellites - big science', Innsbruck, Aug. 2016, eds.: G. Stachowski, E. Poretti, and J. Matthews

We report a simultaneous ground and space-based photometric study of the Beta Cephei star Nu Eridani. Half a year of observations have been obtained by four of the five satellites constituting BRITE-Constellation, supplemented with ground-based photoelectric photometry. We show that carefully combining the two data sets virtually eliminates the aliasing problem that often hampers time-series analyses. We detect 40 periodic signals intrinsic to the star in the light curves. Despite a lower detection limit we do not recover all the pressure and mixed modes previously reported in the literature, but we newly detect six additional gravity modes. This behaviour is a consequence of temporal changes in the pulsation amplitudes that we also detected for some of the p modes. We point out that the dependence of theoretically predicted pulsation amplitude on wavelength is steeper in visual passbands than those observationally measured, to the extent that the three dominant pulsation modes of Nu Eridani would be incorrectly identified using data in optical filters only. We discuss possible reasons for this discrepancy., Comment: 11 pages, 5 figures, 4 tables, accepted for publication in MNRAS

BRITE (BRIght Target Explorer) Constellation, the first nanosatellite mission applied to astrophysical research, is a collaboration among Austria, Canada and Poland. The fleet of satellites (6 launched, 5 functioning) performs precise optical photometry of the brightest stars in the night sky. A pioneering mission like BRITE - with optics and instruments restricted to small volume, mass and power in several nanosatellites, whose measurements must be coordinated in orbit - poses many unique challenges. We discuss the technical issues, including problems encountered during on-orbit commissioning (especially higher-than expected sensitivity of the CCDs to particle radiation). We describe in detail how the BRITE team has mitigated these problems, and provide a complete overview of mission operations. This paper serves as a template for how to effectively plan, build and operate future low-cost niche-driven space astronomy missions., Comment: 54 pages, 12 figures, accepted by PASP

Among the known groups of pulsating stars, $\delta$ Sct stars are one of the least understood. Theoretical models do not predict the oscillation frequencies that observations reveal. Complete asteroseismic studies are necessary to improve these models and better understand the internal structure of these targets. We study the $\delta$ Sct star HD 41641 with the ultimate goal of understanding its oscillation pattern. The target was simultaneously observed by the CoRoT space telescope and the HARPS high-resolution spectrograph. The photometric data set was analyzed with the software package PERIOD04, while FAMIAS was used to analyze the line profile variations. The method of spectrum synthesis was used for spectroscopically determining the fundamental atmospheric parameters and individual chemical abundances. A total of 90 different frequencies was identified and analyzed. An unambiguous identification of the azimuthal order of the surface geometry could only be provided for the dominant p-mode, which was found to be a nonradial prograde mode with m = +1. Using $T_\mathrm{eff}$ and $\log g$, we estimated the mass, radius, and evolutionary stage of HD 41641. We find HD 41641 to be a moderately rotating, slightly evolved $\delta$ Sct star with subsolar overall atmospheric metal content and unexpected chemical peculiarities. HD 41641 is a pure $\delta$ Sct pulsator with p-mode frequencies in the range from 10 d$^{-1}$ to 20 d$^{-1}$. This pulsating star presents chemical signatures of an Ap star and rotational modulation due to surface inhomogeneities, which we consider indirect evidence of the presence of a magnetic field., Comment: 11 pages, 11 figures, accepted for publication in A&A

This paper aims to precisely determine the masses and detect pulsation modes in the two massive components of Beta Cen with BRITE-Constellation photometry. In addition, seismic models for the components are considered and the effects of fast rotation are discussed. This is done to test the limitations of seismic modeling for this very difficult case. A simultaneous fit of visual and spectroscopic orbits is used to self-consistently derive the orbital parameters, and subsequently the masses, of the components. The derived masses are equal to 12.02 +/- 0.13 and 10.58 +/- 0.18 M_Sun. The parameters of the wider, A - B system, presently approaching periastron passage, are constrained. Analysis of the combined blue- and red-filter BRITE-Constellation photometric data of the system revealed the presence of 19 periodic terms, of which eight are likely g modes, nine are p modes, and the remaining two are combination terms. It cannot be excluded that one or two low-frequency terms are rotational frequencies. It is possible that both components of Beta Cen are Beta Cep/SPB hybrids. An attempt to use the apparent changes of frequency to distinguish which modes originate in which component did not succeed, but there is potential for using this method when more BRITE data become available. Agena seems to be one of very few rapidly rotating massive objects with rich p- and g-mode spectra, and precisely known masses. It can therefore be used to gain a better understanding of the excitation of pulsations in relatively rapidly rotating stars and their seismic modeling. Finally, this case illustrates the potential of BRITE-Constellation data for the detection of rich-frequency spectra of small-amplitude modes in massive pulsating stars., Comment: 17 pages (with Appendix), 15 figures, accepted for publication in A&A

Binary stars provide a valuable test of stellar structure and evolution, because the masses of the individual stellar components can be derived with high accuracy and in a model-independent way. In this work, we study Spica, an eccentric double-lined spectroscopic binary system with a beta Cep type variable primary component. We use state-of-the-art modelling tools to determine accurate orbital elements of the binary system and atmospheric parameters of both stellar components. We interpret the short-period variability intrinsic to the primary component, detected on top of the orbital motion both in the photometric and spectroscopic data. The non-LTE based spectrum analysis reveals two stars of similar atmospheric chemical composition consistent with the present day cosmic abundance standard defined by Nieva&Przybilla (2012). The masses and radii of the stars are found to be 11.43+/-1.15 M_sun and 7.21+/-0.75 M_sun, and 7.47+/-0.54 R_sun and 3.74+/-0.53 R_sun for the primary and secondary, respectively. We find the primary component to pulsate in three independent modes, of which one is identified as a radial mode, while the two others are found to be non-radial, low degree l modes. The frequency of one of these modes is an exact multiple of the orbital frequency, and the l=m=2 mode identification suggests a tidal nature for this particular mode. We find a very good agreement between the derived dynamical and evolutionary masses for the Spica system to within the observational errors of the measured masses. The age of the system is estimated to be 12.5+/-1 Myr., Comment: 13 pages, 10 figures, 7 tabels; accepted for publication in the main journal of MNRAS

We report on an analysis of high-precision, multi-colour photometric observations of the rapidly-oscillating Ap (roAp) star $\alpha$ Cir. These observations were obtained with the BRITE-Constellation, which is a coordinated mission of five nanosatellites that collects continuous millimagnitude-precision photometry of dozens of bright stars for up to 180 days at a time in two colours (Johnson B and R). BRITE stands for BRight Target Explorer. The object $\alpha$ Cir is the brightest roAp star and an ideal target for such investigations, facilitating the determination of oscillation frequencies with high resolution. This star is bright enough for complementary interferometry and time-resolved spectroscopy. Four BRITE satellites observed $\alpha$ Cir for 146 d or 33 rotational cycles. Phasing the photometry according to the 4.4790 d rotational period reveals qualitatively different light variations in the two photometric bands. The phased red-band photometry is in good agreement with previously-published WIRE data, showing a light curve symmetric about phase 0.5 with a strong contribution from the first harmonic. The phased blue-band data, in contrast, show an essentially sinusoidal variation. We model both light curves with Bayesian Photometric Imaging, which suggests the presence of two large-scale, photometrically bright (relative to the surrounding photosphere) spots. We also examine the high-frequency pulsation spectrum as encoded in the BRITE photometry. Our analysis establishes the stability of the main pulsation frequency over the last 20 years, confirms the presence of frequency f7, which was not detected (or the mode not excited) prior to 2006, and excludes quadrupolar modes for the main pulsation frequency., Comment: 10 pages, 11 figures, accepted by Astronomy & Astrophysics

Gamma Doradus stars (hereafter gamma Dor stars) are gravity-mode pulsators of spectral type A or F. Such modes probe the deep stellar interior, offering a detailed fingerprint of their structure. Four-year high-precision space-based Kepler photometry of gamma Dor stars has become available, allowing us to study these stars with unprecedented detail. We selected, analysed, and characterized a sample of 67 gamma Dor stars for which we have Kepler observations available. For all the targets in the sample we assembled high-resolution spectroscopy to confirm their F-type nature. We found fourteen binaries, among which four single-lined binaries, five double-lined binaries, two triple systems and three binaries with no detected radial velocity variations. We estimated the orbital parameters whenever possible. For the single stars and the single-lined binaries, fundamental parameter values were determined from spectroscopy. We searched for period spacing patterns in the photometric data and identified this diagnostic for 50 of the stars in the sample, 46 of which are single stars or single-lined binaries. We found a strong correlation between the spectroscopic vsini and the period spacing values, confirming the influence of rotation on gamma Dor-type pulsations as predicted by theory. We also found relations between the dominant g-mode frequency, the longest pulsation period detected in series of prograde modes, vsini, and log Teff., Comment: 61 pages, 61 figures, 6 tables, accepted for publication in ApJS

Context. The analysis of stellar oscillations is one of the most reliable ways to probe stellar interiors. Recent space missions such as Kepler have provided us with an opportunity to study these oscillations with unprecedented detail. For many multi-periodic pulsators such as {\gamma} Doradus stars, this led to the detection of dozens to hundreds of oscillation frequencies that could not be found from ground-based observations. Aims. We aim to detect non-uniform period spacings in the Fourier spectra of a sample of {\gamma} Doradus stars observed by Kepler. Such detection is complicated by both the large number of significant frequencies in the space photometry and by overlapping non-equidistant rotationally split multiplets. Methods. Guided by theoretical properties of gravity-mode oscillation of {\gamma} Doradus stars, we developed a period-spacing detection method and applied it to Kepler observations of a few stars, after having tested the performance from simulations. Results. The application of the technique resulted in the clear detection of non-uniform period spacing series for three out of the five treated Kepler targets. Disadvantages of the technique are also discussed, and include the disability to distinguish between different values of the spherical degree and azimuthal order of the oscillation modes without additional theoretical modelling. Conclusions. Despite the shortcomings, the method is shown to allow solid detections of period spacings for {\gamma} Doradus stars, which will allow future asteroseismic analyses of these stars., Comment: 10 pages, 13 figures, 2 tables. Accepted for publication in Astronomy & Astrophysics

Red giants are evolved stars which exhibit solar-like oscillations. Although a multitude of stars have been observed with space telescopes, only a handful of red-giant stars were targets of spectroscopic asteroseismic observing projects. We search for solar-like oscillations in the two bright red-giant stars $\gamma$ Psc and $\theta^1$ Tau from time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power $\nu_{max}$ and the mean large frequency separation $\Delta\nu$ for both stars. The radial velocities of $\gamma$ Psc and $\theta^1$ Tau were monitored for 120 and 190 days, respectively. Nearly 9000 spectra were obtained. To reach the accurate radial velocities, we used simultaneous thorium-argon and iodine-cell calibration of our optical spectra. In addition to the spectroscopy, we acquired VLTI observations of $\gamma$ Psc for an independent estimate of the radius. Also 22 days of observations of $\theta^1$ Tau with the MOST-satellite were analysed. The frequency analysis of the radial velocity data of $\gamma$ Psc revealed an excess of oscillation power around 32 $\mu$Hz and a large frequency separation of 4.1$\pm$0.1$\mu$Hz. $\theta^1$ Tau exhibits oscillation power around 90 $\mu$Hz, with a large frequency separation of 6.9$\pm$0.2$\mu$Hz. Scaling relations indicate that $\gamma$ Psc is a star of about $\sim$1 M$_\odot$ and $\sim$10 R$_\odot$. $\theta^1$ Tau appears to be a massive star of about $\sim$2.7 M$_\odot$ and $\sim$11 R$_\odot$. The radial velocities of both stars were found to be modulated on time scales much longer than the oscillation periods. While the mass of $\theta^1$ Tau is in agreement with results from dynamical parallaxes, we find a lower mass for $\gamma$ Psc than what is given in the literature. The long periodic variability agrees with the expected time scales of rotational modulation., Comment: 15 pages, 15 figures; accepted for publication in A&A

We demonstrate that a seismic analysis of stars in their earliest evolutionary phases is a powerful method to identify young stars and distinguish their evolutionary states. The early star that is born from the gravitational collapse of a molecular cloud reaches at some point sufficient temperature, mass and luminosity to be detected. Accretion stops and the pre-main sequence star that emerges is nearly fully convective and chemically homogeneous. It will continue to contract gravitationally until the density and temperature in the core are high enough to start nuclear burning of hydrogen. We show that there is a relationship between detected pulsation properties for a sample of young stars and their evolutionary status illustrating the potential of asteroseismology for the early evolutionary phases., Comment: 23 pages, 9 figures, includes Supplementary Material. Science, published in Science Express on July 3, 2014

We used the Ultraviolet and Visual Echelle Spectrograph of the ESO-Very Large Telescope to obtain a high resolution and high signal-to-noise ratio spectrum of Stock 16-12, an early-type star which previous Delta-a photometric observations suggest being a chemically peculiar (CP) star. We used spectral synthesis to perform a detailed abundance analysis obtaining an effective temperature of 8400 +/- 400 K, a surface gravity of 4.1 +/- 0.4, a microturbulence velocity of 3.4 +0.7/-0.3 km/s, and a projected rotational velocity of 68 +/- 4 km/s. We provide photometric and spectroscopic evidence showing the star is most likely a member of the young Stock 16 open cluster (age 3-8 Myr). The probable cluster membership, the star's position in the Hertzsprung-Russell diagram, and the found infrared excess strongly suggest the star is still in the pre-main-sequence (PMS) phase. We used PMS evolutionary tracks to determine the stellar mass, which ranges between 1.95 and 2.3 Msun, depending upon the adopted spectroscopic or photometric data results. Similarly, we obtained a stellar age ranging between 4 and 6 Myr, in agreement with that of the cluster. Because the star's chemical abundance pattern resembles well that known of main sequence CP metallic line (Am) stars, the object sets important constraints to the diffusion theory. Additional spectroscopic and spectropolarimetric data allowed us to conclude that the object is probably a single non-magnetic star., Comment: Accepted for publication in MNRAS; 8 pages, 5 figures, 1 table

BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, the brightness and temperature variations of stars generally brighter than mag(V) ~ 4, with precision and time coverage not possible from the ground. The current mission design consists of six nanosats (hence Constellation): two from Austria, two from Canada, and two from Poland. Each 7 kg nanosat carries an optical telescope of aperture 3 cm feeding an uncooled CCD. One instrument in each pair is equipped with a blue filter, the other with a red filter. Each BRITE instrument has a wide field of view (~24 degrees), so up to about 15 bright stars can be observed simultaneously, sampled in 32 pixel x 32 pixel sub-rasters. Photometry of additional fainter targets, with reduced precision but thorough time sampling, will be possible through onboard data processing. The BRITE sample is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-class stars at the very end of their nuclear burning phases. The goals of BRITE-Constellation are to (1) measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology; (2) look for varying spots on the stars surfaces carried across the stellar disks by rotation, which are the sources of co-rotating interaction regions in the winds of the most luminous stars, probably arising from magnetic subsurface convection; and (3) search for planetary transits., Comment: 23 pages, 12 figures, accepted for publication in the PASP

Star clusters are known as superb tools for understanding stellar evolution. In a quest for understanding the physical origin of magnetism and chemical peculiarity in about 7% of the massive main-sequence stars, we analysed two of the ten brightest members of the ~10 Myr old Galactic open cluster NGC 2264, the early B-dwarfs HD47887 and HD47777. We find accurate rotation periods of 1.95 and 2.64 days, respectively, from MOST photometry. We obtained ESPaDOnS spectropolarimetric observations, through which we determined stellar parameters, detailed chemical surface abundances, projected rotational velocities, and the inclination angles of the rotation axis. Because we found only small (<5 km/s) radial velocity variations, most likely caused by spots, we can rule out that HD47887 and HD47777 are close binaries. Finally, using the least-squares deconvolution technique, we found that both stars possess a large-scale magnetic field with an average longitudinal field strength of about 400 G. From a simultaneous fit of the stellar parameters we determine the evolutionary masses of HD47887 and HD47777 to be 9.4+/-0.7 M0 and 7.6+/-0.5 M0. Interestingly, HD47777 shows a remarkable helium underabundance, typical of helium-weak chemically peculiar stars, while the abundances of HD47887 are normal, which might imply that diffusion is operating in the lower mass star but not in the slightly more massive one. Furthermore, we argue that the rather slow rotation, as well as the lack of nitrogen enrichment in both stars, can be consistent with both the fossil and the binary hypothesis for the origin of the magnetic field. However, the presence of two magnetic and apparently single stars near the top of the cluster mass-function may speak in favour of the latter., Comment: 13 pages, accepted for publication on A&A

PLATO 2.0 has recently been selected for ESA's M3 launch opportunity (2022/24). Providing accurate key planet parameters (radius, mass, density and age) in statistical numbers, it addresses fundamental questions such as: How do planetary systems form and evolve? Are there other systems with planets like ours, including potentially habitable planets? The PLATO 2.0 instrument consists of 34 small aperture telescopes (32 with 25 sec readout cadence and 2 with 2.5 sec candence) providing a wide field-of-view (2232 deg2) and a large photometric magnitude range (4-16 mag). It focusses on bright (4-11 mag) stars in wide fields to detect and characterize planets down to Earth-size by photometric transits, whose masses can then be determined by ground-based radial-velocity follow-up measurements. Asteroseismology will be performed for these bright stars to obtain highly accurate stellar parameters, including masses and ages. The combination of bright targets and asteroseismology results in high accuracy for the bulk planet parameters: 2%, 4-10% and 10% for planet radii, masses and ages, respectively. The planned baseline observing strategy includes two long pointings (2-3 years) to detect and bulk characterize planets reaching into the habitable zone (HZ) of solar-like stars and an additional step-and-stare phase to cover in total about 50% of the sky. PLATO 2.0 will observe up to 1,000,000 stars and detect and characterize hundreds of small planets, and thousands of planets in the Neptune to gas giant regime out to the HZ. It will therefore provide the first large-scale catalogue of bulk characterized planets with accurate radii, masses, mean densities and ages. This catalogue will include terrestrial planets at intermediate orbital distances, where surface temperatures are moderate. Coverage of this parameter range with statistical numbers of bulk characterized planets is unique to PLATO 2.0., Comment: 63 pages, 17 figures, submitted to Experimental Astronomy (ExA)

We outline a proposal to use the Kepler spacecraft in two-wheel mode to monitor a handful of young associations and open clusters, for a few weeks each. Judging from the experience of similar projects using ground-based telescopes and the CoRoT spacecraft, this program would transform our understanding of early stellar evolution through the study of pulsations, rotation, activity, the detection and characterisation of eclipsing binaries, and the possible detection of transiting exoplanets. Importantly, Kepler's wide field-of-view would enable key spatially extended, nearby regions to be monitored in their entirety for the first time, and the proposed observations would exploit unique synergies with the GAIA ESO spectroscopic survey and, in the longer term, the GAIA mission itself. We also outline possible strategies for optimising the photometric performance of Kepler in two-wheel mode by modelling pixel sensitivity variations and other systematics., Comment: 10 pages, 6 figures, white paper submitted in response to NASA call for community input for alternative science investigations for the Kepler spacecraft

We concentrate on an asteroseismological study of HD 261711, a rather hot delta Scuti type pulsating member of the young open cluster NGC 2264 located at the blue border of the instability region. HD 261711 was discovered to be a pre-main sequence delta Scuti star using the time series photometry obtained by the MOST satellite in 2006. High-precision, time-series photometry of HD 261711 was obtained by the MOST and CoRoT satellites in 4 separate new observing runs that are put into context with the star's fundamental atmospheric parameters obtained from spectroscopy. With the new MOST data set from 2011/12 and the two CoRoT light curves from 2008 and 2011/12, the delta Scuti variability was confirmed and regular groups of frequencies were discovered. The two pulsation frequencies identified in the data from the first MOST observing run in 2006 are confirmed and 23 new delta Scuti-type frequencies were discovered using the CoRoT data. Weighted average frequencies for each group are related to l=0 and l=1 p-modes. Evidence for amplitude modulation of the frequencies in two groups is seen. The effective temperature was derived to be 8600$\pm$200 K, log g is 4.1$\pm$0.2, and the projected rotational velocity is 53$\pm$1km/s. Using our Teff value and the radius of 1.8$\pm$0.5 Rsun derived from SED fitting, we get a log L/Lsun of 1.20$\pm$0.14 which agrees well to the seismologically determined values of 1.65 Rsun and, hence, a log L/Lsun of 1.13. The radial velocity of 14$\pm$2 km/s we derived for HD 261711, confirms the star's membership to NGC 2264. Our asteroseismic models suggest that HD 261711 is a delta Scuti-type star close to the zero-age main sequence (ZAMS) with a mass of 1.8 to 1.9Msun. HD 261711 is either a young ZAMS star or a late PMS star just before the onset of hydrogen-core burning., Comment: 12 pages, 13 figures, A&A accepted

Pulsations in pre-main sequence stars have been discovered several times within the last years. But nearly all of these pulsators are of delta Scuti-type. gamma Doradus-type pulsation in young stars has been predicted by theory, but lack observational evidence. We present the investigation of variability caused by rotation and (gammaDoradus-type) pulsation in two pre-main sequence members of the young open cluster NGC2264 using high-precision time series photometry from the CoRoT satellite and dedicated high-resolution spectroscopy. Time series photometry of NGC2264VAS20 and NGC 2264VAS87 was obtained by the CoRoT satellite during the dedicated short run SRa01 in March 2008. NGC2264VAS87 was re-observed by CoRoT during the short run SRa05 in December 2011 and January 2012. Frequency analysis was conducted using Period04 and SigSpec. The spectral analysis was performed using equivalent widths and spectral synthesis. The frequency analysis yielded 10 and 14 intrinsic frequencies for NGC2264VAS20 and NGC2264VAS 87, respectively, in the range from 0 to 1.5c/d which are attributed to be caused by a combination of rotation and pulsation. The effective temperatures were derived to be 6380$\pm$150K for NGC2264VAS20 and 6220$\pm$150K for NGC2264VAS87. Membership of the two stars to the cluster is confirmed independently using X-ray fluxes, radial velocity measurements and proper motions available in the literature. The derived Li abundances of log n(Li)=3.34 and 3.54 for NGC2264VAS20 and NGC2264VAS87, respectively, are in agreement with the Li abundance for other stars in NGC2264 of similar Teff reported in the literature. We conclude that the two objects are members of NGC2264 and therefore are in their pre-main sequence evolutionary stage. Assuming that part of their variability is caused by pulsation, these two stars might be the first pre-main sequence gamma Doradus candidates., Comment: 11 pages, 10 figures, A&A accepted

MOST observations and model analysis of the Herbig Ae star HD 34282 (V1366 Ori) reveal {\delta}-Scuti pulsations. 22 frequencies are observed, 10 of which confirm those previously identified by Amado et al. (2006), and 12 of which are newly discovered in this work. We show that the weighted-average frequency in each group fits the radial p-mode frequencies of viable models. We argue that the observed pulsation spectrum extends just to the edge to the acoustic cut-off frequency and show that this also is consistent with our best-fitting models., Comment: 10 pages, 9 figures

During two weeks of nearly continuous optical photometry of the young open cluster NGC 2244 obtained by the MOST satellite, we discovered two new SPB stars, GSC 00154-00785 and GSC 00154-01871. We present frequency analyses of the MOST light curves of these stars, which reveal two oscillation frequencies (0.61 and 0.71 c/d) in GSC 00154-00785 and two (0.40 and 0.51 c/d) in GSC 00154-01871. These frequency ranges are consistent with g-modes of $\ell \leq 2$ excited in models of main-sequence or pre-main-sequence (PMS) stars of masses 4.5 - 5 $M_{\odot}$ and solar composition $(X, Z)= (0.7, 0.02)$. Published proper motion measurements and radial velocities are insufficient to establish unambiguously cluster membership for these two stars. However, the PMS models which fit best their eigenspectra have ages consistent with NGC 2244. If cluster membership can be confirmed, these would be the first known PMS SPB stars, and would open a new window on testing asteroseismically the interior structures of PMS stars., Comment: accepted for publication in MNRAS

We present high-precision time-series photometry of the classical delta Scuti star HD 144277 obtained with the MOST (Microvariability and Oscillations of STars) satellite in two consecutive years. The observed regular frequency patterns are investigated asteroseismologically. HD 144277 is a hot A-type star that is located on the blue border of the classical instability strip. While we mostly observe low radial order modes in classical delta Scuti stars, HD 144277 presents a different case. Its high observed frequencies, i.e., between 59.9c/d (693.9 microHz) and 71.1c/d (822.8microHz), suggest higher radial orders. We examine the progression of the regular frequency spacings from the low radial order to the asymptotic frequency region. Frequency analysis was performed using Period04 and SigSpec. The results from the MOST observing runs in 2009 and 2010 were compared to each other. The resulting frequencies were submitted to asteroseismic analysis. HD 144277 was discovered to be a delta Scuti star using the time-series photometry observed by the MOST satellite. Twelve independent pulsation frequencies lying in four distinct groups were identified. Two additional frequencies were found to be combination frequencies. The typical spacing of 3.6c/d corresponds to the spacing between subsequent radial and dipole modes, therefore the spacing between radial modes is twice this value, 7.2c/d. Based on the assumption of slow rotation, we find evidence that the two radial modes are the sixth and seventh overtones, and the frequency with the highest amplitude can be identified as a dipole mode. The models required to fit the observed instability range need slightly less metallicity and a moderate enhancement of the helium abundance compared to the standard chemical composition. Our asteroseismic models suggest that HD 144277 is a delta Scuti star close to the ZAMS with a mass of 1.66 solar masses., Comment: 8 pages, 10 figures, accepted by A&A

We present detailed parameter determinations of two chemically normal late A-type stars, HD 32115 and HD 37594, to uncover the reasons behind large discrepancies between two previous analyses of these stars performed with a semi-automatic procedure and a "classical" analysis. Our study is based on high resolution, high signal-to-noise spectra obtained at the McDonald Observatory. Our method is based on the simultaneous use of all available observables: multicolor photometry, pressure-sensitive magnesium lines, metallic lines and Balmer line profiles. Our final set of fundamental parameters fits, within the error bars, all available observables. It differs from the published results obtained with a semi-automatic procedure. A direct comparison between our new observational material and the spectra previously used by other authors shows that the quality of the data is not the origin of the discrepancies. As the two stars require a substantial macroturbulence velocity to fit the line profiles, we concluded that neglecting this additional broadening in the semi-automatic analysis is one origin of discrepancy. The use of FeI excitation equilibrium and of the Fe ionisation equilibrium, to derive effective temperature and surface gravity, respectively, neglecting all other indicators leads to a systematically erroneously high effective temperature. We deduce that the results obtained using only one parameter indicator might be biased and that those results need to be cautiously taken when performing further detailed analyses, such as modelling of the asteroseismic frequencies or characterising transiting exoplanets., Comment: Accepted for publication by MNRAS