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We announce the discovery of pulsations in HD 23642, the only bright eclipsing system in the Pleiades, based on light curves from the Transiting Exoplanet Survey Satellite (TESS). We measure 46 pulsation frequencies and attribute them to δ Scuti pulsations in the secondary component. We find four ℓ = 1 doublets, three of which have frequency splittings consistent with the rotation rate of the star. The dipole mode amplitude ratios are consistent with a high stellar inclination angle and the stellar rotation period agrees with the orbital period. Together, these suggest that the spin axis of the secondary is aligned with the orbital axis. We also determine precise effective temperatures and a spectroscopic light ratio, and use the latter to determine the physical properties of the system alongside the TESS data and published radial velocities. We measure a distance to the system in agreement with the Gaia parallax, and an age of 170 ± 20 Myr based on a comparison to theoretical stellar evolutionary models. [ABSTRACT FROM AUTHOR]

υ  Sgr is the prototype of four known hydrogen-deficient binary (HdB) systems. These are characterized by a hydrogen-deficient A-type primary, variable hydrogen emission lines, and a normally unseen secondary presumed to be an upper main-sequence star. Orbital periods range from tens of days to 360 d. TESS observations of all four HdBs show a flux variation with well-defined period in the range 0.5–0.9 d, too short to be associated with the supergiant primary, and more likely to be the rotation period of the secondary and associated with a chemical surface asymmetry or a low-order non-radial oscillation. The observed rotation period supports a recent analysis of the υ Sgr secondary. The observations give a direct glimpse of the secondary in all four systems, and should help to explain how the primary has been stripped to become a low-mass hydrogen remnant. [ABSTRACT FROM AUTHOR]

The abundance patterns observed in the Sun and in metal-poor stars show a clear odd-even effect. An important question is whether the odd-even effect in solar-metallicity stars is similar to the Sun, or if there are variations that can tell us about different chemical enrichment histories. In this work, we report for the first time observational evidence of a differential odd-even effect in the solar twin HIP 11915, relative to the solar odd-even abundance pattern. The spectra of this star were obtained with high-resolving power (140 000) and signal-to-noise ratio (∼420) using the ESPRESSO spectrograph and the VLT telescope. Thanks to the high spectral quality, we obtained extremely precise stellar parameters (σ(T eff) = 2 K, |$\sigma (\rm {[Fe/H]})$| = 0.003 dex, and σ(log  g) = 0.008 dex). We determine the chemical abundance of 20 elements (Z ≤ 39) with high precision (∼0.01 dex), which shows a strong pattern of the odd-even effect even after performing galactic chemical evolution corrections. The odd-even effect is reasonably well-reproduced by a core-collapse supernova of 13 |$\rm {M_{\odot }}$| and metallicity Z = 0.001 diluted into a metal-poor gas of 1 |$\rm {M_{\odot }}$|⁠. Our results indicate that HIP 11915 has an odd-even effect slightly different than the Sun, thus confirming a different supernova enrichment history. [ABSTRACT FROM AUTHOR]

We present an analysis of the high-mass eclipsing binary system VV Ori based on photometry from the TESS satellite. The primary star (B1 V, 9.5  |$\, {\rm M}_\odot$|⁠) shows β Cephei pulsations and the secondary (B7 V, 3.8  |$\, {\rm M}_\odot$|⁠) is possibly a slowly pulsating B star. We detect 51 significant oscillation frequencies, including two multiplets with separations equal to the orbital frequency, indicating that the pulsations are tidally perturbed. We analyse the TESS light curve and published radial velocities to determine the physical properties of the system. Both stars are only the second of their pulsation type with a precisely measured mass. The orbital inclination is also currently decreasing, likely due to gravitational interactions with a third body. [ABSTRACT FROM AUTHOR]

A 2014 study of the eclipsing binary star 1SWASPJ011351.29+314909.7 (J0113+31) reported an unexpectedly high effective temperature for the M-dwarf companion to the 0.95-M⊙ primary star. The effective temperature inferred from the secondary eclipse depth was ∼600 K higher than the value predicted from stellar models. Such an anomalous result questions our understanding of low-mass stars and might indicate a significant uncertainty when inferring properties of exoplanets orbiting them. We seek to measure the effective temperature of the M-dwarf companion using the light curve of J0113+31 recently observed by the Transiting Exoplanet Survey Satellite (TESS). We use the pycheops modelling software to fit a combined transit and eclipse model to the TESS light curve. To calculate the secondary effective temperature, we compare the best-fitting eclipse depth to the predicted eclipse depths from theoretical stellar models. We determined the effective temperature of the M dwarf to be T eff,2 = 3208 ± 43 K, assuming log  g 2 = 5, [Fe/H] = −0.4, and no alpha-element enhancement. Varying these assumptions changes T eff,2 by less than 100 K. These results do not support a large anomaly between observed and theoretical low-mass star temperatures. [ABSTRACT FROM AUTHOR]

V453 Cyg is an eclipsing binary containing 14 and 11  |$\, {\rm M}_\odot$| stars in an eccentric short-period orbit. We have discovered β Cep-type pulsations in this system using Transiting Exoplanet Survey Satellite data. We identify seven significant pulsation frequencies, between 2.37 and 10.51 d−1, in the primary star. These include six frequencies that are separated by yet significantly offset from harmonics of the orbital frequency, indicating they are tidally perturbed modes. We have determined the physical properties of the system to high precision: V453 Cyg A is the first β Cep pulsator with a precise mass measurement. The system is a vital tracer of the physical processes that govern the evolution of massive single and binary stars. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of the possible future Sun's rotational evolution scenario based on the 8-Gyr-old solar twin HIP 102152. Using HARPS high-cadence observations (and TESS light curves), we analysed the modulation of a variety of activity proxies (Ca  ii  , H  i Balmer, and Na  i lines), finding a strong rotational signal of 35.7 ± 1.4 d (log  B factor ∼ 70, in the case of Ca  ii K line). This value matches with the theoretical expectations regarding the smooth rotational evolution of the Sun towards the end of the main sequence, validating the use of gyrochronology after solar age. [ABSTRACT FROM AUTHOR]

Owing to their simplicity and ease of application, seismic scaling relations are widely used to determine the properties of stars exhibiting solar-like oscillations, such as solar twins and red giants. So far, no seismic scaling relations for determining the ages of red giant stars have been developed. Such relations would be desirable for Galactic Archaeology, which uses stellar ages to map the history of the Milky Way. The ages of red giants must instead be estimated with reference to grids of theoretical stellar models, which can be computationally intensive. Here, I present an exhaustive search for scaling age relations involving different combinations of observable quantities. The candidate scaling relations are calibrated and tested using more than 1000 red giant stars whose ages were obtained via grid-based modelling. I report multiple high-quality scaling relations for red giant branch stars, the best of which are shown to be approximately as accurate as grid-based modelling with typical uncertainties of 15 per cent. Additionally, I present new scaling mass and radius relations for red giants as well. [ABSTRACT FROM AUTHOR]

Spectroscopic equilibrium allows us to obtain precise stellar parameters in Sun-like stars. It relies on the assumption of the iron excitation and ionization equilibrium. However, several works suggest that magnetic activity may affect chemical abundances of young active stars, calling into question the validity of this widely used method. We have tested, for the first time, variations in stellar parameters and chemical abundances for the young solar twin HIP 36515 (∼0.4 Gyr), along its activity cycle. This star has stellar parameters very well established in the literature and we estimated its activity cycle in ∼6 yr. Using HARPS spectra with high resolving power (115 000) and signal-to-noise ratio (∼270), the stellar parameters of six different epochs in the cycle were estimated. We found that the stellar activity is strongly correlated with the effective temperature, metallicity, and microturbulence velocity. The possibility of changes in the Li  i 6707.8 Å line due to flares and star-spots was also investigated. Although the core of the line profile shows some variations with the stellar cycle, it is compensated by changes in the effective temperature, resulting in a non-variation of the Li abundance. [ABSTRACT FROM AUTHOR]

The stellar rotation versus age relation is commonly considered a useful tool to derive reliable ages for Sun-like stars. However, in the light of Kepler data, the presence of apparently old and fast rotators that do not obey the usual gyrochronology relations led to the hypothesis of weakened magnetic breaking in some stars. In this letter, we constrain the solar rotation evolutionary track using solar twins. Predicted rotational periods as a function of mass, age, [Fe/H], and given critical Rossby number (Ro crit) were estimated for the entire rotational sample. Our analysis favours the smooth rotational evolution scenario and suggests that if the magnetic weakened breaking scenario takes place at all, it should arise after Ro crit ≳ 2.29 or ages ≳5.3 Gyr (at 95 per cent confidence level). [ABSTRACT FROM AUTHOR]

Precise stellar masses and radii can be determined using asteroseismology, but their accuracy must be tested against independent estimates. Using radii derived from Gaia DR2 parallaxes, we test the accuracy of asteroseismic radii for a sample of 93 dwarfs based on both individual frequency fitting and the seismic scaling relations. Radii from frequency fitting are about 1 per cent smaller than Gaia radii on average; however, this difference may be explained by a negative bias of |$30\, \mu\mathrm{as}$| in the Gaia parallaxes. This indicates that the radii derived from frequency fitting are accurate to within 1 per cent. The scaling relations are found to overestimate radii by more than 5 per cent, compared to the Gaia radii, at the highest temperatures. We demonstrate that this offset is reduced to 3 per cent after applying corrections based on model frequencies to the scaling relation for Δν, but only when the model frequencies are corrected for the surface effect. With corrections to Δν, the scaling relation gives radii accurate to about 2–3 per cent for dwarfs in the temperature range 5400–6700 K. The remaining offset at the highest temperatures may indicate the need for a correction to the scaling relation for νmax. [ABSTRACT FROM AUTHOR]

We use Gaia Data Release 2 to identify 13 928 white dwarfs (WDs) within 100 pc of the Sun. The exquisite astrometry from Gaia reveals for the first time a bifurcation in the observed WD sequence in both Gaia and the Sloan Digital Sky Survey (SDSS) passbands. The latter is easily explained by a helium atmosphere WD fraction of 36 per cent. However, the bifurcation in the Gaia colour–magnitude diagram depends on both the atmospheric composition and the mass distribution. We simulate theoretical colour–magnitude diagrams for single and binary WDs using a population synthesis approach and demonstrate that there is a significant contribution from relatively massive WDs that likely formed through mergers. These include WD remnants of main-sequence (blue stragglers) and post-main-sequence mergers. The mass distribution of the SDSS subsample, including the spectroscopically confirmed WDs, also shows this massive bump. This is the first direct detection of such a population in a volume-limited sample. [ABSTRACT FROM AUTHOR]

The availability of reliable bolometric corrections and reddening estimates, rather than the quality of parallaxes, will be one of the main limiting factors in determining the luminosities of a large fraction of Gaia stars. With this goal in mind, we provide Gaia G BP, G, and G RP synthetic photometry for the entire MARCS grid and test the performance of our synthetic colours and bolometric corrections against space-borne absolute spectrophotometry. We find indication of a magnitude-dependent offset in Gaia DR2 G magnitudes, which must be taken into account in high-accuracy investigations. Our interpolation routines are easily used to derive bolometric corrections at desired stellar parameters and to explore the dependence of Gaia photometry on T eff, $$\log \,g$$, $$\rm {[Fe/H]}$$, $$[\alpha /\rm {Fe}]$$, and E (B − V). Gaia colours for the Sun and Vega, and T eff-dependent extinction coefficients are also provided. [ABSTRACT FROM AUTHOR]

Understanding the physical process responsible for the transport of energy in the core of α Centauri A is of the utmost importance if this star is to be used in the calibration of stellar model physics. Adoption of different parallax measurements available in the literature results in differences in the interferometric radius constraints used in stellar modelling. Further, this is at the origin of the different dynamical mass measurements reported for this star. With the goal of reproducing the revised dynamical mass derived by Pourbaix & Boffin, we modelled the star using two stellar grids varying in the adopted nuclear reaction rates. Asteroseismic and spectroscopic observables were complemented with different interferometric radius constraints during the optimization procedure. Our findings show that best-fitting models reproducing the revised dynamical mass favour the existence of a convective core (≳70 per cent of best-fitting models), a result that is robust against changes to the model physics. If this mass is accurate, then α Centauri A may be used to calibrate stellar model parameters in the presence of a convective core. [ABSTRACT FROM AUTHOR]

Several recent studies of solar twins in the solar neighbourhood have shown a tight correlation between various elemental abundances and age, in particular [Y/Mg]. If this relation is real and valid for other types of stars as well as elsewhere in the Galaxy, it would provide a very powerful tool to derive ages of stars without the need to resort to determining their masses (evolutionary stage) very precisely. The methodwould also likelywork if the stellar parameters have relatively large errors. The studies presented in the recent literature span a narrow range of [Fe/H]. By studying a larger sample of solar neighbourhood dwarfs with a much larger range of [Fe/H], we find that the relation between [Y/Mg] and age depends on the [Fe/H] of the stars. Hence, it appears that the [Y/Mg]–age relation is unique to solar analogues. [ABSTRACT FROM AUTHOR]

We present the first dynamical determination of the binary parameters of an eclipsing SW Sextantis star in the 3-4 h orbital period range during a low state. We obtained time-resolved optical spectroscopy and photometry of HS 0220+0603 during its 2004-2005 low-brightness state, as revealed in the combined Small & Moderate Aperture Research Telescope System, IAC80 and M1 Group long-term optical light curve. The optical spectra taken during primary eclipse reveal a secondary star spectral type of M5.5 ± 0.5 as derived from molecular band-head indices. The spectra also provide the first detection of a DAB white dwarf in a cataclysmic variable. By modelling its optical spectrum we estimate a white dwarf temperature of 30 000 ± 5000 K. By combining the results of modelling the white dwarf eclipse from ULTRACAM light curves with those obtained by simultaneously fitting the emission- and absorption-line radial velocity curves and I-band ellipsoidal light curves, we measure the stellar masses to be M1 = 0.87 ± 0.09 M⊙ and M2 = 0.47 ± 0.05 M⊙ for the white dwarf and the M dwarf, respectively, and an inclination of the orbital plane of i ≈ 79°. A radius of 0.0103 ± 0.0007 R⊙ is obtained for the white dwarf. The secondary star in HS 0220+0603 is likely too cool and undersized for its mass. [ABSTRACT FROM AUTHOR]

This article investigates the problem of estimating stellar atmospheric parameters from spectra. Feature extraction is a key procedure in estimating stellar parameters automatically. We propose a scheme for spectral feature extraction and atmospheric parameter estimation using the following three procedures: firstly, learn a set of basic structure elements (BSEs) from stellar spectra using an autoencoder; secondly, extract representative features from stellar spectra based on the learned BSEs through some procedures of convolution and pooling; thirdly, estimate stellar parameters (Teff, logg, [Fe/H]) using a back-propagation (BP) network. The proposed scheme has been evaluated on both real spectra from Sloan Digital Sky Survey (SDSS)/Sloan Extension for Galactic Understanding and Exploration (SEGUE) and synthetic spectra calculated from Kurucz's new opacity distribution function (NEWODF) models. The best mean absolute errors (MAEs) are 0.0060 dex for log Teff, 0.1978 dex for log g and 0.1770 dex for [Fe/H] for the real spectra and 0.0004 dex for log Teff, 0.0145 dex for log g and 0.0070 dex for [Fe/H] for the synthetic spectra. [ABSTRACT FROM AUTHOR]

We have analyzed the double-lined eclipsing binary system ASAS J180057-2333.8 from the All Sky Automated Survey (ASAS) catalogue. We measure absolute physical and orbital parameters for this system based on archival V-band and I-band ASAS photometry, as well as on high-resolution spectroscopic data obtained with ESO 3.6 m/HARPS and CORALIE spectrographs. The physical and orbital parameters of the system were derived with an accuracy of about 0.5-3 per cent. The system is a very rare configuration of two bright welldetached giants of spectral types K1 and K4 and luminosity class II. The radii of the stars are R1 = 52.12 ± 1.38 and R2 = 67.63 ± 1.40 R☉ and their masses are M1 = 4.914 ± 0.021 and M2 = 4.875 ± 0.021 M☉. The exquisite accuracy of 0.5 per cent obtained for the masses of the components is one of the best mass determinations for giants. We derived a precise distance to the system of 2.14 ± 0.06 kpc (stat.) ± 0.05 (syst.) which places the star in the Sagittarius-Carina arm. The Galactic rotational velocity of the star is Θs = 258 ± 26 km s-1 assuming Θ0 = 238 km s-1. A comparison with PARSEC isochrones places the system at the early phase of core helium burning with an age of slightly larger than 100 million years. The effect of overshooting on stellar evolutionary tracks was explored using the MESA star code. [ABSTRACT FROM AUTHOR]

The Kepler space mission and its K2 extension provide photometric time series data with unprecedented accuracy. These data challenge our current understanding of the metalliclined A stars (Am stars) for what concerns the onset of pulsations in their atmospheres. It turns out that the predictions of current diffusion models do not agree with observations. To understand this discrepancy, it is of crucial importance to obtain ground-based spectroscopic observations of Am stars in the Kepler and K2 fields in order to determine the best estimates of the stellar parameters. In this paper, we present a detailed analysis of high-resolution spectroscopic data for seven stars previously classified as Am stars. We determine the effective temperatures, surface gravities, projected rotational velocities, microturbulent velocities and chemical abundances of these stars using spectral synthesis. These spectra were obtained with CAOS, a newinstrument recently installed at the observing station of the CataniaAstrophysical Observatory on Mt Etna. Three stars have already been observed during quarters Q0-Q17, namely: HD 180347, HD 181206 and HD 185658, while HD 43509 was already observed during K2 C0 campaign. We confirm that HD 43509 and HD 180347 are Am stars, while HD 52403, HD 50766, HD 58246, HD 181206 and HD 185658 are marginal Am stars. By means of non-LTE (local thermodynamic equilibrium) analysis, we derived oxygen abundances from O I λ7771-5 Å triplet and we also discussed the results obtained with both non-LTE and LTE approaches. [ABSTRACT FROM AUTHOR]

Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated (O - C) diagrams. Analysis of 1952 well-observed fundamentalmode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 yr, leading to a final sample of 12 firm binary candidates. We provide O - C diagrams and binary parameters for this final sample, and also discuss the properties of eight additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that ≳ 4 per cent of the RRL reside in binary systems. [ABSTRACT FROM AUTHOR]

ABSTRACT We report the discovery of low-amplitude gravity-mode oscillations in the massive binary star V380 Cyg, from 180 d of Kepler custom-aperture space photometry and 5 months of high-resolution high signal-to-noise ratio spectroscopy. The new data are of unprecedented quality and allowed the improvement of the orbital and fundamental parameters for this binary. The orbital solution was subtracted from the photometric data and led to the detection of periodic intrinsic variability with frequencies, of which some are multiples of the orbital frequency and others are not. Spectral disentangling allowed the detection of line-profile variability in the primary. With our discovery of intrinsic variability interpreted as gravity-mode oscillations, V380 Cyg becomes an important laboratory for future seismic tuning of the near-core physics in massive B-type stars. [ABSTRACT FROM AUTHOR]

Discovery of the first planetary system by direct imaging, around HR 8799, has made the age determination of the host star a very important task. This determination is the key to deriving accurate masses of the planets and to studying the dynamical stability of the system. The age of this star has been estimated using different procedures. In this Letter we show that some of these procedures have problems and large uncertainties, and the real age of this star is still unknown, needing more observational constraints. Therefore we have developed a comprehensive modelling of HR 8799 and, taking advantage of its γ Doradus-type pulsations, we have estimated the age of the star using asteroseismology. The accuracy in the age determination depends on the rotation velocity of the star, and therefore an accurate value of the inclination angle is required to solve the problem. Nevertheless, we find that the age estimate for this star previously published in the literature ([30, 160] Myr) is unlikely, and a more accurate value might be around a Gyr. This determination has significant implications for the value of the mass of the objects orbiting HR 8799. An age around ≈1 Gyr implies that these objects would be brown dwarfs. [ABSTRACT FROM AUTHOR]

Hoyle & Fowler showed that there could be radiation pressure supported stars (RPSSs) even in Newtonian gravity. Much later, Mitra found that one could also conceive of their general relativistic (GR) version, ‘relativistic radiation pressure supported stars’ (RRPSSs). While RPSSs have , RRPSSs have , where z is the surface gravitational redshift. Here, we elaborate on the formation of RRPSSs during continued gravitational collapse by recalling that a contracting massive star must start trapping radiation as it enters its photon sphere. It is found that, irrespective of the details of the contraction process, the trapped radiation flux should attain the corresponding Eddington value at sufficiently large . This means that continued GR collapse may generate an intermediate RRPSS with before a true black hole state with is formed asymptotically. An exciting consequence of this is that the stellar mass black hole candidates, at the present epoch, should be hot balls of quark–gluon plasma, as has been discussed by Royzen in a recent article entitled ‘QCD against black holes?’. [ABSTRACT FROM AUTHOR]

We report the first resolved bispectrum speckle interferometry of the symbiotic binary CH Cyg. The measured component separation, , is consistent with the one derived from the known spectroscopic orbit and distance. In particular, our result implies a total mass of the binary of , which is in good agreement with the value derived from the spectroscopic orbit solution for the red giant and evolutionary constraints. We also show that the radio jets and the bipolar outflow are not orthogonal to the orbital plane of the binary system. [ABSTRACT FROM AUTHOR]

We derive a new age for the Velorum binary by comparing recent observations to our set of binary models. We find that it is very unlikely that the stars have not interacted, which implies that previous estimates of the age from single-star models of are incorrect. We prefer an older age of that agrees with the age of other lower mass stars in the Vela OB association. We also find that our favoured binary model shows the components of the binary have interacted in a Case B, post-main-sequence, mass-transfer event. During the mass-transfer event, the envelopes of both components are radiative and therefore the damping of tidal forces is relatively weak. This explains why the binary is still eccentric after mass transfer. [ABSTRACT FROM AUTHOR]

Establishing relations between global stellar parameters and asteroseismic quantities can help improve our understanding of stellar astrophysics and facilitate the interpretation of observations. We present an observed relation between the large frequency separation, , and the frequency of maximum power, . We find that , allowing prediction of to about 15 per cent given . Our result is further supported by established scaling relations for and and by extended stellar model calculations, which confirm that can be estimated using this relation for basically any star showing solar-like oscillations in the investigated range . [ABSTRACT FROM AUTHOR]

We address the age rank of the nearest pre-main-sequence (PMS) associations, using low-resolution spectrophotometry to measure gravity-sensitive indices in these stars. We compare spectral index-colour sequences for the PMS populations and rank them according to the strength of their gravity-sensitive features. The age rank using the gravity method is in general agreement with the ranking of these groups suggested by colour–magnitude (CM) diagram placement. Several of the groups have a kinematic origin in the Oph-Sco-Cen OB association. For three of them, their age rank is also in agreement with epochs resulting from a formation scenario for the OB association. [ABSTRACT FROM AUTHOR]

Using a novel technique, which combines previously determined rotation periods with new spectroscopic determinations of projected rotation velocity, we have determined radii for fast-rotating, low-mass M-dwarfs in the young, solar-metallicity open cluster, NGC 2516. The mean radii are larger than model predictions at a given absolute I or K magnitude and also larger than the measured radii of magnetically inactive M-dwarfs; the difference increases from a few per cent to 50 per cent for the lowest luminosity stars in our sample. We show that a simple two-temperature starspot model is broadly capable of explaining these observations, but requires spot coverage fractions of about 50 per cent in rapidly rotating M-dwarfs. [ABSTRACT FROM AUTHOR]

Asymptotic giant branch (AGB) variables are found to obey period–luminosity relations in the mid-infrared (mid-IR) similar to those seen at (2.14 μm), even at 24 μm where emission from circumstellar dust is expected to be dominant. Their loci in the diagrams are essentially the same for the Large Magellanic Cloud (LMC) and for NGC 6522 in spite of different ages and metallicities. There is no systematic trend of slope with wavelength. The offsets of the apparent magnitude versus relations imply a difference between the two fields of 3.8 in distance modulus. The colours of the variables confirm that a principal period with is a necessary condition for detectable mass loss. At the longest observed wavelength, 24 μm, many semiregular variables have dust shells comparable in luminosity to those around Miras. There is a clear bifurcation in LMC colour–magnitude diagrams involving 24 μm magnitudes. [ABSTRACT FROM AUTHOR]

Using Very Large Telescope/Spectrograph for INtegral Field Observation in the Near-Infrared (VLT/SINFONI), we have obtained repeated adaptive-optics assisted, near-infrared spectroscopy of the three central WN6ha stars in the core of the very young (∼1 Myr), massive and dense Galactic cluster NGC 3603. One of these stars, NGC 3603-A1, is a known 3.77 d, double-eclipsing binary, while another one, NGC 3603-C, is one of the brightest X-ray sources among all known Galactic WR stars, which usually is a strong indication for binarity. Our study reveals that star C is indeed an 8.9-d binary, although only the WN6ha component is visible in our spectra; therefore, we temporarily classify star C as an SB1 system. A1, on the other hand, is found to consist of two emission-line stars of similar, but not necessarily of identical spectral type, which can be followed over most the orbit. Using radial velocities for both components and the previously known inclination angle of the system, we are able to derive absolute masses for both stars in A1. We find for the primary and for the secondary component of A1. While uncertainties are large, A1 is intrinsically half a magnitude brighter than WR20a, the current record holder with 83 and , respectively; therefore, it is likely that the primary in A1 is indeed the most massive star weighed so far. [ABSTRACT FROM AUTHOR]

In this Letter, we analyse period–colour and amplitude–colour relations at minimum, mean and maximum V-band light for 6391 RRab stars in the Large Magellanic Cloud obtained by the MACHO project. Specifically, we find that colour and amplitude are nearly independent of period at minimum light, but that there exists a definite relation between period and colour and amplitude and colour at maximum light. These two properties are consistent with earlier work suggesting that these observed properties are, at least to some extent, explained by the application of the Stefan–Boltzmann law and the interaction of the photosphere and hydrogen ionization front at minimum light. When we examine the slope of the period–colour relation as a function of phase, we find that the slope varies significantly with phase and is small for a wide range of phases around minimum light. This suggests that another factor that needs to be considered when trying to understand RR Lyrae observed properties is their behaviour at different phases during a pulsation cycle. [ABSTRACT FROM AUTHOR]

We present a new luminous star in M33 located in the nuclear region. The star shows strong Fe ii and [Fe ii] forest, hydrogen emissions in the spectrum, as well as nebular lines. Ti ii and Si ii lines were detected in absorption, their radial velocity shifted by relative to emission lines. The star is variable over 7 yr with 0.5 mag variations over a year. We studied its spectral energy distribution together with five confirmed luminous blue variables (LBVs) and Var A in M33 using homogeneous data and methods. We found the star's bolometric luminosity to be log L/ , a surface temperature of and blackbody temperatures of two dust components of and 420 K. The new star has properties intermediate between the LBVs and Var A (probable cool hypergiant). At the same time, it has a hot photosphere, LBV-like luminosity and an extensive circumstellar material (strong [Ca ii] lines). In these seven luminous variables in M33, we find the total range of the hot component luminosities is 1.0 dex, but that of the dust components is 2.0 dex. We conclude that the dust phenomenon in the luminous variables is temporary and variable, and that the dust activity may follow strong eruptions. [ABSTRACT FROM AUTHOR]

We have used the Sydney University Stellar Interferometer to measure the angular diameter of β Hydri. This star is a nearby G2 subgiant the mean density of which was recently measured with high precision using asteroseismology. We determine the radius and effective temperature of the star to be (0.9 per cent) and K (0.7 per cent) respectively. By combining the radius with the mean density, as estimated from asteroseismology, we make a direct estimate of the stellar mass. We find a value of (2.8 per cent), which agrees with published estimates based on fitting in the Hertzsprung–Russell diagram, but has much higher precision. These results place valuable constraints on theoretical models of β Hyi and its oscillation frequencies. [ABSTRACT FROM AUTHOR]

We present the results of a magnetic survey of a sample of eight β Cephei stars and 26 slowly pulsating B (SPBs) stars with the FOcal Reducer low dispersion Spectrograph at the Very Large Telescope. A weak mean longitudinal magnetic field of the order of a few hundred Gauss is detected in the β Cephei star and in 13 SPB stars. The star becomes the third magnetic star among the β Cephei stars. Before our study, the star ζ Cas was the only known magnetic SPB star. All magnetic SPB stars for which we gathered several magnetic field measurements show a field that varies in time. We do not find a relation between the evolution of the magnetic field with stellar age in our small sample. Our observations imply that β Cephei and SPB stars can no longer be considered as classes of non-magnetic pulsators, but the effect of the fields on the oscillation properties remains to be studied. [ABSTRACT FROM AUTHOR]