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In this study, we test whether the power law slopes (α F ) for fluxes (F), and (α E ) for energies (E) are universal in their size distributions, N (F) ∝ F − α F and N (E) ∝ E − α E , in astrophysical observations of galactic, extragalactic, and black hole systems. This is a test of fundamental importance for self-organized criticality (SOC) systems. The test decides whether (i) power laws are a natural consequence of the scale-freeness and inherent universality of SOC systems, or (ii) if they depend on more complex physical scaling laws. The former criterion allows quantitative predictions of the power-law-like size distributions, while the latter criterion requires individual physical modeling for each SOC variable and data set. Our statistical test, carried out with 61 published data sets, is consistent with the former option, which implies that observed power laws can simply be derived from the scale-freeness and do not require specific physical models to understand their statistical distributions. The observations show a mean and standard deviation of α F = 1.78 ± 0.29 for SOC fluxes and α E = 1.66 ± 0.22 for SOC fluences, and thus are consistent with the prediction of the fractal-diffusive SOC model, with α F = 1.80 and α E = 1.67. [ABSTRACT FROM AUTHOR]

HD 327083 is a binary system that consists of two supergiant components and exhibits the B[e] phenomenon. In this paper, we report the determination of a new set of the system's fundamental parameters using a combination of photometric and spectroscopic data as well as the Gaia EDR3 distance. We found that the orbital period of the system is 107.68 ± 0.02 days. The spectral line content implies the effective temperatures of ≈7000 K and 25,400 ± 1400 K, while the photometric variations are consistent with the radii of ≈106 R ⊙ and ≈10 R ⊙ for the cool and hot components, respectively. The absorption lines of the cool component show a radial velocity semiamplitude of 48.3 ± 1.7 km s−1, similar to that of the emission lines that originate around the hot component. The inclination of the system to the line of sight is 47 − 20 + 17 °. Modeling of the system's evolutionary history suggests that the components have masses of ∼12.5 M ⊙ and currently undergo mass transfer between them. This configuration, which takes in heating of the surface of the cool component by the radiation from the hot one, can reproduce the photometric and spectroscopic data and is in agreement with previous infrared observations of the circumbinary disk. The results of this study further confirm the hypothesis that the reason for the presence of the B[e] phenomenon in most objects is a consequence of the evolution of various binary systems. [ABSTRACT FROM AUTHOR]

We describe four different approaches for the detection of magnetospheric accretion among Herbig Ae/Be stars with accretion disks. Studies of several unique objects have been carried out. One of the objects is the Herbig Ae star HD101412 with a comparatively strong magnetic field. The second is the early-type Herbig B6e star HD259431. The existence of a magnetosphere in these objects was not recognized earlier. In both cases, a periodicity in the variation of some line parameters, originating near the region of the disk/star interaction, has been found. The third object is the young binary system HD104237, hosting a Herbig Ae star and a T Tauri star. Based on the discovery of periodic variations of equivalent widths of atmospheric lines in the spectrum of the primary, we have concluded that the surface of the star is spotted. Comparing our result with an earlier one, we argue that these spots can be connected with the infall of material from the disk onto the stellar surface through a magnetosphere. The fourth example is the Herbig Ae/Be star HD37806. Signatures of magnetospheric accretion in this object have been identified using a different method. They were inferred from the short-term variability of the He I l5876 line profile forming in the region of the disk/star interaction. [ABSTRACT FROM AUTHOR]

TU Tau (=HD 38218 = HIP 27135) is a binary system consisting of a C-N carbon star primary and an A-type secondary. We report on new photometry and spectroscopy which tracked the recent disappearance of the A-star secondary. The dimming of the A star was gradual and irregular, with one or more brief brightenings, implying the presence of nonhomogeneities in the carbon star outflow. We also present evidence that the A star is actively accreting s -process enriched material from the carbon star and suggest that it will therefore eventually evolve into a Barium giant. This is an important system as well because the A-type star can serve as a probe of the outer atmosphere of the carbon star.

Phase curves, or the change in observed illumination of the planet as it orbits around its host star, help us to characterize their atmospheres. However, the variability of the host star can make their detection challenging. The presence of starspots, faculae, flares, and rotational effects introduce brightness variations that can hide other flux variations related to the presence of an exoplanet: ellipsoidal variation, Doppler boosting, and a combination of reflected light and thermal emission from the planet. Here we present a study to quantify the effect of stellar variability on the detectability of phase curves in the optical. In the first stage we simulated ideal data, with different white noise levels, and with cadences and total duration matching a quarter of the Kepler mission. We performed injection and recovery tests to evaluate the minimum number of planetary orbits that need to be observed in order to determine the amplitude of the phase curve with an accuracy of 15%. We also evaluate the effect of a simplistic stellar variability signal with low amplitude in order to provide strong constraints on the minimum number of orbits needed under these ideal conditions. In the second stage we applied these methods to data from Q9 of the Kepler mission, known for its low instrumental noise. The injection and recovery tests are performed on a selected sample of the less noisy stars in different effective temperature ranges. Even for the shortest explored planet period of 1 day, we find that observing a single orbit of the planet fails to detect accurately more than 90% of the inserted amplitude. The best recovery rates, close to 48%, are obtained after 10 orbits of a 1 day period planet with the largest explored amplitude of 150 ppm. The temperature range of the host stars providing better recovery ratios is 5500 K < Teff < 6000 K. Our results provide guidelines to selecting the best targets in which phase curves can be measured to the greatest accuracy, given the variability and effective temperature of its host star, which is of interest for the upcoming TESS, CHEOPS, and PLATO space missions. [ABSTRACT FROM AUTHOR]

Context. Being the most numerous and oldest stars in the galaxy, M dwarfs are objects of great interest for exoplanet searches. The presence of molecules in their atmosphere complicates our understanding of their atmospheric properties. But great advances have recently been made in the modeling of M dwarfs due to the revision of solar abundances. Aims. We aim to determine stellar parameters of M dwarfs using high resolution spectra (R ∼ 90 000) simultaneously in the visible and the near-infrared. The high resolution spectra and broad wavelength coverage provide an unique opportunity to understand the onset of dust and cloud formation at cool temperatures. Furthermore, this study will help in understanding the physical processes which occur in a cool atmospheres, particularly, the redistribution of energy from the optical to the near-infrared. Methods. The stellar parameters of M dwarfs in our sample have been determined by comparing the high resolution spectra both in the optical and in the near-infrared simultaneously observed by CARMENES with the synthetic spectra obtained from the BT-Settl model atmosphere. The detailed spectral synthesis of these observed spectra both in the optical and in the near-infrared helps to understand the missing continuum opacity. Results. For the first time, we derive fundamental stellar parameters of M dwarfs using the high resolution optical and near-infrared spectra simultaneously. We determine Teff, log g and [M/H] for 292 M dwarfs of spectral type M0 to M9, where the formation of dust and clouds are important. The derived Teff for the sample ranges from 2300 to 4000 K, values of log g ranges from 4.5 ≤ logg ≤ 5.5 and the resulting metallicity ranges from −0.5 ≤ [M/H] ≤ +0.5. We have also explored the possible differences in Teff, log g and [M/H] by comparing them with other studies of the same sample of M dwarfs. [ABSTRACT FROM AUTHOR]

Absorption cells filled with diatomic iodine are frequently employed as wavelength reference for high-precision stellar radial velocity determination due to their long-term stability and low cost. Despite their wide-spread usage in the community, there is little documentation on how to determine the ideal operating temperature of an individual cell. We have developed a new approach to measuring the effective molecular temperature inside a gas absorption cell and searching for effects detrimental to a high-precision wavelength reference, utilizing the Boltzmann distribution of relative line depths within absorption bands of single vibrational transitions. With a high-resolution Fourier transform spectrometer, we took a series of 632 spectra at temperatures between 23 and 66°C. These spectra provide a sufficient basis to test the algorithm and demonstrate the stability and repeatability of the temperature determination via molecular lines on a single iodine absorption cell. The achievable radial velocity precision σRV is found to be independent of the cell temperature and a detailed analysis shows a wavelength dependence, which originates in the resolving power of the spectrometer in use and the signal-to-noise ratio. Two effects were found to cause apparent absolute shifts in radial velocity, a temperature-induced shift of the order of ∼1 m s−1 K−1 and a more significant effect resulting in abrupt jumps of ≥50 m s−1 is determined to be caused by the temperature crossing the dew point of the molecular iodine. [ABSTRACT FROM AUTHOR]

It has been hypothesized that stellar envelopes with positive binding energy may be ejected if the release of recombination energy can be triggered and the calculation of binding energy includes this contribution. The implications of this hypothesis for the evolution of normal hydrogen-rich stars have been investigated, but the implications for helium stars - which may represent mass-transfer or merger remnants in binary star systems-have not. Making a set of model helium stars, we find that those with masses between 0.9 and 2.4M☉ evolve to configurations with positive binding energy envelopes. We discuss consequences of the ejection hypothesis for such stars and possible observational tests of these predictions. [ABSTRACT FROM AUTHOR]

We investigate the masses of 'retired A stars' using asteroseismic detections on seven lowluminosity red-giant and sub-giant stars observed by the NASA Kepler and K2 missions. Our aim is to explore whether masses derived from spectroscopy and isochrone fitting may have been systematically overestimated. Our targets have all previously been subject to longterm radial velocity observations to detect orbiting bodies, and satisfy the criteria used by Johnson et al. to select survey stars which may have had A-type (or early F-type) mainsequence progenitors. The sample actually spans a somewhat wider range in mass, from ≈1 M☉ up to ≈1.7 M☉. Whilst for five of the seven stars the reported discovery mass from spectroscopy exceeds the mass estimated using asteroseismology, there is no strong evidence for a significant, systematic bias across the sample. Moreover, comparisons with other masses from the literature show that the absolute scale of any differences is highly sensitive to the chosen reference literature mass, with the scatter between different literature masses significantly larger than reported error bars. We find that any mass difference can be explained through use of different constraints during the recovery process. We also conclude that underestimated uncertainties on the input parameters can significantly bias the recovered stellar masses, which may have contributed to the controversy on the mass scale for retired A stars. [ABSTRACT FROM AUTHOR]

Little is observationally known about the progenitors of Type Ibc supernovae (SNe) or the typical activity of SNe progenitors in their final years. Here, we analyse deep Large Binocular Telescope imaging data spanning the 4 yr before and after the Type Ibc SN 2012fh using difference imaging. We place 1σ upper limits on the detection of the progenitor star at MU > -3.8, MB > -3.1, MV > -3.8 and MR > -4.0mag. These limits are the tightest placed on a Type Ibc SN to date and they largely rule out single star evolutionary models in favour of a binary channel as the origin of this SN.We also constrain the activity of the progenitor to be small on an absolute scale, with the RMS UBVR optical variability ≲ 2500 L☉ and long-term dimming or brightening trends ≲ 1000 L☉ yr-1 in all four bands. [ABSTRACT FROM AUTHOR]

We present the results of a study of a large sample of A and Am stars with spectral types from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and light curves from Wide Area Search for Planets (WASP). We find that, unlike normal A stars, δ Sct pulsations in Am stars are mostly confined to the effective temperature range 6900 < Teff < 7600 K.We find evidence that the incidence of pulsations inAmstars decreases with increasingmetallicism (degree of chemical peculiarity). The maximum amplitude of the pulsations in Am stars does not appear to vary significantly with metallicism. The amplitude distributions of the principal pulsation frequencies for both A and Am stars appear very similar and agree with results obtained from Kepler photometry. We present evidence that suggests turbulent pressure is the main driving mechanism in pulsating Am stars, rather than the κ-mechanism, which is expected to be suppressed by gravitational settling in these stars. [ABSTRACT FROM AUTHOR]

Kepler data are used to investigate flares in stars of all spectral types. There is a strong tendency across all spectral types for the most energetic flares to occur among the most rapidly rotating stars. Differential rotation could conceivably play an important role in enhancing flare energies. This idea was investigated, but no correlation could be found between rotational shear and the incidence of flares. Inspection of Kepler light curves shows that rotational modulation is very common over the whole spectral type range. Using the rotational light amplitude, the size distribution of star-spots was investigated. Our analysis suggests that stars with detectable flares have spots significantly larger than non-flare stars, indicating that flare energies are correlated with the size of the active region. Further evidence of the existence of spots on A stars is shown by the correlation between the photometric period and the projected rotational velocity. The existence of spots indicates the presence of magnetic fields, but the fact that A stars lack coronae implies that surface convection is a necessary condition for the formation of the corona. [ABSTRACT FROM AUTHOR]

We present the analytic theory of brown dwarf evolution and the lower mass limit of the hydrogen burning main-sequence stars and introduce some modifications to the existing models. We give an exact expression for the pressure of an ideal nonrelativistic Fermi gas at a finite temperature, therefore allowing for nonzero values of the degeneracy parameter. We review the derivation of surface luminosity using an entropy matching condition and the first-order phase transition between the molecular hydrogen in the outer envelope and the partially ionized hydrogen in the inner region. We also discuss the results of modern simulations of the plasma phase transition, which illustrate the uncertainties in determining its critical temperature. Based on the existing models and with some simple modification, we find the maximum mass for a brown dwarf to be in the range 0.064M⊙–0.087M⊙. An analytic formula for the luminosity evolution allows us to estimate the time period of the nonsteady state (i.e., non-main-sequence) nuclear burning for substellar objects. We also calculate the evolution of very low mass stars. We estimate that ≃11% of stars take longer than 107 yr to reach the main sequence, and ≃5% of stars take longer than 108 yr. [ABSTRACT FROM AUTHOR]

Based on high-resolution spectra taken near the He I 6678 Å line for the massive binary system 103 Tau, we have detected a weak absorption component belonging to the binary's secondary component. We have measured the radial velocities of both components, improved the previously known orbital parameters, and determined the new ones. The binary has an orbital period P = 58.305, an orbital eccentricity e = 0.277, a radial velocity semi-amplitude of the bright component K = 44.8 km s, and a component mass ratio M / M = 1.77. The absence of photometric variability and the estimates of physical parameters for the primary component suggest that the binary most likely has a considerable inclination of the orbital plane to the observer, i ≈ 50°−60°. In this case, the secondary component is probably a normal dwarf of spectral type B5-B8. Based on the spectra taken near the H line, we have studied the variability of the emission profile. It is shown to be formed in the Roche lobe of the secondary component, but no traces of active mass exchange in the binary have been detected. [ABSTRACT FROM AUTHOR]

We construct a model atom for Ti I-II using more than 3600 measured and predicted energy levels of Ti I and 1800 energy levels of Ti II, and quantum mechanical photoionization crosssections. Non-local thermodynamical equilibrium (NLTE) line formation for Ti I and Ti II is treated through a wide range of spectral types from A to K, including metal-poor stars with [Fe/H] down to -2.6 dex. NLTE leads to weakened Ti I lines and positive abundance corrections. The magnitude of NLTE corrections is smaller compared to the literature data for FGK atmospheres. NLTE leads to strengthened Ti II lines and negative NLTE abundance corrections. For the first time, we have performed NLTE calculations for Ti I-II in the 6500 = Teff ≤ 13 000 K range. For four A-type stars, we derived in LTE an abundance discrepancy of up to 0.22 dex between Ti I and Ti II, which vanishes in NLTE. For four other A-B stars, with only Ti II lines observed, NLTE leads to a decrease of line-to-line scatter. An efficiency of inelastic Ti I + HI collisions was estimated from an analysis of Ti I and Ti II lines in 17 cool stars with -2.6 ≤ [Fe/H] ≤ 0.0. Consistent NLTE abundances from Ti I and Ti II were obtained by applying classical Drawinian rates for the stars with log g ≥ 4.1, and neglecting inelastic collisions with HI for the very metal-poor (VMP) giant HD 122563. For the VMP turn-off stars ([Fe/H] ≤ -2 and log g ≤ 4.1), we obtained the positive abundance difference Ti I-II already in LTE, which increases in NLTE. Accurate collisional data for Ti I and Ti II are necessary to help solve this problem. [ABSTRACT FROM AUTHOR]

Rotational light modulation in Kepler photometry of K-A stars is used to estimate the absolute rotational shear. The rotation frequency spread in 2562 carefully selected stars with known rotation periods is measured using time-frequency diagrams. Because rotational shear is both a function of effective temperature and rotation rate, it is necessary to separate the two effects by calculating the rotation shear in restricted ranges of effective temperature and rotation period. The shear increases to a maximum in F stars, but decreases somewhat in the A stars. Theoretical models reproduce the variation of rotational shear with effective temperature quite well for all rotation rates. The dependence of the shear on the rotation rate is weak in K and G stars, increases rapidly for F stars and is strongest in A stars. For stars earlier than type K, a discrepancy exists between the predicted and observed variation of shear with rotation rate. [ABSTRACT FROM AUTHOR]

On 2012 June 10, an Earth-grazer meteor which lasted over 17 s with an absolute magnitude of -4.0 ± 0.5 was observed over Spain. This work focuses on the analysis of this rare event which is, to our knowledge, the faintest Earth-grazing meteor reported in the scientific literature, but also the first one belonging to a meteor shower. Thus, the orbital parameters show that the parent meteoroid belonged to the Daytime ζ-Perseid meteoroid stream. According to our calculations, the meteor was produced by a meteoroid with an initial mass ranging between 115 and 1.5 kg. During its encounter with Earth, the particle travelled about 510 km in the atmosphere. Around 260 g were destroyed in the atmosphere during the luminous phase of the event as a consequence of the ablation process. The modified orbit of the remaining material, which left our planet with a fusion crust, is also calculated. [ABSTRACT FROM AUTHOR]

We extend the catalogue of two-dimensional, Point-Spread-Function-corrected de Vacouleurs, Sérsic, de Vacouleurs+Exponential, and Sérsic+Exponential fits of ~7 × 105 galaxies presented in Meert et al. to include the g and i bands. Fits are analysed using the physically motivated flagging system presented in the original text, making adjustments for the differing signal to noise when necessary. We compare the fits in each of the g, r, and i bands. Fixed aperture magnitudes and colours are also provided for all galaxies. The catalogues are available in electronic format. [ABSTRACT FROM AUTHOR]

Context. We present a grid of computed non-local thermodynamic equilibrium (NLTE) equivalent widths (EW) and NLTE abundance corrections for four Ba II lines: 4554, 5853, 6141, and 6496 Å. Aims. The grid can be useful in deriving the NLTE barium abundance in stars having parameters in the following ranges: effective temperature from 4000 K to 6500 K, surface gravity log g from 0 to 5, microturbulent velocity 0 km s-1 to 3 km s-1, metallicity [Fe/H] from -2 to +0.5, and [Ba/Fe] from -0.4 to +0.6. The NLTE abundance can be either derived by EW interpolation (using the observed Ba II line EW) or by using the NLTE correction applied to a previously determined LTE abundance. Methods. Ba II line equivalent widths and the NLTE corrections were calculated using the updated MULTI code and the Ba II atomic model that was previously applied to determine the NLTE barium abundance in different types of stars. Results. The grid is available on-line through the web, and we find that the grid Ba NLTE corrections are almost as accurate as direct NLTE profile fitting (to within 0.05-0.08 dex). For the weakest Ba II line (5853 Å) the LTE abundances almost agree with the NLTE abundances, whereas the other three Ba II lines, 4554, 6141, and 6496 Å, need NLTE corrections even at the highest metallicities tested here. The 4554 Å line is extremely strong and should not be used for abundance analysis above [Fe/H] = -1. Furthermore, we tested the impact of different model atmospheres and spectrum synthesis codes and found average differences of 0.06 dex and 0.09 dex, respectively, for all four lines. At these metallicities we find an average ΔNLTE of ±0.1 dex for the three useful Ba lines for subsolar cool dwarfs. [ABSTRACT FROM AUTHOR]

Context. Since 1995, more than 1500 exoplanets have been discovered around a wide variety of host stars (from M- to A-type stars). Tidal dissipation in stellar convective envelopes is an important factor that shapes the orbital architecture of short-period systems. Aims. Our objective is to understand and evaluate how tidal dissipation in the convective envelope of low-mass stars (from M to F types) depends on their mass, evolutionary stage, and rotation. Methods. Using a simplified two-layer assumption, we analytically compute the frequency-averaged tidal dissipation in the convective envelope. This dissipation is due to the conversion into heat of the kinetic energy of tidal non-wavelike/equilibrium flow and inertial waves because of the viscous friction applied by turbulent convection. Using grids of stellar models allows us to study the variation of the dissipation as a function of stellar mass and age on the pre-main sequence and on the main sequence for stars with masses ranging from 0:4 to 1:4 M☉Results. During their pre-main sequence, all low-mass stars have an increase in the frequency-averaged tidal dissipation for a fixed angular velocity in their convective envelope until they reach a critical aspect and mass ratios (respectivelyα= Rc=Rs and β= Mc=Ms, where Rs; Ms; Rc, and Mc are the star's radius and mass and its radiative core's radius and mass). Next, the dissipation evolves on the main sequence to an asymptotic value that is highest for 0:6 M☉ K-type stars and that then decreases by several orders of magnitude with increasing stellar mass. Finally, the rotational evolution of low-mass stars strengthens the importance of tidal dissipation during the pre-main sequence for star-planet and multiple star systems. Conclusions. As shown by observations, tidal dissipation in stars' convection zones varies over several orders of magnitude as a function of stellar mass, age, and rotation. We demonstrate that i) it reaches a maximum value on the pre-main sequence for all stellar masses and ii) on the main sequence and at fixed angular velocity, it is at a maximum for 0:6 M☉K-type stars and decreases with increasing mass. [ABSTRACT FROM AUTHOR]

Context. We have discovered four new HgMn stars while monitoring a sample of apparently slowly rotating superficially normal bright late-B and early-A stars in the northern hemisphere. Aims. Important classification lines of Hg II and Mn II are found as conspicuous features in the high resolution SOPHIE spectra of these stars (R = 75 000). Methods. Several lines of Hg II, Mn II and Fe II were synthesized using model atmospheres and the spectrum synthesis code SYNSPEC48, including hyperfine structure of various isotopes when relevant. These synthetic spectra were compared to high-resolution observations of these stars that have a high signal-to-noise ratio to derive abundances of these key elements. Results. The four stars are found to have distinct enhancements of Hg and Mn, which shows that they are not superficially normal B and A stars, but are new HgMn stars and need to be reclassified as such. [ABSTRACT FROM AUTHOR]

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims to find sdBs with compact companions such as massive white dwarfs, neutron stars, or black holes. Here we provide classifications, atmospheric parameters, and a complete radial velocity (RV) catalogue containing 1914 single measurements for a sample of 177 hot subluminous stars discovered based on SDSS DR7; 110 stars show significant RV variability, while 67 qualify as candidates. We constrain the fraction of close massive compact companions of hydrogen-rich hot subdwarfs in our sample to be smaller than ~1.3%, which is already close to the theoretical predictions. However, the sample might still contain such binaries with longer periods exceeding ~8 d. We detect a mismatch between the ΔRVmax-distribution of the sdB and the more evolved sdOB and sdO stars, which challenges our understanding of their evolutionary connection. Furthermore, irregular RV variations of unknown origin with amplitudes of up to ~180 km s-1 on timescales of years, days, and even hours have been detected in some He-sdO stars. They might be connected to irregular photometric variations in some cases. [ABSTRACT FROM AUTHOR]

We performed a fine analysis of the normal sharp-lined A0 IV star γ Geminorum with spectra having signal-to-noise ratios at the continuum of 500-1200 that were consistent with previous studies of this series. Our spectra have wavelength ranges of λλ3829-4730, 4873-4931, 4983-5042, and 5070-5210. The spectra measured with the program REDUCE have a two-pixel resolution of 0.072 Å. We used ATLAS9 models and the program WIDTH9 to derive the abundances of the metals. Most derived abundances are close to solar with the abundances of the heaviest elements Zr, Ba, La, Ce, and Nd showing greater than solar values. This suggests by comparison with the abundances of other normal and Am stars that Gem might exhibit an incipient Am star phenomenon. [ABSTRACT FROM AUTHOR]

Context. The 440 Myr old main-sequence A-star Fomalhaut is surrounded by an eccentric debris belt with sharp edges. This sort of a morphology is usually attributed to planetary perturbations, but the orbit of the only planetary candidate detected so far, Fomalhaut b, is too eccentric to efficiently shape the belt. Alternative models that could account for the morphology without invoking a planet are stellar encounters and gas-dust interactions. Aims. We aim to test the possibility of gas-dust interactions as the origin of the observed morphology by putting upper limits on the total gas content of the Fomalhaut belt. Methods. We derive upper limits on the C ıı 158 Îm and O ı 63 Îm emission by using non-detections from the Photodetector Array Camera and Spectrometer (PACS) onboard the Herschel Space Observatory. Line fluxes are converted into total gas mass using the non-local thermodynamic equilibrium (non-LTE) code radex. We consider two different cases for the elemental abundances of the gas: solar abundances and abundances similar to those observed for the gas in the Î Pictoris debris disc. Results. The gas mass is shown to be below the millimetre dust mass by a factor of at least ~3 (for solar abundances) respectively ~300 (for Î Pic-like abundances). Conclusions. The lack of gas co-spatial with the dust implies that gas-dust interactions cannot efficiently shape the Fomalhaut debris belt. The morphology is therefore more likely due to a yet unseen planet (Fomalhaut c) or stellar encounters. [ABSTRACT FROM AUTHOR]

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 γ 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 γ Doradus stars observed by Kepler. Such detection is complicated by both the large number of significant frequencies in the space photometry and by overlapping nonequidistant rotationally split multiplets. Methods. Guided by theoretical properties of gravity-mode oscillation of γ 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 γ Doradus stars, which will allow future asteroseismic analyses of these stars. [ABSTRACT FROM AUTHOR]

We have discovered rotationally split core g-mode triplets and surface p-mode triplets and quintuplets in a terminal age main-sequence A star, KIC 11145123, that shows both δ Sct p-mode pulsations and γ Dor g-mode pulsations. This gives the first robust determination of the rotation of the deep core and surface of a main-sequence star, essentially model independently. We find its rotation to be nearly uniform with a period near 100 d, but we show with high confidence that the surface rotates slightly faster than the core. A strong angular momentum transfer mechanism must be operating to produce the nearly rigid rotation, and a mechanism other than viscosity must be operating to produce a more rapidly rotating surface than core. Our asteroseismic result, along with previous asteroseismic constraints on internal rotation in some B stars, and measurements of internal rotation in some subgiant, giant and white dwarf stars, has made angular momentum transport in stars throughout their lifetimes an observational science. [ABSTRACT FROM PUBLISHER]

Based on the near-infrared spectra of 42 M dwarfs, carbon abundances are determined from the ro-vibrational lines of the CO (2-0) band. We apply Teff values based on the angular diameters if available or use the Teff values in a log Teff-M3.4 relation (M3.4 is the absolute magnitude at 3.4 μm based on the WISE W1 flux and the Hipparcos parallax) to estimate Teff values of objects for which angular diameters are unknown. Also, we discuss briefly the HR diagram of low-mass stars. On the observed spectrum of the M dwarf, the continuum is depressed by the numerous weak lines of H2O and only the depressed continuum or the pseudo-continuum can be seen. On the theoretical spectrum of the M dwarf, the true continuum can be evaluated easily but the pseudocontinuum can also be evaluated accurately thanks to the recent H2O line database. Then spectroscopic analysis of the M dwarf can be done by referring to the pseudocontinuum both on the observed and theoretical spectra. Since the basic principle of the spectroscopic analysis should be the same whether the true- or pseudo-continuum is referred to, the difficulty related to the continuum in cool stars can in principle be overcome. Then, the numerous CO lines can be excellent abundance indicators of carbon, since almost all the carbon atoms are in stable CO molecules which suffer little effect of the uncertainties in photospheric structure, and carbon abundances in late-type stars can best be determined in M dwarfs rather than in solar type stars. The resulting C/Fe ratios for most M dwarfs are nearly constant at about the solar value based on the classical high carbon abundance rather than on the recently revised lower value. This result implies that the solar carbon abundance is atypical for its metallicity among the stellar objects in the solar neighborhood if the downward revised carbon abundance is correct. [ABSTRACT FROM AUTHOR]

An extensive spectroscopic study was carried out for the beryllium abundances of 200 red giants (mostly of late G- and early K-type), which were determined from the near-UV Be II 3131.066 line based on high-dispersion spectra obtained by Subaru/High Dispersion Spectrograph, with an aim of investigating the nature of surface Be contents in these evolved giants; e.g., dependence upon stellar parameters, degree of peculiarity along with its origin and build-up timing. We found that Be is considerably deficient (to widely different degrees from star to star) in the photosphere of these evolved giants by ∼1-3 dex (or more) compared to the initial abundance. While the resulting Be abundances [A(Be)] appear to depend weakly upon Teff, log g, [Fe/H], M, age, and ve sin i, this may be attributed to the metallicity dependence of A(Be) coupled with the mutual correlation between these stellar parameters, since such tendencies almost disappear in the metallicity-scaled Be abundance ([Be/Fe]). By comparing the Be abundances (as well as their correlations with Li and C) to the recent theoretical predictions based on sophisticated stellar evolution calculations, we concluded that such a considerable extent/diversity of Be deficit is difficult to explain only by the standard theory of first dredge-up in the envelope of red giants, and that some extra mixing process (such as rotational or thermohaline mixing) must be responsible, which presumably starts to operate already in the main-sequence phase. This view is supported by the fact that appreciable Be depletion is seen in less evolved intermediate-mass B-A type stars near to the main sequence. [ABSTRACT FROM AUTHOR]

Kepler photometry of A stars shows that a considerable fraction (about 19 per cent) have a peculiar feature in the periodogram. This feature consists of a broad peak, thought to be due to differential rotation in a spotted star, and a sharp peak at slightly higher frequency. The pattern clearly involves some widespread stellar property and the sharp peak implies a strictly coherent periodicity. We investigate the possibility that the periodicity is due to rotation, pulsation or an orbital effect. We argue that neither rotation nor pulsation can provide a suitable, testable, explanation. We suggest that the sharp feature could be due to a planet in synchronous orbit around the rapidly rotating, spotted A star, not necessarily in transit. Spectroscopic observations of sufficient precision are required to falsify this hypothesis. [ABSTRACT FROM AUTHOR]

plays a crucial role in Astrophysics, taking part in the early chemistry responsible for the formation of the stars. It is also one of the most abundant ionic species in hydrogen plasmas. The spectroscopy of the system has been the subject of intensive work in the past. Association processes to formand dissociative recombination with electrons have also been investigated in detail in order to understand the observed abundance of the molecule in the interstellar medium. Besides all these questions, in this work, we review some of the most relevant aspects regarding the dynamics of the H+ + H2reaction and its isotopic variants. A discussion on the most commonly found numerical difficulties in the theoretical study of this reactive collision is included. [ABSTRACT FROM PUBLISHER]

I compared the results of LTE fine analyses for B and A stars based on the newer "precise and accurate" Fe II gf values of Melendez & Barbuy (MB) with those based on the relatively recent major critical compilation of Fuhr & Wiese (FW). Only nonblended Fe II lines with both FW and MB gf values for 34 B and A stars with equivalent widths derived from high dispersion, high (>200) signal-to-noise ratio Dominion Astrophysical Observatory spectra were used. For most stars the standard deviations of the abundances derived from Fe II lines decrease slightly with the MB values, which is the signature of better consistency among the gf values. Then, for stars with many Fe I lines, I performed analyses using all lines with FW gf values and those with only A and B quality gf values and found minor improvements in the latter case. However, the abundances and microturbulences derived from Fe I lines are in better agreement with the Fe II FW results. The discrepancy between the results for Fe I FWand Fe II MB values could be due to NLTE effects on Fe I. A more limited comparison is made with the recent theoretical values of Deb & Hibbert which, when used, show a greater scatter of the derived Fe II gf values and smaller abundances than those obtained with the MB gf values. [ABSTRACT FROM AUTHOR]

With an aim to study whether the close correlation between [Na/H] and [Fe/H] recently found in A-type stars further persists in the regime of B-type stars, the abundances of Na were determined for 30 selected sharp-lined late B-type stars (10000 K ≲ Teff ≲ 14000 K) from the Na i 5890/5896 doublet. These Na abundances were then compared with the O and Fe abundances (derived from the O i6156–8 and Fe ii 6147/6149 lines) showing anti-correlated peculiarities. It turned out that, unlike in the case of A-type stars, [Na/H] is roughly constant at a slightly subsolar level {[Na/H] ∼ −0.2 (±0.2)} without any significant correlation with [Fe/H], which shows considerable dispersion ranging from ∼ −0.6 to ∼ +1.0. This may serve as an important observational constraint for understanding the abundance peculiarities along with the physical mechanism of atomic diffusion in upper main-sequence stars of late A- through late B-type including Am and HgMn stars. [ABSTRACT FROM AUTHOR]

We present an adaptive optics imaging detection of the HD 32297 debris disk at L′ (3.8 μm) obtained with the LBTI/LMIRcam infrared instrument at the Large Binocular Telescope. The disk is detected at signal-to-noise ratio per resolution element ∼3-7.5 from ∼0.″3 to 1.″1 (30-120 AU). The disk at L′ is bowed, as was seen at shorter wavelengths. This likely indicates that the disk is not perfectly edge-on and contains highly forward-scattering grains. Interior to ∼50 AU, the surface brightness at L′ rises sharply on both sides of the disk, which was also previously seen at Ks band. This evidence together points to the disk containing a second inner component located at ≲50 AU. Comparing the color of the outer (50

Young stars with masses 2-8 times solar, the Herbig Ae and Be stars, often show a near-infrared excess too large to explain with a hydrostatically supported circumstellar disk of gas and dust. At the same time, the accretion flow carrying the circumstellar gas to the star is thought to be driven by magnetorotational turbulence, which, according to numerical MHD modeling, yields an extended low-density atmosphere supported by the magnetic fields. We demonstrate that the base of the atmosphere can be optically thick to the starlight and that the parts lying near 1 AU are tall enough to double the fraction of the stellar luminosity reprocessed into the near-infrared. We generate synthetic spectral energy distributions (SEDs) using Monte Carlo radiative transfer calculations with opacities for submicron silicate and carbonaceous grains. The synthetic SEDs closely follow the median Herbig SED constructed recently by Mulders & Dominik and, in particular, match the large near-infrared flux, provided the grains have a mass fraction close to interstellar near the disk's inner rim. [ABSTRACT FROM AUTHOR]

Aims. The goal of our ongoing study of exoplanet host stars is to determine the true multiplicity rate of such stars. For this purpose we aim to research a statistically significant and homogeneously analyzed sample of stars around which planets have been found by the radial velocity or the transiting method. Ultimately, we want to determine if there are significant differences between planets in single- and multiple-star systems. This could indicate different formation scenarios. In this research note, we specifically investigate the companionship of three low-mass stellar candidate companions to exoplanet hosts via second epoch imaging and astrometry. Methods. We used various high-resolution imaging instruments in order to search for low-mass stellar companions to exoplanet host stars. Images were taken at a minimum of two observation epochs to check whether detected companion candidates are co-moving with the primary stars. We used the known photometric data of the primary stars together with theoretical evolutionary models in order to calculate detection limits for all targets and to estimate the mass of confirmed companions. Results. With our astrometric data we can confirm for the first time that the exoplanet host star HAT-P-8 has a low-mass stellar companion with an absolute magnitude in the K-band of 7.37 ± 0.15 mag and an estimated mass of 0.25 M☉. However, in our high-resolution VLT/NACO observation the source appears elongated and could therefore be a close binary. If both of the binary components are equally massive, this binary could have a higher total mass of ∼0.35 M☉. In addition, we were able to calculate detection limits for the HAT-P-30 system and the HD44219 system and showed that companion candidates around these objects are most likely background objects. [ABSTRACT FROM AUTHOR]

We analyze three years of high-resolution spectroscopic data and find radial velocity variations with a characteristic timescale of 100 ± 6 days that are nearly sinusoidal. Simultaneous variations in line-depth ratios imply temperature variations of up to 100 K. No photometric variation is seen on a 100 day timescale. The timescale of the variation and its resonant nature suggest solar-like oscillations driven by large-scale convection. [ABSTRACT FROM AUTHOR]

Highlights: [•] Some stars may have two or more planets stably sharing the same orbit. [•] Results are presented for the reflex motion and tidal effects on such stars. [•] Radial velocities alone can seriously misjudge masses of planets in shared orbits. [•] Combining Doppler data with tidal lightcurves gives accurate masses for both planets. [•] A simple new method is given for adding tidal perturbations from two or more sources. [Copyright &y& Elsevier]

The computation of the outermost layers of a star (the atmosphere) requires to solve in details the radiative transfer equation, whereas an analytical formula provides the radiative flux in optically thick layers, which is the case for the inner structure. Then, to have a complete stellar model from the center up to the optically thin layers, one should compute the inner structure on one hand and the uppermost part on the other, and connect the two in some way. After a non-exhaustive review of what is done with other evolutionary codes, we will describe how we deal with the problems met while performing the junction of an inner structure computed with the Toulouse-Geneva Evolution Code (TGEC) and an ATLAS9 atmosphere. Global behaviour of some physical quantities when considering the complete model will be shown, along with the effect on the oscillation frequencies. [ABSTRACT FROM AUTHOR]

It is clear that in order to explain many observed stellar phenomenae, atomic diffusion must be included in stellar models. Observed surface abundances allow us to constrain other transport processes which compete with atomic diffusion. We will focus on the effect of the flow of matter induced by mass-loss in stellar models. [ABSTRACT FROM AUTHOR]

Atomic diffusion - important in many contexts in stellar astrophysics and an important thread running through this meeting - is most spectacularly observable in the atmospheres of some A stars. The magnetic Ap stars and the non-magnetic Am stars show directly abundance anomalies caused by gravitational settling and radiative levitation. Over the last decade spectroscopic studies have begun to provide maps of abundance distributions in the magnetic Ap stars in three dimensions. Interestingly, high radial overtone p-mode pulsations in roAp stars have also given three-dimensional views of the stellar atmospheres with studies of rotational and line profile variations of pulsation amplitudes and phases. These detailed looks at the effects of microscopic atmospheric changes in the strongly non-LTE and magnetic upper atmospheric layers of Ap stars provide perhaps the most exciting challenge to atomic diffusion theory in terms of detailed explanation and prediction. Am stars were at one time thought not to pulsate because of gravitational settling of He from the He II ionization zone that provides the κ-mechanism driving for δ Sct pulsations in A stars. In the last few years we have found with SuperWASP and Kepler observations that many Am stars do pulsate. More than half of all A stars pulsate at Kepler micromagnitude precision, yet there is a subset of A stars that truly do not pulsate at that level. Are these Am stars with the strongest signature of atomic diffusion? Is atomic diffusion the reason for the pulsational stability of these stars? The answers are not yet known. [ABSTRACT FROM AUTHOR]

This work presents X-Shooter/Very Large Telescope spectra of the prototypical, isolated Herbig Ae stars HD 31648 (MWC 480) and HD 163296 over five epochs separated by timescales ranging from days to months. Each spectrum spans over a wide wavelength range covering from 310 to 2475 nm. We have monitored the continuum excess in the Balmer region of the spectra and the luminosity of 12 ultraviolet, optical, and near-infrared spectral lines that are commonly used as accretion tracers for T Tauri stars. The observed strengths of the Balmer excesses have been reproduced from a magnetospheric accretion shock model, providing a mean mass accretion rate of 1.11 × 10–7 and 4.50 × 10–7M☼ yr–1 for HD 31648 and HD 163296, respectively. Accretion rate variations are observed, being more pronounced for HD 31648 (up to 0.5 dex). However, from the comparison with previous results it is found that the accretion rate of HD 163296 has increased by more than 1 dex, on a timescale of ∼15 yr. Averaged accretion luminosities derived from the Balmer excess are consistent with the ones inferred from the empirical calibrations with the emission line luminosities, indicating that those can be extrapolated to HAe stars. In spite of that, the accretion rate variations do not generally coincide with those estimated from the line luminosities, suggesting that the empirical calibrations are not useful to accurately quantify accretion rate variability. [ABSTRACT FROM AUTHOR]