Search

Stellar multiplicity properties have been studied for the lowest and the highest stellar masses, but intermediate-mass stars from F-type to late A-type have received relatively little attention. Here, we report on a Gemini/NICI snapshot imaging survey of 138 such stars in the young Scorpius–Centaurus (Sco–Cen) region, for the purpose of studying multiplicity with sensitivity down to planetary masses at wide separations. In addition to two brown dwarfs and a companion straddling the hydrogen-burning limit which we reported previously, here we present 26 new stellar companions and determine a multiplicity fraction within 0''.1–5''.0 of 21% ± 4%. Depending on the adopted semimajor axis distribution, our results imply a total multiplicity in the range of∼60%–80%, which further supports the known trend of a smooth continuous increase in the multiplicity fraction as a function of primary stellar mass. A surprising feature in the sample is a distinct lack of nearly equal-mass binaries, for which we discuss possible reasons. The survey yielded no additional companions below or near the deuterium-burning limit, implying that their frequency at >200 AU separations is not quite as high as might be inferred from previous detections of such objects within the Sco–Cen region. [ABSTRACT FROM AUTHOR]

Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing radial velocity (RV) and transit exoplanet surveys and proposed future space missions.Most current estimates of the boundaries of the HZ are based on one-dimensional (1D), cloud-free, climate model calculations by Kasting et al. However, this model used band models that were based on older HITRAN and HITEMP line-by-line databases. The inner edge of the HZ in the Kasting et al. model was determined by loss of water, and the outer edge was determined by the maximum greenhouse provided by a CO2 atmosphere. A conservative estimate for the width of the HZ from this model in our solar system is 0.95-1.67 AU. Here an updated 1D radiative-convective, cloud-free climate model is used to obtain new estimates for HZ widths around F, G, K, and M stars. New H2O and CO2 absorption coefficients, derived from the HITRAN 2008 and HITEMP 2010 line-by-line databases, are important improvements to the climatemodel.According to the newmodel, thewater-loss (inner HZ) and maximum greenhouse (outer HZ) limits for our solar system are at 0.99 and 1.70 AU, respectively, suggesting that the present Earth lies near the inner edge. Additional calculations are performed for stars with effective temperatures between 2600 and 7200 K, and the results are presented in parametric form, making them easy to apply to actual stars. The new model indicates that, near the inner edge of the HZ, there is no clear distinction between runaway greenhouse and water-loss limits for stars with Teff ≲ 5000 K, which has implications for ongoing planet searches around K and M stars. To assess the potential habitability of extrasolar terrestrial planets, we propose using stellar flux incident on a planet rather than equilibrium temperature. This removes the dependence on planetary (Bond) albedo, which varies depending on the host star's spectral type. We suggest that conservative estimates of the HZ (water-loss and maximum greenhouse limits) should be used for current RV surveys and Kepler mission to obtain a lower limit on η⊗, so that future flagship missions like TPF-C and Darwin are not undersized. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may extend further in both directions than the estimates just given. [ABSTRACT FROM AUTHOR]

Context. It is generally accepted that the presence of a giant planet is strongly dependent on the stellar metallicity. A stellar mass dependence has also been investigated, but this dependence does not seem as strong as the metallicity dependence. Even for metallicity, however, the exact form of the correlation has not been established. Aims. In this paper, we test several scenarios for describing the frequency of giant planets as a function of its host parameters. We perform this test on two volume-limited samples (from CORALIE and HARPS). Methods. By using a Bayesian analysis, we quantitatively compared the different scenarios. Results. We confirm that giant planet frequency is indeed a function of metallicity. However, there is no statistical difference between a constant or an exponential function for stars with subsolar metallicities contrary to what has been previously stated in the literature. The dependence on stellar mass could neither be confirmed nor be discarded. [ABSTRACT FROM AUTHOR]

We have performed non-LTE calculations for O I with a multilevel model atom using currently available atomic data for a set of parameters corresponding to stars of spectral types from A to K. Departures from LTE lead to a strengthening of O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The non-LTE correction does not exceed 0.05 dex in absolute value for visible O I lines for main-sequence stars in the entire temperature range. For the infrared O I 7771 Å line, the non-LTE correction can reach −1.9 dex. The departures from LTE are enhanced with increasing temperature and decreasing surface gravity. We have derived the oxygen abundance for three A-type mainsequence stars with reliably determined parameters (Vega, Sirius, HD 32115). For each of the stars, allowance for the departures from LTE leads to a decrease in the difference between the abundances from infrared and visible lines, for example, for Vega from 1.17 dex in LTE to 0.14 dex when abandoning LTE. In the case of Procyon and the Sun, inelastic collisions with HI affect the statistical equilibrium of OI, and agreement between the abundances from different lines is achieved when using Drawin's classical formalism. Based on the O I 6300, 6158, 7771-5, and 8446 Å lines of the solar spectrum, we have derived the mean oxygen abundance log ɛ = 8.74 ± 0.05 using a classical plane-parallel model solar atmosphere and log ɛ = 8.78 ± 0.03 by applying the 3D corrections taken from the literature. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the scientific performance results of pynpoint, our Python-based software package that uses principal component analysis to detect and estimate the flux of exoplanets in two-dimensional imaging data. Recent advances in adaptive optics and imaging technology at visible and infrared wavelengths have opened the door to direct detections of planetary companions to nearby stars, but image processing techniques have yet to be optimized. We show that the performance of our approach gives a marked improvement over what is presently possible using existing methods such as loci. To test our approach, we use real angular differential imaging (ADI) data taken with the adaptive optics-assisted high resolution near-infrared camera NACO at the VLT. These data were taken during the commissioning of the apodizing phase plate (APP) coronagraph. By inserting simulated planets into these data, we test the performance of our method as a function of planet brightness for different positions on the image. We find that in all cases pynpoint has a detection threshold that is superior to that given by our loci analysis when assessed in a common statistical framework. We obtain our best improvements for smaller inner working angles (IWAs). For an IWA of ∼0.29 arcsec we find that we achieve a detection sensitivity that is a factor of 5 better than loci. We also investigate our ability to correctly measure the flux of planets. Again, we find improvements over loci, with pynpoint giving more stable results. Finally, we apply our package to a non-APP data set of the exoplanet β Pictoris b and reveal the planet with high signal-to-noise. This confirms that pynpoint can potentially be applied with high fidelity to a wide range of high-contrast imaging data sets. [ABSTRACT FROM AUTHOR]

ABSTRACT We present an analysis of a high-resolution ( R ∼ 50 000) optical spectrum of the central region of the protoplanetary nebula CRL 2688. This object is thought to have recently moved off the asymptotic giant branch (AGB) and displays abundance patterns of CNO and heavy elements that can provide us with important clues to help us understand the nucleosynthesis, dredge-up and mixing experienced by the envelope of the central star during its AGB stage of evolution. Analysis of the molecular features, presumably originating from circumstellar matter, provides further constraints on the chemistry and velocity of the expanding shell, expelled as a consequence of the strong mass loss experienced by the central star. We confirm that the central star shows a spectrum typical of an F-type supergiant with Teff = 7250 ± 400 K, log g = 0.5 and [Fe/H] = −0.3 ± 0.1 dex. We find that the abundance pattern of this object is characterized by enhancements of carbon ([C/Fe] = 0.6 ± 0.1), nitrogen ([N/Fe] = 1.0 ± 0.3) and Na ([Na/Fe] = 0.7 ± 0.1), similar to other previously known carbon-rich post-AGB stars. Yttrium is also enhanced, while the [Ba/Y] ratio is very low (−1.0), indicating that only the light s-process elements are enhanced. The zinc abundance is found to be normal, [Zn/Fe] = 0.0 ± 0.3, suggesting that there is no depletion of refractory elements. The Hα, Na i and K i resonance lines show prominent emission components, the heliocentric radial velocities of which are offset by −41 ± 3 km s−1 relative to the photospheric metal-absorption lines. The molecular features of C2 and CN also show emission components, the velocities of which are consistent with the emission components of the Hα, Na i and K i lines. On the other hand, their absorption components are more highly blueshifted than the corresponding emission components, which suggests that the regions where the emission and absorption components arise are expanding at different velocities. [ABSTRACT FROM AUTHOR]

We report the discovery of a new stellar companion in the KOI-13 system. KOI-13 is composed of two fast-rotating A-type stars of similar magnitude. One of these two stars hosts a transiting planet discovered by Kepler. We obtained new radial velocity measurements using the SOPHIE spectrograph at the Observatoire de Haute-Provence that reveal an additional companion in this system. This companion has a mass of between 0.4 M⊙ and 1 M⊙ and orbits one of the two main stars with a period of 65.831 ± 0.029 days and an eccentricity of 0.52 ± 0.02. The radial velocities of the two stars are derived using a model of two fast-rotating line profiles. From the residuals, we find a hint of the stellar variations seen in the Kepler light curve, which have an amplitude of about 1.41 km s-1 and a period close to the rotational period. This signal appears to be about three orders of magnitude larger than expected for stellar activity. From the analysis of the residuals, we also put a 3-σ upper limit on the mass of the transiting planet KOI-13.01 of 14.8 MJup and 9.4 MJup, depending on which star hosts the transit. We find that this new companion has no significant impact on the photometric determination of the mass of KOI-13.01 but is expected to affect precise infrared photometry. Finally, using dynamical simulations, we infer that the new companion is orbiting around KOI-13B and that the transiting planet candidate is expected to orbit KOI-13A. Thus, the transiting planet candidate KOI-13.01 is orbiting the main component of a hierarchical triple system. [ABSTRACT FROM AUTHOR]

Aims. In order to search for and study the nature of the low-amplitude and long-periodic radial velocity (RV) variations of massive stars, we have been carrying out a precise RV survey for supergiants that lie near or inside the Cepheid instability strip. Methods. We have obtained high-resolution spectra of α Per (F5 Ib) from November 2005 to September 2011 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy Observatory (BOAO). Results. Our measurements reveal that α Per shows a periodic RV variation of 128 days and a semi-amplitude of 70 m s-1.We find no strong correlation between RV variations and bisector velocity span (BVS), but the 128-d peak is indeed present in the BVS variations among several other significant peaks in periodogram. Conclusions. α Permay have an exoplanet, but the combined data spanning over 20 years seem to suggest that the 128-d RV variations have not been stable on a long-term scale, which is somewhat difficult to reconcile with the exoplanet explanation. We do not exclude the pulsational nature of the 128-d variations in α Per. Although we do not find clear evidence for surface activity or rotational modulations by spots, coupled with the fact that the expected rotation period is ∼130 days the rotational modulation seems to be the most likely cause of the RV variations. More observational data and research are needed to clearly determine the origin of the RV variations in α Per. [ABSTRACT FROM AUTHOR]

ABSTRACT A new catalogue of extrasolar planets is presented by re-analysing a selection of published radial velocity data sets using exofit. All objects are treated on an equal footing within a Bayesian framework to give orbital parameters for 94 exoplanetary systems. Model selection (between one- and two-planet solutions) is then performed using both a visual flagging method and a standard chi-square analysis, with agreement between the two methods for 99 per cent of the systems considered. The catalogue is to be made available online, and this 'proof of concept' study may be maintained and extended in the future to incorporate all systems with publicly available radial velocity data, as well as transit and microlensing data. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a light-curve analysis and radial velocity study of KOI-74, an eclipsing A star + white dwarf binary with a 5.2-d orbit. Aside from new spectroscopy covering the orbit of the system, we used 212 d of publicly available Kepler observations and present the first complete light-curve fitting to these data, modelling the eclipses and transits, ellipsoidal modulation, reflection and Doppler beaming. Markov chain Monte Carlo simulations are used to determine the system parameters and uncertainty estimates. Our results are in agreement with earlier studies, except that we find an inclination of 87°.0 ± 0°.4, which is significantly lower than the previously published value. The altered inclination leads to different values for the relative radii of the two stars and therefore also the mass ratio deduced from the ellipsoidal modulations seen in this system. We find that the mass ratio derived from the radial velocity amplitude ( q= 0.104 ± 0.004) disagrees with that derived from the ellipsoidal modulation ( q= 0.052 ± 0.004 assuming corotation). This was found before, but with our smaller inclination, the discrepancy is even larger than previously reported. Accounting for the rapid rotation of the A-star, instead of assuming corotation with the binary orbit, is found to increase the discrepancy even further by lowering the mass ratio to q= 0.047 ± 0.004. These results indicate that one has to be extremely careful in using the amplitude of an ellipsoidal modulation signal in a close binary to determine the mass ratio, when a proof of corotation is not firmly established. The same problem could arise whenever an ellipsoidal modulation amplitude is used to derive the mass of a planet orbiting a host star that is not in corotation with the planet's orbit. The radial velocities that can be inferred from the detected Doppler beaming in the light curve are found to be in agreement with our spectroscopic radial velocity determination. We also report the first measurement of Rømer delay in a light curve of a compact binary. This delay amounts to −56 ± 17 s and is consistent with the mass ratio derived from the radial velocity amplitude. The firm establishment of this mass ratio at q= 0.104 ± 0.004 leaves little doubt that the companion of KOI-74 is a low-mass white dwarf. [ABSTRACT FROM AUTHOR]

We report the discovery of two low-mass companions to the young A0V star HD 1160 at projected separations of 81 ± 5 AU (HD 1160 B) and 533 ± 25 AU (HD 1160 C) by the Gemini NICI Planet-Finding Campaign. Very Large Telescope images of the system taken over a decade for the purpose of using HD 1160 A as a photometric calibrator confirm that both companions are physically associated. By comparing the system to members of young moving groups and open clusters with well-established ages, we estimate an age of 50-40+50 Myr for HD 1160 ABC. While the UVW motion of the system does not match any known moving group, the small magnitude of the space velocity is consistent with youth. Near-IR spectroscopy shows HD 1160 C to be an M3.5 ± 0.5 star with an estimated mass of 0.22-0.04+0.03M⊙ while NIR photometry of HD 1160 B suggests a brown dwarf with a mass of 33-9+22 MJup. The very small mass ratio (0.014) between the A and B components of the system is rare for A star binaries, and would represent a planetary-mass companion were HD 1160 A to be slightly less massive than the Sun. [ABSTRACT FROM AUTHOR]

ABSTRACT Measurements of the intergalactic medium (IGM) temperature provide a potentially powerful constraint on the reionization history due to the thermal imprint left by the photoionization of neutral hydrogen. However, until recently IGM temperature measurements were limited to redshifts 2 ≤ z≤ 4.8, restricting the ability of these data to probe the reionization history at z > 6. In this work, we use recent measurements of the IGM temperature in the near-zones of seven quasars at z∼ 5.8-6.4, combined with a semi-numerical model for inhomogeneous reionization, to establish new constraints on the redshift at which hydrogen reionization completed. We calibrate the model to reproduce observational constraints on the electron scattering optical depth and the H i photoionization rate, and compute the resulting spatially inhomogeneous temperature distribution at z∼ 6 for a variety of reionization scenarios. Under standard assumptions for the ionizing spectra of Population II sources, the near-zone temperature measurements constrain the redshift by which hydrogen reionization was complete to be zr > 7.9 (6.5) at 68 (95) per cent confidence. We conclude that future temperature measurements around other high-redshift quasars will significantly increase the power of this technique, enabling these results to be tightened and generalized. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the first analysis of spectroscopic and photometric observations of the eclipsing binary star WZ Hor. Observations of the system were made at the Mt. John University Observatory in 2007. Since the light contribution of the secondary component was merely 2–3% of the total light of the system in the optical wavelengths, the radial velocity of the primary component could only be determined using the cross-correlation method. A single-lined spectroscopic orbital solution of WZ Hor was obtained, and the BVRI light curves of the system and radial velocity curve of the primary component were analysed simultaneously using the Wilson–Devinney method. The results describe WZ Hor as a reverse Algol-like binary star with a detached configuration. The following absolute parameters of the components were also derived: M 1 =1.51±0.03M⊙, M 2 =0.66±0.01M⊙, R 1 =1.62±0.02R⊙, R 2 =0.66±0.01R⊙, L 1 =4.93±0.64L⊙ and L 2 =0.09±0.02L⊙. The distance to WZ Hor was calculated as 95±8pc using distance modulus with correction for interstellar extinction, in agreement with the HIPPARCOS value. [Copyright &y& Elsevier]

ABSTRACT We present a novel method to determine eccentricity constraints of extrasolar planets in systems with multiple transiting planets through photometry alone. Our method is highly model independent, making no assumptions about the stellar parameters and requiring no radial velocity, transit timing or occultation events. Our technique exploits the fact the light-curve-derived stellar density must be the same for all planets transiting a common star. Assuming a circular orbit, the derived stellar density departs from the true value by a predictable factor, Ψ, which contains information on the eccentricity of the system. By comparing multiple stellar densities, any differences must be due to eccentricity and thus meaningful constraints can be placed in the absence of any other information. The technique, called 'Multibody Asterodensity Profiling' (MAP), is a new observable which can be used alone or in combination with other observables, such as radial velocities and transit timing variations. An eccentricity prior can also be included as desired. MAP is most sensitive to the minimum pair-combined eccentricity e.g. ( e1+ e2)min. Individual eccentricity constraints are less stringent but an empirical eccentricity posterior is always derivable and is freely available from transit photometry alone. We present a description of our technique using both analytic and numerical implementations, followed by two example analyses on synthetic photometry as a proof of principle. We point out that MAP has the potential to constrain the eccentricity, and thus habitability, of Earth-like planets in the absence of radial velocity data, which is likely for terrestrial-mass objects. [ABSTRACT FROM AUTHOR]

ABSTRACT We present an analysis of the WISE photometric data for 829 stars in the Sco-Cen OB2 association, using the latest high-mass membership probabilities. We detect infrared excesses associated with 135 BAF-type stars, 99 of which are secure Sco-Cen members. There is a clear increase in excess fraction with membership probability, which can be fitted linearly. We infer that 41 ± 5 per cent of Sco-Cen OB2 BAF stars have excesses, while the field star excess fraction is consistent with zero. This is the first time that the probability of non-membership has been used in the calculation of excess fractions for young stars. We do not observe any significant change in excess fraction between the three subgroups. Within our sample, we have observed that B-type association members have a significantly smaller excess fraction than A- and F-type association members. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the discovery of a long-period, rapidly oscillating Ap (roAp) star, HD 177765. Using high-resolution time-series observations obtained with the Ultraviolet and Visual Echelle Spectrograph at the European Southern Observatory Very Large Telescope, we found radial velocity variations with amplitudes 7-150 m s−1 and a period of 23.6 min, exceeding that of any previously known roAp star. The largest pulsation amplitudes are observed for Eu iii, Ce iii and for the narrow core of Hα. We derived the atmospheric parameters and chemical composition of HD 177765, showing this star to be similar to other long-period roAp stars. Comparison with theoretical pulsational models indicates an advanced evolutionary state for HD 177765. Abundance analyses of this and other roAp stars suggest a systematic variation with age of the rare-earth line anomalies seen in cool Ap stars. [ABSTRACT FROM AUTHOR]

ABSTRACT A variation of gravitational redshift, arising from stellar radius fluctuations, will introduce astrophysical noise into radial velocity measurements by shifting the centroid of the observed spectral lines. Shifting the centroid does not necessarily introduce line asymmetries. This is fundamentally different from other types of stellar jitter so far identified, which do result from line asymmetries. Furthermore, only a very small change in stellar radius, ∼0.01 per cent, is necessary to generate a gravitational redshift variation large enough to mask or mimic an Earth-twin. We explore possible mechanisms for stellar radius fluctuations in low-mass stars. Convective inhibition due to varying magnetic field strengths and the Wilson depression of starspots are both found to induce substantial gravitational redshift variations. Finally, we investigate a possible method for monitoring/correcting this newly identified potential source of jitter and comment on its impact for future exoplanet searches. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the discovery of a long-period, rapidly oscillating Ap (roAp) star, HD 177765. Using high-resolution time-series observations obtained with the Ultraviolet and Visual Echelle Spectrograph at the European Southern Observatory Very Large Telescope, we found radial velocity variations with amplitudes 7-150 m s−1 and a period of 23.6 min, exceeding that of any previously known roAp star. The largest pulsation amplitudes are observed for Eu iii, Ce iii and for the narrow core of Hα. We derived the atmospheric parameters and chemical composition of HD 177765, showing this star to be similar to other long-period roAp stars. Comparison with theoretical pulsational models indicates an advanced evolutionary state for HD 177765. Abundance analyses of this and other roAp stars suggest a systematic variation with age of the rare-earth line anomalies seen in cool Ap stars. [ABSTRACT FROM AUTHOR]

ABSTRACT We present three-dimensional spectroscopy of 11 E+A galaxies at z= 0.06-0.12. These galaxies were selected for their strong Hδ absorption but weak (or non-existent) [O ii] λ3727 and Hα emission. This selection suggests that a recent burst of star formation was triggered but subsequently abruptly ended. We probe the spatial and spectral properties of both the young (≲1 Gyr) and old (≳few Gyr) stellar populations. Using the Hδ equivalent widths we estimate that the burst masses must have been at least 10 per cent by mass ( Mburst≳ 1010 M⊙), which is also consistent with the star formation history inferred from the broad-band spectral energy distributions. On average the A stars cover ∼33 per cent of the galaxy image, extending over 2-15 kpc2, indicating that the characteristic E+A signature is a property of the galaxy as a whole and not due to a heterogeneous mixture of populations. In approximately half of the sample, we find that the A stars, nebular emission and continuum emission are not co-located, suggesting that the newest stars are forming in a different place than those that formed ≲1 Gyr ago, and that recent star formation has occurred in regions distinct from the oldest stellar populations. At least 10 of the galaxies (91 per cent) have dynamics that class them as 'fast rotators' with magnitudes, v/σ, λ R and bulge-to-total (B/T) ratio comparable to local, representative ellipticals and S0s. We also find a correlation between the spatial extent of the A stars and the dynamical state of the galaxy such that the fastest rotators tend to have the most compact A star populations, providing new constraints on models that aim to explain the transformation of later type galaxies into early types. Finally, we show that there are no obvious differences between the line extents and kinematics of E+A galaxies detected in the radio (active galactic nucleus, AGN) compared to non-radio sources, suggesting that AGN feedback does not play a dramatic role in defining their properties, and/or that its effects are short. [ABSTRACT FROM AUTHOR]

Context. In previous works of this series, we have shown that late B- and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio Ω/Ωcrit (Ωcrit is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. Aims. We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. Methods. We have gathered v sin i for a sample of 2014 B6- to F2-type stars.We have determined the masses and ages for these objects with stellar evolution models. The (Teff, log L/L☉)-parameters were determined from the uvby-β photometry and the HIPPARCOS parallaxes. Results. The velocity distributions show two regimes that depend on the stellar mass. Stars less massive than 2.5M☉ have a unimodal equatorial velocity distribution and show a monotonical acceleration with age on the main sequence (MS). Stars more massive have a bimodal equatorial velocity distribution. Contrarily to theoretical predictions, the equatorial velocities of stars from about 1.7 M☉ to 3.2 M☉ undergo a strong acceleration in the first third of the MS evolutionary phase, while in the last third of the MS they evolve roughly as if there were no angular momentum redistribution in the external stellar layers. The studied stars might start in the ZAMS not necessarily as rigid rotators, but with a total angular momentum lower than the critical one of rigid rotators. The stars seem to evolve as differential rotators all the way of their MS life span and the variation of the observed rotational velocities proceeds with characteristic time scales δt ≈ 0.2 tMS, where tMS is the time spent by a star in the MS [ABSTRACT FROM AUTHOR]

ABSTRACT We present a novel approach of identifying the Milky Way (MW) and Andromeda (M31) progenitors that could be visible as Lyman Alpha emitters (LAEs) at z∼ 6: we couple a snapshot from the Constrained Local UniversE Simulations (CLUES) project, which successfully reproduces the MW and M31 galaxies situated in their correct environment, to a LAE model. Exploring intergalactic medium (IGM) ionization states ranging from an almost neutral to a fully ionized one, we find that including (excluding) the effects of clustered sources the first Local Group progenitor appears as a LAE for a neutral hydrogen fraction (). This number increases to five progenitors each of the MW and M31 being visible as LAEs for ; the contribution from clustered sources is crucial in making many of the progenitors visible in the Lyα for all the ionization states considered. The stellar mass of the Local Group LAEs ranges between 107.2 and 108 M⊙, the dust mass is between 104.6 and 105.1 M⊙ and the colour excess E( B− V) = 0.03-0.048. We find that the number density of these LAEs is higher than that of general field LAEs (observed in cosmological volumes) by about two (one) orders of magnitude for (0.4). Detections of such high LAE number densities at z∼ 6 would be a clear signature of an overdense region that could evolve and resemble the Local Group volume at z= 0. [ABSTRACT FROM AUTHOR]

The mass of CoRoT-7b, the first transiting super-Earth exoplanet, is still a subject of debate. A wide range of masses have been reported in the literature ranging from as high as 8 M⊕ to as low as 2.3 M⊕. This range in mass is largely due to the activity level of the star that contributes a significant amount of radial velocity (RV) "jitter" and how the various methods correct this jitter. Although most mass determinations give a density consistent with a rocky planet, the lower value permits a bulk composition that can be up to 50% water. We present an analysis of the CoRoT-7b RV measurements that uses very few and simple assumptions in treating the activity signal. By analyzing those RV data for which multiple measurements were made in a given night, we remove the activity related RV contribution without any a priori model. We argue that the contribution of activity to the final RV curve is negligible and that the K-amplitude due to the planet is well constrained. This yields a mass of 7.42 ± 1.21 M⊕ and a mean density of ρ = 10.4 ± 1.8 gm cm-3. CoRoT-7b is similar in mass and radius to the second rocky planet to be discovered, Kepler-10b, and within the errors they have identical bulk densities--they are virtual twins. These bulk densities lie close to the density--radius relationship for terrestrial planets similar to what is seen for Mercury. CoRoT-7b and Kepler-10b may have an internal structure more like Mercury than the Earth. [ABSTRACT FROM AUTHOR]

We use observations from the Hubble Space Telescope Advanced Camera for Surveys (HST/ACS) study of Galactic globular clusters to investigate the spatial distribution of the inner regions of the disrupting Sagittarius dwarf spheroidal galaxy (Sgr). We combine previously published analyses of four Sgr member clusters located near or in the Sgr core (M54, Arp 2, Terzan 7, and Terzan 8) with a new analysis of diffuse Sgr material identified in the background of five low-latitude Galactic bulge clusters (NGC 6624, 6637, 6652, 6681, and 6809) observed as part of the ACS survey. By comparing the bulge cluster color--magnitude diagrams to our previous analysis of the M54/Sgr core, we estimate distances to these background features. The combined data from four Sgr member clusters and five Sgr background features provide nine independent measures of the Sgr distance and, as a group, provide uniformly measured and calibrated probes of different parts of the inner regions of Sgr spanning 20° over the face of the disrupting dwarf. This allows us, for the first time, to constrain the three-dimensional orientation of Sgr's disrupting core and globular cluster system and compare that orientation to the predictions of an N-body model of tidal disruption. The density and distance of Sgr debris are consistent with models that favor a relatively high Sgr core mass and a slightly greater distance (28-30 kpc, with a mean of 29.4 kpc). Our analysis also suggests that M54 is in the lbreground of Sgr by ~2 kpc, projected on the center of the Sgr dSph. While this would imply a remarkable alignment of the cluster and the Sgr nucleus along the line of sight, we cannot identify any systematic effect in our analysis that would falsely create the measured 2 kpc separation. Finally, we find that the cluster Terzan 7 has the most discrepant distance (25 kpc) among the tour Sgr core clusters, which may suggest a different dynamical history than the other Sgr core clusters. [ABSTRACT FROM AUTHOR]

We present an improved formula for the anomalous radial velocity of the star during planetary transits due to the Rossiter-McLaughlin (RM) effect. The improvement comes from a more realistic description of the stellar absorption line profiles, taking into account stellar rotation, macroturbulence, thermal broadening, pressure broadening, and instrumental broadening. Although the formula is derived for the case in which radial velocities are measured by cross-correlation, we show through numerical simulations that the formula accurately describes the cases where the radial velocities are measured with the iodine absorption-cell technique. The formula relies on prior knowledge of the parameters describing macroturbulence, instrumental broadening, and other broadening mechanisms, but even 30% errors in those parameters do not significantly change the results in typical circumstances. We show that the new analytic formula agrees with previous ones that had been computed on a case-by-case basis via numerical simulations. Finally, as one application of the new formula, we reassess the impact of the differential rotation on the RM velocity anomaly. We show that differential rotation of a rapidly rotating star may have a significant impact on future RM observations. [ABSTRACT FROM AUTHOR]

ABSTRACT We have modelled far-UV, UV and optical spectra of a sample of 10 hydrogen-rich central stars of planetary nebulae (CSPN) using stellar atmosphere codes to derive their photospheric and wind parameters. The resulting stellar temperatures range from 40 to 120 kK, well spanning the CSPN evolutionary phase and allowing certain trends to be discerned. In particular, an inhomogeneous wind structure and X-ray emission in the wind are required to match spectral diagnostic lines in many cases. For the majority of the sample, a wind clumping factor of 0.1 ≤ f≤ 0.04 is derived (mainly from the P vλλ1118, 28 and O vλ1371 lines). Such factors correspond to clump densities of ∼10-25 times that of the smooth wind density, with resulting mass-loss rates one-third to one-fifth the smooth wind values, which is of significant consequence to nebular dynamics, stellar and galactic evolution. Furthermore, we find clumping to begin at small radii (∼1.2 R*), as has been found when modelling the winds of (massive) O stars. The inclusion of X-ray fluxes, presumably from shocks, in the model atmosphere calculations is found to improve the fit of the O viλλ1032, 38 line (and other features) for stars with 55 ≤ Teff≤ 80 kK, and to be absolutely necessary to match this feature for the coolest stars in our sample ( Teff≲ 45 kK). These findings suggest that shocks originating from line-driven wind instabilities leading to the formation of clumped winds and X-rays may be a common characteristic of CSPN, as has been found for the winds of massive O-type stars. We also find interesting results for some individual stars. NGC 1360 ( Teff≃ 105 kK) displays the signature of a (previously undetected) weak stellar wind in its O vi 1032, 38 profile, and probably has the lowest mass-loss rate ( M⊙ yr−1) of any known CSPN. In contrast, we find the wind terminal velocity of NGC 2392 ( Teff≃ 45 kK) to be v∞≃ 300 km s−1, one of the slowest CSPN wind known, probably related to its subsolar metallicity. We have included in the model calculations many elements and high-ionization species previously neglected in analyses of this type, providing additional wind diagnostics such as Ne viiλ973 and Ar viiλ1064. The effects of including these as well as other line-blanketing elements are discussed. [ABSTRACT FROM AUTHOR]

ABSTRACT About 4 arcsec south of the young A0-type star HR 7329, a faint companion candidate was found by Lowrance et al. Its spectral type of M7-8 is consistent with a young brown dwarf companion. Here we report 10 new astrometric imaging observations of the pair HR 7329 A and B, obtained with the Hubble Space Telescope and the Very Large Telescope, aimed at showing a common proper motion with high significance and possible orbital motion of B around A. With 11 yr of epoch difference between the first and our last image, we can reject the possibility by more than 21σ that B would be a non-moving background object unrelated to A. We detect no change in position angle and small or no change in separation (2.91 ± 2.41 mas yr−1), so that the orbit of HR 7329 B around A is inclined and/or eccentric and/or the orbital motion is currently only in the radial direction. If HR 7329 B is responsible for the outer radius of the debris disc around HR 7329 A being 24 au, and if HR 7329 B currently is at its apastron at 200 au (4.2 arcsec at 47.7 pc), we determine its pericentre distance to be 71 au, its semimajor axis to be 136 au, and its eccentricity to be e = 0.47. From the magnitude differences between HR 7329 A and B and the 2MASS magnitudes for the HR 7329 A+B system, we can estimate the magnitudes of HR 7329 B ( J = 12.06 ± 0.19, H = 11.75 ± 0.10, Ks = 11.6 ± 0.1, L = 11.1 ± 0.2 mag) and then, with a few otherwise known parameters, its luminosity and mass (20-50 Jupiter masses). In the deepest images available, we did not detect any additional companion candidates up to ≤9 arcsec, but we determined the upper limits in the planetary mass regime. [ABSTRACT FROM AUTHOR]

We present a spectral atlas of 4 B and A stars containing spectra in a poorly studied spectral range of 305-452 nm. The atlas is based on high resolution ( R=60 000) spectra obtained with the 6 meter telescope (SAO, Russia) combined with the NES-spectrograph. The procedure of spectral lines identification and compilation of the atlas is discussed in detail. Using the spectral data we thoroughly investigated the velocity field in expanding atmospheres and envelopes of hot evolved stars β Ori, α Cyg and supergiant KS Per with the extreme hydrogen deficiency. The complete atlas and list of the identified spectral lines will be available via the astronomical database SIMBAD. [ABSTRACT FROM AUTHOR]

We present measurements of dust reddening using the colors of stars with spectra in the Sloan Digital Sky Survey. We measure reddening as the difference between the measured and predicted colors of a star, as derived from stellar parameters from the Sloan Extension for Galactic Understanding and Exploration Stellar Parameter Pipeline. We achieve uncertainties of 56, 34, 25, and 29 mmag in the colors u - g, g - r, r - i, and i - z, per star, though the uncertainty varies depending on the stellar type and the magnitude of the star. The spectrum-based reddening measurements confirm our earlier "blue tip" reddening measurements, finding reddening coefficients different by -3%, 1%, 1%, and 2% in u - g, g - r, r - i, and i - z from those found by the blue tip method, after removing a 4% normalization difference. These results prefer an Rv = 3.1 Fitzpatrick reddening law to O'Donnell or Cardelli et al. reddening laws. We provide a table of conversion coefficients from the Schlegel et al. (SFD) maps of E(B - V) to extinction in 88 bandpasses for four values of Rv, using this reddening law and the 14% recalibration of SFD first reported by Schlafly et al. and confirmed in this work. [ABSTRACT FROM AUTHOR]

BSTRACT We analyse the light curves of over 9000 A-F stars in the first public release of Kepler data and examine the noise properties in constant or nearly constant stars. For the A stars, we find a correlation between the excess power in certain frequency regions and the effective temperature which may be due to granulation. The majority of A-F stars vary with low frequencies (<5 d−1) and low amplitudes (40-150 ppm). The low-frequency variation extends to the hottest A-type stars where the typical amplitude is about 40 ppm. We find that about 8 per cent of A8-A0 stars have light curves resembling those usually attributed to starspots in cool stars, including a few exhibiting travelling waves usually interpreted as differentially rotating starspots. A further 20 per cent of A stars have dominant low frequencies which are visible in the periodogram. If we assume that the dominant low frequency in A-F stars is the rotation frequency, we can calculate the distribution of equatorial rotational velocities given the stellar radii. The resulting distribution matches the distribution of equatorial rotational velocities in field stars of the same spectral type and luminosity class. However, the A8-A0 stars have an excess of slow rotators which can be explained as contamination from horizontal-branch stars. We conclude that the light variations in A-type stars may possibly be due to starspots or other corotating structures and that A-star atmospheres may not be quiescent as previously supposed. We also analyse low frequencies in Kepler A-type δ Sct stars which are too hot to be due to γ Dor pulsations. These do not appear to be due to simple combinations of high-frequency δ Sct modes. Unlike normal A-type stars, the dominant low frequency is close to twice the rotational frequency. In a significant proportion of δ Sct stars there is, in fact, a frequency of smaller amplitude at exactly half the dominant low frequency. There is clearly a quadrupole surface brightness distribution in a significant fraction of these stars, but the amplitudes seem to be too low to be explained as a proximity effect in a binary. [ABSTRACT FROM AUTHOR]

We are investigating the formation and evolution of dust around the hydrogen-deficient supergiants known as R Coronae Borealis (RCB) stars. We aim to determine the connection between the probable merger past of these stars and their current dust-production activities. We carried out high angular resolution interferometric observations of three RCB stars, namely RY Sgr, V CrA and V854 Cen, with the mid-infrared interferometer (MIDI) on the Very Large Telescope Interferometer (VLTI), using two telescope pairs. The baselines ranged from 30 to 60 m, allowing us to probe the dusty environment at very small spatial scales (50 mas or 400). The observations of the RCB star dust environments were interpreted using both geometrical models and one-dimensional radiative transfer codes. From our analysis, we find that asymmetric circumstellar material is apparent in RY Sgr, may also exist in V CrA and is possible for V854 Cen. Overall, we find that our observations are consistent with dust forming in clumps ejected randomly around the RCB star so that over time they create a spherically symmetric distribution of dust. However, we conclude that the determination of whether there is a preferred plane of dust ejection must wait until a time series of observations are obtained. [ABSTRACT FROM AUTHOR]

The reactivity of the thermodynamically stable nanopyroxene cluster MgSiO towards hydrogen and oxygen atoms is studied. Quantum chemical calculations reveal that it can adsorb hydrogen atoms without a barrier, which could catalyze H formation. Furthermore, if we consider consecutive atom adsorption, MgSiO can take up to the equivalent of four units of water (2H + O) before molecular water starts to form preferentially. The resulting superoxygenated nanosilicate cluster (MgSiHO contains only hydroxyl groups and has a high oxygen-to-metal ratio of 2 compared to bulk silicates (1.33-1.5). The hydroxylated cluster readily adsorbs even more oxygen atoms in the form of chemisorbed molecular water; however, the molecular water will readily photodesorb in the diffuse interstellar medium. The large oxygen-uptake capacity of nanosilicates could contribute to the large oxygen depletion observed in diffuse clouds, although depletion into other sources must take place as well. The infrared spectra of the (oxygenated) nanopyroxene are calculated, and we identified its strong infrared transitions. Some of the O-Si-O bending modes have blueshifted from 20 m in bulk silicates to 14-18 m in nanosilicates. The hydroxylated nanopyroxenes all have sharp, strong features in the 9-12 m region and the MgSiHO cluster has a moderately strong feature around 25 m due to frustrated OH rotations. These distinct infrared features may eventually lead to the identification of (hydroxylated) nanosilicates in stellar outflows, interstellar clouds and/or protoplanetary discs. [ABSTRACT FROM AUTHOR]

We present the results of radiation-magnetohydrodynamic simulations of the formation and expansion of H regions and their surrounding photodissociation regions (PDRs) in turbulent, magnetized, molecular clouds on scales of up to 4 pc. We include the effects of ionizing and non-ionizing ultraviolet radiation and X-rays from population synthesis models of young star clusters. For all our simulations we find that the H region expansion reduces the disordered component of the magnetic field, imposing a large-scale order on the field around its border, with the field in the neutral gas tending to lie along the ionization front, while the field in the ionized gas tends to be perpendicular to the front. The highest pressure-compressed neutral and molecular gas is driven towards approximate equipartition between thermal, magnetic and turbulent energy densities, whereas lower pressure neutral/molecular gas bifurcates into, on the one hand, quiescent, magnetically dominated regions and, on the other hand, turbulent, demagnetized regions. The ionized gas shows approximate equipartition between thermal and turbulent energy densities, but with magnetic energy densities that are 1-3 orders of magnitude lower. A high velocity dispersion ( km s) is maintained in the ionized gas throughout our simulations, despite the mean expansion velocity being significantly lower. The magnetic field does not significantly brake the large-scale H region expansion on the length and time-scales accessible to our simulations, but it does tend to suppress the smallest scale fragmentation and radiation-driven implosion of neutral/molecular gas that forms globules and pillars at the edge of the H region. However, the relative luminosity of ionizing and non-ionizing radiation has a much larger influence than the presence or absence of the magnetic field. When the star cluster radiation field is relatively soft (as in the case of a lower mass cluster, containing an earliest spectral type of B0.5), then fragmentation is less vigorous and a thick, relatively smooth PDR forms. [ABSTRACT FROM AUTHOR]

The newly discovered 11-Hz accreting pulsar, IGR J17480−2446, located in the globular cluster Terzan 5, has shown several bursts with a recurrence time as short as a few minutes. The source shows the shortest recurrence time ever observed from a neutron star. Here we present a study of the morphological, spectral and temporal properties of 107 bursts observed by the Rossi X-ray Timing Explorer. The recurrence time and the fluence of the bursts clearly anticorrelate with the increase in the persistent X-ray flux. The ratio between the energy generated by the accretion of mass and that liberated during bursts indicates that helium is ignited in a hydrogen-rich layer. Therefore, we conclude that all the bursts shown by IGR J17480−2446 are Type I X-ray bursts. Pulsations could be detected in all the brightest bursts and no drifts of the frequency are observed within 0.25 Hz of the spin frequency of the neutron star. These are also phase-locked with respect to the pulsations observed during the persistent emission and no rise in the rms associated to the pulse frequency is observed during the burst. This behaviour would favour a scenario where the Type I burst, possibly ignited at the polar caps, immediately propagates to the entire neutron star surface. [ABSTRACT FROM AUTHOR]

We use Monte Carlo simulations to estimate the number of extrasolar planets that are directly detectable in the solar neighborhood using current and forthcoming high-contrast imaging instruments. Our calculations take into consideration the important factors that govern the likelihood for imaging a planet, including the statistical properties of stars in the solar neighborhood, correlations between star and planet properties, observational effects, and selection criteria. We consider several different ground-based surveys, both biased and unbiased, and express the resulting planet yields as a function of stellar mass. Selecting targets based on their youth and visual brightness, we find that strong correlations between star mass and planet properties are required to reproduce high-contrast imaging results to date (i.e., HR 8799, β Pic). Using the most recent empirical findings for the occurrence rate of gas-giant planets from radial velocity (RV) surveys, our simulations indicate that naive extrapolation of the Doppler planet population to semimajor axes accessible to high-contrast instruments provides an excellent agreement between simulations and observations using present-day contrast levels. In addition to being intrinsically young and sufficiently bright to serve as their own beacon for adaptive optics correction, A-stars have a high planet occurrence rate and propensity to form massive planets in wide orbits, making them ideal targets. The same effects responsible for creating a multitude of detectable planets around massive stars conspire to reduce the number orbiting low-mass stars. However, in the case of a young stellar cluster, where targets are approximately the same age and situated at roughly the same distance, MK-stars can easily dominate the number of detections because of an observational bias related to small number statistics. The degree to which low-mass stars produce the most planet detections in this special case depends upon whether multiple formation mechanisms are at work. Upon relaxing our assumption that planets in ultra-wide (a > 100 AU) orbits resemble the RV sample, our simulations suggest that the companions found orbiting late-type stars (AB Pic, 1RXSJ1609, GSC 06214, etc.) are consistent with a formation channel distinct from that of RV planets. These calculations explain why planets have thus far been imaged preferentially around A-stars and K-, M-stars, but no spectral types in between, despite concerted efforts targeting F-, G-stars. [ABSTRACT FROM AUTHOR]

This study is concerned with the early evolution of magnetic fields and differential rotation of intermediate-mass stars which may evolve into Ap stars. We report on simulations of the interplay of differential rotation and magnetic fields, the stability limits and non-linear evolution of such configurations, and the prospects of dynamo action from the unstable cases. The axisymmetric problem delivers a balance between field amplification and back-reaction of the magnetic field on the differential rotation. The non-axisymmetric case involves also the Tayler instability of the amplified toroidal fields. We consider limits for field amplification and apply these to young A stars. Apart from its application to Ap stars, the instability is scrutinized for the fundamental possibility of a dynamo. We are not looking for a dynamo as an explanation for the Ap star phenomenon. The kinetic helicity is concentrated near the tangent cylinder of the inner sphere of the computational domain and is negative in the Northern hemisphere. This appears to be a ubiquitous effect not special to the Tayler instability. The latter is actually connected with a positive current helicity in the bulk of the spherical shell giving rise to a small, but non-vanishing -effect in non-linear evolution of the instability. [ABSTRACT FROM AUTHOR]

We analytically work out the cumulative, i.e. averaged over one orbital revolution, time variations of the radial velocity of a typical S star orbiting the supermassive black hole (SBH) hosted by the Galactic Centre (GC) in Sgr A* caused by several dynamical effects. They are the general relativistic gravitoelectromagnetic (GEM) fields of the SBH, its quadrupole mass moment Q and a diffuse dark matter distribution around the SBH. All of them induce non-zero long-term radial accelerations proportional to the eccentricity e of the orbit. By taking the S2 star, orbiting the SBH along a highly eccentric ellipse with a period and semimajor axis au, we numerically compute the magnitudes of its radial accelerations. The largest effects are due to the general relativistic Schwarzschild-like gravitoelectric (GE) field, with , and the diffuse material distribution, modelled with a Plummer-type mass density profile, with . The effects caused by the general relativistic Kerr-type gravitomagnetic (GM) field and by Q are smaller by orders of magnitude. By assuming an uncertainty in measuring the radial velocities of about 15 km s, the future accuracy in measuring can be evaluated to be of the order of m s over an observational time-span . Currently, the available radial velocity measurements cover just 7 yr. [ABSTRACT FROM AUTHOR]

I report the discovery of two new Galactic Wolf-Rayet stars in Circinus via detection of their C, N and He near-infrared emission lines, using ESO-NTT-SOFI archival data. The H- and K-band spectra of WR 67a and WR 67b indicate that these are Wolf-Rayet stars of WN 6h and WC 8 subtypes, respectively. WR 67a presents a weak-lined spectrum probably reminiscent of young hydrogen-rich main-sequence stars, such as WR 25 in Car OB1 and HD 97950 in NGC 3603. Indeed, this conclusion is reinforced by the close morphological match of the WR 67a H- and K-band spectra with that for WR 21a, a known extremely massive binary system. WR 67b is probably a non-dusty WC 8 Wolf-Rayet star that has an estimated heliocentric distance of , which for its Galactic coordinates puts the star probably in the near portion of the Scutum-Centaurus arm. [ABSTRACT FROM AUTHOR]

While the population of main-sequence debris discs is well constrained, little is known about debris discs around evolved stars. This paper provides a theoretical framework considering the effects of stellar evolution on debris discs, particularly the production and loss of dust within them. Here, we repeat a steady-state model fit to disc evolution statistics for main-sequence A stars, this time using realistic grain optical properties, then evolve that population to consider its detectability at later epochs. Our model predicts that debris discs around giant stars are harder to detect than on the main sequence because radiation pressure is more effective at removing small dust around higher luminosity stars. Just 12 per cent of the first ascent giants within 100 pc are predicted to have discs detectable with Herschel at 160 μm. However, this is subject to the uncertain effect of sublimation on the disc, which we propose can thus be constrained with such observations. Our model also finds that the rapid decline in stellar luminosity results in only very young white dwarfs having luminous discs. As such systems are on average at larger distances they are hard to detect, but we predict that the stellar parameters most likely to yield a disc detection are a white dwarf at 200 pc with cooling age of 0.1 Myr, in line with observations of the helix nebula. Our model does not predict close-in (<0.01 au) dust, as observed for some white dwarfs; however we find that stellar wind drag leaves significant mass (∼10 M), in bodies up to ∼10 m in diameter, inside the disc at the end of the asymptotic giant branch (AGB) phase which may replenish these discs. [ABSTRACT FROM AUTHOR]

The absence of a rigorous proof of the existence of dynamically stable, large-scale magnetic fields in radiative stars has been for many years a missing element in the fossil field theory for the magnetic Ap/Bp stars. Recent numerical simulations, by Braithwaite & Spruit and Braithwaite & Nordlund, have largely filled this gap, demonstrating convincingly that coherent global scale fields can survive for times of the order of the main-sequence lifetimes of A stars. These dynamically stable configurations take the form of magnetic tori, with linked poloidal and toroidal fields, that slowly rise towards the stellar surface. This paper studies a simple analytical model of such a torus, designed to elucidate the physical processes that govern its evolution. It is found that one-dimensional numerical calculations reproduce some key features of the numerical simulations, with radiative heat transfer, Archimedes’ principle, Lorentz force and Ohmic decay all playing significant roles. [ABSTRACT FROM AUTHOR]

We report the discovery of short periodic radial velocity variations in the stars HD 92499 and HD 143487. Both stars show strong magnetic fields and large overabundances of rare earth elements and belong to the class of cool chemically peculiar stars of the main sequence. They are therefore new rapidly oscillating Ap stars. Pulsations were detected from analysis of high time resolution spectra obtained with the European Southern Observatory Very Large Telescope by using a cross-correlation method for large spectral bands and from combinations of lines belonging to rare earth elements. The amplitudes of the pulsations are small and do not exceed several dozens of m s−1 with periods of around 10 min. The detection of such low amplitudes is important for the determination of which magnetic Ap stars pulsate, and which are constant, a distinction important for the understanding of the pulsation driving mechanism in these stars. [ABSTRACT FROM AUTHOR]

A-type stars with their shallow convection zones serve as ideal physics laboratories for stellar atmosphere research. In the absence of large scale mixing, processes such as diffusion, mass loss and accretion leave their characteristic imprint on the chemical composition of the photosphere. This characteristic surface pattern can be studied by means of stellar abundance analysis. However, such patterns can be hidden in the large uncertainties of LTE abundances. Thus, detailed NLTE studies that can push stellar abundance analysis beyond the 0.1 dex uncertainty limit are a pre-requisite for using A star atmospheres as physics laboratories. [ABSTRACT FROM AUTHOR]

We review the literature of high dispersion studies of late B and early A type supergiants to assess the importance of non-LTE abundance calculations for them. Practically we are interested in learning which elements and species have such calculations been performed and then which of these should be implemented in calculations with plane-parallel LTE model atmospheres. The techniques available for the quantitative modeling of these atmospheres are outlined and some recent results are discussed. [ABSTRACT FROM AUTHOR]

With high-resolution spectral observations using a 2.2-m telescope, we found that the Ap star BD+0°4535 has a very strong magnetic field. From Zeeman components of rare earth element spectral lines, we detected an average magnetic field modulus of about 21 kG, although for lines of different chemical elements the estimated magnetic field ranges between 15 and 23 kG. This is a consequence of non-uniform surface distribution of these elements. Considering its possible variation with rotation period, the upper limit of magnetic field is potentially larger than what we have detected. For rare earth elements, large overabundances and ionization disequilibria were found. [ABSTRACT FROM AUTHOR]

The star-formation efficiency (SFE) of a star cluster is thought to be the critical factor in determining if the cluster can survive for a significant (>50 Myr) time. There is an often quoted critical SFE of ∼30% for a cluster to survive gas expulsion. I reiterate that the SFE is not the critical factor; rather, it is the dynamical state of the stars (as measured by their virial ratio) immediately before gas expulsion. If the stars in a star cluster are born in an (even slightly) cold dynamical state, then the survivability of a cluster can be greatly increased. [ABSTRACT FROM AUTHOR]

Among the A/B stars, about 5% host large-scale organised magnetic fields. These magnetic stars show also abundance anomalies in their spectra, and are therefore called the magnetic Ap/Bp stars. Most of these stars are also slow rotators compared to the normal A and B stars. Today, one of the greatest challenges concerning the Ap/Bp stars is to understand the origin of their slow rotation and their magnetic fields. The favoured hypothesis for the latter is that the fields are fosils, which implies that the magnetic fields subsist throughout the different evolutionary phases, and in particular during the premain sequence phase. The existence of magnetic fields at the pre-main sequence phase is also required to explain the slow rotation of Ap/Bp stars. During the last 3 years we performed a spectropolarimetric survey of the Herbig Ae/Be stars in the field and in young clusters, in order to investigate their magnetism and rotation. These investigations have resulted in the detection and/or confirmation of magnetic fields in 8 Herbig Ae/Be stars, ranging in mass from 2 to nearly 15 solar masses. In this paper I will present the results of our survey, as well as their implications for the origin and evolution of the magnetic fields and rotation of the A and B stars. [ABSTRACT FROM AUTHOR]

V440 Per is a Population I Cepheid with a period of 7.57 d and low-amplitude, almost sinusoidal light and radial velocity curves. With no reliable data on the first harmonic, its pulsation mode identification remained controversial. We obtained a radial velocity curve of V440 Per with our new high-precision and high-throughput Poznań Spectroscopic Telescope. Our data reach an accuracy of 130 m s−1 per individual measurement and yield a secure detection of the first harmonic with an amplitude of . The velocity Fourier phase φ21 of V440 Per is inconsistent at the 7.25σ level with those of fundamental-mode Cepheids, implying that the star must be an overtone Cepheid, as originally proposed by Kienzle et al. Thus, V440 Per becomes the longest-period Cepheid with securely established overtone pulsations. We show that a convective non-linear pulsation hydrocode can reproduce the Fourier parameters of V440 Per very well. The requirement to match the observed properties of V440 Per constrains the free parameters of the dynamical convection model used in the pulsation calculations, in particular the radiative loss parameter. [ABSTRACT FROM AUTHOR]

The radiation fluxes inside molecular clouds owing to a neighboring class A star or to isotropic interstellar irradiation are calculated. Radiation within the interval 912 Å < λ < 2067 Å is found to penetrate deeply enough to ensure a radiation dose for water ice on the order of 100 eV/amu or more over the lifetime of the clouds, whether a star formation region is present or not. The possibility is discussed of using these results for an astrophysical interpretation of published data from laboratory experiments on irradiation of ices of the type H2O:CH3OH:NH3:CO. The resulting radiation-chemical transformation of complex organic materials may play an important role in the prebiological evolution of the dust component of molecular clouds. [ABSTRACT FROM AUTHOR]

An analysis of the proper motion measurements of the young stellar objects (YSOs) associated with the cometary globules (CGs) in the Gum Nebula is presented. While earlier studies based on the radial-velocity measurements of the CGs suggested expansion of the system of the CGs, the observed proper motion of the YSOs shows no evidence for expansion. In particular, the kinematics of two YSOs embedded in CGs are inconsistent with the supernova explosion of the companion of ζ Pup, about 1.5 Myr ago being the cause of the expansion of the system of the CGs. YSOs associated with the CGs share the average proper motion of the member stars of the Vela OB2 association. A few YSOs that have relatively large proper motions are found to show relatively low infrared excesses. [ABSTRACT FROM AUTHOR]

We have conducted an astrometric study of the open cluster Lo 807 using proper motion data from UCAC2 catalog. We applied the maximum likelihood method to determine cluster membership by using the proper motion data. The Padova isochrones lines with solar metallicity were fitted upon the Color Magnitude Diagram in near-infrared to derive physical parameters of the cluster. We do not detect significant variable reddening within the cluster. The present result is compared with our previous study. [ABSTRACT FROM AUTHOR]

We have classified and determined the parameters of the evolved close binary MT Ser. Our moderate-resolution spectra covering various phases of the orbital period were taken with the 6-m telescope of the Special Astrophysical Observatory. The spectra of MT Ser freed from the contribution of the surrounding nebula Abell 41 contained no emission lines due to the reflection effect. The radial velocities measured from lines of different elements showed them to be constant on a time scale corresponding to the orbital period. At the same time, we find effects of broadening for the HeII absorption lines, due to the orbital motion of two hot stars of similar types. As a result, we classify MT Ser as a system with two blue subdwarfs after the common-envelope stage. We estimate the component masses and the distance to the object from the Doppler broadening of the HeII lines. We demonstrate that the age of the ambient nebula, Abell 41, is about 35 000 years. [ABSTRACT FROM AUTHOR]