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See detailSpectroscopic survey of Kepler stars. I. HERMES/Mercator observations of A- and F-type stars
Niemczura, E.; Murphy, S. J.; Smalley, B. et al

in Monthly Notices of the Royal Astronomical Society (2015), 450

The Kepler space mission provided near-continuous and high-precision photometry of about 207,000 stars, which can be used for asteroseismology. However, for successful seismic modelling it is equally ... [more ▼]

The Kepler space mission provided near-continuous and high-precision photometry of about 207,000 stars, which can be used for asteroseismology. However, for successful seismic modelling it is equally important to have accurate stellar physical parameters. Therefore, supplementary ground-based data are needed. We report the results of the analysis of high-resolution spectroscopic data of A- and F-type stars from the Kepler field, which were obtained with the HERMES spectrograph on the Mercator telescope. We determined spectral types, atmospheric parameters and chemical abundances for a sample of 117 stars. Hydrogen Balmer, Fe I, and Fe II lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. The atmospheric parameters obtained were compared with those from the Kepler Input Catalogue (KIC), confirming that the KIC effective temperatures are underestimated for A stars. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The analysed sample comprises stars with approximately solar chemical abundances, as well as chemically peculiar stars of the Am, Ap, and Lambda Boo types. The distribution of the projected rotational velocity, Vsini, is typical for A and F stars and ranges from 8 to about 280 km/s, with a mean of 134 km/s. [less ▲]

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See detailHow well can cold dark matter substructures account for the observed radio flux-ratio anomalies
Xu, Dandan; Sluse, Dominique ULg; Gao, Liang et al

in Monthly Notices of the Royal Astronomical Society (2015), 447

Discrepancies between the observed and model-predicted radio flux ratios are seen in a number of quadruply-lensed quasars. The most favoured interpretation of these anomalies is that cold dark matter (CDM ... [more ▼]

Discrepancies between the observed and model-predicted radio flux ratios are seen in a number of quadruply-lensed quasars. The most favoured interpretation of these anomalies is that cold dark matter (CDM) substructures present in lensing galaxies perturb the lens potentials and alter image magnifications and thus flux ratios. So far no consensus has emerged regarding whether or not the predicted CDM substructure abundance fully accounts for the lensing flux anomaly observations. Accurate modelling relies on a realistic lens sample in terms of both the lens environment and internal structures and substructures. In this paper, we construct samples of generalized and specific lens potentials, to which we add (rescaled) subhalo populations from the galaxy-scale Aquarius and the cluster-scale Phoenix simulation suites. We further investigate the lensing effects from subhaloes of masses several orders of magnitude below the simulation resolution limit. The resulting flux-ratio distributions are compared to the currently best available sample of radio lenses. The observed anomalies in B0128+437, B0712+472 and B1555+375 are more likely to be caused by propagation effects or oversimplified/improper lens modelling, signs of which are already seen in the data. Among the quadruple systems that have closely located image triplets/pairs, the anomalous flux ratios of MG0414+0534 can be reproduced by adding CDM subhaloes to its macroscopic lens potential, with a probability of 5-20 per cent; for B0712+472, B1422+231, B1555+375 and B2045+265, these probabilities are only of a few per cent. We hence find that CDM substructures are unlikely to be the whole reason for radio flux anomalies. We discuss other possible effects that might also be at work. [less ▲]

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See detailRotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28° 2561
Wade, G. A.; Barbá, R. H.; Grunhut, J. et al

in Monthly Notices of the Royal Astronomical Society (2015), 447

We report magnetic and spectroscopic observations and modelling of the Of?p star CPD -28° 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic ... [more ▼]

We report magnetic and spectroscopic observations and modelling of the Of?p star CPD -28° 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High-resolution spectropolarimetric data analysed using least-squares deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to phase 0.5 of the spectral ephemeris. Interpreting the 73.41 d period as the stellar rotational period, we have phased the equivalent widths and inferred longitudinal field measurements. The phased magnetic data exhibit a weak sinusoidal variation, with maximum of about 565 G at phase 0.5, and a minimum of about -335 G at phase 0.0, with extrema approximately in phase with the (double-wave) Hα equivalent width variation. Modelling of the Hα equivalent width variation assuming a quasi-3D magnetospheric model produces a unique solution for the ambiguous couplet of inclination and magnetic obliquity angles: (i, β) or (β, i) = (35°, 90°). Adopting either geometry, the longitudinal field variation yields a dipole polar intensity B[SUB]d[/SUB] = 2.6 ± 0.9 kG, consistent with that obtained from direct modelling of the Stokes V profiles. We derive a wind magnetic confinement parameter η[SUB]*[/SUB] ≃ 100, leading to an Alfvén radius R[SUB]A[/SUB] ≃ 3-5R[SUB]*[/SUB], and a Kepler radius R[SUB]K[/SUB] ≃ 20R[SUB]*[/SUB]. This supports a physical scenario in which the Hα emission and other line variability have their origin in an oblique, corotating `dynamical magnetosphere' structure resulting from a magnetically channelled wind. Nevertheless, the details of the formation of spectral lines and their variability within this framework remain generally poorly understood. [less ▲]

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See detailThe non-convex shape of (234) Barbara, the first Barbarian
Tanga, Paolo; Carry, B.; Colas, F. et al

in Monthly Notices of the Royal Astronomical Society (2015)

Asteroid (234) Barbara is the prototype of a category of asteroids that has been shown to be extremely rich in refractory inclusions, the oldest material ever found in the Solar System. It exhibits ... [more ▼]

Asteroid (234) Barbara is the prototype of a category of asteroids that has been shown to be extremely rich in refractory inclusions, the oldest material ever found in the Solar System. It exhibits several peculiar features, most notably its polarimetric behavior. In recent years other objects sharing the same property (collectively known as ”Barbarians”) have been discovered. Interferometric observations in the mid-infrared with the ESO VLTI suggested that (234) Barbara might have a bi-lobated shape or even a large companion satellite. We use a large set of 57 optical lightcurves acquired between 1979 and 2014, together with the timings of two stellar occultations in 2009, to determine the rotation period, spin-vector coordinates, and 3-D shape of (234) Barbara, using two different shape reconstruction algorithms. By using the lightcurves combined to the results obtained from stellar occultations, we are able to show that the shape of (234) Barbara exhibits large concave areas. Possible links of the shape to the polarimetric properties and the object evolution are discussed. We also show that VLTI data can be modeled without the presence of a satellite [less ▲]

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See detailA method to search for large-scale concavities in asteroid shape models
Devogele, Maxime ULg; Rivet, Jean-Pierre; Tanga, Paolo et al

in Monthly Notices of the Royal Astronomical Society (2015)

Light curve inversion is proven to produce an unique model solution only under the hypothesis that the asteroid is convex. However, it was suggested that the resulting shape model, for the case of non ... [more ▼]

Light curve inversion is proven to produce an unique model solution only under the hypothesis that the asteroid is convex. However, it was suggested that the resulting shape model, for the case of non-convex asteroid, is the convex-hull of the true asteroid non-convex shape. While a convex shape is already useful to provide the overall aspect of the target, much information about real shapes is missed, as we know that asteroids are very irregular. It is a commonly accepted evidence that large flat areas sometimes appearing on shapes derived from light curves correspond to concave areas, but this information has not been further explored and exploited so far. We present in this paper a method that allows to predict the presence of concavities from such flat regions. This method analyzes the distribution of the local normals to the facets composing shape models to predict the presence of abnormally large flat surfaces. In order to test our approach, we consider here its application to a large family of synthetic asteroid shapes, and to real asteroids with large scale concavities, whose detailed shape is known by other kinds of observations (radar and spacecraft encounters). The method that we propose is proven to be reliable and capable of providing a qualitative indication of the relevance of concavities on well-constrained asteroid shapes derived from purely photometric data sets. [less ▲]

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See detailSpectral Analysis and Abundances of the Post-HB Star HD 76431
Khalack, V.; Yameogo, B.; LeBlanc, F. et al

in Monthly Notices of the Royal Astronomical Society (2014), 445

HD76431 is a slow rotating post-HB star that shows an underabundance of helium by 0.5 dex relative to the solar value. These observational facts suggest that atomic diffusion could be active in its ... [more ▼]

HD76431 is a slow rotating post-HB star that shows an underabundance of helium by 0.5 dex relative to the solar value. These observational facts suggest that atomic diffusion could be active in its atmosphere. We have used the MMT and Bok spectra to estimate the atmospheric parameters of the target star using the model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC. The derived values of the effective temperature, surface gravity, helium abundance are consistent with those obtained by Ramspeck et al. (2001b). It appears that NLTE effect are not important for HD76431. We have used Stokes I spectra from ESPaDOnS at CFHT to perform an abundance analysis and a search for observational evidence of vertical stratification of the abundance of certain elements. The results of our abundance analysis are in good agreement with previously published data with respect to average abundances. Our numerical simulations show that carbon and nitrogen reveal signatures of vertical abundance stratification in the atmosphere of HD76431. It appears that the carbon abundance increases toward the deeper atmospheric layers. Nitrogen also shows a similar behaviour, but in deeper atmospheric layers we obtain a significant dispersion for the estimates of its abundance. To our knowledge, this is the first demonstration of vertical abundance stratification of metals in a post-HB star and up to now it is the hottest star to show such stratification features. We also report the detection of two SiIII and one TiIII emission lines in the spectra of HD76431 that were not detected in previous studies. [less ▲]

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See detailThree sub-Jupiter-mass planets: WASP-69b & WASP-84b transit active K dwarfs and WASP-70Ab transits the evolved primary of a G4+K3 binary
Anderson, D. R.; Collier Cameron, A.; Delrez, Laetitia ULg et al

in Monthly Notices of the Royal Astronomical Society (2014), 445(2),

We report the discovery of the transiting exoplanets WASP-69b, WASP-70Ab and WASP-84b, each of which orbits a bright star (V ˜ 10). WASP-69b is a bloated Saturn-mass planet (0.26 MJup, 1.06 RJup) in a 3 ... [more ▼]

We report the discovery of the transiting exoplanets WASP-69b, WASP-70Ab and WASP-84b, each of which orbits a bright star (V ˜ 10). WASP-69b is a bloated Saturn-mass planet (0.26 MJup, 1.06 RJup) in a 3.868-d period around an active, ˜1-Gyr, mid-K dwarf. ROSAT detected X-rays 60±27 arcsec from WASP-69. If the star is the source then the planet could be undergoing mass-loss at a rate of ˜1012 g s-1. This is one to two orders of magnitude higher than the evaporation rate estimated for HD 209458b and HD 189733b, both of which have exhibited anomalously large Lyman alpha absorption during transit. WASP-70Ab is a sub-Jupiter-mass planet (0.59 MJup, 1.16 RJup) in a 3.713-d orbit around the primary of a spatially resolved, 9-10-Gyr, G4+K3 binary, with a separation of 3.3 arcsec (>=800 au). WASP-84b is a sub-Jupiter-mass planet (0.69 MJup, 0.94 RJup) in an 8.523-d orbit around an active, ˜1-Gyr, early-K dwarf. Of the transiting planets discovered from the ground to date, WASP-84b has the third-longest period. For the active stars WASP-69 and WASP-84, we pre-whitened the radial velocities using a low-order harmonic series. We found that this reduced the residual scatter more than did the oft-used method of pre-whitening with a fit between residual radial velocity and bisector span. The system parameters were essentially unaffected by pre-whitening. [less ▲]

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See detailA BCool magnetic snapshot survey of solar-type stars
Marsden, S.C.; Petit, P.; Jeffers, S.V. et al

in Monthly Notices of the Royal Astronomical Society (2014), 444

We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature ... [more ▼]

We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs, the mean value of |Bl| (|Bl|mean) was also found to be higher (5.7 G) than |Bl|mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole, |Bl|mean increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and dynamos. [less ▲]

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See detailPlanets and Stellar Activity: Hide and Seek in the CoRoT-7 system
Haywood, R. D.; Cameron, A. C.; Queloz, D. et al

in Monthly Notices of the Royal Astronomical Society (2014), 443(3), 2517-2531

Since the discovery of the transiting Super-Earth CoRoT-7b, several investigations have been made of the number and precise masses of planets present in the system, but they all yield different results ... [more ▼]

Since the discovery of the transiting Super-Earth CoRoT-7b, several investigations have been made of the number and precise masses of planets present in the system, but they all yield different results, owing to the star's high level of activity. Radial velocity (RV) variations induced by stellar activity therefore need to be modelled and removed to allow a reliable detection of all planets in the system. We re-observed CoRoT-7 in January 2012 with both HARPS and the CoRoT satellite, so that we now have the benefit of simultaneous RV and photometric data. We fitted the off-transit variations in the CoRoT lightcurve using a harmonic decomposition similar to that implemented in Queloz et al. (2009). This fit was then used to model the stellar RV contribution, according to the methods described by Aigrain et al. (2011). This model was incorporated into a Monte Carlo Markov Chain in order to make a precise determination of the orbits of CoRoT-7b and CoRoT-7c. We also assess the evidence for the presence of one or two additional planetary companions. [less ▲]

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See detailAbundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD 19400
Hubrig, S.; Castelli, F.; González, J. F. et al

in Monthly Notices of the Royal Astronomical Society (2014), 442

The aim of this study is to carry out an abundance determination, to search for spectral variability and for the presence of a weak magnetic field in the typical PGa star HD 19400. High-resolution, high ... [more ▼]

The aim of this study is to carry out an abundance determination, to search for spectral variability and for the presence of a weak magnetic field in the typical PGa star HD 19400. High-resolution, high signal-to-noise High Accuracy Radial-velocity Planet Searcher (HARPS) spectropolarimetric observations of HD 19400 were obtained at three different epochs in 2011 and 2013. For the first time, we present abundances of various elements determined using an ATLAS12 model, including the abundances of a number of elements not analysed by previous studies, such as Ne I, Ga II, and Xe II. Several lines of As II are also present in the spectra of HD 19400. To study the variability, we compared the behaviour of the line profiles of various elements. We report on the first detection of anomalous shapes of line profiles belonging to Mn and Hg, and the variability of the line profiles belonging to the elements Hg, P, Mn, Fe, and Ga. We suggest that the variability of the line profiles of these elements is caused by their non-uniform surface distribution, similar to the presence of chemical spots detected in HgMn stars. The search for the presence of a magnetic field was carried out using the moment technique and the Singular Value Decomposition (SVD) method. Our measurements of the magnetic field with the moment technique using 22 Mn II lines indicate the potential existence of a weak variable longitudinal magnetic field on the first epoch. The SVD method applied to the Mn II lines indicates <B[SUB]z[/SUB]> = -76 ± 25 G on the first epoch, and at the same epoch the SVD analysis of the observations using the Fe II lines shows <B[SUB]z[/SUB]> = -91 ± 35 G. The calculated false alarm probability values, 0.008 and 0.003, respectively, are above the value 10[SUP]-3[/SUP], indicating no detection. [less ▲]

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See detailColour-magnitude diagrams of transiting Exoplanets - II. A larger sample from photometric distances
Triaud, Amaury H. M. J.; Lanotte, Audrey ULg; Smalley, Barry et al

in Monthly Notices of the Royal Astronomical Society (2014), 444(1), 711-728

CColour-magnitude diagrams form a traditional way of presenting luminous objects in the Universe and compare them to each other. Here, we estimate the photometric distance of 44 transiting exoplanetary ... [more ▼]

CColour-magnitude diagrams form a traditional way of presenting luminous objects in the Universe and compare them to each other. Here, we estimate the photometric distance of 44 transiting exoplanetary systems. Parallaxes for seven systems confirm our methodology. Combining those measurements with fluxes obtained while planets were occulted by their host stars, we compose colour-magnitude diagrams in the near and mid-infrared. When possible, planets are plotted alongside very low mass stars and field brown dwarfs, who often share similar sizes and equilibrium temperatures. They offer a natural, empirical, comparison sample. We also include directly imaged exoplanets and the expected loci of pure blackbodies. Irradiated planets do not match blackbodies; their emission spectra are not featureless. For a given luminosity, hot Jupiters' daysides show a larger variety in colour than brown dwarfs do and display an increasing diversity in colour with decreasing intrinsic luminosity. The presence of an extra absorbent within the 4.5 μm band would reconcile outlying hot Jupiters with ultra-cool dwarfs' atmospheres. Measuring the emission of gas giants cooler than 1000 K would disentangle whether planets' atmospheres behave more similarly to brown dwarfs' atmospheres than to blackbodies, whether they are akin to the young directly imaged planets, or if irradiated gas giants form their own sequence. [less ▲]

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See detailA window on exoplanet dynamical histories: Rossiter-McLaughlin observations of WASP-13b and WASP-32b
Brothwell, R.D.; Watson, C.A.; Hébrard, G. et al

in Monthly Notices of the Royal Astronomical Society (2014), 440(4), 3392-3401

We present Rossiter-McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis (lambda). WASP-13b and ... [more ▼]

We present Rossiter-McLaughlin observations of WASP-13b and WASP-32b and determine the sky-projected angle between the normal of the planetary orbit and the stellar rotation axis (lambda). WASP-13b and WASP-32b both have prograde orbits and are consistent with alignment with measured sky-projected angles of lambda =8°^{+13}_{-12} and lambda =-2°^{+17}_{-19}, respectively. Both WASP-13 and WASP-32 have Teff < 6250 K, and therefore, these systems support the general trend that aligned planetary systems are preferentially found orbiting cool host stars. A Lomb-Scargle periodogram analysis was carried out on archival SuperWASP data for both systems. A statistically significant stellar rotation period detection (above 99.9 per cent confidence) was identified for the WASP-32 system with Prot = 11.6 ± 1.0 days. This rotation period is in agreement with the predicted stellar rotation period calculated from the stellar radius, R*, and vsin i if a stellar inclination of i* = 90° is assumed. With the determined rotation period, the true 3D angle between the stellar rotation axis and the planetary orbit, psi, was found to be psi = 11° ± 14°. We conclude with a discussion on the alignment of systems around cool host stars with Teff < 6150 K by calculating the tidal dissipation time-scale. We find that systems with short tidal dissipation time-scales are preferentially aligned and systems with long tidal dissipation time-scales have a broad range of obliquities. [less ▲]

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See detailA new analysis of quasar polarization alignments
Pelgrims, Vincent ULg; Cudell, Jean-René ULg

in Monthly Notices of the Royal Astronomical Society (2014), 442(1), 1239-1248

We propose a new method to analyse the alignment of optical polarization vectors from quasars. This method leads to a definition of intrinsic preferred axes and to a determination of the probability that ... [more ▼]

We propose a new method to analyse the alignment of optical polarization vectors from quasars. This method leads to a definition of intrinsic preferred axes and to a determination of the probability that the distribution of polarization directions is random. This probability is found to be as low as 0,003 percent for one of the region of redshift. [less ▲]

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See detailTransiting hot Jupiters from WASP-South, Euler and TRAPPIST: WASP-95b to WASP-101b
Hellier, Coel; Anderson, D. R.; Collier Cameron, A. et al

in Monthly Notices of the Royal Astronomical Society (2014)

We report the discovery of the transiting exoplanets WASP-95b, WASP-96b, WASP-97b, WASP-98b, WASP-99b, WASP-100b and WASP-101b. All are hot Jupiters with orbital periods in the range 2.1-5.7 d, masses of ... [more ▼]

We report the discovery of the transiting exoplanets WASP-95b, WASP-96b, WASP-97b, WASP-98b, WASP-99b, WASP-100b and WASP-101b. All are hot Jupiters with orbital periods in the range 2.1-5.7 d, masses of 0.5-2.8 MJup and radii of 1.1-1.4 RJup. The orbits of all the planets are compatible with zero eccentricity. WASP-99b produces the shallowest transit yet found by WASP-South, at 0.4 per cent. The host stars are of spectral type F2-G8. Five have metallicities of [Fe/H] from -0.03 to +0.23, while WASP-98 has a metallicity of -0.60, exceptionally low for a star with a transiting exoplanet. Five of the host stars are brighter than V = 10.8, which significantly extends the number of bright transiting systems available for follow-up studies. WASP-95 shows a possible rotational modulation at a period of 20.7 d. We discuss the completeness of WASP survey techniques by comparing to the HATnet project. [less ▲]

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See detailExtensive study of HD 25558, a long-period double-lined binary with two SPB components
Sódor, Á.; De Cat, P.; Wright, D. J. et al

in Monthly Notices of the Royal Astronomical Society (2014), 438(4), 3535-3556

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ~2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves ... [more ▼]

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ~2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about 9 years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. Eleven independent frequencies were identified in the data. All the frequencies were attributed to one of the two components based on Pixel-by-pixel variability analysis of the line profiles. Spectroscopic and photometric mode identification was also performed for the frequencies of both stars. These results suggest that the inclination and rotation of the two components are rather different. The primary is a slow rotator with ~6 d period, seen at ~60 deg inclination, while the secondary rotates fast with ~1.2 d period, and is seen at ~20 inclination. Spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field can be detected in the primary. [less ▲]

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See detailHigh-frequency A-type pulsators discovered using SuperWASP
Holdsworth, Daniel L.; Smalley, B.; Gillon, Michaël ULg et al

in Monthly Notices of the Royal Astronomical Society (2014)

We present the results of a survey using the WASP archive to search for high-frequency pulsations in F-, A- and B-type stars. Over 1.5 million targets have been searched for pulsations with amplitudes ... [more ▼]

We present the results of a survey using the WASP archive to search for high-frequency pulsations in F-, A- and B-type stars. Over 1.5 million targets have been searched for pulsations with amplitudes greater than 0.5 millimagnitude. We identify over 350 stars which pulsate with periods less than 30 min. Spectroscopic follow-up of selected targets has enabled us to confirm 10 new rapidly oscillating Ap stars, 13 pulsating Am stars and the fastest known δ Scuti star. We also observe stars which show pulsations in both the high-frequency domain and the low-frequency δ Scuti range. This work shows the power of the WASP photometric survey to find variable stars with amplitudes well below the nominal photometric precision per observation. [less ▲]

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See detailErratum: SN 2007uy − metamorphosis of an aspheric Type Ib explosion
Roy, Rupak ULg

in Monthly Notices of the Royal Astronomical Society (2014)

The supernovae (SNe) of Type Ibc are rare and the detailed characteristics of these explosions have been studied only for a few events. Unlike Type II SNe, the progenitors of Type Ibc have never been ... [more ▼]

The supernovae (SNe) of Type Ibc are rare and the detailed characteristics of these explosions have been studied only for a few events. Unlike Type II SNe, the progenitors of Type Ibc have never been detected in pre-explosion images. So, to understand the nature of their progenitors and the characteristics of the explosions, investigation of proximate events are necessary. Here we present the results of multi-wavelength observations of Type Ib \sn\ in the nearby ($\sim$ 29.7 Mpc) galaxy NGC 2770. Analysis of the photometric observations revealed this explosion as an energetic event with peak absolute $R$ band magnitude $-18.5\pm0.16$, which is about one mag brighter than the mean value ($-17.6\pm0.6$) derived for well observed Type Ibc events. The SN is highly extinguished, \ebv\ = 0.63$\pm$0.15 mag, mainly due to foreground material present in the host galaxy. From optical light curve modeling we determine that about 0.3 \msun\ radioactive $^{56}$Ni is produced and roughly 4.4 \msun\ material is ejected during this explosion with liberated energy $\sim 15\times10^{51}$ erg, indicating the event to be an energetic one. Through optical spectroscopy, we have noticed a clear aspheric evolution of several line forming regions, but no dependency of asymmetry is seen on the distribution of $^{56}$Ni inside the ejecta. The SN shock interaction with the circumburst material (CSM) is clearly noticeable in radio follow-up, presenting a Synchrotron Self Absorption (SSA) dominated light curve with a contribution of Free Free Absorption (FFA) during the early phases. Assuming a Wolf-Rayet (WR) star, with wind velocity $\ga 10^3 {\rm km~s}^{-1}$, as a progenitor, we derive a lower limit to the mass loss rate inferred from the radio data as $\dot{M} \ga 2.4\times10^{-5}$ \msun\,~yr$^{-1}$, which is consistent with the results obtained for other Type Ibc SNe bright at radio frequencies. [less ▲]

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See detailWeighted principal component analysis: a weighted covariance eigendecomposition approach
Delchambre, Ludovic ULg

in Monthly Notices of the Royal Astronomical Society (2014), 446(2), 3545-3555

We present a new straightforward principal component analysis (PCA) method based on the diagonalization of the weighted variance-covariance matrix through two spectral decomposition methods: power ... [more ▼]

We present a new straightforward principal component analysis (PCA) method based on the diagonalization of the weighted variance-covariance matrix through two spectral decomposition methods: power iteration and Rayleigh quotient iteration. This method allows one to retrieve a given number of orthogonal principal components amongst the most meaningful ones for the case of problems with weighted and/or missing data. Principal coefficients are then retrieved by fitting principal components to the data while providing the final decomposition. Tests performed on real and simulated cases show that our method is optimal in the identification of the most significant patterns within data sets. We illustrate the usefulness of this method by assessing its quality on the extrapolation of Sloan Digital Sky Survey quasar spectra from measured wavelengths to shorter and longer wavelengths. Our new algorithm also benefits from a fast and flexible implementation. [less ▲]

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See detailEarly-type stars observed in the ESO UVES Paranal Observatory Project - IV. Studies of CN, CH+ and CH in the interstellar medium
Smoker, J.; Ledoux, C.; Jehin, Emmanuel ULg et al

in Monthly Notices of the Royal Astronomical Society (2013)

High spectral resolution (˜80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular ... [more ▼]

High spectral resolution (˜80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular lines CN (3874 Å), CH[SUP]+[/SUP] (3957, 4232 Å) and CH (3886, 4300 Å) towards 74 O- and B-type stellar sightlines. Additionally, archive data are presented for 140 ELODIE early-type stellar sightlines at R = 42 000, plus 25 FEROS at R = 48 000 and 3 UVES at R > 50 000, mainly in the CH[SUP]+[/SUP] (4232 Å) and CH (3886, 4300 Å) transitions. Detection rates are ˜45 per cent for CN and ˜67 per cent for the other lines in the POP sample, and ˜10-15 per cent for CH[SUP]+[/SUP] and CH lines in the additional sample. CH and CH[SUP]+[/SUP] are well correlated between log[N(CH) cm[SUP]-2[/SUP]]˜12-14, implying that these clouds are CH[SUP]+[/SUP]-like CH and not CN-like CH. CH is also very well correlated with Na I D in the range log[N(Na I cm[SUP]-2[/SUP]]) ˜12.2-14.2. A few sightlines show tentative velocity shifts of ˜2 km s[SUP]-1[/SUP] between CH and CH[SUP]+[/SUP], which appear to be caused by differences in component strength in blends, and hence do not provide firm evidence for shocks. Finally, we describe a search for [SUP]13[/SUP]CH[SUP]+[/SUP] in a sightline towards HD 76341. No [SUP]13[/SUP]CH[SUP]+[/SUP] is detected, placing a limit on the [SUP]13[/SUP]CH[SUP]+[/SUP] to [SUP]12[/SUP]CH[SUP]+[/SUP] ratio of ˜0.01. If a formal fit is attempted, the equivalent width ratio in the two isotopes is a factor ˜90 but with large errors. [less ▲]

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See detailUse of the Fourier transform to derive the gravitational lens deflection angle
Wertz, Olivier ULg; Surdej, Jean ULg

in Monthly Notices of the Royal Astronomical Society (2013), 437

Knowing that the gravitational lens deflection angle can be expressed as the convolution product between the dimensionless surface mass density κ(x) and a simple function of the scaled impact parameter ... [more ▼]

Knowing that the gravitational lens deflection angle can be expressed as the convolution product between the dimensionless surface mass density κ(x) and a simple function of the scaled impact parameter vector x, we make use of the Fourier transform to derive its analytical expression for the case of mass distributions presenting a homoeoidal sym- metry. For this family of models, we obtain the expression of the two components of the deflection angle in the form of integrals performed over the radial coordinate ρ. In the limiting case of axially symmetric lenses, we obviously retrieve the well-known relation α(x)∝ M(≤ |x|)x/|x|^2. Furthermore, we derive explicit solutions for the deflection angle characterized by dimensionless surface mass density profiles such as κ ∝ (ρ^2c + ρ^2)^{−ν}; corresponding to the non-singular isothermal ellipsoid (NSIE) model for the particular case ν = 1/2. Let us insist that all these results are obtained without using the complex formal- ism introduced by Bourassa and Kantowski (1973,1975). Further straightforward applica- tions of this Fourier approach are suggested in the conclusions of the present work. [less ▲]

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