References of "Astronomy and Astrophysics"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailFive transiting hot Jupiters discovered using WASP-South, Euler, and TRAPPIST: WASP-119 b, WASP-124 b, WASP-126 b, WASP-129 b, and WASP-133 b
Maxted, P. F. L.; Anderson, D. R.; Collier Cameron, A. et al

in Astronomy and Astrophysics (2016), 591

We have used photometry from the WASP-South instrument to identify 5 stars showing planet-like transits in their light curves. The planetary nature of the companions to these stars has been confirmed ... [more ▼]

We have used photometry from the WASP-South instrument to identify 5 stars showing planet-like transits in their light curves. The planetary nature of the companions to these stars has been confirmed using photometry from the EulerCam instrument on the Swiss Euler 1.2-m telescope and the TRAPPIST telescope, and spectroscopy obtained with the CORALIE spectrograph. The planets discovered are hot Jupiter systems with orbital periods in the range 2.17 to 5.75 days, masses from 0.3 M[SUB]Jup[/SUB] to 1.2 M[SUB]Jup[/SUB] and with radii from 1 R[SUB]Jup[/SUB] to 1.5 R[SUB]Jup[/SUB]. These planets orbit bright stars (V = 11-13) with spectral types in the range F9 to G4. WASP-126 is the brightest planetary system in this sample and hosts a low-mass planet with a large radius (0.3 M[SUB]Jup[/SUB],0.95 R[SUB]Jup[/SUB]), making it a good target for transmission spectroscopy. The high density of WASP-129 A suggests that it is a helium-rich star similar to HAT-P-11 A. WASP-133 A has an enhanced surface lithium abundance compared to other old G-type stars, particularly other planet host stars. These planetary systems are good targets for follow-up observations with ground-based and space-based facilities to study their atmospheric and dynamical properties. Full Tables 2 and 3 are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/591/A55">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/591/A55</A> [less ▲]

Detailed reference viewed: 3 (1 ULg)
Full Text
Peer Reviewed
See detailOrbital, spin state and thermophysical characterization of near-Earth asteroid (3200) Phaethon
Hanus, Josef; Delbo, Marco; Vokrouhlický, D. et al

in Astronomy and Astrophysics (2016)

The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is only at 0.14 au and is associated with the Geminid meteor stream. We aim to use all available disk-integrated optical ... [more ▼]

The near-Earth asteroid (3200) Phaethon is an intriguing object: its perihelion is only at 0.14 au and is associated with the Geminid meteor stream. We aim to use all available disk-integrated optical data to derive reliable convex shape model of Phaethon. By interpreting the available space- and ground-based thermal infrared data and Spitzer spectra using a thermophysical model, we also aim to further constrain its size, thermal inertia, and visible geometric albedo. We apply the convex inversion method to the new optical data obtained by six instruments together with the already existing observations. The convex shape model is then used as an input for the thermophysical modeling. We also study the long-term stability of Phaethon’s orbit and spin axis by a numerical orbital and rotation-state integrator We present a new convex shape model and rotational state of Phaethon – sidereal rotation period of 3.603958(2) h and ecliptic coordinates of the preferred pole orientation of (319◦ , −39◦) with a 5◦ uncertainty. Moreover, we derive its size (D=5.1±0.2 km), thermal inertia (Γ=600±200 J m-2s -1/2K -1), geometric visible albedo (pV=0.122±0.008), and estimate the macroscopic surface roughness. We also find that the Sun illumination at the perihelion passage during past thousands of years is not connected to a specific area on the surface implying non-preferential heating. [less ▲]

Detailed reference viewed: 8 (1 ULg)
Full Text
Peer Reviewed
See detailThe X-ray light curve of the massive colliding wind Wolf-Rayet + O binary WR 21a
Gosset, Eric ULg; Nazé, Yaël ULg

in Astronomy and Astrophysics (2016), 590

Our dedicated XMM-Newton monitoring, as well as archival Chandra and Swift datasets, were used to examine the behaviour of the WN5h+O3V binary WR 21a at high energies. For most of the orbit, the X-ray ... [more ▼]

Our dedicated XMM-Newton monitoring, as well as archival Chandra and Swift datasets, were used to examine the behaviour of the WN5h+O3V binary WR 21a at high energies. For most of the orbit, the X-ray emission exhibits few variations. However, an increase in strength of the emission is seen before periastron, following a 1 /D relative trend, where D is the separation between both components. This increase is rapidly followed by a decline due to strong absorption as the Wolf-Rayet (WR) comes in front. The fitted local absorption value appears to be coherent with a mass-loss rate of about 1 × 10[SUP]-5[/SUP] M[SUB]⊙[/SUB] yr[SUP]-1[/SUP] for the WR component. However, absorption is not the only parameter affecting the X-ray emission at periastron as even the hard X-ray emission decreases, suggesting a possible collapse of the colliding wind region near to or onto the photosphere of the companion just before or at periastron. An eclipse may appear as another potential scenario, but it would be in apparent contradiction with several lines of evidence, notably the width of the dip in the X-ray light curve and the absence of variations in the UV light curve. Afterwards, the emission slowly recovers, with a strong hysteresis effect. The observed behaviour is compatible with predictions from general wind-wind collision models although the absorption increase is too shallow. Based on observations collected at ESO as well as with Swift, Chandra, and the ESA science mission XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). [less ▲]

Detailed reference viewed: 23 (3 ULg)
Full Text
Peer Reviewed
See detailPulsating hot O subdwarfs in ω Centauri: mapping a unique instability strip on the extreme horizontal branch
Randall, S. K.; Calamida, A.; Fontaine, G. et al

in Astronomy and Astrophysics (2016), 589

We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 h of time-series photometry for ... [more ▼]

We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 h of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, T[SUB]eff[/SUB] and log N(He) /N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125 s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48 000 and 54 000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ~2700 s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in log g - T[SUB]eff[/SUB] space. This can be directly compared to the pulsation driving predicted from the Montréal "second-generation" models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well-known instability strip between 29 000-36 000 K where the rapid subdwarf B pulsators are found is complemented by a second one above 50 000 K in the models. While significant challenges remain at the quantitative level, we believe that the same κ-mechanism that drives the pulsations in hot B subdwarfs is also responsible for the excitation of the rapid oscillations observed in the ω Cen variables. Intriguingly, the ω Cen variables appear to form a unique class. No direct counterparts have so far been found either in the Galactic field, nor in other globular clusters, despite dedicated searches. Conversely, our survey revealed no ω Cen representatives of the rapidly pulsating hot B subdwarfs found among the field population, though their presence cannot be excluded from the limited sample. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (proposal IDs 083.D-0833, 386.D-0669, 087.D-0216 and 091.D-0791).The reduced spectra are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A1">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/589/A1</A> [less ▲]

Detailed reference viewed: 13 (2 ULg)
Full Text
Peer Reviewed
See detailLow-rank plus sparse decomposition for exoplanet detection in direct-imaging ADI sequences. The LLSG algorithm
Gómez González, Carlos ULg; Absil, Olivier ULg; Absil, P.-A. et al

in Astronomy and Astrophysics (2016), 589

Context. Data processing constitutes a critical component of high-contrast exoplanet imaging. Its role is almost as important as the choice of a coronagraph or a wavefront control system, and it is ... [more ▼]

Context. Data processing constitutes a critical component of high-contrast exoplanet imaging. Its role is almost as important as the choice of a coronagraph or a wavefront control system, and it is intertwined with the chosen observing strategy. Among the data processing techniques for angular differential imaging (ADI), the most recent is the family of principal component analysis (PCA) based algorithms. It is a widely used statistical tool developed during the first half of the past century. PCA serves, in this case, as a subspace projection technique for constructing a reference point spread function (PSF) that can be subtracted from the science data for boosting the detectability of potential companions present in the data. Unfortunately, when building this reference PSF from the science data itself, PCA comes with certain limitations such as the sensitivity of the lower dimensional orthogonal subspace to non-Gaussian noise. <BR /> Aims: Inspired by recent advances in machine learning algorithms such as robust PCA, we aim to propose a localized subspace projection technique that surpasses current PCA-based post-processing algorithms in terms of the detectability of companions at near real-time speed, a quality that will be useful for future direct imaging surveys. <BR /> Methods: We used randomized low-rank approximation methods recently proposed in the machine learning literature, coupled with entry-wise thresholding to decompose an ADI image sequence locally into low-rank, sparse, and Gaussian noise components (LLSG). This local three-term decomposition separates the starlight and the associated speckle noise from the planetary signal, which mostly remains in the sparse term. We tested the performance of our new algorithm on a long ADI sequence obtained on β Pictoris with VLT/NACO. <BR /> Results: Compared to a standard PCA approach, LLSG decomposition reaches a higher signal-to-noise ratio and has an overall better performance in the receiver operating characteristic space. This three-term decomposition brings a detectability boost compared to the full-frame standard PCA approach, especially in the small inner working angle region where complex speckle noise prevents PCA from discerning true companions from noise. [less ▲]

Detailed reference viewed: 44 (17 ULg)
Full Text
Peer Reviewed
See detailDistant activity of 67P/Churyumov-Gerasimenko in 2014: Ground-based results during the Rosetta pre-landing phase
Snodgrass, Colin; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2016), 588

Context. As the ESA Rosetta mission approached, orbited, and sent a lander to comet 67P/Churyumov-Gerasimenko in 2014, a large campaign of ground-based observations also followed the comet. <BR /> Aims ... [more ▼]

Context. As the ESA Rosetta mission approached, orbited, and sent a lander to comet 67P/Churyumov-Gerasimenko in 2014, a large campaign of ground-based observations also followed the comet. <BR /> Aims: We constrain the total activity level of the comet by photometry and spectroscopy to place Rosetta results in context and to understand the large-scale structure of the comet's coma pre-perihelion. <BR /> Methods: We performed observations using a number of telescopes, but concentrate on results from the 8 m VLT and Gemini South telescopes in Chile. We use R-band imaging to measure the dust coma contribution to the comet's brightness and UV-visible spectroscopy to search for gas emissions, primarily using VLT/FORS. In addition we imaged the comet in near-infrared wavelengths (JHK) in late 2014 with Gemini-S/Flamingos-2. <BR /> Results: We find that the comet was already active in early 2014 at heliocentric distances beyond 4 au. The evolution of the total activity (measured by dust) followed previous predictions. No gas emissions were detected despite sensitive searches. <BR /> Conclusions: The comet maintains a similar level of activity from orbit to orbit, and is in that sense predictable, meaning that Rosetta results correspond to typical behaviour for this comet. The gas production (for CN at least) is highly asymmetric with respect to perihelion, as our upper limits are below the measured production rates for similar distances post-perihelion in previous orbits. Based on observations made with ESO telescopes at the La Silla Paranal Observatory under programme IDs 592.C-0924, 093.C-0593, 094.C-0054, and at Gemini South under GS-2014B-Q-15 and GS-2014B-Q-76. [less ▲]

Detailed reference viewed: 13 (2 ULg)
Full Text
Peer Reviewed
See detailObservational signatures of past mass-exchange episodes in massive binaries: The case of HD 149 404
Raucq, Françoise ULg; Rauw, Gregor ULg; Gosset, Eric ULg et al

in Astronomy and Astrophysics (2016), 588

Context. Mass and momentum exchanges in close massive binaries play an important role in their evolution, and produce several observational signatures such as asynchronous rotation and altered chemical ... [more ▼]

Context. Mass and momentum exchanges in close massive binaries play an important role in their evolution, and produce several observational signatures such as asynchronous rotation and altered chemical compositions, that remain after the stars detach again. Aims: We investigated these effects for the detached massive O-star binary HD 149 404 (O7.5 If + ON9.7 I, P = 9.81 days), which is thought to have experienced a past episode of case A Roche-lobe overflow (RLOF). Methods: Using phase-resolved spectroscopy, we performed the disentangling of the optical spectra of the two stars. The reconstructed primary and secondary spectra were then analysed with the CMFGEN model atmosphere code to determine stellar parameters, such as the effective temperatures and surface gravities, and to constrain the chemical composition of the components. We complemented the optical study with the study of IUE spectra, which we compare to the synthetic binary spectra. The properties of the stars were compared to evolutionary models. Results: We confirmed a strong overabundance in nitrogen ([N/C] ~ 150[N/C][SUB]⊙[/SUB]) for the secondary and a slight nitrogen overabundance ([N/C] ~ 5[N/C][SUB]⊙[/SUB]) for the primary star. Comparing the two stars, we found evidence for asynchronous rotation, with a rotational period ratio of 0.50 ± 0.11. Conclusions: The hypothesis of a past case A RLOF interaction in HD 149 404 is most plausible to explain its chemical abundances and rotational asynchronicity. Some of the observed properties, such as the abundance pattern, are clearly a challenge for current case A binary evolution models, however. [less ▲]

Detailed reference viewed: 31 (8 ULg)
Full Text
Peer Reviewed
See detailTesting the theory of colliding winds: the periastron passage of 9 Sagittarii. I. X-ray and optical spectroscopy
Rauw, Grégor ULg; Blomme, R.; Nazé, Yaël ULg et al

in Astronomy and Astrophysics (2016), 589

Context. The long-period, highly eccentric O-star binary 9 Sgr, known for its non-thermal radio emission and its relatively bright X-ray emission, went through its periastron in 2013. <BR /> Aims: Such an ... [more ▼]

Context. The long-period, highly eccentric O-star binary 9 Sgr, known for its non-thermal radio emission and its relatively bright X-ray emission, went through its periastron in 2013. <BR /> Aims: Such an event can be used to observationally test the predictions of the theory of colliding stellar winds over a broad range of wavelengths. <BR /> Methods: We conducted a multi-wavelength monitoring campaign of 9 Sgr around the 2013 periastron. In this paper, we focus on X-ray observations and optical spectroscopy. <BR /> Results: The optical spectra allow us to revisit the orbital solution of 9 Sgr and to refine its orbital period to 9.1 years. The X-ray flux is maximum at periastron over all energy bands, but with clear differences as a function of energy. The largest variations are observed at energies above 2 keV, whilst the spectrum in the soft band (0.5-1.0 keV) remains mostly unchanged, indicating that it arises far from the collision region, in the inner winds of the individual components. The level of the hard emission at periastron clearly deviates from the 1 /r relation expected for an adiabatic wind-interaction zone, whilst this relation seems to hold at the other phases that are covered by our observations. The spectra taken at phase 0.946 reveal a clear Fe xxv line at 6.7 keV, but no such line is detected at periastron (φ = 0.000), although a simple model predicts a strong line that should be easily visible in the data. <BR /> Conclusions: The peculiarities of the X-ray spectrum of 9 Sgr could reflect the effect of radiative inhibition as well as a phase-dependent efficiency of particle acceleration on the shock properties. [less ▲]

Detailed reference viewed: 19 (4 ULg)
Full Text
Peer Reviewed
See detailHerschel observations of the nebula M1-67 around the Wolf-Rayet star WR 124
Vamvatira-Nakou, C.; Hutsemekers, Damien ULg; Royer, P. et al

in Astronomy and Astrophysics (2016), 588

Infrared Herschel imaging and spectroscopic observations of the nebula M1-67 around the Wolf-Rayet star WR 124 have been obtained along with optical imaging observations. The infrared images reveal a ... [more ▼]

Infrared Herschel imaging and spectroscopic observations of the nebula M1-67 around the Wolf-Rayet star WR 124 have been obtained along with optical imaging observations. The infrared images reveal a clumpy dusty nebula that extends up to 1 pc. The comparison with the optical images shows that the ionized gas nebula coincides with the dust nebula, the dust and the gas being mixed together. A photodissociation region is revealed from the infrared spectroscopic analysis. The analysis of the infrared spectrum of the nebula, where forbidden emission lines of ionized elements were detected, showed that the nebula consists of mildly processed material with the calculated abundance number ratios being N/O = 1.0 ± 0.5 and C/O = 0.46 ± 0.27. Based on a radiative transfer model, the dust mass of the nebula was estimated to be 0.22 M[SUB]⊙[/SUB] with a population of large grains being necessary to reproduce the observations. The comparison of the mass-loss rate and the abundance ratios to theoretical models of stellar evolution led to the conclusion that the nebular ejection took place during a RSG/YSG evolutionary phase of a central star with an initial mass of 32 M[SUB]⊙[/SUB]. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Based in part on observations collected at the European Southern Observatory, La Silla, Chile. [less ▲]

Detailed reference viewed: 16 (3 ULg)
Full Text
Peer Reviewed
See detailHigh spectral resolution monitoring of Nova V339 Delphini with TIGRE (Corrigendum)
De Gennaro Aquino, I.; Schröder, K.-P.; Mittag, M. et al

in Astronomy and Astrophysics (2016), 589

The tags in Table 2, indicating the positions of the most prominent spectral features in Figs. 2a and b, were not corrected during the revision process. We include here the corrected table. The lines ... [more ▼]

The tags in Table 2, indicating the positions of the most prominent spectral features in Figs. 2a and b, were not corrected during the revision process. We include here the corrected table. The lines observed and identified in the spectra and the respective phases remain unchanged. [less ▲]

Detailed reference viewed: 23 (2 ULg)
Full Text
Peer Reviewed
See detailEvidence for the alignment of quasar radio polarizations with large quasar group axes
Pelgrims, Vincent ULg; Hutsemekers, Damien ULg

in Astronomy and Astrophysics (2016)

Recently, evidence has been presented for the polarization vectors from quasars to preferentially align with the axes of the large quasar groups (LQG) to which they belong. This report was based on ... [more ▼]

Recently, evidence has been presented for the polarization vectors from quasars to preferentially align with the axes of the large quasar groups (LQG) to which they belong. This report was based on observations made at optical wavelengths for two large quasar groups at redshift ~1.3. The correlation suggests that the spin axes of quasars preferentially align with their surrounding large-scale structure that is assumed to be traced by the LQGs. Here, we consider a large sample of LQGs built from the Sloan Digital Sky Survey DR7 quasar catalogue in the redshift range 1.0 -􀀀 1.8. For quasars embedded in this sample, we collected radio polarization measurements with the goal to study possible correlations between quasar polarization vectors and the major axis of their host LQGs. Assuming the radio polarization vector is perpendicular to the quasar spin axis, we found that the quasar spin axis is preferentially parallel to the LQG major axis inside LQGs that have at least 20 members. This result independently supports the observations at optical wavelengths. We additionally found that when the richness of an LQG decreases, the quasar spin axis becomes preferentially perpendicular to the LQG major axis and that no correlation is detected for quasar groups with fewer than 10 members. [less ▲]

Detailed reference viewed: 25 (7 ULg)
Full Text
Peer Reviewed
See detailThe dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 AU heliocentric distance range inbound
Moreno, F.; Snodgrass, C.; Hainaut, O. et al

in Astronomy and Astrophysics (2016), 587

Context. The ESA Rosetta spacecraft, currently orbiting around comet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments,particularly ... [more ▼]

Context. The ESA Rosetta spacecraft, currently orbiting around comet 67P/Churyumov-Gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments,particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. <BR /> Aims: To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. <BR /> Methods: A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. <BR /> Results: The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is α = -3, instead of α = -2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 AU, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 AU. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment. [less ▲]

Detailed reference viewed: 9 (1 ULg)
Full Text
Peer Reviewed
See detailFORS2 observes a multi-epoch transmission spectrum of the hot Saturn-mass exoplanet WASP-49b
Lendl, M.; Delrez, Laetitia ULg; Gillon, Michaël ULg et al

in Astronomy and Astrophysics (2016), 587

Context. Transmission spectroscopy has proven to be a useful tool for the study of exoplanet atmospheres, because the absorption and scattering signatures of the atmosphere manifest themselves as ... [more ▼]

Context. Transmission spectroscopy has proven to be a useful tool for the study of exoplanet atmospheres, because the absorption and scattering signatures of the atmosphere manifest themselves as variations in the planetary transit depth. Several planets have been studied with this technique, leading to the detection of a small number of elements and molecules (Na, K, H[SUB]2[/SUB]O), but also revealing that many planets show flat transmission spectra consistent with the presence of opaque high-altitude clouds. <BR /> Aims: We apply this technique to the M[SUB]P[/SUB] = 0.40M[SUB]J[/SUB], R[SUB]p[/SUB] = 1.20R[SUB]J[/SUB], P = 2.78 d planet WASP-49b, aiming to characterize its transmission spectrum between 0.73 and 1 ¯m and search for the features of K and H[SUB]2[/SUB]O. Owing to its density and temperature, the planet is predicted to possess an extended atmosphere and is thus a good target for transmission spectroscopy. <BR /> Methods: Three transits of WASP-49b have been observed with the FORS2 instrument installed at the VLT/UT1 telescope at the ESO Paranal site. We used FORS2 in MXU mode with grism GRIS_600z, producing simultaneous multiwavelength transit light curves throughout the i' and z' bands. We combined these data with independent broadband photometry from the Euler and TRAPPIST telescopes to obtain a good measurement of the transit shape. Strong correlated noise structures are present in the FORS2 light curves, which are due to rotating flat-field structures that are introduced by inhomogeneities of the linear atmospheric dispersion corrector's transparency. We accounted for these structures by constructing common noise models from the residuals of light curves bearing the same noise structures and used them together with simple parametric models to infer the transmission spectrum. <BR /> Results: We present three independent transmission spectra of WASP-49b between 0.73 and 1.02 ¯m, as well as a transmission spectrum between 0.65 and 1.02 ¯m from the combined analysis of FORS2 and broadband data. The results obtained from the three individual epochs agree well. The transmission spectrum of WASP-49b is best fit by atmospheric models containing a cloud deck at pressure levels of 1 mbar or lower. Based on photometric observations made with FORS2 on the ESO VLT/UT1 (Prog. ID 090.C-0758), EulerCam on the Euler-Swiss telescope and the Belgian TRAPPIST telescope.The photometric time series data in this work are only available in electronic form at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A67">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A67</A> [less ▲]

Detailed reference viewed: 2 (1 ULg)
Full Text
Peer Reviewed
See detailWeak magnetic field, solid-envelope rotation, and wave-induced N-enrichment in the SPB star zeta Cassiopeiae
Briquet, Maryline ULg; Neiner, C.; Petit, P. et al

in Astronomy and Astrophysics (2016), 587

Aims. The main-sequence B-type star zeta Cassiopeiae is known as a N-rich star with a magnetic field discovered with the Musicos spectropolarimeter. We model the magnetic field of the star by means of 82 ... [more ▼]

Aims. The main-sequence B-type star zeta Cassiopeiae is known as a N-rich star with a magnetic field discovered with the Musicos spectropolarimeter. We model the magnetic field of the star by means of 82 new spectropolarimetric observations of higher precision to investigate the field strength, topology, and effect. Methods. We gathered data with the Narval spectropolarimeter installed at Télescope Bernard Lyot (TBL; Pic du Midi, France) and applied the least-squares deconvolution technique to measure the circular polarisation of the light emitted from zeta Cas. We used a dipole oblique rotator model to determine the field configuration by fitting the longitudinal field measurements and by synthesizing the measured Stokes V profiles. We also made use of the Zeeman-Doppler imaging technique to map the stellar surface and to deduce the difference in rotation rate between the pole and equator. Results. zeta Cas exhibits a polar field strength B_pol of 100-150 G, which is the weakest polar field observed so far in a massive main-sequence star. Surface differential rotation is ruled out by our observations and the field of zeta Cas is strong enough to enforce rigid internal rotation in the radiative zone according to theory. Thus, the star rotates as a solid body in the envelope. Conclusions. We therefore exclude rotationally-induced mixing as the cause of the surface N-enrichment. We discuss that the transport of chemicals from the core to the surface by internal gravity waves is the most plausible explanation for the nitrogen overabundance at the surface of zeta Cas. [less ▲]

Detailed reference viewed: 40 (3 ULg)
Full Text
Peer Reviewed
See detailMeasuring rotation periods of solar-like stars using TIGRE. A study of periodic CaII H+K S-index variability
Hempelmann, A.; Mittag, M.; Gonzalez-Perez, J. N. et al

in Astronomy and Astrophysics (2016), 586

Context. The rotation period of a star is a key parameter both for the stellar dynamo that generates magnetic fields as well as for stellar differential rotation. <BR /> Aims: We present the results from ... [more ▼]

Context. The rotation period of a star is a key parameter both for the stellar dynamo that generates magnetic fields as well as for stellar differential rotation. <BR /> Aims: We present the results from the first year of monitoring a sample of solar-like stars by the TIGRE facility in Guanajuato (Mexico), which will study rotation in solar analogs. <BR /> Methods: TIGRE is an automatically operating 1.2 m telescope equipped with an Échelle spectrograph with a spectral resolution of 20 000, which covers a spectral range of between 3800 and 8800 Å. A main task is the monitoring the stellar activity of cool stars, mainly in the emission cores of the CaII H and K lines. We observed a number of stars with a sampling between 1-3 days over one year. <BR /> Results: A total number of 95 stars were observed between August 1 2013 and July 31 2014, the total number of spectra taken for this program was appoximately 2700. For almost a third of the sample stars the number of observations was rather low (less than 20), mainly because of bad weather. Fifty-four stars show a periodic signal but often with low significance. Only 24 stars exhibit a significant period. We interpret these signals as stellar rotation. For about half of them the rotation periods were already previously known, in which case our period measurements are usually in good agreement with the literature values. Besides the periodic signals, trends are frequently observed in the time series. <BR /> Conclusions: TIGRE is obviously able to detect stellar rotation periods in the CaII H+K emission cores when the time series contains a sufficient number of data points. However, this is frequently not achievable during the wet summer season in Guanajuato. Hence, future estimates of rotation periods will concentrate on stars that are observable during the winter season from October until April. [less ▲]

Detailed reference viewed: 21 (2 ULg)
Full Text
Peer Reviewed
See detailThe α CrB binary system: A new radial velocity curve, apsidal motion, and the alignment of rotation and orbit axes
Schmitt, J. H. M. M.; Schröder, K.-P.; Rauw, Gregor ULg et al

in Astronomy and Astrophysics (2016), 586

We present a new radial velocity curve for the two components of the eclipsing spectroscopic binary α CrB. This binary consists of two main-sequence stars of types A and G in a 17.3599-day orbit ... [more ▼]

We present a new radial velocity curve for the two components of the eclipsing spectroscopic binary α CrB. This binary consists of two main-sequence stars of types A and G in a 17.3599-day orbit, according to the data from our robotic TIGRE facility that is located in Guanajuato, Mexico. We used a high-resolution solar spectrum to determine the radial velocities of the weak secondary component by cross-correlation and wavelength referencing with telluric lines for the strongly rotationally broadened primary lines (v sin(i) = 138 km s[SUP]-1[/SUP]) to obtain radial velocities with an accuracy of a few hundred m/s. We combined our new RV data with older measurements, dating back to 1908 in the case of the primary, to search for evidence of apsidal motion. We find an apsidal motion period between 6600 and 10 600 yr. This value is consistent with the available data for both the primary and secondary and is also consistent with the assumption that the system has aligned orbit and rotation axes. [less ▲]

Detailed reference viewed: 24 (6 ULg)
Full Text
Peer Reviewed
See detailHot Jupiters with relatives: discovery of additional planets in orbit around WASP-41 and WASP-47
Neveu-VanMalle, M.; Queloz, D.; Anderson, D. R. et al

in Astronomy and Astrophysics (2016), 586

We report the discovery of two additional planetary companions to WASP-41 and WASP-47. WASP-41 c is a planet of minimum mass 3.18 $\pm$ 0.20 M$_{\rm Jup}$ and eccentricity 0.29 $\pm$ 0.02, and it orbits ... [more ▼]

We report the discovery of two additional planetary companions to WASP-41 and WASP-47. WASP-41 c is a planet of minimum mass 3.18 $\pm$ 0.20 M$_{\rm Jup}$ and eccentricity 0.29 $\pm$ 0.02, and it orbits in 421 $\pm$ 2 days. WASP-47 c is a planet of minimum mass 1.24 $\pm$ 0.22 M$_{\rm Jup}$ and eccentricity 0.13 $\pm$ 0.10, and it orbits in 572 $\pm$ 7 days. Unlike most of the planetary systems that include a hot Jupiter, these two systems with a hot Jupiter have a long-period planet located at only $\sim$1 au from their host star. WASP-41 is a rather young star known to be chromospherically active. To differentiate its magnetic cycle from the radial velocity effect induced by the second planet, we used the emission in the H$\alpha$ line and find this indicator well suited to detecting the stellar activity pattern and the magnetic cycle. The analysis of the Rossiter-McLaughlin effect induced by WASP-41 b suggests that the planet could be misaligned, though an aligned orbit cannot be excluded. WASP-47 has recently been found to host two additional transiting super Earths. With such an unprecedented architecture, the WASP-47 system will be very important for understanding planetary migration. [less ▲]

Detailed reference viewed: 49 (4 ULg)
Full Text
Peer Reviewed
See detailCOSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses. XV. Assessing the achievability and precision of time-delay measurements
Bonvin, V.; Tewes, M.; Courbin, F. et al

in Astronomy and Astrophysics (2016), 585

COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed quasars aimed at implementing Refsdal's time-delay method to measure cosmological parameters, in particular H[SUB]0[/SUB]. Given ... [more ▼]

COSMOGRAIL is a long-term photometric monitoring of gravitationally lensed quasars aimed at implementing Refsdal's time-delay method to measure cosmological parameters, in particular H[SUB]0[/SUB]. Given the long and well sampled light curves of strongly lensed quasars, time-delay measurements require numerical techniques whose quality must be assessed. To this end, and also in view of future monitoring programs or surveys such as the LSST, a blind signal processing competition named Time Delay Challenge 1 (TDC1) was held in 2014. The aim of the present paper, which is based on the simulated light curves from the TDC1, is double. First, we test the performance of the time-delay measurement techniques currently used in COSMOGRAIL. Second, we analyse the quantity and quality of the harvest of time delays obtained from the TDC1 simulations. To achieve these goals, we first discover time delays through a careful inspection of the light curves via a dedicated visual interface. Our measurement algorithms can then be applied to the data in an automated way. We show that our techniques have no significant biases, and yield adequate uncertainty estimates resulting in reduced χ[SUP]2[/SUP] values between 0.5 and 1.0. We provide estimates for the number and precision of time-delay measurements that can be expected from future time-delay monitoring campaigns as a function of the photometric signal-to-noise ratio and of the true time delay. We make our blind measurements on the TDC1 data publicly available. [less ▲]

Detailed reference viewed: 18 (2 ULg)
Full Text
Peer Reviewed
See detailAmplitude and frequency variations of oscillation modes in the pulsating DB white dwarf star KIC~08626021. The likely signature of nonlinear resonant mode coupling
Zong, W.; Charpinet, S.; Vauclair, G. et al

in Astronomy and Astrophysics (2016), 585

Context. The signatures of nonlinear effects affecting stellar oscillations are difficult to observe from ground observatories because of the lack of continuous high-precision photometric data spanning ... [more ▼]

Context. The signatures of nonlinear effects affecting stellar oscillations are difficult to observe from ground observatories because of the lack of continuous high-precision photometric data spanning extended enough time baselines. The unprecedented photometric quality and coverage provided by the Kepler spacecraft offers new opportunities to search for these phenomena. Aims: We use the Kepler data accumulated on the pulsating DB white dwarf KIC 08626021 to explore in detail the stability of its oscillation modes, searching, in particular, for evidence of nonlinear behaviors. Methods: We analyze nearly two years of uninterrupted short-cadence data, concentrating on identified triplets that are caused by stellar rotation and that show intriguing behaviors during the course of the observations. Results: We find clear signatures of nonlinear effects that could be attributed to resonant mode coupling mechanisms. These couplings occur between the components of the triplets and can induce different types of behaviors. We first notice that a structure at 3681 μHz, identified as a triplet in previous published studies, is in fact forming a doublet, with the third component being an independent mode. We find that a triplet at 4310 μHz and this doublet at 3681 μHz (most likely the two visible components of an incomplete triplet) have clear periodic frequency and amplitude modulations, which are typical of the so-called intermediate regime of the resonance, with timescales consistent with theoretical expectations. Another triplet at 5073 μHz is likely in a narrow transitory regime in which the amplitudes are modulated while the frequencies are locked. Using nonadiabatic pulsation calculations, based on a model representative of KIC 08626021 to evaluate the linear growth rates of the modes in the triplets, we also provide quantitative information that could be useful for future comparisons with numerical solutions of the amplitude equations. Conclusions: The observed modulations are the clearest hints of nonlinear resonant couplings occurring in white dwarf stars identified so far. These should resonate as a warning to projects that aim at measuring the evolutionary cooling rate of KIC 08626021, and of white dwarf stars in general. Nonlinear modulations of the frequencies can potentially jeopardize any attempt to measure such rates reliably, unless they can be corrected beforehand. These results should motivate further theoretical work to develop the nonlinear stellar pulsation theory. [less ▲]

Detailed reference viewed: 31 (3 ULg)
Full Text
Peer Reviewed
See detailThree irradiated and bloated hot Jupiters:. WASP-76b, WASP-82b, and WASP-90b
West, R. G.; Hellier, C.; Almenara, J.-M. et al

in Astronomy and Astrophysics (2016), 585

We report on three new transiting hot Jupiter planets, discovered from the WASP surveys, which we combine with radial velocities from OHP/SOPHIE and Euler/CORALIE and photometry from Euler and TRAPPIST ... [more ▼]

We report on three new transiting hot Jupiter planets, discovered from the WASP surveys, which we combine with radial velocities from OHP/SOPHIE and Euler/CORALIE and photometry from Euler and TRAPPIST. The planets WASP-76b, WASP-82b, and WASP-90b are all inflated, with radii of 1.7-1.8 R[SUB]Jup[/SUB]. All three orbit hot stars, of type F5-F7, with orbits of 1.8-3.9 d, and all three stars have evolved, post-main-sequence radii (1.7-2.2 R[SUB]⊙[/SUB]). Thus the three planets fit a known trend of hot Jupiters that receive high levels of irradiation being highly inflated. We caution, though, about the presence of a selection effect, in that non-inflated planets around ~2 R[SUB]⊙[/SUB] post-MS stars can often produce transits too shallow to be detected by the ground-based surveys that have found the majority of transiting hot Jupiters. Tables of the photometry and radial velocity are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A126">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/585/A126</A> [less ▲]

Detailed reference viewed: 26 (2 ULg)