ALBERT

Description: WASP-80b is a missing link in the study of exoatmospheres. It falls between the warm Neptunes and the hot Jupiters and is amenable for characterization, thanks to its host star's properties. We observed the planet through transit and during occultation with Warm Spitzer . Combining our mid-infrared transits with optical time series, we find that the planet presents a transmission spectrum indistinguishable from a horizontal line. In emission, WASP-80b is the intrinsically faintest planet whose dayside flux has been detected in both the 3.6 and 4.5 μm Spitzer channels. The depths of the occultations reveal that WASP-80b is as bright and as red as a T4 dwarf, but that its temperature is cooler. If planets go through the equivalent of an L–T transition, our results would imply that this happens at cooler temperatures than for brown dwarfs. Placing WASP-80b's dayside into a colour–magnitude diagram, it falls exactly at the junction between a blackbody model and the T-dwarf sequence; we cannot discern which of those two interpretations is the more likely. WASP-80b's flux density is as low as GJ 436b at 3.6 μm; the planet's dayside is also fainter, but bluer than HD 189733Ab's nightside (in the [3.6] and [4.5] Spitzer bands). Flux measurements on other planets with similar equilibrium temperatures are required to establish whether irradiated gas giants, such as brown dwarfs, transition between two spectral classes. An eventual detection of methane absorption in transmission would also help lift that degeneracy. We obtained a second series of high-resolution spectra during transit, using HARPS. We reanalyse the Rossiter–McLaughlin effect. The data now favour an aligned orbital solution and a stellar rotation nearly three times slower than stellar line broadening implies. A contribution to stellar line broadening, maybe macroturbulence, is likely to have been underestimated for cool stars, whose rotations have therefore been systematically overestimated.

Description: 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 modeling 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  Boo types. The distribution of the projected rotational velocity, v sin i , is typical for A and F stars and ranges from 8 to about 280 km s –1 , with a mean of 134 km s –1 .

Description: We report the identification of 61.45 d –1 (711.2 μHz) oscillations, with amplitudes of 62.6 μmag, in KIC 4768731 (HD 225914) using Kepler photometry. This relatively bright ( V  = 9.17) chemically peculiar star with spectral type A5 Vp SrCr(Eu) has previously been found to exhibit rotational modulation with a period of 5.21 d. Fourier analysis reveals a simple dipole pulsator with an amplitude that has remained stable over a 4-yr time span, but with a frequency that is variable. Analysis of high-resolution spectra yields stellar parameters of T eff  = 8100 ± 200 K, log g  = 4.0 ± 0.2, [Fe/H] = +0.31 ± 0.24 and v sin i  = 14.8 ± 1.6 km s –1 . Line profile variations caused by rotation are also evident. Lines of Sr, Cr, Eu, Mg and Si are strongest when the star is brightest, while Y and Ba vary in antiphase with the other elements. The abundances of rare earth elements are only modestly enhanced compared to other roAp stars of similar T eff and log g . Radial velocities in the literature suggest a significant change over the past 30 yr, but the radial velocities presented here show no significant change over a period of 4 yr.

Description: We investigate the light variations of 15 Am stars using four years of high-precision photometry from the Kepler spacecraft and an additional 14 Am stars from the K2 Campaign 0 field. We find that most of the Am stars in the Kepler field have light curves characteristic of rotational modulation due to star-spots. Of the 29 Am stars observed, 12 are Scuti variables and one is a Doradus star. One star is an eclipsing binary and another was found to be a binary from time delay measurements. Two Am stars show evidence for flares which are unlikely to be due to a cool companion. The fact that 10 out of 29 Am stars are rotational variables and that some may even flare strongly suggests that Am stars possess significant magnetic fields. This is contrary to the current understanding that the enhanced metallicity in these stars is due to diffusion in the absence of a magnetic field. The fact that so many stars are Scuti variables is also at odds with the prediction of diffusion theory. We suggest that a viable alternative is that the metal enhancement could arise from accretion.

Description: We identify stars in the  Sct instability strip that do not pulsate in p modes at the 50-μmag limit, using Kepler data. Spectral classification and abundance analyses from high-resolution spectroscopy allow us to identify chemically peculiar stars, in which the absence of pulsations is not surprising. The remaining stars are chemically normal, yet they are not  Sct stars. Their lack of observed p modes cannot be explained through any known mechanism. However, they are mostly distributed around the edges of the  Sct instability strip, which allows for the possibility that they actually lie outside the strip once the uncertainties are taken into account. We investigated the possibility that the non-pulsators inside the instability strip could be unresolved binary systems, having components that both lie outside the instability strip. If misinterpreted as single stars, we found that such binaries could generate temperature discrepancies of ~300 K – larger than the spectroscopic uncertainties, and fully consistent with the observations. After these considerations, there remains one chemically normal non-pulsator that lies in the middle of the instability strip. This star is a challenge to pulsation theory. However, its existence as the only known star of its kind indicates that such stars are rare. We conclude that the  Sct instability strip is pure, unless pulsation is shut down by diffusion or another mechanism, which could be interaction with a binary companion.

Description: Algol (β Persei) is the prototypical semidetached eclipsing binary and a hierarchical triple system. From 2006 to 2010 we obtained 121 high-resolution and high signal-to-noise ratio échelle spectra of this object. Spectral disentangling yields the individual spectra of all three stars, and greatly improved elements both the inner and outer orbits. We find masses of M A  = 3.39 ± 0.06 M , M B  = 0.770 ± 0.009 M and M C  = 1.58 ± 0.09 M . The disentangled spectra also give the light ratios between the components in the B and V bands. Atmospheric parameters for the three stars are determined, including detailed elemental abundances for Algol A and Algol C. We find the following effective temperatures: T A  = 12 550 ± 120 K, T B  = 4900 ± 300 K and T C  = 7550 ± 250 K. The projected rotational velocities are v A sin i A  = 50.8 ± 0.8  km s –1 , v B sin i B  = 62 ± 2 km s –1 and v C sin i C  = 12.4 ± 0.6 km s –1 . This is the first measurement of the rotational velocity for Algol B, and confirms that it is synchronous with the orbital motion. The abundance patterns of components A and C are identical to within the measurement errors, and are basically solar. They can be summarized as mean metal abundances: [M/H] A  = –0.03 ± 0.08 and [M/H] C  = 0.04 ± 0.09. A carbon deficiency is confirmed for Algol A, with tentative indications for a slight overabundance of nitrogen. The ratio of their abundances is (C/N) A  = 2.0 ± 0.4, half of the solar value of (C/N)  = 4.0 ± 0.7. The new results derived in this study, including detailed abundances and metallicities, will enable tight constraints on theoretical evolutionary models for this complex system.

Description: We present the discovery by the WASP-South survey of WASP-121 b, a new remarkable short-period transiting hot Jupiter. The planet has a mass of $1.183_{-0.062}^{+0.064}$ M Jup , a radius of 1.865 ± 0.044 R Jup , and transits every $1.274\,9255_{-0.000\,0025}^{+0.000\,0020}$ days an active F6-type main-sequence star ( V = 10.4, $1.353_{-0.079}^{+0.080}$ M , 1.458 ± 0.030 R , T eff = 6460 ± 140 K). A notable property of WASP-121 b is that its orbital semimajor axis is only ~1.15 times larger than its Roche limit, which suggests that the planet is close to tidal disruption. Furthermore, its large size and extreme irradiation (~7.1 10 9  erg s –1 cm –2 ) make it an excellent target for atmospheric studies via secondary eclipse observations. Using the TRAnsiting Planets and PlanetesImals Small Telescope, we indeed detect its emission in the z ' -band at better than ~4, the measured occultation depth being 603 ± 130 ppm. Finally, from a measurement of the Rossiter–McLaughlin effect with the CORALIE spectrograph, we infer a sky-projected spin-orbit angle of $257{^{\circ}_{.}} 8_{-5{^{\circ}_{.}} 5}^{+5{^{\circ}_{.}} 3}$ . This result may suggest a significant misalignment between the spin axis of the host star and the orbital plane of the planet. If confirmed, this high misalignment would favour a migration of the planet involving strong dynamical events with a third body.

Description: We present an analysis of the first Kepler K2 mission observations of a rapidly oscillating Ap (roAp) star, HD 24355 ( V = 9.65). The star was discovered in SuperWASP broad-band photometry with a frequency of 224.31 d –1 (2596.18 μHz; P = 6.4 min) and an amplitude of 1.51 mmag, with later spectroscopic analysis of low-resolution spectra showing HD 24355 to be an A5 Vp SrEu star. The high-precision K2 data allow us to identify 13 rotationally split sidelobes to the main pulsation frequency of HD 24355. This number of sidelobes combined with an unusual rotational phase variation show this star to be the most distorted quadrupole roAp pulsator yet observed. In modelling this star, we are able to reproduce well the amplitude modulation of the pulsation, and find a close match to the unusual phase variations. We show this star to have a pulsation frequency higher than the critical cut-off frequency. This is currently the only roAp star observed with the Kepler spacecraft in short cadence mode that has a photometric amplitude detectable from the ground, thus allowing comparison between the mmag amplitude ground-based targets and the μmag spaced-based discoveries. No further pulsation modes are identified in the K2 data, showing this star to be a single-mode pulsator.

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

Description: We describe seven exoplanets transiting stars of brightness V = 10.1–12.4. WASP-130b is a ‘warm Jupiter’ having an orbital period of 11.6 d around a metal-rich G6 star. Its mass and radius (1.23 ± 0.04 M Jup and 0.89 ± 0.03 R Jup ) support the trend that warm Jupiters have smaller radii than hot Jupiters. WASP-131b is a bloated Saturn-mass planet (0.27 M Jup and 1.22 R Jup ). Its large scaleheight and bright ( V = 10.1) host star make it a good target for atmospheric characterization. WASP-132b (0.41 M Jup and 0.87 R Jup ) is among the least irradiated and coolest of WASP planets, having a 7.1-d orbit around a K4 star. WASP-139b is a ‘super-Neptune’ akin to HATS-7b and HATS-8b, being the lowest mass planet yet found by WASP (0.12 M Jup and 0.80 R Jup ). The metal-rich K0 host star appears to be anomalously dense, akin to HAT-P-11. WASP-140b is a 2.4-M Jup planet in an eccentric ( e = 0.047 ± 0.004) 2.2-d orbit. The planet's radius is large (1.4 R Jup ), but uncertain owing to the grazing transit ( b = 0.93). The 10.4-d rotation period of the K0 host star suggests a young age, and the time-scale for tidal circularization is likely to be the lowest of all known eccentric hot Jupiters. WASP-141b (2.7 M Jup , 1.2 R Jup and P = 3.3 d) and WASP-142b (0.84 M Jup , 1.53 R Jup and P = 2.1 d) are typical hot Jupiters orbiting metal-rich F stars. We show that the period distribution within the hot-Jupiter bulge does not depend on the metallicity of the host star.