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We monitored three transits of the giant gas planet around the nearby K dwarf HD 189733 with the ACS camera on the Hubble Space Telescope. The resulting very-high accuracy lightcurve (signal-to-noise ratio near 15 000 on individual measurements, 35 000 on 10-min averages) allows a direct geometric measurement of the orbital inclination, radius ratio and scale of the system: i= 85.68 ±0.04, $R_{\rm pl}/R_{\rm *}$= 0.1572 ±0.0004, $a/R_{\rm *}$= 8.92 ±0.09. We derive improved values for the stellar and planetary radius, R*= 0.755 ±0.011 $R_\odot$, Rpl= 1.154 ±0.017 RJ, and the transit ephemerides, Ttr= 2453931.12048 ±0.00002 + n$\cdot$2.218581 ±0.000002. The HST data also reveal clear evidence of the planet occulting spots on the surface of the star. At least one large spot complex (>80 000 km) is required to explain the observed flux residuals and their colour evolution. This feature is compatible in amplitude and phase with the variability observed simultaneously from the ground. No evidence for satellites or rings around HD 189733bis seen in the HST lightcurve. This allows us to exlude with a high probability the presence of Earth-sized moons and Saturn-type debris rings around this planet. The timing of the three transits sampled is stable to the level of a few seconds, excluding a massive second planet in outer 2:1 resonance.

Context.To expand the range in the colour–magnitude diagram where asteroseismology can be applied, we organized a photometry campaign to find evidence for solar-like oscillations in giant stars in the globular cluster M 4.

We present new results on five of six known SX Phœnicis stars in the core of the globular cluster 47 Tucanae. We give interpretations of the light curves in the Vand Ibands from 8.3 days of observations with the Hubble Space Telescope near the core of 47 Tuc. The most evolved SX Phe star in the cluster is a double-mode pulsator (V2) and we determine its mass to be $(1.54\pm0.05) M_\odot$from its position in the Hertzsprung-Russell diagram and by comparing observed periods with current theoretical pulsation models. For V14 we do not detect any pulsation signal. For the double-mode pulsators V3, V15, and V16 we cannot give a safe identification of the modes. We also describe the photometric techniques we have used to extract the light curves of stars in the crowded core. Some of the SX Phœnicis are saturated and we demonstrate that even for stars that show signs of a bleeding signal we can obtain a point-to-point accuracy of 1-3% .

Aims. We investigate the origin of a flux increase found during a transit of TrES-1, observed with the HST (Hubble Space Telescope). This feature in the HST light curve cannot be attributed to noise and is supposedly a dark area on the stellar surface of the host star eclipsed by TrES-1 during its transit. We investigate the likelihood of two possible hypotheses for its origin. A starspot or a second transiting planet.Methods. We made use of several transit observations of TrES-1 from space with the HST and from ground with the IAC 80-cm telescope (IAC-80). On the basis of these observations we did a statistical study of flux variations in each of the observed events to investigate whether similar flux increases are present in other parts of the data set.Results. The HST observation presents a single clear flux rise during a transit, whereas the ground observations lead to detecting two such events but with low significance. In the case of having observed a starspot in the HST?data, assuming a central impact between the spot and TrES-1, we would obtain a lower limit for the spot radius of 42?000?km. For this radius the spot temperature would be 4690?K, 560?K lower then the stellar surface of 5250?K. For a putative second transiting planet, we can set a lower limit for its radius at 0.37?RJand for periods of less than 10.5?days, we can set an upper limit at 0.72?RJ.Conclusions. Assuming a conventional interpretation, this HST observation then constitutes the detection of a starspot. Alternatively, this flux rise might also be caused by an additional transiting planet. The true nature of the origin can be revealed if a wavelength dependency of the flux rise can be shown or discarded with higher certainty. Additionally, the presence of a second planet can be detected by radial velocity measurements.

Context.Four open clusters are present in the Kepler field of view and timeseries of nearly a year in length are now available. These timeseries allow us to derive asteroseismic global oscillation parameters of red-giant stars in the three open clusters NGC 6791, NGC 6819 and NGC 6811. From these parameters and effective temperatures, we derive masses, radii and luminosities for the clusters as well as field red giants. Aims.We study the influence of evolution and metallicity on the observed red-giant populations. Methods.The global oscillation parameters are derived using different published methods and the effective temperatures are derived from 2MASS colours. The observational results are compared with BaSTI evolution models.Results.We find that the mass has significant influence on the asteroseismic quantities Δνvs. νmaxrelation, while the influence of metallicity is negligible, under the assumption that the metallicity does not affect the excitation/damping of the oscillations. The positions of the stars in the H-R diagram depend on both mass and metallicity. Furthermore, the stellar masses derived for the field stars are bracketed by those of the cluster stars. Conclusions.Both the mass and metallicity contribute to the observed difference in locations in the H-R diagram of the old metal-rich cluster NGC 6791 and the middle-aged solar-metallicity cluster NGC 6819. For the young cluster NGC 6811, the explanation of the position of the stars in the H-R diagram challenges the assumption of solar metallicity, and this open cluster might have significantly lower metallicity [Fe/H] in the range  − 0.3 to  − 0.7 dex. Also, nearly all the observed field stars seem to be older than NGC 6811 and younger than NGC 6791.

Context.The large number of stars for which uninterrupted high-precision photometric timeseries data are being collected with Kepler and CoRoT initiated the development of automated methods to analyse the stochastically excited oscillations in main-sequence, subgiant and red-giant stars.

Context.Clear power excess in a frequency range typical for solar-type oscillations in red giants has been detected in more than 1000 stars, which have been observed during the first 138 days of the science operation of the NASA Kepler satellite. This sample includes stars in a wide mass and radius range with spectral types G and K, extending in luminosity from the bottom of the giant branch up to high-luminous red giants, including the red bump and clump. The high-precision asteroseismic observations with Kepler provide a perfect source for testing stellar structure and evolutionary models, as well as investigating the stellar population in our Galaxy.