Since the discovery of the transiting super-Earth CoRoT-7b, several investigations have yielded different results for the number and masses of planets present in the system, mainly owing to the star's high level of activity. We re-observed CoRoT-7 in January 2012 with both HARPS and CoRoT, so that we now have the benefit of simultaneous radial-velocity and photometric data. This allows us to use the offtransit variations in the star's light curve to estimate the radial-velocity variations induced by the suppression of convective blueshift and the flux blocked by starspots. To account for activity-related effects in the radial-velocities which do not have a photometric signature, we also include an additional activity term in the radial-velocity model, which we treat as a Gaussian process with the same covariance properties (and hence the same frequency structure) as the light curve. Our 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 measure the masses of planets b and c to be 4.73 ± 0.95 M ⊕ and 13.56 ± 1.08 M ⊕ , respectively. The density of CoRoT-7b is (6.61 ± 1.72)(R p /1.58 R ⊕ ) −3 g.cm −3 , which is compatible with a rocky composition. We search for evidence of an additional planet d, identified by previous authors with a period close to 9 days. We are not able to confirm the existence of a planet with this orbital period, which is close to the second harmonic of the stellar rotation at ∼ 7.9 days. Using Bayesian model selection we find that a model with two planets plus activity-induced variations is most favoured.

The Isaac Newton Telescope (INT) Photometric Hα Survey of the Northern Galactic Plane (IPHAS) is a 1800‐deg2 CCD survey of the northern Milky Way spanning the latitude range −5° < b < + 5° and reaching down to r′≃ 20 (10σ). Representative observations and an assessment of point‐source data from IPHAS, now underway, are presented. The data obtained are Wide Field Camera images in the Hα narrow‐band, and Sloan r′ and i′ broad‐band filters. We simulate IPHAS (r′−Hα, r′−i′) point‐source colours using a spectrophotometric library of stellar spectra and available filter transmission profiles: this defines the expected colour properties of (i) solar metallicity stars, without Hα emission, and (ii) emission‐line stars. Comparisons with observations of fields in Aquila show that the simulations of normal star colours reproduce the observations well for all spectral types earlier than M. A further comparison between colours synthesized from long‐slit flux‐calibrated spectra and IPHAS photometry for six objects in a Taurus field confirms the reliability of the pipeline calibration. Spectroscopic follow‐up of a field in Cepheus shows that sources lying above the main stellar locus in the (r′− Hα, r′−i′) plane are confirmed to be emission‐line objects with very few failures. In this same field, examples of Hα deficit objects (a white dwarf and a carbon star) are shown to be readily distinguished by their IPHAS colours. The role IPHAS can play in studies of spatially resolved northern Galactic nebulae is discussed briefly and illustrated by a continuum‐subtracted mosaic image of Shajn 147 (a supernova remnant, 3° in diameter). The final catalogue of IPHAS point sources will contain photometry on about 80 million objects. Used on its own, or in combination with near‐infrared photometric catalogues, IPHAS is a major resource for the study of stellar populations making up the disc of the Milky Way. The eventual yield of new northern emission‐line objects from IPHAS is likely to be an order of magnitude increase on the number already known.

Abstract.A model of solar irradiance variations is presented which is based on the assumption that solar surface magnetism is responsible for all total irradiance changes on time scales of days to years. A time series of daily magnetograms and empirical models of the thermal structure of magnetic features (sunspots, faculae) are combined to reconstruct total (and spectral) irradiance from 1996 to 2002. Comparisons with observational data reveal an excellent correspondence, although the model only contains a single free parameter. This provides strong support for the hypothesis that solar irradiance variations are caused by changes in the amount and distribution of magnetic flux at the solar surface.

The lack of long and reliable time series of solar spectral irradiance (SSI) measurements makes an accurate quantification of solar contributions to recent climate change difficult. Whereas earlier SSI observations and models provided a qualitatively consistent picture of the SSI variability, recent measurements by the SORCE (SOlar Radiation and Climate Experiment) satellite suggest a significantly stronger variability in the ultraviolet (UV) spectral range and changes in the visible and near-infrared (NIR) bands in anti-phase with the solar cycle. A number of recent chemistry-climate model (CCM) simulations have shown that this might have significant implications on the Earth's atmosphere. Motivated by these results, we summarize here our current knowledge of SSI variability and its impact on Earth's climate.

We present a detailed overview of existing SSI measurements and provide thorough comparison of models available to date. SSI changes influence the Earth's atmosphere, both directly, through changes in shortwave (SW) heating and therefore, temperature and ozone distributions in the stratosphere, and indirectly, through dynamical feedbacks. We investigate these direct and indirect effects using several state-of-the art CCM simulations forced with measured and modelled SSI changes. A unique asset of this study is the use of a common comprehensive approach for an issue that is usually addressed separately by different communities.

We show that the SORCE measurements are difficult to reconcile with earlier observations and with SSI models. Of the five SSI models discussed here, specifically NRLSSI (Naval Research Laboratory Solar Spectral Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar Radiation Physical Modelling), and OAR (Osservatorio Astronomico di Roma), only one shows a behaviour of the UV and visible irradiance qualitatively resembling that of the recent SORCE measurements. However, the integral of the SSI computed with this model over the entire spectral range does not reproduce the measured cyclical changes of the total solar irradiance, which is an essential requisite for realistic evaluations of solar effects on the Earth's climate in CCMs.

We show that within the range provided by the recent SSI observations and semi-empirical models discussed here, the NRLSSI model and SORCE observations represent the lower and upper limits in the magnitude of the SSI solar cycle variation.

The results of the CCM simulations, forced with the SSI solar cycle variations estimated from the NRLSSI model and from SORCE measurements, show that the direct solar response in the stratosphere is larger for the SORCE than for the NRLSSI data. Correspondingly, larger UV forcing also leads to a larger surface response.

Finally, we discuss the reliability of the available data and we propose additional coordinated work, first to build composite SSI data sets out of scattered observations and to r...

The Sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radial-velocity (RV) variability. We present HARPS observations of sunlight scattered off the bright asteroid 4/Vesta, from which we deduced the Sun's activity-driven RV variations. In parallel, the HMI instrument onboard the Solar Dynamics Observatory provided us with simultaneous high spatial resolution magnetograms, Dopplergrams, and continuum images of the Sun in the Fe I 6173Å line. We determine the RV modulation arising from the suppression of granular blueshift in magnetised regions and the flux imbalance induced by dark spots and bright faculae. The rms velocity amplitudes of these contributions are 2.40 m s −1 and 0.41 m s −1 , respectively, which confirms that the inhibition of convection is the dominant source of activity-induced RV variations at play, in accordance with previous studies. We find the Doppler imbalances of spot and plage regions to be only weakly anticorrelated. Lightcurves can thus only give incomplete predictions of convective blueshift suppression. We must instead seek proxies that track the plage coverage on the visible stellar hemisphere directly. The chromospheric flux index R HK derived from the HARPS spectra performs poorly in this respect, possibly because of the differences in limb brightening/darkening in the chromosphere and photosphere. We also find that the activity-driven RV variations of the Sun are strongly correlated with its full-disc magnetic flux density, which may become a useful proxy for activity-related RV noise.Based on observations made with the HARPS instrument on the 3.6 m telescope under the program ID 088.C-0323 at Cerro La Silla (Chile), and the Helioseismic and Magnetic Imager onboard the Solar Dynamics Observatory. The HARPS observations, together with tables for the results presented in this paper are available in electronic format at: http://dx.doi.org/10.17630/bb43e6a3-72e0-464c-9fdd-fbe5d3e56a09. The SDO/HMI images can be downloaded from:

18.03.15 KB. Ok to add accepted version to spira

Context. The study of variations in total solar irradiance (TSI) is important for understanding how the Sun affects the Earth's climate. Aims. Full-disk continuum images and magnetograms are now available for three full solar cycles. We investigate how modelled TSI compares with direct observations by building a consistent modelled TSI dataset. The model, based only on changes in the photospheric magnetic flux can then be tested on rotational, cyclical and secular timescales. Methods. We use Kitt Peak and SoHO/MDI continuum images and magnetograms in the SATIRE-S model to reconstruct TSI over cycles 21-23. To maximise independence from TSI composites, SORCE/TIM TSI data are used to fix the one free parameter of the model. We compare and combine the separate data sources for the model to estimate an uncertainty on the reconstruction and prevent any additional free parameters entering the model. Results. The reconstruction supports the PMOD composite as being the best historical record of TSI observations, although on timescales of the solar rotation the IRMB composite provides somewhat better agreement. Further to this, the model is able to account for 92% of TSI variations from 1978 to 2009 in the PMOD composite and over 96% during cycle 23. The reconstruction also displays an inter-cycle, secular decline of 0.20 +0.12 −0.09 W m −2 between cycle 23 minima, in agreement with the PMOD composite. Conclusions. SATIRE-S is able to recreate TSI observations on all timescales of a day and longer over 31 years from 1978. This is strong evidence that changes in photospheric magnetic flux alone are responsible for almost all solar irradiance variations over the last three solar cycles.

Context. The Sun and stars with low magnetic activity levels become photometrically brighter when their activity increases. Magnetically more active stars display the opposite behavior and become fainter when their activity increases. Aims. We reproduce the observed photometric trends in stellar variations with a model that treats stars as hypothetical suns with coverage by magnetic features different from that of the Sun. Methods. The model attributes the variability of stellar spectra to the imbalance between the contributions from different components of the solar atmosphere, such as dark starspots and bright faculae. A stellar spectrum is calculated from spectra of the individual components by weighting them with corresponding disk-area coverages. The latter are obtained by extrapolating the solar dependences of spot and facular disk-area coverages on chromospheric activity to stars with different levels of mean chromospheric activity. Results. We find that the contribution by starspots to the variability increases faster with chromospheric activity than the facular contribution. This causes the transition from faculae-dominated variability and direct activity-brightness correlation to spot-dominated variability and inverse activity-brightness correlation with increasing chromospheric activity level. We show that the regime of the variability also depends on the angle between the stellar rotation axis and the line-of-sight and on the latitudinal distribution of active regions on the stellar surface. Our model can be used as a tool for extrapolating the observed photometric variability of the Sun to Sun-like stars at different activity levels, which makes a direct comparison between solar and stellar irradiance data possible.