Radial velocity surveys have revealed up to now about 115 extra-solar planets, among which a few multi-planetary systems. The discovered planets present a wide variety of orbital elements and masses, which are raising many problems and questions regarding the processes involved in their formation. The statistical analysis of the distributions of orbital elements, planetary masses, and relations between these, is however already giving some strong constraints on the formation of the planetary systems. Furthermore, the study of the planet host stars has revealed the crucial role of the stellar metallicity on the giant planet formation. In this paper we will review the current status of the research on this subject.

I review some possible processes by which planets and brown dwarfs can influence the evolution of their parent evolved stars. As sunlike stars evolve on the red giant branch (RGB) and then on the asymptotic giant branch (AGB), they will interact with their close planets (if exist). The interaction starts with tidal interaction: this will lead the planets to deposit most of their angular momentum to the envelope of the giant, and then spiral-in to the envelope. (Too many papers dealing with close planets [less than about 3-6 AU] around evolved stars neglect tidal interaction, hence their results are questionable.) They may spin-up their parent stars by up to several orders of magnitude. The interaction of substellar objects with evolved star may enhance the mass loss rate, mainly in the equatorial plane. Possible outcomes are: (i) Planetary systems interacting with their parent AGB star may lead to the formation of moderate elliptical planetary nebulae. (ii) RGB stars which lose more mass turn to bluer horizontal branch (HB) stars. Therefore, planets may explain the formation of blue HB stars. This may explain the presence of many blue HB stars in many globular clusters (the planets be the second parameter), and some hot HB stars in the galaxy (sdB stars). (The 8.3 days use of the Hubble Space Telescope in search of planets in a globular clusters with no blue HB stars was a wrong move.) (iii) Most known stars with planets will not form planetary nebulae, because they will lose most of their envelope already on the RGB.

The heavily cratered face of Mercury and the Moon bears mute testimony to the flux of smaller objects that bombarded the inner solar system in the first billion years after the sun formed. A significant fraction of these bodies likely struck the sun, slightly altering its surface abundances of heavy elements. Stellar pollution of this sort can be detected by looking at metallicities of carefully selected populations of stars of varying mass, e.g., in moderate age clusters, by searching for specific patterns in relative abundances in individual stars, or by looking for isotopic anomalies such as 6Li. I describe the current state of such studies.

Extensive spectroscopic studies of stars with and without planets have concluded that stars hosting planets are significantly more metal-rich than those without planets. More subtle trends of different chemical elements begin to appear as the number of detected extrasolar planetary systems continues to grow. I review our current knowledge concerning the observed abundance trends of various chemical elements in stars with exoplanets and their possible implications.

Many of the newly discovered exoplanets are gas giants in close proximity to their parent stars. Therefore, they raise tides on their host stars, and (if similar to Jupiter) will likely have substantial magnetospheres which can interact with stellar magnetic field. Both tidal and magnetospheric interactions can enhance stellar activity levels. An initial search for such planet-induced activity using the Ca ii IR triplet found no clear signal, but recently a more sensitive study using the Ca ii H and K lines has uncovered evidence for planet-enhanced emission on HD 179949, and hints of it in other systems. The phase dependence of the enhanced emission for HD 179949 suggests a magnetospheric interaction. We discuss a simple model of this interaction, the implications of this possible detection for diagnosing exoplanetary magnetospheres, and future observations.

I present a review of observational efforts to study known extrasolar planets by methods that are complementary to the radial velocity technique. I describe the current state of attempts to detect and characterize such planets by astrometry, by reflected light, by thermal emission, by transit photometry, by atmospheric transmission spectroscopy, by planet-induced chromospheric activity, and by long-wavelength radio emission. With a few exceptions, these efforts have yielded only upper limits. Nonetheless, the diversity and vivacity of these pursuits has rapidly pushed many of these techniques into the realm where realistic models of the planets and their atmospheres can now be confronted.

As a planet eclipses its parent star, a dark starspot may be occulted, causing a detectable variation in the light curve. This work describes how features on the surface of a solar-like star can be studied by using planetary transits. Images of the Sun were used in order to simulate such transits, with the planet being modeled as a dark disk at various positions along its orbit. From modeling of these transits it might be possible to infer the physical properties of the spots, such as size, intensity, position, and temperature. Recent transits observations for HD 209458 were used as tests to the model. The results yield that the limb darkening of HD 209458 is not like that of the Sun, but rather follows a quadratic function. The dark features studied have radii varying between 3 — 6 104 km, and probably represent a group of spots, namely an active region. As for the temperature, these spots are hotter than sunspots with a temperature range of 4900-5500 K.

The chemistry of circumstellar disks around young (a few 10 Myr) solar-type stars is mainly driven by the strong UV radiation field of the central star. As a starting point for a detailed UV radiation field, the rocket and satellite observations of the solar chromosphere are used and scaled according to the time-dependent behaviour of stellar activity. The disk chemistry as well as dust and gas temperatures are then derived self-consistently from the model. The results of these calculations can be used for the identification of the most promising gas tracers as well as for the interpretation of present and future observations.

Terrestrial planets in close orbits around magnetic white dwarf stars can be electron-cyclotron maser sources, by analogy to planetary radio emissions generated from the electrodynamic interaction between Jupiter and the Galilean moons. We present predictions of the radio flux densities from white-dwarf/terrestrial-planet systems and discuss a scenario for the formation of these systems.

Astrometric, kinematic, spectroscopic and internal stellar structure data of 59 out of 102, extra-solar planet stars (thereafter ESPs), as yet discovered, are herewith discussed. The remaining 43 have been discarded, because they are not yet subjected to detailed spectroscopic analyses. The assembling of true physical parameters of ESPs has been made with the help of the Hipparcos and the [Fe/H] Catalogues. The retained 59 ESPs, could be divided into three sub-samples: midly metal poor, metal normal and metal enriched ESPs. Three observational (logTeff, Mbol) diagrams for each of the metallicity groups have been constructed and interpreted with the help of theoretical HR diagrams, computed for metal-poor, metal-normal, and metal-rich internal structure models. The age of 47 evolved ESPs of the sample has been estimated from the relevant isochrones. Even if the age difference between some of the ESPs is great, (from 1 to >12 Gyr) stars as young as the Hyades (670 Myr) have not been found. ESPs are biased towards metallicities higher than solar. In this sample the number of ESPs with metallicity [Fe/H]>0 is 2.4 times the number of ESPs with [Fe/H] < 0, whereas the proportion is roughly inverted in a sample of non ESPs.

We report preliminary results of a radial velocity study of the old open cluster NGC 752 using an ensemble mean approach with Hydra multi-fiber spectroscopy on the 3.5-m WIYN telescope. The goal is to detect the higher amplitude extra-solar planetary systems and brown dwarf binaries that might reside in the cluster. The oscillation modes of mid-F stars at the redward edge of the instability strip can also be observed. The observation of NGC 752 is the first step in an ongoing study of a variety of clusters with different ages and metallicities.

Here we present a short progress report of a comprehensive search for variability in the globular cluster 47 Tucanae. Using the MSSSO 40” telescope and a combined V+R filter, we are searching for variability across a 52×52' field centered on the cluster. The main aim is to search for transiting ‘Hot Jupiter’ planets in this cluster, the results of which are still being produced, but a natural side product is a deep catalogue of variable stars within the cluster field. The experiment samples the whole of the cluster (except the inner 5'), thus probing the uncrowded outer regions where the stellar densities are lower, increasing the prospects for the survivability of planetary systems. Half of the currently identified variable stars are new discoveries. We have data for 36,000 stars with masses similar to that of the Sun for the main transit search.

The connection between orbital period variation and magnetic activity cyclic behaviour in close binaries with late-type components is addressed by discussing recent observational studies of Algols, RS CVn's, W UMa's and CVs. A theoretical model based on the Applegate's mechanism seems capable of explaining the observed orbital period modulation in terms of cyclic changes of a gravitational quadrupole moment induced by a magnetic activity cycle affecting one of the binary components. In such a case, the study of orbital period modulations offers a promising tool to investigate hydromagnetic dynamos operating in the interior of active stars, in particular, to address the fundamental question of the interaction between rotation and magnetic fields in nonlinear dynamo regimes. Moreover, interesting applications to planetary systems with a magnetically active central star are discussed.

We report on the results of a multi-wavelength program (X-rays to the near IR) of solar analogs with ages covering ∼0.1—9 Gyr. The chief science goals are to study the solar magnetic dynamo and to determine the radiative and magnetic properties of the Sun during its evolution across the main sequence. The present paper focuses on the latter goal, which has the ultimate purpose of constructing spectral irradiance tables to be used to study and model planetary atmospheres. The results obtained thus far indicate that the young Sun was extremely active, with large flares, massive winds, and high-energy emissions up to 1000 times stronger than presently. The strong radiation and particle emissions inferred should have had major influences on the photochemistry and photo-ionization of paleo-planetary atmospheres and also played an important role in the development of primitive life in the Solar System. Some recent results of the effects of the young Sun's enhanced radiation and particle emissions on the early Solar System planets are discussed.

The Space Telescope Imaging Spectrograph (STIS) obtained high resolution echelle spectra of the nearby G2 V star α Centauri A covering the entire 1133—3150 Â region with very high signal/noise. This data set provides what is probably the best approximation to the spectrum of the Sun viewed as a star, because it is a full disk spectrum with 2.6 km s—1 resolution, accurate absolute fluxes, full UV spectral coverage, high S/N, and low scattered light. In the 1140—1670 Â region we identify 671 emission lines from 37 different atoms and ions and the molecules CO and H2. We make a detailed comparison of the solar and α Cen A spectra in terms of line identification, line widths and Doppler shifts, emission measure distributions, and electron densities.

To explain the heating of stellar chromospheres and transition regions, two classes of heating mechanisms have been considered: dissipation of acoustic and magnetic waves generated in stellar convection zones; and dissipation of currents generated by photospheric motions of surface magnetic fields. The focus of this paper is on the wave heating mechanisms and on recent results which demonstrate that theoretical models of stellar chromospheres based on the wave heating can explain the “basal flux” and the observed Ca II emission in most stars but cannot account for the observed Mg II emission in active stars. The obtained results clearly show that the base of stellar chromospheres is heated by acoustic waves, the heating of the middle and upper chromospheric layers is dominated by magnetic waves associated with magnetic flux tubes, and that other non-wave heating mechanisms are required to explain the structure of the highest layers of stellar chromospheres and transition regions.

Waves at all scales, ranging in wavelength from the size of a loop (fraction of a solar radius) down to the gyroradii of coronal ions (about hundred meters), are believed to play a key role in the transport of mechanical energy from the chromosphere to the Sun's corona and wind, and through the dissipation of wave energy in the heating and sustaining of the solar corona. A concise review of new observations and theories of waves in the magnetically confined (loops) as well as open (holes) corona is given. Evidence obtained from spectroscopy of lines emitted by coronal ions points to cyclotron resonance absorption as a possible cause of the observed emission-line broadenings. Novel remote-sensing solar observations reveal low-frequency loop oscillations as expected from MHD theory, which appear to be excited by magnetic activity in connection with flares and to be strongly damped. Kinetic models of the corona indicate the importance of wave-particle interactions that hold the key to understand ion acceleration and heating by high-frequency waves.

New observational signatures of the heating process(es) have been revealed by space missions including SoHO, TRACE, Yohkoh, and RHESSI. Evidences for heating in the quiet corona, active region loops, and the solar wind are different and must be distinguished. Prime indications come from line broadening and waves, the distribution of temperature and radiation loss in relation to height, the correlation of magnetic flux and brightness, nanoflares and other fluctuations. This review concentrates on microevents observed at coronal temperatures. The reported nanoflares in quiet regions are about 2 orders of magnitude smaller than microflares reported in active regions and exhibit less radio emission. To estimate the impact of these microevents on the corona, the effects from a localized energy release must be considered, regardless of the energy source (reconnection or waves). In particular, the coupling with the chromosphere, i.e. the back-reaction of the chromosphere on coronal energy release, has an important effect on the corona. A necessary requirement for the heating process(es) is to deposit most of the heat in the low corona, but to heat also the upper corona to even higher temperature. Finally, the heating process must be able to account for the coronae of more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun.

We correlate the evolution of the mean X-ray flux, emission measure and temperature (Yohkoh SXT & BCS) with the magnetic flux density (SOHO/MDI) in active region NOAA 7978 from its birth throughout its decay, for five solar rotations. We show that these plasma parameters together with other quantities deduced from them, such as the density and the pressure, follow power-law relationships with the mean magnetic flux density (B). We derive the dependence of the mean coronal heating rate on the magnetic flux density. We use the obtained scaling laws of coronal loops in thermal equilibrium to derive observational estimates of the scaling of the coronal heating with B. These results are used to test the validity of coronal heating models. We find that models based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona. This confirms, with smaller error bars, previous results obtained for individual coronal loops, as well as for the global coronal emission of the Sun and cool stars.

We study the relationship between EUV spectral line intensities and the photospheric magnetic field in solar active regions, using magnetograms from SOHO-MDI and EUV spectra of the Fe XVI 360.8 Â line (2 × 106 K) and the O V 629.7 A line (220,000 K) from the Coronal Diagnostic Spectrometer on SOHO, recorded for several active regions. We overlay and compare spatial patterns of the O V emission and the magnetic flux concentrations, with a 4″ x 4″ spatial resolution, and search for a relationship between the local O V line intensity and the photospheric magnetic flux density in each active region. While this dependence exhibits a certain amount of scatter, it can be represented by a power law fit. The average power index from all regions is 0.7 ± 0.2. Applying static loop models, we derive the dependence of the heating rate on the magnetic flux density, Eh ∝ B0.8, and compare it to the dependence predicted by the coronal heating models.