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The early, active history of our Sun is still not fully understood. Observations of the magnetic fields on active young solar-type stars allow us an insight into the early evolution of our Sun. Here we present Doppler and Zeeman–Doppler images of the young late-F star HIP 71933 (HD 129181) at multiple epochs to add to the growing data about the evolution of magnetic cycles in solar-type stars. Spectroscopic data were obtained over seven epochs spanning 10 yr of observations, with two epochs including spectropolarimetric data. The brightness maps at all epochs show a consistent spot activity in a non-uniform ring at a latitude of approximately +60° with no polar spot present in any epoch. The two magnetic field maps taken ∼2 yr apart show a strong poloidal field configuration with most of the poloidal field energy in the dipolar configuration. The magnetic maps show no evidence of a polarity reversal. We were able to measure the differential rotation from one of the seven epochs using the brightness data finding a dΩ of 0.325 ± 0.01 rad d−1. The values for the rotational period and differential rotation found for HIP 71933 are consistent with values found for other late-F or early-G stars. The dominant poloidal features and the limited spots at the pole are unusual for a rapidly rotating star but not unique. [ABSTRACT FROM AUTHOR]

Solar-type stars, which shed angular momentum via magnetized stellar winds, enter the main sequence with a wide range of rotational periods P rot. This initially wide range of rotational periods contracts and has mostly vanished by a stellar age |$t\sim {0.6}\, {\rm Gyr}$|⁠ , after which Solar-type stars spin according to the Skumanich relation |$P_\text{rot}\propto \sqrt{t}$|⁠. Magnetohydrodynamic stellar wind models can improve our understanding of this convergence of rotation periods. We present wind models of 15 young Solar-type stars aged ∼24 Myr to ∼0.13 Gyr. With our previous wind models of stars aged ∼0.26 and ∼0.6 Gyr we obtain 30 consistent three-dimensional wind models of stars mapped with Zeeman–Doppler imaging – the largest such set to date. The models provide good cover of the pre-Skumanich phase of stellar spin-down in terms of rotation, magnetic field, and age. We find the mass-loss rate |$\dot{M}\propto \Phi ^{{0.9\pm 0.1}}$| with a residual spread of ∼150 per cent and the wind angular momentum loss rate |$\dot{J}\propto {}P_\text{rot}^{-1} \Phi ^{1.3\pm 0.2}$| with a residual spread of ∼500 per cent where Φ is the unsigned surface magnetic flux. When comparing different magnetic field scalings for each single star we find a gradual reduction in the power-law exponent with increasing magnetic field strength. [ABSTRACT FROM AUTHOR]

The study of magnetism in stars close to the transition from fossil to dynamo magnetic fields is important for understanding the nature of the stellar dynamo and dynamics of the outer atmosphere. We present surface magnetic maps for two stars that are located on opposite sides of the suspected transition zone: the chemically peculiar late A-star β Coronae Borealis (A9SrEuCr) and the early F-star σ Bootis (F3V). The large-scale magnetic field reconstructed at six epochs for β Coronae Borealis shows a complex fossil magnetic field, which is highly poloidal, and contains almost half the magnetic energy in higher multipoles (ℓ > 1). In contrast, the single epoch magnetic map for σ Bootis contains a simple surface magnetic topology that is mostly poloidal, and predominantly dipolar, and is consistent with observations of other mature late F-stars. [ABSTRACT FROM AUTHOR]

We present wind models of 10 young Solar-type stars in the Hercules-Lyra association and the Coma Berenices cluster aged around ∼0.26 and ∼0.58 Gyr, respectively. Combined with five previously modelled stars in the Hyades cluster, aged ∼0.63 Gyr, we obtain a large atlas of 15 observationally based wind models. We find varied geometries, multi-armed structures in the equatorial plane, and a greater spread in quantities such as the angular momentum loss. In our models, we infer variation of a factor of ∼6 in wind angular momentum loss |$\dot{J}$| and a factor of ∼2 in wind mass-loss |$\dot{M}$| based on magnetic field geometry differences when adjusting for the unsigned surface magnetic flux. We observe a large variation factor of ∼4 in wind pressure for an Earth-like planet; we attribute this to variations in the 'magnetic inclination' of the magnetic dipole axis with respect to the stellar axis of rotation. Within our models, we observe a tight correlation between unsigned open magnetic flux and angular momentum loss. To account for possible underreporting of the observed magnetic field strength we investigate a second series of wind models where the magnetic field has been scaled by a factor of 5. This gives |$\dot{M}\propto B^{0.4}$| and |$\dot{J}\propto B^{1.0}$| as a result of pure magnetic scaling. [ABSTRACT FROM AUTHOR]

The Kepler mission target star KOI-883 is notable in being a low-mass K2V dwarf with moderately fast 8.99-d rotation and hosting a single transiting hot Jupiter in a 2.69-d orbit. This combination thus presents a particular opportunity to study star-spot activity by using the many deep planetary transits apparent in the light curve to map the stellar surface. The data have been analysed using spot modelling and temporal mapping methods we have used for other Kepler host stars, and a search for flares was conducted. Our results indicate a low-latitude region of the photosphere marked by distinct areas of individual or grouped star-spots with moderately high solar-type differential rotation of 0.102 ± 0.011 rad d−1, but with just two major flares observed across 400 d. These results imply a rotational shear significantly greater than that of our slower rotating Sun. The observed flares are more energetic than typical solar flares, but similar to those of other magnetically active cool dwarfs. [ABSTRACT FROM AUTHOR]

We present an analysis of spectropolarimetric observations of the low-mass weak-line T Tauri stars TWA 25 and TWA 7. The large-scale surface magnetic fields have been reconstructed for both stars using the technique of Zeeman Doppler imaging. Our surface maps reveal predominantly toroidal and non-axisymmetric fields for both stars. These maps reinforce the wide range of surface magnetic fields that have been recovered, particularly in pre-main sequence stars that have stopped accreting from the (now depleted) central regions of their discs. We reconstruct the large scale surface brightness distributions for both stars, and use these reconstructions to filter out the activity-induced radial velocity jitter, reducing the RMS of the radial velocity variations from 495 to 32 m s −1 for TWA 25, and from 127 to 36 m s −1 for TWA 7, ruling out the presence of close-in giant planets for both stars. The TWA 7 radial velocities provide an example of a case where the activity-induced radial velocity variations mimic a Keplerian signal that is uncorrelated with the spectral activity indices. This shows the usefulness of longitudinal magnetic field measurements in identifying activity-induced radial velocity variations. [ABSTRACT FROM AUTHOR]

Little is known of the activity and differential rotation of low luminosity, early M dwarfs from direct observation. We present the first stellar activity analysis of star-spots and faculae for the hot Jupiter hosting M1V dwarf Kepler-45 from |$\it Kepler$| transit light curves. We find star-spot and facula temperatures contrasting a few hundred degrees with the quiet photosphere, hence similar to other early M dwarfs having a convective envelope surrounding a radiative core. Star-spots are prominent close to the centre of the stellar disc, with faculae prominent towards the limbs, similar to what is observed for the Sun. Star-spot and facula mean sizes are about 40 and 45 × 103 km, respectively, and thus faculae occupy a 10 per cent larger surface area than the star-spots. A short-term activity cycle of about 295 d is observed that is reminiscent of those seen for other cool dwarfs. Adopting a solar-type differential rotation profile (faster equatorial rotation than polar rotation), our star-spot and facula temporal mapping indicates a rotation period of 15.520 ± 0.025 d at the transit latitude of −33.2°. From the mean stellar rotation of 15.762 d, we estimate a rotational shear of 0.031 ± 0.004 rad d−1, or a relative differential rotation of 7.8 ± 0.9 per cent. Kepler-45's surface rotational shear is thus consistent with observations and theoretical modelling of other early M dwarfs that indicate a shear of less than 0.045 rad d−1 and no less than 0.03 rad d−1 for stars with similar stellar rotation periods. [ABSTRACT FROM AUTHOR]

Our understanding of planetary systems different to our own has grown dramatically in the past 30 yr. However, our efforts to ascertain the degree to which the Solar system is abnormal or unique have been hindered by the observational biases inherent to the methods that have yielded the greatest exoplanet hauls. On the basis of such surveys, one might consider our planetary system highly unusual – but the reality is that we are only now beginning to uncover the true picture. In this work, we use the full 18-yr archive of data from the Anglo-Australian Planet Search to examine the abundance of 'cool Jupiters' – analogues to the Solar system's giant planets, Jupiter and Saturn. We find that such planets are intrinsically far more common through the cosmos than their siblings, the hot Jupiters. We find that the occurrence rate of such 'cool Jupiters' is |$6.73^{+2.09}_{-1.13}$|  per cent, almost an order of magnitude higher than the occurrence of hot Jupiters (at |$0.84^{+0.70}_{-0.20}$|  per cent). We also find that the occurrence rate of giant planets is essentially constant beyond orbital distances of ∼1 au. Our results reinforce the importance of legacy radial velocity surveys for the understanding of the Solar system's place in the cosmos. [ABSTRACT FROM AUTHOR]

Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here, we present the final data release of the Pan-Pacific Planet Search (PPPS), a 5 yr radial velocity survey using the 3.9 m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight 6 potential substellar-mass companions, which require additional observations to confirm. Correcting for the substantial incompleteness in the sample, we estimate the occurrence rate of giant planets orbiting low-luminosity giant stars to be approximately 7.8 |$^{+9.1}_{-3.3}$|  per cent. This result is consistent with the frequency of such planets found to orbit main-sequence A-type stars, from which the PPPS stars have evolved. [ABSTRACT FROM AUTHOR]

Knowledge of dynamo evolution in solar-type stars is limited by the difficulty of using active region monitoring to measure stellar differential rotation, a key probe of stellar dynamo physics. This paper addresses the problem by presenting the first ever measurement of stellar differential rotation for a main-sequence solar-type star using starspots and faculae to provide complementary information. Our analysis uses modelling of light curves of multiple exoplanet transits for the young solar-type star Kepler-71, utilizing archival data from the Kepler mission. We estimate the physical characteristics of starspots and faculae on Kepler-71 from the characteristic amplitude variations they produce in the transit light curves and measure differential rotation from derived longitudes. Despite the higher contrast of faculae than those in the Sun, the bright features on Kepler-71 have similar properties such as increasing contrast towards the limb and larger sizes than sunspots. Adopting a solar-type differential rotation profile (faster rotation at the equator than the poles), the results from both starspot and facula analysis indicate a rotational shear less than about 0.005 rad d−1, or a relative differential rotation less than 2 per cent, and hence almost rigid rotation. This rotational shear contrasts with the strong rotational shear of zero-age main-sequence stars and the modest but significant shear of the modern-day Sun. Various explanations for the likely rigid rotation are considered. [ABSTRACT FROM AUTHOR]

We present a detailed analysis of high-resolution spectropolarimetric observations of the weak-line T Tauri stars (wTTSs) TWA 9A and V1095 Sco as part of a wider survey of magnetic properties and activity in weak-line T Tauri stars, called MaTYSSE (Magnetic Topologies of Young Stars and the Survival of close-in giant Exoplanets). Our targets have similar masses but differing ages which span the stage of radiative core formation in solar-mass stars. We use the intensity line profiles to reconstruct surface brightness maps for both stars. The reconstructed brightness maps for TWA 9A and V1095 Sco were used to model and subtract the activity-induced jitter, reducing the RMS in the radial velocity measurements of TWA 9A by a factor of ∼7, and for V1095 Sco by a factor of ∼3. We detect significant circular polarization for both stars, but only acquired a high-quality circular polarisation time-series for TWA 9A. Our reconstructed large-scale magnetic field distribution of TWA 9A indicates a strong, non-axisymmetric field. We also analyse the chromospheric activity of both stars by investigating their H α emission, finding excess blue-ward emission for most observations of V1095 Sco, and symmetric, double-peaked emission for TWA 9A, with enhanced emission at one epoch likely indicating a flaring event. [ABSTRACT FROM AUTHOR]

We present a spectropolarimetric snapshot survey of solar-type planet-hosting stars. In addition to 14 planet-hosting stars observed as part of the BCool magnetic snapshot survey, we obtained magnetic observations of a further 19 planet-hosting solar-type stars in order to see if the presence of close-in planets had an effect on the measured surface magnetic field (|Bl|). Our results indicate that the magnetic activity of this sample is congruent with that of the overall BCool sample. The effects of the planetary systems on the magnetic activity of the parent star, if any, are too subtle to detect compared to the intrinsic dispersion and correlations with rotation, age and stellar activity proxies in our sample. Four of the 19 newly observed stars, two of which are subgiants, have unambiguously detected magnetic fields and are future targets for Zeeman-Doppler mapping. [ABSTRACT FROM AUTHOR]

The magnetic fields, activity and dynamos of young solar-type stars can be empirically studied using time series of spectropolarimetric observations and tomographic imaging techniques such as Doppler imaging and Zeeman-Doppler imaging. In this paper, we use these techniques to study the young Sun-like star EK Draconis (SpType: G1.5V, HD 129333) using ESPaDOnS at the Canada-France-Hawaii Telescope and NARVAL at the Télescope Bernard Lyot. This multi-epoch study runs from late 2006 until early 2012. We measure high levels of chromospheric activity indicating an active, and varying, chromosphere. Surface brightness features were constructed for all available epochs. The 2006/2007 and 2008 data show large spot features appearing at intermediate latitudes. However, the 2012 data indicate a distinctive polar spot. We observe a strong, almost unipolar, azimuthal field during all epochs, which is similar to that observed on other Sun-like stars. Using magnetic features, we determined an average equatorial rotational velocity, Ωeq, of ~2.50±0.08 rad d-1. High levels of surface differential rotation were measured with an average rotational shear, ΔΩ, of ~0.27-0.26+0.24 rad d-1. During an intensively observed 3-month period, from 2006 December until 2007 February, the magnetic field went from predominantly toroidal (~80 per cent) to a more balanced poloidal-toroidal (~40-60 per cent) field. Although the large-scale magnetic field evolved over the epochs of our observations, no polarity reversals were found in our data. [ABSTRACT FROM AUTHOR]

We present six epochs of spectropolarimetric observations of the hot-Jupiter-hosting star t Bootis that extend the exceptional previous multiyear data set of its large-scale magnetic field. Our results confirm that the large-scale magnetic field of t Bootis varies cyclicly, with the observation of two further magnetic reversals; between 2013 December and 2014 May and between 2015 January and March. We also show that the field evolves in a broadly solar-type manner in contrast to other F-type stars. We further present new results which indicate that the chromospheric activity cycle and the magnetic activity cycles are related, which would indicate a very rapid magnetic cycle. As an exemplar of long-term magnetic field evolution, t Bootis and this long-term monitoring campaign presents a unique opportunity for studying stellar magnetic cycles. [ABSTRACT FROM AUTHOR]

We report the detection of sixteen binary systems from the Anglo-Australian Planet Search. Solutions to the radial velocity data indicate that the stars have companions orbiting with a wide range of masses, eccentricities and periods. Three of the systems potentially contain brown-dwarf companions while another two have eccentricities that place them in the extreme upper tail of the eccentricity distribution for binaries with periods less than 1000 d. For periods up to 12 years, the distribution of our stellar companion masses is fairly flat, mirroring that seen in other radial velocity surveys, and contrasts sharply with the current distribution of candidate planetary masses, which rises strongly below 10 MJ. When looking at a larger sample of binaries that have FGK star primaries as a function of the primary star metallicity, we find that the distribution maintains a binary fraction of ~43 ± 4 per cent between -1.0 and +0.6 dex in metallicity. This is in stark contrast to the giant exoplanet distribution. This result is in good agreement with binary formation models that invoke fragmentation of a collapsing giant molecular cloud, suggesting that this is the dominant formation mechanism for close binaries and not fragmentation of the primary star's remnant protoplanetary disc. [ABSTRACT FROM AUTHOR]

Observations of the magnetic fields of young solar-type stars provide a way to investigate the signatures of their magnetic activity and dynamos. Spectropolarimetry enables the study of these stellar magnetic fields and was thus employed at the T élescope Bernard Lyot and the Anglo-Australian Telescope to investigate two moderately rotating young Sun-like stars, namely HD 35296 (V119 Tau, HIP 25278) and HD 29615 (HIP 21632). The results indicate that both stars display rotational variation in chromospheric indices consistent with their spot activity, with variations indicating a probable long-term cyclic period for HD 35296. Additionally, both stars have complex, and evolving, large-scale surface magnetic fields with a significant toroidal component. High levels of surface differential rotation were measured for both stars. For the F8V star HD 35296 a rotational shear of ΔΩ = 0.22-0.02+0.04 rad d-1 was derived from the observed magnetic profiles. For the G3V star HD 29615, the magnetic features indicate a rotational shear of ΔΩ = 0.48-0.12+0.11 rad d-1, while the spot features, with a distinctive polar spot, provide a much lower value of ΔΩ of 0.07-0.03+0.10 rad d-1. Such a significant discrepancy in shear values between spot and magnetic features for HD 29615 is an extreme example of the variation observed for other lower mass stars. From the extensive and persistent azimuthal field observed for both targets, it is concluded that a distributed dynamo operates in these moderately rotating Sun-like stars, in marked contrast to the Sun's interface-layer dynamo. [ABSTRACT FROM AUTHOR]

We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs, the mean value of |Bl| (|Bl|mean) was also found to be higher (5.7 G) than |Bl|mean measured for the G-dwarfs (3.2 G) and the F-dwarfs (3.3 G). For the sample as a whole, |Bl|mean increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and dynamos. [ABSTRACT FROM AUTHOR]

We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical (interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40° and 60°, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90° provides the best combination of goodness-of-fit and long-term dynamical stability. [ABSTRACT FROM AUTHOR]

Determining the occurrence rate of "super-Earth" planets (m sin i < 10 M⊕) is a critically important step on the path toward determining the frequency of Earth-like planets (η⊕), and hence the uniqueness of our solar system. Current radial-velocity surveys, achieving precisions of 1 m s-1, are now able to detect super-Earths and provide meaningful estimates of their occurrence rate. We present an analysis of 67 solar-type stars from the Anglo-Australian Planet Search specifically targeted for very high precision observations. When corrected for incompleteness, we find that the planet occurrence rate increases sharply with decreasing planetary mass. Our results are consistent with those from other surveys: in periods shorter than 50days, we find that 3.0% of stars host a giant (msin; > 100 M⊕) planet, and that 17.4% of stars host a planet with msin/ < 10 Me. The preponderance of low-mass planets in short-period orbits is in conflict with formation simulations in which the majority of super-Earths reside at larger orbital distances. This work gives a hint as to the size of η⊕, but to make meaningful predictions on the frequency of terrestrial planets in longer, potentially habitable orbits, low-mass terrestrial planet searches at periods of 100-200 days must be made an urgent priority for ground-based Doppler planet searches in the years ahead. [ABSTRACT FROM AUTHOR]

We present the photometry and spectropolarimetry of the pre-main-sequence star HD 106506. A photometric rotational period of 1.416 0.133 d has been derived using observations at Mount Kent Observatory (MKO). Spectropolarimetric data obtained with the 3.9-m Anglo-Australian Telescope (AAT) were used to derive spot occupancy and magnetic maps of the star through the technique of Zeeman Doppler imaging (ZDI). The resulting brightness maps indicate that HD 106506 displays photospheric spots at all latitudes including a predominant polar spot. Azimuthal and radial magnetic images of this star have been derived, and a significant azimuthal magnetic field is indicated, in line with other active young stars. A solar-like differential rotation law was incorporated into the imaging process. Using Stokes I information the equatorial rotation rate, , was found to be 4.54 0.01 , with a photospheric shear of . This equates to an equatorial rotation period of 1.39 0.01 d, with the equatorial region lapping the poles every d. Using the magnetic features, the equatorial rotation rate, , was found to be 4.51 0.01 , with a photospheric shear of 0.24 0.03 . This differential rotation is approximately four times that observed on the Sun. [ABSTRACT FROM AUTHOR]

Spectropolarimetric observations of the pre-main sequence early-G star HD 141943 were made at three observing epochs (2007, 2009 and 2010). The observations were made using the 3.9-m Anglo-Australian Telescope with the UCLES echelle spectrograph and the SEMPOL spectropolarimeter visitor instrument. The brightness and surface magnetic field topologies (given in Paper I) were used to determine the star's surface differential rotation and reconstruct the coronal magnetic field of the star. The coronal magnetic field at the three epochs shows on the largest scales that the field structure is dominated by the dipole component with possible evidence for the tilt of the dipole axis shifting between observations. We find very high levels of differential rotation on HD 141943 (8 times the solar value for the magnetic features and 5 times solar for the brightness features), similar to that evidenced by another young early-G star, HD 171488. These results indicate that a significant increase in the level of differential rotation occurs for young stars around a spectral type of early-G. We also find for the 2010 observations that there is a large difference in the differential rotation measured from the brightness and magnetic features, similar to that seen on early-K stars, but with the difference being much larger. We find only tentative evidence for temporal evolution in the differential rotation of HD 141943. [ABSTRACT FROM AUTHOR]

Spectroscopic and spectropolarimetric observations of the pre-main sequence early-G star HD 141943 were obtained at four observing epochs (in 2006, 2007, 2009 and 2010). The observations were undertaken at the 3.9-m Anglo-Australian Telescope using the UCLES echelle spectrograph and the SEMPOL spectropolarimeter visitor instrument. Brightness and surface magnetic field topologies were reconstructed for the star using the technique of least-squares deconvolution to increase the signal-to-noise ratio of the data. The reconstructed brightness maps show that HD 141943 had a weak polar spot and a significant amount of low-latitude features, with little change in the latitude distribution of the spots over the 4 yr of observations. The surface magnetic field was reconstructed at three of the epochs from a high-order () spherical harmonic expansion of the spectropolarimetric observations. The reconstructed magnetic topologies show that in 2007 and 2010 the surface magnetic field was reasonably balanced between poloidal and toroidal components. However, we find tentative evidence of a change in the poloidal/toroidal ratio in 2009 with the poloidal component becoming more dominant. At all epochs the radial magnetic field is predominantly non-axisymmetric while the azimuthal field is predominantly axisymmetric with a ring of positive azimuthal field around the pole similar to that seen on other active stars. [ABSTRACT FROM AUTHOR]

In this paper we present chromospheric emission levels of the solar-type stars in the young open clusters IC 2391 and IC 2602. High-resolution spectroscopic data were obtained for over 50 F, G and K stars from these clusters over several observing campaigns using the University College London Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Unlike older clusters, the majority (28/52) of the solar-type stars in the two clusters are rapid rotators with five of the stars being classified as ultra-rapid rotators . The emission levels in the calcium infrared triplet lines were then used as a measure of the chromospheric activity of the stars. When plotted against the Rossby number ( NR), the star's chromospheric emission levels show a plateau in the emission for indicating chromospheric saturation similar to the coronal saturation seen in previously observed X-ray emission from the same stars. However, unlike the coronal emission, the chromospheric emission of the stars shows little evidence of a reduction in emission (i.e. supersaturation) for the ultra-rapid rotators in the clusters. Thus we believe that coronal supersaturation is not the result of an overall decrease in magnetic dynamo efficiency for ultra-rapid rotators. [ABSTRACT FROM AUTHOR]

We have produced brightness and magnetic field maps of the surfaces of CV Cha and CR Cha: two actively accreting G- and K-type T Tauri stars in the Chamaeleon I star-forming cloud with ages of 3–5 Myr. Our magnetic field maps show evidence for strong, complex multipolar fields similar to those obtained for young rapidly rotating main-sequence stars. Brightness maps indicate the presence of dark polar caps and low-latitude spots – these brightness maps are very similar to those obtained for other pre-main-sequence and rapidly rotating main-sequence stars. Only two other classical T Tauri stars have been studied using similar techniques so far: V2129 Oph and BP Tau. CV Cha and CR Cha show magnetic field patterns that are significantly more complex than those recovered for BP Tau, a fully convective T Tauri star. We discuss possible reasons for this difference and suggest that the complexity of the stellar magnetic field is related to the convection zone; with more complex fields being found in T Tauri stars with radiative cores (V2129 Oph, CV Cha and CR Cha). However, it is clearly necessary to conduct magnetic field studies of T Tauri star systems, exploring a wide range of stellar parameters in order to establish how they affect magnetic field generation, and thus how these magnetic fields are likely to affect the evolution of T Tauri star systems as they approach the main sequence. [ABSTRACT FROM AUTHOR]

NRAGE (also known as Maged1, Dlxin) is a member of the MAGE gene family that may play a role in the neuronal apoptosis that is regulated by the p75 neurotrophin receptor (p75NTR). To test this hypothesis in vivo, we generated NRAGE knockout mice and found that NRAGE deletion caused a defect in developmental apoptosis of sympathetic neurons of the superior cervical ganglia, similar to that observed in p75NTR knockout mice. Primary sympathetic neurons derived from NRAGE knockout mice were resistant to apoptosis induced by brain-derived neurotrophic factor (BDNF), a pro-apoptotic p75NTR ligand, and NRAGE-deficient sympathetic neurons show attenuated BDNF-dependent JNK activation. Hair follicle catagen is an apoptosis-like process that is dependent on p75NTR signaling; we show that NRAGE and p75NTR show regulated co-expression in the hair follicle and that identical defects in hair follicle catagen are present in NRAGE and p75NTR knockout mice. Interestingly, NRAGE knockout mice have severe defects in motoneuron apoptosis that are not observed in p75NTR knockout animals, raising the possibility that NRAGE may facilitate apoptosis induced by receptors other than p75NTR. Together, these studies demonstrate that NRAGE plays an important role in apoptotic-signaling in vivo.Cell Death and Differentiation (2008) 15, 1921–1929; doi:10.1038/cdd.2008.127; published online 5 September 2008 [ABSTRACT FROM AUTHOR]

We present Doppler imaging and Balmer line analysis of the weak-line T Tauri star TWA 6. Using these data we have made one of the first attempts to measure differential rotation in a T Tauri star, and the first detection of a slingshot prominence in such a star. We also show the most direct evidence to date of the existence of solar-type plages in a star other than the Sun. Observations were made over six nights: 2006 February 11–13 and 2006 February 18–20, when spectra were taken with the UCL Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Using least-squares deconvolution to improve the effective signal-to-noise ratio we produced two Doppler maps. These show similar features to maps of other rapidly rotating T Tauri stars, i.e. a polar spot with more spots extending out of it down to equator. Comparison of the two maps was carried out to measure the differential rotation. Cross-correlation and parameter fitting indicates that TWA 6 does not have detectable differential rotation. The Balmer emission of the star was studied. The mean Hα profile has a narrow component consistent with rotational broadening and a broad component extending out to ±250 km s−1. The variability in Hα suggests that the chromosphere has active regions that are cospatial with the spots in the photosphere, similar to the ‘plages’ observed on the Sun. In addition the star has at least one slingshot prominence 3 R* above the surface – the first such detection in a T Tauri star. [ABSTRACT FROM AUTHOR]

We have acquired high-resolution echelle spectra of 225 F6-M5 type stars in the Southern hemisphere. The stars are targets or candidates to be targets for the Anglo-Australian Planet Search. Ca ii H& K line cores were used to derive activity indices for all of these objects. The indices were converted to the Mt. Wilson system of measurements and values determined. A number of these stars had no previously derived activity indices. In addition, we have also included the stars from Tinney et al. using our Mt. Wilson calibration. The radial-velocity instability (also known as jitter) level was determined for all 21 planet-host stars in our data set. We find the jitter to be at a level considerably below the radial-velocity signatures in all but one of these systems. 19 stars from our sample were found to be active and thus have high levels of jitter. Radial-velocity analysis for planetary companions to these stars should proceed with caution. [ABSTRACT FROM AUTHOR]

We present the results of a uniform, high-precision spectroscopic metallicity study of 136 G-type stars from the Anglo-Australian Planet Search, 20 of which are known to harbour extrasolar planets (as at 2005 July). Abundances in Fe, C, Na, Al, Si, Ca, Ti and Ni are presented, along with Strömgen photometric metallicities. This study is one of several recent studies examining the metallicities of a sample of planet-host and non-planet-host stars that were obtained from a single sample, and analysed in an identical manner, providing an unbiased estimate of the metallicity trends for planet-bearing stars. We find that non-parametric tests of the distribution of metallicities for planet-host and non-planet-host stars are significantly different at a level of 99.4 per cent confidence. We confirm the previously observed trend for planet-host stars to have higher mean metallicities than non-planet-host stars, with a mean metallicity for planet-host stars of compared with for non-host-stars in our sample. This enrichment is also seen in the other elements studied. Based on our findings, we suggest that this observed enhancement is more likely a relic of the original gas cloud from which the star and its planets formed, rather than being due to ‘pollution’ of the stellar photosphere. [ABSTRACT FROM AUTHOR]

We present spectropolarimetric observations of the young, single early G-dwarf HD 171488. These observations were obtained over a five-night period in 2004 September at the 3.9-m Anglo-Australian Telescope using the SEMPOL spectropolarimeter visitor instrument. Using the technique of least-squares deconvolution to increase the signal-to-noise ratio of the data, we have applied Zeeman Doppler imaging to reconstruct brightness and magnetic surface topologies of the star. The brightness image shows a large polar spot with weaker low- to mid-latitude features, confirming an earlier Doppler imaging observation. The reconstruction of the surface magnetic field shows regions of radial field at all latitudes (except near the pole) and regions of azimuthal field predominantly at high latitudes (60°–70°), with the azimuthal field almost forming a ring around the polar regions. We have incorporated a solar-like differential rotation law into the imaging process to determine the surface differential rotation of cool spots on HD 171488. This gives an equatorial rotation rate of 1.313 ± 0.004 d and a surface shear of rad d−1. This means that the equator of HD 171488 laps the poles every d and that HD 171488 has a photospheric shear approximately seven times the solar value. This is the largest measurement of surface differential rotation yet obtained using the Doppler imaging method and is over twice the value of previously observed early G-dwarfs. [ABSTRACT FROM AUTHOR]

We are about to embark on a project to directly image low-mass companions orbiting within 1.53 of their host stars. Our long-term aim is to reach down into the planetary-mass regime. In order to start this project we have time on the VLT NAOS/CONICA (NACO) facility and in the near future we plan to make use of the Near-Infrared Coronographic Imager (NICI) instrument mounted on Gemini-South. Our targets are F-M type dwarfs, and have been selected from the Anglo-Australian Planet Search (AAPS), Keck and Lick search lists. These surveys have been periodically monitoring over 1200 stars between them for the past $\sim$8 years with precisions typically around 3ms$^{-1}$. Our target list comprises objects which show significant evidence for companions on long-period orbits. Having a priori knowledge of companion characteristics allows us the advantage of prioritising our target list. Given the relatively high incidence of multiple planet systems found so far our search may also serve to provide useful constraints on any large separation, massive companions in our target systems. [ABSTRACT FROM PUBLISHER]

In this paper we present Doppler images of a young active G dwarf (HD 307938) in the southern open cluster IC 2602. Spectroscopic data were obtained over a four-night period in 2000 January at the 3.9-m Anglo-Australian Telescope using the University College London Echelle Spectrograph. Simultaneous photometric observations (in theVandRbands) were obtained at the 1.0-m Australian National University telescope. By applying least-squares deconvolution (LSD) to the 2500+ photospheric lines in each echelle spectrum a single high signal-to-noise ratio LSD profile was produced for each phase of the spectroscopic observations. Maximum-entropy image reconstruction, incorporating both the LSD profiles and the photometric data, was used to produce maps of the surface features of the star, with the inclusion of the photometric data producing an increase (compared with the use of spectroscopic data alone) in the spot occupancy in both low- and mid-latitude regions of the star. The maps show that HD 307938 possesses a large, broken polar spot extending down to∼60° latitude, as well as lower-latitude spots similar to other rapidly rotating G dwarfs. By incorporating a solar-like differential rotation law into the imaging process the surface differential rotation of HD 307938 was determined. This gave a surface shear of(for an inclination angle of 60°). Thus the equator of HD 307938 laps the poles every∼250 d and has a photospheric shear around half that of the Sun. [ABSTRACT FROM AUTHOR]

In this paper, we present new brightness and magnetic surface images of the young K0 dwarfs AB Doradus and LQ Hydrae, and of the K1 subgiant of the RS CVn system HR 1099 (=V711 Tauri), reconstructed from Zeeman–Doppler imaging spectropolarimetric observations collected at the Anglo-Australian Telescope during five observing campaigns (totalling 50 nights), from 1998 January to 2002 January. Along with the older images of the same stars (published in previous papers), our complete data set represents the first long-term series on temporal fluctuations of magnetic topologies of very active stars. All of the magnetic images presented here indicate that large regions with predominantly azimuthal magnetic fields are continuously present at the surfaces of these stars. We take this as further evidence that the underlying dynamo processes that produce them are probably distributed throughout the entire convective zone (and not confined at its base, as in the Sun). We speculate that the radial and azimuthal field maps that we recover correspond, respectively, to the poloidal and toroidal components of the large-scale dynamo field. We find, in particular, that some signatures, for instance the relative fraction of magnetic energy stored in the large-scale poloidal and toroidal field components, and the polarity of the axisymmetric component of the field, are variable with time, and provide potentially fruitful diagnostics for investigating magnetic cycles in active stars other than the Sun. We report here the detection of partial polarity switches in some of the axisymmetric field components of two of our programme stars (AB Dor and LQ Hya), suggesting that the dynamo operating in these stars may be cyclic. [ABSTRACT FROM AUTHOR]

Precise radial velocities from the Anglo-Australian Telescope (AAT) confirm the presence of a rare short-period planet around the K0 giant HD 121056. An independent two-planet solution using the AAT data shows that the inner planet has P = 89.1 ± 0.1 days, and m sin i = 1.35 ± 0.17 MJup. These data also confirm the planetary nature of the outer companion, with m sin i = 3.9 ± 0.6 MJup and a = 2.96 ± 0.16 AU. HD 121056 is the most-evolved star to host a confirmed multiple-planet system, and is a valuable example of a giant star hosting both a short-period and a long-period planet. [ABSTRACT FROM AUTHOR]