3,618 research outputs found
Magnetic fields on young, moderately rotating Sun-like stars - I. HD 35296 and HD 29615
No full textObservations 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 Telescope 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 Delta Omega = 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 Delta Omega = 0.48(-0.12)(+0.11) rad d(-1), while the spot features, with a distinctive polar spot, provide a much lower value of Delta Omega 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
Extrasolar planets around HD 196050, HD 216437 and HD 160691
No full textWe report precise Doppler measurements of the stars HD 216437, HD 196050 and HD 160691 obtained with the Anglo-Australian Telescope using the UCLES spectrometer together with an iodine cell as part of the Anglo-Australian Planet Search. Our measurements reveal periodic Keplerian velocity variations that we interpret as evidence for planets in orbit around these solar type stars. HD 216437 has a period of 1294 ± 250 d, a semi-amplitude of 38 ± 3 m s−1 and an eccentricity of 0.33 ± 0.09. The minimum (M sin i) mass of the companion is 2.1 ± 0.3 MJUP and the semi-major axis is 2.4 ± 0.5 au. HD 196050 has a period of 1300 ± 230 d, a semi-amplitude of 49 ± 8 m s−1 and an eccentricity of 0.19 ± 0.09. The minimum mass of the companion is 2.8 ± 0.5 MJUP and the semi-major axis is 2.4 ± 0.5 au. We also report further observations of the metal-rich planet bearing star HD 160691. Our new solution confirms the previously reported planet and shows a trend indicating a second, longer-period companion. These discoveries add to the growing numbers of mildly eccentric, long-period extrasolar planets around metal-rich Sun-like stars
HD 191939: Three Sub-Neptunes Transiting a Sun-like Star Only 54 pc Away
No full textWe present the discovery of three sub-Neptune-sized planets transiting the nearby and bright Sun-like star HD 191939 (TIC 269701147, TOI 1339), a K_s = 7.18 mag G8 V dwarf at a distance of only 54 pc. We validate the planetary nature of the transit signals by combining 5 months of data from the Transiting Exoplanet Survey Satellite with follow-up ground-based photometry, archival optical images, radial velocities, and high angular resolution observations. The three sub-Neptunes have similar radii (R_b = 3.42^(+0.11)_(-0.11), R_c = 3.23^(+0.11)_(-0.11), R_d = 3.16^(+0.11)_(-0.11) R⊕), and their orbits are consistent with a stable, circular, and coplanar architecture near mean-motion resonances of 1:3 and 3:4 (P_b = 8.88, P_c = 28.58, and P_d = 38.35 days). The HD 191939 system is an excellent candidate for precise mass determinations of the planets with high-resolution spectroscopy due to the host star's brightness and low chromospheric activity. Moreover, the system's compact and near-resonant nature can provide an independent way to measure planetary masses via transit timing variations while also enabling dynamical and evolutionary studies. Finally, as a promising target for multiwavelength transmission spectroscopy of all three planets' atmospheres, HD 191939 can offer valuable insight into multiple sub-Neptunes born from a protoplanetary disk that may have resembled that of the early Sun
HD 35843: A Sun-like Star Hosting a Long-period Sub-Neptune and Inner Super-Earth
No full textWe report the discovery and confirmation of two planets orbiting the metal-poor Sun-like star HD 35843 (TOI 4189). HD 35843 c is a temperate sub-Neptune transiting planet with an orbital period of 46.96 days that was first identified by Planet Hunters TESS. We combine data from TESS and follow-up observations to rule out false-positive scenarios and validate the planet. We then use ESPRESSO radial velocities (RVs) to confirm the planetary nature and characterize the planet’s mass and orbit. Further analysis of these RVs reveals the presence of an additional planet, HD 35843 b, with a period of 9.90 days and a minimum mass of 5.84 ± 0.84 M⊕. For HD 35843 c, a joint photometric and spectroscopic analysis yields a radius of 2.54 ± 0.08 R⊕, a mass of 11.32 ± 1.60 M⊕, and an orbital eccentricity of e = 0.15 ± 0.07. With a bulk density of 3.80 ± 0.70 g cm−3, the planet might be rocky with a substantial H2 atmosphere or it might be a “water world.” With an equilibrium temperature of ∼480 K, HD 35843 c is among the coolest ∼5% of planets discovered by TESS. Combined with the host star’s relative brightness (V = 9.4), HD 35843 c is a promising target for atmospheric characterization that will probe this sparse population of temperate sub-Neptunes
Magnetic fields on young, moderately rotating Sun-like stars - II. EK Draconis (HD 129333)
No full textThe 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 T ' elescope 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, Omega(eq), of similar to 2.50 +/- 0.08 rad d(-1). High levels of surface differential rotation were measured with an average rotational shear, Delta Omega, of similar to 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 (similar to 80 per cent) to a more balanced poloidaltoroidal (similar to 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
TESS Discovery of a Super-Earth and Three Sub-Neptunes Hosted by the Bright, Sun-like Star HD 108236
No full textWe report the discovery and validation of four extrasolar planets hosted by the nearby, bright, Sun-like (G3V) star HD 108236 using data from the Transiting Exoplanet Survey Satellite (TESS). We present transit photometry, reconnaissance, and precise Doppler spectroscopy, as well as high-resolution imaging, to validate the planetary nature of the objects transiting HD 108236, also known as the TESS Object of Interest (TOI) 1233. The innermost planet is a possibly rocky super-Earth with a period of days and has a radius of 1.586 ± 0.098 R ⊕. The outer planets are sub-Neptunes, with potential gaseous envelopes, having radii of R ⊕, 2.72 ± 0.11 R ⊕, and R ⊕ and periods of days, days, and days, respectively. With V and K s magnitudes of 9.2 and 7.6, respectively, the bright host star makes the transiting planets favorable targets for mass measurements and, potentially, for atmospheric characterization via transmission spectroscopy. HD 108236 is the brightest Sun-like star in the visual (V) band known to host four or more transiting exoplanets. The discovered planets span a broad range of planetary radii and equilibrium temperatures and share a common history of insolation from a Sun-like star (R ⋆ = 0.888 ± 0.017 R ⊙, T eff = 5730 ± 50 K), making HD 108236 an exciting, opportune cosmic laboratory for testing models of planet formation and evolution
Vitamin D intake, sun exposure and 25-hydroxy vitamin D status in Peritoneal dialysis (PD) and Haemodialysis (HD) patients
No full textInadequate vitamin D levels have been linked to bone disease but more recently have been associated with wider health implications. Limited studies suggest a high prevalence of Vitamin D deficiency in dialysis patients, although evidence is lacking on whether this is due to dietary restrictions, limited mobility and time outdoors or a combination of these. The aim of this study was to assess the contributions of diet, supplements and sunlight exposure to serum Vitamin D (25(OH)D) levels in dialysis patients. Cross-sectional data were obtained from 30 PD (Mean±SD age 56.9±16.2 y; n=13 male) and 22 HD (Mean±SD age 65.4±14.0 y; n=18 male) patients between 2009 and 2010. Serum 25(OH)D was measured and oral vitamin D intake estimated through a food-frequency-questionnaire and quantifying inactive supplementation. Sunlight exposure was assessed using a validated questionnaire. Prevalence of inadequate/insufficient vitamin D differed between dialysis modality (31% and 43% insufficient (<50nmol/L); 4% and 34% deficient (<25nmol/L) in HD and PD patients respectively (p=0.002)). In HD patients, there was a significant correlation between diet plus supplemental vitamin D intake and 25(OH)D (ρ=0.84, p<0.001). Results suggest a higher frequency of 25(OH)D inadequacy/deficiency in PD compared to HD patients. No other relationships between intake, sun exposure and 25(OH)D were seen. This could reflect limitations of the study design or the importance of other factors such as age, ethnicity and sun protection as interactions in the analysis. Understanding these factors is important given Vitamin D’s emerging status as a biomarker of systemic ill health
Short-interval observational data to inform clinical trial design in Huntington's disease.
No full textOBJECTIVES: To evaluate candidate outcomes for disease-modifying trials in Huntington's disease (HD) over 6-month, 9-month and 15-month intervals, across multiple domains. To present guidelines on rapid efficacy readouts for disease-modifying trials. METHODS: 40 controls and 61 patients with HD, recruited from four EU sites, underwent 3 T MRI and standard clinical and cognitive assessments at baseline, 6 and 15 months. Neuroimaging analysis included global and regional change in macrostructure (atrophy and cortical thinning), and microstructure (diffusion metrics). The main outcome was longitudinal effect size (ES) for each outcome. Such ESs can be used to calculate sample-size requirements for clinical trials for hypothesised treatment efficacies. RESULTS: Longitudinal changes in macrostructural neuroimaging measures such as caudate atrophy and ventricular expansion were significantly larger in HD than controls, giving rise to consistently large ES over the 6-month, 9-month and 15-month intervals. Analogous ESs for cortical metrics were smaller with wide CIs. Microstructural (diffusion) neuroimaging metrics ESs were also typically smaller over the shorter intervals, although caudate diffusivity metrics performed strongly over 9 and 15 months. Clinical and cognitive outcomes exhibited small longitudinal ESs, particularly over 6-month and 9-month intervals, with wide CIs, indicating a lack of precision. CONCLUSIONS: To exploit the potential power of specific neuroimaging measures such as caudate atrophy in disease-modifying trials, we propose their use as (1) initial short-term readouts in early phase/proof-of-concept studies over 6 or 9 months, and (2) secondary end points in efficacy studies over longer periods such as 15 months
Candidate Solar Sibling HD 162826: Color-Magnitude Position Compared to Sun and M67
No full text<p>Color-magnitude position (intrinsic B-V color vs. absolute magnitude) for candidate solar sibling HD 162826, the Sun, and M67 open cluster. HD 162826 is mentioned as a candidate solar sibling by Ramirez et al. 2014 (http://arxiv-web3.library.cornell.edu/abs/1405.1723). Color is from Hipparcos catalog, and absolute magnitude is calculated using V magnitude from Hipparcos catalog and parallax from van Leeuwen (2007). The Sun's color is from Ramirez et al. (2012; ApJ, 752, 5; B-V = 0.653+-0.003) and absolute magnitude is taken from the author's notes on the website https://sites.google.com/site/mamajeksstarnotes/basic-astronomical-data-for-the-sun. I plot stars from the open cluster M67 for comparison as it is probably the best-studied open cluster with an age (~4 Gyr) similar to that of the Sun and HD 162826. BV photometry for M67 members is from Sandquist (2004; MNRAS, 347, 101). I deredden the M67 stars assuming E(B-V) = 0.038 (VandenBerg & Steson 2004; PASP 116, 997) and estimating V-band extinction Av = 0.128 mag, and adopt the distance modulus (9.60 mag) from Sandquist (2004). The red lines are 3.8 Gyr and 4.568 Gyr (solar age) isochrones from Bressan+ (2012; MNRAS, 427, 127), assuming a protosolar metal fraction of Z=0.015. Using the Bressan+ isochrones, M67 does indeed look roughly 3.8 Gyr old, similar to previous estimates. Remarkably, a Bressan+ isochrone for the age and adopted chemical composition of the Sun passes right through the color-magnitude diagram position of the candidate solar sibling HD 162826. Hence, not only is the star remarkably similar in chemical composition to the Sun (Ramirez+2014), but its color-magnitude position appears to be remarkably consistent with have an age similar to the Sun. While HD 162826 appears to be the best "candidate" solar sibling found so far, it is worth keeping in mind that there may be field stars with chemical compositions and ages and velocities similar to the Sun that *didn't* form in the same cluster (e.g. during any ~million-year block in the Milky Way's past, thousands of stars are forming in molecular cloud complexes - many associated with spiral arms - and many will be spawned with similar chemical compositions, ages, and even kinematics, but not necessarily in the same birth cluster). It will be interesting to see if more candidates like HD 162826 are found that match the Sun's chemical composition, age, and velocity so well. <br><br></p
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