Evidence for at least three planet candidates orbiting HD20794

Reproduced with permission from Astronomy & Astrophysics. © 2017 ESO. Published by EDP Sciences.We explore the feasibility of detecting Earth analogs around Sun-like stars using the radial velocity method by investigating one of the largest radial velocities datasets for the one of the most stable radial-velocity stars HD20794. We proceed by disentangling the Keplerian signals from correlated noise and activity-induced variability. We diagnose the noise using the differences between radial velocities measured at different wavelength ranges, so-called "differential radial velocities", as well as the combination of radial velocities measured for other stars to account for instrumental effects. We apply this method to the radial velocities measured by HARPS, and identify four signals at 18, 89, 147 and 330 d. The two signals at periods of 18 and 89 d are previously reported and are better quantified in this work. The signal at a period of about 147 d is reported for the first time, and corresponds to a super-Earth with a minimum mass of 4.59 Earth mass located 0.51 AU from HD20794. We also find a significant signal at a period of about 330 d corresponding to a super-Earth or Neptune in the habitable zone. Since this signal is close to the annual sampling period and significant periodogram power in some noise proxies are found close to this signal, further observations and analyses are required to confirm it. The analyses of the eccentricity and consistency of signals provide weak evidence for the existence of the previously reported 43 d signal and a new signal at a period of about 11.9 d with a semi amplitude of 0.4 m/s. We find that the detection of a number of signals with radial velocity variations around 0.5\,m/s likely caused by low mass planet candidates demonstrates the important role of noise modeling in searching for Earth analogs.Peer reviewe

Color Difference Makes a Difference: Four Planet Candidates around τ Ceti

The removal of noise typically correlated in time and wavelength is one of the main challenges for using the radial-velocity (RV) method to detect Earth analogues. We analyze τ Ceti RV data and find robust evidence for wavelength-dependent noise. We find that this noise can be modeled by a combination of moving average models and the so-called "differential radial velocities." We apply this noise model to various RV data sets for τ Ceti, and find four periodic signals at 20.0, 49.3, 160, and 642 days, which we interpret as planets. We identify two new signals with orbital periods of 20.0 and 49.3 days while the other two previously suspected signals around 160 and 600 days are quantified to a higher precision. The 20.0 days candidate is independently detected in Keck data. All planets detected in this work have minimum masses less than 4M⊕ with the two long-period ones located around the inner and outer edges of the habitable zone, respectively. We find that the instrumental noise gives rise to a precision limit of the High Accuracy Radial Velocity Planet Searcher (HARPS) around 0.2 m s−1. We also find correlation between the HARPS data and the central moments of the spectral line profile at around 0.5 m s−1 level, although these central moments may contain both noise and signals. The signals detected in this work have semi-amplitudes as low as 0.3 m s−1, demonstrating the ability of the RV technique to detect relatively weak signals

Agatha: : disentangling periodic signals from correlated noise in a periodogram framework

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Periodograms are used as a key significance assessment and visualisation tool to display the significant periodicities in unevenly sampled time series. We introduce a framework of periodograms, called "Agatha", to disentangle periodic signals from correlated noise and to solve the 2-dimensional model selection problem: signal dimension and noise model dimension. These periodograms are calculated by applying likelihood maximization and marginalization and combined in a self-consistent way. We compare Agatha with other periodograms for the detection of Keplerian signals in synthetic radial velocity data produced for the Radial Velocity Challenge as well as in radial velocity datasets of several Sun-like stars. In our tests we find Agatha is able to recover signals to the adopted detection limit of the radial velocity challenge. Applied to real radial velocity, we use Agatha to confirm previous analysis of CoRoT-7 and to find two new planet candidates with minimum masses of 15.1 $M_\oplus$ and 7.08 $M_\oplus$ orbiting HD177565 and HD41248, with periods of 44.5 d and 13.4 d, respectively. We find that Agatha outperforms other periodograms in terms of removing correlated noise and assessing the significances of signals with more robust metrics. Moreover, it can be used to select the optimal noise model and to test the consistency of signals in time. Agatha is intended to be flexible enough to be applied to time series analyses in other astronomical and scientific disciplines. Agatha is available at http://www.agatha.herts.ac.uk.Peer reviewe

ROPS: A New Search for Habitable Earths in the Southern Sky

We present the first results from our Red Optical Planet Survey (ROPS) to search for low mass planets orbiting late type dwarfs (M5.5V - M9V) in their habitable zones (HZ). Our observations, with the red arm of the MIKE spectrograph (0.5 - 0.9 microns) at the 6.5 m Magellan Clay telescope at Las Campanas Observatory indicate that >= 92 per cent of the flux lies beyond 0.7 microns. We use a novel approach that is essentially a hybrid of the simultaneous iodine and ThAr methods for determining precision radial velocities. We apply least squares deconvolution to obtain a single high S/N ratio stellar line for each spectrum and cross correlate against the simultaneously observed telluric line profile, which we derive in the same way. Utilising the 0.62 - 0.90 micron region, we have achieved an r.m.s. precision of 10 m/s for an M5.5V spectral type star with spectral S/N ~160 on 5 minute timescales. By M8V spectral type, a precision of ~30 m/s at S/N = 25 is suggested, although more observations are needed. An assessment of our errors and scatter in the radial velocity points hints at the presence of stellar radial velocity variations. Of our sample of 7 stars, 2 show radial velocity signals at 6-sigma and 10-sigma of the cross correlation uncertainties. If the signals are planetary in origin, our findings are consistent with estimates of Neptune mass planets that predict a frequency of 13 - 27 per cent for early M dwarfs.Our current analysis indicates the we can achieve a sensitivity that is equivalent to the amplitude induced by a 6 M_Earth planet orbiting in the habitable zone. Based on simulations, we estimate that <10 M_Earth habitable zone planets will be detected in a new stellar mass regime, with <=20 epochs of observations.Comment: MNRAS accepted: 14 pages, 8 figures, 3 table

A Goldilocks principle for modelling radial velocity noise

F. Feng, M. Tuomi, H. R. A. Jones, R. P. Butler, and S. Vogt, 'A Goldilocks principle for modelling radial velocity noise', MNRAS, Vol. 461 (3): 2440-2452, first published online on 20 June 2016, the version of record is available online at doi: 10.1093/mnras/stw1478. © 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.The doppler measurements of stars are diluted and distorted by stellar activity noise. Different choices of noise models and statistical methods have led to much controversy in the confirmation of exoplanet candidates obtained through analysing radial velocity data. To quantify the limitation of various models and methods, we compare different noise models and signal detection criteria for various simulated and real data sets in the Bayesian framework. According to our analyses, the white noise model tend to interpret noise as signal, leading to false positives. On the other hand, the red noise models are likely to interprete signal as noise, resulting in false negatives. We find that the Bayesian information criterion combined with a Bayes factor threshold of 150 can efficiently rule out false positives and confirm true detections. We further propose a Goldilocks principle aimed at modeling radial velocity noise to avoid too many false positives and too many false negatives. We propose that the noise model with RHK-dependent jitter is used in combination with the moving average model to detect planetary signals for M dwarfs. Our work may also shed light on the noise modeling for hotter stars, and provide a valid approach for finding similar principles in other disciplines.Peer reviewe

Transport dynamics in a complex coastal archipelago

The Archipelago Sea (in the Baltic Sea) is characterised by thousands of islands of various sizes and steep gradients of the bottom topography. Together with the much deeper Åland Sea, the Archipelago Sea acts as a pathway to the water exchange between the neighbouring basins, Baltic proper and Bothnian Sea. We studied circulation and water transports in the Archipelago Sea using a new configuration of the NEMO 3D hydrodynamic model that covers the Åland Sea–Archipelago Sea region with a horizontal resolution of around 500 m. The results show that currents are steered by the geometry of the islands and straits and the bottom topography. Currents are highest and strongly aligned in the narrow channels in the northern part of the area, with the directions alternating between south and north. In more open areas, the currents are weaker with wider directional distribution. During our study period of 2013–2017, southward currents were more frequent in the surface layer. In the bottom layer, in areas deeper than 25 m, northward currents dominated in the southern part of the Archipelago Sea, while in the northern part southward and northward currents were more evenly represented. Due to the variation in current directions, both northward and southward transports occur. During our study period, the net transport in the upper 20 m layer was southward. Below 20 m depth, the net transport was southward at the northern edge and northward at the southern edge of the Archipelago Sea. There were seasonal and inter-annual variations in the transport volumes and directions in the upper layer. Southward transport was usually largest in spring and summer months, and northward transport was largest in autumn and winter months. The transport dynamics in the Archipelago Sea show different variabilities in the north and south. A single transect cannot describe water transport through the whole area in all cases. Further studies on the water exchange processes between the Baltic proper and the Bothnian Sea through the Archipelago Sea would benefit from using a two-way nested model set-up for the region.</p

Systemic Safety in Ranibizumab-Treated Patients with Neovascular Age-Related Macular Degeneration : a Patient-Level Pooled Analysis

Topic: This study evaluated the cardiovascular/cerebrovascular safety profile of ranibizumab 0.5 mg versus sham \ub1 verteporfin in patients with neovascular age-related macular degeneration (nAMD). In addition, comparisons of ranibizumab 0.3 mg with sham and ranibizumab 0.5 mg to 0.3 mg were performed. Clinical Relevance: Intravitreal anti\u2013vascular endothelial growth factor (VEGF) agents carry potential increased systemic risks, including cardiovascular or cerebrovascular events. Pooled safety analyses allow better interpretation of safety outcomes seen in individual clinical trials, especially for less common events. To our knowledge, this is the largest patient-level pooled analysis of patients with nAMD treated with ranibizumab. Methods: Patient-level pooled analysis of data from 7 Genentech- and Novartis-sponsored phase II, III, and IV studies in nAMD that were completed by December 31, 2013. Pairwise comparisons (primary comparison: ranibizumab 0.5 mg [globally approved dose for nAMD] vs. sham or verteporfin) were performed using Cox proportional hazard regression (hazard ratios [HRs], 95% confidence intervals [CIs]) and rates per 100 patient-years. Standardized Medical Dictionary for Regulatory Activities queries (SMQs) and extended searches were used to identify relevant safety endpoints, including arterial thromboembolic events (ATEs), myocardial infarction (MI), stroke or transient ischemic attack (TIA), stroke (excluding TIA), vascular deaths, and major vascular events as defined by the Antiplatelet Trialists\u2019 Collaboration (APTC). Results: The HRs (95% CIs) for the primary comparison of ranibizumab 0.5 mg (n=480) versus sham or verteporfin (n=462) were 1.16 (0.72\u20131.88) for ATE, 1.33 (0.59\u20132.97) for MI, 1.43 (0.54\u20133.77) for stroke excluding TIA, 1.25 (0.61\u20132.55) for stroke or TIA, 0.57 (0.18\u20131.78) for vascular death, and 1.12 (0.64\u20131.98) for APTC events. Hazard ratio 95% CIs included 1, indicating no significant treatment differences, for all endpoints for comparison of ranibizumab 0.5 mg versus sham or verteporfin. Conclusions: The rates of cardiovascular and cerebrovascular events were low in these patients with nAMD and not clinically meaningfully different for patients treated with ranibizumab 0.5 mg versus sham or verteporfin, which supports the favorable benefit\u2013risk profile of ranibizumab in the patient population with nAMD. Pooling these studies allows an analysis with higher power and precision compared with individual study analyses

AD Leonis: Radial Velocity Signal of Stellar Rotation or Spin–Orbit Resonance?

AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days, as well as photometric signals: (1) a short-period signal, which is similar to the radial velocity signal, albeit with considerable variability; and (2) a long-term activity cycle of 4070 ± 120 days. We examine the short-term photometric signal in the available All-Sky Automated Survey and Microvariability and Oscillations of STars (MOST) photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set, which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined High-Accuracy Radial velocity Planet Searcher and High Resolution Echelle Spectrometer radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period, or as a function of extracted wavelength. We consider a variety of starspot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots corotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin–orbit resonance. For such a scenario and no spin–orbit misalignment, the measured v sin i indicates an inclination angle of 15°̣5 ± 2°̣5 and a planetary companion mass of 0.237 ± 0.047 M Jup

In vitro cytotoxicity and surface topography evaluation of additive manufacturing titanium implant materials

Custom-designed patient-specific implants and reconstruction plates are to date commonly manufactured using two different additive manufacturing (AM) technologies: direct metal laser sintering (DMLS) and electron beam melting (EBM). The purpose of this investigation was to characterize the surface structure and to assess the cytotoxicity of titanium alloys processed using DMLS and EBM technologies as the existing information on these issues is scarce. "Processed" and "polished" DMLS and EBM disks were assessed. Microscopic examination revealed titanium alloy particles and surface flaws on the processed materials. These surface flaws were subsequently removed by polishing. Surface roughness of EBM processed titanium was higher than that of DMLS processed. The cytotoxicity results of the DMLS and EBM discs were compared with a "gold standard" commercially available titanium mandible reconstruction plate. The mean cell viability for all discs was 82.6% (range, 77.4 to 89.7) and 83.3% for the control reconstruction plate. The DMLS and EBM manufactured titanium plates were non-cytotoxic both in "processed" and in "polished" forms.Peer reviewe

Precision radial velocities of 15 M5-M9 dwarfs

J. R. Barnes, 'Precision radial velocities of 15 M5-M9 dwarfs', Monthly Notices of the Royal Astronomical Society, Vol. 439 (3): 3094 - 3113, first published online 20 February 2014. The version of record is available online at doi: 10.1093/mnras/stu172 © 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.We present radial velocity measurements of a sample ofM5V-M9Vstars from our Red-Optical Planet Survey, operating at 0.652-1.025 μm. Radial velocities for 15 stars, with rms precision down to 2.5m-1 over a week-long time-scale, are achieved using thorium-argon reference spectra. We are sensitive to planets with mp sin i ≥ 1.5M⊕ (3M⊕ at 2σ) in the classical habitable zone, and our observations currently rule out planets with mp sini ≥ 0.5MJ at 0.03 au for all our targets. A total of 9 of the 15 targets exhibit rms 10M⊕ in 0.03 au orbits. Since the mean rotation velocity is of the order of 8 km-1 for an M6V star and 15 km -1 for M9V, we avoid observing only slow rotators that would introduce a bias towards low axial inclination (i< 90°) systems, which are unfavourable for planet detection. Our targets with the highest v sin i values exhibit radial velocities significantly above the photon-noise-limited precision, even after accounting for v sin i. We have therefore monitored stellar activity via chromospheric emission from the Hα and Ca II infrared triplet lines. A clear trend of log10(LHα/Lbol) with radial velocity rms is seen, implying that significant starspot activity is responsible for the observed radial velocity precision floor. The implication that most late M dwarfs are significantly spotted, and hence exhibit time varying line distortions, indicates that observations to detect orbiting planets need strategies to reliablymitigate against the effects of activity-induced radial velocity variations.Peer reviewe