Search

Context. The stars in the Milky Way thin and thick disks can be distinguished by several properties such as metallicity and kinematics. It is not clear whether the two populations also differ in the properties of planets orbiting the stars. In order to study this, a careful analysis of both the chemical composition and mass detection limits is required for a sufficiently large sample. Currently, this information is still limited only to large radial-velocity (RV) programs. Based on the recently published archival database of the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph, we present a first analysis of low-mass (small) planet occurrence rates in a sample of thin- and thick-disk stars. Aims. We aim to assess the effects of stellar properties on planet occurrence rates and to obtain first estimates of planet occurrence rates in the thin and thick disks of the Galaxy. As a baseline for comparison, we also aim to provide an updated value for the small close-in planet occurrence rate and compare it with the results of previous RV and transit (Kepler) works. Methods. We used archival HARPS RV datasets to calculate detection limits of a sample of stars that were previously analysed for their elemental abundances. For stars with known planets we first subtracted the Keplerian orbit. We then used this information to calculate planet occurrence rates according to a simplified Bayesian model in different regimes of stellar and planet properties. Results. Our results suggest that metal-poor stars and more massive stars host fewer low-mass close-in planets. We find the occurrence rates of these planets in the thin and thick disks to be comparable. In the iron-poor regimes, we find these occurrence rates to be significantly larger at the high-α region (thick-disk stars) as compared with the low-α region (thin-disk stars). In general, we find the average number of close-in small planets (2–100 days, 1–20M⊕) per star (FGK-dwarfs) to be: n¯p = 0.36 ± 0.05, $\bar{n}_{\textrm{p}}\,{=}\,0.36\,{\pm}\,0.05,$ n ¯ p   =   0.36   ±   0.05 , while the fraction of stars with planets is Fh = 0.23−0.03+0.04 $F_{\textrm{h}}\,{=}\,0.23^{+0.04}_{-0.03}$ F h   =   0.23 − 0.03 + 0.04 . Qualitatively, our results agree well with previous estimates based on RV and Kepler surveys. Conclusions. This work provides a first estimate of the close-in small planet occurrence rates in the solar neighbourhood of the thin and thick disks of the Galaxy. It is unclear whether there are other stellar properties related to the Galactic context that affect small-planet occurrence rates, or if it is only the combined effects of stellar metal content and mass. A future larger sample of stars and planets is needed to address those questions. [ABSTRACT FROM AUTHOR]

A low-amplitude periodic signal in the radial velocity (RV) time series of Barnard's Star was recently attributed to a planetary companion with a minimum mass of ~3.2 M⊕ at an orbital period of ~233 days. The relatively long orbital period and the proximity of Barnard's Star to the Sun raises the question whether the true mass of the planet can be constrained by accurate astrometric measurements. By combining the assumption of an isotropic probability distribution of the orbital orientation with the RV-analysis results, we calculated the probability density function of the astrometric signature of the planet. In addition, we reviewed the astrometric capabilities and limitations of current and upcoming astrometric instruments. We conclude that Gaia and the Hubble Space Telescope (HST) are currently the best-suited instruments to perform the astrometric follow-up observations. Taking the optimistic estimate of their single-epoch accuracy to be ~30μas, we find a probability of ~10% to detect the astrometric signature of Barnard's Star b with ~50 individual-epoch observations. In case of no detection, the implied mass upper limit would be ~8 M⊕, which would place the planet in the super-Earth mass range. In the next decade, observations with the Wide-Field Infrared Space Telescope (WFIRST) may increase the prospects of measuring the true mass of the planet to ~99%. [ABSTRACT FROM AUTHOR]

Here, we show that the fundamental Fickian process of diffusion can be equivalently described by a pressureless, compressible, and irrotational flow dynamics, whose effective force is governed by the divergence of the viscous stress tensor. This brings together the seemingly unrelated processes of mass and momentum transports. [ABSTRACT FROM AUTHOR]

In this short paper we examine whether the measurement of Doppler shifts in the solar light reflected off an asteroid surface may improve the accuracy of the determined orbit. Our results suggest it will be worthwhile to use high-resolution spectrographs, of the exoplanet-hunting type, to measure those Doppler shifts. Spectroscopic Doppler shifts might improve the accuracy of Earth-impact predictions, help to recover 'lost' near-Earth objects, and may also significantly enhance the knowledge about dynamics of the Kuiper belt. Future high-resolution spectrographs on the VLT and the E-ELT may thus have an important role in studies of Solar-System dynamics and kinematics. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We propose a new approach to measure differential radial velocities, mainly for single-lined spectroscopic binaries. The proposed procedure –tiravel (Template-Independent RAdial VELocities) – does not rely on a prior theoretical or observed template, but instead looks for a set of relative Doppler shifts that simultaneously optimizes the alignment of all the observed spectra. We suggest a simple measure to quantify this overall alignment and use its maximum to measure the relative radial velocities. As a demonstration, we applytiravel to the observed spectra of three known spectroscopic binaries, and show that in two casestiravel performs as good as the commonly used approach, while in one casetiravel yielded a better orbital solution. [ABSTRACT FROM AUTHOR]

ABSTRACT V621 Persei is a detached eclipsing binary in the open cluster χ Persei, which is composed of an early B-type giant star and a main-sequence secondary component. From high-resolution spectroscopic observations and radial velocities from the literature, we determine the orbital period to be 25.5 d and the primary velocity semi-amplitude to be K= 64.5 ± 0.4 km s−1. No trace of the secondary star has been found in the spectrum. We solve the discovery light curves of this totally eclipsing binary and find that the surface gravity of the secondary star is log gB= 4.244 ± 0.054. We compare the absolute masses and radii of the two stars in the mass-radius diagram, for different possible values of the primary surface gravity, with the predictions of stellar models. We find that log gA≈ 3.55, in agreement with values found from fitting Balmer lines with synthetic profiles. The expected masses of the two stars are 12 and 6 M⊙ and the expected radii are 10 and 3 R⊙. The primary component is near the blue loop stage in its evolution. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper presents a new approach to combining cross-correlation functions. The combination is based on a maximum-likelihood approach and uses a non-linear combination scheme. It can be effective for radial velocity analysis of multi-order spectra, or for analysis of multiple exposures of the same object. Simulations are presented to show the potential of the suggested combination scheme. The technique has already been used to detect a very faint companion of HD 41004. [ABSTRACT FROM AUTHOR]

Focuses on a study which investigated the role of soluble binding proteins, distance and time on the transfer of fatty acids between intracellular membranes. Model structure; Validation of the steady-state model; Discussion of the results.

A letter to the editor is presented commenting on G.N. Ioannou's article on serum bilirubin and risk of colorectal cancer, featured in a 2006 issue.

We introduce an extension of the periodogram concept to time-resolved spectroscopy. USuRPER, the unit-sphere representation periodogram, is a novel technique that opens new horizons in the analysis of astronomical spectra. It can be used to detect a wide range of periodic variability of the spectrum shape. Essentially, the technique is based on representing spectra as unit vectors in a multidimensional hyperspace, hence its name. It is an extension of the phase-distance correlation periodogram we had introduced in previous papers, to very high-dimensional data such as spectra. USuRPER takes the overall shape of the spectrum into account, which means that it does not need to be reduced into a single quantity such as radial velocity or temperature. Through simulations, we demonstrate its performance in various types of spectroscopic variability: single-lined and double-lined spectroscopic binary stars, and pulsating stars. We also show its performance on actual data of a rapidly oscillating Ap star. USuRPER is a new tool to explore large time-resolved spectroscopic databases such as APOGEE, LAMOST, and the RVS spectra of Gaia. We have made a public GitHub repository with a Python implementation of USuRPER available to the community, to experiment with it and apply it to a wide range of spectroscopic time series. [ABSTRACT FROM AUTHOR]

A correction to the article "Template-Independent Radial Velocity measurement" that was published in the 2006 issue is presented.

Aims. We use the recently published database of radial velocities (RVs) that were derived from fifteen years of HARPS/ESO observations to search for planet candidates. Methods. For targets with sufficient RV data, we applied an automated algorithm to identify significant periodic signals and fit a Keplerian model for orbital estimates. We also searched the auxiliary data of stellar-activity indices and compared our findings with existing literature, to detect periodic RV signals that have no counterpart in the activity timeseries. The most convincing signals were then manually inspected to designate additional false planet detection, focusing the search on long-period (P> 1 000 days) massive candidates around FGK dwarf stars. Results. We identified two Jupiter analogs, in orbit around the slightly evolved F8V star HD 103891 and the Solar-like star HD 105779. We used nested sampling to derive their orbital parameters, and found their orbital periods to be 1919 ± 16 days and 2412 ± 54 days, while their minimum masses are 1.44 ± 0.02 MJup and 0.64 ± 0.06 MJup, respectively. While the orbit of HD 103891 b is slightly eccentric (e = 0.31 ± 0.03), that of HD 105779 b is likely circular (e < 0.16). Conclusions. With minimum astrometric signatures of ~59 and ~42 μas, HD 103891 b and HD 105779 b join the growing sample of planets whose exact masses may soon be derived with Gaia astrometry. This finding also highlights the importance of long-term RV surveys to study planetary occurrence beyond the snow line of Solar-like stars. [ABSTRACT FROM AUTHOR]

ABSTRACT We present a new, simple method to predict activity-induced radial velocity (RV) variations using high-precision time series photometry. It is based on insights from a simple spot model, has only two free parameters (one of which can be estimated from the light curve) and does not require knowledge of the stellar rotation period. We test the method on simulated data and illustrate its performance by applying it to MOST/SOPHIE observations of the planet host star HD 189733, where it gives almost identical results to much more sophisticated but highly degenerate models, and synthetic data for the Sun, where we demonstrate that it can reproduce variations well below the m s−1 level. We also apply it to quarter 1 data for Kepler transit candidate host stars, where it can be used to estimate RV variations down to the 2-3 m s−1 level, and show that RV amplitudes above that level may be expected for approximately two-thirds of the candidates we examined. [ABSTRACT FROM AUTHOR]

Abstract: An anticoloring of a graph is a coloring of some of the vertices, such that no two adjacent vertices are colored in distinct colors. The anticoloring problem seeks, roughly speaking, such colorings with many vertices colored in each color. We deal with the anticoloring problem for planar graphs and, using Lipton and Tarjan’s separation algorithm, provide an algorithm with some bound on the error. We also show that, to solve the anticoloring problem for general graphs, it suffices to solve it for connected graphs. [Copyright &y& Elsevier]

We report on photometric follow-up of the recently discovered transiting planet WASP-1b. We observed two transits with the Wise Observatory 1-m telescope, and used a variant of the Eclipsing Binary Orbit Program (ebop) code together with the Sys-Rem detrending approach to fit the light curve. Assuming a stellar mass of , we derived a planetary radius of and mass of . An uncertainty of 15 per cent in the stellar mass results in an additional systematic uncertainty of 5 per cent in the planetary radius and of 10 per cent in planetary mass. Our observations yielded a slightly better ephemeris for the centre of the transit: . The new planet is an inflated, low-density planet, similar to HAT-P-1b and HD 209458b. [ABSTRACT FROM AUTHOR]

We suggest a new algorithm to remove systematic effects in a large set of light curves obtained by a photometric survey. The algorithm can remove systematic effects, such as those associated with atmospheric extinction, detector efficiency, or point spread function changes over the detector. The algorithm works without any prior knowledge of the effects, as long as they linearly appear in many stars of the sample. The approach, which was originally developed to remove atmospheric extinction effects, is based on a lower rank approximation of matrices, an approach which has already been suggested and used in chemometrics, for example. The proposed algorithm is especially useful in cases where the uncertainties of the measurements are unequal. For equal uncertainties, the algorithm reduces to the Principal Component Analysis (PCA) algorithm. We present a simulation to demonstrate the effectiveness of the proposed algorithm and we point out its potential, in the search for transit candidates in particular. [ABSTRACT FROM AUTHOR]

Abstract: We consider scenarios in which a sequence of tests is to be applied to an object; the result of a test may be that a decision (such as the classification of the object) can be made without running additional tests. Thus, one seeks an ordering of the tests that is optimal in some sense, such as minimum expected resource consumption. Sequences of tests are commonly used in computer vision (Paul A. Viola and Michael J. Jones (2001) [15]) and other applications. Finding an optimal ordering is easy when the tests are completely independent. Introducing precedence constraints, we show that the optimization problem becomes NP-hard when the constraints are given by means of a general partial order. Restrictions of the constraints to non-trivial special cases that allow for low-order polynomial-time algorithms are examined. [Copyright &y& Elsevier]

KOI-13 was presented by the Kepler team as a candidate for having a giant planet - KOI-13.01, with an orbital period of 1.7 d and a transit depth of ∼0.8%. We have analyzed the Kepler Q2 data of KOI-13, which was publicly available at the time of the submission of this paper, and derived the amplitudes of the beaming, ellipsoidal and reflection modulations - 8.6± 1.1, 66.8± 1.6 and 72.0 ± 1.5 ppm (parts per million), respectively. After the paper was submitted, Q3 data were released, so we repeated the analysis with the newly available light curve. The results of the two quarters were quite similar. From the amplitude of the beaming modulation we derived a mass of 10 ± 2 MJup for the secondary, suggesting that KOI-13.01 was a massive planet, with one of the largest known radii.We also found in the data a periodicity of unknown origin with a period of 1.0595 d and a peak-to-peak modulation of ∼60 ppm. The light curve of Q3 revealed a few additional small-amplitude periodicities with similar frequencies. It seemed as if the secondary occultation of KOI-13 was slightly deeper than the reflection peak-to-peak modulation by 16.8±4.5 ppm. If real, this small difference was a measure of the thermal emission from the night side of KOI-13.01. We estimated the effective temperature to be 2600 ± 150 K, using a simplistic black-body emissivity approximation. We then derived the planetary geometrical and Bond albedos as a function of the day-side temperature. Our analysis suggested that the Bond albedo of KOI-13.01 might be substantially larger than the geometrical albedo. [ABSTRACT FROM AUTHOR]

This paper presents a new algorithm,trimor, to analyse multi-order spectra of triple systems. The algorithm is an extension oftricor, the three-dimensional correlation technique that derives the radial velocities of triple stellar systems from single-order spectra. The combined correlation derived from many orders enables the detection and the measurement of radial velocities of faint tertiary companions. The paper appliedtrimor to the already available spectra of HD 188753, a well-known triple system, yielding the radial velocities of the faintest star in the system. This rendered the close pair of the triple system a double-lined spectroscopic binary, which led to a precise mass ratio and an estimate of its inclination. The close-pair inclination is very close to the inclination of the wide orbit, consistent with the assertion that this triple system has a close to coplanar configuration. [ABSTRACT FROM AUTHOR]

In the companion article, a framework for structural multiscale geometric organization of subsets of R" and of graphs was introduced. Here, diffusion semigroups are used to generate multiscale analyses in order to organize and represent complex structures. We emphasize the multiscale nature of these problems and build scaling functions of Markov matrices (describing local transitions) that lead to macroscopic descriptions at different scales. The process of iterating or diffusing the Markov matrix is seen as a generalization of some aspects of the Newtonian paradigm, in which local infinitesimal transitions of a system lead to global macroscopic descriptions by integration. This article deals with the construction of fast-order N algorithms for data representation and for homogenization of heterogeneous structures. [ABSTRACT FROM AUTHOR]

We provide a framework for structural multiscale geometric organization of graphs and subsets of W'. We use diffusion semigroups to generate multiscale geometries in order to organize and represent complex structures. We show that appropriately selected eigenfunctions or scaling functions of Markov matrices, which describe local transitions, lead to macroscopic descriptions at different scales. The process of iterating or diffusing the Markov matrix is seen as a generalization of some aspects of the Newtonian paradigm, in which local infinitesimal transitions of a system lead to global macroscopic descriptions by integration. We provide a unified view of ideas from data analysis, machine learning, and numerical analysis. [ABSTRACT FROM AUTHOR]

Gap junctions, composed of connexins, have been shown to suppress transformation in a variety of malignancies and transformed cell types. In addition, transforming factors such as the src oncogene have been shown to directly phosphorylate some connexins (e.g., Cx43) and inhibit coupling. To investigate the role of gap junctions in cell transformsation by v-src , we utilized a clonal cell line derived from Cx43 knockout mice (KoA) that was immortalized, but not transformed. Transfection by v-src induced a marked transformed phenotype characterized by growth in low serum and anchorage-independent conditions. Subsequent transfections by Cx43, Cx32 or vector alone were then tested for their effects on growth. Activity of pp60 v - src was confirmed in all transfectants as well as the ability of pp60 v - src to phosphorylate Cx43 in several clones. Despite the documented effect of pp60 v - src on Cx43 channel closure, modest coupling was still retained in many of the Cx43 and Cx32 transfectants. However, none of the four Cx43 transfected clones showed significant inhibitory effects on proliferation in either anchorage-independent or low serum growth conditions. Of the Cx32 clones, only one in five showed effects on growth in both assays, which was the same ratio observed for the control transfectants. Thus, based on the levels of expression achieved, which were comparable to endogenous levels in established cell lines, neither Cx43 nor Cx32 serve as effective suppressors of the transformed growth phenotype of this v-src expressing cell line. [ABSTRACT FROM AUTHOR]

We present a radial velocity study of the triple-lined system Gliese 644 and derive spectroscopic elements for the inner and outer orbits with periods of 2.965 5 and 627 d. We also utilize old visual data, as well as modern speckle and adaptive optics observations, to derive a new astrometric solution for the outer orbit. These two orbits together allow us to derive masses for each of the three components in the system: M[sub A]=0.410±0.028 (6.9 per cent), M[sub Ba]=0.336±0.016 (4.7 per cent), and M[sub Bb]=0.304±0.014 (4.7 per cent) M[sub ⊙]. We suggest that the relative inclination of the two orbits is very small. Our individual masses and spectroscopic light ratios for the three M stars in the Gliese 644 system provide three points for the mass–luminosity relation near the bottom of the main sequence, where the relation is poorly determined. These three points agree well with theoretical models for solar metallicity and an age of 5 Gyr. Our radial velocities for Gliese 643 and vB 8, two common proper motion companions of Gliese 644, support the interpretation that all five M stars are moving together in a physically bound group. We discuss possible scenarios for the formation and evolution of this configuration, such as the formation of all five stars in a sequence of fragmentation events leading directly to the hierarchical configuration now observed, versus formation in a small N cluster with subsequent dynamical evolution into the present hierarchical configuration. [ABSTRACT FROM AUTHOR]

The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects. Small, sub-kilometre-sized, Kuiper belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Observations at both optical and X-ray wavelengths claim to have detected such occultations, but their implied abundances are inconsistent with each other and far exceed theoretical expectations. Here we report an analysis of archival data that reveals an occultation by a body with an approximately 500-metre radius at a distance of 45 astronomical units. The probability of this event arising from random statistical fluctuations within our data set is about two per cent. Our survey yields a surface density of Kuiper belt objects with radii exceeding 250 metres of , ruling out inferred surface densities from previous claimed detections by more than 5σ. The detection of only one event reveals a deficit of sub-kilometre-sized Kuiper belt objects compared to a population extrapolated from objects with radii exceeding 50 kilometres. This implies that sub-kilometre-sized objects are undergoing collisional erosion, just like debris disks observed around other stars. [ABSTRACT FROM AUTHOR]

A correction to the article "Search for brown-dwarf companions of stars" published in a 2011 issue of the periodical is presented.