The detectability of single- and multiple-planet systems in Gaia data

The all-sky survey of Gaia will generate vast amounts of astrometric data, in which there are expected to be thousands of planets found. Finding a system of $n_\textup{p}$ planets requires fitting of a total $5+7n_\textup{p}$ parameters: five astrometric and seven Keplerian parameters for every planet. The problem is thus highly non-linear and computationally prohibitive. After exploiting the linear properties of the Thiele-Innes constants, the remaining three non-linear parameters still limit the number of stars in the Gaia data that are practicable to probe for planets. The aim of this thesis is to investigate the feasibility of further eliminating two non-linear parameters, which is accomplished by assuming a circular orbit in the fit. If this approach is successful at reliably finding planet candidates even for eccentric orbits, it can possibly be used to expand the number of stars that can be searched for planets in the Gaia data. The approach is tested in simulated Gaia observations of known single- and multiple-planet systems from radial velocity (RV) measurements. Two detection metrics are used to enable comparison with past studies: a simple signal-to-noise (S/N) threshold and a more robust metric based on orbit fitting, the $\Delta\chi^2$ metric. The results indicate that, assuming a circular orbit in the fit, the orbital period can be correctly determined for planets with eccentricity $\lesssim0.8$ in single-planet systems, and $\lesssim0.5$ in multiple-planet systems. It is also found that around one third of the total number of planets in the current RV catalog, and at least one sixth of its multiple-planet system members, can reliably or somewhat reliably be detected and characterized by Gaia.När Tycho Brahe på 1500-talet stod i sin Stjärneborg på ön Ven utanför Landskrona och kartlagde stjärnhimlens rörelser utövade han vad vi i dag kallar för astrometri: att mäta himlakropparnas positioner och rörelser. I ett historiskt skede skulle precisionen i Tychos mätningar komma att knyta ihop astronomin med fysik för första gången. Johannes Kepler, Tychos medhjälpare och efterträdare, kunde med hjälp av Tychos data räkna ut planeternas omloppsbanor kring solen och till slut generalisera dessa till vad som i dag fortsätter vara grundstenarna i den celesta mekaniken, nämligen Keplers lagar. Dessa lagar kom sedan att förklaras av Newtons gravitationslag, varvid astrofysiken såg dagens ljus. Utan tvekan var Tychos noggranna iakttagelser ett viktigt tillskott i denna historiska händelseföljd. I december 2013 skickades den europeiska satelliten Gaia upp, som med sin utomordentliga precision kommer att observera närmare en miljard stjärnor och, likt Tycho, kartlägga deras positioner och rörelser. Precisionen av Gaia är sådan att den hade från Ven kunnat mäta vidden av ett hårstrå som befinner sig i Sundsvall! Detta möjliggör mätningar av de små störningar som Newtons lagar förutsäger att en planet utövar på sin värdstjärna, som förenat med den vida kartläggningen kommer att leda till många nya planetupptäckter. Det har uppskattats att Gaia under sina fem aktiva år kommer att finna och bestämma egenskaperna hos mer än $20\,000$ större planeter kring många olika typer av stjärnor. Ett av problemen för de som jobbar med att skönja planetsignaler ur Gaias data är att det skulle krävas en oerhörd mängd datorkraft om man skulle söka igenom varje en av de miljarder stjärnor Gaia kollar på. Eftersom det inte är praktiskt möjligt, får man istället nöja sig med att söka igenom några av de miljoner stjärnor som man beräknar ha störst sannolikhet att härbärgera planeter. Därför vill man hitta genvägar som gör det möjligt att snabbare upptäcka planetkandidater och således också möjligt att söka igenom fler stjärnor. I denna uppsats görs ett försök att, genom en synbart enkel taktik, hitta en sådan genväg. I algoritmerna som söker efter planeter behöver man i regel ta hänsyn till alla egenskaper hos den omloppsbana man försöker bestämma. Taktiken i denna uppsats är att anta att banan är cirkulär istället för elliptisk. Eftersom en ellips kan se ut på ofantligt många fler sätt än en cirkel blir problemet på detta vis många gånger enklare. Om denna taktik visar sig fungera väl, skulle den kunna göra det praktiskt möjligt att leta efter planetkandidater i ännu fler av stjärnorna i Gaias data. Om Gaia kommer att sätta avtryck i historien återstår att se, men klart är att satelliten, för planetforskningens räkning, kommer att generera en hel del data för ett rikt omfång av planetomgivna stjärnor. Detta kommer att ge oss insikter i fördelningen och egenskaperna av de större planeterna som bland annat kan användas för att testa olika teorier om planetbildning. I vilket fall som helst fortsätter Gaia Tychos tradition att kartlägga himlen med oöverträffad precision, vilket, i ett historiskt perspektiv, kan ha oförutsägbara följder

Optimisation of surface expression using the AIDA autotransporter

<p>Abstract</p> <p>Background</p> <p>Bacterial surface display is of interest in many applications, including live vaccine development, screening of protein libraries and the development of whole cell biocatalysts. The goal of this work was to understand which parameters result in production of large quantities of cells that at the same time express desired levels of the chosen protein on the cell surface. For this purpose, staphylococcal protein Z was expressed using the AIDA autotransporter in <it>Escherichia coli</it>.</p> <p>Results</p> <p>The use of an OmpT-negative <it>E. coli </it>mutant resulted in successful expression of the protein on the surface, while a clear degradation pattern was found in the wild type. The expression in the mutant resulted also in a more narrow distribution of the surface-anchored protein within the population. Medium optimisation showed that minimal medium with glucose gave more than four times as high expression as LB-medium. Glucose limited fed-batch was used to increase the cell productivity and the highest protein levels were found at the highest feed rates. A maintained high surface expression up to cell dry weights of 18 g l^-1could also be achieved by repeated glucose additions in batch cultivation where production was eventually reduced by low oxygen levels. In spite of this, the distribution in the bacterial population of the surface protein was narrower using the batch technique.</p> <p>Conclusions</p> <p>A number of parameters in recombinant protein production were seen to influence the surface expression of the model protein with respect both to the productivity and to the display on the individual cell. The choice of medium and the cell design to remove proteolytic cleavage were however the most important. Both fed-batch and batch processing can be successfully used, but prolonged batch processing is probably only possible if the chosen strain has a low acetic acid production.</p

Severity as a Priority Setting Criterion: Setting a Challenging Research Agenda

Priority setting in health care is ubiquitous and health authorities are increasingly recognising the need for priority setting guidelines to ensure efficient, fair, and equitable resource allocation. While cost-effectiveness concerns seem to dominate many policies, the tension between utilitarian and deontological concerns is salient to many, and various severity criteria appear to fill this gap. Severity, then, must be subjected to rigorous ethical and philosophical analysis. Here we first give a brief history of the path to today’s severity criteria in Norway and Sweden. The Scandinavian perspective on severity might be conducive to the international discussion, given its long-standing use as a priority setting criterion, despite having reached rather different conclusions so far. We then argue that severity can be viewed as a multidimensional concept, drawing on accounts of need, urgency, fairness, duty to save lives, and human dignity. Such concerns will often be relative to local mores, and the weighting placed on the various dimensions cannot be expected to be fixed. Thirdly, we present what we think are the most pertinent questions to answer about severity in order to facilitate decision making in the coming years of increased scarcity, and to further the understanding of underlying assumptions and values that go into these decisions. We conclude that severity is poorly understood, and that the topic needs substantial further inquiry; thus we hope this article may set a challenging and important research agenda

Spatially resolved spectroscopy across stellar surfaces. III. Photospheric Fe I lines across HD189733A (K1 V)

Spectroscopy across spatially resolved stellar surfaces reveals spectral line profiles free from rotational broadening, whose gradual changes from disk center toward the stellar limb reflect an atmospheric fine structure that is possible to model by 3-D hydrodynamics. Previous studies of photospheric spectral lines across stellar disks exist for the Sun and HD209458 (G0 V) and are now extended to the planet-hosting HD189733A to sample a cooler K-type star and explore the future potential of the method. During exoplanet transit, stellar surface portions successively become hidden and differential spectroscopy between various transit phases uncovers spectra of small surface segments temporarily hidden behind the planet. In Paper I, observable signatures were predicted quantitatively from hydrodynamic simulations. From observations of HD189733A with the ESO HARPS spectrometer at R=115,000, profiles for stronger and weaker Fe I lines are retrieved at several center-to-limb positions, reaching adequate S/N after averaging over numerous similar lines. Retrieved line profile widths and depths are compared to synthetic ones from models with parameters bracketing those of the target star and are found to be consistent with 3-D simulations. Center-to-limb changes strongly depend on the surface granulation structure and much greater line-width variation is predicted in hotter F-type stars with vigorous granulation than in cooler K-types. Such parameters, obtained from fits to full line profiles, are realistic to retrieve for brighter planet-hosting stars, while their hydrodynamic modeling offers previously unexplored diagnostics for stellar atmospheric fine structure and 3-D line formation. Precise modeling may be required in searches for Earth-analog exoplanets around K-type stars, whose more tranquil surface granulation and lower ensuing microvariability may enable such detections.Comment: 14 pages, 12 figures, accepted by Astronomy & Astrophysic

Spatially resolved spectroscopy across HD189733 (K1V) using exoplanet transits

For testing 3-dimensional models of stellar atmospheres, spectroscopy across spatially resolved stellar surfaces would be desired with a spectral resolution of $R = 100,000$ or more. Hydrodynamic models predict variations in line profile shapes, strengths, wavelength positions and asymmetries. These variations vary systematically between disk center and limb and as a function of line strength, excitation potential and wavelength region. However, except for a few supergiants and the Sun, current telescopes are not yet capable of resolving any stellar surfaces. One alternative method to resolve distant stellar surfaces, feasible already now, is differential spectroscopy of transiting exoplanet systems. By subtracting in-transit spectra from the spectrum outside of transit, the spectra from stellar surface portions temporarily hidden behind the planet can be disentangled. Since transiting planets cover only a small portion of the stellar surface, the method requires a very high signal-to-noise ratio, obtainable by averaging numerous similar spectral lines. We apply such differential spectroscopy on the 7.7 mag K1V star HD 189733 (‘Alopex’*); its transiting planet covers ∼ 3% of its host star’s surface, which is the deepest known transit among the brighter systems. Archival data from the ESO HARPS spectrometer are used to construct averaged profiles of photospheric Fe I lines, with the aim of comparing spatially resolved profiles to analogous synthetic line profiles computed from the 3-dimensional hydrodynamic CO5BOLD model. * We refer to HD 189733 as ‘Alopex’ (from the Greek ‘αλεπού’), denoting a fox related to the one that gave name to its constellation of Vulpecula

Classification of N=6 superconformal theories of ABJM type

Studying the supersymmetry enhancement mechanism of Aharony, Bergman, Jafferis and Maldacena, we find a simple condition on the gauge group generators for the matter fields. We analyze all possible compact Lie groups and their representations. The only allowed gauge groups leading to the manifest N=6 supersymmetry are, up to discrete quotients, SU(n) x U(1), Sp(n) x U(1), SU(n) x SU(n), and SU(n) x SU(m) x U(1) with possibly additional U(1)'s. Matter representations are restricted to be the (bi)fundamentals. As a byproduct we obtain another proof of the complete classification of the three algebras considered by Bagger and Lambert.Comment: 18 page