Signs of a faint disc population at polluted white dwarfs

Observations of atmospheric metals and dust discs around white dwarfs provide important clues to the fate of terrestrial planetary systems around intermediate mass stars. We present Spitzer IRAC observations of 15 metal polluted white dwarfs to investigate the occurrence and physical properties of circumstellar dust created by the disruption of planetary bodies. We find subtle infrared excess emission consistent with warm dust around KUV 15519+1730 and HS 2132+0941, and weaker excess around the DZ white dwarf G245-58, which, if real, makes it the coolest white dwarf known to exhibit a 3.6 micron excess and the first DZ star with a bright disc. All together our data corroborate a picture where 1) discs at metal-enriched white dwarfs are commonplace and most escape detection in the infrared (possibly as narrow rings), 2) the discs are long lived, having lifetimes on the order of 10^6 yr or longer, and 3) the frequency of bright, infrared detectable discs decreases with age, on a timescale of roughly 500 Myr, suggesting large planetesimal disruptions decline on this same timescale.Comment: 11 pages, 6 figures, 5 tables, MNRAS accepted. Minor changes to match published versio

A Lucky Imaging search for stellar companions to transiting planet host stars

The presence of stellar companions around planet hosting stars influences the architecture of their planetary systems. To find and characterise these companions and determine their orbits is thus an important consideration to understand planet formation and evolution. For transiting systems even unbound field stars are of interest if they are within the photometric aperture of the light curve measurement. Then they contribute a constant flux offset to the transit light curve and bias the derivation of the stellar and planetary parameters if their existence is unknown. Close stellar sources are, however, easily overlooked by common planet surveys due to their limited spatial resolution. We therefore performed high angular resolution imaging of 49 transiting exoplanet hosts to identify unresolved binaries, characterize their spectral type, and determine their separation. The observations were carried out with the Calar Alto 2.2m telescope using the Lucky Imaging camera AstraLux Norte. All targets were imaged in i' and z' passbands. We found new companion candidates to WASP-14 and WASP-58, and we re-observed the stellar companion candidates to CoRoT-2, CoRoT-3, CoRoT-11, HAT-P-7, HAT-P-8, HAT-P-41, KIC 10905746, TrES-2, TrES-4, and WASP-2. We deduce from the stellar density around all sources that two companion candidates out of the targets with the first position measurement (CoRoT-11, HAT-P-41, KIC 10905746, WASP-14 and WASP-58) are probably unbound. In addition, we re-analyse the influence of the sources close to WASP-14 and WASP-58 on the planetary parameters given in the literature and find no significant changes

Spatially resolved spectroscopy of the exoplanet HR 8799 c

HR 8799 is a multi-planet system detected in direct imaging, with three companions known so far. Here, we present spatially resolved VLT/NACO 3.88--4.10 micron spectroscopy of the middle planet, HR 8799 c, which has an estimated mass of ~10 Mjup, temperature of ~1100 K and projected separation of 38 AU. The spectrum shows some differences in the continuum from existing theoretical models, particularly longwards of 4 microns, implying that detailed cloud structure or non-equilibrium conditions may play an important role in the physics of young exoplanetary atmospheres.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter

Evaluation of four methods for the assessment of joint swelling in dogs

Evaluation of joint swelling is an important part of the orthopedic examination and can be used to follow a patient’s progress during rehabilitation and therapy. Usually a swelling is assessed by palpating the joint but a more objective, but still easy to use, method would be preferable. This study seeks to increase the knowledge in veterinary rehabilitation by validating four different measurement tools (three recognized and one novel) for the assessment of elbow joint swelling: palpation, tape measure (circumference and figure eight measurement), slide caliper (craniocaudal and mediolateral positioning) and tonometer. This was achieved by calculating the inter- and intra-rater reliability and correlating the results from the different measurements with each other. The methods with best inter- and intra-rater reliability as well as good correlation among themselves were shown to be slide caliper with craniocaudal positioning, circumference and figure eight. Additional studies, with a larger and more diverse material, ought to investigate these methods further

Hackelselängdens betydelse för tuggtid och foderkonsumtion hos mjölkkor

Today, our cows experience a harder pressure to achieve higher milk yield. To manage this challenge the animal needs first class feeding and treatment. An important aspect of the feeding is to fulfil the need from the cows of especially fiber; and fiber with a sufficient proportion of long particles. Both too much and too little fiber is bad for the wellbeing of the cow, and she might get diseases like acidosis. Many models for feed management have been developed to secure that the animal gets enough of e.g. fiber with a sufficient proportion of long particles. The models describing physical characteristics of NDF have primarily been used in research. However, the new feed evaluating system NORFOR Plan will use the parameter "total chewing time" to secure the value of fiber with sufficient proportion of long particles. Total chewing time is the sum of the eating time and the ruminating time and is measured as minutes per kg dry matter. The aim of my study was to investigate how the physical characteristics of fiber affects the eating behaviour and total chewing time. In the study total chewing time was compared in two silages with similar nutrient composition. The only differences between the two silages were different chopping lengths. Twenty SRB cows in robotic milking (VMS system) was included in the study. They were randomly divided into two groups and feed with the two different silages. The length of the silage harvested with the self load wagon was 58 mm and the length of the silage harvested with the precession chopper was 25 mm arithmetic mean. The total chewing time was measured during at least 23 hours, using an IGER behaviour recorder (Ultrasound advice, London, U.K.). The jaw moment amplitude data were recorded at 20 Hz. Data files were analyzed in software GRAZE version 1,0 (Ultrasound advice, London, U.K.). Bouts of jaw moments were classified as either eating or ruminating. The result of my study implicates that the cows being feed with the longer silage had a tendency for longer total chewing time than the cows feed the precision chopped silage. An observation was that the cows fed with the shorter chopped silage consumed slightly more feed, but no significant differences in total feed consumption between the two groups could be observed.Idag ställs höga krav på att våra mjölkkor ska ha en hög mjölkavkastning och för att lyckas med detta krävs rätt utfodring och skötsel. En viktig aspekt att ta hänsyn till i utfodringen är att se till att deras behov av fiber och struktur säkerställs, då både för mycket och för lite fiber har en direkt inverkan på deras prestation. Exempel på utfodringsrelaterade sjukdomar hos våra nötkreatur är acidos, löpmagsomvridning, trumsjuka och leverförfettning. Strukturen hos ett fodermedel beskriver dels dess fysiska form, partikelstorlek, hur partiklarna är dimensionerade, deras hårdhet och förmåga att motstå mekanisk nedbrytning vid tuggning. En ytterligare viktig faktor vid bestämmandet av ett fodermedels struktur är dess kemiska sammansättning, som kan analyseras som NDF. Hur strukturen i exempelvis ett grovfoder blir, beror av skördesystem och maskintypen bestämmer den teoretiska snittlängden. Partikelstorleken i foder kan bestämmas genom torr och våtsiktning, bildbehandlingsteknik eller manuell sortering. Under årens lopp har det utvecklats olika modeller för att kunna mäta om foderstaten tillför tillräckligt med struktur, men dessa system har främst använts i forskningssyfte men i och med fodervärderingssystemet NORFOR kommer strukturparametern tuggtid att användas för att säkerställa att foderstaten innehåller tillräcklig mängd strukturgivande fiber. Tuggtid mäts som den sammanlagd ät och idisslingstiden och anges minuter per kg torrsubstans. Syftet med detta examensarbete var att studera hur strukturen i grovfodret påverkar tuggtid och konsumtionsmönster. I studien mättes tuggtid, (sammanlagd ät och idisslingstid) för två näringsmässigt identiska ensilage, men med olika hackelselängd. Studien genomfördes på SLU:s försöksgård Kungsängen i Uppsala 20 st SRB kor i stallet för automatisk mjölkning ingick i försöket. De delades in i 2 grupper vilka utfodrades med ensilage av olika hackelselängd. Ensilagen var näringsmässigt identiska men var skördade med snittvagn och exakthackarvagn. Partikellängden var 58 mm för snittvagnen och 25 mm för exakthackarvagnen. Tuggtiden mättes under minst 23 timmar med hjälp av IGER animal behaviour recorder (Ultra sound advice, London, U.K.), beskriven av Rutter et al. (2003). Käkrörelsernas amplitud registrerades vid 20 Hz och analys av käkrörelserna skedde därefter i ett program, IGER Graze™ version 1.0, där sammanlagd ät och idisslingstid kunde utläsas. Resultatet blev att korna som utfodrades med ensilaget med den längre hackelselängden (snittvagnen) hade en tendens till längre tuggtid per kg torrsubstans jämfört med det exakthackade ensilaget. En tendens till skillnad i foderintag fanns mellan grupperna med ett något högre foderintag för kor som fått ensilage skördat med exakthackarvagnen

Formation of stars, substellar objects and exoplanets : Observations of multiplicity

Many nearby stars are part of a binary or multiple system. Details about their history are preserved in their multiplicity characteristics, and observations of binary/multiple star systems provide a way to measure fundamental physical properties of the stars as well as clues to their formation and evolution. Moreover, planet formation and dynamics may also be affected by the presence of a second star, or by giant planets in the same system. In this thesis, high resolution imaging of low-mass stars, planet host stars and a multiple planet system is presented. The results of observations and analyses include the discovery of several previously unknown companion stars and multiplicity statistics for M dwarfs in the largest M dwarf multiplicity survey to date. We also present near-infrared characterization of four close M dwarf systems, previously unknown companion candidates to exoplanet host stars, and investigate how a close companion may affect planet formation. New astrometric data is presented for three of the directly imaged planets in the HR8799 system, and an analysis of a possible orbital configuration of planet HR 8799 d

The frequency and infrared brightness of circumstellar discs at white dwarfs

White dwarfs whose atmospheres are polluted by terrestrial-like planetary debris have become a powerful and unique tool to study evolved planetary systems. This paper presents results for an unbiased Spitzer IRAC search for circumstellar dust orbiting a homogeneous and well-defined sample of 134 single white dwarfs. The stars were selected without regard to atmospheric metal content but were chosen to have 1) hydrogen rich atmospheres, 2) 17 000 K < T_eff < 25 000 K and correspondingly young post main-sequence ages of 15-270Myr, and 3) sufficient far-ultraviolet brightness for a corresponding Hubble Space Telescope COS Snapshot. Five white dwarfs were found to host an infrared bright dust disc, three previously known, and two reported here for the first time, yielding a nominal 3.7% of white dwarfs in this post-main sequence age range with detectable circumstellar dust. Remarkably, complementary HST observations indicate that a fraction of 27% show metals in their photosphere that can only be explained with ongoing accretion from circumstellar material, indicating that nearly 90% of discs escape detection in the infrared, likely due to small emitting surface area. This paper also presents the distribution of disc fractional luminosity as a function of cooling age for all known dusty white dwarfs, suggesting possible disc evolution scenarios and indicating an undetected population of circumstellar discs.Comment: 17 pages, 5 figures and 4 tables. Accepted for publication in MNRA

Uniqueness and Non-uniqueness in the Einstein Constraints

The conformal thin sandwich (CTS) equations are a set of four of the Einstein equations, which generalize the Laplace-Poisson equation of Newton's theory. We examine numerically solutions of the CTS equations describing perturbed Minkowski space, and find only one solution. However, we find {\em two} distinct solutions, one even containing a black hole, when the lapse is determined by a fifth elliptic equation through specification of the mean curvature. While the relationship of the two systems and their solutions is a fundamental property of general relativity, this fairly simple example of an elliptic system with non-unique solutions is also of broader interest.Comment: 4 pages, 4 figures; abstract and introduction rewritte