Molecular Genetic Typing of Staphylococcus aureus from Cows, Goats, Sheep, Rabbits and Chickens

End of project reportsS. aureus can also cause a number of infections in animals such as tick-associated pyaemia in lambs, staphylococcosis in rabbits, septicaemia, abscesses and chondronecrosis in chickens and pneumonia and osteomyelitis complex in turkeys. S. aureus is the most frequent cause of bovine mastitis, a disease that is of economic importance worldwide (Beck et al., 1992). Typically staphylococcal mastitis is chronic in nature, with subclinical mastitis being the most common form

Population and Virulence Factor Analysis of Staphylococcus aureus from Bovine Mastitis.

End of Project ReportsStaphylococcus aureus is a major cause of bovine mastitis and the disease is responsible for substantial economic losses in the dairy industry world-wide. A large number of commonly accepted virulence factors are associated with S. aureus but it is yet to be elucidated which of these are important for infection of the bovine udder. A rational and effective strategy for the control of intramammary infections may need to be directed against clones of S. aureus that commonly cause disease. The objective of this study was to characterise the genetic variance of S. aureus isolate populations from infected udders in Ireland using RAPD-PCR, ribotyping and multilocus enzyme electrophoresis (MLEE). Similar S. aureus isolates collected in the USA were also typed in order to compare strain differences in staphylococcal populations in a different environment. Phenotypic diversity based on a number of presumed virulence factors together with antibiotic sensitivity was examined and correlations between phenotype and genotype were identified, if present. In addition, a pathogenicity island encoding multiple superantigens was completely sequenced and characterised. Knockout mutants of these superantigens were also constructed and in vitro functional analysis performed. Laboratory animal experiments (mice and rabbits) were used to study the relative pathogenicity of individual staphylococcal strains (mice) and also to measure the immunological responses after prolonged exposure to the predominant strains (rabbits)

SpinSpotter: An Automated Algorithm for Identifying Stellar Rotation Periods With Autocorrelation Analysis

Spinspotter is a robust and automated algorithm designed to extract stellar rotation periods from large photometric datasets with minimal supervision. Our approach uses the autocorrelation function (ACF) to identify stellar rotation periods up to one-third the observational baseline of the data. Our algorithm also provides a suite of diagnostics that describe the features in the ACF, which allows the user to fine-tune the tolerance with which to accept a period detection. We apply it to approximately 130,000 main-sequence stars observed by the Transiting Exoplanet Survey Satellite (TESS) at 2-minute cadence during Sectors 1-26, and identify rotation periods for 13,504 stars ranging from 0.4 to 14 days. We demonstrate good agreement between our sample and known values from the literature and note key differences between our population of rotators and those previously identified in the Kepler field, most notably a large population of fast-rotating M dwarfs. Our sample of rotating stars provides a data set with coverage of nearly the entire sky that can be used as a basis for future gyrochronological studies, and, when combined with proper motions and distances from Gaia, to search for regions with high densities of young stars, thus identifying areas of recent star formation and undiscovered moving group members. Our algorithm is publicly available for download and use on GitHub.Comment: 14 pages, 5 figures, Accepted for publication in The Astrophysical Journa

A New Look at T Tauri Star Forbidden Lines: MHD Driven Winds from the Inner Disk

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. We report the first high-resolution ($\Delta v\sim$6\kms) analysis of [S II] $\lambda$4068, [O I] $\lambda$5577, and [O I] $\lambda$6300 lines from a sample of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into three kinematic components: a high-velocity component (HVC) associated with jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We confirm previous findings that many LVCs are blueshifted by more than 1.5 kms$^{-1}$ thus most likely trace a slow disk wind. We further show that the profiles of individual components are similar in the three lines. We find that most LVC-BC and NC line ratios are explained by thermally excited gas with temperatures between 5,000$-$10,000 K and electron densities $\sim10^{7}-10^{8}$ cm$^{-3}$. The HVC ratios are better reproduced by shock models with a pre-shock H number density of $\sim10^{6}-10^{7}$ cm$^{-3}$. Using these physical properties, we estimate $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}$ for the LVC and $\dot{M}_{\rm jet}/\dot{M}_{\rm acc}$ for the HVC. In agreement with previous work, the mass carried out in jets is modest compared to the accretion rate. With the likely assumption that the NC wind height is larger than the BC, the LVC-BC $\dot{M}_{\rm wind}/\dot{M}_{\rm acc}$ is found to be higher than the LVC-NC. These results suggest that most of the mass loss occurs close to the central star, within a few au, through an MHD driven wind. Depending on the wind height, MHD winds might play a major role in the evolution of the disk mass.Comment: 45 pages, 23 figures, and 7 tables, accepted by Ap

A Spectroscopic Survey of Subarcsecond Binaries in the Taurus-Auriga Dark Cloud with the Hubble Space Telescope

We report the results of a spectroscopic survey of 20 close T Tauri binaries in the Taurus-Auriga dark cloud where the separations between primaries and their secondaries are less than the typical size of a circumstellar disk around a young star. Analysis of low-resolution and medium-resolution STIS spectra yields the stellar luminosities, reddenings, ages, masses, mass accretion rates, IR excesses, and emission line luminosities for each star in each pair. We examine the ability of IR color excesses, H-alpha equivalent widths, [O I] emission, and veiling to distinguish between weak emission and classical T Tauri stars. Four pairs have one cTTs and one wTTs; the cTTs is the primary in three of these systems. This frequency of mixed pairs among the close T Tauri binaries is similar to the frequency of mixed pairs in wider young binaries. Extinctions within pairs are usually similar; however, the secondary is more heavily reddened than the primary in some systems, where it may be viewed through the primary's disk. Mass accretion rates of primaries and secondaries are strongly correlated, and H-alpha luminosities, IR excesses, and ages also correlate within pairs. Primaries tend to have somewhat larger accretion rates than their secondaries do, and are typically slightly older than their secondaries according to three different sets of modern pre-main-sequence evolutionary tracks. Age differences for XZ Tau and FS Tau, systems embedded in reflection nebulae, are striking; the secondary in each pair is less massive but more luminous than the primary. The stellar masses of the UY Aur and GG Tau binaries measured from their rotating molecular disks are about 30% larger than the masses inferred from the spectra and evolutionary tracks

Star Spot Induced Radial Velocity Variability in LkCa 19

We describe a new radial velocity survey of T Tauri stars and present the first results. Our search is motivated by an interest in detecting massive young planets, as well as investigating the origin of the brown dwarf desert. As part of this survey, we discovered large-amplitude, periodic, radial velocity variations in the spectrum of the weak line T Tauri star LkCa 19. Using line bisector analysis and a new simulation of the effect of star spots on the photometric and radial velocity variability of T Tauri stars, we show that our measured radial velocities for LkCa19 are fully consistent with variations caused by the presence of large star spots on this rapidly rotating young star. These results illustrate the level of activity-induced radial velocity noise associated with at least some very young stars. This activity-induced noise will set lower limits on the mass of a companion detectable around LkCa 19, and similarly active young stars.Comment: ApJ accepted, 27 pages, 12 figures, aaste

A New Look at T Tauri Star Forbidden Lines: MHD-driven Winds from the Inner Disk

Magnetohydrodynamic (MHD) and photoevaporative winds are thought to play an important role in the evolution and dispersal of planet-forming disks. We report the first high-resolution (∆v ∼ 6 km s−1 ) analysis of [S II] λ4068, [O I] λ5577, and [O I] λ6300 lines from a sample of 48 T Tauri stars. Following Simon et al. (2016), we decompose them into three kinematic components: a high-velocity component (HVC) associated with jets, and a low-velocity narrow (LVC-NC) and broad (LVC-BC) components. We confirm previous findings that many LVCs are blueshifted by more than 1.5 km s−1 thus most likely trace a slow disk wind. We further show that the profiles of individual components are similar in the three lines. We find that most LVC-BC and NC line ratios are explained by thermally excited gas with temperatures between 5,000−10,000 K and electron densities ∼ 107 −108 cm−3 . The HVC ratios are better reproduced by shock models with a pre-shock H number density of ∼ 106 − 107 cm−3 . Using these physical properties, we estimate M˙ wind/M˙ acc for the LVC and M˙ jet/M˙ acc for the HVC. In agreement with previous work, the mass carried out in jets is modest compared to the accretion rate. With the likely assumption that the NC wind height is larger than the BC, the LVC-BC M˙ wind/M˙ acc is found to be higher than the LVC-NC. These results suggest that most of the mass loss occurs close to the central star, within a few au, through an MHD driven wind. Depending on the wind height, MHD winds might play a major role in the evolution of the disk mass

Proper Motions of the HH 47 Jet Observed with the Hubble Space Telescope

We present a proper motion study of the shock waves within the classic stellar jet HH 47 based on Hubble Space Telescope H-alpha and [S II] images of the region taken over two epochs. Individual knots within the jet and in the bow shock/Mach disk working surface of HH 47A move significantly in the five years that separate the images, and the excellent spatial resolution of HST makes it possible to measure the proper motions with enough precision to easily observe differential motions throughout the flow. The bright portion of the jet emerges at 37.5 +/- 2.5 degrees from the plane of the sky with an average velocity of 300 km/s. Dynamical ages of the shock waves in the jet range from a few decades for knots recently ejected by the source to ~ 1300 years for the faint extended bow shock HH 47D. The jet curves, but motions of knots in the jet are directed radially away from the exciting source, and velocity variability in the flow drives the shock waves that heat the jet internally. The jet orientation angle varies with time by about 15 degrees, and currently points to the northwestern portion of a cavity outlined by a reflection nebula, where a quasi-stationary shock deflects the jet. The major working surface HH 47A is more complex than a simple bow shock/Mach disk, and contains numerous clumps that move relative to one another with velocities of ~ +/- 40 km/s. Small clumps or instabilities affect the Mach disk, and dense clumps may move all the way through the working surface to cause the bumpy morphology seen at the bow shock. A localized area between the bow shock and Mach disk varies significantly between the two sets of images.Comment: full resolution figures available at http://sparky.rice.edu/~hartigan/pub.html; Accepted for publication in the Astronomical Journa

A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau

The ~2 Myr old classical T Tauri star CI Tau shows periodic variability in its radial velocity (RV) variations measured at infrared (IR) and optical wavelengths. We find that these observations are consistent with a massive planet in a ~9-day period orbit. These results are based on 71 IR RV measurements of this system obtained over 5 years, and on 26 optical RV measurements obtained over 9 years. CI Tau was also observed photometrically in the optical on 34 nights over ~one month in 2012. The optical RV data alone are inadequate to identify an orbital period, likely the result of star spot and activity induced noise for this relatively small dataset. The infrared RV measurements reveal significant periodicity at ~9 days. In addition, the full set of optical and IR RV measurements taken together phase coherently and with equal amplitudes to the ~9 day period. Periodic radial velocity signals can in principle be produced by cool spots, hot spots, and reflection of the stellar spectrum off the inner disk, in addition to resulting from a planetary companion. We have considered each of these and find the planet hypothesis most consistent with the data. The radial velocity amplitude yields an Msin(i) of ~8.1 M_Jup; in conjunction with a 1.3 mm continuum emission measurement of the circumstellar disk inclination from the literature, we find a planet mass of ~11.3 M_Jup, assuming alignment of the planetary orbit with the disk.Comment: 61 pages, 13 figures, accepted for publication in The Astrophysical Journa