1,137 research outputs found
Muscle fibrils: Solubilization and gel electrophoresis
In a three-year longitudinal intervention study developing an understanding of statisticalliteracy with a cohort of students from Years 4 to 6, teachers delivered lessons fromprovided materials, including scripts and prompts. Besides completing seven majorinvestigations, workbooks, and several in-class assessments, the students undertook foursurveys, from which their overall progress was determined, as well as individual learningprogressions. Findings indicated that despite experiencing the same lessons delivered insimilar ways, students had very different learning progressions. The implications of thesefindings are explored
Extragalactic megahertz-peaked spectrum radio sources at milliarcsecond scales
Extragalactic peaked-spectrum radio sources are thought to be the progenitors
of larger, radio-loud active galactic nuclei (AGN). Synchrotron self-absorption
(SSA) has often been identified as the cause of their spectral peak. The
identification of new megahertz-peaked spectrum sources from the GaLactic and
Extragalactic All-sky Murchison Widefield Array (GLEAM) survey provides an
opportunity to test how radio sources with spectral peaks below 1 GHz fit
within this evolutionary picture. We observed six peaked-spectrum sources
selected from the GLEAM survey, three that have spectral characteristics which
violate SSA and three that have spectral peaks below 230 MHz, with the Very
Long Baseline Array at 1.55 and 4.96 GHz. We present milliarcsecond resolution
images of each source and constrain their morphology, linear size, luminosity,
and magnetic field strength. Of the sources that are resolved by our study, the
sources that violate SSA appear to be compact doubles, while the sources with
peak frequencies below 230 MHz have core-jet features. We find that all of our
sources are smaller than expected from SSA by factors of >20. We also find that
component magnetic field strengths calculated from SSA are likely inaccurate,
differing by factors of >5 from equipartition estimates. The calculated
equipartition magnetic field strengths more closely resemble estimates from
previously studied gigahertz-peaked spectrum sources. Exploring a model of the
interaction between jets and the interstellar medium, we demonstrate that
free-free absorption (FFA) can accurately describe the linear sizes and peak
frequencies of our sources. Our findings support the theory that there is a
fraction of peaked-spectrum sources whose spectral peaks are best modelled by
FFA, implying our understanding of the early stages of radio AGN is incomplete.Comment: Accepted for publication in Astronomy & Astrophysics (A&A) on 16 July
2019. 13 pages, 6 figure
Can we really pick and choose? Benchmarking various selections of Gaia Enceladus/Sausage stars in observations with simulations
Large spectroscopic surveys plus Gaia astrometry have shown us that the inner stellar halo of the Galaxy is dominated by the debris of Gaia Enceladus/Sausage (GES). With the richness of data at hand, there are a myriad of ways these accreted stars have been selected. We investigate these GES selections and their effects on the inferred progenitor properties using data constructed from APOGEE and Gaia. We explore selections made in eccentricity, energy-angular momentum (E-Lz), radial action-angular momentum (Jr-Lz), action diamond, and [Mg/Mn]-[Al/Fe] in the observations, selecting between 144 and 1279 GES stars with varying contamination from in-situ and other accreted stars. We also use the Auriga cosmological hydrodynamic simulations to benchmark the different GES dynamical selections. Applying the same observational GES cuts to nine Auriga galaxies with a GES, we find that the Jr-Lz method is best for sample purity and the eccentricity method for completeness. Given the average metallicity of GES (−1.28 < [Fe/H] < −1.18), we use the z = 0 mass–metallicity relationship to find an average of ∼4 × 108 M⊙. We adopt a similar procedure and derive for the GES-like systems in Auriga and find that the eccentricity method overestimates the true by ∼2.6 × while E-Lz underestimates by ∼0.7 ×. Lastly, we estimate the total mass of GES to be using the relationship between the metallicity gradient and the GES-to-in-situ energy ratio. In the end, we cannot just ‘pick and choose’ how we select GES stars, and instead should be motivated by the science question
Can we really pick and choose? Benchmarking various selections of Gaia Enceladus/Sausage stars in observations with simulations
Large spectroscopic surveys plus Gaia astrometry have shown us that the inner
stellar halo of the Galaxy is dominated by the debris of Gaia Enceladus/Sausage
(GES). With the richness of data at hand, there are a myriad of ways these
accreted stars have been selected. We investigate these GES selections and
their effects on the inferred progenitor properties using data constructed from
APOGEE and Gaia. We explore selections made in eccentricity, energy-angular
momentum (E-Lz), radial action-angular momentum (Jr-Lz), action diamond, and
[Mg/Mn]-[Al/Fe] in the observations, selecting between 144 and 1,279 GES stars
with varying contamination from in-situ and other accreted stars. We also use
the Auriga cosmological hydrodynamic simulations to benchmark the different GES
dynamical selections. Applying the same observational GES cuts to nine Auriga
galaxies with a GES, we find that the Jr-Lz method is best for sample purity
and the eccentricity method for completeness. Given the average metallicity of
GES (-1.28 < [Fe/H] < -1.18), we use the mass-metallicity relationship to
find an average of . We
adopt a similar procedure and derive for the GES-like systems
in Auriga and find that the eccentricity method overestimates the true by while E-Lz underestimates by .
Lastly, we estimate the total mass of GES to be using the relationship between the metallicity gradient and
the GES-to-in-situ energy ratio. In the end, we cannot just `pick and choose'
how we select GES stars, and instead should be motivated by the science
question.Comment: 20 pages, 14 figures, submitted to MNRA
Stellar Systems at Low Radio Frequencies:The Discovery of Radio Exoplanets
For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf — the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star, and our follow-up radial-velocity (RV) observations with Harps-N to confirm the exoplanet's presence. Our study highlights the powerful new and developing synergy between low-frequency radio astronomy and RV observations, with radio emission providing a strong prior on the presence of a short-period planet. I will conclude the talk detailing how the radio detection of an star-exoplanet interaction provides unique information for exoplanet climate and habitability studies, and the extension of our survey to other stellar systems. <p/
Characterization of the sodium layer at Cerro Pachon, and impact on laser guide star performance
Detailed knowledge of the mesospheric sodium layer characteristics is crucial to estimate and optimize the performance of laser guide star (LGS) assisted adaptive optics (AO) systems. In this paper, we present an analysis of two sets of data on the mesospheric sodium layer. The first set comes from a laser experiment that was carried out at Cerro Tololo to monitor the abundance and altitude of the mesospheric sodium in 2001, during six runs covering a period of one year. These data are used to derive the mesospheric sodium column density, the sodium layer thickness and the temporal behaviour of the sodium layer mean altitude. The second set of data was gathered during the first year of the Gemini Multi-Conjugate Adaptive Optics (MCAO) System (GeMS) commissioning and operations. GeMS uses five LGSs to measure and compensate for atmospheric distortions. Analysis of the LGS wavefront sensor (WFS) data provides information about the sodium photon return and the spot elongation seen by the WFS. All these parameters show large variations on a yearly, nightly and hourly basis, affecting the LGS brightness, shape and mean altitude. The sodium photon return varies by a factor of 3-4 over a year, and can change by a factor of 2 over a night. In addition, the comparison of the photon returns obtained in 2001 with those measured a decade later using GeMS shows a significant difference in laser format efficiencies. We find that the temporal power spectrum of the sodium mean altitude follows a linear trend, in good agreement with the results reported by Pfrommer & Hickson
Stellar Systems at Low Radio Frequencies:The Discovery of Radio Exoplanets
For more than thirty years, radio astronomers have searched for auroral emission from exoplanets. With LOFAR we have recently detected strong, highly circularly polarised low-frequency (144 MHz) radio emission associated with a M-dwarf — the expected signpost of such radiation. The star itself is quiescent, with a 130-day rotation period and low X-ray luminosity. In this talk, I will detail how the radio properties of the detection imply that such emission is generated by the presence of an exoplanet in a short period orbit around the star, and our follow-up radial-velocity (RV) observations with Harps-N to confirm the exoplanet's presence. Our study highlights the powerful new and developing synergy between low-frequency radio astronomy and RV observations, with radio emission providing a strong prior on the presence of a short-period planet. I will conclude the talk detailing how the radio detection of an star-exoplanet interaction provides unique information for exoplanet climate and habitability studies, and the extension of our survey to other stellar systems
Milliarcsecond Structures of Variable Peaked-Spectrum Sources
Spectral variability offers a new technique to identify small scale
structures from scintillation, as well as determining the absorption mechanism
for peaked-spectrum (PS) radio sources. In this paper, we present very long
baseline interferometry (VLBI) imaging using the Long Baseline Array (LBA) of
two PS sources, MRC0225-065 and PMNJ0322-4820, identified as spectrally
variable from observations with the Murchison Widefield Array (MWA). We compare
expected milliarcsecond structures based on the detected spectral variability
with direct LBA imaging. We find MRC0225-065 is resolved into three components,
a bright core and two fainter lobes, roughly 430pc projected separation. A
comprehensive analysis of the magnetic field, host galaxy properties, and
spectral analysis implies that MRC0225-065 is a young radio source with recent
jet activity over the last 10^2-10^3years. We find PMNJ0322-4820 is unresolved
on milliarcsecond scales. We conclude PMNJ0322-4820 is a blazar with flaring
activity detected in 2014 with the MWA. We use spectral variability to predict
morphology and find these predictions consistent with the structures revealed
by our LBA images.Comment: Accepted for publication in PASA. 11 pages, 4 figure
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