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public:seminar_abstracts [2018/10/30 15:31]
Mark Magee
public:seminar_abstracts [2019/01/14 17:04] (current)
Krishna Prasad
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 ====== ARC Seminar Abstracts ====== ====== ARC Seminar Abstracts ======
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 +===Energetic particles and star formation =====
 +** Dr Donna Rodgers-Lee** (Hertfordshire)- ARC Seminar Wednesday 16 January 2019 3 pm
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 +There is a growing body of observational evidence to suggest that energetic particles are produced during the low-mass star formation process. Both the young low-mass stars themselves and the jets they power appear to be capable of accelerating particles up to ~GeV energies. These low-energy cosmic rays may be important in determining the ionisation rate in star-forming regions and subsequently the chemical and dynamic evolution of protoplanetary disks.
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 +Here, based on the assumption that young low-mass stars accelerate protons to ~GeV energies, I will discuss our recent work focusing on the ionising effect of these energetic particles in protoplanetary disks, as well as further ways of investigating their transport properties. I will also describe on-going observational efforts to identify further evidence of non-thermal emission from young stellar objects. ​  
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 +===Revealing the Evolution of Comet Nuclei with Ground Photometric Observations =====
 +** Dr Rosita Kokotanekova** (ESO)- ARC Seminar Wednesday 12 December 2018 3 pm
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 +The complex nature of comets has earned them a spot among the most interesting objects in the Solar System. Comets are believed to still preserve information about the physical conditions in the protoplanetary disk. At the same time, they also bear signatures of the epoch of planetary migration ~4 billion years ago, of the time spent in the outer solar system, as well as of their recent activity. In the past three decades, a great progress in untangling the intricate history of comets has come from the in-situ studies during a series of space missions which culminated with the Rosetta mission between 2014 and 2016. However, with no plans for space missions to further comets in the next couple of decades, we have to rely more heavily on telescope observations to reveal new clues on the unanswered questions in cometary science. ​
 +In this talk, I will present results from our effort to study Jupiter-family comet nuclei and their source populations in the Centaur region and the Kuiper Belt from the ground. This work has demonstrated that photometric observations of the rotation and surface properties of comet nuclei can be key for understanding their evolution.
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 +===Internal Gravity Waves in Massive Stars =====
 +** Dr Tamara Rogers** (Newcastle University)- ARC Seminar Wednesday 05 December 2018 1 pm
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 +Internal Gravity Waves (IGW) can lead to angular momentum transport and chemical mixing in stellar interiors. In this talk I will  present numerical simulations of these waves in massive stars and discuss how they might contribute to the understanding of a variety of observational mysteries.  ​
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 +===Unveiling extreme dusty star-formation in the distant Universe =====
 +** Dr Julie Wardlow** (Lancaster University)- ARC Seminar Wednesday 28 November 2018 3.30 pm
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 +In recent years the high-redshift Universe has been increasingly opened to scrutiny at far-infrared wavelengths,​ where cool dust emission from star-formation dominates. The dusty star-forming galaxies (DSFGs), selected at these wavelengths likely represent an important, but short-lived phase in the growth of massive galaxies. These DSFGs often have star-formation rates in excess of ~1000 solar masses per year and are confirmed beyond z~6, although their redshifts and high dust contents make them faint and difficult to study at other wavelengths. I will present results probing their nature and the triggering mechanisms of their immense star-formation rates, using data from ALMA and other leading facilities.
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 +===Transverse Wave Induced Kelvin-Helmholtz Rolls in Spicules =====
 +** Dr Patrick Antolin** (University of St. Andrews)- ARC Seminar Wednesday 21 November 2018 3pm
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 +In addition to their jet-like dynamic behavior, spicules usually exhibit strong transverse speeds, multi-stranded structure, and heating from chromospheric to transition region temperatures. In this work we first analyze Hinode and IRIS observations of spicules and find different behaviors in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models, or long- wavelength torsional Alfvén waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective magnetohydrodynamic (MHD) wave. 
 +By comparing with an idealized 3D MHD simulation combined with radiative transfer modeling, we analyze the role of transverse MHD waves and associated instabilities in spicule-like features. We find that transverse wave induced Kelvin– Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, as seen in some observations. The rapid transverse dynamics and the density and temperature gradients at the spicule boundary lead to ring-shaped Mg II k and Ca II H source functions in the transverse cross-section,​ potentially allowing IRIS to capture the Kelvin–Helmholtz instability dynamics. Twists and currents propagate along the spicule at Alfvénic speeds, and the temperature variations within TWIKH rolls, produce the sudden appearance/​disappearance of strands seen in Doppler velocity and in Ca II H intensity. However, only a mild intensity increase in higher-temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules. ​
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 The infrared (IR) spectra of objects associated with dust and gas – including evolved stars, reflection nebulae, the interstellar medium (ISM), star-forming regions, and galaxies out to redshifts of z ∼ 3 – are dominated by emission bands at 3.3, 6.2, 7.7, 8.6 and 11.2 μm, the so-called unidentified infrared (UIR) bands. They are generally attributed to the IR fluorescence of Polycyclic Aromatic Hydrocarbon molecules (PAHs) UV pumped by nearby massive stars. Hence, the UIR band strengths are used to determine the star formation rate in galaxies, one of the key indicators for understanding galaxy formation and evolution. To date, PAHs are among the largest and most complex molecules known in space and emit up to 10% of the total power output of star-forming galaxies. The infrared (IR) spectra of objects associated with dust and gas – including evolved stars, reflection nebulae, the interstellar medium (ISM), star-forming regions, and galaxies out to redshifts of z ∼ 3 – are dominated by emission bands at 3.3, 6.2, 7.7, 8.6 and 11.2 μm, the so-called unidentified infrared (UIR) bands. They are generally attributed to the IR fluorescence of Polycyclic Aromatic Hydrocarbon molecules (PAHs) UV pumped by nearby massive stars. Hence, the UIR band strengths are used to determine the star formation rate in galaxies, one of the key indicators for understanding galaxy formation and evolution. To date, PAHs are among the largest and most complex molecules known in space and emit up to 10% of the total power output of star-forming galaxies.
 Space-based telescopes such as the Infrared Space Observatory (ISO) and the Spitzer Space Telescope revealed the richness of the PAH spectrum and provided extensive evidence for significant variability in the PAH spectrum from source to source and spatially within sources. In this talk, I will focus on the PAH properties in the reflection nebula NGC2023. I will present spectral maps of NGC2023 obtained with the SL and SH mode of the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. These observations clearly illustrate that the detailed characteristics of the PAH emission features vary across the reflection nebula and that different sets of PAH bands correlate spatially across the nebula. In particular, we conclude that at least 2 spatially distinct components contribute to the 7–9 μm PAH emission. We interpret these differences in spatial behavior in terms of variations in PAH characteristics such as size, charge and structure with the changing environment across the nebula. Space-based telescopes such as the Infrared Space Observatory (ISO) and the Spitzer Space Telescope revealed the richness of the PAH spectrum and provided extensive evidence for significant variability in the PAH spectrum from source to source and spatially within sources. In this talk, I will focus on the PAH properties in the reflection nebula NGC2023. I will present spectral maps of NGC2023 obtained with the SL and SH mode of the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. These observations clearly illustrate that the detailed characteristics of the PAH emission features vary across the reflection nebula and that different sets of PAH bands correlate spatially across the nebula. In particular, we conclude that at least 2 spatially distinct components contribute to the 7–9 μm PAH emission. We interpret these differences in spatial behavior in terms of variations in PAH characteristics such as size, charge and structure with the changing environment across the nebula.
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public/seminar_abstracts.1540913488.txt.gz · Last modified: 2018/10/30 15:31 by Mark Magee

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