This page lists the Seminars that were given at the EAO offices in Hilo or virtually on zoom in 2020. The EAO staff would like to thank all guest speakers and encourage new astronomers/instrument specialists to give talks when visiting.
April 21st, 2pm (HST)
Title: Blowtorch of the Gods – Event Horizon Telescope Observations of the Blazar 3C 279
Geoff Bower, ASIAA
The Event Horizon Telescope is a global submillimeter-wavelength array that produces the highest angular resolution images of black holes. In 2019, the EHT announced an image of the black hole in M87, now also known as Powehi, that showed ring-like emission as the result of strong gravitational lensing. Nearly a year later, the EHT has announced the highest angular resolution image of the blazar 3C 279. Blazars are highly variable active galactic nuclei with relativistic jets that are beamed towards the Earth. The extreme angular resolution of the EHT image reveals the formation of the jet and dynamical evolution on a time scale of days. I will present the new EHT images of 3C 279 and discuss their interpretation as well as discuss the current status of the EHT, including data analysis of other black hole targets and plans for future observations.
March 11th, 2pm (HST)
Title: Dense Molecular Gas and Star Formation in Nearby Galaxies – Results from JCMT large program MALATANG
Xue-Jian Jiang, EAO
The star-formation (SF) process constantly turns gas into stars and drives galaxy formation and evolution. It is, however, not yet fully understood how gas properties affect the ability to form stars. Many studies have shown that the dense molecular gas stands out to have a much tighter and direct connection with SF than that of total gas (HI+ H_2 or only H_2). In this talk, I will review some of the recent observational extragalactic studies relating dens-gas to SF, discuss the challenges in observations, and then present some results from our JCMT large program MALATANG. MALATANG is the first survey to systematically map the distribution of dense-gas line emission out to large galactocentric distances in nearby galaxies. The aim is to bridge the gap, in terms of physical scale and luminosity, between extragalactic (i.e., galaxy-integrated) and Milky Way (i.e., single molecular clouds) observations. Specifically, I will discuss our results on the correlation between dense-gas mass and star-formation-rate, and the relationship between dense gas and stellar surface density.
March 5th, 2020, 1pm (HST)
Title: Spectral analysis of the quiescent low-mass X-ray binary in the globular cluster M30
Coni Echiburu Trujillo, McGill University
Neutron Stars (NSs) are the most extreme directly observable objects in the Universe. Particularly, in their cores, densities overcome the nuclear matter density. Since those conditions cannot be reproduced on Earth, NSs provide a unique laboratory to study the behaviour of matter at such high densities. Measuring the macroscopic properties of neutron stars, such as mass and radius, is helpful to constrain the equation of state of ultra-dense matter. One promising method to constrain neutron star radii consists of the study of low-mass X-ray binaries in quiescence (qLMXB), i.e., during periods of low accretion levels. In quiescence, we can model the surface emission as a single-composition atmosphere dominated by light elements. Moreover, when these systems are located in globular clusters we know the distance to them. In this work, we present a recent Chandra observation of the qLMXB in the globular cluster M30, and we analyze it together with a previous observation in 2001. We fit the thermal emission with light-element composition atmosphere models (hydrogen or helium), including absorption by the interstellar medium, correction for pile-up of X-ray photons in the detector, and a power-law to account for count excesses at high energies. We use a Markov Chain Monte Carlo approach to extract the mass-radius credible intervals for both chemical composition of the atmosphere. The measured radius obtained from a H model is difficult to reconcile with most current physics models and with other NS radii, generally in the 11-14 km range. In contrast, a He atmosphere results in a radius consistent with this range. Finally, we explore possible sources of systematic uncertainty that may result in an underestimation of the radius, identifying the presence of surface temperature inhomogeneities as the most relevant bias.
March 4th, 2020, 2pm (HST)
Title: Providing an Independent Study of Sub-Solar Lunar Spectra and a Possible Hydration Absorption Feature
Patrice Smith, EAO/UH
For the Moon’s continual exploration, an in depth mineralogical map of the surface is being developed. While the Moon was previously considered anhydrous, three spacecraft missions have detected a 3um absorption feature attributed to hydroxyl(OH) and water(H2O ). To access the presence of the location of these quantities as a function of lunar time of day, spectral observations of different parts of the Moon have been done remotely and thermal models are applied to remove thermal excess emission of the Moon in order to reveal possible hydration features. The mapping of these hydration features on the Moon and how they vary in time and space helps to provide insight into which scientific processes are responsible for its presence. Depending on the data used and the model applied, results have differed in the presence of a 3um absorption feature. Here, we present an independent analysis of spectra of the Moon obtained from NASA’s IRTF where we determine if this absorption feature is detected using a newly applied model. Our preliminary results are consistent with a thermally corrected spectra whose applied model’s solution detected hydration throughout different locations on the Moon. Also, the ground-based spectrum is consistent with spectra of the Moon from a NASA mission’s findings. A confirmed detected presence of OH/H2O for the subsolar point would establish hydration of minerals near the lunar noon time of day.
February 26th, 2020, 2pm (HST)
Title: Exploring the properties of pulsar radiation at (sub)millimeter wavelengths
Pablo Torne, EAO/IRAM
Despite successfully using pulsars as high-precision astrophysical tools on a broad variety of science cases, from measuring interstellar medium properties to testing general relativity, the underlying radio emission process of neutron stars remains unknown. No model has yet been capable of predicting all the radio emission characteristics observed in the population of neutron stars, in part due to the wide range of different properties of the sources. Providing additional observational input on the spectrum of emission of radio pulsars at very high frequencies is a way to set constraints on current models, narrowing the path to a better understanding of the physics in pulsar magnetospheres. In this seminar, we will first introduce pulsars and describe some examples on how to constraint and test models. Then, we will review the current status of the research in the (sub)millimeter range of pulsar emission, presenting the challenges in the observations and the existing results on the topic. We will finalise discussing how the JCMT could extend the spectral coverage of ongoing efforts with observations between 1.3 and 0.45 mm.
January 17th, 2020, 2pm (HST)
Title: First confirmed detection of dichroic extinction from a YSO at (sub)mm wavelength with JVLA and ALMA dust polarization observations
Chia-Lin Ko, National Tsing Hua University
The previous SMA 0.87 mm and CARMA 1.3 mm surveys of dust polarization toward protostars (Galametz et al. 2018; Hull et al. 2014) have shown that polarization percentage in general decreases rapidly with total intensity. They also hinted with a dichotomy that the projected polarization E-segments are either parallel or perpendicular to the outflow axes. Based on the JVLA 18-48 GHz and ALMA 230 and 345 GHz polarization observations towards the specific Class 0 YSO, NGC1333 IRAS4A, we conjectured a unified interpretation of these facts based on aligned dust grains with B-field. At 345 GHz, we found that the radial polarization percentage profiles of IRAS4A1 and IRAS4A2 may be consistent with centrally illuminated collapsing cores, which have an hourglass shaped B-field topology, r^-2 volume density profile, and an approximately consistent grain alignment efficiency. The modestly high optical depth leads to the depolarization at the center of IRAS4A2. The much higher optical depth at the center of IRAS4A1 eventually leads to a 90 degree flip of polarization position angles at 230 and 345 GHz with respect to those observed at 18-48 GHz. At 230 and 345 GHz, what we detected were the linear polarization due to dust extinction instead of dust emission. We conclude that the 230/345 GHz polarization observations towards Class 0 YSOs indeed trace B-field, although any dichotomy related to how E-field is aligned with certain prefer axes (e.g., outflow, filament) may be related to the optical thickness of the selected samples.
January 15th, 2020, 3pm (HST)
Title: The fate of the interstellar medium in early-type galaxies
Michal Michalowski, Astronomical Observatory Institute: Adam Mickiewicz University
The way galaxies stop forming new stars (quenching) is a key aspect of galaxy evolution. This is connected with removal of gas, the fuel of star formation. I will review what we know about the mechanism of the removal of interstellar medium (ISM) from galaxies and how fast this process is. I will then present an alternative way to study the ISM removal by selecting dusty early-type galaxies, for which the decrease of gas and dust can be tracked as a function of the age. This led to the first direct measurement of the ISM removal timescale and to the conclusion that the cold ISM is likely removed by feedback from old stellar populations.
January 10th, 2020, 2pm (HST)
Title: Understanding Mass Assembly in Star Formation via Gas Kinematics
Mike Chen, University of Victoria
Stars form from the collapse of dense cores within molecular clouds. How these cores are assembled from a highly turbulent and magnetized medium, however, is not well understood. The ubiquity of filaments in molecular clouds and the tendency to find dense cores along them suggest filaments play a crucial role in core formation (e.g., Andre et al. 2010). Various filament and core formation mechanisms, such as those with convergence flows and gravitational fragmentation, have thus been proposed in response. Here I present observational studies that provide insights into this subject by answering the following questions: 1. do we see velocity gradients in velocity-coherent filaments that may be indicative of accretion flows? 2. are dense cores pressure-confined by their ambient gas? In Perseus NGC 1333, we found velocity gradients on the 0.05 pc scale that are not randomly orientated relative to their filament spines. The magnitudes of these gradients are typically in the range of 1-4 km/s/pc. They tend to increase radially away from the filament spine, suggesting a mass accretion scenario where infalling gas is progressively damped. Moreover, we found dense cores in NGC 1333 to have pressures comparable or less than their surroundings, suggesting they are pressure-confined and may have been formed from convergence flows.