Seminars

The UHH Research Park includes the headquarters for the East Asian Observatory, the Caltech Submillimeter Observatory, Subaru, Gemini, UKIRT, the Smithsonian Submillimeter Array and the Institute for Astronomy, plus the astronomers at the University of Hawaii at Hilo. We are one of the major centres for astronomy in the world and encourage all visitors to the JCMT to take advantage of the proximity of these institutes, and give a seminar while in Hilo. Your talk will be advertised at each of the above institutes.


Upcoming Seminar: October 10th, 2pm (HST)

Discovering high-redshift AGB analogs in nearby metal-poor dwarf galaxies

Location: EAO Office, Hilo

Steven Goldman, Space Telescope Science Institute

The effects of metallicity on both the dust production and mass loss of evolved stars have consequences for stellar masses, stellar lifetimes, the progenitors of core-collapse supernovae, and the origin of dust in the ISM. With the DUST in Nearby Galaxies with Spitzer (DUSTiNGS) survey, we have discovered samples of dusty evolved AGB stars out to the edge of the Local Group, reaching metallicities down to 0.6% solar. This makes them the nearest analogs of AGB stars in high-redshift galaxies. We present the dustiest AGB stars in 10 galaxies from the DUSTiNGS survey and show how the infrared Period-Luminosity (P-L) relation is affected by dust and by metallicity. Using HST and Spitzer photometry we have also discovered both carbon and oxygen-rich AGB candidates in Leo P, the most metal-poor gas-rich galaxy that we can resolve with current instruments. These detections have large implications for the ability of both types to produce dust in metal poor environments and at high redshift, and the ability to use the Mira P-L relation as a distance indicator.

Upcoming Seminar: October 25th, 2pm (HST)

The First Maps of the Dust Mass Absorption Coefficient in Nearby Galaxies

Location: EAO Office, Hilo

Chris Clark, Space Telescope Science Institute

With the advent of large far-infrared and submillimetre facilities such as Herschel, Planck, JCMT, and especially ALMA, dust now provides an indispensable way to study the evolution of galaxies. In particular, our ability to observe large areas of the submillimetre sky quickly (along with the advantageous effects of negative-k-correction and lensing) mean that dust observations are increasingly used as a proxy to study star-formation rates, gas masses, and chemical evolution – which are impractical to observe directly for such substantial numbers of galaxies. However, our ability to exploit dust observations in this way is predicated on a simple assumption – that we can actually use observations of dust emission to infer dust masses. But the dust mass absorption coefficient, κd, is uncertain to (at best!) an order of magnitude. Worse still, this forces us to treat κd as being constant both between galaxies, and within them – which of course cannot be true in reality. Pinning down κd, and how it varies, is therefore vital. By exploiting the fact that the dust-to-metals ratio in galaxies is constrained by observations of elemental depletions, it is possible to empirically determine the value of κd in galaxies. I will present the first ever resolved maps of κd, obtained by applying this method in a pixel-by-pixel manner to nearby galaxies M74 and M83. Our maps show significant variation of κd within these galaxies. Curiously, we find strong evidence that κd anti-correlates with the density of the ISM, which is the opposite behaviour to what is predicted in dust models. However, without abandoning standard assumptions about the ISM, we find no way to avoid drawing this conclusion.

Upcoming Seminar: November 1st, 1pm (HST)

Constraining the properties of interstellar silicate dust using X-ray and infrared spectroscopy

Location: EAO Office, Hilo

Sascha Zeegers, ASIAA

Interstellar silicates are a major component of interstellar dust. Their properties, such as the composition, size distribution of dust grains and internal structure, are important components in many astrophysical models. The infrared and X-ray part of the spectrum provide important tools to understand and constrain these properties. In the soft X-ray band, we can use the unique features in the absorption edges of Si, O, Fe and Mg in the spectra of X-ray binaries to analyse silicates in various environments in the Galaxy, where X-ray binaries serve as background sources to probe the intervening dust along the line of sight. I will present the results of 9 sightlines towards X-ray binaries located in the Central Galactic environment. The study profits from new dust models derived from new laboratory measurements of interstellar dust analogues. The features around 10 and 20 micron in infrared spectra of various sources can also be used to study silicates. I will highlight the possibility of studying the properties of nano silicates using these features. Nano grains may provide insight into the formation of grains in the interstellar medium (ISM), since the observation of these small clusters may point to active grain formation in the ISM. They may also explain the absence of crystalline dust in ISM, since many atoms are near the surface of the grain, distorting the lattice structure, which may make the grains appear amorphous while they are still in their lowest energy configuration.


Where and How:

EAO seminars are (usually) held in the second floor conference room at the East Asia Observatory, 660 N. A’ohoku Place, Hilo, Hawaii. Please note that access to EAO is possible only through the main entrance (through the side doors facing Subaru).

We stream all of our seminars through the Zoom video conferencing application. If you would like to view the seminar via Zoom, links are sent out on the seminar mailing list (see below) or you may contact the helpdesk in advance of the talk and we will make sure that the option is available to you.

A full list of past seminar speakers can be found below for the current and previous years. These pages also contain links to PDF copies of the seminar slides, video recordings of the seminars, and other materials, where available.

To join the Seminar e-mail list:

EAO Seminars are sent out via eao_seminar@eao.hawaii.edu. If you wish to join this seminar list please send an e-mail to eao_seminar-join@eao.hawaii.edu.

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