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: May 2nd, 2017, 2pm (HST)

Observed properties of interstellar filaments

Location: EAO Office, Hilo

Doris Arzoumanian, Nagoya University, Japan

The highly filamentary structure of the interstellar medium is now impressively revealed by Herschel and Planck images tracing the Galactic cold dust emission. Previous observations have shown that clouds are filamentary, however, only recently have interstellar filaments received special attention, thanks to the new observational results on their physical properties.

The analysis of the column density profiles of the filaments derived from Herschel images indicates that they all share a common central width of 0.1 pc, while they span a wide range in length, column density, mass per unit length. The results derived from observations tracing cold dust and gas emission, in total and polarized intensity, suggest that filaments can be divided into two families: On the one hand, low column density, unbound, and quiescent filaments mostly aligned with the local magnetic field orientation, and on the other hand, dense, self-gravitating filaments, mostly perpendicular to the local magnetic field orientation, and fragmented into star forming cores.

I will present the properties of the filamentary structures derived from Herschel, Planck, and molecular line observations, and I will discuss the observational constraints on the formation and evolution of interstellar filaments and their key role in the star formation process.

Upcoming Seminar: May 12th, 2017, 2pm (HST)

HIFI Spectroscopy of H2O Sub-mm Lines in the Nuclei of Actively Star-Forming Galaxies

Location: EAO Office, Hilo

Lijie Liu, University of Oxford, UK

We present a systematic survey of multiple velocity-resolved H2O spectra using Herschel/HIFI towards nine nearby actively star forming galaxies. The ground-state and low-excitation lines (Eup ≤ 130K) show profiles with emission and absorption blended together, while absorption-free medium-excitation lines (130 K ≤ Eup ≤ 350 K) typically display line shapes similar to CO. We analyze the HIFI observation together with archival SPIRE / PACS H2O data using a state-of-the-art 3D radiative transfer code which includes the interaction between continuum and line emission. The water excitation models are combined with information on the dust- and CO spectral line energy distribution to determine the physical structure of the interstellar medium (ISM). We identify two ISM components that are common to all galaxies: A warm (Tdust ∼ 40 − 70 K), dense (n(H) ∼ 105 − 106 cm−3 ) phase which dominates the emission of medium-excitation H2O lines. This gas phase also dominates the FIR emission and the CO intensities for Jup > 8. In addition a cold (Tdust ∼ 20 − 30 K), dense (n(H) ∼ 104 −105 cm−3) more extended phase is present. It outputs the emission in the low-excitation H2O lines and typically also produces the prominent line absorption features. For the two ULIRGs in our sample (Arp 220 and Mrk 231) an even hotter and more compact (Rs ≤ 100 pc) region is present which is possibly linked to AGN activity. We find that collisions dominate the water excitation in the cold gas and for lines with Eup ≤ 300 K and Eup ≤ 800 K in the warm and hot component, respectively. Higher energy levels are mainly excited by IR pumping.

Upcoming Seminar: May 23rd, 2017, 2pm (HST)

The death throes of massive stars

Location: EAO Office, Hilo

Sofia Wallström, ASIAA, Taiwan

Massive evolved stars affect their local surroundings as they go through phases of intense mass-loss and eventually explode as supernovae, adding kinetic energy and freshly synthesised material to the interstellar medium. The circumstellar material ejected by the star affects the shape and evolution of the future supernova remnant, and how the material is incorporated into the interstellar medium. Over time, these processes affect the chemical evolution of the interstellar medium on a galactic scale. This presentation of my thesis work will probe these topics at different stages.

First, CO observations have been used to study the circumstellar environment of a massive star, the yellow hypergiant IRAS 17163-3907. Observations with APEX and ALMA ACA reveal a complex environment with several distinct components: a fast recent stellar wind of 100 km/s, a clumpy CO ring which appears to be a torus ejected by the star several thousand years ago, and a unidirectional bright spur extending from the star to the clumpy ring. These asymmetries are not seen in infrared dust observations, and demonstrate the complexity of massive evolved stars and the need for high resolution molecular observations to understand them.

Second, observations of CO lines in the supernova remnant Cassiopeia A have been used to study the effect of the reverse shock on supernova ejecta. A large column density of warm CO is found, which has most likely re-formed after the passage of the reverse shock. The high temperature and density implies that thermal conduction by electrons may be an important process for the evolution of dense ejecta knots, with implications for the survival of supernova dust.

Finally, the contribution of massive stars to galactic chemical enrichment has been investigated indirectly with measurements of isotopic ratios in a molecular absorber at z=0.68 towards B0218-211. The ratios at z=0.68 are found to be very different from those in the solar neighborhood, but similar to the ratios found in another absorber at z=0.89 and in starburst galaxies. These ratios are interpreted as the signature of enrichment mainly by massive stars.


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).

If you would like to view the seminar via Polycom, please contact the helpdesk well in advance of the talk and we will make sure it’s switched on!

Our Polycom contact details are available on request.

The EAO phone number is: (808) 961-3756. A full list of past seminar speakers can be found here for 2017, here for 2016 and here for 2015.

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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