This pages lists the Seminars that were given at the EAO offices in Hilo in 2015. The EAO staff would like to thank all guest speakers and encourage new astronomers/instrument specialists to give talks when visiting.
December 8th 2015
Title: Observing photoionized gas and star formation in nearby galaxies with ALMA
George Bendo, University of Manchester
While ALMA was designed primarily to detect emission from dust and molecular gas, it is also capable of detecting free-free continuum emission and higher-order recombination line emission from the photoionized gas in star forming regions. These millimetre tracers of star formation are better than most other star formation tracers because they directly trace young photoionizing stars (unlike infrared or radio synchrotron emission) while not being directly affected by dust extinction (as is the case for ultraviolet and optical star formation tracers). In this talk, I will review my work in using ALMA observations to study star formation in nearby galaxies, including discussions on how the ALMA measurements compare with other measurements of star formation, and I will also briefly discuss potential future directions for this line of research.
December 1st 2015
Title: Dust-production rates of AGB stars in the Solar Neighborhood
Alfonso Trejo-Cru, ASIAA, Taiwan
AGB stars are a very important contributor to the total dust mass injected into the ISM in galaxies. Due to foreground extinction and the large uncertainties in the distances for dusty objects, the dust-production rate by AGB stars in the Galaxy remains hard to evaluate. Using the GRAMS model frid, we determine the total dust mass-loss rate from AGB stars in the Milky Way using a 1 kpc distance-limited sample. The last estimate of this dust injection rate was done in the late ’80s. Using new all-sky infrared facilities (WISE, 2MASS, and others), it is possible to provide a better estimate. We also review how this project relates to other ongoing efforts done at the JCMT that also tackle a reasonably large sample of AGB stars.
November 25th 2015
Title: Dense molecular gas in local ULIRGs
Thomas Greve, University College London, UK
The population of nearby gas-rich and highly dust-obscured Ultra Luminous Infrared Galaxies (ULIRGs) provides us with a unique opportunity to study the physical processes governing star formation in kinematically violent and radiation-harsh environments.
As part of the Herschel Comprehensive (U)LIRG Emission Survey (HerCULES) we have obtained observations of the CO rotational ladder from J=4-3 to J=13-12 for a sample of 26 (U)LIRGs. These data have been complemented with JCMT and IRAM 30m observations of the low-J CO lines, thus completing the full CO ladder, as well as of crucial dense gas tracers such as CS, HCN, and HCO+ (and in some cases their isotopologues).
I will discuss some of the first results coming out of this unique data-set, from simple star formation relations (i.e. IR – molecular line luminosity relations) to complex multi-phased Large Velocity Gradient (LVG) radiative transfer modelling that allow us to disentangle different molecular gas phases and possibly different molecular gas heating mechanisms in these galaxies.
November 24th 2015
Title: Detection of water-rich asteroid debris in a metal-polluted white dwarf
Roberto Raddi from the University of Warwick, UK
White dwarfs are the stellar remnants of low- to intermediate-mass stars. The internal structure of white dwarfs is radially stratified due to their strong gravity, and their atmospheres are expected to contain only hydrogen or helium. However, about 30% of the white dwarfs show traces of metals, consistent with recent or ongoing accretion of planetary debris. Ensemble studies and detailed analysis of white dwarf atmospheres have revealed a volatile-poor, rocky origin for the debris, resembling the composition of Solar system meteorites. The chemical signature expressed by the metal abundances and the large amount of hydrogen, mixed within the helium-dominated atmosphere of two white dwarfs, is explained with the accretion of water-rich debris. The comparison of their properties with those of similar stars suggests that the disruption of water-rich asteroids could be common in other planetary systems.
October 30th 2015
Title: Stars of an uncertain age: The problem of determining stellar ages
David Soderblom from Space Telescope Science Institute
Some day fairly soon we can hope to hear an announcement of the signs of life on a planet around another star, and when that happens, our first question will be “How old is that star?” because we will want to place such a discovery in an evolutionary context. But stars do not reveal their ages to us in any direct way and we are left trying to use secondary indicators such as rotation or activity.
Asteroseismology offers a real breakthrough in determining stellar ages, particularly for older solar-type stars, and the oscillations detected by Kepler have been especially critical because of their quality and number. In this talk I will present a framework for understanding the problem of stellar age estimation, the limitations encountered with conventional (pre-seismology) methods, how asteroseismology provides constraints on key physical parameters of stars, and what limitations still exist in the problem of estimating stellar ages.
October 23rd 2015
Title: Astronomy in Antarctica
Professor Walter Gear, Cardiff University, UK
Antarctica is the coldest, driest, windiest continent on earth, which whilst making it inhospitable for humans and most animals, makes it an excellent site for astronomy – indeed the best in the world for some types of observations. Professor Gear will review the geography and properties of Antarctica before describing how own experiences in reaching and spending time at the South Pole, and explaining some of the world-leading astronomical results that have been obtained there. This talk is at a level suitable for all staff.
September 21st 2015
Title: Gas flows in galaxies: galaxy interactions in the SDSS
Dr. Jillian M. Scudder, University of Sussex, UK
Interactions between galaxies in the local universe are well known to trigger significant enhancements to a galaxy’s star formation rate (SFR). It has recently been determined that these interaction-driven SFR enhancements are present over a relatively long time frame. However, the strength of the starburst can still vary wildly from galaxy to galaxy and between interacting systems. The magnitude of this boost to the SFR has been tied to certain parameters of the interaction, such as interaction stage and mass ratio. Even with these parameters accounted for, large residual scatter remains in the observed SFR enhancements. Another parameter which could control the strength of the interaction-triggered SFR enhancement is the gas content of the perturbed galaxies; this parameter has been relatively poorly explored. I will present results from a sample of interacting galaxies selected from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), with new estimates of their HI gas masses from the Jansky Very Large Array (VLA). With the combination of the spectroscopic data from the SDSS and the HI masses from the VLA, we can determine if a strong correlation between star formation enhancement and gas content is present in the observations. To aid in the interpretation of our results, we also make use of a small suite of binary merger simulations. I will present the conclusions drawn from this study, which will help us to understand the role that gas content has upon the star formation rates of interacting galaxies.
September 15th 2015
Title: More from LESS – an ALMA study of LABOCA submillimetre sources
Dr. Alasdair Tomson, Durham University, UK
A significant fraction of star formation at z~2 is known to occur in massive, gas-rich, dust-enshrouded starburst galaxies, which are now routinely detected in deep, large-area surveys in the submillimetre bands. Obtaining a detailed understanding of the physical processes within these galaxies has, however, proved challenging, due to the low angular resolution of the single-dish submillimetre maps in which the sources are first identified, and the difficulty finding counterparts at other wavelengths. In ALMA Cycle 0, we conducted a program of interferometric follow-up observations of 126 single-dish (LABOCA) identified submillimetre sources in the Extended Chandra Deep Field South – the ALESS survey. These high resolution ALMA images — taken in the same band as that in which the sources were first identified — precisely locate the submillimetre galaxy within the large single-dish error circles, providing unambiguous counterpart IDs, and allowing us to study the properties of this population of galaxies in unprecedented detail. In this talk, I will summarize our work on ALESS, and present early results from our sister program, based on SCUBA-2 sources in the UDS field.
July 31st 2015
Title: Of Oceans and Volcanic Islands – How the JCMT came to Mauna Kea
Harry van de Laan
At the end of the 1970s, astronomy in Holland needed access to Northern facilities, from sub-mm through IR and optical wavelengths. The beautiful results from the Westerbork Synthesis Radio Telescope WSRT badly needed complementary data for their astrophysical interpretation.
The effort to achieve this began seriously during the IAU General Assembly in Montreal in 1979. It culminated in the signing of a 30-year Agreement between ZWO-NL and SRC-UK on 18 June 1981. Major goal: to construct, operate and continually update a suite of telescopes on the Observatory del Roque de los Muchachos on La Palma, one of the Spanish Canary Islands in the Atlantic. These UK/NL facilities later became known as the Isaac Newton Group.
Within a month of that fateful signature ceremony, agitation started in Holland, especially at the astronomy institutes of Leiden, Utrecht and Groningen Universities, to construct the 15 m sub-mm telescope in the plan not on La Palma but on Mauna Kea. The rest is history, involving the JCMT and UKIRT.
This exciting story, filled with anecdotes and cliffhangers, will be sketched by the key NL participant, who worked closely with Dr. Harry Atkinson, executive with SRC, and key UK participant.
July 30th 2015
Title: Structure and Dynamics at the Centre of the Milky Way
Andrew Walsh, Curtin University, Australia
The Centre of our Galaxy – the Central Molecular Zone (CMZ), contains 80% of all dense gas in the Galaxy, but holds only about 5% of current star formation. The CMZ is hotter, denser and more turbulent than anywhere else in the Galaxy. It is a truly unique place. It is also important as the CMZ has analogues in other galaxies that are typically used to estimate extragalactic star formation rates. Yet we do not understand the star formation in the CMZ. I will describe the CMZ and present recent models to explain the unusual star formation. I will also introduce a way to make a 3 dimensional model of the CMZ with the hope that this can be used to help us understand how star formation proceeds under extreme circumstances.
July 1st 2015
Title: Proto-brown dwarf candidates in Taurus
Oscar Morata, ASIAA, Taiwan
The formation of brown dwarfs (BDs) is still a highly debated question. Currently, there are two possible scenarios competing to explain BD formation in low-mass star-forming regions: ‘turbulent fragmentation’ of molecular clouds, with the eventual formation of BDs as scaled-down version of low-mass stars, or the ejection of substellar mass fragments from a star cluster or from a protostellar core/circumstellar disk. If BDs form as a scaled-down version of low-mass stars, we should find substellar objects embedded in extended envelopes and with strong accretion and outflow activity. Our group has compiled the best sample of proto-BDs known so far (obtained from Spitzer/IRAC data in the Taurus Molecular Cloud, and with all the objects associated with Herschel submillimeter emission). I will present our latest results, including the detection of thermal radio jets in four of our proto-BD candidates, which favors the formation of BDs as a scaled-down version of low-mass stars.
April 21st 2015
Title: A Low-Frequency Study of the Super-CLASS Supercluster
Christopher Riseley, University of Manchester, UK
The SuperCLASS field is a region of the sky selected for study as part of the e-MERLIN legacy programme. Primarily a target for radio weak lensing study, the field is rich, containing 5 known Abell galaxy clusters, and the opportunity exists for a wide range of ancillary science work. In this talk I will discuss the ongoing low-frequency work, what we can learn about the state of the intracluster medium (ICM) and how this will complement the overall aims of the project. I will also briefly discuss some of the additional objects of interest that I have encountered along the way.
March 20th 2015
Title: Cosmic Evolution with Gas Metallicities of Star-Forming Galaxies
Chun Ly, NASA Postdoctoral Fellow at Goddard Space Flight Center
The chemical enrichment of galaxies, driven by star formation and regulated by gas flows from supernova “feedback” and cosmic accretion, is a key process in galaxy formation. Efforts to study the dependence of the gas-phase oxygen abundance (“metallicity”; Z) against stellar mass (M) and star formation rate (SFR) of galaxies have produced a tight correlation for local star-forming galaxies. In 2010, it was argued that higher redshift galaxies follow this M-Z-SFR relation; however, more recent z~1-2 studies are finding contradicting results. To better understand the M-Z-SFR relation and its redshift dependence, I have conducted three spectroscopic studies at z~1 using the Subaru Deep Field, the DEEP2, and the NewH? Survey. Together, these studies span massive and dwarf galaxies, and galaxies undergoing intense star formation. I will discuss our findings, which have recently been reported in Ly et al. (2014,2015) and de los Reyes, Ly & Lee et al. (2014), and future plans to re-calibrate “strong-line” metallicity diagnostics using a sample with “direct” oxygen abundance measurements from [OIII]4363.