This page lists the Seminars that were given at the EAO offices in Hilo in 2019. The EAO staff would like to thank all guest speakers and encourage new astronomers/instrument specialists to give talks when visiting.
November 1st, 2019, 3pm (HST)
Title: Constraining the properties of interstellar silicate dust using X-ray and infrared spectroscopy
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.
October 25th, 2019, 2pm (HST)
Title: The First Maps of the Dust Mass Absorption Coefficient in Nearby Galaxies
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.
October 10th, 2019, 2pm (HST)
Title: Discovering high-redshift AGB analogs in nearby metal-poor dwarf galaxies
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.
July 26th, 2019, 2pm (HST)
Title: Statistical characteristics of Harp receptors
Taishi Nammoto, UH Hilo
HARP (Heterodyne Array Receiver Program) is a receiver which consists of 16 different receptors. Currently 13 receptors are operational. These receptors are aimed at mapping large areas. The purpose of my project is to enhance the recognition of normal TRX (receiver noise temperature). This allows operators and scientists to figure out whether the receiver works properly or not. Also, characteristics of TRX variation help them to discuss how to deal with issues for operation. In this talk, I’ll analyse the relation between TRX and Lo (Local Oscillator) frequency based on data collected from 2015 to 2019. Specifically some interesting features found on the data will be discussed.
June 12th, 2019, 2pm (HST)
Title: Tracing Historic Mass Loss from Evolved Stars with Thermal Emission from Cold Dust
Thavisha Dharmawardena, ASIAA, Taiwan
Evolved stars play a key role in the life cycle of dust in the universe. Through strong winds and supernovae, they inject the material reprocessed in their cores to the interstellar medium, replenishing the interstellar medium with heavy elements. As evolved stars are so numerous, they are extremely effective in this role. In this talk I will explore the role of historic mass loss. The typical treatment of evolved stars only accounts for present day mass loss or assumes they undergo constant mass loss throughout their lifetime.
Historic mass loss can be effectively traced using thermal emission from the dust which cools down as it moves away from the central star. We exploit Herschel/PACS and JCMT/SCUBA-2 observations to study this historic mass loss. These two sets of observations are especially powerful, tracing the radial variation in the circumstellar envelopes of evolved stars. We establish the presence of variations in mass loss for a sample of Milky Way evolved stars by studying features observed in surface-brightness, temperature, dust mass-column density and spectral index of dust emissivity radial profiles. By comparing these results to predictions for a constant-outflow model I find significant deviations between the total dust masses determined for the two scenarios, demonstrating that the effect of mass loss variation cannot be ignored. We determine the complexities of the detached shell of U Ant with the aid of radiative transfer modelling, prompting the need for further study at higher angular resolution.
The analysis of the sub-mm periodicity of IRC+10216 and o Ceti, two well-known evolved stars, shows that it may be possible to use sub-mm light curves of evolved stars to study the nature of dust formation/destruction in their inner envelope effectively. The optical and sub-mm light curves of IRC+10216 shows an offset in phase of ~ 3/4. Using model predictions and past reports, I find that this is likely due to the relationship between the stellar pulse and the formation/destruction of dust. Moving on from the Milky Way to the Magellanic clouds I stack evolved stars identified in the mid-infrared but not detected in the far-IR from Herschel at 100micron allowing a statistical study of the existence or absence of a far-IR component. We successfully produce detections for the highest mass-loss rate sources, showcasing the merits of the stacking method. Here I emphasise the variations in structure and hence historic mass loss of evolved stars and by doing so highlight the importance of including these variations in studies which include dust production by evolved stars in the future.>
June 4th, 2019, 2pm (HST)
Title: The JCMT BISTRO Survey: Variation of magnetic field and grain aligment properties within the Ophiuchus Molecular Cloud
Kate Pattle, National Tsing Hua University
The role and relative importance of magnetic fields in the late stages of mass assembly within molecular clouds remains highly uncertain. In this talk I will discuss recent results from the JCMT (James Clerk Maxwell Telescope) POL-2 polarimeter and the JCMT BISTRO (B-Fields in Star-Forming Region Observations) survey, which is currently mapping star-forming regions within 2 kpc of the Solar System in submillimetre polarized light. The resolution and sensitivity of the BISTRO observations allows magnetic fields to be traced from low to high densities in star-forming gas, and provides new insights into the depths into molecular clouds to which dust grains are aligned with the magnetic field. I will particularly discuss recent observations of the nearby Ophiuchus molecular cloud, a well-resolved site of low to intermediate-mass star formation. The proximity of this molecular cloud allows for detailed investigation of the variation of magnetic field morphology and dust grain alignment with local environment within an individual star-forming region. Our results demonstrate that the magnetized behaviour of individual star-forming clumps is strongly influenced by local effects and stellar feedback
May 31st, 2019, 2pm (HST)
Title: Morpho-kinematics of oxygen rich AGB star EP Aqr
Tuan-Anh Pham, Vietnam National Space Center
Using ALMA observations in different molecular lines: 12CO(1-0), 12CO(2-1), 13CO(2-1), SiO(5-4), SO2(166,10−175,13) we study the circumstellar envelope of AGB star EP Aqr at different distances to the centre of the star: from few tens to several hundreds au. Complementary, but also significantly different pictures of its morphology and kinematics are drawn. Rotation dominates at distances close to the star photosphere, two narrow polar structures (called jets) are launched from less than 25 au away from the star reaching a velocity of some 20 km/s at a distance of ~100 au and fade away farther out, a radial wind building up at distances up to 300 au from the star, with a larger velocity near polar than equatorial latitudes. The density is maximal at intermediate latitudes. Other features related to temperature, absorption, density and velocity are presented. Plausible interpretations are discussed, in particular assuming the presence of a companion, and underlining the role that the jets are likely to play in the acceleration of the wind.
Note: We apologize but due to technical difficulties the slides cannot be seen clearly in the video. Please download a pdf copy of the slides and follow along if you wish to watch this seminar.
May 3rd, 2019, 2pm (HST)
Title: Dust and Molecular gas in Early-Type Galaxies
Anne Sansom, University of Central Lancashire
Elliptical and lenticular (E/SO) galaxies, collectively known as ETGs, are traditionally thought to be red and dead. However, there is evidence of some cool gas and dust, sometimes seen in absorption as dust lanes in optical images. For late-type galaxies there is a link between the presence of molecular gas and dust, with dust arising mainly from red giant stars and molecular gas and dust forming the sites of the next generation of stars. However, it is less clear how the dust and gas arrived in ETGs. Complete samples are needed to get a clearer picture of the cool ISM properties in E/S0 galaxies. Large surveys with the Herschel Space Observatory gave us the data to look at complete samples of galaxies. We combined data from two such surveys with multi-waveband data from the GAMA survey to uncover the dust properties in ETGs as a function of galaxy characteristics. We show the properties of these dusty ETGs in this talk. Recent follow-on observations with ALMA, for a small sub-sample of these dusty ETGs, will also be presented in this talk, highlighting their molecular gas content and the variety of cool interstellar media found in ETGs.
May 1st, 2019, 2pm (HST)
The exact roles of magnetism and turbulence at different stages of star formation remain poorly understood even today, and it is still not clear from observations in which regime, if any, magnetic fields can effectively counteract gravitational collapse. Nevertheless, the latest generation of polarimeters at far-infrared and submillimeter wavelengths has shown the ubiquity of magnetic fields from the scale of giant molecular clouds to that of protostellar cores. During this talk, I will discuss how our current polarimetric capabilities provide a unique window into the dynamics of star-forming regions when used in combination with spectroscopic data. Specifically, I will present published and on-going results from the BISTRO survey at the James Clerk Maxwell Telescope (JCMT), as well as multi-wavelengths observations using the HAWC+ camera aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). The BISTRO survey in particular is showing that several star-forming regions are only slightly supercritical, with in some cases magnetic fields nearly dominated by their turbulent component. Finally, multi-wavelength polarimetric observations offer a unique opportunity to measure the alignment efficiency of dust grains with interstellar magnetic fields in a variety of extreme environments. These provide a valuable test for grain alignment theories, such as Radiative Alignment Torques (RATs), and will prove particularly helpful in characterizing the range of conditions in which they are most efficient.
April 3rd, 2019, 2pm (HST)
Title: Galaxy evolution studies with the AKARI North Ecliptic Pole survey
Hyunjin Shim, Kyungpook National University
NEP is one of the JCMT large programs started in 2017. The survey is originally based on the mid-infrared survey by the infrared telescope AKARI, providing continuous wavelength coverage through 3-24um. JCMT/SCUBA-2 850um data over this region will enhance the analysis of the infrared luminous galaxies and active galactic nuclei, in the determination of the physical properties such as dust temperature. I will briefly introduce some of the results from the NEP survey.
March 18th, 2019, 2pm (HST)
Title: The Slow Heartbeat of Supermassive Black Hole Fuelling
Alastair Edge, Durham University
I will review the observed variability of the low accretion rate AGN in Brightest Cluster Galaxies (BCGs). From radio/sub-mm monitoring of a sample of several dozen systems over the past decade shows most systems have varied by >30% and many by factors of >2. The implications of this variability, particularly in the sub-mm, will be discussed.
March 13th, 2019, 2pm (HST)
The binary T Tauri system JW 566 in the Orion Molecular Cloud underwent an energetic, short-lived flare observed at 450 and 850 miconrs by SCUBA-2 on 2016 November 26 (UT). The emission faded by nearly 50% during the 31 minute integration. The 850 μm flux corresponds to a radio luminosity of Lν =8× 1019 erg s-1 Hz-1, approximately one order of magnitude brighter (in terms of νLν ) than that of a flare of the young star GMR-A, detected in Orion in 2003 at 3mm. The event may be the most luminous known flare associated with a young stellar object and is also the first coronal flare discovered at submillimeter wavelengths. We interpret this event to be a magnetic reconnection that energized charged particles to emit gyrosynchrotron/synchrotron radiation.
March 5th, 2019, 2pm (HST)
Title: Absorption Lines as a Possible Probe of Protoplanetary Disk Wind
Ziyan Xu, Kavli Institute for Astronomy and Astrophysics
The evolution and dispersal of protoplanetary disks play an important role in planet formation, and are driven by angular momentum transport and mass loss due to disk winds. The angular momentum transport is largely driven by faster magnetized disk wind, while disk mass loss is conventionally considered dominated by slower photoevaporative wind due to high-energy radiation from the central star. Both magnetized and photoevaporative winds have been detected and in most of the cases, the mass flux is measured through analysis of emission lines, and mass loss rates remain uncertain. Absorption lines offer a powerful complement to emission lines, by sampling the wind in our line-of-sight to the emission region. In this talk, I will present an observational analysis of wind absorption in far-ultraviolet stellar spectral lines. I will first present our survey of T Tauri stars by STIS and COS on HST, including C II 1335 doublets and a few other lines. By characterizing CII 1335 doublets, we estimate wind properties including C II column density and wind velocities for components that are considered related to magnetized wind and photoevaporative wind seperately. We then compare our observational results to stellar and disk properties and discuss the implication of our results. I will also present interpretations by forward-modeling wind absorption assuming photoevaporative wind and magneto-photoevaporative wind. I will show that in order to better understand the line profiles, magneto-photoevaporative wind is needed instead of the conventional scenario of pure photoevaporative wind. Our observational results including wind velocity and absorber column density provide potential constraints to mass loss rates.
February 27th, 2019, 2pm (HST)
Title: The relation between molecular clouds and very young stellar clusters
Hongjun Ma, Purple Mountain Observatory, Chinese Academy of Sciences
Most stars in the Galaxy were formed in compact bound stellar clusters or distributed unbound stellar associations. Star clusters are the cradles of star formation and grow within Giant Molecular Clouds. During this process, energy and momentum injected by young stars remove the remaining interstellar material, thus ending further star formation and reducing the gravitational binding energy of the protoclusters. Thus, it is important to study the relationship between the dense molecular clouds and the very young stellar clusters around them. We observed about 40 molecular clouds with young stellar clusters, thirty of which have been observed by JCMT CO(3-2) mapping and SCUBA-2 . I will discuss these data.
February 7th, 2019, 1pm (HST)
Title: Multi-Wavelength Observations of Candidate Starbursting Protoclusters Selected by Planck and Herschel
Tai-An Cheng, Imperial College London
Crossmatching between Planck and Herschel data has revealed a number of candidate high-redshift protoclusters of starbursting galaxies. These starbursting galaxies are believed to be progenitor elliptical galaxies residing in today’s massive galaxy clusters. Hence their studies are important in understanding the formation of elliptical galaxies and galaxy clusters. In this talk, I will first present SCUBA-2 850 micron observations of 13 of our candidate starbursting protoclusters. Besides colors and number counts, we estimate the photometric redshifts, infrared luminosities and star-formation rates (SFRs) of individual 850 micron sources within these candidate protoclusters. We conclude 6 of these 13 candidates are likely to be high-redshift starbursting protoclusters at 2<z<3, while the rest might still be lower-redshift protoclusters having member galaxies bright in other wavelengths. I will next show multi-wavelength studies of our other candidate protoclusters. These include photometric and spectroscopic observations from optical/near-infrared, mid-infrared, millimeter to radio using WHT, VLA, ATCA and IRAM’s 30-m Telescope.
January 22, 2019, Informal Seminar
Title: Revealing the nature of the core through multi-frequency polarization observations with the KVN, SMA, and JCMT
Minchul Kam and Naeun Shin, Seoul National University, South Korea
We study the linear polarization of the radio cores of blazars simultaneously at 22, 43, and 86 GHz with the Korean VLBI Network (KVN) in four epochs between January and June 2017. We investigate the Faraday rotation measure (RM) of the cores; the RM is expected to increase with observing frequency if core positions depend on frequency owing to synchrotron self-absorption. We find a systematic increase of RMs at higher observing frequencies in our targets. The RM–ν relations follow power laws with indices less than 2 which indicates that the geometry of the Faraday rotating media deviates from the conical shape at our observing frequencies. Comparing our KVN data with contemporaneous optical polarization data from the Steward Observatory for a few sources, we find indications that the increase of RM with frequency saturates at frequencies of a few hundred gigahertz. This suggests that blazar cores are physical structures rather than simple τ = 1 surfaces. A single region, e.g., a recollimation shock, might dominate the jet emission downstream of the jet-launching region. However, the saturation frequency we obtained is ambiguous due to the lack of the observing frequencies between 86 GHz and the optical. We expect the SMA and JCMT data will nicely bridge the frequency gap between our 86 GHz and the optical data, and discuss what we can learn more from the KVN, SMA, and JCMT collaboration.