2017 Seminars

This pages lists the Seminars that were given at the EAO offices in Hilo in 2017. The EAO staff would like to thank all guest speakers and encourage new astronomers/instrument specialists to give talks when visiting.

December 21st, 2017, 1pm (HST)

Title: Stellar and Molecular Gas Properties of MaNGA Galaxies

Hsi-An Pan, ASIAA, Taiwan

The galaxy integrated star formation rate(SFR)-stellar mass(M) relation holds important information for understanding the star formation history and evolution of galaxies.Although the SFR-M relation has been reported with a variety of different data sets, their appearance can vary significantly from one to another. In this work, we determine what controls the integrated and the spatially-resolved SFR-M* relation in both star-forming and quiescent galaxies by linking the resolved SFR-M* relation with various galaxy properties such as stellar mass, specific SFR (sSFR), bulge-to-total light ratio, and morphology using MaNGA data (Mapping Nearby Galaxies at APO).

In the second part of the talk, I will introduce the current status of molecular gas observations of MaNGA interacting galaxies using JCMT. Molecular gas represents the material immediately available for forming new stars. A direct comparison between stellar populations and molecular gas is required to understand the star formation in interacting galaxies. We use of CO data to trace molecular gas content in MaNGA interacting galaxies and compare the stellar and gas properties, such as gas fraction and star formation efficiency of gas.

December 18th, 2017, 1pm (HST)

Title: Demonstrating A New Census of INfrared Galaxies with ALMA (DANCING-ALMA). I. FIR Size and Luminosity Relation at z = 0 – 6 Revealed with 1034 ALMA Sources

Seiji Fujimoto, University of Tokyo, Japan

We present the large statistics of the galaxy effective radius in the rest-frame far-infrared (FIR) wavelength Re(FIR) obtained from 1627 deep ALMA 1-mm band maps that become public by 2017 July. Our ALMA sample consists of 1034 sources at z = 0 – 6 that typically have the star-formation rate of ~100-1000 M/yr and the stellar mass of ~1010 – 1011.5 M. We homogeneously derive Re(FIR) and FIR luminosity LFIR of our ALMA sources via the same uv-visibility method with the exponential disk fitting, carefully evaluating the selection and measurement incompletenesses by realistic Monte-Carlo simulations. We find that there is a positive correlation between Re(FIR) and LFIR at the > 99% significance level. The best-fit power-law function, Re(FIR)LFIRα, provides α = 0.28 ± 0.07, and shows that the average Re(FIR) at a fixed LFIR decreases toward high redshifts. The best-fit α and the redshift evolution of Re(FIR) are similar to those of the galaxy effective radius in the rest-frame UV (optical) wavelength Re(UV) (Re(Opt.)) revealed by Hubble Space Telescope (HST) studies. We identify that our ALMA sources have significant trends of Re(FIR)Re(UV) and Re(Opt.), suggesting that dusty starbursts take place in a compact region. Moreover, Re(FIR) of our ALMA sources is comparable to Re(Opt.) of quiescent galaxies at z ~1 – 3 as a function of stellar mass, supporting the evolutionary connection between these two galaxy populations. We also investigate rest-frame UV and optical morphologies of our ALMA sources with deep HST images, and find that ~ 30 – 40% of our ALMA sources are classified as major mergers. This indicates that dusty starbursts are triggered not only by the major mergers but also the other mechanism(s).

November 27th, 2017, 11am (HST)

Title: SPT unlensed protoclusters: a window into the early universe

Emily Pass, University of Waterloo, Canada

The South Pole Telescope’s SPT-SZ 2500 deg2 survey was originally designed to detect overdensities at z ~ 1 using the Sunyaev Zel’dovich effect. However, this data has also been able to be used to create a catalogue of high-redshift dusty star-forming galaxies (DSFGs) that have since received ALMA follow-up. While the majority of these sources are strongly lensed, a subset are unlensed, multi-component sources. These likely z > 4 overdensities may provide views into the early universe, allowing constraints to be placed on structure formation. In this talk, we will discuss the properties of SPT 2349-56, the most thoroughly-investigated member of the SPT unlensed sample and the densest protocluster discovered to date, summarizing our current understanding of protoclusters and highlighting the implications of this discovery. We will also describe our ongoing efforts to characterize the other z > 4 overdensity candidates in the SPT unlensed sample, as well as the future goals of the SPT protocluster project.

November 21st, 2017, 2pm (HST)

Title: Investigating the magnetic fields from diffuse to denser parts of the star forming regions

Archana Soam, KASI, South Korea

Star formation is a long-standing and most exciting fundamental problem to be understood by astrophysicists. Studying star formation in different environments using different astronomical techniques helps in understanding the various important aspects of the process. I mostly worked towards nearby low mass star forming regions which provide fascinating laboratories for studying this process. The two standard theories of star formation investigate the importance of magnetic fields (B-fields) and turbulence in star formation. In my work, I mostly focused on mapping the B-fields towards various star forming regions in different environments viz. molecular clouds in isolation and in HII regions at their different evolutionary stages. This was done using optical, near-IR and sub-mm polarization techniques to map B-fields at parsec to sub-parsec spatial scales (mostly at the distances of Taurus and Orion).

In the B-field-dominated scenario, the cores are envisaged to gradually condense out of a magnetically sub-critical background cloud, through ambipolar diffusion. B-fields are found to be in the star forming regions sitting on the peripheries of HII regions (a.k.a. bright-rimmed clouds) influenced by neighboring high energy sources. B-fields mapped at different wavelength in these clouds have helped in investigating their continuation from diffused to dense regions. I have sampled a number of isolated cores, including those containing very low luminosity objects (VeLLOs) and various BRCs in nearby HII regions. I will present my results based on the observations towards these regions, and will present this work in the context of the JCMT Large Program called BISTRO. Specifically, I am working on SCUBA-2/POL-2 data towards the Oph-B region as a part of this survey. I will present the results obtained and analysis done toward Oph-B. Along with this, I shall briefly introduce the importance of my accepted PI projects on JCMT for SCUBA-2/POL-2 observations towards cores with VeLLOs and some proto-brown dwarf candidates. I will also introduce my accepted Cycle 5 proposal for ALMA Band 6 polarization observations towards these sources.

November 1st, 2017, 2pm (HST)

Title: VALES: The Valparaíso ALMA Line Emission Survey

Tom Hughes, USTC, China, and University of Valparaíso, Chile

I will introduce a new extragalactic survey using ALMA to characterize the content and physical conditions of the multiphase interstellar medium in galaxies at low-intermediate redshifts: the Valparaíso ALMA Line Emission Survey. We use ALMA Band 3 CO(1–0) observations to study the molecular gas content in a sample of 67 dusty normal star-forming galaxies selected from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). We examine the star formation efficiency in these systems and provide a robust linear fit to the Schmidt-Kennicutt relation using the resolved, disk-like galaxies. A significant number of galaxies at z ~ 0.1 present high gas fractions that are similar to those measured in high-redshift systems. We identify a rapid increase of the gas content as a function of redshift. By comparing our CO line observations and Herschel [CII] spectroscopy to the predictions of a photodissociation region (PDR) model, we find that the neutral gas density also rapidly increases as a function of redshift, whereas the incident radiation field remains constant. Finally, we obtain a calibration between the molecular gas content and the estimated dust continuum luminosity. In this talk, I will review these recent results from VALES and the status of our follow-up campaigns.

September 18th, 2017, 2pm (HST)

Title: A high resolution study of the star-formation law: the test case of M33

Tom Williams, Cardiff University, UK

For nearly 2 decades, the Schmidt index of the star-formation law for a range of galaxies has been found to be around 1.4, generally attributed to star-formation timescales being dictated by the free-fall time. However, another school of thought is that star-formation is more closely linked to dense gas, and that this index is closer to 1. Recent work has also shown that on the scale of a giant molecular cloud complex (~100pc), this law breaks down. Using M33 as a laboratory, I have brought together a panchromatic data set from GALEX UV to SCUBA-2 observations to measure star-formation in a variety of ways. HI and CO(2-1) emission have been used to trace atomic and molecular hydrogen, and I also construct dust maps to trace the gas. My work shows that (a) the star-formation law does indeed break down at 100pc scales, and (b) that a linear Schmidt index is appropriate in M33 when considering molecular gas, or the classic 1.4 with total gas.

September 7th, 2017, 2pm (HST)

Title: Extended dust emission from nearby Asymptotic Giant Branch stars

Thavisha Dharmawardena, ASIAA, Taiwan

Asymptotic Giant Branch (AGB) stars are a primary contributor of heavy elements and dust to the Interstellar Medium (ISM). While we are able to accurately measure dust production rates by AGB stars in nearby galaxies, AGB stars within the Milky Way are often overlooked due to the difficulties in obtaining distances. Understanding AGB stellar dust emission properties and mass- loss histories leads to better understanding the ISM evolution of the Milky Way.

We present results of a search for extended dust emission from 15 AGB stars within 500 pc. Observations at 450 μm and 850 μm were carried out using the SCUBA-2 instrument on the James Clerk Maxwell Telescope (JCMT). These observations were combined with Herschel PACS observations at 70μm and 160μm from the MESS survey (Groenewegen M. A. T., et al., 2011, AA, 526; Cox N. L. J., et al., 2012, AA, 537). Using azimuthally-averaged surface brightness vs. radius profiles we determined the extension and percentage flux within the extended component for each source at the four wavelengths. Using these profiles we derived extensions at the 3-sigma level of up to ∼40′′ for SCUBA-2 data and ∼80′′ for PACS data. The fraction of the flux emitted from the extended region is ∼40% for SCUBA-2 data and ∼50% for PACS data. By fitting a modified black body to four-point SEDs at each radial point we derived the temperature, spectral index of dust emissivity (β), and dust column densities, in order to probe the dust mass-loss history, and detect any changes in physical properties of dust as a function radius (and hence, time).

This project is part of the large scale JCMT survey, the Nearby Evolved Star Survey (NESS), which aims to determine the gas and dust return from a volume limited sample of Galactic AGB stars using several sub-mm facilities.

August 30th, 2017, 2pm (HST)

Title: The Atacama Large Millimeter/submillimeter Array (ALMA)

Lars-Ake Nyman, Joint ALMA Observatory, Chile

The Atacama Large Millimeter/submillimeter Array (ALMA) is a versatile mm/sub-mm array for use by the astronomical community. ALMA is located in the Atacama Desert in northern Chile at an elevation of 5000m, and it consists of sixty-six high-precision antennas which can be moved into arrays with baselines up to 16 km. Fifty of these antennas are 12-meter dishes in the 12-m Array, used for sensitive, high-resolution imaging. The remaining sixteen antennas make up the Atacama Compact Array (ACA), also known as the Morita Array, used to enhance wide-field imaging: twelve of those are closely spaced 7-meter antennas (7-m Array), and four are 12-meter antennas for single-dish observations (Total Power Array). ALMA has a collecting area of 6600 m2, an instantaneous bandwidth of 2 × 8 GHz (two polarizations) and a set of receivers for observations between 84 and 950 GHz. During the build-up phase ALMA has already produced transformational science.

Early Science with ALMA started in 2011 with 16 antennas and limited capabilities. ALMA is now in its fifth cycle of operations (Cycle 4) and is expected to reach steady state in Cycle 5. Since Cycle 3 the observing cycles are annual, starting on October 1. During each of the last cycles about 1600 proposals were submitted by the community, and the total oversubscription factor is about a factor 4. Apart from spectral line and continuum observations ALMA now also offers capabilities such as linear polarization, Solar observations and VLBI. Proposal types include regular proposals, Large Programs (> 50h of observing time), target of opportunity and Director’s Discretionary Time proposals.

ALMA data is processed by ALMA staff using both a pipeline and manual data reduction (the latter mainly of data from new capabilities not yet included in the pipeline heuristics). Deliveries include quality assessed images. The proprietary time of the data is one year after delivery, and by now almost all of the Cycle 0, 1 and 2 data is publicly available. So far, ALMA has delivered data to more than 1000 projects that currently have resulted in over 570 refereed publications. There is also an ALMA Development Program led by the community for studies and implementations of improvements to ALMA hardware, software and techniques.

July 7th, 2017, 2pm (HST)

Title: Investigating Dense Gas and Star Formation at Different Scales: from Milky Way Molecular Clouds to the GMCs of the Antennae Galaxies (NGC 4038/39)

Ashley Bemis, McMaster University, Canada

We explore the relationship between dense gas and star formation on a range of physical scales. This range includes individual cores that will go on to form single stellar systems and extends out to giant molecular complexes consisting of hundreds or thousands of such cores within nearby galaxies. We focus on the Antennae system, a nearby galaxy merger, which presents an extreme environment of star formation. We study the relationship between dense gas and star formation in the Antennae galaxies by comparing emission of dense gas tracers, HCN, HCO+, and HNC, from high-resolution ALMA observations to 70-μm infrared observations taken with Herschel PACS. We compare these results to that of nearby molecular clouds, including preliminary results of the Aquila Molecular Complex using JCMT HCN(4-3) data. Combining these results with work on nearby giant molecular clouds in the Milky Way allows us to calibrate observational tracers used to understand the relationship between star formation and dense gas in extragalactic systems.

June 27th, 2017, 2pm (HST)

Title: Transients! in the JCMT-Transient Survey

Greg Herczeg, KIAA, China

Most protostars have luminosities that are significantly fainter than expected from steady accretion over the protostellar lifetime. The solution to this problem may lie in episodic mass accretion — prolonged periods of very low accretion punctuated by short bursts of rapid accretion. However, the evidence for such events is almost entirely indirect. In the EAO-JCMT Survey, “How do stars gain their mass? A JCMT/SCUBA-2 Transient Survey of Protostars in Nearby Star Forming Regions”, we are monitoring monthly with SCUBA-2 the sub-mm emission in eight fields within nearby (< 500 pc) star forming regions to measure the accretion variability of protostars. This survey is the first dedicated survey for sub-mm variability and complements other transient surveys at optical and near-IR wavelengths, which are not sensitive to accretion variability of deeply embedded protostars. In this talk, I will place our survey in the context of past outbursts and discuss our progress in our ongoing program, including one confirmed and several likely sub-mm variables.

June 13th, 2017, 10am (HST)

Title: Low-cost water vapour radiometry: Prospects and progress (Part 1, Part 2)

Tinus Stander and Shaunel Walker, University of Pretoria, South Africa

Ground-based mm-wave water vapour and integrated liquid water radiometers are often used for tropospheric phase, delay and opacity correction in high frequency VLBI. Most current commercial and research instruments follow the same general implementation principle, with seemingly little published efforts toward smaller, low-cost instruments suitable for remote site surveys. This talk will present an overview of a multi-institution project to investigate the incorporation of communications and RADAR system advances into WVR development, as well as present initial progress toward developing a low-cost WVR system.

May 23rd, 2017, 2pm (HST)

Title: The death throes of massive stars

Sofia Wallström, ASIAA

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.

May 12th, 2017, 2pm (HST)

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

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.

May 2nd, 2017, 2pm (HST)

Title: Observed properties of interstellar filaments

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.

March 30th, 2017, 2pm (HST)

Title: Extreme galaxies and their environments

Andrew Blain, University of Leicester, UK

I will describe some of the most remarkable rare objects highlighted by powerful infrared emission from the WISE mission, and their environments seen in JCMT and Spitzer follow-up.

March 21st, 2017, 11am (HST)

Title: An ALMA view of the star forming galaxies associated to a protocluster 4C23.56 at z=2.49

Minju Lee, University of Tokyo / NAOJ, Japan

Galaxies evolve within the cosmic web and the evolution cannot be considered without any affect from the surrounding environment. Galaxy clusters are systems where environmentally driven galaxy evolution may play a profound role. The role of the environment particularly at high redshift is yet unclear. With the accumulating number of studies in ‘general’ fields, we are now trying to understand galaxy evolution within the cosmic web and focussing on dense regions of high redshift Universe. As gas feeds the star forming activity of a galaxy, we first study the cold gas component of the galaxy with ALMA. In this talk, I will present our recent results of a pilot study, with sub-arcsecond observations using ALMA, which are carried out to follow-up Hα emitters (HAEs) associated to a protocluster 4C23.56 that detected with Subaru/MOIRCS, those also have overlaps with several SMGs detected with both ASTE/AzTEC (at 1.1 mm) and JCMT/SCUBA-2. We investigat total gas content, gas fraction and kinematics from CO(3-2) and 1.1 mm dust continuum detections. Our results suggest that massive (> 4×1010 M) star forming galaxies (on the main sequence) appear to evolve somewhat differently compared to field galaxies, in terms of the gas depletion time as a function of stellar mass. I discuss this further with our preliminary analysis on kinematics with higher resolution imaging, to address the potential role of the environment. I will finally conclude my talk with the future observations that we need to investigate further.

February 3rd, 2017, 2pm (HST)

Title: POL-2 & BISTRO: Studying the effects of interstellar magnetic fields

Simon Coudé, University of Montréal, Canada

The new POL-2 polarimeter at the JCMT stands at the forefront of a new generation of millimeter-wavelength polarimeters currently being commissioned around the world. It will open a unique window on the role of magnetism in physical processes of the interstellar medium both within and outside the Galaxy. I will present preliminary results obtained by the POL-2 commissioning team and the Canadian BISTRO team of the 850 µm linear polarisation towards a sample of galactic and extra-galactic sources. These results include the monitoring of rapid variability in the polarisation of four radio-loud active galactic nuclei, which is expected to probe magnetized turbulence in the medium close to their central supermassive black holes. Additionally, I will present polarisation maps for the Bok globule CB 68 and the Barnard 1 star-forming region in Perseus, and discuss how they inform us about the plane-of-sky component of these objects’ magnetic fields in the context of the Radiative Alignment Torque (RAT) theory of grain alignment. Finally, I will compare these POL-2 results with previously published SCUPOL studies.

January 27th, 2017, 4pm (HST)

Title: High resolution ALMA imaging of SMGs

Bitten Gullberg, Durham University, UK

I will present high resolution (0.03″) continuum maps of four z~4 sub-mm galaxies (SMGs) selected from the ALMA-LESS and ALMA-UDS surveys. These cycle 3 observations resolve the gas and dust within the ISM of these galaxies on 0.2 – 1 kpc scales. The data reveal an apparent range of morphologies. Though the continuum morphologies appear to be: smooth and compact of extended and ‘clumpy’, comparison with simulations reveal that all four sources are consistent with exponential disks. From the morphologies and dynamics of the gas and dust, I will show that these SMGs are most likely to contain dust disks which are smooth on scales of ~200 pc.

January 25th, 2017, 2pm (HST)

Title: Resolved gas kinematics and line ratios in a sample of low-redshift extreme line emitters

Hyunjin Shim, Kyungpook National University, Korea

The increase of Hα equivalent width as a function of redshift suggests that the star formation mode in the early Universe was more intense and vigorous compared to that of the present day. How such a strong star formation is powered is still a matter of debate: it is unclear if cold gas accretion or minor merger mechanisms play the dominant role in high-redshift star formation. In this talk, I will address the question by presenting results from Palomar/SWIFT integral field spectroscopy of a sample of low-redshift (z < 0.4) star-forming galaxies with exceptionally large Hα equivalent widths that could be analogs to z > 4 star-forming galaxies. Unlike other recent work that has shown that a significant fraction of z ~ 1 star-forming galaxies have massive rotating disks, only a few of the objects presented here are found to have rotating disks. Velocity dispersion increase due to beam smearing effects does exist, and line ratios suggest high ionization parameters in these galaxies.

January 23rd, 2017, 2pm (HST)

Title: Dynamical Formation of Black Hole Binaries

Hyung Mok Lee, Seoul National University, Korea

The advanced detectors of gravitational waves detected two black hole binary mergers and one candidate. Such binaries are either formed by evolution of binary systems composed of two massive stars of through dynamical processes in dense stellar systems. I will focus on the dynamical scenarios originating from globular clusters. The galactic nuclei star clusters (NC) could also provide suitable environment for the dynamical binary formation, but they are likely to be much less efficient. The spin directions of individual black holes would be random for dynamical binaries. Also we expect the mass ratios of two black holes in binaries would be close to 1. Binaries composed of a black hole and a neutron star will be very rare among dynamical binaries.

January 18th, 2017, 2pm (HST)

Title: Surveys of high- and low-mass cool evolved stars

Peter Scicluna, ASIAA

The mass loss from evolved stars plays a number of key roles in stellar and galactic evolution. As well as being the main source of dust and chemically-enriched material for the ISM, mass-loss is crucial to understanding the final fates of stars. At the high-mass end, mass-loss is the key parameter that determines when a given star will explode as a supernova, and what kind of supernova it will become. Meanwhile for low- and intermediate-mass stars, mass loss on the AGB allows them to avoid this fate. I will discuss a number of ongoing projects, including the first volume-limited sub-mm survey of nearby dusty AGB stars, combining multiple observing facilities to constrain the mass-loss histories of nearby AGB stars, and hence total gas and dust return to the solar neighbourhood, for the first time. I will also present initial results from an optical-IR high-contrast imaging survey of galactic red supergiants (RSGs) which has resulted in the first direct measurement of dust grain sizes in an RSG envelope and the first detection of a candidate disc-like outflow in an RSG; I will then explore the synergies with an ongoing JCMT programme to constrain the processes driving the outflows in these supernova progenitors.

January 12th, 2017, 2pm (HST)

Title: Revealing the circumstellar environment of eruptive young stars

Orsolya Fehér, Konkoly Observatory, Hungary

FU Orionis-type eruptive young stars show episodic, high amplitude optical outbursts, driven by a several magnitudes increase in their accretion rate. It was proposed that the outbursts might be triggered by infall from the envelope and that all low-mass stars go through a period with repetitive outbursts. The outbursts last for a few months / years and undoubtedly play a profound role in increasing the stellar mass, affecting the circumstellar disk (thus even planet formation) and gradually clearing up the envelope.

We present interferometric maps of the millimeter 13CO and C18O line emission around seven northern FU Orionis type targets at ~1000 – 2000 AU resolution. This provides information about the small-scale structure, the physical state and the kinematics of the envelope around these interesting objects. CO emission peaks close to the optical star position were detected at each targets. The envelopes are roughly circular or elliptic and generally have clumpy structures. The heating of the central star can be clearly seen in their excitation temperature maps. The envelope masses are between 0.03 – 1 M and we find a correlation between the detected masses and the shape of the 10-μm silicate feature observed at the stars. This suggests that FUor eruptions may indeed cause envelope dispersal.

Print Friendly, PDF & Email

Comments are closed