Lunch Talk (2014)

Signposts of planets in protoplanetary disks produced by disk-planet interactions may provide us a unique way to probe and study the earliest stages of planet formation. Transitional disks are protoplanetary disks with central depleted regions (cavities), possibly been cleared out by the forming planets. Recently, Subaru directly imaged a number of such disks at near infrared (NIR) wavelengths (the SEEDS project) with high spatial resolution and small inner working angles. Using radiative transfer simulations, we study the structure of these objects by modeling observations at different bands simultaneously. The complexity of transitional disks is reviewed, somewhat unexpectedly, by the variety of features captured in their observations, such as cavities, spiral arms, and other non-smooth/asymmetric structures in the disks, which indicates fundamentally different underlying disk structure, possibly implying different origins of these objects.

We present the phase characteristics study of the ALMA 3 km baseline data. We successfully obtained the spatial structure function of phase fluctuation, which increases as a function of baseline length up to 1.0-1.5 km, and turns to be almost flat at longer baseline. This is the first mm/submm structure function to show the turn-over of the structure function. Furthermore, confirmation of the turn-over indicates that even the ALMA baseline length extended to the planned longest baseline of 15 km, the fringe will be detected at the similar rms phase fluctuation as that at a few km baseline lengths.

Unlike the formation of Solar-type stars, the formation of massive stars (M>8 Msun) is not yet well understood. For Solar-type protostars, the presence of circumstellar or protoplanetary disks which provide a path for mass accretion onto protostars is well established. However, to date only few cases of young massive stars show the evidence of circumstellar disks which might support the idea that a scaled-up version of low-mass star formation could be applied to young massive stars. To what extend this hypothesis can be applied is still unclear and more observational evidences are required to characterize the physical properties of the disk-like structures around massive stars in order to understand how exactly massive stars gain their masses in the equatorial regions. In this lunch talk, I will present high resolution (sub)millimeter interferometric observations of two massive star-forming regions: AFGL 2591 and S255IR. The data imply that massive stars may form via disk accretion in some relatively isolated star-forming cores. Our studies serve as the basis for the coming Atacama Large Millimeter/submillimeter Array (ALMA) studies of massive star formation at very high angular resolution, which is the only instrument that can resolve the sources with great details and provide hints on how exactly massive stars can be formed.

Ring galaxies, a peculiar class of galaxies, contain various ring-like structures with or without clumps, nuclei, companions, or spokes. For example, the famous Cartwheel galaxy, first discovered by Zwicky (1941), shows an outer ring, an inner ring, a nucleus, and spokes (Theys & Spiegel 1976; Fosbury & Hawarden 1977; Higdon 1995). To explain the formation of ring galaxies, Lynds & Toomre (1976) proposed the collision scenario. In this talk, I will introduce the standard classifications of ring galaxies and show our simulations to investigate the formation of collisional ring galaxies.

One of the basic interests in chemistry is finding out geometric structure of molecules and understandings its relation to reactivity. In our study, we couple quantum chemistry methods with nuclear dynamics simulation to provide simple theoretical pictures to understand the curious experimental observations for molecular clusters such as 1) hydrated hydroxide and 2) carbon cation. 1) Hydroxide, OH-, and its hydration state in water have attracted scientific attention due to its fundamental relevance of understanding aqueous chemistry and biology. In our joint theoretical and experimental study for size selected OH-(H2O)n n=2-4 clusters we provide proper spectroscopic assignments to unravel the number of water molecules in the first solvation shell for these clusters in the gas phase. 2) The reactivity of small carbon clusters with simple molecules such as H2, O2, and HCN has attracted interest of the astrophysics and combustion communities. Using ion mobility spectrometry techniques and quantum chemistry calculations, we studied the reaction between linear Cn+ n=4-9 and D2. Interesting odd even alternation in reactivity is shown to be a consequence of alternation in the electronic structure of the linear carbon chain cations.

We present the smoothed-particle hydrodynamics implementation SPHGal which incorporates several recent developments into the GADGET code. This includes a pressure-entropy formulation of SPH with a Wendland kernel, a higher order estimate of velocity gradients, a modified artificial viscosity switch with a strong limiter, and artificial conduction of thermal energy. We conduct a series of idealized hydrodynamic tests and show that while the pressure-entropy formulation is ideal for resolving fluid mixing at contact discontinuities, it performs conspicuously worse when strong shocks are involved due to the large entropy discontinuities. Including artificial conduction at shocks greatly improves the results. We further perform simulations of an isolated Milky Way like disk galaxy and find a feedback-induced instability developing if too much artificial viscosity is introduced. Finally, we compare the accretion behavior of of hot halo gas. The formation of cold blobs, an artifact of simple SPH implementations, can be eliminated efficiently with proper fluid mixing. Based on the performed tests we consider the SPHGal hydrodynamics sufficiently accurate for galaxy formation simulations.

I will introduce our discovery of the [Ne III]3869 emission from the microjets of Sz 102, a low-mass young stellar object in Lupus III. Spectroastrometric analyses of two-dimensional [Ne III] spectra obtained from archival high-dispersion (R ~ 33,000) VLT/UVES data suggest that the emission consists of two velocity components spatially separated by a projected distance of ~60 AU. Both components trace velocity centroids of the known microjets and show large line widths (> 100 km/s) that extend across the systemic velocity, suggesting their potential origins in wide-angle winds that may eventually collimate into jets. The detection of the [Ne III]3869 line with the distinct velocity profile suggests that the emission originates in flows that may have been strongly ionized by deeply embedded hard X-ray sources, most likely generated by magnetic processes. The discovery along with other optical forbidden lines from Sz 102 support the picture of wide-angle winds surrounding magnetic loops in the close vicinity of the young star. Future high sensitivity X-ray imaging and high angular-resolution optical spectroscopy may help confirm the picture proposed.

Challenging the conventional bandwidth limit, we design an extremely wide-band circular waveguide septum polarizer, covering 42% bandwidth, from 77 GHz to 118 GHz, without any high-order resonance. The performance of this polarizer has been verified in between 75 GHz and 115 GHz. The Stokes parameters constructed from the measured data show that the leakages from I to Q are below 2% and the Q − U mutual leakage below 1%. This result removes the major weakness of the septum polarizer and opens up a new domain of astronomical instrumentation for polarization measurement. Despite this polarizer is designed to cover 77-118 GHz, it can be straightforwardly downsized to cover higher frequencies with minor change. The measurement result of a G-band (140-220 GHz) polarizer is also presented.

Type Ia supernovae (SNe) originate from white dwarfs (WDs) in binary systems through either accretion of a stellar companion's material or merger of two WDs. If a surviving stellar companion is found, the former origin is affirmed. I report how we use Hubble Space Telescope observations of Type Ia supernova remnants in the Large Magellanic Cloud to search for surviving companions.

We develop a new Graphics Processing Unit (GPU)-based code, Odyssey, for ray-tracing in curved space-time. The typical order of magnitude of the computation time is about nano-seconds per photon per time step. Together with the Graphic User Interface (GUI) powered by the video accelerated displaying architecture, Odyssey can serve for not only for scientific but for the educational purpose. In this talk, we will briefly introduce the idea of ray-tracing and demonstrate the educational software we designed for visuializing the curved spcetime near a black hole. For example, the silhouette of a black hole, the shape of a hot spot orbiting a black hole, and 3D photon trajectories.

SPHEREx is a proposal to NASA’s SMEX mission (PI: J. Bock, Caltech/JPL), and participation of IAA is now requested. SPHEREx is a near-infrared spectroscopic survey with passively cooled 20 cm telescope which covers 0.75-5 micron. Science targets are Inflationary cosmology, Galactic ice survey and History of galaxy formation survey. Launch on 2020 is scheduled.

ALMA band-1 is the lowest frequency band among ALMA receivers. The microwave monolithic integrated circuit (MMIC) is an attractive technique for circuit design due to its compact size, high performance, and easy to mass production. In this talk, a low noise amplifier (LNA) and a mixer are designed using MMIC technique for ALMA band-1 warm cartridge.

To improve the efficiency and survey speed of a radio telescope, an integrated dual polarization (IDP) receiver for a large format multi-pixel array has been designed by integrating superconductor-insulator-superconductor (SIS) junction mixers with a planar orthomode transducer (OMT) at 350 GHz. The incoming signals from a circular waveguide are separated into two polarizations via orthogonal waveguide probes, and then transmitted to the junctions through the tuning circuit. To suppress resonance, metallic blocks confine the RF signals within the circular waveguide, and a 2μm thick silicon nitride membrane, on which all devices were implemented, was suspended across the circular waveguide. IDP mixers with junction quality factor (Rsg/Rn) of 10 have been fabricated by using standard Nb-based SIS junction technology and SiN/Si membrane process. The double-side-band (DSB) receiver noise temperature (Trx) of both polarizations, measured simultaneously in a 4K cryostat, is approximately 100K at between 332GHz and 372GHz. The isolation of cross polarization is approximately 20dB.

The NanoSIMS is a powerful and very versatile instrument for surface analysis. In this talk, I will give a summary of the underlying principles of Secondary Ion Mass Spectrometry (SIMS) and discuss the setup of the NanoSIMS, in articular. Based on these principles, I will demonstrate the key advantages of the NanoSIMS and its application, as well as key requirements for planning projects and preparing samples.

Luminous galaxies have their luminosity from large population of young and massive stars and/or accreting massive black holes at the nuclei. The high luminosity often results in a large-scale outflow of interstellar medium from around the luminosity source. Cold molecular gas is the most important outflow medium in this negative feedback to the luminosity generation because it is the fuel for star formation and can be the material feeding the central massive black hole. In this lunch talk I will present our ALMA observations of molecular outflow from the most luminous galaxy within z=0.01, NGC 3256. We found dual bipolar molecular outflows with distinctive properties from the two merger nuclei. One of them is particularly noteworthy in that it is a well-collimated bipolar molecular jet having a ~kpc extent and apparent acceleration; its velocity peaks at ~ 2000 km/s at 300 pc from the driving nucleus. Both outflows eject tens of solar masses per year from the nuclei. They are as important as star formation in the gas consumption of the system.

We present combined SMA+ASTE images of the Class I protobinary L1551 IRS 5 in the CS (J = 7--6) line, the submillimeter images of L1551 IRS 5 with the most complete spatial sampling ever achieved (0″.9 -- 36″). The SMA image of L1551 IRS 5 in the 343 GHz dust-continuum emission is also presented, which shows an elongated feature along the northwest to southeast direction (∼160 AU × 80 AU), perpendicular to the associated radio jets. The combined SMA+ASTE images show that the high-velocity (≳1.5 km s−1) CS emission traces the structure of the dust component and shows a velocity gradient along the major axis, which is reproduced by a geometrically-thin Keplerian-disk model with a central stellar mass of ∼0.5 M⊙. The low-velocity (≲1.3 km s−1) CS emission shows an extended (∼1000 AU) feature that exhibits slight south (blueshifted) to north (redshifted) emission offsets, which is modeled with a rotating and infalling envelope with a conserved angular momentum. The rotational motion of the envelope connects smoothly to the inner Keplerian rotation at a radius of ∼64 AU. The infalling velocity of the envelope is ∼three times lower than the free-fall velocity toward the central stellar mass of 0.5 M⊙. These results demonstrate transition from the infalling envelope to the Keplerian disk, consistent with the latest theoretical studies of disk formation. We suggest that sizable (r∼50--200 AU) Keplerian disks are already formed when the protostars are still deeply embedded in the envelopes.

There has been a lot of buzz recently about Microwave Kinetic Inductance Detectors (MKIDs). These superconducting detectors have a wide variety of applications in astronomy, spanning a large range of frequencies from mm-wave to X-ray. The detectors are fast, inherently multiplexed and there is no readout noise. Nevertheless, since the original Day et al. Nature paper, published in 2003, MKIDs have yet to demonstrate their promised potential to the astronomical community. Having spent several years in graduate school working with MKIDs for the mm-wave MUSIC camera, I have a unique point of view in regards to the application of this new technology. In my talk, I will briefly review the basic principles of operation, the range of astronomical applications, give a sample of the current instrumentation efforts employing MKIDs, and review the challenges associated with the fabrication and employment of these detectors.

The center of Milky Way galaxy is the closest galactic nucleus, whose detailed study can help our understanding of galactic nuclei in external galaxies. The central supermassive black hole Sgr A* is accompanied by a circumnuclear disk (CND) composed of molecular and atomic gas located a few pc away. Chemical compositions are affected by energetic events in the Galactic Center such as irradiation from massive stars, black hole activities, SNe, and shocks, and can be good tracers of these events. Combining a chemical abundance model with data from a spectral scan of molecular lines in 80 - 500 GHz range, we attempt to constrain physical conditions surrounding the molecular gas in the southwest lobe of the CND. Although many factors can affect the chemical features, an enhanced cosmic-ray ionization rate and shocks are likely driving forces of chemistry.

The discovery of Sedna, nearly a decade ago, on a highly eccentric orbit beyond the Kuiper belt challenged our understanding of the Solar System. With a perihelion of 76 AU, Sedna is well beyond the reach of the gas-giants and could not be scattered onto its highly eccentric orbit from interactions with Neptune alone. Sedna’s aphelion at ~1000 AU is too far from the edge of the Solar System to feel the perturbing effects of passing stars or galactic tides in the present-day solar neighborhood. Some other mechanism no longer active in the Solar System today is required to emplace Sedna on its orbit. Sedna's origin remains an outstanding question in planetary astronomy. Sedna's presence predicts a population of icy bodies on similar orbits residing past the Kuiper belt detached from the Solar System in what has been called the Inner Oort Cloud. The recent discovery of 2012 VP113 confirms the presence of the Inner Oort Cloud. The orbits of these distant planetoids are dynamically frozen in place providing a fossilized record of their formation. Using dynamical modeling we probe the location of the inner edge of the Inner Oort cloud and its implications for future observational constraints including finding additional Sedna-like bodies. In particular, I will present results constraining the inner edge of the Inner Oort cloud, produced in the proposed formation scenario where stellar encounters early on in an embedded cluster phase of the Solar System, created Sedna-like orbits.

Close to the end of the year 2014, I will give a summary about the projects we have carried out using our NanoSIMS (Secondary Ion Mass Spectrometer) over the past twelve months. This will cover various fields, such as cosmochemistry and geochemistry, as well as microbiology and material sciences. I will demonstrate the versatility of this instrument, look back on the challenges of the last year and give an outlook on the future of our lab.

Recently, massive early-type galaxies have shed their 'red-and-dead' moniker, thanks to the discovery that many host residual star formation. I will show how observations of the cold and warm ISM, combined with simulations and models, can be used to shed light on the mysterious origin of the material which regenerates red-sequence galaxies and changes their late-time evolution. I will then show that star formation in these objects is dynamically suppressed, leading to stars forming with a much lower efficiency than in spiral/starburst galaxies. Star formation is also suppressed in ETGs which have undergone a recent minor merger. These dynamical processes that suppress star formation are likely to be important in other galactic nuclei, and perhaps even in our own Milky Way. Finally I will show that molecular gas is an excellent kinematic tracer, providing a powerful tool for both studying the large scale mass distribution in galaxies (e.g. with the CO Tully Fisher relation), and probing dark objects lurking at the hearts of galaxies. I will show using high-resolution interferometric observations that one can resolve molecular gas kinematics within the sphere of influence of local supermassive black-holes, and present the first ever black-hole mass measured in this manner.

Spirou is the next generation near-infrared spectropolarimeter for CFHT. One of the major science goal is to find the exoplanets in the habitable zones of law mass stars. Fast and stable guiding on target stars plays important role to maintain the high accuracy of line observation. The guiding camera system of Spirou is developed in OIR Lab of ASIAA. In order to evaluate the accuracy and stability of guiding system, we have developed a system of numerical simulation. The system takes inputs as realistic as possible, such as telescope parameters, atmospheric absorption, stellar spectrum, camera parameters, PID control and wind speed. The result of our simulations helped us selecting the best camera system. We are now developing the camera control system and expect test will be allocated in the early next year.

In the local universe, the most massive galaxies are mostly giant ellipticals that show little or no recent star formation. However, many studies have found that massive quiescent galaxies at z > 2 are generally very compact, with effective radii R_e < 2 kpc. Proposed mechanisms to create such compact galaxies from star-forming progenitors generally involve violent, dynamical processes such as gas-rich mergers or dynamical instabilities fed by cold streams. Also, it is now believed that the high-redshift compact galaxies become the cores of the most massive local galaxies after accreting envelopes through minor mergers over cosmic time. However, it is very difficult to study the compact quiescent galaxies at z > 2 in detail because they are faint. Therefore, many recent studies have focused on identifying and characterizing some similar objects at lower redshifts, where images and spectra with high quality are accessible. In this talk, I will present our recent work on 22 compact quiescent galaxies identified between z ~ 0.4 and z ~ 0.9 from several searches of the area common to SDSS and the United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS). I will discuss the formation mechanisms of these galaxies based on our studies of their morphologies and stellar populations.