Lunch Talk (2020)

Angular momentum is one of the most important physical quantities that govern star formation. The initial angular momentum of cores may be responsible for its fragmentation and can have an influence on the size of the protoplanetary disk. To understand how cores obtain their initial angular momentum, it is important to study the angular momentum of filaments where cores form. While a number of theoretical studies on filament rotation exist, there exist little or no precise specific angular momentum measurements in star-forming filaments. In this talk, I will present high-resolution N2D+ ALMA observations of the LBS23 (HH24-HH26) region in Orion B. Our maps provide one of the most precise and reliable measurements of the specific angular momentum in a star-forming filament. We find values of about 2 to 9 x 10^20 cm^2/s, comparable to the value measured in rotating cores with a size similar to our filament width (~ 0.04 pc) in Orion A. Our results suggest that young cores may inherit their angular momentum from their parent filaments. In addition, if time permits I will share some work and planned observations for the first interstellar comet, Borisov.

In this talk, I will give an overview of ALMA data processing status. I will address the issues involved in the past and current cycles, and the efforts we have made to optimize the efficiency of our workflow. There will be time for a discussion session after the talk. Comments and feedbacks from ALMA current and future PIs, as well as ALMA archive users, are most welcome.

Intrinsic alignments (IAs), correlations of galaxy orientations/shapes with surrounding fields such as the mass overdensity, arise due to physical processes during the formation and evolution of galaxies. Thus, investigating IAs in principle enables one to probe galaxy formation and evolution. IAs have been extensively studied also in the context of potential systematic effects in weak-lensing surveys. Besides the two effects above, there is a growing interest of using the galaxy IAs as a tool to extract cosmological information complimentary to galaxy clustering analysis. In a series of recent papers I have developed a comprehensive framework for this purpose: formulation of the IA statistics, investigation of the cosmological information encoded in the IAs, and a forecast study which shows that constraints on cosmological parameters such as dark energy and Hubble parameter can be tighter than those from conventional galaxy clustering analysis alone by a factor of more than 1.5. In this lunch talk I will present a brief overview of these series of work.

夏威夷大島茂納凱亞火山（Mauna Kea）上的天文台群，在過去12月當中，有5個月處於關閉的狀態。去年7-8月期間，新設望遠鏡的爭議及抗議活動達到最高峰，為了確保工作人員的安全，天文台關閉了兩個月。從今年的三月開始，為了防止病毒，也一直關閉至今。 在這演講中，我會快速的說明Mauna Kea 現在的狀況，及我們平時跟關閉時如何操控望遠鏡。

Accretion disks are a common structure in the universe. Young stars grow by accreting the material from the disk that also forms planets. Only in recent years that it is possible to study the detailed structure of these young disks. Yet, it is still not fully understood how disks form around young protostars. By comparing the observed dust and gas structures to numerical models, it might give insights to how the material is transported from the early stages of star formation to the young planet-forming disk. In order to obtain a more complete picture, the dust, gas and ice composition of the young disk is compared with meteorites. The history and physics of star formation can be better understood by knowing the ingredients (dust, ice and gas) of the young disk.<br> Hub-filament system is a morphology commonly seen in star-forming regions, and is often associated with forming protoclusters. Such morphology can be easily produced by simulations via a variety of physical mechanisms, such as fragmentation, cloud-cloud collision, or self-gravitating. It is still challenging to constrain these simulations by observations, as these simulations often predict similar features in one or few physical parameters. To obtain a more complete picture of an object, a systematic analysis using all observable quantities and their cross-correlations is important in characterizing the properties of a system. The parametrization of the observable quantities can be the first step to adopt the machine learning algorithms in comparing the simulation and observations.

This is another talk about those Class 0/I bla bla. But hopefully is more fun.

Understanding the origin of stellar initial mass function (IMF) is a central issue in the study of star formation. The past studies of dense cores reported that the slope of the stellar IMF and core mass function (CMF) are consistent, suggesting that the fundamental mass distribution of stars is determined during the early stage of the core formation. However, dense cores have been observed and studied only in the inner part of the Galactic plane (including the solar neighborhood), which has similar metallicity to that of the solar neighborhood. Thus, an important question to address is whether the same relation between the CMF and stellar IMF holds true even in low-metallicity environments. To solve this question, we performed CO and dust continuum ALMA high-resolution (~0.1 pc scale) mapping observation toward a massive star-forming molecular cloud in the outer Galaxy, which has much lower gas density and lower metallicity (~20 % of the solar neighborhood value) than those in the solar neighborhood . As the results, we successfully detected ~0.1 pc-wide filament structures and ~0.1 pc-scale dense core structures in the outer Galaxy for the first time. We also found that the slope of the CMF in the outer Galaxy is similar to that of the universal IMF. These results suggest that the star-formation processes in the low-metallicity environment follow a universal law.

電腦視覺在近幾年來是個發展快速的領域，生活中常見的如車牌或人臉辨識。在天文觀測上，電腦視覺的發展及應用來的更加久遠。這個演講將簡要說明幾項天文觀測上主要的應用。例如：星系與恆星影像的分辨、光譜相機位置的校正以及多目標光纖模組的定位。

In the search for extrasolar moons, time-domain photometry remains our most valuable asset, in part because there is an abundance of data, and also because exomoons can imprint several independent features in the light curves. In this talk I will discuss the dynamical signatures of exomoons, and highlight some recent work that suggests we should renew our efforts to find exomoons by leveraging these dynamical effects.

Since a significant fraction of stars are in multiple systems, binaries are now a critical component in modern astronomy. Close binaries are the origin of many exotic astronomical events in the Universe, including stellar mergers, type Ia supernovae, and gravitational wave events. On the other extreme, wide binaries are easily disrupted by gravitational perturbations, making them a unique tool to probe the Galactic structures. However, the formation and evolution of close and wide binaries remain an unsolved problem, especially because the age of binaries is difficult to measure. In this talk, I will show how we can learn about the age evolution of close and wide binaries from the Galactic kinematics using the Gaia data. For main-sequence contact binaries, I will discuss when and how they are born and when they merge. By combining Gaia with LAMOST, I will show that the wide binary fraction strongly depends on the metallicity, shedding light on their formation processes. In the end, I will demonstrate how these binaries can help us to understand the mass-radius relation of white dwarfs and planet formation.

Trans-Neptunian objects (TNOs) are the most distant and faintest airless bodies in the Solar System we know so far. As they reflect the Sun's light, the TNOs absolute magnitude estimations must consider i) the geometry of the observation, and ii) the effects of light interaction with the surface. The wide range in color observed from photometric surveys of this population, do not show clear relations with dynamical or physical properties. In this talk I will address the importance of photometric studies in order to estimate the surface composition of TNOs, due to the fact that their spectra are almost featureless. I will talk about the goals of photometric techniques in TNOs composition research, as well as the relation between what we define as absolute colors, and their phase coefficients and albedo.