Lunch Talk (2023)

Protostellar jets are the most intriguing characteristics in the magnetized, accreting young stellar objects. The ejection of jets and accretion outbursts are closely related to the formation of complex organic molecules (COMs) in the class 0/I protostars. However, the launching mechanism of the protostellar jet and its correlation with COMs formation are not constrained observationally. In this presentation, I shall briefly introduce the current theory of jet launching. Then I shall present our recent results on jet/outflow from the high spatial resolution and high sensitivity observations with Atacama Large Millimeter/submillimeter Array (ALMA), which is currently the largest radio interferometry array on Earth. Finally, I shall describe the possible connection of the jet with the accretion burst and formation of complex organic molecules within the disk, which would be the chemical composition of future planets.

Starless cores are the potential sites for star and planet formation. Although we know gravity plays the main role during evolution, the details, in particular the timescale, are not yet well understood. The lifetime suggested by different scenarios could vary by more than a factor of ten. With time-dependent chemical analysis, measuring the chemical timescale of the cores allows us to infer possible evolutionary scenarios. We determine the density, temperature, and molecular abundance profiles of two nearby low-mass starless cores, L1512 and L1498, with dust extinction measurements from near-infrared observations and non-local thermal equilibrium radiative transfer with single-dish radio observations (H2D+ as well as deuterated N-bearing tracers with IRAM30m, JCMT, and GBT). Then we perform chemical modeling of the two targets to measure their chemical timescales (t) using deuterium fractionation as a chemical clock. We find that L1512 is chemically evolved while L1498 is chemically young. This might imply that the magnetic field is stronger in L1512 than in L1498. Consequently, ambipolar diffusion may have slowed the contraction of L1512 or even halted it to the present state.

Planet formation begins with the coagulation of dust grains in protoplanetary disks. Therefore, constraints on the dust size distribution in the disks can provide a clue to understanding planet formation. Previous studies have estimated the dust size distribution using the spectral index derived from multi-wavelength observations or dust polarization observations. However, these studies give different results depending on their methods and model assumptions and do not reach a consensus. In this work, we propose another indirect method to constrain the dust size distribution by using the wavelength dependency of the dust ring widths. In many disks, there are dust and gas rings, and larger dust grains are more effectively trapped in the gas rings, forming narrower dust rings. As a result, the dust rings are expected to appear narrower at longer wavelengths since the observations are sensitive to the dust grains whose size is comparable to the observed wavelength. We analyze high-resolution Band 4 (2.1 mm) and Band 6 (1.3 mm) images of the HD 163296 disk. We find for the first time that the width of the outer dust ring (100 au) appears 1.2 times narrower at the longer wavelength, while the width of the inner ring (67 au) is similar between the two bands. The difference in the ring width depending on the observed wavelength is consistent with the dust trapping scenario in a gas ring. We constrain the maximum dust size a_max and the exponent of the dust size distribution p from the difference in dust ring width between the two bands, together with the spectral index, and found that 1 mm < a_max < 20 mm and p < 3.5 in the inner ring, and a_max > 30 mm and 3.4 < p < 3.6 in the outer ring. These results suggest that the degree of dust growth is spatially dependent, which could affect the formation of planetesimals.

With an emphasis on improving the fidelity even in super-resolution regimes, new imaging techniques have been intensively developed over the last several years, which may provide substantial improvements to the interferometric observation (such as ALMA) of protoplanetary disks (PPDs). In this talk, I will introduce a novel super-resolution imaging technique utilizing sparse modeling to enhance the fidelity and spatial resolution of the ALMA images, as well as its principle. Next, I will turn to our recent results of high-resolution images of 43 Taurus-Auriga protoplanetary disks with spatial resolutions ranging from 0.01 to 0.1 arcseconds (1-14 au at a distance of 140 pc), 2-3 times higher than those obtained from conventional imaging technique. The resolved dust disks have radii that widely range from 8 to 238 au but exhibit a roughly similar average surface brightness temperature of 8 K. The analysis revealed various substructures, such as gap and ring, regardless of disk size. The locations of the gaps show bimodal distribution peaking at 10-20 au and 30-100 au. The locations of gaps and rings show a linear relationship, while several systems do not lie in this correlation. Such outlier’s gap widths are 2-3 times larger than typical sizes on the corresponding locations. Finally, I will discuss two types of these disks with different gap sizes that indicate the presence of two distinct planet-forming mechanisms by assuming that the gaps are carved by planets and that their sizes are proportional to planetary masses.

Understanding orbital evolution and planet formation through the lenses of N-body simulations is crucial for chaotic dynamical systems. On the other hand, atmospheric and climate modeling can provide us with unique insights into atmospheric evolution, habitability, and the observation prospects of rocky extrasolar planets. In this talk, I will present results from two separate studies combining techniques of N-body simulations in conjunction with atmospheric and climate modeling. In the first study, we used a three-dimensional N-Rigid-Body integrator and an intermediately-complex general circulation model to simulate the evolving climates of TRAPPIST-1 e and f with different orbital and spin evolution pathways. We find that sporadic libration and rotation induced by planetary interactions, such as that due to mean motion resonances (MMRs) in compact planetary systems may destabilize attendant exoplanets away from synchronized states (or 1:1 spin-orbit ratio). Planet f perturbed by MMR effects with sporadic spin-variations are colder and dryer compared to their synchronized counterparts due to the zonal drift of the substellar point away from open ocean basins of their initial eyeball states. On the other hand, the differences between perturbed and synchronized planet e are minor due to higher instellation, warmer surfaces, and reduced climate hysteresis. This is the first study to incorporate the time-dependent outcomes of direct gravitational N-Rigid-Body simulations into 3D climate modeling of extrasolar planets and our results show that planets at the outer edge of the habitable zones in compact multi-planet systems are vulnerable to rapid global glaciations. In the absence of external mechanisms such as orbital forcing or tidal heating, these planets could be trapped in permanent snowball states. In a second study, we examine the building blocks of pre-planetary materials using the outputs of an N-body planet formation paradigm and a Python-based volatile accretion model. For Earth-like protoplanets, our results suggest that volatile elemental ratios (e.g., C/N, C/H) are driven by the complex interplay between delivery, atmospheric ablation, and mantle degassing.

We often talk about the star formation history of the Galaxy, but what about the planet formation history of the Milkyway? When did the first planets form in the Galaxy? Did rocky planets form first and gas giants later? Answering these questions is essential for understanding the formation and evolution of exoplanetary systems in the galactic context. Understanding the age distribution of exoplanet host stars and how it relates to the evolution of the Galaxy requires a large statistical study of the exoplanet host stars with uniformly determined ages. However, measuring the ages of the individual main-sequence-stars is challenging. One way to overcome this is to measure the ensemble ages of stars using the dispersion in their peculiar velocities. Stars in the solar neighborhood are known to show a strong correlation between stellar age and velocity dispersion. With Gaia DR3, we have the largest, most accurate measurements of proper motions, parallaxes, and radial velocities of stars, and a large statistical study is now possible. The [Fe/H] in the solar neighborhood also is a strong function of velocity dispersion. Hence studying the velocity dispersion as a function of age and [Fe/H] can help determine the [Fe/H] enrichment history of the Milkyway. From our analysis, we show that as the planet mass increases, the velocity dispersion (age) of the host stars decreases, suggesting that Jupiter-like planets only formed in the last 5-6 Gyr after significant enrichment of the galactic ISM with metals, while rocky planets have been forming for the last 10 Gyr. We further find that debris disks are younger (having smaller velocity dispersion) yet metal-poorer than Jupiter-hosting stars. In this talk, I will discuss our results and, in combination with the velocity dispersion-stellar metallicity relation, examine the implications of our results for planet formation in the context of galactic evolution.

Nanosecond precision in FRB time delay measurements opens up a qualitative new regime for lensing observations. I will outline the many novel applications that may arise in this new lensing paradigm, as well as discuss the necessary theoretical and observational developments needed to take full advantage of lensed FRBs.

The epoch of matter-radiation equality, a fascinating era in the evolution of the Universe, leaves a unique imprint on the matter power spectrum, manifesting as a characteristic turnover. This intriguing feature can serve as an alternative standard ruler, the longest in the cosmos. I will present our latest findings derived from the quasar sample of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). Additionally, I will outline our ongoing endeavors to accurately measure this turnover using the cutting-edge Dark Energy Spectroscopic Instrument (DESI).

Recently, Integral field unit (IFU) spectroscopy has become a powerful tool for understanding the kinematics and morphological features of spatially extended astronomical objects. However, the downside of splitting up photons from an extended source is that the signal weakens and becomes faint, especially when dispersed using a spectrograph. Before analyzing the IFU data scientifically, it needs to be ensured that idealized binning both spatially and spectrally has been done, so that enough spectral signal is present without losing spatial structure information. Additionally, tasks for continuum estimation and spectral line fitting must be automated to ensure that good scientific analysis can be done within a reasonable timescale. Hence, along with other KASI postdocs, I have developed a graphical user interface (GUI) based code, MUSELI, to deal with IFU data from the MUSE instrument installed on the Very Large Telescope (VLT, Paranal, Chile). This python based software deals with multiple complications, such as data cleaning, spatial and spectral binning, and continuum estimation, along with performing spectral line fitting (for gas emission as well as stellar absorption). I have also developed a complementary code MUSELI-DEUX, that is useful for displaying fit results. MUSELI, and its future extension, 'InFUSION' (for dealing with all optical IFU instruments), can be used as an efficient optical IFU analysis tool for on-the-fly calculations, partially similar to CASA in radio astronomy.

I will give a student and beginner friendly introduction to GPU computing. I will discuss the current status of GPU computing, and introduce basic details of commonly available tools. I will talk about consideration for new GPU users and developers and give instruction on typical programming concepts specific to GPUs. The focus will be on central concepts and programming tactics instead of specific code syntax.

Numerical simulations have now shown that Population III (Pop III) stars can form in binaries and small clusters and that these stars can be in close proximity to each other. If so, they could be subject to binary interactions such as mass exchange that could profoundly alter their evolution, ionizing UV and Lyman–Werner photon emission and explosion yields, with important consequences for early cosmological reionization and chemical enrichment. Here we investigate the evolution of Pop III and extremely metal-poor binary stars with the MESA code. We find that interactions ranging from stable mass transfer to common envelope evolution can occur in these binaries for a wide range of mass ratios and initial separations. Mass transfer can nearly double UV photon yields in some of these binaries with respect to their individual stars by extending the life of the companion star, which in turn can enhance early cosmological reionization but also suppress the formation of later generations of primordial stars. Binary interactions can also have large effects on the nucleosynthetic yields of the stars by promoting or removing them into or out of mass ranges for specific SN types. We provide fits to total photon yields for the binaries in our study for use in cosmological simulations.

Infrared dark clouds (IRDCs) are a suitable target for studying the earliest stages of high-mass star formation. Those that are 70 um dark are of special interest because they are apparently the coldest more quiescent clouds. At about 5000 au resolution, we have investigated the kinetic temperature of dense cores determined from formaldehyde (H2CO) emission in 12 IRDCs obtained from the pilot ALMA Survey of 70 um dark High-mass clumps in Early Stages (ASHES). Compared to the 1.3 mm dust continuum and other molecular line emission, such as C18O and deuterated species, we find that H2CO emission is mainly sensitive to the outflow/jet components rather than the quiescent gas expected in the early phases of high-mass star formation. These components show warm-hot gas with temperatures ranging from ~50 to > 200 K. In addition, in some cores we detect compact emission of HC3N J=24-23 and OCS J=18-17, which require high temperatures to be excited (Eu > 100 K). With the supreme sensitivity and angular resolution provided by ALMA, we have discovered that a portion of the embedded cores in 70 um IRDCs have already unexpectedly entered the protostellar phase.

The widespread detection of rings and gaps around T Tauri stars' disks suggests that planet formation may actually start during the protostellar phase. However, unlike T Tauri stars, protostars are still surrounded by dense envelopes of gas and dust. These envelopes can interact with the disks, altering the disk's dynamics, chemistry, and amount of material available for planet formation. Oph IRS63 is one of the youngest protostars with confirmed annular structures in its dust disk, which suggests that planet formation may already be underway. In this talk, I present the first high-resolution observations of the gas environment around Oph IRS63 as part of the eDisk Large ALMA program. This protostar exhibits a shell-like bipolar outflow, streamers connecting a large rotating envelope to the disk, and several small-scale spirals seen toward the edge of the dust continuum. Additionally, I describe the dynamic nature of these large-scale structures and how the mass transfer from the envelope to the disk leads to a mass build-up phase, which could result in disk instabilities.

• The phenomenon of shock breakout is the first electromagnetic signal from CCSN as the shockwave propagates to the stellar surface and the opacity allows radiation to escape. Shock breakout holds vital informations from progenitor star and environments, particularly its final stage of stellar evolution. • To address between 1D rad-hydro simulation and 2D gray simulation, we use CASTRO code MGFLD to simulate 2D cylindrical shock breakout using SN1987a progenitor model from Love-grove et al. 2017, our investigation primarily focus on the structures evolution and angle-dependent luminosity variation curve. • Moreover, our methods extend to complex scenarios including CSM structures and perturbation modes. Additionally, we conduct some RSG, Binary, and 3D simulations. • During this lunch talk, I shall present an introduction to basic ideas of shock breakout, then explain our methodology using CASTRO and share some simulations results, showcasing the evolution of structures and luminosity variation curve.

The Schlegel et al. (1998) Galactic dust reddening map, or the so-called SFD map, has been instrumental for observational astronomy, as extinction correction is needed for accurate photometry in the UV, optical, and near-IR. However, it is known that the SFD map is contaminated by the cosmic infrared background (CIB) due to unresolved dusty galaxies in the large-scale structure, and such a systematic can impact a wide range of precision cosmology experiments. In this talk, I will provide a solution to remove the CIB in SFD, which leads to CSFD, a new, full-sky reddening map that traces the Milky Way dust more faithfully and accurately.

Efficient simulation of multi-scale astrophysical phenomena can be achieved through the application of Adaptive Mesh Refinement (AMR). However, existing AMR libraries often come with usability challenges and limited flexibility. In this presentation, I will introduce SADHANA, a newly developed, in-house block-structured AMR framework designed specifically for astrophysical applications. I will offer an insightful overview of the framework, emphasizing its innovative attributes concerning load balancing, grid connectivity, and boundary delineations. Through demonstrations of hydrodynamic and magnetohydrodynamic test cases, I will showcase the current capabilities of SADHANA. Additionally, I will provide a concise account of the ongoing and prospective advancements within the framework's development pipeline.

Star formation in galaxies is governed by the amount of molecular gas and the efficiency that gas is converted into stars. However, assessing the amount of molecular gas relies on the CO-to-H2 conversion factor (α_CO), which is known to vary with molecular gas conditions like density, temperature, and dynamical state – the same conditions that also alter star formation efficiency. The variation of α_CO, particularly in galaxy centers where α_CO can drop by nearly an order of magnitude, thus causes major uncertainties in current molecular gas and star formation efficiency measurements. Using ALMA observations of multiple 12CO, 13CO, and C18O lines in several barred galaxy centers, we found that α_CO is primarily driven by CO opacity changes and therefore shows strong correlations with observables like velocity dispersion and 12CO/13CO line ratio. Motivated by these results, we have constructed a new α_CO prescription which accounts for emissivity effects in galaxy centers and verified it on a set of barred and non-barred galaxies with measured α_CO values from dust. Applying our new prescription to 65 galaxies from the PHANGS survey, we found an overall 3x higher star formation efficiency in barred galaxy centers than in non-barred centers, and such a trend is obscured when using a MW α_CO or other existing prescriptions. Our results suggest that the high star formation rates observed in barred centers are not simply due to an increased amount of molecular gas but also an enhanced star formation efficiency compared to non-barred centers or disk regions.

The ALMA observations reveal in detail the different structures associated with the star formation processes. In this talk, I will present the ALMA Band 7 observations of the CO molecular line emission of the class 0 protostellar system HH 212. The molecular outflow has a complex structure where we find episodic knots launching from the inner part of the accretion disk, as well as, we observe different CO bow shocks entrained by the SiO jet, and we detect the rotating molecular outflow. Also, I will show ALMA Band 6 observations of the CO molecular line emission of the class II protostellar system HH 30. The molecular outflow presents an internal cavity, as well as multiple outflowing shell structures. We distinguish three different shells with constant expansion and possible rotation signatures. We find that the shells can be explained by magnetocentrifugal disk winds. The multiple shell structure may be the result of episodic ejections of the material from the accretion disk associated with three different epochs.

Gravitationally lensed quasars are valuable astronomical objects that offer unique opportunities for studying galaxy evolution and cosmology. Current and upcoming imaging surveys will contain thousands of new lensed quasars, augmenting the existing sample by an order of magnitude. We report the discovery of new lensed quasars (or candidates) in the HSC and CFIS surveys. Spectroscopic or high-resolution imaging follow up on these newly discovered lensed quasar candidates will further allow their natures to be confirmed.

In this talk, I will discuss the applications of Bayesian surrogate models in two areas of astrophysics. Firstly, I'll demonstrate how we utilize the multi-fidelity multi-scale emulation technique to create a surrogate model (emulator) from cosmological simulations with varying qualities. This approach effectively combines different resolutions and dynamic ranges of simulations, enabling accurate emulation of N-Body simulation codes for future Euclid and Roman galaxy surveys. Additionally, I'll present an example using PRIYA simulations, a galaxy formation suite based on the ASTRID simulation model with varied astrophysical feedback parameters. We apply this model to the eBOSS Lya flux 1D power spectrum and produce new constraints on cosmology. In the second part, I'll discuss how we construct a data-driven surrogate model for quasar emission, employing Bayesian model selection to probabilistically detect damped Lyman alpha absorbers and metal absorbers in SDSS quasar spectra. Our model encodes the full covariance of quasar emissions and the redshift evolution of optical depth, allowing us to provide probabilistic constraints even for low SNR spectra. This technique has been adopted by DESI for producing a damped Lyman alpha catalog, significantly improving the accuracy of the Lya 1D flux power spectrum.

The internal structure of the prestellar core G208.68-19.02-N2 (G208-N2) in the Orion Molecular Cloud 3 (OMC-3) region has been studied with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 6 (1.3mm and 1.1 mm). The dust continuum emission revealed a filamentary structure with a length of ~5000 au and an average H2 volume density of ~6 x 10^7 cm^-3. At the tip of this filamentary structure, a compact "nucleus" is observed, characterized by a radius of ~ 200 au and a mass of ~ 0.1 M_sun. The nucleus exhibits a central density of ~2 x 10^9 cm^-3, following a radial density profile described by a power-law function with an index of -1.87 +/- 0.11. The density scaling of the nucleus is ~3.7 times higher than that of the singular isothermal sphere. This as well as the very low virial parameter of 0.39 suggest that the gravity is dominant over the pressure everywhere in the nucleus. However, there is no sign of CO outflow localized to this nucleus. The filamentary structure is traced by the N2D+ 3--2 emission, but not by the C18O 2--1 emission, implying the significant CO depletion due to high density and cold temperature. Toward the nucleus, the N2D+ also shows the signature of depletion. This could imply either the depletion of the parent molecule, N2, or the presence of the embedded very-low luminosity central source that could sublimate the CO in the very small area. The nucleus in G208-N2 is considered to be a prestellar core on the verge of first hydrostatic core (FHSC) formation or a candidate for the FHSC.

Recent observations of supernovae (SNe) have indicated that a fraction of massive stars possess dense circumstellar medium (CSM) at the moment of their core collapses. They suggest the presence of additional activities of the SN progenitor driving the enhancement of the mass-loss rate, and some physical processes attributing to single star's activities have been considered. In this study, we carry out binary evolutionary simulations of massive stars with the aim of investigating the CSM structure. We show that the mass-transfer rate in a binary can increase at the beginning of the Roche lobe overflow, and this enhancement would be associated with the structure of the CSM before the explosion. We also illustrate that depending on the orbital period of the binary, the density structure of the CSM can have a diverse distribution including shell-like and cliff-like structures. These characteristic structures appear within the lengthscale of ∼10^17cm and could be traced by long-term observations of SNe, if the slow velocity of the CSM is assumed (∼10 km/s). Our results highlight the importance of binary interaction in the aspect of reproducing the diversity of the CSM configuration. In this talk, we will introduce our models for binary evolutionary simulations, resultant CSM structure, and implications for observed SN properties and stellar evolution of massive stars.

The study of complex organic molecules (COMs) in star-forming regions is crucial for understanding the origins and prevalence of life in the universe. This presentation shares findings from a COM survey within the 'ALMA Survey of Orion PGCCs (ALMASOP)' project, focusing on Class 0/I protostellar cores in the Orion molecular cloud complex. We detected a total of 11 hot corinos, with the relative abundances of various COMs to methanol aligning with literature reports. To uncover the underlying physical properties and origin of hot corinos, we applied spectral energy distribution (SED) modeling to our sample. The analysis establishes a correlation between the detectability of hot corinos and the mass of the warm envelope in the protostar, suggesting that hot corinos are a common feature of Class 0/I protostellar cores. Our findings advance our understanding of the chemical composition and physical processes involved in the early stages of star formation and provide observational support for the prevalence of hot corinos in protostellar systems

In the quest to capture direct images of exoplanets in habitable zones, we encounter a formidable challenge—the interference of bright exozodiacal dust, a confounder that significantly diminishes sensitivity. In this talk, we embark on a journey into the intricacies of direct imaging observations in reflected light, focusing on the impact of exozodiacal dust on vortex coronagraphs with varying charge numbers and disk inclinations. As I delve into the simulations, I discover that even modest dust substantially causes bright background brightness within the habitable zone. Astonishingly, the luminosity of this dust can overshadow that of a Jupiter-like planet in a neighboring planetary system by over 2000 times in some extreme cases, posing an obstacle in our pursuit of understanding distant worlds. My analysis highlights the crucial need to account for exozodiacal dust within the inner working angle (IWA), which is often overlooked in conventional studies. Not only does dust alter the contrast curve, demanding a reconsideration of optimal design, but the highly aberrated point spread function (PSF) near the IWA complicates post-processing mitigation strategies. Importantly, my findings reveal that, for high-inclination disks and regions just beyond the IWA, dust can diminish contrast by another factor of three, underscoring the significance of comprehensive exozodiacal dust considerations in mission planning. The discussion will extend beyond the simple estimate of exozodi effects to explore how these phenomena alter the ideal vortex coronagraph designs for direct imaging. Additionally, we will touch upon the assumption of a smooth disk model and the potential complexities that may arise, introducing a layer of realism to my simulations. Join me in unraveling the secrets of exoplanetary imaging, offering insights that shape our understanding of distant worlds and pave the way for more comprehensive strategies for habitable exoplanet detection.

We present NOEMA CO(2-1) observation of nearby Seyfert galaxy NGC 3079, which exhibits both AGN activity and active star formation (SF). By subtracting the best-fitted thick disk component generated by DYSMALPY, we reveal the complex nuclear structures. Furthermore, we visualize the distribution of cold molecular gas (from archive ALMA) and PAH features (from archive JWST) in NGC 7469, another Seyfert galaxy that displays both AGN and SF activities. By extracting spectra from different regions, we discuss the physical properties of the circumnuclear environments. The above studies are conducted with CARTA (Cube Analysis and Rendering Tool for Astronomy) that can enhance the efficiency of analyzing 3D image data. Then, I will briefly show the current CARTA development structure and automatically quality assurance (QA) testing strategy.