1. Testing Fossil System Formation through the Stellar Assembly History of Fossil BCGs

김효원 (Hyowon Kim)

The formation of Brightest Cluster Galaxies (BCGs) in fossil systems is of significant scientific interest, as it directly informs the evolutionary pathways of their host clusters. Fossil clusters, regarded as the most dynamically relaxed and rare systems, exhibit a pronounced deficit of M* galaxies in their luminosity functions compared to normal clusters. This deficiency suggests that fossil BCGs assembled early through major mergers of massive M* galaxies under special conditions, followed primarily by passive growth via dry minor mergers. To test this scenario, we conduct Gemini/GMOS long-slit spectroscopy of two fossil BCG candidates at z ~ 0.36. At these redshifts, fossil BCGs are expected to have largely avoided recent mergers, preserving signatures of their initial assembly in their stellar populations. We will constrain ages and metallicity gradients, providing critical tests of fossil BCG formation hypotheses. In this poster, we will present preliminary results.

 

2. High-Redshift Galaxy Clusters and Large-Scale Structures with Magellan: Prospects for GMT

이성국 (Seong-Kook Lee)

We present a spectroscopic study of high-redshift galaxy cluster candidates selected from multi-band photometric data. Multi-object spectroscopy obtained with IMACS on the Magellan telescope was used to confirm the candidates by identifying spatially and kinematically associated member galaxies. We summarize the properties of the confirmed systems, including their redshifts, galaxy populations, and surrounding environments. We also discuss how this approach may be extended with the Giant Magellan Telescope. The greater sensitivity of GMT will allow spectroscopic follow-up of fainter galaxies and more distant cluster candidates, enabling studies of cluster formation and galaxy evolution at higher redshifts.

 

3. Gemini/GNIRS Near-infrared Spectral Atlas of Type 1 AGNs at z < 0.36

정하영 (Hayeong Jeong)

We present a near-infrared (NIR) spectral atlas of 60 nearby (z < 0.36) and bright (Ks < 13.5 mag) type 1 active galactic nuclei (AGNs) obtained with Gemini North/GNIRS in cross-dispersed mode. The GNIRS spectra cover a wavelength range of 0.85–2.5 μm, which has the advantage of alleviating the effects of dust obscuration while providing important information on the supermassive black hole (SMBH) and the innermost region of the dust torus. To investigate the properties of the SMBH and the dust torus, we measure the line fluxes and full width half maximums (FWHMs) of the NIR hydrogen Paschen lines such as Pα and Pβ. We also find the flat-topped line profiles in the high-order Paschen lines (e.g., Pγ, Pδ, Pε), from which the outer radius of the broad line region (BLR) or the inner radius of the dust torus can be inferred. In future work, we will use these Paschen line measurements to update BH mass estimators with a sample much larger than those used in previous studies and to understand the geometry of dust torus.

 

4. Investigating Resolution-Dependent Biases in Paschen-Line-Based Black Hole Mass Estimates

박준영 (Junyeong Park)

Optical Balmer lines of type-1 active galactic nuclei (AGNs) have been widely used to estimate black hole (BH) masses, but they can be significantly affected by dust extinction. Therefore, infrared (IR) Paschen lines have been used for dust-obscured AGNs to alleviate dust extinction effects. However, the effects of low-resolution IR spectroscopy (e.g., R ~ 750 or 150) have not been fully investigated, even though it may introduce systematic biases in line FWHM and flux measurements. In this study, we compare Paschen line properties derived from high- and low-resolution spectra to investigate resolution-dependent biases. For this purpose, we obtain high-resolution (R ~ 45,000) NIR spectra of 11 low-z type 1 AGNs from IGRINS observation. Using these spectra, we generate low-resolution mock spectra for various observing configurations (e.g., Gemini/GNIRS, AKARI/IRC, and SPHEREx). From this comparison, we find resolution-dependent biases that can introduce systematic bias in BH mass measurements based on Paschen lines. To improve the statistical significance of these results, we plan to expand our sample through additional high-resolution NIR observations across multiple facilities.

 

Oral Presentation

======================== 19 Aug. 2026 (Wed) ========================

Session: Project / Facilities

1. Talk1   International Gemini Observatory

황나래 (Narae Hwang)

We will present the current status and future strategic plan of the International Gemini Observatory, the largest Korean ground-based optical observing facility.

 

2. Talk2   2026 K-GMT Science Program Operation Report

석지연 (Ji Yeon Seok)

I will present the 2026 Korea Gemini Office report for science operations.

 

3. Talk3   LSST: Getting Started and Current Status 

신윤경 (Yun-Kyeong Sheen)

The Legacy Survey of Space and Time (LSST) of the NSF-DOE Vera C. Rubin Observatory has recently started its 10-year-long astronomical observations of the Southern hemisphere.  We will present the current status of the LSST project and the latest news from the Rubin Community Workshop 2026 held in July at SLAC

 

4. Talk4    TBD

이재준 (Jae-joon Lee)

TBD

 

5. Talk5    Development of MagNIFIES/GMTNIRS and Science Opportunities

이호규 (Ho-Gyu Lee)

TBD

 

6. Talk6    GMT 2026: Status and Prospects

박병곤 (Byeong-Gon Park)

TBD

 

Session: High-z / Early Universe

1. Talk1    Galaxies, Bubbles, and Lyman-Alpha: Mapping the Patchy Universe at Cosmic

정인태 (Intae Jung)

The Epoch of Reionization (EoR) marks the Universe’s pivotal phase transition: when the first luminous sources transformed a fog of neutral hydrogen into a transparent, ionized intergalactic medium (IGM). Lyman-alpha (Lyα) emission, the most prominent spectral feature in star-forming galaxies, provides a powerful probe of this process: because it is resonantly scattered by neutral hydrogen, its presence, absence, and spectral shape encode where the IGM is ionized and how ionized bubbles grow. A suite of Lyα observables (e.g., equivalent width, luminosity function, spectral line profile, and damping-wing attenuation) reconstructs both the timeline and topology of reionization and links those maps back to the physics of galaxies and stars. I will discuss what recent discoveries imply about the ionizing sources and geometry of reionization, addressing key physical and observational challenges such as cosmic variance, sight-line dependence, and evolving ISM/CGM conditions. Finally, I will outline future directions aimed at advancing Lyα observations and reionization science toward a more physically grounded and statistically robust view of the Universe’s last major transformation.

 

2. Talk2   Lyman Alpha Blobs in the High-Redshift Universe from the ODIN Survey

문병하 (Byeongha Moon)

Lyα blobs (LABs) are spatially extended Lyα emitting objects embedding multiple galaxies in a high redshift universe. The rarity and association with over-dense regions imply they are proto-group candidates. Therefore, LABs are cosmic laboratories to understand galaxy evolution and association with their underlying large-scale environment. However, their nature and statistical properties are still puzzling due to their small number statistics, strong field-to-field variation, and small survey area. In particular, different survey depths and definitions of the LAB sample make systematic studies challenging (e.g., number density, redshift evolution, luminosity function, clustering). One-hundred-deg^2 DECam Imaging in Narrowbands (ODIN) survey provides a chance to overcome this constraint with the largest survey volume to date at three cosmic slices (z ~ 2.4, 3.1, and 4.5). We have discovered the largest samples of LABs (>400) and confirmed Lyα spectra and protoclusters with large telescopes (e.g., Gemini/GMOS). Thanks to the largest and systematic ODIN samples to date, the first statistical study for LABs finally became possible. Here, we will present an overview of ODIN-LABs and statistical studies. 

 

3. Talk3   The BlueDOG at Cosmic Noon: A Possible Analog to Little Red Dots?

김성재 (Seongjae Kim)

We discovered a hyperluminous dust-obscured galaxy with mysterious blue-excess emission (BlueDOG) in the rest-frame UV of its spectral energy distribution (SED) from a multiwavelength survey in the AKARI Deep Field - South (ADF-S). We present the results of SED analysis with multiwavelength photometric data and spectroscopic analysis, observed with Gemini-S/GMOS, FLAMINGOS-2, to explore the origin of blue-excess emission of a hyperluminous BlueDOG, ADFS-KMTDOG-102, at z=2.6. The SED analysis shows that this BlueDOG is a highly massive system (log M_stellar/M_sun=12.3) with substantial extinction. Additionally, the proportion of the old stellar population exceeds that of the young stellar population, which suggests stellar evolution cumulated from the early Universe. The mass of the supermassive black hole estimated using the extinction-corrected broad H-alpha emission line yields log M_BH/M_sun=10.2. We discuss the similarity between the BlueDOG and "Little Red Dots'" (LRDs), recently discovered with the James Webb Space Telescope, showing SED shapes remarkably similar to those of LRDs. The UV emission line ratios indicate that the emission lines are primarily powered by the central active galactic nuclei (AGN). In contrast, the origin of the blue-excess UV continuum remains ambiguous, since both recent star formation and AGN-induced scattered light are viable explanations, based on the results from the SED fitting and scattered light modeling.

 

4. Talk4   ODIN: Characterizing diffuse Lyα halos around star-forming galaxies at high redshifts

금재염 (Jaeyeom Geum)

Lya halos (LAHs) around star-forming galaxies trace the medium in and around their host halos, offering insights into the baryon cycle that regulates galaxy growth through inflows, outflows, and feedback. The One-hundred-deg2 DECam Imaging in Narrowband survey (ODIN) constructs the largest photometric database of Lya emitters (LAEs) at z=2.4 and 3.1. Using this dataset, we study the evolution of LAHs across the cosmic noon. Here, we present our methodology for cleaning and performing photometry on z=2.4 and 3.1 LAEs in the extended COSMOS, XMM-LSS, and DEEP2-3 field (~26 deg2 in total). Contaminated or saturated sources and possible AGNs (outliers in brightness) are removed, reducing the sample. Background subtraction was recalibrated, followed by scaled median stacking to detect faint LAH, and Markov Chain Monte Carlo (MCMC) fitting to measure the halo scale radius. Comparing the stacked radial profiles in the Lya (N419 and N501) and UV continuum (r) bands, accounting for their point-spread functions, reveals clear LAHs, indicating an extended medium distribution beyond the stars. We also investigate how the LAH scale radius depends on galaxy properties, including UV magnitude, rest-frame equivalent width (EW), and environment, through subsampling analyses.

 

5. Talk5   High-z Quasar Survey with SPHEREx: Synergy with Gemini Telescopes

김용정 (Yongjung Kim)

High-redshift quasars, among the most luminous objects in the early Universe, provide a unique probe of the formation and growth of the earliest supermassive black holes. Owing to strong intergalactic medium attenuation blueward of Lyα at 1216 Å, near-infrared wavelength coverage is essential for identifying quasars at the highest redshifts. SPHEREx, an all-sky near-infrared spectrophotometric survey covering 0.75–5.0 μm, offers a powerful opportunity to search for very bright quasars only a few hundred million years after the Big Bang. In this talk, I will briefly introduce my previous high-redshift quasar survey conducted with support from Gemini and K-GMT, and then present our ongoing SPHEREx-based search for quasars at (z > 7). Starting from the SPHEREx Reference Catalog, we preselect potential high-redshift quasar candidates by requiring optical non-detections and applying dropout-based selection criteria. We then identify plausible candidates in the early SPHEREx data obtained between April and August 2025, and rank them using Lyα-break contrast, spectral-line significance, signal-to-noise ratio, and goodness of fit. Because SPHEREx provides low-resolution spectrophotometry, near-infrared spectroscopy with large telescopes is essential for confirming the redshifts and physical properties of these candidates. I will discuss the most promising candidates and outline our planned Gemini follow-up observations, highlighting the synergy between SPHEREx all-sky discovery and Gemini spectroscopic confirmation for building a new sample of luminous quasars in the early Universe.

 

======================== 20 Aug. 2026 (Thu) ========================

Session: AGN

1. Talk1   Unveiling the AGN Engine with Reverberation Mapping and Its Implications for Black Hole Mass and Growth

우종학 (Jong-Hak Woo)

Reverberation mapping is one of the most powerful tools for probing the central engine of active galactic nuclei (AGNs). In this talk, I will present the Seoul National University AGN Monitoring Projects (SAMP and SAMP-II), our long-term observational campaigns aimed at understanding the structure and kinematics of the broad-line region (BLR). I will highlight the major results from these campaigns and introduce a new black hole mass estimator based on the BLR fundamental plane, which suggests that conventional methods may substantially overestimate black hole masses. Finally, I will discuss the implications of these revised mass estimates for our understanding of black hole growth, particularly in the high-redshift universe.

 

2. Talk2    A spatially and temporally resolved study of local post-starburst AGNs with strong outflows

김창석 (Changseok Kim)

Post-starburst AGNs (PSAs) are ideal laboratories for studying AGN feedback, as they exhibit signatures of both AGN activity and recent quenching. We present spatially resolved properties and global star formation histories (SFHs) for a sample of nine PSAs with ionized outflow signatures (z < 0.2). Using IFU data from Gemini/GMOS and VLT/MUSE, we investigate spatially resolved gas kinematics, stellar populations, and ionization sources. We identify kpc-scale outflows extending over 2-8 kpc in eight PSAs, significantly more extended than those in normal AGNs at comparable luminosities. We directly compare the spatial scales of outflow and post-starburst (PSB) regions to test their co-spatiality. We find that EW(Hd) generally shows a flat radial profile and satisfies the PSB criterion across regions more extended than or comparable to the outflow sizes. Lastly, half of the strong outflow PSAs exhibit a bursty starburst followed by rapid quenching within the last 100-200 Myr, whereas the others have experienced more gradual quenching over a few Gyr. We discuss the implications of these spatially and temporally resolved analyses for AGN feedback scenarios, particularly in the delayed feedback framework.

 

3. Talk3    Probing the Intrinsic Properties and Evolutionary Nature of Red AGNs

김도형 (Dohyeong Kim)

Previous simulation studies have suggested that dust-obscured AGNs represent a transitional phase in which merger-driven star-forming galaxies evolve into unobscured AGNs. In this scenario, AGNs are expected to appear red because of dust extinction from their host galaxies and to exhibit enhanced black hole accretion activity compared with unobscured AGNs. Red AGNs, characterized by their unusually red colors, have therefore long been considered promising candidates for this intermediate dusty phase. However, it remains unclear whether red AGNs truly correspond to young, dust-obscured AGNs, mainly because their intrinsic physical properties have not yet been well established. To address this issue, we investigate both unobscured and red AGNs with three main goals: (i) to derive new black hole mass estimators for obscured AGN studies, for which conventional black hole estimators can be easily affected by dust obscuration; (ii) to examine whether red AGNs host merging black holes; and (iii) to investigate the black hole accretion rates of red AGNs to test whether they exhibit the enhanced activity predicted by simulation studies.

 

Session: Low-z Universe

1. Talk1   Emission line galaxies with Gemini 

심현진 (Hyunjin Shim)

We executed follow-up observations of emission-line galaxy candidates selected by their broad-band colors using Gemini/GMOS, under Band 3 and poor weather conditions. In this talk, we will summarize the results from these previous programs, and discuss future plans to use the capabilities of Gemini for following up on interesting objects selected from large surveys. 

 

2. Talk2   Wide-field Weak Lensing Studies of Galaxy Clusters: Current Status and Future Prospects

조혜전 (Hyejeon Cho)

Wide-field imaging enables weak-lensing studies of galaxy clusters on scales extending from cluster centers to the surrounding large-scale structures. In this talk, I will present an update on our ongoing Subaru Hyper Suprime-Cam weak-lensing program, carried out through the Gemini-Subaru Time Exchange. I will summarize the current status of the program, highlight recent scientific results, and discuss future prospects in the era of Rubin/LSST and upcoming wide-field spectroscopic surveys.

 

3. Talk3   Brightest Cluster Galaxies and Intracluster Light Co-Evolution: Revealed by Rubin LSST Imaging and Gemini GMOS Spectroscopy

유재원 (Jaewon Yoo)

Understanding the co-evolution of brightest cluster galaxies (BCGs) and intracluster light (ICL) is essential for constraining the assembly of galaxy cluster cores, yet observational studies remain limited. We present Gemini/GMOS-S multi-object spectroscopy of a galaxy cluster at z~0.21 selected from Rubin LSST ComCam Data Preview 1 in the ECDFS field. Recent hydrodynamical simulations suggest that, although BCGs and ICL co-evolve, they follow distinct formation pathways: the ICL is predominantly built from stripped stars originating in lower-mass galaxies and is expected to be more metal-poor than the BCG. Direct spectroscopic constraints on the stellar populations across the BCG--ICL transition region, however, remain scarce. Our GMOS observations provide spectroscopic confirmation of cluster members, enabling a robust measurement of the ICL fraction, and deep spectroscopy of the BCG extending into its outskirts. We investigate the metallicity and age gradients across the BCG and the BCG--ICL transition region, and compare the results with predictions from recent numerical simulations. This study represents one of the first spectroscopic investigations of BCG and ICL stellar populations in an LSST-selected galaxy cluster, demonstrating the power of combining deep Rubin imaging with Gemini spectroscopy to probe the assembly history of galaxy clusters.

 

4. Talk4    A Caterpillar in a Cabbage: A Milky-Way Sized HI Reservoir Around an Optically Faint Dwarf Galax

김지인 (Jeein Kim)

We report the detection of an unusually large reservoir of atomic hydrogen (HI) gas spatially coincident with an optically cataloged dwarf galaxy - LEDA 136976. Through follow-up Gemini-N/GMOS spectroscopic observations, we detect various optical emission lines, including Hα, [O III], and [N II], confirming that this HI reservoir is associated with our target. Both HI gas and Hα emission exhibit coherent rotation, leading us to classify the system as a rotating disk dwarf galaxy. Our target shows an HI reservoir comparable in size and mass to the Milky Way, yet its stellar mass is less than 10% of the Milky Way’s, with a high star formation rate (>1.1 Msol/yr). We argue that this system is an early-stage seed galaxy that has recently acquired gas and is entering an active phase of star formation, representing a galaxy population possibly missed by all-sky optical surveys. In this talk, we present this system as a pilot case study of a gas-rich yet optically faint galaxy population that will be discovered in abundance in the coming era of large optical and radio telescopes. 

 

Session: Planetary Atmospheres / Small Bodies

1. Talk1   A Multi-wavelength View of Refractory Cold Trapping in Ultra-hot Jupiter Atmospheres

최연호 (Yeonho Choi)

Ultra-hot Jupiters provide a useful test of whether refractory species remain in the gas phase or are depleted by atmospheric cold trapping. In tidally locked planets, the dayside can vaporize metals, while the nightside or deeper atmosphere may allow condensates to form and settle, selectively removing species such as Ti, Ca, and Fe from the observable atmosphere.

I will present high-resolution results for two ultra-hot Jupiters observed with Gemini instruments. For WASP-33 b, Gemini-N/IGRINS-2 dayside emission spectra reveal volatile molecules and refractory metals, including CO, OH, Mg I, and Ti I. The stellar-normalized refractories-to-Ti ratio shows no clear evidence for strong depletions, suggesting no distinct signature of efficient nightside cold trapping in the pre-eclipse dayside atmosphere.

I will also discuss preliminary Gemini-S/GHOST optical results for WASP-18 b, where refractory species remain detectable despite the planet’s high surface gravity. The recovered metal opacity suggests that these species can survive in the gas phase and contribute to the thermal inversion. Together, these results indicate that refractory cold trapping is not controlled by equilibrium temperature alone, and that multi-wavelength high-resolution spectroscopy is needed to connect refractory chemistry, thermal inversions, gravity, and day-night transport.

 

2. Talk2   Volatile and Refractory Signatures in the Atmosphere of WASP-12 b with Near-Infrared High-Resolution Spectroscopy

계창우 (Changwoo Kye)

Recent studies have suggested that measuring the relative abundances of volatile and refractory elements in exoplanetary atmospheres provides a powerful diagnostics for tracing the formation sites of giant planets. We observed the atmosphere of the ultra-hot Jupiter WASP-12 b using a near-infrared high-resolution spectrograph IGRINS-2 (R ~ 45,000) during post-eclipse phases. We detected signals from volatile molecules and gas-phase iron in the planetary atmosphere. Using the detected signals, we performed a Bayesian retrieval analysis and derived a volatile enrichment of 0.19 × solar, a refractory element enrichment of 0.28 × solar, and a C/O ratio of 0.73. We compared the composition of WASP-12 b with previously observed ultra-hot Jupiters with IGRINS/IGRINS-2. In this distribution, the planets exhibit diverse refractory abundances, whereas their refractory-to-volatile ratios remain consistently super-stellar, showing only minor variations relative to the host stars. This constrained trend can suggest that they may share a common origin located well beyond the CO iceline.

 

3. Talk3    The Asteroid–Comet Continuum as a Future Target for Large Ground-Based Telescopes

진선호 (Sunho Jin)

Rocky asteroids and icy–dusty comets have traditionally been regarded as distinct populations that originated in different regions of the Solar System. However, recent discoveries of objects with intermediate properties, such as active asteroids and asteroids on comet-like orbits, have led to the concept of the asteroid–comet continuum. This framework suggests that asteroids and comets represent end-members of a broader population of planetesimals formed in the early Solar System. In this presentation, I will introduce our previous study of the active asteroid (4015) Wilson–Harrington, in which we used ground-based telescopes to investigate its activation mechanism. I will also discuss future opportunities with large telescopes to further deepen our understanding of the asteroid–comet continuum.

 

4. Talk4   Cometary Ices and Dust Survey: Synergy Between Gemini/GMOS and SPHEREx

임범후 (Bumhoo Lim)

Since its launch in May 2025, the SPHEREx mission has provided an unprecedented near-infrared (0.7–5.0 µm) spectroscopic dataset, enabling the characterization of fundamental cometary volatiles such as H2O, CO2, and CO. However, fully understanding a comet's dynamic ice and dust environment requires complementary deep optical data. In this talk, we highlight the crucial role of Gemini/GMOS in our ongoing cometary survey. To anchor the SPHEREx comet catalog—which expands known volatile abundances to approximately one hundred targets—we conducted contemporaneous, ground-based R-band imaging using Gemini/GMOS. The exceptional optical sensitivity of this instrument is distinctly advantageous, allowing us to robustly constrain vital dust properties, including activity levels, integrated brightness, and coma morphology. This capability effectively grounds the space-based data, resolving SPHEREx’s lower sensitivity to the dust continuum. We present the primary results of this survey, examining the distributions of Dust/H2O, CO/H2O, and CO2/H2O mixing ratios across varying dynamical families and heliocentric distances. Finally, we feature a case study of 2P/Encke—an exceptionally active comet in the inner Solar System—to demonstrate the profound scientific potential of synergizing ground-based Gemini/GMOS imaging with space-based infrared observations.

======================== 21 Aug. 2026 (Fri) ========================

Session: Stellar Evolution / Galactic Environments

1. Talk1   Backlighting Young Stellar Objects in the Central Molecular Zone: An Ensemble-Averaged Abundance Structure of Methanol Ices

안덕근 (Deokkeun An)

The Central Molecular Zone of the Milky Way is one of the nearest laboratories for studying star formation under extreme conditions, but much of its activity is hidden behind heavy extinction. Over the past decade, our group has used large-aperture infrared spectroscopy, including Gemini and Subaru observations, to look through this obscuration and probe the icy material surrounding massive young stellar objects in the Galactic center. By combining multiple backlit sight lines toward different ice-rich sources, we were able to move beyond simple ice detections and recover the internal abundance structure of a representative, ensemble-averaged YSO envelope, revealing how methanol ice changes from the inner, warmer regions to the outer, colder layers. In this talk, I will describe how these observations, made possible through the K-GMT program, allowed us to infer the chemical structure of otherwise unresolved Galactic-center YSOs, and how this work points toward future GMT studies of embedded star formation and interstellar ice chemistry.

 

2. Talk2   Gemini and ALMA: Connecting the Central Circumstellar Regions and Extended Envelopes of Evolved Stars

김효선 (Huosun Kim)

Understanding the physical processes that govern mass loss and the transition from the asymptotic giant branch (AGB) to planetary nebulae requires high-angular-resolution observations across a broad wavelength range, as different diagnostics probe different regions of the circumstellar environment.

CW Leo (IRC+10216), the nearest extreme carbon star, provides a unique laboratory for this approach. ALMA observations have revealed spiral-shell structures in its extended circumstellar envelope, while recent HST and Gemini adaptive-optics observations have uncovered the central regions in unprecedented detail, including the first optical detection of the central star. Combined with Gemini NIFS, GSAOI, and GNIRS observations, these data trace the morphology, physical conditions, and kinematics throughout the central circumstellar regions and the extended envelope, providing new insights into the origin of asymmetric mass loss.

In this talk, I will present recent observational results on CW Leo, highlighting how Gemini adaptive-optics imaging and integral-field spectroscopy complement ALMA observations to reveal the morphology, physical conditions, and kinematics of evolved stars across multiple spatial scales.

 

3. Talk3   Raman spectroscopy of the symbiotic star RR Telescopii Using GHOST

이희원 (Hee-Won Lee)

Most symbiotic stars are wide binary systems consisting of an accreting white dwarf and an evolved mass-losing giant. Accretion is believed to proceed via the gravitational capture of a portion of the slow stellar wind from the giant component. The symbiotic star RR Telescopii is a slow nova that erupted in 1944. Unique spectral features found in RR Tel are Raman-scattered features of far-UV lines that appear in the neighborhood of the Balmer lines. We carried out deep, high-resolution spectroscopy of Raman-scattered He II to find three features formed blueward of H\alpha, H\beta, and H\gamma. We adopt a simple scattering model for the formation of Raman features to compute the Raman conversion efficiencies (RCEs). The observed RCEs are found to differ from our simple scattering geometry, implying that the scattering region consists of various components characterized by several physical parameters. These results establish Raman-scattered He II lines as a powerful tool for spectroscopic tomography, allowing for direct constraints on the structure and kinematics of neutral hydrogen in symbiotic binaries. 

 

4. Talk4   Gemini-S/GMOS Spectroscopy of Transients

이영대 (Youngdae Lee)

We have been conducting prompt spectroscopic follow-up observations of transients within a few days of their discovery using the Gemini South/GMOS Target-of-Opportunity (ToO) program. Gemini spectroscopy of dwarf novae, one of the rapidly evolving transients, provides valuable diagnostics of the secondary stars and accretion disks, offering important constraints on the evolutionary states of these cataclysmic variables (CVs). Our targets also include infant supernovae (SNe) discovered through high-cadence BVI-band optical monitoring by the KMTNet Supernova Program (KSP). For SNe, Gemini spectra enable early classification and measurements of ejecta velocities, chemical compositions, and host-galaxy redshifts. Combined with the densely sampled KSP light curves, these spectroscopic observations provide key insights into the physical properties of SNe and the evolutionary status of the CVs. In this presentation, we highlight the major scientific results from our Gemini ToO program and demonstrate the power of Gemini/GMOS spectroscopy, together with continuous KSP photometric monitoring, for investigating the nature and evolution of astrophysical transients

 

Session: Stellar Population / Galactic Archaeology

1. Talk1    What a stochastic world: Challenges and Limitations in Constraining the Initial Mass Function

임범두 (Beomdu Lim)

To understand the chemical evolution and integrated light of galaxies, two fundamental assumptions are required: the star formation history (SFH) and the initial mass function (IMF). However, disentangling these two factors simultaneously poses a significant challenge. Star clusters, which form in a single, coeval burst of star formation, simplify the SFH into a "single burst" scenario, making them ideal laboratories for isolating and constraining the IMF. Since Salpeter's seminal 1955 work deriving the IMF from field stars in the solar neighborhood, numerous studies have investigated the IMF within coeval stellar systems. While the debate over the universality of the IMF has persisted for decades, its critical importance has resurfaced in the current era of deep-universe observations, where verifying cosmological models is paramount. In this presentation, I will share previous results on the IMF of open clusters within the Galaxy. By combining these results with our recent Gemini-GMOS observations of young stellar clusters in nearby galaxies, I will discuss the ongoing challenges and fundamental limitations encountered in IMF research. 

 

2. Talk2    How can we study planet-host stars with Gemini high-resolution spectrographs?

임동욱 (Dongwook Lim)

As more exoplanets are being discovered in the Milky Way, understanding the detailed properties of their host stars is becoming increasingly important. One key question is whether planets can leave detectable chemical fingerprints in the atmospheres of their host stars. High-resolution spectroscopy of wide binaries using Gemini facilities provides a valuable way to address this question, because the two stars likely formed together from the same natal material, while in some systems only one component is known to host a planet. In such systems, precise differential abundance analysis can offer clues to possible planetary signatures in the atmosphere of the planet-hosting star. High spectral resolution over both optical and near-infrared wavelength regions is essential for this approach. Gemini high-resolution spectrographs provide a powerful opportunity for this purpose. GHOST and MAROON-X can be used to measure abundances of many refractory elements in the optical, while IGRINS-2 allows us to obtain precise abundance measurements for volatile elements in the near-infrared. In this talk, I will introduce our previous study of planet-hosting wide binaries observed with IGRINS, and discuss our future plans to combine GHOST and IGRINS-2 observations to investigate planet-host stars across optical and near-infrared wavelengths.

 

3. Talk3   Derivation of Chemical Abundances via Infrared Spectroscopy for Stars With and Without Planets

윤솔 (Sol Yun)

The chemical composition of a stellar atmosphere retains a record of the formation and evolutionary history of stars and their planetary systems. In particular, elemental abundance ratios such as C/O serve as key diagnostics of the chemical environments in which planets form. Using the Immersion GRating INfrared Spectrometer (IGRINS) on Gemini South, we carry out high-resolution H- and K-band spectroscopy to probe potential chemical differences between stars with and without known planetary companions. We determine stellar atmospheric parameters via synthetic grid fitting and derive CNO abundances from OH, CO, and CN features where reliable constraints are available. Atomic element abundances, including refractory elements such as Mg, Al, and Si, are derived from selected infrared lines, with systematic offsets corrected using an observed solar spectrum. We present the resulting stellar parameters, molecular CNO abundances, and solar-corrected atomic elemental abundances, thereby providing a basis for comparing the chemical properties of stars across different planetary-system populations.

 

4. Talk4   Neutron-capture Signatures of Accreted Halo Building Blocks from Gemini Spectroscopy of Metal-Poor Stars

정미지 (Miji Jeong)

I present a chemodynamical study of 22 metal-poor stars with [Fe/H] < –1.0 selected from the LAMOST survey, based on high-resolution spectra obtained with Gemini-N/GRACES and Gemini-S/GHOST. The aim of this study is to examine whether metal-poor stars associated with different accreted components of the Milky Way halo preserve distinct neutron-capture enrichment signatures. From the spectra, I derive stellar parameters and chemical abundances for light, α, iron-peak, and neutron-capture elements. I compute their dynamical properties using Gaia astrometry and use the resulting orbital parameters to associate the stars with known halo substructures, including Gaia-Sausage-Enceladus, Wukong/LMS-1, and I’itoi. Differences in the abundance trends of [Eu/Fe], [Ba/Eu], [Eu/Mg], and [Ba/Mg] suggest that the accreted halo components did not share a single neutron-capture enrichment history. These results show that the chemodynamical properties of metal-poor stars provide a useful way to trace the enrichment histories of accreted Milky Way building blocks.