arXiv subjects

Jiseop Shin

Publications and source records attributed to Jiseop Shin.

3 recordsLinked to original sources

arXiv2026

Masking Algorithm for CCD Bleeding in Korea Microlensing Telescope Network Images

Astronomical CCD images are often affected by bleeding from bright sources, producing column-aligned streaks that degrade source detection and photometry. We present a pixel-level masking algorithm for bleeding in Korea Microlensing Telescope Network (KMTNet) images, in which these streaks extend along detector columns away from the readout register. The algorithm identifies bleed-generating pixels using a conservative bleeding threshold and a bleeding index that quantifies excess signal along the expected bleeding direction. The extent of each bleed trail is then determined by termination criteria based on a background-relative detection threshold and a continuity condition. To optimize these termination parameters, we generate multiple candidate masks and evaluate them with an F-beta-like score that favors high purity while preserving recovery of sources whose photometry is biased by bleeding. Using the final mask, we apply interpolation-based cleaning and assess the performance in terms of completeness and photometric accuracy in a crowded KMTNet field, using Gaia DR3 as a reference. The source completeness improves from 94.08% to 98.61%, primarily by enabling proper aperture placement that was previously hindered by bleeding. For selected bleeding-affected sources, the root-mean-square photometric offset decreases from 0.623 mag to 0.068 mag. These results demonstrate that the algorithm provides a practical framework for mitigating bleeding artifacts in KMTNet images. We further examine the stability of the algorithm across different observing conditions and discuss limitations of the current masking and cleaning procedure.

astro-ph.IM↗

arXiv2026

KMTNet Synoptic Survey of Southern Sky III: The First Data Release

We present the first public data release (DR1) of the KMTNet Synoptic Survey of Southern Sky (KS4). This deep, wide-field imaging survey covers a southern footprint of -85$^{\circ}$ < Decl. < -28.8$^{\circ}$ in the $B$, $V$, $R$, and $I$ bands using a network of three 1.6-m telescopes. Although primarily designed to secure reference imaging for gravitational wave counterpart identification, DR1 delivers science-ready data for $\sim$4,000 deg$^{2}$ to enable a broad range of astrophysical research. The release includes deep co-added images reaching median 5$\sigma$ depths of 22.0-23.5 AB mag. It is accompanied by two source catalogs containing over 200 million sources with SNR $>5$: an $I$-band-selected forced-photometry catalog optimized for consistent colors, and a band-merged catalog offering enhanced completeness. Validation demonstrates robust data quality, characterized by mean astrometric offsets of $+0.054 \pm 0.129$ arcsec in RA and $-0.015 \pm 0.120$ arcsec in Dec relative to Gaia DR3. {\refbf Photometric uniformity for point sources is maintained within $\pm 0.03$ mag relative to Gaia XP for 97.5--99.8\% of the footprint across all four bands.} A key advantage of KS4 is its uniform and contiguous spatial coverage. It extends to fainter magnitudes than other uniform surveys while filling irregular gaps in existing deep datasets. All data products are publicly available via the CDS and NOIRLab's Astro Data Lab.

astro-ph.IM↗

arXiv2026

KMTNet Synoptic Survey of Southern Sky II: Data Reduction and Real-Time Transient Detection Pipeline

We present a comprehensive pipeline developed for the image processing of the KMTNet Synoptic Survey of the Southern Sky (KS4) Data Release 1. This pipeline encompasses several key processes, including data quality assurance, astrometry, photometric zero-point (ZP) calibration, bad pixel masking, image stacking, and difference image analysis (DIA). The astrometric solutions were validated by cross-matching with the Gaia EDR3 catalog, achieving sub-pixel astrometric accuracy (< 0.4 arcsec). To ensure spatial consistency, we divided each image into multiple subsections and confirmed that astrometric accuracy was maintained even at the edges. We performed a two-stage photometric calibration. Initial ZP solutions were computed for each individual image frame using the APASS DR9 and SkyMapper DR3 catalogs. Subsequently, we corrected residual spatial variations in the stacked images using Gaia XP photometry. This procedure yielded a 5-sigma depth of 22-23 AB mag across the BVRI bands, with root-mean-square errors of approximately 0.03 mag when referenced to Gaia stars in the magnitude range of 14-19 mag. The processed KS4 images span over 4,000 deg^2 of the southern sky, providing reference images suitable for DIA. This publicly available pipeline also supports real-time processing of newly acquired images, enabling prompt transient detection. We demonstrate its effectiveness through successful applications in gravitational-wave follow-up observations.

astro-ph.IM↗