ORCID Profile
0000-0001-9825-7864
Current Organisation
Korea Astronomy and Space Science Institute
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Publisher: Oxford University Press (OUP)
Date: 04-07-2019
Abstract: H2O (22 GHz) and SiO masers (43, 86, 129 GHz) in the bipolar proto-planetary nebula OH 231.8+4.2 were simultaneously monitored using the 21-m antennas of the Korean VLBI Network in 2009–2015. Both species exhibit periodic flux variations that correlate with the central star’s optical light curve, with a phase delay of up to 0.15 for the maser flux variations with respect to the optical light curve. The flux densities of SiO v = 2, J = 1→0 and H2O masers decrease with time, implying that they may disappear in 10–20 years. However, there seems to have been a transient episode of intense H2O maser emission around 2010. We also found a systematic behaviour in the velocity profiles of these masers. The velocities of the H2O maser components appear to be remarkably constant, suggesting ballistic motion for the bipolar outflow in this nebula. On the other hand, those of the SiO maser clumps show a systematic radial acceleration of the in idual clumps, converging to the outflow velocity of the H2O maser clumps. Measuring the full widths at zero power of the detected lines, we estimated the expansion velocities of the compact bipolar outflow traced by H2O maser and SiO thermal line, and discussed the possibility of the expanding SiO maser region in the equatorial direction. All of our analyses support that the central host star of OH231.8 is close to the tip of the AGB phase, and that the mass-loss rate recently started to decrease because of incipient post-AGB evolution.
Publisher: American Astronomical Society
Date: 25-04-2016
Publisher: Cambridge University Press (CUP)
Date: 09-2017
DOI: 10.1017/S1743921317010274
Abstract: The Korean VLBI Network (KVN) is a unique millimeter VLBI system which is consisted of three 21 m telescopes with relatively short baselines. We present the preliminary results of simultaneous monitoring observations of the 22.2 GHz H 2 O and 43.1/42.8/86.2/129.3 GHz SiO masers based on the KVN Key Science Project (KSP). We obtained the astrometrically registered maps of the H 2 O and SiO masers toward nine evolved stars using the source frequency phase referencing method (SFPR). The SFPR maps of the H 2 O and SiO masers enabled us to investigate the spatial structure and kinematics from the SiO to H 2 O maser regions including the development of an outward motion from the ring-like or elliptical structures of SiO masers to the asymmetric structures of the 22.2 GHz H 2 O maser features. In particular, the 86.2/129.3 GHz SiO ( v =1, J =2–1 and J =3–2) masers were clearly imaged toward several objects for the first time. The SiO v =1, J =3–2 maser shows different distributions compared to those of the SiO v =1, 2, J =1–0 and v =1, J =2–1 masers implying a different physical condition.
Publisher: American Astronomical Society
Date: 12-2022
Abstract: We report very long baseline interferometry (VLBI) monitoring observations of the 22 GHz water (H 2 O) masers around the Mira variable BX Cam, which were carried out as a part of the EAVN Synthesis of Stellar Maser Animations project. Data of 37 epochs in total were obtained from 2018 May to 2021 June with a time interval of 3–4 weeks, spanning approximately three stellar pulsation periods ( P = ∼440 days). In particular, the dual-beam system equipped on the VERA stations was used to measure the kinematics and parallaxes of the H 2 O maser features. The measured parallax, π = 1.79 ± 0.08 mas, is consistent with Gaia EDR3 and previously measured VLBI parallaxes within a 1 σ error level. The position of the central star was estimated, based on both the Gaia EDR3 data and the center position of the ring-like 43 GHz silicon-monoxide (SiO) maser distribution imaged with the Korean VLBI Network. The three-dimensional H 2 O maser kinematics indicates that the circumstellar envelope is expanding at a velocity of 13 ± 4 km s −1 , while there are asymmetries in both the spatial and velocity distributions of the maser features. Furthermore, the H 2 O maser animation achieved by our dense monitoring program manifests the propagation of shock waves in the circumstellar envelope of BX Cam.
Publisher: IOP Publishing
Date: 07-2016
Publisher: American Astronomical Society
Date: 15-10-2018
Publisher: Springer Science and Business Media LLC
Date: 28-06-2018
DOI: 10.1038/S41467-018-04767-8
Abstract: The supergiant VX Sagittarii is a strong emitter of both H 2 O and SiO masers. However, previous VLBI observations have been performed separately, which makes it difficult to spatially trace the outward transfer of the material consecutively. Here we present the astrometrically registered, simultaneous maps of 22.2 GHz H 2 O and 43.1/42.8/86.2/129.3 GHz SiO masers toward VX Sagittarii. The H 2 O masers detected above the dust-forming layers have an asymmetric distribution. The multi-transition SiO masers are nearly circular ring, suggesting spherically symmetric wind within a few stellar radii. These results provide the clear evidence that the asymmetry in the outflow is enhanced after the smaller molecular gas clump transform into the inhomogeneous dust layers. The 129.3 GHz maser arises from the outermost region compared to that of 43.1/42.8/86.2 GHz SiO masers. The ring size of the 129.3 GHz maser is maximized around the optical maximum, suggesting that radiative pumping is dominant.
Publisher: Oxford University Press (OUP)
Date: 31-01-2018
DOI: 10.1093/MNRAS/STY239
Publisher: Oxford University Press (OUP)
Date: 12-2014
DOI: 10.1093/PASJ/PSU104
Location: China
Location: Korea, Republic of
No related grants have been discovered for Jaeheon Kim.