한국천문학회지

111

RIGOROUS 'RICH ARGUMENT' IN MICROLENSING PARALLAX

Gould, Andrew
Journal of the Korean astronomical society = 천문학회지
53, n.5
pp.99-102
2020
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I show that when the observables (πE, tE, θE, πs, µs) are well measured up to a discrete degeneracy in the microlensing parallax vector πE, the relative likelihood of the different solutions can be written in closed form Pi = KHiBi, where Hi is the number of stars (potential lenses) having the mass and kinematics of the inferred parameters of solution i and Bi is an additional factor that is formally derived from the Jacobian of the transformation from Galactic to microlensing parameters. Here tE is the Einstein timescale, θE is the angular Einstein radius, and (πs, µs) are the (parallax, proper motion) of the microlensed source. The Jacobian term Bi constitutes an explicit evaluation of the 'Rich Argument', i.e., that there is an extra geometric factor disfavoring large-parallax solutions in addition to the reduced frequency of lenses given by Hi. I also discuss how this analytic expression degrades in the presence of finite errors in the measured observables.

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112

THE FORMATION OF THE DOUBLE GAUSSIAN LINE PROFILES OF THE SYMBIOTIC STAR AG PEGASI

Hyung, Siek
Journal of the Korean astronomical society = 천문학회지
53, n.2
pp.35-42
2020
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We analyze high dispersion emission lines of the symbiotic nova AG Pegasi, observed in 1998, 2001, and 2002. The Hα and Hβ lines show three components, two narrow and one underlying broad line components, but most other lines, such as HI, HeI, and HeII lines, show two blue- and red-shifted components only. A recent study by Lee & Hyung (2018) suggested that the double Gaussian lines emitted from a bipolar conical shell are likely to form Raman scattering lines observed in 1998. In this study, we show that the bipolar cone with an opening angle of 74°, which expands at a velocity of 70 km s-1 along the polar axis of the white dwarf, can accommodate the observed double line profiles in 1998, 2001, and 2002. We conclude that the emission zone of the bipolar conical shell, which formed along the bipolar axis of the white dwarf due to the collimation by the accretion disk, is responsible for the double Gaussian profiles.

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113

A SEARCH FOR EXOPLANETS AROUND NORTHERN CIRCUMPOLAR STARS VI. DETECTION OF PLANETARY COMPANIONS ORBITING THE GIANTS HD 60292 AND HD 112640

Lee, Byeong-Cheol
Journal of the Korean astronomical society = 천문학회지
53, n.1
pp.27-34
2020
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We report the detection of exoplanet candidates in orbits around HD 60292 and HD 112640 from a radial velocity (RV) survey. The stars exhibit RV variations with periods of 495 ±3 days and 613±6 days, respectively. These detections are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory in Korea. The aim of the survey is to search for planetary or substellar companions. We argue that the periodic RV variations are not related to surface inhomogeneities; rather, Keplerian motions of planetary companions are the most likely interpretation. Assuming stellar masses of 1.7 ± 0.2M⊙ (HD 60292) and 1.8 ± 0.2M⊙ (HD 112640), we obtain minimum planetary companion masses of 6.5 ± 1.0MJup and 5.0 ± 1.0MJup, and periods of 495.4 ± 3.0 days and 613.2 ± 5.8 days, respectively.

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114

OGLE-2017-BLG-1049: ANOTHER GIANT PLANET MICROLENSING EVENT

Kim, Yun Hak
Journal of the Korean astronomical society = 천문학회지
53, n.6
pp.161-168
2020
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We report the discovery of a giant exoplanet in the microlensing event OGLE-2017-BLG-1049, with a planet-host star mass ratio of q = 9.53 ± 0.39 × 10-3 and a caustic crossing feature in Korea Microlensing Telescope Network (KMTNet) observations. The caustic crossing feature yields an angular Einstein radius of θE = 0.52 ± 0.11 mas. However, the microlens parallax is not measured because the time scale of the event, tE ≃ 29 days, is too short. Thus, we perform a Bayesian analysis to estimate physical quantities of the lens system. We find that the lens system has a star with mass Mh = 0.55+0.36-0.29 M⊙ hosting a giant planet with Mp = 5.53+3.62-2.87 MJup, at a distance of DL = 5.67+1.11-1.52 kpc. The projected star-planet separation is a⊥ = 3.92+1.10-1.32 au. This means that the planet is located beyond the snow line of the host. The relative lens-source proper motion is μrel ~ 7 mas yr-1, thus the lens and source will be separated from each other within 10 years. After this, it will be possible to measure the flux of the host star with 30 meter class telescopes and to determine its mass.

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115

KMT-2018-BLG-0029LB: A VERY LOW MASS-RATIO Spitzer MICROLENS PLANET

Gould, Andrew
Journal of the Korean astronomical society = 천문학회지
53, n.1
pp.9-26
2020
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At q = 1.81 ± 0.20 × 10-5, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio q of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent 'pile-up' at q = 5-10 ×10-5. The event was observed by Spitzer, yielding a microlens-parallax πE measurement. Combined with a measurement of the Einstein radius θE from finite-source effects during the caustic crossings, these measurements imply masses of the host Mhost = 1.14+0.10-0.12 M⊙ and planet Mplanet = 7.59+0.75-0.69 M⊕, system distance DL = 3.38+0.22-0.26 kpc and projected separation a⊥ = 4.27+0.21-0.23 AU. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.

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116

QUADRUPLY-IMAGED QUASARS: SOME GENERAL FEATURES

Tuan-Anh, P.
Journal of the Korean astronomical society = 천문학회지
53, n.6
pp.149-159
2020
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Gravitational lensing of point sources located inside the lens caustic is known to produce four images in a configuration closely related to the source position. We study this relation in the particular case of a sample of quadruply-imaged quasars observed by the Hubble Space Telescope. Strong correlations between the parameters defining the image configuration are revealed. The relation between the image configuration and the source position is studied. Some simple features of the selected data sample are exposed and commented upon. In particular, evidence is found for the selected sample to be biased in favor of large magnification systems. While having no direct impact on practical analyses of specific systems, our results have pedagogical value and deepen our understanding of the mechanism of gravitational lensing.

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117

SPATIALLY RESOLVED KINEMATICS OF GAS AND STARS IN HIDDEN TYPE 1 AGNS

Son, Donghoon
Journal of the Korean astronomical society = 천문학회지
53, n.5
pp.103-115
2020
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We analyze the spatially resolved kinematics of gas and stars for a sample of ten hidden type 1 AGNs in order to investigate the nature of their central sources and the scaling relation with host galaxy stellar velocity dispersion. We select our sample from a large number of hidden type 1 AGNs, which are identified based on the presence of a broad (full width at half maximum ≳1000 km s-1) component in the Hα line profile and which are frequently mis-classified as type 2 AGNs because AGN continuum and broad emission lines are weak or obscured in the optical spectral range. We used the Blue Channel Spectrograph at the 6.5-m Multiple Mirror Telescope to obtain long-slit data with a spatial scale of 0.3 arcsec pixel-1. We detected broad Hβ lines for only two targets; however, the presence of strong broad Hα lines indicates that the AGNs we selected are all low-luminosity type 1 AGNs. We measured the velocity, velocity dispersion, and flux of stellar continuum and gas emission lines (i.e., Hβ and [O III]) as a function of distance from the center. The spatially resolved gas kinematics traced by Hβ or [O III] are generally similar to the stellar kinematics except for the inner center, where signatures of gas outflows are detected. We compare the luminosity-weighted effective stellar velocity dispersions with the black hole masses and find that our hidden type 1 AGNs, which have relatively low back hole masses, follow the same scaling relation as reverberation-mapped type 1 AGN and more massive inactive galaxies.

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118

SUN FLUX VARIATIONS DUE TO ORBITING PLANETS: THE SOLAR SYSTEM AS A NON-COMPACT PLANETARY SYSTEM

Barbier, Hugo
Journal of the Korean astronomical society = 천문학회지
53, n.3
pp.69-75
2020
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We study the photometric phase curves for the planets of our solar system which can be considered as a prototypical non-compact planetary system. We focus on modeling the small variations caused by three effects: reflection, ellipsoidal, and Doppler beaming. Theoretical predictions for these photometric variations are proposed, considering a hypothetical external observer. Unlike similar studies of multi-planetary systems, the physical and geometrical parameters for each planet of the solar system are well-known. Therefore, we can accurately evaluate the relationships that shape the planetary light curves for a fictitious external observer. Our results suggest that, for all planets, the ellipsoidal effect is very weak while the Doppler beaming effect (DBE) is, in general, dominant. In fact, the DBE seems to be the principal cause of variations of the light curves for the planets of the solar system. However, for Mercury and Venus the Doppler beaming and reflection effects have similar amplitudes. The phase curves obtained for the planets of the solar system show new interesting features of interest for the study of other non-compact planetary systems.

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119

CORE-JET BLENDING EFFECTS IN ACTIVE GALACTIC NUCLEI UNDER THE KOREAN VLBI NETWORK VIEW AT 43 GHZ

Algaba, Juan-Carlos
Journal of the Korean astronomical society = 천문학회지
52, n.2
pp.31-40
2019
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A long standing problem in the study of Active Galactic Nuclei (AGNs) is that the observed VLBI core is in fact a blending of the actual AGN core (classically defined by the <TEX>${\tau}=1$</TEX> surface) and the upstream regions of the jet or optically thin flows. This blending may cause some biases in the observables of the core, such as its flux density, size or brightness temperature, which may lead to misleading interpretation of the derived quantities and physics. We study the effects of such blending under the view of the Korean VLBI Network (KVN) for a sample of AGNs at 43 GHz by comparing their observed properties with observations obtained using the Very Large Baseline Array (VLBA). Our results suggest that the observed core sizes are a factor ~ 11 larger than these of VLBA, which is similar to the factor expected by considering the different resolutions of the two facilities. We suggest the use of this factor to consider blending effects in KVN measurements. Other parameters, such as flux density or brightness temperature, seem to possess a more complicated dependence.

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120

VLBI NETWORK SIMULATOR: AN INTEGRATED SIMULATION TOOL FOR RADIO ASTRONOMERS

Zhao, Zhen
Journal of the Korean astronomical society = 천문학회지
52, n.5
pp.207-216
2019
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In this paper we introduce a software package, the Very long baseline interferometry Network SIMulator (VNSIM), which provides an integrated platform assisting radio astronomers to design Very Long Baseline Interferometry (VLBI) experiments and evaluate the network performance, with a user-friendly interface. Though VNSIM is primarily motivated by the East Asia VLBI Network, it can also be used for other VLBI networks and generic interferometers. The software package not only integrates the functionality of plotting (u, v) coverage, scheduling the observation, and displaying the dirty and CLEAN images, but also adds new features including sensitivity calculations for a given VLBI network. VNSIM provides flexible interactions on both command line and graphical user interface and offers friendly support for log reports and database management. Multi-processing acceleration is also supported, enabling users to handle large survey data. To facilitate future developments and updates, all simulation functions are encapsulated in separate Python modules, allowing independent invoking and testing. In order to verify the performance of VNSIM, we performed simulations and compared the results with other simulation tools, showing good agreement.

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