Dong-Joo Lee

Reclassification of ROTSE-I δ Scuti Stars with Multiband Photometry and Fourier Decomposition

We present new multiband photometric results for 29 ROTSE-I δ Scuti stars and a Fourier decomposition light-curve analysis in order to reclassify their variability types. For the classification between eclipsing and pulsating stars, we use the criterion that pulsating stars have larger amplitude differences between passbands than eclipsing binaries, because the brightness changes in pulsating stars are mainly due to variations in temperature. From this investigation, we find that 24 of our 29 observation targets are W Ursae Majoris type eclipsing binaries. Fourier analysis of the data for all 91 ROTSE-I δ Scuti stars shows that the phase parameters 21 of the high-amplitude δ Scuti variables identified in this study are concentrated around 4.0. This high-probability area characterized by 21 is in good agreement with the finding from OGLE data. Our results suggest that most of the ROTSE-I δ Scuti stars located outside the high-probability area are in fact W UMa type eclipsing binaries.

1SWASP J093010.78+533859.5: A POSSIBLE HIERARCHICAL QUINTUPLE SYSTEM

Among quadruples or higher multiplicity stars, only a few doubly eclipsing binary systems have been discovered. They are important targets for understanding the formation and evolution of multiple stellar systems because we can obtain accurate stellar parameters from photometric and spectroscopic studies. We present the observational results of this kind of rare object, 1SWASP J093010.78+533859.5, for which the doubly eclipsing feature had been detected previously from the SuperWASP photometric archive. Individual point-spread function photometry for two objects with a separation of about 1.9 was performed for the first time in this study. Our time-series photometric data confirms the finding of Lohr et al. that the bright object A is an Algol-type detached eclipsing binary and the fainter B is a W UMa-type contact eclipsing. Using high-resolution optical spectra, we obtained well-defined radial velocity variations of system A. Furthermore, stationary spectral lines were detected that must have originated from a further, previously unrecognized stellar component. It was confirmed by the third object contribution from the light-curve analysis. No spectral feature of system B was detected, probably due to motion blur by long exposure times. We obtained the binary parameters and the absolute dimensions of systems A and B from light-curve synthesis with and without radial velocities, respectively. The primary and secondary components of system A have a spectral type of K1 and K5 main sequences, respectively. Two components of system B have nearly the same type of K3 main sequence. Light variations for both binaries are satisfactorily modeled by using two-spot models with one starspot on each component. We estimated the distances to systems A and B individually. Two systems may have similar distances of about 70xa0pc and seem to be gravitationally bound with a separation of about 130xa0AU. In conclusion, we suggest that 1SWASP J093010.78+533859.5 is a quintuple stellar system with a hierarchical structure of a triple system A(ab)c and a binary system B(ab).

OGLE-2015-BLG-1459L: The Challenges of Exo-Moon Microlensing

Work by K.H.H. was support by KASI grant 2017-1-830-03. Work by W.Z., Y.K.J., and A.G. were supported by AST-1516842 from the US NSF. W.Z., I.G.S., and A.G. were supported by JPL grant 1500811. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. Work by C.H. was supported by the grant (2017R1A4A101517) of National Research Foundation of Korea. The OGLE Team thanks Prof. G. Pietrzynski for his contribution to the collection of the OGLE photometric data. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to AU. The MOA project is supported by JSPS KAKENHI Grant Number JSPS24253004, JSPS26247023, JSPS23340064, JSPS15H00781, and JP16H06287.

The KMTNet/K2-C9 (Kepler) Data Release

We present Korea Microlensing Telescope Network (KMTNet) light curves for microlensing-event candidates in the Kepler K2 C9 field having peaks within 3 effective timescales of the Kepler observations. These include 181 clear microlensing and 84 possible microlensing events found by the KMTNet event finder, plus 56 other events found by OGLE and/or MOA that were not found by KMTNet. All data for the first two classes are immediately available for public use without restriction.

OGLE-2017-BLG-1522: A Giant Planet around a Brown Dwarf Located in the Galactic Bulge

We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of

Korea Microlensing Telescope Network Microlensing Events from 2015: Event-finding Algorithm, Vetting, and Photometry

t_{rm E} sim 7.5

Photometric Properties of the HW Vir-type Binary OGLE-GD-ECL-11388

days. The Einstein radius is unusually small,

OGLE-2016-BLG-1045: A Test of Cheap Space-based Microlens Parallaxes

theta_{rm E} = 0.065,

KMT-2016-BLG-1820 and KMT-2016-BLG-2142: Two Microlensing Binaries Composed of Planetary-mass Companions and Very-low-mass Primaries

mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses

Spitzer Opens New Path to Break Classic Degeneracy for Jupiter-mass Microlensing Planet OGLE-2017-BLG-1140Lb

(M_{rm host}, M_{rm planet})=(46_{-25}^{+79}, 0.75_{-0.40}^{+1.26})~M_{rm J}