Measuring Microlensing Parallax via Simultaneous Observations from Chinese Space Station Telescope and Roman Telescope

Simultaneous observations from two spatially well-separated telescopes can lead to measurements of the microlensing parallax parameter,an important quantity toward the determinations of the lens mass.The separation between Earth and Sun–Earth L2 point,~0.01 au,is ideal for parallax measurements of short and ultra-short(~1 hr to 10 days) microlensing events,which are candidates of free-floating planet (FFP) events.In this work,we study the potential of doing so in the context of two proposed space-based missions,the Chinese Space Station Telescope (CSST) in a low-Earth orbit (LEO) and the Nancy Grace Roman Space Telescope (Roman) at L2.We show that joint observations of the two can directly measure the microlensing parallax of nearly all FFP events with timescales t_(E)■10 days as well as planetary (and stellar binary) events that show caustic crossing features.The potential of using CSST alone in measuring microlensing parallax is also discussed.

Characterizing microlensing planetary system OGLE-2014-BLG-0676Lb with adaptive optics imaging

We constrain the host-star flux of the microlensing planet OGLE-2014-BLG-0676 Lb using adaptive optics(AO)images taken by the Magellan and Keck telescopes.We measure the flux of the light blended with the microlensed source to be K=16.79±0.04 mag and J=17.76±0.03 mag.Assuming that the blend is the lens star,we find that the host is a 0.73_(-0.29)^(+0.14)M_(⊙)star at a distance of2.67_(-1.41)^(+0.77)kpc,where the relatively large uncertainty in angular Einstein radius measurement is the major source of uncertainty.With mass of M_(p)=3.68_(-1.44)^(+0.69)M_J,the planet is likely a"super Jupiter"at a projected separation of r_(⊥)=4.53_(-2.50)^(+1.49)AU,and a degenerate model yields a similar M_p=3.73_(-1.47)^(+0.73)M_(J)at a closer separation of r_(⊥)=2.56_(-1.41)^(+0.84)AU.Our estimates are consistent with the previous Bayesian analysis based on a Galactic model.OGLE-2014-BLG-0676 Lb belongs to a sample of planets discovered in a"secondgeneration"planetary microlensing survey and we attempt to systematically constrain host properties of this sample with high-resolution imaging to study the distribution of planets.

Microlensing bias on the detection of strong lensing gravitational wave

Identifying strong lensing gravitational wave(SLGW)events is of utmost importance in astrophysics as we approach the historic first detection of SLGW amidst the growing number of gravitational wave(GW)events.Currently,one crucial method for identifying SLGW signals involves assessing the overlap of parameters between two GWs.However,the distribution of discrete matter,such as stars and sub-halos,within the strong lensing galaxy can imprint a wave optical(WO)effect on the SLGW waveform.These frequency dependent imprints introduce biases in parameter estimation and impact SLGW identification.In this study,we assess the influence of the stellar microlensing field embedded in a strong lensing galaxy.Our findings demonstrate that the WO effect reduces the detection efficiency of SLGW by 5%-50%for various false alarm probabilities per pair(FAPper pair).Specifically,at an FAPper pairof 10^(-5),the detection efficiency decreases from~10%to~5%.Consequently,the presence of the microlensing field can result in missing half of the strong lensing candidates.Additionally,the microlensing WO effect introduces a noticeable bias in intrinsic parameters,particularly for chirp mass and mass ratio.However,it has tiny influence on extrinsic parameters.Considering all parameters,~30%of events exhibit a 1σparameter bias,~12%exhibit a 2σparameter bias,and~5%exhibit a 3σparameter bias.

Masses for free-floating planets and dwarf planets

The mass and distance functions of free-floating planets(FFPs) would give major insights into the formation and evolution of planetary systems, including any systematic differences between those in the disk and bulge. We show that the only way to measure the mass and distance of individual FFPs over a broad range of distances is to observe them simultaneously from two observatories separated by D ~ O(0.01 au)(to measure their microlens parallax πE) and to focus on the finite-source point-lens(FSPL) events(which yield the Einstein radius θE). By combining the existing KMTNet 3-telescope observatory with a 0.3 m 4 deg2 telescope at L2, of order 130 such measurements could be made over four years, down to about M ~ 6 M⊕for bulge FFPs and M ~ 0.7 M⊕for disk FFPs. The same experiment would return masses and distances for many bound planetary systems. A more ambitious experiment, with two 0.5 m satellites(one at L2 and the other nearer Earth) and similar camera layout but in the infrared, could measure masses and distances of sub-Moon mass objects, and thereby probe(and distinguish between) genuine sub-Moon FFPs and sub-Moon "dwarf planets" in exo-Kuiper Belts and exo-Oort Clouds.

Wave effect of gravitational waves intersected with a microlens field:A new algorithm and supplementary study

The increase in gravitational wave(GW) events has allowed receiving strong lensing image pairs of GWs. However, the wave effect(diffraction and interference) due to the microlens field contaminates the parameter estimation of the image pair, which may lead to a misjudgment of strong lensing signals. To quantify the influence of the microlens field, researchers need a large sample of statistical research. Nevertheless, due to the oscillation characteristic, the Fresnel-Kirchhoff diffraction integral’s computational time hinders this aspect’s study. Although many algorithms are available, most cannot be well applied to the case where the microlens field is embedded in galaxy/galaxy clusters. This work proposes a faster and more accurate algorithm for studying the wave optics effect of microlenses embedded in different types of strong lensing images. Additionally, we provide a quantitative estimation criterion for the lens plane boundary for the Fresnel-Kirchhoff diffraction integral. This algorithm can significantly facilitate the study of wave optics, particularly in the case of microlens fields embedded in galaxy/galaxy clusters.

An Earth-mass planet in a time of COVID-19:KMT-2020-BLG-0414Lb

We report the discovery of KMT-2020-BLG-0414 Lb,with a planet-to-host mass ratio q2=0.9-1.2×10-5=3-4 q⊕at 1σ,which is the lowest mass-ratio microlensing planet to date.Together with two other recent discoveries(4?q/q⊕?6),it fills out the previous empty sector at the bottom of the triangular(log s,log q)diagram,where s is the planet-host separation in units of the angular Einstein radiusθE.Hence,these discoveries call into question the existence,or at least the strength,of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-q planets.Due to the extreme magnification of the event,Amax~1450 for the underlying single-lens event,its light curve revealed a second companion with q3~0.05 and|log s3|~1,i.e.,a factor~10 closer to or farther from the host in projection.The measurements of the microlens parallaxπE and the angular Einstein radiusθE allow estimates of the host,planet and second companion masses,(M1,M2,M3)~(0.3 M⊙,1.0 M⊕,17 MJ),the planet and second companion projected separations,(a⊥,2,a⊥,3)~(1.5,0.15 or 15)au,and system distance DL~1 kpc.The lens could account for most or all of the blended light(I~19.3)and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system.The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events.The detection of this planet,despite the considerable difficulties imposed by COVID-19(two KMT sites and OGLE were shut down),illustrates the potential utility of this program.