Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpitzer Observations of OGLE-2015-BLG-1212 Reveal a New Path to Breaking Strong Microlens Degeneracies
59
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively breaks a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter space. These models clearly indicate that the lens is a stellar binary system possibly located within the bulge of our Galaxy, ruling out the planetary alternative. We argue that several types of discrete degeneracies can be broken via such space-based parallax observations.
rate research
Read More
We report the discovery and the analysis of the short (tE < 5 days) planetary microlensing event, OGLE-2015-BLG-1771. The event was discovered by the Optical Gravitational Lensing Experiment (OGLE), and the planetary anomaly (at I ~ 19) was captured by The Korea Microlensing Telescope Network (KMTNet). The event has three surviving planetary models that explain the observed light curves, with planet-host mass ratio q ~ 5.4 * 10^{-3}, 4.5 * 10^{-3} and 4.5 * 10^{-2}, respectively. The first model is the best-fit model, while the second model is disfavored by Deltachi^2 ~ 3. The last model is strongly disfavored by Deltachi^2 ~ 15 but not ruled out. A Bayesian analysis using a Galactic model indicates that the first two models are probably composed of a Saturn-mass planet orbiting a late M dwarf, while the third one could consist of a super-Jovian planet and a mid-mass brown dwarf. The source-lens relative proper motion is mu_rel ~ 9 mas/yr, so the source and lens could be resolved by current adaptive-optics (AO) instruments in 2021 if the lens is luminous.
Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by exploring different regions of the lens plane and by directly measuring the microlens parallax. We report the discovery of a 30-55$M_J$ brown dwarf orbiting a K dwarf in microlensing event OGLE-2015-BLG-1319. The system is located at a distance of $sim$5 kpc toward the Galactic bulge. The event was observed by several ground-based groups as well as by $Spitzer$ and $Swift$, allowing the measurement of the physical properties. However, the event is still subject to an 8-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either $sim$0.25 AU or $sim$45 AU. This is the first microlensing event observed by $Swift$, with the UVOT camera. We study the region of microlensing parameter space to which $Swift$ is sensitive, finding that while for this event $Swift$ could not measure the microlens parallax with respect to ground-based observations, it can be important for other events. Specifically, for detecting nearby brown dwarfs and free-floating planets in high magnification events.
In this paper, we present the analysis of the binary gravitational microlensing event OGLE-2015-BLG-0196. The event lasted for almost a year and the light curve exhibited significant deviations from the lensing model based on the rectilinear lens-source relative motion, enabling us to measure the microlens parallax. The ground-based microlens parallax is confirmed by the data obtained from space-based microlens observations using the {it Spitzer} telescope. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined up to the two-fold degeneracy: $u_0<0$ and $u_0>0$ solutions caused by the well-known ecliptic degeneracy. It is found that the binary lens is composed of two M dwarf stars with similar masses $M_1=0.38pm 0.04 M_odot$ ($0.50pm 0.05 M_odot)$ and $M_2=0.38pm 0.04 M_odot$ ($0.55pm 0.06 M_odot$) and the distance to the lens is $D_{rm L}=2.77pm 0.23$ kpc ($3.30pm 0.29$ kpc). Here the physical parameters out and in the parenthesis are for the $u_0<0$ and $u_0>0$ solutions, respectively.
We present the MOA Collaboration light curve data for planetary microlensing event OGLE-2015-BLG-0954, which was previously announced in a paper by the KMTNet and OGLE Collaborations. The MOA data cover the caustic exit, which was not covered by the KMTNet or OGLE data, and they provide a more reliable measurement of the finite source effect. The MOA data also provide a new source color measurement that reveals a lens-source relative proper motion of $mu_{rm rel} = 11.8pm 0.8,$mas/yr, which compares to the value of $mu_{rm rel} = 18.4pm 1.7,$mas/yr reported in the KMTNet-OGLE paper. This new MOA value for $mu_{rm rel}$ has an a priori probability that is a factor of $sim 100$ times larger than the previous value, and it does not require a lens system distance of $D_L < 1,$kpc. Based on the corrected source color, we find that the lens system consists of a planet of mass $3.4^{+3.7}_{-1.6} M_{rm Jup}$ orbiting a $0.30^{+0.34}_{-0.14}M_odot$ star at an orbital separation of $2.1^{+2.2}_{-1.0},$AU and a distance of $1.2^{+1.1}_{-0.5},$kpc.
We analyze the binary gravitational microlensing event OGLE-2017-BLG-1130 (mass ratio q~0.45), the first published case in which the binary anomaly was only detected by the Spitzer Space Telescope. This event provides strong evidence that some binary signals can be missed by observations from the ground alone but detected by Spitzer. We therefore invert the normal procedure, first finding the lens parameters by fitting the space-based data and then measuring the microlensing parallax using ground-based observations. We also show that the normal four-fold space-based degeneracy in the single-lens case can become a weak eight-fold degeneracy in binary-lens events. Although this degeneracy is resolved in event OGLE-2017-BLG-1130, it might persist in other events.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
