We present an analysis of the caustic-crossing binary microlensing event OGLE-2017-BLG-0039. Thanks to the very long duration of the event, with a time scale tE ∼ 130 days, the microlens parallax is ...measured precisely despite its low value of . Analysis of the well-resolved caustic crossings during the source star's entrance and exit of the caustic yields an angular Einstein radius of mas. The measured and indicate that the lens is a binary composed of two stars with masses and ∼0.15 M , and is located at a distance of ∼6 kpc. From the color and brightness of the lens estimated from its determined mass and distance, it is expected that ∼2/3 of the I-band blended flux comes from the lens. Therefore, the event is a rare case of a bright lens event for which high-resolution follow-up observations can confirm its nature.
We present a detailed elemental abundance study of 90 F and G dwarf, turn-off, and subgiant stars in the Galactic bulge. Based on high-resolution spectra acquired during gravitational microlensing ...events, stellar ages and abundances for 11 elements (Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Zn, Y and Ba) have been determined. Four main findings are presented: (1) a wide metallicity distribution with distinct peaks at Fe/H = −1.09, −0.63, −0.20, + 0.12, + 0.41; (2) ahigh fraction of intermediate-age to young stars where at Fe/H > 0 more than 35% are younger than 8 Gyr, and for Fe/H ≲ −0.5 most stars are 10 Gyr or older; (3) several episodes of significant star formation in the bulge has been identified: 3, 6, 8, and 11 Gyr ago; (4) tentatively the “knee” in the α-element abundance trends of the sub-solar metallicity bulge is located at a slightly higher Fe/H than in the local thick disk. These findings show that the Galactic bulge has complex age and abundance properties that appear to be tightly connected to the main Galactic stellar populations. In particular, the peaks in the metallicity distribution, the star formation episodes, and the abundance trends, show similarities with the properties of the Galactic thin and thick disks. At the same time, the star formation rate appears to have been slightly faster in the bulge than in the local thick disk, which most likely is an indication of the denser stellar environment closer to the Galactic centre. There are also additional components not seen outside the bulge region, and that most likely can be associated with the Galactic bar. Our results strengthen the observational evidence that support the idea of a secular origin for the Galactic bulge, formed out of the other main Galactic stellar populations present in the central regions of our Galaxy. Additionally, our analysis of this enlarged sample suggests that the (V−I)0 colour of the bulge red clump should be revised to 1.09.
We present the MOA Collaboration light-curve data for the 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 Optical Gravitational Lensing Experiment (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 rel = 11.8 0.8 mas yr−1, which compares to the value of rel = 18.4 1.7 mas yr−1 reported in the KMTNet-OGLE paper. This new MOA value for rel has an a priori probability that is a factor of 100 times larger than the previous value, and it does not require a lens system distance of DL < 1 kpc. Based on the corrected source color, we find that the lens system consists of a planet of mass orbiting a star at an orbital separation of and a distance of .
We present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based
on observations obtained from 13 different telescopes. Intensive coverage of the anomalous
parts of the light ...curve was achieved by automated follow-up observations from the robotic
telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of
an anomalous microlensing event are well covered by follow-up data, allowing us to estimate
the physical parameters of the lens. The strong detection of second-order effects in the event
light curve necessitates the inclusion of longer-baseline survey data in order to constrain
the parallax vector. We find that the event was most likely caused by a stellar binary-lens
with masses M ͙(1) = 0.87 ± 0.12M(☉) and M ͙(2)= 0.77 ± 0.11M(☉). The distance to the lensing
system is 6.41 ± 0.14 kpc and the projected separation between the two components is
13.85 ± 0.16 au. Alternative interpretations are also considered.
We present an analysis of the microlensing event OGLE-2015-BLG-0232. This event is challenging to characterize for two reasons. First, the light curve is not well sampled during the caustic crossing ...due to the proximity of the full Moon impacting the photometry quality. Moreover, the source brightness is difficult to estimate because this event is blended with a nearby K dwarf star. We found that the light-curve deviations are likely due to a close brown dwarf companion (i.e., s = 0.55 and q = 0.06), but the exact nature of the lens is still unknown. We finally discuss the potential of follow-up observations to estimate the lens mass and distance in the future.
MOA-2010-BLG-353Lb: a possible Saturn revealed Rattenbury, N. J; Bennett, D. P; Sumi, T ...
Monthly notices of the Royal Astronomical Society,
11/2015, Letnik:
454, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We report the discovery of a possible planet in microlensing event MOA-2010-BLG-353. This event was only recognized as having a planetary signal after the microlensing event had finished, and ...following a systematic analysis of all archival data for binary lens microlensing events collected to date. Data for event MOA-2010-BLG-353 were only recorded by the high-cadence observations of the OGLE and MOA survey groups. If we make the assumptions that the probability of the lens star hosting a planet of the measured mass ratio is independent of the lens star mass or distance, and that the source star is in the Galactic bulge, a probability density analysis indicates the planetary system comprises a
$0.9^{+1.6}_{-0.53}$
M
Saturn mass planet orbiting a
$0.18^{+0.32}_{-0.11}$
M⊙ red dwarf star,
$6.43^{+1.09}_{-1.15}$
kpc away. The projected separation of the planet from the host star is
$1.72^{+0.56}_{-0.48}$
au. Under the additional assumption that the source is on the far side of the Galactic bulge, the probability density analysis favours a lens system comprising a slightly lighter planet.
ABSTRACT We present the analysis of the planetary microlensing event OGLE-2014-BLG-1760, which shows a strong light-curve signal due to the presence of a Jupiter mass ratio planet. One unusual ...feature of this event is that the source star is quite blue, with . This is marginally consistent with a source star in the Galactic bulge, but it could possibly indicate a young source star on the far side of the disk. Assuming a bulge source, we perform a Bayesian analysis assuming a standard Galactic model, and this indicates that the planetary system resides in or near the Galactic bulge at . It also indicates a host-star mass of , a planet mass of , and a projected star-planet separation of au. The lens-source relative proper motion is mas yr−1. The lens (and stellar host star) is estimated to be very faint compared to the source star, so it is most likely that it can be detected only when the lens and source stars start to separate. Due to the relatively high relative proper motion, the lens and source will be resolved to about ∼46 mas in 6-8 yr after the peak magnification. So, by 2020-2022, we can hope to detect the lens star with deep, high-resolution images.
We present the discovery of a Neptune-mass planet orbiting a 0.8 + or - 0.3Mmiddot in circle star in the Galactic bulge. The planet manifested itself during the microlensing event ...MOA-2011-BLG-028/OGLE-2011-BLG-0203 as a low-mass companion to the lens star. The analysis of the light curve provides the measurement of the mass ratio (1.2 + or - 0.2) x 10 super(-4), which indicates that the mass of the planet is 12-60 Earth masses. The lensing system is located at 7.3 + or - 0.7 kpc away from the Earth near the direction of Baade's Window. The projected separation of the planet at the time of the microlensing event was 3.1-5.2 au. Although the microlens parallax effect is not detected in the light curve of this event, preventing the actual mass measurement, the uncertainties of mass and distance estimation are narrowed by the measurement of the source star proper motion on the OGLE-III images spanning eight years, and by the low amount of blended light seen, proving that the host star cannot be too bright and massive. We also discuss the inclusion of undetected parallax and orbital motion effects into the models and their influence onto the final physical parameters estimates.
We present the analysis of the binary gravitational microlensing event MOA-2015-BLG-020. The event has a fairly long timescale (∼63 days) and thus the light curve deviates significantly from the ...lensing model that is based on the rectilinear lens-source relative motion. This enables us to measure the microlensing parallax through the annual parallax effect. The microlensing parallax parameters constrained by the ground-based data are confirmed by the Spitzer observations through the satellite parallax method. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined. It is found that the binary lens is composed of two dwarf stars with masses and in the Galactic disk. Assuming that the source star is at the same distance as the bulge red clump stars, we find the lens is at a distance . We also provide a summary and short discussion of all of the published microlensing events in which the annual parallax effect is confirmed by other independent observations.
We report the discovery and the analysis of the planetary microlensing event, OGLE-2013-BLG-1761. There are some degenerate solutions in this event because the planetary anomaly is only sparsely ...sampled. However, the detailed light-curve analysis ruled out all stellar binary models and shows the lens to be a planetary system. There is the so-called close/wide degeneracy in the solutions with the planet/host mass ratio of q ∼ (7.0 2.0) × 10−3 and q ∼ (8.1 2.6) × 10−3 with the projected separation in Einstein radius units of s = 0.95 (close) and s = 1.18 (wide), respectively. The microlens parallax effect is not detected, but the finite source effect is detected. Our Bayesian analysis indicates that the lens system is located away from us and the host star is an M/K dwarf with a mass of orbited by a super-Jupiter mass planet with a mass of at the projected separation of . The preference of the large lens distance in the Bayesian analysis is due to the relatively large observed source star radius. The distance and other physical parameters may be constrained by the future high-resolution imaging by large ground telescopes or HST. If the estimated lens distance is correct, then this planet provides another sample for testing the claimed deficit of planets in the Galactic bulge.
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