MOA-2010-BLG-073L: AN M-DWARF WITH A SUBSTELLAR COMPANION AT THE PLANET/BROWN DWARF BOUNDARY

Street, R. A.,Choi, J.-Y.,Tsapras, Y.,Han, C.,Furusawa, K.,Hundertmark, M.,Gould, A.,Sumi, T.,Bond, I. A.,Wouters, D.,Zellem, R.,Udalski, A.,Snodgrass, C.,Horne, K.,Dominik, M.,Browne, P.,Kains, N.,Br IOP Publishing 2013 The Astrophysical journal Vol.763 No.1

<P>We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source light curve, we demonstrate that it is an irregular variable over timescales >200 days. Its dereddened color, (V - I)(S),(0), is 1.221 +/- 0.051 mag, and from our lens model we derive a source radius of 14.7 +/- 1.3 R-circle dot, suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q = 0.0654 +/- 0.0006. The Einstein crossing time of the event, t(E) = 44.3 +/- 0.1 days, was sufficiently long that the light curve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, D-L = 2.8 +/- 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M-L,M-1 = 0.16 +/- 0.03 M-circle dot, while the companion has M-L,M-2 = 11.0 +/- 2.0 M-J, putting it in the boundary zone between planets and brown dwarfs.</P>

GRAVITATIONAL BINARY-LENS EVENTS WITH PROMINENT EFFECTS OF LENS ORBITAL MOTION

Park, H.,Udalski, A.,Han, C.,Gould, A.,Beaulieu, J.-P.,Tsapras, Y.,Szymań,ski, M. K.,Kubiak, M.,Soszyń,ski, I.,Pietrzyń,ski, G.,Poleski, R.,Ulaczyk, K.,Pietrukowicz, P.,Kozłowski, S.,Sk IOP Publishing 2013 The Astrophysical journal Vol.778 No.2

<P>Gravitational microlensing events produced by lenses composed of binary masses are important because they provide a major channel for determining physical parameters of lenses. In this work, we analyze the light curves of two binary-lens events, OGLE-2006-BLG-277 and OGLE-2012-BLG-0031, for which the light curves exhibit strong deviations from standard models. From modeling considering various second-order effects, we find that the deviations are mostly explained by the effect of the lens orbital motion. We also find that lens parallax effects can mimic orbital effects to some extent. This implies that modeling light curves of binary-lens events not considering orbital effects can result in lens parallaxes that are substantially different from actual values and thus wrong determinations of physical lens parameters. This demonstrates the importance of routine consideration of orbital effects in interpreting light curves of binary-lens events. It is found that the lens of OGLE-2006-BLG-277 is a binary composed of a low-mass star and a brown dwarf companion.</P>

OGLE‐2008‐BLG‐510: first automated real‐time detection of a weak microlensing anomaly – brown dwarf or stellar binary?

Bozza, V.,Dominik, M.,Rattenbury, N. J.,Jørgensen, U. G.,Tsapras, Y.,Bramich, D. M.,Udalski, A.,Bond, I. A.,Liebig, C.,Cassan, A.,Fouqué,, P.,Fukui, A.,Hundertmark, M.,Shin, I.‐,G.,Lee, S. Blackwell Publishing Ltd 2012 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.424 No.2

<P><B>ABSTRACT</B></P><P>The microlensing event OGLE‐2008‐BLG‐510 is characterized by an evident asymmetric shape of the peak, promptly detected by the Automated Robotic Terrestrial Exoplanet Microlensing Search (ARTEMiS) system in real time. The skewness of the light curve appears to be compatible both with binary‐lens and binary‐source models, including the possibility that the lens system consists of an M dwarf orbited by a brown dwarf. The detection of this microlensing anomaly and our analysis demonstrate that: (1) automated real‐time detection of weak microlensing anomalies with immediate feedback is feasible, efficient and sensitive, (2) rather common weak features intrinsically come with ambiguities that are not easily resolved from photometric light curves, (3) a modelling approach that finds all features of parameter space rather than just the ‘favourite model’ is required and (4) the data quality is most crucial, where systematics can be confused with real features, in particular small higher order effects such as orbital motion signatures. It moreover becomes apparent that events with weak signatures are a silver mine for statistical studies, although not easy to exploit. Clues about the apparent paucity of both brown‐dwarf companions and binary‐source microlensing events might hide here.</P>

A SUB-SATURN MASS PLANET, MOA-2009-BLG-319Lb

Miyake, N.,Sumi, T.,Dong, Subo,Street, R.,Mancini, L.,Gould, A.,Bennett, D. P.,Tsapras, Y.,Yee, J. C.,Albrow, M. D.,Bond, I. A.,Fouqué,, P.,Browne, P.,Han, C.,Snodgrass, C.,Finet, F.,Furusawa, K IOP Publishing 2011 The Astrophysical journal Vol.728 No.2

<P>We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K-or M-dwarf star in the inner Galactic disk or Galactic bulge. The high-cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high-magnification event approximately 24 hr prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 +/- 0.02) x 10(-4) and a separation of d = 0.97537 +/- 0.00007 in units of the Einstein radius. A Bayesian analysis based on the measured Einstein radius crossing time, t(E), and angular Einstein radius,theta(E), along with a standard Galactic model indicates a host star mass of M-L = 0.38(-0.18)(+0.34) M-circle dot and a planet mass of M-p = 50(-24)(+44)M(circle plus), which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4(-0.6)(+1.2) AU and a distance to the planetary system of D-L = 6.1(-1.2)(+1.1) kpc. This separation is similar to 2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing.</P>

MICROLENSING BINARIES WITH CANDIDATE BROWN DWARF COMPANIONS

Shin, I.-G.,Han, C.,Gould, A.,Udalski, A.,Sumi, T.,Dominik, M.,Beaulieu, J.-P.,Tsapras, Y.,Bozza, V.,Szymań,ski, M. K.,Kubiak, M.,Soszyń,ski, I.,Pietrzyń,ski, G.,Poleski, R.,Ulaczyk, K. IOP Publishing 2012 The Astrophysical journal Vol.760 No.2

<P>Brown dwarfs are important objects because they may provide a missing link between stars and planets, two populations that have dramatically different formation histories. In this paper, we present the candidate binaries with brown dwarf companions that are found by analyzing binary microlensing events discovered during the 2004-2011 observation seasons. Based on the low mass ratio criterion of q < 0.2, we found seven candidate events: OGLE-2004-BLG-035, OGLE-2004-BLG-039, OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334, MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and MOA-201-BLG-278/OGLE-2011-BLG-012N. Among them, we are able to confirm that the companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149 are brown dwarfs by determining the mass of the lens based on the simultaneous measurement of the Einstein radius and the lens parallax. The measured masses of the brown dwarf companions are 0.02 +/- 0.01 M-circle dot and 0.019 +/- 0.002 M-circle dot for MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively, and both companions are orbiting low-mass M dwarf host stars. More microlensing brown dwarfs are expected to be detected as the number of lensing events with well-covered light curves increases with new-generation searches.</P>

<i>SPITZER</i>PARALLAX OF OGLE-2015-BLG-0966: A COLD NEPTUNE IN THE GALACTIC DISK

Street, R. A.,Udalski, A.,Novati, S. Calchi,Hundertmark, M. P. G.,Zhu, W.,Gould, A.,Yee, J.,Tsapras, Y.,Bennett, D. P.,Jørgensen, U. G.,Dominik, M.,Andersen, M. I.,Bachelet, E.,Bozza, V.,Bramich, D. M American Astronomical Society 2016 The Astrophysical journal Vol.819 No.2

<P>We report the detection of a cold Neptune m(planet) = 21 +/- 2M(circle plus) orbiting a 0.38M(circle dot) M dwarf lying 2.5-3.3 kpc toward the Galactic center as part of a campaign combining ground-based and Spitzer observations to measure the Galactic distribution of planets. This is the first time that the complex real-time protocols described by Yee et al., which aim to maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey and follow. up teams successfully combined their efforts within the framework of these protocols to detect this planet. This is the second planet in the Spitzer Galactic distribution sample. Both are in the near. to. mid-disk and are clearly not in the Galactic bulge.</P>

A census of variability in globular cluster M 68 (NGC 4590)

Kains, N.,Arellano Ferro, A.,Figuera Jaimes, R.,Bramich, D. M.,Skottfelt, J.,Jørgensen, U. G.,Tsapras, Y.,Street, R. A.,Browne, P.,Dominik, M.,Horne, K.,Hundertmark, M.,Ipatov, S.,Snodgrass, C.,Steele EDP Sciences 2015 Astronomy and astrophysics Vol.578 No.-

<P>Aims. We analyse 20 nights of CCD observations in the V and I bands of the globular cluster M?68 (NGC 4590) and use them to detect variable objects. We also obtained electron-multiplying CCD (EMCCD) observations for this cluster in order to explore its core with unprecedented spatial resolution from the ground. Methods. We reduced our data using difference image analysis to achieve the best possible photometry in the crowded field of the cluster. In doing so, we show that when dealing with identical networked telescopes, a reference image from any telescope may be used to reduce data from any other telescope, which facilitates the analysis significantly. We then used our light curves to estimate the properties of the RR Lyrae (RRL) stars in M?68 through Fourier decomposition and empirical relations. The variable star properties then allowed us to derive the cluster’s metallicity and distance. Results. M?68 had 45 previously confirmed variables, including 42 RRL and 2 SX Phoenicis (SX Phe) stars. In this paper we determine new periods and search for new variables, especially in the core of the cluster where our method performs particularly well. We detect 4 additional SX Phe stars and confirm the variability of another star, bringing the total number of confirmed variable stars in this cluster to 50. We also used archival data stretching back to 1951 to derive period changes for some of the single-mode RRL stars, and analyse the significant number of double-mode RRL stars in M?68. Furthermore, we find evidence for double-mode pulsation in one of the SX Phe stars in this cluster. Using the different classes of variables, we derived values for the metallicity of the cluster of [Fe/H] = −2.07 ±0.06 on the ZW scale, or −2.20 ±0.10 on the UVES scale, and found true distance moduli μ0 = 15.00±0.11 mag (using RR0 stars), 15.00 ± 0.05 mag (using RR1 stars), 14.97 ±0.11 mag (using SX Phe stars), and 15.00±0.07 mag (using the MV–[Fe/H] relation for RRL stars), corresponding to physical distances of 10.00 ±0.49, 9.99±0.21, 9.84 ±0.50, and 10.00 ±0.30 kpc, respectively. Thanks to the first use of difference image analysis on time-series observations of M?68, we are now confident that we have a complete census of the RRL stars in this cluster.</P>

MOA-2010-BLG-523: “FAILED PLANET” = RS CVn STAR

Gould, A.,Yee, J. C.,Bond, I. A.,Udalski, A.,Han, C.,Jørgensen, U. G.,Greenhill, J.,Tsapras, Y.,Pinsonneault, M. H.,Bensby, T.,Allen, W.,Almeida, L. A.,Bos, M.,Christie, G. W.,DePoy, D. L.,Dong, Subo IOP Publishing 2013 The Astrophysical journal Vol.763 No.2

<P>The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A(max) similar to 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge.</P>

MICROLENSING DISCOVERY OF A TIGHT, LOW-MASS-RATIO PLANETARY-MASS OBJECT AROUND AN OLD FIELD BROWN DWARF

Han, C.,Jung, Y. K.,Udalski, A.,Sumi, T.,Gaudi, B. S.,Gould, A.,Bennett, D. P.,Tsapras, Y.,Szymań,ski, M. K.,Kubiak, M.,Pietrzyń,ski, G.,Soszyń,ski, I.,Skowron, J.,Kozłowski, S.,Poleski IOP Publishing 2013 The Astrophysical journal Vol.778 No.1

<P>Observations of accretion disks around young brown dwarfs (BDs) have led to the speculation that they may form planetary systems similar to normal stars. While there have been several detections of planetary-mass objects around BDs (2MASS 1207-3932 and 2MASS 0441-2301), these companions have relatively large mass ratios and projected separations, suggesting that they formed in a manner analogous to stellar binaries. We present the discovery of a planetary-mass object orbiting a field BD via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is a low secondary/primary mass ratio (0.080 +/- 0.001), relatively tightly separated (similar to 0.87 AU) binary composed of a planetary-mass object with 1.9 +/- 0.2 Jupiter masses orbiting a BD with a mass 0.022M(circle dot). The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the BD host in a manner analogous to planets.</P>

OGLE-2012-BLG-0563Lb: A SATURN-MASS PLANET AROUND AN M DWARF WITH THE MASS CONSTRAINED BY<i>SUBARU</i>AO IMAGING

Fukui, A.,Gould, A.,Sumi, T.,Bennett, D. P.,Bond, I. A.,Han, C.,Suzuki, D.,Beaulieu, J.-P.,Batista, V.,Udalski, A.,Street, R. A.,Tsapras, Y.,Hundertmark, M.,Abe, F.,Bhattacharya, A.,Freeman, M.,Itow, IOP Publishing 2015 The Astrophysical journal Vol.809 No.1

<P>We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio of similar to 1 x 10(-3). Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK'-band images obtained by the Subaru/AO188 and Infrared Camera and Spectrograph instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of spectroscopic information about the source star obtained during the high-magnification state by Bensby et al., we find that the lens system is located at 1.3(-0.8)(+0.6) kpc from us, and consists of an M dwarf (0.34(-0.20)(+0.12)M(circle dot)) orbited by a Saturn-mass planet (0.39(-0.23)(+0.14)M(Jup)) at the projected separation of 0.74(-0.42)(+0.26)AU (close model) or 4.3(-2.5)(+1.5)AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to three, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J - K-s) and (H - K-s) colors of the host star, which are marginally consistent with a low metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2 < m(p)/M-Jup < 1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of similar to 1-2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core-accretion scheme.</P>