We used Keck adaptive optics observations to identify the first planet discovered by microlensing to lie in or near the habitable zone, i.e., at projected separation r sub(perpendicular) = 1.1 + or - ...0.1 AU from its M sub(L) = 0.86 + or - 0.06 M sub(middot in circle) host, being the highest microlensing mass definitely identified. The planet has a mass m sub(p) = 4.8 + or - 0.3 M sub(Jup), and could in principle have habitable moons. This is also the first planet to be identified as being in the Galactic bulge with good confidence: D sub(L) = 7.72 + or - 0.44 kpc. The planet/host masses and distance were previously not known, but only estimated using Bayesian priors based on a Galactic model. These estimates had suggested that the planet might be a super-Jupiter orbiting an M dwarf, a very rare class of planets. We obtained high-resolution JHK images using Keck adaptive optics to detect the lens and so test this hypothesis. We clearly detect light from a G dwarf at the position of the event, and exclude all interpretations other than that this is the lens with high confidence (95%), using a new astrometric technique. The calibrated magnitude of the planet host star is H sub(L) = 19.16 + or - 0.13. We infer the following probabilities for the three possible orbital configurations of the gas giant planet: 53% to be in the habitable zone, 35% to be near the habitable zone, and 12% to be beyond the snow line, depending on the atmospherical conditions and the uncertainties on the semimajor axis.
ABSTRACT
SXP 15.6 is a recently established Be star X-ray binary system in the Small Magellanic Cloud (SMC). Like many such systems, the variable X-ray emission is driven by the underlying behaviour ...of the mass donor Be star. It is shown here that the neutron star in this system is exceptionally close to spin equilibrium averaged over several years, with the angular momentum gain from mass transfer being almost exactly balanced by radiative losses. This makes SXP 15.6 exceptional compared to all other known members of its class in the SMC, all of whom exhibit much higher spin period changes. In this paper, we report on X-ray observations of the brightest known outburst from this system. These observations are supported by contemporaneous optical and radio observations, as well as several years of historical data.
Because of the development of large-format, wide-field cameras, microlensing surveys are now able to monitor millions of stars with sufficient cadence to detect planets. These new discoveries will ...span the full range of significance levels including planetary signals too small to be distinguished from the noise. At present, we do not understand where the threshold is for detecting planets. MOA-2011-BLG-293Lb is the first planet to be published from the new surveys, and it also has substantial follow-up observations. This planet is robustly detected in survey+follow-up data ( Delta chi super(2) ~ 5400). The planet/host mass ratio is q = (5.3 + or - 0.2) x 10 super(-3). The best-fit projected separation is s = 0.548 + or - 0.005 Einstein radii. However, due to the s left right arrow s super(-1) degeneracy, projected separations of s super(-1) are only marginally disfavored at Delta chi super(2) = 3. A Bayesian estimate of the host mass gives ML = 0.43 super(+0.27) sub(-0.17) M sub(middot in circle), with a sharp upper limit of ML < 1.2 M sub(middot in circle) from upper limits on the lens flux. Hence, the planet mass is mp = 2.4 super(+1.5) sub(-0.9) M sub(Jup), and the physical projected separation is either r sub(perpendicular) Asymptotically = to 1.0 AU or r sub(perpendicular) Asymptotically = to 3.4 AU. We show that survey data alone predict this solution and are able to characterize the planet, but the Delta chi super(2) is much smaller ( Delta chi super(2) ~ 500) than with the follow-up data. The Delta chi super(2) for the survey data alone is smaller than for any other securely detected planet. This event suggests a means to probe the detection threshold, by analyzing a large sample of events like MOA-2011-BLG-293, which have both follow-up data and high-cadence survey data, to provide a guide for the interpretation of pure survey microlensing data.
We report the discovery of a young stellar bridge that forms a continuous connection between the Magellanic Clouds. This is the most extensive optical survey of this region to date. We find that the ...young population is present mainly in the western half of the MBR, which, together with the newly discovered young population in the eastern Bridge, form a continuous stream of stars connecting both galaxies along delta ~ -73.5 deg. The young population distribution is clumped, with one of the major densities close to the SMC and the other fairly isolated and located approximately mid-way between the Clouds, which we call the OGLE island. We observe a continuity of red clump stars between the Magellanic Clouds which represent an intermediate-age population. We also see only minor mixing of the old populations of the Clouds in the southern part of the Bridge, represented by the lowest part of the red giant branch.
We report the discovery of a new subclass of double-mode RR Lyrae stars in the Large and Small Magellanic Clouds. The sample of 22 pulsating stars has been extracted from the latest edition of the ...Optical Gravitational Lensing Experiment collection of RR Lyrae variables in the Magellanic System. The stars pulsating simultaneously in the fundamental (F) and first-overtone (1O) modes have distinctly different properties than regular double-mode RR Lyrae variables (RRd stars). The P sub( 1O)/P sub( F) period ratios of our anomalous RRd stars are within a range of 0.725-0.738, while 'classical' double-mode RR Lyrae variables have period ratios in the range of ...0.742-0.748. In contrast to the typical RRd stars, in the majority of the anomalous pulsators, the F-mode amplitudes are higher than the 1O-mode amplitudes. The light curves associated with the F-mode in the anomalous RRd stars show different morphology than the light curves of, both, regular RRd stars and single-mode RRab stars. Most of the anomalous double-mode stars show long-term modulations of the amplitudes (Blazhko-like effect). Translating the period ratios into the abundance parameter, Z, we find for our stars Z ... (0.002, 0.005) -- an order of magnitude higher values than typical for RR Lyrae stars. The mass range of the RRd stars inferred from the W sub( I) versus P sub( F) diagram is (0.55-0.75)...M... These parameters cannot be accounted for with single star evolution assuming a Reimers-like mass-loss. Much greater mass-loss caused by interaction with other stars is postulated. We blame the peculiar pulsation properties of our stars to the parametric resonance instability of the 1O-mode to excitation of the F- and 2O-modes as with the inferred parameters of the stars ... (ProQuest: ... denotes formulae/symbols omitted.)
The dusty aftermath of the V1309 Sco binary merger Nicholls, C. P; Melis, C; Soszy ski, I ...
Monthly notices of the Royal Astronomical Society. Letters,
05/2013, Letnik:
431, Številka:
1
Journal Article
Recenzirano
Odprti dostop
We present mid-IR photometry and spectra of the merged binary V1309 Sco taken between 18 and 23 months after outburst. Strong mid-IR emission and a solid-state absorption feature indicate the ...presence of a significant amount of dust in the circumstellar environment. The absence of detectable mid-IR emission before the outburst suggests that this dust was produced in the eruptive merger event.
Model fits to the solid-state absorption feature constrain the constituent species and column density of the dust around V1309 Sco. We find that the absorption feature can be reproduced by large (3 μm) amorphous pyroxene grains at a temperature of 800 K. This grain size, if confirmed with longer wavelength spectroscopy and modelling, would be suggestive of dust processing in the circumstellar environment. The data in hand do not allow us to discriminate between disc or shell configurations for the dusty material.
ABSTRACT We present the first space-based microlens parallax measurement of an isolated star. From the striking differences in the lightcurve as seen from Earth and from Spitzer ( to the west), we ...infer a projected velocity , which strongly favors a lens in the Galactic Disk with mass and distance . An ensemble of such measurements drawn from our ongoing program could be used to measure the single-lens mass function including dark objects, and also is necessary for measuring the Galactic distribution of planets since the ensemble reflects the underlying Galactic distribution of microlenses. We study the application of the many ideas to break the four-fold degeneracy first predicted by Refsdal 50 years ago. We find that this degeneracy is clearly broken, but by two unanticipated mechanisms: a weak constraint on the orbital parallax from the ground-based data and a definitive measurement of the source proper motion.
ABSTRACT In this paper, we report the discovery of a binary composed of a brown dwarf (BD) and a low-mass M dwarf from observation of the microlensing event OGLE-2014-BLG-0257. The resolution of the ...very brief caustic crossing combined with the detection of subtle continuous deviation in the lensing light curve induced by the Earth's orbital motion enable us to precisely measure both the Einstein radius and the lens parallax , which are the two quantities needed to unambiguously determine the mass and distance to the lens. It is found that the companion is a substellar BD with a mass of ( ) and it is orbiting an M dwarf with a mass of . The binary is located at a distance of 1.25 0.13 kpc toward the Galactic bulge and the projected separation between the binary components is 0.61 0.07 au. The separation scaled by the mass of the host is . Based on the assumption that separations scale with masses, the discovered BD is located in the BD desert. With the growing sample of BDs in various environments, microlensing will provide a powerful probe of BDs in the Galaxy.
ABSTRACT We present the discovery of the first Neptune analog exoplanet or super-Earth with a Neptune-like orbit, MOA-2013-BLG-605Lb. This planet has a mass similar to that of Neptune or a ...super-Earth and it orbits at 9 ∼ 14 times the expected position of the snow line, asnow, which is similar to Neptune's separation of 11 asnow from the Sun. The planet/host-star mass ratio is q = (3.6 0.7) × 10−4 and the projected separation normalized by the Einstein radius is s = 2.39 0.05. There are three degenerate physical solutions and two of these are due to a new type of degeneracy in the microlensing parallax parameters, which we designate "the wide degeneracy." The three models have (i) a Neptune-mass planet with a mass of orbiting a low-mass M-dwarf with a mass of , (ii) a mini-Neptune with orbiting a brown dwarf host with , and (iii) a super-Earth with orbiting a low-mass brown dwarf host with , which is slightly favored. The 3D planet-host separations are au, au, and au, which are , , or times larger than asnow for these models, respectively. Keck adaptive optics observations confirm that the lens is faint. This discovery suggests that low-mass planets with Neptune-like orbits are common. Therefore processes similar to the one that formed Neptune in our own solar system or cold super-Earths may be common in other solar systems.
Abstract
We analyze the microlensing event OGLE-2011-BLG-0173, which shows a small
perturbation at the end of the microlensing event caused by the primary lens. We
consider both binary lens and ...binary source models and explore their
degeneracies, some of which have not previously been recognized. There are two
families of binary lens solutions, one with a mass ratio
q
≈ 4 × 10
−4
and a separation
s
≈ 4.6, and the other with
q
≈ 0.015 and
s
≈ 0.22, i.e., both have companions in the
planetary regime. We search for solutions by using Bayesian analysis that
includes planet frequency as a prior and find that the
s
≈ 4.6 family is the preferred one with a
planet on an orbit of ∼10 au. The degeneracies arise from
a paucity of information on the anomaly, demonstrating that high-cadence
observations are essential for characterizing wide-orbit microlensing planets.
Hence, we predict that the planned
Wide-Field Infrared Survey
Telescope
microlensing survey will be less prone to these
degeneracies than the ongoing ground-based surveys. We discuss the known
low-mass, wide-orbit companions and notice that for the largest projected
separations the mass ratios are either high (consistent with brown dwarf
companions) or low (consistent with Uranus analogs), but intermediate mass
ratios (Jupiter analogs on wide orbits) have not been detected to date, despite
the fact that the sensitivity to such planets should be higher than that of
Uranus analogs. This is therefore tentative evidence of the existence of a
massive ice giant desert at wide separations. On the other hand, given their low
intrinsic detection sensitivity, Uranus analogs may be ubiquitous.
PDF
