On the Nature of XTE J0421+560/CI Camelopardalis Belloni, T; Dieters, S; van den Ancker, M. E ...
Astrophysical journal/The Astrophysical journal,
12/1999, Letnik:
527, Številka:
1
Journal Article
ABSTRACT We report the discovery of a Jupiter-mass planet orbiting an M-dwarf star that gave rise to the microlensing event OGLE-2011-BLG-0265. Such a system is very rare among known planetary ...systems and thus the discovery is important for theoretical studies of planetary formation and evolution. High-cadence temporal coverage of the planetary signal, combined with extended observations throughout the event, allows us to accurately model the observed light curve. However, the final microlensing solution remains degenerate, yielding two possible configurations of the planet and the host star. In the case of the preferred solution, the mass of the planet is , and the planet is orbiting a star with a mass . The second possible configuration (2 away) consists of a planet with and host star with . The system is located in the Galactic disk 3-4 kpc toward the Galactic bulge. In both cases, with an orbit size of 1.5-2.0 AU, the planet is a "cold Jupiter"-located well beyond the "snow line" of the host star. Currently available data make the secure selection of the correct solution difficult, but there are prospects for lifting the degeneracy with additional follow-up observations in the future, when the lens and source star separate.
We present the analysis of MOA-2007-BLG-197Lb, the first brown dwarf companion to a Sun-like star detected through gravitational microlensing. The event was alerted and followed-up photometrically by ...a network of telescopes from the PLANET, MOA, and μFUN collaborations, and observed at high angular resolution using the NaCo instrument at the VLT. From the modelling of the microlensing light curve, we derived basic parameters such as, the binary lens separation in Einstein radius units (s ≃ 1.13), the mass ratio q = (4.732 ± 0.020) × 10-2 and the Einstein radius crossing time (tE ≃ 82 d). Because of this long time scale, we took annual parallax and orbital motion of the lens in the models into account, as well as finite source effects that were clearly detected during the source caustic exit. To recover the lens system’s physical parameters, we combined the resulting light curve best-fit parameters with (J,H,Ks) magnitudes obtained with VLT NaCo and calibrated using IRSF and 2MASS data. From this analysis, we derived a lens total mass of 0.86 ± 0.04 M⊙ and a lens distance of DL = 4.2 ± 0.3 kpc. We find that the companion of MOA-2007-BLG-197L is a brown dwarf of 41 ± 2 MJ observed at a projected separation of a⊥ = 4.3 ± 0.1 AU, and orbits a 0.82 ± 0.04 M⊙ G-K dwarf star. We then placed the companion of MOA-2007-BLG-197L in a mass-period diagram consisting of all brown dwarf companions detected so far through different techniques, including microlensing, transit, radial velocity, and direct imaging (most of these objects orbit solar-type stars). To study the statistical properties of this population, we performed a two-dimensional, non-parametric probability density distribution fit to the data, which draws a structured brown dwarf landscape. We confirm the existence of a region that is strongly depleted in objects at short periods and intermediate masses (P ≲ 30 d, M ~ 30−60 MJ), but also find an accumulation of objects around P ~ 500 d and M ~ 20 MJ, as well as another depletion region at long orbital periods (P ≳ 500 d) and high masses (M ≳ 50 MJ). While these data provide important clues on the different physical mechanisms of formation (or destruction) that shape the brown dwarf desert, more data are needed to establish their relative importance, in particular as a function of host star mass. Future microlensing surveys should soon provide more detections, in particular for red dwarf hosts, thus uniquely complementing the solar-type host sample.
Context. HD179949 is an F8V star, orbited by a close-in giant planet with a period of similar to 3 days. Previous studies suggested that the planet enhances the magnetic activity of the parent star, ...producing a chromospheric hot spot which rotates in phase with the planet orbit. However, this phenomenon is intermittent since it was observed in several but not all seasons. Aims. A long-term monitoring of the magnetic activity of HD179949 is required to study the amplitude and time scales of star-planet interactions. Methods. In 2009 we performed a simultaneous optical and X-ray spectroscopic campaign to monitor the magnetic activity of HD179949 during similar to 5 orbital periods and similar to 2 stellar rotations. We analyzed the Ca II H&K lines as a proxy for chromospheric activity, and we studied the X-ray emission in search of flux modulations and to determine basic properties of the coronal plasma. Results. A detailed analysis of the flux in the cores of the Ca II H&K lines and a similar study of the X-ray photometry shows evidence of source variability, including one flare. The analysis of the time series of chromospheric data indicates a modulation with a similar to 11 days period, compatible with the stellar rotation period at high latitudes. Instead, the X-ray light curve suggests a signal with a period of similar to 4 days, consistent with the presence of two active regions on opposite hemispheres. Conclusions. The observed variability can be explained, most likely, as due to rotational modulation and to intrinsic evolution of chromospheric and coronal activity. There is no clear signature related to the orbital motion of the planet, but the possibility that just a fraction of the chromospheric and coronal variability is modulated with the orbital period of the planet, or the stellar-planet beat period, cannot be excluded. We conclude that any effect due to the presence of the planet is difficult to disentangle.
We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and argue that it is the strongest candidate yet for a bulge planet. Deviations from the single-lens fit are smoothed out by ...finite-source effects and therefore are not immediately apparent from the light curve. Nevertheless, we find that a model in which the primary has a planetary companion is favored over the single-lens model by DELTAchi{sup 2} {approx} 880 for an additional 3 degrees of freedom. Detailed analysis yields a planet/star mass ratio q = (3.3 +- 0.3) x 10{sup -4} and an angular separation between the planet and star within 10% of the angular Einstein radius. The small angular Einstein radius, theta{sub E} = 0.155 +- 0.011 mas, constrains the distance to the lens to be D{sub L} >6.0 kpc if it is a star (M{sub L} >0.08 M{sub sun}). This is the only microlensing exoplanet host discovered so far that must be in the bulge if it is a star. By analyzing VLT NACO adaptive optics images taken near the baseline of the event, we detect additional blended light that is aligned to within 130 mas of the lensed source. This light is plausibly from the lens, but could also be due to a companion to the lens or source, or possibly an unassociated star. If the blended light is indeed due to the lens, we can estimate the mass of the lens, M{sub L} = 0.67 +- 0.14 M{sub sun}, planet mass m = 74 +- 17 M{sub +}, and projected separation between the planet and host, 1.25 +- 0.10 AU, putting it right on the 'snow line'. If not, then the planet has lower mass, is closer to its host and is colder. To distinguish among these possibilities on reasonable timescales would require obtaining Hubble Space Telescope images almost immediately, before the source-lens relative motion of mu= 5 mas yr{sup -1} causes them to separate substantially.
We present an analysis of the anomalous micro-lensing event,MOA-2010-BLG-073, announced by the Micro-lensing 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. We initially explored a number of purely micro-lensing models for the event but found a residual gradient in the data taken prior to and after the event. The Einstein crossing time of the event, tsubE = 44.3 + or - 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, DL = 2.8 + or - 0.4 kpc, and the masses of the lensing objects.
We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of M sub(h) = 0.11 + or - 0.01 M sub(middot in circle) and M sub(p) = 9.2 + or - 2.2 M ...sub(+ in circle), corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at D sub(L) = 0.81 + or - 0.10 kpc with projected separation r sub(bottom) = 0.92 + or - 0.16 AU. Because of the host's a priori unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions.
We analyze MOA-2010-BLG-311, a high magnification (A sub(max) > 600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event ...with both a point lens and a two-body lens model and find that the two-body lens model is a better fit but with only Deltachi super(2) ~ 80. The preferred mass ratio between the lens star and its companion is q = 10 super(-3.7+ or -0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question.
Despite the astrophysical importance of binary star systems, detections are limited to those located in small ranges of separations, distances, and masses and thus it is necessary to use a variety of ...observational techniques for a complete view of stellar multiplicity across a broad range of physical parameters. In this paper, we report the detections and measurements of two binaries discovered from observations of microlensing events MOA-2011-BLG-090 and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by simultaneously measuring the Einstein radius and the lens parallax. The measured masses of the binary components are 0.43 M sub(middot in circle) and 0.39 M sub(middot in circle) for MOA-2011-BLG-090 and 0.57 M sub(middot in circle) and 0.17 M sub(middot in circle) for OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of microlensing in detecting binaries composed of low-mass components. From modeling of the light curves considering full Keplerian motion of the lens, we also measure the orbital parameters of the binaries. The blended light of OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible to check the microlensing orbital solution by follow-up radial-velocity observation. For both events, the caustic-crossing parts of the light curves, which are critical for determining the physical lens parameters, were resolved by high-cadence survey observations and thus it is expected that the number of microlensing binaries with measured physical parameters will increase in the future.
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