693 research outputs found
Microlensing Parallax for Observers in Heliocentric Motion
Motivated by the ongoing Spitzer observational campaign, and the forecoming
K2 one, we revisit, working in an heliocentric reference frame, the geometrical
foundation for the analysis of the microlensing parallax, as measured with the
simultaneous observation of the same microlensing event from two observers with
relative distance of order AU. For the case of observers at rest we discuss the
well known fourfold microlensing parallax degeneracy and determine an equation
for the degenerate directions of the lens trajectory. For the case of observers
in motion, we write down an extension of the Gould (1994) relationship between
the microlensing parallax and the observable quantities and, at the same time,
we highlight the functional dependence of these same quantities from the
timescale of the underlying microlensing event. Furthermore, through a series
of examples, we show the importance of taking into account the motion of the
observers to correctly recover the parameters of the underlying microlensing
event. In particular we discuss the cases of the amplitude of the microlensing
parallax and that of the difference of the timescales between the observed
microlensing events, key to understand the breaking of the microlensing
parallax degeneracy. Finally, we consider the case of the simultaneous
observation of the same microlensing event from ground and two satellites, a
case relevant for the expected joint K2 and Spitzer observational programs in
2016.Comment: Accepted for publication in Ap
Newtonian Limit of Induced Gravity
We discuss the weak-field limit of induced gravity and show that results
directly depend on the coupling and self-interaction potential of the scalar
field. A static spherically symmetric exact solution is found and its conformal
properties are studied. As an application, it is shown that the light
deflection angle and the microlensing quantities can be parametrized by the
coupling of the theory.Comment: 15 pages, LATEX, to appear in Grav & Cos
OGLE-2013-BLG-0911Lb: A Secondary on the Brown-dwarf Planet Boundary around an M Dwarf
We present the analysis of the binary-lens microlensing event OGLE-2013-BLG-0911. The best-fit solutions indicate the binary mass ratio of q 0.03, which differs from that reported in Shvartzvald et al. The event suffers from the well-known close/wide degeneracy, resulting in two groups of solutions for the projected separation normalized by the Einstein radius of s ~ 0.15 or s ~ 7. The finite source and the parallax observations allow us to measure the lens physical parameters. The lens system is an M dwarf orbited by a massive Jupiter companion at very close (M_(host) = 0.30^(+0.08)_(-0.06)M⊙, M_(comp) = 10.1^(+2.9)_(-2.2)M_(Jup), a_(exp) = 0.40^(+0.05)_(-0.04) au) or wide (M_(host) = 0.28^(+0.10)_(-0.08) M⊙, M_(comp) = 9.9^(+3.8)_(-3.5)M_(Jup), a(exp) = 18.0^(+3.8)_(3.5) au) separation. Although the mass ratio is slightly above the planet-brown dwarf (BD) mass-ratio boundary of q = 0.03, which is generally used, the median physical mass of the companion is slightly below the planet-BD mass boundary of 13M_(Jup). It is likely that the formation mechanisms for BDs and planets are different and the objects near the boundaries could have been formed by either mechanism. It is important to probe the distribution of such companions with masses of ~13M_(Jup) in order to statistically constrain the formation theories for both BDs and massive planets. In particular, the microlensing method is able to probe the distribution around low-mass M dwarfs and even BDs, which is challenging for other exoplanet detection methods
Searching for variable stars in the cores of five metal-rich globular clusters using EMCCD observations
Aims. In this paper, we present the analysis of time-series observations from 2013 and 2014 of five metal-rich ([Fe/H] > −1) globular clusters: NGC 6388, NGC 6441, NGC 6528, NGC 6638, and NGC 6652. The data have been used to perform a census of the variable stars in the central parts of these clusters.
Methods. The observations were made with the electron-multiplying charge-couple device (EMCCD) camera at the Danish 1.54 m Telescope at La Silla, Chile, and they were analysed using difference image analysis to obtain high-precision light curves of the variable stars.
Results. It was possible to identify and classify all of the previously known or suspected variable stars in the central regions of the five clusters. Furthermore, we were able to identify and, in most cases, classify 48, 49, 7, 8, and 2 previously unknown variables in NGC 6388, NGC 6441, NGC 6528, NGC 6638, and NGC 6652, respectively. Especially interesting is the case of NGC 6441, for which the variable star population of about 150 stars has been thoroughly examined by previous studies, including a Hubble Space Telescope study. In this paper we are able to present 49 new variable stars for this cluster, of which one (possibly two) are RR Lyrae stars, two are W Virginis stars, and the rest are long-period semi-regular or irregular variables on the red giant branch. We have also detected the first double-mode RR Lyrae in the cluster
Microlensing towards M31 with MDM data
We report the final analysis of a search for microlensing events in the
direction of the Andromeda galaxy, which aimed to probe the MACHO composition
of the M31 halo using data collected during the 1998-99 observational campaign
at the MDM observatory. In a previous paper, we discussed the results from a
first set of observations. Here, we deal with the complete data set, and we
take advantage of some INT observations in the 1999-2000 seasons. This merging
of data sets taken by different instruments turns out to be very useful, the
study of the longer baseline available allowing us to test the uniqueness
characteristic of microlensing events. As a result, all the candidate
microlensing events previously reported turn out to be variable stars. We
further discuss a selection based on different criteria, aimed at the detection
of short--duration events. We find three candidates whose positions are
consistent with self--lensing events, although the available data do not allow
us to conclude unambiguously that they are due to microlensing.Comment: Accepted for publication in Astronomy and Astrophysic
Simultaneous follow-up of planetary transits: revised physical properties for the planetary systems HAT-P-16 and WASP-21
Context. By now more than 300 planets transiting their host star have been
found, and much effort is being put into measuring the properties of each
system. Light curves of planetary transits often contain deviations from a
simple transit shape, and it is generally difficult to differentiate between
anomalies of astrophysical nature (e.g. starspots) and correlated noise due to
instrumental or atmospheric effects. Our solution is to observe transit events
simultaneously with two telescopes located at different observatories. Aims.
Using this observational strategy, we look for anomalies in the light curves of
two transiting planetary systems and accurately estimate their physical
parameters. Methods. We present the first photometric follow-up of the
transiting planet HAT-P-16 b, and new photometric observations of WASP-21 b,
obtained simultaneously with two medium-class telescopes located in different
countries, using the telescope defocussing technique. We modeled these and
other published data in order to estimate the physical parameters of the two
planetary systems. Results. The simultaneous observations did not highlight
particular features in the light curves, which is consistent with the low
activity levels of the two stars. For HAT-P-16, we calculated a new ephemeris
and found that the planet is 1.3 \sigma colder and smaller (Rb = 1.190 \pm
0.037 RJup) than the initial estimates, suggesting the presence of a massive
core. Our physical parameters for this system point towards a younger age than
previously thought. The results obtained for WASP-21 reveal lower values for
the mass and the density of the planet (by 1.0 \sigma and 1.4 \sigma
respectively) with respect to those found in the discovery paper, in agreement
with a subsequent study. We found no evidence of any transit timing variations
in either system.Comment: 8 pages, 6 figures, accepted for publication in A&
Modelling the impact of liner shipping network perturbations on container cargo routing: Southeast Asia to Europe application
Understanding how container routing stands to be impacted by different scenarios of liner shipping network perturbations such as natural disasters or new major infrastructure developments is of key importance for decision-making in the liner shipping industry. The variety of actors and processes within modern supply chains and the complexity of their relationships have previously led to the development of simulation-based models, whose application has been largely compromised by their dependency on extensive and often confidential sets of data. This study proposes the application of optimisation techniques less dependent on complex data sets in order to develop a quantitative framework to assess the impacts of disruptive events on liner shipping networks. We provide a categorization of liner network perturbations, differentiating between systemic and external and formulate a container assignment model that minimises routing costs extending previous implementations to allow feasible solutions when routing capacity is reduced below transport demand. We develop a base case network for the Southeast Asia to Europe liner shipping trade and review of accidents related to port disruptions for two scenarios of seismic and political conflict hazards. Numerical results identify alternative routing paths and costs in the aftermath of port disruptions scenarios and suggest higher vulnerability of intra-regional connectivity
On the mass of the gravitational lenses in LMC
In the self--lensing framework, we estimate the modal values of the mass of
the gravitational lenses found by the MACHO collaboration towards the Large
Magellanic Cloud (LMC). Our results suggest that only the events located near
the center can be identified as a low mass star population belonging to the LMC
disk or bar components.Comment: To appear in the proceedings of the Marcel Grossmann Meeeting
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