From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu May 19 2005 - 07:39:29 PDT
Title: Interpreting microlensing signal in QSO 2237+0305: Stars or planets?
Authors: Rodrigo Gil-Merino and Geraint F. Lewis (University of Sydney)
Comments: 4 pages, 2 figures, A&A Letters accepted; a response to
astro-ph/0503018
\\
The multiply imaged, gravitationally lensed quasar, QSO 2237+0305, has been
the subject of recent optical monitoring campaigns, with its light curves
displaying uncorrelated variability attributed to gravitational microlensing by
masses in the foreground galaxy. Based on these light curves, it has been
claimed that the dominant microlensing population must be a population of
free-floating Jupiter-like objects; such a conclusion is not new, with several
similar claims in the literature. Historically, however, it has been shown that
such conclusions are flawed, with an incorrect interpretation of the complex
caustic network that arises at significant optical depth. This paper examines
this more recent claim, illustrating that it too is flawed.
\\ ( http://arXiv.org/abs/astro-ph/0505372 , 102kb)
Title: Properties of Central Caustics in Planetary Microlensing
Authors: Sun-Ju Chung (1), Cheongho Han (1), Byeong-Gon Park (2), Doeon Kim
(1), Sangjun Kang (3), Yoon-Hyun Ryu (4), Kang Min Kim (2), Young-Beom Jeon
(2), Dong-Wook Lee (5), Kyongae Chang (6), Woo-Baik Lee (2), Yong Hee Kang
(4) ((1) Chungbuk National Univ, (2) Korea Astronomy and Space Science
Institute, (3) Semyung Univ, (4) Kyungpook National Univ, (5) Sejong Univ,
(6) Chongju Univ)
Comments: 5 pages, 4 figures, ApJ accepted
\\
To maximize the number of planet detections, current microlensing follow-up
observations are focusing on high-magnification events which have a higher
chance of being perturbed by central caustics. In this paper, we investigate
the properties of central caustics and the perturbations induced by them. We
derive analytic expressions of the location, size, and shape of the central
caustic as a function of
the star-planet separation, $s$, and the planet/star
mass ratio, $q$, under the planetary perturbative approximation and compare the
results with those based on numerical computations. While it has been known
that the size of the planetary caustic is \propto \sqrt{q}, we find from this
work that the dependence of the size of the central caustic on $q$ is linear,
i.e., \propto q, implying that the central caustic shrinks much more rapidly
with the decrease of $q$ compared to the planetary caustic. The central-caustic
size depends also on the star-planet separation. If the size of the caustic is
defined as the separation between the two cusps on the star-planet axis
(horizontal width), we find that the dependence of the central-caustic size on
the separation is \propto (s+1/s). While the size of the central caustic
depends both on $s$ and q, its
shape defined as the vertical/horizontal width
ratio, R_c, is solely dependent on the planetary separation and we derive an
analytic relation between R_c and s. Due to the smaller size of the central
caustic combined with much more rapid decrease of its size with the decrease of
q, the effect of finite source size on the perturbation induced by the central
caustic is much more severe than the effect on the perturbation induced by the
planetary caustic. Abridged.
\\ ( http://arXiv.org/abs/astro-ph/0505363 , 88kb)
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\\
Paper: astro-ph/0505364
Date: Wed, 18 May 2005 07:14:10 GMT (200kb)
Title: The Effect of Gravity Between Particles on the Shape and Resonant
Structure of Planetary Rings
Authors: A.E. Rosaev (FGUP NPC "NEDRA", Yaroslavl, Russia)
Comments: 10 pages with 7 figures
\\
The resonance perturbation of planetary ring by distant satellite is
considered. The gravity interaction between rings particles is taken into
account. The gravitation interaction between particles in rings can change
shape of non-circular rings, so it is differ from keplerian ellipse. The shift
between simple mean motion resonances and parametric resonance zones is
detected. This shift depends on ring properties.
\\ ( http://arXiv.org/abs/astro-ph/0505364 , 200kb)
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