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# Astrophysics journal club

Summary:
This is the homepage of the of the weekly Astrophysics journal club at the Division of Particle physics and astrophysics at the University of Helsinki.
The meetings are of an unofficial nature and the main driver is to get together and discuss recent interesting papers. This meeting differs from the
Seminar series in that people are not expected to talk about their own research and in that no credits will be awarded to students. The meetings are
open to everyone and the aim is to stimulate discussion about recent results and provide the possibility to  learn about research that is not necessarily
connected to one's own field of expertise.

All topics are welcome ranging from planetary science to larger scales involving stellar  astrophysics, Milky Way studies, galaxies and cosmology.
The only requirement is that the  presented papers should be interesting to a wider audience and that they should be presented  in such a way that also
a non-expert can follow the presentation. In the meetings we discuss one paper each week for about 45 minutes.  All meetings are in English.

Location: Conference room C310 on the third floor.

Time: Thursdays at 10.15-11.00am during term time.

Speakers: Please contact Peter Johansson, Mikael Granvik or Clif Kirkpatrick if you want to present a paper.

Present Program: The next talk will be on the 7th of December

Presenter: Mika Juvela
Paper title: OGLE-2015-BLG-1459L: The Challenges of Exo-Moon Microlensing
Authors: Hwang, K.-H., Udalski, A., Bond, I.A. et al.
Reference: 2017, ApJ submitted, ArXiv: 1711.09651

Abstract: We show that dense OGLE and KMTNet $I$-band survey data require four bodies (sources plus lenses) to explain the microlensing light curve of OGLE-2015-BLG-1459. However, these can equally well consist of three lenses and one source (3L1S), two lenses and two sources (2L2S) or one lens and three sources (1L3S). In the 3L1S and 2L2S interpretations, the host is a brown dwarf and the dominant companion is a Neptune-class planet, with the third body (in the 3L1S case) being a Mars-class object that could have been a moon of the planet. In the 1L3S solution, the light curve anomalies are explained by a tight (five stellar radii) low-luminosity binary source that is offset from the principal source of the event by $\sim 0.17\,{\rm AU}$. These degeneracies are resolved in favor of the 1L3S solution by color effects derived from comparison to MOA data, which are taken in a slightly different ($R/I$) passband. We discuss implications for the observing strategies of current and future ($WFIRST$) observations that would enable them to distinguish among such exotic systems.

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Autumn 2017:

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