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TOPIC: Extrasolar planets in M31


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Astronomers believe they have seen hints of the first planet to be spotted outside of our galaxy.
Situated in the Andromeda galaxy, the planet appears to be about six times the mass of Jupiter.
The method hinges on gravitational lensing, whereby a nearer object can bend the light of a distant star when the two align with an observer.
The results will be published in Monthly Notices of the Royal Astronomical Society (MNRAS).


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Astronomers may have discovered the first planet in another galaxy - thought to be six or seven times the size of Jupiter.
A team of researchers from the University of Zurich in Sweden found what is believed to be a planet in the Milky Way's neighbouring galaxy, Andromeda, the New Scientist magazine reports.


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First extragalactic exoplanet may have been found
We could find planets in other galaxies using today's technology, according to a new simulation. The study gives credence to a tentative detection of a planet in Andromeda, our nearest large galactic neighbour.
The idea is to use gravitational microlensing, in which a distant source star is briefly magnified by the gravity of an object passing in front of it. This technique has already found several planets in our galaxy, out to distances of thousands of light years.
Extending the method from thousands to millions of light years won't be easy, says Philippe Jetzer of the University of Zürich in Switzerland, but it should be possible.

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Title: Pixel-lensing as a way to detect extrasolar planets in M31
Authors: G. Ingrosso, S. Calchi Novati, F. De Paolis, Ph. Jetzer, A.A. Nucita, A.F. Zakharov

We study the possibility to detect extrasolar planets in M31 through pixel-lensing observations. Using a Monte Carlo approach, we select the physical parameters of the binary lens system, a star hosting a planet, and we calculate the pixel-lensing light curve taking into account the finite source effects. Indeed, their inclusion is crucial since the sources in M31 microlensing events are mainly giant stars. Light curves with detectable planetary features are selected by looking for significant deviations from the corresponding Paczynski shapes. We find that the time scale of planetary deviations in light curves increase (up to 3-4 days) as the source size increases. This means that only few exposures per day, depending also on the required accuracy, may be sufficient to reveal in the light curve a planetary companion. Although the mean planet mass for the selected events is about 2 M_Jupiter, even small mass planets (M_P < 20 M_{\oplus}) can cause significant deviations, at least in the observations with large telescopes. However, even in the former case, the probability to find detectable planetary features in pixel-lensing light curves is at most a few percent of the detectable events, and therefore many events have to be collected in order to detect an extrasolar planet in M31. Our analysis also supports the claim that the anomaly found in the candidate event PA-99-N2 towards M31 can be explained by a companion object orbiting the lens star.

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