Highlights - Volume 498-1 (April IV 2009)

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HIGHLIGHTS: this week in A&A

Volume 498-1 (April IV 2009)


In section 1. Letters to the Editor. Subsection 10. Planets and planetary systems

“Photometric and spectroscopic detection of the primary transit of the 111-day-period planet HD 80606 b”, by C. Moutou, G. Hebrard, F. Bouchy, A. Eggenberg, et al., A&A 498, p. L5

With a mass 4 times that of Jupiter, an orbital period of 111 days, and an eccentricity of 0.93, HD 80606b is among the strangest exoplanet known today. Its orbit is extremely elongated, meaning that for a day or so, it comes very close to its star to be heated to 1300°C or so, while for the remaining 110 days, its atmospheric temperature is believed to be around 400°C. Since its discovery by Naef et al. A&A (2001), astronomers have known that the planet had about a 1 to 6 chance of transiting *behind* the star at every orbit (a so-called *secondary* transit). Observing with the Spitzer satellite in the infrared in November 2008, Laughlin et al. (Nature 2009) measured the heat emitted by the planet as it passed close to its star, and were lucky to indeed find the planet passing behind its star. Based on this detection, they estimated that the planet would now have a 1 to 6 chance of transiting *in front* of its star on Feb. 14, 2009 (a so-called *primary* transit). In this issue of A&A, Moutou et al. present observations of the planet on Valentine’s Day with two telescopes at the Observatoire de Haute Provence: the 1.93 and 1.2 meter telescopes. They found that the planet also transits in front of its star! This allowed them to determine its size: with only about 90% that of Jupiter, the planet is surprisingly dense. Their observations also provide a hint that the star's rotation axis and planet orbit are not perpendicular. Both are crucial constraints in understanding the formation of this planet. Most certainly, astronomers will be looking for the next primary and secondary transits of this planet.  


In section 7. Stellar structure and evolution

“From outburst to quiescence: the decay of the transient AXP XTE J1810-197”, F. Bernardini, G.L. Israel, et al., A&A 498, p. 195

The anomalous XR pulsar XTE J1810-197 was observed over a four-year period with XMM-Newton over a range of luminosity of a factor of 100. The paper presents analysis of energy-dependent pulse profiles (from 0.6 - 10 keV) as a function of time and shows that the emission requires a set of three different, but correlated, emission regions (0.19, 0.16, and 0.26 keV)that decayed on different timescales. The coldest region declined in temperature, and the two hotter declined only in size but maintained constant temperature. The authors report the discovery of an apparent cyclotron emission line at 1.1 keV that gives a magnetic field in agreement with the one inferred from spindown, around 2.4E14 G.


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© Astronomy & Astrophysics 2009