HIGHLIGHTS: this week in A&A

02 April 2010 (vol. 512)

 


In section 10. Planets and planetary systems

“The HARPS search for southern extra-solar planets. XX. Planets around the active star BD-08°2823”, by G. Hebrard, et al., A&A 512, A46
“The HARPS search for southern extra-solar planets. XXI. Three new giant planets orbiting the metal-poor stars HD5388, HD181720, and HD190984”, by N.C. Santos, et al., A&A 512, A47
“The HARPS search for southern extra-solar planets. XXII. Multiple planet systems from the HARPS volume limited sample”, by G. Lo Curto, et al., A&A 512, A48

The HARPS spectrograph continues its exploration of planet-bearing stars in the solar neighborhood. In this issue, Lo Curto et al., Santos et al., and Hebrard et al. unveil seven new planetary systems, including four multiple systems with low-mass planets (the lowest with Msini=6.6 Mearth) and three giant planets on very long periods (up to 4885 days!) orbiting metal-deficient stars. These discoveries confirm the tendency of low-mass planets (below the mass of Neptune) to be discovered in multiple systems (as shown by triangles and squares in the figure below). They also confirm that while giant planets are much more frequently found around metal-rich stars, this is not the case for low-mass planets. Altogether, the improvement in sensitivity and increased statistics towards low-mass planets will be crucial for understanding both planetary formation, in general, and the population of planets in our galactic neighborhood.
 

 

In section 10. Planets and planetary systems

“Mapping the methane on Mars”, by S. Fonti and G.A. Marzo, A&A 512, A51

Fonti & Marzo use data acquired by the Thermal Emission Spectrometer onboard the Mars Global Surveyor spacecraft to derive a map of methane production on Mars. The issue is important, as it would have consequences on the geological and possibly biological evolution of the planet. It is also controversial, because the methane absorption at 1304cm-1 is close to several water absorption lines. The authors, however, estimate that water absorption at this wavelength is too weak to contaminate the maps. They also advocate that the water-vapor production observed at other wavelengths is not in phase with their methane production maps.
 

 

In section 10. Planets and planetary systems

“A numerical model of cometary dust coma structures: Application to comet 9P/Tempel”, by J.-B. Vincent, H. Böhnhardt, and L.M. Lara, A&A 512, A60

Comet 9P/Tempel 1 was hit by a 370 kg probe on July 4, 2005, as part of the Deep Impact mission. The comet survived (it weighs about a hundred billion tons), and will be revisited by the Stardust-NExT spacecraft in 2011 for a better look at the impact crater. But for the flyby to be successful, a precise knowledge of the comet's spin is mandatory. Vincent, Böhnhardt, and Lara develop a numerical model for understanding cometary dust structures and apply it to analyzing photographs of 9P/Tempel 1 taken before and after the impact. They thus determine that the comet's spin orientation has not changed between January and August 2005 and that it agreest with Deep-Impact flyby imaging results. They also identify six active regions on the nucleus and show that their model is able to make predictions for the evolution of these structures, an important asset when planning future missions to comets.
 

 

In section 3. Cosmology

“Ly-α escape during cosmological hydrogen recombination: the 3d-1s and 3s-1s two-photon processes”, by J. Chluba and R.A. Sunyaev, A&A 512, A53

The authors have completed a detailed analysis of the role of 3d-1s and 3s-1s two- photon processes during recombination and the formation of the CMB. After formulating the necessary corrections to the Lyman-alpha transfer equation, they perform a series of analytic and numerical calculations designed to show the effect of these two-photon processes. They find that the recombination history is modified at the few percent level. Although minor effects, these corrections will nonetheless be important for any correct interpretation of data from the Planck experiment.
 

 



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