* Astronomy

Title: Search for Giant Planets around White Dwarfs with HST, Spitzer, and VLT
Authors: S. Friedrich (1 and 2), H. Zinnecker (1), S. Correia (1), W. Brandner (3), M. Burleigh (4), M. McCaughrean (5) ((1) Astrophysikalisches Institut Potsdam, (2) Max-Planck-Institut f. Extraterrestrische Physik, (3) Max-Planck-Institut f. Astronomie, (4) Department of Physics & Astronomy, University of Leicester, (5) School of Physics, University of Exeter)

For the last three years we have performed a survey for young ( < 3 Gyrs) giant planets around nearby white dwarfs with HST, Spitzer, and VLT. Direct HST/NICMOS imaging of the seven white dwarfs in the Hyades gave no evidence for companions down to about 10 Jupiter masses and separations larger than 0.5 arcsec (about 25 AU), while VLT/NACO observations revealed a putative companion to a field white dwarf. Second epoch observations with SINFONI on the VLT, however, showed that it is most probably a background star. With IRAC on Spitzer we also found no indications of cool, very low mass companions in our sample of field white dwarfs. The implications of these non-detections are briefly discussed.

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Title: The Possible Belts for Extrasolar Planetary Systems
Authors: Ing-Guey Jiang (1), M. Duncan (2), D.N.C. Lin (3) ((1)National Tsing-Hua University, Taiwan, (2)Queen's University, Canada, (3)UC Santa Cruz, U.S.A.)

More than 100 extrasolar planets have been discovered since 1990s. Different from the solar system, these planets' orbital eccentricities cover a huge range from 0 to 0.7. Incidentally, the first Kuiper Belt Object was discovered in 1992. Thus, an interesting and important question will be whether extrasolar planetary systems could have structures like Kuiper Belt or asteroid belt. We investigate the stability of these planetary systems with different orbital eccentricities by the similar procedures in Rabl & Dvorak (1988) and Holman & Wiegert (1999). We claim that most extrasolar planetary systems can have their own belts at the outer regions. However, we find that the orbits with high--eccentricity is very powerful in depletion of these populations.

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Zooming in on a nearby young star called HD 141569A, astronomers from the National Astronomical Observatory of Japan and the Max Planck Institute for Astronomy used the Subaru telescope on Mauna Kea, Hawai'i, to discover a hole in a disk of gas and dust encircling the star. The existence of this large gap, which is about the size of the orbit of Saturn, supports the theory that this young star ended its infancy abruptly, by ionising and pushing away the gas in the disk from which it was born.
The team, lead by Dr. Miwa Goto and Professor Tomonori Usuda took advantage of the superb spatial resolution attained by the adaptive optics system and the infrared camera and spectrograph (IRCS) on Subaru, to resolve the innermost part of the disk around HD 141569A in emission lines of carbon monoxide in the infrared part of the electromagnetic spectrum. The disk was known to exist from previous studies of the dust around the star. By studying the gas, the new study successfully determined the size of the inner clearing in the disk.



Emission from carbon monoxide (CO) in the disk surrounding HD 141569A, which lies some 320 light-years away from Earth, extends out to a distance fifty times the size of the orbit of Earth. (The distance between Earth and the Sun is called an astronomical unit. In our solar system, the orbital radius of Neptune is about 30 AU). It gradually becomes stronger toward the inner part closest to the star. The emission peaks at around 15 AU, then diminishes to the central star.

"We now know that little gas remains in the inner 11 AU of the disk. In other words, HD 141569A has fully developed a hole at the centre of its molecular gas disk bigger than the size of the orbit of Saturn" - Professor Tomonori Usuda.

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Title: The Planetary Mass Companion 2MASS1207-3932 B: Temperature, Mass and Evidence for an Edge-On Disk
Authors: Subhanjoy Mohanty, Ray Jayawardhana, Nuria Huelamo, Eric Mamajek

We present J-band imaging and H+K-band low-resolution spectroscopy of 2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary mass secondary, we find J = 20.0 ±0.2 mag. The HK spectra of both components imply low gravity, and a dusty atmosphere for the secondary. Comparisons to synthetic spectra yield Teff_A ~ 2550 ±150K, and Teff_B ~ 1600 ±100K, consistent with their late-M and mid-to-late L types. For these Teff, and an age of 5-10 Myrs, evolutionary models imply M_A ~ 24 ±6 M_Jup and M_B ~ 8 ±2 M_Jup. Independent comparisons of these models to the observed colours, spanning ~I to L', also yield the same masses and temperatures. Our primary mass agrees with other recent analyses; however, our secondary mass, while still in the planetary regime, is 2-3 times larger than claimed previously. This discrepancy can be traced to the luminosities: while the absolute photometry and Mbol of the primary agree with theoretical predictions, the secondary is ~ 2.5 ±0.5 mag fainter than expected in all bands from I to L' and in Mbol. This accounts for the much lower secondary mass (and temperature) derived earlier. We argue that this effect is highly unlikely to result from a variety of model-related problems, and is instead real. This conclusion is bolstered by the absence of any luminosity problems in either the primary, or in AB Pic B which we also analyse. We therefore suggest grey extinction in 2M1207B, due to occlusion by an edge-on circum-secondary disk. This is consistent with the observed properties of edge-on disks around T Tauri stars, and with the known presence of a high-inclination evolved disk around the primary. Finally, the system's implied mass ratio of ~0.3 suggests a binary-like formation scenario. .

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