Astrophysics, abstract
astro-ph/0404212

From: Sean Raymond [view email]

Date (v1): Fri, 9 Apr 2004 20:03:38 GMT (38kb)
Date (revised v2): Fri, 24 Feb 2006 16:44:11 GMT (57kb)

Predicting Planets in Known Extra-Solar Planetary Systems III: Forming Terrestrial Planets

Authors: Sean N. Raymond (Colorado), Rory Barnes (Arizona)

Comments: ApJ, accepted -- to appear in June 20 issue

Recent results have shown that many of the known extrasolar planetary systems contain regions which are stable for both Earth-mass and Saturn-mass planets. Here we simulate the formation of terrestrial planets in four planetary systems -- 55 Cancri, HD 38529, HD 37124, and HD 74156 -- under the assumption that these systems of giant planets are complete and that their orbits are well-determined. Assuming the giant planets formed and migrated quickly, then terrestrial planets may form from a second generation of planetesimals. In each case, Moon- to Mars-sized planetary embryos are placed in between the giant planets and evolved for 100 Myr. We find that planets form relatively easily in 55 Cnc, with masses up to 0.6 Earth masses and in some cases substantial water contents and orbits in the habitable zone. HD 38529 is likely to support an asteroid belt but no terrestrial planets of significant mass. No terrestrial planets form in HD 37124 and HD 74156, although in some cases 1-2 lone embryos survive for 100 Myr. If migration occurred later, depleting the planetesimal disk, then massive terrestrial planets are unlikely to form in any of these systems.

http://arxiv.org/abs/astro-ph/0404212

Astrophysics, abstract
astro-ph/0602545

From: Orsola De Marco [view email]

Date: Fri, 24 Feb 2006 18:07:15 GMT (1559kb)

Cloud fragmentation and proplyd-like features in HII regions imaged by HST

Authors: Orsola De Marco, C.R. O'Dell, Pamela Gelfond, R. H. Rubin, S.C.O. Glover

Comments: 51 pages; 19 figures; 5 tables. Accepted by AJ

We have analyzed HST ACS and WFPC2 new and archival images of eight HII regions to look for new proto-planetary disks (proplyds) similar to those found in the Orion Nebula. We find a wealth of features similar in size (though many are larger) to the bright cusps around the Orion Nebula proplyds. None of them, however, contains a definitive central star. From this, we deduce that the new cusps may not be proplyds, but instead are fragments of molecular cloud material. Out of all the features found in the eight HII regions examined, only one, an apparent edge-on silhouette in M17, may have a central star. This feature might join the small number of bona fide proplyds found outside the Orion Nebula, in M8, M20 and possibly in M16. In line with the results found recently by Smith et al. (2005), the paucity of proplyds outside the Orion Nebula, may be explained by their transient nature as well as by the specific environmental conditions under whichthey can be observed.

http://arxiv.org/abs/astro-ph/0602545