15 research outputs found
High-Mass, Four-Planet Models for HR 8799: Constraining the Orbital Inclination and Age of the System
Debates regarding the age and inclination of the planetary system orbiting HR
8799, and the release of additional astrometric data following the discovery of
the fourth planet prompted us to examine the possibility of constraining these
two quantities by studying the long-term stability of this system at different
orbital inclinations and in its high-mass configuration (7-10-10-10 MJup). We
carried out ~1.5 million N-body integrations for different combinations of
orbital elements of the four planets. The most dynamically stable combinations
survived less than ~5 Myr at inclinations of 0{\deg} and 13{\deg}, and 41, 46,
and 31 Myr at 18{\deg}, 23{\deg}, and 30{\deg}, respectively. Given such short
lifetimes and the location of the system on the age-luminosity diagram for
low-mass objects, the most reasonable conclusion of our study is that the
planetary masses are less than 7-10-10-10 MJup and the system is quite young.
Two trends to note from our work are as follows. (1) In the most stable
systems, the higher the inclination, the more the coordinates for planets b and
c diverge from the oldest archival astrometric data (released after we
completed our N-body integrations), suggesting that either these planets are in
eccentric orbits or have lower orbital inclinations than that of planet d. (2)
The most stable systems place planet e closer to the central star than is
observed, supporting the conclusion that the planets are more massive and the
system is young. We present the details of our simulations and discuss the
implications of the results.Comment: Content: 25 pages, 5 figures, 1 table. Submitted for publication on
2012 January 2. Accepted for publication in the Astrophysical Journal on June
7, 2012. File updated June 9, 201
Identification of Nedd4 E3 Ubiquitin Ligase as a Binding Partner and Regulator of MAK-V Protein Kinase
MAK-V/Hunk is a scantily characterized AMPK-like protein kinase. Recent findings identified MAK-V as a pro-survival and anti-apoptotic protein and revealed its role in embryonic development as well as in tumorigenesis and metastasis. However molecular mechanisms of MAK-V action and regulation of its activity remain largely unknown. We identified Nedd4 as an interaction partner for MAK-V protein kinase. However, this HECT-type E3 ubiquitin ligase is not involved in the control of MAK-V degradation by the ubiquitin-proteasome system that regulates MAK-V abundance in cells. However, Nedd4 in an ubiquitin ligase-independent manner rescued developmental defects in Xenopus embryos induced by MAK-V overexpression, suggesting physiological relevance of interaction between MAK-V and Nedd4. This identifies Nedd4 as the first known regulator of MAK-V function