19 research outputs found
Short period line profile and light variations in the Be star ω Orionis
We present the results of a multisite spectroscopic and photometric campaign on the Be star ω Orionis. From the photometry and radial velocity variation of several spectral lines, we confirm that the star is a variable with period . Only one period can be extracted from both the photometric and radial velocity observations. We find that the projected rotational velocity from the helium lines is considerably smaller than from the metal lines . The line profiles show an excess absorption feature moving from blue to red for half the period and from red to blue for the other half of the period. Another excess absorption feature moves exactly out of phase. The excess absorption features are present in photospheric lines as well as in lines which are significantly affected by circumstellar material, such as Hβ. From this we conclude that the periodic variations are most probably associated with corotating circumstellar materia
Light and Life: Exotic Photosynthesis in Binary Star Systems
The potential for hosting photosynthetic life on Earth-like planets within
binary/multiple stellar systems was evaluated by modelling the levels of
photosynthetically active radiation (PAR) such planets receive. Combinations of
M and G stars in: (i) close-binary systems; (ii) wide-binary systems and (iii)
three-star systems were investigated and a range of stable radiation
environments found to be possible. These environmental conditions allow for the
possibility of familiar, but also more exotic forms of photosynthetic life,
such as infrared photosynthesisers and organisms specialised for specific
spectral niches.Comment: Accepted for publication in: Astrobiolog
The Large Magellanic Cloud and the Distance Scale
The Magellanic Clouds, especially the Large Magellanic Cloud, are places
where multiple distance indicators can be compared with each other in a
straight-forward manner at considerable precision. We here review the distances
derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing
Binaries, and show that the results from these distance indicators generally
agree to within their errors, and the distance modulus to the Large Magellanic
Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding
to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing
the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science.
From a presentation at the conference The Fundamental Cosmic Distance Scale:
State of the Art and the Gaia Perspective, Naples, May 201
Geophysical and atmospheric evolution of habitable planets
The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere
Division V: Variable Stars
Contains fulltext :
34844.pdf (Publisher’s version ) (Closed access)Division V, "Variable Stars", consists of Commission 27, also called "Variable Stars" and Commission 42, "Close Binaries". Thus the former deals with stars whose variations are intrinsic, whereas in the latter the variations are caused by the interactions between the components in the binary. It is evident that the definition of the Division is predominantly observational, and there may be cases where the assignment of an object to one of the two commissions might be in doubt (a recent somewhat related example was the first detection of an extra-solar planet, in 54 Pegasi, where intrinsic variability of the star in the form of high-order g modes was also initially suspected)