Found 7 talks width keyword subdwarfs
Planetary systems have been found systematically orbiting main sequence stars and red giants. But the detection of planets per se during the white dwarf phase has been more elusive with only 3 systems. We have, however, ample indirect evidence of the existence of planetary debris around these systems in the form of material acreted onto the white dwarf, disks and even planetesimals. In this talk, I will review how we can put the pieces together: how we can reconcile what we see in white dwarfs with what we can infer regarding the evolution of planetary systems from the main sequence phase.
Wide hot subdwarf B (sdB) binaries with main-sequence companions are outcomes of stable mass transfer from evolved red giants. The orbits of these binaries show a strong correlation between their orbital periods and mass ratios. The origins of this correlation have, so far, been lacking a conclusive explanation.
We have performed a small but statistically significant binary population synthesis study with the binary stellar evolution code MESA. We have used a standard model for binary mass loss and a standard Galactic metallicity history. We have achieved an excellent match to the observed period - mass ratio correlation without explicitly fine-tuning any parameters. Furthermore, our models produce a good match to the observed period - metallicity correlation.
We demonstrate, for the first time, how the metallicity history of the Milky Way is imprinted in the properties of the observed post-mass transfer binaries. We show that Galactic chemical evolution is an important factor in binary population studies of interacting systems containing at least one evolved low-mass (Mi < 1.6 Msol) component. Finally, we provide an observationally supported model of mass transfer from low-mass red giants onto main-sequence stars.
Zoom link: https://rediris.zoom.us/j/98017007654
We report on the discovery of a fourth component in the HD 221356 star system, previously known to be formed by an F8V, slightly metal-poor primary ([Fe/H]= -0.26), and a distant M8V+L3V pair. In our ongoing common proper motion search based on VISTA Hemisphere Survey (VHS) and 2MASS catalogues, we have detected a faint (J = 13.76 ± 0.04 mag) co-moving companion of the F8 star located at a projected distance of ~312 AU. Near-infrared spectroscopy of the new companion indicates an L1±1 spectral type. Using evolutionary models the mass of the new companion is estimated at ~0.08 solar masses, which places the object close to the stellar-substellar borderline. This multiple system provides an interesting example of objects with masses slightly above and below the hydrogen burning mass limit.
The proper characterization of the least massive population of the young Sigma Orionis star cluster is required to understand the form of the cluster mass function and its impact on our comprehension of the substellar formation processes. SOri70 (T5.5±1) and SOri73, two T-type cluster member candidates, would have likely masses between 3 and 7 MJup if their age is 3 Myr. SOri73 awaits confirmation of its methane atmosphere. Here I present the results of a search of T-type objects in an area of ~120 arcmin^2 in the Sigma Orionis cluster, the confirmation of the presence of methane absorption in SOri73 and the study of SOri70 and 73 cluster membership via photometric colors and accurate proper motion analysis. This results would have a dramatic impact in the cluster mass function, in one of the scenarios explored, they suggest a decrease in cluster members with planetary masses in the interval 3.5-6 Mjup.
AbstractIn this Breaking News seminar, I will describe our project dedicated to the search for ultracool low-metallicity dwarfs (or subdwarfs) in the large-scale databases. The highlight of the seminar is the discovery of a mid-L subdwarf, the fifth known to date, and the first one identified in the UKIRT Infrared Deep Sky Survey (UKIDSS). The spectroscopic nature of this subdwarf was confirmed with data obtained with GTC/OSIRIS in April 2009.
AbstractRed Dwarf (dM) stars are the most numerous stars in our Galaxy. These faint, cool, long-lived, and low mass stars make up > 80% of all stars in the Universe. Determining the number of red dwarfs with planets and assessing planetary habitability (a planet’s potential to develop and sustain life) are critically important because such studies would indicate how common life is in the universe. Our program - "Living with a Red Dwarf" addresses these questions by investigating the long-term nuclear evolution and magnetic-dynamo coronal and chromospheric X-ray to Ultraviolet properties of red dwarf stars with widely different ages. The major focus of the program is to study the magnetic-dynamo generated X-ray-Ultraviolet emissions and flare properties of red dwarf stars from youth to old age. Emphasized are how the stellar X-UV emissions, flares & winds affect hosted planets and impact their habitability. We have developed age-rotation-activity relations and also are constructing irradiance tables (X-UV fluxes) that can be used to model the effects of X-UV radiation on planetary atmospheres and on possible life on nearby hosted planets. Despite the earlier pessimistic view that red dwarfs stars are not suitable for habitable planets - mainly because their low luminosities require a hosted planet to orbit quite close (r <0.3 AU) to be sufficiently warm to support life. Our initial results indicate that red dwarf stars (in particular the warmer dM stars) can indeed be suitable hosts for habitable planets capable of sustaining life for hundreds of billion years. Some examples of red dwarf stars currently known to host planets are discussed.
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