Grant: $295,596 - National Science Foundation - Sep. 15, 2009
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Award Description: Stars on the Extended Horizontal Branch (also called subdwarf B or sdB stars) are core—He burning objects with very small H—rich envelope masses. Most red giant stars do not lose their entire envelopes before igniting He, so the sdB stars are somehow special: perhaps they all are members of interacting binary systems in which the companion has helped strip away the envelope. Theories of sdB star origins that involve close binary interactions make definite predictions about the types of companions that should be found, their orbital periods and separations. Observations show that many sdB stars are indeed in close binary systems, usually with white dwarf companions Others are in binary systems with cool main-sequence companions. The latter binaries may be 'close , or not; further evidence on the typical separation of their component stars needs to be established from new observations. Theories also predict that many sdB stars are 'hiding in binaries where the companion stars are somewhat hotter, and lists of such stars are being developed based on observations in the ultraviolet. There is a need to find the ratio of these new hotter companions to the cooler companions in known sdB binaries, and to learn whether these binaries also have separations as predicted by theory. I This work will provide fundamental data that can be used to put the theory of binary star interactions and the origin of sdB stars on a firmer basis. A better understanding of the ages and mass ranges of stars that can become sdBs is important in interpreting the ultraviolet light from galaxies at large look—back times. The work will help to validate, challenge, and ultimately improve binary population synthesis models that are used to predict or understand a wide variety of phenomena in modern astrophysics. This is in addition to the interest in sdBs in their own right, which also offer clues to the evolution of old star clusters.
Project Description: This Project will carry out a program of multi-epoch radial velocity (RV) observations of significant samples of both the composite—spectrum (sdB + cool star) binaries and the binaries with 'hidden sdB stars, to establish whether their orbits are as predicted by theory. Systems for which an acceleration of the RV is found will be followed up to determine full orbits; conversely, if many systems show no detectable acceleration at our low measurement threshold, then this class of binaries cannot have interacted to form the sdB star that we see today, and theory must be modified. The observations will be carried out at the Hobby—Eberly Telescope and at national faeffities. Other sdB stars appear to have resolved (hence non—interacting) companions, which if confirmed can be exploited to learn the distance to the sdB primary and other properties of the binary, such as each system’s metallicity, limits on the original mass of the sdB star, and possibly the age of the binary. Radial velocities, proper motion data and other means wifi be used to confirm association, pair by pair, and true pairs will be studied in detail. In addition, a study wifi be conducted to learn how badly existing catalogs of hot subdwarf stars are biased by selection effects, and how such bias can be accounted for or a catalog that is more representative of the true population of sdB stars can be constructed.
Jobs Summary: Nothing to report currently. (Total jobs reported: 0)
Project Status: Not Started
This award's data was last updated on Sep. 15, 2009. Help expand these official descriptions using the wiki below.