4 research outputs found
Accurate masses and radii of normal stars: modern results and applications
This paper presents and discusses a critical compilation of accurate,
fundamental determinations of stellar masses and radii. We have identified 95
detached binary systems containing 190 stars (94 eclipsing systems, and alpha
Centauri) that satisfy our criterion that the mass and radius of both stars be
known to 3% or better. To these we add interstellar reddening, effective
temperature, metal abundance, rotational velocity and apsidal motion
determinations when available, and we compute a number of other physical
parameters, notably luminosity and distance. We discuss the use of this
information for testing models of stellar evolution. The amount and quality of
the data also allow us to analyse the tidal evolution of the systems in
considerable depth, testing prescriptions of rotational synchronisation and
orbital circularisation in greater detail than possible before. The new data
also enable us to derive empirical calibrations of M and R for single (post-)
main-sequence stars above 0.6 M(Sun). Simple, polynomial functions of T(eff),
log g and [Fe/H] yield M and R with errors of 6% and 3%, respectively.
Excellent agreement is found with independent determinations for host stars of
transiting extrasolar planets, and good agreement with determinations of M and
R from stellar models as constrained by trigonometric parallaxes and
spectroscopic values of T(eff) and [Fe/H]. Finally, we list a set of 23
interferometric binaries with masses known to better than 3%, but without
fundamental radius determinations (except alpha Aur). We discuss the prospects
for improving these and other stellar parameters in the near future.Comment: 56 pages including figures and tables. To appear in The Astronomy and
Astrophysics Review. Ascii versions of the tables will appear in the online
version of the articl
Optical polarimetry: Methods, Instruments and Calibration Techniques
In this chapter we present a brief summary of methods, instruments and
calibration techniques used in modern astronomical polarimetry in the optical
wavelengths. We describe the properties of various polarization devices and
detectors used for optical broadband, imaging and spectropolarimetry, and
discuss their advantages and disadvantages. The necessity of a proper
calibration of the raw polarization data is emphasized and methods of the
determination and subtraction of instrumental polarization are considered. We
also present a few examples of high-precision measurements of optical
polarization of black hole X-ray binaries and massive binary stars made with
our DiPol-2 polarimeter, which allowed us to constrain the sources of optical
emission in black hole X-ray binaries and measure orbital parameters of massive
stellar binaries.Comment: 33 pages, 14 figure; to be published in Astrophysics and Space
Science Library 460, Astronomical Polarisation from the Infrared to Gamma
Ray
Common Envelope Evolution Redux
Common envelopes form in dynamical time scale mass exchange, when the
envelope of a donor star engulfs a much denser companion, and the core of the
donor plus the dense companion star spiral inward through this dissipative
envelope. As conceived by Paczynski and Ostriker, this process must be
responsible for the creation of short-period binaries with degenerate
components, and, indeed, it has proven capable of accounting for short-period
binaries containing one white dwarf component. However, attempts to reconstruct
the evolutionary histories of close double white dwarfs have proven more
problematic, and point to the need for enhanced systemic mass loss, either
during the close of the first, slow episode of mass transfer that produced the
first white dwarf, or during the detached phase preceding the final, common
envelope episode. The survival of long-period interacting binaries with massive
white dwarfs, such as the recurrent novae T CrB and RS Oph, also presents
interpretative difficulties for simple energetic treatments of common envelope
evolution. Their existence implies that major terms are missing from usual
formulations of the energy budget for common envelope evolution. The most
plausible missing energy term is the energy released by recombination in the
common envelope, and, indeed, a simple reformulation the energy budget
explicitly including recombination resolves this issue.Comment: 25 pages, 6 figures. To appear in "Short Period Binary Stars", ed.
E.F. Milone, D.A. Leahy, & D.W. Hobill (Springer