36 research outputs found
Interferometric diameters of five evolved intermediate-mass planet-hosting stars measured with PAVO at the CHARA Array
Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass (∼ 1.5 M⊙) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis (5.12 ± 0.16 R⊙, 4949 ± 58 K), 24 Sextantis (5.49 ± 0.18 R⊙, 4908 ± 65 K), κ Coronae Borealis (4.77 ± 0.07 R⊙, 4870 ± 47 K), HR 6817 (4.45 ± 0.08 R⊙, 5013 ± 59 K), and HR 8461 (4.91 ± 0.12 R⊙, 4950 ± 68 K). We find disagreements of typically 15 per cent in angular diameter and ∼200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly (∼15 per cent) lower masses than generally reported in the literature.Funding for the Stellar Astrophysics Centre is provided by The
Danish National Research Foundation. The research was supported
by the ASTERISK project (ASTERoseismic Investigations with
SONG and Kepler) funded by the European Research Council
(Grant agreement no.: 267864). TRW and VSA acknowledge the support of the Villum Foundation (research grant 10118). DH acknowledges
support by the Australian Research Council’s Discovery
Projects funding scheme (project number DE140101364) and
support by the NASA Grant NNX14AB92G issued through the
Kepler Participating Scientist Program. LC is supported by the
Australian Research Council Future Fellowship FT160100402. MJI
was supported by the Australian Research Council Future Fellowship
FT130100235. Parts of this research were conducted by the
Australian Research Council Centre of Excellence for All Sky Astrophysics
in 3 Dimensions (ASTRO 3D), through project number
CE170100013
Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy
We review HB stars in a broad astrophysical context, including both variable
and non-variable stars. A reassessment of the Oosterhoff dichotomy is
presented, which provides unprecedented detail regarding its origin and
systematics. We show that the Oosterhoff dichotomy and the distribution of
globular clusters (GCs) in the HB morphology-metallicity plane both exclude,
with high statistical significance, the possibility that the Galactic halo may
have formed from the accretion of dwarf galaxies resembling present-day Milky
Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the
second-parameter problem is presented. A technique is proposed to estimate the
HB types of extragalactic GCs on the basis of integrated far-UV photometry. The
relationship between the absolute V magnitude of the HB at the RR Lyrae level
and metallicity, as obtained on the basis of trigonometric parallax
measurements for the star RR Lyrae, is also revisited, giving a distance
modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are
studied. Finally, the conductive opacities used in evolutionary calculations of
low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and
Space Scienc
Hot magnetized nuclear matter: Thermodynamic and saturation properties
We have used a realistic nuclear potential, AV18, and a many body technique,
the lowest order constraint variational (LOCV) approach, to calculate the
properties of hot magnetized nuclear matter. By investigating the free energy,
spin polarization parameter, and symmetry energy, we have studied the
temperature and magnetic field dependence of the saturation properties of
magnetized nuclear matter. In addition, we have calculated the equation of
state of magnetized nuclear matter at different temperatures and magnetic
fields. It was found that the flashing temperature of nuclear matter decreases
by increasing the magnetic field. In addition, we have studied the effect of
the magnetic field on liquid gas phase transition of nuclear matter. The liquid
gas coexistence curves, the order parameter of the liquid gas phase transition,
and the properties of critical point at different magnetic fields have been
calculated.Comment: 30 pages, 13 figures, 2 tables. Accepted for publication in European
Physical Journal