20 research outputs found
Magnetic Field of the Eclipsing M Dwarf Binary YY Gem
YY Gem is a short-period eclipsing binary system containing two nearly
identical, rapidly rotating, very active early-M dwarfs. This binary represents
an important benchmark system for calibrating empirical relations between
fundamental properties of low-mass stars and for testing theories of interior
structure and evolution of these objects. Both components of YY Gem exhibit
inflated radii, which has been attributed to poorly understood magnetic
activity effects. Despite a long history of magnetic activity studies of this
system no direct magnetic field measurements have been made for it. Here we
present a comprehensive characterisation of the surface magnetic field in both
components of YY Gem. We reconstructed the global field topologies with the
help of a tomographic inversion technique applied to high-resolution
spectropolarimetric data. This analysis revealed moderately complex global
fields with a typical strength of 200-300 G and anti-aligned dipolar
components. A complementary Zeeman intensification analysis of the disentangled
intensity spectra showed that the total mean field strength reaches 3.2-3.4 kG
in both components of YY Gem. We used these results together with other recent
magnetic field measurements of M dwarfs to investigate the relation between the
global and small-scale fields in these stars. We also assessed predictions of
competing magnetoconvection interior structure models developed for YY Gem,
finding that only one of them anticipated the surface field strength compatible
with our observations. Results of our star spot mapping of YY Gem do not
support the alternative family of theoretical stellar models which attempts to
explain the radii inflation by postulating a large spot filling factor.Comment: 17 pages, 8 figures; accepted for publication in Ap
Pushing the limit of instrument capabilities
Chemically Peculiar (CP) stars have been subject of systematic research since
more than 50 years. With the discovery of pulsation of some of the cool CP
stars, the availability of advanced spectropolarimetric instrumentation and
high signal- to-noise, high resolution spectroscopy, a new era of CP star
research emerged about 20 years ago. Together with the success in ground-based
observations, new space projects are developed that will greatly benefit for
future investigations of these unique objects. In this contribution we will
give an overview of some interesting results obtained recently from
ground-based observations and discuss on future outstanding Gaia space mission
and its impact on CP star research.Comment: Joint Discussion 04, Secsion 1, To appear in Highlights of Astronomy,
Proc. of the XXVIIth IAU General Assembly, Rio de Janeiro, Brazil, August
2009, 9 page
A self consistent chemically stratified atmosphere model for the roAp star 10 Aquilae
Context: Chemically peculiar A type (Ap) stars are a subgroup of the CP2
stars which exhibit anomalous overabundances of numerous elements, e.g. Fe, Cr,
Sr and rare earth elements. The pulsating subgroup of the Ap stars, the roAp
stars, present ideal laboratories to observe and model pulsational signatures
as well as the interplay of the pulsations with strong magnetic fields and
vertical abundance gradients. Aims: Based on high resolution spectroscopic
observations and observed stellar energy distributions we construct a self
consistent model atmosphere, that accounts for modulations of the
temperature-pressure structure caused by vertical abundance gradients, for the
roAp star 10 Aquilae (HD 176232). We demonstrate that such an analysis can be
used to determine precisely the fundamental atmospheric parameters required for
pulsation modelling. Methods: Average abundances were derived for 56 species.
For Mg, Si, Ca, Cr, Fe, Co, Sr, Pr, and Nd vertical stratification profiles
were empirically derived using the ddafit minimization routine together with
the magnetic spectrum synthesis code synthmag. Model atmospheres were computed
with the LLModels code which accounts for the individual abundances and
stratification of chemical elements. Results: For the final model atmosphere
Teff=7550 K and log g=3.8 were adopted. While Mg, Si, Co and Cr exhibit steep
abundance gradients Ca, Fe and Sr showed much wider abundance gradients between
log tau_5000=-1.5 and 0.5. Elements Mg and Co were found to be the least
stratified, while Ca and Sr showed strong depth variations in abundance of up
to ~ 6 dex.Comment: 9 pages, 15 figure
Abundance and stratification analysis of the CP star HD 103498
Slow rotation and absence of strong mixing processes in atmospheres of
chemically peculiar stars develop ideal conditions for the appearance of
abundance anomalies through the mechanism of microscopic particle diffusion.
This makes these objects look spectroscopically and photometrically different
from their "normal" analogs. As a result, it is often difficult to accurately
determine atmospheric parameters of these stars and special methods are needed
for the consistent analysis of their atmospheres. The main aim of the present
paper is to analyse atmospheric abundance and stratification of chemical
elements in the atmosphere of the chemically peculiar star HD 103498. We find
that two model atmospheres computed with individual and stratified abundances
provide reasonable fit to observed spectroscopic and photometric indicators:
Teff=9300 K, logg=3.5 and Teff=9500K, logg=3.6. It is shown that Mg has a large
abundance gradient in the star's atmosphere with accumulation of Mg ions in the
uppermost atmospheric layers, whereas Si demonstrates opposite behaviour with
accumulation in deep layers. In addition, a detailed non-LTE analysis showed
that none of Mg transitions under consideration is a subject of noticeable
non-LTE effects. Comparing observed photometry transformed to physical units we
estimated the radius of HD 103498 to be between R=(4.56 +/- 0.77)Rsun for
Teff=9300K, logg=3.5 and R=(4.39 +/- 0.75)Rsun for Teff=9500K, logg=3.6 models
respectively. We note that the lack of suitable observations in absolute units
prevents us to uniquely determine the Teff of the star at the current stage of
analysis.Comment: 9 pages, 7 figures and 3 tables, accepted for publication in MNRA
Magnetism in the Brown Dwarf Regime
A suite of discoveries in the last two decades demonstrate that we are now at
a point where incorporating magnetic behavior is key for advancing our ability
to characterize substellar and planetary systems. The next decade heralds the
exciting maturation of the now-burgeoning field of brown dwarf magnetism, and
investing now in brown dwarf magnetism will provide a key platform for
exploring exoplanetary magnetism and habitability beyond the solar system. We
anticipate significant discoveries including: the nature of substellar and
planetary magnetic dynamos, the characterization of exo-aurora physics and
brown dwarf magnetospheric environments, and the role of satellites in
manifestations of substellar magnetic activity. These efforts will require
significant new observational capabilities at radio and near infrared
wavelengths, dedicated long-term monitoring programs, and committed support for
the theoretical modeling efforts underpinning the physical processes of the
magnetic phenomenaComment: Decadal 2020 science white pape
Pushing the limit of instrument capabilities
Chemically Peculiar (CP) stars have been the subject of systematic research for more than 50 years. With the discovery of pulsation of some of the cool CP stars, and the availability of advanced spectropolarimetric instrumentation and high signal-to-noise, high resolution spectroscopy, a new era of CP star research emerged about 20 years ago. Together with the success in ground-based observations, new space projects are developed that will greatly benefit future investigations of these unique objects. In this contribution we will give an overview of some interesting results obtained recently from ground-based observations and discuss the future outstanding Gaia space mission and its impact on CP star researc