267 research outputs found
Cataclysmic Variables — X-rays and Optical Activity in V1223 Sgr and V709 Cas
Intermediate polars are a major fraction of all cataclysmic variables detected by INTEGRAL in hard X-ray. These objects have recently been proposed to be the dominant X-ray source population detected near the Galactic centre, and they also contribute significantly to X-ray diffuse Galactic ridge emission. Nevertheless, only 25% of all known intermediate polars have been detected in hard X-ray. This fact can be related to the activity state of these close interacting binaries.A multi-frequency (from optical to X-ray) investigation of intermediate polars is essential for understanding the physical mechanisms responsible for the observed activity of these objects
Wind mass transfer in S-type symbiotic binaries III. Confirmation of a wind focusing in EG Andromedae from the nebular [OIII]\lambda 5007 line
Context. The structure of the wind from the cool giants in symbiotic binaries
carries important information for understanding the wind mass transfer to their
white dwarf companions and its fuelling. Aims. In this paper, we indicate a
non-spherical distribution of the neutral wind zone around the red giant (RG)
in the symbiotic binary star, EG And. Methods. We achieved this aim by
analysing the periodic orbital variations of fluxes and radial velocities of
individual components of the H and [OIII]5007 lines observed
on our high-cadence medium (R 11 000) and high-resolution (R 38
000) spectra. Results. The asymmetric shaping of the neutral wind zone at the
near-orbital-plane region is indicated by: (i) the asymmetric course of the
H core emission fluxes along the orbit; (ii) the presence of their
secondary maximum around the orbital phase , which is possibly
caused by the refraction effect; and (iii) the properties of the H
broad wing emission originating by Raman scattering on H atoms. The wind is
substantially compressed from polar directions to the orbital plane as
constrained by the location of the [OIII]5007 line emission zones in
the vicinity of the RG at/around its poles. The corresponding mass-loss rate
from the polar regions of Msun/yr is a factor of lower than the average rate of Msun/yr derived from
nebular emission of the ionised wind from the RG. Furthermore, it is two orders
of magnitude lower than that measured in the near-orbital-plane region from
Rayleigh scattering. Conclusions. The startling properties of the nebular
[OIII]5007 line in EG And provides an independent indication of the
wind focusing towards the orbital plane.Comment: 10 pages, 8 figure
Density asymmetry and wind velocities in the orbital plane of the symbiotic binary EG Andromedae
Context. Non-dusty late-type giants without a corona and large-scale
pulsations represent objects that do not fulfil the conditions under which
standard mass-loss mechanisms can be applied efficiently. The driving mechanism
of their winds is still unknown.
Aims. The main goal of this work is to match the radial velocities of
absorbing matter with a depth in the red giant (RG) atmosphere in the S-type
symbiotic star EG And.
Methods. We measured fluxes and radial velocities of ten FeI absorption lines
from spectroscopic observations with a resolution of ~30 000. At selected
orbital phases, we modelled their broadened profiles, including all significant
broadening mechanisms.
Results. The selected FeI absorption lines at 5151 - 6469A, originate at a
radial distance ~1.03 RG radii from its centre. The corresponding radial
velocity is typically ~1 km/s , which represents a few percent of the terminal
velocity of the RG wind. The high scatter of the radial velocities of several
km/s in the narrow layer of the stellar atmosphere points to the complex nature
of the near-surface wind mass flow. The average rotational velocity of 11 km/s
implies that the rotation of the donor star can contribute to observed focusing
the wind towards the orbital plane. The orbital variability of the absorbed
flux indicates the highest column densities of the wind in the area between the
binary components, even though the absorbing neutral material is geometrically
more extended from the opposite side of the giant. This wind density asymmetry
in the orbital plane region can be ascribed to gravitational focusing by the
white dwarf companion.
Conclusions. Our results suggest that both gravitational and rotational
focusing contribute to the observed enhancement of the RG wind towards the
orbital plane, which makes mass transfer by the stellar wind highly efficient.Comment: 12 pages, 10 figure
Feasibility of a community healthy eating and cooking intervention featuring traditional African Caribbean foods from participant and staff perspectives
Culturally appropriate healthy eating resources are intended to help people from different ethnic backgrounds consume diets reflecting government dietary recommendations, yet evidence on use in the target groups is lacking. This study evaluated the feasibility of a new brief culturally appropriate community intervention that aimed to introduce food-based healthy eating and recipe resources featuring African Caribbean foods, which were recently co-developed with people from these ethnic backgrounds. Working with a community organization in the UK, a single-arm study was used to collect verbal data from participants and staff on the acceptability of intervention whilst knowledge, skills and behaviours related to healthy eating were evaluated using pre-, post- and follow-up questionnaires. A total of 30 participants were recruited, and 22 completed all three questionnaires; who were mostly female aged 55 years+ (n = 17) and of African Caribbean ethnicity (45%, n = 10), with 32% (n = 7) reporting no educational attainment. At post-intervention and follow-up, most participants reported high satisfaction (n = 21, 95%) with the intervention sessions and high levels of confidence in using the resources at home within budget. The number of participants who were familiar with the healthy eating guidance featuring Caribbean foods increased from pre- (36%, n = 8) to post-intervention/follow-up (n = 22, 100%) (p < 0.05). Findings suggest the intervention is feasible in a community setting and could help increase awareness and use of culturally appropriate healthy eating guidance amongst a diverse group
T Tauri stars in the SuperWASP and NSVS surveys II. Spectral modelling
We present results from long-term spectroscopic monitoring of 21 T-Tauri stars located in the Taurus–Auriga star-forming region (SFR). We combine medium and high-dispersion Echelle spectroscopy obtained at the Stará Lesná, Skalnaté Pleso (both in Slovakia), and Tautenburg (Germany) observatories with low-resolution flux-calibrated spectra from Asiago (Italy) observatory all taken between 2015 and 2018. We extend the coverage by additional medium-resolution spectra from Stará Lesná obtained in 2022. In the previous paper, we measured photometric periods of these targets in a range of 0.7–3.1 d, which could be due to the rotation of a spotted surface or binarity. Here, we use the broadening-function technique to determine the radial and projected rotational velocities to reveal any close binary companion. Our analysis concludes that no such companion is present with an orbital period equal to the photometric period. We focus our analysis primarily on determining atmospheric parameters such as surface gravity log g, effective temperature Teff, and metallicity [Fe/H]. Additionally, we measure the equivalent width of H α, Li i, and interstellar Na i lines. We also investigate the effect of possible reddening on individual targets and construct the HR diagram of our sample. Using pre-main-sequence evolutionary models, we determine the age of our targets. This analysis hints at ages younger than 50 Myr with mean age 5 ± 3 Myr, masses between 0.75 and 2.10 M⊙, and minimum radii in the range 0.60–3.17 R⊙. Altogether, the results are consistent with expected young stars with larger radii than those of main-sequence stars
On the nature of the candidate T-Tauri star V501 Aurigae
We report new multi-colour photometry and high-resolution spectroscopic
observations of the long-period variable V501 Aur, previously considered to be
a weak-lined T-Tauri star belonging to the Taurus-Auriga star-forming region.
The spectroscopic observations reveal that V501 Aur is a single-lined
spectroscopic binary system with a 68.8-day orbital period, a slightly
eccentric orbit (e ~ 0.03), and a systemic velocity discrepant from the mean of
Taurus-Auriga. The photometry shows quasi-periodic variations on a different,
~55-day timescale that we attribute to rotational modulation by spots. No
eclipses are seen. The visible object is a rapidly rotating (vsini ~ 25 km/s)
early K star, which along with the rotation period implies it must be large (R
> 26.3 Rsun), as suggested also by spectroscopic estimates indicating a low
surface gravity. The parallax from the Gaia mission and other independent
estimates imply a distance much greater than the Taurus-Auriga region,
consistent with the giant interpretation. Taken together, this evidence
together with a re-evaluation of the LiI~6707 and H lines
shows that V501 Aur is not a T-Tauri star, but is instead a field binary with a
giant primary far behind the Taurus-Auriga star-forming region. The large mass
function from the spectroscopic orbit and a comparison with stellar evolution
models suggest the secondary may be an early-type main-sequence star.Comment: 13 pages, 7 figures. Accepted to MNRA
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