381 research outputs found
Separated Fringe Packet Observations with the CHARA Array III. The Very High Eccentricity Binary HR 7345
After an eleven year observing campaign, we present the combined
visual{spectroscopic orbit of the formerly unremarkable bright star HR 7345 (HD
181655, HIP 94981, GJ 754.2). Using the Separated Fringe Packet (SFP) method
with the CHARA Array, we were able to determine a difficult to complete orbital
period of 331.609 +/- 0.004 days. The 11 month period causes the system to be
hidden from interferometric view behind the Sun for 3 years at a time. Due to
the high eccentricity orbit of about 90% of a year, after 2018 January the
periastron phase will not be observable again until late 2021. Hindered by its
extremely high eccentricity of 0.9322 +/- 0.0001, the double-lined
spectroscopic phase of HR 7345 is observable for 15 days. Such a high
eccentricity for HR 7345 places it among the most eccentric systems in catalogs
of both visual and spectroscopic orbits. For this system we determine nearly
identical component masses of 0.941 +/- 0.076 Msun and 0.926 +/- 0.075 Msun as
well as an orbital parallax of 41.08 +/- 0.77 mas.Comment: 20 pages, 3 figures, 4 table
Strong Near-Infrared Emission Interior to the Dust-Sublimation Radius of Young Stellar Objects MWC275 and AB Aur
Using the longest optical-interferometeric baselines currently available, we
have detected strong near-infrared (NIR) emission from inside the
dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our
sub-milli-arcsecond resolution observations unambiguously place the emission
between the dust-destruction radius and the magnetospheric co-rotation radius.
We argue that this new component corresponds to hot gas inside the
dust-sublimation radius, confirming recent claims based on spectrally-resolved
interferometry and dust evaporation front modeling.Comment: 12 pages, 4 figures, Accepted for publication in ApJ
An interferometric study of the post-AGB binary 89 Herculis I Spatially resolving the continuum circumstellar environment at optical and near-IR wavelengths with the VLTI, NPOI, IOTA, PTI, and the CHARA Array
Binary post-AGB stars are interesting laboratories to study both the
evolution of binaries as well as the structure of circumstellar disks. A
multiwavelength high angular resolution study of the prototypical object 89
Herculis is performed with the aim of identifying and locating the different
emission components seen in the SED. A large interferometric data set,
collected over the past decade and covering optical and near-IR wavelengths, is
analyzed with simple geometric models. Combining the interferometric
constraints with the photometry and the optical spectra, we reassess the energy
budget of the post-AGB star and its circumstellar environment. We report the
first (direct) detection of a large (35-40%) optical circumstellar flux
contribution and spatially resolve its emission region. Given this large amount
of reprocessed and/or redistributed optical light, the fitted size of the
emission region is rather compact and fits with(in) the inner rim of the
circumbinary dust disk. This rim dominates our K band data through thermal
emission and is rather compact, emitting significantly already at a radius of
twice the orbital separation. We interpret the circumstellar optical flux as
due to a scattering process, with the scatterers located in the extremely
puffed-up inner rim of the disk and possibly also in a bipolar outflow seen
pole-on. A non-LTE gaseous origin in an inner disk cannot be excluded but is
considered highly unlikely. This direct detection of a significant amount of
circumbinary light at optical wavelengths poses several significant questions
regarding our understanding of both post-AGB binaries and the physics in their
circumbinary disks. Although the identification of the source of
emission/scattering remains inconclusive without further study on this and
similar objects, the implications are manifold.Comment: Accepted for publication in A&A, 16 pages, 15 figure
Residential child and youth care in the Netherlands:Current practices and future perspectives
Residential child and youth care in the Netherlands:Current practices and future perspectives
Pen picture accounts of four young people in the Netherlands’ care system help to focus attention on the needs of young people and their families. This also highlights issues facing the Dutch care system and how it is organised and funded. In one of the world’s most densely populated countries, the child protection and welfare system in the Netherlands focuses on family preservation and community-based interventions. However, the number of young people in out-of-home care facilities has increased over the past decade and a half. The New Act on Care for Children and Young People which came into effect in 2015 has made far-reaching changes to Dutch child and youth care policy, and administrative and financial practices that are now re-located to municipalities
Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties
We present interferometric observations of 7 main-sequence and 3 giant stars
with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA
array. We have directly determined the angular diameters for these objects with
an average precision of 2.3%. We have also computed bolometric fluxes using
available photometry in the visible and infrared wavelengths, as well as
space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos}
parallaxes, we have derived a set of fundamental stellar properties including
linear radius, luminosity and effective temperature. Fitting the latter to
computed isochrone models, we have inferred masses and ages of the stars. The
effective temperatures obtained are in good agreement (at a 3% level) with
nearly-independent temperature estimations from spectroscopy. They validate
recent sixth-order polynomial (B-V)- empirical relations
\citep{Boyajian2012a}, but suggest that a more conservative third-order
solution \citep{vanBelle2009} could adequately describe the
(V-K)- relation for main-sequence stars of spectral type A0 and
later. Finally, we have compared mass values obtained combining surface gravity
with inferred stellar radius (\textit{gravity mass}) and as a result of the
comparison of computed luminosity and temperature values with stellar
evolutionary models (\textit{isochrone mass}). The strong discrepancy between
isochrone and gravity mass obtained for one of the observed stars,
\,Lyr, suggests that determination of the stellar atmosphere parameters
should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Radial Structure in the TW Hya Circumstellar Disk
We present new near-infrared interferometric data from the CHARA array and the Keck Interferometer on the circumstellar disk of the young star, TW Hya, a proposed "transition disk." We use these data, as well as previously published, spatially resolved data at 10 μm and 7 mm, to constrain disk models based on a standard flared disk structure. We find that we can match the interferometry data sets and the overall spectral energy distribution with a three-component model, which combines elements at spatial scales proposed by previous studies: optically thin, emission nearest the star, an inner optically thick ring of emission at roughly 0.5 AU followed by an opacity gap and, finally, an outer optically thick disk starting at ~4 AU. The model demonstrates that the constraints imposed by the spatially resolved data can be met with a physically plausible disk but this requires a disk containing not only an inner gap in the optically thick disk as previously suggested, but also a gap between the inner and outer optically thick disks. Our model is consistent with the suggestion by Calvet et al. of a planet with an orbital radius of a few AU. We discuss the implications of an opacity gap within the optically thick disk
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