Methods used to detect giant exoplanets can be broadly divided into two
categories: indirect and direct. Indirect methods are more sensitive to planets
with a small orbital period, whereas direct ...detection is more sensitive to
planets orbiting at a large distance from their host star. %, and thus on long
orbital period. This dichotomy makes it difficult to combine the two techniques
on a single target at once. Simultaneous measurements made by direct and
indirect techniques offer the possibility of determining the mass and
luminosity of planets and a method of testing formation models. Here, we aim to
show how long-baseline interferometric observations guided by radial-velocity
can be used in such a way. We observed the recently-discovered giant planet
$\beta$ Pictoris c with GRAVITY, mounted on the Very Large Telescope
Interferometer (VLTI). This study constitutes the first direct confirmation of
a planet discovered through radial velocity. We find that the planet has a
temperature of $T = 1250\pm50$\,K and a dynamical mass of $M =
8.2\pm0.8\,M_{\rm Jup}$. At $18.5\pm2.5$\,Myr, this puts $\beta$ Pic c close to
a 'hot start' track, which is usually associated with formation via disk
instability. Conversely, the planet orbits at a distance of 2.7\,au, which is
too close for disk instability to occur. The low apparent magnitude ($M_{\rm K}
= 14.3 \pm 0.1$) favours a core accretion scenario. We suggest that this
apparent contradiction is a sign of hot core accretion, for example, due to the
mass of the planetary core or the existence of a high-temperature accretion
shock during formation.
Context. Extended circumstellar emission has been detected within a few 100 milli-arcsec around >= 10% of nearby main sequence stars using near-infrared interferometry. Follow-up observations using ...other techniques, should they yield similar results or non-detections, can provide strong constraints on the origin of the emission. They can also reveal the variability of the phenomenon. Aims. We aim to demonstrate the persistence of the phenomenon over the timescale of a few years and to search for variability of our previously detected excesses. Methods. Using Very Large Telescope Interferometer (VLTI)/Precision Integrated Optics Near Infrared ExpeRiment (PIONIER) in H band we have carried out multi-epoch observations of the stars for which a near-infrared excess was previously detected using the same observation technique and instrument. The detection rates and distribution of the excesses from our original survey and the follow-up observations are compared statistically. A search for variability of the excesses in our time series is carried out based on the level of the broadband excesses. Results. In 12 of 16 follow-up observations, an excess is re-detected with a significance of >2 sigma, and in 7 of 16 follow-up observations significant excess (>3 sigma) is re-detected. We statistically demonstrate with very high confidence that the phenomenon persists for the majority of the systems. We also present the first detection of potential variability in two sources. Conclusions. We conclude that the phenomenon responsible for the excesses persists over the timescale of a few years for the majority of the systems. However, we also find that variability intrinsic to a target can cause it to have no significant excess at the time of a specific observation.
Aims. In this paper we model, in a self-consistent way, polarimetric, photometric, spectrophotometric and interferometric observations of the classical Be star \(\zeta\) Tauri. Our primary goal is to ...conduct a critical quantitative test of the global oscillation scenario. Methods. We have carried out detailed three-dimensional, NLTE radiative transfer calculations using the radiative transfer code HDUST. For the input for the code we have used the most up-to-date research on Be stars to include a physically realistic description for the central star and the circumstellar disc. We adopt a rotationally deformed, gravity darkened central star, surrounded by a disc whose unperturbed state is given by a steady-state viscous decretion disc model. We further assume that disc is in vertical hydrostatic equilibrium. Results. By adopting a viscous decretion disc model for \(\zeta\) Tauri and a rigorous solution of the radiative transfer, we have obtained a very good fit of the time-average properties of the disc. This provides strong theoretical evidence that the viscous decretion disc model is the mechanism responsible for disc formation. With the global oscillation model we have successfully fitted spatially resolved VLTI/AMBER observations and the temporal V/R variations of the H\(\alpha\) and Br\(\gamma\) lines. This result convincingly demonstrates that the oscillation pattern in the disc is a one-armed spiral. Possible model shortcomings, as well as suggestions for future improvements, are also discussed.
Although debris discs have been detected around a significant number of
main-sequence stars, only a few of them are known to harbour hot dust in their
inner part where terrestrial planets may have ...formed. Thanks to infrared
interferometric observations, it is possible to obtain a direct measurement of
these regions, which are of prime importance for preparing future exo-Earth
characterisation missions. In this context, we have resolved the exozodiacal
dust disc around Vega with the help of infrared stellar interferometry and
estimated the integrated H-band flux originating from the first few AUs of the
debris disc. Using precise H-band interferometric measurements obtained with
the 3-telescope IOTA/IONIC interferometer (Mount Hopkins, Arizona), thorough
modelling of both interferometric data (squared visibility and closure phase)
and spectral energy distribution was performed to constrain the nature of the
near-infrared excess emission. The most straightforward scenario consists in a
compact dust disc producing a thermal emission that is largely dominated by
small grains located between 0.1 and 0.3 AU from Vega and accounting for 1.23
+/- 0.45% of the near-infrared stellar flux for our best-fit model. This flux
ratio is shown to vary slightly with the geometry of the model used to fit our
interferometric data (variations within +/-0.19%). Initially revealed by K-band
CHARA/FLUOR observations, the presence of hot exozodiacal dust in the vicinity
of Vega is confirmed by our H-band IOTA/IONIC measurements at the 3-sigma
level. Whereas the origin of the dust is still uncertain, its presence and the
possible connection with the outer disc suggest that the Vega system is
currently undergoing major dynamical perturbations.
Aims. In this paper we model, in a self-consistent way, polarimetric,
photometric, spectrophotometric and interferometric observations of the
classical Be star $\zeta$ Tauri. Our primary goal is to ...conduct a critical
quantitative test of the global oscillation scenario. Methods. We have carried
out detailed three-dimensional, NLTE radiative transfer calculations using the
radiative transfer code HDUST. For the input for the code we have used the most
up-to-date research on Be stars to include a physically realistic description
for the central star and the circumstellar disc. We adopt a rotationally
deformed, gravity darkened central star, surrounded by a disc whose unperturbed
state is given by a steady-state viscous decretion disc model. We further
assume that disc is in vertical hydrostatic equilibrium. Results. By adopting a
viscous decretion disc model for $\zeta$ Tauri and a rigorous solution of the
radiative transfer, we have obtained a very good fit of the time-average
properties of the disc. This provides strong theoretical evidence that the
viscous decretion disc model is the mechanism responsible for disc formation.
With the global oscillation model we have successfully fitted spatially
resolved VLTI/AMBER observations and the temporal V/R variations of the
H$\alpha$ and Br$\gamma$ lines. This result convincingly demonstrates that the
oscillation pattern in the disc is a one-armed spiral. Possible model
shortcomings, as well as suggestions for future improvements, are also
discussed.
