994 research outputs found
Characterization of exoplanetary systems with the direct imaging technique: towards the first results of SPHERE at the Very Large Telescope
In the year of the 20th anniversary of the discovery of the first extrasolar planet we can count more than 1800 companions found with different techniques. The majority of them are indirect methods that infer the presence of an orbiting body by observing the parent star (radial velocity, transits, astrometry). In this work we explore the technique that permits to directly observe planets and retrieve their spectra, under the conditions that they are bright and far enough from their host star.
Direct imaging is a new technique became possible thanks to a new generation of extreme adaptive optics instruments mounted on 8m class telescopes. On the Very Large Telescope two instruments dedicated to the research for exoplanets with direct imaging are now operative: NACO and SPHERE.
This thesis will describe the development and results of SPHERE from its predecessor NACO to its integration in laboratory and the final on sky results.
Chapter 1 gives a presentation of the exoplanet research, the formation mechanisms, and the characterization of planet atmospheres. Chapter 2 gives a general frame of the two instruments used for the results presented in this thesis: NACO and SPHERE. In Chapter 3 I describe an example of a false positive in the direct imaging technique, found during the survey NACO-Large Program. This work have been published in Zurlo et al. 2013. In Chapter 4 I present the performance of SPHERE, in particular of the subsystems IRDIS and IFS, deeply tested in the laboratory before the shipping to Paranal. This work has been published in Zurlo et al. 2014. Chapter 5 presents a work done to find special targets for the NIRSUR survey, these object are radial velocity long period planets which are observable with SPHERE. In Chapter 6 I present one of the first on sky result, the observations and analysis of the multi-planetary system HR\,8799. In Chapter 7 I give the conclusions and future prospects
The ALMA Early Science View of FUor/EXor objects. IV. Misaligned Outflows in the Complex Star-forming Environment of V1647 Ori and McNeil's Nebula
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations
of the star-forming environment surrounding V1647 Ori, an outbursting FUor/EXor
pre-MS star. Dust continuum and the (J = 2 - 1) CO, CO, CO
molecular emission lines were observed to characterize the V1647 Ori
circumstellar disc and any large scale molecular features present. We detect
continuum emission from the circumstellar disc and determine a radius r = 40
au, inclination i = 17 and total disc mass of
M of ~0.1 M. We do not identify any disc structures
associated with nearby companions, massive planets or fragmentation. The
molecular cloud environment surrounding V1647 Ori is both structured and
complex. We confirm the presence of an excavated cavity north of V1647 Ori and
have identified dense material at the base of the optical reflection nebula
(McNeil's Nebula) that is actively shaping its surrounding environment. Two
distinct outflows have been detected with dynamical ages of ~11,700 and 17,200
years. These outflows are misaligned suggesting disc precession over ~5500
years as a result of anisotropic accretion events is responsible. The
collimated outflows exhibit velocities of ~2 km s, similar in velocity
to that of other FUor objects presented in this series but significantly slower
than previous observations and model predictions. The V1647 Ori system is
seemingly connected by an "arm" of material to a large unresolved structure
located ~20 to the west. The complex environment surrounding V1647 Ori
suggests it is in the early stages of star formation which may relate to its
classification as both an FUor and EXor type object.Comment: 18 pages, 14 figures, 4 tables; accepted for publication in MNRA
The ALMA Early Science View of FUor/EXor Objects - V. Continuum Disc Masses and Sizes
Low-mass stars build a significant fraction of their total mass during short outbursts of enhanced accretion known as FUor and EXor outbursts. FUor objects are characterized by a sudden brightening of ∼5 mag at visible wavelengths within 1 yr and remain bright for decades. EXor objects have lower amplitude outbursts on shorter time-scales. Here we discuss a 1.3 mm Atacama Large Millimeter/submillimeter Array (ALMA) mini-survey of eight outbursting sources (three FUors, four EXors, and the borderline object V1647 Ori) in the Orion Molecular Cloud. While previous papers in this series discuss the remarkable molecular outflows observed in the three FUor objects and V1647 Ori, here we focus on the continuum data and the differences and similarities between the FUor and EXor populations. We find that FUor discs are significantly more massive (∼80–600 MJup) than the EXor objects (∼0.5–40 MJup). We also report that the EXor sources lack the prominent outflows seen in the FUor population. Even though our sample is small, the large differences in disc masses and outflow activity suggest that the two types of objects represent different evolutionary stages. The FUor sources seem to be rather compact (Rc \u3c 20–40 au) and to have a smaller characteristic radius for a given disc mass when compared to T Tauri stars. V1118 Ori, the only known close binary system in our sample, is shown to host a disc around each one of the stellar components. The disc around HBC 494 is asymmetric, hinting at a structure in the outer disc or the presence of a second disc
Detection of Sharp Symmetric Features in the Circumbinary Disk Around AK Sco
The Search for Planets Orbiting Two Stars (SPOTS) survey aims to study the
formation and distribution of planets in binary systems by detecting and
characterizing circumbinary planets and their formation environments through
direct imaging. With the SPHERE Extreme Adaptive Optics instrument, a good
contrast can be achieved even at small (<300 mas) separations from bright
stars, which enables studies of planets and disks in a separation range that
was previously inaccessible. Here, we report the discovery of resolved
scattered light emission from the circumbinary disk around the well-studied
young double star AK Sco, at projected separations in the ~13--40 AU range. The
sharp morphology of the imaged feature is surprising, given the smooth
appearance of the disk in its spectral energy distribution. We show that the
observed morphology can be represented either as a highly eccentric ring around
AK Sco, or as two separate spiral arms in the disk, wound in opposite
directions. The relative merits of these interpretations are discussed, as well
as whether these features may have been caused by one or several circumbinary
planets interacting with the disk.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letters. Minor
(proof-level) corrections implemented in this versio
Near-IR observations of the young star [BHB2007]-1: A sub-stellar companion opening the gap in the disk
The presence of planets or sub-stellar objects still embedded in their native
protoplanetary disks is indirectly suggested by disk sub-structures like gaps,
cavities, and spirals. However, these companions are rarely detected. We
present VLT/NACO high-contrast images in , , , and band
of the young star [BHB2007]-1 probing the inclined disk in scattered light and
revealing the probable presence of a companion. The point source is detected in
the band in spatial correspondence with complementary VLA
observations. This object is constrained to have a mass in the range of 37-47
M and is located at 50 au from the central star, inside the 70 au-large
disk cavity recently imaged by ALMA, that is absent from our NACO data (down to
20 au). This mass range is compatible with the upper end derived from the size
of the ALMA cavity. The NIR disk brightness is highly asymmetric around the
minor axis, with the southern side 5.5 times brighter than the northern side.
The constant amount of asymmetry across all wavelengths suggests that it is due
to a shadow cast by a misaligned inner disk. The massive companion that we
detect could, in principle, explain the possible disk misalignment, as well as
the different cavity sizes inferred by the NACO and ALMA observations. The
confirmation and characterization of the companion is entrusted to future
observations.Comment: 9 pages, 5 figures, 3 tables. Accepted for publication on Ap
Radio-continuum decrements associated to shadowing from the central warp in transition disc DoAr44
Warps have often been used to explain disc properties, but well characterised
examples are important due to their role in disc evolution. Scattered light
images of discs with central gaps have revealed sharp warps, such that the
outer rings are shadowed by tilted inner discs. The near-IR intensity drops
along the ring around TTauri star DoAr44 have been interpreted in terms of a
central warp. We report new ALMA observations of DoAr44 in the continuum at 230
GHz and 350 GHz (at ~10 au), along with a new epoch of SPHERE/IRDIS
differential polarised imaging taken during excellent weather conditions. The
ALMA observations resolve the ring and confirm the decrements proposed from
deconvolution of coarse 336 GHz data. The scattered light image constrains the
dips, which correspond to a misaligned inner disc with a relative inclination
= 21.4 deg. The SPHERE intensity profile shows a
morphological change compared to a previous epoch that may be interpreted as a
variable orientation of the inner disc, from ~30 deg to ~20 deg.
The intensity dips probably correspond to temperature decrements, as their
mm-spectral index, ~2.0 0.1, is indicative
of optically thick emission. The azimuth of the two temperature decrements are
leading clockwise relative to the IR-dips, by = 14.95 deg and =
7.92 deg. For a retrograde disc, such shifts are expected from a thermal lag
and imply gas surface densities of = 117 10 g/cm and
= 48 10 g/cm. A lopsided disc, with contrast ratio
=2.4 0.5, is also consistent with the large continuum crescent.Comment: accepted in MNRA
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