References of "Di Folco, Emmanuel"
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See detailA near-infrared interferometric survey of debris disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR
Absil, Olivier ULg; Defrère, Denis; Coudé du Foresto, Vincent et al

in Astronomy and Astrophysics (2013), 555

Context. Dust is expected to be ubiquitous in extrasolar planetary systems due to the dynamical activity of minor bodies. Inner dust populations are, however, still poorly known due to the high contrast ... [more ▼]

Context. Dust is expected to be ubiquitous in extrasolar planetary systems due to the dynamical activity of minor bodies. Inner dust populations are, however, still poorly known due to the high contrast and small angular separation with respect to their host star. Yet, a proper characterisation of exozodiacal dust is mandatory for the design of future Earth-like planet imaging missions. Aims. We aim to determine the level of near-infrared exozodiacal dust emission around a sample of 42 nearby main sequence stars with spectral types ranging from A to K, and to investigate its correlation with various stellar parameters and with the presence of cold dust belts. Methods. We use high-precision K-band visibilities obtained with the FLUOR interferometer on the shortest baseline of the CHARA array. The calibrated visibilities are compared with the expected visibility of the stellar photosphere to assess the presence of an additional, fully resolved circumstellar emission source. Results. Near-infrared circumstellar emission amounting to about 1% of the stellar flux is detected around 13 of our 42 target stars. Follow-up observations showed that one of them (eps Cep) is associated with a stellar companion, while another one was detected around what turned out to be a giant star (kap CrB). The remaining 11 excesses found around single main sequence stars are most probably due to the presence of hot circumstellar dust, yielding an overall occurrence rate of 28+8-6% for our (biased) sample. We show that the occurrence rate of bright exozodiacal discs correlates with spectral type, K-band excesses being more frequent around A-type stars. It also correlates with the presence of detectable far-infrared excess emission in the case of solar-type stars. Conclusions. This study provides new insights regarding the phenomenon of bright exozodiacal disc, showing that hot dust populations are probably linked to outer dust reservoirs in the case of solar-type stars. In the case of A-type stars, no clear conclusion can be made regarding the origin of the detected near-infrared excesses. [less ▲]

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See detailAladdin nulling instrument
Barillot, Marc; Coudé Du Foresto, Vincent; Surdej, Jean ULg et al

in Spinoglio, L.; Epchtein, N. (Eds.) 3rd ARENA Conference: An Astronomical Observatory at CONCORDIA (Dome C, Antarctica) (2010)

The ALADDIN project aims at detecting warm dust populations around nearby main sequence stars. In order to achieve the significantly improved sensitivity with respect to existing instruments, the ... [more ▼]

The ALADDIN project aims at detecting warm dust populations around nearby main sequence stars. In order to achieve the significantly improved sensitivity with respect to existing instruments, the architecture of the system is focused and optimised for the mission: ALADDIN implements the nulling interferometry technique at the focal plane of a 2-telescope interferometer mounted on a rotating structural beam. Concerning the beam combining nulling instrument, the ALADDIN design is inherited from a Definition Study of the VLTI/GENIE instrument. In this paper, we demonstrate how the ALADDIN instrument preliminary definition can be made simpler and more representative of a space instrument than GENIE thanks to both the outstanding atmospheric properties of Dome C and the dedicated architecture of the system. Finally, we discuss the compatibility of the instrument with the Antarctic environment and constraints, and underline the experimental and industrial know-how learnt from the MAII and PERSEE nulling breadboards in which our Team is also involved. [less ▲]

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See detailAn Interferometric Study of the Fomalhaut Inner Debris Disk. I. Near-Infrared Detection of Hot Dust with VLTI/VINCI
Absil, Olivier ULg; Mennesson, Bertrand; Le Bouquin, Jean-Baptiste et al

in Astrophysical Journal (2009), 704

The innermost parts of dusty debris disks around main-sequence stars are currently poorly known due to the high contrast and small angular separation with their parent stars. Using near-infrared ... [more ▼]

The innermost parts of dusty debris disks around main-sequence stars are currently poorly known due to the high contrast and small angular separation with their parent stars. Using near-infrared interferometry, we aim to detect the signature of hot dust around the nearby A4 V star Fomalhaut, which has already been suggested to harbor a warm dust population in addition to a cold dust ring located at about 140 AU. Archival data obtained with the VINCI instrument at the VLTI are used to study the fringe visibility of the Fomalhaut system at projected baseline lengths ranging from 4 m to 140 m in the K band. A significant visibility deficit is observed at short baselines with respect to the expected visibility of the sole stellar photosphere. This is interpreted as the signature of resolved circumstellar emission, producing a relative flux of 0.88% ± 0.12% with respect to the stellar photosphere. While our interferometric data cannot directly constrain the morphology of the excess emission source, complementary data from the literature allow us to discard an off-axis point-like object as the source of circumstellar emission. We argue that the thermal emission from hot dusty grains located within 6 AU from Fomalhaut is the most plausible explanation for the detected excess. Our study also provides a revised limb-darkened diameter for Fomalhaut (theta_LD = 2.223 ± 0.022 mas), taking into account the effect of the resolved circumstellar emission. Based on observations made with ESO Telescopes at the Paranal Observatory (public VINCI commissioning data). [less ▲]

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See detailHigh dynamic range interferometric observations of exozodiacal discs: performance comparison between ground, space, and Antarctica
Absil, Olivier ULg; Defrere, Denis; Coudé du Foresto, Vincent et al

in Schöller, Markus; Danchi, William; Delplancke, Françoise (Eds.) Optical and Infrared Interferometry (2008, July 01)

The possible presence of large amounts of exozodiacal dust around nearby main sequence stars represents a threat to the detection and characterisation of Earth-like extrasolar planets with future infrared ... [more ▼]

The possible presence of large amounts of exozodiacal dust around nearby main sequence stars represents a threat to the detection and characterisation of Earth-like extrasolar planets with future infrared space interferometers such as DARWIN or TPF. In this paper, we first review the current detection capabilities of ground-based infrared interferometers such as CHARA/FLUOR and the detections of hot dust that have been obtained so far around a few main sequence stars. With the help of realistic instrumental simulations, we then discuss the relative merits of various ground-based sites (temperate and Antarctic) versus space-based observatories for the detection of exozodiacal discs down to a few zodi by interferometric nulling as a preparation to future life-finding missions. In particular, we discuss the performance of four proposed nulling interferometers: GENIE, ALADDIN, PEGASE and FKSI. An optimised strategy for the characterisation of candidate DARWIN/TPF targets is finally proposed. [less ▲]

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See detailA near-infrared interferometric survey of debris disk stars. I. Probing the hot dust content around eps Eridani and tau Ceti with CHARA/FLUOR
Di Folco, Emmanuel; Absil, Olivier ULg; Augereau, J.-C. et al

in Astronomy and Astrophysics (2007), 475

Context: The quest for hot dust in the central region of debris disks requires high resolution and high dynamic range imaging. Near-infrared interferometry is a powerful means to directly detect faint ... [more ▼]

Context: The quest for hot dust in the central region of debris disks requires high resolution and high dynamic range imaging. Near-infrared interferometry is a powerful means to directly detect faint emission from hot grains. Aims: We probed the first 3 AU around tau Ceti and eps Eridani with the CHARA array (Mt Wilson, USA) in order to gauge the 2 mum excess flux emanating from possible hot dust grains in the debris disks and to also resolve the stellar photospheres. Methods: High precision visibility amplitude measurements were performed with the FLUOR single mode fiber instrument and telescope pairs on baselines ranging from 22 to 241 m of projected length. The short baseline observations allow us to disentangle the contribution of an extended structure from the photospheric emission, while the long baselines constrain the stellar diameter. Results: We have detected a resolved emission around tau Cet, corresponding to a spatially integrated, fractional excess flux of 0.98±0.21 × 10[SUP]-2[/SUP] with respect to the photospheric flux in the K'-band. Around eps Eri, our measurements can exclude a fractional excess of greater than 0.6× 10[SUP]-2[/SUP] (3sigma). We interpret the photometric excess around tau Cet as a possible signature of hot grains in the inner debris disk and demonstrate that a faint, physical or background, companion can be safely excluded. In addition, we measured both stellar angular diameters with an unprecedented accuracy: Theta_LD(tau Cet)= 2.015 ± 0.011 mas and Theta_LD(eps Eri)=2.126 ± 0.014 mas. [less ▲]

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See detailDetection of the inner-debris disk of Vega with CHARA/FLUOR
Absil, Olivier ULg; Di Folco, Emmanuel; Mérand, Antoine et al

in Monnier, John; Schöller, Markus; Danchi, Willian (Eds.) Advances in Stellar Interferometry (2006, July 01)

Using the FLUOR beam-combiner installed at the CHARA Array (Mt. Wilson, CA), we have obtained highprecision visibility measurements of Vega, one of the prototypic debris-disk stars, known to be surrounded ... [more ▼]

Using the FLUOR beam-combiner installed at the CHARA Array (Mt. Wilson, CA), we have obtained highprecision visibility measurements of Vega, one of the prototypic debris-disk stars, known to be surrounded by a large amount of cold dust in a ring-like structure at 80-100 AU. The combination of short and long baselines has allowed us to separately resolve the stellar photosphere and the close environment of the star (less than 8 AU). Our observations show a significant deficit in square visibility at short baselines with respect to the expected visibility of a simple UD stellar model (DeltaV2 equal or equivalent to 2%), suggesting the presence of an extended source of emission around Vega. The sparse (u, v) plane coverage does not allow the discrimination between a point source and an extended circumstellar emission as the source of the extended emission. However, we show that the presence of a point-like source within the FLUOR field-of-view (1" in radius, i.e., 7.8 AU at the distance of Vega) is highly unlikely. The excess emission is most likely due to the presence of hot circumstellar dust in the inner part of Vega's debris disk, with a flux ratio of 1.29 plus or minus 0.19% between the integrated dust emission and the stellar photosphere. Complementing this result with archival photometric data in the near- and mid-infrared and taking into account a realistic photospheric model for the rapidly rotating Vega, we derive the expected physical properties of the circumstellar dust by modelling its Spectral Energy Distribution. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations. [less ▲]

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See detailHot Circumstellar Material around Vega
Absil, Olivier ULg; Di Folco, Emmanuel; Mérand, Antoine et al

in Coudé du Foresto, Vincent; Rouan, Daniel; Rousset, Gérard (Eds.) Visions for Infrared Astronomy (2006, March)

Using the FLUOR beam-combiner at the CHARA Array, we have obtained highprecision visibility measurements of Vega, a prototypic debris-disk star. The combination of long and short baselines has allowed us ... [more ▼]

Using the FLUOR beam-combiner at the CHARA Array, we have obtained highprecision visibility measurements of Vega, a prototypic debris-disk star. The combination of long and short baselines has allowed us to separately resolve the stellar photosphere and the close environment of the star (< 8 AU). Our observations show a significant deficit in square visibility at short baselines with respect to the expected visibility of a simple uniform disk stellar model, suggesting the presence of an extended source around Vega. We propose that the excess emission is most likely due to the presence of hot circumstellar dust in the inner part of Vega's debris disk, with a flux ratio of 1.29 ± 0.19% between the integrated dust emission and the stellar photosphere. Using this information together with archival photometric measurements in the nearand mid-infrared, we derive the expected physical properties of the circumstellar dust by modelling its infrared Spectral Energy Distribution. The inferred properties suggest that the Vega system could be currently undergoing major dynamical perturbations. [less ▲]

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