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See detailCharacterization of the low-mass companion around HD 142527 with VLT/SINFONI
Christiaens, Valentin ULg; Casassus, Simon; Absil, Olivier ULg et al

Conference (2016, May 19)

The circumstellar disk of the Herbig Fe star HD 142527 is host to several remarkable features in the context of planetary formation, including a warped inner disk, one of the largest annular gaps, a ... [more ▼]

The circumstellar disk of the Herbig Fe star HD 142527 is host to several remarkable features in the context of planetary formation, including a warped inner disk, one of the largest annular gaps, a prominent dust trap and several spiral arms in its outer disk. A low-mass companion, HD 142527 B, was also found orbiting the primary star at only ~10 au, possibly shaping the inclined inner disk (inclined with respect to the outer disk). This study aims to provide a clarifying answer to the question of the true nature of this companion, which could help explaining its true impact on the peculiar geometry of the disk. We observed the source with VLT/SINFONI in H+K band in pupil-tracking mode. Data were then post-processed with several principal component analysis algorithms based on the principle of Angular Differential Imaging. HD 142527 B is re-detected in most of the H+K spectral channels at a signal-to-noise ratio > 3. This re-detection enables us to extract the first medium-resolution spectrum of a low-mass companion at less than 0.1'' from its central star. The best fit to our spectrum was obtained with a BT-SETTL model spectrum corresponding to a temperature of 3400+-50K and a surface gravity log(g)=2.5+-1.0. Using pre-main sequence tracks, this corresponds to an M3 star with a mass, radius and age of M_B ~0.3 M_Sun, R_B ~ 1.1 R_Sun and 3.6 Myr old, respectively. We also suggest that most of the expected circum-secondary material is at a temperature lower than 1000K, hence not emitting in H and K band, but able to explain the excess measured at L- and M-bands. Based on the new values of radius and mass of the companion, we provide a new estimate for the mass accretion rate on HD 142527 B of ~1% of the accretion rate on the primary, consistent with a non-significant detection in the Brackett-gamma line. This result confirms the efficiency of the pupil-tracking mode implemented on VLT/SINFONI for the spectral characterization of faint companions orbiting very close to their star. [less ▲]

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See detailPluto's atmosphere from stellar occultations in 2012 and 2013
Dias-Oliveira, Alex; Sicardy, Bruno; Lellouch, Emmanuel et al

in Bulletin of the American Astronomical Society (2015, November 01), 47

We present results from two Pluto stellar occultations observed on 18 July 2012 and 04 May 2013, and monitored respectively from five and six sites in South America. Both campaigns involved large ... [more ▼]

We present results from two Pluto stellar occultations observed on 18 July 2012 and 04 May 2013, and monitored respectively from five and six sites in South America. Both campaigns involved large telescopes (including the 8.2-m VLT at ESO/Paranal). The high SNR ratios and multi-chord coverage provide amoung the best Pluto atmospheric profiles ever obtained from the ground.We show that a spherically symmetric, clear (no-haze) and pure N2 atmosphere with a unique temperature profile satisfactorily fits the twelve lightcurves provided by the two events. We find, however, a small but significant increase of pressure of 6% (6-sigma level) between the two dates, with values of 2.16 ± 0.2 and 2.30 ± 0.01 μbar at the reference radius 1275 km, respectively.We provide atmospheric constrains between 1190 km and 1450 km from Pluto's center, and we determine the temperature profile with accuracy of a few km in vertical scale. Our model shows a stratosphere with strong positive gradient between 1190 km (at 36 K, 11 μbar) and r =1215 km (6.0 μbar), where a temperature maximum of 110 K is reached. Above it is a mesosphere with negative thermal gradient of -0.2 K/km up to 1,390 km (0.25 μbar), at which point, the mesosphere connects itself to a more isothermal upper branch at 81 K. This profile provides (assuming no troposphere) a Pluto surface radius of 1190 ± 5 km, consistent with preliminary values obtained by New Horizons. Currently measured CO abundances are too low to explain the negative mesospheric thermal gradient. We explore the possibility of an HCN (recently detected by ALMA) cooling. This model, however, requires largely supersaturated HCN. Zonal winds and vertical compositional variations of the atmosphere are also unable to explain the observed mesospheric trend.These events are the last useful ground-based occultations recorded before the 29 June 2015 occultation observed from Australia and New Zealand, and before the NASA's New Horizons flyby of July 2015. This work can serve as a benchmark in the New Horizons context, enabling comparisons between ground-based and space results concerning Pluto's atmospheric structure and temporal evolution. [less ▲]

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See detailDirect imaging of extra-solar planets in star forming regions. Lessons learned from a false positive around IM Lup.
Mawet, Dimitri; Absil, Olivier ULg; Riaud, Pierre et al

in Astronomy and Astrophysics (2012), 544

Context. Most planet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the ... [more ▼]

Context. Most planet imagers consist of ground-based adaptive optics coronagraphic cameras which are currently limited in contrast, sensitivity and astrometric precision, but advantageously observe in the near-infrared window (1 - 5 µm). Because of these practical limitations, our current observational aim at detecting and characterizing planets puts heavy constraints on target selection, observing strategies, data reduction, and follow-up. Most surveys so far have thus targeted very young systems (1 - 100Myr) to catch the putative remnant thermal radiation of giant planets, which peaks in the near-infrared. They also favor systems in the solar neighborhood (d < 80 pc), which eases angular resolution requirements but also ensures a good knowledge of the distance and proper motion, which are critical to secure the planet status, and enable any subsequent characterization. Aims. Because of their youth, it is very tempting to target the nearby star forming regions, which are typically twice as far as the bulk of objects usually combed for planets by direct imaging. Probing these very interesting reservoirs in practice sets additional constraints that we review in this paper by presenting the planet search that we initiated in 2008 around the disk-bearing T Tauri star IM Lup, which is part of the Lupus star forming region (140-190 pc). Methods. We show and discuss why age determination, the choice of evolutionary model for both the central star and the planet, precise knowledge of the host star proper motion, relative or absolute (between different instruments) astrometric accuracy (including plate scale calibration), and patience are the key ingredients for exoplanet searches around more distant young stars. Results. Unfortunately, most of the time, precision and perseverance are not paying off: we discovered a candidate companion around IM Lup in 2008, which we report here to be a false positive event. We nevertheless review in details the lessons learned from our endeavor, and additionally present the best detection limits ever calculated for IM Lup. We also accessorily report on the successful use of innovative data reduction techniques, such as the damped-LOCI and iterative roll subtraction. [less ▲]

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