An Imaging Survey for Extrasolar Planets around 45 Close, Young Stars with the Simultaneous Differential Imager at the Very Large Telescope and MMT

et al. 2016

A&A

Context. In recent years there have been many attempts to characterize the occurrence and distribution of stellar, brown dwarf (BD), and planetary-mass companions to solar-type stars with the aim of constraining formation mechanisms. From radial velocity observations a dearth of companions with masses between 10-40 M Jupiter has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. Aims. We present a model for the substellar companion mass function (CMF). This model consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the radial velocity measured CMF for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program (NaCo-LP) and the complementary archive datasets, which probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. Methods. We developed a Monte Carlo simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions (mass, semimajor axis, eccentricity, and inclination). Comparing the predictions with the results of the observations, we calculate the likelihood of different models and which models can be ruled out. Results. Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius ( 100 AU) is introduced for the planet separation distribution. Some regions of parameter space can be excluded by the observations. Conclusions. We conclude that the results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 M Jupiter , in agreement with radial velocity measurements. In this picture the dearth of objects in this mass range would naturally arise from the shape of the mass distribution, without the introduction of any distinct formation mechanism for BDs. This kind of model for the CMF allows us to determine the probability for a substellar companion as a function of mass to have formed in a disk or from protostellar core fragmentation, as such mechanisms overlap in this mass range.

“…These constraints on the planet population are consistent with previous survey analyses (Biller et al 2007;Nielsen & Close 2010;Chauvin et al 2010).…”

Section: Discussionsupporting

confidence: 90%

Section: Introductionmentioning

confidence: 99%

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

Reggiani

Meyer

et al. 2016

A&A

“…(b) They inferred the planet population from boundaries in a planet mass-semi major axis grid considering a disk instability model. (c) They performed their analysis using results from surveys of Masciadri et al (2005), Biller et al (2007), and Lafrenière et al (2007). (d) They inferred the planet population from power law distributions with different coefficients of m and a that were used in Cumming et al (2008).…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, numerous large DI surveys to detect giant planet companions have reported null-detections (Masciadri et al 2005;Biller et al 2007;Lafrenière et al 2007;Ehrenreich et al 2010;Chauvin et al 2010;Janson et al 2011;Delorme et al 2012), but this allowed set upper limits to the occurrence of giant planets. Table 1 reports the statistical results of several DI surveys as a function of the sample, separation and mass ranges, and planet distribution.…”

Section: Introductionmentioning

confidence: 99%

A survey of young, nearby, and dusty stars conducted to understand the formation of wide-orbit giant planets

Rameau

Lagrange

et al. 2013

A&A

106

148

Context. Over the past decade, direct imaging has confirmed the existence of substellar companions on wide orbits from their parent stars. To understand the formation and evolution mechanisms of these companions, their individual as well as the full population properties must be characterized. Aims. We aim at detecting giant planet and/or brown dwarf companions around young, nearby, and dusty stars. Our goal is also to provide statistics on the population of giant planets at wide-orbits and discuss planet formation models. Methods. We report the results of a deep survey of 59 stars, members of young stellar associations. The observations were conducted with the ground-based adaptive optics system VLT/NaCo at L -band (3.8 μm). We used angular differential imaging to reach the best detection performances down to the planetary mass regime. A statistical analysis of about 60% of the young and southern A-F stars closer than 65 pc allowed us to derive the fraction of giant planets on wide orbits. We used gravitational instability models and planet population synthesis models following the core-accretion scenario to discuss the occurrence of these companions. Results. We resolve and characterize new visual binaries and do not detect any new substellar companion. The survey's median detection performance reaches contrasts of 10 mag at 0.5 and 11.5 mag at 1.0 . We find the occurrence of planets to be between 10.8 and 24.8% at 68% confidence level assuming a uniform distribution of planets in the interval [1, 13] M J and [1, 1000] AU. Considering the predictions of planetary formation models, we set important constraints on the occurrence of massive planets and brown dwarf companions that would have formed by gravitational instability. We show that this mechanism favors the formation of rather massive clumps (M clump > 30 M J ) at wide (a > 40 AU) orbits, which may evolve dynamically and/or fragment. For the population of close-in giant planets that would have formed by core accretion (without considering any planet -planet scattering), our survey marginally explores physical separations (≤20 AU) and cannot constrain this population. We will have to wait for the next generation of planet finders to start exploring that population, and even for the extremely large telescopes for a more complete overlap with other planet-hunting techniques.

“…The signal of the companion will thus be partially preserved after the subtraction. SDI was first used on the Canada France Hawaii Telescope (CFHT) with the TRIDENT camera (Marois et al 2000(Marois et al , 2003a, with NaCo on the Very Large Telescope (VLT/NaCo; Lenzen et al 2003;Rousset et al 2003) and with the Multiple Mirror Telescope (MMT) A&A 581, A80 (2015) by Close et al (2005) and Biller et al (2007). Recently, Close et al (2014) confirmed a close-in companion around HD 142527 with SDI with MagAO, based on a detection of the Hα emission, not a molecular absorption.…”

Section: Introductionmentioning

confidence: 99%

Detection limits with spectral differential imaging data

Rameau

Lagrange

et al. 2015

A&A

Context. Direct imaging of exoplanets is polluted by speckle noise that severely limits the achievable contrast. Angular and spectral differential imaging have been proposed to make use of the temporal and chromatic properties of the speckles. Both modes, associated with extreme adaptive-optics and coronagraphy, are at the core of the new generation of planet imagers SPHERE and GPI. Aims. We aim to illustrate and characterize the impact of the SDI and SDI+ADI (ASDI) data reduction on the detection of giant planets. We also propose an unbiased method to derive the detection limits from SDI/ASDI data. Methods. Observations of AB Dor B and β Pictoris made with VLT/NaCo were used to simulate and quantify the effects of SDI and ASDI. The novel method is compared to the traditional injection of artificial point sources.Results. The SDI reduction process creates a typical radial positive-negative pattern of any point-source. Its characteristics and its selfsubtraction depend on the separation, but also on the spectral properties of the object. This work demonstrates that the self-subtraction cannot be reduced to a simple geometric effect. As a consequence, the detection performances of SDI observations cannot be expressed as a contrast in magnitude with the central star without the knowledge of the spectral properties of detectable companions. In addition, the residual noise cannot be converted into contrast and physical characteristics (mass, temperature) by standard calibration of flux losses. The proposed method takes the SDI bias into account to derive detection limits without the cost of massively injecting artificial sources into the data. Finally, the sensitivity of ASDI observations can be measured only with a control parameter on the algorithms that controls the minimum rotation that is necessary to build the reference image.