Improving Planet Detection with Disk Modeling: Keck/NIRC2 Imaging of the HD 34282 Single-armed Protoplanetary Disk

Formed in protoplanetary disks around young stars, giant planets can leave observational features such as spirals and gaps in their natal disks through planet–disk interactions. Although such features can indicate the existence of giant planets, protoplanetary disk signals can overwhelm the innate luminosity of planets. Therefore, in order to image planets that are embedded in disks, it is necessary to remove the contamination from the disks to reveal the planets possibly hiding within their natal environments. We observe and directly model the detected disk in the Keck/NIRC2 vortex coronagraph L′-band observations of the single-armed protoplanetary disk around HD 34282. Despite a nondetection of companions for HD 34282, this direct disk modeling improves planet detection sensitivity by up to a factor of 2 in flux ratio and ∼10 M Jupiter in mass. This suggests that performing disk modeling can improve directly imaged planet detection limits in systems with visible scattered light disks, and can help to better constrain the occurrence rates of self-luminous planets in these systems.

Demographics of Exoplanets in Binaries. I. Architecture of S-type Planetary Systems Revealed by the Radial-velocity Sample

Although the sample of exoplanets in binaries has been greatly expanded, the sample heterogeneity and observational bias are obstacles toward a clear figure of exoplanet demographics in the binary environment. To overcome the obstacles, we conduct a statistical study that focuses on S-type (circumstellar) planetary systems detected by the radial-velocity (RV) method. We try to account for observational biases by estimating, from available RV data, planet detection efficiencies for each individual system. Our main results are as follows. (1) Single (resp. multiple) planetary systems are mostly found in close (wide) binaries with separation a B < (>) ∼ 100–300 au. (2) In binaries, single and multiple-planet systems are similar in 1D distributions of mass and period as well as eccentricity (in contrast to the “eccentricity dichotomy” found in single star systems) but different in the 2D period-mass diagram. Specifically, there is a rectangular-shaped gap in the period-mass diagram of single-planet systems but not for multiples. This gap also depends on binary separation and is more prominent in close binaries. (3) There is a rising upper envelope in the period-mass diagram for planets in wide binaries as well as in single stars but not in close binaries. More specifically, there is a population of massive short-period planets in close binaries but almost absent in wide binaries or single stars. We suggest that enhanced planetary migration, collision and/or ejection in close binaries could be the potential underlying explanation for these three features.

Matched filtering with non-Gaussian noise for planet transit detections

We develop a method for planet detection in transit data, which is based on the Matched Filter technique, combined with the Gaussianization of the noise outliers. The method is based on Fourier transforms and is as fast as the existing methods for planet searches. The Gaussinized Matched Filter (GMF) method significantly outperforms the standard baseline methods in terms of the false positive rate, enabling planet detections at up to 30% lower transit amplitudes. Moreover, the method extracts all the main planet transit parameters, amplitude, period, phase, and duration. By comparison to the state of the art Gaussian Process methods on both simulations and real data we show that all the transit parameters are determined with an optimal accuracy (no bias and minimum variance), meaning that the GMF method can be used both for the initial planet detection and the follow-up planet parameter analysis.

The HARPS search for southern extra-solar planets – XLV. Two Neptune mass planets orbiting HD 13808: a study of stellar activity modelling’s impact on planet detection

ABSTRACT We present a comprehensive analysis of 10 yr of HARPS radial velocities (RVs) of the K2V dwarf star HD 13808, which has previously been reported to host two unconfirmed planet candidates. We use the state-of-the-art nested sampling algorithm PolyChord to compare a wide variety of stellar activity models, including simple models exploiting linear correlations between RVs and stellar activity indicators, harmonic models for the activity signals, and a more sophisticated Gaussian process regression model. We show that the use of overly simplistic stellar activity models that are not well-motivated physically can lead to spurious ‘detections’ of planetary signals that are almost certainly not real. We also reveal some difficulties inherent in parameter and model inference in cases where multiple planetary signals may be present. Our study thus underlines the importance both of exploring a variety of competing models and of understanding the limitations and precision settings of one’s sampling algorithm. We also show that at least in the case of HD 13808, we always arrive at consistent conclusions about two particular signals present in the RV, regardless of the stellar activity model we adopt; these two signals correspond to the previously reported though unconfirmed planet candidate signals. Given the robustness and precision with which we can characterize these two signals, we deem them secure planet detections. In particular, we find two planets orbiting HD 13808 at distances of 0.11, 0.26 au with periods of 14.2, 53.8 d, and minimum masses of 11, 10 M⊕.

The effect of late gas disks on the late stages of planet formation

&lt;p&gt;The external supply of gas to planetary atmospheres may be important to set their final compositions. In this talk, I will summarize recent works that quantified in an exoplanetary context, how much gas can be delivered to planets from late gas disks, which appear to be rather ubiquitous around main-sequence stars with bright planetesimal belts. This new gas component is indeed found to be present for tens and sometimes hundreds of millions of years around main-sequence stars. The gas is thought to be released from planetesimals when they collide together in their parent belt, which creates a gas disk (made of volatiles) that can viscously spread further in the system and encounter the already formed planets that can capture this gas, which will affect the primordial atmospheres of these planets. Kral et al. (2020) show that this very late accretion onto planets is very efficient and may allow capturing large quantities of carbon and oxygen (and potentially some nitrogen and hydrogen) leading to new atmospheric masses onto capturing terrestrial planets between that of the Earth's atmosphere to planets with massive atmospheres with sub-Neptune-like pressures. New secondary atmospheres with high metallicities will be created on terrestrial planets bathing in these late gas disks, resetting their primordial compositions inherited from the protoplanetary disk phase, and providing a new birth to planets that lost their atmospheres to photoevaporation or giant impacts. This volatile delivery for tens of Myr may also be favourable to the development of the first bricks of life. It will also affect the metallicity and C/O ratio of giant planets accreting late gas, which is an effect that may be observable in the close future. This very efficient accretion opens the way to a new planet detection method (for planets down to Earth masses at a few au from their stars) that I will present in this talk.&lt;/p&gt;