The β Pictoris system: Setting constraints on the planet and the disk structures at mid-IR wavelengths with NEAR

Abstract

Context. β Pictoris is a young nearby system hosting a well-resolved edge-on debris disk, along with at least two exoplanets. It offers key opportunities for carrying out detailed studies of the evolution of young planetary systems and their shaping soon after the end of the planetary formation phase. Aims. We analyzed high-contrast coronagraphic images of this system, obtained in the mid-infrared, taking advantage of the NEAR experiment using the VLT/VISIR instrument, which provides access to adaptive optics, as well as phase coronagraphy. The goal of our analysis is to investigate both the detection of the planet β Pictoris b and of the disk features at mid-IR wavelengths. In addition, by combining several epochs of observation, we expect to constrain the position of the known clumps and improve our knowledge on the dynamics of the disk. Methods. We observed the β Pictoris system over two nights in December 2019 in the 10–12.5 µm coronagraphic filter. To evaluate the planet b flux contribution, we extracted the photometry at the expected position of the planet and compared it to the flux published in the literature. In addition, we used previous data from T-ReCS and VISIR in the mid-IR, updating the star's distance, to study the evolution of the position of the southwest clump that was initially observed in the planetary disk back in 2003. Results. While we did not detect the planet b, we were able to put constraints on the presence of circumplanetary material, ruling out the equivalent of a Saturn-like planetary ring around the planet. The disk presents several noticeable structures, including the known southwest clump. Using a 16-yr baseline, sampled with five epochs of observations, we were able to examine the evolution of the clump. We found that the clump orbits in a Keplerian motion with a semi-major axis of 56.1−0.3+0.4 au. In addition to the known clump, the images clearly show the presence of a second clump on the northeast side of the disk as well as possibly fainter and closer structures that are yet to be confirmed. Furthermore, we found correlations between the CO clumps detected with ALMA and the northeastern and southwestern clumps in the mid-IR images. Conclusions. If the circumplanetary material were located at the Roche radius, the maximum amount of dust determined from the flux upper limit around β Pictoris b would correspond to the mass of an asteroid of 5 km in diameter. Finally, the Keplerian motion of the southwestern clump is possibly indicative of a yet-to-be detected planet or signals the presence of a vortex.

JWST-TST High Contrast: Asymmetries, Dust Populations, and Hints of a Collision in the β Pictoris Disk with NIRCam and MIRI

“…The cat's tail has not been reported before, despite deep HST observations with several instruments (see, e.g., Burrows et al 1995;Golimowski et al 2006;Apai et al 2015;Ballering et al 2016). There is also no evidence for such structure in ALMA data (Dent et al 2014;Matrà et al 2019), nor any of the ground-based mid-infrared observations (e.g., Telesco et al 2005;Li et al 2012;Skaf et al 2023). There may be faint hints of material near this location in the outermost part of the ¢ L -band imaging presented in Milli et al (2014), but only at the edge of the field of view where PSF subtraction residuals make any potential detection highly uncertain.…”

“…The MIRI data are consistent with that, supporting the inference that the apparent major axis PA does vary with wavelength. At least a partial explanation to this can be found in Skaf et al (2023), where they show in their Figure 6 how the best PA varies for the two different sides of the disk. Besides the IR, the gaseous CO disk in Dent et al (2014) was also inclined ∼4°with respect to the dusty disk, observed in the continuum.…”

“…There are some structures, like the SW dust and CO/C gaseous clumps at around 50-60 au, that are only visible in thermal emission, and are therefore only recovered at longer wavelengths, i.e., mid-infrared (Telesco et al 2005) and submillimeter (Dent et al 2014;Cataldi et al 2018). In recent work, Skaf et al (2023) identified several "clumps" in midinfrared images at locations closer than 5″ to the star. They suggested the main clump, which they locate at ∼52-56 au, has moved when comparing observations spanning 16 yr.…”

“…A clump of excess mid-infrared emission detected on the southwest (SW) side of the disk (Telesco et al 2005;Li et al 2012) has been interpreted as potentially due to the production of dust from a massive collision of very large planetesimals (100 km). Moreover, high-contrast observations from the ground presented in Skaf et al (2023) report a complex structure inwards ∼60 au, with different clumps of material. Recent publications argued whether the main clump's position changes over time as if in Keplerian motion around the star (Skaf et al 2023), consistent with the recent collision hypothesis, or is instead stationary (Han et al 2023).…”

“…Moreover, high-contrast observations from the ground presented in Skaf et al (2023) report a complex structure inwards ∼60 au, with different clumps of material. Recent publications argued whether the main clump's position changes over time as if in Keplerian motion around the star (Skaf et al 2023), consistent with the recent collision hypothesis, or is instead stationary (Han et al 2023). Collisions and outgassing events should release gas as well, and indeed ALMA observations resolved a compact clump of gas spatially colocated with the mid-infrared excess clump, detected first in 12 CO (Dent et al 2014) and subsequently in C I (Cataldi et al 2018).…”