High resolution ALMA and HST images of q$^1$ Eri: an asymmetric debris disc with an eccentric Jupiter

Abstract

We present ALMA 1.3 mm and 0.86 mm observations of the nearby (17.34 pc) F9V star q1 Eri (HD 10647, HR 506). This system, with age ∼1.4 Gyr, hosts a ∼2 au radial velocity planet and a debris disc with the highest fractional luminosity of the closest 300 FGK type stars. The ALMA images, with resolution ∼0. 5, reveal a broad (34-134 au) belt of millimeter emission inclined by 76.7±1.0 degrees with maximum brightness at 81.6±0.5 au. The images reveal an asymmetry, with higher flux near the southwest ansa, which is also closer to the star. Scattered light observed with the Hubble Space Telescope is also asymmetric, being more radially extended to the northeast. We fit the millimeter emission with parametric models and place constraints on the disc morphology, radius, width, dust mass, and scale height. We find the southwest ansa asymmetry is best fitted by an extended clump on the inner edge of the disc, consistent with perturbations from a planet with mass 8 𝑀 ⊕ −11 𝑀 Jup at ∼60 au that may have migrated outwards, similar to Neptune in our Solar System. If the measured vertical aspect ratio of ℎ=0.04±0.01 is due to dynamical interactions in the disc, then this requires perturbers with sizes >1200 km. We find tentative evidence for an 0.86 mm excess within 10 au, 70±22 𝜇Jy, that may be due to an inner planetesimal belt. We find no evidence for CO gas, but set an upper bound on the CO gas mass of 4×10 −6 M ⊕ (3 𝜎), consistent with cometary abundances in the Solar System.

Eccentric debris disc morphologies I: exploring the origin of apocentre and pericentre glows in face-on debris discs

“…Our models have a vertical Gaussian density distribution, defined by the vertical aspect ratio, ℎ = 𝐻/𝑟, where 𝐻 is the absolute vertical height of dust at a radius 𝑟 in the disc. This same parameterisation has been applied previously to model sub-mm ALMA observations (see Marino et al 2016Marino et al , 2018Lovell et al 2021), and is consistent with the expected physical distribution of dust above and below the disc mid-plane. It is possible to show that this vertical structure is a natural consequence of the inclination distribution in the disc (see, for example, Matrà et al 2019).…”

“…Since a linearly rising eccentricity with semi-major axis corresponds to the first-order expansion in 𝑒 for the eccentricity for secularly perturbing external bodies this has important implications for interpreting planetary systems. For example, if a significant pericentre glow was measured in sub-mm observations of a debris disc (in the absence of other disc sub-structures, e.g., clumps inside the belt such as in the case of HD10647, see Lovell et al 2021), this could be consistent with (or due directly to) perturbations from an external eccentric body (such as a massive planet orbiting outside the disc). To add to this final point, whilst pericentre glows can be set up in either e=constant or e=rising discs, by comparing the upper and lower plots of Fig.…”

“…Debris discs are collisionally dominated belts of planetesimals that are observed around ∼20% of main sequence stars (Wyatt 2008;Hughes et al 2018). Their morphologies are diverse with many having now been observed with large scale asymmetries inferred as due to mechanisms such as recent planetesimal collisions (e.g., in Beta Pictoris and HD10647, see Matrà et al 2017;Lovell et al 2021), or from having an underlying eccentric distribution of planetesimals (e.g., Fomalhaut, HR4796, HD202628, and HD38206 see MacGregor et al 2013;Olofsson et al 2019;Faramaz et al 2019;Booth et al 2021). Such eccentric distributions can form through interactions between planetesimals and planets over ∼Myr-Gyr timescales (Mustill & Wyatt 2009); thus understanding the structure of asymmetric debris discs is important to correctly interpret the origin of planetesimal belt morphologies.…”