Multiple Spiral Arms in the Disk around Intermediate-mass Binary HD 34700A

Abstract

We present the first images of the transition disk around the close binary system HD 34700A in polarized scattered light using the Gemini Planet Imager instrument on Gemini South. The J and H band images reveal multiple spiral-arm structures outside a large (R = 0.49 = 175 au) cavity along with a bluish spiral structure inside the cavity. The cavity wall shows a strong discontinuity and we clearly see significant non-azimuthal polarization U φ consistent with multiple scattering within a disk at an inferred inclination ∼42 • . Radiative transfer modeling along with a new Gaia distance suggest HD 37400A is a young (∼5 Myr) system consisting of two intermediate-mass (∼2 M ) stars surrounded by a transitional disk and not a solar-mass binary with a debris disk as previously classified. Conventional assumptions of the dust-to-gas ratio would rule out a gravitational instability origin to the spirals while hydrodynamical models using the known external companion or a hypothetical massive protoplanet in the cavity both have trouble reproducing the relatively large spiral arm pitch angles (∼ 30 • ) without fine tuning of gas temperature. We explore the possibility that material surrounding a massive protoplanet could explain the rim discontinuity after also considering effects of shadowing by an inner disk. Analysis of archival Hubble Space Telescope data suggests the disk is rotating counterclockwise as expected from the spiral arm structure and revealed a new low-mass companion at 6.45 separation. We include an appendix which sets out clear definitions of Q, U, Q φ , U φ , correcting some confusion and errors in the literature.

Irregular Dust Features around Intermediate-mass Young Stars with GPI: Signs of Youth or Misaligned Disks?

“…During the course of the Gemini-LIGHTS survey we published data on resolved ring structures and other scattered light detections from Herbig Ae/Be stars (Monnier et al 2017), and recently we have also presented spectacular structures in the disk around HD 34700 including a bright ring with many spiral arms (Monnier et al 2019). The observed structures typically span several hundred au.…”

“…Our data reduction follows the process in Monnier et al (2017Monnier et al ( , 2019 using the GPI Data Reduction Pipeline (DRP) version 1.4 routines to convert between file types -raw data files, polarization data cubes (podc), and Stokes data cubes (stokesdc) (Maire et al 2010). We also perform stellar polarization corrections and combine multiple data cubes using original routines written in python to manipulate output files from the GPI DRP.…”

“…Similarly to Monnier et al (2019) we expect effects from instrumental polarization to be non-dominant (with systematics on the order of 1% of total intensity and a few percent for Q φ ) and so we have not taken further steps to remove these effects outside the following. We compared results from the DRP with other methods including U φ minimisation (e.g.…”

“…Flux calibration was performed using standard GPI DRP routines to measure the satellite spot flux, as in Monnier et al (2019). For each object all podc were stacked using the primitives "Accumulate Images" and "Combine 3D data cubes" to create a podc made from the mean of all other cubes without rotating to north to prevent effects from the rotation of the detector with respect to the sky, e.g.…”

Using Data Imputation for Signal Separation in High-contrast Imaging

“…However, forward modeling is currently only optimized for unresolved point sources (Marois et al 2010;Pueyo 2016). For resolved circumstellar disks, forward modeling needs assumptions on both morphology and flux (e.g., space-based: Choquet et al 2016Choquet et al , 2017Choquet et al , 2018ground-based: Follette et al 2017;Esposito et al 2018), which is model-dependent thus likely unable to capture the minute irregularly-shaped structures (e.g., the disks in Avenhaus et al 2018;Monnier et al 2019;Garufi et al 2020).…”