The 2020 Eclipse of R Aquarii in the Near-infrared: Mid-eclipse Observations of Disk Distress

Abstract

The Mira in the bright, dusty, symbiotic binary R Aquarii undergoes eclipses of multiyear duration every ∼44 yr by a large, opaque accretion disk. The 2020 eclipse was confirmed by I-band photometry. High-resolution M- and K-band spectra were observed near the midpoint of the eclipse, in 2020 August and September. The 4.5–5.5 μm spectrum during eclipse is a complex blend of disk and Mira features. Continuum emission from the disk region contributes to both the 2.3 μm and 4.6 μm region. The lowest energy vibration-rotation CO lines contain multiple absorption features from ∼780 K gas flowing across the disk away from the Mira. CO fundamental and overtone emission lines are also present. The eccentricity of the orbit results in significant orbital variation in the size of the Roche lobes. At periastron the Roche radius of the secondary is ∼4.0 au, smaller than both the 5 au geometric radius for the disk and estimates for the disk size from models. Fundamental band CO 2–1 emission originates from a thin, eccentric ring with inner radius ∼4.75 au and outer radius ∼6.9 au. The CO emission is identified with regions where the disk has been disrupted near the time of periastron. CO 3–2 fundamental band lines and low-excitation lines in the CO 2–0 and 3–1 overtone bands originate in a Mira-facing spot, 6.3 au from the accretion disk center, near the inner Lagrange point.

Front-row Seat of the Recent R Aqr Periastron Passage: X-Ray Multiepoch Spectral and Spatial Analysis

“…Recent multiwavelength observations (Bujarrabal et al 2018;Teyssier et al 2019;Willson 2020) strongly suggest that the R Aqr WD companion has been approaching or passing through the periastron since late 2018, several years earlier than predicted by the currently available orbit (Willson et al 1981). The dimming of over 2 mag of the optical light curve (V and B magnitudes, normally dominated by Miraʼs 7 mag amplitude variation) shows the signature of powerful recent mass ejection from Mira, resulting in a significant obscuration of the central region of the system, likely caused by a large dust cloud (Sankrit et al 2022) (see however Hinkle et al 2022, where it is suggested that the periastron passage might occur as late as 2024).…”