Nova shells in 3D. I. A catalog of integral field spectroscopic observations

Classical novae eject material during thermonuclear eruptions on the surface of accreting white dwarfs, forming expanding shells (the so-called nova remnants or nova shells). The physical structure and kinematics of nova shells shed light onto the eruption mechanism and binary interaction. Nova shells are typically characterized using direct imaging and spectroscopy, but their intrinsic 3D structure remains poorly constrained. The aim of this work is to present the first 3D catalog of nova shells based on integral field spectroscopic observations, allowing us to investigate the diversity of their physical structures beyond projection effects. We compiled integral-field spectroscopic observations of 19 nova shells obtained with MUSE at the VLT, complemented by new observations obtained with MEGARA at the GTC and WEAVE at the WHT. We constructed 3D visualizations of the emission lines of interest. The 3D visualizations of nova shells reveal a wide variety of structures, including ellipsoidal or spherical (round) shells, ring-like and bipolar features, and clumpy or irregular components. Many of these structures are not evident in two2D projections alone. Approximately 60% of the sample exhibits predominantly ellipsoidal or spherical shapes, while about 30% shows ring-like structures or is bipolar. Several objects show strong line-dependent morphological differences, with the iii or N ii emission lines tracing distinct kinematic components distinct from those in Hα. Compared with imaging studies, integral field spectroscopic observations reveal a larger fraction of bipolar or toroidal nova shells. Their physical structures differ considerably among different emission lines, highlighting distinct excitation mechanisms and physical properties within the ejecta. The comparison of the expansion velocities of nova shells on the plane of the sky and along the line of sight implies that their intrinsic aspect ratios are low, consistent with the conclusions derived from their projected aspect ratios.