Angular Expansion of Nova Shells (2002.06749v2)

Abstract: Nova shells can provide us with important information on their distance, their interactions with the circumstellar and interstellar media, and the evolution in morphology of the ejecta. We have obtained narrow-band images of a sample of five nova shells, namely DQHer, FHSer, TAur, V476Cyg, and V533Her, with ages in the range from 50 to 130 years. These images have been compared with suitable available archival images to derive their angular expansion rates. We find that all the nova shells in our sample are still in the free expansion phase, which can be expected, as the mass of the ejecta is 7-45 times larger than the mass of the swept-up circumstellar medium. The nova shells will keep expanding freely for time periods up to a few hundred years, reducing their time dispersal into the interstellar medium.

• The paper determines that all five studied nova shells continue in a free expansion phase, validated by narrow-band imaging and spectroscopic data.
• It quantifies angular expansion rates, with DQ Her at approximately 0.188 arcseconds per year, aligning observed rates with historical records.
• The findings imply minimal ISM interaction, offering fresh insights into nova ejecta dynamics and their long-term impact on interstellar material.

Angular Expansion of Nova Shells

The paper "Angular Expansion of Nova Shells" examines the angular expansion of a sample of five nova shells: DQ Her, FH Ser, T Aur, V476 Cyg, and V533 Her. The research focuses on understanding the expansion dynamics and morphological evolution of these nova remnants by employing narrow-band imaging techniques across different epochs. This empirical investigation reveals insights into their free expansion phases, the interaction with the interstellar medium (ISM), and subsequent implications on nova shell dispersal.

Main Findings

1. Sample and Methodology: The paper encompasses five nova shells aged between 50 and 130 years, leveraging narrow-band images and historical datasets to draw comparative analyses. The key metric evaluated is the angular expansion rate, which serves as a proxy for understanding the kinematic development of the shells.
2. Free Expansion Dynamics: The research identifies that all studied nova shells remain in the free expansion phase. This observation is linked to the mass of the nova ejecta being significantly larger—by factors ranging from 7 to 45—than the swept-up mass from the circumstellar medium. The findings indicate that the shells will likely continue this undeterred expansion for several centuries before fully dispersing into the ISM.
3. Expansion Rate Quantification: Specific angular expansion rates were determined for the minor axes of the nova shells, which are in good agreement with spectroscopic expansion velocities derived from historical records. For instance, DQ Her exhibited an angular expansion rate of approximately 0.188 arcseconds per year, aligning well with established spectroscopic data. Discrepancies were, however, noted in older spectroscopic data for T Aur and V476 Cyg, which may be attributed to observational limitations.
4. Morphological Characteristics: The nova shells display diverse morphologies, ranging from smooth and elliptical to highly clumpy and knotty patterns. These morphological differences may reflect the varying effects of the post-nova interactions, such as binary star dynamics and fast and slow wind interactions.
5. Implications on Stellar and ISM Interactions: The interactions between nova shell ejecta and the ISM are essential in understanding not only the dynamical aspects but also the enrichment processes. The kinetic energy assessments support the free expansion phase, and the absence of significant deceleration is corroborative of minimal interaction strength with the surrounding ISM.

Implications and Speculations

The results presented in this paper have notable implications for the broader understanding of nova phenomena and their contributions to interstellar material cycling. The persistence of free expansion emphasizes the robustness of ejecta momenta post-eruption and suggests limited influence from environmental factors in the short to medium-term evolutionary phases. Moreover, the paper potentially paves the path for exploring the connection between nova remnants and their contribution to ISM ionization and metallicity enrichment.

The continued free expansion provides a useful contrast for studying planet nebulae and supernova remnants, as the timeframes involved in novae evolution are more accessible. Future work could involve closer analysis of the ISM's role in altering expansion dynamics, particularly with advancements in imaging technologies and data analysis techniques. Understanding the transition to decelerated phases and incorporation into the ISM remains a compelling avenue for further research. This paper contributes valuable data and interpretation to the field of stellar evolution, offering insights into the behaviour of classical novae post-explosion.