Determine the nature and extinction contribution of Cepheid circumstellar envelopes

Determine the actual presence, composition, and contribution to interstellar extinction of circumstellar envelopes around Classical Cepheids, which remain insufficiently characterized for most such stars.

Background

The extinction estimates derived from neighboring field stars do not account for possible extinction produced by material surrounding the Cepheid itself. The paper notes that circumstellar envelopes have been detected around some Cepheids, but their physical nature—particularly whether they are dusty or gaseous—and their effect on ultraviolet and visible extinction remain unresolved. Establishing these properties is important for interpreting discrepancies between direct Cepheid extinction measurements and extinction inferred from nearby field stars, and could also clarify the origin of observed infrared excesses.

References

Many Cepheids are speculated to have CSEs, but their actual presence, composition, and contribution to extinction are not well known for most Cepheids.

— Interstellar extinction of classical Cepheids from neighboring stars I. Methodology and application to 16 Galactic Cepheids  (2609.28406 - Kiviaho et al., 23 Sep 2026) in Section 6.3, “Circumstellar envelopes and small-scale ISM variations”