HR 7355 is a bright, rapidly rotating [[Be star]] located in the constellation [[Hercules]]. It is classified as a [[Gamma Cassiopeiae variable]] (GCAS), a type of eruptive variable star whose brightness fluctuates due to dynamic processes within its circumstellar disk.
Characteristics and Variability: HR 7355 is spectroscopically classified as a B2IVe star, indicating it is a B-type subgiant star with emission lines in its spectrum. The 'e' denotes the presence of a surrounding disk of gas, which is characteristic of Be stars. This disk is formed by material ejected from the star's equator due to its extremely rapid rotation, often exceeding 70% of its critical rotation speed.
As a Gamma Cassiopeiae variable, HR 7355 exhibits irregular and unpredictable changes in its apparent magnitude, typically ranging between 5.0 and 5.5. These variations are attributed to changes in the structure and density of its circumstellar disk, including episodes of mass ejection and absorption. The star's rapid rotation and the presence of this disk are key factors in its observed variability and unique spectral features.
Location and Observation: Situated in the northern celestial hemisphere, HR 7355 is visible to the naked eye under dark sky conditions, although its variability can make it appear slightly brighter or dimmer at different times. Its designation "HR" comes from the [[Harvard Revised Photometry Catalogue]], a star catalog developed at the [[Harvard College Observatory]].