FU FU Ononis stars

- These variables are characterized by gradual increases in brightness by about 6"' in several months, followed by either almost complete constancy at maximum that is sustained for long periods of time or slow decline by lm-2'". Spectral types at maximum are in the range Aea-Gpea. After an outburst, a gradual development of an emission spectrum is observed and the spectral type becomes later. These variables probably mark one of the evolutionary stages of T Tauri-type Orion variables (INT), as evidenced by an outburst on one member, V1057 Cyg, but its decline (2'"5 in 11 years) commenced immediately after maximum brightness was attained. All presently known FU Ori variables are coupled with reflecting cometary nebulae. GCVS

Observation Key

Bright stars ^ Large amplitudes ^^ Long periods <S> Visual

6Orion, the Hunter, usually understood to be the son of Poseidon and a mortal mother.

FU Orionis stars are pre-main sequence (PMS) stars, newly formed out of interstellar matter, that have not yet reached a sufficiently high central temperature to ignite nuclear reactions within their core. As a result of their young age, during their formation stage, the PMS stars receive their energy by release of gravitational energy (Figure 3.1).

PMS stars are usually classified as eruptive variables and within the GCVS they are subdivided into many subgroups that include the FU Ori stars. However, this classification, based strictly upon morphological photometric properties (light curves), is ambiguous and of only limited value.

Within the GCVS, you will find only about 10 FU Ori stars and six are classed as uncertain (FU:). The prototype of this group, FU Orionis is an interesting star that displays a range in brightness from 16T5 to 9™6. At its brightest, this variable is well within the range of binoculars or a small telescope.

0 0

Post a comment