UX Orionis star
The UX Orionis stars ( acronym UXOR ) are a subgroup of variable young stars in and near star formation regions with sharp and deep minima of up to 3 mag . They show a strong infrared excess and the H-alpha - emission lines . Based on the intensity of the lithium lines in their spectra, the age of the UXORs is estimated to be some to 70 million years. The minima, which last only a few days, are the result of a variable extinction in the circumstellar disks around the UX Orionis stars.
properties
spectrum
The properties of their spectra are comparable to those of other groups of young stars with permanent accretion from a circumstellar disk such as the T-Tauri stars or the Herbig-Ae / Be stars . The spectral class of the UXORs is later than A0. The H-alpha emission lines show variable equivalent widths of up to 20 angstroms in their spectra .
Light curve
The light curve is different from minimum to minimum, with the duration of the darkening being a few days. The stars become bluer at the minimum, which is known as blueing . The minima are not predictable, which is why a classic cover light change can be excluded. During the minima, the proportion of polarized light increases . The variability in the optical is anticorrelated with the changes in brightness in the near infrared .
Outside the minima, the UXORs show rapid, irregular variability as is characteristic of the T-Tauri stars and the Herbig-Ae / Be stars.
Interpretation of the light change
The properties of the UX Orionis stars are interpreted as the result of a dusty disk, whereby the star is only visible from the earth through the disk.
The minima in the light curves are interpreted as
- Shadows from incident proto cometary objects
- Coverings by optically thick clouds in an otherwise optically thin disk
- new dust condensation near the dust evaporation line or
- a temporary increase in the thickness of the disc.
The minimum blueing can be modeled quite well as the result of the scattering of light on dust particles. During the minima, P-Cygni profiles appear in the spectrum , which are generated by the gas flowing out. Since the direct light of the star is weakened in the minima, weaker jets or stellar winds become visible in the spectrum.
With older UXORs, where the dust has already been removed by the radiation pressure , the variability no longer occurs near the star. Instead, the absorbing dust in the asteroid belt is formed by collisions between asteroids and dwarf planets like in the debris disks .
Others
With the exception of RZ Piscium , the UX Orionis stars lie within star formation regions or in young open star clusters .
Examples
See also
Individual evidence
- ↑ A. Juhasz et al .: Long-term infrared variability of the UXOri-type star SV Cep . In: Astrophysics. Solar and Stellar Astrophysics . 2006, arxiv : astro-ph / 0612270v1 .
- ↑ VP Grinin, ISPotravnov, and FAMusaev: The evolutionary status of the UX Orionis star RZ Piscium . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1109.2711 .
- ↑ EH Semkov, SP Peneva: Optical Photometry of GM Cep: Evidence for uxor Type of Variability . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1111.2166 .
- ↑ George C. Clayton et al .: HERSCHEL OBSERVATIONS OF A NEWLY DISCOVERED UX ORI STAR IN THE LARGE MAGELLANIC CLOUD . In: Astrophysics. Solar and Stellar Astrophysics . 2010, arxiv : 1008.1945 .
- ↑ WJ de Wit, VP Grinin, IS Potravnov, DN Shakhovskoi, A. Müller, M. Moerchen: An active asteroid belt causing the UX Ori phenomenon in RZ Psc . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1303.4138v1 .