Young star object

Young star object in the complex of Ro Ophiuchus

V1331 Cyg, a young stellar object surrounded by a reflective nebula

Young stellar object ( YSO ) - a star at an early stage of evolution. This class of objects consists of two groups: protostars and stars to the main sequence .

Content

1 Classification by weight
2 Classification by the distribution of energy in the spectrum
3 Features
4 notes

Mass Classification

These objects can be classified according to mass: massive young stellar objects ( Eng. Massive YSOs ), young stellar objects of intermediate mass ( Eng. Intermediate mass YSOs ), brown dwarfs .

Spectrum energy distribution classification

Young stellar objects are usually classified according to a criterion based on the slope of the energy distribution in the spectrum and introduced by C. Lada in 1987. He proposed dividing objects into three classes (I, II, and III) in accordance with the value of the spectral index $\alpha \,$ ${\ displaystyle \ alpha \,}$ : ^[1]

$\alpha ={\frac {d\log(\lambda F_{\lambda })}{d\log(\lambda )}}$ ${\ displaystyle \ alpha = {\ frac {d \ log (\ lambda F _ {\ lambda})} {d \ log (\ lambda)}}}$ .

Here $\lambda \,$ ${\ displaystyle \ lambda \,}$ denotes the wavelength $F_{\lambda }$ ${\ displaystyle F _ {\ lambda}}$ - radiation flux density.

Value $\alpha \,$ ${\ displaystyle \ alpha \,}$ calculated in the wavelength range of 2.2–20 μm (the region of near and medium infrared radiation). F. Andre et al. (1993) proposed class 0: objects with strong submillimeter radiation but weak radiation at ${\lambda }<10$ ${\ displaystyle {\ lambda} <10}$ microns. ^[2] T. Green et al. (1994) added fifth grade for flat-spectrum sources. ^[3]

Class 0 : sources are not detected when ${\lambda }<20$ ${\ displaystyle {\ lambda} <20}$ microns.
Class I : sources possess ${\alpha }>0.3$ ${\ displaystyle {\ alpha}> 0.3}$ .
Flat spectrum sources have $0.3>{\alpha }>-0.3$ ${\ displaystyle 0.3> {\ alpha}> - 0.3}$ .
Class II : sources possess $-0.3>{\alpha }>-1.6$ ${\ displaystyle -0.3> {\ alpha}> - 1.6}$ .
Class III : sources possess ${\alpha }<-1.6$ ${\ displaystyle {\ alpha} <- 1.6}$ .

This classification scheme approximately reflects evolutionary sequence. Class 0 sources are believed to evolve toward a Class I source, destroying the circumstellar membrane. Over time, the star moves to the class of stars to the main sequence.

Features

Young stellar objects are associated with phenomena in the early stages of stellar evolution: jets, bipolar outflows , masers , Herbig-Aro objects , protoplanetary disks .

Notes

↑ Lada, Charles J. Star Formation: From OB Associations to Protostars // Star Forming Regions: Proceedings of the 115th Symposium of the International Astronomical Union Held in Tokyo, Japan, November 11–15, 1985. - Dordrecht: D. Reidel, 1987. - P. 1-17. - ISBN 978-90-277-2388-8 .
↑ Andre, Philippe; Ward-Thompson, Derek; Barsony, Mary. Submillimeter Continuum Observations of ${\rho }$ ${\ displaystyle {\ rho}}$ Ophiuchi A: The Candidate Protostar VLA 1623 and Prestellar Clumps (Eng.) // The Astrophysical Journal : journal. - IOP Publishing 1993. March ( vol. 406 , no. 1 ). - P. 122-141 . - DOI : 10.1086 / 172425 . - .
↑ Greene, Thomas P .; Wilking, Bruce A .; Andre, Philippe; Young, Erick T .; Lada, Charles J. Further Mid-infrared Study of the ${\rho }$ ${\ displaystyle {\ rho}}$ Ophiuchi Cloud Young Stellar Population: Luminosities and Masses of Pre-main-sequence Stars (Eng.) // The Astrophysical Journal : journal. - IOP Publishing 1994 .-- October ( vol. 434 , no. 2 ). - P. 614-626 . - DOI : 10.1086 / 174763 . - .

[Lada1987-1] Lada, Charles J. Star Formation: From OB Associations to Protostars // Star Forming Regions: Proceedings of the 115th Symposium of the International Astronomical Union Held in Tokyo, Japan, November 11–15, 1985. - Dordrecht: D. Reidel, 1987. - P. 1-17. - ISBN 978-90-277-2388-8 .

[Andre1993-2] Andre, Philippe; Ward-Thompson, Derek; Barsony, Mary. Submillimeter Continuum Observations of ${\rho }$ ${\ displaystyle {\ rho}}$ Ophiuchi A: The Candidate Protostar VLA 1623 and Prestellar Clumps (Eng.) // The Astrophysical Journal : journal. - IOP Publishing 1993. March ( vol. 406 , no. 1 ). - P. 122-141 . - DOI : 10.1086 / 172425 . - .

[Greene1994-3] Greene, Thomas P .; Wilking, Bruce A .; Andre, Philippe; Young, Erick T .; Lada, Charles J. Further Mid-infrared Study of the ${\rho }$ ${\ displaystyle {\ rho}}$ Ophiuchi Cloud Young Stellar Population: Luminosities and Masses of Pre-main-sequence Stars (Eng.) // The Astrophysical Journal : journal. - IOP Publishing 1994 .-- October ( vol. 434 , no. 2 ). - P. 614-626 . - DOI : 10.1086 / 174763 . - .