World Library  
Flag as Inappropriate
Email this Article

Young stellar object

Article Id: WHEBN0007205947
Reproduction Date:

Title: Young stellar object  
Author: World Heritage Encyclopedia
Language: English
Subject: Star formation, Circumstellar envelope, Nebular hypothesis, B(e) star, Star
Publisher: World Heritage Encyclopedia

Young stellar object

Small young stellar object known as SSTC2D J033038.2+303212, located in the constellation of Perseus.[1]

Young stellar object (YSO) denotes a star in its early stage of evolution.

This class consists of two groups of objects: protostars and pre–main-sequence stars.


  • Classification by mass 1
  • Classification by spectral energy distribution 2
  • Characteristics 3
  • See also 4
  • References 5

Classification by mass

Sometimes they are divided by mass – massive YSO (MYSO), intermediate mass YSO and brown dwarfs.

Classification by spectral energy distribution

YSO are usually classified using criteria based on the slope of their SED, introduced by Lada C.J. in 1987. He proposed three classes (I, II and III), based on the values of intervals of spectral index \alpha \,:

\alpha=\frac{d\log(\lambda F_\lambda)}{d\log(\lambda)}.

Here \lambda \, is wavelength, and F_\lambda is flux density.

The \alpha \, is calculated in the wavelength interval of 2.2–20 {\mu}m (near- and mid- infrared region). Later Greene et al. in 1994 added a fourth class of "flat spectrum" class sources. In 1993 Andre et al. discovered class 0—objects with strong submillimeter emission, but very faint at {\lambda}<10{\mu}m.

  • Class 0 sources – undetectable at {\lambda}<20{\mu}m
  • Class I sources have {\alpha}>0.3
  • Flat spectrum sources have 0.3>{\alpha}>-0.3
  • Class II sources have -0.3>{\alpha}>-1.6
  • Class III sources have {\alpha}<-1.6

This classification schema roughly reflects evolutionary sequence. It is believed that most deeply embedded Class 0 sources evolve towards Class I stage dissipating their circumstellar envelopes. Eventually they become optically visible on the stellar birthline as pre–main sequence stars.


YSO are also associated with early star evolution phenomena: jets and bipolar outflows, masers, Herbig–Haro objects, and protoplanetary disks (circumstellar disks or proplyds).

See also


  1. ^ "Light and dark". Retrieved 26 August 2014. 
  • Lada, C. J. (1987), IAU Symposium 115: Star Forming Regions, 115, 1
  • Greene, Thomas P.; Wilking, Bruce A.; Andre, Philippe; Young, Erick T.; Lada, Charles J. (1994), Further mid-infrared study of the rho Ophiuchi cloud young stellar population: Luminosities and masses of pre-main-sequence stars, The Astrophysical Journal, vol. 434, pp. 614–626
  • Andre, Philippe; Ward-Thompson, Derek; Barsony, Mary (1993), Submillimeter continuum observations of Rho Ophiuchi A – The candidate protostar VLA 1623 and prestellar clumps, The Astrophysical Journal, vol. 406, pp. 122–141
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from World eBook Library are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.