Star Formation#


Intro paragraph


  • Summary



Orion complex, closest star forming region from the sun.


Fig. 16 Reference#

Spectral Energy Distribution#

[Chiang and Goldreich, 1997]: Hydrostatic, radiative equilibrium disk models, disks encased by thin layer of superheated dust grains, result: disks flare & absorb more stellar radiation than flat disks would, spectral features from dust grains in superheated layer appear in emission if disk is viewed nearly face-on.


Looks like good introduction

Ariane thread for star evolution #

‣ ‣ Black vs Grey body radiation #

A dusty envelope absorbs the stellar photons.

The dust grains re-emit thermal radiation (isotropically).

This dust emission is absorbed by other grains.

This process is reated until the photons escapes from the core.

Because the (radiative) energy is conserved, the temperature of the surface that the observer sees is much lower than that of the star and the characteristic wavelength longer (“redder”).



Insert link toward SED teaching material from Hawai uni

Within dense core

There is 2 parameters often used to describe the SED (Spectral Energy Distribution):

  • Spectral index (class I, II, III)

  • Bolometric temperature (class 0, I) However, SEDs are way too complex to be characterised by a single number and their characterisation are inevitably coarse

Step by Step#

Class 0
Class 1
Class 2
Class 3

First stage of planet formation. Not detectable in the near infrared.

Cold core emit like a grey body

MStar < MCore

More Ressources:


  • Extract picture from article below


[Redaelli et al., 2022]

Protostar begins to emerge and become detectable in the NIR (near Infrared).

Core is dispersing and punctuated by outflows

SED dominated by FIR

protostellar disk to protoplanetary disk in 104 years (ref 4 - 5) This process involve high temperature but while material is accreted by the star the disk mass and temperature decrease.

MStar > MCore


Fig. 17 The Protostar within L1527 source: NASA APOD *2022 November 18 *#

Core has dissipated, the star has reached it’s final mass and is now contracting. The star is now a Pre-Main-Sequence (PMS - ie T Tauri Star or HerbigAe depending on it’s mass).

Infrared excess above photosphere, due to a protoplantary disks.


Circumstellar disk has very little dust (optically thin) and little if any infrared excess.

SED looks like a stellar photosphere.


From Cloud to Disk#

How much of the initial material is reprocessed


  • Ross D/H ratio

    • Energetic processes responsible for H fractionation

Star accretion rate#

Protostars are very hungry babies


Fig. 18 Reference - to find#

Outburst related to accretion

[Kóspál et al., 2023]



Fig. 19 Reference#



Fig. 20 Reference#


[Schneeberger et al., 2023]



Fig. 21 Reference#

Influence of cluster on disk properties#

[Boyden and Eisner, 2022]


The Minimum Mass Solar Nebulae

Definition: litterature Review