In previous episodes …..In previous episodes …..

Stars are formed in the spiral arms of the Galaxy, in the densest and coldest regions of the interstellar medium, which are called Molecular Clouds.

Image: portion of the galactic plane: darker colours indicate higher extinction regions (due to dust in MCs).

Kandori 2007

Star Formation

clustered isolated

Orion

Taurus

Perseus

0.1 pc0.1 pc

• Observationally, two modes of star formation in the Galaxy:

– isolated mode, in dark clouds

– clustered mode, in giant molecular clouds

Dark cloudsDark clouds (10(1033 Msun, 5 pc, 10 K) Msun, 5 pc, 10 K)

Giant Molecular CloudsGiant Molecular Clouds (10(1055 Msun, 100 pc, Msun, 100 pc, 30 K)30 K)

Star Formation: must convert dense cores into stars:

temperature ~10—100 K to >107 K -> 6 o. m.size ~0.5 pc to 2x10-8 (1 Rsun) -> 7 o.m.density 103-4 cm-3 to ~1026 cm-3 -> 22 o.m.

Young starsYoung stars are associated with the are associated with the dense dense corescores in molecular clouds in molecular clouds

The properties of these The properties of these dense cores differdense cores differ for for regions of regions of highhigh and and lowlow mass mass star formation

Low Mass Star Formation ...

Blackbody SpectrumBlackbody Spectrum

SPECTRAL ENERGY DISTRIBUTIONSPECTRAL ENERGY DISTRIBUTION

Spectral Energy Distribution (SED)C

lass

0> 0, peak ~100 m, BB at 10-30 K, Lsmm/Lbol > 0.5%, faint IRcold envelope opt thick in free-fall.powerful and collimated outflows, protostar

= d log F / d log , between 2 and 25 micron

Cla

ss I

>~ 0, flat SED, superposition of BB at different T,IR, faint >~ 0, flat SED, superposition of BB at different T,IR, faint opticalopticalenvelope part. thick + disk.envelope part. thick + disk.Moderate outflowsModerate outflows, evolvedevolved protostarprotostar

C

lass

II

-1.5 <-1.5 < < 0, mid-IR excess compared to BB, optical < 0, mid-IR excess compared to BB, opticalenvelope being disruptedenvelope being disruptedfaint outflow, faint outflow, classical T Tauri, FU Oriclassical T Tauri, FU Ori

C

lass

III

< -1.5, similar to BB, optical< -1.5, similar to BB, opticalstellar photosphere reddened by circumstellar stellar photosphere reddened by circumstellar extinctionextinctiondebris disk, debris disk, weak-line T Tauri, PMSweak-line T Tauri, PMS

Spatial DistributionSpatial Distribution

Hartmann 2003

Class II ~ Class III spatial distribution.

Class I: higher density regions