Astronomy 405Solar System and ISM

Lecture 20

Star Formation and Star Forming Regions

March 1, 2013

How do we know?

• Young stars are seen near molecular clouds.• In infrared light, we can see into the deeper

regions of clouds, and see clusters of young stars with circumstellar material (dust and gas) surrounding them.

• Stars do not live forever, so they must be continuously formed in our galaxy.

Giant Molecular Clouds• Cool: < 100 K

• Dense: 102 – 105 H2 molecules/cm3 (still less dense than our best vacuum)

• Huge: 30 – 300 lyrs across, 105 – 106 solar masses

• CO molecular emission & dust emission trace structure 100 degrees

Infrared image from IRAS

Young Stars

Bright, hot newborn star, partially shrouded by dust

Other newborn stars, reddened by dust

After Shu et al. 1987,Shu et al. 1993

isolated, quasi-static, unbound, isothermal core

Cartoon of Star Formation

simple /Bfield

disk & outflow due to angular momentum

clearing of envelope by wind

grav collapse opposed by turbulence, B field, thermal

planetary system?

Class 0: Youngest stellar objects (> 10 um) Cold black body

Deeply embedded Envelope dominated emission

fux

V IR mm

Class I: Embedded Strong disk and envelope contribution

fux

V IR mm

fux

V IR mm

Class II: Disk dominated Stellar contribution

fux

V IR mm

Class III: Stellar dominated Little dust contribution

Starless cores and protostars with inward (collapse) motions(Gregersen et al. 1997, Mardones et al. 1997, Tafalla et al. 1998, Lee et al. 2001 )

YSO outflows

Alves et al. 2001, O’Dell et al. 1994, Chen et al. 1998, Jayawardhana et al. 1998, Padgett et al. 1999, Burrows et al. 1996, ESO 2000

Majority of T Tauri stars have disks (e.g. Beckwith & Sargent 1996)

HR 4796

HH34

The Expansion of HH30’s Jet

Scattered/Absorbed Light Disks

Massive Star Formation

The Large Magellanic Cloud

Spitzer Space Telescope

• 0.85 meter infrared telescope

• Launched in August 2003

• Cooled to ~1.5 K

MIPSPI: Rieke (UofA)

Imaging at 24, 70, 160 m

IRACPI: Fazio (CfA)

Imaging at 3.6,

4.5, 5.8, 8.0 m

IRSPI: Houck (Cornell)

Spectrographs (4)

5.3-38 m

Spitzer mosaic of the LMC - SAGE

Meixner et al.

Identification of YSOs in the LMC

AGB

Stars

Galaxies

Step 1 (DM of the LMC= 18.5)

Gruendl & Chu 2009, ApJSGruendl & Chu 2009, ApJS

High-mass YSOs

Intermed-Mass YSOs

Step 2

H+CO dss-r H 2MASS J

2MASS K 3.6 4.5 5.8

8.0 24 70

Step 2

H+CO dss-r H ISPI J

ISPI K 3.6 4.5 5.8

8.0 24 70

Step 2

H+CO dss-r H ISPI J

ISPI K 3.6 4.5 5.8

8.0 24 70

Step 2

H+CO dss-r H ISPI J

ISPI K 3.6 4.5 5.8

8.0 24 70

Massive YSO Candidates in the LMC

Source [8]>8 [8]<8

YSO 858 234YSO 303 14YSO 167 >4M >10M

Neb 126 13AGB 110 105PNe 52 9

Galaxy 947 6Galaxy? 126

How Do We Know We Are Right?

• Cycle 4 IRS follow-up observations of ~270 YSO candidates confirmed 95% of them (Seale et al. 2009, ApJ, 699, 150).

• 13 H2O maser sources found coincidence in ~10.

• Identified ~ expected number of background galaxies.

Gravitationally Unstable Regions

<1 (blue)

Gravitationally Unstable Regions

Rafikov 2001

Chen et al. 2009, ApJ, 695, 511

Star Formation in Superbubble N44

3.6, 8.0, 24 um

HST H ISPI J ISPI K SED

A Closer Look at YSOs’ Environments

20" 20"

HST H ISPI J ISPI K SED

A Closer Look at YSOs’ Environments

20" 20"

HST View of YSOsHST View of YSOs’’ Environments Environments

(1)(1) dark clouds, (2) bright-dark clouds, (2) bright-

rimmed rimmed

dust pillars, (3) small compact dust pillars, (3) small compact

HII.HII.

Evolutionary Sequence.Evolutionary Sequence.

YSOs in 30 DorRed: [8.0]< 8 ; Green: [8.0]>8 ; Yellow: [8.0]>8, star + CSD or cHII

HST Images of 30 Dor are availableHST proposals due today at 7pm