Pre-Main Sequence Stars

PHYS390 (Astrophysics)

Professor Lee Carkner

Lecture 13

Pre-Main Sequence

Start to the right of the main sequence

Characteristics: Accretion Magnetic activity

Stage 1 -- Protostellar Core

Age -- IR class -- 0 Infall -- Outflow -- possible Disk -- Magnetic activity -- yes

IR Class

The more IR excess (and the longer its wavelength) the more circumstellar material, the younger the star

Stage 2 -- Protostar

Age -- IR class -- 1 Infall -- Outflow -- strong jet Disk -- Magnetic activity -- strong hard X-ray

emission

Outflow

PMS stars exhibit strong outflows

Winds are similar to scaled up solar wind

Jets are magnetically collimated polar outflows Regulate angular

momentum

Evolutionary Tracks

Hayashi track Most important for low

mass stars

Henyey track Most important for

high mass stars

Stage 4 -- Classical T Tauri Star

Age -- IR class -- 2 Infall -- Outflow -- strong winds Disk -- Magnetic activity -- strong X-ray emission

T Tauri

T Tauri stars are variable stars located near clouds

Classified by width of H line

W > Classical T Tauri (CTT)

W < Weak T Tauri (WTT)

H may be due to disk-star interaction

Disks

Can interact with star and stellar magnetic field

Can magnetically brake star

Forms into planets

Stage 4 -- Weak T Tauri Star

Age -- IR class -- 3 Infall -- Outflow -- weak wind Disk -- Magnetic activity -- strong X-ray activity

and starspots

Magnetic Activity

Exhibited as: Starspots Wind

Stage 5 -- Zero Age Main Sequence

Age -- IR class -- No IR excess Infall -- Outflow -- very weak wind Disk -- Magnetic activity -- weak X-ray emission

High Mass Stars

Herbig Ae/Be stars are high mass version of T Tauri stars

Star forming regions can also contain OB associations

Strong winds can trigger more star formation

IMF

The exact relationship is called the initial mass function

Hard to determine the low mass end

Next Time

Read 13.1, 13.3 Homework: 12.19, 13.2, 13.8