YSOs: Young Stellar Objects

Provide evidence for planet-formingnebular disks around stars

Dusty cocoon surrounding YSO

Different types of YSOs:

1) IR stars2) Proplyds3) Herbig-Haro objects4) T-Tauri stars5) Beta Pictoris systems

Range from protostarsto newly-formed stars

IR stars:infrared protostars

• show excess emission in IR compared to visible wavelengths

• explained by dust cocoons surrounding protostar

• these cocoons obscure the visible light from the central star-like object, but are warmed by that visible light and so radiate in the IR

visible light image IR light image mosaic

IR stars in Orion

IR star DC303.8-14.2

visible light (700 nm),showing dust

IR light (1.65 um), showingring of warmed dust aroundembedded IR star

IR light (2.17 um), showing inner clumps(shocked gas?)

Proplyds: protoplanetary disks

• dusty cocoons seen around YSOs• first seen clearly in the Orion Nebula

Proplyd with evidence for infalling matter (nebular disk shocks)

Disk ~800 AU across

Pattern of methanolemission can be explainedby clumpy accretion ontosurface of disk

Herbig-HaroObjects:

• YSOs withdisks & bipolaroutflows

Bipolar jet

T-Tauri star:catchall term for many types of YSOs

• YSO has not yet ignited H; it follows Hayashi track in luminosity & temperature

• YSO can show evidence for rapid rotation, strong magnetic field, strong stellar winds, short-lived brightness spikes (FU-Orionis outbursts), excess IR emission

H-R diagram showing Hayashitrack (4-7) and Main Sequence trend(grey band)

http://www.go.ednet.ns.ca/~larry/stars/prtostar.html

Beta Pictoris-type system: newly-formed star that still has a surrounding dust disk

• YSO has achieved H to He fusion and falls on Main Sequence trend

• dust disk soon to be destroyed, either by:

stellar winds (material blown out of system)

or

movement to star (e.g., via Poynting-Robertson effect)

colors represent light intensities

waves in disk probably caused by interaction with planets

Dust disk around Beta Pictoris seen edge on