Lecture 11: Observations of Star Formation- Peeking in at the Stellar Nursery

"Space is a hard place to raise a family..."
Elton John, Rocket Man

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Date: March 2, 1995
Reading Assignment: pp. 444-454

Description : observations of star formation

Objectives

be able to describe a T-Tauri star and with what stage of star formation it is associated

be able to describe brown dwarfs

be able to describe the evidence of star fragmentation and collapse in interstellar nebula

be able to describe the observational evidence for protostars

be able to describe the observations of protoplanetary systems

be able to describe how shock waves influnce star formation

be able to describe how star formation may trigger other star formaotn

be able to describe why we find stars in clusters and associations

Lecture Outline

Slide # 1: Observations of Star Formation (GRAPHICS)

Views of the Stellar Nursery

Slide # 2: The HR Diagram (GRAPHICS)

Why?

Slide # 3: Unanswered Questions

Why are 90% of stars on the Main Sequence?

Why is mass so important in determining luminosity?

How can a 1 solar mass star be a red giant, white dwarf, or on the main sequen

Why are red giants and white dwarfs different than MS stars?

Slide # 4: Star Modeling- Laws of Physics

hydrostatic equilibrium

energy transport

energy generation

mass continuity

Slide # 5: Evolutionary Tracks

every star corresponds to place on the HR diagram at any given time

stars may change luminosity or temperature over their lifetime

stars may follow tracks on the HR diagram

Slide # 6: A Simplification

the most important effect is pressure

gas pressure and heat

ignore rotation and magnetic fields

probably less important

Slide # 7: The Steps

gas cloud

fragmentation

protostar

Helmholtz contraction

Hayashi track

ignition

adjustment to the Main Sequence

Slide # 8: Effects Interstellar Dust

stars appear redder

absorbs blue light more than red

appear dimmer

absorbs visible light

star light is polarized

Slide # 9: How do we observe star formation?

found in molecular clouds

lots of dust

Slide # 10: Emission and Excitation

transition between orbitals

produces most visible line emission

spin-flip of electron

HI gas- 21cm line emission (radio)

rotational excitation

molecular emission - radio

thermal emission

peak of stars is in the visible range

peak of protostars is in the infrared

Slide # 11: ZAMS

Zero Age Main Sequence

stars which just arrived on Main Sequence

Slide # 12: Star Formation and Mass

massive stars form rapidly

3 solar mass star = 1 million years to ZAMS

low mass stars form slowly

0.3 solar mass star = 1 billion years to ZAMS

Slide # 13: Observations of Stars Forming

all stages are observed

usually in the same, dense regions

impossible to follow a single star through all stages

1 solar mass = 40 million years to ZAMS

1 astronomer's lifetime < 100 years

Slide # 14: Stage 1: Gas Clouds

high density HI or H2 region

1000 particles per cubic cm

10 parsecs in size

10 K temperature

often Molecular Clouds

a bit cooler and denser than most of the ISM

1 particle per cubic cm

100 K temperature

Slide # 15: Stage 1: Dense Interstellar Clouds

21 cm radio observations of HI regions

gas observed in the galaxy

radio observations of molecular clouds

density and temperature correct for star formation

rotational emission lines

Slide # 16: Radio Telescope Observations (GRAPHICS)

the VLA

Slide # 17: Stage 2: Fragmentation

cloud breaks into pieces

2 solar masses of material

10 6 particles per cubic cm

few one-hundreth's of a parsec

few hundred times the size of solar system

100 K temperature

Slide # 18: Fragmentation (GRAPHICS)

big cloud breaks into many little clouds

Slide # 19: Stage 2: Fragmentation and Collapse

molecular lines indicate contraction

Doppler shift measurements

small fragments observed in some regions

HST observations

Slide # 20: Doppler Shift in Molecular Clouds (GRAPHICS)

evidence of collapse

Slide # 21: M20- the Trifid Nebula (GRAPHICS)

HII region inside a molecular cloud

stages 1, 2, & 7

Slide # 22: HST Image- Orion Nebula (GRAPHICS)

small 1/10 pc fragments

Slide # 23: Stage 3: Protostar

gas cloud heats up

radiation becomes trapped

size of the solar system

10,000 times the size of the Sun

temperature reaches 10,000 K at the core

density 1012 particles per cubic cm

age = 10,000 years

photosphere forms

gas becomes opaque

Slide # 24: Protostar (GRAPHICS)

photosphere forms

Slide # 25: Stage 3: Protostars

Interstellar Masers

density and temperature correct for protostars

radio emission from very dense gas clouds

Slide # 26: Constellation Corner (GRAPHICS)

Constellation De Jour

Slide # 27: Gemini (GRAPHICS)

Feb 15 - 9pm - S - 4.0

Slide # 28: Auriga (GRAPHICS)

Fairfax - 8pm - S - 4.0 - March 5

Slide # 29: Auriga (GRAPHICS)

Fairfax - 8pm - S - 4.0 - March 5

Slide # 30: Stage 4: Kelvin-Helmholtz Contraction

protostar contracts and heats up

core temperature = 1,000,000 K

surface temperature = 3,000 K

size = 50 solar radii

no nuclear reactions yet

very luminous - more than 1,000 solar luminosity

age = 100,000 years

star can be plotted on HR diagram

appears in red giant area

Slide # 31: The HR Diagram (GRAPHICS)

HR diagram

Slide # 32: Stage 4: Kelvin-Helmholtz Contraction

Kleinmann-Low Nebula

warm, small gas cloud

temperature and density close to stage 4

Infrared Stars

stars seen observed only in infrared

surrounded by dust clouds

cool, but very luminous

Slide # 33: Stage 5: Hayashi Track

star contracts, surface temperature rise a small amount

10 times the size of the Sun

surface temperature 4000 K

luminosity = 10 solar luminosity

central temperature = 5,000,000 K

no nuclear reactions

age = 1 million years

luminosity decreases as star shrinks

Slide # 34: The HR Diagram (GRAPHICS)

HR diagram

Slide # 35: Stage 5: Hayashi Track

Barnard 5: infrared source

temperature and luminosity = stage 5

detected in the infrared

Slide # 36: Stage 5: T Tauri Stars

young protostars surrounded by disks

0.5 to 3 million years old

variable activity

bipolar outflows

unstable young star emits strong wind

wind interacts with disk shaped nebula

Slide # 37: T-Tauri Stars (GRAPHICS)

accretion disk around a protostar

Slide # 38: T-Tauri Stars (GRAPHICS)

stellar wind forms- disk causes bipolar flow

Slide # 39: T-Tauri Stars (GRAPHICS)

image

Slide # 40: The HR Diagram (GRAPHICS)

HR diagram

Slide # 41: Stage 7: Adjustments to Main Sequence

star moves to main sequence

star is now a G2V

15,000,000 K core temperature

one solar luminosity

6,000 K surface temperature

central density = 100 gm/cm3

age = 40 million years

star in hydrostatic equilibrium

Slide # 42: Stage 6: Nuclear Ignition

P-P Chain Begins in the Core

core temperature > 10,000,000 K

surface temperature 4,500 K

size = 1.25 solar radii

luminosity = 2/3 solar luminosity

age = 10 million years

star still not in hydrostatic equilibrium

internal structure slightly out of balance

Slide # 43: The HR Diagram (GRAPHICS)

HR diagram

Slide # 44: Star Clusters (GRAPHICS)

the Pleiades - about 90 million years old

Slide # 45: Triggering Star Formation

stars sometimes form spontaneously

density increases, collapse occurs

star formation can also be triggered

shock waves

Slide # 46: Shock Wave

thin shell of gas rushing through space

wave of matter

created by strong energy source

young, hot star

supernova explosions

Slide # 47: Shock Waves

massives stars form

high mass stars form first

shock waves are created

HII regions

supernova explosions

more star formation occurs

Slide # 48: Massive Stars Form (GRAPHICS)

high mass stars form first

Slide # 49: Shock Waves Form (GRAPHICS)

ultraviolet radiation or supernova

Slide # 50: Shock Wave Creates More Star Formation (GRAPHICS)

compression from shock wave

Slide # 51: Emission Nebula (GRAPHICS)

M42 - the Orion Nebula - an HII region

Slide # 52: Supernova Triggered SF? (GRAPHICS)