astr 1040 recitation: cosmic distancezeus.colorado.edu/.../1040-ro-distances_lec_12.pdf · 2014. 4....

ASTR 1040 Recitation:

Cosmic Distance

Ryan Orvedahl

Department of Astrophysical and Planetary Sciences

April 7 & 9, 2014

This Week

Night Observing: Wednesday April 9 (8:30 pm)

Fiske Planetarium: Thursday April 10 (9:30 am)

Heliostat Observing: Thursday April 10 (2:00 - 4:00 pm)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 2 / 24

Today’s Schedule

Past/Current Homework or Lecture Questions?

Density Wave Theory

Standard Candles

Magnitudes

Cosmic Distances

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 3 / 24

Why Spiral Structure? – Density Waves

Gas/Stars move in/out ofdense regions

Gas/stars are pulledtoward high density

Clumping gives rise tospiral structure

Spiral structure has highstar formation

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 4 / 24

Density Waves in Action

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 5 / 24

Density Waves in Action

M51 – WhirlpoolGalaxy

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 6 / 24

Cosmic Distances

The universe is big

How do we know?

We measured it

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 7 / 24

Cosmic Distance Ladder

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 8 / 24

Standard Candles

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 9 / 24

Standard Candles

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 10 / 24

Parallax, α ≥ 10 microarcseconds

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 11 / 24

The Local Neighborhood ∼ 40 pc

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 12 / 24

The Local Bubble ∼ 100 pc

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 13 / 24

Apparent vs Absolute Magnitudes

Apparent Magnitude: m ≡ how bright does it appear

Absolute Magnitude: M ≡ how bright if d = 10 pc

m2 −m1 = 2.5 log10

(f1f2

)= 2.5 log10

(L1

4πd21

4πd22

L2

)M2−M1 = 2.5 log10

(L1L2

)⇒ M?−M� = −2.5 log10

(L?L�

)

Distance modulus: m? −M? = 5 log10

(d?

10 pc

)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 14 / 24

Apparent vs Absolute Magnitudes

Apparent Magnitude: m ≡ how bright does it appear

Absolute Magnitude: M ≡ how bright if d = 10 pc

m2 −m1 = 2.5 log10

(f1f2

)= 2.5 log10

(L1

4πd21

4πd22

L2

)M2−M1 = 2.5 log10

(L1L2

)⇒ M?−M� = −2.5 log10

(L?L�

)

Distance modulus: m? −M? = 5 log10

(d?

10 pc

)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 14 / 24

Apparent vs Absolute Magnitudes

Apparent Magnitude: m ≡ how bright does it appear

Absolute Magnitude: M ≡ how bright if d = 10 pc

m2 −m1 = 2.5 log10

(f1f2

)= 2.5 log10

(L1

4πd21

4πd22

L2

)

M2−M1 = 2.5 log10

(L1L2

)⇒ M?−M� = −2.5 log10

(L?L�

)

Distance modulus: m? −M? = 5 log10

(d?

10 pc

)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 14 / 24

Apparent vs Absolute Magnitudes

Apparent Magnitude: m ≡ how bright does it appear

Absolute Magnitude: M ≡ how bright if d = 10 pc

m2 −m1 = 2.5 log10

(f1f2

)= 2.5 log10

(L1

4πd21

4πd22

L2

)M2−M1 = 2.5 log10

(L1L2

)⇒ M?−M� = −2.5 log10

(L?L�

)

Distance modulus: m? −M? = 5 log10

(d?

10 pc

)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 14 / 24

Apparent vs Absolute Magnitudes

Apparent Magnitude: m ≡ how bright does it appear

Absolute Magnitude: M ≡ how bright if d = 10 pc

m2 −m1 = 2.5 log10

(f1f2

)= 2.5 log10

(L1

4πd21

4πd22

L2

)M2−M1 = 2.5 log10

(L1L2

)⇒ M?−M� = −2.5 log10

(L?L�

)

Distance modulus: m? −M? = 5 log10

(d?

10 pc

)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 14 / 24

Main Sequence Fitting

90% of stars are onthe Main Sequence

Look for paralleltracks on the HRdiagram

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 15 / 24

Main Sequence Fitting

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 16 / 24

Local Galactic Group ∼ 2 Mpc

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 17 / 24

Cepheid Variables

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 18 / 24

Cepheid Variables

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 19 / 24

Cepheid Variables ∼ 50 Mpc

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 20 / 24

Tully-Fisher Relation

Empirical relationshipbetween luminosity andline widths

Measure width of emissionlines (e.g. 21 cm), inferluminosity

Measure apparentmagnitude, calculatedistance

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 21 / 24

Tully-Fisher Relation ∼ 500 Mpc

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 22 / 24

Type Ia Supernovae

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 23 / 24

Type Ia Supernovae

Phillips relationship (1993):

Mmax(B) = −21.726 + 2.698∆m15(B)

R. Orvedahl (CU Boulder) Cosmic Distance Apr 7 & 9 24 / 24