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