a 1020 template study guide 10 star properties

8/12/2019 A 1020 Template Study Guide 10 Star Properties

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ASTR 1020 Study Guide 10

Stellar and Galactic Astronomy

General Properties of Stars


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Stellar Properties IWe have learned about the properties of the Sun such

as distance, luminosity, mass, size, temperature The only star in our solar system

The only star were so close to that we can study its surface indetail

What about all the other stars in the sky? How do the Suns properties compare to those of the other

stars in our solar neighborhood and beyond?

We see the stars in the sky at different brightnesses andcolors. How do these different observed brightnesses and

colors come about? Are all stars pretty much the same or are there different

types with different properties?

What are their spectra like and what can we learn from

them? How do they compare to the Suns?


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Stellar Properties: Parallax I

Review: Parallax, p, = angular shift of a nearby star atdistance d viewed from opposite points of Earths orbit

p = 1/d p is in arcsec, d is in parsec

an object that is 1 parsec(1 pc) awayhas an angular shift of 1 arcsec

In terms of familiar distance units: 1 pc = 3.3 ly = 206,265 AU

All stars (other than Sun) are so faraway that no distance on Earth itselfwould be a large enough baselinefor a measurable parallax

Use Earths orbit as baseline = 1 AU Work out UNL class action question Perspectives

Parallax Animation Ohio State

for a near and a far star
http://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_perspectives.htmlhttp://facstaff.gpc.edu/~ulahaise/astrogeneral/parallax%20animation%20Ohio%20State.gifhttp://facstaff.gpc.edu/~ulahaise/astrogeneral/parallax%20animation%20Ohio%20State.gifhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_perspectives.html


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Stellar Properties: Parallax IINearest Neighbors

Proxima Centauri: p = 0.77 sod = 1.3 pc Member of triple star system

Alpha Centauri

1.3 pc = 4.3 ly = 270,000 AU (~300,000 times Earth Sundistance!) with nearly nothing inbetween

Barnards Star: p = 0.55

so d = 1.8 pc = 6.0 ly ~ 25 30 stars lie within

30 pc (100 ly) of Sun Work out Lecture Tutorial: Parallax and

Distance, any questions ? see instructor Go over UNL class action question Parallax I

NASA

Hawaii.edu
http://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_miscparallax.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_miscparallax.html


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Stellar Properties Practice 10-I

1. A star has a measured parallax of 0.01arcseconds. Given that d = 1/p this parallax

means that the star is ____________.

a) Much closer than 100 pc.

b) Slightly closer than 100 pc.

c) Exactly at 100 pc.d) Slightly further than 100 pc.

e) Much further than 100 pc.


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Stellar Properties Practice 10-II

2. If we were to use Jupiters orbit (about 5 times

larger than Earths orbit)as a baseline to measure

parallax, would we be able to measure the

parallax of more, the same number of, or fewerstars? Explain your reasoning including the effect

of the larger baseline on the parallax shift of a

given star. (Assume that we would use the same instrument withthe same capability on how small an angular shift it can resolve.)


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Stellar Properties Answers 10-I1. A star has a measured parallax of 0.01

arcseconds. Given that d = 1/p this parallax meansthat the star is ____________.

Answer:The relationship d = 1/p is an equality and

100 is the exact inverse of 0.01. This confirms c) ascorrect and proves all others false.

a) Much closer than 100 pc. (false)

b) Slightly closer than 100 pc. (false)

c) Exactly at 100 pc. (correct)

d) Slightly further than 100 pc. (false)

e) Much further than 100 pc. (false)


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Stellar Properties Answers 10-II2. If we were to use Jupiters orbit (about 5 times larger

than Earths orbit) as a baseline to measure parallax, wouldwe be able to measure the parallax of more, the samenumber of, or fewer stars?

Answer:If we increase the baseline by a factor of 5 that means we wouldmeasure a 5 times larger parallax shift for a given star. Since our instrument

has a set lower limit as to how small an angular shift it can still measure, itwould be able to measure shifts of many further stars because the stellarparallaxes would be amplified by a factor of 5. In other words, stars whoseshifts were too small to be measured from Earths orbit will become largeenough to be measured from Jupiters orbit. In essence, we could measurestars up to 5 times further away from Jupiters orbit, a lot more stars than

from Earths orbit.Common misconceptions: We are NOT closer to the stars at Jupiters orbit because

the difference in distance from the Sun averages out over one complete orbit. Jupiter might beever so slightly closer to a given star for half of its orbit but it would be that much furtheraway from the same star for the other half of its orbit. Besides, the difference in distance tothe Sun for planets of our solar system is negligible compared to the huge distances of otherstars from the Sun.


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Stellar Properties: Brightness I

Stellar parallax measurements show that the starsare at different distances from us. In order tocompare the Suns luminosity to that of other starswe need to know how distance affects the intensity

of light from a light source. Example:What do you observe when you shine a

flashlight at your face held at arms length vs.across the room? The farther away the light source, the dimmer it

appears BUT what is the quantitative relationship?

If you double the distance, is the source exactly half asbright? More or less than half as bright?


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Stellar Properties: Brightness II Brightness distance relationship analogies:

We measure the intensity of lightfrom a point light source with thesurface area of a detector at acertain distance. At greater distance, only a

fraction of the light passes throughthe same size area. What fraction?

Spray paint: the paint is thinning out proportional to

the square of the distance! Brightness, b, prop. to

inverse square of distance

b ~ 1/d2

Go over UNL interactives Magnitudes 1, 2, 3a, 3b

Image by John Percy

Dev.physicslab.org
http://astro.unl.edu/interactives/magnitudes/Magnitude1_Distance.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude2_InverseSquare.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude3a_SameDistance.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude3b_SameLuminosity.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude3b_SameLuminosity.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude3a_SameDistance.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude2_InverseSquare.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude1_Distance.html


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Stellar Properties: Brightness IVLuminosity Distance Relationship solved for apparent

brightness:b = L

4d2

Ex.: Stars A and B have the same luminosity. Star A is 4 timesfarther than Star B. Which one is brighter in the sky by how manytimes? Find the ratio of apparent brightnesses: bA/ bB. Since they both have the

same L, the factor of L/4cancels when forming the ratio:

bA = dB2 = 12 = 1

bB dA2 42 16

Star B appears 16 times brighter in the sky than Star A!

Go over UNL class action questions Flux Fraction 1, Flux Fraction 2, and Inverse

Square Flux

Ex.: University of Oregons Inverse Square Simulation(Instructions are at bottom)http://jersey.uoregon.edu/vlab/InverseSquare/index.html
http://astro.unl.edu/classaction/questions/light/ca_light_fluxfraction.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_fluxfraction2.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_inversesquareshells.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_inversesquareshells.htmlhttp://jersey.uoregon.edu/vlab/InverseSquare/index.htmlhttp://jersey.uoregon.edu/vlab/InverseSquare/index.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_inversesquareshells.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_inversesquareshells.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_fluxfraction2.htmlhttp://astro.unl.edu/classaction/questions/light/ca_light_fluxfraction.html


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Stellar Properties: Magnitudes II The magnitude scale is commonly used but it has one big

pitfall: magnitude numbers are in reverseorder! Go over UNL class action question Apparent m and Brightness

Ex.: Take a magnitude 1 star and a magnitude 3 star. Their

difference in magnitude is 2, so

we receive (2.512)(2.512) = 6.310 xmoreenergy from the star with the

lower magnitude!

Bill Lahaise

Esa.int
http://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_appmagbright.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_appmagbright.html


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Stellar Properties: Magnitudes IVEach star has two observed energy values

1) As observed from Earth Brightness, b = energy we receive per (sec cm2)

Apparent magn. m logarithmic equivalent of b

Inverted sign: the larger b the smaller m!!!

2) actual (intrinsic) property of star,independent of observer

Luminosity, L = energy emitted by star per sec

Absolute magn. M logarithmic equivalent of L

Inverted sign: the larger L the smaller M!!!

The Suns absolute M = + 4.83, L = 1Lsun Go over UNL class action questions Suns Relative Luminosity,

Number of Visible Stars
http://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lumfuncsun.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lumfuncnumvisible.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lumfuncnumvisible.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lumfuncsun.html


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Stellar Properties: Magnitudes V

Remember the relationship between L, b, and distance D:

Inverse square law Luminosity perspective: L = b 4D2 Brightness perspective: b = L/4D2

Equivalent relationship between M, m, and D:

Logarithmic law Absolute magnitude perspective:

M = m 5logD + 5

Apparent magnitude perspective:m = M + 5logD 5

Most useful relationship Distance Modulus

m M = 5 log (D/10)

Based on the difference between apparent and absolute magnitude

gives info about the distance of the star

Bill Lahaise


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Stellar Properties: Magnitudes VI

Distance Modulus two versions: 1) Difference between magnitudes: m M = 5 log (D/10)

If m = M, the star appears equally bright as at adistance of 10 pc from us, and m M = 0

The star is exactlyat 10 pc and If m > M, the star appears dimmer in the sky than at

a distance of 10 pc, m M > 0 The star is farther away than 10 pc

If m < M, the star appears brighter in the sky than ata distance of 10 pc, m M < 0 The star is closer than 10 pc

Go over UNL class action questions Brightness & Energy, Magnitude &Distance, and interaction Magnitude 4
http://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_brightenergy.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_magdist.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_magdist.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude4_TenParsecs.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude4_TenParsecs.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_magdist.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_magdist.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_brightenergy.html


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Stellar Properties: Magnitudes VII

2) Distance Modulus solved for distance:

D = 10(m M + 5)/5

If a stars m = M, then the exponent equals 1 and D = 10 pc.

If a stars m > M it is dimmer in the sky than if it were at 10

pc, then it must be farther than 10 pc: The exponent is > 1 so 10(something > 1) = D > 10 pc

If a stars m < M it is brighter in the sky than if it were at 10

pc, then it must be closer than 10 pc:

The exponent is < 1 so 10(something < 1) = D < 10 pc

Go over UNL class action question Distance Modulus, and interaction Magnitudes 5

Work out Lecture Tutorial: Spectroscopic Parallax Part 1: Magnitudes and Star

Distances, any questions ? see instructor

Work out the Stellar Properties/Classification Lab Practice
http://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_disttostar.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude5_DistanceModulusTable.htmlhttp://astro.unl.edu/interactives/magnitudes/Magnitude5_DistanceModulusTable.htmlhttp://astro.unl.edu/classaction/questions/stellarprops/ca_stellarprops_disttostar.html


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Stellar Properties:

Brightness/Magnitudes Practice 10-III

3. To find the luminosity of a star, what twoproperties need to be known?

a. temperature, apparent magnitude

b. radial motion, proper motion

c. distance, brightness

d. temperature, distance

e. distance, absolute magnitude


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Stellar Properties:

Brightness/Magnitudes Practice 10-IV

4. Which stellar property is a measure of theenergy production of a star?

a. size

b. brightness

c. temperature

d. radial velocity

e. luminosity


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Stellar Properties:

Brightness/Magnitudes Practice 10-V

5. Which stellar property is affected by thedistance to the observer?

a. size

b. brightness

c. temperature

d. radial velocity

e. luminosity


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Stellar Properties:

Brightness/Magnitudes Practice 10-VI

6. Which stellar property is described by theAbsolute Magnitude of a star?

a. size

b. brightness

c. temperature

d. radial velocity

e. luminosity


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Stellar Properties: Bright./Magn.

Practice 10-VII

7. Define and distinguish between apparent

magnitude and absolute magnitude. Which

quantity is luminosity most closely related to?


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Stellar Properties: Bright./Mag.

Practice 10-VIII

8) A certain star has an m = 4.5 and an M = -1.0.

This star is at a distance of ________ 10 pc.

A) less than

B) equal to

C) greater than D) not enough info


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Practice 10-IX

9) Another star has an m = 3.8 and an M = 6.2.

This star is at a distance of ________ 10 pc.

A) less than

B) equal to

C) greater than D) not enough info


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Practice 10-X

10) Three stars, A,B and C, have apparentmagnitudes, ma= 2.3, mb= 5.1, and mc= -3.9.What is their correct order from brightest to faintestin the sky?

A) ABC

B) CAB

C) CBA D) BCA

E) BAC


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Practice 10-XI

11) Two stars, D and E, have the same luminosity. So,

if star E is twice as far away from us as star D then

and star E is ________ times as bright as star D.

A) 2

B) 4

C)

D)

E) the same


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Stellar Properties:

Brightness/Magnitudes Answers 10-III

3. To find the luminosity of a star, what twoproperties need to be known?

Answer: Luminosity can be determined from measured brightness anddistance using the relationship L = b 4D2

a. temperature, apparent magnitude (m is a measure of b so thatwould work, but temperature does not false)

b. radial motion, proper motion (none of these work false)

c. distance, brightness (correct, see above) d. temperature, distance (distance works but temperature doesnt

false)

e. distance, absolute magnitude (distance works but M is a measureof luminosity itself so that doesnt work false)


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Stellar Properties:

Brightness/Magnitudes Answer 10-IV

4. Which stellar property is a measure of theenergy production of a star?

Answer:

a. size (the size of the star is one of the consequences of its energyproduction but not a measure of it - false)

b. brightness (the brightness of a star is a combination of its energyproduction and its distance from Earth false)

c. temperature (the temperature is also a consequence of a stars

energy production but not a measure of it false) d. radial velocity (is a measure for how fast the star is moving along

our line of sight, it is unrelated to energy production false)

e. luminosity (the luminosity of a star is a measure of energyproduction because it is defined as the total energy output of thestar per second correct)


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Stellar Properties:

Brightness/Magnitudes Answer 10-V

5. Which stellar property is affected by thedistance to the observer?

Answer:

a. size (the size of a star only depends on its luminosity and temperature, it is anintrinsic property that does not depend on distance false)

b. brightness (the brightness does depend on the distance of the star from Earth.If two stars have an equal luminosity but are at different distances then we willsee the closer star brighter in the sky. Brightness depends on the luminosity andthe inverse square of the distance correct)

c. temperature (temperature is also an intrinsic property of the star that dependson the stars luminosity and size but not on distance false)

d. radial velocity (radial velocity is the speed of the star along our line of sight. Itdoes not depend on the distance of the star false)

e. luminosity (luminosity is a measure of the energy output of the star which is an

intrinsic property that only depends on size and temperature false)


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Stellar Properties:

Brightness/Magnitudes Answer 10-VI

6. Which stellar property is described by the AbsoluteMagnitude of a star?

Answer:absolute magnitude is defined as alogarithmic measure of luminosity which means choice

e) is correct and all other choices are false.

a. size (false)

b. brightness (false) c. temperature (false)

d. radial velocity (false)

e. luminosity (correct)


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Answer 10-VII

7. Define and distinguish between apparent magnitude andabsolute magnitude. Which quantity is luminosity most closelyrelated to?

Answer: Apparent magnitude is a measure for the brightnessof a star in our night sky. It is measured on a scale with lowernumbers for brighter stars and higher numbers for dimmerstars. Two stars that have the same energy output can havedifferent apparent magnitudes when they are at different

distances from the Solar System. Absolute magnitude is ameasure of the actual energy output of a star, the luminosity.The scale is also inverted so that stars with a larger luminosityhave a lower absolute magnitude and stars with a lowerluminosity have a higher absolute magnitude.


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Answer 10-IX9) Another star has an m = 3.8 and an M = 6.2. This star is at adistance of ________ 10 pc.

Answer: At 6.2 the stars absolute M is larger than its apparent m

of 3.8. So it appears brighter in the sky than it would if it were ata distance of 10 pc from Earth. That means it must be at a smallerdistance from Earth than 10 pc.

A) less than (CORRECT, see above)

B) equal to (false, stars m would be equal to its M if it were at

10 pc) C) greater than (false, stars m would be greater than its M if it

were farther)

D) not enough info (false, this question can be answeredknowing m and M)


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Answer 10-X10) Three stars, A,B and C, have apparent magnitudes, ma= 2.3, mb=5.1, and mc= -3.9. What is their correct order from brightest to faintest inthe sky?

Answer: the magnitude scale is in reverse order so stars with a smaller m

are brighter in the sky than stars with a larger m. The correct order frombrightest to faintest starts with the star of smallest magnitude, star C withm = -3.9. Next comes star A with m = 2.3, and the faintest is star B with m= 5.1. Thus, the correct letter sequence is CAB.

A) ABC (false, AB are in correct order but C is out of place)

B) CAB (CORRECT)

C) CBA (false, C is in correct order but A and B are out of place)

D) BCA (false, C and A are in correct order but B is out of place)

E) BAC (false, this is the exact reverse order from what was asked)


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Answer 10-XI11) Two stars, D and E, have the same luminosity. So, if star E is twice asfar away from us as star D then and star E is ________ times as bright asstar D.

Answer: The brightness of a star is inversely proportional to the square of

its distance from us (b prop. 1/d2

). If stars D and E have the sameluminosity they put out an equal amount of energy. If star E is twice as faraway, that factor of 2 in the distance gets inverted and squared (1/22=) to give the factor for how its brightness compares to that of star D.

A) 2

B) 4

C)

D)

E) the same


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Stellar Properties: Spectral Types I

Review: Wiens Law: Temperature of blackbody is

inversely proportional to the wavelength of peak intensityemission

max= 2.9 x 10-3m / T

The Suns surface temperature is 5800K. It emits most ofits energy at 2.9 x 10-3m / 5800K = 0.500 x 10-6m = 500 nm

Green! Remember why we see the

Sun as white?

What color wouldstars be that are Hotter/cooler than the Sun?

Bottom Line:the surface temperature of a star is

strongly related to its color!

PBS - Nova

Broad intensity peak centered on 500 nm.

St ll P ti S t l T II


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Stellar Properties: Spectral Types II

Review:Suns Absorption Spectrum by color and intensity

Guide star light through a spectroscope (prism or diffractiongrating) which breaks it down by wavelength (color).

By color

By intensity Shows absorption lines

as narrow dips

Shows maximumenergy emission asbroad peak in curveof the continuum (peak wavelength related to T, see Wiens Law above)

Absorption lines come from atoms and ions of cooler, dilute gasin Suns atmosphere that absorb narrow wavelengths of theoutgoing photons that are characteristic to their atomic electrontransitions.

Work out UNL ClassAction question Spectra

Both PBS - Nova
http://astro.unl.edu/classaction/questions/sunsolarenergy/ca_sunsolarenergy_spectra.htmlhttp://astro.unl.edu/classaction/questions/sunsolarenergy/ca_sunsolarenergy_spectra.html


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Stellar Properties: Spectral Types III What do the spectra of other stars look like?

What can they tell us about the properties of other stars? Analyze which spectral lines are present and how strong

they are to see if there is a pattern for classification

Historically: first classification scheme was based

on strength of hydrogen (H) lines. Spectral type with strongest H-lines = Type A, with less

strong H-lines = Type B, etc. down the alphabet withdecreasing H-line strength

Big draw back: two groups of stars with weak or no H-lines but otherwise totally different spectra hadneighboring spectral types! Stars with Helium (He) lines at high temperatures

Stars with lines of metals and molecules at low temperatures


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Stellar Properties: Spectral Types IV

Arrows above mark twoH-Balmer lines note their changing width with T.

Psu.edu, smiley by source.

Second classification scheme based on temperature (T) High T:higher energy transitions (ex. Atomic and ionized He),

very weak H-lines

Medium T:strong H-lines,

He lines fading out at

higher T end, metal andmolecular lines are coming

in at lower T end

Low T: get only low energy

transitions (ex. Metal and

molecule lines), very weak

to no H-lines Go over UNL class action questions Line Strength 1, Line Strength 2, Spectral Type

Number Line

Work out Lecture Tutorial: Analyzing Spectra, any questions ? see instructor
http://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_onelinestrength.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_weakerhlines.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_stypenumline.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_stypenumline.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_stypenumline.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_stypenumline.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_weakerhlines.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_onelinestrength.html


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Stellar Properties: Spectral Types V Rearrange spectral types in order of temperature

No alphabetic order anymore, some letters are dropped New sequence: O B A F G K M (hot to cold)

(mnemonic Oh, be afine guy/girl kiss me!)

Bill Lahaise

Betelgeuse = M

Mintaka = O

Rigel = B

Why are their sizes

different from those

below? Different

distances and kinds

of starsstay tuned

Constellation Orion

Galileospendulum.org


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Stellar Properties: Spectral Types VI

Each spectral type is divided into numericalsubtypes:

Ex.: Sun

G2 with a T = 5778 K (5500 C, 9940 C)

Go over UNL class action question Spectral Type Temp.

Bill Lahaise

Spectral types and

selected subtypes are

labeled on the left edgeby Wikipedia

Go over UNL animation

Spectra Explorer
http://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_stypetemps.htmlhttp://astro.unl.edu/classaction/animations/light/spectrum010.htmlhttp://astro.unl.edu/classaction/animations/light/spectrum010.htmlhttp://astro.unl.edu/classaction/animations/light/spectrum010.htmlhttp://astro.unl.edu/classaction/animations/light/spectrum010.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_stypetemps.html


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Stellar Properties: Spectral Type

Practice 10-XII

12) The spectral type sequence OBAFGKM putsstars in order of their

A) temperature B) size

C) luminosity

D) strength of helium lines E) strength of hydrogen lines


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Practice 10-XIII

13) Sort the following spectral types from hottestto coolest: A5, A2, B2, B5.

A) B5, B2, A5, A2 B) B2, B5, A2, A5

C) A2, A5, B2, B5

D) A5, A2, B5, B2 E) B2, A2, B5, A5


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Practice 10-XIV

14) The strongest hydrogen lines are found in______.

A) the hottest types B) the coolest types

C) A types

D) F types E) G types


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Answer 10-XII12) The spectral type sequence OBAFGKM puts stars in order of their

Answer:

A) temperature (CORRECT! The original sequence was in alphabeticalorder and it was based on the strength of the hydrogen lines. This

turned out to be ambiguous and the sequence was rearranged in orderof temperature)

B) size (false, there are larger and smaller stars for each of thespectral types)

C) luminosity (false, some stars with the highest luminosities belong to

type M) D) strength of helium lines (false, only the hottest two spectral types

have He-lines)

E) strength of hydrogen lines (false, see above, totally unrelatedspectral types (the hottest and the coldest) both have weak to nohydrogen lines)

S S


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Answer 10-XIII13) Sort the following spectral types from hottest to coolest: A5, A2, B2,B5.

Answer: The sequence of spectral types from hottest to coolest isOBAFGKM. Each type is subdivided into numerical subtypes from hottest

to coolest 0, 1, 2, , 9. So, type B is hotter than type A, this eliminatesanswers C) and D).

A) B5, B2, A5, A2 (false, type B is hotter than A but subtype 5 iscooler than 2)

B) B2, B5, A2, A5 (CORRECT! B is hotter than A and subtypes 2 arehotter than 5)

C) A2, A5, B2, B5 (false, see above)

D) A5, A2, B5, B2 (false, see above)

E) B2, A2, B5, A5 (false, type A2 is out of order)

S ll S l


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Answer 10-XIV

14) The strongest hydrogen lines are found in ______.

Answer:

A) the hottest types (false, they have weak hydrogen lines)

B) the coolest types (false, they have weak to no hydrogenlines)

C) A types (CORRECT! The original sequence of spectraltypes was in alphabetical order according to the strength

of the hydrogen lines, with type A having the strongesthydrogen lines)

D) F types (false, has slightly weaker H-lines than type A)

E) G types (false, has weaker H-lines than type A)

S ll S ll S


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Stellar Properties: Stellar Sizes I

So far: Stellar properties of stars in our solar

neighborhood that can be directly measured brightness, distance, temperature,

radial velocity (with Doppler shift)

Indirectly determined using the above Luminosity (using brightness and distance)

What about the size of stars? Size cannot be directly measured

generally, stars are so far away thatthey appear as point sources of light

Only exception: Betelgeuse! A super giant 640 ly away from Earth,

photographed by Hubble Space Telescope

in 1996

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Stellar Properties: Stellar Sizes II We can measure T of a star and determine its luminosity

Use Stefans Law that relates energy flux, F, per cm2

to T Review:Stefans Law: F = T4 where is a natural constant

We can multiply the energy flux, F, through 1 cm2by the entire

surface area of the star and thatll equal the luminosity

Surface area of a sphere:4 R2

where R is the radius of the sphere

Bill Lahaise

There is the size

of the star!

Knowing L and T

gets you R!

Stellar Properties Stellar Sizes III


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Stellar Properties: Stellar Sizes III

Stefan-Boltzmann Law: L = (4R2)(T4) Luminosity depends on radius and temperature

Ex.: a smaller, hotter star can have the same L as a cooler, largerstar

Furthermore: L depends on the square of the radiusand

the fourth power of the temperature L is more strongly dependent on T than on R!

Ex.: star A being 4 times smaller than star B only needs to be 2times hotter than star B to have the same luminosity!

With numbers: take the units in comparison to the Sun (i.e. 1

= same value as the Sun, 2 = double the Suns value, etc.) For star A: L = (1Rsun)2x (2Tsun)4= 16 Lsun

For star B: L = (4Rsun)2x (1Tsun)4= 16 Lsun

Go over UNL interactives Luminosity 1, Luminosity 5, and class action questions L-R-T Relation, Stellar Luminosity Comparison
http://astro.unl.edu/interactives/luminosity/Luminosity1_Of_Stars.htmlhttp://astro.unl.edu/interactives/luminosity/Luminosity5_Table.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lrtrelation.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lrtrelation.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lumcomp.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lumcomp.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lrtrelation.htmlhttp://astro.unl.edu/classaction/questions/stellarprops2/ca_stellarprops2_lrtrelation.htmlhttp://astro.unl.edu/interactives/luminosity/Luminosity5_Table.htmlhttp://astro.unl.edu/interactives/luminosity/Luminosity1_Of_Stars.html


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Stellar Properties: Stellar Sizes

Practice 10-XV

15) Stellar sizes practice with the Stefan-

Boltzmann Law:

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Practice 10-XVI

16) Stellar sizes practice with the Stefan-

Boltzmann Law:



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Practice 10-XVII17) Stellar sizes practice with the Stefan-Boltzmann Law:

In reality, T and L can be determined independently.

That makes the radius the sought after quantity.

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Practice 10-XVIII

18) Which of the following statements is true? Thelargest stars are__________.

A) all the hottest stars B) all the coolest stars

C) hot stars with a high luminosity

D) hot stars with a low luminosity E) cool stars with a high luminosity

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Practice 10-XIX

19) Which two properties need to be known todetermine a stars size (radius)?

A) luminosity and temperature B) temperature and distance

C) distance and luminosity

D) luminosity and magnitude E) temperature and spectral type

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Practice 10-XX

20) If two stars have the same luminosity but one

is a K type star and the other is a B star, which

star is larger? How did you determine this?



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Answer 10-XV

15) Two stars, A and B, have the same temperatureof 5000 K but Star A has a larger diameter thanstar B. Which one has the larger luminosity? Answer: Luminosity is proportional to the square of the

radius and the fourth power of the temperature of a star.Stars A and B have the same temperature so that doesntfactor into the difference in luminosity. Star A is larger thanstar B, though, so it will also have a larger luminosity thanstar B. In the house/furnace analogy, star A corresponds to, say, a five

bedroom house (larger R) and star B to a four bedroom house.In order to heat the outside facing rooms of both houses to thesame comfortable temperature, star A needs a larger furnace(L) than star B.

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Answer 10-XVI

16) Two stars, A and B, have the same diameter butstar A has a temperature of 5000 K and star B of10 000 K. Which one has the larger luminosity? Answer: Luminosity is proportional to the square of the

radius and the fourth power of the temperature of a star.Stars A and B have the same diameter so that doesntfactor into the difference in luminosity. Star B is hotter thanstar A, so it will have a larger luminosity than star A. In the house/furnace analogy, stars A and star B are the same

size house. But house A should be heated to regularcomfortable temperature while house B should be heated tomake dessert lizards comfortable. That means house B needs alarger furnace (L) than star A.

Stellar Properties Stellar Sizes


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Answer 10-XVII

17) Stars A and B have the same luminosity butdifferent temperatures. Star A has a temperature of5000 K and star B of 10 000 K. Which star is larger? Answer: Luminosity is proportional to the square of the radius

and the fourth power of the temperature of a star. Stars Aand B have the same luminosity so that doesnt factor into thedifference in sizes. So the product R2T4for star A has to equalthe product of R2T4for B: (RA

2)(TA4) = (RB

2)(TB4). If star B has a

higher temperature than star A then star A must have a largerradius than star B to balance out the equation. In the house/furnace analogy, stars A and star B have the same

size furnace but house Bs outside facing rooms are hotter.Therefore, house A must be larger so that its outside facing roomsare further away from the furnace so they can be cooler.



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Answer 10-XVIII

18) Which of the following statements is true? The largest starsare__________.

Answer:

A) all the hottest stars (false, some of the hottest stars are large but a lot

of the hottest stars are very tiny such as white dwarfs, for example) B) all the coolest stars (false, some of the coolest stars are, indeed, the

largest (the red super giants) but most of the coolest stars are very smallred dwarfs)

C) hot stars with a high luminosity (false, these stars are large but stillsmaller than the red super giants)

D) hot stars with a low luminosity (false, these are the tiny white dwarfs)

E) cool stars with a high luminosity (CORRECT! These are the red supergiants with low surface temperatures and very high luminosities. The onlyway these stars can be so cool with such a high luminosity is that theyare incredibly huge)



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Answer 10-XIX

19) Which two properties need to be known to determine a starssize (radius)?

Answer: this question asks for the Stefan-Boltzmann law: L prop. R2T4

A) luminosity and temperature (CORRECT! When L and T areknown, the above law can be solved for the radius)

B) temperature and distance (false, T is needed but distance isuseless)

C) distance and luminosity (false, L is needed but not distance)

D) luminosity and magnitude (false, L is needed but magnitudeis just another measure of luminosity)

E) temperature and spectral type (false, T is needed but thespectral type is just another measure of temperature)



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Answer 10-XX

20) If two stars have the same luminosity but one

is a K type star and the other is a B star, which

star is larger? How did you determine this?

Stellar Properties: Summary Questions


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p y Practice 10-XXI

star m M sp. type dist. (pc)

A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1

D 1.20 -5.1 B2 II 182

E 4.73 7.0 M1 V 3.48

21) In the table above which star has the highestsurface temperature (disregard the roman numerals in

the sp. type column)?



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Practice 10-XXII


A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1 D 1.20 -5.1 B2 II 182

E 4.73 7.0 M1 V 3.48

22) In the table above which star has the smallestparallax (disregard the roman numerals in the sp. typecolumn)?



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Practice 10-XXIII


A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1 D 1.20 -5.1 B2 II 182

E 4.73 7.0 M1 V 3.48

23) In the table above which star is the brightest in thenight sky (disregard the roman numerals in the sp. typecolumn)?



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Practice 10-XXIV

star m M sp. type dist. (pc) A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1 D 1.20 -5.1 B2 II 182

E 4.73 7.0 M1 V 3.48

24) In the table above which star is the largest(disregard the roman numerals in the spectral typecolumn)?



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Answer 10-XXI star m M sp. Type dist. (pc) A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1

D 1.20 -5.1 B2 II 182 E 4.73 7.0 M1 V 3.48

Answer:

21) In the table above which star has the highest surface

temperature? Surface temperature is given by spectral type from hot to

cool: OBAFGKM with subtypes 0, , 9. The hottest spectraltype listed is B2 for star D, so choice D) is CORRECT.



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Answer 10-XXII star m M sp. type dist. (pc) A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1

D 1.20 -5.1 B2 II 182 E 4.73 7.0 M1 V 3.48

Answer:

22) In the table above which star has the smallest parallax?

The star with the smallest parallax is the star that is furthestaway because the parallactic shift of a star is inverselyproportional to its distance from us. The star at the largestdistance is star D, so choice D) is CORRECT.



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Answer 10-XXIII star m M sp. type dist. (pc) A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 III 95.1

D 1.20 -5.1 B2 II 182

E 4.73 7.0 M1 V 3.48

Answer:

23) In the table above which star is the brightest in the night sky?

The brightness of a star is given by its apparent magnitude, m.The magnitude scale is reversed so the brighter stars have smallerand the dimmer stars have larger magnitudes. Thus, the star withthe smallest m is the brightest star in the sky, star C). So, C) is theCORRECT choice.



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Answer 10-XXIV star m M sp. type dist. (pc) A 3.73 6.1 K2 V 3.28

B 6.32 4.8 G2 V 20.2

C -0.51 -5.4 K0 II 95.1

D 1.20 -5.1 B2 II 182

E 4.73 7.0 M1 V 3.48 Answer:

24) In the table above which star is the largest?

If we disregard the roman numerals for this answer then we can use theconcept of the Stefan-Boltzmann Law where L prop. to the square of R

and the fourth power of T. So, were looking for the coolest possible starwith the highest luminosity (meaning the lowest absolute magnitude, M).That is star C) with M = -5.4 and a spectral type of K0. Then C) isCORRECT. Even though stars A and E are a little cooler than C withspectral types of K2 and M1, they have high Ms which means they have

f f

a 1020 template study guide 10 star properties

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