our universe
DESCRIPTION
OUR UNIVERSE. Week 8. The Sun & the Stars. Visible. UV. Sun’s Structure. Sun’s Structure. The ultra-hot core extends outward from the star's center to about 20% of its radius. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/1.jpg)
OUR UNIVERSEOUR UNIVERSEWeek 8
![Page 2: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/2.jpg)
The Sun & the The Sun & the
Stars.Stars.
Visible UV
![Page 3: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/3.jpg)
Sun’s Structure
![Page 4: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/4.jpg)
Sun’s Structure
The ultra-hot core extends outward from the star's center to about 20% of its radius.
The temperature at the centre of the core is around 15 million kelvin, and it gradually decreases further from the center.
The core is the location within the Sun in which hydrogen fusion occurs.
![Page 5: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/5.jpg)
Above the core is the radiation zone.
It extends from the top of the core outward to about 70% of the Sun's radius.
Temperatures varies from 10 to 5 million kelvin.
Energy is carried through the radiation zone via electromagnetic radiation (photons).
![Page 6: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/6.jpg)
Above the radiation zone, and extending all the way to the "surface" of the Sun, is the convection zone.
This part of the Sun is relatively "cool", with temperatures ranging downward from a peak of around 2 million kelvin.
Energy flows upward through this area in a different manner than in the underlying radiation zone.
![Page 7: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/7.jpg)
Gigantic blobs of matter, heated by the radiation zone below, rise to the Sun's surface, carrying heat with them.
As these blobs of plasma emit their energy into space at the Sun's surface, they cool somewhat;
enough so that their densities increase and they sink back down.
This convective motion is akin to that seen in a lava lamp.
![Page 8: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/8.jpg)
Solar Solar
Granulation Granulation
is due tois due to
convection convection
cellscells
![Page 9: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/9.jpg)
The Sun’s internal StructureThe Sun’s internal Structure
![Page 10: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/10.jpg)
Convection cellsConvection cells
![Page 11: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/11.jpg)
![Page 12: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/12.jpg)
At the topmost boundary of the convection zone lies the photosphere.
The photosphere is often referred to as the "surface" of the Sun.
The photosphere marks an abrupt transition in the optical properties of the material that makes up the Sun.
![Page 13: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/13.jpg)
Below the photosphere, the photons bounce around so much that they don't travel direct paths to viewers on Earth.
Hence we cannot see deeper into the Sun than the photosphere.
So the photosphere is the "visible surface" of the Sun.
The temperature of the photosphere is about 5800 K.
![Page 14: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/14.jpg)
Above the photosphere the Sun's vast “atmosphere” extends outward into interplanetary space.
In the case of the Sun, the density of material in the solar atmosphere is much less than is the case below the photosphere within the Sun's "interior".
Also, the physical properties that control motions of material and the temperatures encountered are far different in the Sun's atmosphere than in the layers of the Sun beneath the photosphere.
![Page 15: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/15.jpg)
There are two major regions within the Sun's atmosphere:
the lower and much smaller chromosphere,
and the upper and much larger corona.
![Page 16: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/16.jpg)
The relatively thin chromosphere is just a few thousand kilometers deep, less than Earth's diameter.
Although temperatures within the Sun gradually decrease as one moves outward,
(from 15 million kelvin in the core to 5,800 kelvin at the photosphere)
they begin to climb once again as we rise through the Sun's atmosphere.
![Page 17: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/17.jpg)
The temperature of the chromosphere increases from 4,300 kelvin (slightly above the photosphere) to around 50,000 kelvin (near the corona).
Powerful magnetic fields in the Sun's atmosphere accelerate the plasma as they transfer energy to it, heating the material in ways that scientists still don't fully understand.
![Page 18: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/18.jpg)
Until relatively recent times, when special filters and space-based telescopes became available, the Sun's atmosphere was only visible during total solar eclipses.
During an eclipse, the chromosphere could be seen as a colorful reddish zone around the edge of the occluded solar disk, thus earning the region its name (Greek "chromos" = "color").
![Page 19: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/19.jpg)
Chromosphere
![Page 20: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/20.jpg)
The Sun's much larger upper atmosphere, the corona, extends unevenly for millions of kilometers into space.
The temperature of the solar atmosphere climbs sharply in a narrow transition region between the chromosphere and the corona.
The temperatures in the corona range from around 800,0000 K to 3 million K
![Page 21: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/21.jpg)
corona,
![Page 22: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/22.jpg)
Matter is continuously flung outward by the Sun.
An electrically charged "soup" of protons, electrons, and lesser numbers of heavier atomic nuclei flows outward into space.
This extremely tenuous plasma is called the solar wind.
In a sense, the solar wind is a vast extension of the Sun's atmosphere.
![Page 23: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/23.jpg)
The solar wind flows past Earth and beyond.
All of the planets are within the gigantic "bubble" of the solar wind.
Eventually, on the far edge of our solar system, the solar wind merges with the outpourings of other stars, and the extended solar atmosphere ends.
![Page 24: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/24.jpg)
The gigantic region within this solar wind "bubble" is called the heliosphere.
The boundary of the heliosphere, where the extended atmosphere of the Sun finally gives way to interstellar space, is called the heliopause.
The location of the heliopause is something like 70AU from the Sun.
![Page 25: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/25.jpg)
Solar Prominence in UVSolar Prominence in UV
![Page 26: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/26.jpg)
SunspotsSunspots
![Page 27: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/27.jpg)
It appears that sunspots are the visible counterparts of magnetic flux tubes in the sun's convective zone that get "wound up" by differential rotation.
![Page 28: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/28.jpg)
![Page 29: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/29.jpg)
Convection cellsConvection cells
![Page 30: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/30.jpg)
Differential rotation causes field Differential rotation causes field
lineslines
to be wrapped around the Sunto be wrapped around the Sun
Sunspots migrate to equator where they cancel Sunspots migrate to equator where they cancel
out and eventually reverse the overall field out and eventually reverse the overall field
![Page 31: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/31.jpg)
If the stress on the tubes reaches a certain limit, they curl up like a rubber band and puncture the sun's surface.
Convection is inhibited at the puncture points; the energy flux from the sun's interior decreases; and with it surface temperature.
![Page 32: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/32.jpg)
Sunspots are depressions on the sun's surface.
Sunspots come in pairs with opposite magnetic polarity.
From cycle to cycle, the polarities of leading and trailing with respect to the solar rotation] sunspots change from north/south to south/north and back.
Sunspots usually appear in groups.
![Page 33: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/33.jpg)
Sunspot Sunspot
Structure Structure
![Page 34: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/34.jpg)
![Page 35: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/35.jpg)
• The sunspot itself can be divided into two parts:
• The central umbra, – which is the darkest part, where the magnetic field
is approximately vertical.
• The surrounding penumbra, – which is lighter, where the magnetic field lines are
more inclined.
![Page 36: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/36.jpg)
• Sunspot activity cycles about every eleven years.
• The point of highest sunspot activity during this cycle is known as Solar Maximum, and the point of lowest activity is Solar Minimum.
• Early in the cycle, sunspots appear in the higher latitudes and then move towards the equator as the cycle approaches maximum.
![Page 37: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/37.jpg)
Sun spots have a 11 year cycle Sun spots have a 11 year cycle
(magnetic field reversal)(magnetic field reversal)
![Page 38: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/38.jpg)
Differential rotation causes field Differential rotation causes field
lineslines
to be wrapped around the Sunto be wrapped around the Sun
Sunspots migrate to equator where they cancel Sunspots migrate to equator where they cancel
out and eventually reverse the overall field out and eventually reverse the overall field
![Page 39: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/39.jpg)
The Solar CoronaThe Solar Corona
Visible
![Page 40: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/40.jpg)
The Solar CoronaThe Solar Corona
Visible
A corona is a type of plasma "atmosphere" of the Sun.
It extends millions of kilometers into space
Most easily seen during a total solar eclipse,
but also observable in a coronagraph.
![Page 41: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/41.jpg)
The Solar CoronaThe Solar Corona
Visible
A corona is a type of plasma "atmosphere" of the Sun.
It extends millions of kilometers into space
Most easily seen during a total solar eclipse,
but also observable in a coronagraph.
![Page 42: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/42.jpg)
Light from the corona comes from three primary sources (called K, F and E), which are called by different names although all of them share the same volume of space.
![Page 43: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/43.jpg)
The K-corona (K for kontinuierlich, "continuous" in German).
Created by sunlight scattering off free electrons;
Doppler broadening of the reflected photospheric absorption lines completely obscures them, giving the spectrum the appearance of a continuum with no absorption lines.
![Page 44: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/44.jpg)
The F-corona (F for Fraunhofer).
Created by sunlight bouncing off dust particles, and is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight;
the F-corona extends to very high elongation angles from the Sun, where it is called the Zodiacal light.
![Page 45: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/45.jpg)
The E-corona (E for emission).
Result from spectral emission lines produced by ions that are present in the coronal plasma;
it may be observed in broad or forbidden or hot spectral emission lines and is the main source of information about the corona's composition.
![Page 46: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/46.jpg)
The Solar The Solar
NeighbourhoodNeighbourhoodTransparency
![Page 47: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/47.jpg)
Transparency
circles at 5, 10, 15 ly
![Page 48: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/48.jpg)
Measuring Measuring
StarsStarsTemperature T Distance d
Luminosity LRadius RMass M
Element Abundances
![Page 49: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/49.jpg)
Measuring StarsMeasuring Stars
Distances (Distances (dd) )
needed for finding needed for finding LL• Stellar parallax (Hipparchos satellite yielded a Stellar parallax (Hipparchos satellite yielded a
revolutionary improvement)revolutionary improvement)• Proper motion studiesProper motion studies• Moving clusters - stars seem to get closer as the Moving clusters - stars seem to get closer as the
cluster recedes.cluster recedes.• Comparison with standard stars of known Comparison with standard stars of known
distancedistance
![Page 50: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/50.jpg)
Measuring Measuring
the Stars.the Stars.
First a Reminder:First a Reminder:
![Page 51: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/51.jpg)
Measuring DistancesMeasuring Distances
using the Earth’susing the Earth’s
orbit around orbit around
the Sun as a the Sun as a
baselinebaseline
![Page 52: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/52.jpg)
Orion’s belt
We only observe a2-dimensional
projection of objects in the sky.
We needWe need
extra information toextra information to
find their position find their position
inin
3-dimensions -3-dimensions -
their distance dtheir distance d
Orion
![Page 53: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/53.jpg)
Distance by Distance by
ParallaxParallax(a) Planet observed from A & B against background of distant stars.(b) Photos taken from A & B
show the planet’s image has moved against the background stars.
dAB2
![Page 54: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/54.jpg)
Distance by Distance by
ParallaxParallax(a) Planet observed from A & B against background of distant stars.(b) Photos taken from A & B
show the planet’s image has moved against the background stars.
dAB2
2tan
ABd
![Page 55: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/55.jpg)
Stellar ParallaxStellar Parallax
![Page 56: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/56.jpg)
Proper MotionProper Motion
The proper motion of a star is its angular change in position over time as seen from the Sun.
It is measured in seconds of arc per year.
![Page 57: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/57.jpg)
Proper MotionProper MotionThis contrasts with radial velocity, which is the time-rate of change in distance toward or away from the viewer.
(usually measured by the Doppler shift)
![Page 58: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/58.jpg)
Proper MotionProper MotionBarnard’s Star (at 1.82 pc, 5.98 ly) Barnard’s Star (at 1.82 pc, 5.98 ly)
moves over 22yrsmoves over 22yrs
by 230by 230 = 3.8´ = 3.8´
1894
1916
![Page 59: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/59.jpg)
Stellar motionStellar motion
vVt
Transverse velocity
(measured by Proper Motion)
Vr
Radial velocity(measured by
DopplerShift)
![Page 60: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/60.jpg)
Stellar Stellar
Motion.Motion.
AnAn
example:example: CentauriCentauri
![Page 61: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/61.jpg)
Measuring Stars.Measuring Stars.
Radius Radius R
![Page 62: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/62.jpg)
Stellar SizesStellar Sizes
Directly from imaging
&Interferometry
Indirectly from Luminosity
![Page 63: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/63.jpg)
The Sun’s RadiusThe Sun’s RadiusDirectly from
imaging
RSun = 6.96108 m
= 109 RE
1 AU = 1.4961011 m
= 215 RE Mercury’s orbit
= 83 Rsun
![Page 64: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/64.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
![Page 65: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/65.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
Stefan’s Law
![Page 66: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/66.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
4TFlux Stefan’s Law
![Page 67: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/67.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
Flux = Power per unit area
![Page 68: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/68.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
Luminosity = Power radiated
![Page 69: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/69.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
Flux = Luminosity per unit area
![Page 70: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/70.jpg)
Directly from Imaging & Interferometry
(but restricted to nearby large stars)(but restricted to nearby large stars)
Stellar RadiiStellar Radii
Indirectly from L & T:
424 TRL starstar
![Page 71: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/71.jpg)
HST Resolves a StarHST Resolves a Star
The Red GiantThe Red GiantBetelgeuseBetelgeuse
in the constellation in the constellation
OrionOrion
![Page 72: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/72.jpg)
Stellar Stellar
SizesSizes
vary vary
greatlygreatly
BetelgeuseBetelgeuse
300 300 R⊙
![Page 73: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/73.jpg)
THETHE END END OF LECTURE 16OF LECTURE 16
![Page 74: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/74.jpg)
OUR UNIVERSEOUR UNIVERSELecture No. 17
![Page 75: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/75.jpg)
Measuring StarsMeasuring Stars..
Temperature Temperature T
( i.e. ( i.e. SurfaceSurface T )
&&
LuminosityLuminosity L
![Page 76: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/76.jpg)
The The
Black BodyBlack Body
SpectrumSpectrum
Here plotted Here plotted
againstagainstwavelength
![Page 77: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/77.jpg)
The Sun’s The Sun’s
continuous continuous
spectrum spectrum
is well is well
approximated approximated
by a by a
Black BodyBlack Body
or or
Planck Planck
SpectrumSpectrum
at 5800 K
![Page 78: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/78.jpg)
A Star’s Colour A Star’s Colour
Depends on its TemperatureDepends on its Temperature
![Page 79: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/79.jpg)
Planck spectrum:Planck spectrum:
& therefore& therefore
the colours of starsthe colours of stars
only depend on only depend on T
T
T
max
1max
![Page 80: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/80.jpg)
Brightness through UBV FiltersBrightness through UBV Filters
Depends on a Star’s TemperatureDepends on a Star’s Temperature
![Page 81: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/81.jpg)
Brightness through UBV FiltersBrightness through UBV Filters
Depends on a Star’s TemperatureDepends on a Star’s Temperature
Use of filters provides a quickUse of filters provides a quick
and convenient method ofand convenient method of
estimating stellar propertiesestimating stellar properties
Each filter samples a different part of the Planckspectrum. The ratio of brightness in B and V filtersdetermines the COLOUR TEMPERATURE
B-V log T
![Page 82: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/82.jpg)
UBV FiltersUBV Filters
are are
supplemented supplemented
with with
8 IR filters8 IR filters
U 360 nmB 420 nmV 540 nmR 700 nm---------------------------------------I 900 nm = 0.90 mJ 1250 nm = 1.25 mK 2200 nm = 2.20 m---------------------------------------L 3400 nm = 3.40 mM 4900 nm = 4.90 m---------------------------------------N 10200 nm = 10.20 mQ 20000 nm = 20.00 m
![Page 83: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/83.jpg)
The Black Body LawsThe Black Body Laws
Stefan-Boltzmann Law for the Flux
Watts m-2
The Total Power L* emitted by a star,
of Radius R* and Area = 4 R*2 is
Watts
4TFlux
42** 4 TRL
![Page 84: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/84.jpg)
Luminosity Luminosity L Watts
needs distanceneeds distance d
&&
brightness (Flux) at Earth brightness (Flux) at Earth (b Watts m-2)
Measuring StarsMeasuring Stars
![Page 85: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/85.jpg)
LUMINOSITY L*
is the Total Power emitted by a star,
of Radius R* and Area = 4 R*2
Watts
42** 4 TRL
![Page 86: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/86.jpg)
The Measured apparent brightness b* is the Flux reaching the Earth at
distance d* from the Star
![Page 87: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/87.jpg)
The Measured apparent brightness b* is the Flux reaching the Earth at
distance d* from the Star
Watts m-22*
** 4 d
Lb
![Page 88: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/88.jpg)
If we Measure both
apparent brightness b*
& distance d*
we obtain Luminosity L*
![Page 89: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/89.jpg)
If we Measure both
apparent brightness b*
& distance d*
we obtain Luminosity L*
Watts*2** 4 bdL
![Page 90: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/90.jpg)
Measuring both d* and the
apparent brightness b* as well as
T (from spectrum) gives us the star’s Radius
42** 4 TRL
![Page 91: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/91.jpg)
Measuring both d* and the
apparent brightness b* as well as
T (from spectrum) gives us the star’s Radius
4*2
* 4 T
LR
![Page 92: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/92.jpg)
The Luminosity is often
found in terms of a standard
star such as the Sun.2
*
** 4 d
Lb
20
00 4 d
Lb
![Page 93: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/93.jpg)
The Luminosityis usually expressed
in terms of the
Solar Luminosity Lsun
For example, a Supergiant :
L*=10 4Lsun
![Page 94: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/94.jpg)
If If distancedistance d not known not known
we must resort to other trickswe must resort to other tricks
e.g. to find the distance of a cluster of e.g. to find the distance of a cluster of
stars, compare its HR diagram with stars, compare its HR diagram with
the standard Main Sequence of Stars the standard Main Sequence of Stars
with known distanceswith known distances
![Page 95: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/95.jpg)
Hertzprung Russell DiagramHertzprung Russell Diagram
![Page 96: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/96.jpg)
![Page 97: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/97.jpg)
RecallRecall
Spectral information from starsSpectral information from stars• Peak Peak or or T = TemperatureT = Temperature• Presence of LinePresence of Line Composition & TComposition & T• Line intensity Composition & TLine intensity Composition & T• Line width T, density, rotation…Line width T, density, rotation…•Doppler shiftDoppler shift Line-of-sight velocity Line-of-sight velocity
![Page 98: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/98.jpg)
Principal Principal
TypesTypes
of Stellar of Stellar
SpectraSpectra
SUN
![Page 99: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/99.jpg)
Principal Types of Stellar SpectraPrincipal Types of Stellar Spectra
35,000 K
3,500 K
3,700 K
5,200 K4,400 K
5,600 K
5,900 K
8,600 K
7,200 K6,500 K
10,800 K
22,000 K
16,400 K
![Page 100: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/100.jpg)
Spectral Classes: O B A F G K Spectral Classes: O B A F G K
MM
![Page 101: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/101.jpg)
Stellar Classification
• Astronomers classify of stars based on their spectral characteristics.
• Based on which atomic excitations are most prominent in the light,
• giving an objective measure of the temperature in this chromosphere.
![Page 102: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/102.jpg)
• Most stars are currently classified using the letters
• O, B, A, F, G, K and M,
• O stars are the hottest and the letter sequence indicates successively cooler stars up to the coolest M class.
![Page 103: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/103.jpg)
• According to an informal tradition:
• O stars are "blue"
• B "blue-white"
• A stars "white"
• F stars "yellow-white"
• G stars "yellow"
• K stars "orange"
• M stars "red“
![Page 104: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/104.jpg)
• Spectral letter is enhanced by a number from 0 to 9 indicating tenths of the range between two star classes.
• E.g., A5 is five tenths between A0 and F0, but A2 is two tenths of the full range from A0 to F0.
![Page 105: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/105.jpg)
• Aditionally, the luminosity class expressed by the Roman numbers I, II, III, IV and V.
• It expressed the width of certain absorption lines in the star's spectrum.
• It has been shown that this feature is a general measure of the size of the star, and thus of the total luminosity output from the star.
![Page 106: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/106.jpg)
• Class I are generally called supergiants,
• class III simply giants and class
• V either dwarfs or more properly main sequence stars.
![Page 107: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/107.jpg)
• For example our Sun has the spectral type G2V,
• (which might be interpreted as "a 'yellow' two tenths towards 'orange' main sequence star“)
• The apparently brightest star Sirius has type A1V.
![Page 108: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/108.jpg)
![Page 109: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/109.jpg)
Spectral Classes: O B A F G K MSpectral Classes: O B A F G K M
++++++++
O BO Be e A FA Fineine G Girlirl K Kississ M Mee
GGirl irl GGuyuy
![Page 110: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/110.jpg)
Strengths of Absorption linesStrengths of Absorption lines
in Stars across the HR Diagramin Stars across the HR Diagram
(which lines dominate depends on temperature)(which lines dominate depends on temperature)
SUN
![Page 111: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/111.jpg)
Principal Types of Stellar SpectraPrincipal Types of Stellar Spectra
35,000 K
3,500 K
3,700 K
5,200 K
4,400 K
5,600 K
5,900 K
8,600 K
7,200 K
6,500 K
10,800 K
22,000 K
16,400 K
Spectral Class
![Page 112: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/112.jpg)
![Page 113: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/113.jpg)
L L etc
P P etc
H H etc
Hydrogen atom Spectral Series
![Page 114: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/114.jpg)
0 2 104
4 104
6 104
8 104
1 105
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
N 1 T( )
N 2 T( )
N 3 T( )
N 4 T( )
N 5 T( )
T
Populations in H levels vs TemperaturePopulations in H levels vs Temperature
Temperature 3000 to 100,000 K
Populationn=1 Ground State
n=3n=4
n=2
n=5
Part shown expandedin the next slide
![Page 115: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/115.jpg)
2 104
4 104
6 104
8 104
1 105
0
0.02
0.04
0.06
N 2 T( )
N 3 T( )
N 4 T( )
N 5 T( )
N 1 T( )
T
Populations showing details for excited states. Populations showing details for excited states.
Temperature 3000 to 100,000 K
Populationn=1
n=3
n=4
n=2
n=5
Note the expanded scale.Note the expanded scale.
![Page 116: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/116.jpg)
• U, B, V filters - colour TemperatureU, B, V filters - colour Temperature• Fit the spectrum to PlanckFit the spectrum to Planck• Detailed modelling of the spectrum line shapes Detailed modelling of the spectrum line shapes
and strengths - this also gives the surface gravity and strengths - this also gives the surface gravity
& the elemental abundances.& the elemental abundances.
Measuring StarsMeasuring Stars
Temperature Temperature T, etc
![Page 117: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/117.jpg)
Element Abundances
Mass fractions: H X~ 0.73, He Y~ 0.25 Metallicity Z ~ 0.02Heavier elements are “Metals”in astronomy
SADSolarAbundanceDistribution
gSun = 274 ms-2 28 gEarth
Measuring StarsMeasuring Stars
![Page 118: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/118.jpg)
The “Cosmic Abundance” of theThe “Cosmic Abundance” of the
Elements determined from the Sun, Stars Elements determined from the Sun, Stars
and Meteoritesand MeteoritesNB: log Abundance
FeCNO
![Page 119: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/119.jpg)
““Cosmic Abundance” of the ElementsCosmic Abundance” of the Elements
NB: log Abundance
Fe
![Page 120: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/120.jpg)
Stars are classified into 2 broad categories depending on
Element Abundances
Population I:H X~ 0.73, He Y~ 0.25 Metallicity Z ~ 0.02
Population II:H X~ 0.75, He Y~ 0.25 Metallicity Z ~ 0.001
SunStars in the disc
of the Galaxy
Globular Cluster Starsin the halo
of the Galaxy
![Page 121: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/121.jpg)
The Herzsprung-Russell DiagramThe Herzsprung-Russell Diagram
![Page 122: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/122.jpg)
Luminosity ClassesLuminosity Classes Sun G2VSun G2V
Vega A0VVega A0V
Barnard’s StarBarnard’s Star
(Dwarf)(Dwarf)
M4VM4V
Betelgeuse Betelgeuse
(Red Giant)(Red Giant)
M2IaM2Ia
supergiants
giants
dwarfs
![Page 123: OUR UNIVERSE](https://reader035.vdocuments.mx/reader035/viewer/2022062410/5681548d550346895dc29b79/html5/thumbnails/123.jpg)
THETHE ENDEND
OF Week 6OF Week 6