Group 22 Jennifer Hare, Sarra Schwartz, Sheba Saroia

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Group 22Jennifer Hare, Sarra Schwartz, Sheba
Saroia

• Solar Neighborhood, Luminosity-Brightness, and
  Stellar Temperature

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Parallax

• Measures the distance of a star in arc seconds
  not degrees
• As observers point of view changes, object
  appears to shift relative to its background
• The parallax is half of this apparent shift
• Distance to star the inverse of the parallax or
  1/parallax

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Luminosity Apparent Brightness

• Luminosity absolute brightness
• Vs Apparent Brightness what we see based on
  distance
• Why?

as luminosity goes up, so
does apparent brightness Apparent brightness
a Luminosity distance 2 as
distance goes up, apparent
brightness goes down
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Apparent Brightness and the Magnitude Scale

• Absolute magnitude- apparent magnitude when seen
  from set distance of 10 pc (really far). Because
  everything viewed from fixed distance, able to
  measure luminosity.
• Magnitude scale- absolute magnitudes of different
  stellar objects (creator of scale Hipparchus)
• 30
• 20
• 10
• 0
• - 10
• - 20
• - 30

DIMMER
POLARIS 2.5
BRIGHTER
THE SUN -26.8
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Stellar TemperatureColor and the Blackbody Curve
FIND TEMPERATURE WITH WEINS LAW AND BLACKBODY
CURVE WHY BLUE STARS ARE HOTTER Shorter
wavelength higher intensity higher
temperature WHY RED STARS ARE COOLER Longer
wavelength lower intensity lower temperature
So, If B (blue) filter picks up more radiation,
then stars temperature is hotter. If V (red)
filter picks up more radiation, then stars
temperature is cooler.
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Absorption/Emission Lines Review
Electrons gain energy through 1) photons and 2)
heat Atomical analysis Photon gets absorbed by
electron So, absorption lines can be seen on the
spectra because light was absorbed Photon gets
released from electron So, emission lines can be
seen on the spectra because light was
released When an element is heated, electrons
get so excited they leave their orbits and atoms
are called ionized (have no electrons). So when
the proton comes along, there are few electrons
to absorb it, resulting in weak or no absorption
lines
photon
e
N
e
photon
Stellar spectra determined by stars temperature
which is reflected by absorption / emission lines
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Stellar TemperatureStellar Spectra
Based on temperature of star, certain elements
show stronger or weaker absorption lines Oh, Be
A Fine Guy, Kiss Me Scientists used to classify
stars based on their hydrogen line intensities,
but now they classify stellar spectra based on
temperature b/c hydrogen line intensity affected
by temperature not the other way around
HIGHER TEMP.
O B A F G K M
30,000 K 20,000 K 10,000 K 7,000 K 6,000 K 4,000
K 3,000 K
LOWER TEMP.
G1 G2 G3 G4 G5G257G681 Hotter star
cooler star
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Lets Sum It Up

• Parallax measures half of observed shift of
  stellar object against its background as viewing
  point changes. Allows us to measure distance from
  earth to stars
• Luminosity is absolute brightness while apparent
  brightness is based on distance
• Magnitude scale based on absolute magnitude
  (distance from 10 pc). Higher magnitude, dimmer/
  Lower magnitude, brighter
• Stellar temperature can be found through Weins
  law and the Blackbody curve (using B and V
  filters)
• Stellar Spectra determined by stars temperature
  which reflected by spectral lines
  (absorption/emission lines)
• THATS IT!!!!!!!!!!! YIPPPEEEEEEE!!!! Any
  questions?