H I

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Mass 35 40 20 lt5
H I H2 H I H II
. basically hydrogen in various forms
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Analysis of absorption features in IR
suggests graphite grains 0.2 m ices
3 m silicates 9 10 m
1 m 10-6 m 10-4cm 10,000 A
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The Free-Fall Time Scale
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Power of observing in the infrared
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When the star first becomes visible it may still
be surrounded by the gas and dust from which it
formed. Often jets are seen.
Because of rotational support matter hangs up in
the equatorial plane forming an accretion
disk. Matter first rains down on the poles, but
then later reverses direction in a strong outflow
called a jet.
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T-Tauri Stars

• Short lived phase in life of stars under 2
  solar masses. Heavier stars evolve quicker
  and start burning by the time the star is
  visible.
• Accretion disks and jets are common features
• Emission and absorption lines
• Powered by gravitational contraction, not
  nuclear burning
• May be forming planetary systems
• High lithium abundance
• Embedded in dense, dusty regions
• Found in association with Herbig-Haro Objects
• Can be highly variable

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T-Tauri Stars
Young binary T-Tauri stars clearing out the disk
around them.
UY Aur
Canadian-French-Hawii Telescope HST composite.
Infrared, 4 arc sec. Flows (300 km s-1) to upper
left and lower right are jets. Greenish region
is an accretion disk (size 150 AU)
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Many Herbig-Haro objects are found in the
vicinity of star forming regions. These pictures
are from the Pelican Nebula. Note the swept back
jets in HH 555.
Herbig-Haro objects are compact emission nebulae
formed when shocks run into the interstellar
medium.
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Protostars start off with very large radii
because they begin as contracting clouds of gas.
They additionally have high luminosities
because they are fully convective (more
about this later) and able to transport the
energy released by gravitational
contraction efficiently to their surface. Most
of the time is spent close to the main sequence.
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Stellar Interiors
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p mv
n(p) is the number of particles with momentum p
per cm3
It is convenient to think of a surface, though
there need not be one. Each particle striking the
surface and bouncing off gives a small
kick. This provides a net force pushing on the
wall. Recall that force is defined as the rate at
which momentum changes.
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Each electron or pair of electrons occupies a
cell of size (Dx)3, but Dx h/p
p would be the same for neutrons or protons but
v would be less.
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At around 107 gm cm-3 the electrons will move
close to the speed of light.
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Ignition happens when the nuclear energy
generation rate becomes comparable to the
luminosity of the contracting proto-star. As we
shall see shortly, nuclear burning rates are very
sensitive to the temperature. Almost all main
sequence stars burn hydrogen in their middles at
temperatures between 1 and 3 x 107 K.
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Combining terms we have
A much more detailed calculation gives 0.08 solar
masses. Protostars lighter than this can never
ignite nuclear reactions. They are known as
brown dwarfs (or planets if the mass is less
than 13 Jupiter masses, or about 0.01 solar
masses.
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14 light years away in the constellation Lepus
orbiting the low mass red star Gliese 229 is the
brown dwarf Gliese 229B. It has a
distance comparable to the orbit of Pluto but a
mass of 20-50 times that of Jupiter.Actually
resolved with the 60 Palomar telescope in 1995
using adaptive optics.
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Spectrum of Gliese 229B