Download Lecture 4-Energy sources

Astronomical Observational Techniques
and Instrumentation
RIT Course Number 1060-771
Professor Don Figer
Energy sources of astronomical objects
1
Aims and outline for this lecture
• describe energy sources of astronomical objects
–
–
–
–
stars: nuclear reactions
protostars: gravitational energy
nebulae/clouds: stellar heating and ionizing radiation
galaxy clusters: shocks
• give case studies of using multiwavelength data to analyze two
star clusters
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Stellar Structure
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Solar Atomic Abundances
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Solar System Atomic Abundances
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Stars: energy source: proton-proton chain
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Stars: energy source: proton-proton chain
PPI (85% for Sun):
H1 + H1 -> D2 + e+ + nu(1) (1.442 MeV)
D2 + H1 -> He3 + gamma (5.493 MeV)
He3 + He3 -> He4 + 2H1 (12.859 MeV)
PPII (15%):
H1 + H1 -> D2 + e+ + nu(1) (1.442 MeV)
D2 + H1 -> He3 + gamma (5.493 MeV)
He3 + He4 -> Be7 + gamma (1.586 MeV)
Be7 + e- -> Li7 + nu(2) (0.861 MeV)
Li7 + H1 -> He4 + He4 (17.347 MeV)
PPIII (0.01%):
H1 + H1 -> D2 + e+ + nu(1) (1.442 MeV)
D2 + H1 -> He3 + gamma (5.493 MeV)
He3 + He4 -> Be7 + gamma (1.586 MeV)
Be7 + H1 -> B8 + gamma (0.135 MeV)
B8 -> Be8 + e+ + nu(3) (followed by spontaneous decay...)
Be8 -> 2He4 (18.074 MeV)
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Stars: energy source: pp chain: Gamow Peak
• Protons in center of star
– have high energies
– have the same charge (they repel each other)
• At sufficiently high energy, particles will fuse.
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Stars: energy source: pp chain timescales
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Stars: energy source: CNO cycle
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Stars: energy source: CNO cycle
12
13
13
14
15
15
1
C+ H
N
1
C+ H
1
N+ H
O
1
N+ H
→
13
→
13
C + e + νe
+2.22 MeV
→
14
N+γ
+7.54 MeV
→
15
O+γ
+7.35 MeV
→
15
→
12
N+γ
+1.95 MeV
+
+
N + e + νe
4
C + He
+2.75 MeV
+4.96 MeV
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Stars: energy source: CNO cycle
• The CNO cycle has several branches that are favored based on
temperature.
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Stars: energy source: CNO vs PP
• The CNO cycle produces more energy than the PP chain at
higher temperatures.
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Betelguese and Rigel in Orion
Betelgeuse: 3,500 K
(a red supergiant)
Rigel: 11,000 K
(a blue supergiant)
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Blackbody curves for hot and cool stars
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Two stars
• Hotter Star emits MUCH more light per unit area  much
brighter at short wavelengths.
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Stars: energy source: Protostars
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Stars: energy source: Gravitational Energy
• As molecular cloud contracts, gravitational potential energy of
particles is converted into kinetic energy.
• With higher kinetic energies, the collision rate between
particles increases, i.e. temperature and thermal radiation
increase.
• At sufficiently high density, the gas becomes opaque to
escaping radiation at shorter wavelengths, making it difficult
to observe the star formation process.
• The radiation generated by gravitational energy cannot
counterbalance the force of gravity of the overlying material.
• Temperature increase until nuclear fusion turns on.
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Star Formation: Hayashi Track
hydrostatic equilibrium
gravitational energy
nuclear fusion
100,000 years from 4 to 6
10 million years from 6 to 7
timescales depend heavily on mass
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Stages of Star Formation on the H-R
Diagram
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Arrival on the Main Sequence
• The mass of the protostar
determines:
– how long the protostar phase will
last
– where the new-born star will land
on the MS
– i.e., what spectral type the star
will have while on the main
sequence
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Protostar Luminosity Derivation
The change in potential energy for a uniform density sphere that
collapses from infinity down to R is :
3 GM 2
U
ergs .
5 R
Assuming that about half of this change is converted to kinetic
energy, and plugging in numbers for the Sun, we find :
kinetic energy ~ 4(10 48 ) ergs.
Assuming that the gas contracts in a hundred thousand years or
so, we find a power of :
4(10 48 ) ergs
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P 5

1
.
2
(
10
) ergs/s  300 L sun .
7
10 yrs  3(10 ) seconds/ye ar
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Star Formation: Gravitational Energy: B68
Optical
1.2 mm Dust Continuum
Near-Infrared
C18O
B68 is thought to be in
hydrostatic equilibrium,
such that the outward
radiation pressure
balances the inward force
of gravity. The cloud
should contract as it
cools/radiates
gravitational energy
converted into kinetic
energy.
N H+
2
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Disks & infrared emission
102
RY Tau x 10
nFn (10-12 W m-2)
104
1
Vega
DL Tau x 2
102
10-2
9700 K
1
10-4
GM Aur / 20
10-2
0.1
1
10 100 1000
Wavelength (mm)
b Pic x 0.1
0.1
1
10 100 1000
Wavelength (mm)
Beckwith & Sargent 1996, Nature, 383, 139-144.
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Spectrum of Protoostar
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McCaughrean et al. 1996
Circumstellar Dust
Vega Disk Detection
l
(mm)
Flux* Contrast
(mJy) Star/Disk
11mm
2.4
1.5x107
22mm
400
2x104
33mm
1300
3x103
Reflected & emitted
light detected with a
simple coronograph.
*per Airy disk
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Star Formation: Debris Disks
BD+31643
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Dust Clouds: energy source
• Dust clouds usually emit radiation that they absorb from stars
(internal or external).
• Young stars are often the internal heat source for star forming
dust clouds, e.g. Sgr B2, W49, W51.
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Dust Clouds: energy source: Sgr B2
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Dust Clouds: energy source: Sgr B2
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Dust Clouds: energy source
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HCHII Regions in Sgr B2
Gaume et al. 1995
• There are ~100 HCHII regions in Sgr B2.
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HCHII Regions in Sgr B2
De Pree et al. 1998
• The clumps break up into even smaller clumps with sizes ~100
AU and densities >107 cm-3.
• Each clump contains an OB star.
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Dust Clouds: energy source: external heating
•
•
•
M0.20-0.033 molecular cloud is warm (molecular emission in contours)
Notice that its surface is ionized (free-free emission in greyscale).
Pistol nebula is also ionized and heated.
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Dust Clouds: energy source: external heating
•
•
•
M0.20-0.033 is externally heated by nearby Quintuplet cluster of massive stars.
Notice that its surface is ionized by the nearby hot stars.
Pistol is ejecta that is ionized/heated by Pistol star.
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Dust Clouds: energy source: external heating: Pa-a
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Nebulae: energy source: stars
• The Pistol nebula is heated by the
Pistol star that resides at its center.
• Note in the figure that the dust
thermal emission peaks in the
mid-infrared, indicating
temperature of a few 100 K.
• The starlight fades in relative
intensity at longer wavelengths.
• Ionized gas emission suggest an
external energy source (other hot
stars in Quintuplet).
3 um
17 um
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Galaxy Clusters: energy source: Shock Heating
A shock increases gas temperatu re,
3 mvu2
T
,
16 k
where m is particle mass and v u is shock velo city.
http://www-astro.physics.ox.ac.uk/~garret/teaching/lecture2.pdf
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Galaxy Clusters: energy source: Shock Heating
• Over last 10 Billion years there have been many galaxy
collisions in galaxy clusters.
• When two galaxies pass through each other stars will continue
on their original path – more or less.
• Interstellar gas clouds collide and cannot pass through each
other.
• They get stripped and pass into the gravitational well of the
cluster.
• This fills with very hot shocked gas over time.
• So hot it emits x-rays.
• Shows matter distribution. (Mostly dark matter again.)
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Galaxy Clusters: energy source: Shock Heating
blue=x-ray
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Multiwavelength View of Energy Sources
red=8um
green=6 cm
blue=20 cm
red=8um
green=5.8um
blue=3.6um
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Multi-wavelength analysis of star clusters:
the cases of GLIMPSE9 and Cl1813-178
Cl1813-178
GLIMPSE9
90 cm
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Cl 1813-175: Multiwavelength Image
Messineo et al. (2008) ApJL, 683, 155
SNR G12.82-0.02
SNR G12.72-0.0
HESS J1813-178
W33
2MASS
3.6 um
8 um
90 cm
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Cl 1813-175: Multiwavelength Plot
74 Chandra point sources from Helfand et al. (2007)
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Cl 1813-175: NIR Spectroscopy
Red supergiant
Blue supergiants
Keck/NIRSPEC high– and low–resolution spectroscopy
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Cl 1813-175: CMD
•
•
•
•
4.7 kpc
6-8 Myr
Ak=0.8 mag
2000-6000 Msun
Chandra data from Helfand et al. (2006)
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Cl 1813-175: distance
• From the radial velocity of star #1, we derive a kinematic
heliocentric distance of 4.7±0.4 kpc by using the rotation curve
of Brand & Blitz (1993).
• We conclude from the CMDs and distance estimates, that the
RSG, the WR star, and the BSGs are all part of the same
stellar cluster. The average spectrophotometric distance of 3.7
± 1.7 kpc is consistent with the kinematic distance 4.7±0.4 kpc
within uncertainties. We assume the kinematic distance.
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Cl 1813-175: age and mass
• We assume coevality of the evolved objects – 1 WR, 1 RSG,
2 BSGs, and several X–ray emitters.
• We conclude that the cluster is 6 − 8 Myr old since this age
allows for the coexistence of both WR and RSG stars.
• Assuming that the other eight X–ray emitters associated with
the cluster, other than the WR star, are BSGs with masses
larger than 20 Msun, and by assuming a Salpeter IMF down to
1.0 Msun, we derive a total initial cluster mass of 2000 Msun.
Messineo et al. (2008, ApJ 683-155)
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24 additional massive stars in CL 11813-178
(Messineo et al. in preparation)
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GLIMPSE9: location (l,b)=(22.76°, -0.40°)
•
HST/NICMOS
•
f.o.v. = 51.5”x51.5”; pixel scale = 0.2”; filters = F160W, F222M
•
exptime = 19.94s, 55.94s
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Age = 6-30 Myr (presence of RSGs)
Ak = 1.6 ± 0.3 mag
#3 4.2 kpc
#4 4.7 kpc
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Cluster surroundings
Blue = 3.6 um
Green = 90 cm
Red = 24 um
Giant Molecular cloud – from CO 10^6 Msun -- 4 SNR remnants
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REG1
REG3
REG4
REG6
Ongoing ESO observations with SINFONI to observe the brightest stars
of REG1, REG3, REG4 and REG6
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GLIMPSE9 and CL1813-178 Summary
• GLIMPSE9 and CL1813-178 are two young clusters.
• The combination of radio and infrared data allowed us to
detect their parental clouds, which appear rich in HII regions
and SNRs.
• With similar studies of other clusters and giant HII regions we
will be able to shed light on the initial masses of the supernova
progenitors, and therefore on the fate of massive stars.
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