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2 Million-K Plasma Pervading
the Orion Nebula
K. Briggs, M. Guedel, Th. Montmerle,
M. Audard, L. Rebull, S. Skinner
HST/STScI
Outline
Motivation
– Why study X-rays?
– Why is Orion Nebula interesting?
– What did we aim to do?
Results
– Hot gas (2 MK) fills nebula (spectrum, low abs, Spitzer)
– Produced by shocked winds from Trapezium
– Low mass of gas in pressure eqm – escaping
Implications:
–
–
–
–
1. Hot gas is a feature of all HMSFRs
2. Young solar system immersed in hot gas
3. Shocked winds play role in shaping all HMSFRs
4. Hot gas flows out and enriches ISM
Kevin Briggs, PSI/ETH
X-rays in star and planet formation
Effects of UV and X-ray radiation
– Heating and ionizing protoplanetary disks
– Driving accretion through disk via
magnetorotational instability
– Driving dispersal of protoplanetary disks
Kevin Briggs, PSI/ETH
X-rays in star and planet formation
Sources of UV and X-ray radiation
– Internal to system
X-rays from magnetic activity on star
UV and X-rays from accretion onto star
X-rays from shocks in out-flowing jets
– External to system
UV from hot, high-mass O stars
X-rays from neighbouring stars
X-rays from shocked winds from high-mass stars?
Kevin Briggs, PSI/ETH
Orion
Rich site of recent star formation
over last few Myr
Orion Nebula Cluster is most
recent (0.5 Myr ago)
Closest HII region with high-mass
O stars (400 pc)
Older generations of young stars
to immediate N and S of ONC
Sun is thought to have been born
in a rich cluster like Orion.
© Till Credner and Sven Kohle
Kevin Briggs, PSI/ETH
Features of the Orion Nebula
COUP field
Kevin Briggs, PSI/ETH
Previous X-ray observations of the Orion
Nebula
Chandra 0.5-8 keV COUP Collaboration
Kevin Briggs, PSI/ETH
Aims of our investigation
Survey of X-ray emission from young stars over range of
ages.
Investigate evolution of X-ray output, energy, flaring rate
in first few Myr.
Investigate dependence of X-ray output, temperature of
X-ray emitting gas on mass, age, accretion-rate, rotation
rate, to understand processes creating X-rays.
Kevin Briggs, PSI/ETH
XMM-Newton
Most sensitive X-ray
observatory
Large field of view (30
arcmin diameter)
3 telescopes, each with EPIC
CCD detector
Measures position, arrival
time and energy of each
detected X-ray photon
Energy range 0.15 – 15 keV
Survey profits from archive
observations of individual
interesting objects (O stars,
outburst T Tauri stars) and
calibration observations
Kevin Briggs, PSI/ETH
XMM Survey of the Orion Nebula
Copyright Anglo-Australian Observatory. Photograph by David Malin.
Kevin Briggs, PSI/ETH
XMM’s New View of the Orion Nebula
Soft diffuse
X-ray emission
Kevin Briggs, PSI/ETH
Physical properties of the X-ray-emitting gas
Kevin Briggs, PSI/ETH
Spectral extraction
Size (d=400 pc)
N
S
Area (pc2)
0.24
1.38
Diameter (pc)
0.6
1.5
0.9-4.0
0.9-4.0
0.22-0.97
1.24-5.5
Depth (pc)
Volume (pc3)
Kevin Briggs, PSI/ETH
Spectral fitting
Spectral
N
S
1.7
2.1
NH
(1020 cm-2)
4.10.7
0.40.5
EM = ne2 V
(1054 cm-3)
1.50.3
1.90.3
LX
(0.1-10 keV,
1031 erg s-1)
2.3
3.2
Te (MK)
Kevin Briggs, PSI/ETH
Derived observational parameters
Derived Quantity
ne (cm-3)
(EM/V)0.5
 (10-23 erg cm3 s-1)
tcool (Myr)
3kT/ne 
Kevin Briggs, PSI/ETH
N
S
0.22-0.47
0.11-0.23
8.28
6.44
0.6-1.3
1.8-3.9
Spatial distribution of X-ray emitting gas
X-ray emission fills a
cavity in IR image
“Lid” or “Veil” of
absorbing material in
front of Trapezium, NH =
4.8 x 1021 cm-2.
Reduces toward SW
X-ray surface
brightness would be 30
times fainter in direction
of Trapezium due to
absorption
Kevin Briggs, PSI/ETH
Spatial distribution of X-ray-emitting gas
Gas extrapolated to full
volume of cavity:
LX = 2 x 1032 erg s-1
MX = 0.07 M
LX (1 Ori C) = 1.9 x 1033 erg s-1
LX (hot stars) = 2.3 x 1033 erg s-1
LX (cool stars) = 3.5 x 1033 erg s-1
(Feigelson et al. 2005, ApJS, 160, 379)
Kevin Briggs, PSI/ETH
Origin of the X-ray-emitting gas
Kevin Briggs, PSI/ETH
Origin of hot gas: The Wind-Blown Bubble
Powerful winds of O
stars
– Mdot ~ 10-6 M yr-1
– Vw > 1500 km s-1
Wind shocked to T > 1
MK: expanding hot
bubble: X-rays
Expanding thin shell of
shocked, swept-up IS
gas: T ~ 104 K
Weaver et al. 1977, ApJ, 218, 377
Kevin Briggs, PSI/ETH
Wind shocks from 1 Ori C (O7 V)
Energetics
Mass loss rate
Mdot
8 x 10-7 M yr-1 *
Terminal velocity
Vw
1650 km s-1 *
Kinetic power
Mdot Vw2/2
7 x 1035 erg s-1
* Leitherer 1988, ApJ, 326, 356
Timescales
Travel time
> 103 x LX
1.5 x 104 yr
< 10-2 tcool
(1.5 pc @ 100 km s-1)
Replenishment
time
105 yr
Kevin Briggs, PSI/ETH
< 0.03 tcool
Outflow of the X-ray-emitting gas
Evidence:
– Low NH toward S
diffuse emission
– Short replenishment
time of X-ray emitting
gas
– Pressure equilibrium
between radio and
X-ray emitting
material
Kevin Briggs, PSI/ETH
Implications
Kevin Briggs, PSI/ETH
Implication 1: Hot gas not only in very
massive star-forming regions
Previously thought supernovae or colliding winds from multiple O stars
needed (Townsley et al. 2003, ApJ, 593, 874)
30 Doradus, LMC, XMM-Newton first-light image
Kevin Briggs, PSI/ETH
Implication 2: Young solar system immersed
in hot, X-ray-emitting gas
But photoionization and heating effects from X-rays on
disks much smaller than from UV irradiation from O stars
(Alexander, Clarke & Pringle 2004, MNRAS, 354, 71)
Kevin Briggs, PSI/ETH
Implication 3: Structure & evolution of the
Orion Nebula
Previously thought UV radiation from Trapezium stars drives structural evolution.
NASA/STScI
Tenorio-Tagle 1979, A&A, 71, 59
Now wind-blown bubble appears to have played significant role.
Kevin Briggs, PSI/ETH
Implication 4: Outflow and enrichment
2MASS near-IR 2 micron
Chandra X-rays 0.5-8 keV
M17, The Omega Nebula (Townsley et al. 2003, ApJ, 593, 874)
Kevin Briggs, PSI/ETH
Implication 4: Outflow and enrichment
Gamma rays indicate
outflow from Orion
Nebula into Eridanus
Superbubble
X-ray outflow carries
– Hot gas
– Fresh nucleosynthetic
products from O stars
(26Al??)
Enrichment of ISM
– Likely common process
throughout Galaxy
Kevin Briggs, PSI/ETH
Conclusions
Orion Nebula filled with X-ray emitting gas at 2 MK.
Originates from shocks in winds of O stars, esp. 1 Ori C.
Hot wind-blown bubbles can occur in all high-mass
SFRs, even with few O stars.
The young solar system was likely immersed in such a
hot gas.
Hot gas flows out of cavity …
… enriching Eridanus superbubble?
Outflows of hot gas are likely common in HII regions,
adding to soft X-ray halo of Galaxy, continuously
enriching ISM.
Kevin Briggs, PSI/ETH