PHOTOELECTRIC CHARGING of DUST GRAINS in PROTOSTELLAR DISKS Prof. Ana I. Gómez de Castro...
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Transcript of PHOTOELECTRIC CHARGING of DUST GRAINS in PROTOSTELLAR DISKS Prof. Ana I. Gómez de Castro...
PHOTOELECTRIC CHARGING of
DUST GRAINS in
PROTOSTELLAR DISKS
Prof. Ana I. Gómez de Castro Universidad Complutense de Madrid
andDr. Andreas Pedersen
Helsinky University
MENU
• Motivation – Protostellar disks:– mass transfer – disk-star interaction
• Photoelectric charging
• Disk atmospheres
• Summary
PROTOSTELLAR DISKs
Dusty disks are observed around protostars with masses < 10 Mo
HH 30
Jet engine (mas-μas scales)
Protostellar disks are formed in the gravitational collapse provided angular momentum is
transported
Mass infall from a rotating core produces a flattened structure
2sr vw
DISK INSTABILITIES
• No hydrodynamical instabilities –
Disks are stable against Rayleigh-Taylor Instabilities
• Gravitational instabilities
• Magnetorotational instability
Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense
Transport can also be allowed by wind ejection that shields the disk
The properties/efficiency of the disk wind is defined by threebasic parameters:
05.1
196229.0
1154.17
125.0
2
,
,
2
,
2
,
,
Aesc
As
Aesc
A
Aesc
Ap
V
C
V
r
V
V
PROTOSTELLAR DISKS IONIZATION
Stellar UV photoionizing photons penetration
Chemical abundances in the disk
Xrays and relativistis particles ionize the interior of the disk
•The electrons will be absorbed by the dense environment producing X-ray radiation
•UV radiation photoionizes the disk atmosphere (MgII)
•UV radiation photodissotiates H2 and produces a faint wind
Transmitted X-ray
THE DUSTY ATMOSPHERES OF DISKS ---- why??
THE PROPERTIES OF THE DUSTY ATMOSPHERE CONTROL:
• WIND EJECTION• DISK PROTECTION AGAINST STELLAR
IONIZATION
AND MAY INFLUENCE THE DISK-STAR BOUNDARY LAYER
Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense
The current paradigma
ISO & Ground-BasedIR Interferometers
XMM-NewtonChandraHubble Space Telescope
WSO-UV
OBJECTIVES
TO EVALUATE THE IMPACT OF THE STELLAR FIELD IN DUST IONIZATION
• PHOTOELECTRIC DISK CHARGING PROFILE
• CHARACTERISTICS OF PHOTOELECTRONS
• RELEVANCE OF PHOTOELECTRIC CHARGING IN DUST GRAINS CHARGING IN PRE-MAIN SEQUENCE SOLAR SYSTEM ANALOGUES
Two populations of photoelectrons
Low energy population E=2.5 eV --- dispersion 1.2eV
High energy population E=5.8eV– dispersion 1.4 eV
•above the photodissotiation threshold of H2 (4.52eV)
•contributes to the ionization of Mg (7.64eV)
DUST CHARGING
egraine
ee JkTrQe
mkT
n
22/1
18
EQUILIBRIUM CONDITION:
Collisional loses by electron impact = Photoelectric charging
Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense
CONCLUSIONS
• DUST CHARGING BY PHOTOELECTRIC EFFECT IS DOMINANT IN THE INNER BORDER OF THE DISK TO Q20-80 e-
• SECONDARY ELECTRONS HAVE ENERGIES HIGH ENOUGH TO PHOTODISSOTIATE H2
• THE ATMOSPHERE OF PROTOSTELLAR DISKS CAN BE CONSIDERED AS METHAL-LIKE
Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense
Disk-star interface
Lovelace et al 1995
1. Field lines are twisted by the differential rotation
2. Toroidal magnetic flux is generated out of the poloidal flux
3. The toroidal field builds up and the associated field pressure tends to push the field lines outward
4. The magnetic link between the star and the disk is eventually broken.
Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense
Engine at work…With disk dynamo Without disk dynamo