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

DISK IONIZATION is fundamental for transport to work

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

UV Radiation from protostars

The photoelectric dust charging profile depends on the UV field

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

DUST CHARGING

PhotoelectricCharging

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

Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense

Engine at work…With disk dynamo Without disk dynamo

Gravitational Engines Prof. Ana I Gómez de Castro – Univ. Complutense

UNKNOWNS

• Current layer & reconnection

• Inner-disk boundary in black-holes

• Blandford-Znayek effect

• Disk ionization degree

• Mass feeding the disk

• Inner disk boundary

• Vertical structure & instabilities

OUTFLOWS DISKS