Transcript Diapositiva 1

Stellar jets (I)
History; Properties from observations
Highly collimated jets (ejected gas; supersonic velocities) are observed
in many classes of astrophysical objects, both stellar and extragalactic
(Livio, 2009):
Stellar
Young Stellar Objects
Massive X-Ray Binaries
Black Hole X-Ray Transients
Low Mass X-Ray Binaries
Symbiotic Stars
Planetary Nebulae Nuclei
Supersoft X-Ray Sources
Recurrent Novae
Pulsars
Extragalactic
Active Galactic Nuclei
Gamma-Ray Bursts
Morphology
HH 111
NGC 6543
M 87
HH
111
Crab
NGC 6543
Crab
Pat Hartigan’s
Home Page
JETS AND DISKS
The emission mechanisms in the different classes of objects are very different.
Also, are very different their dimensions, densities and velocities. Simply
compare YSOs and AGNs.
However, the basic mechanism for the acceleration and collimation of the jet is
likely to be the same in most if not all of the different classes of objects.
Jets most probably requires the
presence of an accretion disk around
the central object for the
acceleration and collimation
mechanism to operate.
In the case of YSOs, accretion disks
are always present in those objects
with jets. Clear examples are HH 30,
DG Tau B, Haro 6-5B and HK Tau.
Jet Origin
Observations indicate that the jet velocity is always of the order of the
escape velocity from the central object. This immediately indicates that most
of the outflow originates at the accretion disk close to the central object.
HST images of HH 30 and DG Tau B indeed show that the jets are emanating
from the central part of the accretion disk.
OPTICAL
• Herbig-Haro Objects; discovered in the early 50s
• First symposium in 1983 (Bohm, ed.)
• 1980s - HH objects part of bipolar outflows
(Dopita; Mundt; Graham; Reipurth)
• Spectroscopy; proper motion studies; modeling
• 1990s - HST …
1994
Herbig & Jones 1981
Bally et al. 2002
HH 212
H2 2,12 mm
(NIR, K-band)
NH3(disk)
protostar
Wiseman, J.
ApJ, 550, L87 (2001)
NEAR-IR
• H2 emission lines discovered in Orion; Gautier 1976
• High-resolution studies of outflows from more embedded
sources!
• 1980s - spectroscopy; molecular shock physics (theory)
• 1990s - First sub-arcsec images; high-resol. spec. (CGS4)
- kinematics and excitation
- numerical simulations; bows; entrainment
Calar Alto
1993
UKIRT
1999
Davis et al. 1994, 2000
(SUB)-MILLIMETRE
• Broad CO lines in Orion (Kwan & Scoville 1976)
• 1980s - CO surveys in the (Snell, Bally, Edwards, Lada)
• 1990s - Higher-energy lines (submm @ JCMT); isotopes;
shock chemistry in outflows; entrainment models
• Interferometry @ Plateau de Bure, CARMA, SMA
- molecular “jets”; study of massive Star-Forming
regions.
Davis & Eisloeffel 1996
Gueth et al. 1998
Beltran et al. 2004
JETS FROM YSOs
Herbig-Haro Objects
The history of jets from YSOs began with the discovery of the Herbig-Haro objects
by George Herbig and Guillermo Haro in the late 40’ s of the past century. These
enigmatic objects showed rather peculiar characteristics: they were small nebulae
(a few tens of arcsec in size), with an strange spectrum (very different from any
known at that time) and, most intriguing, far away from any powering source.
Herbig’s
Catalog
(1974)
HH 1-2
Bally et al. AJ 123, 2627 (2002)
Discovered by:
**G.H.Herbig(1951):
The spectra of two nebulous objects near NGC 1999 (ApJ 113, 697).
On a series of direct photographs taken with the Crosslyer reflector in 1946
and 1947 and centered on the diffuse nebula NGC 1999, there appear several
peculiar nebulous objects. The brightest of these (referred to hereafter as
"No. 1") resembles, on the best plates, a slightly diffuse star with a very short
curved, nebulous "tail" extending for 5" in p.a. 52º. Its visual magnitude was
estimated at the telescope to be near 16. It lies 1'.0 west and 2'.2 south of BD-6
1253, the illuminating star of NGC 1999. Object No.2, which is 0'.1 east and
4'.1 south of BD6 1253, is composed of two faint stars 9" apart, one much
fainter star, and three closely associated semistellar clots of nebulosity; the
entire object would be contained in a circle 20" in diameter. It is superimposed
on much fainter nebulosity in the form of a ring, and slit spectrograms indicate
that still feebler emission nebulosity is present over the entire field. The two
brighter stars in object No.2 were estimated to be about visual magnitude 17.5.
and
**G. Haro ApJ 115, 572 (1952)
In a recently published note G.H.Herbig (ApJ 113,697, 1951) reports the
discovery of three peculiar nebulous objects near NGC 1999 and gives the
spectroscopic description of the two brightest. The writer had independently
discovered these peculiar objects, finding Ha and the [O I] lines at l 6300
and l 6363 in emission in the spectra of them.
First spectrophotometric study by:
Karl-Heinz Böhm (ApJ 123, 379, 1956)
Relative intensities of the emission lines in the spectrum of the brightest
Herbig-Haro Object have been determine from three spectrograms taken by
Herbig in January, 1955.
Therefore, the most obvious means of explaining the ionization is to assume
a strong radiation field in the far ultraviolet. If the radiation is produced by a
"central star" (of solar dimension) in the nebula, a radiation temperature of
24000° K is required to explain the observed ratio of [ O II] and [O III].
BUT :
** Deep optical and NIR images fail to detect the embedded star (inside
the HH nebulosity)
( Haro, G., Minkowski, R.: 1960, The Herbig-Haro objects near NGC 1999, AJ 65,
490).
** Variability of the HH nebulosities:
The nebulosities change their brightness, dissapear and move relative to
Field stars with a scale of time of several yrs
All of this goes in favour of the exciting source being located outside of
the HH nebulosity.
Strom, S. E., Grasdalen, G. L., & Strom, K. M.
Infrared and optical observations of Herbig-Haro objects
ApJ., 191, 111-142 (1974)
HHs=reflection nebulae illuminated by an external source
“old example”
BURNHAM NEBULA (HH 255)
Burnham Nebula was discovered by Burnham
(1984)
as a small nebula some arcsec to the south of
T-Tau.
(Burnham, S.W., Observations of Nebulae with the
36-inch refractor of the Lick Observatory, Pub. Lick
Obs., 2, 1689)
From high-resolution long-slit spectra in the
range 6250-6800 A
Emission nebulosities around T-Tau (Böhm &
Solf 1994
ApJ, 430, 277).
ASSOCIATED WITH TTS
**(Osterbrock, 1958): supersonic gas, ejected by a TTS, excites the
surrounding nebula and produces the observed emission lines.
**Supersonic stellar wind
Radiative shock
interaction with the ambient gas
HH is created
CATALOGS:
*Herbig (1974) ~40 objects
*Reipurth
http://www.astro.umass.edu/catalogs/HHcat/HHintro.html#home
(> 1000, in progress)
Today we know that they are just either the brightest parts of the very
collimated outflows or jets produced by young stellar objects or in the region
of where the jet hits the surrounding medium. The characteristic spectrum is
produced in the cooling region of fast shock waves.
HH 1/ 2
HH 34
Jet properties
A) Morphology
• Bipolar with a slight difference in direction between jet and counterjet.
• Extremely well collimated with small opening angles of no more than a few
degrees. Many are not perfectly straight , but show a gradual change in
direction or bending.
• Lengths around a fraction of a parsec, although, in some cases the jet
can be traced for several parsecs from the source. Widths between 50-500
AU.
• They show a series of bright, almost equidistant, knots inside the body of
the jet.
Highly collimated morphology
wiggling
[SII] CCD image
Acquired with
ACAM (WHT)
HH30
jet/counterjet
system
“JETS” in ORION
HH 270
HH 110
Reipurt &
Bally
HH 270
More “chaotic” morphology
Kno
t
Lack of exciting source?
N
HH 110
[SII] CCD image with
NOT/ALFOSC
~4 ARCMIN
Hartigan et al.
(2005), AJ 130, 2197
“curved”
morphology
+”bow-shock”
Straight
morphology
IWS
Terminal bow-shock
Bow-shock
NIR:
H2
[FeII]
knot
Optical:
[SII]
H
9” (4,000 AU)
HH111
Exciting source: YSO
surounded by a circunstellar
disk
(Orion)
(Reipurth et al. 1999)
Molecular Outflows
High-velocity molecular outflows is a very common phenomenon clearly related
to jets in YSOs. When both phenomena are observed, both coincide in direction
and sense. They are observed in lines of many molecules, most notably in H2
and CO.
Observations
•
Mostly bipolar. Wider and longer than the jet.
•
Velocities in the range from a few km/s to less than a hundred.
•
Sizes ranging from less than 0.1 pc to several parsecs.
•
Kinematical time-scales from about 103 to 105 yr.
•
Masses from a few 10-4 to several hundreds Msun.
Conclusions
•
So massive that they must consist of accelerated ambient molecular
material.
•
The momentum and power of the ionized jet component is usually not
enough for the required acceleration.
•
An additional wide-angle wind is probably required to explain the
observed morphologies and to easy the momentum problem.
Unified model: molecular outflow/
Jet HHs
Optical/Nir wvl
Sub and mm wvl
Formation Mechanism
The most likely mechanism for the launching of the jet from the disk involves
hydromagnetic acceleration and collimation. That is, the outflow is initially
controlled by a strong magnetic field anchored to the disk and the central object.