Transcript Studies of young stellar objects (25+5)

Studying Young Stellar Objects with
the EVLA
Luis F. Rodriguez, CRyA, UNAM
Morelia, México
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Disks and jets in young stars
VLA results
Possibilities with the EVLA
Conclusions
This scheme is supported by observations,
in particular for forming low-mass stars.
JET: removes excess
angular momentum and
magnetic flux, produces
outflows and HH
objects.
DISK: allows
accretion,
planets may
form from it.
DISK
JET
Rodriguez et al. 2008
Gomez et al. (2003)
VLA continuum observations at several
frequencies reveal characteristic spectrum jet+disk.
HH 1-2
VLA 1
VLA 1
“Thermal” jets, systematically found
at the center of low mass star-forming
regions with outflows…
What are the thermal jets?
• (Partially) ionized, collimated outflows that
emanate from young stars.
• Detectable as weak free-free sources.
• They are believed to be the “base” of the large
scale outflow phenomena like the bipolar outflows
and HH systems.
• They are almost always found in the case of lowmass protostars, but rarely in high-mass protostars.
Why are thermal jets rare to find in
association with high mass protostars?
• Different formation mechanism?
• Confusion from bright HII regions in
region?
• Stellar multiplicity a serious problem.
• Molecular outflows (large scale) are,
however, relatively frequent.
HH 80-81 (GGD27)
in L291 dark cloud
Distance 1.7 kpc
(Rodríguez et al. 1980),
Luminosity: 2 x 104
LSol
Star: B0.5 ZAMS
H2O
maser
Thermal
Jet
Gómez et al. (1995)
Marti et al. (1998)
analyzed the
thermal jet over
several years.
Derive
velocities
for knots of
500 km/s.
These
studies will
be much
better with
the EVLA.
Sequence of images of radio jet at 3.6 cm
Curiel et al. (2006)
The EVLA and jet kinematics
• Proper motions now limited by sensitivity:
impossible to detect in weak jets, very
difficult to follow up ejecta that become too
weak with time.
• With the possibility of recombination line
“stacking” we may be able to detect radial
motions, getting 3-D kinematics.
RRL from jets?
Assume electron temperature = 10,000 K,
frequency around 30 GHz, and a linewidth
of 100 km/s:
SL
 0.05
SC
For
SC = 10 mJy
SL
= 0.5 mJy
In the Ka band (26.5 – 40 GHz) you expect a 1-sigma noise of
0.1 mJy for 10 km/s velocity resolution and 12-hour
integration. => You get a modest signal-to-noise of 5. But…
Stacking Radio Recombination Lines
• But, in the Ka band (26.5-40 GHz) you can get 8
alpha RRLs (H62a to H55a) so you gain a factor
of about 3 sensitivity and to an interesting signalto-noise ratio of 15 (spatially integrated line).
• Rotating jets?
• In general, observations of wide lines become
possible with the EVLA (broad line HII regions).
Synchrotron emission in knots?
• It has been argued that there are synchrotron
components in the ejecta from some of
these jets.
• However, only in the case of the jet near
W3(OH) is this clear.
• Other sources are weak and spectral indices
are unreliable. The EVLA will solve this.
Let us now switch to disks…
• Traced by millimeter dust emission and
molecules.
• Expected to be perpendicular to outflow
axis.
L1551 IRS5:
Binary
system with
disks.
VLA 7mm
Lim &
Takakuwa
(2006)
Minus third
component
and jet
contribution
L1551 IRS5: Binary system with jets
VLA 3.6 cm
Rodriguez et al. (2003)
Massive (B0) protostar.
7 mm image suggests
presence of disk, but limited
by signal-to-noise, not by
angular resolution.
Carrasco-Gonzalez et al.
(2009)
HH 111 is a quadrupolar
outflow source. This
quadrupolar structure is
marginally appreciated in the
3.6 cm (free-free emission).
More clearly present in the 7
mm image. Are we seeing in
this image two disks? Or a
disk and a jet? One needs
excellent deep images at
different frequencies to get
spatially-resolved spectral
indices.
HL Tau: Jet and disk
Greaves et al. (2008), Carrasco-Gonzalez et al. (2009)
Possible presence of “gaps” in disk may signal planet formation.
Protoplanets? Images severely limited by signal-to-noise ratio.
The structure of disks can tell us a lot about
how is planet formation taking place…
• According to Durisen (2009) there are two
main models for the formation of giant
planets:
• 1. Core accretion: Will produce gaps in
disks, as possibly observed in HL Tau.
• 2. Disk instability: Will produce spiral
patterns in disk. Has this been observed?
A hint of spiral structure in this 7 mm VLA
image that traces dust? Disk instability?
Rodmann et al. (2006) did
VLA-D survey at 7 mm,
detecting 10 T Tau stars.
Sources resolved at 1” scale,
but little information on
structure.
The EVLA will image this
type of disks with high
fidelity and signal-to-noise
ratio, and provide unique
information on their sizes,
spectral indices, and relation
to possible jets and outflows.
IRAS 16293-2422B
Continuous spectral
index
Studies of spectral
indices as a function of
radius in disk will help
understand problem of
grain growth.
Weak, multiple sources…
VLA-A; 3.6 cm
Weak “companions”
VLA-A; 3.6 cm
IRAS 16457-4742
At a distance of 2.9
kpc, it has a
bolometric
luminosity of 62,000
solar luminosities,
equivalent to an O8
ZAMS star.
VLA images of IRAS 16547-4247
The outflow
carries about 100
solar masses of
gas (most from
ambient cloud)
and has
characteristics of
being driven by
a very luminous
object.
SMA data
Velocity gradient in
SO2 (colors)
suggests total mass
of 20 to 40 solar
masses and a
radius of 1,000 AU
for the disk
(Franco-Hernandez
et al. 2007).
Most massive
young star known
with jets, disk, and
large scale infall.
The EVLA will also be powerful for
the study of more evolved stages.
• Hypercompact HII regions: what is the
nature of their compactness, why some are
variable,…
Component A1 diminish its flux
density between the two epochs
(note years!) Galván-Madrid et al.
NGC 7538 IRS1
Franco-Hernández &
Rodríguez (2004)
The EVLA will
be able to study
these time
variations ina
multifrequency
mode and will
also detect RRLs
from the
componentes,
that are expected
to be weak and
wide.
Still many open questions in star
formation...
• Better cm and mm interferometers will play
a key role in the observational aspect.
• The EVLA will have powerful synergies
with e-MERLIN and ALMA (0.05” angular
resolution over a range of 100 in
frequency).
Thank you