studying young stellar objects with the evla

Studying Young Stellar Objects with Studying Young Stellar Objects with the EVLAthe EVLA

• Disks and jets in young stars

• VLA results

• Possibilities with the EVLA

• Conclusions

Luis F. Rodriguez, CRyA, UNAM Morelia, México

This scheme is supported by observations, in particular for forming low-mass stars.

DISK: allows accretion, planets may form from it.

JET: removes excess angular momentum and magnetic flux, produces outflows and HH objects.

VLA continuum observations at several frequencies reveal characteristic spectrum jet+disk.

JET

DISK

Rodriguez et al. 2008 Gomez et al. (2003)

VLA 1HH 1-2 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 low-mass 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

Gómez et al. (1995)

Thermal Jet

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:

05.0C

L

SS For = 10 mJy

= 0.5 mJy

CS

LS

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 (H62to H55so you gain a factor of about 3 sensitivity and to an interesting signal-to-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

Possible presence of “gaps” in disk may signal planet formation. Protoplanets? Images severely limited by signal-to-noise ratio.

Greaves et al. (2008), Carrasco-Gonzalez et al. (2009)

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.

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.

SMA data

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