Proper Motions of large-scale Optical Outflows Fiona McGroarty, N.U.I. Maynooth

ASGI, Cork 2006

Talk Outline Introduction to star formation and the outflow phase

Parsec-Scale Outflows:

Outflows – What is their function? How do we “see” them?

RESULTS : Examine tangential velocity of the HH objects in the CTTS - driven outflows

RESULTS : Parsec-scale outflows from Classical T Tauri stars (CTTS) with microjets

Observations

Star Formation Process

HR Diagram

Outflow

InfallingEnvelope

Accretion Disk

Bipolar outflows remove excess angular momentum from the forming star

(a) Cores collapse under gravity(b) Protostar and disk form in centre(c) Bipolar outflow forms to disk(d) Infall and outflows stop; star is formed.

Outflows: Functions

Direct optical observations of the star are often impossible but we can observe some of the phenomenon that accompany star formation e.g. outflows

Outflows: Observations Outflows are observed by their interaction with the ambient medium. When optically visible these shocks are known as Herbig-Haro objects

Outflows are mainly observed in lines from CO, H2, optical and various atomic species • CO traces the ambient molecular gas• H2 traces low velocity shocked emission• Optical traces high velocity shocked emission Observe HH shocks in:

[OIII], [SII] and H

HH emission is due to radiative shocks

Shock velocities vary from tens ( 50 kms-1) to hundreds of kms-1

H

[SII]

Structure of Outflows

Knots with “empty space” further out

Jet (~ continuous flow of emission) close to source

Only in the past 10 years that we have Realised that outflows can extend for many parsecs

Can outflows be larger than their parent cloud?

1pc ~ 3 X 1013 km ~ 3.26 light years ~ 206265 AU

Observations: INT Telescope

All observations were taken using the Wide Field Camera (WFC) on the Isaac Newton Telescope, La Palma.

The WFC consists of four 2048 X 4100 pixel CCDs. Each pixel projects to 0.33’’ on the sky. CCDs are aligned to form an approximate square 34’ in size. This is a large enough field of view to find parsec scale outflows, with high enough resolution (0.33”) to see their structure.

Importance of parsec-scale outflows

- Morphology can be used to determine the mass-loss history of the source - Outflows are related to accretion so can deduce if similar accretion rates for different stellar masses (similar star formation process?)

- Are a possible source of turbulence in the parent cloud

- May have a significant effect on subsequent star formation in their vicinity

Typical sources are low-mass, embedded young (forming) stars

Here, look at sources that are not usually associated with parsec-scale outflows – Are parsec-scale outflows ubiquitous?

Classical T Tauri Stars

More evolved, low-mass stars - Classical T Tauri Stars (CTTS)

Accretion decreases with age, does outflow activity decrease?

Previously known to be the sources of “microjets” of ~5’’ - 40’’

Looked at 5 sources – CW Tau, DG Tau, DO Tau, HV Tau C and RW Aur

McGroarty & Ray 2004, A&A, 420, 189

Morphologically : HH826, HH827 and HH829 are extensions of the CW Tau outflow, making it 1pc (24’) in length. The previously known length of the HH220 jet was ~12’’

The curving inverted “S” shape of the assumed outflow is a trend often seen in parsec-scale outflows from Class I YSOs.

The fact that HH827 and HH829 are symmetrically located about CW Tau seemed to strengthen the idea that they are extensions to this outflow.

However my kinematical studies show that HH829 is not driven by CW Tau…..

CW Tau

CW Tau McGroarty, Ray, Froebrich, in preparation

Kinematical studies show HH826 to be driven by CW Tau and if precession is present HH827 is also part of this outflow

For the 5 CTTS-driven outflows observed: Lengths: between 0.3 and 0.5 pc dyn: is of the order of 103 yr

Outflow lengths are comparable to the size of the parent cloud – outflows have “blown out”

However these studies show that HH828 and HH829 are not driven by CW Tau

This reduces the length of this outflow to ~ 0.3pc

Kinematical studies of the CTTS-driven outflowsshow: velocity of micro-jets to be ~200 km/s velocity of distant objects to also be ~ 200 km/s

Is the outflow velocity at the source decreasing over time or does the velocity of the outflow remain approximately constant over these large distances?

CW Tau McGroarty, Ray, Froebrich, in preparation

Need larger data sample and numerical simulations to answer this question

CTTS : Conclusions

Optical evidence for outflows of the order of 0.5pc from from more evolved, classical T Tauri stars These outflows have similar degree of collimation as parsec-scale outflows from younger low-mass sources (Class I) i.e. collimation remains high as the source evolves over ~ 1Myr

Outflow lengths are comparable to parent size cloud “blow out”

Caution is needed when using the apparent alignment of HH objects to derive their sources. However in the absense of kinematical studies it is still the best means of finding potential driving sources

Velocities of ~200 kms-1 are found for the more distant objects, i.e. velocity remains high at large distances from the source