Tigran KhanzadyanCentre for Astronomy, NUIG

ASGI Autumn Meeting at UCC, 3rd of October 2008

Dissection of a Cold, Infalling High-Mass Star-Forming Core

In Collaboration With : Patrick Carolan & Matt Redman (NUIG, Ireland), Mark Thompson (Hertfordshire, UK), Paul Jones & Maria Cunningham (Univ. New South Wales, Australia) and Indra Bains (Swinburne University of Technology, Australia)

Talk Content

• Brief introduction into star-formation (SF).

• Observing the SF, what can be done.

• JCMT 18354-0649S core and our project

• Modelling and understanding “the beast”

Low-Mass High-Mass

FormationSlow vs. Quick

Isolated vs. Crouded

LifeLong vs. Short

Quiet vs. Violent

DeathPlanetary Neb. vs. SN Explosion

If their evolution is different then how about the origin?

High-Mass SF (I)• There is still a debate about the origin of High-Mass

Stars : Mergers vs. Size-up version of Low-Mass SF - both approaches have pros and cons (obviously).

• Many difficulties to trace the high-mass SF in making - complicated environment

• Current understanding is more inclined towards Size-up theory due to the emerging observational evidence - infall and outflow signatures similar to low-mass SF vs. no reliable kinematical evidence for merger theory.

High-Mass SF (II)• If they originate in the same way/conditions where did

the divergence take place?

• What are the chemical and physical processes at play?

• Freeze-out - When the temperature is low enough and the density is high enough the gas will ‘freeze-out’ or stick onto a dust grain (depletion due to freez-out)

• Infall - A starless core will collapse when it loses pressure support

• Outflow - Once Infall starts there has to be outflow to conserve angular momentum

Observing these all ...• Early stage of SF is

Heavily obscured optically so we need to look in the mm part of the spectrum

• We have a choice to study continuum radiation as well as tune into some well know molecular line transitions

JCMT

MOPRAAPEX

ALMA

Kind of Data we get

Bolometers detect thermal continuum emission from the cold dust grains.Temperature Density are calculated from it.

Receivers tune to mm emission lines of gas. Line emission can tell us the chemistry and dynamics. Candidate species would be N2H+, HCO+, HCN, NH3, CO and others ...

Infall Signature

• So can we actually observe the infall motions in the star-forming cores? YES!

• Not only we can observe it, we can actually explain it!

B335

All this was known from Low-Mass SF, how about High-Mass SF?

JCMT 18354-0649S

• First reported by Wu et al, 2005, ApJ, 628, L57 to be a direct indication of infall motions towards high-mass SF core! No objects were detected in any shorter wavelengths at that position - so it’s pretty exciting!

Observing campaign

• So infall in High-Mass SF? - we need more data to get into the mechanism of the process.

• We successfully applied to JCMT (30h), MOPRA(8h) times!

• We obtained lot’s of archive data, JCMT, SPITZER, etc

• We analysed all the data!

R:8p0_G:4p5_B:3p6

1’ 6.98’ x 5.9’

N

EPowered by Aladin

JCMT18354-0649S

G25.4NW

G25.4SE

RGB : SPITZER 3.6μm 4.5μm 8.0μm

Contours:SCUBA 850μm

CO (3-2)

HCN(3-2)

CO (3-2)

C17O(2-1)

HCN(4-3)

HCO+(3-2)

Then comes the model

• After obtaining all these “nice” data-sets we can try to interpret what all these lines mean or we could try to model them by using a 3D, non-LTE radiative transfer code in our disposal (chronologically speaking we had this code before the observations).

• Each cell in the 3D grid is given a temperature, turbulent width, velocity, density and chemical abundance (from data)

• The code calculates level populations and hence emission seen by an observer

• Can load observations into the code and run multiple models

The Model

DensityTemperature

VelocityAbundance

Turbulent width

Described in: Carolan et al, 2008, MNRAS, 383, 705 Keto et al, 2004, ApJ, 613, 355 Rawlings et al, 2004, MNRAS, 351, 1054

The Fit Parameters

MoleculeDensity(cm-3)

Velocitykm/s

Turb. Widthkm/s

Temp. (K)Abundance

n(H2) in cm-3

12CO env. 1 x 106 1 (inf) 1.6 20 1 x 10-6

12CO out 6 x 104 10 1.7 110 2 x 10-5

C17O 1 x 106 1 (inf) 1.6 20 1 x 10-9

C18O 1 x 106 1 (inf) 1.6 20 10 x 10-9

HCN 1 x 106 2 (inf) 1.5 17 1 x 10-11

HCO+ 1 x 106 1 (inf) 0.8 20 90 x 10-11

H13CO+ 1 x 106 1 (inf) 1.4 20 15 x 10-11

So?

• We have quite a good fit on temperature (20K), infall velocity, turbulent width and the density.

• We have a rotation of the cloud about 1km/s.

• We have an outflow and we know the direction, velocity all the essential parameters.

Points to take with you• It is much likely that High-Mass SF is Size-up version of

the Low-Mass SF

• We can use SubMM and MM to carefully dissect the High-Mass SF core in order to learn about the physics and dynamics.

• JCMT 18354-0649S is an example core with infall/outflow motions where we can follow the early stage of High-Mass SF.

• We produced pretty good fit with our 3d non-lte radiative transfer code which reveals quite a good inside of processes occurring in the core. Talk to us if you need more ...

Thanks for your patience!