Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 1

Robert Estalella, Aina Palau, Maite Beltrán (UB)

Paul T. P. Ho (CfA), Henrik Beuther (MPIfA)

IRAS 20343+4129, a puzzling massive star-forming region

UNIVERSITAT DE BARCELONA

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 2

Introduction: modes of star formationIntroduction: modes of star formation

Observationally, there are two modes of star formation in molecular clouds:

clustered mode (e.g. Orion)

isolated mode (e.g. HHL 73)

(Megeath et al. 2005)

(Anglada et al. 1997)

Likely phenomena in clustered mode:● interaction between sources ● outflows● mergings of cloud cores● compression front from high-mass stars

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 3

Introduction: the big question Introduction: the big question

Nobody knows (up to now) the answer, but we can gain insight by:

● characterizing different cluster environments in their first stages of formation, and

● studying the interaction between the members of these environments

Approach and strategy● detect low-mass condensations: high sensitivity● first evolutionary stages: mm/submm range● high-mass star-forming regions farther away than 1 kpc: angular

resolution: 2''-5''

Why do stars preferently form Why do stars preferently form closely packed rather than in closely packed rather than in isolation?isolation?

Source selected from a sample of massive star-forming regions: IRAS 20343+4129

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 4

● 3200 L⊙ at 1.4 kpc in

Cygnus OB2

● 3 bright IR stars, brightest infrared source IRS 3 coincident with a weak cm source

● IRS 1: the most luminous and embedded object of the association?

● N-S bipolar outflow (single dish)

0.05 pc

IRAS 20343+4129IRAS 20343+4129

2MASS composite J, H, K image

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 5

Continuum results (1 mm SMA)Continuum results (1 mm SMA)

cm source (white): associated with IRS 3

1 mm emission (brown): 3 condensations:

● west: mm1-mm4, ~4 M⊙

● east: mm7, ~0.5 M⊙

● north:

mm6/IRS 1, ~0.2-0.5 M⊙

mm5/IRS 1N?grey scale: 2MASS J image

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 6

CO (2-1) results (SMA)CO (2-1) results (SMA)

Low velocity: associated with IRS 1, two elongated structures at both sides of IRS 3

High velocity: bipolar molecular outflow in the east-west direction driven by IRS 1. No evidence of large-scale north-south outflow

high vel

IRS 1 is at the center of symmetry of the outflow

low vel

grey scale: H2 cont + line at 2.12 µm (Kumar et al. 2002)

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 7

The bipolar outflowThe bipolar outflow

CO emission with IRAM 30 m (Beuther et al. 2002) Large-scale blue lobe resolved out by the SMA

Parameters of the outflow discovered toward IRS 1 compared to other outflows:

extended emission

CO(2-1)IRAM 30m

Parameters of IRS 1 outflow in between low-mass and high-mass outflows

high mass

low mass

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 8

Cavity created by IRS 3Cavity created by IRS 3

Observations suggest that IRS 3 is blowing up a shell of surrounding material, and that the dust condensations at both sides of IRS 3 are the result of accumulation of mass.

IRS 3

Snowplow model from Anglada et al. (1995)

Rshell

= 0.07 pc

vshell

= 2 km/s

Pext

(3.3 km/s)2

n0 = 2300 cm-3

twind

= 104 yr

Rmax

= 0.08 pc

assumptions: Derived param.:

low res CO low vel CO cont 1mm

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 9

The nature of IRS 1The nature of IRS 1

IRS 1:● 2MASS very bright

magnitudes● strong IR excess● circumstellar mass at 1 mm ● outflow parameters

SED for IRS 1 typical of Class I:● 1-2 µm: steep >0 profile ● 10-100 µm: >0 profile● Comparison with other SEDs of

Class I sources of different luminosities scaled to the distance of IRAS 20343+4129

IRS 1 is an intermediate-mass Class I source (but the circumstellar mass is low)

Is IRS 1 a high-mass B0 star? (too luminous)

Is IRS 1 a high-mass protostar? (too low circumstellar mass)

Is IRS 1 a low/intermediate-mass protostar?

(IRS 13) 960 L⊙

(IRS 14) 250 L⊙

(IRAS 04016+2610) 4 L⊙

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 10

Star formation: interactions, initial conditionsStar formation: interactions, initial conditions

The most massive source has faint mm emission associated

Other sources around it: different properties at different wavelengths

This suggests continuous star formation, and since N

s(IR) > N

s(mm), that

tlife

(IR) > tlife

(mm)

IRS 3IRS 3

IRS 1

IRS 3 is driving a cavity and accumulating the surrounding material in the walls

Interaction between sources could have triggered star formation in some cases

IRS 1 and IRS 3 could have formed simultaneously (IRS 3 may have not triggered the formation of IRS 1)

Initial conditions are required to explain the overall spatial distribution of the sources

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 11

Number of mm sources Number of mm sources vsvs IR sources IR sources

Median number of mm sources around high-mass protostars: 5Median number of IR sources around high-mass stars: 15

Palau 2006, PhD thesis

Beuther & Schilke 2004

Cesaroni 1999

Why?

Summary of high-mass protostellar objects observed with enough sensitivity to detect low-mass condensations (< 1 M⊙) in the mm range, up to 2006:

(based on very poor statistics!)

See Aina’s presentation

Sensitivity problem? Enough resolution and u-v coverage?

Massive enough regions? Protostars already formed around the high-mass

protostar?Is star formation a continuous process?

Mini Workshop on Star Formation and Astrochemistry. Barcelona, 2006 November 23 12

ConclusionsConclusions

IRAS 20343+4129 is a cluster environment with a variety of sources.

IRS 1, an intermediate-mass Class I source, driving an east-west bipolar CO(2-1) outflow.

IRS 3, seems to drive an expanding shell pushing out the dust condensations detected at both sides of this source.

Our observations suggest that star formation in this cluster environments is a continuous process.

Interaction seems to be important in massive star-forming regions, but initial conditions must be important as well to determine the final distribution of young stellar objects in the cluster environment.