Induced Star Formation in tInduced Star Formation in the Orion and Monoceros he Orion and Monoceros

Molecular CloudsMolecular Clouds

Hsu-Tai Lee and Wen-Ping Chen

National Central University, Institute of Astronomy

OutlineOutline

IntroductionSource of Data and ObservationsIndividual Molecular CloudDiscussion

IntroductionIntroduction

The Orion & Monoceros molecular clouds are 2 nearby active star-forming regions

Orion OB1 association (450 pc)Mon R2 (830 pc)Orion-Eridanus bubble – a series of superno

va explosions in the Orion OB1

Triggered Star FormationTriggered Star Formation

Elmegreen, B. G. 1998, ASP Conf. Ser., 148

Small Scale: Globule-SqueezingIntermediate Scale: Collect and CollapseLarge Scale: Shells and Rings

Small scale triggeringSmall scale triggering

Direct squeezing of pre-existing clouds or globules by high pressure. This includes triggering in bright rims, proplyds, and small cometary globules.

OB stars

Molecular cloud

Young stars

Intermediate scale triggeringIntermediate scale triggering

Compression of a nearby pre-existing cloud from one side, leading to a dense ridge of moving gas.

OB stars

Molecular cloud

Young stars

Large scale triggeringLarge scale triggering

Accumulation of ambient gas into an expanding shell or ring partially surrounding the pressure source, with star formation in the shell or ring presumably triggered by gravitational collapse of swept-up gas.

Pre-Main Sequence StarPre-Main Sequence Star

Classical T Tauri star (CTTS)Strong IR and UV excessStrong emission line

Weak-lined T Tauri star (WTTS)More evolved pre-main sequence starWeak emission lineStrong soft X-ray source

CTTS WTTS

Source of DataSource of Data

2MASS – J (1.25μm), H (1.65μm) and Ks (2.17μm) all sky survey

CO image – Dame, T. M. et al.(2001, ApJ)IRAS 100 μm – Schlegel, D. et al. ( 1998, A

pJ)Hα image – Finkbeiner, D. P. (2003, ApJS)

ObservationsObservations

BAO 2.1m spectroscopic observations in early 2003

Low-resolution spectra have been observed for 32 PMS candidates

24 CTTSs, 4 M stars and 4 carbon starsMost of CTTSs are located at molecular clo

ud; M and carbon stars are not associated with molecular cloud

Hα

Hβ

Maddalena et al. 1986

The Red dots are the CTTSs; blue dots are the O stars.

CO image Hα image

Orion A & B Molecular CloudOrion A & B Molecular Cloud

TheλOri is a O8III star, and it is surrounded by a ring molecular cloud (Duerr, Imhoff, & Lada, 1982, ApJ)

IRAS 100μm Hα image

IC 2118, LDN 1616 IC 2118, LDN 1616 & LDN 1634 & LDN 1634

Hα image IRAS 100μm

LDN 1616

IC 2118LDN 1634

LDN 1652 LDN 1652

Hα image CO image

object scale Pressure source

λOri region S High mass star

IC 2118 region S High mass star

Orion A & B I Superbubble

LDN 1652 L or I Supperbubble

S – small scale triggering; I – intermediate scale triggering; L – large scale triggering

Triggered star formationTriggered star formation

Discussion IDiscussion I

Our selection criterion is good to find CTTSs.For those bright-rimmed clouds associated w

ith both strong Hα and IR emission accompany star formation

High mass star interact with molecular cloud would trigger star formation

Superbubble can also induce star formation hundreds pc away (LDN 1652)

Discussion IIDiscussion II

CTTSs outside the bright-rimmed cloud seem to be older than those inside the bright-rimmed cloud.

Compared with WTTSs, CTTSs are more closer to recent star formation. Our CTTS candidates can be used to trace the nearby star-forming region (< 2 kpc).