Low-Mass Star Formation Low-Mass Star Formation in a Small Group, L1251Bin a Small Group, L1251B

Jeong-Eun LeeJeong-Eun Lee

UCLAUCLA

Why Star Formation?Why Star Formation?

• Stars are one of the Stars are one of the most fundamental most fundamental objects in Astronomy. objects in Astronomy.

• Understanding star Understanding star formation can provide formation can provide important clues for important clues for galaxy evolution, planet galaxy evolution, planet formation, and formation, and ultimately, the origin of ultimately, the origin of life.life.

The Universe

Galaxy

stars

Planet

life

Questions to be answeredQuestions to be answered

• How do dense molecular cores start to How do dense molecular cores start to collapse to form stars?collapse to form stars?

• What are the initial conditions of the What are the initial conditions of the collapse?collapse?

• How is chemical evolution in How is chemical evolution in molecular cores linked to their molecular cores linked to their dynamical evolution?dynamical evolution?

• How do the chemical changes affect How do the chemical changes affect the formation of planets and life?the formation of planets and life?

How to answer those How to answer those questions?questions?• Study more isolated low mass cores Study more isolated low mass cores less complicated and easier to less complicated and easier to

interpret observationsinterpret observations• Combination of continuum and line Combination of continuum and line

observations to provide a coherent, observations to provide a coherent, self-consistent picture of YSOs and self-consistent picture of YSOs and their associated, gaseous their associated, gaseous environments (n, T, v)environments (n, T, v)

The Standard The Standard CartoonCartoon

Observations in L1251BObservations in L1251B• Continuum Continuum 2MASS, IRAC & MIPS(SST), SHARC (CSO), 2MASS, IRAC & MIPS(SST), SHARC (CSO),

SCUBA (JCMT), MAMBO (IRAM), OVRO, SMASCUBA (JCMT), MAMBO (IRAM), OVRO, SMA• Molecular LinesMolecular Lines FCRAO: CS 2-1, HCO+ 1-0, HFCRAO: CS 2-1, HCO+ 1-0, H1313CO+ 1-0, CO+ 1-0,

NN22H+ 1-0, HCN 1-0H+ 1-0, HCN 1-0 CSO: CO 2-1, HCO+ 3-2, DCO+ 3-2CSO: CO 2-1, HCO+ 3-2, DCO+ 3-2

OVRO: NOVRO: N22H+ 1-0, HCO+ 1-0, HH+ 1-0, HCO+ 1-0, H22CO 3CO 31212-2-21111

SMA: CO 2-1, SMA: CO 2-1, 1313CO 2-1, CCO 2-1, C1818O 2-1, NO 2-1, N22D+ 3-2 D+ 3-2 ARO (NRAO): CS 3-2, 5-4ARO (NRAO): CS 3-2, 5-4

L1251 (Sato et al. 1994)L1251 (Sato et al. 1994)

IRAS 22376+7455

SCUBA 850 SCUBA 850 μμm and MIPS 24 m and MIPS 24 μμmm

IRAS 22376+7455

IRAC IRAC 3.63.6, , 4.54.5, & 8.0 μm, & 8.0 μm

IRAS 22376+7455

HH 373

UGC 12160

L1251BL1251B

IRAS 22376+7455

IRAC Color-Color DiagramIRAC Color-Color Diagram

1,2,4,161,2,4,16

7,10,12,13,147,10,12,13,14

3,5,6,8,93,5,6,8,9

Only 1, 2, and 4 have been detected in MIPS 24 Only 1, 2, and 4 have been detected in MIPS 24 μμm.m.

Spectral Spectral Energy Energy DistributioDistributionsns

IRS1IRS1 10 L10 LΘΘ

IRS2IRS2 0.8 L0.8 LΘΘ

IRS4IRS4 1.0 L1.0 LΘΘ

Submillimeter ContinuumSubmillimeter Continuum

Column density peak

Thermally heated350 μm 450 μm

850 μm 1300 μm

gray: K-band contours: submm

OVRO Continuum OVRO Continuum ObservationsObservations

(disk component)(disk component)

gray: 1.3 mm contours: 3.4 mm

gray: 4.5 µm contours: 3.4 mm

IRS1IRS2

IRS3

IRS4

SMA Continuum ObservationsSMA Continuum Observations

gray: 4.5 µm contours: 1.3 mm

IRS1IRS2

IRS3

IRS4

IRS5

IRS6Prestellar Prestellar condensations?condensations?

L1251B is a small group of pre- and L1251B is a small group of pre- and protostellar objects.protostellar objects.

• In L1251B, six sources were detected in all In L1251B, six sources were detected in all IRAC bands. Half of them were classified as IRAC bands. Half of them were classified as Class 0/I candidates, and the other half were Class 0/I candidates, and the other half were classified as Class II candidates.classified as Class II candidates.

• Dust continuum emission maps at 350 and Dust continuum emission maps at 350 and 450 µm have two intensity peaks. The 450 µm have two intensity peaks. The weaker peak is associated with IRS1, but the weaker peak is associated with IRS1, but the stronger peak is located between IRS1 and stronger peak is located between IRS1 and IRS2. The stronger peak has been resolved IRS2. The stronger peak has been resolved to two sources (prestellar objects) in the to two sources (prestellar objects) in the SMA 1.3 mm.SMA 1.3 mm.

Infall Signature in HCO+ 3-Infall Signature in HCO+ 3-22

Outflow in CSO CO 2-Outflow in CSO CO 2-1 and OVRO HCO1 and OVRO HCO++ 1-0 1-0CO 2-1CO 2-1

11

22

K band & HCO+ 1-0

11

22

44

blue component

red component

Thick contours: N2H+

Thin contours: HCO+

Gray: 3 mm continuum

Contours: H2CO

Gray: 1 mm continuum

P-V diagram

OVRO Line ObservationsOVRO Line Observations

11

22

44

11

SMA Line ObservationsSMA Line Observations

11

22

44

A possible formation model of L1251BA possible formation model of L1251B

blueblue

redred

blueblue

redred

L1251B probably formed through collapse of L1251B probably formed through collapse of a rapidly rotating core. a rapidly rotating core.

• Infall signature was detected in optically Infall signature was detected in optically thick lines, and velocity gradients, thick lines, and velocity gradients, indicative of rotation, were measured.indicative of rotation, were measured.

• The large molecular outflow structure may The large molecular outflow structure may be the accumulated result of multiple be the accumulated result of multiple outflows, and IRS4 is possibly triggered to outflows, and IRS4 is possibly triggered to form by the outflow from IRS1.form by the outflow from IRS1.