low-mass star formation in a small group, l1251b jeong-eun lee ucla
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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)
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
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.
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
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.
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