1. Low-Mass Star Formation in a Small Group, L1251B Jeong-Eun Lee UCLA

2. Why Star Formation? Stars are one of the most fundamental objects in Astronomy. Stars are one of the most fundamental objects in Astronomy. Understanding star formation can provide important clues for galaxy evolution, planet formation, and ultimately, the origin of life. Understanding star formation can provide important clues for galaxy evolution, planet formation, and ultimately, the origin of life. The Universe Galaxy stars Planet life

3. Questions to be answered How do dense molecular cores start to collapse to form stars? How do dense molecular cores start to collapse to form stars? What are the initial conditions of the collapse? What are the initial conditions of the collapse? How is chemical evolution in molecular cores linked to their dynamical evolution? How is chemical evolution in molecular cores linked to their dynamical evolution? How do the chemical changes affect the formation of planets and life? How do the chemical changes affect the formation of planets and life?

4. How to answer those questions? Study more isolated low mass cores Study more isolated low mass cores less complicated and easier to interpret observations less complicated and easier to interpret observations Combination of continuum and line observations to provide a coherent, self- consistent picture of YSOs and their associated, gaseous environments (n, T, v) Combination of continuum and line observations to provide a coherent, self- consistent picture of YSOs and their associated, gaseous environments (n, T, v)

5. The Standard Cartoon

6. Observations in L1251B Continuum Continuum 2MASS, IRAC & MIPS(SST), SHARC (CSO), SCUBA (JCMT), MAMBO (IRAM), OVRO, SMA 2MASS, IRAC & MIPS(SST), SHARC (CSO), SCUBA (JCMT), MAMBO (IRAM), OVRO, SMA Molecular Lines Molecular Lines FCRAO: CS 2-1, HCO+ 1-0, H 13 CO+ 1-0, FCRAO: CS 2-1, HCO+ 1-0, H 13 CO+ 1-0, N 2 H+ 1-0, HCN 1-0 N 2 H+ 1-0, HCN 1-0 CSO: CO 2-1, HCO+ 3-2, DCO+ 3-2 CSO: CO 2-1, HCO+ 3-2, DCO+ 3-2 OVRO: N 2 H+ 1-0, HCO+ 1-0, H 2 CO 3 12 -2 11 OVRO: N 2 H+ 1-0, HCO+ 1-0, H 2 CO 3 12 -2 11 SMA: CO 2-1, 13 CO 2-1, C 18 O 2-1, N 2 D+ 3-2 SMA: CO 2-1, 13 CO 2-1, C 18 O 2-1, N 2 D+ 3-2 ARO (NRAO): CS 3-2, 5-4 ARO (NRAO): CS 3-2, 5-4

7. L1251 (Sato et al. 1994) IRAS 22376+7455

8. SCUBA 850 μm and MIPS 24 μm IRAS 22376+7455

9. IRAC 3.6, 4.5, & 8.0 μm IRAS 22376+7455 HH 373 UGC 12160

10. L1251B IRAS 22376+7455

11. IRAC Color-Color Diagram 1,2,4,16 7,10,12,13,14 3,5,6,8,9 Only 1, 2, and 4 have been detected in MIPS 24 μm.

12. Spectral Energy Distributions IRS1 10 L Θ IRS2 0.8 L Θ IRS4 1.0 L Θ

13. Submillimeter Continuum Column density peak Thermally heated 350 μm450 μm 850 μm1300 μm gray: K-band contours: submm

14. OVRO Continuum Observations (disk component) gray: 1.3 mm contours: 3.4 mm gray: 4.5 µm contours: 3.4 mm IRS1 IRS2 IRS3 IRS4

15. SMA Continuum Observations gray: 4.5 µm contours: 1.3 mm IRS1 IRS2 IRS3 IRS4 IRS5 IRS6 Prestellar condensations?

16. L1251B is a small group of pre- and protostellar objects. In L1251B, six sources were detected in all IRAC bands. Half of them were classified as Class 0/I candidates, and the other half were classified as Class II candidates. In L1251B, six sources were detected in all IRAC bands. Half of them were classified as Class 0/I candidates, and the other half were classified as Class II candidates. Dust continuum emission maps at 350 and 450 µm have two intensity peaks. The weaker peak is associated with IRS1, but the stronger peak is located between IRS1 and IRS2. The stronger peak has been resolved to two sources (prestellar objects) in the SMA 1.3 mm. Dust continuum emission maps at 350 and 450 µm have two intensity peaks. The weaker peak is associated with IRS1, but the stronger peak is located between IRS1 and IRS2. The stronger peak has been resolved to two sources (prestellar objects) in the SMA 1.3 mm.

17. Infall Signature in HCO+ 3-2

18. Outflow in CSO CO 2-1 and OVRO HCO + 1-0 CO 2-1 1 2 K band & HCO + 1-0 1 2 4 blue component red component

19. Thick contours: N 2 H + Thin contours: HCO + Gray: 3 mm continuum Contours: H 2 CO Gray: 1 mm continuum P-V diagram OVRO Line Observations 1 2 4 1

20. SMA Line Observations 1 2 4

21. A possible formation model of L1251B blue red blue red

22. L1251B probably formed through collapse of a rapidly rotating core. Infall signature was detected in optically thick lines, and velocity gradients, indicative of rotation, were measured. Infall signature was detected in optically thick lines, and velocity gradients, indicative of rotation, were measured. The large molecular outflow structure may be the accumulated result of multiple outflows, and IRS4 is possibly triggered to form by the outflow from IRS1. The large molecular outflow structure may be the accumulated result of multiple outflows, and IRS4 is possibly triggered to form by the outflow from IRS1.