IRTF Data Archive Program Information

# # Program information file # PROGRAM_ID 2023A023 PROGRAM_TITLE Testing the hierarchical formation scenario using five hierarchical clustering subgroups LP 2442 gp1-gp5 PROGRAM_INV1 Mingjie Jian PROGRAM_INV2 Yifan Wang PROGRAM_INV3 Yanshu Wang PROGRAM_INV4 Xiaoying Pang PROGRAM_INV5 Shih-Yun Tang PROGRAM_SCICAT stellar PROGRAM_ABSTRACT_BEG The formation scenario of the open cluster is now under debate. The monolithic formation scenario assumes that all the member stars in an open cluster are formed in the central part of a molecular cloud, while the hierarchical scenario assumes that stars are formed in both the central part and also in low-density filament networks. Different dynamical and chemical characteristics are expected, with the stars formed under the monolithic scenario having a homogeneous velocity and metallicity, and those formed under the hierarchical scenario would have different velocities and metallicities among subgroups. Here we propose to measure the radial velocity [RV] and metallicity of the stars in the five hierarchical clustering subgroups LP 2442 gp1--gp5 [located near the open cluster LP2442] using the H2 mode of iSHELL on IRTF with a resolution of 38000. Relatively bright FGK-type dwarfs are selected as our target, to obtain spectra with a signal-to-noise ratio [S/N] of 50 or 100, depending on their brightness. Such S/Ns yield an RV precision of ~0.1km/s, which can provide solid evidence of the dynamical situation of these five stellar subgroups. Also, the precision of metallicity for the spectra with S/N=100 is expected to be 0.1 dex, which can reveal the metallicity difference between the subgroups predicted by the hierarchical formation scenario, if any. This observation would determine how these five hierarchical clustering subgroups are formed, whether they will dissipate finally, and provide important information about how the open cluster contributes to the formation of the field stars. PROGRAM_ABSTRACT_END