Searching for Multiple Populations in Star Clusters Using the China Space Station Telescope

Multiple stellar populations(MPs) in most star clusters older than 2 Gyr, as seen by lots of spectroscopic and photometric studies, have led to a significant challenge to the traditional view of star formation. In this field, spacebased instruments, in particular the Hubble Space Telescope(HST), have made a breakthrough as they significantly improved the efficiency of detecting MPs in crowded stellar fields by images. The China Space Station Telescope(CSST) and the HST are sensitive to a similar wavelength interval, but the CSST covers a field of view which is about 5–8 times wider than that of HST. One of its instruments, the Multi-Channel Imager(MCI),will have multiple filters covering a wide wavelength range from NUV to NIR, making the CSST a potentially powerful tool for studying MPs in clusters. In this work, we evaluate the efficiency of the designed filters for the MCI/CSST in revealing MPs in different color–magnitude diagrams(CMDs). We find that CMDs made with MCI/CSST photometry in appropriate UV filters are powerful tools to disentangle stellar populations with different abundances of He, C, N, O and Mg. On the contrary, the traditional CMDs are blind to multiple populations in globular clusters(GCs). We show that CSST has the potential of being the spearhead instrument for investigating MPs in GCs in the next decades.

Two-neutron transfer reactions as a tool to study the interplay between shape coexistence and quantum phase transitions

The atomic mass table presents zones where the structure of the states changes rapidly as a function of the neutron or proton number.Among them,notable examples are the A≈100 Zr region,the Pb region around the neutron midshell(N=104),and the N≈90 rare-earth region.The observed phenomena can be understood in terms of either shape coexistence or quantum phase transitions.The objective of this study is to find an observable that can distinguish between both shape coexistence and quantum phase transitions.As an observable to be analyzed,we selected the two-neutron transfer intensity between the 0+states in the parent and daughter nuclei.The framework used for this study is the Interacting Boson Model(IBM),including its version with configuration mixing(IBM-CM).To generate wave functions of isotope chains of interest needed for calculating transfer intensities,previous systematic studies using IBM and IBM-CM were used without changing the parameters.The results of two-neutron transfer intensities are presented for Zr,Hg,and Pt isotopic chains using IBM-CM.Moreover,for Zr,Pt,and Sm isotopic chains,the results are presented using IBM with only a single configuration,i.e.,without using configuration mixing.For Zr,the two-neutron transfer intensities between the ground states provide a clear observable,indicating that normal and intruder configurations coexist in the low-lying spectrum and cross at A=98→100.This can help clarify whether shape coexistence induces a given quantum phase transition.For Pt,in which shape coexistence is present and the regular and intruder configurations cross for the ground state,there is almost no impact on the value of the two-neutron transfer intensity.Similar is the situation with Hg,where the ground state always has a regular nature.For the Sm isotope chain,which is one of the quantum phase transition paradigms,the value of the two-neutron transfer intensity is affected strongly.