Nova outbursts are the results of thermonuclear runaways,which occur when sufficient material accretes on the surfaces of white dwarfs(WDs).Using the MESA code,we construct a detailed grid for carbon-oxygen and oxygen-neon-magnesium novae.By employing population synthesis methods,we conduct a statistical analysis of the distribution of novae in the Milky Way.In our models,on average,a typical nova system may undergo about8000 eruptions and the Galactic nova rate is~130 yr^(-1).The C,N,and O elements in nova ejecta are strongly affected by the mixing degree between WD core and accreted material.Our results show that the average value of^(12)C/^(13)C in nova ejecta is about an order of magnitude lower than that on the surface of a red giant,that for^(16)O/^(17)O is about 5 times lower,and that for^(14)N/^(15)N is about 1.5 times lower.The annual yields of^(13)C,^(15)N,and^(17)O from nova ejection are larger than those from AGB stars.This indicates that compared to a red giant,nova eruptions are a more important source of the odd-numbered nuclear elements of^(13)C,^(15)N,and^(17)O in the Galactic interstellar medium.
Molecular line emissions are commonly used to trace the distribution and properties of molecular Interstella Medium.However,the emissions are heavily blended on the Galactic disk toward the inner Galaxy because of th relatively large line widths and the velocity overlaps of spiral arms.Structure identification methods based on voxe connectivity in Position-Position-Velocity(PPV)data cubes often produce unrealistically large structures,which i the“over-linking”problem.Therefore,identifying molecular cloud structures in these directions is not trivial.W propose a new method based on Gaussian decomposition and graph theory to solve the over-linking problem named InterStellar Medium Gaussian Component Clustering(ISMGCC).Using the Milky Way Imaging Scrol Painting(MWISP)^(13)CO(1-0)data in the range of 13°.5≤l≤14°.5,|b|≤0°.5,and-100≤V_(lsr)≤+200 km s^(-1),our method identified three hundred molecular gas structures with at least 16 pixels.These structures contain 92%of the total flux in the raw data cube and show single-peaked line profiles on more than 93%of their pixels.Th ISMGCC method could distinguish gas structures in crowded regions and retain most of the flux without globa data clipping or assumptions on the structure geometry,meanwhile,allowing multiple Gaussian components fo complicated line profiles.
