在近代天文學發展中，Ia型超新星作為最被廣泛使用來測量宇宙中天體距離的標準燭光之一。藉由Ia型超新星的觀測，我們發現了如同謎一般的暗能量，其佔據著宇宙大部分的組成，也加速了宇宙的膨脹。儘管如此，我們對於Ia型超新星的成因及其爆發機制的相關知識卻依然是匱乏的，這也為其作為探測暗能量的精準度增添許多不確定性。近期一些研究指出，Ia型超新星光譜中所測得之參數(例如超新星噴發物的速度及超高速噴發物的特徵)可有效使用來了解其爆發背後的物理機制，這些光譜所得出的參數也可直接被用來降低Ia型超新星的光度誤差，並使其距離上的量測更加精確。然而，先前大部分的研究中所使用的超新星樣本數量均為不足 (~100顆超新星)，也只著重在低紅位移 (z<0.1) 超新星上的研究。為了進一步改善這些問題，此研究計畫將使用Pan-STARRS1 (PS1) Medium Deep巡天計畫中所發現的Ia型超新星作為樣本，其中包含約400顆Ia型超新星以及700條可見光波段的光譜，其中最高紅位移的超新星達到z=0.7。此大樣本的光譜分析預期將有效增進我們對於Ia型超新星爆發機制的理解、探索其在不同紅位移間的演化，最終目的為提升其作為探測宇宙暗能量的精準度。 ;Type Ia supernovae (SNe Ia) are superb cosmological probes. After making empirical corrections based on how quickly the SNe fade and their observed colors, SNe Ia are “standardizable” candles from which we can probe the cosmic expansion and constrain the nature of the mysterious dark energy. Despite SNe Ia have been widely used to measure the cosmological parameters, our understanding on their progenitor systems and explosion mechanisms are still poor, which may limit and complicate their usage in cosmology. Recent studies showed evidence that the spectral parameters of SNe Ia (such as ejecta velocities and high-velocity features) can be used as effective tools to differentiate between progenitor scenarios and explosions. They can also be used as parameters in addition to SN light-curve width and color to improve the scatter of luminosities (and thus their distances). However, these studies generally have a relatively small sample size (~100 SNe) and focused on low-redshift (z<0.1) SNe Ia. In this project, we aim to address these issues by studying a large sample of high-redshift SNe Ia discovered by Pan-STARRS1 (PS1) Medium Deep Survey. Our sample contains ~700 optical spectra from ~400 well-observed SNe Ia, with the most distant ones having redshift of ~0.7. The spectroscopic study on these SNe will be crucial to constrain potential evolution of SNe Ia with redshift and further improve their precision as probes of dark energy.
