Near and Far: White Dwarfs, Brown Dwarfs and a New Standard Candle

由这笔拨款资助的科学研究项目将把我们从太阳附近的恒星带到宇宙最遥远的地方。它将利用目前世界上最先进的现代望远镜，证明加拿大对这些前沿设施的贡献是合理的。它将使HQP获得高影响力的国际合作，并提供跨越所有空间和时间的独特科学体验。附近区域：(a)我们能看到恒星的事实意味着它们正在失去能量，因此在进化。对几乎所有的恒星来说，这种能量都是由炽热致密的恒星核心的核反应产生的，核反应消耗了恒星的氢，产生了更重的元素。在这一核过程的最后，恒星将其核燃烧区域上方的所有物质喷射出来，暴露出密度极高、温度极高的核心，然后随着时间的推移慢慢冷却。由此产生的恒星物体被称为白矮星（WD）；通常是太阳质量的一半，半径大约是地球的一半。能够形成WD的最大质量恒星是一个极其重要的数量，所有质量超过这个极限的恒星都会以超新星（SN）的形式爆炸，超新星控制着星系中的化学演化和恒星形成速率。为了确定这个质量上限，我们一直在探索年轻的星团，这些星团包含的大质量恒星是太阳质量的10倍或更多，并确定其中哪些产生了WDs。定位其前身质量超过太阳6倍的WDs是极具挑战性的，但我们一直在开发的一些新想法和技术正在显示出希望。(b)我们成功地在即将发射的詹姆斯·韦伯太空望远镜上获得了20.5小时的时间来搜索（除其他外）非常古老的恒星周围可能存在的行星系统的证据。搜索将在一个古老的星团中进行，用红外（IR）对其WDs进行成像。已知银河系中大约5%的年轻WDs在红外波段异常明亮，这是由于当主星转变为WDs时，行星或小行星被破坏所产生的尘埃。我们的搜索将在这个古老恒星系统的120亿年前的WDs中寻找早期宇宙中行星形成的证据。遥远的区域：测量宇宙膨胀率的哈勃常数是最基本的宇宙学参数之一。目前，标准宇宙学模型的值与局部宇宙的测量值相冲突。提出的原因包括一种或两种技术的系统性偏差，距离校准中低估的不确定性，以及早期宇宙中新物理学的可能性。为了进一步探索这种冲突，我们开发了一种新的距离技术，利用非常明亮的富含碳的红巨星。虽然该方法仍处于起步阶段，但它被证明是非常强大的，并且比标准技术所需的观测时间要少得多。

The research of the scientific program funded by this grant will take us from stars in the neighbourhood of the Sun to the furthest reaches of the universe. It will exploit the most sophisticated modern telescopes currently available to the world community, justifying Canada's contributions to these frontline facilities. It will expose HQP to a high impact international collaboration and provide a unique science experience that spans all of space and time.  The nearby region: (a) The fact that we can see stars means they are losing energy and hence evolving. For almost all stars, this energy is produced by nuclear reactions in the hot dense stellar core which consumes the star's hydrogen and produces heavier elements. At the end of this nuclear processing the star ejects all the material above its nuclear burning region, exposing the extremely dense and hot core which then slowly cools with time. The resulting stellar object is called a white dwarf (WD); typically half the mass of the Sun with a radius roughly that of the Earth. The most massive star capable of forming a WD is an extremely important quantity, all stars more massive than this limit explode as supernovae (SN) which control the chemical evolution and star formation rate in a galaxy. To determine this upper mass limit we have been exploring young star clusters that contain massive stars up to 10 or more times the mass of the Sun and establishing which of them produced WDs. It has been extremely challenging to locate WDs whose progenitor was more than 6 times the mass of the Sun, but some new ideas and techniques we have been developing is showing promise.   (b) We were successful in obtaining 20.5 hours of time on the soon-to-be-launched James Webb Space Telescope to search for (among other things) possible evidence of planetary systems around very old stars. The search will be in an ancient star cluster, imaging its WDs in the infrared (IR). About 5% of young WDs in the galaxy are known to be anomalously bright in the IR due to dust resulting from the destruction of planets or asteroids when the host star transitioned to a WD. Our search will be amongst the 12 billion year WDs in this ancient stellar system looking for evidence of planet formation in the very early universe. The distant region: The Hubble Constant, measuring the expansion rate of the universe, is one of the most fundamental cosmological parameters. Currently, the value from the standard cosmological model is in conflict with measurements in the local universe. Suggested causes range from systematic biases in one or both techniques to underestimated uncertainties in distance calibration, to the possibility of new physics in the early universe. To explore this conflict further we have developed a new distance technique using very luminous carbon-rich red giant stars. While still in its infancy, the method is proving to be extremely powerful and requires significantly less observing time than the standard techniques.