天空中那跳动的心 ∙ 上篇Pumping hearts of the sky Part 1
你也许听说过，我们都来自星尘，没错，这是真的。
As you may have heard before, we are made of star dusts, in fact that’s true.
宇宙中的物质总量总是守恒的，从聚集，变成物质，生存，死亡，分解再结合，所有的物质都在一个循环中。
他们中的一些聚集在一起组成你和我，其他的聚集在一起变成了星星。
Since the total amount of matter in the universe is always conserved, all the materials are in a cycle of gathering to become things, live, die, decompose and recombine. Some of them gathered to assemble you and me, the others gathered to form stars.
在他们变成我们在夜晚空中看到的星星之前，他们会首先相互吸引，成为分子云。
经过数百万年的积累，从星云到原恒星，他们最终进入主序星的阶段，仿佛一个孩子终于走进了人生的下一个阶段，进入了成人世界。
Before turning into the stars that we see in the sky, the matter first attracts each other to become molecular clouds. After millions of years of accumulation, from nebulas to protostars, they finally enter stage of being a main sequence star, like a child walking into the adult world, ready for the next stage of their life.
图为NASA发布的哈勃望远镜拍摄的天鹰星云
Image of Eagle Nubula taken by Hubble from NASA
当恒星进化到了主序阶段，它们的核开始燃烧氢，产生了向外的能量。由于产生能量的不连贯，恒星会膨胀和收缩，由此亮度也会变化。而这种现象的研究被称为星震学，它能帮助科学家从恒星的表面变化来探索恒星的内部。
As stars evolve on to the main sequence, they start to have hydrogen burning in their cores, producing energy that is carried outwards. Due to the difference in the amounts of energy produced in a period of time, the star expands and contracts, causing the brightness to vary. The study of this phenomenon is called asteroseismology, which helps scientist to study inside of stars from their surface changes.
不同质量和年龄的恒星会有各自振动方式。Delta Scuti (δ Scuti) 星，大约质量为1.5-2.5倍太阳质量的主序星，是一群特殊的恒星。它们经常出现在银河系里的各种地方（比如：大麦哲伦星云、球状星团、疏散星团、银河系中心、等等)。
所以通过观察这些 δ Scuti) 星，科学家能够找到强振动和亮度之间的关系，帮助他们计算出这些恒星离我们的距离，更加了解银河系里每个位置。
Stars of different masses and ages all oscillate differently. One class of stars in the main sequence with ~1.5 -2.5 solar mass are called the delta Scuti (δ Scuti) stars. By observing these δ Scutis, scientist would be able to find the relationship between their strongest oscillations and their luminosity, allowing them to calculate the distance to those stars, which appear frequently in the different parts on the milky way (e.g. the Large Magellanic Cloud, globular clusters, open clusters, the Galactic Center).
图为NASA发布的哈勃望远镜拍摄的大麦哲伦星云
Image of the Large Magellanic Cloud taken by Hubble from NASA
要真正了解恒星的振动和它们的基本属性，除了知道它们光度变化的周期，还需要更多细节。要做的就是根据振动发生的频率来分类它们。类太阳的恒星就是这样分析的，但那是因为它们的振动频率分布平均。然而在开普勒任务中发现的δ Scuti里，它们的振动发生频率几乎随机，毫无规律。这样，星震学就无法算出需要研究的恒星的任何信息。
To really understand oscillating stars and their fundamental properties, more details need to be known than just the period-luminosity relations. Oscillations need to be categorized by their frequency of happening. This is often done to solar-like stars, which appear to have oscillations are evenly spread frequencies, however this is not the case with δ Scuti stars observed by the Kepler mission. The data showed the oscillations to be distributed almost randomly, meaning it’s impossible to asteroseismology to carried out on δ Scutis.
新任务，新出发
New Mission, new Way
为了解决这个问题，一组在悉尼的科学家开始了寻找规律振动δ Scuti星的奇妙之旅。虽然刚才说开普勒发现的大多数恒星都只会随机振动，但也发现过少数的有规则频率的恒星。因此，要想观察到规律振动的恒星，第一步就是增加模型中的样本数量，而2018年由SpaceX猎鹰9号火箭发射的TESS任务在这里就非常适合。
In order to solve this problem, a group of scientists based in Sydney set out to find regular oscillations of these δ Scuti stars. Although many found had only random oscillations, stars with regular spacings have also been found before, just with limited numbers. So, for regular patterns into be seen, the first step would be to increase the number of samples in the model and the TESS mission launched in 2018 with a SpaceX Falcon 9 rocket was the perfect fit in this case.
TESS 是一个凌日系外行星巡天卫星，是由美国航天局NASA发射的。最初的目标是用凌日现象研究银河系中20万颗恒星运转以及他们的行星，当然研究的恒星中也包括一些δ Scuti星。
TESS – the Transiting Exoplanet Survey Satellite, launched by NASA, originally designed to explore the transiting exoplanets arounds more than 200 thousand stars in our galaxy, some of them being δ Scutis.
与上篇文章中提到的盖亚任务类似，它能够快速扫描天空并提供宇宙各个方向的数据，不像开普勒只观察浩瀚星空中的一小块区域。话虽如此，来自开普勒的数据在这项研究中依然非常有用。
Operating in a similar way to the Gaia mission mentioned in the previous article, it is able to scan the sky quickly and provide data in all directions of the universe, unlike Kepler only focusing on one patch on the sky. That being said, the data from Kepler is still useful to be included in this research.
视频为TESS的模拟运转影像，它的四个摄像头能全方位的快速扫描外太空，提供更多可以分析的数据
Simulation of TESS in space, it four cameras are able scan the space in all directions quickly, providing accurate data to analysis
从开普勒和TESS的数据中，那组科学家们仅挑选出了拥有高频率的振动的潜在的δ Scuti星（每天至少30次的震动）进行进一步的研究。选择高频是因为，一般在低频的情况下才会出现有规律的震动，这意味着很多恒星在这一方面可能有着共同的特性。因此,为了保证只有δ Scuti星出现在这次研究中，高频振动就变成了那个比较独特的属性，得以用于筛选。经过对整个样本集的筛选，他们挑出了60个有规律间隔振动的候选样本进行下一步的研究。
From the data of Kepler and TESS, the scientist singled out the potential δ Scuti stars with high frequencies of pulsations (30 or more pulsation cycles per day) for further research. The reason for choosing the high frequencies is because, regular pulsations are mainly found to happen at low frequencies, which means it would be a common property for multiple types of variable stars. So, to identify only the δ Scuti stars, a slightly more unique property had to be used. After filtering through the entire sample set, 60 candidates with regularly spaced modes of oscillations were chosen to be in next part of research.
视频为名为HD31901的δ Scuti 星的模拟振动影像，模拟数据来TESS由悉尼的科学家们进行分析后得到的24小时振动模拟
Simulation of HD31901 - a δ Scuti star pulsating based on the star's brightness measured by TESS and analysed by scientists based in Sydney
像δ Scuti星这样的恒星，它们会同一时间有不同频率振动的发生，就像一个管弦乐队同时演奏不同的乐器时候一样。因此，各种振动模式将会在同一个数据中出现，当中隐藏着恒星各种信息。所以，这里用到了échelle图，显示频率的同时也显示了定期间隔的振动模式（Δν）。
因为不同的振动模式来自恒星的不同区域，恒星内部的声速值的变化会最后体现在我们监测到Δν的数据上。而声速变化很重要是因为它包含的着恒星密度的信息。
Stars like δ Scutis have oscillations with different frequencies happening at the same time, like an orchestra playing different instruments at the same time, which creates a range of oscillation modes hidden in the star’s pulsation data we see. So, an échelle diagram is used to show the frequencies, and to determine the regular spacing of the modes of oscillation, Δν.
Because different modes of oscillation come from different parts of the star, the values for the sound-speed would vary inside the stars, shown to us with values of Δν. Here sound-speed variation is important because it carries information on the stellar density.
Échelle图是用来表达恒星中多种频率模式的图，因为混合频率常常会出现各种主序恒星中，所以这种图能很好的帮助分析被研究恒星的振动频率。图中明确了每个不同的频率和规律振动模式的关系。
Échelle diagrams are diagrams designed to show multiple modes of frequencies in stars, since mix modes is common appearing in evolved stars as well as stars in the main sequence. In it, the mode frequencies are plotted as a function of frequency of the regular mode oscillation.
下期揭晓
悉尼科研人员们关于δ Scuti 星的突破性发现！
敬请期待！
Next, we reveal
the revolutionary discoveries of δ Scuti stars
from the team in Sydney!
图片视频来自TESS, MIT, Scitechdaily, NASA官网
部分信息参考来自的悉尼天文研究所团队的 “Very regular high-frequency pulsation modes in young intermediate-mass stars"论文
Pictures and videos from official website of TESS, MIT, Scitechdaily, NASA.
*Parts are from “Very regular high-frequency pulsation modes in young intermediate-mass stars" by the scientist team from Sydney Institute for Astronomy
