人類首次探測到三顆類太陽恒星的恒星風

謝鈺洪

An international research team led by a researcher from the University of Vienna has for the first time directly detected stellar winds from three Sun-like stars by recording the X-ray emission from their astrospheres（星狀體）， and placed restrictions on the mass loss rate of the stars via their stellar winds.

The researchers observed the spectral fingerprints of the oxygen ions（離子） with XMM-Newton and were able to determine the quantity of oxygen and ultimately the total mass of stellar wind emitted by the stars. For the three stars with detected astrospheres， named 70 Ophiuchi， epsilon Eridani， and 61 Cygni， the researchers estimated their mass loss rates to be 66.5±11.1， 15.6±4.4， and 9.6±4.1 times the solar mass loss rate， respectively. This means that the winds from these stars are much stronger than the solar wind， which might be explained by stronger magnetic activity of these stars.

“In the solar system， solar wind charge exchange emission has been observed from planets， and comets，? and provides a natural laboratory to study the solar winds composition，” explains the lead author of the study， Kristina Kislyakova. “Observing this emission from distant stars is much more tricky due to the faintness of the signal. In addition to that， the distance to the stars makes it very difficult to separate the signal emitted by the astrosphere from the actual X-ray emission of the star itself， part of which is “spread” over the field-of-view of the telescope due to instrumental effects.

“We have developed a new algorithm to figure out the stellar and the astrospheric contributions to the emission and detected charge exchange signals originating from stellar wind oxygen ions and the surrounding neutral interstellar medium of three main-sequence stars. This has been the first time X-ray charge exchange emission from astrospheres of such stars has been detected. Our estimated mass loss rates can be used as a benchmark for stellar wind models and expand our limited observational evidence for the winds of Sun-like stars.”

（材料來自Sciencenews網站，有刪改）

1. What can we say about the research？

A. It is a pioneering detection.

B. It is a difficult process.

C. It is a temporary success.

D. It is a massive development.

2. Why are the winds from the three stars much stronger？

A. More accurate observation method.

B. More powerful magnetic activity.

C. Larger amounts of oxygen.

D. Much bigger mass loss.

3. What is paragraph 3 mainly about？

A. The challenges of the observation.

B. The complexity of the solar system.

C. The limitations of the method.

D. The further explanation of the methods.

4. What does the underlined word “benchmark” in paragraph 4 refer to？

A. reference B. test

C. standard D. signal

1. A。解析：細節理解題。材料第一段提到“由維也納大學的一名研究人員領導的一個國際研究小組首次通過記錄三顆類太陽恒星天體的X射線發射，直接探測到它們的恒星風”，由此可知這次觀測具有開創意義。A選項“這是一個開創性的觀測”與材料內容相符，故選A。

2. B。解析：細節理解題。材料第二段最后一句提到“這意味著這些恒星的風比太陽風強得多，這可能是因為這些恒星的磁活動更強”，由此B選項“更強的磁場活動”與材料內容相符，故選B。

3. A。解析：主旨大意題。材料第三段共有三句話，第一句提到“在太陽系中，已經從行星和彗星上觀測到了太陽風的電荷交換發射，并為研究太陽風的成分提供了一個自然實驗室”，第二句和第三句提到“由于信號的微弱性，觀測來自遙遠恒星的這種發射要困難得多。除此之外，由于距離恒星的距離，很難將天體球體發射的信號與恒星本身的實際X射線發射分開，其中一部分由于儀器效應而‘擴散到望遠鏡的視野中”。由此可知第三段主要講述進行該項觀測存在的一些挑戰。A選項“觀測的挑戰”與材料內容相符，故選A。

4. C。解析：詞義猜測題。材料最后一段為研究人員對此次觀測研究的評價，所猜詞的句子提到“我們估計的質量損失率可以作為恒星風模型的基準，并擴展我們對類太陽恒星風的有限觀測證據”。C選項“標準”與材料內容相符，故選C。