★★★

批量審題：

1. The reference to a “l(fā)arger target” serves primarily to suggest why a

信息目的題，一般在定位當(dāng)句可做

2. Information presented in the passage suggests which of the following about blue stragglers??間接細(xì)節(jié)，遇到也不一定好做

3. The passage cites which of the following as evidence undermining the theory presented in the second sentence??直接細(xì)節(jié)+削弱

做題優(yōu)先級要出來，3 1 2

文章分析：

①Hotter and more massive than the Sun, stars called “stragglers” are puzzling to astronomers because such rapidly burning stars would not be expected to persist in ancient star clusters.?②Some researchers believe that the typical blue stragglers formed when two ancient, lower-mass stars collide and merge form more massive, hotter star.?③Peter Leonard theorizes alternatively that in low density globular clusters, where mergers between single stars occur too infrequently to account for the observed quantity of blue stragglers, these stragglers are created instead by a group of stars. ④He suggests that a pair of stars already?orbiting each other presents a?larger target?for a third star or another pair. ⑤Once this new grouping forms, close encounters between the stars could prompt any two to merge as a blue straggler. ⑥Leonard’s model predicts that each blue straggler has a distant orbiting companion—as appears true of many blue stragglers in the M67 cluster of the Milky Way galaxy.

①?觀點，天文學(xué)家們覺得這個現(xiàn)象很奇怪；

② 順承觀點，v1=兩個小的撞成一個大的；

③ PL的轉(zhuǎn)折觀點，v2=不是單個撞的，那樣幾率太小了，應(yīng)該是一群撞的；

④+⑤+⑥?順承觀點，∈v2

①

↓

②? ?? ③

?? ? ? ? ? ?↓
? ??? ? ? ?④→⑤→⑥

題型解析：

1. The reference to a “l(fā)arger target” serves primarily to suggest why a

信息目的題，句內(nèi)局部信息先服務(wù)于句子主干，主干則服務(wù)于邏輯上層

A.blue straggler would be more likely to collide and merge with another star than would be a lower-mass star?沒有證據(jù)/相反，不是bs跟其他的撞

B.pair of stars would be more likely to encounter other stars than would the typical blue straggler?沒有證據(jù)/相反，bs不是撞擊對象

C. pair of stars would be more likely to interact with other stars than would a single star?

D.blue straggler would be more likely to interact with a pair of stars than it would with a third star 同B

E.third star would be more likely to encounter a pair than it would to encountera blue straggler?

其實四個錯誤選項中都有一個相同問題：文中blue straggler都是撞擊結(jié)果，不是撞擊對象。

?

2. Information presented in the passage suggests which of the following about blue stragglers??間接細(xì)節(jié)

A.They?originate?from stars that are hotter and more massive than the Sun.?沒有證據(jù)

B. They are burning more rapidly than other types of stars observed in ancient star clusters.看起來好像沒有證據(jù)，但是屬于第①句的直接推斷，考場上一定記得結(jié)合排除法解題，利用好錯誤標(biāo)簽，單選選最優(yōu)。

C.They are?older?than most other types of stars within the same starcluster.?沒有證據(jù)，甚至相反

D.They are?less numerous?in low-density globular clusters than are pairs of stars.?沒有證據(jù)

E.They generally originate from the?oldest?stars among those found in ancient star clusters.?沒有證據(jù)

?

3. The passage cites which of the following as evidence undermining the theory presented in the second sentence??直接細(xì)節(jié)，對應(yīng)③

A. A discrepancy between the number of mergers between single stars in certain low-density globular clusters and that in?other low-density?globular clusters?沒有證據(jù)

B. A discrepancy between the heat and mass of blue stragglers formed by one type of process and the heat and mass of blue stragglers formed by another type of process?相反/沒有證據(jù)

C. A discrepancy between the frequency of star mergers in low-density globularclusters and those in?high-density globular?clusters?沒有證據(jù)

D. A discrepancy between the amount of heat and mass of ancient single stars and that of blue stragglers?沒有證據(jù)

E. A discrepancy between the number of mergers between single stars in certain star clusters and the number of blue stragglers in those clusters

背景拓展：

A blue straggler is a main-sequence star in an open or globular cluster that is more luminous and bluer than stars at the main sequence turnoff point （主序折向點） for the cluster. Blue stragglers were first discovered by Allan Sandage in 1953 while performing photometry of the stars in the globular cluster M3.

藍(lán)離散星是疏散星團或球狀星團中與其他主序成員成表面溫度較高、光度更高的藍(lán)色恒星。因此，在星團的赫羅圖中，它們的位置有別于星團的其他成員。按理說，光度這樣高的恒星在球狀星團和年老的疏散星團中應(yīng)早已離開主序，進入演化。藍(lán)離散星看似違背了現(xiàn)行恒星演化的標(biāo)準(zhǔn)理論，因為在同時誕生的恒星在赫羅圖上應(yīng)該很明確的位在同一條曲在線，而由此依位置可以測量出它們原始的質(zhì)量。因為藍(lán)離散星偏離了這條曲線，顯示它們在恒星演化中有不同的經(jīng)歷。

以下知識不知道什么時候會有用，但多了解總不會吃虧，假如下次考相關(guān)了呢，不用深究，有個印象就行~

關(guān)于藍(lán)離散星的解釋有很多種，主要分為單星論和多星相互作用論?，F(xiàn)在看來，單星的“返老還童”不太可能，只有多星相互作用更有可能。主要有兩種解釋模型：恒星碰撞和物質(zhì)傳輸。

1?恒星碰撞：

兩顆恒星的合并只會創(chuàng)造出一顆質(zhì)量更大的恒星，這顆恒星的表面溫度會比同年齡的恒星更熱和更亮。如果這種理論是正確的，則藍(lán)離散星就不會成為恒星演化理論上的問題，合并后的恒星在核心會有更多的氫，使它的行為像較年輕的恒星。有證據(jù)支持這種看法，在星團內(nèi)藍(lán)離散星的數(shù)量明顯的與恒星的密集度有關(guān)，越密集處的術(shù)量越多，特別是在球狀星團的核心區(qū)域。因為在單位體積內(nèi)的恒星數(shù)目越多，碰撞和密接的機會越高，而星團內(nèi)確實比其他區(qū)域更容易發(fā)生。

檢驗這種假說的一種方法是研究藍(lán)離散星中的脈動變星。在星震學(xué)中，合并的恒星在脈動上的特性會與一般的恒星有所不同，或許可以測量出其間的差異。盡管在擁擠的區(qū)域中經(jīng)常能找到小光度振幅的藍(lán)離散星，然而，在缺乏明顯的藍(lán)離散脈動星下，脈動的測量是非常困難的。

2?物質(zhì)傳輸：

由一顆大質(zhì)量星和一顆小質(zhì)量星組成的雙星系統(tǒng)，大質(zhì)量星先演化成為超巨星并充滿它的洛希半徑（雙星的允許半徑），這樣就成了一對半相接雙星，紅巨星給沒有演化的小星傳送物質(zhì)，小型的質(zhì)量變大，同時溫度增高（變藍(lán)），光度增高，成為看似“掉隊”的藍(lán)離散星。

最近的研究顯示藍(lán)離散星的碳和氧比附近區(qū)域的其他恒星要少，這意味著一顆恒星的變熱和變藍(lán)是從軌道上的另一顆恒星攫取物質(zhì)所導(dǎo)致的；而質(zhì)量被竊取的恒星會使得原本在深層含有較多碳和氧等重元素的區(qū)域被暴露在表面。

藍(lán)離散星的自轉(zhuǎn)迅速，通常都在太陽的75倍以上，質(zhì)量也是星團中其他成員的2-3倍。