On the Formation of Massive Primordial Stars
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On the Formation of Massive Primordial Stars Kazuyuki Omukai 1,2and Francesco Palla 1omukai@th.nao.ac.jp,palla@arcetri.astro.it ABSTRACT We investigate the formation by accretion of massive primordial protostars in the range 10to 300M ⊙.The high accretion rate used in the models (˙M =4.4×10?3M ⊙yr ?1)causes the structure and evolution to di?er signi?cantly from those of both present-day protostars and primordial zero-age main sequence stars.After an ini-tial expansion of the radius (for M ? 12M ⊙),the protostar undergoes an extended phase of contraction (up to M ??60M ⊙).The stellar surface is not visible throughout most of the main accretion phase,since a photosphere is formed in the infalling en-velope.Also,signi?cant nuclear burning does not take place until a protostellar mass of about 80M ⊙.As the interior luminosity approaches the Eddington luminosity,the protostellar radius rapidly expands,reaching a maximum around 100M ⊙.Changes in the ionization of the surface layers induce a secondary phase of contraction,followed by a ?nal swelling due to radiation pressure when the stellar mass reaches about 300M ⊙.This expansion is likely to signal the end of the main accretion phase,thus setting an upper limit to the protostellar mass formed in these conditions.Subject headings:cosmology:theory —early universe —stars:formation —stars:pre-main-sequence 1.Introduction
Numerical simulations are now beginning to constrain the properties of the sites where star formation ?rst occurred in the post-recombination epoch (e.g.,Abel,Bryan,&Norman 2000;Bromm,Coppi,&Larson 1999,2001;Tsuribe 2001).These works indicate that the fragment mass scale of primordial gas clouds is relatively large (M f ～103M ⊙).On the other hand,the mass of protostellar cores formed inside these fragments is less than 10?2M ⊙at the beginning of the main accretion phase (Palla,Salpeter,&Stahler 1983;Omukai &Nishi 1998).Because of the large reservoir,the cores continue to grow in mass owing to accretion of ambient matter.Eventually,they become ordinary stars that shine by nuclear burning.The fundamental questions are then:
What fraction of the cloud mass can be incorporated into a star?Is there an upper limit to the mass of the primordial stars forming under such circumstances?
In the context of present-day star formation,it is generally believed that stellar activity(ra-diation force,the expansion of an HII region,stellar winds,etc.)of su?ciently massive protostars halts accretion,thereby determining the?nal stellar mass(e.g.,Larson&Starr?eld1971;Nakano, Hasegawa,&Norman1995).Of these processes,radiation force on dust grains appears to be the most e?cient,making spherical accretion above a mass of～15M⊙increasingly di?cult for solar-type metallicities(e.g.,Wol?re&Cassinelli1987),although non-spherical accretion may enhance the maximum stellar mass(Nakano1989).
The main di?erences between primordial and Pop I accreting protostars are the following.First, the opacity of the infalling gas is drastically reduced due to the lack of dust grains.Second,the mass accretion rate,˙M,which is related to the sound speed c s in the protostellar cloud by˙M=c3s/G (e.g.,Stahler,Shu&Taam1980),is substantially higher,because of the high temperature of the primordial clouds,typically T g～1000?1500K over a wide density range(Palla et al.1983). These two properties imply a reduced e?ect of radiation pressure of the protostellar photons and a higher momentum of the in?ow.Thus,reversal of accretion by radiation force alone seems to be less e?cient,and a higher maximum stellar mass is expected(e.g.,Larson&Starr?eld1971).Although qualitatively correct,this prediction has not been substantiated by numerical calculations covering a large mass interval.We still do not know the sequence of events that lead to the termination of the infall at the onset of protostellar surface activity.It is the purpose of this Letter to illustrate the results of such calculations for accreting protostars in the mass range10M⊙to～300M⊙.
2.Numerical Approach
The evolution of low-and intermediate-mass primordial protostars has been followed by Stahler, Palla,&Salpeter(1986,hereafter SPS).In that study,an initially small core of0.01M⊙grows rapidly by accretion at a rate of˙M=4.4×10?3M⊙yr?1,corresponding to the ambient gas temperature.As shown by Omukai&Nishi(1998),this is consistent with the physical conditions in cloud fragments at the time of core formation.The calculation of SPS was terminated at a mass M?=10.5M⊙,when nuclear burning had not yet started and the core was well below the mass scale of the parent cloud.At that point,the protostar was undergoing an internal readjustment due to strong heat transfer,resulting in the appearance of a luminosity wave at the surface and radius swelling.
The basic strategy and equations used here are the same as in SPS.In this scheme,the proto-stellar evolution is treated as a sequence of steady state accretion?ows onto a growing hydrostatic core(see Fig.1of SPS for a de?nition of the various regions).The core is assumed to be in hydro-static equilibrium and the ordinary stellar structure equations are applied.If the gas in front of the accretion shock is optically thin,no envelope model is constructed and the boundary condition
eq.(4a)of SPS is applied at the core surface.In case the preshock gas is optically thick,we integrate the equations inside the radiative precursor from the photosphere to the core surface(see eqs.7a-d of SPS).Outside the photosphere,we assume a free-falling?ow and evaluate at each time the deceleration exerted by radiation pressure.We adopted the same mass accretion rate of ˙M=4.4×10?3M
⊙yr?1as in SPS.The main di?erence with that work is in the use of updated opacity tables:for T<7000K,we take the results of Lenzuni,Cherno?,&Salpeter(1991,compo-sition of X=72,Y=28),and the OPAL opacity at higher temperatures(Iglesias&Rogers1996, with slightly di?erent composition X=70,Y=30).
3.Results
The evolution of primordial protostars in the range0.01M⊙to10.5M⊙has been computed by SPS.According to their results,early in the evolution,the accreted material settles adiabatically. Because of the high value of˙M,the core is surrounded by an optically thick radiative precursor. As the protostar grows,the luminosity increases until the Kelvin-Helmholtz(KH)time scale be-comes shorter than the accretion time.The contraction causes the outward propagation of the accumulated heat as a luminosity wave,which reaches the surface at a core mass of M?～8M⊙. As a result,the radius starts increasing,and the radiative precursor disappears.Owing to the complexity of the internal readjustment caused by the luminosity wave,we decided to follow again this phase and chose the M??8M⊙protostar of SPS as the initial model.
3.1.Overall evolution
The evolution of the core(R?)and photospheric(R ph)radii is presented in Figure1.Initially, the expansion of the core continues from M?=8to11.5M⊙,reaching a maximum value of220R⊙. Then,due to the very short KH time,the protostar starts contracting,and the radiative precursor appears again at a mass of M?=12.4M⊙.Therefore,except for the short interval between M?～8and12M⊙,the optically thick precursor persists throughout the main accretion phase. Unlike the core radius,the photospheric radius steadily expands as the photospheric luminosity (L ph)increases(see Fig.2).The spatial extent of the precursor roughly corresponds to that of the ionized region because the photospheric temperature,T e??6000K,is close to the ionization temperature.However,the present case is di?erent from an ordinary HII region in that here the gas is optically thick to electron scattering and H?bound-free absorption,in addition to Lyman continuum.
The evolution of the interior(L?)and photospheric luminosities divided by the core mass is shown in Figure2.The photospheric luminosity is the sum of L?and L acc,the accretion luminosity. As the luminosity-to-mass ratio L/M?grows,the e?ect of radiation force increases relative to that of gravity.Also,the accretion luminosity L acc?GM?˙M/R?increases as a result of core contraction.
Because of this e?ect and the high accretion rate,L ph approaches the Eddington limit(L Edd)at M?～60M⊙.At this point,the core radius has shrunk to R?～12R⊙,a value which is still higher than that of a zero-age main sequence star(2.8R⊙for a50M⊙star,Marigo et al.2001).
Despite the large increase of the interior luminosity,accretion is not halted by the e?ect of radiation pressure.What happens instead is a second phase of expansion of the surface regions of the core starting at M?～60M⊙(see Fig.1)and a concurrent reduction of the accretion luminosity. The reason for the rapid increase of the radius is the following.While the inner part of the core continues contracting(see the curve of R?(90%)in Fig.1),the interior luminosity L?rises roughly as M2?and becomes close to the Eddington limit at M?～80M⊙.At this time,hydrogen burning begins and core contraction stops.Owing to the high interior luminosity,strong radiation forces act on the thin surface layers,where the opacity sharply peaks due to the ionization of hydrogen and helium.This causes an acceleration of the expansion of the core from～80M⊙to～100M⊙. Then,the ratio L?/M?levels o?at a value close to,but still smaller than,the Eddington limit(see Fig.2)and the radius stops increasing.
From then on,the surface layers of more massive protostars are subject to a delicate balance between the radiation force and the external pressure of the accreting envelope,whereas the interior relaxes toward the structure appropriate to a main sequence star(see the evolution of R?(90%) in Fig.1).The interior luminosity is always close to the Eddington limit and then increases approximately as M?,although the ratio L?/M?keeps increasing slowly.After further shrinking of the core(between100and260M⊙),the photospheric luminosity eventually reaches the Eddington limit.The physical conditions in the surface layers are thus similar to those that occurred at the time of the?rst expansion,but now the course of events is much more dramatic.The interior luminosity L?continues to increase and eventually equals the Eddington limit at～300M⊙.This causes the huge expansion of the outermost layers of the protostar shown in Fig.1,while the interior does not contract anymore.The core runaway signals the end of the accretion phase.
3.2.Evolution of the Core Interior
At the beginning of the calculations,the temperature is highest o?-center(around q≡M/M?～0.1)and the innermost part of the core remains adiabatic.In addition to this thermally inactive part,the core consists of a radiative region and a superadiabatic surface layer.The newly ac-creted material is?rst incorporated into the superadiabatic layer,where the material is heated by radiation.In the radiative relaxation layer,the material loses entropy and contracts.
Because of the o?-center temperature maximum,deuterium burning starts o?-center at about 12M⊙.The deuterium luminosity reaches a maximum between12and16M⊙,but the contribution to the total luminosity is always negligible(<10%).Therefore,unlike Population I and II protostars, in primordial objects deuterium burning does not play an important role.The central inert part persists until the stellar mass reaches～40M⊙,when radiative heating from outside becomes strong
enough and the o?-center temperature maximum disappears.We can see the corresponding sudden rise(drop)of the central temperature(density)in Figure3b.Thereafter,the central temperature continues to rise gradually due to KH contraction.
When the core mass reaches～80M⊙,the central temperature exceeds108K,needed to ignite the3αreactions.Then,enough carbon is built up to drive the CN cycle and signi?cant hydrogen burning ensues(see the sharp rise of L nuc in Figure2).The onset and spread of central convection is shown in Figure3a.Although carbon continues to be synthesized at the center,the growth of the convective core and mixing limits its abundance to values～10?9(see Figure3b).
Before the onset of the CN-cycle,the luminosity is generated mostly by contraction,with a minor contribution of H-burning via the pp-chain.This situation di?ers from the standard ZAMS models studied by several groups who?nd that the CN-cycle dominates the energy budget above ～30M⊙(e.g.Ezer&Cameron1971).Since the high entropy of the accreted matter prevents contraction,the critical mass for the CN-cycle is much higher in the protostellar case.
The radiation?ow is absorbed by the high opacity in the superadiabatic layer.Because of the accumulated radiation energy in these regions,radiation pressure exceeds gas pressure at M?～60M⊙.The radiation dominated region quickly expands as the core mass increases.On the other hand,in the central convective core,the entropy increases in time due to nuclear burning.As a result,the central temperature remains almost constant,whereas the density decreases gradually (see Figure3b).The ratio of radiation to total(gas+radiation)pressure keeps increasing,and eventually the central part becomes dominated by radiation at M?=145M⊙.This region expands rapidly and merges with the outer radiation dominated region at180M⊙.In more massive objects, the internal structure is fully determined by radiation pressure.
4.Discussion
As a result of the high value of the mass accretion rate characteristic of primordial gas clouds, the structural properties of massive protostars have several unique and unexpected features.The evolutionary tracks of the photosphere and core surface in the HR diagram are displayed in Figure 4.The locus of the population III ZAMS stars computed from static models is also shown(Marigo et al.2001;Bromm et al.2001).The e?ective temperature of the protostellar core is computed from the core radius and preshock luminosity.The striking feature of the photospheric track is the almost constant value of the e?ective temperature.The photosphere forms in the accreting envelope,and persists almost throughout the main accretion phase.Because of the sensitivity of the H?bound-free opacity,the temperature is locked at the value of T e??6000K(see eq.23b of SPS).Observationally,primordial protostars of vastly di?erent luminosities should have the same optical colors.On the other hand,the core surface will remain unobservable from outside because of the presence of the optically thick precursor.
From Fig.4we see that the track of the core surface cuts through the ZAMS track of the core
surface at a mass～40M⊙.However,the curve does not join the ZAMS smoothly,but follows a more elaborate path due to the behavior of the mass-radius relation.Therefore,realistic ZAMS models of Pop III stars should start with initial conditions that di?er from those usually adopted on the basis of thermal equilibrium.
Also,the nuclear properties derived from the protostellar phase are quite distinctive.Deu-terium burning and the p-p chain reactions have little e?ect on the evolution.Hydrogen burning due to the CN-cycle begins only at～80M⊙.At this mass,the interior luminosity becomes close to the Eddington limit,so that the surface regions are subject to strong radiation forces.These conditions are favorable to the onset of activity in the form of mass loss.It is clear that continuum radiation driven winds can occur in Pop III protostars.According to the mass-radius relation of Fig.1,there are two critical stages when the conditions become favorable for the onset of a wind: the rapid expansion of the surface layers at M?～80and300M⊙.However,it is only at the highest mass that we expect a major episode of mass loss,since earlier on the interior luminosity always remains slightly below the critical value.Even in this case,however,we anticipate a short lived phase of wind activity related to the small extent of the high opacity surface layer.
Our result of a upper mass limit of～300M⊙is sensitive to the adopted value of the mass accretion rate and to its time evolution.In fact,˙M may not be constant and decrease in time from an even larger initial value(e.g.,Omukai&Nishi1998).Quantitatively,it is di?cult to predict
as a function of˙M without detailed models.However,we can expect the exact values of M max
?
that the evolution obtained here will not change qualitatively.In case of larger values of˙M,the higher luminosity will cause an earlier stripping of the surface layers by radiation pressure.Also, nuclear burning will be postponed at higher masses because of the shorter contraction time scale. On the contrary,for lower accretion rates,the evolution would resemble that of Pop I protostars with the central core smoothly becoming a ZAMS star during the main accretion phase,but with a fundamental di?erence.Because of the lack of grains,the radiative force is not capable to reverse the infall until a very large value of the protostellar mass.Thus,it is evident that there must be a critical value of˙M for the onset of the runaway increase of the protostellar radius that determines the maximum accumulated mass.The existence of this critical behavior will be explored in a forthcoming paper.
This work is supported in part by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists,grant6819.K.O.wishes to thank the director of the Osservatorio di Arcetri for the hospitality during an extended visit in2001.
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Fig.1.—Mass-radius relation for massive primordial protostars.The evolution of the core (solid line)and photospheric (dashed line)radii is shown as a function of the protostellar mass.The circle on the curve of R ?marks the initial model of our calculations.The R ?and R ph curves at smaller masses come from SPS.The dotted lines represent the radii of mass shells containing 90%and 99%,respectively,of the total stellar mass.
Fig.2.—Evolution of the luminosity to mass ratio as a function of mass.The interior and photo-spheric luminosities are displayed by the solid and dotted lines,respectively.The solid horizontal line represents the Eddington luminosity for electron scattering.The nuclear luminosity due to
H-burning is shown by the dashed line.
Fig.3.—The internal structure of the core as a function of mass.(a)Evolution of the nuclear energy and convection as a function of the relative mass q≡M/M?.Regions where the energy generation by D-and H-burning exceeds10%of the average energy generation rate L?/M?are shown as shaded regions The extent of the convective core is illustrated by the short-dashed area.The curve labelled P r=P g is the locus where the radiaton pressure equals gas pressure.Radiation pressure dominates to the right of this curve.(b)Evolution of central density,temperature,and mass fraction of
CN-elements.Each variable is normalized to0.1g cm?3,107K,and10?9,respectively.
Fig.4.—HR diagram for primordial protostars.The evolution of the photosphere and core surface is shown by the thick solid and dashed lines,respectively.For comparison,we also show the locus of the metal-free ZAMS stars(Marigo et al.2001for M?<100M⊙;Bromm,Kudritzki,&Loeb 2001for higher mass).The numbers on both tracks label the value of the core mass(in solar units).
The?lled circles on the dashed line have the same meaning.
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介词后的动词要用—ing形式。介词加代词时，代词要用宾格。例如：give up her（him）这种形式是正确的，而give up she（he）这种形式是错误的。 7.冠词：冠词是指修饰名词，表名词泛指或特指。冠词有a an the 。 8.叹词：叹词表示一种语气。例如：OH. Ya 等 9.连词：连词是指连接两个并列的成分，这两个并列的成分可以是两个词也可以是两个句子。例如：and but or so 。 10.数词：数词是指表示数量关系词，一般分为基数词和序数词 第二章节：英语句子成分 主语：动作的发出者，一般放在动词前或句首。由名词. 代词. 数词. 不定时. 动名词. 或从句充当。 谓语：指主语发出来的动作，只能由动词充当，一般紧跟在主语后面。 宾语：指动作的承受着，一般由代词. 名词. 数词. 不定时. 动名词. 或从句充当. 介词后面的成分也叫介词宾语。 定语：只对名词起限定修饰的成分，一般由形容
六级单词解析造句记忆MNO
M A: Has the case been closed yet? B: No, the magistrate still needs to decide the outcome. magistrate n.地方行政官，地方法官，治安官 A: I am unable to read the small print in the book. B: It seems you need to magnify it. magnify vt.１．放大，扩大；２．夸大，夸张 A: That was a terrible storm. B: Indeed, but it is too early to determine the magnitude of the damage. magnitude n.１．重要性，重大；２．巨大，广大 A: A young fair maiden like you shouldn’t be single. B: That is because I am a young fair independent maiden. maiden n.少女，年轻姑娘，未婚女子 a.首次的，初次的 A: You look majestic sitting on that high chair. B: Yes, I am pretending to be the king! majestic a.雄伟的，壮丽的，庄严的，高贵的 A: Please cook me dinner now. B: Yes, your majesty, I’m at your service. majesty n.１．［Ｍ－］陛下（对帝王，王后的尊称）；２．雄伟，壮丽，庄严 A: Doctor, I traveled to Africa and I think I caught malaria. B: Did you take any medicine as a precaution? malaria n.疟疾 A: I hate you! B: Why are you so full of malice? malice n.恶意，怨恨 A: I’m afraid that the test results have come back and your lump is malignant. B: That means it’s serious, doesn’t it, doctor? malignant a.１．恶性的，致命的；２．恶意的，恶毒的 A: I’m going shopping in the mall this afternoon, want to join me? B: No, thanks, I have plans already. mall n.（由许多商店组成的）购物中心 A: That child looks very unhealthy. B: Yes, he does not have enough to eat. He is suffering from malnutrition.
base on的例句
意见应以事实为根据. 3 来自辞典例句 192. The bombers swooped ( down ) onthe air base. 轰炸机 突袭 空军基地. 来自辞典例句 193. He mounted their engines on a rubber base. 他把他们的发动机装在一个橡胶垫座上. 14 来自辞典例句 194. The column stands on a narrow base. 柱子竖立在狭窄的地基上. 14 来自辞典例句 195. When one stretched it, it looked like grey flakes on the carvas base. 你要是把它摊直, 看上去就象好一些灰色的粉片落在帆布底子上. 18 来自辞典例句 196. Economic growth and human well - being depend on the natural resource base that supports all living systems. 经济增长和人类的福利依赖于支持所有生命系统的自然资源. 12 1 来自辞典例句 197. The base was just a smudge onthe untouched hundred - mile coast of Manila Bay. 那基地只是马尼拉湾一百英里长安然无恙的海岸线上一个硝烟滚滚的污点. 6 来自辞典例句 198. You can't base an operation on the presumption that miracles are going to happen. 你不能把行动计划建筑在可能出现奇迹的假想基础上.
英语造句大全
英语造句大全English sentence 在句子中，更好的记忆单词！ 1、(1)、able adj. 能 句子：We are able to live under the sea in the future. (2)、ability n. 能力 句子：Most school care for children of different abilities. (3)、enable v. 使。。。能句子：This pass enables me to travel half-price on trains. 2、(1)、accurate adj. 精确的句子：We must have the accurate calculation. (2)、accurately adv. 精确地 句子：His calculation is accurately. 3、(1)、act v. 扮演 句子：He act the interesting character. （2）、actor n. 演员 句子：He was a famous actor. (3)、actress n. 女演员 句子：She was a famous actress. (4)、active adj. 积极的 句子：He is an active boy. 4、add v. 加 句子：He adds a little sugar in the milk. 5、advantage n. 优势 句子：His advantage is fight. 6、age 年龄n. 句子：His age is 15. 7、amusing 娱人的adj. 句子：This story is amusing. 8、angry 生气的adj. 句子：He is angry. 9、America 美国n.
(完整版)主谓造句
主语+谓语 1. 理解主谓结构 1) The students arrived. The students arrived at the park. 2) They are listening. They are listening to the music. 3) The disaster happened. 2．体会状语的位置 1) Tom always works hard. 2) Sometimes I go to the park at weekends.. 3) The girl cries very often. 4) We seldom come here. The disaster happened to the poor family. 3. 多个状语的排列次序 1) He works. 2) He works hard. 3) He always works hard. 4) He always works hard in the company. 5) He always works hard in the company recently. 6) He always works hard in the company recently because he wants to get promoted. 4. 写作常用不及物动词 1. ache My head aches. I’m aching all over. 2. agree agree with sb. about sth. agree to do sth. 3. apologize to sb. for sth. 4. appear (at the meeting, on the screen) 5. arrive at / in 6. belong to 7. chat with sb. about sth. 8. come (to …) 9. cry 10. dance 11. depend on /upon 12. die 13. fall 14. go to … 15. graduate from 16. … happen 17. laugh 18. listen to... 19. live 20. rise 21. sit 22. smile 23. swim 24. stay (at home / in a hotel) 25. work 26. wait for 汉译英： 1.昨天我去了电影院。 2.我能用英语跟外国人自由交谈。 3.晚上7点我们到达了机场。 4.暑假就要到了。 5.现在很多老人独自居住。 6.老师同意了。 7.刚才发生了一场车祸。 8.课上我们应该认真听讲。9. 我们的态度很重要。 10. 能否成功取决于你的态度。 11. 能取得多大进步取决于你付出多少努力。 12. 这个木桶能盛多少水取决于最短的一块板子的长度。
初中英语造句
【it's time to和it's time for】 ——————这其实是一个句型,只不过后面要跟不同的东西. ——————It's time to跟的是不定式（to do）.也就是说,要跟一个动词,意思是“到做某事的时候了”.如： It's time to go home. It's time to tell him the truth. ——————It's time for 跟的是名词.也就是说,不能跟动词.如： It's time for lunch.(没必要说It's time to have lunch) It's time for class.(没必要说It's time to begin the class.) They can't wait to see you Please ask liming to study tonight. Please ask liming not to play computer games tonight. Don’t make/let me to smoke I can hear/see you dance at the stage You had better go to bed early. You had better not watch tv It’s better to go to bed early It’s best to run in the morning I am enjoy running with music. With 表伴随听音乐 I already finish studying You should keep working. You should keep on studying English Keep calm and carry on 保持冷静继续前行二战开始前英国皇家政府制造的海报名字 I have to go on studying I feel like I am flying I have to stop playing computer games and stop to go home now I forget/remember to finish my homework. I forget/remember cleaning the classroom We keep/percent/stop him from eating more chips I prefer orange to apple I prefer to walk rather than run I used to sing when I was young What’s wrong with you There have nothing to do with you I am so busy studying You are too young to na?ve I am so tired that I have to go to bed early
The Kite Runner-美句摘抄及造句
《The Kite Runner》追风筝的人--------------------------------美句摘抄 1.I can still see Hassan up on that tree, sunlight flickering through the leaves on his almost perfectly round face, a face like a Chinese doll chiseled from hardwood: his flat, broad nose and slanting, narrow eyes like bamboo leaves, eyes that looked, depending on the light, gold, green even sapphire 翻译：我依然能记得哈桑坐在树上的样子，阳光穿过叶子，照着他那浑圆的脸庞。他的脸很像木头刻成的中国娃娃，鼻子大而扁平，双眼眯斜如同竹叶，在不同光线下会显现出金色、绿色，甚至是宝石蓝。 E.g.: A shadow of disquiet flickering over his face. 2.Never told that the mirror, like shooting walnuts at the neighbor's dog, was always my idea. 翻译：从来不提镜子、用胡桃射狗其实都是我的鬼主意。E.g.:His secret died with him, for he never told anyone. 3.We would sit across from each other on a pair of high
翻译加造句
一、翻译 1. The idea of consciously seeking out a special title was new to me., but not without appeal. 让我自己挑选自己最喜欢的书籍这个有意思的想法真的对我具有吸引力。 2.I was plunged into the aching tragedy of the Holocaust, the extraordinary clash of good, represented by the one decent man, and evil. 我陷入到大屠杀悲剧的痛苦之中，一个体面的人所代表的善与恶的猛烈冲击之中。 3.I was astonished by the the great power a novel could contain. I lacked the vocabulary to translate my feelings into words. 我被这部小说所包含的巨大能量感到震惊。我无法用语言来表达我的感情（心情）。 4，make sth. long to short长话短说 5.I learned that summer that reading was not the innocent(简单的) pastime(消遣) I have assumed it to be., not a breezy, instantly forgettable escape in the hammock(吊床)，( though I’ ve enjoyed many of those too ). I discovered that a book, if it arrives at the right moment, in the proper season, will change the course of all that follows. 那年夏天，我懂得了读书不是我认为的简单的娱乐消遣，也不只是躺在吊床上，一阵风吹过就忘记的消遣。我发现如果在适宜的时间、合适的季节读一本书的话，他将能改变一个人以后的人生道路。 二、词组造句 1. on purpose 特意，故意 This is especially true here, and it was ~. (这一点在这里尤其准确，并且他是故意的) 2.think up 虚构，编造，想出 She has thought up a good idea. 她想出了一个好的主意。 His story was thought up. 他的故事是编出来的。 3. in the meantime 与此同时 助记：in advance 事前in the meantime 与此同时in place 适当地... In the meantime, what can you do? 在这期间您能做什么呢？ In the meantime, we may not know how it works, but we know that it works. 在此期间，我们不知道它是如何工作的，但我们知道，它的确在发挥作用。 4.as though 好像，仿佛 It sounds as though you enjoyed Great wall. 这听起来好像你喜欢长城。 5. plunge into 使陷入 He plunged the room into darkness by switching off the light. 他把灯一关，房
改写句子练习2标准答案
The effective sentences:(improve the sentences!) 1.She hopes to spend this holiday either in Shanghai or in Suzhou. 2.Showing/to show sincerity and to keep/keeping promises are the basic requirements of a real friend. 3.I want to know the space of this house and when it was built. I want to know how big this house is and when it was built. I want to know the space of this house and the building time of the house. 4.In the past ten years,Mr.Smith has been a waiter,a tour guide,and taught English. In the past ten years,Mr.Smith has been a waiter,a tour guide,and an English teacher. 5.They are sweeping the floor wearing masks. They are sweeping the floor by wearing masks. wearing masks,They are sweeping the floor. 6.the drivers are told to drive carefully on the radio. the drivers are told on the radio to drive carefully 7.I almost spent two hours on this exercises. I spent almost two hours on this exercises. 8.Checking carefully,a serious mistake was found in the design. Checking carefully,I found a serious mistake in the design.
用以下短语造句
M1 U1 一. 把下列短语填入每个句子的空白处（注意所填短语的形式变化）： add up (to) be concerned about go through set down a series of on purpose in order to according to get along with fall in love (with) join in have got to hide away face to face 1 We’ve chatted online for some time but we have never met ___________. 2 It is nearly 11 o’clock yet he is not back. His mother ____________ him. 3 The Lius ___________ hard times before liberation. 4 ____________ get a good mark I worked very hard before the exam. 5 I think the window was broken ___________ by someone. 6 You should ___________ the language points on the blackboard. They are useful. 7 They met at Tom’s party and later on ____________ with each other. 8 You can find ____________ English reading materials in the school library. 9 I am easy to be with and _____________my classmates pretty well. 10 They __________ in a small village so that they might not be found. 11 Which of the following statements is not right ____________ the above passage? 12 It’s getting dark. I ___________ be off now. 13 More than 1,000 workers ___________ the general strike last week. 14 All her earnings _____________ about 3,000 yuan per month. 二.用以下短语造句： 1.go through 2. no longer/ not… any longer 3. on purpose 4. calm… down 5. happen to 6. set down 7. wonder if 三. 翻译： 1.曾经有段时间，我对学习丧失了兴趣。（there was a time when…） 2. 这是我第一次和她交流。（It is/was the first time that …注意时态） 3.他昨天公园里遇到的是他的一个老朋友。（强调句） 4. 他是在知道真相之后才意识到错怪女儿了。（强调句） M 1 U 2 一. 把下列短语填入每个句子的空白处（注意所填短语的形式变化）： play a …role (in) because of come up such as even if play a …part (in) 1 Dujiangyan(都江堰) is still ___________in irrigation(灌溉) today. 2 That question ___________ at yesterday’s meeting. 3 Karl Marx could speak a few foreign languages, _________Russian and English. 4 You must ask for leave first __________ you have something very important. 5 The media _________ major ________ in influencing people’s opinion s. 6 _________ years of hard work she looked like a woman in her fifties. 二.用以下短语造句： 1.make (good/full) use of 2. play a(n) important role in 3. even if 4. believe it or not 5. such as 6. because of
英语造句
English sentence 1、(1)、able adj. 能 句子：We are able to live under the sea in the future. (2)、ability n. 能力 句子：Most school care for children of different abilities. (3)、enable v. 使。。。能 句子：This pass enables me to travel half-price on trains. 2、(1)、accurate adj. 精确的 句子：We must have the accurate calculation. (2)、accurately adv. 精确地 句子：His calculation is accurately. 3、(1)、act v. 扮演 句子：He act the interesting character.（2）、actor n. 演员 句子：He was a famous actor. (3)、actress n. 女演员 句子：She was a famous actress. (4)、active adj. 积极的 句子：He is an active boy. 4、add v. 加 句子：He adds a little sugar in the milk. 5、advantage n. 优势 句子：His advantage is fight. 6、age 年龄n. 句子：His age is 15. 7、amusing 娱人的adj. 句子：This story is amusing. 8、angry 生气的adj. 句子：He is angry. 9、America 美国n. 句子：He is in America. 10、appear 出现v. He appears in this place. 11. artist 艺术家n. He is an artist. 12. attract 吸引 He attracts the dog. 13. Australia 澳大利亚 He is in Australia. 14.base 基地 She is in the base now. 15.basket 篮子 His basket is nice. 16.beautiful 美丽的 She is very beautiful. 17.begin 开始 He begins writing. 18.black 黑色的 He is black. 19.bright 明亮的 His eyes are bright. 20.good 好的 He is good at basketball. 21.British 英国人 He is British. 22.building 建造物 The building is highest in this city 23.busy 忙的 He is busy now. 24.calculate 计算 He calculates this test well. 25.Canada 加拿大 He borns in Canada. 26.care 照顾 He cared she yesterday. 27.certain 无疑的 They are certain to succeed. 28.change 改变 He changes the system. 29.chemical 化学药品