文档库 最新最全的文档下载
当前位置:文档库 › Astrometry of circumstellar masers

Astrometry of circumstellar masers

Astrometry of circumstellar masers
Astrometry of circumstellar masers

a r

X

i

v

:a

s t

r o

-

p

h

/

2

8

3

1

7v

1

1

6

A

u

g

2

2

ASTROMETRY OF CIRCUMSTELLAR MASERS H.J.van Langevelde Joint Institute for VLBI in Europe Postbus 2,7990AA Dwingeloo,the Netherlands langevelde@jive.nl W.H.T.Vlemmings Sterrewacht Leiden Niels Bohr weg 2,2300RA Leiden,The Netherlands vlemming@strw.leidenuniv.nl Abstract The circumstellar masers around evolved stars o?er an interesting pos-sibility to measure stellar parameters through VLBI astrometry.In this paper the application of this technique is discussed,including the accu-racy and the uncertainties of the method.The di?erent maser species (OH,H 2O,SiO)have slightly di?erent characteristics and applications.This paper does not concern astrometry of maser spots to study the kinematics of the envelope,but concentrates on attempting to measure the motion of the underlying star.Keywords:masers –stars:circumstellar matter –techniques:interferometric –techniques:astrometry

Introduction

There are a number of scienti?c justi?cations for astrometry of stars with circumstellar masers.Historically,the registration of radio single dish and infrared data was so uncertain that proper identi?cation of maser bearing stars was a problem.Most of these problems have been overcome;the accuracy of connected element interferometers is su?cient to make these identi?cations unambiguously.However,there is still a lot of uncertainty when comparing VLBI data from di?erent experiments.Notably,when maser distributions from di?erent transitions are over-layed,a common origin is usually assumed.Astrometry can be done to do such comparisons properly.

1

2

However,the most tantalizing application of astrometry of circum-stellar masers is the accurate determination of the motion of the star on the sky.Proper motions of a star anywhere in the Galaxy(10km/s at 8kpc corresponds toμ=0.25mas/year)can in principle be obtained with VLBI,as can the parallax for such distances(π=0.125mas).

A direct distance estimate is important for studying the physics of the mass-losing stars.For many Mira variables Hipparcos measured the dis-tance,but for the most enshrouded stars VLBI o?ers the best approach. Both the proper motion and distance are inputs for studying the stellar population and Galactic kinematics(Habing,these proceedings).

In addition,detailed astrometric monitoring of evolved stars could reveal information about the existence of binary components,or even planets in these systems.Moreover,by monitoring its position new facts can be learned about maser physics.Are spots persistent,what (turbulent)motions can be measured,is the brightness a function of stellar cycle?Finally it is worth mentioning that the maser astrometry could tie the observational reference frames,in particular in the infrared where these stars are very bright.

Carrying out astrometric monitoring projects with spectral line VLBI is extensive work that requires some special techniques and assumptions. There are a number of technical advancements and initiatives that will make improvements to this?eld which will make it much more accessible.

1.Methods&Techniques

The most straightforward way of doing VLBI astrometry is to use “phase referencing”to a bright and close calibrator in order to overcome the spatial and temporal?uctuations of the ionosphere and/or tropo-sphere.The calibrator is usually an extragalactic source with a?xed and known position,which is su?ciently bright to calibrate the atmo-spheric and instrumental e?ects within a fraction of the coherence time. Because the modern VLBI correlators have incorporated the best geode-tic models,phase referencing results obtained in this way can be accurate to a few mas.This is already su?cient for a number of applications.In other cases,higher accuracy is required and some adjustments are nec-essary to improve the model.In such cases one probably needs to return to the”totals”in order to use astrometric/geodetic software.To get accuracies below1mas is not trivial;better models of the atmospheric behavior and structure of the reference source are required.

For maser astrometry an additional complication can be that one needs to observe in mixed bandwidth mode,applying a narrow band for the maser detection and simultaneous wide bands for the reference

Astrometry of circumstellar masers3 source.Obviously the maser dictates the observing frequency,which rules out some calibration schemes used in continuum and geodetic VLBI.

Ideally the masers should be bright and persistent.The brightness relates to the size of individual maser features,which sets an upper limit to the resolution one can obtain.A fundamental issue remains to link the motion of the maser spot to the stellar properties.One way forward is to assume that the masers are on a linear path with respect to the star (e.g.a constant out?ow).In this case the parallax of individual spots equals the parallax of the star,and the average motion may be assumed to be the stellar motion.In other cases one may be able to deduce the position of the star from the distribution of the masers,for example when they form a ring.If we can determine the position of the star,one can in principle measure the motion and the parallax.Note that only when one can consistently determine the stellar position with(much)better than1AU accuracy,a useful parallax can be determined.In some cases there is evidence that special maser spots exists that correspond to the stellar continuum ampli?ed by the maser shell.Such spots are then tied very accurately to the stellar position.In other cases one has to worry about the systematic and turbulent motions in the maser shell. In any case,there may be additional motions involved,for example when masers occur in binary stars.

2.OH Masers

The OH masers usually originate in large shells at1000AU from the mass-losing stars.As the out?ow is constant at that point,the maser radiates most e?ectively radially,from the front and back cones of the shell.Three18cm transitions can give reasonably bright maser emission.However,the VLBI spots are usually resolved at20mas, sometimes degraded further by angular broadening in the interstellar medium,notably in the direction of the Galactic centre(Van Langevelde et al.1992).

Although the shells are large,the“ampli?ed stellar image”paradigm makes the OH maser interesting for astrometry.Radio continuum,am-pli?ed by the maser results in a spot that is?xed on the stellar position, bright and persistent.The observation that the most blue-shifted spots in two OH transitions coincides is a very good con?rmation of this idea (Sivagnanam1990).

Recently,comparison of a proper motion study of U Her with Hippar-cos agreed to15mas(van Langevelde et al.2000),thus con?rming that the most blue-shifted and most persistent spot indeed follows the stellar

4

Figure1.Proper motion of the most blue-shifted spot in the1667MHz maser of U Her.A motion ofμvlbi=?15.57±0.56,?9.66±0.61mas/yr and a parallax ofπvlbi=3.85±1.14mas are?tted to the data.For comparison the position of a secondary reference source is also displayed.

trajectory in this case.Therefore the maser motion can be used to ob-tain the parallax and proper motion of the star.U Her was observed10 times in6years on the NRAO VLBA which resulted in the?rst VLBI parallax of a mass-losing star(Fig1;Van Langevelde et al.2000).The motion agrees within the error with the Hipparcos data,from which no reliable parallax could be obtained.

If the ampli?ed stellar image is a general feature in circumstellar OH masers,it will allow astrometric measurements of a large number of stars. However,the modest brightness of OH masers limits the application of this technique to stars closer than1kpc.

3.H2O masers

The22GHz masers are much brighter than the OH masers in circum-stellar shells.Therefore positional accuracies in the order of50μas are in principle achievable.Of course at this high frequency the coherence

Astrometry of circumstellar masers5 time is much shorter and phase referencing VLBI at22GHz is quite a bit more challenging.

Additional complications arise from the fact that the circumstellar H2O masers are rather messy.The structures are often ring-like on scales of100AU,as expected from tangential ampli?cation.However, large departures have been observed,as well as considerable variability. If the structures are persistent enough one can attempt to track individ-ual maser spots over a year and measure the parallax of the star from these(e.g.Kuruyama et al.,these proceedings).If this approach works the water maser observations o?er the interesting possibility to measure parallaxes throughout a large fraction of the Galaxy.

There have been claims that in water masers the ampli?ed stellar im-age can also occur(Marvel1996,Colomer et al.2000).To check this we have observed U Her at22GHz with MERLIN,which yields a com-parable resolution as our previous OH VLBI https://www.wendangku.net/doc/0814263461.html,ing the same position calibrators we?nd,somewhat surprisingly,that the brightest H2O maser coincides with the optical position and the OH image.Al-though the MERLIN observations do not resolve individual maser spots observable with VLBI,we take this as a clue that ampli?cation of back-ground radiation may play a role in water masers too(Fig2;Vlemmings et al.2002).

4.The use of SiO masers

The SiO masers around evolved stars can be even brighter.At43GHz the spots sizes allow10μas accurate positions.At the same time the technical di?culties are considerable.The coherence time is only of the order of a minute and in addition there are fewer suitable extragalactic calibrators.

The masers themselves are located close to the star,within10AU. They are bright and abundant.Monitoring of their structure indicates that the masers are showing motions on the time-scale of the variability of the star(Diamond&Kemball1999).Often these motions are not linear and it will be a challenge to measure a parallax from the combined motions of SiO masers.As the masers are in a ring close to the star, it will be possible to estimate the stellar position from the distribution of SiO masers.The proper motion of the star can be measured this way,even if the individual spots cannot be resolved.Proper motions of individual stars can probably be measured throughout the Galaxy using the43GHz transition.

A very suitable target for stellar astrometry by SiO masers are the Galactic center stars.In this region there is an abundance of maser stars

6

Center at RA 16 25 47.468 DEC 18 53 32.849Peak flux = 1.9579E+06 JY/B*HZ Levs = 1.958E+05 * (1, 3, 5, 7, 9)M i l l i A R C S E C MilliARC SEC 100500-50-100

80

60

40

20

0-20

-40

-60

-80

-100

Figure 2.The location of the U Her H 2O masers with respect to the stellar positions determined from the Hipparcos observations,as determined from phase referencing to an extragalactic calibrator.The star is denoted by two circles indicating the star itself and the stellar radio photo-sphere.The error bars on the maser feature are the errors due to the positional ?tting.The errors on the stellar position are due to the link to the radio-reference frame and due to the errors in the proper motion used to transpose the optical position.The triangle denotes the stellar position when using the phase referencing results on the secondary calibrator.

Astrometry of circumstellar masers7 close together(Sjouwerman,these proceedings).In addition,SgrA*is a suitable calibrator;it is bright at short wavelengths and,as it is is the location of a massive black hole,it is stationary.In fact,an important results from circumstellar maser astrometry is the tie between the IR and radio positions in the Galactic centre.By locking the positions of the IR sources to the radio maser counterparts,it can be shown that the motion of stars in the Galactic centre is consistent with motion around a massive black hole located at the position of SgrA*(Menten et al.1997; Eckart et al.2002).

Several groups have explored the possibility to start monitoring SiO masers in the Galactic centre region with VLBI(Sjouwerman et al.1998; Deguchi,these proceedings;Imai,these proceedings;Reid,private com-munication).The basic goal is to add two more components to the mea-surement of kinematics in this dynamically interesting region(Winnberg, these proceedings).

5.Future

There are many planned improvements of ordinary VLBI that will facilitate more astrometry of circumstellar masers.Several modern,big telescopes are under construction that will observe at high frequencies, necessary for H2O and SiO masers.Disk-based recording systems will improve the reliability and productivity of VLBI,and will be especially advantageous for time consuming astrometric monitoring.In addition there are several indications that the atmospheric modeling can be im-proved considerably.Other improvements of the geodetic models are important too,for example accurate telescope positions.

However,the future for astrometry of masers clearly lies in instru-mental setups that overcome the temporal variability of the atmosphere at high frequencies.Some of this can be done with“cluster–cluster”VLBI,but the dedicated VERA project provides a far more ambitious approach that will soon produce interesting results(Kobayashi&Sasao, these proceedings).

A number of studies are required to establish new techniques for as-trometry of circumstellar masers.Careful analysis of errors and con-sistency checks will be necessary to determine how to use the masers optimally to determine the underlying stellar motions.But in potential this method enables the measurement of proper motions and distances of mass-losing stars throughout the Galaxy.This will progress the study of stellar evolution as well as our knowledge of the structure of the Galaxy.

8

6.Acknowledgements

The National Radio Astronomy Observatory is a facility of the Na-tional Science Foundation operated under cooperative agreement by As-sociated Universities,Inc.MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of PPARC.We acknowledge the continuous support by Phil Diamond, Harm Habing and Richard Schilizzi.

References

Colomer F.,Reid M.J.,Menten K.M.,Bujarrabal V.,2000,AA355979

Diamond P.J.,Kemball A.J.,1999,in“Asymptotic Giant Branch Stars,IAU Sympo-sium#191”,eds Le Bertre,Lebre&Waelkens,p.195

Eckart A.,Genzel R.,Ott T.,Sch¨o del R.,2002,MNRAS331917

Marvel,K.B.,1996,Ph.D.thesis,New Mexico State Univ

Menten K.M.,Reid M.J.,Eckart A.,Genzel R.,1997,ApJ475L111

Sivagnanam P.,Diamond P.J.,Le Squeren A.M.,Biraud F.,1990,AA229171 Sjouwerman L.O.,van Langevelde H.J.,Diamond H.J.,1998,AA339897

Van Langevelde,H.J.,Frail,D.A.,Cordes,J.M.,Diamond,P.J.,1992,ApJ396686 Van Langevelde H.J.,Vlemmings W.,Diamond P.J.,Baudry A.,Beasley A.J.,2000, AA357,945

Vlemmings W.H.T.,Van Langevelde H.J.,Diamond P.J.,2002,AA in press

关于时间管理的英语作文 manage time

How to manage time Time treats everyone fairly that we all have 24 hours per day. Some of us are capable to make good use of time while some find it hard to do so. Knowing how to manage them is essential in our life. Take myself as an example. When I was still a senior high student, I was fully occupied with my studies. Therefore, I hardly had spare time to have fun or develop my hobbies. But things were changed after I entered university. I got more free time than ever before. But ironically, I found it difficult to adjust this kind of brand-new school life and there was no such thing called time management on my mind. It was not until the second year that I realized I had wasted my whole year doing nothing. I could have taken up a Spanish course. I could have read ten books about the stories of successful people. I could have applied for a part-time job to earn some working experiences. B ut I didn’t spend my time on any of them. I felt guilty whenever I looked back to the moments that I just sat around doing nothing. It’s said that better late than never. At least I had the consciousness that I should stop wasting my time. Making up my mind is the first step for me to learn to manage my time. Next, I wrote a timetable, setting some targets that I had to finish each day. For instance, on Monday, I must read two pieces of news and review all the lessons that I have learnt on that day. By the way, the daily plan that I made was flexible. If there’s something unexpected that I had to finish first, I would reduce the time for resting or delay my target to the next day. Also, I would try to achieve those targets ahead of time that I planed so that I could reserve some more time to relax or do something out of my plan. At the beginning, it’s kind of difficult to s tick to the plan. But as time went by, having a plan for time in advance became a part of my life. At the same time, I gradually became a well-organized person. Now I’ve grasped the time management skill and I’m able to use my time efficiently.

英语演讲稿:未来的工作

英语演讲稿:未来的工作 这篇《英语演讲稿范文:未来的工作》,是特地,希望对大家有所帮助! 热门演讲推荐:竞聘演讲稿 | 国旗下演讲稿 | 英语演讲稿 | 师德师风演讲稿 | 年会主持词 | 领导致辞 everybody good afternoon:. first of all thank the teacher gave me a story in my own future ideal job. everyone has a dream job. my dream is to bee a boss, own a pany. in order to achieve my dreams, i need to find a good job, to accumulate some experience and wealth, it is the necessary things of course, in the school good achievement and rich knowledge is also very important. good achievement and rich experience can let me work to make the right choice, have more opportunities and achievements. at the same time, munication is very important, because it determines whether my pany has a good future development. so i need to exercise their municative ability. i need to use all of the free time to learn

关于坚持的英语演讲稿

关于坚持的英语演讲稿 Results are not important, but they can persist for many years as a commemoration of. Many years ago, as a result of habits and overeating formed one of obesity, as well as indicators of overall physical disorders, so that affects my work and life. In friends to encourage and supervise, the participated in the team Now considered to have been more than three years, neither the fine rain, regardless of winter heat, a day out with 5:00 time. The beginning, have been discouraged, suffering, and disappointment, but in the end of the urging of friends, to re-get up, stand on the playground. 成绩并不重要,但可以作为坚持多年晨跑的一个纪念。多年前,由于庸懒习惯和暴饮暴食,形成了一身的肥胖,以及体检指标的全盘失常,以致于影响到了我的工作和生活。在好友的鼓励和督促下,参加了晨跑队伍。现在算来,已经三年多了,无论天晴下雨,不管寒冬酷暑,每天五点准时起来出门晨跑。开始时,也曾气馁过、痛苦过、失望过,但最后都在好友们的催促下,重新爬起来,站到了操场上。 In fact, I did not build big, nor strong muscles, not a sport-born people. Over the past few years to adhere to it, because I have a team behind, the strength of a strongteam here, very grateful to our team, for a long time, we encourage each other, and with sweat, enjoying common health happy. For example, Friends of the several run in order to maintain order and unable to attend the 10,000 meters race, and they are always concerned about the brothers and promptly inform the place and time, gives us confidence and courage. At the same time, also came on their own inner desire and pursuit for a good health, who wrote many of their own log in order to refuel for their own, and inspiring. 其实我没有高大身材,也没健壮肌肉,天生不属于运动型的人。几年来能够坚持下来,因为我的背后有一个团队,有着强大团队的力量,在这里,非常感谢我们的晨跑队,长期以来,我们相互鼓励着,一起流汗,共同享受着健康带来的快

关于管理的英语演讲

1.How to build a business that lasts100years 0:11Imagine that you are a product designer.And you've designed a product,a new type of product,called the human immune system.You're pitching this product to a skeptical,strictly no-nonsense manager.Let's call him Bob.I think we all know at least one Bob,right?How would that go? 0:34Bob,I've got this incredible idea for a completely new type of personal health product.It's called the human immune system.I can see from your face that you're having some problems with this.Don't worry.I know it's very complicated.I don't want to take you through the gory details,I just want to tell you about some of the amazing features of this product.First of all,it cleverly uses redundancy by having millions of copies of each component--leukocytes,white blood cells--before they're actually needed,to create a massive buffer against the unexpected.And it cleverly leverages diversity by having not just leukocytes but B cells,T cells,natural killer cells,antibodies.The components don't really matter.The point is that together,this diversity of different approaches can cope with more or less anything that evolution has been able to throw up.And the design is completely modular.You have the surface barrier of the human skin,you have the very rapidly reacting innate immune system and then you have the highly targeted adaptive immune system.The point is,that if one system fails,another can take over,creating a virtually foolproof system. 1:54I can see I'm losing you,Bob,but stay with me,because here is the really killer feature.The product is completely adaptive.It's able to actually develop targeted antibodies to threats that it's never even met before.It actually also does this with incredible prudence,detecting and reacting to every tiny threat,and furthermore, remembering every previous threat,in case they are ever encountered again.What I'm pitching you today is actually not a stand-alone product.The product is embedded in the larger system of the human body,and it works in complete harmony with that system,to create this unprecedented level of biological protection.So Bob,just tell me honestly,what do you think of my product? 2:47And Bob may say something like,I sincerely appreciate the effort and passion that have gone into your presentation,blah blah blah-- 2:56(Laughter) 2:58But honestly,it's total nonsense.You seem to be saying that the key selling points of your product are that it is inefficient and complex.Didn't they teach you 80-20?And furthermore,you're saying that this product is siloed.It overreacts, makes things up as it goes along and is actually designed for somebody else's benefit. I'm sorry to break it to you,but I don't think this one is a winner.

关于工作的优秀英语演讲稿

关于工作的优秀英语演讲稿 Different people have various ambitions. Some want to be engineers or doctors in the future. Some want to be scientists or businessmen. Still some wish to be teachers or lawers when they grow up in the days to come. Unlike other people, I prefer to be a farmer. However, it is not easy to be a farmer for Iwill be looked upon by others. Anyway,what I am trying to do is to make great contributions to agriculture. It is well known that farming is the basic of the country. Above all, farming is not only a challenge but also a good opportunity for the young. We can also make a big profit by growing vegetables and food in a scientific way. Besides we can apply what we have learned in school to farming. Thus our countryside will become more and more properous. I believe that any man with knowledge can do whatever they can so long as this job can meet his or her interest. All the working position can provide him with a good chance to become a talent. 1 ————来源网络整理,仅供供参考

自我管理演讲稿英语翻译

尊敬的领导,老师,亲爱的同学们, 大家好!我是5班的梁浩东。今天早上我坐车来学校的路上,我仔细观察了路上形形色色的人,有开着小车衣着精致的叔叔阿姨,有市场带着倦容的卖各种早点的阿姨,还有偶尔穿梭于人群中衣衫褴褛的乞丐。于是我问自己,十几年后我会成为怎样的自己,想成为社会成功人士还是碌碌无为的人呢,答案肯定是前者。那么十几年后我怎样才能如愿以偿呢,成为一个受人尊重,有价值的人呢?正如我今天演讲的题目是:自主管理。 大家都知道爱玩是我们孩子的天性,学习也是我们的责任和义务。要怎样处理好这些矛盾,提高自主管理呢? 首先,我们要有小主人翁思想,自己做自己的主人,要认识到我们学习,生活这一切都是我们自己走自己的人生路,并不是为了报答父母,更不是为了敷衍老师。 我认为自主管理又可以理解为自我管理,在学习和生活中无处不在,比如通过老师,小组长来管理约束行为和同学们对自身行为的管理都属于自我管理。比如我们到一个旅游景点,看到一块大石头,有的同学特别兴奋,会想在上面刻上:某某某到此一游话。这时你就需要自我管理,你需要提醒自己,这样做会破坏景点,而且是一种素质低下的表现。你设想一下,如果别人家小孩去你家墙上乱涂乱画,你是何种感受。同样我们把自主管理放到学习上,在我们想偷懒,想逃避,想放弃的时候,我们可以通过自主管理来避免这些,通过他人或者自己的力量来完成。例如我会制定作息时间计划表,里面包括学习,运动,玩耍等内容的完成时间。那些学校学习尖子,他们学习好是智商高于我们吗,其实不然,在我所了解的哪些优秀的学霸传授经验里,就提到要能够自我管理,规范好学习时间的分分秒秒,只有辛勤的付出,才能取得优异成绩。 在现实生活中,无数成功人士告诉我们自主管理的重要性。十几年后我想成为一位优秀的,为国家多做贡献的人。亲爱的同学们,你们们?让我们从现在开始重视和执行自主管理,十几年后成为那个你想成为的人。 谢谢大家!

关于工作的英语演讲稿

关于工作的英语演讲稿 【篇一:关于工作的英语演讲稿】 关于工作的英语演讲稿 different people have various ambitions. some want to be engineers or doctors in the future. some want to be scientists or businessmen. still some wish to be teachers or lawers when they grow up in the days to come. unlike other people, i prefer to be a farmer. however, it is not easy to be a farmer for iwill be looked upon by others. anyway,what i am trying to do is to make great contributions to agriculture. it is well known that farming is the basic of the country. above all, farming is not only a challenge but also a good opportunity for the young. we can also make a big profit by growing vegetables and food in a scientific way. besides we can apply what we have learned in school to farming. thus our countryside will become more and more properous. i believe that any man with knowledge can do whatever they can so long as this job can meet his or her interest. all the working position can provide him with a good chance to become a talent. 【篇二:关于责任感的英语演讲稿】 im grateful that ive been given this opportunity to stand here as a spokesman. facing all of you on the stage, i have the exciting feeling of participating in this speech competition. the topic today is what we cannot afford to lose. if you ask me this question, i must tell you that i think the answer is a word---- responsibility. in my elementary years, there was a little girl in the class who worked very hard, however she could never do satisfactorily in her lessons. the teacher asked me to help her, and it was obvious that she expected a lot from me. but as a young boy, i was so restless and thoughtless, i always tried to get more time to play and enjoy myself. so she was always slighted over by me. one day before the final exam, she came up to me and said, could you please explain this to me? i can not understand it. i

关于时间管理的英语演讲

Dear teacher and colleagues: my topic is on “spare time”. It is a huge blessing that we can work 996. Jack Ma said at an Ali's internal communication activity, That means we should work at 9am to 9pm, 6 days a week .I question the entire premise of this piece. but I'm always interested in hearing what successful and especially rich people come up with time .So I finally found out Jack Ma also had said :”i f you don’t put out more time and energy than others ,how can you achieve the success you want? If you do not do 996 when you are young ,when will you ?”I quite agree with the idea that young people should fight for success .But there are a lot of survival activities to do in a day ,I want to focus on how much time they take from us and what can we do with the rest of the time. As all we known ,There are 168 hours in a week .We sleep roughly seven-and-a-half and eight hours a day .so around 56 hours a week . maybe it is slightly different for someone . We do our personal things like eating and bathing and maybe looking after kids -about three hours a day .so around 21 hours a week .And if you are working a full time job ,so 40 hours a week , Oh! Maybe it is impossible for us at

关于人英语演讲稿(精选多篇)

关于人英语演讲稿(精选多篇) 关于人的优美句子 1、“黑皮小子”是我对在公交车上偶遇两次的一个男孩的称呼代号。一听这个外号,你也定会知道他极黑了。他的脸总是黑黑的;裸露在短袖外的胳膊也是黑黑的;就连两只有厚厚耳垂的耳朵也那么黑黑的,时不时像黑色的猎犬竖起来倾听着什么;黑黑的扁鼻子时不时地深呼吸着,像是在警觉地嗅着什么异样的味道。 2、我不知道,如何诠释我的母亲,因为母亲淡淡的生活中却常常跳动着不一样的间最无私、最伟大、最崇高的爱,莫过于母爱。无私,因为她的爱只有付出,无需回报;伟大,因为她的爱寓于

普通、平凡和简单之中;崇高,是因为她的爱是用生命化作乳汁,哺育着我,使我的生命得以延续,得以蓬勃,得以灿烂。 3、我的左撇子伙伴是用左手写字的,就像我们的右手一样挥洒自如。在日常生活中,曾见过用左手拿筷子的,也有像超级林丹用左手打羽毛球的,但很少碰见用左手写字的。中国汉字笔画笔顺是左起右收,适合用右手写字。但我的左撇子伙伴写字是右起左收的,像鸡爪一样迈出田字格,左看右看,上看下看,每一个字都很难看。平时考试时间终了,他总是做不完试卷。于是老师就跟家长商量,决定让他左改右写。经过老师引导,家长配合,他自己刻苦练字,考试能够提前完成了。现在他的字像他本人一样阳光、帅气。 4、老师,他们是辛勤的园丁,帮助着那些幼苗茁壮成长。他们不怕辛苦地给我们改厚厚一叠的作业,给我们上课。一步一步一点一点地给我们知识。虽然

他们有时也会批评一些人,但是他们的批评是对我们有帮助的,我们也要理解他们。那些学习差的同学,老师会逐一地耐心教导,使他们的学习突飞猛进。使他们的耐心教导培养出了一批批优秀的人才。他们不怕辛苦、不怕劳累地教育着我们这些幼苗,难道不是美吗? 5、我有一个表妹,还不到十岁,她那圆圆的小脸蛋儿,粉白中透着粉红,她的头发很浓密,而且好像马鬓毛一样的粗硬,但还是保留着孩子一样的蓬乱的美,卷曲的环绕着她那小小的耳朵。说起她,她可是一个古灵精怪的小女孩。 6、黑皮小子是一个善良的人,他要跟所有见过的人成为最好的朋友!这样人人都是他的好朋友,那么人人都是好友一样坦诚、关爱相交,这样人与人自然会和谐起来,少了许多争执了。 7、有人说,老师是土壤,把知识化作养分,传授给祖国的花朵,让他们茁壮成长。亦有人说,老师是一座知识的桥梁,把我们带进奇妙的科学世界,让

关于时间的英语演讲稿范文_演讲稿.doc

关于时间的英语演讲稿范文_演讲稿 and organizing people to learn from advanced areas to broaden their horizons in order to understand the team of cadres working conditions in schools, the ministry of education has traveled a number of primary and secondary schools to conduct research, listen to the views of the school party and government leaders to make school leadership cadres receive attention and guidance of the ministry of education to carry out a variety of practical activities to actively lead the majority of young teachers work hard to become qualified personnel and for them to put up the cast talent stage, a single sail swaying, after numerous twists and turns arrived in port, if there is wind, a hand, and naturally smooth arrival and guide students to strive to e xcel, need to nazhen “wind” - teacher. teachers should be ideological and moral education, culture education and the needs of students organically combining various activities for the students or students to carry out their own. for example: school quiz competitions, essay contests, ke benju performances and other activities to enable students to give full play to their talents. teachers rush toil, in order to that will enable students to continue to draw nutrients, to help them grow up healthily and become pillars of the country before. for all students in general education, the government departments have also not forget those who cared about the

关于机会的英语演讲稿

good afternoon everybody! I’m very glad to stand here and give you a short speech about challenge and opportunity,双手交握微笑 So, what’s an opportunity? It’s a great chance to achieve dreams, it’s a platform to show ourselves.Just as now,I’m standing here showing myself,it's one of my dreams,also my opportunity. Then, what about challenge? Challenge is a new or difficult task which test our ability and skill. it is a fighter, a sense of courage, the fearless spirit towards all difficulties, Many people are afraid of being challenged, worrying about change and failure.I used to be a member of them,but now,I find that sth we haven’t done isn’t as difficult as it seems, fear always hindered our courage. Said so much,此刻我最想与你们分享的一句话就是: we should welcome being challenged,and try to enjoy it.它很可能是你进步的机会 Cruel competition isn 't the excuse for failure. No one is regularly on a winner or a loser. To the strong willed, competition is the spring of hope; To the weak minded, it means the winter of despair. So turning into opportunities means taking advantage of these challenges and benefiting from them.In this way,you can be the boss of your life.这句语法有没有错误?指着他,手势 That’s all, thank you!

关于坚持的英语演讲稿

---------------------------------------------------------------范文最新推荐------------------------------------------------------ 1 / 9 关于坚持的英语演讲稿 results are not important, but they can persist for many years as a commemoration of . many years ago, as a result of habits and overeating formed one of obesity, as well as indicators of overall physical disorders, so that affects my work and life. in friends to encourage and supervise, the participated in the team now considered to have been more than three years, neither the fine rain, regardless of winter heat, a day out with 5:00 time. the beginning, have been discouraged, suffering, and disappointment, but in the end of the urging of friends, to re-get up, stand on the playground. in fact, i did not build big, nor strong muscles, not a sport-born people. over the past few years to adhere to it, because i have a team behind, the strength of a strong team here, very grateful to our team, for a long time, we encourage each other, and with sweat, enjoying common health happy. for example, friends of the several run in order to maintain order and unable to attend the 10,000 meters race, and they are always concerned about the brothers and promptly inform the place and

关于生活的英语演讲稿3篇

关于生活的英语演讲稿3篇 无论在学习还是工作中,我们都会接触或用到各类英语演讲,小 到课堂作业和工作汇报,大到会议发言和职位竞选。那么如何才能打造一篇精彩的英语演讲稿呢?下面小编整理了关于生活的英语演讲稿3篇,供你参考。 关于生活的英语演讲稿篇1 My life My future house is wide and spacious. It contains a lot of room such as swim pool, exercise room which contains a plenty of exercise machines, and a big play land so I can play inside the house no matter what time i play, it always open for me. Everything inside the house will be clean of themselves so I don't have to wash them. The tables are new, the computer is the coolest and the tv channels are enjoyable to watch. I want the background of the wall is mysterious and pretty and different in every single room. My future house will prevent the volcano blow and the tsunami or flood attack. It has the emergency exit and security alarm so everything will be safe! 关于生活的英语演讲稿篇2 Choice in My Life

最新-关于职业的英文演讲稿 很好的一篇演讲稿-关于职业 精品

关于职业的英文演讲稿很好的一篇演讲稿-关于职业 我希望今晚探讨的有关话题能涵盖这几个层次,让我们一同度过一个美好的夜晚!(掌声)首先,我谈谈人生的职业定位话题,一个十三岁的小学毕业生和一个研究生同在街边卖雪梨,他们的区别不会太大,那么为什么要读研究生呢?在人事部报到,高中或大学本科或研究生学历,为何在未看你工作能力给你定第一份工资的档次就不一样呢?如果一样,全世界就没有存在那么多学府的必要.今天诸位来到金正集团投身于这里,你是否想过,在这里干多久?想干什么?通过一段时间你会成为什么样的人. 这个公司从97年的几十人发展到今天的几千人,是我们杨总的远见,从这里我们看到,一个人职业定位中你必须把镜头拉长延伸到你的一生.一个人没有事业心的话,他的一生能够参照的只有父母所走的足迹. 导演张艺谋在陕北拍电影时见到一个孩童,夕阳西下骑在牛背上哼着陕北小调,张问﹕\娃,你在干啥?\孩童很悠闲的答﹕\我在放牛!\\为啥放牛?\\放牛挣钱!\\为啥挣钱?\\挣钱娶媳妇!\\娶媳妇干嘛?\\娶媳妇生娃!\\生娃干嘛?\\生娃放牛!\(笑声)八岁的小孩就想好了他一生\职业定位\是从祖辈开始放牛到他放牛,一直处于循环当中.诸位来到这里一定不想继续过放牛-挣钱-娶媳妇-生娃再放牛的生活吧?没有志向的人经常立志. 我有一位拥有硕士学位的同学五年干过十三个行业,基本一无所成,只积累了每个行业不成功的丰富经验.在高科技高速发展的现代社会,往往一个专业足够一个人奋斗一生,在这种分工很细的空间里我们自己的特长在哪里?我们立志在哪个行业干一辈子?你对行业的透彻见解和有所作为令人敬佩和追崇,那你的收入和你的生活才能跟一般人不一样. 所以古人才说﹕\有志之士立长志,无志之士常立志.\(掌声!)如果以一般人同样的工作量、同样的睡眠、同样的娱乐,凭什么比别人成功?吃别人不愿吃的苦,挨别人不愿挨的难,才能享受别人无法享受的生活. 职业定位的准确,关键在立志.毕业于长沙第一师范学校,按理他的职业定位应是老师,但当他十七岁走出韶山时便发自内心立下\身无分文心忧天下\的誓言,这是一个政治家的魄力. 在我们这个行业里,有位著名的广告界人士李光斗,复旦大学毕业的高才生,

相关文档
相关文档 最新文档