Detection of Wolf-Rayet stars in host galaxies of Gamma-Ray Bursts (GRBs) are GRBs produced

唐山“PEP”2024年小学四年级下册英语第1单元真题试卷考试时间：100分钟（总分:110）A卷考试人：_________题号一二三总分得分一、选择题(共计20题，共40分)1、What do we call the process of turning milk into yogurt?A. FermentationB. CoagulationC. PasteurizationD. Homogenization2、选择题：Who is known for saying "I have a dream"?A. Nelson MandelaB. Martin Luther King Jr.C. Albert EinsteinD. Mahatma Gandhi3、What is the name of the telescope that observes ultraviolet light?A. Hubble Space TelescopeB. Chandra X-ray ObservatoryC. Kepler Space TelescopeD. Spitzer Space Telescope4、What is the name of the famous ancient city in Italy?A. PompeiiB. RomeC. HerculaneumD. All of the above5、选择题：What is the capital of Greece?A. AthensB. RomeC. ParisD. MadridWhat do we call the process of breathing?A. RespirationB. DigestionC. CirculationD. Excretion7、Which animal is known for its stripes?A. ElephantB. LionC. ZebraD. Giraffe8、What is the capital city of Burkina Faso?A. OuagadougouB. Bobo DioulassoC. BanforaD. Koudougou9、What do we call a scientist who studies the behavior of animals?A. EthologistB. ZoologistC. EcologistD. Biologist10、What is 5 + 7?A. 10B. 11C. 12D. 1311、选择题：Which season comes after winter?A. FallB. SpringC. SummerD. Monsoon12、选择题：What is 2 + 2?A. ThreeB. FourC. FiveD. SixWhich animal is known for building dams?A. BeaverB. RabbitC. SquirrelD. Fox14、What do we call a piece of furniture we sit on?A. TableB. ChairC. BedD. Couch15、选择题：What do we call the process of cooking food over direct heat?A. BoilingB. BakingC. GrillingD. Steaming16、选择题：What do we call the process of water falling from clouds?A. RainB. SnowC. HailD. Sleet17、What do you call a person who studies plants?A. BotanistB. ZoologistC. BiologistD. Ecologist18、What is the capital of Syria?A. DamascusB. AleppoC. HomsD. Latakia19、What is 2 + 2?A. 3B. 4C. 5D. 620、What is the capital of the USA?A. LondonB. ParisC. Washington,D. C.D. Berlin二、听力题(共计20题，共40分)1、听力题：The chemical symbol for gallium is _____.2、听力题：A strong base can cause chemical ______.3、听力题：The chemical symbol for gold is __________.4、听力题：The stars are ______ (twinkling) in the sky.5、听力题：A __________ is formed when sediments are compacted together.6、听力题：A ______ is a scientific statement that summarizes a pattern.7、听力题：The kitten is ___ in the basket. (sleeping)8、听力题：I want to ___ (go/visit) the museum.9、听力题：Dolphins are known for their ______ behavior.10、听力题：__________ change occurs when ice melts.11、听力题：A _______ can help to demonstrate the principles of fluid dynamics.12、听力题：The capital of Portugal is __________.She is making a ___. (craft)14、听力题：I like to ___ (make) crafts.15、听力题：She enjoys ________ (writing) in her journal.16、听力题：My uncle is a great ____ (listener).17、听力题：A _______ is a process that changes chemical properties.18、听力题：The _____ is the path that comets take around the sun.19、听力题：The _______ of a material is its resistance to flow.20、听力题：I want to ______ how to ride a horse. (learn)三、填空题(共计20题，共10分)1、填空题：The seahorse is known for its unique _______ (外形).2、填空题：I like to go to ______ with my friends.3、填空题：A __________ (聚合反应) creates large molecules from smaller units.4、填空题：The __________ is a region with many active volcanoes. (火山带)5、填空题：A ________ (植物采集) can be educational.6、填空题：They are my . (他们是我的。

o b型恒星的生命历程（中英文实用版）Title: The Lifecycle of an O-type Binary StarTitle: O型双星的生命周期In the vast expanse of the universe, there are numerous types of stars, each with its unique properties and life cycle.Among them, the O-type binary stars, also known as Wolf-Rayet stars, are particularly intriguing due to their high temperatures, intense radiation, and rapid evolution.在宇宙辽阔的空间中，有无数种类的恒星，每一种都有其独特的属性和生命周期。

其中，O型双星，也被称为沃尔夫-拉叶星，因其高温度、强烈辐射和快速演化而特别引人注目。

The formation of an O-type binary star begins with the collision and fusion of gas clouds.These clouds, mainly composed of hydrogen and helium, are propelled by the gravitational pull of neighboring stars and galactic forces.As they collapse under their own weight, they heat up and become dense, eventually leading to the formation of a binary system.O型双星的形成始于气体云的碰撞和融合。

判断野火入侵和动物入侵的设备作文英文回答:Wildfire invasion and animal invasion are two different types of intrusions that require different types of equipment for detection and prevention.To detect and combat wildfire invasion, specialized equipment such as fire alarms, smoke detectors, and heat sensors are essential. These devices are designed to detect the presence of smoke or heat, which are indicators of a potential wildfire. For example, smoke detectors can quickly identify the presence of smoke particles in the air and trigger an alarm to alert residents or authorities. Heat sensors can detect abnormal increases in temperature, which may indicate the presence of a fire. These devices are crucial in providing early warning signs and enabling swift action to prevent the spread of wildfires.On the other hand, animal invasion requires a differentset of equipment for detection and prevention. One of the most common tools used is a wildlife camera, which captures images or videos of animals in their natural habitat. These cameras are often placed in strategic locations to monitor animal activity and identify potential risks. For instance, if there is evidence of animals frequently entering a residential area, measures can be taken to secure the premises and prevent further intrusion. Additionally, motion sensors can be installed to detect movement and trigger alarms if animals are detected in restricted areas.In addition to detection equipment, prevention measures are also necessary to mitigate the risks of both wildfire and animal invasion. For wildfires, fire extinguishers,fire blankets, and fire-resistant materials are essentialin preventing the spread of fires and minimizing damage. These tools can be used to extinguish small fires or create barriers to prevent the flames from spreading. Similarly, for animal invasion, fencing, barriers, and repellents can be used to deter animals from entering restricted areas. For example, electric fences can be installed to prevent animals from accessing certain areas, while repellents canbe used to discourage animals from approaching human settlements.Overall, the equipment required for detecting and preventing wildfire invasion and animal invasion differs based on the nature of the intrusion. While wildfire invasion necessitates the use of fire alarms, smoke detectors, and heat sensors, animal invasion requires wildlife cameras, motion sensors, and preventive measures such as fencing and repellents.中文回答：野火入侵和动物入侵是两种不同类型的侵入，需要不同类型的设备进行检测和防范。

小学下册英语第1单元期中试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.What do we call the planet we live on?A. MarsB. VenusC. EarthD. Jupiter答案:C2.The capital of Kenya is _______.3. A ________ (航空港) is where planes take off and land.4.________ (观赏植物) are often used in landscaping.5.What do you call a person who works with metal?A. BlacksmithB. CarpenterC. ElectricianD. Mason答案:A6. A hydrate is a compound that contains ______ molecules.7.What is 15 + 10?A. 20B. 25C. 30D. 358. A _____ (蚂蚁) works hard to gather food for winter.9.What do we call a sweet food made from cocoa?A. CandyB. ChocolateC. CakeD. Biscuit答案:B10.I can play with my ________ (玩具类型) anywhere.11. A halogen is an element found in group ______ of the periodic table.12.What do we call a person who repairs shoes?A. TailorB. CobblerC. SeamstressD. Artisan答案:B13.What is the name of the first artificial satellite launched into orbit?A. Sputnik 1B. Explorer 1C. Vanguard 1D. Luna 114.What is the season after spring?A. WinterB. SummerC. FallD. Autumn答案:B15.The ancient Sumerians are known for creating the first ________ (城市).16.I found a _______ (古老的) coin.17.Which animal has a long neck?A. ElephantB. GiraffeC. DogD. Cat答案:B18.I like to watch ________ (纪录片) about animals.19.The ice cream is ___. (melting)20.The sunset is _______ (动人的).21.She is wearing a cute ___. (outfit)22.The car is _____ (fast/slow).23. A ______ is a type of bird that can mimic sounds.24.What is 10 - 4?A. 5B. 6C. 7D. 8答案:B25.The rain is ______ on the roof. (falling)26. A _____ (草坪) is perfect for picnics in the park.27.What is the color of an orange?A. BlueB. OrangeC. PurpleD. Green28. A ________ (植物知识普及) can inspire others.29.What do you call a person who plays a musical instrument?A. PainterB. SingerC. MusicianD. Dancer答案:C30.The _______ of a solution tells us how concentrated it is. (浓度)31.What is the main ingredient in falafel?A. LentilsB. ChickpeasC. BeansD. Rice32.The hamster stores food in its ______ (脸颊).33.We enjoy visiting the ___. (aquarium)34. A shooting star is actually a _______ that burns up in the atmosphere.35. A ______ is an animal that can be found in the ocean.36.What is the name of the famous American holiday celebrated on the fourth Thursday in November?A. ThanksgivingB. ChristmasC. New Year'sD. Independence Day答案:A37.Which animal has a long trunk?A. GiraffeB. ElephantC. ZebraD. Lion答案:B38. A solution that can dissolve more solute is called a _______ solution.39.The ________ was a significant movement for women's rights.40.My mom loves to _______ on weekends.41.We have math _____ today. (class)42. A _____ (生态平衡) is essential for a healthy environment.43.The ice cream is ___. (melting)44. A baby cat is called a __________.45.How many days are in a leap year?A. 365B. 366C. 367D. 364答案:B46.What do you call the person who teaches you in school?A. DoctorB. TeacherC. ChefD. Engineer答案:B47.I enjoy planting _____ in the garden.48.Which animal is known as "man's best friend"?A. CatB. DogC. BirdD. Fish49.I can ________ a message.50.__________ are used in the construction industry for insulation.51.What is the name of the fairytale character who climbed a beanstalk?A. JackB. PeterC. HanselD. Gretel52.The __________ (历史的启发性思维) drives innovation.53.I want to ___ a great cook. (become)54.What is the term for the distance light travels in one year?A. Light-YearB. Astronomical UnitC. ParsecsD. Cosmic Yard55.What is the name of the famous volcano in Italy?A. Mount EtnaB. Mount VesuviusC. Mount FujiD. Mount St. Helens答案:B56.The __________ helps to protect the brain.57.What is the name of the fictional land where Peter Pan lives?A. NeverlandB. WonderlandC. OzD. Narnia答案:A58.What is the capital of Portugal?A. LisbonB. MadridC. RomeD. Paris答案:A59.I have a ___ (dream) to travel the world.60.Which flower is known for being red?A. TulipB. RoseC. DaisyD. Sunflower答案:B61.What is the capital of Switzerland?A. ZurichB. GenevaC. BernD. Basel答案:C62.What is the name of the famous American singer known for her powerful voice?A. AdeleB. Whitney HoustonC. Mariah CareyD. Beyoncé答案:B63.What do we call a baby cat?A. KittenB. PuppyC. CubD. Foal答案:A64.The process of making biodiesel involves _______ oils.65.What color is a ripe banana?A. GreenB. YellowC. RedD. Blue66.The dog is _____ with its favorite toy. (playing)67.The ancient Greeks held _______ to honor their gods. (运动会)68.小鱼) plays with its friends in the tank. The ___69.The ______ communicates through sounds.70.What do you call a baby platypus?A. PuggleB. KitC. CalfD. Pup答案:A71.Cleopatra was the last active ruler of the __________ (埃及) dynasty.72.The bird is singing a ______ (happy) song.73.I can ______ (坚持) my beliefs.74.Light pollution makes it difficult to see the stars in an urban _______.75.What is the name of the famous American author known for "Beloved"?A. Toni MorrisonB. Maya AngelouC. Alice WalkerD. Zora Neale Hurston答案:A76.What do you call the hot liquid inside a volcano?A. MagmaB. LavaC. AshD. Gas答案:A77.What is the sound of a sheep?A. MeowB. BarkC. BaaD. Moo答案:C78.What is the name of the famous festival held in Rio de Janeiro?A. CarnivalB. OktoberfestC. DiwaliD. Holi答案:A Carnival79.We can _______ (一起学习) for the exam.80.My best friend is my loyal _______ who always supports me.81.Cosmic rays are high-energy particles that travel through ______.82. A _____ (植物文化交流) fosters appreciation for diversity.83. (Russian) Revolution led to the establishment of the Soviet Union. The ____84.The children are ________ in the playground.85.The ice cream is _____ (cold/warm) and delicious.86.The capital of Canada is _____.87.The _____ (大象) communicates with low-frequency sounds.88.What is the capital of Sri Lanka?A. ColomboB. KandyC. GalleD. Jaffna答案:A89.My sister's name is . (我妹妹的名字是。

a r X i v :a s t r o-ph/12412v119Dec2Can We Date Starbursts?Ariane Lan¸c on 1Observatoire de Strasbourg,11rue de l’Universit´e ,F–67000Strasbourg,France Abstract.Age dating starbursts is an exercise with many caveats.We attempt to summarise a discussion session that was lead along a rather optimistic guideline:the aim was to highlight that current age estimates,despite undeniable uncertainties,do provide constraints on the physics of starbursts.In many cases,better starburst theories will be needed before the improvement of empirical timelines becomes crucial.1Introduction Many questions can be asked about our ability to trace the history of star for-mation (SF)in starbursts.The phrasing chosen by the Organizing Committee of this workshop was “Can we date starbursts ?”.This formulation calls for one of only two answers :yes ,or no ...When hearing the question,one automatically recalls ones most recent conversation about the complexity of starburst galaxies or about uncertainties in stellar population synthesis models.Is there any chance for a positive answer ?In preparing guidelines for the discussion,we took the optimistic approach of attempting to defend a yes .Of course the final answer ended up not being as clear-cut,but some negative intuitions were countered.Clearly,our degree of satisfaction with starburst age or duration measure-ments depends on the intended application.The initial question really holds two:how accurately and reliably can we date starbursts ?and is that sufficient to make astrophysics progress ?Starburst galaxies are composite objects.The SF may occur both in a diffuse mode and in clusters [23].The global duration of active episodes can approach 109yrs,while individual starburst clusters are often thought to form instanta-neously (<106yrs).To avoid confusion in the meaning of the word “starburst”,the following pages deal successively with (i)individual young starburst clusters,(ii)individual intermediate age “post-starburst”clusters that trace starburst ac-tivity of the recent past,and (iii)starburst galaxies as a whole.More extensive reviews and references regarding the age dating of stellar populations can be found in [19],[12],[14]and in this volume.2Individual young clustersThis section focuses on starburst clusters with ages below 107yrs,as observed in large numbers in the main body of starburst galaxies ([7],[29],[1])or in tidal tails of interacting objects ([29],[8]).2 n¸c onThe conditions for cluster age determination are most favourable when the spectroscopic study of individual stars is possible.Until now such studies have been limited to the local neighbourhood of the Milky Way,where many young OB associations exist but massive compact young clusters(as seen in starburst galaxies)are rare/non-existent;30Doradus in the LMC and NGC3603in the Milky Way are the most relevant accessible targets.Nevertheless,the nearby objects highlight some of the difficulties:•Samples of cluster stars with spectroscopically confirmed positions in the Hertzsprung-Russell(HR)diagram are small and strongly affected by stochas-ticfluctuations or spatial variation in the extinction;they are potentially contaminated byfield stars.•Massive star main sequence lifetimes vary between authors by up to∼25%.•Rotation is poorly understood,but rotational velocities above100km/s are the rule in early type stars.Meynet(in[12])shows that the main sequence lifetime of a massive star may be extended by20–25%in case of rotation.•The proportion of double stars and the effect of binarity on evolution are unknown.Binaries are usually neglected in predictions of frequently used properties such as the number fractions of various types of Wolf-Rayet stars. In more distant starburst clusters,one integrates the cluster light.The photo-spheric and wind features in the UV spectrum are considered the most sensitive age indicators and in principle give instantaneous burst ages to within a few Myr[20].The study of line equivalent widths allows similar formal age accura-cies if the light of the whole H II region surrounding the cluster can be summed, the fraction of escaping Lyman continuum photons considered negligible and the continuum contamination by background stars subtracted.The above-mentioned problems associated with rotation,binarity and stellar tracks remain.Charlot(in [19])for instance points out a delay of about0.1dex(25%)between the appear-ance of thefirst red star contributions in two sets of commonly used evolutionary tracks.The risk of stochasticfluctuations between the properties of clusters with identical ages also persists because offluctuations in the small numbers of very luminous stars.Monte Carlo simulations[4]indicate that thesefluctuations con-tribute less than∼1Myr additional uncertainty to the age estimate as long as clusters more massive than104M⊙are considered.How the described sources of uncertainties add up or compensate each other is not known.Today,if telescope time is not a limiting factor,a detailed multi-wavelength study of a young cluster can be thought to provide an age estimate to better than∼50%.Opinions in the workshop audience varied from30%(which I would support at least in favourable cases),to a provocative0.3dex(which are probably realistic at extreme metallicities or in environments of particularly complex structure).Can astrophysical questions be addressed with a50%accuracy in young star-burst cluster ages?Problems of physical interest include SF processes themselves (delay between an external trigger and the onset of SF,formation timescale for massive clusters,propagation of SF within a galaxy)and their effects on the en-Can We Date Starbursts?3 vironment(survival times of molecular clouds around starburst clusters,bubble expansion timescales).Many examples illustrate that spectrophotometric ages,despite the uncer-tainties,provide interesting constraints.Age spreads of several Myr have been found in OB associations([30],[2],[26]),showing that a unique number does not suffice to describe their age.WC/WN star number ratios indicate that spreads of a few Myr may also be relevant to clusters in starburst environments[27]. Rather complex age structures are seen in NGC3606and30Dor.In both cases the massive stars of the youngest,2-3Myr old component,are concentrated in the central few parsecs and surrounded with significantly older components([10], [28]).This situation remains to be convincingly explained by cluster formation models(what are the relative roles of a progressive onset of SF[26],mass seg-regation[24],[13],propagation,merging?).Oey&Massey[25]studied the LH 47/48and the surrounding superbubble in the LMC,and found a significant disagreement between the stellar ages and the bubble properties predicted from a simple dynamical model,calling for more detailed modelling of the reactions of the ISM.Uncertainties in the identification of external triggers and in their onset time dominate in many studies of the initiation of SF in young clusters. Clearly,spectrophotometric dating has been successful in providing otherfields of starburst cluster research with new problems.3Individual post-starburst clustersStar clusters with ages between107and109yrs are useful to relate current SF activity to potential starbursts of the recent past.They are often found together with the young clusters discussed previously.As they do not ionize their surroundings and have already faded at optical wavelengths,they have not yet been searched for and studied as systematically as their younger counterparts.Post-starburst clusters are dominated by B then A type stars in the optical/ near-UV,by red supergiants(RSG)and then giants of the upper asymptotic giant branch(TP-AGB)in the near-IR.The effects of mixing processes,due e.g. to rotation,appear essential to explain the location of B stars in the HR diagram [21];Figueras&Blasi[6]use simulations of the Str¨o mgren photometry of stel-lar populations with reasonable rotation velocity distribution to conclude that photometric ages are affected at the30-50%level.More consistent approaches combining the effects of rotation on internal structure and on observable prop-erties have not yet been systematically applied to age studies.Supergiant counts should be used with caution at non-solar metallicities(Z)as the Z-dependance of the blue/red number ratio is not predicted correctly by models[18].It seems that at Z M31≃Z⊙the RSGs have later spectral types but are only produced for m<15M⊙(age∼12Myr)as opposed to m<25−30M⊙(age∼7Myr)at Z NGC6822≃Z⊙/3[22].Modelling the thermal pulses and the Mira-type pulsa-tion along the TP-AGB,in addition to the early AGB,is essential when studying stars in108−109yr old clusters.Number counts that separate C-rich stars from4 n¸c onO-rich stars of various subtypes then are potential age-indicators(Lan¸c on& Mouhcine,this volume,and references therein).For unresolved solar metallicity clusters younger than∼50Myr,well-isolated from the host galaxy background,the UV features give ages to within∼20% [3].Effects of metallicity are uncertain,but empirical calibrations are being at-tempted(Tremonti,this workshop).The absorption line spectrum(H i and met-als)together with the energy distribution in the Balmer region gives ages to within±30%([7],[11]).Reddening-independent colour-indices in[29]are effi-cient and could be generalised to include near-IRfluxes.Gilbert(this workshop) showed that,at a given metallicity,near-IR spectra of synthetic clusters with ages of10−25Myr(RSG-dominated)and age differences of2−3Myr can be dis-tinguished and sorted.TP-AGB stars leave potentially useful spectral signatures in integrated spectra of slightly older objects([16]).Stochasticfluctuations in the integrated spectrophotometry,that are dominated by the most luminous red stars,add negligible amounts to the other dating errors as long as the clusters contain more than104M⊙of stars[15].Again,when enough telescope time can be obtained to combine several of the above approaches,ages can be expected to within a conservative±50%(25% in favourable cases,0.3dex for sceptical attendees).The ages discussed here are comparable to galaxy interaction timescales and more generally to the duration of starburst activity on galaxy scales.Mihos(this workshop)reminded us that the treatment of the transition from a dynamical perturbation to star formation in dynamical models is simplistic;delays of100 to500Myr are found to be typical before onset of starburst activity.Obvious morphological signatures of an interaction fade away over similar timescales;in the case of NGC4038/39the spectrophotometric age distribution of the clusters is probably a safer indication of a second encounter than model adjustments to the projected system structure.In NGC1614and IC342(Rieke,Genzel,this session)starburst knots form a∼0.5kpc nuclear ring,with younger knots(Hαsources,≤6Myr old)located at larger galactic radii than older ones(RSG hosts,≤7Myr old).No dynamical models are as yet available to explain this situation well enough to require improved spectrophotometric ages.Is the formation of generations of starburst clusters a recurrent phenomenon? When cluster ages become comparable to the dynamical timescales of a galaxy, age differences much shorter than this time cannot be interpreted as separate SF episodes,but rather as one extended one.Therefore a50%precision on the age is sufficient to detect potential separate episodes.Then,attempts to the compare properties of the starburst clusters of the current and the previous active phases must deal with a large variety of dynamical effects that rule the survival/destruction of starburst clusters over timescales of108−109yrs[9]. Uncertainties in those are likely to wash out50%age errors.In this section again,our(biased)approach demonstrates that current age es-timates pose challenging astrophysical problems that are far from being resolved to the point of necessitating better timelines.Can We Date Starbursts?5 4Starburst galaxies at low spatial resolutionLet usfinally question the dating of starburst galaxies observed at a spatial resolution no better than a few100pc,or completely unresolved.Partial spatial resolution has obvious advantages but also has some dangers:aperture mis-match between wavelengths,the likelihood that wavelength-dependent photon-exchanges with regions outside the line of sight(through scattering)falsify energy balances,the possibility that average obscuration curves don’t apply,etc.The youngest and/or least reddened stellar component is usually dominant at UV wavelengths;but underlying“evolved”populations have been found in all star-bursts.Age studies must also aim at determining whether these are part of an extended starburst episode that is still going on,or whether they are remnants of previous,dynamically unrelated star formation.The nuclear starburst in the interacting spiral galaxy NGC7714will be used here for illustration.Integrated photometry is available over the whole electro-magnetic spectrum.Extinction is very inhomogeneous and typically A v∼0.8.A recent study[17]addresses the photometry and the UV+V+near-IR spectra of the central300pc.There,the UV is dominated by a young(∼5Myr old)burst, obviously seen through a hole in the dust distribution;the short wavelengths thus contain no information on putative other young populations,including those required to explain the far-IR emission.The broad band photometry can be adjusted satisfactorily with many models:continuous SF over as little as a few 107yrs or as long as∼109yrs,or a succession of brief bursts:dust distributions provide more than enough degrees of freedom.More stringent constraints come from spectroscopy:the Hubble Space Telescope UV spectrum favours the pres-ence of at least one instantaneous5Myr burst;the Balmer line region rejects the optical predominance of populations younger than∼300Myr or older than ∼900Myr(note that the continuum shape had to be used in addition to the line profiles of the rectified spectrum in order to reach this conclusion);the K band spectrum suggests mixed contributions,as opposed to a population purely dominated by RSG or by TP-AGB stars.The far-IRflux sets a loose upper limit on the amount of heavily obscured young stars,and the reddened Balmer ratio a lower one.The study concludes that starburst activity has been going on with ups and downs over an extended time,and that durations between∼300and ∼900Myr are consistent with the data.This is an age to±50%.The observational constraints on starburst studies can and must still be im-proved,using available instruments;but on the other hand,more dust config-urations and the effects of chemical evolution must be explored systematically, adding even more free parameters.We will thus probably have to bear with ±50%estimates for a while.Is that enough?In the case of NGC7714,it is at least sufficient to point out an astrophysical problem:the comparison of the system morphology with dynamical simulations indicates that the closest encounter with with NGC7715 occured about100Myr ago.The model parameters would allow to increase the time since interaction by about a factor of2,but it seems difficult to reconcile6 n¸c onthis dynamical timescale with the starburst timescales derived from spectropho-tometry.5ConclusionAlthough some workshop participants never accepted age uncertainty estimates below0.3dex,we believe that detailed multiwavelength studies,as possible with current instruments(when access to them is not a limiting factor),allow to reach ±50%,or even better in particularly favourable configurations.The session has allowed many examples to be discussed,and we hope it has conveyed the posi-tive impression that current age determinations,despite their uncertainties,are indeed providing essential constraints on theoretical issues related to starbursts. 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a r X i v :a s t r o -p h /0209259v 1 13 S e p 2002Astronomy &Astrophysics manuscript no.(will be inserted by hand later)A large Wolf-Rayet population in NGC 300uncovered byVLT-FORS2⋆H.Schild 1,P.A.Crowther 2,J.B.Abbott 2,and W.Schmutz 31Institut f¨u r Astronomie,ETH-Zentrum,CH 8092Z¨u rich,Switzerland2Dept of Physics and Astronomy,University College London,Gower St,London WC1E 6BT,United Kingdom 3Physikalisch-Meteorologisches Observatorium,CH-7260Davos,SwitzerlandReceived /AcceptedAbstract.We have detected 58Wolf-Rayet candidates in the central region of the nearby spiral galaxy NGC 300,based on deep VLT-FORS2narrow-band imaging.Our survey is close to complete except for heavily reddened WR stars.Of the objects in our list,16stars were already spectroscopically confirmed as WR stars by Schild &Testor and Breysacher et al.,to which 4stars are added using low resolution FORS2datasets.The WR population of NGC 300now totals 60,a threefold increase over previous surveys,with WC/WN ≥1/3,in reasonable agreement with Local Group galaxies for a moderately sub-solar metallicity.We also discuss the WR surface density in the central region of NGC 300.Finally,analyses are presented for two apparently single WC stars –#29(alias WR3,WC5)and #48(alias WR13,WC4)located close to the nucleus,and at a deprojected radius of 2.5kpc,respectively.These are among the first models of WR stars in galaxies beyond the Local Group,and are compared with early WC stars in our Galaxy and LMC.Key words.galaxies:NGC 300–stars:Wolf-Rayet –stars:fundamental parameters1.IntroductionOver 500Wolf-Rayet stars have been identified in Local Group galaxies,principally the Milky Way,M31and M33.These stars beautifully trace young stellar populations,and their number and distribution reacts sensitively to metallicity,which varies by an order of magnitude from the Small Magellanic Cloud (SMC)to M31.Detailed stud-ies of individual WR stars in Local Group stars have been carried out (e.g.Smartt et al.2001;Crowther 2000;Crowther et al.2002)using 2–4m class telescopes.The availability of 8–10m class telescopes permits the discovery and study of individual stars at greater dis-tances,spanning a greater range of metallicities.As a first application,we present here VLT imaging and spec-troscopy of WR stars in NGC 300,located in the Sculptor group at a distance of 2Mpc (Freedman et al.2001).It’s metallicity is bracketed by the Milky Way and Large Magellanic Cloud (LMC)and therefore we expect a sim-ilarly large number of WR stars in NGC 300.Previous surveys have however failed to identify them.A large pop-ulation might also be anticipated since NGC 300is a late type spiral,reminiscent of M33,which harbours at least2Schild et al.:WR stars in NGC300Fig.1.Finding chart for WR stars/candidates in NGC300.Left:nuclear region,right:area northwest of the nucleus. The horizontal bar represents10′′.North to the top,East to the left.ized by oxygen content.Although there have not beenany recent studies of the NGC300metallicity gradient,Deharveng et al.(1988)used data from Pagel et al.(1979)and Webster&Smith(1983),to imply a range betweenlog(O/H)+12=8.9in its nucleus and8.3in its outer spi-ral arms.Similar conclusions were obtained by Zaritskyet al.(1994)from a recalibration of previous results.Onewould expect a WC/WN ratio of∼1/2from comparisonwith Local Group galaxies,yet the census of WR stars inNGC300indicates WC/WN∼2.Consequently,we mightexpect that the WR population of NGC300is highly in-complete,particularly amongst WN stars.In this paper we present results from a new imag-ing survey of the central region of NGC300with theVery Large Telescope(VLT).New WR candidates areidentified,some of which are spectroscopically confirmed.Spectral types of the latter are discussed,with particularreference to the WC/WN ratio of the inner galaxy.Ananalysis of two apparently single WC stars is presented,one located close to its nucleus,the other at∼50%of theHolmberg radius,ρparisons are made with recentcomparable studies of WC stars in a variety of metallicityenvironments.2.ObservationsWe observed NGC300with the VLT UT2(Kueyen)and Focal Reduced/Low Dispersion Spectrograph#2(FORS2)during2000September2–3.The conditions werephotometric but the seeing was highly variable,changingfrom0.6to3.5′′and we used the instrument accordinglyin imaging and spectroscopic mode.2.1.ImagingWhile the seeing was good(typically0.8′′)we obtainedimages through two interferencefilters with central wave-lengths at4684˚A and4781˚A and band widths of66˚Aand68˚A,respectively.The formerfilter is well matchedto the strong WR emission feature containing the N iiiλ4640,C iiiλ4650,C ivλ4658and He iiλ4686emissionlines.The wavelength range of the latterfilter falls intoa spectral region that is free from emission lines.We col-lected two images in eachfilter with exposure times of600sec.These frames were centred atα:0h54m59.0sandδ:–37◦40′59′′(2000).At mediocre seeing condi-tions short exposures through Bessel B and Vfilters werealso collected.Only one of the V frames was of sufficientquality,but it was slightly offset such that only V-bandmagnitudes of WR candidates with RA larger than00h54m46.7s could be measured.The standard collimator was used,providing afield-of-view of6.8′×6.8′with an image scale of0.2′′/pixel.The detector was a2048×2048Tektronix CCD with24µmpixels.The data were de-biased andflatfielded with framestaken in the following morning twilight.We used theDAOPHOT software package to get relative photometry.These were converted into absolutefluxes with the pho-tometric standard stars in thefield of NGC300listed inPietrzi´n ski et al.(2002a).2.2.SpectroscopyFORS2was used in long slit mode(LSS)to obtainspectroscopy for selected Wolf-Rayet stars and candi-dates.This mode was selected since narrow-band im-Schild et al.:WR stars in NGC3003 Table1.List of Wolf-Rayet stars and candidates in the central regions of NGC300.Two other WR stars are known outside the presentfield–WR8(WN)in Deh30from Schild&Testor(1992)and a WC in Deh24from D’Odorico et al.(1983).Deprojected galactocentric distances are expressed as a fraction of the Holmberg radius(ρ0=9.75′≃5.75 kpc).ST1)Brey2)Remark5) 205442.37-37437.318.93 1.02out0.3353b WC4405442.78-37431.817.880.25out0.3253c WN605444.75-374240.019.030.13out0.26WN115) 1005450.21-374029.719.680.5220.040.1076aWR9I-11205450.53-373826.720.87 1.5722.120.36771405450.62-374021.720.39 1.4921.640.1176b WC4-65) 2305453.11-374347.319.720.0819.710.38882405453.80-374347.220.00 1.5521.340.3890WC5WR22905456.76-374044.019.71 2.5821.610.0898WC4-55) 310550.65-373851.520.74 1.6822.140.31II-134055 3.34-374242.020.36 1.9721.870.35WC5-636055 3.64-374320.018.060.1317.970.4237055 3.75-374251.6blend 2.018.560.3738055 4.09-374318.919.070.6419.530.43WN9-10WR6410559.98-374212.521.640.9522.440.434305512.07-374121.919.840.1219.830.42137d4405512.19-374119.717.710.1917.800.42137d4505512.21-374120.418.550.4018.790.42137dV-14705512.41-374129.019.68 2.9521.190.43137b WC5-6WR13IV-3 4905512.58-374139.518.460.3118.850.45137a WN75305513.23-374139.820.63 1.1221.540.46WN4-65505513.47-374146.320.64 1.8722.300.47WN4-54Schild et al.:WR stars in NGC300Fig.2.Finding chart for WR stars/candidates in the southern spiral arm.The saturated object is the galactic fore-ground star CD−38◦301.The horizontal bar represents10′′.North to the top,East to theleft.Fig.3.Finding chart for WR stars/candidates in the northeast of the nucleus.Some vignetting occurred in the upper left corner(northeast).The horizontal bar represents10′′.North to the top,East to the left.ages were not obtained in advance of the observing run. The300V grating,GG435filter and 1.0′′slit width provided spectroscopy coveringλλ3500–8970at a dis-persion of1.7˚A/pixel,corresponding to a resolution of R=∆λ/λ∼440at5900˚A.Eight targets were observed with this configuration using1800sec exposures,and will be discussed in Sect.4.Generally,two WR stars were ob-served in each observation via a suitable choice of posi-tion angle using the FORS Instrument Mask Simulator (FIMS)software.Relativeflux calibration was achieved using short exposures for standard stars Feige110and LTT1788.Absolute calibration required convolution with b and v(Smith1968)narrow-bandfilters,which were ap-proximated to our m4781photometry.For three stars,higher resolution600R grating obser-vations were obtained,using the GG435filter,coveringSchild et al.:WR stars in NGC3005Fig.4.Finding chart for WR stars/candidates east of the nucleus(top right)and int he H ii regions Deh137(top left),Deh118/119(bottom left)and Deh77/79(bottom right).The horizontal bars represent10′′.North to the top, East to the left.λλ5330–7540,at a dispersion of0.7˚A/pixel,correspond-ing to a resolution of R∼1000at6300˚A.Two1800sec ex-posures were taken before seeing conditions deteriorated.Identicalflux standards were again used with this con-figuration.For all datasets a standard data reduction wascarried out using FIGARO1i.e.,bias subtraction,flatfieldcorrection,extraction,wavelength andflux calibration.6Schild et al.:WR stars in NGC300detected obviously depends on the signal/noise ratio.In this case the signal is theflux difference between on-offframes.Wefirst identified theλ4684emission objects on the difference image.The selection criteria were a stellar appearance and a peak intensity of at least6σ.The prob-ability for any of the listed objects of having indeed a WR excess is therefore very high.For these objects we sub-sequently picked the V,emission(λ4684)and continuum (λ4781)magnitudes from the(rather long)DAOPHOT photometric list.It should be noted that photometry is hampered by a variable background due to unresolved galaxy emission and heavy crowding,which can be particularly severe in OB associations.It follows that while the identification as aλ4684emission object is rather reliable,the quantitative measurement of a WR excess is less certain.Our narrow-band images are complete down to23.7mag while the3σdetection limit was at24.7mag.We present a catalogue of the58WR stars/candidates identified in our images in Table1.We include spectral types taken from the literature,updated in case of revi-sions from our new spectroscopy(see Sect.4),plus as-sociated H ii regions from Deharveng et al.(1988).De-projected galactocentric distances were calculated using parameters from Table1of Deharveng et al.(1988).In Figs.1to4we givefinding charts for the WR candidates. In all of them a horizontal bar is plotted that represents 10′′.The orientation is as usual:North to the top and East to the left.Allfinding charts are from ourλ4684 narrow-bandfilter images.3.2.Nature of candidates39out of our58WR candidates with aλ4684excess are newly identified in this study.We compare theλ4781con-tinuum magnitudes with theλ4684excess in Fig.5.Stars with previous(or new)spectroscopic confirmation are in-dicated,as shown in the key.We include estimates of the absolute magnitudes atλ4781,assuming a distance mod-ulus of26.53mag to NGC300(Freedman et al.2001) and Aλ4781=0.36mag,corresponding to E B−V=0.10mag which is the mean interstellar reddening towards H ii re-gions of NGC300withinρ/ρ0=0.5derived by Deharveng et al.(1988).Fig.5clearly separates the largeλ4684excesses of the visually faint WC and early-type WN stars,from the small excesses of the visually bright late-type WN stars and WR binaries.Approximate line equivalent widths(in˚A)are also presented in thefigure,as estimated from stars in which optical spectroscopy is available(see also Fig.4of Massey&Johnson1998).Such comparisons would repre-sent the sole means by which WR populations might be identified in galaxies which are too distant(or reddened) for confirmatory spectroscopy to be obtained,even with large8–10m telescopes.Previously known WR stars tend to have largeλ4684 excesses of>∼1mag,corresponding to emission parison between theλ4781continuum mag-nitudes of the WR candidates in NGC300and theλ4684 excess(stars).Spectroscopically confirmed WR stars are presented in the key.Approximate absolute magnitudes and line equivalent widths are indicated,as discussed in the text.Three WR stars are not shown in thisfigure–#1(located at the edge of the image surveyed–Fig.1), #37and#51(both are severely blended).lent widths of>∼100˚A.Exceptions include those WR stars which lie in well surveyed OB associations.Wefind six more WR candidates with such a large WR excess(#3, #5,#22,#30,#31and#37).They are rather faint with m4684>20.5mag,which is presumably why they escaped earlier detection.From this sample,#22and#30were observed spectroscopically,such that both were confirmed as WR stars–see Sect4.Single,early-type WC stars haveλ4650–4686emission equivalent widths of>∼1000˚A,and are visually rather faint. Consequently only three WC stars,with an excess of≥2.5 mag are likely to be single,namely#29,#47and#48. Two of these stars are discussed in detail in Sect.5.Other WC stars are almost certainly multiple,or suffer contami-nation from stars along the same line-of-sight.Early-type WN stars possess He iiλ4684emission equivalent widths of100–400˚A,corresponding to excesses of1–2mag.From Fig.5,it is likely that#28and#55are single,whilst others are probably multiple.For those remaining WR candidates with excesses greater than1mag,#5is a strong WC+O candidate,whilst the remainder are prob-able WN+OB systems.There are also a handful of new WR candidates with an excess in the range0.3to1mag(#9,#10,#41,#42, #51,#52and#54),corresponding to emission equivalent widths in the range∼30–100˚A.Their relatively small line strengths suggests that if they are visually bright,with M4781<−6,they are WR binaries(e.g.#11)or single WN7–9stars(e.g.#38).If they are visually faint,they are probably weak-lined single WN stars(e.g.#41).From this group,#9was observed spectroscopically and confirmed as a WN star–see Sect.4.Numbers51and54lie in theSchild etgiant H ii region Deh137while#10is another WRin the nuclear area of NGC300(Fig.1).25WR candidates have aλ4684excessmag.It is possible that some of these stars areline WR/Of stars.Except in one case,they arebright,with M4781<−6,as expected for a WRsingle late WN star,or an extreme O-typestrong He iiλ4686emission(i.e.an Of star).was independently found by Bresolin et al.classified as a WN11star.Ourλ4684excess ofis in close agreement with the spectroscopy ofal.(2002b).This indicates that a He ii excess of∼can be reliably measured with thishence also that Of stars and very late WN starsbe detected.Most candidates from the presentprobably WR rather than Of since,since byHe iiλ4686equivalent widths of the latter do not∼12˚A(Bohannan&Crowther1999).pleteness,Surface Density and the WC/WNRatioIn addition to verifying the likely-hood of whether ourcandidates are genuine WR stars,how complete is oursurvey?The continuumfilter centred at4781˚A lies mid-way between the usual Smith(1968)WR narrow-band b(4270˚A)and v(5160˚A)filters.Typical intrinsic coloursof WC and WNE stars are(b−v)0∼−0.2±0.1,such thatone would expect b−v∼−0.1±0.1mag for WR starsin NGC300,given typical extinctions of E(b−v)∼0.1mag(equivalent to E(B−V)=0.12mag).Consequently,continuumfilter measurements should correspond closely(within∼0.1mag)to b or v magnitudes.i.e.a complete-ness to v=23.7mag will be equivalent to M v∼−3.2mag.According to Table28from van der Hucht(2001),94%of the227known Galactic WR stars are brighterthan M v=−3.5mag,so our census of the central regionof NGC300should be reasonably complete,except thosesuffering from high visual extinction.In Fig.6we plot the WR surface density versus thegalactocentric distance.The WR distribution in the nu-clear region is particularly interesting.While the very cen-tre is apparently free of WR stars wefind a sharp in-crease of the surface density at a galactocentric distance ofabout0.4kpc.Further outside it dropsfirst to a minimumat around1kpc and rises again outwards.Qualitatively,a similar behaviour is observed in our galaxy(van derHucht2001)but in NGC300the drop is much shallower,about−0.3dex between0.5and2kpc instead of−1.5inthe galaxy.The highest surface density in NGC300oc-curs in the Deh137H ii region,alias OB association AS102which contains15WR stars in an area that spans0.3×0.3kpc implying a WR density of about150WRstars/kpc2.Massey&Johnson(1998)compare WR sur-face densities of other Local Group galaxies,such that WRsurface densities range from1/kpc2in the SMC,to2inthe LMC and∼4in M33.the nucleus.Fig.7.The relative number of WC and WN stars in LocalGroup galaxies versus metallicity(Massey2003),supple-mented by NGC300(solid)from the present work.TheWC/WN ratio for IC10is probably an overestimate.As discussed in the introduction,the WC/WN ratio forNGC300prior to the present study,i.e.∼2,was unusuallyhigh relative to more complete surveys of Local Groupgalaxies.Ideally,one might use additional narrow bandfilters at(C iv)λλ5801-12plus a nearby continuum regionto discriminate between WN and WC stars,as recentlycarried out by Royer et al.(2001)for IC10.In the absenceof suchfilters,we have been able to infer likely WN orWC subtypes for those stars without spectroscopy frominspection of Fig.5.We suggest that at least13WR starsin NGC300are WC stars,i.e.12for which spectroscopyis available,plus#5.A further3may host WC binaries,8Schild et al.:WR stars in NGC300Fig.8.Low dispersion FORS2spectroscopy of four previously identified WR stars in NGC300.Fig.9.Low dispersion FORS2spectroscopy of four newly identified WR stars in NGC 300.namely #12,#31,#33,such that the WC/WN ratio for the central regions of NGC 300is ≥12/46=0.3,or more likely ∼15/43=0.35.This falls close to that observed in comparable regions of M33,according to Massey (2003),as illustrated in Fig.7.4.Spectroscopy of Wolf-Rayet stars 4.1.Previously identified WR starsWe present flux calibrated low dispersion FORS2spec-troscopy of four previously observed NGC 300WC stars in Fig.8.These datasets are superior to previous 4m ob-servations,and so allow us to obtain revised spectral types,using the scheme of Crowther et al.(1998).We revise the original classification for #29,alias WR3(Schild &Testor 1991),from WC4–5to WC5since our dataset reveals weak C iii λ5696,with W λ(λ5696)/W λ(λλ5801-12)∼0.1and O iii-v λ5592weak/absent.This star is probably single,given that its emission line spectrum is comparable in strength (e.g.W λ(λλ5801-12)∼800˚A )to apparently single Galactic and LMC WCE stars.A firm classification is possible for #40,alias WR6(Schild &Testor 1992)for which we also assign WC5(updated from WC4–6)since C iii λ5696is again present,with a similar strength to O iii-v λ5592and W λ(λ5696)/W λ(λλ5801-12)∼0.1.#40is almost certainly multiple,since W λ(λ5801-12)∼230˚A .Testor &Schild (1993)previously assigned a WC5spectral type for #24(their WR11),which we revise to WC4,given that W λ(λ5696)/W λ(λλ5801-12)≤0.05.C iv λ5801–12is again unusually weak,with W λ(λ5801-12)∼200˚A indicating either binarity or a line-of-sight companion.The spectral appearance of #48,alias WR13(Testor &Schild 1993),alias IV-3(Breysacher et al.1997)is in marked contrast to the other WCE stars whose spec-troscopy is presented here,with much broader lines –FWHM(λλ5801-12)∼86˚A versus 36–47˚A .Breysacher et al.(1997)interpreted this large FWHM as an indication of a (rare)WO subtype,which possess strong O vi λλ3811-34emission lines,and assigned a WO4spectral type ,whilst our spectroscopy reveals that O vi is weak/absent in #48.Since C iii λ5696is also absent,a WC4spectral type is appropriate.Willis et al.(1992)discuss problems with us-Schild et al.:WR stars in NGC 3009parison between FWHM(C iv λλ5801-12),in ˚A ,and galactocentric distance for early WC stars in NGC 300(solid)and M 33(open,Willis et al.1992),as a fraction of the Holmberg radius.ing FWHM as indicators of spectral type for WC stars in M33.We suspect that #48is single since W λ(λλ5801-12)∼1500˚A .4.2.Newly identified WR starsWe present optical spectroscopy of four newly identifiedNGC 300WR stars in Fig.9,two WN and two WC stars.The WC stars #1and #22are rather similar.They have lines widths which are higher than #48,with FWHM(λλ5801–12)∼91-100˚A ,and similar line strengths,W λ(λλ5801-12)∼500˚A .WC4subtypes are appropriate forboth stars since there is no evidence of C iii λ5696,with O vi λλ3811-34weak.Both stars are probably binaries.The two WN stars #9and #30are early-type,since N v λλ4603-20is prominent,with N iii λλ4634–41weak (#9)or absent (#30).Following the classification scheme of Smith et al.(1998)one obtains a spectral type of WN4–5for #9(N iv λ4058∼N v λλ4603-20),and WN3–4for #30(the region around N iv λ4058is noisy).One cannot use the (primary)He i-ii classification diagnostics for these stars due to the strong nebular contamination,and weak He i λ5876emission.4.3.WC line widthWillis et al.(1992)identified a correlation between line width (FWHM C iv λλ5801-12)and galactocentric dis-tance for WCE stars in M33in the sense that stars at larger galactocentric distance (i.e.lower metallicity)had broader lines than those in the nucleus (with higher metal-licity).We present our measurements for 6WC stars in NGC 300in Fig.10,supplemented by data from Schild&Testor (1991,1992)for #14(WR1)and #47(WR5),and including data from Willis et al.(1992)and refer-ences therein for M33.For NGC 300,there is a very large scatter in FWHM at ρ/ρ0∼0.4,arguing against a tight correlation in general,although the present results are in favour of a deficit of broad-lined WC stars in the nucleus.Nevertheless,firm conclusions await spectroscopy of larger numbers of WC stars in both galaxies.5.Analysis of WC starsAs discussed above in Sect.4,two WC stars in NGC 300are apparently single,and have sufficient quality observa-tions for detailed analyses to be carried out.Ultimately,large numbers of WR stars need to be studied in galax-ies spanning a wide range metallicities to place adequate constraints on evolutionary models.Recent studies,us-ing identical techniques,have been presented for single WC stars in the Milky Way (e.g.Dessart et al.2000),LMC (Crowther et al.2002),M31(Smartt et al.2001)and M33(Abbott et al.2003).We now proceed to study #29(WC5),located close to the nucleus of NGC 300with a probable metallicity of ∼Z ⊙according to 104O /H =7.5−5.3ρ/ρ0(Deharveng et al.1988),and #48(WC4),located at ρ/ρ0=0.43with ∼0.6Z ⊙.5.1.TechniqueWe employ the non-LTE code of Hillier &Miller (1998),which iteratively solves the transfer equation in the co-moving frame subject to statistical and radiative equilib-ria in an expanding,spherically symmetric and steady-state atmosphere.Specific details of the (extremely com-plex)He,C,O,Ne,Si,P,S,Ar,Fe model atoms used for our quantitative analysis are provided in Crowther et al.(2002).We assume that the wind is clumped with a volume filling factor,f ∼0.1.We parameterise the filling factor so that it approaches unity at small velocities.As usual,a series of models were calculated in which stellar parameters (T ∗,log L/L ⊙,v ∞˙M/√10Schild et al.:WR stars in NGC300 The wind ionization balance is ideally selected onthe basis of isolated optical lines from adjacent ioniza-tion stages of carbon and/or helium,e.g.He iλ5876/He iiλ5412.In practice,this was difficult to achieve because ofthe severe blending,so our derived temperature should betreated as approximate.Detection of He iλ5876appearsto be robust in#29,due to its relatively low wind velocity,whilst there is an ambiguity in this feature for#48,sinceit is possible that the observed feature represents the elec-tron scattering wing of C iv for which we have adoptedthefilling factor,f.We also simultaneously match C iiiλ6740and C ivλ5801,the former selected in preferenceto C iiiλ5696which is very sensitive to the exact ion-ization structure(Hillier&Miller1998;Crowther et al.2002).The standard C/He diagnostic,He iiλ5412/C ivλ5471,was used since their relative strengths are insen-sitive to temperature and mass-loss.Oxygen abundanceswere difficult to constrain,since we relied solely on O iii-vλ5592(Crowther et al.2002).Consequently,caution isadvised when comparing the present O/C determinationswith(Galactic and LMC)WC stars for which the superiorλλ2800–3100diagnostics are available.5.2.Results for NGC300#29(WR3,WC5)Our FORS2spectroscopic data of#29is shown in theupper panel of Fig.11.Overall,the spectrum is reason-ably well reproduced by our modelfit,except that the C iiiλ5696profile is strongly underestimated,whilst C iv λλ5801–12is40%too weak.From our recent experienceit is difficult to simultaneously reproduce the strength of C iiiλ5696feature together with other diagnostics in early WC stars.Wefind T∗∼100kK,log(L/L⊙)=5.5, v∞∼2700km s−1,and˙M∼10−4.6M⊙yr−1.We estimate C/He∼0.08by number from He iiλ5412/C ivλ5471.Theweak O iii-vλ5592feature suggests a low oxygen content of O/He≤0.05by number.5.3.Results for NGC300#48(WR13,WC4)We compare our spectroscopy of#48with our synthetic model in the lower panel of Fig.11.Again,reasonably good agreement is achieved,although the broad emis-sion lines of#48hinder detailed comparisons.The blend comprising principally C iiiλ4647–51,C ivλ4660and He iiλ4686is rather too strong in the synthetic model. Our derived parameters are T∗∼95kK,log(L/L⊙)=5.2, v∞∼3750km s−1,and˙M∼10−4.8M⊙yr−1.We esti-mate C/He∼0.5by number,although this ratio should be treated with caution,given the poor quality of the obser-vations–recall#48has the faintest continuum(v=23.5 mag)of all58WR candidates in NGC300.The O iii-v λ5592feature suggests a high oxygen content of O/He≥0.1 by number.Fig.11.Upper panel:Synthetic spectralfit(dotted)to FORS2observations(solid)of NGC300#29(WR3, WC5),de-reddened by E B−V=0.10mag.Close up views of the C iii-iv-He iiλλ4650–4686and C ivλλ5801-12re-gions are indicated.Lower panel:Same for NGC300#48 (WR13,WC4)for a reddening of E B−V=0.15mag.parison with WC stars in the Galaxy and LMC Crowther et al.(2002)recently contrasted the properties of Solar neighbourhood and LMC WC stars,to which we can now add NGC300#29and#48.The upper panel in Fig.12compares(nuclear)luminosities and(C+O)/He abundances for WC stars in the three galaxies.Nuclear luminosities are derived by taking into account the wind blanketing effects discussed by Heger&Langer(1996).In contrast with the results of Heger&Langer,who indicated revisions of up to0.3dex in luminosity,revised mass-loss rates due to clumping yield rather small corrections,typ-ically0.05dex.Current masses of16.3and11.6M⊙are determined for#29and#48,respectively.Crowther et al. (2002)found that low metallicity(LMC)WC stars possess higher luminosities than those at high metallicity(Milky Way).This can be explained since one would require a higher initial mass cut-off,for a massive star to progress through to the WC stage at low metallicity,because of re-duced mass-loss rates during the main-sequence and post-main sequence evolution.The small sample of NGC300。

雷达与蝙蝠关系英语作文Radar and bats, you know, they have a fascinating connection. It's like a real-life version of "imitation is the sincerest form of flattery." But seriously, bats have been using echolocation for centuries, navigating in the dark and hunting for food. And guess what? Radar is a bit like a man-made version of that.Radar, or radio detection and ranging, sends out radio waves and waits for them to bounce back. Just like bats emit sound waves and listen for the echo. But with radar, we can detect objects at great distances and even track their movement. It's incredible how nature inspired this technology.Bats are amazing creatures, flying around in the dead of night, not bumping into anything. They use their echolocation skills to create a mental picture of their surroundings. And we, with all our technology, were able to mimic that and use it for all sorts of things, from weatherforecasting to air traffic control.So, there you have it. Radar and bats: two totally different things, but linked in an interesting way. It's just one example of how nature can provide us with inspiration and ideas that we can then turn into useful tools. And that's pretty cool, don't you think?。

巨大质量恒星列表维基百科，自由的百科全书这是一份有关巨大质量恒星的列表，依太阳质量的多寡排列。

(1 太阳质量= 太阳的质量而不是太阳系的质量)。

恒星质量是恒星最重要的一个因素。

与化学成分的组合，质量能确定一颗恒星的光度，它实际上的大小和它最后的命运。

列在表上的恒星，由于它们的质量非常巨大，到最后大多都会爆发成超新星甚至是极超新星，然后形成黑洞。

目录[隐藏]∙ 1 不确定性和警告∙ 2 恒星演化∙ 3 巨大质量的恒星列表∙ 4 黑洞∙ 5 爱丁顿光度极限∙ 6 参见∙7 外部链接∙8 参考[编辑]不确定性和警告表中所列出的恒星质量都是从理论上推测的，依据的是恒星很难测定的温度和绝对星等。

所有列出的质量都是不确定的：因为都已经将目前的理论和测量技术发挥到了极限，而无论是理论或观测，只要有一个错误，或是两者都错，结果就会不正确。

例如，仙王座VV变星，依据这颗恒星特有的产物审查，质量就可能是太阳的25至40倍，或是100倍。

大质量恒星是很罕见的，表中列出的恒星距离都在数千光年以上，它们孤单的存在着，使距离很难测量。

除了很远之外，这些质量极端巨大的恒星似乎都被喷发出来的气体云气包围着；周围的气体会遮蔽恒星的光度，使原本就很难测量的光度和温度更难测量，并且也使测量他们内部化学成分变成更加复杂的问题。

另一方面，云气的遮蔽也阻碍了观测，而难以确认是一颗大质量恒星，还是多星系统。

下表中必然有一定数量的恒星也许是轨道极近的联星，每一颗恒星的质量必然也不小，但不一定是巨大的质量；这些系统仍然可以二选一的是一颗或多颗大质量恒星，或有许多质量不大的伴星。

因此表中许多恒星的质量经常是目前被研究的主题，质量经常被重测，而且经常被校正。

表中列出的质量中，最可靠的是NGC 3603-A1和WR20a+b，它们是从轨道测量中得到的。

NGC 3603-A1和WR20a+b两者都是联星系统（两颗恒星沿着轨道互绕），运用开普勒行星运动定律，经由研究它们的轨道运动可以测量出两颗恒星各自的质量。

烟台2024年08版小学三年级下册英语第2单元期末试卷考试时间：80分钟（总分:140）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题共100分)1. 听力题：A ______ is an animal that can swim and fly.2. 填空题：I can use my ________ (玩具名称) to create art.3. 填空题：I love to decorate my _________ (玩具房间) with colorful items.4. 选择题：What is the largest animal in the ocean?A. SharkB. WhaleC. DolphinD. Octopus答案: B5. 听力题：Astronomers use spectroscopes to analyze the ______ of light from stars.6. 听力题：She is ___ (laughing/sobbing) at the movie.7. 听力题：The ______ moves slowly and has a shell.8. 填空题：The _______ (The Age of Exploration) opened new lands for colonization and trade.9. 选择题：What is the capital city of India?A. MumbaiB. New DelhiC. KolkataD. Bangalore10. 选择题：What is the capital of Panama?a. Panama Cityb. Colónc. Davidd. Santiago答案:a11. 填空题：The ______ (猪) likes to roll in the mud.12. 选择题：What is the opposite of "clean"?A. DirtyB. NeatC. TidyD. Spotless13. 填空题：The _______ (Mount Rushmore) features the faces of four US presidents.14. 填空题：My dad is a _____ (工程师) involved in technical projects.15. 填空题：We visit the ______ (农场) to learn about agriculture.16. 填空题：A ____(desalinization) plant turns seawater into freshwater.17. 选择题：Which animal is known as man's best friend?A. CatB. DogC. BirdD. Fish答案:B18. 听力题：A base feels slippery and can turn __________ paper blue.19. 选择题：What do you call the main character in a play?A. ActorB. ProtagonistC. DirectorD. Supporting character答案:B20. 听力填空题：I believe in the power of friendship. Friends support each other and share good times. I feel lucky to have a friend like __________ who always makes me smile.21. 填空题：I enjoy riding my ______ around the neighborhood.22. 填空题：The __________ (历史的探讨) encourages inquiry.23. 选择题：What is the capital of Nigeria?A. LagosB. AbujaC. KanoD. Port Harcourt答案:B24. 填空题：Birds can ______ (飞) in the sky.25. 选择题：What do we call a group of stars that form a pattern?A. GalaxyB. ConstellationC. NebulaD. Asteroid26. 听力题：The ancient Greeks held the first Olympic Games in ________.27. 填空题：The __________ (历史的共享) enriches culture.28. 选择题：What is the color of grass?A. BlueB. YellowC. GreenD. Brown答案:C29. 选择题：What is the opposite of old?A. NewB. YoungC. RecentD. Fresh答案:A30. 填空题：I love to ______ (分享) my toys.31. 选择题：What is the name of the main character in "Peter Pan"?A. TinkerbellB. Captain HookC. WendyD. Peter答案:D32. 听力题：I have a new ___. (computer)33. 填空题：The best time of the year is ______ (假期). I can travel and visit my ______ (亲戚). We have so much fun!34. 选择题：What is the term for the distance light travels in one year?A. Light-YearB. Astronomical UnitC. ParsecsD. Cosmic Yard35. 选择题：What do you call a plant that grows in water?A. CactusB. FernC. Aquatic plantD. Tree答案:C36. 选择题：What do you call the process of making cheese?A. FermentationB. CurdlingC. PasteurizationD. Distillation答案:B37. 选择题：How many hours are there in a day?A. 24B. 12C. 36D. 2038. 听力题：The blanket is very ___ (soft/hard).39. 填空题：The _____ (乌龟) basks in the sun on a rock.40. 听力题：A ______ is a large area of land that rises above sea level.41. 听力题：I see a _____ (cat/dog) in the garden.42. 填空题：I enjoy ________ (听故事) before bed.43. 填空题：She is an _____ (科学家) who researches space.44. 选择题：What instrument do you play to make music?A. PencilB. GuitarC. BookD. Chair答案:B45. 选择题：How many points is a touchdown worth in American football?A. 3B. 5C. 6D. 7答案: C46. 选择题：What do you call the outer layer of the Earth?A. CrustB. MantleC. CoreD. Lithosphere答案:A47. 听力题：Chlorine is commonly used as a _____ to disinfect water.48. 选择题：What do we call a piece of fruit that is often orange?A. AppleB. BananaC. OrangeD. Grape49. 填空题：The _____ (蛇) can be found in many different habitats.50. 填空题：I can ______ (做) healthy choices.51. 选择题：What do we call a person who studies the effects of pollution on ecosystems?A. EcologistB. Environmental ScientistC. BiologistD. Chemist答案: A52. 选择题：What is the name of the largest rainforest in the world?A. Amazon RainforestB. Congo RainforestC. TaigaD. Temperate Rainforest53. 听力题：A __________ is a famous site for outdoor festivals.She is _______ (climbing) the stairs.55. 选择题：What is the name of the longest river in South America?A. AmazonB. NileC. MississippiD. Yangtze答案：A56. 填空题：I have a classmate who is really __________ (聪明).57. 听力题：The ability to conduct electricity varies among _____.58. 选择题：What is the capital of Estonia?A. TallinnB. TartuC. NarvaD. Pärnu答案:A59. 填空题：The chef is renowned for his _____ (创新菜肴).60. 填空题：My cousin is a __________ (小提琴演奏者).61. 填空题：The __________ (世界的变化) reflects the impact of human actions.62. 填空题：The _____ (pinecone) falls from pine trees.63. 选择题：What do you call a written work that tells a story?A. PoemB. BookC. ArticleD. Essay答案: BThe giraffe has a very long _________ (脖子).65. 听力题：My friend is a ______. He enjoys building models.66. 填空题:My favorite fruit is ________ because it is sweet.67. 听力题：An acid-base reaction produces ______.68. 选择题：What is the name of the famous clock tower in London?A. Big BenB. Eiffel TowerC. ColosseumD. Statue of Liberty答案:A69. 听力题：I see a _____ bird in the tree. (red/quick/small)70. 听力题：My brother is learning to play the ____ (guitar).71. 听力题：There are many stars in the _____ (sky/sea).72. 选择题：What is 8 x 2?A. 14B. 16C. 18D. 20答案:B73. 听力题：Many species of birds migrate to warmer __________ in winter.74. 听力题：My friend plays on the school ____ (football) team.75. 填空题：My favorite dish is _______ (披萨).The _____ (小马) enjoys running through the fields. 小马喜欢在田野中奔跑。