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GAIA Galaxy Survey a multi-colour galaxy survey with GAIA

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a

rXiv:astro-ph/0110144v2 27 Oct 2001J.Phys.IVFrance1(2008)Pr1-1

c󰀃EDPSciences,LesUlis

GAIAGalaxySurvey:amulti-colourgalaxysurveywithGAIA

MattiaVaccari1

1DipartimentodiAstronomiaandCISAS“GiuseppeColombo”,Universit`adiPadova,Vicolodell’Osservatorio2,I-35122,Padova,Italy(e-mail:vaccari@pd.astro.it)

Abstract

TheperformanceexpectedfromagalaxysurveytobecarriedoutwithGAIA,theGAIAGalaxySurvey,isoutlined.Fromastatisticalmodelofgalaxynumberdensity,sizeandsurfacebrightnessdistribution,andfromdetailednumericalsimulationsbasedonrealimages,itisconservativelyestimatedthatGAIAwouldbeabletodetectandobserveabout3milliongalaxiesbrighterthanV≃17andtoprovidemulti-colourandmulti-epochbroad-bandphotometryofthesewithanend-of-missionangularresolutionof≃0.35arcsecandaphotometricaccuracyofsimeq0.2mag/arcsec2atµV=20mag/arcsec2.Thesubstantialscientificcaseforperformingsuchasurveyandtheadditionaleffortsrequiredintermsofmissionpreparation,operationsandtelemetryarealsodiscussed.

1INTRODUCTION

Sincetheverybeginningofthefeasibilitystudies,theGAIAmissiondesignwasdrivenby

theneedofdeterminingthepositionandthebrightnessofhugenumbersofstarswiththe

uttermostaccuracy.DuringtheConceptandTechnologtStudycompletedinJuly2000(see[9]

and[2]),however,itclearlyemergedthatsuchastar-drivenmissioncouldalsoprovide,several

socalledby-productswhichwouldsubstantiallyenrichitsalreadyimpressivescientificyield.In

particular,itwasrealizedthatthescientificcaseforGAIAimagingofhigh-surfacebrightness

skyregionssuchasthecentralregionsofnearbygalaxieswasdramatic.

Theissuesconnectedwiththisopportunityhavebeenaddressedinacertaindetailina

numberofstudies(see[10],[11],[8]and[12]),andsuchobservationswereincludedinthemission

baselinedesignasdescribedin[2]underthenameofGAIAGalaxySurvey.Inthispaperthe

currentideasontheimplementationofsuchasurveyandontheexpectedperformanceare

presented.

InSection2theoverallstrategyforgalaxydetectionandobservationwithGAIAisoutlined.

InSections3and4thedetectionandobservation,respectively,arediscussedingreaterdetail

andresultsofdedicatedstudiesarepresented.InSection5thesubstantialscientificcasefor

performingsuchasurveyisbrieflysketched,andinSection6theadditionaleffortsrequiredin

termsofmissionpreparation,operationsandtelemetryarediscussed.

Onlythemeasurementofrelativelylargeenhancementsofthesurfacebrightnesswithre-

specttotheskybackgroundisdiscussedhere,althoughitisbelievedthattherathersimilar

issueoftheobservationofGalacticNebulaecouldbeaddressedalongthesamelines.The

measurementofthesurfacebrightnessoftheskybackground,instead,callsforasubstantially

differentapproach,asdescribedin[6].Pr1-2JOURNALDEPHYSIQUEIV

2GALAXYDETECTIONANDOBSERVATIONWITHGAIA

Duringitsscientificoperations,theGAIAsatellitewillcontinuouslyspinaboutitssymmetry

axis,andthechargescontainedintheCCDpixelswillcorrespondinglybeshiftedalong-scanto

integratetheimageforalongerexposuretime,atechniqueknownasTime-DelayIntegration

(TDI).InordertolimittheCCDs’readingfrequencyandthecorrespondingreadnoiseand

telemetryrate,adedicatedCCDreadoutprocesswasdevised,consistingindetectingobjects

astheyenterthefieldofview,determiningtheirposition,magnitudeandsignal-to-noisera-

tio,and,ifthelatterexceedsacertainlimit,collectingdatafromregionsaroundsuchstars

only.Whilethisapproachwasthesubjectofdetailedstudiesasfaraspoint-likeobjectswere

concerned,leadingtothedefinitionoftheAstrotelescopes’focalplaneandtheCCDbinning

strategydescribede.g.in[5],theprocessofgalaxydetectionandobservationcalledfora

ratherdifferentapproachinordertoidentifyandmeasurefaintsurfacebrightnessvariations.

Asfirstsuggestedin[3],galaxiescouldbedetectedintheAstroSkyMapper(ASM)asan

averagesurfacebrightnesssignificantlyinexcessoverthelocalskybackgroundandobserved

indifferentcoloursintheBroadBandPhotometer(BBP).Thisobservingstrategypreventing

fromoptimallyobservingstarswheneveragalaxyisbeingobserved(whichishoweverlessthan

1%percentofthetime),itcouldbeimplementedinoneofthetwoAstrosonly.

Inordertofollowthisgeneralidea,onehadtooptimize:

•thesizeoftheareasoverwhichtheaveragesurfacebrightnessandthelocalskyback-

groundvaluesarecomputed.Itispresentlyenvisagedtodeterminetheformerthrough

trimmedmedianfilteringofASM1samplesof2×2pixelsandthelatteroverafew

degreesofscanwiththesamealgorithm.However,theexactmethodusedtodetermine

thelocalskybackgroundisnotofinterestforourpurposes,sincethereadnoiseisbyfar

thedominantnoisesource.

•thevalueforthedetectionareaandS/Nlimitsothatusefuldataaretransmittedto

thegroundwithoutbeingswampedinlessinterestingdatafromtheMilkyWayorthe

zodiacallight.Thelargerthedetectionarea,thefainterthedetectionlimitcanbefor

objectsofconstantsurfacebrightness,iftheerrorontheskybackgroundisnegligible.

Ontheotherhand,thedetectionareashouldbesmallenoughthatalargenumberof

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高三宇宙奥秘英语阅读理解30题

高三宇宙奥秘英语阅读理解30题

高三宇宙奥秘英语阅读理解30题

1

Black holes are one of the most fascinating and mysterious

phenomena in the universe. A black hole is formed when a massive star

collapses at the end of its life. The gravitational pull of a black hole is so

strong that nothing, not even light, can escape from it.

The formation of a black hole begins with the collapse of a massive

star. As the star runs out of fuel, it can no longer support its own weight

and begins to collapse. The collapse continues until the star reaches a

critical density, at which point it becomes a black hole.

Black holes have several unique characteristics. One of the most

notable is their event horizon, which is the boundary beyond which nothing

can escape. Another characteristic is their intense gravitational field, which

can distort the space and time around them.

广东省湛江市第四中学2023-2024学年高考英语押题试卷含解析

广东省湛江市第四中学2023-2024学年高考英语押题试卷含解析

广东省湛江市第四中学2023-2024学年高考英语押题试卷

考生请注意：

1．答题前请将考场、试室号、座位号、考生号、姓名写在试卷密封线内，不得在试卷上作任何标记。

2．第一部分选择题每小题选出答案后，需将答案写在试卷指定的括号内，第二部分非选择题答案写在试卷题目指定的位置上。

3．考生必须保证答题卡的整洁。考试结束后，请将本试卷和答题卡一并交回。

第一部分 （共20小题，每小题1.5分，满分30分）

1．The coat I bought yesterday is not expensive at all. As a matter of fact, I would gladly have paid ______ for it.

A．as much twice B．much as twice

C．as twice much D．twice as much

2．—Oh, Hannah just told me that she was unable to translate the report into English.

—________She once spent 10 years living in London.

A．Guess what B．Why not C．So what D．How come

3．Peterson, a great archaeologist, said: “Archaeologists have been extremely patient because we were led to believe that

the ministry was ________ this problem, but we feel that we can't wait any longer.”

A．looking out B．bringing out C．carrying out D．sorting out

Mercury is the closest planet to the Sun and the eighth largest

Mercury is the closest planet to the Sun and the eighth largest

Mercury is the closest planet to the Sun and the eighth largest. Mercury

is slightly smaller in diameter than the moons

Ganymede and

Titan but more

than twice as massive.

orbit: 57,910,000 km (0.38 AU) from Sun

diameter: 4,880 km

mass: 3.30e23 kg

In Roman mythology Mercury is the god of commerce, travel and thievery,

the Roman counterpart of the Greek god Hermes, the messenger of the Gods.

The planet probably received this name because it moves so quickly across

the sky.

Mercury has been known since at least the time of the Sumerians (3rd

millennium BC). It was sometimes given separate names for its apparitions

as a morning star and as an evening star.

水星是最接近地球到太阳和第八大。水星是略小，直径比卫星木卫三和土卫六，但两倍多大规模。

轨道： 57,910,000公里（ 0.38 1.00 ）由Sun

直径： 4880公里

质量： 3.30e23公斤

在罗马神话中水星是商业之神，旅行和偷窃，罗马对应的希腊神赫尔墨斯的信使神。该行星可能收到这个名字，因为它动作如此迅速地划过天空。

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2019-2020学年河源市紫金县中山高级中学高三英语三模试题及答案

2019-2020学年河源市紫金县中山高级中学高三英语三模试题及答案

第一部分 阅读（共两节，满分40分）

第一节（共15小题；每小题2分，满分30分）

阅读下列短文，从每题所给的A、B、C、D四个选项中选出最佳选项

A

It’s the time of year when we start hiking. As you pack, remember to bring your smartphone. Whether you’re

going on a short walk or a long trip, there are a handful of apps that can help.

MapMyHike

This app tracks where you're hiking so you have a mapof your route at the end of the hike. It can also track

other fitness information like the distance traveled, speed, pace, and even calories burned. You can save the data

for your hike, so you can always access the route you look as well as track improvements to your workout.

GaiaGPS

You don't always have cellphone service when hiking, but you always want to know where you are. The

GaiaGPS app provides that information. Download maps of different parts of the world, and access the GaiaGPS