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Is dit moontlik vir 'n amateur-sterrekundige om 'n transoplanettransito visueel waar te neem deur die verandering van die helderheid van die ster via waarnemings oor tyd heen, of is die variasie van die helderheid te onbeduidend om gesien te word?
Ek het 'n omvang van 70 mm, maar geen astrofotografie-toerusting of sagteware om data te vergelyk nie. My vraag gaan oor die feit dat ons die helderheidsvariasie mettertyd regtig waarneem soos ons dit op veranderlike sterre sien.
Natuurlik is deurgange waarneembaar met teleskope; dit is die belangrikste metode om eksoplanete op te spoor, sien Wikipedia se Metodes om eksoplanete op te spoor; Transito-fotometrie.
Ongelukkig kan hulle dit net met kragtige toerusting doen. Die grootteverandering wissel van 0 tot 0,03. Dit kan byvoorbeeld nie met 'n 700 mm-teleskoop gesien word nie. Dus is die 70 mm-teleskoop sonder toerusting nie kragtig genoeg nie. Met die teleskoop kan u ongeveer 0,3 grootte verander.
Kan eksoplanet-transisies visueel met amateur-toerusting opgespoor word? Nee. Die grootteverandering is te klein.
Met behoorlike toerusting kan deurgange opgespoor word deur amateurs. Byvoorbeeld, lede van die American Association of Variable Star Observers (AAVSO) versamel data volgens die bladsy Exoplanet Section.
AANKONDIGING: Met die bekendstelling van TESS (Transiting Exoplanet Survey Satellite) sal opvolggrondwaarnemings 'n belangrike deel van die TESS-proses wees om kandidaat-eksoplanete te bevestig. In die besonder sal sulke waarnemings help om vals positiewe en ware transoplanet-transitte te onderskei. Die AAVSO kondig met genoeë aan dat hy 'n program opgestel het wat die deelname van sy lede aan hierdie proses sal vergemaklik.
Alhoewel ek klein in deursnee is, vermoed ek dat 'n teleskoop met 'n deursnee van 70 mm nie heeltemal buite die moontlikheid val nie. Ek vermoed die grootste verskil is dat mense wat die kameras of ander detektors kan bekostig om die metings te neem, ook meer geld aan 'n hoër teleskoop spandeer.
Amateurtoerusting is goed genoeg. Maar jy kan dit nie met 'n blote oog opspoor nie.
Die vloedverandering vir 'n verbygaande eksoplanet in transito is ongeveer 1% ... hoogstens 2% vir die groter eksoplanete - en dit is 'n geleidelike verandering. Dit is 'n verandering wat u nie met die blote oog raaksien nie, maar dit benodig fotografiese toerusting om 'n reeks beelde te skep wat die helderheid van alle sigbare sterre kan ontleed om die variasie in die een interessante op te spoor.
Met 'n gepaste kamera en stabiele montering is u 70mm-teleskoop voldoende om hierdie ligveranderings gedurende 'n paar uur in 'n reeks matige langblootstellingsbeelde op te spoor (blootstellingstyd 'n paar minute elk).
Baie van die professionele grondopname van eksoplanete gebruik nie veel groter teleskope nie (sien byvoorbeeld die HATnet-program). Die verskil is meestal meer in die graad van outomatisering, die sensitiwiteit van fotografiese toerusting en die outomatisering van die verwerkingspyplyn.
Kan ons visuele waarnemings van eksoplaneet met amateurteleskope waarneem? - Sterrekunde
Inleiding
Hierdie handleiding handel oor hoe u ekso-planeet-transitte kan beeld. Beginners sal dit hopelik nuttig vind om hul vaardighede te ontwikkel, en ervare beeldhouers kan ook nuttige wenke kry. Die tutoriaal kan ook help met die ontwikkeling van 'n konsekwente metode wat deur bydraers tot die afdeling toegepas word.
Neem kennis dat bedieners wat aan die ARIEL ExoClock pro-am-projek wil deelneem, besonderhede wil hersien by https://britastro.org/node/20102.
Die totale aantal eksoplanete wat gedurende die afgelope twintig jaar ontdek is, het dramaties gestyg (Figuur 1). Soos gesien kan word, is die meerderheid hiervan met die deurvoermetode ontdek.
Transitte vind plaas wanneer die planeet vanuit ons gesigspunt die gesig van die ster kruis, wat 'n klein maar meetbare duik in die helderheid van die ster veroorsaak. Die belangrikste punte in 'n deurvoer wat nodig is om tydsberekening te meet, word in Figuur 2 getoon. Ingang begin vanaf t1, en teen t2 is die planeet vanuit ons perspektief volledig binne die stertskyf. Dit word omgekeer vir uitgang by t3-t4. Die kromme in die transito word veroorsaak deur die verandering van die helderheid van die ster vanaf sy middelpunt na sy ledemaat, die ledemaat verdonker, en dit verskil vir elke ster en filterkleur wat gebruik word.
Transitte van eksoplaneet word hier in meer besonderhede deur Paul Anthony Wilson verduidelik.
Waarom eksoplanete waarneem?
Met soveel planete ontdek is gedetailleerde opvolgwaarnemings van slegs 'n baie klein persentasie hiervan moontlik met professionele teleskope. Amateurwaarnemers kan dus 'n daadwerklike bydrae lewer tot eksoplanetnavorsing deur sulke waarnemings te maak van bekende ekso-planete wat deurloop.
Die gereelde meting van deurgangstye kan gebruik word om die aanwesigheid van ander onsigbare metgeselle planete af te lei deur middel van variasies (TTV's). Metings oor lang tydperke kan klein veranderinge in 'n wentelperiode van die planete openbaar, wat te wyte is aan 'n baanbreking of selfs verval, aangesien planete 'n stadige spiraal in hul gasheer volg. Hierdie waarnemings bied dus inligting oor die vorming en dinamiese geskiedenis van die planetêre stelsels.
Monitering van gasheersterre van eksoplanet is ook belangrik. Baie gasheersterre is aktief en die grootte van die ster kan die rotasietydperk as gevolg van sterrekolle laat blyk. Dit het belangrike gevolge vir die lang dinamiese stabiliteit van die planete en kan 'n aanduiding wees van interaksie tussen die planeet en die ster vir baie kort tydperk massiewe planete. Verder kan hierdie metings steriele aktiwiteitsiklusse openbaar, nie anders as die twee-jarige siklus van die Son wat 'n impak het op die presisie-transmissiespektroskopie wat gebruik word om die atmosfeer van die planeet te bepaal nie. Daarom kan kennis van hierdie siklusse gebruik word om die tydsberekening van waarnemings op groot grond- of ruimte-gebaseerde teleskope in te lig.
Bogenoemde is goeie wetenskaplike redes om transito-exoplanete te waarneem, maar vergeet waarskynlik nie die belangrikste rede nie; dit is die plesier om 'n ander wêreld te aanskou, want dit wentel om sy eie ster om nie die kans te noem om jouself en ons toerusting na sy perke.
Watter toerusting word benodig?
Byna enige instrument, wat gewoonlik vir amateurs beskikbaar is, kan gebruik word vir transito-fotometrie - van 'n DSLR-kamera met 'n telelens tot 'n 400 mm Schmidt Cassegrain-teleskoop (Figuur 3).
Uiteraard kan 'n groter opening dowwer sterre en kleiner planete waarneem, maar baie deurgange rondom relatief helder sterre bereik 'n diepte van 3%, goed binne die bereik van selfs beskeie teleskope. Aangesien die ster vir 3 + uur aanhoudend waargeneem moet word, is 'n goeie soliede berging met akkurate opsporing noodsaaklik. Gebruik ideaal 'n afgekoelde monochroom CCD-kamera. As u 'n Duitse ekwatoriale berg gebruik, is dit moontlik dat u 'n draai moet maak tydens die waarneming. Probeer om hierdie tyd te bepaal sodat dit nie tydens die kritieke fase van uitbreek / uitgang plaasvind nie. Akkurate tydstempels op u data is van kardinale belang, daarom is dit belangrik om 'n toegewyde sagtewarepakket soos die freeware Dimension 4 te gebruik om u rekenaar se klok aan die begin van elke sessie op te dateer en dan gereeld met tussenposes gedurende die nag. Moenie op u rekenaarbedryfstelsel staatmaak om dit vir u te doen nie.
Watter stelsels maak goeie teikens?
'N Goeie klas planeet om te begin waarneem, is die verbygaande Hot Jupiters. Aangesien hulle naby hul gasheerster is, het baie kort tydperke, dus dit kom gereeld voor en is van korte duur. 'N Lys van sulke planete kan gevind word op exoplanets.org
- Kies 'n tabel
- Kies Hot Jupiters (Figuur 4) in die keuselys Voorbeeldtabelle en Opslaan.
- Klik byvoorbeeld op die kolomopskrif om te kies volgens Orbitale periode
- Data vir die planeet en ster kan verkry word deur op die planeetnaam in die linkerkant te klik
kolom
Hierdie metode vereis 'n mate van sorteer om vas te stel watter planete op u plek beskikbaar is. 'N Eenvoudiger metode is om die transito-voorspeller op die Exoplanet Transit Database (ETD) te gebruik. Om geskikte teikens te lys, kies Voorspellings vir vervoer en voer u Oostelike lengte- en breedtegraad in en klik op Stuur. 'N Lys met stelsels word op die geselekteerde nag aangebied (Figuur 5). Dit wys alle stelsels wat middeldeur is vir voorwerpe bo 20˚. Let daarop dat die tye in UT is, sodat u moet aanpas vir u spesifieke tydsone en BST / Daylight Saving, indien van toepassing.
Hoe u kan besluit watter eksoplanetkandidate moet waarneem deur Paul Anthony Wilson wat data van die exoplanets.org-webwerf gebruik, kan ook help om 'n geskikte teiken te kies.
Ander opsies wat veel groter beheer bied, maar 'n bietjie ingewikkelder is om te gebruik, is die Transit Ephemeris Sakrekenaar en die Transit and Ephemeris Service.
As u 'n exoplanet in die lys aan die linkerkant kies, word die data vir daardie planeet getoon en deur ligkrommes deur te beweeg. 'N Spesifieke ligkromme en gepaardgaande data kan gekies word deur op TRESCA te kliek onder die naam van die indienende sterrekundige soos in hierdie voorbeeld deur Mark Salisbury (Figuur 6).
'N Tipiese waarnemingsessie
Wanneer die waarneming beplan dat dit belangrik is om fotometrie aan weerskante van die verwagte begin- en eindtyd te bekom, kan deurgange baie minute vroeër of later as verwag plaasvind. Hierdie data wat buite vervoer is, kan deur sagteware gebruik word om u data te benadeel as gevolg van veranderende lugmassa. 'N Goeie vuistreël is om die helfte van die verwagte reisduur aan weerskante van die verwagte begin- en eindtyd in ag te neem, alhoewel dit nie altyd prakties is nie, moet u so veel as moontlik buite die dekking van vervoer vervoer.
Sodra u 'n plan en 'n helder nag het, kan u opstel om u teikenvervoer te waarneem. Om die tydreeksfotometrie te verkry, benodig u 'n aaneenlopende reeks beelde, elk van 'n paar sekondes tot 'n paar minute. Die tyd tussen die begin van opeenvolgende beelde staan bekend as die kadens en bevat die blootstellingsduur en die tyd tussen die blootstelling vir aflaai van die beeld. 'N Geskikte kadens word beheers deur twee faktore: die sein-tot-ruis-verhouding (SNR) wat vir u doelwit bereik kan word met u opstelling, en die duur van die snelste veranderende gedeelte van die deurvoer, wat die deurreis / uitgang is. 'N SNR van ongeveer 400 is ideaal en die meeste duur van die binnedringtydperk is 10-30 minute. 'N Duim is om 6-10 metings te probeer verkry gedurende hierdie in- / uitgangsduur. Voor en na vervoer Dit is oor die algemeen beter om hoër SNR metings te hê as meer metings van lae SNR, aangesien dit die verspreiding in die fotometrie verminder, wat akkurater meting van tydsberekening moontlik maak, maar 30 minute beeldvorming gedurende beide hierdie periodes . Onsekerheid in die voorspelde ingangs- / uitgangstye kan 'n langer periode van beeldvorming voorskryf voor en na die vervoer. Sorg dat die tellings per pixel vir u teiken en beplande vergelykingssterre binne die lineêre respons van u CCD-kamera bly. Die blootstellingsduur moet vir alle beelde in die tydreeks dieselfde wees, dus neem die effek van die verandering van lugmassa in ag voordat u begin. As u 'n ster kry wat versadiging op u CCD nader as dit styg, is dit beter om die fokus effens te fokus eerder as om die blootstellingsduur te verander wat gedurende die blootstellingsvolgorde dieselfde moet bly. Analysesagteware kan klein fokusveranderings hanteer deur gebruik te maak van die FWHM-opsporingsvermoë om die grootte van die fotometriese diafragma te bepaal.
Om dieselfde teiken vir baie ure te volg, is goeie opsporing en leiding nodig. Omdat elke pixel in 'n CCD-kamera effens anders reageer, moet die fotometrie met die hoogste akkuraatheid vereis dat die ster gedurende die waarneming op dieselfde pixels bly. Dit is baie veeleisend en word selde bereik, selfs nie in professionele sterrewagte nie, en beoog om die beweging van die ster tot die minimum te beperk.
Een aspek wat vir presisie-fotometrie verslap kan word, is die fokus. Die hoogste presisie-fotometrie word gewoonlik met sterre FWHM in die omgewing van 10 boogsekondes bereik. Defocussing versprei die sterlig oor baie pixels, wat die impak van pixel tot pixelvariasies verminder, maar daar is meer koste verbonde aan die blootstellingstyd en probleme om op die as te lei. Selfs sterre wat effens buite fokus is, kan lei tot verbetering in fotometrie-presisie, mits die SNR-waardes gehandhaaf kan word. Vir die helderste sterre is ontknoping dikwels noodsaaklik om die CCD te versadig.
Vir eenvoudige tydmetings kan ongefilterde waarnemings gebruik word, maar as u van plan is om u gegewens met die van ander waarnemers te kombineer of as deel van 'n pro-am-samewerking werk, moet u 'n standaardfilter gebruik ('n pro-am-projek definieer dikwels 'n voorkeur filterstel). Verdonkering van sterrebeen gee Exoplanet verskillende vorms en dieptes in verskillende filters. Ek sal 'n fotometriese standaard rooi filter soos Cousin Rc of Sloan r aanbeveel. 'N Duidelik-blou-blokkerende (CBb) filter kan ook gebruik word, alhoewel dit nie as 'n standaard beskou word nie. Alle filters verminder die hoeveelheid lig wat die CCD bereik wat langer blootstelling benodig, maar die rooi filters hou 'n aantal ander voordele in. 'N Rooi filter help om die gevolge van skittering (vonkelende sterre) te minimaliseer en bied beter gedefinieerde ingangs- / uitgangsoorgange, wat 'n akkurate meting van deurgangstyds moontlik maak. Die gebruik van 'n filter verminder ook die stelselmatigheid wat deur die verskille in die vergelyking van die sterkleur van u teiken afgestel word.
Vir die tydsberekening van transito is dit noodsaaklik dat u kamera-beheersagteware die aanvangstyd en -duur van die blootstelling akkuraat opneem, aangesien dit deur die fotometriesagteware gebruik word om die blootstelling mid-time te bereken wat as tydstempel vir elke beeld gebruik word.
Die verkryging van kalibrasie-data van hoë gehalte is een van die belangrikste aspekte van 'n eksoplanet waarnemingsessie. Om die beste moontlike resultate te behaal, is dit belangrik dat u wetenskaplike beelde op 'n standaard manier korrek gekalibreer word met vooroordeel, donker en plat veldkorrigering, met die kalibrasierame wat op dieselfde CCD-temperatuur as die wetenskapsraamwerke verkry word. U kan nooit genoeg kalibrasie-data hê nie, so versamel soveel rame as wat u kan (20+ van elk is goed). Die individuele rame moet in die mediaan gekombineer word om die hoofkalibreringslêers te skep voordat dit op u data toegepas word, en bewaar altyd kopieë van die oorspronklike as daar iets verkeerd loop. Die BAA-fotometriehandleiding kan goeie advies gee oor die verkryging en gebruik van kalibrasiegegewens om fotometrie van hoë gehalte te produseer.
Die vervaardiging van 'n ligte kurwe
As alles goed afgeloop het en die weer goed was, sou u nou te min honderd wetenskaplike beelde en gepaardgaande kalibrasie-gegewens moes hê, is dit tyd om dit in 'n transito-ligkromme te verander. Hiervoor beveel ons aan om AstroImageJ (AIJ) te gebruik, 'n dataverminderings- en fotometriepakket wat beide gratis is en spesifiek ontwerp is vir ekso-planeet-transits. Dit kan aanvanklik effens skrikwekkend voorkom, maar daar is baie goeie hulpbronne beskikbaar om te help, soos uiteengesit op die webwerf van die BAA Exoplanet-afdeling se gids / tutoriale.
Figuur 7 toon 'n transito-waarneming van WASP-52b wat op 2 November 2018 vanaf die Verenigde Koninkryk verkry is met behulp van 'n 400mm Orion Optics ODK-teleskoop met 'n ST10XME-kamera en 'n Astrodon Rc-filter. Die swart kolletjies is die fotometriese metings wat van AstroImageJ verkry word met behulp van die proses wat in die teks beskryf word. Die rooi lyn is die beste pas-deurvoermodel van ETD. WASP-52b is 'n uitstekende teiken vir waarneming en wentel om sy 12de sterretjie elke 1,75 dae en lewer 'n transito met 'n diepte van meer as 3%. Let op die sterk verdonkeringseffek van die ledemaat wat sigbaar is as die kromming in die kromming in die basis van die transito. Hierdie effek is die sterkste by korter golflengtes (blou) en die kleinste by langer (rooier) golflengtes, wat die belangrikheid van filters beklemtoon.
Figuur 8 toon 'n fase-gevoude transito-ligkromme van HAT-P-23b. Die oorspronklike data (grys kolletjies) bestaan uit 1755 datapunte geneem uit 11 deurgange waargeneem met die Open University 17,5 ”PIRATE-teleskoop by Observatorios de Canarias op Teide-berg op Tenerife en 'n verdere 6 gange waargeneem deur skrywer met behulp van sy 16 "UK-gebaseerde teleskoop. Die swart kolletjies verteenwoordig vakkies van 25 datapunte en die rooi lyn is die beste pasmodel van Exofast. Die oorblyfsels van die binnegegee data na die Exofast-model is slegs 390 dele per miljoen, vergelykbaar met 'n enkele waarneming vanaf 'n 2m-teleskoop.
Die dataverwerkingsmodule in AIJ bied 'n vinnige en eenvoudige standaard data-vermindering, insluitend die opdatering van FITS-opskrifte en plaatoplossing, wat die fotometrieproses aansienlik vereenvoudig. Die proses vir fotometrie in AIJ word in diepte in die beskikbare literatuur behandel, maar dit laat u toe om 'n fisiese model van die transito by u data in te pas, wat dan gebruik kan word om die kwaliteit van die fotometrie te bepaal. Om 'n model te skep wat pas, is die omlooptydperk, die sterradius en die ledemaatverdonkeringsparameters. Eersgenoemde kan verkry word uit een van die vele aanlyn-katalogusse. Die verdonkering van die ledemate kan verkry word met behulp van die sakrekenaar wat op die Exoplanet Utilities-webwerf gevind word. Binne die AIJ-fotometrie-module voer u u kameraparameters in en kies dan soveel as moontlik vergelykingssterre wat dieselfde helderheid het as u teiken, en verseker dat geen bekende veranderlike sterre is nie. Vir ensemble-fotometrie sal AIJ 'n diafragma-sjabloon skep. Nadat u die fotometrie uitgevoer het, let op die RMS-residuele en BIC-waardes volgens die modelpas en probeer die fotometrie weer en verander die diafragma-instellings totdat u die instellings vind wat beide waardes verminder. Dit is waar die oplossing van die bord vrugte afwerp, aangesien AIJ u sjabloon outomaties weer sal toepas en die sterre sal volg, selfs deur 'n meridiaanflip, wat dit 'n vinnige en eenvoudige proses maak. AIJ bied ook 'n opsie om die fotometrie-diafragma te varieer op grond van die FWHM van elke beeld. Die sagteware laat u toe om deur die vergelykingssterre te gaan en dit een vir een te verwyder om te sien of daar buitensporige geraas by die ligkurwe gevoeg word, en weer kyk of die RMS- en BIC-waardes verminder, vergelykingssterre wat hierdie waardes aansienlik verhoog, weglaat. Volg ten slotte die stappe wat in die AIJ-dokumentasie uiteengesit word om u data in die gewenste formaat te stoor.
Deel van data
Nou het u u deurgangligkromme, moet u dit deel. Dit word aanbeveel dat u u data oplaai na:
a) Die BAA Fotometrie-databasis. 'N Aanmelding is nodig en gebruikershandleidings is beskikbaar via die knoppies Help en opmerkings oor die indien van waarnemings. Data word kwartaalliks na die AAVSO-databasis opgelaai.
c) Die Transiting ExoplanetS CAndidates-projek (TRESCA). Waarnemers kan registreer met behulp van die skakel op hierdie bladsy.
Amateurresultate wat by die ETD ingedien is, het 'n ryk datastel geskep. Hierdie data is deur navorsers in baie tydskrifartikels gebruik.
Besoek die bladsy Gidse / tutoriale op die webwerf van die BAA Exoplanet-afdeling vir hulp met AstroImageJ en ander aspekte van teikenseleksie, beeldvorming en analise
In die besonder word op die publikasie-bladsy gelys:
Transiting Exoplanets deur prof. Carole Haswell uitgegee deur Cambridge University Press, 2010, £ 31,99 (sagteband). Word ook gebruik in die Open University S382 Astrofisika-module
Die Exoplanet Handbook deur Michael Perryman uitgegee deur Cambridge University Press 2018, £ 56,99 (hardeband)
Opmerking: hierdie handleiding is aangepas uit 'n artikel geskryf deur Mark Salisbury en geredigeer deur Roger Dymock, wat in die Exoplanet-afdeling van die BAA-webwerf gevind kan word.
Exoplanet Watch
Wetenskaplikes het die afgelope kwarteeu meer as 4400 eksoplanete ontdek en planete wat om ander sterre wentel. 'N Nuwe projek, genaamd Exoplanet Watch, stel waarnemers met 'n beskeie agterplaasteleskoop en kamera in staat om die klein, dowwe skaduwees wat hierdie planete werp, op te spoor terwyl hulle die gesig van hul sterre kruis.
In werklikheid kan hulle selfs sonder 'n teleskoop deelneem. Met behulp van dataverwerkingsagteware wat deur die program verskaf word, kan hulle 'n tuisrekenaar gebruik om waarnemings van ander te ontleed.
Suksesvolle deelnemers verdien selfs 'n outeurskrediet op 'n gepubliseerde wetenskaplike referaat.
Dit is 'n geleentheid om amateursterrekundiges, of studente, in staat te stel om eksoplanete intyds te ondersoek, "het Tamim Fatahi, 'n junior en rekenaarwetenskap-hoofvak aan die California Polytechnic State University in San Luis Obispo, gehuur vir 'n internskap op die Exoplanet Watch. projek. & quotJy hoef nie ['n gevorderde] graad te hê nie. & quot
Onder leiding van die Universe of Learning-span onder die NASA & # 39 s Science Activation Program, het die nuwe program 'n goeie wetenskaplike doel: om rugsteun te bied aan professionele waarnemende veldtogte op die exoplanet wat groot teleskope op die grond en in die ruimte gebruik.
Om na die skaduwees van eksoplanete te soek, staan bekend as die & quottransit & quot-metode: om die klein duik in sterlig vas te vang terwyl 'n planeet voor sy ster verbygaan. Van die duisende eksoplanete wat tot dusver in ons sterrestelsel bevestig is, is die meeste gevind deur na planetêre en kwotransitte te kyk. & Quot
Om 'n bestaan van 'n planeet en 'n rsquos te bevestig, wil wetenskaplikes so 'n transito meer as een keer waarneem. Deur dit te doen, kan die eienskappe van die planeet onthul word en die deursnee daarvan byvoorbeeld, of die lengte van sy jaar (die tyd wat dit neem om 'n wentelbaan om sy ster te maak) raaksien. Dit is hierdie herhaalde deurgange wat Exoplanet Watch probeer vassteek.
Maar die voorspelling van die volgende deurreis van 'n bepaalde planeet kan 'n moeilike voorstel wees. Die tydsberekening van deurgange is sleg bekend vir baie moontlik teikens.
& quotAs daar 'n onderskatting van 15 minute is van wanneer 'n vervoer sal plaasvind, is dit 'n ekstra 15 minute wat ek moet inbou in my waarnemingscenario, 'het Rob Zellem, 'n sterrekundige van die eksoplaneet by NASA se Jet Propulsion Laboratory en die projekleiding vir Exoplanet Watch.
Vyftien minute klink nie so sleg nie en raak nie geklap totdat u die buitensporige vraag na die waarneming van tyd op instrumente soos die Hubble-ruimteteleskoop oorweeg nie.
& quotTyd op groot teleskope, veral ruimteteleskope, is baie, baie kosbaar, & quot; het Zellem gesê. & quotAs u baie planete waarneem, kan dit [15 minute] baie lank duur. Enige tyd wat vermors word, beteken dat minder wetenskap met die teleskoop gedoen sal word. & Quot
Tik die burgerwetenskaplikes in.
Gewapen met net 'n ses-duim-teleskoop en 'n digitale kamera-aanhangsel, kan u by hul geledere aansluit, op soek na planete en u eie huis in 'n sterrewag verander. Die projek bied aan deelnemers gereelde opdaterings oor sterre waarvoor meer waarnemings nodig is, asook waarskynlike transittye wat hulle kan help verfyn. Hulle & rsquoll ontvang ook gebruikersvriendelike instruksies oor hoe om hul data na die verwerkingsagteware op te laai.
Hierdie waarnemings sal professionele sterrekundiges tyd en hulpbronne bespaar, aangesien hulle uiteindelik hul kragtige instrumente na dieselfde planete draai.
& quotIk is baie lief vir die projek, en ek hou baie daarvan om saam met burgerwetenskaplikes te werk, 'het Marlee Smith, 'n senior aan die Columbia-universiteit en 'n dubbele hoofvak in rekenaarwetenskap en sterrekunde, gesê.
Sy het ook as intern aan die projek gewerk, en haar hulp, tesame met ander stagiairs, was noodsaaklik om Exoplanet Watch gereed te maak vir die beste tyd.
& quot; Ons brei die wetenskap uit na mense wat nie noodwendig dink om wetenskap te doen nie, en altyd wetenskap vir almal te eniger tyd, & quot;
Op soek na ligte kurwes
Smith en die ander het 'n groot deel van hul tyd aan die verbetering van die rekenaarkode, genaamd EXOTIC (vir Exoplanet Transit Interpretation Code), bestee om die waarnemers van tuisgedeeltes in staat te stel om hul data EXOTIC in te voer en dit dan om te sit in & quotlight curves, & quot die brood en botter van eksoplanetjagters.
Wanneer 'n planeet oor die gesig van 'n verre ster begin beweeg, begin die ooreenstemmende ligkromme as 'n plat lyn. Dan neem dit skerp as die planeet na die ster se middelpunt beweeg en 'n klein persentasie van die ster se lig blokkeer.
As die planeet verby die ster se gesig beweeg, styg die lyn weer na sy voorheen plat posisie. Die gevolglike golwende lyn is die planeet se & quotlight-kromme. & Quot
As die ster se deursnee bekend is, openbaar die diepte van die duik die deursnee van die planeet. Hoe groter die planeet, hoe meer sterlig blokkeer dit. Wag vir 'n tweede duik, terwyl die planeet terugkom, en u weet wat die lengte van die planeet is en 'n rit om die ster.
'N Ander intern by die projek, Aaron Tran, het sy somer gewerk aan die sagteware wat die data van amateurteleskope verwerk. Tran, 'n hoofvak in rekenaarwetenskap met 'n belangstelling in sterrekunde, sê hy is geneem met een van die hoofdoelstellings van die projek: om astronomie van eksoplanet toeganklik te maak vir almal.
& quot Die waarneem van eksoplanete met teleskope wat u (internet) koop, in plaas daarvan om een op 'n bergtop te gebruik, was vir my een van die grootste trekpleisters, & quot;
Die beskikbaarstelling van Exoplanet Watch was ook 'n groot trekpleister vir Tiana James, 'n tweedejaarstudent aan die Howard Universiteit in Washington, DC. James, wat ook rekenaarinligtingstelsels en grafiese ontwerp bestudeer, is ook 'n stagiaire wat help om die werf en beginnervriendelik te maak. & quot
En in die gees van die opening van die werf vir almal, ontwikkel sy 'n funksie wat die ligkrommingsdata kan kwotifiseer en aanhaal.
& quot As u die data vir 'n ligkromme invoeg, in plaas daarvan om dit te kan sien, sal dit 'n klankgolf uitstraal, & quot het sy gesê. & quotJy sou dit kon hoor. Dan sou u kon sê: & # 39Ok, dit was waar die ligkromme was. & # 39 Vir blindes is dit 'n wonderlike funksie vir mense met belangstelling. & Quot
Die Exoplanet Watch-span is daartoe verbind om sy wetenskap toeganklik te maak vir almal, sê Rachel Zimmerman-Brachman, 'n spesialis vir openbare betrokkenheid by die Jet Propulsion Laboratory wat haar kundigheid aan die projek verleen.
& ldquoI & rsquom bewusmaking oor die geleentheid vir mense om as burgerwetenskaplikes aan eksoplanetstudies deel te neem, & rdquo het sy gesê. Dit sluit in & praktiese wetenskap en veral eksoplanetwetenskap & ndash wat toeganklik is vir soveel mense as moontlik. & Rdquo
Op soek na planete met 'n steeds groeiende poel van ontluikende sterrekundiges, studente of iemand wat nuuskierig is: Exoplanet Watch is 'n uitnodiging om die heelal te verken.
Wil u ander burgerwetenskaplike geleenthede ondersoek? Besoek die NASA & Citizen Science-portaal.
NASA en rsquos Universe of Learning materials is gebaseer op werk wat deur NASA ondersteun word onder die koöperasie nommer NNX16AC65A aan die Space Telescope Science Institute, wat in vennootskap werk met Caltech / IPAC, Jet Propulsion Laboratory, Centre for Astrophysics | Harvard & amp Smithsonian, en Sonoma State University. Die toekenning is deel van die NASA & rsquos Science Activation-program, wat daarna streef om NASA-wetenskapkenners en -inhoud verder in die leeromgewing effektiewer en doeltreffender met leerders van alle ouderdomme in te stel.
Die beste transito-eksoplanet nog
Deur: Robert Naeye 7 Oktober 2005 
0
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Slegs 0,3 & # 176 reg oos van die bekende Halternevel, M27 in Vulpecula, skyn die ster van HD 7,7 met 'n sterk warm Jupiter in 'n noue wentelbaan. 'N Verkyker is alles wat u nodig het om die ster, 'n ligte oranje, te sien K dwerg 63 ligjare weg. Die ster is op die regte hemelvaart 20h 00.7m, deklinasie + 22 & # 176 43 & # 039 (2000.0 koördinate). Hierdie aansig is 0,9 & # 176 breed. Klik op die prentjie vir 'n aansig 1.3 & # 176 breed. Noord is op, oos is links.
Die Europese planeetjagspan wat deur Michel Mayor (Genève-sterrewag, Switserland) gestig is, het pas 'n nuwe buitesolêre planeet aangekondig wat die gasheerster kruis en # 8212, die negende transito-exoplanet wat tot dusver gevind is. Maar hierdie planeet is spesiaal. Die planeet, wat wentel om die 7,7-grootte tipe-K ster HD 189733 in Vulpecula, bied professionele sterrekundiges hul beste vooruitsigte om die atmosfeer en temperatuur van 'n eksoplanet te bestudeer. Dit gee ook amateurs die maklikste geleentheid om 'n wêreld op te spoor wat om 'n ander ster wentel. Boonop is die gasheerster net 0,3 ° van die Halternevel (M27) geleë, ideaal geleë vir die Noordelike Halfrond waarnemers gedurende die vroeë aand hierdie seisoen.
Met behulp van die 1,9 meter-teleskoop by die Haute-Provence-sterrewag in Frankryk, het die burgemeestersgroep die radiale snelheidsmetode gebruik om die aantrekkingskrag van die planeet op sy gasheerster te ontdek. Hierdie waarnemings het nie net die planeet geopenbaar nie, maar ook aangedui dat die planeet van tyd tot tyd sommige van die ster se lig blokkeer. Opvolgwaarnemings met die 1,2-meter-teleskoop van Haute-Provence bevestig die gange (wat 2 uur duur) en die feit dat die ster se helderheid met 3 persent (0,03) daal elke keer as die planeet die ster se skyf kruis. Dit is die diepste transoplanet-transitte wat nog gesien is.
'N Kunstenaar beeld die nuut ontdekte planeet uit wat deur sy gasheerster, HD 189733, oorgedra word. Die planeet se deursnee is ongeveer 17 persent van die ster en # 039's, wat beteken dat dit ongeveer 3 persent van die ster se lig blokkeer tydens deurgange.
S&T illustrasie deur Gregg Dinderman.
vraestel voorgelê aan Sterrekunde & Astrofisika.
Op grond van die temperatuur van die gasheerster en die skeiding van 0,0313 astronomiese eenhede, moet die planeet se temperatuur 'n paar honderd grade Celsius wees. Dit plaas dit in die klas "baie warm Jupiters" & # 8212 Jupiter-massaplanete wat binne minder as drie dae om hul gasheersterre wentel. Met sy hoë temperatuur is dit amper ondenkbaar dat daar enige lewe op hierdie planeet of enige mane wat daar is, bestaan.
"Hierdie planeet is absoluut fenomenaal vir opvolgwaarnemings," sê David Charbonneau (Harvard-Smithsonian Sentrum vir Astrofisika), wat die ruimteteleskope Hubble en Spitzer gebruik het om die atmosfeer op te spoor en die temperatuur van verskeie ander exo-planete wat deurloop, te meet. Charbonneau se Harvard-kollega, Scott Gaudi, voeg by: "Hierdie planeet gaan 'n goudmyn wees om meer oor planete te leer deur opvolgwaarnemings."
Om verskeie redes is navorsers in ekstase oor die HD 189733-planeet (HD 189733b). Eerstens beteken die ongelooflike strakke wentelbaan gereeld dat dit deurgang vind. Tweedens maak die daling van die helderheid van 3 persent (as gevolg van die relatiewe groot grootte van die planeet ten opsigte van die ster) die vervoer maklik om op te spoor. Derdens is die ster helder, net 63 ligjare van die aarde af, wat beteken dat sterrekundiges 'n hoë sein-ruis-verhouding in hul waarnemings kan bereik. Vierdens waarborg die hoë temperatuur van die planeet dat Spitzer die hitte-uitstoot daarvan kan opspoor, soos die teleskoop vroeër gedoen het vir die transito-exoplanete HD 209458b en TrES-1.
Danksy hierdie gunstige toestande sal navorsing nie net tot professionele sterrekundiges beperk word nie. Die ster self is so helder dat dit met net 'n verkyker gesien kan word. Amateur-sterrekundiges en studente wat klein teleskope gebruik wat met CCD's toegerus is, sal maklik die daling van 3 persent in helderheid wat deur deurgange veroorsaak word, kan meet. 'Heck, hierdie vervoer is so diep van ons mees ervare visueel waarnemers kan dit doen! ”beweer Aaron Price van die American Association of Variable Star Observators.
The little constellation Sagitta, the Arrow, is the key to finding the Dumbbell Nebula, M27 (which glows at 8th magnitude) and its exoplanet-host neighbor star. Sagitta is located 10° north of bright Altair. M27 (at the top left corner here) is located 3.3° north of the point of the Arrow. An old observer's trick: imagine the arrow pivoting counterclockwise around its point through a third of a circle. The Arrow's middle star would then lie right on M27.
Transitsearch.org, has added HD 189733 to his observing list. Transitsearch.org organizes worldwide amateur observing campaigns to catch transiting exoplanets. The next transit occurs at 1:53 UT, October 8th, which is best suited for eastern North America observers. By tracking any slight irregularities in the timing of future transits, professionals and amateurs could detect the gravitational presence of additional planets in the system, including planets with masses as low as Earth's.
"It will be very interesting to get high-quality amateur photometry for additional radius estimates, since like HD 209458b, the HD 189733 planet is clearly larger than predicted by standard models," says Laughlin. "Since high-end amateur setups are reliably observing the HD 149026b transit, whose depth is close to 10 times shallower than the HD 189733 transit, I think we can expect to see some awesome light curves of the transit." Laughlin also notes that amateur observations will reveal whether the star is marred by starspots.
More information about the planet and the discovery team can be found in the Haute-Provence press release.
The Verdict
In general, the reaction of other researchers was positive.
“In principle, the observations are possible, which makes this a tantalizing system,” Kevin Stevenson of the Space Telescope Science Institute told Ars. (Stevenson was not involved in this study but has worked with the lead author in the past.) “However, the authors have made numerous assumptions, which they acknowledge, regarding JWST and the system. Given that we will never find a potentially habitable exoplanet closer than Proxima Centauri b, the risk is certainly worth the rewards.”
Sara Seager of MIT was a bit more cautious. “It looks fine,” she told Ars, though she went on to question “why [the authors] didn’t consider the case of an atmosphere that does not redistribute [heat around the planet]—we will have no way of knowing for sure if they see a signal that looks like a bare rock if it actually is.”
The paper’s lead author, Laura Kreidberg of the University of Chicago, didn't think this was an issue: “I suppose it would be possible to cook up a pathological scenario in which very little heat is transferred (perhaps if the atmosphere were extremely tenuous). But modeling work has shown that for a wide range of atmospheric compositions, the heat circulation is efficient.”
Seager also pointed out that searching for the ozone signal would require up to a hundred hours of observation time. Seager wondered “if it would really be possible to bin together data on that time scale robustly.”
Kreidberg, however, suggested it would be a valuable test of the hardware: “But the tremendous light-gathering power of Webb and the thermal and pointing stability of the telescope are exactly what we need to make these observations successful. But we will definitely want to get test observations of Proxima during the early commissioning phase of JWST to confirm that the detector works at the level of precision required.”
John Mather, the senior project scientist on the James Webb Space Telescope, was also optimistic. “I think the paper in question is pretty good the authors know what they are talking about regarding the planet,” he told Ars. “We definitely did not design the telescope with this target in mind, considering that we started work 21 years ago. We won’t know whether the telescope has the needed stability and sensitivity until after launch. Needless to say we would all like to find out right away, but this is one of the most difficult targets, and it will take a while to learn how to use the equipment in the best possible way. I am certainly optimistic, since we don’t know of anything in the hardware that would prevent the observations.”
Mark Clampin, project scientist for the James Webb Space Telescope at NASA's Goddard Space Flight Center, was enthusiastic (we have more from him below) but shared concerns with Mather about the ozone part. “I think based on this paper alone, the first part of the observation, people would probably want to do. I think that trying to do the ozone observation is something that would probably have to wait until we understand the instruments better.”
And even if we detect ozone, that wouldn’t be a sure sign of life. “I think if you make that observation and you were able to get a positive result, it’s another piece of the puzzle. It’s not the sort of ‘hail Mary.’ I think scientists generally want to see a lot more evidence than just one line. These bio-signatures generally require you to see a number of different lines, different parts of the band.”
Still, Clampin went on to say that, if we did spot ozone, it would inform how we think about the next generation of exoplanet-observing hardware.
Why Is It Important?
Then and Now
In the early 1600s, Johannes Kepler discovered that both Mercury and Venus would transit the sun in 1631. It was fortunate timing: The telescope had been invented just 23 years earlier and the transits wouldn&rsquot happen in the same year again until 13425. Kepler didn&rsquot survive to see the transits, but French astronomer Pierre Gassendi became the first person to see the transit of Mercury (the transit of Venus wasn&rsquot visible from Europe). It was soon understood that transits could be used as an opportunity to measure the apparent diameter &ndash how large a planet appears from Earth &ndash with great accuracy.
In 1677, Edmond Halley observed the transit of Mercury and realized that the parallax shift of the planet &ndash the variation in Mercury&rsquos apparent position against the disk of the sun as seen by observers at distant points on Earth &ndash could be used to accurately measure the distance between the sun and Earth, which wasn&rsquot known at the time.
Today, radar is used to measure the distance between Earth and the sun with greater precision than can be found using transit observations, but the transit of Mercury still provides scientists with opportunities for scientific investigation in two important areas: exospheres and exoplanets.
Exosphere Science
Some objects, like the moon and Mercury, were originally thought to have no atmosphere. But scientists have discovered that these bodies are actually surrounded in an ultra-thin atmosphere of gases called an exosphere. Scientists want to better understand the composition and density of the gases that make up Mercury&rsquos exosphere and transits make that possible.
&ldquoWhen Mercury is in front of the sun, we can study the exosphere close to the planet,&rdquo said NASA scientist Rosemary Killen. &ldquoSodium in the exosphere absorbs and re-emits a yellow-orange color from sunlight, and by measuring that absorption, we can learn about the density of gas there.&rdquo
Exoplanet Discoveries
When Mercury transits the sun, it causes a slight dip in the sun&rsquos brightness as it blocks a tiny portion of the sun's light. Scientists discovered they could use that phenomenon to search for planets orbiting distant stars, called exoplanets, that are otherwise obscured from view by the light of the star. When measuring the brightness of far-off stars, a slight recurring dip in the light curve (a graph of light intensity) could indicate an exoplanet orbiting and transiting its star. NASA&rsquos Kepler mission has found more than 1,000 exoplanets by looking for this telltale drop in brightness.
Additionally, scientists have begun exploring the exospheres of exoplanets. By observing the spectra of the light that passes through an exosphere &ndash similar to how we study Mercury&rsquos exosphere &ndash scientists are beginning to understand the evolution of exoplanet atmospheres as well as the influence of stellar wind and magnetic fields.
See an Exoplanet in Your Telescope!
Around a star slightly smaller than our own sun, about 200 light-years away, orbits a very odd, very big, and very hot planet known as HD80606b. The thing that makes this planet so odd is its highly eccentric orbit (with an eccentricity of 0.93). HD80606b's eccentric orbit takes it very close to its parent star at its lowest point in orbit, about 0.03 AU. During this period of close approach, the planet's atmosphere rises over 1,000 degrees F (555 degrees C) in about 4 hours! Talk about some bad weather! Of course, this enormous temperature swing causes massive storms called shockwave storms , since their winds would be faster than the speed of sound!
So How Could I Possibly See It?
Because of this planet's extremely large size and close orbit, it could actually block out part of its parent star during a transit. This is exactly what is predicted to happen on the evening of February 14, 2009. HD80606b will pass between Earth and its parent star, blocking out a tiny portion of its light. There is a tiny chance that amateur astronomers will be able to detect this event in moderately sized telescopes as a dimming of the star for a few hours on the night of Feb. 14. While it most probably won't be detectable by the human eye, test setups consisting of tracking mounts and CCD cameras could allow amateurs to maybe (just maybe) detect an exoplanet transit at home. Shown below are three finder maps I put together in wide, mid, and close-up views, so anyone can find this star to watch for the event. I'd love to hear any reports of observations of this! (Click to enlarge. Right-click, Save As. and print for use at the scope)
NOTE: If you get any CCD photometry data, please send it to AAVSO and transitsearch.org.
36 comments:
What kind of magnitude drop are we talking about here?
There aren't many estimates available as to the magnitude drop that is expected, but I'd imagine it is going to be on the very edge of perception by amateur telescopes. Still it will be fun to check for it! My thought on it is that it might be comparable to a minima of Algol (if we can see it), so observe it as if it were such an event.
Sean the disk of the planet looks like it's about 1.5% the size of the disk of the star. I'm not sure the exact effect of distance .03-.84 AU, but I expect the closer the planet is to the star the more noticable the effect. I know I'm not set up for that kind of measurement.
I meant I'm not sure the exact distance on the 14th.
Are you going to try? Do you have a test setup in mind?
I would try if I had the equipment and skies. I'll probably be clouded over (Northeast Ohio isn't known for clear winter skies).
Anyways, I'd imagine that the best test setup would be a CCD on a tracking mount that one could use to record precise images of this star. One could then analyze the images for drops in magnitude over the course of the night. Visually, the chances of seeing this effect I admit are very low, especially if the magnitude dip is very small. If I have clear skies, I'm going to try anyways, maybe look back at it every few hours over the course of a night. Not exactly scientific, but hey its what I've got!
Post edited slightly to include the bit about CCD cameras.
Yuck correction. Shouldn't have done the math quickly on a small phone calulator. It's about a million times smaller that 1.5%. I don't think that'll show up.
Oh wow, I guess we can rule out detecting it visually then. Darn, guess I'll have to try again someday when I get a tracking mount and CCD equipment.
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Amateurs Help Discover Transiting Exoplanet
By: Robert Naeye May 23, 2006 0
Kry sulke artikels na u posbus gestuur
Artist Greg Bacon created this impression of the extrasolar planet XO-1b, recently discovered by a team of professional and amateur astronomers. Click on the image to view a larger version.
Courtesy NASA / ESA / Greg Bacon.
XO Project. McCullough and his colleagues monitor the brightnesses of tens of thousands of relatively bright stars (brighter than 12th magnitude) every clear night with two automated 200-millimeter telephoto cameras on Haleakala, a volcano on the Hawaiian island of Maui. The team uses CCD detectors, and sophisticated software to identify potential transiting planets from the vast amount of data.
The XO Project uses this inexpensive telescope to monitor the brightnesses of tens of thousands of stars every night. The telescope consists of two 200-millimeter telephoto camera lenses. The lenses are attached to CCDs, which can measure slight dips in star brightnesses that reveal a transiting planet. The telescope is on the summit of Haleakala, a volcano on Maui.
Courtesy Peter McCullough / Jeffrey Stys / NASA / ESA.
Ron Bissinger in California, Bruce Gary in Arizona, Peter Howell in Massachusetts, and Tonny Vanmunster in Belgium) observed one of the most promising candidates identified by XO: a magnitude-11.3 solar-type star in Corona Borealis named GSC 02041�. The amateur observations revealed the telltale dips of a transiting object only 30 percent larger than Jupiter. The star decreases in brightness by about 2 percent for about 3 hours. The transits occur every 3.94 days — the companion's orbital period.
To make sure the transiting object was a planet and not a low-mass star or brown dwarf (which are about the same size as a gas-giant planet), McCullough conducted follow-up spectral observations with two telescopes at the University of Texas's McDonald Observatory. Sure enough, the spectra proved that the star wobbles back and forth as it its being tugged by a companion with about 90 percent of Jupiter's mass. The XO team had bagged its first planet, which it has named XO-1b.
"The amateurs could not have discovered this planet without my telescope telling them where to look," says McCullough. "But when they found the drops in brightness of XO-1, that was important. We probably could have done this eventually without their assistance, but it certainly accelerated the process. And it's much more fun to do it this way."
"Over several weeks, one by one, I worked through the candidate list and reported negative findings back to the team," writes Bissinger on his Web site. "But as my computer displayed a light curve on the morning of June 23, 2005, after my telescope and CCD camera took 337 one-minute images of one particular candidate throughout the night before, there was little doubt in my mind that a new exoplanet had been discovered."
Amateur astronomer Ron Bissinger obtained this light curve on the night of June 22-23, 2005. The light curve clearly records the dip in brightness of the host star, XO-1, during the transit.
Click on this link to view a strobe movie that shows when the transits of XO-1b are visible from particular locations on Earth.
High precision photometry: detection of exoplanet transits using a small telescope.
The discovery of planets orbiting other stars has to rank as one of the most significant scientific discoveries in modern times. In many ways it confirms strongly suspected ideas that planetary systems are common, however now we have the data to support the conclusion that we live in just one of a plethora of systems scattered through our part of the Milky Way galaxy.
As of 2012 May 12, 612 exoplanet candidates have been discovered (1) and as with many other fields in astronomy, opportunities exist for amateurs to make valuable contributions to their study. The mechanism described here is via the transit method, which makes use of fortuitous circumstances where the orbital plane of a planetary system is coincident with the line of sight of observers on Earth. (2)
Under these circumstances, the star is seen periodically to dim as the planetary companion transits the disc of the star, temporarily blocking some of the observed stellar flux. Typically transit dips amount to less than 20 milli-magnitudes and as a result place exacting requirements on controlling the noise that is inevitably present in the photometric measurement.
This paper describes observations made with fairly modest equipment that yield scientifically useful high precision data and contribute to long term studies of known transiting exoplanet systems.
Objectives and scientific value
Observations of known transiting exoplanets are of particular interest as they allow accurate long term monitoring of any transit timing variations. This can offer information on orbital decay or evolution of closely orbiting planets. It is also a powerful tool to detect anomalies in mid-transit times caused by the gravitational influence of another undetected body in the planetary system. (3)
Observations of exoplanet transits were made at the author's small home observatory in Gothers, St Dennis, Cornwall using a 0.25m Meade LX200 Schmidt-Cassegrain telescope on an EQ6 German Equatorial mount (Figure 1). In order to minimise zero-point errors, targets were chosen which did not require a meridian flip during the transit or for a period of 1 hour before ingress or after egress. The optical system is equipped with a focal reducer to yield a focal ratio f/6.8 and a focal length of approximately 1700mm.
The CCD imager is the QHY6 Pro device, featuring a 752x585 array of 8.6x8.3 micron pixels. The CCD is operated using set point cooling at temperatures between -12 and -15[degrees]C. All observations were taken un-binned, yielding an image scale for all but the first dataset of 1.01"x0.98" per pixel. Images were bias, dark and flat field corrected and no other image enhancements were made.
Autoguiding is helpful in reducing noise generated by spatially imperfect flat field correction. Autoguiding was performed using a QHY5 CMOS detector and the free guiding software package 'PhD'. (4) A separate 100mm diameter, 600mm focal length refractor guidescope was used, and great care was taken to minimise differential flexure through the structure.
A time-series of the selected targets was taken with an exposure time and cadence that depended on the brightness of the objects under study. Basic data on the objects reported in this paper may be found in Table 1.
Exposure times were chosen so that the maximum ADU (analog/digital unit) count remained within the linear portion of the CCD response this corresponds to a value of less than 40,000 ADU for the CCD used. For the brightest targets this can result in a very short exposure time (a few seconds), which introduces an unacceptable component of scintillation noise on such a small aperture. As a result, strategies such as filtering and defocus were used to limit the maximum ADU count and increase exposure times to a few tens of seconds.
For the brighter objects (V<11) any of the standard Johnson/ Cousins V, R, and I photometric bands may be used as the signal-to-noise ratio (SNR) is high even with a large proportion of the spectrum rejected. For fainter objects it is possible to image unfiltered although this can lead to problems due to differential extinction between the target and reference star if their colour indices are significantly different. This leads to a strong baseline curvature on the lightcurve.
While it is possible to model and remove the baseline curvature, a better solution is to use a long-pass filter such as the Kodak Wratten 12, which is inexpensive (less than 10 [pounds sterling]) and easily available (the filter transmission characteristics are shown in Figure 2). The use of this filter minimises differential extinction issues and maximises SNR on the object within reasonable exposure cadence. The root of the differential extinction problem lies in the fact that atmospheric extinction is stronger at the blue end of the spectrum than the red. As observations progress through the night, a blue star will experience a greater variation in magnitude as a function of airmass than a red star. As a result, unless your target and reference stars are of identical colour (which is rare) the differential extinction will cause the baseline magnitude of the target star to appear to change as a function of airmass. The use of a filter that removes much of the blue end of the spectrum (such as the Wratten 12) reduces this effect.
Reduction was performed using standard differential aperture photometry techniques. Comparison stars are selected that are as close as possible in angular separation, colour and brightness to the target. The angular separation should be small, partly as the author owns a small CCD sensor and partly so that transparency variations (such as thin cirrus cloud) are minimised between the target and comparison stars. Brightness differences should also be minimised where possible so that a high SNR may be achieved on both the target and comparison stars, while preventing either from entering the non-linear part of the CCD response.
It is important when undertaking high precision photometry to optimise the measurement aperture of the star image being measured. As the target and reference stars are generally bright, high-SNR objects, it is important to ensure that the measurement aperture is not too small. In particular, variations in seeing will change the diameter of the star's point spread function (PSF) and cause small changes in the proportion of the PSF that falls outside of the measurement aperture. While these changes in measured PSF fraction are small and would not compromise asteroid or variable star photometry, the small variations that are being measured in an exoplanet transit make this effect important.
Typically sky conditions during observations were clear but not always photometric. Airmass was always less than 2: hence observations made at altitudes of greater than 30[degrees].
Photometry was performed using Maxim DL5 and data manipulation using Microsoft Excel.
Model fitting was performed using the transit-fitting tool on the Exoplanet Transit Database (ETD) provided by the variable star section of the Czech Astronomical Society. (6) This is a very useful website which provides a variety of services for the exoplanet observer, including a shared repository for observations.
The ETD tool allows the user to fit their data using a least squares fit to models generated for each transit based on previously measured parameters. Free parameters available for fit optimisation include transit duration, mid-transit time and transit depth. The tool returns the best fitted lightcurve and derived system properties such as measured orbital inclination. (7) It also provides an estimate of residuals and a 'quality' factor that incorporates measurement precision and sampling cadence.
Observing details and photometric accuracy
An analytical assessment of the uncertainties in the photometry is difficult as there are many varied parameters that drive the noise on the signal observed. Thus an estimation of the photometric uncertainties was performed through calculation of standard deviation from the ETD-modelled fit. This method does leave the data subject to uncertainties on the part of the model, however the author feels that this is small compared to that on the photometry.
Table 2 lists summarised data of each observing run and associated photometric uncertainties. Details of comparison stars and all raw data may be accessed via the ETD using the observation reference listed.
The best results using the system described above gave 1-sigma standard deviation values of less than 4 milli-magnitudes on three occasions and
2mmag on one occasion. These were on individual frames without any averaging or stacking applied.
The author feels that while they are already close to the limit in terms of performance, some further optimisation of equipment and imaging strategy could see residuals fall reliably below 2mmag.
The lightcurves of measured transit photometry are presented in Figures 3 to 8. The Figures show individual photometric measurements as a function of time through the predicted transit period. Photometry is normalised to zero for the out-of-transit magnitude. Error bars on the averaged points are of 1 standard deviation from the model fit. The solid yellow line is the fitted model transit found using the ETD tool. Residual baseline curvature is removed using a second order polynomial fit via the ETD tool.
All plots except the last are scaled to the same Y-axes to illustrate the relative transit depths and measurement uncertainties. The last plot GJ436b is of sufficiently high precision that the axes are doubled in scale to better show the shallow transit.
A summary of the transit parameters, compared with predictions based on previously calculated ephemeris data, is seen in Table 3.
This paper reports transit observations for the five extrasolar planets: HAT-P-9b, HAT-P-13b, TrES-1b, TrES-3b and GJ 436b. The use of the model-fitting tool provided by the variable star section of the Czech Astronomical Society allows geometric transit parameters to be calculated from the fitted transit data. These parameters are given in Table 4.
It may be noted that most of the planets studied are slightly larger than Jupiter, with the exception of GJ 436b, a 'hot Neptune-sized' planet orbiting an Mdwarf star in Leo. (8) Without exception, all of the planets studied are in short period orbits, much closer to their parent star than any planets within our own solar system.
Observations reported here demonstrate that telescopes of modest aperture, equipped with relatively low-cost CCD cameras and situated in less than optimal locations, can be used to obtain usefully accurate data on exoplanets transiting stars of 12th magnitude and brighter. These observations are valuable in that they can be incorporated in a worldwide database and used to monitor long-term variations in planetary system behaviour.
Address: 5 Gothers Road, St Dennis, Cornwall PL26 8DF. [[email protected]]
(2) Winn J. N., 'Exoplanet transits and occultations', in Exoplanets, ed. Seager S., University of Arizona Press, 55-77 (2010)
(3) Nascimbeni V. et al., 'TASTE II: A new observational study of transit time variations in HAT-P-13b', Astron. Astrofis. 532, A24 (2011)
(4) Stark C., PhD guiding software, http://www.stark-labs.com/phd guiding.html
(5) Maxim DL, Image processing software by Diffraction Ltd, http://www. cyanogen.com/maxim_main.php
(6) Brat L., Exoplanet Transit Database, http://var2.astro.cz/ETD/ protocol.php
(7) Pejcha O., Exoplanet transit parameters from amateur astronomers' observations, http://var2.astro.cz/ETD/FitProcedureDescriptionPejcha2008.pdf (2008)
(8) Bean J. L. et al., 'A Hubble Space Telescope transit light curve for GJ 436b', Astron. Astrofis. 486, 1039-1046 (2008)
Adv. Astrophysics through backyard telescopes
I have seen articles, videos of people doing stellar spectroscopy (and building databases of star compositions) using grating filters in their medium sized scopes, measuring binary distances and some even measuring exoplanet transits with backyard telescopes. To a guy using machine learning for software based adaptive optics, in a backyard scope. Some truly inspiring things that seemed to be in domain of large observatories only and that more and more amateurs are doing now.
I want to know stories from fellow astronomers on this site, about the most advanced scientific measurement that they have done with their equipment or an observation / image that they are proud of - ( other than seeing Saturn for the first time, which nothing ever tops in life ). or something they have heard or an never tried yet. If possible, please do give some technical details about what key instrument / software / device that you used. It'll might open people, to things they thought weren't possible.
