Tisková zpráva

Světelná ozvěna prozradila vzdálenost hvězdy

Astronomové upřesnili stupnici pro počítání vzdáleností ve vesmíru

11. února 2008

S pomocí dalekohledů ESO astronomové využili přítomnosti světelných ozvěn okolo hvězd k upřesnění vzdáleností cefeid. Cefeidy jsou proměnné hvězdy, které slouží jako majáky při určování vzdáleností ve vesmíru.

Díky novým techonologiím na dalekohledech ESO v La Silla jsme záskali zatím nejpřesnější určení vzdálenosti k cefeidě,“ říká Pierre Kervella, šéfredaktor publikovaných výsledků.

Cefeidy [1] jsou pulzující hvězdy, které se používají k určování vzdáleností ve vesmíru již téměř sto let. Provedené měření je významé hlavně proto, že oproti jiným technikám využívá výhradně geometrické postupy a nespoléhá na hypotetické fyzikální vlastnosti hvězdy.

Tým astronomů studoval hvězdu RS Pup, jasnou cefeidu, která se nachází v souhvězdí Puppis (Lodní záď). Je snadno viditelná i pomocí triedru. RS Pup mění svoji jasnost téměř pětinásobně v periodě 41,4 dne, je 10krát hmotnější, 200krát větší a v průměru 15 000krát svítivější než Slunce. RS Pup je také jediná cefeida, obklopená reflexní mlhovinou [2], jež je tvořena velmi jemným prachem.

Přítomnost mlhoviny umožňuje astronomům pozorovat specifické změny jasnosti cefeidy v podobě světelné ozvěny. Odtud mohou změřit vzdálenost hvězdy. „Světlo, které vychází z hvězdy, prochází mlhovinou a nokonec dopadá do dalekohledu, je mírně zpožděné oproti světlu, které k nám cestuje přímo," vysvětluje Kervella. „Pokud tedy změříme jasnost určité části mlhoviny, získáme stejnou světelnou křivku jako pro cefeidu, ale časově posunutou.“  Světelnou ozvěnou nazýváme právě toto zpoždění jako analogii k tradiční ozvěně, například zvuku, odraženému ode dna studny.

Ze sledování vývoje jasnosti zhuštěniny  v mlhovině odvodíme její vzdálenost od hvězdy. Jednoduše změříme časové zpoždění a vynásobíme jej rychlostí světla (300 000 km/s). Pokud potom známe tuto vzdálenost a příslušnou úhlovou vzdálenost zhuštěniny od hvězdy na obloze, můžeme vypočítat vzdálenost RS Pup. Z pozorování světelné ozvěny na několika místech mlhoviny byla vzdálenost RS Pup stanovena na 6500±90 světelných let.

Znát vzdálenost cefeidy s takovouto přesností je důležité pro upřesnění vztahu mezi periodou a jasností hvězd této třídy,“ říká Kervella. „Tento vztah je klíčový při určování vzdáleností galaxií pomocí cefeid.“ RS Pup se od nás nachází ve čtvrtině vzdálenosti mezi Sluncem a centrem Galaxie a leží uvnitř Mléčné dráhy ve velmi hustě "osídlené" oblasti hvězd.

Poznámky

[1]: Cepheids are rare and very luminous pulsating stars whose luminosity varies in a very regular way. They are named after the star Delta Cephei in the constellation of Cepheus, the first known variable star of this particular type and bright enough to be easily seen with the unaided eye. Almost a century ago, in 1912, American astronomer Henrietta Leavitt published a relation between the intrinsic brightness and the pulsation period of Cepheids, the longer periods corresponding to the brighter stars. This relation still plays today a central role in the extragalactic distance scale.

[2]: The nebula around RS Pup was discovered in 1961 by Swedish astronomer Bengt Westerlund, who later became ESO Director in Chile (1970-74). Shortly after, in 1972, the American astronomer Robert Havlen, then visiting ESO Chile, published the first study of the nebula in the then rather young European journal Astronomy & Astrophysics.

Další informace

"The long-period Galactic Cepheid RS Puppis - I. A geometric distance from its light echoes", P. Kervella et al. is in press in Astronomy and Astrophysics.

Složení týmu: Pierre Kervella and Guy Perrin (LESIA, Observatoire de Paris, France), Antoine Mérand (Center for High Angular Resolution Astronomy, Atlanta, Georgia, USA), László Szabados (Konkoly Observatory, Budapest, Hungary), Pascal Fouqué (Observatoire Midi-Pyrénées, Toulouse, France), David Bersier (Liverpool John Moores University, UK), and Emanuela Pompei (ESO).

 

Kontakty

Pierre Kervella
Observatoire de Paris-Meudon
Paris, France
Tel.: +33 1 45 07 79 66
Email: Pierre.Kervella@obspm.fr

Anežka Srbljanović (press contact Česko)
ESO Science Outreach Network a Astronomical Institute of Czech Academy of Sciences
Tel.: +420 323 620 116
Email: eson-czech@eso.org

Connect with ESO on social media

Toto je překlad tiskové zprávy ESO eso0805. ESON -- ESON (ESO Science Outreach Network) je skupina spolupracovníku z jednotlivých členských zemí ESO, jejichž úkolem je sloužit jako kontaktní osoby pro lokální média.

O zprávě

Tiskové zpráva č.:eso0805cs
Legacy ID:PR 05/08
Jméno:RS Pup, RS Puppis
Typ:Milky Way : Star : Type : Variable
Facility:New Technology Telescope
Instruments:EMMI
Science data:2008A&A...480..167K

Obrázky

The Cepheid star RS Pup
The Cepheid star RS Pup
pouze anglicky
Light echoes in RS Pup
Light echoes in RS Pup
pouze anglicky
Light echoes (artist's impression)
Light echoes (artist's impression)
pouze anglicky
Position of RS Pup in the galaxy (arstist's impression)
Position of RS Pup in the galaxy (arstist's impression)
pouze anglicky

Videa

Light echoes in RS Pup
Light echoes in RS Pup
pouze anglicky
The principle of Light Echoes
The principle of Light Echoes
pouze anglicky

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