An asteroseismic signature of helium ionization
We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent γ is a superposition of two decaying pe...
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| Veröffentlicht in: | Monthly notices of the Royal Astronomical Society 2007-03, Vol.375 (3), p.861-880 |
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| container_title | Monthly notices of the Royal Astronomical Society |
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| creator | Houdek, G. Gough, D. O. |
| description | We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent γ is a superposition of two decaying periodic functions of frequency ν, with ‘frequencies’ that are approximately twice the acoustic depths of the centres of the He i and He ii ionization regions. That variation is probably best exhibited in the second frequency difference Δ2νn, l≡νn−1, l− 2νn, l+νn+1, l. We show how an analytic approximation to the variation of γ leads to a simple representation of this oscillatory contribution to Δ2ν which can be used to characterize the γ variation, our intention being to use it as a seismic diagnostic of the helium abundance of the star. We emphasize that the objective is to characterize γ, not merely to find a formula for Δ2ν that reproduces the data. |
| doi_str_mv | 10.1111/j.1365-2966.2006.11325.x |
| format | Article |
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We show how an analytic approximation to the variation of γ leads to a simple representation of this oscillatory contribution to Δ2ν which can be used to characterize the γ variation, our intention being to use it as a seismic diagnostic of the helium abundance of the star. We emphasize that the objective is to characterize γ, not merely to find a formula for Δ2ν that reproduces the data.</description><subject>Astronomy</subject><subject>Astrophysics</subject><subject>Earth, ocean, space</subject><subject>Exact sciences and technology</subject><subject>Helium</subject><subject>Stars & galaxies</subject><subject>stars: abundances</subject><subject>stars: interiors</subject><subject>stars: oscillations</subject><subject>Sun</subject><subject>Sun: abundances</subject><subject>Sun: oscillations</subject><issn>0035-8711</issn><issn>1365-2966</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2007</creationdate><recordtype>article</recordtype><recordid>eNqNkV9LHDEUxUOx0NX6HYaCvs3uTTLJJC-C-KcWti0VBfEl3M1matbZmTXZoWs_fTOOrCAWzMsNN-f8uPeEkIzCmKYzWYwplyJnWsoxA5Cpy5kYbz6Q0fZhh4wAuMhVSeknshvjAgAKzuSITI6bDOPahTY6H5feZtH_bnDdBZe1VXbnat8tM982_i-uU_lMPlZYR7f_XPfI9fnZ1clFPv359dvJ8TS3EkDkUnFN5wyRaot6DnamLILVfDavtBLMUUZnoKqKKwTnFNN2xirkBRZMoNZ8jxwO3FVoHzoX12bpo3V1jY1ru2gYFKLUvEjCL6-Ei7YLTZotaUouFSt7mhpENu0Zg6vMKvglhkdDwfQxmoXp0zJ9WqaP0TzFaDbJevDMx2ixrgI21scXf1pGcpBJdzTo_vjaPb6bb77_uHy6JgAfAG23-o89f2u8fHD59ImbrQ_DvZElL4W5uLk1t7Qob7g4Nb_4P4tDorc</recordid><startdate>200703</startdate><enddate>200703</enddate><creator>Houdek, G.</creator><creator>Gough, D. 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O.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>An asteroseismic signature of helium ionization</atitle><jtitle>Monthly notices of the Royal Astronomical Society</jtitle><stitle>Monthly Notices of the Royal Astronomical Society</stitle><addtitle>Monthly Notices of the Royal Astronomical Society</addtitle><date>2007-03</date><risdate>2007</risdate><volume>375</volume><issue>3</issue><spage>861</spage><epage>880</epage><pages>861-880</pages><issn>0035-8711</issn><eissn>1365-2966</eissn><coden>MNRAA4</coden><abstract>We investigate the influence of the ionization of helium on the low-degree acoustic oscillation frequencies in model solar-type stars. The signature in the oscillation frequencies characterizing the ionization-induced depression of the first adiabatic exponent γ is a superposition of two decaying periodic functions of frequency ν, with ‘frequencies’ that are approximately twice the acoustic depths of the centres of the He i and He ii ionization regions. That variation is probably best exhibited in the second frequency difference Δ2νn, l≡νn−1, l− 2νn, l+νn+1, l. We show how an analytic approximation to the variation of γ leads to a simple representation of this oscillatory contribution to Δ2ν which can be used to characterize the γ variation, our intention being to use it as a seismic diagnostic of the helium abundance of the star. We emphasize that the objective is to characterize γ, not merely to find a formula for Δ2ν that reproduces the data.</abstract><cop>Oxford, UK</cop><pub>Blackwell Publishing Ltd</pub><doi>10.1111/j.1365-2966.2006.11325.x</doi><tpages>20</tpages><oa>free_for_read</oa></addata></record> |
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| source | Oxford Journals Open Access Collection; Wiley Online Library Journals Frontfile Complete |
| subjects | Astronomy Astrophysics Earth, ocean, space Exact sciences and technology Helium Stars & galaxies stars: abundances stars: interiors stars: oscillations Sun Sun: abundances Sun: oscillations |
| title | An asteroseismic signature of helium ionization |
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