A subdwarf O star (sdO) is a type of hot, but low-mass star. O-type subdwarfs are much dimmer than regular O-type main-sequence stars, but with a brightness about 10 to 100 times that of the Sun,[1] and have a mass approximately half that of the Sun. Their temperature ranges from 40,000 to 100,000 K. Ionized helium is prominent in their spectra. Gravity acceleration is expressed by log g between 4.0 and 6.5.[2] Many sdO stars are moving at high velocity through the Milky Way and are found at high galactic latitudes.[3]
The structure of a subdwarf O star is believed to be a carbon and oxygen core surrounded by a helium burning shell. The spectrum shows that the content is from 50 to 100% helium.[2]
Historyedit
In the early 1970s Greenstein and Sargent measured temperatures and gravity strengths and were able to plot their correct position on the Hertzsprung-Russell diagram. The Palomar-Green survey, Hamburg surveys, Sloan Digital Sky Survey and Supernova Ia Progenitor Survey (ESO-SPY) have documented many of these stars.[4]
There is actually a variety of spectra from the sdO stars. They can be grouped into those with strong helium lines, termed He-sdO, and those with stronger hydrogen lines, H strong sdO. The He-sdO are fairly rare.[4] Usually nitrogen is enriched and carbon depleted. However, there are variations with enhancement in concentration of even numbered elements such as carbon, oxygen, neon, silicon, magnesium or iron.[2]
HIP 52181 pulsates with a frequency of 1.04 milliHertz.[2]
HD 49798 is a carbon poor X-ray binary at 830pc.[3]
US 708 is a hypervelocity star that exceeds the escape velocity of the Milky Way.[5]
Life cycleedit
Planetary nebula remains of a dead giant star leaving behind a Subdwarf O star.[6]
They can be plotted on the Hertzsprung–Russell diagram. They are from two stages in the stellar lifecycle, post–asymptotic giant branch (the luminous sdO), and post–extended horizontal branch compact sdO. The post-AGB stars are expected to be found in planetary nebulas, but only four of the sdO stars are known to be like this. The compact sdOs would be descendants of the B-type subdwarfs. However, statistics do not match sdB. An alternate theory is that sdOs have been formed by coalescing two white dwarfs. This could happen from a close binary that decays due to gravitational waves.[2]
Referencesedit
^Napiwotski, Ralf. "The Origin of Helium Rich Subdwarf O Stars" (PDF). Retrieved 9 June 2011.
^ abcdefRey, Raquel Obeiro. "Asterosismology of Hot Subdwarf Stars" (PDF). Retrieved 9 June 2011.
^ abViotti, R.; D. Cardini; A. Emanuele; M. Badiali. "The Luminosity and Kinematics of a Sample of Hot Subdwarfs" (PDF). pp. 395–396. Retrieved 9 June 2011.
^ abcHeber, Ulrich (September 2009). (PDF). Annual Review of Astronomy and Astrophysics. 47 (1): 211–251. Bibcode:2009ARA&A..47..211H. doi:10.1146/annurev-astro-082708-101836. Archived from the original (PDF) on 21 July 2011. Retrieved 10 June 2011.
^Heber, Uli; Hirsch, Heiko; Edelmann, Heinz; Napiwotzki, Ralf; O'Toole, Simon; Brown, Warren; Altmann, Martin (2008). "Hypervelocity Stars: Young and Heavy or Old and Light?". Hot Subdwarf Stars and Related Objects. 392: 167. arXiv:0805.1050. Bibcode:2008ASPC..392..167H.
^"A Fleeting Moment in Time - European Southern Observatory's Cosmic Gems Programme captures last breath of a dying star". www.eso.org. Retrieved 22 January 2019.
December 18, 2023
subdwarf, star, subdwarf, star, type, mass, star, type, subdwarfs, much, dimmer, than, regular, type, main, sequence, stars, with, brightness, about, times, that, have, mass, approximately, half, that, their, temperature, ranges, from, ionized, helium, promine. A subdwarf O star sdO is a type of hot but low mass star O type subdwarfs are much dimmer than regular O type main sequence stars but with a brightness about 10 to 100 times that of the Sun 1 and have a mass approximately half that of the Sun Their temperature ranges from 40 000 to 100 000 K Ionized helium is prominent in their spectra Gravity acceleration is expressed by log g between 4 0 and 6 5 2 Many sdO stars are moving at high velocity through the Milky Way and are found at high galactic latitudes 3 Schematic cross section of an O type subdwarf Contents 1 Structure 2 History 3 Occurrence 4 Spectrum 5 Examples 6 Life cycle 7 ReferencesStructure editThe structure of a subdwarf O star is believed to be a carbon and oxygen core surrounded by a helium burning shell The spectrum shows that the content is from 50 to 100 helium 2 History editIn the early 1970s Greenstein and Sargent measured temperatures and gravity strengths and were able to plot their correct position on the Hertzsprung Russell diagram The Palomar Green survey Hamburg surveys Sloan Digital Sky Survey and Supernova Ia Progenitor Survey ESO SPY have documented many of these stars 4 Occurrence editSubdwarf O stars are only a third as common as subdwarf B stars 4 Spectrum editThere is actually a variety of spectra from the sdO stars They can be grouped into those with strong helium lines termed He sdO and those with stronger hydrogen lines H strong sdO The He sdO are fairly rare 4 Usually nitrogen is enriched and carbon depleted However there are variations with enhancement in concentration of even numbered elements such as carbon oxygen neon silicon magnesium or iron 2 Examples editHD 128220 was studied by Corrado Bartolini 2 HIP 52181 pulsates with a frequency of 1 04 milliHertz 2 HD 49798 is a carbon poor X ray binary at 830pc 3 US 708 is a hypervelocity star that exceeds the escape velocity of the Milky Way 5 Life cycle edit nbsp Planetary nebula remains of a dead giant star leaving behind a Subdwarf O star 6 They can be plotted on the Hertzsprung Russell diagram They are from two stages in the stellar lifecycle post asymptotic giant branch the luminous sdO and post extended horizontal branch compact sdO The post AGB stars are expected to be found in planetary nebulas but only four of the sdO stars are known to be like this The compact sdOs would be descendants of the B type subdwarfs However statistics do not match sdB An alternate theory is that sdOs have been formed by coalescing two white dwarfs This could happen from a close binary that decays due to gravitational waves 2 References edit Napiwotski Ralf The Origin of Helium Rich Subdwarf O Stars PDF Retrieved 9 June 2011 a b c d e f Rey Raquel Obeiro Asterosismology of Hot Subdwarf Stars PDF Retrieved 9 June 2011 a b Viotti R D Cardini A Emanuele M Badiali The Luminosity and Kinematics of a Sample of Hot Subdwarfs PDF pp 395 396 Retrieved 9 June 2011 a b c Heber Ulrich September 2009 Hot Subdwarf Stars PDF Annual Review of Astronomy and Astrophysics 47 1 211 251 Bibcode 2009ARA amp A 47 211H doi 10 1146 annurev astro 082708 101836 Archived from the original PDF on 21 July 2011 Retrieved 10 June 2011 Heber Uli Hirsch Heiko Edelmann Heinz Napiwotzki Ralf O Toole Simon Brown Warren Altmann Martin 2008 Hypervelocity Stars Young and Heavy or Old and Light Hot Subdwarf Stars and Related Objects 392 167 arXiv 0805 1050 Bibcode 2008ASPC 392 167H A Fleeting Moment in Time European Southern Observatory s Cosmic Gems Programme captures last breath of a dying star www eso org Retrieved 22 January 2019 Retrieved from https en wikipedia org w index php title Subdwarf O star amp oldid 1126571628, wikipedia, wiki, book, books, library,
