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Red clump

January 10, 2023

The red clump is a clustering of red giants in the Hertzsprung–Russell diagram at around 5,000 K and absolute magnitude (MV) +0.5, slightly hotter than most red-giant-branch stars of the same luminosity. It is visible as a denser region of the red-giant branch or a bulge towards hotter temperatures. It is prominent in many galactic open clusters, and it is also noticeable in many intermediate-age globular clusters and in nearby field stars (e.g. the Hipparcos stars).

The red clump is the prominent group of red giant stars at about 5,000 K and 75 L☉.

The red clump giants are cool horizontal branch stars, stars originally similar to the Sun which have undergone a helium flash and are now fusing helium in their cores.

Properties

Red clump stellar properties vary depending on their origin, most notably on the metallicity of the stars, but typically they have early K spectral types and effective temperatures around 5,000 K. The absolute visual magnitude of red clump giants near the sun has been measured at an average of +0.81 with metallicities between −0.6 and +0.4 dex.[1]

There is a considerable spread in the properties of red clump stars even within a single population of similar stars such as an open cluster. This is partly due to the natural variation in temperatures and luminosities of horizontal branch stars when they form and as they evolve, and partly due to the presence of other stars with similar properties.[2] Although red clump stars are generally hotter than red-giant-branch stars, the two regions overlap and the status of individual stars can only be assigned with a detailed chemical abundance study.[3][4]

Evolution

Main article: Horizontal branch
 
Old open clusters showing barely detectable red clumps[5]

Modelling of the horizontal branch has shown that stars have a strong tendency to cluster at the cool end of the zero age horizontal branch (ZAHB). This tendency is weaker in low metallicity stars, so the red clump is usually more prominent in metal-rich clusters. However, there are other effects, and there are well-populated red clumps in some metal-poor globular clusters.[6][7]

Stars with a similar mass to the sun evolve towards the tip of the red-giant branch with a degenerate helium core. More massive stars leave the red-giant branch early and perform a blue loop, but all stars with a degenerate core reach the tip with very similar core masses, temperatures, and luminosities. After the helium flash they lie along the ZAHB, all with helium cores just under 0.5 M☉ and their properties determined mostly by the size of the hydrogen envelope outside the core. Lower envelope masses result in weaker hydrogen shell fusion and give hotter and slightly less luminous stars strung along the horizontal branch. Different initial masses and natural variations in mass loss rates on the red-giant branch cause the variations in the envelope masses even though the helium cores are all the same size. Low-metallicity stars are more sensitive to the size of the hydrogen envelope, so with the same envelope masses they are spread further along the horizontal branch and fewer fall in the red clump.

Although red clump stars lie consistently to the hot side of the red-giant branch that they evolved from, red clump and red-giant-branch stars from different populations can overlap. This occurs in ω Centauri where metal-poor red-giant-branch stars have the same or hotter temperatures as more metal-rich red clump giants.[3]

Other stars, not strictly horizontal branch stars, can lie in the same region of the H-R diagram. Stars too massive to develop a degenerate helium core on the red-giant branch will ignite helium before the tip of the red-giant branch and perform a blue loop. For stars only a little more massive than the sun, around 2 M☉, the blue loop is very short and at a luminosity similar to the red clump giants. These stars are an order of magnitude less common than sun-like stars, even rarer compared to the sub-solar stars that can form red clump giants, and the duration of the blue loop is far less than the time spent by a red clump giant on the horizontal branch. This means that these imposters are much less common in the H–R diagram, but still detectable.[2]

Stars with 2–3 M☉ will also pass through the red clump as they evolve along the subgiant branch. This is again a very rapid phase of evolution, but stars such as OU Andromedae are found in the red clump region (5,500 K and 100 L☉) even though it is thought to be a subgiant crossing the Hertzsprung gap.[2]

Standard candles

In theory, the absolute luminosities of stars in the red clump are fairly independent of stellar composition or age so that consequently they make good standard candles for estimating astronomical distances both within our galaxy and to nearby galaxies and clusters. Variations due to metallicity, mass, age, and extinctions affect visual observations too much for them to be useful, but the effects are much smaller in the infrared. Near infrared I band observations in particular have been used to establish red clump distances. Absolute magnitudes for the red clump at solar metallicity have been measured at −0.22 in the I band and −1.54 in the K band.[8] The distance to the Galactic Center has been measured in this way, giving a result of 7.52 kpc in agreement with other methods.[9]

Red bump

The red clump should not be confused with the "red bump" or red-giant-branch bump, which is a less noticeable clustering of giants partway along the red-giant branch, caused as stars ascending the red-giant branch temporarily decrease in luminosity because of internal convection.[10]

Examples

Many of the bright "red giants" visible in the sky are actually early K class red-clump stars:

Arcturus has sometimes been thought to be a clump giant,[13] but is now more commonly considered to be on the red-giant branch, somewhat cooler and more luminous than a red-clump star.[14]

References

  1. ^ Soubiran, C.; Bienaymé, O.; Siebert, A. (2003). "Vertical distribution of Galactic disk stars". Astronomy and Astrophysics. 398: 141–151. arXiv:astro-ph/0210628. Bibcode:2003A&A...398..141S. doi:10.1051/0004-6361:20021615. S2CID 14060900.
  2. ^ a b c Girardi, Léo (1999). "A secondary clump of red giant stars: Why and where". Monthly Notices of the Royal Astronomical Society. 308 (3): 818–832. arXiv:astro-ph/9901319. Bibcode:1999MNRAS.308..818G. doi:10.1046/j.1365-8711.1999.02746.x. S2CID 3253711.
  3. ^ a b Ree, C. H.; Yoon, S.-J.; Rey, S.-C.; Lee, Y.-W. (2002). "Synthetic Color-Magnitude Diagrams for ω Centauri and Other Massive Globular Clusters with Multiple Populations". Omega Centauri. 265: 101. arXiv:astro-ph/0110689. Bibcode:2002ASPC..265..101R.
  4. ^ Nataf, D. M.; Udalski, A.; Gould, A.; Fouqué, P.; Stanek, K. Z. (2010). "The Split Red Clump of the Galactic Bulge from OGLE-III". The Astrophysical Journal Letters. 721 (1): L28–L32. arXiv:1007.5065. Bibcode:2010ApJ...721L..28N. doi:10.1088/2041-8205/721/1/L28. S2CID 118602293.
  5. ^ Sarajedini, Ata (1999). "WIYN Open Cluster Study. III. The Observed Variation of the Red Clump Luminosity and Color with Metallicity and Age". The Astronomical Journal. 118 (5): 2321–2326. Bibcode:1999AJ....118.2321S. doi:10.1086/301112.
  6. ^ Zhao, G.; Qiu, H. M.; Mao, Shude (2001). "High-Resolution Spectroscopic Observations of Hipparcos Red Clump Giants: Metallicity and Mass Determinations". The Astrophysical Journal. 551 (1): L85. Bibcode:2001ApJ...551L..85Z. doi:10.1086/319832. S2CID 119700315.
  7. ^ d'Antona, Francesca; Caloi, Vittoria (2004). "The Early Evolution of Globular Clusters: The Case of NGC 2808". The Astrophysical Journal. 611 (2): 871–880. arXiv:astro-ph/0405016. Bibcode:2004ApJ...611..871D. doi:10.1086/422334. S2CID 10112905.
  8. ^ Groenewegen, M. A. T. (2008). "The red clump absolute magnitude based on revised Hipparcos parallaxes". Astronomy and Astrophysics. 488 (3): 935–941. arXiv:0807.2764. Bibcode:2008A&A...488..935G. doi:10.1051/0004-6361:200810201. S2CID 118411109.
  9. ^ Nishiyama, Shogo; Nagata, Tetsuya; Sato, Shuji; Kato, Daisuke; Nagayama, Takahiro; Kusakabe, Nobuhiko; Matsunaga, Noriyuki; Naoi, Takahiro; Sugitani, Koji; Tamura, Motohide (2006). "The Distance to the Galactic Center Derived from Infrared Photometry of Bulge Red Clump Stars". The Astrophysical Journal. 647 (2): 1093–1098. arXiv:astro-ph/0607408. Bibcode:2006ApJ...647.1093N. doi:10.1086/505529. S2CID 17487788.
  10. ^ Alves, David R.; Sarajedini, Ata (1999). "The Age-dependent Luminosities of the Red Giant Branch Bump, Asymptotic Giant Branch Bump, and Horizontal Branch Red Clump". The Astrophysical Journal. 511 (1): 225–234. arXiv:astro-ph/9808253. Bibcode:1999ApJ...511..225A. doi:10.1086/306655. S2CID 18834541.
  11. ^ a b Ayres, Thomas R.; Simon, Theodore; Stern, Robert A.; Drake, Stephen A.; Wood, Brian E.; Brown, Alexander (1998). "The Coronae of Moderate-Mass Giants in the Hertzsprung Gap and the Clump". The Astrophysical Journal. 496 (1): 428–448. Bibcode:1998ApJ...496..428A. doi:10.1086/305347.
  12. ^ Sato, Bun'ei; et al. (2007). "A Planetary Companion to the Hyades Giant ε Tauri". The Astrophysical Journal. 661 (1): 527–531. Bibcode:2007ApJ...661..527S. doi:10.1086/513503.
  13. ^ Maeckle, R.; Holweger, H.; Griffin, R.; Griffin, R. (1975). "A model-atmosphere analysis of the spectrum of Arcturus". Astronomy and Astrophysics. 38: 239. Bibcode:1975A&A....38..239M.
  14. ^ Ramírez, I.; Allende Prieto, C. (2011). "Fundamental Parameters and Chemical Composition of Arcturus". The Astrophysical Journal. 743 (2): 135. arXiv:1109.4425. Bibcode:2011ApJ...743..135R. doi:10.1088/0004-637X/743/2/135. S2CID 119186472.

External links

  • Stanek's page on red clumps used for distance measurement

January 10, 2023
clump, clump, clustering, giants, hertzsprung, russell, diagram, around, absolute, magnitude, slightly, hotter, than, most, giant, branch, stars, same, luminosity, visible, denser, region, giant, branch, bulge, towards, hotter, temperatures, prominent, many, g. The red clump is a clustering of red giants in the Hertzsprung Russell diagram at around 5 000 K and absolute magnitude MV 0 5 slightly hotter than most red giant branch stars of the same luminosity It is visible as a denser region of the red giant branch or a bulge towards hotter temperatures It is prominent in many galactic open clusters and it is also noticeable in many intermediate age globular clusters and in nearby field stars e g the Hipparcos stars The red clump is the prominent group of red giant stars at about 5 000 K and 75 L The red clump giants are cool horizontal branch stars stars originally similar to the Sun which have undergone a helium flash and are now fusing helium in their cores Contents 1 Properties 2 Evolution 3 Standard candles 4 Red bump 5 Examples 6 References 7 External linksProperties EditRed clump stellar properties vary depending on their origin most notably on the metallicity of the stars but typically they have early K spectral types and effective temperatures around 5 000 K The absolute visual magnitude of red clump giants near the sun has been measured at an average of 0 81 with metallicities between 0 6 and 0 4 dex 1 There is a considerable spread in the properties of red clump stars even within a single population of similar stars such as an open cluster This is partly due to the natural variation in temperatures and luminosities of horizontal branch stars when they form and as they evolve and partly due to the presence of other stars with similar properties 2 Although red clump stars are generally hotter than red giant branch stars the two regions overlap and the status of individual stars can only be assigned with a detailed chemical abundance study 3 4 Evolution EditMain article Horizontal branch Old open clusters showing barely detectable red clumps 5 Modelling of the horizontal branch has shown that stars have a strong tendency to cluster at the cool end of the zero age horizontal branch ZAHB This tendency is weaker in low metallicity stars so the red clump is usually more prominent in metal rich clusters However there are other effects and there are well populated red clumps in some metal poor globular clusters 6 7 Stars with a similar mass to the sun evolve towards the tip of the red giant branch with a degenerate helium core More massive stars leave the red giant branch early and perform a blue loop but all stars with a degenerate core reach the tip with very similar core masses temperatures and luminosities After the helium flash they lie along the ZAHB all with helium cores just under 0 5 M and their properties determined mostly by the size of the hydrogen envelope outside the core Lower envelope masses result in weaker hydrogen shell fusion and give hotter and slightly less luminous stars strung along the horizontal branch Different initial masses and natural variations in mass loss rates on the red giant branch cause the variations in the envelope masses even though the helium cores are all the same size Low metallicity stars are more sensitive to the size of the hydrogen envelope so with the same envelope masses they are spread further along the horizontal branch and fewer fall in the red clump Although red clump stars lie consistently to the hot side of the red giant branch that they evolved from red clump and red giant branch stars from different populations can overlap This occurs in w Centauri where metal poor red giant branch stars have the same or hotter temperatures as more metal rich red clump giants 3 Other stars not strictly horizontal branch stars can lie in the same region of the H R diagram Stars too massive to develop a degenerate helium core on the red giant branch will ignite helium before the tip of the red giant branch and perform a blue loop For stars only a little more massive than the sun around 2 M the blue loop is very short and at a luminosity similar to the red clump giants These stars are an order of magnitude less common than sun like stars even rarer compared to the sub solar stars that can form red clump giants and the duration of the blue loop is far less than the time spent by a red clump giant on the horizontal branch This means that these imposters are much less common in the H R diagram but still detectable 2 Stars with 2 3 M will also pass through the red clump as they evolve along the subgiant branch This is again a very rapid phase of evolution but stars such as OU Andromedae are found in the red clump region 5 500 K and 100 L even though it is thought to be a subgiant crossing the Hertzsprung gap 2 Standard candles EditIn theory the absolute luminosities of stars in the red clump are fairly independent of stellar composition or age so that consequently they make good standard candles for estimating astronomical distances both within our galaxy and to nearby galaxies and clusters Variations due to metallicity mass age and extinctions affect visual observations too much for them to be useful but the effects are much smaller in the infrared Near infrared I band observations in particular have been used to establish red clump distances Absolute magnitudes for the red clump at solar metallicity have been measured at 0 22 in the I band and 1 54 in the K band 8 The distance to the Galactic Center has been measured in this way giving a result of 7 52 kpc in agreement with other methods 9 Red bump EditThe red clump should not be confused with the red bump or red giant branch bump which is a less noticeable clustering of giants partway along the red giant branch caused as stars ascending the red giant branch temporarily decrease in luminosity because of internal convection 10 Examples EditMany of the bright red giants visible in the sky are actually early K class red clump stars Capella Aa 11 e Tauri 12 b Ceti 11 Arcturus has sometimes been thought to be a clump giant 13 but is now more commonly considered to be on the red giant branch somewhat cooler and more luminous than a red clump star 14 References Edit Soubiran C Bienayme O Siebert A 2003 Vertical distribution of Galactic disk stars Astronomy and Astrophysics 398 141 151 arXiv astro ph 0210628 Bibcode 2003A amp A 398 141S doi 10 1051 0004 6361 20021615 S2CID 14060900 a b c Girardi Leo 1999 A secondary clump of red giant stars Why and where Monthly Notices of the Royal Astronomical Society 308 3 818 832 arXiv astro ph 9901319 Bibcode 1999MNRAS 308 818G doi 10 1046 j 1365 8711 1999 02746 x S2CID 3253711 a b Ree C H Yoon S J Rey S C Lee Y W 2002 Synthetic Color Magnitude Diagrams for w Centauri and Other Massive Globular Clusters with Multiple Populations Omega Centauri 265 101 arXiv astro ph 0110689 Bibcode 2002ASPC 265 101R Nataf D M Udalski A Gould A Fouque P Stanek K Z 2010 The Split Red Clump of the Galactic Bulge from OGLE III The Astrophysical Journal Letters 721 1 L28 L32 arXiv 1007 5065 Bibcode 2010ApJ 721L 28N doi 10 1088 2041 8205 721 1 L28 S2CID 118602293 Sarajedini Ata 1999 WIYN Open Cluster Study III The Observed Variation of the Red Clump Luminosity and Color with Metallicity and Age The Astronomical Journal 118 5 2321 2326 Bibcode 1999AJ 118 2321S doi 10 1086 301112 Zhao G Qiu H M Mao Shude 2001 High Resolution Spectroscopic Observations of Hipparcos Red Clump Giants Metallicity and Mass Determinations The Astrophysical Journal 551 1 L85 Bibcode 2001ApJ 551L 85Z doi 10 1086 319832 S2CID 119700315 d Antona Francesca Caloi Vittoria 2004 The Early Evolution of Globular Clusters The Case of NGC 2808 The Astrophysical Journal 611 2 871 880 arXiv astro ph 0405016 Bibcode 2004ApJ 611 871D doi 10 1086 422334 S2CID 10112905 Groenewegen M A T 2008 The red clump absolute magnitude based on revised Hipparcos parallaxes Astronomy and Astrophysics 488 3 935 941 arXiv 0807 2764 Bibcode 2008A amp A 488 935G doi 10 1051 0004 6361 200810201 S2CID 118411109 Nishiyama Shogo Nagata Tetsuya Sato Shuji Kato Daisuke Nagayama Takahiro Kusakabe Nobuhiko Matsunaga Noriyuki Naoi Takahiro Sugitani Koji Tamura Motohide 2006 The Distance to the Galactic Center Derived from Infrared Photometry of Bulge Red Clump Stars The Astrophysical Journal 647 2 1093 1098 arXiv astro ph 0607408 Bibcode 2006ApJ 647 1093N doi 10 1086 505529 S2CID 17487788 Alves David R Sarajedini Ata 1999 The Age dependent Luminosities of the Red Giant Branch Bump Asymptotic Giant Branch Bump and Horizontal Branch Red Clump The Astrophysical Journal 511 1 225 234 arXiv astro ph 9808253 Bibcode 1999ApJ 511 225A doi 10 1086 306655 S2CID 18834541 a b Ayres Thomas R Simon Theodore Stern Robert A Drake Stephen A Wood Brian E Brown Alexander 1998 The Coronae of Moderate Mass Giants in the Hertzsprung Gap and the Clump The Astrophysical Journal 496 1 428 448 Bibcode 1998ApJ 496 428A doi 10 1086 305347 Sato Bun ei et al 2007 A Planetary Companion to the Hyades Giant e Tauri The Astrophysical Journal 661 1 527 531 Bibcode 2007ApJ 661 527S doi 10 1086 513503 Maeckle R Holweger H Griffin R Griffin R 1975 A model atmosphere analysis of the spectrum of Arcturus Astronomy and Astrophysics 38 239 Bibcode 1975A amp A 38 239M Ramirez I Allende Prieto C 2011 Fundamental Parameters and Chemical Composition of Arcturus The Astrophysical Journal 743 2 135 arXiv 1109 4425 Bibcode 2011ApJ 743 135R doi 10 1088 0004 637X 743 2 135 S2CID 119186472 External links EditStanek s page on red clumps used for distance measurement Retrieved from https en wikipedia org w index php title Red clump amp oldid 1112753112, wikipedia, wiki, book, books, library,

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