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RR Lyrae variable

January 01, 1970

This article is about the variable star class. For the prototype star of the class, see RR Lyrae.

RR Lyrae variables are periodic variable stars, commonly found in globular clusters. They are used as standard candles to measure (extra) galactic distances, assisting with the cosmic distance ladder. This class is named after the prototype and brightest example, RR Lyrae.

The RR Lyrae variable stars fall in a particular area on a Hertzsprung–Russell diagram of color versus brightness.

They are pulsating horizontal branch stars of spectral class A or F, with a mass of around half the Sun's. They are thought to have shed mass during the red-giant branch phase, and were once stars at around 0.8 solar masses.

In contemporary astronomy, a period-luminosity relation makes them good standard candles for relatively nearby targets, especially within the Milky Way and Local Group. They are also frequent subjects in the studies of globular clusters and the chemistry (and quantum mechanics) of older stars.

Discovery and recognition edit

 
H-R diagram for globular cluster M5, with the horizontal branch marked in yellow and known RR Lyrae stars in green

In surveys of globular clusters, these "cluster-type" variables were being rapidly identified in the mid-1890s, especially by E. C. Pickering. Probably the first star definitely of RR Lyrae type found outside a cluster was U Leporis, discovered by J. Kapteyn in 1890. The prototype star RR Lyrae was discovered prior to 1899 by Williamina Fleming, and reported by Pickering in 1900 as "indistinguishable from cluster-type variables".[1]

From 1915 to the 1930s, the RR Lyraes became increasingly accepted as a class of star distinct from the classical Cepheids, due to their shorter periods, differing locations within the galaxy, and chemical differences. RR Lyrae variables are metal-poor, Population II stars.[1]

RR Lyraes have proven difficult to observe in external galaxies because of their intrinsic faintness. (In fact, Walter Baade's failure to find them in the Andromeda Galaxy led him to suspect that the galaxy was much farther away than predicted, to reconsider the calibration of Cepheid variables, and to propose the concept of stellar populations.[1]) Using the Canada-France-Hawaii Telescope in the 1980s, Pritchet & van den Bergh found RR Lyraes in Andromeda's galactic halo[2] and, more recently, in its globular clusters.[3]

Classification edit

The RR Lyrae stars are conventionally divided into three main types,[1] following classification by S.I. Bailey based on the shape of the stars' brightness curves:

  • RRab variables are the most common, making up 91% of all observed RR Lyrae, and display the steep rises in brightness typical of RR Lyrae
  • RRc are less common, making up 9% of observed RR Lyrae, and have shorter periods and more sinusoidal variation
  • RRd are rare, making up between <1% and 30%[4] of RR Lyrae in a system, and are double-mode pulsators, unlike RRab and RRc

Distribution edit

 
RR Lyrae-type variable stars close to the galactic center from the VVV ESO public survey

RR Lyrae stars were formerly called "cluster variables" because of their strong (but not exclusive) association with globular clusters; conversely, over 80% of all variables known in globular clusters are RR Lyraes.[5] RR Lyrae stars are found at all galactic latitudes, as opposed to classical Cepheids, which are strongly associated with the galactic plane.

Because of their old age, RR Lyraes are commonly used to trace certain populations in the Milky Way, including the halo and thick disk.[6]

Several times as many RR Lyraes are known as all Cepheids combined; in the 1980s, about 1900 were known in globular clusters. Some estimates have about 85,000 in the Milky Way.[1]

Though binary star systems are common for typical stars, RR Lyraes are very rarely observed in binaries.[7]

Properties edit

RR Lyrae stars pulse in a manner similar to Cepheid variables, but the nature and histories of these stars is thought to be rather different. Like all variables on the Cepheid instability strip, pulsations are caused by the κ-mechanism, when the opacity of ionised helium varies with its temperature.

RR Lyraes are old, relatively low mass, Population II stars, in common with W Virginis and BL Herculis variables, the type II Cepheids. Classical Cepheid variables are higher mass population I stars. RR Lyrae variables are much more common than Cepheids, but also much less luminous. The average absolute magnitude of an RR Lyrae star is about +0.75, only 40 or 50 times brighter than the Sun.[8] Their period is shorter, typically less than one day, sometimes ranging down to seven hours. Some RRab stars, including RR Lyrae itself, exhibit the Blazhko effect in which there is a conspicuous phase and amplitude modulation.[9]

Period-luminosity relationships edit

 
Typical RR Lyrae light curve

Unlike Cepheid variables, RR Lyrae variables do not follow a strict period-luminosity relationship at visual wavelengths, although they do in the infrared K band.[10] They are normally analysed using a period-colour-relationship, for example using a Wesenheit function. In this way, they can be used as standard candles for distance measurements although there are difficulties with the effects of metallicity, faintness, and blending. The effect of blending can impact RR Lyrae variables sampled near the cores of globular clusters, which are so dense that in low-resolution observations multiple (unresolved) stars may appear as a single target. Thus the brightness measured for that seemingly single star (e.g., an RR Lyrae variable) is erroneously too bright, given those unresolved stars contributed to the brightness determined. Consequently, the computed distance is wrong, and certain researchers have argued that the blending effect can introduce a systematic uncertainty into the cosmic distance ladder, and may bias the estimated age of the Universe and the Hubble constant.[11][12][13]

Recent developments edit

The Hubble Space Telescope has identified several RR Lyrae candidates in globular clusters of the Andromeda Galaxy[3] and has measured the distance to the prototype star RR Lyrae.[14]

The Kepler space telescope provided accurate photometric coverage of a single field at regular intervals over an extended period. 37 known RR Lyrae variables lie within the Kepler field, including RR Lyrae itself, and new phenomena such as period-doubling have been detected.[15]

The Gaia mission mapped 140,784 RR Lyrae stars, of which 50,220 were not previously known to be variable, and for which 54,272 interstellar absorption estimates are available.[16]

References edit

  1. ^ a b c d e Smith, Horace A. (2004). RR Lyrae Stars. Cambridge University Press. ISBN 978-0-521-54817-5.
  2. ^ Pritchet, Christopher J.; Van Den Bergh, Sidney (1987). "Observations of RR Lyrae stars in the halo of M31". Astrophysical Journal. 316: 517. Bibcode:1987ApJ...316..517P. doi:10.1086/165223.
  3. ^ a b Clementini, G.; Federici, L.; Corsi, C.; Cacciari, C.; Bellazzini, M.; Smith, H. A. (2001). "RR Lyrae Variables in the Globular Clusters of M31: A First Detection of Likely Candidates". The Astrophysical Journal. 559 (2): L109. arXiv:astro-ph/0108418. Bibcode:2001ApJ...559L.109C. doi:10.1086/323973. S2CID 48632444.
  4. ^ Christensen-Dalsgaard, J.; Balona, L. A.; Garrido, R.; Suárez, J.C. (Oct 20, 2012). "Stellar Pulsations: Impact of New Instrumentation and New Insights". Astrophysics and Space Science Proceedings. ISBN 978-3-642-29630-7.
  5. ^ Clement, Christine M.; Muzzin, Adam; Dufton, Quentin; Ponnampalam, Thivya; Wang, John; Burford, Jay; Richardson, Alan; Rosebery, Tara; Rowe, Jason; Hogg, Helen Sawyer (2001). "Variable Stars in Galactic Globular Clusters". The Astronomical Journal. 122 (5): 2587–2599. arXiv:astro-ph/0108024. Bibcode:2001AJ....122.2587C. doi:10.1086/323719. S2CID 38359010.
  6. ^ Vozyakova, O. V.; Sefako, R.; Rastorguev, A. S.; Kravtsov, V. V.; Kniazev, A. Y.; Berdnikov, L. N.; Dambis, A. K. (2013-11-11). "RR Lyrae variables: visual and infrared luminosities, intrinsic colours and kinematics". Monthly Notices of the Royal Astronomical Society. 435 (4): 3206–3220. arXiv:1308.4727. doi:10.1093/mnras/stt1514. ISSN 0035-8711.
  7. ^ Hajdu, G.; Catelan, M.; Jurcsik, J.; Dékány, I.; Drake, A.J.; Marquette, B. (2015). "New RR Lyrae variables in binary systems". Monthly Notices of the Royal Astronomical Society. 449 (1): L113–L117. arXiv:1502.01318. Bibcode:2015MNRAS.449L.113H. doi:10.1093/mnrasl/slv024.
  8. ^ Layden, A. C.; Hanson, Robert B.; Hawley, Suzanne L.; Klemola, Arnold R.; Hanley, Christopher J. (August 1996). "The Absolute Magnitude and Kinematics of RR Lyrae Stars via Statistical Parallax". Astron. J. 112: 2110–2131. arXiv:astro-ph/9608108. Bibcode:1996AJ....112.2110L. doi:10.1086/118167. S2CID 8732647.
  9. ^ Szabó, R.; Kolláth, Z.; Molnár, L.; Kolenberg, K.; Kurtz, D. W.; Bryson, S. T.; Benkő, J. M.; Christensen-Dalsgaard, J.; Kjeldsen, H.; Borucki, W. J.; Koch, D.; Twicken, J. D.; Chadid, M.; Di Criscienzo, M.; Jeon, Y.-B.; Moskalik, P.; Nemec, J. M.; Nuspl, J. (2010). "Does Kepler unveil the mystery of the Blazhko effect? First detection of period doubling in Kepler Blazhko RR Lyrae stars". Monthly Notices of the Royal Astronomical Society. 409 (3): 1244. arXiv:1007.3404. Bibcode:2010MNRAS.409.1244S. doi:10.1111/j.1365-2966.2010.17386.x. S2CID 119190883.
  10. ^ Catelan, M.; Pritzl, Barton J.; Smith, Horace A. (2004). "The RR Lyrae Period-Luminosity Relation. I. Theoretical Calibration". The Astrophysical Journal Supplement Series. 154 (2): 633. arXiv:astro-ph/0406067. Bibcode:2004ApJS..154..633C. doi:10.1086/422916. S2CID 119336592.
  11. ^ Majaess, D.; Turner, D.; Gieren, W.; Lane, D. (2012). "The Impact of Contaminated RR Lyrae/Globular Cluster Photometry on the Distance Scale". The Astrophysical Journal Letters. 752 (1): L10. arXiv:1205.0255. Bibcode:2012ApJ...752L..10M. doi:10.1088/2041-8205/752/1/L10. S2CID 118528078.
  12. ^ Lee, Jae-Woo; López-Morales, Mercedes; Hong, Kyeongsoo; Kang, Young-Woon; Pohl, Brian L.; Walker, Alistair (2014). "Toward a Better Understanding of the Distance Scale from RR Lyrae Variable Stars: A Case Study for the Inner Halo Globular Cluster NGC 6723". The Astrophysical Journal Supplement. 210 (1): 6. arXiv:1311.2054. Bibcode:2014ApJS..210....6L. doi:10.1088/0067-0049/210/1/6. S2CID 119280050.
  13. ^ Neeley, J. R.; Marengo, M.; Bono, G.; Braga, V. F.; Dall'Ora, M.; Stetson, P. B.; Buonanno, R.; Ferraro, I.; Freedman, W. L.; Iannicola, G.; Madore, B. F.; Matsunaga, N.; Monson, A.; Persson, S. E.; Scowcroft, V.; Seibert, M. (2015). "On the Distance of the Globular Cluster M4 (NGC 6121) Using RR Lyrae Stars. II. Mid-infrared Period-luminosity Relations". The Astrophysical Journal. 808 (1): 11. arXiv:1505.07858. Bibcode:2015ApJ...808...11N. doi:10.1088/0004-637X/808/1/11. S2CID 117031686.
  14. ^ Benedict, G. Fritz; et al. (January 2002). "Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae". The Astronomical Journal. 123 (1): 473–484. arXiv:astro-ph/0110271. Bibcode:2002AJ....123..473B. doi:10.1086/338087. S2CID 59150013.
  15. ^ Kinemuchi, Karen (2011). "RR Lyrae Research with the Kepler Mission". RR Lyrae Stars. 5: 74. arXiv:1107.0297. Bibcode:2011rrls.conf...74K.
  16. ^ Riello, M.; Evans, D. W.; Szabados, L.; Sarro, L. M.; Regibo, S.; Ridder, J. De; Eyer, L.; Lecoeur-Taibi, I.; Mowlavi, N. (2019-02-01). "Gaia Data Release 2 - Specific characterisation and validation of all-sky Cepheids and RR Lyrae stars". Astronomy & Astrophysics. 622: A60. arXiv:1805.02079. Bibcode:2019A&A...622A..60C. doi:10.1051/0004-6361/201833374. ISSN 0004-6361. S2CID 260496633.

External links edit

  • APOD M3: Inconstant Star Cluster four-frame animation of RR Lyrae variables in globular cluster M3
  • Animation of RR Lyrae-Variables in globular cluster M15
  • Animation with the variable stars RR Lyrae in the center area of the globular cluster M15
  • RR Lyrae stars
  • AAVSO Variable Star of the Season - RR Lyrae
  • OGLE Atlas of Variable Star Light Curves - RR Lyrae stars

January 01, 1970
lyrae, variable, this, article, about, variable, star, class, prototype, star, class, lyrae, periodic, variable, stars, commonly, found, globular, clusters, they, used, standard, candles, measure, extra, galactic, distances, assisting, with, cosmic, distance, . This article is about the variable star class For the prototype star of the class see RR Lyrae RR Lyrae variables are periodic variable stars commonly found in globular clusters They are used as standard candles to measure extra galactic distances assisting with the cosmic distance ladder This class is named after the prototype and brightest example RR Lyrae The RR Lyrae variable stars fall in a particular area on a Hertzsprung Russell diagram of color versus brightness They are pulsating horizontal branch stars of spectral class A or F with a mass of around half the Sun s They are thought to have shed mass during the red giant branch phase and were once stars at around 0 8 solar masses In contemporary astronomy a period luminosity relation makes them good standard candles for relatively nearby targets especially within the Milky Way and Local Group They are also frequent subjects in the studies of globular clusters and the chemistry and quantum mechanics of older stars Contents 1 Discovery and recognition 2 Classification 3 Distribution 4 Properties 5 Period luminosity relationships 6 Recent developments 7 References 8 External linksDiscovery and recognition edit nbsp H R diagram for globular cluster M5 with the horizontal branch marked in yellow and known RR Lyrae stars in green In surveys of globular clusters these cluster type variables were being rapidly identified in the mid 1890s especially by E C Pickering Probably the first star definitely of RR Lyrae type found outside a cluster was U Leporis discovered by J Kapteyn in 1890 The prototype star RR Lyrae was discovered prior to 1899 by Williamina Fleming and reported by Pickering in 1900 as indistinguishable from cluster type variables 1 From 1915 to the 1930s the RR Lyraes became increasingly accepted as a class of star distinct from the classical Cepheids due to their shorter periods differing locations within the galaxy and chemical differences RR Lyrae variables are metal poor Population II stars 1 RR Lyraes have proven difficult to observe in external galaxies because of their intrinsic faintness In fact Walter Baade s failure to find them in the Andromeda Galaxy led him to suspect that the galaxy was much farther away than predicted to reconsider the calibration of Cepheid variables and to propose the concept of stellar populations 1 Using the Canada France Hawaii Telescope in the 1980s Pritchet amp van den Bergh found RR Lyraes in Andromeda s galactic halo 2 and more recently in its globular clusters 3 Classification editThe RR Lyrae stars are conventionally divided into three main types 1 following classification by S I Bailey based on the shape of the stars brightness curves RRab variables are the most common making up 91 of all observed RR Lyrae and display the steep rises in brightness typical of RR Lyrae RRc are less common making up 9 of observed RR Lyrae and have shorter periods and more sinusoidal variation RRd are rare making up between lt 1 and 30 4 of RR Lyrae in a system and are double mode pulsators unlike RRab and RRcDistribution edit nbsp RR Lyrae type variable stars close to the galactic center from the VVV ESO public survey RR Lyrae stars were formerly called cluster variables because of their strong but not exclusive association with globular clusters conversely over 80 of all variables known in globular clusters are RR Lyraes 5 RR Lyrae stars are found at all galactic latitudes as opposed to classical Cepheids which are strongly associated with the galactic plane Because of their old age RR Lyraes are commonly used to trace certain populations in the Milky Way including the halo and thick disk 6 Several times as many RR Lyraes are known as all Cepheids combined in the 1980s about 1900 were known in globular clusters Some estimates have about 85 000 in the Milky Way 1 Though binary star systems are common for typical stars RR Lyraes are very rarely observed in binaries 7 Properties editRR Lyrae stars pulse in a manner similar to Cepheid variables but the nature and histories of these stars is thought to be rather different Like all variables on the Cepheid instability strip pulsations are caused by the k mechanism when the opacity of ionised helium varies with its temperature RR Lyraes are old relatively low mass Population II stars in common with W Virginis and BL Herculis variables the type II Cepheids Classical Cepheid variables are higher mass population I stars RR Lyrae variables are much more common than Cepheids but also much less luminous The average absolute magnitude of an RR Lyrae star is about 0 75 only 40 or 50 times brighter than the Sun 8 Their period is shorter typically less than one day sometimes ranging down to seven hours Some RRab stars including RR Lyrae itself exhibit the Blazhko effect in which there is a conspicuous phase and amplitude modulation 9 Period luminosity relationships edit nbsp Typical RR Lyrae light curve Unlike Cepheid variables RR Lyrae variables do not follow a strict period luminosity relationship at visual wavelengths although they do in the infrared K band 10 They are normally analysed using a period colour relationship for example using a Wesenheit function In this way they can be used as standard candles for distance measurements although there are difficulties with the effects of metallicity faintness and blending The effect of blending can impact RR Lyrae variables sampled near the cores of globular clusters which are so dense that in low resolution observations multiple unresolved stars may appear as a single target Thus the brightness measured for that seemingly single star e g an RR Lyrae variable is erroneously too bright given those unresolved stars contributed to the brightness determined Consequently the computed distance is wrong and certain researchers have argued that the blending effect can introduce a systematic uncertainty into the cosmic distance ladder and may bias the estimated age of the Universe and the Hubble constant 11 12 13 Recent developments editThe Hubble Space Telescope has identified several RR Lyrae candidates in globular clusters of the Andromeda Galaxy 3 and has measured the distance to the prototype star RR Lyrae 14 The Kepler space telescope provided accurate photometric coverage of a single field at regular intervals over an extended period 37 known RR Lyrae variables lie within the Kepler field including RR Lyrae itself and new phenomena such as period doubling have been detected 15 The Gaia mission mapped 140 784 RR Lyrae stars of which 50 220 were not previously known to be variable and for which 54 272 interstellar absorption estimates are available 16 References edit a b c d e Smith Horace A 2004 RR Lyrae Stars Cambridge University Press ISBN 978 0 521 54817 5 Pritchet Christopher J Van Den Bergh Sidney 1987 Observations of RR Lyrae stars in the halo of M31 Astrophysical Journal 316 517 Bibcode 1987ApJ 316 517P doi 10 1086 165223 a b Clementini G Federici L Corsi C Cacciari C Bellazzini M Smith H A 2001 RR Lyrae Variables in the Globular Clusters of M31 A First Detection of Likely Candidates The Astrophysical Journal 559 2 L109 arXiv astro ph 0108418 Bibcode 2001ApJ 559L 109C doi 10 1086 323973 S2CID 48632444 Christensen Dalsgaard J Balona L A Garrido R Suarez J C Oct 20 2012 Stellar Pulsations Impact of New Instrumentation and New Insights Astrophysics and Space Science Proceedings ISBN 978 3 642 29630 7 Clement Christine M Muzzin Adam Dufton Quentin Ponnampalam Thivya Wang John Burford Jay Richardson Alan Rosebery Tara Rowe Jason Hogg Helen Sawyer 2001 Variable Stars in Galactic Globular Clusters The Astronomical Journal 122 5 2587 2599 arXiv astro ph 0108024 Bibcode 2001AJ 122 2587C doi 10 1086 323719 S2CID 38359010 Vozyakova O V Sefako R Rastorguev A S Kravtsov V V Kniazev A Y Berdnikov L N Dambis A K 2013 11 11 RR Lyrae variables visual and infrared luminosities intrinsic colours and kinematics Monthly Notices of the Royal Astronomical Society 435 4 3206 3220 arXiv 1308 4727 doi 10 1093 mnras stt1514 ISSN 0035 8711 Hajdu G Catelan M Jurcsik J Dekany I Drake A J Marquette B 2015 New RR Lyrae variables in binary systems Monthly Notices of the Royal Astronomical Society 449 1 L113 L117 arXiv 1502 01318 Bibcode 2015MNRAS 449L 113H doi 10 1093 mnrasl slv024 Layden A C Hanson Robert B Hawley Suzanne L Klemola Arnold R Hanley Christopher J August 1996 The Absolute Magnitude and Kinematics of RR Lyrae Stars via Statistical Parallax Astron J 112 2110 2131 arXiv astro ph 9608108 Bibcode 1996AJ 112 2110L doi 10 1086 118167 S2CID 8732647 Szabo R Kollath Z Molnar L Kolenberg K Kurtz D W Bryson S T Benko J M Christensen Dalsgaard J Kjeldsen H Borucki W J Koch D Twicken J D Chadid M Di Criscienzo M Jeon Y B Moskalik P Nemec J M Nuspl J 2010 Does Kepler unveil the mystery of the Blazhko effect First detection of period doubling in Kepler Blazhko RR Lyrae stars Monthly Notices of the Royal Astronomical Society 409 3 1244 arXiv 1007 3404 Bibcode 2010MNRAS 409 1244S doi 10 1111 j 1365 2966 2010 17386 x S2CID 119190883 Catelan M Pritzl Barton J Smith Horace A 2004 The RR Lyrae Period Luminosity Relation I Theoretical Calibration The Astrophysical Journal Supplement Series 154 2 633 arXiv astro ph 0406067 Bibcode 2004ApJS 154 633C doi 10 1086 422916 S2CID 119336592 Majaess D Turner D Gieren W Lane D 2012 The Impact of Contaminated RR Lyrae Globular Cluster Photometry on the Distance Scale The Astrophysical Journal Letters 752 1 L10 arXiv 1205 0255 Bibcode 2012ApJ 752L 10M doi 10 1088 2041 8205 752 1 L10 S2CID 118528078 Lee Jae Woo Lopez Morales Mercedes Hong Kyeongsoo Kang Young Woon Pohl Brian L Walker Alistair 2014 Toward a Better Understanding of the Distance Scale from RR Lyrae Variable Stars A Case Study for the Inner Halo Globular Cluster NGC 6723 The Astrophysical Journal Supplement 210 1 6 arXiv 1311 2054 Bibcode 2014ApJS 210 6L doi 10 1088 0067 0049 210 1 6 S2CID 119280050 Neeley J R Marengo M Bono G Braga V F Dall Ora M Stetson P B Buonanno R Ferraro I Freedman W L Iannicola G Madore B F Matsunaga N Monson A Persson S E Scowcroft V Seibert M 2015 On the Distance of the Globular Cluster M4 NGC 6121 Using RR Lyrae Stars II Mid infrared Period luminosity Relations The Astrophysical Journal 808 1 11 arXiv 1505 07858 Bibcode 2015ApJ 808 11N doi 10 1088 0004 637X 808 1 11 S2CID 117031686 Benedict G Fritz et al January 2002 Astrometry with the Hubble Space Telescope A Parallax of the Fundamental Distance Calibrator RR Lyrae The Astronomical Journal 123 1 473 484 arXiv astro ph 0110271 Bibcode 2002AJ 123 473B doi 10 1086 338087 S2CID 59150013 Kinemuchi Karen 2011 RR Lyrae Research with the Kepler Mission RR Lyrae Stars 5 74 arXiv 1107 0297 Bibcode 2011rrls conf 74K Riello M Evans D W Szabados L Sarro L M Regibo S Ridder J De Eyer L Lecoeur Taibi I Mowlavi N 2019 02 01 Gaia Data Release 2 Specific characterisation and validation of all sky Cepheids and RR Lyrae stars Astronomy amp Astrophysics 622 A60 arXiv 1805 02079 Bibcode 2019A amp A 622A 60C doi 10 1051 0004 6361 201833374 ISSN 0004 6361 S2CID 260496633 External links editAPOD M3 Inconstant Star Cluster four frame animation of RR Lyrae variables in globular cluster M3 Animation of RR Lyrae Variables in globular cluster M15 Animation with the variable stars RR Lyrae in the center area of the globular cluster M15 RR Lyrae stars AAVSO Variable Star of the Season RR Lyrae OGLE Atlas of Variable Star Light Curves RR Lyrae stars Retrieved from https en wikipedia org w index php title RR Lyrae variable amp oldid 1172814459, wikipedia, wiki, book, books, library,

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