Scott Jay Kenyon

Last updated
Scott Jay Kenyon
Born
Scott J. Kenyon
NationalityAmerican
Alma mater Arizona State University (1978)
University of Illinois Urbana-Champaign (1983)
Scientific career
Fields Astrophysics:
star formation and planetary formation
Institutions Smithsonian Astrophysical Observatory
Doctoral advisor Ronald F. Webbink

Scott Jay Kenyon (born 1956) is an American astrophysicist. His work has included advances in symbiotic and other types of interacting binary stars, the formation and evolution of stars, and the formation of planetary systems.

Contents

Career

Kenyon received a B.S. in physics from Arizona State University in 1978 and a Ph.D. in astronomy from the University of Illinois Urbana-Champaign in 1983. His doctoral dissertation is titled The Physical Structure of the Symbiotic Stars [1] and was expanded into a book, The Symbiotic Stars. [2] After postdoctoral work at the Center for Astrophysics | Harvard & Smithsonian, including a CfA Fellowship, he joined the scientific staff at the Smithsonian Astrophysical Observatory.[ citation needed ]

Kenyon is a Fellow of the AAAS, a Fellow [3] of the American Physical Society, and is included in the Web of Knowledge index of highly cited researchers. [4]

Scientific work

Kenyon has worked extensively on symbiotic binary stars. [5] His book The Symbiotic Stars was the first to summarize observations and theories for these interacting binaries. [6] The book reviews the general state of knowledge in this field c. 1984 and contains case histories of well-studied binaries [7] and complete references to all papers published on symbiotic stars before c. 1984. [8] With more than 350 citations, [5] the book is a standard in the field.

Kenyon and Lee Hartmann first worked out detailed accretion disk models for pre–main sequence stars and applied these models to optical and infrared spectra of FU Orionis objects. [9] Aside from explaining many details in the spectra of FUors, [9] [10] observations of the size of the disk in FU Orionis match model predictions. [11] Observations of long-term variability in FUors also generally match model predictions. [12] [13] Kenyon and Hartmann used photometric observations and disk models to show that the disks of FUors are surrounded by infalling envelopes with a bipolar cavity. [12] The bipolar cavity is a result of a wind [14] from the disk, which interacts with the surrounding material to produce a bipolar outflow and (perhaps) a Herbig–Haro object,. [10] [15]

Kenyon and Hartmann later developed the first flared accretion disk model to explain the large infrared luminosities of T Tauri stars. [16] In this model, each concentric annulus of the disk is in hydrostatic equilibrium. The surface of the disk then flares upward like the surface of a shallow bowl. A flared disk intercepts and re-radiates more light from the central star than a flat disk, producing a larger predicted infrared luminosity which agrees with observations of T Tauri stars. [16] Theoretical images [17] of edge-on flared disks look identical to actual images, [18] [19] [20] taken with the Hubble Space Telescope, illustrating direct evidence for flared disks. [21]

In 1990, Kenyon, Hartmann, Karen Strom & Steve Strom identified the luminosity problem: protostars in the Taurus-Auriga star-forming region are approximately 10 times less luminous than predicted by star formation theory. [22] In this theory, protostars form by gravitational collapse of a cloud of gas and dust. Over their lifetimes, protostars radiate a total energy comparable to their binding energy. With apparent lifetimes of about 100,000 yr, they have expected luminosities of 10-20 larger than the solar luminosity. Recent observations of larger numbers of protostars with the Spitzer Space Telescope confirm that protostars have typical luminosities closer to the solar luminosity. [23] Kenyon and colleagues identified several possible solutions to this luminosity problem. Adopting larger ages allows protostars to radiate the same amount of energy over a longer time, reducing their average luminosity. If protostars spend a small fraction of their lifetimes at much higher luminosity, as in the FU Orionis stars, then their average luminosity can be much larger than their typical luminosity. McKee & Offner note that ejecting material in a bipolar outflow reduces the expected luminosity of protostars but does not resolve the luminosity problem. [22] Data from Spitzer resolve the luminosity problem by deriving better estimates for the time spent in a high luminosity state and larger ages of 300,000 yr for protostars. [24] This resolution leads to an improved understanding of the early life histories of stars. [22] [24]

Kenyon has developed numerical models for planet formation and applied these calculations to the formation of debris disks [25] and Kuiper belt objects. [26] Kenyon and Ben Bromley have suggested that the dwarf planet Sedna in the outer Solar System might be an exosolar object captured during a close encounter with another planetary system when the Sun was only a few million years old. [27] [28] [29] This capture mechanism might also explain other unusual [dwarf planets] such as (2004) XR 190 [30]

Publications

Here is a cross-section of Kenyon's publications with more than 100 citations.

Related Research Articles

<span class="mw-page-title-main">Star formation</span> Process by which dense regions of molecular clouds in interstellar space collapse to form stars

Star formation is the process by which dense regions within molecular clouds in interstellar space, sometimes referred to as "stellar nurseries" or "star-forming regions", collapse and form stars. As a branch of astronomy, star formation includes the study of the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to the star formation process, and the study of protostars and young stellar objects as its immediate products. It is closely related to planet formation, another branch of astronomy. Star formation theory, as well as accounting for the formation of a single star, must also account for the statistics of binary stars and the initial mass function. Most stars do not form in isolation but as part of a group of stars referred as star clusters or stellar associations.

<span class="mw-page-title-main">Nebular hypothesis</span> Astronomical theory about the Solar System

The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System. It suggests the Solar System is formed from gas and dust orbiting the Sun which clumped up together to form the planets. The theory was developed by Immanuel Kant and published in his Universal Natural History and Theory of the Heavens (1755) and then modified in 1796 by Pierre Laplace. Originally applied to the Solar System, the process of planetary system formation is now thought to be at work throughout the universe. The widely accepted modern variant of the nebular theory is the solar nebular disk model (SNDM) or solar nebular model. It offered explanations for a variety of properties of the Solar System, including the nearly circular and coplanar orbits of the planets, and their motion in the same direction as the Sun's rotation. Some elements of the original nebular theory are echoed in modern theories of planetary formation, but most elements have been superseded.

<span class="mw-page-title-main">Protostar</span> Early stage in the process of star formation

A protostar is a very young star that is still gathering mass from its parent molecular cloud. It is the earliest phase in the process of stellar evolution. For a low-mass star, it lasts about 500,000 years. The phase begins when a molecular cloud fragment first collapses under the force of self-gravity and an opaque, pressure-supported core forms inside the collapsing fragment. It ends when the infalling gas is depleted, leaving a pre-main-sequence star, which contracts to later become a main-sequence star at the onset of hydrogen fusion producing helium.

<span class="mw-page-title-main">Protoplanetary disk</span> Gas and dust surrounding a newly formed star

A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk, while the two are similar. While they are similar, an accretion disk is hotter, and spins much faster. It is also found on black holes, not stars. This process should not be confused with the accretion process thought to build up the planets themselves. Externally illuminated photo-evaporating protoplanetary disks are called proplyds.

<span class="mw-page-title-main">Proplyd</span> Dust ring surrounding large stars thousands of solar radii wide

A proplyd, short for ionized protoplanetary disk, is an externally illuminated photoevaporating protoplanetary disk around a young star. Nearly 180 proplyds have been discovered in the Orion Nebula. Images of proplyds in other star-forming regions are rare, while Orion is the only region with a large known sample due to its relative proximity to Earth.

<span class="mw-page-title-main">FU Orionis star</span>

In stellar evolution, an FU Orionis star is a pre–main-sequence star which displays an extreme change in magnitude and spectral type. One example is the star V1057 Cyg, which became six magnitudes brighter and went from spectral type dKe to F-type supergiant during 1969-1970. These stars are named after their type-star, FU Orionis.

<span class="mw-page-title-main">Sigma Orionis</span> Five-star system in the constellation Orion

Sigma Orionis or Sigma Ori is a multiple star system in the constellation Orion, consisting of the brightest members of a young open cluster. It is found at the eastern end of the belt, south west of Alnitak and west of the Horsehead Nebula which it partially illuminates. The combined brightness of the component stars is magnitude 3.80.

<span class="mw-page-title-main">Alpha Pictoris</span> Brightest star in the southern constellation of Pictor

Alpha Pictoris is the brightest star in the southern constellation of Pictor. It has an apparent visual magnitude of 3.27, which is bright enough to be viewed from urban areas in the southern hemisphere. This star is close enough for its distance to be measured using parallax shifts, which yields a value of roughly 97 light-years from the Sun, with a 5% margin of error. Alpha Pictoris has the distinction of being the south pole star of the planet Mercury.

<span class="mw-page-title-main">Debris disk</span> Disk of dust and debris in orbit around a star

A debris disk, or debris disc, is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks are found around stars with mature planetary systems, including at least one debris disk in orbit around an evolved neutron star. Debris disks can also be produced and maintained as the remnants of collisions between planetesimals, otherwise known as asteroids and comets.

Z Andromedae is a binary star system consisting of a red giant and a white dwarf. It is the prototype of a type of cataclysmic variable star known as symbiotic variable stars or simply Z Andromedae variables. The brightness of those stars vary over time, showing a quiescent, more stable phase and then an active one with a more pronounced variability and stronger brightening and/or dimming.

<span class="mw-page-title-main">HD 100546</span> Star in the constellation Musca

HD 100546, also known as KR Muscae, is a pre-main sequence star of spectral type B8 to A0 located 353 light-years from Earth in the southern constellation of Musca. The star is surrounded by a circumstellar disk from a distance of 0.2 to 4 AU, and again from 13 AU out to a few hundred AU, with evidence for a protoplanet forming at a distance of around 47 AU.

<span class="mw-page-title-main">FU Orionis</span> Variable star in the constellation Orion

FU Orionis is a variable and binary star system in the constellation of Orion, that in 1937 rose in apparent visual magnitude from 16.5 to 9.6, and has since been around magnitude 9. The name FU Orionis is a variable star designation in the Argelander system, which are assigned sequentially as new variables are discovered. FU Orionis is about 1,360 light years distant and is associated with the molecular cloud Barnard 35.

<span class="mw-page-title-main">Orion OB1</span> Hot giant star group

Orion OB1 is a contingent group of several dozen hot giant stars of spectral types O and B in Orion. Associated are thousands of lower-mass stars, and a number of protostars. It is part of the larger Orion molecular cloud complex. Owing to its relative closeness and complexity it is the most closely studied OB association.

<span class="mw-page-title-main">V1057 Cygni</span> Star in the constellation Cygnus

V1057 Cygni is a suspected binary star system in the northern constellation of Cygnus. It is a variable star of the FU Orionis-type, and was the second FU Orionis-type variable to be discovered. The system is located at a distance of approximately 3,000 light years from the Sun, in the North America Nebula. It has an apparent visual magnitude of around 12.4.

<span class="mw-page-title-main">S Ori 70</span> Object in the Orionis cluster in the constellation Orion

S Ori 70 or S Ori J053810.1-023626 is a mid-T type astronomical object in the foreground of the σ Orionis cluster, which is approximately 1,150 light-years from Earth. It was discovered on November 24, 2002 by M. R. Zapatero-Osorio and E. L. Martin's team at the Roque de los Muchachos Observatory. It has yet to be determined if it is a field brown dwarf or a 3-million-year-old planet that is part of a cluster. Near-infrared spectroscopy images taken three years after its discovery led to the first motion measurements for the object. Its behavior is significantly different from what may be expected; it was further described as either a low-gravity atmosphere or an atmosphere with metallicity. The object's small proper motion suggests that it is further away than expected if it were a single field T dwarf.

Pi<sup>1</sup> Orionis Star in the constellation Orion

Pi1 Orionis (π1 Ori, π1 Orionis) is a star in the equatorial constellation of Orion. It is faintly visible to the naked eye with an apparent visual magnitude of 4.74. Based upon an annual parallax shift of 28.04 mas, it is located about 116 light-years from the Sun.

Theta<sup>2</sup> Orionis Star in the constellation Orion

Theta2 Orionis is a multiple star system in the constellation Orion. It is a few arc minutes from its more famous neighbour the Trapezium Cluster, also known as θ1 Orionis.

<span class="mw-page-title-main">V1005 Orionis</span> Young flame star in the constellation of Orion

V1005 Orionis is a young flare star in the equatorial constellation of Orion. It has the identifier GJ 182 in the Gliese–Jahreiß catalogue; V1005 Ori is its variable star designation. This star is too faint to be visible to the naked eye, having a mean apparent visual magnitude of 10.1. It is located at a distance of 79.6 light years from the Sun and is drifting further away with a radial velocity of 19.2 km/s. The star is a possible member of the IC 2391 supercluster.

<span class="mw-page-title-main">CQ Tauri</span> Star in the constellation Taurus

CQ Tauri is a young variable star in the equatorial constellation of Taurus. It is too faint to be visible to the naked eye with an apparent visual magnitude that ranges from 8.7 to 12.25. The distance to this star is approximately 487 light years based on parallax measurements, and it is drifting further away with a radial velocity of ~23 km/s. It appears to be part of the T-association Tau 4. CQ Tauri lies close enough to the ecliptic to undergo lunar occultations.

References

  1. ↑ Kenyon, S. J. (1983). "Physical Nature of the Symbiotic Stars". NASA Astrophysics Data System: 8. Bibcode:1983PhDT.........8K.{{cite journal}}: Cite journal requires |journal= (help)
  2. ↑ Kenyon, S. J. (1986). The Symbiotic Stars. Cambridge University Press. doi:10.1017/CBO9780511586071. ISBN   9780511586071.
  3. ↑ "2013 APS Fellows" . Retrieved 9 February 2014.
  4. ↑ "Index of Highly Cited Researchers". Web of Knowledge. Retrieved 25 October 2012.
  5. 1 2 "S. Kenyon publications on symbiotic stars".
  6. ↑ Selvelli, P. L. (1988). "Book Review: The symbiotic stars". Space Science Reviews. 47 (3–4): 402. Bibcode:1988SSRv...47..402S. doi:10.1007/BF00243559. S2CID   189788657.
  7. ↑ Stickland, D. (August 1987). "Book Review: The symbiotic stars". The Observatory. 107: 170. Bibcode:1987Obs...107..170S.
  8. ↑ Chochol, D. (1988). "Book review: The symbiotic stars". Bulletin of the Astronomical Institutes of Czechoslovakia. 39 (2): 128. Bibcode:1988BAICz..39..128C.
  9. 1 2 Bertout, C. (1989). "T Tauri Stars-Wild as Dust". Annual Review of Astronomy and Astrophysics. 27: 351. Bibcode:1989ARA&A..27..351B. doi:10.1146/annurev.aa.27.090189.002031.
  10. 1 2 Reipurth, B. (1990), "FU Orionis eruptions and early stellar evolution", Flare Stars in Star Clusters, 137: 229, Bibcode:1990IAUS..137..229R
  11. ↑ Malbet, F.; et al. (1998). "FU Orionis Resolved by Infrared Long-Baseline Interferometry at a 2 AU Scale". Astrophysical Journal. 507 (2): L149. arXiv: astro-ph/9808326 . Bibcode:1998ApJ...507L.149M. doi:10.1086/311688. S2CID   14528716.
  12. 1 2 Clarke, C.; G. Lodato; S. Y. Melnikov; M. A. Ibrahimov (2005). "The photometric evolution of FU Orionis objects: disc instability and wind-envelope interaction". Monthly Notices of the Royal Astronomical Society. 361 (3): 942–954. arXiv: astro-ph/0505515 . Bibcode:2005MNRAS.361..942C. doi: 10.1111/j.1365-2966.2005.09231.x . S2CID   15471280.
  13. ↑ Bell, K. R.; D. N. C. Lin (1994). "Using FU Orionis outbursts to constrain self-regulated protostellar disk models". Astrophysical Journal. 427: 987. arXiv: astro-ph/9312015 . Bibcode:1994ApJ...427..987B. doi:10.1086/174206. S2CID   118898339.
  14. ↑ Bastian, U.; R. Mundt (1985). "FU Orionis star winds". Astronomy and Astrophysics. 144: 57. Bibcode:1985A&A...144...57B.
  15. ↑ Reipurth, B. (1985). "Herbig-Haro objects and FU Orionis eruptions The case of HH 57". Astronomy and Astrophysics. 143: 435. Bibcode:1985A&A...143..435R.
  16. 1 2 Chiang, E. I.; P. Goldreich (1997). "Spectral Energy Distributions of T Tauri Stars with Passive Circumstellar Disks". Astrophysical Journal. 490 (1): 368–376. arXiv: astro-ph/9706042 . Bibcode:1997ApJ...490..368C. doi:10.1086/304869. S2CID   5938719.
  17. ↑ Whitney, Barbara A.; Lee Hartmann (1992). "Model scattering envelopes of young stellar objects. I - Method and application to circumstellar disks". Astrophysical Journal. 395: 529. Bibcode:1992ApJ...395..529W. doi:10.1086/171673.
  18. ↑ Burrows, Christopher J.; et al. (1996). "Hubble Space Telescope Observations of the Disk and Jet of HH 30" (PDF). Astrophysical Journal. 473: 437. Bibcode:1996ApJ...473..437B. doi:10.1086/178156. S2CID   51756708.
  19. ↑ Stapelfeldt, Karl R. (1998). "An Edge-On Circumstellar Disk in the Young Binary System HK Tauri". Astrophysical Journal. 502 (1): L65. Bibcode:1998ApJ...502L..65S. doi: 10.1086/311479 .
  20. ↑ Padgett, Deborah L.; et al. (1999). "HUBBLE SPACE TELESCOPE/NICMOS Imaging of Disks and Envelopes around Very Young Stars". Astronomical Journal. 117 (3): 1490–1504. arXiv: astro-ph/9902101 . Bibcode:1999AJ....117.1490P. doi:10.1086/300781. S2CID   16498360.
  21. ↑ Cotera, Angela; et al. (2001). "High-Resolution Near-Infrared Images and Models of the Circumstellar Disk in HH 30". Astrophysical Journal. 556 (2): 958. arXiv: astro-ph/0104066 . Bibcode:2001ApJ...556..958C. doi:10.1086/321627. S2CID   14354548.
  22. 1 2 3 McKee, C. F.; Offner, S.R.R. (2010), "The Luminosity Problem: Testing Theories of Star Formation", Proceedings of the International Astronomical Union, 6: 73–80, arXiv: 1010.4307 , Bibcode:2011IAUS..270...73M, doi:10.1017/S1743921311000202, S2CID   118314634
  23. ↑ Dunham, M.M. (2010). "Evolutionary Signatures in the Formation of Low-Mass Protostars. II. Toward Reconciling Models and Observations". Astrophysical Journal. 710 (1): 470–502. arXiv: 0912.5229 . Bibcode:2010ApJ...710..470D. doi:10.1088/0004-637X/710/1/470. S2CID   14156633.
  24. 1 2 Offner, S. S. R.; McKee, C. F. (2011). "The Protostellar Luminosity Function". Astrophysical Journal. 736 (1): 53. arXiv: 1105.0671 . Bibcode:2011ApJ...736...53O. doi:10.1088/0004-637X/736/1/53. S2CID   118784638.
  25. ↑ Kennedy, G.M.; M.C. Wyatt (2010). "Are debris disks self-stirred?". Monthly Notices of the Royal Astronomical Society. 405 (2): 1253. arXiv: 1002.3469 . Bibcode:2010MNRAS.405.1253K. doi: 10.1111/j.1365-2966.2010.16528.x . S2CID   55055925.
  26. ↑ Goldreich, P.; Lithwick, Y.; Sari, R. (2004). "Planet Formation by Coagulation: A Focus on Uranus and Neptune". Annual Review of Astronomy and Astrophysics. 42 (1): 549–601. arXiv: astro-ph/0405215 . Bibcode:2004ARA&A..42..549G. doi:10.1146/annurev.astro.42.053102.134004. S2CID   5177936.
  27. ↑ Quandt, Matthew (December 2004). "Two Young Stars Scuffle". Astronomy.
  28. ↑ Gugliotta, Guy (13 February 2005). "Distant object could hold secrets to Earth's past". Washington Post.
  29. ↑ Overbye, Dennis (2 December 2004). "Sun Might Have Exchanged Hangers-On With Rival Star". New York Times.
  30. ↑ Spotts, Peter (19 December 2005). "How to explain a mini-planet's odd orbit?". Christian Science Monitor.
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