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Rather close to Earth at a distance of only {{convert|16|pc|ly}} is [[Gliese 758]]. The sunlike pimary star has a [[brown dwarf]] companion, the coldest to have been imaged around a sunlike star in thermal light when it was discovered in 2009.<ref name="ThalmannCarson2009">{{cite journal|last1=Thalmann|first1=C.|last2=Carson|first2=J.|last3=Janson|first3=M.|last4=Goto|first4=M.|last5=McElwain|first5=M.|last6=Egner|first6=S.|last7=Feldt|first7=M.|last8=Hashimoto|first8=J.|last9=Hayano|first9=Y.|last10=Henning|first10=T.|last11=Hodapp|first11=K. W.|last12=Kandori|first12=R.|last13=Klahr|first13=H.|last14=Kudo|first14=T.|last15=Kusakabe|first15=N.|last16=Mordasini|first16=C.|last17=Morino|first17=J.-I.|last18=Suto|first18=H.|last19=Suzuki|first19=R.|last20=Tamura|first20=M.|title=DISCOVERY OF THE COLDEST IMAGED COMPANION OF A SUN-LIKE STAR|journal=The Astrophysical Journal|volume=707|issue=2|date=2009|pages=L123–L127|bibcode=2009ApJ...707L.123T|doi=10.1088/0004-637X/707/2/L123}}</ref>
Rather close to Earth at a distance of only {{convert|16|pc|ly}} is [[Gliese 758]]. The sunlike pimary star has a [[brown dwarf]] companion, the coldest to have been imaged around a sunlike star in thermal light when it was discovered in 2009.<ref name="ThalmannCarson2009">{{cite journal|last1=Thalmann|first1=C.|last2=Carson|first2=J.|last3=Janson|first3=M.|last4=Goto|first4=M.|last5=McElwain|first5=M.|last6=Egner|first6=S.|last7=Feldt|first7=M.|last8=Hashimoto|first8=J.|last9=Hayano|first9=Y.|last10=Henning|first10=T.|last11=Hodapp|first11=K. W.|last12=Kandori|first12=R.|last13=Klahr|first13=H.|last14=Kudo|first14=T.|last15=Kusakabe|first15=N.|last16=Mordasini|first16=C.|last17=Morino|first17=J.-I.|last18=Suto|first18=H.|last19=Suzuki|first19=R.|last20=Tamura|first20=M.|title=DISCOVERY OF THE COLDEST IMAGED COMPANION OF A SUN-LIKE STAR|journal=The Astrophysical Journal|volume=707|issue=2|date=2009|pages=L123–L127|bibcode=2009ApJ...707L.123T|doi=10.1088/0004-637X/707/2/L123}}</ref>


One of the most peculiar systems in Lyra is [[MV Lyrae]], a [[nova-like star]] consisting of a [[red dwarf]] and a [[white dwarf]].<ref name="SkillmanPatterson1995">{{cite journal|last1=Skillman|first1=David R.|last2=Patterson|first2=Joseph|last3=Thorstensen|first3=John R.|title=Superhumps in Cataclysmic Binaries. IV. MV Lyrae|journal=Publications of the Astronomical Society of the Pacific|volume=107|date=1995|pages=545|bibcode=1995PASP..107..545S|doi=10.1086/133590}}</ref> Originally classified as a [[VY Sculptoris star]] due to spending most time at maximum brightness, since around 1979 the system has been dominantly at minimum brightness, with periodic outbursts.<ref name="PavlenkoShugarov1999">{{cite journal |last1=Pavlenko |first1=E. P. |last2=Shugarov |first2=S. Y. |title=Photometric study of the nova-like variable MV Lyrae during an enormous outburst in 1997 |journal=Astronomy and Astrophysics |volume=343 |pages=909–915 |date=1999 |bibcode=1999A&A...343..909P}}</ref> Its nature is still not fully understood.<ref name="LinnellSzkody2005">{{cite journal|last1=Linnell|first1=Albert P.|last2=Szkody|first2=Paula|last3=Gansicke|first3=Boris|last4=Long|first4=Knox S.|last5=Sion|first5=Edward M.|last6=Hoard|first6=D. W.|last7=Hubeny|first7=Ivan|title=MV Lyrae in Low, Intermediate, and High States|journal=The Astrophysical Journal|volume=624|issue=2|date=2005|pages=923–933|bibcode=2005ApJ...624..923L|doi=10.1086/429143}}</ref>
One of the most peculiar systems in Lyra is [[MV Lyrae]], a [[nova-like star]] consisting of a [[red dwarf]] and a [[white dwarf]].<ref name="SkillmanPatterson1995">{{cite journal|last1=Skillman|first1=David R.|last2=Patterson|first2=Joseph|last3=Thorstensen|first3=John R.|title=Superhumps in Cataclysmic Binaries. IV. MV Lyrae|journal=Publications of the Astronomical Society of the Pacific|volume=107|date=1995|pages=545|bibcode=1995PASP..107..545S|doi=10.1086/133590}}</ref> Originally classified as a [[VY Sculptoris star]] due to spending most time at maximum brightness, since around 1979 the system has been dominantly at minimum brightness, with periodic outbursts.<ref name="PavlenkoShugarov1999">{{cite journal |last1=Pavlenko |first1=E. P. |last2=Shugarov |first2=S. Y. |title=Photometric study of the nova-like variable MV Lyrae during an enormous outburst in 1997 |journal=Astronomy and Astrophysics |volume=343 |pages=909–915 |date=1999 |bibcode=1999A&A...343..909P}}</ref> Its nature is still not fully understood.<ref name="LinnellSzkody2005">{{cite journal|last1=Linnell|first1=Albert P.|last2=Szkody|first2=Paula|last3=Gansicke|first3=Boris|last4=Long|first4=Knox S.|last5=Sion|first5=Edward M.|last6=Hoard|first6=D. W.|last7=Hubeny|first7=Ivan|title=MV Lyrae in Low, Intermediate, and High States|journal=The Astrophysical Journal|volume=624|issue=2|date=2005|pages=923–933|bibcode=2005ApJ...624..923L|doi=10.1086/429143}}</ref> Another outbursting star is [[AY Lyrae]], an [[SU Ursae Majoris variable|SU Ursae Majoris]]-type [[dwarf nova]] that has undergone several superoutbursts.<ref name="SzymanskiUndalski1987">{{cite journal |last1=Szymanski |first1=M. |lsat2=Udalski |first2=A. |title=AY Lyrae Superoutburst Photometry |journal=Information Bulletin on Variable Stars |volume=3105 |pages=1 |date=1987 |bibcode=1987IBVS.3105....1S}}</ref>


===Deep-sky objects===
===Deep-sky objects===

Revision as of 16:29, 22 August 2015

For other uses, see Lyra (disambiguation).
Lyra
Constellation
Lyra
List of stars in Lyra
AbbreviationLyr
GenitiveLyrae
Pronunciation/ˈlaɪərə/, genitive /ˈlaɪəriː/
SymbolismLyre, harp
Right ascension18h 14m to 19h 28m
Declination25.66° to 47.71°
QuadrantNQ4
Area286 sq. deg. (52nd)
Main stars5
Bayer/Flamsteed
stars		25
Stars brighter than 3.00m1
Stars within 10.00 pc (32.62 ly)3
Brightest starVega (α Lyr) (0.03m)
Messier objects2
Meteor showersLyrids
June Lyrids
Alpha Lyrids
Bordering
constellations		Draco
Hercules
Vulpecula
Cygnus
Visible at latitudes between +90° and −40°.
Best visible at 21:00 (9 p.m.) during the month of August.
[1]

Lyra (/ˈlaɪərə/; Latin for lyre, from Greek λύρα)[2] is a small constellation. It is one of 48 listed by the 2nd century astronomer Ptolemy, and is one of the 88 constellations recognized by the International Astronomical Union. Lyra was often represented on star maps as a vulture or an eagle carrying a lyre, and hence sometimes referred to as Aquila Cadens or Vultur Cadens. Beginning at the north, Lyra is bordered by Draco, Hercules, Vulpecula, and Cygnus. Lyra is visible from the northern hemisphere from spring through autumn, and nearly overhead, in temperate latitudes, during the summer months. From the southern hemisphere, it is visible low in the northern sky during the winter months.

The lucida or brightest star—and one of the brightest stars in the sky—is the white main sequence star Vega, a corner of the Summer Triangle. Beta Lyrae is the prototype of a class of stars known as Beta Lyrae variables, binary stars so close to each other that they become egg-shaped and material flows from one to the other. Epsilon Lyrae, known informally as the Double Double, is a complex multiple star system. Lyra also hosts the Ring Nebula, the second-discovered and best-known planetary nebula.

History

Lyra can be seen on the right of this c. 1825 star map from Urania's Mirror.

In Greek mythology, Lyra was associated with the myth of Orpheus, the musician who was killed by the Bacchantes. After his death, his lyre was thrown into the river; Zeus sent an eagle to retrieve the lyre, and ordered both of them to be placed in the sky.[citation needed] In Wales, Lyra is known as King Arthur's Harp (Talyn Arthur), and King David's harp [1]. The Persian Hafiz called it the Lyre of Zurah.[2] It has been called the Manger of the Infant Saviour, Praesepe Salvatoris [3].

In the past, Lyra was often represented on star maps as a vulture or an eagle carrying a lyre, either enclosed in its wings, or in its beak. It was sometimes referred to as Aquila Cadens or Vultur Cadens (falling eagle or falling vulture).[3] This historical association is preserved in the name of its brightest star, Vega, which is derived from an Arabic term meaning "swooping eagle."[4]

Vega and its surrounding stars are also treated as a constellation in other cultures. In Australian Aboriginal astronomy, Lyra is known by the Boorong people in Victoria as the Malleefowl constellation.[5] Lyra was known as Urcuchillay by the Incas and was worshipped as an animal deity.[6][7]

Characteristics

Lyra is bordered by Vulpecula to the south, Hercules to the east, Draco to the north, and Cygnus to the west. Covering 286.5 square degrees, it ranks 52nd of the 88 modern constellations in size. It appears prominently in the northern sky during the Nouthern Hemisphere's summer, and the whole constellation is visible for at least part of the year to observers north of latitude 42°S.[8][n 1] Its main asterism consists of six stars,[n 2] and 73 stars in total are brighter than magnitude 6.5.[8] The constellation's boundaries, as set by Eugène Delporte in 1930, are defined by a 17-sided polygon. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 08h 14m and 19h 28m , while the declination coordinates are between +25.66° and +47.71°.[9] The International Astronomical Union (IAU) adopted the three-letter abbreviation "Lyr" for the constellation in 1922.[10]

Notable features

The constellation Lyra as it can be seen by the naked eye.

Stars

See also: List of stars in Lyra

The brightest and by far the most well-known star in the constellation is Vega, a main-sequence star of spectral type A0Va.[11] Only 7.7 parsecs distant,[12] is a Delta Scuti variable, varying between magnitudes −0.02 and 0.07 over 0.2 days.[13] On average, it is the second brightest star of the northern hemisphere (after Arcturus) and the fifth brightest star in all, surpassed only by Arcturus, Alpha Centauri, Canopus, and Sirius. Vega was the pole star in the year 12000 BCE, and will again become the pole star around 14000 CE.

Vega is one of the most-studied of all stars, and has been called "arguably the next most important star in the sky after the Sun".[14] Vega was the first star other than the Sun to be photographed,[15] as well as the first to have a clear spectrum recorded, showing absorption lines for the first time.[16] The star was the first single main-sequence star other than the Sun to be known to emit X-rays,[17] and is surrounded by a circumstellar debris disk, similar to the Kuiper Belt.[18] Vega forms one corner of the famous Summer Triangle asterism; along with Altair and Deneb, these three stars form a prominent triangle during the northern hemisphere summer.

Vega also forms one vertex of a much smaller triangle, along with Epsilon and Zeta Lyrae. Zeta forms a wide binary star visible in binoculars, consisting of an Am star and an F-type subgiant. The Am star has an additional close companion, bringing the total number of stars in the system to three.[19] Epsilon is a more famous wide binary that can even be separated by the naked eye under good conditions. Both components are themselves close binaries which can be seen with telescopes to consist of A- and F-type stars, and a faint star was recently found to orbit component C as well, for a total of five stars.[19]

In contrast to Zeta and Epsilon Lyrae, Delta Lyrae is an optical double, with the two stars simply lying along the same line of sight east of Zeta. The brighter and closer of the two, Delta2 Lyrae, is a 4th-magnitude red bright giant that varies semiregularly by around 0.2 magnitudes[20] with a dominant period of 79 days,[21] while the fainter Delta1 Lyrae is a spectroscopic binary consisting of a B-type primary and an unknown secondary.[19] Both systems, however, have very similar radial velocities, and are the two brightest members of a sparse open cluster known as the Delta Lyrae cluster.[22] South of Delta is Gamma Lyrae, a blue giant and the second-brightest star in the constellation. Around 190 parsecs distant,[12] it has been referred to as a "superficially normal" star.[23]

The final star forming the lyre's figure is Beta Lyrae, also a binary composed of a blue bright giant and an early B-type star. In this case, the stars are so close together that the larger giant is overflowing its Roche lobe and transferring material to the secondary, forming a semidetached system. The secondary, originally the less massive of the two, has accreted so much mass that it is now substantially more massive, albeit smaller, than the primary, and is surrounded by a thick accretion disk.[24] The plane of the orbit is aligned with Earth and the system thus shows eclipses, dropping nearly a full magnitude from its 3rd-magnitude baseline every 13 days,[25] although its period is increasing by around 19 seconds per year.[26] It is the prototype of the Beta Lyrae variables, eclipsing semidetached binaries of early spectral types in which there are no exact onsets of eclipses, but rather continuous changes in brightness.[27]

A long-exposure image of Lyra

Another easy-to-spot variable is the bright R Lyrae, north of the main asterism. Also known as 13 Lyrae, it is a 4th-magnitude red giant semiregular variable that varies by several tenths of a magnitude.[28] Its periodicity is complex, with several different periods of varying lengths, most notably one of 46 days and one of 64 days.[29] Even further north is FL Lyrae, a much fainter 9th-magnitude Algol variable that drops by half a magnitude every 2.18 days during the primary eclipse. Both components are main-sequence stars, the primary being late F-type and the secondary late G-type. The system was one of the first main-sequence eclipsing binaries containing G-type star to have its properties known as well as the better-studied early-type eclipsing binaries.[30]

At the very northernmost edge of the constellation is the even fainter V361 Lyrae, an eclipsing binary that does not easily fall into one of the traditional classes, with features of Beta Lyrae, W Ursae Majoris, and cataclysmic variables.[31][32] It may be a representative of a very brief phase in which the system is transitioning into a contact binary.[33] It can be found less than a degree away from the naked-eye star 16 Lyrae, a 5th-magnitude A-type subgiant[34] located around 37 parsecs distant.[12]

The brightest star not included in the asterism and the westernmost cataloged by Bayer or Flamsteed is Kappa Lyrae, a typical red giant[35] around 77 parsecs distant.[12] Similar bright orange or red giants include the 4th-magnitude Theta Lyrae,[36] Lambda Lyrae,[37] and HD 173780.[35] Lambda is located just south of Gamma, Theta is positioned in the east, and HD 173780, the brightest star in the constellation with no Bayer or Flamsteed designation, is more southernly. Just north of Theta and of almost exactly the same magnitude is Eta Lyrae, a blue subgiant with a near-solar metal abundance.[38] Also nearby is the faint HP Lyrae, a post-asymptotic giant branch (AGB) star that shows variability. The reason for its variability is still a mystery: first cataloged as an eclipsing binary, it was theorized to be an RV Tauri variable in 2002, but if so, it would be by far the hottest such variable discovered.[39]

In the extreme east is RR Lyrae, the prototype of the large class of variables known as RR Lyrae variables, which are pulsating variables similar to Cepheids, but are evolved population II stars of spectral types A and F. Such stars are usually not found in a galaxy's thin disk, but rather in the galactic halo. Such stars serve as standard candles, and thus are a reliable way to calculate distances to the globular clusters in which they reside.[27] RR Lyrae itself varies between magnitudes 7 and 8 while exhibiting the Blazhko effect.[40] The easternmost star designated by Flamsteed, 19 Lyrae, is also a small-amplitude variable, an Alpha2 Canum Venaticorum variable with a period of just over one day.[41]

Another evolved star is the naked-eye variable XY Lyrae, a red bright giant[35] just north of Vega that varies between 6th and 7th magnitudes over a period of 120 days.[42] Also just visible to the naked eye is the peculiar classical Cepheid V473 Lyrae. It is unique in that it is the only known Cepheid in the Milky Way to undergo periodic phase and amplitude changes, analogous to the Blazhko effect in RR Lyrae stars.[43] At 1.5 days, its period was the shortest known for a classical Cepheid at the time of its discovery.[44] W and S Lyrae are two of the many Mira variables in Lyra. W varies between 7th and 12th magnitudes over approximately 200 days,[45] while S, slightly fainter, is a silicate carbon star, likely of the J-type.[46] Another evolved star is EP Lyrae, a faint RV Tauri variable and an "extreme example" of a post-AGB star. It and a likely companion are surrounded by a circumstellar disk of material.[47]

Rather close to Earth at a distance of only 16 parsecs (52 ly) is Gliese 758. The sunlike pimary star has a brown dwarf companion, the coldest to have been imaged around a sunlike star in thermal light when it was discovered in 2009.[48]

One of the most peculiar systems in Lyra is MV Lyrae, a nova-like star consisting of a red dwarf and a white dwarf.[49] Originally classified as a VY Sculptoris star due to spending most time at maximum brightness, since around 1979 the system has been dominantly at minimum brightness, with periodic outbursts.[50] Its nature is still not fully understood.[51] Another outbursting star is AY Lyrae, an SU Ursae Majoris-type dwarf nova that has undergone several superoutbursts.[52]

Deep-sky objects

Messier 56 is composed of a large number of stars, tightly bound to each other by gravity.[53] In Lyra are the objects M56, M57, and Kuiper 90. M56 is a rather loose globular cluster at a distance of approximately 32,900 light-years, with a diameter of about 85 light years. Its apparent brightness is 8.3m.

M57, also known as the "Ring Nebula" and NGC 6720,[54] has a diameter of one light-year and is at a distance of 2,000 light-years from Earth. It is one of the best known planetary nebulae and the second to be discovered; its integrated magnitude is 8.8.[55] It was discovered in 1779 by Antoine Darquier, 15 years after Charles Messier discovered the Dumbbell Nebula.[56] Astronomers have determined that it is between 6,000 and 8,000 years old;[55] it is approximately one light-year in diameter.[57] The outer part of the nebula appears red in photographs because of emission from ionized hydrogen. The middle region is colored green; doubly-ionized oxygen emits greenish-blue light. The hottest region, closest to the central star, appears blue because of emission from helium. The central star itself is a white dwarf with a temperature of 120,000 Kelvin. In telescopes, the nebula appears as a visible ring with a green tinge; it is slightly elliptical because its three-dimensional shape is a torus or cylinder seen from a slight angle.[55] It can be found halfway between Gamma Lyrae and Beta Lyrae.[57]

NGC 6745 is an irregular spiral galaxy in Lyra that is at a distance of 208 million light-years. Several million years ago, it collided with a smaller galaxy, which created a region filled with young, hot, blue stars. Astronomers do not know if the collision was simply a glancing blow or a prelude to a full-on merger, which would end with the two galaxies incorporated into one larger, probably elliptical galaxy.[55]

Exoplanets

In orbit around the orange subgiant star HD 177830 is one of the earliest exoplanets to be detected, HD 177830 b. A jovian-mass planet, it orbits in an eccentric orbit with a period of 390 days.[58] A second planet closer to the star was discovered in 2011.[59] Other exoplanets in Lyra include WASP-3b and TrES-1b.

In January 2010 the Kepler Mission announced the discovery of the additional planets Kepler-7b, Kepler-8b, and three planets around Kepler-9, the first of many in Lyra discovered by the mission, which has a significant part of its field of view in Lyra. Kepler-37 is another star with an exoplanet discovered by Kepler; the planet is the smallest known extrasolar planet known as of February 2013.

In April 2013, it was announced that of the five planets orbiting Kepler-62, at least two -- Kepler-62e and Kepler-62f—are within the boundaries of the habitable zone of that star, where scientists think liquid water could exist, and are both candidates for being a solid, rocky, earth-like planet. The exoplanets are 1.6 and 1.4 times the diameter of Earth respectively, with their star Kepler-62 at a distance of 1,200 light-years.[60]

Notes

  1. ^ While parts of the constellation technically rise above the horizon to observers between 42°S and 64°S, stars within a few degrees of the horizon are to all intents and purposes unobservable.
  2. ^ Assuming the visual double stars Epsilon and Delta Lyrae are counted as single stars

References

  1. ^ Ian Ridpath and Wil Tirion (2007). Stars and Planets Guide, Collins, London. ISBN 978-0-00-725120-9. Princeton University Press, Princeton. ISBN 978-0-691-13556-4.
  2. ^ Lesley Brown: The New Shorter Oxford English Dictionary. Vol. 1: A−M. Clarendon Press, Oxford 1993, p. 1651
  3. ^ "Star Tales - Lyra". Ian Ridpath's Star Tales. Retrieved 17 October 2007.
  4. ^ Ian Ridpath (2002) Stars and Planets, p. 108 [ISBN 0-7894-8988-0].
  5. ^ "World_Archaeological_Congress.pdf" (PDF). The Astronomy of the Boorong. Retrieved 2007-10-17. [dead link]
  6. ^ Allen, Richard Hinckley (March 2003) [1936]. Star Names and Their Meanings. Kessenger Publishing. p. 532. ISBN 978-0-7661-4028-8. Retrieved 2008-03-22.
  7. ^ D'Altroy, Terence N. (2002). "The Inca Pantheon". The Incas. The Peoples of America. Oxford: Blackwell Publishing. p. 149. ISBN 978-0-631-17677-0.
  8. ^ a b Ridpath, Ian. "Constellations: Lacerta–Vulpecula". Star Tales. self-published. Retrieved 25 July 2015.
  9. ^ "Lyra, Constellation Boundary". The Constellations. International Astronomical Union. Retrieved 25 July 2015.
  10. ^ Russell, H. N. (1922). "The New International Symbols for the Constellations". Popular Astronomy. 30: 469–71. Bibcode:1922PA.....30..469R.
  11. ^ Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Robinson, P. E. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637.
  12. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  13. ^ Breger, M. (1979). "Delta Scuti and related stars". Astronomical Society of the Pacific. 91: 5–26. Bibcode:1979PASP...91....5B. doi:10.1086/130433.
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  21. ^ Lloyd, C.; West, K. W. (1996). "Observations of Low-amplitude Late-Type Variables". Information Bulletin on Variable Stars (4335): 1. Bibcode:1996IBVS.4335....1L.
  22. ^ Eggen, O. J. (1968). "Photometric evidence for the existence of a delta Lyrae cluster". Astrophysical Journal. 152: 77. Bibcode:1968ApJ...152...77E. doi:10.1086/149525.
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  25. ^ European Space Agency (1997). The HIPPARCOS and TYCHO catalogues. Astrometric and photometric star catalogues derived from the ESA HIPPARCOS Space Astrometry Mission. Vol. 1200. Netherlands: Noordwijk. Bibcode:1997ESASP1200.....E. ISBN 9290923997.
  26. ^ Zhao, M.; et al. (2008), "First Resolved Images of the Eclipsing and Interacting Binary β Lyrae", The Astrophysical Journal, 684 (2): L95 – L98, arXiv:0808.0932, Bibcode:2008ApJ...684L..95Z, doi:10.1086/592146
  27. ^ a b Otero, S. A.; Watson, C.; Wils, P. "Variable Star Type Designations in the VSX". AAVSO Website. American Association of Variable Star Observers. Retrieved 29 July 2015.
  28. ^ Koen, Chris; Eyer, Laurent (2002). "New periodic variables from the Hipparcos epoch photometry". Monthly Notices of the Royal Astronomical Society. 331 (1): 45–59. Bibcode:2002MNRAS.331...45K. doi:10.1046/j.1365-8711.2002.05150.x.
  29. ^ Percy, John R.; Wilson, Joseph B.; Henry, Gregory W. (2001). "Long‐TermVRIPhotometry of Small‐Amplitude Red Variables. I. Light Curves and Periods". Publications of the Astronomical Society of the Pacific. 113 (786): 983–996. Bibcode:2001PASP..113..983P. doi:10.1086/322153.
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