Editing Serpens (section)

====Head stars====
[[File:SerpensCaputCC.jpg|thumb|left|200px|The constellation Serpens (Caput) as it can be seen by the naked eye|alt=The pattern of stars in Serpens Caput seen with the naked eye, with a triangle marking the head and a line of stars extending down marking the upper body]]
Marking the heart of the serpent is the constellation's brightest star, [[Alpha Serpentis]]. Traditionally called Unukalhai,<ref>{{cite book
  |last1=Kunitzsch |first1=Paul
  |last2=Smart |first2=Tim
  |date = 2006  |edition = 2nd rev.
  |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations
  |publisher = Sky Pub |location = Cambridge, Massachusetts
  |isbn = 978-1-931559-44-7
}}</ref> is a [[red giant]] of [[spectral type]] K2III located approximately 23 parsecs distant with a visual [[apparent magnitude|magnitude]] of 2.630 ± 0.009,<ref name="AlphaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=alf+Ser |title = * Alpha Serpentis – Star in double system|publisher = [[SIMBAD]] | access-date = 18 April 2014}}</ref> meaning it can easily be seen with the naked eye even in areas with substantial light pollution. A faint companion is in orbit around the red giant star,<ref name="Eggleton">{{Cite journal | doi = 10.1111/j.1365-2966.2008.13596.x| title = A catalogue of multiplicity among bright stellar systems| year = 2008| last1 = Eggleton | first1 = P. P.| last2 = Tokovinin | first2 = A. A.| journal = Monthly Notices of the Royal Astronomical Society| volume = 389| issue = 2| pages = 869| doi-access = free| bibcode = 2008MNRAS.389..869E|arxiv = 0806.2878 | s2cid = 14878976}}</ref> although it is not visible to the naked eye. Situated near Alpha is [[Lambda Serpentis]], a magnitude 4.42 ± 0.05 star rather similar to the Sun<ref name="daSilva">{{Cite journal | doi = 10.1051/0004-6361/201118751| title = Accurate and homogeneous abundance patterns in solar-type stars of the solar neighbourhood: A chemo-chronological analysis| journal = Astronomy & Astrophysics| volume = 542| pages = A84| year = 2012| last1 = Da Silva | first1 = R.| last2 = Porto De Mello | first2 = G. F.| last3 = Milone | first3 = A. C.| last4 = Da Silva | first4 = L.| last5 = Ribeiro | first5 = L. S.| last6 = Rocha-Pinto | first6 = H. J. | bibcode = 2012A&A...542A..84D|arxiv = 1204.4433 | s2cid = 118450072}}</ref> positioned only 12 parsecs away.<ref name="LambdaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=lam+Ser |title = * Lambda Serpentis – Star|publisher = SIMBAD | access-date = 20 May 2014}}</ref> It has an exoplanet orbiting around it.<ref>{{citation|arxiv=2105.11583|year=2021|title=The California Legacy Survey. I. A Catalog of 178 Planets from Precision Radial Velocity Monitoring of 719 Nearby Stars over Three Decades|last1=Rosenthal|first1=Lee J.|last2=Fulton|first2=Benjamin J.|last3=Hirsch|first3=Lea A.|last4=Isaacson|first4=Howard T.|last5=Howard|first5=Andrew W.|last6=Dedrick|first6=Cayla M.|last7=Sherstyuk|first7=Ilya A.|last8=Blunt|first8=Sarah C.|last9=Petigura|first9=Erik A.|last10=Knutson|first10=Heather A.|last11=Behmard|first11=Aida|last12=Chontos|first12=Ashley|last13=Crepp|first13=Justin R.|last14=Crossfield|first14=Ian J. M.|last15=Dalba|first15=Paul A.|last16=Fischer|first16=Debra A.|last17=Henry|first17=Gregory W.|last18=Kane|first18=Stephen R.|last19=Kosiarek|first19=Molly|last20=Marcy|first20=Geoffrey W.|last21=Rubenzahl|first21=Ryan A.|last22=Weiss|first22=Lauren M.|last23=Wright|first23=Jason T.|journal=The Astrophysical Journal Supplement Series|volume=255|issue=1 |page=8|doi=10.3847/1538-4365/abe23c|bibcode=2021ApJS..255....8R |s2cid=235186973 |doi-access=free }}</ref> Another [[solar analog]] in Serpens is the primary of [[Psi Serpentis]], a binary star<ref name="Hall">{{Cite journal | doi = 10.1088/0004-6256/138/1/312| title = The Activity and Variability of the Sun and Sun-Like Stars. Ii. Contemporaneous Photometry and Spectroscopy of Bright Solar Analogs| journal = The Astronomical Journal| volume = 138| issue = 1| pages = 312| year = 2009| last1 = Hall | first1 = J. C. | last2 = Henry | first2 = G. W. | last3 = Lockwood | first3 = G. W. | last4 = Skiff | first4 = B. A. | last5 = Saar | first5 = S. H. | bibcode = 2009AJ....138..312H| citeseerx = 10.1.1.216.9004| s2cid = 12332945}}</ref> located slightly further away at approximately 14 parsecs.<ref name="PsiSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=psi+Ser |title = * Psi Serpentis – Double or multiple star|publisher = SIMBAD | access-date = 21 June 2014}}</ref>

[[Beta Serpentis|Beta]], [[Gamma Serpentis|Gamma]], and [[Iota Serpentis]] form a distinctive triangular shape marking the head of the snake, with [[Kappa Serpentis]] (the proper name is Gudja<ref name="IAU-CSN">{{Cite web
  |url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt
  |title=IAU Catalog of Star Names
  |publisher=International Astronomical Union
  |access-date=2018-09-17}}</ref>) being roughly midway between Gamma and Iota. The brightest of the four with an apparent magnitude of roughly 3.67, Beta Serpentis is a white main-sequence star roughly 160 parsecs distant.<ref name="BetaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=bet+Ser |title = * Beta Serpentis – Star in double system|publisher = SIMBAD | access-date = 12 May 2014}}</ref> It is likely that a nearby 10th-magnitude star<ref name="BetaBSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=bet+Ser+B |title = * Beta Serpentis B – Star in double system|publisher = SIMBAD | access-date = 12 May 2014}}</ref> is physically associated with Beta, although it is not certain.<ref name="Shaya">{{Cite journal | doi = 10.1088/0067-0049/192/1/2| title = Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of The Hipparcos Catalogue| journal = The Astrophysical Journal Supplement Series| volume = 192| issue = 1| pages = 2| year = 2011| last1 = Shaya | first1 = E. J. | last2 = Olling | first2 = R. P. | bibcode = 2011ApJS..192....2S|arxiv = 1007.0425 | s2cid = 119226823}}</ref> The [[Mira variable]] [[R Serpentis]], situated between Beta and Gamma, is visible to the naked eye at its maximum of 5th-magnitude, but, typical of Mira variables, it can fade to below magnitude 14.<ref name="RAAVSO">{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=34592 |title=R Serpentis |author=VSX |date=4 January 2010 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=22 May 2014}}</ref> Gamma Serpentis itself is an F-type [[subgiant]] located only 11 parsecs distant and thus is quite bright, being of magnitude 3.84 ± 0.05.<ref name="GammaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=gam+Ser |title = * Gamma Serpentis – Variable star|publisher = SIMBAD | access-date = 22 May 2014}}</ref> The star is known to show [[solar-like oscillations]].<ref name="Bi">{{Cite journal | doi = 10.1086/521575| title = Seismological Analysis of the Stars γ Serpentis and ι Leonis: Stellar Parameters and Evolution| journal = The Astrophysical Journal| volume = 673| issue = 2| pages = 1093–1105| year = 2008| last1 = Bi | first1 = S. -L. | last2 = Basu | first2 = S. | last3 = Li | first3 = L. -H. | bibcode = 2008ApJ...673.1093B| doi-access = free}}</ref> Iota Serpentis is a binary star system.<ref name="Muterspaugh 2010">{{cite journal
 | title=The Phases Differential Astrometry Data Archive. II. Updated Binary Star Orbits and a Long Period Eclipsing Binary
 | last1=Muterspaugh | first1=Matthew W. | last2=Hartkopf | first2=William I.
 | last3=Lane | first3=Benjamin F. | last4=O’Connell | first4=J.
 | last5=Williamson | first5=M. | last6=Kulkarni | first6=S. R.
 | last7=Konacki | first7=Maciej | last8=Burke | first8=Bernard F.
 | last9=Colavita | first9=M. M. | last10=Shao | first10=M.
 | last11=Wiktorowicz | first11=Sloane J. | display-authors=1
 | journal=The Astronomical Journal
 | volume=140 | issue=6 | pages=1623–1630 | year=2010
 | arxiv=1010.4043 | bibcode=2010AJ....140.1623M
 | doi=10.1088/0004-6256/140/6/1623 | s2cid=6030289 }}</ref>

[[Delta Serpentis]], forming part of the body of the snake between the heart and the head, is a multiple star system<ref name="Malkov">{{Cite journal | doi = 10.1051/0004-6361/201219774| title = Dynamical masses of a selected sample of orbital binaries| journal = Astronomy & Astrophysics| volume = 546| pages = A69| year = 2012| last1 = Malkov | first1 = O. Y. | last2 = Tamazian | first2 = V. S.| last3 = Docobo | first3 = J. A.| last4 = Chulkov | first4 = D. A.| bibcode = 2012A&A...546A..69M| doi-access = free}}</ref> positioned around 70 parsecs from Earth. Consisting of four stars, the system has a total apparent magnitude of 3.79 as viewed from Earth,<ref name="DeltaSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=del+Ser |title = * Delta Serpentis – Double or multiple star|publisher = SIMBAD | access-date = 18 May 2014}}</ref> although two of the stars, with a combined apparent magnitude of 3.80, provide nearly all the light.<ref name="DeltaBSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=del+Ser+B |title = * Delta Serpentis B – Star in double system|publisher = SIMBAD | access-date = 18 May 2014}}</ref> The primary, a white subgiant, is a [[Delta Scuti variable]] with an average apparent magnitude of 4.23.<ref name="DeltaAAVSO">{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=34969 |title=Delta Serpentis |author=VSX |date=4 January 2010 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=18 May 2014}}</ref> Positioned very near Delta, both in the night sky and likely in actual space at an estimated distance of around 70 parsecs,<ref name="16Simbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=16+Ser |title = * 16 Serpentis – Star|publisher = SIMBAD | access-date = 24 May 2014}}</ref> is the [[barium star]] [[16 Serpentis]].<ref name="Tomkin">{{Cite journal | doi = 10.1086/164821| title = Heavy-element abundances in the mild barium stars Omicron Virginis and 16 Serpentis| journal = The Astrophysical Journal| volume = 311| pages = 819| year = 1986| last1 = Tomkin | first1 = J. | last2 = Lambert | first2 = D. L. | bibcode = 1986ApJ...311..819T| doi-access = free}}</ref> Another notable variable star visible to the naked eye is [[Chi Serpentis]], an [[Alpha² Canum Venaticorum variable]] situated midway between Delta and Beta which varies from its median brightness of 5.33 by 0.03 magnitudes over a period of approximately 1.5 days.<ref name="ChiAAVSO">{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=34972 |title=Chi Serpentis |author=VSX |date=4 January 2010 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=26 May 2014}}</ref> Chi Serpentis is a [[Ap and Bp stars|chemically peculiar]] star.<ref name=Loden1983>{{citation
 | title=A physical study of the Ursa Major cluster (with special attention to the peculiar A stars)
 | last1=Loden | first1=L. O.
 | journal=Astronomy and Astrophysics Supplement Series
 | volume=53 | date=July 1983 | pages=33–42
 | bibcode=1983A&AS...53...33L | postscript=. }}</ref>

The two stars in Serpens Caput that form part of the Snake's body below the heart are [[Epsilon Serpentis|Epsilon]] and Mu Serpentis, both third-magnitude [[A-type main-sequence star]]s.<ref name="EpsilonSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=eps+Ser |title = * Epsilon Serpentis – Star|publisher = SIMBAD | access-date = 26 May 2014}}</ref><ref name="MuSimbad">{{cite web |url =http://simbad.u-strasbg.fr/simbad/sim-id?Ident=32+Ser |title = * Mu Serpentis – Star|publisher = SIMBAD | access-date = 26 May 2014}}</ref> Both have a peculiarity: Epsilon is an [[Am star]],<ref name="Adelman">{{Cite journal | doi = 10.1046/j.1365-8711.1998.01859.x| title = Elemental abundance analyses with DAO spectrograms -- XX. The early a stars epsilon Serpentis, 29 Vulpeculae and sigma Aquarii| journal = Monthly Notices of the Royal Astronomical Society| volume = 300| issue = 2| pages = 359| year = 1998| last1 = Adelman | first1 = S. J.| last2 = Albayrak | first2 = B.| bibcode = 1998MNRAS.300..359A| doi-access = free}}</ref> while Mu is a binary.<ref name="Gontcharov">{{Cite journal | doi = 10.1016/j.newast.2009.09.006| title = Photocentric orbits from a direct combination of ground-based astrometry with Hipparcos II. Preliminary orbits for six astrometric binaries| journal = New Astronomy| volume = 15| issue = 3| pages = 324–331| year = 2010| last1 = Gontcharov | first1 = G. A. | last2 = Kiyaeva | first2 = O. V. | bibcode = 2010NewA...15..324G|arxiv = 1606.08182 | s2cid = 119252073}}</ref> Located slightly northwest of Mu is [[36 Serpentis]], another A-type main-sequence star. This star also has a peculiarity; it is a binary with the primary component being a [[Lambda Boötis star]], meaning that it has solar-like amounts of [[carbon]], [[nitrogen]], and [[oxygen]], while containing very low amounts of [[iron peak]] elements.<ref name="Nikolov">{{cite journal |last1=Nikolov |first1=G. |last2=Atanasova |first2=E. |last3=Iliev |first3=I. K. |last4=Paunzen |first4=E. |last5=Barzova |first5=I. S. |title=Spectroscopic orbit determination of two metal-weak dwarf stars: HD64491 and HD141851 |journal=Contributions of the Astronomical Observatory Skalnaté Pleso |volume=38 |issue=2 |pages=433–434 |date=April 2008 |bibcode=2008CoSka..38..433N}}</ref> The secondary star has also been a source of X-ray emissions.<ref name=Mason2010>{{cite journal
 | title=Binary Star Orbits. IV. Orbits of 18 Southern Interferometric Pairs
 | display-authors=1 | last1=Mason | first1=Brian D.
 | last2=Hartkopf | first2=William I. | last3=Tokovinin | first3=Andrei
 | journal=The Astronomical Journal
 | volume=140 | issue=3 | pages=735–743 | date=September 2010
 | doi=10.1088/0004-6256/140/3/735 | bibcode=2010AJ....140..735M | doi-access=free }}</ref> [[25 Serpentis]], positioned a few degrees northeast of Mu Serpentis, is a [[spectroscopic binary]]<ref name="Petrie">{{cite journal|last1=Petrie |first1=R. M. |last2=Phibbs |first2=Edgar |title=Redetermination of the Spectrographic Orbits of Iota Pegasi and 25 Serpentis |journal=Publications of the Dominion Astrophysical Observatory Victoria |volume=8 |pages=225–234 |year=1950 |bibcode=1950PDAO....8..225P}}</ref> consisting of a hot [[blue giant|B-type giant]] and an A-type main-sequence star. The primary is a [[slowly pulsating B star]], which causes the system to vary by 0.03 magnitudes.<ref name="25AAVSO">{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=34909 |title=PT Serpentis |author1=VSX |last2=Otero |first2=S. A|date=10 February 2012 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=28 May 2014}}</ref>

Serpens Caput contains many [[RR Lyrae variable]]s, although most are too faint to be seen without professional photography. The brightest is [[VY Serpentis]], only of 10th magnitude. This star's period has been increasing by approximately 1.2 seconds per century.<ref name="Wunder">{{cite journal |last1=Wunder |first1=E. |title=Period Changes of Bright RR Lyrae Stars SU Dra and VY Ser |journal=Information Bulletin on Variable Stars |volume=3669 |issue=1 |page=IBVS Homepage |date=October 1991 |bibcode=1991IBVS.3669....1W }}</ref> A variable star of a different kind is [[Tau4 Serpentis|Tau<sup>4</sup> Serpentis]], a cool red giant that pulsates between magnitudes 5.89 and 7.07 in 87 days.<ref name="Tau4AAVSO">{{cite web|url=http://www.aavso.org/vsx/index.php?view=detail.top&oid=34971 |title=Tau4 Serpentis |author1=VSX |last2=Otero |first2=S. A|date=28 June 2012 |work=AAVSO Website|publisher=American Association of Variable Star Observers|access-date=24 June 2014}}</ref> This star has been found to display an inverse [[P Cygni profile]],<ref name="Kolotilov">{{cite journal |last1=Kolotilov |first1=E. A. |last2=Russev |first2=R. M. |title=Inverse P Cyg Profile of Halpha in the Spectrum of the Red Giant HD 139216 = tau4 Ser |journal=Information Bulletin on Variable Stars |volume=1730 |page=1 |date=January 1980 |bibcode=1980IBVS.1730....1K}}</ref> where cold infalling gas on to the star creates [[redshift]]ed hydrogen absorption lines next to the normal emission lines.<ref name="UToledo">{{cite web|url=http://astro1.physics.utoledo.edu/~megeath/ph6820/lecture7_ph6820.pdf |title=Lecture 7: The Collapse of Cores and Infall |author=Galactic Star and Planet Formation Research Group |publisher=Department of Physics and Astronomy, University of Toledo |access-date=17 July 2015}}</ref>

Several stars in Serpens have been found to have [[exoplanet|planets]]. The brightest, [[Omega Serpentis]], located between Epsilon and Mu, is an [[orange giant]] with a planet of at least 1.7 [[Jupiter]]-masses.<ref name="Sato">{{Cite journal | doi = 10.1093/pasj/65.4.85| title = Planetary Companions to Three Evolved Intermediate-Mass Stars: HD 2952, HD 120084, and ω Serpentis| journal = Publications of the Astronomical Society of Japan| volume = 65| issue = 4| pages = 85| year = 2013| last1 = Sato | first1 = B.| last2 = Omiya | first2 = M.| last3 = Harakawa | first3 = H.| last4 = Liu | first4 = Y. -J. | last5 = Izumiura | first5 = H.| last6 = Kambe | first6 = E.| last7 = Takeda | first7 = Y.| last8 = Yoshida | first8 = M.| last9 = Itoh | first9 = Y.| last10 = Ando | first10 = H.| last11 = Kokubo | first11 = E.| last12 = Ida | first12 = S.| bibcode = 2013PASJ...65...85S|arxiv = 1304.4328 | s2cid = 119248666}}</ref> [[NN Serpentis]], an eclipsing [[Post common envelope binary|post-common-envelope binary]] consisting of a [[white dwarf]] and a [[red dwarf]],<ref name="Parsons">{{Cite journal | doi = 10.1111/j.1365-2966.2009.16072.x| title = Precise mass and radius values for the white dwarf and low mass M dwarf in the pre-cataclysmic binary NN Serpentis| journal = Monthly Notices of the Royal Astronomical Society| volume = 402| issue = 4| pages = 2591| year = 2010| last1 = Parsons | first1 = S. G.| last2 = Marsh | first2 = T. R.| last3 = Copperwheat | first3 = C. M.| last4 = Dhillon | first4 = V. S.| last5 = Littlefair | first5 = S. P.| last6 = Gänsicke | first6 = B. T.| last7 = Hickman | first7 = R.| doi-access = free| bibcode = 2010MNRAS.402.2591P|arxiv = 0909.4307 | s2cid = 15186725}}</ref> is very likely to have two planets causing variations in the period of the eclipses.<ref name="Marsh">{{Cite journal | doi = 10.1093/mnras/stt1903| title = The planets around NN Serpentis: Still there| journal = Monthly Notices of the Royal Astronomical Society| volume = 437| issue = 1| pages = 475| year = 2013| last1 = Marsh | first1 = T. R.| last2 = Parsons | first2 = S. G.| last3 = Bours | first3 = M. C. P.| last4 = Littlefair | first4 = S. P.| last5 = Copperwheat | first5 = C. M.| last6 = Dhillon | first6 = V. S.| last7 = Breedt | first7 = E.| last8 = Caceres | first8 = C.| last9 = Schreiber | first9 = M. R.| doi-access = free| bibcode = 2014MNRAS.437..475M|arxiv = 1310.1391 | s2cid = 53954504| url = http://wrap.warwick.ac.uk/58930/1/WRAP_MNRAS-2014-Marsh-475-88.pdf}}</ref> Although it does not have a planet, the solar analog [[HD 137510]] has been found to have a [[brown dwarf]] companion within the [[brown-dwarf desert]].<ref name="Endl">{{cite journal|doi=10.1086/422310|title=HD 137510: An Oasis in the Brown Dwarf Desert|journal=The Astrophysical Journal|volume=611|issue=2|pages=1121–1124|year=2004|last1=Endl|first1=Michael|last2=Hatzes|first2=Artie P.|last3=Cochran|first3=William D.|last4=McArthur|first4=Barbara|last5=Prieto|first5=Carlos Allende|last6=Paulson|first6=Diane B.|last7=Guenther|first7=Eike|last8=Bedalov|first8=Ana|bibcode=2004ApJ...611.1121E|arxiv = astro-ph/0404584 |s2cid=119062344}}</ref>

[[PSR B1534+11]] is a system consisting of two [[neutron star]]s orbiting each other, one of which is a [[pulsar]] with a period of 37.9 milliseconds. Situated approximately 1000 parsecs distant, the system was used to test [[Albert Einstein]]'s theory of [[general relativity]], validating the system's relativistic parameters to within 0.2% of values predicted by the theory.<ref name="Fonseca">{{Cite journal | doi = 10.1088/0004-637X/787/1/82| title = A Comprehensive Study of Relativistic Gravity Using PSR B1534+12| journal = The Astrophysical Journal| volume = 787| issue = 1| pages = 82| year = 2014| last1 = Fonseca | first1 = E. | last2 = Stairs | first2 = I. H. | last3 = Thorsett | first3 = S. E. | bibcode =  2014ApJ...787...82F|arxiv = 1402.4836 | s2cid = 119198979}}</ref> The [[X-ray]] emission from the system has been found to be present when the non-pulsar star intersects the equatorial [[pulsar wind]] of the pulsar, and the system's orbit has been found to vary slightly.<ref name="Durant">{{Cite journal | doi = 10.1088/0004-637X/741/1/65| title = Orbital Variation of the X-Ray Emission from the Double Neutron Star Binary J1537+1155| journal = The Astrophysical Journal| volume = 741| issue = 1| pages = 65| year = 2011| last1 = Durant | first1 = M. | last2 = Kargaltsev | first2 = O. | last3 = Volkov | first3 = I. | last4 = Pavlov | first4 = G. G. | bibcode = 2011ApJ...741...65D|arxiv = 1108.3330 | s2cid = 119200269}}</ref>