View source for HR 4796

{{Short description|Binary star system in the constellation Centaurus}}
{{Starbox begin
| name = HR 4796
}}
{{Starbox image
| image = [[File:Dust ring around HR 4796A (eso1417a).jpg|250px]]
| caption = A dust ring encircles HR 4796's primary star
}}
{{Starbox observe
| epoch = J2000.0
| constell = [[Centaurus]]
| ra = {{RA|12|36|01.0318}}<ref name="Gaia DR2"/>
| dec = {{DEC|−39|52|10.2226}}<ref name="Gaia DR2"/>
| appmag_v = 5.80<ref name=clpl4_99/>
}}
{{Starbox character
| class    = A0&nbsp;V_+ M2.5&nbsp;V<ref name=aj137_1_53/>
| r-i      =
| v-r      =
| b-v      = +0.01<ref name=clpl4_99/>
| u-b      =
| variable =
}}
{{Starbox astrometry
| radial_v = 9.4<ref name=apjss169_1_105/>
| prop_mo_ra  = {{val|−55.653|0.181}}<ref name="Gaia DR2"/>
| prop_mo_dec = {{val|−23.740|0.230}}<ref name="Gaia DR2"/>
| parallax = 13.9064
| p_error = 0.1349
| parallax_footnote = <ref name="Gaia DR2"/>
| absmag_v = {{Val|1.61|0.11}}<ref name=Gerbaldi1999/>
}}
{{Starbox detail
| component1 = Component A
| mass     = {{nowrap|2.18 ± 0.10}}<ref name=aaas137_273/>
| radius   = 1.68<ref name=aaas137_273/>
| gravity  = 4.43<ref name=aaa490_1_297/>
| luminosity  = 23<ref name=aaas137_273/>
| temperature = 9,378<ref name=aaa490_1_297/>
| metal_fe = –0.03<ref name=aaa490_1_297/>
| rotational_velocity = 152<ref name=aaa463_2_671/>
| age_myr = {{nowrap|8 ± 2}}<ref name=aj137_1_53/>
| component2 = Component B
| mass2    = 0.3<ref name=aaa428_953/>
}}
{{Starbox catalog
| names = [[2MASS]]&nbsp;J12360103-3952102, [[Catalog of Components of Double and Multiple Stars|CCDM]]&nbsp;J12360-3952, [[Durchmusterung|CD]]-39°7717, [[Durchmusterung|CPD]]-39°5622, [[Boss General Catalogue|GC]]&nbsp;17164, [[Henry Draper Catalogue|HD]]&nbsp;109573, [[Hipparcos catalogue|HIP]]&nbsp;61498, [[Bright Star Catalogue|HR]]&nbsp;4796, [[Smithsonian Astrophysical Observatory Star Catalog|SAO]]&nbsp;203621.<ref name=SIMBAD/>
}}
{{Starbox reference
| Simbad = HD+109573
| ARICNS = <!--Code-->
}}
{{Starbox end}}
'''HR 4796''' is a [[binary star|binary star system]] in the southern [[constellation]] of [[Centaurus (constellation)|Centaurus]]. [[Parallax]] measurements put it at a distance of {{Convert|235|ly|pc|abbr=off|lk=on}} from the [[Earth]]. The two components of this system have an [[angular separation]] of 7.7 [[arcsecond]]s, which, at their estimated distance, is equivalent to a [[projected separation]] of about 560 [[Astronomical Unit]]s (AU), or 560 times the separation of the Earth from the Sun.<ref name=aj137_1_53/> The star and its ring resemble an eye, and it is sometimes known by the nickname "[[Eye of Sauron|Sauron's Eye]]".<ref name="Flora Graham">{{cite news |url=https://www.newscientist.com/article/dn25676-eye-of-sauron-star-spotted-by-planethunting-camera.html |title= Eye of Sauron star spotted by planet-hunting camera |author= Flora Graham |date= 4 June 2014 |publisher= New Scientist }}</ref><ref name="NewsCorp Australia">{{cite news |url= http://www.couriermail.com.au/technology/science/saurons-eye-has-been-found-and-its-watching-us-all-from-above-in-the-form-of-ringed-star-hr-4796a/story-fnjwlbuh-1226945497551 |publisher= Courier Mail |title= Sauron's Eye has been found. And it's watching us all, from above, in the form of ringed star HR 4796A |author= NewsCorp Australia |date= 6 June 2014 }}</ref>
==Components==
This is a young system with an estimated age of about 8 million years.<ref name=aj137_1_53/>  The primary member '''A''' has a [[stellar classification]] of A0&nbsp;V, while its smaller companion '''B''' is a [[red dwarf]] with a classification of M2.5&nbsp;V.<ref name=aj137_1_53/> The [[luminosity class]] of 'V' indicates that both stars belong to the [[main sequence]] and are generating energy through the [[thermonuclear fusion]] of hydrogen at their cores. The primary is emitting this energy from its outer envelope at an [[effective temperature]] of about 9,378&nbsp;K, which gives it the white hue characteristic of [[A-type star]]s.<ref name=aaa490_1_297/><ref name=csiro/> It has a radius about 168% of the [[solar radius|radius of the Sun]] and 218% of the [[solar mass|Sun's mass]].<ref name=aaas137_273/> By comparison, the secondary has only 30% of a solar mass. The abundance of elements other than hydrogen or helium, what astronomers term the star's [[metallicity]], is similar to the proportion in the Sun.<ref name=aj137_1_53/>
==Debris disk==
In 1991, the primary was found to have an [[infrared excess|excess of infrared emission]], implying that it has a circumstellar [[debris disk]]. Observations using the Near-Infrared Multi-Object Spectrometer aboard the [[Hubble Space Telescope]] in 2007 indicated that the dust had a reddish spectrum similar to that of [[tholin]]s.<ref name=apjl673_2_L191/> The disk was resolved with the Hubble Space Telescope in 2009, confirming that it exists. Based on these images, the disk has a radius of 75 AU and a width of less than 18.5 AU. It may have some asymmetries and the center appears to be slightly offset from the star. The dust in the disk is likely the result of collisions between larger particles.<ref name=aj137_1_53/> In 2011, observations of the ring offset by the [[Subaru Telescope]] implies that one or more planets would likely exist within gaps tugging at its dust grains.<ref name=subaru/><ref name=apjl743_1_L6/> With a new image in 2014, the configuration and alignment of the dust ring and HR4796A has been nicknamed "[[Eye of Sauron]]".<ref name="Flora Graham"/><ref name="NewsCorp Australia"/>
In 2017 a group using NASA/IRTF and Spitzer infrared spectroscopy of the infrared excess determined that the bright narrow ring is made up of very red devolatilzed cometary material, and that a second faint, hot diffuse dust component likely due to inspiralling material escaping from the ring was present close to the star and evaporating.<ref name="Lisse">{{cite journal|last1=Lisse|first1=C.|last2=Sitko|first2=M.|last3=Marengo|first3=M.|display-authors=etal|title=Infrared Spectroscopy of HR 4796Aʼs Bright Outer Cometary Ring+Tenuous Inner Hot Dust Cloud|journal=The Astronomical Journal|volume=154|issue=5|pages=182|date=November 2017 | doi=10.3847/1538-3881/aa855e | bibcode=2017AJ....154..182L|arxiv=1708.02834|s2cid=119466875 |doi-access=free }}</ref> The discovery of a complex dust structure about 1,600 AU across, enveloping HR 4796A, was announced in March 2018. The structure is believed to have been formed by the pressure of starlight from HR 4796A expelling dust from the debris disk far into space. The structure is much more extended in one direction than the other, possibly due to either the motion of HR 4796A through the interstellar medium, or the gravitational influence of HR 4796B.<ref name="Hille">{{cite web|last1=Hille|first1=Karl|title=Hubble Finds Huge System of Dusty Material Enveloping the Young Star HR 4796A|url=https://www.nasa.gov/feature/goddard/2018/hubble-finds-huge-system-of-dusty-material-enveloping-the-young-star-hr-4796a|website=NASA|date=6 March 2018|access-date=8 March 2018}}</ref>
[[File:Circumstellar Disk Around HR 4796A (Hubble) (2019-29-4504-Image).png|thumb|Hubble image of dust structure surrounding HR 4796A]]
==Kinematics==
The [[space velocity (astronomy)|space velocity]] of HR 4796 in the [[Galactic coordinate system]] is {{nowrap|[''U'', ''V'', ''W'']}} = {{nowrap|[−8.5, −18.3, −3.6] km s<sup>−1</sup>}}. This trajectory and the location of the system suggests that it may be a member of the [[TW Hydrae association]] of stars that share a common origin.<ref name=apjss169_1_105/> A low-mass member of this association, identified as 2MASS J12354893−3950245, may be a tertiary component of the HR 4796 system. It has a [[proper motion]] matching HR 4796, suggesting it is gravitationally bound to the other two stars, and is separated from the pair by a distance of about 13,500&nbsp;AU.<ref name=aaa491_3_829/>
==See also==
* [[Vega]]
==References==
{{reflist|refs=
<ref name=aaa463_2_671>{{citation | last1=Royer | first1=F. | last2=Zorec | first2=J. | last3=Gómez | first3=A. E. | title=Rotational velocities of A-type stars. III. Velocity distributions | journal=Astronomy and Astrophysics | volume=463 | issue= 2 | pages=671–682 |date=February 2007 | doi=10.1051/0004-6361:20065224 | bibcode=2007A&A...463..671R |arxiv = astro-ph/0610785 | s2cid=18475298 }}</ref>
<ref name=clpl4_99>{{citation | last1=Johnson | display-authors=1 | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | pages=99 | date=1966 | bibcode=1966CoLPL...4...99J }}</ref>
<ref name=aj137_1_53>{{citation | display-authors=1 | last1=Schneider | first1=G. | last2=Weinberger | first2=A. J. | last3=Becklin | first3=E. E. | last4=Debes | first4=J. H. | last5=Smith | first5=B. A. | title=STIS Imaging of the HR 4796A Circumstellar Debris Ring | journal=The Astronomical Journal | volume=137 | issue=1 | pages=53–61 |date=January 2009 | doi=10.1088/0004-6256/137/1/53 | bibcode=2009AJ....137...53S |arxiv = 0810.0286 | s2cid=35159109 }}</ref>
<ref name=SIMBAD>{{citation | url=http://simbad.u-strasbg.fr/simbad/sim-id?protocol=html&Ident=HD+109573 | title=HD 109573 -- Star in double system | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | access-date=2007-01-08 }}</ref>
<ref name=apjl673_2_L191>{{cite journal | title=Complex Organic Materials in the Circumstellar Disk of HR 4796A | first1=J. H. | last1=Debes | first2=A. J. | last2=Weinberger | first3=G. | last3=Schneider | arxiv=0712.3283 | journal=Astrophysical Journal Letters | bibcode=2008ApJ...673L.191D | doi=10.1086/527546 | date=2008 | volume=673 | issue=2 | pages=L191 | s2cid=1215872 }}</ref>
<ref name=aaa490_1_297>{{citation | display-authors=1 | last1=Saffe | first1=C. | last2=Gómez | first2=M. | last3=Pintado | first3=O. | last4=González | first4=E. | title=Spectroscopic metallicities of Vega-like stars | journal=Astronomy and Astrophysics | volume=490 | issue=1 | pages=297–305 |date=October 2008 | doi=10.1051/0004-6361:200810260 | bibcode=2008A&A...490..297S |arxiv = 0805.3936 | s2cid=15059920 }}</ref>
<ref name=apjss169_1_105>{{citation | last1=Makarov | first1=Valeri V. | title=Unraveling the Origins of Nearby Young Stars | journal=The Astrophysical Journal Supplement Series | volume=169 | issue=1 | pages=105–119 |date=March 2007 | doi=10.1086/509887 | bibcode=2007ApJS..169..105M | s2cid=119552302 | url=https://authors.library.caltech.edu/17463/1/MAKapjss07.pdf }}</ref>
<ref name=aaa428_953>{{citation | display-authors=1 | last1=Huélamo | first1=N. | last2=Fernández | first2=M. | last3=Neuhäuser | first3=R. | last4=Wolk | first4=S. J. | title=Rotation periods of Post-T Tauri stars in Lindroos systems | journal=Astronomy and Astrophysics | volume=428 | issue=3 | pages=953–967 |date=December 2004 | doi=10.1051/0004-6361:20034442 | bibcode=2004A&A...428..953H |arxiv = astro-ph/0408226 | s2cid=10656237 }}</ref>
<ref name=aaa491_3_829>{{citation | last1=Kastner | first1=J. H. | last2=Zuckerman | first2=B. | last3=Bessell | first3=M. | title=Identification of the TW Hydrae association member 2M1235-39: a tertiary component of the HR 4796 system | journal=Astronomy and Astrophysics | volume=491 | issue=3 | pages=829–831 |date=December 2008 | doi=10.1051/0004-6361:200810580 | bibcode=2008A&A...491..829K |arxiv = 0808.2630 | s2cid=118436645 }}</ref>
<ref name=aaas137_273>{{citation | display-authors=1 | last1=Gerbaldi | first1=M. | last2=Faraggiana | first2=R. | last3=Burnage | first3=R. | last4=Delmas | first4=F. | last5=Gómez | first5=A. E. | last6=Grenier | first6=S. | title=Search for reference A0 dwarf stars: Masses and luminosities revisited with HIPPARCOS parallaxes | journal=Astronomy and Astrophysics Supplement | volume=137 | issue=2 | pages=273–292 |date=June 1999 | doi=10.1051/aas:1999248 | bibcode=1999A&AS..137..273G | doi-access=free }}</ref>
<ref name=subaru>{{cite news | url=http://astronomy.com/News-Observing/News/2012/01/Subarus%20sharp%20eye%20confirms%20signs%20of%20unseen%20planets%20in%20stars%20dust%20ring.aspx | title=Subaru's sharp eye confirms signs of unseen planets in star's dust ring | journal=Astronomy Magazine | date=2012-01-04 }}</ref>
<ref name=apjl743_1_L6>{{citation | display-authors=1 | last1=Thalmann | first1=C. | last2=Janson | first2=M. | last3=Buenzli | first3=E. | last4=Brandt | first4=T. D. | last5=Wisniewski | first5=J. P. | last6=Moro-Martín | first6=A. | last7=Usuda | first7=T. | last8=Schneider | first8=G. | last9=Carson | first9=J. | title=Images of the Extended Outer Regions of the Debris Ring around HR 4796 A | journal=The Astrophysical Journal Letters | volume=743 | issue=1 | page=L6 (2011) |date=December 2011 | doi=10.1088/2041-8205/743/1/L6 | bibcode=2011ApJ...743L...6T |arxiv = 1110.2488 | s2cid=14131310 }}</ref>
<ref name=csiro>{{citation | title=The Colour of Stars | date=December 21, 2004 | work=Australia Telescope, Outreach and Education | publisher=Commonwealth Scientific and Industrial Research Organisation | url=http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html | access-date=2012-01-16 | archive-url=https://web.archive.org/web/20120318151427/http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html | archive-date=March 18, 2012 | url-status=dead }}</ref>
<ref name=Gerbaldi1999>{{citation | display-authors=1
| last1=Gerbaldi | first1=M. | last2=Faraggiana | first2=R.
| last3=Burnage | first3=R. | last4=Delmas | first4=F.
| last5=Gómez | first5=A. E. | last6=Grenier | first6=S.
| title=Search for reference A0 dwarf stars: Masses and luminosities revisited with HIPPARCOS parallaxes
| journal=Astronomy and Astrophysics Supplement | postscript=.
| volume=137 | issue=2 | pages=273–292 |date=June 1999
| doi=10.1051/aas:1999248 | bibcode=1999A&AS..137..273G | doi-access=free }}</ref>
<ref name="Gaia DR2">{{Cite Gaia DR2|6147117727029871360}}</ref>
}}
==External links==
* {{cite web |url=http://www.cnn.com/TECH/space/9804/21/nasa.planets/index.html |title=Birth of a solar system? |access-date=2008-09-10 |publisher=[[CNN]] |date=1998-04-21 }}
* {{cite web |url=http://jumk.de/astronomie/exoplanets/hr-4796.shtml |title=HR 4796 |access-date=2008-09-10 }}
{{Stars of Centaurus}}
{{DEFAULTSORT:HR 4796}}
[[Category:A-type main-sequence stars]]
[[Category:M-type main-sequence stars]]
[[Category:Centaurus]]
[[Category:Henry Draper Catalogue objects|109573]]
[[Category:Hipparcos objects|061498]]
[[Category:Bright Star Catalogue objects|4796]]
[[Category:Circumstellar disks]]
[[Category:Binary stars]]
[[Category:Durchmusterung objects]]