epsilon Coronae Borealis

{{Short description|Multiple star system in the constellation Corona Borealis}}

{{Starbox begin

| name = ε Coronae Borealis

}}

{{Starbox image

| image=

{{Location mark

|image=Corona Borealis constellation map.svg|alt=|float=center|width=260

|label=|position=right

|mark=Red circle.svg|mark_width=10|mark_link=ε CrB

|x=412|y=638

}}

|caption=Location of ε Coronae Borealis (circled)

}}

{{Starbox observe

| epoch = J2000

| constell = Corona Borealis

|ra= {{RA|15|57|35.25147}}

|dec= {{DEC|+26|52|40.3635}}

| appmag_v = 4.13

}}

{{Starbox character

| class = K2 III

| b-v = +1.235

| u-b = +1.28

}}

{{Starbox astrometry

| radial_v = −32.42

| prop_mo_ra = −77.07

| prop_mo_dec = −60.61

| parallax = 13.4922

| p_error = 0.1023

| parallax_footnote = {{Cite Gaia EDR3|1220404653534258816}}

| absmag_v = −0.02

| absmag_bol =

}}

{{Starbox detail

| source =

| mass = {{Val|1.37|0.24}}

| radius = {{val|21.87|0.98|0.99}}

| luminosity_bolometric = {{val|162.9|9.4}}

| temperature = {{Val|4408|109|fmt=commas}}

| gravity = {{Val|1.94|0.15}}

| metal_fe = {{Val|−0.22|0.03}}

| rotation =

| rotational_velocity = 2.4

| age_gyr = {{val|3.24|1.81}}

}}

{{Starbox catalog

| names = 13 Coronae Borealis, BD+27°2558, HD 143107, HIP 78159, HR 5947, SAO 84098, 2MASS J15573523+2652400

}}

{{Starbox reference

|Simbad = eps+CrB

}}

{{Starbox end}}

Epsilon Coronae Borealis, Latinized from ε Coronae Borealis, is a multiple star system in the constellation Corona Borealis located around 230 light-years from the Solar System. It shines with a combined apparent magnitude of 4.13, meaning it is visible to the unaided eye in all night skies except those brightly lit in inner city locations.{{cite web|url=http://www.skyandtelescope.com/resources/darksky/3304011.html?page=1&c=y|title=The Bortle Dark-Sky Scale|last=Bortle|first=John E.|date=February 2001|work=Sky & Telescope|publisher=Sky Publishing Corporation|access-date=2013-02-20|archive-date=2014-03-31|archive-url=https://web.archive.org/web/20140331202746/http://www.skyandtelescope.com/resources/darksky/3304011.html?page=1&c=y|url-status=dead}}

This star has a stellar spectrum matching the class K2III, which indicate it is a giant star that exhausted its hydrogen supply at its core and evolved.{{cite journal|author1=Lee, B.-C. |author2=Han, I. |author3=Park, M.-G. |author4=Mkrtichian, D. E. |author5=Kim, K.-M. |date=2012|title=A planetary companion around the K giant ɛ Corona Borealis|journal=Astronomy & Astrophysics|volume=546|id=A5|pages=5|bibcode=2012A&A...546A...5L|doi=10.1051/0004-6361/201219347|arxiv = 1209.1187 |s2cid=55260442 }} Being 40% more massive than the Sun and 3.2 billion years old, it expanded to over 20 times the Sun's size and cooled to an effective temperature of {{val|fmt=commas|4408|ul=K}}. That is, Epsilon Coronae Borealis's diameter is about one-quarter of Mercury's orbit. The star radiates with 160 times the Sun's luminosity.

Epsilon Coronae Borealis B is a companion star thought to be an orange dwarf of spectral types K3V to K9V that orbits at a distance of 135 astronomical units, completing one orbit every 900 years.

A faint (magnitude 11.5) star, 1.5 arc minutes away, has been called Epsilon Coronae Borealis C although it is only close by line of sight and is unrelated to the system.{{cite web| first1=James B. | last1=Kaler | title=Epsilon and T Coronae Borealis | work=Stars | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/epscrb.html | access-date=16 November 2014|date = 19 August 2011}}SIMBAD, [http://simbad.cfa.harvard.edu/simbad/sim-id?Ident=%402812778&Name=CCDM%20J15576%2b2652C&submit=submit CCDM J15576+2652C -- Star in double system] (accessed 16 November 2014)

Epsilon Coronae Borealis lies one degree north of (and is used as a guide for) the variable T Coronae Borealis.