epsilon Hydri

{{Short description|Star in the constellation Hydrus}}

{{Starbox begin

| name = ε Hydri

}}

{{Starbox image

|image=

{{Location mark

|image=Hydrus constellation map.svg|alt=|float=center|width=280

|label=|position=right

|mark=Red circle.svg|mark_width=10|mark_link=Epsilon Hydri

|x=466|y=510

}}

|caption=Location of ε Hydri (circled)

}}

{{Starbox observe

| epoch = J2000

| constell = Hydrus

| ra = {{RA|02|39|35.36121}}{{cite journal | arxiv=0708.1752 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | year=2007 | last1=Van Leeuwen | first1=F. | s2cid=18759600 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-S?HIP%2012394 Vizier catalog entry]

| dec = {{DEC|-68|16|01.0103}}

| appmag_v = 4.12{{cite journal | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | arxiv=1108.4971 | title=XHIP: An extended hipparcos compilation | journal=Astronomy Letters | volume=38 | issue=5 | pages=331 | year=2012 | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | s2cid=119257644 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=V/137D/XHIP&HIP=12394 Vizier catalog entry]

}}

{{Starbox character

| class = B9 Va

| b-v = −0.06{{cite journal | bibcode=2014JAVSO..42..443M | title=Sloan Magnitudes for the Brightest Stars | journal=The Journal of the American Association of Variable Star Observers | volume=42 | pages=443 | last1=Mallama | first1=A. | year=2014 | issue=2 }}[http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=J/other/JAVSO/42.443/ugriz&HD=016978 Vizier catalog entry]

| u-b = −0.14

}}

{{Starbox astrometry

| radial_v = {{Val|+13.6|0.9}}{{Cite journal | doi=10.1134/S1063773706110065 | bibcode=2006AstL...32..759G| title=Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system| journal=Astronomy Letters| volume=32| issue=11| pages=759–771| year=2006| last1=Gontcharov| first1=G. A.|arxiv = 1606.08053 | s2cid=119231169}}

| prop_mo_ra = +87.30

| prop_mo_dec = +0.09

| parallax = 21.48

| p_error = 0.09

| parallax_footnote =

| absmag_v = +0.78

}}

{{Starbox detail

| mass = 2.64{{cite journal | arxiv=1201.2052 | bibcode=2012A&A...537A.120Z | doi=10.1051/0004-6361/201117691 | title=Rotational velocities of A-type stars | journal=Astronomy & Astrophysics | volume=537 | pages=A120 | year=2012 | last1=Zorec | first1=J. | last2=Royer | first2=F. | s2cid=55586789 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=J/A%2bA/537/A120/table1&HD=16978 Vizier catalog entry]

| radius = 2.2{{cite journal | bibcode=1999A&A...352..555A | arxiv=astro-ph/9911002 | title=Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures | journal=Astronomy and Astrophysics | volume=352 | pages=555–562 | last1=Allende Prieto | first1=C. | last2=Lambert | first2=D. L. | year=1999 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=J/A%2bA/352/555/table1&Name=HIP12394 Vizier catalog entry]

| temperature = {{Val|10970|373|fmt=commas}}{{cite journal | bibcode=2015ApJ...804..146D | doi=10.1088/0004-637X/804/2/146 | arxiv=1501.03154 | title=The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets | journal=The Astrophysical Journal | volume=804 | issue=2 | pages=146 | year=2015 | last1=David | first1=Trevor J. | last2=Hillenbrand | first2=Lynne A. | s2cid=33401607 }} [http://vizier.u-strasbg.fr/viz-bin/VizieR-4?-source=J/ApJ/804/146/table5&HIP=12394 Vizier catalog entry]

| luminosity = 60

| rotational_velocity = 96

| gravity = 4.33

| age_myr = 133

}}

{{Starbox catalog

| names = {{odlist | B=ε Hyi | CPD=−68° 161 | FK5=95 | HD=16978 | HIP=12394 | HR=806 | SAO=248621 | GC=3240 }}

}}

{{Starbox reference

| Simbad = Epsilon+Hydri

}}

{{Starbox end}}

Epsilon Hydri, Latinized from ε Hydri, is a single,{{citation | last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A. | title=A catalogue of multiplicity among bright stellar systems | journal=Monthly Notices of the Royal Astronomical Society | volume=389 | issue=2 | pages=869–879 | date=September 2008 | bibcode=2008MNRAS.389..869E | doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | arxiv=0806.2878 | s2cid=14878976 | postscript=. }} blue-white hued star in the southern constellation of Hydrus. It is a faint star with an apparent visual magnitude of 4.12, but it can be seen with the naked eye. Measurements made by the Hipparcos spacecraft showed an annual parallax shift of 21.48 mas, which provides a distance estimate of 152 light years. The star is moving away from the Sun with a radial velocity of +13.6 km/s. It is a member of the Tucana-Horologium moving group, an association of stars that share a common motion through space.{{citation | title=A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood | display-authors=1 | last1=Bell | first1=Cameron P. M. | last2=Mamajek | first2=Eric E. | last3=Naylor | first3=Tim | journal=Monthly Notices of the Royal Astronomical Society | volume=454 | issue=1 | pages=593–614 | date=November 2015 | doi=10.1093/mnras/stv1981 | doi-access=free | bibcode=2015MNRAS.454..593B | arxiv=1508.05955 }}

The stellar classification for this star is B9 Va, indicating that is it a B-type main-sequence star that is generating energy through hydrogen fusion at its core. It is a young star, just 133 million years in age, and has a high rate of spin with a projected rotational velocity of 96 km/s. This is giving the star a mild oblate shape with an equatorial bulge that is 5% greater than the polar radius.{{Cite journal | title=Interferometric observations of rapidly rotating stars | year=2012 | last1=Belle | first1=G. T. | journal=The Astronomy and Astrophysics Review | volume=20 | issue=1 | pages=51 | doi=10.1007/s00159-012-0051-2 | bibcode=2012A&ARv..20...51V | arxiv=1204.2572 | s2cid=119273474 }} Epsilon Hydri has an estimated 2.64 times the mass of the Sun and 2.2 times the Sun's radius. It is radiating 60 times the Sun's luminosity from its photosphere at an effective temperature of around 10,970 K.