Delta Ursae Minoris

{{Starbox begin

| name=δ Ursae Minoris

}}

{{Starbox image

| image=

{{Location mark

|image=Ursa Minor constellation map.svg|alt=|float=center|width=260

|label=|position=right

|mark=Red circle.svg|mark_width=10|mark_link=δ UMi

|x=423|y=170

}}

|caption=Location of δ Ursae Minoris (circled)

}}

{{Starbox observe

| epoch = J2000

| ra = {{RA|17|32|12.99671}}

| dec = {{DEC|+86|35|11.2584}}

| appmag_v = 4.36

| constell = Ursa Minor

}}

{{Starbox character

| class = A1 Van

| b-v = +0.02

| u-b = +0.03

| variable =

}}

{{Starbox astrometry

| radial_v ={{Val|−7.6|2.7}}

| prop_mo_ra = +10.17

| prop_mo_dec = +53.97

| parallax = 18.95

| p_error = 0.14

| parallax_footnote =

| absmag_v = 0.62

}}

{{Starbox detail

| mass = 2.35

| radius = 2.8

| luminosity = 47.77

| temperature = {{Val|9911|337|fmt=commas}}

| gravity = 4.04

| metal_fe =

| rotation = 19 hours

| rotational_velocity = 154

| age_myr = 327

}}

{{Starbox catalog

| names={{odlist | name=Yildun | name2=Vildiur | name3=Gildun | B=δ UMi | F=23 Ursae Minoris | BD=+86°269 | FK5=913 | HD=166205 | HIP=85822 | HR=6789 | SAO=2937 | GC=24236 }}

}}

{{Starbox reference

| Simbad=del+UMi

}}

Delta Ursae Minoris, Latinized from δ Ursae Minoris, formally named Yildun {{IPAc-en|j|I|l|'|d|V|n}},{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |accessdate=28 July 2016}} is a white-hued star in the northern circumpolar constellation of Ursa Minor, forming the second star in the bear's tail. It is visible to the naked eye with an apparent visual magnitude of 4.36. Based upon an annual parallax shift of 18.95 mas as seen from Earth, it is located 172 light years from the Sun. The star is moving closer to the Sun with a radial velocity of about −8 km/s.

Description

This is an A-type main-sequence star with a stellar classification of A1 Van, where the 'n' indicates "nebulous" absorption lines in the spectrum due to rapid rotation. It is spinning with a projected rotational velocity of 180 km/s, which is giving the star an oblate shape with an equatorial bulge that is an estimated 7% larger than the polar radius. The star is about 327 million years old with 2.35 times the mass of the Sun. It is radiating about 48 times the Sun's luminosity from its photosphere at an effective temperature of 9,911 K.

δ Ursae Minoris has a 12th magnitude common proper-motion companion at an angular separation of 4.5 arc seconds along a position angle of 67.3°, which is a projected separation of 237.4 au at the distance of δ Ursae Minoris. The pair were resolved using adaptive optics. The companion is assumed to be gravitationally bound and to have a mass of approximately {{solar mass|0.16}}.

Nomenclature

δ Ursae Minoris (Latinised to Delta Ursae Minoris) is the star's Bayer designation.

It bore the traditional name Yildun (also spelled Vildiur or Gildun) from the Turkish yıldız "star".{{cite book|author=Richard Hinckley Allen|title=Star-names and Their Meanings|url=https://archive.org/details/bub_gb_5xQuAAAAIAAJ|year=1899|publisher=G.E. Stechert|pages=[https://archive.org/details/bub_gb_5xQuAAAAIAAJ/page/n469 447]–460}} In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN){{citation

| url=https://www.iau.org/science/scientific_bodies/working_groups/280/

| title=IAU Working Group on Star Names (WGSN)

| publisher=International Astronomical Union

| accessdate=22 May 2016 | postscript=. }} to catalogue and standardize proper names for stars. The WGSN approved the name Yildun for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.

References

{{Reflist

| refs =

{{citation

| title=XHIP: An extended hipparcos compilation

| last1=Anderson | first1=E. | last2=Francis | first2=Ch.

| journal=Astronomy Letters

| volume=38 | issue=5 | pages=331 | year=2012

| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015

| arxiv=1108.4971 | s2cid=119257644 | postscript=. }}

{{citation

| title=Star Tales

| first1=Ian | last1=Ridpath

| page=131 | year=1988 | isbn=0718826957

| publisher=James Clarke & Co. | postscript=.

| url=https://books.google.com/books?id=gFrdcTdeVaEC&pg=RA1-PA131 }}

{{cite journal

| last1=De Rosa | first1=R. J. | last2=Patience |first2=J.

| last3=Wilson | first3=P. A. | last4=Schneider | first4=A.

| last5=Wiktorowicz | first5=S. J. | last6=Vigan | first6=A.

| last7=Marois | first7=C. | last8=Song | first8=I.

| last9=MacIntosh | first9=B. | last10=Graham | first10=J. R.

| last11=Doyon | first11=R. | last12=Bessell | first12=M. S.

| last13=Thomas | first13=S. | last14=Lai | first14=O.

| title=The VAST Survey - III. The multiplicity of A-type stars within 75 pc

| journal=Monthly Notices of the Royal Astronomical Society

| volume=437 | issue=2 | pages=1216 | year=2014

| doi=10.1093/mnras/stt1932 | doi-access=free | arxiv=1311.7141

| bibcode=2014MNRAS.437.1216D | s2cid=88503488 }}

{{citation

| title=Interferometric observations of rapidly rotating stars

| last1=Belle | first1=G. T.

| journal=The Astronomy and Astrophysics Review

| volume=20| page=51 | year=2012

| issue=1 | doi=10.1007/s00159-012-0051-2 | bibcode=2012A&ARv..20...51V

| arxiv=1204.2572 | s2cid=119273474 | postscript=. }}

{{cite simbad

| title=del UMa

| access-date=2012-03-04}}

{{citation

| last1=David | first1=Trevor J. | last2=Hillenbrand | first2=Lynne A.

| 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

| bibcode=2015ApJ...804..146D | doi=10.1088/0004-637X/804/2/146

| arxiv=1501.03154 | s2cid=33401607 | postscript=. }}

{{citation

| last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C.

| title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project

| journal=Astronomy & Astrophysics

| volume=546 | id=A61 | pages=14 | date=October 2012

| doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D

| arxiv=1208.3048 | s2cid=59451347 | postscript=. }}

{{citation | postscript=.