9 Hydrae

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

{{Starbox begin}}

{{Starbox observe

| epoch = J2000

| constell = Hydra

| ra = {{RA|08|41|43.33591}}{{cite DR2|5710178952977568000}}

| dec = {{DEC|-15|56|36.1727}}

| appmag_v = 4.866{{cite journal|title=The Tycho-2 catalogue of the 2.5 million brightest stars|author=Høg, E.|display-authors=etal|date=2000|journal=Astronomy and Astrophysics|volume=355|pages=L27–L30|bibcode=2000A&A...355L..27H}}

}}

{{Starbox character

| type = red clump

| class = {{nowrap|K0 III CNII}}{{cite journal|bibcode=1988mcts.book.....H|title=Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Declinations -26°.0 to -12°.0.|journal=Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars|volume=4|author1=Houk, N.|author2=Smith-Moore, M.|year=1988}}

| b-v = +1.07{{cite journal|title=UBVRIJKL Photometry of the Bright Stars|author1=Johnson, H. L.|journal=Communications of the Lunar and Planetary Laboratory|volume=4|pages=99|date=1966|bibcode=1966CoLPL...4...99J}}

| u-b = +0.92

}}

{{Starbox astrometry

| radial_v = {{Val|−1.98|0.12}}

| prop_mo_ra = 3.676

| prop_mo_dec = -97.743

| parallax = 15.9089

| p_error = 0.1297

| parallax_footnote =

| absmag_v = +0.81{{citation | title=XHIP: An extended hipparcos compilation | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | journal=Astronomy Letters | postscript=. | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | arxiv=1108.4971 | doi=10.1134/S1063773712050015 | s2cid=119257644 }}

}}

{{Starbox detail

| source = {{cite journal | bibcode=2008AJ....135..209M | doi=10.1088/0004-6256/135/1/209 | title=Rotational and Radial Velocities for a Sample of 761 Hipparcos Giants and the Role of Binarity | journal=The Astronomical Journal | volume=135 | pages=209–231 | year=2008 | last1=Massarotti | first1=Alessandro | last2=Latham | first2=David W. | last3=Stefanik | first3=Robert P. | last4=Fogel | first4=Jeffrey | issue=1 | doi-access=free }}

| mass = {{Val|1.72|0.46}}{{cite journal|title=Fundamental parameters of nearby stars from the comparison with evolutionary calculations: masses, radii and effective temperatures|author1=Allende Prieto, C.|author2=Lambert, D. L.|journal=Astronomy and Astrophysics|volume=352|pages=555–562|date=1999|bibcode=1999A&A...352..555A|arxiv=astro-ph/9911002}}

| radius = {{Val|11.10|0.15|0.69}}

| temperature = {{Val|4688|5|fmt=commas}}

| luminosity = {{Val|54.445|0.536|0.457}}

| gravity = 2.8

| metal_fe = −0.01

| rotational_velocity = 1.7

| age_gyr =

}}

{{Starbox catalog

|names={{odlist | F=9 Hya | BD=-15°2554 | FK5=2684 | HD=74137 | HIP=42662 | HR=3441 | SAO=154552 }}{{cite simbad | title=9 Hya | access-date=April 26, 2019 }}

}}

{{Starbox reference

|Simbad=9+Hya

}}

{{Starbox end}}

9 Hydrae 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

| doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | postscript=.

| bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 }} star in the equatorial constellation of Hydra, located 205 light years away from the Sun. It is visible to the naked eye as a faint, yellow-orange hued star with an apparent visual magnitude of 4.87. This body is moving closer to the Sun with a heliocentric radial velocity of −2 km/s.

This is an aging giant star with a stellar classification of {{nowrap|K0 III CNII}}, where the suffix notation indicates an overabundance of cyanogen in the spectrum. It is a red clump giant,{{citation

| last1=Alves | first1=David R.

| title=K-Band Calibration of the Red Clump Luminosity

| journal=The Astrophysical Journal

| volume=539 | issue=2 | pages=732–741 | date=August 2000

| doi=10.1086/309278 | bibcode=2000ApJ...539..732A

| arxiv=astro-ph/0003329 | s2cid=16673121

| postscript=. }} which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. The star has 1.7 times the mass of the Sun but, as a consequence of evolving away from the main sequence, its envelope has swollen to 11 times the Sun's radius. It is radiating 54 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,688 K.