Delta Hydrae

{{Short description|Double star system in the constellation Hydra}}

{{Starbox begin

| name = Delta Hydrae

}}

{{Starbox observe

| epoch = J2000.0

| equinox = J2000.0 (ICRS)

| constell = Hydra

| ra = {{RA|08|37|39.36627}}

| dec = {{DEC|+05|42|13.6057}}

| appmag_v = 4.146

}}

{{Starbox character

| component1 = δ Hydrae Aa

| class = A1 Vnn

| b-v = +0.008

| u-b = +0.003

| r-i =

| variable =

}}

{{Starbox astrometry

| radial_v = 4.10

| prop_mo_ra = −70.19

| prop_mo_dec = −7.90

| parallax = 20.34

| p_error = 0.63

| parallax_footnote =

| absmag_v = +0.68

}}

{{Starbox relpos

| primary = δ Hydrae A

| component = δ Hydrae B

| projsep = 147

| angdistsec = {{Val|2.6|0.1}}

| posang = {{Val|265.1|1.0}}

}}

{{Starbox orbit

| reference =

| primary =Aa

| name = Ab

| period_unitless = ~200 days

| axis_unitless = 0.9 AU

}}

{{Starbox detail

| component1 = δ Hydrae Aa

| source =

| mass = 2.43

| radius = 3.1

| luminosity = 42.7

| temperature = 8,995

| gravity =

| metal_fe =

| rotational_velocity = 285

| age_myr = 500

| component2 = δ Hydrae Ab

| mass2 = 0.58

| radius2 = 0.54

| temperature2 = 3,973

| age_myr2 = 500

}}

{{Starbox detail|no_heading=y

| component1 = δ Hydrae B

| mass = 0.44

}}

{{Starbox catalog

| names = δ Hya, 4 Hydrae, BD+06°2001, FK5 1223, HD 73262, HIP 42313, HR 3410, SAO 116965

}}

{{Starbox reference

| Simbad = del+Hya

}}

Delta Hydrae, Latinized from δ Hydrae, is a triple star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 4.146. Based upon an annual parallax shift of 20.34 mas, it is located about 160 light years distant.

Characteristics

This is a hierarchical triple system. δ Hydrae Aa and δ Hydrae Ab form a close binary system with an orbital separation of 0.9 astronomical units, taking about 200 days to complete an orbit. The outer companion, δ Hydrae B, has an angular separation of {{Val|2.6|0.1|u=arc second}} from the Aa–Ab pair, along a position angle of {{Val|265.1|1.0|u=°}}, as of 2003. At the system's distance, this separation translates in a physical projected separation of 147 AU.

The brighter component, δ Hydrae Aa, is an A-type main sequence star with a stellar classification of A1 Vnn. It is spinning rapidly with a projected rotational velocity of 285 km/s. This is giving the star an oblate shape with an equatorial bulge that is 20% larger than the polar radius. It has an estimated 2.43 times the mass of the Sun and 3.1 times the Sun's radius. The star radiates 42.7 times the solar luminosity from its photosphere at an effective temperature of 8,995 K.

Its inner companion, δ Hydrae Ab, is a red dwarf star, with 0.58 times the mass, 0.54 times the Sun's radius, and an effective temperature of 3,973 K. It may form a common envelope system when the primary evolve into a red giant.

The outer companion has a visual magnitude of 11.15. X-ray emissions have been detected from this location in space, which may be coming from a companion star.

Name and etymology

In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, this star was designated Lisan al Shudja, which was translated into Latin as Lingua Hydri, meaning the snake's tongue. This star, along with ε Hya, ζ Hya, η Hya, ρ Hya and σ Hya (Minchir), were Ulugh Beg's Min al Azʽal, "Belonging to the Uninhabited Spot".

According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Min al Azʽal or Minazal were the title for five stars :δ Hya as Minazal I, η Hya as Minazal II, ε Hya as Minazal III, ρ Hya as Minazal IV and ζ Hya as Minazal V (exclude σ Hya)

In Chinese, {{lang|zh|柳宿}} ({{lang|zh-Latn|Liǔ Sù}}), meaning Willow (asterism), refers to an asterism consisting of δ Hydrae, σ Hydrae, η Hydrae, ρ Hydrae, ε Hydrae, ζ Hydrae, ω Hydrae and θ Hydrae{{in lang|zh}} 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}. Consequently, δ Hydrae itself is known as {{lang|zh|柳宿一}} ({{lang|zh-Latn|Liǔ Sù yī}}, {{langx|en|the First Star of Willow}}.){{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0605/ap060528.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 28 日] {{Webarchive|url=https://web.archive.org/web/20110522112415/http://aeea.nmns.edu.tw/2006/0605/ap060528.html |date=2011-05-22 }}

The people of Groote Eylandt called Unwala, "The Crab", for the star cluster including this star, ε Hya, ζ Hya, η Hya, ρ Hya and σ Hya (Minchir).

References

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{{cite simbad

| title=* del Hya

| access-date=2017-01-03 }}

}}