Alpha Hydri

Alpha Hydri
Location of α Hydri (circled)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydrus
Right ascension 01h 58m 46.19467s[1]
Declination −61° 34′ 11.4948″[1]
Apparent magnitude (V) +2.90[2]
Characteristics
Spectral type F0 IV[3]
U−B color index +0.189[4]
B−V color index +0.290[4]
Astrometry
Radial velocity (Rv)+7[5] km/s
Proper motion (μ) RA: +263.66[1] mas/yr
Dec.: +26.77[1] mas/yr
Parallax (π)45.43 ± 0.44 mas[1]
Distance71.8 ± 0.7 ly
(22.0 ± 0.2 pc)
Absolute magnitude (MV)+1.153[6]
Details[3]
Mass2.0[7] M☉
Radius3.040±0.058 R☉
Luminosity21.00±0.75 L☉
Surface gravity (log g)3.67±0.20 cgs
Temperature7,087±47 K
Metallicity [Fe/H]0.07±0.10 dex
Rotational velocity (v sin i)118 km/s
Age810[6] Myr
Other designations
α Hyi, CD−62° 71, GJ 83, HIP 9236, HR 591, SAO 248474[2]
Database references
SIMBADdata

Alpha Hydri, Latinized from α Hydri, is the second brightest star in the southern circumpolar constellation of Hydrus. It is readily visible to the naked eye in locations south of 28°N with an apparent visual magnitude of +2.9. It is sometimes informally known as the Head of Hydrus.[8] This should not be confused with Alpha Hydrae (Alphard) in the constellation Hydra. Alpha Hydri is one of only three stars in the constellation Hydrus that are above the fourth visual magnitude. This star can be readily located as it lies to the south and east of the prominent star Achernar in the constellation Eridanus.[9]

Based upon parallax measurements from the Hipparcos mission, Alpha Hydri is located at a distance of about 71.8 light-years (22.0 parsecs) from Earth. This subgiant star is three[3] times larger and twice as massive as the Sun, with a stellar classification of F0 IV.[3] It is about 810 million years old[6] and is radiating 21 times the Sun's luminosity from its outer atmosphere at an effective temperature of 7,087 K.[3] Alpha Hydri emits X-rays similar to Altair.[10] The space velocity components of this star are [U, V, W] = [−14, −14, -2] km/s.[11]

  1. ^ a b c d e Cite error: The named reference aaa474_2_653 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  3. ^ a b c d e Cite error: The named reference Rains2020 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference gutierrez was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference gcsrv was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference aaa348 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference aass85_3_1015 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference allen1963 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference moore2005 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Schmitt1985 was invoked but never defined (see the help page).
  11. ^ Gliese, W. (1969). Catalogue of Nearby Stars. Karlsruhe.{{cite book}}: CS1 maint: location missing publisher (link)