Alpha Hydri
Template:Location mark Location of α Hydri (circled) | |
| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydrus |
| Right ascension | Template:RA[1] |
| Declination | Template:DEC[1] |
| Apparent magnitude (V) | +2.90[2] |
| Characteristics | |
| Spectral type | F0 IV[3] |
| U−B Template:Engvar | +0.189[4] |
| B−V Template:Engvar | +0.290[4] |
| Astrometry | |
| Radial velocity (Rv) | +7[5] km/s |
| Proper motion (μ) | RA: +263.66 mas/yr[1] Dec.: +26.77 mas/yr[1] |
| Parallax (π) | 45.43±0.44 mas[1] |
| Distance | Template:Rnd ± Template:Rnd ly (Template:Rnd ± Template:Rnd pc) |
| Absolute magnitude (MV) | +1.153[6] |
| Details[7] | |
| Mass | Template:Val Template:Solar mass |
| Radius | Template:Val Template:Solar radius |
| Luminosity | Template:Val[3] Template:Solar luminosity |
| Surface gravity (log g) | Template:Val cgs |
| Temperature | Template:Val K |
| Metallicity [Fe/H] | Template:Val dex |
| Rotational velocity (v sin i) | 118 km/s |
| Age | 810[6] Myr |
| Metallicity [Fe/H] | {{{metal_fe2}}} dex |
| Other designations | |
| Template:Odlist[2] | |
| Database references | |
| SIMBAD | data |
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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 Template:Convert from Earth. This subgiant star is 3.3 times larger and 2.1 as massive as the Sun,[7] 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[3] from its outer atmosphere at an effective temperature of 7,059 K.[7] 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]
Naming
In Chinese caused by adaptation of the European southern hemisphere constellations into the Chinese system, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Snake's Head, refers to an asterism consisting of α Hydri and β Reticuli. Consequently, α Hydri itself is known as Script error: No such module "Lang". (Script error: No such module "Lang"., Template:Langx.)[12]
References
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- ↑ Template:In lang AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 27 日 Template:Webarchive