HD 83953

This article is about I (upper case "i") Hydrae and is not to be confused with l (lower case "L") Hydrae or ι (iota) Hydrae.

HD 83953 (I Hydrae) is a single,^[9] blue-white hued star in the equatorial constellation of Hydra. It is visible to the naked eye, having an apparent visual magnitude of 4.76.^[1] Based upon an annual parallax shift of 6.6 mas,^[2] the distance to this star is estimated as 500 light years. It is moving further from Earth with a heliocentric radial velocity of +16 km/s.^[4]

HD 83953

Observation data Epoch J2000      Equinox J2000
Constellation	Hydra[1]
Right ascension	09h 41m 17.00785s[2]
Declination	−23° 35′ 29.4325″[2]
Apparent magnitude (V)	4.76[1]
Characteristics
Spectral type	B5 V[3]
B−V color index	−0.117±0.015[1]
Astrometry
Radial velocity (Rv)	+16.05±1.5[4] km/s
Proper motion (μ)	RA: −29.969[2] mas/yr Dec.: +1.914[2] mas/yr
Parallax (π)	6.5733±0.2851 mas[2]
Distance	500 ± 20 ly (152 ± 7 pc)
Absolute magnitude (MV)	−1.19[1]
Details
Mass	4.57±0.08[5] M☉
Radius	4.00±0.08[6] R☉
Luminosity	708+60 −55[5] L☉
Surface gravity (log g)	2.54±0.03[6] cgs
Temperature	15,000±150[6] K
Rotational velocity (v sin i)	315[5][7] km/s
Other designations
I Hya, BD−22°2684, HD 83953, HIP 47522, HR 3858, SAO 177840[8]
Database references
SIMBAD	data

This is a B-type main-sequence star with a stellar classification of B5 V.^[3] It has been known to be a Be star since 1926, when an Hβ emission line was discovered in the stellar spectrum by Mount Wilson Observatory.^[10] This energy is coming from a circumstellar envelope of heated gas that has been expelled from the central star and formed a thin orbiting disk.^[11] HD 83953 is spinning rapidly with a projected rotational velocity of 315 km/s, giving the star an oblate shape with an equatorial bulge that is 18% larger than the polar radius.^[7]

HD 83953 has 4.6^[5] times the mass of the Sun and 4.0^[6] times the Sun's radius. It is radiating 708^[5] times the Sun's luminosity from its photosphere at an effective temperature of 15,000 K.^[6]