Upsilon1 Eridani

For other star systems with this Bayer designation, see Upsilon Eridani.

υ^1 Eridanian

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	04^h 33^m 30.55236^s[1]
Declination	−29° 45′ 59.3725″[1]
Apparent magnitude (V)	4.51[2]
Characteristics
Spectral type	K0 III-IV[3]
U−B color index	+0.70[2]
B−V color index	+0.98[2]
Astrometry
Radial velocity (Rv)	+20.89±0.69[4] km/s
Proper motion (μ)	RA: −114.78[1] mas/yr Dec.: −271.79[1] mas/yr
Parallax (π)	25.67 ± 0.24 mas[1]
Distance	127 ± 1 ly (39.0 ± 0.4 pc)
Absolute magnitude (MV)	1.60[4]
Details
Mass	1.54[4] M☉
Radius	7.3[5] R☉
Luminosity	24[4] L☉
Surface gravity (log g)	3.09[4] cgs
Temperature	4,941[4] K
Metallicity [Fe/H]	−0.16±0.08[4] dex
Rotational velocity (v sin i)	2.15[6] km/s
Other designations
υ^1 Eridani, υ^1 Eri, 50 Eridani, CD−30° 1883, HD 29085, HIP 21248, HR 1453, SAO 169570.[7]
Database references
SIMBAD	data

Upsilon¹ Eridani (υ¹ Eri) is a single star in the constellation Eridanus. It has an apparent visual magnitude is 4.51,^[2] which is bright enough to be faintly visible to the naked eye on a clear, dark night. The distance to this star, as determined using the parallax method,^[1] is around 127 light years.

This is an evolved red clump^[8] giant star with a stellar classification of K0III-IV.^[3] The measured angular diameter, after correction for limb darkening, is 1.74±0.02 mas.^[9] At an estimated distance of this star, this yields a physical size of about 7.3 times the radius of the Sun.^[5] It has 154%^[4] of the Sun's mass and radiates 24 times the solar luminosity from its outer atmosphere at an effective temperature of 4,941 K.^[4]

References

1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600.
2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
3. Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal, 132 (1): 161–170, arXiv:astro-ph/0603770, Bibcode:2006AJ....132..161G, doi:10.1086/504637, S2CID 119476992.
4. Luck, R. Earle; Heiter, Ulrike (June 2007), "Giants in the Local Region", The Astronomical Journal, 133 (6): 2464–2486, Bibcode:2007AJ....133.2464L, doi:10.1086/513194.
5. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

   ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(39.0\cdot 1.74\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 14.6\cdot R_{\bigodot }\end{aligned}}}$

6. Hekker, S.; Meléndez, J. (2007). "Precise radial velocities of giant stars. III. Spectroscopic stellar parameters". Astronomy and Astrophysics. 475 (3): 1003. arXiv:0709.1145. Bibcode:2007A&A...475.1003H. doi:10.1051/0004-6361:20078233. S2CID 10436552.
7. "* ups01 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-10-13.
8. Alves, David R. (August 2000), "K-Band Calibration of the Red Clump Luminosity", The Astrophysical Journal, 539 (2): 732–741, arXiv:astro-ph/0003329, Bibcode:2000ApJ...539..732A, doi:10.1086/309278, S2CID 16673121.
9. Richichi, A.; et al. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics, 431 (2): 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039.