Eta Hydrae

η Hydrae
Location of η Hydrae (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 08h 43m 13.47499s[1]
Declination +03° 23′ 55.1867″[1]
Apparent magnitude (V) 4.294[2]
Characteristics
Spectral type B3 V[3]
U−B color index −0.726[2]
B−V color index −0.187[2]
Variable type Candidate β Cep[4]
Astrometry
Proper motion (μ) RA: −19.39[1] mas/yr
Dec.: −1.08[1] mas/yr
Parallax (π)5.56 ± 0.24 mas[1]
Distance590 ± 30 ly
(180 ± 8 pc)
Absolute magnitude (MV)−1.48[5]
Details
Mass7.0±0.1[6] M☉
Radius3.9[7] R☉
Luminosity (bolometric)2,680[8] L☉
Surface gravity (log g)3.933[9] cgs
Temperature18,630±411[9] K
Rotational velocity (v sin i)101±5[9] km/s
Age31.6±3.9[6] Myr
Other designations
η Hya, 7 Hydrae, BD+03°2039, FK5 2687, HD 74280, HIP 42799, HR 3454, SAO 117050[10]
Database references
SIMBADdata

Eta Hydrae (η Hydrae) is a star in the equatorial constellation of Hydra. With an apparent visual magnitude of 4.3,[2] it is visible to the naked eye. However, it is the faintest of the five stars that form the "head" of the hydra.[11] Based upon an annual parallax shift of 5.56 mas,[1] it is located roughly 590 light years from the Sun.

A light curve for Eta Hydrae, plotted from TESS data[12]

This is a B-type main sequence star with a stellar classification of B3V.[3] It has been classified as a candidate Beta Cephei variable with a period of 2.2 days, although this designation was rejected by Stankov and Handler (2005).[4] The spectrum shows a slight underabundance of carbon, compared to the Sun.[13] The star is around 32[6] million years old and is spinning with a projected rotational velocity of 101[9] km/s. It has an estimated seven[6] times the mass of the Sun and nearly four[7] times the Sun's radius. Eta Hydrae radiates 2,680[8] times the solar luminosity from its outer atmosphere at an effective temperature of 18,630[9] K.

  1. ^ a b c d e f Cite error: The named reference vanLeeuwen2007 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference Oja1986 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference Levenhagen2006 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference Stankov2005 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference vonEiff2012 was invoked but never defined (see the help page).
  6. ^ a b c d Cite error: The named reference Tetzlaff2011 was invoked but never defined (see the help page).
  7. ^ a b Cite error: The named reference PasinettiFracassini2001 was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Hohle2010 was invoked but never defined (see the help page).
  9. ^ a b c d e Cite error: The named reference Huang2008 was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Moore2013 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference MAST was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Schnerr2008 was invoked but never defined (see the help page).