3 Equulei

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title: "3 Equulei" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["equuleus", "k-type-giants", "bayer-objects", "flamsteed-objects", "durchmusterung-objects", "henry-draper-catalogue-objects", "bright-star-catalogue-objects", "hipparcos-objects"] description: "K-type giant star in the constellation Equuleus" topic_path: "general/equuleus" source: "https://en.wikipedia.org/wiki/3_Equulei" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary K-type giant star in the constellation Equuleus ::

| name = 3 Equulei | image= |image=Equuleus constellation map.svg|alt=|float=center|width=240 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=3 Equulei |x=594|y=690 |caption=Location of 3 Equulei (circled) | epoch = J2000 | ra = | dec = | appmag_v = 5.593 | constell = Equuleus | type = red giant branch | class = K5 III | b-v = +1.651 | u-b = +1.934 | variable = | radial_v = | prop_mo_ra = +13.115 | prop_mo_dec = +0.752 | parallax = 2.6635 | p_error = 0.0940 | parallax_footnote = | absmag_v = −1.02 | mass = 7.2 | radius = 116 | luminosity = 2,581 | temperature = 4,029 | metal_fe = | gravity = 1.06 | rotational_velocity = 4.6 | age_gyr = | names = ζ Equ, 3 Equ, BD+04°4606, HD 200644, HIP 104031, HR 8066, SAO 126518 | Simbad = 3+Equ 3 Equulei is a single star located in the small northern constellation of Equuleus. It is faintly visible to the naked eye at an apparent visual magnitude of 5.6. Based upon an annual parallax shift of , 3 Equulei is roughly 1,220 ly distant from Earth, give or take a 40 light-year margin of error. At that distance, the apparent brightness of the star is diminished by 0.15 in visual magnitude because of extinction from interstellar gas and dust.

3 Equulei has been referred to in some sources as ζ (Zeta) Equulei, although it was not given that designation by Bayer.

Properties

3 Equulei is an evolved giant star with a stellar classification of K5 III. The measured angular diameter of this star, after correction for limb darkening, is . At the estimated distance of 1,220 light-years, this yields a physical size of about 100 times the radius of the Sun. It is radiating an estimated 2,581 times the luminosity of the Sun from this expanded outer envelope at an effective temperature of . At this temperature, it shines with the orange-hued glow of a K-type star.

References

. The radius (R*) is given by: :\begin{align} 2\cdot R_* & = \frac{(380\cdot 2.44\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \ & \approx 199\cdot R_{\bigodot} \end{align}

References

1. {{cite Gaia DR3. 1733281541754737024
2. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal.
3. (1995). "VizieR Online Data Catalog: Bright Star Catalogue, 5th Revised Ed. (Hoffleit+, 1991)". VizieR On-line Data Catalog: V/50. Originally Published in: 1964BS....C......0H.
4. (January 2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics.
5. (1984). "Standardization of Broadband Photometry of Equatorial Standards". South African Astronomical Observatory Circulars.
6. (September 2008). "A catalogue of multiplicity among bright stellar systems". [[Monthly Notices of the Royal Astronomical Society]].
7. "* 3 Equ".
8. (February 2005). "CHARM2: An updated Catalog of High Angular Resolution Measurements". Astronomy and Astrophysics.
9. (August 2009). "Comparing the Ca ii H and K Emission Lines in Red Giant Stars". Publications of the Astronomical Society of the Pacific.
10. (December 21, 2004). "The Colour of Stars". Commonwealth Scientific and Industrial Research Organisation.
11. (September 2000). "Photometric Variability in a Sample of 187 G and K Giants". The Astrophysical Journal Supplement Series.

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