HD 77361
Star in the constellation Pyxis
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HD 77361 is an orange-hued star in the southern constellation of Pyxis. With an apparent magnitude of 6.187, it can be faintly seen by the naked eye from Earth. As such, it is listed in the Bright Star Catalogue as HR 3597. It is located at a distance of 434 light-years (133 parsecs) according to Gaia DR3 parallax measurements. The star is notable for its unusually high lithium content.
 | |
| Observation data Epoch J2000.0[1] Equinox J2000.0[1] | |
|---|---|
| Constellation | Pyxis |
| Right ascension | 09h 01m 11.41956s[1] |
| Declination | −26° 39′ 49.3773″[1] |
| Apparent magnitude (V) | 6.187[2] |
| Characteristics | |
| Evolutionary stage | RGB[3] |
| Spectral type | K1IIICNII[4] |
| U−B color index | 1.18±0.05[5] |
| B−V color index | 1.165[2] |
| J−H color index | 0.690[6] |
| J−K color index | 0.749[6] |
| Astrometry | |
| Radial velocity (Rv) | −23.17±0.12[7] km/s |
| Proper motion (μ) | RA: 25.441[1] mas/yr Dec.: −53.283[1] mas/yr |
| Parallax (π) | 7.5091±0.0242 mas[1] |
| Distance | 434 ± 1 ly (133.2 ± 0.4 pc) |
| Details[8] | |
| Mass | 1.78 M☉ |
| Luminosity | 74.1+3.5 −3.3 L☉ |
| Surface gravity (log g) | 2.35[9] cgs |
| Temperature | 4,600±90 K |
| Metallicity [Fe/H] | −0.02[9] dex |
| Other designations | |
| CD−26°6647, CPD−26°3737, GC 12478, HD 77361, HIP 44290, HR 3597, SAO 176833, PPM 255522, TIC 37569580, TYC 6593-2444-1, GSC 06593-02444, IRAS 08590-2627, 2MASS J09011142-2639493, Gaia DR2 5649246148871668224[10] | |
| Database references | |
| SIMBAD | data |
Physical properties
This is an aging red-giant branch star (RGB) at the RGB bump,[3] with the spectral type K1III. This means that it has evolved past the main-sequence stage after exhausting its core hydrogen, causing it to bloat into a red giant. It has now reached a point where a discontinuity in hydrogen abundance produced by deep stellar convection results in a short-term decline in energy production, hampering its ascent of the RGB.[11] The "CNII" in its spectral type indicates a strong cyanogen signature in the star's outer atmosphere, as strong as that of a normal K1 bright giant (luminosity class II).[12]
According to a 2020 study,[8] the star has a mass of 1.78 M☉, an effective temperature of roughly 4,600 K (4,330 °C; 7,820 °F), and radiates 74.1 times the luminosity of the Sun from its photosphere. Some earlier publications, however, present smaller values for the mass (1.3±0.2 M☉[5] or 1.5±0.2 M☉[3]), luminosity (45.7 L☉[9]), and temperature (4,370±100 K[5]). The star is slightly poorer in iron than the Sun, with a metallicity of [Fe/H]=−0.02 dex (10−0.02 ≈ 95% solar abundance).
Anomalous abundances
The star is considered a super Li-rich star, a star so enhanced in lithium that its existence cannot be explained by the standard stellar evolution theory.[5] It is thought that the lithium is actively being generated within the star, as unstable beryllium-7 atoms produced in the inner layers well up to the upper atmosphere via an unknown mechanism and then decay into stable lithium-7.[13]
The star also has a very small 12C/13C ratio of 4.3±0.5,[3] compared to 89.4±0.2 of the Sun. It was the first population I super Li-rich low-luminosity low-mass K giant discovered to have such a small 12C/13C ratio.[13]