| |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Mensa |
| Right ascension | 04h58m 17.93697s[2] |
| Declination | −75° 16′ 37.9879″[2] |
| Apparent magnitude (V) | 8.60 - 8.89[3] |
| Characteristics | |
| Spectral type | K1 III/IVe[4] |
| U−B color index | +0.70[5] |
| B−V color index | +1.04[5] |
| Variable type | FK Com[3] |
| Astrometry | |
| Radial velocity (Rv) | −8.5±2.5[6] km/s |
| Proper motion (μ) | RA: −4.149 mas/yr[2] Dec.: −3.077 mas/yr[2] |
| Parallax (π) | 4.5587 ± 0.0161 mas[2] |
| Distance | 715 ± 3 ly (219.4 ± 0.8 pc) |
| Absolute magnitude (MV) | +0.81[7] |
| Details | |
| Mass | 0.983[8] M☉ |
| Radius | 12.3[9] R☉ |
| Luminosity | 68.5[10] L☉ |
| Surface gravity (log g) | 1.63[11] cgs |
| Temperature | 4,691±128[12] K |
| Metallicity [Fe/H] | −0.59[11] dex |
| Rotational velocity (v sin i) | 45±2[13] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
YY Mensae, also known as HD 32918, is a variable star located in the southern circumpolar constellation Mensa. It has an apparent magnitude that fluctuates between 8.6 and 8.9,[3] which is within the visibility of binoculars. Based on parallax measurements from Gaia DR3, it is estimated to be 715 light years distant.[2] It appears to be approaching the Solar System with a heliocentric radial velocityof−8.5 km/s.[6]
This star was known to have an unusual spectrum since the 1970's, but its variability wasn't observed until the 1980's. Collier (1982) found it to be a FK Comae Berenices variable, a class of rapidly rotating giant stars.[15] After a few additional years of observations, HD 32918 was given the variable star designation YY Mensae.[16] A paper in 1987 observed a long and powerful flare coming from the star.[17] X-ray emissions from YY Mensa have been detected in its corona, which may be a result of its fast rotation.[18]
YY Mensae has a stellar classification of K1 III/IVe,[4] indicating an evolved red giant with the blended luminosity class of a giant star and a subgiant. It is chromospherically active and emission lines are also present in its spectra. It has 98% the mass of the Sun[8] but has expanded to 12.3 times its girth.[9] It radiates 68.5 times the luminosity of the Sun[10] from its photosphere at an effective temperatureof4,691 K,[12] giving it an orange hue. Typical for stars its type, YY Mensae spins rapidly, having a projected rotational velocityof45 km/s.[13] The star is metal deficient, having an iron abundance only 26% that of the Sun.[11]
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Audard, M.; Güdel, M.; Skinner, S. L.; Pallavicini, R.; Drake, S. A.; Mewe, R. (December 2002). "Chandra and XMM-Newton X-Ray Spectroscopy of the Hot Corona of YY Mensae". American Astronomical Society Meeting Abstracts. 201: 33.07. Bibcode:2002AAS...201.3307A.
Strassmeier, K.G. (August 2002). "Doppler images of starspots". Astronomische Nachrichten. 323 (3–4): 309–316. Bibcode:2002AN....323..309S. doi:10.1002/1521-3994(200208)323:3/4<309::AID-ASNA309>3.0.CO;2-U. eISSN 1521-3994. ISSN 0004-6337.
Gondoin, P. (December 1999). "Evolution of X-ray activity and rotation on G-K giants". Astronomy and Astrophysics. 352: 217–227. Bibcode:1999A&A...352..217G. ISSN 0004-6361.
Grewing, M.; Bianchi, L.; Cassatella, A. (August 1986). "HD 32918 : Ultraviolet spectrum and optical behaviour". Astronomy and Astrophysics. 164: 31–39. Bibcode:1986A&A...164...31G. ISSN 0004-6361.
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