| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) |
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|---|---|
| Constellation | Serpens |
| Right ascension | 15h 36m 28.1873s[1] |
| Declination | +15° 06′ 05.128″[1] |
| Apparent magnitude (V) | 5.89 to 7.07[2] |
| Characteristics | |
| Spectral type | M5II-III[1] |
| B−V color index | 1.2[1] |
| Variable type | SRB[2] |
| Astrometry | |
| Radial velocity (Rv) | −26 ± 5[1] km/s |
| Proper motion (μ) | RA: −3.41[1] mas/yr Dec.: 9.55[1] mas/yr |
| Parallax (π) | 6.27 ± 1.00[1] mas |
| Distance | approx. 520 ly (approx. 160 pc) |
| Absolute magnitude (MV) | 0.5[3] |
| Other designations | |
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τ4 Ser, Tau4 Serpentis, Tau4 Ser, 17 Serpentis, 17 Ser, τ4 Serpentis, τ4 Ser, Tau4 Serpentis, Tau4 Ser, BD+15 2890, GC 20983, HD 139216, HIP 76423, PPM 131543, SAO 101641.[1]
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| Database references | |
| SIMBAD | data |
Tau4 Serpentis (Tau4 Ser, τ4 Serpentis, τ4 Ser) is a M-type bright giant star in the constellation of Serpens, approximately 520 light-years from the Earth.[1] It is classified as a semiregular late-type variable star, and its magnitude varies between +5.89 and +7.07 with a period of approximately 100 days.[2] τ4 is unique among the stars with the Bayer designation τ Serpentis as being the only one with no HR catalog number.
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