HD 137509
Star in the constellation Apus
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HD 137509 is a star in the southern constellation of Apus, positioned less than a degree from the northern constellation boundary with Triangulum Australe.[13] It has the variable star designation of NN Apodis, or NN Aps for short, and ranges in brightness from an apparent visual magnitude of 6.86 down to 6.93 with a period of 4.4916 days.[7] The star is located at a distance of approximately 647 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +0.50 km/s.[8]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Apus |
| Right ascension | 15h 31m 27.11494s[2] |
| Declination | −71° 03′ 43.6643″[2] |
| Apparent magnitude (V) | 6.86 - 6.92[3] |
| Characteristics | |
| Spectral type | B9p (SiCrFe)[4] B8 He wk SiCrFe[5] |
| B−V color index | −0.125±0.004[6] |
| Variable type | α2 CVn[7] |
| Astrometry | |
| Radial velocity (Rv) | +0.50[8] km/s |
| Proper motion (μ) | RA: −16.276[2] mas/yr Dec.: −15.503[2] mas/yr |
| Parallax (π) | 5.0410±0.0503 mas[2] |
| Distance | 647 ± 6 ly (198 ± 2 pc) |
| Absolute magnitude (MV) | 0.45[6] |
| Details | |
| Mass | 3.43±0.17[9] M☉ |
| Radius | 2.81[10] R☉ |
| Luminosity | 123[6] L☉ |
| Surface gravity (log g) | 4.3[5] cgs |
| Temperature | 13,100±500[5] K |
| Rotation | 4.492 d[9] |
| Rotational velocity (v sin i) | 20±2[5] km/s |
| Age | 124[11] Myr |
| Other designations | |
| NN Aps, CD−70°1302, GC 20810, HD 137509, HIP 76011, SAO 257290[12] | |
| Database references | |
| SIMBAD | data |
In 1973, W. P. Bidelman and D. J. MacConnell found this to be a peculiar A star of the silicon type.[14] During a reclassification of the spectra of southern stars in 1975, A. P. Cowley and N. Houk noted the strength of hydrogen lines and weakness of helium are more typical of a class near B9. It shows a luminosity above the main sequence, which is common for a peculiar A star. The stellar atmosphere appears deficient in helium, but shows a rich variety of metallic lines. However, there are no lines of manganese or mercury, so it's not a Hg–Mn Ap star.[15] HD 137509 is now classified as B9p (SiCrFe)[4] or B8 He wk SiCrFe,[5] matching a late-type, helium-weak Bp star with overabundances of silicon, chromium, and iron.
This star was found to be photometrically variable by L. O. Lodén and A. Sundman in 1989, and a variable spectrum was noted by H. Pedersen in 1979.[14] It has one of the strongest magnetic fields recorded for a chemically peculiar star, measured at around 29 kG,[4] and shows a strong quadrupolar component.[16] Both variances of the star allow its rotation period to be precisely measured.[14] It is classified as a Alpha2 Canum Venaticorum variable.[7] The star is about 124[11] million years old with 3.4[9] times the mass of the Sun and 2.8[10] times the Sun's radius. On average it is radiating ~123[6] times the luminosity of the Sun from its photosphere at an effective temperature of 13,100 K.[5]