HD 49798
Binary star system in the constellation Puppis
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HD 49798 is a binary star in the constellation Puppis about 521 ± 14 parsecs (1,699 ± 46 ly) from Earth. It has an apparent magnitude of 8.3, making it one of the brightest known O class subdwarf stars.[10]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Puppis |
| Right ascension | 06h 48m 04.70015s[2] |
| Declination | −44° 18′ 58.4360″[2] |
| Apparent magnitude (V) | 8.287[3] |
| Characteristics | |
| Spectral type | sdO6p |
| U−B color index | −1.259[3] |
| B−V color index | −0.270[3] |
| Variable type | HMXB[4] |
| Astrometry | |
| Radial velocity (Rv) | 12.10[5] km/s |
| Proper motion (μ) | RA: −4.162[2] mas/yr Dec.: 5.926[2] mas/yr |
| Parallax (π) | 1.9196±0.0501 mas[2] |
| Distance | 1,700±46 ly (521 ± 14 pc)[6] |
| Orbit[6] | |
| Period (P) | 1.547666(6) d |
| Semi-major axis (a) | 2,891,000 ± 15,000 kilometres (0.01933 ± 0.00010 AU) |
| Eccentricity (e) | 0.0 |
| Inclination (i) | 84.5 ± 0.7° |
| Details | |
| sdO5.5[7] | |
| Mass | 1.41 ± 0.02[6] M☉ |
| Radius | 1.08 ± 0.06[6] R☉ |
| Luminosity | 3,943[8] L☉ |
| Surface gravity (log g) | 4.25[8] cgs |
| Temperature | 47,500[8] K |
| WD | |
| Mass | 1.220 ± 0.008[6] M☉ |
| Radius | 3,580[6] km |
| Temperature | 225,000[9] K |
| Rotation | 13.184246634(7) s[6] |
| Other designations | |
| HD 49798, CD-44°2920, SAO 218207, HIP 32602, AAVSO 0645-44 | |
| Database references | |
| SIMBAD | data |
HD 49798 was discovered in 1964 to be a rare hydrogen-deficient O class subdwarf, and was the brightest known at the time.[11] This was identified as a binary star, but the companion could not be detected visually or spectroscopically.[12]
The X-ray source RX J0648.0-4418 was discovered close to HD 49798's location in the sky. Only the space telescope XMM-Newton was able to identify the source. It is a white dwarf with about 1.3 solar masses, in orbit about HD 49798 and rotating once every 13 seconds;[13] this rotation is speeding up by 72.0±0.6 ns per year.[6] This is detected from the 13-second X-ray pulse, which results from the stellar wind accreting onto the compact object.[10] It has been proposed that the white dwarf is surrounded by a debris disk. In this model, the material of the disk would be funneled onto the poles of the dwarf via the magnetic field, which would explain the observed X-ray pulses.[10] This system is considered a likely candidate to explode as a type Ia supernova within a few tens of thousands of years.[14][15]