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HD 49798 is a binary star in the constellation Puppis about 650 parsecs (circa 2119 light-years) from Earth. It has an apparent magnitude of 8.3, making it one of the brightest known O class subdwarf stars.[8]
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Puppis |
| Right ascension | 06h 48m 04.69996s[1] |
| Declination | −44° 18′ 58.4377″[1] |
| Apparent magnitude (V) | 8.287[2] |
| Characteristics | |
| Spectral type | sdO6p |
| U−B color index | −1.259[2] |
| B−V color index | −0.270[2] |
| Variable type | HMXB[3] |
| Astrometry | |
| Radial velocity (Rv) | 12.10[4] km/s |
| Proper motion (μ) | RA: −4.73[1] mas/yr Dec.: 5.39[1] mas/yr |
| Parallax (π) | 1.20 ± 0.50 mas[1] |
| Distance | 650[3] pc |
| Orbit[3] | |
| Period (P) | 1.55 days |
| Eccentricity (e) | 0.0 |
| Inclination (i) | 82° |
| Details | |
| sdO5.5[5] | |
| Mass | 1.50[3] M☉ |
| Radius | 1.45[6] R☉ |
| Luminosity | 3,943[6] L☉ |
| Surface gravity (log g) | 4.25[6] cgs |
| Temperature | 47,500[6] K |
| WD | |
| Mass | 1.28[3] M☉ |
| Radius | 1,600[7] km |
| Temperature | 225,000[7] K |
| Other designations | |
| 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.[9] This was identified as a binary star, but the companion could not be detected visually or spectroscopically.[10]
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.[11] This is detected from the 13-second X-ray pulse, which results from the stellar wind accreting onto the compact object.[8] 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.[8] This system is considered a likely candidate to explode as a type Ia supernova within a few thousand years.[12][13]
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