 A light curve for HD 49798, plotted from TESS data | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Puppis |
| Right ascension | 06 48 04.69996 |
| Declination | −44° 18′ 58.4377″ |
| Apparent magnitude (V) | 8.287 |
| Characteristics | |
| Spectral type | sdO6p |
| U−B color index | −1.259 |
| B−V color index | −0.270 |
| Variable type | HMXB |
| Astrometry | |
| Radial velocity (Rv) | 12.10 km/s |
| Proper motion (μ) | RA: −4.73 mas/yr Dec.: 5.39 mas/yr |
| Parallax (π) | 1.20 ± 0.50 mas |
| Distance | 521 ± 14 pc |
| Orbit | |
| 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 | |
| Mass | 1.41 ± 0.02 M☉ |
| Radius | 1.08 ± 0.06 R☉ |
| Luminosity | 3,943 L☉ |
| Surface gravity (log g) | 4.25 cgs |
| Temperature | 47,500 K |
| WD | |
| Mass | 1.220 ± 0.008 M☉ |
| Radius | 1,604+207 −212 km |
| Temperature | 225,000 K |
| Rotation | 13.184246634(7) s |
| Other designations | |
| HD 49798, CD-44°2920, SAO 218207, HIP 32602, AAVSO 0645-44 | |
| Database references | |
| SIMBAD | data |
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.
HD 49798 was discovered in 1964 to be a rare hydrogen-deficient O class subdwarf, and was the brightest known at the time. This was identified as a binary star, but the companion could not be detected visually or spectroscopically.
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; this rotation is speeding up by 72.0±0.6 ns per year. This is detected from the 13-second X-ray pulse, which results from the stellar wind accreting onto the compact object. 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. This system is considered a likely candidate to explode as a type Ia supernova within a few thousand years.
References
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- Mereghetti, S.; La Palombara, N.; Tiengo, A.; Sartore, N.; Esposito, P.; Israel, G. L.; Stella, L. (2013). "X-ray emission from the luminous O-type subdwarf HD 49798 and its compact companion". Astronomy & Astrophysics. 553: A46. arXiv:1304.1653. Bibcode:2013A&A...553A..46M. doi:10.1051/0004-6361/201321271. S2CID 56402049.
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- ^ Rigoselli, Michela; De Grandis, Davide; Mereghetti, Sandro; Malacaria, Christian (30 May 2023). "Timing the X-ray pulsating companion of the hot subdwarf HD 49798 with NICER". Monthly Notices of the Royal Astronomical Society. 523 (2): 3043–3048. arXiv:2305.15845. doi:10.1093/mnras/stad1611.
- Mereghetti, S.; Tiengo, A.; Esposito, P.; La Palombara, N.; Israel, G. L.; Stella, L. (2009). "An Ultramassive, Fast-Spinning White Dwarf in a Peculiar Binary System". Science. 325 (5945): 1222–1223. arXiv:1003.0997. Bibcode:2009Sci...325.1222M. doi:10.1126/science.1176252. PMID 19729650. S2CID 206521141.
- ^ Kudritzki, R. P.; Simon, K. P. (1978). "Non-LTE analysis of subluminous O-star. The hydrogen-deficient subdwarf O-binary HD 49798". Astronomy and Astrophysics. 70: 653. Bibcode:1978A&A....70..653K.
- ^ Mereghetti, S.; Pintore, F.; Rauch, T.; La Palombara, N.; Esposito, P.; Geier, S.; Pelisoli, I.; Rigoselli, M.; Schaffenroth, V.; Tiengo, A. (2021). "New X-ray observations of the hot subdwarf binary HD 49798/RX J0648.0–4418". Monthly Notices of the Royal Astronomical Society. 504: 920–925. arXiv:2104.03867. doi:10.1093/mnras/stab1004.
- ^ Chen, Wen-Cong (2022). "X-ray pulsar HD 49798: A contracting white dwarf with a debris disk?". Astronomy & Astrophysics. 662: A79. arXiv:2205.09982. Bibcode:2022A&A...662A..79C. doi:10.1051/0004-6361/202243536. S2CID 248965211.
- Jaschek, Mercedes; Jaschek, Carlos (1963). "HD 49798, a New O-Type Subdwarf". Publications of the Astronomical Society of the Pacific. 75 (445): 365. Bibcode:1963PASP...75..365J. doi:10.1086/127968.
- Thackeray, A. D. (1970). "The spectroscopic orbit of the O-type subdwarf HD 49798". Monthly Notices of the Royal Astronomical Society. 150 (2): 215–225. Bibcode:1970MNRAS.150..215T. doi:10.1093/mnras/150.2.215.
- Bisscheroux, B. C.; Pols, O. R.; Kahabka, P.; Belloni, T.; Van Den Heuvel, E. P. J. (1997). "The nature of the bright subdwarf HD 49798 and its X-ray pulsating companion". Astronomy and Astrophysics. 317: 815. Bibcode:1997A&A...317..815B.
- Wang, Bo; Han, Zhanwen (2012). "Progenitors of type Ia supernovae". New Astronomy Reviews. 56 (4): 122. arXiv:1204.1155. Bibcode:2012NewAR..56..122W. doi:10.1016/j.newar.2012.04.001. S2CID 118740933.
- Liu, Dong-Dong; Zhou, Wei-Hong; Wu, Cheng-Yuan; Wang, Bo (2015). "Is the X-ray pulsating companion of HD 49798 a possible type Ia supernova progenitor?". Research in Astronomy and Astrophysics. 15 (11): 1813. arXiv:1504.01461. Bibcode:2015RAA....15.1813L. doi:10.1088/1674-4527/15/11/004. S2CID 118683249.
