HD 49798
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]
Distance650[3] pc
Orbit[3]
Period (P)1.55 days
Eccentricity (e)0.0
Inclination (i)82°
Details
sdO5.5[5]
Mass1.50[3] M☉
Radius1.45[6] R☉
Luminosity3,943[6] L☉
Surface gravity (log g)4.25[6] cgs
Temperature47,500[6] K
WD
Mass1.28[3] M☉
Radius1,600[7] km
Temperature225,000[7] K
Other designations
HD 49798, CD-44°2920, SAO 218207, HIP 32602, AAVSO 0645-44
Database references
SIMBADdata

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]

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]

References

  1. 1 2 3 4 5 Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
  2. 1 2 3 Landolt, Arlo U.; Uomoto, Alan K. (2007). "Optical Multicolor Photometry of Spectrophotometric Standard Stars". The Astronomical Journal. 133 (3): 768–790. arXiv:0704.3030. Bibcode:2007AJ....133..768L. doi:10.1086/510485. S2CID 119672730.
  3. 1 2 3 4 5 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.
  4. ↑ Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
  5. ↑ 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.
  6. 1 2 3 4 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.
  7. 1 2 New X-ray observations of the hot subdwarf binary HD 49798/RX J0648.0–4418, 2021, arXiv:3104.03867
  8. 1 2 3 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.
  9. ↑ 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.
  10. ↑ 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.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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.
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