X-RAY AND OPTICAL OBSERVATIONS OF THE UNIQUE BINARY SYSTEM HD 49798/RX J0648.0-4418

Journal Article · Sat Aug 20 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/737/2/51· OSTI ID:21579974

Mereghetti, S; La Palombara, N; Tiengo, A; Pizzolato, F ^[1]; Esposito, P ^[2]; Woudt, P A ^[3]; Israel, G L; Stella, L ^[4]

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1. INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via E. Bassini 15, I-20133 Milano (Italy)
2. INAF-Osservatorio Astronomico di Cagliari, localita Poggio dei Pini, strada 54, I-09012 Capoterra (Italy)
3. Astronomy Department, and Astrophysics, Cosmology and Gravity Centre, University of Cape Town, Private Bag X3, Rondebosch 7701 (South Africa)
4. INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio Catone (Italy)

We report the results of XMM-Newton observations of HD 49798/RX J0648.0-4418, the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf. The white dwarf rotates very rapidly (P = 13.2 s) and has a dynamically measured mass of 1.28 {+-} 0.05 M{sub sun}. Its X-ray emission consists of a strongly pulsed, soft component, well fit by a blackbody with kT{sub BB} {approx} 40 eV, accounting for most of the luminosity, and a fainter hard power-law component (photon index {approx}1.6). A luminosity of {approx}10{sup 32} erg s{sup -1} is produced by accretion onto the white dwarf of the helium-rich matter from the wind of the companion, which is one of the few hot sub-dwarfs showing evidence of mass loss. A search for optical pulsations at the South African Astronomical Observatory 1.9 m telescope gave negative results. X-rays were also detected during the white dwarf eclipse. This emission, with luminosity 2 x 10{sup 30} erg s{sup -1}, can be attributed to HD 49798 and represents the first detection of a hot sub-dwarf star in the X-ray band. HD 49798/RX J0648.0-4418 is a post-common-envelope binary which most likely originated from a pair of stars with masses {approx}8-10 M{sub sun}. After the current He-burning phase, HD 49798 will expand and reach the Roche lobe, causing a higher accretion rate onto the white dwarf which can reach the Chandrasekhar limit. Considering the fast spin of the white dwarf, this could lead to the formation of a millisecond pulsar. Alternatively, this system could be a Type Ia supernova progenitor with the appealing characteristic of a short time delay, being the descendent of relatively massive stars.

• OSTI ID: 21579974
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 737; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ANGULAR MOMENTUM
COSMIC RADIO SOURCES
DWARF STARS
ELECTROMAGNETIC RADIATION
EMISSION
IONIZING RADIATIONS
LUMINOSITY
OPTICAL PROPERTIES
PARTICLE PROPERTIES
PHYSICAL PROPERTIES
PULSARS
RADIATIONS
SPIN
STARS
WHITE DWARF STARS
X RADIATION