Eclipse studies of the dwarf nova HT Cassiopeiae. I - Observations and system parameters

Horne, K.; Wood, Janet H.; Stiening, R.

doi:10.1086/170426

Cited by 63 publications

(88 citation statements)

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“…For clarity, we also give the results of the piecewise fit to the data in Table 1. The duration of the eclipse in our X-ray light curve is consistent with the white dwarf eclipse observed in the ROSAT and ASCA data (Wood et al 1995;Mukai et al 1997). As in the ASCA data, the eclipse duration that we measure seems to be shorter (but only at the low significance level of ∼1.5σ) with respect to the optical observation (Δφ opt = 0.0493 ± 0.0007 cycles, Horne et al 1991). In addition, for the first time, we have an accurate measure of the ingress and egress durations, the length of which are consistent with the optical counterpart (Δφ 1,2,opt = 0.0086 ± 0.0014 cycles, and Δφ 3,4,opt = 0.0086 ± 0.0012 cycles, Horne et al 1991).…”

Section: Timing Analysissupporting

confidence: 89%

“…(1) one can easily derive the size 5 of the X-ray emitting region of r X = (0.0117 ± 0.0004) R . When this result is compared to the size of the white dwarf (r 0.0118 R ) of Horne et al (1991), it clearly indicates that the size of the X-ray emitting region is comparable to that of the white dwarf, which allows us to tightly constrain the origin of X-rays in HT Cas.…”

Section: Resultsmentioning

confidence: 81%

“…As for many other CVs, HT Cas is a short period binary system (P orb 1.77 h, Borges et al 2008), close to the lower edge of the period gap at ∼2.5 h. The system is characterized by a visual magnitude of ∼16.4 during its quiescent state, relatively rare outbursts (Horne et al 1991), and white dwarf eclipses well observed in several optical campaigns. A detailed analysis of the light curves can be found in Patterson (1981) and Wood et al (1985).…”

Section: Introductionmentioning

confidence: 70%

“…Taking into account the white dwarf spin, the boundary layer luminosity implies that L BL 0.125 L acc for Ω WD 0.5 Ω K (R WD ) (Popham & Narayan 1995). Since the respective best-fit model white dwarf mass and radius of 0.61 M and 0.0118 R are derived from the photometric measurements (Horne et al 1991), one can use the standard accretion scenario (and the bolometric luminosity quoted above) to estimate the mass accretion rate, which, for HT Cas, turns out to be 1.1 × 10 15 g s −1 or, equivalently, 1.7 × 10 −11 M yr −1 assuming Ω WD 0.5 Ω K (R WD ). Of course, since we have neglected the luminosity of the black-body component, the previous estimate for the mass accretion rate must be considered to be a lower limit.…”

Section: Resultsmentioning

confidence: 99%

“…Here, we have increased the radius r of the white dwarf for clarity. Consequently, the two stars are separated by a distance of a cos i, where a 0.658 R and i 81 • are the orbital separation and the inclination angle, respectively (see Horne et al 1991, for more details).…”

Section: Resultsmentioning

confidence: 99%

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The X-ray eclipse of the dwarf nova HT Cassiopeiae observed by theXMM-Newton satellite: spectral and timing analysis

Nucita¹,

Maiolo

Carpano

et al. 2009

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Context.A cataclysmic variable is a binary system consisting of a white dwarf that accretes material from a secondary object via the Roche-lobe mechanism. In the case of long enough observation, a detailed temporal analysis can be performed, allowing the physical properties of the binary system to be determined. Aims. We present an XMM-Newton observation of the dwarf nova HT Cas acquired to resolve the binary system eclipses and constrain the origin of the X-rays observed. We also compare our results with previous ROSAT and ASCA data. Methods. After the spectral analysis of the three EPIC camera signals, the observed X-ray light curve was studied with well known techniques and the eclipse contact points obtained. Results. The X-ray spectrum can be described by thermal bremsstrahlung of temperature kT 1 = 6.89 ± 0.23 keV plus a black-body component (upper limit) with temperature kT 2 = 30 +8 −6 eV. Neglecting the black-body, the bolometric absorption corrected flux is F Bol = (6.5 ± 0.1) × 10 −12 erg s −1 cm −2 , which, for a distance of HT Cas of 131 pc, corresponds to a bolometric luminosity of (1.33 ± 0.02) × 10 31 erg s −1 . In a standard accretion scenario where L BL 0.125L acc assuming Ω WD 0.5Ω K (R WD ), the amount of matter accreting onto the central white dwarf is found to be 1.7 × 10 −11 M yr −1 . The study of the eclipse in the EPIC light curve permits us to constrain the size and location of the X-ray emitting region, which turns out to be close to the white dwarf radius. We measure an X-ray eclipse somewhat smaller (but only at a level of 1.5σ) than the corresponding optical one. If this is the case, we have possibly identified the signature of either high latitude emission or a layer of X-ray emitting material partially obscured by an accretion disk.

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