* Astronomy

Blobrana · L

RE: HT Cassiopeiae

Blobrana · L

The dwarf nova HT Cassiopeiae is in outburst.

Date: 27th August, 2011
Magnitude range: 12.6 - 19.32 V
Period: ? days
Satellite period: 0.0736472031 days
Type: UGSU ?

Position(2000): RA=01 10 12.96 | Dec=+60° 04' 36.3"

Blobrana · L

The eclipsing UGSU dwarf nova HT Cassiopeiae is in outburst.
The magnitude 12.9 outburst was discovered by T. Parson (USA)

Position (2000): RA 01 10 12.96 , Dec +60 04 36.3

Blobrana · L

Title: The X-ray eclipse of the dwarf nova HT CAS observed by the XMM-Newton satellite: spectral and timing analysis
Authors: A.A.Nucita, B.M.T.Maiolo, S.Carpano, G.Belanger, D.Coia, M.Guainazzi, F.de Paolis, G.Ingrosso

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. 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. 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.
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_{-6}^{+8} eV. Neglecting the black-body, the bolometric absorption corrected flux is F^{Bol}=(6.5±0.1) x10^{-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) x10^{31} erg s^{-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 ~= 1.5 \sigma) 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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Blobrana · L

Outburst of the SU UMa type dwarf nova 0103+59 HT HT Cassiopeiae on January 10

HT Cassiopeiae is a faint, eclipsing cataclysmic variable, with a V magnitude of about 16.5 when in quiescence.
In outburst it can brighten to magnitude 12.60

HT Cassiopeiae.kmz

Position (2000): RA 01:10:12.98 Dec. +60:04:35.9

Blobrana · L

Title: Cyclical period changes in HT Cas: a clear difference between systems above and below the period gap
Authors: B. W. Borges, R. Baptista, C. Papadimitriou, O. Giannakis

We report the identification of cyclical changes in the orbital period of the eclipsing cataclysmic variable HT Cas. We measured new white dwarf mid-eclipse timings and combined with published measurements to construct an observed-minus-calculated diagram covering 29 years of observations. The data present cyclical variations that can be fitted by a linear plus sinusoidal function with period 36 yr and semi-amplitude ~ 40 s. The statistical significance of this period by an F-test is larger than 99.9 per cent. We combine our results with those in the literature to revisit the issue of cyclical period changes in cataclysmic variables and their interpretation in terms of a solar-type magnetic activity cycle in the secondary star. A diagram of fractional period change (Delta P/P) versus the angular velocity of the active star (Omega) for cataclysmic variables, RS CVn, W UMa and Algols reveal that close binaries with periods above the gap (secondaries with convective envelopes) satisfy a relationship Delta P/P \propto Omega^{-0.7 ±0.1}. Cataclysmic variables below the period gap (with fully convective secondaries) deviate from this relationship by more than 3-sigma, with average fractional period changes ~ 5 times smaller than those of the systems above the gap.

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