* Astronomy

Blobrana · L

RE: RU Pegasi

Blobrana · L

Title: Roche tomography of cataclysmic variables - V. A high-latitude star-spot on RU Pegasi
Authors: Alexander Dunford, Christopher A Watson, Robert Connon Smith

We present Roche tomograms of the secondary star in the dwarf nova system RU Pegasi derived from blue and red arm ISIS data taken on the 4.2-m William Herschel Telescope. We have applied the entropy landscape technique to determine the system parameters and obtained component masses of M1 = 1.06 Msun, M2 = 0.96 Msun, an orbital inclination angle of i = 43 degrees, and an optimal systemic velocity of gamma = 7 km/s. These are in good agreement with previously published values. Our Roche tomograms of the secondary star show prominent irradiation of the inner Lagrangian point due to illumination by the disc and/or bright spot, which may have been enhanced as RU Peg was in outburst at the time of our observations. We find that this irradiation pattern is axi-symmetric and confined to regions of the star which have a direct view of the accretion regions. This is in contrast to previous attempts to map RU Peg which suggested that the irradiation pattern was non-symmetric and extended beyond the terminator. We also detect additional inhomogeneities in the surface distribution of stellar atomic absorption that we ascribe to the presence of a large star-spot. This spot is centred at a latitude of about 82 degrees and covers approximately 4 per cent of the total surface area of the secondary. In keeping with the high latitude spots mapped on the cataclysmic variables AE Aqr and BV Cen, the spot on RU Peg also appears slightly shifted towards the trailing hemisphere of the star. Finally, we speculate that early mapping attempts which indicated non-symmetric irradiation patterns which extended beyond the terminator of CV donors could possibly be explained by a superposition of symmetric heating and a large spot.

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Blobrana · L

Title: XMM-Newton observations of the dwarf nova RU Peg in quiescence: Probe of the boundary layer
Authors: S. Balman, P. Godon, E.M. Sion, J.-U. Ness, E. Schlegel, P.E. Barrett, P. Szkody

We present an analysis of X-ray and UV data obtained with the XMM-Newton Observatory of the long period dwarf nova RU Peg. RU Peg contains a massive white dwarf, possibly the hottest white dwarf in a dwarf nova, it has a low inclination, thus optimally exposing its X-ray emitting boundary layer, and has an excellent trigonometric parallax distance. We modelled the X-ray data using XSPEC assuming a multi-temperature plasma emission model built from the MEKAL code. We obtained a maximum temperature of 31.7 keV, based on the EPIC MOS1, 2 and pn data, indicating that RU Peg has an X-ray spectrum harder than most dwarf novae, except U Gem. This result is consistent with and indirectly confirms the large mass of the white dwarf in RU Peg. The X-ray luminosity we computed corresponds to a boundary layer luminosity for a mass accretion rate of 2.E-11 Msun/yr (assuming Mwd=1.3Msun), in agreement with an expected quiescent accretion rate. The modelling of the O VIII emission line at 19A as observed by the RGS implies a projected stellar rotational velocity of 695 km/s, i.e. the line is emitted from material rotating at about 936-1245 km/s (for i about 34-48deg) or about 1/6 of the Keplerian speed; this velocity is much larger than the rotation speed of the white dwarf inferred from the FUSE spectrum. Cross-correlation analysis yielded an undelayed component and a delayed component of 116 ±17 sec where the X-ray variations/fluctuations lagged the UV variations. This indicates that the UV fluctuations in the inner disk are propagated into the X-ray emitting region in about 116 sec. The undelayed component may be related to irradiation effects.

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Blobrana · L

The dwarf nova RU Pegasi is in outburst.

Date: 6th August 2011
Magnitude: 9 - 13.2 V
Period: 74.3 days
Satellite orbital Period: 0.3746 days
Type: UGSS

Position (2000): RA 22 14 02.55 | Dec +12° 42' 11.3"

Blobrana · L

The dwarf nova RU Pegasi is in outburst.

Date: 27th April 2010
Magnitude: 9 - 13.2 V
Period: 74.3 days
Satellite orbital Period: 0.3746 days
Type: UGSS

Position (2000): RA 22 14 02.55, Dec +12 42 11.3

Blobrana · L

The dwarf nova RU Pegasi is in outburst.

Date: 16th November 2008
Magnitude: 9 - 13.2 V
Period: 74.3 days
Satellite orbital period: 0.3746 days
Type: UGSS

Position(2000): RA=22h14m02.56s, Dec=+12°42'11.5"