Coordinated UV and optical observations of the AM Herculis object E1405-451 in the high and low states

Maraschi, L.; Treves, A.; Tanzi, E. G.; Mouchet, M.; Lauberts, A.; Motch, C.; Bidaud, J.-M. Bonnet; Phillips, M. M.

doi:10.1086/162494

Cited by 13 publications

(9 citation statements)

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“…Another constraint imposed on the models is the predicted value of the UV flux density. While simultaneous UV observations do not exist for either of our EUVE observations, V834 Cen has been observed numerous times by the International Ultraviolet Explorer (IUE ) (e.g., Nousek & Pravado 1983;Maraschi et al 1984;Takalo & Nousek 1988;Sambruna et al 1991Sambruna et al , 1994. We extracted all of these spectra from the IUE Newly Extracted Spectra (INES) data archive (http://ines.laeff.esa.es/) and determined that the maximum mean flux density in the nominally line-free bandpass at 1300 ± 25 Å is 4 × 10 −14 erg cm −2 s −1 Å−1 .…”

Section: Sw Spectramentioning

confidence: 85%

Extreme Ultraviolet ExplorerPhase‐resolved Spectroscopy of V834 Centauri

Mauche

2002

ApJ

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The Extreme Ultraviolet Explorer (EUVE ) satellite was employed for 5.46 days beginning on 1999 February 9.03 UT to acquire phase-resolved EUV photometric and spectroscopic observations of the AM Her-type cataclysmic variable V834 Centauri. The resulting data are superior to those obtained by EUVE beginning on 1993 May 28.14 UT because the source was approximately three times brighter, the observation was four times longer and dithered, and ASCA observed the source simultaneously. Although we do not understand the EUV light curves in detail, they are explained qualitatively by a simple model of accretion from a ballistic stream along the field lines of a tilted ([β, ψ] ≈ [10 • , 40 • ]) magnetic dipole centered on the white dwarf. In 1993 when the EUV flux was lower, accretion was primarily along the ϕ ≈ ψ ≈ 40 • field line, whereas in 1999 when the EUV flux was higher, accretion took place over a broad range of azimuths extending from ϕ ≈ ψ ≈ 40 • to ϕ ≈ 76 • . These changes in the accretion geometry could be caused by an increase in the mass-accretion rate and/or the clumpiness of the flow. The 75-140Å EUVE spectra are well described by either a blackbody or a pure-H stellar atmosphere absorbed by a neutral hydrogen column density, but constraints on the size of the EUV emission region and its UV brightness favor the blackbody interpretation. The mean 1999 EUV spectrum is best fit by an absorbed blackbody with temperature kT ≈ 17.6 eV, hydrogen column density N H ≈ 7.4 × 10 19 cm −2 , fractional emitting area f ≈ 10 −3 , 70-140Å flux ≈ 3.0 × 10 −11 erg cm −2 s −1 , and luminosity L soft ≈ 7.2 × 10 32 (d/100 pc) 2 erg s −1 . The ratio of the EUV to X-ray luminosities is L soft /L hard ≈ 40, signaling that some mechanism other than irradiation (e.g., blob heating) dominates energy input into the accretion spot. The 1999 SW hardness ratio variation can be explained by minor variations in kT and/or N H , but instead of tracking the SW count rate variation, the hardness ratio variation was sinusoidal, with a minimum (maximum) when the accretion spot was on the near (far) side of the white dwarf, consistent with the trend expected for an atmosphere with an inverted temperature distribution.

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Section: Sw Spectramentioning

confidence: 85%

Extreme Ultraviolet ExplorerPhase‐resolved Spectroscopy of V834 Centauri

Mauche

2002

ApJ

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“…V834 Cen - Maraschi et al (1984)'s blackbody fit to simultaneous optical and IUE low-state spectra gave a T wd = 26 500 K WD within a distance of d = 50 − 200 pc from the low state R and I magnitudes. They noted, however, that the WD interpretation of the UV continuum was somewhat ambiguous, as no broad Lyα absorption was observed.…”

Section: Individual Systemsmentioning

confidence: 94%

“…They noted, however, that the WD interpretation of the UV continuum was somewhat ambiguous, as no broad Lyα absorption was observed. Cropper (1990) applied Bailey's method using K = 13.1, as reported by Maraschi et al (1984) during a high state. This value of K is clearly an upper limit to the K-brightness of the secondary in V834 Cen and therefore the derived distance d = 86 pc is an absolute lower limit.…”

Section: Individual Systemsmentioning

confidence: 99%

Far‐Ultraviolet Spectroscopy of Magnetic Cataclysmic Variables

Araujo-Betancor

Gänsicke

Long

et al. 2005

ApJ

103

110

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We have obtained HST /STIS data for a total of eleven polars as part of a program aimed to compile a homogeneous database of high-quality far-ultraviolet (FUV) spectra for a large number of cataclysmic variables (CVs). Of the eleven polars, eight were found in a state of low accretion activity (V347 Pav, VV Pup, V834 Cen, BL Hyi, MR Ser, ST LMi, RX J1554.2+2721 and V895 Cen) and three in a state of high activity (CD Ind, AN UMa and UW Pic). The STIS spectra of the low-state polars unambiguously reveal the photospheric emission of their white dwarf (WD) primaries. We have used pure hydrogen WD models to fit the FUV spectra of the low-state systems (except RX J1554.2+2721, which is a highfield polar) in order to measure the WD effective temperatures. In all cases, the fits could be improved by adding a second component, which is presumably due to residual accretion onto the magnetic pole of the WD. The WD temperatures obtained range from 10 800 K to 14 200 K for log g = 8.0. Our analysis more than doubles the number of polars with accurate WD effective temperatures. Comparing the WD temperatures of polars to those of non-magnetic CVs, we find that at any given orbital period the WDs in polars are colder than those in non-magnetic CVs. The temperatures of polars below the period gap are consistent with gravitational radiation as the only active angular momentum loss mechanism. The differences in WD effective temperatures between polars and non-magnetic CVs are significantly larger above the period gap, suggesting that magnetic braking in polars might be reduced by the strong field of the primary. We derive distance estimates to the low-state systems from the flux scaling factors of our WD model fits. Combining these distance measurements with those from the literature, we establish a lower limit on the space density of polars of 1.3 × 10 −6 pc −3 .

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“…The Einstein and particularly the EXOSAT satellites have produced a wealth of X-ray data, most of which is still being analysed (in the case of the latter). A particularly useful compilation of the EXOSAT data is given in Mason (1985), although this is by means the full range of observed behaviour. Mason separates his two figures on polars into 'one-pole systems' and 'two-pole systems' (Section 2); this refers to those systems in which one accreting pole is always in view and those in which the two poles are seen alternatively, only one of which is usually accreting (the division depends only on the angles i and # in Equation (30)), These light curves are shown in Figures 25 and 26.…”

Section: The X-ray Light Curves: the Databasementioning

confidence: 99%