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Record 19 of 22
HST Spatially Resolved Spectra of the Accretion Disc and Gas Stream of the Nova-Like Variable UX Ursae Majoris
External Online Source: doi:10.1046/j.1365-8711.1998.01712.x
Author and Affiliation:
Baptista, Raymundo(Santa Catarina Univ., Depto. de Fisica, Florianopolis, Brazil)
Horne, Keith(Saint Andrew's Univ., School of Physics and Astronomy, United Kingdom)
Wade, Richard A.(Pennsylvania State Univ., Dept. of Astronomy and Astrophysics, University Park, PA United States)
Hubeny, Ivan(NASA Goddard Space Flight Center, Greenbelt, MD United States)
Long, Knox S.(Space Telescope Science Inst., Baltimore, MD United States)
Rutten, Rene G. M.(Isaac Newton Group, Santa Cruz de La Palma, Spain)
Abstract: Time-resolved eclipse spectroscopy of the nova-like variable UX UMa obtained with the Hubble Space Telescope/Faint Object Spectrograph (HST/FOS) on 1994 August and November is analysed with eclipse mapping techniques to produce spatially resolved spectra of its accretion disk and gas stream as a function of distance from the disk centre. The inner accretion disk is characterized by a blue continuum filled with absorption bands and lines, which cross over to emission with increasing disk radius, similar to that reported at optical wavelengths. The comparison of spatially resolved spectra at different azimuths reveals a significant asymmetry in the disk emission at ultraviolet (UV) wavelengths, with the disk side closest to the secondary star showing pronounced absorption by an 'iron curtain' and a Balmer jump in absorption. These results suggest the existence of an absorbing ring of cold gas whose density and/or vertical scale increase with disk radius. The spectrum of the infalling gas stream is noticeably different from the disc spectrum at the same radius suggesting that gas overflows through the impact point at the disk rim and continues along the stream trajectory, producing distinct emission down to 0.1 R(sub LI). The spectrum of the uneclipsed light shows prominent emission lines of Lyalpha, N v lambda1241, SiIV Lambda 1400, C IV Lambda 1550, HeII Lambda 1640, and MgII Lambda 2800, and a UV continuum rising towards longer wavelengths. The Balmer jump appears clearly in emission indicating that the uneclipsed light has an important contribution from optically thin gas. The lines and optically thin continuum emission are most probably emitted in a vertically extended disk chromosphere + wind. The radial temperature profiles of the continuum maps are well described by a steady-state disc model in the inner and intermediate disk regions (R greater than or equal to 0.3R(sub LI) ). There is evidence of an increase in the mass accretion rate from August to November (from V = 10 (exp -8.3 +/-0.1) to 10(exp -8.1 +/- 0.1 solar mass yr(exp -1)), in accordance with the observed increase in brightness. Since the UX UMA disc seems to be in a high mass accretion, high-viscosity regime in both epochs, this result suggests that the mass transfer rate of UX UMA varies substantially (approximately equal to 50 per cent) on time-scales of a few months. It is suggested that the reason for the discrepancies between the prediction of the standard disk model and observations is not an inadequate treatment of radiative transfer in the disc atmosphere, but rather the presence of addition important sources of light in the system besides the accretion disk (e.g., optically thin contiuum emission from the disk wind and possible absorption by circumstellar cool gas).
Publication Date: Jan 01, 1998
Document ID:
(Acquired Jun 11, 1999)
Subject Category: ASTRONOMY
Document Type: Reprint
Publication Information: Mon. Not. Royal Astronomical Society; Volume 298; 1079-1091
Contract/Grant/Task Num: NAS5-26555; GO-5488; NAG5-3459; GO-3683.03; CNPq-300-354/96-7
Financial Sponsor: NASA Goddard Space Flight Center; Greenbelt, MD United States
Conselho Nacional de Pesquisas; Sao Paulo, Brazil
Organization Source: NASA Goddard Space Flight Center; Greenbelt, MD United States
Description: 7p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
Availability Source: Other Sources
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