Ultraviolet Temporal Variability of the Peculiar Star R Aquarii

Abstract

This paper is a comprehensive study of all far-UV spectra obtained with the International Ultraviolet Explorer (IUE) satellite of the symbiotic star R Aquarii (R Aqr) covering a 13 yr period between 1979 and 1992. We have analyzed the ultraviolet emission for the compact H II region and the NE and SW extended "jetlike" filamentary structures. The results of our ultraviolet analysis indicate that the H II region and features A, B, and D of the NE jet are increasing in intensity, while the SW counterjet, feature A', has declined in intensity. We have found much stronger evidence that the high ionization lines of N v A.A-1238, 1240 and He II A.1640 in the H II region and NE jet have steadily increased over the entire period of IUE observations. This result could indicate that the ionized region is increasing in excitation. We have found that the observations of the NE jet are consistent with a decreasing electron temperature and increasing line-emitting region, which suggest that the strengthening of emission-line fluxes may be a result of an expanding emitting volume in a post-shocked region. Low-resolution absolute line intensities and wavelengths for the most prominent emission lines in the A.A-1200-3200 wavelength range have been tabulated. In addition, we present plots of the total ultraviolet flux (A.A-1200-3200) and absolute line intensities as a function of time to discern the temporal variability of R Aqr. These plots indicate that the far-UV emission from the NE jet is not variable on a "'1.5 yr timescale as suggested by Kafatos, Michalitsianos, & Hollis. Moreover, we find that the variations in the far-UV emission in R Aqr are not coupled to the 386 day pulsation period of the Mira. Finally, successive ionization levels of carbon, nitrogen, oxygen, and silicon of the NE jet are compared with each other to probe the nature of the ionization source in the NE jet. High-and low-resolution ultraviolet spectra were used to calculate the properties of the emission nebula and hot component. We determined electron densities of ne = 4 x 10 5 em-3 (H II region) and ne = 6 x 10 4 em-3 (NE jet), electron temperatures of T;, "' 20,000 K (H II region) and a high value of 1;, ~ 26,000 K

SPHERE/ZIMPOL observations of the symbiotic system R Aquarii

“…These determinations are mainly based on emission line spectroscopy in the visual range with ground based observations and in the UV with the International Ultraviolet Explorer (IUE) satellite (e.g., Wallerstein & Greenstein 1980;Kaler 1981;Michalitsianos & Kafatos 1982;Kafatos et al 1986;Hollis et al 1991;Burgarella et al 1992;Meier & Kafatos 1995). These spectra cover the central region of R Aqr or/and the NE and SW jet features at separations of ≈5 with typically a spatial resolution of a few arcsec.…”

“…Suggested ionizing sources are either a hot white dwarf T > ∼ 50 000 K (e.g., Meier & Kafatos 1995), or a hot subdwarf T ≈ 40 000 K, L ≈ 10 L , R ≈ 0.1 R (Burgarella et al 1992). In alternative models the UV radiation is proposed to originate from the accretion disk and the boundary layer around a white dwarf or subdwarf with an accretion rate of the orderṀ acc ≈ 10 −8 M yr −1 (e.g., Burgarella et al 1992).…”

“…In alternative models the UV radiation is proposed to originate from the accretion disk and the boundary layer around a white dwarf or subdwarf with an accretion rate of the orderṀ acc ≈ 10 −8 M yr −1 (e.g., Burgarella et al 1992). Estimated values for the number of ionizing photons emitted by the central source are log Q ≈ 42.5 (Meier & Kafatos 1995).…”

Proper motion analysis of the jet of R Aquarii

“…Some of the mechanisms proposed have been based on stellar wind or collision of winds models (e.g., Burgarella et al 1992). Particularly in recent studies, interaction of binary components has been thought to be relevant to the jet formation mechanism and most analyses have utilized the compact companion/accretion disk scenario (e.g., Kellogg et al 2001;Hollis & Koupelis 2000;Meier & Kafatos 1995;Solf 1992;Lehto & Johnson 1992, LJ hereafter;Sopka et al 1982). In these scenarios the matter flowing towards the hot companion is most likely enhanced during periaston passage.…”

A study of the mass loss rates of symbiotic star systems

“…Initially, the mass of the jet was calculated assuming a cylindrical system. This calculation did not take into account the true spatial extent [7], (c) All x-ray quantities are taken or derived from Kellogg et al [11,12], (d) Kafatos et al [10], (e) Meier & Kafatos [13], (f) Hollis et al [8] of the emission. In order to characterize the mass loss in the jet more quantitatively, the Chandra observation was re-analyzed on a pixel by pixel basis to give a tighter estimation of the jet volume hence a tighter mass estimate for the jet in the x-rays.…”