arXiv subjects

Patrick Godon

Publications and source records attributed to Patrick Godon.

At least 19 recordsLinked to original sources

arXiv2026

The instantaneous mass accretion rate of novae in quiescence: - an archival ultraviolet optical spectral analysis

Based on archival spectra, we derive the quiescent instantaneous mass transfer rates in novae using synthetic disk spectra generated with tlusty, Gaia parallax-derived distances, and updated color excess values. Our results for nine novae, based on ultraviolet spectra and on a number of optical spectra, yield mass accretion rates that are higher than those derived from simple integration of the UV and optical luminosity. HR Del, 20 years after its eruption, has a mass transfer rate of $4\times 10^{-7}M_\odot$/yr, and is likely burning the accreting H-rich material. V842 Cen, thought to be a low mass transfer system, has a comparable mass accretion rate. For both novae, the enhanced mass transfer must be self-sustained by a feedback loop. RR Pic, with $\dot{M}\approx 3\times 10^{-8}M_\odot$/yr, is better fitted with an accretion disk where the outer region is heated up to 12,000 K, in agreement with H and He emission lines coming from the outer disk and a large emission region on the leading side of the disk. Such a heated disk also gives a good fit to the spectra of CP Lac, and DI Lac with $\dot{M}\sim4.5$ and $9\times 10^{-9}M_\odot$/yr. V1974 Cyg and V533 Her, with an accretion rate of $\sim 3\times 10^{-9}M_\odot$/yr, have a rather flat spectrum. V446 Her and BK Lyn, caught in a state of low accretion, have the lowest mass accretion rates with $\dot{M} \sim 10^{-9}$ and $\sim 10^{-10}M_\odot$/yr respectively. The higher mass transfer rate systems, with $\dot{M}\approx \sim 10^{-7}M_\odot$/yr, agree with the standard disk model; the remaining systems are better fitted when the outer disk is heated to $\sim 12,000$~K. We suggest that irradiation from the heated WD, inner disk, together with tidal interaction, the bright spot, and material overflowing the disk edge, can increase the temperature of the outer disk.

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arXiv2026

High Resolution X-ray Spectroscopy of the Nova-Like Cataclysmic Variable BZ Cam using Chandra HETG: Diagnosis of the ADAF-like (Advective) Hot Flow

Nova-likes such as BZ Cam are high state Cataclysmic Variables showing hard X-ray emission that can be characterized with advective hot flows in the inner accretion disk. We explore Chandra High Energy Transmission Grating (HETG) observations of BZ~Cam for detailed line diagnosis and ionization conditions in the X-ray regime. We mostly find H- and He-like emission lines of Mg, Si, S, and Fe. All He-like line components of forbidden, intercombination and resonance lines are present. The R ratios of selected lines indicate plasma densities of a few $\times$10$^{12-14}$ cm$^{-3}$ and G ratios reveal temperatures (3-6)$\times$ 10$^6$ K where the Fe lines yield (1-3)$\times$ 10$^7$ K. The H to He line ratios and the R and G ratios show that the plasma is in a nonequilibrium ionization condition, which is consistent with our previous X-ray results and the accretion flow in the X-ray region being an ADAF-like (advective) hot flow. Simultaneous fits of the HEG and MEG spectra or the broadband joint spectra of ROSAT, Chandra zero order and NuSTAR yield temperatures 3.4-6.3 keV using a VNEI model of plasma emission (in XSPEC) or Bremsstrahlung emission. An additional power law is detected above 98\% Confidence Level in the broadband analysis. The orbital variations and the broadband spectra show dipping/veiling of the X-rays and an additional warm absorber model with an ionization parameter log($\xi$) = 2.7 is required at the 3$\sigma$ level, along with the VNEI model where the HEG and MEG simultaneous fits yield the log($\xi$) = 3.6 .

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arXiv2024

X-ray Spectroscopy of the Dwarf Nova Z Chamaeleontis in Quiescence and Outburst Using the XMM-Newton Observatory

We present X-ray spectroscopy of the SU UMa-type dwarf nova (DN) Z Cha using the EPIC and RGS instruments onboard the XMM-Newton Observatory. The quiescent system can be modeled by collisional equilibrium or nonequilibrium plasma models, yielding a kT of 8.2-13.0 keV at a luminosity of (5.0-6.0)$\times$10$^{30}$ erg/s. The spectra yield better reduced $\chi^{2}$ using partial covering absorbers of cold and photoionized nature. The ionized absorber has an equivalent N$_H$=(3.4-5.9)$\times$10$^{22}$ cm$^{-2}$ and a log($\xi$)=3.5-3.7 with (50-60)% covering fraction when VNEI model (XSPEC) is used. The line diagnosis in quiescence shows no resonance lines with only detected forbidden lines of Ne, Mg, Si. The H-like C, O, Ne, and Mg are detected. The strongest line is O VIII with (2.7-4.6)$\times$10$^{-14}$ erg/s/cm$^2$. The quiescent X-ray emitting plasma is not collisional and not in ionization equilibrium which is consistent with hot ADAF-like accretion flows. The line diagnosis in outburst shows He-like O, and Ne with intercombination lines being the strongest along with weaker resonance lines. This indicates the plasma is more collisional and denser, but yet not in a collisional equilibrium, revealing ionization timescales of (0.97-1.4)$\times$10$^{11}$ s cm$^{-3}$. The R-ratios in outburst yield electron densities of (7-90)$\times$10$^{11}$ cm$^{-3}$ and the G-ratios yield electron temperatures of (2-3)$\times$10$^{6}$ K. The outburst luminosity is (1.4-2.5)$\times$10$^{30}$ erg/s. The flow is inhomogeneous in density. All detected lines are narrow with widths limited by the resolution of RGS yielding Keplerian rotational velocities $<$1000 km/s. This is too low for boundary layers, consistent with the nature of ADAF-like hot flows.

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arXiv2022

Characterizing the Advective Hot Flows of Nova-Like Cataclysmic Variables in the X-rays: The case of BZ Cam and V592 Cas

We present a joint spectral analysis of ROSAT PSPC, Swift XRT, and NuSTAR FPMA/B data of the nova-like (NL) cataclysmic variables (CVs), BZ Cam and V592 Cas in the 0.1-78.0 keV band. Plasma models of collisional equilibrium fail to model the 6.0-7.0 iron line complex and continuum with $\chi^2_\nu$ larger than 2.0. Our results show nonequilibrium ionization (NEI) conditions in the X-ray plasma with temperatures of 8.2-9.4 keV and 10.0-12.9 keV for BZ Cam and V592 Cas, respectively. The centroids of He-like and H-like iron ionization lines are not at their equilibrium values as expected from NEI conditions. We find power law spectral components that reveal the existence of scattering and Comptonization with a photon index of 1.50-1.87. We detect a P Cygni profile in the H-like iron line of BZ Cam translating to outflows of 4500-8700 km s$^{-1}$ consistent with the fast winds in the optical and UV. This is the first time such a fast collimated outflow is detected in the X-rays from an accreting CV. An Iron K$\alpha$ line around 6.2-6.5 keV is found revealing the existence of reflection effects in both sources. We study the broadband noise and find that the optically thick disk truncates in BZ Cam and V592 Cas consistent with transition to an advective hot flow structure. V592 Cas also exhibits a quasi-periodic oscillation at 1.4$^{+2.6}_{-0.3}$ mHz. In general, we find that the two NLs portray spectral and noise characteristics as expected from advective hot accretion flows at low radiative efficiency.

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arXiv2022

Hubble Space Telescope STIS Spectroscopy of Nova T Aurigae 1891

T Aurigae is an eclipsing old nova which exploded in 1891. At a Gaia EDR3 distance of 815-871 pc, it is a relatively nearby old nova. Through ultraviolet spectral modeling and using the new precise Gaia distance, we find that the HST/STIS spectrum of T Aurigae is consistent with an accretion disk with a mass transfer rate $\dot{M}$ of the order of $10^{-8}M_{\odot}$/yr, for a white dwarf mass of $M_{\rm wd} \approx 0.7 \pm 0.2 M_{\odot}$, an inclination of $i \sim 60^{\circ}$, and a Gaia distance of of $840_{-25}^{+31}$~pc. The sharp absorption lines of metals cannot form in the disk and are likely forming in material above the disk (e.g. due stream disk overflow), in circumbinary material, and/or in material associated with the ejected shell from the 1891 nova explosion. The saturated hydrogen Ly$\alpha$ absorption feature is attributed to a large interstellar medium hydrogen column density of the order of $10^{21}$cm$^{-2}$ towards T Aur, as corroborated by the value of its reddening $E(B-V)=0.42 \pm 0.08$.

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arXiv2022

White Dwarf Photospheric Abundances in Cataclysmic Variables -- II. White Dwarfs With and Without a Mask

Taking advantage of the now available Gaia EDR3 parallaxes, we carry out an archival {\it Hubble Space Telescope} (HST) far ultraviolet spectroscopic analysis of 10 cataclysmic variable systems, including 5 carefully selected eclipsing systems. We obtain accurate white dwarf (WD) masses and temperatures, in excellent agreement with the masses for 4 of the eclipsing systems. For three systems in our sample, BD Pav, HS 2214, and TT Crt, we report the first robust masses for their WDs. We modeled the absorption lines to derive the WD chemical abundances and rotational velocities for each of the ten systems. As expected, for five higher inclination ($i \gtrsim 75^{\circ}$) systems, the model fits are improved with the inclusion of a cold absorbing slab (an iron curtain masking the WD) with $N_{\rm H} \approx 10^{20}-10^{22}$cm$^{-2}$. Modeling of the metal lines in the HST spectra reveals that 7 of the 10 systems have significant subsolar carbon abundance, and six have subsolar silicon abundance, thereby providing further evidence that CV WDs exhibit subsolar abundances of carbon and silicon. We suggest that strong aluminum absorption lines (and iron absorption features) in the spectra of some CV WDs (such as IR Com) may be due to the presence of a {\it thin} iron curtain ($N_{\rm H}\approx 10^{19}$cm$^{-2}$) rather than to suprasolar aluminum and iron abundances in the WD photosphere. The derived WD (projected) rotational velocities all fall in the range $\approx 100-400$~km/s, all sub-Keplerian similar to the values obtained in earlier studies.

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arXiv2021

The Heating and Pulsations of V386 Serpentis after its 2019 Dwarf Nova Outburst

Following the pulsation spectrum of a white dwarf through the heating and cooling involved in a dwarf nova outburst cycle provides a unique view of the changes to convective driving that take place on timescales of months versus millenia for non-accreting white dwarfs. In 2019 January the dwarf nova V386 Ser (one of a small number containing an accreting, pulsating white dwarf), underwent a large amplitude outburst. Hubble Space Telescope ultraviolet spectra were obtained 7 and 13 months after outburst along with optical ground-based photometry during this interval and high-speed photometry at 5.5 and 17 months after outburst. The resulting spectral and pulsational analysis shows a cooling of the white dwarf from 21,020 K to 18,750 K (with a gravity log(g) = 8.1) between the two UV observations, along with the presence of strong pulsations evident in both UV and optical at a much shorter period after outburst than at quiescence. The pulsation periods consistently lengthened during the year following outburst, in agreement with pulsation theory. However, it remains to be seen if the behavior at longer times past outburst will mimic the unusual non-monotonic cooling and long periods evident in the similar system GW Lib.

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arXiv2021

White Dwarf Photospheric Abundances in Cataclysmic Variables: I. SS Aurigae and TU Mensae

Chemical abundances studies of cataclysmic variables have revealed high nitrogen to carbon ratios in a number of of cataclysmic variable white dwarfs (based on ultraviolet emission and absorption lines), as well as possible carbon deficiency in many secondaries (based on the absence of infrared CO absorption lines). These indicate that the accreted material on the white dwarf surface and the donor itself might be contaminated with CNO processed material. To further understand the origin of this abundance anomaly, there is a need for further chemical abundance study. In the present work, we carry out a far ultraviolet spectral analysis of the extreme SU UMa dwarf nova TU Men and the U Gem dwarf nova SS Aur using archival spectra. We derive the mass and temperature of the WD using the recently available DR2 Gaia parallaxes. The analysis of HST STIS spectra yields a WD mass $M_{\rm wd}=0.77^{+0.16}_{-0.13}M_{\odot}$ with a temperature of $27,750 \pm 1000$~K for TU Men, and a WD mass $M_{\rm wd} \sim 0.80 \pm 0.15$ with a temperature of $\sim 30,000 \pm 1000$~K for SS Aur. However, the analysis of a FUSE spectrum for SS Aur gives to a higher temperature $\sim 33,375 \pm 1875 $~K, yielding to a higher WD mass $\sim 1 \pm 0.25 M_{\odot}$, which could be due to the effect of a second hot emitting component present in the short wavelengths of FUSE. Most importantly, based on the white dwarf far ultraviolet absorption lines, we find that both systems have subsolar carbon and silicon abundances. For TU Men we also find suprasolar nitrogen abundance, evidence of CNO processing.

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arXiv2020

The hydrogen Balmer lines and jump in absorption in accretion disc modeling -- an ultraviolet-optical spectral analysis of the dwarf novae UZ Serpentis and CY Lyrae

The spectra of disc-dominated cataclysmic variables (CVs) often deviate from the spectra of accretion disc models; in particular, the Balmer jump and absorption lines are found to be shallower in the observations than in the models. We carried out a combined ultraviolet-optical spectral analysis of two dwarf novae: UZ Ser in outburst, decline, and quiescence, and CY Lyr on the rise to outburst and in outburst. We fit the Balmer jump and absorption lines, the continuum flux level and slope by adjusting the accretion rate, inclination, and disc outer radius. For both systems we find an accretion rate $\dot{M} \approx 8 \times 10^{-9}M_\odot$/yr in outburst, and $\dot{M} \approx 2-3 \times 10^{-9}M_\odot$/yr for the rise and decline phases. The outer disc radius we derive is smaller than expected ($R_{\rm disc} \approx 0.2a$, where $a$ is the binary separation), except during late rise (for CY Lyr) where $R_{\rm disc}=0.3a$. UZ Ser also reveals a 60,000~K white dwarf. These results show that during a dwarf nova cycle the radius of the disc is the largest just before the peak of the outburst, in qualitative agreement with the disc instability model for dwarf nova outbursts. We suspect that an additional emitting component (e.g. disc wind) is also at work to reduce the slope of the continuum and size of the Balmer jump and absorption lines. We stress that both the outer disc radius and disc wind need to be taken into account for more realistic disc modeling of CVs.

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arXiv2019

Fuse and IUE Spectroscopy of the Prototype Dwarf Nova ER Ursa Majoris During Quiescence

ER Ursae Majoris is the prototype for a subset of SU UMa-type dwarf novae characterized by short cycle times between outburst, high outburst frequency, and ``negative'' superhumps. It suffers superoutbursts every 43 days, lasting 20 days, normal outbursts every 4 days and has an outburst amplitude of 3 magnitudes. We have carried out a far ultraviolet (FUV) spectral analysis of ER UMa in quiescence, by fitting Far Ultraviolet Spectroscopic Explorer (FUSE) and International Ultraviolet Explorer (IUE) spectra with model accretion disks and high gravity photosphere models. Using the Gaia parallax distance and an orbital inclination of $50^{\circ}$, we find that during the brief quiescence of only four days, the accretion rate is $7.3 \times 10^{-11}M_{\odot}$/yr, with the ER UMa white dwarf contributing 55% of the FUV flux and the accretion disk contributing the remaining 45\% of the flux. The white dwarf in ER UMa is markedly hotter (32,000~K) than the other white dwarfs in dwarf novae below the CV period gap which have typical temperatures $\sim$15,000~K. For a higher inclinations of 60 to 75 degrees, the accretion rates that we derive are roughly an order of magnitude higher $1 - 3 \times 10^{-10}M_{\odot}$/yr.

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arXiv2019

FUSE Spectroscopic Analysis of the Slowest Symbiotic Nova AG Peg During Quiescence

We present a far ultraviolet spectroscopic analysis of the slowest known symbiotic nova AG Peg (M3/4III giant + hot white dwarf; P = 818.4 days) which underwent a nova explosion in 1850 followed by a very slow decline that did not end until 1996, marking the beginning of quiescence. The 19 years of quiescence ended in June 2015, when AG Peg exhibited a Z And-type outburst with an optical amplitude of 1.5 magnitudes. We have carried out accretion disk and WD photosphere synthetic spectral modeling of a Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum obtained on June 5.618, 2003 during the quiescence interval 12 years before the 2015 outburst. The spectrum is heavily affected by ISM absorption as well as strong emission lines. We de-reddened the FUSE fluxes assuming E(B-V) = 0.10, which is the maximum galactic reddening in the direction of AG Peg. We discuss our adoption of the pre-Gaia distance over the Gaia parallax. For a range of white dwarf surface gravities and surface temperatures we find that the best-fitting photosphere is a hot WD with a temperature T = 150,000 K, and a low gravity log(g)~6.0-6.5. For a distance of 800 pc, the scaled WD radius is about 0.06 Rsun, giving log(g) = 6.67 for a 0.65 Msun WD mass. The Luminosity we obtain from this model is 1729 Lsun. The hot photosphere models provide better fits than the accretion disk models which have FUV flux deficits toward the shorter wavelengths of FUSE, down to the Lyman Limit. Given the uncertainty of the nature of a true symbiotic accretion disk, and, while a very hot low gravity degenerate star dominates the FUV flux, the presence of a steady-state (standard) accretion disk cannot be summarily ruled out.

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arXiv2018

HST FUV spectroscopy of the short orbital period recurrent nova CI Aql: Implications for white dwarf mass evolution

An HST COS Far UV spectrum (1170 A to 1800 A) was obtained for the short orbital period recurrent novae (T Pyxidis subclass), CI Aquilae. CI Aql is the only classical CV known to have two eclipses of sensible depth per orbit cycle and also have pre- and post-outburst light curves that are steady enough to allow estimates of mass and orbital period changes. Our FUV spectral analysis with model accretion disks and NLTE high gravity photospheres, together with the Gaia parallax, reveal CI Aql's FUV light is dominated by an optically thick accretion disk with an accretion rate of the order of $4\times 10^{-8}$ $M_{\odot}/yr$. Its database of light curves, radial velocity curves, and eclipse timings is among the best for any CV. Its orbit period ($P$), $dP/dt$, and reference time are re-derived via simultaneous analysis of the three data types, giving a dimensionless post-outburst $dP/dt$ of $-2.49\pm 0.95\times 10^{-10}$. Lack of information on loss of orbital to rotational angular momentum leads to some uncertainty in the translation of $dP/dt$ to white dwarf mass change rate, $dM_1/dt$, but within the modest range of $+4.8\times 10^{-8}$ to $+7.8\times 10^{-8}$ $M_{\odot} /yr$. The estimated white dwarf mass change through outburst for CI Aql, based on simple differencing of its pre- and post outburst orbit period, is unchanged from the previously published $+5.3 \times 10^{-6} M_{\odot}$. At the WD's estimated mass increase rate, it will terminate as a Type Ia supernova within 10 million years.

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arXiv2018

L1 Stream Deflection and Ballistic Launching at the Disk Bow Shock: An Absorption-line Velocity Analysis in Semi-detached Binaries

Observations of semi-detached interacting binaries reveal orbital modulation indicating the presence of absorbing material obscuring the disk and accreting primary star at specific orbital phases consistent with L1 stream material overflowing the disk edge. We simulate the L1 stream interaction with the disk using tests particles within the context of the Roche model in the restricted three-body problem. At the disk bow shock the L1 stream particles are deflected and launched onto ballistic trajectories above the disk (as would normally occurs at the front of a detached shock in the hypersonic flow past a blunt body).At a given scale height, the material is assumed to continue without being affected by the disk, while at lower altitude it is being launched at an increasing elevation, as well as gradually being dragged by the Keplerian flow. We follow the stream material ballistic trajectories over the disk surface, where they reach a maximum height z/r at a binary phase $\Phi \sim 0.75$, and land onto the disk at a smaller radius around phase $\Phi \sim 0.5$. The radial velocity for each $L1$ stream ballistic trajectory along the line of sight (of the observer) to the hot inner parts of the disk is computed as a function of the orbital phase for a binary configuration matching the dwarf nova U Geminorum. The computed velocity amplitudes, phases, and pattern match the observed velocity offsets of the metal lines in the FUSE spectrum of U Gem during outburst. As ballistic trajectories are much easier to compute than realistic three-dimensional hydrodynamical simulations, we propose the use of the L1 stream deflection and ballistic launching as a means for the analysis of the absorption lines orbital variability in semi-detached binaries and to assess or confirm, with some limitations, the system parameters such as the mass ratio, inclination, and disk outer radius.

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arXiv2018

The Long-Term Secular Mass Accretion Rate of the Recurrent Nova T Pyxidis

We present Hubble Space Telescope ultraviolet spectroscopy of the recurrent nova T Pyxidis obtained more than 5 years after its 2011 outburst indicating that the system might not have yet reached its deep quiescent state. The ultraviolet data exhibit a 20% decline in the continuum flux from the pre-outburst deep quiescence state to the post-outburst near quiescent state. We suggest that a decline across each recurring nova eruption might help explain the proposed 2mag steady decline of the system since 1866. Using an improved version of our accretion disk model as well as International Ultraviolet Explorer ultraviolet and optical data, and the 4.8 kpc distance, we corroborate our previous findings that the quiescent mass accretion rate in T Pyx is of the order of 1e-6 Solar mass per year. Such a large mass accretion rate would imply that the mass of the white dwarf is increasing with time. However, with the just-release Gaia DR 2 distance of 3.3 kpc (after submission of the first version of this manuscript), we find a mass accretion of the order of 1e-7 Solar mass per year. Our results predict powerful soft X-ray or extreme ultraviolet emission from the hot inner region of the high accretion rate disk. Using constraining X-ray observations and assuming the accretion disk doesn't depart too much from the standard model, we are left with two possible scenarios. The disk either emits mainly extreme ultraviolet radiation which, at a distance of a few kpc, is completely absorbed by the interstellar medium, or the hot inner disk, emitting soft X-rays, is masked by the bulging disk seen at a higher inclination.

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arXiv2017

HST/COS Far Ultraviolet Spectroscopic Analysis of U Geminorum Following a Wide Outburst

We have used HST/COS to obtain a series of 4 FUV (915-2148A) spectroscopic observations of the prototypical dwarf nova U Geminorum during its cooling following a two-week outburst. Our FUV spectral analysis of the data indicates that the white dwarf (WD) cools from a temperature of 41,500 K, 15 days after the peak of the outburst, to 36,250 K, 56 days after the peak of the outburst, assuming a massive WD (log(g)=8.8) and a distance of 100.4 pc. These results are self-consistent with a 1.1 solar mass WD with a 5,000 km radius. The spectra show many absorption lines of but no emission features. We find supra-solar abundances of nitrogen confirming the anomalous high N/C ratio. The FUV lightcurve reveals a 5% modulation with the orbital phase, showing dips near phase 0.25 and 0.75, where the spectra exhibit an increase in the depth of some absorption lines and in particular strong absorption lines from Si, Al, and Ar. The phase dependence we observe is consistent with material overflowing the disk rim at the hot spot, reaching a maximum elevation near phase 0.75, falling back at smaller radii near phase 0.5 where it bounces off the disk surface and again rising above the disk near phase 0.25. There is a large scatter in the absorption lines' velocities, especially for the silicon lines, while the carbon lines seem to match more closely the orbital velocity of the WD. This indicates that many absorption lines are affected by- or form in- the overflowing stream material veiling the WD, making the analysis of the WD spectra more difficult.

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arXiv2017

Modifying the Standard Disk Model for the Ultraviolet Spectral Analysis of Disk-dominated Cataclysmic Variables. I. The Novalikes MV Lyrae, BZ Camelopardalis, and V592 Cassiopeiae

The standard disk is often inadequate to model disk-dominated cataclysmic variables (CVs) and generates a spectrum that is bluer than the observed UV spectra [Puebla et al 2007]. X-ray observations of these systems reveal an optically thin boundary layer (BL) expected to appear as an inner hole in the disk. Consequently, we truncate the inner disk. However, instead of removing the inner disk, we impose the no-shear boundary condition at the truncation radius, thereby lowering the disk temperature and generating a spectrum that better fits the UV data. With our modified disk, we analyze the archival UV spectra of three novalikes that cannot be fitted with standard disks. For the VY Scl systems MV Lyr and BZ Cam, we fit a hot inflated white dwarf WD with a cold modified disk ($\dot{M} \sim $ a few $10^{-9}M_{\odot}$/yr). For V592 Cas, the slightly modified disk ($\dot{M} \sim 6 \times 10^{-9}M_{\odot}$/yr) completely dominates the UV. These results are consistent with Swift X-ray observations of these systems [Balman et al 2014], revealing BLs merged with ADAF-like flows and/or hot coronae, where the advection of energy is likely launching an outflow and heating the WD, thereby explaining the high WD temperature in VY Scl systems. This is further supported by the fact that the X-ray hardness ratio increases with the shallowness of the UV slope in a small CV sample we examine. Furthermore, for 105 disk-dominated systems, the International Ultraviolet Explorer (IUE) spectra UV slope decreases in the same order as the ratio of the X-ray flux to optical/UV flux: from SU UMa's, to U Gem's, Z Cam's, UX UMa's, and VY Scl's.

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arXiv2017

Probing the Accreting Hot Components in Six S-Type Symbiotic Variables

We have carried out a spectroscopic analysis of the far ultraviolet spectra of six symbiotic variables. Two systems, LT Del, which has had one recorded outburst, and BD-21 3873 (= IV Vir) which has had no recorded outburst, are yellow symbiotic systems. Two other systems, V443 Her and RW Hya, have also never had a recorded outburst. Two other symbiotics, StHa190 and CQ Dra, are more strongly interacting with an outburst history. We have studied these systems during their quiescence in order to shed light on the nature of their hot components by fitting their archival far ultraviolet spectra with optically thick accretion disk models and NLTE model white dwarf photospheres. Using the critical advantage offered by extending wavelength coverage down to the Lyman Limit with FUSE spectra, we find that the hot component in RW Hya is a low mass white dwarf with a surface temperature of 160,000K while the symbiotic system CQ Dra is a triple system with a red giant transferring matter to a hot component made up of a cataclysmic variable whose white dwarf has a surface temperature of $\sim$50,000K. Implications are discussed.

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arXiv2017

FUSE Spectroscopy of the Accreting Hot Components in Symbiotic Variables

We have conducted a spectroscopic analysis of the far ultraviolet archival spectra of four symbiotic variables, EG And, AE Ara, CQ Dra and RW Hya. RW Hya and EG And have never had a recorded outburst while CQ Dra and AE Ara have outburst histories. We analyze these systems while they are in quiescence in order to help reveal the physical properties of their hot components via comparisons of the observations with optically thick accretion disk models and NLTE model white dwarf photospheres. We have extended the wavelength coverage down to the Lyman Limit with FUSE spectra. We find that the hot component in RW Hya is a low mass white dwarf with a surface temperature of 160,000K. We re-examine whether or not the symbiotic system CQ Dra is a triple system with a red giant transferring matter to a hot component made up of a cataclysmic variable in which the white dwarf has a surface temperature as low as $\sim$20,000K. The very small size of the hot component contributing to the shortest wavelengths of the FUSE spectrum of CQ Dra agrees with an optically thick and geometrically thin ($\sim$4\% of the WD surface) hot ($\sim 120,000$K) boundary layer. Our analysis of EG And reveals that its hot component is a hot, bare, low mass white dwarf with a surface temperature of 80-95,000K, with a surface gravity $\log(g)= 7.5$. For AE Ara, we also find that a low gravity ($\log(g) \sim 6$) hot ($T \sim 130,000$K) WD accounts for the hot component.

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