scholarly journals Voracious vortices in cataclysmic variables

2020 ◽  
Vol 642 ◽  
pp. A100
Author(s):  
V. V. Neustroev ◽  
S. V. Zharikov
Keyword(s):  
Cataclysmic Variables ◽  
Accretion Disc ◽  
Emission Lines ◽  
Quiescent State ◽  
Doppler Tomography ◽  
Time Resolved ◽  
Balmer Lines ◽  
Cool Gas ◽  
The Right ◽  
Three Body

Context. In Paper I we showed that the accretion disc radius of the dwarf nova HT Cas in its quiescent state has not changed significantly during many years of observations. It has remained consistently large, close to the tidal truncation radius. This result is inconsistent with the modern understanding of the evolution of the disc radius through an outburst cycle. Aims. Spectroscopic observations of HT Cas during its superoutburst offered us an exceptional opportunity to compare the properties of the disc of this object in superoutburst and in quiescence. Methods. We obtained a new set of time-resolved spectra of HT Cas in the middle of its 2017 superoutburst. We used Doppler tomography to map emission structures in the system, which we compared with those detected during the quiescent state. We used solutions of the restricted three-body problem to discuss again the location of emission structures and the disc size of HT Cas in quiescence. Results. The superoutburst spectrum is similar in appearance to the quiescent spectra, although the strength of most of the emission lines decreased. However, the high-excitation lines significantly strengthened in comparison with the Balmer lines. Many lines show a mix of broad emission and narrow absorption components. Hα in superoutburst was much narrower than in quiescence. Other emission lines have also narrowed in outburst, but they did not become as narrow as Hα. Doppler maps of Hα in quiescence and of the Hβ and He I lines in outburst are dominated by a bright emission arc at the right side of the tomograms, which is located at and even beyond the theoretical truncation limit. However, the bulk of the Hα emission in outburst has significantly lower velocities. Conclusions. We show that the accretion disc radius of HT Cas during its superoutburst has become hot but remained the same size as it was in quiescence. Instead, we detected cool gas beyond the Roche lobe of the white dwarf that may have been expelled from the hot disc during the superoutburst.

scholarly journals The tidal disruption event AT 2018hyz – I. Double-peaked emission lines and a flat Balmer decrement

2020 ◽  
Vol 498 (3) ◽  
pp. 4119-4133 ◽  
Author(s):  
P Short ◽  
M Nicholl ◽  
A Lawrence ◽  
S Gomez ◽  
I Arcavi ◽  
...  
Keyword(s):  
Cataclysmic Variables ◽  
Absolute Magnitude ◽  
Emission Lines ◽  
Late Time ◽  
Tidal Disruption ◽  
Broad Emission ◽  
Balmer Lines ◽  
High Cadence ◽  
Balmer Decrement

ABSTRACT We present results from spectroscopic observations of AT 2018hyz, a transient discovered by the All-Sky Automated Survey for Supernova survey at an absolute magnitude of MV ∼ −20.2 mag, in the nucleus of a quiescent galaxy with strong Balmer absorption lines. AT 2018hyz shows a blue spectral continuum and broad emission lines, consistent with previous TDE candidates. High cadence follow-up spectra show broad Balmer lines and He i in early spectra, with He ii making an appearance after ∼70–100 d. The Balmer lines evolve from a smooth broad profile, through a boxy, asymmetric double-peaked phase consistent with accretion disc emission, and back to smooth at late times. The Balmer lines are unlike typical active galactic nucleus in that they show a flat Balmer decrement (Hα/Hβ ∼ 1.5), suggesting the lines are collisionally excited rather than being produced via photoionization. The flat Balmer decrement together with the complex profiles suggests that the emission lines originate in a disc chromosphere, analogous to those seen in cataclysmic variables. The low optical depth of material due to a possible partial disruption may be what allows us to observe these double-peaked, collisionally excited lines. The late appearance of He ii may be due to an expanding photosphere or outflow, or late-time shocks in debris collisions.

scholarly journals Cataclysmic Variables, Hubble-Sandage Variables and η Carinae

1980 ◽  
Vol 88 ◽  
pp. 155-160
Author(s):  
G. T. Bath
Keyword(s):  
Cataclysmic Variables ◽  
Emission Lines ◽  
Quiescent State ◽  
High Luminosity ◽  
Dwarf Novae ◽  
Blue Colour ◽  
External Galaxies ◽  
Distance Indicators ◽  
Colour Indices

The Hubble-Sandage variables are the most luminous stars in external galaxies. They were first investigated by Hubble and Sandage (1953) for use as distance indicators. Their main characteristics are high luminosity, blue colour indices, and irregular variability. Spectroscopically they show hydrogen and helium in emission with occasionally weaker Fell and [Fell], and no Balmer jump (Humphreys 1975, 1978). In this respect they closely resemble cataclysmic variables, particularly dwarf novae. In the quiescent state dwarf novae show broad H and HeI, together with a strong UV continuum. Weak FeII in emission has been observed in U Gem and SS Aur (Warner 1976). The Balmer jump is either not present, or weakly in emission. The principal spectroscopic difference is the increased breadth of the occasionally doubled emission lines.

scholarly journals The hydrogen Balmer lines and jump in absorption in accretion disc modelling – an ultraviolet–optical spectral analysis of the dwarf novae UZ Serpentis and CY Lyrae

2020 ◽  
Vol 494 (4) ◽  
pp. 5244-5258
Author(s):  
Patrick Godon ◽  
Edward M Sion ◽  
Paula Szkody ◽  
William P Blair
Keyword(s):  
Spectral Analysis ◽  
Accretion Rate ◽  
Cataclysmic Variables ◽  
Outer Radius ◽  
Accretion Disc ◽  
Absorption Lines ◽  
Dwarf Novae ◽  
Balmer Lines ◽  
Flux Level ◽  
The Continuum

ABSTRACT 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 (DNe): 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 $\dot{M} \approx 8 \times 10^{-9}\,\mathrm{ M}_\odot\,\mathrm{ yr}^{-1}$ in outburst, and $\dot{M} \approx 2-3 \times 10^{-9}\,\mathrm{ M}_\odot\,\mathrm{ yr}^{-1}$ for the rise and decline phases. The outer disc radius we derive is smaller than expected (Rdisc ≈ 0.2a, where a is the binary separation), except during late rise (for CY Lyr) where Rdisc = 0.3a. UZ Ser also reveals a 60 000 K white dwarf. These results show that during a DN 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 DN 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 modelling of CVs.

scholarly journals Uncovering Flickering in Time-Resolved Spectroscopy for the Nova-like Variable UX Ursa Majoris

1997 ◽  
Vol 163 ◽  
pp. 834-834
Author(s):  
James C. White
Keyword(s):  
Cataclysmic Variables ◽  
Doppler Tomography ◽  
Time Resolved ◽  
Strong Emission ◽  
Secondary Star ◽  
Emission Component ◽  
Early Results ◽  
Usual Location ◽  
Spectroscopic Signatures ◽  
Tomographic Analysis

AbstractThe flickering phenomenon in cataclysmic variables (CVs) is manifest photometrically as variations in system brightness with amplitudes up to about 1 mag and on timescales from seconds to tens of minutes. Although a pronounced characteristic of CVs, flickering has been studied, in general, only tangentially and in the context of overall CV photometric properties. It is usually uncovered in CV photometry, yet my Doppler tomographic analysis of data collected on the KPNO 2.1-meter telescope in 1982 by Schlegel, Honeycutt, and Kaitchuck (1983) for the nova-like variable UX Ursa Majoris suggests that flickering also exists in this system’s spectroscopy.Using the integrated continuum flux from the UX UMa observations and Bruch’s (1992) methodology for classifying high- and low-flicker data, I constructed two data subsets corresponding to high- and low-flicker states. I generated Doppler tomograms of these high- and low-flicker states and interpret differences between the tomograms as spectroscopic signatures of flickering in the system.In UX UMa’s Hβ Doppler tomograms, a small, faint, incomplete ring of emission is visible for both flickering states. Dominating ring emission is strong emission in the (+Vx,+Vy) quadrant. The usual location for Swave emission, in the (−Vx,+Vy) quadrant, is here the region of faintest emission. Differenced Doppler tomograms, produced by subtracting from the tomograms the symmetric ring-emission component, show clear differences between the high- and low-flicker states. Further, these early results suggest Doppler tomography may be a useful technique for studying the secondary stars in CVs imaged in this manner. Enhanced chromospheric activity of the red dwarf companion is clearly visible in the high-flickering state tomogram at (0, Krd) and may, therefore, afford investigators the opportunity to estimate the chromospheric flux and radial velocity of the secondary star.

scholarly journals Analysis of spiral structure in the accretion disc of the nova-like cataclysmic variable EC21178–5417

2019 ◽  
Vol 491 (1) ◽  
pp. 344-355 ◽  
Author(s):  
R Ruiz-Carmona ◽  
Z N Khangale ◽  
P A Woudt ◽  
P J Groot
Keyword(s):  
Spiral Structure ◽  
Relative Strength ◽  
Accretion Disc ◽  
Spectral Lines ◽  
Emission Lines ◽  
Spiral Pattern ◽  
Double Peak ◽  
Doppler Tomography ◽  
Peak Emission ◽  
Armed Spiral

ABSTRACT We present an extensive Doppler tomography study of the eclipsing nova-like EC21178–5417, which exhibits the classic accretion disc signature in the form of double-peak emission lines in its spectrum. Doppler tomograms confirm the presence of a strong, two-armed spiral pattern visible in the majority of the spectral lines studied. This makes EC21178–5417 one of the very few nova-likes that show spiral structure in their discs. We also report night-to-night changes in the position and relative strength of the spiral arms, revealing fluctuations on the conditions in the accretion disc.

scholarly journals Catching VY Sculptoris in a low state

2018 ◽  
Vol 617 ◽  
pp. A16 ◽  
Author(s):  
L. Schmidtobreick ◽  
E. Mason ◽  
S. B. Howell ◽  
K. S. Long ◽  
A. F. Pala ◽  
...  
Keyword(s):  
White Dwarf ◽  
Cataclysmic Variables ◽  
Emission Lines ◽  
High Mass ◽  
Absorption Bands ◽  
Radial Velocity Curve ◽  
Time Resolved ◽  
Time Resolved Spectroscopy ◽  
Secondary Star ◽  
Narrow Emission

Context. In the context of a large campaign to determine the system parameters of high mass transfer cataclysmic variables, we found VY Scl in a low state in 2008. Aims. Making use of this low state, we study the stellar components of the binary with little influence of the normally dominating accretion disc. Methods. Time-resolved spectroscopy and photometry of VY Scl taken during the low state are presented. We analysed the lightcurve and radial velocity curve and use time-resolved spectroscopy to calculate Doppler maps of the dominant emission lines. Results. The spectra show narrow emission lines of Hα, Hβ, He I, Na I D, and Fe II, as well as faint TiO absorption bands that trace the motion of the irradiated secondary star, and Hα and He I emission line wings that trace the motion of the white dwarf. From these radial velocities, we find an orbital period of 3.84 h, and put constraints on binary parameters such as the mass ratio M2/M1 of 0.43 and the inclination of 15°. With a secondary’s mass between 0.3 and 0.35 M⊙, we derive the mass for the white dwarf as M1 = 0.6–1.1 M⊙.

scholarly journals Predicting the broad-lines polarization emitted by supermassive binary black holes

2019 ◽  
Vol 623 ◽  
pp. A56 ◽  
Author(s):  
D. Savić ◽  
F. Marin ◽  
L. Č. Popović
Keyword(s):  
Black Holes ◽  
Emission Lines ◽  
Polarization Angle ◽  
Broad Line ◽  
Line Profiles ◽  
Binary Black Holes ◽  
True Nature ◽  
Line Shapes ◽  
Highly Sensitive ◽  
Balmer Lines

Context. Some Type-1 active galactic nuclei (AGN) show extremely asymmetric Balmer lines with the broad peak redshifted or blueshifted by thousands of km s−1. These AGN may be good candidates for supermassive binary black holes (SMBBHs). The complex line shapes can be due to the complex kinematics of the two broad line regions (BLRs). Therefore other methods should be applied to confirm the SMBBHs. One of them is spectropolarimetry. Aims. We rely on numerical modeling of the polarimetry of binary black holes systems, since polarimetry is highly sensitive to geometry, in order to find the specific influence of supermassive binary black hole (SMBBH) geometry and dynamics on polarized parameters across the broad line profiles. We apply our method to SMBBHs in which both components are assumed to be AGN with distances at the subparsec scale. Methods. We used a Monte Carlo radiative transfer code that simulates the geometry, dynamics, and emission pattern of a binary system where two black holes are getting increasingly close. Each gravitational well is accompanied by its own BLR and the whole system is surrounded by an accretion flow from the distant torus. We examined the emission line deformation and predicted the associated polarization that could be observed. Results. We modeled scattering-induced broad line polarization for various BLR geometries with complex kinematics. We find that the presence of SMBBHs can produce complex polarization angle profiles φ and strongly affect the polarized and unpolarized line profiles. Depending on the phase of the SMBBH, the resulting double-peaked emission lines either show red or blue peak dominance, or both the peaks can have the same intensity. In some cases, the whole line profile appears as a single Gaussian line, hiding the true nature of the source. Conclusions. Our results suggest that future observation with the high resolution spectropolarimetry of optical broad emission lines could play an important role in detecting subparsec SMBBHs.

scholarly journals Spectrophotometry of Supernovae

1974 ◽  
Vol 3 ◽  
pp. 533-544
Author(s):  
R. P. Kirshner
Keyword(s):  
Emission Lines ◽  
Absorption Lines ◽  
Spectral Energy ◽  
Line Profiles ◽  
Energy Distributions ◽  
Maximum Light ◽  
Balmer Lines ◽  
B Lines ◽  
Infrared Triplet ◽  
The Continuum

AbstractAbsolute spectral energy distributions for supernovae of both types I and II have been obtained. These observations demonstrate three facets of supernova spectra. First, both SN I’s and SN II’s have a continuum that varies slowly and uniformly with time, and which carries the bulk of the radiated flux at early epochs. Second, some lines in both SN I’s and SN II’s have P Cygni profiles: broad emissions flanked on their violet edges by broad absorptions. Third, some lines are common to SN I’s and SN II’s and persist throughout the evolution of the spectrum. The continuum temperatures for both SN I’s and SN II’s are about 10000 K at the earliest times of observation and drop in one month’s time to about 6000 K for SN II’s and about 7000 K for SN I’s. After several months, the continuum may cease to carry the bulk of the flux, which might be in emission lines, but continues to exist, as shown by the presence of absorption lines. The P Cygni line profiles indicate expansion velocities of 15000 km s-1 in SN II’s and 20000 km s-11 in the SN I 1972e in NGC 5253. Line identifications for SN II’s include Hα, Hβ, H and K of Ca II, the Ca II infrared triplet at λ8600, the Na I D-lines, the Mg I b-lines at λ5174, and perhaps Fe II. The [O I] lines λλ6300, 6363 and [Ca II] lines λλ7291, 7323 appear after eight months. For SN I’s, the lines identified are H and K of Ca II, the infrared Ca II lines, the Na I D-lines, and the Mg I b-lines. There is some evidence that Balmer lines are present two weeks after maximum. The strong and puzzling λ4600 features drifts with time from λ4600 near maximum light to λ4750 after 400 days.

scholarly journals X-Ray Emission from Flare Stars

1983 ◽  
Vol 71 ◽  
pp. 125-129
Author(s):  
P.C. Agrawal ◽  
A.R. Rao ◽  
B.V. Sreekantan
Keyword(s):  
Emission Lines ◽  
Quiescent State ◽  
X Ray ◽  
Uv Emission ◽  
Chromospheric Emission ◽  
Flare Stars ◽  
Einstein Observatory

Flare stars are a group of mostly dMe stars, which show intense flaring activity in the optical as well as in the radio and X-ray bands. These stars are characterized by the presence of chromospheric emission lines like % and Call H and K which are present even during the quiescent state. The presence of transition regions and coronae have been inferred from the detection of UV emission lines like NV, CIV, SiIV etc. with IUE and X-ray observations made with the Einstein Observatory. We report here X-ray observations of flare stars made with Einstein to measure their coronal X-ray emission during the quiescent state.

scholarly journals Interacting Binaries as Be Stars

1987 ◽  
Vol 92 ◽  
pp. 451-455
Author(s):  
Mirek J. Plavec
Keyword(s):  
Spectral Type ◽  
Binary Stars ◽  
Emission Lines ◽  
Close Binary ◽  
High Electron ◽  
Be Stars ◽  
Close Binary Stars ◽  
High Ionization ◽  
Mass Outflow ◽  
Balmer Lines

AbstractSemidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.

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