We present phase-resolved optical spectroscopy of the eclipsing nova-like cataclysmic variable EC21178-5417 obtained between 2002 and 2013. The average spectrum of EC21178-5417 shows broad double-peaked emission lines from HeII 4686 Å (strongest feature) and the Balmer series. The high-excitation feature, CIII/NIII at 4640-4650 Å, is also present and appears broad in emission. A number of other lines, mostly HeI, are clearly present in absorption and/or emission. The average spectrum of EC21178-5417 taken at different months and years shows variability in spectral features, especially in the Balmer lines beyond H$γ$, from pure line emission, mixed line absorption and emission to pure absorption lines. Doppler maps of the HeII 4686 Å emission reveal the presence of a highly-inclined asymmetric accretion disc and a two spiral arm-like structure, whereas that of the Balmer lines (H$α$ and H$β$) reveal a more circular accretion disc. There is no evidence of a bright spot in the Doppler maps of EC21178-5417 and no emission from the secondary star is seen in the tomograms of the HeII 4686 Å and Balmer lines. Generally, the emission in EC21178-5417 is dominated by emission from the accretion disc. We conclude that EC21178-5417 is a member of the RW Tri or UX UMa sub-type of nova-like variables based on these results and because it shows different spectral characteristics at different dates. This spectral behaviour suggests that EC21178-5417 undergoes distinct variations in mass transfer rate on the observed time scales of months and years.
Cataclysmic variable SDSS J143317.78+101123.3 with P=0.054241 d (78.1-min) was suspected to be a possible dwarf nova of WZ Sge type with the sub-stellar donor, but without detected outbursts so far. Checking the newly available data from ATLAS survey has revealed the outburst by at least 6 magnitudes in September 2020, thus confirming the dwarf nova nature of this object with the brown dwarf secondary. Other projects and individual observers have stopped their monitoring of this target several days before the outburst. This finding strengthens the value of observing the twilight zone by the pr…
We observed the deeply eclipsing SU UMa-type dwarf nova V4140 Sgr and established the very short supercycle of 69.7(3) d. There were several short outbursts between superoutbursts. These values, together with the short orbital period (0.06143 d), were similar to, but not as extreme as, those of ER UMa-type dwarf novae. The object is thus the first, long sought, eclipsing ER UMa-like object. This ER UMa-like nature can naturally explain the high (apparent) quiescent viscosity and unusual temperature profile in quiescence, which were claimed observational features against the thermal-tidal insta…
We present an extensive Doppler tomography study of the eclipsing novalike 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 novalikes 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.
SRGA J115215.0$-$510656: an unusual long-period eclipsing dwarf nova with disc wind signatures
South African Astronomical Observatory（南非天文台）；University of Cape Town（开普敦大学）；University of the Free State（自由州大学）；Dartmouth College（达特茅斯学院）；University of Southampton（南安普顿大学）；University of Johannesburg（约翰内斯堡大学）；Inter-University Centre for Astronomy and Astrophysics (IUCAA)（天文学与天体物理跨大学中心）
We report the analysis of time-series of infrared $JHK_s$ photometry of the dwarf nova V2051 Oph in quiescence with eclipse mapping techniques to investigate structures and the spectrum of its accretion disc. The light curves after removal of the ellipsoidal variations caused by the mass-donor star show a double-wave modulation signalling the presence of two asymmetric light sources in the accretion disc. Eclipse maps reveal two spiral arms on top of the disc emission, one at $R_1= 0.28\pm 0.02 \,R_\mathrm{L1}$ and the other at $R_2= 0.42\pm 0.02 \,R_\mathrm{L1}$ (where $R_\mathrm{L1}$ is the …
Purely photometric models can be used to determine the binary parameters of eclipsing cataclysmic variables with a high degree of precision. However, the photometric method relies on a number of assumptions, and to date there have been very few independent checks of this method in the literature. We present time-resolved spectroscopy of the P=90.9 min eclipsing cataclysmic variable OY Carinae obtained with X-shooter on the VLT, in which we detect the donor star from K I lines in the J-band. We measure the radial velocity amplitude of the donor star K2 = 470.0 +/- 2.7 km/s, consistent with pred…
Long-term Orbital Period Variations of the Eclipsing Dwarf Nova HT Cas
Atatürk University（阿塔图尔克大学）；Türkiye National Observatories, TUG（土耳其国家天文台）；Istanbul University（伊斯坦布尔大学）；National Research Institute of Astronomy and Geophysics (NRIAG)（国家天文地球物理研究所）；Adiyaman University（阿德亚曼大学）
We present results from a study of TESS observations of the eclipsing dwarf nova system Z Cha, covering both an outburst and a superoutburst. We discover that Z Cha undergoes hysteretic loops in eclipse depth - out-of-eclipse flux space in both the outburst and the superoutburst. The direction that these loops are executed in indicates that the disk size increases during an outburst before the mass transfer rate through the disk increases, placing constraints on the physics behind the triggering of outbursts and superoutbursts. By fitting the signature of the superhump period in a flux-phase d…
HS 2325+8205 is a long-period eclipsing dwarf nova with an orbital period above the period gap (Porb>3 h) and is reported to be a Z Cam-type dwarf nova. Based on the photometry of the Transiting Exoplanet Survey Satellite (TESS), the light variation and the quasi-periodic oscillation (QPOs) of HS 2325+8205 are studied. Using Continuous Wavelet Transform (CWT), Lomb-Scargle Periodogram (LSP), and sine fitting methods, we find for the first time that there is a QPOs of ~ 2160s in the long outburst top light curves of HS 2325+8205. Moreover, we find that the oscillation intensity of the QPOs of H…
We present a study of the orbital light curves of the recurrent nova IM Normae since its 2002 outburst. The broad "eclipses" recur with a 2.46 hour period, which increases on a timescale of 1.28(16)x10^6 years. Under the assumption of conservative mass-transfer, this suggests a rate near 10^-7 M_sol/year, and this agrees with the estimated /accretion/ rate of the postnova, based on our estimate of luminosity. IM Nor appears to be a close match to the famous recurrent nova T Pyxidis. Both stars appear to have very high accretion rates, sufficient to drive the recurrent-nova events. Both have qu…
IPHAS J190812.63+045728.1: A deeply eclipsing, X-ray bright cataclysmic variable with frequent outbursts
Universidade Federal de Sergipe（塞尔希培联邦大学）；Observatório Nacional（国家天文台）；Laboratório Nacional de Astrofísica（国家天体物理实验室）；NASA/GSFC（美国宇航局戈达德太空飞行中心）；University of Maryland, Baltimore County（马里兰大学巴尔的摩县分校）；Instituto Nacional de Pesquisas Espaciais（国家空间研究所）
Spectra of 76 known dwarf novae from the LAMOST survey were presented. Most of the objects were observed in quiescence, and about 16 systems have typical outburst spectra. 36 of these systems were observed by SDSS, and most of their spectra are similar to the SDSS spectra. 2 objects, V367 Peg and V537 Peg, are the first to observe their spectra. The spectrum of V367 Peg shows a contribution from a M-type donor and its spectral type could be estimated as M3-5 by combining its orbital period. The signature of white dwarf spectrum can be seen clearly in four low-accretion-rate WZ Sge stars. Other…
Very fast novae are novae which evolve exceptionally quickly (on timescales of only days). Due to their rapid evolution, very fast novae are challenging to detect and study, especially at early times. Here we report the discovery, which was made as part of our Transient UV Objects project, of a probable very fast nova in the nearby spiral galaxy NGC 300. We detected the rise to the peak (which is rarely observed for very fast novae) in the near-ultraviolet (NUV), with the first detection just ~2 hours after the eruption started. The peak and early stages of the decay were also observed in UV a…
We present a comprehensive review of all observations of the eclipsing recurrent Nova LMC 1968 in the Large Magellanic Cloud which was previously observed in eruption in 1968, 1990, 2002, 2010, and most recently in 2016. We derive a probable recurrence time of $6.2 \pm 1.2$ years and provide the ephemerides of the eclipse. In the ultraviolet-optical-IR photometry the light curve shows high variability right from the first observation around two days after eruption. Therefore no colour changes can be substantiated. Outburst spectra from 2016 and 1990 are very similar and are dominated by H and …
