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Register a new userSpectroscopic and Photometric Observations of Dwarf Nova Superoutbursts by the 3.8 m Telescope Seimei and the Variable Star Network
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We present spectroscopic and photometric observations of 17 dwarf-nova superoutbursts obtained by KOOLS-IFU mounted on the 3.8 m telescope Seimei at Okayama Observatory of Kyoto University and through VSNET collaboration. Our spectroscopic observations for six outbursts were performed within 1 d from their optical peak. 11 objects (TCP J00590972+3438357. ASASSN-19ado, TCP J06073081-0101501, ZTF20aavnpug, ASASSN-19ady, MASTER OT J061642.05+435617.9, TCP J20034647+1335125, ASASSN-20kv, ASASSN-20kw, MASTER OT J213908.79+161240.2, and ASASSN-20mf) were previously unknown systems, and our observations enabled quick classification of their transient type. These results illustrate that Seimei telescope has the capability to conduct quick follow-up observations of unknown transients. Our photometric observations yielded that 11 objects are WZ Sge-type dwarf novae and their candidates, and the other six objects are SU UMa-type dwarf novae and their candidates. The He II 4686AA~ emission line was clearly detected among ASASSN-19ado, TCP J06073081-0101501 and MASTER OT J213908.79+161240.2, whose association with a spiral arm structure in an accretion disk has been suggested in the previous studies. Our result suggests that a higher-inclination system shows a stronger emission line of He II 4686AA, as well as larger-amplitude early superhumps.
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We report our photometric and spectroscopic follow-up observations of the superoutbursts of three dwarf novae (GWAC,180415A, GWAC,181017A and GWAC,181211A) identified independently by the Ground Wide-angle Cameras system, one of the ground-based instruments of the China-France SVOM mission. Based on a combination of our photometry and that taken from the AAVSO, our period analysis of the superhumps enables us to determine the mass ratios to be 0.0967-0.1163, 0.1879-0.1883 and 0.0981-0.1173 for GWAC,180415A, GWAC,181017A and GWAC,181211A, respectively. GWAC,180415A can be firmly identified as a WZ sge-type dwarf novae due to its long duration ($sim2$ weeks) multiple rebrightenings with amplitudes of 3-4 magnitudes, the early superhump associated with a double-wave modulation and the low mass ratio. The inferred low mass ratio and location in the $varepsilon-P_{mathrm{orb}}$ diagram suggest that GWAC,181211A is a WZ sge-type dwarf novae candidate. The measured Balmer decrements suggest the Balmer line emission is produced from an optical thick region in GWAC,180415A and GWAC,181017A, and from an optical thin region in GWAC,181211A.
We report multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with Seimei Telescope (6150--7930 {AA}), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700--7500 {AA}), NICER (Neutron Star Interior Composition Explorer; 0.2--12.0 keV), and collaborations of OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total which include ten H$alpha$, four X-ray, and four optical-continuum flares; one of them is a superflare with the total energy of $sim$ 2.0$times$10$^{33}$ erg. We found that (1) during the superflare, the H$alpha$ emission line full width at 1/8 maximum dramatically increases to 14 {AA} from 8 {AA} in the low-resolution spectra (R$sim$ 2000) accompanied with the large white-light flares, (2) some weak H$alpha$/X-ray flares are not accompanied with white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and H$alpha$ intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed by using the RADYN code. As a result of simulations, we found the simulated H$alpha$ line profiles with hard and high-energy non-thermal electron beams are consistent with that of the initial phase line profiles of the superflares, while those with more soft- and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we found that the relation between optical continuum and H$alpha$ intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares.
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 special spectral features worthy of further observations are also noted and discussed. We present a LAMOST spectral atlas of outbursting dwarf novae. 6 objects have the first outburst spectra, and the others were also compared with the published outburst spectra. We argue that these data will be useful for further investigation of the accretion disc properties. The HeII $lambda$4686 emission line can be found in the outburst spectra of seven dwarf novae. These objects are excellent candidates for probing the spiral asymmetries of accretion disc.
We present photometric and spectroscopic follow-up observations of short-period variables discovered in the OmegaWhite survey: a wide-field high-cadence g-band synoptic survey targeting the Galactic Plane. We have used fast photometry on the SAAO 1.0-m and 1.9-m telescopes to obtain light curves of 27 variables, and use these results to validate the period and amplitude estimates from the OmegaWhite processing pipeline. Furthermore, 57 sources (44 unique, 13 also with new light curves) were selected for spectroscopic follow-up using either the SAAO 1.9-m telescope or the Southern African Large Telescope. We find many of these variables have spectra which are consistent with being delta Scuti type pulsating stars. At higher amplitudes, we detect four possible pulsating white dwarf/subdwarf sources and an eclipsing cataclysmic variable. Due to their rarity, these targets are ideal candidates for detailed follow-up studies. From spectroscopy, we confirm the symbiotic binary star nature of two variables identified as such in the SIMBAD database. We also report what could possibly be the first detection of the `Bump Cepheid phenomena in a delta Scuti star, with OW J175848.21-271653.7 showing a pronounced 22% amplitude dip lasting 3 minutes during each pulsational cycle peak. However, the precise nature of this target is still uncertain as it exhibits the spectral features of a B-type star.
We report observations of the flickering variability of the dwarf nova RX And in five bands (UBVRI) on two nights. On 25 October 2019 the brightness of the star was $Bapprox 13.9$ mag, the amplitude of the flickering was 0.47 mag, and we estimate for the flickering source temperature $T_{fl} = 10700 pm 400$ K, and radius $R_{fl} =0.046 pm 0.004$ $R_odot$. On 2 January 2020, the star was about 3 magnitudes brighter ($B approx 10.7$), the amplitude of the flickering was significantly lower (0.07 mag) and we derive for the flickering source $T_{fl} = 9600 pm 700$ K, and radius $R_{fl} = 0.098 pm 0.009$ $R_odot$. The results indicate that 3 magnitudes brightening of the star doubled the radius of the flickering source. The data are available upon request from the authors.
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