EX draconis: using eclipses to separate outside-in and inside-out outbursts

Court, James; Scaringi, Simone; Segura, N. Castro; Long, Knox S.; Maccarone, Thomas J.; Altamirano, D.; Degenaar, N.; Wijnands, Rudy; Shahbaz, T.; Zhan, Zhuchang

doi:10.1093/mnras/staa1042

Cited by 8 publications

(2 citation statements)

References 38 publications

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“…With a steady supply of mass, the inner part of the accretion disk of IW And-type stars can stay in a hot state in both quasi-standstill and brightening phases. Once the mass threshold has been achieved in the outer disk, brightening could occur from inside to outside of the disk, known as insideout brightening (Court et al 2020;Kimura et al 2020a). The brightening event, in fact, shows up in the light curve (for example, see Figure 3 at JD 2,458,565).…”

Section: Photometric Characteristicsmentioning

confidence: 99%

HO Puppis: Not a Be Star, but a Newly Confirmed IW And-type Star

Lee

et al. 2021

ApJ

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HO Puppis (HO Pup) was considered as a Be-star candidate based on its γ Cassiopeiae-type light curve, but lacked spectroscopic confirmation. Using distance measured from Gaia Data Release 2 and the spectral-energydistribution fit on broadband photometry, the Be-star nature of HO Pup is ruled out. Furthermore, based on the 28,700 photometric data points collected from various time-domain surveys and dedicated intensive-monitoring observations, the light curves of HO Pup closely resemble those of IW And-type stars (as pointed out by Kimura et al.), exhibiting characteristics such as a quasi-standstill phase, brightening, and dips. The light curve of HO Pup displays various variability timescales, including brightening cycles ranging from 23 to 61 days, variations with periods between 3.9 days and 50 minutes during the quasi-standstill phase, and a semiregular ∼14 day period for the dip events. We have also collected time-series spectra (with various spectral resolutions), in which Balmer emission lines and other spectral lines expected for an IW And-type star were detected (even though some of these lines were also expected to be present for Be stars). We detect Bowen fluorescence near the brightening phase, and that can be used to discriminate between IW And-type stars and Be stars. Finally, despite only observing for four nights, the polarization variation was detected, indicating that HO Pup has significant intrinsic polarization.

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Section: Photometric Characteristicsmentioning

confidence: 99%

HO Puppis: Not a Be Star, but a Newly Confirmed IW And-type Star

Lee

et al. 2021

ApJ

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“…NSHs have been observed during both DN outbursts and quiescence (e.g., V503 Cyg, Harvey et al 1995;ER UMa, Ohshima et al 2012;BK Lyn, Kato et al 2013;V1504 Cyg, Ohshima et al 2014V344 Lyr, Wood et al 2011;SDSS J210014.12+004446.0, Olech et al 2009;NY Her, Pavlenko et al 2021). However, Ramsay et al (2017) and Court et al (2020) studied Z Cam-type DNe V729 Sgr and EX Dra and both found NSHs only in quiescence and not during outbursts, demonstrating that there is no consensus on the existence of NSHs during DN outbursts. Our recent work found that the NSHs in the Z Cam-type DN AH Her change as the outburst progresses (Sun et al 2023a).…”

Section: Introductionmentioning

confidence: 99%

Nine New Cataclysmic Variable Stars with Negative Superhumps

Sun,

Qian,

Zhu

et al. 2024

ApJ

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Negative superhumps (NSHs) are signals a few percent shorter than the orbital period of a binary star and are considered to originate from the reverse precession of the tilted disk. Based on TESS photometry, we find nine new cataclysmic variable stars with NSHs. Three (ASAS J1420, TZ Per, and V392 Hya) of these stars similar to AH Her still have NSHs during dwarf nova outbursts, and the NSH amplitude varies with the outburst. The variation in the radius of the accretion disk partially explains this phenomenon. However, it does not explain the rebound of the NSH amplitude after the peak of the outburst and the fact that the NSH amplitude of the quiescence is sometimes not the largest, and it is necessary to include the disk instability model (DIM) and add other ingredients. Therefore, we suggest that the variation of NSH amplitude with outburst can be an important basis for studying the origin of NSHs and improving the DIM. The six (ASASSN-V J1137, ASASSN-V J0611, 2MASS J0715, LAMOST J0925, ASASSN-17qj, and ZTF 18acakuxo) remaining stars have been poorly studied, and for the first time we determine their orbital periods, NSHs, and superorbital signal (SOR) periods. The NSH periods and amplitudes of ASASSN-V J1137 and ASASSN-17qj vary with the SOR, and based on the comparison of the observations with the theory, we suggest that a single change in tilted disk angle does not explain the observations of the SOR and that other ingredients need to be considered as well.

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On the nature of the anomalous event in 2021 in the dwarf nova SS Cygni and its multi-wavelength transition

Kimura

Yamada

Nakaniwa

et al. 2021

Publications of the Astronomical Society of Japan

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SS Cyg has long been recognized as the prototype of a group of dwarf novae that show only outbursts. However, this object has entered a quite anomalous event in 2021, which at first appeared to be standstill, i.e., an almost constant luminosity state observed in Z Cam-type dwarf novae. This unexpected event gives us a great opportunity to reconsider the nature of standstill in cataclysmic variables. We have observed this anomalous event and its forerunner, a gradual and simultaneous increase in the optical and X-ray flux during quiescence, through many optical telescopes and the X-ray telescopes NICER and NuSTAR. We have not found any amplification of the orbital hump during quiescence before the anomalous event, which suggests that the mass transfer rate did not significantly fluctuate on average. The estimated X-ray flux was not enough to explain the increment of the optical flux during quiescence via X-ray irradiation of the disk and the secondary star. It would be natural to consider that viscosity in the quiescent disk was enhanced before the anomalous event, which increased mass accretion rates in the disk and raised not only the optical flux but also the X-ray flux. We suggest that enhanced viscosity also triggered the standstill-like phenomenon in SS Cyg, which is considered to be a series of small outbursts. The inner part of the disk would always stay in the outburst state and only its outer part would be unstable against the thermal–viscous instability during this phenomenon, which is consistent with the observed optical color variations. This scenario is in line with our X-ray spectral analyses which imply that the X-ray-emitting inner accretion flow became hotter than usual and vertically expanded, and that it became denser and was cooled down after the onset of the standstill-like state.

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EX draconis: using eclipses to separate outside-in and inside-out outbursts

Cited by 8 publications

References 38 publications

HO Puppis: Not a Be Star, but a Newly Confirmed IW And-type Star

HO Puppis: Not a Be Star, but a Newly Confirmed IW And-type Star

Nine New Cataclysmic Variable Stars with Negative Superhumps

On the nature of the anomalous event in 2021 in the dwarf nova SS Cygni and its multi-wavelength transition

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