Discovery of optical flickering from the symbiotic star EF Aquilae

Zamanov, R.; Boeva, S.; Nikolov, Y.; Petrov, Blagovest; Bachev, R.; Latev, G.; Popov, V.; Stoyanov, K. A.; Bode, M. F.; Martı́, Josep; Tomov, T.; Antonova, A.

doi:10.1002/asna.201713362

Cited by 15 publications

(18 citation statements)

References 44 publications

(58 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our modeling of NuSTAR and other datasets therefore strongly suggest that the X-ray emission in RT Cru originates in the accretion disk boundary layer around a non-magnetic WD. The strong flickering detected (see Section 3.3) in X-rays and UV is also a feature that RT Cru shares with symbiotics, such as RS Oph, T CrB, MWC 560, Z And, V2116 Oph, CH Cyg, o Cet, EF Aql, V648 Car and likely V407 Cyg (Zamanov et al 2017),; all of them powered by accretion through a disk.…”

Section: Evidence For Boundary-layer Origin Of X-ray Emissionmentioning

confidence: 88%

X-ray, UV, and optical observations of the accretion disk and boundary layer in the symbiotic star RT Crucis

Luna

Mukai

Sokoloski

et al. 2018

A&A

View full text Add to dashboard Cite

Compared to mass transfer in cataclysmic variables, the nature of accretion in symbiotic binaries in which red giants transfer material to white dwarfs (WDs) has been difficult to uncover.The accretion flows in a symbiotic binary are most clearly observable, however, when there is no quasi-steady shell burning on the WD to hide them. RT Cru is the prototype of such non-burning symbiotics, with its hard (δ-type) X-ray emission providing a view of its innermost accretion G. J. M. Luna et al.: RT Crucis; X-ray, UV, and optical observations. structures. In the past 20 years, RT Cru has experienced two similar optical brightening events, separated by ∼4000 days and with amplitudes of ∆V∼ 1.5 mag. After Swift became operative, the Burst Alert Telescope (BAT) detector revealed a hard X-ray brightening event almost in coincidence with the second optical peak.Spectral and timing analyses of multi-wavelength observations that we describe here, from NuSTAR, Suzaku, Swift/X-Ray Telescope(XRT) + BAT + UltraViolet Optical Telescope (UVOT) (photometry) and optical photometry and spectroscopy, indicate that accretion proceeds through a disk that reaches down to the white dwarf surface. The scenario in which a massive, magnetic WD accretes from a magnetically truncated accretion disk is not supported. For example, none of our data show the minute-time-scale periodic modulations (with tight upper limits from X-ray data) expected from a spinning, magnetic WD. Moreover, the similarity of the UV and X-ray fluxes, as well as the approximate constancy of the hardness ratio within the BAT band, indicate that the boundary layer of the accretion disk remained optically thin to its own radiation throughout the brightening event, during which the rate of accretion onto the WD increased to 6.7×10 −9 M ⊙ yr −1 (d/2 kpc) 2 . For the first time from a WD symbiotic, the NuSTAR spectrum showed a Compton reflection hump at E> 10 keV, due to hard X-rays from the boundary layer reflecting off of the surface of the WD; the reflection amplitude was 0.77±0.21. The best fit spectral model, including reflection, gave a maximum post-shock temperature of kT =53±4 keV, which implies a WD mass of 1.25±0.02 M ⊙ .Although the long-term optical variability in RT Cru is reminiscent of dwarf-novae-type outbursts, the hard X-ray behavior does not correspond to that observed in well-known dwarf nova.An alternative explanation for the brightening events could be that they are due to an enhancement of the accretion rate as the WD travels through the red giant wind in a wide orbit, with a period of about ∼4000 days. In either case, the constancy of the hard X-ray spectrum while the accretion rate rose suggests that the accretion-rate threshold between a mostly optically thin and thick boundary layer, in this object, may be higher than previously thought.

show abstract

Section: Evidence For Boundary-layer Origin Of X-ray Emissionmentioning

confidence: 88%

X-ray, UV, and optical observations of the accretion disk and boundary layer in the symbiotic star RT Crucis

Luna

Mukai

Sokoloski

et al. 2018

A&A

View full text Add to dashboard Cite

show abstract

“…A comparison of the flickering of EF Aql with that of the symbiotic recurrent nova RS Oph (see fig. 1 in Zamanov et al 2010) shows that in RS Oph the flickering is visible in BVRI bands, while in EF Aql it is not detectable in the I band but clearly visible in B and V bands. In RS Oph, the mass accretion rate is about ∼ 2 × 10 −8 M ⊙ year −1 (Nelson et al 2011).…”

Section: Detection Of Flickering In Ef Aqlmentioning

confidence: 90%

“…There are about 30 symbiotic stars classified as symbiotic Miras (Whitelock 2003). We searched in the Catalogue of Symbiotic Stars (Belczyński et al 2000), for D-type symbiotics with low ionization potential, which are potential candidates for flickering detection.…”

Section: Detection Of Flickering In Ef Aqlmentioning

confidence: 99%

“…and interstellar extinction A V = 0.45(Margon et al 2016), we calculated the dereddened color of the flickering source as (B − V) 0 = 0.35 ± 0.05. For comparison, the average (B − V) 0 color of the flickering source is 0.25 ± 0.21 in the recurrent novae T CrB and RS Oph, and 0.10 ± 0.20 in the cataclysmic variables(Bruch 1992;Zamanov et al 2015). It appears that (B − V) 0 of the flickering source in EF Aql is more similar to the flickering source in T CrB and RS Oph, which also contain a red giant mass donor.4 DISCUSSIONFrom our R-and I-band observations of EF Aql, we measure (R − I) = 3.08 ± 0.06 and (R − I) = 2.93 ± 0.05, for August 28, 2016, and September 4, 2016, respectively.…”

mentioning

confidence: 99%

See 1 more Smart Citation

Discovery of optical flickering from the symbiotic star EF Aquilae

et al. 2017

Self Cite

View full text Add to dashboard Cite

We report optical CCD photometry of the recently identified symbiotic star EF Aql. Our observations in Johnson V and B bands clearly show the presence of stochastic light variations with an amplitude of about 0.2 mag on a time scale of minutes. The observations point toward a white dwarf (WD) as the hot component in the system. It is the 11-th object among more than 200 symbiotic stars known with detected optical flickering. Estimates of the mass accretion rate onto the WD and the mass loss rate in the wind of the Mira secondary star lead to the conclusion that less than 1 per cent of the wind is captured by the WD. Eight further candidates for the detection of flickering in similar systems are suggested.Comment: 5 pages, submitted to A

show abstract

“…The colours of the flickering source in T CrB indicate a temperature of ∼9000 K, which is significantly lower than the average temperature of flickering sources in classical CVs (∼20000 K; Zamanov et al 2015a). Flickering in T CrB seems to originate in the vicinity of the WD (Zamanov & Bruch 1998). The ratio of the amplitude of flickering in T CrB to the average flux remains constant , which according to a model by Bruch & Duschl (1993), means that the size of the boundary layer remains roughly constant.…”

Section: Introductionmentioning

confidence: 89%

Active phases and flickering of a symbiotic recurrent nova T CrB

Iłkiewicz

Mikołajewska

Stoyanov

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

T CrB is a symbiotic recurrent nova known to exhibit active phases, characterised by apparent increases in the hot component temperature and the appearance of flickering, i.e. changes in the observed flux on the time-scale of minutes. Historical UV observations have ruled out orbital variability as an explanation for flickering and instead suggest flickering is caused by variable mass transfer. We have analysed optical and X-ray observations to investigate the nature of the flickering as well as the active phases in T CrB. The spectroscopic and photometric observations confirm that the active phases follow two periods of ∼1000d and ∼5000d. Flickering in the X-rays is detected and follows an amplitude-flux relationship similar to that observed in the optical. The flickering is most prominent at harder X-ray energies, suggesting that it originates in the boundary layer between the accretion disc and the white dwarf. The X-ray radiation from the boundary layer is then reprocessed by a thick accretion disc or a nebula into UV radiation. A more detailed understanding of flickering would benefit from long-term simultaneous X-ray and optical monitoring of the phenomena in symbiotic recurrent novae and related systems such as Z And type symbiotic stars.

show abstract

Discovery of optical flickering from the symbiotic star EF Aquilae

Cited by 15 publications

References 44 publications

X-ray, UV, and optical observations of the accretion disk and boundary layer in the symbiotic star RT Crucis

X-ray, UV, and optical observations of the accretion disk and boundary layer in the symbiotic star RT Crucis

Discovery of optical flickering from the symbiotic star EF Aquilae

Active phases and flickering of a symbiotic recurrent nova T CrB

Contact Info

Product

Resources

About