Phase-resolved spectroscopy of Gaia14aae: line emission from near the white dwarf surface

Green, Matthew; Marsh, T. R.; Steeghs, D.; Breedt, E.; Kupfer, Thomas; Rodríguez‐Gil, P.; Roestel, Jan van; Ashley, R. P.; Wang, L.; Cukanovaite, E.; Outmani, Sabrina

doi:10.1093/mnras/stz469

Cited by 12 publications

(12 citation statements)

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“…For AM CVn binaries with orbital periods 45 min, however, this channel remains a viable option. Indeed, the most precise to date mass and radius measurements of an AM CVn donor star (from the first fully-eclipsing AM CVn binary, Gaia14aae, which has an orbital period of 50 min) agree best with predictions based on the He CV channel (Green et al 2018a(Green et al , 2019.…”

mentioning

confidence: 68%

“…The profile of these helium emission lines is dominated by a strong central spike emission feature with relatively weak emission wings ( Figure 5). Central spike features are seen in many AM CVn binaries, and are emitted from on or near the surface of the accreting white dwarf (Green et al 2019), though the emission mechanism is uncertain. As was noted by Carter et al (2014), the strength of the central spike emission seen here is similar to a number of other longperiod AM CVn binaries, including SDSS J1208+3550 (orbital period 53.0 min; Kupfer et al 2013), SDSS J1137+4054 (59.6 min; Carter et al 2014), and V396 Hya (65.1 min; Ruiz et al 2001;Kupfer et al 2016).…”

Section: Spectroscopymentioning

confidence: 99%

“…The radial velocities (RVs) measured in this way follow a sinusoidal modulation with a semi-amplitude of 5.0 ± 0.2 km/s, around a systemic velocity (γ) which varies between different emission lines. In other AM CVn binaries, central spike γ values have been explained as a combination of an overall gravitational redshift and wavelength-dependent blueshifts arising from the Stark effect (Morales-Rueda et al 2003;Kupfer et al 2016;Green et al 2019). We performed an initial sinusoidal fit to the measured RVs for each line individually, in order to measure γ for each line.…”

Section: Spectroscopymentioning

confidence: 99%

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Spectroscopic and photometric periods of six ultracompact accreting binaries

Green

Marsh

Carter

et al. 2020

Monthly Notices of the Royal Astronomical Society

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ABSTRACT Ultracompact accreting binary systems each consist of a stellar remnant accreting helium-enriched material from a compact donor star. Such binaries include two related sub-classes, AM CVn-type binaries and helium cataclysmic variables, in both of which the central star is a white dwarf. We present a spectroscopic and photometric study of six accreting binaries with orbital periods in the range of 40–70 min, including phase-resolved VLT spectroscopy and high-speed ULTRACAM photometry. Four of these are AM CVn systems and two are helium cataclysmic variables. For four of these binaries we are able to identify orbital periods (of which three are spectroscopic). SDSS J1505+0659 has an orbital period of 67.8 min, significantly longer than previously believed, and longer than any other known AM CVn binary. We identify a Wide-field Infrared Survey Explorer (WISE) infrared excess in SDSS J1505+0659 that we believe to be the first direct detection of an AM CVn donor star in a non-direct impacting binary. The mass ratio of SDSS J1505+0659 is consistent with a white dwarf donor. CRTS J1028–0819 has an orbital period of 52.1 min, the shortest period of any helium cataclysmic variable. MOA 2010-BLG-087 is co-aligned with a K-class star that dominates its spectrum. ASASSN-14ei and ASASSN-14mv both show a remarkable number of echo outbursts following superoutbursts (13 and 10 echo outbursts respectively). ASASSN-14ei shows an increased outburst rate over the years following its superoutburst, perhaps resulting from an increased accretion rate.

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mentioning

confidence: 68%

Section: Spectroscopymentioning

confidence: 99%

Section: Spectroscopymentioning

confidence: 99%

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Spectroscopic and photometric periods of six ultracompact accreting binaries

Green

Marsh

Carter

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Radial velocity measurements show that these lines originate from the white dwarf (Marsh 1999;Roelofs et al 2005;Kupfer et al 2015) and is likely boundary layer emission from the surface of the white dwarf (e.g. Green et al 2019a;Gehron et al 2014).…”

Section: Hementioning

confidence: 98%

“…The second is YZ LMi where the white dwarf is partially eclipsed (Anderson et al 2005;Copperwheat et al 2011). Gaia14aae (ASASSN-14cn), is the only published AM CVn in which the white dwarf is confirmed to be fully eclipsed by the donor (Campbell et al 2015;Green et al 2018aGreen et al , 2019a. Besides these well-studied cases, there are also a number of promising candidates.…”

Section: Eclipsing Am Cvn Systemsmentioning

confidence: 99%

Discovery and characterization of five new eclipsing AM CVn systems

van Roestel,

Kupfer,

Green

et al. 2021

Preprint

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AM CVn systems are ultra-compact, hydrogen-depleted and helium-rich, accreting binaries with degenerate or semi-degenerate donors. We report the discovery of five new eclipsing AM CVn systems with orbital periods of 61.5, 55.5, 53.3, 37.4, and 35.4 minutes. These systems were discovered by searching for deep eclipses in the Zwicky Transient Facility (ZTF) lightcurves of white dwarfs selected using Gaia parallaxes. We obtained phase-resolved spectroscopy to confirm that all systems are AM CVn binaries, and we obtained high-speed photometry to confirm the eclipse and characterize the systems. The spectra of two longperiod systems (61.5 and 53.3 minutes) show many emission and absorption lines, indicating the presence of N, O, Na, Mg, Si, and Ca, and also the K and Zn, elements which have never been detected in AM CVn systems before. By modelling the high-speed photometry, we measured the mass and radius of the donor star, potentially constraining the evolutionary channel that formed these AM CVn systems. We determined that the average mass of the accreting white dwarf is ≈ 0.8 M , and that the white dwarfs in long-period systems are hotter than predicted by recently updated theoretical models. The donors have a high entropy and are a factor of ≈ 2 more massive compared to zero-entropy donors at the same orbital period. The large donor radius is most consistent with He-star progenitors, although the observed spectral features seem to contradict this. The discovery of 5 new eclipsing AM CVn systems is consistent with the known observed AM CVn space density and estimated ZTF recovery efficiency. Based on this estimate, we expect to find another 1-4 eclipsing AM CVn systems as ZTF continues to obtain data. This will further increase our understanding of the population, but will require high precision data to better characterize these 5 systems and any new discoveries.

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Spectroscopy of the helium-rich binary ES Ceti reveals accretion via a disc and evidence of eclipses

Bąkowska

Marsh

Steeghs

et al. 2021

A&A

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Context. Amongst the hydrogen-deficient accreting binaries known as the "AM CVn stars" are three systems with the shortest known orbital periods: HM Cnc (321 s), V407 Vul (569 s) and ES Cet (620 s). These compact binaries are predicted to be strong sources of persistent gravitational wave radiation. HM Cnc and V407 Vul are undergoing direct impact accretion in which matter transferred from their donor hits the accreting white dwarfs directly. ES Cet, is the longest period of the three and is amongst the most luminous AM CVn stars, but it is not known whether it accretes via a disk or direct impact. ES Cet displays strong HeII 4686 line emission, which is sometimes a sign of magnetically-controlled accretion. Peculiarly, although around one third of hydrogen accreting white dwarfs show evidence for magnetism, none have been found amongst helium accretors. Aims. We present the results of Magellan and VLT spectroscopic and spectropolarimetric observing campaigns dedicated to ES Cet with the aim of understanding its accretion structure. Methods. Based on the data collected, we derived trailed spectra, computed Doppler maps of the emission lines, and looked for circular polarisation and variability. Results. We find strong variability in our spectra on the 620 s period. The lines show evidence for double-peaked emission, characteristic for an accretion disc, with an additional component associated with the outermost disc, rather than a direct impact, that is broadly consistent with "S"-wave emission from the gas stream/disc impact region. This confirms beyond any doubt that 620 s is the orbital period of ES Cet. We find no significant circular polarisation (below 0.1 %). The trailed spectra show that ES Cet's outer disc is eclipsed by the mass donor, revealing at the same time that the photometric minimum coincides with the hitherto unrecognised eclipse. Conclusions. ES Cet shows spectroscopic behaviour consistent with accretion via a disc, and is the shortest orbital period eclipsing AM CVn star known.

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Phase-resolved spectroscopy of Gaia14aae: line emission from near the white dwarf surface

Cited by 12 publications

References 53 publications

Spectroscopic and photometric periods of six ultracompact accreting binaries

Spectroscopic and photometric periods of six ultracompact accreting binaries

Discovery and characterization of five new eclipsing AM CVn systems

Spectroscopy of the helium-rich binary ES Ceti reveals accretion via a disc and evidence of eclipses

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