Eclipse Arrival Times Research Articles

The puzzling orbital residuals of XTE J1710–281: Is a Jovian planet orbiting the binary system?

is a transient eclipsing binary system with a period close to 3.28 hours that hosts a neutron star. The average eclipse duration is 420 seconds, and eclipse arrival times reported in the literature span from 1999 to 2017. A previous analysis of the eclipse arrival times using the eclipse timing technique revealed a complex pattern of delays, indicating the presence of three orbital glitches. These glitches correspond to sudden variations in the orbital period and allow for the identification of four distinct epochs, during which the orbital period derivative was estimated to be $-1.8 $ s s$^ $ s s$^ $ s s$^ $, and $0.09 $ s s$^ $, respectively. We reanalyzed the 78 eclipse arrival times spanning 18 years utilizing the eclipse timing technique to derive the corresponding delays as a function of time. We find that the observed delays align well with a fitting model that employs an eccentric sine function characterized by an amplitude of $6.1 0.5$ s, an eccentricity of $0.38 0.17$, and a period of $17.1 1.5$ years. Additionally, we identified the orbital period to be 3.28106345(13) hours, with a reference epoch of $T_0=54112.83200(2)$ MJD. We obtained an upper limit to the orbital period derivative of $3.6 $ s s$^ From the average value of the eclipse duration, we estimate that the companion star has a mass of 0.22 for a neutron star mass of 1.4 and that the inclination of the source is $ degrees. The companion star is in thermal equilibrium. The orbital period derivative is consistent with a conservative mass transfer scenario, where the angular momentum loss due to magnetic braking dominates over gravitational radiation angular momentum loss if the former is present. The eccentric modulation can be explained by a third body with a mass of 2.7 Jovian masses, orbiting with a revolution period close to 17 years and an eccentricity of 0.38.

Anomalous orbital expansion of the low-mass X-ray binary 2A 1822-371: the existence of a circumbinary disk?

Source 2A 1822-371 is an eclipsing low-mass X-ray binary (LMXB) consisting of a neutron star (NS) and a ∼0.5 M⊙donor star in an orbit of 5.57 h. Based on the timing of the eclipse arrival times, this source was found to experience a rapid orbital expansion with an orbital period derivative asṖorb= (1.51 ± 0.05) × 10−10s s−1, implying that the mass-transfer rate is probably higher than at least three times the Eddington accretion rate. The standard magnetic braking (MB) model cannot produce a mass-transfer rate this high. The modified MB model can produce a high mass-transfer rate, resulting in a highṖorb. We propose an alternative model to account for the anomalously high mass-transfer rate andṖorbof 2A 1822-371. During the mass transfer, a tiny fraction of the transferred material is thought to form a circumbinary (CB) disk around the LMXB, which can efficiently extract orbital angular momentum from the system by the interaction between the CB disk and the binary. We used the MESA code to model the formation and evolution of 2A 1822-371 for different CB-disk masses. When the CB-disk mass is 2.3 × 10−8 M⊙, the simulation can reproduce the observed donor-star mass, orbital period, and orbital period derivative. This CB disk can accelerate the evolution of the binary and produce a high mass-transfer rate of 1.9 × 10−7M⊙yr−1, driving the binary to evolve toward a wide-orbit system. Therefore, we propose that CB disks may cause the rapid orbital changes observed in some LMXBs.

Updated orbital ephemeris of the ADC source X 1822-371: a stable orbital expansion over 40 years

Aims. Source X 1822-371 is an eclipsing compact binary system with a period close to 5.57 h and an orbital period derivative Ṗorb of 1.51(7)×10−10 s s−1. The very high value of Ṗorb is compatible with a super-Eddington mass transfer rate from the companion star, as suggested by X-ray and optical data. The XMM-Newton observation taken in 2017 allows us to update the orbital ephemeris and verify whether the orbital period derivative has been stable over the past 40 yr. Methods. We added two new values obtained from the Rossi-XTE (RXTE) and XMM-Newton observations performed in 2011 and 2017, respectively, to the X-ray eclipse arrival times from 1977 to 2008. We estimated the number of orbital cycles and the delays of our eclipse arrival times spanning 40 yr, using as reference time the eclipse arrival time obtained from the RXTE observation taken in 1996. Results. Fitting the delays with a quadratic model, we found an orbital period Porb = 5.57062957(20) h and a Ṗorb value of 1.475(54)×10−10 s s−1. The addition of a cubic term to the model does not significantly improve the fit quality. We also determined a spin-period value of Pspin = 0.5915669(4) s and its first derivative Ṗspin = − 2.595(11) × 10−12 s s−1. Conclusions. Our results confirm the scenario of a super-Eddington mass transfer rate; we also exclude a gravitational coupling between the orbit and the change in the oblateness of the companion star triggered by the nuclear luminosity of the companion star.

On the ephemeris of the eclipsing polar HU Aquarii. II: New eclipse epochs obtained 2014–2018

The magnetic cataclysmic variable HU Aquarii displayed pronounced modulations of its eclipse timing. In recent years, these have been intensively modeled and discussed in the framework of planets orbiting the binary or the Applegate effect. No scenario yielded a unique and satisfactory interpretation of the data. Here, we present 26 new eclipse epochs obtained between 2014 and 2018. The steep and continuous decrease of the orbital period observed in the time interval 2010–2013 has slowed down sometimes before mid 2016. The new slope in the (O − C)‐diagram of eclipse arrival times will further constrain physical models of its complex shape.

A possible solution of the puzzling variation of the orbital period of MXB 1659–298

MXB 1659–298 is a transient neutron-star low-mass X-ray binary system that shows eclipses with a periodicity of 7.1 h. MXB 1659–298 went to outburst in 2015 August, after 14 years of quiescence. We investigate the orbital properties of this source with a baseline of 40 years, obtained by combining the eight eclipse arrival times present in the literature with 51 eclipse arrival times collected during the last two outbursts. A quadratic ephemeris does not fit the delays associated with the eclipse arrival times and the addition of a sinusoidal term with a period of 2.31 ± 0.02 yr is required. We infer a binary orbital period of P = 7.1161099(3) h and an orbital period derivative of |$\dot{P}=-8.5(1.2) \times 10^{-12}$| s s−1. We show that the large orbital period derivative can be explained with a highly non-conservative mass-transfer scenario, in which more than 98 per cent of the mass provided by the companion star leaves the binary system. We predict an orbital period derivative value of |$\dot{P}=-6(3) \times 10^{-12}$| s s−1 and constrain the companion-star mass between 0.3 and 1.2 M⊙. Assuming that the companion star is in thermal equilibrium, the periodic modulation can be due to either a gravitational quadrupole coupling arising from variations of the oblateness of the companion star or the presence of a third body of mass M3 > 21 Jovian masses.

Long-term eclipse timing of white dwarf binaries: an observational hint of a magnetic mechanism at work

We present a long-term programme for timing the eclipses of white dwarfs in close binaries to measure apparent and/or real variations in their orbital periods. Our programme includes 67 close binaries, both detached and semi-detached and with M-dwarfs, K-dwarfs, brown dwarfs or white dwarfs secondaries. In total, we have observed more than 650 white dwarf eclipses. We use this sample to search for orbital period variations and aim to identify the underlying cause of these variations. We find that the probability of observing orbital period variations increases significantly with the observational baseline. In particular, all binaries with baselines exceeding 10 yrs, with secondaries of spectral type K2 -- M5.5, show variations in the eclipse arrival times that in most cases amount to several minutes. In addition, among those with baselines shorter than 10 yrs, binaries with late spectral type (>M6), brown dwarf or white dwarf secondaries appear to show no orbital period variations. This is in agreement with the so-called Applegate mechanism, which proposes that magnetic cycles in the secondary stars can drive variability in the binary orbits. We also present new eclipse times of NN Ser, which are still compatible with the previously published circumbinary planetary system model, although only with the addition of a quadratic term to the ephemeris. Finally, we conclude that we are limited by the relatively short observational baseline for many of the binaries in the eclipse timing programme, and therefore cannot yet draw robust conclusions about the cause of orbital period variations in evolved, white dwarf binaries.

THE FIRST SCIENCE RESULTS FROM SPHERE: DISPROVING THE PREDICTED BROWN DWARF AROUND V471 TAU

Variations of eclipse arrival times have recently been detected in several post common envelope binaries consisting of a white dwarf and a main sequence companion star. The generally favoured explanation for these timing variations is the gravitational pull of one or more circumbinary substellar objects periodically moving the center of mass of the host binary. Using the new extreme-AO instrument SPHERE, we image the prototype eclipsing post-common envelope binary V471 Tau in search of the brown dwarf that is believed to be responsible for variations in its eclipse arrival times. We report that an unprecedented contrast of 12.1 magnitudes in the H band at a separation of 260 mas was achieved, but resulted in a non-detection. This implies that there is no brown dwarf present in the system unless it is three magnitudes fainter than predicted by evolutionary track models, and provides damaging evidence against the circumbinary interpretation of eclipse timing variations. In the case of V471 Tau, a more consistent explanation is offered with the Applegate mechanism, in which these variations are prescribed to changes in the quadrupole moment within the main-sequence star

Cyclic period changes and the light-time effect in eclipsing binaries: A low-mass companion around the system VV Ursae Majoris

In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22±0.17years in the system. The cyclic-variation analysis produces a value of 0.0139day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787±0.02M⊙, and the semi-major axis of its orbit is 10.75AU.

Timing variations in the secondary eclipse of NN Ser

Abstract The eclipsing white dwarf plus main-sequence binary NN Serpentis provides one of the most convincing cases for the existence of circumbinary planets around evolved binaries. The exquisite timing precision provided by the deep eclipse of the white dwarf has revealed complex variations in the eclipse arrival times over the last few decades. These variations have been interpreted as the influence of two planets in orbit around the binary. Recent studies have proved that such a system is dynamically stable over the current lifetime of the binary. However, the existence of such planets is by no means proven and several alternative mechanisms have been proposed that could drive similar variations. One of these is apsidal precession, which causes the eclipse times of eccentric binaries to vary sinusoidally on many year time-scales. In this Letter, we present timing data for the secondary eclipse of NN Ser and show that they follow the same trend seen in the primary eclipse times, ruling out apsidal precession as a possible cause for the variations. This result leaves no alternatives to the planetary interpretation for the observed period variations, although we still do not consider their existence as proven. Our data limit the eccentricity of NN Ser to e < 10−3. We also detect a 3.3 ± 1.0 s delay in the arrival times of the secondary eclipses relative to the best planetary model. This delay is consistent with the expected 2.84 ± 0.04 s Rømer delay of the binary, and is the first time this effect has been detected in a white dwarf plus M dwarf system.

Ole Rømer's method still on the stage: the study of two bound eclipsing binaries in quintuple system V994 Her

More than three hundred years ago, Ole Romer measured the speed of light only by observing the periodic shifting of the observed eclipse arrival times of Jupiter's moons arising from the varying Earth-Jupiter distance. The same method of measuring the periodic modulation of delays is still used in astrophysics. The ideal laboratories for this effect are eclipsing binaries. The unique system V994 Her consists of two eclipsing binaries orbiting each other. However, until now it was not certain whether these are gravitationally bound and what their orbital period is. We show that the system is in fact quintuple and the two eclipsing binaries are orbiting each other with period about 6.3 years. This analysis was made only from studying the periodic modulation of the two periods, when during the periastron passage one binary has an apparently shorter period, while the other one longer, exactly as required by a theory. Additionally, it was found that both inner eclipsing pairs orbit with slightly eccentric orbits undergoing a slow apsidal motions with a period of the order of centuries.

Detailed study of the X-ray and optical/UV orbital ephemeris of X1822–371

Recent studies of the optical/UV and X-ray ephemerides of X1822-371 have found some discrepancies in the value of the orbital period derivative. Because of the importance of this value in constraining the system evolution, we comprehensively analyse all the available optical/UV/X eclipse times of this source to investigate the origin of these discrepancies. We collected all previously published X-ray eclipse times from 1977 to 2008, to which we added the eclipse time observed by Suzaku in 2006. This point is very important to cover the time gap between the last RXTE eclipse time (taken in 2003) and the most recent Chandra eclipse time (taken in 2008). Similarly we collected the optical/UV eclipse arrival times covering the period from 1979 to 2006, adding a further eclipse time taken on 1978 and updating previous optical/UV ephemeris. We compared the X-ray and the optical/UV ephemeris, and finally derived a new ephemeris of the source by combining the eclipse arrival times in the X-ray and optical/UV bands. The X-ray eclipse time delays calculated with respect to a constant orbital period model display a clear parabolic trend, confirming that the orbital period of this source constantly increases at a rate of $\dot{P}_{\rm{orb}} =1.51(7) \times 10^{-10}$ s/s. Combining the X-ray and the optical/UV data sets, we find that $\dot{P}_{\rm{orb}} =1.59(9) \times 10^{-10}$ s/s, which is compatible with the X-ray orbital solution. We also investigate the possible presence of a delay of the optical/UV eclipse with respect to the X-ray eclipse, finding that this delay may not be constant in time. In particular, this variation is compatible with a sinusoidal modulation of the optical/UV eclipse arrival times with respect to the long-term parabolic trend. In this case, the optical/UV eclipse should lag the X-ray eclipse and the time-lag oscillate about an average value. (Abridged)

New ephemeris of the ADC source 2A 1822–371: a stable orbital-period derivative over 30 years

We report on a timing of the eclipse arrival times of the low mass X-ray binary and X-ray pulsar 2A 1822-371 performed using all available observations of the Proportional Counter Array on board the Rossi X-ray Timing Explorer, XMM-Newton pn, and Chandra. These observations span the years from 1996 to 2008. Combining these eclipse arrival time measurements with those already available covering the period from 1977 to 1996, we obtain an orbital solution valid for more than thirty years. The time delays calculated with respect to a constant orbital period model show a clear parabolic trend, implying that the orbital period in this source constantly increases with time at a rate $\dot P_orb = 1.50(7) \times 10^{-10}$ s/s. This is 3 orders of magnitude larger than what is expected from conservative mass transfer driven by magnetic braking and gravitational radiation. From the conservation of the angular momentum of the system we find that to explain the high and positive value of the orbital period derivative the mass transfer rate must not be less than 3 times the Eddington limit for a neutron star, suggesting that the mass transfer has to be partially non-conservative. With the hypothesis that the neutron star accretes at the Eddington limit we find a consistent solution in which at least 70% of the transferred mass has to be expelled from the system.

The Best Brown Dwarf Yet? A Companion to the Hyades Eclipsing Binary V471 Tauri

We have carried out an analysis of about 160 eclipse timings spanning over 30 years of the Hyades eclipsing binary V471 Tauri that shows a long-term quasi-sinusoidal modulation of its observed eclipse arrival times. The O - C values have been analyzed for the effect that arises from the gravitational influence of a tertiary companion. The presence of a third body causes the relative distance of the eclipsing pair to the Earth to change as it orbits the barycenter of the triple system. The result of the analysis of the eclipse times yields a light-time semiamplitude of 137.2 ± 12.0 s, an orbital period of P3 = 30.5 ± 1.6 yr, and an eccentricity of e3 = 0.31 ± 0.04. The mass of the tertiary component is M3 sin i3 0.0393 ± 0.0038 M☉ when a total mass of 1.61 ± 0.06 M☉ for V471 Tau is adopted. For orbital inclinations i3 35°, the mass of the third body would be below the stable hydrogen-burning limit of M ≈ 0.07 M☉, and thus it would be a brown dwarf. In the next several years (near maximum elongation), it should be feasible to obtain IR images and spectra of V471 Tau C that, when combined with the known mass, age, distance, and [Fe/H], will serve as a benchmark for understanding the physical properties and evolution of brown dwarfs.