Mass Donor Star Research Articles

On the Production and Survival of Carbon Fuel for Superbursts on Accreting Neutron Stars: Implications for Mass Donor Evolution

(abridged) We have investigated the physical conditions under which accreting neutron stars can both produce and preserve sufficient quantities of carbon fuel to trigger superbursts. Our models span the plausible ranges of neutron star thermal conductivities, core neutrino emission mechanisms, and areal radii, as well as the CNO abundances in the accreted material. We find that neutron stars that accrete hydrogen-rich material with CNO mass fractions ~ 4 times that of the Sun will exhibit superbursts at accretion rates in the observed range. On this basis, we suggest that the mass donors of superburst systems must have enhanced CNO abundances. The accreted CNO acts only as a catalyst for hydrogen burning via the hot CNO cycle, and therefore it is only the sum of the three elements' mass fractions that is important. Systems that exhibit superbursts are observed to differ from those that do not exhibit superbursts in the nature of their helium-triggered Type I X-ray bursts: the bursts have shorter durations and much greater alpha-values. Increasing the CNO abundance of the accreted material in our models reproduces both of these observations. Many compact binary systems have been observed in which the abundances of the accreting material are distinctly non-solar. Though abundance analyses of the systems that exhibit superbursts currently do not exist, Bowen fluorescence blend profiles of 4U 1636-536 and Ser X-1 suggest that the mass donor stars may indeed have non-solar CNO metallicities. More detailed abundance analyses of the accreting matter in systems that exhibit superbursts are needed to verify our assertion that the matter is rich in CNO elements.

On the origin of the absorption features in SS 433

We present high-resolution optical spectroscopy of the X-ray binary system SS 433, obtained over a wide range of orbital phases. The spectra display numerous weak absorption features, and include the clearest example seen to date of those features (resembling a mid-A type supergiant spectrum), which have previously been associated with the mass-donor star. However, the new data preclude the hypothesis that these features originate solely within the photosphere of the putative mass donor, indicating that there may be more than one region within the system producing an A supergiant-like spectrum, probably an accretion disc wind. Indeed, whilst we cannot confirm the possibility that the companion star is visible at certain phase combinations, it is possible that all supergiant-like features observed thus far are produced solely in a wind. We conclude that great care must be taken when interpreting the behaviour of these weak features.

Identification of the Mass Donor Star’s Spectrum in SS 433

We present spectroscopy of the microquasar SS 433 obtained near primary eclipse and disk precessional phase Psi = 0.0, when the accretion disk is expected to be most ``face-on''. The likelihood of observing the spectrum of the mass donor is maximized at this combination of orbital and precessional phases since the donor is in the foreground and above the extended disk believed to be present in the system. The spectra were obtained over four different runs centered on these special phases. The blue spectra show clear evidence of absorption features consistent with a classification of A3-7 I. The behavior of the observed lines indicates an origin in the mass donor. The observed radial velocity variations are in anti-phase to the disk, the absorption lines strengthen at mid-eclipse when the donor star is expected to contribute its maximum percentage of the total flux, and the line widths are consistent with lines created in an A supergiant photosphere. We discuss and cast doubt on the possibility that these lines represent a shell spectrum rather than the mass donor itself. We re-evaluate the mass ratio of the system and derive masses of 10.9 +/- 3.1 Msun and 2.9 +/- 0.7 Msun for the mass donor and compact object plus disk, respectively. We suggest that the compact object is a low mass black hole. In addition, we review the behavior of the observed emission lines from both the disk/wind and high velocity jets.

The N Enrichment and Supernova Ejection of the Runaway Microquasar LS 5039

We present an investigation of new optical and ultraviolet spectra of the mass donor star in the massive X-ray binary LS 5039. The optical band spectral line strengths indicate that the atmosphere is N-rich and C-poor, and we classify the stellar spectrum as type ON6.5 V((f)). The N-strong and C-weak pattern is also found in the stellar wind P Cygni lines of N V λ1240 and C IV λ1550 (narrow absorption components in the former indicate that the wind terminal velocity is V∞ = 2440 ± 190 km s-1). We suggest that the N enrichment may result from internal mixing if the O star was born as a rapid rotator or the O star may have accreted N-rich gas prior to a common envelope interaction with the progenitor of the supernova. We reevaluated the orbital elements to find an orbital period of P = 4.4267 ± 0.0005 days. We compared the spectral line profiles with new non-LTE line-blanketed model spectra from Lanz and Hubeny, from which we derive an effective temperature Teff = 37.5 ± 1.7 kK, gravity log g = 4.0 ± 0.1, and projected rotational velocity V sin i = 140 ± 8 km s-1. We fitted the UV, optical, and IR flux distribution by using a model spectrum and extinction law with parameters E(B - V) = 1.28 ± 0.02 and R = 3.18 ± 0.07. We confirm the covariability of the observed X-ray flux and stellar wind mass-loss rate derived from the Hα profile, which supports the wind accretion scenario for the X-ray production in LS 5039. Wind accretion models indicate that the compact companion has mass MX/M☉ = 1.4 ± 0.4, consistent with its identification as a neutron star. We argue that the O star has mass in the range 20-35 M☉ (based on a lower limit for the distance and the lack of eclipses). The observed eccentricity and runaway velocity of the binary can be reconciled only if the neutron star received a modest kick velocity due to a slight asymmetry in the supernova explosion (during which more than 5 M☉ was ejected).

The Spectrum of the Mass Donor Star in SS 433

We present results from a short series of blue, moderate resolution spectra of the microquasar binary, SS 433. The observations were made at a time optimized to find the spectrum of the donor star, i.e., when the donor was in the foreground and well above the plane of the obscuring disk. In addition to the well-known stationary and jet emission lines, we find evidence of a weak absorption spectrum that resembles that of an A-type evolved star. These lines display radial velocity shifts opposite to those associated with the disk surrounding the compact star, and they appear strongest when the disk is maximally eclipsed. All these properties suggest that these absorption lines form in the atmosphere of the hitherto unseen mass donor star in SS 433. The radial velocity shifts observed are consistent with a mass ratio M_X / M_O = 0.57 +/- 0.11 and masses of M_O = (19 +/- 7) M_sun and M_X = (11 +/- 5) M_sun. These results indicate that the system consists of an evolved, massive donor and a black hole mass gainer.

The Mass Donor of Scorpius X‐1 Revealed

We present the first detection of the mass donor star in the prototype X-ray binary Scorpius X-1. Phase resolved spectroscopy revealed narrow emission lines components from the irradiated secondary star. Radial velocity fits to the Bowen blend emission are used to establish an absolute orbital ephemeris and derive an accurate value for the systemic velocity; gamma= -113.8 +/- 0.6 km/s. Emission from the irradiated front side of the secondary leads to solid limits to the radial velocity of the mass donor of 87 < K_2 < 148 km/s. In conjunction with an upper limit to the velocity of the primary K_1 < 53 km/s, we derive a firm limit on the mass ratio of Sco X-1 of q < 0.61. % A likely set of system parameters satisfying the various constraints as well as the recent inclination estimate by Fomalont et al. (2001) is K_1=40 km/s, K_2=133 km/s, q=0.30 corresponding to component masses of M_1=1.4M_sun, M_2=0.42 M_sun for an orbital inclination of 38 degrees.

Optical Observations of the Black Hole Candidate GX 339−4 (V821 Arae)

GX 339-4 has long been known as a black hole candidate because of its rapid variability and high/low X-ray states, which are similar to those of Cyg X-1. Although GX 339-4 is assumed to be a binary, the orbital period has not yet been convincingly determined, and hence little is known about the nature of the component stars. In this study simultaneous photometric and spectroscopic observations have been made in an effort to address these problems. Although a definitive period has not been found, we present evidence that it lies near ~0.7 days. The I-band light curve has an amplitude of only ~0.2 mag, with flickering of >0.1 mag superposed, making it difficult to determine the orbital period from light variations alone. The emission-line velocity amplitudes are small, suggesting that GX 339-4 is seen at a low orbital inclination angle. Even though the period is still not determined, the relative phasing of the velocities and light minima are known, since the photometric and spectroscopic observing runs overlapped. Assuming the orbital period is near ~0.7 days, we can set limits on the mass ratio and stellar masses. For reasonable assumptions about the inclination angle, the mass ratio appears to lie between q ~ 3 and 15, where q = MX/Mdonor. If the donor star mass is greater than ~0.3 M⊙, the X-ray source is likely to be a black hole.

Emission from the Secondary Star in the Old Cataclysmic Variable WZ Sagittae

We present the first detection of the mass donor star in the cataclysmic variable WZ Sagittae. Phase-resolved spectroscopy reveals narrow Balmer emission components from the irradiated secondary star during the 2001 outburst. Its radial velocity curve indicates a systemic velocity of -72 ± 3 km s-1 and an apparent velocity amplitude of K = 493 ± 10 km s-1. Doppler tomography reveals a highly asymmetric accretion disk including a significant bright spot contribution 20 days into the outburst. We estimate the apparent primary radial velocity using the Hα tomogram and find K = 37 ± 5 km s-1. Accounting for the likely systematic errors affecting both K1 and K2 measurements, we conservatively derive 493 km s-1 0.70 M☉ and a low-mass secondary with M2 < 0.11 M☉. A nondegenerate mass donor, implying WZ Sge has not yet evolved through its minimum period, is therefore not ruled out by our observations. This would require an improved estimate of K1.

How Evolved are the Mass Donor Stars in Cataclysmic Variables?

Abstract Recent spectroscopic observations have identified several cataclysmic variables non-solar metal abundances. We present theoretical models which examine the level of core evolution expected for CV secondaries prior to contact. Our results indicate that few secondary stars evolve past 10% of their main sequence lifetime prior to the initiation of mass transfer; a result of which is in agreement with present day observations. Thus, the non-solar metal abundances observed must be due to nuclear burning by-products accreted by the secondary star during common envelope sweeping prior to initial contact or ejecta collected during classical nova outbursts.

A mystery solved: the mass ratio of the dwarf nova EM Cygni

We have discovered that the spectrum of the well-known dwarf nova EM Cyg is contaminated by light from a K2–5V star (in addition to the K-type mass donor star). The K2–5V star contributes approximately 16 per cent of the light from the system and if not taken into account has a considerable effect upon radial velocity measurements of the mass donor star. We obtain a new radial velocity amplitude for the mass donor star of K2=202±3 km s−1, compared with the value of K2=135±3 km s−1 obtained in Stover, Robinson & Nather's classic study of EM Cyg. The revised value of the amplitude, combined with a measurement of rotational broadening of the mass donor, v sin i=140±6 km s−1, leads to a new mass ratio of qM2M1=0.88±0.05. This solves a long-standing problem with EM Cyg, because Stover et al.'s measurements indicated a mass ratio q>1, a value that should have led to dynamically unstable mass transfer for the secondary mass deduced by Stover et al. The revised value of the mass ratio, combined with the orbital inclination i=67±2°, leads to masses of 0.99±0.12 M⊙ and 1.12±0.08 M⊙ for the mass donor and white dwarf respectively. The mass donor is evolved, because it has a later spectral type (K3) than its mass would imply. We discuss whether the K star could be physically associated with EM Cyg or not, and present the results of the spectroscopic study.

Echoes from an irradiated disc in GRO J1655-40

We demonstrate correlated rapid variability between the optical/UV and X-ray emission for the first time in a soft X-ray transient, GRO J1655–40: Hubble Space Telescope (HST) light curves show similar features to those seen by the Rossi X-ray Timing Explorer (RXTE), but with mean delay of up to 10–20 s. We interpret the correlations as the result of reprocessing of X-rays into optical and UV emission, with a delay owing to finite light travel time, and thus perform echo mapping of the system. The time-delay distribution has a mean of 14.6 ± 1.4 s and dispersion (i.e. the standard deviation of the distribution) of 10.5 ± 1.9 s at binary phase 0.4. Hence we identify the reprocessing region as the accretion disc rather than the mass donor star.

The Nature and Evolutionary History of GRO J1744−28

GRO J1744-28 is the first known X-ray source to display bursts, periodic pulsations, and quasi-periodic oscillations. This source may thus provide crucial clues that will lead to an understanding of the differences in the nature of the X-ray variability from various accreting neutron stars. The orbital period is 11.8 days, and the measured mass function of 1.31 x 10(exp -4) solar mass is one of the smallest among all known binaries. If we assume that the donor star is a low-mass giant transferring matter through the inner Lagrange point, then we can show that its mass is lower than approximately 0.7 solar mass and probably closer to 0.25 solar mass. Higher mass, but unevolved, donor stars are shown to be implausible. We also demonstrate that the current He core mass of the donor star lies in the range of 0.20-0.25 solar mass. Thus, this system is most likely in the final stages of losing its hydrogen-rich envelope, with only a small amount of mass remaining in the envelope. If this picture is correct, then GRO J1744-28 may well represent the closest observational link that we have between the low-mass X-ray binaries and recycled binary pulsars in wide orbits. We have carried out a series of binary evolution calculations and explored, both systematically and via a novel Monte Carlo approach, the range of initial system parameters and input physics that can lead to the binary parameters of the present-day GRO J1744-28 system. The input parameters include both the initial total mass and the core mass of the donor star, the neutron-star mass, the strength of the magnetic braking, the mass-capture fraction, and the specifics of the core mass/radius relation for giants. Through these evolution calculations, we compute probability distributions for the current binary system parameters (i.e., the total mass, core mass, radius, luminosity, and K-band magnitude of the donor star, the neutron star mass, the orbital inclination angle, and the semimajor axis of the binary). Our calculations yield the following values for the GRO J1744-28 system parameters (with 95% confidence limits in parentheses): donor star mass: 0.24 solar mass (0.2-0.7 solar mass); He core mass of the donor star: 0.22 solar mass (0.20-0.25 solar mass); neutron-star mass: 1.7 solar mass (1.39-1.96 solar mass); orbital inclination angle: 18deg (7deg-22deg); semi- major axis: 64 lt-s (60-67 lt-s); radius of the donor star: 6.2 solar radius(6-9 solar radius); luminosity of donor star: 23 solar luminosity (15-49 solar luminosity), and long-term mass transfer rate at the current epoch: 5 x 10(exp -10)solar mass/yr (2 x 10(exp -10) to 5 x 10(exp -9)solar mass/yr). We deduce that the magnetic field of the underlying neutron star lies in the range of approximately 1.8 x 10(exp 11)G to approximately 7 x 10(exp 11)G, with a most probable value of 2.7 x 10(exp 11)G. This is evidently sufficiently strong to funnel the accretion flow onto the magnetic polar caps and suppress the thermonuclear flashes that would otherwise give rise to the type 1 X-ray bursts observed in most X-ray bursters. We present a simple paradigm for magnetic accreting neutron stars where X-ray pulsars, GRO J1744-28, the Rapid Burster, and the type 1 X-ray bursters may form a continuum of possible behaviors among accreting neutron stars, with the strength of the neutron-star magnetic field serving as a crucial parameter that determines the mode of X-ray variability from a given object.

Super-Eddington Accretion in the Formation of Low-Mass X-ray Binaries and Millisecond Pulsars

AbstractConsiderations of donor star stability, age, and mass transfer rate show that low-mass X-ray binaries and binary millisecond pulsars with orbital periods longer than a few days must have survived an initial phase of super-Eddington mass transfer. We review the physical arguments leading to this conclusion, and examine its implications for the apparent discrepancy between the death rate for low-mass X-ray binaries and the birth rate of binary millisecond pulsars.

Properties of the Exceptionally Long-Period AM Herculis System RX J0515.41+0104.6

view Abstract Citations (8) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Properties of the Exceptionally Long-Period AM Herculis System RX J0515.41+0104.6 Frank, J. ; Lasota, J. -P. ; Chanmugam, G. Abstract We show that the properties of the recently discovered AM Her type cataclysmic variable RX J0515.41+0104.6 can be understood in terms of the standard evolutionary model, which accounts for both the near-synchronism at the observed period and the size of the mass-donor star. We find that either the system is in a low state long enough to bring the white dwarf to synchronism or that the magnetic field of the secondary is strong enough, but not unusually so (≳1 kG), to maintain synchronism at this period and the system may exhibit radio flares. Publication: The Astrophysical Journal Pub Date: November 1995 DOI: 10.1086/176405 Bibcode: 1995ApJ...453..446F Keywords: STARS: BINARIES: CLOSE; STARS: EVOLUTION; STARS: INDIVIDUAL ALPHANUMERIC: RX J0515.41+0104.6; STARS: NOVAE; CATACLYSMIC VARIABLES full text sources ADS | data products SIMBAD (1)

A study of the absorption lines from the donor star in the exotic cataclysmic variable AE Aquarii

We estimate the fundamental system parameters (e.g. mass ratio, inclination, stellar masses) of the unusual cataclysmic variable AE Aquarii by characterizing the behaviour of the mass-donor star. Our analysis focuses on the absorption lines from the donor star, avoiding biases induced by use of the poorly understood emission lines. Using simultaneous high-speed photometry and high-resolution H α spectroscopy, we observed weak absorption lines in AE Aquarii’s spectrum. By modelling these lines we estimate the spectral type of the mass-donor star (K3–K5), its orbital and rotation velocities (K1 ~ 138 ± 6 km s–1, K2 = 157.9 ± 0.8 km s–1; Vrot sin i = 85–108 km s–1), and its contribution to the total flux of the system (69–94 per cent). From K2 and Vrot sin i we derive the mass ratio 0.58 < q ≡ M2/M1 < 0.89, the range depending upon the spectral type and limb darkening. By using K2 and the amplitude of the pulse arrival-time delay curve of Eracleous et al., we estimate the mass ratio of the binary system (q = 0.646 ± 0.013). We also observe variations in the absorption-line flux deficit, and, if interpreted as ellipsoidal variations, their amplitudes suggest an inclination i = 49° ± 15°. However, the deviations from the expected ellipsoidal variations are significant, suggesting a non-uniform distribution of absorption-line strength across the donor star (perhaps indicative of star-spot regions). Realistic probability distributions for the inclination and the stellar masses are derived using a Monte Carlo simulator assuming M1 < 1.4 Mʘ, but with no assumptions about the mass of the donor star. We find M1 = 0.89 ± 0.23 Mʘ, M2 = 0.57 ± 0.15 Mʘ, and further constrain i to 55° ± 7°. We also report the serendipitous discovery of a (previously unknown) eclipsing variable star near AE Aquarii

Flares and Flickering in the Cataclysmic Variable AE Aquarii

Detected from the radio to the γ-ray bands, AE Aquarii is an extraordinary cataclysmic variable. It is a relatively bright (V ∼11.4), non-eclipsing binary with an orbital period of 9h.9. The mass-donor secondary star is of approximate spectral type K5V and contributes about ∼ 80% of the total flux in the optical. While the mass ratio is well determined at q = M2/M1 = 0.646, the individual stellar masses are poorly known since the inclination is unknown. AE Aqr’s flickering behavior is unique among CVs, alternating from periods of very violent activity to near total quiescence. Large amplitude flares have been detected in the radio, optical and UV. Previous work has shown the optical flare spectrum to be similar to stellar flare spectra.Four nights of exactly simultaneous Hα spectroscopy and photometry were obtained on the 2.5 and 1.5m telescopes at Mt. Wilson on 27-30 July 1982. The simultaneity allowed us to renomalize the spectroscopy to agree with the photometry, giving us spectrophotometric data (spectral resolution ∼ 50 km s−, time resolution ∼ 68). A total of ∼ 17h of data were obtained, resulting in 10,098 spectra.

On the mass of the compact object in the black hole binary A0620-00

Multicolor orbital light curves of the black hole candidate binary A0620-00 are presented. The light curves exhibit ellipsoidal variations and a grazing eclipse of the mass donor companion star by the accretion disk. Synthetic light curves were generated using realistic mass donor star fluxes and an isothermal blackbody disk. For mass ratios of q = M sub 1/M sub 2 = 5.0, 10.6, and 15.0 systematic searches were executed in parameter space for synthetic light curves that fit the observations. For each mass ratio, acceptable fits were found only for a small range of orbital inclinations. It is argued that the mass ratio is unlikely to exceed q = 10.6, and an upper limit of 0.8 solar masses is placed on the mass of the companion star. These constraints imply 4.16 +/- 0.1 to 5.55 +/- 0.15 solar masses. The lower limit on M sub 1 is more than 4-sigma above the mass of a maximally rotating neutron star, and constitutes further strong evidence in favor of a black hole primary in this system.