Orbital parameters of supergiant fast X-ray transients

Karino, Shotaro

doi:10.1051/0004-6361/201014917

Cited by 6 publications

(5 citation statements)

References 47 publications

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“…On the other hand, accretion from a spherical wind, even if clumpy, seems unable to reproduce the characteristics of the Xray outbursts, such as the very short duration and strong peak (Romano et al 2009;Karino 2010). An abrupt transition between a region where high accretion rates can be achieved and the rest of the orbit, where accretion is suppressed, would be required.…”

Section: Discussionmentioning

confidence: 99%

Astrophysical parameters of the peculiar X-ray transient IGR J11215−5952

Lorenzo¹,

Negueruela²,

Castro³

et al. 2014

A&A

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Context. The current generation of X-ray satellites has discovered many new X-ray sources that are difficult to classify within the well-described subclasses. The hard X-ray source IGR J11215−5952 is a peculiar transient, displaying very short X-ray outbursts every 165 days. Aims. To characterise the source, we obtained high-resolution spectra of the optical counterpart, HD 306414, at different epochs, spanning a total of three months, before and around the 2007 February outburst with the combined aims of deriving its astrophysical parameters and searching for orbital modulation.Methods. We fit model atmospheres generated with the fastwind code to the spectrum, and used the interstellar lines in the spectrum to estimate its distance. We also cross-correlated each individual spectrum to the best-fit model to derive radial velocities. Results. From its spectral features, we classify HD 306414 as B0.5 Ia. From the model fit, we find T eff ≈ 24 700 K and log g ≈ 2.7, in good agreement with the morphological classification. Using the interstellar lines in its spectrum, we estimate a distance to HD 306414 d > ∼ 7 kpc. Assuming this distance, we derive R * ≈ 40 R and M spect ≈ 30 M (consistent, within errors, with M evol ≈ 38 M , and in good agreement with calibrations for the spectral type). Analysis of the radial velocity curve reveals that radial velocity changes are not dominated by the orbital motion, and provide an upper limit on the semi-amplitude for the optical component K opt < ∼ 11± 6 km s −1 . Large variations in the depth and shape of photospheric lines suggest the presence of strong pulsations, which may be the main cause of the radial velocity changes. Very significant variations, uncorrelated with those of the photospheric lines are seen in the shape and position of the Hα emission feature around the time of the X-ray outburst, but large excursions are also observed at other times. Conclusions. HD 306414 is a normal B0.5 Ia supergiant. Its radial velocity curve is dominated by an effect that is different from binary motion, and is most likely stellar pulsations. The data available suggest that the X-ray outbursts are caused by the close passage of the neutron star in a very eccentric orbit, perhaps leading to localised mass outflow.

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Section: Discussionmentioning

confidence: 99%

Astrophysical parameters of the peculiar X-ray transient IGR J11215−5952

Lorenzo¹,

Negueruela²,

Castro³

et al. 2014

A&A

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“…4) seems to agree with the scenario of a compact star accreting matter from the clumpy wind of the supergiant. Karino (2010) proposes different scenarios for this phenomenon, relating P and e. HD 74194 falls into the SFXT regime, but very near to the unstable orbit region, where stars could evolve towards coalescence.…”

Section: Discussionmentioning

confidence: 99%

The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)

Gamen

Barbá

Walborn

et al. 2015

A&A

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Aims. We present the first orbital solution for the O-type supergiant star HD 74194, which is the optical counterpart of the supergiant fast X-ray transient IGR J08408-4503. Methods. We measured the radial velocities in the optical spectrum of HD 74194, and we determined the orbital solution for the first time. We also analysed the complex Hα profile. Results. HD 74194 is a binary system composed of an O-type supergiant and a compact object in a short-period (P = 9.5436 ± 0.0002 d) and high-eccentricity (e = 0.63 ± 0.03) orbit. The equivalent width of the Hα line is not modulated entirely with the orbital period, but seems to vary in a superorbital period (P = 285 ± 10 d) nearly 30 times longer than the orbital one.

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“…Since SFXTs and faint HMXBs are newly recognized objects, complete parameter sets have not been provided. Additionally, since SFXTs have large eccentricities (Karino 2010), one dimensional approach may be restricted. However, it has been shown that some SG stars hosting SFXTs provide very large wind velocity.…”

Section: Discussionmentioning

confidence: 99%

Bimodality of wind-fed accretion in high-mass X-ray binaries

Karino¹

2014

Publications of the Astronomical Society of Japan

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We study an influence of X-ray photo-ionization from an accreting neutron star in a high mass X-ray binary. Our aim is to unveil a new principle governing X-ray luminosities of X-ray binaries, with a simple analysis of fluid equations simulating line-driven wind flow under influence of X-ray irradiation. In this study, we solve equation of motion of the accretion flow taking into account the line-driven acceleration and X-ray photo-ionization. Under the influence of X-ray irradiation, we find the flow equations take two types of solutions. The first solution is characterized by a slow wind velocity which causes a large accretion rate. The second solution is a fast wind flow which results in a small accretion rate. We find that only the solution with a fast wind and faint X-ray luminosity is a steady solution. On the other hand, slow wind solution with a large X-ray luminosity is not a realizable solution. In bright X-ray binary systems, X-ray luminosity would increase until strong X-ray reduces the line-driven acceleration and causes a stagnation of the wind. This result implies an important consequence that the X-ray luminosity of the wind-fed, X-ray emitting binary will be settled by the wind stagnation limit. At the same time, the fast wind solution with small X-ray luminosity also can be a steady state. Bright X-ray sources, such as Vela X-1, would have limiting luminosities of wind stagnation, while faint systems such a quiescent Super giant Fast X-ray Transients could be on the faint solutions.

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Orbital parameters of supergiant fast X-ray transients

Cited by 6 publications

References 47 publications

Astrophysical parameters of the peculiar X-ray transient IGR J11215−5952

Astrophysical parameters of the peculiar X-ray transient IGR J11215−5952

The eccentric short-period orbit of the supergiant fast X-ray transient HD 74194 (=LM Vel)

Bimodality of wind-fed accretion in high-mass X-ray binaries

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