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Massive Stars & X-Ray Pulsars UvA-DARE (Digital Academic Repository) Massive stars & X-ray pulsars Henrichs, H.F. Publication date 1982 Link to publication Citation for published version (APA): Henrichs, H. F. (1982). Massive stars & X-ray pulsars. General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:03 Oct 2021 103 3 Astron.. Astrophys. 54, 817—822 (1977) ASTRONOMY Y AND D ASTROPHYSICS S Ann Eccentric Close Binary Model for the X Persei System H.. F. Henrichs and E. P. J. van den Heuvel Sterrenkundigg instituut, Universiteit van Amsterdam, Roetersstraat IS, Amsterdam, The Netherlands Receivedd August 2, 1976 Summary.. A model for the X-ray source 3U0352 + 30 discoveryy of the regular X-ray pulsations, such a model connectedd with the 6lh mag O 9.5 V pe star X Per is seemss at present highly unlikely. proposed.. It is suggested that a ~» 1.5 M0 neutron star Whitee et al. (1975, 1976) deduced from the data pulsatingg with a 13T9 period is moving in 22?4 around fromm the Copernicus and Ariel V satellites that the aa relatively normal O 9.5 V star (M~2OM0) in an X-rayy source is pulsating with a 137931 period, which inclined,, slightly eccentric orbit {a^\\2R0\ i<53°; practicallyy excludes a black hole model and indicates «« = 0.1) giving rise to a 22*4 modulation in the X-ray thereforee a model in which the secondary is a white flux,flux, produced by capture of stellar wind material fromdwar ff or a neutron star. This period of 13T9 was also thee main star, which slightly underfills its critical lobe seenn in the Hen A 4686 line of X Per by Liller (1975) att periastron. The apsidal motion of the elliptic orbit andd therefore definitely confirmed the identification mayy explain the 58 ld period observed in the wavelength off X Per with the X-ray source. shiftss of the higher Balmer absorption lines. The system Whitee et al. (1976) also found strong evidence for mightt be very close to tidal instability. Predictions for aa 22M modulation in the mean X-ray intensity and thee X-ray as well as the optical behaviour on the basis suggestedd a number of possible models. Neither of these off the model are given. models,, however, could account for all the observed periodicitiess simultaneously. Notably, the 58 ld pe- Keywords:: galactic X-ray sources — accretion — binaries s riodicityy seems a stumbling block to models involving whitee dwarfs or neutron stars. Garavogliaa and Treves (1976) proposed an accreting whitee dwarf around which in an adiabatic shock the X-rayss are produced, assuming the 22*4 period as 1.. Introduction orbital,, but discarding the 5814 period. Thee identification of the X-ray source 3U0352 + 30 Thee purpose of this paper is first of all to investigate withh the bright peculiar star X Persei seems to be well whetherr the system can be explained in a "classical" establishedd (Hawkins et al., 1975; Liller, 1975; Mason way,, i.e. an accreting neutron star moving around the primaryy star which produces a stellar wind It turns out ett al., 1976 and references quoted therein). d Hutchingss et al. (1974, 1975) studied X Per in the thatt the 1379, 22M and 58 l periodicities easily fit in opticall region and found a 58 ld periodicity in the central suchh a model as a pulse, orbital and apsidal motion wavelengthh of the broad H-Balmer absorption lines period,, respectively, with the main extra condition withh an amplitude of some 60km/s. However, the beingg that the orbit is slightly eccentric. Secondly we otherr absorption or emission tines in the spectrum did investigatee the stability of the system proposed and nott show such a large amplitude (if any). Assuming discusss some aspects of its evolution. Finally we give thatt the origin of these shifts is due to orbital motion somee predictions about the X-ray as well as the optical causedd by a second, unseen, companion one derives from behaviourr of the system starting from this model. thee high mass function (/(M)=17M0) an usually highh mass (at leastt ~- 30 M0) for that companion which 2.. Main Optical and X-ray Data thereforee might be a black hole. The origin of the continuouss X-ray flux was, however, hardly explained Firstt of all let us summarize the main observational (seee Section 6). Especially in view of the subsequent data. Thee optical spectra show a O 9.5 V star with a SendSend offprint requests to: H. F. Henrichs largee variability in the emission features, mainly at 104 4 H.. F. Henrichsand E. P. J. van den Heuvel: An Eccentric Close Binary Model for the X Persei System Ha,, Hft Hy, Hei AA6678, 5875, 5015. Many other Thee projected equatorial velocity of rotation is liness and also the veiling of the spectrum behave very thereforee expected to be irregularlyy in intensity with no clear mutual correlation. iVV sin J' < 320 km/s (2) Forr details the reader is referred to the works of Wacker- lingg (1972), Cowley et al. (1972), Moffat et al. (1973), (assumingg vt-a400km/s, see below) in agreement with Cramptonn and Hutchings (1972) and Hutchings et al. thee observed value. (1975). Lett us now calculate the expected X-ray luminosity Thee projected equatorial rotational velocity derived andd variability. We suppose that mass loss from the fromm Fe /. 4272 and Mg / 4481 lines is ve sin i~ 150 km/s primaryy takes place in the form of a stellar wind, which (Treanor,, 1960) which is consistent with measurements iss reasonable as long as the radius of the primary is off He i, He n, N in and Si iv lines made by Hutchings et al. lesss than the critical Roche lobe radius. In the case of a (1975),, which give i^sini' values of less than 200 km/s. synchronous,, circular orbit we obtain RK„ctkt = 0.598a Thee Balmer absorption lines, however, indicate i?,sini == 6.68 R0. i:400km/ss (Brucato and Kristian, 1972; Hutchings Wee are dealing, however, with an elliptical orbit ett al., 1975). The broad Balmer absorption lines H9, wheree no Roche lobe radius is defined. If we approximate 100 and 11 show cf. Hutchings et al. (1975) evidence for thee critical radius in that case by R,^**—0.598 a(l -e) d aa 58l periodicity in their shift with an amplitude of ??6.011 R0 at periastron, we conclude that no critical approximatelyy 60 km/s. However, such a periodicity lobee overflow will occur as long as Rp<6.0l Re. couldd not be detected with certainty from the behaviour Synchronism—thee rotational angular velocity of the off other spectral lines (see also discussion in Section 6c). primaryy wp is equal to 2n/P, where P is the orbital Notably,, it is very puzzling that neither the He, N or Si period—iss not probable in the case of an elliptical absorptionn lines show this periodicity, whereas these orbit.. Swings (1936) concluded from observations of the liness are expected to be formed in deeper layers i.e. broadeningg of spectral lines for stars in close pairs that too be more closely connected with the star itself. o)o)pp is usually close to the orbital angular velocity of Thee mean X-ray luminosity (Giacconi et al., 1972) thee secondary at periastron, i.e. 33 LLxx = 5 10 erg/s and two periodicities in the intensity l+e2n l+e2n variationss are detected. White et al. (1976) found a (3) ) '' \~e P 13™99 period with an amplitude of ~40%, while the data whichh yields the value for v used in (2). These two alsoo show a periodicity of 22*4 with a 20% intensity e approximationss imply that at periastron the radius of variation.. (Some evidence seemed to indicate that the thee primary is close to its critical radius, while at other latterr period might be 11*2 instead of 22h4, with an orbitall phases the latter will be larger. Thus we adopt irregularr amplitude, but it seems unlikely that this thatt stellar wind is the principal mechanism for mass representss the fundamental period.) Note that no transferr for the proposed model. For simplicity we eclipsess have been observed. considerr a radial outflow of the wind with velocity vv (R),(R), R being the distance from the stellar center. 3.. Estimation of Parameters ww Stellarr wind matter will be captured by the neutron andd Expected X-ray Behaviour starr with an accretion rate S„ which can be calculated Wee shall assume throughout this paper that the 13T9 withh the formulae given by Davidson and Ostriker X-rayy pulses originate from the spin period of a magnetic (1973).. A mean X-ray luminosity of £,^5 1033 erg/s 3 neutronn star.
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