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1.
The analysis of hard X-ray INTEGRAL observations (2003–2008) of superaccreting Galactic microquasar SS433 at precessional phases of the source with the maximum disc opening angle is carried out. It is found that the shape and width of the primary X-ray eclipse are strongly variable, suggesting additional absorption in dense stellar wind and gas outflows from the optical A7I component and the wind–wind collision region. The independence of the observed hard X-ray spectrum on the accretion disc precessional phase suggests that hard X-ray emission (20–100 keV) is formed in an extended, hot, quasi-isothermal corona, probably heated by interaction of relativistic jet with inhomogeneous wind outflow from the precessing supercritical accretion disc. A joint modelling of X-ray eclipsing and precessional hard X-ray variability of SS433 revealed by INTEGRAL by a geometrical model suggests the binary mass ratio   q = mx / m v ≃  0.25–0.5. The absolute minimum of joint orbital and precessional  χ2  residuals is reached at   q ≃ 0.3  . The found binary mass ratio range allows us to explain the substantial precessional variability of the minimum brightness at the middle of the primary optical eclipse. For the mass function of the optical star   f v = 0.268 M⊙  as derived from Hillwig & Gies data, the obtained value of   q ≃ 0.3  yields the masses of the components   mx ≃ 5.3 M⊙, m v ≃ 17.7 M⊙  , confirming the black hole nature of the compact object in SS433.  相似文献   

2.
The variation of the specific intensity across the stellar disc is an essential input parameter in surface brightness reconstruction techniques such as Doppler imaging, where the relative intensity contributions of different surface elements are important in detecting star-spots. We use phoenix and atlas model atmospheres to model light curves derived from high precision (signal-to-noise ratio ≃ 5000) Hubble Space Telescope ( HST ) data of the eclipsing binary SV Cam (F9V+K4V), where the variation of specific intensity across the stellar disc will determine the contact points of the binary system light curve. For the first time, we use χ2 comparison fits to the first derivative profiles to determine the best-fitting model atmosphere. We show the wavelength dependence of the limb darkening and that the first derivative profile is sensitive to the limb-darkening profile very close to the limb of the primary star. It is concluded that there is only a marginal difference (<1σ) between the χ2 comparison fits of the two model atmospheres to the HST light curve at all wavelengths. The usefulness of the second derivative of the light curve for measuring the sharpness of the primary's limb is investigated, but we find that the data are too noisy to permit a quantitative analysis.  相似文献   

3.
We report on high-speed eclipse photometry of the dwarf nova V2051 Oph while it was in a low brightness state, at B  ≃ 16.2 mag. In comparison with the average IUE spectra, the ultraviolet continuum and emission lines appear reduced by factors of, respectively, ≃ 4 and ≃ 5. Flickering activity is mostly suppressed and the light curve shows the eclipse of a compact white dwarf at the disc centre which contributes ≃ 60 per cent of the total light at 3900–4300 Å. We use measurements of contact phases in the eclipse light curve to derive the binary geometry and to estimate masses and relevant dimensions. We find a mass ratio of q  = 0.19 ± 0.03 and an inclination of i  = 83 ± 2°. The masses of the component stars are M 1 = 0.78 ± 0.06 M⊙ and M 2 = 0.15 ± 0.03 M⊙. Our photometric model predicts K 1 = 83 ± 12 km s−1 and K 2 = 436 ± 11 km s−1. The predicted value of K1 is in accordance with the velocity amplitude obtained from the emission lines after a correction for asymmetric line emission in the disc is made. The secondary of V2051 Oph is significantly more massive than the secondaries of the other ultrashort period dwarf novae. V2051 Oph is probably a relatively young system, with a secondary star that has not had enough time to evolve out of thermal equilibrium.  相似文献   

4.
We present a study of a sample of Large Magellanic Cloud red giants exhibiting Long Secondary Periods (LSPs). We use radial velocities obtained from VLT spectral observations and MACHO and OGLE light curves to examine properties of the stars and to evaluate models for the cause of LSPs. This sample is much larger than the combined previous studies of Hinkle et al. and Wood, Olivier & Kawaler.
Binary and pulsation models have enjoyed much support in recent years. Assuming stellar pulsation, we calculate from the velocity curves that the typical fractional radius change over an LSP cycle is greater than 30 per cent. This should lead to large changes in T eff that are not observed. Also, the small light amplitude of these stars seems inconsistent with the radius amplitude. We conclude that pulsation is not a likely explanation for the LSPs. The main alternative, physical movement of the star – binary motion – also has severe problems. If the velocity variations are due to binary motion, the distribution of the angle of periastron in our large sample of stars has a probability of  1.4 × 10−3  that it comes from randomly aligned binary orbits. In addition, we calculate a typical companion mass of  0.09 M⊙  . Less than 1 per cent of low-mass main-sequence stars have companions near this mass  (0.06–0.12 M⊙)  whereas ∼25–50 per cent of low-mass red giants end up with LSPs. We are unable to find a suitable model for the LSPs and conclude by listing their known properties.  相似文献   

5.
We present BeppoSAX observations of Nova Velorum 1999 (V382 Vel), carried out in a broad X-ray band covering 0.1–300 keV only 15 d after the discovery and again after 6 months. The nova was detected at day 15 with the BeppoSAX instruments which measured a flux F x≃1.8×10−11 erg cm−2 s−1 in the 0.1–10 keV range and a 2 σ upper limit F x<6.7×10−12 erg cm−2 s−1 in the 15–60 keV range. We attribute the emission to shocked nebular ejecta at a plasma temperature kT ≃6 keV . At six months no bright component emerged in the 15–60 keV range, but a bright central supersoft X-ray source appeared. The hot nebular component previously detected had cooled to a plasma temperature kT <1 keV . There was strong intrinsic absorption of the ejecta in the first observation and not in the second, because the column density of neutral hydrogen decreased from N (H)≃1.7×1023 to N (H)≃1021 cm−2 (close to the interstellar value). The unabsorbed X-ray flux also decreased from F x=4.3×10−11 to F x≃10−12 erg cm−2 s−1 .  相似文献   

6.
New optical spectroscopy of the high-mass X-ray binary microquasar LS I +61 303 is presented. Eccentric orbital fits to our radial velocity measurements yield updated orbital parameters in good agreement with previous work. Our orbital solution indicates that the periastron passage occurs at radio phase 0.23 and the X-ray/radio outbursts are triggered 2.5–4 d after the compact star passage. The spectrum of the optical star is consistent with a B0 V spectral type and contributes ∼65 per cent of the total light, the remainder being the result of emission by a circumstellar disc. We also measure the projected rotational velocity to be   v sin  i ≃ 113 km s−1  .  相似文献   

7.
We have performed high-speed UBV photometric observations on the peculiar binary V Sagittae. Using three new eclipse timings we update the orbital ephemeris and convert it to a dynamical time-scale (TDB). We also searched for quasi-periodic oscillations but did not detect them. Using the Wilson–Devinney algorithm we have modelled the light curve to find the stellar parameters of V Sge. We find that the system is a detached binary but that the primary star is very close to filling its Roche lobe, while the secondary star fills 90 per cent of its Roche lobe volume. We find temperatures of the primary and the secondary star to be T 1=41 000 K and T 2=22 000 K. We find i =72° and masses of 0.8 M⊙ and 3.3 M⊙ for the primary and secondary stars respectively. De-archived Hubble Space Telescope ( HST ) spectroscopy of V Sge shows evidence of mass loss via a wind or winds. In addition we report radio observations of V Sge during an optical high state at 2 cm, 3.6 cm and 6 cm wavelengths. The 3.6 cm emission is increased by a factor of more than six compared with an earlier detection in a previous optical high state.  相似文献   

8.
A comparison between published field galaxy stellar mass functions (GSMFs) shows that the cosmic stellar mass density is in the range 4–8 per cent of the baryon density (assuming  Ωb= 0.045  ). There remain significant sources of uncertainty for the dust correction and underlying stellar mass-to-light ratio even assuming a reasonable universal stellar initial mass function. We determine the   z < 0.05  GSMF using the New York University Value-Added Galaxy Catalog sample of 49 968 galaxies derived from the Sloan Digital Sky Survey and various estimates of stellar mass. The GSMF shows clear evidence for a low-mass upturn and is fitted with a double Schechter function that has  α2≃−1.6  . At masses below  ∼108.5 M⊙  , the GSMF may be significantly incomplete because of missing low-surface-brightness galaxies. One interpretation of the stellar mass–metallicity relation is that it is primarily caused by a lower fraction of available baryons converted to stars in low-mass galaxies. Using this principle, we determine a simple relationship between baryonic mass and stellar mass and present an 'implied baryonic mass function'. This function has a faint-end slope,  α2≃−1.9  . Thus, we find evidence that the slope of the low-mass end of the galaxy mass function could plausibly be as steep as the halo mass function. We illustrate the relationship between halo baryonic mass function → galaxy baryonic mass function → GSMF. This demonstrates the requirement for peak galaxy formation efficiency at baryonic masses  ∼1011 M⊙  corresponding to a minimum in feedback effects. The baryonic-infall efficiency may have levelled off at lower masses.  相似文献   

9.
We derive the constraints on the mass ratio for a binary system to merge in a violent process. We find that the secondary-to-primary stellar mass ratio should be  0.003 ≲ ( M 2/ M 1) ≲ 0.15  . A more massive secondary star will keep the primary stellar envelope in synchronized rotation with the orbital motion until merger occurs. This implies a very small relative velocity between the secondary star and the primary stellar envelope at the moment of merger, and therefore very weak shock waves, and low-flash luminosity. A too low-mass secondary will release small amount of energy, and will expel small amount of mass, which is unable to form an inflated envelope. It can, however, produce a quite luminous but short flash when colliding with a low-mass main-sequence star.
Violent and luminous mergers, which we term mergebursts, can be observed as V838 Monocerotis-type events, where a star undergoes a fast brightening lasting days to months, with a peak luminosity of up to  ∼106 L⊙  followed by a slow decline at very low effective temperatures.  相似文献   

10.
We present the full VRI light curves and the times of minima of TY UMa to provide a complete photometric solution and a long-term trend of period variation. The light curves show a high degree of asymmetry (the O'Connell effect). The maxima at 0.25 phase (Max I) are 0.021, 0.015, and 0.020 mag fainter than those at 0.75 phase (Max II) in V , R , and I , respectively. The period of TY UMa has varied in a sinusoidal way, superimposed on the long-term upward parabolic variation. The secularly increasing rate of the period is deduced as 1.83 s per century  ( P˙ / P =5.788×10-10 d d-1)  . The period of sinusoidal variation is about 57.4 yr. The spot model has been applied to fit the asymmetric light curves of TY UMa, to explain light variations. By changing only the spot parameters, the model light curves can fit the observed light curves for three epochs. This indicates that the variation of the spot location and size is the main reason for changing the shape of light curves, including two different maxima and the interchanging depths of occultation and transit minima.  相似文献   

11.
We present new infrared photometry of the WC7-type Wolf–Rayet star HD 192641 (WR 137) from 1985 to 1999. These data track the cooling of the dust cloud formed in the 1982–84 dust-formation episode from 1985 to 1991, the increase of the infrared flux from 1994.5 to a new dust-formation maximum in 1997 and its subsequent fading. From these and earlier data we derive a period of 4765±50 d (13.05±0.15 yr) for the dust-formation episodes. Between dust-emission episodes, the infrared spectral energy distribution has the form of a power law, λF λ ∝ λ −1.86. The rising branch of the infrared light curve (1994–97) differs in form from that of the episodic dust-maker WR 125. Time-dependent modelling shows that this difference can be attributed to a different time dependence of dust formation in WR 137, which occurred approximately ∝ t 2 until maximum, whereas that of WR 125 could be described by a step function, akin to a threshold effect. For an adopted distance of 1.6 kpc, the rate of dust formation was found to be 5.0×10−8 M⊙ yr−1 at maximum, accounting for a fraction f C≈1.5×10−3 of the carbon flowing in the stellar wind. The fading branches of the light curves show evidence for secondary 'mini-eruptions' in 1987, 1988 and 1990, behaviour very different from that of the prototypical episodic dust-maker HD 193793 (WR 140), and suggesting the presence in the WR 137 stellar wind of large-scale structures that are crossed by the wind–wind collision region.  相似文献   

12.
We have obtained I -band photometry of the neutron star X-ray transient Aql X-1 during quiescence. We find a periodicity at 2.487 cycles d−1, which we interpret as twice the orbital frequency (19.30±0.05 h). Folding the data on the orbital period, we model the light-curve variations as the ellipsoidal modulation of the secondary star. We determine the binary inclination to be 20°–30° (90 per cent confidence) and also determine the 95 per cent upper limits to the radial velocity semi-amplitude and rotational broadening of the secondary star to be 117 and 50 km s−1, respectively.  相似文献   

13.
Very-high-resolution ( R ∼160 000) spectroscopic observations are presented for the early B-type star, HD 83206. Because it has very sharp metal lines, this star affords an opportunity to test theories of model atmospheres and line formation. Non-LTE model atmosphere calculations have been used to estimate the atmospheric parameters and absolute metal abundances (C, N, O, Mg and Si); an LTE analysis was also undertaken to investigate the validity of this simpler approach and to estimate an iron abundance. For the non-LTE calculations, there is excellent agreement with observations of the Balmer lines H α and H δ and the lines of Si  ii and Si  iii for atmospheric parameters of T eff≃21 700±600 K and log  g ≃4.00±0.15 dex. The agreement is less convincing for the LTE calculations, and a higher gravity is deduced. Careful comparison of the metal line profiles with non-LTE calculations implies that the projected rotational and microturbulent velocities have maximum values of ≃5 and ≃2 km s−1, respectively. The latter value is smaller than has often been adopted in LTE model atmosphere analyses of main-sequence stars. Non-LTE absolute metal abundances are estimated, and a comparison with those for normal B-type stars (deduced using similar non-LTE techniques) shows no significant differences. A comparison of the abundances deduced using non-LTE and LTE calculations implies systematic differences of 0.1–0.2 dex, showing the importance of using a non-LTE approach when accurate absolute abundances are required. Its location in the Hertzsprung–Russell diagram and normal metal abundance lead us to conclude that HD 83206 is probably a main-sequence B-type star. As such, it is among the sharpest-lined young B-type star discovered to date.  相似文献   

14.
Photoelectric UBV photometry and star counts are presented for the previously unstudied open cluster Collinder 236, supplemented by observations for stars near the Cepheid WZ Car. Collinder 236 is typical of groups associated with Cepheids, with an evolutionary age of  (3.2 ± 1.1) × 107 yr  , but it is  1944 ± 71  pc distant, only half the predicted distance to WZ Car. The cluster is reddened by   E ( B − V ) ≃ 0.26  , and has nuclear and coronal radii of   r n≃ 2 arcmin (1.1 pc)  and   R c≃ 8 arcmin (4.5 pc)  , respectively. The Cepheid is not a member of Collinder 236 on the basis of location beyond the cluster tidal radius and implied distance, but its space reddening can be established as   E ( B − V ) = 0.268 ± 0.006  s.e. from five adjacent stars. Period changes in WZ Car studied with the aid of archival data are revised. The period of WZ Car is increasing, its rate of  +8.27 ± 0.19 s yr−1  being consistent with a third crossing of the instability strip.  相似文献   

15.
Based on an extensive grid of stellar models between 13 and  25 M⊙  and a wide range of metallicities, we have studied the light curves of core collapse supernovae, their application to cosmology and their evolutionary effects with redshift. The direct link between the hydrodynamics and radiation transport allows us to calculate monochromatic light curves.
With decreasing metallicity, Z , and increasing mass, progenitors tend to explode as compact blue supergiants (BSG) and produce subluminous supernovae that are approximately 1.5 mag dimmer than normal Type II supernovae (SNe II) with red supergiant (RSG) progenitors. Progenitors with small masses tend to explode as RSGs even at low Z . The consequence for testing the chemical evolution is obvious, namely a strong bias when using the statistics of core collapse supernovae to determine the history of star formation.
Our study is limited in scope with respect to the explosion energies and the production of radioactive Ni. Within the class of extreme SNe II-P supernovae, the light curves are rather insensitive with respect to the progenitor mass and explosion energy compared with analytic models based on parametrized stellar structures. We expect a wider range of brightness due to variations in 56Ni because radioactive energy is a significant source of luminosity. However, the overall insensitivity of light curves may allow their use as quasi-standard candles for distance determination.  相似文献   

16.
The X-ray binary system GX 301−2 consists of a neutron star in an eccentric orbit accreting from the massive early-type star Wray 977. It has previously been shown that the X-ray orbital light curve is consistent with the existence of a gas stream flowing out from Wray 977 in addition to its strong stellar wind. Here, X-ray monitoring observations by the Rossi X-ray Timing Explorer ( RXTE )/All-Sky Monitor and pointed observations by the RXTE /Proportional Counter Array over the past decade are analysed. We analyse both the flux and column density dependence on orbital phase. The wind and stream dynamics are calculated for various system inclinations, companion rotation rates and wind velocities, as well as parametrized by the stream width and density. These calculations are used as inputs to determine both the expected accretion luminosity and the column density along the line-of-sight to the neutron star. The model luminosity and column density are compared to observed flux and column density versus orbital phase, to constrain the properties of the stellar wind and the gas stream. We find that the change between bright and medium intensity levels is primarily due to decreased mass loss in the stellar wind, but the change between medium and dim intensity levels is primarily due to decreased stream density. The mass-loss rate in the stream exceeds that in the stellar wind by a factor of ∼2.5. The quality of the model fits is better for lower inclinations, favouring a higher mass for Wray 977 in its allowed range of  40–60 M⊙  .  相似文献   

17.
The short-period, eclipsing, magnetically active binary system XY UMa has been observed over several orbital cycles at X-ray wavelengths. The X-ray light curves vary owing to obvious flares and other lower level activity on time-scales of days. These data caution against deducing coronal structure on the basis of a single orbit of X-ray data. In contrast to similar binary systems, XY UMa shows no significant X-ray eclipses. This is interpreted as evidence for either extended (> 1  R ⊙) coronae or a compact corona at high, uneclipsed latitudes on the primary star. The extended coronal scenario is favoured by some observational features of other systems such as extended radio coronae, long-duration X-ray flares and cool prominences, but unfavoured by others such as high coronal densities from EUV spectroscopy. A high-latitude compact corona might be associated with the high-latitude starspots seen in many active stars. Nearly simultaneous optical light curves suggest that some equatorial spots were present at the time of the X-ray observations, but fewer than in previous or subsequent years and that high-latitude spots must also be present. It is speculated that the lack of X-ray eclipses and dearth of equatorial, compact coronal regions are associated with a minimum in XY UMa's magnetic activity cycle.  相似文献   

18.
Using improved techniques, high-quality CCD uvbyVI photometry has been obtained for the eclipsing binary HV 982 in the Large Magellanic Cloud (LMC). International Ultraviolet Explorer ultraviolet spectrophotometry was also obtained. These data have been analysed using the Wilson–Devinney synthetic light-curve code and Kurucz low-metallicity model atmospheres as well as the EBOP code. The system is detached and the orbit is eccentric. Apsidal motion is detected with apsidal period 205 ± 7 yr. The effective temperatures of the components are found via flux fitting to be T eff,1 = 28 000 ± 5000 K and T eff,2 = 27 200 ± 5000 K. The large errors result from uncertainties over the appropriate interstellar extinction correction. The system plausibly comprises two ∼ 8 M stars of radius 6–7 R separated by ∼ 30 R. For pedagogical and historical interest, the near simultaneity of the eclipse minima at different wavelengths is used to constrain the constancy of the speed of light with wavelength and the mass of the photon, yielding m γ < 10−41 kg. Because of the great distance to HV 982, this limit is some 102 times smaller than previously achieved with eclipse timings, but it is nevertheless 10 orders of magnitude less stringent than that which is provided by satellite measurements of planetary magnetic fields.  相似文献   

19.
This paper presents a study of the envelope of the young stellar object (YSO) GGD30IR. What distinguishes this from most other YSOs is the elongated absorption feature seen in silhouette against the background emission in the Spitzer Galactic Legacy Infrared Midplane Survey Extraordinaire 8 μm Infrared Array Camera image of the region. The size and the symmetrical placement of GGD30IR in the centre of this feature suggest that it is an extended envelope, perhaps the remnant of the collapse of the GGD30 core. We have used the extinction in the envelope measured from (i) the reduction in the 8 μm background intensity and (ii) field star colour excesses, to estimate the envelope mass, obtaining values of 0.6 ± 0.2 and  0.5 ± 0.3 M⊙  , respectively. To investigate the envelope further, we have obtained Australia Telescope Compact Array 3 mm continuum and HCO+ line observations of the region. The continuum emission at 3 mm arises from both a compact (unresolved; ≤730 au) core embedded in an extended envelope ∼18 000 au × 38 000 au in extent. We estimate the core mass to be 0.11 ± 0.02  M⊙  . The HCO+ emission is extended in a direction perpendicular to the long axis of the envelope, suggesting it comes from an outflow. The spectral energy distribution (SED) provides a 2–24 μm spectral index, α= 1.0, which places GGD30IR in the Class I YSO category. Integrating the SED provides a luminosity of   L *≃ 25 ± 5 L⊙  .  相似文献   

20.
A follow-up survey using the Submillimetre High-Angular Resolution Camera (SHARC-II) at 350 μm has been carried out to map the regions around several 850-μm-selected sources from the Submillimetre HAlf Degree Extragalactic Survey (SHADES). These observations probe the infrared (IR) luminosities and hence star formation rates in the largest existing, most robust sample of submillimetre galaxies (SMGs). We measure 350-μm flux densities for 24 850-μm sources, seven of which are detected at ≥2.5σ within a 10 arcsec search radius of the 850-μm positions. When results from the literature are included the total number of 350-μm flux density constraints of SHADES SMGs is 31, with 15 detections. We fit a modified blackbody to the far-IR (FIR) photometry of each SMG, and confirm that typical SMGs are dust-rich  ( M dust≃ 9 × 108 M⊙)  , luminous  ( L FIR≃ 2 × 1012 L⊙)  star-forming galaxies with intrinsic dust temperatures of ≃35 K and star formation rates of  ≃400 M⊙ yr−1  . We have measured the temperature distribution of SMGs and find that the underlying distribution is slightly broader than implied by the error bars, and that most SMGs are at 28 K with a few hotter. We also place new constraints on the 350-μm source counts, N 350(>25 mJy) ∼ 200–500 deg−2.  相似文献   

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