arXiv subjects

Janusz Ziolkowski

Publications and source records attributed to Janusz Ziolkowski.

10 recordsLinked to original sources

arXiv2022

The Donor of the Black-Hole X-Ray Binary MAXI J1820+070

We estimate the parameters of the donor of the accreting black-hole binary MAXI J1820+070. The measured values of the binary period, rotational and radial velocities and constraints on the orbital inclination imply the donor is a subgiant with the mass of $M_2\approx 0.49^{+0.10}_{-0.10}M_\odot$ and the radius of $R_2\approx 1.19^{+0.08}_{-0.08}R_\odot$. We re-analyze the previously obtained optical spectrum from the Gran Telescopio Canarias, and found it yields a strict lower limit on the effective temperature of $T>4200$ K. We compile optical and infrared fluxes observed during the quiescence of this system. From the minima $r$ and $i$-band fluxes found in Pan-STARSS1 Data Release 2 pre-discovery imaging and for a distance of $D\approx3$ kpc, reddening of $E(B$--$V)=0.23$ and $R_2\approx{1.11R_\odot}$, we find $T\lesssim4230$ K, very close to the above lower limit. For a larger distance, the temperature can be higher, up to about 4500 K (corresponding to a K5 spectral type, preferred by previous studies) at $D=3.5$ kpc, allowed by the Gaia parallax. We perform evolutionary calculations for the binary system and compare them to the observational constraints. Our model fitting the above temperature and radius constraints at $D\approx 3$ kpc has the mass of $0.4M_\odot$, $T\approx4200$ K and solar metallicity. Two alternative models require $D\gtrsim 3.3$--3.4 kpc at $0.4 M_\odot$, $T\approx4500$ K and half solar metallicity, and $0.5M_\odot$, $T\approx4300$ K and solar metallicity. These models yield mass transfer rates of $\sim\!\!10^{-10}M_\odot$/yr, compatible with those based on the estimated accreted mass of $\approx\!2\times 10^{25}$ g and the time between the 2018 discovery and the 1934 historical outburst.

astro-ph.SR↗

arXiv2021

A comment on the properties of the matter flow through the first Langrangian point

We analyse properties of the mass outflow from the Roche-lobe filling component of a semi-detached binary system. We follow the approaches published by Paczyński \& Sienkiewicz and by Lubow \& Shu, which we compare with other simplified approaches. We find that the density of the flow at $L_1$ is orders of magnitude lower than the density on the same equipotential but away from $L_1$. Furthermore, the effective cross section of the flow, after averaging over its profile of the momentum density, is much lower than some published estimates done without accounting for the averaging. Thus, the use of some simplified formulae for the density and the flow cross section can lead to overestimates of the accretion rate and of the mass contained in the $L_1$ regions by very large factors unless they are supported by simultaneous integrations of the equations of stellar structure for the outer layers of the donor.

astro-ph.SR↗

arXiv2020

The nature of the Schoenberg-Chandrasekhar limit

We present a comprehensive description of the Schönberg--Chandrasekhar (S--C) transition, which is an acceleration of the stellar evolution from the nuclear to the thermal time scales occurring when the fractional mass of the helium core reaches a critical value, about 0.1. It occurs in the 1.4 to 7 M$_\odot$ mass range due to impossibility of maintaining the thermal equilibrium after the nuclear energy sources in the core disappear. We present the distributions of the hydrogen abundance, the energy generation rate and the temperature for stars crossing that limit. We confirm that a sharp S--C limit is present for strictly isothermal cores, but it is much smoother for real stars. The way the boundary of the core is defined is important for the picture of this transition. With a strict definition of the core as the region where the helium abundance is close to null, it occurs in an extended range of the fractional core mass of roughly 0.03 to 0.11. The cause of that is a gradual core contraction causing a correspondingly gradual loss of the core isothermality with the increasing core mass. On the other hand, when using definitions allowing for some H abundance in the core, the S--C transition is found to be sharper, at the fractional core mass of between about 0.07 and 0.11. Still, it is more a smooth transition than a sharp limit. We have also searched for specific signatures of that transition, and found that it is associated with the stellar radius first decreasing and then increasing again. We have considered whether the S--C limit can be used as a diagnostic constraining the evolutionary status of accreting X-ray binaries, but found such uses unfounded.

astro-ph.SR↗

arXiv2016

IGR J17451--3022: constraints on the nature of the donor star

We constrain the binary parameters of the eclipsing accreting X-ray binary IGR J17451--3022 and the nature of its donor star. The donor mass, its radius, and the system inclination angle are computed based on the system orbital period and eclipse duration recently reported by Bozzo et al.\ (2016). We find that the donor is most likely a main-sequence star with the mass comprised within the range $\sim$(0.5--$0.8){\rm M}_{\odot}$ and the radius of $\sim\! 0.7{\rm R}_{\odot}$. Assuming that the accreting compact object in IGR J17451--3022 is a neutron star, the duration of the nearly total rectangular eclipses yields the inclination angle of the system of $71^\circ\lesssim i\lesssim 76^\circ$, compatible with the presence of dips in this system. We rule out the presence of either brown or white dwarf. However, we find an alternative possibility that the donor star in IGR J17451--3022 could be a partially stripped giant with a very low mass, $\sim\! 0.2{\rm M}_{\odot}$. This case requires a substantial mass loss prior to the formation of the giant-star He core. According to that solution, the radius would be $\sim\! 0.4{\rm R}_{\odot}$, at $i\sim 80^\circ$. We additionally show that the well-known approximate dependence of the giant-star radius exclusively on its core mass breaks down below $\sim\!0.3{\rm M}_{\odot}$.

astro-ph.HE↗

arXiv2015

On the masses of the components of the V1387 Aql/GRS1915+105 binary system

V1387 Aql (the optical companion to the microquasar GRS1915+105) is a low mass giant. Such star consists of a degenerate, nearly isothermal helium core and a hydrogen rich envelope. Both components are separated by an hydrogen burning shell. The structure of such an object is relatively simple and easy to model. Making use of the observational values of the luminosity and of the radius of V1387 Aql, we determined the mass of this star as equal 0.28+-0.02 solar masses. This determination is relatively precise thanks to high sensitivity of the luminosity of such structure to the mass of the helium core and high sensitivity of its radius to the mass of the envelope. The estimate does not depend on the knowledge of the distance to the system (which is not precisely known). The main source of the uncertainty of my estimate is uncertainty of the effective temperature of V1387 Aql. When the effective temperature will be known more accurately, the mass of V1387 Aql could be determined even more precisely.

astro-ph.SR↗

arXiv2014

Masses of the components of the HDE 226868/Cyg X-1 binary system

Recent determination of the distance to HDE 226868/Cyg X-1 binary system (Reid et al., 2011) and more precise determination of the effective temperature of HDE 226868 (Caballero- Nieves et al., 2009) permit a more accurate estimate of the masses of both components. Using up to date evolutionary models, I obtain a mass range of between 25 to 35 Msun for the mass of the supergiant and between 13 to 23 Msun for the mass of the black hole. Accepting more liberal estimates of uncertainties in both the distance and the effective temperature, one may extend these ranges to 21 to 35 Msun and 10 to 23 Msun for both masses, respectively. The most likely values within these ranges are, respectively, 27 Msun and 16 Msun. The obtained mass of black hole agrees with the value 15 +- 1 Msun suggested by Orosz et al. (2011). However, the value suggested by them for the mass of the supergiant of 19 +- 2 Msun should not be used as such a star violates the mass-luminosity relation for the the massive core hydrogen burning stars. This consideration was not incorporated into the iterative process of Orosz et al. To resolve this violation I consider the possibility that the hydrogen content of HDE 222268 might be lowered as a result of the mass transfer and the induced fast rotation of the mass gainer. I analyzed the evolutionary effects of such situation and found that, while important, they do not invalidate the conclusions listed above. If, as a result of the rotation induced mixing, the present hydrogen content of HDE 226868 is equal about 0.6 (as suggested by some observational data), then its present mass may be somewhat lower: about 24 Msun rather than about 27 Msun.

astro-ph.SR↗

arXiv2011

On the apparent lack of be x-ray binaries with black holes in the galaxy and in the Magellanic clouds

In the Galaxy and in the Magellanic Clouds there are 170 Be X-ray binaries known to-date. Out of those, 111 host a neutron star, and for the reminder the nature of a companion is not known. None, so far, is known to host a black hole. This disparity is referred to as a missing Be -- black hole X-ray binary problem. The stellar population synthesis calculations following the formation of Be X-ray binaries in the Galaxy (Belczynski and Ziolkowski 2009) demonstrate that there is no problem of the missing Be+BH X-ray binaries for the Galaxy (the expected number of Be -- black hole X-ray binaries is 0 to 2, which is entirely consistent with the observed Galactic sample). However, the preliminary calculations for Magellanic Clouds indicate that there is a problem of the missing Be+BH X-ray binaries for the Clouds (the expected number is about 6, while none is observed). We believe, that to remove the discrepancy, one has to take into account a different history of the star formation rate in the Magellanic Clouds, with the respect to the Galaxy. New stellar population synthesis calculations are currently being carried out. An updated (as of November 2011) list of all 170 Be X-ray binaries known presently in the Galaxy and in the Magellanic Clouds is included.

astro-ph.SR↗

arXiv2011

Evolutionary models of the optical component of the LMC X-1/Star 32 binary system

Calculations carried out to model the evolution of Star 32 under different assumptions about the stellar wind mass-loss rate provide robust limits on the present mass of the star. The obtained range is 31 to 35.5 Msun, which is in very good agreement with the orbital solution of Orosz et al., namely 28.3 to 35.3 Msun. The initial mass of Star 32 had to be in the range 35 to 40 Msun and the present age of the system is 3.7 to 4.0 Myr.

astro-ph.SR↗

arXiv2009

On the Apparent Lack of Be X-ray Binaries with Black Holes

In the Galaxy there are 64 Be X-ray binaries known to-date. Out of those, 42 host a neutron star, and for the reminder the nature of a companion is not known. None, so far, is known to host a black hole. There seems to be no apparent mechanism that would prevent formation or detection of Be stars with black holes. This disparity is referred to as a missing Be -- black hole X-ray binary problem. We point out that current evolutionary scenarios that lead to the formation of Be X-ray binaries predict that the ratio of these binaries with neutron stars to the ones with black holes is rather high F_NStoBH=10-50, with the more likely formation models providing the values at the high end. The ratio is a natural outcome of (i) the stellar initial mass function that produces more neutron stars than black holes and (ii) common envelope evolution (i.e. a major mechanism involved in the formation of interacting binaries) that naturally selects progenitors of Be X-ray binaries with neutron stars (binaries with comparable mass components have more likely survival probabilities) over ones with black holes (which are much more likely to be common envelope mergers). A comparison of this ratio (i.e. F_NStoBH=30) with the number of confirmed Be -- neutron star X-ray binaries (42) indicates that the expected number of Be -- black hole X-ray binaries is of the order of only 0-2. This is entirely consistent with the observed Galactic sample.

astro-ph.GA↗

arXiv2008

Masses of Black Holes in the Universe

The different methods of determination of black holes (BHs) masses are presented for three classes of BHs observed in the Universe: stellar mass BHs, intermediate mass BHs (IMBHs) and supermassive BHs (SBHs). The results of these determinations are briefly reviewed: stellar mass BHs are found in the range of about 3 to about 20 solar masses, IMBHs in the range of a few hundreds to a few tens of thousands solar masses (the determinations are much less precise for these objects) and SBHs in the range of about 3x10^5 to about 6x10^10 solar masses.

astro-ph↗