Dust in the disk winds from young stars as a source of the circumstellar extinction     

L. V. Tambovtseva  V. P. Grinin 《Astronomy Letters》2008,34(4):231-240

We consider the problem of dust grain survival in the disk winds from T Tauri and Herbig Ae stars. For our analysis, we have chosen a disk wind model in which the gas component of the wind is heated through ambipolar diffusion to a temperature of ～10⁴ K. We show that the heating of dust grains through their collisions with gas atoms is inefficient compared to their heating by stellar radiation and, hence, the grains survive even in the hot wind component. As a result, the disk wind can be opaque to the ultraviolet and optical stellar radiation and is capable of absorbing an appreciable fraction of it. Calculations show that the fraction of the wind-absorbed radiation for T Tauri stars can be from 20 to 40% of the total stellar luminosity at an accretion rate ? _a = 10^?8-10^?6 M _⊙yr^?1. This means that the disk winds from T Tauri stars can play the same role as the puffed-up inner rim in current accretion disk models. In Herbig Ae stars, the inner layers of the disk wind (r ≤ 0.5 AU) are dust-free, since the dust in this region sublimates under the effect of stellar radiation. Therefore, the fraction of the radiation absorbed by the disk wind in this case is considerably smaller and can be comparable to the effect from the puffed-up inner rim only at an accretion rate of the order of or higher than 10^?6 M _⊙yr^?1. Since the disk wind is structurally inhomogeneous, its optical depth toward the observer can be variable, which should be reflected in the photometric activity of young stars. For the same reason, moving shadows from gas and dust streams with a spiral-like shape can be observed in high-angular-resolution circumstellar disk images.  相似文献   

Modeling the luminosity function of galactic low-mass X-ray binaries     

A. G. Kuranov  K. A. Postnov  M. G. Revnivtsev 《Astronomy Letters》2014,40(1):29-45

The evolution of the family of binaries with a low-mass star and a compact neutron star companion (low-mass X-ray binaries (LMXBs) with neutron stars) ismodeled by the method of population synthesis. Continuous Roche-lobe filling by the optical star in LMXBs is assumed to be maintained by the removal of orbital angular momentum from the binary by a magnetic stellar wind from the optical star and the radiation of gravitational waves by the binary. The developed model of LMXB evolution has the following significant distinctions: (1) allowance for the effect of the rotational evolution of a magnetized compact remnant on themass transfer scenario in the binary, (2) amore accurate allowance for the response of the donor star to mass loss at the Roche-lobe filling stage. The results of theoretical calculations are shown to be in good agreement with the observed orbital period-X-ray luminosity diagrams for persistent Galactic LMXBs and their X-ray luminosity function. This suggests that the main elements of binary evolution, on the whole, are correctly reflected in the developed code. It is shown that most of the Galactic bulge LMXBs at luminosities L _x > 10³⁷ erg s^?1 should have a post-main-sequence Roche-lobe-filling secondary component (low-mass giants). Almost all of the models considered predict a deficit of LMXBs at X-ray luminosities near ～10^36.5 erg s^?1 due to the transition of the binary from the regime of angular momentum removal by a magnetic stellar wind to the regime of gravitational waves (analogous to the widely known period gap in cataclysmic variables, accreting white dwarfs). At low luminosities, the shape of the model luminosity function for LMXBs is affected significantly by their transient behavior-the accretion rate onto the compact companion is not always equal to the mass transfer rate due to instabilities in the accretion disk around the compact object. The best agreement with observed binaries is achieved in the models suggesting that heavy neutron stars with masses 1.4–1.9M _⊙ can be born.  相似文献   

Broadband spectrum of the total X-ray emission from the galaxy M31     

M. G. Revnivtsev  R. A. Sunyaev  R. A. Krivonos  S. S. Tsygankov  S. V. Molkov 《Astronomy Letters》2014,40(1):22-28

We present the results of measurements of the total X-ray flux from the Andromeda galaxy (M31) in the 3-100 keV band based on data from the RXTE/PCA, INTEGRAL/ISGRI, and SWIFT/BAT space experiments. We show that the total emission from the galaxy has a multicomponent spectrum whose main characteristics are specified by binaries emitting in the optically thick and optically thin regimes. The galaxy’s luminosity at energies 20–100 keV gives about 6% of its total luminosity in the 3–100 keV band. The emissivity of the stellar population in M31 is L _{2–20 keV} ～ 1.1 × 10²⁹ erg s^?1 M _⊙ ^?1 in the 2–20 keV band and L _{20–100 keV} ～ 8 × 10²⁷ erg s^?1 M _⊙ ^?1 in the 20–100 keV band. Since low-mass X-ray binaries at high luminosities pass into a soft state with a small fraction of hard X-ray emission, the detection of individual hard X-ray sources in M31 requires a sensitivity that is tens of times better (up to 10^?13 erg s^?1 cm^?2) than is needed to detect the total hard X-ray emission from the entire galaxy. Allowance for the contribution from the hard spectral component of the galaxy changes the galaxy’s effective Compton temperature approximately by a factor of 2, from ～1.1 to ～2.1 keV.  相似文献   

Effect of the reverse shock on the parameters of the observed X-ray emission during the 1998 outburst of CI Camelopardalis     

E. V. Filippova  M. G. Revnivtsev  A. A. Lutovinov 《Astronomy Letters》2009,35(10):688-695

Based on the model of interaction between spherically symmetric expanding matter and the external medium, we have estimated the parameters of the matter heated by the shock that was produced in the envelope ejected by the explosion of a classical nova during its interaction with the stellar wind from the optical companion. Using this model, we have shown that the matter ejected during the outburst in the system CI Camelopardalis had no steep velocity gradients and that the reverse shock could heat the ejected matter only to a temperature of ∼0.1 keV. Therefore, this matter did not contribute to the mean temperature and luminosity of the system observed in the energy range 3–20 keV.  相似文献   

Interaction of the supernova remnant HB3 with the ambient interstellar gas     

I. V. Gosachinskii 《Astronomy Letters》2005,31(3):179-185

The well-known shell supernova remnant (SNR) HB3 is part of a feature-rich star-forming region together with the nebulae W3, W4, and W5. We study the HI structure around this SNR using five RATAN-600 drift curves obtained at a wavelength of 21 cm with an angular resolution of 2′ in one coordinate over the radial-velocity range ?183 to +60 km s^?1 in a wider region of the sky and with a higher sensitivity than in previous works by other authors. The spatial-kinematic distribution of HI features around the SNR clearly shows two concentric expanding shells of gas that surround the SNR and coincide with it in all three coordinates (α, δ, and V). The outer shell has a radius of 133 pc, a thickness of 24 pc, and an expansion velocity of 48 km s^?1. The mass of the gas in it is ≈2.3 × 10⁵M_⊙. For the inner shell, these parameters are 78 pc, 36 pc, 24 km s^{? 1}, and 0.9 × 10⁵M_⊙, respectively. The inner shell is immediately adjacent to the SNR. Assuming that the outer shell was produced by the stellar wind and the inner shell arose from the shock wave of the SNR proper, we estimated the age of the outer shell, ≈1.7 × 10⁶ yr, and the mechanical luminosity of the stellar wind, 1.5 × 10³⁸ erg s^?1. The inner shell has an age of ≈10⁶ yr and corresponds to a total supernova explosion energy of ≈10⁵² erg.  相似文献   

Analysis of HST ultraviolet spectra for T Tauri stars: DR Tau     

A. S. Kravtsova  S. A. Lamzin 《Astronomy Letters》2002,28(10):676-690

We analyze the spectra of DR Tau in the wavelength range 1200 to 3100 Å obtained with the GHRS and STIS spectrographs from the Hubble Space Telescope. The profiles for the C IV 1550 and He II 1640 emission lines and for the absorption features of some lines indicate that matter falls to the star at a velocity ～300 km s^?1. At the same time, absorption features were detected in the blue wings of the N I, Mg I, Fe II, Mg II, C II, and Si II lines, suggesting mass outflow at a velocity up to 400 km s^?1. The C II, Si II, and Al II intercombination lines exhibit symmetric profiles whose peaks have the same radial velocity as the star. This is also true for the emission features of the Fe II and H₂ lines. We believe that stellar activity is attributable to disk accretion of circumstellar matter, with matter reaching the star mainly through the disk and the boundary layer. At the time of observations, the accretion luminosity was L_ac ? 2L_⊙ at an accretion rate ?10^?7M_⊙ yr^?1. Concurrently, a small (<10%) fraction of matter falls to the star along magnetospheric magnetic field lines from a height ～R_*. Within a region of size ?3.5R_*, the disk atmosphere has a thickness ～0.1R_* and a temperature ?1.5 × 10⁴ K. We assume that disk rotation in this region significantly differs from Keplerian rotation. The molecular hydrogen lines are formed in the disk at a distance <1.4 AU from the star. Accretion is accompanied by mass outflow from the accretion-disk surface. In a region of size <10R_*, the wind gas has a temperature ～7000 K, but at the same time, almost all iron is singly ionized by H I L _α photons from inner disk regions. Where the warm-wind velocity reaches ?400 km s^?1, the gas moves at an angle of no less than 30° to the disk plane. We found no evidence of regions with a temperature above 10⁴ K in the wind and leave open the question of whether there is outflow in the H₂ line formation region. According to our estimate, the star has the following set of parameters: M_* ? 0.9M_⊙, R_* ? 1.8R_⊙, L_* ? 0.9L_⊙, and \(A_V \simeq 0\mathop .\limits^m 9\). The inclination i of the disk axis to the line of sight cannot be very small; however, i≤60°.  相似文献   

Properties of Wolf-Rayet stars in eclipsing binary systems     

A. M. Cherepashchuk 《Astrophysics and Space Science》1982,86(2):299-319

The results of investigations of a number of eclipsing Wolf-Rayet binaries are presented. The ‘core’ radiuses, the ‘core’ temperatures and masses of WR stars in the eclipsing WR+OB binary systems V 444 Cyg, CX Cep, CQ Cep, and CV Ser are obtained (see Table I). The results obtained from the light curves analysis of the V 444 Cyg in the range λλ2460 Å-3.5μ give strong evidence for the Beals (1944) model of WR phenomenon. The chromospheric-coronal effects in the WN5 extended atmosphere are not observed up to a distance ofr?20R _⊙. In the Hertzsprung—Russell diagram all the WR stars lie on the left side from the main sequence between the main sequence and the sequence of uniform helium stars (see Figure 9). Their locations are close to those of the helium remnants formed as a result of mass exchange in massive close binary systems. The period variations in the systems V 444 Cyg and CQ Cep have been discovered and a reliable value of the mass loss rateM=10^?5 M _⊙yr^?1 is obtained, for the two WR stars. The results of the photometric and spectroscopic investigations of the WR stars with low mass companions (post X-ray binary stage?) are presented too (see Table II). The masses of the companions are (1–2)M _⊙, their optical luminosity is ～10³⁶, erg s^?1 which implies that these companions cannot be the normal stars. It is possible that these companions are neutron stars accreting from the stellar wind of the WR stars. Low values of the X-ray luminosities of such WR stars with low mass companions imply that the accretion of matter in such systems is distinct from the accretion process in classical X-ray binary systems. It is noted also that the parameters of low massive companions coupled with WR stars are close to those of helium stars.  相似文献   

Analysis of HST and IUE ultraviolet spectra for T Tauri stars: DF Tau     

S. A. Lamzin  A. A. Vittone  L. Errico 《Astronomy Letters》2001,27(5):313-323

We analyze ultraviolet spectra of DF Tau, a binary system whose primary component is a classical T Tauri star. The spectra were obtained from the Hubble Space Telescope and the IUE satellite. The stellar emission in the wavelength range covered is shown to originate in an accretion shock wave. The gas infall velocity is ～250 km s^?1. The accreted-gas density is typically N ₀≤10¹¹ cm^?3, but it can occasionally be higher by one and a half orders of magnitude. The continuum intensity near λ=1900 Å was found to be virtually constant for such a significant change in N ₀. The star’s photometric variability is probably attributable to variations in accreted-gas density and velocity, as well as to variations in the area of a hot spot on the stellar surface and in its orientation relative to the observer. The mean accretion rate is $\dot M \sim 3 \times 10^{ - 9} M_ \odot yr^{ - 1}$ . The interstellar extinction for DF Tau is $A_V \simeq 0\mathop .\limits^m 5$ , the stellar radius is ≤2R _⊙, and the luminosity of the primary component is most likely no higher than 0.3 L _⊙. We argue that the distance to DF Tau is about 70 pc. Upper limits are placed on the primary’s coronal emission measure: EM(T=10⁷ K)<3×10⁵⁴ cm^?3 and EM(T=1.3×10⁶ K)<3×10⁵⁵ cm^?3. Absorption lines originating in the stellar wind were detected in the star’s spectrum. Molecular hydrogen lines have essentially the same radial velocity as the star, but their full width at half maximum is FWHM ?50 km s^?1. We failed to explain why the intensity ratio of the C IV λ1550 doublet components exceeds 2.  相似文献   

The first observation of AX J1749.1-2733 in a bright X-ray state—Another fast transient revealed by INTEGRAL     

S. A. Grebenev  R. A. Sunyaev 《Astronomy Letters》2007,33(3):149-158

An intense outburst of hard radiation (with a peak flux of ～50 mCrab) was detected from the X-ray transient AX J1749.1-2733 by the IBIS/ISGRI gamma-ray telescope onboard the INTEGRAL observatory when the Galactic center field was monitored on September 8–10, 2003. Previously, this source had never been observed in a bright X-ray state. During the outburst, the source’s radiation spectrum was gently sloping and hard (extended to ～100 keV), followed a power law in the standard X-ray energy range, and had an exponential cutoff above 40–50 keV. The spectral hardness decreased with increasing flux. These and other properties described here and the shortness of the outburst (<2 days) allow the source to be attributed to the group of fast X-ray transients many representatives of which have an early O-B supergiant as their optical counterpart. Possible causes of the outbursts of fast transients are discussed. We show that accretion from the supergiant’s stellar wind should have led to intense persistent radiation from transients. The absence of radiation can be explained by the ejection of accreting matter from the system (propeller effect) during its contact with the magnetosphere of a rapidly rotating neutron star. Transient outbursts could originate in sources of this type if the spin period of their neutron star P _s differed only slightly from the critical period P _s ^* ? 3 s at which the propeller effect is still possible. The outburst is triggered by an insignificant rise in the local stellar wind density, by a factor of (P _s ^* /P _s)^7/3. The entire outburst profile cannot be explained by an individual inhomogeneity in the wind, but is the reflection of a long-term (～2 days for AX J1749.1-2733) change in the rate of wind outflow from the supergiant’s surface facing the compact source. The rate of wind outflow could be enhanced through X-ray heating of the supergiant’s surface.  相似文献   

Normal galaxies in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory     

I. G. Prokopenko  M. R. Gilfanov 《Astronomy Letters》2009,35(5):294-304

We analyze the statistical properties of normal galaxies to be detected in the all-sky survey by the eROSITA X-ray telescope of the Spectrum-X-Gamma observatory. With the current configuration and parameters of the eROSITA telescope, the sensitivity of a 4-year-long all-sky survey will be ≈10^?14 erg s^?1 in the 0.5–2 keV band. This will allow ～(1.5–2) × 10⁴ normal galaxies with approximately the same contribution of star-forming and elliptical galaxies to be detected. All galaxies of the X-ray survey are expected to enter into the existing far-infrared (IRAS) or near-infrared (2MASS) catalogs; the sample of star-forming galaxies will be approximately equivalent in sensitivity to the sample of star-forming galaxies in the IRAS catalog of infrared sources. Thus, a large homogeneous sample of normal galaxies with measured X-ray, near-infrared, and far-infrared fluxes will be formed. About 90% of the galaxies in the survey are located within ～200–400 Mpc. A typical (most probable) galaxy will have a luminosity log L _X ～ 40.5–41.0, will be located at a distance of ～70–90 Mpc, and will be either a star-forming galaxy with a star formation rate of ～20M _⊙ yr^?1 whose X-ray emission is produced by ultraluminous X-ray sources (ULXs) or an elliptical galaxy with amass log M _* ～ 11.3 emitting through to a hot interstellar gas. The galaxies within 35 Mpc will collectively contain ～10² ULXs with luminosities log L _X > 40, ～80% of whichwill be the only luminous source in the galaxy. Thus, although the angular resolution of the eROSITA telescope is too low for the luminosity function of compact sources in galaxies to be studied in detail, the survey data will allow one to investigate its bright end and, possibly, to impose constraints on the maximum luminosity of ULXs.  相似文献   

The light curve of supernova 1987A: The structure of the presupernova and radioactive nickel mixing     

V. P. Utrobin 《Astronomy Letters》2004,30(5):293-308

  相似文献   

Symbiotic halo star LT Del: Phase variations of the emission spectrum and parameters of the cool component     

V. P. Arkhipova  V. F. Esipov  N. P. Ikonnikova  G. V. Komissarova  R. I. Noskova 《Astronomy Letters》2011,37(5):343-357

Long-term photometric and spectroscopic observations of the yellow symbiotic star LT Del are analyzed. UBV light curves are presented. Based on the observations of 20 cycles, we have refined the orbital period of the star, P = 476 _· ^d 0 ± 1 _· ^d 0. The brightness has been found to be unstable at some orbital phases with an amplitude up to 0 _· ^m 3. We have measured the fluxes in hydrogen and helium emission lines and in continuum and investigated their relationship to the orbital period. The fluxes in hydrogen and HeI lines follow the UBV light curves in phase; the He II 4686 Å flux does not depend on the phase and is constant within the accuracy of our measurements. The intensity ratio of the 4686 Å andHβ lines changes from 0.2 to 0.9 over the period. We interpret the spectroscopic observations based on the hypothesis of heating and ionization of the stellar wind from a cool component by high-frequency radiation from a hot star with a temperature of 105 K. We have estimated the spectral type of the cool star from our photometry and its continuum energy distribution as a bright K2–4 red giant branch halo star. The bolometric luminosity and mass loss rate have been estimated for the K component to be L _bol ～ 700L _⊙ and \(\dot{M}\) ～ 10^?8 M _⊙ yr^?1, respectively.  相似文献   

Infrared luminosities of local-volume galaxies     

I. D. Karachentsev  A. M. Kutkin 《Astronomy Letters》2005,31(5):299-307

Based on data from the Two-Micrometer All-Sky Survey (2MASS), we analyzed the infrared properties of 451 Local-Volume galaxies at distances D ≤ 10 Mpc. We determined the K-band luminosity function of the galaxies in the range of absolute magnitudes from ?25^m to ?11^m. The local luminosity density within 8 Mpc is 6.8 × 10⁸L_⊙ Mpc^?3, a factor of 1.5 ± 0.1 higher than the global mean K-band luminosity density. We determined the ratios of the virial mass to the K-band luminosity for nearby groups and clusters of galaxies. In the luminosity range from 5 × 10¹⁰ to 2 × 10¹³L_⊙, the dependence log(M/L_K) ∝ (0.27 ± 0.03) log L_K with a dispersion of ～0.1 comparable to the measurement errors of the masses and luminosities of the systems of galaxies holds for the groups and clusters of galaxies. The ensemble-averaged ratio, 〈M/L_K〉 ? (20–25) M_⊙/L_⊙, was found to be much smaller than the expected global ratio, (80–90)M_⊙/L_⊙, in the standard model with Ω_m = 0.27. This discrepancy can be eliminated if the bulk of the dark matter in the Universe is not associated with galaxies and their systems.  相似文献   

Radial pulsations of helium stars with masses from 1 to 10 <Emphasis Type="Italic">M</Emphasis><Subscript>⊙</Subscript>     

Yu. A. Fadeyev  M. F. Novikova 《Astronomy Letters》2003,29(8):522-529

We present the results of our hydrodynamic calculations of radial pulsations in helium stars with masses 1 M_⊙ ≤ M ≤ 10 M_⊙, luminosity-to-mass ratios 1 × 10³L_⊙/M_⊙ ≤ L/M ≤ 2 × 10⁴L_⊙/M_⊙, and effective temperatures 2 × 10⁴ K ≤ T_eff ≤ 10⁵ K for mass fractions of helium Y=0.98 and heavy elements Z=0.02. We show that the lower boundary of the pulsation-instability region corresponds to L/M ～ 10³L_⊙/M_⊙ and that the instability region for L/M ? 5 × 10³L_⊙/M_⊙ is bounded by effective temperatures T_eff ? 3 × 10⁴ K. As the luminosity rises, the instability boundary moves into the left part of the Hertzsprung-Russell diagram and radial pulsations can arise in stars with effective temperatures T_eff ? 10⁵ K at L/M ? 7 × 10³L_⊙/M_⊙. The velocity amplitude for the outer boundary of the hydrodynamic model increases with L/M and lies within the range 200 ? ΔU ? 700 km s^?1 for the models under consideration. The periodic shock waves that accompany radial pulsations cause a significant change of the gas-density distribution in the stellar atmosphere, which is described by a dynamic scale height comparable to the stellar radius. The dynamic instability boundary that corresponds to the separation of the outer stellar atmospheric layers at a superparabolic velocity is roughly determined by a luminosity-to-mass ratio L/M ～ 3 × 10⁴L_⊙/M_⊙.  相似文献   

Relation between the X-ray and optical luminosities in binary systems with accreting nonmagnetic white dwarfs     

M. G. Revnivtsev  E. V. Filippova  V. F. Suleimanov 《Astronomy Letters》2014,40(4):177-184

We investigate the relation between the optical (g-band) and X-ray (0.5–10 keV) luminosities of accreting nonmagnetic white dwarfs. According to the present-day counts of the populations of star systems in our Galaxy, these systems have the highest space density among the close binary systems with white dwarfs. We show that the dependence of the optical luminosity of accreting white dwarfs on their X-ray luminosity forms a fairly narrow one-parameter curve. The typical half-width of this curve does not exceed 0.2–0.3 dex in optical and X-ray luminosities, which is essentially consistent with the amplitude of the aperiodic flux variability for these objects. At X-ray luminosities L _x ～ 10³² erg s^?1 or lower, the optical g-band luminosity of the accretion flow is shown to be related to its X-ray luminosity by a factor ～2–3. At even lower X-ray luminosities (L _x ? 10³⁰ erg s^?1), the contribution from the photosphere of the white dwarf begins to dominate in the optical spectrum of the binary system and its optical brightness does not drop below M _g ～ 13–14. Using the latter fact, we show that in current and planned X-ray sky surveys, the family of accreting nonmagnetic white dwarfs can be completely identified to the distance determined by the sensitivity of an optical sky survey in this region. For the Sloan Digital Sky Survey (SDSS) with a limiting sensitivity m _g ～ 22.5, this distance is ～400–600 pc.  相似文献   

Aperiodic X-ray flux variability of EX Hya and the area of the base of the accretion column at the white dwarf surface     

A. N. Semena  M. G. Revnivtsev 《Astronomy Letters》2014,40(8):475-484

The goal of this paper is to determine the characteristic cooling time of the accretion flowmatter near the surface of the magnetic white dwarf in the binary system EX Hya. Most of the X-ray photons in such binary systems are produced in an optically thin hot plasma with a temperature above 10 keV heated when the matter passes through the shock near the white dwarf surface. The total X-ray luminosity is determined by the matter accumulated below the shock in its cooling time. Thus, the X-ray luminosity variability related to the variations in the accretion rate onto the white dwarf surface must be suppressed at frequencies higher than the inverse cooling time. If the optically thin plasma radiation dominates in the rate of energy losses by the heated matter, which is true for white dwarfs with moderately strong magnetic fields, less than 1–10 MG, then the matter cooling time can give an estimate of the matter density in the accretion column. Given the accretion rate and the matter density in the accretion column at the white dwarf surface, the area of the accretion channel can be estimated. We have analyzed all of the currently available observational data for one of the brightest intermediate polars in the X-ray sky, EX Hya, from the RXTE and XMM-Newton observatories. The power spectra of its aperiodic variability have given an upper limit on the cooling time of the hot plasma: <1.5–2 s. For the observed accretion rate, ×10¹⁵ g s^?1, this corresponds to a matter density below the shock surface ?10¹⁶ cm^?3 and an area of the base of the accretion channel no more than <4.6 × 10¹⁵ cm². Using the information about the maximum geometrical size of the accretion channel obtained by analyzing X-ray eclipses in the binary system EX Hya, we have derived an upper limit on the thickness of the flow over the surface of the magnetosphere near the white dwarf surface, ?3 × 10⁶ cm, and the plasma penetration depth at the magnetospheric boundary, Δr/r ? 6 × 10^?3.  相似文献   

Infrared photometry of Nova Delphini 2013 (=V339 Del) in the first sixty days after its outburst     

O. G. Taranova  A. M. Tatarnikov  V. I. Shenavrin  A. A. Tatarnikova 《Astronomy Letters》2014,40(2-3):120-124

The results of JHKLM photometry for Nova Delphini 2013 obtained in the first sixty days after its outburst are analyzed. Analysis of the energy distribution in a wide spectral range (0.36–5 µm) has shown that the source mimics the emission of normal supergiants of spectral types B5 and A0 for two dates near its optical brightness maximum, August 15.94 UT and August 16.86 UT, respectively. The distance to the nova has been estimated to be D ≈ 3 kpc. For these dates, the following parameters have been estimated: the source’s bolometric fluxes ～9 × 10^?7 and ～7.2 × 10^?7 erg s^?1 cm^?2, luminosities L ≈ 2.5 × 10⁵ L _⊙ and ≈2 × 10⁵ L _⊙, and radii R ≈ 6.3 × 10¹² and ≈1.2 × 10¹³ cm. The nova’s expansion velocity near its optical brightness maximum was ～700 km s^?1. An infrared (IR) excess associated with the formation of a dust shell is shown to have appeared in the energy distribution one month after the optical brightness maximum. The parameters of the dust component have been estimated for two dates of observations, JD2456557.28 (September 21, 2013) and JD2456577.18 (October 11, 2013). For these dates, the dust shell parameters have been estimated: the color temperatures ≈1500 and ≈1200 K, radii ≈6.5 × 10¹³ and 1.7 × 10¹⁴ cm, luminosities ～4 × 10³ L _⊙ and ～1.1 × 10⁴ L _⊙, and the dust mass ～1.6 × 10²⁴ and ～10²⁵ g. The total mass of the material ejected in twenty days (gas + dust) could reach ～1.1 × 10^?6 M _⊙. The rate of dust supply to the nova shell was ～8 × 10^?8 M _⊙ yr^?1. The expansion velocity of the dust shell was about 600 km s^?1.  相似文献   

New probable dwarf galaxies in northern groups of the Local Supercluster     

I. D. Karachentsev  V. E. Karachentseva  W. K. Huchtmeier 《Astronomy Letters》2007,33(8):512-519

We have searched for nearby dwarf galaxies in 27 northern groups with characteristic distances 8–15 Mpc based on the Second Palomar Sky Survey prints. In a total area of about 2000 square degrees, we have found 90 low-surface-brightness objects, more than 60% of which are absent from known catalogs and lists. We have classified most of these objects (～80%) as irregular dwarf systems. The first 21-cm line observations of the new objects with the 100-m Effelsberg radio telescope showed that the typical linear diameters (1–2 kpc), internal motions (～30 km s^?1), and hydrogen masses (～2 × 10⁷ M _⊙) of the new galaxies correspond to those expected for the dwarf population of nearby groups.  相似文献   

Interacting winds in classical nova outbursts     

H. M. Lloyd  T. J. O'Brien  M. F. Bode 《Astrophysics and Space Science》1995,233(1-2):317-321

Classical nova outbursts occur in binary systems containing a white dwarf accretor and a Roche-lobe-filling main-sequence star. The outburst is due to a thermonuclear runaway in the accreted material on the surface of the white dwarf, and results in the ejection of up to 10^–4 M of material at velocities of several hundred to a few thousand kilometres per second. There is now strong evidence that the mass ejection takes place via a wind with secularly increasing velocity. The fast ejecta catches up with slower moving material ejected earlier in the outburst, forming a layer of shock-heated gas which gives rise to a short burst of soft X-ray emission. This emission was observed in V838 Her (Nova Herculis 1991), and was succesfully accounted for by the interacting winds model. In this paper, we present 2.5-D numerical hydrodynamics calculations of interacting winds in novae which consider the effects of the binary system on shaping the mass-loss, and show that many of the features seen in the optical shells of novae many years after outburst can be accounted for.This author is supported by a PPARC research assistantship  相似文献   

Evolution of low-mass close binaries and the problem of orbital period gap in cataclysmic variables     

A. V. Fedorova  L. R. Yungelson 《Astrophysics and Space Science》1984,103(1):125-135

Evolution of close binary composed of a white dwarf primary and a Main-Sequence secondary has been calculated. Angular-momentum loss via gravitational radiation and magnetic stellar wind have been taken into account. We have found that magnetic stellar wind with a rate greater than (10^–10–10^–9)M yr^–1 is able to drive the evolution with mass exchange. If the time-scale of switch-off of wind when the primary becomes fully convective is not longer than 10⁶ yr, mass exchange interrupts due to a contraction of the secondary and the system becomes unobservable. Mass exchange resumes when components approach one another due to loss of momentum via gravitational radiation. The location and width of the thus-arising gap in the orbital periods are comparable to those observed.  相似文献