Photometric variability and evolutionary status of the supergiant with an infrared excess HD 179821=V1427 aquilae

We present new results of our UBV photometry for HD 179821=V1427 Aql, an F supergiant with an infrared excess, from 2000 to 2008. The semiregular low-amplitude (ΔV = 0_. ^m 05−0_. ^m 20) photometric variability of the star with a cycle period from 130 to 200 days is caused by pulsations, along with the instability of a variable stellar wind. V1427 Aql also exhibits a long-term trend in the brightness and colors that is probably attributable to a change in the stellar temperature as a result of mass loss episodes, which cause variations in the continuum formation level. We present the results of our JHKLM photometry for V1427 Aql in 1992–2008. We trace the trend in the near-infrared brightness, which agrees with the long-term variability in the V band. Based on broadband photometry, we have determined the color excess for V1427 Aql: E(B−V) = 0.7. Based on low-resolution spectroscopy, we have estimated the stellar temperature and revealed variability of the Hα line caused by a change in the contribution from the emission component. The hypotheses of whether the star belongs to post-AGB objects or to massive yellow hypergiants are discussed.     

Modeling the Dust Shell of V4334 Sgr

The central star V4334 Sgr (Sakurai's Object) of the planetary nebula PN G010.4+04.4 underwent in 1995–1996 the rare event of a very late helium flash.It is only one of two such events during the era of modern astronomy (the other event was V605 Aql = Nova Aql 1919). All other prominentobjects of that type originate from events several thousands of years ago (e.g. A30, A78). Hence, only snapshots can be modeled for those objects.V4334 Sgr allows for the first time a dynamic consideration of the formation of the dust shell from the beginning.We present here a model which is able to describe the complete photometric behaviorof the object, including the fine structure dips of the optical light curve during the first two years of the mass loss and the dust formation.     

Optimal curve fitting procedures applied to the light curves of classical cepheids

Optimal curve fitting procedures based on the well known Baade/Wesselink methodology have been applied to Stebbinset al.'s 6-colour photometry of the classical cepheids Cep and Aql. Radial velocity data have been represented by a Fourier series, while the brightness temperature at the effective wavelength of observation forms a convenient temperature variable in the fitting function. This fitting function requires the specification of six parameters which thus play the role of unknowns in the optimization problem, though, in fact, all six parameters cannot be independently determined.The formulation involves a simple connection between colours and brightness temperatures, and model stellar atmosphere calculations can provide such a connection. The model stellar atmosphere data of Carbon and Gingerich (1969), which take careful account of line blanketing effects are, to some extent, supported by the results for Aql, though the position is less certain in the case of Cep. On the basis of the Carbon and Gingerich data, and if we take into account various estimates of the interstellar reddening, the absolute magnitudes of Cep and Aql areM _v=–3.57 andM _v=–3.79, respectively; but optimal curve fits would decrease both these values by about 0^m.09.     

The angular momentum loss of low-mass close binary systems

The detailed evolution of low-mass main-sequence stars (M < 1M ) with a compact companion is studied. For angular momentum loss associated with magnetic braking it is found that about 10^–11–10^–12 M yr^–1 in stellar wind loss would be required. This wind is 10²–10³ times stronger than the solar wind, so we believe here magnetic stellar wind is insufficient. It is well known that there is mass outflow in low-mass close binary systems. We believe here that these outflows are centrifugal driven winds from the outer parts of the accretion disks. The winds extract angular momentum from these systems and therefore drive secular evolution. Disk winds are preferred to winds from the secondary, because of the lower disk surface gravity.     

Structure of envelopes ejected by Novae

The paper contains an analysis of the structure of envelopes ejected during the outbursts of Novae. The data used for this purpose: (a) Direct photographs of envelopes and the photographs taken with the use of different colour filters; (b) Spectra of envelopes. The envelope of DQ Her is studied most carefully. The analysis of all available data for the envelopes around DQ Her and V 603 Aql permits us to outline a morphological model of these envelopes, see Figure 3. It appears, that the structure of both these envelopes is approximately identical and that the difference in the observed properties of the photographic images of the nebulae (Figure 2 and Figure 4) is connected with a difference in the orientation of the polar axes of the envelopes relative to the line of sight. The envelope ejected during the outburst of T Aur (Figure 5) reveals the same properties, which are characteristic for the envelopes of DQ Her and V 603 Aql.From this we conclude that the distribution of gases inside the envelopes of the majority of Novae is approximately of the same character. This speaks in favour of the presence of certain forces around many Novae, which guide the motion of ejected plasma along some quite definite directions inside rather small solid angles. It seems that the only conceivable forces of this type may be the forces of a magnetic nature. This hypothesis for example permits us to explain the difference between the envelope of GK Per (Figure 1) and the envelopes of DQ Her, V 603 Aql, T Aur (Figures 2, 4 and 5).Comparing the velocity of expansion of the envelope of DQ Her and the rate of change of its angular size we computed that the distance to DQ Her is equal to 320 pc.On the base of photographs of the envelope of DQ Her it is found that in 1968 the fluxF _H of radiation in the H-line was equal to (6±2)×10^–12 ergs/cm²sec, whereas the mass of the envelope was equal to 10²⁹ G and its electronic concentrationn _e to 2×10³ cm^–3. Several hypotheses, which may explain the stratification of emission from different elements inside the envelope are discussed.     

The Hypothesis of Additional Acceleration in the Motion of Comet Harrington–Abell from Jupiter

By processing 494 observations of Comet Harrington–Abell, we obtained a unified system of elements that includes its turn around the Sun during which it closely approached Jupiter to a minimum distance of 0.037 AU in 1974. A study of the cometary orbit before and after the approach showed that, probably, at the approach of the comet to Jupiter, apart from the well-known gravitational perturbations, its motion was affected by an additional force. An improvement of the cometary orbit by assuming that an additional acceleration inversely proportional to the square of the distance to Jupiter exists in its motion yielded the following values: (4.57 ± 0.42) × 10^–10 and (–7.20 ± 0.42) × 10^–10 AU day^–2 for the radial and transversal acceleration components, respectively. As a plausible explanation of the changes in the cometary orbit, we additionally considered a model based on the hypothesis of partial disintegration of the cometary nucleus. The parameter that characterizes the instant displacement of the center of inertia along the jovicentric radius vector was estimated to be –1.83 ± 0.75 km. Based on a unified numerical theory of cometary motion, we determined the nongravitational parameters using Marsden's model for two periods: A ₁ = (11.68 ± 1.74) × 10^–10 AU day^–2, A ₂ = (0.53 ± 0.0357) × 10^–10 AU day^–2 for 1975–1999 and A ₁ = (5.92 ± 5.86) × 10^–10 AU day^–2, A ₂ = (0.08 ± 0.028) × 10^–10 AU day^–2 for 1955–1969, under the assumption that the nongravitational acceleration changed at the approach of the comet to Jupiter.     

Thermal conduction and modeling of static stellar coronal loops

We have modeled stellar coronal loops in static conditions for a wide range of loop length, plasma pressure at the base of the loop and stellar surface gravity, so as to describe physical conditions that can occur in coronae of stars ranging from low mass dwarfs to giants as well as on a significant fraction of the Main-Sequence stars.Three alternative formulations of heat conduction have been used in the energy balance equation, depending on the ratio ₀/L _Tbetween electron mean free path and temperature scale height: Spitzer's formulation for ₀/L _Tless than 2 × 10^–3, the Luciani, Mora, and Virmont non-local formulation for ₀/L _Tbetween 2 × 10^–3 and 6.67 × 10^–3 and the limited free-streaming formulation for ₀/L _Tlarger than 6.67 × 10^–3.We report the characteristics of all loop models studied, and present examples to illustrate how the temperature and density stratification can be drastically altered by the different conductivity regimes. Significant differences are evident in the differential emission measure distribution vs temperature, an important observable quantity. We also show how physical conditions of coronal plasma, and in particular thermal conduction, change with stellar surface gravity.We have found that, for fixed loop length and stellar gravity, a minimum of loop-top plasma temperature occurs, corresponding to the highest value of base plasma pressure for which the limited free-streaming conduction occurs. This value of temperature satisfies the appropriate scalingT 10^–9 L g, in cgs units.     

Convection regions and coronas of sun and stars

Photospheric models were calculated for 90 stars with effective temperatures between 2500 K and 41600 K for five logg-values ranging from 1 to 5. Molecule formation was taken into account. In order to have an idea about possible instabilities in the different stellar layers some quantities, characteristic for convection and turbulence were calculated, such as the Rayleigh-, Reynolds-, Prandtl- and Péclet-numbers. It turned out that all the investigated stars contain unstable layers, including the hottest. Nevertheless, only stars with effective temperatures of 8300 K or less contain layers where the convective energy transport is important. For all stars the convective velocities were calculated and also the generated mechanical fluxes in the convection zones were tabulated.Under the hypothesis that this mechanical energy flux is responsible for the heating of the corona, coronal models were constructed for the Sun and for some stars with effective temperatures between 5000 K and 8320 K for logg-values of 4 or 5.For Main Sequence stars the largest fluxes are generated in F-stars; stars withT _eff=7130 K and logg=4 possess also the hottest and most dense coronas with a computed temperature of 3.7·10⁶ K and logN _e =10.5.The solar corona computed in this way, on the basis of a photospheric mechanical flux of 0.14·10⁸ erg cm^–2 sec^–1, has a temperature of 1.3·10⁶ K and logN _e =9.8. This density is apparently too high, but even when including in the computations all theoretical refinements proposed in the last few years by various authors it does not appear possible to obtain a solar coronal model with a smaller density.However, when taking into account the inhomogeneous structure of the chromosphere and by associating the calculated mechanical fluxes to the coarse mottles, and lower fluxes to the undisturbed regions we find a mean coronal temperature of 1.1·10⁶ K and a mean logN _e -values of 9. The computed velocity of the solar wind at a distance of 10⁴ km above the photosphere has a value between 7 and 11 km sec^–1. These latter values are in fair agreement with the observations.     

The ratio of total to selective absorption in the Carina OB2 association

Several previous studies in and around the Great Carina nebula (NGC 3372) have strongly indicated an abnormal interstellar extinction law with a high ratio of total to selective absorptionR. In the present study, newUBV photometric data and accurate MK spectral-types of stars in the region of the Carina OB2 association are used to show that (1) Car OB2 is a genuine stellar association located at a distance of 3.2 kpc, and (2) the interstellar extinction law seems to be normal throughout most of the region. A representative value ofR = A _v/E(B – V) = 3.0 is derived for Car OB2 from the variable extinction method.Visiting Astronomer, Cerro Tololo Inter-American Observatory, operated by AURA, Inc. under contract with the National Science Foundation.     

On the further observations ofB E /shell star V 923 Aql

V 923 Aql is one of the candidateB _E stars to be a binary star. In this research, optical and near-infrared spectral measurements of V 923 Aql is presented. V 923 Aql presents variable H Balmer line profiles with shell components. H profiles present R/V, E/C and radial velocity variation. Shell parameters of the envelope are calculated.Near infra-red and optical spectra obtained from Haute-Provence Observatory and bibliographic data obtained from SIMBAD database of C.D.S., Strasbourg Observatory, France.     

The cosmic distance scale

Summary The status of the cosmic distance scale problem in early 1989 is reviewed. Internally consistent distances to Local Group galaxies are given in Tables 5 and 6. Within the Local Group the distance scale is found to be 11±5% smaller than that previously adopted by Sandage and Tammann. Distances to nearby galaxies are used as stepping stones to the Virgo cluster. The interpretation of the Tully-Fisher observations of Virgo spirals is found to be ambiguous because it is not yet clear which spirals are cluster members and which are background objects. Distance estimates of the Virgo cluster obtained by different techniques are listed in Table 11. The distance modulus of the Virgo cluster is found to be 31.5±0.2, corresponding to a distance of 20±2 Mpc. The elliptical galaxies in the core of the Virgo cluster haveV ₀=1200±46 kms^–1, which corresponds toV _LG=1082±48 km s^–1. With an infall velocity of 250±50 km s^–1 this yields a cosmological redshiftV=1332±69 km s^–1, from which a Hubble parameter H₀=67±8 km s^–1 Mpc^–1 is obtained. Space Telescope observations of distant Cepheids, Tully-Fisher observations of spirals in the Hercules eluster, and interference filter observations of Virgo planetary nebulae in the light of [O_III], should soon result in a major improvement in the accuracy with which H₀ is known.     

Vacuum energy in cosmic dynamics

The analysis of the Th/U ratio in meteorites and the evolutionary ages of globular clusters favour values of the cosmic age of (19±5)×10⁹ yr. This evidence together with a Hubble parameterH ₀>70 km s^–1 Mpc^–1=(14×10⁹ yr)^–1 cannot be reconciled in a Friedmann model with =0. It requires a cosmological constant in the order of 10^–56 cm^–2, equivalent to a vacuum density _v =10^–29 g cm^–3 The Friedmann-Lemaître models (>0) with a hot big-bang have been calculated. They are based on a present value of the baryonic matter density of ₀=0.5×10^–30 g cm^–3 as derived from the primordial⁴He and²H abundances.For a Hubble parameter ofH ₀=75 km s^–1 Mpc^–1, our analysis favours a set of models which can be represented by a model with Euclidean metric (density parameter ₀=1.0, deceleration parameterq ₀=–0.93, aget ₀=19.7×10⁹ yr) and by a closed model with perpetual expansion (₀=1.072,q ₀=–1.0, aget ₀=21.4×10⁹ yr). A present density parameter close to one can indeed be expected if the conjecture of an exponential inflation of the very early universe is correct.The possible behaviour of the vacuum density is demonstrated with the help of Streeruwitz' formula in the context of the closed model with an inflationary phase at very early times.     

A period study of V450 Herculis

A detailed period study of the eclipsing binary system V450 Her has been presented. A new period (P= _. ^d 12724) has been given. The period changes in different portions of the O-C diagram, based on new period, have been estimated. The total period change ranges from 3.28×10^–6 d to 7.06×10^–5 d, which is appreciable.     

New activity cycle of the classical symbiotic star V1413 Aql

We present the results of our photometric UBV JHKLM observations in 2008?C2011 for the classical symbiotic star V1413 Aql. At the end of 2008, the hot component of V1413 Aql experienced the next strong outburst (??V > 2 _· ^m 5). According to the photometric criterion (B-V ?? 0 _· ^m 9 ± 0 _· ^m 2), the star was in an active state even in the period preceding the strong 2008 outburst. Two eclipsing minima of the same amplitude were observed for V1413 Aql in 2010 and 2011. Our analysis of the 2011 eclipse has allowed us to estimate the sizes of the components with respect to the orbital semimajor axis if the system is seen edge-on: the radius of the cool component is R _g/a = 0.28 and the radius of the hot component is R _h/a = 0.17. However, judging by the B-V color index, the eclipse may be noncentral.     

The first byurakan Spectral Sky Survey. Blue stellar objects. X. The zone+73°≤σ≤+80°

We present the tenth list of blue stellar objects of the second part of the First Byurakan Spectral Sky Survey (FBS). The list contains 100 objects in the region+73°+80° and3 ^h 30 ^m 18 ^h 30 ^m encompassing an area of 355 square degrees. The objects have stellar V magnitude within the limits 12.0–18.5 and B-V colors between–0.77 and+0.37. Of these 100 objects, 80 were discovered for the first time. We give the equatorial coordinates, stellar V magnitude, color index CI, and preliminary classification of the objects on the basis of low-disperion prismatic spectra. For 29 objects we give approximate types, among which 4 are candidates for quasars, 2 for Seyfert galaxies, 1 for superassociation galaxy IC 381, 18 for white dwarfs, and 4 for cataclysmic variables.Translated fromAstrofizika, Vol. 38, No. 2, 1995.     

The neutrino radiation of collapsing stellar cores and the neutrino burst detected from SN 1987 A

The properties of the neutrino burst generated by massive 1.5–2M collapsing stellar iron-oxygen cores are discussed. Special attention is given to the neutrino heat conductivity theory which allows us to calculate the transport of neutrinos through the collapsing stellar core up to the formation and during the first seconds of cooling of a hot hydrostatic neutron star. The theoretical predictions seem to be in good agreement with both the KAMIOKANDE II and IMB data on the neutrino burst detected from SN 1987A. The most reliable constraint on the neutrino rest mass is shown to bem _v <20–30eV, while the safest upper limit on the neutrino magnetic moment, µ _v < 10^–11 Bohr magnetons, results rather from the cooling of white dwarfs than from the SN 1987A neutrino data.Presented to the 13th International Conference Neutrino-88, Boston, U.S.A., 5–11 June, 1988.     

Photographicuvby photometry of the open cluster M52

Photographicuvby photometry of 15 stars in the open cluster M52 (NGC 7654) has been obtained. The distance modulusV _o–M _v=11.3±0.1 and mean cluster reddeningE(B–V)=0.57 are determined. Some basic physical characteristics of 30 stars with observeduvby values are obtained as well as a numerical estimation of the open cluster age 9.6×10⁷ yr is made.     

An expanding circumstellar cloud of Zeta Aurigae

Strong absorption satellite lines of CaI 6572 were found on spectrograms taken on three successive days just after the fourth contact of the 1971–72 eclipse of Zeta Aurigae. The radial velocities of the satellite lines are –88 km s^–1, –74 km s^–1, and –180 km^–1, respectively, relative to the K-type primary star (K4 Ib). These absorptions should be due to a circumstellar cloud in which the column density of neutral calcium atoms is 1×10¹⁷ cm^–2 and the turbulent velocities come to 20–50 km s^–1. It is suggested that the cloud may be formed by the rocket-effect of the Lyman quanta of the B-type component (B6 V). We estimate the density in the cloud to be 2×10¹¹ atoms cm^–3 fors=10R _K and 2×10¹⁰ atoms cm^–3 fors=10² R _K, wheres denotes the distance of the cloud from the K star andR _K the K star's radius. The mass loss rate of the K-type component is also estimated to be about 10^–7 M yr^–1, assuming that the expansion of the K star occurs isotropically.     

UBV photometry at geographic latitude 69°22′ North

UBV measurements of the light of the night sky in the auroral zone during three seasons are presented. The mean brightness of the night sky in theV band is found to be equal one 18^m1 star (arc sec)^–2, with considerable variations. The observed meanB-V andU-B indicies are +0 _. ^m 7 and –1 _. ^m 6, respectively.Light curves of variable stars during strong auroral activities are also shown. On the basis of measurements we briefly discuss the possibility of accurate stellar photometry in the auroral region.