New orbits of wide visual double stars

Based on photographic and CCD observations with the Pulkovo 26-inch refractor, radial velocity measurements with the 1.5-m RTT-150 telescope (TUBITAK National Observatory, Turkey), and highly accurate observations published in the WDS catalog, we have obtained the orbits of ten wide visual double stars by the apparent motion parameter method. The orientation of the orbits in the Galactic coordinate system has been determined. For the outer pair of the multiple star HIP 12780 we have calculated a family of orbits with a minimum period P = 4634 yr. Two equivalent solutions with the same period have been obtained for the stars HIP 50 (P = 949 yr) and HIP 66195 (P = 3237 yr). We have unambiguously determined the orbits of six stars: HIP 12777 (P = 3327 yr), HIP 15058 (P = 420 yr), HIP 33287 (P = 1090 yr), HIP 48429 (P = 1066 yr), HIP 69751 (P = 957 yr), and HIP 73846 (P = 1348 yr). The orbit of HIP 55068 is orientated perpendicularly to the plane of the sky, P >1000 yr. The star HIP 48429 is suspected to have an invisible companion.     

<Emphasis Type="Italic">UVR</Emphasis> CCD photometry of stars in five sky areas with matched IR/radio sources

Five sky areas about the radio sources ICRS 1254+571, ICRS 1345+125, ICRS 1641+399, ICRS 1732+389, and ICRS 1807+698 were observed with the aim to identify reliably the extragalactic radio sources in these areas with bright infrared objects and objects in the optical range. The test CCD observations were made in the U, V, and R bands of the Johnson system with the 2-meter telescope of the Terskol Peak Observatory (North Caucasus, Russian Federation). The U, V, and B magnitudes and the equatorial coordinates α and δ in the USNO-A2.0 catalog system were determined for objects down to V ≈ 23^m in 8.5′ × 8.5′ areas, and these objects were identified with stars and infrared objects in the 2MASS catalog. The CCD image processing realized within the MIDAS/ROMAFOT program package on the basis of a new method for flat-field elimination is briefly described.     

New spectroscopic observations of the post-AGB star V354 Lac = IRAS 22272+5435

The strongest absorption features with the lower-level excitation potentials χ _low < 1 eV are found to be split in the high-resolution optical spectra of the post-AGB star V354 Lac taken in 2007–2008 with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Main parameters, T _eff =5650 K, log g=0.2, ξ _t =5.0 km/s, and the abundances of 22 chemical elements in the star’s atmosphere are found. The overabundance of the s-process chemical elements (Ba, La, Ce, Nd) in the star’s atmosphere is partly due to the splitting of strong lines of the ions of thesemetals. The peculiarities of the spectrum in the wavelength interval containing the LiI λ 6707 Å line can be naturally explained only by taking the overabundances of the CeII and SmII heavy-metal ions into account. The best agreement with the synthetic spectrum is achieved assuming ?(LiI)=2.0, ?(CeII)=3.2, and ?(SmII)=2.7. The velocity field both in the atmosphere and in the circumstellar envelope of V354 Lac remained stationary throughout the last 15 years of our observations.     

A model of low-mass neutron stars with a quark core

We consider an equation of state that leads to a first-order phase transition from the nucleon state to the quark state with a transition parameter λ>3/2 (λ=ρ_Q/(ρ_N+P₀/c²)) in superdense nuclear matter. Our calculations of integrated parameters for superdense stars using this equation of state show that on the stable branch of the dependence of stellar mass on central pressure dM/dP_c>0) in the range of low masses, a new local maximum with M_max=0.082_⊙ and R=1251 km appears after the formation of a toothlike kink (M=0.08M_⊙, R=205 km) attributable to quark production. For such a star, the mass and radius of the quark core are M_core=0.005M_⊙ and R_core=1.73 km, respectively. In the model under consideration, mass accretion can result in two successive transitions to a quark-core neutron star with energy release similar to a supernova explosion: initially, a low-mass star with a quark core is formed; the subsequent accretion leads to configurations with a radius of ～1000 km; and, finally, the second catastrophic restructuring gives rise to a star with a radius of ～100 km.     

Synchronous <Emphasis Type="Italic">UBVR</Emphasis> photometry and spectroscopy of DI Cephei

We present our synchronous spectroscopy and photometry of DI Cep, a classical T Tauri star. The equivalent widths and radial velocities of the individual components and Hα, Hβ, D1 and D2 Na I, and HeI λ5876 Å emission line profiles exhibit variability. We have found a clear positive correlation between the brightness and equivalent width for the Hα and Hβ emission lines. The photometric and spectroscopic data are satisfactorily described in phases of a 9-day period. The expected magnetic field of the star has been estimated using existing magnetospheric models to be 655–1000 G. The star is suspected to be a binary.     

FG Sge at the stage of dust shell ejection

New photometric observations of the variable star FG Sge, a rapidly evolving planetary nebula nucleus, were performed in 2003–2008. On 230 nights, we obtained 86 UBV and 155 BV RI (or R _c , I _c ) magnitude estimates. The maximum amplitude of the V-band light variations was >8 ^m . Six deep minima and four high maxima were observed. Analysis of the light curve has shown that the pulsation period of the star remained constant since 1991 and was P = 115 days. We have studied the wavelength dependence of the extinction at various phases of the light curve. The blueing of the B-V color at deep minima is interpreted as the result of light scattering in the circumstellar dust shell of the star formed by preceding dust ejections since 1992. Our spectroscopic observations performed on nine nights in 2003–2007 with the 125-cm telescope at the Crimean Station of the Sternberg Institute have confirmed the previously detected intensity variations of the Swan bands and the sodium doublet with brightness. It is noted that the Swan bands originate in the upper atmosphere, the star’s extended envelope, while the sodium doublet originates mainly in the circumstellar shell of FG Sge. We suggest that the star is currently located in the temperature-luminosity diagram at the turning point of the horizontal track of cooling in the direction of hot stars—evolution caused by the last helium shell flash at the planetary nebula stage.     

Ultra-flat galaxies selected from RFGC catalog. III. Star formation rate

We examine the star formation properties of galaxies with very thin disks selected from the Revised FlatGalaxy Catalog (RFGC). The sample contains 333 ultra-flat galaxies (UFG) at high Galactic latitudes, |b| > 10?, with a blue major angular diameter of a ≥ 1.'2, blue and red apparent axial ratios of (a/b)_b > 10, (a/b)_r > 8.5 and radial velocities within 10 000 kms^?1. As a control sample for them we use a population of 722 more thick RFGC galaxies with (a/b)_b > 7, situated in the same volume. The UFG distribution over the sky indicates them as a population of quite isolated galaxies.We found that the specific star formation rate, sSFR _FUV, determined via the FUV GALEX flux, increases steadily from the early type to late type disks for both the UFG and RFGC–UFG samples, showing no significant mutual difference within each morphological type T. The population of UFG disks has the average HI-mass-to-stellarmass ratio by (0.25 ± 0.03) dex higher than that of RFGC–UFG galaxies. Being compared with arbitrary orientated disks of the same type, the ultra-flat edge-on galaxies reveal that their total HI mass is hidden by self-absorption on the average by approximately 0.20 dex.We demonstrate that using the robust stellar mass estimate via 〈B?K〉-color and galaxy type T for the thin disks, together with a nowaday accounting for internal extinction, yields their sSFR quantities definitely lying below the limit of ?9.4 dex (yr^?1). The collected observational data on UFG disks imply that their average star formation rate in the past has been approximately three times the current SFR. The UFG galaxies have also sufficient amount of gas to support their observed SFR over the following nearly 9 Gyrs.     

Stars with Discrepant <Emphasis Type="Italic">v</Emphasis> sin <Emphasis Type="Italic">i</Emphasis> as Derived from the Ca II 3933 and Mg II 4481 Å Lines. VII. HD9531 (SB), HD31592 (SB2), HD129174 (SB?)

In this paper of the series we analyze three stars listed among stars with discrepant v sin i: HD9531 and HD31592, which also show radial velocity variations inherent to spectroscopic binaries, and HD129174 which is an Mn-type star with a possible magnetic field. In HD9531 we confirm the radial velocity derived fromthe hydrogen lines as well as fromthe Ca II line at 3933 Å as variable. The profile of the calcium line also appears variable, and with the estimated magnetic induction B_e = ?630 ± 1340 G, this suggests that the abundance of calcium possibly varies over the surface of the star. We identified the lines of the secondary component in the spectrum of HD31592 revealing thus it is an SB2 binary with B9.5V and A0V components. While the primary star rotates with v sin i = 50 km s^?1, the secondary star is faster with v sin i = 170 km s^?1. We find that only 60% of the Mn lines identified in the spectrum of HD129174 can be fitted with a unique abundance value, whereas the remaining lines are stronger or fainter. We also identified two Xe II lines at 5339.33 Å and 5419.15 Å and estimated their log g f.     

Stars with discrepant <Emphasis Type="Italic">υ</Emphasis> sin <Emphasis Type="Italic">i</Emphasis> as derived from Ca II 3933 and Mg II 4481 Å lines. II. Multiple star HD 90569

Axial rotation of a star plays an important role in its evolution, physical condition in its atmosphere and appearance of its spectrum. Methods of determinations of υ sin i are based on comparison of the observed profiles of spectral lines with theoretical ones. Their accuracy depends on the kind and quality of spectrograms as well as on the algorithms used. A frequently used method is the simple comparing of one line, e.g. the Ca II at 3933 Å or Mg ii at 4481 Å. This however, may result in a false value of υ sin i if low dispersion spectra are used. In this work we studied contemporary CCD as well as older photographic spectra of the multiple star HD90569. We determined the projected rotational velocity value to be υ sin i = 11 km/s. Besides formerly reported enhancing of lines of Cr, Fe, Mn and Sr, we found also large overabundances of rare earths, gallium and platinum. Helium, carbon, nitrogen, oxygen, aluminium, calcium, scandium and nickel are in deficit. The spectrum of the occultation double was not identified to be of the SB2-type, however, there are some observable evidences that the pair creates a binary with a long orbital period. Despite this there are also observations that leave such interpretation uncertain.     

Independent estimate of the interstellar extinction toward FU Ori

Speckle-interferometric observations of FU Ori are performed with the 6-m telescope of the Special Astrophysical Observatory with 600/40 nm and 800/100 nm (central bandwidth/halfwidth) filters. The companion star FU Ori S that was recently discovered at λ >-1.25µm was recorded in observations with the λ/Δλ==800/100 nm filter. The positional parameters and magnitude difference of the companion in the filter considered are found to be θ = (163.9 ± 1.0)°, ρ = (0.493 ± 0.007)″, Δm = 3.96 ± 0.28. An analysis of the spectral energy distribution of the companion implies that for the extinction A _V toward FU Ori to be greater than about 1.6 ^m , i.e., the minimum value required by the available models of the fuor, the spectral type of the companion star must be no later than K3. The reliability of this conclusion and the possible ways for obtaining more accurate estimates of A _V are discussed.     

Variability and rapid evolution of the protoplanetary object IRAS 18062+2410=V886 her

We present our long-term photometric and spectroscopic observations of a high-latitude B supergiant with an infrared excess—the protoplanetary nebula IRAS 18062+2410. OurU BV observations in 2000–2006 have confirmed the rapid irregular photometric variability of the star with a maximum amplitude as high as 0 _. ^m 4 in V that we found previously. The B—V and U—B color indices vary with amplitudes as high as 0 _. ^m 10 and 0 _. ^m 25, respectively, and show no clear correlation with the brightness. Our V-band CCD observations on 11 nights in 2006 have revealed brightness trends during the night. The variability of IRAS18062+2410 is similar in pattern to the light variations in other hot post-AGB objects and some of the nuclei of young planetary nebulae. We assume that pulsations and a variable stellar wind can be responsible for the variability of these stars. In addition to the rapid variability, our 12-year-long observations have revealed a systematic decline in the mean brightness of IRAS 18062+2410. This may be related to a rise in the temperature of the star at constant luminosity as a result of its evolution. Low-resolution spectroscopic observations have shown a systematic increase in the equivalent widths of the Hα, Hβ, [NII]λ6584 Å, OI λ8446 Å, and [OII] λ7320–7330 Å emission lines. The changes in the star’s emission line spectrum are probably caused by an increase in the degree of ionization of the gas shell due to a rise in the temperature of the ionizing star. Our photometric and spectroscopic observations of IRAS 18062+2410 confirm the previously made assumptions that the star evolves very rapidly to the region of planetary nebulae.     

Stars with discrepant <Emphasis Type="Italic">v</Emphasis> sin <Emphasis Type="Italic">i</Emphasis> as derived from the Ca II 3933 and Mg II 4481 Å lines. VI. HD 199892 — an SB2 spectroscopic binary

We analyzed the spectra of a well known SB1 binary HD199892 for which the projected rotational velocity v sin i, introduced in the literature, significantly differs when determined from the lines of Ca II at 3933 Å and ofMg II at 4481 Å. Contrary to the former findings, we discovered the signs of spectral lines of a companion star in the profile of Hβ as well as weak metallic lines in the high resolution high S/N spectra covering the most of the visual region. We estimated the secondary star to be a main sequence A4V star with a mass of 2.2M _⊙ and derived its radial velocity which resulted in the mass of the primary M = 4.6M _⊙. Short sections of the spectra in the Mg II 4481 Å and Ca II 3933 Å regions are analyzed as well.     

Multicolor Photometry and Spectroscopy of the Yellow Supergiant with Dust Envelope HD 179821 = V1427 Aquilae

We present the results of multicolor (UBV JHKLM) photometry (2009–2017) and low-resolution spectroscopy (2016–2017) of the semi-regular variable V1427 Aql = HD 179821, a yellow supergiant with gas-dust envelope. The star displays low-amplitude (ΔV<0 _. ^m 2) semi-periodic brightness variations superimposed on a long-term trend. The light curve shape and timescale change from cycle to cycle. There are temperature variations characteristic for pulsations; brightness oscillations with no significant change of color are also observed. The UBV data for the 2009–2011 interval are well reproduced by a superposition of two periodic components with P = 170^d and 141^d (or P = 217^d—the one year alias of P = 141^d). The variation became less regular after 2011, the timescale increased and exceeded 250^d. Unusual photometric behavior was seen in 2015 when the star brightness increased by 0 _. ^m 25 in the V filter in 130 days and reached the maximum value ever observed in the course of our monitoring since 1990. In 2009–2016 the annual average brightness monotonically increased in V, J, K, whereas it decreased in U and B. The annual average U ? B, B ? V, and J ? K colors grew, the star was getting redder. The cooling and expanding of the star photosphere along with the increasing of luminosity may explain the long-term trend in brightness and colors. Based on our photometric data we suppose that the photosphere temperature decreased by ~400 K in the 2008–2016 interval, the radius increased by ~24%, and the luminosity grew by ~19%. We review the change of annual average photometric data for almost 30 years of observations. Low-resolution spectra in the λ4000?9000 Å wavelength range obtained in 2016–2017 indicate significant changes in the spectrum of V1427 Aql as compared with the 1994–2008 interval, i.e., the Ba II and near-infraredCa II triplet absorptions have gotten stronger while the OI λ7771-4 triplet blend has weakened that points out the decrease of temperature in the region where the absorptions are formed. The evolutionary stage of the star is discussed. We also compare V1427 Aql with post-AGB stars and yellow hypergiants.     

Spectroscopic study of the optical counterpart to the fast X-ray transient IGR J17544-2619 based on observations at the 1.5-m RTT-150 telescope

We present the results of our long-term photometric and spectroscopic observations at the Russian–Turkish RTT-150 telescope for the optical counterpart to one of the best-known sources, representatives of the class of fast X-ray transients, IGR J17544-2619. Based on our optical data, we have determined for the first time the orbital and physical parameters of the binary system by the methods of Doppler spectroscopy.We have calculated theoretical spectra of the optical counterpart by applying non- LTE corrections for selected lines and obtained the parameters of the stellar atmosphere (T _eff = 33 000 K, log g = 3.85, R = 9.5 R _⊙, and M = 23 M _⊙). The latter suggest that the optical star is not a supergiant as has been thought previously.     

Features of magnetic field structures in chemically peculiar stars. IV

We present results of modeling of the sample of magnetic stars. We have obtained such important for magnetic star physics parameters as the mean surface magnetic field B_s, the magnetic field at magnetic poles—B_p, the dipole inclination to the rotation equatorial plane α, and the distance to monopoles from the center of the star Δa. We present some information onmagnetic star physics that helps to understand the derived results better.     

On a family of well behaved perfect fluid balls as astrophysical objects in general relativity

A family of well behaved perfect fluid balls has been derived starting with the metric potential g ₄₄=B(1+Cr ²) ⁿ for all positive integral values of n. For n≥4, the members of this family are seen to satisfy the various physical conditions e.g. c ² ρ≥p≥0,dp/dr<0,dρ/dr<0, along with the velocity of sound \((\sqrt{dp/c^{2}d\rho} )< 1\) and the adiabatic index ((p+c ² ρ)/p)(dp/(c ² dρ))>1. Also the pressure, energy density, velocity of sound and ratio of pressure and energy density are of monotonically decreasing towards the pressure free interface (r=a). The fluid balls join smoothly with the Schwarzschild exterior model at r=a. The well behaved perfect fluid balls so obtained are utilised to construct the superdense star models with their surface density 2×10¹⁴  gm/cm³. We have found that the maximum mass of the fluid balls corresponding to various values of n are decreasing with the increasing values of n. Over all maximum mass for the whole family turns out to be 4.1848M _Θ and the corresponding radius as 19.4144 km while the red shift at the centre and red shift at surface as Z ₀=1.6459 and Z _a =0.6538 respectively this all happens for n=4. It is interesting to note that for higher values of n viz n≥170, the physical data start merging with that of Kuchowicz superdense star models and hence the family of fluid models tends to the Kuchowicz fluid models as n→∞. Consequently the maximum mass of the family of solution can not be less than 1.6096 M _Θ which is the maximum mass occupied by the Kuchowicz superdense ball. Hence each member of the family for n≥4 provides the astrophysical objects like White dwarfs, Quark star, typical neutron star.     

Chemical composition of high proper-motion stars based on short-wavelength optical spectra

The results of spectroscopic observations made with the NES echelle spectrograph of the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences in the wavelength interval of 3550–5100 Å with a spectral resolution of R≥50000 are used to determine the fundamental parameters and atmospheric abundances of more than 20 chemical elements including heavy s- and r-process elements from Sr to Dy for a total of 14 metal-poor G-K-type stars. The abundances of Mg, Al, Sr, and Ba were calculated with non-LTE line-formation effects accounted for. The inferred overabundance of europium with respect to iron agrees with the results obtained for the stars of similar metallicity. The chemical composition of the star BD+80°245 located far from the Galactic plane is typical of stars of the accreted halo: this star exhibits, in addition to the over-deficiency of α-process elements, also the over-deficiency of the γ-process element Ba: [Ba/Fe]= ?1.46. The kinematical parameters and chemical composition imply that the stars studied belong to different Galactic populations. The abundance of the long-living element Th relative to that of the r-process element Eu is determined for six stars using the synthetic-spectrum method.     

High Resolution Optical Spectroscopy of an Intriguing High-Latitude B-Type Star HD119608

We present an LTE analysis of high resolution echelle optical spectra obtained with the 3.9-m Anglo-Australian Telescope (AAT) and the UCLES spectrograph for a B1Ib high galactic latitude supergiant HD119608. A fresh determination of the atmospheric parameters using line-blanketed LTE model atmospheres and spectral synthesis provided T_eff = 23 300 ± 1000 K, log g = 3.0 ± 0.3, and the microturbulent velocity ξ = 6.0 ± 1.0 kms^?1 and [Fe/H] = 0.16. The rotational velocity of the star was derived fromC, O, N, Al, and Fe lines as v sin i = 55.8 ± 1.3 kms^?1. Elemental abundances were obtained for 10 different species. He, Al, and P abundances of the star were determined for the first time. In the spectra, hot post-AGB status as well as the Pop I characteristics of the star were examined. The approximately solar carbon and oxygen abundances, along with mild excess in helium and nitrogen abundances do not stipulate a CNO processed surface composition, hence a hot post-AGB status. The LTE abundances analysis also indicates solar sulphur and moderately enriched magnesium abundances. The average abundances of B dwarfs of well studied OB associations and Population I stars show a striking resemblance to abundances obtained for HD119608 in this study. This may imply a runaway status for the star.     

The evolutionary status of the semiregular variable QY Sge

Repeated spectroscopic observations made with the 6-m telescope of SAO RAS yielded new data on the radial-velocity variability of the anomalous yellow supergiant QY Sge. The strongest and most peculiar feature in its spectrum is the complex profile of NaI D lines, which contains a narrow and a very wide emission components. The wide emission component can be seen to extend from ?170 to +120 km/s, and at its central part it is cut by an absorption feature, which, in turn, is split into two subcomponents by a narrow (16 km/s at r=2.5) emission peak. An analysis of all the Vr values leads us to adopt for the star a systemic velocity of V_r=?21.1 km/s, which corresponds to the position of the narrow emission component of NaI. The locations of emission-line features of NaI D lines are invariable, which point to their formation in regions that are external to the supergiant’s photosphere. Differential line shifts of about 10 km/s are revealed. Emission in the Hα line is weaker than in NaI D lines, it fills the photospheric absorption almost completely. The absorption lines in the spectrum of QY Sge have a substantial width of FWHM ≈ 45 km/s. The method of model atmospheres is used to determine the following parameters: the effective temperature T _eff =6250±150 K, surface gravity l _{g g}=2.0±0.2, and microturbulence velocity ξ _t =4.5±0.5 km/s. The chemical composition of the atmosphere differs only slightly from the solar composition: the metallicity of the star is found to be somewhat higher than the solar metallicity with an average overabundance of iron-peak elements of [Met/H]_⊙=+0.20. The star is found to be slightly overabundant in carbon and nitrogen, [C/Fe]=+0.25, [N/Fe]=+0.27. The α-process elements Mg, Si, and Ca are slightly overabundant, on the average by [α/H]_⊙=+0.12, and sulfur overabundance is higher, [S/α]=+0.29. The strong overabundance of sodium, [Na/Fe]=+0.75, is likely to be due to the dredge-up of the matter processed in the NeNa cycle. Heavy elements of the s-process are underabundant relative to the Sun. On the whole, the observed properties of QY Sge do not give grounds for including this star into the group of RCrB or RVTau-type objects.