Analysis of TESS Field Eclipsing Binary Star V948 Her:A Pulsating or Non-pulsating Star?

Pulsating stars occupy a significant place in the H-R diagram and it was thought that all stars inside the classical instability strip should pulsate.However,re...     

A Photometric Study of the W UMa-type Eclipsing Binary System GSC 0445-1993

Several new light minimum times for the eclipsing binary GSC 0445-1993 have been determined from the observations by Koppelman et al. and the orbital period of this system was revised. A photometric analysis was carried out using the 2003 version of the Wilson-Devinney code. The results reveal that GSC 0445-1993 is a W-type eclipsing binary with a mass ratio of q = 0.323(±0.002) and an over-contact degree of f = 22.8%(±4.2%). A small temperature difference between the components of △T = 135 K and an orbital inclination of i = 65.7°(±0.3°) were obtained. The asymmetry of its light curve (i.e., the O'Connell effect) for this binary star is explained by the presence of a dark spot on the more massive component.     

The phenomenon of the galaxy NGC 6286: A forming polar ring or a superwind?

We present our observations of the pair of interacting galaxies NGC 6285/86 carried out with the 6-m Special Astrophysical Observatory (SAO) telescope using 1D and 2D spectroscopy. The observations of NGC 6286 with a long-slit spectrograph (UAGS) near the Hα line revealed the rotation of the gaseous disk around an axis offset by 5″–7″ from the photometric center and a luminous gas at a distance up to 9 kpc in a direction perpendicular to the galactic plane. Using a multipupil fiber spectrograph (MPFS), we constructed the velocity fields of the stellar and gaseous components in the central region of this galaxy, which proved to be similar. The close radial velocities of the pair and the wide (5′×5′) field of view of the scanning Fabry-Perot interferometer (IFP) allowed us to simultaneously obtain images in the Hα and [N II]λ6583 lines and in the continuum, as well as to construct the radial velocity fields and to map the distribution of the [N II]λ6583/Hα ratio for both galaxies. Based on all these data, we studied the gas kinematics in the galaxies, constructed their rotation curves, and estimated their masses (2 × 10¹¹M_⊙ for NGC 6286 and 1.2 × 10¹⁰M_⊙ for NGC 6285). We found no evidence of gas rotation around the major axis of NGC 6286, which argues against the assumption that this galaxy has a forming polar ring. The IFP observations revealed an emission nebula around this galaxy with a structure characteristic of superwind galaxies. The large [N II]λ6583/Hα ratio, which suggests the collisional excitation of its emission, and the high infrared luminosity are additional arguments for the hypothesis of a superwind in the galaxy NGC 6286. A close encounter between the two galaxies was probably responsible for the starburst and the bipolar outflow of hot gas from the central region of the disk.     

A comparison of different cluster mass estimates: consistency or discrepancy?

Rich and massive clusters of galaxies at intermediate redshift are capable of magnifying and distorting the images of background galaxies. A comparison of different mass estimators among these clusters can provide useful information about the distribution and composition of cluster matter and its dynamical evolution. Using the hitherto largest sample of lensing clusters drawn from the literature, we compare the gravitating masses of clusters derived from the strong/weak gravitational lensing phenomena, from the X-ray measurements based on the assumption of hydrostatic equilibrium, and from the conventional isothermal sphere model for the dark matter profile characterized by the velocity dispersion and core radius of galaxy distributions in clusters. While there is excellent agreement between the weak lensing, X-ray and isothermal sphere model-determined cluster masses, these methods are likely to underestimate the gravitating masses enclosed within the central cores of clusters by a factor of 2–4 as compared with the strong lensing results. Such a mass discrepancy has probably arisen from the inappropriate applications of the weak lensing technique and the hydrostatic equilibrium hypothesis to the central regions of clusters, as well as from assuming an unreasonably large core radius for both luminous and dark matter profiles. Nevertheless, it is pointed out that these cluster mass estimators may be safely applied on scales greater than the core sizes. Namely, the overall clusters of galaxies at intermediate redshift can still be regarded as the dynamically relaxed systems, in which the velocity dispersion of galaxies and the temperature of X-ray emitting gas are good indicators of the underlying gravitational potentials of clusters.     

SWIFT J1749.4-2807: A neutron or quark star?

We investigate a unique accreting millisecond pulsar with X-ray eclipses,SWIFT J1749.4-2807(hereafter J1749),and try to set limits on the binary system by various methods including use of the Roche lobe,the mass-radius relations of both main sequence(MS)and white dwarf(WD)companion stars,as well as the measured mass function of the pulsar.The calculations are based on the assumption that the radius of the companion star has reached its Roche radius(or is at 90%),but the pulsar's mass has not been assumed to be a certain value.Our results are as follows.The companion star should be an MS one.For the case that the radius equals its Roche one,we have a companion star with mass M(～-)0.51 M⊙ and radius Rc(～-)0.52 R⊙,and the inclination angle is i(～-)76.5°; for the case that the radius reaches 90% of its Roche one,we have M(～-)0.43 M⊙,Re()0.44 R⊙ and i(～-)75.7°.We also obtain the mass of J1749,Mp(～-)1 M⊙,and conclude that the pulsar could be a quark star if the ratio of the critical frequency of rotation-mode instability to the Keplerian one is higher than～0.3.The relatively low pulsar mass(about～M⊙)may also challenge the conventional recycling scenario for the origin and evolution of millisecond pulsars.The results presented in this paper are expected to be tested by future observations.     

The stellar system HIP 101227: is it a binary,a triple or a quadruple system?

In this paper, we present the analysis of the stellar system HIP 101227 to determine the actual number of components in the system, and their properties. We use dynamical modeling and complex spectrophotometric(involving atmospheric modeling) techniques with recent data, to determine the physical properties and orbital solution for the system, respectively, with better accuracy than past studies. Based on our analysis, we found that the system is more consistent with being a quadruple rather than a binary or a triple system as suggested by previous studies. The total mass of the system determined from our SED analysis is 3.42 ± 0.20 M, which is distributed almost equally between the four stars. The stars are found to be zero-age main sequence stars; i.e., at the last stage of pre-main sequence, with age less than 200 Myr and spectral types K0. All four stars have very similar physical characteristics, suggesting that the fragmentation process is the most likely theory for the formation and evolution of the system.     

UGC 5119: A galaxy with a stellar polar ring?

We present our photometric BV R_c observations of UGC 5119, a candidate polar-ring galaxy. We have determined its absolute magnitude, \(M_{0,B} = - 20\mathop m\limits_. 3\), and total color indices, \((B - V)_t^0 = + 0\mathop m\limits_. 73 \pm 0\mathop m\limits_. 10\) and \((V - R_c )_t^0 = + 0\mathop m\limits_. 54 \pm 0\mathop m\limits_. 10\). A Fourier analysis of the shape of its isophotes shows that UGC 5119 is most likely an elliptical galaxy with a disk component in the central part and a “boxy” feature on the periphery. At distances larger than 8″, the galaxy exhibits a turn of its major axis and a change in the phase of the fourth harmonic. Assuming the position angle of the major axis to be constant, a stellar ringlike structure is distinguished in the galaxy. The age of the ring stars is the same as that of the stars in the host galaxy. The distinguished ringlike structure cannot be attributed to typical polar rings rich in gas and in young stars.     

A Study of Magnetized White Dwarf+Helium Star Binary Evolution to Type Ⅰa Supernovae

The white dwarf(WD)+helium(He)star binary channel plays an important role in the single degenerate scenario for the progenitors of type Ⅰa supernovae(SNe Ⅰa).Pr...     

Speckle interferometric binary system HD375; Is it a sub-giant binary?

Atmospheric modeling is used to build synthetic spectral energy distributions (SEDs) for the individual components of the speckle interferometric binary system HD375. These synthetic SEDs are combined together for the entire system and compared with its observed SED in an iterative procedure to achieve the best fit. Kurucz blanketed models and the measurements of magnitude differences were used to build these SEDs. The input physical parameters for building these best fitted synthetic SEDs represent adequately enough properties of the system. These parameters are: T _eff ^a = 6100 ± 50 K, T _eff ^b = 5940 ± 50 K, log g _a = 4.01 ± 0.10, log g _b = 3.98 ± 0.10, R _a = 1.93 ± 0.20R _⊙, R _b = 1.83 ± 0.20R _⊙, M _v ^a = 3 _· ^m 26 ± 0.40, M _v ^b = 3 _· ^m 51 ± 0.50, L _a = 4.63 ± 0.80 L _⊙, and L _b = 3.74 ± 0.70 L _⊙, in accordance with the new estimated parallax π = 12.02 ± 0.60 mas. A modified orbit of the system is built and compared with earlier orbits, and the masses of the two components are calculated as M _a = 1.35M _⊙ and M _b = 1.25M _⊙. Based on the estimated physical and geometrical parameters of the system, which are confirmed by synthetic photometry, we suggest that the two components are evolved subgiant (F8.5 IV and G0 IV) stars with the age of 3.5 Gyr, formed by fragmentation.     

The photospheric spectrum of the pre-FUor V1331 CYG: Is it a star or a disk?

The T Tauri variable V1331 Cyg is characterized by an intensive emission spectrum, by signatures of a high rate of mass loss, and also by presence of a circular reflection nebula. According to these characteristics, the star can be considered as a possible pre-FUor star. Up to the present the photospheric spectrum of the star has not been recorded. In this work we analyze the high-resolution spectra of V1331 Cyg that were obtained by G.H. Herbig with the HIRES spectrograph at the Keck-1 telescope in 2004 and 2007. For the first time the numerous photospheric lines of the star have been detected and the spectral class has been estimated, viz., G7-K0 IV. It is revealed that the projection of the rotation velocity is lower than the width of instrumental profile (vsini < 6 km/s); this means that the angle between the stellar axis of rotation and the line of sight is small. The radial velocity of the star derived from the photospheric lines is RV = ?15.0 ± 0.3 km/s. The difference in radial velocities for 2004 and 2007 is lower than the measurement error. The photospheric spectrum is veiled considerably, but the amount of veiling is not the same in different lines. This depends on the line strength in the template spectrum of the G7 IV star: in the weakest lines (EW = 5–10 mÅ in the template spectrum) VF ≈ 1 and it increases up to 4–5 in stronger lines. The H_α and H_β lines demonstrate classical P Cyg profiles, which testifies to an intensive wind with a maximal velocity of about 400 km/s. In addition, the emission lines of Fe II, Mg I and K I and of several other elements are accompanied by a narrow blue-shifted absorption at ?150...?250 km/s. The emission spectrum of V1331 Cyg is rich in the narrow (FWHM = 30–50 km/s) lines of neutral and ionized metals showing the excitation temperature T _exc = 3800 ± 300 K. The stellar mass M* ≈ 2.8M _⊙ and radius R* ≈ 5R _⊙ are estimated.     

Westerlund 1: bound or unbound?

The Galactic open cluster Westerlund 1 (Wd 1) represents the ideal local template for extragalactic young massive star clusters, because it is currently the only nearby young cluster with a mass of ～10⁵?M_⊙. Its proximity makes spatially resolved studies of its stellar population feasible, and additionally permits direct comparison of its properties with measurements of velocity dispersion and dynamical mass for spatially unresolved extragalactic clusters. Recently, we published the dynamical mass estimate based on spectra of four red supergiants. We have now identified six additional stars which allow a determination of radial velocity from the wavelength covered in our VLT/ISAAC near-infrared spectra (CO bandhead region near 2.29 μm), significantly improving statistics. Using a combination of stepping and scanning the slit across the cluster center, we covered an area which included the following suitable spectral types: four red supergiants, five yellow hypergiants, and one B-type emission-line star. Our measured velocity dispersion is 9.2 km?s^?1. Together with the cluster size of 0.86 pc, derived from archival near-infrared SOFI-NTT images, this yields a dynamical mass of 1.5×10⁵ M_⊙. Comparing this to the mass derived via photometry, there is no indication that the cluster is currently undergoing dissolution.     

Autonomous software: Myth or magic?

We discuss work by the eSTAR project which demonstrates a fully closed loop autonomous system for the follow up of possible micro‐lensing anomalies. Not only are the initial micro‐lensing detections followed up in real time, but ongoing events are prioritised and continually monitored, with the returned data being analysed automatically. If the “smart software” running the observing campaign detects a planet‐like anomaly, further follow‐up will be scheduled autonomously and other telescopes and telescope networks alerted to the possible planetary detection.We further discuss the implications of this, and how such projects can be used to build more general autonomous observing and control systems. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The extreme, red afterglow of GRB 060923A: distance or dust?

Gamma-ray bursts (GRBs) are powerful probes of the early Universe, but locating and identifying very distant GRBs remain challenging. We report here the discovery of the K -band afterglow of Swift GRB 060923A, imaged within the first hour post-burst, and the faintest so far found. It was not detected in any bluer bands to deep limits, making it a candidate very high- z burst  ( z ≳ 11)  . However, our later-time optical imaging and spectroscopy reveal a faint galaxy coincident with the GRB position which, if it is the host, implies a more moderate redshift (most likely   z ≲ 2.8  ) and therefore that dust is the likely cause of the very red-afterglow colour. This being the case, it is one of the few instances so far found of a GRB afterglow with high-dust extinction.     

Microlensing variability in FBQ 0951+2635: short-time-scale events or a long-time-scale fluctuation?

We present and analyse new R -band frames of the gravitationally lensed double quasar FBQ 0951+2635. These images were obtained with the 1.5-m AZT-22 Telescope at Maidanak (Uzbekistan) during the 2001–2006 period. Previous results in the R band (1999–2001 period) and the new data allow us to discuss the dominant kind of microlensing variability in FBQ 0951+2635. The time evolution of the flux ratio A / B does not favour the continuous production of short-time-scale (∼months) flares in the faintest quasar component B (crossing the central region of the lensing galaxy). Instead of a rapid variability scenario, the observations are consistent with the existence of a long-time-scale fluctuation. The flux ratio shows a bump during the 2003–2004 period and a quasi-flat trend in more recent epochs. Apart from the global behaviour of A / B , we study the intra-year variability over the first semester of 2004, which is reasonably well sampled. Short-time-scale microlensing is not detected in that period. Additional data in the i band (from new i -band images taken in 2007 with the 2-m Liverpool Robotic Telescope at La Palma, Canary Islands) also indicate the absence of short-time-scale events in 2007.     

The BL Lac Object PKS 0537-441: A Lens or Being Lensed?

1　IntroductionTheBLLacobjectPKS 0 53 7 44 1 (z=0 .896)isoneofthemostluminoussourcesofitsclass.Itshistoricalvariabilityisapprox .Δm =5mag (Stickeletal.,1 993 ) ,whichismuchlargerthantypicallyforBLLacobjects.Duetoitsdistance ,luminosityandstrongvariability,itwasspeculated,whetheritsintrinsicpropertiesmightbemodifiedbygravitational (micro)lensingeffects (e .g .Romeroetal.,1 995,Narayan&Schneider,1 990 ) .Thishasbeentestedbysearchinge .g .forgalaxiesalongtheline of sighttotheBLLac ,howeve…     

BV centauri: dwarf or classical nova?

The similarity in properties of GK Per and BV Cen suggests that the latter may be a classical nova remnant rather than a dwarf nova. Our H and V CCD photometry show no sign of a nova shell but disclose the presence of a close and probably physical companion. BV(RI) _c CCD photometry of the companion, assumed to be a dwarf, givesM _v =3.1±0.3 for BV Cen at quiescence. Even though half of the light in BV Cen comes from the secondary this is much brighter than expected for a dwarf nova and supports the conclusion that BV Cen was an unrecorded nova.