Hβ luminosities of planetary nebula central stars

The determination of the luminosities of planetary nebula central stars from H nebular fluxes is investigated. A correlation is obtained with the luminosities derived from independent stellar parameters. An average scaling factor is determined for H luminosities of optically thick nebulae, as well as correlations of this parameter with the Zanstra He II and H I temperatures.     

Rapid photometric and spectroscopic evolution of the young planetary nebula Hen 3–1357 and its central star SAO 244567

We present the results of spectroscopic and photometric observations for the young compact planetary nebula Hen 3–1357 and its central star SAO 244567. High-resolution spectroscopy has allowed the expansion velocity of the nebula, V _exp = 8.4 ± 1.5 km s^?1, and the heliocentric velocity of the object, V _r = +12.6 ± 1.7 km s^?1, to be determined. The gas shell parameters (N _e , T _e ), the extinction in the Hβ line, and the O, N, Ne, Ar, S, Cl, He, and C abundances have been determined from low-resolution spectra taken in 1992 and 2011. We have found significant changes in the relative intensities of forbidden lines in the spectrum of Hen 3–1357 within the last 20 years: the low-excitation [O I], [O II], and [N II] lines became stronger relative to Hβ by a factor of ～2, while the [O III] lines weakened by a factor of ～ 2, suggesting a decrease in the excitation class of the nebula. The V-band photometry performed under the ASAS-3 program revealed a decline in the yearly mean brightness of SAO 244 567 from 2001 to 2009 by $0_.^m 5$ and rapid variability with an amplitude of a few tenths of a magnitude. Published observational data in a wide spectral range, from the near ultraviolet to the radio band, suggest an appreciable weakening of the flux from the star and the nebula.     

Is the central binary system of the planetary nebula Henize 2–428 a type Ia supernova progenitor?

We critically discuss the recent observations of the binary system at the center of the bipolar planetary nebula Henize 2–428. We find that the proposed explanation of two equal-mass degenerate objects with a total mass larger than the Chandrasekhar limiting mass that supposedly will merge in less than a Hubble time, possibly leading to a SN Ia, is controversial. This hypothesis relies on the assumption that the variability of the He II 5412 Å  spectral line is due to two absorption components. Instead, we propose that it can be accounted for by a broad absorption line from the central system on top of which there is a narrow emission line from the nebula. This prompted us to study if the binary system can be made of a degenerate star and a low-mass main sequence companion, or of two degenerate objects of smaller mass. We find that although both scenarios can account for the existence of two symmetric broad minima in the light curve, the second one agrees better with observations. We thus argue that the claim that Henize 2–428 provides observational evidence supporting the double-degenerate scenario for SN Ia is premature.     

Changes in the spectrum of the recombining planetary nebula He 1–5

In 2008, we observed the spectrum of the planetary nebula He 1–5, which has had no ionization source for more than 50 years. Comparison with the observations performed in 1972–1976 and 1988 shows that the line intensity ratio I(λ5007[O III])/I(Hβ) decreased by a factor of 2.5, the intensity ratio of the red [N II] doublet to Hα was almost constant, and the [S II]-to-Hα intensity ratio may have slightly increased. The observed changes in the spectrum agree, within the limits of the observational errors, with the calculations of gas recombination in a medium-excitation nebula performed by Tylenda in 1980, but the nitrogen line intensities are higher than the calculated ones by 10–15%. This is most likely related to the slightly reduced nitrogen abundance adopted in the model. The onset of nebular recombination dates from the end of the 19th century and is consistent with its estimate from the photometric history of the central star.     

Expansion velocities of the planetary nebula NGC 7009—the high dispersion spectra line profiles

We investigated the line profiles of the high dispersion spectra of He?I, He?II, N?III, [N?II], [O?III], [Ar?III], [Ar?IV], [S?II], [S?III ], and [Cl?IV], secured at the center of the planetary nebula NGC 7009 with the fiber-fed Bohyunsan Echelle Spectrograph (BOES). The expansion velocities for the main shell and the faint outer thin shell were derived based on stronger double Gaussian profiles and the fast blue wing component, respectively. With the Keck 2D spectral images, we set the main shell boundaries as R～4″ and 6″ and the faint outer thin shell boundaries as R～11″ and 13″. The radial variation of expansion velocities of both shells does not follow a linear acceleration. The acceleration of the main shell gas seems to be in a retarded mode, while that of the outer faint shell gas seems to be affected by an additional force. The fast wing component appears also in the He?I, He?II, and N?III line profiles which are likely to have been formed in a compact region, located inside the main shell. The additional deceleration factor, such as the rotation of the central star or the dust gas in the gas shell might cause the non-linear acceleration. Based on the line profiles responsible for the three zones, we conclude that there were at least three major changes occurred in the central star temperature since the first outflow from the central star.     

The putative nebula of the Wolf-Rayet WR 60 star: a case of mistaken identity and reclassification as a new supernova remnant G310.5+0.8

We present narrow band AAO/UKST Hα images and medium and low resolution optical spectra of a nebula shell putatively associated with the Wolf-Rayet star WR 60. We also present the first identification of this shell in the radio regime at 843 MHz and at 4850 MHz from the Sydney University Molonglo Sky Survey (SUMSS), and from the Parkes-MIT-NRAO (PMN) survey respectively. This radio emission closely follows the optical emission. The optical spectra from the shell exhibits the typical shock excitation signatures sometimes seen in Wolf-Rayet stellar ejecta but also common to supernova remnants. A key finding however, is that the WR 60 star, is not, in fact, anywhere near the geometrical centre of the putative arcuate nebula ejecta as had been previously stated. This was due to an erroneous positional identification for the star in the literature which we now correct. This new identification calls into serious question any association of the nebula with WR 60 as such nebula are usually quite well centred on the WR stars themselves. We now propose that this fact combined with our new optical spectra, deeper Hα imaging and newly identified radio structures actually imply that the WR 60 nebula should be reclassified as an unassociated new supernova remnant which we designate G310.5+0.8.     

Searches for HH objects in star formation regions. VII. Herbig-Haro objects in the region of the nebula GM 2–41

Five new Herbig-Haro objects (HH 1036–1040) have been discovered in the neighborhood of the nebula GM 2–41 in a region with an area of 14′ × 14′, at the center of the HII region DR 15 located in the southern periphery of the Cyg OB2 association. Four of them have a complex structure typical of HH flows. Hydrogen molecular emission is detected in the object HH 1036 using archived images from the Spitzer telescope. Two new infrared nebulae illuminated by very red young stellar objects are also found.     

Plasma magnetosphere of rotating magnetized neutron star in the braneworld

Plasma magnetosphere surrounding rotating magnetized neutron star in the braneworld has been studied. For the simplicity of calculations Goldreich-Julian charge density is analyzed for the aligned neutron star with zero inclination between magnetic field and rotation axis. From the system of Maxwell equations in spacetime of slowly rotating star in braneworld, second-order differential equation for electrostatic potential is derived. Analytical solution of this equation indicates the general relativistic modification of an accelerating electric field and charge density along the open field lines by brane tension. The implication of this effect to the magnetospheric energy loss problem is underlined. It was found that for initially zero potential and field on the surface of a neutron star, the amplitude of the plasma mode created by Goldreich-Julian charge density will increase in the presence of the negative brane charge. Finally we derive the equations of motion of test particles in magnetosphere of slowly rotating star in the braneworld. Then we analyze particle motion in the polar cap and show that brane tension can significantly change conditions for particle acceleration in the polar cap region of the neutron star.     

How asteroseismology can constrain the global parameters of solar-like star models

In the previous years, p-mode oscillations (pressure oscillations stochastically excited by convection) have been detected in several solar-like stars thanks to the ground-based spectroscopic and space spectroscopic and photometric observations. We study the importance of seismic constraints on stellar modeling and the impact of their accuracy on reducing the uncertainties of global stellar parameters (i.e. mass, age, etc.). We use the Singular Value Decomposition (SVD) method to analyze the sensitivity of stellar models to seismic constraints. In this context, we construct a grid of evolutionary sequences for solar-like stars with varying age and mass. Around each model of this grid, we evaluate the partial derivatives with respect to a large set of free parameters: mass ?, age τ, mixing-length parameter α, initial helium abundance Y ₀, and initial metallicity Z/X ₀. Masses between 0.9 and 1.55 M _⊙ and central hydrogen abundances from Xc=0.7 to 0.05 have been considered in this study.     

Constraining the gravitational redshift of a neutron star from the Σ-meson well depth

The effect of the Σ-meson well depth on the gravitational redshift is examined within the framework of relativistic mean field theory for the baryon octet system. It is found that, for a stable neutron star, the gravitational redshift increases with the central energy density increase or with the mass increase but decreases as the radius increases. Considering a change of U_S^(N)U_{\Sigma}^{(N)} from −30 MeV to 30 MeV, for a stable neutron star the gravitational redshift near to the maximum mass increases. In addition, it is also found that the growth of the U_S^(N)U_{\Sigma}^{(N)} makes the gravitational redshift as a function of M _max/R increase, the higher the U_S^(N)U_{\Sigma}^{(N)} the less the change in the gravitational redshift.     

Past and future of the central double-degenerate core of Henize 2–428

It has been suggested that Type Ia supernovae(SNe Ia) could be produced in the conditions of the violent merger scenario of the double-degenerate model, in which a thermonuclear explosion could be produced when a double carbon-oxygen white dwarf(CO WD) merges. It has been recently found that the nucleus of the bipolar planetary nebula Henize 2–428 consists of a double CO WD system that has a total mass of^1.76 M⊙, a mass ratio of^1 and an orbital period of^4.2 h, which is the first and only discovered progenitor candidate for an SN Ia predicted by the violent merger scenario. In this work, we aim to reproduce the evolutionary history of the central double CO WD of Henize 2–428. We find that the planetary nebula Henize 2–428 may originate from a primordial binary that has a^5.4 M⊙primary and a^2.7 M⊙secondary with an initial orbital period of^15.9 d. The double CO WD was formed after the primordial binary experienced two Roche-lobe overflows and two common-envelope ejection processes.According to our calculations, it takes about^840 Myr for the double CO WD to merge and form an SN Ia driven by gravitational wave radiation after their birth. To produce the current status of Henize 2–428,a large common-envelope parameter is needed. We also estimate that the rate of SNe Ia from the violent merger scenario is at most 2.9 × 10^-4 yr^-1, and that the delay time is in the range of^90 Myr to the Hubble time.     

Charged analogue of Vlasenko-Pronin superdense star in general relativity

In this article we have derived a set of three static spherical symmetric well behaved solutions of Einstein-Maxwell field equations is obtained for a specific choice of electric field involving a parameter K. The solutions so obtained can be seen as a charge analogue of the neutral solution due to Vlasenko and Pronin. The physical features of solutions so obtained and that of Vlasenko and Pronin are investigated subject to the reality and the causality conditions i.e. Pressure, density (greater than pressure), pressure-density ratio and velocity of sound (less than the velocity of light) are positive and monotonically decreasing and the electric intensity is monotonically increasing in nature away from the centre. The maximum mass and radius occupied by the neutral solution are 2.1434 M _Θ and 16.7300 km respectively. For the charged solution, overall maximum mass and corresponding radius are found to be 6.8714 M _Θ and 20.6166 km respectively (for K=1.343).     

2D hydrodynamic simulations of super star cluster winds in a bimodal regime

It is shown that the winds of very massive and compact clusters evolve in a special bimodal way, such that in which the material deposited by stars into the inner cluster region becomes thermally unstable, forms cold dense clumps, and eventually feeds further episodes of star formation, while the material deposited into the outer region creates a quasi-stationary wind. We perform 2D numerical simulations of such winds using the finite difference hydrodynamic code ZEUS for which the cooling routine has been modified to make it suitable for modelling extremely fast cooling regions. We explore how the fraction of the deposited mass which is accumulated inside the cluster depends on the cluster parameters.     

Solving the mysteries of the diffuse interstellar medium with high-resolution UV spectroscopy

Understanding the complex structure, dynamics, and ionization of gas in the nearby interstellar medium is required before one can realistically model interstellar gas in other galaxies. High-resolution ultraviolet spectra provide the essential data for such studies because the resonance lines of most important atoms, ions, and molecules are located in the ultraviolet, and high spectral resolution is needed to resolve line profiles and determine the velocity structure along a line of sight. I list ten important physical questions concerning interstellar gas that require a more sensitive spectrometer than STIS and the desired spectral resolution to answer these questions.     

Supernova remnants, planetary nebulae and the distance to NGC 4214

We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.     

Spectral and photometric variability of the “runaway” star HD 214930

The paper contains the analysis of spectral and photometric variability of the “runaway” star HD 214930. The previously reported period of 4.7 day of the star’s radial velocity variability is confirmed. Optical photometric variability of the star has not been detected.     

The nature and structure of the emission line nebula K 3-35: a very young planetary nebula with precessing bipolar jet-like outflows?

We present Hα, [N  II ]6583 and 6-cm continuum images of the emission line nebula K 3-35. The optical images reveal an extended nebula (size ≃ 11 × 9 arcsec² in [N  II ]) in which most of the emission originates in a very narrow (width 0.7–1.3 arcsec) S-shaped region which extends almost all along the nebula (≃ 7 arcsec). The 6-cm continuum emission also arises in this narrow region, which is characterized by an exceedingly high point-symmetry and systematic and continuous changes of the orientation with respect to the nebular centre. The properties of the narrow region suggest that it represents a system of precessing bipolar jet-like components. Two low-excitation, compact bipolar knots near the tips of the jet-like components are observed in the deduced [N  II ]/Hα image ratio. These knots may be generated by the interaction of the collimated outflows with surrounding material. A comparison of the optical and radio images shows the existence of differential extinction within the nebula. Maximum extinction is observed in a disc-like region which traces the equator of the elliptical shell previously observed at 20-cm continuum. All available data strongly suggest that K 3-35 is a very young planetary nebula in which we could be observing the first stages of the formation of collimated outflows and point-symmetric structures typically observed in planetary nebulae. The properties of the jet-like components in K 3-35 are in good agreement with models of binary central stars in which highly collimated outflows originate either from a precessing accretion disc or via magnetic collimation in a precessing star.     

Evolutionary studies of the young star clusters: NGC 1960, NGC 2453 and NGC 2384

We report the analysis of the young star clusters NGC 1960, NGC 2453 and NGC 2384 observed in the J (1.12 μm), H (1.65 μm) and K′ (2.2 μm) bands. Estimates of reddening, distance and age as E(B?V)=0.25, d=1380 pc and t=31.6 to 125 Myr for NGC 1960, E(B?V)=0.47, d=3311 pc and t=40 to 200 Myr for NGC 2453 and E(B?V)=0.25, d=3162 pc and t=55 to 125 Myr for NGC 2384 have been obtained. Also, we have extended the color–magnitude diagrams of these clusters to the fainter end and thus extended the luminosity functions to fainter magnitudes. The evolution of the main sequence and luminosity functions of these clusters have been compared with themselves as well as Lyngå 2 and NGC 1582.