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On the post-common-envelope central star of the planetary nebula NGC 2346

On the post-common-envelope central star of the planetary nebula NGC 2346

Central star binarity is now thought to be a key ingredient in under- standing the formation and evolution of a large fraction of planetary nebulae (PNe; Jones & Boffin 2017) – playing an important role in the observed morphologies (Hillwig et al. 2016), chemistry (Wesson et al. 2018), and perhaps even in the planetary nebula luminosity function (PNLF; Ciardullo et al. 2005; Davis et al. 2018). However, very little is known about the processes by which binary stars can produce a PN – particularly the common envelope (CE) phase (see e.g. the review of Ivanova et al. 2013). One particularly interest- ing puzzle is the observed period distribution of post-CE central stars that shows a strong propensity of periods of a few days or less (Jones & Boffin 2017), while models of the CE phase gener- ally predict many more systems at longer periods (see section 4 of De Marco, Hillwig & Smith 2008). As such, the properties of the few longer period systems known, including recent discoveries

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Cluster and nebular properties of the central star-forming region of NGC 1140*

Cluster and nebular properties of the central star-forming region of NGC 1140*

We present new high spatial resolution Hubble Space Telescope/Advanced Camera for Surveys (ACS) imaging of NGC 1140 and high spectral resolution Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectroscopy of its central star-forming region. The central region contains several clusters, the two brightest of which are clusters 1 and 6 from Hunter, O’Connell & Gallagher, located within star-forming knots A and B, respectively. A nebular analysis indicates that the knots have a Large Magellanic Cloud-like metallicity of 12 + log O/H = 8.29 ± 0.09. According to continuum-subtracted Hα ACS imaging, cluster 1 dominates the nebular emission of the brighter knot A. Conversely, negligible nebular emission in knot B originates from cluster 6. Evolutionary synthesis modelling implies an age of 5 ± 1 Myr for cluster 1, from which a photometric mass of (1.1 ± 0.3) × 10 6 M

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IC 4663: the first unambiguous [WN] Wolf-Rayet central star of a planetary nebula

IC 4663: the first unambiguous [WN] Wolf-Rayet central star of a planetary nebula

low. The lack of temporal coverage less than a day also makes this possibility difficult to rule out entirely since the median period of close binary central stars is 0.3–0.4 days (Miszalski et al. 2009a, 2011b). The small variability in the line intensity profile may be explained by either noise in the spectrum or wind turbulence (e.g. Grosdidier, Acker & Moffat 2000, 2001b). There is little historical information on any photometric variability of IC 4663, e.g. whether an LMC-N66-like outburst has occurred. The insensitivity of Shaw & Kaler (1989) to magnitudes fainter than V = 16 provides a rea- sonable lower limit to the central star magnitude in 1989. The very bright nebula precludes measuring central star magnitudes from photographic plate material.

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The G305 star-forming complex: the central star clusters Danks 1 and Danks 2

The G305 star-forming complex: the central star clusters Danks 1 and Danks 2

identified within the Galaxy. It is host to many massive stars at all stages of formation and evolution, from embedded molecular cores to post-main-sequence stars. Here, we present a detailed near-infrared analysis of the two central star clusters Danks 1 and Danks 2, using Hubble Space Telescope+NICMOS imaging and Very Large Telescope+ISAAC spectroscopy. We find that the spectrophotometric distance to the clusters is consistent with the kinematic distance to the G305 complex, an average of all measurements giving a distance of 3.8 ± 0.6 kpc. From analysis of the stellar populations and the pre-main-sequence stars, we find that Danks 2 is the elder of the two clusters, with an age of 3 + −1 3 Myr. Danks 1 is clearly younger with an age of 1.5 +1.5 −0.5 Myr, and is dominated by three very luminous H-rich Wolf–Rayet stars which may have masses 100 M . The two clusters have mass functions consistent with the Salpeter slope, and total cluster masses of 8000 ± 1500 and 3000 ± 800 M for Danks 1 and Danks 2, respectively. Danks 1 is significantly the more compact cluster of the two, and is one of the densest clusters in the Galaxy with log (ρ/M pc −3 ) = 5.5 +0.5 −0.4 . In addition to the clusters, there is a population of apparently isolated Wolf–Rayet stars within the molecular cloud’s cavity. Our results suggest that the star-forming history of G305 began with the formation of Danks 2, and subsequently Danks 1, with the origin of the diffuse evolved population currently uncertain. Together, the massive stars at the centre of the G305 region appear to be clearing away what is left of the natal cloud, triggering a further generation of star formation at the cloud’s periphery.

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VLT / near-Infrared Integral Field Spectrometer Observations of Molecular Hydrogen Lines in the Knots in the Planetary Nebula NGC 7293 (the Helix Nebula)

VLT / near-Infrared Integral Field Spectrometer Observations of Molecular Hydrogen Lines in the Knots in the Planetary Nebula NGC 7293 (the Helix Nebula)

O’Dell, Henney & Ferland (2007) also obtained an excitation temperature of 988 K from 5- to 15-μm spectra in the outer part of the nebula. O’Dell et al. (2007) state that the distance of those slit positions is similar to that of Cox et al. (1998). Although they do not provide detailed information on the slit positions and ob- serving mode for their two Spitzer spectra, the Spitzer archive can provide this, suggesting that their two slit positions are 5.6 and 4.2 arcmin from the central star, and the slit size is 3.6 × 57 arcsec 2 .

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Optical Spectroscopic Monitoring Observations of a T Tauri Star V409 Tau

Optical Spectroscopic Monitoring Observations of a T Tauri Star V409 Tau

We also considered the obscuration of light from the photosphere by the dis- torted disk. AA Tau-like variables show periodic dips in their light curves, which are thought to be caused by the obscuration of light from the photosphere caused by warps in the inner disk. The periods of the dips are typically five to ten days, corresponding to a distance of 0.1 AU between the central star and the in- ner disk for Keplerian rotation [19]. In the case of AA Tau, the luminosity drops by 1.2 magnitude with a period of 8.2 days [8] [20]. It is proposed that the inner disk is distorted by the magnetic field and thus obscures the photosphere. As light from the central star passes through the disk, the intensity decreases un- iformly within a certain wavelength range. As the absorption line weakens, the adjacent continuum light also weakens. As a result, the equivalent width of the absorption line does not change when the photosphere is obscured.

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Modeling and interpretation of images

Modeling and interpretation of images

The most straightforward way to get rid of the central star is to put a small mask in the beam of the telescope which blocks its light. This does, however not automatically get rid of the di ff raction e ff ects around it. Special coronograph masks are developed to reduce the di ff raction e ff ects around the coronograph mask. For example, the apodizing phase plate coronagraph developed by Kenworthy et al. (2010) suppresses all starlight on one side of the image at the cost of a lot of starlight at the other side. This was succesfully used to image a protoplanet candidate embedded inside the protoplanetary disk surrounding HD 100546 (see also Fig. 2 from Quanz et al. 2013).

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The shaping of planetary nebula Sh 2-188 through interaction with the interstellar medium

The shaping of planetary nebula Sh 2-188 through interaction with the interstellar medium

Sh 2 − 188 is an example of strong interaction between a planetary nebula (PN) and the in- terstellar medium (ISM). It shows a single arc-like structure, consisting of several filaments, which is postulated to be the result of motion through the ISM. We present new H α images from the Isaac Newton Telescope Photometric H α Survey of the Northern Galactic Plane which reveal structure behind the filamentary limb. A faint, thin arc is seen opposite the bright limb, in combination forming a closed ring. Behind the faint arc a long wide tail is detected, doubling the size of the nebula. The nebula extends 15 arcmin on the sky in total. We have developed a ‘triple-wind’ hydrodynamical model, comprising of the initial ‘slow’ asymptotic giant branch (AGB) wind and the later ‘fast’ stellar wind (the interacting stellar winds model), plus a third wind reflecting the motion through the ISM. Simulations at various velocities of the central star relative to the ISM indicate that a high velocity of 125 km s −1 is required to reproduce the observed structure. We find that the bright limb and the tail already formed during the AGB phase, prior to the formation of the PN. The closure of the ring arises from the slow–fast wind interaction. Most of the mass lost on the AGB has been swept downstream, providing a potential explanation of the missing-mass problem in PNe. We report a proper motion for the central star of 30 ± 10 mas yr − 1 in the direction of the bright limb. Assuming

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Additions to the genera Asterolibertia and Cirsosia (Asterinaceae, Asterinales), with particular reference to species from the Brazilian Cerrado

Additions to the genera Asterolibertia and Cirsosia (Asterinaceae, Asterinales), with particular reference to species from the Brazilian Cerrado

Description: Colonies epiphyllous, circular or irregular, single or conuent, black, 3–10 mm diam. Hyphae straight, with opposite branches, brown, septate, hyphal cells cylindrical, 4.5–5.5 m diam, smooth. Appressoria numerous, entire, intercalary, elliptical or with a lateral protuberance, unicellular, 10–15 × 7–9 m, brown, penetration peg central on the appressorial cells. Ascomata supercial, thyriothecia, scutiform, on top of a mycelial mat, circular, single to conuent, fringed at the margins, randomly distributed in the colony, 150–207 m diam, opening by a central star-shaped ssure, dark brown; wall textura radiata, with isodiametrical cells. Pseudoparaphyses cylindrical, septate, branched, hyaline, 1–1.5 m wide. Asci bitunicate in structure, ssitunicate, disposed as an upright palisade layer, globose to ovoid, 8-spored, hyaline, 37.5–47.5 × 29–32.5 m. Ascospores oblong to oblong-clavate, ends rounded, straight to slightly arched, 1-septate, constricted at the supramedian septum, hyaline, becoming pale brown to brown at maturity, verruculose, 34–40 × 10–14 m. Asexual morph not seen.

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A 'Rosetta Stone' for protoplanetary disks : the synergy of multi wavelength observations

A 'Rosetta Stone' for protoplanetary disks : the synergy of multi wavelength observations

Many of the uncertainties in our knowledge of disks re- sult from incomplete observations, which lead to de- generacies when interpreting observations e.g. in terms of disk structure, gas/dust ratio, and dust properties. When interpreting dust continuum observations such as the SED or the IR visibilities and closure phases, there is a great degree of freedom in the selection of the dust shape, structure, composition (in particular, for featureless species such as carbon) and dust size distri- bution used to model the data. In addition, gas/dust ratios are usually unknown. Consequently, models are intrinsically degenerated: a large number of models may describe the data equally well. An additional compli- cation comes from the parameter space being strongly non-continuous, so very different geometries, dust prop- erties, and structures may provide a similarly good fit. The stellar properties have a large impact on the disk structure as well as on its observables. The strong UV and X-ray irradiation by the young central star creates complicated and quite unique non-LTE conditions that cannot be studied elsewhere, which is one of the dif- ficulties in understanding disk chemistry. In addition, a good characterization of the star (spectral type, ex- tinction, luminosity, activity) is the only way to obser- vationally constrain many disk properties, such as ages and accretion rates (Sicilia-Aguilar et al. 2006b, 2010; Manara et al. 2012, 2013; Da Rio et al. 2014). The ob- servational impact is larger for the parts of the disk SED for which the star provides a strong contribution, such as the NIR and the UV. The intrinsic variability of young stars is another potential source of inconsistency between non-simultaneous datasets.

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Advection-dominated accretion: A self-similar solution

Advection-dominated accretion: A self-similar solution

Advection-dominated accretion is expected to occur in several astrophysical situations. Thin accretion disks for example exhibit a thermal instability at sufficiently low optical depth, when the cooling through free-free emission is unable to keep up with the viscous energy generation. Numerical models of accretion disks in cataclysmic variables (Narayan & Popham 1993) show that, under the influence of this instability, the disk switches to an advection-dominated flow where only a fraction of the released energy is radiated. A more extreme possibility is that at very low accretion rates the infalling material may never cool sufficiently to collapse to a thin disk, and we could imagine an advection-dominated flow all the way from the outermost radius down to the central star or black hole.

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Multiwavelength Imaging of Planetary Nebulae: Resolving & Disentangling Structure

Multiwavelength Imaging of Planetary Nebulae: Resolving & Disentangling Structure

It is well known that most stars form in pairs, which further supports this hypothesis. Obser- vations of AGB stars have found many with companions that have already begun to play a role in the deformation of the stellar envelope (Le˜ ao et al., 2006; Mayer et al., 2014). Binary companions can also hide themselves by falling into the envelope of the central star. This common envelope binary is expected to accelerate the loss of the AGB envelope by injecting additional energy and momentum. It is in this phase of evolution that jets can form and launch the stellar envelope away from the binary (Soker, 2004; Nordhaus et al., 2007; Tocknell et al., 2014; De Marco et al., 2015). As a result of the common envelope phase, the orbit of the core of the AGB star and the com- panion star shrinks, and in some cases can lead to coalescence. When this happens, the companion star disappears, leaving behind a single star. The only evidence of a companion ever existing is believed to be within the nebula itself. Not only does the morphology inform us of this, but also the chemical composition of the central star. This is how [WR]-type central stars are believed to have formed (De Marco & Soker, 2002; De Marco, 2008; Hajduk et al., 2010).

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Gamma Ray Bursts Generated by Hyper Accreting Kerr Black Hole

Gamma Ray Bursts Generated by Hyper Accreting Kerr Black Hole

We have summarized that high-energy GRBs generated by rotating black hole-accretion disk system. Basic analyses of Figure 1 deduce that accretion lu- minosity drops as we go away from the central Kerr black hole. This probes the energy injection that generates plateau phase as well as x-ray flares. The radia- tion flux as function of emitted photon frequency and energy density explained the engine as accreting compact binary galactic X-ray emitters. The observed luminosity in X-ray ranges for active galactic nuclei tell us, hard X-ray emission from galactic compact binary systems, typical X-ray source binaries, scorpius X-1 [32]. Early X-ray light curve components with large luminosities imply ac- cretion disk radiation of these progenitors where, the total flux is emitted in the soft X-ray energy range shown in Figure 3. Thin disk radiates locally as a black- body above critical frequency as shown in Figure 3, indicate that the total flux is emitted in the soft X-ray range at high frequency due to Poynting, magnetic and radiation pressure fluxes as studied in Equation (51) and the result shown in Figure 3. The spectral evolution resembles that of high energy particle accelera- tion. Particularly, synchrotron and multi-colour blackbody contribution (see Figure 4). The electron energy distribution in the most stable inner radius ( r I )

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The Galah survey: classification and diagnostics with t-SNE reduction of spectral information

The Galah survey: classification and diagnostics with t-SNE reduction of spectral information

Galah is an ongoing high-resolution spectroscopic survey with the goal of disentangling the formation history of the Milky Way using the fossil remnants of disrupted star formation sites that are now dispersed around the Galaxy. It is targeting a randomly selected magnitude-limited ( V „ 14 ) sample of stars, with the goal of observing one million objects. To date, 300,000 spectra have been obtained. Not all of them are correctly processed by parameter estimation pipelines, and we need to know about them. We present a semi-automated classi fi cation scheme that identi fi es different types of peculiar spectral morphologies in an effort to discover and fl ag potentially problematic spectra and thus help to preserve the integrity of the survey results. To this end, we employ the recently developed dimensionality reduction technique t-SNE ( t-distributed stochastic neighbor embedding ) , which enables us to represent the complex spectral morphology in a two-dimensional projection map while still preserving the properties of the local neighborhoods of spectra. We fi nd that the majority ( 178,483 ) of the 209,533 Galah spectra considered in this study represents normal single stars, whereas 31,050 peculiar and problematic spectra with very diverse spectral features pertaining to 28,579 stars are distributed into 10 classi fi cation categories: hot stars, cool metal-poor giants, molecular absorption bands, binary stars, H α/ H β emission, H α/ H β emission superimposed on absorption, H α/ H β P-Cygni, H α/ H β inverted P-Cygni, lithium absorption, and problematic. Classi fi ed spectra with supplementary information are presented in the catalog, indicating candidates for follow-up observations and population studies of the short-lived phases of stellar evolution.

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Design and Implementation of a Practical FTTH Network

Design and Implementation of a Practical FTTH Network

OLT will be deployed in each central office and the quantity will be calculated to satisfy the coverage capacity. Each OLT will connect to the converged Layer 3 switches and then the routers to ITPC PDN network. BRAS will be installed in the core central offices. BRAS are full load configuration with the processing capability of not l ess than 115,000 lines. In the normal status, each BRAS just take the service traffic which belong to the corresponding areas. When one is broken, the other BRAS will take the whole service. AAA is the same with BRAS. EMS remote redundancy is ensuring the reliability.

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High mass star formation through filamentary collapse and clump fed accretion in G22

High mass star formation through filamentary collapse and clump fed accretion in G22

Prevalent fi laments detected in our Galaxy are well- established as some of the main sites for star formation ( André et al. 2010, 2014; Molinari et al. 2010a; Wang et al. 2014, 2015, 2016 ) . Speci fi cally, hub- fi lament systems are frequently reported forming high-mass stars ( e.g., Hennemann et al. 2012; Liu et al. 2012, 2016; Peretto et al. 2013 ) . Converging fl ows detected in several hub- fi lament systems channel gas to the junctions where star formation is often most active ( e.g., Kirk et al. 2013; Peretto et al. 2014; Liu et al. 2016 ) . However, how gas fl ows help individual star-forming cores grow in mass is still poorly understood.

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The Star Scene Modeling and Generation for Hardware in the loop Simulation

The Star Scene Modeling and Generation for Hardware in the loop Simulation

The coordinate system of the star sensor image plane is s-xyz. The origin of the coordinate system is the center of the star sensor. The z-axis is the optical axis of the sensor system. The attitude of the star sensor in the equatorial inertial coordinate system O-XYZ is described by the right ascension angle, α, the declination angle, β, and the rotation angle of the star sensor image plane, κ, as shown in Figure 1.

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The orbital period of V458 Vulpeculae, a post double common envelope nova

The orbital period of V458 Vulpeculae, a post double common envelope nova

Several other systems have been claimed as Type Ia su- pernova progenitors. The subdwarf-B+white dwarf binary KPD 1930+2752 is among the best candidates, but its to- tal mass is very close to the critical mass (Maxted et al. 2000; Ergma et al. 2001; Geier et al. 2007). The first He nova, V445 Puppis, may contain a binary system composed of a massive white dwarf accreting from a helium star com- panion (Woudt et al. 2009). The 3.9-h central binary star of planetary nebula PNG135.9+55.9 (SBS 1150+599A) has also been put forward (Tovmassian et al. 2010). In this case, a post-AGB star and, presumably, a compact companion also amount to a mass just close to the Chandrasekhar limit. An obvious objection to our scenario is the fact that the post-AGB donor star would have to fill its Roche lobe in or- der to sustain mass transfer while it is still contracting. A star filling its Roche lobe must obey an orbital period-mean density law, so we used the evolutionary tracks of Bl¨ ocker (1995) in an attempt to find stellar parameters which fit both the 98-min orbit of V458 Vul and the results of our photoionisation model. We find that a star with an initial and final mass of 3 M ⊙ and 0 . 625 M ⊙ , respectively, on a

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KIC 2856960 : the impossible triple star

KIC 2856960 : the impossible triple star

During our attempts to fit KIC 2856960 two other peculiar prob- lems surfaced that we never resolved. The elusive second compo- nent of the binary is one of these. In all the models that provide a reasonable fit to the dips, star 2 is 2.5 to 4 times smaller than star 1. We mentioned this as the chief drawback of the quadruple models in the previous section, because there star 2’s small radius is out of kilter with its mass. Such unequal ratios are also not favoured by the binary light curve, although in section 3.2 we argued that star spots made the true ratio uncertain. However, there can be no doubt that the two eclipses in the binary light curve have a similar depth, implying a similar surface brightness for each component of the binary. It is then very hard to understand how these two stars, which are most likely unevolved, low mass main-sequence stars, can differ so much in radius.

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A STUDY ON DESIGN AND ANALYSIS OF WEB MART MINING AND ITS RELEVANCE TODAY

A STUDY ON DESIGN AND ANALYSIS OF WEB MART MINING AND ITS RELEVANCE TODAY

The web mart - database schema is designed to make the underlying data structure more comprehensible to users and to simplify the query process. The recommended approach for data warehouse data modeling is to follow a Dimensional Modeling approach-called Star Schema. The star schema has a central fact table with dimension tables at the points of the star. The single fact table’s composite primary key requires a foreign key field corresponding to the primary key field of each dimension table. The dimension tables are hierarchical and thus highly denormalised [4] .A fact table is a primary table in the web mart that contain the business facts, and dimension tables are companion tables to the fact table that represent the business critical dimensions and contain the attributes for the business critical dimensions. The central fact table provides users the ability to do analysis on business facts, and dimensional tables provide users the ability to do analysis on these business facts in various business critical dimensions[10].

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