bluuebunny/crossref_metadata_2025 huggingface dataset:
2(+1?) Binary Central Stars: A Spectroscopic Study
Authors: Exter Katrina , Pollacco Don
Published: July 2016

We report on a study of 3 post common-envelope binary systems; EC 11575-1845, V644 Cas (the central star of the PN HFG 1), and VW Pyx (the central star of K 1–2). These 3 have similar photometric and spectroscopic characteristics. Emission lines from the heated face of the cool star move with different velocities, and the H I lines are very broad with deep absorption component(s) visible at all phases.
The Zanstra Temperatures Revisited
Authors: Gruenwald R. , Viegas S. M.
Published: July 2016

The temperature of the central stars in planetary nebulae is generally obtained by the Zanstra method. This method provides two values for the temperature of a single star: one obtained from the H recombination lines, TZ(H), and another from the He recombination lines, TZ(He II). The ratio (ZR) of these two values can be different from unit, leading to the well-known “Zanstra discrepancy”. The discrepancy is higher for lower temperature stars and the method does not reproduce the high values of stellar temperatures suggested by stellar evolutionary models. In this work a careful analysis of the effect of the optical depth on the determination of the Zanstra temperature is made, using photoionization models. The effects due to deviations from a blackbody spectrum, as well as to the He abundance in the nebulae, are also discussed. We show, quantitatively, that the details of the distribution of the H and He II Zanstra temperatures are mainly explained by an optical depth effect; in particular, the fact that the discrepancy is larger for low stellar temperatures. The results also show that for high stellar temperatures both Zanstra temperatures underestimate the stellar temperature, even for high optical depths. The stellar temperature, as well as the optical depth, can be obtained from a plot of ZR vs. TZ(He II). Since for nebulae of very low optical depth and/or high stellar temperature this plot only provides lower limits for T*, we propose the use of the line intensity ratio He II/He I vs. TZ(He II) diagram for obtaining the stellar temperature, as well as the nebular optical depth. The results of this work has been published in ApJ 543, 889 (2000).
NIR Fabry-Perot Imaging Spectroscopy of PNe
Authors: Arias Lorena , Rosado Margarita
Published: July 2016

In this work we report the radial velocity field of the molecular hydrogen in five planetary nebulae, obtained from scanning Fabry-Perot interferometer observatins at the near-infrared vibrationally excited line H2 S(1) 1-0 at 2.122 μm. Direct images of the nebulae in both transitions of molecular hydrogen S(1) 1-0 and S(1) 2-1 are used in order to discriminate between shocks and fluorescence as the excitation mechanism of the H2. Finally, some physical parameters are derived.
The Molecular Morphology of Evolved Stars
Authors: Fong D. , Meixner M. , Sutton E. C. , Welch W. J.
Published: July 2016

We present 12CO J=1-0 observations of a small sample of evolved stars to investigate the evolution of the molecular envelope from the AGB phase to the formation of the PN.
High Resolution CO Imaging of a Cometary Globule in the Helix Nebula
Authors: Huggins P. J. , Forveille T. , Bachiller R. , Cox P.
Published: July 2016

We report high resolution CO (1–0) line imaging of a prominent cometary globule in the Helix Nebula. The results confirm earlier observations (Huggins et al. 1992) that globules consist of dense condensations of neutral gas embedded in the ionized nebula, and they provide new constraints on the structure and kinematics of the gas.
Astromineralogy: Crystalline silicates
Authors: Molster F. J.
Published: July 2016

Silicates are the most abundant dust component in our Universe. For a long time it was generally assumed that around evolved stars only amorphous silicates were present. The infrared space observatory (ISO; Kessler et al. 1996) discovered that the abundance of crystalline silicates can be quite significant. Thanks to ISO it is now for the first time possible to determine the exact chemical composition of the silicates, and in contrast to the amorphous silicates, the crystalline silicates turned out to be very Fe-poor (i.e. forsterite and enstatite). Careful investigations of the spectra of crystalline silicates in several conditions, both in laboratory and in space, have taken place. It was found that not only the abundance of the crystalline silicates is related to the spatial distribution of the circumstellar dust, but also the shape of the features differs between sources with and without a disk-like dust distribution. Because of the many spectral features of the crystalline silicates one can easily determine temperatures and mass ratios for enstatite and forsterite. But even single features contain interesting information. The position and FWHM of the 69.0 micron forsterite feature, might be used as a new diagnostic of characteristic temperatures of (crystalline) silicate dust, while the 33.6 micron forsterite feature bears evidence for its formation history.
Dust Features in Carbon-rich Planetary Nebulae
Authors: Pei Albertina , Volk Kevin
Published: July 2016

Carbon-rich AGB stars, protoplanetary nebulae (PPNe), and PNe show a variety of dust features attributed to carbon-based compounds. Of particular interest are the three dust features peaking near 21, 26 and 33 μm. The 26 and 33 μm features (collectively the “30 μm feature”; see Volk et al. 2002) are always observed together. The 21 μm feature is weak in the AGB phase and becomes more prominent in the PPN phase, which implies carrier evolution. We wish to see how this evolution continues into the PN phase from detailed modelling of the infrared spectra of PNe.
Temperature Variations from HST Imagery and Spectroscopy of NGC 7009
Authors: Rubin R. H. , Bhatt N. J. , Dufour R. J. , Buckalew B. A. , Barlow M. J. , Liu X.-W. , Storey P. J. , Balick B. , Ferland G. J. , Harrington J. P. , Martin P. G.
Published: July 2016

We obtained new HST/STIS long-slit spectra and WFPC2 imagery of the planetary nebula NGC 7009 in order to obtain high spatial resolution of the intrinsic flux ratio [O III] 4364/5008, which is a well-known diagnostic for electron temperature (Te). Our primary purpose was to quantify Te variations across the nebula. We address whether the observational data support the possibility that the [fractional] mean-square Te variation (t2) (Peimbert 1967) in NGC 7009 may be as large as ~0.1. Such large values are required to reconcile the “abundance dichotomy” by Te variations alone. The abundance dichotomy (discussed by Liu at greater length elsewhere in this volume) refers to the significantly higher heavy element abundances derived from optical recombination lines (e.g., a factor of ~5 for NGC 7009, Liu et al. 1995) compared with the corresponding values deduced from collisionally-excited lines.
Broad Hα wings in Young Planetary Nebulae
Authors: Arrieta Anabel , Torres-Peimbert Silvia
Published: July 2016

In a sample of 30 young planetary nebulae, proto-PNe and other emission line objects we have found 11 young PNe and 2 symbiotic stars that show very broad wings of the emission Hα line (from 800 km s-1 and up to 5100 km s-1). For 7 objects, their first report was in Arrieta & Torres-Peimbert (2002).
Three-Dimensional Monte Carlo Simulations of Ionised Nebulae
Authors: Ercolano Barbara , Morisset Christopher , Barlow Michael J. , Liu Xiao-wei , Storey Peter J.
Published: July 2016

A three-dimensional self-consistent photo-ionisation code is developed using Monte Carlo techniques in order to build realistic models of photoionised nebulae of arbitrary geometry and density distribution. The code's results are benchmarked against those of estabilished codes. Two models are computed for the planetary nebula NGC 3918 using two different density distributions. The results of the two models are compared with the observations.
Raman Scattering and the Hidden He II Emission Region in the Bipolar Planetary Nebula M2-9
Authors: Lee Hee-Won
Published: July 2016

In the spectrum of the young bipolar planetary nebula M2-9, we detected the He II Raman scattered feature at 6545 Å. However, in the same spectrum the He II emission lines at 6527 Å and 6560 Å are absent, which implies that the He II emission region is hidden from our line of sight and that the H I scattering region is pretty much extended not to be obscured entirely. We perform photoionization computations to estimate the physical size of the He II emission line region ≲ 1015 cm in the presence of hot luminous star with T ≳ 105 K and L ≲ 103L⊙.
Keck HIRES Spectra of the Planetary Nebula NGC 7009
Authors: Hyung Siek , Fletcher André , Aller Lawrence H.
Published: July 2016

With strategically important diagnostic lines of, e.g., [O II], [O III] and [S II], secured with the Keck I HIRES, we obtained electron densities and temperatures, while retaining 3-D spatial information for the well-known elliptical nebula NGC 7009: we found that the temperature fluctuations exceeded those reported in the HST imaging study, i.e. Te ~9500 – 11500 K; we also found large velocity dispersions in the [S II] maps (with extremely high density fluctuations, i.e. log Ne = 3.8 – 4.5), but not in the [O II] ones. The [S II] map indicates that this emission is from numerous small-scale blobs of size ~ 1″ spread over a wider region, while [O II] shows no such evidence. The [S II] emission is likely to be due to shock excitation, while the [O II] emission is perhaps due to photoionization.
Analysis of Ultraviolet Absorption Lines in NGC 6543 and NGC 6826
Authors: Bremer M. , Grewing M. , Barnstedt J. , Kappelmann N.
Published: July 2016

During the ORFEUS-SPAS II mission (November 19th - December 7th 1996, aboard the space shuttleColumbia), the elliptical planetary nebulae NGC 6543 and NGC 6826 have been studied with the Echelle spectrometer. The instrumental wavelength range and resolution are 900Å - 1400Å and 0.1Å, respectively (R= 10000), which provides detailed information about emission and absorption lines which are inaccessible for ground-based observations. We present a new analysis of the absorption lines imposed on the spectra of the central stars.
X-ray Aureola of Central Stars
Authors: Oskinova L. , Brown J. C.
Published: July 2016

We report the discovery of a correlation between X-ray luminosity of PNe and bolometric luminosity of central stars from CHANDRA data and discuss briefly its interpretation.
Observations of Planetary Nebulae Haloes
Authors: Corradi Romano L.M.
Published: July 2016

An improved database of ionized haloes around PNe has been built by adding the results of an extensive observational campaign to the data available in the literature. The new observations allowed us to discovered new haloes around CN 1-5, IC 2165, IC 2553, NGC 2792, NGC 2867, NGC 3918, NGC 5979, NGC 6578, PB 4, and possibly IC 1747.

The global sample consists of 29 AGB haloes, that are believed to still contain information about the mass loss from the AGB progenitor star. Six of these haloes show a highly asymmetrical geometry that is tentatively ascribed to the interaction of the stellar outflow with the ISM.

Another 5 PNe show candidate recombination haloes. These are produced by the recombination front that sets up when the stellar luminosity drops in its post-AGB evolution. The resulting, limb-brightened shell resembles a real AGB halo, but is not related to AGB any mass loss event.

Double AGB haloes are found in at least 4 PNe.

For 11 PNe, deep images are available, but no halo is found to a level of ≲ 10-3 the peak surface brightness of the inner nebula.

These observations show us that ionized haloes are a common morphological component of PNe, being found in 70% of elliptical PNe for which adequately deep images exist. Statistical properties of the haloes are briefly discussed. Using the kinematical ages of the haloes and inner nebulae, we conclude that most of the PNe with detected haloes have hydrogen burning central stars.
On the Galactic Evolution of Bipolar Planetary Nebulae
Authors: Durand S. , Köppen J. , Maciel W.
Published: July 2016

Bipolar Planetary Nebulae (hereafter PNe) are almost all of the Type I and have the most massive progenitors among PNe. They are mostly found at very low galactic latitudes and thus are expected to follow rather closely the differential rotation. Moreover since they are strongly suspected to constitute the youngest population among PNe, then some bipolars may have not achieved a complete galactic revolution yet and we can reasonably suppose that some signs of their recent galactic evolution still exist.
HST Observations of Young Planetary Nebulae
Authors: Kwok Sun , Su Kate Y.L. , Sahai Raghvendra
Published: July 2016

Seven compact PNe with high radio surface brightness (and therefore presumably young) were observed with the HST WFPC2 under cycle 8 program 8307 (PI: S. Kwok). Observations were made with three narrow-band filters, F656N (Hα), F658N ([NII]) and F502N ([OIII]). The [NII] images of six of the nebulae are shown in Figure 1.
Formation of the 3-Ring Structure in the PN of the Progenitor of SN 1987A by an MHD Process
Authors: Tanaka Takashi , Washimi Haruichi
Published: July 2016

Optical observations by the HST have shown a fantastic 3-ring structure in the circumstellar space of the SN 1987A. We attempt to reproduce the 3-ring structure from an MHD simulation which takes into account the wind-wind interaction between the slow, magnetized stellar wind generated while the progenitor was a red supergiant (RSG) and the subsequent fast stellar wind ejected from the same star after it had evolved into the blue supergiant (BSG). An important assumption in the simulation is that both the RSG and BSG winds have toroidal magnetic field and coronal holes. The simulation shows that the magnetic pinch effect is essential for the formation of the equatorial ring and that the amplification of initial density asymmetry by the effect of the dynamical interaction is responsible for the formation of two outer rings.
Orientation Effects in Bipolar Planetary Nebulae
Authors: Schwarz Hugo E. , Monteiro Hektor
Published: July 2016

Using a sample of 29 bipolar Planetary Nebulae (BPNe) we show correlations between the luminosity and SED shape with the inclination to the line of sight of the objects polar axes. The presence of an equatorial “doughnut” of material around the central object can explain both these correlations and also and the bipolar shape.
Fractal Analysis of the Helix Nebula (NGC 7293)
Authors: Datta Srabani
Published: July 2016

In this paper, the Helix nebula (NGC 7293) is postulated to be a fractal describable by a Julia set. In order to support this hypothesis, a cometary filament is chosen from the periphery of the shell and is analyzed using an automated software. The box dimension of NGC 7293 is found to be 1.841059.
Velocity Field of the Planetary Nebula Wray 16-423
Authors: Gesicki Krzysztof , Zijlstra Albert A.
Published: July 2016

We have applied the “Torun models” to the PN Wray 16-423, and found evidence for an embedded shock in the nebula.
Morphological and Kinematical Modelling of PNe and Nova Shells Using XSHAPE
Authors: Harman D. J. , Bryce M. , O'Brien T. J. , Meaburn J.
Published: July 2016

XSHAPE has been developed to aid the better understanding of the 3D morphologies and kinematics of PNe and novae, by producing models which closely predict the observed 2D images and long-slit spectra of these objects. Early successes include plausible simulations for the elliptical PN Sa 2-21 and the nova HR Del.
Analysis on Internal Motions of the Halo Planetray Nebula, H4-1
Authors: Otsuka M. , Tamura S. , Yadoumaru Y. , Tajitsu A.
Published: July 2016

Up to now, ten planetary nebulae are regarded as halo planetary nebulae (halo PNe). We obtained low- and moderate-dispersion spectra of the spatially resolved halo planetary nebula H4-1 in the wavelength region of λλ3700-6800 Å with the Cassegrain Spectrograph of 74-inch telescope at Okayama Astronomical Observatory. In the moderate dispersion observation, we were able to obtain [O III] λλ4959,5007 and Hα of H4-1 at several position angles (P.A.). The image was spatially resolved and its apparent angluar size should be less than 10″.0.
Planetary Nebulae as Tracers of Chemical Evolution in External Galaxies
Authors: McCall Marshall L. , Richer Michael G.
Published: July 2016

Thanks to recent advances in instrumentation, metal abundances now can be measured routinely for PNe situated in galaxies beyond the Magellanic Clouds. Consequently, PNe are becoming a valuable tool for studying the chemical evolution of external galaxies, especially those which are not forming stars. Here we review problems and progress in this exciting nascent field of interdisciplinary research.
Oxygen Abundances for the Planetary Nebulae in M32, NGC 185, and NGC 205
Authors: Richer Michael G. , McCall Marshall L.
Published: July 2016

We present spectroscopy of planetary nebulae in M32, NGC 185, and NGC 205. With these new data, spectra exist for 14 planetary nebulae in M32, for 5 planetary nebulae in NGC 185, and 13 planetary nebulae in NGC 205. From these data, oxygen abundances based upon electron temperatures derived from detections of [O III]λ4363 may be derived for 11 planetary nebulae in M32, 5 in NGC 185, and 7 in NGC 205. The mean oxygen abundances and their dispersions based upon these [O III]λ4363 detections are 8.51 ± 0.20, 8.21 ± 0.27, and 8.20 ± 0.24 in M32, NGC 185, and NGC 205, respectively, in the usual 12 + log(O/H) format.

We confirm a previous finding that a significant fraction of the planetary nebulae in M32 have anomalously strong [N II] lines (Stasińska et al. 1998). Seven of the planetary nebulae for which there now exist spectra (half of the total) have I([N II]λ6584)/I(Hβ) > 1.5. These objects are concentrated towards the centre of M32, though less so than the light.

When we combine these new oxygen abundances with extant data, we find that the the same physical processes appear to control the chemical evolution of ellipticals, dwarf spheroidals, and the bulges of spirals. In addition, it is clear that dwarf spheroidals incorporated their metal production into stars much more efficiently than dwarf irregulars, casting more doubt upon an evolutionary link between these two types of dwarf galaxies.
Planetary Nebulae as Extragalactic Distance Indicators
Authors: Ciardullo Robin
Published: July 2016

The planetary nebula luminosity function (PNLF) plays a key role in the distance ladder, as it is the only general purpose standard candle that is applicable to both Pop I and Pop II systems. We review the physics underlying the method, and compare its distances to distances obtained from Cepheids and surface brightness fluctuations (SBF). We show that PNLF distances agree with the geometric distances to the LMC and NGC 4258, and that, on a galaxy-by-galaxy basis, the relative PNLF, Cepheid, and SBF distances are in excellent agreement with no systematic trends. However, even though the PNLF and SBF methods are both calibrated by Cepheids, the PNLF distance scale is ~17% smaller than the SBF scale. We discuss this offset, and examine the possible causes of the discrepancy.
Kinematics of Planetary Nebulae in M51's Tidal Tail
Authors: Feldmeier John J. , Mihos J. Christopher , Durrell Patrick R. , Ciardullo Robin , Jacoby George H.
Published: July 2016

The galaxy pair NGC 5194/95 (M51) is one of the closest and best known interacting systems. Despite its notoriety, however, many of its features are not well studied. Extending westward from NGC 5195 is a low surface brightness tidal tail, which can only be seen in deep broadband exposures. Our previous [O III] λ5007 planetary nebulae (PN) survey of M51 recovered this tidal tail, and presented us with a opportunity to study the kinematics of a galaxy interaction in progress. We report the results of a spectroscopy survey of the PN, aimed at determining their kinematic properties. We then use these data to constrain new self-consistent numerical models of the system.
The Bottom of the Main Sequence and Beyond: Speculations, Calculations, Observations, and Discoveries (1958–2002)
Authors: S. Kumar Shiv
Published: July 2016

In this paper, I briefly review the theoretical and observational work done since 1958 on the gaseous objects with mass below the H-burning limit. Special attention is paid to the theory that I developed during the period 1958–1962 for the hydrogen-rich gaseous objects with mass below the minimum main sequence mass of ~0.08 M⊙. The three main predictions of this theory (Kumar 1962a; Kumar 1962b; Kumar 1963a; Kumar 1963b) are discussed. Fragmentation processes for interstellar clouds are discussed, and it is pointed out that the minimum mass of a gaseous fragment may be as low as 0.001 M⊙. Observational results obtained since 1995 on the luminous and dark objects of very low mass are briefly reviewed. Comments are made on the basic nature of the stars and planets, and it is pointed out that the processes of star formation are fundamentally different from those of planet formation. Arguments are presented to show that some of the very-low-mass dark companions, discovered since 1995, were most probably formed by the star formation processes and not by the planet formation processes.
Evolutionary Models for Low Mass Stars and Brown Dwarfs at Young Ages
Authors: Baraffe Isabelle , Chabrier Gilles , Allard France , Hauschildt Peter
Published: July 2016

We analyse evolutionary tracks at young ages for low mass stars with masses m ≤ 1.4 M⊙ and brown dwarfs down to one mass of Jupiter. We analyse current theoretical uncertainties due to initial conditions. Simple tests on initial conditions show the high uncertainties of models at ages ≲ 1 Myr.
Candidate Brown Dwarfs in Orion OB1b
Authors: Sherry W. H. , Walter F. M. , Wolk S. J.
Published: July 2016

We have photometrically identified eleven candidate brown dwarfs in 0.2 deg2 of the Orion OB1b association. This is consistent with a rising mass function down to ~0.06M⊙. Assuming the IMF of Kroupa (2002) this suggests a population of 40–200 brown dwarfs per deg2 (0.01M<0.075M⊙).
Determination of Substellar Mass Function of Young Open Clusters Using 2MASS and GSC Data
Authors: Tej Anandmayee , C. Sahu Kailash , Chandrasekhar T. , Ashok N. M.
Published: July 2016

We present a statistical method to derive the mass functions of open clusters using sky survey data such as the 2 Micron All Sky Survey (2MASS) and the Guide Star Catalogue (GSC). We have used this method to derive the mass functions in the stellar/substellar regime of three young, nearby open clusters, namely IC 348, σ Orionis and Pleiades. The mass function in the low mass range (M< 0.50M⊙) is appreciably flatter than the stellar Salpeter function for all three open clusters. The contribution of objects below 0.5 M⊙ to the total mass of the cluster is ~40% and the contribution of objects below 0.08 M⊙ to the total is ~4%.
The Substellar Members of the Pleiades
Authors: D. Dobbie Paul , F. Jameson Richard , L. Osborne Samantha , T. Hodgkin Simon , J. Pinfield David
Published: July 2016

We have compiled the largest magnitude limited sample of candidate substellar Pleiads to date. We fit King profiles to their spatial distribution to determine the Pleiades brown dwarf core radius to be Subsequently we have used our improved spatial model to place stringent limits on the shape of the cluster mass function across and below the stellar/substellar regime. We find this to be a power law with index α = 0.41±0.08 (0.3M⊙ ≥M≥ 0.035M⊙). Extrapolation of this mass function to M= 0.012M⊙ indicates that brown dwarfs contribute only ~ 2% to the total mass of the cluster hence we conclude that brown dwarfs do not contribute significantly to disk dark matter.
Non-equilibrium Chemistry in the Atmospheres of Brown Dwarfs
Authors: Saumon D. , Marley M. S. , Lodders K. , Freedman R. S.
Published: July 2016

Carbon monoxide and ammonia have been detected in the spectrum of G1 229B at abundances that differ substantially from those obtained from chemical equilibrium. Vertical mixing in the atmosphere is a mechanism that can drive slowly reacting species out of chemical equilibrium. We explore the effects of vertical mixing as a function of mixing efficiency and effective temperature on the chemical abundances in the atmospheres of brown dwarfs and on their spectra. The models compare favorably with the observational evidence and indicate that vertical mixing plays an important role in brown dwarf atmospheres.
Unified Cloudy Models of L and T Dwarfs: Physical Basis of the Spectral Classification in the Substellar Regime
Authors: Tsuji Takashi
Published: July 2016

Based on a simple thermodynamical argument, we proposed a cloudy model with a warm dust cloud deep in the photosphere. We showed, for the first time, that a single grid of model photospheres (800 ≲ Teff ≳ 2600 K) offers a natural explanation not only for the division of dwarfs cooler than M into the two distinct types L and T but also for the changes of the spectra and colors along the L – T spectral sequence.
The Transition from L to T: Chemistry and Classification
Authors: Geballe T. R. , Fan X. , Golimowski D. A. , Knapp G. R. , Leggett S. K.
Published: July 2016

The growing numbers of brown dwarfs have largely been divided into two new spectral classes, L and T. Subclassification systems for L, based on optical (0.6–1.0 μm) spectra, have existed since 1999, but there is a need for infrared systems for both spectral classes. The differences in the infrared (1.0–2.5 μm) characteristics of L spectra and T spectra observed prior to 2000 are huge, all then-known T dwarfs showing strong methane absorption bands, and all L dwarfs devoid of these bands. However, in the last 2–3 years a significant number of brown dwarfs with infrared spectra in transition between the L and first observed T types have been discovered. The spectra of late L dwarfs and these “transition objects” can be put into a well ordered sequence of increasing H2O and CH4 band strengths and decreasing CO band strengths. Specific infrared spectral indicators have been found that allow the L and T sequences to be linked and the boundary between L and T to be precisely defined. In current T classification schemes the transition objects are defined as early T dwarfs. We recommend that the boundary between the L and T classes be defined as the first appearance of methane absorption just longward of 1.60 μm, in the H band.
The Classification of T Dwarfs
Authors: Burgasser Adam J. , Geballe Thomas R. , Golimowski David A. , Leggett Sandy K. , Davy Kirkpatrick J. , Knapp Gillian R. , Fan Xiaohui
Published: July 2016

The discovery of many cool brown dwarfs similar to Gliese 229B has led to the definition of a new spectral class, the T dwarfs, whose 1–2.5 μm spectra exhibit signatures of CH4 absorption. Two classification schemes have been proposed for these objects by Burgasser et al. and Geballe et al. We discuss and compare these schemes, and describe a joint classification scheme currently in development that closely follows the guidelines of the MK process. We also address future work toward establishing gravity classes, classifying at other wavelengths, and identifying those features that may signify the end of the T spectral class.
The NIRSPEC Brown Dwarf Spectroscopic Survey
Authors: McLean Ian S. , McGovern M. R. , Prato Lisa , Burgasser Adam J. , Davy Kirkpatrick J.
Published: July 2016

This paper describes the status of a new 0.9 – 2.4 μm spectroscopic survey of low-mass stars and brown dwarfs. Flux-calibrated spectra of 30 objects from M6 to T8 have been obtained with a uniform spectral resolution of R=2,000. For the J-band alone, 60 objects have been observed. In addition, we have obtained the first sequence of spectra at R=20,000 (15 km/s) showing the detailed behavior of the J-band potassium doublets over the same range in spectral type. A few sources have been monitored for radial velocity variations, but none have been detected at the ±1–2 km/s level. Preliminary infrared spectral classification indices have been derived and several young brown dwarfs show clear spectral signatures of lower gravity. Our survey will be available on-line in the future.
The First Infrared Parallaxes for T-Dwarfs
Authors: Tinney C. G. , Burgasser A. , Kirkpatrick J. D.
Published: July 2016

We present first results from the first parallax program to use an infrared camera to target the observation of a sample of methane T-dwarfs, using the ESO 3.5m NTT.
H- and K- Band Methane Features in an L Dwarf, 2MASS 0920+35
Authors: Nakajima Tadashi , Tsuji Takashi , Yanagisawa Kenshi
Published: July 2016

We have obtained near-infrared spectra of three L dwarfs discovered by 2MASS, 1146+22 (L3), 1507-16 (L5), and 0920+35 (L6.5). From the comparison of the H and K band spectra of these L dwarfs, we have found the presence of methane absorption in 0920+35. This implies that detectable methane absorption in the H and K bands, usually considered the signature of a T dwarf, can be present in objects classified optically as late L. Methane detection in L dwarfs is consistent with the presence of a dust layer deep in the atmosphere as the unified model of Tsuji suggests. (This work has been published in Nakajima, Tsuji & Yanagisawa (2001).)
Magnetic Activity and Rotation in Brown Dwarfs and Low Mass Stars
Authors: Basri Gibor , Mohanty Subanjoy
Published: July 2016

One of the triumphs of the last 2 decades has been the establishment of the relation between stellar rotation and magnetic activity in solar-type stars. Rapid rotation produces strong activity, which in turn provides magnetic braking to reduce rotation. A solar-type dynamo cannot operate in fully convective stars, so it is of interest to study mid and late M stars. Hints that a dramatic change occurs in very low-mass stars and substellar objects appeared in 1995. The past 7 years have seen substantial progress on this question, with the conclusion that the rotation-activity connection indeed breaks down. As one goes to the bottom of the main sequence and below, the amount of magnetic activity takes a sudden fall, with a concomitant increase in the spindown times of the objects. We summarize these results, and some theoretical work which helps explain them. We also present some remaining mysteries, such as why very young objects seem excessively active, and flaring in objects with no other signs of magnetic activity.
Activity and Kinematics of Late M, L, and T Dwarfs
Authors: Liebert James
Published: July 2016

The kinematics of late M and certainly L dwarfs indicate that they have a mean age of no more than a few Gyr. This result does not rule out a mix of young brown dwarfs and ZAMS stars. Relative Hα emission strengths begin to decline in the late M dwarfs, even though about 100% of the M7-8 dwarfs show the weaker emission. Both the frequency and likely strength of this emission declines with spectral type among the L's and T's. A larger sample of late M and L dwarfs, which may provide more definitive tests of the kinematic and activity properties, is being assembled from our NStars project.

Two unusual objects, one an M9.5e and the other a T6e, show persistent Hα emission at least an order of magnitude stronger than their counterparts of similar spectral type. If these are hypothesized to be very young stellar objects (≲10 Myr) like some observed in Rho Oph, Sigma Ori and Taurus – evolutionary models would require them to have very low masses: In particular, for an entity to fade to a late T dwarf temperature and luminosity within 10 Myr, its mass should be no more than several Jupiters. This seems implausible for an isolated object not near any obvious site of recent star formation. However, our attempt to show that the emission might be due to accretion in a binary system was unsuccessful.
CLOUDS–Continuous Observations of Ultra-cool Dwarfs
Authors: Goldman Bertrand
Published: July 2016

We have established an international collaboration, named CLOUDS, to investigate atmospheric variability in L and T dwarfs. Our aim is to provide continuous and simultaneous observations over a wide range of wavelengths, using various techniques. We observed 15 targets of types between M9.5 to T6.5, from the optical to the mid infrared, in photometry and/or spectroscopy. Here we present the data set.
High Dynamical Range Observations on the VLT
Authors: Lagrange Anne M. ,   the NAOS Consortium,   the NAOS Consortium,   the NAOS Consortium
Published: July 2016

The recently installed Adaptive Optics system NAOS now offers diffraction limited images at the VLT. Together with the CONICA camera, NAOS provides the possibility to perform high dynamical range observations in the near IR domain. We present here NAOS-CONICA (hereafter NACO) capabilities as well as the first images of binaries obtained during NACO commissioning.
Detection of Brown Dwarfs with Astrometric Satellites
Authors: Bernstein Hans-Heinrich
Published: July 2016

The first astrometric procedure for the detection of Brown Dwarfs as a double star component was accomplished for the HIPPARCOS project, using Fourier series for the description of the orbital motion of Brown Dwarfs, in connection with classical least squares techniques for the estimation of all relevant unknowns. The disadvantage of this procedure was an insufficient number of false decisions. Modern techniques of time series analysis allows a much better mathematical treatment of the physical phenomena. With respect to the large number of candidate objects and the enhanced accuracy of the new astrometric satellites, the introduction of a new approach for the astrometric detection of Brown Dwarfs is suggested.
Formation of Substellar Objects: A SIRTF Legacy
Authors: Young C. H. , Guenthner K. M.
Published: July 2016

We present a summary of SIRTF capabilities and the observing strategy for the SIRTF Cores to Disks Legacy Project.
Luminous Blue Variables, cool hypergiants and some impostors in the H-R diagram
Authors: Humphreys Roberta M.
Published: July 2016

Current observations of the S Dor/LBVs and candidates and the implications for their important role in massive star evolution are reviewed. Recent observations of the cool hypergiants are altering our ideas about their evolutionary state, their atmospheres and winds, and the possible mechanisms for their asymmetric high mass loss episodes which may involve surface activity and magnetic fields. Recent results for IRC+10420, ρ Cas and VY CMa are highlighted. S Dor/LBVs in eruption, and the cool hypergiants in their high mass loss phases with their optically thick winds are not what their apparent spectra and temperatures imply; they are then ‘impostors’ on the H-R diagram. The importance of the very most massive stars, like η Carinae and the ‘supernovae impostors’ are also discussed.
Advances in radiatively driven wind models
Authors: Puls Joachim , Repolust Tamara , Hoffmann Tadziu L. , Jokuthy Alexander , Venero Roberto O.J.
Published: July 2016

We report on a re-analysis of the Galactic O-type star sample presented by Puls et al. (1996) by means of non-LTE model atmospheres including line-blocking and line-blanketing. In particular, we concentrate on the question concerning the dependence of the wind-momentum luminosity relation (WLR) on luminosity class. Owing to the line-blanketing, the derived effective temperatures become significantly lower when compared to previous results, whereas the so-called ‘modified wind-momentum rates’ remain roughly at their former values. Therefore, we obtain a new WLR for O-type stars. By comparing these ‘observational’ results with new theoretical predictions and simulations, we conclude that the Hα forming region for objects with Hα in emission might be considerably clumped and thus a larger mass-loss rate than actually present is mimicked. We suggest that the previously found dependence of the WLR on luminosity class is an artefact.
Advances in modeling of Wolf-Rayet stars
Authors: Hillier D. John
Published: July 2016

Due to advances in computer power and numerical techniques non-LTE line-blanketing calculations for Wolf-Rayet (WR) stars are now routine. The incorporation of blanketing has led to significant improvements in spectral analyses, and to a systematic increase in the derived WR luminosities. To make further progress we need to understand the distribution, structure, and strength of inhomogeneities in the stellar wind, and in turn, how these influence diagnostics of WR stellar parameters, and radiative driving. Further, we need to understand the physical process that initiates mass loss in WR stars. Problems with existing wind calculations are examined, and the difficulty of observationally determining the shape of the velocity law around the sonic point is discussed. To determine the wind dynamics around the sonic point, it is essential to include ions with ionization potentials in excess of 300 eV. A recent study of the 07 Iaf+ star AV 83 is discussed. The analysis indicates the existence of a clumped wind, and a relatively slow wind acceleration with the velocity law characterized by β = 2. The importance of extreme Of stars, for understanding both WR and O-type star winds, is stressed. Spectra of such stars show numerous photospheric and wind features, allowing the entire wind to be probed observationally.
High-resolution near-IR imaging of the WCD(+OB) environments: pinwheels
Authors: Tuthill Peter G. , Monnier John D. , Danchi William C. , Turner Nils H.
Published: July 2016

A small number of Wolf-Rayet colliding-wind binaries studied at extremely high angular resolution show elegant dust plumes with an intuitive geometry: that of an Archimedian spiral. A great deal of fundamental information on the binary and the winds is encoded, ultimately teaching us about dust formation and wind-wind collision zones in these fascinating systems. New results are presented summarizing a concerted campaign encompassing a number of systems studied with various techniques over the last five years.
The evolutionary stage of five southern Galactic unclassified B[e] stars
Authors: Fernandes Marcelo Borges , de Araújo Francisco X. , Lamers H.
Published: July 2016

The spectra of stars with the B[e] phenomenon are dominated by features that are related to physical conditions of circumstellar material around these objects and are not intrinsic to the stars. Because of this, they form a very heterogeneous group. This group contains objects with different evolutionary stages. Lamers et al. (1998) have suggested a new designation with five sub-groups, which indicate the evolutionary stage. They are: supergiants, pre-main sequence or Herbig Ae/Be, compact planetary nebulae, symbiotic and unclassified. The unclassified group has many objects that need a better study to resolve their evolutionary status. Forbidden lines can be a useful tool to solve this problem. They can give informations about chemical composition, ionization and density of the circunstellar medium and probably the evolutionary phase of these objects. We analize spectra of some galactic objects, obtained with the feros and b&c spectrographs at the 1.52m telescope in ESO (La Silla-Chile), with a special focus on the forbidden lines. We have studied the spectra of five B[e] stars of uncertain evolutionary stage. We find that one of them is a pre-WN star, the other four are supergiant B[e] stars.
Emission-line-profile variability as a contraint on the structure and dynamics of hot star winds
Authors: Dessart Luc , Owocki Stanley P.
Published: July 2016

We present theoretical calculations of emission-line-profile variability (LPV), based on radiation hydrodynamics simulations of the infamous radiative instability of hot star winds. We demonstrate that spherically symmetric wind structures (shells) cannot account for the observed profile variability at line center. Hence, we resort to a model that breaks-up the wind volume into a number of independent star-centered cones. The essential approximation made here is that each of these cones can be described by a structure calculated with a one-dimensional (1d) radiation hydrodynamics model. Such pseudo-3d ‘patch’-method leads to a satisfactory reproduction of the fundamental characteristics of LPV observed in O-type and Wolf-Rayet star optical spectra: the low-level fluctuations in the profile centre region, a migration of variable sub-peaks from line center to edge, that mimics the underlying wind acceleration. Our method highlights the correlation between the velocity scale of profile sub-peaks at line center and the lateral extent of wind structures, while at line edge it reflects the intrinsic radial velocity dispersion of emitting clumps. However, our model fails to reproduce the increase in this characteristic velocity scale from line center to edge, which we believe is a shortcoming of our purely 1d hydrodynamics approach.
Grain formation in post-shocked wind collisions of massive binary systems
Authors: Falceta-Gonçalves Diego , Jatenco-Pereira Vera , Abraham Zulema
Published: July 2016

Massive binary star systems are not uncommon, and neither the supersonic collision of their winds. In the present work we study these shocks and the further consequences on wind structure. The post-shock gas is a warm and high-density environment, which allows dust to form and grow. We show that this growth is fast, of just a few hours. An application to η Car shows that, probably, the decline of X-rays fluxes observed in its light curve is the consequence of its high absorption in periodic dust formation events, at periastron passage.
Wolf-Rayet star parameters from spectral analyses
Authors: Hamann Wolf-Rainer , Gräfener Götz , Koesterke Lars
Published: July 2016

The Potsdam non-LTE code for expanding atmospheres, which accounts for clumping and iron-line blanketing, has been used to establish a grid of model atmospheres for WC stars. A parameter degeneracy is discovered for early-type WC models which do not depend on the ‘stellar temperature’. 15 Galactic WC4-7 stars are analyzed, showing a very uniform carbon abundance (He:C = 55:40) with only few exceptions.
Unusual 2001 periastron passage in the colliding-wind binary WR 140 (WC7pd+O4-5)
Authors: Marchenko Sergey V. , Moffat Anthony F.J. , Panov Kiril P. , Seggewiss Wilhelm , Zubko Victor G.
Published: July 2016

The massive, long-period and highly-eccentric (P = 2899 d, e = 0.88), colliding-wind binary WR 140 (WC7pd+O4-5) may be regarded as a clock-work for its predictable, repeatable IR outbursts related to dust formation right after each periastron passage. However, the 2001 periastron passage broke this monotonic trend. Our UBV photometry, completely covering the past nine years, shows a series of quasi-regular fadings starting ~ 2 months after periastron passage (Φ ≃ 0.02-0.05). Preliminary analysis points to dust as a probable cause of the eclipse-like behavior of the system, while the oscillating pattern hints towards instabilities in the wind-wind collision zone. At the same time, contemporaneous spectroscopy shows nothing unusual aside of the strong, but short-lived signs of wind-wind interaction (Φ ≃ 0.99-1.02).
X-ray line profiles from structured stellar winds
Authors: Oskinova Lidia M. , Feldmeier Achim , Hamann Wolf-Rainer
Published: July 2016

Absorbing material compressed in a number of thin shells is effectively less opaque for X-rays than smoothly distributed gas. The calculated X-ray emission-line profiles are red-shifted if the emission arises from the starward side of the shells.
A critical comparison of spectroscopic and evolutionary masses for O-type binary systems
Authors: Penny Laura R. , Gies Douglas R. , Bagnuolo William G. , Wise John H. , Herrero Artemio , Stickland David J. , Lloyd Chris
Published: July 2016

We have embarked on a program to directly compare spectroscopic and evolutionary masses with those obtained from a combination of spectroscopic and photometric orbital solutions for O-type binary systems. The ability to directly determine the spectroscopic masses of the individual components of O-type binary systems has been difficult, because of the severe line blending that is present in these systems. Doppler tomography is an iterative scheme, that uses an ensemble of spectra to reconstruct the individual component spectra. These individual spectra can then be analyzed.
In hot pursuit of the hidden companion of η Carinae: an X-ray determination of the wind parameters
Authors: Pittard Julian M. , Corcoran Michael F.
Published: July 2016

We perform X-ray spectral fits to a recently obtained Chandra grating spectrum of η Carinae, one of the most massive and powerful stars in the Galaxy and which is strongly suspected to be a colliding wind binary system. The good fit that we obtain gives us further confidence in the binary hypothesis, and we find M ≈ 2.5 × 10–4 M⊙ yr–1 for the mass loss rate of η Car.
High-resolution X-ray imaging of the colliding wind shock in WR 147 (WN8(h)+B0.5V)
Authors: Pittard Julian M. , Stevens Ian R. , Williams Peredur M. , Pollock Andrew M.T. , Skinner Steven L. , Corcoran Michael F. , Moffat Anthony F.J.
Published: July 2016

We present the results of a high-resolution Chandra X-ray image of the Wolf-Rayet binary system WR 147, which consists of a WN8 star and an early-type companion located 0″.6 to its north. The image provides the first direct evidence for spatially extended X-ray emission in an early-type binary system, and shows that the emission peaks north of the WN8 star and close to the position of the radio bow shock. Simulated X-ray images of the wind-wind collision have a fwhm consistent with the data, but cannot account for the full spatial extension, unless emission from the stars is also included.
Dynamical simulations of magnetically channeled line-driven stellar winds
Authors: ud-Doula Asif , Owocki Stanley P.
Published: July 2016

We present numerical magnetohydrodynamic simulations of the effect of stellar dipole magnetic fields on line-driven wind outflows from hot, luminous stars. Unlike previous fixed-field analyses, the simulations here take full account of the dynamical competition between field and flow, and thus apply to a full range of magnetic field strength, and within both closed and open magnetic topologies. A key result is that the overall degree to which the wind is influenced by the field depends largely on a single, dimensionless, ‘wind magnetic confinement parameter’, η* = B2eqR2*/Mv∞, which characterizes the ratio between magnetic field energy density and kinetic energy density of the wind. For weak confinement η* ≤ 1, the field is fully opened by the wind outflow, but nonetheless for confinements as small as η* = 1/10 can have a significant back-influence in enhancing the density and reducing the flow speed near the magnetic equator. For stronger confinement η* > 1, the magnetic field remains closed over a limited range of latitude and height about the equatorial surface, but eventually is opened into a nearly radial configuration at large radii. Within closed loops, the flow is channeled toward loop tops into shock collisions that are strong enough to produce hard X-rays, with the stagnated material then pulled by gravity back onto the star in quite complex and variable inflow patterns. Within open field flow, the equatorial channeling leads to oblique shocks that are again strong enough to produce X-rays, and also lead to a thin, dense, slowly outflowing ‘disk’ at the magnetic equator. The polar flow is characterized by a faster-than-radial expansion that is more gradual than anticipated in previous 1d flow-tube analyses, and leads to a much more modest increase in terminal speed (< 30%), consistent with observational constraints. Overall, the results here provide a dynamical groundwork for interpreting many types of observations, e.g., UV line-profile variability; red-shifted absorption or emission features; enhanced density-squared emission; and X-ray emission, that might be associated with perturbation of hot-star winds by surface magnetic fields.