A statistical analysis of circumstellar material in Type Ia supernovae

A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass-loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the European Southern Observatory Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (∼20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to redshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption and SNe Ia displaying blueshifted narrow Na I D absorption features have broader light curves. The strength of the Na I D absorption is stronger in SNe Ia displaying blueshifted Na I D absorption features than those without blueshifted features, and the strength of the blueshifted Na I D is correlated with the B − V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests that there are at least two distinct populations of normal, cosmologically useful SNe Ia.

EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems

The star 1SWASP J024743.37-251549.2 was recently discovered to be a binary star in which an A-type dwarf star eclipses the remnant of a disrupted red giant star (WASP 0247-25 B). The remnant is in a rarely observed state evolving to higher effective temperatures at nearly constant luminosity prior to becoming a very low mass white dwarf composed almost entirely of helium, i.e. it is a pre-helium white dwarf (pre-He-WD). We have used the photometric database from theWide Angle Search for Planets (WASP) to find 17 eclipsing binary stars with orbital periods P = 0.7-2.2 d with similar light curves to 1SWASP J024743.37-251549.2. The only star in this group previously identified as a variable star is the brightest one, EL CVn, which we adopt as the prototype for this class of eclipsing binary star. The characteristic light curves of EL CVn-type stars show a total eclipse by an A-type dwarf star of a smaller, hotter star and a secondary eclipse of comparable depth to the primary eclipse. We have used new spectroscopic observations for six of these systems to confirm that the companions to the A-type stars in these binaries have very low masses (≈0.2M⊙). This includes the companion to EL CVn which was not previously known to be a pre-He-WD. EL CVn-type binary star systems will enable us to study the formation of very low mass white dwarfs in great detail, particularly in those cases where the pre-He-WD star shows non-radial pulsations similar to those recently discovered in WASP0247-25 B. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Characterizing K2 Planet Discoveries: A super-Earth transiting the bright K-dwarf HIP 116454

We report the first planet discovery from the two-wheeled Kepler (K2) mission: HIP 116454 b. The host star HIP 116454 is a bright (V = 10.1, K = 8.0) K1 dwarf with high proper motion and a parallax-based distance of 55.2 +/- 5.4 pc. Based on high-resolution optical spectroscopy, we find that the host star is metal-poor with [Fe/H]= -0.16 +/- 0.08 and has a radius R-star = 0.716 +/- 0.024 R-circle dot and mass M-star = 0.775 +/- 0.027M(circle dot). The star was observed by the Kepler spacecraft during its Two-Wheeled Concept Engineering Test in 2014 February. During the 9 days of observations, K2 observed a single transit event. Using a new K2 photometric analysis technique, we are able to correct small telescope drifts and recover the observed transit at high confidence, corresponding to a planetary radius of R-p = 2.53 +/- 0.18 R-circle plus. Radial velocity observations with the HARPS-N spectrograph reveal a 11.82 +/- 1.33 M-circle plus planet in a 9.1 day orbit, consistent with the transit depth, duration, and ephemeris. Follow-up photometric measurements from the MOST satellite confirm the transit observed in the K2 photometry and provide a refined ephemeris, making HIP 116454 b amenable for future follow-up observations of this latest addition to the growing population of transiting super-Earths around nearby, bright stars.

PESSTO monitoring of SN 2012hn: further heterogeneity among faint Type I supernovae

We present optical and infrared monitoring data of SN 2012hn collectedby the Public European Southern Observatory Spectroscopic Survey forTransient Objects. We show that SN 2012hn has a faint peak magnitude(MR ˜ -15.65) and shows no hydrogen and no clearevidence for helium in its spectral evolution. Instead, we detectprominent Ca II lines at all epochs, which relates this transient topreviously described `Ca-rich' or `gap' transients. However, thephotospheric spectra (from -3 to +32 d with respect to peak) of SN2012hn show a series of absorption lines which are unique and a redcontinuum that is likely intrinsic rather than due to extinction. Linesof Ti II and Cr II are visible. This may be a temperature effect, whichcould also explain the red photospheric colour. A nebular spectrum at+150 d shows prominent Ca II, O I, C I and possibly Mg I lines whichappear similar in strength to those displayed by core-collapsesupernovae (SNe). To add to the puzzle, SN 2012hn is located at aprojected distance of 6 kpc from an E/S0 host and is not close to anyobvious star-forming region. Overall SN 2012hn resembles a group offaint H-poor SNe that have been discovered recently and for which aconvincing and consistent physical explanation is still missing. Theyall appear to explode preferentially in remote locations offset from amassive host galaxy with deep limits on any dwarf host galaxies,favouring old progenitor systems. SN 2012hn adds heterogeneity to thissample of objects. We discuss potential explosion channels includingHe-shell detonations and double detonations of white dwarfs as well aspeculiar core-collapse SNe.

On the progenitor of the Type Ic SN 2013dk in the Antennae galaxies

We report the results of our search for the progenitor candidate of SN 2013dk, a Type Ic supernova (SN) that exploded in the Antennae galaxy system. We compare pre-explosion Hubble Space Telescope (HST) archival images with SN images obtained using adaptive optics at the ESO Very Large Telescope. We isolate the SN position to within 3σ uncertainty radius of 0.02 arcsec and show that there is no detectable point source in any of the HST filter images within the error circle. We set an upper limit to the absolute magnitude of the progenitor to be MF555W ≳ -5.7, which does not allow Wolf-Rayet (WR) star progenitors to be ruled out. A bright source appears 0.17 arcsec away, which is either a single bright supergiant or compact cluster, given its absolute magnitude of MF555W = -9.02 ± 0.28 extended wings and complex environment. However, even if this is a cluster, the spatial displacement of SN 2013dk means that its membership is not assured. The strongest statement that we can make is that in the immediate environment of SN 2013dk (within 10 pc or so), we find no clear evidence of either a point source coincident with the SN or a young stellar cluster that could host a massive WR progenitor.

Ultraluminous Supernovae as a New Probe of the Interstellar Medium in Distant Galaxies

We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and Gemini spectroscopy of an ultraluminous supernova (ULSN; dubbed PS1-11bam) at a redshift of z = 1.566 with a peak brightness of M UV ≈ -22.3 mag. PS1-11bam is one of the highest redshift spectroscopically confirmed SNe known to date. The spectrum exhibits broad absorption features typical of previous ULSNe (e.g., C II, Si III), and strong and narrow Mg II and Fe II absorption lines from the interstellar medium (ISM) of the host galaxy, confirmed by an [O II]λ3727 emission line at the same redshift. The equivalent widths of the Fe II λ2600 and Mg II λ2803 lines are in the top quartile of the quasar intervening absorption system distribution, but are weaker than those of gamma-ray burst intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy in pre-explosion Pan-STARRS1 data and find that its UV spectral energy distribution is best fit with a young stellar population age of τ* ≈ 15-45 Myr and a stellar mass of M * ≈ (1.1-2.6) × 109 M ⊙ (for Z = 0.05-1 Z ⊙). The star formation rate inferred from the UV continuum and [O II]λ3727 emission line is ≈10 M ⊙ yr-1, higher than in previous ULSN hosts. PS1-11bam provides the first direct demonstration that ULSNe can serve as probes of the ISM in distant galaxies. The depth and red sensitivity of PS1 are uniquely suited to finding such events at cosmologically interesting redshifts (z ~ 1-2); the future combination of LSST and 30 m class telescopes promises to extend this technique to z ~ 4.

The white dwarf's carbon fraction as a secondary parameter of Type Ia supernovae

Context. Binary stellar evolution calculations predict thatChandrasekhar-mass carbon/oxygen white dwarfs (WDs) show a radiallyvarying profile for the composition with a carbon depleted core. Manyrecent multi-dimensional simulations of Type Ia supernovae (SNe Ia),however, assume the progenitor WD has a homogeneous chemicalcomposition.
Aims: In this work, we explore the impact ofdifferent initial carbon profiles of the progenitor WD on the explosionphase and on synthetic observables in the Chandrasekhar-mass delayeddetonation model. Spectra and light curves are compared to observationsto judge the validity of the model.
Methods: The explosion phaseis simulated using the finite volume supernova code Leafs, which isextended to treat different compositions of the progenitor WD. Thesynthetic observables are computed with the Monte Carlo radiativetransfer code Artis. Results: Differences in binding energies ofcarbon and oxygen lead to a lower nuclear energy release for carbondepleted material; thus, the burning fronts that develop are weaker andthe total nuclear energy release is smaller. For otherwise identicalconditions, carbon depleted models produce less 56Ni.Comparing different models with similar 56Ni yields showslower kinetic energies in the ejecta for carbon depleted models, butonly small differences in velocity distributions and line velocities inspectra. The light curve width-luminosity relation (WLR) obtained formodels with differing carbon depletion is roughly perpendicular to theobserved WLR, hence the carbon mass fraction is probably only asecondary parameter in the family of SNe Ia.
Tables 3 and 4 are available in electronic form at http://www.aanda.org

Magnetospheric Structure and Atmospheric Joule Heating of Habitable Planets Orbiting M-dwarf Stars

We study the magnetospheric structure and the ionospheric Joule Heating of planets orbiting M-dwarf stars in the habitable zone using a set of magnetohydrodynamic models. The stellar wind solution is used to drive a model for the planetary magnetosphere, which is coupled with a model for the planetary ionosphere. Our simulations reveal that the space environment around close-in habitable planets is extreme, and the stellar wind plasma conditions change from sub- to super-Alfvénic along the planetary orbit. As a result, the magnetospheric structure changes dramatically with a bow shock forming in the super-Alfvénic sectors, while no bow shock forms in the sub-Alfvénic sectors. The planets reside most of the time in the sub-Alfvénic sectors with poor atmospheric protection. A significant amount of Joule Heating is provided at the top of the atmosphere as a result of the intense stellar wind. For the steady-state solution, the heating is about 0.1%-3% of the total incoming stellar irradiation, and it is enhanced by 50% for the time-dependent case. The significant Joule Heating obtained here should be considered in models for the atmospheres of habitable planets in terms of the thickness of the atmosphere, the top-side temperature and density, the boundary conditions for the atmospheric pressure, and particle radiation and transport. Here we assume constant ionospheric Pedersen conductance similar to that of the Earth. The conductance could be greater due to the intense EUV radiation leading to smaller heating rates. We plan to quantify the ionospheric conductance in future study.

Quiescent and flaring X-ray emission from the nearby M/T dwarf binary SCR 1845-6357

Aims: X-ray emission is an important diagnostics to study magnetic activity in very low mass stars that are presumably fully convective and have an effectively neutral photosphere. Methods: We investigate an XMM-Newton observation of SCR 1845-6357, a nearby, ultracool M 8.5 / T 5.5 dwarf binary. The binary is unresolved in the XMM detectors, but the X-ray emission is very likely from the M 8.5 dwarf. We compare its flaring emission to those of similar very low mass stars and additionally present an XMM observation of the M 8 dwarf VB 10. Results: We detect quasi-quiescent X-ray emission from SCR 1845-6357 at soft X-ray energies in the 0.2-2.0 keV band, as well as a strong flare with a count rate increase of a factor of 30 and a duration of only 10 min. The quasi-quiescent X-ray luminosity of log LX = 26.2 erg/s and the corresponding activity level of log LX/Lbol = -3.8 point to a fairly active star. Coronal temperatures of up to 5 MK and frequent minor variability support this picture. During the flare, which is accompanied by a significant brightening in the near-UV, plasma temperatures of 25-30 MK are observed and an X-ray luminosity of LX = 8 × 1027 erg/s is reached. Conclusions: The source SCR 1845-6357 is a nearby, very low mass star that emits X-rays at detectable levels in quasi-quiescence, implying the existence of a corona. The high activity level, coronal temperatures and the observed large flare point to a rather active star, despite its estimated age of a few Gyr.

M Dwarf Flare Continuum Variations on One-second Timescales: Calibrating and Modeling of ULTRACAM Flare Color Indices

We present a large data set of high-cadence dMe flare light curves obtained with custom continuum filters on the triple-beam, high-speed camera system ULTRACAM. The measurements provide constraints for models of the near-ultraviolet (NUV) and optical continuum spectral evolution on timescales of ≈1 s. We provide a robust interpretation of the flare emission in the ULTRACAM filters using simultaneously obtained low-resolution spectra during two moderate-sized flares in the dM4.5e star YZ CMi. By avoiding the spectral complexity within the broadband Johnson filters, the ULTRACAM filters are shown to characterize bona fide continuum emission in the NUV, blue, and red wavelength regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and the blue/red flux ratio provides an estimate for the color temperature of the optical continuum emission. We present a new “color-color” relationship for these continuum flux ratios at the peaks of the flares. Using the RADYN and RH codes, we interpret the ULTRACAM filter emission using the dominant emission processes from a radiative-hydrodynamic flare model with a high nonthermal electron beam flux, which explains a hot, T ≈ 104 K, color temperature at blue-to-red optical wavelengths and a small Balmer jump ratio as observed in moderate-sized and large flares alike. We also discuss the high time resolution, high signal-to-noise continuum color variations observed in YZ CMi during a giant flare, which increased the NUV flux from this star by over a factor of 100. Based on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium, based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofsica de Canarias, and observations, and based on observations made with the ESO Telescopes at the La Silla Paranal Observatory under programme ID 085.D-0501(A).

Spectro-imagerie optique à faible flux et comparaison de la cinématique Ha et HI d'un échantillon de galaxies proches

Un nouveau contrôleur de EMCCD (Electron multiplying Charge Coupled Device) est présenté. Il permet de diminuer significativement le bruit qui domine lorsque la puce EMCCD est utilisé pour du comptage de photons: le bruit d'injection de charge. À l'aide de ce contrôleur, une caméra EMCCD scientifique a été construite, caractérisée en laboratoire et testée à l'observatoire du mont Mégantic. Cette nouvelle caméra permet, entre autres, de réaliser des observations de la cinématique des galaxies par spectroscopie de champ intégral par interférométrie de Fabry-Perot en lumière Ha beaucoup plus rapidement, ou de galaxies de plus faible luminosité, que les caméras à comptage de photon basées sur des tubes amplificateurs. Le temps d'intégration nécessaire à l'obtention d'un rapport signal sur bruit donné est environ 4 fois moindre qu'avec les anciennes caméras. Les applications d'un tel appareil d'imagerie sont nombreuses: photométrie rapide et faible flux, spectroscopie à haute résolution spectrale et temporelle, imagerie limitée par la diffraction à partir de télescopes terrestres (lucky imaging), etc. D'un point de vue technique, la caméra est dominée par le bruit de Poisson pour les flux lumineux supérieurs à 0.002 photon/pixel/image. D'un autre côté, la raie d'hydrogène neutre (HI) à 21 cm a souvent été utilisée pour étudier la cinématique des galaxies. L'hydrogène neutre a l'avantage de se retrouver en quantité détectable au-delà du disque optique des galaxies. Cependant, la résolution spatiale de ces observations est moindre que leurs équivalents réalisés en lumière visible. Lors de la comparaison des données HI, avec des données à plus haute résolution, certaines différences étaient simplement attribuées à la faible résolution des observations HI. Le projet THINGS (The HI Nearby Galaxy Survey a observé plusieurs galaxies de l'échantillon SINGS (Spitzer Infrared Nearby Galaxies Survey). Les données cinématiques du projet THIGNS seront comparées aux données cinématiques obtenues en lumière Ha, afin de déterminer si la seule différence de résolution spatiale peut expliquer les différences observées. Les résultats montrent que des différences intrinsèques aux traceurs utilisées (hydrogène neutre ou ionisé), sont responsables de dissemblances importantes. La compréhension de ces particularités est importante: la distribution de la matière sombre, dérivée de la rotation des galaxies, est un test de certains modèles cosmologiques.

Cinématique haute résolution des galaxies de l'échantillon SINGS et observations du H[alpha] profond de la galaxie NGC 7793

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Analyse cinématique de l'hydrogène ionisé et étude du gaz ionisé diffus de trois galaxies du Groupe Sculpteur : NGC253, NGC300 et NGC247

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Photometric and fundamental plane studies of galaxies

Determining the morphological parameters that describe galaxies has always been a challenging task. The studies on the correlations between different photometric as well as spectroscopic parameters of the galaxies help in understanding their structure, properties of the stars and gas which constitute the galaxy, the various physical and chemical processes which determine the properties, and galaxy formation and evolution. In the last few decades, the advent of Charge Coupled Devices (CCDs) and near infrared arrays ha\·e provided quick and reliable digitized data acquisition, in the optical and near infrared bands. This has provided an avalanche of data, which can be processed using sophisticated image analysis techniques to obtain information about the morphology of galaxies. The photometric analysis performed in this thesis involve the extraction of structural parameters of early type gala.xies imaged in the near infrared K (2.2ttm) band, obtaining correlations between these, parameters and using them to constrain the large scale properties of galaxi,~s.

Development of mechanical methods for cell-tray propagation and field transplanting of dwarf napiergrass (Pennisetum purpureum Schumach.)

Since dwarf napiergrass (Pennisetum purpureum Schumach.) must be propagated vegetatively due to lack of viable seeds, root splitting and stem cuttings are generally used to obtain true-to-type plant populations. These ordinary methods are laborious and costly, and are the greatest barriers for expanding the cultivation area of this crop. The objectives of this research were to develop nursery production of dwarf napiergrass in cell trays and to compare the efficiency of mechanical versus manual methods for cell-tray propagation and field transplanting. After defoliation of herbage either by a sickle (manually) or hand-mowing machine, every potential aerial tiller bud was cut to a single one for transplanting into cell trays as stem cuttings and placed in a glasshouse over winter. The following June, nursery plants were trimmed to a 25–cm length and transplanted in an experimental field (sandy soil) with 20,000 plants ha^(−1) either by shovel (manually) or Welsh onion planter. Labour time was recorded for each process. The manual defoliation of plants required 44% more labour time for preparing the stem cuttings (0.73 person-min. stemcutting^(−1)) compared to using hand-mowing machinery (0.51 person-min. stem-cutting^(−1)). In contrast, labour time for transplanting required an extra 0.30 person-min. m^(−2) (14%) using the machinery compared to manual transplanting, possibly due to the limited plot size for machinery operation. The transplanting method had no significant effect on plant establishment or plant growth, except for herbage yield 110 days after planting. Defoliation of herbage by machinery, production using a cell-tray nursery and mechanical transplanting reduced the labour intensity of dwarf napiergrass propagation.