3,102 research outputs found
Vacuum ultraviolet photoabsorption spectra of nitrile ices for their identification on Pluto
Icy bodies, such as Pluto, are known to harbor simple and complex molecules. The recent New Horizons flyby of Pluto has revealed a complex surface composed of bright and dark ice surfaces, indicating a rich chemistry based on nitrogen (N2), methane (CH4), and carbon monoxide (CO). Nitrile (CN) containing molecules such as acetonitrile (CH3CN), propionitrile (CH3CH2CN), butyronitrile (CH3CH2CH2CN), and isobutyronitrile ((CH3)2CHCN) are some of the nitrile molecules that are known to be synthesized by radiative processing of such simple ices. Through the provision of a spectral atlas for such compounds we propose that such nitriles may be identified from the ALICE payload on board New Horizons</i
SiFTO: An Empirical Method for Fitting SNe Ia Light Curves
We present SiFTO, a new empirical method for modeling type Ia supernovae (SNe
Ia) light curves by manipulating a spectral template. We make use of
high-redshift SN observations when training the model, allowing us to extend it
bluer than rest frame U. This increases the utility of our high-redshift SN
observations by allowing us to use more of the available data. We find that
when the shape of the light curve is described using a stretch prescription,
applying the same stretch at all wavelengths is not an adequate description.
SiFTO therefore uses a generalization of stretch which applies different
stretch factors as a function of both the wavelength of the observed filter and
the stretch in the rest-frame B band. We compare SiFTO to other published
light-curve models by applying them to the same set of SN photometry, and
demonstrate that SiFTO and SALT2 perform better than the alternatives when
judged by the scatter around the best fit luminosity distance relationship. We
further demonstrate that when SiFTO and SALT2 are trained on the same data set
the cosmological results agree.Comment: Modified to better match published version in Ap
Near-infrared observations of type Ia supernovae: The best known standard candle for cosmology
We present an analysis of the Hubble diagram for 12 Type Ia supernovae (SNe
Ia) observed in the near-infrared J and H bands. We select SNe exclusively from
the redshift range 0.03 < z < 0.09 to reduce uncertainties coming from peculiar
velocities while remaining in a cosmologically well-understood region. All of
the SNe in our sample exhibit no spectral or B-band light-curve peculiarities
and lie in the B-band stretch range of 0.8-1.15. Our results suggest that SNe
Ia observed in the near-infrared (NIR) are the best known standard candles. We
fit previously determined NIR light-curve templates to new high-precision data
to derive peak magnitudes and to determine the scatter about the Hubble line.
Photometry of the 12 SNe is presented in the natural system. Using a standard
cosmology of (H_0, Omega_m, Lambda) = (70,0.27,0.73) we find a median J-band
absolute magnitude of M_J = -18.39 with a scatter of 0.116 and a median H-band
absolute magnitude of M_H = -18.36 with a scatter of 0.085. The scatter in the
H band is the smallest yet measured. We search for correlations between
residuals in the J- and H-band Hubble diagrams and SN properties, such as SN
colour, B-band stretch and the projected distance from host-galaxy centre. The
only significant correlation is between the J-band Hubble residual and the J-H
pseudo-colour. We also examine how the scatter changes when fewer points in the
near-infrared are used to constrain the light curve. With a single point in the
H band taken anywhere from 10 days before to 15 days after B-band maximum light
and a prior on the date of H-band maximum set from the date of B-band maximum,
we find that we can measure distances to an accuracy of 6%. The precision of
SNe Ia in the NIR provides new opportunities for precision measurements of both
the expansion history of the universe and peculiar velocities of nearby
galaxies.Comment: 6 pages, 2 figures. Accepted for publication in MNRA
Spectral Models for Early Time SN 2011fe Observations
We use observed UV through near IR spectra to examine whether SN 2011fe can
be understood in the framework of Branch-normal SNe Ia and to examine its
individual peculiarities. As a benchmark, we use a delayed-detonation model
with a progenitor metallicity of Z_solar/20. We study the sensitivity of
features to variations in progenitor metallicity, the outer density profile,
and the distribution of radioactive nickel. The effect of metallicity
variations in the progenitor have a relatively small effect on the synthetic
spectra. We also find that the abundance stratification of SN 2011fe resembles
closely that of a delayed detonation model with a transition density that has
been fit to other Branch-normal Type Ia supernovae. At early times, the model
photosphere is formed in material with velocities that are too high, indicating
that the photosphere recedes too slowly or that SN 2011fe has a lower specific
energy in the outer ~0.1 M_sun than does the model. We discuss several
explanations for the discrepancies. Finally, we examine variations in both the
spectral energy distribution and in the colors due to variations in the
progenitor metallicity, which suggests that colors are only weak indicators for
the progenitor metallicity, in the particular explosion model that we have
studied. We do find that the flux in the U band is significantly higher at
maximum light in the solar metallicity model than in the lower metallicity
model and the lower metallicity model much better matches the observed
spectrum.Comment: 9 pages, 14 figures, MNRAS, in press, fixed typ
Capture and inception of bubbles near line vortices
Motivated by the need to predict vortex cavitation inception, a study has been conducted to investigate bubble capture by a concentrated line vortex of core size rcrc and circulation Γ0Γ0 under noncavitating and cavitating conditions. Direct numerical simulations that solve simultaneously for the two phase flow field, as well as a simpler one-way coupled point-particle-tracking model (PTM) were used to investigate the capture process. The capture times were compared to experimental observations. It was found that the point-particle-tracking model can successfully predict the capture of noncavitating small nuclei by a line vortex released far from the vortex axis. The nucleus grows very slowly during capture until the late stages of the process, where bubble/vortex interaction and bubble deformation become important. Consequently, PTM can be used to study the capture of cavitating nuclei by dividing the process into the noncavitating capture of the nucleus, and then the growth of the nucleus in the low-pressure core region. Bubble growth and deformation act to speed up the capture process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87832/2/022105_1.pd
Optical and near infrared observations of SN 2014ck: an outlier among the Type Iax supernovae
We present a comprehensive set of optical and near-infrared photometric and
spectroscopic observations for SN 2014ck, extending from pre-maximum to six
months later. These data indicate that SN 2014ck is photometrically nearly
identical to SN 2002cx, which is the prototype of the class of peculiar
transients named SNe Iax. Similar to SN 2002cx, SN 2014ck reached a peak
brightness mag, with a post-maximum decline-rate mag. However, the spectroscopic sequence shows
similarities with SN 2008ha, which was three magnitudes fainter and faster
declining. In particular, SN 2014ck exhibits extremely low ejecta velocities,
km s at maximum, which are close to the value measured for
SN 2008ha and half the value inferred for SN 2002cx. The bolometric light curve
of SN 2014ck is consistent with the production of of Ni. The spectral identification of several iron-peak
features, in particular Co II lines in the NIR, provides a clear link to SNe
Ia. Also, the detection of narrow Si, S and C features in the pre-maximum
spectra suggests a thermonuclear explosion mechanism. The late-phase spectra
show a complex overlap of both permitted and forbidden Fe, Ca and Co lines. The
appearance of strong [Ca~II] 7292, 7324 again mirrors the
late-time spectra of SN 2008ha and SN 2002cx. The photometric resemblance to SN
2002cx and the spectral similarities to SN 2008ha highlight the peculiarity of
SN 2014ck, and the complexity and heterogeneity of the SNe Iax class.Comment: MNRAS Accepted 2016 March 22. Received 2016 March
Constraining Type Ia supernova models: SN 2011fe as a test case
The nearby supernova SN 2011fe can be observed in unprecedented detail.
Therefore, it is an important test case for Type Ia supernova (SN Ia) models,
which may bring us closer to understanding the physical nature of these
objects. Here, we explore how available and expected future observations of SN
2011fe can be used to constrain SN Ia explosion scenarios. We base our
discussion on three-dimensional simulations of a delayed detonation in a
Chandrasekhar-mass white dwarf and of a violent merger of two white
dwarfs-realizations of explosion models appropriate for two of the most
widely-discussed progenitor channels that may give rise to SNe Ia. Although
both models have their shortcomings in reproducing details of the early and
near-maximum spectra of SN 2011fe obtained by the Nearby Supernova Factory
(SNfactory), the overall match with the observations is reasonable. The level
of agreement is slightly better for the merger, in particular around maximum,
but a clear preference for one model over the other is still not justified.
Observations at late epochs, however, hold promise for discriminating the
explosion scenarios in a straightforward way, as a nucleosynthesis effect leads
to differences in the 55Co production. SN 2011fe is close enough to be followed
sufficiently long to study this effect.Comment: Accepted for publication in The Astrophysical Journal Letter
The Supernova Legacy Survey 3-year sample: Type Ia Supernovae photometric distances and cosmological constraints
We present photometric properties and distance measurements of 252 high
redshift Type Ia supernovae (0.15 < z < 1.1) discovered during the first three
years of the Supernova Legacy Survey (SNLS). These events were detected and
their multi-colour light curves measured using the MegaPrime/MegaCam instrument
at the Canada-France-Hawaii Telescope (CFHT), by repeatedly imaging four
one-square degree fields in four bands. Follow-up spectroscopy was performed at
the VLT, Gemini and Keck telescopes to confirm the nature of the supernovae and
to measure their redshifts. Systematic uncertainties arising from light curve
modeling are studied, making use of two techniques to derive the peak
magnitude, shape and colour of the supernovae, and taking advantage of a
precise calibration of the SNLS fields. A flat LambdaCDM cosmological fit to
231 SNLS high redshift Type Ia supernovae alone gives Omega_M = 0.211 +/-
0.034(stat) +/- 0.069(sys). The dominant systematic uncertainty comes from
uncertainties in the photometric calibration. Systematic uncertainties from
light curve fitters come next with a total contribution of +/- 0.026 on
Omega_M. No clear evidence is found for a possible evolution of the slope
(beta) of the colour-luminosity relation with redshift.Comment: (The SNLS Collaboration) 40 pages, 32 figures, Accepted in A&
Single-cell mass cytometry reveals complex myeloid cell composition in active lesions of progressive multiple sclerosis
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