91 research outputs found
Distance determination to 12 Type II-P Supernovae using the Expanding Photosphere Method
We use early-time photometry and spectroscopy of 12 Type II plateau
supernovae (SNe IIP) to derive their distances using the expanding photosphere
method (EPM). We perform this study using two sets of Type II supernova (SN II)
atmosphere models, three filter subsets (, , ), and
two methods for the host-galaxy extinction, which leads to 12 Hubble diagrams.
We find that systematic differences in the atmosphere models lead to 50%
differences in the EPM distances and to a value of between 52 and
101 . Using the filter subset we obtain the
lowest dispersion in the Hubble diagram, { mag}. We
also apply the EPM analysis to the well-observed SN IIP 1999em. With the
filter subset we derive a distance ranging from 9.3 0.5 Mpc to
13.9 1.4 Mpc depending on the atmosphere model employed.Comment: Accepted for publication in the Astrophysical Journa
The Type II supernovae 2006V and 2006au: two SN 1987A-like events
Supernova 1987A revealed that a blue supergiant (BSG) star can end its life
as a core-collapse supernova (SN). SN 1987A and other similar objects exhibit
properties that distinguish them from ordinary Type II Plateau (IIP) SNe, whose
progenitors are believed to be red supergiants (RSGs). Similarities among
1987A-like events include a long rise to maximum, early luminosity fainter than
that of normal Type IIP SNe, and radioactivity acting as the primary source
powering the light curves. We present and analyze two SNe monitored by the
Carnegie Supernova Project that are reminiscent of SN 1987A. Optical and
near-infrared (NIR) light curves, and optical spectroscopy of SNe 2006V and
2006au are presented. These observations are compared to those of SN 1987A, and
are used to estimate properties of their progenitors. Both objects exhibit a
slow rise to maximum and light curve evolution similar to that of SN 1987A. At
the earliest epochs, SN 2006au also displays an initial dip which we interpret
as the signature of the adiabatic cooling phase that ensues shock break- out.
SNe 2006V and 2006au are both found to be bluer, hotter and brighter than SN
1987A. Spectra of SNe 2006V and 2006au are similar to those of SN 1987A and
other normal Type II objects, although both consistently exhibit expansion
velocities higher than SN 1987A. Semi-analytic models are fit to the UVOIR
light curve of each object from which physical properties of the progenitors
are estimated. This yields ejecta mass estimates of about 20 solar masses,
explosion energies of 2 - 3 x 10^51 erg, and progenitor radii of 75 - 100 solar
radii for both SNe. The progenitors of SNe 2006V and 2006au were most likely
BSGs with a larger explosion energy as compared to that of SN 1987A.Comment: 21 pages,15 figures, accepted for publication in A&A, 25 October 201
Convergence towards a European strategic culture? A constructivist framework for explaining changing norms.
The article contributes to the debate about the emergence of a European strategic culture to underpin a European Security and Defence Policy. Noting both conceptual and empirical weaknesses in the literature, the article disaggregates the concept of strategic culture and focuses on four types of norms concerning the means and ends for the use of force. The study argues that national strategic cultures are less resistant to change than commonly thought and that they have been subject to three types of learning pressures since 1989: changing threat perceptions, institutional socialization, and mediatized crisis learning. The combined effect of these mechanisms would be a process of convergence with regard to strategic norms prevalent in current EU countries. If the outlined hypotheses can be substantiated by further research the implications for ESDP are positive, especially if the EU acts cautiously in those cases which involve norms that are not yet sufficiently shared across countries
The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system
Short-period high-amplitude pulsating stars of Population I ( Sct
stars) and II (SX Phe variables) exist in the lower part of the classical
(Cepheid) instability strip. Most of them have very simple pulsational
behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is
a unique object among them, being an extreme metal-deficient field
high-amplitude SX Phe variable with a large number of frequencies. Based on a
frequency analysis, a pulsational interpretation was previously given. aims
heading (mandatory) We attempt to interpret the long-term behaviour of the
residuals that were not taken into account in the previous Observed-Calculated
(O-C) short-term analyses. methods heading (mandatory) An investigation of the
O-C times has been carried out, using a data set based on the previous
published times of light maxima, largely enriched by those obtained during an
intensive multisite photometric campaign of BL Cam lasting several months.
results heading (mandatory) In addition to a positive (161 3) x 10
yr secular relative increase in the main pulsation period of BL Cam, we
detected in the O-C data short- (144.2 d) and long-term ( 3400 d)
variations, both incompatible with a scenario of stellar evolution. conclusions
heading (mandatory) Interpreted as a light travel-time effect, the short-term
O-C variation is indicative of a massive stellar component (0.46 to 1
M_{\sun}) with a short period orbit (144.2 d), within a distance of 0.7 AU
from the primary. More observations are needed to confirm the long-term O-C
variations: if they were also to be caused by a light travel-time effect, they
could be interpreted in terms of a third component, in this case probably a
brown dwarf star ( 0.03 \ M_{\sun}), orbiting in 3400 d at a
distance of 4.5 AU from the primary.Comment: 7 pages, 5 figures, accepted for publication in A&
SN 2009E: a faint clone of SN 1987A
In this paper we investigate the properties of SN 2009E, which exploded in a
relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest
1987A-like supernova discovered so far. Spectroscopic observations which
started about 2 months after the supernova explosion, highlight significant
differences between SN 2009E and the prototypical SN 1987A. Modelling the data
of SN 2009E allows us to constrain the explosion parameters and the properties
of the progenitor star, and compare the inferred estimates with those available
for the similar SNe 1987A and 1998A. The light curve of SN 2009E is less
luminous than that of SN 1987A and the other members of this class, and the
maximum light curve peak is reached at a slightly later epoch than in SN 1987A.
Late-time photometric observations suggest that SN 2009E ejected about 0.04
solar masses of 56Ni, which is the smallest 56Ni mass in our sample of
1987A-like events. Modelling the observations with a radiation hydrodynamics
code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an
initial radius of ~7 x 10^12 cm and an ejected mass of ~19 solar masses. The
photospheric spectra show a number of narrow (v~1800 km/s) metal lines, with
unusually strong Ba II lines. The nebular spectrum displays narrow emission
lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively
strong compared to the [Ca II] doublet. The overall spectroscopic evolution is
reminiscent of that of the faint 56Ni-poor type II-plateau supernovae. This
suggests that SN 2009E belongs to the low-luminosity, low 56Ni mass, low-energy
tail in the distribution of the 1987A-like objects in the same manner as SN
1997D and similar events represent the faint tail in the distribution of
physical properties for normal type II-plateau supernovae.Comment: 19 pages, 9 figures (+7 in appendix); accepted for publication in A&A
on 3 November 201
Spectropolarimetry of the Type II Supernovae 1997ds, 1998A, and 1999gi
We present single-epoch spectropolarimetry of the Type II supernovae (SNe II)
1997ds, 1998A, and 1999gi. SN 1997ds and SN 1998A were both observed during the
early photospheric phase, while spectropolarimetry of SN 1999gi was obtained
near the start of the transition to the nebular phase. Uncorrected for
interstellar polarization (ISP), SN 1997ds is characterized by p_V = 0.85 +/-
0.02%, SN 1998A has p_V = 0.24 +/- 0.05%, and SN 1999gi is polarized at p_V =
5.72 +/- 0.01%. The low continuum polarization inferred for SN 1997ds and SN
1998A and the amplitude of polarization modulations across strong line features
are consistent with those measured at similar epochs for SN 1987A and the Type
II-plateau SN 1999em, and supports the growing consensus that core-collapse
events with hydrogen envelopes substantially intact at the time of explosion
are not significantly aspherical during the early photospheric phase.
The spectral shape of the high continuum polarization of SN 1999gi closely
resembles a ``Serkowski'' ISP curve, and is inconsistent with the
wavelength-independent nature of electron scattering expected for an aspherical
SN atmosphere. Since Galactic reddening is minimal along this line-of-sight,
the majority of the observed polarization in SN 1999gi is believed to be due to
ISP of the host galaxy, although significant (up to p = 2%) intrinsic
polarization cannot be ruled out. The potential power of SN spectropolarimetry
to study the properties of interstellar dust in external galaxies is described
and applied to the SN 1999gi data, where it is shown that if the polarization
is indeed predominantly interstellar in origin, then R_V = 3.0 +/- 0.2 for the
dust along this line-of-sight in NGC 3184.Comment: 34 pages (13 Figures, 2 Tables). Accepted by PAS
The compound machinery of government: The case of seconded officials in the European commission
This article explores the compound machinery of government. Attention is directed toward decision making within the core executive of the European Union - the European Commission. The article studies seconded national civil servants (SNEs) hired on short-term contracts. The analysis benefits from an original and rich body of surveys and interview data derived from current and former SNEs. The decision-making dynamics of SNEs are shown to contain a compound mix of departmental, epistemic, and supranational dynamics. This study clearly demonstrates that the socializing power of the Commission is conditional and only partly sustained when SNEs exit the Commission. Any long-lasting effect of socialization within European Union's executive machinery of government is largely absent. The compound decision-making dynamics of SNEs are explained by (1) the organizational affiliations of SNEs, (2) the formal organization of the Commission apparatus, and (3) only partly by processes of resocialization of SNEs within the Commission
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