290 research outputs found
The type IIb SN 2008ax: the nature of the progenitor
A source coincident with the position of the type IIb supernova (SN) 2008ax
is identified in pre-explosion Hubble Space Telescope (HST) Wide Field
Planetary Camera 2 observations in three optical filters. We identify and
constrain two possible progenitor systems: (i) a single massive star that lost
most of its hydrogen envelope through radiatively driven mass loss processes,
prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen
envelope, and (ii) an interacting binary in a low mass cluster producing a
stripped progenitor. Late time, high resolution observations along with
detailed modelling of the SN will be required to reveal the true nature of this
progenitor star.Comment: 5 pages, 2 figures, resolution of figure 1 reduced, figure 2 revised,
some revision following referee's comments, accepted for publication in MNRAS
letter
Does a Nursing Associate Programme Team Work and Leadership Module Make a Difference to Student Nursing Associate Self-reported Leadership Skills? A Mixed-methods Study
Background: Leadership is an essential element in the skills of healthcare professionals at all levels. This is true for Registered Nurses as well as Nursing Associates, who are registered professionals with a two-year foundation degree programme as role preparation. Objective: This paper reports a study examining potential gains that might accrue from leadership and team-working module in year two of the Nursing Associate Foundation Degree programme at one university in the South West of England. Methods: We conducted a mixed-methods study in the summer of 2020, with a pre- and post-module survey using the Student Leadership Inventory – Self, and a virtual focus group on the video conferencing software Zoom ™. Results: The survey results showed a statistically significant difference between Student Nurse Associates’ scores before and after the module, with a moderate effect size. The virtual focus group confirmed benefits that included growing personal confidence amongst those that attended and that they could identify leadership styles and team dynamics in practice. Conclusion: As effective leadership is associated with patient safety and quality of care, we conclude that not only has this module been effective, but also that such preparation for practice can have important real-world impacts beyond the classroom. </jats:sec
Probing the Rotational Velocity of Galactic WO Stars with Spectropolarimetry
Oxygen sequence Wolf-Rayet stars (WO) are thought to be the final evolution phase of some high-mass stars, as such they may be the progenitors of Type Ic SNe as well as potential progenitors of broad-lined Ic and long gamma-ray bursts. We present the first spectropolarimetric observations of the Galactic WO stars WR93b and WR102 obtained with FORS1 on the Very Large Telescope. We find no sign of a line effect, which could be expected if these stars were rapid rotators. We also place constraints on the amplitude of a potentially undetected line effect. This allows us to derive upper limits on the possible intrinsic continuum polarization and find Pcont \u3c 0.077 per cent and Pcont \u3c 0.057 per cent for WR93b and WR102, respectively. Furthermore, we derive upper limits on the rotation of our WO stars by considering our results in the context of the wind compression effect. We estimate that for an edge-on case the rotational velocity of WR93b is vrot \u3c 324 km s−1 while for WR102 vrot \u3c 234 km s−1. These correspond to values of vrot/vcrit \u3c 19 per cent and j) \u3c 18.0 cm2 s−1 for WR93b and 2 s−1 for WR102. The upper limits found on vrot/vcrit and log(j) for our WO stars are therefore similar to the estimates calculated for Galactic Wolf-Rayet (WR) stars that do show a line effect. Therefore, although the presence of a line effect in a single WR star is indicative of fast rotation, the absence of a line effect does not rule out significant rotation, even when considering the edge-on scenario
An Upper Mass Limit on a Red Supergiant Progenitor for the Type II-Plateau Supernova SN 2006my
We analyze two pre-supernova (SN) and three post-SN high-resolution images of
the site of the Type II-Plateau supernova SN 2006my in an effort to either
detect the progenitor star or to constrain its properties. Following image
registration, we find that an isolated stellar object is not detected at the
location of SN 2006my in either of the two pre-SN images. In the first, an
I-band image obtained with the Wide-Field and Planetary Camera 2 on board the
Hubble Space Telescope, the offset between the SN 2006my location and a
detected source ("Source 1") is too large: > 0.08", which corresponds to a
confidence level of non-association of 96% from our most liberal estimates of
the transformation and measurement uncertainties. In the second, a similarly
obtained V-band image, a source is detected ("Source 2") that has overlap with
the SN 2006my location but is definitively an extended object. Through
artificial star tests carried out on the precise location of SN 2006my in the
images, we derive a 3-sigma upper bound on the luminosity of a red supergiant
that could have remained undetected in our pre-SN images of log L/L_Sun = 5.10,
which translates to an upper bound on such a star's initial mass of 15 M_Sun
from the STARS stellar evolutionary models. Although considered unlikely, we
can not rule out the possibility that part of the light comprising Source 1,
which exhibits a slight extension relative to other point sources in the image,
or part of the light contributing to the extended Source 2, may be due to the
progenitor of SN 2006my. Only additional, high-resolution observations of the
site taken after SN 2006my has faded beyond detection can confirm or reject
these possibilities.Comment: Minor text changes from Version 1. Appendix added detailing the
determination of confidence level of non-association of point sources in two
registered astronomical image
SN 2007uy - metamorphosis of an aspheric Type Ib explosion
The supernovae of Type Ibc are rare and the detailed characteristics of these
explosions have been studied only for a few events. Unlike Type II SNe, the
progenitors of Type Ibc have never been detected in pre-explosion images. So,
to understand the nature of their progenitors and the characteristics of the
explosions, investigation of proximate events are necessary. Here we present
the results of multi-wavelength observations of Type Ib SN 2007uy in the nearby
( 29.5 Mpc) galaxy NGC 2770. Analysis of the photometric observations
revealed this explosion as an energetic event with peak absolute R band
magnitude , which is about one mag brighter than the mean value
() derived for well observed Type Ibc events. The SN is highly
extinguished, E(B-V) = 0.630.15 mag, mainly due to foreground material
present in the host galaxy. From optical light curve modeling we determine that
about 0.3 M radioactive Ni is produced and roughly 4.4
M material is ejected during this explosion with liberated energy
erg, indicating the event to be an energetic one.
Through optical spectroscopy, we have noticed a clear aspheric evolution of
several line forming regions, but no dependency of asymmetry is seen on the
distribution of Ni inside the ejecta. The SN shock interaction with the
circumburst material is clearly noticeable in radio follow-up, presenting a
Synchrotron Self Absorption (SSA) dominated light curve with a contribution of
Free Free Absorption (FFA) during the early phases. Assuming a WR star, with
wind velocity \ga 10^3 {\rm km s}^{-1}, as a progenitor, we derive a lower
limit to the mass loss rate inferred from the radio data as \dot{M} \ga
2.4\times10^{-5} M, yr, which is consistent with the results
obtained for other Type Ibc SNe bright at radio frequencies.Comment: 22 pages, 13 figures, accepted for publication in MNRA
Supernova 2012ec: Identification of the progenitor and early monitoring with PESSTO
We present the identification of the progenitor of the Type IIP SN 2012ec in
archival pre-explosion HST WFPC2 and ACS/WFC F814W images. The properties of
the progenitor are further constrained by non-detections in pre-explosion WFPC2
F450W and F606W images. We report a series of early photometric and
spectroscopic observations of SN 2012ec. The r'-band light curve shows a
plateau with M(r')=-17.0. The early spectrum is similar to the Type IIP SN
1999em, with the expansion velocity measured at Halpha absorption minimum of
-11,700 km/s (at 1 day post-discovery). The photometric and spectroscopic
evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days
post-explosion (<6d). We derive a luminosity for the progenitor, in comparison
with MARCS model SEDs, of log L/Lsun = 5.15+/-0.19, from which we infer an
initial mass range of 14-22Msun. This is the first SN with an identified
progenitor to be followed by the Public ESO Spectroscopic Survey of Transient
Objects (PESSTO).Comment: 6 pages, 3 figures, MNRAS accepte
Using Spatial Distributions to Constrain Progenitors of Supernovae and Gamma Ray Bursts
We carry out a comprehensive theoretical examination of the relationship
between the spatial distribution of optical transients and the properties of
their progenitor stars. By constructing analytic models of star-forming
galaxies and the evolution of stellar populations within them, we are able to
place constraints on candidate progenitors for core-collapse supernovae (SNe),
long-duration gamma ray bursts, and supernovae Ia. In particular we first
construct models of spiral galaxies that reproduce observations of
core-collapse SNe, and we use these models to constrain the minimum mass for
SNe Ic progenitors to approximately 25 solar masses. Secondly, we lay out the
parameters of a dwarf irregular galaxy model, which we use to show that the
progenitors of long-duration gamma-ray bursts are likely to have masses above
approximately 43 solar masses. Finally, we introduce a new method for
constraining the time scale associated with SNe Ia and apply it to our spiral
galaxy models to show how observations can better be analyzed to discriminate
between the leading progenitor models for these objects.Comment: 18 pages, 19 figures, ApJ, in pres
Probing the rotational velocity of Galactic WO stars with spectropolarimetry
Oxygen sequence Wolf-Rayet stars (WO) are thought to be the final evolution phase of some high-mass stars, as such they may be the progenitors of Type Ic SNe as well as potential progenitors of broad-lined Ic and long gamma-ray bursts. We present the first spectropolarimetric observations of the Galactic WO stars WR93b and WR102 obtained with FORS1 on the Very Large Telescope. We find no sign of a line effect, which could be expected if these stars were rapid rotators. We also place constraints on the amplitude of a potentially undetected line effect. This allows us to derive upper limits on the possible intrinsic continuum polarization and find Pcont < 0.077 per cent and Pcont < 0.057 per cent for WR93b and WR102, respectively. Furthermore, we derive upper limits on the rotation of our WO stars by considering our results in the context of the wind compression effect. We estimate that for an edge-on case the rotational velocity of WR93b is vrot < 324 km s−1 while for WR102 vrot < 234 km s−1. These correspond to values of vrot/vcrit < 19 per cent and <10 per cent, respectively, and values of log(j) < 18.0 cm2 s−1 for WR93b and <17.6 cm2 s−1 for WR102. The upper limits found on vrot/vcrit and log(j) for our WO stars are therefore similar to the estimates calculated for Galactic Wolf-Rayet (WR) stars that do show a line effect. Therefore, although the presence of a line effect in a single WR star is indicative of fast rotation, the absence of a line effect does not rule out significant rotation, even when considering the edge-on scenario
Did the progenitor of SN 2011dh have a binary companion?
We present late-time Hubble Space Telescope ultraviolet (UV) and optical observations of the site of SN 2011dh in the galaxy M51, ∼1164 days post-explosion. At the supernova (SN) location, we observe a point source that is visible at all wavelengths, which is significantly fainter than the spectral energy distribution (SED) of the yellow supergiant progenitor observed prior to explosion. The previously reported photometry of the progenitor is, therefore, completely unaffected by any sources that may persist at the SN location after explosion. In comparison with the previously reported late-time photometric evolution of SN 2011dh, we find that the light curve has plateaued at all wavelengths. The SED of the late-time source is clearly inconsistent with an SED of stellar origin. Although the SED is bright at UV wavelengths, there is no strong evidence that the late-time luminosity originates solely from a stellar source corresponding to the binary companion, although a partial contribution to the observed UV flux from a companion star cannot be ruled out
SN 2008in—Bridging the Gap between Normal and Faint Supernovae of Type IIP
We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M61. Photometric data in the X-ray, ultraviolet, and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ~98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. indicates that it is a less energetic event (~5 × 10^(50) erg). However, the light curve indicates that the production of radioactive ^(56)Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of AV ~ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized ^(56)Ni mass of ~0.015 M_☉. Employing semi-analytical formulae derived by Litvinova and Nadezhin, we derived a pre-SN radius of ~126 R_☉, an explosion energy of ~5.4 × 10^(50) erg, and a total ejected mass of ~16.7 M_☉. The latter indicates that the zero-age main-sequence mass of the progenitor did not exceed 20 M_☉. Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity ([O/H] ~ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star
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