581 research outputs found
The Unusually Luminous Extragalactic Nova SN 2010U
We present observations of the unusual optical transient SN 2010U, including
spectra taken 1.03 days to 15.3 days after maximum light that identify it as a
fast and luminous Fe II type nova. Our multi-band light curve traces the fast
decline (t_2 = 3.5 days) from maximum light (M_V = -10.2 mag), placing SN 2010U
in the top 0.5% of the most luminous novae ever observed. We find typical
ejecta velocities of approximately 1100 km/s and that SN 2010U shares many
spectral and photometric characteristics with two other fast and luminous Fe II
type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme
luminosity of this nova, the maximum magnitude vs. rate of decline relationship
indicates a massive white dwarf progenitor with a low pre-outburst accretion
rate. However, this prediction is in conflict with emerging theories of nova
populations, which predict that luminous novae from massive white dwarfs should
preferentially exhibit an alternate spectral type (He/N) near maximum light.Comment: 16 pages, 16 figures. Submitted to the Astrophysical Journa
A Study of the Type II-P Supernova 2003gd in M74
We present photometric and spectroscopic data of the type II-P supernova
2003gd, which was discovered in M74 close to the end of its plateau phase. SN
2003gd is the first type II supernova to have a directly confirmed red
supergiant progenitor. We compare SN 2003gd with SN 1999em, a similar type II-P
supernova, and estimate an explosion date of 18th March 2003. We determine a
reddening towards the supernova of E(B-V) = 0.14+/-0.06, using three different
methods. We also calculate three new distances to M74 of 9.6+/-2.8 Mpc,
7.7+/-1.7 Mpc and 9.6+/-2.2 Mpc. The former was estimated using the
Standardised Candle Method (SCM), for type II supernovae, and the latter two
using the Brightest Supergiants Method (BSM). When combined with existing
kinematic and BSM distance estimates, we derive a mean value of 9.3+/-1.8 Mpc.
SN 2003gd was found to have a lower tail luminosity compared to other
``normal'' type II-P SNe bringing into question the nature of this supernova.
We present a discussion concluding that this is a ``normal'' type II-P
supernova which is consistent with the observed progenitor mass of 8(+4/-2) Mo.Comment: 23 pages, 24 figures to appear in MNRA
Star Formation in the Most Distant Molecular Cloud in the Extreme Outer Galaxy: A Laboratory of Star Formation in an Early Epoch of the Galaxy's Formation
We report the discovery of active star formation in Digel's Cloud 2, which is
one of the most distant giant molecular clouds known in the extreme outer
Galaxy (EOG). At the probable Galactic radius of ~20 kpc, Cloud 2 has a quite
different environment from that in the solar neighborhood, including lower
metallicity, much lower gas density, and small or no perturbation from spiral
arms. With new wide-field near-infrared (NIR) imaging that covers the entire
Cloud 2, we discovered two young embedded star clusters located in the two
dense cores of the cloud. Using our NIR and 12CO data as well as HI, radio
continuum, and IRAS data in the archives, we discuss the detailed star
formation processes in this unique environment. We show clear evidences of a
sequential star formation triggered by the nearby huge supernova remnant, GSH
138-01-94. The two embedded clusters show a distinct morphology difference: the
one in the northern molecular cloud core is a loose association with
isolated-mode star formation, while the other in the southern molecular cloud
core is a dense cluster with cluster-mode star formation. We propose that high
compression by the combination of the SNR shell and an adjacent shell caused
the dense cluster formation in the southern core. Along with the low
metallicity range of the EOG, we suggest that EOG could be an excellent
laboratory for the study of star formation processes, such as those triggered
by supernovae, that occured during an early epoch of the Galaxy's formation. In
particular, the study of the EOG may shed light on the origin and role of the
thick disk, whose metallicity range matches with that of the EOG well.Comment: Accepted by The Astrophysical Journal (18 pages, 9 figures; a version
w/full-resolution color figures is available at
http://www.ioa.s.u-tokyo.ac.jp/~naoto/papers/apj.cl2_quirc/ms2p_final.pdf
Interacting supernovae and supernova impostors. SN 2007sv: the major eruption of a massive star in UGC 5979
We report the results of the photometric and spectroscopic monitoring
campaign of the transient SN 2007sv. The observables are similar to those of
type IIn supernovae, a well-known class of objects whose ejecta interact with
pre-existing circum-stellar material. The spectra show a blue continuum at
early phases and prominent Balmer lines in emission, however, the absolute
magnitude at the discovery of SN 2007sv (M_R = - 14.25 +/- 0.38) indicate it to
be most likely a supernova impostor. This classification is also supported by
the lack of evidence in the spectra of very high velocity material as expected
in supernova ejecta. In addition we find no unequivocal evidence of broad lines
of alpha - and/or Fe-peak elements. The comparison with the absolute light
curves of other interacting objects (including type IIn supernovae) highlights
the overall similarity with the prototypical impostor SN 1997bs. This supports
our claim that SN 2007sv was not a genuine supernova, and was instead a
supernova impostor, most likely similar to the major eruption of a luminous
blue variable.Comment: Accepted for publication in MNRAS. 15 pages, 11 figures, 5 table
Zooming In on the Progenitors of Superluminous Supernovae With the HST
We present Hubble Space Telescope (HST) rest-frame ultraviolet imaging of the
host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including
11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the
superb angular resolution of HST, we characterize the galaxies' morphological
properties, sizes and star formation rate (SFR) densities. We determine the
supernova (SN) locations within the host galaxies through precise astrometric
matching, and measure physical and host-normalized offsets, as well as the SN
positions within the cumulative distribution of UV light pixel brightness. We
find that the host galaxies of H-poor SLSNe are irregular, compact dwarf
galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived SFR
densities are high ( ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe
form in overdense environments. Their locations trace the UV light of their
host galaxies, with a distribution intermediate between that of long-duration
gamma-ray bursts (LGRBs) (which are strongly clustered on the brightest regions
of their hosts) and a uniform distribution (characteristic of normal
core-collapse SNe), though cannot be statistically distinguished from either
with the current sample size. Taken together, this strengthens the picture that
SLSN progenitors require different conditions than those of ordinary
core-collapse SNe to form, and that they explode in broadly similar galaxies as
do LGRBs. If the tendency for SLSNe to be less clustered on the brightest
regions than are LGRBs is confirmed by a larger sample, this would indicate a
different, potentially lower-mass progenitor for SLSNe than LRGBs.Comment: ApJ in press; matches published version. Minor changes following
referee's comments; conclusions unchange
Sensing the gas metal arc welding process
Control of gas metal arc welding (GMAW) requires real-time sensing of the process. Three sensing techniques for GMAW are being developed at the Idaho National Engineering Laboratory (INEL). These are (1) noncontacting ultrasonic sensing using a laser/EMAT (electromagnetic acoustic transducer) to detect defects in the solidified weld on a pass-by-pass basis, (2) integrated optical sensing using a CCD camera and a laser stripe to obtain cooling rate and weld bead geometry information, and (3) monitoring fluctuations in digitized welding voltage data to detect the mode of metal droplet transfer and assure that the desired mass input is achieved
The Anomaly in the Candidate Microlensing Event PA-99-N2
The lightcurve of PA-99-N2, one of the recently announced microlensing
candidates towards M31, shows small deviations from the standard Paczynski
form. We explore a number of possible explanations, including correlations with
the seeing, the parallax effect and a binary lens. We find that the
observations are consistent with an unresolved RGB or AGB star in M31 being
microlensed by a binary lens. We find that the best fit binary lens mass ratio
is about one hundredth, which is one of most extreme values found for a binary
lens so far. If both the source and lens lie in the M31 disk, then the standard
M31 model predicts the probable mass range of the system to be 0.02-3.6 solar
masses (95 % confidence limit). In this scenario, the mass of the secondary
component is therefore likely to be below the hydrogen-burning limit. On the
other hand, if a compact halo object in M31 is lensing a disk or spheroid
source, then the total lens mass is likely to lie between 0.09-32 solar masses,
which is consistent with the primary being a stellar remnant and the secondary
a low mass star or brown dwarf. The optical depth (or alternatively the
differential rate) along the line of sight toward the event indicates that a
halo lens is more likely than a stellar lens provided that dark compact objects
comprise no less than 15 per cent (or 5 per cent) of haloes.Comment: Latex, 23 pages, 9 figures, in press at The Astrophysical Journa
Hydrogen-Poor Superluminous Supernovae and Long-Duration Gamma-Ray Bursts Have Similar Host Galaxies
We present optical spectroscopy and optical/near-IR photometry of 31 host
galaxies of hydrogen-poor superluminous supernovae (SLSNe), including 15 events
from the Pan-STARRS1 Medium Deep Survey. Our sample spans the redshift range
0.1 < z < 1.6 and is the first comprehensive host galaxy study of this specific
subclass of cosmic explosions. Combining the multi-band photometry and
emission-line measurements, we determine the luminosities, stellar masses, star
formation rates and metallicities. We find that as a whole, the hosts of SLSNe
are a low-luminosity ( ~ -17.3 mag), low stellar mass ( ~ 2 x 10^8
M_sun) population, with a high median specific star formation rate ( ~ 2
Gyr^-1). The median metallicity of our spectroscopic sample is low, 12 +
log(O/H}) ~ 8.35 ~ 0.45 Z_sun, although at least one host galaxy has solar
metallicity. The host galaxies of H-poor SLSNe are statistically distinct from
the hosts of GOODS core-collapse SNe (which cover a similar redshift range),
but resemble the host galaxies of long-duration gamma-ray bursts (LGRBs) in
terms of stellar mass, SFR, sSFR and metallicity. This result indicates that
the environmental causes leading to massive stars forming either SLSNe or LGRBs
are similar, and in particular that SLSNe are more effectively formed in low
metallicity environments. We speculate that the key ingredient is large core
angular momentum, leading to a rapidly-spinning magnetar in SLSNe and an
accreting black hole in LGRBs.Comment: ApJ in press; updated to match accepted version. Some additional data
added, discussion of selection effects expanded; conclusions unchanged. 22
pages in emulateapj forma
Observations of the GRB afterglow ATLAS17aeu and its possible association with GW170104
We report the discovery and multi-wavelength data analysis of the peculiar
optical transient, ATLAS17aeu. This transient was identified in the skymap of
the LIGO gravitational wave event GW170104 by our ATLAS and Pan-STARRS
coverage. ATLAS17aeu was discovered 23.1hrs after GW170104 and rapidly faded
over the next 3 nights, with a spectrum revealing a blue featureless continuum.
The transient was also detected as a fading x-ray source by Swift and in the
radio at 6 and 15 GHz. A gamma ray burst GRB170105A was detected by 3
satellites 19.04hrs after GW170104 and 4.10hrs before our first optical
detection. We analyse the multi-wavelength fluxes in the context of the known
GRB population and discuss the observed sky rates of GRBs and their afterglows.
We find it statistically likely that ATLAS17aeu is an afterglow associated with
GRB170105A, with a chance coincidence ruled out at the 99\% confidence or
2.6. A long, soft GRB within a redshift range of would be consistent with all the observed multi-wavelength data. The
Poisson probability of a chance occurrence of GW170104 and ATLAS17aeu is
. This is the probability of a chance coincidence in 2D sky location
and in time. These observations indicate that ATLAS17aeu is plausibly a normal
GRB afterglow at significantly higher redshift than the distance constraint for
GW170104 and therefore a chance coincidence. However if a redshift of the faint
host were to place it within the GW170104 distance range, then physical
association with GW170104 should be considered.Comment: 16 pages, 6 figures, accepted to Ap
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