1,596 research outputs found
The Great Eruption of Eta Carinae
During the years 1838-1858, the very massive star {\eta} Carinae became the
prototype supernova impostor: it released nearly as much light as a supernova
explosion and shed an impressive amount of mass, but survived as a star.1 Based
on a light-echo spectrum of that event, Rest et al.2 conclude that "a new
physical mechanism" is required to explain it, because the gas outflow appears
cooler than theoretical expectations. Here we note that (1) theory predicted a
substantially lower temperature than they quoted, and (2) their inferred
observational value is quite uncertain. Therefore, analyses so far do not
reveal any significant contradiction between the observed spectrum and most
previous discussions of the Great Eruption and its physics.Comment: To appear in Nature, a brief communication arising in response to
Rest et al. 2012. Submitted to Nature February 17, 201
On the Interpretation of Supernova Light Echo Profiles and Spectra
The light echo systems of historical supernovae in the Milky Way and local
group galaxies provide an unprecedented opportunity to reveal the effects of
asymmetry on observables, particularly optical spectra. Scattering dust at
different locations on the light echo ellipsoid witnesses the supernova from
different perspectives and the light consequently scattered towards Earth
preserves the shape of line profile variations introduced by asymmetries in the
supernova photosphere. However, the interpretation of supernova light echo
spectra to date has not involved a detailed consideration of the effects of
outburst duration and geometrical scattering modifications due to finite
scattering dust filament dimension, inclination, and image point-spread
function and spectrograph slit width. In this paper, we explore the
implications of these factors and present a framework for future resolved
supernova light echo spectra interpretation, and test it against Cas A and SN
1987A light echo spectra. We conclude that the full modeling of the dimensions
and orientation of the scattering dust using the observed light echoes at two
or more epochs is critical for the correct interpretation of light echo
spectra. Indeed, without doing so one might falsely conclude that differences
exist when none are actually present.Comment: 18 pages, 22 figures, accepted for publication in Ap
Application of remote sensing technology in South Dakota to assess wildlife habitat change, describe meandering lakes, improve agricultural censusing, map Aspen, and quantify cell selection criteria for spatial data
There are no author-identified significant results in this report
A pulsed, mono-energetic and angular-selective UV photo-electron source for the commissioning of the KATRIN experiment
The KATRIN experiment aims to determine the neutrino mass scale with a
sensitivity of 200 meV/c^2 (90% C.L.) by a precision measurement of the shape
of the tritium -spectrum in the endpoint region. The energy analysis of
the decay electrons is achieved by a MAC-E filter spectrometer. To determine
the transmission properties of the KATRIN main spectrometer, a mono-energetic
and angular-selective electron source has been developed. In preparation for
the second commissioning phase of the main spectrometer, a measurement phase
was carried out at the KATRIN monitor spectrometer where the device was
operated in a MAC-E filter setup for testing. The results of these measurements
are compared with simulations using the particle-tracking software
"Kassiopeia", which was developed in the KATRIN collaboration over recent
years.Comment: 19 pages, 16 figures, submitted to European Physical Journal
Light echoes reveal an unexpectedly cool Eta Carinae during its 19th-century Great Eruption
Eta Carinae (Eta Car) is one of the most massive binary stars in the Milky
Way. It became the second-brightest star in the sky during its mid-19th century
"Great Eruption," but then faded from view (with only naked-eye estimates of
brightness). Its eruption is unique among known astronomical transients in that
it exceeded the Eddington luminosity limit for 10 years. Because it is only 2.3
kpc away, spatially resolved studies of the nebula have constrained the ejected
mass and velocity, indicating that in its 19th century eruption, Eta Car
ejected more than 10 M_solar in an event that had 10% of the energy of a
typical core-collapse supernova without destroying the star. Here we report the
discovery of light echoes of Eta Carinae which appear to be from the 1838-1858
Great Eruption. Spectra of these light echoes show only absorption lines, which
are blueshifted by -210 km/s, in good agreement with predicted expansion
speeds. The light-echo spectra correlate best with those of G2-G5 supergiant
spectra, which have effective temperatures of ~5000 K. In contrast to the class
of extragalactic outbursts assumed to be analogs of Eta Car's Great Eruption,
the effective temperature of its outburst is significantly cooler than allowed
by standard opaque wind models. This indicates that other physical mechanisms
like an energetic blast wave may have triggered and influenced the eruption.Comment: Accepted for publication by Nature; 4 pages, 4 figures, SI: 6 pages,
3 figures, 5 table
Observation of light echoes around very young stars
The goal of the paper is to present new results on light echoes from young
stellar objects. Broad band CCD images were obtained over three months at
one-to-two week intervals for the field of NGC 6726, using the large
field-of-view remotely-operated telescope on top of Cerro Burek. We detected
scattered light echoes around two young, low-amplitude, irregular variable
stars. Observations revealed not just one, but multiple light echoes from
brightness pulses of the T Tauri star S CrA and the Herbig Ae/Be star R CrA.
Analysis of S CrA's recurring echoes suggests that the star is located 138 +/-
16 pc from Earth, making these the closest echoes ever detected. The
environment that scatters the stellar light from S CrA is compatible with an
incomplete dust shell or an inclined torus some 10,000 AU in radius and
containing M_{\sun} of dust. The cause of such
concentration at 10,000AU from the star is unknown. It could be the
remnant of the envelope from which the star formed, but the distance of the
cloud is remarkably similar to the nominal distance of the Oort cloud to the
Sun, leading us to also speculate that the dust (or ice) seen around S CrA
might have the same origin as the Solar System Oort cloud.Comment: A&A, in press Received: 16 March 2010 / Accepted: 01 June 201
Triplets of Quasars at high redshift I: Photometric data
We have conducted an optical and infrared imaging in the neighbourhoods of 4
triplets of quasars. R, z', J and Ks images were obtained with MOSAIC II and
ISPI at Cerro Tololo Interamerican Observatory. Accurate relative photometry
and astrometry were obtained from these images for subsequent use in deriving
photometric redshifts. We analyzed the homogeneity and depth of the photometric
catalog by comparing with results coming from the literature. The good
agreement shows that our magnitudes are reliable to study large scale structure
reaching limiting magnitudes of R = 24.5, z' = 22.5, J = 20.5 and Ks = 19.0.
With this catalog we can study the neighbourhoods of the triplets of quasars
searching for galaxy overdensities such as groups and galaxy clusters.Comment: The paper contains 12 figures and 3 table
The host galaxy and late-time evolution of the Super-Luminous Supernova PTF12dam
Super-luminous supernovae of type Ic have a tendency to occur in faint host
galaxies which are likely to have low mass and low metallicity. PTF12dam is one
of the closest and best studied super-luminous explosions that has a broad and
slowly fading lightcurve similar to SN 2007bi. Here we present new photometry
and spectroscopy for PTF12dam from 200-500 days (rest-frame) after peak and a
detailed analysis of the host galaxy (SDSS J142446.21+461348.6 at z = 0.107).
Using deep templates and image subtraction we show that the full lightcurve can
be fit with a magnetar model if escape of high-energy gamma rays is taken into
account. The full bolometric lightcurve from -53 to +399 days (with respect to
peak) cannot be fit satisfactorily with the pair-instability models. An
alternative model of interaction with a dense CSM produces a good fit to the
data although this requires a very large mass (~ 13 M_sun) of hydrogen free
CSM. The host galaxy is a compact dwarf (physical size ~ 1.9 kpc) and with M_g
= -19.33 +/- 0.10, it is the brightest nearby SLSN Ic host discovered so far.
The host is a low mass system (2.8 x 10^8 M_sun) with a star-formation rate
(5.0 M_sun/year), which implies a very high specific star-formation rate (17.9
Gyr^-1). The remarkably strong nebular lines provide detections of the [O III]
\lambda 4363 and [O II] \lambda\lambda 7320,7330 auroral lines and an accurate
oxygen abundance of 12 + log(O/H) = 8.05 +/- 0.09. We show here that they are
at the extreme end of the metallicity distribution of dwarf galaxies and
propose that low metallicity is a requirement to produce these rare and
peculiar supernovae.Comment: 20 pages, 12 figures, 8 tables, accepted for publication to MNRA
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