359 research outputs found
An infrared-submillimeter study of star-forming regions selected by the ISOSS 170um survey
Using the ISOPHOT Serendipity Survey (ISOSS) at 170um a sample of galactic
star-forming regions exhibiting very cold dust temperatures (< 20 K) and high
masses (> 100 M_sun) has been established. We characterise the star-forming
content of five regions that were selected as potential sites for early stage
high-mass star formation using SCUBA (JCMT) and Spitzer observations. In every
region we identify one to four submillimeter clumps with projected sizes
between 0.1 and 0.4 pc. The dust temperatures range from 11.6 to 21.3 K and the
estimated clump masses are 2 to 166 M_sun. Towards the majority of
submillimeter peaks we find point sources in the near- to mid-infrared. Most
are interpreted as low-mass young stellar objects but we also detect very red
sources. They probably represent very young and deeply embedded protostars that
continue to accrete clump material and may reach higher masses. Several
candidate intermediate-mass proto- or pre-main-sequence stars embedded in the
clumps are identified. A subset of four clumps may be massive enough (> 100
M_sun) to form high-mass stars and accompanying clusters. The absence of
stellar precursors with current masses in the high-mass regime leave the type
of star formation occuring in the clumps unsettled. We confirm the presence of
large fractions of cold material as derived from large-scale far-infrared
measurements which dominates the emission of most clumps and suggests that the
star-forming process will continue.Comment: 11 pages, 11 figures, accepted for publication in A&
Constraints on the nature of dust particles by infrared observations
The far-infrared (FIR) emissivity of dust is an important parameter
characterizing the physical properties of the grains. With the availability of
stellar databases and far-infrared data from Infrared Space Observatory (ISO)
it is possible to compare the optical and infrared properties of dust, and
derive the far-infrared emissivity with respect to the optical extinction.
In this paper we present the results of a systematic analysis of the FIR
emissivity of interstellar clouds observed with ISOPHOT (the photometer onboard
ISO) at least at two infrared wavelengths, one close to ~100um and one at
200um. We constructed FIR emission maps, determined dust temperatures, created
extinction maps using 2MASS survey data, and calculated far-infrared emissivity
for each of these clouds. We present the largest homogeneously reduced database
constructed so far for this purpose. During the data analysis special care was
taken on possible systematic errors. We find that far-infrared emissivity has a
clear dependence on temperature.
The emissivity is enhanced by a factor of usually less than 2 in the low dust
temperature regime of 12K<=T_d<=14K. This result suggests larger grain sizes in
those regions. However, the emissivity increase of typically below 2 restricts
the possible grain growth processes to ice-mantle formation and coagulation of
silicate grains, and excludes the coagulation of carbonaceous particles on the
scales of the regions we investigated.
In the temperature range 14K<=T_d<=16K a systematic decrease of emissivity is
observed with respect to the values of the diffuse interstellar matter.
Possible scenarios for this behaviour are discussed in the paper.Comment: Accepted for publication in MNRA
Framing vulnerability, risk and societal responses: the MOVE framework
The paper deals with the development of a general as well as integrative and holistic framework to systematize and assess vulnerability, risk and adaptation. The framework is a thinking tool meant as a heuristic that outlines key factors and different dimensions that need to be addressed when assessing vulnerability in the context of natural hazards and climate change. The approach underlines that the key factors of such a common framework are related to the exposure of a society or system to a hazard or stressor, the susceptibility of the system or community exposed, and its resilience and adaptive capacity. Additionally, it underlines the necessity to consider key factors and multiple thematic dimensions when assessing vulnerability in the context of natural and socio-natural hazards. In this regard, it shows key linkages between the different concepts used within the disaster risk management (DRM) and climate change adaptation (CCA) research. Further, it helps to illustrate the strong relationships between different concepts used in DRM and CCA. The framework is also a tool for communicating complexity and stresses the need for societal change in order to reduce risk and to promote adaptation. With regard to this, the policy relevance of the framework and first results of its application are outlined. Overall, the framework presented enhances the discussion on how to frame and link vulnerability, disaster risk, risk management and adaptation concepts
"Last-Mile" preparation for a potential disaster
Extreme natural events, like e.g. tsunamis or earthquakes, regularly lead to catastrophes with dramatic consequences. In recent years natural disasters caused hundreds of thousands of deaths, destruction of infrastructure, disruption of economic activity and loss of billions of dollars worth of property and thus revealed considerable deficits hindering their effective management: Needs for stakeholders, decision-makers as well as for persons concerned include systematic risk identification and evaluation, a way to assess countermeasures, awareness raising and decision support systems to be employed before, during and after crisis situations. The overall goal of this study focuses on interdisciplinary integration of various scientific disciplines to contribute to a tsunami early warning information system. In comparison to most studies our focus is on high-end geometric and thematic analysis to meet the requirements of small-scale, heterogeneous and complex coastal urban systems. Data, methods and results from engineering, remote sensing and social sciences are interlinked and provide comprehensive information for disaster risk assessment, management and reduction. In detail, we combine inundation modeling, urban morphology analysis, population assessment, socio-economic analysis of the population and evacuation modeling. The interdisciplinary results eventually lead to recommendations for mitigation strategies in the fields of spatial planning or coping capacity
The Cassiopeia A Supernova was of Type IIB
Cassiopeia A is one of the youngest supernova remnants known in the Milky Way
and a unique laboratory for supernova physics. We present an optical spectrum
of the Cassiopeia A supernova near maximum brightness, obtained from
observations of a scattered light echo - more than three centuries after the
direct light of the explosion swept past Earth. The spectrum shows that
Cassiopeia A was a type IIb supernova and originated from the collapse of the
helium core of a red supergiant that had lost most of its hydrogen envelope
prior to exploding. Our finding concludes a longstanding debate on the
Cassiopeia A progenitor and provides new insight into supernova physics by
linking the properties of the explosion to the wealth of knowledge about its
remnant.Comment: 17 pages, 4 figures, including online supporting material; to be
published in Science on 30 May 200
JWST/NIRSpec Observations of the Coldest Known Brown Dwarf
We present 1-5um spectroscopy of the coldest known brown dwarf, WISE
J085510.83-071442.5 (WISE 0855), performed with the Near-Infrared Spectrograph
(NIRSpec) on board the James Webb Space Telescope (JWST). NIRSpec has
dramatically improved the measurement of spectral energy distribution of WISE
0855 in terms of wavelength coverage, signal-to-noise ratios, and spectral
resolution. We have performed preliminary modeling of the NIRSpec data using
the ATMO 2020 models of cloudless atmospheres, arriving at a best fitting model
that has T_eff=285 K. That temperature is ~20 K higher than the value derived
by combining our luminosity estimate with evolutionary models (i.e., the radius
in the model fit to the SED is somewhat smaller than expected from evolutionary
models). Through comparisons to the model spectra, we detect absorption in the
fundamental band of CO, which is consistent with an earlier detection in a
ground-based spectrum and indicates the presence of vertical mixing. Although
PH_3 is expected in Y dwarfs that experience vertical mixing, it is not
detected in WISE 0855. Previous ground-based M-band spectroscopy of WISE 0855
has been cited for evidence of H_2O ice clouds, but we find that the NIRSpec
data in that wavelength range are matched well by our cloudless model. Thus,
clear evidence of H_2O ice clouds in WISE 0855 has not been identified yet, but
it may still be present in the NIRSpec data. The physical properties of WISE
0855, including the presence of H_2O clouds, can be better constrained by more
detailed fitting with both cloudless and cloudy models and the incorporation of
unpublished 5-28um data from the Mid-infrared Instrument on JWST.Comment: Astronomical Journal, in pres
JWST/NIRSpec Observations of the Planetary Mass Companion TWA 27B
We present 1-5um spectroscopy of the young planetary mass companion TWA 27B
(2M1207B) performed with NIRSpec on board the James Webb Space Telescope. In
these data, the fundamental band of CH_4 is absent and the fundamental band of
CO is weak. The nondetection of CH_4 reinforces a previously observed trend of
weaker CH_4 with younger ages among L dwarfs, which has been attributed to
enhanced non-equilibrium chemistry among young objects. The weakness of CO may
reflect an additional atmospheric property that varies with age, such as the
temperature gradient or cloud thickness. We are able to reproduce the broad
shape of the spectrum with an ATMO cloudless model that has T=1300 K,
non-equilibrium chemistry, and a temperature gradient reduction caused by
fingering convection. However, the fundamental bands of CH_4 and CO are
somewhat stronger in the model. In addition, the model temperature of 1300 K is
higher than expected from evolutionary models given the luminosity and age of
TWA 27B (T=1200 K). Previous models of young L-type objects suggest that the
inclusion of clouds could potentially resolve these issues; it remains to be
seen whether cloudy models can provide a good fit to the 1-5um data from
NIRSpec. TWA 27B exhibits emission in Paschen transitions and the He I triplet
at 1.083um, which are signatures of accretion that provide the first evidence
of a circumstellar disk. We have used the NIRSpec data to estimate the
bolometric luminosity of TWA 27B (log L/L_sun=-4.466+/-0.014), which implies a
mass of 5-6 MJup according to evolutionary models.Comment: Astrophysical Journal Letters, in pres
Tycho Brahe's 1572 supernova as a standard type Ia explosion revealed from its light echo spectrum
Type Ia supernovae (SNe Ia) are thermonuclear explosions of white dwarf stars
in close binary systems. They play an important role as cosmological distance
indicators and have led to the discovery of the accelerated expansion of the
Universe. Among the most important unsolved questions are how the explosion
actually proceeds and whether accretion occurs from a companion or via the
merging of two white dwarfs. Tycho Brahe's supernova of 1572 (SN 1572) is
thought to be one of the best candidates for a SN Ia in the Milky Way. The
proximity of the SN 1572 remnant has allowed detailed studies, such as the
possible identification of the binary companion, and provides a unique
opportunity to test theories of the explosion mechanism and the nature of the
progenitor. The determination of the yet unknown exact spectroscopic type of SN
1572 is crucial to relate these results to the diverse population of SNe Ia.
Here we report an optical spectrum of Tycho Brahe's supernova near maximum
brightness, obtained from a scattered-light echo more than four centuries after
the direct light of the explosion swept past Earth. We find that SN 1572
belongs to the majority class of normal SNe Ia. The presence of a strong Ca II
IR feature at velocities exceeding 20,000 km/s, which is similar to the
previously observed polarized features in other SNe Ia, suggests asphericity in
SN 1572.Comment: 15 pages, 3 figures - accepted for publication in Natur
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