51 research outputs found
SIMBA's view of the epsilon Eri disk
We present the first observational confirmation for an extended circumstellar
dust disk around epsilon Eri. The observations were obtained with the bolometer
array SIMBA at the 15 m radio telescope SEST in Chile and measure the dust
continuum at 1.2 mm. The emission, with a total flux of 21.4 mJy and a rms of
2.2 mJy/beam, is resolved to a deconvolved size of 27.4 arcsec which
corresponds to 88 AU. No clear indication for a ring-like disk structure is
seen, possibly also due to the telescope's large beam width of 24 arcsec.
Models of the object's spectral energy distribution from IR to mm-wavelengths
show that the emission can also be explained by a simple disk model. We further
demonstrate the strong influence of noise and propose to be cautious with
interpretations of the ring substructure.Comment: To appear in A&A Letters, in pres
Carbon in different phases ([CII], [CI], and CO) in infrared dark clouds: Cloud formation signatures and carbon gas fractions
Context: How do molecular clouds form out of the atomic phase? And what are
the relative fractions of carbon in the ionized, atomic and molecular phase?
These are questions at the heart of cloud and star formation. Methods: Using
multiple observatories from Herschel and SOFIA to APEX and the IRAM 30m
telescope, we mapped the ionized, atomic and molecular carbon ([CII]@1900GHz,
[CI]@492GHz and C18O(2-1)@220GHz) at high spatial resolution (12"-25") in four
young massive infrared dark clouds (IRDCs). Results: The three carbon phases
were successfully mapped in all four regions, only in one source the [CII] line
remained a non-detection. Both the molecular and atomic phases trace the dense
structures well, with [CI] also tracing material at lower column densities.
[CII] exhibits diverse morphologies in our sample, from compact to diffuse
structures probing the cloud environment. In at least two out of the four
regions, we find kinematic signatures strongly indicating that the dense gas
filaments have formed out of a dynamically active and turbulent
atomic/molecular cloud, potentially from converging gas flows. The
atomic-to-molecular carbon gas mass ratios are low between 7% and 12% with the
lowest values found toward the most quiescent region. In the three regions
where [CII] is detected, its mass is always higher by a factor of a few than
that of the atomic carbon. The ionized carbon emission depends as well on the
radiation field, however, we also find strong [CII] emission in a region
without significant external sources, indicating that other processes, e.g.,
energetic gas flows can contribute to the [CII] excitation as well.Comment: 15 pages, 18 figures, accepted by Astronomy & Astrophysics, a higher
resolution version can be found at
http://www.mpia.de/homes/beuther/papers.htm
Fragmentation and dynamical collapse of the starless high-mass star-forming region IRDC18310-4
Aims: We study the fragmentation and dynamical properties of a massive
starless gas clump at the onset of high-mass star formation. Methods: Based on
Herschel continuum data we identify a massive gas clump that remains
far-infrared dark up to 100mum wavelengths. The fragmentation and dynamical
properties are investigated by means of Plateau de Bure Interferometer and
Nobeyama 45m single-dish spectral line and continuum observations. Results: The
massive gas reservoir fragments at spatial scales of ~18000AU in four cores.
Comparing the spatial extent of this high-mass region with intermediate- to
low-mass starless cores from the literature, we find that linear sizes do not
vary significantly over the whole mass regime. However, the high-mass regions
squeeze much more gas into these similar volumes and hence have orders of
magnitude larger densities. The fragmentation properties of the presented
low-to high-mass regions are consistent with gravitational instable Jeans
fragmentation. Furthermore, we find multiple velocity components associated
with the resolved cores. Recent radiative transfer hydrodynamic simulations of
the dynamic collapse of massive gas clumps also result in multiple velocity
components along the line of sight because of the clumpy structure of the
regions. This result is supported by a ratio between viral and total gas mass
for the whole region <1. Conclusions: This apparently still starless high-mass
gas clump exhibits clear signatures of early fragmentation and dynamic collapse
prior to the formation of an embedded heating source. A comparison with regions
of lower mass reveals that the linear size of star-forming regions does not
necessarily have to vary much for different masses, however, the mass
reservoirs and gas densities are orders of magnitude enhanced for high-mass
regions compared to their lower-mass siblings.Comment: 11 pages, 10 figures, accepted to Astronomy and Astrophysics,
high-resolution version with all figures included can be found at
http://www.mpia.de/homes/beuther/papers.htm
Kinematic structure of massive star-forming regions - I. Accretion along filaments
The mid- and far-infrared view on high-mass star formation, in particular
with the results from the Herschel space observatory, has shed light on many
aspects of massive star formation. However, these continuum studies lack
kinematic information.
We study the kinematics of the molecular gas in high-mass star-forming
regions.
We complemented the PACS and SPIRE far-infrared data of 16 high-mass
star-forming regions from the Herschel key project EPoS with N2H+ molecular
line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+
hyperfine structure, we produced column density, velocity, and linewidth maps.
These were correlated with PACS 70micron images and PACS point sources. In
addition, we searched for velocity gradients.
For several regions, the data suggest that the linewidth on the scale of
clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and
G11.11 show two velocity components along several lines of sight. We find that
all regions with a diameter larger than 1pc show either velocity gradients or
fragment into independent structures with distinct velocities. The velocity
profiles of three regions with a smooth gradient are consistent with gas flows
along the filament, suggesting accretion flows onto the densest regions.
We show that the kinematics of several regions have a significant and complex
velocity structure. For three filaments, we suggest that gas flows toward the
more massive clumps are present.Comment: accepted by A&
ISM conditions in z~0.2 Lyman-Break Analogs
We present an analysis of far--infrared (FIR) [CII] and [OI] fine structure
line and continuum observations obtained with /PACS, and CO(1-0)
observations obtained with the IRAM Plateau de Bure Interferometer, of Lyman
Break Analogs (LBAs) at . The principal aim of this work is to
determine the typical ISM properties of Main Sequence (MS)
galaxies, with stellar masses between and ,
which are currently not easily detectable in all these lines even with ALMA and
NOEMA. We perform PDR modeling and apply different IR diagnostics to derive the
main physical parameters of the FIR emitting gas and dust and we compare the
derived ISM properties to those of galaxies on and above the MS at different
redshifts. We find that the ISM properties of LBAs are quite extreme (low gas
temperature, high density and thermal pressure) with respect to those found in
local normal spirals and more active local galaxies. LBAs have no [CII] deficit
despite having the high specific star formation rates (sSFRs) typical of
starbursts. Although LBAs lie above the local MS, we show that their ISM
properties are more similar to those of high-redshift MS galaxies than of local
galaxies above the main sequence. This data set represents an important
reference for planning future ALMA [CII] observations of relatively low-mass MS
galaxies at the epoch of the peak of the cosmic star formation.Comment: 19 pages, 12 Figures,8 Tables, Accepted for publication in A&
Kinematic structure of massive star-forming regions - I. Accretion along filaments
The mid- and far-infrared view on high-mass star formation, in particular
with the results from the Herschel space observatory, has shed light on many
aspects of massive star formation. However, these continuum studies lack
kinematic information.
We study the kinematics of the molecular gas in high-mass star-forming
regions.
We complemented the PACS and SPIRE far-infrared data of 16 high-mass
star-forming regions from the Herschel key project EPoS with N2H+ molecular
line data from the MOPRA and Nobeyama 45m telescope. Using the full N2H+
hyperfine structure, we produced column density, velocity, and linewidth maps.
These were correlated with PACS 70micron images and PACS point sources. In
addition, we searched for velocity gradients.
For several regions, the data suggest that the linewidth on the scale of
clumps is dominated by outflows or unresolved velocity gradients. IRDC18454 and
G11.11 show two velocity components along several lines of sight. We find that
all regions with a diameter larger than 1pc show either velocity gradients or
fragment into independent structures with distinct velocities. The velocity
profiles of three regions with a smooth gradient are consistent with gas flows
along the filament, suggesting accretion flows onto the densest regions.
We show that the kinematics of several regions have a significant and complex
velocity structure. For three filaments, we suggest that gas flows toward the
more massive clumps are present.Comment: accepted by A&
Variability and multi-periodic oscillations in the X-ray light curve of the classical nova V4743 Sgr
The classical nova V4743 Sgr was observed with XMM-Newton for about 10 hours
on April 4 2003, 6.5 months after optical maximum. At this time, this nova had
become the brightest supersoft X-ray source ever observed. We present the
results of a time series analysis performed on the X-ray light curve obtained
in this observation, and in a previous shorter observation done with Chandra 16
days earlier. Intense variability, with amplitude as large as 40% of the total
flux, was observed both times. Similarities can be found between the two
observations in the structure of the variations. Most of the variability is
well represented as a combination of oscillations at a set of discrete
frequencies lower than 1.7 mHz. At least five frequencies are constant over the
16 day time interval between the two observations. We suggest that a periods in
the power spectrum of both light curves at the frequency of 0.75 mHz and its
first harmonic are related to the spin period of the white dwarf in the system,
and that other observed frequencies are signatures of nonradial white dwarf
pulsations. A possible signal with a 24000 sec period is also found in the
XMM-Newton light curve: a cycle and a half are clearly identified. This period
is consistent with the 24278 s periodicity discovered in the optical light
curve of the source and thought to be the orbital period of the nova binary
system.Comment: In press in Monthly Notices of the Royal Astronomical Societ
Lynds 1622: a nearby star forming cloud projected on Orion B?
We present results of optical spectroscopic and photometric observation of
the pre-main sequence stars associated with the cometary shaped dark cloud
Lynds 1622, and 12CO and 13CO observations of the cloud. We determined the
effective temperatures and luminosities of 14 pre-main sequence stars
associated with the cloud from their positions in the Hertzsprung--Russell
diagram, as well as constructed their spectral energy distributions using
optical, 2MASS and Spitzer IRAC and MIPS data. We derived physical parameters
of L1622 from the molecular observations. Our results are not compatible with
the assumption that L1622 lies on the near side of the Orion-Eridanus loop, but
suggest that L1622 is as distant as Orion B. At a distance of 400 pc the mass
of the cloud, derived from our CO data, is 1100 solar masses, its star
formation efficiency is 1.8%, and the average age of its low-mass pre-main
sequence star population is about 1 million years.Comment: 13 pages, 9 figures, 4 tables; accepted by MNRA
Parameterizing the interstellar dust temperature
The temperature of interstellar dust particles is of great importance to
astronomers. It plays a crucial role in the thermodynamics of interstellar
clouds, because of the gas-dust collisional coupling. It is also a key
parameter in astrochemical studies that governs the rate at which molecules
form on dust. In 3D (magneto)hydrodynamic simulations often a simple expression
for the dust temperature is adopted, because of computational constraints,
while astrochemical modelers tend to keep the dust temperature constant over a
large range of parameter space. Our aim is to provide an easy-to-use parametric
expression for the dust temperature as a function of visual extinction () and to shed light on the critical dependencies of the dust temperature on
the grain composition. We obtain an expression for the dust temperature by
semi-analytically solving the dust thermal balance for different types of
grains and compare to a collection of recent observational measurements. We
also explore the effect of ices on the dust temperature. Our results show that
a mixed carbonaceous-silicate type dust with a high carbon volume fraction
matches the observations best. We find that ice formation allows the dust to be
warmer by up to 15% at high optical depths ( mag) in the
interstellar medium. Our parametric expression for the dust temperature is
presented as , where is in units of the Draine (1978) UV fieldComment: 16 pages, 17 figures, 4 tables. Accepted for publication in A&A.
Version 2: the omission of factor 0.921 in equation 4 is correcte
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