2,059 research outputs found
Fragmentation, infall, and outflow around the showcase massive protostar NGC7538 IRS1 at 500 AU resolution
Aims: Revealing the fragmentation, infall, and outflow processes in the
immediate environment around massive young stellar objects is crucial for
understanding the formation of the most massive stars. Methods: With this goal
in mind we present the so far highest spatial-resolution thermal submm line and
continuum observations toward the young high-mass protostar NGC7538 IRS1. Using
the Plateau de Bure Interferometer in its most extended configuration at 843mum
wavelength, we achieved a spatial resolution of 0.2"x0.17", corresponding to
~500AU at a distance of 2.7\,kpc. Results: For the first time, we have observed
the fragmentation of the dense inner core of this region with at least three
subsources within the inner 3000 AU. The outflow exhibits blue- and red-shifted
emission on both sides of the central source indicating that the current
orientation has to be close to the line-of-sight, which differs from other
recent models. We observe rotational signatures in northeast-southwest
direction; however, even on scales of 500 AU, we do not identify any Keplerian
rotation signatures. This implies that during the early evolutionary stages any
stable Keplerian inner disk has to be very small (<=500 AU). The high-energy
line HCN(4-3)v2=1 (E_u/k=1050K) is detected over an extent of approximately
3000 AU. In addition to this, the detection of red-shifted absorption from this
line toward the central dust continuum peak position allows us to estimate
infall rates of ~1.8x10^(-3)Msun/yr on the smallest spatial scales. Although
all that gas will not necessarily be accreted onto the central protostar,
nevertheless, such inner core infall rates are among the best proxies of the
actual accretion rates one can derive during the early embedded star formation
phase. These data are consistent with collapse simulations and the observed
high multiplicity of massive stars.Comment: Accepted for Astronomy & Astrophysics, 8 pages, also available at
http://www.mpia.de/homes/beuther/papers.htm
Photovoltaic effect in ferroelectric ceramics
The ceramic structure was simulated in a form that is more tractable to correlation between experiment and theory. Single crystals (of barium titanate) were fabricated in a simple corrugated structure in which the pedestals of the corrugation simulated the grain while the intervening cuts could be filled with materials simulating the grain boundaries. The observed photovoltages were extremely small (100 mv)
Development of Analytical Methods for the Determination of Methylarginines in Serum
Nitric oxide (NO) plays a crucial role in numerous physiological pathways including the regulation of the endothelium that lines blood vessels throughout the body. Therefore, in order to maintain good endothelial health, there must be a careful homeostasis of NO. Under pathological conditions that impair the production of NO, endothelial function is disrupted which can result in various pathologies including cardiovascular diseases (CVDs) and respiratory disorders. A class of endogenous compounds that inhibit the enzyme responsible for NO synthesis in vivo are the methylated arginines (MAs). Given their propensity for attenuating NO production, it comes as no surprise that MAs have been implicated in several diseases. Increased blood concentrations of asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), and monomethylarginine (MMA) have been reported in patients suffering from CVDs. However, despite evidence demonstrating the link between MAs and these diseases, no diagnostic concentrations have yet been established. The goal of this work was to develop an analytical method capable of rapidly determining the concentrations of MAs in blood samples so that threshold concentrations indicative of disease could be established. Further efforts were then made to fabricate a point-of-care device that could be used in a clinical setting to measure MAs as a means of preventative diagnostics. Analyzing components in a serum sample is a very challenging endeavor because of the incredible complexity of the sample matrix. To alleviate matrix interferents, a method was developed to rapidly isolate MAs from serum using a newly developed heating procedure. The sample was immersed in a boiling water bath which caused it to solidify. Solvent was then added to the congealed serum and briefly homogenized to permit solid-liquid extraction to take place. After a brief incubation period at room temperature, the sample was centrifuged to sediment the aggregated serum proteins, leaving the small molecules of interest in the supernatant. The supernatant was then derivatized with naphthalene-2,3-dicarboxaldehyde to label the MAs for analysis by capillary electrophoresis (CE) with fluorescence detection. A CE method was developed using sulfobutylether-b-cyclodextrin and dimethylsulfoxide as buffer modifiers to obtain good resolution between the MAs and the other components in serum-derived samples. Under optimized conditions, baseline resolution was achieved which allowed precise quantitation of the MAs. The separation method was then transferred to a microchip electrophoresis (MCE) device that made it possible to perform the same analysis more rapidly on a smaller, portable device. MAs were separated using this MCE platform as a first step towards the development of a point-of-care device to perform clinical analyses on-chip
Chemical evolution in the early phases of massive star formation II: Deuteration
The chemical evolution in high-mass star-forming regions is still poorly
constrained. Studying the evolution of deuterated molecules allows to
differentiate between subsequent stages of high-mass star formation regions due
to the strong temperature dependence of deuterium isotopic fractionation. We
observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass
protostellar objects, 11 hot molecular cores and 9 ultra-compact HII regions in
the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO+ and N2D+
as well as their non-deuterated counterpart. The overall detection fraction of
DCN, DNC and DCO+ is high and exceeds 50% for most of the stages. N2D+ was only
detected in a few infrared dark clouds and high-mass protostellar objects. It
can be related to problems in the bandpass at the frequency of the transition
and to low abundances in the more evolved, warmer stages. We find median D/H
ratios of ~0.02 for DCN, ~0.005 for DNC, ~0.0025 for DCO+ and ~0.02 for N2D+.
While the D/H ratios of DNC, DCO+ and N2D+ decrease with time, DCN/HCN peaks at
the hot molecular core stage. We only found weak correlations of the D/H ratios
for N2D+ with the luminosity of the central source and the FWHM of the line,
and no correlation with the H2 column density. In combination with a previously
observed set of 14 other molecules (Paper I) we fitted the calculated column
densities with an elaborate 1D physico-chemical model with time-dependent
D-chemistry including ortho- and para-H2 states. Good overall fits to the
observed data have been obtained the model. It is one of the first times that
observations and modeling have been combined to derive chemically based
best-fit models for the evolution of high-mass star formation including
deuteration.Comment: 26 pages, 16 figures, accepted at A&
The Herschel/PACS view of disks around low-mass stars in Chamaleon-I
Circumstellar disks are expected to be the birthplaces of planets. The
potential for forming one or more planets of various masses is essentially
driven by the initial mass of the disks. We present and analyze Herschel/PACS
observations of disk-bearing M-type stars that belong to the young ~2 Myr old
Chamaleon-I star forming region. We used the radiative transfer code RADMC to
successfully model the SED of 17 M-type stars detected at PACS wavelengths. We
first discuss the relatively low detection rates of M5 and later spectral type
stars with respect to the PACS sensitivity, and argue their disks masses, or
flaring indices, are likely to be low. For M0 to M3 stars, we find a relatively
broad range of disk masses, scale heights, and flaring indices. Via a
parametrization of dust stratification, we can reproduce the peak fluxes of the
10 m emission feature observed with Spitzer/IRS, and find that disks
around M-type stars may display signs of dust sedimentation. The Herschel/PACS
observations of low-mass stars in Cha-I provide new constraints on their disk
properties, overall suggesting that disk parameters for early M-type stars are
comparable to those for more massive stars (e.g., comparable scale height and
flaring angles). However, regions of the disks emitting at about 100 m may
still be in the optically thick regime, preventing direct determination of disk
masses. Thus the modeled disk masses should be considered as lower limits.
Still, we are able to extend the wavelength coverage of SED models and start
characterizing effects such as dust sedimentation, an effort leading the way
towards ALMA observations of these low-mass stars
Far-infrared photometric observations of the outer planets and satellites with Herschel-PACS
We present all Herschel PACS photometer observations of Mars, Saturn, Uranus,
Neptune, Callisto, Ganymede, and Titan. All measurements were carefully
inspected for quality problems, were reduced in a (semi-)standard way, and were
calibrated. The derived flux densities are tied to the standard PACS photometer
response calibration, which is based on repeated measurements of five fiducial
stars. The overall absolute flux uncertainty is dominated by the estimated 5%
model uncertainty of the stellar models in the PACS wavelength range between 60
and 210 micron. A comparison with the corresponding planet and satellite models
shows excellent agreement for Uranus, Neptune, and Titan, well within the
specified 5%. Callisto is brighter than our model predictions by about 4-8%,
Ganymede by about 14-21%. We discuss possible reasons for the model offsets.
The measurements of these very bright point-like sources, together with
observations of stars and asteroids, show the high reliability of the PACS
photometer observations and the linear behavior of the PACS bolometer source
fluxes over more than four orders of magnitude (from mJy levels up to more than
1000 Jy). Our results show the great potential of using the observed solar
system targets for cross-calibration purposes with other ground-based,
airborne, and space-based instruments and projects. At the same time, the PACS
results will lead to improved model solutions for future calibration
applications.Comment: 25 pages, 11 figures, 11 table
Infrared variability, maser activity, and accretion of massive young stellar objects
Methanol and water masers indicate young stellar objects. They often exhibit
flares, and a fraction shows periodic activity. Several mechanisms might
explain this behavior but the lack of concurrent infrared (IR) data complicates
to identify the cause. Recently, 6.7 GHz methanol maser flares were observed,
triggered by accretion bursts of high-mass YSOs which confirmed the IR-pumping
of these masers. This suggests that regular IR changes might lead to maser
periodicity. Hence, we scrutinized space-based IR imaging of YSOs associated
with periodic methanol masers. We succeeded to extract the IR light curve from
NEOWISE data for the intermediate mass YSO G107.298+5.639. Thus, for the first
time a relationship between the maser and IR variability could be established.
While the IR light curve shows the same period of ~34.6 days as the masers, its
shape is distinct from that of the maser flares. Possible reasons for the IR
periodicity are discussed.Comment: 4 pages, 3 figures, to be published in: Proceedings IAU Symposium 336
"Astrophysical Masers: Unlocking the Mysteries of the Universe", Editors: A.
Tarchi, M.J. Reid & P. Castangia, updated version with hyperlinks adde
Characterization of Infrared Dark Clouds -- NH Observations of an Absorption-contrast Selected IRDC Sample
Despite increasing research in massive star formation, little is known about
its earliest stages. Infrared Dark Clouds (IRDCs) are cold, dense and massive
enough to harbour the sites of future high-mass star formation. But up to now,
mainly small samples have been observed and analysed. To understand the
physical conditions during the early stages of high-mass star formation, it is
necessary to learn more about the physical conditions and stability in
relatively unevolved IRDCs. Thus, for characterising IRDCs studies of large
samples are needed. We investigate a complete sample of 218 northern hemisphere
high-contrast IRDCs using the ammonia (1,1)- and (2,2)-inversion transitions.
We detected ammonia (1,1)-inversion transition lines in 109 of our IRDC
candidates. Using the data we were able to study the physical conditions within
the star-forming regions statistically. We compared them with the conditions in
more evolved regions which have been observed in the same fashion as our sample
sources. Our results show that IRDCs have, on average, rotation temperatures of
15 K, are turbulent (with line width FWHMs around 2 km s), have ammonia
column densities on the order of cm and molecular hydrogen
column densities on the order of cm. Their virial masses are
between 100 and a few 1000 M. The comparison of bulk kinetic and
potential energies indicate that the sources are close to virial equilibrium.
IRDCs are on average cooler and less turbulent than a comparison sample of
high-mass protostellar objects, and have lower ammonia column densities. Virial
parameters indicate that the majority of IRDCs are currently stable, but are
expected to collapse in the future.Comment: 21 pages, 11 figures, 7 tables. Paper accepted for publication in
Astronomy & Astrophysic
Chemical evolution in the early phases of massive star formation. I
Understanding the chemical evolution of young (high-mass) star-forming
regions is a central topic in star formation research. Chemistry is employed as
a unique tool 1) to investigate the underlying physical processes and 2) to
characterize the evolution of the chemical composition. We observed a sample of
59 high-mass star-forming regions at different evolutionary stages varying from
the early starless phase of infrared dark clouds to high-mass protostellar
objects to hot molecular cores and, finally, ultra-compact HII regions at 1mm
and 3mm with the IRAM 30m telescope. We determined their large-scale chemical
abundances and found that the chemical composition evolves along with the
evolutionary stages. On average, the molecular abundances increase with time.
We modeled the chemical evolution, using a 1D physical model where density and
temperature vary from stage to stage coupled with an advanced gas-grain
chemical model and derived the best-fit chi^2 values of all relevant
parameters. A satisfying overall agreement between observed and modeled column
densities for most of the molecules was obtained. With the best-fit model we
also derived a chemical age for each stage, which gives the timescales for the
transformation between two consecutive stages. The best-fit chemical ages are
~10,000 years for the IRDC stage, ~60,000 years for the HMPO stage, ~40,000
years for the HMC stage, and ~10,000 years for the UCHII stage. The total
chemical timescale for the entire evolutionary sequence of the high-mass star
formation process is on the order of 10^5 years, which is consistent with
theoretical estimates. Furthermore, based on the approach of a multiple-line
survey of unresolved data, we were able to constrain an intuitive and
reasonable physical and chemical model. The results of this study can be used
as chemical templates for the different evolutionary stages in high-mass star
formation.Comment: 31 pages, 11 figures, 21 tables, accepted by A&A; typos adde
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