439 research outputs found
A cold complex chemistry toward the low-mass protostar B1-b: evidence for complex molecule production in ices
Gas-phase complex organic molecules have been detected toward a range of
high- and low-mass star-forming regions at abundances which cannot be explained
by any known gas-phase chemistry. Recent laboratory experiments show that UV
irradiation of CH3OH-rich ices may be an important mechanism for producing
complex molecules and releasing them into the gas-phase. To test this ice
formation scenario we mapped the B1-b dust core and nearby protostar in CH3OH
gas using the IRAM 30m telescope to identify locations of efficient non-thermal
ice desorption. We find three CH3OH abundance peaks tracing two outflows and a
quiescent region on the side of the core facing the protostar. The CH3OH gas
has a rotational temperature of ~10 K at all locations. The quiescent CH3OH
abundance peak and one outflow position were searched for complex molecules.
Narrow, 0.6-0.8 km s-1 wide, HCOOCH3 and CH3CHO lines originating in cold gas
are clearly detected, CH3OCH3 is tentatively detected and C2H5OH and HOCH2CHO
are undetected toward the quiescent core, while no complex molecular lines were
found toward the outflow. The core abundances with respect to CH3OH are ~2.3%
and 1.1% for HCOOCH3 and CH3CHO, respectively, and the upper limits are
0.7-1.1%, which is similar to most other low-mass sources. The observed complex
molecule characteristics toward B1-b and the pre-dominance of HCO-bearing
species suggest a cold ice (below 25 K, the sublimation temperature of CO)
formation pathway followed by non-thermal desorption through e.g. UV photons
traveling through outflow cavities. The observed complex gas composition
together with the lack of any evidence of warm gas-phase chemistry provide
clear evidence of efficient complex molecule formation in cold interstellar
ices.Comment: 23 pages, 7 figures, accepted for publication in Ap
Cepheid and Tip of the Red Giant Branch Distances To the Dwarf Irregular Galaxy IC10
We present color-magnitude diagrams and luminosity functions of stars in the
nearby galaxy IC 10, based on VI CCD photometry acquired with the COSMIC
prime-focus camera on the Palomar 5m telescope. The apparent I-band luminosity
function of stars in the halo of IC 10 shows an identifiable rise at I~21.7
mag. This is interpreted as being the tip of the red giant branch (TRGB) at
M_V~-4 mag. Since IC 10 is at a very low Galactic latitude, its foreground
extinction is expected to be high and the uncertainty associated with that
correction is the largest contributor to the error associated with its distance
determination. Multi-wavelength observations of Cepheid variable stars in IC 10
give a Population I distance modulus of 24.1 +- 0.2 mag, which corresponds to a
linear distance of 660 +- 66 kpc for a total line-of-sight reddening of E(B-V)
= 1.16 +- 0.08 mag, derived self-consistently from the Cepheid data alone.
Applying this Population I reddening to the Population II halo stars gives a
TRGB distance modulus of 23.5 +- 0.2 mag, corresponding to 500 +- 50 kpc. We
consider this to be a lower limit on the TRGB distance. Reconciling the Cepheid
and TRGB distances would require that the reddening to the halo is
E(B-V) = 0.31 mag lower than that into the main body of the galaxy.
This then suggests that the Galactic extinction in the direction of IC10 is
(B-V) ~ 0.85
Cold gas as an ice diagnostic toward low mass protostars
Up to 90% of the chemical reactions during star formation occurs on ice
surfaces, probably including the formation of complex organics. Only the most
abundant ice species are however observed directly by infrared spectroscopy.
This study aims to develop an indirect observational method of ices based on
non-thermal ice desorption in the colder part of protostellar envelopes. For
that purpose the IRAM 30m telescope was employed to observe two molecules that
can be detected both in the gas and the ice, CH3 OH and HNCO, toward 4 low mass
embedded protostars. Their respective gas-phase column densities are determined
using rotational diagrams. The relationship between ice and gas phase
abundances is subsequently determined. The observed gas and ice abundances span
several orders of magnitude. Most of the CH3OH and HNCO gas along the lines of
sight is inferred to be quiescent from the measured line widths and the derived
excitation temperatures, and hence not affected by thermal desorption close to
the protostar or in outflow shocks. The measured gas to ice ratio of ~10-4
agrees well with model predictions for non-thermal desorption under cold
envelope conditions and there is a tentative correlation between ice and gas
phase abundances. This indicates that non-thermal desorption products can serve
as a signature of the ice composition. A larger sample is however necessary to
provide a conclusive proof of concept.Comment: accepted by A&A letters, 10 pages including 5 figure
An interferometric study of the low-mass protostar IRAS 16293-2422: small scale organic chemistry
Aims: To investigate the chemical relations between complex organics based on
their spatial distributions and excitation conditions in the low-mass young
stellar objects IRAS 16293-2422 A and B. Methods: Interferometric observations
with the Submillimeter Array have been performed at 5''x3'' resolution
revealing emission lines of HNCO, CH3CN, CH2CO, CH3CHO and C2H5OH. Rotational
temperatures are determined from rotational diagrams when a sufficient number
of lines are detected. Results: Compact emission is detected for all species
studied here. For HNCO and CH3CN it mostly arises from source A, CH2CO and
C2H5OH have comparable strength for both sources and CH3CHO arises exclusively
from source B. HNCO, CH3CN and CH3CHO have rotational temperatures >200 K. The
(u,v)-visibility data reveal that HNCO also has extended cold emission.
Conclusions: The abundances of the molecules studied here are very similar
within factors of a few to those found in high-mass YSOs. Thus the chemistry
between high- and low-mass objects appears to be independent of luminosity and
cloud mass. Bigger abundance differences are seen between the A and B source.
The HNCO abundance relative to CH3OH is ~4 times higher toward A, which may be
due to a higher initial OCN- ice abundances in source A compared to B.
Furthermore, not all oxygen-bearing species are co-existent. The different
spatial behavior of CH2CO and C2H5OH compared with CH3CHO suggests that
hydrogenation reactions on grain-surfaces are not sufficient to explain the
observed gas phase abundances. Selective destruction of CH3CHO may result in
the anti-coincidence of these species in source A. These results illustrate the
power of interferometric compared with single dish data in terms of testing
chemical models.Comment: 11 pages, 15 figures, accepeted by A&
Distorted HI Gas in the Widely Separated LIRG Arp 256
We present new interferometric HI and CO (1-0) observations of the luminous
infrared source, Arp 256. Arp 256 consists of two spiral galaxies in an early
stage of merging, with a projected nuclear separation of 29 kpc (54") and an
infrared luminosity of 2.0E11 L_sun. Despite the large separation of the
galaxies' nuclei and mildly disrupted stellar components, the HI disks are
found to be strongly disrupted, and the southern galaxy in Arp 256 shows an
elevated star formation efficiency, which is consistent with a nuclear
starburst. Both of these results run contrary to expectations, posing
interesting questions on the physical mechanisms involved in stimulating star
formation during an interaction.Comment: 19 pages, 7 figures. Accepted for publication in AJ. Author added.
Full resolution figures available at
http://astro.uchicago.edu/home/web/jchen/arp25
State of the art in bile analysis in forensic toxicology
AbstractIn forensic toxicology, alternative matrices to blood are useful in case of limited, unavailable or unusable blood sample, suspected postmortem redistribution or long drug intake-to-sampling interval. The present article provides an update on the state of knowledge for the use of bile in forensic toxicology, through a review of the Medline literature from 1970 to May 2015. Bile physiology and technical aspects of analysis (sampling, storage, sample preparation and analytical methods) are reported, to highlight specificities and consequences from an analytical and interpretative point of view. A table summarizes cause of death and quantification in bile and blood of 133 compounds from more than 200 case reports, providing a useful tool for forensic physicians and toxicologists involved in interpreting bile analysis. Qualitative and quantitative interpretation is discussed. As bile/blood concentration ratios are high for numerous molecules or metabolites, bile is a matrix of choice for screening when blood concentrations are low or non-detectable: e.g., cases of weak exposure or long intake-to-death interval. Quantitative applications have been little investigated, but small molecules with low bile/blood concentration ratios seem to be good candidates for quantitative bile-based interpretation. Further experimental data on the mechanism and properties of biliary extraction of xenobiotics of forensic interest are required to improve quantitative interpretation
Distribution of dust clouds around the central engine of NGC 1068
We studied the distribution of dust clouds around the central engine of NGC
1068 based on shifted-and-added 8.8 - 12.3 micron (MIR) multi-filter images and
3.0 - 3.9 micron (L-band) spectra obtained with the Subaru Telescope. In a
region of 100 pc (1.4") around the central peak, we successfully constructed
maps of color temperatures and emissivities of the MIR and L-band continua as
well as the 9.7 micron and 3.4 micron dust features with spatial resolutions of
26 pc (0.37") in the MIR and 22 pc (0.3") in the L-band. Our main results are:
1) color temperature of the MIR continuum scatters around the thermal
equilibrium temperature with the central engine as the heat source while that
of the L-band continuum is higher and independent upon distance from the
central engine; 2) the peak of the 9.7 micron silicate absorption feature is
shifted to a longer wavelength at some locations; 3) the ratio of the optical
depths of the dust features is different from the Galactic values and show
complicated spatial distribution; and 4) there is a pie shaped warm dust cloud
as an enhancement in the emissivity of the MIR continuum extending about 50 pc
to the north from the central engine. We speculate that material falls into the
central engine through this cloud.Comment: 26 pages, 9 figures. Accepted for publication on Ap
Complex molecules toward low-mass protostars: the Serpens core
Gas-phase complex organic molecules are commonly detected toward high-mass
protostellar hot cores. Detections toward low-mass protostars and outflows are
comparatively rare, and a larger sample is key to investigate how the chemistry
responds to its environment. Guided by the prediction that complex organic
molecules form in CH3OH-rich ices and thermally or non-thermally evaporate with
CH3OH, we have identified three sight-lines in the Serpens core - SMM1, SMM4
and SMM4-W - which are likely to be rich in complex organics. Using the IRAM
30m telescope, narrow lines (FWHM of 1-2 km s-1) of CH3CHO and CH3OCH3 are
detected toward all sources, HCOOCH3 toward SMM1 and SMM4-W, and C2H5OH not at
all. Beam-averaged abundances of individual complex organics range between 0.6
and 10% with respect to CH3OH when the CH3OH rotational temperature is applied.
The summed complex organic abundances also vary by an order of magnitude, with
the richest chemistry toward the most luminous protostar SMM1. The range of
abundances compare well with other beam-averaged observations of low-mass
sources. Complex organic abundances are of the same order of magnitude toward
low-mass protostars and high-mass hot cores, but HCOOCH3 is relatively more
important toward low-mass protostars. This is consistent with a sequential ice
photochemistry, dominated by CHO-containing products at low temperatures and
early times.Comment: 20 pages, including 5 figures. Accepted for publication in Ap
Detection of CI in absorption towards PKS 1830-211 with the eSMA
We report the first science observations and results obtained with the
"extended" SMA (eSMA), which is composed of the SMA (Submillimeter Array), JCMT
(James Clerk Maxwell Telescope) and CSO (Caltech Submillimeter Observatory).
Redshifted absorptions at z=0.886 of CI (^3P_1 - ^3P_0) were observed with the
eSMA with an angular resolution of 0.55"x0.22" at 1.1 mm toward the
southwestern image of the remarkable lensed quasar PKS 1830-211, but not toward
the northeastern component at a separation of ~1". Additionally, SMA
observations of CO, 13CO and C18O (all J=4-3) were obtained toward this object:
CO was also detected toward the SW component, but none of the isotopologues
were. This is the first time [CI] is detected in this object, allowing the
first direct determination of relative abundances of neutral atomic carbon to
CO in the molecular clouds of a spiral galaxy at z>0.1. The [CI] and CO
profiles can be decomposed into two and three velocity components respectively.
We derive C/CO column density ratios ranging from <0.5 (representative of dense
cores) to ~2.5 (close to translucent clouds values). This could indicate that
we are seeing environments with different physical conditions or that we are
witnessing chemical evolution of regions where C has not completely been
converted into CO.Comment: 6 pages using emulateapj, 3 tables, 2 figures ; accepted for
publication in ApJ
Identifying Old Tidal Dwarf Irregulars
We examine the observational consequences of the two possible origins for
irregular galaxies: formation from collapse of a primordial cloud of gas early
in the age of the Universe, and formation from tidal tails in an interaction
that could have occured any time in the history of the Universe. Because the
formation from tidal tails could have occurred a long time ago, proximity to
larger galaxies is not sufficient to distinguish tidal dwarfs from traditional
dwarfs. We consider the effects of little or no dark matter on rotation speeds
and the Tully-Fisher relationship, the metallicity-luminosity relationship,
structure, and stellar populations. From these selection criteria, we identify
a small list of dwarf irregular galaxies that are candidates for having formed
as tidal dwarfs.Comment: ApJ, to appear September 20, 200
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