29 research outputs found
Complex Organic Molecules at High Spatial Resolution Toward Orion-KL I: Spatial Scales
Here we present high spatial resolution (<1 arcsecond) observations of
molecular emission in Orion-KL conducted using the Combined Array for Research
in Millimeter-Wave Astronomy (CARMA). This work was motivated by recent
millimeter continuum imaging studies of this region conducted at a similarly
high spatial resolution, which revealed that the bulk of the emission arises
from numerous compact sources, rather than the larger-scale extended structures
typically associated with the Orion Hot Core and Compact Ridge. Given that the
spatial extent of molecular emission greatly affects the determination of
molecular abundances, it is important to determine the true spatial scale for
complex molecules in this region. Additionally, it has recently been suggested
that the relative spatial distributions of complex molecules in a source might
give insight into the chemical mechanisms that drive complex chemistry in
star-forming regions. In order to begin to address these issues, this study
seeks to determine the spatial distributions of ethyl cyanide [C2H5CN],
dimethyl ether [(CH3)2O], methyl formate [HCOOCH3], formic acid [HCOOH],
acetone [(CH3)2CO], SiO, methanol [CH3OH], and methyl cyanide [CH3CN] in
Orion-KL at \lambda = 3 mm. We find that for all observed molecules, the
molecular emission arises from multiple components of the cloud that include a
range of spatial scales and physical conditions. Here we present the results of
these observations and discuss the implications for studies of complex
molecules in star-forming regions.Comment: Accepted for publication in the Astrophysical Journal Supplement;
Part 1 of a 2 paper series; 37 page
First Acetic Acid Survey with CARMA in Hot Molecular Cores
Acetic acid (CHCOOH) has been detected mainly in hot molecular cores
where the distribution between oxygen (O) and nitrogen (N) containing molecular
species is co-spatial within the telescope beam. Previous work has presumed
that similar cores with co-spatial O and N species may be an indicator for
detecting acetic acid. However, does this presumption hold as higher spatial
resolution observations become available of large O and N-containing molecules?
As the number of detected acetic acid sources is still low, more observations
are needed to support this postulate. In this paper, we report the first acetic
acid survey conducted with the Combined Array for Research in Millimeter-wave
Astronomy (CARMA) at 3 mm wavelengths towards G19.61-0.23, G29.96-0.02 and IRAS
16293-2422. We have successfully detected CHCOOH via two transitions toward
G19.61-0.23 and tentatively confirmed the detection toward IRAS 16293-2422 A.
The determined column density of CHCOOH is 2.0(1.0)
cm and the abundance ratio of CHCOOH to methyl formate (HCOOCH)
is 2.2(0.1) toward G19.61-0.23. Toward IRAS 16293 A, the
determined column density of CHCOOH is 1.6
cm and the abundance ratio of CHCOOH to methyl formate (HCOOCH)
is 1.0 both of which are consistent with abundance
ratios determined toward other hot cores. Finally, we model all known line
emission in our passband to determine physical conditions in the regions and
introduce a new metric to better reveal weak spectral features that are blended
with stronger lines or that may be near the 1-2 detection limit.Comment: 28 pages, 8 figures, accepted for publication in the ApJ; Revised
citation in session 2, references remove
Observational Results of a Multi-Telescope Campaign in Search of Interstellar Urea [(NH)CO]
In this paper, we present the results of an observational search for gas
phase urea [(NH)CO] observed towards the Sgr B2(N-LMH) region. We show
data covering urea transitions from 100 GHz to 250 GHz from five
different observational facilities: BIMA, CARMA, the NRAO 12 m telescope, the
IRAM 30 m telescope, and SEST. The results show that the features ascribed to
urea can be reproduced across the entire observed bandwidth and all facilities
by best fit column density, temperature, and source size parameters which vary
by less than a factor of 2 between observations merely by adjusting for
telescope-specific parameters. Interferometric observations show that the
emission arising from these transitions is cospatial and compact, consistent
with the derived source sizes and emission from a single species. Despite this
evidence, the spectral complexity, both of (NH)CO and of Sgr B2(N),
makes the definitive identification of this molecule challenging. We present
observational spectra, laboratory data, and models, and discuss our results in
the context of a possible molecular detection of urea.Comment: 38 pages, 9 Figures, accepted in the Astrophysical Journa
A systematic analysis of host factors reveals a Med23-interferon-λ regulatory axis against herpes simplex virus type 1 replication
Herpes simplex virus type 1 (HSV-1) is a neurotropic virus causing vesicular oral or genital skin lesions, meningitis and other diseases particularly harmful in immunocompromised individuals. To comprehensively investigate the complex interaction between HSV-1 and its host we combined two genome-scale screens for host factors (HFs) involved in virus replication. A yeast two-hybrid screen for protein interactions and a RNA interference (RNAi) screen with a druggable genome small interfering RNA (siRNA) library confirmed existing and identified novel HFs which functionally influence HSV-1 infection. Bioinformatic analyses found the 358 HFs were enriched for several pathways and multi-protein complexes. Of particular interest was the identification of Med23 as a strongly anti-viral component of the largely pro-viral Mediator complex, which links specific transcription factors to RNA polymerase II. The anti-viral effect of Med23 on HSV-1 replication was confirmed in gain-of-function gene overexpression experiments, and this inhibitory effect was specific to HSV-1, as a range of other viruses including Vaccinia virus and Semliki Forest virus were unaffected by Med23 depletion. We found Med23 significantly upregulated expression of the type III interferon family (IFN-λ) at the mRNA and protein level by directly interacting with the transcription factor IRF7. The synergistic effect of Med23 and IRF7 on IFN-λ induction suggests this is the major transcription factor for IFN-λ expression. Genotypic analysis of patients suffering recurrent orofacial HSV-1 outbreaks, previously shown to be deficient in IFN-λ secretion, found a significant correlation with a single nucleotide polymorphism in the IFN-λ3 (IL28b) promoter strongly linked to Hepatitis C disease and treatment outcome. This paper describes a link between Med23 and IFN-λ, provides evidence for the crucial role of IFN-λ in HSV-1 immune control, and highlights the power of integrative genome-scale approaches to identify HFs critical for disease progression and outcome
MULTI-RESOLUTION STUDIES OF COMPLEX MOLECULES IN HIGH MASS STAR FORMING REGIONS
Author Institution: Department of Astronomy, University of Illinois, 1002 W. Green St., Urbana, IL 61801After our successful molecular studies of the high mass star forming region Orion-KL (Friedel \& Widicus Weaver 2012, ApJS, 201, 17; Widicus Weaver \& Friedel 2012, ApJS, 201, 16) we have observed three more high mass star forming regions (W3, W75N, and W51). The purpose of these observations is to further constrain the physical conditions under which the different complex organic molecules form and survive. The results of these observations as well as their impact on current molecular formation models will be presented
COSMOLOGICAL NUCLEOSYNTHESIS: THE LITHIUM PROBLEM
Author Institution: Department of Astronomy, University of Illinois, 1002 W. Green St.; Urbana, IL 61801A measurement of the primordial Lithium abundance would give a significant observational constraint to current big-bang nucleosynthesis models. Deuterium and helium abundances agree closely with predictions of current cosmological models, however, the predicted primordial lithium abundance is a factor of two above current measurements of the stellar lithium abundance obtained from optical spectroscopy of halo star atmospheres. Current optical measurements of stellar lithium abundances are subject to significant systematic uncertainties. Millimeter wavelength observations of the =0, LiH rotational line, red-shifted from its rest frequency near 444 GHz, where it is significantly absorbed in the atmosphere, offer the opportunity to measure interstellar LiH abundance and isotopic ratios in extra-galactic sources. However, these observations have been difficult with older millimeter-wavelength telescopes and arrays, and a search and tentative (2-3 sigma) detection has been reported only towards one source: the lens B0218+357 (Combes \& Wiklind 1998, AALett, 334, L81). We will present the results of our search for LiH and LiH toward several extragalactic sources
A Survey of Large Molecules toward the Protoplanetary Nebula CRL 61 8
We present the results of our survey toward the protoplanetary nebula CRL 618 for several large, highly saturated, oxygen bearing organic molecules of biological importance including acetaldehyde (CH3CHO), acetic acid (CH3OOH), dimethyl ether (CH3OCH3), ethanol (CH3CH2OH), formic acid (HCOOH) and methyl formate (HCOOCH3); large carbon chain molecules including methyl cyanide (CH3CN) , methylcyanoacetylene (CH3C3N), cyanoacetylene (HC3N), cyanodiacetylene (HC5N), and C6H; and finally smaller molecules including SO-34, SO2, O(C-34)S and MgNC. No biologically important organic molecules were detected. However, we report the first interferometric detections of CH3CN and vibrationally excited HC3N and HC5N toward this source. The temperature and distribution of CH3CN toward CRL 618 indicates it is formed in the outer envelope surrounding the UC HII region. Furthermore, the P-Cygni line profile and corresponding channel maps of vibrationally excited HC5N supports its distribution in the extended envelope expanding radially from the central star. The detection of vibrationally excited HC3N confirmed the temperature structure and column density of HC3N in the inner envelope found by Wyrowski and colleagues (2003). Finally, our observations clearly indicate that CRL 618 is a good source of large carbon chain species but is a very poor source to detect or produce organic species of biological importance