1,048 research outputs found
Structure and chemistry in the northwestern condensation of the Serpens molecular cloud core
We present single-dish and interferometric observations of gas and dust in the core of the Serpens molecular cloud, focusing on the northwestern condensation. Single-dish molecular line observations are used to probe the structure and chemistry of the condensation while high-resolution images of CS and CH_(3)0H are combined with continuum observations from λ = 1.3 mm to λ = 3.5 cm to study the subcondensations and overall distribution of dust. For the northwestern condensation, we derive a characteristic density of 3 x 10^5 cm^(-3) and an estimated total mass of approximately 70 M_â. We find compact molecular emission associated with the far-infrared source S68 FIRS 1, and with a newly detected subcondensation named S68 N. Comparison of the large-and small-scale emission reveals that most of the material in the northwest condensation is not directly associated with these compact sources, suggesting a youthful age for this region. CO J = 1 approaches 0 observations indicate widespread outflow activity. However, no unique association of embedded objects with outflows is possible with our observations. The SiO emission is found to be extended with the overall emission centered about S68 FIRS 1; the offset of the peak emission from all of the known continuum sources and the coincidence between the blueshifted SiO emission and blueshifted high-velocity gas traced by CO and CS is consistent with formation of SiO in shocks. Derived abundances of CO and HCO^(+) are consistent with quiescent and other star-forming regions while CS, HCN, and H2CO abundances indicate mild depletions within the condensation. Spectral energy distribution fits to S68 FIRS 1 indicate a modest luminosity (50-60 L_â), implying that it is a low-mass (0.5-3 M_â) young stellar object. Radio continuum observations of the triple source toward S68 FIRS 1 indicate that the lobe emission is varying on timescales †1 yr while the central component is relatively constant over ~14 yr. The nature of a newly detected compact emission region, S68 N, is less certain due to the absence of firm continuum detections; based on its low luminosity (<5 L_â) and strong molecular emission, S68 N may be prestellar subcondensation of gas and dust
Senior Programmers: Characteristics of Elderly Users from Stack Overflow
In this paper we presents results of research about elderly users of Stack
Overflow (Question and Answer portal for programmers). They have different
roles, different main activities and different habits. They are an important
part of the community, as they tend to have higher reputation and they like to
share their knowledge. This is a great example of possible way of keeping
elderly people active and helpful for society
Use of soft contact lenses as a means for corneal restabilization after discontinuing hard contract lens wear
The study consisted of ll symptomatic full time hard contact lens wearers who were refitted with hydrogel lenses in a corneal re-stabilization program. The purpose of this study was t o determine the degree of problems the eye care practitioner could expect if he or she should choose such a program. The study showed that the hydrogel lens problems encountered depended on the amount of corneal deformation induced by the hard lenses
Highâcontiguity genome assembly of the chemosynthetic gammaproteobacterial endosymbiont of the cold seep tubeworm Lamellibrachia barhami
Symbiotic relationships between vestimentiferan tubeworms and chemosynthetic Gammaproteobacteria build the foundations of many hydrothermal vent and hydrocarbon seep ecosystems in the deep sea. The association between the vent tubeworm Riftia pachyptila and its endosymbiont Candidatus Endoriftia persephone has become a model system for symbiosis research in deepâsea vestimentiferans, while markedly fewer studies have investigated symbiotic relationships in other tubeworm species, especially at cold seeps. Here we sequenced the endosymbiont genome of the tubeworm Lamellibrachia barhami from a cold seep in the Gulf of California, using shortâ and longâread sequencing technologies in combination with HiâC and Dovetail Chicago libraries. Our final assembly had a size of ~4.17 MB, a GC content of 54.54%, 137X coverage, 4153 coding sequences, and a CheckM completeness score of 97.19%. A single scaffold contained 99.51% of the genome. Comparative genomic analyses indicated that the L. barhami symbiont shares a set of core genes and many metabolic pathways with other vestimentiferan symbionts, while containing 433 unique gene clusters that comprised a variety of transposases, defenceârelated genes and a lineageâspecific CRISPR/Cas3 system. This assembly represents the most contiguous tubeworm symbiont genome resource to date and will be particularly valuable for future comparative genomic studies investigating structural genome evolution, physiological adaptations and hostâsymbiont communication in chemosynthetic animalâmicrobe symbioses
Correction of SOHO CELIAS/SEM EUV Measurements saturated by extreme solar flare events
The solar irradiance in the Extreme Ultraviolet (EUV) spectral bands has been
observed with a 15 sec cadence by the SOHO Solar EUV Monitor (SEM) since 1995.
During remarkably intense solar flares the SEM EUV measurements are saturated
in the central (zero) order channel (0.1 -- 50.0 nm) by the flare soft X-ray
and EUV flux. The first order EUV channel (26 -- 34 nm) is not saturated by the
flare flux because of its limited bandwidth, but it is sensitive to the arrival
of Solar Energetic Particles (SEP). While both channels detect nearly equal SEP
fluxes, their contributions to the count rate is sensibly negligible in the
zero order channel but must be accounted for and removed from the first channel
count rate. SEP contribution to the measured SEM signals usually follows the
EUV peak for the gradual solar flare events. Correcting the extreme solar flare
SEM EUV measurements may reveal currently unclear relations between the flare
magnitude, dynamics observed in different EUV spectral bands, and the measured
Earth atmosphere response. A simple and effective correction technique based on
analysis of SEM count-rate profiles, GOES X-ray, and GOES proton data has been
developed and used for correcting EUV measurements for the five extreme solar
flare events of July 14, 2000, October 28, November 2, November 4, 2003, and
January 20, 2005. Although none of the 2000 and 2003 flare peaks were
contaminated by the presence of SEPs, the January 20, 2005 SEPs were unusually
prompt and contaminated the peak. The estimated accuracy of the correction is
about 7.5% for large X-class events.Comment: To appear in Astron. Nachr. /A
An absolutely calibrated survey of polarized emission from the northern sky at 1.4 GHz
A new polarization survey of the northern sky at 1.41 GHz is presented. The
observations were carried out using the 25.6m telescope at the Dominion Radio
Astrophysical Observatory in Canada, with an angular resolution of 36 arcmin.
The data are corrected for ground radiation to obtain Stokes U and Q maps on a
well-established intensity scale tied to absolute determinations of zero
levels, containing emission structures of large angular extent, with an rms
noise of 12 mK. Survey observations were carried out by drift scanning the sky
between -29 degr and +90 degr declination. The fully sampled drift scans,
observed in steps of 0.25 degr to 2.5 degr in declination, result in a northern
sky coverage of 41.7% of full Nyquist sampling. The survey surpasses by a
factor of 200 the coverage, and by a factor of 5 the sensitivity, of the
Leiden/Dwingeloo polarization survey (Spoelstra 1972) that was until now the
most complete large-scale survey. The temperature scale is tied to the
Effelsberg scale. Absolute zero-temperature levels are taken from the
Leiden/Dwingeloo survey after rescaling those data by the factor of 0.94. The
paper describes the observations, data processing, and calibration steps. The
data are publicly available at http://www.mpifr-bonn.mpg.de/div/konti/26msurvey
or http://www.drao.nrc.ca/26msurvey.Comment: 18 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
Methanol maps of low-mass protostellar systems: the Serpens Molecular Core
Observations of Serpens have been performed at the JCMT using Harp-B. Maps
over a 4.5'x5.4' region were made in a frequency window around 338 GHz,
covering the 7-6 transitions of methanol. Emission is extended over each
source, following the column density of H2 but showing up also particularly
strongly around outflows. The rotational temperature is low, 15-20 K, and does
not vary with position within each source. The abundance is typically 10^-9 -
10^-8 with respect to H2 in the outer envelope, whereas "jumps" by factors of
up to 10^2 -10^3 inside the region where the dust temperature exceeds 100 K are
not excluded. A factor of up to ~ 10^3 enhancement is seen in outflow gas. In
one object, SMM4, the ice abundance has been measured to be ~ 3x10^-5 with
respect to H2 in the outer envelope, i.e., a factor of 10^3 larger than the
gas-phase abundance. Comparison with C18O J=3-2 emission shows that strong CO
depletion leads to a high gas-phase abundance of CH3OH not just for the Serpens
sources, but for a larger sample of protostars. The observations illustrate the
large-scale, low-level desorption of CH3OH from dust grains, extending out to
and beyond 7500 AU from each source, a scenario which is consistent with
non-thermal (photo-)desorption from the ice. The observations also illustrate
the usefulness of CH3OH as a tracer of energetic input in the form of outflows,
where methanol is sputtered from the grain surfaces. Finally, the observations
provide further evidence of CH3OH formation through CO hydrogenation proceeding
on grain surfaces in low-mass envelopes.Comment: Accepted for publication in A&A
Young Stars and Protostellar Cores near NGC 2023
We investigate the young (proto)stellar population in NGC 2023 and the L 1630
molecular cloud bordering the HII region IC 434, using Spitzer IRAC and MIPS
archive data, JCMT SCUBA imaging and spectroscopy as well as targeted BIMA
observations of one of the Class 0 protostars, NGC 2023 MM1. We have performed
photometry of all IRAC and MIPS images, and used color-color diagrams to
identify and classify all young stars seen within a 22'x26' field along the
boundary between IC 434 and L 1630. For some stars, which have sufficient
optical, IR, and/or sub-millimeter data we have also used the online SED
fitting tool for a large 2D archive of axisymmetric radiative transfer models
to perform more detailed modeling of the observed SEDs. We identify 5
sub-millimeter cores in our 850 and 450 micron SCUBA images, two of which have
embedded class 0 or I protostars. Observations with BIMA are used to refine the
position and characteristics of the Class 0 source NGC 2023 MM 1. These
observations show that it is embedded in a very cold cloud core, which is
strongly enhanced in NH2D. We find that HD 37903 is the most massive member of
a cluster with 20 -- 30 PMS stars. We also find smaller groups of PMS stars
formed from the Horsehead nebula and another elephant trunk structure to the
north of the Horsehead. We refine the spectral classification of HD 37903 to B2
Ve. Our study shows that the expansion of the IC 434 HII region has triggered
star formation in some of the dense elephant trunk structures and compressed
gas inside the L 1630 molecular cloud. This pre-shock region is seen as a
sub-millimeter ridge in which stars have already formed. The cluster associated
with NGC 2023 is very young, and has a large fraction of Class I sources.Comment: 21 pages, 11 figures. Accepted for publication in A&A Replaced with
higher resolution figure
- âŠ