58 research outputs found
MSX versus IRAS Two-Color Diagrams and the CSE-Sequence of Oxygen-Rich Late-Type Stars
We present MSX two-color diagrams that can be used to characterize
circumstellar environments of sources with good quality MSX colors in terms of
IRAS color regions for oxygen-rich stars. With these diagrams we aim to provide
a new tool that can be used to study circumstellar environments and to improve
detection rates for targeted surveys for circumstellar maser emission similar
to the IRAS two-color diagram. This new tool is especially useful for regions
in the sky where IRAS was confused, in particular in the Galactic plane and
bulge region. Unfortunately, using MSX colors alone does not allow to
distinguish between carbon-rich and oxygen-rich objects. An application of this
tool on 86 GHz SiO masers shows that for this type of masers an instantaneous
detection rate of 60% to 80% can be achieved if target sources are selected
according to MSX color (region).
Our investigations may have revealed an error in the MSX point source catalog
version 2.3. That is, the photometry of the 21.3 m (MSX E filter) band for
most weak 8.28 m (or MSX A filter) band sources seems off by about a
factor two (0.5--1 magnitude too bright).Comment: accepted to Astrophysical Journal, 11 pages, 11 figs of which 1 in
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Color processing in the early visual system of Drosophila
Color vision extracts spectral information by comparing signals from photoreceptors with different visual pigments. Such comparisons are encoded by color-opponent neurons that are excited at one wavelength and inhibited at another. Here, we examine the circuit implementation of color-opponent processing in the Drosophila visual system by combining two-photon calcium imaging with genetic dissection of visual circuits. We report that coloropponent processing of UVshort/blue and UVlong/green is already implemented in R7/R8 inner photoreceptor terminals of "pale'' and "yellow'' ommatidia, respectively. R7 and R8 photoreceptors of the same type of ommatidia mutually inhibit each other directly via HisCl1 histamine receptors and receive additional feedback inhibition that requires the second histamine receptor Ort. Color-opponent processing at the first visual synapse represents an unexpected commonality between Drosophila and vertebrates; however, the differences in the molecular and cellular implementation suggest that the same principles evolved independently
Detection of H2D+ in a massive prestellar core in Orion B
Aims. The purpose of this study is to examine the prediction that the deuterated H3+ ion, H2D+, can be found exclusively in the coldest regions of molecular cloud cores. This is also a feasibility study for the detection of the ground-state line of ortho-H2D+ at 372 GHz with APEX. Methods. The 1(10)-1(11) transition of H2D+ at 372 GHz was searched towards selected positions in the massive star forming cloud OriB9, in the dark cloud L183, and in the low- to intermediate mass star-forming cloud R CrA. Results. The line was detected in cold, prestellar cores in the regions of OriB9 and L183, but only upper limits were obtained towards other locations which either have elevated temperatures or contain a newly born star. The H2D+ detection towards OriB9 is the first one in a massive star-forming region. The fractional ortho-H2D+ abundances (relative to H2) are estimated to be about 1.0E-10 in two cold cores in OriB9, and 3.0E-10 in the cold core of L183. Conclusions. The H2D+ detection in OriB9 shows that also massive star forming regions contain very cold prestellar cores which probably have reached matured chemical composition characterized, e.g., by a high degree of deuterium fractionation. Besides as a tracer of the interior parts of prestellar cores, H2D+ may therefore be used to put contraints on the timescales related to massive star formation
Mining the UKIDSS GPS: star formation and embedded clusters
Data mining techniques must be developed and applied to analyse the large
public data bases containing hundreds to thousands of millions entries. The aim
of this study is to develop methods for locating previously unknown stellar
clusters from the UKIDSS Galactic Plane Survey catalogue data. The cluster
candidates are computationally searched from pre-filtered catalogue data using
a method that fits a mixture model of Gaussian densities and background noise
using the Expectation Maximization algorithm. The catalogue data contains a
significant number of false sources clustered around bright stars. A large
fraction of these artefacts were automatically filtered out before or during
the cluster search. The UKIDSS data reduction pipeline tends to classify
marginally resolved stellar pairs and objects seen against variable surface
brightness as extended objects (or "galaxies" in the archive parlance). 10% or
66 x 10^6 of the sources in the UKIDSS GPS catalogue brighter than 17
magnitudes in the K band are classified as "galaxies". Young embedded clusters
create variable NIR surface brightness because the gas/dust clouds in which
they were formed scatters the light from the cluster members. Such clusters
appear therefore as clusters of "galaxies" in the catalogue and can be found
using only a subset of the catalogue data. The detected "galaxy clusters" were
finally screened visually to eliminate the remaining false detections due to
data artefacts. Besides the embedded clusters the search also located locations
of non clustered embedded star formation. The search covered an area of 1302
square degrees and 137 previously unknown cluster candidates and 30 previously
unknown sites of star formation were found
Physical properties of dense cores in Orion B9
We aim to determine the physical and chemical properties of dense cores in
Orion B9. We observed the NH3(1,1) and (2,2), and the N2H+(3-2) lines towards
the submm peak positions. These data are used in conjunction with our LABOCA
870 micron dust continuum data. The gas kinetic temperature in the cores is
between ~9.4-13.9 K. The non-thermal velocity dispersion is subsonic in most of
the cores. The non-thermal linewidth in protostellar cores appears to increase
with increasing bolometric luminosity. The core masses are very likely drawn
from the same parent distribution as the core masses in Orion B North. Starless
cores in the region are likely to be gravitationally bound, and thus
prestellar. Some of the cores have a lower radial velocity than the systemic
velocity of the region, suggesting that they are members of the "low-velocity
part" of Orion B. The observed core-separation distances deviate from the
corresponding random-like model distributions. The distances between the
nearest-neighbours are comparable to the thermal Jeans length. The fractional
abundances of NH3 and N2H+ in the cores are ~1.5-9.8x10^{-8} and
~0.2-5.9x10^{-10}, respectively. The NH3 abundance appears to decrease with
increasing H2 column and number densities. The NH3/N2H+ column density ratio is
larger in starless cores than in cores with embedded protostars. The core
population in Orion B9 is comparable in physical properties to those in nearby
low-mass star-forming regions. It is unclear if the origin of cores could be
explained by turbulent fragmentation. On the other hand, many of the core
properties conform with the picture of dynamic core evolution. The Orion B9
region has probably been influenced by the feedback from the nearby Ori OB 1b
group, and the fragmentation of the parental cloud into cores could be caused
by gravitational instability.Comment: 17 pages, 11 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysics. Version 2: minor language corrections adde
A (sub)millimetre study of dense cores in Orion B9
We aim to further constrain the properties and evolutionary stages of dense
cores in Orion B9. The central part of Orion B9 was mapped at 350 micron with
APEX/SABOCA. A sample of nine cores in the region were observed in C17O(2-1),
H13CO+(4-3) (towards 3 sources), DCO+(4-3), N2H+(3-2), and N2D+(3-2) with
APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA
870-micron dust continuum data. Many of the LABOCA cores show evidence of
substructure in the higher-resolution SABOCA image. In particular, we report on
the discovery of multiple very low-mass condensations in the prestellar core
SMM 6. Based on the 350-to-870 micron flux density ratios, we determine dust
temperatures of ~7.9-10.8 K, and dust emissivity indices of ~0.5-1.8. The CO
depletion factors are in the range ~1.6-10.8. The degree of deuteration in N2H+
is ~0.04-0.99, where the highest value (seen towards the prestellar core SMM 1)
is, to our knowledge, the most extreme level of N2H+ deuteration reported so
far. The level of HCO+ deuteration is about 1-2%. We also detected D2CO towards
two sources. The detection of subcondensations within SMM 6 shows that core
fragmentation can already take place during the prestellar phase. The origin of
this substructure is likely caused by thermal Jeans fragmentation of the
elongated parent core. A low depletion factor and the presence of gas-phase
D2CO in SMM 1 suggest that the core chemistry is affected by the nearby
outflow. The very high N2H+ deuteration in SMM 1 is likely to be remnant of the
earlier CO-depleted phase.Comment: 20 pages, 10 figures, 10 tables. Accepted for publication in
Astronomy and Astrophysic
86 GHz SiO maser survey of late-type stars in the Inner Galaxy. I. Observational data
We present 86 GHz (v = 1, J = 2 -1) SiO maser line observations with the IRAM
30-m telescope of a sample of 441 late-type stars in the Inner Galaxy (-4 degr
< l < +30 degr). These stars were selected on basis of their infrared
magnitudes and colours from the ISOGAL and MSX catalogues. SiO maser emission
was detected in 271 sources, and their line-of-sight velocities indicate that
the stars are located in the Inner Galaxy. These new detections double the
number of line-of-sight velocities available from previous SiO and OH maser
observations in the area covered by our survey and are, together with other
samples of e.g. OH/IR stars, useful for kinematic studies of the central parts
of the Galaxy.Comment: 15 pages, 12 figures, accepted by A&A Journa
Prestellar and protostellar cores in Ori B9
The aims of this study are to determine the properties and spatial
distribution of dense cores in Ori B9, and to estimate their ages and dynamical
timescales. The cloud was mapped in the 870 micron continuum with APEX/LABOCA,
and selected positions were observed in the lines of N2H+ and N2D+ using
IRAM-30m. These were used together with our previous H2D+ observations.
Moreover, archival FIR Spitzer/MIPS maps were combined with the LABOCA map to
distinguish between pre- and protostellar cores, and to estimate the
evolutionary stages of protostars. Twelve dense cores were detected at 870
micron in the Ori B9 cloud. The submm cores constitute ~4% of the total mass of
the Ori B9 region. There is an equal number of pre- and protostellar cores. Two
of the submm sources, which we call SMM 3 and SMM 4, are previously unknown
Class 0 candidates. We found a moderate degree of deuteration in N2H+
(0.03-0.04). There is, furthermore, evidence for N2H+ depletion in the core SMM
4. We derive a relatively high degree of ionization (~10^-7) in the clump
associated with IRAS 05405-0117. The ambipolar diffusion timescales for two of
the cores are ~70-100 times longer than the free-fall time. The distribution
and masses of dense cores in Ori B9 are similar to those observed in more
active regions in Orion, where the statistical core properties have been
explained by turbulent fragmentation. The 50/50 proportions of pre- and
protostellar cores suggest that duration of the prestellar phase is comparable
to the free-fall time. This timescale can be questioned, however, on the basis
of chemical data on the IRAS 05405-0117 region. A possible explanation is that
this survey samples only the densest, i.e., dynamically most advanced cores.Comment: 17 pages, 8 figures, 9 tables. Revised version accepted for
publication in A&A (Figs. 1, 3, and 7 revised, minor revisions in Sect. 5.2,
updated reference information
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