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 $\mu$m (MSX E filter) band for most weak 8.28 $\mu$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 colo

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

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