Small-area molecular clouds without shielding

Using the IRAM 30m telescope two molecular structures have been detected which cover very small areas, FWHM<1'. The clouds have velocities of v_lsr~5kms and linewidth of dv~0.8km/s; thus they belong most likely to the Milky Way. Applying standard conversion factors one finds that even at the upper distance limit of 2200pc the structures are low mass objects (M=(1-6)x10^{-4}(d/100pc)^2Msun) which are not gravitationally virialized. HI 21cm line data towards the clouds show no prominent HI clouds. The total HI column densities for both structures are below N(HI)<2.1x10^{20}cm^{-2}, corresponding to A_V<0.2mag, assuming a standard gas-to-dust ratio. IRAS 100micron data towards the structures show also only low emission, consistent with low extinction. Unless there is unseen cold dust associated with the structures this shielding is too low for the structures to survive the interstellar radiation field for a long time. The detection of 2 such structures in a rather limited sample of observations suggests that they could be a rather common feature in the interstellar medium, however, so far not recognized as such due to the weakness of their lines and their small extent.Comment: 4 pages, 3 figures, accepted by Astronomy & Astrophysics (Letters

A candidate protostellar object in the L1457 / MBM12 cloud

The association of young T Tauri stars, MBM12A, indicates that L1457 was forming stars not too long ago. With our study we want to find out whether or not there are still signs for ongoing star formation in that cloud. Using the Max-Planck-Millimeter-Bolometer MAMBO at the IRAM 30m telescope we obtained a map of about 8' by 8' centered on L1457 in the dust continuum emission at 230 GHz. Towards the most intense regions in our bolometer map we obtained spectra at high angular resolution in the CS (2-1) and the N2H+(1-0) lines using the IRAM 30m telescope. We find that the cold dust in L1457 is concentrated in several small cores with high H2 column densities and solar masses. The density profiles of the cores are inconsistent with a sphere with constant density. These cores are closer to virial equilibrium than the cloud as a whole. Data from the VLA and Spitzer archives reveal two point sources in the direction of one dust core. One of the sources is probably a distant quasar, whereas the other source is projected right on a local maximum of our dust map and shows characteristics of a protostellar object.Comment: 4 pages, 4 figures, accepted by Astronomy & Astrophysic

Observations of CO in the Magellanic irregular galaxy NGC 55

The content of molecular gas in galaxies, mainly H2, is one of the key observations necessary for the understanding of star formation processes and history. As the CO molecule is the most widely distributed molecule after H2 and has easily observable mm lines, it is used as a tracer for the molecular gas. CO was detected towards the direction where the H alpha and 6 cm radio continuum emission is strongest (Hummel et al. 1986). Here, researchers present the Gaussian line parameters in tabular form. The distribution of CO corresponds well with the intense HI cloud near the bar of NGC 55. The extent of the CO cloud is about 975 pc perpendicular to the major axis. As the radio continuum and the H alpha emission also peaks in this region, it is most probably associated with the star forming region in NGC 55. Assuming that the molecular gas is in virial equilibrium, researchers derive a mass of about 8 times 10(exp 7) solar magnitude. The molecular mass found indicates that the conversion factor for the molecular mass in Irr galaxies as inferred from CO line emission is indeed higher by up to a factor of 20 compared to the canonical value for the Galaxy

Partners in crime – How cabbage seed weevil assists brassica pod midge in damaging pods of winter oilseed rape in fields in Southern Sweden

The brassica pod midge (Dasineura brassicae) has emerged as an important pest causing problems in Winter Oilseed Rape (WOSR) (Brassica napus ssp. napus) production in Southern Sweden during recent years. Adult female D. brassicae oviposit into WOSR pods. After hatching from the eggs, the D. brassicae larvae feed on the inside of the pod, causing deformation and premature opening of the pod, which can result in dramatic yield losses. As the ovipositor of the adult female D. brassicae is too weak to pierce WOSR pod walls, oviposition is mostly done in pre-damaged WOSR pods. Most of these damages that are utilized for oviposition by D. brassicae are caused by the cabbage seed weevil (Ceutorhynchus obstrictus). The weevil feeds on the WOSR pods, thereby causing damages that facilitate oviposition by D. brassicae. Pest control measures are therefore directed against C. obstrictus as the brassica pod midge is extremely difficult to control. More information about the phenology and the combined effect of the two insect species is needed in order to create pest control as sustainable as possible. In this study, C. obstrictus and D. brassicae were monitored during six weeks from May until June 2019 in 20 different WOSR fields around Scania, the southernmost province of Sweden. Different active (visual count) and passive (yellow pan traps, yellow sticky traps) monitoring methods were used to assess the abundance of C. obstrictus and D. brassicae in the 20 WOSR fields and the effect of their presence on the amount of pod damage by D. brassicae. Trap samples were collected weekly and analyzed in the laboratory. At the end of the study period, pod damage was assessed in each field. The number of captured insects of the two species was very low in comparison with previous studies from the last two years, so was the percentage of pod damage. Phenology of C. obstrictus deviated from the expected pattern: Usually the cabbage seed weevil can be observed in a WOSR field earlier in the season than the pod gall midge. In this study C. obstrictus captures peaked 2-3 weeks later than D. brassicae captures, presumably creating less oviposition possibilities for D. brassicae. Nonetheless, the brassica pod midge could benefit from the presence of the cabbage seed weevil – significant correlations between abundance of C. obstrictus monitored in the field border and pod damage caused by D. brassicae inside the field were found. Insecticide treatment showed no effect as the amount of pod damage inside an insecticide-free control zone did not differ from the amount of pod damage outside the insecticide free control zone. Nonetheless, insecticides had been used by the farmers, indicating the need for development of more refined and more rapidly available monitoring and decision tools for farmers to improve IPM strategies for pest control of C. obstrictus and D. brassicae and to reduce insecticide use.Skidgallmyggan (Dasineura brassicae) har nyligen blivit en viktig skadegörare på raps (Brassica napus ssp. napus) och har de senaste åren orsakat stora skador i höstrapodlingar i Södra Sverige. D. brassicae-honor lägger ägg i höstrapsskidor och de nykläckta larverna äter på insidan av rapsskidan. Larvernas gnag påverkar rapsskidan så att den blir deformerad och spricker i förtid. Detta kan resultera i stora skördeförluster. D. brassicae-honans äggläggningsrör är för svagt för att genomborra rapsskidans vägg och äggen läggs därför oftast i redan skadade rapsskidor. De flesta av dessa skador på rapsskidor som kan utnyttjas för äggläggning av D. brassicae-honor är gjorda av blygrå rapsviveln (Ceutorhynchus obstrictus). När viveln äter på rapsskidorna uppstår gnagskador som kan gynna äggläggningen av D. brassicae. Växtskyddsåtgärder riktas därför mot C. obstrictus, eftersom skidgallmyggan är extremt svårkontrollerad. Det behövs mer kunskap om fenologin och den kombinerade påverkan av de två insektsarterna för att kunna utforma västskyddsåtgärder så hållbart som möjligt. I denna studie blev C. obstrictus och D. brassicae övervakad i 20 olika höstrapsfält över hela Skåne under 6 veckor från maj till juni 2019. Olika aktiva (räkna vivlar på plantan) och passiva (gulskålar och gula klisterskivor) övervakningsmetoder användes för att uppskatta abundans av C. obstrictus och D. brassicae i de 20 höstrapsfälten och för att undersöka hur abundans av de båda insektsarterna hänger ihop med omfattningen av skador på höstrapsskidor orsakad av D. brassicae. Fällfångster samlades veckovis och räknades på labb. I slutet av undersökningsperioden genomfördes en skadegradering i varje fält. Antal fångade insekter från de två undersökta arterna samt omfattningen av skador på höstrapsskidor orsakad av D. brassicae var väldigt få i jämförelse med studier från de två föregående år. C. obstrictus fenologi avvek från det förväntade mönstret: Vanligtvis observeras blygrå rapsvivel i ett höstrapsfält tidigare på säsongen än skidgallmyggan. I denna studie nådde fångsterna av C. obstrictus sin topp 2–3 veckor senare än D. brassicae fångster. Förmodligen förvärrade detta möjligheter till äggläggning för D. brassicae. Skidgallmyggan verkar ha kunnat dra nytta av blygrå rapsvivelns närvaro ändå: signifikanta korrelationer hittades mellan förekomsten av C. obstrictus i fältkanten och skador på höstrapsskidor orsakad av D. brassicae inuti fältet. Kemisk bekämpning med insekticider verkar inte ha gett effekt, eftersom skadorna på rapsskidorna inuti och utanför en insekticidfri kontrollruta inte skiljde sig åt. Att kemisk bekämpning med insekticider ändå har utförts av jordbrukarna tyder på att övervakningsmetoder kan behöva förfinas för att ge jordbrukarna beslutsunderlag för att förbättra IPM strategier mot C. obstrictus och D. brassicae och minska insekticidanvändningen

Chemical and physical small-scale structure in a pre-stellar core

We present a comparative study of several molecular lines and of the dust contiunuum at 1.2mm in a pre-stellar core that is embedded in the Galactic cirrus cloud MCLD123.5+24.9. Previous studies found that the core is gravitationally stable and shows signs of inward motion. Using the Owens Valley (OVRO) and Plateau de Bure (PdB) interferometers we obtained high-angular resolution maps of the core in the carbon monosulfide CS 2-1 and the cyanoacetylene HC3N 10-9 transitions. Together with CS 5-4, C34S 3-2, and bolometer data obtained with the IRAM 30m telescope, we analyse the excitation conditions and the structural properties of the cloud. On the one hand, the new CS 2-1 observations reveal significant substructure on a scale of about 7", i.e., the beam size, corresponding to about 1050 AU at an adopted distance of 150pc. On the other hand, the interferometric observations in the HC3N 10-9 transition shows just one single well resolved clump in the inner part of the core. This core is well described by an intensity profile following from a centrally peaked volume density distribution. We find no evidence for depletion of CS onto dust grains. The inward motion seen in the CS 2-1 occurs one-sided from the middle of the filamentary cloud towards the HC3N core.Comment: 8 pages, 8 figures, accepted by A&

Molecular hydrogen as baryonic dark matter

High-angular resolution CO observations of small-area molecular structures (SAMS) are presented. The feature-less structures seen in the single-dish measurements break up into several smaller clumps in the interferometer map. At an adopted distance of 100pc their sizes are of order a few hundred AU, some of which are still unresolved at an angular resolution of about 3". The clumps have a fractal structure with a fractal index between 1.7 and 2.0. Their kinetic temperature is between 7K and 18K. Adopting standard conversion factors masses are about 1/10 Jupiter-masses for individual clumps and densities are higher than 20000cm^{-3}. The clumps are highly overpressured and it is unknown what creates or maintains such structures.Comment: 8 pages, 1 figure, accepted by Astrophysical Journal Letter

Molecular gas in blue compact dwarf galaxies

Blue compact dwarf galaxies (BCDGs) are currently undergoing strong bursts of star formation. Nevertheless, only a few of them have been clearly detected in CO, which is thought to trace the "fuel" of star formation: H_2. In this paper, we present a deep search for CO J=1-->0 and J=2-->1 emission lines in a sample of 8 BCDGs and two companions. Only 2 of them (Haro 2 and UM 465) are detected. For the other galaxies we have obtained more stringent upper limits on the CO luminosity than published values. We could not confirm the previously reported ``detection'' of CO for the galaxies UM 456 and UM 462. We analyze a possible relation between metallicity, CO luminosity, and absolute blue magnitude of the galaxies. We use previously determined relations between X = N(H_2)/I_CO and the metallicity to derive molecular cloud masses or upper limits for them. With these ``global'' X_CO values we find that for those galaxies which we detect in CO, the molecular gas mass is similar to the HI mass, whereas for the non-detections, the upper limits on the molecular gas masses are significantly lower than the HI mass. Using an LVG (Large Velocity Gradient) model we show that X_CO depends not only on metallicity, but also on other physical parameters such as volume density and kinetic temperature, which rises the question on the validity of ``global'' X_CO factors.Comment: 9 pages, 6 figures, to be published on MNRA

Cold dust and its relation to molecular gas in the dwarf irregular galaxy NGC 4449

We present observations of the dwarf irregular galaxy NGC 4449 at 850 $\mu$m and 450 $\mu$m obtained with SCUBA at the JCMT. The distribution of the cold dust agrees well with that of the CO and H$\alpha$ emission. To explain the integrated mm- through far-infrared continuum spectrum three dust components are required, with temperatures of 16 K, 39 K and 168 K, respectively. The dust mass is dominated by the cold dust component; we derive a total dust mass of \~3.8 x10^6 Msun, and with the local gas-to-dust ratio of ~130 a total gas mass of M(HI+H_2}~4.9 x 10^8 Msun. Comparison with the HI mass leads to a total molecular gas mass of ~3.4 x 10^8 Msun. We derive a conversion factor of the CO line intensity to molecular hydrogen column density XCO = N(H_2)/I(CO) which is at least 11 times larger than the Galactic value. These values are in accord with the lower metallicity of NGC 4449.Comment: 6 pages, 2 figures, accepted for publication in A&

ORFEUS II echelle spectra: Absorption by H_2 in the LMC

We present the first detection of molecular hydrogen (H_2) UV absorption profiles on the line of sight to the LMC. The star LH 10:3120 in the LMC was measured with the ORFEUS telescope and the Tuebingen echelle spectrograph during the space shuttle mission of Nov./Dec. 1996. 16 absorption lines from the Lyman band are used to derive the column densities of H_2 for the lowest 5 rotational states in the LMC gas. For these states we find a total column density of N(H_2)=6.6 x 10^18$ cm^-2 on this individual line of sight. We obtain equivalent excitation temperatures of T < 50 K for the rotational ground state and T = 470 K for 0 < J < 6 by fitting the population densities of the rotational states to theoretical Boltzmann distributions. We conclude that UV pumping dominates the population of the higher rotational levels, as known from the H_2 gas in the Milky Way. (Research supported in part by the DARA)Comment: Astronomy & Astrophysics, Letter, in pres