383 research outputs found

    A deep wide-field sub-mm survey of the Carina Nebula complex

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    The Great Nebula in Carina is a superb location in which to study the physics of violent massive star-formation and the resulting feedback effects, including cloud dispersal and triggered star-formation. In order to reveal the cold dusty clouds in the Carina Nebula complex, we used the Large APEX Bolometer Camera LABOCA at the APEX telescope to map a 1.25 deg x 1.25 deg (= 50 x 50 pc^2) region at 870 micrometer. From a comparison to Halpha images we infer that about 6% of the 870 micrometer flux in the observed area is likely free-free emission from the HII region, while about 94% of the flux is very likely thermal dust emission. The total (dust + gas) mass of all clouds for which our map is sensitive is ~ 60 000 Msun, in good agreement with the mass of the compact clouds in this region derived from 13CO line observations. We generally find good agreement in the cloud morphology seen at 870 micrometer and the Spitzer 8 micrometer emission maps, but also identify a prominent infrared dark cloud. Finally, we construct a radiative transfer model for the Carina Nebula complex that reproduces the observed integrated spectral energy distribution reasonably well. Our analysis suggests a total gas + dust mass of about 200000 Msun in the investigated area; most of this material is in the form of molecular clouds, but a widely distributed component of (partly) atomic gas, containing up to ~ 50% of the total mass, may also be present. Currently, only some 10% of the gas is in sufficiently dense clouds to be immediately available for future star formation, but this fraction may increase with time owing to the ongoing compression of the strongly irradiated clouds and the expected shockwaves of the imminent supernova explosions.Comment: Accepted for publication in Astronomy & Astrophysics; high-quality pre-prints can be obtained from http://www.usm.uni-muenchen.de/people/preibisch/publications.htm

    A multiwavelength study of the star forming region IRAS 18544+0112

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    This work aims at investigating the molecular and infrared components in the massive young stellar object (MYSO) candidate IRAS 18544+0112. The purpose is to determine the nature and the origin of this infrared source. To analyze the molecular gas towards IRAS 18544+0112, we have carried out observations in a 90" x 90" region around l = 34.69, b = -0.65, using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3-2, 13CO J=3-2, HCO+ J=4-3 and CS J=7-6 lines with an angular resolution of 22". The infrared emission in the area has been analyzed using 2MASS and Spitzer public data. From the molecular analysis, we find self-absorbed 12CO J=3-2 profiles, which are typical in star forming regions, but we do not find any evidence of outflow activity. Moreover, we do not detect either HCO+ J=4-3 or CS J=7-6 in the region, which are species normally enhanced in molecular outflows and high density envelopes. The 12CO J=3-2 emission profile suggests the presence of expanding gas in the region. The Spitzer images reveal that the infrared source has a conspicuous extended emission bright at 8 um with an evident shell-like morphology of ~ 1.5 arcmin in size (~ 1.4 pc at the proposed distance of 3 kpc) that encircles the 24 um emission. The non-detection of ionized gas related to IRAS 18544+0112, together with the fact that it is still embedded in a molecular clump suggest that IRAS 18544+0112, has not reached the UCHII region stage yet. Based on near infrared photometry we search for YSO candidates in the region and propos that 2MASS 18565878+0116233 is the infrared point source associated with IRAS 18544+0112. Finally, we suggest that the expansion of a larger nearby HII region, G034.8-0.7, might be related to the formation of IRAS 18544+0112.Comment: 14 pages, accepted for publication in A&A. Figures degraded to reduce file siz

    Multi-frequency study of supernova remnants in the Large Magellanic Cloud. Confirmation of the supernova remnant status of DEM L205

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    We present new X-ray and radio data of the LMC SNR candidate DEM L205, obtained by XMM-Newton and ATCA, along with archival optical and infrared observations. We use data at various wavelengths to study this object and its complex neighbourhood, in particular in the context of the star formation activity, past and present, around the source. We analyse the X-ray spectrum to derive some remnant's properties, such as age and explosion energy. Supernova remnant features are detected at all observed wavelengths: soft and extended X-ray emission is observed, arising from a thermal plasma with a temperature kT between 0.2 keV and 0.3 keV. Optical line emission is characterised by an enhanced [SII]/Halpha ratio and a shell-like morphology, correlating with the X-ray emission. The source is not or only tentatively detected at near-infrared wavelengths (< 10 microns), but there is a detection of arc-like emission at mid and far-infrared wavelengths (24 and 70 micron) that can be unambiguously associated with the remnant. We suggest that thermal emission from dust heated by stellar radiation and shock waves is the main contributor to the infrared emission. Finally, an extended and faint non-thermal radio emission correlates with the remnant at other wavelengths and we find a radio spectral index between -0.7 and -0.9, within the range for SNRs. The size of the remnant is ~79x64 pc and we estimate a dynamical age of about 35000 years. We definitely confirm DEM L205 as a new SNR. This object ranks amongst the largest remnants known in the LMC. The numerous massive stars and the recent outburst in star formation around the source strongly suggest that a core-collapse supernova is the progenitor of this remnant. (abridged)Comment: 11 pages, 6 figures, accepted for publication in A&

    A molecular outflow evidencing star formation activity in the vicinity of the HII region G034.8-0.7 and the SNR W44

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    This work aims at investigating the molecular gas component in the vicinity of two young stellar object (YSO) candidates identified at the border of the HII region G034.8-0.7 that is evolving within a molecular cloud shocked by the SNR W44. The purpose is to explore signatures of star forming activity in this complex region. We performed a near and mid infrared study towards the border of the HII region G034.8-0.7 and observed a 90" X 90" region near 18h 56m 48s, +01d 18' 45" (J2000) using the Atacama Submillimeter Telescope Experiment (ASTE) in the 12CO J=3--2, 13CO J=3--2, HCO+ J=4--3 and CS J=7--6 lines with an angular resolution of 22". Based on the infrared study we propose that the source 2MASS 18564827+0118471 (IR1 in this work) is a YSO candidate. We discovered a bipolar 12CO outflow in the direction of the line of sight and a HCO+ clump towards IR1, confirming that it is a YSO. From the detection of the CS J=7--6 line we infer the presence of high density (>10^7 cm^-3) and warm (>60 K) gas towards IR1, probably belonging to the protostellar envelope where the YSO is forming. We investigated the possible genetic connection of IR1 with the SNR and the HII region. By comparing the dynamical time of the outflows and the age of the SNR W44, we conclude that the possibility of the SNR has triggered the formation of IR1 is unlikely. On the other hand, we suggest that the expansion of the HII region G034.8-0.7 is responsible for the formation of IR1 through the "collect and collapse" process.Comment: 19 pages, 14 figures. Figures degraded to reduce file size. Accepted 06/02/2009 for publication in A&

    Terminating ley with mid-summer bare fallow controls Elymus repens

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    The results of this study suggest that mid-summer bare fallow is a relative effective way to reduce the amount of Elymus repens when terminating ley. Early started stubble cultivation is also less sensitive to moist weather, leaving more time for exhausting the rhizome reserves of E. repens. Stubble cultivation and catch crop do increase the costs but not as much as bare fallowing for the whole summer would do. Additionally, mid summer bare fallow allows harvesting one forage yield prior to bare fallowing

    Tekoäly ja syväoppiminen synteettisen biologian työkaluna

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    Tiivistelmä. Synteettinen biologia tarkoittaa biologisten järjestelmien tutkimusta keinotekoisten organismien avulla. Synteettisen biologian ala on alkuajoistaan lähtien kärsinyt orgaanisten järjestelmiensä vaatimien standardoitujen komponenttien puutteellisesta tuntemuksesta sekä niiden luomisen korkeista kustannuksista. Ongelmaa on kuitenkin ajan kuluessa helpottanut biologian ja tietotekniikan alojen lisääntynyt yhteensovittaminen sekä tietolaitteiden laskentatehon nopea kasvu. Tämä on luonut pohjan myös esimerkiksi korkean suorituskyvyn sekvensointimenetelmille ja tekoälypohjaisille tehokkaille työkaluille. Synteettinen biologia on hyötynyt merkittävästi tekoälyn laajamittaisesta käyttöönotosta ja sen tuomista mahdollisuuksista useissa biologian sekä synteettisen biologian alojen sovelluksissa. Tekoäly on mahdollistanut esimerkiksi biomolekyylien rakenteiden ja vuorovaikutuksien perinpohjaisemman selvittämisen sekä synteettisten biokomponenttien tehokkaamman suunnittelun ja luomisen. Esimerkiksi kohdespesifisten synteettisten proteiinien luominen on jo mahdollista. Synteettisiä geenejä ja niiden säätelyalueita kyetään rakentamaan proteiinisynteesin hallitsemiseksi. Myös kokonaisten geenipiirien ja yksinkertaisten genomien suunnittelu on mahdollista esimerkiksi uudenlaisten protosolujen, eli yksinkertaistettujen synteettisten organismien toteuttamista varten. Tämän kehityksen ansiosta pystymme luomaan entistä monimutkaisempia synteettisen biologian järjestelmiä biologisten prosessien ymmärtämisen parantamiseksi sekä niiden hyödyntämiseksi esimerkiksi lääketieteen tai bioteollisuuden tarpeisiin. Synteettisen biologian alalla on kuitenkin edelleen suuria haasteita tekoälyn täysimittaisen potentiaalin hyödyntämisessä. Tietoteknisten standardien yhteensovittaminen synteettisen biologian prosessien ja järjestelmien kanssa vaatii edelleen paljon työtä. Tekoälymallien koulutusta varten tarvitaan riittävästi laadukasta dataa. Tekoälytyökalut sekä niiden paljastamien yhä monimutkaisempien kokonaisuuksien käsittely ja ymmärtäminen voi vaatia entistä enemmän resursseja sekä organisaatio- että yksilötasolla. Etenkin syväoppivien tekoälymallien seurauksena tutkimuskohteisiin liittyvien ongelmien ulottuvuudet sekä niiden vaatima laskentateho voi kasvaa merkittävästi. Teknisten haasteiden lisäksi myös yhteiskunnalliset haasteet ovat merkittäviä. Synteettisen biologian ja tekoälyn herättämät eettiset kysymykset aiheuttavat yhä enemmän julkista keskustelua. Kansainvälinen lainsäädäntö ja yhteiset standardit ovatkin keskeisessä asemassa näiden voimakkaiden tieteenalojen hallitun kehittämisen takaamiseksi

    A Critical Examination of the X-Wind Model for Chondrule and Calcium-rich, Aluminum-rich Inclusion Formation and Radionuclide Production

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    Meteoritic data, especially regarding chondrules and calcium-rich, aluminum-rich inclusions (CAIs), and isotopic evidence for short-lived radionuclides (SLRs) in the solar nebula, potentially can constrain how planetary systems form. Intepretation of these data demands an astrophysical model, and the "X-wind" model of Shu et al. (1996) and collaborators has been advanced to explain the origin of chondrules, CAIs and SLRs. It posits that chondrules and CAIs were thermally processed < 0.1 AU from the protostar, then flung by a magnetocentrifugal outflow to the 2-3 AU region to be incorporated into chondrites. Here we critically examine key assumptions and predictions of the X-wind model. We find a number of internal inconsistencies: theory and observation show no solid material exists at 0.1 AU; particles at 0.1 AU cannot escape being accreted into the star; particles at 0.1 AU will collide at speeds high enough to destroy them; thermal sputtering will prevent growth of particles; and launching of particles in magnetocentrifugal outflows is not modeled, and may not be possible. We also identify a number of incorrect predictions of the X-wind model: the oxygen fugacity where CAIs form is orders of magnitude too oxidizing; chondrule cooling rates are orders of magnitude lower than those experienced by barred olivine chondrules; chondrule-matrix complementarity is not predicted; and the SLRs are not produced in their observed proportions. We conclude that the X-wind model is not relevant to chondrule and CAI formation and SLR production. We discuss more plausible models for chondrule and CAI formation and SLR production.Comment: Accepted for publication in The Astrophysical Journa
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