Phenolics, depsides and triterpenes from the chilean lichen pseudocyphellaria nudata (zahlbr.) D.J. Galloway

Indexación: ScieloThe lichen Pseudocyphellaria nudata is a species endemic to southern South América. From the lichen tallus, methyl orsellinate, 2-methoxy-3,6-dimethyl-4-hydroxybenzaldehyde, methyl-evernate, tenuiorin, hopan-6ß,22-diol and hopan-6α,76,22-triol were isolated and identified as the main lichen constituents. This is the first report of the occurrence of 2-methoxy-3,6-dimethyl-4-hydroxybenzaldehyde in lichens.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=s0717-97072008000300017&nrm=is

The Magellanic Bridge cluster NGC 796: Deep optical AO imaging reveals the stellar content and initial mass function of a massive open cluster

NGC 796 is a massive young cluster located 59 kpc from us in the diffuse intergalactic medium of the 1/5-1/10 $Z_{\odot}$ Magellanic Bridge, allowing to probe variations in star formation and stellar evolution processes as a function of metallicity in a resolved fashion, providing a link between resolved studies of nearby solar-metallicity and unresolved distant metal-poor clusters located in high-redshift galaxies. In this paper, we present adaptive optics $gri$H$\alpha$ imaging of NGC 796 (at 0.5", which is ~0.14 pc at the cluster distance) along with optical spectroscopy of two bright members to quantify the cluster properties. Our aim is to explore if star formation and stellar evolution varies as a function of metallicity by comparing the properties of NGC 796 to higher metallicity clusters. We find from isochronal fitting of the cluster main sequence in the colour-magnitude diagram an age of 20$^{+12}_{-5}$ Myr. Based on the cluster luminosity function, we derive a top-heavy stellar initial mass function (IMF) with a slope $\alpha$ = 1.99$\pm$0.2, hinting at an metallicity and/or environmental dependence of the IMF which may lead to a top-heavy IMF in the early Universe. Study of the H$\alpha$ emission line stars reveals that Classical Be stars constitute a higher fraction of the total B-type stars when compared with similar clusters at greater metallicity, providing some support to the chemically homogeneous theory of stellar evolution. Overall, NGC 796 has a total estimated mass of 990$\pm200$ $M_{\odot}$, and a core radius of 1.4$\pm$0.3 pc which classifies it as a massive young open cluster, unique in the diffuse interstellar medium of the Magellanic Bridge.Comment: Accepted for publication in the Astrophysical Journal. Contains 14 pages, 11 figures, and 3 table

Studying the Molecular Ambient towards the Young Stellar Object EGO G35.04-0.47

We are performing a systematic study of the interstellar medium around extended green objects (EGOs), likely massive young stellar objects driving outflows. EGO G35.04-0.47 is located towards a dark cloud at the northern-west edge of an HII region. Recently, H2 jets were discovered towards this source, mainly towards its southwest, where the H2 1-0 S(1) emission peaks. Therefore, the source was catalogued as the Molecular Hydrogen emission-line object MHO 2429. In order to study the molecular ambient towards this star-forming site, we observed a region around the aforementioned EGO using the Atacama Submillimeter Telescope Experiment in the 12CO J=3--2, 13CO J=3--2, HCO+ J=4--3, and CS J=7--6 lines with an angular and spectral resolution of 22" and 0.11 km s-1, respectively. The observations revealed a molecular clump where the EGO is embedded at v_LSR ~ 51 km s-1, in coincidence with the velocity of a Class I 95 GHz methanol maser previously detected. Analyzing the 12CO line we discovered high velocity molecular gas in the range from 34 to 47 km s-1, most likely a blueshifted outflow driven by the EGO. The alignment and shape of this molecular structure coincide with those of the southwest lobe of MHO 2429 mainly between 46 and 47 km s-1, confirming that we are mapping its CO counterpart. Performing a SED analysis of EGO G35.04-0.47 we found that its central object should be an intermediate-mass young stellar object accreting mass at a rate similar to those found in some massive YSOs. We suggest that this source can become a massive YSO.Comment: accepted to be published in PASJ - 24 September 201

Molecular gas associated with IRAS 10361-5830

We analyze the distribution of the molecular gas and the dust in the molecular clump linked to IRAS 10361-5830, located in the environs of the bubble-shaped HII region Gum 31 in the Carina region, with the aim of determining the main parameters of the associated material and investigating the evolutionary state of the young stellar objects identified there. Using the APEX telescope, we mapped the molecular emission in the J=3-2 transition of three CO isotopologues, 12CO, 13CO and C18O, over a 1.5' x 1.5' region around the IRAS position. We also observed the high density tracers CS and HCO+ toward the source. The cold dust distribution was analyzed using submillimeter continuum data at 870 \mu\ obtained with the APEX telescope. Complementary IR and radio data at different wavelengths were used to complete the study of the ISM. The molecular gas distribution reveals a cavity and a shell-like structure of ~ 0.32 pc in radius centered at the position of the IRAS source, with some young stellar objects (YSOs) projected onto the cavity. The total molecular mass in the shell and the mean H$_2$ volume density are ~ 40 solar masses and ~(1-2) x 10$^3$ cm$^{-3}$, respectively. The cold dust counterpart of the molecular shell has been detected in the far-IR at 870 \mu\ and in Herschel data at 350 \mu. Weak extended emission at 24 \mu\ from warm dust is projected onto the cavity, as well as weak radio continuum emission. A comparison of the distribution of cold and warm dust, and molecular and ionized gas allows us to conclude that a compact HII region has developed in the molecular clump, indicating that this is an area of recent massive star formation. Probable exciting sources capable of creating the compact HII region are investigated. The 2MASS source 10380461-5846233 (MSX G286.3773-00.2563) seems to be responsible for the formation of the HII region.Comment: Accepted in A&A. 11 pages, 10 Postscript figure

12CO and 13CO J=3-2 observations toward N11 in the Large Magellanic Cloud

After 30 Doradus, N11 is the second largest and brightest nebula in the LMC. This large nebula has several OB associations with bright nebulae at its surroundings. N11 was previously mapped at the lowest rotational transitions of $^{12}$CO (J=1--0 and 2--1), and in some particular regions pointings of the $^{13}$CO J=1--0 and 2--1 lines were also performed. Using ASTE we mapped the whole extension of the N11 nebula in the $^{12}$CO J=3--2 line, and three sub-regions in the $^{13}$CO J=3--2 line. The regions mapped in the $^{13}$CO J=3--2 were selected based on that they may be exposed to the radiation at different ways: a region lying over the nebula related to the OB association LH10 (N11B), another one that it is associated with the southern part of the nebula related to the OB association LH13 (N11D), and finally a farther area at the southwest without any embedded OB association (N11I). We found that the morphology of the molecular clouds lying in each region shows some signatures that could be explained by the expansion of the nebulae and the action of the radiation. Fragmentation generated in a molecular shell due to the expansion of the N11 nebula is suggested. The integrated line ratios $^{12}$CO/$^{13}$CO show evidences of selective photodissociation of the $^{13}$CO, and probably other mechanisms such as chemical fractionation. The CO contribution to the continuum at 870 $\mu$m was directly derived. The distribution of the integrated line ratios $^{12}$CO J=3--2/2--1 show hints of stellar feedback in N11B and N11D. The ratio between the virial and LTE mass (M$_{\rm vir}$/M$_{\rm LTE}$) is higher than unity in all analyzed molecular clumps, which suggests that the clumps are not gravitationally bounded and may be supported by external pressure. A non-LTE analysis suggests that we are mapping gas with densities about a few 10$^{3}$ cm$^{-3}$.Comment: Accepted to be published in A&A. Figures were degrade

Quantum Interference and Decoherence in Single-Molecule Junctions: How Vibrations Induce Electrical Current

Quantum interference effects and decoherence mechanisms in single-molecule junctions are analyzed employing a nonequilibrium Green's function approach. Electrons tunneling through quasi-degenerate states of a nanoscale molecular junction exhibit interference effects. We show that electronic-vibrational coupling, inherent to any molecular junction, strongly quenches such interference effects. As a result, the electrical current can be significantly larger than without electronic-vibrational coupling. The analysis reveals that the quenching of quantum interference is particularly pronounced if the junction is vibrationally highly excited, e.g. due to current-induced nonequilibrium effects in the resonant transport regime.Comment: 11 pages, 4 figure

A view of Large Magellanic Cloud HII regions N159, N132, and N166 through the 345 GHz window

We present results obtained towards the HII regions N159, N166, and N132 from the emission of several molecular lines in the 345 GHz window. Using ASTE we mapped a 2.4' $\times$ 2.4' region towards the molecular cloud N159-W in the $^{13}$CO J=3-2 line and observed several molecular lines at an IR peak very close to a massive young stellar object. $^{12}$CO and $^{13}$CO J=3-2 were observed towards two positions in N166 and one position in N132. The $^{13}$CO J=3-2 map of the N159-W cloud shows that the molecular peak is shifted southwest compared to the peak of the IR emission. Towards the IR peak we detected emission from HCN, HNC, HCO$^{+}$, C$_{2}$H J=4-3, CS J=7-6, and tentatively C$^{18}$O J=3-2. This is the first reported detection of these molecular lines in N159-W. The analysis of the C$_{2}$H line yields more evidence supporting that the chemistry involving this molecular species in compact and/or UCHII regions in the LMC should be similar to that in Galactic ones. A non-LTE study of the CO emission suggests the presence of both cool and warm gas in the analysed region. The same analysis for the CS, HCO$^{+}$, HCN, and HNC shows that it is very likely that their emissions arise mainly from warm gas with a density between $5 \times 10^5$ to some $10^6$ cm$^{-3}$. The obtained HCN/HNC abundance ratio greater than 1 is compatible with warm gas and with an star-forming scenario. From the analysis of the molecular lines observed towards N132 and N166 we propose that both regions should have similar physical conditions, with densities of about 10$^3$ cm$^{-3}$.Comment: accepted in MNRAS (October 5, 2015

Molecular gas and star formation towards the IR dust bubble S24 and its environs

We present a multi-wavelength analysis of the infrared dust bubble S24, and its environs, with the aim of investigating the characteristics of the molecular gas and the interstellar dust linked to them, and analyzing the evolutionary status of the young stellar objects (YSOs) identified there. Using APEX data, we mapped the molecular emission in the CO(2-1), $^{13}$CO(2-1), C$^{18}$O(2-1), and $^{13}$CO(3-2) lines in a region of about 5'x 5' in size around the bubble. The cold dust distribution was analyzed using ATLASGAL and Herschel images. Complementary IR and radio data were also used.The molecular gas linked to the S24 bubble, G341.220-0.213, and G341.217-0.237 has velocities between -48.0 km sec$^{-1}$ and -40.0 km sec$^{-1}$. The gas distribution reveals a shell-like molecular structure of $\sim$0.8 pc in radius bordering the bubble. A cold dust counterpart of the shell is detected in the LABOCA and Herschel images.The presence of extended emission at 24 $\mu$m and radio continuum emission inside the bubble indicates that the bubble is a compact HII region. Part of the molecular gas bordering S24 coincides with the extended infrared dust cloud SDC341.194-0.221. A cold molecular clump is present at the interface between S24 and G341.217-0.237. As regards G341.220-0.213, the presence of an arc-like molecular structure at the northern and eastern sections of this IR source indicates that G341.220-0.213 is interacting with the molecular gas. Several YSO candidates are found to be linked to the IR extended sources, thus confirming their nature as active star-forming regions. The total gas mass in the region and the H$_2$ ambient density amount to 10300 M$_{\odot}$ and 5900 cm$^{-3}$, indicating that G341.220-0.213, G341.217-0.237, and the S24 HII region are evolving in a high density medium. A triggering star formation scenario is also investigated.Comment: 17 pages, 16 figures. Submitted to A&A. Revised according to the referee repor