Studying the interstellar medium to look for relics of triggered star formation among stellar clusters

Evidence of triggered star formation at large spatial scales involving stellar clusters is scarce. We investigate a Galactic region (l = 130°.0, b = 0°.35) populated by several open stellar clusters that according to the last Gaia data release, are located at a distance of about 2.9 kpc. By analysing the interstellar medium (ISM) at infrared, centimeter, and millimeter wavelengths towards this group of clusters we discovered a shell of material of about 2° in size at the same distance. We suggest that the shell, mainly observed at 12 μm and in the H i emission at 21 cm, was generated by the action of massive stars belonging to clusters Berkeley 7 and UBC 414, which lie at its centre. Five clusters (MWSC0152, Czernik 6, Czernik 7, Berkeley 6, NGC 663, and NGC 654) lie at the border of this shell. From the comparison between the dynamical time of the discovered H i shell and the analysis of the ages of stellar populations in these clusters, we conclude that the expansion of the shell could have triggered in the past the formation of stars in some of them. We point out that in order to find physical evidence supporting a genetic connection between stellar clusters, it is necessary not only to study the individual clusters and their stellar populations, but also to investigate their surrounding ISM at a large spatial scale.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Granada, Anahi. Universidad Nacional de Rio Negro. Sede Andina. Laboratorio de Procesamiento de Señales Aplicadas y Computacion de Alto Rendimiento.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Areal, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Studying the molecular gas towards a bright rimmed cloud at the infrared dust bubble N30

We present a study on the molecular gas towards a bright-rimmed cloud located to the north of theinfrared dust bubble N30. Using the emission from the12CO,13CO, and C18O J=3?2 line, together with infraredand radio continuum data, we characterized the bubble and the related molecular cloud. In addition, we showan analysis of the behaviour of the abundance ratio13CO/C18O towards the bright-rimmed cloud, and we searchfor clues on recent star-formation.Fil: Solernó, A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Areal, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina61º Reunión Anual Asociación Argentina de AstronomíaViedmaArgentinaAsociación Argentina de Astronomí

SNR Puppis A: molecular gas possibly associated with the brightest X-ray feature

We analize the 12CO emission towards the brightest X-ray knot in the supernova remnant (SNR) Puppis A. The observations were performed with the SEST telescope in the 12CO J=1--0 and 2--1 lines (beams of 45" and 23" respectively). We discovered a compact molecular clump near the radio and X-ray maxima and calculated its physical parameters. From the comparison with Chandra X-ray data we conclude that this molecular clump lies in front of Puppis A along the line of sight. The possibilities of a recent interaction between the SNR and the molecular gas are analyzed.Se analiza la emisión del 12CO en la región más brillante de emisión de rayos X del remanente de supernova (RSN) Puppis A. Las observaciones fueron realizadas en las transiciones J=1–0 y 2–1 con el telescopio sueco SEST con resoluciones angulares de 45′′ y 23′′ respectivamente para ambas líneas. Se descubrio la presencia de un grumo molecular compacto cerca del máximo en radio y en rayos X. Se calculan los parámetros físicos de dicha componente molecular. De la comparación con datos en rayos X del satélite Chandra se concluye que dicho grumo molecular se encuentra por delante del RSN Puppis A a lo largo de la visual. Se analiza la posibilidad de una reciente interacción entre el frente de choque del RSN y el gas molecular.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Reynoso, Estela Marta. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96-0.02

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96-0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13/18) toward this region, we used 12CO J = 3-2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3-2 data from the 13CO/C18O (J = 3-2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2-1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13/18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13/18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13/18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13/18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Areal, María Belén. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

Discovering a misaligned CO outflow related to the red MSX source G034.5964-01.0292

Aims. The red MSX source G034.5964-01.0292 (MSXG34), catalogued as a massive young stellar object, was observed in molecular lines with the aim of discovering and studying molecular outflows. Methods. We mapped a region of 3′× 3′ centred at MSXG34 using the Atacama Submillimeter Telescope Experiment in the 12CO J = 3–2 and HCO+J = 4–3 lines with an angular and spectral resolution of 22′′ and 0.11 km s-1. Additionally, public 13CO J = 1–0 and near-IR UKIDSS data obtained from the Galactic Ring Survey and the WFCAM Sciencie Archive were analysed. Results. We found that the 12CO spectra towards the YSO present a self-absorption dip, as is common in star-forming regions, and spectral wings that indicate outflow activity. The HCO+ was detected only towards the MSXG34 position at vLSR ~ 14.2 km s-1, in coincidence with the 12CO absorption dip and approximately with the velocity of previous ammonia observations. HCO+ and NH3 are known to be enhanced in molecular outflows. When we analysed the spectral wings of the 12CO line, we discovered misaligned red- and blue-shifted molecular outflows associated with MSXG34. The near-IR emission shows a cone-like nebulosity composed of two arc-like features related to the YSO, which might be due to a cavity cleared in the circumstellar material by a precessing jet. This can explain the misalignment in the molecular outflows. From the analysis of the 13CO J = 1–0 data we suggest that the YSO is very likely related to a molecular clump ranging between 10 and 14 km s-1. This suggests that MSXG34, with an associated central velocity of about 14 km s-1, may be located in the background of this clump. Thus, the blue-shifted outflow is probably deflected by the interaction with dense gas along the line of sight. From a spectral energy distribution analysis of MSXG34 we found that its central object probably is an intermediate-mass protostar.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Petriella, Alberto. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Rubio, M.. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; Chile. Universidad de Chile; Chil

Exploring the 13CO/C18O abundance ratio towards Galactic young stellar objects and H II regions

Aims. Determining molecular abundance ratios is important not only for the study of Galactic chemistry, but also because they are useful to estimate physical parameters in a large variety of interstellar medium environments. One of the most important molecules for tracing the molecular gas in the interstellar medium is CO, and the 13CO/C18O abundance ratio is usually used to estimate molecular masses and densities of regions with moderate to high densities. Nowadays isotope ratios are in general indirectly derived from elemental abundances ratios. We present the first 13CO/C18O abundance ratio study performed from CO isotope observations towards a large sample of Galactic sources of different natures at different locations. Methods. To study the 13CO/C18O abundance ratio, we used 12CO J = 3 - 2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3 - 2 data from the 13CO/C18O (J = 3 - 2) Heterodyne Inner Milky Way Plane Survey, and some complementary data extracted from the James Clerk Maxwell Telescope database. We analyzed a sample of 198 sources composed of young stellar objects (YSOs), and HII and diffuse HII regions as catalogued in the Red MSX Source Survey in 27°.5 < l < 46°; .5 and /b/ < 0° .5. Results. Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5 kpc. We found that YSOs have, on average, lower 13CO/C18O abundance ratios than HII and diffuse HII regions. Taking into account that the gas associated with YSOs should be less affected by the radiation than in the case of the others sources, selective far-UV photodissociation of C18O is confirmed. The 13CO/C18O abundance ratios obtained in this work are systematically lower than those predicted from the known elemental abundance relations. These results will be useful in future studies of molecular gas related to YSOs and HII regions based on the observation of these isotopes.Fil: Areal, María Belén. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Paron, Sergio Ariel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Celis Peña, Mariela Fernanda. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin

A bright-rimmed cloud sculpted by the Hii region Sh2-48

Aims. To characterize a bright-rimmed cloud embedded in the Hii region Sh2-48 searching for evidence of triggered star formation. Methods. We carried out observations towards a region of 20 × 20 centered at RA=18h 22m 11.39s , dec.=-14 350 24.8100(J2000) using the Atacama Submillimeter Telescope Experiment (ASTE; Chile) 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 about 2200 . We also present radio continuum observations at 5 GHz carried out with the Jansky Very Large Array (JVLA; EEUU) interferometer with a synthetized beam of 700 × 500 . The molecular transitions are used to study the distribution and kinematics of the molecular gas of the bright-rimmed cloud. The radio continuum data is used to characterize the ionized gas located at the illuminated border of this molecular condensation. Combining these observations with infrared public data allows us to build up a comprehensive picture of the current state of star formation within this cloud. Results. The analysis of our molecular observations reveals the presence of a relatively dense clump with n(H2) ~ 3 × 103cm−3, located in projection onto the interior of the Hii region Sh2-48. The emission distribution of the four observed molecular transitions has, at VLSR ~ 38 kms−1, morphological anti-correlation with the bright-rimmed cloud as seen in the optical emission. From the new radio continuum observations we identify a thin layer of ionized gas located at the border of the clump which is facing to the ionizing star. The ionized gas has an electron density of about 73 cm−3 which is a factor three higher than the typical critical density (nc ~ 25 cm−3) above which an ionized boundary layer can be formed and be maintained. This fact supports the hypothesis that the clump is being photoionized by the nearby O9.5V star, BD-14 5014. From the evaluation of the pressure balance between the ionized and molecular gas, we conclude that the clump would be in a pre-pressure balance state with the shocks being driven into the surface layer. Among the five YSO candidates found in the region, two of them (class I), are placed slightly beyond the bright rim suggesting that their formation could have been triggered via the radiation-driven implosion process.Fil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentina;Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentina; Universidad de Chile;Fil: Giacani, Elsa Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentina;Fil: Rubio, M.. Universidad de Chile. Departamento de Astronomía; Chile;Fil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentina

The interstellar medium and the massive stellar content towards the SNR G18.1-0.1 and neighbouring H II regions

We perform a multiwavelength study of the SNR G18.1-0.1 and nearby several H II regions (infrared dust bubbles N21 and N22, and the H II regions G018.149-00.283 and G18.197-00.181). Our goal is to provide observational evidence supporting the view that massive stars are usually born in clusters from the same molecular cloud, which then produce, along their evolution, different neighbouring objects such as H II regions, interstellar bubbles and supernova remnants (SNRs). We suggest that the objects analysed in this work belong to a same complex located at the distance of about 4 kpc. Using molecular data we inspected the interstellar medium towards this complex and from optical and X-ray observations we looked for OB-type stars in the region. Analysing public 13 CO J = 1-0 data we found several molecular structures very likely related to the H II region/SNR complex. We suggest that the molecular gas is very likely being swept and shaped by the expansion of the H II regions. From spectroscopic optical observations obtained with the 2.15-m telescope at CASLEO, Argentina, we discovered three O-type stars very likely exciting the bubbles N21 and N22, and an uncatalogued H II region northwards of bubble N22, respectively. Also we found four B0-5 stars, one towards the bubble N22 and the others within the H II region G18.149-0.283. By inspecting the Chandra Source Catalogue we found two-point X-ray sources and suggest that one of them is an early O-type star. Finally, we inspected the large-scale interstellar medium around this region. We discovered a big molecular shell of about 70 × 28 pc in which the analysed complex appears to be located in its southern border.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentina. Universidad de Buenos Aires; ArgentinaFil: Weidmann, Walter Alfredo. Universidad Nacional de Cordoba. Observatorio Astronomico de Cordoba;Fil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); ArgentinaFil: Albacete Colombo, Juan Facundo. Universidad Nacional del Comahue; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Pichel, Ana Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio(i); Argentin

Cyano radical emission at small spatial scales towards massive protostars

Context. The cyano radical (CN), one of the first detected interstellar molecular species, is a key molecule in many astrochemical chains. In particular, it is detected towards molecular cores, the birth places of stars, and it is involved in the rich chemistry that takes place at these sites. Aims. At present, there are not many studies on the emission of this molecular species at small spatial scales towards massive young stellar objects. We therefore present a high-angular resolution CN study towards a sample of massive protostars, with the aim of unveiling the spatial distribution at the small scale of the emission of this radical in relation to star-forming processes. Methods. The interstellar CN has a strong emission line at the rest frequency 226 874.764 MHz, thus we searched for observing projects in the Atacama Large Millimeter Array (ALMA) database regarding high-mass star-forming regions observed at Band 6. The used data set was observed in ALMA Cycle 3 with angular and spectral resolutions of 0.′′7 and 1.13 MHz, respectively. A sample of ten high-mass star-forming regions located in the first Galactic quadrant were selected on the basis that they present a clear emission of CN at the mentioned frequency. Results. We found that the CN traces both molecular condensations and the diffuse and extended gas surrounding them. In general, the molecular condensations traced by the maximums of the CN emission do not spatially coincide with the peaks of the continuum emission at 1.3 mm, which trace the molecular cores where massive stars are born. Based on the presence or lack of near-IR emission associated with such cores, we suggest that our sample is composed of sources at different stages of evolution. The CN is present in all sources, suggesting that this radical may be ubiquitous along the different star formation stages, and hence it may be involved in different chemical reactions occurring during the period of star formation. Additionally, other molecules such as CH3OCHO and CH2CHCN were detected towards the continuum peaks of some of the analysed cores. We found that the missing flux coming from extended spatial scales that are filtered out by the interferometer is an important issue to take into account in the analysis of some spectral features and the spatial distribution of the emission.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Marinelli Andino, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Areal, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Martinez, Naila Constanza. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentin

The southern molecular environment of SNR G18.8+0.3

In a previous paper we have investigated the molecular environment towardsthe eastern border of the SNR G18.8+0.3. Continuing with the study of thesurroundings of this SNR, in this work we focus on its southern border, whichin the radio continuum emission shows a very peculiar morphology with acorrugated corner and a very flattened southern flank. We observed two regionstowards the south of SNR G18.8+0.3 using the Atacama Submillimeter TelescopeExperiment (ASTE) in the 12CO J=3-2. One of these regions was also surveyed in13CO and C18O J=3-2. The angular and spectral resolution of these observationswere 22", and 0.11 km/s. We compared the CO emission to 20 cm radio continuummaps obtain as part of the Multi-Array Galactic Plane Imaging Survey (MAGPIS)and 870 um dust emission extracted from the APEX Telescope Large Area Survey ofthe Galaxy. We discovered a molecular feature with a good morphologicalcorrespondence with the SNR´s southernmost corner. In particular, there areindentations in the radio continuum map that are complemented by protrusions inthe molecular CO image, strongly suggesting that the SNR shock is interactingwith a molecular cloud. Towards this region we found that the 12CO peak is notcorrelated with the observed 13CO peaks, which are likely related to a nearby Hii region. Regarding the most flattened border of SNR G18.8+0.3, where aninteraction of the SNR with dense material was previously suggested, our 12COJ=3-2 map show no obvious indication that this is occurring.Fil: Paron, Sergio Ariel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Celis Peña, Mariela Fernanda. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Ortega, Martin Eduardo. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Petriella, Alberto. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Rubio, M.. Universidad de Chile. Facultad de Ciencias Fisicas y Matematicas; ChileFil: Dubner, Gloria Mabel. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Giacani, Elsa Beatriz. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentin