J/A+A/612/A117ivo://CDS.VizieR/J/A+A/612/A117doi:10.26093/cds/vizier.36120117CDSAreal M.B.Paron S.Celis Pena M.Ortega M.E.2018-09-10T08:11:26Z2018-09-07T12:08:13ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.fryoung-stellar-objectsh-ii-regionsco-line-emissionchemical-abundancesAims. 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 ^13^CO/C^18^O 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 ^13^CO/C^18^O 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 ^13^CO/C^18^O abundance ratio, we used ^12^CO J=3-2 data obtained from the CO High-Resolution Survey, ^13^CO and C^18^O J=3-2 data from the ^13^CO/C^18^O (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{deg}<=l<=46.5{deg} and |b|<0.5{deg}. Results. Most of the analyzed sources are located in the galactocentric distance range 4.0-6.5kpc. We found that YSOs have, on average, lower ^13^CO/C^18^O 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 C^18^O is confirmed. The ^13^CO/C^18^O 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.2018A&A...612A.117Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/612/A117CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/ApJS/208/11 : The Red MSX Source Survey: massive protostars (Lumsden+, 2013)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/612/A117https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/612/A117http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/612/A117https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/612/A117https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/612/A117http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/612/A117GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapRadiodefaultJ/A+A/612/A117/tableaLine parameters for the CO isotopes (table A1) and results (table A2)SimbadNameSimbad column added by the CDSmeta.idcharTexExcitation temperatureKphys.atmol.excitationfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRedMSXDisplay the Red MSX survey data (Lumsden et al., 2013, Cat. J/ApJS/208/11meta.ref.urlcharSeqSequential numbermeta.recordintSourceSource name (GLLL.llll+BB.bbbbA),meta.id;meta.maincharTypeSource type (G1)src.classcharDgalGalactocentric distancekpcpos.distancefloatv12Central LSR velocity of ^12^CO linekm/sphys.veloc;pos.lsrfloatdv12LSR velocity of ^12^CO line dispersionkm/sphys.veloc.dispersionfloatTmb12Peak main brightness temperature of ^12^CO line (1)Kphys.temperaturefloatv13Central LSR velocity of ^13^CO linekm/sphys.veloc;pos.lsrfloatdv13LSR velocity of ^13^CO line dispersionkm/sphys.veloc.dispersionfloatTmb13Peak main brightness temperature of ^13^CO line (1)Kphys.temperaturefloatI13Velocity-integrated line emission of ^13^CO (2)K.km/sspect.line.intensityfloatv18LSR velocity of C^18^O linekm/sphys.veloc;pos.lsrfloatdv18LSR velocity of C^18^O linekm/sphys.veloc.dispersionfloatTmb18Peak main brightness temperature of C^18^O line (1)Kphys.temperaturefloatI18Velocity-integrated line emission of C^18^O (2)K.km/sspect.line.intensityfloatI13/I18Integrated line ratio, ^13^CO/C^18^Ospect.line.intensity;arith.ratiofloattau13Optical depth of ^13^COphys.absorption.opticalDepthfloatN13Column density of ^13^CO1e+16cm**-2phys.columnDensityfloattau18Optical depth of C^18^Ophys.absorption.opticalDepthfloatN18Column density of C^18^O1e+16cm**-2phys.columnDensityfloatN13/N18Abundance ratio, N(^13^CO)/N(C^16^O)phys.abund;arith.ratiofloat