A 1.85-m mm-submm Telescope for Large-Scale Molecular Gas Surveys in 12CO, 13CO, and C18O (J = 2a€“1)

摘要

Wehavedevelopedanewmm-submmtelescopewithadiameterof1.85-minstalledattheNobeyamaRadioObservatory.ThescientificgoalistopreciselyrevealthephysicalpropertiesofmolecularcloudsintheMilkyWayGalaxybyobtainingalarge-scaledistributionofmoleculargas,whichcanalsobecomparedwithlarge-scaleobservationsatvariouswavelengths.Thetargetfrequencyis$$sim$$230a€‰GHz;simultaneousobservationsatthemolecularrotationallinesof$$J=$$2a€“1ofthreecarbonmonoxideisotopes($$^{12}$$CO,$$^{13}$$CO,C$$^{18}$$O)areachievedwithabeamsize(HPBW)of2$${.}{}^prime$$7.Inordertoaccomplishthesimultaneousobservations,wehavedevelopedwaveguide-typesideband-separatingSISmixerstoobtainspectraseparatelyintheupperandlowersidebands.AFourierdigitalspectrometerwitha1a€‰GHzbandwidthhaving16384channelsisinstalled,andthebandwidthofthespectrometerisdividedintothreeparts,correspondingtoeachofthethreespectra;theIFsystemhasbeendesignedsoastoinjectthesethreelinesintothespectrometer.AflexibleobservationsystemwascreatedmainlyinPythononLinuxPCs,enablingeffectiveOTF(On-The-Fly)scansforlarge-areamapping.Thetelescopeisenclosedinaradomewithamembranecoveredtopreventanyharmfuleffectsofsunlight,strongwind,andprecipitationinordertominimizeerrorsinthetelescopepointing,andtostabilizethereceiverandtheIFdevices.From2011November,westartedscienceoperation,resultinginalarge-scalesurveyoftheOrionA/Bclouds,CygnusOB7,GalacticPlane,Taurus,andsoon.Wealsoupdatedthereceiversystemfordual-polarizationobservations.