Cold complex organic molecules toward low-mass protostars

Cold complex organic molecules toward low-mass protostars

Cold complex organic molecules toward low-mass protostars


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Cold complex organic moleculestoward low-mass protostars andoutflowsÖberg et al. 2011Nienke van der MarelLeiden ObservatoryAugust 11 th , 2011ESACNienke van der Marel, 11-08-2011

Contents●●●●●●●●●Star formationAstrochemistryComplex organic moleculesLab resultsObservationsData reductionResultsComparison with other studiesConclusionsNienke van der Marel, 11-08-2011

Star formation●Many changes intemperature,density andchemistry duringstar formationprocessHogerheijde, 1997Nienke van der Marel, 11-08-2011

Star formation●Low mass●High mass– < 8 Mo– > 8 Mo– Slow evolution– Fast evolution– Low luminosity– High luminosity– Less complicatedmechanisms– More complicatedmechanisms– Complexmolecules?– Many complexmolecules (hot)Nienke van der Marel, 11-08-2011

Astrochemistry●●●●●> 150 different moleculesdetectedConditions in space: low T, n=> formation ánd destructionreactions slow!Tracers of physical conditionsGas and solid phase (ice)Approach: observations,modeling and lab experimentsNienke van der Marel, 11-08-2011

Astrochemistry●●●Dust grains veryimportantGas-grain/ice chemistry=> formation (larger)moleculesMost abundant ice: H 2ONienke van der Marel, 11-08-2011

Astrochemistry●Ice processes– Freeze out– Formation– Desorption (sublimation)●Triggering factors– Temperature– UV radiation– Atom bombardments– Shocks●Main observablesare desorbed gasphase molecules!Nienke van der Marel, 11-08-2011

Complex organic molecules●●Molecules with >6 atomsFormation in gas-phase & in ice (thermal)Öberg et al 2009Nienke van der Marel, 11-08-2011

Complex organic molecules●Long time thought: only complex organics inhot cores (high mass) => warm chemistry● Detections in low mass protostars rare (4)=> some kind of cold chemistry has to exist!Nienke van der Marel, 11-08-2011

Lab results●●Lab experiments ice(Öberg et al 2009)Freeze out CH 3OHand CO/CH 3OHice in UHV setup(Sackler labLeiden)Nienke van der Marel, 11-08-2011

Lab results●●●UV irradiation=> production complex organic moleculesat low (

Lab resultsÖberg et al 2009Nienke van der Marel, 11-08-2011

Motivation●●Understanding formation in low mass=> Need for larger sample!Observation demands:– Low mass protostellar environments– Very abundant CH 3OH– Submm telescope– Spectral settings with several complex organictarget molecule transitions– Long integration times: lines weak!Nienke van der Marel, 11-08-2011

Observations●●●Targets: two protostars+ one outflow inSerpens (d=250 pc)- SMM1 (30 Lo)- SMM4 (5 Lo)- SMM4-WRich in CH 3OH~ 30% wrt H 2O iceSingle pointingNienke van der Marel, 11-08-2011Kristensen et al 2010Pontoppidan et al 2004

Observations●Main target molecules (network)– CH 3OCH 3– dimethylether– HCOOCH 3– methylformate– CH 3CHO – acetaldehydeNienke van der Marel, 11-08-2011

Data analysis●●●Many potentialdetections inspectral rangeSmoothing0.1 to 0.4 km/srms ~10 mKDetections & upperlimitsNienke van der Marel, 11-08-2011

Results●Compare to CH 3OH:Nienke van der Marel, 11-08-2011– FWHM Derive originatingregion

Results●CH 3OH convolved to 17”/28” beam => eq.abundant => origin in envelope, not core●●CH 3OH 8 transitions => derive T rotCalculate column densitiesusing T rotfrom CH 3OH lines (10-15 K)●Derive ratio complex/CH 3OH (CC)Nienke van der Marel, 11-08-2011

Results● CC = 5 - 22%●Results consistent with cold UVphotochemistry:– CC ratio largest for SMM1 (most luminous)– (HCOOCH 3+CH 3CHO)/CH 3OCH 3~ 3 (coldchemistry => CH 3OCH 3forms after COdesorption)Nienke van der Marel, 11-08-2011

Results●Desorption mechanisms– Thermal– UV: only surface layer! (lab)– Outflow shocks: entire ice mantle!●●Abundance ratios depend on desorptionmechanism and formation structureMore modeling required to constrain formation,layer structure, desorption processesNienke van der Marel, 11-08-2011

Comparison with other studiesRelative abundances similar for low and high mass!Nienke van der Marel, 11-08-2011

Comparison with other studies●●HCOOCH 3> CH 3OCH 3for cold chemistryHCOOCH 3< CH 3OCH 3for hot core/high masswith high T=> support for sequential formation withHCOOCH 3formed in colder CO-rich ice andCH 3OCH 3in warmer CO-poor iceNienke van der Marel, 11-08-2011

Comparison with other studiesNienke van der Marel, 11-08-2011Öberg et al 2009

Comparison with other studiesLow THigh TNienke van der Marel, 11-08-2011

Conclusions●●●Complex organics can be detected in cold gas.Abundances of complex organics are similarfor high-mass hot cores and low-massprotostars and outflows, although thechemical mechanisms are different.HCOOCH 3/CH 3OCH 3is larger in low-masssources. This supports a sequential formationof complex molecules for CO-rich and COpooriceNienke van der Marel, 11-08-2011

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