Astronomy&Astrophysicsmanuscriptno.marce˙anions˙space (cid:13)c ESO2008 February2,2008 LE − ⋆ Search for anions in molecular sources: C H detection in L1527 4 M.Agu´ndez1,J.Cernicharo1,M.Gue´lin2,M.Gerin3,M.C.McCarthy4 andP.Thaddeus4 1 DepartamentodeAstrof´ısicaMoleculareInfrarroja,InstitutodeEstructuradelaMateria,CSIC,Serrano121,28006Madrid,Spain; e-mail:[email protected], [email protected] 8 2 InstitutdeRadioastronomieMillime´trique,300ruedelaPiscine,38406St.Martind’He´res,France;e-mail:[email protected] 0 3 LERMA,UMR8112,CNRS,ObservatoiredeParisandE´coleNormaleSupe´rieure,24Ruel’Homond,75231Paris,Francee-mail: 0 [email protected] 2 4 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA e-mail: [email protected], [email protected] n a Received;accepted J 8 ABSTRACT 1 Aims.WepresenttheresultsofasearchforthenegativeionC H−invariousdarkclouds,lowmassstar-formingregionsandphoton- 4 ] dominatedregions(PDRs).WehavealsosearchedforC H−,C H−andCN−insomeofthesources. 6 2 h Methods.Themillimeter-waveobservationswerecarriedoutwiththeIRAM-30mtelescope. p Results.Wedetect C H−,through theJ=9-8andJ=10-9rotationaltransitions, inthelowmassstar-formingregionL1527. We 4 - thusconfirmthetentativedetectionoftheJ=9-8linerecentlyreportedtowardthissource.The[C H−]/[C H]ratiofoundis0.011%, o 4 4 whichisslightlylowerthanthevalueobservedinIRC+10216,0.024%,butabovethe3σupperlimitwederiveinTMC-1,<0.0052 r t %.Wehavealsoderivedanupperlimitforthe[C H−]/[C H]ratiointheHorseheadNebula,andforvariousanion-to-neutralratiosin s 6 6 theobservedsources.Theseresultsarecomparedwithrecentchemicalmodels. a [ Keywords.Astrochemistry—ISM:molecules—ISM:individual(L1527)—radiolines:ISM 2 v 4 1. Introduction tachmentratecoefficientsseemstobethecrucialparametercon- 7 trollingthe anion-to-neutralratio. Millaretal. (2007) have cal- 1 We have learnt that negatively charged molecules are present culated such rate coefficientsand constructedchemical models 1 in the interstellar medium. Following the laboratory detection whichpredictanionstobeabundantindarkcloudsandPDRs. 2. of the series of hydrocarbon anions C2nH− (n = 1, 2, 3, 4; To explore how ubiquitous and abundant molecular anions 1 McCarthyetal. 2006; Guptaetal. 2007; Bru¨nkenetal. 2007a) are in theinterstellar mediumwe havesearchedforC H− with 7 andofthesmallestmemberoftheisoelectronicseriesC2n+1N− theIRAM-30mtelescopetowardvariousdarkclouds,l4owmass 0 (n = 0; Gottliebetal. 2007), astronomical searches have suc- star-formingregionsandPDRs.WehavealsosearchedforCN−, v: ceeded in detecting the three largest anions of the first series C H−andC H−insomeofthesources.InthisLetterwepresent in the C-rich envelope around the evolved star IRC +10216, 2 6 i theresultsofthesesearches,whichhaveledto thepositivede- X C6H− and C8H− in the dark cloud TMC-1, and C6H− toward tectionofC H− inthelowmassstar-formingregionL1527. 4 r thelowmassstar-formingregionL1527(McCarthyetal.,2006; a Cernicharoetal., 2007; Remijanetal., 2007; Bru¨nkenetal., 2007b; Sakaietal., 2007a). The smallest members of each se- 2. Observations ries,C H− andCN−,remainundetectedinspace. 2 It has been found that the abundance of the larger anions TheobservationswerecarriedoutwiththeIRAM-30mtelescope C H− andC H− representsasubstantialfractionofthatoftheir from 24th July to 2nd August 2007. We searched for molecu- 6 8 neutralcounterparts(afewpercent)whilethesmallerC H− has lar anions in the starless cores: TMC-1 (at the cyanopolyyne 4 anabundancemuchlowerthanC H(0.024%inIRC+10216). peak), Barnard 1 (at the B1-b core) and L134N; and in the 4 Thus, the anion-to-neutral ratio decreases when moving from lowmassstar-formingregionsL1527andL483,attheposition largetosmallspecies.Thistrendwaspredictedmanyyearsago of their embedded IRAS sources. In PDRs, molecular anions by Herbst (1981), who discussed the formation and potential are predicted to have a peak abundance in the low extinction, detectability of molecular anions in interstellar clouds. It was AV∼1.5-3, interface where the transition of C+ to CO occurs pointed out that the efficiency of electron radiative attachment (Millaretal., 2007). We thus searched for anions toward such greatly increases for species with a high electron affinity, such positionsinthreePDRs:theHorseheadNebulaattheso-called astheradicalsC HandC N,andwithalargenumberofvi- IR peak where the greatest hydrocarbon emission is observed 2n 2n+1 brationalstates,i.e.alargesize.Thus,theelectronradiativeat- (Teyssieretal., 2004; Petyetal., 2005), the Orion Bar at the (CO)positionwhereCF+ wasdiscovered(Neufeldetal.,2006), andthereflectionnebulaNGC7023attheso-calledPDR peak Sendoffprintrequeststo:M.Agu´ndez ⋆ Basedonobservations carriedoutwiththeIRAM30mtelescope. whereCO+hasbeenobserved(Fuente&Mart´ın-Pintado,1997). IRAM is supported by INSU/CNRS (France), MPG (Germany) and WeusedSISreceiversoperatingat3mmand1mminsingle- IGN(Spain). sidebandmodewithimagerejections>20dBat3mmand≥10 2 Agu´ndezetal.:Searchforanionsinmolecularsources Table1.Observedlineparameters Frequency T∗A ∆v VLSR RT∗Adv Source Molecule Transition (MHz) (mK) (kms−1) (kms−1) (mKkms−1) η c b TMC-1e C H N=9-8J=9.5-8.5d 85634.012 678(12) 0.58(8) +5.83(4) 417(11) 0.82 4 C H N=9-8J=8.5-7.5d 85672.578 626(11) 0.58(8) +5.74(4) 386(10) 0.82 4 C H− J=9-8 83787.263 1.5a — — 2.8b 0.82 4 CN− J=2-1 224525.061 7.8a — — 14.5b 0.59 C H− J=3-2 249824.940 3.5a — — 6.6b 0.53 2 Barnard1e C H N=9-8J=9.5-8.5d 85634.012 145(9) 1.21(7) +6.79(5) 186(8) 0.82 4 C H N=9-8J=8.5-7.5d 85672.578 133(8) 1.09(7) +6.64(5) 154(7) 0.82 4 C H− J=9-8 83787.263 1.2a — — 4.4b 0.82 4 CN− J=2-1 224525.061 2.8a — — 10.3b 0.59 C H− J=3-2 249824.940 7.9a — — 29b 0.53 2 L134N C H N=9-8J=9.5-8.5 85634.012 131(7) 0.33(4) +2.47(4) 46(5) 0.82 4 C H N=9-8J=8.5-7.5 85672.578 122(6) 0.29(4) +2.38(4) 38(4) 0.82 4 C H− J=9-8 83787.263 2.9a — — 2.9b 0.82 4 CN− J=2-1 224525.061 14a — — 14b 0.59 L1527e C H− J=9-8 83787.263 13(2) 0.62(9) +5.80(3) 8(1) 0.82 4 C H− J=10-9 93096.551 11(2) 0.59(9) +5.90(4) 7(1) 0.81 4 C H N=9-8J=9.5-8.5d 85634.012 947(11) 0.74(6) +5.95(2) 747(11) 0.82 4 C H N=9-8J=8.5-7.5d 85672.578 871(11) 0.77(6) +5.89(2) 712(11) 0.82 4 C H N=11-10J=11.5-10.5d104666.566 681(10) 0.75(6) +5.92(2) 542(10) 0.79 4 C H N=11-10J=10.5-9-5d 104705.109 656(10) 0.70(6) +5.88(2) 487(10) 0.79 4 C H N=12-11J=12.5-11.5 114182.516 712(14) 0.61(4) +5.93(3) 462(13) 0.78 4 C H N=12-11J=11.5-10.5 114221.039 663(13) 0.58(4) +5.85(3) 406(12) 0.78 4 CN− J=2-1 224525.061 2.3a — — 5.5b 0.59 C H− J=3-2 249824.940 3.5a — — 6.7b 0.53 2 L483e C H N=9-8J=9.5-8.5d 85634.012 387(15) 0.60(6) +5.27(4) 249(12) 0.82 4 C H N=9-8J=8.5-7.5d 85672.578 332(15) 0.70(6) +5.33(4) 249(12) 0.82 4 C H− J=9-8 83787.263 4.5a — — 9.3b 0.82 4 CN− J=2-1 224525.061 11.5a — — 28b 0.59 Horseheade C H N=9-8J=9.5-8.5d 85634.012 199(10) 0.86(8) +10.72(4) 181(9) 0.82 4 C H N=9-8J=8.5-7.5d 85672.578 155(8) 0.81(8) +10.69(4) 133(9) 0.82 4 C H 2Π J=29.5-28.5fd 81777.898 13(2) 0.93(16) +10.76(8) 13(2) 0.82 6 3/2 C H 2Π J=29.5-28.5ed 81801.254 10(2) 0.97(21) +10.81(9) 11(2) 0.82 6 3/2 C H− J=9-8 83787.263 1.9a — — 5.0b 0.82 4 C H− J=30-29 82608.285 1.5a — — 4.6b 0.82 6 CN− J=2-1 224525.061 2.2a — — 4.9b 0.59 OrionBare C H N=9-8J=9.5-8.5d 85634.012 58(5) 1.86(11) +10.77(6) 116(7) 0.82 4 C H N=9-8J=8.5-7.5d 85672.578 55(10) 2.54(13) +10.60(9) 149(8) 0.82 4 C H− J=9-8 83787.263 1.2a — — 8.4b 0.82 4 CN− J=2-1 224525.061 3.2a — — 18b 0.59 NGC7023e,f CN− J=2-1 224525.061 6.4a — — 16.4b 0.59 C H− J=3-2 249824.940 9.5a — — 20b 0.53 2 N.– The line parameters have been obtained from Gaussian fits. Number in parentheses are 1σ uncertain- ties in units of the last digits. The observed positions are: TMC-1 α =04h41m41.9s, δ =+25◦41′27.0′′; 2000.0 2000.0 Barnard 1 α =03h33m20.8s, δ =+31◦07′34.0′′; L134N α =15h54m06.6s, δ =-02◦52′19.1′′; 2000.0 2000.0 2000.0 2000.0 L1527 α =04h39m53.9s, δ =+26◦03′11.0′′; L483 α =18h17m29.8s, δ =-04◦39′38.3′′; Horsehead 2000.0 2000.0 2000.0 2000.0 α =05h40m53.7s, δ =-02◦28′04.0′′; Orion Bar α =05h35m22.8s, δ =-05◦25′01.0′′; and NGC 7023 2000.0 2000.0 2000.0 2000.0 α =21h01m32.6s,δ =+68◦10′27.0′′. 2000.0 2000.0 armsnoiseaveragedoverthelinewidth.b3σupperlimitassumingthesamelinewidthastheneutral.cη isB /F ,i.e. b eff eff theratioofT∗ toT .d Lineobserved withaspectral resolutionof80kHz.e TheN=2-1J=5/2-3/2 transitionofCNat A mb 226.8GHzwasobservedinthissourcewithaS/Nratiohigherthan6;linewidthsare0.58kms−1inTMC-1,1.15kms−1 inBarnard1,0.75kms−1inL1527,0.76kms−1inL483,0.70kms−1intheHorsehead,1.76kms−1intheOrionBar,and 0.80kms−1inNGC7023. f TheN=3-2transitionofC Hat262.0GHzwasobservedinNGC7023withaS/Nratiohigher 2 than20andalinewidthof0.65kms−1. dBat1mm.Systemtemperatureswere100-140Kat3mmand every1-2hoursobservingnearbyplanetsorquasars.Thelistof 300-500 K at 1 mm. An autocorrelator was used as the back observedmoleculesandtransitionsisgiveninTable1. end. The spectral resolution at 3 mm was 40 kHz (∼ 0.13 km s−1), exceptforsome observationsofneutralspeciesforwhich 3. Resultsanddiscussion 80 kHz was used (see Table 1), and 80 kHz at 1 mm (∼ 0.10 kms−1).Weusedthefrequencyswitchingtechniquewithafre- MostoftheobservingtimewasdedicatedtothesearchforC H− 4 quency throw of 7.14 MHz. Pointing and focus were checked in TMC-1 and L1527,and for C H− in the Horsehead Nebula. 6 WecouldonlydetectC H− inL1527throughtheJ=9-8andJ 4 = 10-9rotationallines(shownin Fig.1 ata spectralresolution Agu´ndezetal.:Searchforanionsinmolecularsources 3 cations B+ (k ), neutral atoms N0 (k ), and by photodetach- B+ N0 ment (Γ ). Carbon chain anions are known to react rapidly ph withHandOatoms,andsomewhatmoreslowlywithNatoms (Eichelbergeretal., 2007). Assuming rather standard rate con- stants for the other destruction processes (k = 10−7 cm3 s−1 B+ and Γ from Millaretal. 2007), we may use the observed ph [A−]/[A] ratio to derive the relevant electron attachment rate constant k (A). This approach was used by Cernicharoetal. ea (2007) in the context of a chemical model of IRC +10216 to derivek (C H)andk (C H).Herewehaverevisedthatmodel, ea 4 ea 6 includinglossofanionsbyreactionwithatomsotherthanH,to arriveat: k (C H) = 2.5 × 10−8 (T/300)−1/2 cm3s−1 ea 8 k (C H) = 1.4 × 10−8 (T/300)−1/2 cm3s−1 ea 6 (2) k (C H) = 9 × 10−11 (T/300)−1/2 cm3s−1 ea 4 k (C H) < 1.5 × 10−11 (T/300)−1/2 cm3s−1 ea 2 Thevaluesofk (C H)andk (C H)attemperaturesof10- ea 4 ea 6 30 K are similar to those derived in Cernicharoetal. (2007). There exists a clear correlation between the value of k and ea theobservedanion-to-neutralratio,whichsimplyindicatesthat Fig.1.J=9-8andJ=10-9transitionsofC H−observedtoward the latter is mostly controlled by the electron attachment reac- 4 L1527in13.8hand22.1hofintegrationtimerespectively. tion,thedestructionprocessesbeingassumedsimilarforallan- ions.Therateconstantsk obtainedforC HandC Hareofthe ea 6 8 same order of magnitude as the theoretical values reported by of 40 kHz) which are observed with a signal-to-noise ratio in Millaretal.(2007),althoughthevalueforC Hismorethanone T∗ of6and5respectively.Wethusconfirmthetentativedetec- 4 A order of magnitude lower than the theoretical one. In fact, the tion of the J = 9-8line announcedby Sakaietal. (2007a). The chemicalmodelsofMillaretal.(2007)systematicallyoveresti- lines have a Gaussian-like profile with a width of 0.6 km s−1 matetheanion-to-neutralratioforC H−.Theycalculatevalues and are centered at a source velocity of +5.85 km s−1. Similar of the [C H−]/[C H] ratio in IRC +140216, in TMC-1 (at early linepropertiesarealsofoundforC H(seeTable1),forC Hand 4 4 4 6 time) and in the Horsehead Nebula of 0.77 %, 0.13 % and 3.5 C H−(Sakaietal.,2007a),andforothercarbonchainsobserved 6 %respectively,whicharehigherbyafactorof20-100thanthe in L1527(Sakaietal., 2007b). The rmsnoiselevelsreachedin values derived from observations (see Table 3). It seems that the other searches for anions, a few mK in T∗ in most of the A the theory of electron radiative attachment (Terzieva&Herbst, cases,aregiveninTable1. 2000)failsforsmallmolecules(themuchlowerdipolemoment We have calculated beam averaged column densities (see of C H comparedto C H and C H could play a role in dimin- Table 2) under the LTE approximation. In L1527, the column 4 6 8 ishingtheefficiencyforelectronattachment;see Bru¨nkenetal. density of C H− is 1.6 × 1010 cm−2 and that of C H is 1.5 × 4 4 2007b), or that there are important destruction processes for 1014cm−2.Therotationaltemperature(T )obtainedforC His rot 4 small anions so far not considered (e.g. reaction with neutral 14.1±1.6K,whileinthecaseofC H− thetwoobservedlines 4 molecules). suggestsavalueof14Kwhichisinagreementwiththatfound ThepresenceofmolecularanionsseemstobefavoredinIRC forC H.IntherestofthecasesT hasbeenfixed:forthedense 4 rot +10216, where three different anions have been observed with coresL1527andL483we assumedthatT is equalto thegas rot relatively high anion-to-neutral ratios, compared to the other kinetic temperature, 14 K and 10 K respectively (Sakaietal., sources.The ratios are in particularlargerin IRC +10216than 2007b;Tafallaetal.,2000),andadoptedT =5Kforthecold rot inTMC-1,mostprobablyduetoalargerionizationdegreeinthe darkcloudsandT =15KforthePDRs. rot former. The anion-to-neutralratios derived in varioussources from thisandpreviousworksaregiveninTable3.IntheC H−series, ComparingthedensecoresTMC-1andL1527,wenotethat the ratios(orlimitsto ratios) observedforC H− andnC H− are molecular anions are present at a higher level in the latter, as 6 8 indicatedbythe larger[C H−]/[C H] and[C H−]/[C H]ratios. alwaysabove1%.Theyareabouttwoordersofmagnitudelower 6 6 4 4 forC H−andevensmallerforC H−(atleastinIRC+10216).In This has been interpreted by Sakaietal. (2007a) as due to a theca4seofthe[CN−]/[CN]ratio2,thelowestupperlimitsderived higher gas density in L1527 (∼ 106 cm−3; Sakaietal. 2007b) comparedto thatin TMC-1(104 cm−3). An increasein the gas (0.2 % for the lowest) are less constraining than in the case of C H−. density makes the abundance of H atoms decrease more than 2 thatofelectrons1.ThusaccordingtoEq.1(thetermΓ /ndrops The anion-to-neutralratio maybe expressed in terms of the ph foradensecloudshieldedfromUVphotons,)thisresultsinan processes of formation and destruction of the anion. In steady increaseoftheanion-to-neutral-ratiowhichapproachesitsmax- statewehave(seeCernicharoetal.2007): imum value k /k , achieved in the limit when reactions with ea B+ [A−] k [e−] cationsdominatethe destructionof anions,i.e. k [B+] ≫ k [A] = k [B+]+kea [N0]+Γ /n (1) [N0]andassuming[B+]=[e−]. B+ N0 B+ N0 ph where n is the gas volume density and it is assumed that the 1 ItispredictedthatinadensecloudthefractionalabundanceofH anion A− forms by attachment of an electron e− on A (with atomsvarieswiththegasdensityastheinversewhilethatofelectrons a rate constant kea) and can be destroyed by reactions with variesonlyastheinverseofthesquareroot(seee.g.Floweretal.2007). 4 Agu´ndezetal.:Searchforanionsinmolecularsources Table3.Anion-to-neutralratios(in%)invariousmolecularsources IRC+10216 TMC-1 Barnard1 L134N L1527 L483 Horsehead OrionBar NGC7023 [C H−]/[C H]..... <0.0030(1,2) <0.033(6,7)<0.048(6,7) <0.25(9,10) <0.0036(6,7) <0.035(6) 2 2 [C H−]/[C H]..... 0.024 (3) <0.0052(6) <0.024(6) <0.062(6) 0.011 (6) <0.033(6) <0.033(6) <0.064(6) 4 4 [C H−]/[C H]..... 6.2-8.6(3,4) 1.6 (8) 9.3 (11) <8.9 (6) 6 6 [C H−]/[C H]..... 26 (5) 4.6 (8) 8 8 [CN−]/[CN]........ <0.52 (1) <1.9 (6) <0.40(6) <6.5 (6,10) <0.20 (6) <1.3 (6) <0.55(6) <0.17(6) <2.6 (6) R.–(1)unpublishedIRAM-30mdata;(2)Cernicharoetal.2000;(3)Cernicharoetal.2007;(4)Kasaietal.2007;(5)Remijanetal. 2007;(6)Thiswork;(7)Sakaietal.2007b;(8)Bru¨nkenetal.2007b;(9)Morisawaetal.2005;(10)Dickensetal.2000;(11)Sakaietal.2007a. Table2.Columndensities the anion-to-neutral ratio for C H− in the Horsehead Nebula. 4 The discrepancy could lie in the value of k (C H) used in the ea 4 Source Molecule T (K) N(1010cm−2) models,whichisprobablytoolarge.InthecaseofC H−,thepre- rot 6 TMC-1 C H− (C H) 5.0a (5.0a) <3.7b (71000) dictedratio(470%)islargerthanourupperlimitbyafactorof 4 4 CN− (CN) 5.0a (5.0a) <140b (4700) 50.Thefactthatchemicalmodelsreproducemuchbettertheob- C2H− 5.0a <22b served[C6H−]/[C6H]ratioinIRC+10216andTMC-1(withina Barnard1 C4H− (C4H) 5.0a (5.0a) <6b (25000) factorof4)thanintheHorseheadNebulasuggeststhatinPDRs CN− (CN) 5.0a (5.0a) <84b (21000) theglobaldestructionrateoftheanioncouldbeunderestimated. C H− 5.0a <15b 2 This study has shown that molecular anions, despite the L134N C H− (C H) 5.0a (5.0a) <3.8b (6100) 4 4 weaknessoftheirmillimeteremission,maybeusedtoprobethe CN− 5.0a <130b chemicalandphysicalconditionsofinterstellarclouds(seealso L1527 C H− (C H) 13.6 (14.1) 1.6 (15000) 4 4 Floweretal.2007).Furtherlaboratoryandtheoreticalworkare CN− (CN) 14.0a (14.0a) <9.8b (>4800) C H− 14.0a <1.8b necessaryforamorecompleteinterpretationoftheastronomical 2 L483 C H− (C H) 10.0a (10.0a) <2.3b (6900) observations. 4 4 CN− (CN) 10.0a (10.0a) <90b (>7100) Whilewewerewritingupthisletter,webecameawareofa Horsehead C H− (C H) 15.0a (15.0a) <1.0b (3000) paperbySakaietal.(2007c)reportingthetentativedetectionof C46H− (C46H) 15.0a (15.0a) <8.0b (90) the C4H− J = 9-8line in L1527.Theyderivea columndensity CN− (CN) 15.0a (15.0a) <12b (2200) of 1.1 × 1010 cm−2 which is in good agreementwith the value OrionBar C H− (C H) 15.0a (15.0a) <1.6b (2500) obtainedbyus. 4 4 CN− (CN) 15.0a (15.0a) <46b (27000) NGC7023 CN− (CN) 15.0a (15.0a) <37b (1400) Acknowledgements. WewouldliketothanktheIRAMstaffandthe30mtele- C H− (C H) 15.0a (15.0a) <3.1b (8900) scopeoperators fortheir assistance duringtheobservations andN.Marcelino 2 2 N.– Parameters for the neutral species are given in parentheses. forusefuladvicesonthefrequencyswitchingobservingmode.Wealsothank the anonymous referee forhelpful suggestions. Weacknowledge N.Sakai, T. µ(C H−)=3.1D;µ(C H−)=6.2D;µ(C H−)=8.2D;µ(CN−)=0.65 2 4 6 Sakai and S. Yamamoto for communicating their observational results prior D.aAssumedrotationaltemperature.b3σupperlimit. topublication. This workhas been supported bySpanish MECtrough grants AYA2003-2785,AYA2006-14876andESP2004-665andbySpanishCAMun- derPRICITprojectS-0505/ESP-0237(ASTROCAM).MAalsoacknowledges AninterestingdifferencebetweenTMC-1andL1527isthat grantAP2003-4619fromSpanishMEC. the former is a starless quiescent core while the latter har- borsanembeddedprotostar(IRAS04368+2557)with anasso- References ciated bipolar outflow and an infalling envelope of about 30” (Ohashietal.,1997).Theoutflowisrevealedinthehighveloc- Bru¨nken,S.,Gottlieb,C.A.,Gupta,H.,etal.2007a,A&A,464,L33 ity (∼ 3 kms−1) wingsof some molecularlinessuch as HCO+ Bru¨nken,S.,Gupta,H.,Gottlieb,C.A.,etal.2007b,ApJ,664,L43 Cernicharo,J.,Gue´lin,M.,&Kahane,C.2000,A&AS,142,181 J=1-0 (Sakaietal., 2007b). These wings are not present in the Cernicharo,J.,Gue´lin,M.,Agu´ndez,M.,etal.2007,A&A,467,L37 C4H− lines, which rules out the presence of a substantial frac- Dickens,J.E.,Irvine,W.M.,Snell,R.L.,etal.ApJ,542,870 tionofanionmoleculesintheoutflow.Thegravitationalinfallis Eichelberger,B.,Snow,T.P.,Barckholtz,C.,&Bierbaum,V.M.2007,ApJ,667, indicatedbythetwo-peakasymmetry,withabrighterbluepeak, 1283 Flower,D.R.,PineaudesForeˆts,G.,&Walmsley,C.M.2007,A&A,474,923 intheprofilesofsomeopticallythicklinesofc-C H andH CO 3 2 2 Fuente,A.,&Mart´ın-Pintado,J.1997,ApJ,477,L107 (Myersetal., 1995). Such a profile is not visible in any of the Gottlieb, C. A., Bru¨nken, S., McCarthy, M., C., & Thaddeus, P. 2007, C4HandC4H− linesobservedinL1527,althoughtheyareopti- J.Chem.Phys.,126,191101 cally thin.Smallmappingobservationsofthe N=9-8transition Gupta,H.,Bru¨nken,S.,Tamassia,F.,etal.2007,ApJ,655,L57 indicates that C H has an extended distribution (∼ 40”) in all Herbst,E.1981,Nature,289,656 4 Kasai,Y.,Kagi,E.,&Kawaguchi,K.2007,ApJ,661,L61 directionsaroundtheprotostarandthatthelinewidthincreases McCarthy,M.C.,Gottlieb, C.A.,Gupta,H.,&Thaddeus,P.2006,ApJ,652, when approaching to the central position (Sakaietal., 2007b). L141 This latter signature was also observed by Myersetal. (1995) Millar,T.J.,Walsh,C.,Cordiner,M.A.,etal.2007,ApJ,662,L87 in the c-C H 2 -1 line and was interpretedas due to infall Morisawa,Y.,Hoshina,H.,Kato,Y.,etal.2005,PASJ,57,325 3 2 1,2 0,1 motion.Unfortunately,the ratherweak C H− linesobservedin Myers,P.C.,Bachiller,R.,Caselli,P.,etal.1995,ApJ,449,L65 4 Neufeld,D.A.,Schilke,P.,Menten,K.M.,etal.2006,A&A,454,L37 L1527leavelittlechancetomaptheiremission. Ohashi,N.,Hayashi,M.,Ho,P.T.P.,&Momose,M.1997,ApJ,475,211 In the PDRs, the upperlimits onthe anion-to-neutralratios Pety,J.,Teyssier,D.,Fosse´,D.,etal.2005,A&A,435,885 are not as low as in the rest of the sources due to the lower Remijan,A.J.,Hollis,J.M.,Lovas,F.J.,etal.2007,ApJ,664,L47 Sakai,N.,Sakai,T.,Osamura,Y.,&Yamamoto,S.2007a,ApJ,667,L65 abundanceofcarbonchains.Nevertheless,wefindvaluesmuch Sakai, N., Sakai, T., Hirota, T., & Yamamoto, S. 2007b, ApJ, preprint lower than those predicted by chemical models. In particular, doi:10.1086/’523635’ Millaretal. (2007) overestimate by more than a factor of 100 Sakai,N.,Sakai,T.,&Yamamoto,S.2007c,ApJ,inpress Agu´ndezetal.:Searchforanionsinmolecularsources 5 Tafalla,M.,Myers,P.C.,Mardones,D.,&Bachiller,R.2000,A&A,359,967 Terzieva,R.,&Herbst,E.2000,Int.J.MassSpectr.,201,135 Teyssier,D.,Fosse´,D.,Gerin,M.,etal.2004,A&A,417,135