The r-Process and Chronometers

We present detailed abundance observations of the metal-poor ([Fe/H] = --2.0) Galactic halo star BD+17 3248. We have detected gold in this star, for the first time in any halo star. We also detected a weak line at 3859.60 A in the spectrum of BD+17 3248 th

Ther-ProcessandChronometers

JohnJ.Cowan1,ChristopherSneden

12andJamesW.Truran3

arXiv:astro-ph/0204294v1 17 Apr 2002DepartmentofPhysicsandAstronomy,UniversityofOklahoma,Norman,OK730192DepartmentofAstronomyandMcDonaldObservatory,UniversityofTexas,Austin,TX787123DepartmentofAstronomy&Astrophysics,UniversityofChicago,Chicago,IL606371IntroductionWehavebeenexaminingtheabundancedistributionsinmetal-poorGalactichalostarstryingtoidentify,andunderstand,thesignaturesoftheslow-andrapid-neutroncaptureprocesses(i.e.,thes-andther-process).DetailedstudieshavebeenmadeofthestarsCS22892–052andHD115444[3].Inourlatestworkwehaveaddedtothislistthemetal-poor([Fe/H]=–2.0)halostarBD+17 32482ObservationsandAbundanceTrendsinBD+17 3248Usingbothground-based(KeckandMcDonald)andspace-based(HubbleSpaceTelescope,HST)observationswehaveobtainedhighresolution,highsignal-to-noisespectraofBD+17 3248.TheelementgoldhasbeendetectedinBD+17 3248asshowninFigure1.ThisHSTSTISobservationshowsacomparisonbetweenBD+17 3248andHD122563.Whilethespectraappearsomewhatsimilarinthisregion,thisisduetothecomplexsetofabsorptionlinesthatcontributetothetotalfeaturenearthiswavelength.Speci cally,thereisanOHlinenearthe2675.94 Agoldline.ThisresultsinsomeblendingofthegoldfeatureforBD+17 3248.TheOHabsorption,however,ismuchstrongerthroughouttheUVspectrumofHD122563andissolelyrepsonsibleforthestronglineat2676.0 Ainthisstar.Wenotethatthethisgold

detectioninBD+17 3248isthe rstinanymetal-poorhalostars.

WeshowinFigure2theentireabundancedistributionofBD+17 3248.Thisincludestheelementuranium.Wehavedetectedaweaklineat3859.60 AinthespectrumofBD+17 3248thatwetentativelyidentifywiththiselement.Thiswouldbeonlythesecondsuchdetection,afterCayreletal.inanymetal-poorhalostars.

WenoteinFigure2thattheheavierneutron-captureelements,Z≥56,includingnowthe3rdr-processpeakelements,allfallonthescaledsolarsystemr-processdistribution.ThisisthesamepatternthatwasseenpreviouslyinCS22892–052andHD115444[6].Thisstronglysuggestsarobustprocessfortheproductionoftheseheavierneutron-captureelements.VeryrecentlytheeuropiumisotopicabundancefractionshavebeendeterminedforBD+17 3248,CS22892–052andHD115444[7].Thosefractionsareallinexcellentagreementwitheachotherandwiththeirvaluesinthesolarsystem.Thus,thereappearstobeaconsistencyintheproductionoftheheavierneutron-captureelementsand,atleastforeuropium,theisotopes.WealsonotethetrendofthelighterneutroncaptureelementsinFigure2.SimilarlytothecaseofCS22892–052,theelementswithZ=40–50inBD+17 3248fallbelowthescaledsolarsystemcurvethat tstheheavierneutron-captureelements.Thismightbeexplained

第1页下一页