Exploring the Low-Mass Initial Mass Function in Young Clusters and Star-Forming Regions Andrew Burgess To cite this version: Andrew Burgess. Exploring the Low-Mass Initial Mass Function in Young Clusters and Star-Forming Regions. Astrophysics [astro-ph]. Université de Grenoble, 2010. English. tel-00576460 HAL Id: tel-00576460 https://tel.archives-ouvertes.fr/tel-00576460 Submitted on 14 Mar 2011 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. UNIVERSITE´ DE GRENOBLE THESE` pour obtenir le grade de DOCTEUR DE L’UNIVERSITE´ DE GRENOBLE Sp´ecialit´e: ASTROPHYSIQUE ET MILIEUX DILUES´ Arrˆet´es minist´eriels du 7 aoˆut 2006 pr´esent´ee et soutenue publiquement par A.S.M.BURGESS le 15i`eme decembre´ 2010 Exploring the Low-Mass Initial Mass Function in Young Clusters and Star-Forming Regions1 - Exploration de la fonction de faible masse initiale dans les amas jeunes et les regions´ de formation stellaire Th`ese dirig´ee par Jerome Bouvier et coridig´ee par Estelle Moraux JURY M. Jean-Louis MONIN Pr´esident Mme. France ALLARD Rapporteur M. Eduardo MARTIN´ Rapporteur M. J´erˆome BOUVIER Examinateur M. Nicolas LODIEU Examinateur Mme. Estelle MORAUX Examinateur Th`ese pr´epar´ee au sein du Laboratoire d’Astrophysique et Observatoire de Grenoble dans l’Ecole´ Doctorale de Physique UMR-5571 (OSUG/UJF/CNRS), BP 53, F-38041 Grenoble Cedex 9 1Based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Research supported by the Marie Curie Research Training Network ”CONSTELLATION” under grant no. MRTN-CT-2006-035890 2 Exploring the Low-Mass Initial Mass Function in Young Clusters and Star-Forming Regions Andrew S. M. Burgess A thesis submitted to the University of Joseph Fourier in accordance with the requirements of the degree of Doctor of Philosophy in the Ecole Doctorale Laboratoire d’Astrophysique et Observatoire de Grenoble 414 Rue de la Piscine Domaine Universitaire 38400 Saint-Martin d’Heres´ FRANCE 15th October 2010 ∼ 50, 000 words Abstract The determination of the lower-end of the initial mass function (IMF) provides strong constraints on star formation theories. We report here on a search for isolated planetary-mass objects in the 3 Myr-old star-forming region IC 348 and on a wider survey of the 30 Myr-old open cluster IC 4665. IC 4665 is a fairly young (∼30Myr) star cluster and is 356pc distant towards the constellation Ophiuchus. Proper motion is low at -4 to -7.5 mas/yr and extinction is also low and present at AV ∼ 0.59 ± 0.15 mag. WIRCam Y , J, H and Ks observations were made using the CFHT and spanned 10 cluster fields (of total footprint ∼1.1sq.deg) and two control fields of 20′x20′ each. Colour/magnitude diagrams were used to compare the catalogue objects to the 30 and 50 Myr BT-SETTL models for photometric selection. Further colour/colour diagrams were then iteratively used to further filter these objects into a final cluster candidate member list, with 590 unique objects. Contamination by field stars can be assessed using the control fields and M- and L- dwarf space densities. This part requires further analysis. Probing into the lowest-mass end of the IMF in IC 348 required deep, narrowband CH4off and CH4on images. These were were obtained with CFHT/WIRCam over 0.11 sq.deg. over the ′ central part of IC 348, along with z , J, H and Ks band images. Young T-dwarfs were identified from their 1.69 µm methane absorption bands. Three faint T-dwarf candidates were detected with CH4on−CH4off colours >0.4 mag. Extinction was estimated for each candidate and lies in the range AV ∼ 5 − 12 mag. Comparisons with T-dwarf spectral models, and colour/colour and colour/magnitude diagrams, reject two of the three candidates because of their extreme z′ − J blueness. The one remaining object is not thought to be a foreground field dwarf because of a number density argument and also its strong extinction AV ∼ 12 mag, or thought to be a background field T-dwarf which would be expected to be much fainter. Models and diagrams give this object a preliminary T6 spectral type. With a few Jupiter masses, the young T-dwarf candidate reported here is potentially amongst the youngest, lowest mass objects detected in a star-forming region so far. Its frequency is consistent with the extrapolation of current lognormal IMF estimates down to the planetary mass domain. iii Le Resum´ e´ en Franc¸ais La d´etermination de l’extr´emit´einf´erieure de la fonction de masse initiale (FMI) pr´evoit de fortes contraintes sur les th´eories de la formation des ´etoiles. IC4665 est un amas d’´etoile jeune (30Myr) et il a situe 356pc de la Terre. L’extinction est AV ∼ 0.59 ± 0.15 mag. WIRCam Y, J, H et K observations ont ´et´efaites par le CFHT et a comprise 10 champs (de 1.1sq.deg totale) et deux zones de contrle de 20’x20’ chacun. Diagrammes couleur/magnitude et couleur/couleur ont ´et´eutilis´ees pour comparer les candidats s´electionn´es par les mod`eles BT-SETTL 30 et 50Myr. Les images CH4off et CH4on ont ´et´eobtenus avec CFHT/WIRCam plus 0.11 sq.deg. dans IC348. Naines-T ont ensuite ´et´eidentifi´es `apartir de leur couleur de 1.69µm d’absorption du m´ethane et trois candidats nain-T ont ´et´etrouv´ee avec CH4on−CH4 >0.4 mag. Extinction a ´et´e estim´ee `aAV ∼ 5 − 12 mag. Les comparaisons avec les naines-T mod`eles, et des diagrammes couleur/couleur et magnitude, rejeter 2 entre 3 candidats en raison de leur extrˆeme z′ − J coleur. L’objet reste n’est pas consid´er´ecomme un nain avant l’amas en raison d’un argument de densit´e en nombre ou l’extinction forte AV ∼ 12 mag, ni d’ˆetre un champ de fond nain-T qui serait devrait ˆetre beaucoup plus faible. Les mod`eles et les sch´emas de donner cet objet un type T6 pr´eliminaires spectrale. Avec un peu de la masse de Jupiter, ce jeune candidat nain-T est potentiellement parmi les plus jeunes, des objets de masse plus faible d´etect´ee dans une r´egion de formation d’´etoiles `ace jour. Sa fr´equence est conforme `al’extrapolation du courant lognormal FMI estime `aau domaine de masse plan´etaire Contents Abstract.......................................... iii TableofContents .................................... vii ListofFigures...................................... xi ListofTables ....................................... xv Acknowledgments.................................... xvii 1 Introduction and Review 1 1.1 Overview ...................................... 1 1.2 Introduction.................................... 3 1.2.1 Temperature & Luminosity . 4 1.2.2 Absorption&Emission .......................... 7 1.2.3 Extinction & Reddening . 8 1.3 Stellar and Sub-Stellar Mass Objects . ........ 12 1.3.1 StellarObjects ............................... 12 1.3.2 Sub-StellarObjects. 12 1.3.3 Models ................................... 14 1.3.4 Youth & Gravity Considerations . 18 1.4 Initial Mass Function (IMF) . 18 1.4.1 Observations ................................ 20 1.4.2 Formation Mechanisms & Simulations . 22 1.5 Motivation...................................... 25 1.5.1 Observational Strategy . 26 1.6 Summary ...................................... 28 1.7 R´esum´e ....................................... 31 2 Data Acquisition and Pipeline Development 33 2.1 Instrumentation & Observations . ...... 34 2.1.1 Principal Observatory - Canada France Hawaii Telescope(CFHT) . 34 2.1.2 ObservedData ............................... 38 vii 2.2 Infrared Surveys & Astronomical Databases . ......... 45 2.2.1 2MicronAllSkySurvey(2MASS). 45 2.2.2 UKIRT Infrared Deep Sky Survey (UKIDSS) . 45 2.2.3 Spitzer Space Telescope . 46 2.2.4 Online Respositories . 47 2.3 PipelineDevelopment. 48 2.3.1 SExtractor First-Pass . 49 2.3.2 SExtractor Optimisation . 50 2.3.3 Point Source Function Extractor (PSFEx) . ...... 53 2.3.4 PSFExOptimisation ............................ 55 2.3.5 SExtractor Second-Pass . 55 2.3.6 Catalogue Amalgamation . 56 2.3.7 Calibration ................................. 56 2.4 Summary ...................................... 62 2.5 R´esum´e ....................................... 63 3 Sub-Stellar Census of the Open Cluster IC 4665 65 3.1 Introduction.................................... 66 3.1.1 TheOpenClusterIC4665 ...... ...... ..... ...... .. 67 3.2 Object Catalogue Extraction . ..... 71 3.2.1 DataTesting ................................ 71 3.2.2 Specifics of Object Detection . 72 3.2.3 Flags .................................... 74 3.3 Calibration ..................................... 75 3.3.1 Short&LongAmalgamation. 81 3.3.2 Completeness................................ 82 3.4 CandidateSelection... ..... ...... ...... ..... ..... 87 3.4.1 Colour/Magnitude Diagram Selection . ..... 87 3.4.2 Colour/Colour Diagram Selection . 88 3.4.3 CandidateCleaning. 88 3.5 Discussion...................................... 92 3.5.1 RecoveredKnownMembers . 92 3.5.2 Selection Considerations . 92 3.5.3 Contamination ............................... 94 3.6 Summary ...................................... 96 3.7 R´esum´e ....................................... 97 4 Young T-dwarf Candidates in IC 348 99 4.1 Introduction & Context . 99 4.1.1 Searching for T-dwarfs . 100 4.1.2 The Young Star-Forming Region IC 348 . 101 4.2 SpecificDataTreatment. 103 4.2.1 Photometric Catalogue . 104 4.2.2 Photometric Comparison . 104 4.2.3 MethanePhotometry ............................ 106 4.3 Results........................................ 109 4.3.1 T-dwarf Candidate Selection . 109 4.3.2 Reddening & Spectral Type Estimates .