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Looking for brown dwarfs in wide field surveys: Extending CFBDS to the Near InfraRed Philippe Delorme St Andrews University Research Fellow working with:

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Presentation on theme: "Looking for brown dwarfs in wide field surveys: Extending CFBDS to the Near InfraRed Philippe Delorme St Andrews University Research Fellow working with:"— Presentation transcript:

1 Looking for brown dwarfs in wide field surveys: Extending CFBDS to the Near InfraRed Philippe Delorme St Andrews University Research Fellow working with: T.Forveille, X.Delfosse (LAOG)‏, C. Willott(U Toronto), C.Reylé(LAOB), L. Albert (CFHT), E. Artigau(Gemini)‏

2 Canada-France Brown Dwarfs Survey => Looks for brown dwarfs in a wide field far-red survey => Carried out by CFHT, 3.6 m telescope => Uses Megacam, 1x1 degree optical camera => Covers about 900 sq degrees in i,z => Over 50 000 000 astrophysical sources: Wealth of deep optical data CFBDS(1/6)Ultracool Dwarfs in the NIR

3 Science objectives(1/2)‏ Constrain stellar formation models at substellar masses =>Young clusters: ~constrained =>Field: Biased by low statistics and age-mass degeneracy - Objects from the solar neigbourhood : ''average'' of the disc Need to build a large sample discovered in a simple and homogeneous way CFBDS(2/6)Ultracool Dwarfs in the NIR

4 Link stellar atmosphere with planetary atmospheres => Y dwarfs, the missing link between stars and planets. => Put constraints on theoretical models: probe the temperature range between the coldest brown dwarfs (600-700K) and Jupiter (100K). From Burgasser et al, 2003 From Kulkarni, 1997 Science objectives ‏(2/2)‏ CFBDS(3/6)Ultracool Dwarfs in the NIR

5 Analysis principle =>Candidate identification in far-red (CFHT). Good i'-z' dynamics L/T dwarfs: i-z > 1.5 Our selection: i-z > 1.7 Spectral type i'-z' color CFBDS(4/6)Ultracool Dwarfs in the NIR

6 Analysis summary Candidate selection * PSF fitting analysis using our modified * PSF fitting analysis using our modified Sextractor on i' and z' images. => ~50000 sources per square degree * Selection of red candidates and filtering based on the c 2 from the PSF-fitting = > 10-50 candidates per square degree * Visual inspection of our candidates, supernovae and asteroid rejection = > 1-3 candidates per square degree * J-band follow-up to confirm candidates = > ~0.5 brown dwarfs per square degree CFBDS(5/6)Ultracool Dwarfs in the NIR * Injection of fake brown dwarfs modelled from the local PSF into science images = > average completeness of ~75% for a magnitude limited sample

7 Results Summary All objects with J-band follow-up Photometric follow-up of the most promising (stars). Up to now, ~50% of T dwarfs have spectra. ~300 L dwarfs 40 T dwarfs spectra (Albert et al, in prep)‏ From Albert et al, in prep. CFBDS(6/6)Ultracool Dwarfs in the NIR

8 CFBDS-Wircam Survey

9 Brown dwarfs luminosity function Problem of low stat at the faint end. CFBDS: 2 Bds later than T8 ---> ~100 Bds in the same temperature range within 15 pc of the sun ! Need to find more ultracool Bds in a statistically-friendly survey From Reyle et al, in prep. CFBDSUltracool Dwarfs in the NIR(1/7)

10 Why a wircam extension to CFBDS? Keep CFBDS advantages: * Optical data: Strong * Optical data: Strong selection criteria => 42 T dwarfs observed in spectroscopy = 42T dwarfs confirmed * Candidates are bright enough in NIR for such spectroscopic characterization * Simple color-color selection criteria: possible to derive reliable completeness => Use fake brown dwarfs modelled from the local PSF injected in science images. * Good for statistics! Overcome CFBDS main drawback: * Not sensitive enough to l ater than T8 dwarfs: few photons left in the far-red! =>Need NIR detection ! backed by CFBDS homogeneous deep optical data CFBDSUltracool Dwarfs in the NIR(2/7)

11 Analysis Principle CFBDSUltracool Dwarfs in the NIR(3/7) => similar to CFBDS z-J selection instead of i-z Our selection: z-J>3.5 High completeness

12 Analysis summary Candidate selection * PSF fitting analysis using our modified * PSF fitting analysis using our modified Sextractor on z' and J images. => ~30000 sources per square degree * Selection of red candidates and filtering based on the c 2 from the PSF-fitting = > 3-10 candidates per square degree * Visual inspection of our candidates, supernovae and asteroid rejection = > 0-2 candidates per square degree * J-band follow-up to confirm candidates = > ~0.25 T dwarfs per square degree CFBDSUltracool Dwarfs in the NIR(4/7) * Injection of fake brown dwarfs modelled from the local PSF into science images = > To add to the pipeline! First estimates >~80% completeness for z-J>3.8

13 Wircam survey status * Wircam J-band observations of CFBDS fields =>180 sq degrees observed, more data to come. * J vega =19.6 at 10 sigmas => 4-8 times CFBDS sensitivity to ultracool brown dwarfs. * Most earlier than T7 dwarfs have z' band counterpart =>Ultracool brown dwarfs are J-band dropouts * Short J-band follow-up at NTT to eliminate artefacts =>H and K photometry to start physical characterization CFBDSUltracool Dwarfs in the NIR(5/7)

14 Preliminary results * Reduction and analysis pipeline working * Selects candidates with z-J>3.5 * First follow up of candidates in a pilot 24 degrees area in march 2009 * Confirmed 6 T dwarfs and one ultracool brown dwarf * Spectroscopic characterisation with ongoing DDT observations CFBDSUltracool Dwarfs in the NIR(6/7)

15 Summary CFBDS found a steep increase at the faint-end of the luminosity function This draws on only 2 identifications CFBDSUltracool Dwarfs in the NIR(7/7) The wircam extension will discover more ultracool brown dwarfs *It will provide stronger statistical significance * Possibility to find even cooler objects and probe new atmosphere temperature range Very preliminary results: 1 ultracool dwarf on 24 sq degrees: Either we keep being lucky either there are many cool brown dwarfs to discover in the close solar neighbourhood !

16 Thanks for your attention

17 Etoiles artificielles IntroductionAnalyse d'image(13/15)RésultatsPerspectives

18 Complétude et contamination: résultats Pourcentage d'étoiles artificielles identifiées par Sextractor et sélectionnées par le pipeline standard, par intervalle de couleur et de magnitude. IntroductionAnalyse d'image(15/15)RésultatsPerspectives

19 From cool brown dwarfs to giant planets: more and more complex atmosphere chemistry ! From Lodders et al.2006 From brown dwarfs to planets Dust clouds ~2000K CH 4 Absorption ~1400K NH 3 Absorption ~500K-600K ? The Survey(4/9)Ultracool Dwarfs

20 From cool brown dwarfs to giant planets: Age, mass, temperature From Lyon Model The Survey(5/9)Ultracool Dwarfs

21 Spectral indices Flux ratio centered on molecular absorption bands. => Trace associated physical parameters. The SurveyUltracool Dwarfs(2/6)

22 Discovery of the coldest brown dwarf Spectral indices of CFBDS0059 compared with those of the coldest BD known. From Delorme et al, 2008a The SurveyUltracool Dwarfs(3/6)

23 A new absorption band From Delorme et al, 2008a Left: H-band binned spectra of ultra-cool BDs. Right: Model spectra with (red) and without (black) ammonia absorption. The SurveyUltracool Dwarfs(4/6)

24 Is this actually NH 3 ? Left: Flux ratio between CFBDS0059 and Gl570D (black) together with NH 3 transmission (red). Right: Same with water transmission (red)‏ From Delorme et al, 2008a Left: Flux ratio between ULAS0034 and Gl570D (black) together with NH 3 transmission (red). Right: Same with water transmission (red)‏ The SurveyUltracool Dwarfs(5/6)

25 M, L and T dwarfs Naine M Naine L Naine T Introduction(2/7)Analyse d'imageRésultatsPerspectives

26 J-band follow-up i'-z'candidates are: - Brown dwarfs and high redshift quasars - Contamination: M dwarfs and false detections Color-color diagram J band follow-up allows to confirm or discard candidates. => Collaboration with quasar specialists. From Delorme et al, 2008b The Survey(8/9)Ultracool Dwarfs

27 J-band photometry: sample entirely followed-up Resulats as of 01/09/2008 Color-color diagram of the first 200 square degree completely followed-up. Dashed ligne : Average color of know object. Gray area: color scattering of known objects. The SurveyGeneral Results(1/3)Ultracool Dwarfs

28 Sextractor and image analysis Candidates filtering - Color: i'-z'>1.7 - Signal to noise: mag error < 0.1 in z' band - Chi2 filtering in z' - No bad pixels or cosmic rays - No saturation And of course a final visual check IntroductionImage AnalysisResultsDevelopments Chi2 used for filtering candidates: In red, selection without chi2, on 70 sq deg. In blue, selection on 70 sq deg, with chi2 filtering. In green, remaining candidates after manual analysis, including removing some PSF like contamination.

29 Une naine T binaire Suivi sytématique en optique adaptative LGS des naines T CFBDS les plus proches. => Collaboration avec Mike Liu (IFA)‏ IntroductionAnalyse d'imageRésultats(10/11)Perspectives Séparation : 0.055 '' Naines T2.5 + T6.5 Période estimée: 10-20 ans Masse dynamique ! D'après Liu et al, en préparation

30 Fit de PSF et photométrie d'ouverture Image BruteModèle de PSFRésidus IntroductionAnalyse d'image(3/15)RésultatsPerspectives

31 Analyse visuelle * Elimination des supernovae, astéroïdes, rayons cosmiques et mauvais pixels. => images à des dates différentes. IntroductionAnalyse d'image(8/15)RésultatsPerspectives

32 Fonction de luminosité préliminaire des naines brunes du champ. Répartition en distance des naines brunes de l'échantillon avant (traits pleins) et après correction de la complétude et de la contamination (pointillés)‏ Fonction de luminosité préliminaire en bande z' des naines brunes du champ à partir de l'analyse du CFBDS. IntroductionAnalyse d'imageRésultatsPerspectives(1/4)‏ D'après Reylé, Delorme et al, en préparation

33  Les naines T tardives et Y sont beaucoup plus lumineuses en bande J  180 degrés carrés couverts en bande J sur des champs observés par le CFBDS en bande z'.  Les images du CFBDS assurent une détection à mieux que 5 s de toutes les naines plus précoces que T7.  Attentes: 2 à 6 naines Y et plusieurs dizaines de naines T. Un survey wircam ciblé sur les naines Y IntroductionAnalyse d'imageRésultatsPerspectives(3/4)‏

34 z-J Vs Y-J

35 L Dwarfs with subsolar metallicity photometric indicators Search for early L subbdwarfs hampered by late M contamination. Search for late L/early T subdwarfs showed some possible candidates: ongoing observations. Mid and late T are systematically observed in spectroscopy. 2/11 Color-color plot of CFBDS candidates

36 Notre relevé: le CFBDS Couvre ~2.5% du ciel. Origines des données: CFHTLS (1/3), RCS-2(1/4), temps PI (le reste) Introduction(7/7)Analyse d'imageRésultatsPerspectives D'après Delorme et al, 2008b

37 A puzzling T dwarf CFBDS1500 – black- stands out among others CFBDS T dwarfs Discrepancies in every spectroscopic band No 1.25 μ m Potassium doublet Many clues point toward sub- solar metallicity 3/11

38 Kinematics: CFBDS1500 facts Very high apparent proper motion: RA: +0.709 ".yr -1 DEC: -0.165 ".yr -1 How distant is it? => Photometric distance is 40-65 pcs => Velocity is in the 135-225 km.s -1 range Very high absolute proper motion points toward an old object, likely with low metallicity. 4/11

39 Kinematics: population statistics We favored the 40-50 pcs range since subsolar metallicity decreases flux. Left: Besancon model stellar population modelisation. Red: thin disc, green: thick disc, blue: halo. Age and average metallicity of Milky Way's populations from Robin et al, 2003. Besancon stellar population model was used to derive the kinematic probability that CFBDS1500 belongs to a given population. 5/11

40 Spectral type estimation Spectral indices range from T3 to T6 Comparison to templates spectra is also confusing: Y-band: earlier than T3 J-band: T4 H-band: T5 K-band: later than T6 Metallicity strongly modifies Y and K bands flux. Spectral type from J and H points to T4 to T5 6/11

41 Physical parameters(1/2)‏ Teff and Log g grids from Burrows et al, 2006, anchored on SDSS1254 parameters. In red: M/H=-0.5, in black: M/H=0. 2MASS0937 is likely the most metal-deficient T dwarf known: M/H=-0.2, Teff=800 and Log g= 5.4 according to Burgasser et al, 2006. 2MASS2254 is the T4 solar-metallicity templates that we use to fit CFBDS1500. 7/11

42 Physical parameters(2/2)‏ Metallicity color grid for CFBDS1500 and 2MASS0937. The parameter space of log g for CFBDS1500 is restricted to ~5.5 Points to CFBDS1500 being more metal deficient than 2MASS0937, by ~0.2dex Derived physical parameters: Log g~5.5, Teff~1025K, M/H~ -0.3 to -0.4 Slightly lower gravity favors M/H~-0.4 to -0.5 8/11

43 Potassium doublet Up: J-band comparison between CFBDS1500 and 2MASS2254. Down: Model J-band spectra for CFBDS1500 and 2MASS2254 parameters. Gravity alone cannot account for the potassium doublet disappearance. Potassium points to M/H= -0.5 Redward shift of J-band peak predicted by models is not observed. 9/11

44 Comparison to models Up: Whole NIR comparison between CFBDS1500 and 2MASS2254. Down: Model NIR spectra for CFBDS1500 and 2MASS2254 parameters. Low metallicity models do not fit the whole CFBDS1500 spectra. Qualitative evolution in Y, H and K band well matched Redward shift of J-band and blueward shift of H band are not observed. 10/11

45 Summary 11/11 CFBDS1500 is the lowest metallicity T dwarf observed. New benchmark on the way toward T subdwarfs Matches many model predictions but not all Derived parameters are: M/H = [-0.3,-0.5] Log g = [5.4,5.5] Teff = [1000K-1050K] Without taking into account systematic errors from models CFBDS1500 likely belongs to the thick disc : Age = ~11Gyrs

46 Quasars ! Une collaboration fructueuse: répartition de l'analyse et des observations. IntroductionAnalyse d'image(11/15)RésultatsPerspectives Optical spectroscopy of 4 z>6 QSOs (D'après Willott et al, 2007)‏ D'après Willott, Delorme et al, 2007


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