A W 2 ONLY SEARCH FOR LATE T AND Y DWARFS IN WISE Joana Gomes University of Hertfordshire David Pinfield, Avril Day-Jones, Ben Burningham, Maria Teresa Ruiz, Sandy Leggett, Ruby Kurtev, Mariuz Gromadzki, Cátia Cardoso, Nicolas Lodieu

O VERVIEW Introduction Candidate selection Rejection methods Results Summary and future work

Y DWARFS 14 Y dwarfs discovered (Cushing et al. 2011, Kirkpatrick et al. 2012, Tinney et al. 2012) Extremely red colours (W1-W2 > 3) Mainzer et al. 2011

Y DWARFS 14 Y dwarfs discovered (Cushing et al. 2011, Kirkpatrick et al. 2012, Tinney et al. 2012) Extremely red colours (W1-W2 > 3) Cushing et al. 2011

W HAT DO THEY LOOK LIKE ? Cushing et al. 2011

C ANDIDATE SELECTION 1.Select W2 detections with S/N ≥ 10. In WISE this corresponds to W2 = [15 – 15.7]. Taking into account Y colours: W1 – W2 > 3.9 W2 – W3 = [ ] W2 – W4 ≥ 5 it means we do not expect detections, at a level of 2 , in the W1,W3 and W4 bands. 2. No 2MASS source within 3 arcseconds of WISE source 3. Measured in at least 8 individual exposures 4. Removed sources towards redenned regions of sky

C ONTROL S AMPLE Control sample of isolated, point- like, non-variable and non-moving sources. Combination of SDSS and WISE: Avoided galactic latitudes g < 20 g – r < 0.3 proper motions > 20 mas yr -1 cross-match with 1 arcsecond to avoid mis-matches avoid quasars with colour cuts Wu et al. 2012

1 – Profile fit photometry rejection method Assess how point-like each source is. R EJECTION METHODS 6067 sources 4673 sources 3263 sources 904 sources 52 sources

1 – Profile fit photometry rejection method Assess how point-like each source is. R EJECTION METHODS 6067 sources 4673 sources 3263 sources 904 sources 52 sources

R EJECTION METHODS 2 –Photometric uncertainty rejection method Compares the integrated flux uncertainty (w2sigmpro) with the standard deviation of W2 fluxes from the individual exposures (w2sip1) 6067 sources 4673 sources 3263 sources 904 sources 52 sources

R EJECTION METHODS 3 – Detection number rejection method Fraction of individual W2 frames in which the source is detected 6067 sources 4673 sources 3263 sources 904 sources 52 sources

V ISUAL INSPECTION 6067 sources 4673 sources 3263 sources 904 sources 52 sources Excluded: artefacts (such as diffraction spikes, optical ghosts, glints, halo associations) blended sources extended structures (galaxies, nebulae)

E XPANDING THE SEARCH Extended the analysis to S/N = [8 – 10] After applying rejection methods – 3252 sources Compare the separation of the sources with the proximity to a 2MASS bright source – most of the sources are halo associations. S/N > 10 = 52 S/N = [8-10] = 106 Total = 158 candidates

N EW SAMPLE S/N > out of 52 candidates in K12 S/N = [8-10] - only 8 out of 106 in K12 Difference comes from the criterion that defines the minimum number of individual exposures where the source should be detected.

A DDITIONAL P HOTOMETRY We have used multiple facilities in our ongoing follow-up campaign. UKIDSS/UHS and VISTA surveys J-band at FourStar, Magellan telescope J-band at NICS, TNG telescope J-band at HAWK-I, VLT Mid-IR obtained at the Spitzer, [3.6] and [4.5] bands Low-RES spectroscopy, with FIRE, Magellan telescope

R ESULTS – C ANDIDATE 1 Top: WISE W2 and W2 Bottom: FourStar and UKIDSS Source not detected in Y, H and K bands (LAS) Combining UKIDSS and FourStar we find p.m = 1.3 arcsec yr -1 W1 – W2 > 3.27 J – W2 =.489 ± 0.15 [3.6] – [4.5] = 1.99 ±0.04 Spectral type of T9 or later.

R ESULTS – C ANDIDATE 2 The brightest new object in the sample with W2 = Proper motion estimated with different combinations of epochs. Final result obtained with UKIDSS and HAWK-I images. p.m. = 1.89 ± 0.04 arcsec yr -1 Spitzer ch1 (2013.1)Spitzer ch2 (2013.1)

S PECTROSCOPY NIR spectrum obtained with FIRE

C OMPARING WITH T9 AND Y0 T9 ± 0.5 dwarf NIR spectrum obtained with FIRE

K INEMATICS Distances estimated with the relations between absolute magnitude and spectral type considering single object and binarity. J + H band distances – pc Y + mid-IR distances pc Space motion suggesting it's a thick disk/halo candidate.

C OLOURS Comparison sample from Leggett et al Peculiar Y-J and H-W2 colours

C ONCLUSIONS We developed a new method to identify late T and Y dwarfs in the WISE database. Identified 158 candidates, with 90% falling outside the K12 criteria in the lowest S/N sample Discovery of a thick disk/halo candidate with spectral type T9 ± 0.5 Obtain a higher S/N spectrum of Candidate 2 and a spectrum for Candidate 1. Obtain parallaxes measurements for the Candidate 2 in order to put better constraints on distance. Continue the follow up campaign and assess the nature of other interesting candidates. F UTURE WORK

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