A W2 ONLY SEARCH FOR LATE T AND Y DWARFS IN WISE

Joana GomesUniversity of Hertfordshire

David Pinfield, Avril Day-Jones, Ben Burningham, Maria Teresa Ruiz, Sandy Leggett, Ruby Kurtev, Mariuz

Gromadzki, Cátia Cardoso, Nicolas Lodieu

OVERVIEW

• 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

CANDIDATE SELECTION1. Select W2 detections with S/N ≥ 10. In WISE this corresponds

to W2 = [15 – 15.7]. Taking into account Y colours:

W1 – W2 > 3.9W2 – W3 = [1.7-2.6]

W2 – W4 ≥ 5

it means we do not expect detections, at a level of 2s, 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

1 – Profile fit photometry rejection method

Assess how point-like each source is.

REJECTION METHODS 6067 source

s

4673sources

3263sources

904sources

52 sources

1 – Profile fit photometry rejection method

Assess how point-like each source is.

REJECTION METHODS 6067 sources

4673source

s

3263sources

904sources

52 sources

REJECTION METHODS2 –Photometric uncertainty rejection method

Compares the integrated flux uncertainty (w2sigmpro) with the standard deviation of W2 fluxes from the individual exposures (w2sip1)

6067 sources

4673sources

3263source

s

904sources

52 sources

REJECTION METHODS3 – Detection number rejection method

Fraction of individual W2 frames in which the source is detected

6067 sources

4673sources

3263sources

904source

s

52 sources

VISUAL INSPECTION 6067 sources

4673sources

3263sources

904sources

52 source

s

Excluded:• artefacts (such as diffraction spikes, optical ghosts, glints, halo associations)• blended sources• extended structures (galaxies, nebulae)

EXPANDING 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 = 52S/N = [8-10] = 106

Total = 158 candidates

NEW SAMPLES/N > 10 - 29 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.

ADDITIONAL PHOTOMETRYWe 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

RESULTS – CANDIDATE 1

Top: WISE W2 and W2Bottom: 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 > 3.27J – W2 = .489 ± 0.15[3.6] – [4.5] = 1.99 ±0.04

Spectral type of T9 or later.

RESULTS – CANDIDATE 2

The brightest new object in the sample with W2 = 14.96

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)

COMPARING WITH T9 AND Y0T9 ± 0.5 dwarf

NIR spectrum obtained with FIRE

KINEMATICSDistances estimated with the relations between absolute magnitude and spectral type considering single object and binarity.

J + H band distances – 17-52 pc

Y + mid-IR distances 13-23 pc

Space motion suggesting it's a thick disk/halo candidate.

COLOURSComparison sample from Leggett et al. 2013

Peculiar Y-J and H-W2 colours

CONCLUSIONS• 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.

FUTURE WORK

THANK

YOU!