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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
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OVERVIEW
• Introduction
• Candidate selection
• Rejection methods
• Results
• Summary and future work
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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
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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
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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
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1 – Profile fit photometry rejection method
Assess how point-like each source is.
REJECTION METHODS 6067 source
s
4673sources
3263sources
904sources
52 sources
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1 – Profile fit photometry rejection method
Assess how point-like each source is.
REJECTION METHODS 6067 sources
4673source
s
3263sources
904sources
52 sources
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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
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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
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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)
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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
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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.
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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
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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.
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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)
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COMPARING WITH T9 AND Y0T9 ± 0.5 dwarf
NIR spectrum obtained with FIRE
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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.
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COLOURSComparison sample from Leggett et al. 2013
Peculiar Y-J and H-W2 colours
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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
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THANK
YOU!