J/ApJ/889/74 Spitzer follow-up of Y brown dwarfs (Meisner+, 2020)
Expanding the Y dwarf census with Spitzer follow-up of the coldest CatWISE
solar neighborhood discoveries.
Meisner A.M., Caselden D., Kirkpatrick J.D., Marocco F., Gelino C.R.,
Cushing M.C., Eisenhardt P.R.M., Wright E.L., Faherty J.K., Koontz R.,
Marchese E.J., Khalil M., Fowler J.W., Schlafly E.F.
<Astrophys. J., 889, 74 (2020)>
=2020ApJ...889...74M 2020ApJ...889...74M
ADC_Keywords: Stars, brown dwarf; Stars, Y-type; Stars, T-type;
Photometry, infrared; Spectral types; Proper motions
Keywords: Brown dwarfs; Y dwarfs; Solar neighborhood; T dwarfs; Proper motions
Abstract:
We present Spitzer 3.6 and 4.5µm follow-up of 170 candidate
extremely cool brown dwarfs newly discovered via the combination of
Wide-field Infrared Survey Explorer (WISE) and NEOWISE imaging at
3-5µm. CatWISE, a joint analysis of archival WISE and NEOWISE data,
has improved upon the motion measurements of AllWISE by leveraging a
>10x time baseline enhancement, from 0.5yr (AllWISE) to 6.5yr
(CatWISE). As a result, CatWISE motion selection has yielded a large
sample of previously unrecognized brown dwarf candidates, many of
which have archival detections exclusively in the WISE 4.6µm (W2)
channel, suggesting that they could be both exceptionally cold and
nearby. Where these objects go undetected in WISE W1 (3.4µm),
Spitzer can provide critically informative detections at 3.6µm. Of
our motion-confirmed discoveries, 17 have a best-fit Spitzer
[3.6]-[4.5] color most consistent with spectral type Y. It is likely
that CWISEP J144606.62-231717.8 (µ∼1.3yr-1) is the reddest, and
therefore potentially coldest, member of our sample with a very
uncertain [3.6]-[4.5] color of 3.71±0.44mag. We also highlight our
highest proper-motion discovery, WISEA J153429.75-104303.3, with
µ∼2.7yr-1. Given that the prior list of confirmed and presumed Y
dwarfs consists of just 27 objects, the Spitzer follow-up presented in
this work has substantially expanded the sample of identified Y
dwarfs. Our new discoveries thus represent significant progress toward
understanding the bottom of the substellar mass function,
investigating the diversity of the Y dwarf population, and selecting
optimal brown dwarf targets for James Webb Space Telescope spectroscopy.
Description:
Our Spitzer follow-up observations presented throughout this work were
acquired as part of program 14034 (PI: Meisner). See Section 4.
For southern targets, we acquired follow-up J-band imaging at Gemini
South. Through program GS-2019A-Q-316 (PI: C. R. Gelino), we obtained
FLAMINGOS-2 J-band photometry for 16 of the discoveries presented in
this paper. See Section 9.1.
For northern targets, we obtained follow-up J-band imaging with the
Wide Field Infrared Camera (WIRC) at the Palomar Hale 200 inch
telescope (PI: F. Marocco). See Section 9.2.
We searched the entire WFCAM Science Archive (WSA) and VISTA Science
Archive (VSA) for UKIRT/WFCAM and VISTA VIRCAM JHK/Ks counterparts to
our brown dwarf candidates. See Section 9.3.2.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 134 169 WISE & Spitzer photometry
table3.dat 78 510 WISE W2 positions used in joint WISE+Spitzer
linear motion fits
table4.dat 85 166 Recalibrated Spitzer ch2 positions
table7.dat 120 169 WISE+Spitzer linear motion fitting results
table9.dat 113 96 NIR photometry from Gemini, Palomar, UKIRT, and
VISTA for motion-confirmed targets
table11.dat 114 111 Derived properties for motion-confirmed targets
with Spitzer imaging available
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See also:
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
II/328 : AllWISE Data Release (Cutri+ 2013)
II/359 : The VISTA Hemisphere Survey (VHS) catalog DR4.1 (McMahon+, 2013)
II/343 : VIKING catalogue data release 2 (Edge+, 2016)
II/357 : The Dark Energy Survey (DES): Data Release 1 (Abbott+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
II/363 : The band-merged unWISE Catalog (Schlafly+, 2019)
II/365 : The CatWISE2020 catalog (updated version 28-Jan-2021) (Marocco+, 2020)
J/AJ/124/1190 : Northern high proper motion stars in DSS (Lepine+, 2002)
J/other/ARA+A/43.195 : L and T dwarf stars (Kirkpatrick, 2005)
J/ApJ/651/502 : Spitzer IRAC photometry of M, L, and T dwarfs (Patten+, 2006)
J/AJ/137/1 : PMs and astrometry of late-type dwarfs (Faherty+, 2009)
J/ApJS/197/19 : First brown dwarfs discovered by WISE (Kirkpatrick+, 2011)
J/ApJS/201/19 : Hawaii Infrared Parallax Program. I. (Dupuy+, 2012)
J/AJ/144/148 : IR photometry of brown dwarf and Hyper-LIRG (Griffith+, 2012)
J/ApJ/753/156 : T/Y brown dwarfs with WISE photometry (Kirkpatrick+, 2012)
J/ApJS/205/6 : T dwarf population revealed by WISE (Mace+, 2013)
J/ApJ/783/122 : AllWISE motion survey (Kirkpatrick+, 2014)
J/ApJ/781/4 : Phot. of high proper motion objects from WISE (Luhman, 2014)
J/ApJ/792/30 : NEOWISE magnitudes for near-Earth objects (Mainzer+, 2014)
J/ApJS/224/36 : The AllWISE motion survey (AllWISE2) (Kirkpatrick+, 2016)
J/ApJ/817/112 : NEOWISE/AllWISE high proper motion objects (Schneider+, 2016)
J/ApJ/867/109 : Spitzer observations of Y and T dwarfs (Martin+, 2018)
J/ApJS/240/19 : Parallaxes of late-T and Y dwarfs (Kirkpatrick+, 2019)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Source identifier
28 A1 --- m_Name [SN] Components on Name
30 A1 --- f_Name [b] Flag on Name (1)
32- 34 A3 --- Motion? Motion confirmed? (yes=114 occurrences)
36 A1 --- l_W1mag Limit flag on W1mag
38- 43 F6.3 mag W1mag [15.71/19.42] WISE 3.4 micron band magnitude
45- 49 F5.3 mag e_W1mag [0.02/0.6]? Uncertainty in W1mag
51 A1 --- f_W1mag [a] Flag on W1mag (1)
53- 58 F6.3 mag W2mag [14.46/16.84] WISE 4.6 micron band magnitude
60- 64 F5.3 mag e_W2mag [0.015/0.3] Uncertainty in W2mag
66 A1 --- l_W1-W2 Limit flag on W1-W2
68- 72 F5.3 mag W1-W2 [1.15/3.3] WISE (W1-W2) color
74- 78 F5.3 mag e_W1-W2 [0.025/0.6]? Uncertainty in W1-W2
80- 87 A8 --- AOR Spitzer AOR identifier
89- 94 F6.3 mag 3.6mag [15.21/19.52]? Spitzer/IRAC 3.6um band magnitude
96-100 F5.3 mag e_3.6mag [0.016/0.5]? Uncertainty in 3.6mag
102-107 F6.3 mag 4.5mag [14.43/18.01]? Spitzer/IRAC 4.5um band magnitude
109-113 F5.3 mag e_4.5mag [0.017/0.08]? Uncertainty in 4.5mag
115-119 F5.3 mag 3.6-4.5 [0.33/3.71]? Spitzer/IRAC 3.6-4.5 band color
121-125 F5.3 mag e_3.6-4.5 [0.024/0.5]? Uncertainty in 3.6-4.5
127-134 A8 --- Method Search method (2)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
a = WISE photometry may be contaminated by blending.
b = Object is scheduled for p14034 Spitzer observations in the near future,
but does not yet have Spitzer photometry available.
Note (2): The search method names listed in this column are defined in
Sections 4.1-4.3, which also contain explanations of each search's
moving object candidate selection procedure.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Source identifier
29- 38 F10.6 deg RAdeg Right Ascension in decimal degrees (ICRS) (G1)
40- 49 F10.6 deg DEdeg [-84/79.6] Declination in decimal degrees
(ICRS) (G1)
51- 54 I4 mas e_RAdeg [94/2005] Uncertainty in RAdeg
56- 59 I4 mas e_DEdeg [101/2048] Uncertainty in DEdeg
61- 69 A9 --- Time Time slice (1)
71- 78 F8.2 d MJD [55231.08/58315.04] Mean modified Julian Date
--------------------------------------------------------------------------------
Note (1): See Section 8.3 and Table 5 for discussion and definitions of the
WISE time slices used for W2 astrometry.
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Source identifier
28 A1 --- m_Name [SN] Components on Name
30- 37 I8 --- AOR [3862272/68733952] Spitzer AOR identifier
39- 50 F12.8 deg RAdeg Right Ascension in decimal degrees (ICRS) (G1)
52- 63 F12.8 deg DEdeg [-84/79.6] Declination in decimal degrees (ICRS)
(G1)
65- 67 I3 mas e_RAdeg [21/145] Uncertainty in RAdeg
69- 71 I3 mas e_DEdeg [20/131] Uncertainty in DEdeg
73- 80 F8.2 d MJD [52975.74/58711.09] Modified Julian Date
82 I1 --- Meth [1/9] Method number (1)
84- 85 I2 --- Ncal [5/92] Number of Gaia DR2 calibrators (2)
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Note (1): The astrometric calibrator selection "method number" here refers to
the method number listed in Table 6 and explained in Section 8.4.1:
--------------------------------------------------------------------
Method Min. Min. BCD Gaia PM Ncalib,min Number of
number chi2 S/N Cov. Frac. required AORs
--------------------------------------------------------------------
1 100 1.0 Yes 10 67
2 50 1.0 Yes 10 28
3 30 1.0 Yes 5 57
4 100 1.0 No 10 1
5 50 1.0 No 10 0
6 30 1.0 No 5 6
7 100 0.5 Yes 10 0
8 50 0.5 Yes 10 0
9 30 0.5 Yes 5 5
--------------------------------------------------------------------
Note (2): Used for Spitzer 4.5 micron band astrometric recalibration of each
AOR, as discussed in Section 8.4.1.
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Byte-by-byte Description of file: table7.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Source identifier
28 A1 --- m_Name Component on Name
30- 40 F11.7 deg RAdeg Right Ascension in decimal degrees (ICRS)
at Ep=MJD
42- 52 F11.7 deg DEdeg [-84/79.6] Declination in decimal degrees (ICRS)
at Ep=MJD
54- 56 I3 mas e_RAdeg [21/223] Uncertainty in RAdeg
58- 60 I3 mas e_DEdeg [20/238] Uncertainty in DEdeg
62- 69 F8.2 d MJD [53261.59/58656.23] MJD
71- 75 I5 mas/yr pmRA [-1254/1138] Proper motion along RA
77- 79 I3 mas/yr e_pmRA [16/186] Uncertainty in pmRA
81- 85 I5 mas/yr pmDE [-2387/518] Proper motion along DE
87- 89 I3 mas/yr e_pmDE [17/190] Uncertainty in pmDE
91- 94 I4 mas/yr pmTot [9/2697] Total proper motion
96- 98 I3 mas/yr e_pmTot [17/189] Uncertainty in pmTot
100-105 F6.1 --- Chi2MM [0.1/2684.6] Significance of motion metric
107-111 F5.2 --- Chi2 [0.0/54.35]? Model χ2
113-114 I2 --- dof [0/20] Number of degrees of freedom
116-120 F5.2 --- rChi2 [0.0/14.92]? Reduced χ2 (4)
--------------------------------------------------------------------------------
Note (4): The reduced χ2 of the linear motion fit, defined as
χν2=χ2/(dof).
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Byte-by-byte Description of file: table9.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Name of the source
29 A1 --- l_Jmag Limit flag on Jmag
31- 35 F5.2 mag Jmag [16.9/22.36]? MKO J-band magnitude (1)
37- 40 F4.2 mag e_Jmag [0.01/0.6]? Uncertainty on the Jmag
42 A1 --- f_Jmag Flag on Jmag
44- 54 A11 --- r_Jmag Origin of Jmag
56 A1 --- l_Hmag Limit flag on Hmag
58- 62 F5.2 mag Hmag [18.01/19.79]? MKO H-band magnitude (1)
64- 67 F4.2 mag e_Hmag [0.03/0.34]? Uncertainty on the Hmag
69- 74 A6 --- r_Hmag Origin of Hmag
76 A1 --- l_Kmag Limit flag on Kmag
78- 82 F5.2 mag Kmag [17.92/18.79]? MKO K band magnitude (1)
84- 87 F4.2 mag e_Kmag [0.12/0.18]? Uncertainty on the Kmag
89- 93 A5 --- r_Kmag Origin of Kmag
95 A1 --- l_Ksmag Limit flag on Ksmag
97- 101 F5.2 mag Ksmag [17.39/18.99]? Ks-band magnitude
103- 106 F4.2 mag e_Ksmag [0.07/0.38]? Uncertainty on the Ksmag
108- 113 A6 --- r_Ksmag Origin of Ksmag
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Note (1): To calibrate the photometry in each target's field using 2MASS, we
applied the color transformation equation from Hodgkin+ (2009):
JMKO=J2MASS-0.065x(J2MASS-H2MASS) Equation (3)
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Byte-by-byte Description of file: table11.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 27 A27 --- Name Name of the source
29- 30 A2 --- l_SpT [≥ ] Limit flag on SpT
32- 35 F4.1 --- SpT [3.5/11] Spectral type (phototype) (1)
37 A1 --- f_SpT Flag on SpT
39- 43 F5.2 mag 4.5Mag [12.25/16.23] Spitzer/IRAC Ch2 (4.5um) band
absolute magnitude (Mch2)
45- 48 F4.2 mag e_4.5Mag [0.23/0.64]? Negative uncertainty on 4.5Mag
50- 53 F4.2 mag E_4.5Mag [0.23/0.7]? Positive uncertainty on 4.5Mag
55 A1 --- l_Dist Limit flag on Dist
57- 61 F5.1 pc Dist [8.3/124.8] Distance
63- 66 F4.1 pc e_Dist [1.3/13.2]? Negative uncertainty on Dist
68- 71 F4.1 pc E_Dist [1.5/14.6]? Positive uncertainty on Dist
73 A1 --- l_Teff Limit flag on Teff
75- 78 I4 K Teff [341/1073]? Effective temperature
80- 82 I3 K e_Teff [81/102]? Negative uncertainty on Teff
84- 86 I3 K E_Teff [81/109]? Positive uncertainty on Teff
88- 92 F5.2 mag Hch2 [15.33/22.92] Reduced proper motion (Hch2)
94- 97 F4.2 mag e_Hch2 [0.05/0.41] Negative uncertainty on Hch2
99- 102 F4.2 mag E_Hch2 [0.05/0.5] Positive uncertainty on Hch2
104 A1 --- l_Vtan Limit flag on Vtan
106- 108 I3 km/s Vtan [14/485] Tangential velocity
110- 111 I2 km/s e_Vtan [3/76]? Negative uncertainty on Vtan
113- 114 I2 km/s E_Vtan [3/79]? Positive uncertainty on Vtan
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Note (1): Photometric spectral type values are defined such that SpT=6 for T6,
SpT=7 for T7, ..., SpT=11 for Y1.
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Global notes:
Note (G1): All Gaia-recalibrated W2 and ch2 (RA, DEC) coordinates quoted
throughout the paper are in the International Celestial Reference
System (ICRS). The Spitzer and WISE positions reported in Tables 3 and
4 are relative rather than absolute; we did not attempt to correct for
the typically very small parallaxes of our astrometric calibration
sources. See Section 8.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Oct-2021