-
Ben Burningham,
C. V. Cardoso,
L. Smith,
S. K. Leggett,
R. L. Smart,
A. W. Mann,
S. Dhital, P. W. Lucas,
C. G. Tinney,
D. J. Pinfield, [......],
J. J. Fortney,
J. Gomes,
M. Ishii,
H. R. A. Jones,
M. Liu,
A. Magazzu,
F. Marocco,
D. N. Murray,
B. Rojas-Ayala,
M. Tamura
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of 76 new T dwarfs from the UKIDSS Large Area Survey
(LAS). Near-infrared broad and narrow-band photometry and spectroscopy are
presented for the new objects, along with WISE and warm-Spitzer photometry.
Proper motions for 128 UKIDSS T dwarfs are presented from a new two epoch LAS
proper motion catalogue. We use these motions to identify two new benchmark
systems: LHS 6176AB, a T8+M4 pair and HD118865AB, a T5.5+F8 pair. Using age
constraints from the primaries and evolutionary models to constrain the radii
we have estimated their physical properties from their bolometric luminosity.
We compare the colours and properties of known benchmark T dwarfs to the latest
model atmospheres and draw two principal conclusions. Firstly, it appears that
the H - [4.5] and J - W2 colours are more sensitive to metallicity than has
previously been recognised, such that differences in metallicity may dominate
over differences in Teff when considering relative properties of cool objects
using these colours. Secondly, the previously noted apparent dominance of young
objects in the late-T dwarf sample is no longer apparent when using the new
model grids and the expanded sample of late-T dwarfs and benchmarks. This is
supported by the apparently similar distribution of late-T dwarfs and
earlier-type T dwarfs on reduced proper motion diagrams that we present.
Finally, we present updated space densities for the late-T dwarfs, and compare
our values to simulation predictions and those from WISE.
04/2013;
-
N. Lodieu,
B. Burningham,
A. Day-Jones,
R. -D. Scholz,
F. Marocco,
S. Koposov,
D. Barrado y Navascues, P. W. Lucas,
P. Cruz,
J. Lillo, [......],
R. Rebolo,
V. J. S. Bejar,
S. Boudreault,
J. P. Emerson,
M. Banerji,
E. Gonzalez-Solares,
S. T. Hodgkin,
R. McMahon,
J. Canty,
C. Contreras
[show abstract]
[hide abstract]
ABSTRACT: The aim of the project is to improve our current knowledge of the density of
T dwarfs and the shape of the substellar initial mass function by identifying a
magnitude-limited sample of T dwarfs in the full southern sky.
We present the results of a photometric search aimed at discovering cool
brown dwarfs in the Southern sky imaged at infrared wavelengths by the Visible
and Infrared Survey Telescope for Astronomy (VISTA) and the Wide Infrared
Survey Explorer (WISE) satellite mission. We combined the first data release
(DR1) of the VISTA Hemisphere Survey (VHS) and the WISE preliminary data
release to extract candidates with red mid-infrared colours and near- to
mid-infrared colours characteristics of cool brown dwarfs.
The VHS DR1 vs WISE search returned tens of T dwarf candidates, 13 of which
are presented here, including two previously published in the literature and
five new ones confirmed spectroscopically with spectral types between T4.5 and
T8. We estimate that the two T6 dwarfs lie within 16 pc and the T4.5 within 25
pc. The remaining three are 30-50 pc distant. The only T7 dwarf in our sample
is the faintest of its spectral class with J=19.28 mag. The other six T dwarf
candidates remain without spectroscopic follow-up. We also improve our
knowledge on the proper motion accuracy for three bright T dwarfs by combining
multi-epoch data from public databases (DENIS, 2MASS, VHS, WISE, Spitzer).
10/2012;
-
S. Catalan,
P. -E. Tremblay,
D. J. Pinfield,
L. C. Smith,
Z. H. Zhang,
R. Napiwotzki,
F. Marocco,
A. C. Day-Jones,
J. Gomes,
K. P. Forde, P. W. Lucas,
H. R. A. Jones
[show abstract]
[hide abstract]
ABSTRACT: We report the identification of LSR J0745+2627 in the United Kingdom InfraRed
Telescope Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) as a cool
white dwarf with kinematics and age compatible with the thick-disk/halo
population. LSR J0745+2627 has a high proper motion (890 mas/yr) and a high
reduced proper motion value in the J band (H_J=21.87). We show how the
infrared-reduced proper motion diagram is useful for selecting a sample of cool
white dwarfs with low contamination. LSR J0745+2627 is also detected in the
Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer
(WISE). We have spectroscopically confirmed this object as a cool white dwarf
using X-Shooter on the Very Large Telescope. A detailed analysis of its
spectral energy distribution reveals that its atmosphere is compatible with a
pure-H composition model with an effective temperature of 3880+-90 K. This
object is the brightest pure-H ultracool white dwarf (Teff<4000 K) ever
identified. We have constrained the distance (24-45 pc), space velocities and
age considering different surface gravities. The results obtained suggest that
LSR J0745+2627 belongs to the thick-disk/halo population and is also one of the
closest ultracool white dwarfs.
09/2012;
-
R. K. Saito,
D. Minniti,
B. Dias,
M. Hempel,
M. Rejkuba,
J. Alonso-Garcia,
B. Barbuy,
M. Catelan,
J. P. Emerson,
O. A. Gonzalez, P. W. Lucas,
M. Zoccali
[show abstract]
[hide abstract]
ABSTRACT: The Milky Way (MW) bulge is a fundamental Galactic component for
understanding the formation and evolution of galaxies, in particular our own.
The ESO Public Survey VISTA Variables in the Via Lactea is a deep near-IR
survey mapping the Galactic bulge and southern plane. Data taken during 2010-11
covered 315 deg2 in the bulge area in the JHKs bands. We used VVV data for the
whole bulge area as a single and homogeneous data set to build for the first
time a single colour-magnitude diagram (CMD) for the entire Galactic bulge.
Photometric data in the JHKs bands were combined to produce a single and huge
data set containing 173.1M+ sources in the three bands. Selecting only the data
points flagged as stellar, the total number of sources is 84.0M+. We built the
largest CMDs published up to date, containing 173.1+ million sources for all
data points, and more than 84.0 million sources accounting for the stellar
sources only. The CMD has a complex shape, mostly owing to the complexity of
the stellar population and the effects of extinction and reddening towards the
Galactic centre. The red clump (RC) giants are seen double in magnitude at b ~
-8-10 deg, while in the inner part (b ~ 3deg) they appear to be spreading in
colour, or even splitting into a secondary peak. The analysis of the outermost
bulge area reveals a well-defined sequence of late K and M dwarfs, seen at
(J-Ks) ~ 0.7-0.9 mag and Ks~14 mag. The interpretation of the CMD yields
important information about the MW bulge, showing the fingerprint of its
structure and content. We report a well-defined red dwarf sequence in the
outermost bulge, which is important for the planetary transit searches of VVV.
The double RC in magnitude seen in the outer bulge is the signature of the
X-shaped MW bulge, while the spreading of the RC in colour are caused by
reddening effects.
08/2012;
-
E. B. Amôres,
L. Sodré,
D. Minniti,
M. V. Alonso,
N. Padilla,
S. Gurovich,
V. Arsenijevic,
E. J. Tollerud,
A. Rodríguez-Ardila,
J. Díaz Tello, P. W. Lucas
[show abstract]
[hide abstract]
ABSTRACT: Vista Variables in The Via Lactea (VVV) is an ESO variability survey that is
performing observations in near infrared bands (ZYJHKs) towards the Galactic
bulge and part of the disk with the completeness limits at least 3 mag deeper
than 2MASS. In the present work, we searched in the VVV survey data for
background galaxies near the Galactic plane using ZYJHKs photometry that covers
1.636 square degrees. We identified 204 new galaxy candidates by analyzing
colors, sizes, and visual inspection of multi-band (ZYJHKs) images. The galaxy
candidates colors were also compared with the predicted ones by star counts
models considering a more realistic extinction model at the same completeness
limits observed by VVV. A comparison of the galaxy candidates with the expected
one by Milennium simulations is also presented. Our results increase the number
density of known galaxies behind the Milky Way by more than one order of
magnitude. A catalog with galaxy properties including ellipticity, Petrosian
radii and ZYJHKs magnitudes is provided, as well as comparisons of the results
with other surveys of galaxies towards Galactic plane.
06/2012;
-
D. J. Pinfield,
B. Burningham,
N. Lodieu,
S. K. Leggett,
C. G. Tinney,
L. van Spaandonk,
F. Marocco,
R. Smart,
J. Gomes,
L. Smith, [......],
A. C. Katsiyannis,
S. Catalan,
C. Cardoso,
J. R. A. Clarke,
S. Folkes,
M. C. Galvez-Ortiz,
D. Homeier,
J. S. Jenkins,
H. R. A. Jones,
Z. H. Zhang
[show abstract]
[hide abstract]
ABSTRACT: We have searched the WISE first data release for widely separated (<10,000AU)
late T dwarf companions to Hipparcos and Gliese stars. We have discovered a new
binary system containing a K-band suppressed T8p dwarf WISEP J1423+0116 and the
mildly metal poor ([Fe/H]=-0.38+-0.06) primary BD+01 2920 (Hip 70319), a G1
dwarf at a distance of 17.2pc. This new benchmark has Teff=680+-55K and a mass
of 20-50 Mjup. Its spectral properties are well modelled except for known
discrepancies in the Y and K bands. Based on the well determined metallicity of
its companion, the properties of BD+01 2920B imply that the currently known T
dwarfs are dominated by young low-mass objects. We also present an accurate
proper motion for the T8.5 dwarf WISEP J075003.84+272544.8.
01/2012;
-
R. K. Saito,
M. Hempel,
D. Minniti, P. W. Lucas,
M. Rejkuba,
I. Toledo,
O. A. Gonzalez,
J. Alonso-Garcia,
M. J. Irwin,
E. Gonzalez-Solares, [......],
J. Stead,
A. W. Stephens,
M Tamura,
C. Tappert,
M. A. Thompson,
E. Valenti,
L. Vanzi,
N. A. Walton,
W. Weidmann,
A. Zijlstra
[show abstract]
[hide abstract]
ABSTRACT: The ESO Public Survey VISTA Variables in the Via Lactea (VVV) started in
2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane
region and is expected to run for ~5 years. In this paper we describe the
progress of the survey observations in the first observing season, the
observing strategy and quality of the data obtained. The observations are
carried out on the 4-m VISTA telescope in the ZYJHKs filters. In addition to
the multi-band imaging the variability monitoring campaign in the Ks filter has
started. Data reduction is carried out using the pipeline at the Cambridge
Astronomical Survey Unit. The photometric and astrometric calibration is
performed via the numerous 2MASS sources observed in each pointing. The first
data release contains the aperture photometry and astrometric catalogues for
348 individual pointings in the ZYJHKs filters taken in the 2010 observing
season. The typical image quality is ~0.9-1.0". The stringent photometric and
image quality requirements of the survey are satisfied in 100% of the JHKs
images in the disk area and 90% of the JHKs images in the bulge area. The
completeness in the Z and Y images is 84% in the disk, and 40% in the bulge.
The first season catalogues contain 1.28x10^8 stellar sources in the bulge and
1.68x10^8 in the disk area detected in at least one of the photometric bands.
The combined, multi-band catalogues contain more than 1.63x10^8 stellar
sources. About 10% of these are double detections due to overlapping adjacent
pointings. These overlapping multiple detections are used to characterise the
quality of the data. The images in the JHKs bands extend typically ~4 mag
deeper than 2MASS. The magnitude limit and photometric quality depend strongly
on crowding in the inner Galactic regions. The astrometry for Ks=15-18 mag has
rms ~35-175 mas.
11/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present a detailed study of a dust-obscured Galactic star cluster Mercer 5 ([MCM2005b] 5) in an extremely crowded field in the Milky Way. Near-infrared (near-IR) photometry from United Kingdom Infrared Digital Sky Surveys (UKIDSS) and the Son of ISAAC on the New Technology Telescope (SofI/NTT), combined with near-IR spectroscopy also from SofI, indicates that it is almost certainly a Galactic globular cluster, located at the edge of the Galactic bulge. The cluster suffers ∼9 mag of visual extinction, with strong evidence for an extinction gradient across the cluster. A simulation of the differential reddening in the cluster using empirical data from NGC 6539 (chosen because it had high signal-to-noise ratio data and low field star contamination) as a template mimics the observations extremely well. This simulation and other arguments are used to indicate that the most prominent clump of stars in the colour–magnitude diagrams is a horizontal branch clump. On this basis we conclude that the cluster is at a distance of ∼5.5 kpc and suffers from visual extinction ranging from ∼8.5 to ∼12.5 mag. Alternative explanations for its nature, such as a young cluster or an old open cluster, are much less likely, on the grounds of no visible main sequence or stars with IR excesses for the former and location versus lifetime arguments for the latter.
Monthly Notices of the Royal Astronomical Society 07/2011; 416(1):465 - 478. · 4.90 Impact Factor
-
D. J. Pinfield,
A. C. Day-Jones,
B. Burningham,
S. K. Leggett,
H. Beaumont,
M. Tamura,
C. G. Tinney,
M. C. Liu,
D. Homeier,
N. Lodieu, [......], P. W. Lucas,
M. Ishi,
R. G. McMahon,
P. C. Hewett,
M. R. Zapatero-Osorio,
E. L. Martin,
B. P. Venemans,
D. Barrado,
Z. Zhang,
M. Morales-Calderon
[show abstract]
[hide abstract]
ABSTRACT: This paper discusses benchmark brown dwarfs in various environments, and
focuses on those in wide binary systems. We present a summary of the
recently discovered T dwarf population from the UKIDSS Large Area
Survey, and describe the constraints that it places on our knowledge of
the sub-stellar initial mass function. We also present some exciting
results from our ongoing search for wide companions to this sample, that
has so far revealed an M4-T8.5 binary system at ˜12 parsecs and
also the first ever Tdwarf-white dwarf binary system. The T dwarfs in
these binaries have their properties constrained by the primary object
and are thus benchmark objects that are already testing the predictions
of theoretical model atmospheres.
06/2011; 16:06002.
-
D. N. Murray,
B. Burningham,
H. R. A. Jones,
D. J. Pinfield, P. W. Lucas,
S. K. Leggett,
C. G. Tinney,
A. C. Day-Jones,
D. J. Weights,
N. Lodieu,
J. A. Pérez Prieto,
E. Nickson,
Z. H. Zhang,
J. R. A. Clarke,
J. S. Jenkins,
M. Tamura
[show abstract]
[hide abstract]
ABSTRACT: We have used blue near-infrared colours to select a group of 12 spectroscopically confirmed United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) T dwarfs later than T4. From amongst these, we identify the first two kinematic halo T-dwarf candidates. Blue near-infrared colours have been attributed to collisionally induced hydrogen absorption, which is enhanced by either high surface gravity or low metallicity. Proper motions are measured and distances estimated, allowing the determination of tangential velocities. U and V components are estimated for our objects by assuming Vrad= 0. From this, ULAS J0926+0835 is found to have U= 62 km s−1 and V=−140 km s−1, and ULAS J1319+1209 is found to have U= 192 km s−1 and V=−92 km s−1. These values are consistent with potential halo membership. However, these are not the bluest objects in our selection. The bluest is ULAS J1233+1219, with J−K=−1.16 ± 0.07, and surprisingly this object is found to have young disc-like U and V. Our sample also contains Hip 73786B, companion to the metal-poor K5 dwarf Hip 73786. Hip 73786 is a metal-poor star, with [Fe/H] =−0.3 ± 0.1 and is located at a distance of 19 ± 0.7 pc. U, V, W space velocity components are calculated for Hip 73786A and B, finding that U=−48 ± 7 km s−1, V=−75 ± 4 km s−1 and W=−44 ± 8 km s−1. From the properties of the primary, Hip 73786B is found to be at least 1.6-Gyr old. As a metal-poor object, Hip 73786B represents an important addition to the sample of known T dwarf benchmarks.
Monthly Notices of the Royal Astronomical Society 06/2011; 414(1):575 - 586. · 4.90 Impact Factor
-
Ben Burningham, P. W. Lucas,
S. K. Leggett,
R. Smart,
D. Baker,
D. J. Pinfield,
C. G. Tinney,
D. Homeier,
F. Allard,
Z. H. Zhang,
J. Gomes,
A. C. Day-Jones,
H. R. A. Jones,
G. Kovács,
N. Lodieu,
F. Marocco,
D. N. Murray,
B. Sipőcz
[show abstract]
[hide abstract]
ABSTRACT: We have carried out a search for late-type T dwarfs in the UKIRT Infrared Deep Sky Survey Galactic Plane Survey 6th Data Release. The search yielded two persuasive candidates, both of which have been confirmed as T dwarfs. The brightest, UGPS J0521+3640, has been assigned the spectral type T8.5 and appears to lie at a distance of 7–9 pc. The fainter of the two, UGPS J0652+0324, is classified as a T5.5 dwarf and lies at an estimated distance of 28–37 pc. Warm-Spitzer observations in IRAC channels 1 and 2, taken as part of the GLIMPSE360 Legacy Survey, are available for UGPS J0521+3640 and we used these data with the near-infrared spectroscopy to estimate its properties. We find best-fitting solar metallicity BT-Settl models for Teff= 600 and 650 K and log g= 4.5 and 5.0. These parameters suggest a mass between 14 and 32MJ for an age between 1 and 5 Gyr. The proximity of this very cool T dwarf, and its location in the Galactic plane, makes it an ideal candidate for high-resolution adaptive optics imaging to search for cool companions.
Monthly Notices of the Royal Astronomical Society Letters 06/2011; 414(1):L90 - L94.
-
[show abstract]
[hide abstract]
ABSTRACT: We use the clump giants of the disk as standard candles calibrated from
Hipparcos parallaxes in order to map their distribution with two new near-IR
surveys of the Galactic plane: UKIDSS-GPS and VVV. We explore different
selection cuts of clump giants. We conclude that there is an edge of the
stellar disk of the Milky Way at R=13.9+/-0.5kpc along various lines of sight
across the galaxy. The effect of the warp is considered, taking fields at
different longitudes and above and below the plane. We demonstrate that the
edge of the stellar disk of the Milky Way can now be mapped in the near
infrared in order to test different models, and to establish our own place
within the galaxy.
05/2011;
-
M. Catelan,
D. Minniti, P. W. Lucas,
J. Alonso-Garcia,
R. Angeloni,
J. C. Beamin,
C. Bonatto,
J. Borissova,
C. Contreras,
N. Cross, [......],
F. Mauro,
C. Moni Bidin,
C. Navarrete,
P. Perez,
K. Pichara,
M. Read,
M. Rejkuba,
R. K. Saito,
S. E. Sale,
I. Toledo
[show abstract]
[hide abstract]
ABSTRACT: Vista Variables in the Via Lactea (VVV) is an ESO Public Survey that is
performing a variability survey of the Galactic bulge and part of the inner
disk using ESO's Visible and Infrared Survey Telescope for Astronomy (VISTA).
The survey covers 520 deg^2 of sky area in the ZYJHK_S filters, for a total
observing time of 1929 hours, including ~ 10^9 point sources and an estimated ~
10^6 variable stars. Here we describe the current status of the VVV Survey, in
addition to a variety of new results based on VVV data, including light curves
for variable stars, newly discovered globular clusters, open clusters, and
associations. A set of reddening-free indices based on the ZYJHK_S system is
also introduced. Finally, we provide an overview of the VVV Templates Project,
whose main goal is to derive well-defined light curve templates in the near-IR,
for the automated classification of VVV light curves.
05/2011;
-
Ben Burningham,
S. K. Leggett,
D. Homeier,
D. Saumon, P. W. Lucas,
D. J. Pinfield,
C. G. Tinney,
F. Allard,
M. S. Marley,
H. R. A. Jones,
D. N. Murray,
M Ishii,
A. C. Day-Jones,
J. Gomes,
Z. H. Zhang
[show abstract]
[hide abstract]
ABSTRACT: We present near-infrared photometry and spectroscopy, and warm-Spitzer IRAC
photometry of the young very cool T dwarf Ross 458C, which we have typed as
T8.5p. By applying the fiducial age constraints (< 1Gyr) imposed by the
properties of the active M dwarf Ross 458A, we have used these data to
determine that Ross 458C has Teff = 695 \pm 60K, log g = 4.0 - 4.7 and an
inferred mass of 5-20 MJup. We have compared fits of the near-infrared spectrum
and IRAC photometry to the BT Settl and Saumon & Marley model grids, and have
found that both sets provide best fits that are consistent with our derived
properties, whilst the former provide a marginally closer match to the data for
all scenarios explored here. The main difference between the model grids arises
in the 4.5{\mu}m region, where the BT Settl models are able to better predict
the flux through the IRAC filter, suggesting that non-equilibrium effects on
the CO-CO2 ratio are important for shaping the mid-infrared spectra of very
cool T dwarfs. We have also revisited the issue of dust opacity in the spectra
of Ross 458C that was raised by Burgasser et al (2010). We have found that the
BT Settl models which also incorporate a condensate cloud model, provide a
better match to the near-infrared spectrum of this target than the Saumon &
Marley model with fsed = 2, and we briefly discuss the influence of condensate
clouds on T dwarf spectra.
03/2011;
-
D. N. Murray,
B. Burningham,
H. R. A. Jones,
D. J. Pinfield, P. W. Lucas,
S. K. Leggett,
C. G. Tinney,
A. C. Day-Jones,
D. J. Weights,
N. Lodieu,
J. A. Perez Prieto,
E. Nickson,
Z. H. Zhang,
J. R. A. Clarke,
J. S. Jenkins,
M Tamura
[show abstract]
[hide abstract]
ABSTRACT: We have used blue near-infrared colours to select a group of 12
spectroscopically-confirmed UKIDSS T dwarfs later than T4. From amongst these
we identify the first two kinematic halo T-dwarf candidates. Blue near-infrared
colours have been attributed to collisionally-induced hydrogen absorption,
which is enhanced by either high surface gravity or low metallicity. Proper
motions are measured and distances estimated, allowing the determination of
tangential velocities. U and V components are estimated for our objects by
assuming radial velocity = 0 km/s. From this, ULAS J0926+0835 is found to have
U=62 km/s and V=-140km/s and ULAS J1319+1209 is found to have U=192 km/s and
V=-92 km/s. These values are consistent with potential halo membership.
However, these are not the bluest objects in our selection. The bluest is ULAS
J1233+1219, with J-K=-1.16 +/- 0.07, and surprisingly this object is found to
have young disc-like U and V. Our sample also contains Hip 73786B, companion to
the metal-poor K5 dwarf Hip 73786. Hip 73786 is a metal-poor star, with
[Fe/H]=-0.3 and is located at a distance of 19 pc. U, V, W space velocity
components are calculated for Hip 73786A and B, finding that U=-48 +/- 7 km/s,
V=-75 +/- 4 km/s and W=-44 +/- 8 km/s. From the properties of the primary, Hip
73786B is found to be at least 1.6 Gyr old. As a metal poor object, Hip 73786B
represents an important addition to the sample of known T dwarf benchmarks.
01/2011;
-
Boletin de la Asociacion Argentina de Astronomia La Plata Argentina. 01/2011; 54:293-296.
-
D Minniti,
J ~J Clariá,
R ~K Saito,
M Hempel, P ~W Lucas,
M Rejkuba,
I Toledo,
O ~A Gonzalez,
J {Alonso-Garc'i}a,
M ~J Irwin, [......],
A ~C Schröder,
M Smith,
L Sodré Jr,
A ~W Stephens,
N ~A Walton,
A ~A Zijlstra,
M Tamura,
C Tappert,
M ~A Thompson,
L Vanzi
Boletin de la Asociacion Argentina de Astronomia La Plata Argentina. 01/2011; 54:265-276.
-
J Borissova,
J ~R ~A Clarke,
C Bonatto,
A -N Chené,
E Bica,
R Kurtev,
R Barbá,
D Minniti,
F Peñaloza,
M Catelan, P ~W Lucas,
F Mauro,
C Moni Bidin,
D Geisler,
V ~D Ivanov,
G Baume,
C Feinstein
Boletin de la Asociacion Argentina de Astronomia La Plata Argentina. 01/2011; 54:277-280.
-
N. R. Deacon,
D. J. Pinfield, P. W. Lucas,
Michael C. Liu,
M. S. Bessell,
B. Burningham,
M. C. Cushing,
A. C. Day-Jones,
S. Dhital,
N. M. Law,
A. K. Mainzer,
Z. H. Zhang
[show abstract]
[hide abstract]
ABSTRACT: Widefield surveys have always provided a rich hunting ground for the coolest stars and brown dwarfs. The single epoch surveys at the beginning of this century greatly expanded the parameter space for ultracool dwarfs. Here we outline the science possible from new multi-epoch surveys which add extra depth and open the time domain to study. Comment: 12 pages, 1 figure, Contribution to Proceedings of Cool Stars 16
12/2010;
-
S. K. Leggett,
L. Albert,
E. Artigau,
Ben Burningham,
X. Delfosse,
P. Delorme,
T. Forveille, P. W. Lucas,
M. S. Marley,
D. J. Pinfield,
C. Reyle,
D. Saumon,
R. L. Smart,
S. J. Warren
[show abstract]
[hide abstract]
ABSTRACT: Mid-infrared data, including Spitzer warm-IRAC [3.6] and [4.5] photometry, is critical for understanding the cold population of brown dwarfs now being found, objects which have more in common with planets than stars. As effective temperature (T_eff) drops from 800 K to 400 K, the fraction of flux emitted beyond 3 microns increases rapidly, from about 40% to >75%. This rapid increase makes a color like H-[4.5] a very sensitive temperature indicator, and it can be combined with a gravity- and metallicity-sensitive color like H-K to constrain all three of these fundamental properties, which in turn gives us mass and age for these slowly cooling objects. Determination of mid-infrared color trends also allows better exploitation of the WISE mission by the community. We use new Spitzer Cycle 6 IRAC photometry, together with published data, to present trends of color with type for L0 to T10 dwarfs. We also use the atmospheric and evolutionary models of Saumon & Marley to investigate the masses and ages of 13 very late-type T dwarfs, which have H-[4.5] > 3.2 and T_eff ~ 500 K to 750 K. Comment: To be published in the on-line version of the Proceedings of Cool Stars 16 (ASP Conference Series). This is an updated version of Leggett et al. 2010 ApJ 710 1627; a photometry compilation is available at http://www.gemini.edu/staff/sleggett
12/2010;
