238 research outputs found
WISEP J180026.60+013453.1: A Nearby Late L Dwarf Near the Galactic Plane
We report a nearby L7.5 dwarf discovered using the Preliminary Data Release
of the Wide-field Infrared Survey Explorer (WISE) and the Two Micron All-Sky
Survey (2MASS). WISEP J180026.60+013453.1 has a motion of 0.42 arcsec/yr and an
estimated distance of 8.8 \pm 1.0 pc. With this distance, it currently ranks as
the sixth closest known L dwarf, although a trigonometric parallax is needed to
confirm this distance. It was previously overlooked because it lies near the
Galactic Plane (b=12). As a relatively bright and nearby late L dwarf with
normal near-infrared colors, W1800+0134 will serve as a benchmark for studies
of cloud-related phenomena in cool substellar atmospheres.Comment: 12 pages, 2 figure, accepted to the Astronomical Journal (AJ
C stars in the outer spheroid of NGC 6822
From a 2 x 2 degree survey of NGC 6822 we have previously established that
this Local Group dwarf irregular galaxy possesses a huge spheroid having more
than one degree in length. This spheroid is in rotation but its rotation curve
is known only within ~15' from the center. It is therefore critical to identify
bright stars belonging to the spheroid to characterize, as far as possible, its
outer kinematics. We use the new wide field near infrared imager CPAPIR,
operated by the SMARTS consortium, to acquire J, Ks images of two 34.8' x 34.8'
areas in the outer spheroid to search for C stars. The colour diagram of the
fields allows the identification of 192 C stars candidates but a study of the
FWHM of the images permits the rejection of numerous non-stellar objects with
colours similar to C stars. We are left with 75 new C stars, their mean Ks
magnitude and mean colour are similar to the bulk of known NGC 6822 C stars.
This outer spheroid survey confirms that the intermediate-age AGB stars are a
major contributor to the stellar populations of the spheroid. The discovery of
some 50 C stars well beyond the limit of the previously known rotation curve
calls for a promising spectroscopic follow-up to a major axis distance of 40'.Comment: 13 page
The ultracool eld dwarfs luminosity function from the Canada-France Brown Dwarf Survey
The Canada-France Brown Dwarf Survey is a wide eld survey for cool brown
dwarfs conducted with the MegaCam camera on the CFHT telescope. Our objectives
are to nd ultracool brown dwarfs and to constrain the eld brown dwarf mass
function from a large and homogeneous sample of L and T dwarfs. We identify
candidates in CFHT/Megacam i' and z' images and follow them up with pointed NIR
imaging on several telescopes. Our survey has to date found 50 T dwarfs
candidates and 170 L or late M dwarf candidates drawn from a larger sample of
1300 candidates with typical ultracool dwarfs i'-z' colours, found in 900
square degrees. We currently have completed the NIR follow-up on a large part
of the survey for all candidates from the latest T dwarfs known to the late L
color range. This allows us to build on a complete and well de ned sample of
ultracool dwarfs to investigate the luminosity function of eld L and T dwarfs.Comment: Cool Stars XV conference. to appear in proceedings of Cool Stars XV
Conferenc
Spitzer Mid-Infrared Photometry of 500 - 750 K Brown Dwarfs
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/slegget
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An optimal point spread function subtraction algorithm for high-contrast imaging: a demonstration with angular differential imaging
Direct imaging of exoplanets is limited by bright quasi-static speckles in the point spread function (PSF) of the central star. This limitation can be reduced by subtraction of reference PSF images. We have developed an algorithm to construct an optimal reference PSF image from an arbitrary set of reference images. This image is built as a linear combination of all available images and is optimized independently inside multiple subsections of the image to ensure that the absolute minimum residual noise is achieved within each subsection. The algorithm developed is completely general and can be used with many high contrast imaging observing strategies, such as angular differential imaging (ADI), roll subtraction, spectral differential imaging, reference star observations, etc. The performance of the algorithm is demonstrated for ADI data. It is shown that for this type of data the new algorithm provides a gain in sensitivity by up 22 to a factor 3 at small separation over the algorithm previously used
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