617 research outputs found
The Gemini NICI Planet-Finding Campaign: Discovery of a Close Substellar Companion to the Young Debris Disk Star PZ Tel
We report the discovery of a tight substellar companion to the young solar
analog PZ Tel, a member of the Beta Pictoris moving group observed with high
contrast adaptive optics imaging as part of the Gemini NICI Planet-Finding
Campaign. The companion was detected at a projected separation of 16.4 +/- 1.0
AU (0.33 +/- 0.01") in April 2009. Second-epoch observations in May 2010
demonstrate that the companion is physically associated and shows significant
orbital motion. Monte Carlo modeling constrains the orbit of PZ Tel B to
eccentricities > 0.6. The near-IR colors of PZ Tel B indicate a spectral type
of M7+/-2 and thus this object will be a new benchmark companion for studies of
ultracool, low-gravity photospheres. Adopting an age of 12 +8 -4 Myr for the
system, we estimate a mass of 36 +/- 6 Mjup based on the Lyon/DUSTY
evolutionary models. PZ Tel B is one of few young substellar companions
directly imaged at orbital separations similar to those of giant planets in our
own solar system. Additionally, the primary star PZ Tel A shows a 70 um
emission excess, evidence for a significant quantity of circumstellar dust that
has not been disrupted by the orbital motion of the companion.Comment: 15 pages, 4 figures, to appear in ApJ Letter
A Spectroscopic Binary at the M/L Transition
We report the discovery of a single-lined spectroscopic binary with an Ultra
Cool Dwarf (UCD) primary with a spectral type between M8 and L0.5. This system
was discovered during the course of an ongoing survey to monitor L dwarfs for
radial velocity variations and is the first known small separation (a<1 AU)
spectroscopic binary among dwarfs at the M/L transition. Based on
radial-velocity measurements with a typical precision of 300 m/s we estimate
the orbital parameters of this system to be P=246.73+/-0.49 d, a1
sin(i)=0.159+/-0.003 AU, M2 sin(i)=0.2062 (M1+M2)^(2/3)+/-0.0034 M_{\sun}.
Assuming a primary mass of M1=0.08M_{\sun} (based on spectral type), we
estimate the secondary minimum mass to be M2 sin(i)=0.054 M_{\sun}. With future
photometric, spectroscopic, and interferometric observations it may be possible
to determine the dynamical masses of both components directly, making this
system one of the best characterized UCD binaries known.Comment: 11 pages, 2 figures. Accepted for publication in ApJ Letter
A Search for Planets Transiting the M Dwarf Debris Disk Host, AU Microscopii
We present high cadence, high precision multi-band photometry of the young,
M1Ve, debris disk star, AU Microscopii. The data were obtained in three
continuum filters spanning a wavelength range from 4500\AA to 6600\AA, plus
H, over 28 nights in 2005. The lightcurves show intrinsic stellar
variability due to starspots with an amplitude in the blue band of 0.051
magnitudes and a period of 4.847 days. In addition, three large flares were
detected in the data which all occur near the minimum brightness of the star.
We remove the intrinsic stellar variability and combine the lightcurves of all
the filters in order to search for transits by possible planetary companions
orbiting in the plane of the nearly edge-on debris disk. The combined final
lightcurve has a sampling of 0.35 minutes and a standard deviation of 6.8
millimags (mmag). We performed Monte Carlo simulations by adding fake transits
to the observed lightcurve and find with 95% significance that there are no
Jupiter mass planets orbiting in the plane of the debris disk on circular
orbits with periods, P days. In addition, there are no young
Neptune-like planets (with radii 2.5 smaller than the young Jupiter) on
circular orbits with periods, P days.Comment: accepted to MNRA
Seventy-One New L and T Dwarfs from the Sloan Digital Sky Survey
We present near-infrared observations of 71 newly discovered L and T dwarfs,
selected from imaging data of the Sloan Digital Sky Survey (SDSS) using the
i-dropout technique. Sixty-five of these dwarfs have been classified
spectroscopically according to the near-infrared L dwarf classification scheme
of Geballe et al. and the unified T dwarf classification scheme of Burgasser et
al. The spectral types of these dwarfs range from L3 to T7, and include the
latest types yet found in the SDSS. Six of the newly identified dwarfs are
classified as early- to mid-L dwarfs according to their photometric
near-infrared colors, and two others are classified photometrically as M
dwarfs. We also present new near-infrared spectra for five previously published
SDSS L and T dwarfs, and one L dwarf and one T dwarf discovered by Burgasser et
al. from the Two Micron All Sky Survey. The new SDSS sample includes 27 T
dwarfs and 30 dwarfs with spectral types spanning the complex L-T transition
(L7-T3). We continue to see a large (~0.5 mag) spread in J-H for L3 to T1
types, and a similar spread in H-K for all dwarfs later than L3. This color
dispersion is probably due to a range of grain sedimentation properties,
metallicity, and gravity. We also find L and T dwarfs with unusual colors and
spectral properties that may eventually help to disentangle these effects.Comment: accepted by AJ, 18 pages, 10 figures, 5 tables, emulateapj layou
Companions of Stars: From Other Stars to Brown Dwarfs to Planets: The Discovery of the First Methane Brown Dwarf
The discovery of the first methane brown dwarf provides a framework for
describing the important advances in both fundamental physics and astrophysics
that are due to the study of companions of stars. I present a few highlights of
the history of this subject along with details of the discovery of the brown
dwarf Gliese 229B. The nature of companions of stars is discussed with an
attempt to avoid biases induced by anthropocentric nomenclature. With the newer
types of remote reconnaissance of nearby stars and their systems of companions,
an exciting and perhaps even more profound set of contributions to science is
within reach in the near future. This includes an exploration of the diversity
of planets in the universe and perhaps soon the first solid evidence for
biological activity outside our Solar System.Comment: 31 pages, 13 figure
A Resolved Millimeter Emission Belt in the AU Mic Debris Disk
We present imaging observations at 1.3 millimeters of the debris disk
surrounding the nearby M-type flare star AU Mic with beam size 3 arcsec (30 AU)
from the Submillimeter Array. These data reveal a belt of thermal dust emission
surrounding the star with the same edge-on geometry as the more extended
scattered light disk detected at optical wavelengths. Simple modeling indicates
a central radius of ~35 AU for the emission belt. This location is consistent
with the reservoir of planetesimals previously invoked to explain the shape of
the scattered light surface brightness profile through size-dependent dust
dynamics. The identification of this belt further strengthens the kinship
between the debris disks around AU Mic and its more massive sister star beta
Pic, members of the same ~10 Myr-old moving group.Comment: 10 pages, 2 figures. Accepted for publication in ApJ Letter
Sub-Pixel Response Measurement of Near-Infrared Sensors
Wide-field survey instruments are used to efficiently observe large regions
of the sky. To achieve the necessary field of view, and to provide a higher
signal-to-noise ratio for faint sources, many modern instruments are
undersampled. However, precision photometry with undersampled imagers requires
a detailed understanding of the sensitivity variations on a scale much smaller
than a pixel. To address this, a near-infrared spot projection system has been
developed to precisely characterize near-infrared focal plane arrays and to
study the effect of sub-pixel non uniformity on precision photometry.
Measurements of large format near-infrared detectors demonstrate the power of
this system for understanding sub-pixel response.Comment: 9 pages, 13 figures, submitted to PAS
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