40 research outputs found
Characterizing the Cool KOIs II. The M Dwarf KOI-254 and its Hot Jupiter
We report the confirmation and characterization of a transiting gas giant
planet orbiting the M dwarf KOI-254 every 2.455239 days, which was originally
discovered by the Kepler mission. We use radial velocity measurements, adaptive
optics imaging and near infrared spectroscopy to confirm the planetary nature
of the transit events. KOI-254b is the first hot Jupiter discovered around an
M-type dwarf star. We also present a new model-independent method of using
broadband photometry to estimate the mass and metallicity of an M dwarf without
relying on a direct distance measurement. Included in this methodology is a new
photometric metallicity calibration based on J-K colors. We use this technique
to measure the physical properties of KOI-254 and its planet. We measure a
planet mass of Mp = 0.505 Mjup, radius Rp = 0.96 Rjup and semimajor axis a =
0.03 AU, based on our measured stellar mass Mstar = 0.59 Msun and radius Rstar
= 0.55 Rsun. We also find that the host star is metal-rich, which is consistent
with the sample of M-type stars known to harbor giant planets.Comment: AJ accepted (in press
Characterization the Cool KOIs. II. The M Dwarf KOI-254 and its Hot Jupiter
We report the confirmation and characterization of a transiting gas giant planet orbiting the M dwarf KOI-254 every 2.455239 days, which was originally discovered by the Kepler mission. We use radial velocity measurements, adaptive optics imaging, and near-infrared spectroscopy to confirm the planetary nature of the transit events. KOI-254 b is the first hot Jupiter discovered around an M-type dwarf star. We also present a new model-independent method of using broadband photometry to estimate the mass and metallicity of an M dwarf without relying on a direct distance measurement. Included in this methodology is a new photometric metallicity calibration based on J ā K colors. We use this technique to measure the physical properties of KOI-254 and its planet. We measure a planet mass of M_P = 0.505 M_(Jup), radius R_P = 0.96 R_(Jup), and semimajor axis a = 0.030 AU, based on our measured stellar mass M_* = 0.59 M_ā and radius R_* = 0.55 R_ā. We also find that the host star is metal-rich, which is consistent with the sample of M-type stars known to harbor giant planets
Visual orbit of GJ 164 AB
We report seven successful observations of the astrometric binary GJ 164 AB
system with aperture masking interferometry. The companion, with a near
infrared contrast of 5:1 was detected beyond the formal diffraction limit.
Combined with astrometric observations from the literature, these observations
fix the parallax of the system, and allow a model-independent mass
determination of both components. We find the mass of GJ 164B to be 0.086 \pm
0.007 M_{\sun}. An infrared spectroscopic study of a sample of M-Dwarfs
outlines a method for calibrating metallicity of M-Dwarfs. Results from the
newly commissionned TripleSpec spectrograph reveal that the GJ 164 system is at
least of Solar metallicity. Models are not consistent with color and mass,
requiring a very young age to accommodate a secondary too luminous, a scenario
ruled out by the kinematics.Comment: 9 pages, 8 figures. Submitted to Ap
Evidence for an FU Orionis-like Outburst from a Classical T Tauri Star
We present pre- and post-outburst observations of the new FU Orionis-like
young stellar object PTF 10qpf (also known as LkHa 188-G4 and HBC 722). Prior
to this outburst, LkHa 188-G4 was classified as a classical T Tauri star on the
basis of its optical emission-line spectrum superposed on a K8-type
photosphere, and its photometric variability. The mid-infrared spectral index
of LkHa 188-G4 indicates a Class II-type object. LkHa 188-G4 exhibited a steady
rise by ~1 mag over ~11 months starting in Aug. 2009, before a subsequent more
abrupt rise of > 3 mag on a time scale of ~2 months. Observations taken during
the eruption exhibit the defining characteristics of FU Orionis variables: (i)
an increase in brightness by > 4 mag, (ii) a bright optical/near-infrared
reflection nebula appeared, (iii) optical spectra are consistent with a G
supergiant and dominated by absorption lines, the only exception being Halpha
which is characterized by a P Cygni profile, (iv) near-infrared spectra
resemble those of late K--M giants/supergiants with enhanced absorption seen in
the molecular bands of CO and H_2O, and (v) outflow signatures in H and He are
seen in the form of blueshifted absorption profiles. LkHa 188-G4 is the first
member of the FU Orionis-like class with a well-sampled optical to mid-infrared
spectral energy distribution in the pre-outburst phase. The association of the
PTF 10qpf outburst with the previously identified classical T Tauri star LkHa
188-G4 (HBC 722) provides strong evidence that FU Orionis-like eruptions
represent periods of enhanced disk accretion and outflow, likely triggered by
instabilities in the disk. The early identification of PTF 10qpf as an FU
Orionis-like variable will enable detailed photometric and spectroscopic
observations during its post-outburst evolution for comparison with other known
outbursting objects.Comment: 14 pages, 11 figures, ApJ accepte
Stellar and Planetary Characterization of the Ross 128 Exoplanetary System from APOGEE Spectra
The first detailed chemical abundance analysis of the M dwarf (M4.0)
exoplanet-hosting star Ross 128 is presented here, based upon near-infrared
(1.5--1.7 \micron) high-resolution (22,500) spectra from the
SDSS-APOGEE survey. We determined precise atmospheric parameters =3231100K, log=4.960.11 dex and chemical abundances of eight
elements (C, O, Mg, Al, K, Ca, Ti, and Fe), finding Ross 128 to have near solar
metallicity ([Fe/H] = +0.030.09 dex). The derived results were obtained
via spectral synthesis (1-D LTE) adopting both MARCS and PHOENIX model
atmospheres; stellar parameters and chemical abundances derived from the
different adopted models do not show significant offsets. Mass-radius modeling
of Ross 128b indicate that it lies below the pure rock composition curve,
suggesting that it contains a mixture of rock and iron, with the relative
amounts of each set by the ratio of Fe/Mg. If Ross 128b formed with a sub-solar
Si/Mg ratio, and assuming the planet's composition matches that of the
host-star, it likely has a larger core size relative to the Earth. The derived
planetary parameters -- insolation flux (S=1.790.26) and
equilibrium temperature (=29410K) -- support previous findings
that Ross 128b is a temperate exoplanet in the inner edge of the habitable
zone.Comment: Accepted in ApJLetters, 3 figures, 2 tables, 12 page
Characterizing the Cool KOIs III. KOI-961: A Small Star with Large Proper Motion and Three Small Planets
We present the characterization of the star KOI 961, an M dwarf with transit
signals indicative of three short-period exoplanets, originally discovered by
the Kepler Mission. We proceed by comparing KOI 961 to Barnard's Star, a
nearby, well-characterized mid-M dwarf. By comparing colors, optical and
near-infrared spectra, we find remarkable agreement between the two, implying
similar effective temperatures and metallicities. Both are metal-poor compared
to the Solar neighborhood, have low projected rotational velocity, high
absolute radial velocity, large proper motion and no quiescent H-alpha
emission--all of which is consistent with being old M dwarfs. We combine
empirical measurements of Barnard's Star and expectations from evolutionary
isochrones to estimate KOI 961's mass (0.13 +/- 0.05 Msun), radius (0.17 +/-
0.04 Rsun) and luminosity (2.40 x 10^(-3.0 +/- 0.3) Lsun). We calculate KOI
961's distance (38.7 +/- 6.3 pc) and space motions, which, like Barnard's Star,
are consistent with a high scale-height population in the Milky Way. We perform
an independent multi-transit fit to the public Kepler light curve and
significantly revise the transit parameters for the three planets. We calculate
the false-positive probability for each planet-candidate, and find a less than
1% chance that any one of the transiting signals is due to a background or
hierarchical eclipsing binary, validating the planetary nature of the transits.
The best-fitting radii for all three planets are less than 1 Rearth, with KOI
961.03 being Mars-sized (Rp = 0.57 +/- 0.18 Rearth), and they represent some of
the smallest exoplanets detected to date.Comment: Accepted to Ap
LHS 1815b: The First Thick-disk Planet Detected by TESS
We report the first discovery of a thick-disk planet, LHS 1815b (TOI-704b, TIC 260004324), detected in the Transiting Exoplanet Survey Satellite (TESS) survey. LHS 1815b transits a bright (V = 12.19 mag, K = 7.99 mag) and quiet M dwarf located 29.87 Ā± 0.02 pc away with a mass of 0.502 Ā± 0.015 M oĖ and a radius of 0.501 Ā± 0.030 R oĖ. We validate the planet by combining space- and ground-based photometry, spectroscopy, and imaging. The planet has a radius of 1.088 Ā± 0.064 R ā with a 3Ļ mass upper limit of 8.7 M ā. We analyze the galactic kinematics and orbit of the host star LHS 1815 and find that it has a large probability (P thick/P thin = 6482) to be in the thick disk with a much higher expected maximal height (Z max = 1.8 kpc) above the Galactic plane compared with other TESS planet host stars. Future studies of the interior structure and atmospheric properties of planets in such systems using, for example, the upcoming James Webb Space Telescope, can investigate the differences in formation efficiency and evolution for planetary systems between different Galactic components (thick disks, thin disks, and halo)