67 research outputs found
Spectro-Thermometry of M dwarfs and their candidate planets: too hot, too cool, or just right?
We use moderate-resolution spectra of nearby late K and M dwarf stars with
parallaxes and interferometrically determined radii to refine their effective
temperatures, luminosities, and metallicities. We use these revised values to
calibrate spectroscopic techniques to infer the fundamental parameters of more
distant late-type dwarf stars. We demonstrate that, after masking out poorly
modeled regions, the newest version of the PHOENIX atmosphere models accurately
reproduce temperatures derived bolometrically. We apply methods to late-type
hosts of transiting planet candidates in the Kepler field, and calculate
effective temperature, radius, mass, and luminosity with typical errors of 57
K, 7%, 11%, and 13%, respectively. We find systematic offsets between our
values and those from previous analyses of the same stars, which we attribute
to differences in atmospheric models utilized for each study. We investigate
which of the planets in this sample are likely to orbit in the circumstellar
habitable zone. We determine that four candidate planets (KOI 854.01, 1298.02,
1686.01, and 2992.01) are inside of or within 1-sigma of a conservative
definition of the habitable zone, but that several planets identified by
previous analyses are not (e.g. KOI 1422.02 and KOI 2626.01). Only one of the
four habitable-zone planets is Earth sized, suggesting a downward revision in
the occurrence of such planets around M dwarfs. These findings highlight the
importance of measuring accurate stellar parameters when deriving parameters of
their orbiting planets.Comment: 17 pages, 16 figures, accepted to ApJ. Added requisite significant
Figures to Equations 6-8. Fixed a formatting error in the machine readable
tables. All spectra now downloadable from
http://www.as.utexas.edu/~amann/files/th_spec
Protoplanetary Disk Demographics with ALMA.
Ph.D. Thesis. University of HawaiÊ»i at MÄnoa 2017
An ALMA Survey of Protoplanetary Disks in the Orionis Cluster
The Orionis cluster is important for studying protoplanetary disk
evolution, as its intermediate age (3-5 Myr) is comparable to the median
disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas
in 92 protoplanetary disks around Orionis members with
. Our observations cover the 1.33 mm continuum
and several CO lines: out of 92 sources, we detect 37 in the mm
continuum and six in CO, three in CO, and none in CO.
Using the continuum emission to estimate dust mass, we find only 11 disks with
, indicating that after only a few Myr of
evolution most disks lack sufficient dust to form giant planet cores. Stacking
the individually undetected continuum sources limits their average dust mass to
5 lower than that of the faintest detected disk, supporting theoretical
models that indicate rapid dissipation once disk clearing begins. Comparing the
protoplanetary disk population in Orionis to those of other
star-forming regions supports the steady decline in average dust mass and the
steepening of the - relation with age; studying these
evolutionary trends can inform the relative importance of different disk
processes during key eras of planet formation. External photoevaporation from
the central O9 star is influencing disk evolution throughout the region: dust
masses clearly decline with decreasing separation from the photoionizing
source, and the handful of CO detections exist at projected separations
pc. Collectively, our findings indicate that giant planet formation is
inherently rare and/or well underway by a few Myr of age.Comment: 16 pages, 9 figures; published in AJ; The full machine readable
tables can be obtained by downloading and extracting the gzipped tar source
file listed under "Other formats.
The gold standard: accurate stellar and planetary parameters for eight Kepler M dwarf systems enabled by parallaxes
We report parallaxes and proper motions from the Hawaii Infrared Parallax Program for eight nearby M dwarf stars with transiting exoplanets discovered by Kepler. We combine our directly measured distances with mass-luminosity and radiusâluminosity relationships to significantly improve constraints on the host starsâ properties. Our astrometry enables the identification of wide stellar companions to the planet hosts. Within our limited sample, all the multi-transiting planet hosts (three of three) appear to be single stars, while nearly all (four of five) of the systems with a single detected planet have wide stellar companions. By applying strict priors on average stellar density from our updated radius and mass in our transit fitting analysis, we measure the eccentricity probability distributions for each transiting planet. Planets in single-star systems tend to have smaller eccentricities than those in binaries, although this difference is not significant in our small sample. In the case of Kepler-42bcd, where the eccentricities are known to be â0, we demonstrate that such systems can serve as powerful tests of M dwarf evolutionary models by working in Lâ â Ïâ space. The transit-fit density for Kepler- 42bcd is inconsistent with model predictions at 2.1Ï (22%), but matches more empirical estimates at 0.2Ï (2%), consistent with earlier results showing model radii of M dwarfs are underinflated. Gaia will provide high-precision parallaxes for the entire Kepler M dwarf sample, and TESS will identify more planets transiting nearby, late-type stars, enabling significant improvements in our understanding of the eccentricity distribution of small planets and the parameters of late-type dwarfs.Support for Program number HST-HF2-51364.001-A was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper. URL: http://www.tacc.utexas.edu. (HST-HF2-51364.001-A - NASA through Space Telescope Science Institute; NAS5-26555 - NASA; NNX09AF08G - NASA Office of Space Science; NASA Science Mission directorate
New insights into the nature of transition disks from a complete disk survey of the Lupus star forming region
Transition disks with large dust cavities around young stars are promising
targets for studying planet formation. Previous studies have revealed the
presence of gas cavities inside the dust cavities hinting at recently formed,
giant planets. However, many of these studies are biased towards the brightest
disks in the nearby star forming regions, and it is not possible to derive
reliable statistics that can be compared with exoplanet populations. We present
the analysis of 11 transition disks with large cavities (>20 AU radius) from a
complete disk survey of the Lupus star forming region, using ALMA Band 7
observations at 0.3" (22-30 AU radius) resolution of the 345 GHz continuum,
13CO and C18O 3-2 observations and the Spectral Energy Distribution of each
source. Gas and dust surface density profiles are derived using the
physical-chemical modeling code DALI. This is the first study of transition
disks of large cavities within a complete disk survey within a star forming
region. The dust cavity sizes range from 20-90 AU radius and in three cases, a
gas cavity is resolved as well. The deep drops in gas density and large dust
cavity sizes are consistent with clearing by giant planets. The fraction of
transition disks with large cavities in Lupus is ~11%, which is inconsistent
with exoplanet population studies of giant planets at wide orbits. Furthermore,
we present a hypothesis of an evolutionary path for large massive disks
evolving into transition disks with large cavities.Comment: 29 pages, 15 figures, Accepted by Ap
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