12,862 research outputs found
The Densities of Planets in Multiple Stellar Systems
We analyze the effect of companion stars on the bulk density of 29 planets
orbiting 15 stars in the Kepler field. These stars have at least one stellar
companion within 2", and the planets have measured masses and radii, allowing
an estimate of their bulk density. The transit dilution by the companion star
requires the planet radii to be revised upward, even if the planet orbits the
primary star; as a consequence, the planetary bulk density decreases. We find
that, if planets orbited a faint companion star, they would be more
volatile-rich, and in several cases their densities would become
unrealistically low, requiring large, inflated atmospheres or unusually large
mass fractions in a H/He envelope. In addition, for planets detected in radial
velocity data, the primary star has to be the host. We can exclude 14 planets
from orbiting the companion star; the remaining 15 planets in seven planetary
systems could orbit either the primary or the secondary star, and for five of
these planets the decrease in density would be substantial even if they orbited
the primary, since the companion is of almost equal brightness as the primary.
Substantial follow-up work is required in order to accurately determine the
radii of transiting planets. Of particular interest are small, rocky planets
that may be habitable; a lower mean density might imply a more volatile-rich
composition. Reliable radii, masses, and thus bulk densities will allow us to
identify which small planets are truly Earth-like.Comment: Accepted by AJ; 22 page
Spectroscopic Observations of Twenty-one Faint Cataclysmic Variables Candidates
We provide the first minimum light spectroscopic observations for 21
previously known or suspected faint cataclysmic variable candidates. The
sources were selected from the Downes et al. (2001) living edition catalog and
the identified candidates have minimum light magnitudes of V~18-22. We confirm
15 of the candidates to be cataclysmic variables.Comment: 10 pages, 4 figures, accepted by A&
Color and Variability Characteristics of Point Sources in the Faint Sky Variability Survey
We present an analysis of the color and variability characteristics for point
sources in the Faint Sky Variability Survey (FSVS). The FSVS cataloged ~23
square degrees in BVI filters from ~16--24 mag to investigate variability in
faint sources at moderate to high Galactic latitudes. Point source completeness
is found to be >83% for a selected representative sample (V=17.5--22.0 mag,
B-V=0.0--1.5) containing both photometric B, V detections and 80% of the
time-sampled V data available compared to a basic internal source completeness
of 99%. Multi-epoch (10--30) observations in V spanning minutes to years
modeled by light curve simulations reveal amplitude sensitivities to
0.015--0.075 mag over a representative V=18--22 mag range. Periodicity
determinations appear viable to time-scales of an order 1 day or less using the
most sampled fields (~30 epochs). The fraction of point sources is found to be
generally variable at 5--8% over V=17.5--22.0 mag. For V brighter than 19 mag,
the variable population is dominated by low amplitude (<0.05 mag) and blue
(B-V<0.35) sources, possibly representing a population of gamma Doradus stars.
Overall, the dominant population of variable sources are bluer than B-V=0.65
and have Main Sequence colors, likely reflecting larger populations of RR
Lyrae, SX Phe, gamma Doradus, and W UMa variables.Comment: 34 pages, 16 figures, accepted in A
Snowpack ground truth: Radar test site, Steamboat Springs, Colorado, 8-16 April 1976
Ground-truth data taken at Steamboat Springs, Colorado is presented. Data taken during the period April 8, 1976 - April 16, 1976 included the following: (1) snow depths and densities at selected locations (using a Mount Rose snow tube); (2) snow pits for temperature, density, and liquid water determinations using the freezing calorimetry technique and vertical layer classification; (3) snow walls were also constructed of various cross sections and documented with respect to sizes and snow characteristics; (4) soil moisture at selected locations; and (5) appropriate air temperature and weather data
A Search for Variable Stars and Planetary Occultations in NGC2301 I: Techniques
We observed the young open cluster NGC 2301 for 14 nights in Feb. 2004 using
the orthogonal transfer CCD camera (OPTIC). We used PSF shaping techniques
("square stars") during the observations allowing a larger dynamic range (4.5
magnitudes) of high photometric precision results (2 mmag) to be obtained.
These results are better than similar observing campaigns using standard CCD
imagers. This paper discusses our observational techniques and presents initial
results for the variability statistics found in NGC 2301. Details of the
variability statistics as functions of color, variability type, stellar type,
and cluster location will appear in paper II
High spectral resolution time-resolved optical spectroscopy of V893 Sco
We present high resolution time-resolved optical spectra of the high
inclination short orbital period dwarf nova V893 Sco. We performed spectral
analysis through radial velocity measurements, Doppler mapping, and ratioed
Doppler maps. Our results indicate that V893 Sco's accretion disk is dissimilar
to WZ Sge's accretion disk, and does not fit any of the current accretion disk
models. We derive the system parameters M1 and i, and present evidence for V893
Sco as a very young cataclysmic variable and an ER UMa star. We advance the
hypothesis that all ER UMa stars may be newly formed cataclysmic variables.Comment: 23 pages (total), 8 figures, accepted by Ap
Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters
In this work, we quantify the effect of an unresolved companion star on the derived stellar parameters of the primary star if a blended spectrum is fit assuming the star is single. Fitting tools that determine stellar parameters from spectra typically fit for a single star, but we know that up to half of all exoplanet host stars may have one or more companion stars. We use high-resolution spectra of planet host stars in the Kepler field from the California-Kepler Survey to create simulated binaries; we select eight stellar pairs and vary the contribution of the secondary star, then determine stellar parameters with SpecMatch-Emp and compare them to the parameters derived for the primary star alone. We find that, in most cases, the effective temperature, surface gravity, metallicity, and stellar radius derived from the composite spectrum are within 2–3σ of the values determined from the unblended spectrum, but the deviations depend on the properties of the two stars. Relatively bright companion stars that are similar to the primary star have the largest effect on the derived parameters; in these cases, the stellar radii can be overestimated by up to 60%. We find that metallicities are generally underestimated, with values up to eight times smaller than the typical uncertainty in [Fe/H]. Our study shows that follow-up observations are necessary to detect or set limits on stellar companions of planetary host stars so that stellar (and planet) parameters are as accurate as possible
On the new short orbital period cataclysmic variable Halpha0242-2802
We present results from our phase-resolved spectroscopy of the newly
identified cataclysmic variable Halpha0242-2802. Halpha0242-2802 was identified
from a deep UK Schmidt Halpha-R band survey as a candidate cataclysmic
variable. Although initial spectroscopy revealed an optical spectrum very
similar to that of the famous short orbital period system WZ Sge, the analysis
of our data shows that this is not the case. Halpha0242-28 differs from WZ Sge
in both the accretion disk structure and the orbital period. In particular,
Halpha0242-28 appears to be a system which has not reached the orbital period
minimum, yet.Comment: 9 pages, 6 figures. In pres
Unresolved Binary Exoplanet Host Stars Fit as Single Stars: Effects on the Stellar Parameters
In this work we quantify the effect of an unresolved companion star on the
derived stellar parameters of the primary star if a blended spectrum is fit
assuming the star is single. Fitting tools that determine stellar parameters
from spectra typically fit for a single star, but we know that up to half of
all exoplanet host stars may have one or more companion stars. We use
high-resolution spectra of planet host stars in the Kepler field from the
California-Kepler Survey to create simulated binaries; we select 8 stellar
pairs and vary the contribution of the secondary star, then determine stellar
parameters with SpecMatch-Emp and compare them to the parameters derived for
the primary star alone. We find that in most cases the effective temperature,
surface gravity, metallicity, and stellar radius derived from the composite
spectrum are within 2-3 of the values determined from the unblended
spectrum, but the deviations depend on the properties of the two stars.
Relatively bright companion stars that are similar to the primary star have the
largest effect on the derived parameters; in these cases the stellar radii can
be overestimated by up to 60%. We find that metallicities are generally
underestimated, with values up to 8 times smaller than the typical uncertainty
in [Fe/H]. Our study shows that follow-up observations are necessary to detect
or set limits on stellar companions of planetary host stars so that stellar
(and planet) parameters are as accurate as possible.Comment: Accepted by ApJ; 20 page
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