547 research outputs found
Understanding The Effects Of Stellar Multiplicity On The Derived Planet Radii From Transit Surveys: Implications for Kepler, K2, and TESS
We present a study on the effect of undetected stellar companions on the
derived planetary radii for the Kepler Objects of Interest (KOIs). The current
production of the KOI list assumes that the each KOI is a single star. Not
accounting for stellar multiplicity statistically biases the planets towards
smaller radii. The bias towards smaller radii depends on the properties of the
companion stars and whether the planets orbit the primary or the companion
stars. Defining a planetary radius correction factor , we find that if the
KOIs are assumed to be single, then, {\it on average}, the planetary radii may
be underestimated by a factor of . If typical
radial velocity and high resolution imaging observations are performed and no
companions are detected, this factor reduces to . The correction factor is dependent upon the primary
star properties and ranges from for A and F
stars to for K and M stars. For missions like
K2 and TESS where the stars may be closer than the stars in the Kepler target
sample, observational vetting (primary imaging) reduces the radius correction
factor to . Finally, we show that if the
stellar multiplicity rates are not accounted for correctly, occurrence rate
calculations for Earth-sized planets may overestimate the frequency of small
planets by as much as \%.Comment: 10 pages, 6 Figures, Accepted for publication in The Astrophysical
Journal (Fix typo in Equation 6 of original astroph submission; correction
also submitted to Journal
Masses, Luminosities, and Orbital Coplanarities of the mu Orionis Quadruple Star System from PHASES Differential Astrometry
mu Orionis was identified by spectroscopic studies as a quadruple star
system. Seventeen high precision differential astrometry measurements of mu Ori
have been collected by the Palomar High-precision Astrometric Search for
Exoplanet Systems (PHASES). These show both the motion of the long period
binary orbit and short period perturbations superimposed on that caused by each
of the components in the long period system being themselves binaries. The new
measurements enable the orientations of the long period binary and short period
subsystems to be determined. Recent theoretical work predicts the distribution
of relative inclinations between inner and outer orbits of hierarchical systems
to peak near 40 and 140 degrees. The degree of coplanarity of this complex
system is determined, and the angle between the planes of the A-B and Aa-Ab
orbits is found to be 136.7 +/- 8.3 degrees, near the predicted distribution
peak at 140 degrees; this result is discussed in the context of the handful of
systems with established mutual inclinations. The system distance and masses
for each component are obtained from a combined fit of the PHASES astrometry
and archival radial velocity observations. The component masses have relative
precisions of 5% (component Aa), 15% (Ab), and 1.4% (each of Ba and Bb). The
median size of the minor axes of the uncertainty ellipses for the new
measurements is 20 micro-arcseconds. Updated orbits for delta Equulei, kappa
Pegasi, and V819 Herculis are also presented.Comment: 12 Pages, Accepted for publication in A
Assessing the Effect of Stellar Companions from High-Resolution Imaging of Kepler Objects of Interest
We report on 176 close (<2") stellar companions detected with high-resolution
imaging near 170 hosts of Kepler Objects of Interest. These Kepler targets were
prioritized for imaging follow-up based on the presence of small planets, so
most of the KOIs in these systems (176 out of 204) have nominal radii <6 R_E .
Each KOI in our sample was observed in at least 2 filters with adaptive optics,
speckle imaging, lucky imaging, or HST. Multi-filter photometry provides color
information on the companions, allowing us to constrain their stellar
properties and assess the probability that the companions are physically bound.
We find that 60 -- 80% of companions within 1" are bound, and the bound
fraction is >90% for companions within 0.5"; the bound fraction decreases with
increasing angular separation. This picture is consistent with simulations of
the binary and background stellar populations in the Kepler field. We also
reassess the planet radii in these systems, converting the observed
differential magnitudes to a contamination in the Kepler bandpass and
calculating the planet radius correction factor, . Under the assumption that planets in bound binaries are equally
likely to orbit the primary or secondary, we find a mean radius correction
factor for planets in stellar multiples of . If stellar
multiplicity in the Kepler field is similar to the solar neighborhood, then
nearly half of all Kepler planets may have radii underestimated by an average
of 65%, unless vetted using high resolution imaging or spectroscopy.Comment: 23 pages, 12 figures. Accepted for publication in The Astronomical
Journa
Detection of Planetary and Stellar Companions to Neighboring Stars via a Combination of Radial Velocity and Direct Imaging Techniques
13 pages, 6 figures, 4 tables, accepted for publication in the Astronomical Journal (submitted 25 Feb 2019; accepted 28 April 2019). Machine readable tables and Posteriors from the RadVel fits are available here: http://stephenkane.net/rvfits.tarThe sensitivities of radial velocity (RV) surveys for exoplanet detection are extending to increasingly longer orbital periods, where companions with periods of several years are now being regularly discovered. Companions with orbital periods that exceed the duration of the survey manifest in the data as an incomplete orbit or linear trend, a feature that can either present as the sole detectable companion to the host star, or as an additional signal overlain on the signatures of previously discovered companion(s). A diagnostic that can confirm or constrain scenarios in which the trend is caused by an unseen stellar rather than planetary companion is the use of high-contrast imaging observations. Here, we present RV data from the Anglo-Australian Planet Search (AAPS) for 20 stars that show evidence of orbiting companions. Of these, six companions have resolved orbits, with three that lie in the planetary regime. Two of these (HD 92987b and HD 221420b) are new discoveries. Follow-up observations using the Differential Speckle Survey Instrument (DSSI) on the Gemini South telescope revealed that 5 of the 20 monitored companions are likely stellar in nature. We use the sensitivity of the AAPS and DSSI data to place constraints on the mass of the companions for the remaining systems. Our analysis shows that a planetary-mass companion provides the most likely self-consistent explanation of the data for many of the remaining systems.Peer reviewedFinal Accepted Versio
Religious Extremism and Global Violence: What We Knew before September 11 and Why We Ignored It
Observations of Binary Stars with the Differential Speckle Survey Instrument. VII. Measures from 2010 September to 2012 February at the WIYN Telescope
We report on speckle observations of binary stars carried out at the WIYN
Telescope over the period from September 2010 through February 2012, providing
relative astrometry for 2521 observations of 883 objects, 856 of which are
double stars and 27 of which are triples. The separations measured span a range
of 0.01 to 1.75 arc seconds. Wavelengths of 562 nm, 692 nm, and 880 nm were
used, and differential photometry at one or more of these wavelengths is
presented in most cases. Sixty-six components were resolved for the first time.
We also estimate detection limits at 0.2 and 1.0 arc seconds for high-quality
observations in cases where no companion was seen, a total of 176 additional
objects. Detection limits vary based on observing conditions and
signal-to-noise ratio, but are approximately 4 magnitudes at 0.2 arc seconds
and 6 magnitudes at 1.0 arc seconds on average. Analyzing the measurement
precision of the data set, we find that the individual separations obtained
have linear measurement uncertainties of approximately 2 mas, and photometry is
uncertain to approximately 0.1 magnitudes in general. This work provides
fundamental, well-calibrated data for future orbit and mass determinations, and
we present three first orbits and total mass estimates of nearby K-dwarf
systems as examples of this potential
Discovery of a compact companion to a nearby star
Radial velocity (RV) searches for exoplanets have surveyed many of the nearest and brightest stars for long-term velocity variations indicative of a companion body. Such surveys often detect high-amplitude velocity signatures of objects that lie outside the planetary mass regime, most commonly those of a low-mass star. Such stellar companions are frequently discarded as false-alarms to the main science goals of the survey, but high-resolution imaging techniques can be employed to either directly detect or place significant constraints on the nature of the companion object. Here, we present the discovery of a compact companion to the nearby star HD 118475. Our Anglo-Australian Telescope RV data allow the extraction of the full Keplerian orbit of the companion, which is found to have a minimum mass of 0.445 M⊙. Follow-up speckle imaging observations at the predicted time of maximum angular separation rule out a main-sequence star as the source of the RV signature at the 3.3σ significance level, implying that the companion must be a low-luminosity compact object, most likely a white dwarf. We provide an isochrone analysis combined with our data that constrain the possible inclinations of the binary orbit. We discuss the eccentric orbit of the companion in the context of tidal circularization timescales and show that non-circular orbit was likely inherited from the progenitor. Finally, we emphasize the need for utilizing such an observation method to further understand the demographics of white dwarf companions around nearby stars
The POKEMON Speckle Survey of Nearby M dwarfs. I. New Discoveries
M dwarfs are favorable targets for exoplanet detection with current
instrumentation, but stellar companions can induce false positives and inhibit
planet characterization. Knowledge of stellar companions is also critical to
our understanding of how binary stars form and evolve. We have therefore
conducted a survey of stellar companions around nearby M dwarfs, and here we
present our new discoveries. Using the DSSI speckle imager at the 4.3-meter
Lowell Discovery Telescope, and the similar NESSI instrument at the 3.5-meter
WIYN telescope, we carried out a volume-limited survey of M-dwarf multiplicity
to 15 parsecs, with a special emphasis on including the later M dwarfs that
were overlooked in previous surveys. Additional brighter targets at larger
distances were included for a total sample size of 1070 M dwarfs. Observations
of these 1070 targets revealed 26 new companions; 22 of these systems were
previously thought to be single. If all new discoveries are confirmed, then the
number of known multiples in the sample will increase by 7.6%. Using our
observed properties, as well as the parallaxes and 2MASS K magnitudes for these
objects, we calculate the projected separation, and estimate the mass ratio and
component spectral types, for these systems. We report the discovery of a new
M-dwarf companion to the white dwarf Wolf 672 A, which hosts a known M-dwarf
companion as well, making the system trinary. We also examine the possibility
that the new companion to 2MASS J13092185-2330350 is a brown dwarf. Finally, we
discuss initial insights from the POKEMON survey.Comment: 23 pages, 6 figures, 5 table
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