117 research outputs found
KOI-1003: A new spotted, eclipsing RS CVn binary in the Kepler field
Using the high-precision photometry from the Kepler space telescope,
thousands of stars with stellar and planetary companions have been observed.
The characterization of stars with companions is not always straightforward and
can be contaminated by systematic and stellar influences on the light curves.
Here, through a detailed analysis of starspots and eclipses, we identify
KOI-1003 as a new, active RS CVn star---the first identified with data from
Kepler. The Kepler light curve of this close binary system exhibits the
system's primary transit, secondary eclipse, and starspot evolution of two
persistent active longitudes. The near equality of the system's orbital and
rotation periods indicates the orbit and primary star's rotation are nearly
synchronized ( days; days). By assuming the secondary star is on the main sequence, we suggest
the system consists of a subgiant primary and
a main-sequence companion. Our work gives a
distance of pc and an age of Gyr,
parameters which are discrepant with previous studies that included the star as
a member of the open cluster NGC 6791.Comment: 21 pages, 19 figures, accepted to Ap
Imaging starspot evolution on Kepler target KIC 5110407 using light curve inversion
The Kepler target KIC 5110407, a K-type star, shows strong quasi-periodic
light curve fluctuations likely arising from the formation and decay of spots
on the stellar surface rotating with a period of 3.4693 days. Using an
established light-curve inversion algorithm, we study the evolution of the
surface features based on Kepler space telescope light curves over a period of
two years (with a gap of .25 years). At virtually all epochs, we detect at
least one large spot group on the surface causing a 1-10% flux modulation in
the Kepler passband. By identifying and tracking spot groups over a range of
inferred latitudes, we measured the surface differential rotation to be much
smaller than that found for the Sun. We also searched for a correlation between
the seventeen stellar flares that occurred during our observations and the
orientation of the dominant surface spot at the time of each flare. No
statistically-significant correlation was found except perhaps for the very
brightest flares, suggesting most flares are associated with regions devoid of
spots or spots too small to be clearly discerned using our reconstruction
technique. While we may see hints of long-term changes in the spot
characteristics and flare statistics within our current dataset, a longer
baseline of observation will be needed to detect the existence of a magnetic
cycle in KIC 5110407.Comment: 32 pages, 15 figures, accepted to Ap
Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: II. omicron Draconis, a Candidate for Recent Low-Mass Companion Ingestion
To measure the stellar and orbital properties of the metal-poor RS CVn binary
o Draconis (o Dra), we directly detect the companion using interferometric
observations obtained with the Michigan InfraRed Combiner at Georgia State
University's Center for High Angular Resolution Astronomy (CHARA) Array. The
H-band flux ratio between the primary and secondary stars is the highest
confirmed flux ratio (370 +/- 40) observed with long-baseline optical
interferometry. These detections are combined with radial velocity data of both
the primary and secondary stars, including new data obtained with the
Tillinghast Reflector Echelle Spectrograph on the Tillinghast Reflector at the
Fred Lawrence Whipple Observatory and the 2-m Tennessee State University
Automated Spectroscopic Telescope at Fairborn Observatory. We determine an
orbit from which we find model-independent masses and ages of the components
(M_A = 1.35 +\- 0.05 M_Sun, M_B = 0.99 +\- 0.02 M_Sun, system age = 3.0 -\+ 0.5
Gyr). An average of a 23-year light curve of o Dra from the Tennessee State
University Automated Photometric Telescope folded over the orbital period newly
reveals eclipses and the quasi-sinusoidal signature of ellipsoidal variations.
The modeled light curve for our system's stellar and orbital parameters confirm
these ellipsoidal variations due to the primary star partially filling its
Roche lobe potential, suggesting most of the photometric variations are not due
to stellar activity (starspots). Measuring gravity darkening from the average
light curve gives a best-fit of beta = 0.07 +\- 0.03, a value consistent with
conventional theory for convective envelope stars. The primary star also
exhibits an anomalously short rotation period, which, when taken with other
system parameters, suggests the star likely engulfed a low-mass companion that
had recently spun-up the star.Comment: 14 pages, 13 figures, Accepted to Ap
Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: I. sigma Geminorum
To measure the properties of both components of the RS CVn binary sigma
Geminorum (sigma Gem), we directly detect the faint companion, measure the
orbit, obtain model-independent masses and evolutionary histories, detect
ellipsoidal variations of the primary caused by the gravity of the companion,
and measure gravity darkening. We detect the companion with interferometric
observations obtained with the Michigan InfraRed Combiner (MIRC) at Georgia
State University's Center for High Angular Resolution Astronomy (CHARA) Array
with a primary-to-secondary H-band flux ratio of 270+/-70. A radial velocity
curve of the companion was obtained with spectra from the Tillinghast Reflector
Echelle Spectrograph (TRES) on the 1.5-m Tillinghast Reflector at Fred Lawrence
Whipple Observatory (FLWO). We additionally use new observations from the
Tennessee State University Automated Spectroscopic and Photometric Telescopes
(AST and APT, respectively). From our orbit, we determine model-independent
masses of the components (M_1 = 1.28 +/- 0.07 M_Sun, M_2 = 0.73 +/- 0.03
M_Sun), and estimate a system age of 5 -/+ 1 Gyr. An average of the 27-year APT
light curve of sigma Gem folded over the orbital period (P = 19.6027 +/- 0.0005
days) reveals a quasi-sinusoidal signature, which has previously been
attributed to active longitudes 180 deg apart on the surface of sigma Gem. With
the component masses, diameters, and orbit, we find that the predicted light
curve for ellipsoidal variations due to the primary star partially filling its
Roche lobe potential matches well with the observed average light curve,
offering a compelling alternative explanation to the active longitudes
hypothesis. Measuring gravity darkening from the light curve gives beta < 0.1,
a value slightly lower than that expected from recent theory.Comment: Accepted to ApJ, 11 pages, 6 figures, 8 table
EXPRES. II. Searching for Planets Around Active Stars: A Case Study of HD 101501
By controlling instrumental errors to below 10 cm/s, the EXtreme PREcision
Spectrograph (EXPRES) allows for a more insightful study of photospheric
velocities that can mask weak Keplerian signals. Gaussian Processes (GP) have
become a standard tool for modeling correlated noise in radial velocity
datasets. While GPs are constrained and motivated by physical properties of the
star, in some cases they are still flexible enough to absorb unresolved
Keplerian signals. We apply GP regression to EXPRES radial velocity
measurements of the 3.5 Gyr old chromospherically active Sun-like star, HD
101501. We obtain tight constraints on the stellar rotation period and the
evolution of spot distributions using 28 seasons of ground-based photometry, as
well as recent data. Light curve inversion was carried out on both
photometry datasets to reveal the spot distribution and spot evolution
timescales on the star. We find that the m/s rms radial velocity
variations in HD 101501 are well-modeled with a GP stellar activity model
without planets, yielding a residual rms scatter of 45 cm/s. We carry out
simulations, injecting and recovering signals with the GP framework, to
demonstrate that high-cadence observations are required to use GPs most
efficiently to detect low-mass planets around active stars like HD 101501.
Sparse sampling prevents GPs from learning the correlated noise structure and
can allow it to absorb prospective Keplerian signals. We quantify the moderate
to high-cadence monitoring that provides the necessary information to
disentangle photospheric features using GPs and to detect planets around active
stars.Comment: 25 pages, 16 figures, accepted to A
Contemporaneous Imaging Comparisons of the Spotted Giant sigma Geminorum Using Interferometric, Spectroscopic, and Photometric Data
Nearby active stars with relatively rapid rotation and large starspot structures offer the opportunity to compare interferometric, spectroscopic, and photometric imaging techniques. In this paper, we image a spotted star with three different methods for the first time. The giant primary star of the RS Canum Venaticorum binary sigma. Geminorum (sigma Gem) was imaged for two epochs of interferometric, high-resolution spectroscopic, and photometric observations. The light curves from the reconstructions show good agreement with the observed light curves, supported by the longitudinally consistent spot features on the different maps. However, there is strong disagreement in the spot latitudes across the methods.Peer reviewe
Amicus Brief: Kumho Tire v. Carmichael
This brief addresses the issue of jury performance and jury responses to expert testimony. It reviews and summaries a substantial body of research evidence about jury behavior that has been produced over the past quarter century. The great weight of that evidence challenges the view that jurors abdicate their responsibilities as fact finders when faced with expert evidence or that they are pro-plaintiff, anti-defendant, and anti-business.
The Petitioners and amici on behalf of petitioners make a number of overlapping, but empirically unsupported, assertions about jury behavior in response to expert testimony, namely that juries are frequently incapable of critically evaluation expert testimony, are easily confused, give inordinate weight to expert testimony, are awed by science, defer to the opinions of unreliable experts, and, implicitly, that in civil trials juries tilt in favor of plaintiffs and against corporations
Erratum to: 36th International Symposium on Intensive Care and Emergency Medicine
[This corrects the article DOI: 10.1186/s13054-016-1208-6.]
Partners No More: Relational Transformation and the Turn to Litigation in Two Conservationist Organizations
The rise in litigation against administrative bodies by environmental and other political interest groups worldwide has been explained predominantly through the liberalization of standing doctrines. Under this explanation, termed here the floodgate model, restrictive standing rules have dammed the flow of suits that groups were otherwise ready and eager to pursue. I examine this hypothesis by analyzing processes of institutional transformation in two conservationist organizations: the Sierra Club in the United States and the Society for the Protection of Nature in Israel (SPNI). Rather than an eagerness to embrace newly available litigation opportunities, as the floodgate model would predict, the groups\u27 history reveals a gradual process of transformation marked by internal, largely intergenerational divisions between those who abhorred conflict with state institutions and those who saw such conflict as not only appropriate but necessary to the mission of the group. Furthermore, in contrast to the pluralist interactions that the floodgate model imagines, both groups\u27 relations with pertinent agencies in earlier eras better accorded with the partnership-based corporatist paradigm. Sociolegal research has long indicated the importance of relational distance to the transformation of interpersonal disputes. I argue that, at the group level as well, the presence or absence of a (national) partnership-centered relationship determines propensities to bring political issues to court. As such, well beyond change in groups\u27 legal capacity and resources, current increases in levels of political litigation suggest more fundamental transformations in the structure and meaning of relations between citizen groups and the state
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