7,742 research outputs found
The Lick-Carnegie Survey: Four New Exoplanet Candidates
We present new precise HIRES radial velocity (RV) data sets of five nearby
stars obtained at Keck Observatory. HD 31253, HD 218566, HD 177830, HD 99492
and HD 74156 are host stars of spectral classes F through K and show radial
velocity variations consistent with new or additional planetary companions in
Keplerian motion. The orbital parameters of the candidate planets in the five
planetary systems span minimum masses of M sin i = 27.43 M_{earth} to M sin i =
8.28 M_{jup}, periods of 17.05 to 4696.95 days and eccentricities ranging from
circular to extremely eccentric (e ~ 0.63). The 5th star, HD 74156, was known
to have both a 52-day and a 2500-day planet, and was claimed to also harbor a
3rd planet at 336d, in apparent support of the "Packed Planetary System"
hypothesis. Our greatly expanded data set for HD 74156 provides strong
confirmation of both the 52-day and 2500-d planets, but strongly contradicts
the existence of a 336-day planet, and offers no significant evidence for any
other planets in the system.Comment: 13 pages, 15 figures. Accepted for publication in ApJ. Fixed typos in
Table 2. Additional material at http://www.ucolick.org/~smeschia/4planet.ph
Color Difference Makes a Difference: Four Planet Candidates around Ï Ceti
The removal of noise typically correlated in time and wavelength is one of the main challenges for using the radial-velocity (RV) method to detect Earth analogues. We analyze Ï Ceti RV data and find robust evidence for wavelength-dependent noise. We find that this noise can be modeled by a combination of moving average models and the so-called "differential radial velocities." We apply this noise model to various RV data sets for Ï Ceti, and find four periodic signals at 20.0, 49.3, 160, and 642 days, which we interpret as planets. We identify two new signals with orbital periods of 20.0 and 49.3 days while the other two previously suspected signals around 160 and 600 days are quantified to a higher precision. The 20.0 days candidate is independently detected in Keck data. All planets detected in this work have minimum masses less than 4Mâ with the two long-period ones located around the inner and outer edges of the habitable zone, respectively. We find that the instrumental noise gives rise to a precision limit of the High Accuracy Radial Velocity Planet Searcher (HARPS) around 0.2 m sâ1. We also find correlation between the HARPS data and the central moments of the spectral line profile at around 0.5 m sâ1 level, although these central moments may contain both noise and signals. The signals detected in this work have semi-amplitudes as low as 0.3 m sâ1, demonstrating the ability of the RV technique to detect relatively weak signals
Biology and population dynamics of cowcod (Sebastes levis) in the southern California Bight
Cowcod (Sebastes levis) is a large (100-cm-FL), long-lived (maximum observed age 55 yr) demersal rockfish taken in multispecies commercial and recreational fisheries off
southern and central California. It lives at 20â500 m depth: adults (>44 cm TL) inhabit rocky areas at 90â300 m and juveniles inhabit fine sand and clay at 40â100 m. Both sexes have similar growth and maturity. Both sexes recruit to the fishery before reaching full maturity. Based on age and growth data, the natural mortality rate is about M =0.055/yr, but the estimate is uncertain. Biomass, recruitment, and mortality during 1951â98 were estimated in a delay-difference model with catch data and abundance indices. The same model gave less precise estimates for 1916â50 based on catch data and assumptions about virgin biomass and recruitment such as used in stock reduction analysis. Abundance indices, based on rare event data, included a habitat-areaâweighted index of recreational
catch per unit of fishing effort (CPUE index values were 0.003â0.07 fish per angler hour), a standardized
index of proportion of positive tows in CalCOFI ichthyoplankton survey data (binomial errors, 0â13% positive
tows/yr), and proportion of positive tows for juveniles in bottom trawl surveys (binomial errors, 0â30% positive tows/yr). Cowcod are overfished in the southern California Bight; biomass during the 1998 season was about 7% of the virgin level and recent catches have been near 20 metric tons (t)/yr. Projections based on recent recruitment levels indicate that biomass will decline at catch levels > 5 t/yr. Trend data indicate that recruitment will be poor in
the near future. Recreational fishing effort in deep water has increased and has become more effective for catching
cowcod. Areas with relatively high catch rates for cowcod are fewer and are farther offshore. Cowcod die after capture
and cannot be released alive. Two areas recently closed to bottom fishing will help rebuild the cowcod stock
Sources of Differences in On-Orbit Total Solar Irradiance Measurements and Description of Proposed Laboratory Intercomparison
There is a 5 W/sq m (about 0.35 %) difference between current on-orbit Total Solar Irradiance (TSI) measurements. On 18-20 July 2005, a workshop was held at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland that focused on understanding possible reasons for this difference, through an examination of the instrument designs, calibration approaches, and appropriate measurement equations. The instruments studied in that workshop included the Active Cavity Radiometer Irradiance Monitor III (ACRIM III) on the Active Cavity Radiometer Irradiance Monitor SATellite (ACRIMSAT), the Total Irradiance Monitor (TIM) on the Solar Radiation and Climate Experiment (SORCE), the Variability of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and Heliospheric Observatory (SOHO), and the Earth Radiation Budget Experiment (ERBE) on the Earth Radiation Budget Satellite (ERBS). Presentations for each instrument included descriptions of its design, its measurement equation and uncertainty budget, and the methods used to assess on-orbit degradation. The workshop also included a session on satellite- and ground-based instrument comparisons and a session on laboratory-based comparisons and the application of new laboratory comparison techniques. The workshop has led to investigations of the effects of diffraction and of aperture area measurements on the differences between instruments. In addition, a laboratory-based instrument comparison is proposed that uses optical power measurements (with lasers that underEll the apertures of the TSI instruments), irradiance measurements (with lasers that overfill the apertures of the TSI instrument), and a cryogenic electrical substitution radiometer as a standard for comparing the instruments. A summary of the workshop and an overview of the proposed research efforts are presented here
Mapping Large-Scale CO Depletion in a Filamentary Infrared Dark Cloud
Infrared Dark Clouds (IRDCs) are cold, high mass surface density and high
density structures, likely to be representative of the initial conditions for
massive star and star cluster formation. CO emission from IRDCs has the
potential to be useful for tracing their dynamics, but may be affected by
depleted gas phase abundances due to freeze-out onto dust grains. Here we
analyze C18O J=1-0 and J=2-1 emission line data, taken with the IRAM 30m
telescope, of the highly filamentary IRDC G035.39.-0033. We derive the
excitation temperature as a function of position and velocity, with typical
values of ~7K, and thus derive total mass surface densities, Sigma_C18O,
assuming standard gas phase abundances and accounting for optical depth in the
line, which can reach values of ~1. The mass surface densities reach values of
~0.07 g/cm^2. We compare these results to the mass surface densities derived
from mid-infrared (MIR) extinction mapping, Sigma_SMF, by Butler & Tan, which
are expected to be insensitive to the dust temperatures in the cloud. With a
significance of >10sigma, we find Sigma_C18O/Sigma_SMF decreases by about a
factor of 5 as Sigma increases from ~0.02 to ~0.2 g/cm^2, which we interpret as
evidence for CO depletion. Several hundred solar masses are being affected,
making this one of the most massive clouds in which CO depletion has been
observed directly. We present a map of the depletion factor in the filament and
discuss implications for the formation of the IRDC.Comment: 9 pages, accepted to ApJ, Mac users: Figure 1 is best viewed with
Adobe acroread rather than previe
An Overview of Suomi NPP VIIRS Calibration Maneuvers
The first Visible Infrared Imager Radiometer Suite (VIIRS) instrument was successfully launched on-board the Suomi National Polar-orbiting Partnership (SNPP) spacecraft on October 28, 2011. Suomi NPP VIIRS observations are made in 22 spectral bands, from the visible (VIS) to the long-wave infrared (LWIR), and are used to produce 22 Environmental Data Records (EDRs) with a broad range of scientific applications. The quality of these VIIRS EDRs strongly depends on the quality of its calibrated and geo-located Sensor Date Records (SDRs). Built with a strong heritage to the NASA's EOS MODerate resolution Imaging Spectroradiometer (MODIS) instrument, the VIIRS is calibrated on-orbit using a similar set of on-board calibrators (OBC), including a solar diffuser (SD) and solar diffuser stability monitor (SDSM) system for the reflective solar bands (RSB) and a blackbody (BB) for the thermal emissive bands (TEB). On-orbit maneuvers of the SNPP spacecraft provide additional calibration and characterization data from the VIIRS instrument which cannot be obtained pre-launch and are required to produce the highest quality SDRs. These include multi-orbit yaw maneuvers for the characterization of SD and SDSM screen transmission, quasi-monthly roll maneuvers to acquire lunar observations to track sensor degradation in the visible through shortwave infrared, and a driven pitch-over maneuver to acquire multiple scans of deep space to determine TEB response versus scan angle (RVS). This paper pro-vides an overview of these three SNPP calibration maneuvers. Discussions are focused on their potential calibration and science benefits, pre-launch planning activities, and on-orbit scheduling and implementation strategies. Results from calibration maneuvers performed during the Intensive Calibration and Validation (ICV) period for the VIIRS sensor are illustrated. Also presented in this paper are lessons learned regarding the implementation of calibration spacecraft maneuvers on follow-on missions
A 'Performative' Social Movement: The Emergence of Collective Contentions within Collaborative Governance
The enmeshment of urban movements in networks of collaborative governance has been characterised as a process of co-option in which previously disruptive contentions are absorbed by regimes and reproduced in ways that do not threaten the stability of power relations. Applying a theoretical framework drawn from feminist philosopher Judith Butler this paper directs attention to the development of collective oppositional identities that remain embedded in conventional political processes. In a case study of the English tenants' movement, it investigates the potential of regulatory discourses that draw on market theories of performative voice to offer the collectivising narratives and belief in change that can generate the emotional identification of a social movement. The paper originates the concept of the âperformative social movementâ to denote the contentious claims that continue to emerge from urban movements that otherwise appear quiescent
Ten New and Updated Multi-planet Systems, and a Survey of Exoplanetary Systems
We present the latest velocities for 10 multi-planet systems, including a
re-analysis of archival Keck and Lick data, resulting in improved velocities
that supersede our previously published measurements. We derive updated orbital
fits for ten Lick and Keck systems, including two systems (HD 11964, HD 183263)
for which we provide confirmation of second planets only tentatively identified
elsewhere, and two others (HD 187123, and HD 217107) for which we provide a
major revision of the outer planet's orbit. We compile orbital elements from
the literature to generate a catalog of the 28 published multiple-planet
systems around stars within 200 pc. From this catalog we find several
intriguing patterns emerging: - Including those systems with long-term radial
velocity trends, at least 28% of known planetary systems appear to contain
multiple planets. - Planets in multiple-planet systems have somewhat smaller
eccentricities than single planets. - The distribution of orbital distances of
planets in multi-planet systems and single planets are inconsistent:
single-planet systems show a pile-up at P ~ 3 days and a jump near 1 AU, while
multi-planet systems show a more uniform distribution in log-period. In
addition, among all planetary systems we find: - There may be an emerging,
positive correlation between stellar mass and giant-planet semi-major axis. -
Exoplanets more massive than Jupiter have eccentricities broadly distributed
across 0 < e < 0.5, while lower-mass exoplanets exhibit a distribution peaked
near e = 0.Comment: ApJ accepted. v.2 makes minor corrections to author list, citations,
and provides a stable set of orbital parameters for HD 183263 in Table 1. v.3
makes preprint consistent with ApJ version, minor changes to wording, orbital
parameters of HD 217107 and HD 187123c in Table
Comparison of Two Methodologies for Calibrating Satellite Instruments in the Visible and Near Infrared
Traditionally, satellite instruments that measure Earth-reflected solar radiation in the visible and near infrared wavelength regions have been calibrated for radiance response in a two-step method. In the first step, the spectral response of the instrument is determined using a nearly monochromatic light source, such a lamp-illuminated monochromator. Such sources only provide a relative spectral response (RSR) for the instrument, since they do not act as calibrated sources of light nor do they typically fill the field-of-view of the instrument. In the second step, the instrument views a calibrated source of broadband light, such as lamp-illuminated integrating sphere. In the traditional method, the RSR and the sphere spectral radiance are combined and, with the instrument's response, determine the absolute spectral radiance responsivity of the instrument. More recently, an absolute calibration system using widely tunable monochromatic laser systems has been developed, Using these sources, the absolute spectral responsivity (ASR) of an instrument can be determined on a wavelength-hy-wavelength basis. From these monochromatic ASRs. the responses of the instrument bands to broadband radiance sources can be calculated directly, eliminating the need for calibrated broadband light sources such as integrating spheres. Here we describe the laser-based calibration and the traditional broad-band source-based calibration of the NPP VIIRS sensor, and compare the derived calibration coefficients for the instrument. Finally, we evaluate the impact of the new calibration approach on the on-orbit performance of the sensor
Magnetic fields and differential rotation on the pre-main sequence I: The early-G star HD 141943 - brightness and magnetic topologies
Spectroscopic and spectropolarimetric observations of the pre-main sequence
early-G star HD 141943 were obtained at four observing epochs (in 2006, 2007,
2009 and 2010). The observations were undertaken at the 3.9-m Anglo-Australian
Telescope using the UCLES echelle spectrograph and the SEMPOL
spectropolarimeter visitor instrument. Brightness and surface magnetic field
topologies were reconstructed for the star using the technique of least-squares
deconvolution to increase the signal-to-noise of the data.
The reconstructed brightness maps show that HD 141943 had a weak polar spot
and a significant amount of low latitude features, with little change in the
latitude distribution of the spots over the 4 years of observations. The
surface magnetic field was reconstructed at three of the epochs from a high
order (l <= 30) spherical harmonic expansion of the spectropolarimetric
observations. The reconstructed magnetic topologies show that in 2007 and 2010
the surface magnetic field was reasonably balanced between poloidal and
toroidal components. However we find tentative evidence of a change in the
poloidal/toroidal ratio in 2009 with the poloidal component becoming more
dominant. At all epochs the radial magnetic field is predominantly
non-axisymmetric while the azimuthal field is predominantly axisymmetric with a
ring of positive azimuthal field around the pole similar to that seen on other
active stars.Comment: 18 pages, 17 figures, accepted by MNRA
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