adsabs/AstroCLIMB huggingface dataset:
Paper: An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE
Authors: John Rankin, Fabio Muleri, Allyn F. Tennant, Matteo Bachetti, Enrico Costa, Alessandro Di Marco, Sergio Fabiani, Fabio La Monaca, Paolo Soffitta, Antonino Tobia, Alessio Trois, Fei Xie, Luca Baldini, Niccolò Di Lalla, Alberto Manfreda, Stephen L. O'Dell, Matteo Perri, Simonetta Puccetti, Brian D. Ramsey, Carmelo Sgrò, Martin C. Weisskopf
Figure caption: Observation at 2.8 keV consisting of 104 iterations with 107 events in each iteration. The predicted distribution of the observed values (orange line) is compared with the fit to the observed distribution (red line). The former has a larger width, because it accounts for the fact that, in correcting, we are subtracting an estimate of spurious modulation and not its true value. This causes a shift between the true modulation (vertical line) and the center of the observed distribution.
Paper: An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE
Authors: John Rankin, Fabio Muleri, Allyn F. Tennant, Matteo Bachetti, Enrico Costa, Alessandro Di Marco, Sergio Fabiani, Fabio La Monaca, Paolo Soffitta, Antonino Tobia, Alessio Trois, Fei Xie, Luca Baldini, Niccolò Di Lalla, Alberto Manfreda, Stephen L. O'Dell, Matteo Perri, Simonetta Puccetti, Brian D. Ramsey, Carmelo Sgrò, Martin C. Weisskopf
Figure caption: Comparison of modulation corrected using the true and observed energy using a 3.5M event Monte Carlo simulation of a Crab-like spectrum. The plot on the left compares the spectra, and the one on the right the Stokes parameters of the observation. Spurious modulation is first summed by interpolating the calibration maps using the true energy (given in input to the Monte Carlo), and then subtracted by interpolating using the measured energy. As can be seen, the offset in the correction due to the discrepancy between the two energy estimates is negligible.
Paper: An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE
Authors: John Rankin, Fabio Muleri, Allyn F. Tennant, Matteo Bachetti, Enrico Costa, Alessandro Di Marco, Sergio Fabiani, Fabio La Monaca, Paolo Soffitta, Antonino Tobia, Alessio Trois, Fei Xie, Luca Baldini, Niccolò Di Lalla, Alberto Manfreda, Stephen L. O'Dell, Matteo Perri, Simonetta Puccetti, Brian D. Ramsey, Carmelo Sgrò, Martin C. Weisskopf
Figure caption: Modulation of low-polarization flat-field laboratory sources at various energies. One value is referred to the global decoupling; the other two values are the application of the photon-by-photon algorithm to the flat fields at the two rotation angles (named eps1 and eps2) at which this measurement was acquired (hence the two values). All three values are compatible.
Paper: An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE
Authors: John Rankin, Fabio Muleri, Allyn F. Tennant, Matteo Bachetti, Enrico Costa, Alessandro Di Marco, Sergio Fabiani, Fabio La Monaca, Paolo Soffitta, Antonino Tobia, Alessio Trois, Fei Xie, Luca Baldini, Niccolò Di Lalla, Alberto Manfreda, Stephen L. O'Dell, Matteo Perri, Simonetta Puccetti, Brian D. Ramsey, Carmelo Sgrò, Martin C. Weisskopf
Figure caption: Spectra of the Ca X-ray tube with the modulation computed in energy bins. The colored points are corrected for spurious modulation using the photon-by-photon correction which therefore is sensitive to the different energies), while the gray points are uncorrected. The corrected points are compatible with 0 as expected for the Ca X-ray tube, while for the uncorrected points, the decreasing trend of spurious modulation with energy is evident.
Paper: An Algorithm to Calibrate and Correct the Response to Unpolarized Radiation of the X-Ray Polarimeter Onboard IXPE
Authors: John Rankin, Fabio Muleri, Allyn F. Tennant, Matteo Bachetti, Enrico Costa, Alessandro Di Marco, Sergio Fabiani, Fabio La Monaca, Paolo Soffitta, Antonino Tobia, Alessio Trois, Fei Xie, Luca Baldini, Niccolò Di Lalla, Alberto Manfreda, Stephen L. O'Dell, Matteo Perri, Simonetta Puccetti, Brian D. Ramsey, Carmelo Sgrò, Martin C. Weisskopf
Figure caption: Same as Figure 7, but for the modulation factor (obtained by dividing the source modulation of the polarized measurements by the source polarization, as in Equation (1)).
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Residual maps for observations taken in i (catalog position minus observed position). The left and right panels display the maps for R.A. and decl., respectively. The CCD manufacturing process leads to discontinuities between regions on the CCD 1024 × 512 pixels in size, evident in the maps. The large hole in the center of each map corresponds to the portion of the CCD not used in the astrometric calibrations due to the bright out-of-focus images of the target star.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Close-up under the neutral-density spot of the image displayed in Figure 1, using a log scaling to highlight low-level features in the image.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Same as Figure 3, but for observations taken in z.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: The slope and intercept values for the DCR fits for the ensemble of i images, plotted against refraction. The black lines are the fits to the ensemble, used to apply DCR corrections in i. Blue circles were included in the fits, and orange squares were iteratively rejected as greater than 3σ outliers.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Typical survey image, taken through the i filter. The color bar indicates the nonlinear scaling used to highlight various features in the image.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Differences between Gaia EDR3 and UBAD individual-frame positions vs. Gaia G magnitude for a clean set of i observations (R.A. in the top panel, decl. in the bottom panel). The black points are observations for the main survey, while the gray points are for the faint survey extension, used only in this figure. The blue line is the median difference for stars in the main survey. The solid and dotted orange lines indicate the median and interquartile range, respectively, of the differences in bins of 100 stars in G.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Same as Figure 9, but for z observations.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Histograms of the differences between Gaia and UBAD positions for a clean set of i observations. The differences in R.A. and decl. are shown in the top and bottom panels, respectively.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Same as Figure 11, but for z observations.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Offsets in declination between Gaia and UBAD positions as a function of declination, after correction for the median offsets. The orange solid and dashed lines are the median and interquartile range of the offsets, respectively, in bins of 200 stars.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Differences between Gaia and UBAD positions (Gaia − UBAD, R.A. in the top panel, decl. in the bottom panel), normalized by the expected error in the differences. The black points are the individual stars. The blue and orange points are the mean and rms differences, respectively, in equal-sized bins in G. The rms values should be near one (indicated by the dotted cyan line). The dashed cyan line is a reference line at zero normalized error.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Same as Figure 5, but for the z images.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Distribution of the number of calibration stars used on each image in the survey. An additional 18 observations have more than 150 calibration stars.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Distribution of the rms residuals for the astrometric solutions for all images in the survey, separately in R.A. and decl.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Same as Figure 25, but for the 33 stars whose fits exclude the Hipparcos-2 position. There are an additional two and one unplotted stars with errors greater than 10 mas yr−1 in R.A. and decl., respectively.
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Distributions of catalog proper-motion errors for the 331 stars whose fits include the Hipparcos-2 position (R.A. in top panel, decl. in bottom panel).
Paper: Accurate Ground-based Astrometry of Naked-eye Stars: The United States Naval Observatory Bright-star Astrometric Database
Authors: Jeffrey A. Munn, John P. Subasavage, Hugh C. Harris, Trudy M. Tilleman
Figure caption: Distributions of catalog position errors (R.A. in top panel, decl. in bottom panel). There are an additional two and four unplotted stars with errors greater than 4.5 mas in R.A. and decl., respectively.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: Model comparisons for Spitzer 3.6 μm (top) and 4.5 μm (bottom) phase variations of XO-3b. The best-fit astrophysical model to the Spitzer data obtained using different detector models and phase variation models are shown here. Each column indicates the detector model used. The rows indicate the phase variation model used and whether or not a prior was imposed on the secondary eclipse depth. The ΔBIC from the preferred solution of each fit is indicated in each box and the opacity of the background of each box reflects fit preference (darker is better). The eclipse depth for each fit is denoted by f  p , in parts per mille. Top: the fit using a first-order PLD with a 5 × 5 stamp using a first-order sinusoidal model is preferred. In principle, the shape of the best-fit phase curve is dependent on the models and priors chosen. Fortunately, the shape of the first-order phase variation model is robust against the choice of detector model and prior on the secondary eclipse depth. Bottom: the preferred fit uses a first-order PLD with a 3 × 3 stamp and a second-order sinusoidal model. Note that the shape of the 4.5 μm phase curves is robust against prior and model choices, but the 3.6 μm phase-curve shape is not.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: The yellow (left) and red (right) line and swath represent the brightness temperature and uncertainties of XO-3b based on the Spitzer 3.6 μm and 4.5 μm observations, respectively. The dark yellow and red dashed lines represent the energy balance model fits to the temperature curves. The light gray lines represent the time of secondary eclipse and the dark gray line indicates the transit time. The vertical brown line represents the periastron passage. In both panels, the gray transparent curve represent the limiting case with a short advective timescale τ adv ≪ τ rad ≪ P and the pink transparent line represents the limiting case of a short radiative timescale, τ rad = 0.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: One-dimensional atmospheric model at apoapse and periapse. The model predicts that incoming shortwave radiation from the star is deposited entirely at pressures P < 10 bars above the isothermal region. An approximate infrared photosphere is indicated by the red swath from 0.01 to 1 bar.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: Red-noise test for our best-fit models as a function of bin size for 3.6 μm (left) and 4.5 μm (right) fit. We binned the data into bins of different sizes, N binned, and computed the binned residuals rms. The lighter shaded area is the uncertainty that the MC3 package computed (Cubillos et al. 2017). The gray line represents the expected decrease in rms if the residuals are purely white noise. We find that there is significant red noise in the residuals of the 3.6 μm fit, while the residuals of the 4.5 μm fit are less correlated. The vertical dashed line represents the number of bins contained in the duration of an eclipse depth.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: General circulation model (GCM) thermal phase-curve predictions for the 3.6 μm (left) and 4.5 μm (right) Spitzer bandpasses. The colored swaths represent the 1σ uncertainties of the best-fit Spitzer phase curves. The gray swath represents the magnitude of the orbit-to-orbit variability seen in the GCM. The large discrepancy between the 3.6 μm Spitzer phase curve and GCM predictions is likely due to issues with the observations. At 4.5 μm, our model correctly predicts the cooling rate of the planet between eclipse and transit, but underestimates its heating rate between transit and eclipse.The dashed black lines represents the EBM fit to each Spitzer phase curve.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: The best-fit models to the 3.6 and 4.5 μm observations are presented in the left and right panels, respectively. The vertical dashed lines represent the AOR breaks and the dark vertical lines represent the time of periapse passage. The raw photometry is plotted in the top panels in pale yellow and red while the best-fit signal, F total, is shown in dark yellow and red. The corrected photometry is shown in the second panels in pale yellow and red and the best-fit astrophysical models are shown in darker colors. The third panels are a zoomed-in version of the second panels to more clearly show the phase variations. The last panels shows the residuals. Note that the 3.6 μm and 4.5 μm channels data were fitted independently.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: Published Spitzer/IRAC secondary eclipse depths are shown along with our new eclipse depths. Gray dashed lines show notional eclipse spectra if the star and planet radiate as blackbodies with T eff,* = 6885 K and planetary dayside temperature T day = [2000, 2342, 2600] K. The deeper 3.6 μm eclipse depth in comparison to the 4.5 μm eclipse depth rules out the thermal inversion reported by Machalek et al. (2010): water vapor opacity dictates that the 3.6 μm photons originate from deeper in the atmosphere than those at 4.5 μm.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: Temperature (color scale) and winds (arrows) at the ≈10 mbar and ≈120 mbar level of our 1 × solar model at snapshots corresponding to apoapse (left) and periapse (right). The substellar longitude is indicated by the solid vertical line. At periapse, the model exhibits a large temperature contrast between the dayside and nightside of the planet. At apoapse, the temperature gradient is attenuated and the predominant wind zonal and meridional flows are suppressed.
Paper: Thermal Phase Curves of XO-3b: An Eccentric Hot Jupiter at the Deuterium Burning Limit
Authors: Lisa Dang, Taylor J. Bell, Nicolas B. Cowan, Daniel Thorngren, Tiffany Kataria, Heather A. Knutson, Nikole K. Lewis, Keivan G. Stassun, Jonathan J. Fortney, Eric Agol, Gregory P. Laughlin, Adam Burrows, Karen A. Collins, Drake Deming, Diana Jovmir, Jonathan Langton, Sara Rastegar, Adam P. Showman
Figure caption: SPCA analysis of the secondary eclipse obtained as part of the 2010 partial phase curve of XO-3b at 3.6 μm with Spitzer. The detrended data are connected with a pale orange line. The dark line represents the best-fit astrophysical model and the orange circles represent the binned calibrated photometry in 20 bins. The bottom panel shows the residuals of the SPCA fit.
Paper: Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades
Authors: Philip S. Muirhead, Jason Nordhaus, Maria R. Drout
Figure caption: Phase-folded light curve of V471 Tau. (a) Full orbital phase showing the normalized K2 data (blue, offset for clarity), the best-fitting stellar-variability model (orange, offset for clarity), the K2 data divided by the variability model (gray), and the best-fitting eclipse model (red). Gaps in the data near-zero phase correspond to periodic anomalous data points removed from the light curve (see text). (b) Insert showing the ingress of the white-dwarf occultation. (c) Insert showing the white-dwarf transit and the best-fitting eclipse model with and without gravitational microlensing (red and dashed red, respectively).
Paper: Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades
Authors: Philip S. Muirhead, Jason Nordhaus, Maria R. Drout
Figure caption: Radial-velocity measurements of the component stars of V471 Tau. Green circles show measurements of the main-sequence star from the literature (Bois et al. 1988), blue diamonds show measurements of the white dwarf from the literature (O’Brien et al. 2001), and orange squares show measurements from this effort using a custom reduction of archival HST-STIS observations. The best-fitting models for the main-sequence star (solid gray) and white dwarf (dashed gray) are shown. The fitted radial-velocity zero points for each data set have been subtracted from the measurements and model.
Paper: Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades
Authors: Philip S. Muirhead, Jason Nordhaus, Maria R. Drout
Figure caption: Density of samples of the posterior probability distribution for fitted parameters. Highest density regions correspond to higher likelihood parameters. Histograms at the top capture the marginalized posterior probability distribution for a given parameter. Dashed lines indicate the 16%, 50%, and 84% quantile locations. Red lines and square indicate the values for the sample with the highest posterior probability. This figure was made using corner (Foreman-Mackey 2016).
Paper: Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades
Authors: Philip S. Muirhead, Jason Nordhaus, Maria R. Drout
Figure caption: Far-ultraviolet spectrum of V471 Tau. An archival Hubble Space Telescope spectra acquired with the Space Telescope Imaging Spectrograph (STIS) is shown in blue. In orange we show our best-fitting model to the Stark-broadened wings of the white dwarf’s Lyα absorption line, ignoring regions contaminated by chromospheric emission and interstellar absorption.
Paper: Revised Stellar Parameters for V471 Tau, A Post-common Envelope Binary in the Hyades
Authors: Philip S. Muirhead, Jason Nordhaus, Maria R. Drout
Figure caption: Measurements for the radius and mass of the main-sequence component of V471 Tau (circle, square) compared to MIST evolutionary models (assuming [Fe/H] = 0.0). Top: radius vs. age, colored by mass. Bottom: radius vs. mass, showing the MIST model for ages between 650 and 850 Myr. The dots indicate the MIST model values, the square indicates our measurement for the main-sequence star, and the circle indicates a previous measurement from the literature (O’Brien et al. 2001).