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(color online) Type Ia supernova Hubble diagram, showing luminosity distance vs. redshift. The data points shown are from the original supernova surveys 2,3 that established the cosmic acceleration. The supernovae at higher redshift are ∼ 20% fainter than would be expected in a matter-dominated critical density Universe (the dashed curve). The orange bar corresponds to a 1% flux uncertainty, which is the calibration target for next-generation measurements to constrain the nature of dark energy. (From Riess, 12 used with permission.)
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Measurements of the luminosity of Type Ia supernovae versus redshift provided the original evidence for the accelerating expansion of the Universe and the existence of dark energy. Despite substantial improvements in survey methodology, systematic uncertainty in flux calibration dominates the error budget for this technique, exceeding both statisti...
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... density, matter dominated (Ω matter = 1), Universe (where Ω denotes dimensionless cosmic density normalized to the critical density). Thus, the cosmic expansion is seen to be accelerating -a phenomenon presumed to be due to a still-mysterious dark energy. The initial supernova datasets that indicated a nonzero dark energy content are shown in Fig. ...
Citations
... It serves as a distant 95 in situ reference for a compact astronomical telescope. One of the largest remaining sources of systematic uncertainty when observing stellar sources from the ground is the Earth's atmosphere transmission (Stubbs and Tonry, 2012;Stubbs and Brown, 2015;Li et al., 2016). It is dependent on many environmental conditions and processes, including: absorption and scattering by molecular constituents (O 2 , O 3 , and others), absorption by PWV, scattering by aerosols, and shadowing by larger ice crystals and water droplets in clouds that is independent of wavelength and responsible for gray extinction (Burke et al., 2010(Burke et al., , 2017. ...
Infrared thermal cameras offer reliable means of assessing atmospheric conditions by measuring the downward radiance from the sky, facilitating their usage in cloud monitoring endeavors. Precise identification and detection of clouds in images pose great challenges stemming from the indistinct boundaries inherent to cloud formations. Various methodologies for segmentation have been previously suggested. Most of them rely on color as the distinguishing criterion for cloud identification in the visible spectral domain and thus lack the ability to detect cloud structure on gray-scaled images with satisfying accuracy. In this work, we propose a new complete deep-learning framework to perform image classification and segmentation with Convolutional Neural Networks. We demonstrate the effectiveness of this technique by conducting a series of tests and validations on self-captured infrared sky images. Our findings reveal that the models can effectively differentiate between image types and accurately capture detailed cloud structure information at the pixel level, even when trained with a single binary ground-truth mask per input sample. The classifier model achieves an excellent accuracy of 99 % in image type distinction, while the segmentation model attains a mean pixel accuracy of 94 % on our dataset. We emphasize that our framework exhibits strong viability and can be used for infrared thermal ground-based cloud monitoring operations over extended durations. We expect to take advantage of this framework for astronomical applications by providing cloud cover selection criteria for ground-based photometric observations within the StarDICE experiment.
... Knowledge of instrumental passbands is particularly useful when attempting to determine magnitudes of sources having SEDs that are dissimilar to standard flux calibration stars, as in the case of SNe Ia cosmology. With the advent of large-scale transient surveys such as Rubin Legacy Survey of Space and Time (Ivezić et al. 2019; Ivezić & the LSST Science Collaboration 2013) (LSST) undertaken by Rubin Observatory, the number of Type Ia SNe will be large enough that systematic calibration uncertainty will become the limiting factor in the determination of cosmological parameters (Stubbs & Brown 2015). Additionally, state-of-the-art survey calibration schemes, such as the Forward Global Calibration Method (Burke et al. 2017), can take passband measurements as inputs, thereby increasing the accuracy and precision of survey measurements by accounting for the variations in the spectra of field stars. ...
... A calibration system that can be taken to different telescopes is of critical importance to SN cosmology in particular, as photometric calibration has been and remains a major factor in determining cosmological parameters (Betoule et al. 2014;Scolnic et al. 2014Scolnic et al. , 2018Stubbs & Brown 2015). In support of this mission, our group intends to undertake a series of measurements on a representative group of telescopes that have played significant roles in SN measurements. ...
With the increasingly large number of Type Ia supernova being detected by current-generation survey telescopes, and even more expected with the upcoming Rubin Observatory Legacy Survey of Space and Time, the precision of cosmological measurements will become limited by systematic uncertainties in flux calibration rather than statistical noise. One major source of systematic error in determining SNe Ia color evolution (needed for distance estimation) is uncertainty in telescope transmission, both within and between surveys. We introduce here the Collimated Beam Projector (CBP), which is meant to measure a telescope transmission with collimated light. The collimated beam more closely mimics a stellar wave front as compared to flat-field-based instruments, allowing for more precise handling of systematic errors such as those from ghosting and filter angle-of-incidence dependence. As a proof of concept, we present CBP measurements of the StarDICE prototype telescope, achieving a standard (1 σ ) uncertainty of 3% on average over the full wavelength range measured with a single beam illumination.
... With the advent of large-scale transient surveys such as Rubin Legacy Survey of Space and Time 4, 5 (LSST) undertaken by Rubin Observatory, the number of Type Ia supernovae will be large enough that systematic calibration uncertainty will become the limiting factor in the determination of cosmological parameters. 6 Additionally, state of the art survey calibration schemes, such as the Forward Global Calibration Method, 7 can take passband measurements as inputs, thereby increasing the accuracy and precision of survey measurements by accounting for the variations in the spectra of field stars. ...
... Although the specification published in the 6514 datasheet provides only measurement accuracy (not precision), the manufacturer indicates that the value is intended to be understood as total measurement uncertainty, including both precision and accuracy 4 . We therefore use the datasheet's uncertainty formula for the 2 µC range given by σ PD = 0.01Q PD + 500 pC (6) as the uncertainty on the photodiode charge measurement. We keep the bias part of the formula in order to account for its variation throughout the experiment time span. ...
... A calibration system that can be taken to different telescopes is of critical importance to supernova cosmology in particular, as photometric calibration has been and remains a major factor in determining cosmological parameters. 2,6,26,27 In support of this mission, our group intends to undertake a series of measurements on a representative group of telescopes that have played significant roles in supernova measurements. In addition to our CBP, Rubin Observatory has also procured a CBP. ...
With the increasingly large number of type Ia supernova being detected by current-generation survey telescopes, and even more expected with the upcoming Rubin Observatory Legacy Survey of Space and Time, the precision of cosmological measurements will become limited by systematic uncertainties in flux calibration rather than statistical noise. One major source of systematic error in determining SNe Ia color evolution (needed for distance estimation) is uncertainty in telescope transmission, both within and between surveys. We introduce here the Collimated Beam Projector (CBP), which is meant to measure a telescope transmission with collimated light. The collimated beam more closely mimics a stellar wavefront as compared to flat-field based instruments, allowing for more precise handling of systematic errors such as those from ghosting and filter angle-of-incidence dependence. As a proof of concept, we present CBP measurements of the StarDICE prototype telescope, achieving a standard (1 sigma) uncertainty of 3 % on average over the full wavelength range measured with a single beam illumination.
... Sub-percent global photometric standardization has been challenging in the past, but is now in high demand for several ongoing scientific studies. For instance, photometric calibration is the major source of uncertainty in the use of Type Ia supernovae as probes of the history of cosmic expansion to infer the properties of the dark energy (Betoule et al. 2014;Scolnic et al. 2015Scolnic et al. , 2019Scolnic et al. , 2022Stubbs & Brown 2015;Brout et al. 2022). Experiments that require accurate and reliable photoredshift determination, such as weak lensing tomography and baryonic acoustic oscillation analysis with the VRO (Gorecki et al. 2014), are also limited by systematic uncertainties arising from their relative photometric calibration. ...
We verified for photometric stability a set of DA white dwarfs with Hubble Space Telescope magnitudes from the near-ultraviolet to the near-infrared and ground-based spectroscopy by using time-spaced observations from the Las Cumbres Observatory network of telescopes. The initial list of 38 stars was whittled to 32 final ones, which comprise a high-quality set of spectrophotometric standards. These stars are homogeneously distributed around the sky and are all fainter than r ∼ 16.5 mag. Their distribution is such that at least two of them would be available to be observed from any observatory on the ground at any time at airmass less than 2. Light curves and different variability indices from the Las Cumbres Observatory data were used to determine the stability of the candidate standards. When available, Pan-STARRS1, Zwicky Transient Facility, and TESS data were also used to confirm the star classification. Our analysis showed that four DA white dwarfs may exhibit evidence of photometric variability, while a fifth is cooler than our established lower temperature limit, and a sixth star might be a binary. In some instances, due to the presence of faint nearby red sources, care should be used when observing a few of the spectrophotometric standards with ground-based telescopes. Light curves and finding charts for all the stars are provided.
... Fortunately there are paths forward for each of these. For survey flux calibration, dedicated programs are needed, and there are currently multiple paths underway to improve the fundamental calibration of SN Ia samples and how they are tied to various other samples (e.g., Regnault et al. 2015;Stubbs & Brown 2015;Narayan et al. 2019). There is also ongoing work (G. ...
We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from z = 0.001 to 2.26. This work features an increased sample size from the addition of multiple cross-calibrated photometric systems of SNe covering an increased redshift span, and improved treatments of systematic uncertainties in comparison to the original Pantheon analysis, which together result in a factor of 2 improvement in cosmological constraining power. For a flat ΛCDM model, we find Ω M = 0.334 ± 0.018 from SNe Ia alone. For a flat w 0 CDM model, we measure w 0 = −0.90 ± 0.14 from SNe Ia alone, H 0 = 73.5 ± 1.1 km s ⁻¹ Mpc ⁻¹ when including the Cepheid host distances and covariance (SH0ES), and w 0 = − 0.978 − 0.031 + 0.024 when combining the SN likelihood with Planck constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both w 0 values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a flat w 0 w a CDM universe, and measure w a = − 0.1 − 2.0 + 0.9 from Pantheon+ SNe Ia alone, H 0 = 73.3 ± 1.1 km s ⁻¹ Mpc ⁻¹ when including SH0ES Cepheid distances, and w a = − 0.65 − 0.32 + 0.28 when combining Pantheon+ SNe Ia with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one-third of the total uncertainty in the measurement of H 0 and cannot explain the present “Hubble tension” between local measurements and early universe predictions from the cosmological model.
... Sub-percent global photometric standardization has been challenging in the past, but is now in high demand for several ongoing scientific studies. For instance, photometric calibration is the major source of uncertainty in the use of Type Ia supernovae as probes of the history of cosmic expansion to infer the properties of the dark energy (Betoule et al. 2014;Scolnic et al. 2015;Stubbs & Brown 2015;Scolnic et al. 2019Scolnic et al. , 2021Brout et al. 2021). Experiments that require accurate and reliable photo-redshift determination, such as weak lensing tomography and baryonic acoustic oscillation analysis with the Vera Rubin Observatory (Gorecki et al. 2014), are also limited by systematic uncertainties arising from their relative photometric calibration. ...
We verified for photometric stability a set of DA white dwarfs with Hubble Space Telescope magnitudes from the near-ultraviolet to the near-infrared and ground-based spectroscopy by using time-spaced observations from the Las Cumbres Observatory network of telescopes. The initial list of 38 stars was whittled to 32 final ones which comprise a high quality set of spectrophotometric standards. These stars are homogeneously distributed around the sky and are all fainter than r ~ 16.5 mag. Their distribution is such that at least two of them would be available to be observed from any observatory on the ground at any time at airmass less than two. Light curves and different variability indices from the Las Cumbres Observatory data were used to determine the stability of the candidate standards. When available, Pan-STARRS1, Zwicky Transient Facility and TESS data were also used to confirm the star classification. Our analysis showed that four DA white dwarfs may exhibit evidence of photometric variability, while a fifth is cooler than our established lower temperature limit, and a sixth star might be a binary. In some instances, due to the presence of faint nearby red sources, care should be used when observing a few of the spectrophotometric standards with ground-based telescopes. Light curves and finding charts for all the stars are provided.
... Precise absolute flux calibration of astronomical spectra is crucial for understanding the nature of cosmic sources. For example, the most precise flux determinations are essential for the interpretation of the supernova data that measure the accelerating expansion rate of the universe (Scolnic et al. 2014;Stubbs & Brown 2015) and for understanding the nature of exoplanet host stars (Tayar et al. 2022). White dwarf (WD) model atmosphere calculations for the three CALSPEC 4 primary WD standards, G191B2B, GD153, and GD71, define the shape of the instrumental flux calibrations and of the spectral energy distributions (SEDs), i.e., flux (or flux density) as a function of wavelength from 0.115 to 2.5 μm for the instruments on the Hubble Space Telescope (HST) and for the CALSPEC flux scale (Bohlin et al. , 2020, while the absolute flux levels depend on SI-traceable measurements of Sirius and Vega (Bohlin 2014;Bohlin et al. 2020). ...
An accurate tabulation of stellar brightness in physical units is essential for a multitude of scientific endeavors. The HST/CALSPEC database of flux standards contains many stars with spectral coverage in the 0.115–1 μ m range, with some extensions to longer wavelengths of 1.7 or 2.5 μ m. Modeled flux distributions to 32 μ m for calibration of JWST complement the shorter-wavelength HST measurements. Understanding the differences between IRAC observations and CALSPEC models is important for science that uses IR fluxes from multiple instruments, including JWST. The absolute flux of Spitzer IRAC photometry at 3.6–8 μ m agrees with CALSPEC synthetic photometry to 1% for the three prime HST standards: G191B2B, GD153, and GD71. For a set of 17–22 A-star standards, the average IRAC difference rises from agreement at 3.6 μ m to 3.4% ± 0.1% brighter than CALSPEC at 8 μ m. For a smaller set of G-type stars, the average of the IRAC photometry falls below CALSPEC by as much as 3.7% ± 0.3% for IRAC1, while one G-type star, P330E, is consistent with the A-star ensemble of IRAC/CALSPEC ratios.
... Precise absolute flux calibration of astronomical spectra is crucial for understanding the nature of cosmic sources. For example, the most precise flux determinations are essential for the interpretion of the supernova data that measure the accelerating expansion rate of the universe (Scolnic et al. 2014;Stubbs & Brown 2015) and for understanding the nature of exoplanet host stars (Tayar et al. 2020). White dwarf (WD) model atmosphere calculations for the three CALSPEC 1 primary WD standards, G191B2B, GD153, and GD71, define the shape of the instrumental flux calibrations and of the spectral energy distributions (SEDs), i.e. flux (or flux density) as a function of wavelength from 0.115 to 2.5 µm for the instruments on the Hubble Space Telescope (HST) and for the CALSPEC flux scale (Bohlin et al. , 2020, while the absolute flux levels depend on SI-traceable measurements of Sirius and Vega (Bohlin 2014;Bohlin et al. 2020). ...
An accurate tabulation of stellar brightness in physical units is essential for a multitude of scientific endeavors. The HST/CALSPEC database of flux standards contains many stars with spectral coverage in the 0.115--1 \micron\ range with some extensions to longer wavelengths of 1.7 or 2.5 \micron. Modeled flux distributions to 32 \micron\ for calibration of JWST complement the shorter wavelength HST measurements. Understanding the differences between IRAC observations and CALSPEC models is important for science that uses IR fluxes from multiple instruments, including JWST. The absolute flux of Spitzer IRAC photometry at 3.6--8 \micron\ agrees with CALSPEC synthetic photometry to 1\% for the three prime HST standards G191B2B, GD153, and GD71. For a set of 17--22 A-star standards, the average IRAC difference rises from agreement at 3.6 \micron\ to 3.4 $\pm$0.1\% brighter than CALSPEC at 8 \micron. For a smaller set of G-stars, the average of the IRAC photometry falls below CALSPEC by as much as 3.7 $\pm$0.3\% for IRAC1, while one G-star, P330E, is consistent with the A-star ensemble of IRAC/CALSPEC ratios.
... With larger datasets, modeling of many of the SN and host population related systematics will naturally improve. On the other hand, for flux calibration, dedicated programs are needed and thankfully there are multiple paths to improving the fundamental calibration of SN Ia samples and how they are tied to various other samples (e.g., Regnault et al. 2015;Narayan et al. 2019;Stubbs & Brown 2015). ...
We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from $z=0.001$ to 2.26. This work features an increased sample size, increased redshift span, and improved treatment of systematic uncertainties in comparison to the original Pantheon analysis and results in a factor of two improvement in cosmological constraining power. For a Flat$\Lambda$CDM model, we find $\Omega_M=0.338\pm0.018$ from SNe Ia alone. For a Flat$w_0$CDM model, we measure $w_0=-0.89\pm0.13$ from SNe Ia alone, H$_0=72.86^{+0.94}_{-1.06}$ km s$^{-1}$ Mpc$^{-1}$ when including the Cepheid host distances and covariance (SH0ES), and $w_0=-0.978^{+0.024}_{-0.031}$ when combining the SN likelihood with constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both $w_0$ values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a Flat$w_0w_a$CDM universe, and measure $w_a=-0.4^{+1.0}_{-1.8}$ from Pantheon+ alone, H$_0=73.40^{+0.99}_{-1.22}$ km s$^{-1}$ Mpc$^{-1}$ when including SH0ES, and $w_a=-0.65^{+0.28}_{-0.32}$ when combining Pantheon+ with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one third of the total uncertainty in the measurement of H$_0$ and cannot explain the present "Hubble tension" between local measurements and early-Universe predictions from the cosmological model.
... These measurements are complicated by many effects such as the differential atmospheric absorption between the standard lamp and the standard star light (whose correction requires a precise knowledge of the atmospheric transmission as a function of wavelength), the brigthness difference between the two sources and the need to characterize the telescope/detector throughput. Early results have not been followed by many modern comparisons of laboratory standards to stars (Bohlin et al. 2014), even if new methods have been proposed (Smith et al. 2009), and this technique has been superseded by different approaches, nicely described in Stubbs & Brown (2015), based on calibrated detectors or on theoretical knowledge of the physics of hydrogen. In fact, as mentioned in Zimmer et al. (2016), over the last decades the National Institute for Standards and Technology 19 put aside emissive standards in favour of detector standards, such as silicon and In-GaAs photodiodes (Larason et al. 1996;Yoon et al. 2003), that have been calibrated against primary optical standards (Brown et al. 2006;Smith et al. 2009). ...
We present Johnson-Kron-Cousins BVRI photometry of 228 candidate spectrophotometric standard stars for the external (absolute) flux calibration of Gaia data. The data were gathered as part of a ten-year observing campaign with the goal of building the external grid of flux standards for Gaia and we obtained absolute photometry, relative photometry for constancy monitoring, and spectrophotometry. Preliminary releases of the flux tables were used to calibrate the first two Gaia releases. This paper focuses on the imaging frames observed in good sky conditions (about 9100). The photometry will be used to validate the ground-based flux tables of the Gaia spectrophotometric standard stars and to correct the spectra obtained in non-perfectly photometric observing conditions for small zeropoint variations. The absolute photometry presented here is tied to the Landolt standard stars system to $\simeq$1 per cent or better, depending on the photometric band. Extensive comparisons with various literature sources show an overall $\simeq$1 per cent agreement, which appears to be the current limit in the accuracy of flux calibrations across various samples and techniques in the literature. The Gaia photometric precision is presently of the order of 0.1 per cent or better, thus various ideas for the improvement of photometric calibration accuracy are discussed.
