A Correction for GALEX Spectroscopic UV Flux Distributions from Comparisons with CALSPEC and IUE

Bohlin, R. C.; Bianchi, Luciana

doi:10.3847/1538-3881/aafdb8

Cited by 3 publications

(2 citation statements)

References 31 publications

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“…After instrument commissioning the detection efficiency values in Figure 3 were multiplied by 0.7 when a preliminary comparison of observations of the star HD 30836 (π 4 Ori), which were made by allowing it to drift across the entrance slits of the spectrometers during commissioning, with published irradiance values from International Ultraviolet Explorer (IUE; Boggess et al, 1978; Bohlin, 1996; Bohlin & Bianchi, 2018) suggested that the ground calibration had overestimated instrument responsivity. This factor has been revised to 0.78 and 0.85 for Channel A and Channel B, respectively, based on above‐the‐atmosphere occultation observations of multiple stars (see section 4.7).…”

Section: Prelaunch Performancementioning

confidence: 99%

Global‐Scale Observations of the Limb and Disk Mission Implementation: 1. Instrument Design and Early Flight Performance

et al. 2020

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The Global-scale Observations of the Limb and Disk (GOLD) is a National Aeronautics and Space Administration mission of opportunity designed to study how the Earth's ionosphere-thermosphere system responds to geomagnetic storms, solar radiation, and upward propagating atmospheric tides and waves. GOLD employs an instrument with two identical ultraviolet spectrographs that make observations of the Earth's thermosphere and ionosphere from a commercial communications satellite owned and operated by Société Européenne des Satellites (SES) and located in geostationary orbit at 47.5°west longitude (near the mouth of the Amazon River). They make images of atomic oxygen 135.6 nm and N 2 Lyman-Birge-Hopfield (LBH) 137-162 nm radiances of the entire disk that is observable from geostationary orbit and on the near-equatorial limb. They also observe occultations of stars to measure molecular oxygen column densities on the limb. Here, we provide an overview of the instrument and compare its prelaunch and early flight measurement performance. Direct comparison of LBH spectra of an electron lamp taken before launch with spectra on orbit provides evidence that both cascade and direct excitation are important sources of thermospheric LBH emission. Plain Language Summary The Global-scale Observations of the Limb and Disk (GOLD) is aNational Aeronautics and Space Administration mission of opportunity designed to study how the Earth's ionosphere-thermosphere system responds to geomagnetic storms, solar radiation, and upward propagating tides on time scales as short as 30 min. GOLD employs two identical ultraviolet spectrographs that make observations of the Earth's thermosphere and ionosphere from a commercial communications satellite owned and operated by SES and located in geostationary orbit at 47.5°west longitude (near the mouth of the Amazon River). They make images of atomic oxygen 135.6 nm and N 2 LBH radiances of the entire disk that is observable from geostationary orbit and on the near-equatorial limb. They also observe occultations of stars to measure molecular oxygen column densities on the limb. Here we describe the GOLD instrument including its optical system and detector. Its performance was characterized in the lab before launch. We compare measurements of laboratory sources made then to observations of the thermosphere after launch and find good agreement.

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Section: Prelaunch Performancementioning

confidence: 99%

Global‐Scale Observations of the Limb and Disk Mission Implementation: 1. Instrument Design and Early Flight Performance

et al. 2020

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“…Milone et al (1981) obtained a series of spectra of AI Phe during primary minimum with the International Ultraviolet Explorer (IUE) satellite. We downloaded the data from the IUE NEWSIPS archive 2 and applied the wavelength-dependent corrections suggested by Bohlin & Bianchi (2019) to put the flux on the CALSPEC scale. We created three trapezoidal filters with which to integrate the IUE spectra, the properties of which are given in Table 2.…”

Section: Ultraviolet Photometry and Flux Ratiosmentioning

confidence: 99%

Fundamental effective temperature measurements for eclipsing binary stars – I. Development of the method and application to AI Phoenicis

Miller

Maxted

Smalley

2020

Monthly Notices of the Royal Astronomical Society

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Stars with accurate and precise effective temperature (Teff) measurements are needed to test stellar atmosphere models and calibrate empirical methods to determine Teff. There are few standard stars currently available to calibrate temperature indicators for dwarf stars. Gaia parallaxes now make it possible, in principle, to measure Teff for many dwarf stars in eclipsing binaries. We aim to develop a method that uses high-precision measurements of detached eclipsing binary stars, Gaia parallaxes and multi-wavelength photometry to obtain accurate and precise fundamental effective temperatures that can be used to establish a set of benchmark stars. We select the well-studied binary AI Phoenicis to test our method, since it has very precise absolute parameters and extensive archival photometry. The method uses the stellar radii and parallax for stars in eclipsing binaries. We use a Bayesian approach to obtain the integrated bolometric fluxes for the two stars from observed magnitudes, colours and flux ratios. The fundamental effective temperature of two stars in AI Phoenicis are 6199 ± 22 K for the F7 V component and 5094 ± 16 K for the K0 IV component. The zero-point error in the flux scale leads to a systematic error of only 0.2% (≈ 11 K) in Teff. We find that these results are robust against the details of the analysis, such as the choice of model spectra. Our method can be applied to eclipsing binary stars with radius, parallax and photometric measurements across a range of wavelengths. Stars with fundamental effective temperatures determined with this method can be used as benchmarks in future surveys.

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Ultraviolet extinction correlation with 3D dust maps using white dwarfs

Sahu,

Tremblay,

Lallement

et al. 2024

Monthly Notices of the Royal Astronomical Society

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Accurate astrometric and photometric measurements from Gaia have led to the construction of 3D dust extinction maps which can now be used for estimating the integrated extinctions of Galactic sources located within 5 kpc. These maps based on optical observations may not be reliable for use in the ultraviolet (UV) which is more sensitive to reddening. Past studies have focused on studying UV extinction using main-sequence stars but lack comparison with 3D dust maps. White dwarfs with well-modeled hydrogen-dominated (DA) atmospheres provide an advantage over main-sequence stars affected by magnetic activity. In this work, we study the variation of UV extinction with 3D dust maps utilising HST and GALEX observations of DA white dwarfs located within 300 pc. We used HST COS spectroscopic data of 76 sight lines to calculate the optical extinction from Si ii column densities and validate our results with the kinematic model predictions of the local interstellar medium. Also, we combined GALEX and Gaia photometric observations of 1158 DA white dwarfs to study UV reddening by comparing observed and modeled colour-colour relations. We calculated GALEX non-linearity corrections and derived reddening coefficients (R(NUV − G) = 6.52 ± 1.53 and R(FUV − G) = 6.04 ± 2.41) considering their variations with optical extinction (AV < 0.1 mag), and found them to be in good agreement with known extinction laws. HST analysis suggests a positive bias of 0.01–0.02 mag in the optical extinction from 3D maps depending on the Galactic latitude. These results independently confirm the validity of 3D dust maps to deredden the optical and UV observations of white dwarfs.

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A Correction for GALEX Spectroscopic UV Flux Distributions from Comparisons with CALSPEC and IUE

Cited by 3 publications

References 31 publications

Global‐Scale Observations of the Limb and Disk Mission Implementation: 1. Instrument Design and Early Flight Performance

Global‐Scale Observations of the Limb and Disk Mission Implementation: 1. Instrument Design and Early Flight Performance

Fundamental effective temperature measurements for eclipsing binary stars – I. Development of the method and application to AI Phoenicis

Ultraviolet extinction correlation with 3D dust maps using white dwarfs

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