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At least 1,513 records · Page 84
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DOE OSTI2017

New Precision Orbits of Bright Double-lined Spectroscopic Binaries. X. HD 96511, HR 7578, and KZ Andromedae

From an extensive number of newly acquired radial velocities we determine the orbital elements for three late-type dwarf systems, HD 96511, HR 7578, and KZ And. The orbital periods are 18.89737 ± 0.00002, 46.81610 ± 0.00006, and 3.0329113 ± 0.0000005 days, respectively, and all three systems are eccentric, although KZ And is just barely so. We have detected lines of the secondary of HD 96511 for the first time. The orbital dimensions ( a {sub 1} sin i and a {sub 2} sin i ) and minimum masses ( m {sub 1} sin{sup 3} i and m {sub 2} sin{sup 3} i ) of the binary components all have accuracies of 0.2% or better. Extensive photometry of the chromospherically active binary HR 7578 confirms a rather long rotation period of 16.446 ± 0.002 days and that the K3 V components do not eclipse. We have estimated the basic properties of the stars in the three systems and compared those results with evolutionary tracks. The results for KZ And that we computed with the revised Hipparcos parallax of van Leeuwen produce inconsistencies. That parallax appears to be too large, and so, instead, we used the original Hipparcos parallax of the common proper motion primary, which improves the results, although some problems remain.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

The Globular Cluster NGC 6402 (M14). II. Variable Stars

We present time-series BVI photometry for the Galactic globular cluster NGC 6402 (M14). The data consist of ∼137 images per filter, obtained using the 0.9 and 1.0 m SMARTS telescopes at the Cerro Tololo Inter-American Observatory. The images were obtained during two observing runs in 2006–2007. The image-subtraction package ISIS, along with DAOPHOT II/ALLFRAME, was used to perform crowded-field photometry and search for variable stars. We identified 130 variables, eight of which are new discoveries. The variable star population is comprised of 56 ab-type RR Lyrae stars, 54 c-type RR Lyrae, 6 type II Cepheids, 1 W UMa star, 1 detached eclipsing binary, and 12 long-period variables. We provide Fourier decomposition parameters for the RR Lyrae, and discuss the physical parameters and photometric metallicity derived therefrom. The M14 distance modulus is also discussed, based on different approaches for the calibration of the absolute magnitudes of RR Lyrae stars. The possible presence of second-overtone RR Lyrae in M14 is critically addressed, with our results arguing against this possibility. By considering all of the RR Lyrae stars as members of the cluster, we derive 〈P{sub ab}〉=0.589 days. This, together with the position of the RR Lyrae stars of both Bailey types in the period–amplitude diagram, suggests an Oosterhoff-intermediate classification for the cluster. Such an intermediate Oosterhoff type is much more commonly found in nearby extragalactic systems, and we critically discuss several other possible indications that may point to an extragalactic origin for this cluster.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

LHS 1610A: A Nearby Mid-M Dwarf with a Companion That Is Likely a Brown Dwarf

We present the spectroscopic orbit of LHS 1610A, a newly discovered single-lined spectroscopic binary with a trigonometric distance placing it at 9.9 ± 0.2 pc. We obtained spectra with the TRES instrument on the 1.5 m Tillinghast Reflector at the Fred Lawrence Whipple Observatory located on Mt. Hopkins in AZ. We demonstrate the use of the TiO molecular bands at 7065–7165 Å to measure radial velocities and achieve an average estimated velocity uncertainty of 28 m s{sup −1}. We measure the orbital period to be 10.6 days and calculate a minimum mass of 44.8 ± 3.2 M {sub Jup} for the secondary, indicating that it is likely a brown dwarf. We place an upper limit to 3σ of 2500 K on the effective temperature of the companion from infrared spectroscopic observations using IGRINS on the 4.3 m Discovery Channel Telescope. In addition, we present a new photometric rotation period of 84.3 days for the primary star using data from the MEarth-South Observatory, with which we show that the system does not eclipse.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Absolute Dimensions and Evolutionary Status of the Semi-detached Algol W Ursae Minoris

Double-lined eclipsing binaries allow accurate and direct determination of fundamental parameters such as mass and radius for each component, and they provide important constraints on the stellar structure and evolution models. In this study, we aim to determine a unique set of binary parameters for the Algol system W UMi and to examine its evolutionary status. New high-resolution time-series spectroscopic observations were carried out during 14 nights from 2008 April to 2011 March, and a total of 37 spectra were obtained using the Bohyunsan Optical Echelle Spectrograph. We measured the radial velocities (RVs) for both components, and the effective temperature of the primary star was found to be T {sub eff,1} = 9310 ± 90 K by a comparison of the observed spectra and the Kurucz models. The physical parameters of W UMi were derived by an analysis of our RV data together with the multi-band light curves of Devinney et al. The individual masses, radii, and luminosities of both components are M {sub 1} = 3.68 ± 0.10 M {sub ⊙} and M {sub 2} = 1.47 ± 0.04 M {sub ⊙}, R {sub 1} = 3.88 ± 0.03 R {sub ⊙} and R {sub 2} = 3.13 ± 0.03 R {sub ⊙}, and L {sub 1} = 102 ± 1 L {sub ⊙} and L {sub 2} = 7.3 ± 0.1 L {sub ⊙}, respectively. A comparison of these parameters with theoretical stellar models showed that the primary component lies in the main-sequence band, while the less massive secondary is noticeably evolved. The results indicate that the initially more massive star became the present secondary by losing most of its own mass via mass transfer to the companion (present primary).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

An Improved Transit Measurement for a 2.4 R{sub ⊕} Planet Orbiting A Bright Mid-M Dwarf K2–28

We present a new Spitzer transit observation of K2–28b, a sub-Neptune (R {sub p} = 2.45 ± 0.28 R {sub ⊕}) orbiting a relatively bright (V {sub mag} = 16.06, K {sub mag} = 10.75) metal-rich M4 dwarf (EPIC 206318379). This star is one of only seven with masses less than 0.2 M{sub ⊙} known to host transiting planets, and the planet appears to be a slightly smaller analogue of GJ 1214b (2.85±0.20 R{sub ⊕}). Our new Spitzer observations were taken two years after the original K2 discovery data and have a significantly higher cadence, allowing us to derive improved estimates for this planet’s radius, semimajor axis, and orbital period, which greatly reduce the uncertainty in the prediction of near future transit times for the James Webb Space Telescope (JWST) observations. We also evaluate the system’s suitability for atmospheric characterization with JWST and find that it is currently the only small (<3 R{sub ⊕}) and cool (<600 K) planet aside from GJ 1214b with a potentially detectable secondary eclipse. We also note that this system is a favorable target for near-infrared radial velocity instruments on larger telescopes (e.g., the Habitable Planet Finder on the Hobby–Eberly Telescope), making it one of only a handful of small, cool planets accessible with this technique. Finally, we compare our results with the simulated catalog of the Transiting Exoplanet Survey Satellite (TESS) and find K2–28b to be representative of the kind of mid-M systems that should be detectable in the TESS sample.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

New Variable Stars in NGC 6652 and Its Background Sagittarius Stream

We conducted a variable star search on the metal-rich Galactic globular cluster NGC 6652 using archival Gemini-S/Gemini Multiobject Spectrograph data. We report the discovery of nine new variable stars in the NGC 6652 field, of which we classify six as eclipsing binaries and one as an SX Phoenicis star, leaving two variables without classification. Using proper motions from Gaia DR2 and Hubble Space Telescope, albeit with some uncertainties, we find that the cluster, the field, and the background Sagittarius stream each have three of these variables. We also reassess the membership of known variables based on the Gaia proper motions, confirming the existence of one RR Lyrae star in the cluster.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

A Comprehensive Study of Three Early-type Contact Twin Binaries: CT Tau, GU Mon, and V701 Sco

Three eclipsing binaries, CT Tau, GU Mon, and V701 Sco, are early-type contact binaries with infrared excess from circumbinary matter. We present the multi-color photometry for CT Tau and GU Mon, whose spectral types of B1V are identified by the low-precision spectra. Combining these new light curves (LCs) with previously reported LCs and radial velocity curves, we perform a synthesized analysis to estimate/update the stellar absolute parameters of the three systems. Their mass ratios are close to unity (i.e., q ≃ 1), which indicates that the binary system comprising of twin components may be undergoing a slow Case A mass transfer. From the period analysis, the light–time orbit in the (O - C) curve may result from the third condense companion around the binary system although no evidence could be provided by the third light ℓ {sub 3}. From the spectral energy distribution for three binaries, the excess infrared (IR) emissions are above the photospheric emissions, which can be seen at the 22.1 μm for CT Tau and GU Mon, and 11.6 μm, 14.5 μm, and 22.1 μm for V701 Sco, respectively. This kind of infrared excess for the early-type star may be attributed to the circumbinary matter by stellar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Smaller than Expected Bright-spot Offsets in Spitzer Phase Curves of the Hot Jupiter Qatar-1b

We present Spitzer full-orbit thermal phase curves of the hot Jupiter Qatar-1b, a planet with the same equilibrium temperature—and intermediate surface gravity and orbital period—as the well-studied planets HD 209458b and WASP-43b. We measure secondary eclipse depths of 0.21 ± 0.02% at 3.6 μm and 0.30 ± 0.02% at 4.5 μm, corresponding to dayside brightness temperatures of 1542{sub −31}{sup +32} K and 1557{sub −36}{sup +35} K, respectively, consistent with a vertically isothermal dayside. The respective nightside brightness temperatures are 1117{sub −71}{sup +76} and 1167{sub −74}{sup +69} K, in line with a trend that hot Jupiters all have similar nightside temperatures. We infer a Bond albedo of 0.12{sub −0.16}{sup +0.14} and a moderate day–night heat recirculation efficiency, similar to HD 209458b. General circulation models for HD 209458b and WASP-43b predict that their bright spots should be shifted east of the substellar point by tens of degrees, and these predictions were previously confirmed with Spitzer full-orbit phase curve observations. The phase curves of Qatar-1b are likewise expected to exhibit eastward offsets. Instead, the observed phase curves are consistent with no offset: 11° ± 7° at 3.6 μm and −4° ± 7° at 4.5 μm. The discrepancy in circulation patterns between these three otherwise similar planets points to the importance of secondary parameters like rotation rate and surface gravity, and the presence or absence of clouds, in determining atmospheric conditions on hot Jupiters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Optical to Near-infrared Transmission Spectrum of the Warm Sub-Saturn HAT-P-12b

We present the transmission spectrum of HAT-P-12b through a joint analysis of data obtained from the Hubble Space Telescope Space Telescope Imaging Spectrograph and Wide Field Camera 3 and Spitzer, covering the wavelength range 0.3–5.0 μm. We detect a muted water vapor absorption feature at 1.4 μm attenuated by clouds, as well as a Rayleigh scattering slope in the optical indicative of small particles. We interpret the transmission spectrum using both the state-of-the-art atmospheric retrieval code SCARLET and the aerosol microphysics model CARMA. These models indicate that the atmosphere of HAT-P-12b is consistent with a broad range of metallicities between several tens to a few hundred times solar, a roughly solar C/O ratio, and moderately efficient vertical mixing. Cloud models that include condensate clouds do not readily generate the submicron particles necessary to reproduce the observed Rayleigh scattering slope, while models that incorporate photochemical hazes composed of soot or tholins are able to match the full transmission spectrum. From a complementary analysis of secondary eclipses by Spitzer, we obtain measured depths of 0.042% ± 0.013% and 0.045% ± 0.018% at 3.6 and 4.5 μm, respectively, which are consistent with a blackbody temperature of 890{sup +60} {sub −70} K and indicate efficient day–night heat recirculation. HAT-P-12b joins the growing number of well-characterized warm planets that underscore the importance of clouds and hazes in our understanding of exoplanet atmospheres.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Long-term Photometry and Orbital Period Change of the W UMa–type Binary v0599 Aur: Evidence of about 11 yr Magnetic-activity Cycle

Combining all available photometric data from various surveys and literature with our observations, we present 10 sets of light curves for the eclipsing binary V0599 Aur covering a timescale of 20 yr. During the last two decades, the O’Connell effect continuously varied and went through at least two flips between positive and negative effects. The photometric solutions from our two sets of multicolored light curves show that V0599 Aur is a W-type shallow contact binary with an active spot on the secondary. Its absolute parameters are determined by combining the Gaia distance with the photometric solutions. The period investigation reveals a secular decrease and a cyclic variation in its orbital period. The former mainly originates from the mass transfer from the more massive secondary to the less massive primary. The latter can be preferentially explained as a result of cyclic magnetic activity of the secondary, with three observational supports: (1) the existence and evolution of an active spot suggested by the long-term photometry, (2) periodic variation in both the O’Connell effect and relative luminosity, and (3) weak correlations between O’Connell effect/relative luminosity changes and cyclic period variation. Together with the cyclic period variation and its theoretical reasonability by Applegate’s mechanism, we suggest that the secondary of V0599 Aur is a solar-type magnetic-activity star with an approximately 11 yr active cycle. Furthermore, by combining the secular period decrease with the Roche-lobe model, we infer that V0599 Aur is evolving from the marginal contact state controlled by thermal relaxation oscillation theory to the overcontact state.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Asteroid Rotation Period Survey Using the China Near-Earth Object Survey Telescope (CNEOST)

We initiated the bilateral collaboration between the Lulin Observatory and the Purple Mountain Observatory to collect asteroid lightcurves using the Chinese Near-Earth Object Survey Telescope at the Xuyi Observation Station. The primary goal of this collaboration was to discover super-fast rotators (SFRs) and study their physical properties. Two campaigns have been conducted: (a) a survey of ∼45 deg{sup 2} using 8 minute cadence during 2017 February 26–March 2, and (b) a survey of ∼60 deg{sup 2} using 10 minute cadence during 2018 March 9–12. Our samples are mainly main-belt asteroids and some Hildas and Jupiter Trojans. Out of 4522 collected lightcurves, 506 reliable rotation periods were obtained. Among the reliable rotation periods, we found 16 candidates with a possible rotation period of <2.2 hr, in which (134291) 2006 DZ6 shows a very convincing folded lightcurve and the other 15 candidates only have a likely trend. Further confirmation is needed for the rotation periods of these SFR candidates. In addition, (2280) Kunikov seems to have an eclipsing feature on its lightcurve with a relatively long rotation period suggesting that it is likely a fully synchronized binary asteroid. When the preliminary spin-rate distributions were carried out for asteroids using different sizes, no obvious difference was found.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Follow-up Studies of Five Cataclysmic Variable Candidates Discovered by LAMOST

We report follow-up observations of five cataclysmic variable candidates from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) published by Hou et al. LAMOST J024048.51+195226.9 is the most unusual of the five; an early-M type secondary star contributes strongly to its spectrum, and its spectral and photometric behavior are strikingly reminiscent of the hitherto-unique propeller system AE Aqr. We confirm that a 7.34 hr period discovered in the Catalina survey data is orbital. Another object, LAMOST J204305.95+341340.6, appears to be a near twin of the novalike variable V795 Her, with an orbital period in the so-called 2–3 hr “gap.” LAMOST J035913.61+405035.0 is evidently an eclipsing, weakly outbursting dwarf nova with a 5.48 hr period. Our spectrum of LAMOST J090150.09+375444.3 is dominated by a late-type secondary and shows weak, narrow Balmer emission moving in phase with the absorption lines, but at lower amplitude; we do not see the He ii λ4686 emission evident in the published discovery spectrum. We again confirm that a period from the Catalina data, in this case 6.80 hr, is orbital. LAMOST J033940.98+414805.7 yields a radial-velocity period of 3.54 hr, and its spectrum appears to be typical of novalike variables in this period range. The spectroscopically selected sample from LAMOST evidently includes some interesting cataclysmic variables that have been unrecognized until now, apparently because of the relatively modest range of their photometric variations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Integrating Light Curve and Atmospheric Modeling of Transiting Exoplanets

Spectral retrieval techniques are currently our best tool to interpret the observed exoplanet atmospheric data. Said techniques retrieve the optimal atmospheric components and parameters by identifying the best fit to an observed transmission/emission spectrum. Over the past decade, our understanding of remote worlds in our galaxy has flourished thanks to the use of increasingly sophisticated spectral retrieval techniques and the collective effort of the community working on exoplanet atmospheric models. A new generation of instruments in space and from the ground is expected to deliver higher quality data in the next decade; it is therefore paramount to upgrade current models and improve their reliability, their completeness, and the numerical speed with which they can be run. In this paper, we address the issue of reliability of the results provided by retrieval models in the presence of systematics of unknown origin. More specifically, we demonstrate that if we fit directly individual light curves at different wavelengths (L-retrieval), instead of fitting transit or eclipse depths, as it is currently done (S-retrieval), the said methodology is more sensitive against astrophysical and instrumental noise. This new approach is tested, in particular, when discrepant simulated observations from Hubble Space Telescope/Wide Field Camera 3 and Spitzer/IRAC are combined. We find that while S-retrievals converge to an incorrect solution without any warning, L-retrievals are able to flag potential discrepancies between the data sets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Mathematical Underpinnings of the Multiwavelength Structure of the Tip of the Red Giant Branch

We consider the application of the tip of the red giant branch (TRGB) in the optical and in the near-infrared for the determination of distances to nearby galaxies. We analyze ACS VI (F555W and F814W) data and self-consistently cross-calibrate WFC3-IR JH (F110W and F120W) data using an absolute magnitude calibration of M {sub I} = −4.05 mag as determined in the Large Magellanic Cloud using detached eclipsing binary star geometric parallaxes. We demonstrate how the optical and near-infrared calibrations of the TRGB method are mathematically self-consistent, and illustrate the mathematical basis and relations among these multiwavelength calibrations. We go on to present a method for determining the reddening, extinction, and the true modulus to the host galaxy using multiwavelength data. The power of the method is that with high-precision data, the reddening can be determined using the TRGB stars themselves, and decreases the systematic (albeit generally small) uncertainty in distance due to reddening for these halo stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Phase Modeling of the TRAPPIST-1 Planetary Atmospheres

Transiting compact multiplanet systems provide many unique opportunities to characterize the planets, including studies of size distributions, mean densities, orbital dynamics, and atmospheric compositions. The relatively short orbital periods in these systems ensure that events requiring specific orbital locations of the planets (such as primary transit and secondary eclipse points) occur with high frequency. The orbital motion and associated phase variations of the planets provide a means to constrain the atmospheric compositions through measurement of their albedos. Here we describe the expected phase variations of the TRAPPIST-1 system and times of superior conjunction when the summation of phase effects produce maximum amplitudes. We also describe the infrared flux emitted by the TRAPPIST-1 planets and the influence on the overall phase amplitudes. We further present the results from using the global circulation model ROCKE-3D to model the atmospheres of TRAPPIST-1e and TRAPPIST-1f assuming modern Earth and Archean atmospheric compositions. These simulations are used to calculate predicted phase curves for both reflected light and thermal emission components. We discuss the detectability of these signatures and the future prospects for similar studies of phase variations for relatively faint M stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Short-period Variability in the Globular Cluster NGC 419 and the SMC Field

Delta Scuti (δ Sct) stars have been extensively studied in our Galaxy but far less in extragalactic systems. Here we study the population of δ Sct variables in NGC 419, an intermediate-age globular cluster of the Small Magellanic Cloud (SMC), using g, r, and i Gemini-S/Gemini Multi-Object Spectrograph (GMOS) time-series observations. Our goal is to study the role of such variables in the cluster extended main-sequence turnoff (MSTO). We report the discovery of 54 δ Sct stars and three eclipsing binaries in the NGC 419 field. We find only a handful of the δ Sct stars at the MSTO of NGC 419, while the majority are fainter, indicating that the cluster is younger (≲1.2 Gyr) than previously thought. Considering their radial distribution, we identify only six δ Sct stars as probable members of NGC 419, while the 48 remaining are likely δ Sct stars of the SMC field. Cluster δ Sct stars appear close to the red edge of the MSTO, supporting the idea that the extended MSTO has its origin in an age spread. The 48 field δ Sct stars represent the largest detection of δ Sct stars made in the SMC. The period distribution of these newly detected δ Sct stars (0.04 day ≲ P ≲ 0.15 day) is similar to that detected in other systems. The amplitude distribution (0.05 mag ≲ Δr ≲ 0.60 mag) is likely biased because of the lack of low-amplitude stars. We finally use the δ Sct stars to calculate distances using different period–luminosity relations. The average distance moduli obtained are 18.76 ± 0.14 mag for NGC 419 and 18.86 ± 0.11 mag for the SMC field, which agree with previous measurements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

BVR{sub c}I{sub c} Observations, Third-body Orbital Study, and Analysis of the UV Leo-type, Pre-W UMA Binary V642 Virginis

V642 Vir is a polar spotted, well-detached, UV Leo-type, low-mass, pre-WUMa (T1 ~ 4250K, ~K6V) eclipsing binary. It was observed in 2020 April, May, and June at the Dark Sky Observatory in North Carolina, USA with the 0.81 m reflector of Appalachian State University. A total of 88 timings were used in our 22-year period study which included 12 Transiting Exoplanet Survey Satellite (TESS) timings. The O - C plots show a low-amplitude oscillation of residuals that points to the existence of an orbiting third body, a dwarf of minimum mass, 0.15 M {sub ⊙} in an eccentric orbit (e = 0.41), with an orbital period of 20.07 yr. The odd light curves of V642 Virginis indicate that it has polar spots similar to UV Leo and the recently published V1023 Per. Its present large polar spot region indicates that it must have a strong magnetic field and that it is synchronously rotating. The BVR{sub c}I{sub c} simultaneous Wilson–Devinney Program solution gives a detached binary (primary and secondary components are underfilling their respective Roche Lobes, with 76% and 78% fill outs respectively). The cool spot region models near the pole of the primary component (centered at 10° colatitude) and is angled toward the secondary component. Its large radius (68°) and T-fact (T{sub spot}/T{sub surface} = 0.69) also attest to the conclusion of the strength of the magnetic field. The small ΔT in the components (~318 K) and mass ratio near unity (0.9542 ± 0.0005) show that the stars are similar in spectral type (secondary ~K9V). The inclination is high, ~86.87 ± 0.04°, yet there is no time of constant light due to the two stars’ essentially equal radii.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Physical and Visual Evaluation of Filters for Direct Observation of the Sun and the International Standard ISO 12312-2:2015

We investigated the compliance of 43 commercially available solar filters (eclipse glasses) with the ISO 12312-2:2015 standard by measuring their spectral transmittances (280–2000 nm) and calculating their luminous, solar ultraviolet A, ultraviolet B, and infrared (IR) transmittances. We also evaluated the filters for usability by observing the full midday Sun and rating the view on a seven-point balanced scale, from “far too dark, details seen only with great difficulty” to “far too light, uncomfortable to view the Sun.” The mean ratings of two observers, one experienced and one inexperienced in solar observing, differed by 0.28 (95% confidence interval of the mean = 0.26). The inexperienced observer tended to be less accepting of high transmittances. All 43 solar filters complied with the UV and IR requirements. Eighteen filters passed the luminous transmittance requirements, and 24 were borderline too light or too dark. Seven of the 15 solar filters with a luminous transmittance darker than the requirement were rated as acceptable. One filter that passed and another that was borderline too light were rated as too light or far too light. The ISO 12312-2 limits derive from welding filter standards and do not represent an appropriate evidence base for direct solar viewing. This work provides the evidence base for a maximum 0.0012% and a minimum 0.00004% luminous transmittance for solar filters. The results of this study also support the use of welding filters between shades 12 and 16. Lighter welding filters are more acceptable than solar filters of the same luminous transmittance.

79 ASTRONOMY AND ASTROPHYSICS↗