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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Hubble Space Telescope Eclipse Observations of the Nova Like Cataclysmic Variable UX Ursae Majoris

We present and analyze Hubble Space Telescope observations of the eclipsing nova-like cataclysmic variable UX UMa obtained with the Faint Object Spectrograph. Two eclipses each were observed with the G160L grating (covering the ultraviolet waveband) in 1994 August and with the PRISM (covering the near-ultraviolet to near-infrared) in November of the same year. The system was about 50% brighter in November than in August, which, if due to a change in the accretion rate, indicates a fairly substantial increase in Mass accretion by about 50%. The eclipse light curves are qualitatively consistent with the gradual occultation of an accretion disk with a radially decreasing temperature distribution. The light curves also exhibit asymmetries about mideclipse that are likely due to a bright spot at the disk edge. Bright-spot spectra have been constructed by differencing the mean spectra observed at pre- and posteclipse orbital phases. These difference spectra contain ultraviolet absorption lines and show the Balmer jump in emission. This suggests that part of the bright spot may be optically thin in the continuum and vertically extended enough to veil the inner disk and/or the outflow from UX UMa in some spectral lines. Model disk spectra constructed as ensembles of stellar atmospheres provide poor descriptions of the observed posteclipse spectra, despite the fact that UX UMa's light should be dominated by the disk at this time. Suitably scaled single temperature model stellar atmospheres with T(sub eff) approximately equals 12,500-14,500 K actually provide a better match to both the ultraviolet and optical posteclipse spectra. Evidently, great care must be taken in attempts to derive accretion rates from comparisons of disk models to observations. One way to reconcile disk models with the observed posteclipse spectra is to postulate the presence of a significant amount of optically thin material in the system. Such an optically thin component might be associated with the transition region ("chromosphere") between the disk photosphere and the fast wind from the system whose presence has been suggested by Knigge and Drew. In any event, the wind/ chromosphere is likely to be the region in which many, if not most, of the UV lines are formed. This is clear from the plethora of emission lines that appear in the mideclipse spectra, some of which appear as absorption features in spectra taken at out-of-eclipse orbital phases.

Knigge, Christian↗
NASA NTRS1999

Total Solar Eclipse of 2001 June 21

On 2001 June 21, a total eclipse of the Sun will be visible from within a narrow corridor which traverses the Southern Hemisphere. The path of the Moon's umbral shadow begins in the South Atlantic, crosses southern Africa and Madagascar, and ends at sunset in the Indian Ocean. A partial eclipse will be seen within the much broader path of the Moon's penumbral shadow, which includes eastern South America and the southern two thirds of Africa. Detailed predictions for this event are presented and include besselian elements, geographic coordinates of the path of totality, physical ephemeris of the umbra, topocentric limb profile corrections, local circumstances for approximately 350 cities, maps of the eclipse path, weather prospects, the lunar limb profile and the sky during totality. Tips and suggestions are also given on how to safely view and photograph the eclipse.

Espenak, Fred↗
NASA NTRS2002

Annular and Total Solar Eclipses of 2003

On Saturday, 2003 May 31, an annular eclipse of the Sun will be visible from a broad corridor that traverses the North Atlantic. The path of the Moon's antumbral shadow begins in northern Scotland, crosses Iceland and central Greenland, and ends at sunrise in Baffin Bay (Canada). A partial eclipse will be seen within the much broader path of the Moon's penumbral shadow, which includes most of Europe, the Middle East, central and northern Asia, and northwestern North America. The trajectory of the Moon's shadow is quite unusual during this event. The shadow axis passes to the far north where it barely grazes Earth's surface. In fact, the northern edge of the antumbra actually misses Earth so that one path limit is defined by the day/night terminator rather than by the shadow's upper edge. As a result, the track of annularity has a peculiar "D" shape that is nearly 1200 kilometers wide. Since the eclipse occurs just three weeks prior to the northern summer solstice, Earth's northern axis is pointed sunwards by 22.8 deg. As seen from the Sun, the antumbral shadow actually passes between the North Pole and the terminator. As a consequence of this extraordinary geometry, the path of annularity runs from east to west rather than the more typical west to east. The event transpires near the Moon's ascending node in Taurus five degrees north of Aldebaran. Since apogee occurs three days earlier (May 28 at 13 UT), the Moon's apparent diameter (29.6 arc-minutes) is still too small to completely cover the Sun (31.6 arc-minutes) resulting in an annular eclipse.

Espenak, Fred↗
NASA NTRS2019

Libration Orbit Eclipse Avoidance Maneuver Study for the James Webb Space Telescope Mission

Mission analysis of libration orbit trajectories at Sun-Earth/Moon L2 typically includes predictions of lunar and Earth eclipses during the mission life-time. The NASA James Webb Space Telescope (JWST) trajectory, by design, avoids these eclipses by pruning its launch window. In an off-nominal scenario where an eclipse is predicted, a maneuver strategy is needed. In this paper, trade studies are examined for JWST that characterize the burn magnitude, location, and epochs of multiple maneuver plans to avoid an eclipse. The results enable analysts to explore the space of feasible maneuver strategies during routine operations.

Maneuver design↗
NASA NTRS2021

Triply eclipsing triple stars in the northern TESS fields: TICs 193993801, 388459317, and 52041148

In this work we report the discovery and analysis of three new triply eclipsing triple star systems found with the TESS mission during its observations of the northern skies: TICs 193993801, 388459317, and 52041148. We utilized the TESS precision photometry of the binary eclipses and third-body eclipsing events, ground-based archival and follow-up photometric data, eclipse timing variations, archival spectral energy distributions, as well as theoretical evolution tracks in a joint photodynamical analysis to deduce the system masses and orbital parameters of both the inner and outer orbits. In one case (TIC 193993801) we also obtained radial velocity measurements of all three stars. This enabled us to `calibrate' our analysis approach with and without `truth' (i.e., RV) data. We find that the masses are good to 1-3% accuracy with RV data and 3-10% without the use of RV data. In all three systems we were able to find the outer orbital period before doing any detailed analysis by searching for a longer-term periodicity in the ASAS-SN archival photometry data -- just a few thousand ASAS-SN points enabled us to find the outer periods of 49.28 d, 89.86 d, and 177.0 d, respectively. From our full photodynamical analysis we find that all three systems are coplanar to within 1 ∘ −3 ∘ . The outer eccentricities of the three systems are 0.003, 0.10, and 0.62, respectively (i.e., spanning a factor of 200). The masses of the three stars {Aa, Ab, and B} in the three systems are: {1.31, 1.19, 1.34}, {1.82, 1.73, 2.19}, and {1.62, 1.48, 2.74} M ⊙ , respectively.

Tamás Borkovits↗
NASA NTRSDate not supplied

Thermal Band Observations of the May 2022 Total Lunar Eclipse by the Landsat Thermal Infrared Sensors

The Thermal Infrared Sensor (TIRS) instruments on board Landsat 8 and Landsat 9 provide routine thermal band image measurements of the Earth for the Landsat program. Although these observatories are specifically designed for mapping the Earth’s surface from their 705-km altitude orbits, they were recently utilized to image the Moon during the total lunar eclipse of May 2022. The full Moon is frequently used as a calibration target for Landsat. However, the imaging of the lunar eclipse provided a unique opportunity to gather accurate temporal thermal band data over the full lunar disc as solar illumination is removed. This campaign required a large effort by the Landsat Flight Operations teams to coordinate acquisitions and technical constraints on both observatories to capture the long temporal extent of the eclipse. The result of this effort was a series of resolved thermal images of the Moon at discrete times as the Earth’s shadow swept across the lunar surface through the start, partial, and total phases of the eclipse. This sequence of images showed an overall drop in surface temperature from approximately 370 K to 180 K in about 300 minutes as solar insolation was removed. Furthermore, the spatial distribution of cooling rates from this unique event provided information about different material properties (density and thermal inertia) across the lunar surface and showed a clear distinction among mare, highlands, and impact craters.

Matthew Montanaro↗
DOE OSTI2015

The Kepler eclipsing system KIC 5621294 and its substellar companion

We present the physical properties of KIC 5621294, showing light and timing variations from the Kepler photometry. Its light curve displays partial eclipses and the O’Connell effect, with Max II fainter than Max I, which was fitted quite well by applying third-body and spot effects to the system. The results indicate that the eclipsing pair is a classical Algol-type system with parameters of q = 0.22, i = 76.°8, and Δ(T{sub 1}−T{sub 2}) = 4235 K, in which the detached primary component fills about 77% of its limiting lobe. Striking discrepancies exist between the primary and secondary eclipse times obtained with the method of Kwee and van Woerden. These are mainly caused by surface inhomogeneities due to spot activity detected in our light curve synthesis. The 1253 light curve timings from the Wilson–Devinney code were used for a period study. It was found that the orbital period of KIC 5621294 has varied due to periodic variation overlaid on a downward parabola. The sinusoidal variation with a period of 961 days and a semi-amplitude of 22.5 s most likely arises from a light-time effect due to a third component with a mass of M{sub 3}sini{sub 3} = 46.9 M{sub Jup}, which is in good agreement with that calculated from the light curve itself. If its orbital inclination is larger than about 40°, the mass of the circumbinary object would possibly match a brown dwarf. The parabolic variation could not be fully explained by either a mass transfer between the binary components or angular momentum via magnetic braking. It is possible that the parabola may be the only observed part of a period modulation caused by the presence of another companion in a wider orbit.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A systematic retrieval analysis of secondary eclipse spectra. II. A uniform analysis of nine planets and their C to O ratios

Secondary eclipse spectroscopy provides invaluable insights into the temperatures and compositions of exoplanetary atmospheres. We carry out a systematic temperature and abundance retrieval analysis of nine exoplanets (HD 189733b, HD 209458b, HD 149026b, GJ436b, WASP-12b, WASP-19b, WASP-43b, TrES-2b, and TrES-3b) observed in secondary eclipse using a combination of space- and ground-based facilities. Our goal with this analysis is to provide a consistent set of temperatures and compositions from which self-consistent models can be compared and to probe the underlying processes that shape these atmospheres. This paper is the second in a three part series of papers exploring the retrievability of temperatures and abundances from secondary eclipse spectra and the implications of these results for the chemistry of exoplanet atmospheres. In this investigation we present a catalogue of temperatures and abundances for H{sub 2}O, CH{sub 4}, CO, and CO{sub 2}. We find that our temperatures and abundances are generally consistent with those of previous studies, although we do not find any statistically convincing evidence for super-solar C to O ratios (e.g., solar C/O falls in the 1σ confidence intervals in eight of the nine planets in our sample). Furthermore, within our sample we find little evidence for thermal inversions over a wide range of effective temperatures (with the exception of HD 209458b), consistent with previous investigations. The lack of evidence for inversions for most planets in our sample over such a wide range of effective temperatures provides additional support for the hypothesis that TiO is unlikely to be the absorber responsible for the formation of these inversions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The ARAUCARIA project. OGLE-LMC-CEP-1718: An exotic eclipsing binary system composed of two classical overtone cepheids in a 413 day orbit

We have obtained extensive high-quality spectroscopic observations of the OGLE-LMC-CEP-1718 eclipsing binary system in the Large Magellanic Cloud that Soszyński et al. had identified as a candidate system for containing two classical Cepheids in orbit. Our spectroscopic data clearly demonstrate binary motion of the Cepheids in a 413 day eccentric orbit, rendering this eclipsing binary system the first ever known to consist of 2 classical Cepheid variables. After disentangling the four different radial velocity variations in the system, we present the orbital solution and the individual pulsational radial velocity curves of the Cepheids. We show that both Cepheids are extremely likely to be first overtone pulsators and determine their respective dynamical masses, which turn out to be equal to within 1.5%. Since the secondary eclipse is not observed in the orbital light curve, we cannot derive the individual radii of the Cepheids, but the sum of their radii derived from the photometry is consistent with overtone pulsation for both variables. The existence of two equal-mass Cepheids in a binary system having different pulsation periods (1.96 and 2.48 days, respectively) may pose an interesting challenge to stellar evolution and pulsation theories, and a more detailed study of this system using additional data sets should yield deeper insight about the physics of stellar evolution of Cepheid variables. Future analysis of the system using additional near-infrared photometry might also lead to a better understanding of the systematic uncertainties in current Baade-Wesselink techniques of distance determinations to Cepheid variables.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Calibrating the updated overshoot mixing model on eclipsing binary stars: HY Vir, YZ Cas, χ{sup 2} Hya, and VV Crv

Detached eclipsing binary stars with convective cores provide a good tool to investigate convective core overshoot. It has been performed on some binary stars to restrict the classical overshoot model which simply extends the boundary of the fully mixed region. However, the classical overshoot model is physically unreasonable and inconsistent with helioseismic investigations. An updated model of overshoot mixing was established recently. There is a key parameter in the model. In this paper, we use observations of four eclipsing binary stars, i.e., HY Vir, YZ Cas, χ{sup 2} Hya, and VV Crv, to investigate a suitable value for the parameter. It is found that the value suggested by calibrations on eclipsing binary stars is the same as the value recommended by other methods. In addition, we have studied the effects of the updated overshoot model on the stellar structure. The diffusion coefficient of convective/overshoot mixing is very high in the convection zone, then quickly decreases near the convective boundary, and exponentially decreases in the overshoot region. The low value of the diffusion coefficient in the overshoot region leads to weak mixing and a partially mixed overshoot region. Semi-convection, which appears in the standard stellar models of low-mass stars with convective cores, is removed by partial overshoot mixing.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

BD Andromedae: A new short-period RS CVn eclipsing binary star with a distant tertiary body in a highly eccentric orbit

A photometric study of BD And was made through the analysis of two sets of new BVR light curves. The light curves with migrating photometric waves outside eclipse show that BD And is a short-period RS CVn-type binary star. The analysis of all available timings reveals that the orbital period has varied in a strictly cyclical way with a period of 9.2 yr. The periodic variation most likely arises from the light-time effect due to a tertiary moving in a highly elliptical orbit (e {sub 3} = 0.76). The Applegate mechanism could not operate properly in the eclipsing pair. The light curves were modeled with two large spots on the hotter star and a large third light amounting to about 14% of the total systemic light. BD And is a triple system: a detached binary system consisting of two nearly equal solar-type stars with an active primary star and a G6-G7 tertiary dwarf. The absolute dimensions of the eclipsing pair and tertiary components were determined. The three components with a mean age of about 5.8 Gyr are located at midpositions in main-sequence bands. The radius of the secondary is about 17% larger than that deduced from stellar models. The orbital and radiometric characteristics of the tertiary are intensively investigated. One important feature is that the mutual inclination between two orbits is larger than 60°, implying that Kozai cycles had occurred very efficiently in the past. The possible past and future evolutions of the BD And system, driven by KCTF and MBTF, are also discussed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Near-infrared brightness of the Galilean satellites eclipsed in Jovian shadow: A new technique to investigate Jovian upper atmosphere

Based on observations from the Hubble Space Telescope and the Subaru Telescope, we have discovered that Europa, Ganymede, and Callisto are bright around 1.5 μm even when not directly lit by sunlight. The observations were conducted with non-sidereal tracking on Jupiter outside of the field of view to reduce the stray light subtraction uncertainty due to the close proximity of Jupiter. Their eclipsed luminosity was 10{sup –6}-10{sup –7} of their uneclipsed brightness, which is low enough that this phenomenon has been undiscovered until now. In addition, Europa in eclipse was <1/10 of the others at 1.5 μm, a potential clue to the origin of the source of luminosity. Likewise, Ganymede observations were attempted at 3.6 μm by the Spitzer Space Telescope, but it was not detected, suggesting a significant wavelength dependence. It is still unknown why they are luminous even when in the Jovian shadow, but forward-scattered sunlight by hazes in the Jovian upper atmosphere is proposed as the most plausible candidate. If this is the case, observations of these Galilean satellites while eclipsed by the Jovian shadow provide us with a new technique to investigate the Jovian atmospheric composition. Investigating the transmission spectrum of Jupiter by this method is important for investigating the atmosphere of extrasolar giant planets by transit spectroscopy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

A search for planetary eclipses of white dwarfs in the Pan-STARRS1 medium-deep fields

We present a search for eclipses of ∼1700 white dwarfs (WDs) in the Pan-STARRS1 medium-deep fields. Candidate eclipse events are selected by identifying low outliers in over 4.3 million light curve measurements. We find no short-duration eclipses consistent with being caused by a planetary size companion. This large data set enables us to place strong constraints on the close-in planet occurrence rates around WDs for planets as small as 2 R {sub ⊕}. Our results indicate that gas giant planets orbiting just outside the Roche limit are rare, occurring around less than 0.5% of WDs. Habitable-zone super-Earths and hot super-Earths are less abundant than similar classes of planets around main-sequence stars. These constraints provide important insight into the ultimate fate of the large population of exoplanets orbiting main-sequence stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

HERCULES X-1: USING ECLIPSE TO MEASURE THE X-RAY CORONA

Observations of HZ Her/Her X-1 by the Rossi X-ray Timing Explorer during High State X-ray eclipses are analyzed. After a sharp ingress caused by the neutron star receding behind the companion star HZ Her, X-ray flux smoothly declines to a minimum at mid-eclipse. It then increases smoothly until egress. The mid-eclipse flux implies an extended emission region around the neutron star that is larger than that of HZ Her. The constancy of the X-ray softness ratio is consistent with electron scattering by an ionized corona. The corona is modeled as spherically symmetric with a power-law density profile. We find a best fit of ∝r {sup –1.25} with a normalization of ≅ 10{sup 12} cm{sup –3} at r = 2 × 10{sup 10} cm. The corona could either be in hydrostatic equilibrium, with heating by Compton scattering, a fast outflow, with a high mass-loss rate of ∼10{sup 18} gm s{sup –1}, or a hybrid, with an inner hydrostatic region and outer slow flow with a low mass-loss rate. A brightening at orbital phase 0.94 is suggested to be caused by the impact of the accretion stream with the accretion disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The mass–radius relation of young stars. I. USCO 5, an M4.5 eclipsing binary in upper Scorpius observed by K2

We present the discovery that UScoCTIO 5, a known spectroscopic binary in the Upper Scorpius star-forming region (P = 34 days, M{sub tot}sin(i)=0.64 M{sub ⊙}), is an eclipsing system with both primary and secondary eclipses apparent in K2 light curves obtained during Campaign 2. We have simultaneously fit the eclipse profiles from the K2 light curves and the existing RV data to demonstrate that UScoCTIO 5 consists of a pair of nearly identical M4.5 stars with M{sub A}=0.329±0.002 M{sub ⊙}, R{sub A}=0.834±0.006 R{sub ⊙}, M{sub B}=0.317±0.002 M{sub ⊙}, and R{sub B}=0.810±0.006 R{sub ⊙}. The radii are broadly consistent with pre-main-sequence ages predicted by stellar evolutionary models, but none agree to within the uncertainties. All models predict systematically incorrect masses at the 25%–50% level for the HR diagram position of these mid-M dwarfs, suggesting significant modifications to mass-dependent outcomes of star and planet formation. The form of the discrepancy for most model sets is not that they predict luminosities that are too low, but rather that they predict temperatures that are too high, suggesting that the models do not fully encompass the physics of energy transport (via convection and/or missing opacities) and/or a miscalibration of the SpT–T{sub eff} scale. The simplest modification to the models (changing T{sub eff} to match observations) would yield an older age for this system, in line with the recently proposed older age of Upper Scorpius (τ ∼ 11 Myr).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Spitzer secondary eclipse observations of five cool gas giant planets and empirical trends in cool planet emission spectra

In this work we present Spitzer 3.6 and 4.5 μm secondary eclipse observations of five new cool (<1200 K) transiting gas giant planets: HAT-P-19b, WASP-6b, WASP-10b, WASP-39b, and WASP-67b. We compare our measured eclipse depths to the predictions of a suite of atmosphere models and to eclipse depths for planets with previously published observations in order to constrain the temperature- and mass-dependent properties of gas giant planet atmospheres. We find that the dayside emission spectra of planets less massive than Jupiter require models with efficient circulation of energy to the night side and/or increased albedos, while those with masses greater than that of Jupiter are consistently best-matched by models with inefficient circulation and low albedos. At these relatively low temperatures we expect the atmospheric CH{sub 4}/CO ratio to vary as a function of metallicity, and we therefore use our observations of these planets to constrain their atmospheric metallicities. We find that the most massive planets have dayside emission spectra that are best-matched by solar metallicity atmosphere models, but we are not able to place strong constraints on metallicities of the smaller planets in our sample. Interestingly, we find that the ratio of the 3.6 and 4.5 μm brightness temperatures for these cool transiting planets is independent of planet temperature, and instead exhibits a tentative correlation with planet mass. If this trend can be confirmed, it would suggest that the shape of these planets’ emission spectra depends primarily on their masses, consistent with the hypothesis that lower-mass planets are more likely to have metal-rich atmospheres.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A study for testing the Kerr metric with AGN iron line eclipses

Recently, two of us have studied iron line reverberation mapping to test black hole candidates, showing that the time information in reverberation mapping can better constrain the Kerr metric than the time-integrated approach. Motivated by this finding, here we explore the constraining power of another time-dependent measurement: an AGN iron line eclipse. An obscuring cloud passes between the AGN and the distant observer, covering different parts of the accretion disk at different times. Similar to the reverberation measurement, an eclipse might help to better identify the relativistic effects affecting the X-ray photons. However, this is not what we find. In our study, we employ the Johannsen-Psaltis parametrisation, but we argue that our conclusions hold in a large class of non-Kerr metrics. We explain our results pointing out an important difference between reverberation and eclipse measurements.

79 ASTRONOMY AND ASTROPHYSICS↗