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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,585 records · Page 88
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DOE OSTI2017

A Measurement of Radius Inflation in the Pleiades and Its Relation to Rotation and Lithium Depletion

Precise measurements of eclipsing binary parameters and statistical studies of young clusters have suggested that some magnetically active low-mass dwarfs possess radii inflated by ∼5%–15% relative to theoretical expectations. If true, this effect should be pronounced in young open clusters, due to the rapid rotation and strong magnetic activity of their most extreme members. We explore this possibility by determining empirical radii for 83 members of the nearby Pleiades open cluster, using spectral energy distribution fitting to establish F{sub bol} with a typical accuracy of ≈3% together with color and spectro-photometric indices to determine T{sub eff}. We find several Pleiades members with radii inflated above radius-T{sub eff} models from state-of-the-art calculations, and apparent dispersions in radii for the K-dwarfs of the cluster. Moreover, we demonstrate that this putative radius inflation correlates strongly with rotation rate, consistent with inflation of young stars by magnetic activity and/or starspots. We argue that this signal is not a consequence of starspot-induced color anomalies, binarity, or depth effects in the cluster, employing Gaia DR1 distances as a check. Finally, we consider the lithium abundances of these stars, demonstrating a triple correlation between rotation rate, radius inflation, and enhanced lithium abundance. Our result—already significant to ∼99.99% confidence—provides strong support for a magnetic origin of the inflated radii and lithium dispersion observed in young, low-mass stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Hubble Space Telescope Ultraviolet Light Curves Reveal Interesting Properties of CC Sculptoris and RZ Leonis

Time-tag ultraviolet data obtained on the Hubble Space Telescope in 2013 reveal interesting variability related to the white dwarf spin in the two cataclysmic variables RZ Leo and CC Scl. RZ Leo shows a period at 220 s and its harmonic at 110 s, thus identifying it as a likely Intermediate Polar (IP). The spin signal is not visible in a short single night of ground-based data in 2016, but the shorter exposures in that data set indicate a possible partial eclipse. The much larger UV amplitude of the spin signal in the known IP CC Scl allows the spin of 389 s, previously only seen at outburst, to be visible at quiescence. Spectra created from the peaks and troughs of the spin times indicate a hotter temperature of several thousand degrees during the peak phases, with multiple components contributing to the UV light.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Large Magellanic Cloud Near-infrared Synoptic Survey. IV. Leavitt Laws for Type II Cepheid Variables

We present time-series observations of Population II Cepheids in the Large Magellanic Cloud at near-infrared (JHK {sub s}) wavelengths. Our sample consists of 81 variables with accurate periods and optical (VI) magnitudes from the OGLE survey, covering various subtypes of pulsators (BL Herculis, W Virginis, and RV Tauri). We generate light-curve templates using high-quality I-band data in the LMC from OGLE and K {sub s}-band data in the Galactic bulge from VISTA Variables in Via Láctea survey and use them to obtain robust mean magnitudes. We derive period–luminosity (P–L) relations in the near-infrared and Period–Wesenheit (P–W) relations by combining optical and near-infrared data. Our P–L and P–W relations are consistent with published work when excluding long-period RV Tauris. We find that Pop II Cepheids and RR Lyraes follow the same P–L relations in the LMC. Therefore, we use trigonometric parallax from the Gaia DR1 for VY Pyx and the Hubble Space Telescope parallaxes for k Pav and 5 RR Lyrae variables to obtain an absolute calibration of the Galactic K {sub s}-band P–L relation, resulting in a distance modulus to the LMC of μ{sub LMC}=18.54±0.08 mag. We update the mean magnitudes of Pop II Cepheids in Galactic globular clusters using our light-curve templates and obtain distance estimates to those systems, anchored to a precise late-type eclipsing binary distance to the LMC. We find that the distances to these globular clusters based on Pop II Cepheids are consistent (within 2σ) with estimates based on the M{sub V}-[Fe/H] relation for horizontal branch stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

HAT-P-67b: An Extremely Low Density Saturn Transiting an F-subgiant Confirmed via Doppler Tomography

We report the discovery of HAT-P-67b, which is a hot-Saturn transiting a rapidly rotating F-subgiant. HAT-P-67b has a radius of R p =2.085$_{-0.071}^{+0.096}$ R J , and orbites a M * =1.642$_{-0.072}^{+0.155}$ M ⊙ , R * =2.546$_{-0.084}^{ +0.099}$ R ⊙ host star in a ~4.81 day period orbit. We place an upper limit on the mass of the planet via radial velocity measurements to be M{sub p}<0.59 M{sub J}, and a lower limit of >0.056 M{sub J} by limitations on Roche lobe overflow. Despite being a subgiant, the host star still exhibits relatively rapid rotation, with a projected rotational velocity of vsinI * =35.8±1.1 km s -1 , which makes it difficult to precisely determine the mass of the planet using radial velocities. We validated HAT-P-67b via two Doppler tomographic detections of the planetary transit, which eliminate potential eclipsing binary blend scenarios. The Doppler tomographic observations also confirm that HAT-P-67b has an orbit that is aligned to within 12°, in projection, with the spin of its host star. HAT-P-67b receives strong UV irradiation and is among one of the lowest density planets known, which makes it a good candidate for future UV transit observations in the search for an extended hydrogen exosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315

The masses, atmospheric makeups, spin–orbit alignments, and system architectures of extrasolar planets can be best studied when the planets orbit bright stars. We report the discovery of three bodies orbiting HD 106315, a bright (V = 8.97 mag) F5 dwarf targeted by our K2 survey for transiting exoplanets. Two small transiting planets are found to have radii 2.23{sub −0.25}{sup +0.30} R{sub ⊕} and 3.95{sub −0.39}{sup +0.42} R{sub ⊕} and orbital periods 9.55 days and 21.06 days, respectively. A radial velocity (RV) trend of 0.3 ± 0.1 m s{sup −1} day{sup −1} indicates the likely presence of a third body orbiting HD 106315 with period ≳160 days and mass ≳45 M {sub ⊕}. Transits of this object would have depths ≳0.1% and are definitively ruled out. Although the star has v sin i = 13.2 km s{sup −1}, it exhibits a short-timescale RV variability of just 6.4 m s{sup −1}. Thus, it is a good target for RV measurements of the mass and density of the inner two planets and the outer object’s orbit and mass. Furthermore, the combination of RV noise and moderate v sin i makes HD 106315 a valuable laboratory for studying the spin–orbit alignment of small planets through the Rossiter–McLaughlin effect. Space-based atmospheric characterization of the two transiting planets via transit and eclipse spectroscopy should also be feasible. This discovery demonstrates again the power of K2 to find compelling exoplanets worthy of future study.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Photometric Study of Fourteen Low-mass Binaries

New CCD photometric observations of fourteen short-period low-mass eclipsing binaries (LMBs) in the photometric filters I, R, and V were used for a light curve analysis. A discrepancy remains between observed radii and those derived from the theoretical modeling for LMBs, in general. Mass calibration of all observed LMBs was performed using only the photometric indices. The light curve modeling of these selected systems was completed, yielding the new derived masses and radii for both components. We compared these systems with the compilation of other known double-lined LMB systems with uncertainties of masses and radii less then 5%, which includes 66 components of binaries where both spectroscopy and photometry were combined together. All of our systems are circular short-period binaries, and for some of them, the photospheric spots were also used. A purely photometric study of the light curves without spectroscopy seems unable to achieve high enough precision and accuracy in the masses and radii to act as meaningful test of the M–R relation for low-mass stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Hubble COS Spectroscopy of the Dwarf Nova CW Mon: The White Dwarf in Quiescence?

We present a synthetic spectral analysis of the HST COS spectrum of the U Geminorum-type dwarf nova CW Mon, taken during quiescence as part of our COS survey of accreting white dwarfs (WDs) in Cataclysmic Variables. We use a synthetic photosphere and optically thick accretion disk spectra to model the COS spectrum as well as archival IUE spectra obtained decades ago, when the system was in an even deeper quiescent state. Assuming a reddening of E(B−V) = 0.06, an inclination of 60° (CW Mon has eclipses of the accretion disk), and a WD mass of 0.8 M{sub ⊙}, our results indicate the presence of a 22–27,000 K WD and a low mass accretion rate M-dot ≲10{sup −10} M{sub ⊙} yr{sup −1}, for a derived distance of ∼200 to ∼300 pc.

79 ASTRONOMY AND ASTROPHYSICS↗
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).

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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.

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