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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

New Blue and Red Variable Stars in NGC 247

Images recorded with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South are combined with archival images from other facilities to search for variable stars in the southern half of the nearby disk galaxy NGC 247. Fifteen new periodic and nonperiodic variables are identified. These include three Cepheids with periods <25 days, four semiregular variables, one of which shows light variations similar to those of R CrB stars, five variables with intrinsic visible/red brightnesses and colors that are similar to those of luminous blue variables (LBVs), and three fainter blue variables, one of which may be a noneclipsing close binary system. The S Doradus instability strip defines the upper envelope of a distinct sequence of objects on the (i, g-i) color–magnitude diagram (CMD) of NGC 247. The frequency of variability of an amplitude ≥0.1 magnitude in the part of the CMD that contains LBVs over the seven-month period when the GMOS images were recorded is ~0.2. The light curve of the B[e] supergiant J004702.18–204739.9, which is among the brightest stars in NGC 247, is also examined. Low-amplitude variations on day-to-day timescales are found, coupled with a systematic trend in mean brightness over a six-month time interval.

47 OTHER INSTRUMENTATION↗
DOE OSTI2025

Ecosystem leaf area, gross primary production, and evapotranspiration responses to wildfire in the Columbia River basin

Wildfires impact vegetation mortality and productivity and are increasing in intensity, frequency, and spatial area in the western United States. The rates of vegetation recovery after fires play a major role in the reestablishment of biomass and ecosystem functioning (e.g., structure, resilience, and productivity), but such recovery rates are poorly understood. Here we use remotely sensed data products from the Moderate Resolution Imaging Spectroradiometer (MODIS) to quantify the resistance and resilience of leaf area index (LAI), gross primary production (GPP), and evapotranspiration (ET) to 138 wildfires of various burn severity across the Columbia River basin (CRB) of the Pacific Northwest in 2015. Increasing burn severity caused lower resistance and resilience for all three variables. Resistance and resilience are highest in grasslands, intermediate in savanna, and lowest in needleleaf evergreen forests, consistent with the adaptation of these vegetation types to fire. LAI has consistently lower resistance and resilience than GPP and ET, which is consistent with physical and physiological mechanisms that compensate for reduced LAI. Resilience is influenced by precipitation, vapor pressure deficit (VPD), and burn severity across all three vegetation types; however, burn severity plays a more minor role in grasslands. Increasing wildfire severity will reduce the resistance and resilience and lengthen the recovery time of vegetation structure and fluxes with climate change, with significant consequences for the provision of ecosystem functioning and implications for model predictions.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1969

Infrared excess of RY Sgr.

IR excess of R CrB type variable star RY Sgr, noting visual brightness and radiation in 2.0-3.4 micron range

Feast, M. W.↗
NASA NTRS1974

Infrared stars in binary systems

The peculiar F-type supergiant HD 101584, which has a large and unusual infrared excess, is discussed along with the possibility that the infrared radiation could be accounted for by a cool companion. The peculiar F supergiants 89 Her, v Sgr, and R CrB are also considered as possible binary systems containing an infrared star. It is pointed out that all four of these stars have infrared excesses with characteristics similar to the infrared radiation from several cool objects which are known single stars.

Humphreys, R. M.↗
NASA NTRS1976

Isotopic abundances of Hg in mercury stars inferred from the Hg II line at 3984 A

Wavelengths of the Hg II absorption feature at 3984 A in 30 Hg stars are distributed uniformly from the value for the terrestrial mix to a value that corresponds to nearly pure Hg-204. The wavelengths are correlated loosely with effective temperatures inferred from Q(UBV). Relative isotopic abundances derived from partially resolved profiles of the 3984-A line in iota CrB, chi Lup, and HR 4072 suggest that mass-dependent fractionation has occurred in all three stars. It is supposed that such fractionation occurs in all Hg stars, and a scheme whereby isotopic compositions can be inferred from a comparison of stellar wavelengths and equivalent widths with those calculated for a family of fractionated isotopic mixes. Theoretical profiles calculated for the derived isotopic composition agree well with high-resolution interferometric profiles obtained for three of the stars.

White, R. E.↗
NASA NTRS1977

The ultraviolet spectra of four binaries observed with the S59 spectrometer

Ultraviolet spectra of Omicron And, Alpha CrB, Eta Ori A, and Alpha Vir, which were obtained with the S59 spectrometer at a resolution of 1.7 A in three 100-A-wide regions centered at 2110, 2454, and 2825 A, have been studied for the presence or absence of effects due to their binary nature. As may have been anticipated from their orbital and other characteristics, no indication of strong binary interactions were seen in these observations. However, there are certain spectral peculiarities suggesting the possibility of modifications of spectral classifications for some of these objects. A rather unusual spectral behavior in Alpha Vir is also noted. In addition, based primarily on a review of available literature, attention is drawn to a remarkable property of the third component in Eta Ori A.

Herczeg, T. J.↗
NASA NTRS1977

Genesis of howardites, diogenites, and eucrites

The reported investigation was mainly concerned with the precise determinations of major-, minor-, and trace-element abundances, especially the REE abundances in the bulk howardites in order to establish the bulk rock composition for the future chemical-mineralogical, petrographic studies of different rock types on the chemically unique howardites and diogenites if they exist. From the chemical data for the major-element abundances and the REE patterns of the howardites analyzed, it is evident that these howardites are predominantly composed of eucritic and diogenitic components. The analytical results for howardites and diogenites are shown in two tables together with the results for CRB-1. The chondritic normalized K, Sr, Ba, REE, Hf, and Sc abundances of these howardites are plotted in two graphs.

Fukuoka, T.↗
NASA NTRS1982

Observations of mass accretion in binary stars

Results from high resolution observations of eight close binary stars (TX UMa, U CrB, CX Dra, TT Hya, AU Mon, KX And, HR 2142, and phi Per) are presented. Variable absorption lines, indicative of mass flow, are observed in all systems expect phi Per. Emission lines are seen in KX And and phi Per. Variable high ionization features (NV, SiIV, and CIV) are seen in TX UMa, UCrB, CX Dra, and AU Mon. The observations are modeled using the calculations of Lubow and Shu.

Polidan, R. S.↗
NASA NTRS1983

Spectrophotometric observations of symbiotic stars and related objects

Calibrated optical spectrophotometric observations of 16 symbiotic and symbiotic-like objects are presented. The objects observed include Z And, T CrB, CH Cyg, CI Cyg, V1016 Cyg, V1329 Cyg, AG Dra, YY Her, RS Oph, XX Oph, AG Peg, AX Per, CL Sco, HM Sge, AS 289, and M1-2. Integrated emission-line intensities are tabulated for comparison with ultraviolet and infrared data, as well as with previous optical studies. The reddening to each of the objects is derived by assuming that Balmer lines are emitted in their case B recombination ratios. However, the values so derived are often systematically higher than reddening estimates from the ultraviolet 2200 A feature. Comparisons with the available data from other wavelength ranges are noted.

Blair, W. P.↗
NASA NTRS1983

Detection of an X-ray flare in the RS CVn binary Sigma Corona Borealis

The first observation of a time-resolved X-ray flare in an RS CVn binary is reported. The X-ray flare was detected from the RS CVn binary Sigma CrB on August 17, 1980 during the course of a long pointed-mode observation with the Monitor Proportional Counter on the Einstein Observatory. The flare commenced at about 11:12 UT and lasted for about 205 minutes. During the flare the count rate increased by a factor of five from a quiescent state value of 0.3 count/s to a peak value of 1.5 count/s in the 1.2-10.2-keV energy band. The source spectrum during the flare was found to be considerably harder than that observed in the quiescent state. Details of the various characteristics of the X-ray flare are described.

Agrawal, P. C.↗
NASA NTRS1985

Dual polarization VLBI observations of stellar binary systems at 5 GHz

The binary systems Sigma CrB, SZ Psc, HR 1099, UX Ari, HR 5110, Algol, and Cyg X-1 are characterized in terms of marcsec-scale radio structure on the basis of dual-polarization observations at 4.969-4.997 GHz, obtained with an international VLBI array comprising the 100-m Effelsberg, 36-m Haystack, 42-m Green Bank, 26-m Fort Davis, 130-m-equivalent VLA, and 40-m Owens Valley telescopes (system temperatures 40-70 K) at 22-14 h UT on July 26-27, 1983. The data are presented in graphs and tables and discussed in detail. Single Gaussian brightness distributions with theta(FWHM) = 0.5-2.0 marcsec and brightness temperatures (2-200) x 10 to the 8th K are determined for four sources; core-halo structures are found for UX Ari and Algol; and an upper limit of 50 microarcsec is established for the angular separation of the regions of left and right circular polarization. The gross features seen in RS CVn systems are explained in terms of a simple expanding-coronal-loop model of flare events.

Mutel, R. L.↗
NASA NTRS1986

IRAS observations of R Coronae Borealis - Detection and study of a fossil shell

IRAS observations of the extreme hydrogen-deficient supergiant R CrB are presented and discussed. The star is surrounded by an enormous cool dust cloud which is tentatively identified as a fossil remnant of the hydrogen-rich envelope of the star. The angular extent of the emission corresponds to a linear extent of 8 pc, 20 times larger than the largest previously known shell around a late-type star. The radiating material is distributed very symmetrically over a wide range of radial distances from the star. The dust temperature is nearly constant throughout the extended shell. The total mass in the shell is about 0.3 solar mass. The ejection process appears to have occurred in a spherically symmetric fashion with a nearly constant mass loss rate and expansion velocity over a period of about 150,000 yr, terminating about 26,000 yr ago.

Gillett, F. C.↗
NASA NTRS1987

The fading of R Coronae Borealis

Using the International Ultraviolet Explorer (IUE) low-resolution spectra were obtained of R CrB, the prototype of its class of variable stars, shortly after the beginning of its 1983-84 minimum and during its rise to maximum again. The behavior of the spectra during the rise to maximum is similar to the behavior of the spectra of RY Sgr during a similar phase in 1979-80. The extinction data have been analyzed using Mie theory and are consistent with the stellar photosphere being obscured by 20-nm glassy carbon particles. The observations during the decline to minimum show substantial spectral variations which cannot be explained in terms of simple continuum absorption. An interpretation of the observed behavior in terms of a model incorporating an occulting cloud and circumstellar emission is offered.

Holm, A. V.↗
NASA NTRS1988

R Coronae Borealis dust ejections - A preferred plane?

Spectropolarimetric observations of R Coronae Borealis obtained during the brightness minimum of 1986 are presented. When combined with previous polarization observations of brightness minima, the distribution of observations in the Q-U plane suggests that ejections of dust clouds occur in a preferred plane about the star, in contrast to the standard model for the R CrB-type stars, which holds that clouds are ejected from all parts of the stellar surface. The possibility of an ejection mechanism connected with nonradial pulsations is discussed as the most likely explanation of the preferred plane.

Stanford, S. A.↗
NASA NTRS1988

V482 Cygni - An R Coronae Borealis star in a quadruple system

Observations of the R CrB variable star V482 Cyg, obtained with the University of Rochester 32 x 32 InSb array camera at the NASA IR Telescope Facility on Mauna Kea on August 20, 1984, are reported. The data-reduction and analysis procedures are described in detail, and the results are presented in tables and maps. V482 Cyg is shown to be a member of a quadruple system or perhaps a small obscured cluster. Parameters determined include distance 1.7 kpc, circumstellar-shell temperature 800 K, and absolute magnitude M(V) = -2.8.

Gaustad, John E.↗
NASA NTRS1988

Ultraviolet spectroscopy of R Coronae Borealis

Observations of the hydrogen-deficient supergiant R CrB were obtained with the IUE over an interval of 54 days in order to study the nature of this star's irregular, small-amplitude variations in light. By chance, the series of observations coincided with a dip in the light intermediate between the normal fluctuations and the deep declines associated with the formation of an obscuring dust cloud. High-resolution spectra have been used to search for radial velocity variations, while low-resolution spectra yield ultraviolet light curves down to 1810 A. Both types of spectra have been analyzed for indications of temperature changes. It is found that a combination of photospheric temperature variation and variable extinction is necessary to account for the details of the observations. A simple, ad hoc, periodic model is presented in which the amount of obscuring dust varies in proportion to the drop in temperature, but at a later time, reproduces the wavelength dependence of both the amplitudes and phase shifts of the light curves. The radial velocities are consistent with pulsation being responsible for the temperature variation.

Holm, A. V.↗
NASA NTRS1989

Coronal activity in F-, G-, and K-type stars. IV - Evidence for expanding loop geometries in stellar coronae

A detailed analysis is presented of X-ray spectra of Capella and of Sigma2 CrB. The spectra of both stars are compatible with coronae consisting of two different ensembles of static loops with different maximum temperatures and ratios of the cross sectional areas at the loop top and at the footpoint. The cool (5 MK) loop components in both stars show evidence of relatively strong expansion with height. The hot (30 MK) components appear to expand much less.

Schrijver, C. J.↗