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At least 1,567 records · Page 87
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DOE OSTI2025

47 Tuc in Rubin Data Preview 1. Exploring Early LSST Data and Science Potential

We present analyses of the early data from Rubin Observatory’s Data Preview 1 (DP1) for the field of the globular cluster 47 Tuc. The DP1 data set for 47 Tuc includes four nights of observations from the Rubin Commissioning Camera (LSSTComCam), covering multiple bands (ugriy). We address challenges of crowding in the inner region of the cluster and toward the SMC in DP1, and demonstrate improved star–galaxy separation by fitting fifth-degree polynomials to the stellar loci in color–color diagrams and applying multidimensional sigma clipping. We compile a catalog of 3576 probable 47 Tuc member stars selected via a combination of isochrone, Gaia proper-motion, and color–color space matched filtering. We explore the sources of photometric scatter in the 47 Tuc color–color sequence, evaluating contributions from various potential sources, including differential extinction within the cluster. Finally, of the 72 well-characterized variables in the field, we recover three known variable stars, including two RR Lyrae and one eclipsing binary, in the coadd-based object catalog, and identify 62 in the difference image-based object catalog. Although the DP1 lightcurves have sparse temporal sampling, they appear to follow the patterns of densely sampled literature lightcurves well. Despite some data limitations for crowded-field stellar analysis, DP1 demonstrates the promising scientific potential for future LSST data releases.

Choi, Yumi [NSF National Optical-Infrared Astronom↗
DOE OSTI2024

DMTN-221: Periodicity Analysis in Alert Production

The baselined timeseries features to be computed in Alert Production include a Lomb-Scargle periodogram ran on two classes of variable systems: RR Lyrae and Eclipsing Binaries. Based on a simulated LSST-like cadence light curves taken from the Extended LSST Astronomical Time-series Classification Challenge (ELAsTiCC) we perform an end-to-end test to characterize the periodicity recovery on the Alert Production multi-band light curves. In both variable classes, we found that a single-band Lomb-Scargle implementation yields to a low fraction of recovered periods, with a significant preference on the simple periodic phenomena such as RR Lyrae. We also investigated the results from a multi-band Lomb-Scargle and found an increased fraction of recovered periodicities above 15% for the eclipsing binaries, and over 80$\%$ for the RR Lyrae stars. Our findings suggest that a multi-band Lomb-Scargle should be implemented for searching periodic phenomena through AP. We also asses the computational and scientific performance of several configurations on simulated alert data and find that our current configuration scales linearly with the number of detections while assuming an heuristic frequency grid.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Ultraviolet photometry of the eclipsing variable CW Cephei

A series of photometric observations was made of the eclipsing variable CW Cephei on the OAO 2. Approximate elements were derived from the eclipse depths and shape of the secondary. Persistent asymmetries and anomalous light variations, larger than the expected experimental error, were also found, subsequent ground-based observations show H alpha entirely in emission, indicating the presence of an extended gaseous system surrounding one or both components. A detailed comparison was made of the flux distribution of the binary relative to that for the nominally unreddened stars delta Pic, BlIII, and eta Aur, B3V, to investigate the effects of interstellar extinction. The resultant extinction curves, normalized at a wavelength of 3330 A, show a relatively smooth increase with decreasing wavelength.

Sobieski, S.↗
NASA NTRS1972

Identification of the X-ray pulsar in Hercules: A new optical pulsar

A series of photographic, photoelectric, and spectroscopic observations beginning June 1, 1972 has led to the optical identification of Her X-1 (2U 1705 + 34), a pulsed X-ray source in an eclipsing binary system, with the thirteenth magnitude blue variable star HZ Herculis. The detection of optical pulses at the frequency of the X-ray pulsar on three nights makes the identification conclusive and establishes HZ Her as the second known optical pulsar. The strength of the optical pulses may be correlated with the orbital phase but is not obviously related to the high or low intensity states of the X-ray source.

Davidsen, A.↗
NASA NTRS1974

Structural and spectral studies of sunspots

Observations of umbral cores, both by multicolor photometry and by narrow band photometry in the vicinity of the sodium D lines, are described, and evidence is given which supports the validity of many umbral models, each of which describes different aspects of the observed umbral cores. Theoretical studies carried on at the observatory include the following: (1) Zeeman profiles of the sodium D sub 2 line and other lines; (2) turbulent heat conduction, sound waves, and the missing flux in sunspots; (3) chromospheric heating above spots by Alfven waves; (4) magnetic convection in the sun and solar neutrinos; (5) models of starspots on flare stars; (5) starspots on the primaries of contact binary systems; and (6) implications of starspots on red dwarfs.

Wyller, A. A.↗
NASA NTRS1976

Skylab ultraviolet stellar spectra - Cool stars with hot secondaries

A hot companion to the G5 III star HR 3080, a single-line spectroscopic binary, has been discovered from spectra in the vacuum-ultraviolet. The companion must be a subdwarf or pre-white dwarf. A list of previously known systems of the zeta Aur and VV Cep type observed with the ultraviolet spectrograph on Skylab is also given.

Parsons, S. B.↗
NASA NTRS1981

New insight into the physics of atmospheres of early type stars

The phenomenon of mass loss and stellar winds from hot stars are discussed. The mass loss rate of early type stars increases by about a factor of 100 to 1000 during their evolution. This seems incompatible with the radiation driven wind models and may require another explanation for the mass loss from early type stars. The winds of early type stars are strongly variable and the stars may go through active phases. Eclipses in binary systems by the stellar winds can be used to probe the winds. A few future IUE studies are suggested.

Lamers, H. J. G. L. M.↗
NASA NTRS1983

Discovery of 13.5 s X-ray pulsations from LMC X-4 and an orbital determination

X-ray pulsations with a 13.5-sec period have been detected from the 1.4-d X-ray binary LMC X-4. By measuring the apparent pulse period at several binary orbital phases, and assuming the orbit to be nearly circular, the semimajor axis of the orbit is determined to be 30 + or - 5 ly-sec. This result, together with a revised orbital velocity amplitude of 37.9 + or - 2.4 km/sec, and other available information, suffice for the determination of the component masses of the binary system and the radius of the companion star. The mass of the neutron star is found to be 1.6 +1.0 -0.5 solar masses, while the mass, radius, and effective temperature of the companion star indicate that it may be undermassive for its luminosity.

Kelley, R. L.↗
NASA NTRS1983

On the origin of the 6.1-ms pulsar

A quantitative model is presented to account for the observed features of the binary pulsar PSR1953+53. A lower giant branch star is suggested to have evolved on a nuclear time scale while orbiting a neutron star, with mass transfer to the neutron star commencing when the giant attained its Roche lobe. A radius-core mass relationship was used to examined the processes that occurred after the hydrogen atmosphere was drained off to the neutron star. Tidal dissipation has circularized the orbit of the companion during mass transfer, while the orbit expanded. Accretion torques caused spin-up of the neutron star, which had a magnetic moment of no more than 3 x 10 to the 27th G/cu cm. The drained star became a degenerate dwarf with very faint luminosity, which accounts for no visual companion having been observed to date.

Joss, P. C.↗
NASA NTRS1984

New syndrome decoding techniques for the (n, k) convolutional codes

This paper presents a new syndrome decoding algorithm for the (n, k) convolutional codes (CC) which differs completely from an earlier syndrome decoding algorithm of Schalkwijk and Vinck. The new algorithm is based on the general solution of the syndrome equation, a linear Diophantine equation for the error polynomial vector E(D). The set of Diophantine solutions is a coset of the CC. In this error coset a recursive, Viterbi-like algorithm is developed to find the minimum weight error vector (circumflex)E(D). An example, illustrating the new decoding algorithm, is given for the binary nonsystemmatic (3, 1)CC. Previously announced in STAR as N83-34964

Reed, I. S.↗
NASA NTRS1985

Two new color-selected magnetic DA white dwarfs

The discovery of two magnetic white dwarfs culled from blue star surveys is reported. The surveys were carried out with the Mount Lemnon 1.5-meter reflecting telescope attached to a two-holer polarimeter/photometer. Spectral observations of the objects, (PG 1533 - 057, and K813 - 14), indicate the presence of hydrogen and Zeeman components. On the basis of dipolar field simulations, it is shown that PG 1533 - 057 has a polar field strength of 31 megagauss (MG) while K813 - 14 has a polar field strength of 29 MG. A third known white dwarf has a polar field strength of 18 MG. All the dwarfs had temperatures in the 11,000-20,000 K range. The possibility that a significant fraction of isolated magnetic degenerate stars could be the progeny of magnetic accreting binary systems is considered.

Liebert, J.↗
NASA NTRS1985

The newly discovered eclipsing supergiant 22 Vulpeculae

Spectra obtained with the IUE satellite have led to the discovery that 22 Vul is an atmospheric eclipsing binary belonging to the zeta Aurigae class of stars. The system is the first found with a G-type primary (G3 Ib-II), while the spectral type of the secondary is the latest (B9) and its period is the shortest (249 days) of any of the classical members of the group. Out-of-eclipse spectra, atmospheric eclipse phases and totality observations are discussed. Comparisons are made with other systems.

Ake, T. B.↗
NASA NTRS1988

Radio emission from RS CVn binaries. III - A VLA survey of 103 systems

The paper presents a 5 GHz radio survey of 103 close late-type stellar binaries. Fifty-three of the 103 candidate stars were detected above an average detection threshold of 0.4 mJy. The median observed radio luminosity is compared with total bolometric luminosity, rotational period, color index (B-V), and Rossby number.

Morris, D. H.↗
NASA NTRS1990

Gas dynamics, accretion, and evolution of Algols: Initial results for three representative systems

IUE (International Ultraviolet Explorer) observations were made around the orbits of three Algol-type binaries: R Arae, U Cephei and Algol. These stars were selected to represent, respectively, the rapid, moderate and slow phases of mass transfer and mass loss in Algols. The data was obtained to derive maps of gas flow and mass loss, to study accretion processes and kinetic heating, and to investigate the importance of magnetic fields in these systems. Continuous observations were made from GSFC and VILSPA over 4 1/3 consecutive days during 10 to 14 Sep. 1989. A total of 100 spectra are obtained. This is the first time that Algol systems are observed continuously over their orbits with IUE. Initial results from this program are discussed.

Gimenez, A.↗
NASA NTRS1992

The origin of planets orbiting millisecond pulsars

A model for the formation of planets around millisecond pulsar which no longer have stellar companions is suggested. Detailed hydrodynamical models are presented which suggest that planet formation can occur either in a low-mass X-ray binary progenitor to a progenitor of a star-vaporizing millisecond pulsar when the neutron star is accreting material driven off its companion by X-ray irradiation or after a pulsar has formed and is vaporizing its companion. In both cases a circumbinary disk is created in which planets can form on a timescale of 10 exp 5 to 10 exp 6 yrs and the planets can survive a second phase in which the companion star moves toward the pulsar and is completely vaporized.

Tavani, Marco↗
NASA NTRS1992

Presupernova evolution in massive interacting binaries

The way in which binary interaction affects the presupernova evolution of massive close binaries and the resulting supernova explosions is investigated systematically by means of a Henyey-type stellar evolution code that was modified to allow its application to binary stellar evolution calculations. The code makes it possible to trace the effects of mass and angular momentum loss from the binary, as well as mass transfer within the binary system. It is found that a large number of binary scenarios can be distinguished, depending on the type of binary interaction and the evolutionary stage of the supernova progenitor at the time of the interaction. Monte Carlo simulations are performed to estimate the frequencies of the occurrence of various scenarios. It is found that, because of a previous binary interaction, 15-30 percent of all massive stars (with initial masses greater than about 8 solar masses) become helium stars, and another 5 percent of all massive stars end their lives as blue supergiants rather than as red supergiants.

Podsiadlowski, PH.↗
NASA NTRS1995

Selected highlights from the Extreme Ultraviolet Explorer

We present a few scientific highlights from the Extreme Ultraviolet Explorer (EUVE) all-sky and deep surveys, from the EUVE Righ Angle Program, and from the EUVE Guest Observer Program. The First EUVE Source Catalog includes 410 extreme ultraviolet (EUV) sources detected in the initial processing of the EUVE all-sky data. A program of optical identification indicates that counterparts include cool star coronae, flare stars, hot white dwarfs, central stars of planetary nebulae, B star photospheres and winds, an X-ray binary, extragalactic objects (active galactic nuclei, BL Lacertae), solar system objects (Moon, Mars, Io,), supernova remnants, and two novae.

Bowyer, S.↗
NASA NTRS1995

An extended galactic population of low-luminosity x-ray sources (CVs?) and the diffuse x-ray background

The incompatibility of the properties of the X-ray background (XRB) with active galactic nuclei (AGNs) contributing approximately greater than 60% at energies of a few keV has often been interpreted as being due to a substantial contribution of a new population of yet unrecognized X-ray sources. The existence of such population has been recently suggested also by an analysis of very deep ROSAT observations which revealed a considerable excess of faint X-ray sources over that expected from QSO evolution models, and that the average spectrum of the resolved sources becomes harder with decreasing flux limit. These sources could be extragalactic in origin, but if they make a substantial contribution to the XRB then they must exhibit much weaker clustering than galaxies or QSOs in order to be consistent with the stringent constraints on source clustering imposed by autocorrelation analyses of the unresolved XRB. We investigate the possibility that the indicated new population of X-ray sources is Galactic in origin. Examining spherical halo and thick disk distributions, we derive the allowed properties of such populations which would resolve the discrepancy found in the number counts of faint sources and be consistent with observational constraints on the total background intensity, the XRB anisotropy, the number of unidentified bright sources, the Galaxy's total X-ray luminosity, and with the results of fluctuation analyses of the unresolved XRB. We find that a flattened Galactic halo (or a thick disk) distribution with a scale height of a few kpc is consistent with all the above requirements. The typical X-ray luminosity of the sources is approximately equal to 10(exp 30-31)ergs/s in the 0.5-2 keV band, the number density of sources in the solar vicinity is approximately 10(exp -4.5)pc(exp -3), their total number in the Galaxy is approximately 10(exp 8.5), and their total contribution to the Galaxy's X-ray luminosity is approximately 10(exp 39) ergs/s. We discuss the possible nature of these soures, including their being subdwarfs, low mass x-ray binaries (LMXBs), massive black holes, and old neutron stars. We argue that the inferred X-ray and optical luminosities of these sources, the slope of their energy spectrum, and the derived local number density and spatial distribution are all consistent with their being intrinsically faint cataclysmic variables with low accretion rates. We suggest a few possibilities for the origin of such population, including an origin from disrupted globular clusters or dark clusters. We make predictions and suggest tests that could either confirm or rule out our proposal in the near future.

Maoz, Eyal↗