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1

Nucleosynthesis of Li-7 in flares on UV Ceti stars  

NASA Technical Reports Server (NTRS)

The possible production of Li-7 by nuclear reactions in UV Ceti flares has been considered. By utilizing solar observations and theory, a relationship is derived between flare energy and production rates for Li-7; approximately 100 erg of total flare energy is found to denote the formation of a Li-7 atom. Based on this value and best estimates of UV Ceti-type flare rates, it is concluded that less than 10% of the Li-7 observed in the intestellar medium may have been produced by this mechanism. Formation of significant amounts of interstellar deuterium by this method is ruled out.

Karpen, J. T.; Worden, S. P.

1979-01-01

2

Catalog of Binary UV Ceti Type Flare Stars  

NASA Astrophysics Data System (ADS)

This catalog* provides an easy access to the basic astrophysical and dynamical characteristics of nearby (d<25 pc) visual binary systems (pairs) in which at least one component is a UV Cet type flare star. It contains 138 such pairs (111 flare stars) of which 31 pairs have known orbital parameters. Along with parallax mainly (but not only) taken from SIMBAD, apparent and absolute magnitudes of each component, spectral types for all primaries and the vast majority of secondaries are given. On the basis of cataloged data, absolute brightness vs. spectral type and mass vs. spectral type relations for flare and non-flare stars are constructed. It is shown that flare and non-flare stars cannot be distinguished on the absolute brightness vs. spectral type plane. Comparison between photometric and dynamical masses suggests that photometric mass of flare stars can be estimated using the mass vs. absolute brightness relation of non-flare stars.*The catalog is available only in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr or via http://vizier.u-strasbg.fr/viz-bin/VizieR

Tamazian, V. S.; Malkov, O. Yu.

2014-12-01

3

VizieR Online Data Catalog: Binary UV Ceti type flare stars catalog (Tamazian+, 2014)  

NASA Astrophysics Data System (ADS)

A catalogue of nearby UV Ceti type flare stars in (137) visual binary systems is presented in the form of two separate tables of information. The catalogue has developed from Catalogue and Bibliography of UV Cet stars (Gershberg et al., 1999, Cat. J/A+AS/139/555) and the list of nearby flare stars (Pettersen, 1991MmSAI..62..217P) by including more recent and additional information from catalogues of binary stars (WDS, Mason et al., 2001-2014, Cat. B/wds; ORB6, Hartkopf et al. 2006-2014; DM3, Mason+ 2006-2014) and data from the Catalog of Nearby Stars, Preliminary 3rd Version (Gliese et al., 1991, Cat. V/70), from Hipparcos, the New Reduction (van Leeuwen 2007, Cat. I/311) and from SIMBAD. Some issues relating to the mass, luminosity and spectrum relations of flare stars are also discussed. (2 data files).

Tamazian, V.; Malkov, O.

2015-01-01

4

The statistical analyses of flares detected in B band photometry of UV Ceti type stars  

NASA Astrophysics Data System (ADS)

In this study, we present the unpublished flare data collected from 222 flares detected in the B band observations of five stars and the results derived by statistical analysis and modeling of these data. Six basic properties have been found with a statistical analysis method applied to all models and analyses for the flares detected in the B band observation of UV Ceti type stars. We have also compared the U and B bands with the analysis results. This comparison allowed us to evaluate the methods used in the analyses. The analyses provided the following results. (1) The flares were separated into two types, fast and slow flares. (2) The mean values of the equivalent durations of the slow and the fast flares differ by a factor of 16.2 ± 3.7. (3) Regardless of the total flare duration, the maximum flare energy can reach a different Plateau level for each star. (4) The Plateau values of EV Lac and EQ Peg are higher than the others. (5) The minimum values of the total flare duration increase toward the later spectral types. This value is called the Half-Life value in models. (6) Both the maximum flare rise times and the total flare duration obtained from the observed flares decrease toward the later spectral types.

Dal, H. A.; Evren, S.

2012-05-01

5

Microwave emission from late-type dwarf stars UV Ceti and YZ Canis Minoris  

NASA Astrophysics Data System (ADS)

Simultaneous high-resolution observations of two late-type dwarf stars, UV Cet and YZ CMi, at 6 and 20 cm are presented. These observations put sufficient constraints on existing interpretations to conclude that the quiescent microwave emission from these stars is due to gyrosynchrotron radiation of nonthermal electrons having a power-law energy distribution. From the lifetime of 1 hr of the nonthermal particles against radiation and collision losses, a magnetic field of a few thousand gauss on the photosphere of these stars is estimated. The observations indicate that the ambient density in the coronae of YZ CMi is an order of magnitude higher than that of UV Cet.

Kundu, M. R.; Shevgaonkar, R. K.

1985-10-01

6

A NEW METHOD FOR CLASSIFYING FLARES OF UV Ceti TYPE STARS: DIFFERENCES BETWEEN SLOW AND FAST FLARES  

SciTech Connect

In this study, a new method is presented to classify flares derived from the photoelectric photometry of UV Ceti type stars. This method is based on statistical analyses using an independent samples t-test. The data used in analyses were obtained from four flare stars observed between 2004 and 2007. The total number of flares obtained in the observations of AD Leo, EV Lac, EQ Peg, and V1054 Oph is 321 in the standard Johnson U band. As a result flares can be separated into two types, slow and fast, depending on the ratio of flare decay time to flare rise time. The ratio is below 3.5 for all slow flares, while it is above 3.5 for all fast flares. Also, according to the independent samples t-test, there is a difference of about 157 s between equivalent durations of slow and fast flares. In addition, there are significant differences between amplitudes and rise times of slow and fast flares.

Dal, H. A.; Evren, S., E-mail: ali.dal@ege.edu.t [Department of Astronomy and Space Sciences, University of Ege, Bornova, 35100 Izmir (Turkey)

2010-08-15

7

Detection of a compact companion of the mild barium star Xi-1 Ceti  

NASA Technical Reports Server (NTRS)

In the present paper, the observation of a white dwarf companion of the mild Ba star Xi-1 Ceti (= 65 Ceti = HR 649 = HD 13611) is reported, taking into account also the properties of the mild Ba star and of its companion. The UV spectrum of Xi-1 Ceti is discussed along with an interpretation of this spectrum. Attention is given to the effective temperature of the companion, the absorption bands in the spectrum, the radius and mass of the Xi-1 Ceti companion, and questions regarding the obscuration of the companion by the atmosphere of the Ba star. It is found that the overall energy distribution of the Xi-1 Ceti companion can best be matched with a 14,000 K DA white dwarf of log g = 8 or less. However, the absolute intensity is too small and would require a radius too small and a mass too large for such a gravity.

Bohm-Vitense, E.; Johnson, H. R.

1985-01-01

8

The Asteroseismology of ZZ Ceti star GD1212  

E-print Network

The ZZ Ceti star GD 1212 was detected to have 19 independent modes from the two-wheel-controlled Kepler Spacecraft in 2014. By asymptotic analysis, we identify most of pulsation modes. We find out two set of complete triplets, and four sets of doublet which are interpreted as rotation modes with $l=1$. For the other five modes, the four modes $f_{13}$, $f_{15}$, $f_{16}$ and $f_{4}$ are identified as ones with $l=2$; and the mode $f_{7}$ is identified to be the one with $l=1$. Meanwhile we derive a mean rotation period of $6.65\\pm0.21$ h for GD 1212 according to the rotation splitting. Using the method of matching the observed periods to theoretical ones, we obtain the best-fitting model with the four parameters as $M_{\\rm{*}}/M_{\\rm{\\odot}} = 0.775$, $T_{\\rm{eff}} = 11400$ K, $\\log (M_{\\rm{H}}/M_{\\rm{*}}) = -5.0$, $\\log (M_{\\rm{He}}/M_{\\rm{*}})=-2.5$ for GD 1212. We find that due to the gradient of C/O abundance in the interior of white dwarf, some modes can not propagate to the stellar interior, which leads...

Guifang, Lin; Jie, Su

2015-01-01

9

Asteroseismological Study of Massive ZZ Ceti Stars with Fully Evolutionary Models  

NASA Astrophysics Data System (ADS)

We present the first asteroseismological study for 42 massive ZZ Ceti stars based on a large set of fully evolutionary carbon-oxygen core DA white dwarf models characterized by a detailed and consistent chemical inner profile for the core and the envelope. Our sample comprises all of the ZZ Ceti stars with spectroscopic stellar masses between 0.72 and 1.05 M ? known to date. The asteroseismological analysis of a set of 42 stars enables study of the ensemble properties of the massive, pulsating white dwarf stars with carbon-oxygen cores, in particular the thickness of the hydrogen envelope and the stellar mass. A significant fraction of stars in our sample have stellar mass that is high enough to crystallize at the effective temperatures of the ZZ Ceti instability strip, which enables us to study the effects of crystallization on the pulsation properties of these stars. Our results show that the phase diagram presented in Horowitz et al. seems to be a good representation of the crystallization process inside white dwarf stars, in agreement with the results from white dwarf luminosity function in globular clusters.

Romero, A. D.; Kepler, S. O.; Córsico, A. H.; Althaus, L. G.; Fraga, L.

2013-12-01

10

Ultraviolet Spectra of Star-Grazing Comets in the 49 Ceti Disk System  

NASA Astrophysics Data System (ADS)

49 Ceti is a young star that hosts a debris disk with an unusually large amount of carbon monoxide gas. This excess gas has been attributed to frequent collisions of comets within the disk. (Zuckerman & Song, 2012). Since 49 Ceti disk is nearly edge-on to our line of sight, it is a prime target to observe disk gas and evaporated material from star-grazing comets using absorption spectroscopy, as shown by detection of time-variable circumstellar absorption in optical spectra of the star (Montgomery & Welsh 2012). Here we discuss ultraviolet spectra of 49 Ceti taken using the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS) during two separate visits six days apart. The spectra show time-variable and highly Doppler shifted absorption features from ionized gaseous species. The maximum velocity of the time-variable gas corresponds to a minimum distance from the star of 0.06 AU. These features very likely come from star-grazing comets. Lower limits on element abundances in the gas were found using the apparent optical depth method. The variable comet gas appears carbon rich, despite the disk gas as a whole showing strong absorption features from both carbon and oxygen (Roberge et al., 2014, in press).

Miles, Brittany E.; Roberge, Aki; Welsh, Barry

2015-01-01

11

The effective temperature of Wolf 485A and the statistics of ZZ Ceti stars  

NASA Astrophysics Data System (ADS)

High-speed photometry shows that the bright DA white dwarf Wolf 485A is not a variable star, with an upper limit on the semi-amplitudes of luminosity variations of 0.0005 mag in the period range characteristic of the ZZ Ceti stars. However, its time-averaged multichannel color index (G-R) places it in the instability strip. If confirmed, this result would make Wolf 485A an important object, the lone counterexample to the assertion that all DA white dwarfs evolve to become nonradial pulsators as they enter the ZZ Ceti instability strip. New photometric and spectrophotometric observations conclusively show, however, that the effective temperature of Wolf 485A is around 15,000 K, substantially above the blue edge of the instability strip (Te approximately 13,000 K). The source of this discrepancy most probably lies in erroneous multichannel colors for that object.

Wesemael, F.; Fontaine, G.

1985-01-01

12

X-ray emission from an Ap star /Phi Herculis/ and a late B star /Pi Ceti/  

NASA Technical Reports Server (NTRS)

Using the HEAO 1 soft X-ray sky survey, a search was conducted for X-ray emission from 18 stars in the spectral range B5-A7. The detection of 0.25 keV X-ray sources consistent with the positions of Pi Ceti, a normal B7 V star, and Phi Herculis, a classic Ap star was reported. The detection of these stars argues for large mass motions in the upper layers of stars in this spectral range, and argues against radiative diffusion as the source of abundance anomalies in Ap stars.

Cash, W.; Snow, T. P., Jr.; Charles, P.

1979-01-01

13

Gravity-Modes in ZZ Ceti Stars: IV. Amplitude Saturation by Parametric Instability  

E-print Network

ZZ Ceti stars exhibit small amplitude photometric pulsations in multiple gravity-modes. We demonstrate that parametric instability, a form of resonant 3-mode coupling, limits overstable modes to amplitudes similar to those observed. In particular, it reproduces the observed trend that longer period modes have larger amplitudes. Parametric instability involves the destabilization of a pair of stable daughter modes by an overstable parent mode. The 3-modes must satisfy exact angular selection rules and approximate frequency resonance. The lowest instability threshold for each parent mode is provided by the daughter pair that minimizes $(\\delta\\omega^2+\\gamma_d^2)/\\kappa^2$, where $\\kappa$ is the nonlinear coupling constant, $\\delta\\omega$ is the frequency mismatch, and $\\gamma_d$ is the energy damping rate of the daughter modes. The overstable mode's amplitude is maintained at close to the instability threshold value. Although parametric instability defines an upper envelope for the amplitudes of overstable modes in ZZ Ceti stars, other nonlinear mechanisms are required to account for the irregular distribution of amplitudes of similar modes and the non-detection of modes with periods longer than $1,200\\s$. Resonant 3-mode interactions involving more than one excited mode may account for the former. Our leading candidate for the latter is Kelvin-Helmholtz instability of the mode-driven shear layer below the convection zone.

Yanqin Wu; Peter Goldreich

2000-03-12

14

Gravity-Modes in ZZ Ceti Stars: I.Quasiadiabatic Analysis of Overstability  

E-print Network

We analyze the stability of g-modes in variable white dwarfs with hydrogen envelopes. In these stars, the radiative layer contributes to mode damping because its opacity decreases upon compression and the amplitude of the Lagrangian pressure perturbation increases outward. The overlying convective envelope is the seat of mode excitation because it acts as an insulating blanket with respect to the perturbed flux that enters it from below. A crucial point is that the convective motions respond to the instantaneous pulsational state. Driving exceeds damping by as much as a factor of two provided $\\omega\\tau_c\\geq 1$, where $\\omega$ is the radian frequency of the mode and $\\tau_c\\approx 4\\tau_{th}$ with $\\tau_{th}$ being the thermal time constant evaluated at the base of the convective envelope. As a white dwarf cools, its convection zone deepens, and modes of lower frequency become overstable. However, the deeper convection zone impedes the passage of flux perturbations from the base of the convection zone to the photosphere. Thus the photometric variation of a mode with constant velocity amplitude decreases. These factors account for the observed trend that longer period modes are found in cooler DAVs. The linear growth time, ranging from hours for the longest period observed modes ($P\\approx 20$ minutes) to thousands of years for those of shortest period ($P\\approx 2 $ minutes), probably sets the time-scale for variations of mode amplitude and phase. This is consistent with observations showing that longer period modes are more variable than shorter period ones. Our investigation confirms many results obtained by Brickhill in his pioneering studies of ZZ Cetis.

Peter Goldreich; Yanqin Wu

1998-04-28

15

Cooling time of shock-heated gas in the atmospheres of Mira Ceti long-period variable stars  

NASA Astrophysics Data System (ADS)

The eventual cooling of post-shock gas before the temperature returns to its unperturbed value is studied in a model for a stationary shock in the atmosphere of a Mira Ceti variable star. The cooling time of the gas as a function of the current temperature is calculated. The cooling time is compared to the period of the brightness variations of Mira variables, for which the phase dependence of emission-line intensities is known. In most cases, the gas does not have time to cool to the temperature of the "photosphere"—the region where the molecular absorption bands are formed. Therefore, the shock propagates in subphotospheric layers. This is confirmed by previously published high-resolution spectra, which show absorption lines of molecules superimposed on emission lines.

Belova, O. M.; Bychkov, K. V.; Rudnitskii, G. M.

2014-12-01

16

A 40 Myr OLD GASEOUS CIRCUMSTELLAR DISK AT 49 CETI: MASSIVE CO-RICH COMET CLOUDS AT YOUNG A-TYPE STARS  

SciTech Connect

The gaseous molecular disk that orbits the main-sequence A-type star 49 Ceti has been known since 1995, but the stellar age and the origin of the observed carbon monoxide molecules have been unknown. We now identify 49 Ceti as a member of the 40 Myr old Argus Association and present a colliding comet model to explain the high CO concentrations seen at 49 Ceti and the 30 Myr old A-type star HD 21997. The model suggests that massive-400 Earth mass-analogs of the Sun's Kuiper Belt are in orbit around some A-type stars, that these large masses are composed primarily of comet-like objects, and that these objects are rich in CO and perhaps also CO{sub 2}. We identify additional early-type members of the Argus Association and the Tucana/Horologium and Columba Associations; some of these stars display excess mid-infrared emission as measured with the Widefield Infrared Survey Explorer.

Zuckerman, B. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Song, Inseok, E-mail: ben@astro.ucla.edu, E-mail: song@physast.uga.edu [Department of Physics and Astronomy, University of Georgia, Athens, GA 30602-2451 (United States)

2012-10-20

17

Gravity-Modes in ZZ Ceti Stars III. Eigenvalues and Eigenfuctions  

E-print Network

We report on numerical calculations of nonadiabatic eigenvalues and eigenfunctions for g-modes in ZZ Ceti variables. The spectrum of overstable $l=1$ modes delineates the instability strip. Its blue edge occurs where $\\omega \\tau_c \\approx 1$ for the $n=1$ mode. Here $\\omega$ is radian frequency and $\\tau_c$ is about four times the thermal timescale at the bottom of the surface convection zone. As a ZZ Ceti cools, its convection zone deepens, longer period modes become overstable, but the critical value of $\\omega\\tau_c$ separating overstable and damped modes rises. The latter is a consequence of enhanced radiative damping for modes which propagate immediately below the convection zone. The critical value of $\\omega\\tau_c$ is of observational significance because modes with the smallest value of $\\omega\\tau_c$ are most observable photometrically. Maximum periods for overstable modes predicted for our cooler model envelopes are about a factor two longer than the observational upper limit of $1,200\\s$. We assess a number of plausible resolutions for this discrepancy among which convective overshoot and nonlinear saturation look promising. The nonadiabatic eigenfunctions enable us to predict relative amplitudes and phases of photospheric variations of flux and velocity, quantities made accessible by recent observations. We also present asymptotic formula for damping rates of high order modes, a result of consequence for future investigations of nonlinear saturation of the amplidues of overstable modes.

Yanqin Wu; Peter Goldreich

1998-12-03

18

Gamma Ray Bursts and CETI  

Microsoft Academic Search

Gamma ray burst sources are isotropically distributed. They could be located at distances 1000 AU. (Katz (4)) GRB signals have many narrow peaks that are unresolved at the millisecond time resolution of existing observations. (1) CETI could use stars as gravitational lenses for interstellar gamma ray laser beam communication. Much better time resolution of GRB signals could rule out (or

19

Gravity-modes in ZZ Ceti Stars. II. Effects of Turbulent Dissipation  

E-print Network

We investigate dynamical interactions between turbulent convection and g-mode pulsations in ZZ Ceti variables (DAVs). Since our understanding of turbulence is rudimentary, we are compelled to settle for order of magnitude results. A key feature of these interactions is that convective response times are much shorter than pulsation periods. Thus the dynamical interactions enforce near uniform horizontal velocity inside the convection zone. They also give rise to a narrow shear layer in the region of convective overshoot at the top of the radiative interior. Turbulent damping inside the convection zone is negligible for all modes, but that in the region of convective overshoot may be significant for a few long period modes near the red edge of the instability strip. These conclusions are in accord with those reached earlier by Brickhill. Our major new result concerns nonlinear damping arising from the Kelvin-Helmholtz instability of the aforementioned shear layer. Amplitudes of overstable modes saturate where dissipation due to this instability balances excitation by convective driving. This mechanism of amplitude saturation is most effective for long period modes, and it may play an important role in defining the red edge of the instability strip.

P. Goldreich; Y. Wu

1998-10-02

20

No first ionization potential fractionation in the active stars AR Piscium and AY Ceti  

NASA Astrophysics Data System (ADS)

Context: The comparison of coronal and photospheric abundances in cool stars is an essential question to resolve. In the Sun an enhancement of the elements with low first ionization potential (FIP) is observed in the corona with respect to the photosphere. Stars with high levels of activity seem to show a depletion of elements with low FIP when compared to solar standard values; however, the few cases of active stars in which photospheric values are available for comparison lead to confusing results, and an enlargement of the sample is mandatory for solving this longstanding problem. Aims: We calculate in this paper the photospheric and coronal abundances of two well known active binary systems, AR Psc and AY Cet, to get further insight into the complications of coronal abundances. Methods: Coronal abundances of 9 elements were calculated by means of the reconstruction of a detailed emission measure distribution, using a line-based method that considers the lines from different elements separately. Photospheric abundances of 8 elements were calculated using high-resolution optical spectra of the stars. Results: The results once again show a lack of any FIP-related effect in the coronal abundances of the stars. The presence of metal abundance depletion (MAD) or inverse FIP effects in some stars could stem from a mistaken comparison to solar photospheric values or from a deficient calculation of photospheric abundances in fast-rotating stars. Conclusions: The lack of FIP fractionation seems to confirm that Alfvén waves combined with pondermotive forces are dominant in the corona of active stars. Tables 2 and 3 are only available in electronic form at http://www.aanda.org

Sanz-Forcada, J.; Affer, L.; Micela, G.

2009-10-01

21

UV-bright stars in globular clusters  

NASA Technical Reports Server (NTRS)

This paper highlights globular cluster studies with Ultraviolet Imaging Telescope (UIT) in three areas: the discrepancy between observed ultraviolet HB magnitudes and predictions of theoretical HB models; the discovery of two hot subdwarfs in NGC 1851, a globular not previously known to contain such stars; and spectroscopic follow up of newly identified UV-bright stars in M79 and w Cen. I also present results of a recent observation of NGC 6397 with the Voyager ultraviolet spectrometer.

Landsman, Wayne B.

1994-01-01

22

Tau Ceti: our nearest cousin  

NASA Astrophysics Data System (ADS)

The 10 Gyr old G8V star ?Ceti is the closest Solar analogue. It harbors the less massive exo-Kuiper belt detected so far among debris disks stars. With a total disk mass only ten times larger than that of our Kuiper belt, it represents a case study of evolved debris disks. Whether its disk has been continuously eroded by steady-state collisions of planetesimals or recently regenerated by a dynamical instability remains a puzzling question. The detection of the dust points to the existence of (undetected) planetary bodies, which are expected to sculpt the belt and may scatter material inwards to the terrestrial planet region, where hot dust is also observed. Unfortunately, the disk morphology remains unknown. We report a recent Herschel PACS (70? and 160?)detection of a 15 au ring-like structure which is in conflict with the earlier SCUBA discovery. The disk is partly resolved by Herschel and we derive its morphology and the dust properties from the images and SED analysis with the GraTer modeling code. ?Ceti is a unique laboratory to highlight the long-term dynamical evolution of planetary systems and may represent an alternative outcome to the evolution of our Solar system.

Di Folco, E.; Péricaud, J.; Augereau, J.-C.; Marshall, J.

2014-12-01

23

Mean ZZ Ceti pulsation period gauges stellar temperature  

E-print Network

The mean pulsation period of ZZ Ceti stars increases with decreasing effective temperature as we traverse from the blue to the red edge of the instability strip. This well-established correlation between the mean period and spectroscopic temperature suggests that the mean period could be utilized as a tool to measure the relative temperature of the star independent of spectroscopy. Measuring the pulsation periods of a ZZ Ceti star is a simple, model-independent, and straight forward process as opposed to a spectroscopic determination of its temperature. Internal uncertainties in determining the spectroscopic temperature of a ZZ Ceti star are at least 200K, 15% of the 1350K width of the instability strip. The uncertainties in determining the mean period arise mostly from amplitude modulation in the pulsation spectrum and are smaller than 100s for 91% of the ZZ Ceti stars, temperature indicator rather than conventional spectroscopy. Presently we only claim that the relative temperatures of ZZ Ceti stars derived by using the mean pulsation period are certainly as good as and perhaps about 15% better than spectroscopy.

Anjum S. Mukadam; M. H. Montgomery; A. Kim; D. E. Winget; S. O. Kepler; J. C. Clemens

2006-12-15

24

UV spectroscopy of young star clusters  

NASA Astrophysics Data System (ADS)

We propose to take spectra of young star clusters (t < 1 Gyr) in the Magellanic Clouds. These data will serve to improve and extend the calibration of the UV spectral index system for stellar population models, which we have built with IUE spectra from the data bases of Fanelli et al. (1992) and Cassatella et al. (1987). We have developed evolutionary population synthesis models of the most relevant absorption features of stellar systems with ages in the range 1 Myr to 1 Gyr, covering the most important elements including C, Si, Fe and Mg (Nieves & Maraston 2004). The new data will allow the calibration of these spectral indices for different chemical abundances and ages. The calibrated stellar population models will provide an important tool to interpret spectra of high redshift galaxies

Maraston, Claudia

25

Multicolour photometry of EO Ceti (PB 8783)  

NASA Astrophysics Data System (ADS)

We present the first-look analysis of the high-speed multicolour photometry of the bright V361 Hya-type star EO Ceti ( m V=12.3). The observations were gathered with the three-channel ULTRACAM instrument attached to the 4.2-m William Herschel Telescope. The data set has a total time span of 6.2 d and consists of 31 h simultaneous three colour photometry. The main power regions in all three colours are the same as previously reported in the white light photometric campaigns on EO Ceti. We calculate the frequencies, amplitudes and phases of the significant modes in three colours of the SDSS system, r', g' and u'. The amplitudes of the detected modes are the highest in the u' lightcurve, and the phases are the same in all three colours within the measurement accuracy. The amplitudes of the highest signal-to-noise modes show time variability in all three colours. We analyse the amplitude and phase variations of the five highest signal-to-noise modes in different colours. Even though the amplitudes show variations from night to night, the amplitude ratios are found to be constant to within 2 ? level. This result is promising as it allows us to compare the observed amplitude ratios with theoretically calculated amplitude ratios. This may further constrain the mode identification of the highest amplitude modes in EO Ceti and let us test the proposed seismic and binary evolution models.

Vu?kovi?, M.; Østensen, R. H.; Aerts, C.; Dhillon, V. S.; Marsh, T. R.

2010-10-01

26

ASCA X-ray spectra of the active single stars Beta Ceti and pi(1) Ursae Majoris  

NASA Technical Reports Server (NTRS)

We present X-ray spectra obtaiined by ASCA of two single, active stars, the G dwarf pi(1) UMa, and the G9/K0 giant Beta Cet. The spectra of both stars require the presence of at least two plasma components with different temperatures, 0.3-0.4 keV and approximately 0.7 keV, in order for acceptable fits to be obtained. The spectral resolving power and signal-to-noise ratio of the solid state imaging spectrometer (SIS) spectra allow us to formally constrain the coronal abundances of a number of elements. In Beta Cet, we find Mg to be overabundant, while other elements such as O, Ne, and N are underabundant, relative to the solar photospheric values. From the lower signal-to-noise ratio SIS spectrum of pi(1) UMa, we find evidence for underabundances of O, Ne, and Fe. These results are discussed in the context of the present understanding of elemental abundances in solar and stellar coronae.

Drake, S. A.; Singh, K. P.; White, N. E.; Simon, Theodore

1994-01-01

27

A Comparison of the Outer Atmosphere of the ``Flat Activity'' Star ? Ceti (G8 V) with the Sun (G2 V) and ? Centauri A (G2 V)  

NASA Astrophysics Data System (ADS)

Driven by the desire to understand the roles of acoustic and magnetic mechanisms in heating the outer atmospheres of Sun-like stars, we compare solar UV spectra with archival STIS spectra from the Hubble Space Telescope of ? Cen A (G2 V) and new STIS spectra of the extremely inactive dwarf star ? Cet (G8 V, V=3.5). The activity of ? Cet shows occasional rotational modulations but no long-term cyclic variation. It may be in a phase analogous to the solar Maunder minimum. Solar disk center intensities from both the HRTS instrument and the SUMER instrument on SOHO were converted to Sun-as-a-star fluxes by using center-to-limb data from Dammasch and colleagues. The derived solar flux spectrum represents conditions near the minimum of the solar magnetic activity cycle. We find that the ? Cet line profiles differ systematically from those of the Sun and ? Cen A. While lines formed in the middle chromospheres appear similar, the entire emission from the upper chromosphere to the middle transition region of ? Cet has lower flux densities by factors of ~2, the line widths are significantly narrower, and, uniquely, the transition region lines are not significantly redshifted. The soft X-ray surface flux of ? Cet, measured between 0.1 and 2.4 keV, is ~9×103 ergs cm-2 s-1, several times smaller than the median solar value. We also find that the UV spectrum of ? Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun is in an intermediate phase of its activity cycle but that its coronal emission may be somewhat smaller. We discuss the implications of these results for magnetic fields and heating mechanisms in the stars and speculate that ? Cet's UV spectrum might represent the solar spectrum during a grand minimum phase.

Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres, Thomas R.

2004-07-01

28

Brucella ceti and Brucellosis in Cetaceans  

PubMed Central

Since the first case of brucellosis detected in a dolphin aborted fetus, an increasing number of Brucella ceti isolates has been reported in members of the two suborders of cetaceans: Mysticeti and Odontoceti. Serological surveys have shown that cetacean brucellosis may be distributed worldwide in the oceans. Although all B. ceti isolates have been included within the same species, three different groups have been recognized according to their preferred host, bacteriological properties, and distinct genetic traits: B. ceti dolphin type, B. ceti porpoise type, and B. ceti human type. It seems that B. ceti porpoise type is more closely related to B. ceti human isolates and B. pinnipedialis group, while B. ceti dolphin type seems ancestral to them. Based on comparative phylogenetic analysis, it is feasible that the B. ceti ancestor radiated in a terrestrial artiodactyl host close to the Raoellidae family about 58 million years ago. The more likely mode of transmission of B. ceti seems to be through sexual intercourse, maternal feeding, aborted fetuses, placental tissues, vertical transmission from mother to the fetus or through fish or helminth reservoirs. The B. ceti dolphin and porpoise types seem to display variable virulence in land animal models and low infectivity for humans. However, brucellosis in some dolphins and porpoises has been demonstrated to be a severe chronic disease, displaying significant clinical and pathological signs related to abortions, male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings, and death. PMID:22919595

Guzmán-Verri, Caterina; González-Barrientos, Rocío; Hernández-Mora, Gabriela; Morales, Juan-Alberto; Baquero-Calvo, Elías; Chaves-Olarte, Esteban; Moreno, Edgardo

2012-01-01

29

A Complete UV Atlas of Standard Stars  

NASA Technical Reports Server (NTRS)

This program is an Astrophysics Data Program (ADP) contract, together with a follow-on contract (S- 57791 -Z), intended to produce a comprehensive ultraviolet spectral atlas of stars based on the data in the IUE Final Archive. The data in the Final Archive were uniformly processed by the NEWSIPS pipeline system. The NEWSIPS gives an improved signal-to-noise ratio for the data that will be especially beneficial to low signal portions of the spectra; and it also gives more accurate fluxes for stars by adopting the latest absolute calibration and measured instrument parameters. Therefore, this atlas provides more uniform and accurate data than the version previously published.

Wu, Chi-Chao

1999-01-01

30

DISCOVERY OF A ZZ CETI IN THE KEPLER MISSION FIELD  

SciTech Connect

We report the discovery of the first identified pulsating DA white dwarf, WD J1916+3938 (Kepler ID 4552982), in the field of the Kepler mission. This ZZ Ceti star was first identified through ground-based, time-series photometry, and follow-up spectroscopy confirms that it is a hydrogen-atmosphere white dwarf with T {sub eff} = 11,129 {+-} 115 K and log g = 8.34 {+-} 0.06, placing it within the empirical ZZ Ceti instability strip. The object shows up to 0.5% amplitude variability at several periods between 800 and 1450 s. Extended Kepler observations of WD J1916+3938 could yield the best light curve, to date, of any pulsating white dwarf, allowing us to directly study the interior of an evolved object representative of the fate of the majority of stars in our Galaxy.

Hermes, J. J.; Winget, D. E. [Department of Astronomy, University of Texas at Austin, Austin, TX 78712 (United States); Mullally, Fergal; Howell, Steve B. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Oestensen, R. H.; Bloemen, S. [Instituut voor Sterrenkunde, K.U. Leuven, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Williams, Kurtis A. [Department of Physics and Astronomy, Texas A and M University-Commerce, Commerce, TX 75428 (United States); Telting, John [Nordic Optical Telescope, 38700 Santa Cruz de La Palma (Spain); Southworth, John [Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom); Everett, Mark, E-mail: jjhermes@astro.as.utexas.edu [National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)

2011-11-01

31

UV properties of hot stars in NGC 6752  

NASA Technical Reports Server (NTRS)

The UV properties of hot stars found in the center of NGC 6752 are compared with those outside the core. Few, if any, faint sdB stars are found in the central region, whereas they occur in significant numbers far from the core. A statistically complete photographic survey is used to demonstrate that the faint blue stars in NGC 6752 occur in greater numbers with increasing distance form the center, and the International Ultraviolet Explorer (IUE) findings extend this result all the way to the center of the cluster. A similar phenomenon has been observed optically in other clusters, such as M15.

Altner, Bruce

1990-01-01

32

Elemental abundance analyses with DAO spectrograms. VII - The late normal B stars Pi Ceti, 134 Tauri, 21 Aquilae, and Nu Capricorni and the use of Reticon spectra  

NASA Technical Reports Server (NTRS)

This paper presents elemental abundance analyses of sharp-lined normal late B stars. These stars exhibit mostly near-solar abundances, but each star also shows a few abundances which are a factor of 2 less than solar. The coadded photographic spectrograms are supplemented with Reticon data. A comparison of 261 equivalent widths on 2.4 A/mm spectra of sharp-lined B and A stars shows that the Reticon equivalent widths are about 95 percent of the coadded equivalent mean. The H-gamma profiles of the coadded and Reticon spectra for eight sharp-lined stars show generally good agreement. The generally high quality of the coadded data produced from 10 or more spectrograms is confirmed using the REDUCE graphics-oriented computed reduction code. For five stars, metal lines which fall in the gap between the U and V plates are analyzed using Reticon data.

Adelman, Saul J.

1991-01-01

33

An Evolutionary Sequence for Herbig Ae\\/be Stars Derived from UV Data  

Microsoft Academic Search

Based on the study of 35 Herbig Ae\\/Be stars in the UV using IUE data, this study proposes an evolutionary sequence for the circumstellar matter surrounding these objects. This sequence has two distinct phases each with unique underlying physics: (1) the UV Broad Line stars have extremely broad bands of absorption arising mainly from the metastable states of Fe II

Jeffrey Michael Silvis

1995-01-01

34

HAZMAT I: The Evolution of X-ray, Far-UV and Near-UV Emission from Early M Stars  

NASA Astrophysics Data System (ADS)

With the recent discoveries of several super-earths orbiting M dwarfs well within their habitable zones (0.1 to 0.4 AU), and with many more such planets to come, it is critical to assess the evolution of the high-energy radiation environment of these systems. We have begun the HAZMAT (HAbitable Zones and M dwarf Activity across Time) program by first measuring the drop in near-UV and far-UV flux in early M stars from 10 Myr to several Gyr using photometry from NASA's Galaxy Evolution Explorer (GALEX). We focus this study on the confirmed low-mass members of nearby young moving groups, the Hyades cluster, and old field stars. We show a relatively slow decline in UV flux up until at least 650 Myr with a sharper drop in the old M dwarfs. Yet without confirmed M dwarfs in nearby star clusters with ages of 1-2 Gyr, mapping the precise evolution at these older ages is not currently possible. The UV data also provide much-needed constraints to M dwarf upper-atmosphere models, which are currently insufficient for predicting UV emission from M dwarfs. Our analysis will aid empirically motivated upper-atmospheric modeling for the young and old M stars, which can then be used to predict the extreme-UV fluxes most critical to the evolution of a planetary atmosphere. (See HAZMAT II abstract by Peacock et al.) The HAZMAT program is the first comprehensive study of the UV history of M stars.

Shkolnik, E.; Barman, T.

2014-03-01

35

UV observations of sdB stars and prospects of WSO-UV mission for such studies  

NASA Astrophysics Data System (ADS)

The hot subdwarf B (sdB) stars are considered to be core He-burning stars with surface temperatures T eff up to 40 000 K and log g?5. They are UV bright and ultraviolet observatories have a significant impact on studies of these objects. Using the technical characteristics of the instruments of the World Space Observatory-Ultraviolet ( WSO-UV) mission and data from previous UV studies of sdBs we estimate the limiting apparent magnitudes for these stars that can be observed with the signal-to-noise ratio required in fine spectroscopic analysis. WSO-UV is an international space observatory for observation in UV spectral range 100-350 nm, that is beyond the reach of ground-based instruments but where most of astrophysical processes can be efficiently studied with unprecedented capability. The WSO-UV project is currently funded by national space agencies of Russia and Spain with participation of Germany, Ukraine and China. The WSO-UV consists of a 1.7 m aperture telescope (under responsibility of Russia) with instrumentation designed to carry out high resolution spectroscopy, long-slit low resolution spectroscopy and direct sky imaging. The WSO-UV Ground Segment is under development by Spain and Russia. They will coordinate the Mission and Science Operations and provide the satellite tracking stations for the project. The WSO-UV will work as a targeted scientific observatory. The scientific program of the observatory is open to excellent scientific projects from the world-wide community and occupies up to 40% of total observational time.

Sachkov, Mikhail

2010-10-01

36

HAZMAT. I. The Evolution of Far-UV and Near-UV Emission from Early M Stars  

NASA Astrophysics Data System (ADS)

The spectral energy distribution, variability, and evolution of the high-energy radiation from an M dwarf planet host is crucial in understanding the planet's atmospheric evolution and habitability and in interpreting the planet's spectrum. The star's extreme-UV (EUV), far-UV (FUV), and near-UV (NUV) emission can chemically modify, ionize, and erode the atmosphere over time. This makes determining the lifetime exposure of such planets to stellar UV radiation critical for both the evolution of a planet's atmosphere and our potential to characterize it. Using the early M star members of nearby young moving groups, which sample critical ages in planet formation and evolution, we measure the evolution of the GALEX NUV and FUV flux as a function of age. The median UV flux remains at a "saturated" level for a few hundred million years, analogous to that observed for X-ray emission. By the age of the Hyades Cluster (650 Myr), we measure a drop in UV flux by a factor of 2-3 followed by a steep drop from old (several Gyrs) field stars. This decline in activity beyond 300 Myr follows roughly t -1. Despite this clear evolution, there remains a wide range, of 1-2 orders of magnitude, in observed emission levels at every age. These UV data supply the much-needed constraints to M dwarf upper-atmosphere models, which will provide empirically motivated EUV predictions and more accurate age-dependent UV spectra as inputs to planetary photochemical models. Based on observations made with the NASA Galaxy Evolution Explorer (GALEX). GALEX was operated for NASA by the California Institute of Technology under NASA contract NAS5-98034.

Shkolnik, Evgenya L.; Barman, Travis S.

2014-10-01

37

UV habitability and dM stars: an approach for evaluation of biological survival  

NASA Astrophysics Data System (ADS)

Dwarf M stars comprise about 75 percent of all stars in the galaxy. For several years planets orbiting M stars have been discarded as suitable places for development of life. This paradigm now has changed and terrestrial-type planets within liquid-water habitable zones (LW-HZ) around M stars are reconsidered as possible hosts for life as we know it. Nevertheless, large amount of UV radiation is emitted during flares by this stars, and it is uncertain how these events could affect biological systems. In particular UV-C ? < 290nm) exhibits the most damaging effects for living organisms. To analyze the hypothesis that UV could set a limit for the development of extraterrestrial life, we studied the effect of UV-C treatment on halophile archaea cultures. Halophile archaea are extremophile organisms, they are exposed to intense solar UV radiation in their natural environment so they are generally regarded as relatively UV tolerant. Halophiles inhabits in hipersaline environments as salt lakes but also have been found in ancient salt deposits as halites and evaporites on Earth. Since evaporites have been detected in Martian meteorites, these organisms are proposed as plausible inhabitants of Mars-like planets. Our preliminary results show that even after UV damage, the surviving cells were able to resume growth with nearly normal kinetics.

Abrevaya, Ximena C.; Cortón, Eduardo; Mauas, Pablo J. D.

2010-02-01

38

Recent Massive Star Formation in NGC1068 Derived from UV/H? Comparisons  

NASA Astrophysics Data System (ADS)

We present broadband ultraviolet images of NGC1068 made at 152 and 249nm with 3 arcsec resolution. The images were made using the Ultraviolet Imaging Telescope (UIT) in December 1990. The UV images are compared with ground-based H? images having comparable resolution. Although the overall brightness distributions are similar in the UV and in H? , we find significant differences when we compare the images in detail. In particular, the extremely luminous UV region 10 arcsec NW of the active nucleus is unremarkable in H? . Several other regions are observed with differing UV and H? appearances. We use the UV/H? ratio in different regions to explore the recent star formation history of NGC1068. Although both the UV light and the H? emission trace the young stellar population, the H? tends to fade more quickly as the ionizing stars evolve off the main sequence; the UV continuum emission lasts longer, as it originates from a broader range of stellar ages and temperatures. Thus, the `knots' which are UV-bright but H? -weak are probably regions currently containing young stars with intermediate masses (5-15 M_?). Alternatively, the `knots' may have formed with a truncated IMF. We compare our observations to population synthesis models of Fanelli \\it et al. to determine ages of the star- forming regions and to constrain the IMF in selected regions of NGC1068.

Neff, S. G.; Fanelli, M. N.; Roberts, L. J.; Cheng, K. P.; Hintzen, P. M. N.; Smith, E. P.; Smith, A. M.; Stecher, T. P.; Bohlin, R. C.; O'Connell, R. W.; Roberts, M. S.

1993-12-01

39

An Evolutionary Sequence for Herbig Ae\\/Be Stars Based on UV Data  

Microsoft Academic Search

This work represents a systematic study of the differences found in the UV spectra of 37 Herbig Ae\\/Be stars, involving over 800 spectra. By examining spectral and continuum differences between the members of this set of stars it is possible to construct an evolutionary sequence. This evolutionary sequence is supported by data from other bandpasses. Furthermore, there is a radical

Jms Silvis

1994-01-01

40

The possible nature of the high-velocity OB stars - Hot UV-bright stars in the galactic disk  

NASA Astrophysics Data System (ADS)

It is suggested that many of the high-velocity, low surface gravity, early-type stars are Old Disk Population objects in the same evolutionary phase as the hot UV-bright stars in globular clusters. The bimodal Gaussian fits to the peculiar radial velocity distribution result in Gaussian distribution values of 13 km/s and 28 km/s which are typical of extreme Population I objects and of the Old Disk Population. An analysis of the kinematics of a sample of OB stars indicates solar motion and mean peculiar velocities typical of Population I objects; it is concluded that up to 39 percent of the O-type and 11 percent of the B-type stars may be Old Disk Population objects, referred to as Disk-UV-bright stars.

Carrasco, L.; Bisiacchi, G. F.; Firmani, C.; Costero, R.; Cruz-Gonzalez, C.

1980-12-01

41

A High-Resolution UV Spectral Atlas for Mira Variable Stars  

NASA Astrophysics Data System (ADS)

The ultraviolet (UV) spectra of Mira variable stars have been studied for nearly three decades. The International Ultraviolet Explorer (IUE) space telescope observed these stars at both low and high dispersion. Later the Hubble Space Telescope (HST) obtained high-dispersion spectra both with the High Resolution Spectrograph (HRS) and the Space Telescope Imaging Spectrograph (STIS). This paper displays a STIS spectrum of the cool Mira-type variable star R Leo taken on 31 December 1998. On this date R Leo was at phase 0.37 in its light-curve cycle. This spectrum shows a large number of emission lines and identifications are made for nearly 200 of these features. Many of these emission lines were previously unrecorded in IUE and HRS spectra of Miras, such as the Fe II (UV33, 35, 158, 160, 161, 180, 181), Mn II (UV38), V II (UV43, 73), Zr II (UV58), and the Ni II (UV36) multiplets. The electron density diagnostic multiplet of C II] (UV0.01) gives an electron density of 10^{9} cm^{-3} for R Leo at this phase. This is similar to the electron density found for the Mira star R Hya at phase 0.26 obtained with a HST/HRS spectrum. Finally, the photospheric spectrum was detected from 2980 Å (the long wavelength cut-off) down to 2450 Å.

Luttermoser, D. G.

2009-09-01

42

UV and FIR selected star-forming galaxies at z=0: differences and overlaps  

E-print Network

We study two samples of local galaxies, one is UV (GALEX) selected and the other FIR (IRAS) selected, to address the question whether UV and FIR surveys see the two sides ('bright' and 'dark') of the star formation of the same population of galaxies or two different populations of star forming galaxies. No significant difference between the L$_{tot}$ ($=L_{60}+L_{FUV}$) luminosity functions of the UV and FIR samples is found. Also, after the correction for the `Malmquist bias' (bias for flux limited samples), the FIR-to-UV ratio v.s. L$_{tot}$ relations of the two samples are consistent with each other. In the range of $9 \\la \\log(L_{tot}/L_\\sun) \\la 12$, both can be approximated by a simple linear relation of $\\log (L_{60}/L_{FUV})=\\log(L_{tot}/L_\\sun)-9.66$. These are consistent with the hypothesis that the two samples represent the same population of star forming galaxies, and their well documented differences in L$_{tot}$ and in FIR-to-UV ratio are due only to the selection effect. A comparison between the UV luminosity functions shows marginal evidence for a population of faint UV galaxies missing in the FIR selected sample. The contribution from these 'FIR-quiet' galaxies to the overall UV population is insignificant, given that the K-band luminosity functions (i.e. the stellar mass functions) of the two samples do not show any significant difference.

C. Kevin Xu; Veronique Buat; Jorge Iglesias-Páramo; Tsutomu T. Takeuchi; Tom A. Barlow; Luciana Bianchi; Jose Donas; Karl Forster; Timothy M. Heckman; Patrick N. Jelinsky; Young-Wook Lee; Barry F. Madore; Roger F. Malina; D. Christopher Martin; Bruno Milliard; Patrick Morrissey; R. Michael Rich; Susan G. Neff; David Schiminovich; Oswald H. W. Siegmund; Todd Small; Alex S. Szalay; Barry Y. Welsh; Ted K. Wyder; Sukyoung Yi

2006-04-04

43

SATURATION LEVELS FOR WHITE-LIGHT FLARES OF FLARE STARS: VARIATION OF MINIMUM FLARE DURATION FOR SATURATION  

SciTech Connect

Taking into account results obtained from models and from statistical analyses of obtained parameters, we discuss flare activity levels and flare characteristics of five UV Ceti stars. We present the parameters of unpublished flares detected over two years of observations of V1005 Ori. We compare parameters of the U-band flares detected over several seasons of observations of AD Leo, EV Lac, EQ Peg, V1054 Oph, and V1005 Ori. Flare frequencies calculated for all program stars and maximum energy levels of the flares are compared, and we consider which is the most correct parameter as an indicator of flare activity levels. Using the One Phase Exponential Association function, the distributions of flare equivalent duration versus flare total duration are modeled for each program star. We use the Independent Samples t-Test in the statistical analyses of the parameters obtained from the models. The results reveal some properties of flare processes occurring on the surfaces of UV Ceti type stars. (1) Flare energies cannot be higher than a specific value regardless of the length of the flare total duration. This must be a saturation level for white-light flares occurring in flare processes observed in the U band. Thus, for the first time it is shown that white-light flares have a saturation in a specific energy range. (2) The span values, which are the difference between the equivalent durations of flares with the shortest and longest total durations, are almost equal for each star. (3) The half-life values, minimum flare durations for saturation, increase toward the later spectral types. (4) Both maximum total durations and maximum rise times computed from the observed flares decrease toward the later spectral types among the UV Ceti stars. According to the maximum energy levels obtained from the models, both EV Lac and EQ Peg are more active than the other three program stars, while AD Leo is the most active flare star according to the flare frequencies.

Dal, H. A.; Evren, S., E-mail: ali.dal@ege.edu.tr [Department of Astronomy and Space Sciences, University of Ege, Bornova, 35100 Izmir (Turkey)

2011-02-15

44

HAZMAT I: The Evolution of Far- and Near-UV Emission from Early M Stars  

NASA Astrophysics Data System (ADS)

With the recent discoveries of several super-earths orbiting M dwarfs well within their habitable zones (0.1 to 0.4 AU), and with many more such planets to come, it is critical to assess the evolution of the high-energy radiation environment of these systems. We have begun the HAZMAT (Habitable Zones and M dwarf Activity across Time) program by first measuring the drop in near-UV and far-UV flux in early M stars from 10 Myr to several Gyr using photometry from NASA's Galaxy Evolution Explorer (GALEX). We focus this study on the confirmed low-mass members of nearby young moving groups, the Hyades cluster, and old field stars. We show a relatively slow decline in UV flux up until at least 650 Myr with a sharper drop in the old M dwarfs. Yet without confirmed M dwarfs in nearby star clusters with ages of 1-2 Gyr, mapping the precise evolution at these older ages is not currently possible. The UV data also provide much-needed constraints to M dwarf upper-atmosphere models, which are insufficient for predicting UV emission from M dwarfs. Our analysis will produce empirically-motivated chromospheric profiles for the young and old M stars, which can then be used to predict the extreme-UV fluxes most critical to the evolution of a planetary atmosphere. The HAZMAT program is the first comprehensive study of the UV history of M stars, and will ultimately tell us if a planet in the canonical habitable zone can indeed be habitable.

Shkolnik, Evgenya; Barman, T. S.; Peacock, S.

2014-01-01

45

Legacy ExtraGalactic UV Survey (LEGUS): The HST View of Star Formation in Nearby Galaxies  

NASA Astrophysics Data System (ADS)

The Treasury program LEGUS (HST/GO-13364) is the first HST UV Atlas of nearby galaxies, and is aimed at the thorough investigation of star formation and its relation with galaxy environment, from the scales of individual stars to those of ~kpc clustered structures. The 154-orbits program is obtaining NUV,U,B,V,I images of 50 star-forming galaxies in the distance range 4-12 Mpc, covering the full range of morphology, star formation rate (SFR), mass, metallicity, internal structure, and interaction state found in the local Universe. The imaging survey will yield accurate recent (<50 Myr) star formation histories (SFHs) from resolved massive stars, and the extinction-corrected ages and masses of star clusters and associations. These extensive inventories of massive stars, clustered systems, and SFHs will be used to: (1) quantify how the clustering of star formation evolves both in space and in time; (2) discriminate among models of star cluster evolution; (3) investigate the effects of SFH on the UV SFR calibrations; (4) explore the impact of environment on star formation and cluster evolution across the full range of galactic and ISM properties. LEGUS observations will inform theories of star formation and galaxy evolution, and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of the clumpy star formation at high redshift. LEGUS will generate the most homogeneous high-resolution, wide-field UV dataset to date, building and expanding on the GALEX legacy. Data products that will be delivered to the community include: catalogs of massive stars and star clusters, catalogs of star cluster properties (ages, masses, extinction), and a one-stop shop for all the ancillary data available for this well-studied galaxy sample. LEGUS will provide the reference survey and the foundation for future observations with JWST and with ALMA. This abstract accompanies another one from the same project, and presents the status of the project, its structure, and the data products that will be delivered to the community; the other abstract presents the science goals of LEGUS and how these will be addressed by the HST observations.

Calzetti, Daniela; Lee, J. C.; Adamo, A.; Aloisi, A.; Andrews, J. E.; Brown, T. M.; Chandar, R.; Christian, C. A.; Cignoni, M.; Clayton, G. C.; Da Silva, R. L.; de Mink, S. E.; Dobbs, C.; Elmegreen, B.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gallagher, J. S.; Gouliermis, D.; Grebel, E.; Herrero-Davo`, A.; Hilbert, B.; Hunter, D. A.; Johnson, K. E.; Kennicutt, R.; Kim, H.; Krumholz, M. R.; Lennon, D. J.; Martin, C. D.; Nair, P.; Nota, A.; Pellerin, A.; Prieto, J.; Regan, M. W.; Sabbi, E.; Schaerer, D.; Schiminovich, D.; Smith, L. J.; Thilker, D. A.; Tosi, M.; Van Dyk, S. D.; Walterbos, R. A.; Whitmore, B. C.; Wofford, A.

2014-01-01

46

The UVMag space project: UV and visible spectropolarimetry of massive stars  

NASA Astrophysics Data System (ADS)

UVMag is a medium-size space telescope equipped with a high-resolution spectropolarimetrer working in the UV and visible domains. It will be proposed to ESA for a future M mission. It will allow scientists to study all types of stars as well as e.g. exoplanets and the interstellar medium. It will be particularly useful for massive stars, since their spectral energy distribution peaks in the UV. UVMag will allow us to study massive stars and their circumstellar environment (in particular the stellar wind) spectroscopically in great details. Moreover, with UVMag's polarimetric capabilities we will be able, for the first time, to measure the magnetic field of massive stars simultaneously at the stellar surface and in the wind lines, i.e. to completely map their magnetosphere.

Neiner, Coralie; Neiner

2015-01-01

47

Stroemgren photometry of ZZ Ceti and other DA white dwarfs  

SciTech Connect

Stroemgren colors for a sample of 71 stars classified as DA white dwarfs are presented. Comparison with the recent model atmospheres of the Kiel group indicates that the average gravity of 63 stars of the sample is log g = 7.98 +- 0.31, with no indication of a dependence on the effective temperature. This is consistent with the theoretical expectation that white dwarfs evolve at constant gravity. Correlations between Stroemgren colors and Greenstein multichannel colors are also given, using 52 stars that have been observed in common in the two systems. These correlations are used to compare the data with a second set of model atmospheres computed by Shipman. Contrary to what has been suggested in the past, no fundamental differences are found when confronting the Stroemgren data with the DA model atmospheres of Shipman or those of the Kiel group. Finally, observations of 11 pulsating objects reveal the existence of a narrow instability strip in the range 13 000 K> or approx. =T/sub e/> or approx. =11 000 K in a ((u-b), (b-y)) two-color diagram. The present results add evidence to the contention that all DA white dwarfs evolve to become ZZ Ceti pulsators in the instability strip.

Fontaine, G.; Bergeron, P.; Lacombe, P.; Lamontagne, R.; Talon, A.

1985-06-01

48

Constraining Models of Evolved UV-Bright Stars in the M31 Bulge  

NASA Astrophysics Data System (ADS)

We aim to use HST observations of M31 to generate the definitive data set for modeling the population of the UV-bright stars that contribute to the UV flux in old stellar populations (i.e., the "UV excess" seen in some elliptical galaxies and spiral bulges).We propose to place stringent observational constraints on the post-AGB (P-AGB) and post-early AGB (PE-AGB) phases of stellar evolution using a UV survey of M31's bulge. M31 is a critical laboratory for testing these models, as it hosts an old, metal-rich stellar population with high stellar densities such that even rare evolutionary phases are well-represented.We will (1) assemble a catalog of UV-bright stars in the center of M31 in F336W and F225W, extending out to ~0.7 kpc, to sample stellar populations with different metallicities; and (2) image a smaller 0.9 sqr-arcmin strip with ACS/SBC in F140LP, to image the regions with the highest density of rapidly-evolving P-AGB stars. The FUV imaging will allow us to separate the P-AGB from the PE-AGB. These observations will include thousands of UV-bright stars, increasing the size of existing samples by orders of magnitude.These new observations will drive revisions in models for post-HB evolution, which we will merge into new isochrone libraries and stellar population synthesis codes. The revisions will have important implications for AGB evolution, spectral evolution models of galaxies, and for mass loss on the RGB. The observations will also have a direct impact on interpreting (1) the UV flux from old stellar populations; (2) the emission line flux from M31's nuclear spiral; and (3) models of dust heating by old stellar populations.

Rosenfield, Philip

2014-10-01

49

Simultaneous UV and optical study of O star winds and UV and optical covariability of O star winds  

NASA Technical Reports Server (NTRS)

Simultaneous ultraviolet and optical observations of 10 bright O stars were organized in several observing campaigns lasting 3-6 days each. The observing campaigns included 12 observatories in the Northern hemisphere obtaining high resolution spectroscopy, photometry, and polarimetry, as well as 24-hour coverage with the IUE (International Ultraviolet Explorer) observatory. Over 600 high dispersion SWP spectra were acquired with IUE at both NASA and VILSPA for the completion of this work. The massive amount of data from these observing campaigns, both from IUE and the ground-based instruments, has been reduced and analyzed. The accompanying paper describes the data acquisition, analysis, and conclusions of the study performed. The most important results of this study are the strong confirmation of the ubiquitous variability of winds of O stars, and the critical correlation between rotation of the star and the wind variability as seen in the ultraviolet and optical spectral lines.

Nichols, Joy S.

1995-01-01

50

Interstellar C_2 Molecule Detected in UV Spectra of Reddened Stars  

E-print Network

$C_2$ molecule is sometimes considered as a crucial component of carriers of some diffuse interstellar bands. Using UV data achieved by spectrometer STIS fed with HST we detected interstellar $C_2$ lines for few reddened target stars. We tried to verify the idea that intensity of $C_2$ lines around 2313 \\AA is correlated with some diffuse interstellar bands.

M. Dyrka; B. Wszolek

2007-12-10

51

Heavy-elements in metal-poor stars: an UV perspective  

NASA Astrophysics Data System (ADS)

The site(s) of the r-process(es) is(are) not completely defined, and several models have been proposed. Observed abundances are the best clues to bring some light to this field, especially the study of the extremely metal-poor (EMP) Galactic halo stars. Many elements can be measured using ground-based facilities already available, but the ultraviolet window also presents a rich opportunity in terms of chemical abundances of heavy elements. In fact, for some elements only the UV transitions are strong enough to be useful. Focusing on the project of the Cassegrain U-Band Brazilian Spectrograph (CUBES), we discuss the science case for heavy elements in metal-poor stars, describing the useful lines of trans-Fe elements present in the UV region. Lines in the far UV are also discussed.

Siqueira-Mello, C.; Barbuy, B.

2014-11-01

52

Surface Abundance Patterns in A-Type Stars from UV Spectral Synthesis  

NASA Astrophysics Data System (ADS)

In this poster, we present results from a program whose goals are to (1) examine the degree to which current LTE atmosphere models can reproduce the complex UV spectra (1200-3200 A) of the A-type stars; in order to (2) develop better estimates of the physical properties, including composition, for specific target stars with available archival UV data; and (3) examine the abundance patterns revealed from a large group of normal and peculiar A-type stars to gain insight into the processes driving the compositional anomalies often observed in this spectral domain. We use the ATLAS9 atmospheric structure models from R.L. Kurucz, the spectral synthesis program SPECTRUM from R. Gray, and a new atomic line list developed from data in the VALD and NIST archives. For most of the stars, the data are high-dispersion spectrophotometry from the IUE satellite, although in several cases very high quality HST spectroscopy from GHRS and STIS are available. In addition to measurements of effective temperature, surface gravity, mictrotubulence velocity, and rotational velocity, we are also able to determine abundances for over 30 elements per star, including CNO, the light metals, the Fe group, and a number of heavy elements. We illustrate the striking abundance patterns for a number of stars, including members of the Am and HgMn classes, along with several ``normal'’ and ``superficially normal'’ stars. This research has been supported by NASA Astrophysics Data Program grant NX08AJ62G.

Fitzpatrick, Edward L.

2011-05-01

53

GHRS Profiles of Hot UV Lines in T Tauri Stars  

NASA Astrophysics Data System (ADS)

We present the first good line profiles of ``transition region'' lines in ``typical'' T Tauri stars. In particular, we discuss the C IV and Si IV doublets at 1400 Angstroms and 1550 Angstroms for BP Tau, DF Tau, DR Tau, and RW Aur. These line profiles were obtained with the GHRS on HST, and they are supplemented with concurrent observations of the Mg II doublet at 2800 Angstroms and various optical lines such as H? , H? , the Ca II infrared triplet, Na D, and He I at 5876 Angstroms. The C IV emission profiles have broad wings indicative of high velocity gas (+/-200 km/s). For DR Tau and RW Aur the velocity structure seen in C IV is similar to that seen in H? and Mg II. Line flux ratios imply that the gas is close to optically thin in the C IV lines. In addition, blueshifted absorption may be present in 3 of the 4 stars. The Si IV profiles are narrower than the C IV profiles, but still broader than expected from a classical transition region. There is also evidence of a ``stellar'' (very narrow) component in several of the profiles. This is particularly striking for RW Aur, where the weaker line has a distinct narrow core, while the stronger line is broad and has a flat top. Furthermore, the broad (500 km/s) Si IV emission in RW Aur is significantly redshifted. In each of the stars, the Mg II profile looks very similar to the H? profile, and C IV and Ca II bear an intriguing relation to each other. We do not claim to fully understand these profiles yet, but it is obvious that they are primarily formed outside the stellar atmosphere.

Valenti, J. A.; Basri, G.; Walter, F.; Hartmann, L.; Calvet, N.

1993-12-01

54

Extreme Carbon Overabundance in the 49 Ceti Circumstellar Gas  

NASA Astrophysics Data System (ADS)

We present analysis of C and O absorption in high-resolution HST-STIS FUV spectra of the nearby A1V star 49 Ceti. This disk system is one of the few showing the dust properties of a debris disk, but harboring relatively abundant molecular gas more characteristic of a low-mass protoplanetary disk. Since the disk is nearly edge-on, the line-of-sight to the central star passes through the disk, permitting sensitive probes of the circumstellar gas with absorption spectroscopy.Our FUV spectra show many narrow circumstellar gas lines arising from several atomic species, including neutral carbon (a gas not seen in the local ISM) and neutral oxygen. We present an estimate of the total carbon column density in the line-of-sight gas and limits on the oxygen column density. Comparing the carbon abundance to a previous measurement of the line-of-sight iron abundance, we see that the carbon is extremely overabundant relative to the solar abundance. A similar overabundance is seen in the Beta Pic disk gas, where the carbon brakes other gases from being rapidly blown out by radiation pressure. The carbon in the 49 Cet gas may play a similar role.

Roberge, Aki; Welsh, Barry; Kamp, Inga; Weinberger, Alycia J.; Grady, Carol A.

2015-01-01

55

Star Formation and Dust Attenuation Properties in Galaxies from a Statistical UV-to-FIR Analysis  

E-print Network

We study two galaxy samples selected in ultraviolet (UV) and in far-infrared (FIR) for which the spectral energy distributions (SEDs) from the far UV (FUV) to the FIR are available. We compare the observed SEDs to modelled SEDs with several star formation histories (SFHs; decaying star formation rate plus burst) and attenuation laws (power law + 2175 Angstroem bump). The Bayesian method allows to estimate statistically the best parameters by comparing each observed SED to the full set of 82800 models. We reach the conclusion that the UV dust attenuation cannot be estimated correctly from an SED analysis if the FIR information is not used. The deduced dispersion is larger than with the FIR data and the distribution is not symetrically distributed about zero: there is an over-estimation for UV-selected galaxies and an under-estimation for FIR-selected galaxies. The output from the analysis process suggests that UV-selected galaxies have attenuation laws in average similar to the LMC extinction while FIR-selected galaxy attenuation laws more resemble the MW extinction law. The dispersion about the average relation in the Log(Fdust/Ffuv) vs. FUV-NUV diagram (once the main relation with FUV-NUV is accounted for) is explained by two other parameters: the slope of the attenuation law and the instantaneous birthrate parameter b_0 for UV-selected galaxies and the same ones plus the strength of the bump for the FIR-selected galaxies. We propose a recipe to estimate the UV dust attenuation for UV-galaxies only (that should be used whenever the FIR information is not available because the resulting Afuv is poorly defined with an uncertainty of about 0.32): A_{FUV} = 1.4168 (FUV-NUV)^2 + 0.3298 (NUV-I)^2 + 2.1207 (FUV-NUV) + 2.7465 (NUV-I) + 5.8408

Denis Burgarella; Veronique Buat; Jorge Iglesias-Paramo

2005-04-20

56

UV Variability in Two Peculiar Emission Stars in the Magellanic Clouds  

NASA Astrophysics Data System (ADS)

The peculiar emission star SMC S-18 is characterized by a variety of spectral properties in the UV and optical that suggest high mass loss rates, turbulence from wide emission lines and indications of both high and low density material in the stellar neighborhood. S 18 is by far the most peculiar emission star studied in the Small Magellanic Cloud with IUE, because it exhibits significant temporal variations on timescales of months in high ionization emission lines of C IV 1548,1550 and He II 1640, and particularly N V 1245,1249. However, the UV emission line spectrum of SMC S-18 is strikingly similar to another recently observed peculiar star LMC " Anonymous" (Sanduleak's Star in the Large Magellanic Cloud). Sanduleak's star in the LMC appears deficient in carbon, while three stages nitrogen, together with doubly ionized Helium, dominate the far-UV 1200-2000 wavelength range. Strong N V 1239,1243 emission in contrast to the relatively weak C IV emission in LMC 5 "Anonymous" indicates that a highly ionized gas at approximately -10^5K gives rise to the chemically peculiar spectrum of the object, and suggests the presence of CNO processed material that is expected during advanced stages of evolution. We suspect that the emission line spectrum of Sanduleak's Star (in the LMC) is variable, since it is strikingly similar (based on the one IUE spectrum that exists of this object) to the UV emission line spectrum of SMC S18. We request IUE observing time in order to determine if the UV emission line spectrum of LMC "Anonymous" shares similar temporal variability as found for its counterpart in the SMC. If variability which is suggested from optical observations is confirmed in high excitation UV emission lines, the distinguishing characteristics of SMC S-18 and LMC "Anonymous" could indicate the existence of a highly evolved group of peculiar emission stars which are unique to the Magellanic Clouds, our observing program, justification and method of data analysis are discussed.

Michalitsianos, Andrew G.

57

Star Bursts in the UV Bright Interacting Galaxies NGC 3395 & 3396  

NASA Astrophysics Data System (ADS)

We have obtained ultraviolet and visible wavelength images for the interacting galaxies, NGC 3395 and 3396, using the Space Telescope Imaging Spectrograph on Hubble Space Telescope. IUE observations (Kinney et al. 1993) indicate that both of these galaxies have strong UV emission. Ground based spectra display evidence of extensive star formation. The visible images were obtained using the CCD detector and filter F28X50LP (central wavelength ~ 7230 Angstroms , FWHM ~ 1998 Angstroms). The ultraviolet images were obtained using the F25QTZ filter with the far-UV MAMA detector (central wavelength ~ 1595 Angstroms , FWHM ~ 206 Angstroms), and the F25CN182 filter with the near-UV MAMA detector (central wavelength ~ 2010 Angstroms, FWHM ~ 681 Angstroms). The data were reduced and analyzed using standard IRAF and STSDAS packages and customized software routines. This work has been supported in part by NASA, under contract NAS5-31231. We will present luminosities, luminosity functions, sizes and colors for the UV bright star forming regions. Stellar populations and ages of these knots will be constrained by comparison with star burst models (Leitherer et al. 1999). We will discuss the dependence of the characteristics of the knots on position in the galaxies and the possible relationship to the tidal interaction.

Hancock, M.; Weistrop, D.; Nelson, C. H.

2000-05-01

58

Winds of metal-poor OB stars: Updates from HST-COS UV spectroscopy  

NASA Astrophysics Data System (ADS)

In the race to break the SMC frontier and reach metallicity conditions closer to the First Stars the information from UV spectroscopy is usually overlooked. New HST-COS observations of OB stars in the metal-poor galaxy IC1613, with oxygen content ~1/10 solar, have proved the important role of UV spectroscopy to characterize blue massive stars and their winds. The terminal velocities (??) and abundances derived from the dataset have shed new light on the problem of metal-poor massive stars with strong winds. Furthermore, our results question the ??-? esc and ??-Z scaling relations whose use in optical-only studies may introduce large uncertainties in the derived mass loss rates and wind-momenta. Finally, our results indicate that the detailed abundance pattern of each star may have a non-negligible impact on its wind properties, and scaling these as a function of one single metallicity parameter is probably too coarse an approximation. Considering, for instance, that the [?/Fe] ratio evolves with the star formation history of each galaxy, we may be in need of updating all our wind recipes.

García, M.; Herrero, A.; Najarro, F.; Lennon, D. J.; Urbaneja, M. A.

2015-01-01

59

A Comparison of UV and H? Star Formation Rates In Intermediate Redshift Galaxies  

NASA Astrophysics Data System (ADS)

We present results of a study which directly compares star formation rates (SFRs) based on two commonly used indicators, the UV non-ionizing continuum and H-alpha nebular emission, for star-forming galaxies at z 0.8. Using UV data from the GALEX ultra-deep imaging survey in the Extended Groth Strip (EGS), Hubble Deep Field North (HDFN), and COSMOS fields, we construct a PSF-based UV flux catalog, which effectively deals with object blending. In the EGS and HDFN regions, we extract H-alpha fluxes from new near-IR (NIR) narrowband imaging observations obtained with the PISCES NIR camera on the 2.3m Bok telescope on Kitt Peak. For the COSMOS field, H-alpha fluxes are extracted from new NIR narrowband imaging observations taken with the NEWFIRM NIR camera on the Kitt Peak 4m. From the rest-frame far-UV flux and UV slope, we calculate dust-corrected UV SFRs. We also calculate SFRs from H-alpha fluxes, corrected for 1 magnitude of extinction. For galaxies at z 0.8, we examine the correlation between dust-corrected UV and H-alpha SFRs, and compare with previous results at lower redshifts. Walton's research was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation through Scientific Program Order No. 3 (AST-0243875) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF, and The Observatories of the Carnegie Institute of Washington.

Walton, Josiah; Salim, S.; Lee, J.; Ly, C.; Finn, R.; Moore, C.; Dale, D.; McCarthy, D.; Kulesa, C.; Kennefick, J.

2009-01-01

60

UV spectra of T Tau stars from hubble space telescope  

NASA Astrophysics Data System (ADS)

HST/GHRS spectra of 5 classical T Tau stars (CTTSs) in the 1150-2800 spectral band were analyzed in detail for the first time. Profiles of optically thin Si III] 1892 and C III] 1909 lines in RU Lup and RY Tau spectra are asymmetric and have FWHM > 100 km s-1 which definitely excludes their origin in chromospheric regions. It appeared possible to reproduce observed profiles in the framework of an accretion shock model. A flare-like event was detected in the case of RY Tau accompanied with a redshift of CIV 1550 and He II 1640 line profiles. A number of strong lines of molecular hydrogen were found: they originated in CTTS circumstellar envelopes and L quanta pumped by accretion shock. CTTSs L luminosity can reach 10% of the observed bolometric luminosity. It is shown that Fe II absorption lines originating in CTTS stellar wind along with H2 emission lines can significantly disturb profiles of C IV 1550 and Si IV 1400 lines. We also found Fe II fluorescent emission lines in RW Aur and BP Tau spectra originating in stellar wind and also pumped by L.

Lamzin, S. A.

2001-08-01

61

The Dearth of UV-bright Stars in M32: Implications for Stellar Evolution Theory  

NASA Technical Reports Server (NTRS)

Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained deep far ultraviolet images of the compact elliptical galaxy M32. When combined with earlier near-ultraviolet images of the same field, these data enable the construction of an ultraviolet color-magnitude diagram of the hot horizontal branch (HB) population and other hot stars in late phases of stellar evolution. We find few post-asymptotic giant branch (PAGB) stars in the galaxy, implying that these stars either cross the HR diagram more rapidly than expected, and/or that they spend a significant fraction of their time enshrouded in circumstellar material. The predicted luminosity gap between the hot HB and its AGB-Manque (AGBM) progeny is less pronounced than expected, especially when compared to evolutionary tracks with enhanced helium abundances, implying that the presence of hot HB stars in this metal-rich population is not due to (Delta)Y/(Delta)Z greater than or approx. 4. Only a small fraction (approx. 2%) of the HB population is hot enough to produce significant UV emission, yet most of the W emission in this galaxy comes from the hot HB and AGBM stars, implying that PAGB stars are not a significant source of W emission even in those elliptical galaxies with a weak W excess. Subject headings: galaxies: evolution - galaxies: stellar content - galaxies: individual (M32) - stars: evolution - stars: horizontal branch

Sweigart, Allen V.; Kimble, Randy A.; Bowers, Charles W.

2008-01-01

62

Is the SDSS ZZ Ceti instability strip really pure?  

NASA Astrophysics Data System (ADS)

We propose to obtain SNR > 60 optical spectra of the DA white dwarf stars for which the Sloan Digital Sky Survey spectra indicated temperatures inside de ZZ Ceti instability strip, but time series photometry show they are not variables. The Sloan spectra have insufficient SNR, specially below 4000A, where there are hydrogen lines whose strength can be used to measure surface gravity accurately. Theoretically and observationally, the location of the instability strip depends both on temperature and mass. To use the properties derived from the pulsating stars as applying to all white dwarf stars, and their progenitors, we must demonstrate pulsation is a normal evolutionary state. As the instability strip is only 1200K wide, accurate temperatures and log g must be obtained and therefore the spectra must include the log g sensitive lines Hgamma to H9. White dwarf stars, the objects of this proposal, are the end point of evolution of around 97% of all stars born. As they cool, they pass through instability strips, where they are seen as multi-periodic pulsators. Each pulsation is an independent measurement, placing another constraint on the stellar properties. Pulsations allow the determination of the stellar compositional layers, including the core, crucial to understand the progenitor's evolution, from AGB to planetary nebulae nuclei, "born again" phase, and their possible evolution to SNIa through accretion. As white dwarf progenitors lose at least half of their masses before turning into white dwarfs, they contribute to the interstellar medium enrichment, and measuring their structure in detail will allow us to decode nuclear reaction rates and convection, which determine their evolution. Pulsating white dwarf stars are also laboratories for physics at high densities as crystallization, neutrino cooling, and axion emission. White dwarf cooling, also measured through pulsations, allows an independent measurement of the age of the galactic components and was the first to indicate an age of 13 Gyr to the Universe, back in 1987. Now that we have observed white dwarf stars in all the components of our galaxy, possible differences in component ages are detectable. Our goal is to determine if the instalibity strip is pure, implying the information we obtain on the variables applies to white dwarf stars in general. As these stars are on average fainter than g=18.2, we require blue sensitive 8m class telescope.

de Souza Oliveira, Kepler

2006-08-01

63

The Intrinsic EUV, Lyman-alpha, and UV Emission from Exoplanet Host Stars  

NASA Astrophysics Data System (ADS)

The chemical composition and mass loss from exoplanet atmospheres is driven largely by the ultraviolet and extreme ultraviolet (EUV) radiation from their host stars. In particular, such important molecules as H2O, CO2, and CH4 are photodissociated primarily by radiation in the Lyman-alpha line, and planetary exospheres are heated primarily by EUV radiation from the host star, producing expansion and mass loss. Unfortunately, most of the host star radiation in the Lyman-alpha line is removed by hydrogen in the interstellar medium, and the EUV emission between 400 and 912 Angstroms is absorbed by interstellar hydrogen. We have developed a variety of techniques for inferring the intrinsic Lyman-alpha and EUV emission from main sequence stars with spectral types F5 to M5. We find that the ratios of the EUV flux to Lyman-alpha and the Lyman-alpha flux to other emission lines are relatively insensitive to spectral type and activity. We therefore propose formulae for estimating the intrinsic emission from exoplanet host stars. We present results from our HST observing program MUSCLES that provides near-UV and far-UV spectra of M dwarf exoplanet host stars. We also present a preliminary non-LTE chromosphere model for an M dwarf host star. This combination of HST spectra, host star models, and estimated intrinsic Lyman-alpha and EUV emission provides essential input for the computation of photochemical models of exoplanet atmospheres. This work is supported by the Space Telescope Science Institute and NASA grants.

Linsky, Jeffrey; France, K.; Fontenla, J.

2014-01-01

64

UV spectroscopy as main diagnostic access to hot-star winds  

NASA Astrophysics Data System (ADS)

Winds from hot stars are best explored with spectroscopy in the UV, where the resonance lines from abundant ions may show up with P Cygni profiles. Massive stars possess strong winds during their whole lifetime from the main sequence to supernova explosion. Low mass stars become sufficiently hot only in the late stage of their evolution, and can develop strong winds during the phase of central stars of planetary nebulae. The fundamental stellar and wind parameters can be determined from careful spectroscopic analysis, with help of sophisticated atmosphere models, such as our Potsdam Wolf-Rayet (PoWR) code for expanding atmosphere in non-LTE. The inferred chemical abundances of evolved stars allow to test stellar evolutionary models. A current question concerns the effect of wind inhomogeneities, the so-called micro- and macro-clumping, on the empirical mass-loss rate diagnostics. The true mass-loss rates are an important input for modeling the stellar evolution, feedback, and the understanding of the chemical galactic evolution. This whole field of research crucially depends on the availability of UV instruments. With the foreseeable end of HST, a new mission is urgently needed.

Hamann, Wolf-Rainer; Oskinova, Lidia

65

Stellar Parameters of Wolf-Rayet Stars from Far-UV to Mid-IR Observations  

E-print Network

Recent results for Galactic and Magellanic Cloud Wolf-Rayet stars are summarised based on line blanketed, clumped model atmospheres together with UV, optical and IR spectroscopy. The trend towards earlier WN and WC spectral types with decreasing metallicity is explained via the sensitivity of classification diagnostics to abundance/wind density, such that WR mass-loss rates are metallicity dependent. Pre-supernovae masses for WC stars are determined, in reasonable agreement with CO-cores of recent Type-Ic SN.

Paul A Crowther

2002-07-26

66

The optical/UV excess of isolated neutron stars in the RCS model  

E-print Network

The X-ray dim isolated neutron stars (XDINSs) are peculiar pulsar-like objects, characterized by their very well Planck-like spectrum. In studying their spectral energy distributions, the optical/UV excess is a long standing problem. Recently, Kaplan et al. (2011) have measured the optical/UV excess for all seven sources, which is understandable in the resonant cyclotron scattering (RCS) model previously adressed. The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources . The flat spectrum of RX J2143.0+0654 may due to contribution from bremsstrahlung emission of the electron system in addition to the RCS process.

Tong, H; Song, L M

2011-01-01

67

Resolving the Dusty Debris Disk of 49 Ceti  

NASA Astrophysics Data System (ADS)

Understanding the dispersal of primordial gas and dust from circumstellar disks is necessary for determining the timeline for giant planet formation. While the current assumption is that the gas and dust evolve simultaneously, there are a few systems that defy this paradigm. The nearby A star 49 Ceti, at a distance of 61 pc, hosts one of only a few known circumstellar disks that exhibits the dust qualities of an older debris disk but still displays a substantial mass of molecular gas, a characteristic normally associated with youth. We present Atacama Large Millimeter/Submillimeter Array (ALMA) observations at 850?m and a spatial resolution of 0.47x0.39 arcsec that resolve emission from the dust disk for the first time. To investigate the properties of the dust grains and the morphology of the disk, we simultaneously model the high-resolution ALMA data and the unresolved spectral energy distribution (SED). The detected emission reveals a disk that extends from 1.16±0.12AU to 286±7AU with an increase in surface density at 113±2AU that is viewed at an inclination of 79.6±.4°. The increase in surface density corresponds to the inner radius of the gas disk, hinting that similar mechanisms may be responsible for sculpting the gas and dust disks at this late stage of disk evolution.

Lieman-Sifry, Jesse; Hughes, A. Meredith

2015-01-01

68

Cross-Correlation Analysis of UV Profile Variations and Nonradial Pulsations in Be Stars  

NASA Technical Reports Server (NTRS)

This study is an investigation of the role of photospheric nonradial pulsations in the mass loss processes of Be stars. Some 18 Be stars were the focus of intensive, multi-wavelength campaigns between 1985 and 1996 with the NASA/ESA International Ultraviolet Explorer Satellite (IUE) . The campaigns were designed to monitor variations in the UV flux and stellar wind lines with near simultaneous, high signal-to-noise, optical spectroscopy of photospheric lines. The high quality, ground-based spectra were required to record the subtle, blue-to-red moving bump patterns in spectral line profiles that result from nonradial pulsations. We found that the same fine variations in the UV photospheric lines can be extracted from noisy IUE spectra by cross-correlating each target spectrum with a narrow-lined standard spectrum. Time series analyses of the cross-correlation functions then reveal the periodic signals, amplitudes, phases, and modal identifications of the pulsations. Our goals are to compare such results from UV and optical time series in order to model the stellar photospheric temperature and velocity fluctuations, and to search for correlated UV wind line variations to determine whether there is a connection between pulsation and mass loss.

Gies, Douglas R.

2001-01-01

69

Characterizing Extragalactic Star Formation with GALEX Legacy Photometric Analysis of UV-Bright Stellar Complexes  

NASA Astrophysics Data System (ADS)

At the close of nearly a decade of observing, GALEX has accumulated an unprecedented archive of ultraviolet (UV) images revealing both the scope and intricacy of star formation (SF) in many thousands of galaxies inhabiting the local universe. If the observed hierarchical SF morphology can be quantified systematically, and physically interpreted with multi-wavelength ancillary data and modeling, then the low redshift GALEX legacy will approach completion. However, the GALEX GR6 pipeline database contains a highly incomplete census of young stellar complexes even for very well-studied galaxies. We propose to apply a dedicated photometry algorithm that has been optimized for measuring the properties of irregularly shaped sources in crowded galaxy images containing spatially variant, diffuse intra-clump emission. Structures will be selected in the UV, but we will compile UV-visible-MIR SEDs for each detection utilizing Pan-STARRS1+SDSS and WISE data. These SEDs will then be fit using population-synthesis models to derive estimated stellar mass, age, and extinction. Processing will be completed for the entire diameter-limited GALEX Large Galaxy Atlas (GLGA) sample of 20,000+ galaxies, at a variety of standardized spatial resolutions. Although the precise categorization of the cataloged substructures will depend on galaxy distance, the outcome of our analysis will be a catalog similar to the stellar association surveys of past decades for very nearby galaxies based on resolved stars (e.g. van den Bergh 1964, Hodge 1986, Efremov et al. 1987), except that our investigation will probe a galaxy sample of dramatically larger size using the integrated UV light from such groupings of young stars. Our algorithm is multi-scale in nature and will thus preserve the hierarchical properties of the stellar distribution, by linking sub-clumps to their larger-scale parent feature(s). The resulting database will be a fundamental resource for follow-up multi-wavelength studies probing SF-driven galaxy evolution using both existing NASA databases and operating instruments, in addition to upcoming space telescopes. While a legacy of our project will be the hierarchical photometric database (disseminated via MAST and NED) which supports extragalactic community science, our own goals from the proposed comprehensive measurements address some vital issues: (i) Currently there is controversy regarding the power-law slope of the empirical star formation law (SFL). Is there constant star formation efficiency above the HI-to-H_2 transition gas surface density (implying ~unity slope, see papers by Bigiel et al. and Leroy et al.), or is the SFL relation a stronger function of gas density with a super-linear form (as observed by Kennicutt et al. 2007)? Liu et al. (2011) have shown that the answer may depend critically on whether or not diffuse emission underlying star-forming substructures is removed. Our analysis will allow firm resolution of this issue, as we will also apply our photometry algorithm to Spitzer imaging for a subset of our sample galaxies, thus providing background-subtracted L(UV) and L(IR) measurements for substructures which can then be compared to existing and forthcoming (ALMA) CO imaging. (ii) We will also verify/calibrate our SED-fit based determination of age, extinction, and mass for UV-bright structures via direct comparison to the ground-truth stemming from resolved stellar populations (e.g. in ANGST galaxies) and also high-resolution HST UV-optical star cluster surveys (further out in the Local Volume). (iii) Finally, we will measure the diffuse UV fraction in a few hundred of the nearest galaxies (accounting for variation tied only to spatial resolution), trying to ascertain the characteristic fraction in galaxies of different Hubble type and dust-to-gas ratio. Systematic local variations in diffuse fraction and color will also be quantified as a function of environment.

Thilker, David

70

Peculiarities of the UV Continuum Energy Distribution for T Tauri Stars  

NASA Astrophysics Data System (ADS)

In the UV spectra of BP Tau, GW Ori, T Tau, and RY Tau obtained with the Hubble Space Telescope, we detected an inflection near 2000 Angstrems in the F^clambda(lambda) curve that describes the continuum energy distribution. The inflection probably stems from the fact that the UV continuum in these stars consists of two components: the emission from an optically thick gas with T < 8000 K and the emission from a gas with a much higher temperature. The total luminosity of the hot component is much lower than that of the cool component, but the hot-gas radiation dominates at lambda < 1800 Angstrems. Previously, other authors have drawn a similar conclusion for several young stars from low-resolution IUE spectra. However, we show that the short-wavelength continuum is determined from these spectra with large errors. We also show that, for three of the stars studied (BP Tau, GW Ori, and T Tau), the accretion-shock radiation cannot account for the observed dependence F^clambda(lambda) in the ultraviolet. We argue that more than 90% of the emission continuum in BP Tau at lambda > 2000 Angstrems originates not in the accretion shock but in the inner accretion disk. Previously, a similar conclusion was reached for six more classical T Tau stars. Therefore, we believe that the high-temperature continuum can be associated with the radiation from the disk chromosphere. However, it may well be that the stellar chromosphere is its source.

Kravtsova, A. S.; Lamzin, S. A.

2003-09-01

71

Molecular gas properties of UV-bright star-forming galaxies at low redshift  

NASA Astrophysics Data System (ADS)

Lyman break analogues (LBAs) are a population of star-forming galaxies at low redshift (z ˜ 0.2) selected in the ultraviolet (UV). These objects present higher star formation rates and lower dust extinction than other galaxies with similar masses and luminosities in the local universe. In this work, we present results from a survey with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) array to detect CO(1-0) emission in LBAs, in order to analyse the properties of the molecular gas in these galaxies. Our results show that LBAs follow the same Schmidt-Kennicutt law as local galaxies. On the other hand, they have higher gas fractions (up to 66 per cent) and faster gas depletion time-scales (below 1 Gyr). These characteristics render these objects more akin to high-redshift star-forming galaxies. We conclude that LBAs are a great nearby laboratory for studying the cold interstellar medium in low-metallicity, UV-bright compact star-forming galaxies.

Gonçalves, Thiago S.; Basu-Zych, Antara; Overzier, Roderik A.; Pérez, Laura; Martin, D. Christopher

2014-08-01

72

Does UV CETI Suffer from the MAD Syndrome?  

NASA Technical Reports Server (NTRS)

Data have been reduced and partially analyzed and models have been fitted. ASCA data indicate a metal-poor corona, with metals down by a factor of 3 or more relative to the photospheric values. EUVE data show a FIP effect, which is expected if the metals are enhanced rather than depleted. An absolute measure of the metal abundance has not yet been performed for the EUVE data. Either the FIP effect is in operation in the presence of a global depletion of metals, or the ASCA analysis is giving the wrong answer. The latter could be the case if the plasma models applied are incomplete. Further investigation into this is warranted prior to publication.

Drake, Jeremy

2000-01-01

73

Does UV CETI Suffer from the MAD Syndrome?  

NASA Technical Reports Server (NTRS)

Photometric data have been analysed and searched for events of flaring and other variability. Some flaring has been detected, though probably not at a level that will hinder our continuing spectral analysis. X-ray diagnostics for the very hot coronal emission measure are under investigation in order to determine whether or not the very hot coronal plasma contributes significantly to the observed X-ray flux in the EUV. The key test of the MAD syndrome lies in whether or not the coronal lines indicate a depletion in met- als in the corona relative to the underlying photosphere. While some progress has been made in this direction, not as much work has been accomplished as expected due to the increasing commitments of the PI to the CXO project as it nears launch. A no-cost extension has been granted in order to further the analysis and carry out the next stages of the investigation: to construct an emission measure distribution with which to compute a synthetic continuum to compare with the observed continuum.

Drake, Jeremy

1999-01-01

74

Does UV CETI Suffer from the Mad Syndrome?  

NASA Technical Reports Server (NTRS)

Photometric data have been analyzed and searched for events of flaring and other variability. Some flaring has been detected, though probably not at a level that will hinder our continuing spectral analysis. X-ray diagnostics for the very hot coronal emission measure are under investigation in order to determine whether or not the very hot coronal plasma contributes significantly to the observed X-ray flux in the (EUV) Extreme Ultraviolet Radiation. The key test of the MAD syndrome lies in whether or not the coronal lines indicate a depletion in metals in the corona relative to the underlying photosphere.

Drake, Jeremy

1999-01-01

75

Spectroscopic diagnostics of UV power and accretion in T Tauri stars  

NASA Astrophysics Data System (ADS)

It is known that in the upper atmospheres of the Sun and some late-type stars there is a systematic relationship between the optically thin total radiated power and the power emitted by single spectral lines. Using recently derived emission-measure distributions from IUE spectra for BP Tau, CV Cha, RY Tau, RU Lupi and GW Ori, we demonstrate that this is also true for classical T Tauri stars (CTTSs). As in the solar case it is found that the CIV resonance doublet at 1548 Å is also the most accurate indicator of the total radiated power from the atmospheres of CTTSs. Since the total radiated-power density in CTTSs exceeds that of the Sun by over three orders of magnitude we derive new analytic expressions that can be used to estimate the values for these stars. We also discuss the implications of these results with regard to the influence or absence of accretion in this sample of stars and suggest that the method can be used to infer properties of the geometrical structure of the emission regions. As a demonstration case we also use archived HST-GHRS data to estimate the total radiative losses in the UV emitting region of BP Tau. We find values of 4.57 × 109 erg cm-2 s-1 and 5.11 × 1032 erg s-1 dependent on the geometry of the emission region. These results are several orders of magnitude larger than would be expected if the UV emission came primarily from an atmosphere covered in solar-like active regions and are closer to values associated with solar flares. They lead to luminosity estimates of 0.07 and 0.13 Lsolar, respectively, which are in broad agreement with results obtained from theoretical accretion shock models. Taken together they suggest that accretion may well be the dominant contributor to the UV emission in BP Tau.

Brooks, D. H.; Costa, V. M.

2003-02-01

76

DK UMa: A Star on the Ascent  

NASA Technical Reports Server (NTRS)

DK UMa (= 24 UMa = HD 82210) is a G4 IV-III star. According to its M(sub v) and B - V color, it is located at the base of the red giant branch, having recently exited from the Hertzsprung Gap. Now poised to start its first ascent along the giant branch, DK UMa is at a significant juncture in its post-main-sequence evolution, offering an important evolutionary comparison for magnetic activity with stars like 31 Comae, which is just entering the Hertzsprung Gap, and older stars like the Hyades giants or P Ceti, which have passed the tip of the giant branch and lie in the so-called 'clump'. As part of a major survey of the ultraviolet and X ray properties of a well-defined sample of evolved giant stars, DK UMa was observed with the Extreme Ultraviolet Explorer (EUVE) spacecraft in March 1997, for a total exposure time of 230 kiloseconds. A plot of the extracted short-wavelength (SW) spectrum of this star is shown, where it is compared with similar EUVE exposures for other yellow and red giant stars in the activity survey. In terms of the spectral lines of different ionization stages present in these spectra, the transition region and coronal temperature of DK UMa appears to be intermediate between those of 31 Com and P Ceti. Combining the relative strengths of the EUVE lines with Hubble Space Telescope (HST) data at near UV wavelengths and with ROSAT X-ray fluxes, the differential emission measure (DEM) distributions of these stars form a sequence in coronal temperature, which peaks at 10(exp 7.2) K for 31 Com, at 10(exp 6.8) K for B Ceti, and at intermediate temperatures for DK UMa - consistent with the evolutionary stages represented by the three stars. The integrated fluxes of the strongest emission lines found in the EUVE spectrum of DK UMa are listed, again compared with similar measurements for other giant stars that were observed in the course of other EUVE Guest Observer programs.

Simon, Theodore

1999-01-01

77

Correlation of MgII(h+k) UV Resonance Lines and Rotational Period in G-type Stars  

NASA Astrophysics Data System (ADS)

We present preliminary results of an investigation aimed at establishing the correlation between the mid-UV MgII h and k lines and the rotational period of G-Type stars. We collected the high resolution spectra of a small sample of stars extracted from the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST) archives. The far more intense MgII lines with respect to CaII appear well correlated with rotational period, showing very little scatter. These UV features seems to be a promising tool for dating stars on the main sequence.

Olmedo, M.; Chávez, M.; Bertone, E.

2013-04-01

78

Sizing Up Dwarf Galaxies at z > 1: UV Colors, Stellar Masses and Star Formation Rates  

NASA Astrophysics Data System (ADS)

Deep HST imaging allows the detection and study of dwarf galaxies at z > 1. Our recent multiwavelength analyses of continuum and Ly-alpha selected galaxies in the Hubble UltraDeep Field (HUDF) and CANDELS fields reveals a diversity of physical properties. We show that these galaxies are on the whole bluer than comparable luminosity galaxies in the local universe, although they are as diverse in their UV colors as local dwarf galaxies. On the SFR-M* diagram, Ly-alpha selected galaxies fall above the main sequence, implying bursty star formation. In this presentation, we illustrate that low luminosity continuum selected galaxies appear to lie on the main sequence, suggesting a more quiescent evolution. The systematic study of low luminosity galaxies spanning the epoch of peak cosmic star formation will elucidate the mechanisms of formation and evolution for the bulk of the present day galaxy population.

UVUDF Team

2015-01-01

79

HAZMAT II: Modeling the Evolution of Extreme-UV Radiation from M Stars  

NASA Astrophysics Data System (ADS)

M dwarf stars make up nearly 75% of the Milky Way's stellar population. Due to their low luminosities, the habitable zones around these stars are very close in (~0.1-0.4 AU), increasing the probability of finding terrestrial planets located in these regions. While there is evidence that stars emit their highest levels of far and near ultraviolet (FUV; NUV) radiation in the earliest stages of their evolution while planets are simultaneously forming and accumulating their atmospheres, we are currently unable to directly measure the extreme UV radiation (EUV). High levels of EUV radiation can alter the abundance of important molecules such as H2O, changing the chemistry in extrasolar planet atmospheres. Most previous stellar atmosphere models under-predict FUV and EUV emission from M dwarfs; here we present new models for M stars that include prescriptions for the hot, lowest density, atmospheric layers (chromosphere, transition region and corona), from which this radiation is emitted. By comparing our model spectra to GALEX near and far ultraviolet fluxes, we are able to predict the evolution of EUV radiation for M dwarfs from 10 Myr - 1 Gyr. This research is the next major step in the HAZMAT (HAbitable Zones and M dwarf Activity across Time) project to analyze how the habitable zone evolves with the evolving properties of stellar and planetary atmospheres.

Peacock, Sarah; Barman, Travis S.; Shkolnik, Evgenya

2015-01-01

80

HST UV Imaging of Brightest Cluster Galaxies in CLASH: AGN Feedback and Star Formation in the Universe's Most Massive Galaxies  

NASA Astrophysics Data System (ADS)

Rest-frame far-UV imaging of cluster galaxies typically don't show very much! But radio-bright Brightest Cluster Galaxies in cool-core X-ray clusters are often but not always also UV-excess sources, with UV luminosities exceeding that expected from an evolved stellar population. The UV excess is consistent with 1-10 solar masses per year of unattenuated, recently-formed stars. For a few of these BCGs, we have Spitzer photometry showing even higher obscured star formation rates, approaching 100 sols/yr. For "red and dead" galaxies, these are quite busy. The HST imagery show a rich diversity in UV morphologies: diffuse, clumpy, filaments, bars within the central 10 kpc. This star formation is the result of imperfect quenching of star formation by the central supermassive black hole in these galaxies. The connection between the dusty, star-forming gas and the hot intracluster gas is clear but the nature of the relationship is not.

Donahue, Megan; CLASH

2013-01-01

81

X-ray properties of UV-selected star forming galaxies at z~1 in the Hubble Deep Field North  

E-print Network

We present an analysis of the X-ray emission from a large sample of ultraviolet (UV) selected, star forming galaxies with 0.74UV and X-ray is expected to be predominantly due to star formation. Stacking the X-ray flux from 216 galaxies in the soft and hard bands produces significant detections. The derived mean 2-10 keV rest-frame luminosity is 2.97+/-0.26x10^(40) erg/s, corresponding to an X-ray derived star formation rate (SFR) of 6.0+/-0.6 Msolar/yr. Comparing the X-ray value with the mean UV derived SFR, uncorrected for attenuation, we find that the average UV attenuation correction factor is \\~3. By binning the galaxy sample according to UV magnitude and colour, correlations between UV and X-ray emission are also examined. We find a strong positive correlation between X-ray emission and rest-frame UV emission. A correlation between the ratio of X-ray-to-UV emission and UV colour is also seen, such that L(X)/L(UV) increases for redder galaxies. Given that X-ray emission offers a view of star formation regions that is relatively unaffected by extinction, results such as these can be used to evaluate the effects of dust on the UV emission from high-z galaxies. For instance we derive a relationship for estimating UV attenuation corrections as a function of colour excess. The observed relation is inconsistent with the Calzetti et al. (2000) reddening law which over predicts the range in UV attenuation corrections by a factor of ~100 for the UV selected z~1 galaxies in this sample (abridged).

E. S. Laird; K. Nandra; K. L. Adelberger; C. C. Steidel; N. A. Reddy

2005-01-19

82

UV diagnostic of porosity-free mass-loss estimates in B stars  

E-print Network

We seek to establish evidence in UV P Cygni line profiles that the signs of wind clumping and porosity vary with velocity. We aim to demonstrate empirically that while at most wind velocities optically thick clumps cover only a fraction of the stellar surface, close to the terminal velocity where narrow absorption components (NACs) appear in UV lines the covering factor is approximately unity. SEI line-synthesis models are used to determine the radial optical depths of blue and red components of the SiIV 1400 resonance line doublet in a sample of 12 B0 to B4 supergiants. We focus on stars with well developed NACs and relatively low terminal velocity so that the SiIV doublet components can be treated as radiatively decoupled and formed independently. For all 12 stars the mean optical depth ratio of the blue to red components is closer to ~ 2 (i.e. the ratio of oscillator strengths) in the NACs than at intermediate and lower velocities. The product of mass-loss rate and Si^3+ ion fraction calculated from the NA...

Prinja, Raman

2013-01-01

83

The Origin and Nature of UV Bright stars in Globular Clusters II  

NASA Astrophysics Data System (ADS)

We propose an investigation of the UV-bright stellar populations of NGC 1904, NGC 6254, and NGC 5904. These are Galactic globular clusters that are known to be bright at far-UV wavelengths, with the two known to possess extended blue HB tails. These observations will complement data obtained during Cycle 5 and during the UIT Astro-1 flight in December 1990. The object of this investigation is twofold: {a} to explore the relationship between the HB mass distribution in clusters with blue HB tails {BT clusters} to the clusters' structural and dynamical properties and {b} to gain further samples of blue straggler stars in the cores of such clusters. These observations will allow a probe of the variation in mass loss processes close to the tip of the red giant branch. The clusters have been selected as follows: NGC 1904 and NGC 6254 are similar in HB morphology to NGC 6205 for which we have scheduled Cycle 5 observations, and are both more centrally concentrated. In addition, UIT observations indicate a deficit of blue HB stars in the core of NGC1904. NGC 5904 has similar metallicity and concentration to both NGC 1904 & NGC 6254, and was observed by the ANS to be brighter in the far-UV than its optical HB morphology suggests. Our original target list contained also NGC 6266, which has a larger continuous range in HB colour than any other cluster, extending from the red to the blue extreme, and would have provided information about a cluster with high HB mass dispersion. However the exposure times that we derived in Phase 1 using the WFPC2 Exposure Time Calculator provided by the STScI resulted significantly underestimated because of an error in the ETC. As a result of that, we decided to drop NGC 6266, which is highly reddened and requires long exposure times, in order to obtain acceptably good photometric quality on the other 3 clusters.

Ferraro, Francesco

1996-07-01

84

Star formation rate in galaxies from UV, IR, and H-alpha estimators  

E-print Network

Infrared (IR) luminosity of galaxies originating from dust emission can be used as an indicator of the star formation rate (SFR). Inoue et al. (2000, IHK) have derived a formula for the conversion from IR luminosity to SFR by using the following three quantities: the fraction of Lyman continuum luminosity absorbed by gas (f), the fraction of UV luminosity absorbed by dust (epsilon), and the fraction of dust heating from old (>10^8 yr) stellar populations (eta). We develop a method to estimate those three quantities based on the idea that the various way of SFR estimates should return the same SFR. After applying our method to samples of galaxies, the following results are obtained. First, our method is applied to star-forming galaxies, finding that f~0.6, epsilon~0.5, and eta~0.4 as representative values. Next, we apply the method to a starburst sample, which shows larger extinction than the star-forming galaxy sample. With the aid of f, epsilon, and eta, we estimate reliable SFRs. Moreover, the H-alpha luminosity, if the H-alpha extinction is corrected by using the Balmer decrement, is suitable for a statistical analysis of SFR, because the same correction factor for the Lyman continuum extinction is applicable to both normal and starburst galaxies over all the range of SFR. The metallicity dependence of f and epsilon is also tested: Only the latter proves to have a correlation with metallicity. As an extension of our result, we show that all UV, H-alpha, and IR comoving luminosity densities at z=0 give a consistent SFR (~ 3x10^{-2}h M_sun/Mpc^3). Useful formulae for SFR estimate are listed.

Hiroyuki Hirashita; Veronique Buat; Akio K. Inoue

2003-08-29

85

Recent Optical and UV Emission Line Variability in the Symbiotic Star CH CYG  

NASA Astrophysics Data System (ADS)

The symbiotic star CH Cygni has shown abrupt changes in the emission profiles of H? , He I 5875 Angstroms, and the Na I D-lines. CCD echelle spectra obtained at Ritter Observatory between Jun. 30 and Oct. 4 1993 show a single strong emission line at H? , with an essentially constant profile. From Oct. 8 through Dec. 12 1993 additional ``emission'' components formed and faded on a time scale of days on the blue wing of H? at velocities from -45 to -275 km/s. Whether these components are truly emission lines or windows in an absorbing curtain is unclear. The blue wing and continuum, out to at least -500 km/s, were also variable while the red wing and continuum remained unchanged. On Oct. 8 the FWHM of the He I 5875 Angstroms emission line doubled and a P-Cyg absorption component abruptly formed at -200 km/s. The Na I D-lines were then seen in emission with P-Cyg structure developing over the next week. The width and strength of these P-Cyg absorption features were variable through Dec. 12. In addition an IUE high dispersion spectrum was obtained on Nov. 25 1993 showing similar P-Cyg structure in the Mg II h&k doublet and the Fe II UV multiplets. These UV emission lines show an increase in flux while the UV continuum indicates an increasingly optically thick shell phase when compared with spectra from May 1993. The optical and UV spectra will be presented and discussed.

Aufdenberg, J. P.; Gordon, K. D.; Bopp, B. W.

1994-05-01

86

Astroinformatics for the Flare Stars in Stellar Clusters and Associations  

NASA Astrophysics Data System (ADS)

Applying the subjects of Astroinformatics to the data concerning the photographic observations of the flare stars in stellar clusters and associations we aim to enable extracting unrevealed knowledge for this type of variable stars, as well as to re-use the accumulated observing material (photographic plates) already in digital form, supplying digital curation. The database for the detected photographically flare stars (UV Ceti type variability with designations in the General Catalogue of Variable Stars - UV and UVn) in stellar clusters and associations as the Pleiades, Orion M42/M43, Taurus Dark Clouds, Cygnus NGC 7000, Praesepe, NGC 2264, Cygnus IC 1318, Coma Open Cluster, Alpha Perseus Cluster, Scorpius-Ophiuchus, and others, is present. The metadata records for the flare stars and their registered flare-events is described, as well as the access, data mining, possibilities for information searches, and flare stars plate visualization. The automated flare stars search, started on the basis of scanned flare stars monitoring plates of the Rozhen Observatory obtained with the 50/70/172 cm Schmidt telescope in the period 1979 - 1995, is expected to increase the number of discovered flares compared to the visual inspection by a blink-comparator done before in the observatory.

Tsvetkova, K.

2012-01-01

87

Ten years of the international review meetings on Communication with Extraterrestrial Intelligence /CETI/  

NASA Technical Reports Server (NTRS)

The development of ideas on CETI within the international community over the past five years is reviewed, and the outlook for future CETI activities is discussed. The growth of review sessions on CETI held annually by the International Academy of Astronautics (IAA) is considered, with particular attention given to the issue of radio frequency allocation for the search for extraterrestrial intelligence. CETI activities outside the IAA are then examined, including the Viking search for life on Mars, Project Orion for the detection of extrasolar planetary systems, SETI programs undertaken in the U.S. and Soviet Union, and the development of multispectral spectrum analyzers and signal processors. The expected future development of CETI strategies, techniques and instrumentation as well as popular and scientific interest in SETI are discussed, and it is noted that the IAA sessions remain the only regular international forum for the exchange of data on all aspects of CETI.

Pesek, R.; Billingham, J.

1981-01-01

88

Star Formation in the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this Field on the star-forming interstellar medium. Following previous researchers such as Habing (1968), we calculate the average interstellar radiation field at the Solar Circle of the Galaxy. However, our new calculations follow more closely the time dependence of the field at any point. We show that there is a significant difference between the mean field and the median field, and that there are substantial fluctuations of the field (on timescales of order 100 million years) at a given point. Far Ultraviolet Radiation (FUV, photon energies of 6 eV - 13.6 eV) has been recognized as the main source of heating of the neutral interstellar gas. Given the pressure of the interstellar medium (ISM) the FUV field determines whether the thermal balance of the neutral gas results in cold (T approximately 50 - 100 K) clouds (CNM), warm (T about 10,000 K) (WNM), for a combination of the two (the two phase ISM) We present results for the time history of the FUV field for points in the local ISM of the Milky Way Galaxy. The presence of this fluctuating heating rate converts CNM to WNM and vice versa. We show how to calculate the average fractions of the gas in the CNM and WNM when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties (i.e. mean density and composition) and on the FUV-sources (i.e. the star formation rate, or the IMF, or the size distribution of associations) is a basic step in building any detailed model of the large scale behavior of the ISM and the mutual relation between the ISM and the SFR.

Hollenbach, David; Parravano, A.; McKee, C.; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

89

Living with an Old Red Dwarf: X-ray-UV Emissions of Kapteyn’s Star - Effects of X-UV radiation on Habitable Zone Planets hosted by old Red Dwarf Stars  

NASA Astrophysics Data System (ADS)

Red dwarfs (dM) stars make up over 75% of the local stellar population and a significant fraction (~40-50%) are older than the Sun. Because of the high frequency of red dwarfs and their longevity (> 50 Gyr), there is a greater possibility of more advanced life in red dwarf-exoplanet systems. MEarths, UVES, SDSS-III, and the upcoming TESS mission are some surveys that are targeting red dwarfs in the search for hosted potentially habitalble planets. As part of Villanova's 'Living with a Red Dwarf' program, we have obtained HST-COS Ultraviolet spectra (1150-3000A) and Chandra X-ray observations of Kapteyn's star (GJ 191; M1 V, V = 8.85 mag , d = 12.76 +/- 0.05 ly). Kapyteyn's Star is important for the study of old red dwarfs because it is the nearest (Pop II) halo star with a radial velocity of +245.2 km/s and an estimated age of 11.2 +/-0.9 Gyrs. Recently Kapteyn's Star was found to host two super-Earth mass planets - one of these is orbiting inside the star's Habitable Zone (Anglada-Escude' 2014: MNRAS 443, L89). In our program, Kapteyn's star is the oldest red dwarf and as such serves as an anchor for our age, rotation, and activity relations. The spectra obtained from HST/COS provide one of the cleanest measurements of the important HI Lyman-alpha 1215.6 A emission flux for red dwarfs. This is due to the large Doppler shift from the high radial velocity, separating the stellar Ly-alpha emission from by the Ly-alpha ISM and local geo-coronal sources. These observations further provide calibrations at the old age/low rotation/low activity extremes for our relations. As the nearest and brightest old red dwarf star, Kapteyn's Star also provides insights into its magnetic properties to investigae coronal x-ray and UV emission for the large population of old, slowly rotating red dwarf stars. Kapteyn's star also serves as a proxy for the numerous metal-poor old disk - Pop II M dwarfs by providing information about X-UV emissions. This information is crucial for determining X-ray-UV irradiances for habitable zone planets hosted by these old numerous, cool low luminosity stars.We gratefully acknowledge the support from NSF/RUI Grant AST-1009903, NASA/Chandra Grants GO2-13020X, and HST-GO-13020

Guinan, Edward F.; Durbin, Allyn J.; Engle, Scott G.

2015-01-01

90

The Pulsating White Dwarf Stars  

Microsoft Academic Search

We present a summary of what is currently known about the three distinct families of isolated pulsating white dwarfs. These are the GW Vir stars (He\\/C\\/O-atmosphere stars with Teff ~= 120,000 K), the V777 Her stars (He-atmosphere, Teff ~= 25,000 K), and the ZZ Ceti stars (H-atmosphere, Teff ~= 12,000 K), all showing multiperiodic luminosity variations caused by low-order and

G. Fontaine; P. Brassard

2008-01-01

91

UV to Mid-IR Observations of Star-forming Galaxies at z~2: Stellar Masses and Stellar Populations  

E-print Network

We present the broad-band UV through mid-infrared spectral energy distributions (SEDs) of a sample of 72 spectroscopically-confirmed star-forming galaxies at z=2.30+/-0.3. Located in a 72 arcmin-squared field centered on the bright background QSO, HS1700+643, these galaxies were pre-selected to lie at z~2 based solely on their rest-frame UV colors and luminosities, and should be representative of UV-selected samples at high redshift. In addition to deep ground-based photometry spanning from 0.35-2.15 microns, we make use of Spitzer/IRAC data, which probes the rest-frame near-IR at z~2. The range of stellar populations present in the sample is investigated with simple, single-component stellar population synthesis models. Emphasizing stellar mass estimates, which are less subject to systematic uncertainties than other parameters, we find =10.32+/-0.51 for the sample. Allowing for the possibility of episodic star formation, we find that typical galaxies in our sample could contain up to three times more stellar mass in an old underlying burst than what was inferred from single-component modeling. In contrast, mass estimates for the most massive galaxies in the sample (M*>10^11 Msun) are fairly insensitive to the method used to model the stellar population. Galaxies in this massive tail, which are also the oldest objects in the sample, could plausibly evolve into the passive galaxies discovered at z~1.7 with near-IR selection techniques. In the general framework of hierarchical galaxy formation and mergers, which implies episodic star-formation histories, galaxies at high redshift may pass in and out of UV-selected and near-IR color-selected samples as they evolve from phases of active star formation to quiescence and back again (Abridged).

Alice E. Shapley; Charles C. Steidel; Dawn K. Erb; Naveen A. Reddy; Kurt L. Adelberger; Max Pettini; Pauline Barmby; Jiasheng Huang

2005-03-22

92

UV spectral variability in the Herbig Ae star HR 5999. 11: The accretion interpretation  

NASA Technical Reports Server (NTRS)

We report recent IUE high- and low-dispersion observations with the IUE long wavelength camera (LWP) and short wavelength camera (SWP) of the Herbig Ae star HR 5999. We have found a dramatic change in the structure of the Mg II h and k lines (2795.5, 2802.7 A) along with some continuum flux excesses especially at the short end of the SWP camera. LWP high dispersion observations of HR 5999 obtained between 1979 and 1990, at times of comparatively low UV continuum fluxes, exhibit P Cygni type m profiles in the Mg II resonance doublet. In contrast, observations made from September 1990 through March 16-18, 1992, with high W continuum fluxes, present Mg II lines with reverse P Cygni profiles indicative of some active episodic accretion. Accreting gas can also be detected in the additional red wings of the various Fe II and Mn II absorption lines, with velocities up to +300-350 km/s (September 1990). By September 10, 1992 the Mg II profile had returned to the type III P Cygni profile similar to those from earlier spectra. The correlation between the presence of large column densities of accreting gas and the continuum light variations supports suggestions by several authors that HR 5999 is surrounded by an optically thick, viscously heated accretion disk. Detection of accreting gas in the line of sight to HR 5999 permits us to place constraints on our viewing geometry for this system. A discussion is included comparing the spectral and physical similarities between HR 5999 and the more evolved proto-planetary candidate system, beta Pictoris.

Perez, M. R.; Grady, C. A.; The, P. S.

1993-01-01

93

Far-UV Continuum as a Diagnostic for Temperature Structure in the Atmospheres of G-type Stars  

NASA Astrophysics Data System (ADS)

Investigations of IUE ultraviolet spectra of field G and K-type stars (Morossi et al. 1993, Morossi et al. 1998, Franchini et al. 1998a) showed that the spectral energy distributions (SED's) of cool stars present a significant excess in the UV with respect to the fluxes predicted by the atmosphere models characterized by a monotonic decrease of temperature. We combine HST, IUE and visual observations to construct accurate SED's to be used for deriving empirical estimate of the temperature distribution in the atmosphere of G-type stars. Template objects are used to compare pure LTE model predictions with those from semi-empirical structures designed for the solar case (Vernazza et al. 1981). Particular attention is devoted to the determination of the position of the temperature minimum layer by computing ``semi-empirical Tmin models'' (Morossi et al. 1993 and Franchini et al. 1998b).

Morossi, C.; Franchini, M.; Malagnini, M. L.; Chavez, M. A.

2003-10-01

94

VizieR Online Data Catalog: Far-UV spectral atlas of O-type stars (Smith, 2012)  

NASA Astrophysics Data System (ADS)

In this paper, we present a spectral atlas covering the wavelength interval 930-1188Å for O2-O9.5 stars using Far-Ultraviolet Spectroscopic Explorer archival data. The stars selected for the atlas were drawn from three populations: Galactic main-sequence (classes III-V) stars, supergiants, and main-sequence stars in the Magellanic Clouds, which have low metallicities. For several of these stars, we have prepared FITS files comprised of pairs of merged spectra for user access via the Multimission Archive at Space Telescope (MAST). We chose spectra from the first population with spectral types O4, O5, O6, O7, O8, and O9.5 and used them to compile tables and figures with identifications of all possible atmospheric and interstellar medium lines in the region 949-1188Å. Our identified line totals for these six representative spectra are 821 (500), 992 (663), 1077 (749), 1178 (847), 1359 (1001), and 1798 (1392) lines, respectively, where the numbers in parentheses are the totals of lines formed in the atmospheres, according to spectral synthesis models. The total number of unique atmospheric identifications for the six main-sequence O-star template spectra is 1792, whereas the number of atmospheric lines in common to these spectra is 300. The number of identified lines decreases toward earlier types (increasing effective temperature), while the percentages of "missed" features (unknown lines not predicted from our spectral syntheses) drop from a high of 8% at type B0.2, from our recently published B-star far-UV atlas (Cat. J/ApJS/186/175), to 1%-3% for type O spectra. The percentages of overpredicted lines are similar, despite their being much higher for B-star spectra. (4 data files).

Smith, M. A.

2012-10-01

95

Building up a database of spectro-photometric standard stars from the UV to the near-IR: a status report!  

E-print Network

Building up a database of spectro-photometric standard stars from the UV to the near-IR: a status. Currently no such set of standard stars covering the near-IR is available. Our strategy is to extend the useful range of existing well-established optical flux standards into the near-IR by means of integral

Liske, Jochen

96

The helium-to-hydrogen ratio of the UV-bright star Barnard 29 of Messier 13  

NASA Astrophysics Data System (ADS)

Barnard 29 is the most luminous UV-bright star of the globular cluster Messier 13. Comparison of its reddening corrected optical region spectrophotometry and IUE low dispersion fluxes and its H-gamma profile with the predictions of metal-poor model atmospheres having the metallicity of M 13 indicated Teff = 20250 K, log g = 3.15. Observations of He I lambda(4026) taken with echelle spectrograph of the Multi-Mirror telescope using a Reticon detector show that He/H = 0.055 +/- 0.020. Some astrophysical implications of this result are discussed.

Adelman, S. J.; Aikman, G. C. L.; Hayes, D. S.; Philip, A. G. D.; Sweigart, A. V.

1994-02-01

97

The WiggleZ Dark Energy Survey: star formation in UV-luminous galaxies from their luminosity functions  

NASA Astrophysics Data System (ADS)

We present the ultraviolet (UV) luminosity function of galaxies from the GALEX Medium Imaging Survey with measured spectroscopic redshifts from the first data release of the WiggleZ Dark Energy Survey. Our sample consists of 39 996 NUV < 22.8 emission line galaxies in the redshift range 0.1 < z < 0.9. This sample selects galaxies with high star formation rates: at 0.6 < z < 0.9 the median star formation rate is at the upper 95th percentile of optically selected (r < 22.5) galaxies and the sample contains about 50 per cent of all NUV < 22.8, 0.6 < z < 0.9 starburst galaxies within the volume sampled. The most luminous galaxies in our sample ( - 21.0 > MNUV > -22.5) evolve very rapidly with a number density declining as (1 + z)5±1 from redshift z = 0.9 to 0.6. These starburst galaxies (MNUV < -21 is approximately a star formation rate of 30 M? yr-1) contribute about 1 per cent of cosmic star formation over the redshift range z = 0.6-0.9. The star formation rate density of these very luminous galaxies evolves rapidly, as (1 + z)4±1. Such a rapid evolution implies that the majority of star formation in these large galaxies must have occurred before z = 0.9. We measure the UV luminosity function in ?z = 0.05 redshift intervals spanning 0.1 < z < 0.9, and provide analytic fits to the results. Our measurements of the luminosity function over this redshift range probe further into the bright end (1-2 mag further) than previous measurements, e.g. Arnouts et al., Budavári et al. and Treyer et al., due to our much larger sample size and sampled volume. At all redshifts z > 0.55 we find that the bright end of the luminosity function is not well described by a pure Schechter function due to an excess of very luminous (MNUV < -22) galaxies. These luminosity functions can be used to create a radial selection function for the WiggleZ survey or test models of galaxy formation and evolution. Here we test the AGN feedback model in Scannapieco, Silk & Bouwens, and find that this AGN feedback model requires AGN feedback efficiency to vary with one or more of the following: stellar mass, star formation rate and redshift.

Jurek, Russell J.; Drinkwater, Michael J.; Pimbblet, Kevin; Glazebrook, Karl; Blake, Chris; Brough, Sarah; Colless, Matthew; Contreras, Carlos; Couch, Warrick; Croom, Scott; Croton, Darren; Davis, Tamara M.; Forster, Karl; Gilbank, David; Gladders, Mike; Jelliffe, Ben; Li, I.-hui; Madore, Barry; Martin, D. Christopher; Poole, Gregory B.; Pracy, Michael; Sharp, Rob; Wisnioski, Emily; Woods, David; Wyder, Ted K.; Yee, H. K. C.

2013-09-01

98

UV Spectral Slope and Dust Attenuation of Faint Star-Forming Galaxies at 1 < z < 3 Behind the Lensing Cluster A1689  

NASA Astrophysics Data System (ADS)

Based on our recent study on the galaxy cluster Abell 1689, the faint star-forming galaxies (MUV ? -18) account for the majority of ultraviolet luminosity density at the peak epoch of star formation activity. In this study, we provide a comprehensive measurement of the rest-frame UV spectral slopes of the faint star-forming galaxies at the corresponding epoch. We combine very deep HST/WFC3 UVIS photometry in F225W, F275W and F336W bands with HST/ACS optical and HST/WFC3 IR images. The high magnification from the lensing cluster Abell 1689, enables us to extend our study down to a very faint UV absolute magnitude MUV=-12 (?0.001L*z=1). We find more than 150 faint galaxies in the range 1 ? z ? 3 based on a photometric redshift selection technique. We study the trends of UV continuum slope with luminosity and redshift. These faint galaxies follow the same trends as seen in the other studies, where galaxies get bluer as their UV luminosities decrease. Using the results of a hydro-dynamical simulation of dwarf galaxies with bursty star formation history, we investigate the intrinsic scatter in the UV continuum color measurements. We determine the level of dust attenuation with luminosity and redshift, but also consider other factors that may affect the dust extinction such as metallicity and star formation history.

Alavi, Anahita; Siana, Brian D.; Dominguez, Alberto; Richard, Johan; Rafelski, Marc; Stark, Daniel

2015-01-01

99

VizieR Online Data Catalog: Synthetic UV spectra of massive stars (Leitherer+ 1995)  

NASA Astrophysics Data System (ADS)

An atlas of synthetic ultraviolet spectra of a population of massive stars is presented. The spectra are based on a stellar library of IUE high-dispersion spectra of O and Wolf-Rayet stars, coupled to an evolutionary synthesis code. Later spectral types are included via low-dispersion spectra. Line profiles of N V lambda 1240, Si IV lambda 1400, C IV lambda 1550, He II lambda 1640, and N IV lambda 1720 have been computed for star-formation histories and initial mass functions typically found in starburst regions. It is found that the lines are sensitive indicators for the presence or absence of massive stars. C IV lambda 1550 is the strongest stellar line in the ultraviolet spectrum of a typical starburst. If O stars with zero-age main-sequence masses above 50M? are present, C IV always shows a P Cygni profile. In the absence of such stars, only a blue-shifted absorption is present. During later epochs of the starburst, when late-O/early-B stars dominate, an unshifted photospheric absorption appears. Si IV lambda 1400 shows a conspicuous wind profile when luminous O supergiants are present. A strong P Cygni profile is found only for an instantaneous burst observed at 3 to 5Myr, which has a top-heavy IMF. The velocity of the blueshifted absorption is strongly correlated with the age and the upper cutoff mass (or slope) of the IMF. N V lambda 1240 traces the most massive stars and behaves rather similar to Si IV lambda 1400. Its usefulness as an indicator of very massive stars is limited due to the strong blending effect of the nearby Ly-alpha line. Nevertheless, strong N V lambda 1240 emission in a starburst suggests the presence of stars with masses in excess of 60M?. He II lambda 1640 and N IV lambda 1720 are produced by very hot and luminous O and Wolf-Rayet stars. Both lines can have weak absorption or emission in a typical starburst but are predicted to be observable only under rare circumstances, such as in an instantaneous burst at t{approx.}3Myr. The profiles presented in the atlas can be compared to high-quality ultraviolet observations of galaxies with active star formation in order to constrain the massive star population. The atlas is published in its entirety in computer-readable form in the AAS CD-ROM series, Vol. 5. (1 data file).

Leitherer, C.; Robert, C.; Heckman, T. M.

1996-02-01

100

MEASURING THE EVOLUTIONARY RATE OF COOLING OF ZZ Ceti  

SciTech Connect

We have finally measured the evolutionary rate of cooling of the pulsating hydrogen atmosphere (DA) white dwarf ZZ Ceti (Ross 548), as reflected by the drift rate of the 213.13260694 s period. Using 41 yr of time-series photometry from 1970 November to 2012 January, we determine the rate of change of this period with time to be dP/dt = (5.2 {+-} 1.4) Multiplication-Sign 10{sup -15} s s{sup -1} employing the O - C method and (5.45 {+-} 0.79) Multiplication-Sign 10{sup -15} s s{sup -1} using a direct nonlinear least squares fit to the entire lightcurve. We adopt the dP/dt obtained from the nonlinear least squares program as our final determination, but augment the corresponding uncertainty to a more realistic value, ultimately arriving at the measurement of dP/dt = (5.5 {+-} 1.0) Multiplication-Sign 10{sup -15} s s{sup -1}. After correcting for proper motion, the evolutionary rate of cooling of ZZ Ceti is computed to be (3.3 {+-} 1.1) Multiplication-Sign 10{sup -15} s s{sup -1}. This value is consistent within uncertainties with the measurement of (4.19 {+-} 0.73) Multiplication-Sign 10{sup -15} s s{sup -1} for another similar pulsating DA white dwarf, G 117-B15A. Measuring the cooling rate of ZZ Ceti helps us refine our stellar structure and evolutionary models, as cooling depends mainly on the core composition and stellar mass. Calibrating white dwarf cooling curves with this measurement will reduce the theoretical uncertainties involved in white dwarf cosmochronometry. Should the 213.13 s period be trapped in the hydrogen envelope, then our determination of its drift rate compared to the expected evolutionary rate suggests an additional source of stellar cooling. Attributing the excess cooling to the emission of axions imposes a constraint on the mass of the hypothetical axion particle.

Mukadam, Anjum S.; Fraser, Oliver; Riecken, T. S.; Kronberg, M. E. [Department of Astronomy, University of Washington, Seattle, WA 98195 (United States); Bischoff-Kim, Agnes [Georgia College and State University, Milledgeville, GA 31061 (United States); Corsico, A. H. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata (Argentina); Montgomery, M. H.; Winget, D. E.; Hermes, J. J.; Winget, K. I.; Falcon, Ross E.; Reaves, D. [Department of Astronomy, University of Texas at Austin, Austin, TX 78759 (United States); Kepler, S. O.; Romero, A. D. [Universidade Federal do Rio Grande do Sul, Porto Alegre 91501-970, RS (Brazil); Chandler, D. W. [Meyer Observatory, Central Texas Astronomical Society, 3409 Whispering Oaks, Temple, TX 76504 (United States); Kuehne, J. W. [McDonald Observatory, Fort Davis, TX 79734 (United States); Sullivan, D. J. [Victoria University of Wellington, P.O. Box 600, Wellington (New Zealand); Von Hippel, T. [Embry-Riddle Aeronautical University, 600 South Clyde Morris Boulevard, Daytona Beach, FL 32114 (United States); Mullally, F. [SETI Institute, NASA Ames Research Center, MS 244-30, Moffet Field, CA 94035 (United States); Shipman, H. [Delaware Asteroseismic Research Center, Mt. Cuba Observatory, Greenville, DE 19807 (United States); and others

2013-07-01

101

UV Continuum Slope and Dust Obscuration from z ~ 6 to z ~ 2: The Star Formation Rate Density at High Redshift  

NASA Astrophysics Data System (ADS)

We provide a systematic measurement of the rest-frame UV continuum slope ? over a wide range in redshift (z ~ 2-6) and rest-frame UV luminosity (0.1 L* z = 3 to 2 L* z = 3) to improve estimates of the star formation rate (SFR) density at high redshift. We utilize the deep optical and infrared data (Advanced Camera for Surveys/NICMOS) over the Chandra Deep Field-South and Hubble Deep Field-North Great Observatories Origins Deep Survey fields, as well as the UDF for our primary UBVi "dropout" Lyman Break Galaxy sample. We also use strong lensing clusters to identify a population of very low luminosity, high-redshift dropout galaxies. We correct the observed distributions for both selection biases and photometric scatter. We find that the UV-continuum slope of the most luminous galaxies is substantially redder at z ~ 2-4 than it is at z ~ 5-6 (from ~-2.4 at z ~ 6 to ~-1.5 at z ~ 2). Lower luminosity galaxies are also found to be bluer than higher luminosity galaxies at z ~ 2.5 and z ~ 4. We do not find a large number of galaxies with ?'s as red as -1 in our dropout selections at z ~ 4, and particularly at z gsim 5, even though such sources could be readily selected from our data (and also from Balmer Break Galaxy searches at z ~ 4). This suggests that star-forming galaxies at z gsim 5 almost universally have very blue UV-continuum slopes, and that there are not likely to be a substantial number of dust-obscured galaxies at z gsim 5 that are missed in "dropout" searches. Using the same relation between UV-continuum slope and dust extinction as has been found to be appropriate at both z ~ 0 and z ~ 2, we estimate the average dust extinction of galaxies as a function of redshift and UV luminosity in a consistent way. As expected, we find that the estimated dust extinction increases substantially with cosmic time for the most UV luminous galaxies, but remains small (lsim2 times) at all times for lower luminosity galaxies. Because these same lower luminosity galaxies dominate the luminosity density in the UV continuum, the overall dust extinction correction remains modest at all redshifts and the evolution of this correction with redshift is only modest. We include the contribution from ultra-luminous IR galaxies in our SFR density estimates at z ~ 2-6, but find that they contribute only ~20% of the total at z ~ 2.5 and lsim10% at z gsim 4. Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 7235, 7817, 9425, 9575, 9797, 9803, 9978, 9979, 10189, 10339, 10340, 10403, 10504, 10530, 10632, 10872, 10874, 11082, and 11144.

Bouwens, R. J.; Illingworth, G. D.; Franx, M.; Chary, R.-R.; Meurer, G. R.; Conselice, C. J.; Ford, H.; Giavalisco, M.; van Dokkum, P.

2009-11-01

102

UV Spectroscopy of Metal-Poor Massive Stars in the Small Magellanic Cloud  

E-print Network

The Hubble Space Telescope has provided the first clear evidence for weaker winds of metal-poor massive stars in the Small Magellanic Cloud, confirming theoretical predictions of the metallicity dependence of mass-loss rates and wind terminal velocities. For lower luminosity O-type stars however, derived mass-loss rates are orders of magnitude lower than predicted, and are at present unexplained.

Daniel J. Lennon

2007-07-16

103

The Copernicus observations - Interstellar or circumstellar material. [UV spectra of early stars  

NASA Technical Reports Server (NTRS)

It is suggested that the sharp absorption lines observed in the ultraviolet spectra of early-type stars by the Copernicus satellite may be entirely accounted for by the circumstellar material in the H II regions and associated transition zones around the observed stars. If this interpretation is correct, the Copernicus results yield little information on the state of any interstellar (as opposed to circumstellar) gas and, in particular, shed little light on the degree of element depletion in interstellar space.

Steigman, G.; Strittmatter, P. A.; Williams, R. E.

1975-01-01

104

Star Formation in Nearby EarlyType Galaxies: Mapping in UV, Optical, and CO  

E-print Network

. Emsellem, R. Bacon et al: MNRAS 369, 497 (2006) 5. E. Emsellem, M. Cappellari, R.F. Peletier et al: MNRASStar Formation in Nearby Early­Type Galaxies: Mapping in UV, Optical, and CO M. Bureau 1 , R. Bacon 2 , M. Cappellari 3 , F. Combes 4 , R.L. Davies 1 , P.T. de Zeeuw 3 , E. Emsellem 2 , J. Falc

Bureau, Martin

105

FUSE Observations of the UV-bright Star vZ 1128 in the Globular Cluster M 3  

NASA Astrophysics Data System (ADS)

We present an abundance analysis of the UV-bright star vZ 1128 in the Globular Cluster M 3 based on Far Ultraviolet Spectroscopic Explorer (FUSE) observations. vZ 1128 is a post-asymptotic giant branch star with an effective temperature of about 35,000 K and a gravity of log g = 4.0. The FUSE spectrum shows photospheric lines from CIII, NIII, NIV, OIII, SiIII, SiIV, PIV, PV, SIV, SV, and SVI. No photospheric lines from iron peak elements or beyond are observed. Using NLTE models, we find that the abundance of C, N, O, Si, P, and S relative to hydrogen is a factor 3 to 100 lower than the solar abundance. Adopting the cluster iron abundance ([Fe/H] = -1.57) for the star, we derive C, N, O, Si, P, and S abundances of [X/Fe] = -0.6, 0.9, 0.2, -0.4, -0.3, and 0.2, respectively. These values are consistent with those measured for red giants in M 3, except for [Si/Fe], which is low by roughly 0.7 dex.

Chayer, P.; Dixon, W. V.; Torres, L.; Rivera, J. M.

2005-12-01

106

UV-Absorbent Lignin-Based Multi-Arm Star Thermoplastic Elastomers.  

PubMed

Lignin-grafted copolymers, namely lignin-graft-poly(methyl methacrylate-co-butyl acrylate) (lignin-g-P(MMA-co-BA)), are synthesized via "grafting from" atom transfer radical polymerization (ATRP) with the aid of lignin-based macroinitiators. By manipulating the monomer feed ratios of MMA/BA, grafted copolymers with tunable glass transition temperatures (-10-40 °C) are obtained. These copolymers are evaluated as sustainable thermoplastic elastomers (TPEs). The results suggest that the mechanical properties of these TPEs lignin-g-P(MMA-co-BA) copolymers are improved significantly by comparing with those of linear P(MMA-co-BA) copolymer counterparts, and the elastic strain recovery is nearly 70%. Lignin-g-P(MMA-co-BA) copolymers exhibit high absorption in the range of the UV spectrum, which might allow for applications in UV-blocking coatings. PMID:25545630

Yu, Juan; Wang, Jifu; Wang, Chunpeng; Liu, Yupeng; Xu, Yuzhi; Tang, Chuanbing; Chu, Fuxiang

2015-02-01

107

New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey  

Microsoft Academic Search

We are searching for new He atmosphere white dwarf pulsators (DBVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better known cousins, the H atmosphere white dwarf pulsators (DAVs or ZZ Ceti stars). Since the evolution of white dwarf stars is characterized

A. Nitta; S. J. Kleinman; J. Krzesinski; S. O. Kepler; T. S. Metcalfe; Anjum S. Mukadam; Fergal Mullally; R. E. Nather; Denis J. Sullivan; Susan E. Thompson; D. E. Winget

2009-01-01

108

Near-UV Observations of HD221170: New Insights into the Nature of r-Process-Rich Stars  

E-print Network

Employing high resolution spectra obtained with the near-UV sensitive detector on the Keck I HIRES, supplemented by data obtained with the McDonald Observatory 2-d coude, we have performed a comprehensive chemical composition analysis of the bright r-process-rich metal-poor red giant star HD221170. Analysis of 57 individual neutral and ionized species yielded abundances for a total of 46 elements and significant upper limits for an additional five. Model stellar atmosphere parameters were derived with the aid of ~200 Fe-peak transitions. From more than 350 transitions of 35 neutron-capture (Z > 30) species, abundances for 30 neutron-capture elements and upper limits for three others were derived. Utilizing 36 transitions of La, 16 of Eu, and seven of Th, we derive ratios of log epsilon(Th/La) = -0.73 (sigma = 0.06) and log epsilon(Th/Eu) = -0.60 (sigma = 0.05), values in excellent agreement with those previously derived for other r-process-rich metal-poor stars such as CS22892-052, BD+17 3248, and HD115444. Based upon the Th/Eu chronometer, the inferred age is 11.7 +/- 2.8 Gyr. The abundance distribution of the heavier neutron-capture elements (Z >= 56) is fit well by the predicted scaled solar system r-process abundances, as also seen in other r-process-rich stars. Unlike other r-process-rich stars, however, we find that the abundances of the lighter neutron-capture elements (37 < Z < 56) in HD221170 are also statistically in better agreement with the abundances predicted for the scaled solar r-process pattern.

Inese I. Ivans; Jennifer Simmerer; Christopher Sneden; James E. Lawler; John J. Cowan; Roberto Gallino; Sara Bisterzo

2006-04-08

109

Extragalactic Backgrounds in the Far UV and Exploring Star Formation at High Redshifts with Gamma-ray Observations  

NASA Technical Reports Server (NTRS)

The determination of the intergalactic photon densities from the FIR to the UV which is produced by stellar emission and dust reradiation at various redshifts can provide an independent measure of the star formation history of the universe. Using recent Spitzer and GALEX data in conjunction with other observational inputs, Stecker, Malkan and Scully have calculated the intergalactic photon density as a function of both energy and redshift for 0 < zeta < 6 for photon energies from 0.003 eV to the Lyman limit cutoff at 13.6 eV in a ACDM universe with Omega(sub Lambda) = 0.7 and Omega(sub m) = 0.3. Their results are based on backwards evolution models for galaxies which were developed by Malkan and Stecker previously. The calculated background SEDs at zeta = 0 are in good agreement with the present observational data and limits. The calculated intergalactic photon densities as a function of redshift were used to predict to extend the absorption of high energy 7-rays in intergalactic space from sources such as blazars and quasars, this absorption being produced by interactions the y-rays with the intergalactic FIR-UV photons having the calculated densities. The results are in excellent agreement with absorption features found in the low gamma-ray spectra of Mkn 421, Mkn 501 at, zeta = 0.03 and PKS

Stecker, Floyd W.

2006-01-01

110

FUV, UV, and Optical Observations of the He-sdO Star BD+39 3226  

NASA Astrophysics Data System (ADS)

Based on observations carried out with the Far Ultraviolet Spectroscopic Explorer, the Space Telescope Imaging Spectrograph, the MMT Observatory, and the Keck telescope HIRES spectrograph, we present a spectral analysis of the He-sdO star BD+39 3226. By fitting the MMT spectrum we obtain a gravity that is 0.7 dex higher than the one reported in the literature. The new atmospheric parameters will have an impact on the measurement of the HI column density toward BD+39 3226, and by this very fact on the deuterium abundance. The high-resolution spectra show stellar absorption lines coming from C, N, O, Si, P, S, Fe, and Ni. The spectra also show lines from heavy elements such as Ge, As, and Sn. On the other hand, neither Zr nor Pb absorption lines are detected. The non-detection of lead in BD+39 3226 indicates that the star does not belong to the newly discovered group of lead-rich He-sdO stars. P.C. is supported by the Canadian Space Agency under a Public Works and Government Services of Canada contract.

Chayer, Pierre; Green, E. M.; Fontaine, G.

2014-01-01

111

Automated ground-based star-pointing UV -visible spectrometer for stratospheric measurements.  

PubMed

A novel automated ground-based star-pointing spectrometer system has been constructed for long-term deployment in Antarctica. Similar to our earlier stellar system, a two-dimensional detector array measures the spectra of the star and the adjacent sky, so that auroral emission from the sky can be subtracted from the stellar signal. Some new features are an altitude -azimuth pointing mirror, so that the spectrometer does not move; slip rings to provide its power thereby avoiding flexing of cables and restriction of all-around viewing; and a glazed enclosure around the mirror to ensure protection from rain and snow, made from flat plates to avoid changing the focal length of the telescope. The optical system can also view sunlight scattered from the zenith sky. The system automatically points and tracks selected stars and switches to other views on command. The system is now installed at Halley in Antarctica, and some preliminary measurements of ozone from Antarctica are shown. PMID:18259452

Roscoe, H K; Taylor, W H; Evans, J D; Tait, A M; Freshwater, R; Fish, D; Strong, E K; Jones, R L

1997-08-20

112

Preparation of a Far-UV Spectral and Line Atlas for B stars near the Main Sequence  

NASA Astrophysics Data System (ADS)

B type stars are major contributors to the total far-UV (949-1225 Å) flux produced in the Milky Way and external galaxies. The final reprocessing of the FUSE satellite dataset, together with the existing archives of the HST/STIS, IUE, and the Copernicus Atlas of ? Sco, permit the construction of a high dispersion atlas of 10 sharp-lined B stars near the main sequence (mostly class III-V). Our atlas segregates the H I and molecular H2 and photospheric lines and, thanks to the synspec synthesis program, lists essentially all noticeable absorption features with known oscillator strengths for specta of types B0, B2, and B8-B9. The atlas will allow the identification of anomalous features in other B-type spectra and the selection of line proxies to compute Teff, anomalous abundance patterns, and possible departures of atmospheric T(?)'s from nonstandard gradients. We discuss the input constituents for this atlas, show examples of atlas panels, and we display line identifications for the three spectral types noted above. The ~4300 lines we have identified comprise over 12% of the features in our line library. We have been unable to identify fewer than 5% of the visible features in the ? Sco spectrum, and fewer still in the B8 spectrum. Comparable numbers of lines are overpredicted in our syntheses.

Smith, Myron A.

2009-05-01

113

Completing The Characterization Of Stellar Populations In The Galaxy: Final Catalogs Of Unique Galex Uv Sources And Of Milky Way Hot Stars.  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer (GALEX) has performed the first extensive surveys in the Ultraviolet (UV), filling the last gap in our view of the sky across the electromagnetic spectrum. Its legacy is an unprecedented database with more than 200 million source measurements in far-UV and near-UV. The UV surveys offer unique sensitivity for identifying and studying selected classes of astrophysical objects, both stellar and extra- galactic, notably hot stars, star-forming galaxies, and QSOs (redshift ?sssim2.4). In order to examine the overall content and distribution of UV sources over the sky, and to classify them by astrophysical class, we propose to construct final catalogs of UV unique sources with homogeneous quality (eliminating duplicate measurements of the same source, excluding artifacts, adding science flags, etc). Such catalogs will facilitate a variety of science investigations on UV-selected samples by the community, in addition to our own science goal, as well as planning of observations with future instruments. We will build the catalogs (high-level science product) using recipes developed for our early version (Bianchi et al. 2011a) but with expanded tools, science flags, and corollary data, in addition to the much larger area coverage with respect to our early version. To facilitate UV source classification and characterization, we will also match the catalogs of unique UV sources with existing ground-based surveys, adding optical and infrared magnitudes to the two UV GALEX magnitudes, and construct flags to identify sources with multiple matches. These products will allow us (and the community) to extract UV-selected samples for several projects. We will use our catalogs for our own science goal: an unbiased census of Milky Way hot white dwarfs (WD). Hot WDs are elusive at all wavelengths except the UV, given their very high temperatures to which optical colors are insensitive, and low optical luminosity. From our proposed UV catalogs we will be able to identify and characterize unbiased samples of such stars; we expect to increase known samples by two orders of magnitudes, as shown by our preliminary work on early data releases. Such hot-WD census over most of the sky, reaching WDs with small radii out to large distances along low-extinction sight-lines, detecting rare halo objects, will include in particular the hottest and highest-mass WDs, elusive in optical searches, and hot-WD in binaries (where the hot component is undetectable without UV data, as the flux at longer wavelengths is dominated by the cooler companion). We will compare the derived hot- WD counts with Milky Way models to constrain statistically a yet obscure phase of stellar evolution, the Initial-Final Mass Relation, of paramount relevance for understanding late phases of stellar evolution and the yield of chemical elements. The intrinsic overall distribution of hot stars reflects the Galactic structure; the number counts of both Galactic and extra-galactic UV sources are modulated by the Milky Way dust extinction, to which the UV data are also very sensitive. We will also gain insight on the Milky Way dust distribution, independently from other methods. All resulting catalogs will be made publicly available from existing VO sites (MAST, SIMBAD/Vizier, US-VAO), after publication, and immediately from our web site (http://dolomiti.pha.jhu.edu/uvsky) with related tools. Our early-release catalogs are already online at MAST and Vizier and are amply used by the community.

Bianchi, Luciana

114

Sensitivity of biosignatures on Earth-like planets orbiting in the habitable zone of cool M-dwarf Stars to varying stellar UV radiation and surface biomass emissions  

NASA Astrophysics Data System (ADS)

We find that variations in the UV emissions of cool M-dwarf stars have a potentially large impact upon atmospheric biosignatures in simulations of Earth-like exoplanets i.e. planets with Earth's development, and biomass and a molecular nitrogen-oxygen dominated atmosphere. Starting with an assumed black-body stellar emission for an M7 class dwarf star, the stellar UV irradiation was increased stepwise and the resulting climate-photochemical response of the planetary atmosphere was calculated. Results suggest a “Goldilocks” effect with respect to the spectral detection of ozone. At weak UV levels, the ozone column was weak (due to weaker production from the Chapman mechanism) hence its spectral detection was challenging. At strong UV levels, ozone formation is stronger but its associated stratospheric heating leads to a weakening in temperature gradients between the stratosphere and troposphere, which results in weakened spectral bands. Also, increased UV levels can lead to enhanced abundances of hydrogen oxides which oppose the ozone formation effect. At intermediate UV (i.e. with ×10 the stellar UV radiative flux of black body Planck curves corresponding to spectral class M7) the conditions are “just right” for spectral detection. Results suggest that the planetary ozone profile is sensitive to the UV output of the star from ~200-350 nm.We also investigated the effect of increasing the top-of-atmosphere incoming Lyman-? radiation but this had only a minimal effect on the biosignatures since it was efficiently absorbed in the uppermost planetary atmospheric layer, mainly by abundant methane. Earlier studies have suggested that the planetary methane is an important stratospheric heater which critically affects the vertical temperature gradient, hence the strength of spectral emission bands. We therefore varied methane and nitrous oxide biomass emissions, finding e.g. that a lowering in methane emissions by ×100 compared with the Earth can influence temperature hence have a significant effect on biosignature spectral bands such as those of nitrous oxide. Our work emphasises the need for future missions to characterise the UV of cool M-dwarf stars in order to understand potential biosignature signals.

Grenfell, J. L.; Gebauer, S.; v. Paris, P.; Godolt, M.; Rauer, H.

2014-08-01

115

Wind/jet Formation in T Tauri Stars: Theory versus UV Observations  

NASA Astrophysics Data System (ADS)

Observations of the base of protostellars jet carried out with HST-STIS are presented. The Si III] and CIII] profiles are analized for 6 T Tauri stars (TTSs). It is found that the line emission is produced in the stellar atmosphere and in the base of the optical jet. The presence of a low density (104-105 cm-3) envelope is detected. High densities (˜ 1010 cm-3) of the line formation region are confirmed for RU Lup. These results are compared with the theoretical predictions of magneto- centrifugal disk winds. It is shown that densities above 108 cm-3 cannot be produced by disk winds. The main spectral signature of disk winds is shown to be the presence of asymmetric absorption components in the blue-wing of strong resonance lines. The strength of the components depends on the inclination and on the accretion rate.

Gomez de Castro, A. I.; Verdugo, E.; Ferro-Fontan, C.

2003-10-01

116

MODELING THE NEAR-UV BAND OF GK STARS. II. NON-LTE MODELS  

SciTech Connect

We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent non-local thermodynamic equilibrium (NLTE), and compare them to the LTE grid of Short and Hauschildt (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T({tau}) relation) and the SED as a finely sampled function of T{sub eff}, log g, and [A/H] among solar metallicity and mildly metal-poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best-fit T{sub eff} values that are 30-90 K lower than those provided by LTE models, while providing greater consistency between log g values, and, for Arcturus, T{sub eff} values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best-fit T{sub eff} values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue-band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant. We compare our derived T{sub eff} values to several other spectroscopic and photometric T{sub eff} calibrations for red giants, including one that is less model dependent based on the infrared flux method (IRFM). We find that the NLTE models provide slightly better agreement to the IRFM calibration among the warmer stars in our sample, while giving approximately the same level of agreement for the cooler stars.

Ian Short, C.; Campbell, Eamonn A. [Department of Astronomy and Physics and Institute for Computational Astrophysics, Saint Mary's University, Halifax, NS B3H 3C3 (Canada); Pickup, Heather [Department of Physics and Astronomy, University of Waterloo, Waterloo, ON (Canada); Hauschildt, Peter H., E-mail: ishort@ap.smu.ca, E-mail: yeti@hs.uni-hamburg.de [Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg (Germany)

2012-03-10

117

Investigation Jet Rotation in Young Stars via High Resolution UV Spectra  

NASA Astrophysics Data System (ADS)

In recent years we have successfully harnessed the high resolution of STIS in the optical to reveal asymmetries in Doppler shifts transverse to the flow direction in 8 T Tauri jets {Bacciotti ea 2002; Woitas ea 2005; Coffey ea 2004; 2007}. We interpret the findings, just 100 AU above the disk, as signatures of jet rotation. The significance of these results is considerable. They form the only existing observational indications supporting the theory that jets extract angular momentum from star-disk systems. Furthermore, they hold the potential to discriminate between the main model contenders: X-wind and Disk-wind {Ferreira ea 2006}. Although our results are encouraging, it is evident that we are only marginally resolving the effects of rotation because of the limiting resolution {spatially and spectrally} of STIS in the optical. Therefore, in Cycle 12 we proposed to extend this study into the near-ultraviolet {NUV}, giving double the spatial and spectral resolution {proposal ID 9807}. Unfortunately, only 3 targets in our survey were observed before the failure of STIS {Coffey ea 2007}. Nevertheless, the results were very exciting. Agreement was found between the optical and NUV results in terms of the magnitude and sense of the Doppler shift gradient across the jet. Furthermore, the NUV lines indicated that the observed high velocity gas was launched from about 0.2-0.5 AU, compared to the lower velocity gas traced in optical lines which originates from as far as 2 AU. This puts a strong contraint on MHD launch models, and indeed holds the potential to differentiate between them. Given that the strength of a rotation argument lies in the survey nature of the findings, we need to resume this program in order to see if the same rotation signatures are commonly seen in the NUV, as they are in the optical. Furthermore, the higher spatial and spectral resolution of STIS in the NUV will allow us to more accurately quantify the variation in toroidal velocity as a function of distance from the jet axis. This study will provide an invaluable statistical argument to support the fact that we are indeed observing jet rotation. Such a conclusion is critical to providing observational backing to the widely accepted but untested theory of magnetocentrifugal ejection.

Bacciotti, Francesca

2009-07-01

118

Brucella ceti from two striped dolphins stranded on the Apulia coastline, Italy.  

PubMed

Since 1994, when Brucella ceti was first isolated from an aborted dolphin fetus, several cases have been reported worldwide. The first case of B. ceti in the Mediterranean (and in Italy), however, was recorded only in 2012, off the coast of Tuscany. Extensive studies, using serological and microbiological methods, have documented this bacterium in dolphins and demonstrated its zoonotic potential. We describe the typing of two B. ceti strains isolated from striped dolphins (Stenella coeruleoalba) stranded on the southern Apulia coastline. B. ceti isolates were conventionally typed, and then genotyped by both the multilocus sequence typing (MLST) and the multilocus variable number of tandem repeats typing (MLVA) methodologies to infer phylogeny and potential epidemiological links between the two cases. The two isolates were identified through MLST analysis as belonging to the common sequence type 26 (ST26), while MLVA analysis, having established that the two isolates have identical profiles, assigned them to a novel genotype within cluster A - a unique representative of a new Mediterranean subcluster. The results thus revealed a link between the two cases studied, demonstrating the usefulness of MLST and MLVA for the epidemiological investigation of brucellae among marine mammals. PMID:24324028

Garofolo, Giuliano; Zilli, Katiuscia; Troiano, Pasquale; Petrella, Antonio; Marotta, Francesca; Di Serafino, Gabriella; Ancora, Massimo; Di Giannatale, Elisabetta

2014-02-01

119

A Theoretical Domain for Flare Stars in the HR Diagram  

Microsoft Academic Search

IT has been suggested several times1 that the flare activity observed in flash and U V Ceti stars is of a nature similar to that of solar flares. In this communication I shall adhere to this point of view, which, together with present ideas about the Helmholtz-Kelvin phases of stellar evolution, will permit us to understand, in a simple manner,

Arcadio Poveda

1964-01-01

120

Herschel Detection of Dust Emission from UV-luminous Star-forming Galaxies at 3.3 <~ z <~ 4.3  

NASA Astrophysics Data System (ADS)

We report the Herschel/SPIRE detection of dust emission arising from UV-luminous (L >~ L*) star-forming galaxies at 3.3 <~ z <~ 4.3. Our sample of 1913 Lyman break galaxy (LBG) candidates is selected over an area of 5.3 deg2 in the Boötes field of the NOAO Deep Wide-Field Survey. This is one of the largest samples of UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel/SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of (3-5) × 1011 L ? and 60%-70% of their star formation obscured by dust. The FIR SEDs peak at ?rest >~ 100 ?m suggesting dust temperatures (Td = 27-30 K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX ? L IR/L UV) is low (?3-4) compared with that observed for z ? 2 LBGs (IRXz ~ 2 ? 7.1 ± 1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV-luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.

Lee, Kyoung-Soo; Alberts, Stacey; Atlee, David; Dey, Arjun; Pope, Alexandra; Jannuzi, Buell T.; Reddy, Naveen; Brown, Michael J. I.

2012-10-01

121

Herschel Detection of Dust Emission from UV-Luminous Star-Forming Galaxies at 3.3  

NASA Astrophysics Data System (ADS)

We report the Herschel SPIRE detection of dust emission arising from UV-luminous (L> L*) star-forming galaxies at 3.3UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of 3-5x 10^11L_sun and 60-70% of their star-formation obscured by dust. The FIR SEDs peak at lambda_res 100um, suggesting dust temperatures (T_d=27-30K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX=L_IR/L_UV) is low 3-4) compared with that observed for 2 LBGs (IR 7.1+/-1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.

Lee, Kyoung-Soo; Alberts, S.; Atlee, D. W.; Dey, A.; Pope, A.; Jannuzi, B.; Reddy, N. A.; Brown, M. J.

2013-01-01

122

C IV and Si IV in IUE spectra of normal B8-A0 stars: UV identified Be/Ae stars  

NASA Technical Reports Server (NTRS)

Archival IUE high dispersion spectra of 42 B6-A2 stars within 200 pc were surveyed. Five of the program stars show significant C IV and Si IV absorption. All of the stars with detected C IV have v sin i less than or = 190 km/sec. Sharp absorption cores are present in Si II lambda 1533 in 3 of the objects, indicating that these are previously unrecognized shell stars. Three of the stars have variable or asymmetric C IV profiles which are consistent with the C IV and Si IV being produced in stellar winds. One star has C IV in the form of a shortward-shifted discrete absorption component, similar to those observed in Be stars. The data are compared with similar data for Be and B shell stars.

Chiu, Weihsueh A.; Grady, C. A.; Bruhweiler, Frederick C.

1988-01-01

123

Signals embedded in the radial velocity noise. Periodic variations in the ? Ceti velocities  

NASA Astrophysics Data System (ADS)

Context. The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. Aims: We study an extensive set of radial velocities for the star HD 10700 (? Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. Methods: We performed Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reached our goal by adding artificial signals to the "flat" radial velocity data of HD 10700 and by seeing which one of our statistical noise models receives the greatest posterior probabilities while still being able to extract the artificial signals correctly from the data. We utilised various noise components to assess properties of the noise in the data and analyse the HARPS, AAPS, and HIRES data for HD 10700 to quantify these properties and search for previously unknown low-amplitude Keplerian signals. Results: According to our analyses, moving average components with an exponential decay with a timescale from a few hours to few days, and Gaussian white noise explains the jitter the best for all three data sets. Fitting the corresponding noise parameters results in significant improvements of the statistical models and enables the detection of very weak signals with amplitudes below 1 m s-1 level in our numerical experiments. We detect significant periodicities that have no activity-induced counterparts in the combined radial velocities. Three of these signals can be seen in the HARPS data alone, and a further two can be inferred by utilising the AAPS and Keck data. These periodicities could be interpreted as corresponding to planets on dynamically stable close-circular orbits with periods of 13.9, 35.4, 94, 168, and 640 days and minimum masses of 2.0, 3.1, 3.6, 4.3, and 6.6 M?, respectively. Radial velocities are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A79

Tuomi, M.; Jones, H. R. A.; Jenkins, J. S.; Tinney, C. G.; Butler, R. P.; Vogt, S. S.; Barnes, J. R.; Wittenmyer, R. A.; O'Toole, S.; Horner, J.; Bailey, J.; Carter, B. D.; Wright, D. J.; Salter, G. S.; Pinfield, D.

2013-03-01

124

The Observation of the Nearby Universe in UV and in FIR: an evidence for a moderate extinction in present day star forming galaxies  

E-print Network

We study the FIR and UV-visible properties of nearby star forming galaxies. This comparison is performed using the local luminosity functions at UV and FIR wavelengths and on individual starburst galaxies for which photometric data from UV to NIR and FIR are available. The comparison of the FIR and UV local luminosity functions argues for a moderate extinction in nearby disk galaxies. For a sample of 22 starburst galaxies, it is found that the UV(912-3650AA), the visible(3600-12500 AA) and the NIR(12500-22000 AA) wavelength range contribute 30%, 50% and 20% respectively to the total emerging stellar emission. The mean ratio of the dust to bolometric luminosity of these galaxies is 0.37+/-0.22 similar to the ratio found for normal spiral galaxies. The mean extinction at 2000AA is found to be ~1.2mag although with a large dispersion. The conversion factor of the stellar emission into dust emission is found to correlate with the luminosity of the galaxies, brighter galaxies having a higher conversion factor. We conclude that a very large conversion of the stellar light into dust emission can no longer be assumed as a general property of starburst galaxies at least in the local Universe. We compare the UV properties of our local starburst galaxies to those of high redshift galaxies. The larger extinction found in the distant galaxies is consistent with the trend we find for the nearby starburst galaxies namely the brighter the galaxies the lower the escape fraction of stellar light.

Veronique Buat; Denis Burgarella

1998-03-13

125

A Far Ultraviolet Study of the Hot White Dwarf in the Dwarf Nova WW Ceti  

E-print Network

We present a synthetic spectral analysis of IUE archival and FUSE FUV spectra of the peculiar dwarf nova WW Ceti. During the quiescence of WW Ceti, a white dwarf with Twd=26,000K can account for the FUV flux and yields the proper distance. However, the best agreement with the observations is provided by a two-temperature white dwarf model with a cooler white dwarf at Twd=25,000K providing 75% of the FUV flux and a hotter region (accretion belt or optically thick disk ring) with T=40,000K contributing 25% of the flux for the proper distance. We find from the FUSE spectrum that the white dwarf is rotating with a projected rotational velocity V sin{i} = 600 km/s. Our temperature results provide an additional data point in the distribution of Twd versus orbital period above the CV period gap where few Twds are available.

P. Godon; L. Seward; E. M. Sion; P. Szkody

2006-02-06

126

A Far Ultraviolet Study of the Hot White Dwarf in the Dwarf Nova WW Ceti  

E-print Network

We present a synthetic spectral analysis of IUE archival and FUSE FUV spectra of the peculiar dwarf nova WW Ceti. During the quiescence of WW Ceti, a white dwarf with Twd=26,000K can account for the FUV flux and yields the proper distance. However, the best agreement with the observations is provided by a two-temperature white dwarf model with a cooler white dwarf at Twd=25,000K providing 75% of the FUV flux and a hotter region (accretion belt or optically thick disk ring) with T=40,000K contributing 25% of the flux for the proper distance. We find from the FUSE spectrum that the white dwarf is rotating with a projected rotational velocity V sin{i} = 600 km/s. Our temperature results provide an additional data point in the distribution of Twd versus orbital period above the CV period gap where few Twds are available.

Godon, P; Sion, E M; Szkody, P

2006-01-01

127

Complete Genome Sequences of Fish Pathogenic Weissella ceti Strains WS74 and WS105.  

PubMed

We describe here the genome sequencing and annotation of Weissella ceti strains WS74 and WS105, isolated from diseased rainbow trout in Brazil. The two genomes were sequenced with an Ion Torrent personal genome machine (PGM) using a fragment library. The genomes of strains WS74 and WS105 consist of circular chromosomes 1,389,513 bp and 1,390,396 bp long, respectively, both presenting a G+C content of 40.75%. PMID:25323710

Figueiredo, H C P; Leal, C A G; Dorella, F A; Carvalho, A F; Soares, S C; Pereira, F L; Azevedo, V A C

2014-01-01

128

Complete Genome Sequences of Fish Pathogenic Weissella ceti Strains WS74 and WS105  

PubMed Central

We describe here the genome sequencing and annotation of Weissella ceti strains WS74 and WS105, isolated from diseased rainbow trout in Brazil. The two genomes were sequenced with an Ion Torrent personal genome machine (PGM) using a fragment library. The genomes of strains WS74 and WS105 consist of circular chromosomes 1,389,513 bp and 1,390,396 bp long, respectively, both presenting a G+C content of 40.75%. PMID:25323710

Leal, C. A. G.; Dorella, F. A.; Carvalho, A. F.; Soares, S. C.; Pereira, F. L.; Azevedo, V. A. C.

2014-01-01

129

Understanding the atmospheric structure of T Tauri stars - II. UV spectroscopy of RY Tau, BP Tau, RU Lupi, GW Ori and CV Cha  

NASA Astrophysics Data System (ADS)

We report results from our study of International Ultraviolet Explorer (IUE) data of a group of T Tauri stars (TTS). Comparisons between UV-line fluxes in these stars and in the Sun indicate very high levels of activity in their atmospheres and comparatively higher electron densities. Spectroscopic diagnostic line ratios indicate densities over an order of magnitude higher than in the `quiet' Sun at `transition region' temperatures. At these densities, metastable levels can attain comparable populations to the ground level and ionization fractions can be altered as a result of the sensitivity of dielectronic recombination. In Brooks et al. we improved the treatment of these effects using the adas software package, the atomic models and data of which are based on collisional-radiative theory. Here we extend the analysis to a sample of five TTS: RY Tau, BP Tau, RU Lupi, GW Ori and CV Cha. Using these models and data we derive the emission measure (EM) distribution for each star in the sample. We find that the decrease in EM with increasing temperature appears to be sharper than that found in previous work. In comparison with the Sun, the results suggest that the UV emission is formed in a region with a steeper density or volume gradient. We find mismatches between the theoretical and observed fluxes which cannot be explained by density effects and thus must be a result of uncertainties in the atomic data, unreliabilities in the fluxes or the failure of physical assumptions in the method. We have made a series of tests and comparisons, including examination of opacity effects, and these clearly favour the latter explanation. They also lead us to suggest the presence of two separate components in the UV emission for each of the TTS, although the case of CV Cha is more ambiguous. This supports and extends the earlier work of Jordan & Kuin on RU Lupi. Interestingly, we find that the EM distribution for GW Ori has values at least 10 times larger than those of RY Tau, which appears to have approximately the same electron density. A similar difference is found between CV Cha and RU Lupi. Following geometrical arguments, we suggest that the UV emission in GW Ori and CV Cha is formed in a more extended region than in the other three stars.

Brooks, D. H.; Costa, V. M.; Lago, M. T. V. T.; Lanzafame, A. C.

2001-10-01

130

HERSCHEL DETECTION OF DUST EMISSION FROM UV-LUMINOUS STAR-FORMING GALAXIES AT 3.3 {approx}< z {approx}< 4.3  

SciTech Connect

We report the Herschel/SPIRE detection of dust emission arising from UV-luminous (L {approx}> L*) star-forming galaxies at 3.3 {approx}< z {approx}< 4.3. Our sample of 1913 Lyman break galaxy (LBG) candidates is selected over an area of 5.3 deg{sup 2} in the Booetes field of the NOAO Deep Wide-Field Survey. This is one of the largest samples of UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel/SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of (3-5) Multiplication-Sign 10{sup 11} L{sub Sun} and 60%-70% of their star formation obscured by dust. The FIR SEDs peak at {lambda}{sub rest} {approx}> 100 {mu}m suggesting dust temperatures (T{sub d} = 27-30 K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX {identical_to} L{sub IR}/L{sub UV}) is low ( Almost-Equal-To 3-4) compared with that observed for z Almost-Equal-To 2 LBGs (IRX{sub z{approx}2} Almost-Equal-To 7.1 {+-} 1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV-luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.

Lee, Kyoung-Soo [Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907 (United States); Alberts, Stacey; Pope, Alexandra [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Atlee, David; Dey, Arjun; Jannuzi, Buell T. [National Optical Astronomy Observatory, Tucson, AZ 85726 (United States); Reddy, Naveen [Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 (United States); Brown, Michael J. I. [School of Physics, Monash University, Clayton, Victoria 3800 (Australia)

2012-10-20

131

Asteroseismology of DAV White Dwarf Stars  

SciTech Connect

The author reviews the seismological structural determinations of ZZ Ceti stars done to date, and supplement these with additional preliminary determinations of his own. He compares the constraints on the hydrogen layer mass to see what trends emerge and also determines if the observed hydrogen layer masses are consistent with proposed theories. He then looks ahead to the prospects of further DAV white dwarf seismology.

Bradley, Paul A.

1997-12-31

132

Discovering Mira Ceti: Celestial Change and Cosmic Continuity  

NASA Astrophysics Data System (ADS)

In the short narrative that follows I introduce two new heroes. Although we begin with Fabricius's first sighting in 1596, the new pivot point in the drama is the collaboration between Hevelius and Boulliau that began around 1660. As it happens, Learned Europe paid little attention to Mira in the generation after the first scattered sightings of 1596, indeed, nearly 70 years passed before the New Star was given a working identity. Like Columbus discovering America, Fabricius and Holwarda saw different things - for convenience, I call them Fabricius's Star and Holwarda's Star. Hevelius's Historiola (Danzig, 1662) and Boulliau's Ad astronomos (Paris, 1667) presented a different vision. It made Mira famous. As I shall argue, if Hevelius gave Mira a history, Boulliau gave Mira a future.5 In the end, the New Star not only challenged the ancient cosmos, it became an enduring icon for the New Science, a returning reminder of celestial continuity and cosmic order.

Hatch, Robert Alan

133

DUST ATTENUATION IN UV-SELECTED STARBURSTS AT HIGH REDSHIFT AND THEIR LOCAL COUNTERPARTS: IMPLICATIONS FOR THE COSMIC STAR FORMATION RATE DENSITY  

SciTech Connect

We present a new analysis of the dust obscuration in starburst galaxies at low and high redshifts. This study is motivated by our unique sample of the most extreme UV-selected starburst galaxies in the nearby universe (z < 0.3), found to be good analogs of high-redshift Lyman break galaxies (LBGs) in most of their physical properties. We find that the dust properties of the Lyman break analogs (LBAs) are consistent with the relation derived previously by Meurer et al. (M99) that is commonly used to dust-correct star formation rate (SFR) measurements at a very wide range of redshifts. We directly compare our results with high-redshift samples (LBGs, 'BzK', and submillimeter galaxies at z {approx} 2-3) having IR data either from Spitzer or Herschel. The attenuation in typical LBGs at z {approx} 2-3 and LBAs is very similar. Because LBAs are much better analogs to LBGs compared to previous local star-forming samples, including M99, the practice of dust-correcting the SFRs of high-redshift galaxies based on the local calibration is now placed on a much more solid ground. We illustrate the importance of this result by showing how the locally calibrated relation between UV measurements and extinction is used to estimate the integrated, dust-corrected SFR density at z {approx_equal} 2-6.

Overzier, Roderik A.; Wang Jing [Max-Planck-Institut for Astrophysics, D-85748 Garching (Germany); Heckman, Timothy M. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Armus, Lee; Howell, Justin [Spitzer Science Center, Caltech, MS 220-6, Pasadena, CA 91125 (United States); Buat, Veronique [Laboratoire d'Astrophysique de Marseille, OAMP, Universite Aix-marseille, CNRS, 38 rue Frederic Joliot-Curie, 13388 Marseille Cedex 13 (France); Meurer, Gerhardt [ICRAR/University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Seibert, Mark [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Siana, Brian; Goncalves, Thiago S.; Martin, D. Christopher; Neill, James D. [California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States); Basu-Zych, Antara [NASA Goddard Space Flight Center, Laboratory for X-ray Astrophysics, Greenbelt, MD 20771 (United States); Charlot, Stephane [PMC Univ Paris 06, UMR7095, Institut d'Astrophysique de Paris, F-75014 Paris (France); Rich, R. Michael [Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562 (United States); Salim, Samir [National Optical Astronomical Observatories, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Schiminovich, David, E-mail: overzier@mpa-garching.mpg.de [Department of Astronomy, Columbia University, MC 2457, 550 West 120th Street, New York, NY 10027 (United States)

2011-01-01

134

X-Ray and Radio Emission from UV-Selected Star Forming Galaxies at Redshifts 1.5  

E-print Network

We have examined the stacked radio and X-ray emission from UV-selected galaxies spectroscopically confirmed to lie between redshifts 1.5 < z < 3.0 in the GOODS-North field to determine their average extinction and star formation rates (SFRs). The X-ray and radio data are obtained from the Chandra 2 Msec survey and the Very Large Array, respectively. There is a good agreement between the X-ray, radio, and de-reddened UV estimates of the average SFR for our sample of z~2 galaxies of ~50 solar masses per year, indicating that the locally-calibrated SFR relations appear to be statistically valid from redshifts 1.5 < z < 3.0. We find that UV-estimated SFRs (uncorrected for extinction) underestimate the bolometric SFRs as determined from the 2-10 keV X-ray luminosity by a factor of ~4.5 to 5.0 for galaxies over a large range in redshift from 1.0 < z < 3.5.

Naveen A. Reddy; Charles C. Steidel

2004-01-21

135

The blue UV slopes of z~4 Lyman break galaxies: implications for the corrected star formation rate density  

Microsoft Academic Search

We plan to analyse dust extinction in Lyman Break Galaxies (LBGs) by introducing a new and more reliable approach to their selection and to the characterization of their distribution of UV slopes beta, using deep IR images from HST. We exploit deep WFC3 IR observations of the ERS and HUDF fields over GOODS-South, combined with HST-ACS optical data, to select

M. Castellano; A. Fontana; A. Grazian; L. Pentericci; P. Santini; A. Koekemoer; S. Cristiani; A. Galametz; S. Gallerani; E. Vanzella; K. Boutsia; S. Gallozzi; R. Maiolino; N. Menci

2011-01-01

136

ACCESS - II. A complete census of star formation in the Shapley supercluster - UV and IR luminosity functions  

NASA Astrophysics Data System (ADS)

We present panoramic Spitzer/MIPS mid- and far-infrared (MIR/FIR) and GALEX ultraviolet imaging of the most massive and dynamically active system in the local Universe, the Shapley supercluster at z= 0.048, covering the five clusters that make up the supercluster core. We combine these data with existing spectroscopic data from 814 confirmed supercluster members to produce the first study of a local rich cluster including both ultraviolet and infrared luminosity functions (LFs). This joint analysis allows us to produce a complete census of star formation (both obscured and unobscured), extending down to star formation rates (SFRs) ˜0.02-0.05 M? yr-1, and quantify the level of obscuration of star formation among cluster galaxies, providing a local benchmark for comparison to ongoing and future studies of cluster galaxies at higher redshifts with Spitzer and Herschel. The GALEX near-ultraviolet (NUV) and far-ultraviolet (FUV) luminosity functions (LFs) obtained have steeper faint-end slopes than the local field population, due largely to the contribution of massive, quiescent galaxies at MFUV?-16. The 24- and 70-?m galaxy LFs for the Shapley supercluster instead have shapes fully consistent with those obtained for the Coma cluster and for the local field galaxy population. This apparent lack of environmental dependence for the shape of the FIR luminosity function suggests that the bulk of the star-forming galaxies that make up the observed cluster infrared LF have been recently accreted from the field and have yet to have their star formation activity significantly affected by the cluster environment. We estimate a global SFR of 327 M? yr-1 over the whole supercluster core, of which just ˜20 per cent is visible directly in the ultraviolet continuum and ˜80 per cent is reprocessed by dust and emitted in the infrared. The level of obscuration (LIR/LFUV) in star-forming galaxies is seen to increase linearly with LK over 2 orders of magnitude in stellar mass.

Haines, C. P.; Busarello, G.; Merluzzi, P.; Smith, R. J.; Raychaudhury, S.; Mercurio, A.; Smith, G. P.

2011-03-01

137

THE UV LUMINOSITY FUNCTION OF STAR-FORMING GALAXIES VIA DROPOUT SELECTION AT REDSHIFTS z {approx} 7 AND 8 FROM THE 2012 ULTRA DEEP FIELD CAMPAIGN  

SciTech Connect

We present a catalog of high-redshift star-forming galaxies selected to lie within the redshift range z {approx_equal} 7-8 using the Ultra Deep Field 2012 (UDF12), the deepest near-infrared (near-IR) exposures yet taken with the Hubble Space Telescope (HST). As a result of the increased near-IR exposure time compared to previous HST imaging in this field, we probe {approx}0.65 (0.25) mag fainter in absolute UV magnitude, at z {approx} 7 (8), which increases confidence in a measurement of the faint end slope of the galaxy luminosity function. Through a 0.7 mag deeper limit in the key F105W filter that encompasses or lies just longward of the Lyman break, we also achieve a much-refined color-color selection that balances high redshift completeness and a low expected contamination fraction. We improve the number of dropout-selected UDF sources to 47 at z {approx} 7 and 27 at z {approx} 8. Incorporating brighter archival and ground-based samples, we measure the z {approx_equal} 7 UV luminosity function to an absolute magnitude limit of M{sub UV} = -17 and find a faint end Schechter slope of {alpha}=-1.87{sup +0.18}{sub -0.17}. Using a similar color-color selection at z {approx_equal} 8 that takes our newly added imaging in the F140W filter into account, and incorporating archival data from the HIPPIES and BoRG campaigns, we provide a robust estimate of the faint end slope at z {approx_equal} 8, {alpha}=-1.94{sup +0.21}{sub -0.24}. We briefly discuss our results in the context of earlier work and that derived using the same UDF12 data but with an independent photometric redshift technique.

Schenker, Matthew A.; Ellis, Richard S. [Department of Astrophysics, California Institute of Technology, MC 249-17, Pasadena, CA 91125 (United States); Robertson, Brant E.; Schneider, Evan [Department of Astronomy and Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Ono, Yoshiaki; Ouchi, Masami; Stark, Daniel P. [Institute for Cosmic Ray Research, University of Tokyo, Kashiwa City, Chiba 277-8582 (Japan); McLure, Ross J.; Dunlop, James S.; Bowler, Rebecca A. A.; Curtis-Lake, Emma; Rogers, Alexander B.; Cirasuolo, Michele [Institute for Astronomy, University of Edinburgh, Edinburgh EH9 3HJ (United Kingdom); Koekemoer, Anton [Space Telescope Science Institute, Baltimore, MD 21218 (United States); Charlot, Stephane [UPMC-CNRS, UMR7095, Institut d'Astrophysique de Paris, F-75014 Paris (France); Furlanetto, Steven R., E-mail: schenker@astro.caltech.edu [Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA 90095 (United States)

2013-05-10

138

Whole-Genome Sequence of Weissella ceti Strain WS08, Isolated from Diseased Rainbow Trout in Brazil  

PubMed Central

We report here the complete genome sequence of Weissella ceti strain WS08, an emerging pathogen to farm-raised rainbow trout. The genome of strain WS08 is composed of a circular chromosome with 1,355,853 bp and a G+C content of 40.78%. PMID:25146147

Leal, G.; Pereira, F. L.; Soares, S. C.; Dorella, F. A.; Carvalho, A. F.; Pereira, U. P.; Azevedo, V. A. C.

2014-01-01

139

Quantitative UV spectroscopy of early O stars on the Magellanic Clouds: The determination of the stellar metallicities  

NASA Technical Reports Server (NTRS)

Ultraviolet spectra of four O stars in the Magellanic Clouds obtained with the faint object spectrograph of the Hubble Space Telescope are analyzed with respect to their metallicity. The metal abundances are derived from the stellar parameters and the mass loss rate with a two step procedure: hydrodynamic radiation-driven wind models with metallicity as a free parameter are constructed to fit the observed wind momentum rate and thus yield a dynamical metallicity, and synthetic spectra are computed for different metal abundances and compared to the observed spectra in order to obtain a spectroscopic metallicity.

Haser, Stefan M.; Pauldrach, Adalbert W. A.; Lennon, Danny J.; Kudritzki, Rolf-Peter; Lennon, Maguerite; Puls, Joachim; Voels, Stephen A.

1997-01-01

140

A search variability in the UV spectrum of Pi Aquarii and Fe 3 shell lines of Be stars  

NASA Technical Reports Server (NTRS)

Several short U1 and U2 observations of Be stars are obtained with the Copernicus satellite. Pi Aquarii (B1 IV-Ve) is observed with the U1 and U2 spectrometers. These scans are compared with earlier observations. Variations in the strengths and profiles of selected shell and photospheric features are examined. In order to study possible changes in the temperature of the circumstellar envelope, features covering a wide range in ionization are observed. Included in the observing program are lines of O VI, N V, Si IV, Si III, S III, Fe III, and N I.

1984-01-01

141

Uv Observations of Geminga  

NASA Astrophysics Data System (ADS)

The gamma-ray source Geminga (identified with the X-ray source 1E0630+178) is a near-by neutron star detected as a 237 ms pulsar in both the X-ray and gamma-ray region of the spectrum (Halpern and Holt, 1992). It is not detected as a radio pulsar, however. We will observe the proposed optical counterpart of Geminga (star G" in the list of Halpern and Tytler, 1988) in the UV (140 - 300 nm) with the High Speed Photometer in an attempt to detect the 237 ms pulsation. An offset of 1.3 arcmin from GSC 01333.01169 will be required to acquire G". A positive detection of the 237 ms period will confirm the identity of G" as Geminga and extend our knowledge of the spectrum of a neutron star into the UV; a negative result may place important constraints on the standard model of neutron star emission.

Holt, Stephen

1991-07-01

142

REST-FRAME UV-OPTICALLY SELECTED GALAXIES AT 2.3 {approx}< z {approx}< 3.5: SEARCHING FOR DUSTY STAR-FORMING AND PASSIVELY EVOLVING GALAXIES  

SciTech Connect

A new set of color selection criteria (VJL) analogous with the BzK method is designed to select both star-forming galaxies (SFGs) and passively evolving galaxies (PEGs) at 2.3 {approx}< z {approx}< 3.5 by using rest-frame UV-optical (V - J versus J - L) colors. The criteria are thoroughly tested with theoretical stellar population synthesis models and real galaxies with spectroscopic redshifts to evaluate their efficiency and contamination. We apply the well-tested VJL criteria to the HST/WFC3 Early Release Science field and study the physical properties of selected galaxies. The redshift distribution of selected SFGs peaks at z {approx} 2.7, slightly lower than that of Lyman break galaxies at z {approx} 3. Comparing the observed mid-infrared fluxes of selected galaxies with the prediction of pure stellar emission, we find that our VJL method is effective at selecting massive dusty SFGs that are missed by the Lyman break technique. About half of the star formation in massive (M{sub star} > 10{sup 10} M{sub Sun }) galaxies at 2.3 {approx}< z {approx}< 3.5 is contributed by dusty (extinction E(B - V) > 0.4) SFGs, which, however, only account for {approx}20% of the number density of massive SFGs. We also use the mid-infrared fluxes to clean our PEG sample and find that galaxy size can be used as a secondary criterion to effectively eliminate the contamination of dusty SFGs. The redshift distribution of the cleaned PEG sample peaks at z {approx} 2.5. We find six PEG candidates at z > 3 and discuss possible methods to distinguish them from dusty contamination. We conclude that at least part of our candidates are real PEGs at z {approx} 3, implying that these types of galaxies began to form their stars at z {approx}> 5. We measure the integrated stellar mass density (ISMD) of PEGs at z {approx} 2.5 and set constraints on it at z > 3. We find that the ISMD grows by at least about a factor of 10 in 1 Gyr at 3 < z <5 and by another factor of 10 in the next 3.5 Gyr (1 < z < 3).

Guo Yicheng; Giavalisco, Mauro; Cassata, Paolo; Williams, Christina C.; Salimbeni, Sara [Astronomy Department, University of Massachusetts, 710 N. Pleasant Street, Amherst, MA 01003 (United States); Ferguson, Henry C.; Koekemoer, Anton; Grogin, Norman A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Dickinson, Mark [NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Chary, Ranga-Ram [Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125 (United States); Messias, Hugo [Centro de Astronomia e Astrofisica da Universidade de Lisboa, Observatorio Astronomico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa (Portugal); Tundo, Elena [INAF-Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste (Italy); Lin Lihwai [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan (China); Lee, Seong-Kook [School of Physics, Korea Institute for Advanced Study, Hoegiro 87, Dongdaemun-Gu, Seoul 130-722 (Korea, Republic of); Fontana, Adriano; Grazian, Andrea [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I00040 Monteporzio (Italy); Kocevski, Dale [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Lee, Kyoung-Soo [Yale Center for Astronomy and Astrophysics, Department of Physics, Yale University, New Haven, CT 06520 (United States); Villanueva, Edward [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101-1292 (United States); Van der Wel, Arjen, E-mail: yicheng@astro.umass.edu [Max-Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

2012-04-20

143

Time-Resolved Ultraviolet Spectroscopy of the SW Sex Star DW UMa: Confirmation of a Hidden White Dwarf and the UV Counterpart to Phase 0.5 Absorption Events  

E-print Network

We present time-resolved, ultraviolet (UV) spectroscopy of the SW Sex star DW UMa in the high state. We confirm that, shortward of 1500 \\AA, the high-state, UV continuum level is lower than the white dwarf (WD)-dominated low-state level. We also do not see the WD contact phases in the high state eclipse light curves. These results confirm our earlier finding that the WD in this system is hidden from view in the high state. Based on this, we caution that eclipse mapping of high-inclination SW Sex stars in the high state may yield incorrect or misleading results. In the context of DW UMa, we demonstrate explicitly that distance estimates obtained by recent eclipse mapping studies cannot be reconciled with the WD-dominated low-state spectrum. We also show that the fluxes of the UV emission lines in the high state drop near orbital phase 0.5. This is the first detection of a UV counterpart to the class-defining phase 0.5 absorption seen in the optical emission lines of SW Sex stars.

Christian Knigge; Sofia Araujo-Betancor; Boris T. Gaensicke; Knox S. Long; Paula Szkody; D. W. Hoard; R. I. Hynes; V. S. Dhillon

2004-10-12

144

Time-Resolved Ultraviolet Spectroscopy of the SW Sex Star DW UMa: Confirmation of a Hidden White Dwarf and the UV Counterpart to Phase 0.5 Absorption Events  

E-print Network

We present time-resolved, ultraviolet (UV) spectroscopy of the SW Sex star DW UMa in the high state. We confirm that, shortward of 1500 \\AA, the high-state, UV continuum level is lower than the white dwarf (WD)-dominated low-state level. We also do not see the WD contact phases in the high state eclipse light curves. These results confirm our earlier finding that the WD in this system is hidden from view in the high state. Based on this, we caution that eclipse mapping of high-inclination SW Sex stars in the high state may yield incorrect or misleading results. In the context of DW UMa, we demonstrate explicitly that distance estimates obtained by recent eclipse mapping studies cannot be reconciled with the WD-dominated low-state spectrum. We also show that the fluxes of the UV emission lines in the high state drop near orbital phase 0.5. This is the first detection of a UV counterpart to the class-defining phase 0.5 absorption seen in the optical emission lines of SW Sex stars.

Knigge, C; Gänsicke, B T; Long, K S; Szkody, P; Hoard, D W; Hynes, R I; Dhillon, V S; Knigge, Christian; Araujo-Betancor, Sofia; Gaensicke, Boris T.; Long, Knox S.; Szkody, Paula

2004-01-01

145

VizieR Online Data Catalog: PHAT X. UV-IR photometry of M31 stars (Williams+, 2014)  

NASA Astrophysics Data System (ADS)

The data for the Panchromatic Hubble Andromeda Treasury (PHAT) survey were obtained from 2010 July 12 to 2013 October 12 using the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC), the Wide Field Camera 3 (WFC3) IR (infrared) channel, and the WFC3 UVIS (ultraviolet-optical) channel. The observing strategy is described in detail in Dalcanton et al. (2012ApJS..200...18D). A list of the target names, observing dates, coordinates, orientations, instruments, exposure times, and filters is given in Table 1. Using the ACS and WFC3 cameras aboard HST, we have photometered 414 contiguous WFC3/IR footprints covering 0.5deg2 of the M31 star-forming disk. (4 data files).

Williams, B. F.; Lang, D.; Dalcanton, J. J.; Dolphin, A. E.; Weisz, D. R.; Bell, E. F.; Bianchi, L.; Byler, N.; Gilbert, K. M.; Girardi, L.; Gordon, K.; Gregersen, D.; Johnson, L. C.; Kalirai, J.; Lauer, T. R.; Monachesi, A.; Rosenfield, P.; Seth, A.; Skillman, E.

2015-01-01

146

VizieR Online Data Catalog: UV spectra of the central star of Sh 2-216 (Rauch+, 2007)  

NASA Astrophysics Data System (ADS)

We perform a comprehensive spectral analysis of LS V +46 21 in order to compare its photospheric properties to theoretical predictions from stellar evolution theory as well as from diffusion calculations. LS V +46 21 is the DAO-type central star of the planetary nebula Sh 2-216. High-resolution, high-S/N ultraviolet observations obtained with FUSE and STIS aboard the HST as well as the optical spectrum have been analyzed in order to determine the photospheric parameters and the spectroscopic distance. We performed a detailed spectral analysis of the ultraviolet and optical spectrum by means of state-of-the-art NLTE model-atmosphere techniques. >From the NIV-NV, OIV-OVI, SiIV-SiV, and FeV-FeVII ionization equilibria, we determined an effective temperature of 95+/-2kK with high precision. The surface gravity is logg=6.9+/-0.2. An unexplained discrepancy appears between the spectroscopic distance d=224+46-58pc and the parallax distance d=129+6-5pc of LS V +46 21. For the first time, we have identified Mg IV and Ar VI absorption lines in the spectrum of a hydrogen-rich central star and determined the Mg and Ar abundances as well as the individual abundances of iron-group elements (Cr, Mn, Fe, Co, and Ni). With the realistic treatment of metal opacities up to the iron group in the model-atmosphere calculations, the so-called Balmer-line problem (found in models that neglect metal-line blanketing) vanishes. Spectral analysis by means of NLTE model atmospheres has presently arrived at a high level of sophistication, which is now hampered largely by the lack of reliable atomic data and accurate line-broadening tables. Strong efforts should be made to improve upon this situation. (5 data files).

Rauch, T.; Ziegler, M.; Werner, K.; Kruk, J. W.; Oliveira, C. M.; Vande Putte, D.; Migniani, R. P.; Kerber, F.

2007-05-01

147

Characterization of Weissella ceti infections in Brazilian rainbow trout, Oncorhynchus mykiss (Walbaum), farms and development of an oil-adjuvanted vaccine.  

PubMed

Weissella ceti is an emerging bacterial pathogen that affects rainbow trout, Oncorhynchus mykiss (Walbaum), farms. The aims of this study were to genotype W. ceti strains isolated from distinct geographical origins and to determine the efficacy of an oil-adjuvanted vaccine against the disease. Between 2010 and 2012, outbreaks were recorded in five Brazilian farms, and 34 W. ceti isolates were genetically characterized by repetitive extragenic palindromic PCR, enterobacterial repetitive intergenic consensus sequences PCR and pulsed-field gel electrophoresis. Two different W. ceti vaccines were tested: an aqueous-based whole-cell inactivated vaccine (bacterin) and oil-adjuvanted vaccine. Their efficacy was evaluated in rainbow trout at 30 and 60 days post-vaccination (d.p.v.). W. ceti was found to be a highly homogeneous population in Brazil, with clonally related genotypes. Oil-adjuvanted vaccine exhibited the best (P < 0.05) protection against disease, reaching relative percentage survival (RPS)values of 92% at 30 and 60 d.p.v. Bacterin resulted in RPS values of 67% and 58% at day 30 and 60, respectively. The oil-adjuvanted vaccine provided effective protection against W. ceti infection in rainbow trout. PMID:24661016

Costa, F A A; Leal, C A G; Schuenker, N D; Leite, R C; Figueiredo, H C P

2015-03-01

148

EFFECTS OF CLOUDS AND TROPOSPHERIC AIR QUALITY ON SURFACE UV AT 6 UV RESEARCH SITES  

EPA Science Inventory

This document provides a summary of results of the EPA STAR funded proposal “Effects of Clouds and Tropospheric Pollution on Surface UV at six EPA UV Research Sites”. This project worked to provide high quality UV spectral solar irradiance, erythema (UV Index), oz...

149

UV-TO-FIR ANALYSIS OF SPITZER/IRAC SOURCES IN THE EXTENDED GROTH STRIP. II. PHOTOMETRIC REDSHIFTS, STELLAR MASSES, AND STAR FORMATION RATES  

SciTech Connect

Based on the ultraviolet to far-infrared photometry already compiled and presented in a companion paper (Paper I), we present a detailed spectral energy distribution (SED) analysis of nearly 80,000 IRAC 3.6 + 4.5 {mu}m selected galaxies in the Extended Groth Strip. We estimate photometric redshifts, stellar masses, and star formation rates (SFRs) separately for each galaxy in this large sample. The catalog includes 76,936 sources with [3.6] {<=} 23.75 (85% completeness level of the IRAC survey) over 0.48 deg{sup 2}. The typical photometric redshift accuracy is {Delta}z/(1 + z) = 0.034, with a catastrophic outlier fraction of just 2%. We quantify the systematics introduced by the use of different stellar population synthesis libraries and initial mass functions in the calculation of stellar masses. We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies, based on several sets of dust emission templates and SFR indicators. We evaluate the systematic differences and goodness of the different SFR estimations using the deep FIDEL 70 {mu}m data available in the Extended Groth Strip. Typical random uncertainties of the IR-bases SFRs are a factor of two, with non-negligible systematic effects at z {approx}> 1.5 observed when only MIPS 24 {mu}m data are available. All data products (SEDs, postage stamps from imaging data, and different estimations of the photometric redshifts, stellar masses, and SFRs of each galaxy) described in this and the companion paper are publicly available, and they can be accessed through our the Web interface utility Rainbow-navigator.

Barro, G.; Perez-Gonzalez, P. G.; Gallego, J.; Villar, V.; Zamorano, J. [Departamento de Astrofisica, Facultad de CC. Fisicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Ashby, M. L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Kajisawa, M.; Yamada, T. [Astronomical Institute, Tohoku University, Aramaki, Aoba, Sendai 9808578 (Japan); Miyazaki, S. [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)

2011-04-01

150

The Effect of Crystallization on the Pulsations of White Dwarf Stars  

Microsoft Academic Search

We consider the pulsational properties of white dwarf star models with\\u000atemperatures appropriate for the ZZ Ceti instability strip and with masses\\u000alarge enough that they should be substantially crystallized. Our work is\\u000amotivated by the existence of a potentially crystallized DAV, BPM 37093, and\\u000athe expectation that digital surveys in progress will yield many more such\\u000amassive pulsators.\\u000a A

M. H. Montgomery; D. E. Winget

1999-01-01

151

Modelling UV sky for future UV missions  

NASA Astrophysics Data System (ADS)

Software simulators are now widely used in all areas of science, especially in application to astronomical missions: from instrument design to mission planning, and to data interpretation. We present a simulator to model the diffuse ultraviolet sky, where the different contributors are separately calculated and added together to produce a sky image of the size specified by the instrument requirements. Each of the contributors to the background, instrumental dark current, airglow, zodiacal light and diffuse galactic light, is dependent on various factors. Airglow is dependent on the time of day, zodiacal light on the time of year, angle from the Sun and from the ecliptic, and diffuse UV emission depends on the look direction. To provide a full description of any line of sight, we have also added stars. The diffuse UV background light can dominate in many areas of the sky and severely impact space telescopes viewing directions due to over brightness. The simulator, available as a downloadable package and as a simple web-based tool, can be applied to separate missions and instruments. For demonstration, we present the example used for two UV missions: the UVIT instrument on the Indian ASTROSAT mission to be launched in the next year and a prospective wide-field mission to search for transients in the UV.

Sreejith, A. G.; Safanova, M.; Mohan, R.; Murthy, Jayant

152

Chromospherically active stars. 11: Giant with compact hot companions and the barium star scenario  

NASA Technical Reports Server (NTRS)

We have determined spectroscopic orbits for three chromsopherically active giants that have hot compact companions. They are HD 160538 (KO III + wd, P = 904 days), HD 165141 (G8 III + wd, P approximately 5200 days), and HD 185510 (KO III + sdB, P = 20.6619 days). By fitting an IUE spectrum with theoretical models, we find the white dwarf companion of HD 165141 has a temperature of about 35,000 K. Spectral types and rotational velocities have been determined for the three giants and distances have been estimated. These three systems and 39 Ceti are compared with the barium star mass-transfer scenario. The long-period mild barium giant HD 165141 as well as HD 185510 and 39 Ceti, which have relatively short periods and normal abundance giants, appear to be consistent with this scenario. The last binary, HD 160538, a system with apparently near solar abundances, a white dwarf companion, and orbital characteristics similar to many barium stars, demonstrates that the existence of a white dwarf companion is insufficient to produce a barium star. The paucity of systems with confirmed white dwarf companions makes abundance analyses of HD 160538 and HD 165141 of great value in examining the role of metallicity in barium star formation.

Fekel, Francis C.; Henry, Gregory W.; Busby, Michael R.; Eitter, Joseph J.

1993-01-01

153

UV Throughput  

NASA Astrophysics Data System (ADS)

This proposal is designed to perform a check of the UV throughput during Cycle 7 and is loosely based on the Cycle 5 and 6 UV throughput programs {6186, 6936} as well as past Lyman alpha proposals {5778 and 7018}. The Cycle 7 program is designed to verify that the spectral response curve in the UV has not changed appreciably since the Cycle 6 measurements and that the contamination effects remain essentially same. The Lyman alpha observations will provide a check for possible contamination on the pickoff mirror.

Baggett, Sylvia

1997-07-01

154

Predicting UV sky for future UV missions  

NASA Astrophysics Data System (ADS)

Software simulators are now widely used in all areas of science, especially in application to astronomical missions: from instrument design to mission planning, and to data interpretation. We present a simulator to model the diffuse ultraviolet sky, where the different contributors are separately calculated and added together to produce a sky image of the size specified by the instrument requirements. Each of the contributors to the background, instrumental dark current, airglow, zodiacal light and diffuse Galactic light, depends on different factors. Airglow is dependent on the time of day; zodiacal light depends on the time of year, angle from the Sun and from the ecliptic; diffuse UV emission depends on the line of sight. To provide a full description of the sky along any line of sight, we have also added stars. The UV background light can dominate in many areas of the sky and severely limit viewing directions due to overbrightness. The simulator, available as a downloadable package and as a web-based tool, can be applied to preparation of real space missions and instruments. For demonstration, we present the example use for the two near-future UV missions: UVIT instrument on the Indian Astrosat mission and a new proposed wide-field (?1000 square degrees) transient explorer satellite.

Safonova, M.; Mohan, R.; Sreejith, A. G.; Murthy, Jayant

2013-02-01

155

Complete Genome Sequence of a Brucella ceti ST26 Strain Isolated from a Striped Dolphin (Stenella coeruleoalba) on the Coast of Italy  

PubMed Central

Brucella spp. are important pathogens affecting a wide range of terrestrial and aquatic animals. We report the complete and annotated genome sequence of Brucella ceti ST26 strain TE10759-12, isolated from a striped dolphin (Stenella coeruleoalba) stranded along the Italian shoreline in March of 2012. PMID:24604638

Marcacci, Maurilia; Orsini, Massimiliano; Zilli, Katiuscia; Di Giannatale, Elisabetta; Garofolo, Giuliano; Cammà, Cesare

2014-01-01

156

Complete Genome Sequence of a Brucella ceti ST26 Strain Isolated from a Striped Dolphin (Stenella coeruleoalba) on the Coast of Italy.  

PubMed

Brucella spp. are important pathogens affecting a wide range of terrestrial and aquatic animals. We report the complete and annotated genome sequence of Brucella ceti ST26 strain TE10759-12, isolated from a striped dolphin (Stenella coeruleoalba) stranded along the Italian shoreline in March of 2012. PMID:24604638

Ancora, Massimo; Marcacci, Maurilia; Orsini, Massimiliano; Zilli, Katiuscia; Di Giannatale, Elisabetta; Garofolo, Giuliano; Cammà, Cesare

2014-01-01

157

Amphritea ceti sp. nov., isolated from faeces of Beluga whale (Delphinapterus leucas).  

PubMed

A Gram-stain-negative, aerobic, non-spore-forming, non-flagellated and rod-shaped or ovoid bacterial strain, designated RA1(T), was isolated from faeces collected from Beluga whale (Delphinapterus leucas) in Yeosu aquarium, South Korea. Strain RA1(T) grew optimally at 25 °C, at pH 7.0-8.0 and in the presence of 2.0?% (w/v) NaCl. Neighbour-joining, maximum-likelihood and maximum-parsimony phylogenetic trees based on 16S rRNA gene sequences revealed that strain RA1(T) joins the cluster comprising the type strains of three species of the genus Amphritea, with which it exhibited 95.8-96.0?% sequence similarity. Sequence similarities to the type strains of other recognized species were less than 94.3?%. Strain RA1(T) contained Q-8 as the predominant ubiquinone and summed feature 3 (C16?:?1?7c and/or C16?:?1?6c), C18?:?1?7c and C16?:?0 as the major fatty acids. The major polar lipids of strain RA1(T) were phosphatidylethanolamine, phosphatidylglycerol, two unidentified lipids and one unidentified aminolipid. The DNA G+C content of strain RA1(T) was 47.4 mol%. The differential phenotypic properties, together with the phylogenetic distinctiveness, revealed that strain RA1(T) is separated from other species of the genus Amphritea. On the basis of the data presented, strain RA1(T) is considered to represent a novel species of the genus Amphritea, for which the name Amphritea ceti sp. nov. is proposed. The type strain is RA1(T) (?=?KCTC 42154(T)?=?NBRC 110551(T)). PMID:25237149

Kim, Young-Ok; Park, Sooyeon; Kim, Doo Nam; Nam, Bo-Hye; Won, Sung-Min; An, Du Hae; Yoon, Jung-Hoon

2014-12-01

158

Local Interstellar Medium Properties and Deuterium Abundances for the Lines of Sight Toward HR 1099, 31 Comae, beta Ceti, and beta Cassiopeiae  

NASA Technical Reports Server (NTRS)

We analyze Goddard High-Resolution Spectrograph data to infer the properties of local interstellar gas and the Deuterium/Hydrogen (D/H) ratio for lines of sight toward four nearby late-type stars-HR 1099, 31 Comae, beta Ceti, and beta Cassiopeiae. The data consist of spectra of the hydrogen and deuterium Lyman-(alpha) lines, and echelle spectra of the Mg IIh and k lines toward all stars except beta Cas. Spectra of the RS CVn-type spectroscopic binary system HR 1099 were obtained near opposite quadratures to determine the intrinsic stellar emission line profile and the interstellar absorption separately. Multiple-velocity components were found toward HR 1099 and beta Cet. The spectra of 31 Com and beta Cet are particularly interesting because they sample lines of sight toward the north and south Galactic poles, respectively, for which H I and D I column densities were not previously available. The north Galactic pole appears to be a region of low hydrogen density like the 'interstellar tunnel' toward epsilon CMa. The temperature and turbulent velocities of the Local InterStellar Medium (LISM) that we measure for the lines of sight toward HR 1099, 31 Com, beta Cet, and beta Cas are similar to previously measured values (T approx.7000 K and xi = 1.0-1.6 km/s). The deuterium/hydrogen ratios found for these lines of sight are also consistent with previous measurements of other short lines of sight, which suggest D/H approx. 1.6 x 10(sup -5). In contrast, the Mg abundance measured for the beta Cet line of sight (implying a logarithmic depletion of D(Mg) = +0.30 +/- 0.15) is about 5 times larger than the Mg abundance previously observed toward alpha Cen, and about 20 times larger than all other previous measurements for the LISM. These results demonstrate that metal abundances in the LISM vary greatly over distances of only a few parsecs.

Piskunov, Nikolai; Wood, Brian E.; Linsky, Jeffrey L.; Dempsey, Robert C.; Ayres, Thomas R.

1997-01-01

159

Draft Genome Sequences of Brucella suis Biovar 4 Strain NCTC 10385, Brucella ceti Strain NCTC 12891T, Brucella inopinata Strain CAMP 6436T, and Brucella neotomae Strain ATCC 23459T  

PubMed Central

With the aim of developing quantitative PCR methods for the detection and differentiation of Brucella species, the genomes of Brucella ceti, Brucella inopinata, Brucella netotomae, and Brucella suis biovar 4 were sequenced and analyzed. PMID:25278518

Ferrari, Sevinc; Lindberg, Martina; Bäckman, Stina; Kaden, Rene

2014-01-01

160

UV Properties of Galactic Globular Clusters  

Microsoft Academic Search

We propose to collect deep far and near-UV images of 35 Galactic globular clusters (GCs). This will be the largest homogeneous dataset ever produced on the UV photometric properties of Galactic GCs and will allow a full characterization of their hot stellar contents. For all the targets, horizontal branch (HB) stars will be clearly resolved, so that the data will

Ricardo Schiavon

2004-01-01

161

A Steep Faint-End Slope of the UV Luminosity Function at z~2-3: Implications for the Global Stellar Mass Density and Star Formation in Low Mass Halos  

E-print Network

We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (alpha) of the UV LF at redshifts 1.92000 spectroscopic redshifts and ~31000 LBGs in 31 spatially-independent fields over a total area of 3261 arcmin^2. These data allow us to select galaxies to 0.07L* and 0.10L* at z~2 and z~3, respectively. A maximum likelihood analysis indicates steep values of alpha(z=2)=-1.73+/-0.07 and alpha(z=3)=-1.73+/-0.13. This result is robust to luminosity dependent systematics in the Ly-alpha equivalent width and reddening distributions, is similar to the steep values advocated at z>4, and implies that ~93% of the unobscured UV luminosity density at z~2-3 arises from sub-L* galaxies. With a realistic luminosity dependent reddening distribution, faint to moderately luminous galaxies account for >70% and >25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.92 contrasts with the shallower value inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low mass halos capable of supporting star formation at z<2. [Abridged

Naveen A. Reddy; Charles C. Steidel

2008-10-15

162

Formation of cerium titanate, CeTi 2 O 6 , in sol–gel films studied by XRD and FAR infrared spectroscopy  

Microsoft Academic Search

The process of formation of cerium titanate films as a function of annealing temperature and composition has been studied\\u000a by combining X-ray diffraction analysis and far infrared spectroscopy. The films have been prepared by a sol–gel synthesis\\u000a using metal chlorides as precursors; the synthesis allows obtaining cerium titanate films upon annealing in air. A brannerite\\u000a type, CeTi2O6, phase has been

Tongjit Kidchob; Luca Malfatti; Daniela Marongiu; Stefano Enzo; Plinio Innocenzi

2009-01-01

163

UV variability in BP Tau  

NASA Astrophysics Data System (ADS)

We report the variations of the UV spectrum of BP Tau from 5 to 19 January, 1992 when the star was monitored with IUE during 2 rotation periods. Our data indicate that lines that can be excited by recombination processes, such as those from O I and He II have periodic-like light curves, whereas lines that are only collisionally excited do not follow a periodic-like trend. These results agree with the expectations of the magnetically channelled accretion models.

Gomez de Castro, Ana I.; Franqueira, Mercedes; Petitjean, Patrick

164

UV SPECTRAL SYNTHESIS OF VEGA  

SciTech Connect

We show that the UV spectrum (1280-3200 A) of the 'superficially normal' A-star Vega, as observed by the International Ultraviolet Explorer (IUE) satellite at a resolution comparable to the star's rotational broadening width, can be fit remarkably well by a single-temperature synthetic spectrum based on LTE atmosphere models and a newly constructed UV line list. If Vega were a normal, equator-on, slow-rotating star, then its spectrum and our analysis would indicate a temperature of T{sub eff} {approx_equal}9550 K, surface gravity of log g {approx_equal}3.7, general surface metallicity of [m/H] {approx_equal}-0.5, and a microturbulence velocity of v{sub turb} {approx_equal}2.0 km s{sup -1}. Given its rapid rotation and nearly pole-on orientation, however, these parameters must be regarded as representing averages across the observed hemisphere. Modeling the complex UV line spectrum has allowed us to determine the specific surface abundances for 17 different chemical elements, including CNO, the light metals, and the iron group elements. The resultant abundance pattern agrees in general with previous results, although there is considerable scatter in the literature. Despite its peculiarities, Vega has turned out to provide a powerful test of the extent of our abilities to model the atmospheric properties of the early A-stars, particularly the detailed UV line spectrum. The value of the measurements from this pilot study will increase as this analysis is extended to more objects in the rich high-dispersion IUE data archive, including both normal and peculiar objects.

Fitzpatrick, E. L., E-mail: edward.fitzpatrick@villanova.ed [Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States)

2010-12-20

165

The UV Side of BOSS Galaxies  

NASA Astrophysics Data System (ADS)

We exploit stellar population models of absorption line indices in the ultraviolet to assess their power in determining physical properties of the stellar populations of galaxies. We use a system of 8 indices between 2200–3200 A, tracing several chemical elements including Mg and Fe. We apply these models to a large sample of z ˜ 0.6 massive galaxies from the SDSS-III/BOSS survey using both individual spectra and stacks. We find qualitative agreement between stellar ages derived from UV absorption indices and those from full broadband Spectral Energy Distribution (SED) fitting. We also find evidence for old stars contributing to the UV, rather than new star formation.

Le Cras, C.; Maraston, C.; Thomas, D.

2014-09-01

166

The UV Upturn: From M32 to Distant Clusters  

E-print Network

I review the observational constraints on the stars responsible for the upturn in the UV spectra of ellipticals, ranging from galaxies in the local Universe to distant clusters. In nearby galaxies, this UV upturn is produced by a minority population of extreme horizontal branch (EHB) stars, with the large variations observed in the UV-to-optical flux ratio driven by variations in the number of EHB stars, and not the type of UV-bright stars. Deep UV images of the nearest elliptical galaxy, M32, show that it has a well-populated EHB, even though it has the weakest UV upturn of any known elliptical galaxy. However, M32 suffers from a striking dearth of the hot post-HB stars expected from canonical evolutionary theory. As we observe to larger lookback times in more distant galaxy clusters, the UV upturn fades, as predicted by theories of stellar and galactic evolution, but does so gradually. Because the EHB stars do not appear suddenly in the Universe, their presence is likely driven by a large dispersion in the parameters that govern HB morphology.

Thomas M. Brown

2003-08-28

167

UV measurements of the local SFR  

NASA Astrophysics Data System (ADS)

Because of its strong interest in itself and for comparison to the hi-z Universe, the rest-UV approach to the global SFR in the local Universe has motivated a long standing effort to overcome the difficulties inherent to observations from space. This brief review focuses on the results obtained from wide-band observations on ``normally star forming" galaxies, which show only moderate dust attenuation and may well host the bulk of the star formation activity in the local Universe (Strong starbursts are addressed by Tim Heckman, this Session). The wide-band rest-UV approach is first illustrated with results on the major characteristics of star formation in nearby individual galaxies, their variations along the Hubble sequence and their links with the gas content and galaxy parameters. The availability of a few genuine rest-UV selected galaxies samples at reshifts below 0.5 has opened the door to the first statistical approaches to the global star formation parameters in the local Universe. The results address the derivation of the FUV luminosity function, the global star formation intensity, the influence of environment, and the amount of star formation that could be hidden to rest-UV selected samples. Along the talk, the rest-UV approach to SFR is compared to other young population tracers. We expose its strengths and weaknesses, and stress how complementary data available in the local Universe helps find a way around the major limitations to the accuracy (namely the dust attenuation-see also Daniella Calzetti this Session, the metallicity effects, the IMF scatter and the microhistory- see also Richard Ellis, this Session). We end with some perspectives promised by GALEX. Funding by CNES and CNRS is acknowledged.

Milliard, B.; Donas, J.; Buat, V.; Deharveng, J.-M.

2001-05-01

168

UV-based therapy.  

PubMed

UV phototherapy has a long history of use for the treatment of select diseases in dermatology. Its use has evolved into more effective and targeted modalities, including psoralen + UV-A photochemotherapy, narrowband UV-B, excimer laser, and UV-A1 phototherapy. With its proven record of efficacy and safety, UV phototherapy is an excellent option in the treatment of an ever-growing number of skin conditions. PMID:24891061

Totonchy, Mariam B; Chiu, Melvin W

2014-07-01

169

Optical, UV and Radio Observations of RS Canum Venaticorum  

NASA Astrophysics Data System (ADS)

Preliminary results are reported on optical, UV and radio observations of the binary system RS Canum Venaticorum carried out in March 1984, as a part of the international coordinated programme on solar-like activity in late type stars.

Catalano, S.; Rodono, M.; Linsky, J. L.; Carpenter, K.; Gibson, D.; Gary, D.; Butler, J.

170

Magnetic Interaction between Stars and Hot Jupiters as Observed in Ca II H & K Emission - An Update  

NASA Astrophysics Data System (ADS)

We monitored the chromospheric activity in the Ca II H & K lines of 13 solar-type stars (including the Sun); 8 of them over three years at the CFHT and 5 in a single run at the VLT. Ten of the 13 targets have close planetary companions. All of the stars observed at the CFHT show long-term (months to years) changes in H & K intensity levels. Four stars display short-term (days) cyclical activity. For two, HD 73256 and ? 1 Ceti, the activity is likely associated with an active region rotating with the star, however, the flaring in excess of the rotational modulation may be associated with a hot jupiter. A planetary companion remains an unconfirmed possibility for ? 1 Ceti. For the other two, HD 179949 and ? And, the cyclic variation is synchronized to the hot jupiter's orbit. For both stars this synchronicity with the orbit is clearly seen in two out of three epochs. The effect is only marginal in the third epoch at which the seasonal level of chromospheric activity had changed for both stars. Short-term chromospheric activity appears weakly dependent on the mean K-line reversal intensities for the sample of 13 stars. Also, a suggestive correlation exists with the Mpsini of the star's hot jupiter. Because of their small separation (? 0.1 AU), hot jupiters lie within the Alfvén radius of their host stars which allows a direct magnetic interaction with the stellar surface. This work opens up the possibility of characterizing planet-star interactions with implications for extrasolar planet magnetic fields.

Shkolnik, E.; Walker, G. A. H.; Bohlender, D. A.; Gu, P.-G.; Kürster, M.

2004-12-01

171

UV excess galaxies: Wolf-Rayet galaxies  

E-print Network

We discuss V and R band photometry for 67% of the Sullivan et al. 2000 SA57 ultraviolet-selected galaxy sample. In a sample of 176 UV-selected galaxies, Sullivan et al. 2000 find that 24% have (UV-B) colors too blue for consistency with starburst spectral synthesis models. We propose that these extreme blue, UV excess galaxies are Wolf-Rayet (WR) galaxies, starburst galaxies with strong UV emission from WR stars. We measure a median (V-R)=0.38+-0.06 for the UV-selected sample, bluer than a sample optically selected at R but consistent with starburst and WR galaxy colors. We demonstrate that redshifted WR emission lines can double or triple the flux through the UV bandpass at high redshifts. Thus the (UV-B) color of a WR galaxy can be up to 1.3 mag bluer at high redshift, and the expected selection function is skewed to larger redshifts. The redshift distribution of the extreme blue, UV excess galaxies matches the selection function we predict from the properties of WR galaxies.

Warren R. Brown; Scott J. Kenyon; Margaret J. Geller; Daniel G. Fabricant

2000-07-20

172

The Spectroscopic Orbit of SAO 167450, Visual Companion of AA Ceti  

NASA Astrophysics Data System (ADS)

We have determined a spectroscopic orbit for SAO 167450, which is the visual secondary of the W UMa-type eclipsing binary AA Cet, and so the system is quadruple. Radial velocities from the coudé feed and 4 m telescopes at Kitt Peak National Observatory produce an orbit with a period of 25.68 days and an eccentricity of 0.50. We classify both the primary and secondary as G0 subgiant/dwarf stars and find that they are somewhat metal rich relative to the Sun. The high lithium abundances of both components argue that the stars are less than 1 Gyr old. If the components are dwarfs, they are pseudosynchronously rotating, while if they are subgiants, they are rotating more slowly than pseudosynchronous. We very roughly estimate a period of 5,000-15,000 yr for the visual pair. Although it has been suggested that in a multiple system, the combination of Kozai cycles and tidal friction may produce contact binaries, the separation between the visual components in this system appears to be much too large to accomplish that result.

Fekel, Francis C.; Willmarth, Daryl W.

2009-12-01

173

Ultraviolet (UV) Stellar Astronomy - Skylab Experiment S019  

NASA Technical Reports Server (NTRS)

This 1970 photograph shows Skylab's Ultraviolet (UV) Stellar Astronomy experiment, a scientific airlock-based facility/experiment that would study UV spectra of early-type stars and galaxies. The Marshall Space Flight Center had program management responsibility for the development of Skylab hardware and experiments.

1970-01-01

174

WX Ceti: a closer look at its behaviour in quiescence and outburst  

NASA Astrophysics Data System (ADS)

Context: WX Cet is a dwarf nova with rare outbursts of large amplitude. Aims: We compile the available data of WX Cet, compare the results with other SU UMa stars, and discuss our findings in the context of current theories of superhumps and superoutbursts to progress with our understanding of SU UMa stars. Methods: We analyse all recorded outbursts of WX Cet, based on the AAVSO archive and other published sources, and present new CCD photometry during two recent superoutbursts, including the determination of the corresponding periodicities. We perform numerical disc instability model calculations and compare its predictions with the observations. Results: WX Cet is a SU UMa type dwarf nova with a superoutburst cycle of 880 days on average, and short eruptions every 200 days. It seems that the outburst cycle length increased by nearly a factor of 2 during the past 70 years. According to our numerical simulations, this can be explained in the context of the disc instability model by assuming enhanced mass transfer during outburst and a decreasing mean mass transfer rate during the last decades. Using the data available, we refine the orbital period of WX Cet to 0.0582610± 0.0000002 days and interpret the orbital hump found in quiescence as emission from the hot spot. During two recent superoutbursts in July 2001 and December 2004 we observed superhumps, with a rather large positive period derivative of dot P_s/Ps = 1.6× 10-4, present only during the first 9 days of a superoutburst. Afterwards and during decline from the "plateau" phase, a constant superhump period of about 0.05922 days was observed. Late superhumps are present for at least 12 days after the decline from the "plateau", with a period of 0.05927 days. We find this phenomenology difficult to interpret in the context of the standard explanation for superhumps, i.e. the thermal tidal instability model. Conclusions: .We interpret the long-term light curve of WX Cet as the result of a significantly decreasing mean mass transfer rate. Highlighting the complexity of the observed superhump light curves, we emphasise the importance of WX Cet for a proper understanding of the SU UMa star outburst physics and the evolution of ultra-short period cataclysmic variables. Based on observations obtained at ESO La Silla, Las Campanas Observatory, Cerro Armazones Observatory, and the University of Concepción. The data are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/463/1053

Sterken, C.; Vogt, N.; Schreiber, M. R.; Uemura, M.; Tuvikene, T.

2007-03-01

175

A search for nearby young stars among the flare stars  

E-print Network

Flare stars were discovered in the late 1940s in the solar vicinity and were named UV Cet-type variables (classical FSs). Among the FSs within 100 pc we search for young stars. For the search we take spectra with sufficient resolution to resolve Lithium at 6707 \\AA and Calcium at 6718 \\AA of all the stars. The real young stars are prime targets for the search of extra-solar planets by direct imaging.

Brigitte König; Ralph Neuhäuser; Valeri Hambaryan

2001-06-11

176

UvAScriptieprijs 2014 UvAscriptieprijs  

E-print Network

bijlagen (zie 2.5) digitaal gestuurd te worden naar scriptieprijsalumni@uva.nl (zoveel mogelijk in één volgende adres: UvA Bureau Alumnirelaties en Universiteitsfonds T.a.v.: Jury Uv met bijlagen vervolgens door aan het secretariaat van de jury (scriptieprijsalumni@uva.nl). 2

van Rooij, Robert

177

New Pulsating DB White Dwarf Stars from the Sloan Digital Sky Survey  

E-print Network

We are searching for new He atmosphere white dwarf pulsators (DBVs) based on the newly found white dwarf stars from the spectra obtained by the Sloan Digital Sky Survey. DBVs pulsate at hotter temperature ranges than their better known cousins, the H atmosphere white dwarf pulsators (DAVs or ZZ Ceti stars). Since the evolution of white dwarf stars is characterized by cooling, asteroseismological studies of DBVs give us opportunities to study white dwarf structure at a different evolutionary stage than the DAVs. The hottest DBVs are thought to have neutrino luminosities exceeding their photon luminosities (Winget et al. 2004), a quantity measurable through asteroseismology. Therefore, they can also be used to study neutrino physics in the stellar interior. So far we have discovered nine new DBVs, doubling the number of previously known DBVs. Here we report the new pulsators' lightcurves and power spectra.

A. Nitta; S. J. Kleinman; J. Krzesinski; S. O. Kepler; T. S. Metcalfe; Anjum S. Mukadam; Fergal Mullally; R. E. Nather; Denis J. Sullivan; Susan E. Thompson; D. E. Winget

2008-09-04

178

UV water disinfector  

DOEpatents

A UV disinfector with a gravity driven feed water delivery system and an air-suspended bare UV lamp are disclosed. The disinfector is hydrodynamically optimized with a laminerizing, perforated baffle wall, beveled treatment chamber, and outlet weir. 7 figs.

Gadgil, A.; Garud, V.

1998-07-14

179

UV opportunities at ESO  

NASA Astrophysics Data System (ADS)

After summarizing the UV capabilities available at the Paranal observatory, the perspectives for additional UV instruments are discussed. When considering that most likely the E-ELT will not be optimized for UV, and that HST operations will be soon discontinued, UV instruments at the VLT may represent the best capabilities for the ESO community for a few years. In particular the cases of spectroscopy close to the atmospheric cutoff and Blue diffraction limited imaging show a great scientific potential.

Pasquini, Luca

2014-11-01

180

The History of Variable Stars: A Fresh Look  

NASA Astrophysics Data System (ADS)

(Abstract only) For historians of astronomy, variable stars are important for a simple reason - stars change. But good evidence suggests this is a very modern idea. Over the millennia, our species has viewed stars as eternal and unchanging, forever fixed in time and space - indeed, the Celestial Dance was a celebration of order, reason, and stability. But everything changed in the period between Copernicus and Newton. According to tradition, two New Stars announced the birth of the New Science. Blazing across the celestial stage, Tycho's Star (1572) and Kepler's Star (1604) appeared dramatically - and just as unexpectedly - disappeared forever. But variable stars were different. Mira Ceti, the oldest, brightest, and most controversial variable star, was important because it appeared and disappeared again and again. Mira was important because it did not go away. The purpose of this essay is to take a fresh look at the history of variable stars. In re-thinking the traditional narrative, I begin with the first sightings of David Fabricius (1596) and his contemporaries - particularly Hevelius (1662) and Boulliau (1667) - to new traditions that unfolded from Newton and Maupertuis to Herschel (1780) and Pigott (1805). The essay concludes with important 19th-century developments, particularly by Argelander (1838), Pickering (1888), and Lockyer (1890). Across three centuries, variable stars prompted astronomers to re-think all the ways that stars were no longer "fixed." New strategies were needed. Astronomers needed to organize, to make continuous observations, to track changing magnitudes, and to explain stellar phases. Importantly - as Mira suggested from the outset - these challenges called for an army of observers with the discipline of Spartans. But recruiting that army required a strategy, a set of theories with shared expectations. Observation and theory worked hand-in-hand. In presenting new historical evidence from neglected printed sources and unpublished manuscripts, this essay aims to offer a fresh look at the history of variable stars.

Hatch, R. A.

2012-06-01

181

Measurements of the UV Upturn in Local and Intermediate-Redshift Ellipticals  

E-print Network

The rest-frame UV contains the most sensitive indicators of age for elliptical galaxies. While the near-UV flux from young ellipticals isolates the main sequence turnoff, the far-UV flux in old ellipticals is dominated by hot horizontal branch (HB) stars. This evolved population was first revealed by early UV observations showing a sharp flux increase shortward of rest-frame 2500 A, subsequently dubbed the "UV upturn." The phenomenon has since been characterized in many local ellipticals, and measurements at intermediate redshifts are now underway. Once ellipticals reach ages of 5-10 Gyr, stellar and galactic evolution theories predict that the UV-to-optical flux ratio can increase by orders of magnitude over timescales of a few Gyr, making the UV upturn the most rapidly evolving feature of these galaxies. It is thus expected to fade dramatically with increasing redshift. I review the imaging and spectroscopic evidence for the nature of the UV upturn in nearby ellipticals, and then present observations that measure the UV upturn at an epoch significantly earlier than our own. Far-UV data from the HUT demonstrate that the spectra of nearby ellipticals are dominated by hot HB stars. FOC UV imaging of M32 and the M31 bulge detected the UV-bright phases of post-HB stars, but did not reach the HB itself. Recent STIS observations were the first to image the hot HB and post-HB stars in the center of the nearest elliptical galaxy, M32; these observations also show a striking lack of UV-bright post-AGB stars. FOC observations of Abell 370, a rich galaxy cluster at z=0.375, show that giant ellipticals at a lookback time of 4 Gyr can exhibit strong UV luminosity, with no evidence of evolution in the UV upturn between this epoch and our own, thus implying a high redshift of formation (z_f > 4).

Thomas M. Brown

1999-05-28

182

Solar UV variability  

NASA Technical Reports Server (NTRS)

Measurements from the Solar Backscatter Ultraviolet (SBUV) provide solar UV flux in the 160 to 400 nm wavelength range, backed up by independent measurement in the 115 to 305 nm range from the Solar Mesosphere Explorer (SME). The full disc UV flux from spatially resolved measurements of solar activity was modeled, which provides a better understanding of why the UV variations have their observed temporal and wavelength dependencies. Long term, intermediate term, and short term variations are briefly examined.

Donnelly, Richard F.

1989-01-01

183

Intergalactic Star Formation  

E-print Network

Star formation in interacting systems may take place in various locations, from the dust--enshrouded core of Ultraluminous Infrared Galaxies to more unusual places such as the debris of colliding galaxies expelled into the intergalactic medium. Determining whether star-formation proceeds in the latter environment, far from the parent galaxies, in a similar way as in spiral disks has motivated the multi--wavelength study presented here. We collected VLA/HI, UV/GALEX, optical Halpha and MIR/Spitzer images of a few nearby interacting systems chosen for their prominent "intergalactic" star formation activity. Preliminary results on the spectacular collisional HI ring around NGC 5291 are presented.

Pierre-Alain Duc; Meederic Boquien; Jonathan Braine; Elias Brinks; Ute Lisenfeld; Vassilis Charmandaris

2006-10-13

184

Observing the First Stars in Luminous, Red Galaxies  

NASA Technical Reports Server (NTRS)

Modern cosmological simulations predict that the first stars are to be found today in luminous, red galaxies. Although observing such stars individually against a background of younger, metal-rich stars is impossible, the first stars should make their presence known by their strong, line-free ultraviolet flux. We have found evidence for a UV-bright stellar population in Sloan spectra of LRG's at z=0.4-0.5. We present arguments for interpreting this UV-bright stellar population as the oldest stars, rather than other types of stellar populations (e.g. young stars or blue straggler stars in the dominant, metal-rich stellar population

Heap, Sally; Lindler, Don

2010-01-01

185

Multi-Wavelength Constraints on the Cosmic Star Formation History from Spectroscopy: the Rest-Frame UV, H-alpha, and Infrared Luminosity Functions at Redshifts 1.9  

E-print Network

We use a sample of rest-frame UV selected and spectroscopically observed galaxies at redshifts 1.9UV, H-alpha, and infrared (IR) luminosity functions (LFs) at these redshifts. Our sample is by far the largest of its kind, with over 2000 spectroscopic redshifts in the range 1.9UV-bright galaxies over what was inferred in early z~3 LBG studies. The UV LF appears to undergo little evolution between z~4 and z~2. Corrected for extinction, the UV luminosity density (LD) at z~2 is at least as large as the value at z~3 and a factor of ~9 larger than the value at z~6, primarily reflecting an increase in the number density of bright galaxies between z~6 and z~2. Our analysis yields the first constraints anchored by extensive spectroscopy on the IR and bolometric LFs for faint and moderately luminous (L[bol]<10^12 L_sun) galaxies. Adding the IR to the emergent UV luminosity, incorporating independent measurements of the LD from ULIRGs, and assuming realistic dust attenuation values for UV-faint galaxies, indicates that galaxies with L[bol]<10^12 L_sun account for ~80% of the bolometric LD and SFRD at z~2-3. Our multi-wavelength constraints on the global SFRD indicate that approximately one-third of the present-day stellar mass density was formed in sub-ultraluminous galaxies between redshifts z=1.9-3.4. [Abridged

Naveen A. Reddy; Charles C. Steidel; Max Pettini; Kurt L. Adelberger; Alice E. Shapley; Dawn K. Erb; Mark Dickinson

2007-06-27

186

Child universes UV regularization?  

E-print Network

It is argued that high energy density excitations, responsible for UV divergences in quantum field theories, including quantum gravity, are likely to be the source of child universes which carry them out of the original space time. This decoupling prevents these high UV excitations from having any influence on physical amplitudes. Child universe production could therefore be responsible for UV regularization in quantum field theories which takes into account gravitational effects. Also child universe production in the last stages of black hole evaporation, the prediction of absence of tranplanckian primordial perturbations, connection to the minimum length hypothesis and in particular connection to the maximal curvature hypothesis are discussed.

E. I. Guendelman

2007-03-26

187

The LMC UV Extinction Curve Re--visisted  

NASA Astrophysics Data System (ADS)

As part of an on--going effort to quantify the extinction properties in the Local Group, we have re--analyzed the LMC UV extinction curve. UV extinction curves have been contstructed via the pair method using the most highly reddened stars from Fitzpatrick (1985, ApJ 299,219) as well as five new reddened stars for which archival IUE spectra exist. In addition to constructing average LMC extinction curves, we have taken advantage of the improved signal--to--noise in the NEWSIPS IUE reduction to examine several stars with large reddening on an individual basis. We find less regional difference between the star--forming 30 Dor region and the remainder of the LMC as compared to Fitzpatrick (1985) and several stars have extinction curves remarkably similar to the average Galactic curve, most notably SK -69 210 whose projected position places it on the western edge of 30 Dor near the LH 89 OB association. In an effort to quantify the dependence of the UV extinction curve in the LMC on the environment (eg. star--formation) we collect data from the literature on individual lines of sight to several of our reddened stars.

Misselt, K. A.; Clayton, G. C.; Gordon, K. D.

1998-09-01

188

Detecting UV Light  

NSDL National Science Digital Library

Students learn about ultraviolet light in this Moveable Museum unit, where they detect UV rays and then explore ways to block them. The four-page PDF guide includes suggested general background readings for educators, activity notes, step-by-step directions, and information about where to obtain supplies. Students make a bracelet from beads that respond to UV light by changing color, and test it in different light environments.

189

Star formation in dwarf galaxies  

NASA Astrophysics Data System (ADS)

In this thesis, we examine the star formation history and stellar feedback effects of dwarf galaxies under the influence of extragalactic ultraviolet radiation, as well as the evolution of residual gas within tidally-limited dwarf galaxies and globular clusters. Previous work has indicated that the background UV flux can easily ionize the gas within typical dwarf galaxies, delaying or even preventing cooling and star formation within them. Many dwarf galaxies within the Local Group are, however, observed to contain multiple generations of stars, the oldest of which formed in the early epochs of cosmic evolution, when the background UV flux was intense. In order to address this paradox, we consider the dynamical evolution of gas in dwarf galaxies using a one-dimensional, spherically symmetric, Lagrangian numerical scheme which also computes the effects of radiative transfer and photoionization. We include in the scheme a physically-motivated star formation recipe and consider the effects of feedback. This scheme allows us to follow the history of the gas and of star formation within dwarf galaxies, as influenced by both external and internal UV radiation. Our results indicate that star formation in the severe environment of dwarf galaxies is a difficult and inefficient process. In potentials with total mass less than a few 106 M? , and velocity dispersion less than a few km s-1 , residual gas is efficiently photoionized by cosmic background UV radiation. For intermediate mass systems, such as the dSphs around the Galaxy, star formation can proceed within early cosmic epochs despite the intense background UV flux. Triggering processes such as merger events, collisions, and tidal disturbance can lead to density enhancements, reducing the recombination timescale, allowing gas to cool and star formation to proceed. However, the star formation and gas retention efficiency may vary widely in galaxies with similar dark matter potentials, because they depend on many factors, such as the baryonic fraction, external perturbation, IMF, and background UV intensity. We suggest that the presence of very old stars in these dwarf galaxies indicates that their initial baryonic to dark matter content was comparable to the cosmic value. This constraint suggests that the initial density fluctuation of baryonic matter may be correlated with that of the dark matter. For the more massive dwarf elliptical galaxies, the star formation efficiency and gas retention rate is much higher. Their mass to light ratio is regulated by star formation feedback, and is expected to be nearly independent of their absolute luminosity. The results of our theoretical models reproduce the observed M/L - Mupsilon correlation. (Abstract shortened by UMI.)

Dong, Shawfeng

190

UV Spectral Synthesis of Sirius A  

NASA Astrophysics Data System (ADS)

UV Spectral Synthesis of Sirius A We report the first results from a study of the fundamental physical properties of the A1 V star Sirius A. Using archival spectrophotometric data from the Hubble Space Telescope's STIS spectrograph, we have produced a synthetic UV spectrum of the star. The data were obtained at medium resolution with the G160M, G200M, and G270M gratings (FWHM 15 km/s) and cover the wavelength range 1265-3200 Angstroms. The synthetic spectrum was constructed using Kurucz's ATLAS9 LTE stellar atmospheric models and Hubeny's SYNSPEC spectral synthesis program and is a function of the star's effective temperature, surface gravity, microturbulence velocity, rotational velocity, radial velocity, and chemical composition. A chi2-minimization program was used to find the values of these parameters which produce the best match of the synthetic spectrum with the observed spectrum. In addition to determining the stellar properties, this program can illuminate - and help rectify - deficiencies in the spectral line database used to construct the synthetic spectra. In this poster, we illustrate the first results from this program, including the quality of the match between the observed and computed spectra and the elemental abundance profile of Sirius A, including CNO, the light metals (e.g., Si and Al), and the Fe group.

McClain, Timothy; Fitzpatrick, E.

2010-01-01

191

UBVR Imaging of UV Bright Interacting Galaxies  

NASA Astrophysics Data System (ADS)

Interacting galaxies are often found to contain UV-bright knots which are the sites of very recent or ongoing star-formation. To investigate the stellar populations of these complexes we have obtained UBVR images of several interacting or morphologically disturbed UV bright galaxies (NGC 3395/6, NGC 3991/4/5, NGC 4194, NGC 6090). Images of IRAS 15179+3956, an interacting galaxy in the Bootes Void, were also obtained. The images were made with the 2048x 2048 CCD camera on the 1-meter telescope at the Mount Laguna Observatory. Colors and magnitudes of star-forming regions in these objects will be presented and used to study how their properties change with age and position within each galaxy and how star-formation propagates through the system. This is part of an ongoing study of starburst galaxies that will include STIS (Space Telescope Imaging Spectrograph) longslit spectroscopy of a subset of these galaxies. Mount Laguna Observatory is operated jointly by San Diego State University and the University of Illinois. This research is supported in part by NASA under contract NAS 5-31231.

Nelson, C. H.; Weistrop, D.; Angione, R.; Cruzen, S.; Kaiser, M. E.

1997-12-01

192

Filling the gap --near UV, optical and near IR extinction  

NASA Astrophysics Data System (ADS)

We propose a SNAP program to obtain STIS low resolution near-UV, optical and near-IR (G430L and G750L) spectra for a set of O7-B7 class III-V stars in the Galaxy and Magellanic Clouds with available IUE or HST/STIS UV spectropotometry, optical photometry and 2MASS IR photometry. Together with the existing data, the new observations will provide complete photometric and spectrophotometric coverage from 1150 to 10000 A and enable us to produce complete extinction curves from the far-UV to the near-IR, with well-determined values of R(V). The proposed set of 150 program sight lines includes the full range of interstellar extinction curve types from both the Galaxy and the Magellanic Clouds. The new data will allow us to examine variability in the near-UV through near-IR spectral regions, including the UV-optical "knee", and the "Very Broad Structure" and to verify the applicability of the near IR extinction law recently derived by Fitzpatrick and Massa (2009). We will examine the response of these features to different interstellar environments and their relationship to other curve features. These are largely unexplored aspects of the extinction curves which will provide additional constraints on the properties of interstellar grains. The curves will be derived using model atmospheres for the program stars, eliminating the need for standard stars.

Massa, Derck

2014-10-01

193

Hubble Space Telescope Observations of UV Oscillations in WZ Sagittae During the Decline from Outburst  

E-print Network

We present a time series analysis of Hubble Space Telescope observations of WZ Sge obtained in 2001 September, October, November and December as WZ Sge declined from its 2001 July superoutburst. Previous analysis of these data showed the temperature of the white dwarf decreased from ~29,000 K to ~18,000 K. In this study we binned the spectra over wavelength to yield ultraviolet light curves at each epoch that were then analyzed for the presence of the well-known 27.87 s and 28.96 s oscillations. We detect the 29 s periodicity at all four epochs, but the 28 s periodicity is absent. The origin of these oscillations has been debated since their discovery in the 1970s and competing hypotheses are based on either white dwarf non-radial g-mode pulsations or magnetically-channelled accretion onto a rotating white dwarf. By analogy with the ZZ Ceti stars, we argue that the non-radial g-mode pulsation model demands a strong dependence of pulse period on the white dwarf's temperature. However, these observations show t...

Welsh, W F; Godon, P; Gänsicke, B T; Knigge, C; Long, K S; Szkody, P

2003-01-01

194

Silicon carbide UV photodiodes  

Microsoft Academic Search

SiC photodiodes were fabricated using 6 H single-crystal wafers. These devices have excellent UV responsivity characteristics and very low dark current even at elevated temperatures. The reproducibility is excellent and the characteristics agree with theoretical calculations for different device designs. The advantages of these diodes are that they will operate at high temperatures and are responsive between 200 and 400

D. M. Brown; E. T. Downey; M. Ghezzo; J. W. Kretchmer; R. J. Saia; Y. S. Liu; J. A. Edmond; G. Gati; J. M. Pimbley; W. E. Schneider

1993-01-01

195

Deep UV HST Imaging in Abel 1689  

NASA Astrophysics Data System (ADS)

We have obtained a deep (30-orbit) Hubble Space Telescope WFC3/UVIS F275W image of Abell 1689, a massive cluster at z=0.183, and one of the best studied HST targets for lensing surveys. We use the new UV data, in conjunction with existing high resolution optical and IR data to constrain the residual star-formation in the cluster early-type galaxy population, determine the ages of young stellar populations, providing insight into the buildup of the cluster red sequence.

Scarlata, Claudia; Siana, B. D.; Richard, J.; Stark, D.; Teplitz, H. I.; Desai, V.; Dominguez, A.; Alavi, A.; Robertson, B. E.

2013-01-01

196

Hot Subdwarf Stars  

NASA Astrophysics Data System (ADS)

Hot subdwarf stars (sdBs, sdOs) are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. They are found in all Galactic stellar populations and are sufficiently common to account for the UV-upturn of early-type galaxies. About half of the sdBs reside in close binaries; companions are white dwarfs or low-mass main-sequence stars. Binary population-synthesis models explain naturally the actual sdB binary fractions of field and globular cluster stars as well as of He-sdOs if white-dwarf mergers are considered. Hot helium flashes explain the chemical composition of He-sdOs. Asteroseismology of a dozen pulsating sdB stars allowed determination of their masses and detection of a planet to V391 Peg. The discoveries of an sdO star unbound to the Galaxy, potential SN Ia progenitors and probably a hidden population of neutron stars or black hole companions have great impact on astrophysics at large.

Heber, Ulrich

2009-09-01

197

Deep UV Luminosity Functions at the Infall Region of the Coma Cluster  

NASA Technical Reports Server (NTRS)

We have used deep GALEX observations at the infall region of the Coma cluster to measure the faintest UV luminosity functions (LFs) presented for a rich galaxy cluster thus far. The Coma UV LFs are measured to M(sub uv) = -10.5 in the GALEX FUV and NUV bands, or 3.5 mag fainter than previous studies, and reach the dwarf early-type galaxy population in Coma for the first time. The Schechter faint-end slopes (alpha approximately equal to -1.39 in both GALEX bands) are shallower than reported in previous Coma UV LF studies owing to a flatter LF at faint magnitudes. A Gaussian-plus-Schechter model provides a slightly better parametrization of the UV LFs resulting in a faint-end slope of alpha approximately equal to -1.15 in both GALEX bands. The two-component model gives faint-end slopes shallower than alpha = -1 (a turnover) for the LFs constructed separately for passive and star forming galaxies. The UV LFs for star forming galaxies show a turnover at M(sub UV) approximately equal to -14 owing to a deficit of dwarf star forming galaxies in Coma with stellar masses below M(sub *) = 10(sup 8) solar mass. A similar turnover is identified in recent UV LFs measured for the Virgo cluster suggesting this may be a common feature of local galaxy clusters, whereas the field UV LFs continue to rise at faint magnitudes. We did not identify an excess of passive galaxies as would be expected if the missing dwarf star forming galaxies were quenched inside the cluster. In fact, the LFs for both dwarf passive and star forming galaxies show the same turnover at faint magnitudes. We discuss the possible origin of the missing dwarf star forming galaxies in Coma and their expected properties based on comparisons to local field galaxies.

Hammer, D. M.; Hornschemeier, A. E.; Salim, S.; Smith, R.; Jenkins, L.; Mobasher, B.; Miller, N.; Ferguson, H.

2011-01-01

198

Evolutionary and pulsational properties of low-mass white dwarf stars with oxygen cores resulting from close binary evolution  

E-print Network

The present work is designed to explore the evolutionary and pulsational properties of low-mass white dwarfs with carbon/oxygen cores. In particular, we follow the evolution of a 0.33 Msun white dwarf remnant in a self-consistent way with the predictions of nuclear burning, element diffusion and the history of the white dwarf progenitor. Attention is focused on the occurrence of hydrogen shell flashes induced by diffusion processes during cooling phases. The evolutionary stages prior to the white dwarf formation are also fully accounted for by computing the conservative binary evolution of an initially 2.5-Msun Pop. I star with a 1.25 Msun companion, and period P_i= 3 days. Evolution is followed down to the domain of the ZZ Ceti stars on the white dwarf cooling branch. We find that chemical diffusion induces the occurrence of an additional hydrogen thermonuclear flash which leads to stellar models with thin hydrogen envelopes. As a result, a fast cooling is encountered at advanced stages of evolution. In addition, we explore the adiabatic pulsational properties of the resulting white dwarf models. As compared with their helium-core counterparts, low-mass oxygen-core white dwarfs are characterized by a pulsational spectrum much more featured, an aspect which could eventually be used for distinguishing both types of stars if low-mass white dwarfs were in fact found to pulsate as ZZ Ceti-type variables. Finally, we perform a non-adiabatic pulsational analysis on the resulting carbon/oxygen low-mass white dwarf models.

L. G. Althaus; A. H. Corsico; A. Gautschy; Z. Han; A. M. Serenelli; J. A. Panei

2003-09-09

199

An X-ray Study of Massive Star Forming Regions with Chandra.  

E-print Network

??Massive stars are characterized by powerful stellar winds, strongultraviolet (UV) radiation, and consequently devastating supernovaeexplosions, which have a profound influence on their natal clouds andgalaxy… (more)

Wang, Junfeng

2007-01-01

200

uv preilluminated gas switches  

Microsoft Academic Search

We have designed, built, and characterized uv preilluminated gas switches for a trigger circuit and a low inductance discharge circuit. These switches have been incorporated into a 54 x 76 x 150 cm pulser module to produce a 1 Ma output current rising at 5 x 10¹² amps\\/sec with 1 ns jitter. Twenty such modules will be used on the

L. P. Bradley; E. L. Orham; I. F. Stowers; J. R. Braucht

1980-01-01

201

The Galaxy Evolution Explorer (GALEX). Its legacy of UV surveys, and science highlights  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer (GALEX) imaged the sky in the Ultraviolet (UV) for almost a decade, delivering the first sky surveys at these wavelengths. Its database contains far-UV (FUV, ? eff˜1528 Å) and near-UV (NUV, ? eff˜2310 Å) images of most of the sky, including deep UV-mapping of extended galaxies, over 200 million source measurements, and more than 100,000 low-resolution UV spectra. The GALEX archive will remain a long-lasting resource for statistical studies of hot stellar objects, QSOs, star-forming galaxies, nebulae and the interstellar medium. It provides an unprecedented road-map for planning future UV instrumentation and follow-up observing programs in the UV and at other wavelengths. We review the characteristics of the GALEX data, and describe final catalogs and available tools, that facilitate future exploitation of this database. We also recall highlights from the science results uniquely enabled by GALEX data so far.

Bianchi, Luciana

2014-11-01

202

UVS is rare in seabirds  

Microsoft Academic Search

Ultraviolet-sensitive vision (UVS), believed to have evolved from an ancestral state of violet-sensitive vision (VS), is widespread among terrestrial birds, where it is thought to play a role in orientation, foraging, and sexual selection. Less is known, however, about the distribution and significance of UVS in seabirds. To date UVS has been definitively demonstrated only in two families (Laridae and

Gabriel E. Machovsky Capuska; Leon Huynen; David Lambert; David Raubenheimer

2011-01-01

203

Rest-frame UV Spectra of the most UV luminous Lyman Break Galaxies at z~3  

NASA Astrophysics Data System (ADS)

We propose to carry out long-slit deep optical (rest frame ultraviolet (UV)) spectroscopic observations of three most UV luminous Lyman break galaxies (LBGs) at z~3 with GMOS-S. We have carried out wide-field multicolor surveys of LBGs covering >300 deg^2, increasing the survey volume by 2 orders of magnitude larger than previous surveys. Our initial observations have revealed eight extremely UV luminous galaxies with r~21-22.3, more than 2 magnitudes brighter than typical LBGs. We will observe three faintest galaxies in this sample with r~22. At L ~ 7.5 L^*, they represent the rarest and most intensive star forming systems in the early Universe. With the deep spectroscopy, we will investigate the nature of these galaxy systems, which was proposed to be comprised of multiple galaxies by previous optical spectroscopic observations. Combining previous faint LBG sample, the proposed observations will build up a perfect sample to provide enough dynamic range of star formation rate (SFR) to study the correlation between galactic-scale outflows velocity and SFR in LBGs at z~2-3 for the first time.

Bian, Fuyan; Fan, Xiaohui; Jiang, Linhua; McGreer, Ian

2011-08-01

204

The UV Scattering Halo of the Central Source Associated with Eta Carinae  

NASA Technical Reports Server (NTRS)

Eta Carinae is one of the most massive and luminous stars within our galaxy. It consists of a compact central source which suffers circumstellar and interstellar extinction, local dense knots which emit strong narrow nebular-like emission lines, and an outer dusty nebula called the Homunculus. The optical spectrum of the central star, first observed directly and without obvious nebular contamination by the HST, can be modeled successfully using a hot star with a radius (at the wind sonic point) of 60\\,R\\odot. The central star is losing mass, via a dense stellar wind, at the prodigious rate of 10(exp -3)\\,M\\odot/yr. Its effective temperature is low (< 10,000\\,K), and is determined entirely by the wind properties. Until now the UV spectrum has not been explained. We show that HST UV spectrum, and the FUSE FUV spectrum, can both be understood using the same underlying model that explains the optical spectrum. To do so, however, it is necessary to take into account the occultation of the central source by dust. It is also important to realize that in the UV, the HST is partially resolving the central source. Due to strong mass loss, the wind is optically thick in UV resonance lines even at large radii. The UV resonance lines are responsible for the UV halo seen around Eta Carinae, and provide a partial explanation of why Eta Carinae can even be seen at UV wavelengths.

Hillier, D. J.; Davidson, K.; Gull, T. R.; Humphreys, R. M.; Iping, R.; Sonneborn, G.

2004-01-01

205

Far UV Spectroscopy of eta Carinae  

NASA Technical Reports Server (NTRS)

We present the first high spectral resolution observations of the Luminous Blue Variable eta Carinae between the Lyman limit and 1180 Angstroms. High resolution spectra (R approximately 20,000) were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite on Feb. 1 and Mar. 20, 2000. The observations were made with a 30x30 arcsec aperture and includes the entire Homunculus region. However, the spatial extent of the far UV flux is consistent with a point source. With the limited spatial resolution of the FUSE instrument, we can only constrain the far UV emission to be within +/-5 arcsec of the star. The far UV spectrum of eta Car is dominated by strong absorption features of molecular hydrogen. The observed flux level at 1150 Angstroms is approximately 4\\times 10(exp 12) erg/sq cm/s/Angstrom and decreases approximately linearly to approximately 920 Angstroms where converging HI and HII features completely blanket the spectrum. These observations were obtained as part of the FUSE Early Release Observation program.

Iping, R. C.; Sonneborn, G.; Massa, D.; Hutchings, J. B.; Gull, T. R.; Fisher, Richard (Technical Monitor)

2000-01-01

206

Far UV Spectroscopy of eta Carinae  

NASA Technical Reports Server (NTRS)

We present the first high spectral resolution observations of the Luminous Blue Variable eta Carinae between the Lyman limit and 1180 A. High resolution spectra (R approx. 20,000) were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite on Feb. 1 and Mar. 20, 2000. The observations were made with a 30 x 30 arcsec aperture and includes the entire Homunculus region. However, the spatial extent of the far UV flux is consistent with a point source. With the limited spatial resolution of the FUSE instrument, we can only constrain the far UV emission to be within +/- 5 arcsec of the star. The far UV spectrum of eta Car is dominated by strong absorption features of molecular hydrogen. The observed flux level at 1150A is approx. 4 times 10(exp 12) erg /cm(exp -2) /sec(exp -1) / A(exp -1) and decreases approximately linearly to approx. 920 A where converging H1 and H2 features completely blanket the spectrum. These observations were obtained as part of the FUSE Early Release Observation program.

Iping, R. C.; Sonneborn, G.; Massa, D. L.; Hutchings, J. B.; Gull, T. R.; Fisher, Richard R. (Technical Monitor)

2000-01-01

207

Panchromatic Hubble Andromeda Treasury (PHAT): Tests of UV Flux-Based SFR Estimates  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV) flux is often used to trace and quantify recent star formation in nearby and distant galaxies. With new observations of resolved stars in the disk of M31 from the Panchromatic Hubble Andromeda Treasury (PHAT), we are able to test the validity of estimating ages and masses of stellar populations based on integrated UV flux. We use a maximum likelihood color-magnitude diagram fitting method (Dolphin, 2002), optimized to fit the main sequence, with the PHAT optical photometry to measure recent (within the last ~200 Myr) star formation histories and extinctions for 33 UV-bright regions in a 7.4 kpc2 area. With these results, we draw comparisons with single-age characterizations of these regions derived from integrated NUV and FUV GALEX flux by Kang et al. (2009). This study is the beginning of our effort to investigate all UV-bright regions within the entire PHAT survey area.

Simones, Jacob; Weisz, D. R.; Skillman, E. D.; Dalcanton, J.; Dolphin, A. E.; Williams, B. F.; PHAT Team

2013-01-01

208

Accretion and UV Variability in BP Tauri  

NASA Astrophysics Data System (ADS)

BP Tau is one of the few classical T Tauri stars for which the presence of a hot spot in the surface has been reported without ambiguity. The most likely source of heating is gravitational energy released by the accreting material as it shocks with the stellar surface. This energy is expected to be radiated mainly at UV wavelengths. In this work we report the variations of the UV spectrum of BP Tau for 1992 January 5-19, when the star was monitored with IUE during two rotation periods. Our data indicate that lines that can be excited by recombination processes, such as those from O I and He II, have periodic-like light curves, whereas lines that are only collisionally excited do not follow a periodic-like trend. These results agree with the expectations of the magnetically channeled accretion models. The kinetic energy released in the accretion shocks is expected to heat the gas to temperatures of ~106 K, which henceforth produces ionizing radiation. The UV (Balmer) continuum and the O I and He II lines are direct outputs of the recombination process. However, the C IV, Si II, and Mg II lines are collisionally excited not only in the shock region but also in inhomogeneous accretion events and in the active (and flaring) magnetosphere, and therefore their light curves are expected to be blurred by these irregular processes. We also report the detection of warm infalling gas from the presence of redshifted (81 km s-1) absorption components in some of the high-resolution Mg II profiles available in the IUE and Hubble Space Telescope archives. Based on observations made with the International Ultraviolet Explorer (IUE) and with the NASA/ESA Hubble Space Telescope (HST) obtained from the HST data archive at the Space Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Gómez de Castro, Ana I.; Franqueira, M.

1997-06-01

209

Spectroscopic Observations of Nearby Low Mass Stars  

NASA Astrophysics Data System (ADS)

Young low-mass stars are known to be bright in X-ray and UV due to a high level of magnetic activity. By cross-correlating the GALEX Catalog with the WISE and 2MASS Point Source Catalogs, we have identified more than 2,000 stars whose UV excesses suggest ages in the 10-100 Myr range. We used the Shane 3-m telescope at Lick Observatory on Mount Hamilton, California to observe some of these 2,000 stars spectroscopically. We measured the equivalent width of lithium at 6708 A absorption and H-alpha emission lines. Out of a total of 122 stars observed with the Kast grating spectrometer, we find that roughly 10% have strong lithium absorption features. The high percentage of stars with lithium present is further evidence of the importance of UV emission as a youth indicator for low-mass stars. In addition, we used high-resolution spectra obtained with the Hamilton echelle spectrograph to determine radial velocities for several UV-bright stars. These radial velocities will be useful for the calculation of Galactic UVW space velocities for determination of possible moving group membership. This work is supported by NASA Astrophysics Data Analysis Program award NNX12AH37G to RIT and UCLA and Chilean FONDECYT grant 3130520 to Universidad de Chile. This submission presents work for the GALNYSS project and should be linked to abstracts submitted by David Rodriguez, Laura Vican, and Joel Kastner.

Vican, Laura; Zuckerman, B. M.; Rodriguez, D.

2014-01-01

210

Full-Stokes UV and visible spectropolarimeter for spatial application  

NASA Astrophysics Data System (ADS)

UVMag is a project of a space mission equipped with a high-resolution spectropolarimeter working in the UV and visible range. This M-size mission will be proposed to ESA. The main goal of UVMag is to measure the magnetic fields, winds and environment of all types of stars to reach a better understanding of stellar formation and evolution. The groundbreaking combination of a UV and visible observation will allow the scientists to study the star and its environment simultaneously. The baseline wavelength window for spectropolarimetry is between 117nm and 870nm, in order to observe the polarization state in many important spectral lines. We also aim at extending the window down to 90 nm at least in spectroscopy. The UV domain contains key atomic and molecular transitions, for example for hot stars, and is the best domain to study Sun-like stars or white dwarfs. The instrumental challenge for this mission is to design a high-resolution space spectropolarimeter measuring the full-Stokes vector of the observed star in a huge spectral range from FUV to the limit between visible and NIR. This spectral range is the main difficulty because of the lack of birefringent and transparent materials working at FUV and visible wavelengths at the same time. As the instrument will be launched into space, the polarimetry module has to be robust and therefore use if possible only static elements. I will present some concepts that we studied to build such a system, using spatial or temporal modulation or channeled polarimetry. The output of the full-Stokes robust polarimeter will correspond to the entrance slit of a high-resolution echelle spectrometer, which will disperse the echelle orders into several UV and visible detectors.

Pertenais, Martin; Neiner, Coralie; Petit, Pascal; Pares, Laurent

211

Problems in abundance determination from UV spectra of hot supergiants  

NASA Astrophysics Data System (ADS)

We present measurements of equivalent widths of the UV, presumably photospheric lines: C III 1247 Å, N III 1748 Å, N III 1752 Å, N IV 1718 Å and He II 1640 Å in high-resolution IUE spectra of 24 galactic OB supergiants. Equivalent widths measured from the observed spectra have been compared with their counterparts in the Tlusty NLTE synthetic spectra. We discuss possibilities of static plan-parallel model to reproduce observed UV spectra of hot massive stars and possible reasons why observations differ from the model so much.

Dekovi?, M. Sarta; Kotnik-Karuza, D.; Jurki?, T.; Prester, D. Dominis

2010-03-01

212

Relations between mid-IR dust emission and UV extinction  

NASA Astrophysics Data System (ADS)

We present a comparison of Spitzer mid-IR emission spectral features and UV extinction properties for sight lines to stars at high Galactic latitude which lie beyond the bulk of the Milky Way dust layer. For these sight lines the emission and extinction sample the same dust. The dust emission is described by the Draine & Li (2007) PAH model with the addition of a continuum component which removes residual Zodiacal light contributions. The derived emission parameters are compared to the different Fitzpatrick & Massa (1990) parameters which describe the shapes of UV extinction curves. Results from this comparison will be discussed.

Massa, Derck; Fitzpatrick, E. L.; Gordon, K. D.

2014-01-01

213

Holographic UV laser microsurgery  

PubMed Central

Abstract We use a spatial light modulator (SLM) to diffract a single UV laser pulse to ablate multiple points on a Drosophila embryo. This system dynamically generates a phase hologram for ablating a user-defined pattern fast enough to be used with living, and thus moving, tissue. We demonstrate the ability of this single-pulse multi-point system to perform two experiments that are very difficult for conventional microsurgery—isolating single cells in vivo and measuring fast retractions from large incisions. PMID:21991551

Jayasinghe, Aroshan K; Rohner, Jason; Hutson, M Shane

2011-01-01

214

Uvs Nuur, Mongolia  

NASA Technical Reports Server (NTRS)

The Uvs Nuur Basin in Mongolia and the Russian Federation is the northernmost of the enclosed basins of Central Asia. It takes its name from Uvs Nuur Lake, a large, shallow and very saline lake, very important for migrating birds. Inscribed as a UNESCO World Heritage Site in 2003, the site is made up of twelve protected areas representing major biomes of eastern Eurasia. The steppe ecosystem supports a rich diversity of birds and the desert is home to a number of rare gerbil, jerboas and the marbled polecat. The mountains are an important refuge for the endangered snow leopard, mountain sheep, and the Asiatic ibex.

The image covers an area of 46 x 47.8 km, was acquired on September 4, 2001, and is located near 50.3 degrees north latitude, 90.7 degrees east longitude.

The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

2007-01-01

215

UV Curable Polyimides  

NASA Technical Reports Server (NTRS)

The development of UV curable polyimides for high-temperature applications is a growing area of research activity. The objective of this technology is an attempt to bypass many of the issues associated with "typical" high-temperature polymers. For example, the use of toxic or mutagenic monomers (i.e., many aromatic diamines) can be prevented. Also, it proves to be a viable means in circumventing the problems associated with high-processing temperature of polymers, which cause thermally induced processing stresses (i.e., microcracking). The approach that we have been pursuing is Diels-Alder Polymerization. In this approach, we are generating dienes with light instead of heat. This process is called photoenolization. Several bismaleimides and bisacrylates are used as the dienophiles. The method is fairly general and a wide variety of diketones and bismaleimides can be used. UV curability processes are advantageous due to the following: (1) With such a wide variety of monomers, it allows for the use of nontoxic/nonmutagenic monomers; (2) Polyimides cure at room temperature, which reduces thermally induced stresses; (3) It reduces processing and tooling cost; (4) There are many potential applications for this technology, i.e., thin films as alignment layers for LC displays, photoresists, and photonic material as well as a potential market for use as adhesives.

Meador, Michael; Oliver, Thomas

2001-01-01

216

Binary stars and the UVX in early-type galaxies  

NASA Astrophysics Data System (ADS)

We use the Hernández-Pérez and Bruzual (HB13) stellar population synthesis models to study the role of interacting binary pairs as progenitors of extreme horizontal branch (EHB) stars. We assemble a sample of 3417 early-type galaxies observed both in the optical (SDSS-DR8) and the UV (GALEX-GR6). The galaxies in our sample can be classified according to their position in the colour-colour diagram as UV-weak or red-sequence galaxies (˜48 per cent), UV-strong or UVX galaxies (˜9 per cent), and recent star-forming galaxies (˜43 per cent). Analysing this sample using the HB13 models for various choices of basic model parameters, we conclude that (a) the UVr colours of UV-weak and UV-strong galaxies are reproduced by the models as long as the fraction of binary stars is at least 15 per cent. (b) Higher metallicity models (Z = 0.02 and 0.03) reproduce the colours of UV-weak and UV-strong galaxies better than lower Z models. The Z = 0.03 model is slightly bluer than the Z = 0.02 model in the UV-strong region, indicating a weak relationship between UVX and Z. (c) The strength of UVX increases with age in the model population. This is at variance with the results of other models that include binary stars as progenitors of EHB stars.

Hernández-Pérez, Fabiola; Bruzual, Gustavo

2014-11-01

217

Hot Stars in Globular Cluster - A Spectroscopist's View  

E-print Network

Globular clusters are ideal laboratories to study the evolution of low-mass stars. In this work we concentrate on three types of hot stars observed in globular clusters: horizontal branch stars, UV bright stars, and white dwarfs. After providing some historical background and information on gaps and blue tails we discuss extensively hot horizontal branch stars in metal-poor globular clusters, esp. their abundance anomalies and the consequences for the determination of their atmospheric parameters and evolutionary status. Hot horizontal branch stars in metal-rich globular clusters are found to form a small, but rather inhomogeneous group that cannot be explained by one evolutionary scenario. Hot UV bright stars show a lack of classic post-AGB stars that may explain the lack of planetary nebulae in globular clusters. Finally we discuss first results of spectroscopic observations of white dwarfs in globular clusters.

S. Moehler

2001-05-09

218

Exocomets and variable circumstellar gas absorption in the debris disks of nearby A-type stars  

NASA Astrophysics Data System (ADS)

Over the past five years, more than a dozen new star systems have been discovered that are similar to the famous and well-described Beta Pictoris system. Like Beta Pictoris, these systems include a young A-type star, a circumstellar gas-poor debris disk, and infalling exocomets. The presence of comets has been inferred from night-to-night changes in the absorption-line characteristics of the circumstellar disk CaII K-line at 3933Å towards these stars. As described by the Falling Evaporated Bodies model of Beust et al (1990, 1998), comet-like planetesimals residing in the outer regions of the dust disk are perturbed into eccentric star-grazing orbits by the action of either mutual collisions or by the gravitational influence of an accompanying massive exoplanet. The plume of gas is liberated at the comet’s close approach to the star.We present new high resolution absorption spectra of the CaII K line recorded over several nights towards the nearby and young (< 50 Myr) A-type stars HD 80007 and HD 109573. Both stars exhibit circumstellar absorption variability that is similar to that frequently observed in other `exocomet-systems’, such as Beta Pictoris and 49 Ceti. We also present a list of the physical characteristics of ~40 A-type stars with associated debris disks that possess circumstellar absorption spectra of the CaII K-line observed by us over several nights. Using all of these data we comment on which stellar parameter(s) seem to be the most important in determining whether or not exocomets will be detected in a given system.

Montgomery, Sharon Lynn; Welsh, Barry; Bukoski, Benjamin; Strausbaugh, Sarah

2015-01-01

219

UV extinction and IR emission in diffuse H2 regions  

NASA Astrophysics Data System (ADS)

During this period, much work was spent in an attempt to use theoretical UV line indices as a basis for spectral calibration of the program stars. Five line indices are shown as functions of effective temperature and log g, calculated with the spectral synthesis programs of Kurucz. Open stars and circles are observed values from Fanelli et al., using the spectral class-effective temperature calibration of Schmidt-Kaler. We conclude that these line indices may be used to determine an effective stellar temperature, but with uncertainties of approximately a few thousand degrees. Also, for the hotter stars, theoretical line opacities are systematically low compared to observations. We have also found that Kurucz's new models appear to represent hot stars very well, even at far-UV wavelengths. This is shown in an example where two spectra of mu Col (spectral class 09.5 V) are compared to a synthetic spectrum for Teff = 33,000 K, log g = 4.0. Also shown (uppermost curve) is an empirical estimate of the intrinsic flux distribution for 09.5 V stars from Papaj, Wegner, and Krelowski.

Aannestad, Per A.

220

UV extinction and IR emission in diffuse H2 regions  

NASA Technical Reports Server (NTRS)

During this period, much work was spent in an attempt to use theoretical UV line indices as a basis for spectral calibration of the program stars. Five line indices are shown as functions of effective temperature and log g, calculated with the spectral synthesis programs of Kurucz. Open stars and circles are observed values from Fanelli et al., using the spectral class-effective temperature calibration of Schmidt-Kaler. We conclude that these line indices may be used to determine an effective stellar temperature, but with uncertainties of approximately a few thousand degrees. Also, for the hotter stars, theoretical line opacities are systematically low compared to observations. We have also found that Kurucz's new models appear to represent hot stars very well, even at far-UV wavelengths. This is shown in an example where two spectra of mu Col (spectral class 09.5 V) are compared to a synthetic spectrum for T(sub eff) = 33,000 K, log g = 4.0. Also shown (uppermost curve) is an empirical estimate of the intrinsic flux distribution for 09.5 V stars from Papaj, Wegner, and Krelowski.

Aannestad, Per A.

1994-01-01

221

Reinvestigating the Lambda Boo Stars  

NASA Astrophysics Data System (ADS)

The peculiar nature of Lambda Bootis was first introduced in 1943. Subsequently, Lambda Boo stars have been slowly recognized as a group of A-type Population I dwarfs that show mild to extreme deficiencies of iron-peak elements, although C, N, O, and S can be near solar. MK classification criteria include broad hydrogen lines, a weak metallic-line spectrum compared to MK standards, coupled with a particularly weak Mg II 4481 line. This intriguing stellar class has recently regained the spotlight because of the directly imaged planets around a confirmed Lambda Boo star-HR 8799 and a probable Lambda Boo star-Beta Pictoris. The possible link between Lambda Boo stars and planet-bearing stars motivates us to study Lambda Boo stars systematically. However, Lambda Boo candidates published in the literature have been selected using widely different criteria. The Lambda Boo class has become somewhat of a "grab bag" for any peculiar A-type stars that didn't fit elsewhere. In order to determine the origin of Lambda Boo stars’ low abundances and to better discriminate between theories explaining the Lambda Boo phenomenon, a refined working definition of Lambda Boo stars is needed. We have re-evaluated all published Lambda Boo candidates and their existing spectra. After applying a consistent set of optical/UV classification criteria, we identified over 60 confirmed and over 20 probable Lambda Boo stars among all stars that have been suggested as Lambda Boo candidates. We are obtaining new observations for those probable Lambda Boo stars. We also have explored the possible link between debris disks and Lambda Boo Stars.

Cheng, Kwang-Ping; Corbally, C. J.; Gray, R. O.; Murphy, S.; Neff, J. E.; Desai, A.; Newsome, I.; Steele, P.

2014-01-01

222

Phantom without UV pathology  

E-print Network

We present a simple model in which the weak energy condition is violated for spatially homogeneous, slowly evolving fields. The excitations about Lorentz-violating background in Minkowski space do not contain ghosts, tachyons or superluminal modes at spatial momenta ranging from some low scale epsilon to the UV cutoff scale, while tachyons and possibly ghosts do exist at p^2 < epsilon^2. We show that in the absence of other matter, slow roll cosmological regime is possible; in this regime p+rho<0, and yet homogeneity and isotropy are not completely spoiled (at the expence of fine-tuning), since for given conformal momentum, the tachyon mode grows for short enough period of time.

V. A. Rubakov

2006-05-17

223

The diffuse UV background  

NASA Technical Reports Server (NTRS)

The diffuse radiation field in the UV (900-3,000 A) affects the structure of galactic molecular clouds and conveys important information concerning the physical characteristics and spatial distribution of gas and dust in the universe. Continuum emission in this range is probably dominated by interstellar dust scattering in our galaxy. For view directions and angular resolutions allowing observations in the rifts between galactic dust clouds, the background due to the integrated light of spiral galaxies may be detected, providing important information on their structure and evolution. The redshifted emission from an intergalactic medium may be observable in the regions between nearby bright galaxies. Present observations provide weak constraints on the radiation field required to ionize the intergalactic medium at the level required by the Gunn-Peterson test.

Paresce, F.; Jakobsen, P.

1980-01-01

224

Micro UV detector  

NASA Astrophysics Data System (ADS)

A lightweight, tactical biological agent detection network offers the potential for a detect-to-warn capability against biological aerosol attacks. Ideally, this capability can be achieved by deploying the sensors upwind from the protected assets. The further the distance upwind, the greater the warning time. The technological challenge to this concept is the biological detection technology. Here, cost, size and power are major factors in selecting acceptable technologies. This is in part due to the increased field densities needed to cover the upwind area and the fact that the sensors, when deployed forward, must operate autonomously for long periods of time with little or no long-term logistical support. The Defense Advanced Research Project Agency"s (DARPA) Solid-state Ultraviolet Optical Source (SUVOS) program offers an enabling technology to achieving a detector compatible with this mission. As an optical source, these devices emit excitation wavelengths known to be useful in the detection of biological aerosols. The wavelength band is absorbed by the biological aerosol and results in visible fluorescence. Detection of a biological aerosol is based on the observed intensity of this fluorescence signal compared to a background reference. Historically this has been accomplished with emission sources that are outside the boundaries for low cost, low power sensors. The SUVOS technology, on the other hand, provides the same basic wavelengths needed for the detection process in a small, low power package. ECBC has initiated an effort to develop a network array based on micro UV detectors that utilize the SUVOS technology. This paper presents an overview of the micro UV detector and some of the findings to date. This includes the overall design philosophy, fluid flow calculations to maximize presentation of aerosol particles to the sources, and the fluorescence measurements.

Cabalo, Jerry B.; Sickenberger, Richard; Underwood, William J.; Sickenberger, David W.

2004-09-01

225

Micro-UV detector  

NASA Astrophysics Data System (ADS)

A lightweight, tactical biological agent detection network offers the potential for a detect-to-warn capability against biological aerosol attacks. Ideally, this capability can be achieved by deploying the sensors upwind from the protected assets. The further the distance upwind, the greater the warning time. The technological challenge to this concept is the biological detection technology. Here, cost, size and power are major factors in selecting acceptable technologies. This is in part due to the increased field densities needed to cover the upwind area and the fact that the sensors, when deployed forward, must operate autonomously for long periods of time with little or no long-term logistical support. The Defense Advanced Research Project Agency"s (DARPA) Solid-state Ultraviolet Optical Source (SUVOS) program offers an enabling technology to achieving a detector compatible with this mission. As an optical source, these devices emit excitation wavelengths known to be useful in the detection of biological aerosols. The wavelength band is absorbed by the biological aerosol and results in visible fluorescence. Detection of a biological aerosol is based on the observed intensity of this fluorescence signal compared to a background reference. Historically this has been accomplished with emission sources that are outside the boundaries for low cost, low power sensors. The SUVOS technology, on the other hand, provides the same basic wavelengths needed for the detection process in a small, low power package. ECBC has initiated an effort to develop a network array based on micro UV detectors that utilize the SUVOS technology. This paper presents an overview of the micro UV detector and some of the findings to date. This includes the overall design philosophy, fluid flow calculations to maximize presentation of aerosol particles to the sources, and the fluorescence measurements.

Cabalo, Jerry B.; Sickenberger, Richard; Underwood, William J.; Sickenberger, David W.

2004-12-01

226

Interstellar Extinction Toward Young Stars  

NASA Astrophysics Data System (ADS)

We present work on a molecular hydrogen (H2) fluorescence model to characterize the ultraviolet (UV) extinction curve along the line of sight towards young stars with circumstellar disks. Stellar UV radiation plays a strong role in heating the disk gas and driving chemical reactions, so it is important to measure the UV extinction curve in order to reconstruct the intrinsic stellar UV flux impacting the disk. To measure the extinction, we compare modeled H2 fluorescence spectra to observed H2 lines. Lyman-alpha radiation from the stars pumps electronic transitions of H2 in the disk, and we model the flux that is re-emitted through the subsequent fluorescent cascade. We then extract the extinction along the line-of-sight over the 1100-1700 Angstrom wavelength region from the difference between the modeled H2 fluorescence and the HST-COS data. The shape of the extinction curve allows us to characterize the dust grain distribution in the intervening material as well as to recover the intrinsic spectral energy distribution of the stars over a wide wavelength range.

McJunkin, Matthew; France, Kevin

2015-01-01

227

Star Formation and Feedback in Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

We examine the star formation history and stellar feedback effects of dwarf galaxies under the influence of extragalactic ultraviolet radiation. Previous work has indicated that the background UV flux can easily ionize the gas within typical dwarf galaxies, delaying or even preventing cooling and star formation within them. Many dwarf galaxies within the Local Group are, however, observed to contain multiple generations of stars, the oldest of which formed in the early epochs of cosmic evolution, when the background UV flux was intense. In order to address this paradox, we consider the dynamical evolution of gas in dwarf galaxies using a one-dimensional, spherically symmetric, Lagrangian numerical scheme to compute the effects of radiative transfer and photoionization. We include a physically motivated star formation recipe and consider the effects of feedback. This scheme allows us to follow the history of the gas and of star formation within dwarf galaxies, as influenced by both external and internal UV radiation. Our results indicate that star formation in the severe environment of dwarf galaxies is a difficult and inefficient process. In potentials with total mass less than a few times 106 Msolar and velocity dispersion less than a few kilometers per second, residual gas is efficiently photoionized by cosmic background UV radiation. Since the density scale height of the gas within these galaxies is comparable to their size, gas may be tidally removed from them, leaving behind starless residual dark matter clumps. For intermediate-mass systems, such as the dSphs around the Galaxy, star formation can proceed within early cosmic epochs despite the intense background UV flux. Triggering processes such as merger events, collisions, and tidal disturbance can lead to density enhancements, reducing the recombination timescale, allowing gas to cool and star formation to proceed. However, the star formation and gas retention efficiency may vary widely in galaxies with similar dark matter potentials because they depend on many factors, such as the baryonic fraction, external perturbation, initial mass function, and background UV intensity. We suggest that the presence of very old stars in these dwarf galaxies indicates that their initial baryonic-to-dark matter content was comparable to the cosmic value. This constraint suggests that the initial density fluctuation of baryonic matter may be correlated with that of the dark matter. For the more massive dwarf elliptical galaxies, the star formation efficiency and gas retention rate are much higher. Their mass-to-light ratio is regulated by star formation feedback and is expected to be nearly independent of their absolute luminosity. The results of our theoretical models reproduce the observed (M/L)-Mv correlation.

Dong, Shawfeng; Lin, D. N. C.; Murray, S. D.

2003-10-01

228

UV Light for Processing Foods  

Microsoft Academic Search

Ultraviolet light (UV) light holds considerable promise in food processing as an alternative to traditional thermal processing. Its applications include pasteurization of juices, post lethality treatment for meats, treatment of food contact surfaces and to extend the shelf-life of fresh produce. This paper will review published studies and commercial applications that utilize UV treatment for solid and liquid foods. Designs

Tatiana Koutchma

2008-01-01

229

A predicted new population of UV-faint galaxies at z ? 4  

NASA Astrophysics Data System (ADS)

We show that a bursty model of star formation explains several puzzling observations of high-redshift galaxies. We begin by showing that because the observed star formation rate integrated over a Hubble time exceeds the observed stellar mass by an order of magnitude, the specific star formation rate requires a duty-cycle of ˜10 per cent. We use the specific star formation rate to calibrate a merger-driven model of star formation regulated by supernova feedback, and reproduce the star formation rate density and stellar mass functions of galaxies at 4 ? z ? 7. The specific star formation rate is predicted not to evolve rapidly with either mass or redshift at z ? 4, consistent with observation. This is in contrast to expectations from hydrodynamical simulations where star formation closely follows accretion rate, and increases strongly towards high redshift. Bursty star formation explains the observation that there is not enough stellar mass at z ˜ 2-4 to account for all star formation observed. A duty-cycle of ˜10 per cent implies that there could be 10 times the number of known high-redshift galaxies at fixed stellar mass that have not yet been detected through UV selection. We therefore predict the possible existence of an undetected population of UV-faint galaxies that accounts for most of the stellar mass density at z ˜ 4-8.

Wyithe, J. Stuart B.; Loeb, Abraham; Oesch, Pascal A.

2014-04-01

230

III-Nitride UV Devices  

NASA Astrophysics Data System (ADS)

The need for efficient, compact and robust solid-state UV optical sources and sensors had stimulated the development of optical devices based on III-nitride material system. Rapid progress in material growth, device fabrication and packaging enabled demonstration of high efficiency visible-blind and solar-blind photodetectors, deep-UV light-emitting diodes with emission from 400 to 250 nm, and UV laser diodes with operation wavelengths ranging from 340 to 350 nm. Applications of these UV optical devices include flame sensing; fluorescence-based biochemical sensing; covert communications; air, water and food purification and disinfection; and biomedical instrumentation. This paper provides a review of recent advances in the development of UV optical devices. Performance of state-of-the-art devices as well as future prospects and challenges are discussed.

Asif Khan, M.; Shatalov, M.; Maruska, H. P.; Wang, H. M.; Kuokstis, E.

2005-10-01

231

WSO-UV progress and expectations  

NASA Astrophysics Data System (ADS)

The World Space Observatory Ultraviolet (WSO-UV) is the space mission that will grant access to the ultraviolet (UV) range in the post Hubble epoch. WSO-UV is equipped with instrumentation for imaging and spectroscopy and it is fully devoted to UV astronomy. In this article, we outline the WSO-UV mission model and present the current status of the project.

Shustov, Boris; Gómez de Castro, Ana I.; Sachkov, Mikhail; Moisheev, Alexander; Kanev, Evgeny; López-Santiago, Javier; Malkov, Oleg; Nasonov, Dmitry; Belén Perea, G.; Sánchez, Néstor; Savanov, Igor; Shugarov, Andrey; Sichevskiy, Sergey; Vlasenko, Oleg; Yañez, Javier

2014-11-01

232

UvA huisstijlsjablonen | Word 2012 gebruikshandleiding  

E-print Network

UvA huisstijlsjablonen | Word 2012 gebruikshandleiding Versie 29 januari 2013 #12;Pagina 2....................................................................................................................................... 9 #12;Pagina 3 Inleiding Via de UvA-werkplek is een basisset UvA Sjablonen /UvA Templates beschikbaar in Word. Met UvA Sjablonen is het maken van brieven, faxen, memo's, agenda's, verslagen en

van Rooij, Robert

233

Large-scale asymmetries in the winds of (binary) AGB stars  

NASA Astrophysics Data System (ADS)

Observations of 78 Asymptotic Giant Branch (AGB) stars and Red Supergiants were carried out with the PACS photometer on-board Herschel as part of the MESS (Mass loss of Evolved StarS) program. For about 60% of these objects, the dusty wind differs from spherically symmetric and reveals a complex morphology. The majority of these asymmetries are caused by a rather simple incident, the interaction of the stellar wind with the interstellar medium. A bow shock is formed in direction of the stellar motion where the two media interact. However, also much more irregular shapes are encountered in the sample. These structures are often related to the binarity of the stellar system. Accreted material by the companion can cause nova outbursts or bipolar outflows which are relatively common. A rather rare encounter are Archimedean spirals that are imprinted in the wind which are now found for a handful of objects, among W Aquilae observed with Herschel and R Sculptoris with ALMA. The most complicated structures in the MESS sample indicate the interplay of multiple interacting influences. A prominent case is o Ceti (Mira). Its exceptionally high space motion produces a strong bow shock and its white dwarf companion drags an Archimedean spiral into the deformed stellar wind bubble and pierces it with a fast bipolar outflow.

Mayer, A.; Jorissen, A.; Kerschbaum, F.; Ottensamer, R.; Nowotny, W.; Aringer, B.; Paladini, C.; Mecina, M.; Pourbaix, D.; Groenewegen, M.; Mohamed, S.

2014-04-01

234

UV light from old stellar populations: the HST and GALEX eyes on globular clusters.  

NASA Astrophysics Data System (ADS)

The UV properties of old stellar populations have been subject of intense scrutiny from the late sixties, when the UV-upturn in early type galaxies was first discovered. Because of their proximity and relative simplicity, Galactic globular clusters (GGCs) are ideal local templates to understand how the integrated UV light is driven by hot stellar populations, primarily horizontal branch stars and their progeny. Our understanding of such stars is still plagued by theoretical uncertainties, which are partly due to the absence of an accurate, comprehensive, statistically representative homogeneous data-set. To move a step forward on this subject, we have combined the HST and GALEX capabilities and collected the largest data-base ever obtained for GGCs in UV. This data-base is best suited to provide insights on the HB second parameter problem and on the first stages of GCs formation and chemical evolution and to understand how they are linked to the observed properties of extragalactic systems.

Dalessandro, Emanuele

235

AN IUE ATLAS OF PREMAIN-SEQUENCE STARS. II. FAR-ULTRAVIOLET ACCRETION DIAGNOSTICS IN T TAURI STARS  

Microsoft Academic Search

We use our ultraviolet (UV) atlas of premain-sequence stars constructed from all useful, short- wavelength, low-resolution spectra in the International Ultraviolet Explorer (IUE) satellite Final Archive to analyze the short-wavelength UV properties of 49 T Tauri stars (TTSs). We compare the line and continuum —uxes in these TTSs with each other and with previously published parameters of these systems, including

CHRISTOPHER M. JOHNS-KRULL; JEFF A. VALENTI; JEFFREY L. LINSKY

236

Are all Trapezium stars magnetic?  

NASA Astrophysics Data System (ADS)

Recent X-ray observations of unprecedented length (10 days) of the Orion Nebula Cluster with the Chandra satellite (the COUP project) have revealed X-ray flares on the light-curves of late-B and A stars, as well as two new cases of rotational modulation, in addition to the already known case of the O7 star ?1 OriC. We show that the X-ray emission of A stars (which have neither deep outer convective zones nor strong UV radiation) when detected must be due to the solar-like magnetic activity of unresolved late-type companions, and that most, if not all, of the O and early B stars of the Trapezium may be magnetized and emit X-rays by magnetically channelled wind shocks.

Montmerle, T.

237

Hot Massive Stars: The Impact of HST  

E-print Network

We review the contribution of Hubble Space Telescope to the study of hot, luminous stars. Optical and IR imaging have permitted spatially resolved observations of young, massive clusters within Local Group galaxies, such as R136, NGC 3603 and Arches, revealing unprecedented concentrations of very massive O stars. UV spectroscopy of field OB stars in the Magellanic Clouds have provided suitable templates for interpretation of metal-poor star-forming galaxies at high-redshift. Spectacular imaging provides the detailed structure of ejecta nebulae from individual stars, including the Homunculus associated with eta Carinae and M1-67, associated with a Wolf-Rayet star. HST has permitted individual massive stars to be spatially resolved in giant HII regions located beyond the Local Group, such as NGC 604, plus individual clusters, dominated by the light of massive stars within starburst galaxies at larger distances, such as NGC 3125. UV spectroscopy of young, massive clusters in the extremely metal-poor HII galaxy I Zw 18 include signatures of large numbers of Wolf-Rayet stars.

Paul A. Crowther

2007-06-30

238

Hot Massive Stars: The Impact of HST  

NASA Astrophysics Data System (ADS)

We review the contribution of Hubble Space Telescope to the study of hot, luminous stars. Optical and IR imaging have permitted spatially resolved observations of young, massive clusters within Local Group galaxies, such as R136, NGC 3603 and Arches, revealing unprecedented concentrations of very massive O stars. UV spectroscopy of field OB stars in the Magellanic Clouds have provided suitable templates for interpretation of metal-poor star-forming galaxies at high-redshift. Spectacular imaging provides the detailed structure of ejecta nebulae from individual stars, including the Homunculus associated with ? Carinae and M1-67, associated with a Wolf-Rayet star. HST has permitted individual massive stars to be spatially resolved in giant HII regions located beyond the Local Group, such as NGC 604, plus individual clusters, dominated by the light of massive stars within starburst galaxies at larger distances, such as NGC 3125. UV spectroscopy of young, massive clusters in the extremely metal-poor HII galaxy I Zw 18 include signatures of large numbers of Wolf-Rayet stars.

Crowther, Paul A.

239

Hot Stars in the Galactic Halo  

NASA Astrophysics Data System (ADS)

Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars in the halo; 32. Baade-Wesselink analyses of field vs. cluster RR lyrae variables; 33. The rotation of population II A stars; 34. Horizontal branch stars and possibly related objects; 35. A new group of post-AGB objects - the hot carbon-poor stars; 36. MK classifications of hot stars in the halo 37. Photometry of XX Virginis and V716 Ophiuchi and the period luminosity relations of type II cepheids; 38. Rotation and oxygen line strengths in blue horizontal branch stars; Part V. Miscellaneous: 39. UBV CCd photometry of the halo of M31; 40. Can stars still form in the galactic halo?; 41. The ultraviolet imaging telescope on the Astro -1 and Astro -2 missions; 42. Are analogues of hot subdwarf stars responsible for the UVX phenomenon in galaxy nucleli; 43. A survey for field BHB stars outside the solar circle; 44. Post-AGB A and F supergiants as standard candles; 45. The extended horizontal-branch: a challenge for stellar evolution theory; 46. Astronomical patterns in fractals: the work of A. G. Davis Philip on the Mandelbrot Set; Part VI. Summary: 47. Final remarks; Author index; Subject index.

Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

2011-03-01

240

Hot Stars in the Galactic Halo  

NASA Astrophysics Data System (ADS)

Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars in the halo; 32. Baade-Wesselink analyses of field vs. cluster RR lyrae variables; 33. The rotation of population II A stars; 34. Horizontal branch stars and possibly related objects; 35. A new group of post-AGB objects - the hot carbon-poor stars; 36. MK classifications of hot stars in the halo 37. Photometry of XX Virginis and V716 Ophiuchi and the period luminosity relations of type II cepheids; 38. Rotation and oxygen line strengths in blue horizontal branch stars; Part V. Miscellaneous: 39. UBV CCd photometry of the halo of M31; 40. Can stars still form in the galactic halo?; 41. The ultraviolet imaging telescope on the Astro -1 and Astro -2 missions; 42. Are analogues of hot subdwarf stars responsible for the UVX phenomenon in galaxy nucleli; 43. A survey for field BHB stars outside the solar circle; 44. Post-AGB A and F supergiants as standard candles; 45. The extended horizontal-branch: a challenge for stellar evolution theory; 46. Astronomical patterns in fractals: the work of A. G. Davis Philip on the Mandelbrot Set; Part VI. Summary: 47. Final remarks; Author index; Subject index.

Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

1994-08-01

241

Hubble Space Telescope Observations of UV Oscillations in WZ Sagittae During the Decline from Outburst  

E-print Network

We present a time series analysis of Hubble Space Telescope observations of WZ Sge obtained in 2001 September, October, November and December as WZ Sge declined from its 2001 July superoutburst. Previous analysis of these data showed the temperature of the white dwarf decreased from ~29,000 K to ~18,000 K. In this study we binned the spectra over wavelength to yield ultraviolet light curves at each epoch that were then analyzed for the presence of the well-known 27.87 s and 28.96 s oscillations. We detect the 29 s periodicity at all four epochs, but the 28 s periodicity is absent. The origin of these oscillations has been debated since their discovery in the 1970s and competing hypotheses are based on either white dwarf non-radial g-mode pulsations or magnetically-channelled accretion onto a rotating white dwarf. By analogy with the ZZ Ceti stars, we argue that the non-radial g-mode pulsation model demands a strong dependence of pulse period on the white dwarf's temperature. However, these observations show the 29 s oscillation is independent of the white dwarf's temperature. Thus we reject the white dwarf non-radial g-mode pulsation hypothesis as the sole origin of the oscillations. It remains unclear if magnetically-funnelled accretion onto a rapidly rotating white dwarf (or belt on the white dwarf) is responsible for producing the oscillations. We also report the detection of a QPO with period ~18 s in the September light curve. The amplitudes of the 29 s oscillation and the QPO vary erratically on short timescales and are not correlated with the mean system brightness nor with each other.

W. F. Welsh; E. M. Sion; P. Godon; B. T. Gansicke; C. Knigge; K. S. Long; P. Szkody

2003-09-19

242

Cubesat-based UV astronomy  

NASA Astrophysics Data System (ADS)

Development of UV astronomy can be traced to go in one main direction: launching even larger telescopes to ensure an as high as possible photon collecting area. This trend causes inevitably escalating mission costs and this, in the present environment of diminishing research budgets, is the main reason for not having as many UV astronomy missions as one would like. I propose an alternative paradigm based on developing UV missions based on the cubesat technology. This allows a very significant cost reduction by basing the platform on custom off-the-shelf (COTS) components, at the price of small collecting apertures. I discuss possible topics that could benefit from such an approach.

Brosch, Noah

243

STAR FORMATION IN ATOMIC GAS  

SciTech Connect

Observations of nearby galaxies have firmly established, over a broad range of galactic environments and metallicities, that star formation occurs exclusively in the molecular phase of the interstellar medium (ISM). Theoretical models show that this association results from the correlation between chemical phase, shielding, and temperature. Interstellar gas converts from atomic to molecular only in regions that are well shielded from interstellar ultraviolet (UV) photons, and since UV photons are also the dominant source of interstellar heating, only in these shielded regions does the gas become cold enough to be subject to Jeans instability. However, while the equilibrium temperature and chemical state of interstellar gas are well correlated, the timescale required to reach chemical equilibrium is much longer than that required to reach thermal equilibrium, and both timescales are metallicity-dependent. Here I show that the difference in timescales implies that, at metallicities below a few percent of the solar value, well shielded gas will reach low temperatures and proceed to star formation before the bulk of it is able to convert from atomic to molecular. As a result, at extremely low metallicities, star formation will occur in a cold atomic phase of the ISM rather than a molecular phase. I calculate the observable consequences of this result for star formation in low-metallicity galaxies, and I discuss how some current numerical models for H{sub 2}-regulated star formation may need to be modified.

Krumholz, Mark R., E-mail: krumholz@ucolick.org [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2012-11-01

244

Limits of detection in debris disks around young stars with NaCo/Sparse Aperture Masking observations  

NASA Astrophysics Data System (ADS)

To understand the formation and evolution of solar systems and planets formations in the stars neighbourhood, we need to obtain information of their state at different time of their evolution. Here, we focus on debris disks around young stars aged of ten to few tens of Myr, we analyze NaCo/Sparse Aperture Masking (SAM) observations in the L' band (3.8 ?m) of eight objects (beta Pictoris, AU Mic, 49 Ceti, eta Tel, Fomalhaut, G Lupi, HD182327 and HR8799). The aim is to get limits of detection about the mass of the debris orbiting around their stars. The SAM technique consists in transforming a single telescope into a Fizeau interferometer using a non redundant mask inserted in a pupil plane of the instrument. The analysis of the observations was completed with the sparse aperture mode pipeline. Interference fringes are fitted to obtain complex visibilities of the object, then the closure phases are calibrated and evaluated. Finally, a map of the detection limits is obtained as it is related to the closure phases previously estimated. In order to obtain an estimation of the mass corresponding to the luminosity measured with the reduction pipeline we are using theoretical isochrones interpolated into synthetic color tables. The results are maps of detection limits in unit of Jupiter Mass in a range of up to 450 mas around the stars.

Gauchet, L.; Lacour, S.

2014-09-01

245

The massive star IMF  

E-print Network

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a "universal" Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lower M_up and/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich HII regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit on M_up of >~ 60--90 Msun.

Daniel Schaerer

2002-08-12

246

Mass loss from cool stars  

NASA Technical Reports Server (NTRS)

The properties of cool stellar winds are discussed, summarizing the results of observations obtained with the IUE satellite since its launch in 1978. The advantages of the UV spectral region for studying mass loss in cool stars are outlined; the evidence for mass outflow in objects spanning the cool half of the H-R diagram is reviewed; techniques and results of mass-loss-rate computations based on UV data are examined; detailed studies of single stars and binaries are described; the primary achievements of the IUE are listed; and a number of outstanding problems are briefly considered. Diagrams, graphs, sample spectra, and tables of numerical data are included. The mass-loss rates and wind velocities for Zeta Aur and VV Cep binaries are found to have ranges of about (6-1000) x 10 to the -9th solar mass/yr and 10-160 km/s, respectively.

Dupree, A. K.; Reimers, D.

1987-01-01

247

The Carbon Mira UV Aurigae and its Companion  

NASA Astrophysics Data System (ADS)

The carbon Mira UV Aur (photometric period 394 days) and its companion present several interesting spectroscopic issues. The late B-type companion, at a separation of 3farcs36, is seen through at least two shells expanding from the C9-type primary, as evidenced by a series of narrow, displaced absorption features at the D1,2 lines of Na I. The (projected) expansion velocity of the fastest shell is about 116 km s-1, much larger than the typical outflow velocity of about 15 km s-1 seen in C-type giants, but reminiscent of the velocities observed in the envelope of another C-type Mira, V Hya. Emission lines of H, Ca II, and Na I are present in UV Aur A; its Balmer emission lines are heavily mutilated by overlying C-type absorptions (much as is seen in Me-type Miras), so they must be formed at a lower level. UV Aur B offers the opportunity to test a speculation that the carriers of the diffuse interstellar bands (DIBs), believed to be a family of carbon-containing polyatomic molecules, may be formed in cool, carbon-rich stars. Moderately strong DIBs are indeed present in the spectrum of UV Aur B at about the same strength and velocity seen in nearby (in the sky) B-type stars. But the essential question is, are DIBs present in the outflow from UV Aur A, at the velocities of the Na I shell components? The answer is no, at least at the level permitted by the signal-to-noise ratio of these Keck/HIRES spectrograms.

Herbig, G. H.

2009-11-01

248

High Temporal Resolution Spectroscopic Observations of the Flare Star V1054 Oph  

E-print Network

of the are (UV Cet type) star V1054 Oph (Wolf 630AB), classi#12;ed as a dM3.5e visual binary system. Intermediate (red-shifted) lines are observed as well. Keywords: stars: V1054 Oph, stars: ares: spectroscopic, stars: activity, stars: late-type 1. Introduction V1054 Oph (GJ 644, Wolf 630AB) is a close visual

Complutense de Madrid, Universidad

249

UVS is rare in seabirds.  

PubMed

Ultraviolet-sensitive vision (UVS), believed to have evolved from an ancestral state of violet-sensitive vision (VS), is widespread among terrestrial birds, where it is thought to play a role in orientation, foraging, and sexual selection. Less is known, however, about the distribution and significance of UVS in seabirds. To date UVS has been definitively demonstrated only in two families (Laridae and Sternidae), although indirect evidence has been used to argue for a more widespread occurrence. In this study we analyzed short-wavelength sensitive (SWS1) opsin DNA sequences to determine the distribution of ancestral (VS) and derived (UVS) amino acid spectral tuning sites in 16 seabird species representing 8 families with diverse ecological niches. Our results revealed sequences associated with UVS pigments (UVSs) in the Black-backed gull (Larus dominicanus), providing further evidence of its widespread occurrence within the Laridae. The Caspian tern (Hydroprogne caspia) and White-fronted tern (Sterna striata), however, were found to have VSs, suggesting an evolutionary reversion to the ancestral state within Sternidae. VSs were also detected in an additional six families. Our results raise interesting questions about the functions of UV vision in marine environments. PMID:21527267

Machovsky Capuska, Gabriel E; Huynen, Leon; Lambert, David; Raubenheimer, David

2011-06-21

250

Exoplanet Host Star Radiation and Plasma Environment  

NASA Astrophysics Data System (ADS)

Radiation from host stars controls the planetary energy budget, photochemistry in planetary atmospheres, and mass loss from the outer layers of these atmospheres. Stellar optical and infrared radiation, the major source of energy for the lower atmosphere and planetary surfaces, increases slowly as stars evolve from the Zero-Age-Main-Sequence. Ultraviolet radiation, including the Lyman-? emission line that dominates the UV spectrum of M dwarf stars, controls photochemical reactions of important molecules, including H2O, CO2, and CH4. Extreme ultraviolet and X-radiation from host stars ionizes and heats the outer layers of planetary atmospheres driving mass loss that is rapid for close-in Jupiter-like planets. The strength of the stellar UV, EUV, and X-radiation depends on stellar activity, which decays with time as stellar rotation decreases. As a result, the evolution of an exoplanet's atmosphere depends on the evolution of its host star. We summarize the available techniques for measuring or estimating the X-ray, EUV, and UV radiation of host stars with different spectral types and ages.

Linsky, Jeffrey L.; Güdel, Manuel

251

STATISTICAL PROPERTIES OF GALACTIC {delta} SCUTI STARS: REVISITED  

SciTech Connect

We present statistical characteristics of 1578 {delta} Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodriguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of {delta} Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodriguez's work. All the {delta} Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing {delta} Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

Chang, S.-W.; Kim, D.-W.; Byun, Y.-I. [Department of Astronomy, Yonsei University, Seoul 120-749 (Korea, Republic of); Protopapas, P., E-mail: seowony@galaxy.yonsei.ac.kr, E-mail: kim@mpia-hd.mpg.de [Harvard Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)

2013-05-15

252

VUV-UV absorption spectroscopy of DNA and UV screens suggests strategies for UV resistance during evolution and space travel  

Microsoft Academic Search

Early life on Earth had to cope with harsh conditions, including full spectrum solar UV. Since DNA absorbs in the highly energetic UV-C and VUV, solar irradiation was likely an obstacle to the expansion of life on Earth, until biological mechanisms evolved to cope with UV liability (including the biosynthesis of UV screens) and ozone (derived from oxygen produced by

Andreja Zalar; David Tepfer; Søren V. Hoffmann; Albert Kollmann; Sydney Leach

2007-01-01

253

HST/COS Observations of O(He) Stars  

NASA Astrophysics Data System (ADS)

The four known O(He) stars are the only amongst the hottest post-AGB stars (Teff>100,000 K) whose atmospheres are composed of almost pure helium. This chemistry markedly differs from that of the hydrogen-deficient post-AGB evolutionary sequence with objects that have carbon-dominated atmospheres (namely PG 1159 stars and Wolf-Rayet type central stars). While PG 1159 and Wolf-Rayet stars are the result of a (very) late helium-shell flash, this scenario cannot explain the O(He) stars. Instead, they are possibly double-degeneratemergers. We speculate that the four O(He) stars represent evolved RCrB stars, which also have helium-dominated atmospheres. We present UV spectroscopy of the O(He) stars based on recently performed HST/COS observations.

Rauch, T.; Werner, K.

2010-11-01

254

A Type Stars as Probes of the Local Interstellar Medium  

NASA Technical Reports Server (NTRS)

With the aim to sample the Local Interstellar Medium (LISM), it was proposed to use A stars as targets. The Mg II UV lines seem to be the best interstellar absorption candidates. Several hundreths of A stars can be reached within 100 pc. First preliminary results (20 lines of sight) are presented, based on previous Copernicus and actual IUE observations.

Ferrero, R. F.; Ferlet, R.; Vidal-Madjar, A.

1984-01-01

255

Star formation in hosts of young radio galaxies  

E-print Network

We present near ultraviolet imaging with the Hubble Space Telescope Advanced Camera for Surveys, targeting young radio galaxies (Gigahertz Peaked Spectrum and Compact Steep Spectrum sources), in search of star formation regions in their hosts. We find near UV light which could be the product of recent star formation in eight of the nine observed sources. However, observations at other wavelengths and colors are needed to definitively establish the nature of the observed UV light. In the CSS sources 1443+77 and 1814--637 the near UV light is aligned with and is co-spatial with the radio source, and we suggest that in these sources the UV light is produced by star formation triggered and/or enhanced by the radio source.

A. Labiano; C. P. O'Dea; P. D. Barthel; W. H. de Vries; S. A. Baum

2005-12-02

256

Legacy ExtraGalactic UV Survey (LEGUS): Revolutionary UV astronomy  

NASA Astrophysics Data System (ADS)

The Treasury program LEGUS (HST/GO-13364) is a 154-orbit Hubble Space Telescope survey that is obtaining HST/WFC3 and HST/ACS NUV, U, B, V, and I-band imaging of 50 star-forming galaxies at distances of 4-12 Mpc. The LEGUS targets have been carefully selected to uniformly sample a full range of global galaxy properties such as morphology, star formation rate, mass, metallicity, internal structure, and interaction state.We provide a first taste of the type and quality of the data products that will be made available to the community through the website legus.stsci.edu. The data includes: state of the art science-ready mosaics in five wavelengths; band-merged catalogs of stellar sources (including location and photometry), band-merged catalogs of star clusters (locations, photometry, aperture corrections), catalogs of star cluster properties (ages, masses, extinction). and ancillary data available for this galaxy sample such as GALEX, Spitzer and WISE imaging.The above catalogs will enable a wide range of scientific applications, including color-magnitude diagrams and color-color diagrams of both stars and clusters, to derive star formation histories, cluster formation histories, the evolution of stars/association/cluster clustering, and the dependence of these on galactic environment. These are only a few of the potential applications enabled by a diverse sample like LEGUS.

Ubeda, Leonardo

2014-06-01

257

High Power UV LED Industrial Curing Systems  

Microsoft Academic Search

UV curing is a green technology that is largely underutilized because UV radiation sources like Hg Lamps are unreliable and difficult to use. High Power UV LEDs are now efficient enough to replace Hg Lamps, and offer significantly improved performance relative to Hg Lamps. In this study, a modular, scalable high power UV LED curing system was designed and tested,

Karlicek; F. Robert; Robert Sargent

2012-01-01

258

UV-VIS Varian Cary 50 Series  

E-print Network

UV-VIS Varian Cary 50 Series Spectrophotometer #12;2 1947 Cary 11 UV-Vis 1954 Cary 14 UV commercial recording UV-Vis spectrophotometer, a Cary 11, to Mellon Institute in Pittsburgh, USA on occasion must push a spectrophotometer to the very limits of its performance capability to obtain

Magee, Joseph W.

259

The DQ Herculis stars  

NASA Technical Reports Server (NTRS)

We review the properties of the DQ Herculis stars: cataclysmic variables containing an accreting, magnetic, rapidly rotating white dwarf. These stars are characterized by strong X-ray emission, high-excitation spectra, and very stable optical and X-ray pulsations in their light curves. There is considerable resemblance to their more famous cousins, the AM Herculis stars, but the latter class is additionally characterized by spin-orbit synchronism and the presence of strong circular polarization. We list eighteen stars passing muster as certain or very likely DQ Her stars. The rotational periods range from 33 s to 2.0 hr. Additional periods can result when the rotating searchlight illuminates other structures in the binary. A single hypothesis explains most of the observed properties: magnetically channeled accretion within a truncated disk. Some accretion flow still seems to proceed directly to the magnetosphere, however. The white dwarfs' magnetic moments are in the range 10(sup 32) - 10(sup 34) G cc, slightly weaker than in AM Her stars but with some probable overlap. The more important reason why DQ Hers have broken synchronism is probably their greater accretion rate and orbital separation. The observed L(sub x)/L(sub V) values are surprisingly low for a radially accreting white dwarf, suggesting that most of the accretion energy is not radiated in a strong shock above the magnetic pole. The fluxes can be more satisfactorily explained if most of the radial infall energy manages to bypass the shock and deposit itse lf directly in the white dwarf photosphere, where it should emerge as extreme ultraviolet (EUV) radiation. This also provides an adequate source of ionizing photons to power the high-excitation optical and UV emission lines. This is probably the DQ Her analog to the famous 'soft X-ray excess' in AM Her stars. However, unlike the AM Her case, this radiation has not been directly observed, so the analogy must not (yet) be embraced too firmly. There is some conventional wisdom today which segregates the short-period from the long-period DQ Her stars. But the observational grounds for this distinction are slim, except in one respect: X-ray emission from short-period systems appears to be weaker and softer. This must be due to the shallower depth of the potential well, and/or the greater difficulty the fast rotators have in enforcing radial accretion flow.

Patterson, Joseph

1994-01-01

260

Testing White Dwarf Crystallization Theory with Asteroseismology of the Massive Pulsating DA Star BPM 37093  

E-print Network

It was predicted more than 40 years ago that the cores of the coolest white dwarf stars should eventually crystallize. This effect is one of the largest sources of uncertainty in white dwarf cooling models, which are now routinely used to estimate the ages of stellar populations in both the Galactic disk and the halo. We are attempting to minimize this source of uncertainty by calibrating the models, using observations of pulsating white dwarfs. In a typical mass white dwarf model, crystallization does not begin until the surface temperature reaches 6000-8000 K. In more massive white dwarf models the effect begins at higher surface temperatures, where pulsations are observed in the ZZ Ceti (DAV) stars. We use the observed pulsation periods of BPM 37093, the most massive DAV white dwarf presently known, to probe the interior and determine the size of the crystallized core empirically. Our initial exploration of the models strongly suggests the presence of a solid core containing about 90% of the stellar mass, which is consistent with our theoretical expectations.

T. S. Metcalfe; M. H. Montgomery; A. Kanaan

2004-03-09

261

Planetary nebulae and the death of stars  

Microsoft Academic Search

The database on planetary nebulae (PN) is summarized in terms of the known facts of the processes of planetary formation. Approximately 1500 PN have been observed in the Galaxy, most taking either a bilobed or circularly symmetric form. The matter is 90 percent hydrogen heated by UV light from a central star to surface temperatures ranging from 25,000-100,000 K. The

J. B. Kaler

1986-01-01

262

UV Disinfection System for Cabin Air  

Microsoft Academic Search

Ultraviolet (UV) radiation is commonly used for disinfection of water. As a result of advancements made in the last 10-15 years, the analysis and design of UV disinfection systems for water is well developed. UV disinfection is also used for disinfection of air; however, despite the fact the UV-air systems have a longer record of application than UV-water systems, the

Soojung Lim

2008-01-01

263

UvA Template Manual A basic set of UvA Templates is available in Word via UvA-Workspace. UvA Templates  

E-print Network

UvA Template Manual A basic set of UvA Templates is available in Word via UvA-Workspace. UvA information concerning the corporate identity, e.g. creating PowerPoint presentations, can be found via www.uva.nl/huisstijl On starting Word, you will see UvA Templates below the toolbar in the upper left hand side of the screen. Next

van Rooij, Robert

264

A Global Perspective on Star Formation  

E-print Network

We outline a method to infer the global history of star formation in galaxies with input only from absorption-line observations of quasars. The application of the method to existing data leads to the conclusion that most stars formed at relatively low redshifts (z <~ 2). We combine the global rate of star formation with stellar population synthesis models to compute the mean comoving emissivity and mean intensity of background radiation from far-UV to far-IR wavelengths. These predictions are consistent with all the available measurements and observational limits, including recent results from HST and COBE.

S. Michael Fall

1996-11-20

265

Plasmon-enhanced UV photocatalysis  

SciTech Connect

We report plasmonic nanoparticle enhanced photocatalysis on titanium dioxide (TiO{sub 2}) in the deep-UV range. Aluminum (Al) nanoparticles fabricated on TiO{sub 2} film increases the reaction rate of photocatalysis by factors as high as 14 under UV irradiation in the range of 260–340?nm. The reaction efficiency has been determined by measuring the decolorization rate of methylene blue applied on the TiO{sub 2} substrate. The enhancement of photocatalysis shows particle size and excitation wavelength dependence, which can be explained by the surface plasmon resonance of Al nanoparticles.

Honda, Mitsuhiro; Saito, Yuika, E-mail: yuika@ap.eng.osaka-u.ac.jp; Kawata, Satoshi [Department of Applied Physics, Osaka University, Suita, Osaka 565-0871 (Japan); Kumamoto, Yasuaki [Nanophotonics Laboratory, RIKEN, Wako, Saitama 351-0198 (Japan); Taguchi, Atsushi [Nanophotonics Laboratory, RIKEN, Wako, Saitama 351-0198 (Japan); Department of Mechanical Systems Engineering, School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

2014-02-10

266

Constraining Galaxy Evolution Using Observed UV-Optical Spectra  

NASA Technical Reports Server (NTRS)

Our understanding of galaxy evolution depends on model spectra of stellar populations, and the models are only as good as the observed spectra and stellar parameters that go into them. We are therefore evaluating modem UV-optical model spectra using Hubble's Next Generation Spectral Library (NGSL) as the reference standard. The NGSL comprises intermediate-resolution (R is approximately 1000) STIS spectra of 378 stars having a wide range in metallicity and age. Unique features of the NGSL include its broad wavelength coverage (1,800-10,100 A) and high-S/N, absolute spectrophotometry. We will report on a systematic comparison of model and observed UV-blue spectra, describe where on the HR diagram significant differences occur, and comment on current approaches to correct the models for these differences.

Heap, Sally

2007-01-01

267

Stationary Star  

NSDL National Science Digital Library

This is an activity about star movement due to the Earth's rotation. Learners will utilize the Sky Tonight online program to find the star that appears stationary in our night sky. They will then draw conclusions about the Earthâs rotation based on the position changes of certain stars. This activity requires the use of a computer with Internet access. This activity is Sky Tonight Activity 2 in a larger resource, Space Update.

268

Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, aren’t doing much of anything. In this video, Jonathan’s investigations reveal a slow-motion predator that hunts and attacks its prey. Traveling the world, Jonathan investigates sea stars from the tropics to the Antarctic and uses time-lapse photography to reveal an amazing complexity to the world of the sea star. Please see the accompanying study guide for educational objectives and discussion points.

2012-07-28

269

Comparison Of UV And H-alpha SFR Indicators At Intermediate Redshift: Extraction Of GALEX UV Fluxes  

NASA Astrophysics Data System (ADS)

We present preliminary results of an on-going study of the systematics between two commonly used star formation rate (SFR) indicators, UV and H-alpha emission, at z 0.8. This poster reports on the construction of a PSF-based flux catalog, which effectively deals with object blending, using data from the GALEX ultra-deep imaging survey in the Extended Groth Strip. A companion poster presents the work done to extract H-alpha fluxes from new near-IR narrowband imaging observations in the same region. From the rest-frame far-UV flux and the UV slope, we calculate dust-corrected SFRs. For galaxies at z 0.8 having spectroscopic redshifts in DEEP2, our UV SFRs are compared to those obtained in the H-alpha analysis. We hope our study aids in a better understanding of these two indicators, since the systematics of both have not been extensively studied in the intermediate and high redshift regimes. Walton's research was supported by the NOAO/KPNO Research Experiences for Undergraduates (REU) Program which is funded by the National Science Foundation through Scientific Program Order No. 3 (AST-0243875) of the Cooperative Agreement No. AST-0132798 between the Association of Universities for Research in Astronomy (AURA) and the NSF.

Walton, Josiah; Esselman, A.; Salim, S.; Lee, J.

2007-12-01

270

The Birth of the Universe and the Fate of the Earth: UV Photons Meet Stan  

E-print Network

contain signatures of planets, particularly around compact UV-luminous objects such white dwarfs. Stars becomes a white dwarf? With the GALEX photon data set, we can measure the distribution function of planets around white dwarfs and begin to answer this question. Even more recently, astronomers have discovered

Columbia University

271

Scintillating Stars  

NSDL National Science Digital Library

Often, a bright planet that is visible over the horizon will be mistaken for a star. Some believe they can tell the difference between a star and a planet because stars twinkle, or scintillate , and planets do not. In actuality however, both will twinkle because any light that passes through our atmosphere, whether it be reflected from a planet or generated by a star, will be interfered with by the atmospheric elements. This month's column sheds light on this "scintillating" subject and engages students in a research activity that revolves around the question: Is Pluto a planet?

Riddle, Bob

2003-02-01

272

Neutron Stars  

NASA Technical Reports Server (NTRS)

Neutron stars were discovered almost 40 years ago, and yet many of their most fundamental properties remain mysteries. There have been many attempts to measure the mass and radius of a neutron star and thereby constrain the equation of state of the dense nuclear matter at their cores. These have been complicated by unknown parameters such as the source distance and burning fractions. A clean, straightforward way to access the neutron star parameters is with high-resolution spectroscopy. I will present the results of searches for gravitationally red-shifted absorption lines from the neutron star atmosphere using XMM-Newton and Chandra.

Cottam, J.

2007-01-01

273

Lucky Star  

NSDL National Science Digital Library

Watch this video from Cyberchase and then play the Lucky Star game! The Lucky Star game show the will ask you math-related questions and give you four possible answers to choose from. Your goal is to answer the questions correctly and score as many points as you can. You can score points during two different rounds: the pick-a-star round and the lightning round. During the pick-a-star round you have as much time as you want to answer the questions. During the lightning round you have to think fast in order to earn the points. Good luck!

2008-01-01

274

8, 27452769, 2008 Personal UV  

E-print Network

Chemistry and Physics Discussions Personal UV exposure on a ski-field at an alpine site A. M. Siani 1 , G. R) of two groups of volunteers (ski instructors and skiers) at the Alpine site of La Thuile (Valle d on the ski-fields are often significantly higher than those on horizontal surfaces. Given the high levels

Paris-Sud XI, Université de

275

UV Treatment for Small Systems  

EPA Science Inventory

The Center for Environmental Education, Conservation and Research (CECIA) at InterAmerican University of Puerto Rico (IAUPR) has organized the 10th CECIA-IAUPR Biennial Symposium on Potable Water Issues in Puerto Rico. This presentation on UV Treatment for Small Systems will be ...

276

Near UV Aerosol Group Report  

NASA Technical Reports Server (NTRS)

2012-13 Report of research on aerosol and cloud remote sensing using UV observations. The document was presented at the 2013 AEROCENTER Annual Meeting held at the GSFC Visitors Center, May 31, 2013. The Organizers of the meeting are posting the talks to the public Aerocentr website, after the meeting.

Torres, Omar

2013-01-01

277

Star Life  

NSDL National Science Digital Library

Visitors to this site can follow the life cycle of a star, beginning with its formation from matter exploded outward by the Big Bang, followed by its expansion into a red giant as nuclear "fuel" is consumed, and ending with its "death" in a supernova, after which it becomes a neutron star or black hole.

278

The GALEX Extended Mission: Surveying UV Tracers of the Hidden Side of Galaxy Evolution  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer (GALEX) continues its surveys of the ultraviolet sky. GALEX surveys have supported the following galaxy evolution investigations: calibrating UV as a star formation rate tracer, using wide and deep surveys to measure star formation history, studying the evolution of dust extinction and metallicity, selecting and analyzing galaxies in transitory states, finding local analogs to Lyman Break Galaxies, probing and time-dating star formation in a wide variety of physical regimes. Our continuing mission is focussed on relating star formation history and galaxy evolution paths to the properties of dark matter halos and their assembly history, and on beginning to relate the evolution of galaxies to that of black holes and the intergalactic medium. GALEX has proven that the UV is an ideal band to find and map star formation in low mass, low density objects, and potentially in primordial gas. With future UV missions it may be possible to map emission from the intergalactic and circum-galactic medium, and make a definitive connection between galaxy evolution and the cooling, accretion, heating, and enrichment of gas in the cosmic web.

Christopher Martin, D.

2010-06-01

279

Possible Sources of UV Radiation in Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

We have compiled a sample of 519 nearby (z < 0.13) elliptical galaxies, selected by matching the Galaxy Evolution Explorer (GALEX) Medium Imaging Survey (MIS) with the Sloan Digital Sky Survey (SDSS) Fourth Data Release (DR4). Our galaxies are bright, with r < 16.8 and have FUV (far ultraviolet) an NUV (near ultraviolet) emission. We build a UV Color Magnitude Relation (CMR) using GALEX and SDSS photometric bands, and analyze the evolution of this CMR for these galaxies using stellar population synthesis models. We find that these galaxies may have suffered a small amount of recent residual star formation (1-2% of the galaxy mass). Extreme Horizontal Branch (EHB) stars can explain galaxies with 4 < NUV-r < 5.4.

Hernández, F. C.; Bruzual, G.

2009-05-01

280

Star Formation and Cooling in CLASH Brightest Cluster Galaxies  

NASA Astrophysics Data System (ADS)

We present new constraints on star-formation in the brightest cluster galaxies (BCGs) of the 20 X-ray selected CLASH galaxy clusters. Using 16 HST passbands, we find evidence for significant UV and H? +[NII] emission in ˜ 50% of these intermediate redshift (˜ 0.2 - 0.6) BCGs. The emission appears to come from regions with morphologically irregular knots and filaments. The UV and H? fluxes are well correlated with one another. The extinction-corrected luminosities are consistent with the Kennicutt law for continuous star formation. For the largest emission structures we observe, we estimate that the SFRs are 100-200 Msun yr-1, under the assumption that the UV and H? emission is solely due to star formation. We hypothesize that the structures we observe are either direct features of a cooling mechanism in the cores of these clusters or are a direct consequence of the processes that regulate the cooling. Using data from the ACCEPT catalog of Chandra observations of these clusters, we find a correlation between the UV luminosity and several X-ray derived ICM properties. In particular, we find a possible scaling between either the UV or H?+[NII] luminosity and the 1 Gyr cooling radius. These UV and H? features are surprisingly prevalent in the CLASH sample and this new study provides us with new constraints on the physics of gas flows and star formation in cluster cores.

Fogarty, Kevin; Postman, Marc; Donahue, Megan; Moustakas, John

2014-06-01

281

Near-simultaneous ultraviolet and optical spectrophotometry of T Tauri stars  

NASA Technical Reports Server (NTRS)

A set of near-simultaneous ultraviolet and optical spectra and UBVR(J)I(J) photometry of five T Tauri stars has been analyzed for the shape of the energy distribution shortward of 3000 A. The far-ultraviolet continua of these stars are very much stronger than the level of light scattered from longer wavelengths in the IUE spectrograph. The results, expressed as two-color plots, show that the UV colors of T Tauri stars differ significantly from those expected from their optical spectral types. Although these particular K-type T Tauri stars are not extreme members of the class, they have the UV colors of A stars. The spectral shape of this UV excess is approximately that expected from published chromospheric models of T Tauri stars.

Goodrich, Robert W.; Herbig, G. H.

1986-01-01

282

Mapping the Dark Matter From UV Light at High Redshift: An Empirical Approach to Understand Galaxy Statistics  

SciTech Connect

We present a simple formalism to interpret the observations of two galaxy statistics, the UV luminosity function (LF) and two-point correlation functions for star-forming galaxies at z {approx} 4, 5 and 6 in the context of {Lambda}CDM cosmology. Both statistics are the result of how star formation takes place in dark matter halos, and thus are used to constrain how UV light depends on halo properties, in particular halo mass. The two physical quantities we explore are the star formation duty cycle, and the range of UV luminosity that a halo of mass M can have (mean and variance). The former directly addresses the typical duration of star formation activity in halos while the latter addresses the averaged star formation history and regularity of gas inflow into these systems. In the context of this formalism, we explore various physical models consistent with all the available observational data, and find the following: (1) the typical duration of star formation observed in the data is {approx}< 0.4 Gyr (1{sigma}), (2) the inferred scaling law between the observed L{sub UV} and halo mass M from the observed faint-end slope of the luminosity functions is roughly linear out to M {approx} 10{sup 11.5} - 10{sup 12} h{sup -1} M{sub {circle_dot}} at all redshifts probed in this work, and (3) the observed L{sub UV} for a fixed halo mass M decreases with time, implying that the star formation efficiency (after dust extinction) is higher at earlier times. We explore several different physical scenarios relating star formation to halo mass, but find that these scenarios are indistinguishable due to the limited range of halo mass probed by our data. In order to discriminate between different scenarios, we discuss the possibility of using the bright-faint galaxy cross-correlation functions and more robust determination of luminosity-dependent galaxy bias for future surveys.

Lee, Kyoung-Soo; /Yale Ctr. Astron. Astrophys.; Giavalisco, Mauro; /Massachusetts U., Amherst; Conroy, Charlie; /Princeton U. Observ.; Wechsler, Risa H; /KIPAC, Menlo Park; Ferguson, Henry C.; Somerville, Rachel S.; /Baltimore, Space Telescope Sci.; Dickinson, Mark E.; /NOAO, Tucson; Urry, Claudia M.; /Yale Ctr. Astron. Astrophys.

2009-08-03

283

UV-Luminosity Function to z 3 with the UKIDSS UDS Survey  

NASA Astrophysics Data System (ADS)

The star formation history is a key-element to understand galaxy evolution and formation. Recent studies have shown that the star-formation rate peaks at redshift z=1-3 and then decline to its local value. The physical processes responsible for the sudden quenching of star-formation are still unknown. In order to better understand the origin of these effects, we propose in this study to use the UV-luminosity as an indicator of the Star-formation rate. We take advantage of our deep NIR/optical data from the UKIDSS-UDS/SXDS survey and our very deep CFHT U-band data to compute the luminosity function of galaxies at z=1-3. Fitting the Schechter parameters to integrate luminosity density to explore the evolution of the Star-formation rate.

Lo, C.-M.; Foucaud, S.; Grützbauch, R.; Hartley, W.; Simpson, C.; Almaini, O.

2013-10-01

284

Tunable UV source for UV fluorescence remote sensing  

SciTech Connect

Efficient generation of ultraviolet radiation tunable over the 240--410 nm range has been achieved in a system suitable for ultraviolet (uv) fluorescence remote sensing. Light from an Optical Parametric Oscillator/Amplifier turning in the 0.7--2.1 {mu}m range is mixed with the second or third harmonic from a Nd:YAG laser, to obtain up to 30 mJ of broadly tunable output in the ultraviolet.

Mead, R.D.; Lowenthal, D.D. [Aculight Corp., Bellevue, WA (United States); Raymond, T.D.; Alford, W.J.; Smith, A.V.; Johnson, M.S. [Sandia National Labs., Albuquerque, NM (United States)

1994-08-01

285

UV Spectroscopy of Newly Discovered Tidal Disruption Flares  

NASA Astrophysics Data System (ADS)

When a star passes within the sphere of disruption of a massive black hole, tidal forces will overcome self-gravity and unbind the star. While approximately half of the stellar debris is ejected at high velocities, the remaining material remains bound to the black hole and accretes, resulting in a luminous, long-lived transient known as a tidal disruption flare (TDF). Aside from serving as a unique laboratory for accretion physics, TDFs offer the hope of measuring black hole masses in galaxies much too distant for resolved kinematic studies. In the simplest analytic models, the black hole mass should scale as dt^2, where dt is the time delay between the disruption and the start of the flare. Two primary factors have so far limited precise black hole mass estimates from current TDF searches: 1) The difficulty of distinguishing a bona fide TDF from the many other transients that can occur in galactic nuclei; 2) Determing the nature of the disrupted star from the observed electromagnetic signal (in particular the presence or absence of H in optical spectra). Here we request non-disruptive ToO spectra of two nearby TDF candidates in the UV with STIS. Our objectives are to search for unique "smoking gun" signatures of the tidal disruption process, and to constrain the geometry and composition of the newly formed accretion disk (and hence the disrupted star). Much like type Ia supernovae, these observations will furthermore serve as a cornerstone for future high-redshift TDF discoveries by LSST, where the rest-frame UV emission is redshifted into the optical bandpass.

Cenko, Stephen

2014-10-01

286

Physics of Electrodeless UV Lamps and Applications of UV Radiation  

NASA Astrophysics Data System (ADS)

Electrodeless discharge microwave powered ultraviolet limps are a special class of high power incoherent UV sources, conceptualized forty years ago for industrial processing applications. Because of the nonimaging character of the applications, the need for measuring averaged properties of the lamps' exceeds the motivation to obtain detailed space-resolved discharge parameters. This writing discusses measurements of the average plasma temperature of a 5.8kW high pressure mercury bulb and a XeCl* excimer bulb driven by the microwaves of the same power. First method is based on the black body radiance fit to the self-absorbed 185nm and 254nm mercury lines. The second method is essentially Boltzmann plot method applied to the roto-vibrational levels of B1/2 - X1/2 XeCl* molecular transition with a maximum at 308nm. We also present a procedure for evaluation of effectiveness of different bulb spectra to the given UV curing chemistry system independent from the Beer-Lambert law. Conversely, the procedure can be used for the optimization of the chemistry to the chosen UV lamp radiance spectrum.

Cekic, Miodrag; Ruckman, Mark

2004-12-01

287

PULSED UV: REALITIES OF ENHANCED DISINFECTION  

EPA Science Inventory

Quantitative measurements of the light output from low pressure (LP), medium pressure (MP) and the pulsed UV lamps were made using calibrated spectrometry, chemical actinometry and biodosimetry approaches to compare their relative efficiency in producing germicidal UV energy. Fur...

288

Exploding star  

NASA Astrophysics Data System (ADS)

Three astronomers report that the star Eta Carinae, 100 times more massive than the sun, is nearing its life expectancy and will explode sometime in the next 10,000 years. Until now, astronomers have been unable to discern whether the star was in the process of being born, was a middle-aged star with an unusual outflow of material, or an aged star about to explode.The huge star is coming to the end of what is considered a normal lifetime—about 2 million years—for a star of its size, according to Kris Davidson at the University of Minnesota, Nolan R. Walborn (presently at the Goddard Space Flight Center) of Cerro Tololo Inter-American Observatory, and Theodore R. Gull at Goddard. When Eta Carinae explodes, the astronomers report, it could emit more light than all the hundreds of billions of other stars in the galaxy for weeks. The expected explosion, or supernova, could produce a bright point of light that would be visible in broad daylight, they add.

289

Star-Forming or Starbursting? The Ultraviolet Conundrum  

NASA Astrophysics Data System (ADS)

Compared to starburst galaxies, normal star-forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-? diagram (the IR/UV ratio "IRX" versus the UV color "?"). To investigate the causes of this larger dispersion and attempt to isolate second parameters, we have used GALEX UV, ground-based optical, and Spitzer infrared imaging of eight nearby galaxies, and examined the properties of individual UV and 24 ?m selected star-forming regions. We concentrated on star-forming regions, in order to isolate simpler star formation histories than those that characterize whole galaxies. We find that (1) the dispersion is not correlated with the mean age of the stellar populations; (2) a range of dust geometries and dust extinction curves are the most likely causes for the observed dispersion in the IRX-? diagram, (3) together with some potential dilution of the most recent star-forming population by older unrelated bursts, at least in the case of star-forming regions within galaxies; and (4) we also recover some general characteristics of the regions, including a tight positive correlation between the amount of dust attenuation and the metal content. Although generalizing our results to whole galaxies may not be immediate, the possibility of a range of dust extinction laws and geometries should be accounted for in the latter systems as well.

Boquien, M.; Calzetti, D.; Kennicutt, R.; Dale, D.; Engelbracht, C.; Gordon, K. D.; Hong, S.; Lee, J. C.; Portouw, J.

2009-11-01

290

T Tauri stars observing campaign  

NASA Astrophysics Data System (ADS)

Darryl Sergison (University of Exeter) has requested AAVSO assistance with a campaign he is carrying out on five T Tauri stars. This study is the one for which AAVSO observers carried out a preliminary campaign last year (see Alert Notice 473 and Special Notice #306). The star list is revised and expanded from last year's list of targets. This campaign will run from now at least through the end of the 2013-2014 observing season. This is part of an on-going study into the nature of pre-main-sequence low mass stars, using time series optical spectroscopy and UV-Visual-IR photometry and offers a great opportunity for professional-amateur collaboration as the objects (with V magnitudes of 10-13) are well within the reach of photometry by small telescopes. Amateur observations are uniquely useful in the study of chaotically variable young stars as they offer crucial datapoints in the light curve between observations made by professional telescopes. Targets are BP Tau, DN Tau, V827 Tau, V1068 Tau, and V1264 Tau. Finder charts with sequences may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details and instructions.

Waagen, Elizabeth O.

2013-12-01

291

8, 119, 2008 UV doses during  

E-print Network

ACPD 8, 1­19, 2008 UV doses during psoriasis climate therapy at Gran Canaria L. T. N. Nilsen et al Chemistry and Physics Discussions Estimated UV doses to psoriasis patients during climate therapy at Gran Correspondence to: L. T. N. Nilsen (lill.tove.nilsen@nrpa.no) 1 #12;ACPD 8, 1­19, 2008 UV doses during psoriasis

Paris-Sud XI, Université de

292

UV disinfection system for cabin air  

Microsoft Academic Search

The air of indoor cabin environments is susceptible to contamination by airborne microbial pathogens. A number of air treatment processes are available for inactivation or removal of airborne pathogens; included among these processes is ultraviolet (UV) irradiation. The effectiveness of UV-based processes is known to be determined by the combined effects of UV dose delivery by the reactor and the

Soojung Lim; Ernest R. Blatchley III

2009-01-01

293

Instant colour photography: chemistry and UV stabilization  

Microsoft Academic Search

An ultraviolet (UV) screening agent precursor, dinonylphenylisophthalate, applied as a component of a surface coating on instant colour positive photographic prints stabilizes the dyes that are used and prevents the fading of colour that otherwise occurs. It is believed that upon exposure to UV light the ester precursor rearrangesin situ to form substituted benzophenones, which are effective UV screening agents.

A. M. Usmani; I. O. Salyer

1983-01-01

294

How the First Stars Regulated Local Star Formation I: Radiative Feedback  

E-print Network

We present numerical simulations of how a 120 M$_\\odot$ primordial star regulates star formation in nearby cosmological halos at $z \\sim$ 20 by photoevaporation. Our models include nine-species primordial chemistry and self-consistent multifrequency conservative transfer of UV photons with all relevant radiative processes. Whether or not new stars form in halos clustered around a Population III star ultimately depends on their core densities and proximity to the star. Diffuse halos with central densities below 2 - 3 cm$^{-3}$ are completely ionized and evaporated anywhere in the cluster. Evolved halos with core densities above 2000 cm$^{-3}$ are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse as quickly as they would in its absence. Star formation in halos of intermediate density can be either promoted or suppressed depending on how the I-front remnant shock compresses, deforms and enriches the core with H$_2$. We find that the 120 M$_\\odot$ star photodissociates H$_2$ in most halos in the cluster but that catalysis by H- restores it a few hundred kyr after the death of the star, with little effect on star formation. Our models exhibit significant departures from previous one-dimensional spherically-symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.

Daniel Whalen; Brian W. O'Shea; Joseph Smidt; Michael L. Norman

2007-08-12

295

IUE observations of symbiotic stars  

NASA Technical Reports Server (NTRS)

The main photometric and spectroscopic characteristics in the ultraviolet and visual range of the most extensively studied symbiotic stars are reviewed. The main data obtained with IUE concern: (1) the determination of the shape of the UV continuum, which, in some cases, proves without doubt the presence of a hot companion; and the determination of the interstellar extinction by means of the lambda 2200 feature; (2) the measurement of emission lines, which enables us to derive the electron temperature and density of the circumstellar envelope, and, taken together with those lines observed in the visual, give more complete information on which spectroscopic mechanisms operate in the envelope; (3) the observation of absorption lines in the UV, which are present in just a few cases.

Hack, M.

1982-01-01

296

Measuring Boron Abundances in Rapidly Rotating Early-B Stars  

NASA Astrophysics Data System (ADS)

We discuss the modeling techniques we have developed to measure boron abundances using crowded, badly blended, and modest resolution UV spectra of rapidly rotating early-B stars. Hi-resolution echelle spectra of narrow-lined stars are first used as templates for improving the atomic data and spectral synthesis. This allows the same fitting techniques to then be used for the more blended spectra. We also present our results for boron abundances for a large sample of early-B stars and discuss implications for models of mixing in the envelopes of rapidly rotating stars.

Proffitt, Charles R.

2015-01-01

297

Far-UV variability of 0 CR B in 1985-86 - A progression toward higher velocities  

NASA Astrophysics Data System (ADS)

New far UV observations of ? CrB obtained with the IUE in 1985 - 1986 are presented. They show that the far UV spectrum of that star has usually continued to exhibit the apparently low excitation state observed from mid-84 to mid-85. However, the C IV resonance lines are occasionally conspicuous and exhibit an even higher outflow velocity than during the preceding epochs of variation, when the C IV resonance lines were strong and frequently present. Such a long term progression toward higher expansion velocities has not yet been observed in any other Be star.

Doazan, V.; Rusconi, L.; Sedmak, G.; Thomas, R. N.

1987-02-01

298

Classifying stars  

NSDL National Science Digital Library

You will be able to describe the H-R diagram and explain how astronomers use it. The most important characteristics for classifying stars are: a) Color b) Temperature c) Size d) Composition e) Brightness The classification scheme that we currently use is the H-R diagram which is in the Earth Science Reference Tables (ESRT). The H-R diagram groups stars by surface temperature compared to their luminosity. 1)Today you will be reading a short tutorial ...

B, Mr.

2007-11-10

299

Tycho's Star  

NASA Astrophysics Data System (ADS)

A supernova remnant in Cassiopeia, 7.7° north of ? Cas, which suddenly appeared as a brilliant naked-eye star in November 1572 and reached a maximum apparent magnitude of -3.5. Until its disappearance 16 months later, it was extensively studied by the Danish astronomer Tycho Brahe (1546-1601), who described its early appearance as follows: `Initially, the new star was brighter than any other fixe...

Murdin, P.

2000-11-01

300

The Galaxy Evolution Explorer (GALEX): A New View of the UV Universe  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer (GALEX) has surveyed the ultraviolet sky for almost nine years. GALEX surveys have supported numerous galaxy evolution investigations: calibrating UV as a star formation rate tracer, using wide and deep surveys to measure star formation history, studying the evolution of dust extinction and metallicity, selecting and analyzing galaxies in transitory states, finding local analogs to Lyman Break Galaxies, probing and time-dating star formation in a wide variety of physical regimes, and probing star formation properties in low mass, low density settings. Archival data will support more complex investigations such as relating star formation history and galaxy evolution paths to the properties of dark matter halos and their assembly history, and beginning to relate the evolution of galaxies to that of black holes and the intergalactic medium. Over and above GALEX's study of galaxy evolution the surveys have: found all UV bright QSOs at low and high redshift, discovering tidal capture flares from inactive black holes, discovering shock breakout flashes from distant supernovae, selecting a sample of galaxies for Baryon Acoustic Oscillation surveys, and in our own Milky Way, discovering and diagnosing spectacular new stellar wind nebulae from aging, mass- losing stars.

Wyder, Ted; Martin, Christopher

2012-07-01

301

UV blocking filters for polymeric films  

NASA Technical Reports Server (NTRS)

The concept of incorporating UV screening agents in silicone resins as a means of protecting underlying solar cell covers and adhesives from UV degradation is presented. A silicone hard-coat resin incorporating a UV screening agent was selected as a suitable coating material for PFA Teflon solar cell covers. Consideration is given to fabrication procedures and techniques for introduction of the UV screening agents into silicone resins and application of these UV-inhibited coatings to the Teflons. Some preliminary environmental tests, such as thermal shock and temperature humidity, were conducted.

Rayl, G. J.

1979-01-01

302

STARS no star on Kauai  

SciTech Connect

The island of Kuai, home to the Pacific Missile Range Facility, is preparing for the first of a series of Star Wars rocket launches expected to begin early this year. The Strategic Defense Initiative plans 40 launches of the Stategic Target System (STARS) over a 10-year period. The focus of the tests appears to be weapons and sensors designed to combat multiple-warhead ICBMs, which will be banned under the START II Treaty that was signed in January. The focus of this article is to express the dubious value of testing the STARS at a time when their application will not be an anticipated problem.

Jones, M.

1993-04-01

303

IR/UV and UV/UV double-resonance study of guaiacol and eugenol dimers  

NASA Astrophysics Data System (ADS)

Guaiacol (2-methoxyphenol) and eugenol (4-allyl-2-methoxyphenol) molecules are biologically active phenol derivatives with an intramolecular -OH⋯OCH3 hydrogen bond (H bond). Pulsed supersonic expansions of mixtures of either of the two molecules with He yield weakly bound homodimers as well as other higher-order complexes. A number of complementary and powerful laser spectroscopic techniques, including UV-UV and IR-UV double resonances, have been employed to interrogate the species formed in the expansion in order to get information on their structures and spectroscopic properties. The interpretation of the spectra of eugenol dimer is complex and required a previous investigation on a similar but simpler molecule both to gain insight into the possible structures and support the conclusions. Guaiacol (2-methoxyphenol) has been used for that purpose. The combination of the broad laser study combined with ab initio calculations at the Becke 3 Lee-Yang-Parr/6-31+G(d) level has provided the isomer structures, the potential-energy wells, and shed light on the inter- and intramolecular interactions involved. Guaiacol homodimer has been shown to have a single isomer whereas eugenol dimer has at least two. The comparison between the computed geometries of the dimers, their respective energies, and the vibrational normal modes permits the identification of the spectra.

Longarte, Asier; Redondo, Carolina; Fernández, José A.; Castaño, Fernando

2005-04-01

304

The Physical Nature of Rest-UV Galaxy Morphology During the Peak Epoch of Galaxy Formation  

E-print Network

Motivated by the irregular and little-understood morphologies of z ~ 2 - 3 galaxies, we use non-parametric coefficents to quantify the morphologies of 216 galaxies which have been spectroscopically confirmed to lie at redshifts z = 1.8 - 3.4 in the GOODS-N field. Using measurements of ultraviolet (UV) and optical spectral lines, multi-band photometric data, and stellar population models we statistically assess possible correlations between galaxy morphology and physical observables such as stellar mass, star formation rate, and the strength of galaxy-scale outflows. We find evidence that dustier galaxies have more nebulous UV morphologies and that larger, more luminous galaxies may drive stronger outflows, but otherwise conclude that UV morphology is either statistically decoupled from the majority of physical observables or determined by too complex a combination of physical processes to provide characterizations with predictive power. Given the absence of strong correlations between UV morphology and physical parameters such as star formation rates, we are therefore unable to support the hypothesis that morphologically irregular galaxies predominantly represent major galaxy mergers. Comparing galaxy samples, we find that IR-selected BzK galaxies and radio-selected submillimeter galaxies (SMGs) have UV morphologies similar to the optically selected sample, while distant red galaxies (DRGs) are more nebulous.

David R. Law; Charles C. Steidel; Dawn K. Erb; Max Pettini; Naveen A. Reddy; Alice E. Shapley; Kurt L. Adelberger; David J. Simenc

2006-10-24

305

High Power UV LED Industrial Curing Systems  

SciTech Connect

UV curing is a green technology that is largely underutilized because UV radiation sources like Hg Lamps are unreliable and difficult to use. High Power UV LEDs are now efficient enough to replace Hg Lamps, and offer significantly improved performance relative to Hg Lamps. In this study, a modular, scalable high power UV LED curing system was designed and tested, performing well in industrial coating evaluations. In order to achieve mechanical form factors similar to commercial Hg Lamp systems, a new patent pending design was employed enabling high irradiance at long working distances. While high power UV LEDs are currently only available at longer UVA wavelengths, rapid progress on UVC LEDs and the development of new formulations designed specifically for use with UV LED sources will converge to drive more rapid adoption of UV curing technology. An assessment of the environmental impact of replacing Hg Lamp systems with UV LED systems was performed. Since UV curing is used in only a small portion of the industrial printing, painting and coating markets, the ease of use of UV LED systems should increase the use of UV curing technology. Even a small penetration of the significant number of industrial applications still using oven curing and drying will lead to significant reductions in energy consumption and reductions in the emission of green house gases and solvent emissions.

Karlicek, Robert, F., Jr; Sargent, Robert

2012-05-14

306

UV-B radiation at Penang  

NASA Astrophysics Data System (ADS)

A new series of measurements including global and UV radiation was initiated in 1994 at Penang. These high quality data were used to study diurnal and seasonal variations. The mean daily total UV-B and global radiation is about 1.43×10 4 J and 1.77×10 7 J, respectively. Maximum radiation values for both the UV-B and global radiation are received in March and September. The daily total global radiation shows a bigger seasonal variation than UV-B radiation. On clear days, the erythemal UV radiation flux is in the high or extreme range for about 5 h beginning at around 1030 hours throughout the year. Penang (5.3°N) and Natal (6°S) are found to exhibit similar daily maximum erythemal UV irradiance values. A simple empirical relationship for the noontime UV-B flux and global irradiance in the equatorial/tropical regions has been established.

Ilyas, Mohammad; Pandy, Arunasala; Hassan, Syed Idris Syed

307

Electron stars for holographic metallic criticality  

E-print Network

We refer to the ground state of a gravitating, charged ideal fluid of fermions held at a finite chemical potential as an `electron star'. In a holographic setting, electron stars are candidate gravity duals for strongly interacting finite fermion density systems. We show how electron stars develop an emergent Lifshitz scaling at low energies. This IR scaling region is a consequence of the two way interaction between emergent quantum critical bosonic modes and the finite density of fermions. By integrating from the IR region to an asymptotically AdS_4 spacetime, we compute basic properties of the electron stars, including their electrical conductivity. We emphasize the challenge of connecting UV and IR physics in strongly interacting finite density systems.

Sean A. Hartnoll; Alireza Tavanfar

2011-01-06

308

THE EFFECTIVE TEMPERATURES OF HOT STARS. II. THE EARLY-O TYPES1 Miriam Garcia2  

E-print Network

Center for Astrophysical Sciences, Department of Physics and Astronomy, The Johns Hopkins University early-O type stars by analyzing their UV and far-UV spectra from the Far Ultraviolet Spectroscopic Explorer (905­1187 8), the International Ultraviolet Explorer, the Hubble Space Telescope STIS

Bianchi, Luciana

309

Massive star forming regions from the local Universe to high redshift \\Lambda  

E-print Network

). Due to their intense EUV--UV radiation field massive stars ionise the surrounding interstellar medium to the UV ionising background radiation and are possibly also the source of cosmological re­ionisation (ISM) creating thus H ii regions and the diffuse ISM in galaxies, they contribute non negligibly

Schaerer, Daniel

310

UV radiation as biologic limit in the origin and development of life in extrasolar planets  

NASA Astrophysics Data System (ADS)

In this work, we displayed a new biological criterion that restricts the traditional habitable zone. We set the internal boundary of this new UV habitable zone from the maximum radiation that tolerates the DNA and its external boundary from the levels of UV radiation needed in the biogenesis processes. We also analyzed the evolution of the habitable zones according to the variation of the stellar luminosity throughout the main sequence stage. We evaluated these criteria in those planetary stars that were observed by IUE satellite. FULL TEXT IN SPANISH

Buccino, A. P.; Mauas, P. J. D.; Lemarchand, G. A.

311

Small observatories for the UV  

NASA Astrophysics Data System (ADS)

We describe concepts for small space telescopes that are able to provide significant UV science and can be realized with small (but realistic) budgets. The concepts are based on nano-satellites carrying small optics, with no redundancy, without producing intermediate models prior to flight model, and using COTS (custom off-the-shelf) components. We describe a few concepts of deployable optics that could provide large collecting areas and high angular resolution while packaged in the small volume of a nano-satellite. We point out areas where technological development is still required.

Brosch, Noah; Balabanov, Vladimir; Behar, Ehud

2014-11-01

312

Transdermal Penetration of UV Filters  

Microsoft Academic Search

A penetration study of 2-ethylhexyl-4-methoxycinnamate (EHMC), 4-methyl benzylidenecamphor (MBC), butyl methoxydibenzoylmethane (BMBM), 2-ethylhexyl-2,4,5-trimethoxycinnamate (EHTMC) and di(2-ethylhexyl)-2,4,5-trimethoxybenzalmalonate (TMB) through baby mouse skin (Mus musculus Linn.) was carried out using a vertical Franz diffusion cell. At 4.4 mg\\/cm2 coverage of UV filter on the skin, 2.98 ± 0.38, 1.15 ± 0.14 and 0.80 ± 0.28% of the applied EHMC, MBC and BMBM

P. Klinubol; P. Asawanonda; S. P. Wanichwecharungruang

2008-01-01

313

Of-type stars HD 16691 and HD 190429 show WN-like spectra in infrared K band  

NASA Technical Reports Server (NTRS)

We present 2 micrometer K-band spectra of two early-type Of stars that have infrared emission-line morphology similar to that of WN stars. Archival International Ultraviolet Explorer (IUE) spectra of these two stars indicate they appear to be Of type, rather than WN. Recently acquired optical spectra of these stars are quantitatively similar to that in the past, namely, Of attributes. We suggest that these two Of stars have stellar wind characteristics closer to WN type than other Of stars. We discuss the consequences for K-band classification of highly obscured hot stars that might not otherwise be visible in optical or UV wavelengths.

Conti, Peter S.; Hanson, Margaret Murray; Morris, Patrick W.

1995-01-01

314

Coronal Structures in Cool Stars  

NASA Technical Reports Server (NTRS)

We have extended our study of the structure of coronas in cool stars to very young stars still accreting from their surrounding disks. In addition we are pursing the connection between coronal X-rays and a powerful diagnostic line in the infrared, the He I 10830Angstrom transition of helium. Highlights of these are summarized below including publications during this reporting period and presentations. Spectroscopy of the infrared He I (lambda10830) line with KECK/NIRSPEC and IRTF/CSHELL and of the ultraviolet C III (lambda977) and O VI (lambda1032) emission with FUSE reveals that the classical T Tauri star TW Hydrae exhibits P Cygni profiles, line asymmetries, and absorption indicative of a continuous, fast (approximately 400 kilometers per second), hot (approximately 300,000 K) accelerating outflow with a mass loss rate approximately 10(exp -11)-10(exp -12) solar mass yr(sup -1) or larger. Spectra of T Tauri N appear consistent with such a wind. The source of the emission and outflow seems restricted to the stars themselves. Although the mass accretion rate is an order of magnitude less for TW Hya than for T Tau, the outflow reaches higher velocities at chromospheric temperatures in TW Hya. Winds from young stellar objects may be substantially hotter and faster than previously thought. The ultraviolet emission lines, when corrected for absorption are broad. Emission associated with the accretion flow and shock is likely to show turbulent broadening. We note that the UV line widths are significantly larger than the X-ray line widths. If the X-rays from TW Hya are generated at the accretion shock, the UV lines may not be directly associated with the shock. On the other hand, studies of X-ray emission in young star clusters, suggest that the strength of the X-ray emission is correlated with stellar rotation, thus casting doubt on an accretion origin for the X-rays. We are beginning to access the infrared spectral region where the He I 108308Angstroms transition occurs. This line is particularly useful as a diagnostic of coronal radiation since it is formed by recombination following photoionization of neutral helium by coronal X-rays. Because the lower level of the transition is metastable, infrared radiation from the stellar photosphere is absorbed which provides a diagnostic of atmospheric dynamics. This transition is useful both in young stars in the T Tauri phase and in active cool star binaries. We will investigate the influence of coronal x-rays on the strength of this transition.

Oliversen, Ronald (Technical Monitor); Dupree, Andrea K.

2005-01-01

315

X-shooter Science Verification Proposal A special co-moving white dwarfmain sequence pair  

E-print Network

: The white dwarf (WD) WD 1401-147 and the main sequence (MS) star HD 122750 form a co-moving proper motion) white dwarfs, the so-called ZZ Ceti stars. On the other hand, the only information available on the MS, but it is also a ZZ Ceti variable. ZZ Ceti stars are non-radially pulsating (g-mode) hydrogen (DA) white dwarfs

Liske, Jochen

316

Transdermal penetration of UV filters.  

PubMed

A penetration study of 2-ethylhexyl-4-methoxycinnamate (EHMC), 4-methyl benzylidenecamphor (MBC), butyl methoxydibenzoylmethane (BMBM), 2-ethylhexyl-2,4,5-trimethoxycinnamate (EHTMC) and di(2-ethylhexyl)-2,4,5-trimethoxybenzalmalonate (TMB) through baby mouse skin (Mus musculus Linn.) was carried out using a vertical Franz diffusion cell. At 4.4 mg/cm(2) coverage of UV filter on the skin, 2.98 +/- 0.38, 1.15 +/- 0.14 and 0.80 +/- 0.28% of the applied EHMC, MBC and BMBM were detected in the receptor fluid at 24 h after application. Penetrations of UV filter in an ethanolic solution and lotion forms were comparable. EHTMC and TMB showed insignificant penetration across the baby mouse skins. Baby mouse skins kept at 4, -20 and -80 degrees C gave similar EHMC penetration results. Penetrations of EHMC, BMBM, EHTMC and TMB across human epidermis were carried out upon 5 volunteers using the suction blister technique. The results also confirmed the significant penetrations of EHMC and BMBM and the insignificant penetrations of EHTMC and TMB. PMID:17912021

Klinubol, P; Asawanonda, P; Wanichwecharungruang, S P

2008-01-01

317

Tomographic separation of composite spectra. The components of Plaskett's Star  

NASA Technical Reports Server (NTRS)

The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correlation analysis, which showed that the secondary produces significant lines in the UV, indicates that the mass ratio is q = 1.18 + or - 0.12 (secondary slightly more massive). A tomography algorithm was used to produce the separate spectra of the two stars in six spectral regions. The interpolated spectral classifications of the primary and secondary, 07.3 I and 06.2 I, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. The intensity ratio of the stars in the UV is 0.53 + or - 0.05 (primary brighter). The secondary lines appear rotationally broadened, and the projected rotational velocity V sin i for this star is estimated to be 310 + or - 20 km/s. The possible evolutionary history of this system is discussed through a comparison of the positions of the components and evolutionary tracks in the H-R diagram.

Bagnuolo, William G., Jr.; Gies, Douglas R.; Wiggs, Michael S.

1991-01-01

318

Fe I lines in late type stellar UV spectra.  

NASA Astrophysics Data System (ADS)

It has been suggested that Fe I lines may constitute a major part of the many absorption lines observed in the (near-UV) solar spectrum and in those of late type stars. We use the table of Fe I lines recently measured in the laboratory by Nave et al. (1994) and examine the solar spectrum between 2756-2831A observed by us previously with the highest spectral resolution to date, R=1.75x10^5^. We exploit this existing observation since only such high spectral resolution allows sufficient isolation of weak lines in an underlying haze of absorption features. In this solar spectrum we detect ~90% of the tabulated Fe I lines. Investigations of this kind are relevant, for instance, to primordial abundances of beryllium and boron in late type metal poor halo stars requiring complete model atmosphere line opacities and discrimination of possible line blending. We illustrate the case of Be with the spectrum of the late type star HD 165908 observed with R=~5x10^4^.

Greve, A.; McKeith, C. D.

1995-10-01

319

T Tauri stars observing campaign  

NASA Astrophysics Data System (ADS)

Darryl Sergison (U. Exeter) requested AAVSO assistance with a campaign he is organizing on six T Tauri stars (RY Tau, DN Tau, DR Tau, and three to be announced). In September/October 2013 he and his Ph.D. supervisor Tim Naylor (U. Exeter) are undertaking a study into the nature of pre-main-sequence low mass stars, using time series optical spectroscopy and UV-Visual-IR photometry to build a clearer picture of the environment around young solar-type stars and characterize their various disc, accretion, and outflow structures. To begin building light curves in advance of the official study, visual observations and BVRcIc CCD photometry are requested from now through the 2013-2014 observing season at least. They are hoping to investigate periodicity for a range of phenomena on timescales of months to hours, so visual estimates ranging from monthly to twice in a night are requested. For photometry, low cadence is useful, higher cadence (hourly or long time series) is better! Spectroscopy is also requested, particularly around H-alpha (6563Å) if the resolution is greater than a few thousand. Finder charts with sequences may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp). Observations should be submitted to the AAVSO International Database. See full Alert Notice for more details.

Waagen, Elizabeth O.

2012-11-01

320

Energy Star  

E-print Network

ENERGY STAR ENERGY TARGETS ESL-KT-12-10-08 CATEE 2012: Clean Air Through Energy Efficiency Conference, Galveston, TX, October 9-11, 2012 POP QUIZ!!!! What is EUI?? Energy Use Intensity Do you know the EUI and any of the buildings you designed... Efficiency Conference, Galveston, TX, October 9-11, 2012 The CFLs in an ENERGY STAR qualified light fixture only need to be changed once every 8 years on average, compared with an annual ladder-climb for incandescent light bulbs. 6 CONSIDERING TIME...

Reihl, K.; Tullos, A.

2012-01-01

321

UV filters for lighting of plants  

NASA Technical Reports Server (NTRS)

The wavelength dependent interaction of biological systems with radiation is commonly described by appropriate action spectra. Particularly effective plant responses are obtained for ultraviolet (UV) radiation. Excess shortwave UV-B radiation will induce genetic defects and plant damage. Besides the ecological discussion of the deleterious effects of the excess UV radiation there is increasing interest in horticultural applications of this spectral region. Several metabolic pathways leading to valuable secondary plant products like colors, odors, taste, or resulting in mechanical strength and vitality are triggered by UV radiation. Thus, in ecologically as well as in economically oriented experiments the exact generation and knowledge of the spectral irradiance, particularly near the UV absorption edge, is essential. The ideal filter 'material' to control the UV absorption edge would be ozone itself. However, due to problems in controlling the toxic and chemically aggressive, instable gas, only rather 'small ozone filters' have been realized so far. In artificial plant lighting conventional solid filter materials such as glass sheets and plastic foils (celluloseacetate or cellulosetriacetate) which can be easily handled have been used to absorb the UV-C and the excess shortwave UV-B radiation of the lamp emissions. Different filter glasses are available which provide absorption properties suitable for gradual changes of the spectral UV-B illumination of artificial lighting. Using a distinct set of lamps and filter glasses an acceptable simulation of the UV-B part of natural global radiation can be achieved. The aging of these and other filter materials under the extreme UV radiation in the lamphouse of a solar simulator is presently unavoidable. This instability can be dealt with only by a precise spectral monitoring and by replacing the filters accordingly. For this reason attempts would be useful to develop real ozone filters which can replace glass filters. In any case chamber experiments require a careful selection of the filter material used and must be accompanied by a continuous UV-B monitoring.

Doehring, T.; Koefferlein, M.; Thiel, S.; Seidlitz, H. K.; Payer, H. D.

1994-01-01

322

UV-Induced Cell Death in Plants  

PubMed Central

Plants are photosynthetic organisms that depend on sunlight for energy. Plants respond to light through different photoreceptors and show photomorphogenic development. Apart from Photosynthetically Active Radiation (PAR; 400–700 nm), plants are exposed to UV light, which is comprised of UV-C (below 280 nm), UV-B (280–320 nm) and UV-A (320–390 nm). The atmospheric ozone layer protects UV-C radiation from reaching earth while the UVR8 protein acts as a receptor for UV-B radiation. Low levels of UV-B exposure initiate signaling through UVR8 and induce secondary metabolite genes involved in protection against UV while higher dosages are very detrimental to plants. It has also been reported that genes involved in MAPK cascade help the plant in providing tolerance against UV radiation. The important targets of UV radiation in plant cells are DNA, lipids and proteins and also vital processes such as photosynthesis. Recent studies showed that, in response to UV radiation, mitochondria and chloroplasts produce a reactive oxygen species (ROS). Arabidopsis metacaspase-8 (AtMC8) is induced in response to oxidative stress caused by ROS, which acts downstream of the radical induced cell death (AtRCD1) gene making plants vulnerable to cell death. The studies on salicylic and jasmonic acid signaling mutants revealed that SA and JA regulate the ROS level and antagonize ROS mediated cell death. Recently, molecular studies have revealed genes involved in response to UV exposure, with respect to programmed cell death (PCD). PMID:23344059

Nawkar, Ganesh M.; Maibam, Punyakishore; Park, Jung Hoon; Sahi, Vaidurya Pratap; Lee, Sang Yeol; Kang, Chang Ho

2013-01-01

323

Modelling the variability of the CP star \\varphi Dra  

NASA Astrophysics Data System (ADS)

\\varphi Draconis is one of the brightest known CP stars. We model its light variability using the horizontal distribution of chemical elements in the stellar atmosphere derived from abundance maps. Those elements cause redistribution of the energy from the short-wavelength part of the UV spectrum to longer wavelengths. We compute a grid of LTE model atmospheres, and synthesize a theoretical light curve. The results obtained from our computations are in a very good agreement with the observed variability of the star.

Prvák, M.; Krti?ka, J.; Mikulášek, Z.; Lüftinger, T.; Liška, J.

2014-11-01

324

Very Massive Stars in the Primitive Galaxy, IZw 18  

NASA Technical Reports Server (NTRS)

IZw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass greater than 10(exp 9) Msun, strong photoionizing radiation, no galactic outflow, and very low metallicity,log(O/H)+12=7.2. We will describe the properties and evolutionary status of very massive stars in IZw 18, based on UV photometry of individual stars in I Zw 18 and analysis of unresolved ultraviolet spectra of IZw 18-NW obtained with HST.

Heap, Sara

2012-01-01

325

New technologies for UV detectors  

NASA Technical Reports Server (NTRS)

Several technologies are currently being developed, leading to substantial improvements in the performance of UV detectors or significant reductions in power or weight. Four technologies discussed are (1) thin-film coatings to enhance the UV sensitivity of CCD's, (2) highly innovative magnet assemblies that dramatically reduce weight and result in virtually no external flux, (3) new techniques for curving microchannel plates (MCP's) so that single plates can be used to prevent ion feedback and present highly localized charge clouds to an anode structure, and (4) high-performance alternatives to glass-based MCP's. In item (2), for example, very robust magnets are made out of rare earth materials such as samarium cobalt, and cladding magnets are employed to prevent flux from escaping from the detector into the external environment. These new ultralight magnet assemblies are able to create strong, exceptionally uniform magnetic fields for image intensification and focusing of photoelectrons. The principle advantage of such detectors is the quantum efficiencies of 70-80 percent obtained throughout ultraviolet wavelengths (900-2000 A), the highest of any device. Despite the improvements achieved under item (3), high-performance alternatives to conventional glass-based MCP's potentially offer three distinct new advantages that include (1) a 30-100-fold improvement in dynamic range resulting in correspondingly higher signal-to-noise ratios, (2) the use of pure dielectric and semiconductor materials that will not outgas contaminants that eventually destroy photocathodes, and (3) channels that have constant spacing providing long-ranged order since the plates are made using photolithography techniques from the semiconductor industry. The manufacturers of these advanced-technology MCP's, however, are a couple of years away from actually producing a functioning image intensifier. In contrast to the use of CCD's for optical, ground based observations, there is no single detector technology in the ultraviolet that dominates or is as universally suitable for all applications. Thus, several technological problems, recent advances, and the impact that these new enabling technologies represent for UV applications are addressed.

Joseph, C. L.

1993-01-01

326

Blue and UV Semiconductor Lasers  

NASA Astrophysics Data System (ADS)

Despite many technological difficulties the group III nitrides: GaN, AlN and InN and their alloys are primary candidates for electro-optical coherent light sources. In the recent years the research and technology of the nitride based continuous wave (CW) laser diodes (LDs) led to creation of blue-violet coherent light sources of power up to 200 mW. The progress has been attained by using various ways to attack the main obstacles in the technology of these devices such as insufficient size of high quality lattice matched substrates, low p-doping efficiency of Mg acceptor, poor contact to p-type semiconductor and low efficiency of radiative recombination. The two different approaches were used to overcome the substrate problem: hetero-epitaxy and homoepitaxy. Homoepitaxy used high pressure GaN high quality crystals. Heteroepitaxy used sapphire, SiC or GaAs substrates and very sophisticated techniques of reduction of the dislocation density. The low p-doping efficiency by using Mg acceptor is related to creation of Mg--H complexes due to hydrogen presence during the growth of laser diode quantum structures. In addition, Mg acceptor has low efficiency due to its high energy. High Mg concentrations can be obtained by using either MOCVD or ammonia source MBE growth. An alternative route is to use hydrogen-free plasma activated MBE (PA-MBE) method. The recent advances and the prospects of both approaches will be discussed. Solid AlGaInN solution offers a possibility to cover wide spectral range, starting from near UV to blue, green and red. Arsenide based laser diodes (LDs) are efficient coherent red light sources. Therefore, nitride based LDs are considered to be devices of choice for green, blue and UV spectral range. So far only blue and violet laser has been realized. The progress toward green and UV lasers is far less spectacular. The results in all these areas and future prospects will be discussed.

Krukowski, S.; Skierbiszewski, C.; Perlin, P.; Leszczynski, M.; Bockowski, M.; Porowski, S.

2006-04-01

327

Rocket instrument for far-UV spectrophotometry of faint astronomical objects.  

PubMed

A sensitive sounding rocket instrument for moderate (~10-A) resolution far-UV (lambda1160-lambda1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employs a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed. PMID:20220923

Hartig, G F; Fastie, W G; Davidsen, A F

1980-03-01

328

The Slow Death (or Rebirth?) of Extended Star Formation in z~0.1 Green Valley Early-Type Galaxies  

E-print Network

UV observations in the local universe have uncovered a population of early-type galaxies with UV flux consistent with low-level recent or ongoing star formation. We present resolved UV-optical photometry of a sample of 19 SDSS early-type galaxies at z~0.1 drawn from the sample originally selected by Salim & Rich (2010) to lie in the bluer part of the green valley in the UV-optical color-magnitude diagram as measured by GALEX. Utilizing high-resolution HST far-UV imaging provides unique insight into the distribution of UV light in these galaxies, which we call "extended star-forming early-type galaxies" (ESF-ETGs) because of extended UV emission that is indicative of recent star formation. The UV-optical color profiles of all ESF-ETGs show red centers and blue outer parts. Their outer colors require the existence of a significant underlying population of older stars in the UV-bright regions. Analysis of stacked SDSS spectra reveals weak LINER-like emission in their centers. Using a cross-matched SDSS DR7/G...

Fang, Jerome J; Salim, Samir; Graves, Genevieve J; Rich, R Michael

2012-01-01

329

Star Power  

ScienceCinema

The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

None

2014-11-18

330

Star Power  

NSDL National Science Digital Library

In this activity, learners create a star show and discover how they can prevent light pollution. Using simple materials, learners first design constellation boxes. Next, learners use their constellation boxes and desk lamps to explore how city lights impact the visibility of constellations. Finally, learners design shields to reduce light pollution and increase the visibility of constellations.

Twin Cities Public Television

2010-01-01

331

Brittle Star  

USGS Multimedia Gallery

A tiny brittle star (the central disc is smaller than a dime) clings to the branches of a soft coral in a sample bucket brought into the shipboard laboratory from a submersible dive. This creature makes its home on the deep, dark ocean floor. ...

332

Star Power  

SciTech Connect

The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

None

2014-10-17

333

STAR Highlights  

E-print Network

We report selected results from STAR collaboration at RHIC, focusing on jet-hadron and jet-like correlations, quarkonium suppression and collectivity, di-electron spectrum in both p+p and Au+Au, and higher moments of net-protons as well as azimuthal anisotropy from RHIC Beam Energy Scan program.

Hiroshi Masui; for the STAR Collaboration

2011-06-29

334

X-rays from accretion shocks in T Tauri stars: The case of BP Tau  

NASA Astrophysics Data System (ADS)

We present an XMM-Newton observation of the classical T Tauri star BP Tau. In the XMM-Newton RGS spectrum the O vii triplet is clearly detected with a very weak forbidden line indicating high plasma densities and/or a high UV flux environment. At the same time concurrent UV data point to a small hot spot filling factor suggesting an accretion funnel shock as the site of the X-ray and UV emission. Together with the X-ray data on TW Hya these new observations suggest such funnels to be a general feature in classical T Tauri stars.

Schmitt, J. H. M. M.; Robrade, J.; Ness, J.-U.; Favata, F.; Stelzer, B.

2005-03-01

335

Empirical wind models from detailed UV-line FITS - Tau Scorpii  

NASA Astrophysics Data System (ADS)

Lamers and Rogerson (1978) have conducted a study of the main-sequence BO star Tau Sco. However, the line formation was calculated according to the Sobolev approximation method, and the line fit was, therefore, restricted to the blue wings of the UV resonance lines. The present investigation of this star is based on an employment of the comoving-frame (CMF) method, which was extended to the treatment of overlapping doublets. It has been shown by Hamann (1980) that the results of the CMF method may differ considerably from those of the Sobolev procedure. It is found in the current investigation that the observed UV resonance lines of Tau Sco are well reproduced by theoretical profiles. The CMF calculations allow for a fit of the entire profile range and a correct treatment of the doublets. An empirical model which distinguishes three zones is derived. The line fits firmly establish a large microturbulence of 100 km/s in zones I and II.

Hamann, W.-R.

336

UV and optical spectrum variability of T Tau and RY Tau  

NASA Astrophysics Data System (ADS)

In this report we have presented results of spectral observations of classical T Tauri type stars T Tau and RY Tau. Observational dates were obtained from following sources: spectrograms of the UV range from the IUE archive data, and spectrograms of the visual range obtained in the 2 m telescope of ShAO of the NAS of Azerbaijan (Ismailov et al. 2010). For both of stars on the Scargle method we have searched a periodicity of variations in equivalent widths of emission lines in the optical and UV ranges. In the RY Tau firstly was detected the periodic variability in MgII ?2800 Å emission doublet intensities with a period of 23 days. The observed period had also revealed with the equivalent widths and displacements of components of H? and H+H? and K CaII emission.

Ismailov, N. Z.; Quliyev, N. Kh.; Khalilov, O. V.; Adigezalzade, H. N.

2013-03-01

337

How Does Abundance Affect the Strength of UV Emission in Elliptical Galaxies?  

NASA Technical Reports Server (NTRS)

This program used the Far Ultraviolet Spectroscopic Explorer (FUSE) to observe elliptical galaxies with the intention of measuring the chemical abundances in their hot stellar populations. It was designed to complement an earlier FUSE program that observed elliptical galaxies with strong UV emission. The current program originally planned observations of two ellipticals with weak UV emission (M32 and M49). Once FUSE encountered pointing control problems in certain regions of the sky (particularly Virgo, which is very unfortunate for the study of ellipticals in general), M49 was replaced with the bulge of M31, which has a similar UV-to-optical flux ratio as the center of M49. As the closest elliptical galaxy and the one with the weakest UV-to-optical flux ratio, M32 was an obvious choice of target, but M49 was the ideal complementary target, because it has a very low reddening (unlike M32). With the inability of FUSE to point at Virgo, nearly all of the best elliptical galaxies (bright galaxies with low foreground extinction) were also lost, and this severely hampered three FUSE programs of the PI, all focused on the hot stellar populations of ellipticals. M31 was the best replacement for M49, but like M32, it suffers from significant foreground reddening. Strong Galactic ISM lines heavily contaminate the FUSE spectra of M31 and M32. These ISM lines are coincident with the photospheric lines from the stellar populations (whereas M49, with little foreground ISM and significant redshift, would not have suffered from this problem). We have reduced the faint (and thus difficult) data for M31 and M32, producing final co-added spectra representing all of the exposures, but we have not yet finished our analysis, due to the complication of the contaminating ISM. The silver lining here is the set of CHI lines at 1175 Angstroms, which are not significantly contaminated by the ISM. A comparison of the M31 spectrum with other galaxies observed by FEE showed a surprising result: the hot stars in M31 seem to have a similar carbon abundance to those stars in galaxies with much brighter UV emission. The fraction of these hot stars in a population should be a strong function of chemical abundances, so this finding warrants further exploration, and we are proceeding with our analysis. Because the UV emission in these galaxies comes from a population of extreme horizontal branch stars, the PI (Brown) presented this result at a June 2003 conference on such stars.

Sonneborn, George (Technical Monitor); Brown, Thomas

2005-01-01

338

ApJ submitted June 20, 2008 Obscured star formation in intermediate-density environments: A  

E-print Network

study of the Abell 901/902 supercluster Anna Gallazzi1 , Eric F. Bell1 , Christian Wolf2 , Meghan E have red optical colors at intermediate and high densities. These red systems are not star- bursting. More than half of the red star-forming galax- ies have low IR-to-UV luminosity ratios, relatively high

Balogh, Michael L.

339

Hubble Space Telescope Imaging of Star-forming Galaxies at Redshifts Z > 3  

Microsoft Academic Search

We present Hubble Space Telescope images of star-forming galaxies at redshifts z > 3. These galaxies have been selected using ground-based images and color criteria sensitive to the presence of a Lyman discontinuity in the otherwise flat (in fnu_ units) UV spectral energy distribution of unreddened star formation. The spectroscopic confirmation of these z > 3 galaxies is reported in

Mauro Giavalisco; Charles C. Steidel; F. Duccio Macchetto

1996-01-01

340

Expression of cloned bacteriophage T4 uvsW and uvsY genes in rec+ and rec- Escherichia coli  

SciTech Connect

Chimeric plasmids containing the uvsY uvsW region of the T4 genome were examined for the expression of these genes. Certain of these plasmids were shown to express the uvsY or the uvsW gene products by their ability to complement the UV sensitivity of infecting uvsW or uvsY mutant phage. Also, a chimeric plasmid containing both the uvsW and uvsY genes increases the survival of UV-irradiated, methyl methane sulfonate- or ethyl methane sulfonate-treated recA hosts.

DeVries, J.K.; Wallace, S.S.

1983-09-01

341

Study of Implosion in Wire Arrays with UV interferometry and Faraday Rotation Diagnostics  

NASA Astrophysics Data System (ADS)

The implosion stage in wire arrays was studied with UV interferometry and Faraday rotation diagnostics at the wavelength of 266 nm implemented at the 1 MA Zebra pulsed power generator at UNR. Al cylindrical, star, and planar wire arrays were investigated. UV interferometry allows direct study of electron plasma density > 10^20 cm-3. Measurement of higher density is limited by spatial resolution, plasma motion, and plasma opacity at 266 nm. The density of the non-imploded plasma was measured at different times during the implosion stage. The first results from the UV Faraday rotation diagnostics are presented. Comparison of Faraday images with shadowgrams and interferograms allow measurement of current in the imploding plasma and non-imploded material in wire arrays.

Anderson, Austin; Papp, Daniel; Altemara, Sara; Ivanov, Vladimir

2012-10-01

342

Fiber optic systems in the UV region  

NASA Astrophysics Data System (ADS)

Mainly due to the unexpected progress in manufacturing of solarization-reduced all-silica fibers, new fiber-optic applications in the UV-region are feasible. However, the other components like the UV-sources and the detector- systems have to be improved, too. Especially, the miniaturization is very important fitting to the small-sized fiber-optic assemblies leading to compact and mobile UV- analytical systems. Based on independent improvements in the preform and fiber processing, UV-improved fibers with different properties have been developed. The best UV-fiber for the prosed applications is selectable by its short and long-term spectral behavior, especially in the region from 190 to 350 nm. The spectrum of the UV-source and the power density in the fiber have an influence on the nonlinear transmission and the damaging level; however, hydrogen can reduce the UV-defect concentration. After determining the diffusion processes in the fiber, the UV-lifetime in commercially available all-silica fibers can be predicted. Newest results with light from deuterium-lamps, excimer- lasers and 5th harmonics of Nd:YAG laser will be shown. Many activities are in the field of UV-sources. In addition to new UV-lasers like the Nd:YAG laser at 213 nm, a new low- power deuterium-lamp with smaller dimensions has been introduced last year. Properties of this lamp will be discussed, taking into account some of the application requirements. Finally, some new applications with UV-fiber optics will be shown; especially the TLC-method can be improved significantly, combining a 2-row fiber-array with a diode-array spectrometer optimized for fiber-optics.

Huebner, Michael; Meyer, H.; Klein, Karl-Friedrich; Hillrichs, G.; Ruetting, Martin; Veidemanis, M.; Spangenberg, Bernd; Clarkin, James P.; Nelson, Gary W.

2000-05-01

343

Dissecting the Star Formation Within Late-Type Galaxies  

NASA Astrophysics Data System (ADS)

The past decade has brought the discovery and characterization of star-forming galaxies in the distant universe, detected through signatures of their rest-frame UV emission. One question about these galaxies is whether the UV continuum is a complete and unbiased picture of the star formation activity. Late-type galaxies are the best local analog candidates to the star formation occuring in galaxies in the distant universe. While samples reaching ~1000 galaxies at high redshift have been constructed, local samples are comparatively small. Early Spitzer observations have generated several large, general surveys the IR properties of nearby galaxies, but these survey inadequately sample the wide range of UV/Halpha/IR properties of late-type galaxies, so it is difficult to assess any trends---or to identify which kinds of local galaxies are the best analogs to the distant ones. In fact, late-type galaxies show so little self-similarity, that large samples of them are needed to span the full, multi-dimensional parameter space of those galaxy properties. We propose to fill-in this gap by obtaining IRAC and MIPS 3-24um images of a large sample of late-type galaxies (T>7) that all have UV (and many have Halpha) imaging already publicly-available in the HST archive. The result will be a wide and varied sample spanning many magnitudes of galaxy luminosity, star formation rate, stellar ages, metallicities, and merger activity. We will trace out the star formation activity in a variety of environments, and combine this with high-resolution HST imaging in order to dissect the processes occuring within those regions. The loss of HST's STIS, CTE degradation of WFPC-2, and uncertainity over WFC-3 all mean that our proposed sample is the complete list of galaxies with high spatial resolution UV images from HST. Our proposal will generate a generally useful Great Observatories dataset on star formation in late-type galaxies.

Fazio, Giovanni; Jansen, Rolf; Pahre, Michael; Windhorst, Rogier

2007-05-01

344

Are Dusty Galaxies Blue? Insights on UV Attenuation from Dust-selected Galaxies  

NASA Astrophysics Data System (ADS)

Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates (SFRs). While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15-500 ?m in the COSMOS field, in particular making use of Herschel imaging, and a rich data set on local galaxies, we find an empirical variation in the relationship between the rest-frame UV slope (?) and the ratio of infrared-to-ultraviolet emission (L IR/L UV ? IRX) as a function of infrared luminosity, or total SFR. Both locally and at high-z, galaxies above SFR >~ 50 M ? yr–1 deviate from the nominal IRX-? relation toward bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of Lt1% at z <~ 4-10, providing independent verification that contamination from very dusty foreground galaxies is low in Lyman-break galaxy searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g., galaxies with >50 M ? yr–1, are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z ~ 2 exhibit steady-state star formation in secular disks.

Casey, C. M.; Scoville, N. Z.; Sanders, D. B.; Lee, N.; Cooray, A.; Finkelstein, S. L.; Capak, P.; Conley, A.; De Zotti, G.; Farrah, D.; Fu, H.; Le Floc'h, E.; Ilbert, O.; Ivison, R. J.; Takeuchi, T. T.

2014-12-01

345

UV-BIOMETER - A BROAD-BAND INSTRUMENT COMPLEMENTING OZONE MEASUREMENTS WITH GROUND BASED UV EXPOSURE  

Microsoft Academic Search

Stratospheric ozone is known to be the most important atmospheric factor determining clear sky UV-B radiation reaching the Earth's surface. The potential increase of UV-B exposure is the cause of mounting concern about the ozone layer. There are, however, other effects that influence the UV radiative energy transfer: cloud cover, aerosols, tropospheric ozone, and other gaseous pollutants. The relationships between

Daniel Berger; Marian Morys

346

Photoconduction studies on GaN nanowire transistors under UV and polarized UV illumination  

E-print Network

Photoconduction studies on GaN nanowire transistors under UV and polarized UV illumination Song Han carried out with single crystal GaN nanowires. The nanowire transistors exhibited a sub- stantial increase was demonstrated and studied for GaN nanowires working as polarized UV detectors. The nanowire conductance varied

Zhou, Chongwu

347

Spectroscopy: Star Light, Star Bright  

NSDL National Science Digital Library

This is a student reading about the different types of spectra: continuous, absorption, and emission. Learners will read about the differences between each and see graphical representations of each. This activity is from the Stanford Solar Center's All About the Sun: Sun and Stars activity guide for Grades 5-8 and can also accompany the Stanford Solar Center's Build Your Own Spectroscope activity.

348

Converting neutron stars into strange stars  

NASA Technical Reports Server (NTRS)

If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

Olinto, A. V.

1991-01-01

349

Star formation and the ages of stars  

NASA Astrophysics Data System (ADS)

In this contribution we illustrate how the knowledge of the ages of stars is important to constrain star formation processes. We focus on two specific cases: star formation around the supermassive black hole at the center of the Galaxy and triggered star formation on the borders of Hii regions.

Martins, F.

2014-11-01

350

USGS Tunison Lab's New UV Treatment Facility  

USGS Multimedia Gallery

This photo shows an interior view of the USGS Tunison Lab's new UV water treament facility. The UV treatment system is on the bottom left of the photo. A new, sophisticated fish rearing facility in Cortland, N.Y. will help restore Atlantic salmon, bloater, and lake herring to Lake Ontario, strength...

351

Reconstruction of solar UV irradiance since 1974  

Microsoft Academic Search

Variations of the solar UV irradiance are an important driver of chemical and physical processes in the Earth's upper atmosphere and may also influence global climate. Here we reconstruct solar UV irradiance in the range 115–400 nm over the period 1974–2007 by making use of the recently developed empirical extension of the Spectral And Total Irradiance Reconstruction (SATIRE) models employing

N. A. Krivova; S. K. Solanki; T. Wenzler; B. Podlipnik

2009-01-01

352

On the Future of Ultraviolet (uv) Astronomy  

Microsoft Academic Search

The UV range supplies a richness of experimental data which is unmatched by any other domain for the study of hot plasma with temperatures in between 10^4 K and 10^5 K; the high excitation lines and the resonance lines of the most abundant species in the Universe are observed in UV. Plasma at these temperatures is observed in all astrophysical

A. I. Gómez de Castro; W. Wamsteker

2004-01-01

353

TOMS UV Algorithm: Problems and Enhancements. 2  

NASA Technical Reports Server (NTRS)

Satellite instruments provide global maps of surface ultraviolet (UV) irradiance by combining backscattered radiance measurements with radiative transfer models. The models are limited by uncertainties in input parameters of the atmosphere and the surface. We evaluate the effects of possible enhancements of the current Total Ozone Mapping Spectrometer (TOMS) surface UV irradiance algorithm focusing on effects of diurnal variation of cloudiness and improved treatment of snow/ice. The emphasis is on comparison between the results of the current (version 1) TOMS UV algorithm and each of the changes proposed. We evaluate different approaches for improved treatment of pixel average cloud attenuation, with and without snow/ice on the ground. In addition to treating clouds based only on the measurements at the local time of the TOMS observations, the results from other satellites and weather assimilation models can be used to estimate attenuation of the incident UV irradiance throughout the day. A new method is proposed to obtain a more realistic treatment of snow covered terrain. The method is based on a statistical relation between UV reflectivity and snow depth. The new method reduced the bias between the TOMS UV estimations and ground-based UV measurements for snow periods. The improved (version 2) algorithm will be applied to re-process the existing TOMS UV data record (since 1978) and to the future satellite sensors (e.g., Quik/TOMS, GOME, OMI on EOS/Aura and Triana/EPIC).

Krotkov, Nickolay; Herman, Jay; Bhartia, P. K.; Seftor, Colin; Arola, Antti; Kaurola, Jussi; Kroskinen, Lasse; Kalliskota, S.; Taalas, Petteri; Geogdzhaev, I.

2002-01-01

354

UV RADIATION MEASUREMENTS/ATMOSPHERIC CHARACTERIZATION  

EPA Science Inventory

Because exposure to ultraviolet (UV) radiation is an ecosystem stressor and poses a human health risk, the National Exposure Research Laboratory (NERL) has undertaken a research program to measure the intensity of UV-B radiation at various locations throughout the U.S. In Septem...

355

8, 59195938, 2008 Distribution of UV  

E-print Network

probability levels of snow cover occurrence as criterion for the snow effect incorporation in the model biological effects on life ecosystems. Overexpo- sure to solar UV radiation can exhibit instantly (as e of photosynthetic activity of plants) (WMO, 2003). From the latter point of view, the20 knowledge on typical UV

Paris-Sud XI, Université de

356

Compact hybrid IR\\/UV biological sensor  

Microsoft Academic Search

The sensor is a hybrid IR\\/UV lidar system that maps aerosol clouds, measures cloud wind speed and direction, and determines whether the cloud fluoresces. It is being developed by EOO, Inc. and SRI International under a DARPA SBIR. The hybrid IR\\/UV lidar system was conceived to operate from a small UAV platform for tactical battlefield missions. The IR sensor can

Donald A. Leonard; James F. Shaw; Christopher Smith; Paul J. Titterton; Norm Neilson; Russ Scofield; Sylvie A. Carlisle; Russell E. Warren; David E. Cooper

1999-01-01

357

Solar UV Radiation and the Origin of Life On Earth  

NASA Technical Reports Server (NTRS)

We have embarked on a program aimed at understanding the atmosphere of the early Earth, because of its importance as a greenhouse, radiation shield and energy source for life. Here, we give a progress report on the first phase of this program to establish the UV radiation from the early Sun. We have obtained ultraviolet spectra (STIS, FUSE, EUVE) of carefully selected nearby, young solar-type stars, which act as surrogates for the early Sun We are making detailed non-LTE analyses of the spectra and constructing models of their photospheres + chromospheres. Once validated, these models will allow us to extrapolate our theoretical spectra to other metallicities and to unobserved spectral regions.

Heap, S. R.; Lanz, T.; Hubeny, I.; Gaidos, E.; Oegerle, William R. (Technical Monitor)

2002-01-01

358

Solar UV Radiation and the Origin of Life on Earth  

NASA Technical Reports Server (NTRS)

We have embarked on a program aimed at understanding the atmosphere of the early Earth, because of its importance as a greenhouse, radiation shield, and energy source for life. Here, we give a progress report on the first phase of this program: to establish the UV radiation from the early Sun. We are presently obtaining ultraviolet spectra (STIS, FUSE, EUVE) of carefully selected nearby, young solar-type stars, which act as surrogates for the early Sun. We are currently making detailed non-LTE analyses of the spectra and constructing models of their photospheres + chromospheres. once validated, these models will allow us to extrapolate our theoretical spectra to unobserved spectral regions, and to proceed to the next step: to develop photochemical models of the pre-biotic and Archean atmosphere of the Earth.

Heap, S. R.; Gaidos, E.; Hubeny, I.; Lanz, T. M.; Fisher, Richard R. (Technical Monitor)

2001-01-01

359

Modeling UV-FIR SEDs of Starburst Galaxies with DIRTY  

NASA Astrophysics Data System (ADS)

We apply the DIRTY model to a small sample of nearby starburst galaxies. The DIRTY model is a three-dimensional Monte Carlo radiative transfer code. The model self-consistently includes dust heating and emission, fully accounting for the effects of the transient heating of small grains. Dust self-absorption is also accounted for by treating photons emitted by the dust as an additional heating source and adopting an iterative radiative transfer scheme. The UV to far IR SEDs of the galaxies are well reproduced using DIRTY, and quantitative information including star formation rates, dust masses, and dust temperatures are derived. The ability to accurately reproduce the full SED of starburst galaxies is discussed in the context of modeling galaxies at high redshift.

Misselt, K. A.; Gordon, K. D.; Clayton, G. C.

2000-12-01

360

Modelling the UV/X-ray cosmic background with CUBA  

NASA Astrophysics Data System (ADS)

In this paper, I will describe the features of the numerical code CUBA, aimed at the solution of the radiative transfer equation in a cosmological context. CUBA will be soon available for public use at the URL http://pitto.mib.infn.it/~haardt/, allowing for several user-supplied input parameters, such as favourite cosmology, luminosity functions, Type II object evolution, stellar spectra, and many others. I will also present some new results of the UV/X-ray cosmic background as produced by the observed populations of QSOs and star forming galaxies, updating and extending our previous works. The background evolution is complemented with a number of derived quantities such as the ionization and thermal state of the IGM, the HeII opacity, the HI and HeII ionization rates, and the HI, HeII and Compton heating rates.

Haardt, F.; Madau, P.

361

Tomographic separation of composite spectra - The components of the O-star spectroscopic binary AO Cassiopeiae  

NASA Technical Reports Server (NTRS)

The UV photospheric lines of the short-period, double-lined O-star spectroscopic binary AO Cas are analyzed. Archival data from IUE (16 spectra uniformly distributed in orbital phase) were analyzed with a tomography algorithm to produce the separate spectra of the two stars in six spectral regions. The spectral classifications of the primary and secondary, O9.5 III and O8 V, respectively, were estimated through a comparison of UV line ratios with those in spectral standard stars. An intensity ratio of 0.5-0.7 (primary brighter) at 1600 A is compatible with the data.

Bagnuolo, William G., Jr.; Gies, Douglas R.

1991-01-01

362

Stars : the end of a star  

NSDL National Science Digital Library

What happens during the death of a star? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the final processes of stars. Here students read about low-mass, medium-mass, and massive stars. Low-mass stars produce white dwarfs. A pop-up window describes how white dwarfs form. Medium-mass stars produce neutron stars and supernova. Pop-up information explains the supernova process. Massive stars undergo carbon burning. An interactive lab activity presents students the opportunity to predict temperature, pressure, and gravity changes that occur during carbon fusion. In a final lab activity, students compare initial star size with the type of death that occurs. Activity questions about star death are provided for each star size and are recordable and printable. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)

2003-01-01

363

UV Induced Oxidation of Nitric Oxide  

NASA Technical Reports Server (NTRS)

Nitric oxide in a gaseous stream is converted to nitrogen dioxide using oxidizing species generated at least in part using in situ UV radiation sources. The sources of the oxidizing species include oxygen and/or hydrogen peroxide. The oxygen may be a component of the gaseous stream or added to the gaseous stream, preferably near a UV radiation source, and is converted to ozone by the UV irradiation. The hydrogen peroxide is decomposed through a combination of vaporization and UV irradiation. The hydrogen peroxide is preferably stored at stable concentration levels, i.e., approximately 50% by volume and increased in concentration in a continuous process preceding vaporization within the flow channel of the gaseous stream and in the presence of the UV radiation sources.

Parrish, Clyde, F. (Inventor); Luecke, Dale E. (Inventor)

2007-01-01

364

UV Microspot Irradiator at Columbia University  

PubMed Central

The Radiological Research Accelerator Facility (RARAF) at Columbia University has recently added a UV microspot irradiator to a microbeam irradiation platform. This UV microspot irradiator applies multiphoton excitation at the focal point of an incident laser as the source for cell damage, and with this approach, a single cell within a 3D sample can be targeted and exposed to damaging UV. The UV microspot’s ability to impart cellular damage within 3D is an advantage over all other microbeam techniques, which instead impart damage to numerous cells along microbeam tracks. This short communication is an overview and a description of the UV microspot including the following applications and demonstrations of selective damage to live single cell targets: DNA damage foci formation, patterned irradiation, photoactivation, targeting of mitochondria, and targeting of individual cardiomyocytes in the live zebrafish embryo. PMID:23708525

Bigelow, Alan W.; Ponnaiya, Brian; Targoff, Kimara L.; Brenner, David J.

2013-01-01

365

IUE observations of new A star candidate proto-planetary systems  

NASA Technical Reports Server (NTRS)

As a result of the detection of accreting gas in the A5e PMS Herbig Ae star, HR 5999, most of the observations for this IUE program were devoted to Herbig Ae stars rather than to main sequence A stars. Mid-UV emission at optical minimum light was detected for UX Ori (A1e), BF Ori (A5e), and CQ Tau (F2e). The presence of accreting gas in HD 45677 and HD 50138 prompted reclassification of these stars as Herbig Be stars rather than as protoplanetary nebulae. Detailed results are discussed.

Grady, Carol A.

1994-01-01

366

Are Dusty Galaxies Blue? Insights on UV Attenuation from Dust-Selected Galaxies  

NASA Astrophysics Data System (ADS)

Galaxies’ rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates. While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-z, here we investigate attenuation in dusty, star-forming galaxies (DSFGs) selected at far- infrared wavelengths. By combining multiwavelength coverage across 0.15–500 ?m in the COSMOS field, in particular making use of Herschel imaging, and a rich dataset on local galaxies, we find a empirical variation in the relationship between rest-frame UV slope (?) and ratio of infrared-to- ultraviolet emission (LIR/LUV?IRX) as a function of infrared luminosity, or total star formation rate, SFR. Both locally and at high-z, galaxies above SFR ˜> 50 M? yr?1 deviate from the nominal IRX–? relation towards bluer colors by a factor proportional to their increasing IR luminosity. We also estimate contamination rates of DSFGs on high-z dropout searches of <<1% at z= 4 ? 10, providing independent verification that contamination from very dusty foreground galaxies is low in LBG searches. Overall, our results are consistent with the physical interpretation that DSFGs, e.g. galaxies with > 50 M? yr?1, are dominated at all epochs by short-lived, extreme burst events, producing many young O and B stars that are primarily, yet not entirely, enshrouded in thick dust cocoons. The blue rest-frame UV slopes of DSFGs are inconsistent with the suggestion that most DSFGs at z ~ 2 exhibit steady-state star formation in secular disks.

Casey, Caitlin; Scoville, Nicholas; Sanders, David B.; Lee, Nicholas; Cooray, Asantha R.; Capak, Peter L.; Conley, Alexander J.; De Zotti, Gianfranco; Farrah, Duncan; Fu, Hai; Le Floc'h, Emeric; Ilbert, Olivier; Ivison, Rob; Takeuchi, Tsutomu T.

2015-01-01

367

STAR FORMATION IN THE OUTER DISKS OF SPIRAL GALAXIES: ULTRAVIOLET AND H{alpha} PHOTOMETRY  

SciTech Connect

We present an analysis of ultradeep UV and H{alpha} imaging of five nearby spiral galaxies to study the recent star formation in the outer disk. Using azimuthally averaged ellipse photometry as well as aperture photometry of individual young stellar complexes, we measure how star formation rates (SFRs) and UV and H{alpha} colors vary with radius. We detect azimuthally averaged UV flux to {approx}1.2-1.4 R{sub 25} in most galaxies; at the edge of the detected UV disk, the surface brightnesses are 28-29 mag arcsec{sup -2}, corresponding to SFR surface densities of {approx}3 Multiplication-Sign 10{sup -4} M{sub Sun} yr{sup -1} kpc{sup -2}. Additionally, we detect between 120 and 410 young stellar complexes per galaxy, with a significant number of detections out to {approx}1.5 R{sub 25}. We measure radial FUV-NUV profiles, and find that the dispersion in the UV colors of individual young stellar complexes increases with radius. We investigate how radial variations in the frequency of star formation episodes can create color gradients and increasing dispersion in the UV colors of star-forming regions, like those observed in our study. Specifically, we use recently published, high spatial and temporal resolution measurements of {Sigma}{sub SFR} throughout the disk of M33 to estimate the frequency of star formation episodes throughout the disk of a typical spiral galaxy. We use stellar synthesis models of these star formation histories (SFHs) to measure the variations in UV colors and find that we can replicate large dispersions in UV colors based on episodic SFHs.

Barnes, Kate L.; Van Zee, Liese [Department of Astronomy, Indiana University, Bloomington, IN 47405 (United States); Skillman, Evan D., E-mail: barneskl@astro.indiana.edu, E-mail: vanzee@astro.indiana.edu, E-mail: skillman@astro.umn.edu [Department of Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)

2011-12-20

368

UV-optical from space  

NASA Technical Reports Server (NTRS)

The following subject areas are covered: (1) the science program (star formation and origins of planetary systems; structure and evolution of the interstellar medium; stellar population; the galactic and extragalactic distance scale; nature of galaxy nuclei, AGNs, and QSOs; formation and evolution of galaxies at high redshifts; and cosmology); (2) implementation of the science program; (3) the observatory-class missions (HST; LST - the 6m successor to HST; and next-generation 16m telescope); (4) moderate and small missions (Delta-class Explorers; imaging astrometric interferometer; small Explorers; optics development and demonstrations; and supporting ground-based capabilities); (5) prerequisites - the current science program (Lyman-FUSE; HTS optimization; the near-term science program; data analysis, modeling, and theory funding; and archives); (6) technologies for the next century; and (7) lunar-based telescopes and instruments.

Illingworth, Garth; Savage, Blair; Angel, J. Roger; Blandford, Roger D.; Boggess, Albert; Bowyer, C. Stuart; Carruthers, George R.; Cowie, Lennox L.; Doschek, George A.; Dupree, Andrea K.

1991-01-01

369

Testing the Disk-Locking Paradigm: An Association Between U-V Excess and Rotation in NGC 2264  

E-print Network

We present some results from a UVI photometric study of a field in the young open cluster NGC 2264 aimed, in part, at testing whether accretion in pre-main sequence stars is linked to rotation. We confirm that U-V excess is well correlated with H-alpha equivalent width for the stars in our sample. We show that for the more massive stars in the cluster sample (roughly 0.4-1.2 M_sun) there is also a significant association between U-V excess and rotation, in the sense that slow rotators are more likely to show excess U-band emission and variability. This constitutes significant new evidence in support of the disk-locking paradigm.

Cassandra Fallscheer; William Herbst

2006-07-10

370

A stellar population synthesis model for the study of ultraviolet star counts of the Galaxy  

NASA Astrophysics Data System (ADS)

Context. Galaxy Evolution Explorer (GALEX), the first all sky imaging ultraviolet (UV) satellite, has imaged a large part of the sky providing an excellent opportunity for studying UV star counts. Combining photometry from the different wavelengths in the infrared (from Wide-field Infrared Survey (WISE) and Two Micron All Sky Survey (2MASS)) to UV allows us to extract a real star catalogue from the GALEX source catalogue. Aims: The aim of our study is to investigate in detail the observed UV star counts obtained by GALEX vis-à-vis the model simulated catalogues produced by the Besançon model of stellar population synthesis in various Galactic directions, and to explore the potential for studying the structure of our Galaxy from images in multiple near-UV (NUV) and far-UV (FUV) filters of the forthcoming Ultraviolet Imaging Telescope (UVIT) to be flown onboard Astrosat. Methods: We have upgraded the Besançon model of stellar population synthesis to include the UV bands of GALEX and UVIT. Depending on the availability of contiguous GALEX, Sloan Digital Sky Survey (SDSS), WISE, and 2MASS overlapping regions, we have chosen a set of 19 GALEX fields which spread over a range of Galactic directions. We selected a sample of objects from the GALEX database using the CASjobs interface and then cross-matched them with the WISE+2MASS and SDSS catalogues. The UV stars in the GALEX catalogue are identified by choosing a suitable infrared (IR) colour, J - W1 (W1 is a WISE band at 3.4 ?m), which corresponds to a temperature range from 1650 K to 65 000 K. The IR colour cut method, which is used for the first time for separation of stars, is discussed in comparison with the GALEX+SDSS star counts method. Results: We present the results of the UV star counts analysis carried out using the data from GALEX. We find that the Besançon model simulations represent the observed star counts of both the GALEX All-sky Imaging Survey and Medium Imaging Survey well within the error bars in various Galactic directions. Based on the analysis of the model FUV - NUV colour, we separated out white dwarfs of the disc and blue horizontal branch stars of the halo from the observed sample by selecting a suitable FUV - NUV colour. Conclusions: The Besançon model is now ready for further comparisons in the UV domain and will be used for prospective studies for the UVIT instrument to be flown onboard Astrosat.

Pradhan, Ananta C.; Ojha, Devendra K.; Robin, Annie C.; Ghosh, Swarna K.; Vickers, John J.

2014-05-01

371

A database of UV variables from the GALEX surveys  

NASA Astrophysics Data System (ADS)

We present the first part of a comprehensive study to search for variability in the UV GALEX archive. GALEX provided photometric measurements for over 200 million objects in FUV and NUV, from sky surveys with different depth and coverage. In this work we extract 410,408 unique sources showing variability (?NUV?0.6 mag , ?FUV?0.4 mag) in both NUV and FUV from a total of 2,106,816 measurements. We restrict our analysis to 7264 sources that have at least 30 measurements, sampled with serendipitous time coverage. This first sample selection includes both extragalactic sources and Milky Way stellar objects, displaying both periodic and non-periodic variability, of various types including RR Lyrae, flare stars, transients, and eclipsing binaries. Amplitudes of magnitude variations are found from our minimum selection threshold up to several magnitudes. We describe the selection criteria and procedures, we characterize the main classes of variables within the sample, and present the layout of the resulting catalog which will be also made available as on-line resource. Beyond our immediate goals of discovering and characterizing UV-selected variables, this work provides synergy with existing and planned surveys at other wavelengths (e.g. SDSS, PanSTARRS, LSST, GAIA).

Conti, Alberto; Bianchi, Luciana; Chopra, Nitish; Orio, Marina; Shiao, Bernie

2014-03-01

372

Flight Performance of UV Filters on the ALEXIS Satellite  

SciTech Connect

The ALEXIS (Array of Low-Energy X-ray Imaging Sensors) mission, serving as the first dedicated all-sky monitor in the extreme UV, has been collecting data since its launch in 1993. ALEXIS operates in a 70{degree} inclination orbit at an altitude of 800 km. The ALEXIS science mission is to observe the cosmic UV background and to study variability of EUV sources. The ALEXIS experiment is composed of six telescopes. Although the telescopes were only designed for a one-year technology verification mission, they are still functioning with much the same effectiveness as at the beginning of the mission. The telescopes comprise: (1) layered synthetic microstructure (LSM) spherical mirrors, (2) thin foil filters, and (3) microchannel plate (MCP) detectors, all enshrouded within the telescope body. The LSM mirrors select the bandpass for each telescope, while rejecting some of the HeII 304{angstrom} geocoronal radiation. The filters, constructed either from aluminum/carbon or Lexan/titanium/boron, serve to strongly reject the geocoronal radiation, as well as longer wavelength emission from bright OB stars. Each telescope detector consists of two plates, the outermost of which is curved to accurately match the spherical focal surface of the mirror. By reviewing the ground and flight histories, this paper analyzes the flight performance of the filters, including the effects of long term exposure and the formation of pinholes.

Bloch, J.J.; Roussel-Dupre, D.; Starin, S.

1999-07-08

373

Interstellar iron and manganese - UV oscillator strengths and abundances  

NASA Technical Reports Server (NTRS)

Observations of 16 UV resonance lines of Fe II and six of Mn II in five stars are used to derive new f-values for the lines of these species at wavelengths lower than 1300 A. Values of forbidden lines Fe/H and Mn/H are derived. These new values are used to reassess mean depletions and range of variations in depletions for several lines of sight. On an integrated line-of-sight basis, depletions of Fe and Mn show larger variations than P, Cl, or Zn. The mean local depletion forbidden line Fe/H is 1.65, in interstellar gas. One Fe II line, 2366.864 A, has never been detected. Its f-value is shown to be much lower than previously thought. This line is therefore not useful for interstellar studies at the present time. It is suggested that the true wavelength of 1142 A of Fe II, from UV multiplet 10, is 1142.285 A.

Lugger, P.; Barker, E.; York, D. G.; Oegerle, W.

1982-01-01

374

UV/Vis/NIR Spectroelectrochemistry  

NASA Astrophysics Data System (ADS)

Voltammetric techniques used in electrochemistry monitor the flow of current as a function of potential, time, and mass transport. A huge variety of different experiments are possible, giving information about reaction energies, reaction intermediates, and the kinetics of a process [1-4]. However, additional data are often required and are accessible, in particular, via in situ spectroelectrochemical approaches. By coupling a spectroscopic technique such as UV/Vis/NIR spectroscopy [5, 6] to an electrochemical experiment, a wealth of complementary information as a function of the potential, time, and mass transport is available. In a recently published book dedicated to spectroelectrochemical techniques [7] the diversity of methods and new chemical information obtained is apparent. Both spectroscopic information about short-lived unstable intermediates and spectroscopic information disentangling the composition of complex mixtures of reactants can be obtained. Figure II.6.1 shows a schematic diagram for the case of a computer-controlled potentiostat system connected to a conventional electrochemical cell (working electrode WE, reference electrode RE, counter electrode CE) and simultaneously controlling the emitter and detector of a spectrometer. This kind of experimental arrangement allows the electrochemical and the spectroscopic data to be recorded simultaneously and, therefore, in contrast to the analysis of two independent data sets, direct correlation of data as a function of time and potential is possible.

Neudeck, Andreas; Marken, Frank; Compton, Richard G.

375

Photometric Analysis of UV Piscium  

NASA Astrophysics Data System (ADS)

We present light curves and analyses of the RS CVn eclipsing system UV Psc. Greenwood (1981, M.S. thesis San Diego State University) obtained uvby photoelectric data at Mount Laguna Observatory in 1980 using the 0.4-m telescope. Because this system has a strongly variable light curve and the data is unpublished, we reanalysed these data using the physically more realistic models of Wilson-Devinney and the ELC program (Orosz, J. A., & Hauschildt, P. H. 2000 A&A, 364, 265). Both modeling programs yielded similar results, which were also consistent with other published results (Kjurkchieva, et al. 2005 AJ, 129, 1084). The determination of the global parameters was somewhat affected by the night to night variations typical of RS CVn systems. A new time of primary minimum was determined. This determination was consistent with other minima reported during this time period (Shengbang, et al. 1999, Ap&SS, 266, 259). This work was supported in part through an REU grant (AST-0453609) to SDSU.

Kaplan, Kyle; Angione, R.; Sievers, J.

2007-12-01

376

Massive Star Forming Regions: from diagnostic tools to derived properties  

E-print Network

The current state-of-the-art of multi-wavelength diagnostic tools (evolutionary synthesis, photoionisation models) for massive star forming regions (HII regions, starbursts, etc.) and some of their input physics (especially model atmospheres) is reviewed. Analysis of stellar populations based on integrated spectra from both stellar features and nebular emission lines from the UV to IR are summarised. We stress the importance of "template" studies at various scales (from individual stars to well studied galaxies) and various wavelengths, to understand the processes operating in massive star forming regions and to reliably derive their properties.

Daniel Schaerer

2000-07-20

377

UV disinfection system for cabin air  

NASA Astrophysics Data System (ADS)

The air of indoor cabin environments is susceptible to contamination by airborne microbial pathogens. A number of air treatment processes are available for inactivation or removal of airborne pathogens; included among these processes is ultraviolet (UV) irradiation. The effectiveness of UV-based processes is known to be determined by the combined effects of UV dose delivery by the reactor and the UV dose-response behavior of the target microbe(s). To date, most UV system designs for air treatment have been based on empirical approaches, often involving crude representations of dose delivery and dose-response behavior. The objective of this research was to illustrate the development of a UV system for disinfection of cabin air based on well-defined methods of reactor and reaction characterization. UV dose-response behavior of a test microorganism was measured using a laboratory (bench-scale) system. Target microorganisms (bacterial spores) were first applied to membrane filters at sub-monolayer coverage. The filters were then transferred to a humidity chamber at fixed relative humidity (RH) and allowed to equilibrate with their surroundings. Microorganisms were then subjected to UV exposure under a collimated beam. The experiment was repeated at RH values ranging from 20% to 100%. UV dose-response behavior was observed to vary with RH. For example, at 100% RH, a UV dose of 20 mJ/cm 2 accomplished 99.7% (2.5 log10 U) of the Bacillus subtilis spore inactivation, whereas 99.94% (3.2 log10 U) inactivation was accomplished at this same UV dose under 20% RH conditions. To determine reactor behavior, UV dose-response behavior was combined with simulated results of computational fluid dynamics (CFD) and radiation intensity field models. This modeling approach allowed estimating the UV dose distribution delivered by the reactor. The advantage of this approach is that simulation of many reactor configurations can be done in a relatively short period of time. Moreover, by following this approach of "numerical prototyping", it is possible to "build" and analyze several virtual reactors before the construction of a physical prototype. As such, this procedure allows effective development of efficient reactors.

Lim, Soojung; Blatchley, Ernest R.

2009-10-01

378

Nitrogen abundances in Planet-harbouring stars  

E-print Network

We present a detailed spectroscopic analysis of nitrogen abundances in 91 solar-type stars, 66 with and 25 without known planetary mass companions. All comparison sample stars and 28 planet hosts were analysed by spectral synthesis of the near-UV NH band at 3360 \\AA observed at high resolution with the VLT/UVES,while the near-IR NI 7468 \\AA was measured in 31 objects. These two abundance indicators are in good agreement. We found that nitrogen abundance scales with that of iron in the metallicity range -0.6 exoplanets is the high [Fe/H] extension of the curve traced by the comparison sample of stars with no known planets. A comparison of our nitrogen abundances with those available in the literature shows a good agreement.

A. Ecuvillon; G. Israelian; N. C. Santos; M. Mayor; R. J. García López; S. Randich

2004-01-20

379

Overview of the observations of symbiotic stars  

NASA Technical Reports Server (NTRS)

The term Symbiotic stars commonly denotes variable stars whose optical spectra simultaneously present a cool absorption spectrum (typically TiO absorption bands) and emission lines of high ionization energy. This term is now used for the category of variable stars with composite spectrum. The main spectral features of these objects are: (1) the presence of the red continuum typical of a cool star, (2) the rich emission line spectrum, and (3) the UV excess, frequently with the Balmer continuum in emission. In addition to the peculiar spectrum, the very irregular photometric and spectroscopic variability is the major feature of the symbiotic stars. Moreover, the light curve is basic to identify the different phases of activity in a symbiotic star. The physical mechanisms that cause the symbiotic phenomenon and its variety are the focus of this paper. An astronomical phenomenon characterized by a composite stellar spectrum with two apparently conflicting features, and large variability has been observed. Our research set out to find the origin of this behavior and, in particular, to identify and measure the physical mechanism(s) responsible for the observed phenomena.

Viotti, Roberto

1993-01-01

380

UV Disinfection System for Cabin Air  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV) radiation is commonly used for disinfection of water. As a result of advancements made in the last 10-15 years, the analysis and design of UV disinfection systems for water is well developed. UV disinfection is also used for disinfection of air; however, despite the fact the UV-air systems have a longer record of application than UV-water systems, the methods used to analyze and design UV-air disinfection systems remain quite empirical. It is well-established that the effectiveness of UV-air systems is strongly affected by the type of microorganisms, the irradiation level/type (lamp power and wavelength), duration of irradiation (exposure time), air movement pattern (mixing degree), and relative humidity. This paper will describe ongoing efforts to evaluate, design and test a UV-air system based on first principles. Specific issues to be addressed in this work will include laboratory measurements of relevant kinetics (i.e., UV dose-response behavior) and numerical simulations designed to represent fluid mechanics and the radiation intensity field. UV dose-response behavior of test microorganism was measured using a laboratory (bench-scale) system. Target microorganisms (e.g., bacterial spores) were first applied to membrane filters at sub-monolayer coverage. The filters were then transferred to an environmental chamber at fixed relative humidity (RH) and allowed to equilibrate with their surroundings. Microorganisms were then subjected to UV exposure under a collimated beam. The experiment was repeated at RH values ranging from 20% to 100%. UV dose-response behavior was observed to vary with RH. For example, at 100% RH, a UV dose of 20 mJ/cm2 accomplished 90% (1 log10 units) of the B. subtilis spore inactivation, whereas 99 % (2 log10 units) inactivation was accomplished at this same UV dose under 20% RH conditions. However, at higher doses, the result was opposite of that in low dose. Reactor behavior is simulated using an integrated application of computational fluid dynamics (CFD) and radiation intensity field models. These simulations followed a Lagrangian approach, wherein the UV radiation intensity field was mapped onto simulated particle trajectories for prediction of the UV dose delivered to each particle. By repeating these calculations for a large number of simulated particle trajectories, an estimate of the UV dose distribution delivered by the reactor can be made. In turn, these dose distribution estimates are integrated with the UV dose-response behavior described above to yield an estimate of microbial inactivation accomplished by the reactor. This modeling approach has the advantage of allowing simulation of many reactor configurations in a relatively short period of time. Moreover, by following this approach of "numerical prototyping," it is possible to "build" and analyze several virtual reactors before the construction of a physical prototype. As such, this procedure allows effective development of efficient reactors.

Lim, Soojung

381

UV-Visible Spectroscopic Method and Models for Assessment and Monitoring of Harmful Algal Blooms  

NASA Technical Reports Server (NTRS)

The development of an enhanced predictive and early warning capability for the occurrence and impact of harmful algal blooms (HABs) would be of great benefit to coastal communities. A critical issue for early detection and monitoring of HABs is the need to detect harmful algal species within a mixed-species phytoplankton assemblage. Possession of UV-absorbing compounds called mycosporine-like amino acids (MAAs) may be one factor that allows HAB species to out-compete their phytoplankton neighbors. Possession of MAAs, which we believe can be inferred from strong UV-absorption signals in phytoplankton absorption coefficients, can be used as a flag for potential HAB outbreak. The goal of this project was to develop a solar simulating UV-visible incubator to grow HAB dinoflagellates, to begin MAA analysis of samples collected on global cruises, and to carry out initial experiments on HAB dinoflagellate species in pure culture. Our scientific objectives are to quantify MAA production and spectral induction mechanisms in HAB species, to characterize spectral absorption of MAAs, and to define the ecological benefit of MAAs (i.e. photoprotection). Data collected on cruises to the global oceans will be used to parameterize phytoplankton absorption in the UV region, and this parameterization could be incorporated into existing models of seawater optical properties in the UV spectral region. Data collected in this project were used for graduate fellowship applications by Elizabeth Frame. She has been awarded an EPA STAR fellowship to continue the work initiated by this project.

Mitchell, B. Greg

2000-01-01

382

Skin ?-endorphin mediates addiction to UV light.  

PubMed

UV light is an established carcinogen, yet evidence suggests that UV-seeking behavior has addictive features. Following UV exposure, epidermal keratinocytes synthesize proopiomelanocortin (POMC) that is processed to melanocyte-stimulating hormone, inducing tanning. We show that, in rodents, another POMC-derived peptide, ?-endorphin, is coordinately synthesized in skin, elevating plasma levels after low-dose UV. Increases in pain-related thresholds are observed and reversed by pharmacologic opioid antagonism. Opioid blockade also elicits withdrawal signs after chronic UV exposure. This effect was sufficient to guide operant behavioral choices to avoidance of opioid withdrawal (conditioned place aversion). These UV-induced nociceptive and behavioral effects were absent in ?-endorphin knockout mice and in mice lacking p53-mediated POMC induction in epidermal keratinocytes. Although primordial UV addiction, mediated by the hedonic action of ?-endorphin and anhedonic effects of withdrawal, may theoretically have enhanced evolutionary vitamin D biosynthesis, it now may contribute to the relentless rise in skin cancer incidence in humans. PMID:24949966

Fell, Gillian L; Robinson, Kathleen C; Mao, Jianren; Woolf, Clifford J; Fisher, David E

2014-06-19

383

The winds of O-stars. II - The terminal velocities of stellar winds of O-type stars  

NASA Astrophysics Data System (ADS)

The SEI method (Lamers et al., 1987) is used to obtain P Cygni profiles of the UV resonance lines of C IV, N V, and S IV and of the subordinate UV lines of N IV and C III observed in the spectra of 27 O-type stars. Theoretical profiles which include the turbulence effects agree well with the observations, and they can account for the deep absorption troughs, the shape of the violet absorption wings, and the wavelength of the emission peak. The resulting terminal velocities of the stellar winds are found to be systematically lower by about 400 km/s than previous estimates obtained using the Sobolev approximation (Castor and Lamers, 1979), suggesting that the narrow absorption components, observed in the UV resonance lines of O and B stars, reach the terminal velocity of the winds.

Groenewegen, M. A. T.; Lamers, H. J. G. L. M.; Pauldrach, A. W. A.

1989-08-01

384

The winds of O-stars. II - The terminal velocities of stellar winds of O-type stars  

NASA Technical Reports Server (NTRS)

The SEI method (Lamers et al., 1987) is used to obtain P Cygni profiles of the UV resonance lines of C IV, N V, and S IV and of the subordinate UV lines of N IV and C III observed in the spectra of 27 O-type stars. Theoretical profiles which include the turbulence effects agree well with the observations, and they can account for the deep absorption troughs, the shape of the violet absorption wings, and the wavelength of the emission peak. The resulting terminal velocities of the stellar winds are found to be systematically lower by about 400 km/s than previous estimates obtained using the Sobolev approximation (Castor and Lamers, 1979), suggesting that the narrow absorption components, observed in the UV resonance lines of O and B stars, reach the terminal velocity of the winds.

Groenewegen, M. A. T.; Lamers, H. J. G. L. M.; Pauldrach, A. W. A.

1989-01-01

385

The sun, our star  

NASA Astrophysics Data System (ADS)

Observational data, analytical models, and instrumentation used to study the sun and its evolution are detailed, and attention is given to techniques for converting solar energy to useful power on earth. The star ignited when the mutual gravitational attractions of dust and vapor in a primordial cloud in the Galaxy caused an in-rush of accelerating particles which eventually became dense enough to ignite. The heat grew until inward rushing matter was balanced by outward moving radiative forces. The planets formed from similar debris, and solar radiation is suggested to have triggered the chemical reactions giving rise to life on earth. Visual, spectroscopic, coronagraphic, and UV observations of the sun from the ground and from spacecraft, particularly Skylab, are described, together with features of the solar surface, magnetic field, sunspots, and coronal loops. Models for the processes that occur in the solar interior are explored, as are the causes of solar flares. Attention is given to solar cells, heliostat arrays, wind turbines, and water turbines as means to convert, either directly or indirectly, the earth-bound solar energy to electrical and thermal power. Finally, the life cycle of the sun, about 9 billion yr in duration, is summarized, noting the current status of midlife.

Noyes, R. W.

386

UV Spectrum of the Massive X-ray Binary LS 5039  

NASA Astrophysics Data System (ADS)

LS 5039 is a massive X-ray binary with non-thermal radio emission, relativistic jets, and probably high energy Gamma- ray emission. It appears to be one of the closest of the Galactic microquasars, stellar-sized engines that produce relativistic jets like extragalactic quasars. We recently discovered that the system is a 4.1 day binary with a very eccentric orbit {indicating large mass loss in the supernova event that gave birth to the system}. The companion is probably a neutron star, but a black hole companion is viable if the system inclination is small. Here we propose to obtain the first UV observations of the binary to determine fundamental properties about the O6.5 V{{f}} optical star and the mass transfer process. The UV spectrophotometry will allow us to measure accurately the interstellar extinction and system distance, and the unreddened spectrum will provide information on the optical star's effective temperature, spectral classification, and surface abundances. The stellar wind lines in the FUV provide the means to measure the O- star's wind terminal velocity and mass loss rate, and these parameters will allow us to determine if the X-ray luminosity can be generated by wind accretion alone. We plan to observe these wind lines at both orbital conjunction phases to search for evidence of changes in the wind structure caused by proximity to the X-ray source's radiation field, accretion disk wind, and jets.

Gies, Douglas

2002-07-01

387

Estrogenic activity of UV filter mixtures  

SciTech Connect

UV-absorbing chemicals (UV filters) are widely used for protection against UV radiation in sunscreens and in a variety of cosmetic products and materials. Depending on the breadth and factor of UV protection, they are added as single compounds or as a combination thereof. Some UV filters have estrogenic activity, but their activity and interactions in mixtures are largely unknown. In this work, we analyzed 8 commonly used UV filters, which are pure or partial hER{alpha} agonists, for their estrogenic activity in equieffective mixtures in a recombinant yeast assay carrying the human estrogen receptor alpha (hER{alpha}). Mixtures of two, four and eight UV filters alone, or in combination with 17 {beta} estradiol (E2), were assessed at different effect levels and no-observed-effect-concentrations (NOEC). Predictions of the joint effects of these mixtures were calculated by employing the concentration addition (Canada) and independent action (IA) model. Most binary mixtures comprising of pure hER{alpha} agonists showed a synergistic activity at all mixture combinations. Only in combination with benzophenone-1, antagonistic activity was observed at some effect levels. All mixtures of four or eight, pure or pure and partial hER{alpha} agonists, alone or including E2, showed synergistic activity at concentrations giving an increase of 10% of basal activity (BC10). This occurred even at concentrations that were at the NOEC level of each single compound. Hence, there were substantial mixture effects even though each UV filter was present at its NOEC level. These results show that significant interactions occur in UV filter mixtures, which is important for the hazard and risk assessments of these personal care products.

Kunz, Petra Y. [University of Applied Sciences Northwestern Switzerland (FHNW), School of Life Sciences, Institute of Ecopreneurship, Gruendenstrasse 40, CH-4132 Muttenz (Switzerland) and University of Zuerich, Institute of Plant Biology, Limnology, CH-8802 Kilchberg (Switzerland)]. E-mail: petra.kunz@fhnw.ch; Fent, Karl [University of Applied Sciences Northwestern Switzerland (FHNW), School of Life Sciences, Institute of Ecopreneurship, Gruendenstrasse 40, CH-4132 Muttenz (Switzerland) and Swiss Federal Institute of Technology (ETH), Department of Environmental Sciences, CH-8092 Zurich (Switzerland)]. E-mail: karl.fent@bluewin.ch

2006-11-15

388

Triggered Star Formation by Massive Stars  

NASA Astrophysics Data System (ADS)

We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the ? Ori region, Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars and Herbig Ae/Be stars tend to line up between luminous O stars and bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively younger they are. Our positional and chronological study lends support to the validity of the radiation-driven implosion mechanism, where the Lyman continuum photons from a luminous O star create expanding ionization fronts to evaporate and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive pressure then causes dense clumps to collapse, prompting the formation of low-mass stars on the cloud surface (i.e., the bright rim) and intermediate-mass stars somewhat deeper in the cloud. These stars are a signpost of current star formation; no young stars are seen leading the ionization fronts further into the cloud. Young stars in bright-rimmed or comet-shaped clouds are likely to have been formed by triggering, which would result in an age spread of several megayears between the member stars or star groups formed in the sequence.

Lee, Hsu-Tai; Chen, W. P.

2007-03-01

389

Triggered Star Formation by Massive Stars  

E-print Network

We present our diagnosis of the role that massive stars play in the formation of low- and intermediate-mass stars in OB associations (the Lambda Ori region, Ori OB1, and Lac OB1 associations). We find that the classical T Tauri stars and Herbig Ae/Be stars tend to line up between luminous O stars and bright-rimmed or comet-shaped clouds; the closer to a cloud the progressively younger they are. Our positional and chronological study lends support to the validity of the radiation-driven implosion mechanism, where the Lyman continuum photons from a luminous O star create expanding ionization fronts to evaporate and compress nearby clouds into bright-rimmed or comet-shaped clouds. Implosive pressure then causes dense clumps to collapse, prompting the formation of low-mass stars on the cloud surface (i.e., the bright rim) and intermediate-mass stars somewhat deeper in the cloud. These stars are a signpost of current star formation; no young stars are seen leading the ionization fronts further into the cloud. Young stars in bright-rimmed or comet-shaped clouds are likely to have been formed by triggering, which would result in an age spread of several megayears between the member stars or star groups formed in the sequence.

Hsu-Tai Lee; W. P. Chen

2009-02-03

390

Preparation of Ce3+-activated UV-emitting fluoride phosphors  

NASA Astrophysics Data System (ADS)

One step, wet chemical synthesis of several Ce3+ activated fluorides is described. Intense ultraviolet (UV) emission is observed in most cases. It is suggested that this emission can be used to obtain UV-emitting lamps for UV phototherapy.

Belsare, P. D.; Joshi, C. P.; Moharil, S. V.; Kondawar, V. K.; Muthal, P. L.; Dhopte, S. M.

391

Star Formation Histories in CLASH Brightest Cluster Galaxies  

NASA Astrophysics Data System (ADS)

The CLASH sample of 25 lensing galaxy clusters contains 11 Brightest Cluster Galaxies (BCG) that exhibit significant unobscured (>5 Msol yr-1) star formation activity. The star formation is inferred from UV emission and from evidence for H-alpha filaments as detected in the ACS and WFC3 observations. We use photometry from the 16-band CLASH imaging along with spectra from the SOAR and SDSS telescopes to examine the star formation histories of these galaxies. Using SED fits to synthetic stellar population and nebular emission models, we constrain the burst histories of the two most UV and H-alpha luminous BCGs in our sample, RXJ1532.9+3021 and MACS1931.8-2635. The BCG in both of these clusters have reddening-corrected UV estimates of star formation rates in excess of 100 solar masses per year. We model the timescales and sizes of the starbursts that can account for the photometric and spectroscopic properties in these BCGs and create maps of their stellar properties on scales of ~350 pc. These maps reveal recent bursts occurring in elongated filaments on relatively long (~0.5-1.0 Gyr) timescales. In addition, we constrain the star formation properties of all of the remaining BCGs in the CLASH sample. These results and their implications for BCG formation and evolution will be presented.

CLASH Science Team

2015-01-01

392

UV LEDs for high-current operation  

NASA Astrophysics Data System (ADS)

In this paper we report on results of development of ultraviolet light-emitting diodes (UV LEDs) based on GaN/AlGaN heterostructures grown on Al2O3 (0001) substrates by chloride-hydride vapour phase epitaxy (CHVPE). Both UV LED heterostructures and packaged dies are investigated. UV LEDs proved performance capability at current density up to 125 A/cm2 and revealed wall-plug efficiency (WPE) of 1.5% at operating current of 20 mA.

Kurin, S. Yu; Antipov, A. A.; Roenkov, A. D.; Barash, I. S.; Helava, H. I.; Menkovich, E. A.; Tarasov, S. A.; Lamkin, I. A.; Shmidt, N. M.; Makarov, Yu N.

2013-08-01

393

Personal UV biodosimeter for healthy indoor tanning  

NASA Astrophysics Data System (ADS)

The practice of indoor tanning has led to the development of a large artificial tanning industry. In addition to psychological benefits, exposure to UVB light helps the body produce the activated form of vitamin D, which is necessary for many cellular functions. But uncontrolled tanning and UV overexposure can increase the risk of skin cancer. For direct checkout of the vitamin D synthetic capacity of a UV source the bio-equivalent UV dosimeter has been developed that is based on the same molecular photochemistry from which vitamin D is photosynthesized in human skin and makes possible both instrumental and visual indication of vitamin D synthesis.

Terenetskaya, I. P.; Orlova, T. N.

2008-04-01

394

UV Stable High Birefringence Liquid Crystals  

NASA Astrophysics Data System (ADS)

High birefringence and low viscosity nematic liquid crystal single compounds and mixtures were developed and their properties evaluated. The UV stability of the single isothiocyanianes liquid crystal compounds was studied by different methods. Excellent UV durability of some of the single high birefringence isothiocyanianes was discovered. The new eutectic liquid crystal mixtures based on these compounds were tested in comparison to commercial high birefringence Merck’s E44. Our new mixtures exhibit similar birefringence, ˜4 times lower visco-elastic coefficient and significantly better UV stability than E44 mixture.

Gauza, Sebastian; Wen, Chien-Hui; Tan, Bijun; Wu, Shin-Tson

2004-10-01

395

First Spectacular Panoramic UV Images of the Magellanic Clouds from GALEX  

NASA Astrophysics Data System (ADS)

We present the first complete, panoramic ultraviolet maps of the Large and Small Magellanic Clouds obtained from by the Galaxy Evolution Explorer (GALEX) near the end of its mission. These are the deepest and highest quality UV images yet obtained for the Clouds. We present first scientific results including measurements of total and local star formation rates across the Clouds and their outskirts, and a detailed view of specific star-forming regions and the interplay of gas, dust and young stars. We also discuss the novel techniques used to build these maps — a challenge for the standard GALEX — pipeline with observations that routinely far exceeded the GALEX bright source limits. These images provide a powerful legacy data set for the GALEX mission. This work was supported by NASA ADAP grant NNX14AF81G.

Schiminovich, David; Seibert, Mark; GALEX Science Team

2015-01-01

396

Legacy Extragalactic UV Survey (LEGUS) With the Hubble Space Telescope. I. Survey Description  

NASA Astrophysics Data System (ADS)

The Legacy ExtraGalactic UV Survey (LEGUS) is a Cycle 21 Treasury program on the Hubble Space Telescope aimed at the investigation of star formation and its relation with galactic environment in nearby galaxies, from the scales of individual stars to those of ˜kiloparsec-size clustered structures. Five-band imaging from the near-ultraviolet to the I band with the Wide-Field Camera 3 (WFC3), plus parallel optical imaging with the Advanced Camera for Surveys (ACS), is being collected for selected pointings of 50 galaxies within the local 12 Mpc. The filters used for the observations with the WFC3 are F275W(?2704 Å), F336W(?3355 Å), F438W(?4325 Å), F555W(?5308 Å), and F814W(?8024 Å) the parallel observations with the ACS use the filters F435W(?4328 Å), F606W(?5921 Å), and F814W(?8057 Å). The multiband images are yielding accurate recent (?50 Myr) star formation histories from resolved massive stars and the extinction-corrected ages and masses of star clusters and associations. The extensive inventories of massive stars and clustered systems will be used to investigate the spatial and temporal evolution of star formation within galaxies. This will, in turn, inform theories of galaxy evolution and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of star formation at high redshift. This paper describes the survey, its goals and observational strategy, and the initial scientific results. Because LEGUS will provide a reference survey and a foundation for future observations with the James Webb Space Telescope and with ALMA, a large number of data products are planned for delivery to the community. Based on observations obtained with the NASA/ESA Hubble Space Telescope at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy under NASA Contract NAS 5-26555.

Calzetti, D.; Lee, J. C.; Sabbi, E.; Adamo, A.; Smith, L. J.; Andrews, J. E.; Ubeda, L.; Bright, S. N.; Thilker, D.; Aloisi, A.; Brown, T. M.; Chandar, R.; Christian, C.; Cignoni, M.; Clayton, G. C.; da Silva, R.; de Mink, S. E.; Dobbs, C.; Elmegreen, B. G.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gallagher, J. S., III; Gouliermis, D. A.; Grebel, E. K.; Herrero, A.; Hunter, D. A.; Johnson, K. E.; Kennicutt, R. C.; Kim, H.; Krumholz, M. R.; Lennon, D.; Levay, K.; Martin, C.; Nair, P.; Nota, A.; Östlin, G.; Pellerin, A.; Prieto, J.; Regan, M. W.; Ryon, J. E.; Schaerer, D.; Schiminovich, D.; Tosi, M.; Van Dyk, S. D.; Walterbos, R.; Whitmore, B. C.; Wofford, A.

2015-02-01

397

Binary stars.  

PubMed

Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars. PMID:17749544

Paczynacuteski, B

1984-07-20

398

Sun, UV Radiation and Your Eyes  

MedlinePLUS

... cause painful damage called snow blindness . The Sun, UV Radiation and Your Eyes Summer Sun Eye Safety Winter Sun Eye Safety Indoor Tanning Eye Safety Solar Eclipse Eye Safety Snow Blindness Who is at ...

399

Genetics Home Reference: UV-sensitive syndrome  

MedlinePLUS

... making proteins that are involved in repairing damaged DNA. DNA can be damaged by UV rays from the ... free radicals. Cells are usually able to fix DNA damage before it causes problems. If left uncorrected, ...

400

UV RESEARCH - FUNDED AND IN HOUSE EFFORTS  

EPA Science Inventory

The National Risk Management research Laboratory (NRMRL) has performed or funded limited in-house and extramural research on the disinfection of CCL listed organisms using ultraviolet (UV) irradiation. In addition, multiple extramural efforts have been funded to assess operation...

401

UV Curable Coatings in Aluminum Can Production  

E-print Network

based coatings. The Coors Brewing Company Can Manufacturing Plant has been utilizing this technology in full scale aluminum can production since 1975, and therefore has had the opportunity to evaluate practical operations of the UV technology...

Donhowe, E. T.

402

Are Main-Sequence K-type Stars the "Goldilocks" Stars for Hosting Long-term Habitable Planets  

NASA Astrophysics Data System (ADS)

Main-sequence K-type (dwarf K = dK) stars have masses and luminosities ranging from ˜0.6-0.85 M? and ˜0.1-0.45 L?. In addition, dK stars have significantly longer main-sequence lifetimes than our Sun -- lasting ˜20-50 billion yrs. Moreover, these cool, low luminosity orange dwarfs are much more numerous (˜6-10×) than solar-type stars and also have been found to host an increasing number of planets. Their liquid-water habitable zones (HZs) extend from ˜0.4-1.2 AU. Because dK-stars evolve more slowly than G-stars, their HZs are essentially fixed for billions of years. As an extension of the Villanova "Sun in Time" program, we have been studying the suitability of dK stars as hosts to habitable planets. To this end we have measured the coronal X-ray and chromospheric emissions of dK0-8 stars with wide ranges of age, rotation, and magnetic-dynamo generated coronal and chromospheric X-UV activity. We have established well defined age-rotation-activity relations for this sample. We have used archival X-ray (mostly ROSAT) and UV data (from FUSE and IUE). The rotation periods were determined using photometry from starspot modulations. Although their optical luminosities remain essentially fixed up to ˜10+ Gyrs, the magnetic dynamo X-UV radiances decay rapidly with age. Young dK stars rotate rapidly and have correspondingly strong magnetic dynamos and strong coronal X-ray and chromospheric UV emissions (as well as frequent flaring). Here we discuss the suitability of dK stars as hosts for life-supporting planets where long-term life is sustainable and compare them with properties of planets hosted by G and M-type stars. From this study we conclude that these orange dwarf stars may be the best choices for hosting planets with evolved, complex life. This research is supported by grants from NSF/RUI (AST5-07542) and NASA/FUSE (NNG04G0386) which we gratefully acknowledge.

Wolfe, Aaron; Guinan, E. F.; Datin, K. M.; DeWarf, L. E.; Engle, S. G.

2010-01-01

403

The UV Properties of Core Collapse Supernovae  

NASA Astrophysics Data System (ADS)

With the advent of robotic telescope transient surveys in the 1990's, the study of Supernovae (SNe) in the optical and infrared wavelengths underwent a revolution as the number of SNe discovered per year increased by well over an order of magnitude in the ensuing decade. UV studies of these objects lagged behind their optical/NIR counterparts, however, due to a limited observing capability. With the launch of Swift in 2005 a similar revolution took place in the UV as it was finally possible to regularly obtain well-sampled UV and optical observations with the Swift UV/Optical Telescope (UVOT; ?c = 1928, 2246, 2600 Å). In 2007 Swift/UVOT observed SN 2007pk, which was at the time the earliest observed Type IIn SNe in the UV, and whose study led us to understand the need for a more comprehensive sampling of Core Collapse Supernovae (CCSNe) observations than had previously been performed. Using data from Swift’s launch to the end of 2012, we produce a study of the UV characteristics of CCSNe, dependant upon SNe subtype. We find that at early times or around peak magnitude, contingent upon subtype, a majority of the supernovae flux can occur in the UV regime. However, due to ground based observing constraints this flux often goes unmeasured. This missing flux, and associated corrections, has implications for SNe explosion models which use bolometric light curves to examine factors including: supernovae explosion energy, progenitor radius, CSM winds, and metallicity. We then calculate bolometric light curves for this sample of CCSNe, along with empirical UV-corrections from these for bolometric light curves that have been generated without UV data. We then refine these corrections using a smaller sample of Type IIP SNe from the Carnegie Supernovae Project that overlap with Swift observations, resulting in bolometric light curves with a comprehensive UV-NIR coverage. Finally, using recent numerical simulations we compare variations in observed model light curves due to progenitor differences with observed UV data. Support for this work is sponsored at PSU and SwRI by the NASA ADP grant NNX12AE21G.

Pritchard, Tyler A.; Roming, P.

2014-01-01

404

Star formation in the hosts of GHz peaked spectrum and compact steep spectrum radio galaxies  

E-print Network

AIMS: Search for star formation regions in the hosts of potentially young radio galaxies (Gigahertz Peaked Spectrum and Compact Steep Spectrum sources). METHODS: Near-UV imaging with the Hubble Space Telescope Advanced Camera for Surveys.} RESULTS: We find near-UV light which could be the product of recent star formation in eight of the nine observed sources, though other explanations are not currently ruled out. The UV luminosities of the GPS and CSS sources are similar to those of a sample of nearby large scale radio galaxies. Stellar population synthesis models are consistent with a burst of recent star formation occuring before the formation of the radio source. However, observations at other wavelengths and colors are needed to definitively establish the nature of the observed UV light. In the CSS sources 1443+77 and 1814-637 the near-UV light is aligned with and is co-spatial with the radio source. We suggest that in these sources the UV light is produced by star formation triggered and/or enhanced by the radio source.

A. Labiano; C. P. O'Dea; P. D. Barthel; W. H. de Vries; S. A. Baum

2007-01-22

405

STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS  

SciTech Connect

Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 {mu}m, H{alpha}, and UV down to rates of 0.03 M{sub Sun} yr{sup -1}. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 {mu}m and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies.

Tyler, K. D.; Rieke, G. H. [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Bai, L. [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street Room 101, Toronto, Ontario M5S 3H4 (Canada)

2013-08-20

406

UV-B signaling in maize  

PubMed Central

Plants have evolved adaptations to environmental factors, including UV-B present in solar radiation. Deployment of specific adaptive phenotypes to avoid or repair UV-B damage requires physiological and developmental acclimation to variable UV-B fluence. To gain a better understanding of the events in UV-B acclimation, we have analyzed a 5min to 6h time course of transcriptome and metabolome responses in irradiated and shielded leaves and in immature maize ears to unravel the systemic physiological and developmental responses in exposed and shielded organs. Within 10 min of UV-B exposure, transcripts are changed not only in irradiated leaves, but also in shielded tissues. The number of UV-B-regulated transcripts rapidly increases with exposure length. Interestingly, after 10 min of exposure, the overlap in transcriptome changes in irradiated and shielded organs is significant; while, after 6h of UV-B, most transcripts are specific for each tissue under study. We suggest that early events in all tissues may be elicited by common signaling pathways, while at longer exposure times responses become more organ-specific. Our working hypothesis is that mobile signaling molecules are generated in irradiated organs to elicit the initial responses. We found several metabolites that rapidly change after different treatments during the timecourse; myoinositol is one candidate metabolite based on its rapid modulation in all organs. There is also support from RNA profiling: after 1h UV-B, transcripts for myoinositol-1-phosphate synthase are decreased in both irradiated and shielded leaves suggesting downregulation of biogenesis. PMID:22105027

Casati, Paula; Morrow, Darren J.; Fernandes, John; Walbot, Virginia

2011-01-01

407

Reconstruction of solar UV irradiance since 1974  

Microsoft Academic Search

Variations of the solar UV irradiance are an important driver of chemical and\\u000aphysical processes in the Earth's upper atmosphere and may also influence\\u000aglobal climate. Here we reconstruct solar UV irradiance in the range 115-400 nm\\u000aover the period 1974-2007 by making use of the recently developed empirical\\u000aextension of the SATIRE models employing SUSIM data. The evolution of

N. A. Krivova; S. K. Solanki; T. Wenzler; B. Podlipnik

2009-01-01

408

Bactericidal effectiveness of modulated UV light  

SciTech Connect

Studies were designed to evaluate the effectiveness of pulsed modulated UV light waveforms for killing bacteria. Exposure of five strains of bacteria to the modulated information encoded in the light decreased the colony population from a confluent lawn to less than 20 colonies. However, approximately 2,000 colonies survived treatment with the same intensity and time of exposure to UV light lacking the modulated information.

Bank, H.L.; John, J.; Schmehl, M.K.; Dratch, R.J. (Medical Univ. of South Carolina, Charleston (USA))

1990-12-01

409

Electrodeless microwave source of UV radiation  

NASA Astrophysics Data System (ADS)

The parameters of an electrodeless microwave low-pressure discharge in an Ar + Hg vapor mixture are studied, the design of a UV radiation source for water disinfection is suggested, and its main characteristics are presented. The domestic microwave oven ( f = 2.45 GHz; N = kW) is used as a microwave radiation source. The maximal UV power at wavelength ? = 254 nm amounts to 120-130 W.

Barkhudarov, E. M.; Kozlov, Yu. N.; Kossyi, I. A.; Malykh, N. I.; Misakyan, M. A.; Taktakishvili, I. M.; Khomichenko, A. A.

2012-06-01

410

UV-UV hole burning and IR dip spectroscopy of homophenylalanine by laser desorption supersonic jet technique  

NASA Astrophysics Data System (ADS)

Conformer selected electronic and vibrational spectra of homophenylalanine, phenylalanine analogue molecule, were measured by UV-UV hole burning and IR dip spectroscopy combined with laser desorption technique. 10 conformers were found by UV-UV hole burning spectroscopy and their structures were assigned by IR dip and UV absorption spectra with aid of quantum chemical calculations in both S0 and S1. This study shows that the combination of simulated IR and UV spectra is powerful to assign flexible molecules.

Sohn, Woon Yong; Ishiuchi, Shun-ichi; Çarçabal, Pierre; Oba, Hikari; Fujii, Masaaki

2014-12-01

411

Neutrino signatures from the first stars  

SciTech Connect

Evidence from the Wilkinson Microwave Anisotropy Probe (WMAP) polarization data indicates that the Universe may have been reionized at very high redshift. It is often suggested that the ionizing UV flux originates from an early population of massive or very massive stars. Depending on their mass, such stars can explode either as type II supernovae or pair-instability supernovae, or may entirely collapse into a black hole. The resulting neutrino emission can be quite different in each case. We consider here the relic neutrino background produced by an early burst of Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z < or approx. 6, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at z{approx}10-20. We find that although the high redshift burst of Population III stars does lead to an appreciable flux of neutrinos at relatively low energy (E{sub {nu}}{approx_equal}1 MeV), the observable neutrino flux is dominated by the normal mode of star formation. We also find that predicted fluxes are at the present level of the SuperK limit. As a consequence, the supernova relic neutrino background has a direct impact on models of chemical evolution and/or supernova dynamics.

Daigne, Frederic; Vangioni, Elisabeth [Institut d'Astrophysique de Paris, UMR 7095, CNRS, Universite Pierre et Marie Curie-Paris VI, 98 bis bd Arago, F-75014, Paris (France); Olive, Keith A. [William I. Fine Theoretical Physics Institute, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Sandick, Pearl [Department of Physics, School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455 (United States)

2005-11-15

412

The Rest-frame Ultraviolet Spectra of UV-selected Active Galactic Nuclei at z ~ 2-3  

NASA Astrophysics Data System (ADS)

We present new results for a sample of 33 narrow-lined UV-selected active galactic nuclei (AGNs), identified in the course of a spectroscopic survey for star-forming galaxies at z ~ 2-3. The rest-frame UV composite spectrum for our AGN sample shows several emission lines characteristic of AGNs, as well as interstellar absorption features detected in star-forming Lyman break galaxies (LBGs). We report a detection of N IV] ?1486, which has been observed in high-redshift radio galaxies, as well as in rare optically selected quasars. The UV continuum slope of the composite spectrum is significantly redder than that of a sample of non-AGN UV-selected star-forming galaxies. Blueshifted Si IV absorption provides evidence for outflowing highly ionized gas in these objects at speeds of ~103 km s-1, quantitatively different from what is seen in the outflows of non-AGN LBGs. Grouping the individual AGNs by parameters such as the Ly? equivalent width, redshift, and UV continuum magnitude allows for an analysis of the major spectroscopic trends within the sample. Stronger Ly? emission is coupled with weaker low-ionization absorption, which is similar to what is seen in the non-AGN LBGs, and highlights the role that cool interstellar gas plays in the escape of Ly? photons. However, the AGN composite does not show the same trends between Ly? strength and extinction seen in the non-AGN LBGs. These results represent the first such comparison at high redshift between star-forming galaxies and similar galaxies that host AGN activity. Based, in part, on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

Hainline, Kevin N.; Shapley, Alice E.; Greene, Jenny E.; Steidel, Charles C.

2011-05-01

413

Synthesis of UV-curable tung oil and UV-curable tung oil based alkyd  

Microsoft Academic Search

Two UV-curable tung oil-based resins were synthesized via a Diels–Alder cycloaddition. An UV-curable tung oil (UVTO) was prepared from bodied tung oil and trimethylolpropane trimethacrylate (TMPTMA). An inhibitor, phenothiazine, was added to avoid homopolymerization of TMPTMA. The UV-curable tung oil alkyd (UVTA) was prepared from the monoglyceride process and then reacted with TMPTMA via the Diels–Alder reaction similar to the

Narin Thanamongkollit; Kent R. Miller; Mark D. Soucek

414

A survey of ultraviolet circumstellar absorption lines in the spectra of early Be and shell stars  

NASA Technical Reports Server (NTRS)

Copernicus UV data are used to examine the rich shell absorption spectra between 1120 and 1140 A in 17 Be and shell stars. Previous observations of the program stars are reviewed, the general appearance of the shell spectra between 1120 and 1140 A is described, and the shell spectra are compared with the spectra of four bright B-type supergiants in the same wavelength region. The line strengths are analyzed to determine quantitative shell strengths and shell column densities; the shell line velocities are discussed in the context of different models. It is shown that UV shell lines can exist in stars with no visible-wavelength shell features, that Fe III shell lines dominate the spectra between 1120 and 1140 A in Be and shell stars with circumstellar absorption features, and that the spectra of Be and shell stars in this region strongly resemble those of supergiants of similar effective temperature.

Snow, T. P., Jr.; Mathieu, R. D.; Peters, G. J.

1979-01-01

415

A Swift/UVOT NUV Study of RR Lyrae Stars in the Globular Cluster M3  

NASA Astrophysics Data System (ADS)

We present the first results of a program to monitor RR Lyrae stars in globular clusters with the Swift Ultraviolet Optical Telescope. Although variable stars have their strongest pulsations in the UV, no comprehensive catalog of NUV light curves has ever been produced for RR Lyrae stars. We present uvm2 light curves for 124 variable star candidates in the globular cluster M3. We show that the RR Lyrae stars have strong pulsations in the NUV, with amplitudes up to three magnitudes. We show that the RR Lyrae follow period-amplitude relations in the NUV similar to those they follow in the optical. Our data hint at the existence of a period-metallicity-luminosity relationship in the UV that would make RR Lyrae even more useful standard candles.

Porterfield, Blair; Siegel, M.; Swift; UVOT

2014-01-01

416

Star formation in infrared bright and infrared faint starburst interacting galaxies  

NASA Technical Reports Server (NTRS)

Short wavelength IUE spectra of Arp 248b and UGC 8315N are combined with optical spectra and interpreted using a combination of spectrum synthesis and spectral diagnostics to place constraints on the massive star populations of the central regions of these galaxies and to deduce information about the star formation histories in the last 10(exp 8) years. The authors find that both galaxies have substantial fractions of their optical light coming from massive stars and that Arp 248b may be dominated in the UV by WR stars. The UV spectra are dominated by radiation from evolved massive stars and the authors place and age on the burst in Arp 248b of a few tens of millions of years.

Lamb, Susan A.; Bushouse, Howard A.; Towns, John W.

1990-01-01

417

Relation between UV suppression of polarity in phi X174 and UV sensitivity of rho mutants.  

PubMed

The suppression of polarity by UV irradiation was similar to the suppression by rho mutants. This was demonstrated for a polar nonsense mutant of phage phi X174. Treatment of the host for 30 min with 100 micrograms of the radiomimetic drug mitomycin C per ml was about as effective as 550 J of UV irradiation per m2 in relieving polarity. The shape of the UV survival curves for rho mutants could be linked to a proposed mechanism of UV relief of polarity. Host cell reactivation of phage lambda and W-reactivation of phage G4 were unaffected by rho mutations. UV suppression of polarity is independent of the Hcr- and RecA- phenotypes. An explanation for the UV sensitivity of rho mutants is provided, and several ways are considered in which UV irradiation may deplete cellular rho activity and thereby cause UV relief of polarity. We propose a novel theory that relates the UV inactivation of normal repair-proficient cells to a decrease in rho activity. PMID:6453239

Fassler, J S; Tessman, I

1981-03-01

418

Star Search  

NSDL National Science Digital Library

In this online activity, learners can test their skills at finding constellations in the northern hemisphere's night sky. Learners can choose during which season to look, and then look for four constellations in that season. The simulation shows a simple representation of the night sky with key stars highlighted. Use this as a practice before going outside or just to give learners an idea of the difficulties involved in identifying constellations. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.

Science, American A.

2009-01-01

419

Detection of H2 Emission from Mira B in UV Spectra from the Hubble Space Telescope  

E-print Network

We present ultraviolet spectra of Mira's companion star from the Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope (HST). The companion is generally assumed to be a white dwarf surrounded by an accretion disk fed by Mira's wind, which dominates the UV emission from the system. The STIS UV spectrum is dominated by numerous, narrow H2 lines fluoresced by H I Ly-alpha, which were not detected in any o