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1

A search for X rays from UV Ceti flare stars  

NASA Technical Reports Server (NTRS)

A search of the MIT/OSO-7 data has been made for evidence of X-ray emission from flares of UV Ceti flare stars. Observations from McDonald Observatory have been used to identify the times of optical flares. The only instance of coincident coverage occurred on 1974, January 21, UT at 03:43:26 GMT for a flare of YZ CMi with a u magnitude increment of 0.86. No radio coverage of this particular event was obtained. Upper limits (3 sigma) of 0.8, 1.0, and 0.7 photons/sq cm sec on the observed X-ray flux have been set for the energy ranges greater than 15, greater than 3, and 1-10 keV, respectively.

Crannell, C. J.; Markert, T. H.; Moffett, T. J.; Spangler, S. R.

1975-01-01

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

Simultaneous radio and optical observations of UV Ceti-type flare stars  

NASA Technical Reports Server (NTRS)

The UV Ceti-type stars, YZ Canis Minoris, AD Leonis, and Wolf 424 AB, were monitored for 57.8 hours from January 15 to February 22, 1974, using the 1000-foot (305-m) radio telescope at Arecibo, Puerto Rico, and the 91-cm or 76-cm reflector at McDonald Observatory. Radio observations were made at frequencies of 430, 318, and 196 MHz, and optical monitoring was done in the Johnson U or B band, the Stromgren u band, or white light. During the period of simultaneous observations, 62 optical flares were detected. A total of 13 RF flares were independently identified, of which 10 reached maximum flux within 10 min of the peak time of an optical flare. Using times of optical-flare events as reference data, an additional 15 cases of radio enhancements associated with optical flares are identified. The most probable delay interval between the optical-flare maximum and 318-MHz radio peak was found to be 0 to 5 min, with the optical flare occurring first. Aside from this statistical delay of peak occurrence and a general tendency for radio and optical flares to be associated, no systematic correlations of optical and radio amplitudes or morphology were found. The possible consequences of the radio emission's being due to a coherent process are discussed.

Spangler, S. R.; Moffett, T. J.

1976-01-01

5

Does UV Ceti Suffer from the MAD Syndrome?  

NASA Astrophysics Data System (ADS)

We propose to obtain an EUV spectrum of the nearby flare star UV Ceti with the EUVE spectrometer. UV Ceti is the lowest mass star within the reach of the EUVE spectrometer, and it is of particular interest to study this protypical flare star with respect to recent suggestions of elemental underabundances of active stars. Our spectral analysis of X-ray spectra of UV Ceti obtained with the ROSAT PSPC and ASCA SIS does suggest significant metal underabundances, however, these analyses heavily rely on the spectral modelling of - in comparison to the spectral resolution achievable with EUVE - lower resolution data. In addition we expect to be able to derive differential emission measure distributions and coronal densities if the Fe XIV lines at 211 and 264 Angstroms can be detected. Finally, the proposed EUVE observations of UV Ceti will provide an unprecedented opportunity to study the coronal output on time scales from hours to weeks.

Drake, Jeremy J.

6

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

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

NEW CHEMICAL PROFILES FOR THE ASTEROSEISMOLOGY OF ZZ CETI STARS  

SciTech Connect

We compute new chemical profiles for the core and envelope of white dwarfs appropriate for pulsational studies of ZZ Ceti stars. These profiles are extracted from the complete evolution of progenitor stars, evolved through the main sequence and the thermally pulsing asymptotic giant branch (AGB) stages, and from time-dependent element diffusion during white dwarf evolution. We discuss the importance of the initial-final mass relationship for the white dwarf carbon-oxygen composition. In particular, we find that the central oxygen abundance may be underestimated by about 15% if the white dwarf mass is assumed to be the hydrogen-free core mass before the first thermal pulse. We also discuss the importance for the chemical profiles expected in the outermost layers of ZZ Ceti stars of the computation of the thermally pulsing AGB phase and of the phase in which element diffusion is relevant. We find a strong dependence of the outer layer chemical stratification on the stellar mass. In particular, in the less massive models, the double-layered structure in the helium layer built up during the thermally pulsing AGB phase is not removed by diffusion by the time the ZZ Ceti stage is reached. Finally, we perform adiabatic pulsation calculations and discuss the implications of our new chemical profiles for the pulsational properties of ZZ Ceti stars. We find that the whole g-mode period spectrum and the mode-trapping properties of these pulsating white dwarfs as derived from our new chemical profiles are substantially different from those based on chemical profiles widely used in existing asteroseismological studies. Thus, we expect the asteroseismological models derived from our chemical profiles to be significantly different from those found thus far.

Althaus, L. G.; Corsico, A. H.; Romero, A. D.; Miller Bertolami, M. M. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, (1900) La Plata (Argentina); Bischoff-Kim, A. [Department of Chemistry, Physics and Astronomy, CBX 82, Georgia College and State University, Milledgeville, GA 31061 (United States); Renedo, I.; Garcia-Berro, E., E-mail: althaus@fcaglp.unlp.edu.a [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, c/Esteve Terrades 5, 08860 Castelldefels (Spain)

2010-07-10

9

New analysis of ZZ Ceti star PG 2303+243  

NASA Astrophysics Data System (ADS)

The new photometric observations of PG 2303+243 were obtained in 2012 during a campaign carried out with three telescopes. The analysis of these observations is presented in this paper. We identified l = 1 and l = 2 pulsation modes. The pulsation periods were compared with theoretical ones for models of ZZ Ceti stars. This allowed us to estimate the physical parameters of PG 2303+243. The star seems to be cooler and has thicker hydrogen layer than it was thought before. We have derived M */M ? = 0.66, T eff = 11014 K and log(M H/M *)=-4.246 for this star.

Pakštien?, E.; Laugalys, V.; Qvam, J.; Boyle, R. P.

2014-02-01

10

New chemical profiles for the asteroseismology of ZZ Ceti stars  

E-print Network

We compute new chemical profiles for the core and envelope of white dwarfs appropriate for pulsational studies of ZZ Ceti stars. These profiles are extracted from the complete evolution of progenitor stars, evolved through the main sequence and the thermally-pulsing asymptotic giant branch (AGB) stages, and from time-dependent element diffusion during white dwarf evolution. We discuss the importance of the initial-final mass relationship for the white dwarf carbon-oxygen composition. In particular, we find that the central oxygen abundance may be underestimated by about 15% if the white dwarf mass is assumed to be the hydrogen-free core mass before the first thermal pulse. We also discuss the importance for the chemical profiles expected in the outermost layers of ZZ Ceti stars of the computation of the thermally-pulsing AGB phase and of the phase in which element diffusion is relevant. We find a strong dependence of the outer layer chemical stratification on the stellar mass. In particular, in the less massi...

Althaus, L G; Bischoff-Kim, A; Romero, A D; Renedo, I; García-Berro, E; Bertolami, M M Miller

2010-01-01

11

Seismological studies of ZZ Ceti stars. I. The model grid and the application to individual stars  

E-print Network

We calculate and explore an extensive adiabatic model grid for pulsating white dwarfs with H dominated atmospheres, the ZZ Ceti stars. We also compared the computed modes with the observed ones for five ZZ Ceti stars that are a representative sample of the whole class of pulsators. We describe our new approach for seismological studies, using the relative observed amplitudes to give weights for the periods in the fit and the external mass and temperature determinations as a guide. Our seismological study is clear evidence that seismology is indeed a powerful tool in the study of stellar structure and evolution.

B. G. Castanheira; S. O. Kepler

2007-12-12

12

An Inventory of Gas in a Debris Disk: Far-UV Spectroscopy of 49 Ceti  

NASA Astrophysics Data System (ADS)

Debris disks stand between gas-rich protoplanetary disks and mature planetary systems, shedding light on the late stages of planetary system formation. Their dust component has been extensively studied, yet has provided little information about disk chemical composition. More information can be provided by their gas content, but astonishingly little is known about it. Only one debris disk has a fairly complete inventory of its gas, which is surprisingly carbon-rich {Beta Pictoris; Roberge et al. 2006}. Basic questions remain unanswered. What are the typical gas-to-dust mass ratios in debris disks? What is the chemical composition of debris gas and its parent material? The answers to these questions have profound implications for terrestrial planet assembly and the origins of planetary atmospheres.Most detections of debris gas were achieved with line-of-sight UV/optical absorption spectroscopy of edge-on disks, using the central star as the background source. This technique is far more sensitive to small amounts of gas than current emission line studies. The far-UV bandpass is particularly important, since strong transitions of abundant atomic, ionic, and molecular species lie there. We propose extending our intriguing studies of the Beta Pic gas with STIS far-UV spectroscopy of a highly promising debris disk system, 49 Ceti. This well-known disk is edge-on and contains CO gas {e.g. Hughes et al. 2008}. We plan to measure column densities of the most important gas species {CI, CII, OI, CO, SiII, and FeII}, find the relative elemental gas abundances, and determine the total gas mass using a powerful gas disk modeling code {ProDiMo; Woitke, Kamp, & Thi 2009}.

Roberge, Aki

2012-10-01

13

The Pulsations of Zz-Ceti Stars - Part Six - the Amplitude Spectra  

NASA Astrophysics Data System (ADS)

Amplitude spectra of the fight curves of ZZ Ceti stars often show peaks at harmonic frequencies and at `cross-frequencies' which are related to the frequencies of the dominant peaks by expressions of the form ?mf1 + nf2? where m and n are small integers and f1, f2 are the frequencies of the dominant peaks. These peaks can be understood in terms of a model of the ionization zone of a pulsating ZZ Ceti star which has been described in previous papers. For stars where the (rotational) fine structure of the amplitude spectra is resolved, comparison with the model calculations provides a means of identifying the degree l of the excited modes.

Brickhill, A. J.

1992-12-01

14

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

15

Preliminary identification of the observed pulsation modes of ZZ Ceti star KUV 03442+0719  

NASA Astrophysics Data System (ADS)

KUV 03442+0719 is a ZZ Ceti star originally discovered in 2005. We performed observations for it in 2010, 2011 and 2012. From the three years’ Fourier transform spectra, a total number of 43 pulsation periods are detected. We found out a set of complete quintuplets, five sets of incomplete quintuplets and two sets of incomplete triplets among these periods. They are interpreted as rotational splits of l=2 and l=1 modes. We thus derive a mean rotation period of 6.71 ± 0.11 h from the values of splitting spacing. We perform asymptotic analysis to get preliminary identification of the observed pulsation modes.

Su, J.; Li, Y.; Fu, J.-N.

2014-11-01

16

Seismological procedures for ZZ Ceti stars and an application to G 117-B15A  

SciTech Connect

In this paper, we outline the procedure for seismological analysis of the ZZ Ceti stars, which are pulsating white dwarfs with hydrogen atmospheres. We use G 117-B15A as the example for this process and derive constraints on the mass and internal structure. The hydrogen layer mass is either about 10(-4)M* or 10(-7)M* depending on whether the l = 1 mode near 215 s is k = 2 or k = 1, respectively. In both cases, the best fitting mass is 0.60M solar, in agreement with spectroscopic log g values.

Bradley, P.A.

1997-06-01

17

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

18

Gamma Ray Bursts and CETI  

E-print Network

Gamma ray burst sources are isotropically distributed. They could be located at distances $\\sim 1000$ AU. (Katz \\cite{JK92}) GRB signals have many narrow peaks that are unresolved at the millisecond time resolution of existing observations. \\cite{JK87} 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 confirm?) the speculative hypothesis that GRB = CETI.

Frank D. Smith Jr

1993-02-10

19

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

20

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

21

New evolutionary models for massive ZZ Ceti stars. II. The effects of crystallization on their pulsational properties  

NASA Astrophysics Data System (ADS)

In view of recent claims that asteroseismology could supply invaluable insight into the crystallization process occurring in the interiors of massive white dwarf stars, we present in this work new pulsational calculations for improved carbon-oxygen DA white dwarf models suitable for the study of massive ZZ Ceti stars. The background models employed in this study, presented in detail in a recent paper by Althaus et al. (\\cite{Althaus2003}, A&A, 404, 593), are the result of the complete evolution of massive white dwarf progenitors from the zero-age main sequence through the Asymptotic Giant Branch (AGB) and mass loss phases to the white dwarf regime. Abundance changes are accounted for by means of a full coupling between nuclear evolution and time-dependent mixing due to convection, salt fingers, and diffusive overshoot. In addition, time-dependent element diffusion for multicomponent gases has been considered during the white dwarf evolution. Crystallization and chemical rehomogenization due to phase separation upon crystallization in the core of our models have been fully considered. The effects of crystallization on the period spectrum of these massive white dwarf models are assessed by means of a detailed pulsational analysis of linear, nonradial, adiabatic gravity modes. To properly account for the effects of the presence of a solid phase in the models we impose special conditions on the oscillation eigenfunctions at the solid-liquid interface. We find that the theoretical pulsation spectrum is strongly modified when crystallization is considered, in particular concerning the mode trapping properties of the equilibrium models. We show that the strong mode trapping seen in the models with overshooting can be reproduced by means of a simple analytical model. We also discuss at some length the implications of our study for BPM 37093, the most massive ZZ Ceti star presently known. In particular, we attempt to place constraints on the physical processes occurring prior to the formation of this white dwarf. We find that if BPM 37093 has a stellar mass of ?1.00 M?, its observed spectrum could bear the signature of overshoot episodes during the helium core burning.

Córsico, A. H.; Althaus, L. G.; Montgomery, M. H.; García-Berro, E.; Isern, J.

2005-01-01

22

UV habitable zones around M stars  

Microsoft Academic Search

During the last decade there was a change in paradigm, which led to consider that terrestrial-type planets within liquid-water habitable zones (LW-HZ) around M stars can also be suitable places for the emergence and evolution of life. Since many dMe stars emit large amount of UV radiation during flares, in this work we analyze the UV constrains for living systems

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas

2007-01-01

23

UV Astronomy: Stars from Birth to Death  

Microsoft Academic Search

The Joint Discussion on UV Astronmy: Stars from Birth to Death was held during the IAU General Assembly of 2006, in August 2006. It was aimed to provide a forum where the accomplishments of UV astrophysics could be highlighted and a new roadmap for the future discussed. This meeting focussed in particular on stellar astrophysics. The understanding of stellar physics

Ana I. Gómez de Castro; Martin A. Barstow

2007-01-01

24

Ceti Mensa  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site]

Released 1 June 2004 This image was collected January 29, 2004 during southern summer season. The local time at the image location was about 4 pm. The image shows an area in the Ceti Mensa region.

The THEMIS VIS camera is capable of capturing color images of the martian surface using its five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from the use of multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

Image information: VIS instrument. Latitude -5.2, Longitude 283.6 East (76.4 West). 38 meter/pixel resolution.

Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

2004-01-01

25

Characterizing the pulsations of the ZZ Ceti star KUV 02464+3239  

E-print Network

We present the results on period search and modeling of the cool DAV star KUV 02464+3239. Our observations resolved the multiperiodic pulsational behaviour of the star. In agreement with its position near the red edge of the DAV instability strip, it shows large amplitude, long period pulsation modes, and has a strongly non-sinusoidal light curve. We determined 6 frequencies as normal modes and revealed remarkable short-term amplitude variations. A rigorous test was performed for the possible source of amplitude variation: beating of modes, effect of noise, unresolved frequencies or rotational triplets. Among the best-fit models resulting from a grid search, we selected 3 that gave l=1 solutions for the largest amplitude modes. These models had masses of 0.645, 0.650 and 0.680 M_Sun. The 3 `favoured' models have M_H between 2.5x10^-5 - 6.3x10^-6 M_* and give 14.2 - 14.8 mas seismological parallax. The 0.645 M_Sun (11400 K) model also matches the spectroscopic log g and T_eff within 1 sigma. We investigated th...

Bognár, Z; Bradley, P A; Bischoff-Kim, A

2009-01-01

26

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

27

Understanding the dynamical structure of pulsating stars. HARPS spectroscopy of the ? Scuti stars ? Puppis and DX Ceti  

NASA Astrophysics Data System (ADS)

Context. High-resolution spectroscopy is a powerful tool to study the dynamical structure of a pulsating star's atmosphere. Aims: We aim at comparing the line asymmetry and velocity of the two ? Sct stars ? Pup and DX Cet with previous spectroscopic data obtained on classical Cepheids and ? Cep stars. Methods: We obtained, analysed and discuss HARPS high-resolution spectra of ? Pup and DX Cet. We derived the same physical quantities as used in previous studies, which are the first-moment radial velocities and the bi-Gaussian spectral line asymmetries. Results: The identification of f = 7.098 d-1 as a fundamental radial mode and the very accurate Hipparcos parallax promote ? Pup as the best standard candle to test the period-luminosity relations of ? Sct stars. The action of small-amplitude nonradial modes can be seen as well-defined cycle-to-cycle variations in the radial velocity measurements of ? Pup. Using the spectral-line asymmetry method, we also found the centre-of-mass velocities of ? Pup and DX Cet, V? = 47.49 ± 0.07 km s-1 and V? = 25.75 ± 0.06 km s-1, respectively. By comparing our results with previous HARPS observations of classical Cepheids and ? Cep stars, we confirm the linear relation between the atmospheric velocity gradient and the amplitude of the radial velocity curve, but only for amplitudes larger than 22.5 km s-1. For lower values of the velocity amplitude (i.e., <22.5 km s-1), our data on ? Pup seem to indicate that the velocity gradient is null, but this result needs to be confirmed with additional data. We derived the Baade-Wesselink projection factor p = 1.36 ± 0.02 for ? Pup and p = 1.39 ± 0.02 for DX Cet. We successfully extended the period-projection factor relation from classical Cepheids to ? Scuti stars. This work is based on observations made with the 3.6 m telescope at La Silla Observatory under the ESO Large Programme LP185.D-0056.

Nardetto, N.; Poretti, E.; Rainer, M.; Guiglion, G.; Scardia, M.; Schmid, V. S.; Mathias, P.

2014-01-01

28

Updates on the Asteroseismological Study of the ZZ Ceti Star R548: Determination of the Bulk Core Composition  

NASA Astrophysics Data System (ADS)

We present a progress report on the detailed asteroseismological analysis of the pulsating white dwarf R548 with the use of the forward method. ZZ Ceti variables are nonradially g-mode pulsating white dwarfs with a hydrogen-dominated atmosphere. The low-amplitude and "simple" pulsator R548 is an ideal candidate for carrying on a complete asteroseismological analysis as five independent frequencies are unequivocally singled out. Using the successful double-optimization technique that has been applied and refined on pulsating hot B subdwarfs for more than a decade, we are capable of unraveling global structural parameters. Taking advantage of independent measurements of spectroscopic temperature and surface gravity, we investigate the constraints on the envelope layering and the bulk composition of the core of R548.

Giammichele, N.; Fontaine, G.; Brassard, P.

2014-04-01

29

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

30

The Challenge of Explaining the Nonlinear Features in the Light Curve of the ZZ Ceti Star G117-B15A  

NASA Astrophysics Data System (ADS)

We present our response to a challenge raised publicly during the Barcelona EUROWD08 workshop concerning the modeling of nonlinearities observed in the light curves of pulsating white dwarfs. We have been able to explain quite successfully the nonlinear structure observed in the ZZ Ceti star G117-B15A, which was chosen at the outset because it was supposed to be an easy case. This was done on the basis of the nonlinear approach developed in Brassard, Fontaine, & Wesemael (1995), which includes explicitly the nonlinear response of the emergent flux to temperature variations, unlike the method used by our respected opponent, Dr. Mike Montgomery. The latter did not provide a response in Tübingen, so we must presume that he has not pursued this any further. Anticipating that this could happen, we did test on our own the method proposed by our opponent, only to find out that it is impossible, on its basis, to reproduce quantitatively the nonlinear structure observed in the ``easy star'' G117-B15A. Our point is that the nonlinear response of the flux should never be neglected in modeling of this kind.

Fontaine, G.; Brassard, P.

2010-11-01

31

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

32

The UV-Bright Stars of Omega Centauri  

NASA Astrophysics Data System (ADS)

During the first flight of the ASTRO observatory in 1990 December, we obtained a 1620 A image of the globular cluster Omega Centauri using the Ultraviolet Imaging Telescope (UIT). This image revealed that Omega Cen contains a rich population of "UV-bright" stars. We have previously obtained IUE spectra of six UV-bright stars discovered on the UIT image and have found a variety of spectra probably indicative of different evolutionary states. Two stars (ROA 5342 and Dk 3873) have sdO spectra indicative of very high temperatures, while the two core UV-bright stars have spectra similar to main-sequence B stars. Only one star (ROA 3596) appears have the luminosity expected of a classical post-AGB star. We now propose to obtain IUE low-dispersion spectra of four additional UV bright stars in Omega Cen. Three of the stars (UIT-151, UIT-1435 and Dickens 3089) are known from comparison of UIT and ground-based photometry to be quite hot (>> 20000 K) although such broad-band photometry can only set a lower limit on their effective temperature. We will use the IUE spectra to determine the effective temperature and luminosity of these stars, in order to help determine their evolutionary status. Our combined survey of 11 UV-bright stars in a single cluster should yield insights concerning the late evolution of low mass stars, and may provide clues to the origin of the ultraviolet light in elliptical galaxies.

Landsman, Wayne B.

33

The UV-Bright Stars of Omega Centauri  

NASA Astrophysics Data System (ADS)

During the first flight of the ASTRO observatory in 1990 December, we obtained a 1620 A image of the globular cluster Omega Centauri using the Ultraviolet Imaging Telescope (UIT). This image revealed that Omega Cen contained numerous "UV-bright" stars. We subsequently obtained IUE discretionary time to study two UV-bright stars found within 2' of the center of Omega Cen. We found that these stars were insufficiently luminous to be postAGB stars, and suggested that they could be evolved hot horizontal branch stars or postearly AGB stars. We now propose to obtain IUE low-dispersion spectra of four additional UV-bright stars in Omega Cen. Three of the stars (ROA 5342, ROA 5857, and Dickens 3873) are known from comparison of UIT and ground-based photometry to be quite hot (>> 20000 K) although such broad-band photometry can only set a lower limit on their effective temperature. We will use the IUE spectra to determine the effective temperature and luminosity of these stars, in order to help determine their evolutionary status. Our results will yield insights concerning the the late evolution of low mass stars, and may provide clues to the origin of the ultraviolet light in elliptical galaxies.

Landsman, Wayne B.

34

A Complete UV Atlas of Standard Stars  

NASA Technical Reports Server (NTRS)

The general objective of this project is to provide a comprehensive ultraviolet spectral atlas of stars based on the data in the IUE Final Archive. The data have been uniformly processed by the IUE 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. Our new atlas, therefore, provides more uniform and accurate data than the version previously published. In addition, considerable efforts were devoted to obtain reliable spectral types, V,B-V, and E(B-V). Our goal is to provide the information which can be used with reasonable confidence by scientists.

Wu, Chi-Chao

2000-01-01

35

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

36

Suggested UV spectral classification criteria for A stars  

NASA Technical Reports Server (NTRS)

Criteria for determining effective temperature and electron density independently of abundances, for A, late B, and F stars are given. Comparison of IUE data with standard classification techniques, shows that for late B and A stars, temperature classification by UV spectra is more sensitive than classification using visual spectra. The long wavelength wing of the Lyman is recommended for these stars. For A and F stars, the ratio of the Mg (2580 A) and Mg+ (2800A) resonance lines gives a good temperature/electron density (ne) criterion which is nearly independent of metal abundance (Z). The SiI discontinuities give an excellent temperature classification for A and F stars, but it is dependent on Z and ne. If the absolute intensities of either of the Mg lines are added to the criteria, three classification criteria for a three dimensional classification, according to temperature, ne and Z, are obtained.

Boehm-Vitense, E.

1982-01-01

37

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

38

Physical Properties of Known Exoplanet and Host Stars Within Ten Parsecs: X-ray/UV Fluxes, Rotation, Ages, and Potential of Habitability  

NASA Astrophysics Data System (ADS)

We have compiled a catalogue of all exoplanets and their host stars within ten parsecs (32.6 ly) from the Sun. In addition to the physical properties of the exoplanets: estimated mass, orbital period, etc; we have compiled the properties of the host stars. These include: spectral class, effective temperature, luminosity, metallicity, period of rotation, etc. For the stars that have X-Ray observations and UV spectrophotometry, we have measured the X-UV irradiances at the distance of the exoplanets orbiting them. In addition, we estimated the ages of the stellar systems using our Rotation-Age-Activity relationship developed at Villanova over the last ten years. These results were used to evaluate the potential habitability of the exoplanets with particular attention is paid to stars with Super-Earth planets orbiting within the habitable zones of their host stars. These include GJ 581, GJ 876, Tau Ceti, and HD 20794. We focus on the GJ 581 system, since it contains at least two Super-Earth exoplanets on the inner and outer boundaries of the habitable zone (GJ 581c and GJ 581d respectively), and because the host star has recently been observed with the SWIFT satellite and detected to be an X-Ray source with a log(LX 26.1 erg/s (Vitale and France A&A 2013). We also utilized the recently secured FUV-UV HIST/COS spectrophotometry (France et al. ApJ 2013) to compute X-Ray to UV irradiances at GJ 581c and GJ 581d. In addition to the XUV irradiance studies, we have estimated the age of the GJ 581 system from the: rotational period, Lyman Alpha Emission, Mg-II emission, Ca-II emission; using our Rotation-Age-Activity relationship from our Living with a Red Dwarf program. We calculate an average age determination of 7.5±2 Gyr. We discuss how these results affect the relevance of these stars as potential destinations of interstellar travel in the future. We acknowledge the support for this study from NSF/RUI grant AST-1009903, and NASA/CHANDRA GO1-12024X, GO2-13020X and HST-GO-13020.01-A.

Kullberg, Evan; Guinan, E. F.; Engle, S. G.

2014-01-01

39

Symbiotic stars in X-rays and UV  

NASA Astrophysics Data System (ADS)

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. I will describe the detection with the Swift/XRT of 14 white dwarf symbiotics that were not previously known to be X-ray sources. The 14 new X-ray detections were the result of a survey of more than 50 symbiotic stars using Swift fill-in programs during three years. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. Simultaneous Swift/UVOT data allowed us to find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, the UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk.

Luna, G. J. M.; Sokoloski, J. L.; Mukai, K.; Nelson, T.; Nuñez, N. E.

2014-10-01

40

On the Purity of the ZZ Ceti Instability Strip: Discovery of More Pulsating DA White Dwarfs on the Basis of Optical Spectroscopy  

NASA Astrophysics Data System (ADS)

We report the discovery of two new ZZ Ceti pulsators, LP 133-144 and HE 1258+0123, selected on the basis of model atmosphere fits to optical spectroscopic data. The atmospheric parameters for LP 133-144 (Teff=11,800+/-200 K and logg=7.87+/-0.05) and for HE 1258+0123 (Teff=11,410+/-200 K and logg=8.04+/-0.05) place them within the empirical boundaries of the ZZ Ceti instability strip. This brings the number of known ZZ Ceti stars to a total of 36, a quarter of which have now been discovered using the spectroscopic approach for estimating their atmospheric parameters. This method has had a 100% success rate so far in predicting the variability of candidate ZZ Ceti stars. We have also analyzed additional spectra of known nonvariable white dwarfs in the vicinity of the ZZ Ceti instability strip. Our study further strengthens the idea that ZZ Ceti stars occupy a pure region in the logg-Teff plane, a region where no nonvariable stars are found. This result supports the thesis that ZZ Ceti pulsators represent a phase through which all DA stars must evolve. Based, in part, on observations gathered at the European Southern Observatory, La Silla, Chile.

Bergeron, P.; Fontaine, G.; Billères, M.; Boudreault, S.; Green, E. M.

2004-01-01

41

Chromospheres of Various Cool Stars from Models of the UV  

NASA Astrophysics Data System (ADS)

One important clue to the physical mechanism of chromospheric heating in the Sun is provided by the well-known widespread presence of chromospheres in most cool stars. Recent UV observations are shedding more light into the characteristics of these chromospheres and transition-regions. The physical modeling of these, combined with the older, observations provides much less ambiguous constraints than the Ca II line and other visible data could provide. We are building this new generation of models that are providing interesting trends that give clues on the atmospheric parameters where physical mechanisms of chromospheric and coronal heating operate.We will present some of the current results and will point to some of the trends that are starting to emerge. This is of course an ongoing topic and much remains to be learnt.

Fontenla, John; France, Kevin; Linsky, Jeff; Vieytes, Mariela; Witbrod, Jeese

2015-04-01

42

UV Continua of Cluster OB Stars in the Wing of the SMC  

NASA Astrophysics Data System (ADS)

Many investigators have found that the UV color temperatures of galactic O stars are generally well below the effective temperatures of the stars as inferred from optical line spectra and Zanstra colors. The difference is so severe that even the earliest O stars have UV continua, normalized at V, no brighter than early B main sequence stars. The effects of two possible explanations for the relatively cool continua, wind blanketing and non-LTE line blanketing, should be dependent on the stellar metal content. In particular, the winds of early-type stars with lower metallicity should be weaker and less effective at scattering radiation back onto the photosphere. The net effect should be reduced surface heating and consequently steeper UV continua than stars of galactic abundance. We propose to measure the UV continua of main sequence O and B stars in two lightly reddened clusters in the extreme wing of the SMC. Our observations will allow a precise test of these theories. With a much lower metallicity in the SMC compared to the Galaxy, line- and wind blanketing effects should be greatly reduced. If neither of these mechanisms are shaping the UV continua, the color temperatures of the O stars should be as cool as the B stars. Restricting our target stars to a single lightly reddened association will limit the uncertainties in dereddening the spectra.

Bohm-Vitense, Erika

43

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

44

A Spectroscopic Reconnaissance of Selected UV-Bright Stars  

NASA Astrophysics Data System (ADS)

We have obtained low-dispersion spectra for 62 ``Lanning'' stars. These stars show ultraviolet excesses based on photographic plates double--exposed in the U and B passbands. Thirty--five Lanning stars brighter than B = 13 were observed with the GoldCam spectrograph at the KPNO 2.1m telescope, covering 3875--7530 Å with a resolution of 4.5 Å. Twenty--seven Lanning stars with B between 13 and 16 were observed with the Marcario Low Resolution Spectrograph (LRS) at the Hobby-Eberly Telescope, covering 4260--7245 Å with a resolution of 4.9 Å. The stars were drawn from Papers I, II and (mostly) V by Lanning (1973) and Lanning & Meakes (1994, 2000). One--dimensional spectra were extracted and flux--calibrated. The similar--resolution digital Library of Stellar Spectra (Jacoby, Hunter & Christian 1984) was used as a source of ``standard'' spectra for classification purposes. Both the standard spectra and the Lanning star spectra were approximately flattened, and rough classification was carried out by eye. The brighter sample includes a number of late F/early G stars (possibly metal--weak) with relatively few high--gravity stars, while the fainter sample shows the reverse. We interpret this as a result of ``deselection'' by interstellar reddening of stars beyond a certain distance in these Milky Way fields. Thus fainter stars in the sample are typically of lower intrinsic luminosity. Several unusual spectra, including composite hot+cool systems, emission line stars, a He--strong star, and the exciting star of an H II region were found and will be discussed. The fraction of Lanning stars that are ``interesting'' in these ways is significant.

Lanning, H. H.; Wade, R. A.; Eracleous, M.

2001-05-01

45

Dust-Induced Systematic Errors in UV-Derived Star Formation Rates  

E-print Network

Rest-frame far-ultraviolet (FUV) luminosities form the `backbone' of our understanding of star formation at all cosmic epochs. FUV luminosities are typically corrected for dust by assuming that extinction indicators which have been calibrated for local starbursting galaxies apply to all star-forming galaxies. I present evidence that `normal' star-forming galaxies have systematically redder UV/optical colors than starbursting galaxies at a given FUV extinction. This is attributed to differences in star/dust geometry, coupled with a small contribution from older stellar populations. Folding in data for starbursts and ultra-luminous infrared galaxies, I conclude that SF rates from rest-frame UV and optical data alone are subject to large (factors of at least a few) systematic uncertainties because of dust, which cannot be reliably corrected for using only UV/optical diagnostics.

Eric F. Bell

2002-07-18

46

THE PANCHROMATIC HUBBLE ANDROMEDA TREASURY. I. BRIGHT UV STARS IN THE BULGE OF M31  

SciTech Connect

As part of the Panchromatic Hubble Andromeda Treasury multi-cycle program, we observed a 12' Multiplication-Sign 6.'5 area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of {approx}4000 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes: Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars, and AGB-manque stars. P-AGB stars are the end result of the asymptotic giant branch (AGB) phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manque (together referred to as the hot post-horizontal branch; HP-HB) stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or {alpha} abundances when the mass loss on the red giant branch is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot (extreme) horizontal branch (EHB) stars and their progeny. We construct the first radial profiles of these stellar populations and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting only the progeny of the EHB stars that are the likely source of the UV excess. We calculate that only a few percent of main-sequence stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of low-mass X-ray binaries. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.

Rosenfield, Philip; Johnson, L. Clifton; Dalcanton, Julianne J.; Williams, Benjamin F.; Gilbert, Karoline M. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Girardi, Leo [Osservatorio Astronomico di Padova-INAF, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy); Bressan, Alessandro [SISSA, Via Bonomea 265, 34136 Trieste (Italy); Lang, Dustin [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Guhathakurta, Puragra; Dorman, Claire E. [UCO/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Howley, Kirsten M. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Lauer, Tod R.; Olsen, Knut A. G. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109 (United States); Bianchi, Luciana [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Caldwell, Nelson [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street Cambridge, MA 02138 (United States); Dolphin, Andrew [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Kalirai, Jason [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Larsen, Soren S. [Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC Utrecht (Netherlands); Rix, Hans-Walter [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); and others

2012-08-20

47

Non-LTE modeling of the near UV band of late-type stars  

E-print Network

We investigate the ability of both LTE and Non-LTE models to fit the near UV band absolute flux distribution and individual spectral line profiles of three standard stars for which high quality spectrophotometry and high resolution spectroscopy are available: The Sun (G2 V), Arcturus (K2 III), and Procyon (F5 IV-V). We investigate 1) the effect of the choice of atomic line list on the ability of NLTE models to fit the near UV band flux level, 2) the amount of a hypothesized continuous thermal absorption extinction source required to allow NLTE models to fit the observations, and 3) the semi-empirical temperature structure required to fit the observations with NLTE models and standard continuous near UV extinction. We find that all models that are computed with high quality atomic line lists predict too much flux in the near UV band for Arcturus, but fit the warmer stars well. The variance among independent measurements of the solar irradiance in the near UV is sufficiently large that we cannot definitely conclude that models predict too much near UV flux, in contrast to other recent results. We surmise that the inadequacy of current atmospheric models of K giants in the near UV band is best addressed by hypothesizing that there is still missing continuous thermal extinction, and that the missing near UV extinction becomes more important with decreasing effective temperature for spectral classes later than early G, suggesting a molecular origin.

C. Ian Short; P. H. Hauschildt

2008-11-07

48

The UV-Bright Stars of Omega Centauri  

NASA Astrophysics Data System (ADS)

Images of the globular cluster Omega Centauri obtained with the Ultraviolet Imaging Telescope (UIT) in 1990 revealed numerous hot stars more luminous than zero-age horizontal branch (Whitney et al. 1994, AJ, 108, 1350). We have obtained CTIO 4m and IUE low-dispersion spectra of seven of the brightest stars in the Whitney et al. catalog. The target stars include UIT-1 and UIT-2 in the core of Omega Cen (Landsman et al. 1992 ApJL, 395, L21), as well as ROA 5342, Dk 3873, and Dk 3089 from the catalog of Dickens (1988). All of the target stars are found to be radial velocity members of the cluster. Three of the stars (ROA 5342, UIT-151, Dk 3873) show strong He II lines in their spectra and are probably very hot (> 50,000 K) post-AGB stars. The remaining four stars show strong He I lines, and UIT-1 also shows numerous nitrogen lines. We present results of an atmospheric analysis to constrain the reddening, effective temperatures, and helium abundances.

Landsman, W. B.; Crotts, A.; O'Connell, R. W.; Whitney, J. H.; Lanz, T.; Stecher, T. P.

1995-05-01

49

Synthetic UV spectra of massive stars (Leitherer+ 1995)  

Microsoft Academic Search

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,

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

1996-01-01

50

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

2015-01-01

51

RU Lupi? A UV spectroanalysis of an adolescent star  

NASA Astrophysics Data System (ADS)

We present an HST/STIS E140M spectrum of the CTTS RU Lupi. The UV spectrum of RU Lupi is dominated by emission lines, including tracers of hot accreting gas and cool molecular gas. We also detect a strong continuum and wind absorption features. We analyze 90 fluorescent H2 emission lines, and use them to reconstruct the intrinsic Ly-alpha profile.

Herczeg, G.; Walter, F.; Linsky, J. L.; Ardila, D.; Brown., A.; Gahm, G.; Johns-Krull, C.; Lissauer, J.; Simon, M.; Valenti, J. A.; Wood, B. E.

2003-12-01

52

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

53

Optical Observations of the Cataclysmic Variable FL Ceti, Evidence for a Decrease in Orbital Period  

NASA Astrophysics Data System (ADS)

FL Ceti is a short period cataclysmic variable star belonging to the highly magnetic subclass of polars. Our one second time resolution light curves show dramatic eclipses, as well as a well defined ingress and egress features. We collected 35 hours of broad band optical photometry on FL Ceti at the 82" reflector in the McDonald Observatory. We observed 23 eclipses of the system in 2011. Combining timings of these eclipses with previously publish data we obtain preliminary evidence which indicate that the orbital period of the system is decreasing. We discuss the implications for the derived period derivative and mass transfer rate. This research is supported in part by NSF grant 0958783.

Gomez, Sebastian; Mason, P. A.; Robinson, E. L.

2014-01-01

54

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

55

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

56

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

57

Biological damage of UV radiation in environments of F-type stars  

NASA Astrophysics Data System (ADS)

I investigate the general astrobiological significance of F-type main-sequence stars with special consideration to stellar evolutionary aspects due to nuclear evolution. DNA is taken as a proxy for carbon-based macromolecules following the assumption that exobiology is most likely based on hydrocarbons. The DNA action spectrum is utilized to represent the relative damage of the stellar UV radiation. Planetary atmospheric attenuation is taken into account in the form of parameterized attenuation functions. My work is motivated by previous studies indicating that the UV environment of solar-like stars is one of the most critical elements in determining the habitability of exoplanets and exomoons. It contributes further to the exploration of the exobiological suitability of stars that are hotter and emit much higher photospheric UV fluxes than the Sun. I found that the damage inflicted on DNA for planets at Earth-equivalent positions is between 2.5 and 7.1 times higher than for solar-like stars, and there are intricate relations for the time-dependence of damage during stellar main-sequence evolution. If atmospheric attenuation is included, however, less damage is obtained in alignment to the attenuation parameters. Also, the outer part of late F-type stars have similar UV conditions to Earth. Therefore, F-type circumstellar environments should not be excluded from candidates for habitable places on the grounds of higher stellar UV emission than the Sun. Besides the extensive theoretical component of this study, emphasis is furthermore placed on applications to observed planetary systems including CoRoT-3, WASP-14, HD 197286, HD 179949, upsilon And, and HD 86264.

Sato, Satoko

58

The accuracy of the UV continuum as an indicator of the star formation rate in galaxies  

NASA Astrophysics Data System (ADS)

The rest-frame intrinsic UV luminosity is often used as an indicator of the instantaneous star formation rate (SFR) in a galaxy. While it is in general a robust indicator of the ongoing star formation activity, the precise value of the calibration relating the UV luminosity to the SFR (B?) is sensitive to various physical properties, such as the recent star formation and metal enrichment histories, along with the choice of stellar initial mass function (IMF). The distribution of these properties for the star-forming galaxy population then suggests that the adoption of a single calibration is not appropriate unless properly qualified with the uncertainties on the calibration. We investigate, with the aid of the GALFORM semi-analytic model of galaxy formation, the distribution of UV-SFR calibrations obtained using realistic star formation and metal enrichment histories. At z = 0, we find that when the IMF is fixed (to the Kennicutt IMF), the median calibration is Bfuv = 0.9 where SFR/[M? yr-1] = B? × 10-28 × L?/[erg s-1 Hz-1]. However, the width of the distribution Bfuv suggests that for a single object there is around a 20 per cent intrinsic uncertainty (at z = 0, rising to ?30 per cent at z = 6) on the SFR inferred from the FUV luminosity without additional constraints on the star formation history or metallicity. We also find that the median value of the calibration Bfuv is correlated with the SFR and redshift (at z > 3) raising implications for the correct determination of the SFR from the UV.

Wilkins, Stephen M.; Gonzalez-Perez, Violeta; Lacey, Cedric G.; Baugh, Carlton M.

2012-12-01

59

Fast transition between Classical and Weak lined T Tauri stars due to external UV dissipation  

E-print Network

The discovery of optical jets immersed in the strong UV radiation field of the Rosette Nebula sheds new light on, but meanwhile poses challenges to, the study of externally irradiated jets. The jet systems in the Rosette are found to have a high state of ionization and show unique features. In this paper, we investigate the evolutionary status of the jet driving sources for young solar-like stars. To our surprise, these jet sources indicate unexpected near infrared properties with no excess emission. They are bathed in harsh external UV radiation such that evaporation leads to a fast dissipation of their circumstellar material. This could represent a transient phase of evolution of young solar-like stars between classical and weak lined T Tauri stars. Naked T Tauri stars formed in this way have indistinguishable evolutionary ages from those of classical T Tauri stars resulting from the same episode of star formation. However, it would be hard for such sources to be identified if they are not driving an irradiated jet in a photoionized medium.

J. Z. Li; T. A. Rector

2007-02-09

60

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

61

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

62

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

63

Restframe UV colors of 1 < z < 4 star-forming galaxies in the Hubble Ultraviolet UltraDeep Field (UVUDF)  

NASA Astrophysics Data System (ADS)

Restframe UV color is represented by the UV continuum slope, beta, which is sensitive to a galaxy's stellar age and dust reddening. We measure the correlation of beta with redshift, luminosity and stellar mass for galaxies in the range 1 < z_phot < 4, using new deep UV imaging in the Hubble Ultradeep Field. Our results probe evolution of the UV continuum across the epoch of peak star-formation in the universe and provide a context for interpreting recent studies of higher redshift star-forming galaxies.

Kurczynski, Peter; Gawiser, E. J.; Teplitz, H. I.; Rafelski, M.; Finkelstein, S. L.; UVUDF Team

2014-01-01

64

Comparing H-alpha, UV, and Far-IR Star Formation Rates of Galaxies at 2  

NASA Astrophysics Data System (ADS)

We use a unique sample of 262 star-forming galaxies selected during the epoch of peak cosmic star formation to infer star-formation rates and dust reddening, and to investigate the validity of the local star-formation calibrations at high redshift. The sample contains galaxies at redshifts 2.08UV continuum and Spitzer/MIPS 24 micron measurements in order to examine the bolometric star-formation rates and dust attenuation. We discuss the comparison of these three complementary star-formation rate indicators in the context of the star-formation histories of the galaxies, and the implications for inferring star-formation rates and reddening at high redshift.

Shivaei, Irene; Reddy, N.

2013-01-01

65

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

66

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

67

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

68

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

69

VLBI Studies of Mira's (o Ceti) Stellar Envelope  

NASA Astrophysics Data System (ADS)

Over a period of six months in 1999-2000, six epochs of VLBA data at 7mm (43 GHz) were taken of J = 1 to 0, v=1 and v=2 SiO maser emission around Mira (o Ceti). Images were created from each epoch and compared to study the motion of the masing regions within Mira's stellar envelope. In each transition, the masing regions appeared in a broken, 2 to 3 AU ring about the star. Mira's sparse SiO maser shell contrasts with the contiguous rings seen from such AGB stars as R Cas and TX Cam. The data encompass a period of time in which Mira peaks in visual wavelengths. The peak for the SiO masers lagged behind the visual peak, as expected. However, this lag was different between the v=1 and v=2 vibrational states. These images, which resemble a stop-action movie of Mira's masing regions, are the highest fidelity look into its envelope achieved to date.

Gardner, J. M.; Phillips, R. B.; Boboltz, D. A.

2000-12-01

70

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

71

Morphology and Morphometry of Ceti Mensa, West Candor Chasma, Mars  

NASA Astrophysics Data System (ADS)

We use high-resolution topographic data to examine the morphology and morphometry of Ceti Mensa (CM), a feature comprised of layered units on the floor of West Candor Chasma in the Valles Marineris (VM), Mars.

Gaddis, L. R.; Skinner, J.; Hare, T.; Kirk, R.; Titus, T.; Weller, L.; Neukum, G.

2006-03-01

72

Star Formation Rates in Cooling Flow Clusters: A UV Pilot Study with Archival XMM-Newton Optical Monitor Data  

NASA Technical Reports Server (NTRS)

We have analyzed XMM-Newton Optical Monitor (OM) UV (180-400 nm) data for a sample of 33 galaxies. 30 are cluster member galaxies, and nine of these are central cluster galaxies (CCGs) in cooling flow clusters having mass deposition rates which span a range of 8 - 525 solar mass per year. By comparing the ratio of UV to 2MASS J band fluxes, we find a significant UV excess in many, but not all, cooling flow CCGs, a finding consistent with the outcome of previous studies based on optical imaging data (McNamara & O Connell 1989; Cardiel, Gorgas, & Aragon-Salamanca 1998; Crawford et al. 1999). This UV excess is a direct indication of the presence of young massive stars, and therefore recent star formation, in these galaxies. Using the Starburst99 spectral energy distribution (SED) model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2 - 219 solar mass per year for the cooling flow sample. For 2/3 of this sample it is possible to equate Chandra/XMM cooling flow mass deposition rates with UV inferred star formation rates, for a combination of starburst lifetime and IMF slope. This is a pilot study of the well populated XMM UV cluster archive and a more extensive follow up study is currently underway.

Hicks, A. K.; Mushotzky, R.

2005-01-01

73

Star Formation Rates in Cooling Flow Clusters: A UV Pilot Study with Archival XMM-Newton Optical Monitor Data  

NASA Technical Reports Server (NTRS)

We have analyzed XMM-Newton Optical Monitor (OM) UV (180-400 nm) data for a sample of 33 galaxies. 30 are cluster member galaxies, and nine of these are central cluster galaxies (CCGs) in cooling flow clusters having mass deposition rates which span a range of 8 - 525 Solar Mass/yr. By comparing the ratio of UV to 2MASS J band fluxes, we find a significant UV excess in many, but not all, cooling flow CCGs, a finding consistent with the outcome of previous studies based on optical imaging data (McNamara & O'Connell 1989; Cardiel, Gorgas, & Aragon-Salamanca 1998; Crawford et al. 1999). This UV excess is a direct indication of the presence of young massive stars, and therefore recent star formation, in these galaxies. Using the Starburst99 spectral energy distribution (SED) model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2 - 219 solar Mass/yr for the cooling flow sample. For 2/3 of this sample it is possible to equate Chandra/XMM cooling flow mass deposition rates with UV inferred star formation rates, for a combination of starburst lifetime and IMF slope. This is a pilot study of the well populated XMM UV cluster archive and a more extensive follow up study is currently underway.

Hicks, A. K.; Mushotzky, R.

2006-01-01

74

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

75

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

76

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

77

Very Short-Duration UV-B Optical Flares in RS CVn-type Star Systems  

NASA Astrophysics Data System (ADS)

Very short duration UV-B optical flares were observed during a high-cadence search for conventional flares on three RS CVn type stars: AR Lac, II Peg, and UX Ari. A statistical criterion was developed for isolating these short-duration optical flares from random photon events. Five flares, ranging in duration from 30 to 85 ms with peaks 0.29-0.51 mag. above the mean, were detected within the 132 hours of monitoring time. The time resolution of the observations was 5 ms for AR Lac and 10 ms for II Peg and UX Ari.

Vander Haagen, G. A.

2013-06-01

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.

Kurczynski, Peter; Gawiser, Eric J.; Rafelski, Marc; Teplitz, Harry I.; de Mello, Duilia F.; Finkelstein, Steven L.; Gardner, Jonathan P.; Koekemoer, Anton M.; Soto, Emmaris; 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

The Chemical Composition of {\\tau} Ceti and Possible Effects on Terrestrial Planets  

E-print Network

{\\tau} Ceti (HD10700), a G8 dwarf with solar mass of 0.78, is a close (3.65 pc) sun-like star where 5 possibly terrestrial planet candidates (minimum masses of 2, 3.1, 3.5, 4.3, and 6.7 Earth masses) have recently been discovered. We report abundances of 23 elements using spectra from the MIKE spectrograph on Magellan. Using stellar models with the abundances determined here, we calculate the position of the classical habitable zone with time. At the current best fit age, 7.63 Gy, up to two planets (e and f) may be in the habitable zone, depending on atmospheric properties. The Mg/Si ratio of the star is found to be 1.78, which is much greater than for Earth (about 1.2). With a system that has such an excess of Mg to Si ratio it is possible that the mineralogical make-up of planets around {\\tau} Ceti could be significantly different from that of Earth, with possible oversaturation of MgO, resulting in an increase in the content of olivine and ferropericlase compared with Earth. The increase in MgO would have ...

Pagano, Michael; Young, Patrick A; Shim, Sang-Heon

2015-01-01

82

Structural Relations of a Sulfate-bearing Unit near Ceti Mensa, Candor Chasma, Mars  

NASA Astrophysics Data System (ADS)

A mapped kieserite unit within Ceti Mensa is unconformable to units that comprise Ceti Mensa. This fits a model of ILD deposition in which Ceti Mensa is a fault-bound block emplaced during ancestral basin formation, while kieserite units are late.

Fueten, F.; Stesky, R.; MacKinnon, P.; Hauber, E.; Gwinner, K.; Scholten, F.; Zegers, T. E.

2008-03-01

83

NLTE Analysis of the Hot sdO Star Bd+28°4211: The UV Spectrum  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of the UV spectrum of the calibration star BD+28°4211 using high-quality spectra obtained with the HST and FUSE satellites. To this aim, we compare quantitatively the observed data with model spectra obtained from state-of-the-art non-LTE metal line-blanketed model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC. We thus determine in a self-consistent way the abundances of 11 elements with well-defined lines in the UV. The derived abundances range from about solar to 1/10 solar and the overall quality of the derived spectral fits is very satisfying. Our analysis can be used to constrain rather tightly the effective temperature of BD+28°4211 to a value of Teff = 82,000±5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2-0.1+0.3. Assuming that the Hipparcos measurement for BD+28°4211 is fully reliable and that our model atmospheres are reasonably realistic, we can reconcile our spectroscopic constraints with the available parallax measurement only if the mass of BD+28°4211 is significantly less than the canonical value of 0.5 M? for a representative post-EHB star.

Latour, M.; Fontaine, G.; Chayer, P.; Brassard, P.; Green, E.

2014-04-01

84

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

85

Magnetic field structure in single late-type giants: ? Ceti in 2010-2012  

NASA Astrophysics Data System (ADS)

Aims: We study the behavior of the magnetic field and the line activity indicators of the single late-type giant ? Ceti. Using spectropolarimetric data, we aim to reconstruct the magnetic field structure on the star's surface and to present the first magnetic maps for ? Ceti. Methods: The data were obtained using two spectropolarimeters - Narval at the Bernard Lyot Télescope, Pic du Midi, France, and ESPaDOnS at CFHT, Hawaii. Thirty-eight circularly-polarized spectra have been collected in the period June 2010-January 2012. The least square deconvolution method was applied for extracting high signal-to-noise ratio line profiles, from which we measured the surface-averaged longitudinal magnetic field Bl. Chromospheric activity indicators CaII K, H?, CaII IR (854.2 nm), and radial velocity were simultaneously measured, and their variability was analyzed along with the behavior of Bl. The Zeeman Doppler imaging (ZDI) inversion technique was employed for reconstructing the large-scale magnetic field and two magnetic maps of ? Ceti are presented for two periods (June 2010-December 2010 and June 2011-January 2012). Results: The Bl stays with a same positive polarity for the whole observational period and shows significant variations in the interval 0.1-8.2 G. The behavior of the line activity indicators is in good agreement with the Bl variations. Searching for periodic signals in the Stokes V time series, we found a possible rotation period of 215 days. The two ZDI maps show a mainly axisymmetric and poloidal magnetic topology and a simple surface magnetic field configuration dominated by a dipole. Little evolution is observed between the two maps, in spite of a 1 yr interval between both subsets. We also use state-of-the-art stellar evolution models to constrain the evolutionary status of ? Ceti. We derive a mass of 3.5 M? and propose that this star is already in the central helium-burning phase. Conclusions: Considering all our results and the evolutionary status of the star, we suggest that dynamo action alone may not be efficient enough to account for the high magnetic activity of ? Ceti. As an alternate option, we propose that it is a descendant of an Ap star presently undergoing central helium-burning and still exhibiting a remnant of the Ap star magnetic field. Based on observations obtained at the Bernard Lyot Télescope (TBL, Pic du Midi, France) of the Midi-Pyrénées Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and Université de Toulouse, and at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.Table 1 is available in electronic form at http://www.aanda.org

Tsvetkova, S.; Petit, P.; Aurière, M.; Konstantinova-Antova, R.; Wade, G. A.; Charbonnel, C.; Decressin, T.; Bogdanovski, R.

2013-08-01

86

Elemental abundance analyses with DAO spectrograms: XXX. The middle B through early A stars ?2 Ceti (B9 III), 21 Aquilae (B8 II-III), ? Aquilae (B5 III), and ? Delphini (A2V)  

NASA Astrophysics Data System (ADS)

This series of high quality elemental abundance analyses of mostly main-sequence band normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with the analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (? 200) spectrograms obtained with CCD detectors at the long camera of the Coudé spectrograph of the 1.22-m Dominion Astrophysical Observatory telescope. Here we reanalyze 21 Aql with better quality spectra and increase the number of stars consistently analyzed in the spectral range B5 to A2 by analyzing three new stars for this series. In the early A stars the normal and non-mCP stars have abundances with overlapping ranges. But more stars are needed especially in the B5 to B9 range. ?2 Cet on average has a solar composition with a few abundances outside the solar range while both 21 Aql and ? Aql have abundances marginally less than solar. The abundances of ? Del are greater than solar with a few elements such as Ca being less than solar. It is an Am star. Table 3 is only available in electronic form at the CDS via http://cdsarc.u-strasbg.fr/ftp/cats/J/other/AN/331/378

Adelman, S. J.; Westbrook, P. C.; Gulliver, A. F.

2010-04-01

87

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

88

Investigating H$\\alpha$, UV, and IR star-formation rate diagnostics for a large sample of z ~ 2 galaxies  

E-print Network

We use a sample of 262 spectroscopically confirmed star-forming galaxies at redshifts $2.08\\leq z\\leq 2.51$ to compare H$\\alpha$, UV, and IR star-formation-rate diagnostics and to investigate the dust properties of the galaxies. At these redshifts, the H$\\alpha$ line shifts to the $K_{s}$-band. By comparing $K_{s}$-band photometry to underlying stellar population model fits to other UV, optical, and near-infrared data, we infer the H$\\alpha$ flux for each galaxy. We obtain the best agreement between H$\\alpha$- and UV-based SFRs if we assume that the ionized gas and stellar continuum are reddened by the same value and that the Calzetti attenuation curve is applied to both. Aided with MIPS 24$\\mu$m data, we find that an attenuation curve steeper than the Calzetti curve is needed to reproduce the observed IR/UV ratios of galaxies younger than 100 Myr. Furthermore, using the bolometric star-formation rate inferred from the UV and mid-IR data (SFR$_{IR}$+SFR$_{UV}$), we calculated the conversion between the H$\\alp...

Shivaei, Irene; Steidel, Charles C; Shapley, Alice E

2015-01-01

89

Line driven winds, ionizing fluxes and UV-spectra of hot stars at extremely low metallicity  

NASA Astrophysics Data System (ADS)

Wind models of very massive stars with metallicities in a range from 10-4 - 1.0 Z? are presented using a new treatment of radiation driven winds with depth dependent radiative force multipliers and a comprehensive list of more than two million of spectral lines in non-LTE. The models yield mass-loss rates, wind velocities, wind momenta and wind energies as a function of metallicity and can be used to discuss the influence of stellar winds on the evolution of very massive stars in the early universe and on the interstellar medium in the early phases of galaxy formation. It is shown that the normal scaling laws, which predict stellar mass-loss rates and wind momenta to decrease as a power law with metal abundance break down at a certain threshold. The new wind models are applied to calculate ionizing fluxes and observable UV-spectra of very massive stars as a function of metallicity using the WM-basic code developed by Pauldrach et al. (2001), and the efffects of metallicity are discussed.

Kudritzki, Rolf-Peter

90

A finding list of faint UV-bright stars in the galactic plane, 2  

NASA Technical Reports Server (NTRS)

Fifty-three UV-bright stars have been found on three two-color 48-in. Schmidt plates centered on the galactic plane. The sources detected range in U-B color from near U- B = 0 to U - B = -1.5, and in magnitude from m(sub B) approximately = 10 to approximately 21. Some of the more interesting sources are discussed, and finding charts are included for all sources listed. Additionally, follow-up spectroscopic and postitional information is provided for several objects first listed in Paper I of this series. One new cataclysmic variable discovered during the course of this portion of the survey has been published previously and is discussed herein.

Lanning, Howard H.; Meakes, Michael

1994-01-01

91

The Helium-Rich Cataclysmic Variable ES Ceti  

E-print Network

We report photometry of the helium-rich cataclysmic variable ES Ceti during 2001-2004. The star is roughly stable at V ~ 17.0 and has a light curve dominated by a single period of 620 s, which remains measurably constant over the 3 year baseline. The weight of evidence suggests that this is the true orbital period of the underlying binary, not a "superhump" as initially assumed. We report GALEX ultraviolet magnitudes, which establish a very blue flux distribution (F_nu ~ nu^1.3), and therefore a large bolometric correction. Other evidence (the very strong He II 4686 emission, and a ROSAT detection in soft X-rays) also indicates a strong EUV source, and comparison to helium-atmosphere models suggests a temperature of 130+-10 kK. For a distance of 350 pc, we estimate a luminosity of (0.8-1.7)x10^34 erg/s, yielding a mass accretion rate of (2-4)x10^-9 M_sol/yr onto an assumed 0.7 M_sol white dwarf. This appears to be about as expected for white dwarfs orbiting each other in a 10 minute binary, assuming that mass transfer is powered by gravitational radiation losses. We estimate mean accretion rates for other helium-rich cataclysmic variables, and find that they also follow the expected M-dot ~ P_o^-5 relation. There is some evidence (the lack of superhumps, and the small apparent size of the luminous region) that the mass transfer stream in ES Cet directly strikes the white dwarf, rather than circularizing to form an accretion disk.

Catherine Espaillat; Joseph Patterson; Brian Warner; Patrick Woudt

2004-12-02

92

UV Habitability of Possible Exomoons in Observed F-star Planetary Systems  

E-print Network

In the present study we explore the astrobiological significance of F-type stars of spectral type between F5 V and F9.5 V, which possess Jupiter-type planets within or close to their climatological habitable zones. These planets, or at least a subset of them, may also possess rocky exomoons, which potentially offer habitable environments. Our work considers eight selected systems. The Jupiter-type planets in these systems are in notably different orbits with eccentricities ranging from 0.08 to 0.72. Particularly, we consider the stellar UV environments provided by the photospheric stellar radiation in regard to the circumstellar habitability of the system. According to previous studies, DNA is taken as a proxy for carbon-based macromolecules following the paradigm that extraterrestrial biology might be based on hydrocarbons. Thus, the DNA action spectrum is utilized to represent the impact of the stellar UV radiation. Atmospheric attenuation is taken into account based on parameterized attenuation functions. ...

Sato, Satoko

2015-01-01

93

IUE observations of WX Ceti in outburst  

NASA Technical Reports Server (NTRS)

IUE observations of the peculiar dwarf nova WX Ceti roughly two weeks into a rare outburst, the first since 1963, are obtained. The SWP and LWP observations are very similar to other erupting dwarf novae, both in the line and continuum spectrum. The C IV 1549 A doublet displays blueshifted absorption, indicating the presence of a wind which has a terminal velocity of either 3150 km/s or 5450 km/s; the two possible values are due to an uncertain interpretation of features in the blue wing of the line. The line may also show a weak, redshifted emission, completing a P Cygni profile. The derived mass-loss of 0.7-2.2 x 10 to the -11th solar masses/yr is quite typical of dwarf novae in outburst. Thus, despite the unusual photometric properties of this system, long recurrence time, large amplitude outbursts, and long duration eruptions, the IUE observations reveal that the physical characteristics of the outburst are fairly typical of dwarf novae.

Downes, Ronald A.

1990-01-01

94

Evolution over time of magnetic dynamo driven UV emissions of dG-M stars and effects on hosted planets  

NASA Astrophysics Data System (ADS)

The evolution over time of the magnetic activity and the resulting X-ray and UV coronal and chromospheric emissions of main-sequence dG, dK, and dM stars with widely different ages will be discussed. Young cool stars spin rapidly and have correspondingly very robust magnetic dynamos and strong coronal and chromospheric X-ray - UV (XUV) emissions. However, these stars spin-down with time as they lose angular momentum via magnetized winds and their magnetic generated activity and emission decrease. For example, the study of solar proxies shows that the young Sun was rotating more than ten times faster than today and had correspondingly very high levels of magnetic activity and very intense X-ray - UV (XUV) emissions. Studies of dK-dM stars over a wide range of ages and rotations show similar (but not identical) behavior. Particular emphasis will be given to discussing the effects that UV emissions have on the atmospheres and evolution of solar system planets as well as the increasing number of exoplanets found hosted by dG-dM stars. The results from modeling the early atmospheres of Venus, Earth and Mars using recently determined XUV irradiances and winds of the young Sun are also briefly discussed. For example, the loss of water from juvenile Venus and Mars can be explained by action of the strong XUV emissions and robust winds of the young Sun. We also examine the effects of strong X-ray and UV coronal and chromospheric emissions (and frequent flares) that dM stars may have on possible planets orbiting within their habitable zones (HZ) - located close to the low luminosity host stars (0.05 < HZ < 0.4 AU). Dwarf M stars make interesting targets for further study because of their deep convective zones, efficient dynamos and strong XUV emissions. Furthermore, a large fraction of dM stars are very old (>5 Gyr), which present possibilities for the development of highly advanced modes of intelligent life on planets that may orbit them. This research is supported by grants from NASA and utilizes data from the IUE, FUSE, HST, EUVE, ROSAT, XMM, and the Chandra Missions. We are very grateful for this support.

Guinan, E. F.; Ribas, I.; Engle, S. G.

2006-08-01

95

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

96

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

97

The winds of O-stars. I - An analysis of the UV line profiles with the SEI method  

NASA Technical Reports Server (NTRS)

The theoretical UV P Cygni profiles of the UV resonance lines for C IV, N V, Si IV, C III, and N IV of 26 O-type stars and one B star were calculated using the SEI method described by Lamers et al. (1987), taking into account the effects of turbulence in the wind, limb darkening, photospheric lines, and interstellar Ly alpha. The results were compared with profiles observed with the IUE satellite. The profile fits were found to be very accurate, showing significant improvement over previously obtained fits with the Sobolev (1958) method. The SEI method and the line fitting analysis are described and the results are presented in terms of the column densities and distributions of absorbing atoms, and the velocity laws.

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

1989-01-01

98

First Detection of UV emission from a Detached Dust Shell: GALEX Observations of the Carbon AGB Star U Hya  

E-print Network

We present the discovery of an extended ring of ultraviolet emission surrounding the AGB star U Hya in archival observations performed by the Galaxy Evolution Explorer (GALEX). This is the third discovery of extended UV emission from a carbon AGB star and the first from an AGB star with a detached shell. From imaging and photometric analysis of the FUV and NUV images, we determined that the ultraviolet ring has a radius of $\\sim 110^{\\prime\\prime}$, thus indicating that the emitting material is likely associated with the detached shell seen in the infrared. We find that scattering of the central point source of NUV and FUV emission by the dust shell is negligible. Moreover, we find that scattering of the interstellar radiation field by the dust shell can contribute at most $\\sim10%$ of the FUV flux. Morphological and photometric evidence suggests that shocks caused by the star's motion through space and, possibly, shock-excited H$_2$ molecules are the most likely origins of the UV flux. In contrast to previou...

Sanchez, E; Ramstedt, S; Stassun, K G

2014-01-01

99

VLBI Studies of Mira's (o Ceti) Stellar Envelope  

Microsoft Academic Search

Over a period of six months in 1999-2000, six epochs of VLBA data at 7mm (43 GHz) were taken of J = 1 to 0, v=1 and v=2 SiO maser emission around Mira (o Ceti). Images were created from each epoch and compared to study the motion of the masing regions within Mira's stellar envelope. In each transition, the masing

J. M. Gardner; R. B. Phillips; D. A. Boboltz

2000-01-01

100

High Velocity Interstellar Lines and Temporal Variations in the UV Spectra of Stars in the Carina Nebula  

NASA Astrophysics Data System (ADS)

UV observations of 4 stars in the Carina Nebula region have been obtained with STIS at a resolution of R ~ 110,000. All four stars demonstrate numerous high velocity components extending over ranges ~ +/- 200 km/sec. In particular two observations of the star CPD -59 2603 have been obtained 22 months apart and demonstrate substantial variations in the intensities of the high velocity components of Mg II 2796.35, 2803.53 and Mg I 2852.96 lines. The origin of the variations is discussed. Furthermore, there is a marked similarity in the shape of the absorption features with those seen in narrow-lines QSO systems, which may shed light on the origin of these features. This work was supported by NASA through the STIS GTO funding.

Danks, A. C.; Walborn, N. R.; Vieira, G. L.; Gales, J. M.; Landsman, W. B.; Garcia, B.; Hulbert, S. J.

2000-05-01

101

Faulting of ILD Deposits on Ceti Mensa, Western Candor Chasma, Mars  

NASA Astrophysics Data System (ADS)

Active normal faulting within Ceti Mensa continued until at least 1.4 km of ILD material was deposited. Only a thin layer of ILD material postdates fault motion. The domal topography of Ceti Mensa may reflect the inward tilt of two fault blocks.

Fueten, F.; Stesky, R.; MacKinnon, P.; Hauber, E.; Gwinner, K.; Scholten, F.; Zegers, T.; Neukum, G.; HRSC Co-Investigator Team

2007-03-01

102

A Morphological Study of UV-Bright Stars and Emission Nebulae in a Selection of Star Formation Regions in M31  

NASA Astrophysics Data System (ADS)

Using the data from the NOAO Local Group Survey, we have measured the H? fluxes of 291 nebulae associated with 21 of the van den Bergh OB associations. We have combined these data together with six-color HST WFPC2 photometry, in order to identify the most UV-bright stars in the region. The simple purpose of this article is to explore the spatial relationships between these components. We find that there are basically three types of H?-hot star morphology. One type consists of a very bright H II region, with a tightly spaced group of hot stars at or near its center; we refer to these as monolithic structures. A second common arrangement is that of a ringlike bubble structure with an often-empty central area, where the hot stars are concentrated. We construct simple models of these objects, which show that their photometric profiles are like those of spherical shells. We refer to these as bubble structures A third morphology is a scattered distribution of small nebulae with a few hot stars that are widely spaced; these are called dispersed structures. We suggest that this sequence may be an evolutionary one.

Hodge, Paul W.; Krienke, O. Karl; Luciana, Bianchi

2011-06-01

103

Far-UV radiation from hot subdwarf stars in early-type galaxies  

NASA Astrophysics Data System (ADS)

Far-ultraviolet (FUV) excess is crucial to our understanding of early-type galaxies and it is widely believed that the FUV radiation originates mainly from hot subwarf stars. Hot subdwarf stars may form from binary interactions or from single star evolution. In the binary channel, a star near the tip of the first giant branch (FGB) may get its envelope removed by its companion via stable Roche lobe overflow or common envelope ejection, and then evolves to a hot subdwarf star (Han et al. 2002, 2003, 2007). Such a process does not depend much on metallicity.

Han, Zhanwen; Chen, Xuefei

2015-03-01

104

UV-B and B-band Optical Flare Search in AR Lacertae, II Pegasi, and UX Arietis Star Systems  

NASA Astrophysics Data System (ADS)

A high-cadence search was conducted on the known RS CVn-type flare stars AR Lac, II Peg, and UX Ari. Two optical flares were observed in the B-band on AR Lac at 5 milliseconds (ms) resolution for a rate of 0.04 fl/hr. Flare energy of the two B-band fast-flares ranged from 0.55 to 16.7 × 1033 ergs. The UV-B and B-band search of II Peg for 44.5 hours at 5 and 10 ms resolution and UV-B band search of UX Ari for 25.6 hours at 10 ms resolution detected no flare activity.

Vander Haagen, G. A.

2013-11-01

105

Chromospherically active stars. VI - HD 136901 = UV CrB: A massive ellipsoidal K giant single-lined spectroscopic binary  

NASA Technical Reports Server (NTRS)

The variable star HD 136901 = UV CrB is a chromospherically active K2 III single-lined spectroscopic binary with an orbital period of 18.665 days. It has modest-strength Ca H and K emission and UV features, while H-alpha is a strong absorption feature containing little or no emission. The inclination of the system is 53 + or - 12 deg. The v sin i of the primary is 42 + or - 2 km/s, resulting in a minimum radius of 15.5 + or - 0.8 solar. When compared with the Roche lobe radius, this results in a mass ratio of 2.90 or larger. Additional constraints indicate that the secondary has a mass between 0.85 and 1.25 solar. Thus, the mass of the primary is at least 2.5 solar and probably is in the range 2.5-4 solar.

Fekel, Francis C.; Kirkpatrick, J. Davy; Yang, Xinxing; Strassmeier, Klaus G.

1989-01-01

106

Transition from star-like to crew-cut micelles induced by UV radiation.  

PubMed

In the present article, the effect of UV on PS-b-PMMA micelles in solution is discussed. Micellar solutions of the amphiphilic poly(styrene-b-methylmethacrylate) block copolymer in selective solvent (methanol for the PMMA block) were exposed to UV radiation, which has simultaneously led to cross linking of the micellar core (PS) and degradation of the micellar corona (PMMA). The kinetics of such process were investigated in situ by means of dynamic light scattering, allowing the measurement of hydrodynamic radius as a function of UV exposure time. Results indicate that the size of micelles has decreased with UV exposure time down to a minimum value. Such reduced size resulted from PMMA degradation, which later promoted aggregation and coagulation because the micellar core was no longer well protected by PMMA. Addition of good solvent for both blocks (toluene) to non-UV exposed micelles has led to core swelling (PS) and, ultimately, system disassembly (free copolymer chain). The effect of adding toluene on the UV-exposed micelles has only caused core swelling as a consequence of the PS cross-linking. PMID:24370401

Fayad, Samira Jamil; Minatti, Edson; Soldi, Valdir; Borsali, Redouane

2014-02-15

107

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

108

A Non-LTE Analysis of the Hot Subdwarf O Star BD+28°4211. I. The UV Spectrum  

NASA Astrophysics Data System (ADS)

We present a detailed analysis of the UV spectrum of the calibration star BD+28°4211 using high-quality spectra obtained with the Hubble Space Telescope and Far-Ultraviolet Spectroscopic Explorer satellites. To this aim, we compare quantitatively the observed data with model spectra obtained from state-of-the-art non-LTE metal line-blanketed model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC. We thus determine in a self-consistent way the abundances of 11 elements with well-defined lines in the UV, namely those of C, N, O, F, Mg, Si, P, S, Ar, Fe, and Ni. The derived abundances range from about solar to 1/10 solar. We find that the overall quality of the derived spectral fits is very satisfying. Our spectral analysis can be used to constrain rather tightly the effective temperature of BD+28°4211 to a value of T eff = 82, 000 ± 5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2_{-0.1}^{+0.3}. Assuming that the Hipparcos measurement for BD+28°4211 is fully reliable and that our model atmospheres are reasonably realistic, we can reconcile our spectroscopic constraints with the available parallax measurement only if the mass of BD+28°4211 is significantly less than the canonical value of 0.5 M ? for a representative post-extended horizontal branch star.

Latour, M.; Fontaine, G.; Chayer, P.; Brassard, P.

2013-08-01

109

Overtures to the pulsational instability of ZZ Ceti variables  

E-print Network

Results of nonradial, nonadiabatic pulsation calculations on hydrogen-rich white dwarf models are presented. In contrast to earlier attempts, the modeling builds on hydrodynamically simulated convective surface layers supplemented with standard interior models. Based on our stellar models and despite of various simple attempts to couple convection and pulsation we could not reproduce theoretically the presently adopted location of the observed blue edge of the ZZ Ceti variables. When the convective efficiency is high enough we found a sensitive dependence of the stability properties of the g-modes on the pulsational treatment of shear within the convection zone.

Alfred Gautschy; Hans-Günter Ludwig; Bernd Freytag

1995-07-26

110

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

111

MASTER: new UV-type variable star and 2 OH masers' optical variability  

NASA Astrophysics Data System (ADS)

MASTER OT J110235.37+271333.0 - UV Cet type MASTER-Tunka auto-detection system ( Lipunov et al., Advances in Astronomy, MASTER Global Robotic Net, 2010 ) discovered OT source at (RA, Dec) = 11h 02m 35.37s +27d 13m 33.0s on 2015-02-23.73913 UT.

Shurpakov, S.; Balanutsa, P.; Gress, O.; Lipunov, V.; Gorbovskoy, E.; Antipin, S.; Tiurina, N.; Kornilov, V.; Kuznetsov, A.; Shumkov, V.; Chazov, V.; Vladimirov, V.; Ivanov, K.; Budnev, N.; Yazev, S.; Poleshchuk, V.; Konstantinov, E.; Chuvalaev, O.; Tlatov, A.; Dormidontov, D.; Senik, V.; Parkhomenko, A.; Yurkov, V.; Sergienko, Y.; Gabovich, A.; Krushinsky, V.; Zalozhnih, I.; Popov, A.; Bourdanov, A.

2015-02-01

112

Spectroscopy of high proper motion stars in the ground-based UV  

NASA Astrophysics Data System (ADS)

Based on high quality spectral data (spectral resolution R?60000) within the wavelength range of 3550-5000 Å we determined main parameters (effective temperature, surface gravity, microturbulent velocity, and content of chemical elements including heavy metals from Sr to Dy) for 14 metal-deficient G-K stars with large proper motions. The stars studied have a high range of metallicity: [Fe/H]=-0.3÷-2.9. Abundances of Mg, Al, Sr and Ba were calculated with non-LTE line-formation effects accounted for. The abundance both of radioactive element Th and the r-process element Eu were determined through synthetic spectrum calculations. We selected stars that belong to different galactic populations according to the kinematical criterion and parameters determined by us. We found that the studied stars with large proper motions refer to different components of the Galaxy: thin, thick disks and halo. The chemical composition of the star BD+80° 245 far from the galactic plane agrees with its belonging to the accreted halo. For the giant HD 115444 we obtained [Fe/H]=-2.91, an underabundance of Mn, an overabundance of heavy metals from Ba to Dy, and especially a high excess of the r-process element europium: [Eu/Fe]=+1.26. Contrary to its chemical composition typical for halo stars, HD 115444 belongs to the disc population according to its kinematic parameters.

Klochkova, V.; Mishenina, T.; Korotin, S.; Marsakov, V.; Panchuk, V.; Tavolganskaya, N.; Usenko, I.

2011-09-01

113

Curing the UV/IR mixing for field theories with translation-invariant star products  

SciTech Connect

The ultraviolet/infrared (UV/IR) mixing of noncommutative field theories has been recently shown to be a generic feature of translation-invariant associative products. In this paper we propose to take into account the quantum corrections of the model to modify in this way the noncommutative action. This idea was already used to cure the UV/IR mixing for theories on Moyal space. We show that in the present framework also, this proposal proves successful for curing the mixing. We achieve this task by explicit calculations of one and higher loops Feynman amplitudes. For the sake of completeness, we compute the form of the new action in the matrix base for the Wick-Voros product.

Tanasa, Adrian [Centre de Physique Theorique, CNRS UMR 7644, Ecole Polytechnique, 91128 Palaiseau (France); Institutul de Fizica si Inginerie Nucleara Horia Hulubei, P.O. Box MG-6, 077125 Magurele (Romania); Vitale, Patrizia [Laboratoire de Physique Theorique, Universite Paris XI, 91405 Orsay Cedex (France); Dipartimento di Scienze Fisiche, Universita di Napoli Federico II and INFN, Sezione di Napoli, Via Cintia 80126 Napoli (Italy)

2010-03-15

114

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

115

Curing the UV/IR mixing for field theories with translation-invariant $\\star$ products  

E-print Network

The ultraviolet/infrared (UV/IR) mixing of noncommutative field theories has been recently shown to be a generic feature of translation- invariant associative products. In this paper we propose to take into account the quantum corrections of the model to modify in this way the noncommutative action. This idea was already used to cure the UV/IR mixing for theories on Moyal space. We show that in the present framework also, this proposal proves successful for curing the mixing. We achieve this task by explicit calculations of one and higher loops Feynman amplitudes. For the sake of completeness, we compute the form of the new action in the matrix base for the Wick-Voros product.

Adrian Tanasa; Patrizia Vitale

2010-02-15

116

Comparison of stars and decaying neutrinos as additional sources of Intergalactic UV background  

Microsoft Academic Search

A numerical calculation of properties of finite absorbers and of\\u000aintergalactic medium based on photoionization equilibrium is performed to\\u000aconfront alternative UV sources in addition to quasars. It is seen that a\\u000aspectrum including a large peak around the HI ionization energy due to decaying\\u000aneutrinos is too soft in the region up to the HeI edge to explain the

Luis Masperi; Sandra Savaglio

1996-01-01

117

CETIS: COMPLEX EFFLUENTS TOXICITY INFORMATION SYSTEM. DATA ENCODING GUIDELINES AND PROCEDURES  

EPA Science Inventory

The computerized Complex Effluent Toxicity Information System (CETIS) data base includes data extracted from aquatic bioassay reprints as well as facility and receiving water information. Data references are obtained from both published papers and from unpublished results of test...

118

Fracture Orientations Within HiRISE Images of Ceti Mensa, West Candor Chasma, Mars  

NASA Astrophysics Data System (ADS)

Fracture morphology and orientations measured within HiRISE images around Ceti Mensa show a large variation in orientation and are generally not parallel to the proposed trend of the major basin-forming faults.

Birnie, C.; Fueten, F.; Stesky, R.; Hauber, E.; Zegers, T.; Gwinner, K.

2010-03-01

119

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

120

THE NEWLY DISCOVERED PULSATING LOW-MASS WHITE DWARFS: AN EXTENSION OF THE ZZ CETI INSTABILITY STRIP  

SciTech Connect

In light of the exciting discovery of g-mode pulsations in extremely low-mass, He-core DA white dwarfs, we report on the results of a detailed stability survey aimed at explaining the existence of these new pulsators as well as their location in the spectroscopic Hertzsprung-Russell diagram. To this aim, we calculated some 28 evolutionary sequences of DA models with various masses and chemical layering. These models are characterized by the so-called ML2/{alpha} = 1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We pulsated the models with the nonadiabatic code MAD, which incorporates a detailed treatment of time-dependent convection. On the other hand, given the failure of all nonadiabatic codes, including MAD, to account properly for the red edge of the strip, we resurrect the idea that the red edge is due to energy leakage through the atmosphere. We thus estimated the location of that edge by requiring that the thermal timescale in the driving region-located at the base of the H convection zone-be equal to the critical period beyond which l = 1 g-modes cease to exist. Using this approach, we find that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip, including the low-gravity, low-temperature regime where the three new pulsators are found. We also account for the relatively long periods observed in these stars, and thus conclude that they are true ZZ Ceti stars, but with low masses.

Van Grootel, V.; Dupret, M.-A. [Institut d'Astrophysique et de Geophysique de l'Universite de Liege, Allee du 6 Aout 17, B-4000 Liege (Belgium)] [Institut d'Astrophysique et de Geophysique de l'Universite de Liege, Allee du 6 Aout 17, B-4000 Liege (Belgium); Fontaine, G.; Brassard, P., E-mail: valerie.vangrootel@ulg.ac.be [Departement de Physique, Universite de Montreal, Succ. Centre-Ville, C.P. 6128, Montreal, QC H3C 3J7 (Canada)

2013-01-01

121

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

122

Evolution over Time of Magentic Dynamo Driven UV & X-ray Emissions of dG-M Stars and Effects on Hosted Planets  

NASA Astrophysics Data System (ADS)

The evolution over time of the magnetic activity and the resulting X-ray and UV coronal and chromospheric emissions of main-sequence dG, dK, and dM stars with widely different ages are discussed. Young cool stars spin rapidly and have correspondingly very robust magnetic dynamos and strong coronal and chromospheric X-ray - UV (XUV) emissions. However, these stars spin-down with time as they lose angular momentum via magnetized winds and their magnetic generated activity and emissions significantly decrease. Studies of dK-dM stars over a wide range of ages and rotations show similar (but not identical) behavior. Particular emphasis is given to discussing the effects that XUV emissions have on the atmospheres and evolution of solar system planets as well as the increasing number of extrasolar planets found hosted by dG-dM stars. The results from modeling the early atmospheres of Venus, Earth and Mars using recently determined XUV irradiances and inferred winds of the young Sun are also briefly discussed. For example, the loss of water from juvenile Venus and Mars can be explained by action of the strong XUV emissions and robust winds of the young Sun. We also examine the effects of strong X-ray and UV coronal and chromospheric emissions (and frequent flares) that dM stars have on possible planets orbiting within their shrunken habitable zones (HZs) - located close to the low luminosity host stars (HZ ? 0.4 AU). Dwarf M stars make interesting targets for further study because of their deep outer convective zones (CZs), efficient dynamos, frequent flares and strong XUV emissions. Furthermore, a large fraction of dM stars are very old (>5 Gyr), which present intriguing possibilities for the development of highly advanced modes of intelligent life on planets that may orbit them.

2007-07-01

123

Hubble Space Telescope STIS Spectroscopy of the White Dwarfs in the Ultrashort-Period Dwarf Novae VY Aquarii and WX Ceti  

NASA Astrophysics Data System (ADS)

We present the results of a multicomponent synthetic spectral analysis of Hubble Space Telescope (HST) STIS spectra of the ultrashort-period dwarf novae VY Aqr and WX Ceti during their deep quiescence following their last superoutburst. The white dwarf in these extremely low accretion rate systems dominates the far-UV light. We find that the accreting white dwarfs in VY Aqr and WX Ceti are remarkably similar. Both systems contain white dwarfs with Teff=13,000-13,500 K, a rotation velocity below 800-1200 km s-1, and subsolar metallicity. Both white dwarfs are better fitted with a two-temperature white dwarf plus accretion belt model in which part of the white dwarf is cooler and ``slowly'' rotating and part is hotter, smaller, and spinning at the Keplerian speed. We discuss the implications of the surface temperatures we have derived for the white dwarfs in VY Aqr, WX Ceti, and the nine other WZ Sge-like dwarf novae below the period gap which have been observed with HST. Their surface temperatures cluster closely around 15,000 K and their orbital periods are between 1.3 and 1.5 hr. We show that long-term compressional heating due to time-averaged accretion is the mechanism responsible for the clustering around 15,000 K. The time-averaged accretion rate corresponding to this cluster of observed temperatures is almost precisely what is predicted if gravitational wave emission is driving mass transfer below the period gap. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Sion, Edward M.; Szkody, Paula; Cheng, Fuhua; Gänsicke, Boris T.; Howell, Steve B.

2003-02-01

124

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

125

New binaries among UV-selected, hot subdwarf stars and population properties  

E-print Network

We have measured the orbital parameters of seven close binaries, including six new objects, in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from ~0.17 to 3 d. One new system, GALEX J2205-3141, shows reflection on a M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low mass white dwarf (GALEX J0805-1058) paired with an unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses...

Kawka, A; O'Toole, S; Nemeth, P; Burton, D; Kotze, E; Buckley, D A H

2015-01-01

126

UV-CONTINUUM SLOPES AT z {approx} 4-7 FROM THE HUDF09+ERS+CANDELS OBSERVATIONS: DISCOVERY OF A WELL-DEFINED UV COLOR-MAGNITUDE RELATIONSHIP FOR z {>=} 4 STAR-FORMING GALAXIES  

SciTech Connect

Ultra-deep Advanced Camera for Surveys (ACS) and WFC3/IR HUDF+HUDF09 data, along with the wide-area GOODS+ERS+CANDELS data over the CDF-S GOODS field, are used to measure UV colors, expressed as the UV-continuum slope {beta}, of star-forming galaxies over a wide range of luminosity (0.1L*{sub z=3} to 2L*{sub z=3}) at high redshift (z {approx} 7 to z {approx} 4). {beta} is measured using all ACS and WFC3/IR passbands uncontaminated by Ly{alpha} and spectral breaks. Extensive tests show that our {beta} measurements are only subject to minimal biases. Using a different selection procedure, Dunlop et al. recently found large biases in their {beta} measurements. To reconcile these different results, we simulated both approaches and found that {beta} measurements for faint sources are subject to large biases if the same passbands are used both to select the sources and to measure {beta}. High-redshift galaxies show a well-defined rest-frame UV color-magnitude (CM) relationship that becomes systematically bluer toward fainter UV luminosities. No evolution is seen in the slope of the UV CM relationship in the first 1.5 Gyr, though there is a small evolution in the zero point to redder colors from z {approx} 7 to z {approx} 4. This suggests that galaxies are evolving along a well-defined sequence in the L{sub UV}-color ({beta}) plane (a 'star-forming sequence'?). Dust appears to be the principal factor driving changes in the UV color {beta} with luminosity. These new larger {beta} samples lead to improved dust extinction estimates at z {approx} 4-7 and confirm that the extinction is essentially zero at low luminosities and high redshifts. Inclusion of the new dust extinction results leads to (1) excellent agreement between the star formation rate (SFR) density at z {approx} 4-8 and that inferred from the stellar mass density; and (2) to higher specific star formation rates (SSFRs) at z {approx}> 4, suggesting that the SSFR may evolve modestly (by factors of {approx}2) from z {approx} 4-7 to z {approx} 2.

Bouwens, R. J.; Franx, M.; Labbe, I.; Smit, R. [Leiden Observatory, Leiden University, NL-2300 RA Leiden (Netherlands); Illingworth, G. D.; Oesch, P.A.; Gonzalez, V.; Magee, D. [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Trenti, M. [Center for Astrophysics and Space Astronomy, University of Colorado, 389-UCB, Boulder, CO 80309 (United States); Van Dokkum, P. [Department of Astronomy, Yale University, New Haven, CT 06520 (United States); Carollo, C. M. [Institute for Astronomy, ETH Zurich, 8092 Zurich (Switzerland)

2012-08-01

127

UV-continuum Slopes at z ~ 4-7 from the HUDF09+ERS+CANDELS Observations: Discovery of a Well-defined UV Color-Magnitude Relationship for z >= 4 Star-forming Galaxies  

NASA Astrophysics Data System (ADS)

Ultra-deep Advanced Camera for Surveys (ACS) and WFC3/IR HUDF+HUDF09 data, along with the wide-area GOODS+ERS+CANDELS data over the CDF-S GOODS field, are used to measure UV colors, expressed as the UV-continuum slope ?, of star-forming galaxies over a wide range of luminosity (0.1L* z = 3 to 2L* z = 3) at high redshift (z ~ 7 to z ~ 4). ? is measured using all ACS and WFC3/IR passbands uncontaminated by Ly? and spectral breaks. Extensive tests show that our ? measurements are only subject to minimal biases. Using a different selection procedure, Dunlop et al. recently found large biases in their ? measurements. To reconcile these different results, we simulated both approaches and found that ? measurements for faint sources are subject to large biases if the same passbands are used both to select the sources and to measure ?. High-redshift galaxies show a well-defined rest-frame UV color-magnitude (CM) relationship that becomes systematically bluer toward fainter UV luminosities. No evolution is seen in the slope of the UV CM relationship in the first 1.5 Gyr, though there is a small evolution in the zero point to redder colors from z ~ 7 to z ~ 4. This suggests that galaxies are evolving along a well-defined sequence in the L UV-color (?) plane (a "star-forming sequence"?). Dust appears to be the principal factor driving changes in the UV color ? with luminosity. These new larger ? samples lead to improved dust extinction estimates at z ~ 4-7 and confirm that the extinction is essentially zero at low luminosities and high redshifts. Inclusion of the new dust extinction results leads to (1) excellent agreement between the star formation rate (SFR) density at z ~ 4-8 and that inferred from the stellar mass density; and (2) to higher specific star formation rates (SSFRs) at z >~ 4, suggesting that the SSFR may evolve modestly (by factors of ~2) from z ~ 4-7 to z ~ 2. 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 11563 and 9797.

Bouwens, R. J.; Illingworth, G. D.; Oesch, P. A.; Franx, M.; Labbé, I.; Trenti, M.; van Dokkum, P.; Carollo, C. M.; González, V.; Smit, R.; Magee, D.

2012-08-01

128

UV circular polarisation in star formation regions: the origin of homochirality?  

E-print Network

Ultraviolet circularly polarised light has been suggested as the initial cause of the homochirality of organic molecules in terrestrial organisms, via enantiomeric selection of prebiotic molecules by asymmetric photolysis. We present a theoretical investigation of mechanisms by which ultraviolet circular polarisation may be produced in star formation regions. In the scenarios considered here, light scattering produces only a small percentage of net circular polarisation at any point in space, due to the forward throwing nature of the phase function in the ultraviolet. By contrast, dichroic extinction can produce a fairly high percentage of net circular polarisation (~10%) and may therefore play a key role in producing an enantiomeric excess.

Lucas, P W; Bailey, J; Chrysostomou, A; Gledhill, T M; McCall, A; Bailey, Jeremy; Chrysostomou, Antonio; Call, Alan Mc

2003-01-01

129

UV circular polarisation in star formation regions: the origin of homochirality?  

E-print Network

Ultraviolet circularly polarised light has been suggested as the initial cause of the homochirality of organic molecules in terrestrial organisms, via enantiomeric selection of prebiotic molecules by asymmetric photolysis. We present a theoretical investigation of mechanisms by which ultraviolet circular polarisation may be produced in star formation regions. In the scenarios considered here, light scattering produces only a small percentage of net circular polarisation at any point in space, due to the forward throwing nature of the phase function in the ultraviolet. By contrast, dichroic extinction can produce a fairly high percentage of net circular polarisation (~10%) and may therefore play a key role in producing an enantiomeric excess.

P. W. Lucas; J. H. Hough; Jeremy Bailey; Antonio Chrysostomou; T. M. Gledhill; Alan McCall

2003-08-18

130

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

131

The outer disks of Herbig stars from the UV to NIR  

NASA Astrophysics Data System (ADS)

Spatially-resolved imaging of Herbig stars and related objects began with HST, but intensified with commissioning of high-contrast imagers on 8-m class telescopes. The bulk of the data taken from the ground have been polarized intensity imagery at H-band, with the majority of the sources observed as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey. Sufficiently many systems have been imaged that we discuss disk properties in scattered, polarized light in terms of groups defined by the IR spectral energy distribution. We find novel phenomena in many of the disks, including spiral density waves, and discuss the disks in terms of clearing mechanisms. Some of the disks have sufficient data to map the dust and gas components, including water ice dissociation products.

Grady, C.; Fukagawa, M.; Maruta, Y.; Ohta, Y.; Wisniewski, J.; Hashimoto, J.; Okamoto, Y.; Momose, M.; Currie, T.; McElwain, M.; Muto, T.; Kotani, T.; Kusakabe, N.; Feldt, M.; Sitko, M.; Follette, K.; Bonnefoy, M.; Henning, T.; Takami, M.; Karr, J.; Kwon, J.; Kudo, T.; Abe, L.; Brandner, W.; Brandt, T.; Carson, J.; Egner, S.; Goto, M.; Guyon, O.; Hayano, Y.; Hayashi, M.; Hayashi, S.; Hodapp, K.; Ishii, M.; Iye, M.; Janson, M.; Kandori, R.; Knapp, G.; Kuzuhara, M.; Matsuo, T.; Miyama, S.; Morino, J.-I.; Moro-Martín, A.; Nishimura, T.; Pyo, T.-S.; Serabyn, E.; Suenaga, T.; Suto, H.; Suzuki, R.; Takahashi, Y. H.; Takato, N.; Terada, H.; Thalmann, C.; Tomono, D.; Turner, E. L.; Watanabe, M.; Yamada, T.; Takami, H.; Usuda, T.; Tamura, M.

2015-02-01

132

Modeling the near-UV Band of GK Stars. II. Non-LTE Models  

NASA Astrophysics Data System (ADS)

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 & Hauschildt (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T(?) relation) and the SED as a finely sampled function of T 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 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 eff values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best-fit T 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 eff values to several other spectroscopic and photometric T 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.

Short, C. Ian; Campbell, Eamonn A.; Pickup, Heather; Hauschildt, Peter H.

2012-03-01

133

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

134

Diagnostic tools for rapid detection and quantification of Weissella ceti NC36 infections in rainbow trout.  

PubMed

Weissellosis of rainbow trout is caused by the Gram-positive bacteria Weissella ceti and has been reported in China, Brazil and the United States. This disease can result in high mortality in market-sized fish and thus can cause significant economic loss. Thus far, phenotypic characterization and 16S rRNA sequencing have been used to confirm a Weissellosis diagnosis. Here, we present the development of PCR-based diagnostic tools for the rapid identification and quantification of W. ceti within bacteriological culture and infected tissues. A duplex PCR, which amplifies both genus- and strain-specific targets, positively identifies isolates as W. ceti NC36. A qPCR assay was also developed to quantify pathogen load from infected tissues, using a W. ceti NC36 unique locus. A proof of concept study was performed to demonstrate that quantification using traditional plate count methods and qPCR were significantly correlated when assessed from infected brain and spleen tissue. These tools were also used to confirm diagnosis of Weissellosis in a commercial rainbow trout farm during an outbreak investigation. These are the first diagnostic tools developed for identification and quantification of W. ceti infection within rainbow trout, contributing to rapid Weissellosis diagnosis, enhanced pathogen surveillance and epidemiological studies. PMID:25470116

Snyder, A K; Hinshaw, J M; Welch, T J

2015-02-01

135

The UV properties of E+A galaxies: constraints on feedback-driven quenching of star formation  

NASA Astrophysics Data System (ADS)

We present the first large-scale study of E+A galaxies that incorporates photometry in the ultraviolet (UV) wavelengths. E+A galaxies are `post-starburst' systems, with strong Balmer absorption lines indicating significant recent star formation, but without [OII] and H? emission lines which are characteristic of ongoing star formation. The starburst that creates the E+A galaxy typically takes place within the last Gyr and creates a high fraction (20-60 per cent) of the stellar mass in the remnant over a short time-scale (<0.1 Gyr). We find a tight correlation between the luminosity of our E+A galaxies and the implied star formation rate (SFR) during the starburst. While low-luminosity E+As [M(z) > -20] exhibit implied SFRs of less than 50Msolaryr-1, their luminous counterparts [M(z) < -22] show SFRs greater than 300 and as high as 2000Msolaryr-1, suggesting that luminous and ultra-luminous infrared galaxies in the low-redshift Universe could be the progenitors of massive nearby E+A galaxies. We perform a comprehensive study of the characteristics of the quenching that truncates the starburst in E+A systems. We find that, for galaxies less massive than 1010Msolar, the quenching efficiency decreases as the galaxy mass increases. However, for galaxies more massive than 1010Msolar, this trend is reversed and the quenching efficiency increases with galaxy mass. Noting that the mass threshold at which this reversal occurs is in excellent agreement with the mass above which active galactic nuclei (AGN) become significantly more abundant in nearby galaxies, we use simple energetic arguments to show that the bimodal behaviour of the quenching efficiency is consistent with AGN and supernovae (SN) being the principal sources of negative feedback above and below M ~ 1010Msolar, respectively. The arguments assume that quenching occurs through the mechanical ejection or dispersal of the gas reservoir and that, in the high-mass regime (M > 1010Msolar), the Eddington ratios in this sample of galaxies scale as M?, where 1 < ? < 3. Finally, we use our E+A sample to estimate the time it takes for galaxies to migrate from the blue cloud to the red sequence. We find migration times between 1 and 5 Gyr, with a median value of 1.5 Gyr.

Kaviraj, S.; Kirkby, L. A.; Silk, J.; Sarzi, M.

2007-12-01

136

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

137

Meningoencephalitis and arthritis associated with Brucella ceti in a short-beaked common dolphin (Delphinus delphis).  

PubMed

Brucella species infection in marine mammal species has been reported to have a global distribution. In 2007, the description of Brucella ceti was published and formally adopted for those isolates originating from cetaceans and pathologic lesions similar to those seen in terrestrial mammals infected with Brucella spp. have been associated with its isolation. Brucella ceti infection specific to the central nervous system has been described in two species of cetacean: striped dolphins (Stenella coeruleoalba) in Europe and Costa Rica and an Atlantic white-sided dolphin (Lagenorhynchus acutus) in the UK. We describe the first report, to our knowledge, of B. ceti-associated meningitis and arthritis in a third species, the short-beaked common dolphin (Delphinus delphis), in an animal that stranded in the UK. PMID:23778612

Davison, Nicholas J; Barnett, James E F; Perrett, Lorraine L; Dawson, Claire E; Perkins, Matthew W; Deaville, Robert C; Jepson, Paul D

2013-07-01

138

Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk  

NASA Technical Reports Server (NTRS)

We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the “Gas in Protoplanetary Systems” (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 micron; 49 Cet is significantly extended in the 70 micron image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O i] 63 micron and [C ii] 158 micron. The C ii line was detected at the 5 sigma level—the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the Oi line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C ii emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.

Roberge, A.; Kamp, I.; Montesinos, B.; Dent, W. R. F.; Meeus, G.; Donaldson, J. K.; Olofsson, J.; Moor, A.; Augereau, J.-C.; Howard, C.; Eiroa, C.; Thi, W.-F.; Ardila, D. R.; Sandell, G.; Woitke, P.

2013-01-01

139

HERSCHEL OBSERVATIONS OF GAS AND DUST IN THE UNUSUAL 49 Ceti DEBRIS DISK  

SciTech Connect

We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the ''Gas in Protoplanetary Systems'' (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 {mu}m; 49 Cet is significantly extended in the 70 {mu}m image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O I] 63 {mu}m and [C II] 158 {mu}m. The C II line was detected at the 5{sigma} level-the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the O I line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C II emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.

Roberge, A. [Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States); Kamp, I. [Kapteyn Astronomical Institute, University of Groningen, 9700 AV Groningen (Netherlands); Montesinos, B. [Departamento de Astrofisica, Centro de Astrobiologia (INTA-CSIC), ESAC Campus, PO Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Dent, W. R. F. [ALMA, Avda Apoquindo 3846, Piso 19, Edificio Alsacia, Las Condes, Santiago (Chile); Meeus, G.; Eiroa, C. [Departmento Fisica Teorica, Facultad de Ciencias, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain); Donaldson, J. K. [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Olofsson, J. [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117, Heidelberg (Germany); Moor, A. [Konkoly Observatory of the Hungarian Academy of Sciences, P.O. Box 67, H-1525 Budapest (Hungary); Augereau, J.-C.; Thi, W.-F. [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d'Astrophysique de Grenoble, UMR 5274, F-38041, Grenoble (France); Howard, C.; Sandell, G. [SOFIA-USRA, NASA Ames Research Center, Building N232, PO Box 1, Moffett Field, CA 94035 (United States); Ardila, D. R. [NASA Herschel Science Center, California Institute of Technology, 1200 E. California Blvd., Mail Stop 220-6, Pasadena, CA 91125 (United States); Woitke, P., E-mail: Aki.Roberge@nasa.gov [University of Vienna, Department of Astronomy, Tuerkenschanzstr. 17, A-1180, Vienna (Austria)

2013-07-01

140

The UV colours of high-redshift early-type galaxies: evidence for recent star formation and stellar mass assembly over the last 8 billion years  

NASA Astrophysics Data System (ADS)

We combine deep optical and NIR (UBVRIzJK) photometry from the Multiwavelength Survey by Yale-Chile (MUSYC) with redshifts from the COMBO-17 survey to perform a large-scale study of the rest-frame ultraviolet (UV) properties of 674 high-redshift (0.5 < z < 1) early-type galaxies, drawn from the Extended Chandra Deep Field-South (E-CDFS). Galaxy morphologies are determined through visual inspection of Hubble Space Telescope (HST) images taken from the GEMS survey. We harness the sensitivity of the UV to young (<1-Gyr old) stars to quantify the recent star formation history of early-type galaxies across a range of luminosities [-23.5 < M(V) < -18]. Comparisons to simple stellar populations forming at high redshift indicate that ~1.1 per cent of early-types in this sample are consistent with purely passive ageing since z = 2 - this value drops to ~0.24 per cent and ~0.15 per cent for z = 3 and 5, respectively. Parametrizing the recent star formation (RSF) in terms of the mass fraction of stars less than a Gyr old, we find that the early-type population as a whole shows a typical RSF between 5 and 13 per cent in the redshift range 0.5 < z < 1. Early-types on the broad UV `red sequence' show RSF values less than 5 per cent, while the reddest early-types (which are also the most luminous) are virtually quiescent with RSF values of ~1 per cent. In contrast to their low-redshift (z < 0.1) counterparts, the high-redshift early-types in this sample show a pronounced bimodality in the rest-frame UV-optical colour, with a minor but significant peak centred on the blue cloud. Furthermore, star formation in the most active early-types is a factor of 2 greater at z ~ 0.7 than in the local universe. Given that evolved sources of UV flux (e.g. horizontal branch stars) should be absent at z > 0.5, implying that the UV is dominated by young stars, we find compelling evidence that early-types of all luminosities form stars over the lifetime of the Universe, although the bulk of their star formation is already complete at high redshift. This `tail-end' of star formation is measurable and not negligible, with luminous [-23 < M(V) < -20.5] early-types potentially forming 10-15 per cent of their mass since z = 1, with less luminous early-types [M(V) > -20.5] potentially forming 30-60 per cent of their mass after z = 1. This, in turn, implies that intermediate-age stellar populations should be abundant in local early-type galaxies, as expected in hierarchical cosmology.

Kaviraj, S.; Khochfar, S.; Schawinski, K.; Yi, S. K.; Gawiser, E.; Silk, J.; Virani, S. N.; Cardamone, C. N.; van Dokkum, P. G.; Urry, C. M.

2008-07-01

141

The debris disc of solar analogue ? Ceti: Herschel observations and dynamical simulations of the proposed multiplanet system  

NASA Astrophysics Data System (ADS)

? Ceti is a nearby, mature G-type star very similar to our Sun, with a massive Kuiper Belt analogue and possible multiplanet system that has been compared to our Solar system. We present Herschel Space Observatory images of the debris disc, finding the disc is resolved at 70 ?m and 160 ?m, and marginally resolved at 250 ?m. The Herschel images and infrared photometry from the literature are best modelled using a wide dust annulus with an inner edge between 1 and 10 au and an outer edge at ˜55 au, inclined from face-on by 35° ± 10°, and with no significant azimuthal structure. We model the proposed tightly packed planetary system of five super-Earths and find that the innermost dynamically stable disc orbits are consistent with the inner edge found by the observations. The photometric modelling, however, cannot rule out a disc inner edge as close to the star as 1 au, though larger distances produce a better fit to the data. Dynamical modelling shows that the five-planet system is stable with the addition of a Neptune or smaller mass planet on an orbit outside 5 au, where the radial velocity data analysis would not have detected a planet of this mass.

Lawler, S. M.; Di Francesco, J.; Kennedy, G. M.; Sibthorpe, B.; Booth, M.; Vandenbussche, B.; Matthews, B. C.; Holland, W. S.; Greaves, J.; Wilner, D. J.; Tuomi, M.; Blommaert, J. A. D. L.; de Vries, B. L.; Dominik, C.; Fridlund, M.; Gear, W.; Heras, A. M.; Ivison, R.; Olofsson, G.

2014-11-01

142

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

143

VizieR Online Data Catalog: The anomalous Cepheid XZ Ceti (Szabados+, 2007)  

NASA Astrophysics Data System (ADS)

Photometric and radial velocity data of the anomalous Cepheid XZ Ceti are given. The photometric data cover one week, the spectroscopic radial velocity observations were secured during two observing runs in 2004-2005. All data were obtained with the equipments of the Siding Spring Observatory, Australia. (2 data files).

Szabados, L.; Kiss, L. L.; Derekas, A.

2006-10-01

144

Slippery Slopes on Ceti Mensa, West Candor Chasma, Mars: Analysis of a Lobate Deposit  

NASA Astrophysics Data System (ADS)

A lobate deposit on the north side of Ceti Mensa is composed of rounded blocks that appear to have slid on a malleable substrate. Sliding features elsewhere on the mensa suggest that gravity gliding contributed to the domal shape of this ILD stack.

Lucchitta, B. K.

2010-03-01

145

Large-scale Star Formation Triggering in the Low-mass Arp 82 System: A Nearby Example of Galaxy Downsizing Based on UV/Optical/Mid-IR Imaging  

E-print Network

As part of our Spitzer Spirals, Bridges, and Tails project to help understand the effects of galaxy interactions on star formation, we analyze GALEX ultraviolet, SARA optical, and Spitzer infrared images of the interacting galaxy pair Arp 82 (NGC 2535/6) and compare to a numerical simulation of the interaction. We investigate the multiwavelength properties of several individual star forming complexes (clumps). Using optical and UV colors, EW(Halpha), and population synthesis models we constrain the ages of the clumps and find that the median clump age is about 12 Myr. The clumps have masses ranging from a few times 10^6 to 10^9 solar masses. In general, the clumps in the tidal features have similar ages to those in the spiral region, but are less massive. The 8 micron and 24 micron luminosities are used to estimate the far-infrared luminosities and the star formation rates of the clumps. The total clump star formation rate is 2.0+/-0.8 solar masses per year, while the entire Arp 82 system is forming stars at a rate of 4.9+/-2.0 solar masses per year. We find, for the first time, stars in the HI arc to the southeast of the NGC 2535 disk. Population synthesis models indicate that all of the observed populations have young to intermediate ages. We conclude that although the gas disks and some old stars may have formed early-on, the progenitors are late-type or low surface brightness and the evolution of these galaxies was halted until the recent encounter.

Mark Hancock; Beverly J. Smith; Curtis Struck; Mark L. Giroux; Philip N. Appleton; Vassilis Charmandaris; William T. Reach

2006-10-13

146

When people say they see a shooting star after noticing a momentary streak of light in the night sky, what  

E-print Network

(pronounced "my-rah") is also known as Omicron Ceti. Mira is the only normal star known to have a tail. You- years from Earth. If you could see the star and its tail with your naked eyes, it would be as long is called a stellar wind. Like the bow wave of a boat traveling through water, a bow shock forms ahead

147

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

148

UV CONTINUUM SLOPE AND DUST OBSCURATION FROM z approx 6 TO z approx 2: THE STAR FORMATION RATE DENSITY AT HIGH REDSHIFT  

SciTech Connect

We provide a systematic measurement of the rest-frame UV continuum slope beta over a wide range in redshift (z approx 2-6) and rest-frame UV luminosity (0.1 L* {sub z} {sub =} {sub 3} to 2 L* {sub z={sub 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 approx 2-4 than it is at z approx 5-6 (from approx-2.4 at z approx 6 to approx-1.5 at z approx 2). Lower luminosity galaxies are also found to be bluer than higher luminosity galaxies at z approx 2.5 and z approx 4. We do not find a large number of galaxies with beta's as red as -1 in our dropout selections at z approx 4, and particularly at z approx> 5, even though such sources could be readily selected from our data (and also from Balmer Break Galaxy searches at z approx 4). This suggests that star-forming galaxies at z approx> 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 approx> 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 approx 0 and z approx 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 (approx<2 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 approx 2-6, but find that they contribute only approx20% of the total at z approx 2.5 and approx<10% at z approx> 4.

Bouwens, R. J.; Illingworth, G. D. [Astronomy Department, University of California, Santa Cruz, CA 95064 (United States); Franx, M. [Leiden Observatory, University of Leiden, Postbus 9513, 2300 RA Leiden (Netherlands); Chary, R.-R. [Divison of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Meurer, G. R.; Ford, H. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Conselice, C. J. [University of Nottingham, School of Physics and Astronomy, Nottinghm NG7 2RD (United Kingdom); Giavalisco, M. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Van Dokkum, P. [Department of Astronomy, Yale University, New Haven, CT (United States)

2009-11-01

149

Sub-mm Observation of Vega-like Stars  

NASA Astrophysics Data System (ADS)

We observed eight Vega-like stars at 850 ?m with SCUBA on the JCMT at Mauna Kea, Hawaii; all are predicted to have high dust content. We marginally detected 49 Ceti (4 ?), previously detected in CO (Zuckerman et al. 1995). We derive a dust mass of ˜8 Mmoon, resulting in a gas-to-dust ratio of ˜ 20. We also detected HD 627, but the emission is extended and centered east of the star, suggesting interstellar rather than circumstellar origin.

Song, I.; Sandell, G.; Friberg, P.

2004-12-01

150

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

151

UV Luminosity Functions at z~4, 5, and 6 from the HUDF and other Deep HST ACS Fields: Evolution and Star Formation History  

E-print Network

We use the ACS BViz data from the HUDF and all other deep HST ACS fields (including the GOODS fields) to find large samples of star-forming galaxies at z~4 and z~5 and to extend our previous z~6 sample. These samples contain 4671, 1416, and 627 B, V, and i dropouts, respectively, and reach to extremely low luminosities (0.01-0.04 L* or M(UV)~-16 to -17), allowing us to determine the rest-frame UV luminosity function (LF) and faint-end slope alpha at z~4-6 to high accuracy. We find faint-end slopes alpha of -1.73+/-0.05 at z~4, -1.66+/-0.09 at z~5, and -1.74+/-0.16 at z~6 -- suggesting that the faint-end slope is very steep and shows little evolution with cosmic time. We find that M*(UV) brightens considerably in the 0.7 Gyr from z~6 to z~4 (by ~0.7 mag from M*=-20.24+/-0.19 to M*=-20.98+/-0.10). The observed increase in the characteristic luminosity over this range is almost identical to that expected for the halo mass function -- suggesting that the observed evolution is likely due to the hierarchical coalescence and merging of galaxies. The evolution in phi* is not significant. The UV luminosity density at z~6 is modestly lower (0.45+/-0.09 times) than that at z~4 (integrated to -17.5 AB mag) though a larger change is seen in the dust-corrected star-formation rate density. We thoroughly examine published LF results and assess the reasons for their wide dispersion. We argue that the results reported here are the most robust available. The extremely steep faint-end slopes alpha found here suggest that lower luminosity galaxies play a significant role in reionizing the universe. Finally, we consider recent search results for galaxies at z~7-8 and use them to extend our estimates of the evolution in M* from z~7-8 to z~4.

Rychard J. Bouwens; Garth D. Illingworth; Marijn Franx; Holland Ford

2007-11-12

152

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

153

Star formation in NGC 4449: MAMA-detector UV imagery and Fabry-Perot Balmer-line imagery  

NASA Technical Reports Server (NTRS)

Using far-ultraviolet (FUV) and Balmer-line imagery, we investigate the star formation history of 22 large OB complexes in the Magellanic irregular galaxy NGC 4449. The FUV luminosity of NGC 4449 is comparable to those of late-type spirals and is greater than that of the LMC by approximately 2.4 mag, indicating substantial star formation in the last 10(exp 8) yr. FUV data were taken using a sounding-rocket telescope with a Multianode Microchannel Array (MAMA) detector, and Balmer-line data were taken using the Goddard Fabry-Perot Imager. The resulting imagery shows bright, roughly coincident FUV and H alpha sources throughout the extent of the visible galaxy. We model these sources using cluster-evolution codes. Although all sources are a few Myr old, clear age differences are found. In particular, several of the most recently active star formation regions are located together in the galaxy's northern periphery, which is apparently coincident with a large H I reservoir. The brightest and most massive OB complexes are found along the northeast-southwest surface brightness ridgeline (the 'bar'). Over the entire galaxy, star formation rates are consistent on timescales of 10(exp 6), 10(exp 8), and 10(exp 9) yr. A history of recent star formation is suggested with two main episodes, one predominantly in the bar ending approximately 5 Myr ago, and an ongoing one associated with an observed H I cloud.

Hill, Robert S.; Home, Allen T.; Smith, Andrew M.; Bruhweiler, Fred C.; Cheng, K.P.; Hintzen, Paul M. N.; Oliversen, Ronald J.

1994-01-01

154

A NON-LTE ANALYSIS OF THE HOT SUBDWARF O STAR BD+28 Degree-Sign 4211. I. THE UV SPECTRUM  

SciTech Connect

We present a detailed analysis of the UV spectrum of the calibration star BD+28 Degree-Sign 4211 using high-quality spectra obtained with the Hubble Space Telescope and Far-Ultraviolet Spectroscopic Explorer satellites. To this aim, we compare quantitatively the observed data with model spectra obtained from state-of-the-art non-LTE metal line-blanketed model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC. We thus determine in a self-consistent way the abundances of 11 elements with well-defined lines in the UV, namely those of C, N, O, F, Mg, Si, P, S, Ar, Fe, and Ni. The derived abundances range from about solar to 1/10 solar. We find that the overall quality of the derived spectral fits is very satisfying. Our spectral analysis can be used to constrain rather tightly the effective temperature of BD+28 Degree-Sign 4211 to a value of T{sub eff} = 82, 000 {+-} 5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2{sub -0.1}{sup +0.3}. Assuming that the Hipparcos measurement for BD+28 Degree-Sign 4211 is fully reliable and that our model atmospheres are reasonably realistic, we can reconcile our spectroscopic constraints with the available parallax measurement only if the mass of BD+28 Degree-Sign 4211 is significantly less than the canonical value of 0.5 M{sub Sun} for a representative post-extended horizontal branch star.

Latour, M.; Fontaine, G.; Brassard, P. [Departement de Physique, Universite de Montreal, Succ. Centre-Ville, C.P. 6128, Montreal, QC H3C 3J7 (Canada); Chayer, P., E-mail: marilyn@astro.umontreal.ca [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)

2013-08-20

155

The UV Luminosity Function of Star-forming Galaxies via Dropout Selection at Redshifts z ~ 7 and 8 from the 2012 Ultra Deep Field Campaign  

NASA Astrophysics Data System (ADS)

We present a catalog of high-redshift star-forming galaxies selected to lie within the redshift range z ~= 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 ~0.65 (0.25) mag fainter in absolute UV magnitude, at z ~ 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 ~ 7 and 27 at z ~ 8. Incorporating brighter archival and ground-based samples, we measure the z ~= 7 UV luminosity function to an absolute magnitude limit of M UV = -17 and find a faint end Schechter slope of \\alpha =-1.87^{+0.18}_{-0.17}. Using a similar color-color selection at z ~= 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 ~= 8, \\alpha =-1.94^{+0.21}_{-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.; Robertson, Brant E.; Ellis, Richard S.; Ono, Yoshiaki; McLure, Ross J.; Dunlop, James S.; Koekemoer, Anton; Bowler, Rebecca A. A.; Ouchi, Masami; Curtis-Lake, Emma; Rogers, Alexander B.; Schneider, Evan; Charlot, Stephane; Stark, Daniel P.; Furlanetto, Steven R.; Cirasuolo, Michele

2013-05-01

156

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

157

The UV Continuum of z > 1 Star-forming Galaxies in the Hubble Ultraviolet UltraDeep Field  

NASA Astrophysics Data System (ADS)

We estimate the UV continuum slope, ?, for 923 galaxies in the range 1 < z < 8 in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at 1 < z < 2 down to an absolute magnitude M_UV= -14({\\sim} 0.006\\, L^*_{z=1}; 0.02\\, L^*_{z=0}), comparable to dwarf galaxies in the local universe. We combine deep HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data from HST/WFC3/IR (HUDF12). Galaxies in the range 1 < z < 2 are significantly bluer than local dwarf galaxies. We find their mean (median) values = - 1.382(- 1.830) ± 0.002 (random) ± 0.1 (systematic). We find comparable scatter in ? (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than z > 2 galaxies. We study the trends of ? with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, d?/dM = -0.11 ± 0.01, and no evolution in d?/dM with redshift. A modest increase in dust reddening with redshift and luminosity, ?E(B - V) ~ 0.1, and a comparable increase in the dispersion of dust reddening at z < 2, appears likely to explain the observed trends. At z > 2, we find trends that are consistent with previous works; combining our data with the literature in the range 1 < z < 8, we find a color evolution with redshift, d?/dz = -0.09 ± 0.01 for low luminosity (0.05 L^*_{z=3}), and d?/dz = -0.06 ± 0.01 for medium luminosity (0.25 L^*_{z=3}) galaxies.

Kurczynski, Peter; Gawiser, Eric; Rafelski, Marc; Teplitz, Harry I.; Acquaviva, Viviana; Brown, Thomas M.; Coe, Dan; de Mello, Duilia F.; Finkelstein, Steven L.; Grogin, Norman A.; Koekemoer, Anton M.; Lee, Kyoung-soo; Scarlata, Claudia; Siana, Brian D.

2014-09-01

158

Dust-obscured star formation and the contribution of galaxies escaping UV/optical color selections at z ~ 2  

NASA Astrophysics Data System (ADS)

Context. A substantial amount of the stellar mass growth across cosmic time occurred within dust-enshrouded environments. So far, identification of complete samples of distant star-forming galaxies from the short wavelength range has been strongly biased by the effect of dust extinction. Nevertheless, the exact amount of star-forming activity that took place in high-redshift dusty galaxies but that has currently been missed by optical surveys has barely been explored. Aims: Our goal is to determine the number of luminous star-forming galaxies at 1.5 ? z ? 3 that are potentially missed by the traditional color selection techniques because of dust extinction. We also aim at quantifying the contribution of these sources to the IR luminosity and cosmic star formation density at high redshift. Methods: We based our work on a sample of 24 ?m sources brighter than 80 ?Jy and taken from the Spitzer survey of the COSMOS field. Almost all of these sources have accurate photometric redshifts. We applied to this mid-IR selected sample the BzK and BM/BX criteria, as well as the selections of the IRAC peakers and the Optically-Faint IR-bright (OFIR) galaxies. We analyzed the fraction of sources identified with these techniques. We also computed 8 ?m rest-frame luminosity from the 24 ?m fluxes of our sources, and considering the relationships between L8 ?m and LPa? and between L8 ?m and LIR, we derived ?IR and then ?SFR for our MIPS sources. Results: The BzK criterion offers an almost complete (~90%) identification of the 24 ?m sources at 1.4 < z < 2.5. In contrast, the BM/BX criterion misses 50% of the MIPS sources. We attribute this bias to the effect of extinction, which reddens the typical colors of galaxies. The contribution of these two selections to the IR luminosity density produced by all the sources brighter than 80 ?Jy are on the same order. Moreover the criterion based on the presence of a stellar bump in their spectra (IRAC peakers) misses up to 40% of the IR luminosity density, while only 25% of the IR luminosity density at z ~ 2 is produced by OFIR galaxies characterized by extreme mid-IR to optical flux ratios. Conclusions: Color selections of distant star-forming galaxies must be used with care given the substantial bias they can suffer. In particular, the effect of dust extinction strongly affects the completeness of identifications at the bright end of the bolometric luminosity function, which implies large and uncertain extrapolations to account for the contribution of dusty galaxies missed by these selections. In the context of forthcoming facilities that will operate at long wavelengths (e.g., JWST, ALMA, SAFARI, EVLA, SKA), this emphasizes the importance of minimizing the extinction biases when probing the activity of star formation in the early Universe.

Riguccini, L.; Le Floc'h, E.; Ilbert, O.; Aussel, H.; Salvato, M.; Capak, P.; McCracken, H.; Kartaltepe, J.; Sanders, D.; Scoville, N.

2011-10-01

159

Estimation of Mass-Loss Rates from Emission Line Profiles in the UV Spectra of Cool Stars  

NASA Technical Reports Server (NTRS)

The photon-scattering winds of cool, low-gravity stars (K-M giants and supergiants) produce absorption features in the strong chromospheric emission lines. This provides us with an opportunity to assess important parameters of the wind, including flow and turbulent velocities, the optical depth of the wind above the region of photon creation, and the star's mass-loss rate. We have used the Lamers et al. Sobolev with Exact Integration (SEI) radiative transfer code along with simple models of the outer atmospheric structure to compute synthetic line profiles for comparison with the observed line profiles. The SEI code has the advantage of being computationally fast and allows a great number of possible wind models to be examined. We therefore use it here to obtain initial first-order estimates of the wind parameters. More sophisticated, but more time-consuming and resource intensive calculations will be performed at a later date, using the SEI-deduced wind parameters as a starting point. A comparison of the profiles over a range of wind velocity laws, turbulence values, and line opacities allows us to constrain the wind parameters, and to estimate the mass-loss rates. We have applied this analysis technique (using lines of Mg II, 0 I, and Fe II) so far to four stars: the normal K5-giant alpha Tau, the hybrid K-giant gamma Dra, the K5 supergiant lambda Vel, and the M-giant gamma Cru. We present in this paper a description of the technique, including the assumptions which go into its use, an assessment of its robustness, and the results of our analysis.

Carpenter, K. G.; Robinson, R. D.; Harper, G. M.

1999-01-01

160

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

161

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...

162

Chemical composition of AY Ceti: A flaring, spotted star with a white dwarf companion  

NASA Astrophysics Data System (ADS)

The detailed chemical composition of the atmosphere AY Cet (HD 7672) is determined from a high-resolution spectrum in the optical region. The main atmospheric parameters and the abundances of 22 chemical elements, including key species such as 12C, 13C, N, and O, are determined. A differential line analysis gives T_eff=5080 K, log g=3.0, [Fe/H]=-0.33, [C/Fe]=-0.17, [N/Fe]=0.17, [O/Fe]=0.05, C/N=1.58, and 12C/13C=21. Despite the high chromospheric activity, the optical spectrum of AY Cet provides a chemical composition typical for first ascent giants after the first dredge-up.

Tautvaišien?, G.; Barisevi?ius, G.; Berdyugina, S.; Ilyin, I.; Chorniy, Y.

2011-12-01

163

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

164

A Unique Gas-Rich Debris Disk: Herschel Imaging and Spectroscopy of 49 Ceti  

NASA Technical Reports Server (NTRS)

Gas-poor debris disks represent a fundamentally different class of circumstellar disk than gas-rich protoplanetary disks. Their gas probably originates from the same source as the dust, i.e. planetesimal destruction, but the low gas densities make it difficult to detect. So far, Herschel has detected far-IR gas emission from only one or two debris disks, Beta Pictoris being one of them. Here we present Herschel GASPS observations of a well-known debris disk system, 49 Ceti. The dust disk is spatially resolved in thermal emission at 70 _m. Most interestingly, weak far-IR gas emission is detected. Preliminary modeling suggests that reconciling the sub-mm CO emission seen from this system with the far-IR gas detection and upper limits requires a low gas-to-dust ratio and possibly an unusual gas composition.

Roberge, Aki

2012-01-01

165

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

166

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

167

Chromospherically active stars. 6: Giants with compact hot companions and the barium star scenario  

NASA Technical Reports Server (NTRS)

We have determined spectroscopic orbits for three chromospherically active giants that have hot compact companions. They are HD 160538 (K0 III + wd, P = 904 days), HD 165141 (G8 III + wd, P approximately 5200 days), and HD 185510 (K0 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 35000 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

168

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

169

Exploring high temperature magnetic order in CeTi1-xScxGe  

NASA Astrophysics Data System (ADS)

We studied the magnetic, transport, and thermodynamic properties of the alloy CeTi1-xScxGe in order to shed some light into the origin of the exceptionally large antiferromagnetic (AFM) ordering temperature TN = 47 K in pure CeScGe. We observed a complex magnetic phase diagram, which present an interesting dichotomy: Despite strong changes in the nature of the ordered state, from ferromagnetic (FM) for x <= 0.55 to AFM for x > 0.55, the ordering temperature increases smoothly and continuously from TC = 7 K at x = 0.25 to TN = 47 K at x = 1. Within the AFM regime we observe a metamagnetic transition at a critical field increasing from H = 0 at x ? 0.55 to ?0 * H ? 6 Tesla at x = 1. Furthermore a second transition appears at TL <= TN for x >= 0.65. In contrast to observations in CeRh2Si2 or CeRh3B2, we found no evidence for a strong hybridization of the 4f electrons at large Sc contents. Therefore the exceptionally large TN of CeScGe could be attributed to the unusually strong RKKY interaction in this type of compounds.

Sereni, J. G.; Pedrazzini, P.; Gómez Berisso, M.; Chacoma, A.; Encina, S.; Gruner, T.; Caroca-Canales, N.; Geibel, C.

2015-03-01

170

UV Radiation  

NSDL National Science Digital Library

The sun radiates energy over a broad spectrum of wavelengths. Ultraviolet (UV) radiation, which has a shorter wavelength than either visible blue or violet light, is responsible for sunburn and other adverse health effects. Fortunately for life on Earth, our atmospheres stratospheric ozone layer shields us from most UV radiation. What gets through the ozone layer, however, can cause the following problems, particularly for people who spend substantial time outdoors: Skin cancer, Suppression of the immune system, Cataracts, and Premature aging of the skin.Because of these serious health effects, you should limit your exposure to UVradiation and protect yourself when outdoors.

U.S. Environmental Protection Agency (; )

2008-04-25

171

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

172

The presence of Brucella ceti ST26 in a striped dolphin (Stenella coeruleoalba) with meningoencephalitis from the Mediterranean Sea.  

PubMed

Brucella spp. was isolated from brain, lung and intestinal lymph nodes of a dead adult male striped dolphin (Stenella coeruleoalba) found stranded on the Tyrrhenian coast (Tuscany, Italy) of the Mediterranean Sea in February 2012. Brucella spp. was associated with moderate to severe lesions of meningoencephalitis. A co-infection by Toxoplasma gondii was also demonstrated at brain level by means of molecular and histopathologic methods. The Brucella isolate was further characterized based on a fragment-specific polymerase chain reaction (PCR) approach, consisting of a set of five specific PCRs, targeting specific chromosomal IS711 locations for marine mammal Brucellae, as described previously. The isolate was thus classified as Brucella ceti I; V fragment-positive (or B. ceti dolphin type), according to previous studies. Multi Locus Sequence Analysis demonstrated that the isolate belongs to Sequence Type 26, while omp2 (omp2a and omp2b genes) sequence analysis further confirmed the isolate belonged to this group of strains. This is the first report of Brucella spp. from marine mammals in the Mediterranean Sea, and represents a further observation that this strain group is associated with hosts of the Family Delphinidae, and particularly with the striped dolphins, also in the Mediterranean area, thus constituting a further biological hazard of concern for this vulnerable subpopulation. PMID:23419820

Alba, Patricia; Terracciano, Giuliana; Franco, Alessia; Lorenzetti, Serena; Cocumelli, Cristiano; Fichi, Gianluca; Eleni, Claudia; Zygmunt, Michel S; Cloeckaert, Axel; Battisti, Antonio

2013-05-31

173

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

174

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

175

LEGUS: Legacy ExtraGalactic UV Survey  

NASA Astrophysics Data System (ADS)

We propose to build the first HST UV Atlas of 50 nearby star-forming galaxies, carefully selected to span the full range of morphology, star formation rate {SFR}, mass, metallicity, internal structure, and interaction state found in the local Universe. In combination with archival and new optical {UBVI} WFC3/ACS data, the requested WFC3/UV images are key for deriving accurate recent {<50 Myr} star formation histories {SFHs} from resolved massive stars, and the extinction-free 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. These are only a few of the science opportunities enabled by LEGUS. The astronomical community will add many more: 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. LEGUS will populate the HST Archive with unique data, that will be ready for immediate use by the community through the extensive data products we will deliver, and will provide a unique foundation for future observations with JWST and ALMA.

Calzetti, Daniela

2013-10-01

176

UV Menace  

NSDL National Science Digital Library

UV Menace is part of an online series of modules entitled Exploring the Environment. Emphasizing an integrated approach to environmental Earth Science education through problem-based learning, this module asks students to learn about stratospheric ozone depletion and its effects, then determine future measures that will be needed to correct the current situation. Students will find extensive coverage of the Earth's hydrosphere, lithosphere, atmosphere, anthrosphere, and biosphere. They use this information to evaluate the current status of the Montreal Protocol and determine if it is adequate. If not, students must develop the changes they feel are necessary. There is an online glossary and links for further research and information, teacher resources, and a reference on problem-based learning.

177

Star Journey  

NSDL National Science Digital Library

This National Geographic web-site contains information about the Hubble Space Telescope (HST) along with a star chart and facts about objects in the night sky. The HST section contains details about the building and structure of the HST, how it captures light, positioning the HST to targets, instruments used to record and measure infrared through UV wavelengths, how the HST is powered and communicates with the Earth. Star Attractions discusses properties of constellations, the Milky Way galaxy, other galaxies, star clusters and nebulae. This information is then put together on the National Geographic Star Chart. This chart contains maps of the heavens for the northern and southern hemispheres. The chart contains constellation names, location of stars and other objects, and links to HST images of various galaxies and objects on the chart with names and detailed descriptions. There is an image index to find HST images from the site, details about chart symbol meanings, and links for more information.

Carolyn Anderson

178

Early-type stars observed in the ESO UVES Paranal Observatory Project: I -- Interstellar Na I UV, Ti II and Ca II K observations  

E-print Network

We present an analysis of interstellar Na I (lambda=3302.37\\AA, 3302.98\\AA), Ti II (lambda=3383.76\\AA) and Ca II K (lambda=3933.66\\AA) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the UVES Paranal Observatory Project, at a spectral resolution of 3.75km/s and with mean signal to noise ratios per pixel of 260, 300 and 430 for the Na I, Ti II and Ca II observations, respectively. Interstellar features were detected in all but one of the Ti II sightlines and all of the Ca II sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, H I column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the Na I column density as an indicator of that for H I. In general we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium and also that the Ti II/Ca II ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general interstellar medium conditions of the Galactic disc.

I. Hunter; J. V. Smoker; F. P. Keenan; C. Ledoux; E. Jehin; R. Cabanac; C. Melo; S. Bagnulo

2006-01-17

179

Peering through the holes: the far-UV color of star-forming galaxies at z ~ 3-4 and the escaping fraction of ionizing radiation  

NASA Astrophysics Data System (ADS)

Aims: We aim to investigate the effect of the escaping ionizing radiation on the color selection of high-redshift galaxies and identify candidate Lyman-continuum (LyC) emitters. Methods: We used the intergalactic medium (IGM) prescription of Inoue et al. (2014, MNRAS, 442, 1805) and galaxy synthesis models of Bruzual & Charlot (2003, MNRAS, 344, 1000) to properly treat the ultraviolet stellar emission and the stochasticity of the intergalactic transmission and mean free path in the ionizing regime. Color tracks were computed by turning the escape fraction fesc of ionizing radiation on or off. Results: At variance with recent studies, a careful treatment of IGM transmission leads to no significant effects on the high-redshift broad-band color selection, even adopting the most extreme ionizing emission model (with an age of 1 Myr, zero dust, and metallicity Z/Z? = 0.02). The decreasing mean free path of ionizing photons with increasing redshift further diminishes the contribution of the LyC to broad-band colors. We demonstrate that prominent LyC sources can be selected under suitable conditions by calculating the probability of a null escaping ionizing radiation. This was performed by running ad hoc Monte Carlo simulations anchored to the observed photometry, exploring the stochasticity of the IGM, and comparing the simulated and observed colors that encompass the Lyman edge. The method was applied to a sample of galaxies extracted from the GOODS-S field. A known LyC source at z = 3.795 was successfully recovered as a LyC-emitter candidate, and another convincing candidate at z = 3.212 is reported. A detailed analysis of the two sources (including their variability and morphology) suggests a possible mixture of stellar and non-stellar (AGN) contribution in the ultraviolet. Conclusions: The classical broad-band color selection of 2.5 < z < 4.5 galaxies does not prevent the inclusion of LyC emitters in the selected samples. High fesc in relatively bright galaxies (L > 0.1L?) could be favored by the presence of a faint active galactic nucleus (AGN) that is not easily detected at any wavelength. A hybrid stellar and non-stellar (AGN) ionizing emission could coexist in these systems and explain the tensions found among the UV excess and the stellar population synthesis models reported in literature.

Vanzella, E.; de Barros, S.; Castellano, M.; Grazian, A.; Inoue, A. K.; Schaerer, D.; Guaita, L.; Zamorani, G.; Giavalisco, M.; Siana, B.; Pentericci, L.; Giallongo, E.; Fontana, A.; Vignali, C.

2015-04-01

180

Symbiotic stars  

NASA Astrophysics Data System (ADS)

Observations of symbiotic stars (SSs) obtained with the IUE satellite since its launch in 1978 are reviewed. The general features of SS spectra are discussed (IR emission from a cool highly evolved star and UV emission from a nebula ionized by a source of 100,000 K or hotter), and the astrophysical interest of SSs is indicated. Particular attention is given to the S-type SSs AG Peg, AR Pav, Z And, HBV 475, AG Dra, and CH Cyg; the D-type SSs R Aqr, V 1016 Cyg, and RR Tel; SSs in other galaxies; the UV continuum, emisssion lines, abundances, electron temperatures, Doppler shifts, and Doppler broadening and line profiles; and theoretical models based on multispectral information. Sample spectra, graphs, and tables listing SS parameter values are provided.

Nussbaumer, Harry; Stencel, Robert E.

181

UVMag: a UV and optical spectropolarimeter for stellar physics  

NASA Astrophysics Data System (ADS)

UVMag is a space project currently under R&D study. It consists in a medium-size telescope equipped with a spectropolarimeter to observe in the UV and optical wavelength domains simultaneously. Its first goal is to obtain time series of selected magnetic stars over their rotation period, to study them from their surface to their environment, in particular their wind and magnetospheres. As the star rotates it will be possible to reconstruct 3D maps of the star and its surroundings. The second goal of UVMag is to obtain two observations of a large sample of stars to construct a new database of UV and optical spectropolarimetric measurements.

Neiner, Coralie; Petit, Pascal; Parès, Laurent; Parès

2014-08-01

182

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.

183

Statistical error analysis in CCD time-resolved photometry with applications to variable stars and quasars  

NASA Technical Reports Server (NTRS)

Differential photometric time series obtained from CCD frames are tested for intrinsic variability using a newly developed analysis of variance technique. In general, the objects used for differential photometry will not all be of equal magnitude, so the techniques derived here explicitly correct for differences in the measured variances due to photon statistics. Other random-noise terms are also considered. The technique tests for the presence of intrinsic variability without regard to its random or periodic nature. It is then applied to observations of the variable stars ZZ Ceti and US 943 and the active extragalactic objects OQ 530, US 211, US 844, LB 9743, and OJ 287.

Howell, Steve B.; Warnock, Archibald, III; Mitchell, Kenneth J.

1988-01-01

184

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

185

UV water disinfector  

DOEpatents

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

Gadgil, Ashok (El Cerrito, CA); Garud, Vikas (Bombay, IN)

1998-07-14

186

Intrinsically variable stars  

NASA Technical Reports Server (NTRS)

The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.

Bohm-Vitense, Erika; Querci, Monique

1987-01-01

187

Pulsational mode-typing in line profile variables. I - Four Beta Cephei stars  

NASA Technical Reports Server (NTRS)

The detailed variations of line profiles in the Beta Cephei-type variable stars Gamma Pegasi, Beta Cephei, Delta Ceti and Sigma Scorpii are modeled throughout their pulsation cycles in order to classify the dominant pulsation mode as radial or nonradial. High-dispersion Reticon observations of the variables were obtained for the Si III line at 4567 A, and line profiles broadened by radial or nonradial pulsations, rotation and radial-tangential macroturbulence were calculated based on a model atmosphere. It is found that only a radial pulsation mode can reproduce the radial velocity amplitude, changes in line asymmetry and uniform line width observed in all four stars. Results are in agreement with the color-to-light arguments of Stamford and Watson (1978), and suggest that radial pulsation plays the dominant role in the observed variations in most Beta Cephei stars. Evidence for shocks or moving shells is also found in visual line data for Sigma Scorpii and an ultraviolet line of Beta Cephei, together with evidence of smooth, secular period changes in Beta Cephei and Delta Ceti.

Campos, A. J.; Smith, M. A.

1980-01-01

188

UV-Visible Spectroscopy  

NSDL National Science Digital Library

This webpage, part of a larger project "Understanding Chemistry", provides an introduction to UV-visible spectroscopy suitable for use in introductory chemistry and introductory analytical chemistry courses. The pages discuss UV-visible light, absorption, Beer's law, the double-beam spectrometer, and introduce some standard applications of UV-vis spectroscopy.

Clark, Jim

189

UV color-color relation of early-type galaxies  

NASA Astrophysics Data System (ADS)

The ultraviolet (UV) color-color relation of early-type galaxies (ETGs) in the nearby universe (0.05 < z < 0.12) is re-examined with the latest GALEX GR6 and SDSS DR7 data. By drawing the FUV - NUV (as a measure of UV temperature) versus FUV - r (as a measure of UV amplitude) color-color diagram for the morphologically-cleaned, spectroscopically-cleaned sample of ~3700 quiescent ETGs, we find that the ``old and dead`` ETGs consist of a well-defined sequence in UV colors, the ``UV red sequence'', so that the stronger UV excess galaxies should have a harder UV spectral shape systematically. However, the observed UV spectral slope is too steep to be reproduced by the canonical models in which the UV flux is mainly controlled by age or metallicity parameters. The observed data support the helium enhancement scenario in which the UV spectral shape of UV upturn (FUV - NUV < 0.9; FUV - r ~ 6) galaxies may be governed by the minority population of helium-enhanced horizontal-branch (HB) stars.

Ree, Chang H.; Jeong, Hyunjin; Oh, Kyuseok; Chung, Chul; Lee, Joon Hyeop; Kim, Sang Chul; Kyeong, Jaemann

2015-03-01

190

Hot Stars in Globular Clusters  

E-print Network

Blue horizontal branch and UV bright stars in several globular clusters are analysed spectroscopically and the results are compared with predictions of stellar evolutionary theory. We find that the distribution of temperatures and surface gravities of the blue HB stars may be explained by the effects of deep mixing. The masses derived for these stars are too low unless one uses the long distance scale for globular clusters. First results on blue HB stars in metal rich clusters are presented. Analyses of hot UV bright stars in globular clusters uncovered a lack of genuine post-asymptotic giant branch stars which may explain the lack of planetary nebulae in globular clusters seen by Jacoby et al. (1997). Abundance analyses of post-AGB stars in two globular clusters suggest that gas and dust may separate during the AGB phase.

S. Moehler

1998-12-08

191

Precise radial velocities of giant stars. VI. A possible 2:1 resonant planet pair around the K giant star ? Ceti  

NASA Astrophysics Data System (ADS)

We report the discovery of a new planetary system around the K giant ? Cet (HIP 5364, HD 6805, HR 334) based on 118 high-precision optical radial velocities taken at Lick Observatory since July 2000. Since October 2011 an additional nine near-infrared Doppler measurements have been taken using the ESO CRIRES spectrograph (VLT, UT1). The visible data set shows two clear periodicities. Although we cannot completely rule out that the shorter period is due to rotational modulation of stellar features, the infrared data show the same variations as in the optical, which strongly supports that the variations are caused by two planets. Assuming the mass of ? Cet to be 1.7 M?, the best edge-on coplanar dynamical fit to the data is consistent with two massive planets (mb sini = 2.6 ± 0.2 MJup, mc sini = 3.3 ± 0.2 MJup), with periods of Pb = 407 ± 3 days and Pc = 740 ± 5 days and eccentricities of eb = 0.12 ± 0.05 and ec = 0.08 ± 0.04. These mass and period ratios suggest possible strong interactions between the planets, and a dynamical test is mandatory. We tested a wide variety of edge-on coplanar and inclined planetary configurations for stability, which agree with the derived radial velocities. We find that for a coplanar configuration there are several isolated stable solutions and two well defined stability regions. In certain orbital configurations with moderate eb eccentricity, the planets can be effectively trapped in an anti-aligned 2:1 mean motion resonance that stabilizes the system. A much larger non-resonant stable region exists in low-eccentricity parameter space, although it appears to be much farther from the best fit than the 2:1 resonant region. In all other cases, the system is categorized as unstable or chaotic. Another conclusion from the coplanar inclined dynamical test is that the planets can be at most a factor of ~1.4 more massive than their suggested minimum masses. Assuming yet higher inclinations, and thus larger planetary masses, leads to instability in all cases. This stability constraint on the inclination excludes the possibility of two brown dwarfs, and strongly favors a planetary system. Based on observations collected at Lick Observatory, University of California.Based on observations collected at the European Southern Observatory, Chile, under program IDs 088.D-0132, 089.D-0186, 090.D-0155 and 091.D-0365.

Trifonov, Trifon; Reffert, Sabine; Tan, Xianyu; Lee, Man Hoi; Quirrenbach, Andreas

2014-08-01

192

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

193

EVOLUTION OF THE SOLAR ACTIVITY OVER TIME AND EFFECTS ON PLANETARY ATMOSPHERES. II. {kappa}{sup 1} Ceti, AN ANALOG OF THE SUN WHEN LIFE AROSE ON EARTH  

SciTech Connect

The early evolution of Earth's atmosphere and the origin of life took place at a time when physical conditions at the Earth were radically different from its present state. The radiative input from the Sun was much enhanced in the high-energy spectral domain, and in order to model early planetary atmospheres in detail, a knowledge of the solar radiative input is needed. We present an investigation of the atmospheric parameters, state of evolution, and high-energy fluxes of the nearby star {kappa}{sup 1} Cet, previously thought to have properties resembling those of the early Sun. Atmospheric parameters were derived from the excitation/ionization equilibrium of Fe I and Fe II, profile fitting of H{alpha}, and the spectral energy distribution. The UV irradiance was derived from Far-Ultraviolet Spectroscopic Explorer and Hubble Space Telescope data, and the absolute chromospheric flux from the H{alpha} line core. From careful spectral analysis and the comparison of different methods, we propose for {kappa}{sup 1} Cet the following atmospheric parameters: T{sub eff} = 5665 {+-} 30 K (H{alpha} profile and energy distribution), log g = 4.49 {+-} 0.05 dex (evolutionary and spectroscopic), and [Fe/H] = +0.10 {+-} 0.05 (Fe II lines). The UV radiative properties of {kappa}{sup 1} Cet indicate that its flux is some 35% lower than the current Sun's between 210 and 300 nm, it matches the Sun's at 170 nm, and increases to at least 2-7 times higher than the Sun's between 110 and 140 nm. The use of several indicators ascribes an age to {kappa}{sup 1} Cet in the interval {approx}0.4-0.8 Gyr and the analysis of the theoretical Hertzsprung-Russell diagram (H-R) suggests a mass {approx}1.04 M{sub sun}. This star is thus a very close analog of the Sun when life arose on Earth and Mars is thought to have lost its surface bodies of liquid water. Photochemical models indicate that the enhanced UV emission leads to a significant increase in photodissociation rates compared with those commonly assumed of the early Earth. Our results show that reliable calculations of the chemical composition of early planetary atmospheres need to account for the stronger solar photodissociating UV irradiation.

Ribas, I.; Garces, A. [Institut de Ciencies de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5, parell, 2a pl., E-08193 Bellaterra (Spain); Porto de Mello, G. F.; Ferreira, L. D. [Universidade Federal do Rio de Janeiro, Observatorio do Valongo, Ladeira do Pedro Antonio 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Hebrard, E.; Selsis, F. [Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France); Catalan, S. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Do Nascimento, J. D.; De Medeiros, J. R., E-mail: iribas@ice.csic.e, E-mail: garces@ice.csic.e, E-mail: gustavo@astro.ufrj.b, E-mail: leticia@astro.ufrj.b, E-mail: franck.selsis@obs.u-bordeaux1.f, E-mail: eric.hebrard@obs.u-bordeaux1.f, E-mail: s.catalan@herts.ac.u, E-mail: dias@dfte.ufrn.b, E-mail: renan@dfte.ufrn.b [Departamento de Fisica, Universidade Federal do Rio Grande do Norte, CEP: 59072-970, Natal, RN (Brazil)

2010-05-01

194

WSO-UV project  

NASA Astrophysics Data System (ADS)

During last three decades, astronomers have enjoyed continuous access to the 100-300 nm ultraviolet (UV) spectral range where the resonance transitions of the most abundant atoms and ions (at temperatures between 3000 and 300 000 K) reside. This UV range is not accessible from ground-based facilities. The successful International Ultraviolet Explorer (IUE) observatory, the Russian ASTRON mission and successor instruments such as the Galaxy Evolution Explorer (GALEX) mission or the COS and STIS spectrographs on-board the Hubble Space Telescope (HST) prove the major impact of observations in the UV wavelength range in modern astronomy. Future access to space-based observatories is expected to be very limited. For the next decade, the post-HST era, the World Space Observatory - Ultraviolet (WSO-UV) will be the only 2-m class UV telescope with capabilities similar to the HST. WSO-UV will be equipped with instruments for imaging and spectroscopy and it will be a facility dedicated, full-time, to UV astronomy. In this article, we briefly outline the current status of the WSO-UV mission and the science management plan.

Sachkov, Mikhail; Shustov, Boris; Gómez de Castro, Ana Ines

2014-03-01

195

Effective temperatures of AP stars  

NASA Astrophysics Data System (ADS)

A new method of determination of the effective temperatures of Ap stars is suggested in which at first the temperature of a model best reproducing the observed visual energy distribution is determined and then a correction to this temperature resulting from the UV flux deficit is added. The method is calibrated on a sample of stars with energy distributions known from the UV to the red. It is shown that the obtained effective temperatures of hotter stars agree well with the relation found by Lanz (1985). An extension of his relation toward cooler temperatures is given.

Stepien, K.; Dominiczak, R.

1989-07-01

196

Star Formation in Clusters  

Microsoft Academic Search

HST is very well tailored for observations of extragalactic star clusters. One obvious reason is HST's high spatial resolution, but equally important is the wavelength range offered by the instruments on board HST, in particular the blue and near-UV coverage which is essential for age-dating young clusters. HST observations have helped establish the ubiquity of young massive clusters (YMCs) in

SØREN S. LARSEN; Karl-Schwarzschild Strasse

2004-01-01

197

UV Cas: Photometry, Polarization, and Spectrum near Maximum Light  

NASA Astrophysics Data System (ADS)

The UBV observations of UV Cas during 1996-1999 show mostly irregular light variations. The VB light variations on time scales from one day to two weeks have a smaller amplitude than those on longer time scales. The amplitude of the UBV light variations on time scales from 20 to 200 days reaches 0.4, 0.3, and 0.2 mag, respectively. The colors of UV Cas do not correspond to G5 supergiants, but are more similar to the colors of G0 I stars at substantial U-B color excesses. A comparison of the energy distribution for UV Cas, as constructed from the broadband UBVRI observations in 1982, with the energy distribution for G0 supergiants reveals enhanced near-infrared and ultraviolet emission, which can be attributed to unusual chemical composition of the star. The polarization of light from UV Cas in quiescence is mainly interstellar in origin, although the presence of weak intrinsic polarization produced by the gas-dust circumstellar medium cannot be ruled out either. The strength of CI lines in the spectrum of UV Cas confirms that it belongs to R CrB stars, as well as the conclusion of Orlov and Rodriguez that carbon is appreciably overabundant. The atmospheric metal underabundance in UV Cas may be larger than has been thought previously. The line broadening is sigma = 10.7 km/s. The star's effective temperature appears to be higher than 5500 K. The radial velocity of UV Cas measured from metal and carbon lines is -31.17 +/- 0.38 km/s. The NaI D lines have a split profile, with the two absorbing clouds observed toward UV Cas at distances < 1 kpc and 1.5-2.5 kpc from the Sun contributing to its components.

Doroshenko, V. T.; Efimov, Yu. S.; Rosenbush, A. E.

2000-07-01

198

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

199

A Marvelous Star in M33  

NASA Astrophysics Data System (ADS)

The end stages of stellar evolution release heavy element enriched dust into the interstellar medium where it is eventually incorporated into star formation regions and later generations of stars. As low mass stars go through this process they bloat in size, pulsate, and expel dust and gas before ultimately transforming into planetary nebulae (PNe). A classic example of this stage of evolution is the well studied class of pulsating stars, the Mira variables. Prior to expelling a PNe, these objects go through a short (tens of thousands of years) stage of evolution where they undergo episodic mass loss and become enshrouded in dust. We report the discovery of an unusual Mira star within the M33 galaxy; IRAC 0134+3029. The source is heavily obscured in the visible, indicating large amounts of enshrouding dust. In addition, Spitzer Space Telescope spectroscopy and imaging show strong thermal emission as well as absorption features from silicates. Examination of the properties of IRAC 0134 suggests that it is the extragalactic analog of the well known "extreme" Mira OH26.5+0.6. We compare spectra and photometry of IRAC 0134 to observations of OH26.5+.6 as well as to the prototype of the Mira class, Omicron Ceti. We also discuss some contradictory archival observations of these objects and suggest possible explanations. This work is based upon observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. The authors were supported in part through contracts 1256406 and 1215746 issued by JPL/Caltech to the University of Minnesota.

Polomski, Elisha; Gehrz, R. D.; McQuinn, K.; Paffel, F.; Woodward, C. E.

2012-05-01

200

The First Stars  

E-print Network

The formation of the first generations of stars at redshifts z > 15-20 signaled the transition from the simple initial state of the universe to one of increasing complexity. We here review recent progress in understanding the assembly process of the first galaxies, starting with cosmological initial conditions and modelling the detailed physics of star formation. In particular, we study the role of HD cooling in ionized primordial gas, the impact of UV radiation produced by the first stars, and the propagation of the supernova blast waves triggered at the end of their brief lives. We conclude by discussing how the chemical abundance patterns observed in extremely low-metallicity stars allow us to probe the properties of the first stars.

Jarrett L. Johnson; Thomas H. Greif; Volker Bromm

2008-02-01

201

The Controversial Nature of the Diffuse UV Emission in Galaxies: Exploring NGC300  

NASA Astrophysics Data System (ADS)

The wealth of data produced over the past decade by sensitive IR and wide-field UV space facilities has ushered a new era for studies of star formation in galaxies, both at the whole-galaxy and sub-galactic (<~kpc) scale. These data underscore the difficulty of using standard methods, including the dust-corrected UV light, to measure star formation within galaxies, owing to the local variations in stellar population and dust properties. The UV should be a direct tracer of young stellar populations and recent star formation, yet UV colors in the 'diffuse' interarm regions of spiral galaxies are unusually red relative to those of spiral arms, even after accounting for dust attenuation. This suggests a complex mix of moderately aged stars and dust, plus perhaps scattered light. We will unveil the origin of those UV colors with new ACS far-UV (FUV) and WFC3 near-UV (NUV) images of the nearby, prototypical spiral NGC300, which will be combined with B,V,I archival images. By exploiting the dust-insensitivity of the HST FUV-NUV color for resolved stars, we will obtain a census of both O and B stars in order to: (1) uncover the nature of the UV-emitting interarm stellar populations, while estimate the true diffuse fraction; (2) constrain the extinction law in both interarm+arm regions; (3) place UV-based SFR indicators on a secure footing for use both at low and high redshift. The angular resolution and UV capabilities of HST are crucial for this project. By directly addressing the use and limitations of UV colors to trace young stellar populations and dust attenuation in galaxies, this project maximizes the return from the large investment of HST time devoted to high-z surveys.

Thilker, David

2014-10-01

202

Are You UV Safe?  

NSDL National Science Digital Library

Students may be slathered with SPF 30 sunscreen all summer at the beach or pool, but what do they know about ultraviolet (UV) light radiation and absorption? How could we help them find out the science behind this important health precaution? We found the perfect opportunity when we developed this series of practical strategies to promote students' investigation skills. We integrated several scientific processes into a lesson on UV light radiation and absorption for fourth-grade students and preservice elementary methods students. These teaching tools help students develop their abilities to ask testable questions, plan and design investigations, and interpret what they find.

Brenda Capobianco

2006-09-01

203

UV actinometer film  

NASA Technical Reports Server (NTRS)

Cumulative UV radiation can be measured by low-cost polymer film that is unaffacted by visible light. Useful for virtually any surface, film can help paint and plastics manufacturers determine how well their products stand up against UV radiation. Actinometer film uses photochemically sensitive compound that changes its chemical composition in response to solar radiation. Extent of chemical conversion depends on length exposure and can be measured by examining film sample with spectrophotometer. Film can be exposed from several seconds up to month.

Coulbert, C. D.; Gupta, A.; Pitts, J.

1980-01-01

204

Are You UV Safe?  

ERIC Educational Resources Information Center

Students may be slathered with SPF 30 sunscreen all summer at the beach or pool, but what do they know about ultraviolet (UV) light radiation and absorption? The authors of this article found the perfect opportunity to help students find out the science behind this important health precaution, when they developed a series of practical strategies…

Capobianco, Brenda; Thiel, Elizabeth Andrew

2006-01-01

205

Essential UV Observations of Eta Carinae's Change of State  

NASA Astrophysics Data System (ADS)

Eta Carinae is now passing though a critical phase in its evolution as it recovers from its ''Great Eruption'' 170 years ago. About 12 years ago we began to see a dramatic and unpredicted change in eta Car's long-term behavior. The brightening rate suddenly accelerated, so by 2010 the central star had brightened by more than a factor of four in the near-UV. Between 2003 and 2010 the stellar-wind emission lines weakened by factors of 2 to 4( ) implying a rapid decrease in its mass loss rate. Eta Car is unsteadily returning to its pre-eruptive state, but the rapidity since 2000 has been astonishing. The recent secular changes are much stronger in the UV than at optical wavelengths, but no UV data have been obtained since 2010 and no far-UV observations since 2004. The extraordinary brightening and changes in the wind are fundamental and must indicate basic changes in the outer structure of this circa-130 Msun star. Therefore, this proposal focuses on the rapid secular changes rather than the expected 2014.6 periastron passage. This is primarily a UV problem, though longer wavelengths are also worthwhile. Fresh observations must be done early in Cycle 21 before the approaching periastron alters the system. Our highest priorities are the UV brightening and the long term changes in the wind.

Mehner, Andrea

2014-10-01

206

A connection between the instability strips of ZZ Ceti and V777 Herculis white dwarfs. Pulsating accreting GW Lib white dwarfs  

NASA Astrophysics Data System (ADS)

Aims: We aim to determine the theoretical instability strips of white dwarfs with diverse H and He content in their atmospheres, from a solar composition to a H-depleted atmosphere. Pulsators with mixed H-He atmospheres are indeed known to exist, and these are the white dwarfs in cataclysmic accreting systems of the GW Lib type. We thus also aim to determine the range of periods of excited pulsation modes, and to qualitatively compare these to the observed periods in GW Lib white dwarf pulsators. Methods: In the first full nonadiabatic stability analysis of pulsators of this kind, we applied a time-dependent convection treatment and an energy leakage argument to compute, for cooling models of white dwarfs with various masses and envelope compositions, the location of the blue and the red edges, as well as the properties of pulsation modes. Results: We find that our derived instability strips form a true continuum in the log g-Teff plane and that their individual location depends uniquely on the assumed atmospheric composition, from the solar composition models at low effective temperatures to the H-depleted models at much higher temperatures. Taking into account our previous results from the ZZ Ceti (pure H atmosphere) and V777 Her (pure He atmosphere) white dwarf pulsators, this implies that all of these instability domains are connected via the same fundamental driving mechanism. Applying our results to the case of white dwarf pulsators of the GW Lib type, we find that our theoretical instability strips can qualitatively account for all of the known cases. The computed range of periods of excited modes also compares qualitatively very well to the observed ones. Conclusions: The GW Lib pulsators are very similar in nature to ZZ Ceti and V777 Her white dwarfs. It is the diverse chemical compositions in their atmosphere and envelope that defines their specific pulsation properties. Beyond GW Lib pulsators, white dwarfs can sometimes exhibit mixed H-He atmospheres, such as in the recently found proto-He white dwarf pulsators. Our results open the way towards quantitative asteroseismology of these various kinds of white dwarfs.

Van Grootel, V.; Fontaine, G.; Brassard, P.; Dupret, M.-A.

2015-03-01

207

Characterising exoplanets and their environment with UV transmission spectroscopy  

E-print Network

Exoplanet science is now in its full expansion, particularly after the CoRoT and Kepler space missions that led us to the discovery of thousands of extra-solar planets. The last decade has taught us that UV observations play a major role in advancing our understanding of planets and of their host stars, but the necessary UV observations can be carried out only by HST, and this is going to be the case for many years to come. It is therefore crucial to build a treasury data archive of UV exoplanet observations formed by a dozen "golden systems" for which observations will be available from the UV to the infrared. Only in this way we will be able to fully exploit JWST observations for exoplanet science, one of the key JWST science case.

Fossati, L; Ehrenreich, D; Haswell, C A; Kislyakova, K G; Lammer, H; Etangs, A Lecavelier des; Alibert, Y; Ayres, T R; Ballester, G E; Barnes, J; Bisikalo, D V; Collier, A; Cameron,; Czesla, S; Desert, J -M; France, K; Guedel, M; Guenther, E; Helling, Ch; Heng, K; Homstrom, M; Kaltenegger, L; Koskinen, T; Lanza, A F; Linsky, J L; Mordasini, C; Pagano, I; Pollacco, D; Rauer, H; Reiners, A; Salz, M; Schneider, P C; Shematovich, V I; Staab, D; Vidotto, A A; Wheatley, P J; Wood, B E; Yelle, R V

2015-01-01

208

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

209

Discrete Scale Relativity And SX Phoenicis Variable Stars  

E-print Network

Discrete Scale Relativity proposes a new symmetry principle called discrete cosmological self-similarity which relates each class of systems and phenomena on a given Scale of nature's discrete cosmological hierarchy to the equivalent class of analogue systems and phenomena on any other Scale. The new symmetry principle can be understood in terms of discrete scale invariance involving the spatial, temporal and dynamic parameters of all systems and phenomena. This new paradigm predicts a rigorous discrete self-similarity between Stellar Scale variable stars and Atomic Scale excited atoms undergoing energy-level transitions and sub-threshold oscillations. Previously, methods for demonstrating and testing the proposed symmetry principle have been applied to RR Lyrae, Delta Scuti and ZZ Ceti variable stars. In the present paper we apply the same analytical methods and diagnostic tests to a new class of variable stars: SX Phoenicis variables. Double-mode pulsators are shown to provide an especially useful means of testing the uniqueness and rigor of the conceptual principles and discrete self-similar scaling of Discrete Scale Relativity.

R. L. Oldershaw

2009-06-18

210

UV curable materials development  

SciTech Connect

Adhesives, coatings, and inks were selected for evaluation based on literature search and possible production applications. A differential photocalorimeter was used to measure degree of cure and allow prediction of optimum processing conditions. UV cure equipment were characterized and the ability to size equipment to specific materials cure needs established. Adhesion tests procedures were developed for the adhesives and solvent resistance testing procedures developed for the coatings and inks.

Parker, B.G.

1996-12-01

211

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

212

Enhanced UV Inactivation of Adenoviruses under Polychromatic UV Lamps?  

PubMed Central

Adenovirus is recognized as the most UV-resistant waterborne pathogen of concern to public health microbiologists. The U.S. EPA has stipulated that a UV fluence (dose) of 186 mJ cm?2 is required for 4-log inactivation credit in water treatment. However, all adenovirus inactivation data to date published in the peer-reviewed literature have been based on UV disinfection experiments using UV irradiation at 253.7 nm produced from a conventional low-pressure UV source. The work reported here presents inactivation data for adenovirus based on polychromatic UV sources and details the significant enhancement in inactivation achieved using these polychromatic sources. When full-spectrum, medium-pressure UV lamps were used, 4-log inactivation of adenovirus type 40 is achieved at a UV fluence of less than 60 mJ cm?2 and a surface discharge pulsed UV source required a UV fluence of less than 40 mJ cm?2. The action spectrum for adenovirus type 2 was also developed and partially explains the improved inactivation based on enhancements at wavelengths below 230 nm. Implications for water treatment, public health, and the future of UV regulations for virus disinfection are discussed. PMID:17933932

Linden, Karl G.; Thurston, Jeanette; Schaefer, Raymond; Malley, James P.

2007-01-01

213

Deep Galex Imaging of the Isolated Extended-Uv Disks of CIG96 and CIG812  

NASA Astrophysics Data System (ADS)

We propose to obtain deep GALEX images of the isolated galaxies CIG96 and CIG812. These galaxies are part of the AMIGA project (Analysis of the Interstellar Medium of Isolated Galaxies) and constitute the first two well-defined isolated galaxies where extended-UV emission has been identified. The images here requested will allow us (1) to confirm the nature of these objects are extended-UV-disk galaxies, (2) to study the star formation threshold and law in combination with already-obtained VLA HI maps, and (3) to investigate the role of internal processes in the triggering of the star formation in extended-UV disks.

Gil de Paz, Armando

214

Observations of the diffuse UV radiation field  

NASA Technical Reports Server (NTRS)

Spectra are presented for the diffuse UV radiation field between 1250 to 3100 A from eight different regions of the sky, which were obtained with the Johns Hopkins UVX experiment. UVX flew aboard the Space Shuttle Columbia (STS-61C) in January 1986 as part of the Get-Away Special project. The experiment consisted of two 1/4 m Ebert-Fastie spectrometers, covering the spectral range 1250 to 1700 A at 17 A resolution and 1600 to 3100 A at 27 A resolution, respectively, with a field of view of 4 x .25 deg, sufficiently small to pick out regions of the sky with no stars in the line of sight. Values were found for the diffuse cosmic background ranging in intensity from 300 to 900 photons/sq cm/sec/sr/A. The cosmic background is spectrally flat from 1250 to 3100 A, within the uncertainties of each spectrometer. The zodiacal light begins to play a significant role in the diffuse radiation field above 2000 A, and its brightness was determined relative to the solar emission. Observed brightnesses of the zodiacal light in the UV remain almost constant with ecliptic latitude, unlike the declining visible brightnesses, possibly indicating that those (smaller) grains responsible for the UV scattering have a much more uniform distribution with distance from the ecliptic plane than do those grains responsible for the visible scattering.

Murthy, Jayant; Henry, R. C.; Feldman, P. D.; Tennyson, P. D.

1989-01-01

215

UV matters in shoaling decisions  

PubMed Central

Shoaling behaviour in fish is influenced by numerous factors, such as familiarity, kinship, group size and shoal composition. Grouping decisions are based on both olfactory and visual cues. The visual system of many vertebrates is extended into the ultraviolet (UV) wave range as in three-spined sticklebacks (Gasterosteus aculeatus, L.). We investigated whether the presence or absence of UV wavelengths has an influence on shoaling behaviour in this species. Reproductively non-active three-spined sticklebacks were given the choice between two shoals, equal in numbers of individuals, which could be seen either through a UV-transmitting [UV(+)] or a UV-blocking [UV(?)] filter. Test fish preferred to join the shoal seen under UV(+) conditions. Due to differences in quantal flux between the UV(+) and UV(?) filters used, control experiments with neutral-density optical filters were performed in order to clarify the role of luminance. Here, test fish spent significantly more time near shoals that were seen in a darker environment, suggesting a potential trade-off between UV radiation and lower brightness during shoal choice. To our knowledge, these results demonstrate for the first time that shoaling decisions are influenced by UV wavelengths. PMID:16618679

Modarressie, Ricarda; Rick, Ingolf P; Bakker, Theo C.M

2005-01-01

216

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

217

UV immobilized phospholipid bilayers  

SciTech Connect

Dinitrophenyl phosphotidylethanolamine-containing bilayers have been immobilized on carbon-shadowed support films by UV irradiation of the first monolayer transferred to the support film. The immobilized bilayer is capable of allowing bound protein (anti-DNP antibody) to organize into 2-D arrays in the presence of organic solvents such as acetonitrile and dilute concentrations of detergents such as beta-octyl glucoside. The ability of the bilayers to remain attached to supports under various conditions that include organic solvents and detergents as well as divalent ions is of potential interest in the study of protein crystallization and particularly in the study of membrane proteins.

Uzgiris, E.E.

1987-08-14

218

Extreme Horizontal Branch Stars in Passively Evolving Early Type Galaxies  

NASA Astrophysics Data System (ADS)

We study the effects of including binary star evolution in population synthesis models. We use the Hurley et al. (2002) code to compute binary star evolutionary tracks, and follow the procedure by Han et al. (2002), in particular, the two 2HeWD merger channel, to form EHB stars from a binary pair. We apply the resulting models to study UV excess ETGs.

Hernández-Pérez, Fabiola; Bruzual, Gustavo

2015-03-01

219

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

220

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

221

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

NASA Astrophysics Data System (ADS)

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-Msolar 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-Msolar Population I star with a 1.25-Msolar companion, and with period Pi= 3 d. 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.

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

2004-01-01

222

The UV enigma of post-starburst galaxies  

NASA Astrophysics Data System (ADS)

We have studied the panchromatic broad-band properties from the FUV to the MIR of a sample of 808 post-starburst galaxies. We find that in the optical and near-IR bands post-starburst galaxies (PSGs) form a remarkably uniform class of objects and that, on average, simple populations synthesis models (SSP) reproduce very well the SEDs of PSGs over a broad wavelength range, but not in the UV. We also find that, while the photometric variance in the optical and near-IR properties of the sample is small and comparable to the observational errors, both in the UV and the mid-IR the observed variance is much larger than the errors. We find a strong correlation between the UV fluxes and those in the mid-IR, indicating that the large variance in UV properties of PSGs could be related to a non-uniform distribution of dust covering the intermediate age populations. The disagreement between models and observations in the UV could be due to inadequate modelling; to the contribution of AGB and post-AGB stars; or to a non-uniform distribution of dust; possibly all three. Further progress in understanding this important class of galaxies, therefore, requires at the same time better modelling and better observations in the UV and mid-IR.

Melnick, Jorge; De Propris, Roberto

2014-11-01

223

Nuclear-induced UV fluorescence  

Microsoft Academic Search

An investigation of nuclear pumping of ultraviolet (UV) fluorescent gases that can be used to power the optically pumped atomic iodine laser is discussed. This laser utilizes 230-330-nm UV irradiance to dissociate compounds such as CF3I or C3F7 I, resulting in lasing on the 52P1\\/2-52P3\\/2 transition of atomic iodine at 1.31 ?m. UV fluorescence can be produced by the interaction

W. H. Williams; G. H. Miley

1989-01-01

224

Star clusters  

Microsoft Academic Search

Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which

M. Gieles

2006-01-01

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.

2004-09-01

226

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

227

UV Emission in Type Ia Supernova Elliptical Host Galaxies  

NASA Astrophysics Data System (ADS)

The current use of Type Ia supernova (SN Ia) as standard candles is to measure the dark energy equation-of-state to better than 10%. However, we still lack a clear understanding of their progenitor systems. We analyze the host galaxies of type Ia Supernova (SN Ia) discovered by the ESSENCE survey using UV and optical data, as studying the environments of SN Ia is a great way to understand the progenitors. We developed a new method for determining the SED and rest-frame magnitudes of the host galaxies and we use empirical relations to derive stellar mass and star-formation rate (SFR) measurements of the host galaxies. We find a high rate of UV emission in our passive galaxies, suggesting current star-formation in these galaxies.

Tucker, Brad E.

2015-03-01

228

Photosynthesis via Mineral Fluorescence in Harsh UV Radiation Environments  

NASA Astrophysics Data System (ADS)

Before the development of a protective ozone layer about two billion years ago, the surface ultraviolet flux on Earth would have restricted ancient life to environments that offered some protection from direct solar radiation, such as the deep ocean or under or within rocks. In environments where the visible solar radiation would have been reduced to levels too low for photosynthesis, visible fluorescence resulting from UV irradiation of minerals may have provided a useable energy source. We are investigating the possibility that photosynthesis can occur without direct sunlight, if certain minerals are present that can absorb UV radiation and fluoresce in the visible. There are several common minerals(e.g. fluorite, calcite) that emit strong visible radiation under both short- and long-wave UV light, as well as some that only emit visible radiation under specific UV wavelengths. We will test a variety of minerals that fluoresce at wavelengths utilized by microbial chlorophylls and accessory pigments, and by simulating endolithic communities living under a few centimeters or millimeters of rock, we will measure the intensity of fluorescence and UV radiation received at various depths. We plan to simulate a variety of environments where the surface UV radiation may have a significant impact on the survival of life. These include the early Earth and present-day Mars(where the atmosphere would offer little to no protection against biologically damaging UV radiation), as well as extrasolar planets(a terrestrial planet in the habitable zone around an M-type star, for example, would be subject to an intense UV flux due to high flare activity). If mineral fluorescence proves to be a viable survival mechanism for photosynthetic organisms in harsh radiation environments, there are many implications for the study of ancient life on Earth as well as the search for life elsewhere.

Barge, L. M.; Nealson, K.

2005-12-01

229

MEASURING GALAXY STAR FORMATION RATES FROM INTEGRATED PHOTOMETRY: INSIGHTS FROM COLOR-MAGNITUDE DIAGRAMS OF RESOLVED STARS  

SciTech Connect

We use empirical star formation histories (SFHs), measured from Hubble-Space-Telescope-based resolved star color-magnitude diagrams, as input into population synthesis codes to model the broadband spectral energy distributions (SEDs) of 50 nearby dwarf galaxies (6.5 < log M{sub *}/M{sub Sun} < 8.5, with metallicities {approx}10% solar). In the presence of realistic SFHs, we compare the modeled and observed SEDs from the ultraviolet (UV) through near-infrared and assess the reliability of widely used UV-based star formation rate (SFR) indicators. In the FUV through i bands, we find that the observed and modeled SEDs are in excellent agreement. In the Spitzer 3.6 {mu}m and 4.5 {mu}m bands, we find that modeled SEDs systematically overpredict observed luminosities by up to {approx}0.2 dex, depending on treatment of the TP-AGB stars in the synthesis models. We assess the reliability of UV luminosity as a SFR indicator, in light of independently constrained SFHs. We find that fluctuations in the SFHs alone can cause factor of {approx}2 variations in the UV luminosities relative to the assumption of a constant SFH over the past 100 Myr. These variations are not strongly correlated with UV-optical colors, implying that correcting UV-based SFRs for the effects of realistic SFHs is difficult using only the broadband SED. Additionally, for this diverse sample of galaxies, we find that stars older than 100 Myr can contribute from <5%-100% of the present day UV luminosity, highlighting the challenges in defining a characteristic star formation timescale associated with UV emission. We do find a relationship between UV emission timescale and broadband UV-optical color, though it is different than predictions based on exponentially declining SFH models. Our findings have significant implications for the comparison of UV-based SFRs across low-metallicity populations with diverse SFHs.

Johnson, Benjamin D. [Institute d'Astrophysique de Paris, CNRS, UPMC, 98bis Bd Arago, F-75014 Paris (France); Weisz, Daniel R.; Dalcanton, Julianne J.; Johnson, L. C.; Williams, Benjamin F. [Department of Astronomy, Box 351580, University of Washington, Seattle, WA 98195 (United States); Dale, Daniel A. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Dolphin, Andrew E. [Raytheon, 1151 E. Hermans Road, Tucson, AZ 85756 (United States); Gil de Paz, Armando [CEI Campus Moncloa, UCM-UPM, Departamento de Astrofisica y CC. de la Atmosfera, Facultad de CC. Fisicas, Universidad Complutense de Madrid, Avda. Complutense s/n, E-28040 Madrid (Spain); Kennicutt, Robert C. Jr. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Lee, Janice C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Skillman, Evan D. [Department of Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Boquien, Mederic [Marseille Universite, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, F-13388 Marseille (France)

2013-07-20

230

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

231

Triggered Star Formation in the Environment of Young Massive Stars  

E-print Network

Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (called IVINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula (M16) or the Horsehead Nebula B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

M. Gritschneder; T. Naab; F. Heitsch; A. Burkert

2006-09-26

232

8, 33573381, 2008 UV irradiances  

E-print Network

effects: on the one hand, UV radiation is able to cause health damages reaching from sun burn to skin). In contrast, the influence of the orienta- tion of the skin relative to the sun has hardly been considered calculating the impact of UV radiation on biological systems, such as for instance the human skin or eye, in5

Paris-Sud XI, Université de

233

The FIREBall fiber-fed UV spectrograph  

NASA Astrophysics Data System (ADS)

FIREBall (Faint Intergalactic Redshifted Emission Balloon) had a successful first engineering flight in July of 2007 from Palestine, Texas. Here we detail the design and construction of the spectrograph. FIREBall consists of a 1m telescope coupled to a fiber-fed ultraviolet spectrograph flown on a short duration balloon. The spectrograph is designed to map hydrogen and metal line emission from the intergalactic medium at several redshifts below z=1, exploiting a small window in atmospheric oxygen absorption at balloon altitudes. The instrument is a wide-field IFU fed by almost 400 fibers. The Offner mount spectrograph is designed to be sensitive in the 195-215nm window accessible at our altitudes of 35-40km. We are able to observe Ly?, as well as OVI and CIV doublets, from 0.3 < z < 0.9. Observations of UV bright B stars and background measurements allow characterization of throughput for the entire system and will inform future flights.

Tuttle, Sarah E.; Schiminovich, David; Milliard, Bruno; Grange, Robert; Martin, D. Christopher; Rahman, Shahinur; Deharveng, Jean-Michel; McLean, Ryan; Tajiri, Gordon; Matuszewski, M.

2008-07-01

234

Substantial reservoirs of molecular hydrogen in the debris disks around young stars.  

PubMed

Circumstellar accretion disks transfer matter from molecular clouds to young stars and to the sites of planet formation. The disks observed around pre-main-sequence stars have properties consistent with those expected for the pre-solar nebula from which our own Solar System formed 4.5 Gyr ago. But the 'debris' disks that encircle more than 15% of nearby main-sequence stars appear to have very small amounts of gas, based on observations of the tracer molecule carbon monoxide: these observations have yielded gas/dust ratios much less than 0.1, whereas the interstellar value is about 100 (ref. 9). Here we report observations of the lowest rotational transitions of molecular hydrogen (H2) that reveal large quantities of gas in the debris disks around the stars beta Pictoris, 49 Ceti and HD135344. The gas masses calculated from the data are several hundreds to a thousand times greater than those estimated from the CO observations, and yield gas/dust ratios of the same order as the interstellar value. PMID:11343110

Thi, W F; Blake, G A; van Dishoeck, E F; van Zadelhoff, G J; Horn, J M; Becklin, E E; Mannings, V; Sargent, A I; van Den Ancker, M E; Natta, A

2001-01-01

235

Substantial reservoirs of molecular hydrogen in the debris disks around young stars  

NASA Technical Reports Server (NTRS)

Circumstellar accretion disks transfer matter from molecular clouds to young stars and to the sites of planet formation. The disks observed around pre-main-sequence stars have properties consistent with those expected for the pre-solar nebula from which our own Solar System formed 4.5 Gyr ago. But the 'debris' disks that encircle more than 15% of nearby main-sequence stars appear to have very small amounts of gas, based on observations of the tracer molecule carbon monoxide: these observations have yielded gas/dust ratios much less than 0.1, whereas the interstellar value is about 100 (ref. 9). Here we report observations of the lowest rotational transitions of molecular hydrogen (H2) that reveal large quantities of gas in the debris disks around the stars beta Pictoris, 49 Ceti and HD135344. The gas masses calculated from the data are several hundreds to a thousand times greater than those estimated from the CO observations, and yield gas/dust ratios of the same order as the interstellar value.

Thi, W. F.; Blake, G. A.; van Dishoeck, E. F.; van Zadelhoff, G. J.; Horn, J. M.; Becklin, E. E.; Mannings, V.; Sargent, A. I.; van Den Ancker, M. E.; Natta, A.

2001-01-01

236

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

237

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

238

[Ozone decline and UV increase].  

PubMed

The following results have been obtained from long-term observations on the ozone layer and UV at the Meteorological Observatory Hohenpeigenberg:The seasonally varying decline of the ozone layer determines the maximum exposure to UV. Since ozone decline shows the highest rates in the spring months the UV exposure has most strongly increased in this time of the year. This is especially important because in spring the human skin is not adapted to UV exposure. Weather changes from day to day can induce rapid ozone reductions in spring about -30% which in turn is followed by an increase in UV of about 40%. Clouds, especially the transparent cirrus clouds (high clouds consisting of ice particles) have increased in frequency during spring and fall while a decrease is observed in summer. This change in cloudiness reduces the daily UV dose in spring and fall while it is enhanced in summer. With increasing height above sea level UV rises by roughly 10% per 1000 m (rule of thumb). Snow reflects the UV-radiation by up to 80% enhancing the UV-doses at relevant conditions. Strong volcano eruptions destroy ozone in the stratosphere additionally during 1-2 years after the eruption. Therafter the ozone layer recovers. In April 1993, after the eruption of Mt. Pinatubo (1991), the UV burden was still 40% higher than average. Miniholes and streamers can appear unexpected on a short-time scale and cross over Central Europe within 1-2 days, thus enhancing UV irradiation. The human skin reacts to UV exposure depending on the type of skin. The campaign "Sonne(n) mit Verstand" of the Bavarian Ministries for Environment, for Health and for Education informs about the danger of UV radiation (see www.sonne-mit-ver-stand.de). The German Weather Service informs the public on present developments of the ozone layer and relevant topics byits ozone bulletin, which is also available via internet under (www.dwd.de/deFundE/Observator/MOHp/hp2/ozon/bulletin.htm). PMID:14770335

Winkler, P; Trepte, S

2004-02-01

239

THE STAR FORMATION LAW AT LOW SURFACE DENSITY  

SciTech Connect

We investigate the nature of the star formation law at low gas surface densities using a sample of 19 low surface brightness (LSB) galaxies with existing H I maps in the literature, UV imaging from the Galaxy Evolution Explorer satellite, and optical images from the Sloan Digital Sky Survey. All of the LSB galaxies have (NUV - r) colors similar to those for higher surface brightness star-forming galaxies of similar luminosity indicating that their average star formation histories are not very different. Based upon four LSB galaxies with both UV and far-infrared (FIR) data, we find FIR/UV ratios significantly less than 1, implying low amounts of internal UV extinction in LSB galaxies. We use the UV images and H I maps to measure the star formation rate (SFR) and hydrogen gas surface density within the same region for all the galaxies. The LSB galaxy star formation rate surface densities lie below the extrapolation of the power law fit to the SFR surface density as a function of the total gas density for higher surface brightness galaxies. Although there is more scatter, the LSB galaxies also lie below a second version of the star formation law in which the SFR surface density is correlated with the gas density divided by the orbital time in the disk. The downturn seen in both star formation laws is consistent with theoretical models that predict lower star formation efficiencies in LSB galaxies due to the declining molecular fraction with decreasing density.

Wyder, Ted K.; Martin, D. Christopher; Barlow, Tom A.; Foster, Karl; Friedman, Peter G.; Morrissey, Patrick; Neill, James D. [California Institute of Technology, MC 278-17, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Neff, Susan G. [Laboratory for Astronomy and Solar Physics, NASA Goddard Space Flight Center, Greenbelt, MD, 20771 (United States); Schiminovich, David [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Seibert, Mark; Madore, Barry F. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Bianchi, Luciana [Center for Astrophysical Sciences, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218 (United States); Donas, Jose; Milliard, Bruno [Laboratoire d'Astrophysique de Marseille, BP 8, Traverse du Siphon, 13376 Marseille Cedex 12 (France); Heckman, Timothy M.; Szalay, Alex S. [Department of Physics and Astronomy, Johns Hopkins University, Homewood Campus, Baltimore, MD 21218 (United States); Lee, Young-Wook; Yi, Sukyoung K. [Center for Space Astrophysics, Yonsei University, Seoul 120-749 (Korea, Republic of); Rich, R. Michael [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)

2009-05-10

240

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

241

Strange stars  

NASA Technical Reports Server (NTRS)

Strange matter, a form of quark matter that is postulated to be absolute stable, may be the true ground stage of the hadrons. If this hypothesis is correct, neutron stars may convert to 'strange stars'. The mass-radius relation for strange stars is very different from that of neutron stars; there is no minimum mass, and for mass of 1 solar mass or less, mass is proportional to the cube of the radius. For masses between 1 solar mass and 2 solar masses, the radii of strange stars are about 10 km, as for neutron stars. Strange stars may have an exposed quark surface, which is capable of radiating at rates greatly exceeding the Eddington limit, but has a low emissivity for X-ray photons. The stars may have a thin crust with the same composition as the preneutron drip outer layer of a conventional neutron star crust. Strange stars cool efficiently via neutrino emission.

Alcock, Charles; Farhi, Edward; Olinto, Angela

1986-01-01

242

Criteria for the spectral classification of B stars in the ultraviolet  

NASA Technical Reports Server (NTRS)

A set of criteria for the classification of G stars from UV spectra alone, using standards drawn form the optical region, is developed. About 100 stars having normal MK spectral types in the range B0-B8, III-V, have been classified. The UV spectral types are found to be very consistent with the optical MK types, implying that it is possible to do two-dimensional spectral classification in the UV without any knowledge of the optical spectrum.

Rountree, Janet; Sonneborn, George

1991-01-01

243

Stars and Star Myths.  

ERIC Educational Resources Information Center

Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

Eason, Oliver

244

The Moon in the UV  

NASA Astrophysics Data System (ADS)

While the Moon has been observed in the UV for decades, the real utility of this spectral region for unlocking some of the Moon’s secrets has only recently been understood. Previously the domain of atmospheric studies, the UV has now emerged as an important spectral region for studying surfaces. The ultraviolet regime is very sensitive to both space weathering effects and composition, including hydration. This presentation will cover a review of early UV lunar observations (e.g., Apollo 17, International Ultraviolet Explorer), as well as early laboratory studies that first shone a light on the importance of this spectral region. The Lyman Alpha Mapping Project (LAMP) instrument, currently in orbit on the Lunar Reconnaissance Orbiter (LRO) spacecraft, is providing critical mapping capabilities of UV signatures, including signals from the permanently shadowed regions of the poles. I will discuss some of these exciting results, and extend these to implications for other airless bodies in the solar system.

Hendrix, Amanda

2014-11-01

245

Health Effects of UV Radiation  

MedlinePLUS

Fact Sheet Download the Health Effects of Overexposure to the Sun (PDF) Ozone layer depletion decreases our atmosphere’s natural protection from the sun’s harmful ultraviolet (UV) radiation. This Web page provides an overview of ...

246

UV clothing and skin cancer.  

PubMed

Skin cancer incidence in Croatia is steadily increasing in spite of public and governmental permanently measurements. It is clear that will soon become a major public health problem. The primary cause of skin cancer is believed to be a long exposure to solar ultraviolet (UV) radiation. The future designers of UV protective materials should be able to block totally the ultraviolet radiation. The aim of this paper is to present results of measurements concerning UV protecting ability of garments and sun-screening textiles using transmission spectrophotometer Cary 50 Solarscreen (Varian) according to AS/NZS 4399:1996; to show that standard clothing materials are not always adequate to prevent effect of UV radiation to the human skin; and to suggest the possibilities for its improvement for this purpose. PMID:21302719

Tarbuk, Anita; Grancari?, Ana Marija; Situm, Mirna; Martinis, Mladen

2010-04-01

247

Ultraviolet observations of Be stars /Review paper/  

NASA Technical Reports Server (NTRS)

In the last decade twelve major space experiments have observed Be stars in the UV region of the spectrum. The characteristics of the experiments are listed in a table. The studies were conducted with the aid of two rockets, five astronomical satellites, three manned satellites, and one planetary probe. Another table shows the name and the spectral type of the bright Be stars observed in the UV. Approaches concerning a system for ultraviolet spectral classification are discussed. Attention is also given to aspects of mass loss, the effects of rapid rotation, and the properties of the shell.

Heap, S. R.

1976-01-01

248

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

249

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

250

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

251

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

252

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

253

Exploring Ultraviolet (UV) light from the Sun  

NSDL National Science Digital Library

In this outdoor activity, learners explore UV rays from the Sun and ways to protect against these potentially harmful rays. Learners use "detectors" (UV beads) at five different stations, including sunscreen, water, sunglasses, shade and full sun, to explore what conditions block UV rays. Learners will observe that different materials block UV rays to different extents. After the activity, learners can use pipe-cleaners or strings to attach the "UV detectors" to a purse or shoelace and continue detecting UV wherever they go (optional). This activity can be conducted indoors by using an opened sunny window or a UV light bulb/blacklight to imitate the Sun.

2012-06-26

254

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

255

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

256

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

257

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

258

Hybrid Stars  

E-print Network

Recently there have been important developments in the determination of neutron star masses which put severe constraints on the composition and equation of state (EOS) of the neutron star matter. Here we study the effect of quark and nuclear matter mixed phase on mass radius relationship of neutron stars employing recent models from two classes of EOS's and discuss their implications.

Ashok Goyal

2003-03-21

259

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

260

Circumpolar Stars  

Microsoft Academic Search

Stars that never set as seen from a particular location. The requirement for this to happen is that the star's polar distance is less than the observer's latitude---thus from a location in latitude 52° North, stars of NPD less than 52° (i.e. with declinations of between 0° and +38°) are circumpolar and will be seen to circle around the north

P. Murdin

2000-01-01

261

UV Raman spectroscopy of hydrocarbons.  

PubMed

In this paper, the UV Raman spectra of a large number of saturated and alkyl-substituted monocyclic, bicyclic and polycyclic aromatic hydrocarbons are obtained at 220 and 233 nm excitation wavelengths. Also included are nitrogen- and sulphur-containing hydrocarbons. The spectra obtained are fluorescence free, even for such highly fluorescent compounds as perylene, consistent with earlier reports of UV Raman spectra of hydrocarbons. The hydrocarbon UV Raman spectra exhibit greatly improved signal-to-noise ratio when in the neat liquid or solution state compared with the neat solid state, suggesting that some surface degradation occurs under the conditions used here. Assignments are given for most of the bands and clear marker bands for the different classes of hydrocarbons are readily observable, although their relative intensities vary greatly. These results are discussed in the context of structure and symmetry to develop a consistent, molecular-based model of vibrational group frequencies. PMID:15482987

Loppnow, G R; Shoute, L; Schmidt, K J; Savage, A; Hall, R H; Bulmer, J T

2004-11-15

262

Hot Stars: Old-Fashioned or Trendy?  

E-print Network

Spectroscopic analyses with the intention of the interpretation of the UV-spectra of the brightest stars as individuals - supernovae - or as components of star-forming regions - massive O stars - provide a powerful tool with great astrophysical potential for the determination of extragalactic distances and of the chemical composition of star-forming galaxies even at high redshifts. The perspectives of already initiated work with the new generation of tools for quantitative UV-spectroscopy of Hot Stars that have been developed during the last two decades are presented and the status of the continuing effort to construct corresponding models for Hot Star atmospheres is reviewed. Because the physics of the atmospheres of Hot Stars are strongly affected by velocity expansion dominating the spectra at all wavelength ranges, hydrodynamic model atmospheres for O-type stars and explosion models for Supernovae of Type Ia are necessary as basis for the synthesis and analysis of the spectra. It is shown that stellar parameters, abundances and stellar wind properties can be determined by the methods of spectral diagnostics already developed. Additionally, it will be demonstrated that models and synthetic spectra of Type Ia Supernovae of required quality are already available that make it possible to tackle the question of whether Supernovae Ia are standard candles in a cosmological sense and the SN-luminosity distances thus indicate accelerated expansion of the universe.

A. W. A. Pauldrach

2003-01-16

263

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

264

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

265

The role of UV-optical obscuration in starburst galaxies  

NASA Technical Reports Server (NTRS)

The starburst phenomenon was viewed as increasingly important since the recognition that some galaxies have regions in which stars are forming so rapidly that a transient event must be seen. Such starbursts populate samples of galaxies selected either for UV or IR excess, and some were found from IRAS source identifications that must be quite heavily obscured at optical wavelengths. Many interpretations of the physical conditions in these objects and their stellar populations have relied on scaling from models of individual H II regions, and this certainly seems justified from the gross appearance of the optical spectra and IR spectral shapes. Collection of complementary UV, optical, and near-IR data is presented on a set of starbursts, with a preliminary analysis of models for more realistic internal structure.

Keel, William C.

1991-01-01

266

Hadron star models. [neutron stars  

NASA Technical Reports Server (NTRS)

The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as about 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

Cohen, J. M.; Boerner, G.

1974-01-01

267

Parameters and Winds of Hot Massive Stars  

Microsoft Academic Search

Over the last years a new generation of model atmosphere codes, which include the effects of metal line-blanketing of millions of spectral lines in NLTE, has been used to re-determine the properties of massive stars through quantitative spectral analysis methods applied to optical, IR and UV spectra. This has resulted in a significant change of the effective temperature scale of

R.-P. Kudritzki; M. A. Urbaneja

2006-01-01

268

Deep X-ray and UV Surveys of Galaxies with Chandra, XMM-Newton, and GALEX  

NASA Technical Reports Server (NTRS)

Only with the deepest Chandra surveys has X-ray emission from normal and star forming galaxies (as opposed to AGN, which dominate the X-ray sky) been accessible at cosmologically interesting distances. The X-ray emission from accreting binaries provide a critical glimpse into the binary phase of stellar evolution and studies of the hot gas reservoir constrain past star formation. UV studies provide important, sensitive diagnostics of the young star forming populations and provide the most mature means for studying galaxies at 2 < zeta < 4. This talk will review current progress on studying X-ray emission in concert with UV emission from normal/star-forming galaxies at higher redshift. We will also report on our new, deep surveys with GALEX and XMM-Newton in the nearby Coma cluster. These studies are relevant to DEEP06 as Coma is the nearest rich cluster of galaxies and provides an important benchmark for high-redshift studies in the X-ray and UV wavebands. The 30 ks GALEX (note: similar depth to the GALEX Deep Imaging Survey) and the 110 ks XMM observations provide extremely deep coverage of a Coma outskirts field, allowing the construction of the UV and X-ray luminosity function of galaxies and important constraints on star formation scaling relations such as the X-ray-Star Formation Rate correlation and the X-ray/Stellar Mass correlation. We will discuss what we learn from these deep observations of Coma, including the recently established suppression of the X-ray emission from galaxies in the Coma outskirts that is likely associated with lower levels of past star formation and/or the results of tidal gas stripping.

Hornschemeier, Ann

2006-01-01

269

UV-induced skin damage  

Microsoft Academic Search

Solar radiation induces acute and chronic reactions in human and animal skin. Chronic repeated exposures are the primary cause of benign and malignant skin tumors, including malignant melanoma. Among types of solar radiation, ultraviolet B (290–320 nm) radiation is highly mutagenic and carcinogenic in animal experiments compared to ultraviolet A (320–400 nm) radiation. Epidemiological studies suggest that solar UV radiation

M. Ichihashi; M. Ueda; A. Budiyanto; T. Bito; M. Oka; M. Fukunaga; K. Tsuru; T. Horikawa

2003-01-01

270

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 ...

271

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

272

Multifrequency observations of symbiotic stars  

NASA Technical Reports Server (NTRS)

The discovery of symbiotic stars is described, and the results of multifrequency observations made during the past two decades are presented. Observational data identify symbiotic stars as long-period binary systems that can be divided into two basic physical classes: detached symbiotics containing a red giant (or a Mira variable), and semidetached symbiotics containing a lobe-filling red giant and a solar-type main sequence star. Three components are typically observed: (1) the cool giant component with an effective temperature of 2500-4000 K, which can be divided by the IR spectral classification into normal M giants (S-types) and heavily reddened Mira variables (D-types); (2) the hot companion displaying a bright blue continuum at UV wavelengths, which is sometimes also an X-ray source; and (3) a gaseous nebula enveloping the binary.

Kenyon, Scott J.

1988-01-01

273

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

274

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 Earth’s 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.

2012-08-03

275

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

276

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

277

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...

278

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

279

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?

Bob Riddle

2003-02-01

280

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

281

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

282

Fluorine in extremely hot post-AGB stars  

E-print Network

We have discovered lines of highly ionized fluorine (Fv and Fvi) in the far-UV spectra of extremely hot (Teff=85,000--150,000 K) post-AGB stars. Our sample comprises H-rich central stars of planetary nebulae as well as H-deficient PG1159 stars. We performed non-LTE calculations and find strong F overabundances (up to 10**-4 by mass, i.e., 250 times solar) in a number of PG1159 stars, while F is essentially solar in the H-rich stars. Since PG1159 stars are believed to exhibit intershell matter of the preceding AGB phase on their surface, their chemical analyses allow for a direct insight into nucleosynthesis processes during the AGB phase. The high F abundances in PG1159 stars confirm the conclusion from abundance determinations in giants, that F is synthesized in AGB stars and that the F enrichment in the intershell must be very high.

K. Werner; T. Rauch; J. W. Kruk

2004-12-10

283

Luminous stars in galactic supernova remnants  

NASA Technical Reports Server (NTRS)

It is shown that luminous stars should be expected in the vicinity of supernova remnants. Luminous stars within the maximum optical areas of supernova remnants are tabulated from catalogs, and an excitation parameter is correlated with the spectral classification of such stars when their UV flux excites H II regions to produce nebular thermal bremsstrahlung. The correlations indicate that the presence of a ZAMS star of type 08 to 05 is necessary to produce thermal bremsstrahlung equal to the observed flux density at 1 GHz. Optical components of seven other supernova remnants are discussed, and it is concluded that gross uncertainties in the distance moduli of both stars and supernova remnants prevent any associations from being made.

Johnson, H. M.

1975-01-01

284

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

285

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

286

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 2, circa 1947. In 1966 Cary merged into Varian and in 1972 the Cary operation moved from Monrovia to Varian's main facilities in Palo Alto, California. In 1982 the Cary operation was moved to the Varian

Magee, Joseph W.

287

UV protective coatings: A botanical approach  

Microsoft Academic Search

Solar UV radiation is harmful to many biological systems, as well as all kind of technical applications. UV protective coatings are commonly utilised to shield many susceptible substances. In an attempt to learn from nature we demonstrate that for the Pinus mugo subsp. mugo (dwarf mountain pine) the cuticular wax layer provides UV protection. This biological coating contains chromophores that

J. F. Jacobs; G. J. M. Koper; W. N. J. Ursem

2007-01-01

288

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

289

Experimenting with UV-sensitive Beads  

NSDL National Science Digital Library

Participants will experiment with ultraviolet light sensitive plastic beads, which are generally white but turn colors when exposed to UV light. Participants are informed about the nature and risks of UV light and are asked to be the scientist to explore what types of materials keep the beads, and hence the user, safe from UV light.

290

MULTISPECTRAL UV FLUORESCENCE ANALYSIS OF PAINTED SURFACES  

Microsoft Academic Search

ABSTRACT A novel system has been developed to acquire digital multis- pectral ultraviolet (UV) induced visible fluorescence images ofpaintings. We present here the image processing needed to understand and further process the acquired multispectral UV fluorescence images. 1.,INTRODUCTION Observations of an ,artwork under UV light have been car- ried on since the end of the twenties. Traditionally this diag- nostic

A. Pelagotti; L. Pezzati; A. Piva; A. Del Mastio

2006-01-01

291

UV-B Biodosimetry in Turfgrass Canopies  

Microsoft Academic Search

and Lindow, 1995). Radiation in the UV spectrum ac- counts for less than 9% of the total incoming solar Phylloplane microorganisms are affected by ultraviolet (UV) radia- energy, but it has deleterious effects on all biological tion penetrating into plant canopies, but data as to the relationships between microorganism activity and canopy UV levels is lacking. systems. Wavelengths shorter than

G. Y. Yuen; C. C. Jochum; L. J. Giesler; M. D. Shulski; E. A. Walter-Shea; K. G. Hubbard; G. L. Horst

2002-01-01

292

CO map and steep Kennicutt-Schmidt relation in the extended UV disk of M 63  

NASA Astrophysics Data System (ADS)

Results from the UV satellite GALEX revealed surprisingly large extensions of disks in some nearby spiral galaxies. While the H? emission, the usual tracer of star formation, drops down at the border of the isophotal radius, r25, the UV emission extends out to 3 to 4 times this radius and often covers a significant fraction of the H I area. M 63 is a remarkable example of a spiral galaxy with one of the most extended UV disks, so it offers the opportunity to search for the molecular gas and characterize the star formation in outer disk regions as revealed by the UV emission. We obtained deep CO(1-0) and CO(2-1) observations on the IRAM 30 m telescope along the major axis of the M 63 disk from the center out to the galactocentric radius rgal = 1.6 r25 and over a bright UV region at rgal = 1.36 r25. CO(1-0) is detected all along the M 63 major axis out to r25, and CO(2-1) is confined to rgal = 0.68 r25, which may betray lower excitation temperatures in the outer disk. CO(1-0) is also detected in the external bright UV region of M 63. This is the fourth molecular gas detection in the outskirts of nearby spirals. The radial profiles of the CO emission and of the H?, 24 ?m, NUV and FUV star formation tracers and H I taken from the literature show a severe drop with the galactocentric radius, such that beyond r25 they are all absent with the exception of a faint UV emission and H I. The CO emission detection in the external UV region, where the UV flux is higher than the UV flux observed beyond r25, highlights a tight correlation between the CO and UV fluxes, namely the amount of molecular gas and the intensity of star formation. This external UV region is dominated by the atomic gas, suggesting that H I is more likely the precursor of H2 rather than the product of UV photodissociation. A broken power law needs to be invoked to describe the Kennicutt-Schmidt (K-S) relation of M 63 from the center of the galaxy out to rgal = 1.36 r25. While all along the major axis out to r25, the K-S relation is almost linear (with a slope of nearly 1 in log space), in the external UV region the SFR regime is highly nonlinear and characterized by a steep K-S relation (with a slope much higher than 1 in log space) and very low star formation efficiency. Based on observations carried out with the IRAM 30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).

Dessauges-Zavadsky, M.; Verdugo, C.; Combes, F.; Pfenniger, D.

2014-06-01

293

Research on UV scattering communication  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV) scattering communication is a broadcast communication mode of information transmission by particles in the atmosphere scattering effect on the blind band ultraviolet light, there are many advantages such as unaffected by electromagnetic radiation, good confidentiality, non-line-of sight communication. This type communication mainly used in a short distance, secure communication, which was superior to no line communication in aspect of anti-jamming and secrecy. Firstly the military requirement of UV scattering communication is analyzed in this paper, The development trend is introduced, then the composition and working principle of ultraviolet scattering communication system are also discussed, The key influential factors of UV communication system path transmission loss effects on parameters such as receiver, transmitter and received beam divergence angle, pitch angle and the communication distance were analyzed. Attenuation was quantitatively simulated under different atmospheres, communication patterns and structure parameters. The results show that: transmission distance increases with increasing beam divergence angle and decreasing field angle. And the received view angle of influence on the communication distance is far greater than the emission beam divergence angle; transmission distance increases with increasing beam divergence angle and decreasing field and field angle effects on communication distance is greater than beam divergence angle.

Dong, Ke-yan; Lou, Yan; Ding, Ying; Wang, Shuo; Wang, Hongliang; Jiang, Hui-lin

2013-08-01

294

Photolytic degradation of sulfamethoxazole and trimethoprim using UV-A, UV-C and vacuum-UV (VUV).  

PubMed

The photolytic degradation of the non-degradable pharmaceuticals sulfamethoxazole (SMX) and trimethoprim (TMP) in an aqueous solution was investigated using three kinds of low-pressure mercury lamp UV-A (352 nm), UV-C (254 nm), and vacuum-UV (VUV, 185 nm and 254 nm). The degradation rates were highly dependent on the target compounds as well as the UV sources. No degradation of the target compounds was observed using UV-A treatment, because there was no overlap between the UV-A emission spectrum and absorption spectrum of the target compounds. On the other hand, UVC and VUV revealed higher reactivity. The results also indicated that SMX had a greater potential to react photochemically than TMP. Among the UV sources, VUV was the most effective process for the degradation of target compounds. Furthermore, the addition of oxidants such as hydrogen peroxide (H2O2) and sodium persulfate (Na2S2O8) to the reaction system improved the overall degradation rate significantly.The experimental results for the VUV-irradiated samples with the addition of methanol as a hydroxyl radical scavenger revealed that hydroxyl radicals contribute significantly to the elimination of the target compound. Overall, the degradation rate of the target compounds was in the order: VUV = UV-C > UV-A for sulfamethoxazole and VUV/H2O2 > VUV/ Na2S2O8 > VUV >UV-C >UV-A for trimethoprim. PMID:25594122

Kim, Hyun Young; Kim, Tae-Hun; Yu, Seungho

2015-01-01

295

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

NASA Astrophysics Data System (ADS)

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 photosynthesis) accumulated in the stratosphere. In an effort to better understand the UV liability of DNA, we used synchrotron light to measure VUV-UV absorption spectra (125-340 nm) for DNA and its components (oligonucleotides and mononucleotides). We also measured VUV-UV absorption spectra for potential and known UV screens, including amino acids, proteins, amines (including polyamines), scytonemin, mycosporine-like amino acids, ?- carotene, melanin and flavonoids. Among these, flavonoids seem remarkably suited to protecting DNA in the VUV-UV. Flavonoids accumulate in seed coats, where they confer resistance to monochromatic UV (254 nm) and polychromatic UV (200-400 nm). We discuss these findings in relation to the origin and evolution of life and its potential dispersal through space.

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

2007-09-01

296

Double stars  

Microsoft Academic Search

The work devoted to the identification of double and multiple stars for the Hipparcos input catalog is presented. Ground based observations, and photometric and astrometric aspects are included. The aim of the work is to improve the main stream of the data reduction. The tasks performed by the input catalog (INCA) double star working groups are reported. The contents of

J. Dommanget

1989-01-01

297

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.

298

Rogue Star  

NSDL National Science Digital Library

This program calculates and depicts the effects of a rogue star coming through our solar system. Users adjust the date, the rogue star's mass, approach distance in astronomical units (AU) and flyby speed to run an animation of what would happen to the planets under the specified conditions.

Douglas Hamilton

299

An ultraviolet line list for O star spectra  

NASA Technical Reports Server (NTRS)

Archival high dispersion UV spectra obtained by the IUE satellite, together with laboratory data for the Fe peak ions, reveal more than 550 identifiable spectral features in the far-UV region in the cases of the O subdwarfs BD +75 deg 325 and BD +28 deg 4211, as well as the sharp lined main sequence star HD 46202. The wide range of effective temperatures of the selected stars makes this spectral line identification list suitable for use with all stars of spectral type O. The most numerous of the features identified are those of the lines attributed to iron atoms, with each of the spectra studied exhibiting three levels of ionization that range from Fe III to Fe V for the coolest O star, HD 46202, and Fe IV through Fe VI for the hottest O star, BD +28 4211.

Dean, C. A.; Bruhweiler, F. C.

1985-01-01

300

Searching for Flaring Activity on the STAR Star Gamma CAS  

NASA Astrophysics Data System (ADS)

Gamma Cas is one of the most active of the classical Be stars,showing pronounced optical emission lines as well as variableoptical, UV and X-ray continua. The X-ray variability is oftenassumed to be caused by the interaction of the stellar windwith a hypothetical degenerate companion. Recent evidence,however, suggests that the X-rays may be generated by flare-like activity originating in localized regions on the surfaceof the star (Smith, 1995). This interpretation is based on avariety of evidence, including FUV continuum variationsobserved with Voyager and transient emission and absorptionfeatures in various optical spectral lines seen from theground. The observations are far from conclusive, however. Inthe proposed observations we will use the GHRS to obtain highquality UV spectral time sequences, which will allow us totest the flare/active region hypothesis. Flares are commonlyassumed to be related to magnetic energy releases. If flaresand active regions are proven to exist on Be stars, it willhave a dramatic influence on the theoretical interpretation ofthe Be phenomena.

Smith, Myron

1995-07-01

301

Star dust.  

PubMed

Infrared astronomy has shown that certain classes of stars are abundant producers of refractory grains, which condense in their atmospheres and are blown into interstellar space by the radiation pressure of these stars. Metallic silicates of the kind that produce terrestrial planets are injected by the oxygen-rich stars and carbon and its refractories by carbon stars. Much of the interstellar dust may be produced by this mechanism. A number of "infrared stars" are completely surrounded by their own dust, and a few of these exhibit a unique morphology that suggests the formation of a planetary system or a stage in the evolution of a planetary nebula. Certain novae also condense grains, which are blown out in their shells. In our own solar system, comets are found to contain the same silicates that are present elsewhere in the galaxy, suggesting that these constituents were present in the primeval solar nebula. PMID:17732279

Ney, E P

1977-02-11

302

A Spectral Atlas of lambda Bootis Stars  

NASA Astrophysics Data System (ADS)

Since the discovery of lambda Bootes stars, a permanent confusion about their classification can be found in literature. This group of non-magnetic, Population I, metal-poor A to F-type stars, has often been used as some sort of trash can for "exotic" and spectroscopically dubious objects. Some attempts have been made to establish a homogeneous group of stars which share the same common properties. Unfortunately, the flood of "new" information (e.g. UV and IR data) led again to a whole zoo of objects classified as lambda Bootes stars, which, however, are apparent non-members. To overcome this unsatisfying situation, a spectral atlas of well established lambda Bootes stars for the classical optical domain was compiled. It includes intermediate dispersion (40 and 120 Å mm^{-1}) spectra of three lambda Bootes, as well as appropriate MK standard stars. Furthermore, "suspicious" objects, such as shell and Field Horizontal Branch stars, have been considered in order to provide to classifiers a homogeneous reference. As a further step, a high resolution (8 Å mm^{-1}) spectrum of one "classical" lambda Bootes star in the same wavelength region (3800-4600 Å) is presented. In total, 55 lines can be used for this particular star to derive detailed abundances for nine heavy elements (Mg, Ca, Sc, Ti, Cr, Mn, Fe, Sr and Ba).

Paunzen, E.; Heiter, U.

2014-06-01

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

Diurnal changes in epidermal UV transmittance of plants in naturally high UV environments.  

PubMed

Studies were conducted on three herbaceous plant species growing in naturally high solar UV environments in the subalpine of Mauna Kea, Hawaii, USA, to determine if diurnal changes in epidermal UV transmittance (T(UV)) occur in these species, and to test whether manipulation of the solar radiation regime could alter these diurnal patterns. Additional field studies were conducted at Logan, Utah, USA, to determine if solar UV was causing diurnal T(UV) changes and to evaluate the relationship between diurnal changes in T(UV) and UV-absorbing pigments. Under clear skies, T(UV), as measured with a UV-A-pulse amplitude modulation fluorometer for leaves of Verbascum thapsus and Oenothera stricta growing in native soils and Vicia faba growing in pots, was highest at predawn and sunset and lowest at midday. These patterns in T(UV) closely tracked diurnal changes in solar radiation and were the result of correlated changes in fluorescence induced by UV-A and blue radiation but not photochemical efficiency (F(v)/F(m)) or initial fluorescence yield (F(o)). The magnitude of the midday reduction in T(UV) was greater for young leaves than for older leaves of Verbascum. Imposition of artificial shade eliminated the diurnal changes in T(UV) in Verbascum, but reduction in solar UV had no effect on diurnal T(UV) changes in Vicia. In Vicia, the diurnal changes in T(UV) occurred without detectable changes in the concentration of whole-leaf UV-absorbing compounds. Results suggest that plants actively control diurnal changes in UV shielding, and these changes occur in response to signals other than solar UV; however, the underlying mechanisms responsible for rapid changes in T(UV) remain unclear. PMID:18346077

Barnes, Paul W; Flint, Stephan D; Slusser, James R; Gao, Wei; Ryel, Ronald J

2008-06-01

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

The ultraviolet-bright stars of Omega Centauri, M3, and M13  

NASA Technical Reports Server (NTRS)

Two new UV-bright stars detected within 2 arcmin of the center of Omega Cen are spectroscopically investigated with the short-wavelength spectrograph of the IUE. The IUE spectra of the UV-bright stars UIT-1 and UIT-2 in the core of Omega Cen superficially resemble those of Population I mid-B stars. The absorption lines of the core UV-bright stars are significantly weaker than in Population I stars, consistent with their membership in the cluster. Synthetic spectra calculated from low-metallicity Kurucz model stellar atmospheres are compared with the spectra. These objects are insufficiently luminous to be classical hydrogen-burning post-AGB stars. They may be evolved hot horizontal branch stars which have been brightened by more than 3 mag since leaving the zero-age horizontal branch. It is inferred from the spectra and luminosity of the core UV-bright stars that similar objects could provide the source of the UV light in elliptical galaxies.

Landsman, Wayne B.; O'Connell, Robert W.; Whitney, Jonathan H.; Bohlin, Ralph C.; Hill, Robert S.; Maran, Stephen P.; Parise, Ronald A.; Roberts, Morton S.; Smith, Andrew A.; Stecher, Theodore P.

1992-01-01

307

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

308

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

309

Star Formation and Feedback in Dwarf Galaxies  

E-print Network

We examine the star formation history and stellar feedback effects of dwarf galaxies under the influence of extragalactic ultraviolet radiation. 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. Our results indicate that star formation in the severe environment of dwarf galaxies is a difficult and inefficient process. For intermediate mass systems, such as the dSphs around the Galaxy, star formation can proceed with in 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 $M/L-M_v$ correlation.

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

2003-12-08

310

Influence of UV activity on the Spectral Fingerprints of Earth-like Planets around M dwarfs  

NASA Astrophysics Data System (ADS)

A wide range of potentially rocky transiting planets in the habitable zone (HZ) have been detected by Kepler as well as ground-based searches. The spectral type of the host star will influence our ability to detect atmospheric features with future space and ground based missions like JWST, GMT and E-ELT. Particularly the active and inactive M stars are a stellar class, covering a wide range of UV luminosity, that will influence the detectability of habitable conditions. The UV emission from a planet's host star dominates the photochemistry and thus the resultant observable spectral features. Using the latest UV spectra obtained by Hubble as well as IUE, we model Earth-like planets orbiting a wide range of M-dwarfs from M0 to M9 for both active and inactive stars. These planets are the first ones that should become available to observations with JWST and E-ELT. A wide range of such targets will soon be identified in our Solar Neighborhood by the 2017 TESS mission.

Rugheimer, Sarah; Kaltenegger, Lisa; Segura, Antigona; Mohanty, Subhanjoy

2014-06-01

311

XMM-Newton and VLA Observations of the Variable Wolf-Rayet Star EZ CMa: Evidence for a Close Companion?  

E-print Network

XMM-Newton and VLA Observations of the Variable Wolf-Rayet Star EZ CMa: Evidence for a Close of the Wolf-Rayet star EZ CMa (HD 50896) obtained with XMM-Newton and the VLA. This WN4 star exhibits optical and UV variability at a period of 3.765 d whose cause is unknown. Binarity may be responsible

Guedel, Manuel

312

UV emission from young and middle-aged pulsars: Connecting X-rays with the optical  

E-print Network

We present the UV spectroscopy and timing of three nearby pulsars (Vela, B0656+14 and Geminga) recently observed with the Space Telescope Imaging Spectrograph. We also review the optical and X-ray properties of these pulsars and establish their connection with the UV properties. We show that the multiwavelengths properties of neutron stars (NSs) vary significantly within the sample of middle-aged pulsars. Even larger differences are found between the thermal components of Ge-minga and B0656+14 as compared to those of radio-quiet isolated NSs. These differences could be attributed to different properties of the NS surface layers.

O. Kargaltsev; G. G. Pavlov

2006-09-25

313

The secrets of T Pyx: I. UV observations  

E-print Network

We have studied the UV spectral behavior of the recurrent nova T Pyx during 16 years of IUE observations. We examined both the IUE line-by-line images and the extracted spectra in order to understand the reality and the origin of the observed spectral variations. The UV continuum of T Pyx has remained nearly constant in slope and intensity over this time interval, without any indication of long-term trends. The reddening determined from the UV data is E(B-V}=0.25 \\pm 0.02. The best single-curve fit to the dereddened UV continuum is a power-law distribution $\\propto \\lambda^{-2.33}$. The tail of this curve agrees well with the B, V, and J magnitudes of T Pyx, indicating that the contribution of the secondary star is negligible. One peculiar aspect of T Pyx is that most emission lines (the strongest ones being those of CIV 1550 and HeII 1640) show substantial changes both in intensity and detectability, in contrast to the near constancy of the continuum. Several individual spectra display emission features that are difficult to identify, suggesting a composite spectroscopic system. We tentatively ascribe the origin of these transient emission features either to loops and jets from the irradiated secondary or to moving knots of the surrounding nebula that are (temporarily) projected in front of the system. The inspection of all IUE line-by-line images has led to the detection of emission spikes outside the central strip of the spectrum, which in some cases seem associated to known emission features in the (main) spectrum. A comparison with other ex-novae reveals a surprising similarity to the spectrum of the very-slow nova HR Del, whose white dwarf primary has a mass that is allegedly about one half that of T Pyx.

Roberto Gilmozzi; Pierluigi Selvelli

2006-10-02

314

Solar UV Radiation and the Origin of Life on Earth  

NASA Technical Reports Server (NTRS)

We have started a comprehensive, interdisciplinary study of the influence of solar ultraviolet radiation on the atmosphere of of the early Earth. We plan to model the chemistry of the Earth atmosphere during its evolution, using observed UV flux distributions of early solar analogs as boundary conditions in photochemical models of the Earth's atmosphere. The study has four distinct but interlinked parts: (1) Establishing the radiation of the early Sun; (2) Determining the photochemistry of the early Earth's atmosphere; (3) Estimating the rates of H2 loss from the atmosphere; and (4) Ascertaining how sensitive is the photochemistry to the metallicity of the Sun. We are currently using STIS and EUVE to obtain high-quality far-UV and extreme-UV observations of three early-solar analogs. We will perform a detailed non-LTE study of each stars, and construct theoretical model photosphere, and an empirical model chromospheres, which can be used to extrapolate the continuum to the Lyman continuum region. Given a realistic flux distribution of the early Sun, we will perform photochemical modeling of weakly reducing primitive atmospheres to determine the lifetime and photochemistry of CH4. In particular, we will make estimates of the amount of CH4 present in the prebiotic atmosphere, and estimate the atmospheric CH4 concentration during the Late Archean (2.5-3.0 b.y. ago) and determine whether it would have been sufficiently abundant to help offset reduced solar luminosity at that time. Having obtained a photochemical model, we will solve for the concentrations of greenhouse gasses and important pre-biotic molecules, and perform a detailed radiative transfer calculations to compute the UV flux reaching the surface.

Heap, Sara R.; Hubeny, Ivan; Lanz, Thierry; Gaidos, Eric; Kasting, James; Fisher, Richard R. (Technical Monitor)

2000-01-01

315

Massive star-formation regions in the Magellanic Clouds  

SciTech Connect

Optical and UV spectroscopy of stars from six compact, luminous groups or clusters in the SMC and LMC is presented. The groups are characterized by high concentrations of nebulosity or starlight confined to areas smaller than 30 arcsec on a side, in which some stars can be resolved. The spectra and fluxes are used to derive luminosities and effective temperatures for the stars. Spectroscopic and stellar wind properties are also noted. It is found that the stars are all of O and B-type, with low extinction. The stars generally have little or no sign of stellar winds, and often have spectral peculiarities, such as weak lines or mixed spectral indicators. Most spectra have strong, broad Ly-alpha absorption, and some have broad Ca II absorption. The stars are placed on the H-R diagram, and it is argued that some of them are massive stars in pre-main-sequence stages of their evolution. 8 references.

Hutchings, J.B.; Thompson, I.B.

1988-08-01

316

Criteria for the spectral classification of B stars in the ultraviolet  

Microsoft Academic Search

A set of criteria for the classification of G stars from UV spectra alone, using standards drawn form the optical region, is developed. About 100 stars having normal MK spectral types in the range B0-B8, III-V, have been classified. The UV spectral types are found to be very consistent with the optical MK types, implying that it is possible to

Janet Rountree; George Sonneborn

1991-01-01

317

Stars equilibrium  

NSDL National Science Digital Library

What causes the fusion reaction in a star's core? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to processes inside a star. Students read about the equilibrium process in a star, in which outward gas pressure equals inward gravitational pressure. Then, an interactive lab activity offers students the opportunity to predict temperature, pressure, and gravity changes that occur during equilibrium. The chemical reactions of the fusion process are presented, and more specific detailed reactions are available in a pop-up box. Student practice quizzes about the equilibrium process and pressure and gravity interactions inside the star are included, as are answers. Copyright 2005 Eisenhower National Clearinghouse

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

2003-01-01

318

HST UV polarimetry of AGNs  

NASA Astrophysics Data System (ADS)

We present the results of HST/FOS UV spectropolarimetry and FOC imaging polarimetry of radio galaxies and Seyfert 2 galaxies. The FOS data of narrow-line radio galaxies are discussed based on the following two observed facts. One is that the scattering regions are very extended (a few kpc to over 10kpc). The other is that the polarized continuum has a spectral shape similar to or slightly redder than quasar continua. The latter fact favors electrons as the dominant scatterers rather than dust grains. In this case, however, due to the observed large size of the scattering region, the mass of the scattering gas is estimated to be uncomfortably large. Combining our UV data with previous optical/infrared polarimetry data, we infer instead that the scattering would be often caused by opaque dust clouds, which will show apparently grey scattering. With dust, the large mass problem can be avoided, due to its higher scattering efficiency. However, we still cannot rule out the possibility of electron scattering, which could imply the existence of a large gas mass surrounding these radio galaxies. The FOC imaging polarimetry data are also discussed in terms of the nature of scatterers and environment using our multi-color images.

Kishimoto, M.; Antonucci, R.; Cimatti, A.; Hurt, T.; Dey, A.; van Breugel, W.; Spinrad, H.; Kay, L.; Cohen, R.; Krolik, J.

2000-12-01

319

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 ...

Mr. B

2007-11-10

320

Tycho's Star  

Microsoft Academic Search

A supernova remnant in Cassiopeia, 7.7° north of alpha 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

P. Murdin

2000-01-01

321

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

322

Star clusters  

NASA Astrophysics Data System (ADS)

Star clusters are observed in almost every galaxy. In this thesis we address several fundamental problems concerning the formation, evolution and disruption of star clusters. From observations of (young) star clusters in the interacting galaxy M51, we found that clusters are formed in complexes of stars and star clusters. These complexes share similar properties with giant molecular clouds, from which they are formed. Many (70%) of the young clusters will not survive the fist 10 Myr, due to the removal of left over gas. We study the evolution of clusters that have survived this first 10 Myr, to become bound star clusters that have cleared their primordial gas content. We determined the life time of such star clusters in M51 and the solar neighbourhood and compare these values, including existing values from literature, to the results of N-body simulations. These simulations consider realistic star clusters, with a stellar initial mass function, stellar evolution, accurate treatments of binaries and the tidal field of the host galaxy. We found that the observed disruption times of clusters in the solar neighbourhood and M51 are shorter than predicted by the simulations by a factor of 5 and 10, respectively. We studied the effect of additional perturbations by spiral arm crossings and encounters with giant molecular clouds with N-body simulations. We found that the mass loss due to these external perturbations, combined with the mass loss due to stellar evolution and the galactic tidal field can explain the observed disruption times. The star clusters in the solar neighbourhood have much lower masses than the young clusters observed in merging and interacting galaxies. We show that this can be largely explained by size-of-sample effects, that is, when more star clusters are observed, the chance of finding a more massive one is higher. However, we showed that there can exist a physical maximum to the cluster mass, which should be observable in the cluster luminosity function. We found this observational signature in the luminosity function of clusters in M51. A comparison to a cluster population model, that was developed for this thesis research, suggests that the maximum cluster mass in M51 is 5x10^5 solar masses. In the merging Antennae galaxies a similar luminosity function was observed. However, the maximum mass is four times higher there, suggesting that the maximum mass depends on galactic environment.

Gieles, M.

2006-10-01

323

Chemical abundances in Hg-Mn stars  

NASA Technical Reports Server (NTRS)

An abundance analysis has been conducted of 21 elements in 21 Hg-Mn, two Si-Cr, and six normal stars using model atmospheres and high-dispersion spectroscopy in the visible and UV. Manganese line strengths imply abundances that correlate well with stellar effective temperature. Within the studied sample of Hg-Mn stars there appears to be no correlation of abundances of any element with projected rotational velocity. Abundances in several Hg-Mn stars show patterns that are probably consistent with diffusion but difficult to reconcile with equilibrium nucleosynthesis. In general, no combination of gross stellar physical parameters is sufficient to characterize the patterns of line strengths observed in Hg-Mb Hg-Mn stars.

Heacox, W. D.

1979-01-01

324

Electron stars for holographic metallic criticality  

SciTech Connect

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{sub 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.

Hartnoll, Sean A.; Tavanfar, Alireza [Center for the Fundamental Laws of Nature, Harvard University, Cambridge, Massachusetts 02138 (United States)

2011-02-15

325

Potential fingerprints detection using UV spectral imaging  

NASA Astrophysics Data System (ADS)

Spectral imaging technology research is becoming more extensive in the field of examination of material evidence. UV spectral imaging technology is an important part of the full spectrum of imaging technology. This paper summarizes the application of the results of UV imaging technology in the field of evidence examination, explores the common object of potential fingerprints of UV spectra characteristic for the research objectives, which shows the potential traces of criminal using the ultraviolet spectrum imaging method.

Huang, Wei; Yang, Zhichao; Xu, Xiaojing; Guo, Jingjing

2012-11-01

326

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

327

UV-Induced Cell Death in Plants.  

PubMed

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

328

HST images of Jupiter's UV aurora  

NASA Astrophysics Data System (ADS)

One of the brightest and most variable UV emissions in the solar system comes from Jupiter's UV aurora. The auroras have been imaged with each camera on HST, starting with the pre-COSTAR FOC and continuing with increasing sensitivity to the present with STIS. This paper presents a short overview of the scientific results on Jupiter's aurora obtained from HST UV images and spectra, plus a short dicussion of Saturn's aurora.

Clarke, John T.

329

The UV Index and Sun Protection  

NSDL National Science Digital Library

This site from the Government of Canada provides educational materials on the UV index (created from data from thirteen monitoring sites across Canada), UV radiation, ozone, and issues in weather and ozone depletion. It is intended to create awareness of health risks of UV radiation by offering activities for children and reading materials for adults on the matter. A summary of UV radiation and ozone science, information on ozone and radiation monitoring activities by Canada and the US, and links to data sets and publications are given. Among the "bells and whistles" are a printable poster and coloring pages for children and RealPlayer movies.

330

Induction and construct UV protective yeast plasmid.  

PubMed

In this study, we apply concepts of synthetic biology in combination with conventional methods to assemble different genetic components to construct yeast resistant to UV radiation, and to induce production of anti-UV proteins. This work combines sequences of different promoters, STRESS-proteins, heat shock protein (HSP), kinase proteins, alcohol dehydrogenase protein (ADH), ribosomal binding sites, fluorescent reporter proteins, terminators, and a synthetic ribosomal switch. The aim of this investigation was to induce an anti-UV proteins, and to construct an anti-UV yeast plasmid to be used for protection of skin cells against UV radiation. This investigation demonstrates induction and construction of anti-UV genes and production of their corresponding proteins. Cultures of Saccharomyces cerevisiae (ATCC # 66348) were exposed to short-wave UV radiation and were then subjected to time-PCR to assess specific gene expression. Proteins were identified using two dimensional difference gel electrophoresis (2D DIGE) and LC-MS/MS. Different up-regulated and down-regulated proteins were identified. Highly expressed identified proteins were cloned into S. cerevisiae using a synthetic biology approach. Extracts from UV-induced genetically transformed yeasts were used to protect skin cell cultures (ATCC #2522-CRL) in vitro. Both microscopic analysis and an apoptosis assay showed protection of the skin cell cultures against UV radiation. PMID:23665192

Cuero, Raul; McKay, David S

2013-07-10

331

Is UV ornamentation an amplifier in swordtails?  

PubMed

Do distinct male morphs use the same ornaments in different ways? Female preference for UV ornamentation and male activity was examined in two different male size classes of the swordtail Xiphophorus nigrensis: intermediate and large. UV ornamentation is preferred by females for both size classes, while high male activity is not. Large males have significantly greater intensity and saturation of UV reflectance for several body regions. Despite this difference in signal strength, intermediate sized males garnered a greater gain in female attention for UV ornamentation relative to large males. The differential payoff may be a result of different interactions between ornamentation and activity between the size classes. Females show significant preference for UV-ornamented intermediate males only when they are more active than their rival and not when the UV-ornamented male is less active, indicating that behavior might serve as an amplifier of UV ornamentation in this class. Meanwhile, large males gain from their UVornamentation only when they are less active than their rival, failing to support behavior as an amplifier for UV ornamentation in this size class. This interaction between size class and activity is significant, and suggests that UV and/or behavior play different roles for alternative male morphs competing for female attention. PMID:18248249

Cummings, Molly E; García de León, Francisco J; Mollaghan, Diane M; Ryan, Michael J

2006-01-01

332

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

333

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

334

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

335

YOUNG, ULTRAVIOLET-BRIGHT STARS DOMINATE DUST HEATING IN STAR-FORMING GALAXIES  

SciTech Connect

In star-forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAHs), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region-the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the IR emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star-forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.

Law, Ka-Hei [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Gordon, Karl D. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Misselt, K. A., E-mail: klaw@pha.jhu.edu, E-mail: kgordon@stsci.edu, E-mail: misselt@as.arizona.edu [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2011-09-10

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

Measurements of UV radiation on rotating vertical plane at the ALOMAR Observatory (69° N, 16° E), Norway, June 2007  

NASA Astrophysics Data System (ADS)

Erythemaly weighted UV and total UV-A irradiance measured at the ALOMAR (Arctic Lidar Observatory for Middle Atmosphere Research; 69° N, 16° E) in June 2007 by two Kipp & Zonen UV broadband meters type, UV-S-EA-T, are examined. One unit is mounted on rotating vertical plane and the other is permanently fixed horizontally. The UV broadband meters measure simultaneously to compare UV irradiances on vertical and horizontal planes. The entire range of such relative exposure variations during clear-sky and overcast conditions over ALOMAR in the period March June 2007 is examined using STAR and Radonic1 model (developed at the Meteorological Institute, University of Munich) for various action spectra: erythema, UV-A, and vitamin D3. The model and observations support that the daily means of relative exposures are quite stable, i.e., vary within the range 0.4 0.6 with the mean around 0.5 when the averaged intra-day, day-to-day, and seasonal changes of the relative erythemal exposures are considered. It seems that multiplication of the daily mean dose from a broadband meter placed horizontally by the factor of 0.5 gives reasonable estimation of the daily mean exposure on a vertically oriented receiver randomly oriented towards the Sun. The model studies during clear-sky conditions show that the extreme value and daily variability of relative exposure are the highest for UV-A, next for erythemal UV, then for vitamin D3 weighed UV irradiance. The minima of relative exposure (~0.20 0.30) are almost the same for all weighting functions. The comparison of model simulations and measurements suggests that specific cloud configuration could lead to significant enhancement of UV exposure of rotating receiver.

Sobolewski, P.; Krzy?cin, J. W.; Jaroslawski, J.; Stebel, K.

2008-06-01

338

Star formation in HI debris  

NASA Astrophysics Data System (ADS)

We propose to use GALEX observations to search for evidence of star formation in the intergalatic HI clouds of nearby galaxy systems. The method, identifying starburst sources (the so called intergalactic HII regions) coincident with HI clouds, has been recently used to demonstrate significant star formation outside of galaxies in Stephan's quintet. Mendes de Oliveira et al. 2004, (see also http://www.gemini.edu/project/announcements/press/2004-7.html) found several candidates of such star-forming regions using multi-slit spectroscopy which were confirmed by the GALEX pre-release observations of this spectacular interacting group. For this proposal we chose eight nearby systems (z < 3200 km/s), most of which are interacting or merging, which contain intergalactic HI clouds. They were selected from the HI Rogues Gallery of HI maps of galaxies and groups (http://www.nrao.edu/astrores/HIrogues/). Our main goal is to measure or set limits on the UV flux for the intergalactic HII regions that may be present in intergalactic HI clouds, in order to determine their ages and masses. Finding widespread, young, star-forming regions in the eight HI intergalactic clouds, indicating `in situ' formation of these objects, will be strong evidence that this is an efficient mechanism for producing and mixing metals in the intergalactic medium. This may have been even more important in the early universe, when galaxy-galaxy interactions were more frequent and tidal debris more common.

Oliveira, Claudia

339

Hot Post-AGB Stars  

NASA Astrophysics Data System (ADS)

From the study of IRAS sources with far-IR colors similar to planetary nebulae (PNe), several proto-planetary nebulae with hot (OB) post-AGB central stars have been detected. These stars form an evolutionary link between the cooler G,F,A supergiant stars that have evolved off the Asymptotic Giant Branch (AGB) and the hot (OB) central stars of PNe. The optical spectra of these objects show strong Balmer emission lines and in some cases low excitation nebular emission lines such as [NII] and [SII] superposed on the OB stellar continuum. The absence of of [OIII] 5007Å line and the presence of low excitation nebular emission lines indicate that photoionisation has just started. The UV(IUE) spectra of some of these objects revealed violet shifted stellar wind P-Cygni profiles of CIV, SiIV and NV, indicating hot and fast stellar wind and post-AGB mass loss. These objects appear to be rapildy evolving into the early stages of PNe similar to that observed in the case of Hen1357 IRAS 17119-5926 (Stingray Nebula) and IRAS 18062+2410 SAO85766.

Parthasarathy, M.; Gauba, G.; Fujii, T.; Nakada, Y.

2001-08-01

340

UV/Optical Detections of Candidate Tidal Disruption Events by GALEX and CFHTLS  

NASA Astrophysics Data System (ADS)

We present two luminous UV/optical flares from the nuclei of apparently inactive early-type galaxies at z=0.37 and 0.33 that have the radiative properties of a flare from the tidal disruption of a star. In this paper we report the second candidate tidal disruption event discovery in the UV by the GALEX Deep Imaging Survey and present simultaneous optical light curves from the CFHTLS Deep Imaging Survey for both UV flares. The first few months of the UV/optical light curves are well fitted with the canonical t-5/3 power-law decay predicted for emission from the fallback of debris from a tidally disrupted star. Chandra ACIS X-ray observations during the flares detect soft X-ray sources with Tbb=(2-5)×105 K or ?>3 and place limits on hard X-ray emission from an underlying AGN down to LX(2-10 keV)<~1041 ergs s-1. Blackbody fits to the UV/optical spectral energy distributions of the flares indicate peak flare luminosities of >~1044-1045 ergs s-1. The temperature, luminosity, and light curves of both flares are in excellent agreement with emission from a tidally disrupted main-sequence star onto a central black hole of several times 107 Msolar. The observed detection rate of our search over ~2.9 deg 2 of GALEX Deep Imaging Survey data spanning from 2003 to 2007 is consistent with tidal disruption rates calculated from dynamical models, and we use these models to make predictions for the detection rates of the next generation of optical synoptic surveys. Some of the data presented herein were 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 the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

Gezari, S.; Basa, S.; Martin, D. C.; Bazin, G.; Forster, K.; Milliard, B.; Halpern, J. P.; Friedman, P. G.; Morrissey, P.; Neff, S. G.; Schiminovich, D.; Seibert, M.; Small, T.; Wyder, T. K.

2008-04-01

341

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

342

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

343

SWIRE Stars  

NASA Astrophysics Data System (ADS)

We propose IRS lo-res spectroscopy of 21 carefully selected stars from the SWIRE survey which show excess emission above the expected photospheric levels at 24um. This program differs from many extensive Spitzer stellar surveys, such as the FEPS legacy program and the MIPS GTO VLS survey in that the targets are not preselected. We hope through this approach to start to: 1) characterize the galactic population of stars with excesses at 24um; 2) to discover and identify rare transitional objects, such as protoplanetary nebulae; and 3) to test the inferences drawn from the targeted surveys. We will augment the Spitzer spectroscopy with 6.5 hrs. of visible spectroscopy from NOAO designed to permit classification of the stars. The type of program we undertake here exploits the unique discovery potential of the Spitzer mission.

Werner, Michael; Morales, Farisa; Padgett, Deborah; Stauffer, John

2006-05-01

344

Massive stars  

NASA Astrophysics Data System (ADS)

We describe the present state of massive star research seen from the viewpoint of stellar evolution, with special emphasis on close binaries. Statistics of massive close binaries are reasonably complete for the Solar neighbourhood. We defend the thesis that within our knowledge, many scientific results where the effects of binaries are not included, have an academic value, but may be far from reality. In chapter I, we summarize general observations of massive stars where we focus on the HR diagram, stellar wind mass loss rates, the stellar surface chemistry, rotation, circumstellar environments, supernovae. Close binaries can not be studied separately from single stars and vice versa. First, the evolution of single stars is discussed (chapter I). We refer to new calculations with updated stellar wind mass loss rate formalisms and conclusions are proposed resulting from a comparison with representative observations. Massive binaries are considered in chapter II. Basic processes are briefly described, i.e. the Roche lobe overflow and mass transfer, the common envelope process, the spiral-in process in binaries with extreme mass ratio, the effects of mass accretion and the merging process, the implications of the (asymmetric) supernova explosion of one of the components on the orbital parameters of the binary. Evolutionary computations of interacting close binaries are discussed and general conclusions are drawn. The enormous amount of observational data of massive binaries is summarized. We separately consider the non-evolved and evolved systems. The latter class includes the semi-detached and contact binaries, the WR binaries, the X-ray binaries, the runaways, the single and binary pulsars. A general comparison between theoretical evolution and observations is combined with a discussion of specially interesting binaries: the evolved binaries HD 163181, HD 12323, HD 14633, HD 193516, HD 25638, HD 209481, ? Per and silon Sgr; the WR+OB binary V444 Cyg; the high mass X-ray binaries Vela X-1, Wray 977, Cyg X-1; the low mass X-ray binaries Her X-1 and those with a black hole candidate; the runaway ? Pup, the WR+compact companion candidates Cyg X-3, HD 50896 and HD 197406. We finally propose an overall evolutionary model of massive close binaries as a function of primary mass, mass ratio and orbital period. Chapter III deals with massive star population synthesis with a realistic population of binaries. We discuss the massive close binary frequency, mass ratio and period distribution, the observations that allow to constrain possible asymmetries during the supernova explosion of a massive star. We focuss on the comparison between observed star numbers (as a function of metallicity) and theoretically predicted numbers of stellar populations in regions of continuous star formation and in starburst regions. Special attention is given to the O-type star/WR star/red supergiant star population, the pulsar and binary pulsar population, the supernova rates.

Vanbeveren, D.; De Loore, C.; Van Rensbergen, W.

345

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

346

Beryllium and Boron abundances in population II stars  

NASA Technical Reports Server (NTRS)

The scientific focus of this program was to undertake UV spectroscopic abundance analyses of extremely metal poor stars with attention to determining abundances of light elements such as beryllium and boron. The abundances are likely to reflect primordial abundances within the early galaxy and help to constrain models for early galactic nucleosynthesis. The general metal abundances of these stars are also important for understanding stellar evolution.

1995-01-01

347

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

348

Photoionization of Clustered Halos by the First Stars  

Microsoft Academic Search

We present numerical simulations of the photoevaporation of cosmological halos clustered around a 120 M⊙ primordial star, confining our study to structures capable of hosting Population III star formation. The calculations include self-consistent multifrequency conservative transfer of UV photons together with nine-species primordial chemistry and all relevant radiative processes. The ultimate fates of these halos varies with central density and

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

2008-01-01

349

Parameters and Winds of Hot Massive Stars  

Microsoft Academic Search

Over the last years a new generation of model atmosphere codes, which include\\u000athe effects of metal line-blanketing of millions of spectral lines in NLTE, has\\u000abeen used to re-determine the properties of massive stars through quantitative\\u000aspectral analysis methods applied to optical, IR and UV spectra. This has\\u000aresulted in a significant change of the effective temperature scale of

ROLF P. KUDRITZKI; MIGUEL A. URBANEJA

2006-01-01

350

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

351

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

352

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

353

UV curable polyurethane-based microspheres  

Microsoft Academic Search

Radiation curable polyurethane-based microspheres were prepared by modifying conventional procedures for preparing anionic polyurethane dispersions. Vinyl groups were introduced to the side chains and the ends of the polyurethane main chains. Photoinitiators and multifunctional acrylate oligomers were incorporated into each microsphere. The curing behavior of the films obtained from these microspheres under UV were studied. The MEK resistance of UV

Masakazu Hirose; Jianhui Zhou; Fumiyuki Kadowaki

1999-01-01

354

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...

355

UV-B EFFECTS ON TERRESTRIAL ECOSYSTEMS  

EPA Science Inventory

Dpeletion of stratospheric O3 layer should result in enhanced levels of ultraviolet-B (UV-B) radiation at the earth's surface compared to present, with potentially damaging effects on biological systems. his paper briefly summarizes some key findings for UV-B effects on terrestri...

356

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...

357

Skin cancer and solar UV radiation  

Microsoft Academic Search

Ultraviolet (UV) radiation in sunlight is the most prominent and ubiquitous physical carcinogen in our natural environment. It is highly genotoxic but does not penetrate the body any deeper than the skin. Like all organisms regularly exposed to sunlight, the human skin is extremely well adapted to continuous UV stress. Well-pigmented skin is clearly better protected than white Caucasian skin.

F. R. de Gruijl

1999-01-01

358

Are natural lipids UV-screening agents?  

Microsoft Academic Search

Isolated lipids from Deinococcus radiodurans were reconstituted at final concentrations of 1 mg\\/ml into dioleoyl phosphatidyl choline (DOPC) vesicles and assayed for the ability to protect cells of Escherichia coli against killing by UV light (254 nm). Values of D37 (UV dose required to reduce the number of surviving cells to 37% of the original number) were calculated from killing

Jeff Reeve; Lorraine H. Kligman; Robert Anderson

1990-01-01

359

On $?$-Deformation and UV/IR Mixing  

E-print Network

We examine the UV/IR mixing property on a $\\kappa$-deformed Euclidean space for a real scalar $\\phi^4$ theory. All contributions to the tadpole diagram are explicitly calculated. UV/IR mixing is present, though in a different dressing than in the case of the canonical deformation.

Harald Grosse; Michael Wohlgenannt

2005-09-08

360

UV Modulation of Subcutaneous Fat Metabolism  

Microsoft Academic Search

Adipose tissue is not a homogeneous organ. Visceral fat accumulation is associated with atherosclerosis and metabolic syndrome, but peripheral subcutaneous (SC) fat accumulation may be protective. Human skin is continuously exposed to UV light. UV can penetrate the epidermis and into the mid-dermis, but not into the SC fat tissue of human skin. However, we here show that SC fat

Eun Ju Kim; Yeon Kyung Kim; Ji Eun Kim; Sojeong Kim; Min-Kyoung Kim; Chi-Hyun Park; Jin Ho Chung

2011-01-01

361

UV microspot irradiator at Columbia University.  

PubMed

The Radiological Research Accelerator Facility 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 a live zebrafish embryo. PMID:23708525

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

2013-08-01

362

UV sensors based on liquid crystals mixtures  

NASA Astrophysics Data System (ADS)

The Erythemal Response Spectrum is a scientific expression that describes the sensitivity of the skin to the ultraviolet radiation. The skin sensitivity strongly depends on the UV wavelength: a long exposition to UV radiation causes erythema once a threshold dose has been exceeded. In the past years several devices have been developed in order to monitor the UV exposure, most of them are based on inorganic materials that are able to mimic the human skin behaviour under UV radiation. We present a new device based on liquid crystals technology. The sensor is based on a liquid crystalline mixture that absorbs photons at UV wavelength and emits them at a longer one. This system presents several innovative features: the absorption range of the mixture can be varied to be sensitive to different wavelengths, the luminescence intensity can be tuned, the system can be implemented on flexible devices.

Chanishvili, Andro; Petriashvili, Gia; Chilaya, Guram; Barberi, Riccardo; De Santo, Maria P.; Matranga, Mario A.; Ciuchi, F.

2006-04-01

363

Instrumentation of the WSO-UV project  

NASA Astrophysics Data System (ADS)

Dedicated to spectroscopic and imaging observations of the ultraviolet sky, the World Space Observatory - Ultraviolet mission is a Russian-Spanish collaboration. The project consists of a 1.7m telescope with instrumentation able to perform: a) high resolution (R ?50 000) spectroscopy by means of two echellé spectrographs covering the 115-310 nm spectral range; b) long slit (1x75 arcsec) low resolution (R ˜ 1000) spectroscopy with a near-UV channel and a far-UV channel to cover the 115-305 nm spectral range; c) near-UV and a far-UV imaging channels covering the 115-320 nm wavelength range; d) slitless spectroscopy with spectral resolution of about 500 in the full 115-320 nm spectral range. Here we present the WSO-UV focal plane instruments, their status of implementation, and the expected performances.

Sachkov, Mikhail; Shustov, Boris; Gómez de Castro, Ana Inés.

2014-07-01

364

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

365

First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group  

NASA Astrophysics Data System (ADS)

First-Ever Census of Variable Mira-Type Stars in Galaxy Outsidethe Local Group Summary An international team led by ESO astronomer Marina Rejkuba [1] has discovered more than 1000 luminous red variable stars in the nearby elliptical galaxy Centaurus A (NGC 5128) . Brightness changes and periods of these stars were measured accurately and reveal that they are mostly cool long-period variable stars of the so-called "Mira-type" . The observed variability is caused by stellar pulsation. This is the first time a detailed census of variable stars has been accomplished for a galaxy outside the Local Group of Galaxies (of which the Milky Way galaxy in which we live is a member). It also opens an entirely new window towards the detailed study of stellar content and evolution of giant elliptical galaxies . These massive objects are presumed to play a major role in the gravitational assembly of galaxy clusters in the Universe (especially during the early phases). This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory . PR Photo 14a/03 : Colour image of the peculiar galaxy Centaurus A . PR Photo 14b/03 : Location of the fields in Centaurus A, now studied. PR Photo 14c/03 : "Field 1" in Centaurus A (visual light; FORS1). PR Photo 14d/03 : "Field 2" in Centaurus A (visual light; FORS1). PR Photo 14e/03 : "Field 1" in Centaurus A (near-infrared; ISAAC). PR Photo 14f/03 : "Field 2" in Centaurus A (near-infrared; ISAAC). PR Photo 14g/03 : Light variation of six variable stars in Centaurus A PR Photo 14h/03 : Light variation of stars in Centaurus A (Animated GIF) PR Photo 14i/03 : Light curves of four variable stars in Centaurus A. Mira-type variable stars Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred (0.3%) displays brightness variations and is referred to by astronomers as a "variable star". The percentage is much higher among large, cool stars ("red giants") - in fact, almost all luminous stars of that type are variable. Such stars are known as Mira-variables ; the name comes from the most prominent member of this class, Omicron Ceti in the constellation Cetus (The Whale), also known as "Stella Mira" (The Wonderful Star). Its brightness changes with a period of 332 days and it is about 1500 times brighter at maximum (visible magnitude 2 and one of the fifty brightest stars in the sky) than at minimum (magnitude 10 and only visible in small telescopes) [2]. Stars like Omicron Ceti are nearing the end of their life. They are very large and have sizes from a few hundred to about a thousand times that of the Sun. The brightness variation is due to pulsations during which the star's temperature and size change dramatically. In the following evolutionary phase, Mira-variables will shed their outer layers into surrounding space and become visible as planetary nebulae with a hot and compact star (a "white dwarf") at the middle of a nebula of gas and dust (cf. the "Dumbbell Nebula" - ESO PR Photo 38a-b/98 ). Several thousand Mira-type stars are currently known in the Milky Way galaxy and a few hundred have been found in other nearby galaxies, including the Magellanic Clouds. The peculiar galaxy Centaurus A ESO PR Photo 14a/03 ESO PR Photo 14a/03 [Preview - JPEG: 400 x 451 pix - 53k [Normal - JPEG: 800 x 903 pix - 528k] [Hi-Res - JPEG: 3612 x 4075 pix - 8.4M] ESO PR Photo 14b/03 ESO PR Photo 14b/03 [Preview - JPEG: 570 x 400 pix - 52k [Normal - JPEG: 1140 x 800 pix - 392k] ESO PR Photo 14c/03 ESO PR Photo 14c/03 [Preview - JPEG: 400 x 451 pix - 61k [Normal - JPEG: 800 x 903 pix - 768k] ESO PR Photo 14d/03 ESO PR Photo 14d/03 [Preview - JPEG: 400 x 451 pix - 56k [Normal - JPEG: 800 x 903 pix - 760k] Captions : PR Photo 14a/03 is a colour composite photo of the peculiar galaxy Centaurus A (NGC 5128) , obtained with the Wide-Field Imager (WFI) cam

2003-05-01

366

Filamentary star formation in a unique environment  

NASA Astrophysics Data System (ADS)

The most spectacular examples of star formation outside of galactic disks occur in the vicinities of some brightest cluster galaxies (BCGs) in rich, X-ray bright ‘cool core’ galaxy clusters. We present the results of HST optical and UV photometry of massive star formation that is occurring at large projected distances 20 kpc) from the centre of the BCG NGC 1275 in the Perseus cluster. The star formation is occurring in situ in an extensive filamentary nebulosity which engulfs the host galaxy. Powerful AGN feedback is responsible for distributing the cool gas to large radii which then sits in the hot, high pressure intra-cluster medium. We model the ages and masses of the young star clusters and determine that the star-forming filaments switched on ~50 Myrs ago and are currently feeding the growth of the NGC 1275 stellar halo at a rate of 2-3 solar masses per year. Star formation in filamentary nebulae surrounding BCGs could lead to dynamically hot, spatially extended stellar halos and globular cluster systems. This mode of star-formation may also be important in early galaxy formation where powerful AGN are common and the pressurised external atmospheres in these systems may be supplied by the in-falling intergalactic medium.

Canning, Rebecca

2014-08-01

367

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

368

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

369

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

370

Addressable Micromachined UV Light Sources for Active Patterning  

Microsoft Academic Search

This paper presents a programmable UV light source array which can generate a patterned UV light for various applications. While all existing excimer lasers or UV light sources are based on a static compositional patterning, the UV light source array presented in this paper can be used to define arbitrary patterns in real-time. As a demonstration, UV light source arrays

Yoonsu Choi; Ravikanth Devireddy; Youngdo Jung; A. Bruno Frazier

2007-01-01

371

The star sky atlas  

Microsoft Academic Search

This atlas consists of 20 star charts together with a stellar catalogue. A booklet with explanations to the star sky atlas and to the stellar catalogue is included. The charts of the atlas contain stars to visual magnitude 6.5. The total number of stars is ?8,500. The star charts also contain star clusters, nebulae and galaxies. The atlas is referred

V. K. Abalakin

1991-01-01

372

Seeing Stars  

Microsoft Academic Search

Seeing Stars is written for astronomers, regardless of the depth of their theoretical knowledge, who are taking their first steps in observational astronomy. Chris Kitchin and Bob Forrest - both professional astronomers - take a conducted tour of the night sky and suggest suitable observing programmes for everyone from beginners to experts. How is this book different? We are all

Chris Kitchin; Robert W. Forrest

1998-01-01

373

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

374

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

375

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

376

Star quality.  

PubMed

Around 150 wards are participating in the voluntary Star Wards scheme to provide mental health inpatients with more activities with therapeutic value. Suggested activities range from a library, to horse riding Internet access and comedy. Service users are particularly keen to have more exercise, which can be a challenge in inpatient settings. PMID:17970387

Dent, Emma

2007-09-20

377

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. ...

378

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

379

Plant responses to UV-B irradiation are modified by UV-A irradiation  

SciTech Connect

The increasing UV-B radiation (0.28-0.32 [mu]m) reaching the earth's surface is an important concern. Plant response in artificial UV-B irradiation studies has been difficult to assess, especially regarding photosynthetic pigments, because the fluorescent lamps also produce UV-A (0.32-0.40[mu]m) radiation which is involved with blue light in pigment synthesis. Both UV-A and UV-B irradiances were controlled in two glasshouse experiments conducted under relatively high PPFD (> 1300[mu]mol m[sup [minus]2] s[sup [minus]1]) at two biologically effective daily UV-B irradiances (10.7 and 14.1 kJ m[sup [minus]2]); UV-A irradiances were matched in Controls ([approximately]5, 9 kJ m[sup [minus]2]). Normal, chlorophyll-deficient, and flavonoid-deficient isolines of soybean cultivar, Clark, were utilized. Many growth/ pigment variables exhibited a statistically significant interaction between light quality and quantity: in general, UV-A radiation moderated the damaging effects of UV-B radiation. Regression analyses demonstrated that a single negative function related photosynthetic efficiency to carotenoid Content (r[sup 2] =0.73, P[le]0.001), implying a [open quotes]cost[close quotes] in maintaining carotenoids for photoprotection. A stomatal limitation to photosynthesis was verified and carotenoid content was correlated with UV-B absorbing compound levels, in UV-B irradiated plants.

Middleton, E.M.; Teramura, A.H. (NASA/Goddard Space Flight Center, Greenbelt, MD (United States) Univ. of Maryland, College Park (United States))

1993-06-01

380

Young stars in nearby early-type galaxies: The GALEX-SAURON perspective  

NASA Astrophysics Data System (ADS)

Recent studies from the Galaxy Evolution Explore (GALEX) ultraviolet (UV) data reveal that the recent star formation is more common in early-type galaxies (ETGs) that we used to believe (Jeong et al. 2007). Here we used the unique GALEX UV data on existing SAURON IFU-studied galaxies and combined these two datasets (UV and IFU) to find where photometric anomalies occur. One of the highlights of our study is the work on the Fundamental Plane (FP). The tilt and scatter found in optical FPs have been an issue. From our sample of 34 ETGs, we found that most of the tilt and scatter are caused by the minority ETGs which have been forming stars recently at very low level (see figure 1). Using our UV FPs, we found a strong evidence for star formation history being the main source of the mystery (Jeong et al. 2009).

Jeong, Hyunjin; Yi, Sukyoung K.; Bureau, Martin; Davies, Roger L.

2015-03-01

381

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

382

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

383

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

384

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

385

Overview of SPICAV occultation results for the UV channel  

NASA Astrophysics Data System (ADS)

The SPICAV instrument onboard the Venus Express spacecraft is a multi-channel suite cov-ering the far ultraviolet to the mid-infrared. In this presentation, we will focus on the results obtained by the UV channel during stellar occultations observations. Stellar occultation tech-nique possesses well-known advantages: self-calibration, low sensitivity to instrument aging, simple laws of radiative transfer. In addition, occultation with stars permit to cover a broad range of latitudes at any given season and they provide optimal geometrical registration. Since Venus Express orbit insertion, several hundreds of occultations have been performed by SPI-CAV, yielding profiles of atmospheric constituents between 80 and 140 km. In the SPICAV UV range, CO2 possesses a broad signature shortward of 200 nm which allows one to retrieve CO2 concentration and subsequently to deduce atmospheric pressure and temperature profiles in the upper mesosphere and in the thermosphere. The Venusian thermosphere shows excessive variability, with the equivalent of more than three scale heights change in density in less than a few days. No other spectral signature besides that of CO2 and haze particles was expected to appear in SPICAV ultraviolet spectra at this altitude range but a consistent search was undertaken, revealing the presence of aan ozone at 100 km (¡108 cm-3) and of sulfur dioxide above 90 km at a concentration of 0.1 to 1 ppm.

Montmessin, Franck; Bertaux, Jean-Loup; Belyaev, Denis; Marcq, Emmanuel; Korablev, Oleg; Vandaele, Ann-Carine; Fedorova, Anna

386

Implications of Ultraviolet Imaging Telescope observations for star formation histories in NGC 1275  

NASA Technical Reports Server (NTRS)

We discuss UV imagery of NGC 1275 obtained using the Goddard Ultraviolet Imaging Telescope. We are able to study the UV morphology down to mu 249 of about 25 mag/sq arcsec. There are significant nonaxisymmetric structures in the UV continuum associated with the low-velocity filament system. Continuum from the high-velocity system may also be present. The large aperture UV colors indicate that although the mass function extends to about 5 solar masses, more massive objects are not present. This implies either a cessation of star formation during the last 50-100 Myr or a truncated initial mass function.

Smith, Eric P.; O'Connell, Robert W.; Bohlin, Ralph C.; Cheng, Kwang-Ping; Cornett, Robert H.; Hill, Jesse K.; Hill, Robert S.; Hintzen, Paul; Landsman, Wayne B.; Neff, Susan G.

1992-01-01

387

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

388

UV radiation: balancing risks and benefits.  

PubMed

We use action spectra published by the International Commission on Illumination to examine diurnal, seasonal and latitudinal variations in erythemally weighted (sunburning) UV-a health risk, and vitamin D-weighted UV-a health benefit. Vitamin D-weighted UV is more strongly dependent on ozone and solar zenith angle. Consequently, its diurnal, seasonal and geographic variability is more pronounced than for erythemally weighted UV. We then investigate relationships between the two quantities. An algorithm is developed and used to relate vitamin D production to the widely used UV index, to help the public to optimize their exposure to UV radiation. In the summer at noon, there should at mid-latitudes be sufficient UV to photosynthesize optimal vitamin D in approximately 1 min for full body exposure, whereas skin damage occurs after approximately 15 min. Further, while it should be possible to photosynthesize vitamin D in the winter at mid-latitudes, the amount of skin that must be exposed is larger than from the hands and face alone. This raises the question of whether the action spectrum for vitamin D production is correct, since studies have reported that production of vitamin D is not possible in the winter at mid-latitudes. PMID:18657052

McKenzie, Richard L; Liley, J Ben; Björn, Lars Olof

2009-01-01

389

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

390

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

391

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

392

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

393

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.

2012-08-03

394

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

395

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.

396

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

397

H2 in the UV-rich Environment of Orion's Veil  

NASA Astrophysics Data System (ADS)

Understanding the physics of molecular gas, almost by definition, requires understanding the physics of molecular hydrogen. H2 is the most abundant molecule in molecular clouds, the formation of H2 initiates the transition from warmer atomic to cooler molecular gas, and H2 serves as a catalyst in the formation of other molecules like CO that are widely used to study star-forming regions. It is no exaggeration to say that a fundamental understanding of the earliest phases of star formation is impossible without a fundamental understanding of the physics of H2. In this presentation, we will present high-resolution UV absorption spectroscopy towards the Trapezium stars in the Orion Nebula. Using the STIS E140H setting of HST, we now have an S/N = 50 - 150 spectral dataset between 1133 - 1335 Angstroms, with a spectral resolution of 2.5 km/s. This dataset will allow us to determine the H2 column density in a PDR which has a very low H2 column density (H2/H(tot) < 10^-5). By observing the column density of high rotational/vibrational levels of H2, and combining the observations a detailed model of ISM physics using Cloudy, we hope to better understand the physics of H2 in high-UV flux environments, which has applications to star-forming environments at the galactic and extra-galactic level.

Abel, Nicholas; Ferland, Gary J.; O'Dell, C. R.; Troland, Thomas H.

2014-06-01

398

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

399

Christmas star.  

NASA Astrophysics Data System (ADS)

There are continuous attempts to identify the legendary Christmas Star with a real astronomical event accompanying the birth of Jesus from Nazareth. Unfortunately, the date of birth is difficult to establish on the basis of historical records with better accuracy than a few years. During that period a number of peculiar astronomical events were observed and it seem to be impossible to identify the right one unambiguously.

Bia?a, J.

400

Recombination Lines of Embedded Star Clusters  

E-print Network

Aims. We are trying to probe conditions in the youngest super star clusters, those still embedded in dense obscuring clouds. Methods. The hydrogen recombination lines in the radio and infrared can be observed through the obscuration, as the optical and UV lines cannot, and give us the kinematics of the ionized gas. Results. The line profiles of the clusters resemble superpositions of the lines of many very young ultra-compact or hyper-compact HII regions. This can be explained if each OB star is individually embedded in dense material which it is accreting, even as it ionizes. Conclusions. We speculate on what this implies for the status and evolutionary state of cluster stars.

S. C. Beck

2008-08-13

401

UV Impacts Avoided by the Montreal Protocol  

NASA Technical Reports Server (NTRS)

Temporal and geographical variabilities in the future "World Expected" UV environment are compared with the "World Avoided", which would have occurred without the Montreal Protocol on protection of the ozone layer and its subsequent amendments and adjustments. Based on calculations of clear-sky UV irradiances, the effects of the Montreal Protocol have been hugely beneficial to avoid the health risks, such as skin cancer, which are associated with high UV, while there is only a small increase in health risks, such as vitamin D deficiency, that are associated with low UV. However, interactions with climate change may lead to changes in cloud and albedo, and possibly behavioural changes which could also be important.

Newman, Paul; McKenzie, Richard

2010-01-01

402

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...

403

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

404

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

405

Some physical properties of UV galaxies  

NASA Astrophysics Data System (ADS)

Observational data on galaxies displaying ultraviolet excesses in their spectra included in a survey compiled at the Byurakan Astrophysical Observatory are considered and discussed. The characteristic physical properties of active galaxies with UV excesses are considered, as well as the unusual morphologies in their central regions. In spite of numerous studies of these galaxies, their physical nature remains incompletely understood. The results of the analysis of the problems associated with the peculiarities of UV galaxies are presented.

Khachikyan, E. E.; Danelyan, M. R.

2014-08-01

406

Surface evaluation of UV-degraded contamination  

NASA Technical Reports Server (NTRS)

Three different areas of work were accomplished under this contract: (1) contamination testing and evaluation; (2) UV irradiation testing; and (3) surface evaluation testing. Contamination testing was generally performed in the In-Situ Contamination Effects Facility at Marshall Space Flight Center (MSFC). UV irradiation testing was also performed primarily at MSFC, utilizing facilities there. Finally, the surface evaluation was done at facilities at UAH Center for Applied Optics.

Connatser, Robert; Hadaway, James B.

1992-01-01

407

Photochemical degradation of ciprofloxacin in UV and UV/H?O? process: kinetics, parameters, and products.  

PubMed

Photochemical degradation of fluoroquinolone ciprofloxacin (CIP) in water by UV and UV/H?O? were investigated. The degradation rate of CIP was affected by pH, H?O? dosage, as well as the presence of other inorganic components. The optimized pH value and H?O? concentration were 7.0 and 5 mM. Carbonate and nitrate both impeded CIP degradation. According to liquid chromatography-tandem mass spectrometry analysis, four and 16 products were identified in UV and UV/H?O? system, respectively. Proposed degradation pathways suggest that reactions including the piperazinyl substituent, quinolone moiety, and cyclopropyl group lead to the photochemical degradation of CIP. Toxicity of products assessed by Vibrio qinghaiensis demonstrated that UV/H?O? process was more capable on controlling the toxicity of intermediates in CIP degradation than UV process. PMID:23054793

Guo, Hong-Guang; Gao, Nai-Yun; Chu, Wen-Hai; Li, Lei; Zhang, Yong-Ji; Gu, Jin-Shan; Gu, Yu-Liang

2013-05-01

408

Star clusters in the Whirlpool Galaxy  

NASA Astrophysics Data System (ADS)

This thesis presents the results of observational studies of the star cluster population in the interacting spiral galaxy M51, also known as the Whirlpool galaxy. Observations taken by the Hubble Space Telescope in the optical and the near-UV are used to determine fundamental properties of the star clusters, such as their ages, masses, radii and their spatial distribution. We study how these properties are related and how they depend on different environmental conditions in the galaxy, such as galactocentric radius and the distance from the spiral arms. By comparing the properties of the young star clusters to the properties of the giant molecular clouds from which they form, we study the process of star formation indirectly. We determine the radius distribution of 1284 young star clusters, which is different compared to the radius distribution of the giant molecular clouds. This suggests that during the formation of star clusters their radii change in a non-uniform way. The majority of the youngest star clusters are found in the spiral arms and these clusters are slightly more compact compared to older star clusters in the interarm regions. We discover a peculiar, fuzzy object with a projected position close to the nucleus of M51. After considering different scenarios for this object, we conclude that this object is most likely a fuzzy star cluster in front of the disc, with an age of 1.4 Gyr. The spatial distribution of the young star clusters is analysed using two-point autocorrelation functions. From this we find that the positions of the star clusters show a hierarchy with a fractal dimension similar to that of the turbulent interstellar medium in other galaxies, suggesting that star formation is hierarchical with a universal fractal dimension. Exploiting different multi-wavelength datasets we compare the positions of current star formation sites and recently formed star clusters younger than 10 Myr. A quantitative comparison between star and cluster formation is used to study the rapid dispersion, also called infant mortality, of young star clusters. Both star and cluster formation peak in the spiral arms and in the centre of the galaxy, but also at a galactocentric radius of 2.5 and 5 kpc, which is likely caused by the presence of the 4:1 resonance and the corotation radius, respectively. We derive the star cluster formation efficiency, which is the fraction of star formation that takes place in the star clusters we observe. We correct this fraction for selection effects by use of the cluster initial mass function, which we derive from our new data. We conclude that 20% of the star formation takes place in the form of star clusters. The remaining 80% takes place in a dispersed way, suggesting that the infant mortality can be as high as 80% and occuring on timescales of less than 10 Myr.

Scheepmaker, R. A.

2009-06-01

409

Disk Evaporation in Star Forming Regions  

NASA Technical Reports Server (NTRS)

Young stars produce sufficient ultraviolet photon luminosity and mechanical luminosity in their winds to significantly affect the structure and evolution of the accretion disks surrounding them. The Lyman continuum photons create a nearly static, ionized, isothermal 10(exp 4) K atmosphere forms above the neutral disk at small distances from the star. Further out, they create a photoevaporative flow which relatively rapidly destroys the disk. The resulting slow (10-50 km/s) ionized outflow, which persists for approx. greater than 10(exp 5) years for disk masses M(sub d) approx. 0.3M(sub *), may explain the observational characteristics of many ultracompact HII regions. We compare model results to the observed radio free-free spectra and luminosities of ultracompact HII regions and to the interesting source MWC349, which is observed to produce hydrogen masers. We apply the results to Ae and Be stars in order to determine the lifetimes of disks around such stars. We also apply the results to the early solar nebula to explain the the dispersal of the solar nebula and the differences in hydrogen content in the giant planets. Finally, we model the small bright objects ("proplyds") observed in the Orion Nebula as disks around young, low mass stars which are externally illuminated by the UV photons from the nearby massive star Theta(sup 1) C.

Hollenbach, David; DeVincenzi, Donald L. (Technical Monitor)

2000-01-01

410

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

411

Measuring the Evolution of the UV Upturn  

NASA Astrophysics Data System (ADS)

We propose far-ultraviolet observations of CL1358+62, a rich, well-studied cluster of galaxies at z =0.33. These observations will provide the first completely unambiguous measurement of far-UV emission in quiescent ellipticals at moderate redshift. Theoretically, the strength of far-UV emission {relative to flux at longer wavelengths} is the most rapidly evolving feature in elliptical galaxies. Models suggest that this ``UV upturn'' can change by a factor of 25 over a few Gyr, and it is expected to fade rapidly with increasing redshift. Surprisingly, the Faint Object Camera {FOC} found strong far-UV emission in four elliptical galaxies at z=0.375, suggesting no evolution in this diagnostic between our own epoch and one 4 Gyr earlier. However, the FOC measurement was particularly susceptible to systematic errors, and it was limited to a small number of galaxies in just one cluster. In contrast to the FOC results, recent Space Telescope Imaging Spectrograph {STIS} observations at z=0.55 obtained very weak detections of ellipticals at higher redshift, as expected for ellipticals much younger than those in our own epoch. Observations with the STIS far-UV camera are not subject to the uncertainties of the FOC measurements, because the STIS camera is blind to flux at longer wavelengths. Our observations of CL1358+62 will unambiguously test the apparent lack of evolution in the UV upturn over the past 4 Gyr.

Brown, Thomas

2000-07-01

412

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.

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

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.

Fogarty, Kevin; Postman, Marc; Donahue, Megan; Moustakas, John; Connor, Thomas; Clash Science Team

2015-01-01

415

When Stars Collide  

E-print Network

When two stars collide and merge they form a new star that can stand out against the background population in a starcluster as a blue straggler. In so called collision runaways many stars can merge and may form a very massive star that eventually forms an intermediate mass blackhole. We have performed detailed evolution calculations of merger remnants from collisions between main sequence stars, both for lower mass stars and higher mass stars. These stars can be significantly brighter than ordinary stars of the same mass due to their increased helium abundance. Simplified treatments ignoring this effect give incorrect predictions for the collision product lifetime and evolution in the Hertzsprung-Russell diagram.

E. Glebbeek; O. R. Pols

2007-10-09

416

Effect of UV irradiation on the apoptosis and necrosis of Jurkat cells using UV LEDs  

NASA Astrophysics Data System (ADS)

Phototherapy is a very effective method for treating most of the incurable skin diseases. A fluorescent light bulb is used as a conventional UV light source for this type of therapy. However, infrared radiation from the light source sometimes causes serious problems on patient's health. In addition, the normal part of the skin is irradiated when a large fluorescent light bulb is used. Moreover, a conventional UV irradiation system is heavy and has a short lifetime and a high electrical power consumption. Therefore, a new UV light source for solving the problems of phototherapy is required. To realize low-power-consumption, lightweight and long-lifetime systems, group III nitride-based UV-A1 light-emitting diodes (LEDs) were investigated. We examined the UV LED irradiation of Jurkat cell, which is a tumor cell and more sensitive to UV light than a healthy cell. The numbers of apoptotic and necrotic cells were confirmed to be the same using a UV LED and a conventional lamp system. The UV LED showed the possibility of realizing a new UV light source for phototherapy.

Inada, Shunko A.; Amano, Hiroshi; Akasaki, Isamu; Morita, Akimichi; Kobayashi, Keiko

2009-02-01