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1

The Galactic Orbits of Nearby UV Ceti Stars  

NASA Astrophysics Data System (ADS)

The galactic orbits of 93 UV Ceti stars of the solar neighborhood have been numerically integrated. The UV Ceti stars studied are those of the working list for which Poveda et al. (1996a) determined kinematic properties and ages. All stars are contained within 25 pc of the Sun (? ? 0.04''), and values for their distances, proper motions and radial velocities are available for them (Gliese & Jahreiss 1991). The galactic potential model of Allen & Santillán (1991) was used, and the orbits were integrated for times similar to the age of the old disk. The galactic orbital parameters are obtained. The orbits are all regular, and the values found for the orbital parameters are similar to those characteristic of the classic young thin disk. The vertical scale height found for the whole sample is 115 pc. However, the orbital parameters found for the 7 objects with extreme kinematic characteristics recognized in Poveda et al. are markedly different from those of the rest of the flare stars; in particular, their orbital eccentricities are larger than 0.3. The vertical scale height of the sample excluding the anomalous objects is just 103 pc. Consequently, we propose that the anomalous objects belong to the thick disk, which may be characterized by either e? 0.3 or | zmax | > 400 pc.

Allen, C.; Herrera, M. A.

1998-04-01

2

The galactic orbits of nearby UV Ceti stars  

NASA Astrophysics Data System (ADS)

The galactic orbits of 93 UV Ceti stars of the solar neighborhood have been numerically integrated. The UV Ceti stars studied are those of the working list for which Poveda et al. (1996) determined kinematic properties and ages. All stars are contained within 25 pc of the sun, and values for their distances, proper motions and radial velocities are available for them (Gliese & Jahreiss 1991). The galactic potential model of Allen & Santillan (1991) was used, and the orbits were integrated for times similar to the age of the old disk. The galactic orbital parameters are obtained. The orbits are all regular, and the values found for the orbital parameters are similar to those characteristic of the classic young thin disk. The vertical scale height found for the whole sample is 115 pc. However, the orbital parameters found for the 7 objects with extreme kinematic characteristics recognized in Poveda et al. are markedly different from those of the rest of the flare stars; in particular, their orbital eccentricities are larger than 0.3. The vertical scale height of the sample excluding the anomalous objects is just 103 pc. Consequently, we propose that the anomalous objects belong to the thick disk, which may be characterized by either e >= 0.3 or |z max| > 400 pc.

Allen, C.; Herrera, M. A.

1998-11-01

3

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

4

Stellar Flares on the Dme Stars Prox CEN and UV Ceti  

Microsoft Academic Search

We are proposing to observe two nearby flare stars, Prox Cen (1.3 pc) and UV Ceti (2.6 pc). XTE will be used to search for non-thermal impulsive emission either directly at higher energies or indirectly by measuring discontinuities in the temporal evolution of the thermal emission. The linkage of HXR bursts and SXR discontinuities is evident in many solar flares.

Bernhard Haisch

1996-01-01

5

A search for centimetric wavelength emission from UV Ceti stars  

NASA Technical Reports Server (NTRS)

Simultaneous radio and optical observations were obtained on three UV Cet flare stars: YZ CMi, AD Leo, and Wolf 424. The total simultaneous monitoring time was 33.9 hours during which time 41 optical flares were detected. Two enhancements were detected at 1420 MHz in close temporal association with optical flares, but are of uncertain validity. The results presented indicate that 1420 MHz emission during a typical stellar flare is less than 0.10 Jy.

Moffett, T. J.; Helmken, H. F.; Spangler, S. R.

1978-01-01

6

Microwave observations of the flare stars UV Ceti, AT Microscopii, and AU Microscopii  

NASA Technical Reports Server (NTRS)

The results of observations of three red dwarf flare star systems, UV Ceti, AT Mic, and AU Mic, made in February and March of 1985, are reported. Flaring was detected from all three systems, and quiescent emission from UV Cet and AU Mic. Models for the quiescent microwave-emitting corona of UV Cet are discussed. The gravitational scale height in current models is similar to or larger than the height of the corona, which is a striking difference from the case of the solar corona and confirms that magnetic structures are required to confine the radio-emitting corona. The role of precipitation into the chromosphere of the energetic particles in such a corona is explored, and it is shown that for plausible parameters it may be the dominant energy loss mechanism.

Kundu, M. R.; Jackson, P. D.; White, S. M.; Melozzi, M.

1987-01-01

7

A search for X-rays from UV Ceti flare stars  

NASA Technical Reports Server (NTRS)

A search of MIT/OSO-7 data was made for evidence of X-ray emission from flares of UV Ceti flare stars. Observations from McDonald Observatory were 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 delta m(u)=0.86 flare of YZ CMi. 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 were set for the energy ranges greater than or approximately equal to 15, greater than or approximately equal to 3, and 1-10 keV, respectively.

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

1975-01-01

8

Coherent cyclotron maser radiation from UV Ceti  

Microsoft Academic Search

Recent images in the radio of UV Ceti show two intense emission regions above the magnetic poles of the star. The emission is overwhelmingly right hand circularly polarized with 100% right hand polarization at 3 cm and 6 cm wavelengths during flares. This high degree of polarization rules out gyrosynchrotron emission. In this article we propose that such emission can

R. Bingham; R. A. Cairns; B. J. Kellett

2001-01-01

9

ZZ Ceti Stars  

NASA Astrophysics Data System (ADS)

ZZ Ceti is the generic name for pulsating WHITE DWARFS of type DA, which have a pure hydrogen outer layer composition. This name is equivalent to DAV (for variable DA white dwarfs) frequently used in the literature....

Vauclair, G.; Murdin, P.

2000-11-01

10

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

11

Chromospheric Mass Motions during a Flare on Uv Ceti,  

National Technical Information Service (NTIS)

Simultaneous optical and IUE observations of a flare on UV Ceti in 1980 are reported. The IUE spectra show only slight increase of C IV line emission. The optical spectrophotometric observations show, from Balmer line profiles, turbulent broadening in qui...

K. J. H. Phillips G. E. Bromage P. L. Dufton F. P. Keenan A. E. Kingston

1988-01-01

12

Flare Activity on UV Ceti: Visible and IUE Observations,  

National Technical Information Service (NTIS)

Simultaneous far-ultraviolet (IUE) spectroscopy and optical photometry and spectrophotometry of a flare on UV Ceti are reported. The flare reached Delta U = 2 sup m but showed only modest enhancements in the IUE spectra. The optical spectrophotometry indi...

K. J. H. Phillips G. E. Bromage P. L. Dufton F. P. Keenan A. E. Kingston

1988-01-01

13

Discovery of eleven new ZZ Ceti stars  

NASA Astrophysics Data System (ADS)

We report the discovery of eleven new ZZ Cetis using telescopes at OPD (Observatório do Pico dos Dias/LNA) in Brazil, the 4.1 m SOAR (Southern Astrophysical Research) telescope at Cerro Pachon, Chile, and the 2.1 m Otto Struve telescope at McDonald observatory. The candidates were selected from the SDSS (Sloan Digital Sky Survey) and SPY (ESO SN Ia progenitor survey), based on their Teff obtained from optical spectra fitting. This selection criterion yields the highest success rate of detecting new ZZ Cetis, above 90% in the Teff range from 12 000 to 11 000 K. We also report on a DA not observed to vary, with a Teff placing the star close to the blue edge of the instability strip. Among our new pulsators, one is slightly cooler than this star for which pulsations were not detected. Our observations are an important constraint on the location of the blue edge of the ZZ Ceti instability strip. Partially based on observations at Observatório do Pico dos Dias/LNA, the Southern Astrophysical Research telescope, a collaboration between CNPq-Brazil, NOAO, UNC and MSU, and McDonald Observatory of the University of Texas at Austin.

Castanheira, B. G.; Kepler, S. O.; Mullally, F.; Winget, D. E.; Koester, D.; Voss, B.; Kleinman, S. J.; Nitta, A.; Eisenstein, D. J.; Napiwotzki, R.; Reimers, D.

2006-04-01

14

Mira Ceti and the Star of Bethlehem  

NASA Astrophysics Data System (ADS)

We consider the probability that the Gospel of Matthew could report the earliest observation of Mira Ceti. Some biblical remarks have to be considered in order to distinguish a scientific text in the modern acceptation and the content of Gospels regarding some astronomical arguments. Mira fulfills the basic requirements to be the Star of Bethlehem as described in the Gospel according to Matthew (Mt 2:1-12). In fact it was visible at least two times with a time interval (not specified in Mt text) in which it disappeared. Moreover Mira was close to the position were the triple conjunction of Jupiter and Saturn occurred in the years 7-6 b. C. and it could be observed during that period by ancient astronomers. The discovery of Mira in 1596 and its second observation 12.5 years later, made by David Fabricius, occurred when Jupiter approached it. Because of those reasons we study the maxima of Mira in order to evaluate both the frequency of one and of two consecutive bright apparitions eventually as observed by the Magi. We did an evaluation of the correlation between two following maxima in order to verify the probability of occurrence of two consecutive bright maxima, because that condition would have been indeed the most favorable for the candidature of Mira as the Bethlehem Star. Analyzing the maxima of Mira we found a probability of seeing it brighter than alpha Ceti once every 21 years. In this case, as in February 1997, Mira can be detected at the first sight as a new component near the most significant asterism in its zone, composed by alpha, gamma and delta Ceti. This condition could have happened in the case of the Bethlehem Star. We found also a correlation between the magnitude of two consecutive maxima: if a bright maximum occurs it is more probable that the following is a faint one.

Sigismondi, Costantino

15

AY Ceti - A flaring, spotted star with a hot companion  

NASA Technical Reports Server (NTRS)

AY Ceti is a late-type single-line spectroscopic binary, a bright X-ray source (L/x/ equal to about 1.5 x 10 to the 31st ergs/s), and a spotted star, as evidenced by its prominent photometric wave. In this paper, observations made with the IUE satellite and the VLA radio interferometer are reported. The 1200-2000 A UV spectrum of AY Cet shows a hot stellar continuum and a very broad Ly-alpha absorption line from a previously unobserved white dwarf secondary. The UV spectrum can be matched to the energy distribution of a (T/eff/ = 18,000 K, log g = 8) model atmosphere. Superposed on this hot continuum are high-excitation emission lines typical of chromospheres and transition regions of active late-type stars, e.g., the spotted RS CVn binaries. It is concluded that the bright lines and soft X-ray emission of AY Cet arise from the cool primary star, rather than from mass transfer and accretion onto the secondary as has recently been proposed for the similar system 56 Peg. Two strong radio flares on AY Cet were observed. The second was rapidly variable and left-hand circularly polarized at levels up to pi(c) = 86 + or - 5 percent at 20 cm wavelength. The most likely emission mechanism is an electron-cyclotron maser.

Simon, T.; Fekel, F. C., Jr.; Gibson, D. M.

1985-01-01

16

AY Ceti: A flaring, spotted star with a hot companion  

SciTech Connect

AY Ceti is a late-type single-line spectroscopic binary, a bright X-ray source (L/sub x/roughly-equal1.5 x 10/sup 31/ ergs s/sup -1/), and a spotted star, as evidenced by its prominent photometric wave. In this paper, we report on observations made with the IUE satellite and the VLA radio interferometer. The 1200--2000 A UV spectrum of AY Cet shows a hot stellar continuum and a very broad Ly..cap alpha.. absorption line from a previously unobserved white dwarf secondary. The UV spectrum can be matched to the energy distribution of a (T/sub eff/ = 18,000 K, log g = 8) model atmosphere. Superposed on this hot continuum are high-excitation emission lines typical of chromospheres and transition regions of active late-type stars, e.g., the spotted RS CVn binaries. We conclude that the bright lines and soft X-ray emission of AY Cet arise from the cool primary star, rather than from mass transfer and accretion onto the secondary as has recently been proposed for the similar system 56 Peg. Two strong radio flares on AY Cet were observed. The second was rapidly variable and left-hand circularly polarized at levels up to ..pi../sub c/ = 86 +- 5% at 20 cm wavelength. The most likely radio emission mechanism is an electron-cyclotron maser.

Simon, T.; Fekel F.C. Jr.; Gibson, D.M.

1985-08-01

17

Pioneer 10 observations of the Beta Cephei stars Gamma Pegasi and Delta Ceti  

NASA Technical Reports Server (NTRS)

The results of analyzing broad-band Pioneer 10 photometric observations of the low-amplitude pulsating Beta Cephei stars Gamma Pegasi and Delta Ceti are reported. Periods and light curve amplitudes of 3.649 + or - 0.020 hr, 0.05 + or - 0.02 mag for Gamma Peg and 3.869 + or - 0.020 hr, 0.13 + or - 0.02 mag for Delta Ceti are obtained; a power spectrum analysis of the data reveals no other periods. No evidence is found for a phase shift between the light curve maxima in the UV and visible regions. The observed amplitudes combined with published visual and near-UV data suggest a flux and temperature variability of about 200 solar luminosities and 250 K for Gamma Peg and about 600 solar luminosities and 450 K for Delta Cet. These results are compared with others obtained with satellite and ground-based instrumentation.

Peters, Geraldine J.; Ogawa, H. S.; Judge, K. S.; Judge, D. L.

1987-01-01

18

Multiwavelength Studies of Mira Ceti-type Variable Stars  

NASA Astrophysics Data System (ADS)

Since 1994, observations of a sample of about 20 Mira Ceti-type and semiregular variables have been carried out in three spectral ranges: radio (H2O maser line ? = 1.35cm), optical (spectroscopy and U BV photometry) and infrared (JHKLM photometry). Time series of the H? emission intensity and H2O line flux, covering several periods of the stars, have been obtained. Correlation of the intensity variations of the H2O maser with optical variability in the maser stars RR Aql, U Ori, VX Sgr and others was confirmed. One of the most interesting results is the flare of the H2O maser emission in R Leo, which happened in autumn 1997, 14 months after a flare of the H? emission.

Esipov, V. F.; Pashchenko, M. I.; Rudnitskij, G. M.; Kozin, M. V.; Lekht, E. E.; Nadjip, A. E.; Fomin, S. V.

19

Shock-induced polarized hydrogen emission lines in the Mira star o Ceti  

Microsoft Academic Search

Context. In the spectra of variable pulsating stars, especially Mira stars, the detection of intense hydrogen emission lines has been explained by the presence of a radiative and hypersonic shock wave, periodically propagating throughout the stellar atmosphere. Previous observation of the Mira star o Ceti around one of its brightest maximum light led to the detection of a strong level

N. Fabas; A. Lèbre; D. Gillet

2011-01-01

20

Six New ZZ Ceti Stars from the SPY and the HQS Surveys  

NASA Astrophysics Data System (ADS)

We report on the discovery of six new ZZ Ceti stars. They were selected as candidates based on preparatory photometric observations of objects from the Hamburg Quasar Survey (HQS), and based on the spectra of the Supernova Ia Progenitor Survey (SPY). Time-series photometry of 19 candidate stars was carried out at the Nordic Optical Telescope (NOT) at Roque de Los Muchachos Observatory, Spain. The new variables are relatively bright, 15.4Ceti star that shows photospheric CaII in its spectrum.

Voss, B.; Koester, D.; Østensen, R.; Napiwotzki, R.; Homeier, D.; Reimers, D.

2007-09-01

21

14 Ceti: a probable Ap-star-descendant entering the Hertzsprung gap  

NASA Astrophysics Data System (ADS)

Context. 14 Ceti is a subgiant star of F spectral class that displays variations in the S-index of its Ca ii H & K lines and an X-ray emission that is stronger than the mean observed for its spectral class, which may be due to some magnetic activity. Aims: We attempt to Zeeman-detect and study the magnetic field of 14 Ceti and to infer its origin. Methods: We used the spectropolarimeter Narval at the Telescope Bernard Lyot, Pic du Midi Observatory, and the least squares deconvolution method to create high signal-to-noise ratio Stokes V profiles. We derived the surface-averaged longitudinal magnetic field Bl. We also measured the S-index, and the radial velocity for each observation. Results: 14 Ceti is Zeeman-detected for the 30 observed dates spanning from August 2007 to January 2012. The average longitudinal magnetic field does not reverse its sign, reaches about -35 G, and shows some month-long-timescale variations in our 2008 and 2011-2012 observations. The S-index follows the same long-term trend as Bl. 14 Ceti is confirmed as a single star without H-K emission cores. The strength of the observed surface magnetic field of 14 Ceti is one order of magnitude greater than the observed one for late F main-sequence stars, and is comparable to the values measured in the active late F pre-main-sequence star HR 1817. On the other hand, taking into account the post-main-sequence evolution of an Ap star, an oblique rotator model can explain the strength of the magnetic field of 14 Ceti. The variations with a timescale of months observed for both the Bl and S-index could be due to the rotation. Conclusions: The most probable scenario to explain our observations appears to be that 14 Ceti is the descendant of a cool Ap star. Based on data obtained using the Télescope Bernard Lyot at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse, France.

Aurière, M.; Konstantinova-Antova, R.; Petit, P.; Charbonnel, C.; Van Eck, S.; Donati, J.-F.; Lignières, F.; Roudier, T.

2012-07-01

22

Asteroseismological Study of Massive ZZ Ceti Stars with Fully Evolutionary Models  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

23

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

24

Shock-induced polarized hydrogen emission lines in the Mira star o Ceti  

NASA Astrophysics Data System (ADS)

Context. In the spectra of variable pulsating stars, especially Mira stars, the detection of intense hydrogen emission lines has been explained by the presence of a radiative and hypersonic shock wave, periodically propagating throughout the stellar atmosphere. Previous observation of the Mira star o Ceti around one of its brightest maximum light led to the detection of a strong level of linear polarization associated to Balmer emissions, although the origin of this phenomenon is not fully explained yet. Aims: With the help of spectropolarimetry, we propose to investigate the nature of shock waves propagating throughout the stellar atmosphere and present, for o Ceti (the prototype of Mira stars), a full observational study of hydrogen emission lines formed in the radiative region of such a shock. Methods: Using the instrument NARVAL mounted on the Télescope Bernard Lyot (TBL) in Pic du Midi Observatory (France), we performed a spectropolarimetric monitoring of o Ceti during three consecutive pulsation cycles. For this survey, the four Stokes parameters (I for intensity, Q and U for linear polarization, and V for circular polarization) were systematically collected, with a particular emphasis on the maxima of luminosity, i.e. when a radiative shock wave is supposed to emerge from the photosphere and starts to propagate outward. Results: On hydrogen Balmer lines, over a large part of the luminosity cycle, we report clear detection of polarimetric structures in Q and U Stokes spectra (and also in V Stokes spectra but to a lesser extent). We report a temporal evolution of these spectropolarimetric signatures, which appear strongly correlated to the presence of an intense shock wave responsible for the hydrogen emission lines. We establish that the hydrogen lines are polarized by a physical process inherent to the mechanism responsible for the emission line formation: the shock wave itself. Two mechanisms are thus considered: a global one that implies a polarization induced by some giant convective cells located around the photosphere and a local one that implies a charge separation due to the passage of the shock wave, inducing an electrical current. Combined with the existing turbulence, this may generate a magnetic field, hence polarization. Based on spectropolarimetric observations obtained at the Télescope Bernard Lyot (TBL at Observatoire du Pic du Midi, CNRS and Université de Toulouse, France).

Fabas, N.; Lèbre, A.; Gillet, D.

2011-11-01

25

Massive stars in the UV  

Microsoft Academic Search

We emphasize in this paper the importance of the UV range for our knowledge of massive stars and the fundamental role played\\u000a by past and present space-based UV capabilities (IUE, HST, FUSE and others). Based on a review of the work developed in the\\u000a last years and the state of the art situation for quantitative spectroscopy of massive stars, we

F. Najarro; A. Herrero; E. Verdugo

26

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

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

UV Astronomy: Stars from Birth to Death  

NASA Astrophysics Data System (ADS)

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 is at the very base of our understanding of the Universe. The chemical evolution of the Universe is controlled by stars. Supernovae are prime distance indicators that have allowed to measure the evolution of the curvature of the Universe and to detect the existence of dark energy. The development of life sustaining system depends strongly on the evolution of stars like our Sun. Some of the most extreme forms of matter in the Universe, the densest and more strongly magnetized, are the magnetars, debris of stellar evolution. The excellent contributions presented in this Joint Discussion dealt with the many aspects of stellar astrophysics from the analysis of dissipative processes in the atmosphere of cool stars and their impact on the evolution of the planetary systems to the study of the atmospheres and winds of the hot massive stars or the determination of the abundances in white dwarfs. The physics of disks, its role in the evolution of binary systems, and the formation of supernovae were among the main topics treated in the meeting. We should also not forget the role of starbursts and, in general, high mass stars in the chemical evolution of galaxies. The metallicity gradient in the Galaxy is traced in the UV spectrum of planetary nebulae. The evolution of young planetary disks and the role of the central stars in the photoevaporation of the giant gaseous planets that have been detected recently. The book contains a summary of the numerous and high quality contributions to this Joint Discussion classified in five chapters: * Chapter 1: Star Formation and Young Stellar Objects * Chapter 2: Life in Main Sequence * Chapter 3: Star Death * Chapter 4: Compact Objects * Chapter 5: The impact of stellar astrophysics in understanding the formation of life sustainable systems; That correspond to the five sessions held during the meeting. A summary of the current status of UV astronomy and the discussions that took place during the XXVIth I. A. U. General Assembly can be found in Highlights of Astronomy, Volume 14.

Gómez de Castro, Ana I.; Barstow, Martin A.

29

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

30

Constraining the Evolution of ZZ Ceti  

NASA Technical Reports Server (NTRS)

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt 5 (5.5 plus or minus 1.9) x 10(exp -15) ss(sup -1), after correcting for proper motion. Our results are consistent with previous P values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is |P||P(raised dot)|greater than or equal to 1.2 Gyr, comparable to the theoretical cooling timescale for the star. Our current stability limit for the period 213.13 s is only slightly less than the present measurement for another DAV, G117-B15A, for the period 215.2 s, establishing this mode in ZZ Ceti as the second most stable optical clock known, comparable to atomic clocks and more stable than most pulsars. Constraining the cooling rate of ZZ Ceti aids theoretical evolutionary models and white dwarf cosmochronology. The drift rate of this clock is small enough that we can set interesting limits on reflex motion due to planetary companions.

Mukadam, Anjum S.; Kepler, S. O.; Winget, D. E.; Nather, R. E.; Kilic, M.; Mullally, F.; vonHippel, T.; Kleinman, S. J.; Nitta, A.; Guzik, J. A.

2003-01-01

31

Physical parameters and chemical abundances of ? Ceti  

NASA Astrophysics Data System (ADS)

A detailed spectroscopic study of a ? Cephei variable star, ? Ceti, is presented. Physical fundamental parameters are estimated from the best fitting of 26 neutral helium lines and Balmer profiles: effective temperature, superficial gravity and projected rotation velocity. Non-LTE abundances of He, C, N, O, Ne, Mg, Al, Si, P, S, Ar and Fe are achieved using model atmospheres with updated atomic data. Our analysis show an N-enrichment and Fe overabundance, with [O/Fe]? -0.73 dex, confirming this object to be a metal-rich star, which is a requirement for the ?-mechanism to trigger the pulsations observed in ? Cephei stars.

Levenhagen, R. S.; Künzel, R.; Leister, N. V.

2013-01-01

32

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

33

Quantitative Asteroseismology: Determination of the Core Composition and Layering of the ZZ Ceti Star R 548. Part II  

NASA Astrophysics Data System (ADS)

We present a preview of a detailed asteroseismological study of the pulsating white dwarf R548 based on fits to newly detected periods and the use of the forward method. We first exploited a very high S/N photometric data set gathered with the CFHT/LAPOUNE combination, and isolated five secure independent periods for seismic modeling with spherical models. The details of this frequency extraction analysis having been summarized elsewhere, we now turn to a brief description of the seismic analysis per se. Using a method that has been developed and refined over more than a decade for applications to pulsating hot subdwarf stars mostly, we computed several million models during the course of an automatic and objective search in parameter space for the optimal model. Combining our results with independent spectroscopic constraints, we find that the global structural parameters of R548 can be well determined, including the envelope layering and the bulk composition of the core.

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

2013-01-01

34

Binary Population Synthesis, Sdb Stars and the UV Upturn  

NASA Astrophysics Data System (ADS)

We aim to use the methods of binary population synthesis (BPS) to study the ultraviolet upturn (UVX) in the spectra of giant elliptical galaxies with emphasis being placed on those binary channels which could lead to the formation of stars that can account for it. This project will combine Sukyoung Yi's single star population synthesis methodology with that of Zhanwen Han's binary population synthesis methods in order to provide a more coherent study of the origin of the UV upturn, the focus being on sdB stars as the possible source of the UV upturn. The primary approach of the project will be to explore the UV upturn, with sdBs included, for several different metallicities in order to examine the UVX in composite populations.

Brown, D.; Yi, S.; Han, Z.; Yoon, S.-J.

35

Time distribution of flare events on UV Cet stars  

Microsoft Academic Search

A statistical analysis of the flare data on three UV Cet stars obtained at Catania Observatory in the indicated periods-UV Cet (1968–1976), EQ Peg (1969–1975) and YZ CMi (1968–1976)-is presented. The distributions of the four variables (i) ?, the time elapsed from the start of a continuous observation interval to the occurrence of the first flare; (ii) ?, the time

V. Pazzani; M. Rodono

1981-01-01

36

The ZZ Ceti Instability Strip and Stellar Convection  

NASA Astrophysics Data System (ADS)

ZZ Ceti stars are variable white dwarfs of spectral type DA. The theoretically predicted instability strip depends on several uncertain assumptions, most importantly the efficiency of convective energy transport. Empirical determinations from optical spectra are not as accurate as desirable, because the Balmer lines reach maximum strengths within the instability strip and vary only little with temperature. The UV spectrum is much better suited since we have recently improved the quantitative description of the quasi-molecular satellite features, that vary strongly with temperature. The analysis of G117-B15A (in several studies defining the hot edge of the instability strip), which was observed by us in Cycle 2 confirms that an accuracy of 200 K or better can be achieved. It also shows that convection must be more efficient than normally assumed, and that the temperature of G117-B15A is 1000 K lower than determined previously, raising the question that perhaps GD165, the last remaining hot edge candidate with relatively uncertain temperature determination, defines the blue edge.

Koester, Detlev

1995-07-01

37

Mass loss from Be stars derived from UV spectra  

NASA Astrophysics Data System (ADS)

The present investigation considers the interpretation of UV line profiles of some Be stars obtained with the International Ultraviolet Explorer (IUE) spacecraft, giving particular attention to Pi Aqr. The mass-loss rates are estimated using the Sobolev approximation and assuming that the observed asymmetric UV lines are formed in an expanding envelope above and below the considered denser equatorial region. A mass-loss rate of 2.4 x 10 to the -9th solar mass per year is derived for Pi Aqr. The derived value for Pi Aqr is comparable to that deduced for Gamma Cas by Hensberge et al. (1980) and to that deduced for the BOV star Tau Sco by Lamers and Rogerson (1978).

de Freitas Pacheco, J. A.

1982-05-01

38

Shock induced polarized hydrogen emission lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Télescope Bernard Lyot in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Fabas, N.; Lèbre, A.; Gillet, D.

2010-12-01

39

Shock-Induced Polarized Hydrogen Emission Lines in Omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Fabas, N.; Lèbre, A.; Gillet, D.

2011-04-01

40

Shock-Induced Polarized Hydrogen Emission Lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Lèbre, A.; Fabas, N.; Gillet, D.

2011-12-01

41

Mapping the ZZ Ceti Instability Strip: Discovery of Six New Pulsators  

Microsoft Academic Search

As part of an ongoing program to better map the empirical instability strip of pulsating ZZ Ceti white dwarfs, we present a brief progress report based on our last observing season. We discuss here high-speed photometric measurements for six new pulsators. These stars were selected on the basis of preliminary measurements of their effective temperatures and surface gravities, which placed

A. Gianninas; P. Bergeron; G. Fontaine

2006-01-01

42

Shock-induced polarized hydrogen emission lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

Hydrogen emission lines in Mira variable stars are a well-known phenomenon whose origin has been established as related to the propagation of radiative hypersonic shock waves throughout the stellar atmosphere. A polarimetric observation by McLean and Coyne [1] made on omicron Ceti (the prototype of Mira variable stars) has revealed the existence of linear polarization signatures associated with Balmer emission lines. However, the polarizing mechanism has never been properly explained so far. The study presented here is the first of its kind since it displays the results of a spectropolarimetric survey of omicron Ceti in the Balmer lines. The survey was made with the NARVAL spectropolarimeter (Telescope Bernard Lyot, France) in full Stokes mode. We did not just confirm the appearance of this polarization but we also and above all showed the temporal variation of the linear polarization in the lines. We conclude that the polarizing mechanism is definitely intrinsic to the shock wave propagation throughout the stellar atmosphere of Mira and give some leads about the nature of this mechanism.

Fabas, N.; Lèbre, A.; Gillet, D.

2012-05-01

43

Energy spectrum of UV Cet stars and the physical meaning of some statistical characteristics of such stars  

SciTech Connect

On the basis of the observed power-law energy spectrum of the flares of stars of teh UV Cet type, some statistical characteristics of the activity of such stars are considered. It is shown that the mean amplitude of the flares is determined primarily by the amplitude of the weakest flare detected in the given star so that the mean amplitude cannot serve as a measure of the flare activity of the star. The mean frequency of flares detected in flare stars depends on the absolute magnitude of the star and this dependence is determined both by the change in the threshold of flare detection as well as by the real changes in the activity level. The catalog of Haro, Chavira and Gonzalez of flare stars in the Pleiades was used to construct the luminosity function of such stars in this cluster.

Gershberg, R.E.

1985-11-01

44

A UV Imaging Survey of IR-Bright Star- Forming Galaxies  

NASA Astrophysics Data System (ADS)

We propose to carry out a UV{ 1, 600 Angstrom} snapshot imaging survey with STIS of all the actively star-forming galaxies detected by ISO at Lambda>170 Mum and closer than cz=9000 km/s. The sample covers a large region in the parameter's space of morphology, luminosity, metallicity, and star formation intensity. The multiwavelength {UV/far-IR} information will be exploited to address open issues on low- and high-redshift star formation and on the dust/star- formation interconnection. The ISO galaxies will be used as low-redshift benchmarks to explore the relationship between the Lyman-break galaxies at z 3 and the SCUBA sources. The conditions for the escape of UV light from a `dusty' galaxy will be investigated as a function of the sample parameters. UV-bright structures will be measured and used to quantify the fractions of nuclear and disk emission, the fraction of star formation in massive clusters and the properties of those star clusters, the structural properties of star forming bars, rings, and tidally-driven star formation in IR-bright galaxies. Given the breadth of scientific applications and the relevance of this unique dataset for upcoming instruments and missions, including mid/far-IR ones like SIRTF, we propose this project as a Service to the Community and will release immediately the UV images in the public domain.

Calzetti, Daniela

2000-07-01

45

Characteristics of activity energetics of the UV cet-type flare stars  

Microsoft Academic Search

A quantitative comparison of energetics of different manifestations of the activity of the UV Cet-type flare stars — sporadic flares, quiet chromospheres and coronae and stellar spots — have been carried out. On the basis of a statistical analysis of about 1800 flares registered for 23 flare stars, the energy spectra of flares have been constructed and time-averaged powers of

R. E. Gershberg; N. I. Shakhovskaia

1983-01-01

46

The Panchromatic Hubble Andromeda Treasury: Bright UV Stars in the Bulge of M31  

NASA Astrophysics Data System (ADS)

As part of the Panchromatic Hubble Andromeda Treasury (PHAT) multi-cycle program, we observed a 12? × 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 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes, including Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars and AGB-manque stars. P-AGB stars are the end result of the AGB phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manque (together referred to as 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 ? abundances when the mass loss on the RGB is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot horizontal branch stars (EHB) 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 the progeny of the EHB stars that are the likely source of the UVX. We calculate that only a few percent of MS 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 LMXBs. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.

Rosenfield, Philip; Johnson, L.; Girardi, L.; Dalcanton, J. J.; Bressan, A.; Lang, D.; Williams, B. F.; Howley, K. M.; Guhathakurta, P.; Panchromatic Hubble Andromeda Treasury Survey Team

2012-01-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

48

Mining the HST "Advanced Spectral Library (ASTRAL) - Hot Stars": The High Definition UV Spectrum of the Ap Star HR 465  

NASA Astrophysics Data System (ADS)

The "Advanced Spectral Library (ASTRAL) Project: Hot Stars" is a Hubble Space Telescope (HST) Cycle 21 Treasury Program (GO-13346: Ayres PI). It is designed to collect a definitive set of representative, high-resolution ( 30,000-100,000), high signal/noise (S/N>100), and full UV coverage 1200 - 3000 A) spectra of 21 early-type stars, utilizing the high-performance Space Telescope Imaging Spectrograph (STIS). The targets span the range of spectral types between early-O and early-A, including both main sequence and evolved stars, fast and slow rotators, as well as chemically peculiar (CP) and magnetic objects. These extremely high-quality STIS UV echelle spectra will be available from the HST archive and, in post-processed and merged form, at http://casa.colorado.edu ayres/ASTRAL/. The UV "atlases" produced by this program will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years to come. We offer a first look at one of the earliest datasets to come out of this observing program, a "high definition" UV spectrum of the Ap star HR 465, which was chosen as a prototypical example of an A-type magnetic CP star. HR 465 has a global magnetic field of ~2200 Gauss. Earlier analyses of IUE spectra show strong iron-peak element lines, along with heavy elements such as Ga and Pt, while being deficient in the abundance of some ions of low atomic number, such as carbon. We demonstrate the high quality of the ASTRAL data and present the identification of spectral lines for a number of elements. By comparison of the observed spectra with calculated spectra, we also provide estimates of element abundances, emphasizing heavy elements, and place these measurements in the context of earlier results for this and other Ap stars.

Carpenter, Kenneth G.; Ayres, T. R.; Nielsen, K. E.; Kober, G. V.; Wahlgren, G. M.; Adelman, S. J.; Cowley, C. R.

2014-01-01

49

UV Bright-Star Spectrophotometric Supplement (Macau-Hercot+ 1978)  

NASA Astrophysics Data System (ADS)

This catalogue is a supplement of the Ultraviolet Bright Star Spectrophotometric Catalogue (=III/39A). It contains observations carried out by the S2/68 Ultraviolet Sky Survey Telescope (UVSST) aboard the ESRO satellite TD-1. The data presented in this supplement were obtained during the second and third observation periods, which lasted from 19 February 1973 to 30 September 1973 and from 16 February to 6 May 1974. The S2/68 experiment has been described by Boksenberg et al. (=1973MNRAS.163..291B) Owing to the optical scanning mode, most of the stars observed during the first observational period, the spectra of which are included in the "Ultraviolet Bright-Star Spectrophotometric Catalogue", were seen again by the telescope. This supplement, however, has been limited to the spectra of stars that were not observed during the first period. The data reduction and selection criteria are identical to those underlying the main Catalogue and hence the data presented in the Supplement are directly comparable with those in the main Catalogue. The Supplement contains data for 435 stars. For a statistical summary of the observed stars, see the tables I and II in the published version of the Supplement. The spectrum scanning itself was achieved by the movement of a star image across the wide entrance slot of the spectrophotometer, which caused the corresponding spectrum image to pass over the three exit slits in the direction of dispersion. The motion of the primary image during each detector integration interval (0.148 s) was equivalent to 19.4 A, depending on the channel. The wavelength range covered was 1350 - 2550 A. The passband of the photometer channel, defined by a glass transmission filter and the photocathode tube response, was centered at 2740 A and had a full width at half height of 310 A. (1 data file).

Macau-Hercot, D.; Jamar, C.; Monfils, A.; Thompson, L.; Houziaux, L.; Wilson, R.

1995-10-01

50

The ultraviolet variability of AY Ceti  

NASA Technical Reports Server (NTRS)

AY Cet is a single-line binary comprised of a spotted G5 III primary and a white dwarf secondary. A series of UV spectra have been obtained with the IUE satellite on five different dates covering a substantial part of the optical cycle of the primary star. No evidence that the continuum or the Ly-alpha absorption line of the secondary star varied is found. There were significant changes in the strengths of the UV emission lines, but the variations were only weakly correlated with either the orbital phase of the binary or the rotational phase of the primary. The UV emission lines were especially strong near maximum visual brightness at a time when the starspot(s) on the primary was least visible. The enhanced line emission is attributed to a flare event on the primary, most likely at a high-latitude site close to the pole of this star. The UV radiative losses of this flare were comparable with those of flares previously observed on the RC CVn variables Lambda And and HR 1099.

Simon, Theodore; Sonneborn, George

1987-01-01

51

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

52

Long-Term Variability in o Ceti and Other Mira Variables: Signs of Supergranular Convection?  

NASA Astrophysics Data System (ADS)

We describe our study of long-term variability of o Ceti (Mira A), the prototype of the Mira-type pulsating stars. Our study was originally undertaken to search for coherent long-period variability, but the results of our analysis didn't uncover this. However, we detected a low-frequency ``red noise'' in the Fourier spectrum of the o Ceti century-long light curve. We have since found similar behavior in other Miras and pulsating giant stars and have begun a study of a large sample of Mira variables. Similar red noise has been previously detected in red supergiants and attributed to supergranular convection. Its presence in Miras suggests the phenomenon may be ubiquitous in cool giant pulsators. These results support high-angular resolution observations of Miras and supergiants showing asymmetries in their surface brightness distributions, which may be due to large supergranular convection cells. Theoretical modeling, and numerical simulations of pulsation processes in late-type giants and supergiants should therefore take into account the effects of deep convection and large supergranular structures, which in turn may provide important insights into the behavior of Miras and other giant and supergiant pulsators. In this work, we summarize our results for o Ceti, present preliminary results of our broader study of Mira variables, and discuss how the results of this study may be used by future studies of AGB variables.

Templeton, Matthew R.; Karovska, Margarita

2009-09-01

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

Two-color photographic observations of flare stars in Cygnus  

NASA Astrophysics Data System (ADS)

Parallel observations made in U and in the visible photographic range of the luminosities and colors of stellar flares in the Cygnus region are presented. Observations covering a period of 73 h were obtained by the 40- and 20-inch telescopes of the Biurakan Astrophysical Observatory for nine flares from eight stars, and flare light curves were determined by the use of an iris photometer. The flare emission of the stars is observed to be consistently bluer than the normal stellar emission, as observed in the classic flare star UV Ceti and flare stars in the Pleiades. The light curve of the flare of the star B 9 is also noted to exhibit an extraordinarily long maximum, remaining practically constant for 1 h 30 min.

Tsvetkov, M.; Erastova, L. K.

55

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

56

Variability of the UV Spectrum of the Symbiotic Star Bf Cygni,  

National Technical Information Service (NTIS)

The symbiotic star BF Cygni was monitored by IUE in low and high resolution since July 1986 to cover a full photometric period. In order to study the long-term UV variability of the system, spectra were used with archive data taken during the period 1979 ...

R. Gonzalez-Riestra A. Cassatella T. Fernandez-Castro

1988-01-01

57

Star formation rate in galaxies from UV, IR, and Halpha estimators  

Microsoft Academic Search

Infrared (IR) luminosity of galaxies originating from dust thermal emission can be used as an indicator of the star formation rate (SFR). Inoue et al. (\\\\cite{inoue00}, IHK) have derived a formula for the conversion from dust IR luminosity to SFR by using the following three quantities: the fraction of Lyman continuum luminosity absorbed by gas (f), the fraction of UV

Hiroyuki Hirashita; Veronique Buat; A. K. Inoue

2003-01-01

58

Quantifying Star Formation in Early-Type Galaxies using Spatially-Resolved UV-Optical Photometry  

NASA Astrophysics Data System (ADS)

Our understanding of star formation in nearby early-type galaxies (ETGs) has evolved rapidly in recent years, due to new UV data from GALEX and HST. Contrary to the classical notion of them being old, passively-evolving systems, recent work has demonstrated widespread late-epoch star formation in ETGs, which builds ~20% of their stellar mass after 1, via minor mergers between ETGs and gas-rich dwarfs. While survey data from GALEX has indicated the average properties of star formation in the ETG population as a whole, I demonstrate how spatially-resolved UV studies can offer detailed insights into the star formation histories of individual galaxies, using an HST-WFC3 case study of NGC 4150. Using a pixel-by-pixel analysis in 5 WFC3 filters, spanning UV to i-band, reveals a central 0.9 Gyr old young stellar population, with a median metallicity of 0.5 solar, that contributes around 3% of the stellar mass and coincides spatially with a small, kinematically-decoupled core (indicating a recent minor merger). Assuming that the metallicity of the young stars traces the gas-phase metallicity of the satellite that fuels the star formation, we use the mass-metallicity relation to estimate the mass ratio of the merger to be ~1:20. An WFC3 study of globular clusters reveals a substantial population of young star clusters coincident with the central region of star formation and indicates that the bulk of the stellar mass in this galaxy probably formed 6-8 Gyrs in the past. This study demonstrates the utility of high-resolution imaging from future instruments such as the extremely large telescopes. (Based on Early Release Science observations by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this program.)

Kaviraj, Sugata

2013-01-01

59

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

60

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

61

StarCAT: STIS UV echelle spectra of stars (Ayres, 2010)  

NASA Astrophysics Data System (ADS)

StarCAT is a Cycle 14 Legacy Archival project supported by the Guest Investigator program of Hubble Space Telescope (HST). The objective of StarCAT was to create an easily accessible catalog of high resolution spectral observations of targets broadly identified as "stars," collected by Space Telescope Imaging Spectrograph (STIS) from the time of its installation in 1997, during Hubble Servicing Mission 2, to its shutdown in 2004 August. StarCAT is available through an interface maintained at the Multimission Archive at Space Telescope (MAST): http://archive.stsci.edu/prepds/starcat (3 data files).

Ayres, T. R.

2010-04-01

62

Spectral classification criteria for some early type stars in the UV region/atl>  

NASA Astrophysics Data System (ADS)

The aim of this paper is to get new critertia for spectral classification of some early type stars which depend on the flux in the UV region ? ? 1500-2500 by carrying out spectrophotometric analysis of observational ultraviolet data of stars obtained by the S2/68 Ultraviolet Sky Survey Telescope (UVSST) aboard the European Space Research Organization (ESRO) Satellite TD1. We have developed these new criteria based on the Intrinsic Ultraviolet Colour Index (IUI), and the Intrinsic Flux Ratio (IFR). Using these quantities we are going to represent the results of spectral classification of 323 early type stars mainly from spectral type B and A. The results of calculations of the Intrinsic Flux Ratios for the stars under investigation together with their Colour Temperatures (Tc) are given. Comparison between our suggested two new criteria with the MK classification system and Cucchairo (1980) classification system was carried out.

Hamdy, M. A.; Abo Elazm, M. S.; Saad, S. M.; Nafie, H. O.; Abdel Baeth, H. E.

63

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

64

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

65

DK UMa: A Star on the Ascent  

NASA Technical Reports Server (NTRS)

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

Simon, Theodore

1999-01-01

66

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

67

Radiative Transfer SPH Simulations of UV Feedback on Pop III Star Formation  

NASA Astrophysics Data System (ADS)

To explore the radiative feedback from first stars on the subsequent Pop III star formation in a Lambda-CDM universe, we perform high-resolution cosmological SPH simulations coupled with radiative transfer of UV radiation, using FIRST simulator. In the simulations, the baryon mass resolution is 0.3 Msolar and the number of particles is several 105 respectively for baryon and dark matter component. We assume that several collapsing cores form in a Pop III object and one of them evolves into a first star, and then investigate the evolution of other collapsing cores with paying special attention to the radiation hydrodynamic feedback. As a result, it is shown that other collapsing cores are impervious to the negative radiative feedbacks of H2 photodissociation and photoevapolation, but can continue to collapse due to the shielding of UV radiation, consistent with the results of Susa & Umemura (2006). This result implies that all collapsing cores in a Pop III object can evolve into stars.

Sato, Daisuke; Umemura, Masayuki; Susa, Hajime; Suwa, Tamon

2008-03-01

68

Star Formation in the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV radiation field, and the effect of this field on the star-forming interstellar medium (ISM). There are substantial fluctuations of the UV radiation field in space (scales of 100's of parsecs) and time (time-scales of order 100 million years) at the solar circle. The Far Ultraviolet (FUV) (6 eV< hv < 13.6 eV) field and the pressure determines whether the thermal balance of the neutral gas results in cold clouds or warm (T - 10(exp 4) neutral medium. We show how to calculate the average fractions of the gas in the cold and warm phases when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties and on the FUV sources is a basic step in building a model of the large scale behavior of the ISM and the mutual relation between the ISM and the star formation rate. Application is made to observations of spiral galaxies which correlate the star formation rate per unit area with the surface density of the gas. We acknowledge support from the NASA Astrophysical Theory program.

Hollenbach, David; Parravano, Antonio; McKee, Christopher H.; Fonda, Mark (Technical Monitor)

2001-01-01

69

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

70

Simultaneous UV-optical observations of isolated T-Tauri stars: The V4046 SGR CASE  

NASA Astrophysics Data System (ADS)

It is suggested that a group of a southern T-Tauri stars presented by V 4046 Sgr (HDE 319139), Co-2711363, AS 218, and TW Hya, located relatively far from any known dark or molecular clouds, were formed in very small clouds leaving almost no residuals, instead of having escaped from a cloud as suggested in the past of a similar isolated T-Tauri type star (FK Ser). Star V 4046 Sgr is the only group that is double and that presents a large far infrared residual measured from IRAS. Simultaneous observations of V 4046 Sgr in the UV obtained with the IUE and in the optical range by ground based observations are presented.

de La Reza, R.; Quast, G.; Torres, C. A. O.; Mayor, M.; Meylan, G.; Llorente de Andres, F.

1986-09-01

71

Far-UV spectral atlas of O-type stars (Smith, 2012)  

NASA Astrophysics Data System (ADS)

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

Smith, M. A.

2012-10-01

72

Omicron Ceti light curves, 1838-2000  

NASA Astrophysics Data System (ADS)

This monograph contains light curves of the Mira prototype Omicron Ceti from 1838 through 2000 (JD 2392720-2451910). The AAVSO historical light curve from 1838 through 2000 of 10-day means of observations is presented. This light curve has been included to give a more complete picture of Omicron Ceti's behavior. The observations used to create the historical light curve have been compiled from the AAVSO archives. Pages 2 through 14 contain expanded computer-generated light curves for the interval 1966-2000 (JD 2439295-2451910), with each observation plotted separately. Data may be visual; photoelectric photometry (V); B, V, R, I, or unfiltered CCD; photographic; and/or photovisual. A key to the symbols appearing in each light curve is given at the top of each page. Very dense concentrations of observations made at the same magnitude at very close intervals may appear in the light curves as solid horizontal lines. The line running through parts of the data represents 10-day means; mean magnitudes were calculated when there was more than one positive visual observation in each of two or more consecutive 10-day intervals. Observations are plotted Julian date versus magnitude, and the start of each year (January 1) is indicated along the upper axis.

Mattei, Janet A.; Menali, H. Gamze; Waagen, Elizabeth O.

73

Young stars in nearby early-type galaxies: SED fitting based on ultraviolet (UV) and optical imaging  

NASA Astrophysics Data System (ADS)

Recent studies from the Galaxy Evolution Explore (GALEX) ultraviolet (UV) data have demonstrated that the recent star formation is more common in early-type galaxies (ETGs) than we used to believe. The UV is one order of magnitude more sensitive than the optical to the presence of young stellar populations. The near-ultraviolet (NUV) lights of ETGs, especially, are used to reveal their residual star formation history. Here we used the GALEX UV data of 34 nearby early-type galaxies from the SAURON sample, all of which have optical data from MDM Observatory. At least 15% of the galaxies in this sample show blue UV-optical colours suggesting recent star formation (Jeong et al. 2009). These NUV blue galaxies are generally low velocity dispersion systems and change the slopes of scaling relations (colour-magnitude relations and fundamental planes) and increase the scatters. To quantify the amount of recent star formation in our sample, we assume two bursts of star formation, allowing us to constrain the age and mass fraction of the young component pixel by pixel (Jeong et al. 2007). The pixel-by-pixel SED fitting based on UV and optical imaging reveals that the mass fraction of young (< 1 Gyr old) stars in ETGs varies between 1 and 3% in the nearby universe (Jeong et al. in prep.). We will compare our results with the prediction from the hierarchical merger paradigm to understand the mechanism of low-level recent star formation observed in early-type galaxies.

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

2012-08-01

74

The instability strip of ZZ Ceti white dwarfs. I. Introduction of time-dependent convection  

NASA Astrophysics Data System (ADS)

Aims: The determination of the location of the theoretical ZZ Ceti instability strip in the log g - Teff diagram has remained a challenge over the years due to the lack of a suitable treatment for convection in these stars. For the first time, a full nonadiabatic approach including time-dependent convection is applied to ZZ Ceti pulsators, and we provide the appropriate details related to the inner workings of the driving mechanism. Methods: We used the nonadiabatic pulsation code MAD with a representative evolutionary sequence of a 0.6 M? DA white dwarf. This sequence is made of state-of-the-art models that include a detailed modeling of the feedback of convection on the atmospheric structure. The assumed convective efficiency in these models is the so-called ML2/? = 1.0 version. We also carried out, for comparison purposes, nonadiabatic computations within the frozen convection approximation, as well as calculations based on models with standard grey atmospheres. Results: We find that pulsational driving in ZZ Ceti stars is concentrated at the base of the superficial H convection zone, but at depths, near the blue edge of the instability strip, somewhat larger than those obtained with the frozen convection approach. Despite the fact that this approach is formally invalid in such stars, particularly near the blue edge of the instability strip, the predicted boundaries are not dramatically different in both cases. The revised blue edge for a 0.6 M? model is found to be around Teff = 11 970 K, some 240 K hotter than the value predicted within the frozen convection approximation, in rather good agreement with the empirical value. On the other hand, our predicted red edge temperature for the same stellar mass is only about 5600 K (80 K hotter than with the frozen convection approach), much lower than the observed value. Conclusions: We correctly understand the development of pulsational instabilities of a white dwarf as it cools at the blue edge of the ZZ Ceti instability strip. Our current implementation of time-dependent convection however still lacks important ingredients to fully account for the observed red edge of the strip. We will explore a number of possibilities in the future papers of this series.

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

2012-03-01

75

UV Extinction Properties of Dust in a Region of Active Star Formation  

NASA Astrophysics Data System (ADS)

This proposal requests low-dispersion IUE observations of several dark cloud lines of sight (E(B - V) ~ 0.6 - 1.0) toward the GMC complex Cygnus X. IRAS images of the southwest region of this well known GMC reveals a shell structure superimposed on a field of hot young stars, known as the Cyg OB1 association. Saken et al. (1992) have found this well defined structure is visible in the ratio of the 60 microns to 100 microns Skyflux images. One scenario proposed by Saken et al. for seeing the cavity is that the small grains, the source of most of the 60 micron emission, have been destroyed by the strong stellar radiation field. The young galactic star clusters NGC 6913 (M 29), Berkeley 86 and IC 4996 make up the nuclei of the expansive star forming region of Cyg OB1 and are the best candidates to lie within the infrared structure. A study of the UV extinction properties of these stars would be sampling the dust responsible for the IRAS feature. This would enable us to test models of dust physical and chemical characteristics by fitting the curves to the models of Draine & Lee (1984) to see if this sightline shows evidence of an altered chemistry or size distribution. By choosing a few stars from each cluster to study, we can 1) determine the nature of the dust in different regions of the IRAS feature, and 2) compare the extinction curves of stars within the same cluster to determine the variability over small angles. No stars in the open galactic clusters NGC 6913, Berkeley 86 or IC 4996 have ever been observed with the IUE.

Clayton, Geoffrey C.

76

Constraints for models of Be stars derived from UV and IRAS observations  

NASA Technical Reports Server (NTRS)

The effect of different geometrical models (disk and circumstellar shell) on the mass loss determinations of Be stars is investigated. The characteristics of the disk and circumstellar shell models are described. The models are applied to the analysis of the column density derived from the UV lines and emission measurements derived from IRAS observations of 10 Be stars, and the mass loss rate for these stars are calculated. It is observed that the mass loss rates obtained from the circumstellar shell model are a factor of 0.01 smaller than those of the disk model; the mass of the IR emitting region is three times larger in the shell model than that in the disk model; and the radial outflow velocity of the IR emitting region for the shell model is of the order of 0.01 km/sec and for the disk model of the order of 10 km/sec. It is noted that the UV and IRAS observations can be analyzed using the two models if the proper geometry is considered.

Lamers, H. J. G. L. M.; Waters, L. B. F. M.

1987-01-01

77

Star Formation In the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

We examine the formation of massive stars in the Galaxy, the resultant fluctuating UV (ultraviolet) radiation field, and the effect of this field on the star-forming interstellar medium. There are substantial fluctuations of the UV radiation field in space (scales of 100's of parsecs) and time (time-scales of order 100 million years). The FUV (far ultraviolet) (6 eV less than hv less than 13.6 eV) field and the pressure determines whether the thermal balance of the neutral gas results in cold clouds or warm (T approx. 10(exp 4) K) neutral medium. We show how to calculate the average fractions of the gas in the cold and warm phases when the interstellar gas is subject to this fluctuating FUV field. The knowledge of how these fractions depend on the gas properties and on the FUV sources is a basic step in building a model of the large scale behavior of the ISM (interstellar medium) and the mutual relation between the ISM and the star formation rate.

Hollenbach, David; Parravano, Antonio; McKee, Christopher H.; DeVincenzi, D. (Technical Monitor)

2002-01-01

78

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

79

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

80

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

NASA Astrophysics Data System (ADS)

We have analyzed XMM-Newton Optical Monitor UV (180-400 nm) data for a sample of 33 galaxies. Thirty are cluster member galaxies, and nine are central cluster galaxies (CCGs) in cooling flow clusters having mass deposition rates between 8 and 525 Msolar yr-1. 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, consistent with several previous studies based on optical imaging data (McNamara & O'Connell Cardiel et al.; Crawford et al.). This UV excess is a direct indication of the presence of young massive stars and, therefore, recent star formation. Using the Starburst99 model of continuous star formation over a 900 Myr period, we derive star formation rates of 0.2-219 Msolar yr-1 for the cooling flow sample. For two-thirds 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.

2005-12-01

81

The formation of hot subdwarf stars and its implications for the UV-upturn phenomenon of elliptical galaxies  

NASA Astrophysics Data System (ADS)

In this paper, we review the formation scenario for field hot subdwarf stars and extreme horizontal branch stars in globular clusters and discuss how the scenario helps us to understand the UV-upturn phenomenon of elliptical galaxies. It is widely accepted that field hot subdwarf stars originate from binary evolution via the following three channels, common envelope evolution channel for hot subdwarf binaries with short orbital periods, stable Roche lobe overflow channel for hot subdwarf binaries with long orbital periods, and the double helium white dwarf merger channel for single hot subdwarfs. Such a scenario can also explain the lack of binarity of extreme horizontal branch stars in globular clusters. We have applied, in an a priori way, the scenario to the study of UV-upturn phenomenon of elliptical galaxies via an evolutionary population synthesis approach and found that the UV-upturn can be naturally explained. This has major implications for understanding the evolution of UV-upturn and elliptical galaxies in general. In particular, it implies that the UV-upturn is not a sign of age, as had been postulated previously, and should not be strongly dependent on the metallicity of the population, but exists universally from dwarf ellipticals to giant ellipticals. The above a priori UV-upturn model is supported by recent GALEX observations and has been applied to naturally explain the colours of both dwarf ellipticals and giant ellipticals without the requirement of dichotomy between their stellar population properties.

Han, Z.; Podsiadlowski, P.; Lynas-Gray, A.

2010-10-01

82

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

83

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

NASA Astrophysics Data System (ADS)

Infrared (IR) luminosity of galaxies originating from dust thermal emission can be used as an indicator of the star formation rate (SFR). Inoue et al. (\\cite{inoue00}, IHK) have derived a formula for the conversion from dust 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 (ga 108 yr) stellar populations (eta ). We develop a method to estimate those three quantities based on the idea that the various way of SFR estimates from ultraviolet (UV) luminosity (2000 Å luminosity), H? luminosity, and dust IR luminosity should return the same SFR. After applying our method to samples of galaxies, the following results are obtained in our framework. First, our method is applied to a sample of 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 are able to estimate reliable SFRs from UV and/or IR luminosities. Moreover, the H? luminosity, if the H? 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 (i.e. 1/f)} 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, the local (z=0) comoving density of SFR can be estimated with our dust extinction corrections. We show that all UV, H? , and IR comoving luminosity densities at z=0 give a consistent SFR per comoving volume ( ~ 3x 10-2h M_sun yr-1 Mpc-3). Useful formulae for SFR estimate are listed. Tables 1 and 2, and Appendix A are only available in electronic form at http://www.edpsciences.org

Hirashita, H.; Buat, V.; Inoue, A. K.

2003-10-01

84

THE AVERAGE PHYSICAL PROPERTIES AND STAR FORMATION HISTORIES OF THE UV-BRIGHTEST STAR-FORMING GALAXIES AT z {approx} 3.7  

SciTech Connect

We investigate the average physical properties and star formation histories (SFHs) of the most UV-luminous star-forming galaxies at z {approx} 3.7. Our results are based on the average spectral energy distributions (SEDs), constructed from stacked optical-to-infrared photometry, of a sample of the 1913 most UV-luminous star-forming galaxies found in 5.3 deg{sup 2} of the NOAO Deep Wide-Field Survey. We find that the shape of the average SED in the rest optical and infrared is fairly constant with UV luminosity, i.e., more UV-luminous galaxies are, on average, also more luminous at longer wavelengths. In the rest UV, however, the spectral slope {beta} ({identical_to} dlogF{sub {lambda}}/dlog{lambda}; measured at 0.13 {mu}m < {lambda}{sub rest} < 0.28 {mu}m) rises steeply with the median UV luminosity from -1.8 at L {approx} L* to -1.2 (L {approx} 4-5L*). We use population synthesis analyses to derive their average physical properties and find that (1) L{sub UV} and thus star formation rates (SFRs) scale closely with stellar mass such that more UV-luminous galaxies are also more massive, (2) the median ages indicate that the stellar populations are relatively young (200-400 Myr) and show little correlation with UV luminosity, and (3) more UV-luminous galaxies are dustier than their less-luminous counterparts, such that L {approx} 4-5L* galaxies are extincted up to A(1600) = 2 mag while L {approx} L* galaxies have A(1600) = 0.7-1.5 mag. We argue that the average SFHs of UV-luminous galaxies are better described by models in which SFR increases with time in order to simultaneously reproduce the tight correlation between the UV-derived SFR and stellar mass and their universally young ages. We demonstrate the potential of measurements of the SFR-M{sub *} relation at multiple redshifts to discriminate between simple models of SFHs. Finally, we discuss the fate of these UV-brightest galaxies in the next 1-2 Gyr and their possible connection to the most massive galaxies at z {approx} 2.

Lee, Kyoung-Soo; Glikman, Eilat [Yale Center for Astronomy and Astrophysics, Department of Physics, Yale University, New Haven, CT 06520 (United States); Dey, Arjun; Reddy, Naveen; Jannuzi, Buell T. [National Optical Astronomy Observatory, Tucson, AZ 85726 (United States); Brown, Michael J. I. [School of Physics, Monash University, Clayton, Victoria 3800 (Australia); Gonzalez, Anthony H. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Cooper, Michael C.; Fan Xiaohui; Bian Fuyan [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, MS 169-327, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Brodwin, Mark [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Cooray, Asantha [School of Physical Sciences, University of California, Irvine, CA 92697 (United States)

2011-06-01

85

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

86

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

87

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

88

FUV/UV/Optical Observations of the symbiotic star AG DRA  

NASA Astrophysics Data System (ADS)

We present spectroscopic data of AG Draconis covering the far-ultraviolet (FUV), ultraviolet (UV) and optical regions and obtained during the Astro-2 Space Shuttle astronomy mission in March 1995, approximately eight months after peak light of the system's most recent outburst. We have supplemented these data with UV -- FUV archival data obtained with the IUE and ORFEUS satellites. We discuss these data in the light of the strength of the nebular emission from this object, in particular from the higher excitation lines, and the physical conditions estimated from the emission line diagnostics. Additional information provided via. the Raman-scattering of OVI 1032, 1038 emission lines will also be discussed in comparison with recent results for the symbiotic nova RR Tel (Espey, B.R., et al. 1995, ApJ 454, L61). Using the high resolution ORFEUS data obtained during a Space Shuttle mission in the fall of 1993, combined with more recent UV and ground-based data, we discuss likely origins for the strong nebular emission features and the relative importance of the contributions of the winds from the hot star and the cool giant, and the shocked region between them. This work is supported by NASA contract NAS 5-27000 to the Johns Hopkins University. and by Astro-2 Guest Investigator grants NAG 8-1049 and NAG 8-1073 to Espey and Schulte-Ladbeck, respectively.

Espey, B. R.; Birriel, J.; Schulte-Ladbeck, R. E.; Johnson, J. J.; Schmidt, H. M.; Schild, H.

1995-12-01

89

The Instability Strip of ZZ Ceti White Dwarfs and Its Extension to the Extremely Low Mass Pulsators  

NASA Astrophysics Data System (ADS)

The determination of the location of the theoretical ZZ Ceti instability strip in the log g - Teff diagram has remained a challenge over the years, due to the lack of a suitable treatment for convection in these stars. We report here a detailed stability survey over the whole ZZ Ceti regime, including the very low masses where three pulsators have recently been found. With this in mind, we computed twenty-nine evolutionary sequences of DA models with various masses and chemical layering. These models are characterized by the so-called ML2/? = 1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We computed power spectra for these models with the Liège nonadiabatic pulsation code MAD, which is the only one to conveniently incorporate a full time-dependent convection treatment and, thus, provides the best available description of the blue edge of the instability strip. On the other hand, given the failure of all nonadiabatic codes to properly account for the red edge of the strip, including MAD, we tested the idea that the red edge is due to energy leakage through the atmosphere. Using this approach, we found that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip.

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

2013-12-01

90

Some results of the cooperative photometric observations of the UV Cet-type flare stars in the years 1967–71  

Microsoft Academic Search

The list of the cooperative photometric observations of the UV Cet-type flare stars that have been organized during the years 1967 to 1971 by the Working Group on Flare Stars of the IAU Commission 27 is given. The completeness and reliability of the data obtained are evaluated by comparing simultaneous observations at different observatories. the statistical analysis of the UV

R. E. Gershberg

1972-01-01

91

Anomalously bright UV lines of Fe II as a probe of gas condensations in the vicinity of hot stars  

NASA Astrophysics Data System (ADS)

Two UV lines of Fe II at 2507/2509 Å are extremely bright in spatially resolved HST/STIS spectra of dense gas condensations (the so called Weigelt blobs) close to the central star of ? Carinae. The lines also appear unresolved in HST/FOS spectra of the star AE And. Under normal conditions the lines should hardly be observable. Based on recent studies of the formation of the ?ambda?ambda2507/2509 lines as part of a radiative cycle driven by HLy? pumping and including stimulated emission we propose the possibility of using them as a probe of non-homogeneities in gas condensations located outside hot, massive stars.

Johansson, S.; Letokhov, V. S.

2003-12-01

92

FOS observations of G117-B15A and the blue edge of the ZZ Ceti instability strip  

NASA Astrophysics Data System (ADS)

From an analysis of Faint-Object-Spectrograph (FOS) observations of G117-B15A, one of the hottest members of the ZZ Ceti class, we derive an effective temperature of 12,250 +/- 125 K. Since several other DA near the blue edge of the instability strip must have very similar temperatures according to their UV spectra, it is likely that the blue edge is lower than assumed until now. The spectrum can only be fitted, if we assume a relatively high convective efficiency, corresponding to a mixing-length parameter of about 2.

Koester, D.; Allard, N. F.; Vauclair, G.

1994-11-01

93

Star Formation in the Galaxy and the Fluctuating UV Radiation Field  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

94

Quantitative technetium abundances in the long-period variables Chi Cygni and Omicron Ceti  

NASA Astrophysics Data System (ADS)

The authors have analyzed spectra of 2.4 Å mm-1 dispersion to derive abundances of V, Zr, Nb, and Tc in ? Cygni, ? Ceti, and R Lyrae. They find a large Tc abundance in ? Cyg and a smaller amount of Tc in Mira. Accompanying the enhanced Tc in Mira is a surprisingly low abundance of Nb. The enhancement of Tc in ? Cyg can be explained as part of a general enhancement of heavy elements by neutron capture which is characteristic of S and MS stars. For Mira the explanation is less obvious because there is no apparent enhancement of heavy elements except for Tc. The depletion of Nb leads the authors to suggest that a very small pulse of neutrons could be responsible for this apparent anomaly.

Dominy, James F.; Wallerstein, George

1986-11-01

95

Panchromatic Hubble Andromeda Treasury (PHAT): Comparing Ages and Masses of GALEX UV-Bright Regions and Resolved Stars  

NASA Astrophysics Data System (ADS)

The Panchromatic Hubble Andromeda Treasury (PHAT) offers a rich set of multi-wavelength HST imaging (UV through near-IR) with which to study the resolved populations in the disk of M31. This provides a unique opportunity to investigate how well integrated UV flux can be used to estimate various properties (e.g., age, mass, and extinction) of the underlying stellar populations. Kang et al. (2009) measured the total NUV and FUV GALEX flux within a set of UV-bright regions in M31 and used stellar population models to estimate ages and masses. In this followup study, we use a maximum likelihood color-magnitude diagram fitting technique with the optical photometry of resolved stars in the PHAT survey to measure the star formation histories (mass formed as a function of age) within the same UV-bright regions. We compare our results with the ages, masses, and extinction values derived by Kang et al. from integrated UV flux. Support for this work was provided by NASA through grant GO-12055 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555.

Skillman, Evan D.; Simones, J.; Weisz, D. R.; Dalcanton, J. J.; Williams, B. F.; PHAT Team

2012-01-01

96

UV Observations of the Symbiotic Star AR PAV in Eclipse & Two Mass-Transfer X-Ray Binaries  

NASA Astrophysics Data System (ADS)

Previous IUE observations of the eclipse egress of the symbiotic binary AR Pav show that the hot secondary and high excitation emission line region are not eclipsed during the optical totality. Further uv observations nearer the center of eclipse are required to determine the distribution, structure and physical conditions of the disk surrounding the hot star. UV observations of two unusual xray sources with high mass-transfer rates will also be obtained to investigate variations on the time scales of a few days to a few weeks.

Cowley, Anne P.

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

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

NASA Astrophysics Data System (ADS)

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.

1989-09-01

99

X-ray and Hubble/COS UV Measures of Kapteyn's Star: A Crucial Proxy of X-UV Irradiances for Old Red Dwarf Stars that May Host Habitable Zone Planets  

NASA Astrophysics Data System (ADS)

Red dwarfs (dM) stars make up over 80% of the local stellar population and a significant fraction of them are old (age > 4 Gyr). Because of the high frequency of red dwarfs and their longevity, there is a greater possibility of more advanced life in red dwarf planet systems. MEarths, UVES, SDSS-III, and the upcoming TESS mission are some surveys that are targeting these objects. As part of Villanova’s Living with a Red Dwarf program, we have obtained HST/COS spectra and Chandra X-ray observations of Kapteyn's star (M1V, V = 8.853, d = 12.76 +/- 0.05 ly, P_rot = 195 days). This star is crucial to the study of old red dwarfs as it is the nearest halo star with a radial velocity of +245.2 km/s and an estimated age of 10-12 Gyr. 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 Lyman-alpha emission for red dwarfs. This is due to Doppler shift from the high radial velocity, separating the Lyman-alpha line from emission produced by the ISM and geocoronal sources. These observations further provide calibration at the old age/low rotation/low activity extremes for our relations. They also provide insights into the magnetic properties as investigating coronal x-ray and UV emission in very old, slowly rotating dM stars. Kapteyn’s star also serves as a proxy for metal-poor old disk/Pop II M dwarfs by providing information about X-UV emissions. This information is crucial for determining X-UV irradiances of possible habitable zone planets hosted by old red dwarfs. We gratefully acknowledge the support from NSF/RUI Grant AST-1009903, NASA/Chandra Grants GO1-12124X and GO2-13020X, and HST-GO-13020.

Durbin, Allyn J.; Guinan, E. F.; Engle, S. G.

2014-01-01

100

Measuring the Evolutionary Rate of Cooling of ZZ Ceti  

NASA Astrophysics Data System (ADS)

We have finally measured the evolutionary rate of cooling of the pulsating hydrogen atmosphere white dwarf ZZ Ceti (R548), as reflected by the 213.13260694 s period. Using 41 years of time-series photometry from 1970 to 2011, we determine its rate of change of period with time to be dP/dt = (3.0 ± 1.4) × 10-15 s/s with the O-C method and (3.23 ± 0.87) × 10-15 s/s using the nonlinear least squares fit, after correcting for proper motion. We augment the uncertainty to a more realistic value and arrive at the evolutionary cooling rate of (3.2 ± 1.2) × 10-15 s/s for ZZ Ceti, consistent with the measurement of (4.19 ± 0.73) × 10-15 s/s for G117-B15A.

Mukadam, A. S.; Kim, A.; Montgomery, M. H.; Córsico, A. H.; Kepler, S. O.; Romero, A. D.; Winget, D. E.; Fraser, O.; Riecken, T. S.; Kronberg, M. E.; Hermes, J. J.; Winget, K. I.; Falcon, R. E.; Chandler, D. W.; Kuehne, J. W.; Sullivan, D. J.; Reaves, D.; von Hippel, T.; Mullally, F.; Shipman, H.; Thompson, S. E.; Silvestri, N. M.; Hynes, R. I.

2013-01-01

101

Weissella ceti sp. nov., isolated from beaked whales (Mesoplodon bidens).  

PubMed

During an investigation into the microbiota of beaked whales (Mesoplodon bidens), nine isolates were obtained from different organs of four animals. The isolates were Gram-positive-staining, catalase-negative, short rod-shaped or coccoid organisms. A phylogenetic analysis based on 16S rRNA gene sequences of these isolates allocated them to the genus Weissella, showing 96.3 % and 96.0 % 16S rRNA gene sequence similarity with Weissella viridescens NRIC 1536(T)and Weissella minor NRIC 1625(T), respectively. On the basis of phenotypic, physiological and phylogenetic evidence, it is proposed that the new isolates from whales represent a novel species of the genus Weissella, Weissella ceti sp. nov. The type strain of Weissella ceti is 1119-1A-09(T) ( = CECT 7719(T) = CCUG 59653(T)). PMID:21216921

Vela, A I; Fernández, A; de Quirós, Y Bernaldo; Herráez, P; Domínguez, L; Fernández-Garayzábal, J F

2011-11-01

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

STAR FORMATION AND UV COLORS OF THE BRIGHTEST CLUSTER GALAXIES IN THE REPRESENTATIVE XMM-NEWTON CLUSTER STRUCTURE SURVEY  

SciTech Connect

We present UV broadband photometry and optical emission-line measurements for a sample of 32 brightest cluster galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM-Newton Optical Monitor, supplemented by existing archival Galaxy Evolution Explorer photometry. We detected H{alpha} and forbidden line emission in seven (22%) of these BCGs, in optical spectra obtained using the Southern Astrophysical Research Goodman spectrograph. All of these emission-line BCGs occupy clusters classified as cool cores (CCs) based on the central cooling time in the cluster core, for an emission-line incidence rate of 70% for BCGs in REXCESS CC clusters. Significant correlations between the H{alpha} equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H{alpha} emitters inhabit systems with short central cooling times and high central intracluster medium densities. Estimates of the star formation rates based on H{alpha} and UV excesses are consistent with each other in these seven systems, ranging from 0.1to8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray-selected samples ({approx}35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples ({approx}10%-15%). The UV-optical colors (UVW1 - R {approx}4.7 {+-} 0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no trend in UV-optical colors with optical luminosity, R-K color, X-ray temperature, redshift, or offset between X-ray centroid and X-ray peak ((w)). The lack of such trends in these massive galaxies, particularly the ones lacking emission lines, suggests that the proportion of UV-emitting (200-300 nm) stars is insensitive to galaxy mass, cluster mass, cluster relaxation, and recent evolution, over the range of this sample.

Donahue, Megan; Bruch, Seth; Wang, Emily; Voit, G. Mark; Hicks, Amalia K. [Physics and Astronomy Department, Michigan State University, East Lansing, MI 48824-2320 (United States); Haarsma, Deborah B. [Calvin College, 1734 Knollcrest Circle SE, Grand Rapids, MI 48546 (United States); Croston, Judith H. [School of Physics and Astronomy, University of Southampton, Southampton SO17 1SJ (United Kingdom); Pratt, Gabriel W. [Laboratoire AIM, IRFU/Service dAstrophysique-CEA/DSM-CNRS-Universite Paris Diderot, Bt. 709, CEA-Saclay, F-91191, Gif-sur-Yvette Cedex (France); Pierini, Daniele; Boehringer, Hans [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstr., 85748 Garching (Germany); O'Connell, Robert W., E-mail: donahue@pa.msu.ed [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States)

2010-06-01

104

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

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

105

UV-bright Clumps in Star-forming Galaxies at 0.5  

NASA Astrophysics Data System (ADS)

A common feature of star-forming galaxies (SFGs) at z>1 is the existence of giant star-forming clumps, with typical size of 1 kpc and mass of 10^{7-9} solar mass. These clumps, prominent and most easily detected in the rest-frame UV images, are fundamental to our understanding of the evolution of early gas-rich disks, accretion history of galaxies, and formation of bulges. However, their origin and evolution are still unclear. It is not even clear if they resemble the star-burst regions or bulges of today's galaxies. To understand the evolution and duration of this clumpy star formation mode, a complete census on clumpy galaxies at all redshifts with rest-frame UV observations is needed. We will use the CANDELS data in the GOODS-S and UDS fields to address one essential question: the frequency of clumps in SFGs at 0.5UV images by an automated clump finder, with the detection ability and completeness well evaluated by fake clumpy galaxies. We will present the fractional UV luminosity function of clumps in different redshift and stellar mass bins and study the fraction of star formation that the clumps contribute to their host galaxies. We will also compare the observations with our hydrodynamic cosmological simulations.

Guo, Yicheng; Koo, D. C.; Primack, J. R.; CANDELS Collaboration

2014-01-01

106

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

107

The Newly Discovered Pulsating Low-mass White Dwarfs: An Extension of the ZZ Ceti Instability Strip  

NASA Astrophysics Data System (ADS)

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/? = 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.; Fontaine, G.; Brassard, P.; Dupret, M.-A.

2013-01-01

108

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...

109

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

110

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

111

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

NASA Astrophysics Data System (ADS)

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

Roscoe, Howard K.; Taylor, William H.; Evans, Jon D.; Tait, Andy M.; Freshwater, Ray; Fish, Debbie; Strong, E. Kimberly; Jones, Rod L.

1997-08-01

112

Mass loss from inhomogeneous hot star winds. II. Constraints from a combined optical/UV study  

NASA Astrophysics Data System (ADS)

Context. Mass loss is essential for massive star evolution, thus also for the variety of astrophysical applications relying on its predictions. However, mass-loss rates currently in use for hot, massive stars have recently been seriously questioned, mainly because of the effects of wind clumping. Aims: We investigate the impact of clumping on diagnostic ultraviolet resonance and optical recombination lines often used to derive empirical mass-loss rates of hot stars. Optically thick clumps, a non-void interclump medium, and a non-monotonic velocity field are all accounted for in a single model. The line formation is first theoretically studied, after which an exemplary multi-diagnostic study of an O-supergiant is performed. Methods: We used 2D and 3D stochastic and radiation-hydrodynamic wind models, constructed by assembling 1D snapshots in radially independent slices. To compute synthetic spectra, we developed and used detailed radiative transfer codes for both recombination lines (solving the "formal integral") and resonance lines (using a Monte-Carlo approach). In addition, we propose an analytic method to model these lines in clumpy winds, which does not rely on optically thin clumping. Results: The importance of the "vorosity" effect for line formation in clumpy winds is emphasized. Resonance lines are generally more affected by optically thick clumping than recombination lines. Synthetic spectra calculated directly from current radiation-hydrodynamic wind models of the line-driven instability are unable to in parallel reproduce strategic optical and ultraviolet lines for the Galactic O-supergiant ? Cep. Using our stochastic wind models, we obtain consistent fits essentially by increasing the clumping in the inner wind. A mass-loss rate is derived that is approximately two times lower than what is predicted by the line-driven wind theory, but much higher than the corresponding rate derived when assuming optically thin clumps. Our analytic formulation for line formation is used to demonstrate the potential importance of optically thick clumping in diagnostic lines in so-called weak-winded stars and to confirm recent results that resonance doublets may be used as tracers of wind structure and optically thick clumping. Conclusions: We confirm earlier results that a re-investigation of the structures in the inner wind predicted by line-driven instability simulations is needed. Our derived mass-loss rate for ? Cep suggests that only moderate reductions of current mass-loss predictions for OB-stars are necessary, but this nevertheless prompts investigations on feedback effects from optically thick clumping on the steady-state, NLTE wind models used for quantitative spectroscopy.

Sundqvist, J. O.; Puls, J.; Feldmeier, A.; Owocki, S. P.

2011-04-01

113

The IUE-UV spectrum of the CP2 star HR465  

NASA Astrophysics Data System (ADS)

Consideration is given to eleven high resolution IUE spectra of the chemically peculiar star HR 465 obtained between 1979 and 1982. The spectra are compared to those of Pi Cet, Nu Cap, Vega, HD 101065, alpha exp 2 CVn, Kappa Cnc, HR 4072, and HR 7775. About 2500 lines are identified in the HR 465 spectra. Most of these lines belong to iron-peak elements, especially Fe II. The presence of other ions, including Ni II, Zn II, Ga II, Nb II, Eu II, and Eu III, is examined. It is shown that the rare-earth elements that are strong in the optical spectra of HR 465 are very weak, if present, in the IUE region. Lines of Pt II are found for HR 465. The results also suggest that Au II, Hg II, and Bi II are probably present.

Fuhrmann, K.

1989-11-01

114

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

115

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

116

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

SciTech Connect

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

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

2012-03-10

117

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

NASA Astrophysics Data System (ADS)

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 ?m 49 Cet is significantly extended in the 70 ?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 ?m and [C II] 158 ?m. The C II line was detected at the 5? 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.; Kamp, I.; Montesinos, B.; Dent, W. R. F.; Meeus, G.; Donaldson, J. K.; Olofsson, J.; Moór, A.; Augereau, J.-C.; Howard, C.; Eiroa, C.; Thi, W.-F.; Ardila, D. R.; Sandell, G.; Woitke, P.

2013-07-01

118

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

119

Crystallization kinetics study of cerium titanate CeTi2O6  

NASA Astrophysics Data System (ADS)

Cerium titanate CeTi2O6 has been investigated recently for its photocatalytic activity and as a safe analogue to actinide-containing brannerite-like titanates (UTi2O6, PuTi2O6, e.g.) which are intensively studied because of their use for storing nuclear waste. In this paper we report on the monoclinic phase CeTi2O6 obtained from the Ti-Ce oxide mixture prepared by a reverse micelles directed sol-gel method and subsequently annealed. The kinetics of the isothermal crystallization process is investigated by means of Johnson-Mehl-Avrami-Kolmogorov equation. The effective activation energy of the formation of CeTi2O6 particles, which is an important parameter for its synthesis, is estimated.

Valeš, Václav; Mat?jová, Lenka; Mat?j, Zden?k; Brunátová, Tereza; Holý, Václav

2014-02-01

120

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

121

DUST OBSCURATION AND METALLICITY AT HIGH REDSHIFT: NEW INFERENCES FROM UV, H{alpha}, AND 8 {mu}m OBSERVATIONS OF z {approx} 2 STAR-FORMING GALAXIES  

SciTech Connect

We use a sample of 90 spectroscopically confirmed Lyman break galaxies with Halpha measurements and Spitzer MIPS 24 {mu}m observations to constrain the relationship between rest-frame 8 {mu}m luminosity (L{sub 8}) and star formation rate (SFR) for L* galaxies at z {approx} 2. We find a tight correlation with 0.24 dex scatter between L{sub 8} and H{alpha} luminosity/SFR for z {approx} 2 galaxies with 10{sup 10} L{sub sun} {approx}< L{sub IR} {approx}< 10{sup 12} L{sub sun}. Employing this relationship with a larger sample of 392 galaxies with spectroscopic redshifts, we find that the UV slope beta can be used to recover the dust attenuation of the vast majority of moderately luminous L* galaxies at z {approx} 2 to within a 0.4 dex scatter using the local correlation. Separately, young galaxies with ages {approx}<100 Myr appear to be less dusty than their UV slopes would imply based on the local trend and may follow an extinction curve that is steeper than what is typically assumed. Consequently, very young galaxies at high redshift may be significantly less dusty than inferred previously. Our results provide the first direct evidence, independent of the UV slope, for a correlation between UV and bolometric luminosity (L{sub bol}) at high redshift, in the sense that UV-faint galaxies are on average less infrared and less bolometrically luminous than their UV-bright counterparts. The L{sub bol}-L{sub UV} relation indicates that as the SFR increases, L{sub UV} turns over (or 'saturates') around the value of L* at z {approx} 2, implying that dust obscuration may be largely responsible for modulating the bright end of the UV luminosity function. Finally, dust attenuation is found to correlate with oxygen abundance at z {approx} 2. Accounting for systematic differences in local and high-redshift metallicity calibrations, we find that L* galaxies at z {approx} 2, while at least an order of magnitude more bolometrically luminous, exhibit ratios of metals to dust that are similar to those of local starbursts. This result is expected if high-redshift galaxies are forming their stars in a less metal-rich environment compared to local galaxies of the same luminosity, thus naturally leading to a redshift evolution in both the bolometric luminosity-metallicity and bolometric luminosity-obscuration relations.

Reddy, Naveen A. [National Optical Astronomy Observatory, 950 N Cherry Ave., Tucson, AZ 85719 (United States); Erb, Dawn K. [University of California at Santa Barbara, Santa Barbara, CA 93106 (United States); Pettini, Max [Institute of Astronomy, Madingley Road, Cambridge CB3 OHA (United Kingdom); Steidel, Charles C. [California Institute of Technology, MS 105-24, Pasadena, CA 91125 (United States); Shapley, Alice E. [University of California at Los Angeles, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095 (United States)

2010-04-01

122

Variation of the flare energy spectrum during the activity cycle of the UV Cet-type stars.  

NASA Astrophysics Data System (ADS)

A study is made of the variation of the flare energy spectrum of the flare star EV Lac during the activity cycle of this star, based on the homogeneous series of observational data obtained at the Stephanion Observatory. The spectrum varies significantly during the 5 year activity cycle of this star. Analogous variation is also observed in the time-averaged rate of flare energy release of the star.

Mavridis, L. N.; Avgoloupis, S.

123

Stars  

NASA Astrophysics Data System (ADS)

We will begin our study with a more or less superficial inspection of the "forest" of stars that we see in the skies. The first thing we notice is that, as sources of light, they are much weaker than the Sun. Second, their apparent colors vary; from a bluish-white in most of them to a reddish-yellow, which is rarer. There is also a third aspect, though it is not very obvious to the naked eye: most of the stars group themselves in small families of two, three or more members. A good example is the Alpha Centauri, the closest star to us, which, in fact, is a triple system of stars. Another is the group of 7 stars that make up the Pleiades, which will be discussed later on. In fact, almost half of the stars are double systems with only two members, called binary stars. Most of these double stars, though together, are separated by several astronomical units (one astronomical unit, AU, is the distance from Earth to the sun: see Chapter 1), and revolve around each other over periods of several years. And yet the revolutions of some binary stars, separated by much smaller distances, occur in only a few hours! These stars are so close to each other that they can share enveloping material. Often this exchange occurs in a somewhat violent manner. Local explosions may occur, expelling matter away from the system. In other binary systems, where one of the components is a very compact, dense star, companion material flows more calmly, making up a light disk around the compact star.

Capelato, Hugo Vicente

1999-01-01

124

A line identification study of the IUE SWP high dispersion spectrum of the UV-bright star Barnard 29 of Messier 13  

NASA Technical Reports Server (NTRS)

A line identification study was performed of the coaddition of three SWP high dispersion IUE exposures of the UV-bright star Barnard 29 of Messier 13. One of these images took two IUE shifts. The previous study by de Boer and Savage (1983) was extended and stellar lines of C I, C II, C III, C IV, N I, N III, O I, O III, O IV,Al III, Si II, Si III, Si IV, P III, S II, and S III and interstellar lines of C I, C II, C IV, N I, N III, N IV, N V, O I, Al II, Al III, Si II, Si IV, S II, and Fe II were found. These lines are the strongest expected lines in a hot Population II star. Apparent intensity minima corresponding to interstellar features are noted, especially those matching a high velocity cloud found by de Boer and Savage.

Adelman, S. J.; Cacciari, C.; Leckrone, D. S.

1991-01-01

125

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

126

Catalina Sky Survey observations of GRB130505B - a UV Ceti variable?  

NASA Astrophysics Data System (ADS)

We have inspected images from the Catalina Sky Survey (http://nesssi.cacr.caltech.edu/catalina/20010510/105101010504100001p.html) at the position of the suspected Galactic transient GRB130505B (Serino et al., GCN circ. 14586). The source's location was observed 363 times between 2004-03-27 and 2013-02-17. We find one clear detection on MJD=55204.38265, when PSF-like a source was present with V=~18.4.

De Pasquale, M.; Oates, S.; Drake, A.; Kocevski, D.; D'Avanzo, P.; Melandri, A.; Evans, P.; Marshall, F. E.

2013-05-01

127

Photometric activity of the Herbig Be star MWC 297 over 25 years  

NASA Astrophysics Data System (ADS)

The photometric behavior of the hot, young Herbig Be starMWC 297 on various time scales is studied using published data, as well as new observations. The series of photometric observations covers about 25 years. Over this time, the star showed low-amplitude (? V ? 0.3 m ) irregular variabilitymodulated by large-scale cyclic variabilitywith an amplitude close to 0.2 m and a period (or quasi-period) of 5.4±0.1 yr. A detailed seasonal analysis of the data shows that the light curve of MWC 297 displays two types of photometric features: low-amplitude Algol-like fading with an amplitude close to 0.2 m and low-amplitude flares resembling the flares of UV Ceti stars, but being more powerful and having longer durations. The variations of the stellar brightness are accompanied by variations of the B- V and V - R colors: when the brightness decreases, B- V decreases, while V - R increases (the star reddens). The reddening law is close to the standard interstellar reddening law. Although the character of the brightness variability ofMWC 297 resembles the photometric activity of UX Ori type stars, which is due to variations of their circumstellar extinction, its scale is very far from the scales observed for UX Ori stars. It is difficult to reconcile the level of photometric activity with the idea that MWC 297 is observed through its own gas-dust disk viewed almost edge-on, as has been suggested in several studies.

Barsunova, O. Yu.; Mel'nikov, S. Yu.; Grinin, V. P.; Katysheva, N. A.; Shugarov, S. Yu.

2013-02-01

128

A model for the origin of the anomalous and very bright UV lines of Fe II in gaseous condensations of the star ? Carinae  

NASA Astrophysics Data System (ADS)

We present a qualitative physical model of the origin of two very bright UV lines of Fe II at 2507-2509 Å, present in high-resolution spectra of gaseous condensations (blobs) close to the central star of eta Carinae. The spectra have been obtained with the Hubble Space Telescope (HST). The model is based on a type of Bowen mechanism with selective photoexcitation of Fe II by a broad HLyalpha profile, generated in the HII region and diffusely transferred to the optically thick HI region. The frequency distribution by large Doppler diffusion into the HI region provides a substantial broadening of HLyalpha , which makes it possible to selectively photo-excite short-lived (~1 ns) states at 11.2 eV in Fe II. Within the frame of the present model the intense HLyalpha radiation induces a depletion of the lower, long-lived (~1 ms) level of the strong UV lines by photoionization. The subsequent recombination of Fe III explains the appearance of the ``forest'' of narrow Fe II lines. The possibility of a cyclic process is also discussed, where HLyalpha induces depletion to bound states, which have fast decays in the far-UV to the lower state of the Bowen pumping channel.

Johansson, S.; Letokhov, V. S.

2001-10-01

129

Variations in the spatial distribution of 11 Micron radiation from omicron Ceti. [infrared interferometry  

NASA Technical Reports Server (NTRS)

The spatial distribution of 11 micron radiation from omicron Ceti was observed at various phases of its light cycle using a stellar interferometer. Changes were seen which can be attributed to variation in the strength of thermal emission from circumstellar dust relative to the stellar continuum at 11 microns. These changes are shown to be correlated with the changes in luminosity of micron Ceti in such a way that dust grain emission at 11 microns was increased more than the continuum during the period of maximum luminosity. The degree of the change in dust grain emission implies that the maximum dust temperature is in the range of 500 K to 700 K during minimum stellar luminosity.

Sutton, E. C.; Storey, J. W. V.; Townes, C. H.; Spears, D. L.

1977-01-01

130

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

131

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

132

Catalogue and bibliography of the UV Cet-type flare stars and related objects in the solar vicinity  

Microsoft Academic Search

This new catalogue of flare stars includes 463 objects. It contains astrometric, spectral and photometric data as well as information on the infrared, radio and X-ray properties and general stellar parameters. From the total reference list of about 3400 articles, partial lists selected by objects, authors, key words and by any pairs of these criteria can be obtained Tables 1,

R. E. Gershberg; M. M. Katsova; M. N. Lovkaya; A. V. Terebizh; N. I. Shakhovskaya

1999-01-01

133

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

134

The origin of the anomalous intensity ratio between very bright UV FeII lines and their satellites in gaseous condensations close to the star eta Carinae  

NASA Astrophysics Data System (ADS)

We present a model that explains the anomalous intensity ratios between each of two very bright UV lines of Fe II at 2507 Å and 2509 Å and its corresponding satellite line, observed in HST spectra of a compact gaseous condensation (blob B) in the vicinity of the star protect eta Car.The model is based on the assumption that the FeII transitions have a substantial optical thickness, which varies as a result of the photodepletion of the long-lived lower states, c4F7/2,9/2, by the intense Lyalpha radiation. In conditions where the photodepletion rates of these two states differ, the resonance scattering lengths of the spectral lines become different as well. In the presence of a weak, nonresonant (continuous) absorption, this gives rise to a difference in attenuation between the spectral lines (the Hummer effect (Hummer 1968)). It is the combination of these two effects that explains the anomalous (as compared with laboratory data) intensity ratios observed in the two pairs of UV FeII lines. Ionization channels of stimulated photodepletion by the Lyalpha radiation, including the possible role of autoionization levels, are considered.

Klimov, V.; Johansson, S.; Letokhov, V. S.

2002-04-01

135

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

136

Toward an Empirical Determination of the ZZ Ceti Instability Strip  

Microsoft Academic Search

We present atmospheric parameters for a large sample of DA white dwarfs that are known to be photometrically constant. For each star, we determine the effective temperature and surface gravity by comparing high signal-to-noise ratio optical spectra to the predictions of detailed model atmosphere calculations. We also report the successful prediction and detection of photometric variability in G232-38 based on

A. Gianninas; P. Bergeron; G. Fontaine

2005-01-01

137

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

138

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

139

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

NASA Technical Reports Server (NTRS)

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

1984-01-01

140

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

SciTech Connect

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

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

2012-04-20

141

Rest-frame UV-Optically Selected Galaxies at 2.3 <~ z <~ 3.5: Searching for Dusty Star-forming and Passively Evolving Galaxies  

NASA Astrophysics Data System (ADS)

A new set of color selection criteria (VJL) analogous with the BzK method is designed to select both star-forming galaxies (SFGs) and passively evolving galaxies (PEGs) at 2.3 <~ z <~ 3.5 by using rest-frame UV-optical (V - J versus J - L) colors. The criteria are thoroughly tested with theoretical stellar population synthesis models and real galaxies with spectroscopic redshifts to evaluate their efficiency and contamination. We apply the well-tested VJL criteria to the HST/WFC3 Early Release Science field and study the physical properties of selected galaxies. The redshift distribution of selected SFGs peaks at z ~ 2.7, slightly lower than that of Lyman break galaxies at z ~ 3. Comparing the observed mid-infrared fluxes of selected galaxies with the prediction of pure stellar emission, we find that our VJL method is effective at selecting massive dusty SFGs that are missed by the Lyman break technique. About half of the star formation in massive (M star > 1010 M ?) galaxies at 2.3 <~ z <~ 3.5 is contributed by dusty (extinction E(B - V) > 0.4) SFGs, which, however, only account for ~20% of the number density of massive SFGs. We also use the mid-infrared fluxes to clean our PEG sample and find that galaxy size can be used as a secondary criterion to effectively eliminate the contamination of dusty SFGs. The redshift distribution of the cleaned PEG sample peaks at z ~ 2.5. We find six PEG candidates at z > 3 and discuss possible methods to distinguish them from dusty contamination. We conclude that at least part of our candidates are real PEGs at z ~ 3, implying that these types of galaxies began to form their stars at z >~ 5. We measure the integrated stellar mass density (ISMD) of PEGs at z ~ 2.5 and set constraints on it at z > 3. We find that the ISMD grows by at least about a factor of 10 in 1 Gyr at 3 < z <5 and by another factor of 10 in the next 3.5 Gyr (1 < z < 3).

Guo, Yicheng; Giavalisco, Mauro; Cassata, Paolo; Ferguson, Henry C.; Williams, Christina C.; Dickinson, Mark; Koekemoer, Anton; Grogin, Norman A.; Chary, Ranga-Ram; Messias, Hugo; Tundo, Elena; Lin, Lihwai; Lee, Seong-Kook; Salimbeni, Sara; Fontana, Adriano; Grazian, Andrea; Kocevski, Dale; Lee, Kyoung-Soo; Villanueva, Edward; van der Wel, Arjen

2012-04-01

142

Novel Chemical Synthesis and Characterization of CeTi2O6 Brannerite.  

PubMed

Cerium titanate CeTi2O6 was prepared by a new soft chemistry route in aqueous solution. A suite of characterization techniques, including X-ray diffraction, thermal analysis, vibrational spectroscopy, and scanning and transmission electron spectroscopy, were employed to investigate the brannerite structure formation and its bulk properties. The synthesized powder formed the brannerite crystal structure upon calcination at temperatures as low as 800 °C. Samples sintered at 1350 °C possess a high level of crystallinity. X-ray absorption near-edge structure results indicate the presence of six-coordinated Ce(4+) in the brannerite samples. PMID:24926643

Kong, Linggen; Gregg, Daniel J; Karatchevtseva, Inna; Zhang, Zhaoming; Blackford, Mark G; Middleburgh, Simon C; Lumpkin, Gregory R; Triani, Gerry

2014-07-01

143

Magnetic field and activity of the single late-type giant ? Ceti  

NASA Astrophysics Data System (ADS)

We present the behavior of the magnetic field and activity indicators of the single late-type giant ? Ceti in the period June 19, 2010 - December 14, 2010. We used spectropolarimetric data obtained with two telescopes -- the NARVAL spectropolarimeter at Télescope Bernard Lyot, Pic du Midi, France and the ESPaDOnS spectropolarimeter at CFHT, Hawaii. The data were processed using the method of Least Square Deconvolution which enables to derive the mean photospheric profiles of Stokes I and V parameters. We measured the surface-averaged longitudinal magnetic field B_{l}, which varies in the interval 0.1 - 8.2 G, the line activity indicators CaII K, H?, CaII IR (854.2 nm), and radial velocity. By analyzing the B_{l} variations, a possible rotational period P = 118 days was identified. A single, large magnetic spot, which dominates the field topology, is a possible explanation for the B_{l} and activity indicator variations of ? Ceti.

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

144

O-star winds in the Magellanic Clouds and the Milky Way. A modified empirical analysis of UV P-Cygni profiles.  

NASA Astrophysics Data System (ADS)

UV P-Cygni profiles of OB-stars in the Magellanic Clouds (observed with HST), and the galaxy (observed with IUE) are analyzed empirically using a line formation procedure similar to the one described by Lamers et al. (1987). The assumption of a constant microturbulence vturb throughout the wind is dropped and replaced by a radially increasing turbulence parameter vturb(v), thus improving the fit for the emission peaks substantially, and at the same time avoiding the need for a justification of extremely supersonic turbulence in the vicinity of the wind's sonic point. The Sobolev optical depth is determined iteratively at fixed velocities in the wind, which removes the bias introduced by the choice of a specific parameterization function. Where it was possible and necessary a full photospheric spectrum was used to illuminate the wind line. The terminal velocities v? are found to be largest in the Galaxy, smallest in the Small Magellanic Cloud, and intermediate or similar to galactic in the Large Cloud.

Haser, S. M.; Puls, J.; Kudritzki, R.-P.

145

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

146

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

147

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

148

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

149

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...

150

Uv Upturn of Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

We investigate the UV upturn phenomenon of elliptical galaxies by applying the binary model of hot subdwarfs of Han et al. (2002, 2003). Preliminary results show that the model provides a natural explanation for the UV upturn phenomenon and that the model could be used to detect low level recent star formation.

Han, Z.; Podsiadlowski, Ph.; Lynas-Gray, A. E.

151

UV/H? Turmoil  

NASA Astrophysics Data System (ADS)

A great deal of our understanding of star formation in the local universe has been built upon an extensive foundation of H? observational studies. However, recent work in the ultraviolet (UV) with GALEX has shown that star formation rates (SFRs) inferred from H? in galactic environments characterized by low stellar and gas densities tend to be less than those based on the UV luminosity. The origin of the discrepancy is actively debated because one possible explanation is that the stellar initial mass function is systematically deficient in high mass stars in such environments. In this contribution, we summarize our work on this topic using a dwarf galaxy dominated sample of ˜300 late-type galaxies in the 11 Mpc Local Volume. The sample allows us to examine the discrepancy between H? and UV SFRs using a statistical number of galaxies with activities less than 0.1 M? yr-1. A range of potential causes for such an effect are reviewed. We find that while the IMF hypothesis is not inconsistent with our observations, alternate explanations remain that must be investigated further before a final conclusion can be drawn.

Lee, J. C.; de Paz, A. G.; Tremonti, C.; Kennicutt, R.; Loval Volume Legacy Team

2011-06-01

152

UV spectral analysis of very hot H-deficient [WCE]-type central stars of planetary nebulae: NGC 2867, NGC 5189, NGC 6905, Pb 6 and Sand 3  

NASA Astrophysics Data System (ADS)

We analysed ultraviolet Far Ultraviolet Spectroscopic Explorer, International Ultraviolet Explorer, and Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra of five of the hottest [WCE]-type central stars of planetary nebulae: NGC 2867, NGC 5189, NGC 6905, Pb 6, and Sand 3. The analysis leveraged on our grid of CMFGEN synthetic spectra, which covers the parameter regime of hydrogen-deficient central stars of planetary nebulae and allows a uniform and systematic study of the stellar spectra. The stellar atmosphere models calculated by us include many elements and ionic species neglected in previous analyses, which allowed us to improve the fits to the observed spectra considerably and provided an additional diagnostic line: the Ne VII ?973 Å, which had not been modelled in [WCE] spectra and which presents, in these stars, a strong P-Cygni profile. We report newly derived photospheric and wind parameters and elemental abundances. The central stars of NGC 2867, NGC 5189, and Pb 6 had their temperatures revised upward in comparison with previous investigations and we found the carbon to helium mass ratio of the sample objects to span a wide range of values, 0.42 < C: He < 1.96. Modelling of the Ne VII ?973 Å P-Cygni profile indicated strong neon overabundances for the central stars of NGC 2867, NGC 5189, NGC 6905, and Pb 6, with Ne mass fractions between 0.01 and 0.04. Nitrogen abundances derived by us for the central stars of NGC 5189, Pb 6, and Sand 3 are higher than previous determinations by factors of 3, 10, and 14, respectively.

Keller, Graziela R.; Bianchi, Luciana; Maciel, Walter J.

2014-08-01

153

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

PubMed

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

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

2014-01-01

154

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

155

Herschel PEP/HerMES: the redshift evolution (0 ? z ? 4) of dust attenuation and of the total (UV+IR) star formation rate density  

NASA Astrophysics Data System (ADS)

Using new homogeneous luminosity functions (LFs) in the far-ultraviolet (FUV) from VVDS and in the far-infrared (FIR) from Herschel/PEP and Herschel/HerMES, we studied the evolution of the dust attenuation with redshift. With this information, we were able to estimate the redshift evolution of the total (FUV + FIR) star formation rate density (SFRDTOT). By integrating SFRDTOT, we followed the mass building and analyzed the redshift evolution of the stellar mass density (SMD). This article aims at providing a complete view of star formation from the local Universe to z ~ 4 and, using assumptions on earlier star formation history, compares this evolution with previously published data in an attempt to draw a homogeneous picture of the global evolution of star formation in galaxies. Our main conclusions are that: 1) the dust attenuation AFUV is found to increase from z = 0 to z ~ 1.2 and then starts to decrease until our last data point at z = 3.6; 2) the estimated SFRD confirms published results to z ~ 2. At z > 2, we observe either a plateau or a small increase up to z ~ 3 and then a likely decrease up to z = 3.6; 3) the peak of AFUV is delayed with respect to the plateau of SFRDTOT and a probable origin might be found in the evolution of the bright ends of the FUV and FIR LFs; 4) using assumptions (exponential rise and linear rise with time) for the evolution of the star formation density from z = 3.6 to zform = 10, we integrated SFRDTOT and obtained a good agreement with the published SMDs. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

Burgarella, D.; Buat, V.; Gruppioni, C.; Cucciati, O.; Heinis, S.; Berta, S.; Béthermin, M.; Bock, J.; Cooray, A.; Dunlop, J. S.; Farrah, D.; Franceschini, A.; Le Floc'h, E.; Lutz, D.; Magnelli, B.; Nordon, R.; Oliver, S. J.; Page, M. J.; Popesso, P.; Pozzi, F.; Riguccini, L.; Vaccari, M.; Viero, M.

2013-06-01

156

UV-to-FIR Analysis of Spitzer\\/IRAC Sources in the Extended Groth Strip. II. Photometric Redshifts, Stellar Masses, and Star Formation Rates  

Microsoft Academic Search

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 mum 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.

Guillermo Barro; P. G. Pérez-González; Jesus Gallego; M. L. N. Ashby; Masaru Kajisawa; Satoshi Miyazaki; Victor Villar; Toru Yamada; Jaime Zamorano

2011-01-01

157

New Variable Stars Discovered from the Western Italian Alps I. Observations from Fields 12hr < RA < 24hr  

NASA Astrophysics Data System (ADS)

We present 20 new variable stars discovered at the Astronomical Observatory of the Autonomous Region of the Aosta Valley in the course of observations carried out from April to October 2010. The list of the newly discovered stars comprises 19 pulsating variables (two of them should be classified as Delta Scuti and 16 as Mira Ceti-type/Semi-Regular pulsators), and one W UMa eclipsing binary system. Our proposed variability classification relies on the properties of the optical differential light curves that we obtained using less than 1-meter class telescopes.

Damasso, Mario; Giacobbe, Paolo; Toso, Giorgio; Calcidese, Paolo; Bernagozzi, Andrea; Bertolini, Enzo; Sozzetti, Alessandro; Lattanzi, Mario G.; Perdoncin, Matteo; Smart, R.

2011-04-01

158

Symbiotic stars  

NASA Technical Reports Server (NTRS)

The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

Kafatos, M.; Michalitsianos, A. G.

1984-01-01

159

The thermal and spatial structure of the solar corona over the cycle and its implication for the coronae of inactive stars  

NASA Astrophysics Data System (ADS)

We use spectral (SOHO/SUMER and Hinode/EIS) and imaging (Hinode/XRT and SDO/AIA) solar coronal data to systematically measure the thermal structure of different types of solar features (coronal hole, quiet Sun, X-ray bright points, active regions...), and how they vary over the solar cycle. We use a combination of these structures to construct a model for the quiet corona of the inactive G8V star tau Ceti, which is a candidate stellar analog of a solar magnetic minimum. Since tau Ceti is significantly metal-poor relative to the Sun, we reconstruct the solar results with corresponding lower metallicities to generate more appropriate coronal structures.

Testa, P.; Landi, E.; Saar, S.

2012-12-01

160

Quantitative asteroseismology: Determination of the core composition and layering of the ZZ Ceti star R548. Part I  

NASA Astrophysics Data System (ADS)

We present a detailed asteroseismological study of the pulsating white dwarf R548 based on fits to newly detected periods and the use of the forward method. In this first part, we concentrate on the frequency extraction analysis. Based on an unexploited CFHT/LAPOUNE broadband photometric campaign of high S/N, we are able to obtain a finer frequency spectrum and uncover two triplets, two doublets, and two singlets. The low-amplitude and "simple" pulsator R548 is an ideal candidate for carrying on a complete asteroseismological analysis within the framework of the adiabatic approximation to obtain optimized structural parameters, including the envelope layering and the bulk composition of the core.

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

2013-03-01

161

3 Ms in the Life of ? Ceti: Sustained Flare Activity on a Clump Giant Detected by the Extreme Ultraviolet Explorer  

NASA Astrophysics Data System (ADS)

A 34 day Extreme Ultraviolet Explorer (EUVE) pointing on the ``clump'' giant ? Ceti (HD 4128; K0 III) recorded a series of striking coronal flare events, reminiscent of a singular outburst seen previously from ? Velorum (HD 93497; G6 III + dF). The recent flaring episode contrasts with a more placid behavior in a 6 day EUVE observation of ? Cet 6 years earlier. The average 70-180 Å Deep Survey count rate in the new observation is twice as high, and the 75-150 Å spectrum displays a distinct hardening. The discovery of sustained flare activity on ? Cet raises the possibility that such episodes are more common than suspected among the core helium-burning giants and sharpens the puzzle of the survival of magnetic activity beyond helium flash.

Ayres, Thomas R.; Osten, Rachel A.; Brown, Alexander

2001-11-01

162

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

163

Cool luminous stars  

NASA Technical Reports Server (NTRS)

The consequences of magnetic fields for the atmospheres of cool stars are addressed based on IUE and Einstein Observatory observations. Gross atmospheric structure data for cool luminous stars are discussed, and the relevance of the observations for the energy balance and nonradiative heating rates is considered. Data from X-ray fluxes, low dispersion UV spectra, and high dispersion spectra in the region of the Mg II resonance lines are presented. New results on cool star atmospheres provided by high dispersion UV spectra are considered, including those pertaining to spectral line identification, identification of emission components in close binary systems, densities and atmospheric extension, emission line widths, properties of stellar winds as derived from IUE data, and systematic flows of transition region plasma. An explanation for the observed spectra of cool giants and supergiants is proposed in terms of active, quiet, and hybrid stars.

Linsky, J. L.

1982-01-01

164

UV SPECTRAL SYNTHESIS OF VEGA  

SciTech Connect

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

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

2010-12-20

165

Hiden Star Formation: The Ultraviolet Perspective  

Microsoft Academic Search

Many recent estimates of the star formation rate density at high redshift rely on rest-frame ultraviolet (UV) data. These are highly sensitive to dust absorption. Applying a correlation between the far-infrared (FIR) to UV flux ratio and UV color found in a local starbursts to galaxy samples out to z ~ 3, one can account for most of the FIR

G. R. Meurer; T. M. Heckman; M. Seibert; J. D. Goldader; D. Calzetti; D. Sanders; C. C. Steidel

2000-01-01

166

The ultraviolet reddening of Be stars  

NASA Astrophysics Data System (ADS)

The UV extinction of several bright Be stars is examined in light of Schild's (1978) demonstration of their intrinsic (B-V) color excess. Stars possessing this excess are found not to have the 0.22-micron bump associated with Bless and Savage's (1972) interstellar reddening law. The bright Be stars studied are HD 30076, HD 58011, HD 63462, and HD 105435.

Schild, R.

1983-04-01

167

Chromospheres of Cool Stars.  

National Technical Information Service (NTIS)

Progress in understanding the nature and origin of cool star chromospheres and transition regions since the launch of IUE is reviewed. While previous observations in the visible and UV regions laid the foundations for present work, the nature of the IUE i...

C. Jordan

1986-01-01

168

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

169

UV activity indicators  

NASA Astrophysics Data System (ADS)

In Order to continue the work displayed in Buccino & Mauas(2003) and Buccino (2003), we have calculated the index Mg II (Xhk) on 1640 high resolution IUE spectra of 269 main sequence stars of spectral classes F, G and K. From this set of observations, we found an exponential relation between the continuum UV flux and the color (B-V). Contrary to Schrijver et al (1989), who assumed that the continuum UV flux depended on the color following the relation found by Rutten (1984) for the visible one, i.e. the logarithm of the flux is proportional to a polynomial of third order with the color. Nevertheless, the exponential relation flux in the continuous UV and the color (B-V) fits far better to our data that the given one by Rutten (1984). Obtained this dependency for the ultraviolet continuum flux, the index Xhk can be obtained from the single flux in the lines core, allowing to calculate the index of Mg II for those spectra where the continuum is very dark and so the relation signal noise is very low. As it were already reported in previous works (Rutten (1991), Schrijver (1992)), we found a minimum basal flux in the Mg II h and k lines core due to the cromospheric heating by disipation of acustics waves. From this minimum flux, we calculated minimum index of activity that satisfactorily fits to the minimum values of the indexes calculated on the 1640 spectra like quotient between the flux in the line core and the continuous one.

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

170

IUE observations of the high-velocity symbiotic star AG Draconis. III. A compendium of 17 years of UV monitoring, and comparison with optical and X-ray observations  

NASA Astrophysics Data System (ADS)

We present the first extensive analysis of the ultraviolet observations with the IUE mission of the high velocity symbiotic system AG Draconis, covering the period June 1979-February 1996 which included three active phases of the system with six light maxima. The low resolution IUE line and continuum fluxes are compared with optical observations and with archival X-ray data. The analysis of the IUE observations near minimum (quiescence) led us to find that during the orbital motion the hot WD component is not eclipsed, in agreement with a non large inclination of the binary orbit. The larger modulation of the N v, C iV, He ii, and O i lines with respect to the intercombination lines may indicate that the former are formed in a region near the line connecting the two stars, probably slightly receding, while the latter lines originate in an extended ionized nebula surrounding the white dwarf. Large orbit-to-orbit variation are probably associated with fluctuation of the K-star wind density. From the He ii line we determine for the WD during quiescence a Zanstra temperature of 109600+/-5400çK, implying, at a distance of 2.5 kpc, a radius of 0.08+/-0.01 Rsun, and a luminosity of 900+/-200 Lsun. During the different outbursts AG Dra displayed a variety of behaviours. According to the strength of the He ii/FUV continuum ratio we have identified cool and hot outbursts. In fact, during the ``minor'' 1985-1986 outbursts the peak fluxes of the high ionization emission lines was comparable with those during the 1980-83 and 1994-95 major outbursts. The white dwarf temperature decreased to about 90000çK during the ``cool'' outbursts, while it increased to 120000-130000çK during the 1985-86 ``hot'' outbursts. The behaviour during the major (``cool'') outbursts is explained by expansion and cooling of the white dwarf atmosphere, which explains the marked anticorrelation between optical/UV and X-ray fluxes. The minimum X-ray flux observed also during the minor (``hot'') outbursts might be attributed to the increased opacity of the WD envelope and wind to photons shortward the N(+4) ionization limit. We also note that the beginning of the last activity phase of AG Dra was marked by the temporary appearance in July 1994 of strong P Cygni absorptions in the high ionization resonance lines with quite high terminal velocities of at least 700 km s(-1) . Based on observations made with the International Ultraviolet Explorer collected at the Villafranca Satellite Tracking Station and retrieved from the IUE-INES Archive, on ROSAT observations, and on optical observations collected at the Asiago Observatory of the Padova Astronomical Observatory.

González-Riestra, R.; Viotti, R.; Iijima, T.; Greiner, J.

1999-07-01

171

Correlation of Maxima in Long-Period Variable Stars: From Eddington to Present Time  

NASA Astrophysics Data System (ADS)

Eddington during the years of pioneering in General Relativity worked also in observational statistics of variable stars, and proposed a model for Cepheids' pulsation. The statistical analysis of time series of long-period variable stars (Mira): Mira Ceti and ? Cygni made by Eddington and Plakidis in 1929 has been extended to luminosities dominion and to R Leonis and R Hydrae. The difference between consecutive maxima ?M is negatively correlated with the magnitude M of the first maximum of the pair. Bright maxima are preferentially followed by dim ones, excepted for R Hydrae. It shows a possible two-periods time pattern of its maxima, which makes easier predictions of its maxima. Our two-points correlation analysis is still not enough to give a satisfactory predictive model of maxima sequence.

Sigismondi, Costantino

2006-02-01

172

Mass loss from evolved stars. II - Radio continuum emission and evolution to planetary nebulae  

NASA Technical Reports Server (NTRS)

The radio continuum properties of cool evolved stars are investigated from the viewpoint of mass loss mechanisms and evolution through the planetary nebula stage. The VLA was used to search 32 high mass loss rate objects for 6-cm continuum emission, leading to the detection of NGC 7027, CRL 618, R Aqr, IRC + 10216, and Omicron Ceti. The evolution of such objects to the planetary nebula stage was studied by calculating the propagation of an ionization front into the remnant neutral envelope that is produced by continuous mass loss in the red giant stage. It is found that none of the stars has a hot, compact companion, except for the known cases of R Aqr and Mira, and that envelope fractional ionization is in most cases as small as less than about 0.001.

Spergel, D. N.; Giuliani, J. L., Jr.; Knapp, G. R.

1983-01-01

173

Ce-Ti amorphous oxides for selective catalytic reduction of NO with NH3: confirmation of Ce-O-Ti active sites.  

PubMed

The amorphous Ce-Ti mixed oxides were reported to be catalysts for selective catalytic reduction of NO(x) with NH(3), in which Ce and not Ti acts as their solvent in spite of the fact that Ce is low in content. The amorphous catalysts were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with selective area electron diffraction (SAED). The Ce-Ti amorphous oxide shows higher activity than its crystalline counterpart at lower temperatures. Moreover, the presence of small CeO(2) crystallites as for the impregnated sample is deleterious to activity. The Ce-O-Ti short-range order species with the interaction between Ce and Ti in atomic scale was confirmed for the first time to be the active site using temperature programmed reduction with H(2) (H(2)-TPR), in situ FTIR spectra of NO adsorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine-structure (XAFS). Lastly, the Ce-O-Ti structure was directly observed by field-emission TEM (FETEM). PMID:22888951

Li, Ping; Xin, Ying; Li, Qian; Wang, Zhongpeng; Zhang, Zhaoliang; Zheng, Lirong

2012-09-01

174

Wf/pc Cycle 1 Calib: 4-CHIP UV Calibration  

NASA Astrophysics Data System (ADS)

THIS PROGRAM CALIBRATES THE QE OF THE WFC AND PC IN THE ULTRAVIOLET (F194W, F230W, AND F284W). This calibration is done for each CCD detector using exposures of a UV flux standard star. This program is intended for use only during a UV campaign.

MacKenty, John

1991-07-01

175

Wf/pc Cycle 2 Calib: Single Chip UV Calibration  

NASA Astrophysics Data System (ADS)

THIS PROGRAM CALIBRATES THE QE OF THE WFC AND PC IN THE ULTRAVIOLET (F194W, F230W, AND F284W). This calibration is done using exposures of a UV flux standard star. This program is intended for use only following a UV decontamination.

MacKenty, John

1992-07-01

176

Evolution of the Solar Activity Over Time and Effects on Planetary Atmospheres. II. ?1 Ceti, an Analog of the Sun when Life Arose on Earth  

NASA Astrophysics Data System (ADS)

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 ?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?, 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? line core. From careful spectral analysis and the comparison of different methods, we propose for ?1 Cet the following atmospheric parameters: T eff = 5665 ± 30 K (H? 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 ?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 ?1 Cet in the interval ~0.4-0.8 Gyr and the analysis of the theoretical Hertzsprung-Russell diagram (H-R) suggests a mass ~1.04 M 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. Based on spectroscopic observations collected at the Observatório do Pico dos Dias (OPD), operated by the Laboratório Nacional de Astrofísica, CNPq, Brazil, at the European Southern Observatory (ESO), within the ON/ESO and ON/IAG agreements, under FAPESP project no. 1998/10138-8, and with the Hubble Space Telescope.

Ribas, I.; Porto de Mello, G. F.; Ferreira, L. D.; Hébrard, E.; Selsis, F.; Catalán, S.; Garcés, A.; do Nascimento, J. D., Jr.; de Medeiros, J. R.

2010-05-01

177

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

178

Hot Subdwarf Stars  

NASA Astrophysics Data System (ADS)

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

Heber, Ulrich

2009-09-01

179

UV-based therapy.  

PubMed

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

Totonchy, Mariam B; Chiu, Melvin W

2014-07-01

180

Birds, berries and UV  

NASA Astrophysics Data System (ADS)

The problem of UV vision in vertebrates is briefly discussed in its historical context. For example, UV vision has been demonstrated in some birds by several authors. Hence the reflectances of plumage, petals of bird-pollinated flowers and of berries in the near UV may play an important rôle within the visual environment of birds. Some data obtained by means of UV photography are presented, and it is shown, that the waxlayer of glaucous fruits is highly reflective in the UV.

Burkhardt, Dietrich

1982-04-01

181

Radiative and Kinetic Feedback by Low-Mass Primordial Stars  

NASA Astrophysics Data System (ADS)

Ionizing UV radiation and supernova (SN) flows amidst clustered minihalos at high redshift regulated the rise of the first stellar populations in the universe. Previous studies have addressed the effects of very massive primordial stars on the collapse of nearby halos into new stars, but the absence of the odd-even nucleosynthetic signature of pair-instability SNe in ancient metal-poor stars suggests that Population III stars may have been less than 100 M sun. We extend our earlier survey of local UV feedback on star formation to 25-80 M sun stars and include kinetic feedback by SNe for 25-40 M sun stars. We find radiative feedback to be relatively uniform over this mass range, primarily because the larger fluxes of more massive stars are offset by their shorter lifetimes. Our models demonstrate that prior to the rise of global UV backgrounds, Lyman-Werner (LW) photons from nearby stars cannot prevent halos from forming new stars. These calculations also reveal that violent dynamical instabilities can erupt in the UV radiation front enveloping a primordial halo, but that they ultimately have no effect on the formation of a star. Finally, our simulations suggest that relic H II regions surrounding partially evaporated halos may expel LW backgrounds at lower redshifts, allowing stars to form that were previously suppressed. We provide fits to radiative and kinetic feedback on star formation for use in both semianalytic models and numerical simulations.

Whalen, Daniel; Hueckstaedt, Robert M.; McConkie, Thomas O.

2010-03-01

182

Statistical Properties of Galactic ? Scuti Stars: Revisited  

NASA Astrophysics Data System (ADS)

We present statistical characteristics of 1578 ? 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 Rodríguez 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 ? 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 Rodríguez's work. All the ? 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 ? 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.; Protopapas, P.; Kim, D.-W.; Byun, Y.-I.

2013-05-01

183

Star Formation  

NASA Astrophysics Data System (ADS)

Stars are one of the most important constituents of the Universe, and understanding their formation is crucial to many areas of astrophysics. Stars form from dense molecular gas, and they tend not to form in isolation. Stars often form in binary and multiple systems, and these systems tend to form in clusters with 102-105 members. Stars also form with a wide range of masses, from substellar brown dwarfs with masses < 0. 1 M ? to massive stars > 100 M ?, and wherever stars form the distribution of their masses seems always to be the same. This chapter will review our current understanding of star formation from cold gas to young star clusters.

Goodwin, Simon

184

UVMag: a UV+visible spectropolarimeter to study stellar magnetospheres  

NASA Astrophysics Data System (ADS)

In the last decade magnetic fields have been detected in basically all types of stars. These discoveries gave rise to innovative studies on the mapping of magnetic fields and on their impact on stellar environment. To go even further, the UVMag international consortium proposes to combine UV and visible spectropolarimetry. The UV domain allows us to study stellar winds, while the optical domain allows us to study the stellar surface. With UV and visible spectropolarimetry we can then study magnetospheres as a whole and do this over a complete stellar rotation period thanks to a space mission. UV and visible spectropolarimetry can of course also address many other stellar physics issues.

Neiner, C.

2012-12-01

185

Protosteller Disks Under the Influence of Winds and UV Radiation  

NASA Technical Reports Server (NTRS)

Star formation and the creation of protostellar disks generally occur in a crowded environment. Nearby young stars and protostars can influence the disks of their closets neighbors by a combination of outflows and hard radiation. The central stars themselves can have a stellar wind and may produce sufficient UV and X-ray to ultimately destroy their surrounding disks. Here we describe the results of numerical simulations of the influence that an external UV source and a central star's wind can have on its circumstellar disk. The numerical method (axial symmetry assumed) is described elsewhere. We find that protostellar disks will be destroyed on a relatively short time scale ( 10(sup 5)yr) unless they are well shielded from O-stars. Initially isotropic T-Tauri winds do not significantly influence their disks, but instead are focused toward the rotation axis by the disk wind from photoevaporation.

Yorke, H. W.

2003-01-01

186

Hubble Space Telescope spectroscopy of OB stars in M31  

NASA Technical Reports Server (NTRS)

We have obtained UV spectra of two luminous hot stars in M31 with the Hubble Space Telescope. The stars are of late O and WN spectral type and lie on opposite sides of M31. We derive UV extinction curves for M31 which differ from both the Galaxy and the LMC. We find differences between the IS absorbers in both lines of sight in M31 and in the Galactic halo. The stellar wind-driven mass loss of the stars is found to be 10 times lower than in similar Galactic stars. One star appears to be an eclipsing W-R binary.

Hutchings, J. B.; Bianchi, L.; Lamers, H. J. G. L. M.; Massey, P.; Morris, S. C.

1992-01-01

187

The Star Formation Rate In Nearby Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

Small amounts of star formation in normal elliptical galaxies are suggested by several results: some surprisingly young ages from optical line-index dating; cooling X-ray gas; and mid-IR dust emission. Previously, it was difficult to detect low levels of star formation, but UV imaging with WFPC3 will permit us to conclusively identify individual O/B stars in nearby normal ellipticals by their UV colors and magnitudes. This technique is orders of magnitude more sensitive than previous methods, allowing detections of star formation to levels of 1E-4 Msolar/yr. Proof of concept is provided by a very long UV ACS observation of M87 that revealed many O/B stars. We propose observations of four normal ellipticals where recent star formation is likely. This will yield their star formation rates and the locations of such activity.;

Bregman, Joel

2008-07-01

188

Strange stars  

Microsoft Academic Search

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

Charles Alcock; Edward Farhi; Angela Olinto

1986-01-01

189

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

190

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

191

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

192

Be Stars  

NASA Astrophysics Data System (ADS)

A Be star (pronounced `bee-ee' star) is a non-supergiant B-type star whose spectrum displays or has displayed one or more Balmer lines in emission and Be is the notation for the spectral classification of such a star (see also CLASSIFICATION OF STELLAR SPECTRA). `Classical' Be stars are believed to have acquired the circumstellar (CS) material that produces the Balmer emission through ejection of...

Peters, G.; Murdin, P.

2000-11-01

193

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

2012-09-20

194

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

195

A Comparison of Star Formation Rate Indicators for Galaxies  

NASA Astrophysics Data System (ADS)

With the multi-wavelength data from UV to sub-millimeter in the region of H-ATLAS (Herschel Astrophysical Terahertz Large Area Survey) Science Demonstration Phase (SDP), in combination with the population synthesis model and dust model, the total infrared luminosities of the galaxies were calculated. On this basis, for respectively the strong and weak star-forming galaxies, we studied the differences in the star formation rates calculated by the UV luminosity, infrared luminosity and H? line, as well as the intrinsic physical origin of such differences. It was found that for the galaxies of strong star-formation activity, the 3 kinds of star formation rate indicators give the basically consistent results with a small dispersion. But at the end of high star formation rate, the star formation rate calculated by the UV luminosity is slightly smaller than that calculated by the H?-line ?ux; at the end of low star formation rate, the UV indicator tends to be greater than the H? indicator; and at both ends, the infrared indicator and H? indicator have no significant difference. For the weak star-forming galaxies, significant differences exist among the 3 kinds of indicators, and there is a rather large dispersion. The dispersions and systematic difference of the star formation rates calculated by the UV luminosity and H? line increase with the galactic age and mass. The main cause for the increased systematic difference is that when the extinction of an weak star-forming galaxy is calibrated by its UV continuum spectral slope ?, the UV extinction of the galaxy is overestimated, it makes the UV luminosity tends to be large after the extinction correction. In addition, the star formation rates (H?) of weak starforming galaxies in the MPA/JHU (Max Planck Institute for Astrophysics/Johns Hopkins University) database are generally less than the real values.

Fan, Dong-xin; Li, Jin-rong; Pan, Zhi-zheng; Shi, Fei; Fang, Guan-wen; Kong, Xu

2013-04-01

196

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

197

Spectroscopic Observations of Nearby Low Mass Stars  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

198

Far-UV Radiation of the Early Sun  

NASA Technical Reports Server (NTRS)

Far-UV radiation is responsible for the photolysis of important greenhouse gases such as CO2, NH3 (ammonia), CH4 (methane) and more generally, the global UV photochemistry of the early atmosphere. In our project, we are concentrating on the young Sun's effect on methane, since UV sunlight (lambda less than 1450 Angstroms) was the main destruction mechanism for methane in the early Earth's atmosphere. Since the UV luminosity of the early Sun cannot be calculated a priori; it can only be estimated from observations of stars similar to the young Sun. We report our results based on Hubble + FUSE spectra of stars selected from Gaidos (1998) Catalog of Nearby Young Solar Analogs (YSA's).

Heap, Sally

2005-01-01

199

Ultraviolet properties of the symbiotic stars  

NASA Technical Reports Server (NTRS)

A general discussion of the UV spectra of symbiotic stars, including both the emission lines and the continua, is presented, with AG Pegasi considered as an illustrative example. It is noted that the IUE observations of the symbiotics have revealed UV properties which rival the diversity of the optical features. Nevertheless, the UV data have for the first time permitted the hot component to be studied relatively uncontaminated by the giant companion, which dominates the optical regime. The UV observations provide convincing evidence that many of the symbiotics have hot stellar companions embedded in the enshrouding nebula or accretion shell formed from the wind from one or possibly both of the components.

Slovak, M. H.; Lambert, D. L.

1982-01-01

200

STAR Publications  

Cancer.gov

STAR Publications The following citations are of reports that have been published in the scientific literature concerning the Study of Tamoxifen and Raloxifene (STAR). The citations are listed in reverse chronological order.

201

Science with a Wide-field UV Transient Explorer  

NASA Astrophysics Data System (ADS)

The time-variable electromagnetic sky has been well-explored at a wide range of wavelengths. In contrast, the ultra-violet (UV) variable sky is relatively poorly explored, even though it offers exciting scientific prospects. Here, we review the potential scientific impact of a wide-field UV survey on the study of explosive and other transient events, as well as known classes of variable objects, such as active galactic nuclei and variable stars. We quantify our predictions using a fiducial set of observational parameters which are similar to those envisaged for the proposed ULTRASAT mission. We show that such a mission would be able to revolutionize our knowledge about massive star explosions by measuring the early UV emission from hundreds of events, revealing key physical parameters of the exploding progenitor stars. Such a mission would also detect the UV emission from many tens of tidal-disruption events of stars by supermassive black holes at galactic nuclei and enable a measurement of the rate of such events. The overlap of such a wide-field UV mission with existing and planned gravitational-wave and high-energy neutrino telescopes makes it especially timely.

Sagiv, I.; Gal-Yam, A.; Ofek, E. O.; Waxman, E.; Aharonson, O.; Kulkarni, S. R.; Nakar, E.; Maoz, D.; Trakhtenbrot, B.; Phinney, E. S.; Topaz, J.; Beichman, C.; Murthy, J.; Worden, S. P.

2014-04-01

202

STAR System.  

ERIC Educational Resources Information Center

The STAR System is a developmental guidance approach to be used with elementary school children in the 5th or 6th grades. Two basic purposes underlie STAR: to increase learning potential and to enhance personal growth and development. STAR refers to 4 basic skills: sensory, thinking, adapting, and revising. Major components of the 4 skills are:…

Doverspike, James E.

203

A Survey of UV Interstellar Absorption Lines with STIS  

Microsoft Academic Search

We are using HST to conduct a survey of UV spectra of 21 stars over the wavelength intervals 1160 to 1361 Angstroms and 1626 to 1906 Angstroms, using the highest resolution echelle gratings of STIS (E140H and E230H) and its narrowest entrance aperture (0.1x 0.03 arc sec). The target stars were selected according to the criteria (1) spectral type earlier

E. B. Jenkins; T. M. Tripp; C. W. Bowers; F. Roesler; R. J. Reynolds; L. M. Haffner

1999-01-01

204

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

205

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

206

NGC 4656UV: A UV-SELECTED TIDAL DWARF GALAXY CANDIDATE  

SciTech Connect

We report the discovery of a UV-bright tidal dwarf galaxy (TDG) candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet, we investigate the gas kinematics and stellar properties of this system. The H I morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M{sub Sun} yr{sup -1} from the far-ultraviolet flux and measure a total H I mass of 3.8 Multiplication-Sign 10{sup 8} M{sub Sun} for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low-metallicity system whose only major burst of star formation occurred within the last {approx}260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object-whether it is tidal or pre-existing in origin-in the context of its metallicity being a factor of 10 lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates.

Schechtman-Rook, Andrew; Hess, Kelley M., E-mail: andrew@astro.wisc.edu, E-mail: hess@ast.uct.ac.za [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States)

2012-05-10

207

Are all Trapezium stars magnetic?  

NASA Astrophysics Data System (ADS)

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

Montmerle, T.

208

Ground-State SiO Maser Emission toward Evolved Stars  

NASA Astrophysics Data System (ADS)

We have made the first unambiguous detection of vibrational ground-state maser emission from 28SiO toward six evolved stars. Using the Very Large Array (VLA), we simultaneously observed the v=0,J=1-0, 43.4 GHz ground-state transitions and the v=1,J=1-0, 43.1 GHz first excited-state transitions of 28SiO toward the oxygen-rich evolved stars IRC +10011, o Ceti, W Hya, RX Boo, NML Cyg, and R Cas and the S-type star ? Cyg. We detected at least one v=0 SiO maser feature from six of the seven stars observed, with peak maser brightness temperatures ranging from 10,000 to 108,800 K. In fact, four of the seven v=0 spectra show multiple maser peaks, a phenomenon that has not been previously observed. Ground-state thermal emission was detected for one of the stars, RX Boo, with a peak brightness temperature of 200 K. Comparing the v=0 and v=1 transitions, we find that the ground-state masers are much weaker, with spectral characteristics different from those of the first excited-state masers. For four of the seven stars, the velocity dispersion is smaller for the v=0 emission than for the v=1 emission; for one star, the dispersions are roughly equivalent; and for two stars (one of which is RX Boo), the velocity spread of the v=0 emission is larger. In most cases, the peak flux density in the v=0 emission spectrum does not coincide with the v=1 maser peak. Although the angular resolution of these VLA observations was insufficient to completely resolve the spatial structure of the SiO emission, the SiO spot maps produced from the interferometric image cubes suggest that the v=0 masers are more extended than their v=1 counterparts.

Boboltz, D. A.; Claussen, M. J.

2004-06-01

209

Optical and ultraviolet spectroscopy of three F + B binary stars  

NASA Astrophysics Data System (ADS)

Optical and ultraviolet spectroscopy is presented for three F + B objects that are members of the first group of strongly interacting, F II + B systems. The data obtained confirm that HD 59771, HD 242257, and CoD -30 5135 are all binary star systems consisting of a luminous F-type component and a B star. Strong, variable H-alpha emission is seen in all the stars. It is found that the UV spectrum of HD 59771 resembles the spectrum of HD 207739. CoD -30 5135 has the most dramatic mid-UV spectrum seen among the scores of observed cool + hot star systems.

Bopp, Bernard W.; Dempsey, Robert C.; Parsons, Sidney B.

1991-05-01

210

Time-resolved UV spectroscopy of BE Ursae Majoris  

NASA Technical Reports Server (NTRS)

Far-ultraviolet spectra have been obtained of the eclipsing, hot subdwarf binary, BE UMa, with phase coverage in the 2.3-day orbital period concentrated near minimum light. No clearly phase-related spectra changes were found, but the UV continuum appeared to be in a highly variable state, with changes of a factor of two occurring on a time scale of hours. The hot star in this system may be one of the few known PG1159-035 variables, which show nonradial pulsations. If so, this is the first such star known in a binary system and thus should be important for determining the physical properties of these stars.

Hutchings, J. B.; Cowley, A. P.

1985-01-01

211

Star-Forming or Starbursting? The Ultraviolet Conundrum  

Microsoft Academic Search

Compared to starburst galaxies, normal star-forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-beta diagram (the IR\\/UV ratio \\

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

2009-01-01

212

Massive star formation in galaxies with excess ultraviolet emission  

NASA Astrophysics Data System (ADS)

From an analysis of almost 2000 Galaxy Evolution Explorer images of galaxies with morphological types ranging from E to Sab, we have found a significant subset (28 per cent) that show ultraviolet (UV) emission outside R25. We have obtained H? imaging of 10 such galaxies, and found that their star formation rates are similar in the UV and in H?, with values ranging from a few tenths to a few M? yr-1. Probably because our sample selection is biased towards star-forming galaxies, these rates are comparable to those found in disc galaxies, although the star formation rates of the elliptical galaxies in our sample are well below 1 M? yr-1. We confirm that the extended UV emission in our sample is caused by massive star formation in outer spiral arms and/or outer (pseudo) rings, rather than by alternative mechanisms such as the UV upturn.

Erroz-Ferrer, Santiago; Knapen, Johan H.; Mohd Noh Velastín, Elena A. N.; Ryon, Jenna E.; Hagen, Lea M. Z.

2013-12-01

213

Stationary Star  

NSDL National Science Digital Library

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

214

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

215

UV, stress and aging  

PubMed Central

Skin is a model of choice in studies on aging. Indeed, skin aging can be modulated by internal and external factors, reflecting its complexity. Two types of skin aging have been identified: intrinsic, mainly genetically determined and extrinsic—also called "photo-aging"—resulting on the impact of environmental stress and more precisely of UV rays. Simplified in vitro models, based on cellular senescence, have been developed to study the relationship between UV and aging. These models vary on the cell type (fibroblasts or keratinocytes, normal or immortalized) and the type of UV used (UVA or UVB).

Debacq-Chainiaux, Florence; Leduc, Cedric; Verbeke, Alix; Toussaint, Olivier

2012-01-01

216

Radiative regulation of Population III star formation  

NASA Astrophysics Data System (ADS)

We explore the impact of ultraviolet (UV) radiation from massive Population III (Pop III) stars of 25, 40, 80 and 120Msolar on the subsequent Pop III star formation. In this paper, particular attention is paid to the dependence of radiative feedback on the mass of source Pop III star. UV radiation from the source star can work to impede the secondary star formation through the photoheating and photodissociation processes. Recently, Susa and Umemura have shown that the ionizing radiation alleviates the negative effect by H2-dissociating radiation from 120Msolar Pop III star, since an H2 shell formed ahead of an ionizing front can effectively shield H2-dissociating radiation. On the other hand, it is expected that the negative feedback by H2-dissociating radiation can be predominant if a source star is less massive, since a ratio of the H2-dissociating photon number to the ionizing photon number becomes higher. In order to investigate the radiative feedback effects from such less massive stars, we perform three-dimensional radiation hydrodynamic simulations, incorporating the radiative transfer effect of ionizing and H2-dissociating radiation. As a result, we find that if a source star is less massive than ~25Msolar, the ionizing radiation cannot suppress the negative feedback of H2-dissociating radiation. Therefore, the fate of the neighbouring clouds around such less massive stars is determined solely by the flux of H2-dissociating radiation from source stars. By making analytic estimates of H2 shell formation and its shielding effect, we derive the criteria for radiation hydrodynamic feedback depending on the source star mass.

Hasegawa, K.; Umemura, M.; Susa, H.

2009-05-01

217

Advanced Spectral Library (ASTRAL): Cool stars edition  

NASA Astrophysics Data System (ADS)

ASTRAL is a project to create high-resolution, high-S/N UV (1150-3200 Å) atlases of bright stars utilizing {HST}/STIS. During Cycle 18 (2010-2011), eight cool star targets were observed, including key objects like Procyon and Betelgeuse, churning through 146 orbits in the process. The new spectral atlases are publically available through the project website. Data were obtained with the Hubble Space Telescope.

Ayres, T. R.

2013-02-01

218

X-ray sources in regions of star formation. II - The pre-main-sequence G star HDE 283572  

NASA Technical Reports Server (NTRS)

This paper reports the detection of HDE 283572, a ninth-magnitude G star 8 arcmin south of RY Tau, as a bright X-ray source. The observations reveal this object to be a fairly massive (about 2 solar masses) pre-main-sequence star associated with the Taurus-Auriga star formation complex. It exhibits few of the characteristics of the classical T Tauri stars and is a good example of a 'naked' T Tauri star. The star is a mid-G subgiant, of about three solar radii and rotates with a period of 1.5 d. The coronal and chromospheric surface fluxes are similar to those of the most active late type stars (excluding T Tauri stars). The X-ray and UV lines most likely arise in different atmospheric structures. Radiative losses are some 1000 times the quiet solar value and compare favorably with those of T Tauri stars.

Walter, F. M.; Brown, A.; Linsky, J. L.; Rydgren, A. E.; Vrba, F.

1987-01-01

219

Detecting UV Light  

NSDL National Science Digital Library

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

220

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. M.; Groenewegen, M.; Mohamed, S.

2014-04-01

221

The evolution of protostellar disks under the influence of external UV radiation and central stellar winds  

NASA Technical Reports Server (NTRS)

The evolution and appearance of circumstellar disks in star forming regions can be influenced strongly by the radiation from nearby hot stars. Here we describe the results of numerical simulations of the evolution of protostellar disks and their immediate surroundings under the influence of external UV radiation.

Yorke, H. W.; Richling, S.

2001-01-01

222

Star Images, Star Performances (College Course File).  

ERIC Educational Resources Information Center

Describes a course that focuses attention on the position of the actor, especially the star actor, in cinematic and television signification. Divides the course into three sections: "The Star System,""Stars as Images," and "Star Performance." (RS)

Butler, Jeremy G.

1990-01-01

223

Ultraviolet photometry with the Astronomical Netherlands Satellite /ANS/ - Faint blue stars in the halo  

NASA Technical Reports Server (NTRS)

Blue stars at high galactic latitudes have been observed with the UV telescope on board ANS. In this paper a subset of the collected data pertaining to the cooler stars is discussed. Most of them have energy distributions in general agreement with the visual spectral type. One star is exceptionally blue, and of seven possible horizontal-branch stars, two have UV energy distributions distinct from main-sequence stars in the sense that they have an excess at 1550 A and a large Balmer jump.

De Boer, K. S.; Wesselius, P. R.

1980-01-01

224

UV-upturn of elliptical galaxies model (Han+, 2007)  

NASA Astrophysics Data System (ADS)

A long-standing problem in the study of elliptical galaxies is the far-ultraviolet (FUV) excess in their spectra (also known as UV-upturn, UV rising-branch, UV rising flux, or UVX). While it is now clear that this UV excess is caused by an old population of hot helium-burning stars without large hydrogen-rich envelopes. We have developed an evolutionary population synthesis (EPS) model for the FUV excess of elliptical galaxies based on the binary model of Han et al. (2002MNRAS.336..449H and 2003MNRAS.341..669H) for the formation of hot subdwarfs in our Galaxy. We give the colour evolution of a simple stellar population (SSP) (including binaries) of 1010M{sun} for our standard simulation set. We have also compiled a file for the SED evolution, in which the SEDs without binary interactions are also supplied. (4 data files).

Han, Z.; Podsiadlowski, P.; Lynas-Gray, A. E.

2007-10-01

225

HIRES Dust Imaging of the NGC 6334 Star Forming Complex  

NASA Technical Reports Server (NTRS)

We present here our final report for the NASA grant "HIRES Dust Imaging of the NGC 6334 Star Forming Complex." This project was designed to study the photodissociation regions surrounding several OB stars in this cloud complex. NGC 6334 is unique in having at least seven distinct massive star forming regions in the same molecular cloud complex. The obvious advantage of studying young stars in the same molecular complex is that the stars all formed in the same global environment. Consequently, global factors like density waves, abundances, global magnetic field strength, and age of the parental molecular cloud cannot contribute to the differences among the star forming regions. Instead, the differences must arise only from local effects such as the mass, age, and UV fields of the individual stars. A study of NGC 6334 will greatly simplify the general problem of comparing different star formation regions by eliminating global effects.

Jackson, James M.

1997-01-01

226

Degradation of antipyrine by UV, UV/H?O? and UV/PS.  

PubMed

Degradation of antipyrine (AP) in water by three UV-based photolysis processes (i.e., direct UV, UV/H?O?, UV/persulfate (UV/PS)) was studied. For all the oxidation processes, the AP decomposition exhibited a pseudo-first-order kinetics pattern. Generally, UV/H?O? and UV/PS significantly improved the degradation rate relevant to UV treatment alone. The pseudo-first-order degradation rate constants (kobs) were, to different degrees, affected by initial AP concentration, oxidant dose, pH, UV irradiation intensity, and co-existing chemicals such as humic acid, chloride, bicarbonate, carbonate and nitrate. The three oxidation processes followed the order in terms of treatment costs: UV/PS>UV>UV/H?O? if the energy and chemical costs are considered. Finally, the AP degradation pathways in the UV/H?O? and UV/PS processes are proposed. Results demonstrated that UV/H?O? and UV/PS are potential alternatives to control water pollution caused by emerging contaminants such as AP. PMID:23892168

Tan, Chaoqun; Gao, Naiyun; Deng, Yang; Zhang, Yongji; Sui, Minghao; Deng, Jing; Zhou, Shiqing

2013-09-15

227

Conference on Faint Blue Stars, 2nd, Tucson, AZ, June 1-5, 1987, Proceedings  

SciTech Connect

Recent observational and theoretical investigations of faint blue population II and degenerate stars are discussed in reviews and reports. Topics addressed include stellar parameters for post-AGB stars, four-color observations of field horizontal-branch stars, observations of UV-bright stars in Galactic globular clusters, and quantitative spectroscopy of PN central stars. Consideration is given to the physics of cool white dwarfs, nonradial pulsations of hot evolved stars, the Schmidt high-Galactic-latitude survey, normal B stars at very large distances from the Galactic plane, and IUE observations of the ZZ Cet instability strip.

Philip, A.G.D.; Hayes, D.S.; Liebert, J.W.

1987-01-01

228

Neutron stars  

NASA Astrophysics Data System (ADS)

Neutron stars are laboratories for dense matter and gravitational physics. Observations of neutron stars from sources such as radio pulsars, low-mass X-ray binaries, X-ray bursts and thermally-emitting neutron stars are setting bounds to neutron star masses, radii, rotation rates, temperatures and ages. Mass measurements constrain the equation of state at the highest densities and set firm bounds to the highest possible density of cold matter. Radii constrain the equation of state in the vicinity of the nuclear saturation density and yield information about the density dependence of the nuclear symmetry energy. Laboratory measurements and theoretical studies of pure neutron matter are in remarkable agreement with observational bounds.

Lattimer, James M.

2014-05-01

229

DETECTING STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES WITH GALEX  

SciTech Connect

We present the results of GALEX observations of 17 cool core (CC) clusters of galaxies. We show that GALEX is easily capable of detecting star formation in brightest cluster galaxies (BCGs) out to z {>=} 0.45 and 50-100 kpc. In most of the CC clusters studied, we find significant UV luminosity excesses and colors that strongly suggest recent and/or current star formation. The BCGs are found to have blue UV colors in the center which become increasingly redder with radius, indicating that the UV signature of star formation is most easily detected in the central regions. Our findings show good agreement between UV star formation rates and estimates based on H{alpha} observations. IR observations coupled with our data indicate moderate-to-high dust attenuation. Comparisons between our UV results and the X-ray properties of our sample suggest clear correlations between UV excess, cluster entropy, and central cooling time, confirming that star formation is directly and incontrovertibly related to the cooling gas.

Hicks, A. K.; Donahue, M. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320 (United States); Mushotzky, R., E-mail: ahicks@alum.mit.ed, E-mail: donahue@pa.msu.ed, E-mail: richard@astro.umd.ed [Goddard Space Flight Center, Code 662, Greenbelt, MD, 20771 (United States)

2010-08-20

230

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

NASA Astrophysics Data System (ADS)

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

Bianchi, Luciana

2014-04-01

231

Highly ionized stellar winds in Be stars. II - Winds in B6-B9.5e stars  

NASA Technical Reports Server (NTRS)

The results of a UV survey of stellar winds and circumstellar shells in 40 B6-B9.5e stars covering luminosity classes V-III are presented. A graph is presented of the region from 1520-1560 A, which includes both the Si II UV multiplet 2 transitions and the C IV resonance transition for selected Be stars in the sample. The detection of shortward-shifted discrete component absorption features in nine of the program stars suggests that the material is produced in a stellar wind, which attains velocities of at least a few hundred km/s.

Grady, C. A.; Sonneborn, George; Bjorkman, K. S.; Snow, T. P.; Shore, Steven N.

1989-01-01

232

UnISIS: Laser Guide Star and Natural Guide Star Adaptive Optics System  

Microsoft Academic Search

UnISIS (University of Illinois Seeing Improvement System) is a versatile adaptive optics system mounted on a large optics bench at the coudé focus of the Mount Wilson 2.5-m telescope. It was designed to have both laser guide star (LGS) and natural guide star (NGS) adaptive optics capabilities. The LGS side of the system relies on a pulsed UV laser with

Laird A. Thompson; Scott W. Teare; Yao-Heng Xiong; Richard M. Castle; Abhijit Chakraborty; Robert A. Gruendl; Robert W. Leach

2009-01-01

233

Revisiting binary stars in population synthesis models  

NASA Astrophysics Data System (ADS)

We report results of a population synthesis model that follows the evolution of single and binary stars. In this model, we include the two He white dwarfs merger channel, suggested by Han et al., for the formation of extreme horizontal branch (EHB) stars. The physical parameters of the resulting EHB stars are derived from the Bag of Stellar Tracks and Isochrones data base by Pietrinferni et al., and are thus realistic and observationally supported. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary stars or their products, e.g., EHB stars in the ultraviolet (UV) of early-type galaxies (ETGs). We reproduce successfully the observed colour-magnitude diagram and spectral energy distribution of the metal-rich open cluster NGC 6791. The stellar population in this cluster may be archetypal of the stellar population in ETGs that show the UV excess phenomenon. Our models should be appropriate to study the UV upturn in ETGs.

Hernández-Pérez, Fabiola; Bruzual, Gustavo

2013-05-01

234

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

235

New UV Detector Concepts  

NASA Astrophysics Data System (ADS)

BOLD (Blind to the Optical Light Detectors) is an international initiative dedicated to the development of novel imaging detectors for UV solar observations. It relies on the properties of wide-bandgap semiconductor materials (in particular diamond and Al-Ganitrides). This investigation is proposed in view of the Solar Orbiter UV instruments, for which the expected benefits of the new sensors, visible blindness and radiation hardness, will be highly valuable. Despite various advances in the technology of imaging detectors over the last few decades, the present UV imagers based on silicon CCDs or microchannel plates exhibit limitations which are inherent to their actual material and technology. Yet the utmost spatial resolution, fast temporal cadence, sensitivity, and photometric accuracy will all be decisive for forthcoming solar space missions. The advent of imagers made of large wide-bandgap semiconductors would surmount many present weaknesses. This would open up new scientific prospects and, by simplifying their design, would even make the instruments cheaper. As for the Solar Orbiter, the aspiration for wide-bandgap semiconductor-based UV detectors is still more desirable because the spacecraft will approach the Sun where heat and radiation fluxes are high. We describe the motivations leading to such new developments, and present a programme to achieve revolutionary flight cameras within the Solar Orbiter schedule.

Hochedez, J.-F.; Schuhle, U.; Lemaire, P.

236

Silicon carbide UV photodiodes  

Microsoft Academic Search

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

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

1993-01-01

237

Infrared photometry of the RS CVn binaries. III - JHK light curves of UV PSC  

NASA Astrophysics Data System (ADS)

The infrared observation of UV Psc were made in October 1978, September 1979, and November and December 1979 with an MKII infrared photometer. The photometer, detector, filters, and telescope are the same as those described by Glass (1973). The photometric measures were made in relation to HR 434; its infrared magnitudes are compared with the magnitudes of Glass's 1974 standard stars, and their magnitude differences were constant to high accuracy throughout the periods of observation. A comparison star (HR 434) not as faint as the program star and not of the same spectral type was selected in order to save observing time, which was used in obtaining more frequent observations of UV Psc. Another reason for using a bright comparison star is that the errors introduced into infrared differential photometry at 7 m or 8 m in K would be worse than those introduced because of the nonsimilarity of magnitudes and colors of the standard star and program binary.

Antonopoulou, E.

1983-09-01

238

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

239

Far UV Spectroscopy of eta Carinae  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

240

Far UV Spectroscopy of eta Carinae  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

241

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

242

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

NASA Astrophysics Data System (ADS)

We present numerical simulations of how a 120 Msolar primordial star regulates star formation in nearby cosmological halos at z~20 by photoevaporation. Our models include nine-species primordial chemistry and self-consistent multifrequency conservative transfer of UV photons with all relevant radiative processes. Whether or not new stars form in halos clustered around a Population III star ultimately depends on their core densities and proximity to the star. Diffuse halos with central densities below 2-3 cm-3 are completely ionized and evaporated anywhere in the cluster. Evolved halos with core densities above 2000 cm-3 are impervious to both ionizing and Lyman-Werner flux at most distances from the star and collapse as quickly as they would in its absence. Star formation in halos of intermediate density can be either promoted or suppressed depending on how the ionization front (I-front) remnant shock compresses, deforms, and enriches the core with H2. We find that the 120 Msolar star photodissociates H2 in most halos in the cluster, but that catalysis by H- restores it a few hundred kiloyears after the death of the star, with little effect on star formation. Our models exhibit significant departures from previous one-dimensional, spherically symmetric simulations, which are prone to serious errors due to unphysical geometric focusing effects.

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

2008-06-01

243

Key problems in cool-star astrophysics  

NASA Astrophysics Data System (ADS)

Selected key problems in cool-star astrophysics are reviewed, with emphasis on the importance of new ultraviolet missions to tackle the unresolved issues. UV spectral signatures are an essential probe of critical physical processes related to the production and transport of magnetic energy in astrophysical plasmas ranging, for example, from stellar coronae, to the magnetospheres of magnetars, and the accretion disks of protostars and Active Galactic Nuclei. From an historical point of view, our comprehension of such processes has been closely tied to our understanding of solar/stellar magnetic activity, which has its origins in a poorly understood convection-powered internal magnetic dynamo. The evolution of the Sun's dynamo, and associated magnetic activity, affected the development of planetary atmospheres in the early solar system, and the conditions in which life arose on the primitive Earth. The gradual fading of magnetic activity as the Sun grows old likewise will have profound consequences for the future heliospheric environment. Beyond the Sun, the magnetic activity of stars can influence their close-in companions, and vice versa. Cool star outer atmospheres thus represent an important laboratory in which magnetic activity phenomena can be studied under a wide variety of conditions, allowing us to gain insight into the fundamental processes involved. The UV range is especially useful for such studies because it contains powerful diagnostics extending from warm (˜ 104 K) chromospheres out to hot (1 10 MK) coronae, and very high-resolution spectroscopy in the UV has been demonstrated by the GHRS and STIS instruments on HST but has not yet been demonstrated in the higher energy EUV and X-ray bands. A recent example is the use of the hydrogen Ly? resonance line—at 110 000 resolution with HST STIS—study, for the first time, coronal winds from cool stars through their interaction with the interstellar gas. These winds cannot be detected from the ground, for lack of suitable diagnostics; or in the X-rays, because the outflowing gas is too thin. A 2m class UV space telescope with high resolution spectroscopy and monitoring capabilities would enable important new discoveries in cool-star astronomy among the stars of the solar neighborhood out to about 150 pc. A larger aperture facility (4 6 m) would reach beyond the 150 pc horizon to fainter objects including young brown dwarfs and pre-main sequence stars in star-forming regions like Orion, and magnetic active stars in distant clusters beyond the Pleiades and ? Persei. This would be essential, as well, to characterize the outer atmospheres of stars with planets, that will be discovered by future space missions like COROT, Kepler, and Darwin.

Pagano, Isabella; Ayres, Thomas R.; Lanzafame, Alessandro C.; Linsky, Jeffrey L.; Montesinos, Benjamín; Marcello-Rodonò

2006-06-01

244

Subdwarf B and O Stars: Which Evolutionary Pathways?  

NASA Astrophysics Data System (ADS)

Hot subdwarf stars (spectral types subdwarf B and O) are long lived stars producing a large amount of UV radiation. This makes them excellent candidates to explain the UV radiation observed in old populations. However, the origin of both classes of hot subdwarfs is unclear. I review possible single star and binary channels. High resolution observations of hot subdwarfs taken in the course of the Supernova type Ia Progenitor surveY (SPY) are presented. The SPY observations are used for a systematic assessment of the frequency of close binaries among hot subdwarfs. Results are a high binary fraction among the subdwarf B stars - albeit not as high as in a previous investigation, but a very low binary frequency in helium-rich hot subdwarf O stars. Implications for the evolutionary status of hot subdwarfs are discussed.

Napiwotzki, R.

2009-03-01

245

Chameleon stars  

SciTech Connect

We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.

Dzhunushaliev, Vladimir [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Folomeev, Vladimir [Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Singleton, Douglas [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Physics Department, CSU Fresno, Fresno, California 93740-8031 (United States)

2011-10-15

246

uv preilluminated gas switches  

SciTech Connect

We have designed, built, and characterized uv preilluminated gas switches for a trigger circuit and a low inductance discharge circuit. These switches have been incorporated into a 54 x 76 x 150 cm pulser module to produce a 1 Ma output current rising at 5 x 10/sup 12/ amps/sec with 1 ns jitter. Twenty such modules will be used on the Nova Inertial Confinement Fusion Laser System for plasma retropulse shutters.

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

1980-06-03

247

Dynamic UV microstereolithography  

Microsoft Academic Search

A new process of microstereolithography to manufacture freeform solid three-dimensional micro-components with outer dimensions in the millimetre size range is presented. The process, based on the use of a liquid crystal display as a dynamic mask generator, works with conventional industrial UV-sensitive stereolithographic materials. The main innovation of the process consists in using the optical frequency up-conversion of images from

S. Monneret; H. Le Gall; V. Badé; F. Devaux; A. Mosset; E. Lantz

2002-01-01

248

The Environment of the Optically Brightest Herbig Ae Star, HD 104237  

Microsoft Academic Search

We investigate the environment of the nearest Herbig Ae star, HD 104237, with a multiwavelength combination of optical coronagraphic, near-IR, and mid-IR imaging supported by optical, UV, and far-ultraviolet spectroscopy. We confirm the presence of T Tauri stars associated with the Herbig Ae star HD 104237, noted by Feigelson et al. We find that two of the stars within 15\\

C. A. Grady; B. Woodgate; Carlos A. O. Torres; Th. Henning; D. Apai; J. Rodmann; Hongchi Wang; B. Stecklum; H. Linz; G. M. Williger; A. Brown; E. Wilkinson; G. M. Harper; G. J. Herczeg; A. Danks; G. L. Vieira; E. Malumuth; N. R. Collins; R. S. Hill

2004-01-01

249

Images in the rocket ultraviolet - Star formation and extinction in the M51 system  

NASA Technical Reports Server (NTRS)

UV images of M51 with up to 15 arcsec resolution were obtained by a rocket-borne telescope. The bandwidth was 970 A with maximum response at 2650 A. The two most prominent features of M51 in the UV are the bright central region and a region of intense star formation about 2.5 NE of the nucleus toward the companion NGC 5195. This complex is the source of 20 percent of the total UV flux in M51. The companion is much less prominent in the UV than in optical bands. Spiral arms show much higher contrast in UV and U bands than in the R band. The nuclear region in the UV band shows clumped emission from probable star-forming regions, possibly associated with the inner Lindblad resonance. These regions are probably the UV counterparts of FIR sources discovered in an EW scan across the nucleus. UV/U colors of most bright H II regions with known extinction are consistent with O star spectra reddened by amounts estimated from radio and Balmer line measurements. However, some of the brightest H II regions have redder UV/U colors, probably indicating the presence of cooler stars which contribute in the U band. CO and IR observations indicate that the companion NGC 5195 may be a reddened starburst in spite of its faintness in the UV.

Bohlin, Ralph C.; Cornett, Robert H.; Hill, Jesse K.; O'Connell, Robert W.; Stecher, Theodore P.

1990-01-01

250

Fundamental parameters of Wolf-Rayet stars. III. The evolutionary status of WNL stars.  

NASA Astrophysics Data System (ADS)

New high S/N optical observations of 9 Galactic WNL (WN7-8) stars are presented. The spectra have been analysed using tailored non-LTE model atmospheres by Crowther et al. (1994c). Here we use the derived stellar parameters and abundances for a thorough investigation of the evolutionary status and mass-loss properties of WNL stars. We have identified two distinct groups of WNL stars from their observed properties. The WNL+abs and WN7 stars have high luminosities (log L/Lsun_~5.9) and form a continuity in morphology and physical parameters from the Of stars. They appear to be intimately related to these stars, confirming the suspicion of Walborn (1973) and are descended from extremely massive progenitors (M_initial_>60Msun_) through the sequence O->Of->WNL+abs->WN7(->WNE)->WC->SN. In contrast, the evolutionary sequence for WN8 stars is identified as O->LBV or RSG->WN8->WNE->WC->SN. These stars, with lower luminosities (log L/Lsun_~5.5), are descended from less massive stars, and have either red supergiant (RSG, 25Msun_stars have in common with LBVs, e.g. spatial distribution, association with ejecta nebulae, low binary frequency, large photometric variability. We also find that those stars with the highest terminal velocities (WN7+abs stars) have the lowest variability while the WN8 stars and LBVs (low wind velocities) are the most variable. The smooth progression of mass loss properties from O supergiants to WNL stars found by Lamers & Leitherer (1993) is confirmed with the WNL+abs stars lying intermediately between the WN8 stars and O stars. The spectroscopic differences between Ofpe and WNL+abs stars appear to be attributable principally to a difference in wind density. This naturally explains the often ambiguous Of-WN spectral classification of some Of and WNL stars (Conti & Bohannan 1989). Finally, interstellar reddenings are determined using two independent methods based on the model atmosphere continuum distributions and the observed ubv colours. We find that the UV reddening towards WR25 (WN7+abs) is highly anomalous (R=4.6), confiming the findings of Tapia et al. (1988) for stars in Tr 16 in the Carina nebula.

Crowther, P. A.; Smith, L. J.; Hillier, D. J.; Schmutz, W.

1995-01-01

251

Enhanced UV inactivation of adenoviruses under polychromatic UV lamps.  

PubMed

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

2007-12-01

252

Ultraviolet interstellar extinction toward 1367 stars observed by ANS  

NASA Technical Reports Server (NTRS)

Five-band UV photometry is used to investigate the character of interstellar extinction toward 1367 stars of spectral type B3 and earlier, with observations producing a galactic average of 5.11, 4.78, 6.52, 4.10 and 1.95 at 1550, 1800, 2200, 2500, and 3300 A, respectively. Differences in the strengths of the UV extinction features of these stars appear to be independent, since objects with either strong or weak 2200 A extinction can have strong, normal or weak far-UV extinction. Further investigation reveals that some of the deviant stars are embedded in localized regions whose average extinction curves diverge dramatically from the galactic mean. The anomalous extinction of these regions attests to localized inhomogeneities in the UV characteristics of interstellar dust. Because the evaluation of UV extinction toward a particular star would be more accurate if based on the average curve of the region immediately surrounding that star rather than that of the entire Galaxy, it is recommended that the galactic average presented be used with caution to correct astronomical data of individual objects.

Meyer, D. M.; Savage, B. D.

1981-01-01

253

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. ...

2010-04-15

254

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

255

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

2014-05-01

256

STAR-FORMING OR STARBURSTING? THE ULTRAVIOLET CONUNDRUM  

SciTech Connect

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

Boquien, M.; Calzetti, D.; Hong, S. [University of Massachusetts, Department of Astronomy, LGRT-B 619E, Amherst, MA 01003 (United States); Kennicutt, R. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Dale, D. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Engelbracht, C.; Portouw, J. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Gordon, K. D. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Lee, J. C., E-mail: boquien@astro.umass.ed [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2009-11-20

257

UV matters in shoaling decisions.  

PubMed

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

2006-04-01

258

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

259

Tracing the Extreme Edges of Galaxies in UV and HI  

NASA Astrophysics Data System (ADS)

One of the most surprising discoveries of the GALEX mission is without doubt the discovery of extended star formation disks in nearby galaxies. Detailed comparisons with new, high-sensitivity, high-resolution VLA HI data from "The HI Nearby Galaxy Survey" (THINGS), which are beautifully matched to GALEX in its spatial resolution (6"), provide strong evidence for a well defined Schmidt Law, with no lower bound, i.e. no star formation threshold (SFT), yet detected. Comparisons are limited by the GALEX data though (with exposure times of 1.5 ks per galaxy), but indicate that there is even more extended star formation occurring at progressively lower HI column densities. To investigate this phenomenon further, we have selected a sample of 8 galaxies spanning a diverse range of galaxy parameters. For those galaxies we are requesting UV exposures with an increased signal-to-noise ratio by a factor of 3 (an additional 12 ks per object), in order to be able to probe in a systematic way and for the first time a part of the UV parameter space investigated in only one other galaxy before (NGC 300). This will allow us to push the UV detection limit significantly below the canonical 5.6E20 per cm**2 HI column density SFT.

Bigiel, Frank

260

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.

261

Holographic UV laser microsurgery  

PubMed Central

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

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

2011-01-01

262

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

263

Converting neutron stars into strange stars  

NASA Technical Reports Server (NTRS)

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

Olinto, A. V.

1991-01-01

264

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

265

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

266

UV extinction and IR emission in diffuse H2 regions  

NASA Technical Reports Server (NTRS)

HII regions occupy a unique position in our understanding of the physical relationships between stars, the interstellar medium, and galactic structure. Observations show a complex interaction between a newly formed hot star and its surroundings. In particular, the ultraviolet radiation from the stars modifies the pre-existing dust, which again affects both the amount of ionizing radiation absorbed by the gas, and the infrared spectrum emitted by the heated dust. The aim of this project was to use UV and far-UV observations to gain information on the nebular dust, and to use this dust to model the far-IR emission, for a consistent picture of a few selected diffuse HII regions. Using archival data from the IUE and Voyager data banks and computed model atmospheres, we have deduced extinction curves for early-types stars. The requisite spectral resolution turned out to be a major task. We have successfully modelled these curves in terms of a multi-component, multi-size distribution of dust grains, and interpret the differences in the curves as primarily due to the presence or non-presence of intermediate size grains (0.01 to 0.04 micron). Much smaller (0.005 micron) grains must also be present. Finally, we have made calculations of the temperature fluctuations and the corresponding infra-red emission in such small grains.

Aannestad, Per A.

1994-01-01

267

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

268

UV Curable Polyimides  

NASA Technical Reports Server (NTRS)

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

Meador, Michael; Oliver, Thomas

2001-01-01

269

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

270

UV extinction properties of carina nebular dust  

NASA Technical Reports Server (NTRS)

I have performed an analysis of the UV extinction by dust along the line of sight to the young open cluster Tr 16. The observed curves are parameterized in order to extract quantitative information about the structure of the curves. Furthermore, by constructing differential extinction curves, obtained by differencing curves for stars which lie within a few arc seconds of each other on the sky, I was able to obtain a curve which is free of the effects of foreground extinction, and represents the extinction by the dust in the Tr 16 molecular cloud. I then show that this curve is nearly identical to one due to dust in the Orion molecular cloud. This result shows that dust in the Carina arm exhibits the same behavior as that in the local arm.

Massa, Derck

1993-01-01

271

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.

2008-08-01

272

New Star Formation in NGC 3690  

NASA Astrophysics Data System (ADS)

NGC 3690 is a system of merging spiral galaxies located in Ursa Major about 150 million light years away from Earth. A significant burst of star formation has occurred as a result of these merging galaxies. HST observations in the B,I, and far-UV bands reveal active star formation within this pair of luminous infrared galaxies (LIRGs), which are factories of star birth, primary sources of thermal energy emission in the far-infrared spectrum, and characterized by the abundant presence of dust in the interstellar medium. Significant amounts of dust poses as an observation obstacle, and hinders us from seeing processes of star formation inside the merging system at visible wavelengths using optical telescopes. Dust re-emits absorbed starlight (i.e. UV radiation) as thermal infrared emission which can be seen by radio telescopes (the VLA, VLBA, and ALMA to name a few). One of my primary goals is to determine approximate ages of star clusters in the NGC 3690 system, which has had six supernovae within the last fifteen years.

Abdullah, Ajamu

2014-01-01

273

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

NASA Astrophysics Data System (ADS)

The hot stars responsible for the UV upturn phenomenon are key indicators of age and abundance for the stellar populations in ellipticals. These stars are well-isolated in the FUSE wavelength range from the cooler main sequence stars that complicate interpretation at wavelengths longer than 2000 Angstroms. The strength of the UV upturn correlates well with optical metallicity indices, but these optical indices trace abundances in the cool population, not the hot stars that produce the UV emission, so the relation between abundance and UV upturn remains unclear. We are currently obtaining FUSE observations of two giant elliptical galaxies with strong UV emission NGC 4649 and NGC 1399. For the next cycle, we propose complementary observations of two ellipticals with weak emission NGC 221 and NGC 4472. Although NGC 221 is a fundamental testing ground for theories of stellar and galactic evolution, its spectrum has never been measured below Lyman alpha. The galaxy is unique because it the closest and most metal-poor elliptical, with the weakest measured UV upturn. NGC 4472 was observed by the Hopkins Ultraviolet Telescope, but at considerably lower signal-to-noise and resolution than possible with FUSE. With FUSE data, the absorption lines of C, N, and Si prevalent in the far-UV will provide invaluable composition diagnostics for the hot stellar populations in ellipticals. Furthermore, FUSE is uniquely qualified to measure the Lyman series, an important diagnostic of effective temperature and surface gravity. FUSE presents the opportunity to understand the role of abundance in the UV upturn phenomenon.

Brown, Thomas M.

274

UV radiation from the young sun and oxygen and ozone levels in the prebiological palaeoatmosphere  

NASA Technical Reports Server (NTRS)

UV measurements of young T-Tauri stars, resembling the sun at an age of a few million years, have recently been made with the International Ultraviolet Explorer. They indicate that young stars emit up to 10,000 times more UV than the present sun. The implications for the origin and evolution of O2 and O3 in the prebiological palaeoatmosphere are presented here. The results of photochemical calculations indicate that the O2 surface mixing ratio was a factor 10,000-1,000,000 times greater than the standard value of 10 to the -15. This new value reconciles the simultaneous existence of oxidized iron and reduced uranium.

Canuto, V. M.; Levine, J. S.; Augustsson, T. R.; Imhoff, C. L.

1982-01-01

275

Standard stars for photometry of comets  

NASA Technical Reports Server (NTRS)

Magnitudes are presented in 10 bandpasses for 63 stars that can be used as standards in photometric observations of comets. The bandpasses are, in addition to those for three (UV, blue, and red) continuum points, those which measure C2, C3, CN, CO(+), H2O(+), OH, and NH emissions. After correction for extinction, the derived magnitudes were transformed to a zero point such that all filters showed magnitude 5.88 for the star HD 3379. The internal agreement among the present observations and the agreement obtained between the observations and independently published measures indicate that the derived magnitudes are generally accurate to + or - 0.01 mag.

Osborn, Wayne H.; A'Hearn, Michael F.; Carsenty, Uri; Millis, Robert L.; Schleicher, David G.

1990-01-01

276

Seismic telescope for astrophysical research from space (STARS) triply reflecting telescope: a space instrument for astrophysics.  

PubMed

We describe the characteristics of the wide-field, triply reflecting telescope adopted for the European Space Agency project STARS (seismic telescope for astrophysical research from space), operating in the visible and UV range. PMID:18264439

Badiali, M; Amoretti, M

1997-12-01

277

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

278

Long Baseline Interferometric Observations of the Spatial Distribution of Dust Surrounding Late-Type Stars at 11 microns  

NASA Astrophysics Data System (ADS)

The spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) operating at a wavelength 11.15 microns. Radiative transfer modeling of visibility curves obtained by the ISI has yielded estimates of the inner radii of the dust shells, the optical depth at 11 microns, and the temperature of the dust at the inner radii. For stars in which the dust is resolved, estimates of the stellar diameter and temperature have also been made for those stars not seen in visible light. Roughly speaking two classes of stars have been found. One class has inner radii of their dust shells very close to the photospheres of the stars themselves (2-5 stellar radii) and at a higher temperature ( ~ 1300 K) than previously measured. This class includes VY CMa, NML Tau, IRC +10216, and o Ceti. For the latter two the visibility curves change with the luminosity phase of the star and new dust appears to form at still smaller radii during minimum luminosity. The second class of stars has dust shells with substantially larger inner radii (as large as 1 arcsec) and very little dust close to the stars, and includes alpha Ori, alpha Sco, alpha Her, and chi Cyg, This indicates sporadic production of dust and little or no recent dust formation. In addition to the stars mentioned above a still larger study of such stars is underway and visibility curves for some of this larger group will be reported. In some cases a rather advanced radiative transfer model based on the work of Wolfire and Cassinelli (Ap. J. 310, 207, 1986) has been used which self-consistently calculates the temperature distribution and infrared spectrum of the star plus dust shell based on the optical properties of the grains, including grain size distributions and chemistry. For alpha Ori, we have shown that a dust distribution that fits its 11 microns visibility curve very well also produces excellent agreement with its IRAS Low Resolution Spectrum, as well as 8.7 microns and 10.4 microns visibility curves obtained by Dyck and Benson (1992, Astron. J in press).

Danchi, W. C.; Greenhill, L.; Bester, M.; Degiacomi, C. G.; Townes, C. H.

1992-12-01

279

Ultraviolet Imaging Telescope images - Limits on recent star formation in Holmberg IX  

NASA Technical Reports Server (NTRS)

Ultraviolet Imaging Telescope near-UV and far-UV images of Holmberg IX show no OB associations. Relative fluxes measured for the galaxy as a whole in the UV and optical B and V bands are consistent with models in which about 0.6-0.7 of the V flux is from an old population of age 10 Gyr, while the remainder is from stars of age 20-200 Myr, which also contribute 0.80 of the near-UV flux and 0.99 of the far-UV flux. Individual stars measured in B and V appear to be evolved stars of mass about 12 solar masses and age about 20 Myr belonging to the youngest population in the galaxy.

Hill, Jesse K.; Gessner, Susan E.; Bohlin, Ralph C.; Cheng, Kwang-Ping; Hintzen, Paul M. N.; O'Connell, Robert W.; Roberts, Morton S.; Smith, Andrew M.; Smith, Eric P.; Stecher, Theodore P.

1993-01-01

280

Nebular UV Absorption Lines in Planetary Nebulae  

NASA Astrophysics Data System (ADS)

We propose to continue our Cycle 1 program of studying the Lyman and Werner bands of H_2, seen in absorption against the UV continua of planetary nebula central stars, which arise within neutral-molecular envelopes surrounding the ionized gas. These are the pump lines for a fluorescent cascade of near-infrared emission lines which are observed in many planetary nebulae. By observing the UV lines we can probe the chemical and thermal structure of the envelopes, as well as measure molecular column densities and clarify the excitation processes for the infrared lines. In Cycle 1 we were granted time for three targets, one of which was successfully observed shortly before submission of this proposal. Although the data were not yet available for examination, similar target observed by the project team revealed a rich set of H_2 circumstellar absorption features, demonstrating the feasibility of our program. FUSE spectra also include absorption features from atomic species such as O I and C II, which give rise to important far-infrared fine-structure cooling lines that likewise have been observed from planetary nebulae. In Cycle 2, we add as a secondary goal a search for nebular components of the O VI 032, 1038 AA absorption lines, which trace the presence of hot shocked gas, in nebulae with anomalously strong optical recombination lines of ions of oxygen and nitrogen. This will test a plausible hypothesis for the origin of this anomaly.

Dinerstein, Harriet

281

Diffuse UV Background Radiation  

NASA Astrophysics Data System (ADS)

The diffuse UV sky is expected to glow with significant amounts of starlight that is scattered from the interstellar dust. The albedo and scattering pattern of the dust in the ultraviolet are both well established, and are both fairly independent of wavelength from 912 Å to 3000 Å. We present 1943 Voyager spectra of the diffuse cosmic background radiation from 500 Å to 1200 Å, and we compare their brightnesses, and their distribution on the sky, to those observed (Murthy et al., ApJ 724, 1389, 2010) from the GALEX mission at longer wavelengths (1530 Å). Significant differences appear, suggesting that background radiation components in addition to dust-scattered starlight may be present in both spectral regions.

Conn Henry, Richard; Murthy, J.

2012-01-01

282

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

283

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

284

A catalog of ultraviolet interstellar extinction excesses for 1415 stars  

NASA Technical Reports Server (NTRS)

Ultraviolet interstellar extinction excesses are presented for 1415 stars with spectral types B7 and earlier. The excesses with respect to V are derived from Astronomical Netherlands Satellite (ANS) 5-channel UV photometry at central wavelengths of approximately 1550, 1800, 2500, and 3300 A. A measure of the excess extinction in the 2200-A extinction bump is also given. The data are valuable for investigating the systematics of peculiar interstellar extinction and for studying the character of UV interstellar extinction in the general direction of stars for which the extinction-curve shape is unknown.

Savage, B. D.; Massa, D.; Meade, M.; Wesselius, P. R.

1985-01-01

285

The UV-metallicity Characteristics Of UCDs, GCs And dEs In The Fornax Cluster  

NASA Astrophysics Data System (ADS)

The remarkable variation of UV-optical ratios in elliptical galaxies suggests that the observed "UV-excess" may be uniquely sensitive to their star formation histories and chemical enrichment. While the stellar evolutionary phase responsible for creating this "excess" is fairly well understood (He-rich, hot-HB stars), the UV emission of an integrated stellar population and its dependence on global characteristics such as metallicity is far more complex. Because they are mostly simple stellar populations with small dispersion in age and abundance, globular clusters (GCs) have been considered good calibrators for understanding these global characteristics. The GCs of M87 appear to follow a far-UV-metallicity relation (FUV - Mg_2) similar to Milky Way GCs, but distinct from that observed for ellipticals.Ultra-compact dwarf galaxies (UCDs) may provide an alternative, more luminous calibrator of the UV-excess in early-type galaxies. Near- and far-UV GALEX imaging provides tantalising hints that at least some UCDs exhibit a "UV-excess" comparable to the UV-luminous GCs in M87. I will present the FUV - Mg_2 relation for Fornax Cluster UCDs from GALEX imaging and our Magellan/IMACS spectroscopy, and compare them with NGC1399 GCs and cluster dE,Ns. By combining GALEX imaging with our optical g,r,i imaging, I will also show that the UV-optical properties of Fornax UCDs and NGC1399 GCs, provide an efficient tool for discriminating between new candidates and foreground stars in ground based images.

Karick, Arna; Gregg, M.

2009-01-01

286

FUV Detection of the Primary Star of eta Carinae  

NASA Astrophysics Data System (ADS)

Using FUSE data, Iping et al (2005, ApJ 633, L37) report a direct detection of the elusive hot companion of eta Car. We argue, however, that much of the observed emission represents the primary star, with no proof that any of it comes from a secondary star. The hypothetical companion should dominate the ionizing radiation below 912 A, but this is not true for wavelengths around 1100 A observed with FUSE. Moreover, since a companion's UV would be partially reprocessed by the primary star's wind, any detection is likely to be ambiguous.The non-spherical primary wind allows production of strong UV radiation at low latitudes (Smith et al 2003, ApJ 586, 432), an effect that spherical models don't include. The N II 1085 feature, the relatively slow wind velocities seen by FUSE, and other details are characteristic of the primary wind, not the secondary. Zanella et al. (1984, A&A 137, 79) suggested that eta Car's far UV disappears during a spectroscopic event due to a shell ejection. The FUSE observations may be regarded as confirmation of that conjecture, which made no reference to a secondary star. The 2003 spectroscopic event was probably a mass ejection or a wind-disturbance episode, not merely an eclipse as assumed by Iping et al. A hot companion star seems likely to account for the ionizing UV and the X-ray variability, but the FUSE data do not confirm its existence.

Davidson, K.; Smith, N.

2006-06-01

287

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

288

STAR FORMATION EFFICIENCY IN THE COOL CORES OF GALAXY CLUSTERS  

SciTech Connect

We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and H{alpha} (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to H{alpha} luminosity, the UV spectral energy distribution, and the far-UV and H{alpha} morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given H{alpha} luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/H{alpha} ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) {approx} 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from {approx}0.05 M{sub sun} yr{sup -1} in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to {approx}5 M{sub sun} yr{sup -1} in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, H{alpha}, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14{sup +18}{sub -8}%. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard; Reynolds, Christopher [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Rupke, David S. N., E-mail: mcdonald@astro.umd.edu, E-mail: veilleux@astro.umd.edu [Department of Physics, Rhodes College, Memphis, TN 38112 (United States)

2011-06-20

289

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

290

The UV Interstellar Extinction Properties in M31  

NASA Astrophysics Data System (ADS)

Radiative transfer modeling of external galaxies indicates that the "standard" Milky-Way-type dust extinction relation does not provide the best fit to many extragalactic SEDs. SMC-type dust is often a better fit. Therefore, studies of Local Group galaxies, where the dust properties can be directly measured, are very important to assess the variations in interstellar dust extinction from galaxy to galaxy, and also within a single galaxy. The UV extinction properties of the Milky Way and two sub-Solar metallicity galaxies, the LMC and SMC, have been well studied. However, little is known about other galaxies in the Local Group. Fifteen years ago, we did a "pilot study" using HST/FOS of UV extinction toward a very small sample of OB stars in the high metallicity galaxy, M31. We derived an average M31 extinction curve from only three sightlines that had an overall wavelength dependence similar to that of the average Galactic extinction curve, but potentially possessed a weaker 2175 A bump. While the extinction curves calculated from these data provided a proof-of-concept, the study suffered from low S/N, low extinction, and poorly matched pairs of reddened and unreddened stars. In this new study, we obtained low resolution UV spectra of a sample of reddened and lightly reddened OB stars in M31 with HST/STIS to improve our knowledge of the wavelength dependence of interstellar dust extinction. We will present UV extinction curves that have been constructed for seven reddened sightlines in M31, and compare the wavelength dependence of extinction in M31 with that seen in the Milky Way, LMC, and SMC.

Clayton, Geoffrey C.; Gordon, K. D.; Bianchi, L.; Bohlin, R.; Massa, D.; Fitzpatrick, E. L.; Wolff, M. J.

2014-01-01

291

Detection of H2 in UV Absorption in the LMC  

NASA Astrophysics Data System (ADS)

Molecular hydrogen (H2) is the most abundant molecule in the interstellar medium. It therefore plays an important role in the physics and chemistry of the interstellar gas. The cool gas component of H2 only can be studied through UV absorption lines near 1000 A. The presence of H2 in the Milky Way has been demonstrated with the Copernicus satellite in the early seventies. Because of technical limits of former UV satellites, the measurement of H2 in the local neighbourhood of the Milky Way via UV spectroscopy had not been possible until the ORFEUS space shuttle mission in 1996. Based on measurements with the ORFEUS far UV echelle spectrograph, we present the first detection of H2 in absorption in the Large Magellanic Cloud (LMC) in the spectrum of the O5 star LH 10:3120. The LMC gas component in the absorption lines at 270 km s-1 is clearly separated from the galactic one at 0 km s-1. The quantitative analysis of the identified absorption lines leads to column densities between 1017 and 1019 cm-2 for the lowest four rotational states. Moreover, we derive a high equivalent excitation temperature of more than 1000 K for J=1,2,3. We therefore conclude that strong UV pumping influences the population of the rotational states of H2 in the LMC gas in the direction of LH 10:3120.

Richter, P.; de Boer, K. S.; Bomans, D. J.; Heithausen, A.; Koornneef, J.

292

Detailed FUSE Study of a Star Behind the Cygnus Loop  

Microsoft Academic Search

We will observe an sdOB star behind the Cygnus Loop supernova remnant to study the line-of-sight interstellar medium structures toward and through this prototypical remnant. The star was identified from Ultraviolet Imaging Telescope UV imaging and lies behind the bright NE Cygnus Loop filaments. New ground-based data and a preliminary FUSE Cycle 3 spectrum (program C052) demonstrate conclusively that the

W. Blair

2003-01-01

293

STARS: the Stellar Absorption and Refraction Sensor  

Microsoft Academic Search

The Stellar Absorption and Refraction Sensor (STARS) is a compact, large-aperture instrument that combines a UV-IR imaging spectrograph with a co-aligned visible-light imager to make simultaneous absorptive and refractive stellar occultation measurements. The absorption measurements provided by the spectrograph allow the determination of vertical profiles of atmospheric constituents. The coincident refraction observations made by the image yield high-precision measurements of

Jeng-Hwa Yee; Daniel Morrison; Graham A. Murphy; M. F. Morgan; David C. Humm; Peter R. Silverglate; Ronald Vervack; Larry J. Paxton

2002-01-01

294

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

295

DB Pulsating Stars  

NASA Astrophysics Data System (ADS)

Pulsating WHITE DWARF stars with nearly pure helium atmospheres exist in a narrow temperature range near 25 000 K. At this writing, there are eight of these stars known. Collectively, they go by two names: the V777 Her stars, named after the VARIABLE STAR designation of the first known star in the class, and the more informative name, the DBV stars. The name DBV follows the standard convention fo...

Winget, D.; Murdin, P.

2000-11-01

296

Deep UV LEDs  

NASA Astrophysics Data System (ADS)

Deep ultraviolet (DUV) photons interact strongly with a broad range of chemical and biological molecules; compact DUV light sources could enable a wide range of applications in chemi/bio-sensing, sterilization, agriculture, and industrial curing. The much shorter wavelength also results in useful characteristics related to optical diffraction (for lithography) and scattering (non-line-of-sight communication). The family of III–N (AlGaInN) compound semiconductors offers a tunable energy gap from infrared to DUV. While InGaN-based blue light emitters have been the primary focus for the obvious application of solid state lighting, there is a growing interest in the development of efficient UV and DUV light-emitting devices. In the past few years we have witnessed an increasing investment from both government and industry sectors to further the state of DUV light-emitting devices. The contributions in Semiconductor Science and Technology 's special issue on DUV devices provide an up-to-date snapshot covering many relevant topics in this field. Given the expected importance of bulk AlN substrate in DUV technology, we are pleased to include a review article by Hartmann et al on the growth of AlN bulk crystal by physical vapour transport. The issue of polarization field within the deep ultraviolet LEDs is examined in the article by Braut et al. Several commercial companies provide useful updates in their development of DUV emitters, including Nichia (Fujioka et al ), Nitride Semiconductors (Muramoto et al ) and Sensor Electronic Technology (Shatalov et al ). We believe these articles will provide an excellent overview of the state of technology. The growth of AlGaN heterostructures by molecular beam epitaxy, in contrast to the common organo-metallic vapour phase epitaxy, is discussed by Ivanov et al. Since hexagonal boron nitride (BN) has received much attention as both a UV and a two-dimensional electronic material, we believe it serves readers well to include the article by Jiang et al on using BN for UV devices; potentially as a p-type wide band gap semiconductor contact. Finally, an in-depth discussion of one DUV application in defense, the non-line-of-sight (NLOS) communication, is given by Drost and Sadler. Overall, we believe that this special issue of Semiconductor Science and Technology provides a useful overview of the state-of-art in the field on DUV materials and devices. In view of the rapidly growing interest in this field, the demonstrated enhanced device performance, and the wide range of applications, this special issue can be considered a very timely contribution. Finally, we would like to thank the IOP editorial staff, in particular Alice Malhador, for their support and also like to thank all contributors for their efforts to make this special issue possible.

Han, Jung; Amano, Hiroshi; Schowalter, Leo

2014-06-01

297

Synthetic UV spectra of starburst regions with massive close binaries  

NASA Astrophysics Data System (ADS)

We present the evolution of synthetic ultraviolet spectra of starburst regions having a significant fraction of binaries. The population synthesis program uses an extended library of stellar evolutionary tracks of single stars and binaries computed with the most recent stellar wind mass loss rates during RSG, LBV and WR stages. In the case of binaries we account in detail for the effects of Roche lobe overflow, mass transfer and mass accretion, common envelope evolution, the spiral-in process, asymmetric kicks to neutron stars as a result of their supernova explosion, etc. The most important synthesized line pyrofiles are those of Si IV ?1400 and C IV ?1550, two P Cygni lines prominent in O stars. The main effect of the close binaries is to extend the UV bright lifetime of the starburst due to the appearance of accretion stars. But more importantly, our computations show that a spectrum of a single star model of about 6 Myr old is effectively undistinguishable from that of a binary rich model of about 10 Myr old. This indicates a possible age degeneracy, reminiscent of the influence of binaries on the commonly used optical age indicator W (H?).

Belkus, Houria; van Bever, J.; Vanbeveren, D.; van Rensbergen, W.

298

Synthetic UV spectra of starburst regions with massive close binaries  

NASA Astrophysics Data System (ADS)

We present the evolution of synthetic ultraviolet spectra of starburst regions having a significant fraction of binaries. The population synthesis program uses an extended library of stellar evolutionary tracks of single stars and binaries computed with the most recent stellar wind mass loss rates during RSG, LBV and WR stages. In the case of binaries we account in detail for the effects of Roche lobe overflow, mass transfer and mass accretion, common envelope evolution, the spiral-in process, asymmetric kicks to neutron stars as a result of their supernova explosion, etc. The most important synthesized line profiles are those of SiIV?1400 and CIV?1550, two P-Cygni lines prominent in O-type stars. The main effect of the close binaries is to extend the UV bright lifetime of the starburst due to the appearance of accretion stars. But more importantly, our computations show that a spectrum of a single star model of about 6 Myr old is effectively undistinguishable from that of a binary rich model of about 10 Myr old. This indicates a possible age degeneracy, reminiscent of the influence of binaries on the commonly used optical age indicator WH?.

Belkus, Houria; van Bever, Joris; Vanbeveren, Dany; van Rensbergen, Walter

299

Solar-blind UV region and UV detector development objectives  

NASA Astrophysics Data System (ADS)

The vulnerability of aircraft to missile attacks is briefly sketched. Aircraft and helicopter defensive electronic self- protection systems against missile attacks including passive and active radar and IR countermeasures are summarized. Radar and IR missile threat warnings are outlined. The development of UV missile threat warning is recounted. UV missile warning coverage is defined. UV missile plume photon emission is addressed. Solar UV emission and atmospheric transmission is reviewed. An AF atmospheric computer program called PLEXUS is applied to the UV spectral region to obtain the atmospheric transmission along paths extending from the upper atmosphere to the lower atmosphere. These atmospheric transmission numbers are used to evaluate the number of solar photons propagating through the upper atmosphere to lower tactical altitudes and into a UV missile-warning sensor viewing the sun directly. These numerical evaluations are accomplished in one- nanometer wide wavelength bins. The results are presented in a number of figures, which then serve to define the solar blind UV region. Detector spectral development objectives are then presented based on the results shown in the figures.

Schreiber, Peter; Dang, Tuoc; Pickenpaugh, Thad; Smith, Gary; Gehred, Paul; Litton, Cole

1999-04-01

300

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

301

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

302

Origin of Hot Subluminous Horizontal-Branch Stars in (omega) Centauri and NGC 2808.  

National Technical Information Service (NTIS)

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet (UV) color magnitude diagrams of both (omega) Cen and NGC 2808. In order to explore the evolutionary status of these subluminous stars, we hav...

A. V. Sweigart T. M. Brown T. Lanz W. B. Landsman I. Hubeny

2001-01-01

303

IUE observations of new A star candidate proto-planetary systems  

NASA Technical Reports Server (NTRS)

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

Grady, Carol A.

1994-01-01

304

Star Search  

NSDL National Science Digital Library

In this online activity, learners can test their skills at finding constellations in the northern hemisphere's night sky. Learners can choose during which season to look, and then look for four constellations in that season. The simulation shows a simple representation of the night sky with key stars highlighted. Use this as a practice before going outside or just to give learners an idea of the difficulties involved in identifying constellations. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.

Science, American A.

2009-01-01

305

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.

306

Future Far-UV Studies of Hot White Dwarfs  

NASA Astrophysics Data System (ADS)

We are beginning to understand the evolution of the hot white dwarfs, but even with telescopes such as IUE and HST, we have still only observed a modest number of the most interesting objects with the spectral resolution and signal-to-noise required. This is in part arises from the intense competition for HST time, against both optical and IR observations as well as other far-UV bids. A key requirement of any new far-UV telescope is sufficient sensitivity to observe most of the ~100 or so brightest hot white dwarfs at high spectral resolution. A spectral resolving power of at least 30,000 is required for studies of white dwarfs. First it is necessary to detect and resolve photospheric, circumstellar and interstellar absorption features. Interstellar/circumstellar features may have several components that can only be separated in velocity space. For example, it is interesting to note that IUE was unable to resolve the photospheric and circumstellar CIV components of G191-B2B, discovered by the HST STIS instrument, leading to a serious overestimate of the carbon abundance in this star. There may be similar components in other stars observed only by IUE. In those stars that have highly stratified atmospheres, the detailed shape of the absorption lines is sensitive to the atmospheric structure. High-resolution observations of the line shapes can provide us with a direct probe of atmospheric structure.

Barstow, M. A.

307

Chemical abundances of 451 stars (Neves+, 2009)  

NASA Astrophysics Data System (ADS)

The file table1.dat lists the parameters used to assign the Galactic population to which each star belongs. Columns 2, 3, and 4 list the U,V and W velocities relative to the local standard of rest (LSR). Columns 5, 6, and 7 list the Gaussian distributions of each population: thin disc, thick disc, and halo, respectively. In Cols. 8 and 9, we provide the relative probabilities of the thick disc relative to the thin disc and of the thick disc relative to the halo. The last column depicts the probable population where each star belongs. The file table3.dat lists the derived abundances of the elements, rms, and number of measured lines for each star. (3 data files).

Neves, V.; Santos, N. C.; Sousa, S. G.; Correia, A. C. M.; Israelian, G.

2009-05-01

308

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

309

An overview investigation of Be/Shell stars  

NASA Astrophysics Data System (ADS)

Be/Shell stars as hot massive type stars are one of the most important stellar groups through the global universe contents. They are important sources of UV photons, so they are playing an important role in the heating and ionizing the interstellar environment up to few hundred parsecs. We here represent an overview investigation of the Be/Shell stars using the last decades “ground and space” observations with high sensitivity, high signal to noise ratio and the new applied techniques in addition to the recent developments of advanced models.

Saad, S. M.; Hamdy, M. A.; Abolazm, M. S.

2012-12-01

310

The Magnetic Fields and Magnetospheres of Hot Stars  

NASA Astrophysics Data System (ADS)

Strong advances in direct evidence of magnetic fields in hot massive stars have been possible thanks to the new generation of high-resolution spectropolarimeters such as ESPaDOnS (on the Canada-France-Hawaii Telescope) or HARPSpol (on the 3.6m ESO telescope). UV and optical high-resolution spectroscopy has also been very useful to study the magnetospheres of massive stars. In this contribution I review the observing tools and our current knowledge concerning the detection and characterization of the magnetic fields and magnetospheres in hot stars.

Alecian, E.

2012-12-01

311

O stars and Wolf-Rayet stars  

NASA Technical Reports Server (NTRS)

Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (editor); Thomas, Richard (editor)

1988-01-01

312

THE CHEMICAL COMPOSITIONS OF VARIABLE FIELD HORIZONTAL-BRANCH STARS: RR LYRAE STARS  

SciTech Connect

We present a detailed abundance study of 11 RR Lyrae ab-type variables: AS Vir, BS Aps, CD Vel, DT Hya, RV Oct, TY Gru, UV Oct, V1645 Sgr, WY Ant, XZ Aps, and Z Mic. High-resolution and high signal-to-noise ratio echelle spectra of these variables were obtained with the 2.5 m du Pont telescope at the Las Campanas Observatory. We obtained more than 2300 spectra, roughly 200 spectra per star, distributed more or less uniformly throughout the pulsational cycles. A new method has been developed to obtain the initial effective temperatures of our sample stars at a specific pulsational phase. We find that the abundance ratios are generally consistent with those of similar metallicity field stars in different evolutionary states and throughout the pulsational cycles for RR Lyrae stars. TY Gru remains the only n-capture enriched star among the RRab in our sample. A new relation is found between microturbulence and effective temperature among stars of the horizontal-branch population. In addition, the variation of microturbulence as a function of phase is empirically shown to be similar to the theoretical variation. Finally, we conclude that the derived T{sub eff} and log g values of our sample stars follow the general trend of a single mass evolutionary track.

For Biqing; Sneden, Christopher [Department of Astronomy, University of Texas, Austin, TX 78712 (United States); Preston, George W., E-mail: biqing.for@uwa.edu.au [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)

2011-12-01

313

Highly divergent homogenizers for UV and deep UV  

Microsoft Academic Search

For many applications such as lithography and material processing, the hsaping and homogenization of a UV or Deep UV source needed. Often the divergence angle needed is fairly large ($GTR5 degree(s)half angle). This can be very difficult using diffractive homogenizers, especially when the divergence needed approaches 10 degree(s)half angle. Presented in this paper is a new technique that has the

David R. Brown

2000-01-01

314

A binary model for the UV-upturn of elliptical galaxies  

NASA Astrophysics Data System (ADS)

The discovery of a flux excess in the far-ultraviolet (FUV) spectrum of elliptical galaxies was a major surprise in 1969. While it is now clear that this UV excess is caused by an old population of hot helium-burning stars without large hydrogen-rich envelopes, rather than young stars, their origin has remained a mystery. Here we show that these stars most likely lost their envelopes because of binary interactions, similar to the hot subdwarf population in our own Galaxy. We have developed an evolutionary population synthesis model for the FUV excess of elliptical galaxies based on the binary model developed by Han et al. for the formation of hot subdwarfs in our Galaxy. Despite its simplicity, it successfully reproduces most of the properties of elliptical galaxies with a UV excess: the range of observed UV excesses, both in (1550 - V) and (2000 - V), and their evolution with redshift. We also present colour-colour diagrams for use as diagnostic tools in the study of elliptical galaxies. The model has major implications for understanding the evolution of the UV excess and of elliptical galaxies in general. In particular, it implies that the UV excess is not a sign of age, as had been postulated previously, and predicts that it should not be strongly dependent on the metallicity of the population, but exists universally from dwarf ellipticals to giant ellipticals.

Han, Z.; Podsiadlowski, Ph.; Lynas-Gray, A. E.

2007-09-01

315

Lifestyles of the Stars.  

ERIC Educational Resources Information Center

Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)

National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

316

StarHeads  

NSDL National Science Digital Library

StarHeads, the last product of the Star*s Family is now available at the Centre de Donnees astronomiques de Strasbourg (CDS). StarHeads gives access to about 400 individual pages of astronomers and space scientists, and this figure is rapidly growing. Forms based browser is required.

317

Ultraviolet Radiation Exposure from UV-Transilluminators  

Microsoft Academic Search

UV-transilluminators use ultraviolet radiation (UVR) to visualize proteins, DNA, RNA, and their precursors in a gel electrophoresis procedure. This study was initiated to evaluate workers' exposure to UVR during their use of UV-transillumin- ators. The levels of irradiance of UV-A, UV-B, and UV-C were determined for 29 UV-transilluminators at arbitrary measuring locations of 6, 25, 62, and 125 cm from

Farhang Akbar-Khanzadeh; Mahdi Jahangir-Blourchian

2005-01-01

318

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

319

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

320

UV-LED photopolymerised monoliths.  

PubMed

For the first time photopolymerisation of polymer monoliths has been realised with UV-light emitting diodes (LEDs) as light source and demonstrated with polymethacrylate monoliths created in fused silica capillaries and plastic chips. PMID:18575635

Abele, Silvija; Nie, Fu-Qiang; Foret, Frantisek; Paull, Brett; Macka, Mirek

2008-07-01

321

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

322

Photometry in UV astronomical images of extended sources in crowded field using deblended images in optical visible bands as Bayesian priors  

Microsoft Academic Search

Photometry of astrophysical sources, galaxies and stars, in crowded field images, if an old problem, is still a challenging goal, as new space survey missions are launched, releasing new data with increased sensibility, resolution and field of view. The GALEX mission, observes in two UV bands and produces deep sky images of millions of galaxies or stars mixed together. These

D. Vibert; M. Zamojski; S. Conseil; A. Llebaria; S. Arnouts; B. Milliard; M. Guillaume

2009-01-01

323

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

324

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

325

The UV and optical properties of Old Novae  

NASA Astrophysics Data System (ADS)

We have examined the UV and optical properties of twenty old-novae observed with IUE. The de-reddened continuum energy distribution of all stars is well described by a power-law distribution F?˜?-? with ? ranging from 0.0 (GK Per) to 2.7 (V841 Oph). Our new values of EB-V have led to new estimates of the UV luminosities which range from less than 1 L? (DQ Her) to as much as 70 L? (HR Del and T Pyx). A tight correlation exists between LUV and MVmin, and both these quantities show a definite correlation with the system inclination angle cos i, with the notable exceptions of the extra slow nova HR Del and of the recurrent nova T Pyx that are too bright.

Selvelli, P.; Gilmozzi, R.

2005-08-01

326

Performance Results from In-Flight Commissioning of the Juno Ultraviolet Spectrograph (Juno-UVS)  

NASA Astrophysics Data System (ADS)

We present a description of the Juno ultraviolet spectrograph (Juno-UVS), results from the successful in-flight commissioning performed between December 5th and 13th 2011, and some predictions of future Jupiter observations. Juno-UVS is a modest power (9.0 W) ultraviolet spectrograph based on the Alice instruments now in flight aboard the European Space Agency’s Rosetta spacecraft, NASA’s New Horizons spacecraft, and the LAMP instrument aboard NASA’s Lunar Reconnaissance Orbiter. However, unlike the other Alice spectrographs, Juno-UVS sits aboard a rotationally stabilized spacecraft. The planned 2 rpm rotation rate for the primary mission results in integration times per spatial resolution element per spin of only 17 ms. Thus, data was retrieved from many spins and then remapped and co-added to build up integration times on bright stars to measure the effective area, spatial resolution, map out scan mirror pointing positions, etc. The Juno-UVS scan mirror allows for pointing of the slit approximately ±30° from the spacecraft spin plane. This ability gives Juno-UVS access to half the sky at any given spacecraft orientation. We will describe our process for solving for the pointing of the scan mirror relative to the Juno spacecraft and present our initial half sky survey of UV bright stars complete with constellation overlays. The primary job of Juno-UVS will be to characterize Jupiter’s UV auroral emissions and relate them to in situ particle measurements. The ability to point the slit will facilitate these measurements, allowing Juno-UVS to observe the surface positions of magnetic field lines Juno is flying through giving a direct connection between the particle measurements on the spacecraft to the observed reaction of Jupiter’s atmosphere to those particles. Finally, we will describe planned observations to be made during Earth flyby in October 2013 that will complete the in-flight characterization.

Greathouse, Thomas K.; Gladstone, G. R.; Davis, M. W.; Slater, D. C.; Versteeg, M. H.; Persson, K. B.; Winters, G. S.; Persyn, S. C.; Eterno, J. S.

2012-10-01

327

UV Morphology and Demographics of Galaxies in the Green Valley  

NASA Astrophysics Data System (ADS)

We discuss the demographics of galaxies chosen to be in the the so-called "Green Valley", a sparsely populated color-selected transition region between the "Blue Plume" (generally populated by actively star-forming spiral and irregular galaxies) and the "Red Sequence" (populated by elliptical and S0/lenticular galaxies). We are in the process of describing, typing and classifying these galaxies according to their UV morphology in an attempt to evaluate the likely physical mechanism(s) leading to their departure from the two main regions in which the majority of other galaxies are found.

Ryon, Jenna E.; Zernow, L.; Seibert, M.; Neill, D.; Madore, B. F.

2010-01-01

328

Herschel's Star Gages  

NSDL National Science Digital Library

The EJS Herschel's Star Gages Model illustrates William Herschel's methods of "star gages" by which he attempted to map out the shape of our galaxy in 1785. Herschel's star gages (sic) relied on two important assumptions: that Herschel's telescope (his "large 20 foot" with an 18.5 inch aperture) could see to the ends of the galaxy, and that within the galactic system stars are distributed uniformly. If the first assumption holds then the stars seen in the telescope all lie within a conical region of space with the apex at the telescope and the base at the edge of the galaxy. If the second assumption holds then the number of stars seen in the telescope is proportional to the volume of this cone. Since the volume of the cone is proportional to the cube of its height, the distance to the galactic edge in any direction is proportional to the cube root of the number of stars seen in that direction. This simulation allows the user to use Herschel's method of star gages to map out the shape of an artificial "star system" for which Herschel's assumptions are valid. One window shows the view through a telescope, with a slider to change the telescopes direction (around a single fixed axis). Another window shows a 3D view of the star system, showing either all of the stars in the system or only those stars visible through the telescope. A third window shows a plot of the star gages. Plotting star gages for many different directions maps out a cross-section of the star system. An optional slider allows the user to decrease the distance to at which stars are no longer visible, and a menu allows the user to select a star system in which the stars are not distributed uniformly. These options let the user explore how violations of Herschel's two fundamental assumptions invalidate his star gage method.

Timberlake, Todd

2011-05-28

329

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

330

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

331

Observations of stellar winds in early type stars  

NASA Technical Reports Server (NTRS)

The presented review is mainly concerned with the massive population I stars of spectral type OB and the Wolf-Rayet (WR) class. It is pointed out that stellar winds are a ubiquitous phenomenon among the early type stars. Methods to determine the mass loss rate are discussed, taking into account the UV method, the optical method, the infrared method, and the radio method. Current beliefs about early type stars are considered. It is thought that all have stellar winds. The winds are primarily driven by radiation pressure from the UV lines, but other, as yet unknown factors, may determine the density and hence the rates. The stellar winds are highly ionized, more so than would be inferred from their continuum radiation temperatures. The ionization equilibrium in the winds is affected by local X rays which have been detected by the Einstein satellite. Unresolved issues are also pointed out.

Conti, P. S.

1981-01-01

332

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

333

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

NASA Astrophysics Data System (ADS)

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

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

1989-08-01

334

Dispersal of Disks Around Young Stars  

NASA Technical Reports Server (NTRS)

We review the evidence pertaining to the lifetimes of planet-forming disks and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source, 2) close stellar encounters, 3) stellar winds, and 4) photoevaporation by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the inner disk (r < or approx. equals 10 AU), while photoevaporation is the principal process of disk dispersal outside of r > or approx. equals 10 AU for low mass stars. Disk dispersal timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed the solar nebula is called into question. 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

2001-01-01

335

Dispersal of Disks Around Young Stars  

NASA Technical Reports Server (NTRS)

We review the evidence pertaining to the lifetimes of planet-forming disks and discuss possible disk dispersal mechanisms: 1) viscous accretion of material onto the central source; 2) close stellar encounters; 3) stellar winds; and 4) photoevaporation by ultraviolet radiation. We focus on 3) and 4) and describe the quasi-steady state appearance and the overall evolution of disks under the influence of winds and radiation from the central star and of radiation from external OB stars. Viscous accretion likely dominates disk dispersal in the inner disk (r approx. or less than 10 AU), while photoevaporation is the principal process of disk dispersal outside of r approx. or greater than 10 AU for low mass stars. Disk dispersal timescales are compared and discussed in relation to theoretical estimates for planet formation timescales. Photoevaporation may explain the large differences in the hydrogen content of the giant planets in the solar system. The commonly held belief that our early sun's stellar wind dispersed he solar nebula is called into question. 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 (ultraviolet) photons from the nearby massive star Theta(1)C.

Hollenbach, David; DeVincenzi, D. (Technical Monitor)

2002-01-01

336

High-power UV lamps for industrial UV curing applications  

NASA Astrophysics Data System (ADS)

UV Curing is highly adaptable to printing, coating, decorating and assembling of a great variety of products and materials owing to some of its key attributes, it is: a low temperature process, a high speed process, and a solventless process--cure is by polymerization rather than by evaporation. The latest developments in UV lamps for industrial processing are presented. Among these are: (1) the selection and control of the lamp emission spectra to match the optical properties of the film and its photoinitiator, (2) sustained high power lamp operation at 6 kilowatts, and (3) the use of absorptive dichroic reflectors to manage the relative components of UV and infrared energy in the highly focused radiation delivered to surfaces being processed.

Stowe, Richard W.

1996-11-01

337

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

NASA Astrophysics Data System (ADS)

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

Wyder, Ted; Martin, Christopher

2012-07-01

338

UV technologies in water purification systems  

Microsoft Academic Search

A Abbssttrraacctt:: UV technologies are being increasingly used in water purification systems, taking advantage of the germicidal properties of UV and also its effect in reducing organic contaminants. This paper discusses the effectiveness of using UV technologies along a water purification chain and the parameters and configurations to be considered when selecting UV lamps for water purification systems. Also described

Ichiro Kano; Daniel Darbouret; Stéphane Mabic

339

Wolf-Rayet stars  

NASA Technical Reports Server (NTRS)

The properties and evolutionary status of WR stars are examined, reviewing the results of recent observational and theoretical investigations. Topics discussed include spectral types and line strengths, magnitudes and colors, intrinsic variability, IR and radio observations, X-ray observations, the Galactic distribution of WR stars, WR stars in other galaxies, and WR binaries. Consideration is given to the inferred masses, composition, and stellar winds of WR stars; model atmospheres; WR stars and the Galactic environment; and WR stars as a phase of stellar evolution. Diagrams, graphs, and tables of numerical data are provided.

Abbott, David C.; Conti, Peter S.

1987-01-01

340

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.

Nasa

2012-06-26

341

T Tauri stars pictured at ultraviolet and x-rays  

NASA Astrophysics Data System (ADS)

Newly calibrated IUE spectra and ROSAT data for a sample of T Tauri stars have been investigated. In the ultraviolet band a complete spectral atlases for our sample of stars is presented. We have identified the main spectral lines and the continuous emission. While for some stars the continuum is well explained by the sum of the stellar black body emission plus a hydrogenic component with a temperature in the range 1.4 to 5 × 104 K, there are however others which require a third component, i.e., black body emission at temperatures in the range 5900--9700 K covering a few percent of the stellar surface. In addition, we have utilised the observed line fluxes together with Emission Measure techniques to derive the temperature structure in the atmosphere of the stars. The behaviour of the stars is analysed showing noticeable differences. For the star LkH? 264 we have also established the connection between the UV analysis into optical ranges in terms of the continuum. The combined emission in the UV also fits the observed optical continuum well and we conclude that this star is an analogue of the Sun but displaying a much higher level of activity. The stars in the sample have also been studied in X-ray allowing for some newly detections. Also fundamental parameters have been derived. Within the sample we analysed in more detail those stars for which there are more than one set of observations and looked for X-ray variability. Three stars in our sample, V410 Tau, TW Hya and CS Cha, allow a detailed spectral analysis and we have also searched for variability, both short- and long-term within the limits of the data. The results of the spectral analysis for these stars can be successfully described by a model of emission from two-temperature, hot, optically thin plasma in collisional equilibrium. We have established the connection from the UV to the X-ray band extending the spectroscopic analysis from regions with plasma at temperatures below 104K to regions at ?107K. From comparison with the Sun we concluded that the behaviour of the stars can be tentatively classified in three types.

Costa, Vitor

2000-07-01

342

A 'Rosetta Stone' to Interpret the UV-HST Photometry of Multiple Stellar Populations in Globular Clusters  

NASA Astrophysics Data System (ADS)

In this proposal we intend to firmly identify the chemical species responsible for the UV and UV-optical color differences exhibited by the multiple stellar populations harboured by two Galactic globular clusters: omega Centauri and 47 Tucanae, one with highly helium enriched sub-populations {omega Centauri}, the other not.We plan to collect ultraviolet STIS spectra for stars in the crowded cores of the clusters, where HST photometry is already available for thousands of stars in more than 10 filters, from F225W to F850LP. This WFC3+ACS photometric database has allowed us to show that UV colors are remarkably effective in separating the different cluster sub-populations, and with the proposed STIS spectroscopy we can quantify the chemical abundance differences among such sub-populations, most notably in Nitrogen and Oxygen. The resulting calibration of the UV colors in terms of CNO abundances will provide a new effective tool for the chemical characterization of large numbers of globular cluster stars belonging to the various sub-populations in each cluster, and to better isolate the specific role of the helium abundance.The plan is to observe at least one star for each of the main principal stellar sub-populations in each of the two clusters. These objects are selected on the basis of their accurate photometry and astrometry already in hand, based on existing UV-HST images.

Renzini, Alvio

2010-07-01

343

UnISIS: Laser Guide Star and Natural Guide Star Adaptive Optics System  

NASA Astrophysics Data System (ADS)

UnISIS (University of Illinois Seeing Improvement System) is a versatile adaptive optics system mounted on a large optics bench at the coudé focus of the Mount Wilson 2.5-m telescope. It was designed to have both laser guide star (LGS) and natural guide star (NGS) adaptive optics capabilities. The LGS side of the system relies on a pulsed UV laser with raw power of 30 W capable of creating an artificial laser star via Rayleigh scattering 18 km above the telescope. The LGS system can work at temporal response rates as high as 333 Hz-limited by the UV laser pulse rate-and the NGS system can work at rates up to 1.4 kHz. Each side of the system has its own high-speed wavefront sensor that runs separately, but in the LGS mode the NGS wavefront sensor is converted into a natural star tip-tilt sensor. The deformable mirror is conjugate to the telescope's primary mirror and has one of the most densely packed sets of actuators of any adaptive optics system currently in operation. This paper provides details of the UnISIS design and describes key updates we have made to the system. We show NGS AO-corrected images from the sky from the 900 nm K band.

Thompson, Laird A.; Teare, Scott W.; Xiong, Yao-Heng; Castle, Richard M.; Chakraborty, Abhijit; Gruendl, Robert A.; Leach, Robert W.

2009-05-01

344

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

345

UV Eclipse Spectroscopy of Accretion Disk Winds  

NASA Astrophysics Data System (ADS)

We shall monitor wind-formed UV lines in the highly inclined disk-accreting CV, UX UMa as they are eclipsed by the companion star. By measuring the way in which lines from several different ionic species change in shape and strength as the wind is progressively covered, we will probe its ionisation structure as well as its geometry and kinematics. The data will be compared with the results of Monte Carlo simulation of the line profiles to provide quantitative constraints on outflow collimation, acceleration, and mass- loss rate. Our goal is to build a full and self consistent model for the wind and to determine where in the system the wind originates {e.g. white dwarf, boundary layer, or disk}. We will then be in a position to investigate what drives the wind and the effect it has on the underlying accretion disk structure. The proposal builds on highly successful observations of UX UMa begun by us in Cycle 2 in a restricted wavelength range. Repairs to the GHRS now permit its full potential for such a study to be realised. This is a carryover of part of GHRS proposal 6079 modified to use STIS.

Mason, Keith

1997-12-01

346

Classification and properties of UV extinction curves  

NASA Astrophysics Data System (ADS)

The catalog of Savage et al. (\\cite{ref27}) reporting colour excesses of 1415 stars from ANS photometry offers the opportunity to deeply investigate the characteristics of UV extinction curves which differ from the standard extinction of the diffuse interstellar medium. To this aim we have selected a sample of 252 curves, which have been compared with the relations derived by Cardelli et al. (\\cite{ref4}; CCM in the following) for a variety of R_V values in the range 2.4-5 and have been classified as normal if they fit at least one of the CCM curves or anomalous otherwise. We find that normal curves with small R_V are just as numerous as those with large R_V. The anomalous objects are arranged into two groups according to the strength of the bump at 0.217 mu . For a given value of c_2 this increases along the sequence: type A anomalous, normals and type B anomalous, suggesting that this sequence should correspond to an increase of the amount of small grains along the sightline. Considerations concerning the environmental characteristics indicate that the anomalous behaviour is not necessarily tied to the existence of dense gas clouds along the line of sight.

Barbaro, G.; Mazzei, P.; Morbidelli, L.; Patriarchi, P.; Perinotto, M.

2001-01-01

347

First detection of nonflare microwave emissions from the coronae of single late-type dwarf stars  

NASA Technical Reports Server (NTRS)

Results are presented of a search for nonflare microwave radiation from the coronae of nearby late-type dwarf stars comparable to the sun: single stars without evidence for either a large wind or circumstellar envelope. The observing program consisted of flux measurements of six stars over a 24-h period with the VLA in the C configuration at a wavelength of 6 cm with 50 MHz bandwidth. Positive detections at 6 cm were made for Chi 1 Ori (0.6 mJy) and the flare star UV Cet (1.55 mJy), and upper limits were obtained for the stars Pi 1 UMa, Xi Boo A, 70 Oph A and Epsilon Eri. It is suggested that Chi 1 Ori, and possibly UV Cet, represent the first detected members of a new class of radio sources which are driven by gyroresonance emission, i.e. cyclotron emission from nonrelativistic Maxwellian electrons.

Gary, D. E.; Linsky, J. L.

1981-01-01

348

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

349

Hierarchical Star Formation in LEGUS Galaxies  

NASA Astrophysics Data System (ADS)

Star formation generally follows a hierarchical distribution in galaxies from kpc scales in giant star complexes down to sub-pc scales in embedded clusters. This hierarchy corresponds to a power law distribution function for the number of star forming regions as a function of size or luminosity. Using the Legacy ExtraGalactic Ultraviolet Survey (LEGUS), we examine six galaxies, NGC 1566, NGC 1705, NGC 2500, NGC 5253, NGC 5477, and IC 4247, which span types from grand design and flocculent spirals to irregulars and starburst irregulars. Power law size and luminosity distributions were measured from Gaussian-blurred images in the NUV and UV using SExtractor. Slopes ranged from -1 to -1.8, with the steepest slopes corresponding to the starburst galaxies. The slopes did not vary from the NUV to the UV. The fraction of light contained within the largest scales ranged from 85 to 95 percent, independent of galaxy type. We acknowledge support from grant HST-GO-13364.

Elmegreen, Debra M.; Elmegreen, Bruce

2014-06-01

350

Habitability around F-type stars  

NASA Astrophysics Data System (ADS)

We explore the general astrobiological significance of F-type main-sequence stars with masses between 1.2 and 1.5 M ?. Special consideration is given to stellar evolutionary aspects due to nuclear main-sequence evolution. DNA is taken as a proxy for carbon-based macromolecules following the paradigm that extraterrestrial biology may be most likely based on hydrocarbons. Consequently, the DNA action spectrum is utilized to represent the impact of the stellar ultraviolet (UV) radiation. Planetary atmospheric attenuation is taken into account based on parameterized attenuation functions. We found that the damage inflicted on DNA for planets at Earth-equivalent positions is between a factor of 2.5 and 7.1 higher than for solar-like stars, and there are intricate relations for the time-dependence of damage during stellar main-sequence evolution. If attenuation is considered, smaller factors of damage are obtained in alignment to the attenuation parameters. This work is motivated by earlier studies indicating that the UV environment of solar-type stars is one of the most decisive factors in determining the suitability of exosolar planets and exomoons for biological evolution and sustainability.

Sato, S.; Cuntz, M.; Guerra Olvera, C. M.; Jack, D.; Schröder, K.-P.

2014-07-01

351

UV photolysis using a micromanipulated optical fiber to deliver UV energy directly to the sample  

Microsoft Academic Search

UV photolysis of caged molecules is a powerful method for studying cellular signaling. However, UV energy is often delivered through the microscope objective which can make certain experiments difficult. We have evaluated the utility of delivering UV pulses directly to the sample through an optical fiber. Visible (635 nm) and UV (337 nm) lasers were coupled into a UV transmitting

Vladimir Parpura; Philip G. Haydon

1999-01-01

352

STRONG VARIABLE ULTRAVIOLET EMISSION FROM Y GEM: ACCRETION ACTIVITY IN AN ASYMPTOTIC GIANT BRANCH STAR WITH A BINARY COMPANION?  

SciTech Connect

Binarity is believed to dramatically affect the history and geometry of mass loss in asymptotic giant branch (AGB) and post-AGB stars, but observational evidence of binarity is sorely lacking. As part of a project to look for hot binary companions to cool AGB stars using the Galaxy Evolution Explorer archive, we have discovered a late-M star, Y Gem, to be a source of strong and variable UV emission. Y Gem is a prime example of the success of our technique of UV imaging of AGB stars in order to search for binary companions. Y Gem's large and variable UV flux makes it one of the most prominent examples of a late-AGB star with a mass accreting binary companion. The UV emission is most likely due to emission associated with accretion activity and a disk around a main-sequence companion star. The physical mechanism generating the UV emission is extremely energetic, with an integrated luminosity of a few x L{sub sun} at its peak. We also find weak CO J = 2-1 emission from Y Gem with a very narrow line profile (FWHM of 3.4 km s{sup -1}). Such a narrow line is unlikely to arise in an outflow and is consistent with emission from an orbiting, molecular reservoir of radius 300 AU. Y Gem may be the progenitor of the class of post-AGB stars which are binaries and possess disks but no outflows.

Sahai, Raghvendra [Jet Propulsion Laboratory, MS 183-900, California Institute of Technology, Pasadena, CA 91109 (United States); Neill, James D. [California Institute of Technology, 1200 E. California Blvd. MC278-17, Pasadena, CA 91125 (United States); Gil de Paz, Armando [Dpto. de Astrofisica, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Sanchez Contreras, Carmen [Astrobiology Center (CSIC-INTA), ESAC campus, E-28691 Villanueva de la Canada, Madrid (Spain)

2011-10-20

353

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

354

LSPR enhanced MSM UV photodetectors.  

PubMed

We fabricated localized surface plasmon resonance enhanced UV photodetectors on MOCVD grown semi-insulating GaN. Plasmonic resonance in the UV region was attained using 36 nm diameter Al nanoparticles. Extinction spectra of the nanoparticles were measured through spectral transmission measurements. A resonant extinction peak around 300 nm was obtained with Al nanoparticles. These particles gave rise to enhanced absorption in GaN at 340 nm. Spectral responsivity measurements revealed an enhancement factor of 1.5. These results provided experimental verification for obtaining field enhancement by using Al nanoparticles on GaN. PMID:23080432

Butun, Serkan; Cinel, Neval A; Ozbay, Ekmel

2012-11-01

355

Star Formation in Galaxies  

NASA Technical Reports Server (NTRS)

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

1987-01-01

356

Open Star Clusters  

NSDL National Science Digital Library

This site offers information about the formation of star clusters, the pleiades, how to calculate star cluster distances, and much more. There are also some great images that techers can use on this website.

2005-02-11

357

'Polaris, Mark Kummerfeldt's Star, and My Star.'  

ERIC Educational Resources Information Center

In most astronomy courses, descriptions of stars and constellations reveal the western European origins of the astronomers who named them. However, it is suggested that a study of non-western views be incorporated into astronomy curricula. Descriptions of various stars and constellations from different cultures and instructional strategies are…

McLure, John W.

1984-01-01

358

Southern Cool Stars Misclassified as Carbon Stars  

NASA Astrophysics Data System (ADS)

We report a list of 24 red stars classified as carbon stars by one author. Close examination of them on near-IR objective-prism plates reveals that they are of M type or earlier. Three are variable in the ASAS-3 Catalog.

MacConnell, D. J.

2006-01-01

359

A star tracking algorithm suitable for star sensor  

NASA Astrophysics Data System (ADS)

The sufficient attitude knowledge including location of recognized stars in star image can be obtained with Lost-in-Space case. In order to make use of the sufficient attitude knowledge, the star sensor may work in star tracking case. To achieve this, a star tracking algorithm is proposed in this paper. The previous location of recognized stars in star image may be used to obtain location of observed star in proper region of current star image with the star tracking algorithm. The simulations and real sky experiment results show that the star tracking algorithm proposed in this paper not only improves update rate of star sensor, but also avoids fault star pattern recognition. Finally, a star sensor featuring star tracking algorithm proposed in this paper was for on-orbit demonstration.

Li, Baohua; Zhang, Yingchun; Li, Huayi; Wang, Changhong

2007-03-01

360

Spectroscopy of be stars  

NASA Astrophysics Data System (ADS)

This chapter describes non supergiant B-type stars that show emission lines, called Be stars. The emission is caused by the presence of a circumstellar decretion disk. Many physical phenomena are thought to be involved in these stars, such as rapid rotation, pulsations and magnetic fields, and give rise to variations. Spectroscopy is used as a diagnostic tool to study Be stars, by professional astronomers as well as by amateurs.

Neiner, C.

2011-04-01

361

Chromospheres of Coronal Stars  

NASA Technical Reports Server (NTRS)

We summarize the main results obtained from the analysis of ultraviolet emission line profiles of coronal late-type stars observed with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. The excellent GHRS spectra provide new information on magnetohydrodynamic phenomena in the chromospheres and transition regions of these stars. One exciting new result is the discovery of broad components in the transition region lines of active stars that we believe provide evidence for microflare heating in these stars.

Linsky, Jeffrey L.; Wood, Brian E.

1996-01-01

362

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

363

Far ultraviolet colors of B and Be stars  

NASA Astrophysics Data System (ADS)

A far-UV color index, G, which is free of interstellar reddening effects is applied to TD-1 satellite observations of B and Be stars listed in the catalogs of Jamar et al. (1976) and Macau-Hercot et al. (1978). The expressions defining G(in terms of the wavelengths 146, 235, and 274 nm) and the S70 index of spectral type are set forth. Tables of mean and individual-star G and S70 indices and plots of G versus S70, Delta-G versus spectral type, Delta-G versus H-alpha and H-beta intensity, and G versus V(sin i) are presented and discussed. The Be stars are classified as strong if they show strong Balmer emission, some Paschen and Fe II emission, and IR excess; otherwise they are 'weak'. Weak Be stars are found to have G similar to that of B stars, while G in strong Be stars is either much more negative or much less negative than in the B stars. No correlation is found between G and V(sin i) for either B or Be stars.

Zorec, J.; Divan, L.; Briot, D.

1983-09-01

364

Supernova Star Maps  

NSDL National Science Digital Library

This fun astronomy activity allows learners to experience finding stars in the night sky that will eventually go supernova. This activity is perfect for a star party outdoors. The PDF contains step-by-step instructions, photos, presentation tips, ready-to-print star maps, and links to background information.

Pacific, Astronomical S.

2008-01-01

365

Star Field Simulator.  

National Technical Information Service (NTIS)

A Star Field Simulator has been developed to serve as a source of radiation for the ASTRO Star Tracker. The star tracker and simulator are components of a motion compensation test facility located at Marshall Space Flight Center in Huntsville, Alabama. Pr...

1985-01-01

366

Main Sequence Stars  

NSDL National Science Digital Library

This website from the Australian Telescope Outreach and Education Group provides a thorough introduction to the life and death of stars. The website uses text, diagrams, and images to help explain how stars evolve. Highlights include a discussion of stellar fusion reactions and also a straightforward calculation of the lifetime of a star.

2007-06-12

367

Life Cycles of Stars  

NSDL National Science Digital Library

This Powerpoint presentation inroduces younger students to the life cycles of stars. Topics include stellar nurseries, types of stars, supernovae, the fates of stars of either high or low mass, and the creation of heavier elements by continued fusion of successively heavier elements.

368

America's Star Libraries  

ERIC Educational Resources Information Center

"Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

Lyons, Ray; Lance, Keith Curry

2009-01-01

369

The detection of ultraviolet photospheric absorption in the spectra of two Wolf-Rayet stars  

NASA Technical Reports Server (NTRS)

Narrow, unshifted UV absorption lines, principally of Fe v, have been detected in the spectra of two Wolf-Rayet stars, HD 93162 (WN7) and HD 193793 (WC7). Both stars are known to show upper Balmer-line absorption but exhibit no periodic Doppler shifts that might indicate the presence of a companion. If intrinsic to the Wolf-Rayet stars, these lines presumably form near the base of the envelope in the photosphere. The potential significance of absorption-line studies of Wolf-Rayet stars is discussed.

Fitzpatrick, E. L.

1982-01-01

370

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

371

UV stabilization of isosorbide polycarbonates  

US Patent & Trademark Office Database

Provided herein are polymeric compositions that are suitable protected from UV-induced discoloration and degradation. Such resins comprise an isosorbide polymer and one or more hindered amines. These resin compositions are useful in the manufacture of various shaped, formed and/or molded articles.

2014-01-21

372

UV photobiochemistry under space conditions  

NASA Astrophysics Data System (ADS)

The response of spores of Bacillus subtilis, cells of Deinococcus radiodurans and conidia of Aspergillus ochraceus to actual and simulated space conditions (UV in combination with long-term exposure to extremely dry conditions, including vacuum) has been studied: The following effects have been analyzed: decrease of viability, occurrence of DNA double strand breaks, formation of DNA-protein cross-links and DNA-DNA cross-links. All organisms show an increased sensitivity to UV light in extreme dryness (dry argon or vacuum) compared to an irradiation in aqueous suspension. The UV irradiation leads in all cases to a variety of DNA lesions. Very conspicuous is the occurrence of double strand breaks. Most of these double strand breaks are produced by incomplete repair of other lesions, especially base damages. The increase in DNA lesions can be correlated to the loss in viability. The specific response of the chromosomal DNA to UV irradiation in extreme dryness, however, varies from species to species and depends on the state of dehydration. The formation of DNA double strand breaks and DNA-protein cross-links prevails in the case of B. subtilis spores. In cells of Deinococcus radiodurans DNA-DNA cross-links often predominate, in conidia of Aspergillus ochraceus double strand breaks. The results obtained by direct exposure to space conditions (EURECA mission and D2 mission) largely agree with the laboratory data.

Dose, K.; Bieger-Dose, A.; Dillmann, R.; Gill, M.; Kerz, O.; Klein, A.; Stridde, C.

373

Cool stars, stellar systems, and the sun; Proceedings of the 6th Cambridge Workshop, Seattle, WA, Sept. 18-21, 1989  

NASA Technical Reports Server (NTRS)

The present conference on cool stars, stellar systems, and the sun encompasses stellar chromospheres and coronae, binary stars, the stellar evolution of contracting stars and red giants, stellar evolution abundances of the elements, mass loss and envelopes, and stellar pulsation. Specific issues addressed include theories regarding the acoustic and magnetic heating of stellar chromospheres and coronae, stellar granulation, wave heating in magnetic flux tubes, observations of the solar Ca-II lines, longitudinal-transverse magnetic tube waves in the solar atmosphere, radio emission from rapidly rotating cool giant stars, and spot temperatures and area coverages on active dwarf stars. Also addressed are the optical and UV spectra of RS-CVn stars, emission lines from T-Tauri stars, the spectroscopy of HR1614 group stars, red giants in external galaxies, the rotation of evolved stars, the transition from red giant to planetary nebula, and radiative transfer in the dynamic atmospheres of variable stars.

Wallerstein, George (editor)

1990-01-01

374

X-ray sources in regions of star formation. III - Naked T Tauri stars associated with the Taurus-Auriga complex  

NASA Technical Reports Server (NTRS)

Ground-based and IRAS optical and IR spectroscopic and photometric observations are reported for 90 stars in or near 59 Einstein Observatory X-ray error circles in the Tau-Aur region. The data are presented in extensive tables and sample spectra and characterized in detail, with particular attention to 28 newly discovered 'naked' T Tau stars, which are shown to be normal stars with no significant IR or UV excess and ages of 1-40 Myr. These stars are found to outnumber normal T Tau stars by a factor of 10 in an area near the Tau-Aur dark clouds, and it is argued that their evolution toward the ZAMS is typical for low-mass stars. The implications of this finding for the time scales of circumstellar-disk dissipation and planet formation are discussed.

Walter, Frederick M.; Brown, A.; Mathieu, R. D.; Myers, P. C.; Vrba, F. J.

1988-01-01

375

Simulated versus observed UV emission at high redshift: a hint for a clumpy interstellar medium?  

NASA Astrophysics Data System (ADS)

We discuss the rest-frame UV emission between 5 < z < 7 from the MareNostrum High-z Universe, an smoothed particle hydrodynamics simulation done with more than 2 billion particles. Cosmological simulations of galaxy formation generally overpredict the UV rest-frame luminosity function at high redshift, both at the bright and faint ends. In this Letter, we explore a dust attenuation model where a larger extinction is applied to star populations younger than a given age, mimicking the effect of a clumpy interstellar medium. We show that this scenario fits reasonably well both the UV luminosity functions and the UV continuum slopes derived from observations. The model assumes a large obscuration for stars younger than 25 Myr from the gas clouds where they should be embedded at their formation time. We find that the optical depth in these clouds should be between 30 and 100 times larger than the mean optical depth for the homogeneous part of the interstellar medium. These values are one order of magnitude larger than those estimated in local galaxies. Therefore, we conclude that ? cold dark matter predictions for the high-z UV emission can accommodate the current observations if we consider a dust extinction model based on the assumption of a clumpy environment at high redshift.

Forero-Romero, Jaime E.; Yepes, Gustavo; Gottlöber, Stefan; Knollmann, Steffen R.; Khalatyan, Arman; Cuesta, Antonio J.; Prada, Francisco

2010-03-01

376

The Correlation of UV Extinction and IR Emission in Bright Visual Reflection Nebulae  

NASA Astrophysics Data System (ADS)

Reflection nebulae are natural laboratories for the study of interstellar grains. To investigate the variation in ultraviolet extinction with infrared emission, we propose to obtain lowdispersion IUE observations of latetype B stars within several bright visual reflection nebulae. Our proposed observations will compliment existing data obtained previously by IUE for reflection nebulae excited by early-type B stars. In addition, our proposal compliments the earlier infrared studies of reflection nebulae (Sellgren, Luan, & Werner 1990, Casey 1991) by adopting a parametric decomposition of UV extinction (Fitzpatrick and Massa 1990). A parametric study of UV extinction and IR emission must necessarily precede a detailed analysis of optical nebular grain properties or dusty nebular environments. Recent models of interstellar grains predict systematic variations in UV extinction with variations in the abundance of very small grains (Desert, Boulanger, and Puget 1990) and/or variations in equilibrium grain temperature (Hecht 1986). A systematic study of nebular UV extinction and IR emission will test many of these predictions. If galactic extinction results from the superposition of distinct grain populations, then we expect to find correlated variations between observations of UV extinction and IR emission in bright visual reflection nebulae.

Casey, Sean C.

377

Strange Quark Star Crusts  

SciTech Connect

If strange quark matter is absolutely stable, some neutron stars may be strange quark stars. Strange quark stars are usually assumed to have a simple liquid surface. We show that if the surface tension of droplets of quark matter in the vacuum is sufficiently small, droplets of quark matter on the surface of a strange quark star may form a solid crust on top of the strange quark star. This solid crust can significantly modify the predictions for the photon emission for the surface in an observable way.

Steiner, Andrew W. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States)

2007-02-27

378

Neutron Star Collision  

NSDL National Science Digital Library

Systems of orbiting neutron stars are born when the cores of two old stars collapse in supernova explosions. Neutron stars have the mass of our Sun but are the size of a city, so dense that boundaries between atoms disappear. Einsteins theory of general relativity predicts that the orbit shrinks from ripples of space-time called gravitational waves. After about 1 billion simulation years, the two neutron stars closely circle each other at 60,000 revolutions per minute. The stars finally merge in a few milliseconds, sending out a burst of gravitational waves.

Bock, Dave; Shalf, John; Swesty, Doug; Calder, Alan; Wang, Ed

1999-01-21

379

The Near-Ultraviolet Continuum of Late-Type Stars  

NASA Astrophysics Data System (ADS)

Analyses of the near-ultraviolet continuum of late-type stars have led to controversial results regarding the performance of state-of-the-art model atmospheres. The release of the homogeneous International Ultraviolet Explorer (IUE) final archive and the availability of the high-accuracy Hipparcos parallaxes provide an opportunity to revisit this issue, as accurate stellar distances make it possible to compare observed absolute fluxes with the predictions of model atmospheres. The near-UV continuum is highly sensitive to Teff and [Fe/H], and once the gravity is constrained from the parallax, these parameters may be derived from the analysis of low-dispersion, long-wavelength (2000-3000 Å) IUE spectra for stars previously studied by Alonso, Arribas, & Martínez-Roger using the Infrared Flux Method (IRFM). A second comparison is carried out against the stars spectroscopically investigated by Gratton, Carretta, & Castelli. It is shown that there is a good agreement between Teff values obtained from the IRFM and those from the near-UV continuum, and a remarkable correspondence between observed and synthetic fluxes for stars with 4000 K<=Teff<=6000 K of any metallicity and gravity. These facts suggest that model atmospheres provide an adequate description of the near-UV continuum forming region and that the opacities involved are essentially understood.

Allende Prieto, Carlos; Lambert, David L.

2000-05-01

380

A complete census of massive star formation in M31 and M33: The relation between star formation and ISM properties  

NASA Astrophysics Data System (ADS)

We utilize GALEX FUV and NUV observations (Thilker et al. 2004), WSRT and VLA HI mosaics, published CO data, plus Spitzer (MIPS) and ISO imagery of M31 and M33 to measure the spatial distribution of extinction-corrected star formation rate (SFR) and gas surface density. The powerful combination of UV and IR datasets allows us to firmly constrain the SFR over a comprehensive range of galactic environments, from relatively unobscured locales to highly extincted clusters embedded in the spiral arms. With this complete census of massive star forming regions, we re-examine the relationship between the multi-phase ISM and recent star formation activity, focusing on the Schmidt Law and well-known star formation thresholds. This project is complementary to the companion poster of Gordon et al. which compares IR, H-alpha, and UV SFR tracers in M31.

Thilker, D. A.; Bianchi, L.; Braun, R.; Gordon, K.; Rieke, G.; Krause, O.; Engelbracht, C.; Hines, D.; Hinz, J.; Misselt, K.; Perez-Gonzalez, P.; Su, K.; Young, E.; Latter, W.; Levine, D.; Stolovy, S.; Noriega-Crespo, A.; Werner, M.; Mould, J.; Barmby, P.; Willner, S.; GALEX Science Team

2004-12-01

381

Detailed FUSE Study of a Star Behind the Cygnus Loop  

NASA Astrophysics Data System (ADS)

We will observe an sdOB star behind the Cygnus Loop supernova remnant to study the line-of-sight interstellar medium structures toward and through this prototypical remnant. The star was identified from Ultraviolet Imaging Telescope UV imaging and lies behind the bright NE Cygnus Loop filaments. New ground-based data and a preliminary FUSE Cycle 3 spectrum (program C052) demonstrate conclusively that the star is behind the supernova remnant. This is the first FUV background source known for the Cygnus Loop. We will re-observe this star to obtain improved signal-to-noise ratio data, and will also observe optically-emitting filaments directly adjacent, making a combined emission-absorption line study of the region possible. These two nearly complementary ways of studying the same region will provide the most detailed look to date at the workings of the Cygnus Loop blast wave as it encounters an interstellar cloud.

Blair, W.

382

Identification of the 1600A feature in Lambda Bootis stars  

NASA Astrophysics Data System (ADS)

The nature of the absoprtion feature near 1600A in ? Bootis stars, which is one of the strongest features in these objects, is a longstanding puzzle. In this study we demonstrate that it is caused by quasimolecular absorption leading to a satellite in the Lyman ? profile due to perturbations by neutral hydrogen. This feature has also been observed in the hydrogen-rich DA white dwarfs. The satellite is not observable in normal A stars because of the extremely strong distortion of the UV flux by metal lines, especially of C, Si, and Fe. Although the C abundance seems to be close to solar in ? Bootis stars, the Si, Fe, and other metal abundances are sufficiently reduced to make the feature visible. For the same reason the feature is conspicuous in metal-deficient horizontal branch stars of spectral type A.

Holweger, H.; Koester, D.; Allard, N. F.

1994-10-01

383

The chemical abundances of the Ap star HD94660  

NASA Astrophysics Data System (ADS)

In this work I present the determination of chemical abundances of the Ap star HD94660, a possible rapid oscillating star. As all the magnetic chemically peculiar objects, it presents CNO underabundance and overabundance of iron peak elements of ˜100 times and of rare earths up to 4 dex with respect to the Sun. The determination was based on the conversion of the observed equivalent widths into abundances simultaneously to the determination of effective temperature and gravity. Since the Balmer lines of early type stars are very sensitive to the surface gravity while the flux distribution is sensitive to the effective temperature, I have adopted an iterative procedure to match the H? line profile and the observed UV-Vis-NIR magnitudes of HD94660 looking for a consistency between the metallicity of the atmosphere model and the derived abundances. From my spectroscopic analysis, this star belongs to the no-rapid oscillating class.

Giarrusso, M.

2014-05-01

384

Predicted UV properties of very metal-poor starburst galaxies  

NASA Astrophysics Data System (ADS)

Aims: We study the expected properties of starburst galaxies in order to provide the point of reference for interpretation of high-z galaxy surveys and of very metal-poor galaxies. We concentrate mainly on the UV characteristics such as the ionizing spectra, the UV continuum, the Ly? and He ii ?1640 line and two-photon continuum emission. Methods: We use evolutionary synthesis models covering metallicities from Pop III to solar and a wide range of IMFs. We also combine the synthetic SEDs with the CLOUDY photoionization code for more accurate predictions of nebular emission, and to study possible departures from case B assumed in the synthesis models. Results: The ionizing fluxes, UV continuum properties, and predicted Ly? and He ii ?1640 line strengths are presented for synthesis models covering a wider range of parameter space than our earlier calculations. Strong departures from case B predictions are obtained for Ly? and 2? continuum at low metallicities. At low nebular densities both are shown to be enhanced proportionally to the mean energy carried by the Lyman continuum photons emitted by the ionizing source. Larger Ly? equivalent widths are therefore predicted at low metallicity. The He ii ?1640 line can be weaker than case B predicts (in terms of flux as well as the equivalent width) due to its ionization parameter dependence and to the enhanced underlying 2? continuum. Conclusions: Our results have implications for the interpretation of star-forming metal-poor and/or high redshift galaxies, for galaxies among the Ly? emitters (LAE) and Lyman Break galaxy (LBG) populations, and for searches of Population III stars in the distant Universe. The full set of model results is available at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/523/A64

Raiter, A.; Schaerer, D.; Fosbury, R. A. E.

2010-11-01

385

Ponderable soliton stars  

NASA Technical Reports Server (NTRS)

The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

Chiu, Hong-Yee

1990-01-01

386

Negative infrared flares of flare stars  

SciTech Connect

The basic formulation of the so-called fast electron hypothesis is presented. According to this hypothesis, the optical flares of UV Cet-type stars are caused by the inverse compton effect, i.e., nonthermal interactions of infrared photons with fast electrons (E equal to about 1.5 MeV), as well as nonthermal bremsstrahlung. The spontaneous appearance of fast electrons on the outer regions of the star is the essence of the flare. The fast electron hypothesis elicits two important predictions: (1) the possibility of X-ray emission during the stellar flares and (2) the inevitability of negative infrared flares. Both predictions are confirmed by direct observations. The importance of negative infrared flares is especially striking; it may be taken as convincing evidence that the inverse Compton effect may really work in the stellar atmospheres. 25 references.

Gurzadian, G.A.

1988-09-01

387

Hot, Massive Stars in I Zw 18  

NASA Technical Reports Server (NTRS)

I Zw 18 is one of the most primitive blue, compact dwarf galaxies. The ionized gas in I Zw 18 has a low oxygen abundance (O approx.1/30 Osun) and nitrogen abundance (N-1/100 Nsun) (Pequignot 2008). We have obtained a far-UV spectrum of the northwest massive star cluster of I Zw 18 using Hubble's Cosmic Origins Spectrograph (COS). The spectrum is compatible with continuous star-formation over the past approx.10 Myr, and a very low metallicity, log Z/Zsun 1.7, although the stellar surface may be enhanced in carbon. Stellar wind lines are very weak, and the edge velocity of wind lines is very low (approx.250 km/s).

Heap, Sara R.; Lindler, D.; Malumuth, E.

2011-01-01

388

Plaskett's Star (HD 47129): Still More Curious  

NASA Astrophysics Data System (ADS)

The properties of the components of Plaskett's Star (HD 47129) have been the subject of a continuing controversy for over seven decades. In a recent paper, Bagnuolo, Gies, & Wiggs analyzed a set of 17 UV spectra of this object from IUE archives. A tomography algorithm was used to produce the individual spectra of the two components. The physical properties of the stars were estimated including the mass ratio (q = 1.18), the UV intensity ratio (rUV = 0.53), the interpolated MK types (07.3 I and 06.2 I, respectively), and the rotational velocities (v sin i ? 88 km s-1 and 310 km s-1, respectively). These properties of the primary and secondary of RD 47129 were questioned by Underhill based on visual spectra. We now present reconstructions of the component spectra in four visual wavebands with data obtained using the CHARA 1 m Multiple Telescope Telescope (MTT). Data were taken at nine epochs well distributed in orbital phase about the 14.4 day period and separated with a tomography algorithm. An analysis produces results consistent with those of Bagnuolo, Gies, & Wiggs. Specifically, we find that the secondary is roughly 1-1.5 subclasses earlier than the primary (O7 vs. O8.5 from He II ?4542: He I ?4471 ratio. The intensity ratio in the visual is about 0.5 (primary brighter). The mass ratio appears to be similar to that estimated from the UV lines (q = 1.18). The primary lines are sharp and are compatible with a relatively low rotational velocity from the primary: V sin i = 105 km s-1. The secondary lines appear to be rotationally broadened, and we estimate that V sin i = 370 km s-1 for this star. We suggest that the main reason for the discrepancy between our interpretation and Underhill's is abundance differences in the stars. Specifically, the primary appears to be depleted in C and O and enriched in N. We briefly discuss the implications for the evolutionary history of this interesting binary.

Bagnuolo, William G., Jr.; Barry, Donald J.

1996-09-01

389

Highly divergent homogenizers for UV and deep UV  

NASA Astrophysics Data System (ADS)

For many applications such as lithography and material processing, the hsaping and homogenization of a UV or Deep UV source needed. Often the divergence angle needed is fairly large ($GTR5 degree(s)half angle). This can be very difficult using diffractive homogenizers, especially when the divergence needed approaches 10 degree(s)half angle. Presented in this paper is a new technique that has the ability to homogenize and shape a deep UV source by more than 10 degree(s)half angle. This technique uses a deep ($GTR10 waves) microstructure that bends the light by the required amount. The fabrication of this microstructure is practical only with gray scale or analog lithography. With gray scale lithography, complicated smooth surface relief structures are possible in one lithography step. Older fabrication methods have good design freedom in the two dimensions associated with the plane of the wafer or optic but have limited design freedom in the dimension of the microstructure depth. Gray scale lithography opens up this dimension of the micro optic as a design freedom making higher performance micro optics possible and economical. Design, fabrication, modeling and test results will be discussed.

Brown, David R.

2000-10-01

390

DETECTION OF IRON IN PG1159 STARS  

SciTech Connect

Up to now, iron had not been found in any hydrogen-deficient (pre-) white dwarf of spectral type PG1159, despite intense searching in a number of objects. Consequently, an iron deficiency was claimed, in some cases at least 1 dex. The primary indicators were UV lines of Fe VII. Therefore, the search was confined to relatively cool PG1159 stars (T{sub eff} {approx}<150,000 K), otherwise Fe is too strongly ionized for a significant population of Fe VII. In this Letter, we announce the discovery of iron in the very hottest PG1159 stars (T{sub eff} = 150,000-200,000 K; RX J2117.1+3412, K 1-16, Longmore 4, NGC 246, H1504+65), based on the identification of the Fe X {lambda}{lambda}979.3, 1022.9 lines in spectra obtained with the Far Ultraviolet Spectroscopic Explorer. Surprisingly, our analysis results in a solar iron abundance for these stars. It is conspicuous that they are among the most massive PG1159 stars (0.71-0.82 M{sub sun}), in contrast to those objects for which strongest Fe deficiency was claimed (0.53-0.56 M{sub sun}).

Werner, Klaus; Rauch, Thomas [Institute for Astronomy and Astrophysics, Kepler Center for Astro and Particle Physics, Eberhard Karls University Tuebingen, Sand 1, 72076 Tuebingen (Germany); Kruk, Jeffrey W., E-mail: werner@astro.uni-tuebingen.d [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)

2010-08-10

391

A Spectral Survey of Evolved Stars  

NASA Astrophysics Data System (ADS)

We report a spectral line survey of the circumstellar envelopes of evolved stars using the Arizona Radio Observatory 12 m and 10 m telescopes, covering the frequency ranges from 71-161 GHz and 218-268GHz. Our sample consists of the AGB stars IRC 10216 and CIT 6, the proto-planetary nebula AFGL 2688, and the young planetary nebula NGC 7027. The data allow us to investigate the chemistry processes in different physical environments and evolutionary stages. A total of more than 500 emission features (mostly rotational transitions of molecules) are detected in the survey. Our observations show that the sources in different evolutionary stages have remarkably different chemical composition. As a star evolves from AGB stage to proto-planetary nebula, the abundances of Si-bearing molecules (SiO, SiCC, and SiS) decrease, while the abundances of some long-chain molecules, such as CH3CN, C4H, and HC3N, increase. After further evolution to the planetary nebula stage, the abundances of neutral molecules decrease, and the emission from molecular ions becomes more intense. These differences can be attributed to the changes of the role that dust, stellar wind, shock wave, and UV/X-ray from the central star play in different evolutionary stages. These results will provide significant constraints on models of circumstellar chemistry.

Kwok, Sun; Zhang, Y.; Trung, D. V.

2007-12-01

392

The AFP-675 Far Ultraviolet Cameras experiment - Observations of the far-UV space environment  

NASA Technical Reports Server (NTRS)

The NRL's Far UV Cameras experiment flew aboard the Shuttle Orbiter on STS-39, in 1991: obtaining 105-200 nm measurements of the upper atmosphere, astronomical targets, and the Shuttle environment. Attention is presently given to observations of O2 density vs altitude in the nighttime atmosphere, the nocturnal ionosphere, Space Shuttle FUV glow, and photometry for both the stars and diffuse sources of 12 star fields at high and low galactic latitudes. The first FUV observations of the extended region of reflection nebulosity in Scorpius are included.

Carruthers, George R.; Morrill, Jeff S.; Dohne, Brian C.; Christensen, Susan A.

1993-01-01

393

What the UV SED Tells us About Stellar Populations and Galaxies  

NASA Technical Reports Server (NTRS)

The UV SED parameter b as in f(sub 1) 1(sup b), is commonly used to estimate fundamental properties of high-redshift galaxies including age and metallicity. However, sources and processes other than age and metallicity can influence the value of b. We use the local starforming dwarf galaxy, I Zw 18, in a case study to investigate uncertainties in age and metallicity inferred from b due errors or uncertainties in: mode of star formation (instantaneous starburst vs. continuous SF), dust extinction, nebular continuous emission (2-photon emission, Balmer continuum flux), and presence of older stars.

Heap, Sara R.

2011-01-01

394

Rocket instrument for far-UV spectrophotometry of faint astronomical objects  

NASA Technical Reports Server (NTRS)

A sensitive sounding rocket instrument for moderate (about 10-A) resolution far-UV (1160-1750-A) spectrophotometry of faint astronomical objects has been developed. The instrument employes a photon-counting microchannel plate imaging detector and a concave grating spectrograph behind a 40-cm Dall-Kirkham telescope. A unique remote-control pointing system, incorporating an SIT vidicon aspect camera, two star trackers, and a tone-encoded command telemetry link, permits the telescope to be oriented to within 5 arc sec of any target for which suitable guide stars can be found. The design, construction, calibration, and flight performance of the instrument are discussed.

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

1980-01-01

395

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

PubMed

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

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

1980-03-01

396

UV Filters for Lighting of Plants.  

National Technical Information Service (NTIS)

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 ...

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

1994-01-01

397

UV Laser Ablation of Electronically Conductive Polymers.  

National Technical Information Service (NTIS)

The UV laser ablation of thin polypyrrole and polyaniline films coated on an insulating substrate is described. UV laser ablation is used to pattern the conductive polymer coating; patterns with submillimeter features are easily obtained with edge resolut...

L. S. Van Dyke C. J. Brumlik Z. Yu G. J. Collins C. R. Martin

1992-01-01

398

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...

399

UV and Optical Detectors: Status and Prospects  

NASA Technical Reports Server (NTRS)

UV and visible detectors - status and prospects. The status and prospects for UV and visible detectors for space astrophysics missions will be described, based on the findings of the NASA working group roadmap report, hopefully updated.

Woodgate, Bruce; Oegerle, William (Technical Monitor)

2002-01-01

400

An Ultraviolet Investigation of Activity on Exoplanet Host Stars  

NASA Astrophysics Data System (ADS)

Using the far-UV (FUV) and near-UV (NUV) photometry from the NASA Galaxy Evolution Explorer (GALEX), we searched for evidence of increased stellar activity due to tidal and/or magnetic star-planet interactions (SPI) in the 272 known FGK planetary hosts observed by GALEX. With the increased sensitivity of GALEX, we are able probe systems with lower activity levels and at larger distances than what has been done to date with X-ray satellites. We compared samples of stars with close-in planets (a < 0.1 AU) to those with far-out planets (a > 0.5 AU) and looked for correlations of excess activity with other system parameters. This statistical investigation found no clear correlations with a, Mp , or Mp /a, in contrast to some X-ray and Ca II studies. However, there is tentative evidence (at a level of 1.8?) that stars with radial-velocity-(RV)-detected close-in planets are more FUV-active than stars with far-out planets, in agreement with several published X-ray and Ca II results. The case is strengthened to a level of significance to 2.3? when transit-detected close-in planets are included. This is most likely because the RV-selected sample of stars is significantly less active than the field population of comparable stars, while the transit-selected sample is similarly active. Given the factor of 2-3 scatter in fractional FUV luminosity for a given stellar effective temperature, it is necessary to conduct a time-resolved study of the planet hosts in order to better characterize their UV variability and generate a firmer statistical result. Based on observations made with the NASA Galaxy Evolution Explorer. GALEX is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034.

Shkolnik, Evgenya L.

2013-03-01

401

AN ULTRAVIOLET INVESTIGATION OF ACTIVITY ON EXOPLANET HOST STARS  

SciTech Connect

Using the far-UV (FUV) and near-UV (NUV) photometry from the NASA Galaxy Evolution Explorer (GALEX), we searched for evidence of increased stellar activity due to tidal and/or magnetic star-planet interactions (SPI) in the 272 known FGK planetary hosts observed by GALEX. With the increased sensitivity of GALEX, we are able probe systems with lower activity levels and at larger distances than what has been done to date with X-ray satellites. We compared samples of stars with close-in planets (a < 0.1 AU) to those with far-out planets (a > 0.5 AU) and looked for correlations of excess activity with other system parameters. This statistical investigation found no clear correlations with a, M{sub p} , or M{sub p} /a, in contrast to some X-ray and Ca II studies. However, there is tentative evidence (at a level of 1.8{sigma}) that stars with radial-velocity-(RV)-detected close-in planets are more FUV-active than stars with far-out planets, in agreement with several published X-ray and Ca II results. The case is strengthened to a level of significance to 2.3{sigma} when transit-detected close-in planets are included. This is most likely because the RV-selected sample of stars is significantly less active than the field population of comparable stars, while the transit-selected sample is similarly active. Given the factor of 2-3 scatter in fractional FUV luminosity for a given stellar effective temperature, it is necessary to conduct a time-resolved study of the planet hosts in order to better characterize their UV variability and generate a firmer statistical result.

Shkolnik, Evgenya L., E-mail: shkolnik@lowell.edu [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States)

2013-03-20

402

Mg II h + k Flux - Rotational Period Correlation for G-type Stars  

NASA Astrophysics Data System (ADS)

We present an analysis of the correlation between the mid-UV Mg II h and k emission lines and measured rotational periods of G-type stars. Based on IUE and HST high resolution spectra of a sample of 36 stars, we derive an exponential function that best represents the correlation. We find that the variation of the Mg II h + k fluxes is about a factor of 2.5 larger than that of Ca II H + K, indicating that the UV features are more sensitive to the decline of Prot. The comparison of UV-predicted rotational periods with those derived from empirical Prot - Ca II H + K flux calibrations are consistent, with some scatter at large periods, where the emissions are less intense. We present newly derived rotational periods for 15 G-type stars.

Olmedo, Manuel; Chávez, Miguel; Bertone, Emanuele; De la Luz, Víctor

2013-12-01

403

Protein Determination by UV Absorption  

Microsoft Academic Search

\\u000a Quantitation of the amount of protein in a solution is possible in a simple spectrometer. Absorption of radiation in the near\\u000a UV by proteins depends on the Tyr and Trp content (and to a very small extent on the amount of Phe and disulfide bonds). Therefore\\u000a the A\\u000a 280 varies greatly between different proteins (for a 1 mg\\/mL solution, from

Alastair Aitken; Michèle Learmonth

404

Protein Determination by UV Absorption  

Microsoft Academic Search

\\u000a Quantitation of the amount of protein in a solution is possible in a simple spectrometer. Absorption of radiation in the near\\u000a UV by proteins depends on the Tyr and Trp content (and to a very small extent on the amount of Phe and disulfide bonds). Therefore\\u000a the A280 varies greatly between different proteins (for a 1 mg\\/mL solution, from 0

Alastair Aitken; Michèle P. Learmonth

405

Spectrum Synthesis of UV Ga II and Ga III Lines Compared to IUE Observations of HD 25823 and HD 17081.  

National Technical Information Service (NTIS)

The exceptional overabundance of gallium in the magnetic silicon star HD 25823 was studied using the strongest UV Ga II and Ga III lines in IUE spectra. Atomic data were collected to perform an LTE synthetic calculation of the spectral ranges 1406 to 1422...

R. Freire-ferrero M. C. Artu

1986-01-01

406

UV filters for lighting of plants  

Microsoft Academic Search

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

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

1994-01-01

407

Modulation of Immune Function by UV Radiation  

Microsoft Academic Search

In addition to its carcinogenic activity, ultraviolet (UV) radiation is capable of modifying certain immunologic reactions. Immunologic alterations induced in mice by UV radiation include both local and distant effects. Local alterations result from a direct effect of UV radiation on an immune reaction that takes place at the site of irradiation. Distant alterations are those in which exposure of

Margaret L. Kripke; Warwick L. Morison

1985-01-01