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1

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

2

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

3

FUSE Observations of the Classical dMe Flare Star UV Ceti  

NASA Astrophysics Data System (ADS)

We propose to use FUSE in the TTAG observing mode to observe the classical dMe flare star UV Ceti. This is one of the most active of all flare stars and so provides the best opportunity of obtaining large flares, with enough photons to examine the time history of the event. FUSE is an excellent instrument for investigating flares, since the prominent CIII and O IV lines are formed in the transition region and lower corona, where the flare events are thought to originate. These lines not only provide valuable density diagnostics, but are also sufficiently resolved by FUSE to allow an investigation of turbulence and flows during the larger events. The goals of the program are to understand (1) the dynamics of the flares, (2) the relation between flare occurrence rate and energy released, (3) the physical characteristics within the flare region, (4) the properties of the continuum emission and 5) the characteristics of the quiescent emission.

Robinson, L.

4

Quiescent and flaring radio emission from the flare stars AD Leonis, EQ Pegasi, UV Ceti, Wolf 630, YY Geminorum and YZ Canis Minoris  

NASA Astrophysics Data System (ADS)

Observations of the flare stars AD Leo, EQ Peg, UV Cet, Wolf 630, YY Gem, and YZ CMi at 6 and 20 cm wavelengths are presented. These observations display how a sample of the more active radio flare stars behave over periods of several hours. An extensive time analysis at five minute resolution, to investigate the typical variability of these stars, is presented together with a ten-second-resolution time analysis for periods of enhanced activity. Highlights are the enhanced 6-cm activity from both components of the UV Ceti system, quiescent emission from UV Ceti at 20 cm (which has a higher flux than the quiescent emission at 6 cm), the possible detection of polarized quiescent emission, a 20-cm flare from AD Leo in which the polarization changes sign during the rise phase of the flare, and a relatively high level of 6-cm emission from AD Leo.

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

1989-02-01

5

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

NASA Astrophysics Data System (ADS)

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

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

1985-10-01

6

A search for slowly varying radio continuum emission from UV Ceti stars  

NASA Technical Reports Server (NTRS)

The paper presents results of a search conducted at the Arecibo Observatory for variable 430-MHz emission from the active flare stars EQ Peg, YZ CMi, and AD Leo. No statistically significant evidence for slowly varying emission is found to a level of 0.05 Jy for AD Leo, 0.018-0.021 Jy for YZ CMi, and 0.009-0.018 Jy for EQ Peg. Upper limits of about 10 trillion K are determined for the brightness temperature of active radio regions on these stars at the time of the observations.

Spangler, S. R.; Shawhan, S. D.

1976-01-01

7

Observations of H-beta and He II 4686-A lines in the flare spectra of UV Ceti type stars  

NASA Astrophysics Data System (ADS)

Spectroscopic observations and photoelectric B system observations of the flare stars AD Leo, DT Vir, YZ CMi and UV Cet are reported. Three flares of AD Leo and three flares of YZ CMi were recorded. In two flares of AD Leo and two flares of YZ CMi the increase of the central intensity of H? was observed 10 - 20 minutes before the flare maxima. The emission line He II ?4686 was found neither in the quiet state of the stars nor during the flares. The following conclusions are drawn: 1) preflares are characterized by a prevailing increase of the line emission; 2) the emission wings of H? occur during the flare maxima owing to the Stark effect and mass motions; 3) only a very weak He II ?4686 emission may appear during the flare maxima due to cascade recombinations of He III caused by the increase of the X-ray flux.

Petrov, P. P.; Chugainov, P. F.; Shcherbakov, A. G.

8

Discovery of eleven new ZZ Ceti stars  

E-print Network

We report the discovery of eleven new ZZ Cetis using telescopes at OPD (Observat\\'orio 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 12000 to 11000 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 a little bit 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.

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

2005-11-29

9

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

Microsoft Academic Search

We calculate and explore an extensive adiabatic model grid for pulsating white dwarfs with hydrogen-dominated atmospheres, the ZZ Ceti stars. We also compared the computed modes with the observed ones for five ZZ Ceti stars that are a representative sample of the whole class of pulsators. We describe our new approach for seismological studies, using the relative observed amplitudes to

B. G. Castanheira; S. O. Kepler

2008-01-01

10

Co-ordinated VLA and EXOSAT observations of the flare stars UV Ceti, EQ Pegasi, YZ Canis Minoris, and AD Leonis  

NASA Astrophysics Data System (ADS)

The authors have observed four flare stars (UV Cet, EQ Peg, YZ CMi and AD Leo) simultaneously with the VLA and the EXOSAT satellite over continuous periods of 7 - 10 h. This is the first time that flare stars were observed simultaneously in X-rays and at microwave frequencies with high sensitivity instrumentation. All stars were detected both at the quiescent level and during flares. Although considerable activity in both X-rays and in the radio was found, there was little correlation between the two wavelength domains. The auhors discuss the significance of these observations for coronal activity in red dwarf flare stars.

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

1988-04-01

11

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

Microsoft Academic Search

We calculate and explore an extensive adiabatic model grid for pulsating\\u000awhite dwarfs with H dominated atmospheres, the ZZ Ceti stars. We also compared\\u000athe computed modes with the observed ones for five ZZ Ceti stars that are a\\u000arepresentative sample of the whole class of pulsators. We describe our new\\u000aapproach for seismological studies, using the relative observed amplitudes

B. G. Castanheira; S. O. Kepler

2007-01-01

12

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

E-print Network

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

Castanheira, B G

2007-01-01

13

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

NASA Astrophysics Data System (ADS)

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

Castanheira, B. G.; Kepler, S. O.

2008-03-01

14

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

E-print Network

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

B. G. Castanheira; S. O. Kepler

2007-12-12

15

A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti  

E-print Network

The A star 49 Ceti, at a distance of 61 pc, is unusual in retaining a substantial quantity of molecular gas while exhibiting dust properties similar to those of a debris disk. We present resolved observations of the disk around 49 Ceti from the Submillimeter Array in the J=2-1 rotational transition of CO with a resolution of 1.0x1.2 arcsec. The observed emission reveals an extended rotating structure viewed approximately edge-on and clear of detectable CO emission out to a distance of ~90 AU from the star. No 1.3 millimeter continuum emission is detected at a 3-sigma sensitivity of 2.1 mJy/beam. Models of disk structure and chemistry indicate that the inner disk is devoid of molecular gas, while the outer gas disk between 40 and 200 AU from the star is dominated by photochemistry from stellar and interstellar radiation. We determine parameters for a model that reproduces the basic features of the spatially resolved CO J=2-1 emission, the spectral energy distribution, and the unresolved CO J=3-2 spectrum. We investigate variations in disk chemistry and observable properties for a range of structural parameters. 49 Ceti appears to be a rare example of a system in a late stage of transition between a gas-rich protoplanetary disk and a tenuous, virtually gas-free debris disk.

A. M. Hughes; D. J. Wilner; I. Kamp; M. R. Hogerheijde

2008-03-24

16

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

17

THE STRUCTURE OF THE ZZ CETI STARS L 19-2 AND GD165  

SciTech Connect

We infer the structure of the ZZ Ceti stars L 19-2 and GD 165 by comparing the observed periods with periods predicted from an extensive grid of evolutionary white dwarf models. The observed period structure of these two stars is similar, and the models for both stars have a helium layer mass of about 10{sup {minus}2}M* and a hydrogen layer mass of about 10{sup {minus}4}M*. The core of these models is 20:80 C/O that extends to 0.60 to 0.65M* with a linear ramp to pure carbon by 0.90M*. The differences in the observed effective temperature, log g, and periods imply different stellar masses for these two stars. L 19-2 has a favored stellar mass of 0.72M{circle_dot} and GD 165 has a favored stellar mass range of 0.65 to 0.68M*.

P. BRADLEY

2000-11-01

18

The Effects of Crystallization on the Pulsational Properties of Massive ZZ Ceti Stars  

NASA Astrophysics Data System (ADS)

We present pulsational calculations for improved carbon-oxygen DA white dwarf (WD) models suitable for massive ZZ Ceti stars. The background models employed in this study are the result of the complete evolution of massive WD progenitors from the zero-age main sequence through the Asymptotic Giant Branch (AGB) and mass loss phases to the WD regime (Althaus et al. 2003). Abundance changes are accounted for by means of a full coupling between nuclear evolution and time-dependent mixing due to convection and diffusive overshoot. In addition, time-dependent element diffusion for multicomponent gases has been considered during the WD evolution. Crystallization and chemical rehomogenization due to phase separation upon crystallization in the core of our models have been fully considered. We discuss the implications of our study for BPM 37093, the most massive ZZ Ceti star presently known. In particular, we attempt to place constraints on the physical processes occurring prior to the formation of this WD. We find that if BPM 37093 has a stellar mass of ? 1.00 M?, its observed spectrum could bear the signature of overshoot episodes during the helium core burning.

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

2005-07-01

19

Asteroseismology of the Crystallized ZZ Ceti Star BPM 37093: A Different View  

NASA Astrophysics Data System (ADS)

BPM 37093 is a pulsating white dwarf of the ZZ Ceti type massive enough to have undergone partial crystallization. Metcalfe et al. recently claimed to have measured the fraction of crystallized matter in that star on the basis of asteroseismological techniques and determined a value upward of 90%. If true, this is a most significant achievement, well worthy of further scrutiny. In this spirit, we have reexamined the data available-eight periods-with our own independent model-building code and period-matching code in parameter space. In contrast to the above authors, we find that the likely value of the fraction of solidified matter in BPM 37093 is substantially less than 90%, but also that we cannot pin it down with any reasonable accuracy. Our results instead suggest that the value probably lies between 32% and 82%, depending on the unknown chemical composition of the core. We stress that, in principle, asteroseismology can be used to derive the fundamental parameters of BPM 37093, possibly including its core composition, but that, in this specific case, the information contained in the current period data appears insufficient. Indeed, we find full families of different models in parameter space that provide equally valid matches to the available period data. We suggest that the ``lack of information'' that appears to characterize the set of eight observed periods in BPM 37093 is related to the fact that these periods all correspond to high-order modes reaching into the asymptotic regime (k>>1). We also point out that asteroseismology cannot provide a direct test of crystallization theory; the crystallized mass fraction is merely a secondary quantity derived by fixing the interior equation of state of the models and using the inferred fundamental parameters (including the core composition).

Brassard, P.; Fontaine, G.

2005-03-01

20

Gamma Ray Bursts and CETI  

E-print Network

Gamma ray burst sources are isotropically distributed. They could be located at distances $\\sim 1000$ AU. (Katz \\cite{JK92}) GRB signals have many narrow peaks that are unresolved at the millisecond time resolution of existing observations. \\cite{JK87} CETI could use stars as gravitational lenses for interstellar gamma ray laser beam communication. Much better time resolution of GRB signals could rule out (or confirm?) the speculative hypothesis that GRB = CETI.

Frank D. Smith Jr

1993-02-10

21

Asteroseismology of the Crystallized ZZ Ceti Star BPM 37093: A Different View (Part II)  

NASA Astrophysics Data System (ADS)

BPM 37093 is a pulsating white dwarf of the ZZ Ceti type massive enough to have undergone partial crystallization. Recently, on the basis of asteroseismological techniques, Metcalfe et al. (2004) claimed to have measured the fraction of crystallized matter in BPM 37093, a value upward of 90%. If true, this is a most significant achievement, well worthy of further scrutiny. In this spirit, we have reexamined the data available -- 8 periods -- with our own independent model building code and period matching code in parameter space. We present the second and final part of the results of our investigations in this communication.

Fontaine, G.; Brassard, P.

2005-07-01

22

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

SciTech Connect

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

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

2012-10-20

23

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

NASA Astrophysics Data System (ADS)

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

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

2005-01-01

24

Coordinated photometry, spectroscopy and X-ray observations of flare stars.  

NASA Astrophysics Data System (ADS)

The authors have compared the characteristics of flare activity in UV Ceti and YZ CMi. Almost continuous variability is seen in H? and U-band flux in both stars but only in UV Ceti does this correlate strongly with soft X-rays. The relative fluxes in the Balmer emission lines indicates higher densities in the chromospheres of these two dMe stars as compared to the Sun.

Butler, C. J.; Doyle, J. G.; Foing, B. H.; Rodono, M.

25

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

NASA Astrophysics Data System (ADS)

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

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

2009-10-01

26

Solar-like oscillations in the G8 V star tau Ceti  

E-print Network

We used HARPS to measure oscillations in the low-mass star tau Cet. Although the data were compromised by instrumental noise, we have been able to extract the main features of the oscillations. We found tau Cet to oscillate with an amplitude that is about half that of the Sun, and with a mode lifetime that is slightly shorter than solar. The large frequency separation is 169 muHz, and we have identified modes with degrees 0, 1, 2, and 3. We used the frequencies to estimate the mean density of the star to an accuracy of 0.45% which, combined with the interferometric radius, gives a mass of 0.783 +/- 0.012 M_sun (1.6%).

T. C. Teixeira; H. Kjeldsen; T. R. Bedding; F. Bouchy; J. Christensen-Dalsgaard; M. S. Cunha; T. Dall; S. Frandsen; C. Karoff; M. J. P. F. G. Monteiro; F. P. Pijpers

2008-11-24

27

UV-bright stars in globular clusters  

NASA Technical Reports Server (NTRS)

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

Landsman, Wayne B.

1994-01-01

28

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

29

High temporal resolution spectroscopic observations of UV Cet type flare stars  

NASA Astrophysics Data System (ADS)

We present the first results of a high temporal resolution spectroscopic monitoring of the UV Ceti-type flare stars EQ Vir, DK Leo, CR Dra, DT Vir, CE Boo, VV Lyn, DP Dra, V1054 Oph, AD Leo, BL Lyn and YZ CMi. The observations were done using the IDS spectrograph at the 2.5 m Isaac Newton Telescope (INT) of the El Roque de los Muchachos Observatory (La Palma, Canary Islands, Spain). Intermediate resolution spectra, including the Balmer series from H? to H11 as well as the He I ?4026 AA and the Ca II H & K lines, were taken using the R1200B dispersion grating (reciprocal dispersion of 0.48 AA/pixel). The great number of spectra taken each night with high temporal resolution (exposure times as short as 60 s) allows us to analyse the time evolution of the emission lines in order to identify flares. Other variations at different scales have been also observed. A comparison between all the observed stars have been done. Finally, for the strongest flares or changes, we study differences on the behaviour of the lines of interest.

Crespo-Chacón, I.; Montes, D.; Fernández-Figueroa, M. J.; López-Santiago, J.

2005-03-01

30

Modeling of PMS Ae\\/Fe stars using UV spectra  

Microsoft Academic Search

Context: .Spectral classification of AeFe stars, based on visual observations, may lead to ambiguous conclusions. Aims: . We aim to reduce these ambiguities by using UV spectra for the classification of these stars, because the rise of the continuum in the UV is highly sensitive to the stellar spectral type of A\\/F-type stars. Methods: . We analyse the low-resolution UV

P. F. C. Blondel; H. R. E. Tjin A. Djie

2006-01-01

31

Discovery of fourteen new ZZ Cetis with SOAR  

E-print Network

We report the discovery of fourteen new ZZ Cetis with the 4.1m Southern Astrophysical Research telescope, at Cerro Pachon, in Chile. The candidates were selected from the SDSS (Sloan Digital Sky Survey) DA white dwarf stars with Teff obtained from the optical spectra fit, inside the ZZ Ceti instability strip. Considering these stars are multi-periodic pulsators and the pulsations propagate to the nucleus of the star, they carry information on the structure of the star and evolution of the progenitors. The ZZ Cetis discovered till 2003 are mainly within 100 pc from the Sun, and probe only the solar vicinity. The recently discovered ones, and those reported here, may sample a distinct population as they were selected mainly perpendicular to the galactic disk and cover a distance up to ~400pc.

S. O. Kepler; B. G. Castanheira; M. F. O. Saraiva; A. Nitta; S. J. Kleinman; F. Mullally; D. E. Winget; D. J. Eisenstein

2005-07-20

32

The UV-Bright Stars of Omega Centauri  

NASA Astrophysics Data System (ADS)

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

Landsman, Wayne B.

33

UV and radiofrequency observations of Wolf-Rayet stars.  

NASA Technical Reports Server (NTRS)

Available spectrometric and photometric observations of Wolf-Rayet stars by the OAO 2 spacecraft in the UV range are discussed along with radio astronomical observations of W stars with symmetrical nebulae around them. The scanned spectrum of the WN5 star HD 50896 between 1200 and 1900 A is illustrated together with the photometered spectrum of the WN6 star HD 192163 from 1330 to 3320 A. RF observations of NGC 6888 around HD 192163 are examined relative to interpretation of the properties of a WN6 star ejecting mass into a nebular shell.

Johnson, H. M.

1973-01-01

34

A Complete UV Atlas of Standard Stars  

NASA Technical Reports Server (NTRS)

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

Wu, Chi-Chao

1999-01-01

35

UV properties of hot stars in NGC 6752  

NASA Technical Reports Server (NTRS)

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

Altner, Bruce

1990-01-01

36

A Complete UV Atlas of Standard Stars  

NASA Technical Reports Server (NTRS)

The general objective of this project is to provide a comprehensive ultraviolet spectral atlas of stars based on the data in the IUE Final Archive. The data have been uniformly processed by the IUE NEWSIPS pipeline system. The NEWSIPS gives an improved signal to noise ratio for the data that will be especially beneficial to low signal portions of the spectra; and it also gives more accurate fluxes for stars by adopting the latest absolute calibration and measured instrument parameters. Our new atlas, therefore, provides more uniform and accurate data than the version previously published. In addition, considerable efforts were devoted to obtain reliable spectral types, V,B-V, and E(B-V). Our goal is to provide the information which can be used with reasonable confidence by scientists.

Wu, Chi-Chao

2000-01-01

37

Volatile-rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk  

NASA Astrophysics Data System (ADS)

We present Hubble Space Telescope Space Telescope Imaging Spectrograph far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing submillimeter CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight C I column density, estimated the total carbon column density, and set limits on the O I column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of ? Pictoris.

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

2014-11-01

38

Volatile-Rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk  

E-print Network

We present Hubble Space Telescope STIS far-UV spectra of the edge-on disk around 49 Ceti, one of the very few debris disks showing sub-mm CO emission. Many atomic absorption lines are present in the spectra, most of which arise from circumstellar gas lying along the line-of-sight to the central star. We determined the line-of-sight CI column density, estimated the total carbon column density, and set limits on the OI column density. Surprisingly, no line-of-sight CO absorption was seen. We discuss possible explanations for this non-detection, and present preliminary estimates of the carbon abundances in the line-of-sight gas. The C/Fe ratio is much greater than the solar value, suggesting that 49 Cet harbors a volatile-rich gas disk similar to that of Beta Pictoris.

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

2014-01-01

39

UV emission and Star Formation in Stephan's Quintet  

E-print Network

we present the first GALEX UV images of the well known interacting group of galaxies, Stephan's Quintet (SQ). We detect widespread UV emission throughout the group. However, there is no consistent coincidence between UV structure and emission in the optical, H\\alpha, or HI. Excluding the foreground galaxy NGC7320 (Sd), most of the UV emission is found in regions associated with the two spiral members of the group, NGC7319 and NGC7318b, and the intragroup medium starburst SQ-A. The extinction corrected UV data are analyzed to investigate the overall star formation activity in SQ. It is found that the total star formation rate (SFR) of SQ is 6.69+-0.65 M_\\sun/yr. Among this, 1.34+-0.16 M_sun/yr is due to SQ-A. This is in excellent agreement with that derived from extinction corrected H\\alpha luminosity of SQ-A. The SFR in regions related to NGC 7319 is 1.98+-0.58 M_\\sun/yr, most of which(68%) is contributed by the disk. The contribution from the 'young tail' is only 15%. In the UV, the 'young tail' is more extended (~100 kpc) and shows a loop-like structure, including the optical tail, the extragalactic HII regions recently discovered in H\\alpha, and other UV emission regions discovered for the first time. The UV and optical colors of the 'old tail' are consistent with a single stellar population of age t ~10^{8.5+-0.4} yrs. The UV emission associated with NGC 7318b is found in a very large (~80 kpc) disk, with a net SFR of 3.37+-0.25 M_sun/yr. Several large UV emission regions are 30 -- 40 kpc away from the nucleus of NGC7318b. Although both NGC7319 and NGC7318b show peculiar UV morphology, their SFR is consistent with that of normal Sbc galaxies, indicating that the strength of star formation activity is not enhenced by interactions.

C. Kevin Xu; Jorge Iglesias-Paramo; Denis Burgarella; R. Michael Rich; Susan G. Neff; Sebastien Lauger; Tom A. Barlow; Luciana Bianchi; Yong-Ik Byun; Karl Forster; Peter G. Friedman; Timothy M. Heckman; Patrick N. Jelinsky; Young-Wook Lee; Barry F. Madore; Roger F. Malina; D. Christopher Martin; Bruno Milliard; Patrick Morrissey; David Schiminovich; Oswald H. W. Siegmund; Todd Small; Alex S. Szalay; Barry Y. Welsh; Ted K. Wyder

2004-11-12

40

Star formation in extended UV disk {XUV-disk} galaxies  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer {GALEX} has discovered the existence of extended UV-disk {XUV-disk} galaxies. This class of intriguing spiral galaxies is distinguished by UV-bright regions of star formation located at extreme galactocentric radii, commonly reaching many times the optical extent of each target. XUV-disks represent a population of late-type galaxies still actively building, or significantly augmenting, their stellar disk in the outer, low-density environment. Prior to GALEX, such regions were considered to be far more stable against star formation than now realized. Our work on these targets has led to the recognition of the XUV phenomenon as probing a diverse population of galaxies which, although having certain commonality in terms of their present XUV star formation, have apparently experienced different star formation histories {as judged by their outer disk UV-optical colors and morphology}. In ordinary spirals, disk formation occurred at a much earlier epoch, making today's XUV-disks useful templates for commonplace, high z galaxies. The diverse XUV-disks in our sample may represent snapshots of different phases in the disk building process. We seek to characterize the demographics of star forming regions occupying this environmental range, especially in contrast to their inner disk counterparts. HST imaging is needed to accurately characterize the massive stars and clusters which have, in fact, managed to form. The GALEX observations are limited by 5" resolution. Deep ACS FUV, B, V, I, and H-alpha imaging {along with parallel WFPC2 data} will allow: {1} photometric classification of the OB star population, {2} constraint on the cluster mass function and age distribution, {3} critical accounting for possible leakage of Lyman continuum photons in a porous ISM or an IMF change, and {4} population synthesis modeling of the field SFH on Gyr timescales. We benefit from extensive archival HST observations of our target galaxies, although the outer disk has yet to be probed.

Thilker, David

2006-07-01

41

DISCOVERY OF A ZZ CETI IN THE KEPLER MISSION FIELD  

SciTech Connect

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

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

2011-11-01

42

Joint Discussion 4 UV astronomy: stars from birth to death  

NASA Astrophysics Data System (ADS)

The scientific program is presented as well a the abstracts of the contributions. An extended account is published in “The Ultraviolet Universe: stars from birth to death” (Ed. Gómez de Castro) published by the Editorial Complutense de Madrid (UCM), that can be accessed by electronic format through the website of the Network for UV Astronomy (www.ucm.es/info/nuva). There are five telescopes currently in orbit that have a UV capability of some description. At the moment, only FUSE provides any medium- to high-resolution spectroscopic capability. GALEX, the XMM UV-Optical Telescope (UVOT) and the Swift. UVOT mainly delivers broad-band imaging, but with some low-resolution spectroscopy using grisms. The primary UV spectroscopic capability of HST was lost when the Space Telescope Imaging Spectrograph failed in 2004, but UV imaging is still available with the HST-WFPC2 and HST-ACS instruments. With the expected limited lifetime of sl FUSE, UV spectroscopy will be effectively unavailable in the short-term future. Even if a servicing mission of HST does go ahead, to install COS and repair STIS, the availability of high-resolution spectroscopy well into the next decade will not have been addressed. Therefore, it is important to develop new missions to complement and follow on from the legacy of FUSE and HST, as well as the smaller imaging/low resolution spectroscopy facilities. This contribution presents an outline of the UV projects, some of which are already approved for flight, while others are still at the proposal/study stage of their development. This contribution outlines the main results from Joint Discussion 04 held during the IAU General Assembly in Prague, August 2006, concerning the rationale behind the needs of the astronomical community, in particular the stellar astrophysics community, for new UV instrumentation. Recent results from UV observations were presented and future science goals were laid out. These goals will lay the framework for future mission planning.

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

2007-08-01

43

Joint Discussion 4 UV astronomy: stars from birth to death  

Microsoft Academic Search

The scientific program is presented as well a the abstracts of the contributions. An extended account is published in ``The Ultraviolet Universe: stars from birth to death'' (Ed. Gómez de Castro) published by the Editorial Complutense de Madrid (UCM), that can be accessed by electronic format through the website of the Network for UV Astronomy (www.ucm.es\\/info\\/nuva). There are five telescopes

Ana I. Gómez de Castro; Martin A. Barstow

2007-01-01

44

Time variations of UV emission features of Be stars  

NASA Technical Reports Server (NTRS)

The UV spectra of three Be stars (gamma Cas, sigma Tau, eta Cen) were studied. Of the six Be stars observed in the first four lines of the Balmer series, three stars showed at least one of the Balmer lines to be variable in the equivalent width amounting to a few percent with time scales of 3 to 30 minutes. Photoelectric spectrum scans of five southern Wolf-Rayet stars showed night-to-night variations. A simple model is proposed to account for the behavior of these emission lines. Scans of gamma square Vel showed rapid variations of emission strengths of He II 4686 and C III - IV 4650. These variations have time scales of 1 minute and longer. Night-to-night variations were also found. Scans of four Be stars in H alpha showed a definite variation of 3 to 4 percent, with time scales of 1 minute and longer in sigma Tau. In 48 Per and kappa Dra the variations are not as well established. No variation of any significance was found for nu Gem.

Bahng, J. D. R.

1975-01-01

45

Photoelectric monitoring of flare stars AD Leo, EV Lac and YZ CMi from 1980 to 1984  

NASA Astrophysics Data System (ADS)

Simultaneous UBV observations of UV Ceti-type flare stars were performed at Tokyo Astronomical Observatory's Okayama Station during 1980-1984. The stars observed were AD Leo, EV Lac, and YZ CMi. A three-color simultaneous photometer with an unrefrigerated EMI 6256 photomultiplier was used. The integrated intensity for each flare computed by integrated U, B, and V light curves in the relative intensity scale is given.

Ichimura, Kihachiro; Shimizu, Yasuhiro

1986-07-01

46

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

47

Time distribution of flare events on UV CET stars  

NASA Astrophysics Data System (ADS)

The flare occurrence on UV Cet, EQ Peg, and YZ CMi is studied by a statistical analysis of observational data based on four variables. The variables include: time elapsed from the start of a continuous observation period to the occurrence of the first flare; time interval between consecutive flares; the number of flares occurring in time periods of given duration; and the ratio of the number of flares observed in each continuous observation period to that expected for a Poisson process. Results indicate that the time sequence of flares on the stars studied does not have a Poisson distribution.

Pazzani, V.; Rodono, M.

1981-07-01

48

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

NASA Astrophysics Data System (ADS)

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

Shkolnik, E.; Barman, T.

2014-03-01

49

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

NASA Astrophysics Data System (ADS)

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

Shkolnik, Evgenya L.; Barman, Travis S.

2014-10-01

50

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

51

Star-Pointing UV-Visible Spectrometer for Remote-Sensing of the Stratosphere.  

National Technical Information Service (NTIS)

We have constructed a novel instrument for ground-based remote sensing, by mounting a UV-visible spectrometer on a telescope and observing the absorption by atmospheric constituents of light from stars. Potentially, the instrument can observe stratospheri...

H. K. Roscoe, R. A. Freshwater, R. L. Jones, D. J. Fish, J. E. Harries

1994-01-01

52

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

E-print Network

The spectral energy distribution, variability and evolution of the high-energy radiation from an M dwarf planet host is crucial in understanding the planet's atmospheric evolution and habitability and in interpreting the planet's spectrum. The star's extreme-UV (EUV), far-UV (FUV) and near-UV (NUV) emission can chemically modify, ionize, and erode the atmosphere over time. This makes determining the lifetime exposure of such planets to stellar UV radiation critical for both the evolution of a planet's atmosphere and our potential to characterize it. Using the early M star members of nearby young moving groups (YMGs), which sample critical ages in planet formation and evolution, we measure the GALEX NUV and FUV flux as a function of age. The median UV flux remains at a "saturated" level for a few hundred million years, analogous to that observed for X-ray emission. By the age of the Hyades Cluster (650 Myr), we measure a drop in UV flux by a factor of 2-3 followed by a steep drop from old (several Gyrs) field ...

Shkolnik, Evgenya L

2014-01-01

53

UV Spectral Classification and Opacity in Magellanic Cloud OB Stars: Implications for Modeling Young Starbursts  

Microsoft Academic Search

Examination of archival Hubble Space Telescope (HST) spectra shows that the UV classifications of Magellanic Cloud O and B stars are consistent with those of Neubig and Bruhweiler (1997,1999) using International Ultraviolet Explorer (IUE) data. It also reveals previously unrecognized, strong UV line-blanketing by Fe-peak elements in two spectral regions. This is most noticable in SMC O stars with low

M. Smith Neubig; F. C. Bruhweiler; R. Cecil; J. Eaton

1999-01-01

54

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

NASA Astrophysics Data System (ADS)

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

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

2010-02-01

55

Recent star formation in nearby 3CR radio-galaxies from UV HST observations  

Microsoft Academic Search

We analyzed HST images of 31 nearby (z ≲ 0.1) 3CR radio-galaxies. We compared their UV and optical images to detect evidence of recent star formation. Six objects were excluded because they are highly nucleated or had very low UV count rates. After subtracting the emission from their nuclei and\\/or jets, 12 of the remaining 25 objects, presenting an UV\\/optical

R. D. Baldi; Alessandro Capetti

2008-01-01

56

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

E-print Network

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

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

2006-04-04

57

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

SciTech Connect

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

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

2012-08-20

58

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

NASA Astrophysics Data System (ADS)

As part of the Panchromatic Hubble Andromeda Treasury multi-cycle program, we observed a 12' × 6farcm5 area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of ~4000 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes: Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars, and AGB-manqué stars. P-AGB stars are the end result of the asymptotic giant branch (AGB) phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manqué (together referred to as the hot post-horizontal branch; HP-HB) stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or ? abundances when the mass loss on the red giant branch is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot (extreme) horizontal branch (EHB) stars and their progeny. We construct the first radial profiles of these stellar populations and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting only the progeny of the EHB stars that are the likely source of the UV excess. We calculate that only a few percent of main-sequence stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of low-mass X-ray binaries. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

Rosenfield, Philip; Johnson, L. Clifton; Girardi, Léo; Dalcanton, Julianne J.; Bressan, Alessandro; Lang, Dustin; Williams, Benjamin F.; Guhathakurta, Puragra; Howley, Kirsten M.; Lauer, Tod R.; Bell, Eric F.; Bianchi, Luciana; Caldwell, Nelson; Dolphin, Andrew; Dorman, Claire E.; Gilbert, Karoline M.; Kalirai, Jason; Larsen, Søren S.; Olsen, Knut A. G.; Rix, Hans-Walter; Seth, Anil C.; Skillman, Evan D.; Weisz, Daniel R.

2012-08-01

59

UV fluxes and effective temperatures of extreme helium stars  

NASA Technical Reports Server (NTRS)

Low resolution IUE spectra of a complete ensemble of extreme helium stars are presented and their appearance in comparison with normal stars is discussed. Effective temperatures from these observations by means of line blanketed model atmospheres are determined. It is found that the temperatures are in accordance with earlier results from ground based observations.

Schoenberner, D.; Drilling, J. S.; Lynas-Gray, A. E.; Heber, U.

1982-01-01

60

The UV-Bright Stars of Omega Centauri  

NASA Astrophysics Data System (ADS)

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

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

1995-05-01

61

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

62

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

E-print Network

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

C. Ian Short; P. H. Hauschildt

2008-11-07

63

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

64

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

SciTech Connect

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

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

2011-02-15

65

Deriving extinction laws with O stars: from the IR to the UV  

E-print Network

We have recently derived a family of extinction laws for 30 Doradus that provides better fits to the optical photometry of obscured stars in the Galaxy and the LMC. Simultaneously, we are extending our Galactic O-Star Spectroscopic Survey (GOSSS) to fainter, more extinguished stars to obtain accurate spectral types for massive stars with more than 6 magnitudes of $V$-band extinction. I have combined both lines of research with 2MASS, WISE, and Spitzer photometry to obtain the 1-10 micron extinction law for O stars in the solar neighborhood. I present these results and compare them with the extinction laws in the same wavelength range derived from late-type stars and H II regions. I also discuss plans to extend the newly derived optical-IR extinction laws to the UV.

Apellániz, J Maíz

2014-01-01

66

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

Microsoft Academic Search

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.

Daisuke Sato; Masayuki Umemura; Hajime Susa; Tamon Suwa

2008-01-01

67

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

68

Imitation is the sincerest form of flattery: is 49 Ceti the new Beta Pictoris?  

NASA Astrophysics Data System (ADS)

The young (40Myr) A1-type star 49 Ceti is thought to possess many of the same physical characteristics as Beta Pictoris, whose circumstellar gas and debris dust disks are the most well-studied of all exoplanet systems. As part of a campaign to monitor circumstellar activity in the gas disk(s) surrounding 49 Ceti, we present ground-based high spectral resolution observations (R ~ 60,000) of the visible circumstellar absorption lines recorded in conjunction with ultraviolet observations using the STIS instrument on HST in August 2013 (see presentation by Roberge et al at this conference). Our data, which spans a 6-week observational period, reveals significant variability in the properties of the circumstellar gas absorption which can be attributed to evaporating ionized Ca gas liberated by Kuiper Belt-like objects as they fall towards the central star. Similar behavior has been routinely observed towards Beta Pictoris. However, unlike Beta Pictoris we have observed anomalous behavior of the NaI and CaII IR-triplet lines in this extremely ‘active” debris disk system of 49 Ceti.

Welsh, Barry; Montgomery, S. L.; Alu, D.; Lallement, R.

2014-01-01

69

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

70

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

NASA Astrophysics Data System (ADS)

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

Rosenfield, Philip

2014-10-01

71

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

72

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

NASA Technical Reports Server (NTRS)

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

Nichols, Joy S.

1995-01-01

73

A star-pointing UV-visible spectrometer for remote-sensing of the stratosphere  

NASA Technical Reports Server (NTRS)

We have constructed a novel instrument for ground-based remote sensing, by mounting a UV-visible spectrometer on a telescope and observing the absorption by atmospheric constituents of light from stars. Potentially, the instrument can observe stratospheric O3, NO3, NO2, and OClO.

Roscoe, Howard K.; Freshwater, Ray A.; Jones, Rod L.; Fish, Debbie J.; Harries, John E.; Wolfenden, Roger; Stone, Phillip

1994-01-01

74

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

NASA Astrophysics Data System (ADS)

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

Siqueira-Mello, C.; Barbuy, B.

2014-11-01

75

The missing UV opacity and the colours of solar-type stars  

NASA Astrophysics Data System (ADS)

A simple method is proposed to take into account the "missing UV opacity" in solar-type stars. It is shown that the mere inclusion of that UV opacity through a very simple formula is sufficient to bring the theoretical colours in agreement with observed ones for stars of different metal abundances and belonging to the spectral range from mid-F to late-G. Synthetic colours computed in the Geneva and UBV systems reproduce the various observed relations satisfactorily. The relations based on these colours allow reliable estimates of effective temperatures, surface gravities and metal abundances of stars. In addition, solar colours are obtained and three more solar twin candidates are proposed.

Magain, P.

1983-06-01

76

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

NASA Astrophysics Data System (ADS)

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

Sato, Satoko

77

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

78

UV spectra of T Tau stars from hubble space telescope  

NASA Astrophysics Data System (ADS)

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

Lamzin, S. A.

2001-08-01

79

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

80

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

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

81

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

E-print Network

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

Paul A Crowther

2002-07-26

82

The Formation of Massive Primordial Stars in the Presence of Moderate UV Backgrounds  

NASA Astrophysics Data System (ADS)

Radiative feedback produced by stellar populations played a vital role in early structure formation. In particular, photons below the Lyman limit can escape the star-forming regions and produce a background ultraviolet (UV) flux, which consequently may influence the pristine halos far away from the radiation sources. These photons can quench the formation of molecular hydrogen by photodetachment of H–. In this study, we explore the impact of such UV radiation on fragmentation in massive primordial halos of a few times 107 M ?. To accomplish this goal, we perform high resolution cosmological simulations for two distinct halos and vary the strength of the impinging background UV field in units of J 21 assuming a blackbody radiation spectrum with a characteristic temperature of T rad = 104 K. We further make use of sink particles to follow the evolution for 10,000 yr after reaching the maximum refinement level. No vigorous fragmentation is observed in UV-illuminated halos while the accretion rate changes according to the thermal properties. Our findings show that a few 102-104 solar mass protostars are formed when halos are irradiated by J 21 = 10-500 at z > 10 and suggest a strong relation between the strength of the UV flux and mass of a protostar. This mode of star formation is quite different from minihalos, as higher accretion rates of about 0.01-0.1 M ? yr–1 are observed by the end of our simulations. The resulting massive stars are potential cradles for the formation of intermediate-mass black holes at earlier cosmic times and contribute to the formation of a global X-ray background.

Latif, M. A.; Schleicher, D. R. G.; Bovino, S.; Grassi, T.; Spaans, M.

2014-09-01

83

The formation of massive primordial stars in the presence of moderate UV backgrounds  

E-print Network

Radiative feedback from populations II stars played a vital role in early structure formation. Particularly, photons below the Lyman limit can escape the star forming regions and produce a background ultraviolet (UV) flux which consequently may influence the pristine halos far away from the radiation sources. These photons can quench the formation of molecular hydrogen by photo-detachment of $\\rm H^{-}$. In this study, we explore the impact of such UV radiation on fragmentation in massive primordial halos of a few times $\\rm 10^{7}$~M${_\\odot}$. To accomplish this goal, we perform high resolution cosmological simulations for two distinct halos and vary the strength of the impinging background UV field in units of $\\rm J_{21}$. We further make use of sink particles to follow the evolution for 10,000 years after reaching the maximum refinement level. No vigorous fragmentation is observed in UV illuminated halos while the accretion rate changes according to the thermal properties. Our findings show that a few 10...

Latif, M A; Bovino, S; Grassi, T; Spaans, M

2014-01-01

84

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

E-print Network

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 Millimetre-wave Astronomy (CARMA) 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%) 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-luminous compact star-forming galaxies.

Gonçalves, T S; Overzier, R A; Pérez, L; Martin, D C

2014-01-01

85

Spectroscopic diagnostics of UV power and accretion in T Tauri stars  

NASA Astrophysics Data System (ADS)

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

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

2003-02-01

86

Modeling the near-UV band of GK stars, Paper I: LTE models  

E-print Network

We present a grid of LTE atmospheric models and synthetic spectra that cover the spectral class range from mid-G to mid-K, and luminosity classes from V to III, that is dense in Teff sampling (Delta Teff=62.5 K), for stars of solar metallicity and moderately metal poor scaled solar abundance ([A/H]=0.0 and -0.5). All models have been computed with two choices of atomic line list: a) the "big" line lists of Kurucz (1992) that best reproduce the broad-band solar blue and near UV flux level, and b) the "small" lists of Kurucz & Peytremann (1975) that provide the best fit to the high resolution solar blue and near-UV spectrum. We compare our model SEDs to a sample of stars carefully selected from the large catalog of uniformly re-calibrated spectrophotometry of Burnashev (1985) with the goal of determining how the quality of fit varies with stellar parameters, especially in the historically troublesome blue and near-UV bands. We confirm that our models computed with the "big" line list recover the derived Tef...

Short, C Ian

2010-01-01

87

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

88

Unveiling and Dereddening Classical T Tauri Stars Using Simultaneous UV and Optical Spectra  

NASA Astrophysics Data System (ADS)

T Tauri stars (TTSs) are low-mass, pre-main sequence stars that exhibit a variety of interesting spectral characteristics. One of the defining features of a classical TTS (CTTS) is the presence of an ultraviolet and optical excess continuum that is believed to form as the result of accreting circumstellar disk material that shocks at the photosphere of the star, heating the material to ~106 K. The excess emission results in the TTS spectrum being veiled, i.e. the photospheric absorption features appear to be filled in and are thus shallower than they would be in an unveiled spectrum. Correctly de-veiling TTSs is vital in determining the extinction to these systems. The amount of extinction in turn determines the correction that must be applied to emission at shorter wavelengths where veiling measurements are not possible due to the lack of stellar continuum. We present veiling and extinction measurements to a small sample of CTTS using low resolution, flux calibrated spectra that are simultaneous across the wavelengths 1800-8500 Å. By measuring the extinction with optical data taken simultaneously with the UV observations, we are able to generate accurate estimates of the extinction-corrected UV flux that is unaffected by variability, which in turn places more precise constraints on relationships between single colors and accretion luminosity.

Cauley, Paul W.; Hartigan, P. M.; Johns-Krull, C. M.

2013-01-01

89

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

90

Abundances of UV bright stars in globular clusters. I. ROA 5701 in omega Centauri and Barnard 29 in M 13  

E-print Network

Two UV brights stars in globular clusters, ROA 5701 (omega Cen) and Barnard 29 (M 13) are analysed from high-resolution UV and optical spectra. The main aim is the measurement of iron abundances from UV spectra obtained with the HST-GHRS. In addition atmospheric parameters and abundances for He, C, N, O, and Si are derived from optical spectra (ESO CASPEC) for ROA 5701 or taken from literature for Barnard 29. Both stars are found to be post-asymptotic giant branch stars. Surprisingly, their iron abundances lie significantly below the cluster abundance in both cases. Barnard 29 lies 0.5 dex below the iron abundance derived for giant stars in M 13 and the iron abundance of ROA 5701 is the lowest of any star in omega Cen analysed so far. Barnard 29 shows the same abundance pattern as the red giant stars in M 13, except for its stronger iron deficiency. The iron depletion could be explained by gas-dust separation in the AGB progenitor's atmosphere, if iron condensed into dust grains which were then removed from the atmosphere by a radiatively driven wind. The interpretation of the abundance pattern for ROA 5701 is hampered by the star-to-star abundance variations seen in omega Cen, but its abundance pattern appears to be consistent with the gas-dust separation scenario.

S. Moehler; U. Heber; M. Lemke; R. Napiwotzki

1998-09-10

91

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

92

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

93

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

94

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

E-print Network

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

Prinja, Raman

2013-01-01

95

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

96

Young Stars in Old Galaxies: A UV Imaging Survey of the Sauron Galaxy Sample  

NASA Astrophysics Data System (ADS)

Simultaneously constraining the dynamics and stellar populations of galaxies is essential to understand their mass assembly and star formation histories. The SAURON Team has surveyed the two dimensional stellar/ionized-gas kinematics and stellar populations of a representative sample of 72 nearby early-type galaxies. It revealed a great dynamical diversity, discovering numerous central disks and kinematically decoupled components. The limited optical line strength diagnostics indicate that most (but not all) galaxies have homogeneously old stellar populations. By combining GALEX far-ultraviolet (FUV) and near-ultraviolet (NUV) imaging with SAURON data, we aim here to more reliably constrain the incidence, rate, and spatial distribution of recent and ongoing star formation in early-type galaxies, and to quantify those as function of luminosity, Hubble type, and environment. Of particular interest is whether star formation is closely associated with the kinematic (sub-)structures detected. Other important goals include measuring the spatial extent of the enigmatic UV-upturn population, identifying the orbital families populated by young stars and constraining their migration patterns, and testing the reliability and limitations of line strength-based methods to detect young populations. Progress toward those goals was achieved with Cycle 1 data, but we now request to complete the sample by observing galaxies originally planned for the GALEX Nearby Galaxies Survey (NGS). The combined SAURON and GALEX data will provide by far the best determination of the relative roles of merger-induced and passive star formation in early-type galaxies today, and they will give us a unique glimpse into the future of those objects.

Bureau, Martin

97

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

98

Astroinformatics for the Flare Stars in Stellar Clusters and Associations  

NASA Astrophysics Data System (ADS)

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

Tsvetkova, K.

2012-01-01

99

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

100

Observations of the UV-Bright Star BS in 47 Tucanae with the Hopkins Ultraviolet Telescope  

NASA Astrophysics Data System (ADS)

The UV-bright star BS in the globular cluster 47 Tuc was observed with the Hopkins Ultraviolet Telescope (HUT) during the Astro-2 space shuttle mission in 1995 March. The resulting spectrum extends from the interstellar cutoff at 912 Angstroms to 1850 Angstroms with a resolution of ~ 3 Angstroms. It shows numerous absorption features, but no significant emission features other than terrestrial airglow lines. Detailed fitting of Kurucz stellar atmosphere models using a chi (2) minimization technique indicates Teff = 11,000 K, log g = 2.5, and log Z/Z_? = -1.0. The Kurucz model which best fits the observed spectrum overpredicts the flux in the Lyman gamma to Lyman beta region by nearly a factor of three, suggesting that opacity effects not included in the models are important even at this relatively low temperature. Assuming a distance of 4.6 +/- 1.0 kpc, we estimate the stellar luminosity to be log L/L_? = 3.1 +/- 0.2. These atmospheric parameters place the star on the Schonberner post-AGB evolutionary tracks. The Hopkins Ultraviolet Telescope Project is supported by NASA contract NAS 5-27000 to The Johns Hopkins University.

Dixon, W. V.; Davidsen, A. F.; Ferguson, H. C.

1995-05-01

101

Determination of the age of stellar aggregates and flare stars of the galactic field  

NASA Astrophysics Data System (ADS)

On the basis of the relationship between the age and the magnitude of the maximal flare amplitude in flare stars found previously by the author we propose a method of determining the age of aggregates. Using new observational data relative to flares in U and B we determine the age of the Cyg T1 association (3.4 · 10 6 years), which differs only slightly from an earlier estimate. We give estimated upper bounds for the ages of some flare stars in the solar neighborhood: UV Ceti, EV Lac, AD Leo, EG Peg, and YZ CMi, and also for seven flare stars of the galactic field. It follows from these results that the ages vary noticeably.

Parsamyan, E. S.

1995-07-01

102

The GOODS UV Legacy Fields: A Full Census of Faint Star-Forming Galaxies at z~0.5-2  

NASA Astrophysics Data System (ADS)

Deep HST imaging has shown that the overall star formation density and UV light density at z>3 is dominated by faint, blue galaxies. Remarkably, very little is known about the equivalent galaxy population at lower redshifts. Understanding how these galaxies evolve across the epoch of peak cosmic star-formation is key to a complete picture of galaxy evolution. While we and others have been making every effort to use existing UV imaging data, a large fraction of the prior data were taken without post-flash and are not photometric. We now propose to obtain a robust legacy dataset for a complete census of faint star-forming galaxies at z~0.5-2, akin to what is achieved at z>3, using the unique capabilities of the WFC3/UVIS camera to obtain very deep UV imaging to 27.5-28.0 mag over the CANDELS Deep fields in GOODS North and South. We directly sample the FUV at z>~0.5 and we make these prime legacy fields for JWST with unique and essential UV/blue HST coverage. Together with the exquisite ancillary multi-wavelength data at high spatial resolution from ACS and WFC3/IR our program will result in accurate photometric redshifts for very faint sources and will enable a wealth of research by the community. This includes tracing the evolution of the FUV luminosity function over the peak of the star formation rate density from z~3 down to z~0.5, measuring the physical properties of sub-L* galaxies, and characterizing resolved stellar populations to decipher the build-up of the Hubble sequence from sub-galactic clumps. The lack of a future UV space telescope makes the acquisition of such legacy data imperative for the JWST era and beyond.

Oesch, Pascal

2014-10-01

103

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

104

UV excess measures of accretion onto young very low-mass stars and brown dwarfs  

E-print Network

Low-resolution spectra from 3000-9000 AA of young low-mass stars and brown dwarfs were obtained with LRIS on Keck I. The excess UV and optical emission arising in the Balmer and Paschen continua yields mass accretion rates ranging from 2e-12 to 1e-8 Mo/yr. These results are compared with {\\it HST}/STIS spectra of roughly solar-mass accretors with accretion rates that range from 2e-10 to 5e-8 Mo/yr. The weak photospheric emission from M-dwarfs at <4000 A leads to a higher contrast between the accretion and photospheric emission relative to higher-mass counterparts. The mass accretion rates measured here are systematically 4-7 times larger than those from H-alpha emission line profiles, with a difference that is consistent with but unlikely to be explained by the uncertainty in both methods. The accretion luminosity correlates well with many line luminosities, including high Balmer and many He I lines. Correlations of the accretion rate with H-alpha 10% width and line fluxes show a large amount of scatter. Our results and previous accretion rate measurements suggest that accretion rate is proportional to M^(1.87+/-0.26) for accretors in the Taurus Molecular Cloud.

Gregory J. Herczeg; Lynne A. Hillenbrand

2008-01-23

105

Design and Implementation of the Widefield High-resolution UV\\/Optical Star Formation Camera for the THEIA Mission  

Microsoft Academic Search

The Star Formation Camera (SFC) is a wide-field ( 15'x19', > 280 arcmin2), high-resolution (18x18 mas pixels) UV\\/optical dichroic camera for the 4-m THEIA space telescope concept. SFC will deliver diffraction-limited images at lambda > 300 nm in both a Blue (190--517nm) and a Red (517--1075nm) Channel simultaneously. Our aim is to conduct a comprehensive and systematic study of the

Paul A. Scowen; R. Jansen; M. Beasley; S. Macenka; S. Shaklan; D. Calzetti; S. Desch; A. Fullerton; J. Gallagher; S. Malhotra; M. McCaughrean; S. Nikzad; R. O'Connell; S. Oey; D. Padgett; J. Rhoads; A. Roberge; O. Siegmund; N. Smith; D. Stern; J. Tumlinson; R. Windhorst; R. Woodruff; D. Spergel; K. Sembach

2009-01-01

106

The solar-exoplanet-host-star connection: measurements, reconstruction, and estimates of the UV, Lyman-alpha, and EUV radiation emitted by exoplanet host stars  

NASA Astrophysics Data System (ADS)

One of the important ways in which host stars influence their exoplanets is through photochemistry in their atmospheres. For example, the photodissociation of such important molecules in exoplanet atmospheres as H2O, CO2, and CH4 is primarily controlled by Lymanalpha and FUV radiation from the host stars. Photochemistry of oxygen and ozone is controlled by NUV radiation. EUV radiation photoionizes H and other atoms, heats the outer atmospheres, and thereby drives mass loss from exoplanets. Photodissociation of H2O and CO2 liberates oxygen without the need for life forms and thus complicates the use of oxygen and ozone as biosignatures. The COS instrument on HST has now obtained UV spectra of a number of M dwarfs host stars. The Lyman-alpha line, which is important for G stars but completely dominates the UV emission of M dwarfs, is attenuated by interstellar absorption. I will present techniques for reconstructing or estimating the stellar emission in this line. The EUV emission can be estimated by comparison with Lymanalpha and other emission lines. These recent developments now make it feasible to evaluate the radiation received by exoplanets and to compute realistic models of the chemistry of exoplanet atmospheres.

Linsky, J.

2014-03-01

107

Predictions for the intrinsic UV continuum properties of star forming galaxies and the implications for inferring dust extinction  

E-print Network

The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function (IMF) and to the recent star formation and metal enrichment histories of a galaxy. Using the galform semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z=0, parameterised by the power law index beta, has a standard deviation of sigma_beta=0.30. This suggests an uncertainty on the inferred UV attenuation of A_fuv=0.7$ (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quan...

Wilkins, Stephen M; Lacey, Cedric G; Baugh, Carlton M

2012-01-01

108

Predictions for the intrinsic UV continuum properties of star-forming galaxies and the implications for inferring dust extinction  

NASA Astrophysics Data System (ADS)

The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star-forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function and to the recent star formation and metal enrichment histories of a galaxy. Using the GALFORM semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z= 0, parametrized by the power-law index ?, has a standard deviation of ??? 0.30. This suggests an uncertainty on the inferred ultraviolet (UV) attenuation of Afuv? 0.7 (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quantities irrespective of the sample size or quality of the photometry. Our results suggest that in some cases the attenuation by dust has been incorrectly estimated.

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

2012-08-01

109

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

110

Radio stars; Proceedings of the Workshop on Stellar Continuum Radio Astronomy, Boulder, CO, August 8-10, 1984  

NASA Astrophysics Data System (ADS)

Papers are presented on radio-observable processes in stars, stochastic electron acceleration in stellar coronae, corotating interaction regions in stellar winds, damping of the magnetoionic Z mode, and electron-cyclotron maser emission during solar and stellar flares. Also considered are radio emission from the winds of single stars, as well as from circumstellar envelopes, AG Pegasi, L1551 IRS5, premain sequence stars and associated structures, P Cygni, Cyg OB2 No. 5, Theta(1)A Orionis, Gamma(2) Vel, symbiotic stars, and VV Cephei-type binaries. Papers are also presented on emission from flare stars and RS CVn systems, early-type stars, AM Herculis, the late-type dwarf stars UV Ceti and YZ CMi, AU Mic, dMe stars, solar-type stars, A and B stars, active late-type giants in binary systems, RS CVn binaries, W UMa Systems, and from strong X-ray sources. Also considered are parameters of the SS433 accretion disk, the confirmation of Cygnus X-3 radio periodicity, a variable Rho P Ophiuchi cloud radio star, microwave spectroscopic deduction of coronal magnetic fields, and a technique for removing confusion sources from VLA data. Other topics include stellar radio emission theoretical problems, high-angular resolution studies, and the time-resolution domain.

Hjellming, R. M.; Gibson, D. M.

111

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

112

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

NASA Astrophysics Data System (ADS)

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

Smith, M. A.

2012-10-01

113

Observations of Flare Activity on Selected DME Flare Stars  

NASA Astrophysics Data System (ADS)

Optical and ultraviolet spectroscopy can enable the assessment of the physical conditions characterizing a stellar flare atmosphere and thereby potentially elucidate the possible radiative and hydrodynamic transport mechanisms operative during stellar flares. Observations of flares on M dwarf stars offers the opportunity to obtain detailed information on a solar-like phenomenon as it presumably occurs on many stars, but can presently only be observed on the cool dMe stars due to the highly favorable contrast between the UV and near UV bright flare emission and the faint quiescent background. We therefore propose to acquire timeresolved, low dispersion, large aperture SWP and LWR observations simultaneously with moderate resolution (3-4A) spectrophotometric optical observations of stellar flare events. We also will attempt to coordinate simultaneous VLA (radio corona) observations. We intend to monitor two highly flare active systems; the binary UV Ceti (GL65AB) system and the single flare star YZ CMi (GL 285). We wish to ascertain the dominant radiative transport mechanism that gives rise to the UV and optical continuum emission during flares as well as assess the relative energy balance in these wavelength regions. Furthermore, we will utilize density diagnostics and emission mesure analysis techniques developed for solar observations. In addition, we will infer flare X-ray luminosities from the enhancement of the He II 1640 recombination line. The UV data and inferred X-ray data will ultimately be used to determine the applicability of flare loop models. All data obtained in this program will be used as input for the construction of semiempirical flare atmospheres.

Giampapa, Mark S.

114

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

Mukadam, Anjum S.; Bischoff-Kim, Agnes; Fraser, Oliver; Córsico, A. H.; Montgomery, M. H.; Kepler, S. O.; Romero, A. D.; Winget, D. E.; Hermes, J. J.; Riecken, T. S.; Kronberg, M. E.; Winget, K. I.; Falcon, Ross 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.

2013-07-01

115

Microwave Observations of Red Dwarf Flare Stars  

NASA Astrophysics Data System (ADS)

Observations of AD Leo, EQ Peg AB, L726-8AB (B = UV Ceti), Wolf 630AB, YY Gem and YZ CMi were made on March 22, 1985 in the 6 and 20 cm wavelength bands using the Very Large Array with hybrid A/B configuration.

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

116

Using nonradial pulsations to determine the envelope composition of very evolved stars  

SciTech Connect

Recent observational and theoretical studies of the ZZ Ceti variables (DA degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (DO degenerate dwarfs) have shown them to be pulsating in nonradial g/sup +/-modes. The pulsation mechanism has been identified for each class of variable star and, in all cases, involves predictions of the stars envelope composition. The ZZ Ceti variables must have pure hydrogen surface layers, the DBV stars must have pure helium surface layers, and the GW Vir stars must have carbon and oxygen rich surface layers. 44 refs.

Starrfield, S.

1986-07-07

117

Simultaneous UV-Optical Observations of Isolated T-Tauri Stars: The V4046 Sgr Case.  

National Technical Information Service (NTIS)

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, in...

R. Delareza, G. Quast, C. A. Torres, M. Mayor, G. Meylan

1986-01-01

118

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

E-print Network

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

Adrian Tanasa; Patrizia Vitale

2009-12-01

119

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

120

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

121

Design and Implementation of the Widefield High-resolution UV/Optical Star Formation Camera for the THEIA Mission  

NASA Astrophysics Data System (ADS)

The Star Formation Camera (SFC) is a wide-field ( 15'x19', > 280 arcmin2), high-resolution (18x18 mas pixels) UV/optical dichroic camera for the 4-m THEIA space telescope concept. SFC will deliver diffraction-limited images at lambda > 300 nm in both a Blue (190--517nm) and a Red (517--1075nm) Channel simultaneously. Our aim is to conduct a comprehensive and systematic study of the astrophysical processes and environments relevant for the births and life cycles of stars and their planetary systems, and to investigate and understand the range of environments, feedback mechanisms, and other factors that most affect the outcome of the star and planet formation process. We present the design and performance specifications resulting from the implementation study of the camera, conducted under NASA's Astrophysics Space Mission Concept Studies program, which is intended to assembly realistic options for mission development over the next decade. The result is a lightweight, low-cost instrument that will provide deep, high-resolution imaging across a wide angular field enabling a wide variety of community science as well as completing the core science that drives the design of the camera. The technology associated with the camera is next generation but still relatively high TRL, allowing a low-risk solution with moderate technology development investment over the next 10 years. The completed study will be used as input to not only the NASA decadal strategic planning process but also to the NAS Decadal Survey on Astronomy. This work has been supported by NASA-GSFC contract NNX08AK79G.

Scowen, Paul A.; Jansen, R.; Beasley, M.; Macenka, S.; Shaklan, S.; Calzetti, D.; Desch, S.; Fullerton, A.; Gallagher, J.; Malhotra, S.; McCaughrean, M.; Nikzad, S.; O'Connell, R.; Oey, S.; Padgett, D.; Rhoads, J.; Roberge, A.; Siegmund, O.; Smith, N.; Stern, D.; Tumlinson, J.; Windhorst, R.; Woodruff, R.; Spergel, D.; Sembach, K.

2009-01-01

122

Modeling the near-UV band of GK stars, Paper III: Dependence on abundance pattern  

E-print Network

We extend the grid of NLTE models presented in Paper II to explore variations in abundance pattern in two ways: 1) The adoption of the Asplund et al. (2009) (GASS10) abundances, 2) For stars of metallicity, [M/H], of -0.5, the adoption of a non-solar enhancement of alpha-elements by +0.3 dex. Moreover, our grid of synthetic spectral energy distributions (SEDs) is interpolated to a finer numerical resolution in both T_eff (Delta T_eff = 25 K) and log g (Delta log g = 0.25). We compare the values of T_eff and log g inferred from fitting LTE and Non-LTE SEDs to observed SEDs throughout the entire visible band, and in an ad hoc "blue" band. We compare our spectrophotometrically derived T_eff values to a variety of T_eff calibrations, including more empirical ones, drawn from the literature. For stars of solar metallicity, we find that the adoption of the GASS10 abundances lowers the inferred T_eff value by 25 - 50 K for late-type giants, and NLTE models computed with the GASS10 abundances give T_eff results that ...

Short, C Ian

2013-01-01

123

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

NASA Astrophysics Data System (ADS)

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

Bianchi, Luciana

124

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

125

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

NASA Astrophysics Data System (ADS)

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

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

2003-10-01

126

Star Formation History of CALIFA galaxies in the optical and UV  

NASA Astrophysics Data System (ADS)

CALIFA is a spectroscopic survey of 600 nearby galaxies (0.005 < z < 0.03). CALIFA provides a unique and very useful set of data for galaxies covering the color-magnitude diagram from Mr = -23 mag to Mr = -18 mag, a large range of masses (109-12 M_{odot}) and morphological types (from E to Sc), and allow us to obtain the spatially resolved properties of galaxies. The spectral range of the CALIFA sample is ideal for studying stellar populations because it contains the Balmer series and the 4000 Å break, among other useful tracers. However, there are age-metallicity-extinction degeneracies, which produce uncertainties in estimation of the physical properties of the stellar population. So we combine CALIFA spectroscopic data with photometric data in the ultraviolet range obtained with the GALEX mission in order to break these degeneracies, including data that provide additional information about the young stellar populations, which contribute to a lesser extent in the optical range. We perform a full spectral synthesis at the optical range plus the two UV GALEX filters with a new version of the fitting code STARLIGHT.

López-Fernández, R.; González Delgado, R. M.; Cid Fernandes, R.; Pérez, E.; García Benito, R.

2014-10-01

127

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

128

Mon. Not. R. Astron. Soc. 000, 000{000 (0000) Printed 25 October 1998 (MN L A T E X style le v1.4) Surface Imaging of Long-Period Variable Stars.  

E-print Network

physical origin. Key words: stars: { imaging { stars: individual: o Ceti { stars: individual: R Leo { stars 1998 November 99; in original form 1998 May 30 ABSTRACT The photospheric surfaces of #12;ve long with the presence of bright compact features, individually contributing between 5 and 20 % of the total stellar ux

Tuthill, Peter

129

Photometric investigations of UV Cet type flare stars with 3×10-7sec time resolution on a 6-m telescope  

Microsoft Academic Search

In 1982 - 1985, electrophotometrical observations of eight flare stars of the UV Cet type have been carried out with the 3×10-7sec time resolution at the 6-m telescope of the Special Astrophysical Observatory. Using the apparatus and program complex MANIA during 35 hours of patrol observations, the authors have registered about 120 stellar flares, mainly at V577 Mon, Wolf 424

G. M. Beskin; R. E. Gershberg; S. I. Neizvestnyj; V. L. Plakhotnichenko; L. A. Pustil'Nik; V. F. Shvartsman

1990-01-01

130

Photometrical investigations of the UV Cet type flare stars with the 3×10-7sec time resolution at the 6-metre telescope  

Microsoft Academic Search

In 1982 - 85 electrophotometrical observations of 8 flare stars of the UV Cet type have been carried out with the 3×10-7sec time resolution at the 6-m telescope of the Special Astrophysical Observatory. Using the apparatus and program complex MANIA during 35 hours of patrol observations, the authors have registered about 120 stellar flares, mainly at V577 Mon, Wolf 424

G. M. Beskin; R. E. Gershberg; S. I. Neizvestnyj; V. L. Plakhotnichenko; L. A. Pustil'Nik; V. F. Shvartsman

1988-01-01

131

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

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

132

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

133

A Comprehensive COS Study of the Magnetic Dynamos, Rotations, UV Irradiances and Habitability of dM Stars with a Broad Span of Ages  

NASA Astrophysics Data System (ADS)

We propose HST/COS FUV spectrophotometry of a carefully selected sample of 9 dM1-5 stars with recently reliably determined ages ranging from 1-12 Gyr. This program complements our Chandra Cycle 13 program of the same targets to determine their coronal X-ray properties. Ages {of all but one star} have recently been firmly determined from memberships in wide binaries with white dwarf {WD} companions having reliable cooling time+main-sequence evolution ages {Zhao et al. 2012, Garces et al 2011}. Until these studies, reliable age determinations for dM stars >2 Gyr were nearly impossible. However, we can now carry out a comprehensive UV study of dM star atmospheres across nearly the full age-range of the current Universe. The primary goals are 1} to study the evolution of their dynamo-generated X-ray and UV {XUV} emissions with age/rotation and to better define the heating and energetics of their atmospheres {via Age-Rotation-Activity-XUV Irradiance relations} and 2} to study the effects of the XUV radiation on planets hosted by red dwarfs. The COS UV spectral region contains numerous important diagnostic emission lines for characterizing the energy transfer and atmospheric structure, while line ratios yield valuable information about the electron density. Further, these data {when combined with our coronal X-ray measures} are also important for gauging dM star XUV emissions - critical for assessing the photochemical & photoionization evolution of planetary atmospheres and ionospheres that in turn strongly affect the possible development of life on hosted extrasolar planets. We are requesting a total of 19 HST orbits to achieve the science goals of the program.

Guinan, Edward

2012-10-01

134

Observations of late-type stars with hot companions  

NASA Astrophysics Data System (ADS)

International Ultraviolet Explorer and Astronomical Netherlands Satellite observations of the hot companions of omicron Ceti, epsilon Aur, and pi Pup are discussed. Observations of HD 62001, the central star of the nebula VV 1-7 are also reported. The nebula VV 1-7 which is present on the Palomar blueprint is not present on the ESO blueprints.

Gilra, D.; Wesselius, P. R.; Rao, N. K.

1980-04-01

135

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

136

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

137

The Debris Disk of Solar Analogue $\\tau$ Ceti: Herschel Observations and Dynamical Simulations of the Proposed Multiplanet System  

E-print Network

$\\tau$ Ceti is a nearby, mature G-type star very similar to our Sun, with a massive Kuiper Belt analogue (Greaves et al. 2004) and possible multiplanet system (Tuomi et al. 2013) that has been compared to our Solar System. We present Herschel Space Observatory images of the debris disk, finding the disk is resolved at 70 and 160 microns, and marginally resolved at 250 microns. The Herschel images and infrared photometry from the literature are best modelled using a wide dust annulus with an inner edge between 1-10 AU and an outer edge at ~55 AU, inclined from face-on by 35$\\pm$10 degrees, and with no significant azimuthal structure. We model the proposed tightly-packed planetary system of five super-Earths and find that the innermost dynamically stable disk orbits are consistent with the inner edge found by the observations. The photometric modelling, however, cannot rule out a disk inner edge as close to the star as 1 AU, though larger distances produce a better fit to the data. Dynamical modelling shows tha...

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

2014-01-01

138

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

PubMed

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

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

2014-02-01

139

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

NASA Astrophysics Data System (ADS)

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

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

2001-10-01

140

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  

E-print Network

We analysed UV FUSE, IUE, and HST/STIS 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 $\\lambda$ 973 $\\mathrm{\\AA}$, 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 ...

Keller, Graziela R; Maciel, Walter J

2014-01-01

141

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

142

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

SciTech Connect

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

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

2011-01-01

143

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

PubMed Central

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

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

2014-01-01

144

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

PubMed

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

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

2014-01-01

145

Long-Term Study of the Starspot Activity on the Eclipsing Short-Period RS Canum Venaticorum Star UV Piscium  

NASA Astrophysics Data System (ADS)

We present optical photometry of the short period eclipsing RS CVn system, UV Piscium for the years 1966-1984. After removing the spot effects from the light curves of Vivekananda Rao and Sarma (1981), we analyzed the cleaned data to obtain system parameters. For each light curve, we model the distortion waves in order to study the behaviour of starspots in this system.

Vivekananda Rao, P.; Radhika, P.

146

How temperature influences the stoichiometry of CeTi2O6  

NASA Astrophysics Data System (ADS)

Of the many materials examined for the sequestration of nuclear waste, Ti oxides have received considerable attention. Brannerite (UTi2O6), in particular, has been studied extensively for this application. The Ce analogue of this material (CeTi2O6) has been widely investigated instead of the actinide versions owing to the reduced safety hazards and because Ce has similar crystal chemistry to U and Pu. In this study, examination of Ti K-, Ce L3-, and Ce M4,5-edge XANES spectra lead to the conclusion that CeTi2O6 was O-deficient when synthesized at high temperature and then quench cooled, and that the degree of O-deficiency was reduced upon post-annealing at lower temperatures. These observations can be ascribed to a temperature-dependant Ce3+/Ce4+ redox couple. This investigation suggests that Ce-containing materials may not properly simulate the actinide-bearing analogues; however, CeTi2O6 could be useful for other applications, such as catalysis.

Huynh, Lana T.; Eger, Shaylin B.; Walker, James D. S.; Hayes, John R.; Gaultois, Michael W.; Grosvenor, Andrew P.

2012-06-01

147

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

148

Photometrical investigations of the UV Cet type flare stars with the 3×10-7sec time resolution at the 6-metre telescope.  

NASA Astrophysics Data System (ADS)

In 1982 - 85 electrophotometrical observations of 8 flare stars of the UV Cet type have been carried out with the 3×10-7sec time resolution at the 6-m telescope of the Special Astrophysical Observatory. Using the apparatus and program complex MANIA during 35 hours of patrol observations, the authors have registered about 120 stellar flares, mainly at V577 Mon, Wolf 424 = FL Vir, CN Leo and UV Cet. The methods of observations and statistical treatment of data are given. The main results are: (1) no fine structure within the time scale 10-6 - 10-1s is found; (2) the shortest times of statistically significant brightness variations are 0.3 - 0.8 s and inherent in a phase of a fast flaring up; these values fit the prediction of the gasodynamical model of flares; (3) the life time of significant details at maxima and descending branches of flare light curves reliably exceed 0.5 s; (4) the flares with a total duration of several seconds are registered, their fading phases seem to be determined by a relaxation time of matter heated in a flare; (5) the energetics of the faintest flares registered in the observations is compatible with the energetics of the solar subflares; (6) the upper limit of a total power of stellar microflares is less than the time averaged power of flares which are individually registered and therefore there is no reason to suggest that microflares play the main role in stellar corona heating.

Beskin, G. M.; Gershberg, R. E.; Neizvestnyj, S. I.; Plakhotnichenko, V. L.; Pustil'Nik, L. A.; Shvartsman, V. F.

149

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

150

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

151

The UV to hard X-ray continuum of a Seyfert galaxy scrutinized by XMM and NuSTAR  

NASA Astrophysics Data System (ADS)

We propose to perform a unique XMM-NuSTAR monitoring with 5 repeated observations of 20 ks spaced by a few days of the Seyfert galaxy NGC 4593. This is the best Seyfert candidate to obtain high sensitivity measurements on a day time scale over the entire high energy spectrum. This is an absolute prerequisite 1) to correctly disentangle the different spectral components present in this energy band, and 2) to reveal their complex interdependences and variability behavior. This study will allow us i) to constrain the physical parameters of the Comptonizing corona; ii) to investigate the nature of the soft X-ray excess; iii) to put firm conclusions on the distance, nature and geometry of the reflecting material(s).

Petrucci, Pierre-Olivier

2013-10-01

152

Novel chemical synthesis and characterization of CeTi(2)O(6) 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

153

Photometric investigations of UV Cet type flare stars with 3×10-7sec time resolution on a 6-m telescope.  

NASA Astrophysics Data System (ADS)

In 1982 - 1985, electrophotometrical observations of eight flare stars of the UV Cet type have been carried out with the 3×10-7sec time resolution at the 6-m telescope of the Special Astrophysical Observatory. Using the apparatus and program complex MANIA during 35 hours of patrol observations, the authors have registered about 120 stellar flares, mainly at V577 Mon, Wolf 424 = FL Vir, CN Leo and UV Cet. The methods of observations and statistical treatment of data are given. The main results are as follows: 1) no fine structure within the time scale 10-6 - 10-1sec is found in flares; 2) the shortest times of statistically significant brightness variations are 0.3 - 0.8 sec, inherent in a phase of a fast flaring-up; these values fit the prediction of the gasdynamical model of flares; 3) the lifetime of significant details at maxima and descending branches of flare light curves reliably exceed 0.5 sec; 4) the flares with a total duration of several seconds are registered, their fading phases seem to be determined by a relaxation time of matter heated in a flare; 5) the energetics of the faintest flares registered in the observations is compatible with the energetics of the solar subflares; 6) the upper limit of the total power of stellar microflares is less than the time-averaged power of flares which are individually registered, and therefore there is no reason to suggest that microflares play the main role in stellar corona heating.

Beskin, G. M.; Gershberg, R. E.; Neizvestnyj, S. I.; Plakhotnichenko, V. L.; Pustil'Nik, L. A.; Shvartsman, V. F.

154

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

E-print Network

We estimate the UV continuum slope, $\\beta$, for 923 galaxies in the range $1 = -1.382~(-1.830)\\pm0.002$ (random) $\\pm0.1$ (systematic). We find comparable scatter in $\\beta$ (standard deviation = 0.43) to local dwarf galaxies and 30% larger scatter than $z>2$ galaxies. We study the trends of $\\beta$ with redshift and absolute magnitude for binned sub-samples and find a modest color-magnitude relation, $d\\beta/dM = -0.11 \\pm 0.01$ and no evolution in $d\\beta/dM$ with redshift. A modest increase in dust reddening with redshift and luminosity, $\\Delta E(B-V) \\sim 0.1$, and a comparable increase in the dispersion of dust reddening at $z2$, we find trends that are consistent with previous works; combining our data with the literature in the range $1

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

2014-01-01

155

Intercombinational Line Profiles in the UV Spectra of T Tauri Stars and Analysis of the Accretion Zone  

NASA Astrophysics Data System (ADS)

We have analyzed for the first time profiles of the SiIII 1892 Å and CIII 1909 Å intercombinational lines in HST spectra of the stars RY Tau and RU Lup. The widths of these optically thin lines exceeded 400 km/s, ruling out formation in the stellar chromosphere. Since the intensity of the Si line exceeds that of the C line, it is unlikely that a large fraction of the observed line flux is formed in a stellar wind. The observed profiles can be reproduced in the framework of an accretion shock model if the velocity field in the accretion zone is appreciably nonaxisymmetric. In this case, the line profiles should display periodic variations, which can be used to determine the accretion zone geometry and the topology of the magnetic field near the stellar surface; corresponding formulas are presented. In addition, periodic variations of the 0.3 0.7 keV X-ray flux should be observed.

Lamzin, S. A.

2000-05-01

156

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

157

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

PubMed

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

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

2014-01-01

158

Observations of H-beta and He II lambda 4686 lines in the spectra of flares of UV Cet-type stars  

NASA Astrophysics Data System (ADS)

The main results of 45.4 hours of continuous spectroscopic and photoelectric B-band observations of AD Leo, DT Virgo, and YZ CMi are discussed. In two AD Leo flares and two YZ CMi flares, an increase of the central intensity of H-beta was observed 10-20 min before the maximum B-band brightness. The spectra of one AD Leo flare and one YZ CMi flare definitely indicate the formation of broad wings of H-beta occurring mainly during flare maximum. These flares surpass the other four in total optical energy. The Stark effect seems to be the most appropriate explanation for the origin of the wings. The upper limit of the equivalent widths of the He II wavelength 4686 line was higher than that in the quiet state. The equivalent width values cannot be explained by the cascade recombination mechanism if the ratio of optical and X-ray luminosities is nearly the same for all flares of UV Cet-type stars.

Chugainov, P. F.; Petrov, P. P.; Scherbakov, A. G.

159

Uv Observations of Geminga  

NASA Astrophysics Data System (ADS)

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

Holt, Stephen

1991-07-01

160

White Dwarf Stars (With 37 figures)  

NASA Astrophysics Data System (ADS)

Introduction White Dwarfs as Useful Stars Origins: the Clue of White Dwarf Masses The Main Channel Why Such a Narrow Mass Distribution? Observed Properties of White Dwarfs Discovery of White Dwarfs Finding White Dwarfs White Dwarf Colors and the White Dwarf Luminosity Function White Dwarf Optical Spectra Distribution of Spectral Types with Effective Temperatures Magnetic White Dwarfs Pulsating White Dwarfs Physics of White Dwarf Interiors Equation of State Heat Transport in Degenerate Matter Nonideal Effects Specific Heat White Dwarf Formation and Early Cooling Thermal Pulses on the AGB Departure from the AGB The PNN Phase Nuclear Shutdown and Neutrino Cooling Chemical Evolution of White Dwarfs Diffusive Processes Accretion of "Fresh" ISM vs. Mass Loss Convection Chemical Evolution Scenarios White Dwarf Cooling and the White Dwarf Luminosity Function A Simplified Cooling Model Complications: Neutrinos and Crystallization Realistic Cooling Calculations Construction of Theoretical Luminosity Functions The Age of the Galactic Disk Nonradial Oscillations of White Dwarfs: Theory Review of Observations Hydrodynamic Equations Local Analysis and the Dispersion Relation g-mode Period Spacings Mode Trapping Rotational and Magnetic Splitting The Seismological Toolbox Pulsating White Dwarfs The Whole Earth Telescope PG 1159 Stars and Pulsating PNNs GD 358: A Pulsating DB White Dwarf The ZZ Ceti Stars Astrophysical Applications of White Dwarfs Stellar Evolution as a Spectator Sport The White Dwarf Luminosity Function and Our Galaxy White Dwarfs and Cluster Ages The Planetary Nebula Luminosity Function and Galaxy Distances Driving and Damping of Pulsations and Convective Efficiency in - White Dwarfs Ceti Stars Final Thoughts References

Kawaler, Steven D.

161

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

162

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...

163

From Cosmic Dawn to Our Solar System: A Next-Generation UV--Optical Space Facility for the Study of Star Formation  

E-print Network

for the births and life cycles of stars and their planetary systems, and to in- vestigate and understand of Star Formation Rolf A. Jansen1 , Paul Scowen1 , Matt Beasley2 , D. Calzetti3 , S. Desch1 , A. Fullerton's ASMCS program), and a proposed concept for a dedicated 1.65 m Star Formation Observatory. Our aim

Jansen, Rolf Arthur

164

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

165

Modelling UV sky for future UV missions  

NASA Astrophysics Data System (ADS)

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

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

166

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

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

167

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

PubMed Central

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

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

2014-01-01

168

Predicting UV sky for future UV missions  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

169

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

PubMed Central

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

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

2014-01-01

170

Massive Stars: Stellar Populations  

Microsoft Academic Search

Massive stars dominate the chemical and dynamical evolution of the ISM, and ultimately of their parent galaxy and the universe, because of their fast evolution and intense supersonic winds. Four decades ago, the first rocket UV spectra of massive stars revealed the importance of mass loss and began to change our understanding of their evolution. Recently, advances in stellar modeling,

Luciana Bianchi

2007-01-01

171

The outburst of Nova CSS 081007:030559+054715 (HV Ceti)  

NASA Astrophysics Data System (ADS)

Aims: The outburst of nova CSS 081007:030559+054715 (HV Cet) was extensively followed by Swift to study the evolution of its X-ray and UV emission. Methods: We obtained Swift X-ray and UV observations, at times with high cadence, over an interval of 266 days and analysed the temporal and spectral properties of the object. Optical polarisation measurements were also obtained, but no significant circular polarisation was identified. UV data from GALEX and AAVSO optical data were investigated in addition. Results: A variable supersoft source was discovered, with a 1.77 d periodic modulation in its X-ray, UV and optical emission, in phase across all three bands. High cadence observations revealed a declining trend of the X-ray modulation amplitude, while the UV oscillation became stronger over this interval; the UV data also show occasional secondary minima. The X-ray and UV flux declines sharply ~150 days after discovery (the date of optical outburst peak is uncertain). While bright, the UV and, to a lesser extent, the X-ray light curves show two cycles of a ~40-50 day modulation. We believe the 1.77 d modulation to be orbital, likely caused by structured disc-rim occultation. The X-ray spectra were soft at all times, with negligible flux above 1 keV. These spectra were fitted with an NLTE white dwarf model atmosphere of kT = 60-80 eV, with no spectral changes related to the 1.77 d or possible ~40-day periodicities seen. A Cloudy model demonstrated that it is possible to account for the UV flux through the reprocessing of X-rays. The UV flux is far in excess of the soft X-ray spectral component. We propose that the apparently sub-Eddington white dwarf luminosity is due to permanent obscuration by the accretion disc rim: we see only X-rays scattered by optically thin plasma interior to the disc rim, whereas the UV flux is mostly created by reprocessing in the disk rim interior surface. The in-phase 1.77 d UV and X-ray modulation is caused by the region in which the gas stream from the secondary raises the disc rim, the maximum X-ray obscuration coinciding with the minimum aspect of the UV reprocessing area. In summary, HV Cet had characteristics of both classical novae and persistent super-soft X-ray sources.

Beardmore, A. P.; Osborne, J. P.; Page, K. L.; Hakala, P. J.; Schwarz, G. J.; Rauch, T.; Balman, S.; Evans, P. A.; Goad, M. R.; Ness, J.-U.; Starrfield, S.; Wagner, R. M.

2012-09-01

172

Evolution of UV-Irradiated Protoplanetary Disks  

NASA Astrophysics Data System (ADS)

Most stars are born in transient clusters within OB associations. Within the first few million years of birth, stars and their protoplanetary disks can be exposed to intense UV radiation, close-passages of sibling stars, stellar winds, and supernova explosions. Disk photo-ablation may promote the rapid formation of kilometer-scale planetesimals by preferentially removing gas and small grains, and enhancing the relative abundance of centimeter and meter-scale bodies. Disk perturbations produced by close-by passages of sibling stars or binary companions can trigger tidally induced shocks which anneal grains. Close-by supernovae can inject live radioactive species such as 26Al and 60Fe either before or after the formation of a low-mass star and its disk. Intense UV radiation from the pre-supernova blue-supergiant and Wolf-Rayet phases of the most massive stars can result in enhanced disk photo-ablation.

Bally, J.; Moeckel, N.; Throop, H.

2005-12-01

173

LEGUS: Legacy ExtraGalactic UV Survey  

NASA Astrophysics Data System (ADS)

We propose to build the first HST UV Atlas of 50 nearby star-forming galaxies, carefully selected to span the full range of morphology, star formation rate {SFR}, mass, metallicity, internal structure, and interaction state found in the local Universe. In combination with archival and new optical {UBVI} WFC3/ACS data, the requested WFC3/UV images are key for deriving accurate recent {<50 Myr} star formation histories {SFHs} from resolved massive stars, and the extinction-free ages and masses of star clusters and associations. These extensive inventories of massive stars, clustered systems, and SFHs will be used to: {1} quantify how the clustering of star formation evolves both in space and in time; {2} discriminate among models of star cluster evolution; {3} investigate the effects of SFH on the UV SFR calibrations; {4} explore the impact of environment on star formation and cluster evolution across the full range of galactic and ISM properties. These are only a few of the science opportunities enabled by LEGUS. The astronomical community will add many more: LEGUS observations will inform theories of star formation and galaxy evolution, and improve the understanding of the physical underpinning of the gas-star formation relation and the nature of the clumpy star formation at high redshift. LEGUS will generate the most homogeneous high-resolution, wide-field UV dataset to date, building and expanding on the GALEX legacy. LEGUS will populate the HST Archive with unique data, that will be ready for immediate use by the community through the extensive data products we will deliver, and will provide a unique foundation for future observations with JWST and ALMA.

Calzetti, Daniela

2013-10-01

174

Solar UV dose patterns in Italy.  

PubMed

Since 1992 solar ultraviolet (UV) spectral irradiance (290-325 nm) has been measured at two Italian stations of Rome (urban site) and Ispra (semirural site) using Brewer spectrophotometry. The data collected under all sky conditions, are compared with the output of a sophisticated radiative transfer model (System for Transfer of Atmospheric Radiation--STAR model). The STAR multiple scattering scheme is able to cope with all physical processes relevant to the UV transfer through the atmosphere. The experience so far acquired indicates that, in spite of the unavoidable uncertainties in the input parameters (ozone, aerosol, surface albedo, pressure, temperature, relative humidity, cloud cover), measured and computed clear sky iradiances are in reasonable agreement. The STAR model is applied to build up the solar UV geographic patterns in Italy: the daily dose in the range 290-325 nm is computed at about 70 sites where a thorough and homogeneous climatology is available. For each month the concept of an idealized "standard day" is introduced and the surface distribution of solar UV field determined. The map of solar UV patterns for Italy, available for the first time, meets the study requirements in the field of skin and eye epidemiology, as well as in other investigations dealing with the impact of UV on the biosphere. The results are interpreted in terms of atmospheric and meteorological parameters modulating UV radiation reaching the ground. PMID:10857363

Meloni, D; Casale, G R; Siani, A M; Palmieri, S; Cappellani, F

2000-06-01

175

Hot Stars in Globular Clusters  

E-print Network

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

S. Moehler

1998-12-08

176

UV Menace  

NSDL National Science Digital Library

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

177

The UV Side of BOSS Galaxies  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

178

Optical, UV and Radio Observations of RS Canum Venaticorum  

NASA Astrophysics Data System (ADS)

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

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

179

Intergalactic Star Formation  

E-print Network

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

Duc, P A; Braine, J; Brinks, E; Lisenfeld, U; Charmandaris, V; Duc, Pierre-Alain; Boquien, Meederic; Braine, Jonathan; Brinks, Elias; Lisenfeld, Ute; Charmandaris, Vassilis

2006-01-01

180

Intergalactic Star Formation  

E-print Network

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

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

2006-10-13

181

The First Stars  

E-print Network

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

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

2008-02-01

182

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

1990-12-01

183

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

1991-07-01

184

UV excess galaxies: Wolf-Rayet galaxies  

E-print Network

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

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

2000-05-26

185

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

186

The 90-day report for SL4 experiment S019: UV stellar astronomy  

NASA Technical Reports Server (NTRS)

The use of Experiment S019 to obtain moderate dispersion stellar spectra extending down to 1300A with sufficient spectral resolution to permit the study of ultraviolet (UV) line spectra and of spectral energy distributions of early-type stars is studied. Data obtained from this experiment should be of sufficient accuracy to permit detailed physical analysis of individual stars and nebulae, but an even more basic consideration is the expectation of obtaining spectra of a sufficient number of stars so that a statistically meaningful survey may be made of the UV spectra of a wide variety of star types. These should include all luminosity classes of spectral types O, B and A, as well as peculiar stars such as Wolf-Rayet stars and Ap or Am stars. An attempt was also made to obtain, in the no-prism mode, low dispersion UV spectra in a number of Milky Way star fields and in nearby galaxies.

1974-01-01

187

Magnetism in Massive Stars  

NASA Astrophysics Data System (ADS)

Stars with mass more than 8 solar masses end their lives as neutron stars, which we mostly observe as highly magnetized objects. Where does this magnetic field come from? Such a field could be formed during the collapse, or is a (modified) remnant of a fossil field since the birth of the star, or otherwise generated by a dynamo during its lifetime in the pre-collapse stages. The answer is unknown, but traditionally magnetic massive stars should not exist since they do not have a convective layer such as the Sun. In the last decade, however, a number of magnetic massive stars have been found, which likely possess a stable field from their birth, and indirect evidence is accumulating that localized fields can indeed be generated during the main-sequence lifetime and beyond. These observational facts opened a new field of research, which is the topic of this review. Among the indirect evidence is a large range of observational phenomena among O and B stars that cannot be explained without the presence of surface magnetic fields. These phenomena include photospheric turbulence, wind clumping, cyclic wind variability observed in UV lines, other types of wind variability in optical lines, anomalous X-ray emission, and non-thermal emission in the radio region. A summary of the properties of observed magnetic massive OB stars is given and the role of magnetic fields in massive stars will be discussed, including how to identify new magnetic candidates.

Henrichs, H. F.

2012-12-01

188

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

189

UV opportunities at ESO  

NASA Astrophysics Data System (ADS)

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

Pasquini, Luca

2014-11-01

190

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

191

GALEX Catalog of UV Point Sources in M33  

E-print Network

The hottest stars ($>$10,000 K), and by extension typically the most massive ones, are those that will be prevalent in the ultraviolet (UV) portion of the electromagnetic spectrum, and we expect numerous B, O, and Wolf-Rayet stars to be bright in UV data. In this paper, we update the previous UV catalog of M33, created using the Ultraviolet Imaging Telescope (UIT), using data from the Galaxy Evolution Explorer (GALEX). We utilize PSF photometry to better handle the crowded regions in the galaxy, and benefit from GALEX's increased sensitivity compared to UIT. We match our detections with data from the Local Group Galaxies Survey (LGGS) to create a catalog with photometry spanning from the far-UV through the optical for a final list of 24738 sources. All of these sources have far-UV (FUV; 1516A), near-UV (NUV; 2267A), and V data, and a significant fraction also have U, B, R, and I data as well. We compare these sources to a catalog of known Wolf-Rayet stars in M33 and find that we recover 114 of 206 stars with ...

Mudd, Dale

2014-01-01

192

The Star Formation Camera  

Microsoft Academic Search

The Star Formation Camera (SFC) is a wide-field (~15'x19, >280 arcmin^2), high-resolution (18x18 mas pixels) UV\\/optical dichroic camera designed for the Theia 4-m space-borne space telescope concept. SFC will deliver diffraction-limited images at lambda > 300 nm in both a blue (190-517nm) and a red (517-1075nm) channel simultaneously. Our aim is to conduct a comprehensive and systematic study of the

Paul A. Scowen; Rolf Jansen; Matthew Beasley; Daniela Calzetti; Steven Desch; Alex Fullerton; John Gallagher; Doug Lisman; Steve Macenka; Sangeeta Malhotra; Mark McCaughrean; Shouleh Nikzad; Robert O'Connell; Sally Oey; Deborah Padgett; James Rhoads; Aki Roberge; Oswald Siegmund; Stuart Shaklan; Nathan Smith; Daniel Stern; Jason Tumlinson; Rogier Windhorst; Robert Woodruff

2009-01-01

193

UV Radiative Feedback on High-Redshift Proto-Galaxies  

E-print Network

We use three-dimensional hydrodynamic simulations to investigate the effects of a transient photoionizing ultraviolet (UV) flux on the collapse and cooling of pregalactic clouds. These clouds have masses in the range 10^5 -10^7 M_sun, form at high redshifts (z>18), are assumed to lie within the short-lived cosmological HII regions around the first generation of stars. In addition, we study the combined effects of this transient UV flux and a persistent Lyman-Werner (LW) background from distant sources. In the absence of a LW background, we find that a critical specific intensity of J_UV ~ 0.1 x 10^-21 ergs s^-1 cm^-2 Hz^-1 sr^-1 demarcates a transition from net negative to positive feedback for the halo population. A weaker UV flux stimulates subsequent star formation inside the fossil HII regions, by enhancing the H_2 molecule abundance. A stronger UV flux significantly delays star-formation by reducing the gas density, and increasing the cooling time, at the centers of collapsing halos. At a fixed J_UV, the sign of the feedback also depends strongly on the density of the gas at the time of UV illumination. Regardless of the whether the feedback is positive or negative, we find that once the UV flux is turned off, its impact stars to diminish after ~30% of the Hubble time. In the more realistic case when a LW background is present, with J_LW > 0.01 x 10^-21 ergs s^-1 cm^-2 Hz^-1 sr^-1, strong suppression persists down to the lowest redshift (z=18) in our simulations. Finally, we find evidence that heating and photoevaporation by the transient UV flux renders the ~10^6 M_sun halos inside fossil HII regions more vulnerable to subsequent H_2 photo-dissociation by a LW background.

Andrei Mesinger; Greg Bryan; Zoltan Haiman

2006-04-07

194

Discrete Scale Relativity And SX Phoenicis Variable Stars  

E-print Network

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

R. L. Oldershaw

2009-06-18

195

Solar UV variability  

NASA Technical Reports Server (NTRS)

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

Donnelly, Richard F.

1989-01-01

196

Old stellar systems in UV: resolved and integrated properties  

NASA Astrophysics Data System (ADS)

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

Dalessandro, E.

2014-11-01

197

Photo-dissociated and Photoionized Regions Around Main Sequence Stars  

Microsoft Academic Search

Molecular Clouds are the sites were stars are formed. The birth of a star results in a strong UV flux that propagates through the cold molecular material, dissociating and ionizing the gas. A shell of ionized gas (an HII region) forms around the star, both of which are encapsulated by a shell of photo-dissociated gas (the PDR). The extent of

Rosa Izela Diaz-Miller

1998-01-01

198

Review: Magnetic fields of O stars  

E-print Network

Since 2002, strong, organized magnetic fields have been firmly detected at the surfaces of about 10 Galactic O-type stars. In this paper I will review the characteristics of the inferred fields of individual stars, as well as the overall population. I will discuss the extension of the 'magnetic desert', first inferred among the A-type stars, to O stars up to 60 solar masses. I will discuss the interaction of the winds of the magnetic stars with the fields above their surfaces, generating complex 'dynamical magnetosphere' structures detected in optical and UV lines, and in X-ray lines and continuum. Finally, I will discuss the detection of a small number of variable O stars in the LMC and SMC that exhibit spectral characteristics analogous to the known Galactic magnetic stars, and that almost certainly represent the first known examples of extra-Galactic magnetic stars.

Wade, G A

2014-01-01

199

WSO-UV project  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

200

NGC 4656UV: A UV-selected Tidal Dwarf Galaxy Candidate  

NASA Astrophysics Data System (ADS)

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 ? yr-1 from the far-ultraviolet flux and measure a total H I mass of 3.8 × 108 M ? 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 ~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. Based in part 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.

Schechtman-Rook, Andrew; Hess, Kelley M.

2012-05-01

201

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

202

Mid-UV Determination of Elliptical Galaxy Abundances and Ages  

E-print Network

We investigate the effects of abundance and age on the mid-UV spectra and Mg_{2} strengths of stellar populations using simple population synthesis models. These models are used to constrain the star formation history of four nearby elliptical galaxies and spiral bulges. The mid-UV (1800 - 3200 \\AA) light of evolved stellar populations (> 1 Gyr) is dominated by the main sequence turn-off, unlike the optical light which is dominated by the red giant branch. A detailed investigation of the mid-UV features of elliptical galaxies may help break the age-metallicity degeneracy that plagues optical techniques. Also, a better understanding of this wavelength region is useful for the studies of 0.5 $\\leq$ z $\\leq$ 1.5 galaxies for which the rest frame mid-UV is redshifted into the visible. We create simple, single age (3-20 Gyr), single metallicity (Z = 0.0004 - 0.05) spectral energy distributions (SEDs) extending into the UV using the Kurucz model stellar fluxes. Comparison to standard stars' mid-UV spectra reveals that the Kurucz model fluxes accurately model a blend feature of FeI and MgI at 2538 {\\AA} (Bl2538) and the slope of the continuum between 2600 and 3100 {\\AA} (S2850). We find that our simple single age, single metallicity SEDs agree well with these mid-UV features of globular clusters. However, the majority of the galaxies do not agree with the Bl2538, S2850, and Mg_{2} values given by these simple models. The mid-UV features appear to require both an old metal-rich and a small old metal-poor (Z $\\leq$ 0.001) population. Despite being limited by the quality of the model stellar fluxes, our study has yielded two promising mid-UV spectral diagnostics (Bl2538 and S2850) and suggests unique and complex star formation histories for elliptical galaxies.

Jennifer M. Lotz; Henry C. Ferguson; Ralph C. Bohlin

1999-11-12

203

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

204

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

NASA Astrophysics Data System (ADS)

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

Thilker, David

2014-10-01

205

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

206

Hot Stars in Globular Cluster - A Spectroscopist's View  

E-print Network

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

S. Moehler

2001-05-09

207

Dynamic UV microstereolithography  

NASA Astrophysics Data System (ADS)

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 the visible to the UV range in order to overcome the opacity of LCD's in the UV domain. 400 × 400 points up-converted images have been obtained to generate solid three-dimensional objects.

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

2002-12-01

208

Child universes UV regularization?  

E-print Network

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

E. I. Guendelman

2007-03-21

209

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.

210

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

NASA Astrophysics Data System (ADS)

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

Massa, Derck

2014-10-01

211

Binary stars and the UVX in early-type galaxies  

NASA Astrophysics Data System (ADS)

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

Hernández-Pérez, Fabiola; Bruzual, Gustavo

2014-11-01

212

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

PubMed

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

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

2001-01-01

213

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

SciTech Connect

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

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

2013-07-20

214

The UV Upturn In Elliptical Galaxies And Environmental Effects  

NASA Astrophysics Data System (ADS)

It is suspected that the ultraviolet (UV) upturn phenomenon in elliptical galaxies and extended horizontal-branch stars in globular clusters have a common origin. An extremely high abundance of helium (Y 0.4) allows for a working hypothesis, but its origin is unclear. Peng & Nagai (2009) proposed that primordial helium sedimentation in dark haloes over cosmic timescales may lead to extreme helium abundances in galaxy cluster centers. In this scenario UV upturn should be restricted to brightest cluster galaxies (BCGs) only. This is a clear and testable prediction. We present tests of this hypothesis using galaxy clusters from Yoon et al. (2008) that were detected by both the Sloan Digital Sky Survey and the Galaxy Evolution Explorer Medium Imaging Survey. Using a new UV classification scheme based on far-UV, near-UV, and optical photometry we found only 5% of cluster elliptical galaxies show a UV upturn, while 27% and 68% are classified as "recent star-formation" and "UV-weak" ellipticals, respectively. The data reveal a modest positive dependence of the UV upturn fraction on galaxy velocity dispersion, which is in agreement with the earlier findings of Burstein et al. (1988) and possibly with the helium sedimentation theory. However, we do not see any dependency on rank or luminosity of galaxies. Besides, BCGs do not show any marked difference in UV upturn fraction or strength, which is inconsistent with the prediction. We conclude that the aforementioned helium sedimentation theory and its inferred environmental effects are not supported by the available data.

Yi, Sukyoung; Lee, J.; Sheen, Y.; Jeong, H.; Suh, H.; Oh, K.

2012-01-01

215

THE STAR FORMATION LAW AT LOW SURFACE DENSITY  

SciTech Connect

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

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

2009-05-10

216

Hot Massive Stars: The Impact of HST  

E-print Network

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

Paul A. Crowther

2007-06-30

217

Essential UV Observations of Eta Carinae's Change of State  

NASA Astrophysics Data System (ADS)

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

Mehner, Andrea

2014-10-01

218

The Star Formation Camera  

E-print Network

The Star Formation Camera (SFC) is a wide-field (~15'x19, >280 arcmin^2), high-resolution (18x18 mas pixels) UV/optical dichroic camera designed for the Theia 4-m space-borne space telescope concept. SFC will deliver diffraction-limited images at lambda > 300 nm in both a blue (190-517nm) and a red (517-1075nm) channel simultaneously. Our aim is to conduct a comprehensive and systematic study of the astrophysical processes and environments relevant for the births and life cycles of stars and their planetary systems, and to investigate and understand the range of environments, feedback mechanisms, and other factors that most affect the outcome of the star and planet formation process. This program addresses the origins and evolution of stars, galaxies, and cosmic structure and has direct relevance for the formation and survival of planetary systems like our Solar System and planets like Earth. We present the design and performance specifications resulting from the implementation study of the camera, conducted ...

Scowen, Paul A; Beasley, Matthew; Calzetti, Daniela; Desch, Steven; Fullerton, Alex; Gallagher, John; Lisman, Doug; Macenka, Steve; Malhotra, Sangeeta; McCaughrean, Mark; Nikzad, Shouleh; O'Connell, Robert; Oey, Sally; Padgett, Deborah; Rhoads, James; Roberge, Aki; Siegmund, Oswald; Shaklan, Stuart; Smith, Nathan; Stern, Daniel; Tumlinson, Jason; Windhorst, Rogier; Woodruff, Robert

2009-01-01

219

Models of H2 Fluorescence in the UV spectrum of the CTTS TW Hya  

Microsoft Academic Search

Strong UV emission lines produced in accretion shocks of classical T Tauri stars significantly affect the chemistry of the circumstellar disks. The surface layers of the disk close to the star are analgous to a photo-dissociation region, only controlled by line rather than continuum emission. A broad Ly-alpha emission line incident on surface layers of the disk photoexcites the warm

Gregory J. Herczeg; Brian E. Wood; Jeffrey L. Linsky; J. A. Valenti; C. M. Johns-Krull

2003-01-01

220

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

E-print Network

observed and recorded by the Galaxy Evolution Explorer (GALEX) ultraviolet space telescope (Martin et al, including surprising last flares from stars falling into supermassive black holes. In this era of exoplanet contain signatures of planets, particularly around compact UV-luminous objects such white dwarfs. Stars

Columbia University

221

STAR FORMATION IN ATOMIC GAS  

SciTech Connect

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

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

2012-11-01

222

Are You UV Safe?  

NSDL National Science Digital Library

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

Capobianco, Brenda; Thiel, Elizabeth A.

2006-09-01

223

Ultraviolet observations of Be stars /Review paper/  

NASA Technical Reports Server (NTRS)

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

Heap, S. R.

1976-01-01

224

UV Observations of the Galaxy Cluster Abell 1795 with the Optical Monitor on XMM-Newton  

NASA Technical Reports Server (NTRS)

We present the results of an analysis of broad band UV observations of the central regions of Abell 1795 observed with the optical monitor on XMM-Newton. As have been found with other UV observations of the central regions of clusters of galaxies, we find evidence for star formation. However, we also find evidence for absorption in the cD galaxy on a more extended scale than has been seen with optical imaging. We also report the first UV observation of part of the filamentary structure seen in H-alpha, X-rays and very deep U band imaging. The part of the filament we see is very blue with UV colours consistent with a very early (O/B) stellar population. This is the first direct evidence of a dominant population of early type stars at the centre of Abell 1795 and implies very recent star formation. The relationship of this emission to emission at other wavebands is discussed.

Mittaz, J. P. D.; Kaastra, J. S.; Tamura, T.; Fabian, A. C.; Mushotzky, F.; Peterson, J. R.; Ikebe, Y.; Lumb, D. H.; Paerels, F.; Stewart, G.

2000-01-01

225

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

226

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

227

From Cosmic Dawn to Our Solar System: A Next-Generation UVOptical Space Facility for the Study of Star Formation  

E-print Network

study of the astrophys- ical processes and environments relevant for the births and life cycles of stars of Star Formation Rolf Jansen, Paul Scowen (Arizona State University), Matthew Beasley (University)) Star Formation Observatory Star Formation Camera Abstract We summarize our science case for a UV

Jansen, Rolf Arthur

228

Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, arenât doing much of anything. In this video, Jonathanâs investigations reveal a slow-motion predator that hunts and attacks its prey. Traveling the world, Jonathan investigates sea stars from the tropics to the Antarctic and uses time-lapse photography to reveal an amazing complexity to the world of the sea star. Please see the accompanying study guide for educational objectives and discussion points.

Productions, Jonathan B.

2010-10-06

229

Hot Stars: Old-Fashioned or Trendy?  

E-print Network

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

A. W. A. Pauldrach

2002-12-10

230

Hot Massive Stars: The Impact of HST  

E-print Network

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

Crowther, Paul A

2007-01-01

231

Scintillating Stars  

NSDL National Science Digital Library

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

Riddle, Bob

2003-02-01

232

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

233

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

NASA Astrophysics Data System (ADS)

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

Bianchi, Luciana

2014-11-01

234

STATISTICAL PROPERTIES OF GALACTIC {delta} SCUTI STARS: REVISITED  

SciTech Connect

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

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

2013-05-15

235

Full-Stokes UV and visible spectropolarimeter for spatial application  

NASA Astrophysics Data System (ADS)

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

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

236

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

237

Binary Stars behind the Vela Super Nova Remnant  

Microsoft Academic Search

Spectroscopic observations of a pair of double stars behind the Vela SNR, in the UV provide information on the variations of the intersteallar medium composition, spatially and because these stars have been observed earlier by GHRS the data will also provide a measure of temporal variations. The Vela SNR is close and movement of the ISM infront perpendicular to the

Anthony Danks

1999-01-01

238

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

239

UV curable materials development  

SciTech Connect

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

Parker, B.G.

1996-12-01

240

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

241

Multifrequency observations of symbiotic stars  

NASA Technical Reports Server (NTRS)

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

Kenyon, Scott J.

1988-01-01

242

A Global Perspective on Star Formation  

E-print Network

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

S. Michael Fall

1996-11-20

243

The UV-Excess survey of the northern Galactic plane  

NASA Astrophysics Data System (ADS)

The UV-Excess survey of the northern Galactic plane images a 10° × 185° wide band, centred on the Galactic equator using the 2.5-m Isaac Newton Telescope in four bands (I5875) down to ~21-22 mag ( in I5875). The setup and data reduction procedures are described. Simulations of the colours of main-sequence stars, giant, supergiants, DA and DB white dwarfs and AM Canum Venaticorum stars are made, including the effects of reddening. A first look at the data of the survey (currently 30 per cent complete) is given.

Groot, Paul J.; Verbeek, Kars; Greimel, Robert; Irwin, Mike; González-Solares, Eduardo; Gänsicke, Boris T.; de Groot, Eelco; Drew, Janet; Augusteijn, Thomas; Aungwerojwit, Amornrat; Barlow, Mike; Barros, Susana; van den Besselaar, Else J. M.; Casares, Jorge; Corradi, Romano; Corral-Santana, Jesús M.; Deacon, Niall; van Ham, Wilbert; Hu, Haili; Heber, Uli; Jonker, Peter G.; King, Rob; Knigge, Christian; Mampaso, Antonio; Marsh, Tom R.; Morales-Rueda, Luisa; Napiwotzki, Ralf; Naylor, Tim; Nelemans, Gijs; Oosting, Tim; Pyrzas, Stylianos; Pretorius, Magaretha; Rodríguez-Gil, Pablo; Roelofs, Gijs H. A.; Sale, Stuart; Schellart, Pim; Steeghs, Danny; Szyszka, Cezary; Unruh, Yvonne; Walton, Nicholas A.; Weston, Simon; Witham, Andrew; Woudt, Patrick; Zijlstra, Albert

2009-10-01

244

Fluorine in extremely hot post-AGB stars  

E-print Network

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

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

2004-12-10

245

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

246

Biologically weighted personal UV dosimetry.  

PubMed

People are exposed to natural or artificial UV radiation in different ways; unintentionally or intentionally, at their workplace on their spare time. To quantify the amount of individual UV exposure, a personal dosimetry is necessary. In research, polysulphone film (PSF) dosimeters are the most frequently used personal UV dosimeters. We use calculated weighting factors in the measurement processing of polysulphone film dosimeters. The special weighting factor transforms the dosimeter reading from an equivalent UV dose to the biologically effective UV dose. The factor depends on the investigated problem (action spectrum of the photobiological effect and spectral distribution of the incident UV source), the calibration of PSF was carried out once by a monochromatic radiation (gamma = 295 nm). The equivalent dose readings are available from this calibration curve for any investigated question. A presented result of this method is the seasonal measurement of erythemally effective UV exposure by ambient solar radiation, and the individual exposure level in a "normal" person concerning UV exposure and also in groups with the risk of a lack of sunshine. Further applications are occupational measurements of the risk of health damage by UV radiation (with respect to the limit of the maximum permissible 8 h-exposure according to IRPA/INIRC-guidelines). We controlled the extent of UV exposure in workers in the area of arc welding workplaces. The biological weighting of PSF readings simplifies a routine use of PSF in personal UV monitoring to investigators without the expending special measurement technology (e.g. spectroradiometer). PMID:8988614

Knuschke, P; Barth, J

1996-10-01

247

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

248

UV-B induced morphogenesis  

PubMed Central

Low levels of ultraviolet (UV)-radiation alter the morphology of plants. UV-B exposure can lead to shorter petioles and shorter, narrower and/or thicker leaf blades. The resulting decrease in leaf area has been associated with inhibitory UV-B effects on biomass accumulation. In Arabidopsis, UV-B effects on leaf area have variously been attributed to altered cell division, cell expansion or combinations of these two processes. A dedicated UV-B sensory system, crosstalk between flavonoids and auxins, endoreduplication and generic Stress Induced Morphogenic Responses (SIMR) have all been proposed to contribute to the UV-B phenotype. Here, we propose that UV-mediated morphogenesis, rather than being controlled by a single regulatory pathway, is controlled by a regulatory blur involving multiple compensatory molecular and physiological feedback interactions. PMID:22899069

Jansen, Marcel A.K.; Coffey, Aoife M.; Prinsen, Els

2012-01-01

249

The Impact of UV Irradiance on the Composition of Exoplanets  

NASA Astrophysics Data System (ADS)

A majority of extrasolar giant planets are within a few hundredths of an AU from their parent star. Their proximity subjects them to high amounts of UV flux compared to what bodies in our own solar system receive. Therefore, we expect photochemistry to play a significant role in the composition of their visible atmospheres. Here we will present photochemical results that demonstrate the effects of different UV fields for F, G, K and M stars using HD189733b and GJ436b as examples. Effects of different eddy mixing strengths and metallicty will also be investigated as they determine where the boundary between thermochemistry and transport occurs and thus determine the bulk composition of the visible atmosphere.

Line, Michael R.; Chen, P.; Yung, Y. L.

2010-10-01

250

Which Stars Go BOOM?  

NASA Astrophysics Data System (ADS)

Intermediate mass stars with M = 6 to 10 Msun will end their lives by either losing mass quiescently and forming massive white dwarfs or by exploding as core collapse type II supernovae. The critical mass separating these two stellar evolution channels is not only a fundamental threshold of stellar astrophysics, but is a crucial ingredient to generate reliable galaxy evolution simulations. Given the steepness of the stellar IMF, small changes in the critical mass directly affects chemical evolution scenarios, energetics, and feedback relations. Although most astronomers reference the critical mass at M = 8 Msun, there is a lack of robust theoretical or observational confirmation of this number. We propose to measure the critical mass directly by verifying the end products of stellar evolution in four rich, young, co-eval stellar populations. With ages of 25 to 60 Myr and total stellar masses >10,000 Msun, the Magellanic Cloud globular clusters NGC 1818, NGC 330, NGC 1805, and NGC 2164 have present-day main-sequence turnoff masses of M = 6.2, 7.2, 8.5, and 9.8 Msun, respectively. Existing photometry verifies that each cluster has a rich upper main sequence of massive stars, and therefore would have formed dozen(s) of stars above the present day turnoff. If those stars did not explode as core collapse supernovae, they will populate a clear blue white dwarf cooling sequence. Our experiment uses the full power, wavelength coverage, and resolution of HST/WFC3 to detect these cooling sequences in high-precision, UV-sensitive color-magnitude diagrams.

Kalirai, Jason

2014-10-01

251

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

252

The UV enigma of post-starburst galaxies  

NASA Astrophysics Data System (ADS)

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

Melnick, Jorge; De Propris, Roberto

2014-11-01

253

Holographic UV laser microsurgery  

PubMed Central

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

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

2011-01-01

254

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

255

Stars equilibrium  

NSDL National Science Digital Library

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

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

2003-01-01

256

Possible causes for wide depresssion appearance in ultraviolet spectra of B- and A-stars. I. Abundance anomalies in stellar atmospheres.  

NASA Astrophysics Data System (ADS)

A brief survey of observational data related to energy distribution in UV spectra of hot stars is presented, indicating wide depression for a part of normal B- and A-stars and particularly for Ap-stars. The observed depressions may be connected with the overabundance of elements in stellar atmospheres. To check this assumption synthetic spectra in three UV intervals (2350 - 2380), 2245 - 2275 and 1810 - 1840 Å) and one optical interval (4500 - 4530 Å) are calculated for different element abundances in stellar atmospheres. It was shown that UV flux deficiency for Ap-stars can be explained by the metal overabundance intrinsic for such stars. In the case of normal stars permissible variations of metal abundances may explain the appearance of UV flux deficiency (or its excess) for A-stars and probably for latest B-stars. This mechanism fails at higher temperatures.

Lyubimkov, L. S.; Lafarli, A. M.

257

Star fruit  

Microsoft Academic Search

The carambola or star fruit belongs to the Oxalidaceae family, species Averrhoa carambola. Slices cut in cross-section have the form of a star (Figure 1). It is believed to have originated in Ceylon and the Moluccas\\u000a but it has been cultivated in southeast Asia and Malaysia for many centuries. It is commonly grown in some provinces in southern\\u000a China, in

Miguel M. Neto; Ruither O. Carolino; Norberto P. Lopes; Norberto Garcia-Cairasco

258

UV detectors for spectrographs of WSO-UV project  

NASA Astrophysics Data System (ADS)

The WUVS (WSO-UV Ultra Violet Spectrographs) consists of two high resolution spectrographs (R=50000) covering the Far-UV range of 115-176 nm and the Near-UV range of 174-310 nm, and a long-slit spectrograph (R=1000) covering the wavelength range of 115-305 nm. Significant progress in the CCD development gives a possibility to use back-illuminated CCD detectors with anti-reflection coating for observations in the UV. These detectors are under construction by e2v company (UK) based on their heritage of detectors production for numerous space missions including those for UV- and far-UV. The main parameters of WUVS detector subsystems are described.

Shugarov, A.; Savanov, I.; Sachkov, M.; Jerram, P.; Moody, I.; Pool, P.; Turner, P.; Pittock, R.; Kuzin, S.; Waltham, N.

2014-04-01

259

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

260

Activity on young stars.  

NASA Astrophysics Data System (ADS)

Simultaneous photometry and spectroscopy were made of 6 young stars during two observing periods mainly to study short-term variability on time-scales from minutes to a few hours. The material includes two classical T Tauri stars (CTTS): SY Ori and VW Cha; three T Tauri stars with weak emission line spectra (WTTS): San 1, SZ Cha and ADA 481 and one post-T Tauri candidate: HD 70309B. Both UBV and Stroemgren photometry was made. In the visible spectral region we resolved rapid fluctuations - events - with total amplitudes of about 5% (0.05 magnitudes). In the ultraviolet, the corresponding limit of detection was usually <=10%. On the basis of totally about 100 hours of monitoring we conclude that the normal state of these stars is that they are completely constant in brightness or that they vary only slowly with small amplitudes over several hours. Only a few percent of the time, on the average, is a given star caught at brightness changes >=0.2mag. during one night. No event reached a total amplitude of >=0.3mag. VW Cha is the most active star, but no events were seen on SY Ori and HD 70309B. This confirms earlier indications that powerful "flaring" on T Tauri stars is not frequent. We make a detailed study of all events and find two types of slow events, usually with d(U or u)/dt<=0.1mag/hour. One is caused by changes in the continuous emission (the veiling) superimposed on the stellar photospheric spectrum and operates mainly on VW Cha. These events have nothing to do with stellar surface flares of the type observed on flare stars and we suggest that they originate from inhomogeneous mass accretion from a circumstellar disk to the stellar surface. The time-scales support models with magnetically controlled accretion along the stellar dipole field to rings or spots at the stellar surface. The other type of event appears to originate from relatively rapid changes in the opacity of circumstellar dust in the line-of-sight to the star. This effect dominates on SZ Cha, a WTTS surrounded by a substantial dust reservoir. Also for the rapid events we distinguish two types. On two WTTS we detected a few flare-like events produced by a sudden increase in emission in the Balmer continuum and the Balmer lines and no detectable change of the continuum long-ward of the Balmer jump. With only UBV photometry the Balmer flares could erronously been interpreted as very hot blackbody radiators. We suggest that these events are genuine surface flares with total energies of 10^33^ to 10^34^erg, and discuss the implication of energy supply. On ADA 481 we detected 2 flare-like events in white light. If these are due to the ignition of a source of blackbody radiation, the inferred temperature of the flare is low compared to what is normally observed for flare stars. Even though the events are rare and have small total amplitudes in UV, they are extremely powerful, with the same total energies as the largest flares seen on flare stars. The flare stars may show much larger changes in UV, but the difference comes from the lower contrast of the flares on the TTS. If all TTS have surface magnetic activity similar to the flare stars, only the radii being larger, then we conclude that the frequency distribution of the flare-like events on WTTS are similar to flare stars in the field, but much higher than for the dwarfs in the Pleiades. No flare-like event was seen on the CTTS and we discuss possible implications. For the long-term changes (over days) we conclude that very dark spots on the rotating surfaces of SY Ori and San 1 dominates, while VW Cha varies because of variable veiling, but with an uncertain period. For SZ Cha variable circumstellar extinction operates, also in phase with the hydrogen line absorption. The situation for ADA 481 is still unclear. HD 70309B did not vary.

Gahm, G. F.; Loden, K.; Gullbring, E.; Hartstein, D.

1995-09-01

261

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

262

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

263

Star Formation in the Intergalactic Medium  

NASA Astrophysics Data System (ADS)

Recent observations have shown that star formation may occur in the intergalactic medium outside any pre-existing stellar structure. Many of such giant HII complexes are progenitors of super star clusters or -- if they are very luminous -- dwarf galaxies, and are associated with tidal debris found in the vicinity of interacting systems. How star formation proceeds in this particular, though simple environment, is so far unknown. We propose to image with GALEX two interacting systems showing tidal tails solely made of ejected gaseous material, in which we have already detected the formation of star-forming tidal dwarf galaxies. Both systems (NGC 5291 and NGC 4694/VCC 2062) lie in the outskirts of clusters of galaxies. Their UV fluxes will complement our multi-wavelength data set on these objects; they will be used to (1) study the recent star formation history and in particular infer the onset of the starburst actvity in the tidal tails (2) determine the UV SFR which we will compare with that derived in the optical and infrared, thus giving hints on the extinction law (3) estimate the star formation efficiency and compare it with that measured in grand design spirals and in classical dwarf galaxies.

Lisenfeld, Ute

264

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

NASA Astrophysics Data System (ADS)

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

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

2004-04-01

265

Precision radial-velocity measurements on bright Sun-like stars  

NASA Astrophysics Data System (ADS)

We at PRL have initiated for the first time in India an Exoplanet search program using the precision Radial Velocity (RV) technique. The program is called PARAS (PRL Advanced Radial-velocity All-sky Search) and consists of a high resolution, optical fiber-fed, cross-dispersed, Echelle spectrograph. The spectrograph works at a resolution (R) of 67000, in the wavelength range of 3700 Å -- 8400 Å and is coupled with the PRL Mt. Abu 1.2~m telescope. We present here time series RV measurements on RV standard stars like sigma Draconics, 47 UMa and tau Ceti at 2 to sub-2m/s precision. Thus, in principle PARAS can detect exoplanets of masses down to 10 Earth mass at 0.1AU distances or less around 1 to 0.5 Solar Mass stars. Since many of the bright G and K dwarfs are yet to be surveyed at sub-2m/s RV precision at high cadence, this opens up new science opportunities for highly stabilized high resolution spectrographs like PARAS attached to 1m-class telescopes. The PARAS echelle spectrograph is installed in a temperature controlled chamber (0.03C rms at 25C) and inside a vacuum vessel for both temperature and pressure stability.

Dixit, Vaibhav; Chaturvedi, Priyanka; Chakraborty, Abhijit; Mahadevan, Suvrath; Roy, Arpita; Dongre, Varun

266

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

267

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

268

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

269

UVMag: stellar formation, evolution, structure and environment with space UV and visible spectropolarimetry  

NASA Astrophysics Data System (ADS)

Important insights into the formation, structure, evolution and environment of all types of stars can be obtained through the measurement of their winds and possible magnetospheres. However, this has hardly been done up to now mainly because of the lack of UV instrumentation available for long periods of time. To reach this aim, we have designed UVMag, an M-size space mission equipped with a high-resolution spectropolarimeter working in the UV and visible spectral range. The UV domain is crucial in stellar physics as it is very rich in atomic and molecular lines and contains most of the flux of hot stars. Moreover, covering the UV and visible spectral domains at the same time will allow us to study the star and its environment simultaneously. Adding polarimetric power to the spectrograph will multiply tenfold the capabilities of extracting information on stellar magnetospheres, winds, disks, and magnetic fields. Examples of science objectives that can be reached with UVMag are presented for pre-main sequence, main sequence and evolved stars. They will cast new light onto stellar physics by addressing many exciting and important questions. UVMag is currently undergoing a Research & Technology study and will be proposed at the forthcoming ESA call for M-size missions. This spectropolarimeter could also be installed on a large UV and visible observatory (e.g. NASA's LUVOIR project) within a suite of instruments.

Neiner, C.; Baade, D.; Fullerton, A.; Gry, C.; Hussain, G.; Lèbre, A.; Morin, J.; Petit, P.; Sundqvist, J. O.; ud-Doula, A.; Vidotto, A. A.; Wade, G. A.

2014-11-01

270

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

271

The friendly stars  

NASA Astrophysics Data System (ADS)

Describes prominent stars such as Vega, Arcturus, and Antares and means of identifying them, discusses the constellations in which they are located, and explains star names, stellar light, distances between stars, and types of stars.

Martin, Martha Evans

272

Energy Star  

E-print Network

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

Reihl, K.; Tullos, A.

2012-01-01

273

The Fundamental Parameters of Massive Stars  

NASA Astrophysics Data System (ADS)

We analyzed far-UV (FUSE), UV (HST, IUE) and optical spectra of hot massive stars in the Milky Way with non-LTE, line-blanketed models with sphericity and expanding winds. We were able to reconcile previously discrepant diagnostics from H? to highly ionized transitions (e.g. OVI and NV) with a revised treatement of soft X-rays from shocks and clumping in the stellar wind. These effects could be constrained uniquely by combining lines in the FUSE range and at longer wavelenghs. We derived Teff and luminosity values lower than canonical values, and refined measurements of mass-loss rate. The Teff recalibration of O-type stars has relevant implications for our understanding of massive star evolution and energy balance of HII regions. Mass loss is a major source of uncertainty in our current knowledge of massive stars evolution, and a consistent derivation of mass-loss rate from optical and far-UV lines is an important step forward.

Bianchi, Luciana; Herald, James; Garcia, Miriam

2009-05-01

274

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

275

The imprint of accretion on the UV spectrum of young stellar objects: an X-Shooter view  

NASA Astrophysics Data System (ADS)

The evolution of protoplanetary disks is regulated by its interaction with the central forming star. This interaction happens through accretion of matter from the disk onto the star, and its most significant signatures are the continuum excess in the UV part of the spectrum and the presence of various emission lines. With the VLT/X-Shooter spectrograph, the excess emission in the UV due to accretion can being studied simultaneously with the signatures in the visible and in the near-infrared, giving a simultaneous and complete view of this phenomenon. Here we present some results we obtained using observation and modeling of the UV-excess in young forming stars, which are: (1) the determination of stellar and accretion properties in candidate older accreting young stellar objects and (2) the study of the star-disk interaction in the early stages of planetary system evolution in transitional disk systems.

Manara, Carlo Felice; Testi, Leonardo

2014-11-01

276

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

277

Star Power  

ScienceCinema

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

None

2014-11-18

278

STAR Highlights  

E-print Network

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

Hiroshi Masui; for the STAR Collaboration

2011-06-29

279

Star Power  

NSDL National Science Digital Library

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

Television, Twin C.

2010-01-01

280

Chemical abundances in Hg-Mn stars  

NASA Technical Reports Server (NTRS)

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

Heacox, W. D.

1979-01-01

281

Electron stars for holographic metallic criticality  

E-print Network

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

Sean A. Hartnoll; Alireza Tavanfar

2010-08-17

282

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

283

WSO-UV progress and expectations  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

284

Estrogenic activity of UV filter mixtures  

Microsoft Academic Search

UV-absorbing chemicals (UV filters) are widely used for protection against UV radiation in sunscreens and in a variety of cosmetic products and materials. Depending on the breadth and factor of UV protection, they are added as single compounds or as a combination thereof. Some UV filters have estrogenic activity, but their activity and interactions in mixtures are largely unknown. In

Petra Y.. Kunz; Karl. Fent

2006-01-01

285

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

286

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

287

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.

288

Coordinated X-ray, ultraviolet and optical observations of T Tauri stars.  

NASA Astrophysics Data System (ADS)

Within the framework of a large campaign of observations of RU Lupi in X-ray, UV and optical, the authors present some partial results of their observations. Some theoretical considerations on T Tauri stars are given.

Giovannelli, F.; Bisnovatyj-Kogan, G. S.; Golynskaya, I. M.; Kurt, V. G.; Lamzin, S. A.; Mizyakina, T. A.; Shafer, E. Yu.; Shamolin, V. M.; Sheffer, E. K.; Smirnoff, A. S.; Smirnov, A. S.; Vittone, A. A.

289

Star formation and the ages of stars  

NASA Astrophysics Data System (ADS)

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

Martins, F.

2014-11-01

290

Stars : the end of a star  

NSDL National Science Digital Library

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

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

2003-01-01

291

Christmas star.  

NASA Astrophysics Data System (ADS)

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

Bia?a, J.

292

Energy distribution monitoring of the T Tauri star RU LUPI  

NASA Astrophysics Data System (ADS)

Simultaneous UV, optical and IR energy distributions of RU Lupi are presented for the period 1984-1986. The observations were obtained with the IUE satellite and optical and IR telescopes. Variations are detected in UV and optical regions. In addition, a large flare was observed on June 30, 1986. The results agree with those of Gahm et al. (1974) and suggest that the main cause of variability in RU Lupi is strong activity in the star's surface layers.

Giovannelli, F.; Vittone, A. A.; Errico, L.; Rossi, C.

293

Planck stars  

E-print Network

A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density --not by size-- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

Rovelli, Carlo

2014-01-01

294

Planck stars  

E-print Network

A star that collapses gravitationally can reach a further stage of its life, where quantum-gravitational pressure counteracts weight. The duration of this stage is very short in the star proper time, yielding a bounce, but extremely long seen from the outside, because of the huge gravitational time dilation. Since the onset of quantum-gravitational effects is governed by energy density ---not by size--- the star can be much larger than planckian in this phase. The object emerging at the end of the Hawking evaporation of a black hole can then be larger than planckian by a factor $(m/m_{\\scriptscriptstyle P})^n$, where $m$ is the mass fallen into the hole, $m_{\\scriptscriptstyle P}$ is the Planck mass, and $n$ is positive. We consider arguments for $n=1/3$ and for $n=1$. There is no causality violation or faster-than-light propagation. The existence of these objects alleviates the black-hole information paradox. More interestingly, these objects could have astrophysical and cosmological interest: they produce a detectable signal, of quantum gravitational origin, around the $10^{-14} cm$ wavelength.

Carlo Rovelli; Francesca Vidotto

2014-01-25

295

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

296

The Moon in the UV  

NASA Astrophysics Data System (ADS)

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

Hendrix, Amanda

2014-11-01

297

HARPS spectropolarimetry of O and B-type stars  

E-print Network

Our knowledge of the presence and the strength of magnetic fields in massive O and B-type stars remains very poor. Recent observations indicate that the presence of magnetic fields is responsible for a wide range of phenomena observed in massive stars at different wavelengths, such as chemical peculiarity, excess of emission in UV-wind lines and periodic UV wind-line variability, unusual X-ray emission, and cyclic variability in Halpha and He II 4686. However, it is difficult to establish relationships to multiwavelength diagnostics, as the strength of the detected magnetic fields and their geometry differ from one star to the other. In this work, we present new magnetic field measurements in a number of O and B-type stars of different classification observed with HARPS in spectropolarimetric mode.

Hubrig, S; Ilyin, I; Curto, G Lo

2013-01-01

298

HARPS spectropolarimetry of O and B-type stars  

NASA Astrophysics Data System (ADS)

Our knowledge of the presence and strengths of magnetic fields in massive O- and B-type stars remains very poor. Recent observations indicate that the presence of a magnetic field is responsible for a wide range of phenomena that are observed in massive stars at different wavelengths, such as chemical peculiarity, excess emission in UV-wind lines and periodic UV wind-line variability, unusual X-ray emission, and cyclic variability in H? and in He II ? 4686 Å. However, it is difficult to establish relationships involving multiwavelength diagnostics, because the strengths and the geometry of the magnetic fields that have been detected differ from one star to another. This paper presents new measurements of magnetic fields in a number of O- and B-type stars of various classifications, observed with HARPS in spectropolarimetric mode.

Hubrig, S.; Schöller, M.; Ilyin, I.; Lo, Curto G.

2014-11-01

299

White light with UV LEDs  

Microsoft Academic Search

The advantages of near UV LED chips with phosphors for white light generation are discussed. Recently developed UV LED excitable phosphor blends are presented. Monte Carlo simulations suggest low color point variation (entirely within the first MacAdam oval) for the standard LED chip bin (400-410 nm), compared to high color point variation (outside the fourth MacAdam oval) for the standard

Emil Radkov; Rebecca Bompiedi; Alok M. Srivastava; Anant A. Setlur; Charles A. Becker

2004-01-01

300

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

301

The detection of M-dwarf UV flare events in the GALEX data archives  

E-print Network

We present the preliminary results from implementing a new software tool that enables inspection of time-tagged photon data for the astronomical sources contained within individual GALEX ultraviolet images of the sky. We have inspected the photon data contained within 1802 GALEX images to reveal rapid, short-term (<500 sec) UV source variability in the form of stellar flares. The mean associated change in NUV magnitude due to this flaring activity is 2.7+/-0.3 mag. A list of 49 new UV variable-star candidates is presented, together with their associated Sloan Digital Sky Survey (SDSS) photometric magnitudes. From these data we can associate the main source of these UV flare events with magnetic activity on M-dwarf stars. Photometric parallaxes have been determined for 32 of these sources, placing them at distances ranging from approximately 25 to 1000pc. The average UV flare energy for these flare events is 2.5E30 ergs, which is of a similar energy to that of U-band, X-ray and EUV flares observed on many local M-dwarf stars. We have found that stars of classes M0 to M5 flare with energies spanning a far larger range and with an energy approximately 5 times greater than those of later (M6 to M8) spectral type.

Barry Y. Welsh; Jonathan M. Wheatley; Mark Seibert; Stanley E. Browne; Andrew A. West; Oswald H. W. Siegmund; Tom A. Barlow; Karl Forster; Peter G. Friedman; D. Christopher Martin; Patrick Morrissey; Todd Small; Ted Wyder; David Schiminovich; Susan Neff; R. Michael Rich

2006-05-12

302

The UV-IR Energy Budget and Far-Infrared Emission in Spiral Galaxies  

Microsoft Academic Search

We use available ultraviolet imagery and HIRES processing of IRAS data to examine the energy balance in spatially-resolved spiral galaxies, using the UV data to constrain the dominant energy input to the dust more tightly than possible from optical data. The improved resolution of the HIRES output allows separation of individual clumps of star-forming regions in the disks of nearby

L. V. Jones; W. C. Keel

1994-01-01

303

When Stars Collide  

E-print Network

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

E. Glebbeek; O. R. Pols

2007-10-09

304

Very Massive Stars in the Primitive Galaxy, IZw 18  

NASA Technical Reports Server (NTRS)

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

Heap, Sara

2012-01-01

305

Beryllium and Boron abundances in population II stars  

NASA Technical Reports Server (NTRS)

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

1995-01-01

306

Modelling the variability of the CP star \\varphi Dra  

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

307

Hot Stars: Old-Fashioned or Trendy? (With 24 Figures)  

NASA Astrophysics Data System (ADS)

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

Pauldrach, A. W. A.

308

Triggered Star Formation by Massive Stars  

E-print Network

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

Hsu-Tai Lee; W. P. Chen

2005-09-13

309

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

Microsoft Academic Search

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

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

2007-01-01

310

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

311

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

312

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

313

The Evolution of Planetary Systems: A FUSE Legacy View of Accretion and Stellar Activity for Young A Stars  

Microsoft Academic Search

Far Ultraviolet Spectroscopic Explorer (FUSE) far-UV (FUV) spectra provide an unique view of accretion and stellar activity in nearby, minimally reddened pre-main sequence stars. We present first results of the FUSE Legacy study of young, intermediate-mass stars. The FUSE data show that over 1--10 Myr, Herbig Ae stars closely resemble classical T Tauri stars by having FUV excess light and

G. M. Williger; C. A. Grady; B. E. Woodgate; J.-C. Bouret; A. Roberge; M. Sahu

2004-01-01

314

The effect of UV-B and UV-C radiation on sugar beet leaves  

Microsoft Academic Search

Summary The effect of UV-C (254 nm) and UV-B (290–320 nm) radiation on leaves ofBeta vulgaris L. at the ultrastructural level was investigated. Although the damage caused by UV-C radiation was more striking than that resulting from UV-B radiation, several structural changes were seen in the UV-B treated material. Generally the effects of UV-B and UV-C radiation were different, suggesting

Janet French Bornman; Ray F. Evert; Robert J. Mierzwa

1983-01-01

315

LUCI (Lunar UV Cosmic Imager): Opportunities for UV Astronomy from Commercial Lunar Missions.  

NASA Astrophysics Data System (ADS)

There seems to be a general consensus that for the UV astronomy, there is no alternative to orbital space observatories. Though the Moon was proposed as a prime site for astronomy nearly 50 years ago, the success of space-based observatories at a fraction of the cost of a lunar base has diverted the attention away from lunar surface as a platform for science to rather studying the Moon and its environment from near-Earth or lunar orbits. However, the unprecedented mission opportunities for astronomy on/from the Moon realized with the surge of privately-funded space flights, have renewed the concept of the Moon as the next place to go. Here we describe a low-cost wide-field UV imager (LUCI) to observe in a far-UV (130--180 nm) from the Moon as a primary payload to an Indian Google Lunar X PRIZE Team INDUS lander. We consider an initial fixed zenith pointing and a scanning mode with the option to allow observations of different attitudes. Pointing towards intermediate ecliptic latitudes (50 deg. or higher) ensures that Sun is at least 40 deg. off the line of sight at all times. This way, the telescope can cover higher galactic latitudes as well as parts of Galactic plane. With ~7 sq. deg. FOV, LUCI may expect to see as many as 11-14 transients from flaring stars or collisions in planetary systems per exposure, which can last 5 to 7 hours due to the slow sidereal movement of lunar sky. LUCI will also be a key instrument in the attitude determination of the lander, where initial data from the sun sensors and Earth antenna will be combined with first LUCI's images of the stellar field to determine the precise location and attitude of the lander. We describe in details the telescope design and delineate our scientific objectives.

Chechin, Leonid

316

High Power UV LED Industrial Curing Systems  

Microsoft Academic Search

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

Karlicek; F. Robert; Robert Sargent

2012-01-01

317

8, 2145, 2008 Measurements of UV  

E-print Network

of total ozone. Statistical model will allow to reconstruct (or monitor) vitamin D3 weighted UV irradiances and surface UV variability and led to establishing the ozone and UV global observing network. MonitoringACPD 8, 21­45, 2008 Measurements of UV radiation on rotating vertical plane P. Sobolewski et al

Paris-Sud XI, Université de

318

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

319

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

320

Optical, UV, and EUV Oscillations of SS Cygni in Outburst  

SciTech Connect

I provide a review of observations in the optical, UV (HST), and EUV (EUVE and Chandra LETG) of the rapid periodic oscillations of nonmagnetic, disk-accreting, high mass-accretion rate cataclysmic variables (CVs), with particular emphasis on the dwarf nova SS Cyg in outburst. In addition, I drawn attention to a correlation, valid over nearly six orders of magnitude in frequency, between the frequencies of the quasi-periodic oscillations (QPOs) of white dwarf, neutron star, and black hole binaries. This correlation identifies the high frequency quasi-coherent oscillations (so-called ''dwarf nova oscillations'') of CVs with the kilohertz QPOs of low mass X-ray binaries (LMXBs), and the low frequency and low coherence QPOs of CVs with the horizontal branch oscillations (or the broad noise component identified as such) of LMXBs. Assuming that the same mechanisms produce the QPOs of white dwarf, neutron star, and black hole binaries, this correlation has important implications for QPO models.

Mauche, C W

2003-12-19

321

Star formation rate and metallicity of damped Lyman? absorbers in cosmological SPH simulations  

Microsoft Academic Search

We study the distribution of the star formation rate (SFR) and metallicity of damped Lyman-? absorbers (DLAs) in the redshift range z = 0 4.5 using cosmological smoothed particle hydrodynamics (SPH) simulations of thecold dark matter model. Our simulations include standard radiative cooling and heating with a uniform UV background, star formation, supernova (SN) feedback, as well as a phenomenological

K. Nagamine; V. Springel; L. Hernquist

322

Star formation - An overview  

NASA Technical Reports Server (NTRS)

Methods for studying star formation are reviewed. Stellar clusters and associations, as well as field stars, provide a fossil record of the star formation process. Regions of current star formation provide a series of snapshots of different epochs of star formation. A simplified picture of individual star formation as it was envisioned in the late 1970s is contrasted with the results of recent observations, in particular the outflow phenomenon.

Evans, N. J., II

1985-01-01

323

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

324

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

325

UV Spectroscopy of Newly Discovered Tidal Disruption Flares  

NASA Astrophysics Data System (ADS)

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

Cenko, Stephen

2014-10-01

326

Disk Evaporation in Star Forming Regions  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

327

Formation of Massive Stars via Accretion  

E-print Network

The collapse of massive molecular clumps can produce high mass stars, but the evolution is not simply a scaled-up version of low mass star formation. Outflows and radiative effects strongly hinder the formation of massive stars via accretion. A necessary condition for accretion growth of a hydrostatic object up to high masses M > 20 M_sun (rather than coalescence of optically thick objects) is the formation of and accretion through a circumstellar disk. Once the central object has accreted approximately 10 M_sun it has already evolved to core hydrogen-burning; the resultant main sequence star continues to accrete material as it begins to photoevaporate its circumstellar disk (and any nearby disks) on a timescale of 100,000 years, similar to the accretion timescale. Until the disk(s) is (are) completely photoevaporated, this configuration is observable as an ultra-compact HII region (UCHII). The final mass of the central star (and any nearby neighboring systems) is determined by the interplay between radiation acceleration, UV photoevaporation, stellar winds and outflows, and the accretion through the disk. Several aspects of this evolutionary sequence have been simulated numerically, resulting in a "proof of concept". This scenario places strong constraints on the accretion rate necessary to produce high mass stars and offers an opportunity to test the accretion hypothesis.

Harold W. Yorke

2003-12-23

328

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

329

On stars and Steiner stars Adrian Dumitrescu  

E-print Network

On stars and Steiner stars Adrian Dumitrescu Csaba D. T´oth Guangwu Xu§ March 9, 2009 Abstract A Steiner star for a set P of n points in Rd connects an arbitrary point in Rd to all points of P, while a star connects one of the points in P to the remaining n - 1 points of P. All connections are realized

Dumitrescu, Adrian

330

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

E-print Network

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

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

2005-03-07

331

White light with UV LEDs  

NASA Astrophysics Data System (ADS)

The advantages of near UV LED chips with phosphors for white light generation are discussed. Recently developed UV LED excitable phosphor blends are presented. Monte Carlo simulations suggest low color point variation (entirely within the first MacAdam oval) for the standard LED chip bin (400-410 nm), compared to high color point variation (outside the fourth MacAdam oval) for the standard bin (460-470 nm) and typical phosphors, modeled as Gaussians of realistic spectral width and targeting the 3000K ANSI color point (x=0.440, y=0.403). A discussion of the full LED package performance is also offered.

Radkov, Emil; Bompiedi, Rebecca; Srivastava, Alok M.; Setlur, Anant A.; Becker, Charles A.

2004-01-01

332

Dissecting the star formation history of starburst galaxies: the case of NGC 7673  

Microsoft Academic Search

We have collected archival data on NGC 7673 to constrain the star formation history that produced the young star clusters and the field stellar population in this galaxy during the last 2 Gyr. We have considered the sample of 50 star clusters detected by Hubble Space Telescope\\/WFPC2 in the UV,V and I bands and estimated their age, intrinsic reddening and

A. Pasquali; P. Castangia

2008-01-01

333

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

334

The UV Galaxy Luminosity Function in the Local Universe from GALEX Data  

E-print Network

We present the results of a determination of the galaxy luminosity function at ultraviolet wavelengths at redshifts of $z=0.0-0.1$ from GALEX data. We determined the luminosity function in the GALEX FUV and NUV bands from a sample of galaxies with UV magnitudes between 17 and 20 that are drawn from a total of 56.73 deg^2 of GALEX fields overlapping the b_j-selected 2dF Galaxy Redshift Survey. The resulting luminosity functions are fainter than previous UV estimates and result in total UV luminosity densities of 10^(25.55+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 and 10^(25.72+/-0.12) ergs s^-1 Hz^-1 Mpc^-3 at 1530 Ang. and 2310 Ang., respectively. This corresponds to a local star formation rate density in agreement with previous estimates made with H-alpha-selected data for reasonable assumptions about the UV extinction.

Ted K. Wyder; Marie A. Treyer; Bruno Milliard; David Schiminovich; Stéphane Arnouts; Tamás Budavári; Tom A. Barlow; Luciana Bianchi; Yong-Ik Byun; José Donas; Karl Forster; Peter G. Friedman; Timothy M. Heckman; Patrick N. Jelinsky; Young-Wook Lee; Barry F. Madore; Roger F. Malina; D. Christopher Martin; Patrick Morrissey; Susan G. Neff; R. Michael Rich; Oswald H. W. Siegmund; Todd Small; Alex S. Szalay; Barry Y. Welsh

2004-11-13

335

Ultraviolet continuum of a sample of Be stars  

Microsoft Academic Search

IUE spectra obtained in the low dispersion mode were used to analyze the energy distributions in the UV of Alpha Draconis, Tau Orionis, 53 Persei, 48 Librae, Pi Aquarii, and 27 Canis Majoris. Absolute fluxes were determined. The effective temperatures and gravity of the model atmospheres which provide the best fit to the spectra of these stars are presented. Alpha

A. E. Ringuelet; M. Rovira; J. M. Fontenla

1981-01-01

336

Nature of star-forming rings in S0 galaxies  

NASA Astrophysics Data System (ADS)

Lenticular galaxies are a morphological class of disc galaxies that in general lacks current star formation and extended gaseous discs. However recent ultraviolet (UV) surveys have revealed extended UV discs and rings even among these `red and dead' galaxies, and their origin is now still unclear. We have studied the nature of the outer star-forming, UV-detected rings in four unbarred S0 galaxies by undertaking their long-slit spectroscopy with the focal reducer SCORPIO of the Russian 6-m telescope. Gaseous discs in NGC 252 and in NGC 4513 have decoupled kinematics, and the ionized gas of their rings is certainly excited by young stars. Just these two galaxies belong to galaxy groups. Two other, quite isolated S0 galaxies with the UV rings, IC 522 and NGC 446, demonstrate the shock-dominated gas excitation in the UV-detected rings, so their rings may probably have impact origin. However, in all four galaxies the ionized gas reveals the oxygen abundance close to the solar one, so the hypothesis of gas accretion from cosmological filaments seems to be unfavourable. Rather another large galaxy may be a donor of outer gas in the galaxies of our sample.

Ilyina, M. A.; Sil'chenko, O. K.; Afanasiev, V. L.

2014-03-01

337

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

338

Near UV Aerosol Group Report  

NASA Technical Reports Server (NTRS)

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

Torres, Omar

2013-01-01

339

Reliability of deep UV LEDs  

Microsoft Academic Search

We report on reliability of deep UV (DUV) LEDs with wavelengths ranging from 235 nm to 310 nm. For longer wavelength DUV LEDs, the operation lifetime (50% decrease of output power) exceeds 5,000 hours. The current-voltage characteristics and the emission spectrum remain nearly unchanged during the degradation process. The degradation is sensitive to the operating temperature. The low frequency noise

M. Shatalov; Yu. Bilenko; R. Gaska; S. L. Rumyantsev; M. Shur

2009-01-01

340

UV Treatment for Small Systems  

EPA Science Inventory

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

341

The size, shape and temperature of the stars  

NASA Astrophysics Data System (ADS)

The development of techniques for measuring the size, shape, and temperature of stars is traced. Astrometric measurements were first performed with stone arrangements such as those at Stonehenge, followed by mechanical devices like those Tycho Brahe used. The telescope was invented in the 17th century and was coupled with the spectrograph in the 19th century. Angular sizes of stars were measured with the invention of the stellar interferometer in 1920, the first star measured being Betelgeuse, which varies from 200-300 times the size of the sun. Main sequence, i.e., hydrogen-burning stars, have been most characterized. An intensity interferometer was eventually developed and compensated for atmospheric perturbations that severely limited the performance of the stellar interferometer; the new instrument permitted interferometry of main sequence stars. Other such data have been gathered by speckle interferometry and the International UV Explorer satellite, and further space-based data will be garnered with the Hipparchos satellite.

Brown, R. H.

342

Ultraviolet observations of hot stars with circumstellar dust shells  

NASA Technical Reports Server (NTRS)

Absolute fluxes over the wavelength range 1200-3200 A are presented for 13 normal early-type stars and 12 early-type stars known to have large IR excess; the data were obtained to study the UV spectral modifications produced by absorbing circumstellar dust particles. It is found that all the Be/shell stars whose spectral types are later than B6 exhibit greatly enhanced line absorption due to circumstellar Fe II. The circumstellar gaseous line absorption in stars cooler than B6 severely complicates the study of circumstellar dust absorption. However, those B and A stars that exhibit the circumstellar 9.7-micron emission feature have a very large increase in circumstellar absorption for 1800 A; such absorption is expected from circumstellar silicate particles.

Sitko, M. L.; Meade, M. R.; Savage, B. D.

1981-01-01

343

Counting Your Lucky Stars  

NSDL National Science Digital Library

In this activity, learners sample a star field to estimate the number of stars in the universe. This activity simulates how astronomers use sampling instead of census (counting) to more easily collect data in space. Learners predict, count, approximate, and average the number of stars in a Star Field Sheet.

Ricles, Shannon; Hatok, Tim; Taylor, Berlina

2013-01-30

344

Extragalactic Star Clusters: the Resolved Star Approach  

NASA Astrophysics Data System (ADS)

The physical processes leading to the dissolution of star clusters is a topic barely studied and still not understood. We started a pilot project to develop a new approach to directly detect and study the properties of stellar clusters while they are being destroyed. Our technique currently under development makes use of the exceptional spatial resolution and sensitivity of the ACS camera onboard HST to resolve individual stars in nearby galaxies. PSF stellar photometry and color-magnitude diagrams allows us to separate the most massive stars (more likely to be in clusters) from the star field background. While applying the method to the normal spiral galaxy NGC1313, we found that the method of studying star clusters through resolved stars in nearby galaxies is even more powerful than we first expected. The stellar maps obtained for NGC1313 show that a large fraction of early B-type stars contained in the galaxy are already part of the star field background rather that being in star clusters. Such stars live for 5 to 25 Myr. Since most stars form in clusters, the presence of such massive stars in the field means that they must have left their birthplace very rapidly. It also means that the processes involved in the dissolution of the clusters are extremely efficient. The only plausible explanation for so many young stars to be in the field background is the infant mortality of star clusters. We will present the latest results on the two galaxies NGC 1313 and IC 2475 and discuss the potential of the new approach for studying extragalactic stellar clusters.

Pellerin, Anne; Meyer, M. J.; Jason, H.; Calzetti, D.

2006-12-01

345

UVMag: stellar formation, evolution, structure and environment with space UV and visible spectropolarimetry  

E-print Network

Important insights into the formation, structure, evolution and environment of all types of stars can be obtained through the measurement of their winds and possible magnetospheres. However, this has hardly been done up to now mainly because of the lack of UV instrumentation available for long periods of time. To reach this aim, we have designed UVMag, an M-size space mission equipped with a high-resolution spectropolarimeter working in the UV and visible spectral range. The UV domain is crucial in stellar physics as it is very rich in atomic and molecular lines and contains most of the flux of hot stars. Moreover, covering the UV and visible spectral domains at the same time will allow us to study the star and its environment simultaneously. Adding polarimetric power to the spectrograph will multiply tenfold the capabilities of extracting information on stellar magnetospheres, winds, disks, and magnetic fields. Examples of science objectives that can be reached with UVMag are presented for pre-main sequence,...

Neiner, C; Fullerton, A; Gry, C; Hussain, G; Lebre, A; Morin, J; Petit, P; Sundqvist, J O; ud-Doula, A; Vidotto, A A; Wade, G A

2014-01-01

346

Habitable Niches In Single and Binary Star Systems  

NASA Astrophysics Data System (ADS)

We investigate habitable niches, defined as locations with optimum conditions for complex life to exist. The recent discovery of planets in several binaries motivates this study to examine favorable habitability circumstances in both single and binary star systems. Stellar evolution calculations are used to model time dependent stellar luminosity, UV flux, photo-synthetic flux and atmospheric water photolysis. Tidal interactions such as synchronization timescales, heat generation, and forcing frequency are also investigated. An Earth-analogue planet in the habitable zone of a 0.8 solar mass star is well suited for complex life. Several high quality niches are available to planets in habitable zones of binaries. For example, orbiting a pair of twin stars each 0.75 solar masses with a binary period of ten days will provide ample photo-synthetic radiation without an overdose of UV radiation, and tidal effects mimicking the Earth-Moon. A solar like star with a close red dwarf companion, like the recently discovered Kepler 47, provides a high quality niche because both stars are relatively long lived and the habitable zone has abundant photo-synthetic light while avoiding harmful UV light. A similar niche exists with a sun like star, which in turn is orbited by a distant red dwarf, providing a roughly annual enhanced red photo-synthetic flux. Also, moons orbiting Jupiter mass planets may exist within habitable zones of both single and binary stars. Such moons might be synchronized to the planet rather than the star. Due to the abundance of binary systems and the presence of high quality niches; binaries may harbor a significant fraction of inhabited planets within the universe. The present study allows for selection of the best habitability follow up targets for large telescopes.

Clark, Joni; Mason, P. A.

2013-01-01

347

IntrAst2 (Petrovay) Variable stars VARIABLE STARS  

E-print Network

IntrAst2 (Petrovay) Variable stars VARIABLE STARS Definitions: (a) Stars displaying brightness variations (in the optical domain) All stars are variables (a matter of sensitivity only). (b) Stars) A variable star is what is listed in GCVS or VSX GCVS: General Catalogue of Variable Stars; http

Petrovay, Kristóf

348

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

349

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

E-print Network

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, $\\lambda$$_{eff}$ $\\sim$ 1528\\AA) and near-UV (NUV, $\\lambda$$_{eff}$ $\\sim$ 2310\\AA) 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

2014-01-01

350

The (BETA) Pictoris Phenomenon Among Herbig Ae/Be Stars  

NASA Technical Reports Server (NTRS)

We present a survey of high dispersion UV and optical spectra of Herbig Ae/Be (HAeBe) and related stars. We find accreting, circumstellar gas over the velocity range +100 to +400 km/s, and absorption profiles similar to those seen toward Beta Pic, in 36% of the 33 HAeBe stars with IUE data as well as in 3 non-emission B stars. We also find evidence of accretion in 7 HAeBe stars with optical data only. Line profile variability appears ubiquitous. As a group, the stars with accreting gas signatures have higher v sin i than the stars with outflowing material, and tend to exhibit large amplitude (greater than or equal to 1(sup m)) optical light variations. All of the program stars with polarimetric variations that are anti-correlated with the optical light, previously interpreted as the signature of a dust disk viewed close to equator-on, also show spectral signatures of accreting gas. These data imply that accretion activity in HAeBe stars is preferentially observed when the line of sight transits the circumstellar dust disk. Our data imply that the spectroscopic signatures of accreting circumstellar material seen in Beta Pic are not unique to that object, but instead are consistent with interpretation of Beta Pic as a comparatively young A star with its associated circumstellar disk.

Grady, C. A.; Perez, M. R.; Talavera, A.; Bjorkman, K. S.; deWinter, D.; The, P.-S.; Molster, F. J.; vandenAncker, M. E.; Sitko, M. L.; Morrison, N. D.; Beaver, M. L.; McCollum, B.; Castelaz, M. W.

1996-01-01

351

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

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

352

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

353

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

354

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...

355

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

356

XI UV Laser Trigger System  

SciTech Connect

The X1 accelerator project at Sandia National Laboratory/New Mexico utilizes SF6 insulated, multi-stage, UV laser triggered gas switches. A 265 nm UV laser system was designed and built to generate eight simultaneous output pulses of 10 mJ each with a 13 nsec pulse width. A 1061 nm solid-state Nd:Cr:GSGG laser was frequency quadrupled using a two-stage doubling process. The 1061 nm fundamental laser energy was frequency doubled with a KTP crystal to 530 nm, achieving 65% conversion efficiency. The 530 nm output was frequency doubled with KD*P crystal to 265 nm, achieving conversion efficiency of 31%. The 265 nm beam pulse was split into eight parallel channels with a system of partially reflecting mirrors. Low timing jitter and stable energy output were achieved. The entire optical system was packaged into a rugged, o-ring sealed, aluminum structure 10''x19''x2.75''. The size of the electronics was 12''x8''x8''. Subsequent accelerator system requirements dictated a redesign of the triggering system for an output beam with less angular divergence. An unstable, crossed porro prism resonator was designed and incorporated into the system. The beam divergence of the redesigned system was successfully decreased to 0.97 mrad in the UV. The resulting frequency doubling efficiencies were 55% to 530 nm and 25% to 265 nm. The optical output remained at 10 mJ in each channel with an 11 nsec pulse width.

Brickeen, B.K.; Morelli, G.L.; Paiva, R.A.; Powell, C.A.; Sundvold, P.D.

1999-01-26

357

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

358

8, 119, 2008 UV doses during  

E-print Network

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

Paris-Sud XI, Université de

359

UV-B Biodosimetry in Turfgrass Canopies  

Microsoft Academic Search

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

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

2002-01-01

360

Sterilization Using 365 nm UV-LED  

Microsoft Academic Search

There are several methods used for sterilization. In those methods chlorine, heat and UV rays are traditionally used. In recent years, the UV sterilization is taken notice as a sterilization method that the sterilized object does not change in quality and is environment-friendly. In this paper, an UV-LED is focused because it does not contain harmful substance and has longer

Noriyuki YAGI; Mirei MORI; Akiko HAMAMOTO; Masayuki NAKANO; Masatake AKUTAGAWA; Souko TACHIBANA; Akira TAKAHASHI; Toshitaka IKEHARA; Yohsuke KINOUCHI

2007-01-01

361

8, 41554198, 2008 UV albedo of arctic  

E-print Network

ACPD 8, 4155­4198, 2008 UV albedo of arctic snow in spring O. Meinander et al. Title Page Abstract Chemistry and Physics Discussions UV albedo of arctic snow in spring O. Meinander 1 , A. Kontu 1 , K­4198, 2008 UV albedo of arctic snow in spring O. Meinander et al. Title Page Abstract Introduction

Paris-Sud XI, Université de

362

Experimenting with UV-sensitive Beads  

NSDL National Science Digital Library

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

363

StarCAT: A CATALOG OF SPACE TELESCOPE IMAGING SPECTROGRAPH ULTRAVIOLET ECHELLE SPECTRA OF STARS  

SciTech Connect

StarCAT is a catalog of high resolution ultraviolet spectra of objects classified as 'stars', recorded by Space Telescope Imaging Spectrograph (STIS) during its initial seven years of operations (1997-2004). StarCAT is based on 3184 echelle observations of 545 distinct targets, with a total exposure duration of 5.2 Ms. For many of the objects, broad ultraviolet coverage has been achieved by splicing echellegrams taken in two or more FUV (1150-1700 A) and/or NUV (1600-3100 A) settings. In cases of multiple pointings on conspicuously variable sources, spectra were separated into independent epochs. Otherwise, different epochs were combined to enhance the signal-to-noise ratio (S/N). A post-facto correction to the calstis pipeline data sets compensated for subtle wavelength distortions identified in a previous study of the STIS calibration lamps. An internal 'fluxing' procedure yielded coherent spectral energy distributions (SEDs) for objects with broadly overlapping wavelength coverage. The best StarCAT material achieves 300 m s{sup -1} internal velocity precision; absolute accuracy at the 1 km s{sup -1} level; photometric accuracy of order 4%; and relative flux precision several times better (limited mainly by knowledge of SEDs of UV standard stars). While StarCAT represents a milestone in the large-scale post-processing of STIS echellegrams, a number of potential improvements in the underlying 'final' pipeline are identified.

Ayres, Thomas R. [Center for Astrophysics and Space Astronomy, 389 UCB, University of Colorado, Boulder, CO 80309 (United States)], E-mail: Thomas.Ayres@Colorado.edu

2010-03-01

364

Nearby candidate dust-disk pre-main-sequence solar-mass stars  

E-print Network

I have isolated a population of numerous F stars that appear to be pre-main-sequence (PMS). The candidate PMS stars have been identified using CM diagram, reddening, flux excess in the UV and near-infrared, and luminosity anomaly. Negative luminosity anomaly and excessive UV flux for many of these stars is suggestive of accretion disks, while the NIR excess is indicative in many cases of the presence of dust disk thermal emission. Observed overluminosity of many PMS candidates is consistent with their pre-main-sequence status. The bulk of the PMS candidates is located within 200 pc, exhibiting strong association with regions of star formation that are numerous between ~130 to 180 pc. The number of PMS candidates plummets redward of the spectral type ~ F5. This effect may provide important clues for understanding the evolution of PMS stars in the solar-mass range.

A. A. Suchkov

2002-10-25

365

A Swift/UVOT NUV Study of RR Lyrae Stars in the Globular Cluster M3  

NASA Astrophysics Data System (ADS)

We present the first results of a program to monitor RR Lyrae stars in globular clusters with the Swift Ultraviolet Optical Telescope. Although variable stars have their strongest pulsations in the UV, no comprehensive catalog of NUV light curves has ever been produced for RR Lyrae stars. We present uvm2 light curves for 124 variable star candidates in the globular cluster M3. We show that the RR Lyrae stars have strong pulsations in the NUV, with amplitudes up to three magnitudes. We show that the RR Lyrae follow period-amplitude relations in the NUV similar to those they follow in the optical. Our data hint at the existence of a period-metallicity-luminosity relationship in the UV that would make RR Lyrae even more useful standard candles.

Porterfield, Blair; Siegel, M.; Swift; UVOT

2014-01-01

366

Star formation in infrared bright and infrared faint starburst interacting galaxies  

NASA Technical Reports Server (NTRS)

Short wavelength IUE spectra of Arp 248b and UGC 8315N are combined with optical spectra and interpreted using a combination of spectrum synthesis and spectral diagnostics to place constraints on the massive star populations of the central regions of these galaxies and to deduce information about the star formation histories in the last 10(exp 8) years. The authors find that both galaxies have substantial fractions of their optical light coming from massive stars and that Arp 248b may be dominated in the UV by WR stars. The UV spectra are dominated by radiation from evolved massive stars and the authors place and age on the burst in Arp 248b of a few tens of millions of years.

Lamb, Susan A.; Bushouse, Howard A.; Towns, John W.

1990-01-01

367

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

368

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

NASA Astrophysics Data System (ADS)

Early life on Earth had to cope with harsh conditions, including full spectrum solar UV. Since DNA absorbs in the highly energetic UV-C and VUV, solar irradiation was likely an obstacle to the expansion of life on Earth, until biological mechanisms evolved to cope with UV liability (including the biosynthesis of UV screens) and ozone (derived from oxygen produced by photosynthesis) accumulated in the stratosphere. In an effort to better understand the UV liability of DNA, we used synchrotron light to measure VUV-UV absorption spectra (125-340 nm) for DNA and its components (oligonucleotides and mononucleotides). We also measured VUV-UV absorption spectra for potential and known UV screens, including amino acids, proteins, amines (including polyamines), scytonemin, mycosporine-like amino acids, ?- carotene, melanin and flavonoids. Among these, flavonoids seem remarkably suited to protecting DNA in the VUV-UV. Flavonoids accumulate in seed coats, where they confer resistance to monochromatic UV (254 nm) and polychromatic UV (200-400 nm). We discuss these findings in relation to the origin and evolution of life and its potential dispersal through space.

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

2007-09-01

369

First View of the Accretion Disks in Normal Symbiotic Stars  

NASA Astrophysics Data System (ADS)

Accretion disks in symbiotic stars are often hidden by the optical emission from the red-giant companion, UV from the ionized nebula, and soft X-rays from colliding winds. A survey of symbiotic with Swift, however, has revealed that the accretion disk dominates above 2 keV and in the rapidly variable portion of the UV. To determine the basic properties of the large, wind- fed accretion disks around the white dwarfs in symbiotic, we propose X-ray and UV observations with XMM-Newton of the two most promising targets from our Swift survey. Only XMM can provide the sensitive, contiguous, multi-wavelength observations to determine the accretion rates, characterize the properties of the UV flickering and test our conclusion that hard X-rays originate in the innermost accretion disk.

Sokoloski, Jennifer

2013-10-01

370

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

371

GAS, STARS, AND STAR FORMATION IN ALFALFA DWARF GALAXIES  

SciTech Connect

We examine the global properties of the stellar and H I components of 229 low H I mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H I masses <10{sup 7.7} M{sub Sun} and H I line widths <80 km s{sup -1}. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M{sub *}) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M{sub *} obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M{sub *} {approx}< 10{sup 8} M{sub Sun} is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper H I mass limit yields the selection of a sample with lower gas fractions for their M{sub *} than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H I depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that H I disks are more extended than stellar ones.

Huang Shan; Haynes, Martha P.; Giovanelli, Riccardo [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Brinchmann, Jarle [Sterrewacht Leiden, Leiden University, NL-2300 RA Leiden (Netherlands); Stierwalt, Sabrina [Spitzer Science Center, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Neff, Susan G., E-mail: shan@astro.cornell.edu, E-mail: haynes@astro.cornell.edu, E-mail: riccardo@astro.cornell.edu, E-mail: jarle@strw.leidenuniv.nl, E-mail: sabrina@ipac.caltech.edu, E-mail: susan.g.neff@nasa.gov [NASA GSFC, Code 665, Observational Cosmology Lab, Greenbelt, MD 20771 (United States)

2012-06-15

372

Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies  

NASA Technical Reports Server (NTRS)

We examine the global properties of the stellar and Hi components of 229 low H i mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H i masses <10(sup 7.7) solar mass and Hi line widths <80 kilometers per second. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M*) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M* obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M* approximately less than10(exp 8)M(sub 0) is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper Hi mass limit yields the selection of a sample with lower gas fractions for their M* than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H i depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that Hi disks are more extended than stellar ones.

Huang, Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G.

2012-01-01

373

The secrets of T Pyx: I. UV observations  

E-print Network

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

Roberto Gilmozzi; Pierluigi Selvelli

2006-10-02

374

An Investigation of the Loss of Planet-Forming Potential in Intermediate-Sized Young Embedded Star Clusters  

Microsoft Academic Search

A large fraction of stars forming in our galaxy are born within clusters embedded in giant molecular clouds. In these environments, the background UV radiation fields impinging upon circumstellar disks can often dominate over the radiation fields produced by each disk's central star. As a result, this background radiation can drive the evaporation of circumstellar disks and lead to the

Lisa Holden; Edward Landis; Jeremy Spitzig; Fred C. Adams

2011-01-01

375

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

PubMed

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

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

2008-06-01

376

High Power UV LED Industrial Curing Systems  

SciTech Connect

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

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

2012-05-14

377

Habitat of early life: Solar X-ray and UV radiation at Earth's surface 43.5 billion years ago  

E-print Network

here, including the effects of flares and activity cycles, using a solar-like star that has the sameHabitat of early life: Solar X-ray and UV radiation at Earth's surface 4­3.5 billion years ago of the circumstances under which life formed on Earth. The quantity that is received depends on two main variables

Utrecht, Universiteit

378

The UV-Infrared Energy Budget in Spiral Galaxies: Is There a Single Dominant Grain-Heating Population?  

Microsoft Academic Search

We consider the energy balance between absorption of radiation from various stellar populations by dust grains and far-infrared (FIR) emission from heated grains. We use HIRES processing of the IRAS data for improved spatial resolution along with optical, Halpha , and archival UV imagery to trace stellar populations of different characteristic ages testing the assertion that OB stars dominate the

L. V. Jones; W. C. Keel

1996-01-01

379

Astronomy: A Star Party  

NSDL National Science Digital Library

This lesson is designed to teach students about the functions of a telescope, the daylight uses of a telescope, the parts of the telescope, and to identify and view certain stars and planets during a star party at night.

380

Stars in Nutrition & Cancer  

Cancer.gov

Stars in Nutrition & Cancer Soy and Cancer: Wish You Were Young Again Star Speaker Stephen Barnes, PhD Professor, Department of Pharmacology and Toxicology University of Alabama Birmingham Birmingham, Alabama Meeting Date Monday, October 04, 2010

381

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

382

Models of H2 Fluorescence in the UV spectrum of the CTTS TW Hya  

NASA Astrophysics Data System (ADS)

Strong UV emission lines produced in accretion shocks of classical T Tauri stars significantly affect the chemistry of the circumstellar disks. The surface layers of the disk close to the star are analgous to a photo-dissociation region, only controlled by line rather than continuum emission. A broad Ly-? emission line incident on surface layers of the disk photoexcites the warm H2, producing Lyman-band H2 emission. We model this H2 fluorescence to determine the temperature and depth of the warm molecular layer. We compare these models to H2 fluorescence observed in the UV spectra of the CTTS TW Hya obtained with HST/STIS and FUSE. We discuss applications of this model, including disk truncation, disk height and disk dissipation. See: Paper I: http://xxx.lanl.gov/abs/astro-ph/0201319, in ApJ 10 June 2002.

Herczeg, Gregory J.; Wood, Brian E.; Linsky, Jeffrey L.; Valenti, J. A.; Johns-Krull, C. M.

383

Microbial UV fluence-response assessment using a novel UV-LED collimated beam system.  

PubMed

A research study has been performed to determine the ultraviolet (UV) fluence-response of several target non-pathogenic microorganisms to UV light emitting diodes (UV-LEDs) by performing collimated beam tests. UV-LEDs do not contain toxic mercury, offer design flexibility due to their small size, and have a longer operational life than mercury lamps. Comsol Multiphysics was utilized to create an optimal UV-LED collimated beam design based on number and spacing of UV-LEDs and distance of the sample from the light source while minimizing the overall cost. The optimized UV-LED collimated beam apparatus and a low-pressure mercury lamp collimated beam apparatus were used to determine the UV fluence-response of three surrogate microorganisms (Escherichia coli, MS-2, T7) to 255 nm UV-LEDs, 275 nm UV-LEDs, and 254 nm low-pressure mercury lamps. Irradiation by low-pressure mercury lamps produced greater E. coli and MS-2 inactivation than 255 nm and 275 nm UV-LEDs and similar T7 inactivation to irradiation by 275 nm UV-LEDs. The 275 nm UV-LEDs produced more efficient T7 and E. coli inactivation than 255 nm UV-LEDs while both 255 nm and 275 nm UV-LEDs produced comparable microbial inactivation for MS-2. Differences may have been caused by a departure from the time-dose reciprocity law due to microbial repair mechanisms. PMID:21220143

Bowker, Colleen; Sain, Amanda; Shatalov, Max; Ducoste, Joel

2011-02-01

384

Dynamical Young Star Masses  

NASA Astrophysics Data System (ADS)

Mass is a star's most important property, once composition has been established, and determines the entire life trajectory of an object. Only a couple dozen young stars have absolute dynamical mass measurements, and many of those are imprecise. We propose to observe ~17 young close visual binaries in the Taurus star forming region to advance our knowledge of young star masses. We will use NIRSPEC in high-resolution mode behind the adaptive optics system on the Keck II telescope.

Prato, Lisa; Schaefer, Gail; Simon, Michal

2013-08-01

385

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

NASA Technical Reports Server (NTRS)

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

Sonneborn, George (Technical Monitor); Brown, Thomas

2005-01-01

386

UV and Optical Surface Photometry of NGC 1068 from UIT and Ground-Based Observations  

NASA Astrophysics Data System (ADS)

We present a photometric analysis of ultraviolet (UV) and optical image data for NGC 1068. The UV data were obtained by the Ultraviolet Imaging Telescope (UIT) in two bands: far-UV (FUV), lambda_ {eff} ~ 1520 \\ Angstroms, and near-UV (NUV), lambda_ {eff} ~ 2490 \\ Angstroms. Associated optical CCD images in the B and R bandpasses were obtained at KPNO and at Mt. Laguna Observatory of San Diego State University. Using annular aperture photometry and isophotal fitting techniques, we derive structural parameters such as disk scale lengths, central surface brightness, luminosity, and isophotal diameters. The radial brightness profile is best described by two components with a distinct break at r ~ 90('') (6.5 kpc). This break is present in the NUV, B, and R bands, with the NUV bandpass being the most pronounced. Both components are consistent with an exponentially declining light profile, with the outer component (90('') < r < \\ ~ 200('') ) showing a more shallow gradient. Maps of the UV-optical color distribution (muv -- moptical) reveal the dust distribution, the underlying old stellar population and areas of recent massive star formation. The broken circumnuclear ring of luminous knots appears blue in UV-optical colors. However, their FUV -- NUV colors are more complex; exhibiting a range of colors, - 0.5 < FUV -- NUV < +0.5, most likely produced by patchy extinction. These maps also show a uniform red disk at r > 50('') (3.5 kpc) with a NUV -- B color ~ 1.4 mags and a NUV -- R color ~ 2.9 mags.

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

1993-12-01

387

Small observatories for the UV  

NASA Astrophysics Data System (ADS)

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

Brosch, Noah; Balabanov, Vladimir; Behar, Ehud

2014-11-01

388

The LINUS UV imaging spectrometer  

NASA Astrophysics Data System (ADS)

We present an overview of the Naval Postgraduate School's new LINUS instrument. This is a spectral imager designed to observe atmospheric gas plumes by means of absorption spectroscopy, using background Rayleigh-scattered daylight as an illumination source. It is a pushbroom instrument, incorporating a UV-intensified digital camera, interchangeable gratings and filters, and a DC servo-controlled image scanning system. LINUS has been developed to operate across both the near-ultraviolet and the short visible wavelength portions of the spectrum in overlapping passbands. This paper provides an outline of LINUS's design, operation and capabilities, and it summarizes results from initial laboratory and field trials.

Davis, D. S.; Harkins, Richard M.; Olsen, Richard C.

2003-09-01

389

Eclipsing Binary Stars  

NSDL National Science Digital Library

Eclipsing Binary Stars model simulates the detection of eclipsing binary stars. In this method, the light curve from the combination of the two stars, and how it changes over time due to each star transiting (or being occulted or eclipsing the other), is observed and then analyzed. In this simulation each star orbits the other in circular motion via Kepler's third law.  When one star passes in front of the other (transits), it blocks part of the starlight of the other star. This decrease in starlight is shown on the graph.  In the simulation the binary star system is shown as seen from Earth (edge on view) and from overhead, but magnified greatly, and with the star sizes not shown to the scale of the orbit. The mass, radius, and temperature of each star can be changed. The simulation uses either simple 3D or Java 3D (if installed) to render the view the stars. If Java 3D is not installed, the simulation defaults to simple 3D using Java. The Eclipsing Binary Stars model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_astronomy_eclipsing_binaries.jar file will run the program if Java is installed.

Belloni, Mario

2010-07-15

390

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

391

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

392

Rotation-Activity-Age Relations of Sun-like Stars: In Search of the Much Coveted Solar Twin  

Microsoft Academic Search

We present the current results of our ongoing investigation of the coronal (X-ray; Einstein\\/ROSAT), transition region (FUV; IUE\\/FUSE), and chromospheric (FUV-UV; IUE) emissions of single solar-type stars. By considering only main-sequence stars in a restricted range of spectral types ranging from F8 V to G8 V and stars with measured rotation periods, we have focused on the role of rotation

R. T. Hamilton; E. F. Guinan; L. E. DeWarf

2003-01-01

393

IC 3418: STAR FORMATION IN A TURBULENT WAKE  

SciTech Connect

Galaxy Evolution Explorer observations of IC 3418, a low surface brightness galaxy in the Virgo Cluster, revealed a striking 17 kpc UV tail of bright knots and diffuse emission. H{alpha} imaging confirms that star formation is ongoing in the tail. IC 3418 was likely recently ram pressure stripped on its first pass through Virgo. We suggest that star formation is occurring in molecular clouds that formed in IC 3418's turbulent stripped wake. Tides and ram pressure stripping (RPS) of molecular clouds are both disfavored as tail formation mechanisms. The tail is similar to the few other observed star-forming tails, all of which likely formed during RPS. The tails' morphologies reflect the forces present during their formation and can be used to test for dynamical coupling between molecular and diffuse gas, thereby probing the origin of the star-forming molecular gas.

Hester, Janice A.; Neill, James D.; Wyder, Ted K.; Martin, D. Christopher [California Institute of Technology, Pasadena, CA 91125 (United States); Seibert, Mark; Madore, Barry F. [Observatories of the Carnegie Institute of Washington, Pasadena, CA 91101 (United States); Gil de Paz, Armando [Dpto. de Astrofisica, Universidad Computense de Madrid, Madrid 28040 (Spain); Schiminovich, David [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Rich, R. Michael, E-mail: jhester@srl.caltech.ed [Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095 (United States)

2010-06-10

394

Massive stars and star clusters in the Antennae galaxies  

E-print Network

Large numbers of young stars are formed in merging galaxies, such as the Antennae galaxies. Most of these stars are formed in compact star clusters (i.e., super star clusters), which have been the focus of a large number of studies. However, an increasing number of projects are beginning to focus on the individual stars as well. In this contribution, we examine a few results relevant to the triggering of star and star cluster formation; ask what fraction of stars form in the field rather than in clusters; and begin to explore the demographics of both the massive stars and star clusters in the Antennae.

Bradley C. Whitmore

2006-12-22

395

THE EFFECTS OF EPISODIC STAR FORMATION ON THE FUV-NUV COLORS OF STAR FORMING REGIONS IN OUTER DISKS  

SciTech Connect

We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and H? colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; ? model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and H? observations in the literature. We find significant dispersion in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10{sup –8} to 4 × 10{sup –9} yr{sup –1}. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L{sub H{sub ?}}/L{sub FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing ? and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ?2 × 10{sup –6} M{sub ?} yr{sup –1}, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical evolution of spiral galaxies.

Barnes, Kate L.; Van Zee, Liese [Department of Astronomy, Indiana University, Bloomington, IN 47405 (United States); Dowell, Jayce D., E-mail: barneskl@astro.indiana.edu, E-mail: vanzee@astro.indiana.edu, E-mail: jdowell@unm.edu [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131 (United States)

2013-09-20

396

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

397

VLA observation of dMe stars  

NASA Astrophysics Data System (ADS)

We present new VLA radio observations of a sample of dMe stars in X, U, K, and Q bands (from 8.4 to 43 GHz) obtained during an observing campaign in 1996 April-June. The aim of the project was to determine the spectral energy distributions of late-type dwarf flare stars to investigate the possible existence of an inversion of the spectrum slope at frequencies higher than 8 GHz. We also tried to constrain the possible emission mechanism at radio frequencies. We have detections in X band (8.4 GHz), for three sources (UV Cet, V 1054 Oph, and EV Lac), while all of our other measurements are upper limits. We discuss how the weak radio emission of some sources (e.g. AU Mic) and the coronal plasma properties deduced from X-ray observations constrain the coronal magnetic field properties.

Leto, G.; Pagano, I.; Linsky, J. L.; Rodonò, M.; Umana, G.

2000-07-01

398

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

E-print Network

Galaxies' rest-frame ultraviolet (UV) properties are often used to directly infer the degree to which dust obscuration affects the measurement of star formation rates. While much recent work has focused on calibrating dust attenuation in galaxies selected at rest-frame ultraviolet wavelengths, locally and at high-$z$, here we investigate attenuation in dusty, star-forming galaxies (DSFGs) selected at far-infrared wavelengths. By combining multiwavelength coverage across 0.15--500\\,$\\mu$m in the COSMOS field, in particular making use of {\\it Herschel} imaging, and a rich dataset on local galaxies, we find a empirical variation in the relationship between rest-frame UV slope ($\\beta$) and ratio of infrared-to-ultraviolet emission ($L_{\\rm IR}/L_{\\rm UV}\\equiv\\,IRX$) as a function of infrared luminosity, or total star formation rate, SFR. Both locally and at high-$z$, galaxies above SFR$\\gt$50\\,M$_\\odot$\\,yr$^{-1}$ deviate from the nominal $IRX-\\beta$ relation towards bluer colors by a factor proportional to the...

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

2014-01-01

399

Bursting dwarf galaxies from the far-UV and deep surveys  

E-print Network

The far-ultraviolet (UV) counts and the deep optical spectroscopic surveys have revealed an unexpected number of very blue galaxies (vBG). Using constraints from the UV and optical, we apply the galaxy evolution model PEGASE (Fioc & Rocca-Volmerange 1997, hereafter FRV) to describe this population with a cycling star formation. When added to normally evolving galaxy populations, vBG are able to reproduce UV number counts and color distributions as well as deep optical redshift distributions fairly well. Good agreement is also obtained with optical counts (including the Hubble Deep Field). The number of vBG is only a small fraction of the number of normal galaxies, even at faintest magnitudes. In our modelling, the latter explain the bulk of the excess of faint blue galaxies in an open Universe. The problem of the blue excess remains in a flat Universe without cosmological constant.

Michel Fioc; Brigitte Rocca-Volmerange

1997-09-08

400

Making Sense of the Rest-Frame UV Spectra of Galaxies  

NASA Technical Reports Server (NTRS)

Spectroscopic surveys of galaxies at z=1 or more will bring the rest-frame ultraviolet into view of large, ground-based telescopes. This spectral region is rich in diagnostics, but these diagnostics have not yet been calibrated in terms of the properties of the responsible stellar population(s). Such calibrations are now possible with Hubble's Next Generation Spectral Library (NGSL). The NGSL contains UV-optical spectra (0.2- 1.0 microns) of 378 stars having a wide range in temperature, luminosity, and metallicity. Because of the broad wavelength coverage of NGSL spectra, it is possible to derive the basic stellar parameters from the optical spectral region (0.35 - 1.0 microns) and use them to calibrate UV spectral diagnostics. In this talk, I will describe the NGSL and our preliminary calibration of UV spectral diagnostics, focusing on the MgII and MgI resonance lines and the 2640-Angstrom break.

Heap, Sara R.

2007-01-01

401

Vega-like stars  

NASA Astrophysics Data System (ADS)

The results on Vega-like stars obtained with ISO are discussed. We find that the incidence of Vega-like disks is approximately 21% on average, with some dependency upon the spectral type. While young stars do more frequently show disks than old stars, there is no clear trend in the amount of dust seen at different ages. We also discuss the discovery of a Vega-like disk associated with ?1Cnc, a star which is know to be orbited by a planet. Finally we show preliminary results on HD 207129, an old G star with a very prominent IR excess.

Dominik, C.; Habing, H. J.; Laureijs, R. J.; Jourdain de Muizon, M.; Bouchet, P.; Heske, A.; Kessler, M. F.; Leech, K.; Metcalfe, L.; Salama, A.; Siebenmorgen, R.; Trams, N. R.

1999-03-01

402

The most luminous stars.  

PubMed

Stars with individual luminosities more than a million times that of the sun are now being studied in a variety of contexts. Observational and theoretical ideas about the most luminous stars have changed greatly in the past few years. They can be observed spectroscopically even in nearby galaxies. They are not very stable; some have had violent outbursts in which large amounts of mass were lost. Because of their instabilities, these stars do not evolve to become red superglants as less luminous stars do. Theoretical scenarios for the evolution of these most massive stars depend on the effects of turbulence and mixing combined with high radition densities. PMID:17801579

Humphreys, R M; Davidson, K

1984-01-20

403

Stars and Constellations  

NSDL National Science Digital Library

This site from Jim Kaler, a Professor of Astronomy at the University of Illinois, is geared toward amateur and budding astronomers. Kaler offers detailed but non-technical descriptions of selected stars and a link to a photo of their respective constellations. Another section of the site, The Natures of Stars, consists of basic overviews of key concepts. The star descriptions are interesting to beginner and avid starwatchers alike, but the photos would benefit perhaps from superimposed arrows or other finding aids. The Stars site grows by one celestial body each week: the Star of the Week from Kaler's other site, Skylights.

Kaler, James, B.

404

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

405

The Ultraviolet Sky: final catalogs of unique UV sources from GALEX, and characterization of the UV-emitting sources across the sky, and of the Milky Way extinction  

NASA Astrophysics Data System (ADS)

The legacy of the Galaxy Evolution Explorer (GALEX), which imaged the sky at Ultraviolet (UV) wavelengths for about 9 years, is its unprecedented database with more than 200 million source measurements in far-UV (FUV) and near-UV (NUV), as well as wide-field imaging of extended objects. GALEX's data, the first substantial sky surveys at UV wavelengths, offer an unprecedented view of the sky and a unique opportunity for an unbiased characterization of several classes of astrophysical objects, such as hot stars, QSOs at red-shift about 1, UV-peculiar QSOs, star-forming galaxies, among others. Bianchi et al. (2013, J. Adv. Space Res. (2013), DOI: http://dx.doi.org/10.1016/j.asr.2013.07.045) have constructed final catalogs of UV sources, with homogeneous quality, eliminating duplicate measurements of the same source ('unique' source catalogs), and excluding rim artifacts and bad photometry. The catalogs are constructed improving on the recipe of Bianchi et al. 2011 (MNRAS, 411, 2770, which presented the earlier version of these catalogs) and include all data for the major surveys, AIS and MIS. Considering the fields where both FUV and NUV detectors were exposed, the catalogs contain about 71 and 16.6 million unique sources respectively. We show several maps illustrating the content of UV sources across the sky, globally, and separately for bright/faint, hot, stellar/extragalactic objects. We matched the UV-source catalogs with optical-IR data from the SDSS, GSC2, 2MASS surveys. We are also in the process of matching the catalogs with preliminary PanSTARRS1 (PS1) 3pi survey photometry which already provides twice the sky coverage of SDSS, at slightly fainter magnitude limits. The sources' SED from FUV to optical wavelengths enables classification, derivation of the object physical parameters, and ultimately also a map of the Milky Way extinction. The catalogs will be available on MAST, Vizier (where the previous version already is), and in reduced form (for agile downloading), with related tools, from the author web site " http://dolomiti.pha.jhu.edu/uvsky "

Bianchi, Luciana; Conti, A.; Shiao, B.; Keller, G. R.; Thilker, D. A.

2014-01-01

406

The Carina Nebula: A Laboratory for Feedback and Triggered Star Formation  

NASA Astrophysics Data System (ADS)

The Carina Nebula (NGC 3372) is our richest nearby laboratory in which to study feedback through UV radiation and stellar winds from very massive stars during the formation of an OB association, at an early phase before supernova explosions have disrupted the environment. This feedback is triggering new generations of star formation around the periphery of the nebula, while simultaneously evaporating the gas and dust reservoirs out of which young stars are trying to accrete. Carina is currently powered by UV radiation from 65 O-type stars and 3 WNH stars, but for most of its lifetime when its most massive star (? Carinae) was on the main-sequence, the Carina Nebula was powered by 70 O-type stars that produced a hydrogen ionizing luminosity 150 times stronger than in the Orion Nebula. At a distance of 2.3 kpc, Carina has the most extreme stellar population within a few kpc of the Sun, and suffers little interstellar extinction. It is our best bridge between the detailed star-formation processes that can be studied in nearby regions like Orion, and much more extreme but also more distant regions like 30 Doradus. Existing observations have only begun to tap the tremendous potential of this region for understanding the importance of feedback in star formation --- it will provide a reservoir of new discoveries for the next generation of large ground-based telescopes, space telescopes, and large submillimeter and radio arrays.

Smith, N.; Brooks, K. J.

2008-12-01

407