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Sample records for uv ceti stars

  1. A search for X rays from UV Ceti flare stars

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  2. VizieR Online Data Catalog: Catalog of binary UV Ceti stars (Tamazian+, 2014)

    NASA Astrophysics Data System (ADS)

    Tamazian, V.; Malkov, O.

    2015-01-01

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

  3. A search for X-rays from UV Ceti flare stars

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  4. MAXI/GSC detection of a large X-ray flare from the active star binary UV Ceti

    NASA Astrophysics Data System (ADS)

    Negoro, H.; Nakahira, S.; Ueno, S.; Tomida, H.; Kimura, M.; Ishikawa, M.; Mihara, T.; Sugizaki, M.; Serino, M.; Morihana, K.; Yamamoto, T.; Sugimoto, J.; Takagi, T.; Matsuoka, M.; Kawai, N.; Morii, M.; Usui, R.; Ishikawa, K.; Yoshida, A.; Sakamoto, T.; Nakano, Y.; Tsunemi, H.; Sasaki, M.; Nakajima, M.; Asada, M.; Ueda, Y.; Hiroi, K.; Shidatsu, M.; Sato, R.; Kawamuro, T.; Tsuboi, Y.; Higa, M.; Yamauchi, M.; Nishimura, Y.; Hanayama, T.; Yoshidome, K.; Ogawa, Y.; Yamaoka, K.

    2012-12-01

    At 00:21 UT of December 23, 2012, the MAXI/GSC transient alert system triggered on enhanced X-ray emission from the position consistent with the active dMe star binary UV Ceti. The 2-10 keV flux averaged over the 56-second triangular transit was about 169 25 mCrab, corresponding to an X-ray luminosity of about 3.5e30 ergs/s for 2.7 pc distance. Note that the luminosity is larger than that of an X-ray flare (~2e29 erg/s) detected with Chandra in 2001 (Audard et al.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  6. Discovery of eleven new ZZ Ceti stars

    NASA Astrophysics Data System (ADS)

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

    2006-04-01

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

  7. Mira Ceti and the Star of Bethlehem

    NASA Astrophysics Data System (ADS)

    Sigismondi, Costantino

    2014-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  9. Amplitude Modulation in the ZZ Ceti Star GD 244

    NASA Astrophysics Data System (ADS)

    Bognár, Zs.; Paparó, M.; Molnár, L.; Plachy, E.; Sódor, Á.

    2015-06-01

    Previous studies of GD 244 revealed seven pulsation frequencies (two doublets and three single periods) in the light variations of the star. The data obtained at McDonald Observatory between 2003 and 2006, and our additional measurements in 2006 and 2007 at Konkoly Observatory, allow the investigation of the long-term pulsational behaviour of GD 244. We found that the 307.1 s period component of one of the doublets show long-term, periodic amplitude modulation with a time scale of ˜ 740 days. Possible explanations are that nonlinear resonant mode coupling is operating among the rotationally split frequency components, or two modes, unresolved in the yearly data are excited at ˜ 307.1 s. This is the first time that such long-term periodic amplitude modulation is published on a ZZ Ceti star.

  10. A Convective Model for Light Curves of ZZ Ceti Stars

    NASA Astrophysics Data System (ADS)

    Falcn, N.

    2005-07-01

    The erratic behavior of the luminosity in ZZ Ceti light curves may be explained in terms of the sum of several convective fluctuations, where the heat flux is propagated in time by thermal waves. We present simulations of the light curves of GD29-38, GD 358, and HL Tau-76.

  11. The search for ZZ Ceti stars in the original Kepler mission

    NASA Astrophysics Data System (ADS)

    Greiss, S.; Hermes, J. J.; Gänsicke, B. T.; Steeghs, D. T. H.; Bell, Keaton J.; Raddi, R.; Tremblay, P.-E.; Breedt, E.; Ramsay, G.; Koester, D.; Carter, P. J.; Vanderbosch, Z.; Winget, D. E.; Winget, K. I.

    2016-04-01

    We report the discovery of 42 white dwarfs in the original Kepler mission field, including nine new confirmed pulsating hydrogen-atmosphere white dwarfs (ZZ Ceti stars). Guided by the Kepler-Isaac Newton Telescope Survey, we selected white dwarf candidates on the basis of their U - g, g - r, and r - Hα photometric colours. We followed up these candidates with high-signal-to-noise optical spectroscopy from the 4.2-m William Herschel Telescope. Using ground-based, time series photometry, we put our sample of new spectroscopically characterized white dwarfs in the context of the empirical ZZ Ceti instability strip. Prior to our search, only two pulsating white dwarfs had been observed by Kepler. Ultimately, four of our new ZZ Cetis were observed from space. These rich data sets are helping initiate a rapid advancement in the asteroseismic investigation of pulsating white dwarfs, which continues with the extended Kepler mission, K2.

  12. Asteroseismological Study of Massive ZZ Ceti Stars with Fully Evolutionary Models

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  13. Asteroseismological study of massive ZZ Ceti stars with fully evolutionary models

    SciTech Connect

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

    2013-12-10

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  15. The effective temperature of the white-dwarf star and ZZ Ceti candidate Wolf 485A

    NASA Technical Reports Server (NTRS)

    Digel, S. W.; Shipman, H. L.

    1984-01-01

    Previous multichannel observations of W485A (WD 1327-08) have placed it in the instability strip, the effective temperature range 11,000-13,000 K. In the instability strip, most of the stars (the ZZ Ceti stars) are variable, but W485A has not been detected to be variable. In this paper, high-resolution spectra of W485A and improved hydrogen-line broadening routines are used in the ATLAS model-atmospheres program to find the temperature of W485A; the estimate of effective temperature most consistent with the other data on the star is 14,600 K, outside the instability strip.

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

    SciTech Connect

    Bradley, P.A.

    1997-06-01

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

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

    NASA Technical Reports Server (NTRS)

    Bradley, P. A.

    1997-01-01

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

  18. Asteroseismological constraints on the structure of the ZZ Ceti star HL Tau 76

    NASA Astrophysics Data System (ADS)

    Pech, D.; Vauclair, G.; Dolez, N.

    2006-01-01

    This paper reports the results derived from an asteroseismological study of the cool ZZ Ceti star HL Tau 76. A grid of models has been computed in a parameter space covering the range of log g and Teff, formerly determined by spectroscopy, and a large range of hydrogen mass fraction. The adiabatic non-radial oscillations for all the models have been computed for the modes of degrees ?=1 and ?=2. An algorithm based on a ? 2 test was applied to evaluate the quality of the fit between observed and theoretical periods. This method resulted in selecting a best fitting model for which the average relative matching of the periods is 0.7%. Then, a detailed comparison between the observed and the computed periods for the ?=1 and ?=2 modes of the best fitting model was achieved in order to identify as many observed modes as possible. To perform this identification we used the calculated periods for which we applied the rotational splitting as deduced from the observations. Through this process we identify the 36 independent modes observed in HL Tau 76. The best fitting model for HL Tau 76 is well constrained due to the large number of oscillations detected in this ZZ Ceti star. The main stellar parameters of HL Tau 76 derived from this analysis are: the total mass Mstar=0.575 0.005 M?, the hydrogen mass fraction qH, estimated as thick as 2.35 0.10 10-4. The helium mass fraction consistent with qH must be qHe=~1 10-2. The method is not sensitive to Teff variations in the narrow domain of temperature derived from spectroscopy for HL Tau 76. The best adjustment is found however for Teff= 11 375 K. The other derived stellar parameters are the luminosity (L/L?= 0.00389) and the radius (R/R?= 0.0162). We note some trends in the fit of the observed periods with the computed ones which suggest that the rotational splitting could be non-uniform and that the large amplitude modes might contain information on the convection-driven excitation mechanism.

  19. Whole Earth telescope observations of the ZZ Ceti star HL Tau 76

    NASA Astrophysics Data System (ADS)

    Dolez, N.; Vauclair, G.; Kleinman, S. J.; Chevreton, M.; Fu, J. N.; Solheim, J.-E.; Gonzlez Perez, J. M.; Ulla, A.; Fraga, L.; Kanaan, A.; Reed, M.; Kawaler, S.; O'Brien, M. S.; Metcalfe, T. S.; Nather, R. E.; Sanwal, D.; Klumpe, E. W.; Mukadam, A.; Wood, M. A.; Ahrens, T. J.; Silvestri, N.; Sullivan, D.; Sullivan, T.; Jiang, X. J.; Xu, D. W.; Ashoka, B. N.; Leibowitz, E.; Ibbetson, P.; Ofek, E.; Kilkenny, D.; Meitas, E. G.; Alisauskas, D.; Janulis, R.; Kalytis, R.; Moskalik, P.; Zola, S.; Krzesinski, J.; Ogloza, W.; Handler, G.; Silvotti, R.; Bernabei, S.

    2006-01-01

    This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 ?Hz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and those present in earlier data, which do not show up in the 1999 data set, we find a total of 43 independent frequencies. This makes HL Tau 76 the richest ZZ Ceti star in terms of number of observed pulsation modes. We use those pulsation frequencies to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 cover a wide range of periods between 380 s and 1390 s. We propose an identification for 39 of those 43 frequencies in terms of ?=1 and ?=2 non-radial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a moderately "thick" hydrogen mass fraction log qH ? -7.0. The results presented in this paper constitute a starting point for a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.

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

    SciTech Connect

    Zuckerman, B.; Song, Inseok E-mail: song@physast.uga.edu

    2012-10-20

    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.

  1. Solar-like oscillations in the G8 V star ? Ceti

    NASA Astrophysics Data System (ADS)

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

    2009-01-01

    We used HARPS to measure oscillations in the low-mass star ? Cet. Although the data were compromised by instrumental noise, we have been able to extract the main features of the oscillations. We found ? 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 ?Hz, 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? (1.6%). Based on observations collected at the European Southern Observatory, La Silla, Chile (ESO Programme 74.D-0380).

  2. Whole Earth Telescope Observations of the ZZ Ceti Star HL Tau 76

    NASA Astrophysics Data System (ADS)

    Vauclair, G.; Wet Collaboration

    2005-07-01

    This paper analyses the Whole Earth Telescope observations of HL Tau 76 obtained in 1996 and in 1999. In the 1999 data, we find as much as 80 significant frequencies in the power spectrum, of which 33 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and in earlier data, we find a total of 40 independent modes. We use those modes to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 covers a wide range of periods between 380 s and 1390 s. We propose an identification for many of those modes in terms of ?=1 and ?=2 nonradial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a ``thick'' hydrogen mass fraction -4.5? log qH ?-4.0. These results have to be confirmed by a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  4. UV-bright stars in globular clusters

    NASA Technical Reports Server (NTRS)

    Landsman, Wayne B.

    1994-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Fontaine, G.; Brassard, P.

    2010-11-01

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

  6. Constraining the Evolution of ZZ Ceti

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  7. Tau Ceti: our nearest cousin

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  9. Stellar Winds of Hot Stars - Diagnostics from UV spectra

    NASA Astrophysics Data System (ADS)

    Hamann, Wolf-Rainer; Oskinova, Lidia

    2012-07-01

    All non-degenerate stars with the maximum of their spectral energy distribution in the UV range drive strong winds. Massive stars possess strong winds during their whole lifetime from the main sequence to supernova explosion. Low mass stars become sufficiently hot only in the late stage of their evolution, and can develop strong winds during the phase of central stars of planetary nebulae. The spectroscopic signatures from hot star winds are best explored in the UV range, where a couple of resonance lines from abundant ions may show up with P Cygni profiles. The fundamental stellar and wind parameters can be determined from careful spectroscopic analysis, with help of sophisticated atmosphere models, such as our Potsdam Wolf-Rayet (PoWR) code for expanding atmosphere in non-LTE. We use PoWR to analyze the UV spectra of massive stars as well as sdO-type stars and central stars of planetary nebulae. I will briefly review our recent work on the analysis of UV spectra of stellar winds. The inferred chemical abundances of evolved stars allow to test stellar evolutionary models. A current question concerns the effect of wind inhomogeneities, the so-called micro- and macro-clumping, on the empirical mass-loss rate diagnostics. The true mass-loss rates are an important input for modeling the stellar evolution, feedback, and the understanding of the chemical galactic evolution.

  10. VOLATILE-RICH CIRCUMSTELLAR GAS IN THE UNUSUAL 49 CETI DEBRIS DISK

    SciTech Connect

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

    2014-11-20

    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 β Pictoris.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    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(sub I) column density, estimated the total carbon column density, and set limits on the O(sub 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 Beta Pictoris.

  12. Brucella ceti and Brucellosis in Cetaceans

    PubMed Central

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

    2012-01-01

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

  13. A Complete UV Atlas of Standard Stars

    NASA Technical Reports Server (NTRS)

    Wu, Chi-Chao

    1999-01-01

    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.

  14. DISCOVERY OF A ZZ CETI IN THE KEPLER MISSION FIELD

    SciTech Connect

    Hermes, J. J.; Winget, D. E.; Mullally, Fergal; Howell, Steve B.; Oestensen, R. H.; Bloemen, S.; Williams, Kurtis A.; Telting, John; Southworth, John; Everett, Mark

    2011-11-01

    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.

  15. A Complete UV Atlas of Standard Stars

    NASA Technical Reports Server (NTRS)

    Wu, Chi-Chao

    2000-01-01

    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.

  16. Suggested UV spectral classification criteria for A stars

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, E.

    1982-01-01

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

  17. Interferometric observations of Mira (Omicron Ceti)

    NASA Technical Reports Server (NTRS)

    Quirrenbach, A.; Mozurkewich, D.; Armstrong, J. T.; Johnston, K. J.; Colavita, M. M.; Shao, M.

    1992-01-01

    The long-period variable Mira Omicron Ceti has been observed at 800 nm wavelength with the Mk III Optical Interferometer at photometric phases 0 = 0.96, 0.05, and 0.14 in 1990; some additional data were taken in 1989. The star is not spherically symmetric, and temporal variations of the size and the position angle of the asymmetry are detected. The visibility data can be represented by two uniform elliptical disks, which could correspond to different layers in Mira's atmosphere. If the size variations are interpreted in terms of physical motion of the emitting material, an infall velocity of about 15 km/s around phi = 0 is derived.

  18. The UV + IR Hybrid Star Formation Rate Across NGC6946

    NASA Astrophysics Data System (ADS)

    Eufrasio, Rafael T.; Lehmer, Bret; Dwek, Eli; Arendt, Richard G.

    2016-01-01

    Knowledge of the star formation rate (SFR) of galaxies is essential to understand galaxy evolution and thus determining reliable, simple tracers of star-forming activity is of paramount importance to astrophysics. For instance, intrinsic ultraviolet (UV) emission from young stars is an excellent tracer of the SFR. Observed UV luminosities, however, have been strongly attenuated by intervening interstellar dust. Since emission from hot dust is readily available from IRAS, Spitzer, and WISE, it is common practice to combine mid-IR emission (around 25 ?m) with observed UV in order to obtain an SFR diagnostic of the form Lobs(FUV) + acorr Lobs(25 ?m). Conventionally, a single correction acorr, previously determined for a sample of galaxies, is used. Here we test the reliability of this hybrid SFR diagnostic, allowing for a variable correction factor acorr. For this, we have performed broadband UV-to-IR SED fittings in order to model the star formation histories across the spiral galaxy NGC6946. We have obtained SFRs and stellar masses across the galaxy, from physical scales of 5 kpc down to 500 pc. We find that acorr varies significantly across the galaxy and increases with increasing specific star formation rate (sSFR), the ratio of SFR and stellar mass (or the ratio of young and old stars). The correction acorr does not seem to be correlated to the amount of attenuation AV. Variation of acorr is most likely caused by different mixes of young and old stellar populations across the galaxy. This finding agrees well with our previous results for the interacting spiral galaxy NGC 6872, for which we have demonstrated the variation of acorr and a its correlation with sSFR. Our results show the need of caution when using only two broadband filters in order to determine SFR of individual galaxies or sub-galactic regions. The dust emission most likely overestimates SFR for highly star-forming, high sSFR regions, and underestimates it for more quiescent, low sSFR regions.

  19. Calibrating UV Star Formation Rates for Dwarf Galaxies from STARBIRDS

    NASA Astrophysics Data System (ADS)

    McQuinn, Kristen B. W.; Skillman, Evan D.; Dolphin, Andrew E.; Mitchell, Noah P.

    2015-08-01

    Integrating our knowledge of star formation (SF) traced by observations at different wavelengths is essential for correctly interpreting and comparing SF activity in a variety of systems and environments. This study compares extinction corrected integrated ultraviolet (UV) emission from resolved galaxies with color-magnitude diagram (CMD) based star formation rates (SFRs) derived from resolved stellar populations and CMD fitting techniques in 19 nearby starburst and post-starburst dwarf galaxies. The data sets are from the panchromatic Starburst Irregular Dwarf Survey and include deep legacy GALEX UV imaging, Hubble Space Telescope optical imaging, and Spitzer MIPS imaging. For the majority of the sample, the integrated near-UV fluxes predicted from the CMD-based SFRsusing four different modelsagree with the measured, extinction corrected, integrated near-UV fluxes from GALEX images, but the far-UV (FUV) predicted fluxes do not. Furthermore, we find a systematic deviation between the SFRs based on integrated FUV luminosities and existing scaling relations, and the SFRs based on the resolved stellar populations. This offset is not driven by different SF timescales, variations in SFRs, UV attenuation, nor stochastic effects. This first comparison between CMD-based SFRs and an integrated FUV emission SFR indicator suggests that the most likely cause of the discrepancy is the theoretical FUV-SFR calibration from stellar evolutionary libraries and/or stellar atmospheric models. We present an empirical calibration of the FUV-based SFR relation for dwarf galaxies, with uncertainties, which is 53% larger than previous relations. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST-ECF/ESA), and the Canadian Astronomy Data Centre (CADC/NRC/CSA).

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

    NASA Technical Reports Server (NTRS)

    Adelman, Saul J.

    1991-01-01

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

  1. The Instability Strip of ZZ Ceti White Dwarfs

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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 low and extremely low masses. We computed to this aim 29 evolutionary sequences of DA models with various masses, chemical layering, and core compositions. These models are characterized by the so-called ML2/α=1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We computed pulsation 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 account properly 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.

  2. Time variations of UV emission features of Be stars

    NASA Technical Reports Server (NTRS)

    Bahng, J. D. R.

    1975-01-01

    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.

  3. A big flare from UV Ceti

    NASA Astrophysics Data System (ADS)

    Ishikawa, M.; Kawagoe, Uchida A.; Tsuboi, Y.; Ueno, S.; Tomida, H.; Nakahira, S.; Kimura, M.; Nakagawa, Y. E.; Mihara, T.; Sugizaki, M.; Morii, M.; Serino, M.; Sugimoto, J.; Takagi, T.; Yoshikawa, A.; Matsuoka, M.; Kawai, N.; Usui, R.; Yoshii, T.; Tachibana, Y.; Yoshida, A.; Sakamoto, T.; Nakano, Y.; Kawakubo, Y.; Ohtsuki, H.; Tsunemi, H.; Sasaki, M.; Negoro, H.; Nakajima, M.; Fukushima, K.; Onodera, T.; Suzuki, K.; Ueda, Y.; Shidatsu, M.; Kawamuro, T.; Hori, T.; Higa, M.; Yamauchi, M.; Yoshidome, K.; Ogawa, Y.; Yamada, H.; Morooka, Y.; Yamaoka, K.

    2014-03-01

    On 2014-03-29 15:21 (UT) UT (=MJD 56745.640), the MAXI/GSC transient alert system triggered on enhanced X-ray emission at (R.A., Dec) = (24.687 deg, -18.012 deg) = (01 38 44.88, -18 00 43.2) (J2000) with a statistical 90% C.L. ...

  4. UV-selected Young Massive Star Cluster Populations in Nearby Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Smith, Linda J.

    2015-08-01

    The Legacy ExtraGalactic UV Survey (LEGUS) is an HST Treasury program aimed at the investigation of star-formation and its relationship to environment in nearby galaxies. The results of a UV-selected study of young massive star clusters in a sample of nearby galaxies (< 10 Mpc) using detections based on the WFC3/UVIS F275W filter will be presented. Previous studies have used V or I-band detections and tend to ignore clusters younger than 10 Myr old. This very young population, which represents the most recent cluster-forming event in the LEGUS galaxies will be discussed.This poster is presented on behalf of the LEGUS team (PI Daniela Calzetti).

  5. Chromospheres of Various Cool Stars from Models of the UV

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  6. HAZMAT. I. The evolution of far-UV and near-UV emission from early M stars

    SciTech Connect

    Shkolnik, Evgenya L.; Barman, Travis S. E-mail: barman@lpl.arizona.edu

    2014-10-01

    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 {sup –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.

  7. KIC 4552982: Outbursts and Asteroseismology from the Longest Pseudo-continuous Light Curve of a ZZ Ceti

    NASA Astrophysics Data System (ADS)

    Bell, Keaton J.; Hermes, J. J.; Bischoff-Kim, A.; Moorhead, Sean; Montgomery, M. H.; stensen, Roy; Castanheira, Barbara G.; Winget, D. E.

    2015-08-01

    We present the Kepler light curve of KIC 4552982, the first ZZ Ceti (hydrogen-atmosphere pulsating white dwarf star) discovered in the Kepler field of view. Our data span more than 1.5 years, with a 86% duty cycle, making it the longest pseudo-continuous light curve ever recorded for a ZZ Ceti. This extensive data set provides the most complete coverage to date of amplitude and frequency variations in a cool ZZ Ceti. We detect 20 independent frequencies of variability in the data that we compare with asteroseismic models to demonstrate that this star has a mass M*> 0.6 M?. We identify a rotationally split pulsation mode and derive a probable rotation period for this star of 17.47 0.04 hr. In addition to pulsation signatures, the Kepler light curve exhibits sporadic, energetic outbursts that increase the stars relative flux by 2%-17%, last 4-25 hr, and recur on an average timescale of 2.7 days. These are the first detections of a new dynamic white dwarf phenomenon that may be related to the pulsations of this relatively cool (Teff =10,860 120 K) ZZ Ceti star near the red edge of the instability strip.

  8. Ultraviolet Morphology and Unobscured UV Star Formation Rates of CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Donahue, Megan; Connor, Thomas; Fogarty, Kevin; Li, Yuan; Voit, G. Mark; Postman, Marc; Koekemoer, Anton; Moustakas, John; Bradley, Larry; Ford, Holland

    2015-06-01

    Brightest cluster galaxies (BCGs) are usually quiescent, but many exhibit star formation. Here we exploit the opportunity provided by rest-frame UV imaging of galaxy clusters in the Cluster Lensing and Supernovae with Hubble (CLASH) Multi-Cycle Treasury Project to reveal the diversity of UV morphologies in BCGs and to compare them with recent simulations of the cool, star-forming gas structures produced by precipitation-driven feedback. All of the CLASH BCGs are detected in the rest-frame UV (280 nm), regardless of their star formation activity, because evolved stellar populations produce a modest amount of UV light that traces the relatively smooth, symmetric, and centrally peaked stellar distribution seen in the near infrared. Ultraviolet morphologies among the BCGs with strong UV excesses exhibit distinctive knots, multiple elongated clumps, and extended filaments of emission that distinctly differ from the smooth profiles of the UV-quiet BCGs. These structures, which are similar to those seen in the few star-forming BCGs observed in the UV at low redshift, are suggestive of bi-polar streams of clumpy star formation, but not of spiral arms or large, kiloparsec-scale disks. Based on the number of streams and lack of culprit companion galaxies, these streams are unlikely to have arisen from multiple collisions with gas-rich galaxies. These star-forming UV structures are morphologically similar to the cold-gas structures produced in simulations of precipitation-driven active galactic nucleus feedback in which jets uplift low-entropy gas to greater altitudes, causing it to condense. Unobscured star formation rates estimated from CLASH UV images using the Kennicutt relation range up to 80 {{M}? } y{{r}-1} in the most extended and highly structured systems. The circumgalactic gas-entropy threshold for star formation in CLASH BCGs at z 0.2-0.5 is indistinguishable from that for clusters at z\\lt 0.2.

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

    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.

  10. UV Spectroscopy of the Central Star of Planetary Nebulae A43

    NASA Astrophysics Data System (ADS)

    Ringat, E.; Friederich, F.; Rauch, T.; Werner, K.; Kruk, J. W.

    About 25% of all post-AGB stars are hydrogen-deficient, e.g. the PG 1159 stars with a typical abundance pattern He:C:O = 33:50:17 (by mass). Only four of about 40 known PG 1159 stars exhibit H in their spectra. The exciting star of the planetary nebula A 43 is one of these so-called hybrid PG 1159 stars. We present preliminary results of an on-going spectral analysis by means of NLTE model-atmosphere techniques based on UV spectra obtained with FUSE, HST/GHRS, and IUE as well as on optical observations.

  11. Infant Mortality of Star Clusters: on the Origin of the Diffuse UV Emission

    NASA Astrophysics Data System (ADS)

    Pellerin, A.; Meyer, M. J.; Harris, J.; Calzetti, D.

    2009-03-01

    We present HST images in which we discovered the presence of a large number of massive stars in the field of the two galaxies NGC 1313 and NGC 4449. These massive stars, not in obvious groups or clusters, are known to produce a significant amount of UV radiation, and to live for at most 25 Myr. We think that these stars are the main source of diffuse UV emission first observed by Meurer et al. (1995) in starburst galaxies. We also propose that the infant mortality of star clusters, an early evolutionary stage of star clusters which kills 90% of them within 10 Myr, is a physical process that can explain how these young stars could end up in the field so quickly. We will also present preliminary stellar 2-points correlation functions for the two galaxies.

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

    SciTech Connect

    Rosenfield, Philip; Johnson, L. Clifton; Dalcanton, Julianne J.; Williams, Benjamin F.; Gilbert, Karoline M.; Girardi, Leo; Bressan, Alessandro; Lang, Dustin; Guhathakurta, Puragra; Dorman, Claire E.; Lauer, Tod R.; Olsen, Knut A. G.; Bell, Eric F.; Bianchi, Luciana; Caldwell, Nelson; Dolphin, Andrew; Kalirai, Jason; Larsen, Soren S.; Rix, Hans-Walter; and others

    2012-08-20

    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.

  13. The Chemical Composition of ? Ceti and Possible Effects on Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Pagano, Michael; Truitt, Amanda; Young, Patrick A.; Shim, Sang-Heon

    2015-04-01

    ? Ceti (HD10700), a G8 dwarf with mass 0.78 M ? , is a close (3.65 pc) Sun-like star where five possibly terrestrial planet candidates (minimum masses of 2, 3.1, 3.5, 4.3, and 6.7 M \\oplus ) have recently been discovered. We report abundances of 23 elements using spectra from the MIKE spectrograph on Magellan. We find [Fe/H] = -0.49 and {{T}eff}=5387 K. Using stellar models with the abundances determined here, we calculate the position of the classical habitable zone (HZ) with time. At the current best fit age, 7.63-1.5+0.87 Gy, up to two planets (e and f) may be in the HZ, depending on atmospheric properties. The Mg/Si ratio of the star is found to be 1.78, which is much greater than for Earth (1.2). With a system that has such an excess of Mg/Si ratio it is possible that the mineralogical make-up of planets around ? Ceti could be significantly different from that of Earth, with possible oversaturation of MgO, resulting in an increase in the content of olivine and ferropericlase compared with Earth. The increase in MgO would have a drastic impact on the rheology of the mantles of the planets around ? Ceti.

  14. UV Surface Environment of Earth-like Planets Orbiting FGKM Stars through Geological Evolution

    NASA Astrophysics Data System (ADS)

    Rugheimer, S.; Segura, A.; Kaltenegger, L.; Sasselov, D.

    2015-06-01

    The UV environment of a host star affects the photochemistry in the atmosphere, and ultimately the surface UV environment for terrestrial planets and therefore the conditions for the origin and evolution of life. We model the surface UV radiation environment for Earth-sized planets orbiting FGKM stars in the circumstellar Habitable Zone for Earth through its geological evolution. We explore four different types of atmospheres corresponding to an early-Earth atmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to present-day levels at 2.0 Gyr ago, 0.8 Gyr ago, and modern Earth. In addition to calculating the UV flux on the surface of the planet, we model the biologically effective irradiance, using DNA damage as a proxy for biological damage. We find that a pre-biotic Earth (3.9 Gyr ago) orbiting an F0V star receives 6 times the biologically effective radiation as around the early Sun and 3520 times the modern Earth-Sun levels. A pre-biotic Earth orbiting GJ 581 (M3.5 V) receives 300 times less biologically effective radiation, about 2 times modern Earth-Sun levels. The UV fluxes calculated here provide a grid of model UV environments during the evolution of an Earth-like planet orbiting a range of stars. These models can be used as inputs into photo-biological experiments and for pre-biotic chemistry and early life evolution experiments.

  15. UV Spectrophotometry of the Hottest Stars from the Southern HK Survey

    NASA Astrophysics Data System (ADS)

    Drilling, John S.; Beers, Timothy C.

    1995-06-01

    Low-resolution UV spectra have been obtained with the long- and short-wavelength lUE cameras for seven of the hottest stars identified in the ongoing HK objective-prism/interference-filter survey begun by Beers, Preston, & Shectman. These stars are a subset of a sample of some 25,000 stars at high galactic latitude whose objective-prism spectra indicate that they are hotter than the Population II main-sequence turnoff in the magnitude range 11 ≤ B ≤ 15.5. The UV fluxes have been corrected for interstellar reddening using a standard reddening law, and comparison of the integrated fluxes in the two lUE cameras indicates that the effective temperatures of these stars range from 40,000 K to 80,000 K. The UV absorption spectra of six of the seven stars are characterized by a strong He II λ1640 line and 3-n series of He II. Five of these stars show strong C IV λ1550 absorption. The low-resolution UV spectrum of the remaining object is featureless.

  16. Habitable zones and UV habitable zones around host stars

    NASA Astrophysics Data System (ADS)

    Guo, Jianpo; Zhang, Fenghui; Zhang, Xianfei; Han, Zhanwen

    2010-01-01

    Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged. And if it is too weak, the synthesis of many biochemical compounds cannot go along. We try to obtain the continuous ultraviolet habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary ultraviolet radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable zones of host stars with masses from 0.08 to 4.00 M ⊙. For the host stars with effective temperatures lower than 4,600 K, the ultraviolet habitable zones are closer than the habitable zones. For the host stars with effective temperatures higher than 7,137 K, the ultraviolet habitable zones are farther than the habitable zones. For a hot subdwarf as a host star, the distance of the ultraviolet habitable zone is about ten times more than that of the habitable zone, which is not suitable for the existence of life.

  17. The Disk and Planets of Solar Analogue τCeti

    NASA Astrophysics Data System (ADS)

    Lawler, S. M.; Francesco, J. Di; Kennedy, G.; Sibthorpe, B.; Booth, M.; Vandenbussche, B.; Matthews, B.; Tuomi, M.

    2015-01-01

    τ Ceti is a nearby, mature star very similar to our Sun, with a massive Kuiper belt analogue tep{Greavesetal2004} and possible multiplanet system tep{Tuomietal2013} that has been compared to our Solar System. We present infrared and submillimeter observations of the debris disk from the Herschel Space Observatory and the James Clerk Maxwell Telescope (JCMT). We find the best model of the disk is a wide annulus ranging from 5-55 AU, inclined from face-on by 30°. tet{Tuomietal2013} report five possible super-Earths tightly nestled inside 1.4 AU, and we model this planetary system and place dynamical constraints on the inner edge of the disk. We find that due to the low masses and fairly circular orbits of the planets, the disk could reach as close to the star as 1.5 AU, with some stable orbits even possible between the two outermost planets. The photometric modelling cannot rule out a disk inner edge as close to the star as 1 AU, though 5-10 AU produces a better fit to the data. Dynamical modelling shows that the 5 planet system is stable with the addition of a Saturn-mass planet on an orbit outside 5 AU, where the Tuomi et al. analysis would not have detected a planet of this mass.

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

    NASA Astrophysics Data System (ADS)

    Maz Apellniz, J.

    2015-05-01

    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 ({http://adsabs.harvard.edu/abs/2011hsa6.conf..467M}{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.

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

    NASA Technical Reports Server (NTRS)

    Nichols, Joy S.

    1995-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Rosenfield, Philip

    2014-10-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

  2. Extreme horizontal branch stars - Puzzling objects dominating the UV-light in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Geier, Stephan

    2015-08-01

    Extreme horizontal branch stars (also known as hot subdwarf stars, sdO/Bs) are located at the bluest extension of the horizontal branch in the HR-diagram. They burn helium in their cores and are the sources of the UV-excess in elliptical galaxies and other old stellar populations. However, the formation of those stars is still unclear. SdO/B stars in the field show a high binary fraction and are likely formed via binary interactions with low-mass stars, substellar objects or compact stellar remnants. Similar objects in globular clusters on the other hand have a significantly lower binary fraction and might therefore be formed in a different way. I will review the state-of-the-art and confront theories of sdO/B formation with most recent observational evidence.

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

    NASA Astrophysics Data System (ADS)

    Siqueira-Mello, C.; Barbuy, B.

    2014-11-01

    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.

  4. UV stars and the interstellar medium - A statistical time-dependent model

    NASA Technical Reports Server (NTRS)

    Lyon, J.

    1975-01-01

    A statistical time-dependent model for the effects on the interstellar gas of the ionizing radiation from UV stars is presented. The radiation from the stars is assumed to be emitted as monochromatic bursts at random times and locations. The thermal and ionization history of the gas is followed in a Monte Carlo simulation. Probability densities as well as mean values for the ionization fraction, temperature, and other observable quantities are derived. The fluctuations in observed quantities due to the stochastic nature of the model are estimated. Models of the interstellar medium perpendicular to the galactic plane are developed and compared with observations. The action of the UV stars can explain the bulk properties of the interstellar gas toward the galactic poles and is consistent with the Copernicus satellite observations toward lambda Scorpii.

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

    NASA Astrophysics Data System (ADS)

    Sato, Satoko

    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.

  6. KIC 4552982: outbursts and pulsations in the longest-ever pseudo-continuous light curve of a ZZ Ceti

    NASA Astrophysics Data System (ADS)

    Bell, K. J.; Hermes, J. J.; Bischoff-Kim, A.; Moorhead, S.; Castanheira, B. G.; Montgomery, M. H.; Winget, D. E.

    2015-09-01

    KIC 4552982 was the first ZZ Ceti (hydrogen-atmosphere pulsating white dwarf) identified to lie in the Kepler field, resulting in the longest pseudo-continuous light curve ever obtained for this type of variable star. In addition to the pulsations, this light curve exhibits stochastic episodes of brightness enhancement unlike any previously studied white dwarf phenomenon. We briefly highlight the basic outburst and pulsation properties in these proceedings.

  7. Discovery of a nitrogen-rich UV-bright star in the globular cluster M5

    SciTech Connect

    Bohlin, R.C.; Cornett, R.H.; Hill, J.K.; Smith, A.M.; Stecher, T.P.; Sweigart, A.V.

    1983-04-15

    Ultraviolet images of the globular cluster M5 (NGC 5904) obtained with a rocket-borne telescope show a hot and luminous star approx.20'' from the cluster center. Spectra of this UB-bright star, obtained with the International Ultraviolet Explorer satellite in the low-resolution mode, reveal an energy distribution very similar to that of ..mu.. Col, a Population I O9.5 IV star with T/sub eff/ = 35,000 K and log g = 4.19, except for the absence of metallic line blanketing. Assuming an effective temperature of 35,000 K for the UV-bright star, we find L = 1800 L/sub sun/, M/sub bol/ = -3.40, R = 1.15 R/sub sun/, and log g = 4.04. The N V lambda1240 line is much stronger in the UV-bright star than in ..mu.. Col, indicating that the CNO cycle has converted the envelope C and O into N. A single emission line at the wavelength of the N IV intercombination line is also present, suggesting the possible existence of a planetary nebula. The mass-luminosity relation for asymptotic giant branch stars gives M = 0.53 M/sub sun/, imply a mass of 0.08 M/sub sun/ since the horizontal-branch phase.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    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

  10. UV spectroscopy as main diagnostic access to hot-star winds

    NASA Astrophysics Data System (ADS)

    Hamann, Wolf-Rainer; Oskinova, Lidia

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

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

    SciTech Connect

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

    2014-09-01

    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{sup –}. In this study, we explore the impact of such UV radiation on fragmentation in massive primordial halos of a few times 10{sup 7} M {sub ☉}. 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 {sub 21} assuming a blackbody radiation spectrum with a characteristic temperature of T {sub rad} = 10{sup 4} 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 10{sup 2}-10{sup 4} solar mass protostars are formed when halos are irradiated by J {sub 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 {sub ☉} yr{sup –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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    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.

  13. Identification of Faint UV Images using the Guide Star Plate Archive

    NASA Astrophysics Data System (ADS)

    Smart, R. L.; Shara, M.; Milliard, B.

    1994-05-01

    We have used images from the FOCA balloon borne middle UV imaging telescope as a test of the optical - ultraviolet identification abilities of the proposed Joint Ultraviolet Nightsky Observer mission (JUNO). The precision of the FOCA object centering is 3'' and the resolution (FWHM) is 12''; as such optical identification is required for meaningful source identifications. The magnitude range we are examining extends to 18 in the UV which corresponds to a required visible magnitude limit of 22. The only sources of all-sky optical coverage at this magnitude limit are the Palomar and UK/ESO surveys. We have therefore made use of the Guide Star Plate Archive to both optically identify the UV sources and provide basic color and proper motion information on those images. This application of all-sky surveys is an obvious and increasingly important use of such datasets. We present preliminary results and discuss the problems encountered.

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

    NASA Astrophysics Data System (ADS)

    Thilker, David

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

  15. Star Formation in the Galaxy and the Fluctuating UV Radiation Field

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  16. Predicting the Extreme-UV and Lyman-? Fluxes Received by Exoplanets from their Host Stars

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey L.; France, Kevin; Ayres, Thomas R.

    2015-01-01

    Extreme-UV (EUV) radiation from the chromospheres, transition regions, and coronae of host stars (spectral types F, G, K, and M) ionize and heat the outer atmospheres of exoplanets leading to mass loss that is observed during transits and can change the exoplanet's atmosphere. Lyman-? emission from host stars controls the photochemistry in the upper layers of planetary atmospheres by photodissociating important molecules including H_2O, CO_2, CH_4, thereby increasing the oxygen and ozone mixing ratios important for habitability. Both the EUV and strong Lyman-? radiation are largely absorbed by the interstellar medium and must be reconstructed or estimated to understand the radiation environment of exoplanets. In two recent papers, tet{Linsky2013} and tet{Linsky2014}, we have presented robust methods for predicting the intrinsic Lyman-? and EUV fluxes from main sequence cool stars. Solar models and satellite observations (HST, FUSE, and EUVE) provide tests for the feasibility of these methods.

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

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    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 Tlescope, 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 Tlescope (TBL, Pic du Midi, France) of the Midi-Pyrnes Observatory, which is operated by the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France and Universit 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

  18. UV escape fraction and dust distribution of star forming galaxies at z=0-3: a new dust attenuation model

    NASA Astrophysics Data System (ADS)

    Kusakabe, Haruka; Shimasaku, Kazuhiro; shimizu, ikkoh

    2015-08-01

    In star-forming galaxies, a relatively small fraction of UV radiation from young stars can escape dust absorption, with the remaining being re-emitted in IR. The UV escape fraction, fUV, is thus a key parameter determining the shape of galaxy SEDs. However, it is not well known how the fUV of galaxies depends on global parameters of the dust in them such as total mass and whether the depencence evolves with time. Addressing this question is important also for galaxy formation models in which simple, untested prescriptions of dust attenuation such as a uniform dust slab are often used, because different prescriptions can give very different multiband properties of model galaxies. In this study, we use ~140 normal star-forming galaxies (~110 at z~0 and ~30 at z~1-3) with fUV and dust-mass measurements to examine the dependence of fUV (at ~1500A) on total dust mass and galaxy size. In addition to an expected, but weak, anti-correlation of fUV against total dust mass, we find a relatively tight anti-correlation against the characteristic surface dust mass density, Sigma_d, defined as the total dust mass divided by the area enclosing half of the UV luminosity. This is interesting because the actual distributions of dust and young stars are far from smooth on small scales. Galaxies at all redshifts follow a common (anti-)correlation between fUV and Sigma_d, suggesting that the geometrical distributions of dust and young stars do not significantly change with redshift. This anti-correlation can be explained not by a unform slab or its variants but by a model where dust and young stars are well mixed and have the same exponential profile. We implement this model in Shimizu et al.'s cosmological hydrodynamics simulations and discuss predicted multiband galaxy properties.

  19. Star Formation In the Galaxy and the Fluctuating UV Radiation Field

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    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.

  20. Does UV CETI Suffer from the MAD Syndrome?

    NASA Technical Reports Server (NTRS)

    Drake, Jeremy

    1999-01-01

    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.

  1. Does UV CETI Suffer from the MAD Syndrome?

    NASA Technical Reports Server (NTRS)

    Drake, Jeremy

    2000-01-01

    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.

  2. Does UV CETI Suffer from the Mad Syndrome?

    NASA Technical Reports Server (NTRS)

    Drake, Jeremy

    1999-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Hicks, A. K.; Mushotzky, R.

    2005-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Hicks, A. K.; Mushotzky, R.

    2006-01-01

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

  5. MID-IR LUMINOSITIES AND UV/OPTICAL STAR FORMATION RATES AT z < 1.4

    SciTech Connect

    Salim, Samir; Dickinson, Mark; Michael Rich, R.; Charlot, Stephane; Lee, Janice C.; Schiminovich, David; Perez-Gonzalez, Pablo G.; Ashby, Matthew L. N.; Noeske, Kai; Papovich, Casey; Weiner, Benjamin J.; Faber, S. M.; Frayer, David T.; Walton, Josiah M.; Chary, Ranga-Ram; Bundy, Kevin; Koekemoer, Anton M.

    2009-07-20

    Ultraviolet (UV) nonionizing continuum and mid-infrared (IR) emission constitute the basis of two widely used star formation (SF) indicators at intermediate and high redshifts. We study 2430 galaxies with z < 1.4 in the Extended Groth Strip with deep MIPS 24 {mu}m observations from FIDEL, spectroscopy from DEEP2, and UV, optical, and near-IR photometry from the AEGIS. The data are coupled with dust-reddened stellar population models and Bayesian spectral energy distribution (SED) fitting to estimate dust-corrected star formation rates (SFRs). In order to probe the dust heating from stellar populations of various ages, the derived SFRs were averaged over various timescales-from 100 Myr for 'current' SFR (corresponding to young stars) to 1-3 Gyr for long-timescale SFRs (corresponding to the light-weighted age of the dominant stellar populations). These SED-based UV/optical SFRs are compared to total IR luminosities extrapolated from 24 {mu}m observations, corresponding to 10-18 {mu}m rest frame. The total IR luminosities are in the range of normal star-forming galaxies and luminous IR galaxies (10{sup 10}-10{sup 12} L{sub sun}). We show that the IR luminosity can be estimated from the UV and optical photometry to within a factor of 2, implying that most z < 1.4 galaxies are not optically thick. We find that for the blue, actively star-forming galaxies the correlation between the IR luminosity and the UV/optical SFR shows a decrease in scatter when going from shorter to longer SFR-averaging timescales. We interpret this as the greater role of intermediate age stellar populations in heating the dust than what is typically assumed. Equivalently, we observe that the IR luminosity is better correlated with dust-corrected optical luminosity than with dust-corrected UV light. We find that this holds over the entire redshift range. Many so-called green valley galaxies are simply dust-obscured actively star-forming galaxies. However, there exist 24 {mu}m detected galaxies, some with L{sub IR}>10{sup 11} L{sub sun}, yet with little current SF. For them a reasonable amount of dust absorption of stellar light (but presumably higher than in nearby early-type galaxies) is sufficient to produce the observed levels of IR, which includes a large contribution from intermediate and old stellar populations. In our sample, which contains very few ultraluminous IR galaxies, optical and X-ray active galactic nuclei do not contribute on average more than {approx}50% to the mid-IR luminosity, and we see no evidence for a large population of 'IR excess' galaxies.

  6. Discovery of a nitrogen-rich UV-bright star in the globular cluster M5

    NASA Technical Reports Server (NTRS)

    Bohlin, R. C.; Smith, A. M.; Stecher, T. P.; Sweigart, A. V.; Cornett, R. H.; Hill, J. K.

    1983-01-01

    Observations of a UV bright source in the globular cluster M5 using instrumentation on the Black Brant rocket are reported. Imagery was obtained by two cameras operating at 1540 A and 2360 A and bandpasses of 350 A and 880 A. The instruments are prototypes for cameras to be flown with the Spacelab. The UV-emitting object in the cluster was located off-center. Comparison of the data with data from the IUE for short-wavelength radiation indicated a temperature in the range 25,000-50,000 K, with a dereddened flux for the continuum near 1550 A of 4.2 x 10 to the -13th ergs/sq cm per sec per A. The object is concluded to be a post-AGB star with an envelope which has experienced CNO processing.

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

    NASA Astrophysics Data System (ADS)

    Vander Haagen, G. A.

    2013-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  9. Predicting dust extinction properties of star-forming galaxies from H?/UV ratio

    NASA Astrophysics Data System (ADS)

    Koyama, Yusei; Kodama, Tadayuki; Hayashi, Masao; Shimakawa, Rhythm; Yamamura, Issei; Egusa, Fumi; Oi, Nagisa; Tanaka, Ichi; Tadaki, Ken-ichi; Takita, Satoshi; Makiuti, Sin'itirou

    2015-10-01

    Using star-forming galaxies sample in the nearby Universe (0.02 < z < 0.10) selected from the Sloan Digital Sky Survey (DR7) and Galaxy Evolution Explorer all-sky survey (GR5), we present a new empirical calibration for predicting dust extinction of galaxies from the H?-to-FUV flux ratio. We find that the H? dust extinction (AH?) derived with H?/H? ratio (Balmer decrement) increases with increasing H?/UV ratio as expected, but there remains a considerable scatter around the relation, which is largely dependent on stellar mass and/or H? equivalent width (EWH?). At fixed H?/UV ratio, galaxies with higher stellar mass (or galaxies with lower EWH?) tend to be more highly obscured by dust. We quantify this trend and establish an empirical calibration for predicting AH? with a combination of H?/UV ratio, stellar mass, and EWH?, with which we can successfully reduce the systematic uncertainties accompanying the simple H?/UV approach by 15-30 per cent. The new recipes proposed in this study will provide a convenient tool for predicting dust extinction level of galaxies particularly when Balmer decrement is not available. By comparing AH? (derived with Balmer decrement) and AUV (derived with IR/UV luminosity ratio) for a subsample of galaxies for which AKARI far-infrared photometry is available, we demonstrate that more massive galaxies tend to have higher extra extinction towards the nebular regions compared to the stellar continuum light. Considering recent studies reporting smaller extra extinction towards nebular regions for high-redshift galaxies, we argue that the dust geometry within high-redshift galaxies resembles low-mass galaxies in the nearby Universe.

  10. NLTE Analysis of the Hot sdO Star Bd+284211: The UV Spectrum

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    We present a detailed analysis of the UV spectrum of the calibration star BD+284211 using high-quality spectra obtained with the HST and FUSE satellites. To this aim, we compare quantitatively the observed data with model spectra obtained from state-of-the-art non-LTE metal line-blanketed model atmospheres and synthetic spectra calculated with TLUSTY and SYNSPEC. We thus determine in a self-consistent way the abundances of 11 elements with well-defined lines in the UV. The derived abundances range from about solar to 1/10 solar and the overall quality of the derived spectral fits is very satisfying. Our analysis can be used to constrain rather tightly the effective temperature of BD+284211 to a value of Teff = 82,0005000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2-0.1+0.3. Assuming that the Hipparcos measurement for BD+284211 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+284211 is significantly less than the canonical value of 0.5 M? for a representative post-EHB star.

  11. The Lives and Deaths of Planets and Stars in the Value-Added UV Photon Catalog

    NASA Astrophysics Data System (ADS)

    Hogg, David

    The lives and deaths of planets and stars in the Value-Added UV Photon Catalog Over its lifetime, the GALEX satellite has detected nearly two trillion photons with its ultraviolet- sensitive, photon-counting detectors. This time-tagged data set remains largely unexplored time-variable science. This proposal is to extract and calibrate the full photon time stream from the GALEX raw data products and to use that time stream to make discoveries in two rapidlydeveloping areas of astrophysical research: exoplanets around hot white dwarf stars and prompt ultraviolet emission from supernovae. It is only around white dwarf stars that rocky planets in the habitable zone generate frequent eclipses at large depth and with high likelihood. Theories of planet formation and evolution, now confronted with heterogeneous exoplanet discoveries around main-sequence stars, make strong predictions about planets around white dwarf stars, establishing unique and sensitive tests for ultraviolet surveys. Almost every GALEX pointing contains a bright white dwarf in the field of view. This project would be the first ever photon-limited and ultraviolet search for exoplanet eclipses. A preliminary study by the proposers has discovered new white-dwarf--main-sequence-star eclipsing binaries (and confirmed known systems) using time-resolved GALEX images, but because a calibrated photon stream is not available, it has not been possible to reach the photon limit. This proposal is to calibrate the photon time stream and perform the first UV search for planets, moons and asteroids around white dwarfs and other blue stars. The project will produce a statistically complete sample of exoplanets around white dwarfs and a similarly complete sample of binary stars. Although any exoplanet system is interesting in its own right, the proposers will also produce a probabilistic estimate of the frequency with which stellar remnants host planets of different kinds at different radii. Supernovae models have long predicted a "shock breakout" flash or prompt emission at ignition. The first shock- breakout detection in the UV was discovered a few years ago, in GALEX data with poor time resolution. Models of the prompt emission during shock-breakout predict that a photonlimited search will detect new events in the calibrated photon time stream. Using the same data set as that produced for exoplanet discovery, these predictions will be tested. Once again, each such event is individually interesting, but another outcome is an estimate of the frequency as a function of flash and host-galaxy properties, especially fluence and redshift. This study will employ generative modeling of the photon time stream--explicit approximation of the probability of the data given the model--using the latest models for exoplanet transits and supernovae prompt flares. Essential for obtaining high purity is to compete these models with models of more mundane or alternative phenomena that are confusing, including stellar variability of various kinds and hardware artifacts. Early results indicate that candidate lists can be produced with high completeness and purity. In addition to the exoplanet and supernova deliverables, the project will produce a publicly available, curated photon time stream (coordinates and time of arrival for every GALEX photon) along with the spacecraft field-of-view and sensitivity information that make it useful. It will also produce improved spacecraft calibration information, including especially improved flat-field modeling in the focal plane, and a time- and position-dependent sky background rate estimate. The proposed scientific investigations and deliverable data products will permit new kinds of timedomain astrophysics projects (including many ex-post-facto studies), and improve dramatically the legacy value of all GALEX data

  12. Characterizing Dust Attenuation in Local Star-forming Galaxies: UV and Optical Reddening

    NASA Astrophysics Data System (ADS)

    Battisti, A. J.; Calzetti, D.; Chary, R.-R.

    2016-02-01

    The dust attenuation for a sample of ∼10,000 local (z ≲ 0.1) star-forming galaxies is constrained as a function of their physical properties. We utilize aperture-matched multiwavelength data available from the Galaxy Evolution Explorer and the Sloan Digital Sky Survey to ensure that regions of comparable size in each galaxy are being analyzed. We follow the method of Calzetti et al. and characterize the dust attenuation through the UV power-law index, β, and the dust optical depth, which is quantified using the difference in Balmer emission line optical depth, {τ }Bl={τ }{{H}β }-{τ }{{H}α }. The observed linear relationship between β and {τ }Bl is similar to the local starburst relation, but the large scatter (σint = 0.44) suggests that there is significant variation in the local universe. We derive a selective attenuation curve over the range 1250 Å < λ < 8320 Å and find that a single attenuation curve is effective for characterizing the majority of galaxies in our sample. This curve has a slightly lower selective attenuation in the UV compared to previously determined curves. We do not see evidence to suggest that a 2175 Å feature is significant in the average attenuation curve. Significant positive correlations are seen between the amount of UV and optical reddening and galaxy metallicity, mass, star formation rate (SFR), and SFR surface density. This provides a potential tool for gauging attenuation where the stellar population is unresolved, such as at high z.

  13. Effect of UV Radiation on the Spectral Fingerprints of Earth-like Planets Orbiting M Stars

    NASA Astrophysics Data System (ADS)

    Rugheimer, S.; Kaltenegger, L.; Segura, A.; Linsky, J.; Mohanty, S.

    2015-08-01

    We model the atmospheres and spectra of Earth-like planets orbiting the entire grid of M dwarfs for active and inactive stellar models with Teff = 2300 K to Teff = 3800 K and for six observed MUSCLES M dwarfs with UV radiation data. We set the Earth-like planets at the 1 AU equivalent distance and show spectra from the visible to IR (0.4-20 ?m) to compare detectability of features in different wavelength ranges with the James Webb Space Telescope and other future ground- and spaced-based missions to characterize exo-Earths. We focus on the effect of UV activity levels on detectable atmospheric features that indicate habitability on Earth, namely, H2O, O3, CH4, N2O, and CH3Cl. To observe signatures of lifeO2/O3 in combination with reducing species like CH4we find that early and active M dwarfs are the best targets of the M star grid for future telescopes. The O2 spectral feature at 0.76 ?m is increasingly difficult to detect in reflected light of later M dwarfs owing to low stellar flux in that wavelength region. N2O, another biosignature detectable in the IR, builds up to observable concentrations in our planetary models around M dwarfs with low UV flux. CH3Cl could become detectable, depending on the depth of the overlapping N2O feature. We present a spectral database of Earth-like planets around cool stars for directly imaged planets as a framework for interpreting future light curves, direct imaging, and secondary eclipse measurements of the atmospheres of terrestrial planets in the habitable zone to design and assess future telescope capabilities.

  14. Brucella ceti Infection in Harbor Porpoise (Phocoena phocoena)

    PubMed Central

    Brenez, Cecile; Fretin, David; Godfroid, Jacques; Haelters, Jan; Jacques, Thierry; Kerckhof, Francis; Mast, Jan; Sarlet, Michael; Coignoul, Freddy L.

    2010-01-01

    We describe Brucella sp. infection and associated lesions in a harbor porpoise (Phocoena phocoena) found on the coast of Belgium. The infection was diagnosed by immunohistochemistry, transmission electron microscopy, and bacteriology, and the organism was identified as B. ceti. The infections location in the porpoise raises questions of abortion and zoonotic risks. PMID:21122233

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

    NASA Technical Reports Server (NTRS)

    Lanning, Howard H.; Meakes, Michael

    1994-01-01

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

  16. Gamma-Ray Bursts Trace UV Metrics of Star Formation over 3 < z < 5

    NASA Astrophysics Data System (ADS)

    Greiner, J.; Fox, D. B.; Schady, P.; Krühler, T.; Trenti, M.; Cikota, A.; Bolmer, J.; Elliott, J.; Delvaux, C.; Perna, R.; Afonso, P.; Kann, D. A.; Klose, S.; Savaglio, S.; Schmidl, S.; Schweyer, T.; Tanga, M.; Varela, K.

    2015-08-01

    We present the first uniform treatment of long duration gamma-ray burst (GRB) host galaxy detections and upper limits over the redshift range 3star formation (SF). We contribute deep imaging observations of 13 GRB positions yielding the discovery of 8 new host galaxies. We use this data set in tandem with previously published observations of 31 further GRB positions to estimate or constrain the host galaxy rest-frame ultraviolet (UV; λ =1600 Å) absolute magnitudes MUV. We then use the combined set of 44 MUV estimates and limits to construct the MUV luminosity function (LF) for GRB host galaxies over 3-15.6 mag, and with extrapolations of the assumed Schechter-type LF well beyond this range. We review proposed astrophysical and observational biases for our sample, and find that they are for the most part minimal. We therefore conclude, as the simplest interpretation of our results, that GRBs successfully trace UV metrics of cosmic SF over the range 3star formation processes from z≈ 3 out to the highest redshifts. Partly based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under IDs 089.A-0120(A) and 091.A-0786(A).

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

    NASA Technical Reports Server (NTRS)

    Pesek, R.; Billingham, J.

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Oesch, Pascal

    2014-10-01

    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.

  20. Investigating H?, UV, and IR Star-formation Rate Diagnostics for a Large Sample of z ? 2 Galaxies

    NASA Astrophysics Data System (ADS)

    Shivaei, Irene; Reddy, Naveen A.; Steidel, Charles C.; Shapley, Alice E.

    2015-05-01

    We use a sample of 262 spectroscopically confirmed star-forming galaxies at redshifts 2.08?slant z?slant 2.51 to compare H?, ultraviolet (UV), and IR star formation rate (SFR) diagnostics and to investigate the dust properties of the galaxies. At these redshifts, the H? line shifts to the {{K}s} band. By comparing {{K}s}-band photometry to underlying stellar population model fits to other UV, optical, and near-infrared data, we infer the H? flux for each galaxy. We obtain the best agreement between H?- and UV-based SFRs if we assume that the ionized gas and stellar continuum are reddened by the same value and that the Calzetti attenuation curve is applied to both. Aided with MIPS 24 ?m data, we find that an attenuation curve steeper than the Calzetti curve is needed to reproduce the observed IR/UV ratios of galaxies younger than 100 Myr. Furthermore, using the bolometric SFR inferred from the UV and mid-IR data (SFRIR+SFRUV), we calculated the conversion between the H? luminosity and SFR to be (7.5+/- 1.3) {{10}-42} for a Salpeter initial mass function, which is consistent with the Kennicutt conversion. The derived conversion factor is independent of any assumption of the dust correction and is robust to stellar population model uncertainties.

  1. The effective temperature and surface gravity of the UV-bright star Barnard 29 of Messier 13

    NASA Technical Reports Server (NTRS)

    Adelman, Saul J.; Aikman, G. C. L.

    1987-01-01

    Comparison of optical region spectrophotometry, IUE low dispersion fluxes, and the H-gamma profile with the predictions of metal-poor model atmospheres were used to derive the photospheric parameters of the UV-bright star Barnard 29. These were found to be T(eff) - 20, 250 K, log g - 3.15 after the application of reddening corrections. A solar He/H ratio and the metallicity of Messier 13 were assumed.

  2. VizieR Online Data Catalog: Optical spectra of 7 hot UV bright stars in GC (Moehler+, 1998)

    NASA Astrophysics Data System (ADS)

    Moehler S., Landsman W., Napiwotzki R.

    2015-11-01

    Optical low-resolution spectra of 7 UV bright stars in globular clusters are presented together with the atmospheric parameters derived from them. The following globular clusters have been observed: NGC2808, NGC6121, NGC6723, NGC6752. The continuum of the spectra has ben normalized and they were resampled to laboratory wavelengths. Effective temperatures, surface gravities, and helium abundances were derived from line profile fits. (2 data files).

  3. On the Discovery of Massive ZZ Ceti Variables and the Peculiar Light Curve of SDSS J1529

    NASA Astrophysics Data System (ADS)

    Curd, Brandon; Kilic, Mukremin; Gianninas, Alex

    2016-01-01

    We report the discovery of pulsations in three hydrogen atmosphere white dwarfs with masses greater than one solar mass. We identified these white dwarfs through SDSS Data Release 7 spectroscopy. All three objects show monoperiodic oscillations with periods ranging from 203 s to 11 min. With follow-up observations of the confirmed ZZ Ceti stars, it should be possible to detect lower amplitude pulsation modes in order to conduct an in depth asteroseismological analysis and estimate the fraction of their core mass that is crystallized. We also present and discuss the peculiar light curve of J1529, which shows eclipse-like events every 38 min. We compare the light curve of J1529 to that of GD 394 which has similar characteristics (despite being four times hotter) which are thought to be caused by a metal-rich dark spot on the star's surface.

  4. Comparing FIR, UV and SED star formation rates for IR-luminous galaxies at 1?z?2 in CANDELS

    NASA Astrophysics Data System (ADS)

    Pforr, Janine; Dickinson, Mark; Kartaltepe, Jeyhan; Inami, Hanae; Penner, Kyle

    2015-08-01

    Galaxy formation and evolution studies rely on the robust determination of galaxy properties such as stellar masses and star formation rates (SFR). One the one hand these are important to distinguish between star bursting galaxies, normally star forming galaxies and those in the process of quenching and reveal the underlying processes causing these phenomena. On the other hand, they are crucial to derive reliable estimates of global properties like the star formation rate density of the Universe and the stellar mass assembly. We exploit the excellent multi-wavelength data in the GOODS-S, GOODS-N, UDS and COSMOS CANDELS fields ranging from deep ground and space-based optical data, deep-NIR HST data from CANDELS to the deepest FIR PACS data available from CANDELS-Herschel and Pep/GOODS-Herschel to estimate SFRs of IR-luminous galaxies between redshift 1 and 2. We determine SFRs in three different ways:1) from SED-fitting to the optical/IR multi-wavelength data, 2) from far-IR luminosities using 24 micron and Herschel PACS fluxes and 3) from UV slope and UV luminosity measurements. While for the majority of objects the different estimates agree very well, we find a subsample of outliers that are classified as pseudo-quiescent by the SED-fit. We present possible reasons for these misclassifications as well as potential remedies.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Smith, M. A.

    2012-10-01

    In this paper, we present a spectral atlas covering the wavelength interval 930-1188 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 949-1188. 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).

  7. Probing the Peak Epoch of Cosmic Star Formation (1Star-forming Galaxies Behind the Lensing Clusters: UV Luminosity Function and the Dust Attenuation

    NASA Astrophysics Data System (ADS)

    Alavi, Anahita; Siana, Brian D.; Richard, Johan; Rafelski, Marc; Jauzac, Mathilde; Limousin, Marceau; Stark, Daniel; Teplitz, Harry I.

    2016-01-01

    Obtaining a complete census of cosmic star formation requires an understanding of faint star-forming galaxies that are far below the detection limits of current surveys. To search for the faint galaxies, we use the power of strong gravitational lensing from foreground galaxy clusters to boost the detection limits of HST to much fainter luminosities. Using the WFC3/UVIS on board the HST, we obtain deep UV images of 4 lensing clusters with existing deep optical and near-infrared data (three from Frontier Fields survey). Building multiband photometric catalogs and applying a photometric redshift selection, we uncover a large population of dwarf galaxies (-18.5star formation (1star-forming galaxies keeps increasing steeply toward very faint magnitudes (MUV=-12.5). As an important implication of a steep faint-end slope LF, we show that the faint galaxies (-18.5UV background (>50%) at these redshifts. We use this unique sample to investigate further the various properties of dwarf galaxies as it is claimed to deviate from the trends seen for the more massive galaxies. Recent hydro-dynamical simulations and observations of local dwarfs show that these galaxies have episodic bursts of star formation on short time scales (< 10 Myr). We find that the bursty star formation histories (SFHs) cause a large intrinsic scatter in UV colors (β) at MUV > -16, comparing a sample of low mass galaxies from simulations with bursty SFHs with our comprehensive measurements of the observed β values. As this scatter can also be due to the dust extinction, we distinguish these two effects by measuring the dust attenuation using Balmer decrement (Hα/Hβ) ratios from our MOSFIRE/Keck spectroscopy.

  8. Measuring the Evolutionary Rate of Cooling of ZZ Ceti

    NASA Astrophysics Data System (ADS)

    Mukadam, Anjum S.; Bischoff-Kim, Agnes; Fraser, Oliver; Crsico, 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

    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.

  9. The MOSDEF Survey: The Strong Agreement between Hα and UV-to-FIR Star Formation Rates for z ~ 2 Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Shivaei, Irene; Kriek, Mariska; Reddy, Naveen A.; Shapley, Alice E.; Barro, Guillermo; Conroy, Charlie; Coil, Alison L.; Freeman, William R.; Mobasher, Bahram; Siana, Brian; Sanders, Ryan; Price, Sedona H.; Azadi, Mojegan; Pasha, Imad; Inami, Hanae

    2016-04-01

    We present the first direct comparison between Balmer line and panchromatic spectral energy distribution (SED)-based star formation rates (SFRs) for z∼ 2 galaxies. For this comparison, we used 17 star-forming galaxies selected from the MOSFIRE Deep Evolution Field (MOSDEF) survey, with 3σ detections for Hα and at least two IR bands (Spitzer/MIPS 24 μm and Herschel/PACS 100 and 160 μm, and in some cases Herschel/SPIRE 250, 350, and 500 μm). The galaxies have total IR (8–1000 μm) luminosities of ∼ {10}11.4{--}{10}12.4 {L}ȯ and SFRs of ∼ 30{--}250 {M}ȯ {{yr}}-1. We fit the UV-to-far-IR SEDs with flexible stellar population synthesis (FSPS) models—which include both stellar and dust emission—and compare the inferred SFRs with the SFR(Hα, Hβ) values corrected for dust attenuation using Balmer decrements. The two SFRs agree with a scatter of 0.17 dex. Our results imply that the Balmer decrement accurately predicts the obscuration of the nebular lines and can be used to robustly calculate SFRs for star-forming galaxies at z∼ 2 with SFRs up to ∼ 200 {M}ȯ {{yr}}-1. We also use our data to assess SFR indicators based on modeling the UV-to-mid-IR SEDs or by adding SFR(UV) and SFR(IR), for which the latter is based on the mid-IR only or on the full IR SED. All these SFRs show a poorer agreement with SFR(Hα, Hβ) and in some cases large systematic biases are observed. Finally, we show that the SFR and dust attenuation derived from the UV-to-near-IR SED alone are unbiased when assuming a delayed exponentially declining star formation history. Based on observations made with the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration.

  10. Radiation-driven winds of hot luminous stars. 12: A first step towards detailed UV-line diagnostics of O-stars

    NASA Astrophysics Data System (ADS)

    Pauldrach, A. W. A.; Kudritzki, R. P.; Puls, J.; Butler, K.; Hunsinger, J.

    1994-03-01

    Improved radiation driven wind models are constructed to calculate detailed synthetic UV spectra of hot luminous stars. The model improvements comprise: a very detailed multilevel non-local thermodynamic equilibrium (NLTE) treatment of 29 of the most important ionization stages, in particular C, N, O and Fe using accurate atomic data; the approximate inclusion of EUV radiation by shock heated matter in the ionization rates and a simple simulation of photospheric line blocking. The direct ionization by EUV shock radiation has important effects on the lines of the highest ionization stages, whereas line blocking is needed to reproduce the lowest stages of ionization that are observed. A detailed comparison between observed and calculated synthetic spectra of two O-stars, zeta Puppis in the Galaxy and Melnick 42 in the LMC, has been carried out.

  11. The grey extinction and starburst-like dust in the star cluster NGC 3603 from UV to optical

    NASA Astrophysics Data System (ADS)

    Pang, Xiaoying; Pasquali, Anna; Grebel, Eva K.

    2015-08-01

    The young massive star cluster NGC 3603 hosts 10 times more OB stars than the Orion Nebula Cluster. The strong radiation field of OB stars ionizes and sweeps away the ISM, and generates a cavity around the cluster where the gas reddening is lowest (Pang et al. 2011). To investigate the dust grains properties in NGC 3603, we use photometry in the F220W, F250W, F330W, F435W filters from the HRC/ACS/HST and photometry in the F555W, F675W, and F814W filters from the WFPC2/HST to derive individual stellar reddenings and extinctions for stars inside the cluster. The mean reddening and visual extinction for about a hundred main-sequence member stars inside the cluster is E(F435W-F555W)=1.33±0.12 mag and A(F555W)=4.72±0.10 mag, respectively. After correcting for foreground reddening, the total to selective extinction ratio is R(F555W)=3.75±0.87 in the cluster. The variation of A(F555W) and R(F555W) is larger in the innermost region than in the outer part, implying that the column density of dust within NGC 3603 and possibly the size of dust grains vary along different lines of sight, resulting in a clumpy dust distribution across the cluster. This could be the result of stellar feedback from massive stars, which is destroying small grains to make the size distribution in favour of large grains, or grows small grains by condensing material onto their surface (De Marchi et al. 2013). The cluster extinction curve [E(λ - F555W)/E(F435W - F555W)] at UV wavelengths tends to be greyer than the average Galactic extinction laws from Cardelli et al. (1989) and Fitzpatrick et al. (1999). It is closer to the extinction law derived by Calzetti et al. (2000) for starburst galaxies, where the 0.2175 μm bump is absent. Previous studies found that the strength of the 0.2175 μm bump decreases when dust is mostly composed of large grains, which absorb less UV radiation than smaller grains (Pierini et al. 2005). This indicates an anomalous extinction in NGC 3603, which may due to the clumpy dust distribution within the cluster, and the size of dust grains being larger than the average Galactic ISM. Further UV observations (λ<2000A) are needed in order to quantify the size distribution of dust grains in NGC 3606.

  12. Utilizing Synthetic Spectra to Refine Lambda Boo Stars' UV Classification Criteria

    NASA Astrophysics Data System (ADS)

    Cheng, Kwang-Ping; Neff, James E.; Johnson, Dustin; Tarbell, Erik; Romo, Christopher; Steele, Patricia; Gray, Richard O.; Corbally, Christopher J.

    2016-01-01

    Lambda Boo-type stars are a group of late B to early F-type Population I dwarfs that show deficiencies of iron-peak elements (up to 2 dex), but their C, N, O, and S abundances are near solar. This stellar class has recently regained the spotlight because of the directly-imaged planets around a confirmed Lambda Boo star, HR 8799, and a suggested Lambda Boo star Beta Pictoris. The discovery of a giant asteroid belt around Vega, another possible Lambda Boo star, also suggests hidden planets. This possible link between Lambda Boo stars and planet-bearing stars motivates us to study Lambda Boo stars systematically. Since the peculiar nature of the prototype Lambda Bootis was first noticed in 1943, Lambda Boo candidates published in the literature have been selected using widely different criteria. The Lambda Boo label has been applied to almost any peculiar A-type stars that do not fit elsewhere. In order to determine the origin of Lambda Boo stars' unique abundance pattern and to better discriminate between theories explaining the Lambda Boo phenomenon, a consistent working definition of Lambda Boo stars is needed. We have re-evaluated all published Lambda Boo candidates and their available ultraviolet and visible spectra. Using observed and synthetic spectra, we explored the classification of Lambda Boo stars and developed quantitative criteria that discriminate metal-poor stars from bona fide Lambda Boo stars. With model spectra, we demonstrated that the (C I 1657 Angstrom)/ (Al II 1671 Angstrom) line ratio is the best single criterion to distinguish between Lambda Boo stars and metal weak stars, and that one cannot use a single C I/Al II cut-off value as a Lambda Boo classification criterion. The C I/Al II cut-off value is a function of a star's effective temperature and metallicity. Using these stricter Lambda Boo classification criteria, we concluded that neither Beta Pictoris nor Vega should be classified as Lambda Boo stars.

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Vander Haagen, G. A.

    2013-11-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  16. 3D-HST emission line galaxies at z ∼ 2: discrepancies in the optical/UV star formation rates

    SciTech Connect

    Zeimann, Gregory R.; Ciardullo, Robin; Gebhardt, Henry; Gronwall, Caryl; Schneider, Donald P.; Hagen, Alex; Bridge, Joanna S.; Trump, Jonathan R.; Feldmeier, John

    2014-08-01

    We use Hubble Space Telescope near-IR grism spectroscopy to examine the Hβ line strengths of 260 star-forming galaxies in the redshift range 1.90 < z < 2.35. We show that at these epochs, the Hβ star formation rate (SFR) is a factor of ∼1.8 higher than what would be expected from the systems' rest-frame UV flux density, suggesting a shift in the standard conversion between these quantities and SFR. We demonstrate that at least part of this shift can be attributed to metallicity, as Hβ is more enhanced in systems with lower oxygen abundance. This offset must be considered when measuring the SFR history of the universe. We also show that the relation between stellar and nebular extinction in our z ∼ 2 sample is consistent with that observed in the local universe.

  17. A New Analysis of the Two Classical ZZ Ceti White Dwarfs GD 165 and Ross 548. I. Photometry and Spectroscopy

    NASA Astrophysics Data System (ADS)

    Giammichele, N.; Fontaine, G.; Bergeron, P.; Brassard, P.; Charpinet, S.; Pfeiffer, B.; Vauclair, G.

    2015-12-01

    We present the first of a two-part seismic analysis of the two bright hot ZZ Ceti stars GD 165 and Ross 548. In this first part, we report the results of frequency extraction exercises based on time-series data sets of exceptional quality. We uncovered up to 13 independent pulsation modes in GD 165, regrouped into six main frequency multiplets. These include 9 secure (signal-to-noise ratio, S/N > 4) detections and 4 possible ones (4 ≥ S/N ≥ 3). Likewise, we isolated 11 independent modes in Ross 548 (9 secure and 2 possible detections), also regrouped into 6 multiplets. The multiplet structure is likely caused by rotational splitting. We also provide updated estimates of the time-averaged atmospheric properties of these two pulsators in the light of recent developments on the front of atmospheric modeling for DA white dwarfs.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    Context. Study of the dust extinction in high-redshift galaxies is fundamental to obtaining an estimate of the corrected star formation rate density (SFRD) and to put constraints on galaxy evolution models. Aims: We plan to analyse dust extinction in Lyman break galaxies (LBGs) by introducing a new and more reliable approach to their selection and to the characterization of their distribution of UV slopes ?, using deep IR images from HST. We fully discuss the methodology and the results, focusing on a robust sample of z ~ 4 LBGs. Methods: We exploit deep WFC3 IR observations of the ERS and HUDF fields over GOODS-South, combined with HST-ACS optical data, to select z ~ 4 LBGs through a new (B - V) vs. (V - H) colour diagram. The UV slope of the selected galaxies is robustly determined by a linear fit over their observed I,Z,Y,J magnitudes, coherently with the original definition of ?. The same fit is used to determine their rest-frame UV magnitudes M1600 through a simple interpolation. We estimate the effect of observational uncertainties with detailed simulations that we also exploit, under a parametric maximum-likelihood approach, to constrain the probability density function of UV slopes PDF(?) as a function of rest-frame magnitude. Results: We find 142 robust LBGs in the ERS and 25 in the HUDF field, limiting our sample to S/N(H) > 10 objects. Our newly defined criteria improve the selection of z ~ 4 LBGs and allow us to exclude red interlopers at lower redshifts, especially z ~ 3-3.5 objects. We show that using a linear fit to estimate ? and accurately characterizing observational effects are required in this kind of analysis of flux-limited samples. We find that z ~ 4 LBGs are characterized by blue UV slopes, suggesting a low dust extinction: all L < L? galaxies have an average UV slope ??? ? -2.1, while brighter objects are only slightly redder (??? ? -1.9). We find an intrinsic dispersion ?0.3 for PDF(?) at all magnitudes. The SFRD at z ~ 4 corrected according to these estimates turns out to be lower than previously found: log(SFRD) ? -1.09 M?/yr/Mpc3. Finally, we discuss how the UV slope of z ~ 4 galaxies changes as a function of the dust-corrected UV magnitude (i.e. SFR). We show that most galaxies with high SFR (?80 M?/yr) are highly extincted objects. Among galaxies with lower SFR, we detect many with a much lower amount of reddening, although current observational limits prevent us from detecting those with high extinction, if they exist.

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

    EPA Science Inventory

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  1. The MUSCLES Treasury Survey: Intrinsic Lyα Profile Reconstructions and UV, X-ray, and Optical Correlations of Low-mass Exoplanet Host Stars

    NASA Astrophysics Data System (ADS)

    Youngblood, Allison; France, Kevin; Parke Loyd, R. O.

    2016-01-01

    UV stellar radiation can significantly impact planetary atmospheres through heating and photochemistry, even regulating production of potential biomarkers. Cool stars emit the majority of their UV radiation in the form of emission lines, and the incident UV radiation on close-in habitable-zone planets is significant. Lyα (1215.67 Å) dominates the 912 - 3200 Å spectrum of cool stars, but strong absorption from the interstellar medium (ISM) makes direct observations of the intrinsic Lyα emission of even nearby stars challenging. The MUSCLES Hubble Space Telescope Treasury Survey (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems) has completed observations of 7 M and 4 K stars hosting exoplanets (d < 22 pc) with simultaneous X-ray and ground-based optical spectroscopy for many of the targets. We have reconstructed the intrinsic Lyα profiles using an MCMC technique and used the results to estimate the extreme ultraviolet (100 - 911 Å) spectrum. We also present empirical relations between chromospheric UV and optical lines, e.g., Lyα, Mg II, Ca II H & K, and Hα, for use when direct UV observations of low-mass exoplanet host stars are not possible. The spectra presented here will be made publicly available through MAST to support exoplanet atmosphere modeling.

  2. A Non-LTE Analysis of the Hot Subdwarf O Star BD+284211. I. The UV Spectrum

    NASA Astrophysics Data System (ADS)

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

    2013-08-01

    We present a detailed analysis of the UV spectrum of the calibration star BD+284211 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+284211 to a value of T eff = 82, 000 5000 K. We also estimate conservatively that its surface gravity falls in the range log g = 6.2_{-0.1}^{+0.3}. Assuming that the Hipparcos measurement for BD+284211 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+284211 is significantly less than the canonical value of 0.5 M ? for a representative post-extended horizontal branch star.

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  4. MEASURING THE EVOLUTIONARY RATE OF COOLING OF ZZ Ceti

    SciTech Connect

    Mukadam, Anjum S.; Fraser, Oliver; Riecken, T. S.; Kronberg, M. E.; Bischoff-Kim, Agnes; Corsico, A. H.; Montgomery, M. H.; Winget, D. E.; Hermes, J. J.; Winget, K. I.; Falcon, Ross E.; Reaves, D.; Kepler, S. O.; Romero, A. D.; Chandler, D. W.; Kuehne, J. W.; Sullivan, D. J.; Von Hippel, T.; Mullally, F.; Shipman, H.; and others

    2013-07-01

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

  5. Isolation of Brucella ceti from a Long-finned Pilot Whale (Globicephala melas) and a Sowerby's Beaked Whale (Mesoploden bidens).

    PubMed

    Foster, Geoffrey; Whatmore, Adrian M; Dagleish, Mark P; Baily, Johanna L; Deaville, Rob; Davison, Nicholas J; Koylass, Mark S; Perrett, Lorraine L; Stubberfield, Emma J; Reid, Robert J; Brownlow, Andrew C

    2015-10-01

    Brucella ceti is an emerging zoonotic pathogen that has been recovered from several species of cetaceans in the world's oceans over the past 20 yr. We report the recovery of B. ceti from a Sowerby's beaked whale (Mesoploden bidens) and a long-finned pilot whale (Globicehala melas). Recovery from the testis of a long-finned pilot whale provides further evidence of potential for B. ceti infection to impact the reproductive success of cetaceans, many of which are threatened species. The addition of another two cetacean species to the growing number from which B. ceti has been recovered also further emphasizes the concern for human infections with this organism. PMID:26285099

  6. Enhanced optical transmission through a star-shaped bull's eye at dual resonant-bands in UV and the visible spectral range.

    PubMed

    Nazari, Tavakol; Khazaeinezhad, Reza; Jung, Woohyun; Joo, Boram; Kong, Byung-Joo; Oh, Kyunghwan

    2015-07-13

    Dual resonant bands in UV and the visible range were simultaneously observed in the enhanced optical transmission (EOT) through star-shaped plasmonic structures. EOTs through four types of polygonal bull's eyes with a star aperture surrounded by the concentric star grooves were analyzed and compared for 3, 4, 5, and 6 corners, using finite difference time domain (FDTD) method. In contrast to plasmonic resonances in the visible range, the UV-band resonance intensity was found to scale with the number of corners, which is related with higher order multipole interactions. Spectral positions and relative intensities of the dual resonances were analyzed parametrically to find optimal conditions to maximize EOT in UV-visible dual bands. PMID:26191917

  7. UV Snapshot of Low-redshift Massive Star-forming Galaxies: Searching for the Analogs of High-redshift Clumpy Galaxies

    NASA Astrophysics Data System (ADS)

    Guo, Yicheng

    2013-10-01

    Most galaxies at z>1 with Milky Way stellar masses are actively forming stars at rates 10-100x higher than that of our Milky Way. More surprising was the discovery that most of the star formation resides among giant star-forming clumps. The origin, properties, and evolution of these clumps remain under debate, yet they are vital to our understanding of initial bulge formation, the evolution of early gas-rich disks, and the cold gas accretion history of galaxies. Because these clumps are often visible only in the rest-frame UV, they are easily detected in observed optical images of high redshift galaxies. But at low redshifts {0.05star-forming clumps is only possible with HST UV imaging. The number of current identified clumpy galaxies at 0.05star formation from high redshifts to today. To remedy this deficiency, we propose an UV snapshot survey to image a representative sample of 136 massive star-forming galaxies at 0.05star formation {SF} within these clumpy galaxies. HST's access to deep UV imaging at the required high-spatial resolution to detect and resolve local clumps is unique. The high-resolution UV images of our sample will serve as an invaluable legacy dataset for further extragalactic studies for years to come.

  8. Total ozone measured during EASOE by a UV-visible spectrometer which observes stars

    SciTech Connect

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

    1994-06-22

    This paper presents the results of ground based measurement of column ozone from Abisko, Sweden (68.4[degrees]N), by means of a novel absorption spectroscopy technique. The instrument uses starlight, and moon glow as sources of UV and visible light for the absorption technique. These measurements were compared with ozonesonde measurements, and with space borne instruments.

  9. (F)UV spectral analysis of 15 extremely hot, hydrogen-rich central stars of planetary nebulae

    NASA Astrophysics Data System (ADS)

    Ziegler, Marc; Rauch, Thomas; Werner, Klaus; Kruk, Jeffrey W.

    2012-08-01

    We present results of a (F)UV spectral analysis of 15 hot, hydrogen-rich central stars of planetary nebulae (CSPNe) of DAO-type (A 7, A 31, A 35, A 39, NGC 3587, NGC 6720, NGC 6853, NGC 7293, PuWe 1, Sh 2-174) and O(H)-type (A 36, Lo 1, LSS 1362, NGC 1360, NGC 4361). The sample covers a wide range of parameters (T eff ~ 70-130 kK, log g = 5.4-7.4). It represents different stages of post-AGB evolution. The derived stellar parameters are crucial constraints for AGB nucleosynthesis and stellar evolutionary calculations. Detailed spectral analyses using fully line-blanketed NLTE model atmospheres including 23 elements from hydrogen to nickel are performed. Additional modeling of the ISM line absorption enables to unambigiously identify nearly all observed lines and to improve both, the photospheric as well as the ISM model.

  10. The star formation rate cookbook at 1 < z < 3: Extinction-corrected relations for UV and [OII]?3727 luminosities

    NASA Astrophysics Data System (ADS)

    Talia, M.; Cimatti, A.; Pozzetti, L.; Rodighiero, G.; Gruppioni, C.; Pozzi, F.; Daddi, E.; Maraston, C.; Mignoli, M.; Kurk, J.

    2015-10-01

    Aims: In this paper we use a well-controlled spectroscopic sample of galaxies at 1 star formation rate (SFR) estimators. In particular, we use infrared (IR) data to derive empirical calibrations to correct ultraviolet (UV) and [OII]?3727 luminosities for dust extinction and dust-corrected estimates of SFR. Methods: We selected 286 star-forming galaxies with spectroscopic redshift 1 UV and [OII]?3727 luminosities for dust extinction. Results: Through the analyses of the correlations between different dust attenuation probes, a set of relations is provided that allows the recovery of the total unattenuated SFR for star-forming galaxies at 1 UV and [OII]?3727 luminosities. The relation between AIRX and UV continuum slope (?) was tested for our sample and found to be broadly consistent with the literature results at the same redshift, though with a larger dispersion with respect to UV-selected samples. We find a correlation between the rest-frame equivalent width of the [OII]?3727 line and ?, which is the main result of this work. We therefore propose the rest-frame equivalent width of the [OII]?3727 line as a dust attenuation probe and calibrate it through AIRX, though the assumption of a reddening curve is still needed to derive the actual attenuation towards the [OII]?3727 line (A[OII]). We tested the issue of differential attenuation towards stellar continuum and nebular emission: our results are in line with the traditional prescription of extra attenuation towards nebular lines. Finally, we use our set of cross-calibrated SFR estimates to look at the relation between SFR and stellar mass. The galaxies in our sample show a close linear relation (? = 0.3 dex) at all redshifts with a slope ~0.7-0.8, which confirms several previous results. Appendix A is available in electronic form at http://www.aanda.org

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  12. A New Analysis of the Two Classical ZZ Ceti White Dwarfs GD 165 and Ross 548. II. Seismic Modeling

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    We present the second of a two-part seismic analysis of the bright, hot ZZ Ceti stars GD 165 and Ross 548. In this second part, we report the results of detailed searches in parameter space for identifying an optimal model for each star that can account well for the observed periods, while being consistent with the spectroscopic constraints derived in our first paper. We find optimal models for each target that reproduce the six observed periods well within ∼0.3% on the average. We also find that there is a sensitivity on the core composition for Ross 548, while there is practically none for GD 165. Our optimal model of Ross 548, with its thin envelope, indeed shows weight functions for some confined modes that extend relatively deep into the interior, thus explaining the sensitivity of the period spectrum on the core composition in that star. In contrast, our optimal seismic model of its spectroscopic sibling, GD 165 with its thick envelope, does not trap/confine modes very efficiently, and we find weight functions for all six observed modes that do not extend into the deep core, hence accounting for the lack of sensitivity in that case. Furthermore, we exploit after the fact the observed multiplet structure that we ascribe to rotation. We are able to map the rotation profile in GD 165 (Ross 548) over the outermost ∼20% (∼5%) of its radius, and we find that the profile is consistent with solid-body rotation.

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

    NASA Technical Reports Server (NTRS)

    Stecker, Floyd W.

    2006-01-01

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

  14. Constraints on hot star X-ray source characteristics from combinded analysis of X-ray and UV observations

    NASA Technical Reports Server (NTRS)

    Macfarlane, J. J.

    1994-01-01

    Results from wind ionization calculations are presented which show how the P-Cygni profiles of 'superionized' species such as O VI can provide information about the X-ray source characteristics of early-type stars. Using detailed radiative and atomic physics models, we find that a significant source of X-ray emission from zeta Pup comes from a region in the wind located within rougly 1 to 2 stellar radii of the photosphere. Our results suggest that X-rays sources in which emission occurs exclusively at large radii (r greater than or approximately equal to a few R(sub *)) are inconsistent with UV P-Cygni profiles for O VI. Instead, we find that X-ray emission from shocks distributed throughout the lower regions of the wind (r approximately equal to 1-2 R(sub *)) is consistent with both X-ray and UV data, as well as mass loss rates deduced from radio and H-alpha observations.

  15. Dust Attenuation of the Nebular Regions of z ~ 2 Star-forming Galaxies: Insight from UV, IR, and Emission Lines

    NASA Astrophysics Data System (ADS)

    De Barros, S.; Reddy, N.; Shivaei, I.

    2016-04-01

    We use a sample of 149 spectroscopically confirmed UV-selected galaxies at z ∼ 2 to investigate the relative dust attenuation of the stellar continuum and the nebular emission lines. For each galaxy in the sample, at least one rest-frame optical emission line (Hα/[N ii] λ6583 or [O iii] λ5007) measurement has been taken from the litterature, and 41 galaxies have additional Spitzer/MIPS 24 μm observations that are used to infer infrared luminosities. We use a spectral energy distribution (SED) fitting code that predicts nebular line strengths when fitting the stellar populations of galaxies in our sample, and we perform comparisons between the predictions of our models and the observed/derived physical quantities. We find that on average our code is able to reproduce all the physical quantities (e.g., UV β slopes, infrared luminosities, emission line fluxes), but we need to apply a higher dust correction to the nebular emission compared to the stellar emission for the largest star formation rate (SFR) (log SFR/M⊙ yr‑1 > 1.82, Salpeter initial mass function). We find a correlation between SFR and the difference in nebular and stellar color excesses, which could resolve the discrepant results regarding nebular dust correction at z ∼ 2 from previous studies.

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

    PubMed

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

    2015-02-01

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

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

    NASA Astrophysics Data System (ADS)

    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

    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.

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

    NASA Astrophysics Data System (ADS)

    Kawka, A.; Vennes, S.; O'Toole, S.; Nmeth, P.; Burton, D.; Kotze, E.; Buckley, D. A. H.

    2015-07-01

    We have measured the orbital parameters of seven close binaries, including six new objects, in a radial velocity survey of 38 objects comprising a hot subdwarf star with orbital periods ranging from 0.17 to 3 d. One new system, GALEX J2205-3141, shows reflection on an M dwarf companion. Three other objects show significant short-period variations, but their orbital parameters could not be constrained. Two systems comprising a hot subdwarf paired with a bright main-sequence/giant companion display short-period photometric variations possibly due to irradiation or stellar activity and are also short-period candidates. All except two candidates were drawn from a selection of subluminous stars in the Galaxy Evolution Explorer ultraviolet sky survey. Our new identifications also include a low-mass subdwarf B star and likely progenitor of a low-mass white dwarf (GALEX J0805-1058) paired with an unseen, possibly substellar, companion. The mass functions of the newly identified binaries imply minimum secondary masses ranging from 0.03 to 0.39 M?. Photometric time series suggest that, apart from GALEX J0805-1058 and J2205-3141, the companions are most likely white dwarfs. We update the binary population statistics: close to 40 per cent of hot subdwarfs have a companion. Also, we found that the secondary mass distribution shows a low-mass peak attributed to late-type dwarfs, and a higher mass peak and tail distribution attributed to white dwarfs and a few spectroscopic composites. Also, we found that the population kinematics imply an old age and include a few likely halo population members.

  19. UV Absorption Lines as Metallicity Estimator and the Metal Content of Star-forming Galaxies at z=5

    NASA Astrophysics Data System (ADS)

    Faisst, Andreas; Capak, Peter L.; Davidson, Iary; Kakazu, Yuko; Salvato, Mara; Laigle, Clotilde; Onodera, Masato; Masters, Daniel; COSMOS Team

    2016-01-01

    Probing the metal content of high redshift galaxies is essential to study their formation and evolution in the early universe. However, the spectral features used to measure the metallicity are shifted out of the wavelength range of current spectrographs at high-z and therefore alternative methods must be used.We measure the relation between four prominent UV absorption complexes and metallicity for more than 50 local galaxies and, by using a sample of more than 20 galaxies at z ~ 2 - 3, verify that this relation holds up to z ˜ 3. We then apply this method to a sample of ˜ 220 galaxies at 3.5 < z < 6.0 in COSMOS, for which unique UV spectra from DEIMOS and accurate stellar mass estimates from SPLASH are available. The z ~ 5 galaxies at 9 < log(m/M⊙) < 11 are characterized by 0.3 - 0.4 dex (in units of 12 + log(O/H)) lower metallicities than galaxies at z ˜ 2 but comparable to z ˜ 3 - 3.5 galaxies. In the same stellar mass range, we do not find a significant relation between stellar mass and metallicity (MZ relation), suggesting that the MZ relation at z ~ 5 is very shallow or breaking down. Since we verify a correlation between dust obscuration (measured by β) and UV absorption strength (i.e., metallicity), we argue that the process of dust production and metal enrichment in the first billion years of galaxy formation is more stochastic than at later times. Using a "bathtub" model approach, we find that an exponential build up of stellar mass within a short time of several 100 Myr can explain a shallow MZ relation at z ˜ 5. Furthermore, we find a weak anti-correlation between star-formation rates and UV absorption strength (i.e., metallicity), indicative of these galaxies being fueled by the inflow of pristine (metal-poor) gas. The galaxy sample presented in this work is unique to further test these scenarios using ALMA and the upcoming James Webb Space Telescope.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

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

    SciTech Connect

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

    2013-07-01

    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.

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

    PubMed

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

    2013-07-01

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

  3. The outer disks of Herbig stars from the UV to NIR

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

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

  4. GalevNB: a conversion from N-BODY simulations to observations—its application on the study of UV-excess in star clusters

    NASA Astrophysics Data System (ADS)

    Pang, Xiaoying; Olczak, Christoph; Guo, Difeng; Spurzem, Rainer

    2015-08-01

    We present GalevNB (Galev for N-body simulations), an utility that converts fundamental stellar properties of N-body simulations into observational properties using the GALEV (GAlaxy EVolutionary synthesis models) package, and thus allowing direct comparisons between observations and N-body simulations. It works by converting fundamental stellar properties, such as stellar mass, temperature, luminosity and metallicity into observational magnitudes for a variety of filters of mainstream instruments/telescopes, such as HST, ESO, SDSS, 2MASS, etc., and into spectra that spans from far-UV (90 Å) to near-IR (160 μm). As an application, we use GalevNB to investigate the secular evolution of spectral energy distribution (SED) and color-magnitude diagram (CMD) of a simulated star cluster over a few hundred million years. The model cluster in this work is evolved using the most recent version of NBODY6++ utilizing many GPU cores in parallel to accelerate multi-node multi-core simulations (Wang et al. 2015), which is the MPI parallel version based on the state-of-the-art direct N-body integrator NBODY6GPU. With the results given by GalevNB, we discover an UV-excess in the integrated SED of the cluster over the whole simulation time. We also identify four candidates that contribute to the FUV peak, core helium burning stars, thermal pulsing asymptotic giant branch (TPAGB) stars, white dwarfs and naked helium stars. Among them, TAGB is a favorable candidate from theoretical point of view (O’connell 1999). On the contrary, white dwarf’s candidate position is controversial (Magris & Bruzual 1993, Landsman et al. 1998) because of low luminosity. The life time of massive star descendants: core helium burning stars and naked helium stars, is very short. Though both of they are very bright at the UV at the early age, their short-term emission makes them become insignificant candidates.

  5. 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

    Bouwens, R. J.; Franx, M.; Labbe, I.; Smit, R.; Illingworth, G. D.; Oesch, P.A.; Gonzalez, V.; Magee, D.; Van Dokkum, P.; Carollo, C. M.

    2012-08-01

    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.

  6. THE UV CONTINUUM OF z > 1 STAR-FORMING GALAXIES IN THE HUBBLE ULTRAVIOLET ULTRADEEP FIELD

    SciTech Connect

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

    2014-09-20

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

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

    SciTech Connect

    Ian Short, C.; Campbell, Eamonn A.; Pickup, Heather; Hauschildt, Peter H. E-mail: yeti@hs.uni-hamburg.de

    2012-03-10

    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.

  8. Analysis of flares in the chromosphere and corona of main- and pre-main-sequence M-type stars

    NASA Astrophysics Data System (ADS)

    Crespo-Chacón, I.

    2015-11-01

    This Ph.D. Thesis revolves around flares on main- and pre-main-sequence M-type stars. We use observations in different wavelength ranges with the aim of analysing the effects of flares at different layers of stellar atmospheres. In particular, optical and X-ray observations are used so that we can study how flares affect, respectively, the chromosphere and the corona of stars. In the optical range we carry out a high temporal resolution spectroscopic monitoring of UV Ceti-type stars aimed at detecting non-white-light flares (the most typical kind of solar flares) in stars other than the Sun. With these data we confirm that non-white-light flares are a frequent phenomenon in UV Ceti-type stars, as observed in the Sun. We study and interpret the behaviour of different chromospheric lines during the flares detected on AD Leo. By using a simplified slab model of flares (Jevremović et al. 1998), we are able to determine the physical parameters of the chromospheric flaring plasma (electron density and electron temperature), the temperature of the underlying source, and the surface area covered by the flaring plasma. We also search for possible relationships between the physical parameters of the flaring plasma and other properties such as the flare duration, area, maximum flux and released energy. This work considerably extends the existing sample of stellar flares analysed with good quality spectroscopy in the optical range. In X-rays we take advantage of the great sensitivity, wide energy range, high energy resolution, and continuous time coverage of the EPIC detectors - on-board the XMMNewton satellite - in order to perform time-resolved spectral analysis of coronal flares. In particular, in the UV Ceti-type star CC Eri we study two flares that are weaker than those typically reported in the literature (allowing us to speculate about the role of flares as heating agents of stellar atmospheres); while in the pre-main-sequence M-type star TWA 11B (with no signatures of having an accretion disk) we carry out a detailed analysis of an extremely long rise phase and of a shorter, weaker flare (allowing us to compare the results with those reported for young stars but surrounded by disks). Assuming multitemperature models to describe the coronal flaring plasma, we have calculated the metal abundance, the electron temperatures and the respective emission measures by fitting the spectra with the Astrophysical Plasma Emission Code included in the XSPEC software, which calculates spectral models for hot, optically thin plasmas. Moreover, we are able to estimate the size of the flaring loops by using theoretical models. These sizes give us an idea about the extent of the corona. For those flares in which heating does not entirely drive the flare evolution we use the models reported by Reale (2007) and Reale et al. (1997) for the rise and decay phases, respectively, including the effect of sustained heating during the decay. Instead, the stellar version of the Kopp & Poletto (1984)'s solar two-ribbon flare model (Poletto et al. 1988) is used when the residual heating completely drives the flare over the plasma cooling. Later, we apply the so-called RTV scaling laws (Rosner et al. 1978) and other fundamental laws of physics to determine additional characteristics of the plasma contained in the flaring loops (electron density and pressure), as well as the volume of the flaring region, the heating rate per unit volume, and the strength of the magnetic field required to confine this plasma. Making some assumptions we are also able to estimate the number of loops involved in the observed flares and the kind of magnetic structures present in the atmosphere of these types of stars. Finally, we discuss and interpret the results in the context of solar and stellar flares reported so far.

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

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

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

    PubMed

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

    2014-02-01

    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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Weissellosis in rainbow trout is caused by the gram-positive bacteria Weissella ceti and has been reported in China, Brazil and the United States. This disease can result in high mortality in market-sized fish and thus causes significant losses. Thus far, phenotypic characterization and 16S rRNA seq...

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

    NASA Astrophysics Data System (ADS)

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

    2008-07-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  14. Discovering Mira Ceti: Celestial Change and Cosmic Continuity

    NASA Astrophysics Data System (ADS)

    Hatch, Robert Alan

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  16. How temperature influences the stoichiometry of CeTi2O6

    NASA Astrophysics Data System (ADS)

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

    2012-06-01

    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.

  17. Far-UV Spectroscopy of the Planet-hosting Star WASP-13: High-energy Irradiance, Distance, Age, Planetary Mass-loss Rate, and Circumstellar Environment

    NASA Astrophysics Data System (ADS)

    Fossati, L.; France, K.; Koskinen, T.; Juvan, I. G.; Haswell, C. A.; Lendl, M.

    2015-12-01

    Several transiting hot Jupiters orbit relatively inactive main-sequence stars. For some of those, the {log}{R}{HK}\\prime activity parameter lies below the basal level (-5.1). Two explanations have been proposed so far: (i) the planet affects the stellar dynamo, (ii) the {log}{R}{HK}\\prime measurements are biased by extrinsic absorption, either by the interstellar medium (ISM) or by material local to the system. We present here Hubble Space Telescope/COS far-UV spectra of WASP-13, which hosts an inflated hot Jupiter and has a measured {log}{R}{HK}\\prime value (-5.26), well below the basal level. From the star's spectral energy distribution we obtain an extinction E(B - V) = 0.045 ± 0.025 mag and a distance d = 232 ± 8 pc. We detect at ≳4σ lines belonging to three different ionization states of carbon (C i, C ii, and C iv) and the Si iv doublet at ˜3σ. Using far-UV spectra of nearby early G-type stars of known age, we derive a C iv/C i flux ratio-age relation, from which we estimate WASP-13's age to be 5.1 ± 2.0 Gyr. We rescale the solar irradiance reference spectrum to match the flux of the C iv 1548 doublet. By integrating the rescaled solar spectrum, we obtain an XUV flux at 1 AU of 5.4 erg s-1 cm-2. We use a detailed model of the planet's upper atmosphere, deriving a mass-loss rate of 1.5 × 1011 g s-1. Despite the low {log}{R}{HK}\\prime value, the star shows a far-UV spectrum typical of middle-aged solar-type stars, pointing toward the presence of significant extrinsic absorption. The analysis of a high-resolution spectrum of the Ca ii H&K lines indicates that the ISM absorption could be the origin of the low {log}{R}{HK}\\prime value. Nevertheless, the large uncertainty in the Ca ii ISM abundance does not allow us to firmly exclude the presence of circumstellar gas. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from MAST 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. These observations are associated with program #13859.

  18. HST/COS Observations of the UV-Bright Star Y453 in the Globular Cluster M4 (NGC 6121)

    NASA Astrophysics Data System (ADS)

    Dixon, William V. D.; Chayer, Pierre; Benjamin, Robert A.

    2016-01-01

    Post-AGB stars represent a short-lived phase of stellar evolution during which stars cross the optical color-magnitude diagram from the cool, red tip of the assymptotic giant branch (AGB) to the hot, blue tip of the white-dwarf cooling curve. Their surface chemistry reflects the nuclear-shell burning, mixing, and mass-loss processes characteristic of AGB stars, and their high effective temperatures allow the detection of elements that are unobservable in cool giants. Post-AGB stars in globular clusters offer the additional advantages of known distance, age, and initial chemistry. To better understand the AGB evolution of low-mass stars, we have observed the post-AGB star Y453 in the globular cluster M4 (NGC 6121) with the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope. The star, which has an effective temperature of at least 60,000 K, shows absorption from He, C, N, O, Ne, Si, S, Ti, Cr, Mn, Fe, Co, Ni, and Ga. While the star's C and O abundances are consistent with those measured in a sample of nitrogen-poor RGB stars in M4, its N abundance is considerably enhanced. The star's low C abundance suggests that it left the AGB before the onset of third dredge-up.This work was supported by NASA grant HST-GO-13721.001-A to the University of Wisconsin, Whitewater. P.C. is supported by the Canadian Space Agency under a contract with NRC Herzberg Astronomy and Astrophysics.

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

    SciTech Connect

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

    2012-10-20

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

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

  1. First report of Brucella ceti-associated meningoencephalitis in a long-finned pilot whale Globicephala melas.

    PubMed

    Davison, Nicholas J; Brownlow, Andrew; McGovern, Barry; Dagleish, Mark P; Perrett, Lorraine L; Dale, Emma-Jane; Koylass, Mark; Foster, Geoffrey

    2015-10-27

    Fatal Brucella ceti infection with histological lesions specific to the central nervous system has been described in only 3 species of cetaceans: striped dolphins Stenella coeruleoalba, Atlantic white-sided dolphins Lagenorhynchus acutus and short-beaked common dolphins Delphinus delphis. This paper describes the first report of a B. ceti-associated meningoencephalitis in a long-finned pilot whale Globicephala melas, showing the increasing range of species susceptibility. Brucella was recovered in larger numbers from cerebrospinal fluid than from brain tissue and is the sample of choice for isolation. PMID:26503778

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

    SciTech Connect

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

    2013-08-20

    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.

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

    NASA Astrophysics Data System (ADS)

    Schenker, Matthew A.; Robertson, Brant E.; Ellis, Richard S.; Ono, Yoshiaki; McLure, Ross J.; Dunlop, James S.; Koekemoer, Anton; Bowler, Rebecca A. A.; Ouchi, Masami; Curtis-Lake, Emma; Rogers, Alexander B.; Schneider, Evan; Charlot, Stephane; Stark, Daniel P.; Furlanetto, Steven R.; Cirasuolo, Michele

    2013-05-01

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

  4. 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

    Schenker, Matthew A.; Ellis, Richard S.; Robertson, Brant E.; Schneider, Evan; Ono, Yoshiaki; Ouchi, Masami; Stark, Daniel P.; McLure, Ross J.; Dunlop, James S.; Bowler, Rebecca A. A.; Curtis-Lake, Emma; Rogers, Alexander B.; Cirasuolo, Michele; Koekemoer, Anton; Charlot, Stephane; Furlanetto, Steven R.

    2013-05-10

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

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

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

    NASA Technical Reports Server (NTRS)

    1984-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1997-01-01

    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.

  8. Simultaneous spectroscopic and photoelectric observations of Beta Cephei stars. IV - Delta Ceti

    NASA Astrophysics Data System (ADS)

    Kubiak, M.; Seggewiss, W.

    Two nights of radial velocity observations and three nights of uvby photometry show unusually large radial velocity amplitude and normal amplitude of brightness. Present data confirm former determination of secular period increase equal 0.46 s/century and the average value of phase lag between radial velocity and light curves equals to 0.23. The phase lag in the epoch of the present observations was close to 0.25.

  9. Determination of the Core Composition of ZZ Ceti Stars through Seismic Means

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    As we know, the exact chemical profile in the core of a white dwarf is still very much uncertain, and comparing results from different investigators yields significant differences with the addition of the numerical noise coming from the accumulated uncertainties through all the various stages of pre-white dwarf evolution. We believe that until significant progress is made on that front, we can only probe the bulk core composition as a whole. In effect, the low sensitivity of the pulsation periods on the core composition can be exploited as long as we rely on the detection of confined modes that have relatively large amplitudes in the core. We show that the bulk composition of Ross 548 can be effectively determined, while that of GD 165 is not easily pinned down due to the lack of detected confined modes in that latter case.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  12. White Dwarf Stars (With 37 figures)

    NASA Astrophysics Data System (ADS)

    Kawaler, Steven D.

    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

  13. The UV Continuum of z Greater Than 1 Star-Forming Galaxies in the Hubble Ultraviolet Ultradeep Field

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  14. Pulsational analyses of post planetary nebula central stars and degenerate dwarfs

    NASA Technical Reports Server (NTRS)

    Starrfield, Sumner

    1987-01-01

    Recent observational and theoretical studies of the ZZ Ceti variabls (DA degenerate dwarfs), the DBV variables (DB degenerate dwarfs), and the GW Vir variables (D0 degenerate dwarfs) have shown them to be pulsating in nonradial g-modes. The pulsation mechanism has been identified for each class of variable star. For the ZZ Ceti and DBV variables it is both the kappa and gamma effects in the partial-ionization regions of either H or He and also a a recently identified pulsation-driving mechanism called 'convection blocking'. For the GW Vir variables, it is the kappa and gamma effects in the partial-ionization region of C and O. The ZZ Ceti variables must have pure H surface layers, the DBV stars must have pure He surface layers, and the GW Vir stars must have C- and O-rich surface layers with only a small amount of He present. The accuracy of the prediction for the GW Vir stars is limited by the lack of observational determinations of their luminosity, effective temperature, and composition.

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

    NASA Technical Reports Server (NTRS)

    Roberge, Aki

    2012-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

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

    SciTech Connect

    Barro, G.; Perez-Gonzalez, P. G.; Gallego, J.; Villar, V.; Zamorano, J.; Ashby, M. L. N.; Kajisawa, M.; Yamada, T.; Miyazaki, S.

    2011-04-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Barro, G.; Prez-Gonzlez, P. G.; Gallego, J.; Ashby, M. L. N.; Kajisawa, M.; Miyazaki, S.; Villar, V.; Yamada, T.; Zamorano, J.

    2011-04-01

    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 ?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 deg2. The typical photometric redshift accuracy is ?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 ?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 gsim 1.5 observed when only MIPS 24 ?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.

  20. Long-term polarization observations of Mira variable stars suggest asymmetric structures

    NASA Astrophysics Data System (ADS)

    Neilson, Hilding R.; Ignace, Richard; Henson, Gary D.

    2014-02-01

    Mira and semi-regular variable stars have been studied for centuries but continue to be enigmatic. One unsolved mystery is the presence of polarization from these stars. In particular, we present 40 years of polarization measurements for the prototype o Ceti and V CVn and find very different phenomena for each star. The polarization fraction and position angle for Mira is found to be small and highly variable. On the other hand, the polarization fraction for V CVn is large and variable, from 2-7%, and its position angle is approximately constant, suggesting a long-term asymmetric structure. We suggest a number of potential scenarios to explain these observations.

  1. 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...

  2. 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...

  3. Exploring high temperature magnetic order in CeTi1-xScxGe

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    We studied the magnetic, transport, and thermodynamic properties of the alloy CeTi1-xScxGe in order to shed some light into the origin of the exceptionally large antiferromagnetic (AFM) ordering temperature TN = 47 K in pure CeScGe. We observed a complex magnetic phase diagram, which present an interesting dichotomy: Despite strong changes in the nature of the ordered state, from ferromagnetic (FM) for x <= 0.55 to AFM for x > 0.55, the ordering temperature increases smoothly and continuously from TC = 7 K at x = 0.25 to TN = 47 K at x = 1. Within the AFM regime we observe a metamagnetic transition at a critical field increasing from H = 0 at x ≈ 0.55 to μ0 * H ≈ 6 Tesla at x = 1. Furthermore a second transition appears at TL <= TN for x >= 0.65. In contrast to observations in CeRh2Si2 or CeRh3B2, we found no evidence for a strong hybridization of the 4f electrons at large Sc contents. Therefore the exceptionally large TN of CeScGe could be attributed to the unusually strong RKKY interaction in this type of compounds.

  4. Detection of Variable Gaseous Absorption Features in the Debris Disks Around Young A-type Stars

    NASA Astrophysics Data System (ADS)

    Montgomery, Sharon L.; Welsh, Barry Y.

    2012-10-01

    We present medium resolution (R=60,000) absorption measurements of the interstellar Ca II K line observed towards five nearby A-type stars (49 Ceti, 5 Vul, ? Cyg, 2 And, and HD 223884) suspected of possessing circumstellar gas debris disks. The stars were observed on a nightly basis during a six night observing run on the 2.1-meter Otto Struve telescope at the McDonald Observatory, Texas. We have detected nightly changes in the absorption strength of the Ca II K line observed near the stellar radial velocity in three of the stars (49 Ceti, i Cyg and HD 223884). Such changes in absorption suggest the presence of a circumstellar (atomic) gas disk around these stars. In addition to the absorption changes in the main Ca II K line profile, we have also observed weak transient absorption features that randomly appear at redshifted velocities in the spectra of 49 Ceti, 5 Vul, and 2 And. These absorption features are most probably associated with the presence of falling evaporated bodies (exo-comets) that liberate evaporating gas on their approach to the central star. This now brings the total number of systems in which exocomet activity has been observed at Ca II or Na I wavelengths on a nightly basis to seven (? Pic, HR 10, HD 85905, ? Car, 49 Ceti, 5 Vul, and 2 And), with 2 And exhibiting weaker and less frequent changes. All of the disk systems presently known to exhibit either type of short-term variability in Ca II K line absorption are rapidly rotating A-type stars (V sin i>120 km s-1). Most exhibit mid-IR excesses, and many of them are very young (<20 Myr), thus supporting the argument that many of them are transitional objects between Herbig Ae and ""Vega-like"" A-type stars with more tenuous circumstellar disks. No mid-IR excess (due to the presence of a dust disk) has yet been detected around either 2 And or HD 223884, both of which have been classified as ? Btis-type stars. This may indicate that the observed changes in gas absorption for these two stars may not be due to circumstellar activity, but may instead be associated with the stars'' episodic mass loss and passage though low-density interstellar clouds.

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

    PubMed

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

    2014-12-01

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

  6. 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)

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

    1997-01-01

    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.

  7. Identification of new fluorescence processes in the UV spectra of cool stars from new energy levels of Fe II and Cr II

    NASA Technical Reports Server (NTRS)

    Johansson, Sveneric; Carpenter, Kenneth G.

    1988-01-01

    Two fluorescence processes operating in atmospheres of cool stars, symbiotic stars, and the Sun are presented. Two emission lines, at 1347.03 and 1360.17 A, are identified as fluorescence lines of Cr II and Fe II. The lines are due to transitions from highly excited levels, which are populated radiatively by the hydrogen Lyman alpha line due to accidental wavelength coincidences. Three energy levels, one in Cr II and two in Fe II, are reported.

  8. FUSE, STIS and Keck spectroscopic analysis of the UV-bright star vZ 1128 in M3 (NGC 5272)

    NASA Astrophysics Data System (ADS)

    Chayer, P.; Dixon, W. V.; Fullerton, A. W.; Ooghe-Tabanou, B.; Reid, I. N.

    2015-09-01

    We present a spectral analysis of the ultraviolet-bright star vZ 1128 in M3 based on observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space Telescope Imaging Spectrograph (STIS), and the Keck High Resolution Echelle Spectrometer (HIRES). By fitting the H I, He I, and He II lines in the Keck spectrum with non-local thermodynamic equilibrium H-He models, we obtain Teff = 36 600 K, log g = 3.95, and log N(He)/N(H) = -0.84. The star's FUSE and STIS spectra show photospheric absorption from C, N, O, Al, Si, P, S, Fe, and Ni. No stellar features from elements beyond the iron peak are observed. Both components of the N V λ1240 doublet exhibit P Cygni profiles, indicating a weak stellar wind, but no other wind features are seen. The star's photospheric abundances appear to have changed little since it left the red giant branch (RGB). Its C, N, O, Al, Si, Fe, and Ni abundances are consistent with published values for the red giant stars in M3, and the relative abundances of C, N, and O follow the trends seen on the cluster RGB. In particular, its low C abundance suggests that the star left the asymptotic giant branch before the onset of third dredge-up.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  10. Pulsating or not? A search for hidden pulsations below the red edge of the ZZ Ceti instability strip

    NASA Astrophysics Data System (ADS)

    Kotak, R.; van Kerkwijk, M. H.; Clemens, J. C.; Bida, T. A.

    2002-09-01

    The location of the red edge of the ZZ Ceti instability strip is defined observationally as being the lowest temperature for which a white dwarf with a H-rich atmosphere (DA) is known to exhibit periodic brightness variations. Whether this cut-off in flux variations is actually due to a cessation of pulsation or merely due to the attenuation of any variations by the convection zone, rendering them invisible, is not clear. The latter is a theoretical possibility because with decreasing effective temperature, the emergent flux variations become an ever smaller fraction of the amplitude of the flux variations in the interior. In contrast to the flux variations, the visibility of the velocity variations associated with the pulsations is not thought to be similarly affected. Thus, models imply that were it still pulsating, a white dwarf just below the observed red edge should show velocity variations. In order to test this possibility, we used time-resolved spectra of three DA white dwarfs that do not show photometric variability, but which have derived temperatures only slightly lower than the coolest ZZ Ceti variables. We find that none of our three targets show significant periodic velocity variations, and set 95% confidence limits on amplitudes of 3.0, 5.2, and 8.8 km s-1. Thus, for two out of our three objects, we can rule out velocity variations as large as 5.4 km s-1 observed for the strongest mode in the cool white dwarf pulsator ZZ Psc. In order to verify our procedures, we also examined similar data of a known ZZ Ceti, HL Tau 76. Applying external information from the light curve, we detect significant velocity variations for this object with amplitudes of up to 4 km s-1. Our results suggest that substantial numbers of pulsators having large velocity amplitudes do not exist below the observed photometric red edge and that the latter probably reflects a real termination of pulsations. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  11. Discovery of five new massive pulsating white dwarf stars

    NASA Astrophysics Data System (ADS)

    Castanheira, B. G.; Kepler, S. O.; Kleinman, S. J.; Nitta, A.; Fraga, L.

    2013-03-01

    Using the SOuthern Astrophysical Research telescope (SOAR) Optical Imager at the SOAR 4.1 m telescope, we report on the discovery of five new massive pulsating white dwarf stars. Our results represent an increase of about 20 per cent in the number of massive pulsators. We have detected both short and long periods, low and high amplitude pulsation modes, covering the whole range of the ZZ Ceti instability strip. In this paper, we present a first seismological study of the new massive pulsators based on the few frequencies detected. Our analysis indicates that these stars have masses higher than average, in agreement with the spectroscopic determinations. In addition, we study for the first time the ensemble properties of the pulsating white dwarf stars with masses above 0.8 M?. We found a bimodal distribution of the main pulsation period with the effective temperature for the massive DAVs, which indicates mode selection mechanisms.

  12. UV observations of x ray binaries

    NASA Technical Reports Server (NTRS)

    Raymond, John C.

    1990-01-01

    IUE (International Ultraviolet Explorer) has observed both high and low mass x ray binaries throughout its life. The UV spectra of high mass systems reveal the nature of the massive companion star and the effects of the x ray illumination of the stellar wind. In loss mass systems, the x ray illuminated disk or companion star dominates the UV light. System parameters and the characteristics of the accretion disk can be inferred.

  13. Intrinsically variable stars

    NASA Technical Reports Server (NTRS)

    Bohm-Vitense, Erika; Querci, Monique

    1987-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  15. Hydrogen Lines in Mira Stars Through Interferometry and Polarimetry

    NASA Astrophysics Data System (ADS)

    Fabas, N.; Chiavassa, A.; Millour, F.; Wittkowski, M.

    2015-12-01

    Balmer lines in emission are the most prominent features in Mira stars spectra and have a strong potential as a proxy to study the lower atmosphere's dynamics. In Fabas et al. ([1]), we accumulated spectropolarimetric observations of Balmer lines in emission. As the shock is propagating outwards, linear polarization rate increases and the angle of this polarization evolves. Assuming that linear polarization arises from anisotropic scattering, it has the potential of telling us about the geometric structure of the shock as it propagates and the study of such atmospheric structures can typically be performed with interferometry. In 2012, AMBER data on the Mira star omicron Ceti were collected in which the Brackett γ line is studied. The data show signatures in the interferometric observables around this line. Olivier Chesneau was in the jury evaluating the PhD thesis of N. Fabas and he was seduced by the idea to study these shock waves with interferometry and use polarimetry as a complementary study.

  16. Evolution of UV-Irradiated Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  18. Merging Galaxies as Probes of the Main-Sequence and the Evolution of Star Formation Rates: UV-FIR Observations and Simulations

    NASA Astrophysics Data System (ADS)

    Smith, Howard; Martinez, R.; Hung, C.; Hayward, Christopher; Zezas, A.; Lanz, L.; Ashby, M. L. N.; Rosenthal, L.; Weiner, A.

    2015-08-01

    The study of merging galaxies sheds light not only the processes that drive U/LIRGs, both local and at high-z, but also on the parameters that lead to a galaxy having a main-sequence or starburst character, on the role of its AGN, on the diagnostic kinematic signatures, on the development of galactic winds, and on evolutionary trends. We have reduced and analyzed multi-wavelength (GALEX to Herschel) datasets on a large sample of merging galaxies in many stages of interaction, and used a variety of SED modeling routines (MAGPHYS, CHIBURST, CIGALE) to derive the key physical parameters. To compare and contrast these observations, we prepared and analyzed a large set of merger simulations with hydrodynamic codes, and used the SUNRISE radiative transfer to calculate the radiative output at every step and viewing angle of each merging pair; we include variations on the character of the ISM and the strength of the AGN. We will discuss our results, the evolutionary development of star formation and the "main-sequence, and comment on constraints associated with using photometric measures to infer the physical conditions.

  19. Hot evolved stars in massive galaxies

    NASA Astrophysics Data System (ADS)

    Le Cras, Claire; Maraston, Claudia; Thomas, Daniel

    2015-08-01

    It is believed that HB stars and their progeny are responsible for the increase in UV flux found in elliptical galaxies, a phenomenon known as the UV upturn. These stars undergo different evolutionary paths depending on their temperature, with the redder stars evolving as bright P-AGB stars, possibly forming planetary nebulae, before eventually descending the white dwarf cooling curve. We exploit a theoretical model of stellar populations incorporating a hot P-AGB component with a fuel calibrated UV upturn and a system of UV absorption line indices to investigate the redshift at the onset of the UV upturn in massive galaxies. We analyse a large sample of massive galaxy spectra taken from the Sloan Digital Sky Survey (SDSS) -III / Baryon Oscillator Spectroscopic Survey (BOSS). We find up to 47% of our working sample to contain a contribution from old UV bright stars with the majority of old populations contributing up to 30% of the galaxy's stellar mass.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  1. The History of Variable Stars: A Fresh Look

    NASA Astrophysics Data System (ADS)

    Hatch, R. A.

    2012-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  3. Deep UV photometry of galaxies & the extragalactic UV background

    NASA Astrophysics Data System (ADS)

    Martin, Chris; Milliard, Bruno; Viton, Maurice; Donas, Jose

    1997-05-01

    We have performed multifiber spectroscopy of UV-selected galaxies obtained by the balloon-borne FOCA telescope. 55 galaxies were found in 0.25 square degrees. The number-magnitude, redshift, and color distributions show that strong evolution is occurring in the UV-selected population. A mildly luminosity-dependent model normalized to the star formation history derived from optical surveys is a good fit to the distribution. Keck spectroscopy reveals that galaxies in the high-redshift tail are both dwarfs and giants, including ``giant starburst'' galaxies. One third of these high-redshift galaxies have companions inside 100 kpc consistent with being dynamically bound. The results are consistent with current limits on the extragalactic UV background.

  4. UV SPECTRAL SYNTHESIS OF VEGA

    SciTech Connect

    Fitzpatrick, E. L.

    2010-12-20

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

  5. The wings of the calcium infrared triplet lines in solar-type stars

    NASA Astrophysics Data System (ADS)

    Smith, G.; Drake, J. J.

    1987-07-01

    Profiles of the IR triplet lines of ionized Ca (8494, 8542, and 8662 A) have been calculated in the LTE approximation using model atmospheres representative of solar-type stars. The depth of absorption in the line wings is found to be particularly insensitive to surface gravity. Provided that the relative abundance (RA) of Ca is consistent with the metallicity of the model atmosphere, the depth of absorption becomes more sensitive to metallicity with increasing effective temperature. These conclusions have been tested against accurate measurements of IR triplet line profiles in Tau Ceti (G8 V) and Eta Cas A (G0 V). Using spectra recorded at a dispersion of 1 A/mm and with S/N of about 100, the T(eff), log g, Fe/H, and Ca/H were derived. Line profiles in Tau Ceti were found to be extremely narrow, indicating low rotational and turbulent broadening. The difference in RA between Ca and Fe in this star is consistent with other recent analyses of metal-deficient dwarfs in the Galactic disk. If the RAs of the alpha-particle elements are assumed to follow the Ca abundance rather than the Fe abundance, there is good agreement between observed and calculated profiles. In the case of Eta Cas A, where there appears to be no difference in RA between Ca and Fe, a small discrepancy between observed and calculated line wings is found.

  6. Winds of Binary AGB Stars as Observed by Herschel

    NASA Astrophysics Data System (ADS)

    Mayer, A.; Jorissen, A.; Kerschbaum, F.; Ottensamer, R.; Me?ina, M.; Paladini, C.; Cox, N. L. J.; Nowotny, W.; Aringer, B.; Pourbaix, D.; Mohamed, S.; Siopis, C.; Groenewegen, M. A. T.

    2015-08-01

    We present Herschel/PACS observations of the large-scale environments of binary AGB stars as part of the Mass-loss of Evolved StarS (MESS) sample. From the literature we found 18 of the objects to be members of physically bound multiple systems. Several show a large-scale far-IR emission which differs significantly from spherical symmetry. A probable cause is the gravitational force of the companion on the stellar AGB wind and the mass-losing star itself. A spiral pattern is thereby imprinted in the dusty stellar wind. The most remarkable structures are found around o Ceti, W Aquil, R Aquarii, and ?1 Gruis. The environments of o Cet and W Aql show a spiral pattern while the symbiotic nature of R Aqr is revealed as two opposing arms which reflect a nova outburst. The emission around ?1 Gru is dominated by two structures, a disk and an arc, which are presumably not caused by the same companion. We found evidence that ?1 Gru is a hierarchical triple system in which a close companion attracts the AGB wind onto the orbital plane and the outer companion forms a spiral arm. These far-IR observations underline the role of a companion as a major external influence in creating asymmetric winds in the AGB phase, even before the star becomes a planetary nebula (PN).

  7. A Marvelous Star in M33

    NASA Astrophysics Data System (ADS)

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

    2012-05-01

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

  8. Age derivation from UV absorption indices and the effect of the UV upturn.

    NASA Astrophysics Data System (ADS)

    Le Cras, Claire; Maraston, Claudia; Thomas, Daniel

    2015-08-01

    We exploit stellar population models of absorption line indices in the ultraviolet to assess their power in determining the age of the stellar populations in galaxies. We focus in particular on features that can differentiate between an old UV bright population, contributing to the UV upturn, and a young population due to recent star formation. We use a system of 8 indices between 2200 - 3200A , tracing several chemical elements including Mg and Fe. We apply these models to a large sample of z ~ 0.6 massive galaxies from the Sloan Digital Sky Survey (SDSS) - III / Baryon Oscillation Spectroscopic Survey (BOSS) to derive the ages of the UV bright populations. We find a subset of our indices to be non-degenerate between old and young UV ages allowing us to find evidence for old stars contributing to the UV, rather than new star formation. We find up to 47% of our working sample to contain a contribution from old UV bright stars, with those found to have higher contributing mass fractions being on average more massive and redder than those with lower mass fractions.

  9. 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

    Ribas, I.; Garces, A.; Porto de Mello, G. F.; Ferreira, L. D.; Hebrard, E.; Selsis, F.; Catalan, S.; Do Nascimento, J. D.; De Medeiros, J. R. E-mail: garces@ice.csic.e E-mail: leticia@astro.ufrj.b E-mail: eric.hebrard@obs.u-bordeaux1.f E-mail: dias@dfte.ufrn.b

    2010-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

    MacKenty, John

    1990-12-01

    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.

  11. Wf/pc Cycle 2 Calib: Single Chip UV Calibration

    NASA Astrophysics Data System (ADS)

    MacKenty, John

    1991-07-01

    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.

  12. Ultraviolet (UV) Stellar Astronomy - Skylab Experiment S019

    NASA Technical Reports Server (NTRS)

    1970-01-01

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

  13. UV Spectral Templates for High-Redshift Galaxies

    NASA Technical Reports Server (NTRS)

    Heap, Sara; Lindler, Don; Lanz, Thierry

    2003-01-01

    New instrumentation such as DEIMOS on Keck-II now enable deep spectral surveys, and thereby samples of galaxies at younger ages. At a redshift, z = 1, all galaxies are less than 6 Gyr old and hence, have not yet formed horizontal-branch stars. Also, at z = 1, the restframe-UV comes into view, and with it, a new set of spectral diagnostics. UV spectral features are especially important because most of the UV flux comes from stars at the main-sequence turnoff (MSTO). Hence, UV spectral diagnostics enable the ages of z = 1 galaxies to be estimated directly from MSTO stars. In preparation for these high-redshift spectral surveys, we are developing UV spectral templates for stellar populations younger than 6 Gyr using UV-optical spectra of stars observed by HST/STIS. We are also planning to supplement these observations with theoretical spectral grids of stars of various metallicities. In this paper, we present a progress report on the observation-based spectral templates and spectral diagnostics.

  14. GALEX catalogue of UV point sources in M33

    NASA Astrophysics Data System (ADS)

    Mudd, Dale; Stanek, K. Z.

    2015-07-01

    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 to numerous B, O and WR (WR) stars to be bright in UV data. In this paper, we update the previous point source UV catalogue of M33, created using the Ultraviolet Imaging Telescope (UIT), using data from the Galaxy Evolution Explorer (GALEX). We utilize point spread function photometry to optimally photometer sources in the crowded regions of the galaxy, and benefit from GALEX's increased sensitivity compared to UIT. We match our detections with data from the Local Group Galaxies Survey to create a catalogue with photometry spanning from the far-UV through the optical for a final list of 24 738 sources. All of these sources have far-UV (FUV; 1516 ), near-UV (NUV; 2267 ) and V data, and a significant fraction also have U, B, R and I data as well. We also present an additional 3000 sources that have no matching optical counterpart. We compare all of our sources to a catalogue of known WR stars in M33 and find that we recover 114 of 206 stars with spatially-coincident UV point sources. Additionally, we highlight and investigate those sources with unique colours as well as a selection of other well-studied sources in M33.

  15. UV Extinction in High Latitude Clouds

    NASA Astrophysics Data System (ADS)

    Welty, Daniel E.

    We propose to determine the UV extinction in one nearby high latitude molecular cloud (HLC) by obtaining low-dispersion spectra of a B3V star located behind the cloud's dense, molecular core. As a class, the HLC's are both relatively nearby (within ~200 pc) and isolated, with little confusion from other clouds along the same lines of sight; they are thus excellent candidates for comparing the emission and absorption characteristics of individual interstellar clouds. Comparison of the UV extinction with the infrared emission observed by IRAS should provide constraints on the relative contributions of very small grains and polycyclic aromatic hydrocarbons to both phenomena, which may in turn lead to better understanding of the relationships among AV, Iv(100micron), and cloud mass and of what role shocks may have played in the formation of the HLC's. In addition, knowledge of the UV extinction is essential for understanding the ambient radiation field in the cloud core, and thus for the ionization equilibrium, abundances, and molecular chemistry in these diffuse high latitude clouds.The primary star to be observed, HD 210121, is perhaps the earliest type star known to be located behind the dense core of an HLC, and thus may provide a unique opportunity for reliably determining the UV extinction in an HLC. The bright B7IVe star omicron Aqr is apparently located behind a more diffuse part of this particular HLC; we thus plan to compare both high and low dispersion spectra of the two stars to explore the differences in both extinction and abundances between the dense and diffuse parts of this cloud.

  16. UV Observations of Collisional Ring Galaxies

    NASA Astrophysics Data System (ADS)

    Appleton, Philip

    We propose to image 12 of the largest known collisional ring galaxies with GALEX to directly measure the escaping UV radiation from bright blue outer rings and fainter interior regions. The observations will allow us to 1) compare the direct UV measures of the ring star formation rates (SFR) with SFR derived from our extensive multi-wavelength (optical, IR, radio) data on many of the same systems, 2) explore secondary star formation interior to the brighter outer rings predicted by models to occur in spokes, filaments and inner rings and c) search for UV counterparts to non-stellar (i.e. accretion-driven) sources in the outer rings, by analogy with the recently discovery of a dozen extremely luminous X-rays sources found in the Cartwheel ring, and numerous sources in Arp 284. UV observations should be capable of separating intermediate-mass black-hole candidates from more traditional O/B associations by virtue of their expected high UV luminosities. Although relatively rare locally, ring galaxies are more common at high redshift, and their study may represent one of the few ways of probing the physical condition in the outer regions of high-z disks.

  17. UV water disinfector

    DOEpatents

    Gadgil, A.; Garud, V.

    1998-07-14

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

  18. UV water disinfector

    DOEpatents

    Gadgil, Ashok; Garud, Vikas

    1998-07-14

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

  19. RADIATIVE AND KINETIC FEEDBACK BY LOW-MASS PRIMORDIAL STARS

    SciTech Connect

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

    2010-03-20

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

  20. Statistical Properties of Galactic ? Scuti Stars: Revisited

    NASA Astrophysics Data System (ADS)

    Chang, S.-W.; Protopapas, P.; Kim, D.-W.; Byun, Y.-I.

    2013-05-01

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

  1. Strange stars

    NASA Technical Reports Server (NTRS)

    Alcock, Charles; Farhi, Edward; Olinto, Angela

    1986-01-01

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

  2. UV color-color relation of early-type galaxies

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  3. Stars and Star Myths.

    ERIC Educational Resources Information Center

    Eason, Oliver

    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

  4. Stars and Star Myths.

    ERIC Educational Resources Information Center

    Eason, Oliver

    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…

  5. Be Stars

    NASA Astrophysics Data System (ADS)

    Peters, G.; Murdin, P.

    2000-11-01

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

  6. Reinvestigating the Lambda Boo Stars

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  7. VizieR Online Data Catalog: Star-forming galaxies in the Coma Cluster (Donas+, 1995)

    NASA Astrophysics Data System (ADS)

    Donas, J.; Milliard, B.; Laget, M.

    1995-05-01

    In a field of 1deg radius centered in the Coma cluster of galaxies, UV (?=2000 A) observations with a 40-cm balloon-borne imaging telescope (FOCA) have provided a list of 442 UV sources brighter than mUV=18, which are identified in the Godwin (1983) catalogue. 254 are identified as galaxies, 178 as star-like objects and 10 as galaxy-star pairs, unresolved in the UV image. (2 data files).

  8. Far-UV Radiation of the Early Sun

    NASA Technical Reports Server (NTRS)

    Heap, Sally

    2005-01-01

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

  9. Old stellar systems in UV: resolved and integrated properties

    NASA Astrophysics Data System (ADS)

    Dalessandro, E.

    2014-11-01

    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.

  10. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  11. Science with a wide-field UV transient explorer

    SciTech Connect

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

    2014-04-01

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

  12. Co-spatial Long-slit UV/Optical Spectra of Ten Galactic Planetary Nebulae with HST/STIS. II. Nebular Models, Central Star Properties, and He+CNO Synthesis

    NASA Astrophysics Data System (ADS)

    Henry, R. B. C.; Balick, B.; Dufour, R. J.; Kwitter, K. B.; Shaw, R. A.; Miller, T. R.; Buell, J. F.; Corradi, R. L. M.

    2015-11-01

    The goal of the present study is twofold. First, we employ new HST/STIS spectra and photoionization modeling techniques to determine the progenitor masses of eight planetary nebulae (IC 2165, IC 3568, NGC 2440, NGC 3242, NGC 5315, NGC 5882, NGC 7662, and PB 6). Second, for the first time we are able to compare each objects observed nebular abundances of helium, carbon, and nitrogen with abundance predictions of these same elements by a stellar model that is consistent with each objects progenitor mass. Important results include the following: (1) the mass range of our objects central stars matches well with the mass distribution of other central stars of planetary nebulae and white dwarfs; (2) He/H is above solar in all of our objects, in most cases likely due to the predicted effects of first dredge-up; (3) most of our objects show negligible C enrichment, probably because their low masses preclude third dredge-up; (4) C/O versus O/H for our objects appears to be inversely correlated, which is perhaps consistent with the conclusion of theorists that the extent of atmospheric carbon enrichment from first dredge-up is sensitive to a parameter whose value increases as metallicity declines; (5) stellar model predictions of nebular C and N enrichment are consistent with observed abundances for progenitor star masses ?1.5 M?. Finally, we present the first published photoionization models of NGC 5315 and NGC 5882. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.

  13. The Hubble Deep UV Legacy Survey (HDUV)

    NASA Astrophysics Data System (ADS)

    Montes, Mireia; Oesch, Pascal

    2015-08-01

    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. Here, we present a new HST WFC3/UVIS program, the Hubble Deep UV (HDUV) legacy survey. The HDUV is a 132 orbit program to obtain deep imaging in two filters (F275W and F336W) over the two CANDELS Deep fields. We will cover ~100 arcmin2 sampling the rest-frame far-UV at z>~0.5, this will provide a unique legacy dataset with exquisite HST multi-wavelength imaging as well as ancillary HST grism NIR spectroscopy for a detailed study of faint, star-forming galaxies at z~0.5-2. The HDUV will enable a wealth of research by the community, which 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. This poster provides an overview of the HDUV survey and presents the reduced data products and catalogs which will be released to the community, reaching down to 27.5-28.0 mag at 5 sigma. By directly sampling the rest-frame far-UV at z>~0.5, this will provide a unique legacy dataset with exquisite HST multi-wavelength imaging as well as ancillary HST grism NIR spectroscopy for a detailed study of faint, star-forming galaxies at z~0.5-2. The HDUV will enable a wealth of research by the community, which 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. This poster provides an overview of the HDUV survey and presents reduced data products and catalogs which will be released to the community.

  14. UV LED Space Qualification

    NASA Astrophysics Data System (ADS)

    Buchman, Saps; Sun, K.; Leindecker, N.; Higuchi, S.; Byer, R.; Goebel, J.

    2009-01-01

    Electric charges induced by cosmic rays tend to accumulate on the free floating proof mass at the core of a drag-free satellite. The Lorentz force will affect stationarity of the proof mass. Generation of photoelectrons via ultraviolet (UV) light is an effective method of charge management. Previous missions have relied on mercury lamps as a UV light source. We have proposed the use of UV LEDs as a source for UV light generation, because they have significantly lower mass and power requirements. Since 2005, we have conducted systematic UV LED power and spectral lifetime tests. The UV LED has now been operated more than 16,668 hours (as of submission of this abstract) without significant power decay. At the 10,000 hour mark, the UV LED spectral shift was measured to be approximately 1 nm towards shorter wavelengths. To fully simulate the space environment, we have initiated another UV LED lifetime test in 1E-7 torr vacuum chamber starting in January 2008. Thus far the UV LED output has been stable without noticeable degradation. We have conducted a large dose radiation test using an accelerator source for 59.0 64.8 MeV proton generation. For proton flux from 10E10 to 2E12 protons per square centimeter, there was no significant power drop and spectral shift for UV LED light output, This level of radiation test exceeded 100 years of radiation dose at deep space LISA orbits. The combination of the successful tests in power lifetime, spectral stability, and radiation hardness have proven that UV LED should be the primary choice for the charge management system for LISA and other high precision space flights.

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

    PubMed

    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

    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

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  17. Largescale Self-Regulation in Star-Forming Systems

    NASA Astrophysics Data System (ADS)

    Cammerer, M.; Shchekinov, Y.

    1994-03-01

    A model with stimulation and inhibition of star formation (SF) by interstellar UV-radiation (A> 912 A) and X-rays is considered. Both UV and X-rays have large free path in the intercloud medium (lUV = (?n0)-1 ? 300 pc) and are able to synchronize star formation on large scales. The main suggestion is that UV radiation generated by newly born massive stars induces a contraction of optically thick interstellar clouds and it results in formation of stars of the next generation. This positive feedback ensures the growth of star formation rate on spatial scales of the order of lUV in a time scale close to the time of pre-mainsequence evolution of massive stars (? 3 Myr) so that star formation process propagates through the system with a velocity of 100 km s-1. Such a process will be observed as a global quasy-synchronous starburst. On the other hand X-ray photons, for which interstellar clouds are optically thin, can depress star formation by heating the cloud gas. Thus, there is a negative feedback with long-range action - X-ray emission produced by massive stars of previous generation exploding as SNe. The competition between positive and negative feedbacks produces the onset of an oscillatory global SF regime.

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

    SciTech Connect

    Schechtman-Rook, Andrew; Hess, Kelley M. E-mail: hess@ast.uct.ac.za

    2012-05-10

    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.

  19. Extreme Be stars in the Magellanic Clouds

    NASA Technical Reports Server (NTRS)

    Garmany, C. D.; Humphreys, R. M.

    1985-01-01

    In the course of a spectroscopic investigation of the O-type stars in the Magellanic Clouds, a population of luminous Be stars was serendipitously encountered. They are here referred to as extreme Be stars, following the terminology used by Schild (1966) for a population of Be stars in the region of h and Chi Persei which lie significantly above the main sequence. As members of the Clouds, their luminosities and intrinsic colors can be determined directly. A comparison of these new high-luminosity Be stars with known H-beta-emission-line supergiants in the Clouds is made in both the optical and UV spectral regions. The Galactic counterparts of these Be stars are also discussed. Although these Be stars are an average of several magnitudes brighter than those in the Galaxy, this may in part be a selection effect.

  20. Mass loss from extreme helium stars

    NASA Astrophysics Data System (ADS)

    Heber, U.; Hamann, W. R.; Schonberner, D.

    1982-06-01

    Indications of mass loss were found in the UV spectra of stars HD 160641, BD-9 4395 and BD+10 2179, obtained with IUE in high resolution. The observed ionization fractions were compared with warm, cool and corona models. Mass loss rates for the three stars were derived and compared with theoretical predictions as well as with empirical correlations established for early stars of normal composition. Mass loss rates for the helium stars have an order of magnitude similar to that of massive stars of similar luminosity. However, the mass loss must depend on a second parameter, radius or effective temperature, i.e., cooler stars have smaller mass loss. Because the extreme helium stars probably develop towards the left in the HR diagram, results imply that they also increase their mass loss with time.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  2. UV (200 nm) observation of the A2111 galaxies cluster

    NASA Astrophysics Data System (ADS)

    Donas, J.; Viton, M.; Martin, C.; Milliard, B.

    1997-05-01

    An ultraviolet image of the Butcher-Oemler cluster A2111 (z=0.229) has been obtained with the FOCA balloon-borne telescope. In this UV magnitude-limited sample, 19 galaxies are found at the cluster redshift from a follow-up with the Norris spectroscope at the Palomar 5m telescope, some of them lie as far as ~7 Mpc (H0=50, q0=0.1) from the cluster center. Comparison with the Coma cluster shows that UV-luminous A2111 galaxies are 0.7 mag brighter in UV, indicating that the star formation rate is twice as high in these galaxies.

  3. Interstellar Extinction Toward Young Stars

    NASA Astrophysics Data System (ADS)

    McJunkin, Matthew; France, Kevin

    2015-01-01

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

  4. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

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

    2011-03-01

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

  5. Star Formation Across Galactic Environments

    NASA Astrophysics Data System (ADS)

    Young, Jason

    2013-01-01

    I present here parallel investigations of star formation in AGN-free and quasar host galaxies. These environments are both insightful; quasars are among the most violent objects known, reshaping their host galaxies, while my sample of AGN-free star-forming galaxies ranges from systems larger than the Milky Way to dwarf star-forming galaxies. The AGN-free galaxies are drawn from the KPNO International Spectroscopic Survey, an Hα-selected, volume-limited survey was designed to avoid continuum luminosity bias. This work studies the KISS galaxies in mid- and far-IR using Spitzer IRAC and MIPS photometry. These IR bands are interesting because the UV light from young stars is reprocessed into thermal emission in the far-IR (24μm MIPS) by dust and into vibrational transition features in the mid-IR (8.0μm IRAC) by polycyclic aromatic hydrocarbons (PAHs). This work examines the efficiencies of PAH and dust emission as tracers of star-formation. I find that the efficiency of PAH as a star-formation tracer varies with galactic stellar mass, while thermal dust has no systematic dependance on galactic mass. My study of quasar host galaxies utilizes images of eight PG quasars from the WFPC2 and NICMOS instruments aboard HST. I use narrow-band images centered on the Hβ, [OII]λ3727, [OIII]λ5007, and Paα emission lines to construct extinction and star formation maps. Additionally, I use line-ratio maps to distinguish AGN-powered line emission from star formation powered line emission. I find star formation, albeit at rates are lower than expected, suggesting that quasar host galaxies are dynamically more advanced than suspected. Seven of the galaxies have higher mass-specific star-formation rates. Additionally, I see evidence of shocked gas, supporting the hypotheses from earlier works that AGN activity quenches star formation in host galaxies by disrupting gas reservoirs.

  6. Local character of the highest antiferromagnetic temperature of Ce systems in Sc-rich CeTi1 -xScxGe

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    The highest antiferromagnetic (AFM) temperature in Ce based compounds has been reported for CeScGe with TN=47 K , but its local or itinerant nature has not been deeply investigated yet. In order to shed more light into this unusually high ordering temperature we have investigated structural, magnetic, transport, and thermal properties of CeTi1 -xScxGe alloys within the range of stability of the CeScSi-type structure: 0.25 ?x ?1 . Along this concentration range, this strongly anisotropic system presents a complex magnetic phase diagram with a continuous modification of its magnetic behavior, from ferromagnetism for 0.25 ?x ?0.50 (with 7 K?TC?16 K ) to AFM for 0.60 ?x ?1 (with 19 K?TN?47 K ). The onset of the AFM phase is associated to a metamagnetic transition with a critical field increasing from Hcr=0 at x ?0.55 to ?6 T at x =1 , coincident with an increasing contribution of the first excited crystal electric field doublet. At a critical point xcr?0.65 a second transition appears at TL?TN . In contrast to observations in itinerant systems like CeRh2Si2 or CeRh3B2 , no evidences for significant hybridization of the 4 f electrons at large Sc contents were found. Therefore, the exceptionally large TN of CeScGe can be attributed to an increasing Ruderman-Kittel-Kasuya-Yosida interaction between Ce double layers as Sc content grows.

  7. Optical and ultraviolet spectroscopy of three F + B binary stars

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  8. Optical and ultraviolet spectroscopy of three F + B binary stars

    NASA Astrophysics Data System (ADS)

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

    1991-05-01

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

  9. UV doses worldwide.

    PubMed

    Godar, Dianne E

    2005-01-01

    UV radiation affects human health. Human exposure to UV radiation causes a few beneficial health effects like vitamin D3 formation but it causes many detrimental health effects: sunburn, ocular damage, photoaging, immune suppression, DNA damage and skin cancer. In countries with fair-skinned populations, skin cancer is the most diagnosed of all cancers. In the United States in 2002, there were over one million new skin cancer cases. That means one out of every 285 people got skin cancer. Skin cancer of fair-skinned individuals is increasing at an alarming rate (4-6% per year) around the world and has now reached so-called "pandemic" proportions. Thus, it is important to know what UV doses people around the world get throughout their lives. This review covers how the outdoor UV doses are weighted for different biological effects, the most commonly used measuring devices for terrestrial and personal UV doses, the natural and other effects on terrestrial and personal UV doses, the time people spend outside, their ambient exposures and the terrestrial and personal UV doses of adult outdoor and indoor workers as well as children and adolescents around the world. Overall, outdoor-working adults get about 10%, while indoor-working adults and children get about 3% (2-4%) of the total available annual UV (on a horizontal plane). People's UV doses increase with increasing altitude and decreasing latitude; most indoor-working adult Europeans get 10,000-20,000 J/m2 per year, Americans get 20,000-30,000 J/m2 per year and Australians are estimated to get 20,000-50,000 J/m2 per year (excluding vacation, which can increase the dose by 30% or more). PMID:15819599

  10. UV Extinction in High Latitude Clouds. II

    NASA Astrophysics Data System (ADS)

    Welty, Daniel E.

    We propose to determine the LTV extinction in a number of nearby high latitude molecular clouds (HLC's) by obtaining low-dispersion spectra of early B stars located behind the clouds. The HLC's are nearby (typically within -200 pc) and isolated, with little confusion from other clouds along the same lines of sight; they are thus excellent candidates for comparing the emission and absorption characteristics of individual interstellar clouds. Comparison of the LTV extinction with the infrared emission observed by IRAS should provide constraints on the grain size and composition distributions, and may lead to better understanding of the relationships among AV, Iv (100 microns) and cloud mass and of what role shocks may have played in the formation or the HLC's. Knowledge of the UV extinction is also essential for understanding the ambient radiation field in the cloud cores, and thus for studies of the ionization equilibrium, abundances, and molecular chemistry. The UV extinction curve obtained during the previous year for HD 210121, a B3 V star located behind the dense core of an HLC is among the steepest known in the Galaxy. Additional early B stars have been identified in the vicinities of other HLC's; we would like to extend our study of the extinction characteristics of these objects to determine whether such extreme extinction is a common feature, thus perhaps providing clues to understanding the IR emission and enhanced molecular abundances.

  11. THE STAR FORMATION LAW AT LOW SURFACE DENSITY

    SciTech Connect

    Wyder, Ted K.; Martin, D. Christopher; Barlow, Tom A.; Foster, Karl; Friedman, Peter G.; Morrissey, Patrick; Neill, James D.; Neff, Susan G.; Schiminovich, David; Seibert, Mark; Madore, Barry F.; Bianchi, Luciana; Donas, Jose; Milliard, Bruno; Heckman, Timothy M.; Szalay, Alex S.; Lee, Young-Wook; Yi, Sukyoung K.; Rich, R. Michael

    2009-05-10

    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.

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

    SciTech Connect

    Johnson, Benjamin D.; Weisz, Daniel R.; Dalcanton, Julianne J.; Johnson, L. C.; Williams, Benjamin F.; Dale, Daniel A.; Dolphin, Andrew E.; Gil de Paz, Armando; Lee, Janice C.; Skillman, Evan D.; Boquien, Mederic

    2013-07-20

    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.

  13. STAR FORMATION IN ATOMIC GAS

    SciTech Connect

    Krumholz, Mark R.

    2012-11-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Massa, Derck

    2014-10-01

    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.

  15. UV signature mutations.

    PubMed

    Brash, Douglas E

    2015-01-01

    Sequencing complete tumor genomes and exomes has sparked the cancer field's interest in mutation signatures for identifying the tumor's carcinogen. This review and meta-analysis discusses signatures and their proper use. We first distinguish between a mutagen's canonical mutationsdeviations from a random distribution of base changes to create a pattern typical of that mutagenand the subset of signature mutations, which are unique to that mutagen and permit inference backward from mutations to mutagen. To verify UV signature mutations, we assembled literature datasets on cells exposed to UVC, UVB, UVA, or solar simulator light (SSL) and tested canonical UV mutation features as criteria for clustering datasets. A confirmed UV signature was: ?60% of mutations are C?T at a dipyrimidine site, with ?5% CC?TT. Other canonical features such as a bias for mutations on the nontranscribed strand or at the 3' pyrimidine had limited application. The most robust classifier combined these features with criteria for the rarity of non-UV canonical mutations. In addition, several signatures proposed for specific UV wavelengths were limited to specific genes or species; UV's nonsignature mutations may cause melanoma BRAF mutations; and the mutagen for sunlight-related skin neoplasms may vary between continents. PMID:25354245

  16. Star Mapper

    NASA Technical Reports Server (NTRS)

    1983-01-01

    A COSMIC (Computer Software Management and Information Center) program known as Skymap Star Catalog and Data Base provides a very accurate star map. The data assists Perkin Elmer Corporation in designing an optical system of proper size and field of view, and confirms the design integrity of star sensors which are very accurate and represent a major advance in optical technology. Perkin Elmer is the prime contractor for the optical telescope assembly of NASA's space telescope.

  17. Neutron Stars

    NASA Technical Reports Server (NTRS)

    Cottam, J.

    2007-01-01

    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.

  18. Mass loss from cool stars

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.; Reimers, D.

    1987-01-01

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

  19. The DQ Herculis stars

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph

    1994-01-01

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

  20. IR emission and UV extinction in two open clusters

    NASA Technical Reports Server (NTRS)

    Hackwell, James A.; Hecht, James H.

    1989-01-01

    Recent models of interstellar extinction have shown the importance of understanding both the UV and IR properties of interstellar dust grains. IRAS data have shown variations in 60 and 100 micron emissions presumably due to the presence of IR cirrus, while recent observations in the UV by Fitzpatrick and Massa have identified components in the UV extinction curve which vary in different star regions. A Draine and Anderson model connects these results by proposing that different size variations in interstellar grains would cause distinct changes in both the IR emission and the UV extinction. In order to test this model it is necessary to make observations in well defined locations away from peculiar extinction regions. In the infrared this means looking away from the galactic plane so as to limit non-local sources of IR radiation. Two open clusters that are out of the galactic plane and which contain a number of late B and early A stars suitable for UV extinction studies, and whose IRAS data show variations in the 60/100 micron ratio were studied. Based on the Drain and Anderson model, variations were expected in their UV extinction curves that correlate with the IR cirrus emission.

  1. Essential UV Observations of Eta Carinae's Change of State

    NASA Astrophysics Data System (ADS)

    Mehner, Andrea

    2014-10-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1987-01-01

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

  4. Radio stars.

    PubMed

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars. PMID:17836594

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

    NASA Astrophysics Data System (ADS)

    Gauchet, L.; Lacour, S.

    2014-09-01

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

  6. Extraordinary Views of Ordinary Galaxies: Multiwavelength Measures of Star Formation

    NASA Astrophysics Data System (ADS)

    Johnson, Benjamin D.; Schiminovich, D.; GALEX Science Team

    2007-05-01

    Testing models of galaxy evolution requires the accurate conversion of observable properties (such as color) to physical parameters (such as star formation history). One of the primary obstacles to these conversions is the presence of dust attenuation. To empirically constrain the effect of attenuation on derived physical parameters I have assembled a sample of 1000 SDSS spectroscopically observed galaxies that have been deeply imaged with GALEX in the UV and Spitzer in the IR. I use the UV through IR data to show how the entire spectral energy distribution (not just a single color) varies as a function of the relevant galaxy parameters such as dust attenuation, star formation history, and stellar mass. I show how these variations can be used to constrain and inform models of galaxy spectra, including dust attenuation. I have used the average UV through IR SEDs to derive a low resolution dust attenuation curve for blue-sequence galaxies. I explore the relation of UV and IR emission to star formation and dust attenuation, accounting for the contribution old star heating to the IR luminosity. I find that a large fraction of the IR luminosity of red galaxies may be contributed by absorption of optical light from older stars. I also compare the IR and UV measures of star formation and attenuation to optical measures, such as H-alpha luminosity, finding good agreement for rapidly star-forming blue galaxies. This work was supported by NASA GSRP grant NNG05GO43H

  7. Exoplanet Host Star Radiation and Plasma Environment

    NASA Astrophysics Data System (ADS)

    Linsky, Jeffrey L.; Gdel, Manuel

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

  8. Star dust.

    PubMed

    Ney, E P

    1977-02-11

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

  9. Star Images, Star Performances (College Course File).

    ERIC Educational Resources Information Center

    Butler, Jeremy G.

    1990-01-01

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

  10. STATISTICAL PROPERTIES OF GALACTIC {delta} SCUTI STARS: REVISITED

    SciTech Connect

    Chang, S.-W.; Kim, D.-W.; Byun, Y.-I.; Protopapas, P. E-mail: kim@mpia-hd.mpg.de

    2013-05-15

    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.

  11. Photometry of symbiotic stars - an international campaign IV. Z And, EG And, R Aqr, UV Aur, TX CVn, T CrB, BF Cyg, CH Cyg, CI Cyg, V 1016 Cyg, AG Dra, CQ DRA (4 Dra), YY Her, V 443 Her, SS Lep, AG Peg, AX Per, FG Sge, V 1017 Sgr, FG SER (AS 296), PU Vul, AS 338, AS 360, MWC 560, GH Gem, He2-468

    NASA Astrophysics Data System (ADS)

    Hric, V.; Skopal, A.; Urban, Z.; Komzik, R.; Luthardt, R.; Papousek, J.; Hanzl, D.; Blanco, C.; Niarchos, P.; Velic, Z.; Schweitzer, E.

    1993-07-01

    We present new observations of 26 symbiotic and symbiotic-like stars. The photoelectric UBV observations were made during the years 1982-92, the photographic in 1989-92 and visual in 1989-92. The most interesting results can be summarized as follows: EG And: There is an apparent increase in all three colours corresponding to the ascending branch of the secondary minimum. UV Aur: The long-term photoelectric photometry supports our earlier identification of the red giant component as the primary cause of light variations. BF Cyg: UBV data cover well the last active phase of the star with maximum around 1990 July. CH Cyg: The photoelectric data cover the sudden light brightening starting in Feb-Mar 1992 and decline in Sep 1992. CI Cyg: Long-term UBV observations are presented. AG Dra: UBV photometry cover almost all the interval since the last outburst. CQ Dra: The star's brightness has been decreasing monotonically during the present observational period. AX Per: Our UBV data reveal an outburst (maximum around Nov 1989) with a total of five minima occurring during the observational interval.

  12. Two UV colours of the central part of M 31

    NASA Technical Reports Server (NTRS)

    Deharveng, J. M.; Laget, M.; Monnet, G.; Vuillemin, A.

    1976-01-01

    Two photographs of the galaxy M 31 have been obtained in the far UV with a Faust rocket experiment and in the near UV with the S 183 experiment aboard Skylab. Only the central part of the galaxy is detected. Reductions provide both the energy received and the angular area over M 31 from which it is emitted. The UV flux is brighter than expected from extrapolation of the visible spectrum. The distribution below 300 A is rather flat and different from previous OAO-2 observations. These results, combined with Lyman continuum flux evaluation, are used to discuss the temperature and the age of the stars which may be responsible for this anomalous UV distribution.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

    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.

  15. Integrated UV fluxes and the HB morphology of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Landsman, W. B.; Catelan, M.; O'Connell, R. W.; Pereira, D.; Stecher, T. P.

    2001-12-01

    The UV ( ~ 1500 ) flux of a globular cluster will be dominated by its blue horizontal branch (HB) population, provided that such a population is present. Thus, the integrated UV - V color of a globular cluster can provide an indication of its HB morphology, without the need to resolve the cluster into a color-magnitude diagram. To date, UV photometry of extragalactic clusters are available for only a few globulars in M31 (e.g. Bohlin et al. 1993, ApJ, 417, 127), but additional UV photometry of extragalactic globulars is soon expected from GALEX (Yi et al. 2001, AAS, 198, 5501), and from STIS FUV-MAMA observations of M87 (HST program 8643). Here we calibrate the relation between UV flux and HB morphology for Galactic globular clusters. The OAO-2 and ANS data tabulated by deBoer (1985, A&A, 142, 321) are supplemented with photometry of 14 globular clusters observed with the Ultraviolet Imaging Telescope (UIT), and a few cluster cores observed with the STIS FUV-MAMA. The UIT data is especially useful since its 40' diameter FOV was sufficient to completely encompass most of the observed clusters, while allowing isolation of hot field and UV-bright stars. We compare the observed Galactic UV color - HB morphology relation with synthetic HB models as a function of age and metallicity. We also estimate the effect of radiative levitation of heavy metals in hot HB stars (e.g. Moehler et al. 2000, , A&A, 360, 120) on the integrated UV flux. This work is funded by STScI grant GO-8358.01.

  16. Are You UV Safe?

    ERIC Educational Resources Information Center

    Capobianco, Brenda; Thiel, Elizabeth Andrew

    2006-01-01

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

  17. Are You UV Safe?

    ERIC Educational Resources Information Center

    Capobianco, Brenda; Thiel, Elizabeth Andrew

    2006-01-01

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

  18. Ultraviolet Imaging Telescope photometry of massive stars - The OB association NGC 206 in M31

    NASA Technical Reports Server (NTRS)

    Hill, Jesse K.; Pfarr, Barbara B.; Bohlin, Ralph C.; Isensee, Joan E.; O'Connell, Robert W.; Neff, Susan G.; Roberts, Morton S.; Smith, Andrew M.; Stecher, Theodore P.

    1992-01-01

    The Ultraviolet Imaging Telescope (UIT) obtained UV images of the giant M31 OB association NGC 206. Magnitudes in bands at 1520 and 2490 A were obtained for 30 massive stars, which demonstrate the effectiveness of UIT for photometry of moderately crowded hot stars to V about 21. The UV colors and magnitudes observed for stars in NGC 206 place them in the region of the color magnitude diagram occupied by evolutionary models for 30-60 solar mass stars, after correcting for extinction. The brighter stars are systematically redder than the fainter stars, indicating that they are supergiants of age about 4 Myr, while the fainter, bluer stars are nearer age zero. The relative numbers of probable supergiants measured by us and the number of probable main-sequence O stars measured from optical images are in agreement with the relative lifetimes. Calculated UIT colors are presented for a library of standard star spectra constructed from IUE and ground-based observations.

  19. Searching for Star Formation in the Smith Cloud

    NASA Astrophysics Data System (ADS)

    Baker, Ashley; Stark, D.; Kannappan, S.

    2013-01-01

    Recent discoveries of star formation in regions previously thought impossible implies new criteria for where stars can form. The Smith Cloud, a high velocity cloud (HVC) primarily comprised of neutral hydrogen located 12 kpc away in the halo of the Milky Way, meets these criteria by having a large reservoir of gas and the tidal pull of the Milky Way as a mechanism for perturbing the gas. We obtained GALEX NUV magnitudes for stars in the field of the Smith Cloud. These sources were matched with WISE and 2MASS catalogs to obtain infrared magnitudes. We determined the expected colors of young stars in these wavelength bands using synthetic spectral libraries. By comparing the observed UV and IR colors of stars to the expected colors of young stars, while also comparing star positions to existing 21cm data, we aim to isolate possible recent star formation in the Smith Cloud.

  20. TP-AGB Stars in M31: Results from PHAT

    NASA Astrophysics Data System (ADS)

    Girardi, L.; Beerman, L. C.; Boyer, M. L.; Dalcanton, J. J.; Dolphin, A.; Fouesnaeu, M.; Hamren, K.; Johnson, L. C.; Lang, D.; Lewis, A.; Marigo, P.; Rosenfield, P.; Senchyna, P.; Seth, A. C.; Veyette, M.; Weisz, D. R.; Williams, B. F.

    2015-08-01

    The Panchromatic Hubble Andromeda Treasury (PHAT) is an HST multi-cycle treasury program that mapped one-third of M31 from the UV through the near-IR. It provides photometry in up to 6 filters for about 117 million stars distributed across 20 kpc of the M31 disk, with a spatial resolution comparable to that routinely attained for the Magellanic Clouds from the ground. These data are revolutionising our view of the spatial distribution of stars and dust across M31. Here we present an overview of PHAT data and results, with a focus on the thermally-pulsing asymptotic giant branch (TP-AGB) stars. We comment on (1) the overall spatial distribution of TP-AGB stars as compared to stars of the red giant branch (RGB); (2) the detection of a dramatic drop in the C/M ratio toward the inner M31 disk; (3) the large population of TP-AGB stars in star clusters; (4) an improved view of the planetary nebula population; and (5) the unusual populations of UV-bright stars in the M31 bulge, which correspond to either post-AGB or "failed-AGB stars. These rich datasets allow us to test the evolution of TP-AGB stars in a metal-rich and star-forming environment, avoiding the incompleteness and distance uncertainties that severely limit similar studies in the Milky Way.

  1. Chemical and UV Mutagenesis.

    PubMed

    Bose, Jeffrey L

    2016-01-01

    The ability to create mutations is an important step towards understanding bacterial physiology and virulence. While targeted approaches are invaluable, the ability to produce genome-wide random mutations can lead to crucial discoveries. Transposon mutagenesis is a useful approach, but many interesting mutations can be missed by these insertions that interrupt coding and noncoding sequences due to the integration of an entire transposon. Chemical mutagenesis and UV-based random mutagenesis are alternate approaches to isolate mutations of interest with the potential of only single nucleotide changes. Once a standard method, difficulty in identifying mutation sites had decreased the popularity of this technique. However, thanks to the recent emergence of economical whole-genome sequencing, this approach to making mutations can once again become a viable option. Therefore, this chapter provides an overview protocol for random mutagenesis using UV light or DNA-damaging chemicals. PMID:25646611

  2. A Spectral Atlas of lambda Bootis Stars

    NASA Astrophysics Data System (ADS)

    Paunzen, E.; Heiter, U.

    2014-06-01

    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).

  3. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Lige (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99-2 in the LMC. PR Photo 09c/03: Nebula near the hot binary star BAT99-49 in the LMC. PR Photo 09d/03: The N44C Nebula in the LMC. Four unique images of highly excited nebulae in the Magellanic Clouds ESO PR Photo 09a/03 ESO PR Photo 09a/03 [Preview - JPEG: 400 x 472 pix - 74k [Normal - JPEG: 800 x 943 pix - 720k] [Full-Res - JPEG: 1200 x 1414 pix - 1.2M] ESO PR Photo 09b/03 ESO PR Photo 09b/03 [Preview - JPEG: 400 x 466 pix - 70k [Normal - JPEG: 800 x 931 pix - 928k] [Full-Res - JPEG: 1200 x 1397 pix - 1.8M] ESO PR Photo 09c/03 ESO PR Photo 09c/03 [Preview - JPEG: 400 x 469 pix - 74k [Normal - JPEG: 800 x 937 pix - 1.1M] [Full-Res - JPEG: 1200 x 1405 pix - 2.2M] ESO PR Photo 09d/03 ESO PR Photo 09d/03 [Preview - JPEG: 400 x 473 pix - 28k [Normal - JPEG: 800 x 945 pix - 368k] [Full-Res - JPEG: 1200 x 1418 pix - 600k] Captions: PR Photo 09a/03 is a reproduction of a "near-true" three-colour composite image of the highly excited nebula around the hot double star AB7 in the Small Magellanic Cloud (SMC), obtained in January 2002 with the FORS1 multi-mode instrument at the 8.2-m VLT MELIPAL telescope at the Paranal Observatory (Chile). It is based on three exposures through narrow-band optical (interference) filters that isolate the light from specific atoms and ions. In this rendering, the blue colour represents the light from singly ionized Helium (He II; wavelength 468.6 nm; exposure time 30 min), green corresponds to doubly ionized oxygen ([O III]; 495.7 + 500.7 nm; 5 min) and red to hydrogen atoms (H; H-alpha line at 656.2 nm; 5 min). Of these three ions, He II is the tracer of high excitation, i.e. the bluest areas of the nebula are the hottest. The sky field measures 400 x 400 arcsec2; the original pixel size on the 2k x 2k CCD is 0.23 arcsec. North is up and east to the left. Before combination, the CCD frames were flat-fielded and cleaned of cosmic-rays. Moreover, the stars in the blue (He II) image were removed in order to provide a clearer view of the surrounding nebular emission. The reproduced brightness is proportional to the square-root of the actual intensity; this increases the "dynamical range" of the image, i.e. it shows better areas of very different brightness. PR Photo 09b/03 is a similar reproduction of the sky area with the nebula near the Wolf-Rayet (WR) star BAT99-2 in the LMC. The filters are the same, but the exposure times were 60, 5 and 5 min for the blue, green and red exposures, respectively. PR Photo 09c/03 shows, in the same way, the nebula around the hot double star BAT99-49 in the LMC. The filters are the same, but the exposure times were 45, 5 and 5 min for the blue, green and red exposures, respectively. Finally, PR Photo 09d/03 shows the N44C nebula in the LMC, photographed through the same optical filters with exposure times of 20, 5 and 5 min for the blue, green and red exposures, respectively. The sky field measures 208 x 208 arcsec2. The above collection of impressive VLT colour photos is unique. They show some of the highest excitation nebulae in the Magellanic Clouds (MCs), two satellite galaxies of our own Milky Way. They may be enjoyed for their beauty alone. However, each of them also carries a message about the depicted objects, their properties and evolutionary state. In fact, they represent the spectacular and visible result of a dedicated research programme begun by an international team of astronomers from Belgium and the United States of America [1], and aimed at unravelling the secrets of unsually hot nebulae. What makes them shine? From where come the enormous energies needed to make these nebulae glow in the light of ionized helium atoms? Emission nebulae Nebulae are huge clouds of gas and dust, the cosmic material from which stars and planets form, cf. the Appendix. Many of them emit their own light, and are then called emission nebulae. Astronomers distinguish between Planetary Nebulae (PNe), Supernova Remnants (SNRs) and "normal" emission nebulae or "HII regions" (pronounced "Eitch-two"). PNe result from the death of comparatively light stars, similar to our Sun, while SNRs originate from the explosive death of heavier stars. The collision between the surrounding interstellar matter and that ejected by the dying star, accompanied by the intense radiation from the hot stellar remnant (white dwarf, neutron star) excites the gas and makes it shine brightly. But the radiation of young hot stars embedded in an interstellar cloud is also able to heat the surrounding gas, resulting in the apparition of another type of emission nebula, that shines mostly in the light of ionized hydrogen (H) atoms. Such nebulae are therefore often referred to as "HII regions". The well-known Orion Nebula is an outstanding example of that type of nebula, cf. ESO PR Photos 03a-c/01. Highly excited nebulae The hotter the central object of an emission nebula, whether a white dwarf, a neutron star or just a young star, the hotter and more excited will be the surrounding nebula. The word "excitation" refers to the degree of ionization of the nebular gas. The more energetic the impinging particles and radiation, the more electrons will be lost and higher is the degree of excitation. Only in the most excited nebulae is there enough ultraviolet energy to completely ionize the helium atoms. When these ions subsequently capture an electron, this process gives rise to the characteristic radiation of single ionized helium (HeII). A particularly useful way to trace the very highest excitation areas is thus to map the distribution of HeII by means of imaging or spectroscopic observations that are sensitive to the radiation from these helium ions, for example at a particular wavelength in blue light (468.6 nm). It is common to detect the presence of HeII in Planetary Nebulae around extremely hot white dwarf stars, but not in "normal" HII regions. However, a few otherwise seemingly normal HII regions reveal the characteristics of high excitation. One of them is located in our own Milky Way galaxy, another has been found in the nearby galaxy IC 1613, and five others are situated in the Magellanic Clouds. Astronomers have also detected the presence of HeII ions in a number of remote galaxies undergoing a phase of intense star formation ("starburst galaxies") and in the vicinity of ultraluminous X-ray sources in very distant galaxies. What is going on in those remote objects in the early Universe? Do we see the action of young and very hot stars or is something unknown going on? What can the existence of those hot nebulae in young galaxies tell about the evolution of our own Milky Way? Searching for the energy source We would like to know, but those distant nebulae are unfortunately too faint to be studied in any reasonable detail, even by means of the largest available telescopes. The only way forward is therefore to look closer at the nearest ones in the hope that they will provide clues about the processes leading to the observed high excitation and thus help to better understand their cousins in those distant galaxies. There appears to be three possible answers to the basic question about the nature of the energetic sources that heat these strange emission nebulae: * very fast particles: if there is in the area a fast-moving gas (more than 100 km/s), the shock created by the impact of this material is able to heat the ambient interstellar medium sufficiently to produce a HeII nebula. * ultraviolet emission from massive stars: according to the most recent model calculations, even the most massive O-type stars do not emit enough ultraviolet light to ionize a sufficient number of helium atoms in the surrounding nebula to produce a detectable HeII nebula. However, some of the hottest stars of the so-called Wolf-Rayet (W-R) type (that are the evolved descendants of O-stars) may produce enough high energy emission to completely ionize the helium atoms in their surroundings. * intense X-ray emission: close binary stars in which one component is a "compact" object (a white dwarf, a neutron star, or a black hole) and the other an "ordinary" star can produce an intense X-ray emission. This happens because the compact object is so dense and massive that it siphons off matter from its companion star - astronomers refer to this as an accretion process, sometimes also called "stellar cannibalism". When the "stolen" matter approaches the compact object, it gradually heats up and may reach temperatures of millions of degrees. It then emits X-rays. At the same time, ultraviolet radiation is also emitted, which may produce high excitation regions in the surrounding nebula. This scenario can also explain the association of HeII nebulae with ultraluminous X-ray sources in other galaxies. VLT observations of highly excited nebulae in the MCs Observations of a number of highly excited nebulae in the Magellanic Clouds were carried out by a team composed of Belgian and American astronomers [1] in January 2002, by means of the FORS1 multi-mode instrument at the 8.2-m VLT MELIPAL telescope. Detailed images were obtained through various special optical filters - they bring into light the complex structure of these nebulae and reveal for the first time the exact morphology of the high excitation zones. Some of exposures have been combined to produce the colour photos shown in PR Photos 09a-d/03. Here, the blue colour traces the exceptional HeII emission, whilst the red and green correspond to the more common nebular emissions from atomic hydrogen and doubly-ionized oxygen, respectively. All four nebulae shown were found to be associated with very hot stars. They carry rather prosaic names: BAT99-2 and BAT99-49, AB7 and N44C Star #2 [2]. The first three of these objects contain some of the highly evolved massive stars, of the so-called Wolf-Rayet (WR) type, while the fourth is an mid-age massive star, of type O. Massive stars, with masses more than 20 times that of the Sun, are very bright (100,000 to 10 million times brighter than the Sun), very blue and very hot, with surface temperatures of a few tens of thousands of degrees. Another property of these exceptional stars is their very strong stellar winds: they continuously eject energetic particles - like the "solar wind" from the Sun - but some 10 to 1000 million times more intensely than our star! These powerful winds exert an enormous pressure on the surrounding interstellar material and forcefully shape those clouds into "bubbles". These photos have now provided the astronomers with sufficient information to understand exactly what is going on in three of those unusual nebulae - while one case still remains ambiguous. The nebulae around BAT99-2, BAT99-49 and AB7 BAT99-2 (cf. PR Photo 09b/03) is one of the hottest WR-stars known in the Large Magellanic Cloud (LMC). Before this star reached this phase of its short life, the strong stellar wind from its progenitor O-type star swept the interstellar medium and created a "bubble", much like a snowplough pushes aside the snow on a road. Part of this "bubble" can still be seen as a large half-ring to the south of the star. When the star did become a WR, the increasingly intense stellar wind impacted on the material previously ejected from the star. This created a new bubble, now visible as a small arc-like structure to the north-west of the star. We are appparently witnessing an ongoing merger of these two bubbles. With its strong ultraviolet (UV) radiation, BAT99-2 is strongly heating its immediate surroundings, in particular the above mentioned arc-like feature that, due to the resulting high excitation, is seen as a violet-pink region in the colour image. The entire field is very complex - the presence of a supernova remnant (SNR) is revealed by a few faint red filaments rather close to the high excitation nebula, to the north-west of the arc-like structure. AB7 (PR Photo 09a/03) and BAT99-49 (PR Photo 09c/03) are both binary stars, consisting of one WR-star and a companion O-type star. Like in the case of BAT99-2, the strong UV-radiation from their WR-star has created HeII nebulae around them, well visible in the photos by their blue colour. AB7 is particularly remarkable: the associated huge nebula and HeII region indicate that this star is one of the, if not THE, hottest WR-star known so far, with a surface temperature in excess of 120,000 degrees! Just outside this nebula, a small network of green filaments is visible - they are the remains of another supernova explosion. The new VLT images, complemented with VLT spectra, demonstrate that these stars are indeed the source of the observed ionization. These very first maps of the HeII emission unveil the as yet undiscovered complex structure of those highly excited nebulae. Moreover, the new observations provide the first accurate determination of the true ionizing power of these exceptional stars. They allow a direct measurement of the otherwise unobservable intensity of the far-UV emission of WR stars. The new observations have clearly identified the ultraviolet emission of very massive stars as the energy source in these three nebulae. Using the latest theoretical models to interpret these unique data, the Belgian astronomers and their American collaborator were also able to show that all of these stars are hotter than 90,000 degrees! The N44C nebula The fourth photo, PR Photo 09d/03, shows the very peculiar nebula N44C in the LMC. There is a beautiful (blue) HeII nebula near the two central stars. It is very different from the larger, "normal" HII region that is delimited by the light from atomic hydrogen (red) and doubly-ionized oxygen (green): this hot central region of N44C rather appears to "enshroud" the stars like a veil. There is a mystery, though. With a temperature of "only" a few tens of thousand degrees, even the hottest of the two stars, an O-type star (the upper one), cannot possibly be responsible for this inner high excitation nebula [3]. Moreover, no fast motions have so far been detected in the vicinity. Some astronomers have suggested that N44C is a "fossil X-ray nebula". What does that mean ? It may well be that this O-type star is not alone, but actually possesses a compact companion. The X-ray emission from such a binary may not be constant. During their orbital motion, the two stars can move away from each other, and the larger separation may cause the X-ray emission to stop (because of the cessation of accretion of matter onto the compact object). In this case, the observed high excitation nebula could still persist for a short period of time as a "fossil" of the previous X-ray ionized nebula. Later, that part of the nebula would then gradually disappear. However, to the astonishment of the astronomers, the present VLT observations show little or no variation in the HeII emission. Thus the above described "fossil X-ray nebula" explanation does not appear to be completely adequate and the cause of the high excitation in N44C remains a challenge to astronomers. "You can't win them all", says Yal Naz. "We were able to fully understand three nebulae, but we must now look more closely at N44C. I would not be surprised, if we will be able to solve this riddle by means of additional VLT observations." More information The information contained in this press release is based on two research articles to be published in the European research journal "Astronomy & Astrophysics", one of which is available at the preprint website at the Institut d'Astrophysique et de Gophysique de Lige (Belgium). Notes [1]: The team consists of Yal Naz, Grgor Rauw, Jean Manfroid and Jean-Marie Vreux (Lige Institute, Belgium), and You-Hua Chu (University of Illinois, USA). [2]: The names of these stars refer to the research papers in which they were first decribed. BAT99-2 and BAT99-49 are nos. 2 and 49 in the list published by Breysacher, Azzopardi and Testor (A&AS, 137, 117, 1999), AB7 is star no. 7 in the list by Azzopardi and Breysacher (A&A, 75, 120, 1979) and N44C Star #2 is included in a paper by Stasinska, Testor and Heydari-Malayeri (A&A, 170, L4, 1986). [3]: Consequently, contrary to what was possible in the other three nebulae, the observed extent of that nebula does not allow measuring the temperature of the hot O-type star. Contact Yal Naz Institut d'Astrophysique et de Gophysique Lige, Belgium Phone: +32 4 366 97 20 email: naze@astro.ulg.ac.be Appendix: Different types of nebulae   Nebulae are huge clouds of gas and dust, the cosmic material from which stars and planets form. Most of them belong to five main categories, each representing a different physical state. Two of these do not shine by their own light, but three others do. Dark nebulae and reflection nebulae If the gas does not emit visible light by itself, astronomers talk about dark nebulae or reflection nebulae. The former block the light from objects behind them, and they are therefore seen as dark regions in the sky - famous examples are the Barnard 68 "globule" (cf. ESO ESO PR 01/01 and ESO PR Photos 29a-c/99) and the "Horsehead Nebula" (ESO PR Photos 02a-b/02). Contrarily, reflection nebulae appear as bright areas in the sky because their dust particles reflect the light emitted by nearby stars. A good example is the nebulae surrounding some of the brightest stars in the "Pleiades" stellar cluster or in the southern Chamaeleon I area, cf. ESO PR Photo 17c/99. Emission nebulae Other nebulae emit visible light of their own. Astronomers distinguish between Planetary Nebulae (PNs), Supernova Remnants (SNRs) and "normal" emission nebulae or "HII regions" (pronounced "Eitch-two"). When stars die, they eject copious amounts of matter into neighbouring space. These ejecta collide with and heat the surrounding interstellar matter. This is sometimes accompanied by intense radiation from the hot stellar remnant at the centre. These processes excite the interstellar gas (and the ejecta) so that they shine brightly. In the case of lighter stars like the Sun, the remnant object is a hot "white dwarf", a star barely larger than the Earth and the surrounding nebula is called a "Planetary Nebula (PN)". This historical term refers to the planet-like appearance of such a nebula in a small telescope. A fine example is the "Dumbbell Nebula", photographed by the VLT in 1998, cf. ESO PR Photos 38a-b/98. On the other hand, heavier stars explode violently - such dramatic events are seen as supernovae - and leave behind a exceedingly hot and dense, rotating "neutron star" of diameter 10-20 km (or, in the case of the heaviest stars, presumably a "black hole") as well as a surrounding nebula, the supernova remnant (SNR). A famous example is the "Crab Nebula" from the supernova that exploded in the year 1054, cf. ESO PR Photos 40f-i/99. Finally, the radiation of young hot stars embedded in an interstellar cloud is also able to heat the surrounding gas, resulting in the apparition of an emission nebula, that shines mostly in the light of ionized hydrogen (H) atoms. Such nebulae are therefore often referred to as "HII regions". The well-known Orion Nebula is an outstanding example of that type of nebula, cf. ESO PR Photos 03a-c/01.

  4. UV curable materials development

    SciTech Connect

    Parker, B.G.

    1996-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  6. Standardization of UV LED measurements

    NASA Astrophysics Data System (ADS)

    Eppeldauer, G. P.; Larason, T. C.; Yoon, H. W.

    2015-09-01

    Traditionally used source spectral-distribution or detector spectral-response based standards cannot be applied for accurate UV LED measurements. Since the CIE standardized rectangular-shape spectral response function for UV measurements cannot be realized with small spectral mismatch when using filtered detectors, the UV measurement errors can be several times ten percent or larger. The UV LEDs produce broadband radiation and both their peaks or spectral bandwidths can change significantly. The detectors used for the measurement of these LEDs also have different spectral bandwidths. In the discussed example, where LEDs with 365 nm peak are applied for fluorescent crack-recognition using liquid penetrant (non-destructive) inspection, the broadband radiometric LED (signal) measurement procedure is standardized. A UV LED irradiance-source was calibrated against an FEL lamp standard to determine its spectral irradiance. The spectral irradiance responsivity of a reference UV meter was also calibrated. The output signal of the reference UV meter was calculated from the spectral irradiance of the UV source and the spectral irradiance responsivity of the reference UV meter. From the output signal, both the integrated irradiance (in the reference plane of the reference meter) and the integrated responsivity of the reference meter were determined. Test UV meters calibrated for integrated responsivity against the reference UV meter, can be used to determine the integrated irradiance from a field UV source. The obtained 5 % (k=2) measurement uncertainty can be decreased when meters with spectral response close to a constant value are selected.

  7. UV-spektra frn Hubble-teleskopet avsljar en stjrna i Vargen som lagrar tunga isotoper av mycket tunga grundmnen.

    NASA Astrophysics Data System (ADS)

    Johansson, S. E.; Leckrone, D. S.; Wahlgren, G. M.

    1994-09-01

    UV spectra from the Hubble Space Telescope reveal a star that stores heavy isotopes of very heavy elements. Atomic and plasma physics arguments for UV spectroscopy from space borne observatories are given. As an example, the authors discuss the analysis of high resolution spectra of the chemically peculiar star ? Lupi, obtained with the Hubble Space Telescope, in terms of identification of spectral lines of very heavy elements.

  8. Lyman-Werner UV escape fractions from primordial haloes

    NASA Astrophysics Data System (ADS)

    Schauer, Anna T. P.; Whalen, Daniel J.; Glover, Simon C. O.; Klessen, Ralf S.

    2015-12-01

    Population III (Pop III) stars can regulate star formation in the primordial Universe in several ways. They can ionize nearby haloes, and even if their ionizing photons are trapped by their own haloes, their Lyman-Werner (LW) photons can still escape and destroy H2 in other haloes, preventing them from cooling and forming stars. LW escape fractions are thus a key parameter in cosmological simulations of early reionization and star formation but have not yet been parametrized for realistic haloes by halo or stellar mass. To do so, we perform radiation hydrodynamical simulations of LW UV escape from 9-120 M⊙ Pop III stars in 105-107 M⊙ haloes with ZEUS-MP. We find that photons in the LW lines (i.e. those responsible for destroying H2 in nearby systems) have escape fractions ranging from 0 to 85 per cent. No LW photons escape the most massive halo in our sample, even from the most massive star. Escape fractions for photons elsewhere in the 11.18-13.6 eV energy range, which can be redshifted into the LW lines at cosmological distances, are generally much higher, being above 60 per cent for all but the least massive stars in the most massive haloes. We find that shielding of H2 by neutral hydrogen, which has been neglected in most studies to date, produces escape fractions that are up to a factor of 3 smaller than those predicted by H2 self-shielding alone.

  9. Unveiling the nature of ultraluminous X-ray sources via UV spectroscopy

    NASA Astrophysics Data System (ADS)

    Grise, Fabien

    2013-10-01

    Our recent HST/Chandra study of the ultraluminous X-ray source {ULX} in NGC 5408 showed that the X-ray/UV/optical/NIR spectral energy distribution {SED} is consistent with emission from an irradiated accretion disk, while the UV/optical/NIR SED alone can also be explained as a B0I supergiant star. If the accretion disk dominates in the far-UV, then we expect to see a wealth of spectral lines features in the far-UV spectrum. If, instead, the far-UV light arises from an early B supergiant, we expect to see UV lines with strong P-Cygni profiles. To determine the physical origin of the UV/optical/NIR emission, we propose to take a deep look at the far-UV spectrum of the ULX using the unique capabilities of the Cosmic Origins Spectrograph. The spectrum obtained will definitively distinguish between an irradiated accretion disk and a supergiant companion star. Detection of UV lines is likely one of the only direct ways to constrain the physical nature of ultraluminous X-ray sources.

  10. Ultraviolet observations of galaxies in nearby clusters. III. Star-forming galaxies in the Coma cluster.

    NASA Astrophysics Data System (ADS)

    Donas, J.; Milliard, B.; Laget, M.

    1995-11-01

    In a field of 1deg radius centered in the Coma cluster of galaxies, UV (?=2000A) observations with a 40-cm balloon-borne imaging telescope (FOCA) have provided a list of 442 UV sources brighter than m_UV_=18, which are identified in the Godwin et al. (1983) catalogue. 254 are identified as galaxies, 178 as star-like objects and 10 as galaxy-star pairs, unresolved in the UV image. The 254 galaxies fall into two sub-groups. The galaxies brighter than b=17 define a sequence in the (b-r,m_UV_-b) color-color diagram which is well fitted by the models of Bruzual & Charlot (1993); most are cluster members. The galaxies fainter than b=17 show distinctly (m_UV_-b) colors bluer than the former group at the same (b-r); most of them are likely background late-type galaxies. Notably, a significant fraction of the 178 star-like objects have UV magnitudes and colors similar to that of the second group of galaxies; ground-based spectroscopy is required to determine their nature and/or membership. In the UV sample, 61 galaxies have radial velocities consistent with cluster membership. Among them, nearly half are blue (m_UV_-b<1), star-forming galaxies. Their cumulated UV fluxes lead to a star formation rate of ~23h^-2^Msun_/yr. Their velocity distribution shows an unexpected concentration near 7500 km/s and a void in the 6000-7000km/s range. The other half contains red galaxies (m_UV_-b>1) with little or no recent star formation. All early-type galaxies brighter than b=14.5 are detected in UV and have a median color (m_UV_-b)=3.0 in agreement with the representative spectral distribution of an elliptical compiled from IUE. 17 early-types galaxies which have spectroscopic data in the sample of Caldwell et al. (1993) show a correlation between the (m_UV_-b) color and the H? (absorption line) equivalent width; some, with (m_UV_-b)<1, would imply that the last starburst event is younger than 1 Gyr or that a residual star-formation is still present. The median UV flux and the fraction of blue star-forming galaxies which are cluster members show an enhancement at ~25'(0.5h^-1^Mpc) from the cluster center, suggesting that a global physical process might induce star formation in a rich cluster such as Coma.

  11. UV Emission in Type Ia Supernova Elliptical Host Galaxies

    NASA Astrophysics Data System (ADS)

    Tucker, Brad E.

    2015-03-01

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

  12. Eta Carinae: The Central Star

    NASA Astrophysics Data System (ADS)

    Hillier, D. J.; Davidson, K.; Kazunori Ishibashi, K.; Gull, T.

    1999-12-01

    Recent HST STIS observations have revealed the spectrum of the central star in Eta Carinae for the first time. These observations clearly show that the optical spectrum of the central star is dominated by emission lines of H, He 1, and Fe 2. Its spectrum is qualitatively similar to the extreme P Cygni star HDE 316285. Using the non-LTE atmosphere code of Hillier and Miller (1998) we have performed a spectroscopic investigation of the central star. Previously measured IR fluxes indicate that the luminosity of the system is approximately 5x 106 Lsun (for a distance of d=2.5 kpc), which we adopt as the luminosity of the central star. An excellent fit is obtained to the emission line spectrum using a mass loss rate of 10-3Msun yr-1, a terminal wind velocity of 500 kms-1, and a solar Fe abundance (by mass). Due to degeneracies in the model it is difficult to constrain both the effective temperature and the H/He abundance ratio. The most significant discrepancy is that the strength of the P Cygni absorption components is overestimated, particularly on the Fe 2\\ emission lines. These discrepancies may be due to asymmetries in the stellar wind and/or time variability. There may also be a problem for our models in matching the UV spectrum shortward of 1600 Angstroms, but STIS observations of the central star are not yet available, while earlier GHRS observations may be contaminated by nebula emission and/or a companion star. We discuss the implications of our results for the current evolutionary status of ? Car, and for the binary model of Damineli et al. (1997). This research was supported in part by NASA through a grant from the STScI, which is operated by AURA, under NASA contract NAS5-26555. Additional support was provided by NASA grant NAG5-8211.

  13. UV matters in shoaling decisions

    PubMed Central

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

    2005-01-01

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

  14. UV Radiation and the Skin

    PubMed Central

    D’Orazio, John; Jarrett, Stuart; Amaro-Ortiz, Alexandra; Scott, Timothy

    2013-01-01

    UV radiation (UV) is classified as a “complete carcinogen” because it is both a mutagen and a non-specific damaging agent and has properties of both a tumor initiator and a tumor promoter. In environmental abundance, UV is the most important modifiable risk factor for skin cancer and many other environmentally-influenced skin disorders. However, UV also benefits human health by mediating natural synthesis of vitamin D and endorphins in the skin, therefore UV has complex and mixed effects on human health. Nonetheless, excessive exposure to UV carries profound health risks, including atrophy, pigmentary changes, wrinkling and malignancy. UV is epidemiologically and molecularly linked to the three most common types of skin cancer, basal cell carcinoma, squamous cell carcinoma and malignant melanoma, which together affect more than a million Americans annually. Genetic factors also influence risk of UV-mediated skin disease. Polymorphisms of the melanocortin 1 receptor (MC1R) gene, in particular, correlate with fairness of skin, UV sensitivity, and enhanced cancer risk. We are interested in developing UV-protective approaches based on a detailed understanding of molecular events that occur after UV exposure, focusing particularly on epidermal melanization and the role of the MC1R in genome maintenance. PMID:23749111

  15. Chameleon stars

    SciTech Connect

    Dzhunushaliev, Vladimir; Folomeev, Vladimir; Singleton, Douglas

    2011-10-15

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

  16. Subdwarf B and O Stars: Which Evolutionary Pathways?

    NASA Astrophysics Data System (ADS)

    Napiwotzki, R.

    2009-03-01

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

  17. UV observations of two extremely helium rich stars

    NASA Astrophysics Data System (ADS)

    Heber, U.; Schonberner, D.

    1980-04-01

    Ultraviolet spectrograms of BD + 10 deg 2179 and BD - 9 deg 4395 were obtained with the International Ultraviolet Explorer in the low resolution mode. No evidence for mass loss was found. The observations were analyzed by comparison with detailed LTE-model fluxes including 800 atomic transitions. The results confirm earlier analyses of visual spectra.

  18. An Atlas of GALEX UV Images of Interacting Galaxies

    NASA Astrophysics Data System (ADS)

    Giroux, M. L.; Smith, B. J.; Struck, C.; Hancock, M.; Hurlock, S.

    2010-06-01

    We present GALEX ultraviolet images from a survey of strongly interacting galaxy pairs, and compare with images at other wavelengths. The tidal features are particularly striking in the UV images. Numerous knots of star formation are visible throughout the disks and the tails and bridges. We also identify a possible `Taffy' galaxy in our sample, which may have been produced by a head-on collision between two disk galaxies.

  19. UV Photography Shows Hidden Sun Damage

    MedlinePLUS

    ... skin UV photography shows hidden sun damage UV photography shows hidden sun damage A UV photograph gives ... developing skin cancer and prematurely aged skin. Normal photography UV photography 18 months of age: This boy's ...

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

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

    SciTech Connect

    Bohlin, R.C.; Cornett, R.H.; Hill, J.K.; O'connell, R.W.; Stecher, T.P. ST Systems Corp., Lanham, MD Virginia Univ., Charlottesville NASA, Goddard Space Flight Center, Greenbelt, MD )

    1990-03-01

    UV images of M51 with up to 15 arcsec resolution were obtained by a rocket-borne telescope. The bandwidth was 970 A with maximum response at 2650 A. The two most prominent features of M51 in the UV are the bright central region and a region of intense star formation about 2.5 NE of the nucleus toward the companion NGC 5195. This complex is the source of 20 percent of the total UV flux in M51. The companion is much less prominent in the UV than in optical bands. Spiral arms show much higher contrast in UV and U bands than in the R band. The nuclear region in the UV band shows clumped emission from probable star-forming regions, possibly associated with the inner Lindblad resonance. These regions are probably the UV counterparts of FIR sources discovered in an EW scan across the nucleus. UV/U colors of most bright H II regions with known extinction are consistent with O star spectra reddened by amounts estimated from radio and Balmer line measurements. However, some of the brightest H II regions have redder UV/U colors, probably indicating the presence of cooler stars which contribute in the U band. CO and IR observations indicate that the companion NGC 5195 may be a reddened starburst in spite of its faintness in the UV. 55 refs.

  2. Near-simultaneous ultraviolet and optical spectrophotometry of T Tauri stars

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  3. Population studies I. The Bidelman-MacConnell ''weak-metal'' stars

    SciTech Connect

    Norris, J.; Bessell, M.S.; Pickles, A.J.

    1985-07-01

    We present BVRI and DDO photometry for 309 of the Bidelman-MacConnell ''weak-metal'' stars, together with radial velocities for most of the stars that have (Fe/H)< or =-0.8. Photometric taxonomy is used to classify the sample as giants, dwarfs, red horizontal-branch stars, UV-bright stars, etc., and various calibrations have been adopted to determine (Fe/H), M/sub V/, space motions, and orbital eccentricity e.

  4. Massive star-formation regions in the Magellanic Clouds

    SciTech Connect

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

    1988-08-01

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

  5. Star Power

    SciTech Connect

    2014-10-17

    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.

  6. Star Power

    ScienceCinema

    None

    2014-11-18

    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.

  7. Brittle Star

    USGS Multimedia Gallery

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

  8. Ultraviolet interstellar extinction toward 1367 stars observed by ANS

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1995-01-01

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

  10. UV detectors for spectrographs of WSO-UV project

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

    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.

  11. UV Curable Polyimides

    NASA Technical Reports Server (NTRS)

    Meador, Michael; Oliver, Thomas

    2001-01-01

    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.

  12. Uvs Nuur, Mongolia

    NASA Technical Reports Server (NTRS)

    2007-01-01

    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.

  13. IUE observations of symbiotic stars

    NASA Technical Reports Server (NTRS)

    Hack, M.

    1982-01-01

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

  14. Coronal Structures in Cool Stars

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

    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.

  15. Electron stars for holographic metallic criticality

    SciTech Connect

    Hartnoll, Sean A.; Tavanfar, Alireza

    2011-02-15

    We refer to the ground state of a gravitating, charged ideal fluid of fermions held at a finite chemical potential as an ''electron star.'' In a holographic setting, electron stars are candidate gravity duals for strongly interacting finite fermion density systems. We show how electron stars develop an emergent Lifshitz scaling at low energies. This IR scaling region is a consequence of the two-way interaction between emergent quantum critical bosonic modes and the finite density of fermions. By integrating from the IR region to an asymptotically AdS{sub 4} spacetime, we compute basic properties of the electron stars, including their electrical conductivity. We emphasize the challenge of connecting UV and IR physics in strongly interacting finite density systems.

  16. Chemical abundances in Hg-Mn stars

    NASA Technical Reports Server (NTRS)

    Heacox, W. D.

    1979-01-01

    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.

  17. UV extinction and IR emission in diffuse H2 regions

    NASA Technical Reports Server (NTRS)

    Aannestad, Per A.

    1994-01-01

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

  18. Characterizing Pale Blue Dots Around FGKM Stars

    NASA Astrophysics Data System (ADS)

    Rugheimer, Sarah; Kaltenegger, Lisa; Sasselov, Dimitar; Segura, Antigona

    2015-12-01

    Exoplanet characterization of small rocky worlds will be a main focus in the coming decades. For future telescopes like JWST and UVOIR/HDST, an exoplanet’s host star will influence our ability to detect and interpret spectral features, including biosignatures. We present a complete suit of stellar models and a grid of model atmospheres for Earth-like planets at equivalent stages of geological evolution in their HZ for stellar effective temperature from Teff = 2300K to 7000K, sampling the entire FGKM stellar type range. Since M dwarfs are simultaneously the most numerous in the universe, the most active, and the most likely stars to host terrestrial exoplanets, we focus in particular on the range of UV emission possible in each sub M spectral class. The UV emission from a planet's host star dominates the photochemistry and thus the resultant observable spectral features of the planet. Using the latest UV spectra obtained by HST and IUE we model the effect of stellar activity on Earth-like planets. We also model the amount of UV flux reaching the surface for Earth-like planets at various geological epochs ranging from a pre-biotic world through the rise of oxygen and for Earth-like planets orbiting FGKM stars at equivalent stages of evolution. When modeling the remotely detectable spectra of these planets we focus on the primary detectable atmospheric features that indicate habitability on Earth, namely: H2O, CO2, O3, CH4, N2O and CH3Cl. We model spectra of Earth-like planets orbiting our grid of FGKM stars in the VIS/NIR (0.4 - 4 μm) and the IR (5 - 20 μm) range as input for future missions and concepts like UVOIR/HDST and JWST.

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

    NASA Astrophysics Data System (ADS)

    Dalessandro, Emanuele

    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.

  20. Converting neutron stars into strange stars

    NASA Technical Reports Server (NTRS)

    Olinto, A. V.

    1991-01-01

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

  1. UV doses of young adults.

    PubMed

    Godar, Dianne E; Urbach, Frederick; Gasparro, Francis P; van der Leun, Jan C

    2003-04-01

    Since 1986, people have been informed that they get about 80% of their lifetime ultraviolet (UV) dose by the age of 18. This belief originated from the mathematical conclusion that diligent use of sunscreens (sun protection factor 15 or higher) during the first 18 years of life would reduce the lifetime incidence of nonmelanoma skin cancers by 78%. These data were misconstrued to mean that individuals also got about 80% of their lifetime dose of UV by the age of 18 (linear relationship). However, these calculations were based on the incidence of nonmelanoma skin cancers being related to the square of the UV dose. Careful analysis of UV exposure data shows that Americans actually get less than 25% of their lifetime UV dose by the age of 18. This finding also appears to be true worldwide because Australia, UK and The Netherlands report a similar UV exposure pattern. UV-initiated damage early in life can be promoted by subsequent exposures to progress into tumors later in life. For example, the nonmelanoma skin cancer, squamous cell carcinoma, is dependent on the cumulative UV dose. Thus, a better educational approach for reducing skin cancers would be to instruct fair-skinned individuals to protect themselves throughout their lives from being exposed to too much UV radiation. PMID:12733658

  2. T Tauri stars observing campaign

    NASA Astrophysics Data System (ADS)

    Waagen, Elizabeth O.

    2012-11-01

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

  3. Hybrid Stars

    SciTech Connect

    Menezes, D.P.; Providencia, C.

    2004-12-02

    In the present paper we calculate the properties of hybrid stars, namely, its gravitational, baryonic masses and central energy densities by solving the Tolman-Volkoff-Oppenheimer equations, which were derived from Einstein's equations for compact stellar objects. In order to obtain these properties, an adequate equation of state (EOS) is necessary. Hybrid stars are formed when a phase transition to a deconfined phase is thermodinamically possible. In this work we have used the non-linear Walecka model for the hadron matter and the MIT Bag (unpaired quark phase) and the Nambu-Jona-Lasinio (NJL) models for the quark matter in order to build the appropriate equations of state for the mixed phase constituted by hadrons and quarks in {beta}-equilibrium.

  4. Micro UV detector

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

    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.

  5. Micro-UV detector

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    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.

  6. Christmas star.

    NASA Astrophysics Data System (ADS)

    Biała, J.

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

  8. Ultraviolet spectroscopy of the outer layers of stars

    NASA Technical Reports Server (NTRS)

    Snow, T. P., Jr.; Linsky, J. L.

    1980-01-01

    Ultraviolet observations of the extended atmospheres and circumstellar envelopes of early-type and cool stars are reviewed. UV spectra of OB stars have shown that mass loss occurs in virtually all these stars and in many Be stars, and the Copernicus satellite has also provided information on the physical conditions and variability of the winds. The winds have been interpreted in terms of hot coronal wind models, imperfect flow models and radiation pressure models, and estimates of mass loss ranging from 10 to the -10th to 9 x 10 to the -6th solar masses/year have been obtained. Further UV data of faint stars, additional wavelengths and time variability are required. Recent UV and X-ray experiments have detected stellar chromospheres, transition regions coronas and winds in cool stars. Semiempirical line-profile and line-flux models and purely theoretical atmospheric models have been constructed to explain chromosphere, corona and wind data, and future observations of the physical properties of stellar chromospheres, coronas and winds, terms in the energy balance equation, stellar activity and its long-term variability and atmospheric modifications due to the presence of companion stars are proposed for such missions as Spacelab.

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

    NASA Technical Reports Server (NTRS)

    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

    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.

  10. New Star Formation in NGC 3690

    NASA Astrophysics Data System (ADS)

    Abdullah, Ajamu

    2014-01-01

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

  11. Standard stars for photometry of comets

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  12. Mass loss from extreme helium stars

    NASA Astrophysics Data System (ADS)

    Hamann, W.-R.; Schoenberner, D.; Heber, U.

    1982-12-01

    Indications of mass loss are found in the UV spectra of three extreme helium stars (HD 160641, BD -9 deg 4395, and BD +10 deg 2179) obtained with the IUE in high resolution. These three stars are found to lose mass with rates of roughly 10 to the -9th solar mass/yr. These rates have approximately the same order-of-magnitude as expected for 'normal' stars with similar luminosities (about 10,000 solar luminosities), though the final velocities of the winds are distinctly smaller in the case of these three extreme helium stars. Hence, it is stated as a general result that, in first-order approximation, mass loss rates are independent of the internal structure, evolutionary history, and chemical composition of the star. In addition, within the present sample, the mass loss rates show a decrease with increasing radius, whereas the mass and luminosity of the three program stars are similar. This behavior contradicts all theoretical predictions as well as empirical correlations obtained for early-type stars of normal composition.

  13. The UV Interstellar Extinction Properties in M31

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  14. Star ratings. Stars of wonder.

    PubMed

    Dawes, David

    2002-09-12

    Analysis of trusts that changed their star-rating over the past two years indicates that a change of chief executive was not a significant factor. The length of time in post and the experience of the chief executive were also insignificant. This has serious implications for the theory behind franchising and the evaluation of franchised trusts. Holding chief executives to account for the organisation's performance within their first 12 months is unlikely to be effective. PMID:12357738

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  16. Deep UV LEDs

    NASA Astrophysics Data System (ADS)

    Han, Jung; Amano, Hiroshi; Schowalter, Leo

    2014-06-01

    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.

  17. III-Nitride UV Devices

    NASA Astrophysics Data System (ADS)

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

    2005-10-01

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

  18. The kinematics and dynamics of OH masers in circumstellar envelopes of AGB stars

    NASA Astrophysics Data System (ADS)

    Gerard, E.

    Among circumstellar molecular lines, the OH lines at 18 cm wavelength are the strongest and the most stable. The maser emission often consists of narrow and intense features which may be used to detect possible secular velocity shifts (accelerations) over months or years. Spectral features of OH masers in Mira and OH/IR stars often appear and disappear and vary in intensity. Such variations are generally correlated with the stellar light cycle but also occur from cycle to cycle. They are commonly attributed to the pumping mechanism. Hence, blended lines often show apparent velocity shifts. But with high signal-to-noise ratio and high spectral resolution, it may be possible to isolate individual components which have lifetimes of the order of several years and retain the same polarization characteristics like in Mira Ceti. Thus, one should be able to trace their motion through the circumstellar envelopes by combining high spectral resolution observations with single antennas and high spatial resolution observations with interferometers. Such measurements carried out at regular intervals should provide both the radial acceleration and the transverse displacement of those OH clumps. They are also indispensable to sort out the periodic changes due to the stellar light cycle. Finally, the strong Zeeman splitting of the OH lines should shed light on the magnetic field structure of the envelope. A few examples are taken from the long term monitoring of several circumstellar OH masers with the Nanccay Radio Telescope.

  19. The mechanisms of UV mutagenesis.

    PubMed

    Ikehata, Hironobu; Ono, Tetsuya

    2011-01-01

    Ultraviolet (UV) light induces specific mutations in the cellular and skin genome such as UV-signature and triplet mutations, the mechanism of which has been thought to involve translesion DNA synthesis (TLS) over UV-induced DNA base damage. Two models have been proposed: "error-free" bypass of deaminated cytosine-containing cyclobutane pyrimidine dimers (CPDs) by DNA polymerase ?, and error-prone bypass of CPDs and other UV-induced photolesions by combinations of TLS and replicative DNA polymerases--the latter model has also been known as the two-step model, in which the cooperation of two (or more) DNA polymerases as misinserters and (mis)extenders is assumed. Daylight UV induces a characteristic UV-specific mutation, a UV-signature mutation occurring preferentially at methyl-CpG sites, which is also observed frequently after exposure to either UVB or UVA, but not to UVC. The wavelengths relevant to the mutation are so consistent with the composition of daylight UV that the mutation is called solar-UV signature, highlighting the importance of this type of mutation for creatures with the cytosine-methylated genome that are exposed to the sun in the natural environment. UVA has also been suggested to induce oxidative types of mutation, which would be caused by oxidative DNA damage produced through the oxidative stress after the irradiation. Indeed, UVA produces oxidative DNA damage not only in cells but also in skin, which, however, does not seem sufficient to induce mutations in the normal skin genome. In contrast, it has been demonstrated that UVA exclusively induces the solar-UV signature mutations in vivo through CPD formation. PMID:21436607

  20. A catalog of ultraviolet interstellar extinction excesses for 1415 stars

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

  1. Binary stars.

    PubMed

    Paczynacuteski, B

    1984-07-20

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

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  3. [Ozone decline and UV increase].

    PubMed

    Winkler, P; Trepte, S

    2004-02-01

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

  4. Eutactic star closest to a given star

    SciTech Connect

    Gomez, A.; Torres, M.; Aragon, J. L.

    2007-05-15

    A eutactic star is a set of M vectors in R{sup n} (M>n) that are projections of M orthogonal vectors in R{sup M}. Eutactic stars have remarkable properties that have been exploited in several fields such as crystallography, graph theory, wavelets, and quantum measurement theory. In this work we show that given an arbitrary star of vectors, there exists a closest eutactic star in the Frobenius norm. An algorithm for calculating this star is presented. Additionally, the distance between both stars provides a new measure of eutacticity.

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

    SciTech Connect

    Law, Ka-Hei; Gordon, Karl D.; Misselt, K. A. E-mail: kgordon@stsci.edu

    2011-09-10

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

  6. Modelling the variability of the CP star \\varphi Dra

    NASA Astrophysics Data System (ADS)

    Prvk, M.; Krti?ka, J.; Mikulek, Z.; Lftinger, T.; Lika, J.

    2014-11-01

    \\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.

  7. Beryllium and Boron abundances in population II stars

    NASA Technical Reports Server (NTRS)

    1995-01-01

    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.

  8. Very Massive Stars in the Primitive Galaxy, IZw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara

    2012-01-01

    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.

  9. The Formation Mechanism of Helium-Rich Subdwarf B Stars

    NASA Astrophysics Data System (ADS)

    Brown, Thomas M.

    Subdwarf B stars in the Galactic field are the metal-rich counterparts to the extreme horizontal branch stars found in globular clusters, and they are the dominant source of UV emission in old elliptical galaxies. They are distinguished by their high effective temperature T_eff > 25,000 K) and surface gravity (log g > 5). The sdB stars all show significant abundance anomalies most are extremely deficient in helium and heavy elements, but a minority are helium-rich. Deficiencies in helium and heavy elements have been attributed to gravitational settling, but the helium-enriched members of the class present a puzzling exception, because radiative levitation should be too weak to prevent gravitational settling. We hypothesize that these helium-rich sdB stars are the result of a delayed helium-core flash on the white dwarf cooling curve. The convective zone produced by this flash will penetrate the hydrogen envelope, mixing hydrogen into the hot helium-burning interior, where is rapidly consumed. The resulting star should show greatly enhanced helium and carbon with respect to the other heavy elements. This phenomenon is analogous to the born again scenario for producing hydrogen-deficient R CrB stars following a very late helium-shell flash. To test this hypothesis, we propose FUSE observations of three helium-rich sdB stars. FUSE observations will provide the first far-UV spectra of this unusual class of stars.

  10. The Galaxy UV Luminosity Function before the Epoch of Reionization

    NASA Astrophysics Data System (ADS)

    Mason, Charlotte A.; Trenti, Michele; Treu, Tommaso

    2015-11-01

    We present a model for the evolution of the galaxy ultraviolet (UV) luminosity function (LF) across cosmic time where star formation is linked to the assembly of dark matter halos under the assumption of a mass-dependent, but redshift-independent, efficiency. We introduce a new self-consistent treatment of the halo star formation history, which allows us to make predictions at z > 10 (lookback time ?500 Myr), when growth is rapid. With a calibration at a single redshift to set the stellar-to-halo mass ratio, and no further degrees of freedom, our model captures the evolution of the UV LF over all available observations (0 ? z ? 10). The significant drop in luminosity density of currently detectable galaxies beyond z 8 is explained by a shift of star formation toward less massive, fainter galaxies. Assuming that star formation proceeds down to atomic cooling halos, we derive a reionization optical depth ? ={0.056}-0.010+0.007, fully consistent with the latest Planck measurement, implying that the universe is fully reionized at z={7.84}-0.98+0.65. In addition, our model naturally produces smoothly rising star formation histories for galaxies with L ? L* in agreement with observations and hydrodynamical simulations. Before the epoch of reionization at z > 10 we predict the LF to remain well-described by a Schechter function, but with an increasingly steep faint-end slope (? -3.5 at z 16). Finally, we construct forecasts for surveys with James Webb Space Telescope (JWST) and Wide-field Infrared Survey Telescope (WFIRST) and predict that galaxies out to z 14 will be observed. Galaxies at z > 15 will likely be accessible to JWST and WFIRST only through the assistance of strong lensing magnification.

  11. Star clusters in the Whirlpool Galaxy

    NASA Astrophysics Data System (ADS)

    Scheepmaker, R. A.

    2009-06-01

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

  12. UV Photography Shows Hidden Sun Damage

    MedlinePLUS

    ... Kids’ zone Video library Find a dermatologist UV photography shows hidden sun damage A UV photograph gives ... developing skin cancer and prematurely aged skin. Normal photography UV photography 18 months of age: This boy's ...

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

    NASA Technical Reports Server (NTRS)

    Hornschemeier, Ann

    2006-01-01

    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.

  14. Red Leak Characterization for the WFPC2 UV Filters

    NASA Astrophysics Data System (ADS)

    Lim, P. L.; Chiaberge, M.; Biretta, J.; di Nino, D.

    2009-12-01

    We characterize the red leaks for all eight WFPC2 UV filters (F122M, F160BW, F170W, F185W, F218W, F250W, F300W, and F336W). We crossed each UV filter with three broad band optical filters (F450W, F606W, and F814W) in order to isolate different spectral regions in the red leak. We observed 15 Mon, an O7Ve-type star, using five different pointings to position the star at different locations on three WFPC2 chips (PC1, WF2, and WF3) to study possible filter inhomogeneities. We also observed g Gem, a K4III-type star, with WF3 as a follow-up to further study selected filters. Our results for F160BW, F170W, F300W, and F336W show good agreement (within 20%) between the observed off-band count rates and those predicted by SYNPHOT. Filters F185W, F218W, and F255W showed significant discrepancies between the observed and predicted values (20% to 250%); we derived new throughput curves for these filters, and delivered them to CDBS. The F122M filter shows evidence for a long-term throughput decline and will require additional studies beyond the scope of this report.

  15. The Void Galaxy Survey: Star Formation Properties

    NASA Astrophysics Data System (ADS)

    Beygu, B.; Kreckel, K.; van der Hulst, J. M.; Jarrett, T. H.; Peletier, R.; van de Weygaert, R.; van Gorkom, J. H.; Aragon-Calvo, M. A.

    2016-02-01

    We study the star formation properties of 59 void galaxies as part of the Void Galaxy Survey (VGS). Current star formation rates are derived from H? and recent star formation rates from near-UV imaging. In addition, infrared 3.4 ?m, 4.6 ?m, 12 ?m and 22 ?m WISE emission is used as star formation and mass indicator. Infrared and optical colours show that the VGS sample displays a wide range of dust and metallicity properties. We combine these measurements with stellar and H I masses to measure the specific SFRs (SFR/M_{*}) and star formation efficiencies (SFR/M_{H I}). We compare the star formation properties of our sample with galaxies in the more moderate density regions of the cosmic web, `the field'. We find that specific SFRs of the VGS galaxies as a function of stellar and H I mass are similar to those of the galaxies in these field regions. Their SFR? is slightly elevated than the galaxies in the field for a given total H I mass. In the global star formation picture presented by Kennicutt-Schmidt, VGS galaxies fall into the regime of low average star formation and correspondingly low H I surface density. Their mean SFR? /M_H I and SFR? /M_{*} are of the order of 10^{-9.9} yr^{-1}. We conclude that while the large scale underdense environment must play some role in galaxy formation and growth through accretion, we find that even with respect to other galaxies in the more mildly underdense regions, the increase in star formation rate is only marginal.

  16. Deep GALEX UV Survey of the Kepler Field. I. Point Source Catalog

    NASA Astrophysics Data System (ADS)

    Olmedo, Manuel; Lloyd, James; Mamajek, Eric E.; Chvez, Miguel; Bertone, Emanuele; Martin, D. Christopher; Neill, James D.

    2015-11-01

    We report observations of a deep near-ultraviolet (NUV) survey of the Kepler field made in 2012 with the Galaxy Evolution Explorer (GALEX) Complete All-Sky UV Survey Extension (CAUSE). The GALEX-CAUSE Kepler survey (GCK) covers 104 square degrees of the Kepler field and reaches a limiting magnitude of NUV ? 22.6 at 3?. Analysis of the GCK survey has yielded a catalog of 669,928 NUV sources, of which 475,164 are cross-matched with stars in the Kepler Input Catalog. Approximately 327 of 451 confirmed exoplanet host stars and 2614 of 4696 candidate exoplanet host stars identified by Kepler have NUV photometry in the GCK survey. The GCK catalog should enable the identification and characterization of UV-excess stars in the Kepler field (young solar-type and low-mass stars, chromospherically active binaries, white dwarfs, horizontal branch stars, etc.), and elucidation of various astrophysics problems related to the stars and planetary systems in the Kepler field.

  17. The Moon in the UV

    NASA Astrophysics Data System (ADS)

    Hendrix, Amanda

    2014-11-01

    While the Moon has been observed in the UV for decades, the real utility of this spectral region for unlocking some of the Moons 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.

  18. The sun, our star

    NASA Astrophysics Data System (ADS)

    Noyes, R. W.

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

  19. Modelling of variability of the chemically peculiar star ? Draconis

    NASA Astrophysics Data System (ADS)

    Prvk, M.; Lika, J.; Krti?ka, J.; Mikulek, Z.; Lftinger, T.

    2015-12-01

    Context. The presence of heavier chemical elements in stellar atmospheres influences the spectral energy distribution of stars. An uneven surface distribution of these elements, together with flux redistribution and stellar rotation, are commonly believed to be the primary causes of the variability of chemically peculiar (CP) stars. Aims: We aim to model the photometric variability of the CP star ? Dra based on the assumption of inhomogeneous surface distribution of heavier elements and compare it to the observed variability of the star. We also intend to identify the processes that contribute most significantly to its photometric variability. Methods: We use a grid of TLUSTY model atmospheres and the SYNSPEC code to model the radiative flux emerging from the individual surface elements of ? Dra with different chemical compositions. We integrate the emerging flux over the visible surface of the star at different phases throughout the entire rotational period to synthesise theoretical light curves of the star in several spectral bands. Results: The synthetic light curves in the visible and in the near-UV regions are in very good agreement with the observed variability of the star. The lack of usable far-UV measurements of the star precludes making any conclusions about the correctness of our model in this spectral region. We also obtained 194 new BVRI observations of ? Dra and improved its rotational period to P = 1 ? 716500(2). Conclusions: We show that the inhomogeneous distribution of elements, flux redistribution, and rotation of the star are fully capable of explaining the stellar variability in the visible and the near-UV regions. The flux redistribution is mainly caused by bound-free transitions of silicon and bound-bound transitions of iron. BVRI photometry of Phi Dra is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A17

  20. Applying Machine Learning to Star Cluster Classification

    NASA Astrophysics Data System (ADS)

    Fedorenko, Kristina; Grasha, Kathryn; Calzetti, Daniela; Mahadevan, Sridhar

    2016-01-01

    Catalogs describing populations of star clusters are essential in investigating a range of important issues, from star formation to galaxy evolution. Star cluster catalogs are typically created in a two-step process: in the first step, a catalog of sources is automatically produced; in the second step, each of the extracted sources is visually inspected by 3-to-5 human classifiers and assigned a category. Classification by humans is labor-intensive and time consuming, thus it creates a bottleneck, and substantially slows down progress in star cluster research.We seek to automate the process of labeling star clusters (the second step) through applying supervised machine learning techniques. This will provide a fast, objective, and reproducible classification. Our data is HST (WFC3 and ACS) images of galaxies in the distance range of 3.5-12 Mpc, with a few thousand star clusters already classified by humans as a part of the LEGUS (Legacy ExtraGalactic UV Survey) project. The classification is based on 4 labels (Class 1 - symmetric, compact cluster; Class 2 - concentrated object with some degree of asymmetry; Class 3 - multiple peak system, diffuse; and Class 4 - spurious detection). We start by looking at basic machine learning methods such as decision trees. We then proceed to evaluate performance of more advanced techniques, focusing on convolutional neural networks and other Deep Learning methods. We analyze the results, and suggest several directions for further improvement.

  1. Overview of the observations of symbiotic stars

    NASA Technical Reports Server (NTRS)

    Viotti, Roberto

    1993-01-01

    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.

  2. X-ray emission from stars

    NASA Astrophysics Data System (ADS)

    Vaiana, G. S.

    1981-11-01

    Data from the Einstein Observatory are examined to discover the processes which lead to the appearance of stellar surface activity. Previous astrophysical observations are reviewed, including stellar X ray, UV, Ca II, H, and K emissions observations, and monitoring of the solar corona. All stars have been observed to emit X rays at one time or another, and the Einstein spacecraft has furnished data on X ray emission and stellar rotation, Ca II, H, and K emission from late-type stars, X ray emission from early-type stars and pre-main-sequence stars, and has provided evidence that X rays are not emitted by stellar winds. Stellar coronae have been identified as the source of the X ray emission in pre-main-sequence stars, and correlations have been found between the level of X ray emission and the rotation rate in late-type stars. Further attention is given to the capture of the energy of infalling and outgassing material by the stellar magnetic fields, and purposes of the AXAF orbiting instrument to be launched by the Shuttle are discussed, specifically for stellar X ray spectrographic observations.

  3. Disk Evaporation in Star Forming Regions

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

  4. Fast and Furious: X-Rays and UV from the WASP-18 System.

    NASA Astrophysics Data System (ADS)

    Pillitteri, Ignazio

    2012-09-01

    Recent observations demonstrate that magnetic and tidal interactions between hot-Jupiters and their host stars manifest as X-ray emission. These interactions, which are a strong function of separation, should accelerate the dynamical evolution of the planet while simultaneously disguising signs of age in the host star. We propose to study the X-ray and UV signatures of star planet interaction in WASP-18, an F6 star with an extreme hot Jupiter orbiting in less than one day at a distance of only 3.5 stellar radii. We ask a 90 ks ACIS-Chandra observation to observe the entire orbit for evidence of phase dependent interactions. Five HST orbits of COS FUV spectroscopy will reveal SPI effects in the chromosphere on transition region of the star.

  5. Chemical Abundances in Three Population II Stars

    NASA Astrophysics Data System (ADS)

    Bonifacio, Piercarlo

    The purpose of this thesis is to describe the abundance analysis of three Pop II stars. Chapter one is a historical review aimed at illustrating how the present-day concepts on stellar populations and the formation of the chemical elements came about. Chapter 2 describes the current views on the chemical an dynamical history of the Galaxy. Chapter 3 contains a brief description of two classes of Pop II stars: blue HB stars and extremely metal-poor G-type stars. The stars which are the object of this thesis belong to these two classes. Feige 86 is a field HB star which has an anomalous chemical composition. We shall argue, in chapter 6, that it represents a Pop II analogue of the Pop I CP stars. Instead CS 22881-39 and CS 22885-96 are ``normal'' G-type giants whose peculiarity is that the iron abundance is some two orders of magnitude below that of the most metal poor globular clusters. This metal deficiency is taken as evidence that these stars were formed out of extremely metal-poor gas, and is not attributed to some sort of atmospheric peculiarity as is the case for the anomalous abundances of Feige 86. Chapter 4 reviews some of the methods used to fix the atmospheric parameters of B-type and G-type stars. Chapter 5 is devoted to the study of the far UV spectrum of the Pop I B-type star Iota Her. The reason for performing this study, and for including it in this thesis, is to provide a ``standard'' spectrum against which the spectrum of ``peculiar'' objects, such as Feige 86, may be compared. This ``standard'' spectrum also provides an ideal test ground for the spectrum synthesis code used throughout this work. Chapter 6 describes the abundance analysis of Feige 86. Chapter 7 describes the abundance analysis of CS 22881-39 and CS 22885-96. In the appendices we provide plots of the UV spectra of Iota Her and Feige 86.

  6. UVS is rare in seabirds.

    PubMed

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

    2011-06-21

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

  7. IUE observations of new A star candidate proto-planetary systems

    NASA Technical Reports Server (NTRS)

    Grady, Carol A.

    1994-01-01

    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.

  8. An ultraviolet-selected galaxy redshift survey: new estimates of the local star formation rate

    NASA Astrophysics Data System (ADS)

    Treyer, Marie A.; Ellis, Richard S.; Milliard, Bruno; Donas, Jose; Bridges, Terry J.

    1998-10-01

    We present the first results of an ongoing spectroscopic survey of galaxies selected in the rest frame ultraviolet (UV). The source catalogue has been constructed from a flux-limited sample of stars, galaxies and QSOs imaged at 2000Angstroms in Selected Area 57 with the FOCA balloon-borne imaging camera. Accurate positions for the UV sources have been obtained by matching with optical counterparts using APM scans of the Palomar Sky Survey limited at B20.5. Here we present results derived from optical spectroscopy conducted with the WIYN telescope and the WHT for 142 faint sources. The redshift distribution for this UV-selected sample extends over 0UV-optical colours bluer than normal Hubble sequence galaxies. Such UV-selected surveys are thus a very efficient way to locate and study intermediate-redshift galaxies undergoing intense star formation. Although our sample is currently small, we derive a rest frame UV luminosity function with a steep faint-end slope consistent with that found for late-type galaxies in optical samples. However, the integrated luminosity density derived implies a volume-averaged star formation rate higher than other recent estimates, assuming a normal initial mass function. If representative of other UV fields, as suggested by UV number count studies, our data imply that the local abundance of star-forming galaxies may have been underestimated, and consequently claims for strong evolution in the global star formation rate in the range 0UV-selected sample is likely to reveal important information on the declining population of star-forming galaxies of all types.

  9. The stellar wind of hot subdwarf stars

    NASA Astrophysics Data System (ADS)

    La Palombara, Nicola

    2010-10-01

    All we know about hot subdwarf (sd) stars is based on studies in the optical and UV domain, while none of them has been detected at X-rays. The only exception is the sdO binary HD49798, in which the WD companion shows a significant X-ray emission, due to the matter accreted from the sd primary. A recent XMM observation of this source has revealed a significant X-ray emission also during the eclipse phase, when the WD is obscured by the primary subdwarf, thus suggesting that the observed X-ray flux is due to the subdwarf itself. In order to investigate if also other sdO stars are characterized by an intrinsic X-ray emission, we propose to observe BD+37 442: it is a nearby and bright sdO star with a strong stellar wind, therefore it is the best candidate to perform this type of search.

  10. Radiation driven winds of hot stars: Theory of O-star atmospheres as a spectroscopic tool

    NASA Astrophysics Data System (ADS)

    Pauldrach, A. W. A.; Feldmeier, A.; Puls, J.; Kudritzki, R. P.

    1993-03-01

    The status of the continuing effort to construct radiation driven wind models for O-Stars atmospheres is reviewed. Emphasis is given to several problems relating to the fomation of UV line spectra the use of accurate atomic data, the inclusion of EUV radiation by shock heated matter, the simulation of photospheric line blocking. A new tool for O-star diagnostics is presented. This is based on the use of wind models to calculate synthetic high resolution spectra covering the observable UV region. A comparison with observed spectra then gives physical constraints on the properties of stellar winds and stellar parameters, additionally abundances can be determined. The astrophysical potential of this method is demonstrated by an application to two Of-stars, the galactic O4f-star ?-Puppis and the LMC O3f-star Melnick 42. With regard to effective temperatures and gravities, the results from the application of classical methods to the analysis of photospheric lines are only partially verified. Explanations for the shortcomings of classical NLTE methods are discussed.

  11. Radiation driven winds of hot stars: theory of O-Star atmospheres as a spectroscopic tool.

    NASA Astrophysics Data System (ADS)

    Pauldrach, A. W. A.; Feldmeier, A.; Puls, J.; Kudritzki, R. P.

    The status of the continuing effort to construct radiation driven wind models for O-Stars atmospheres is reviewed. Emphasis is given to several problems relating to the fomation of UV line spectra the use of accurate atomic data, the inclusion of EUV radiation by shock heated matter, the simulation of photospheric line blocking. A new tool for O-star diagnostics is presented. This is based on the use of wind models to calculate synthetic high resolution spectra covering the observable UV region. A comparison with observed spectra then gives physical constraints on the properties of stellar winds and stellar parameters, additionally abundances can be determined. The astrophysical potential of this method is demonstrated by an application to two Of-stars, the galactic O4f-star ? Puppis and the LMC O3f-star Melnick 42. With regard to effective temperatures and gravities, the results from the application of classical methods to the analysis of photospheric lines are only partially verified. Explanations for the shortcomings of classical NLTE methods are discussed.

  12. Spectroscopic Observations of Low-Mass Stars in the GALNYSS Survey

    NASA Astrophysics Data System (ADS)

    Vican, Laura; Zuckerman, Ben M.; Rodriguez, David

    2016-01-01

    Young, low-mass stars are known to be bright in X-ray and UV due to their high levels of magnetic activity. By cross-correlating the GALEX Catalog with the 2MASS Point Source Catalog, we have identified a list of over 2,000 stars whose UV excesses suggest that they are in the 10-100 Myr age range. We used several medium and high-resolution spectrometers in the Northern and Southern hemisphere to obtain optical spectra of ~500 of these stars. By measuring their lithium equivalent widths and H? emission, we have been able to confirm the youth of many stars in our catalog. Furthermore, we were able to measure radial velocities and UVW galactic space velocities for stars with high-resolution spectra, and were able to place some of these stars in nearby young moving groups.

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

    SciTech Connect

    Lee, Kyoung-Soo; Giavalisco, Mauro; Conroy, Charlie; Wechsler, Risa H; Ferguson, Henry C.; Somerville, Rachel S.; Dickinson, Mark E.; Urry, Claudia M.; /Yale Ctr. Astron. Astrophys.

    2009-08-03

    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.

  14. O stars and Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  15. The Chemical Compositions of Variable Field Horizontal-branch Stars: RR Lyrae Stars

    NASA Astrophysics Data System (ADS)

    For, Bi-Qing; Sneden, Christopher; Preston, George W.

    2011-12-01

    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 eff and log g values of our sample stars follow the general trend of a single mass evolutionary track.

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

    SciTech Connect

    For Biqing; Sneden, Christopher; Preston, George W.

    2011-12-01

    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.

  17. The role of UV-optical obscuration in starburst galaxies

    NASA Technical Reports Server (NTRS)

    Keel, William C.

    1991-01-01

    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.

  18. Constraining Galaxy Evolution Using Observed UV-Optical Spectra

    NASA Technical Reports Server (NTRS)

    Heap, Sally

    2007-01-01

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

  19. Lifestyles of the Stars.

    ERIC Educational Resources Information Center

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

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

  20. Egyptian "Star Clocks"

    NASA Astrophysics Data System (ADS)

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  1. Extragalactic Star Clusters: the Resolved Star Approach

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-10-01

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

  3. The bolometric and UV attenuation in normal spiral galaxies of the Herschel Reference Survey

    NASA Astrophysics Data System (ADS)

    Viaene, S.; Baes, M.; Bendo, G.; Boquien, M.; Boselli, A.; Ciesla, L.; Cortese, L.; De Looze, I.; Eales, S.; Fritz, J.; Karczewski, O. Ł.; Madden, S.; Smith, M. W. L.; Spinoglio, L.

    2016-02-01

    The dust in nearby galaxies absorbs a fraction of the UV-optical-near-infrared radiation produced by stars. This energy is consequently re-emitted in the infrared. We investigate the portion of the stellar radiation absorbed by spiral galaxies from the Herschel Reference Survey (HRS) by modelling their UV-to-submillimetre spectral energy distributions. Our models provide an attenuated and intrinsic spectral energy distribution (SED), from which we find that on average 32% of all starlight is absorbed by dust. We define the UV heating fraction as the percentage of dust luminosity that comes from absorbed UV photons and find this to be 56%, on average. This percentage varies with morphological type, with later types having significantly higher UV heating fractions. We find a strong correlation between the UV heating fraction and specific star formation rate and provide a power-law fit. Our models allow us to revisit the IRX - AFUV relations, and derive these quantities directly within a self-consistent framework. We calibrate this relation for different bins of NUV - r colour and provide simple relations to relate these parameters. We investigated the robustness of our method and conclude that the derived parameters are reliable within the uncertainties that are inherent to the adopted SED model. This calls for a deeper investigation of how well extinction and attenuation can be determined through panchromatic SED modelling. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

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

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

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

  5. Neutrino signatures from the first stars

    SciTech Connect

    Daigne, Frederic; Vangioni, Elisabeth; Olive, Keith A.; Sandick, Pearl

    2005-11-15

    Evidence from the Wilkinson Microwave Anisotropy Probe (WMAP) polarization data indicates that the Universe may have been reionized at very high redshift. It is often suggested that the ionizing UV flux originates from an early population of massive or very massive stars. Depending on their mass, such stars can explode either as type II supernovae or pair-instability supernovae, or may entirely collapse into a black hole. The resulting neutrino emission can be quite different in each case. We consider here the relic neutrino background produced by an early burst of Population III stars coupled with a normal mode of star formation at lower redshift. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star formation histories constrained to reproduce the observed star formation rate at redshift z < or approx. 6, the observed chemical abundances in damped Lyman alpha absorbers and in the intergalactic medium, and to allow for an early reionization of the Universe at z{approx}10-20. We find that although the high redshift burst of Population III stars does lead to an appreciable flux of neutrinos at relatively low energy (E{sub {nu}}{approx_equal}1 MeV), the observable neutrino flux is dominated by the normal mode of star formation. We also find that predicted fluxes are at the present level of the SuperK limit. As a consequence, the supernova relic neutrino background has a direct impact on models of chemical evolution and/or supernova dynamics.

  6. A Review in Mixed Chemistry of Low Mass Evolved Stars

    NASA Astrophysics Data System (ADS)

    Guzman-Ramirez, L.

    2015-12-01

    During the late stages of their evolution, Sun-like stars bring the products of nuclear burning to the surface. Although there is a chemical dichotomy between oxygen-rich and carbon-rich evolved stars, the dredge-up itself has never been directly observed. In the last three decades, however, a few stars have been shown to display both carbon- and oxygen-rich material in their circumstellar envelopes. These phenomena is seen in both Galactic Disk and Bulge planetary nebulae. For the Galactic Disk objects the mixed chemistry phenomenon is best explained through a recent dredge-up of carbon produced by nucleosynthesis inside the star during the Asymptotic Giant Branch that changed the surface chemistry of the star. On the contrary, we conclude that the mixed chemistry phenomenon occurring in the Galactic Bulge planetary nebulae is best explained through hydrocarbon chemistry in an ultraviolet (UV)-irradiated, dense torus.

  7. X-ray emission of hot subdwarf stars

    NASA Astrophysics Data System (ADS)

    La Palombara, Nicola

    2011-10-01

    While several hot subdwarf stars have been deeply investigated in the optical and UV domain, only the sdO stars HD49798 and BD+37 442 have been detected at X-rays. In both cases the measured value of log(fx/fbol) is about -7, in agreement with the average value found in the standard OB stars: therefore it is interesting to investigate if this is a common property of the sdO stars. To this aim, we propose to observe with XMM-Newton the sdO stars BD+28 4211, BD+75 325, BD+37 1977 and BD-03 2179, since they are the best candidate to perform this type of search: they are optically bright (V = 9-10) and are characterized by a high temperature (Teff > 45000 K), thus implying an estimated X-ray flux high enough to be detectable with a XMM-Newton observation.

  8. Neutron Stars and NuSTAR

    NASA Astrophysics Data System (ADS)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses among all classes of neutron star binaries. Intrigued by this diversity - which points to diverse birth masses - we undertook a systematic survey to measure the masses of neutron stars in nine high-mass X-ray binaries. In this thesis, I present results from this ongoing project. While neutron stars formed the primary focus of my work, I also explored other topics in compact objects. Appendix A describes the discovery and complete characterization of a 1RXS J173006.4+033813, a polar cataclysmic variable. Appendix B describes the discovery of a diamond planet orbiting a millisecond pulsar, and our search for its optical counterpart.

  9. Symbiotic Stars in X-rays

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

    Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of 9 white dwarf symbiotics that were not previously known to be X-ray sources and one that was previously detected as a supersoft X-ray source. The 9 new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. Swift/XRT detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component, which we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component, which likely arises in a region where low-velocity shocks produce X-ray emission, i.e. a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the alpha/beta/gamma classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new sigma classification for sources with hard X-ray emission from the innermost accretion region. Since we have identified the elusive accretion component in the emission from a sample of symbiotic stars, our results have implications for the understanding of wind-fed mass transfer in wide binaries, and the accretion rate in one class of candidate progenitors of type Ia supernovae.

  10. Star Formation Histories in CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  11. Mapping H_2 Emission Around T Tauri Stars

    NASA Astrophysics Data System (ADS)

    Johns-Krull, Christopher

    1997-07-01

    We will study the distribution of circumstellar dust and molecular {H_2} gas around six classical T Tauri stars {cTTS}. We will probe both the near circumstellar environment {the accretion disk} as well as the environment further out where strong winds from these stars may be interacting with remnants of the cloud material from which they formed. The primary goal is to map the distribution of the molecular gas around cTTS. All our proposed targets show UV fluorescent H_2 emission {Johns-Krull et al. 1997; Valenti et al. 1997}, and are therefore expected to show IR molecular hydrogen emission. These images will reveal what fraction of the H_2 emission is produced in the warm circumstellar disks surrounding young these stars. The morphology of the extended emission will constrain collimation processes that focus the outflows from these stars. Combined with our UV data, these observations will allow us to test the thermal+fluorescent excitation model of molecular hydrogen {Black & van Dishoeck 1987}. These data, combined with future HST UV imaging and long-slit spectroscopy {STIS and ground-based IR} will provide very tight constraints on the physical conditions and excitation mechanisms present in the gaseous circumstellar environments of these stars.

  12. STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2013-08-20

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

  13. UV Spectroscopy of the Hot, Helium-Core White Dwarf Companion in HR 1608

    NASA Astrophysics Data System (ADS)

    Torres, Guillermo

    2003-07-01

    We propose to observe the FUV spectrum of the hot, helium-core white dwarf in the binary system HR 1608 in order to determine if there are suitable spectral lines to obtain a radial velocity orbit for the white dwarf star. The primary star in this system, with spectral type K0 IV, dominates the spectrum at visual wavelengths. At a temperature of around 25, 000 K, however, the white dwarf outshines the primary in the UV. The orbital motion of the primary star has been monitored for seven years with the CfA Digital Speedometer at Oak Ridge Observatory in Harvard, MA. In addition, the Hipparcos team noted excess scatter in the astrometric solution which, though unexplained at the time, we now know to be due to the orbital motion. Combining the astrometric and spectroscopic data, we have solved for the orbital elements, including the inclination of the system. In order to obtain a dynamical mass for the star, the orbital motion of both stars must be observed, thus the need for monitoring the white dwarf in the UV. As the first step in this endeavor, we propose to obtain a STIS spectrum of the white dwarf star to discover if there are spectral lines with which its radial velocity could be measured precisely enough to calculate a dynamical mass.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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--vis the model simulated catalogues produced by the Besanon 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 Besanon 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 Besanon 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 Besanon 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-01-01

    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.

  16. Plasmon-enhanced UV photocatalysis

    SciTech Connect

    Honda, Mitsuhiro; Saito, Yuika Kawata, Satoshi; Kumamoto, Yasuaki; Taguchi, Atsushi

    2014-02-10

    We report plasmonic nanoparticle enhanced photocatalysis on titanium dioxide (TiO{sub 2}) in the deep-UV range. Aluminum (Al) nanoparticles fabricated on TiO{sub 2} film increases the reaction rate of photocatalysis by factors as high as 14 under UV irradiation in the range of 260340?nm. The reaction efficiency has been determined by measuring the decolorization rate of methylene blue applied on the TiO{sub 2} substrate. The enhancement of photocatalysis shows particle size and excitation wavelength dependence, which can be explained by the surface plasmon resonance of Al nanoparticles.

  17. Guanine tautomerism revealed by UV-UV and IR-UV hole burning spectroscopy

    NASA Astrophysics Data System (ADS)

    Nir, E.; Janzen, Ch.; Imhof, P.; Kleinermanns, K.; de Vries, M. S.

    2001-09-01

    The vibronic spectrum of laser desorbed and jet cooled guanine consists of bands from three different tautomers of guanine as revealed by UV-UV and IR-UV double resonance spectroscopy. 1-methylguanine, in which the Keto-Enol tautomerism is blocked, shows hole burning spectra from the 9H-and 7H-Keto form. A comparison of the vibronic pattern of the different tautomers demonstrates that the vibronic spectrum built on the redmost guanine band at 32 870 cm-1 (electronic origin 0) can be traced back to the 9H-Enol tautomer, while the spectra built on the origins at 0+404 cm-1 and 0+1044 cm-1 stem from the two Keto tautomers. The IR-UV double resonance spectra of the OH-and NH-stretch vibrations of the different tautomers support this assignment. The UV and IR spectra can be partly assigned by comparison with ab initio calculated vibrational frequencies and with the help of deuteration experiments.

  18. Ultraviolet and X-ray Activity and Flaring on Low-Mass Exoplanet Host Stars

    NASA Astrophysics Data System (ADS)

    France, Kevin; Parke Loyd, R. O.; Brown, Alexander

    2015-08-01

    The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. High-energy photons (X-ray to NUV) from these stars regulate the atmospheric temperature profiles and photochemistry on orbiting planets, influencing the production of potential “biomarker” gases. We present results from the MUSCLES Treasury Survey, an ongoing study of time-resolved UV and X-ray spectroscopy of nearby M and K dwarf exoplanet host stars. This program uses contemporaneous Hubble Space Telescope and Chandra (or XMM) observations to characterize the time variability of the energetic radiation field incident on the habitable zones planetary systems at d < 15 pc. We find that all exoplanet host stars observed to date exhibit significant levels of chromospheric and transition region UV emission. M dwarf exoplanet host stars display 30 - 2000% UV emission line amplitude variations on timescales of minutes-to-hours. The relative flare/quiescent UV flux amplitudes on old (age > 1 Gyr) planet-hosting M dwarfs are comparable to active flare stars (e.g., AD Leo), despite their lack of flare activity at visible wavelengths. We also detect similar UV flare behavior on a subset of our K dwarf exoplanet host stars. We conclude that strong flares and stochastic variability are common, even on “optically inactive” M dwarfs hosting planetary systems. These results argue that the traditional assumption of weak UV fields and low flare rates on older low-mass stars needs to be revised.

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

    NASA Astrophysics Data System (ADS)

    Renzini, Alvio

    2011-10-01

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

  20. Star Clusters in Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Vetens, Sidney David; Crocker, Alison Faye

    2016-01-01

    Star formation rates in early-type galaxies are notoriously hard to determine because of their very low specific star formation rates. For this project, we use Hubble Space Telescope photometric data in 4-5 visible and near-UV filters to measure the young stellar clusters in nine early-type galaxies. Aperture photometry colors were compared to colors from synthetic photometry produced by the Flexible Stellar Population Synthesis code (Conroy et. al, ApJ 699, 486-506 (2009)), using a chi-squared likelihood method to estimate the age, metallicity and extinction for each cluster. Masses were determined using the best-fit model, the distance to each galaxy and the measured fluxes. Young clusters were selected below a cutoff age of 100 Myr, and star formation rates for each galaxy were then calculated as the combined mass of the young clusters divided by the cutoff age. Star formation rates computed in this way are far below those computed using the 22 micron emission. While some completeness effects are biasing the cluster-estimated SFRs low, the extreme difference (two orders of magnitude) may also point to SFR overestimation due to contamination from older stars in the 22 micron SFRs.

  1. Dispersal of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2001-01-01

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

  2. Dispersal of Disks Around Young Stars

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    Results from the UV satellite GALEX revealed surprisingly large extensions of disks in some nearby spiral galaxies. While the Hα 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 Hα, 24 μm, 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).

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  5. Near UV Aerosol Group Report

    NASA Technical Reports Server (NTRS)

    Torres, Omar

    2013-01-01

    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.

  6. 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 ...

  7. UV photobiochemistry under space conditions

    NASA Astrophysics Data System (ADS)

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

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

  8. The sn stars - Magnetically controlled stellar winds among the helium-weak stars

    NASA Technical Reports Server (NTRS)

    Shore, Steven N.; Brown, Douglas N.; Sonneborn, George

    1987-01-01

    The paper reports observations of magnetically controlled stellar mass outflows in three helium-weak sn stars: HD 21699 = HR 1063; HD 5737 = Alpha Scl; and HD 79158 = 36 Lyn. IUE observations show that the C IV resonance doublet is variable on the rotational timescale but that there are no other strong-spectrum variations in the UV. Magnetic fields, which reverse sign on the rotational timescale, are present in all three stars. This phenomenology is interpreted in terms of jetlike mass loss above the magnetic poles, and these objects are discussed in the context of a general survey of the C IV and Si IV profiles of other more typical helium-weak stars.

  9. Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Tan, J. C.; Beltrn, M. T.; Caselli, P.; Fontani, F.; Fuente, A.; Krumholz, M. R.; McKee, C. F.; Stolte, A.

    The enormous radiative and mechanical luminosities of massive stars impact a vast range of scales and processes, from the reionization of the universe, to the evolution of galaxies, to the regulation of the interstellar medium, to the formation of star clusters, and even to the formation of planets around stars in such clusters. Two main classes of massive star formation theory are under active study: core accretion and competitive accretion. In core accretion, the initial conditions are self-gravitating, centrally concentrated cores that condense with a range of masses from the surrounding, fragmenting clump environment. They then undergo relatively ordered collapse via a central disk to form a single star or a small-N multiple. In this case, the prestellar core mass function has a similar form to the stellar initial mass function. In competitive accretion, the material that forms a massive star is drawn more chaotically from a wider region of the clump without passing through a phase of being in a massive, coherent core. In this case, massive star formation must proceed hand in hand with star cluster formation. If stellar densities become very high near the cluster center, then collisions between stars may also help to form the most massive stars. We review recent theoretical and observational progress toward understanding massive star formation, considering physical and chemical processes, comparisons with low and intermediate-mass stars, and connections to star cluster formation.

  10. Habitability around F-type stars

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  11. A search for rapid pulsations among nine luminous Ap stars

    NASA Astrophysics Data System (ADS)

    Freyhammer, L. M.; Kurtz, D. W.; Cunha, M. S.; Mathys, G.; Elkin, V. G.; Riley, J. D.

    2008-04-01

    The rapidly oscillating Ap (roAp) stars are of importance for studying the atmospheric structure of stars where the process of chemical element diffusion is significant. We have performed a survey for rapid oscillations in a sample of nine luminous Ap stars, selected from their location in the colour-magnitude diagram as more evolved main-sequence Ap stars that are inside the instability strip for roAp stars. Until recently this region was devoid of stars with observed rapid pulsations. We used the Very Large Telescope UV-Visual Echelle Spectrograph to obtain high time resolution spectroscopy to make the first systematic spectroscopic search for rapid oscillations in this region of the roAp instability strip. We report nine null detections with upper limits for radial velocity amplitudes of 20-65ms-1 and precisions of ? = 7-20ms-1 for combinations of Nd and Pr lines. Cross-correlations confirm these null results. At least six stars are magnetic and we provide magnetic field measurements for four of them, of which three are newly discovered magnetic stars. It is found that four stars have magnetic fields smaller than ~2kG, which according to theoretical predictions might be insufficient for suppressing envelope convection around the magnetic poles for more evolved Ap stars. Suppression of convection is expected to be essential for the opacity mechanism acting in the hydrogen ionization zone to drive the high-overtone roAp pulsations efficiently. Our null results suggest that the more evolved roAp stars may require particularly strong magnetic fields to pulsate. Three of the studied stars do, however, have magnetic fields stronger than 5kG. Based on observations collected at the European Southern Observatory, Paranal, Chile, as part of programmes 075.D-0145 (A), 078.D-0080(A), 072.D-0138(A) and 077.D-0150(A). E-mail: lmfreyhammer@uclan.ac.uk

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

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

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

  13. Gas, Stars, and Star Formation in Alfalfa Dwarf Galaxies

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

    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.

  14. GAS, STARS, AND STAR FORMATION IN ALFALFA DWARF GALAXIES

    SciTech Connect

    Huang Shan; Haynes, Martha P.; Giovanelli, Riccardo; Brinchmann, Jarle; Stierwalt, Sabrina; Neff, Susan G. E-mail: haynes@astro.cornell.edu E-mail: jarle@strw.leidenuniv.nl E-mail: susan.g.neff@nasa.gov

    2012-06-15

    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.

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

    SciTech Connect

    Sahai, Raghvendra; Neill, James D.; Gil de Paz, Armando; Sanchez Contreras, Carmen

    2011-10-20

    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.

  16. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

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

  17. Astrophysics: Stars fight back

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.

    2014-12-01

    Galaxies contain fewer stars than predicted. The discovery of a massive galactic outflow of molecular gas in a compact galaxy, which forms stars 100 times faster than the Milky Way, may help to explain why. See Letter p.68

  18. QCD in Neutron Stars and Strange Stars

    SciTech Connect

    Weber, Fridolin; Negreiros, Rodrigo

    2011-05-24

    This paper provides an overview of the possible role of Quantum Chromo Dynamics (QCD) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than even the most stable atomic nucleus, {sup 56}Fe. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

  19. Chromospheres of Coronal Stars

    NASA Technical Reports Server (NTRS)

    Linsky, Jeffrey L.; Wood, Brian E.

    1996-01-01

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

  20. Dibaryons in neutron stars

    NASA Technical Reports Server (NTRS)

    Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.

    1991-01-01

    The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.

  1. Tunable UV source for UV fluorescence remote sensing

    SciTech Connect

    Mead, R.D.; Lowenthal, D.D.; Raymond, T.D.; Alford, W.J.; Smith, A.V.; Johnson, M.S.

    1994-08-01

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

  2. America's Star Libraries

    ERIC Educational Resources Information Center

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "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…

  3. Managing the star performer.

    PubMed

    Hills, Laura

    2013-01-01

    Our culture seems to be endlessly fascinated with its stars in entertainment, athletics, politics, and business, and holds fast to the idea that extraordinary talent accounts for an individual's extraordinary performance. At first glance, managing a star performer in your medical practice may seem like it would be an easy task. However, there's much more to managing a star performer than many practice managers realize. The concern is how to keep the star performer happy and functioning at a high level without detriment to the rest of the medical practice team. This article offers tips for practice managers who manage star performers. It explores ways to keep the star performer motivated, while at the same time helping the star performer to meld into the existing medical practice team. This article suggests strategies for redefining the star performer's role, for holding the star performer accountable for his or her behavior, and for coaching the star performer. Finally, this article offers practical tips for keeping the star performer during trying times, for identifying and cultivating new star performers, and for managing medical practice prima donnas. PMID:23767124

  4. America's Star Libraries

    ERIC Educational Resources Information Center

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "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

  5. Spots on Am stars

    NASA Astrophysics Data System (ADS)

    Balona, L. A.; Catanzaro, G.; Abedigamba, O. P.; Ripepi, V.; Smalley, B.

    2015-04-01

    We investigate the light variations of 15 Am stars using four years of high-precision photometry from the Kepler spacecraft and an additional 14 Am stars from the K2 Campaign 0 field. We find that most of the Am stars in the Kepler field have light curves characteristic of rotational modulation due to star-spots. Of the 29 Am stars observed, 12 are ? Scuti variables and one is a ? Doradus star. One star is an eclipsing binary and another was found to be a binary from time delay measurements. Two Am stars show evidence for flares which are unlikely to be due to a cool companion. The fact that 10 out of 29 Am stars are rotational variables and that some may even flare strongly suggests that Am stars possess significant magnetic fields. This is contrary to the current understanding that the enhanced metallicity in these stars is due to diffusion in the absence of a magnetic field. The fact that so many stars are ? Scuti variables is also at odds with the prediction of diffusion theory. We suggest that a viable alternative is that the metal enhancement could arise from accretion.

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

    NASA Astrophysics Data System (ADS)

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

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

  7. 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...

  8. Magnitude calibration of a fixed head star tracker using Astro-1 flight data

    NASA Technical Reports Server (NTRS)

    Rakoczy, John M.; West, Mark E.

    1992-01-01

    The Astro-1 UV astronomy mission was hampered by the failures of the automatic star acquisition procedure. The acquisition procedure depended on the Instrument Pointing Subsystem's Fixed Head Star Trackers (FHST) to acquire, track and identify guidestars of known visual magnitude. During the Astro-1 mission it was suspected that the star magnitudes measured by the FHST were much lower than predicted. A postflight investigation of the Astro-1 flight data confirmed and quantified this suspicion. Star magnitude calibration curves computed from the flight data depict the variance from the preflight calibration curves. These results are helping engineers to plan improvements to the acquisition procedure for the upcoming Astro-2 mission.

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

    NASA Technical Reports Server (NTRS)

    Fitzpatrick, E. L.

    1982-01-01

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

  10. Investigation of the shell stars omicron and theta Per, and of the eclipsing binary beta Lyr

    NASA Technical Reports Server (NTRS)

    Plavec, M.

    1975-01-01

    All three stars showed rather complicated spectra, which require a very detailed spectroscopic analysis. The far UV spectrum of Beta Lyrae is clearly peculiar, with a multitude of emission lines not observed on any other star so far scanned with Copernicus. This made this star at once the most interesting and also, in a sense, easier to study. The other two stars display a spectrum rich in absorption lines, some of them being fairly broad (as expected for photospheric lines of rapidly rotating objects), some sharp. The later were clearly non-photospheric lines. An attempt was made to distinguish the circumstellar from the interstellar components.

  11. Ultraviolet Extinction Curves For Nearby T Tauri Stars

    NASA Astrophysics Data System (ADS)

    McJunkin, Matthew; France, Kevin

    2016-01-01

    We present empirically-derived fits to the ultraviolet (UV) extinction curves along the line of sight towards young stars with circumstellar disks. Stellar UV radiation plays a strong role in heating the disk gas and driving chemical reactions. Thus, it is important to measure the UV extinction curve in order to reconstruct the intrinsic UV flux irradiating the disk, thereby enabling accurate photochemical modeling of the planet-forming environment. To measure the extinction, we first compare modeled H2 fluorescence spectra to observed H2 lines. Lyman-alpha radiation from the stars pumps electronic transitions of H2 in the disk, and we model the flux that is re-emitted through the subsequent fluorescent cascade. We then extract an initial extinction curve over the 1100-1700 Angstrom wavelength region from the difference between the modeled H2 fluorescence and the HST data. To account for self-absorption in the disk by the optically thick H2, we divide this initial extinction curve by the transmission in each fluorescence line. We then fit the resulting interstellar extinction curve with an interstellar reddening model characterized by an Av and Rv value. The shape of the extinction curve allows us to characterize the dust grain distribution in the intervening material as well as to recover the intrinsic spectral energy distribution of the stars over a wide wavelength range.

  12. UV curable pressure sensitive adhesives

    SciTech Connect

    Glotfelter, C.A.

    1995-12-01

    Pressure sensitive adhesives (PSA`s) have become a ubiquitous element in our society, so much so, that the relative status of a society can be determined by the per capita consumption of PSA`s. We discuss new monomers as components of PSA formulations which enable adhesion to be achieved on a variety of substrates. Since solventless coating systems are desirable, the UV PSA market is of utmost importance to meeting the strict environmental guidelines now being imposed worldwide. In addition, highly ethoxylated monomers have shown promise in water dispersed PSA formulations, and a self-emulsifying acrylate monomer has been developed to offer dispersive abilities without using traditional emulsifying agents. This talk will focus on the effects of the materials described on properties of adhesive strength and shear strength in UV PSA formulations.

  13. Strange Quark Star Crusts

    SciTech Connect

    Steiner, Andrew W.

    2007-02-27

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

  14. The Old Feeble Transition Regions and Coronae of Solar-like Dwarf Stars in the Arcturus Moving Group

    NASA Astrophysics Data System (ADS)

    Brown, Alexander; Hodges-Kluck, E. J.; Ayres, T. R.; Harper, G. M.

    2012-05-01

    Old dwarf stars have generally spun down significantly thus dampening one of the main contributors (rotation) to solar-like alpha-omega magnetic dynamo activity. Studying how stellar activity on stars older than the Sun changes in terms of the chromospheric/transition-region/coronal temperature structure and how much energy is radiated as a function of temperature provides important constraints on how solar-like dynamos work. Stars with different metallicities provide information on how the radiative cooling channels control the temperature structure. We have measured fluxes and profiles of FUV emission lines using the HST COS spectrograph and the broad-band X-ray fluxes using Chandra ACIS-S for a sample of old inactive dwarfs. Our sample comprises five members of the 7-8 Gyr Arcturus Moving Group --- HD90508/LHS2266 (F9 V/M4 V, [Fe/H] = -0.4), HD65583 (G8 V, Fe/H]=-0.7), and HD145417 (K0 V, [Fe/H]=-1.4) --- plus three well-studied comparison stars -- HD103095 (G8 V, [Fe/H]=-1.4), Tau Ceti (G8 V, [Fe/H]=-0.4), and the Quiet Sun (G2 V, [Fe/H]=0.0). In this poster we provide estimates of atmospheric radiative losses as a function of temperature and metallicity. The atmospheres of these low-metallicity stars are more heavily weighted towards cooler temperatures than those of more active stars or even the Sun. Chromospheric emission lines, e.g. C I lines, are far stronger relative transition region lines, e.g C IV. Similarly the X-ray data provide detections for all the targets but with primarily very soft (0.3-0.5 keV) photons and imply "coronal" temperatures of less than 1 MK. While the temperature distributions are cooler, the overall integrated X-ray and FUV luminosities are similar to those of the "Quiet Sun" -- implying that similar amounts of non-radiative energy input are being dissipated. This work is supported by NASA GALEX grant NNX06AB46G, HST grants GO-11555 and GO-11829, and Chandra grants GO6-7018X, GO7-8020X, and GO9-0021X to the University of Colorado.

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

    NASA Astrophysics Data System (ADS)

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

    1988-07-01

    The authors report results from a multispectral investigation of stellar counterparts of X-ray sources in the general region of the Taurus-Auriga star-formation complex. They discuss 28 new low-mass pre-main-sequence "naked T Tauri" stars, bringing the census of naked T Tauri stars to 44 in the Tau-Aur region. The authors discuss the optical spectra and the optical and near-IR colors. They show that these stars are basically normal stars with ages of 1 - 40106yr. There is no evidence for IR or UV excesses. Chromospheric and coronal surface fluxes are comparable to those of the most active main-sequence stars and the RS CVn systems. The authors show that the chromospheric fluxes do not increase for stellar ages <108yr, confirming the postulated exponential decay of stellar activity.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  17. XI UV Laser Trigger System

    SciTech Connect

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

    1999-01-26

    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.

  18. The High-Energy Radiation Environment of Planets around Low-Mass Stars

    NASA Astrophysics Data System (ADS)

    Shkolnik, Evgenya; Miles, Brittany; Barman, Travis; Peacock, Sarah

    2015-12-01

    Low-mass stars are the dominant planet hosts averaging about one planet per star. Many of these planets orbit in the canonical habitable zone (HZ) of the star where, if other conditions allowed, liquid water may exist on the surface.A planet’s habitability, including atmospheric retention, is strongly dependent on the star’s ultraviolet (UV) emission, which chemically modifies, ionizes, and even erodes the atmosphere over time including the photodissociation of important diagnostic molecules, e.g. H2O, CH4, and CO2. The UV spectral slope of a low-mass star can enhance atmospheric lifetimes, and increase the detectability of biologically generated gases. But, a different slope may lead to the formation of abiotic oxygen and ozone producing a false-positive biosignature for oxygenic photosynthesis. Realistic constraints on the incident UV flux over a planet’s lifetime are necessary to explore the cumulative effects on the evolution, composition, and fate of a HZ planetary atmosphere.NASA’s Galaxy Evolution Explorer (GALEX) provides a unique data set with which to study the broadband UV emission from many hundreds of M dwarfs. The GALEX satellite has imaged nearly 3/4 of the sky simultaneously in two UV bands: near-UV (NUV; 175-275 nm) and far-UV (FUV; 135-175 nm). With these data these, we are able to calculate the mean UV emission and its level of variability at these wavelengths over critical planet formation and evolution time scales to better understand the probable conditions in HZ planetary atmospheres.In the near future, dedicated CubeSats (miniaturized satellites for space research) to monitor M dwarf hosts of transiting exoplanets will provide the best opportunity to measure their UV variability, constrain the probabilities of detecting habitable (and inhabited) planets, and provide the correct context within which to interpret IR transmission and emission spectroscopy of transiting exoplanets.

  19. The chemical abundances of the Ap star HD94660

    SciTech Connect

    Giarrusso, M.

    2014-05-09

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

  20. IC 3418: STAR FORMATION IN A TURBULENT WAKE

    SciTech Connect

    Hester, Janice A.; Neill, James D.; Wyder, Ted K.; Martin, D. Christopher; Seibert, Mark; Madore, Barry F.; Gil de Paz, Armando; Schiminovich, David; Rich, R. Michael

    2010-06-10

    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.

  1. What the UV SED Tells us About Stellar Populations and Galaxies

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.

    2011-01-01

    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.

  2. A Star's Close Encounter

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Annotated Version

    The potential planet-forming disk (or 'protoplanetary disk') of a sun-like star is being violently ripped away by the powerful winds of a nearby hot O-type star in this image from NASA's Spitzer Space Telescope. At up to 100 times the mass of sun-like stars, O stars are the most massive and energetic stars in the universe.

    The O star can be seen to the right of the image, as the large orange spot with the white center. To the left, the comet-like structure is actually a neighboring solar system that is being destroyed by the O star's powerful winds and intense ultraviolet light.

    In a process called 'photoevaporation,' immense output from the O star heats up the nearby protoplanetary disk so much that gas and dust boil off, and the disk can no longer hold together. Photon (or light) blasts from the O star then strip the potential planet-forming disk off its neighbor star by blowing away evaporated material. This effect is illustrated in the smaller system's comet-like structure.

    The system is located about 2,450 light-years away in the star-forming cloud IC 1396. The image was taken with Spitzer's multiband imaging photometer instrument at 24 microns. The picture is a pseudo-color stretch representing intensity. Yellow and white represent hot areas, whereas purple and blue represent relatively cooler, fainter regions.

  3. A SECOND NEUTRON STAR IN M4?

    SciTech Connect

    Kaluzny, J.; Rozanska, A.; Rozyczka, M.; Krzeminski, W.; Thompson, Ian B.

    2012-05-01

    We show that the optical counterpart of the X-ray source CX 1 in M4 is a {approx}20th magnitude star, located in the color-magnitude diagram on (or very close to) the main sequence of the cluster, and exhibiting sinusoidal variations of the flux. We find the X-ray flux to be also periodically variable, with X-ray and optical minima coinciding. Stability of the optical light curve, lack of UV-excess, and unrealistic mean density resulting from period-density relation for semidetached systems speak against the original identification of CX 1 as a cataclysmic variable. We argue that the X-ray active component of this system is a neutron star (probably a millisecond pulsar).

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

    SciTech Connect

    Wallerstein, G.

    1990-01-01

    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.

  5. Ultraviolet Synthetic Spectra for Three Lambda Bootis Stars

    NASA Astrophysics Data System (ADS)

    Cheng, Kwang-Ping; Neff, James E.; Gray, Richard O.; Corbally, Christopher J.; Johnson, Dustin; Tarbell, Erik

    2015-01-01

    Lambda Boo-type stars are a group of late B to early F-type Population I dwarfs that show mild to extreme deficiencies of iron-peak elements (up to 2 dex), but their C, N, O, and S abundances are near solar. We show that the International Ultraviolet Explorer (IUE) spectra (1280-3200 A) of Lambda Bootis, 29 Cygni (a "confirmed" Lambda Boo star), and Vega (a "mild" Lambda Boo star) can be fit remarkably well by single-temperature synthetic spectra. We computed the full resolution synthetic ultraviolet (UV) spectrum covering the IUE wavelength range using Gray's Stellar Spectral Synthesis Program SPECTRUM. To improve the synthetic spectra, we generated a grid of LTE atmosphere models with the appropriate stellar parameters using ATLAS9 and the existing Castelli and Kurucz 2004 models. One of the improvements of their opacity distribution functions (ODFs) is the addition to the line blanketing near 1400 A and 1600 A by the quasi-molecular absorptions of atomic hydrogen undergoing collisions with protons and other neutral hydrogen atoms. New-ODF fluxes reproduce the ultraviolet observations of Lambda Boo stars in a more realistic way than previous computations. We also constructed our own UV line list for the relevant set of absorption features. Modeling the UV line spectra of Lambda Boo stars allows us to confirm their published surface abundances, including CNO and the iron group elements. It also provides further insight into their photospheric conditions (e.g., Teff, log g, [M/H], micro turbulent velocity, etc.). About 40 percent of the published Lambda Boo candidates have existing IUE spectra. We plan to follow this pilot study and perform UV spectral synthesis for all of them.

  6. Ponderable soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

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

  7. Ponderable soliton stars

    NASA Astrophysics Data System (ADS)

    Chiu, Hong-Yee

    1990-12-01

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

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

    SciTech Connect

    Barnes, Kate L.; Van Zee, Liese; Dowell, Jayce D. E-mail: vanzee@astro.indiana.edu

    2013-09-20

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-09-01

    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.

  10. Advanced Spectral Library II: Hot Stars

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas

    2013-10-01

    Stars are the bright matter of the Universe. Without them, it would be a dull and dreary place indeed: no light, no heavy elements, no planets, no life. It also is safe to say that stellar spectroscopy is a cornerstone of astrophysics, providing much of what we know concerning temperatures and masses of stars, their compositions, planets, and the dynamics and evolution of the galaxies they inhabit. This is especially true for the satellite ultraviolet, owing to the rich collection of atomic and ionic transitions found there. Unfortunately, the archive of Space Telescope Imaging Spectrograph rarely achieves the high S/N of the best ground-based spectra, and relatively few objects have the full wavelength coverage for which the powerful, highly multiplexed, second generation Hubble instrument was designed. Our aim is to collect STIS UV echelle spectra - comparable in S/N and resolution to the best ground-based material - for a diverse sample of representative stars, to build an Advanced Spectral Library; a foundation for astrophysical exploration: stellar, interstellar, and beyond. Our first effort, in Cycle 18, involved cool stars. Now we turn attention to the hot side of the H-R diagram.Our Treasury program will provide detailed stellar "atlases," based on advanced processing of the STIS echellegrams. Members of our broad collaboration will analyze these data for specific purposes, such as dynamics of O-star mass-loss; detection of rare species in sharp-lined B stars; and properties and kinematics of local interstellar clouds; but public release {based on the "ASTRAL-I" model} will enable many other investigations by a much wider community, for decades to come.

  11. Dispersal of Disk Around Young Stars

    NASA Technical Reports Server (NTRS)

    DeVincenzi, Donald L.; Hollenbach, David

    2000-01-01

    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 per second) ionized outflow, which persists for greater than or equal to 10(exp 5) years for disk masses Md approx. 0.3M*, 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 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.

  12. The NuSTAR Serendipitous Survey

    NASA Astrophysics Data System (ADS)

    Lansbury, George B.; NuSTAR

    2015-01-01

    A great breakthrough in studying the cosmic X-ray background (CXB) population is the Nuclear Spectroscopic Telescope Array (NuSTAR), the first focusing X-ray observatory with high sensitivity at > 10 keV. Here we present results from the NuSTAR serendipitous survey, the largest area (~7 deg2) component of the NuSTAR extragalactic survey programme. The source statistics are relatively good for a high energy X-ray survey, with ~150 detections and ~100 spectroscopically identified sources to-date. Studying the X-ray emission at > 10 keV, where X-rays from the central black hole are relatively unabsorbed, allows intrinsic properties such as column densities and luminosities to be well constrained. The X-ray analysis is supplemented by broad-band UV to mid-IR spectral energy distribution (SED) analyses. The dominant source population sampled by the NuSTAR serendipitous survey is quasars with L(10-40)keV > 1044 erg/s. This population is broadly similar to the population of nearby high-energy selected AGNs sampled by Swift/BAT, but scaled up in luminosity and mass.

  13. Solar UV Radiation and the Origin of Life on Earth

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  14. UV blocking filters for polymeric films

    NASA Technical Reports Server (NTRS)

    Rayl, G. J.

    1979-01-01

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

  15. UV and optical spectrum variability of T Tau and RY Tau

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

  16. AN ULTRAVIOLET INVESTIGATION OF ACTIVITY ON EXOPLANET HOST STARS

    SciTech Connect

    Shkolnik, Evgenya L.

    2013-03-20

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

  17. High Power UV LED Industrial Curing Systems

    SciTech Connect

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

    2012-05-14

    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.

  18. UV irradiation responses in Giardia intestinalis.

    PubMed

    Einarsson, Elin; Svrd, Staffan G; Troell, Karin

    2015-07-01

    The response to ultraviolet light (UV) radiation, a natural stressor to the intestinal protozoan parasite Giardia intestinalis, was studied to deepen the understanding of how the surrounding environment affects the parasite during transmission. UV radiation at 10 mJ/cm(2) kills Giardia cysts effectively whereas trophozoites and encysting parasites can recover from UV treatment at 100 mJ/cm(2) and 50 mJ/cm(2) respectively. Staining for phosphorylated histone H2A showed that UV treatment induces double-stranded DNA breaks and flow cytometry analyses revealed that UV treatment of trophozoites induces DNA replication arrest. Active DNA replication coupled to DNA repair could be an explanation to why UV light does not kill trophozoites and encysting cells as efficiently as the non-replicating cysts. We also examined UV-induced gene expression responses in both trophozoites and cysts using RNA sequencing (RNA seq). UV radiation induces small overall changes in gene expression in Giardia but cysts show a stronger response than trophozoites. Heat shock proteins, kinesins and Nek kinases are up-regulated, whereas alpha-giardins and histones are down-regulated in UV treated trophozoites. Expression of variable surface proteins (VSPs) is changed in both trophozoites and cysts. Our data show that Giardia cysts have limited ability to repair UV-induced damage and this may have implications for drinking- and waste-water treatment when setting criteria for the use of UV disinfection to ensure safe water. PMID:25825252

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

    PubMed

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

    2008-06-01

    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

  20. IUE and Einstein survey of late-type giant and supergiant stars and the dividing line

    NASA Astrophysics Data System (ADS)

    Haisch, Bernhard M.; Bookbinder, Jay A.; Maggio, A.; Vaiana, G. S.; Bennett, Jeffrey O.

    1990-10-01

    Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a trend involving a steeply-dropping upper envelope of the transition region line fluxes, f(line)/f(V), as the dividing line is approached. This suggests that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to this steep gradient region. The results confirm the rotation-activity connection for stars in this region of the H-R diagram.

  1. IUE and Einstein survey of late-type giant and supergiant stars and the dividing line

    SciTech Connect

    Haisch, B.M.; Bookbinder, J.A.; Maggio, A.; Vaiana, G.S.; Bennett, J.O. Smithsonian Astrophysical Observatory, Cambridge, MA Osservatorio Astronomico, Palermo Colorado Univ., Boulder )

    1990-10-01

    Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a trend involving a steeply-dropping upper envelope of the transition region line fluxes, f(line)/f(V), as the dividing line is approached. This suggests that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to this steep gradient region. The results confirm the rotation-activity connection for stars in this region of the H-R diagram. 67 refs.

  2. IUE and Einstein survey of late-type giant and supergiant stars and the dividing line

    NASA Technical Reports Server (NTRS)

    Haisch, Bernhard M.; Bookbinder, Jay A.; Maggio, A.; Vaiana, G. S.; Bennett, Jeffrey O.

    1990-01-01

    Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a trend involving a steeply-dropping upper envelope of the transition region line fluxes, f(line)/f(V), as the dividing line is approached. This suggests that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to this steep gradient region. The results confirm the rotation-activity connection for stars in this region of the H-R diagram.

  3. Novel Radiation Sources in Vacuum UV and Near UV

    NASA Astrophysics Data System (ADS)

    Peng, Sheng; Ametepe, Joseph; Manos, Dennis

    2004-05-01

    Ultraviolet (UV) light induced or enhanced chemical reactions have many advanced applications. This causes excimer lamps which deliver high power, large area UV radiations in demand. There have been extensive studies on rare gas or mixtures of rare gas halogen in different excimer lamps. But experimental data for high pressure KrI (iodine in krypton) spectra are scarce partially because the transitions B->X (191nm) and B->A (225nm) are usually very weak. We designed a new prototype of rf lamp for this study. This lamp has its electrodes outside the plasma for longer lamp lifetime. It is capable of studying most rf excited gas discharge and efficient enough for weak emissions like KrI. Detailed features of KrI spectrum from 160nm to 360nm were obtained. The wavelength and intensity variation of with pressure was modeled using a set of coupled kinetic equations. Molecular orbits of KrI were calculated in Gaussian 03. A semi-classical approach was used to study the line shape of the broad band emission and an explicit expression was obtain for KrI.

  4. Physiological responses of Scenedesmus quadricauda (Chlorophyceae) to UV-A and UV-C light.

    PubMed

    Kovcik, Jozef; Klejdus, Borivoj; Backor, Martin

    2010-01-01

    Despite intensive research focused on the effects of UV-B, deeper metabolic responses to UV-A and UV-C are still scarce. Besides, especially microalgal species had to develop efficient protective features in comparison with tissue structure of vascular plants. We exposed axenic cultures of Scenedesmus quadricauda (Chlorophyceae) to UV-A (366 nm) and UV-C (254 nm) light over 1 h. Both wavelengths stimulated increase in soluble proteins, superoxide radical and hydrogen peroxide, but had a nonsignificant effect on cell viability. Within 17 detected free amino acids, five (including proline) increased in response to UV-A while only aspartic acid and histidine increased in UV-C treatment. Total soluble phenols and flavonoids were influenced neither by UV-A nor by UV-C while selected flavonols (quercetin and kaempferol) decreased in UV-A and were not detected in UV-C treatment. Benzoic acid derivatives increased preferentially after UV-A illumination (vanillic acid and vanillin) while cinnamic derivatives (caffeic, chlorogenic and p-coumaric acids) decreased in both UV-A and UV-C. It is concluded that UV light stimulated oxidative stress while exposure time was not sufficient to stimulate larger changes in phenolic metabolites. Present findings in the context of available data and with emphasis on phenolics in algae are discussed. PMID:20202162

  5. Color excesses, intrinsic colors, and absolute magnitudes of Galactic and Large Magellanic Cloud Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

    Vacca, William D.; Torres-Dodgen, Ana V.

    1990-01-01

    A new method of determining the color excesses of WR stars in the Galaxy and the LMC has been developed and is used to determine the excesses for 44 Galactic and 32 LMC WR stars. The excesses are combined with line-free, narrow-band spectrophotometry to derive intrinsic colors of the WR stars of nearly all spectral subtypes. No correlation of UV spectral index or intrinsic colors with spectral subtype is found for the samples of single WN or WC stars. There is evidence that early WN stars in the LMC have flatter UV continua and redder intrinsic colors than early WN stars in the Galaxy. No separation is found between the values derived for Galactic WC stars and those obtained for LMC WC stars. The intrinsic colors are compared with those calculated from model atmospheres of WR stars and generally good agreement is found. Absolute magnitudes are derived for WR stars in the LMC and for those Galactic WR stars located in clusters and associations for which there are reliable distance estimates.

  6. Are dusty galaxies blue? Insights on UV attenuation from dust-selected galaxies

    SciTech Connect

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

    2014-12-01

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

  7. The unusual interacting S star binary HR 1105

    NASA Technical Reports Server (NTRS)

    Ake, Thomas B., III; Johnson, Hollis R.; Bopp, Bernard W.

    1994-01-01

    IUE observations of HR 1105 over its 596-day orbit show strong orbital modulation of both continuum and emission lines. These are most intense just before both conjunctions and nearly disappear near quadratures, the most intense phase being just before the hot component passes in front of the S star. High dispersion observations exhibit a blue-shifted absorption feature in Mg II, representing an outflow of material of about 55 km/s. These observations are consistent with the UV source being an optically thin gas stream between the components of the system, which is partially eclipsed when the S star is in front.

  8. Environmentally driven star formation during a super galaxy group merger

    NASA Astrophysics Data System (ADS)

    Monroe, Jonathan; Tran, Kim-Vy; Gonzalez, Anthony H.

    2016-01-01

    We find evidence for outside-in growth of galaxies within a merging super galaxy group at a redshift of z~0.37. We utilize Hubble Space Telescope imaging in rest-frame UV and visual to measure color gradients across the super group and internally within 138 individual galaxies that are spectroscopically confirmed members. The group members show enhanced star formation at intermediate environmental densities. The high resolution imaging shows that the group galaxies have bluer disks, i.e. most of the new stars are forming in the disk which supports outside-in growth. These disk-dominated galaxies will likely fade to become S0 members.

  9. WO-Type Wolf-Rayet Stars: the Last Hurrah of the Most Massive Stars?

    NASA Astrophysics Data System (ADS)

    Massey, Philip

    2014-10-01

    WO-type Wolf-Rayet (WR) stars are considered the final evolutionary stage of the highest mass stars, immediate precursors to Type Ic (He-poor) core-collapse supernovae. These WO stars are rare, and until recently only 6 were known. Our knowledge about their physical properties is mostly based on a single object, Sand 2 in the LMC. It was the only non-binary WO star both bright and unreddened enough that its FUV and NUV spectra could be obtained by FUSE and HST/FOS. A non-LTE analysis showed that Sand 2 is very hot and its (C+O)/He abundance ratio is higher than that found in WC-type WRs, suggesting it is indeed highly evolved. However, the O VI resonance doublet in the FUV required a considerably cooler temperature (120,000 K) model than did the optical O VI lines (170,000 K). Further, the enhanced chemical abundances did not match the predictions of stellar evolutionary models. Another non-LTE study found a 3x higher (C+O)/He abundance ratio and a cooler temperature. We have recently discovered two other bright, single, and lightly reddened WOs in the LMC, allowing us to take a fresh look at these important objects. Our newly found WOs span a range in excitation type, from WO1 (the highest) to WO4 (the lowest). Sand 2 is intermediate (WO3). We propose to use COS to obtain FUV and NUV data of all three stars for as comprehensive a study as is currently possible. These UV data will be combined with our optical Magellan spectra for a detailed analysis with CMFGEN with the latest atomic data. Knowing the degree of chemical evolution of these WO stars is crucial to determining their evolutionary status, and thus in understanding the final stages of the most massive stars.

  10. The impact of stellar activity on X-ray and UV transits

    NASA Astrophysics Data System (ADS)

    Llama, Joe; Shkolnik, Evgenya

    2015-12-01

    X-ray and UV observations of transiting exoplanets have revealed the presence of extended atmospheres around a number of systems. At high energies, stellar radiation is absorbed high up in the planetary atmosphere, making X-ray and UV observations a potential tool for investigating the upper atmospheres of exoplanets. However, at these high energies, stellar activity can dramatically impact the observations. At short wavelengths the star appears limb-brightened, and active regions appear as bright features on the stellar disk. These will impact both the transit depth and shape, affecting our ability to measure the true planet-to-star radius ratio.I will show results of simulate exoplanet transit light curves using Solar data obtained in the soft X-ray and UV by NASAs Solar Dynamics Observatory to investigate the impact of stellar activity at these wavelengths. By using a limb-brightened transit model coupled with disk resolved Solar images in the X-ray, extreme- and far-UV I will show how both occulted and unocculted active regions can mimic an inflated planetary atmosphere by changing the depth and shape of the transit profile. I will also show how the disk integrated Lyman-alpha Solar irradiance varies on both short and long timescales and how this variability can impact our ability to recover the true radius ratio of a transiting exoplanet.Finally, I will present techniques on how to overcome these effects to determine the true planet-to-star radius in X-ray and UV observations.

  11. Arches showing UV flaring activity

    NASA Technical Reports Server (NTRS)

    Fontenla, J. M.

    1988-01-01

    The UVSP data obtained in the previous maximum activity cycle show the frequent appearance of flaring events in the UV. In many cases these flaring events are characterized by at least two footpoints which show compact impulsive non-simultaneous brightenings and a fainter but clearly observed arch developes between the footpoints. These arches and footpoints are observed in line corresponding to different temperatures, as Lyman alpha, N V, and C IV, and when observed above the limb display large Doppler shifts at some stages. The size of the arches can be larger than 20 arcsec.

  12. The LINUS UV imaging spectrometer

    NASA Astrophysics Data System (ADS)

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

    2003-09-01

    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.

  13. Spectrophotometric Studies of Carbon Wolf-Rayet Stars

    NASA Astrophysics Data System (ADS)

    Brownsberger, Kenneth Robert

    1995-01-01

    Using multi-band spectra of 90 Carbon Wolf-Rayet (WC) stars, this Ph.D. thesis investigates the relationships between various emission line and continuum features of WC star winds and how these relationships compare with theoretical wind models. Numerous ultraviolet (UV) observations from the International Ultraviolet Explorer (IUE) archives have been combined with ground-based optical and near-infrared (NIR) data to give a spectral range for many WC stars spanning from 1200 to 10,200 A. The power-law distribution of Wolf -Rayet (W-R) continua are utilized to estimate line-of-sight interstellar reddening and spectral indices of WC stars. Relatively constant strengths of several emission lines in single early-type WC stars (WCE) are used to compute intrinsic line fluxes, absolute magnitudes and distances for Galactic WCE stars. These lines are also used to estimate magnitude differences in WCE+OB systems, and to compute absolute magnitudes and distances for these systems. Lastly, WCE emission line strengths are compared with values from published WCE wind structure models. The unfortunate result is that these models do not adequately predict line strengths for most emission features in WCE stars.

  14. Observed Effects of of Star-Planet Interaction

    NASA Astrophysics Data System (ADS)

    Wolk, Scott; Pillitteri, Ignazio; Poppenhaeger, Katja

    2015-08-01

    Since soon after the discover of Hot Jupiters, it has been suspected that interaction of these massive bodies with their host stars could give rise to observable signals. We discuss the observational evidence for star-planet interactions (SPI) of tidal and magnetic origin observed in X-rays and FUV. Hot Jupiters can significantly affect the activity of their host stars through tidal and magnetic interaction, leading to both an increased or a decreased stellar activity depending on the internal structure of the host star and the properties of the hosted planet. In HD 189733 X-ray and FUV flares are preferentially in a very restricted range of planetary phases. Matsakos et al. (2015) show, using MHD simulations, that planetary gas can be liberated, forming a stream of gas that gets compressed and accrete onto the star with a phase lag of 70-90 degrees . This scenario explains many features observed both in X-rays and FUV (Pillitteri et al. 2015). On the other hand, WASP-18, an F6 star with a massive hot Jupiter, there are no signs of activity in X-rays or UV. Several age indicators (isochrone fitting, Li abundance) point to a young age (in 0.5-2 Gyr) and thus significant activity was expected. In this system, tidal SPI between the star and the very close-in and massive planet can destroy the formation of magnetic dynamo and thus nullify the stellar activity.

  15. The First Stars

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2010-10-01

    The standard cosmological model predicts that the first cosmological objects are formed when the age of the universe is a few hundred million years. Recent theoretical studies and numerical simulations consistently suggest that the first objects are very massive primordial stars. We introduce the key physics and explain why the first stars are thought to be massive, rather than to be low-mass stars. The state-of-the-art simulations include all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to very high ``stellar'' densities. Evolutionary calculations of the primordial stars suggest the formation of massive blackholes in the early universe. Finally, we show the results from high-resolution simulations of star formation in a low-metallicity gas. Vigorous fragmentation is triggered in a star-forming gas cloud at a metallicity of as low as Z = 10-5Zsolar.

  16. Cooling of dense stars

    NASA Technical Reports Server (NTRS)

    Tsuruta, S.

    1972-01-01

    Cooling rates were calculated for neutron stars of about one solar mass and 10 km radius, with magnetic fields from zero to about 10 to the 14th power gauss, for extreme cases of maximum and zero superfluidity. The results show that most pulsars are so cold that thermal ionization of surface atoms would be negligible. Nucleon superfluidity and crystallization of heavy nuclei were treated quantitatively, and more realistic hadron star models were chosen. Cooling rates were calculated for a stable hyperon star near the maximum mass limit, a medium weight neutron star, and a light neutron star with neutron-rich heavy nuclei near the minimum mass limit. Results show that cooling rates are a sensitive function of density. The Crab and Vela pulsars are considered, as well as cooling of a massive white dwarf star.

  17. The Slow Death (Or Rebirth?) of Extended Star Formation in z ~ 0.1 Green Valley Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Fang, Jerome J.; Faber, S. M.; Salim, Samir; Graves, Genevieve J.; Rich, R. Michael

    2012-12-01

    UV observations in the local universe have uncovered a population of early-type galaxies with UV flux consistent with low-level recent or ongoing star formation. Understanding the origin of such star formation remains an open issue. We present resolved UV-optical photometry of a sample of 19 Sloan Digital Sky Survey (SDSS) early-type galaxies at z ~ 0.1 drawn from the sample originally selected by Salim & Rich to lie in the bluer part of the green valley in the UV-optical color-magnitude diagram as measured by the Galaxy Evolution Explorer (GALEX). Utilizing high-resolution Hubble Space Telescope (HST) far-UV imaging provides unique insight into the distribution of UV light in these galaxies, which we call "extended star-forming early-type galaxies" (ESF-ETGs) because of extended UV emission that is indicative of recent star formation. The UV-optical color profiles of all ESF-ETGs show red centers and blue outer parts. Their outer colors require the existence of a significant underlying population of older stars in the UV-bright regions. An analysis of stacked SDSS spectra reveals weak LINER-like emission in their centers. Using a cross-matched SDSS DR7/GALEX GR6 catalog, we search for other green valley galaxies with similar properties to these ESF-ETGs and estimate that ?13% of dust-corrected green valley galaxies of similar stellar mass and UV-optical color are likely ESF-candidates, i.e., ESF-ETGs are not rare. Our results are consistent with star formation that is gradually declining in existing disks, i.e., the ESF-ETGs are evolving onto the red sequence for the first time, or with rejuvenated star formation due to accreted gas in older disks provided that the gas does not disrupt the structure of the galaxy and the resulting star formation is not too recent and bursty. ESF-ETGs may typify an important subpopulation of galaxies that can linger in the green valley for up to several Gyrs, based on their resemblance to nearby gas-rich green valley galaxies with low-level ongoing star formation.

  18. Scientific problems addressed by the Spektr-UV space project (world space Observatory—Ultraviolet)

    NASA Astrophysics Data System (ADS)

    Boyarchuk, A. A.; Shustov, B. M.; Savanov, I. S.; Sachkov, M. E.; Bisikalo, D. V.; Mashonkina, L. I.; Wiebe, D. Z.; Shematovich, V. I.; Shchekinov, Yu. A.; Ryabchikova, T. A.; Chugai, N. N.; Ivanov, P. B.; Voshchinnikov, N. V.; Gomez de Castro, A. I.; Lamzin, S. A.; Piskunov, N.; Ayres, T.; Strassmeier, K. G.; Jeffrey, S.; Zwintz, S. K.; Shulyak, D.; Gérard, J.-C.; Hubert, B.; Fossati, L.; Lammer, H.; Werner, K.; Zhilkin, A. G.; Kaigorodov, P. V.; Sichevskii, S. G.; Ustamuich, S.; Kanev, E. N.; Kil'pio, E. Yu.

    2016-01-01

    The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory—Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115-310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems.

  19. U Gem Stars

    NASA Astrophysics Data System (ADS)

    Kaitchuck, R.; Murdin, P.

    2000-11-01

    U Geminorum (U Gem) is the prototype for one subclass of dwarf nova (DN) systems. U Gem stars, like other DNs, brighten by factors of hundreds to thousands, sometimes in just a few hours. The eruptions recur quasi-periodically on intervals of weeks to years, with durations from a few days to a few weeks. U Gem stars, like all cataclysmic variables, are BINARY STAR systems consisting of a low-ma...

  20. First supernova companion star found

    NASA Astrophysics Data System (ADS)

    2004-01-01

    Supernova 1993J exploding hi-res Size hi-res: 222 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Supernova 1993J exploding (artist’s impression) New observations with the Hubble Space Telescope allow a look into a supernova explosion under development. In this artist’s view the red supergiant supernova progenitor star (left) is exploding after having transferred about 10 solar masses of hydrogen gas to the blue companion star (right). This interaction process happened over about 250 years and affected the supernova explosion to such an extent that SN 1993J was later known as one of the most peculiar supernovae ever seen. Supernova 1993J exploding hi-res Size hi-res: 4200 kb Credits: ESA and Justyn R. Maund (University of Cambridge) The site of the Supernova 1993J explosion A virtual journey into one of the spiral arms of the grand spiral Messier 81 (imaged with the Isaac Newton Telescope on La Palma, left) reveals the superb razor-sharp imaging power of the NASA/ESA Hubble Space Telescope (Hubble’s WFPC2 instrument, below). The close-up (with Hubble’s ACS, to the right) is centred on the newly discovered companion star to Supernova 1993J that itself is no longer visible. The quarter-circle around the supernova companion is a so-called light echo originating from sheets of dust in the galaxy reflecting light from the original supernova explosion. Supernova 1993J explosing site hi-res Size hi-res: 1502 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Close-up of the Supernova 1993J explosion site (ACS/HRC image) This NASA/ESA Hubble Space Telescope image shows the area in Messier 81 where Supernova 1993J exploded. The companion to the supernova ‘mother star’ that remains after the explosion is seen in the centre of the image. The image is taken with Hubble’s Advanced Camera for Surveys and is a combination of four exposures taken with ACS’ High Resolution Camera. The exposures were taken through two near-UV filters (250W, 2100 seconds and 330W, 1200 seconds) shown in purple and blue, a deep blue filter (435W, 1000 seconds) shown in green and a green filter (555W, 1120 seconds) shown in red. The quarter-circle around the supernova companion is a so-called light echo originating from sheets of dust in the galaxy reflecting light from the original supernova explosion. The timing of the appearance of these echoes can be used to map out the dust structure around the supernova. The light echo was detected in late 2002 and early 2003 by two competing groups of scientists. Messier 81 spiral arm (WFPC2 image) hi-res Size hi-res: 1502 kb Credits: ESA and Justyn R. Maund (University of Cambridge) Messier 81 spiral arm (WFPC2 image) This NASA/ESA Hubble Space Telescope image shows a small portion of one of Messier 81’s spiral arms. It extends about 0.03 x 0.03 degrees. The supernova companion is the bluish star in the upper right hand corner. Dust lanes in the spiral arms of the galaxy are seen, as well as many other stars and a few star forming nebulae. The image is composed of four separate exposures from the ESO/ST-ECF Archive through a blue filter, a green filter, a red filter and a near-infrared filter. The image was taken with Hubble’s Wide Field and Planetary Camera 2. Acknowledgement: Bob Kirshner (Harvard University, USA) Grand Spiral Messier 81 (ground-based) hi-res Size hi-res: 1502 kb Credits: ESA/INT/DSS2 Grand Spiral Messier 81 (ground-based) This ground-based image shows the spiral galaxy Messier 81 in its entirety. The image is a combination of exposures from the Isaac Newton Telescope on La Palma (courtesy of Jonathan Irwin) and Digitized Sky Survey 2 images. The dynamic duo, Messier 81 and 82 (ground-based) hi-res Size hi-res: 1502 kb Credits: Robert Gendler (http://www.robgendlerastropics.com) The dynamic duo, Messier 81 and 82 (ground-based) This wide-angle image taken by astrophotographer Robert Gendler shows the amazing duo of Messier 81 (right) and Messier 82 (left). These two mighty galaxies in the Plough (Ursa Major) belong to some of the most famous and beloved galaxies known to amateur astronomers. This may be one of the reasons that Supernova 1993J was discovered by the Spanish amateur astronomer Francisco Garcia Diaz and not a professional astronomer. The violent star-forming activity in the neighbouring Messier 82 gives rise to a strong galactic wind that is spewing knotty filaments of hydrogen and nitrogen gas (seen in red) out of its centre. Supernovae are some of the most significant sources of chemical elements in the Universe, and they are at the heart of our understanding of the evolution of galaxies. Supernovae are some of the most violent events in the Universe. For many years astronomers have thought that they occur in either solitary massive stars (Type II supernovae) or in a binary system where the companion star plays an important role (Type I supernovae). However no one has been able to observe any such companion star. It has even been speculated that the companion stars might not survive the actual explosion... The second brightest supernova discovered in modern times, SN 1993J, was found in the beautiful spiral galaxy M81 on 28 March 1993. From archival images of this galaxy taken before the explosion, a red supergiant was identified as the mother star in 1993 - only the second time astronomers have actually seen the progenitor of a supernova explosion (the first was SN 1987A, the supernova that exploded in 1987 in our neighbouring galaxy, the Large Magellanic Cloud). Initially rather ordinary, SN 1993J began to puzzle astronomers as its ejecta seemed too rich in the chemical element helium and instead of fading normally it showed a bizarre sharp increase in brightness. The astronomers realised that a normal red supergiant alone could not have given rise to such a weird supernova. It was suggested that the red supergiant orbited a companion star that had shredded its outer layers just before the explosion. Ten years after this cataclysmic event, a European/University of Hawaii team of astronomers has now peered deep into the glowing remnants of SN 1993J using the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS) and the giant Keck telescope on Mauna Kea in Hawaii. They have discovered a massive star exactly at the position of the supernova that is the long sought companion to the supernova progenitor. This is the first supernova companion star ever to be detected and it represents a triumph for the theoretical models. In addition, this observation allows a detailed investigation of the stellar physics leading to supernova explosions. It is now clear that during the last 250 years before the explosion 10 solar masses of gas were torn violently from the red supergiant by its partner. By observing the companion closely in the coming years it may even be possible to detect a neutron star or black hole emerge from the remnants of the explosion ‘in real time’. Given the paucity of observations of supernova progenitor systems this result, published in Nature on 8 January 2004, is likely to “be crucial to understanding how very massive stars explode and why we see such peculiar supernovae” according to first author Justyn R. Maund from the University of Cambridge, UK. Stephen Smartt, also from the University of Cambridge, says “Supernova explosions are at the heart of our understanding of the evolution of galaxies and the formation of chemical elements in the Universe. It is essential that we know what type of stars produce them.” For the last ten years astronomers have believed that they could understand the very peculiar behaviour of 1993J by invoking the existence of a binary companion star and now this picture has proved correct. According to Rolf Kudritzki from the University of Hawaii “The combination of the outstanding spatial resolution of Hubble and the huge light gathering power of the Keck 10m telescope in Hawaii has made this fantastic discovery possible.” Supernovae occur when a star of more than about eight times the mass of the Sun reaches the end of its nuclear fuel reserves and can no longer produce enough energy to keep the star from collapsing under its own immense weight. The core of the star collapses, and the outer layers are ejected in a fast-moving shock wave. This huge energy release causes the visible supernova we see. While astronomers are convinced that observations will match this theoretical model, they are in the embarrassing position that they have confidently identified only two stars that later exploded as supernovae - the precursors of supernovae 1987A and 1993J. There have been more than 2000 supernovae discovered in galaxies beyond the Milky Way and there appear to be about eight distinct sub-classes. However identifying which stars produce which flavours has proved incredibly difficult. This team has now embarked on a parallel project with the Hubble Space Telescope to image a large number of galaxies and then wait patiently for a supernova to explode. Supernovae appear in spiral galaxies like M81 on average once every 100 years or so. The team, led by Stephen Smartt, hope to increase the numbers of supernova progenitors known from 2 to 20 over the next five years. Notes for editors The team is composed of Stephen J. Smartt and Justyn R. Maund (University of Cambridge, UK), Rolf. P. Kudritzki (University of Hawaii, USA), Philipp Podsiadlowski (University of Oxford, UK) and Gerry F. Gilmore (University of Cambridge, UK). Animations of the discovery and general Hubble Space Telescope background footage are available from http://www.spacetelescope.org/video/heic0401_vnr.html

  1. THE FAR-INFRARED, UV, AND MOLECULAR GAS RELATION IN GALAXIES UP TO z = 2.5

    SciTech Connect

    Nordon, R.; Lutz, D.; Saintonge, A.; Berta, S.; Wuyts, S.; Foerster Schreiber, N. M.; Genzel, R.; Magnelli, B.; Poglitsch, A.; Popesso, P.; Rosario, D.; Sturm, E.; Tacconi, L. J.

    2013-01-10

    We use the infrared excess (IRX) FIR/UV luminosity ratio to study the relation between the effective UV attenuation (A {sub IRX}) and the UV spectral slope ({beta}) in a sample of 450 1 < z < 2.5 galaxies. The FIR data are from very deep Herschel observations in the GOODS fields that allow us to detect galaxies with star formation rates (SFRs) typical of galaxies with log(M {sub *}) > 9.3. Thus, we are able to study galaxies on and even below the main SFR-stellar mass relation (main sequence). We find that main-sequence galaxies form a tight sequence in the IRX-{beta} plane, which has a flatter slope than commonly used relations. This slope favors a Small-Magellanic-Cloud-like UV extinction curve, though the interpretation is model dependent. The scatter in the A {sub IRX}-{beta} plane correlates with the position of the galaxies in the SFR-M {sub *} plane. Using a smaller sample of galaxies with CO gas masses, we study the relation between the UV attenuation and the molecular gas content. We find a very tight relation between the scatter in the IRX-{beta} plane and the specific attenuation S{sub A} , a quantity that represents the attenuation contributed by the molecular gas mass per young star. S{sub A} is sensitive to both the geometrical arrangement of stars and dust and to the compactness of the star-forming regions. We use this empirical relation to derive a method for estimating molecular gas masses using only widely available integrated rest-frame UV and FIR photometry. The method produces gas masses with an accuracy between 0.12 and 0.16 dex in samples of normal galaxies between z {approx} 0 and z {approx} 1.5. Major mergers and submillimeter galaxies follow a different S{sub A} relation.

  2. The UV to Near-IR Optical Properties of PAHs: A Semi-Empirical Model

    NASA Technical Reports Server (NTRS)

    Mattioda, A. L.; Allamandola, L. J.; Hudgins, D. M.

    2005-01-01

    Interstellar Polycyclic Aromatic Hydrocarbon (PAH) infrared emission features represent an important and unique diagnostic tool of the chemical and physical conditions throughout the universe. However, one challenge facing the widely accepted PAH emission model has been the detection of infrared features in regions of low UV flux. Utilizing recently published laboratory Near Infrared VIR) PAH ion absorption data measured in our laboratory, we build upon previous models for PAH ion absorption in the UV-Vis to extrapolate a new model which incorporates PAH ion absorption in the NIR. This model provides a basis for comparing the relative energy absorption of PAH ions in the UV-Vis and NIR regions for a wide variety of stellar types. This model demonstrates that the radiation from late-type stars can pump the mid-IR PAH features.

  3. The MUSCLES Treasury Survey: Temporally- and Spectrally-Resolved Irradiance from Low-mass Exoplanet Host Stars

    NASA Astrophysics Data System (ADS)

    France, Kevin; Parke Loyd, R. O.; Youngblood, Allison; Linsky, Jeffrey; MUSCLES Treasury Survey Team

    2016-01-01

    The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. High-energy photons (X-ray to near-UV; 5 - 3200 Ang) from these stars regulate the atmospheric temperature profiles and photochemistry on orbiting planets, influencing the production of potential "biomarker" gases. It has been shown that the atmospheric signatures of potentially habitable planets around low-mass stars may be significantly different from planets orbiting Sun-like stars owing to the different UV spectral energy distribution. I will present results from a panchromatic survey (Hubble/Chandra/XMM/optical) of M and K dwarf exoplanet hosts, the MUSCLES Treasury Survey (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems). We reconstruct the Lyman-alpha and extreme-UV (100-900 Ang) radiation lost to interstellar attenuation and create 5 Angstrom to 5 micron stellar irradiance spectra; these data will be publically available as a High-Level Science Product on MAST. We find that all low-mass exoplanet host stars exhibit significant chromospheric/transition region/coronal emission -- no "UV inactive" M dwarfs are observed. The F(far-UV)/F(near-UV) flux ratio, a driver for possible abiotic production of the suggested biomarkers O2 and O3, increases by ~3 orders of magnitude as the habitable zone moves inward from 1 to 0.1 AU, while the incident far-UV (912 - 1700 Ang) and XUV (5 - 900 Ang) radiation field strengths decrease by factors of a few across this range. Far-UV flare activity is common in 'optically inactive' M dwarfs; statistics from the entire sample indicate that large UV flares (E(300 - 1700 Ang) >= 10^31 erg) occur several times per day on typical M dwarf exoplanet hosts.

  4. Strange Nonchaotic Stars

    NASA Astrophysics Data System (ADS)

    Lindner, John F.; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G.; Ditto, William L.

    2015-08-01

    Exploiting the unprecedented capabilities of the planet-hunting Kepler space telescope, which stared at 150 000 stars for four years, we discuss recent evidence that certain stars dim and brighten in complex patterns with fractal features. Such stars pulsate at primary and secondary frequencies whose ratios are near the famous golden mean, the most irrational number. A nonlinear system driven by an irrational ratio of frequencies is generically attracted toward a “strange” behavior that is geometrically fractal without displaying the “butterfly effect” of chaos. Strange nonchaotic attractors have been observed in laboratory experiments and have been hypothesized to describe the electrochemical activity of the brain, but a bluish white star 16 000 light years from Earth in the constellation Lyra may manifest, in the scale-free distribution of its minor frequency components, the first strange nonchaotic attractor observed in the wild. The recognition of stellar strange nonchaotic dynamics may improve the classification of these stars and refine the physical modeling of their interiors. We also discuss nonlinear analysis of other RR Lyrae stars in Kepler field of view and discuss some toy models for modeling these stars.References: 1) Hippke, Michael, et al. "Pulsation period variations in the RRc Lyrae star KIC 5520878." The Astrophysical Journal 798.1 (2015): 42.2) Lindner, John F., et al. "Strange nonchaotic stars." Phys. Rev. Lett. 114, 054101 (2015)

  5. Massive soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  6. CSTAR star catalogue development

    NASA Technical Reports Server (NTRS)

    Uhde-Lacovara, J. A.

    1986-01-01

    The Continuous Stellar Tracking Attitude Reference (CSTAR) system is an in-house project for the Space Station to provide high accuracy, drift free attitude and angular rate information for the GN&C system. Constraints exist on the star catalogue incorporated in the system. These constraints include the following: mass memory allocated for catalogue storage, star tracker imaging sensitivity, the minimum resolvable separation angle between stars, the width of the field of view of the star tracker, and the desired number of stars to be tracked in a field of view. The Smithsonian Astrophysical Observatory (SAO) catalogue is the basis reference for this study. As it stands, the SAO does not meet the requirements of any of the above constraints. Star selection algorithms have been devised for catalogue optimization. Star distribution statistics have been obtained to aid in the development of these rules. VAX based software has been developed to implement the star selection algorithms. The software is modular and provides a design tool to tailor the catalogue to available star tracker technology. The SAO catalogue has been optimized for the requirements of the present CSTAR system.

  7. Delta Scuti stars: Theory

    NASA Technical Reports Server (NTRS)

    Guzik, J. A.

    1998-01-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.

  8. Introduction to neutron stars

    NASA Astrophysics Data System (ADS)

    Lattimer, James M.

    2015-02-01

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  9. Delta Scuti stars: Theory

    SciTech Connect

    Guzik, J.A.

    1998-03-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one`s understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying {delta} Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for {delta} Scuti stars, using FG Vir, {delta} Scuti, and CD-24{degree} 7599 as examples.

  10. Introduction to neutron stars

    SciTech Connect

    Lattimer, James M.

    2015-02-24

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  11. Massive soliton stars

    NASA Astrophysics Data System (ADS)

    Chiu, Hong-Yee

    1990-05-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  12. Fast pulsars, strange stars

    SciTech Connect

    Glendenning, N.K.

    1990-02-01

    The initial motivation for this work was the reported discovery in January 1989 of a 1/2 millisecond pulsar in the remnant of the spectacular supernova, 1987A. The status of this discovery has come into grave doubt as of data taken by the same group in February, 1990. At this time we must consider that the millisecond signal does not belong to the pulsar. The existence of a neutron star in remnant of the supernova is suspected because of recent observations on the light curve of the remnant, and of course by the neutrino burst that announced the supernova. However its frequency is unknown. I can make a strong case that a pulsar rotation period of about 1 ms divides those that can be understood quite comfortably as neutron stars, and those that cannot. What we will soon learn is whether there is an invisible boundary below which pulsar periods do not fall, in which case, all are presumable neutron stars, or whether there exist sub- millisecond pulsars, which almost certainly cannot be neutron stars. Their most plausible structure is that of a self-bound star, a strange-quark-matter star. The existence of such stars would imply that the ground state of the strong interaction is not, as we usually assume, hadronic matter, but rather strange quark matter. Let us look respectively at stars that are bound only by gravity, and hypothetical stars that are self-bound, for which gravity is so to speak, icing on the cake.

  13. 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)

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

    2014-01-01

    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