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NASA NTRS2016

Local starburst galaxies and their descendants. Statistics from the Sloan Digital Sky Survey

Despite strong interest in the starburst phenomenon in extragalactic astronomy, the concept remains ill-defined. Here we use a strict definition of starburst to examine the statistical properties of starburst galaxies in the local universe. We also seek to establish links between starburst galaxies, post-starburst (hereafter postburst) galaxies, and active galaxies. Data were selected from the Sloan Digital Sky Survey DR7. We applied a novel method of treating dust attenuation and derive star formation rates, ages, and stellar masses assuming a two-component stellar population model. Dynamical masses are calculated from the width of the H-alpha line. These masses agree excellently with the photometric masses. The mass (gas+stars) range is approximately 10( exp 9) - 10(exp 11.5) solar mass. As a selection criterion for starburst galaxies, we use, the birthrate parameter, b = SFR/SFR, requiring that b is greater than 3. For postburst galaxies, we use, the equivalent width of Hdelta in absorption with the criterion EW (sub Hdelta_abs) is greater than 6 A. Results. We find that only 1% of star-forming galaxies are starburst galaxies. They contribute 3-6% to the stellar production and are therefore unimportant for the local star formation activity. The median starburst age is 70 Myr roughly independent of mass, indicating that star formation is mainly regulated by local feedback processes. The b-parameter strongly depends on burst age. Values close to b = 60 are found at ages approximately 10 Myr, while almost no starbursts are found at ages greater than 1 Gyr. The median baryonic burst mass fraction of sub-L galaxies is 5% and decreases slowly towards high masses. The median mass fraction of the recent burst in the postburst sample is 5-10%. A smaller fraction of the postburst galaxies, however, originates in non-bursting galaxies. The age-mass distribution of the postburst progenitors (with mass fractions is greater than 3%) is bimodal with a break at logM(solar mass ) 10.6, above which the ages are doubled. The starburst and postburst luminosity functions (LFs) follow each other closely until M(sub r ) (is) approximately -21, when active galactic nuclei (AGNs) begin to dominate. The postburst LF continues to follow the AGN LF, while starbursts become less significant. This suggests that the number of luminous starbursts is underestimated by about one dex at high luminosities, because of having large amounts of dust and/or being outshone by an AGN. It also indicates that the starburst phase preceded the AGN phase. Finally, we look at the conditions for global gas outflow caused by stellar feedback and find that massive starburst galaxies are susceptible to such outflows.

Statistical distributions↗
NASA NTRS2011

Suzaku Observations of the Ultracompact Binary System 4U1626-67

The accretion-powered pulsar 4U1626-67 experienced a new torque reversal at the beginning of 2008, after about 18 years of steadily spinning down. We present a spectral analysis of this source using two pointed observations performed by Suzaku in 2006 March and in 2010 September. We confirm with Suzaku the presence of a strong emission-line complex centered on 1 keV, with the strongest line being the hydrogen-like Ne Ly- alpha at 1.025(1.5) keV. We were able to resolve this complex with up to eight emission lines. A dramatic increase of the equivalent width of the Ne Ly-alpha 1.021 keV after the 2008 torque reversal occurred, reaching almost the same value measured by ASCA in 1993. In addition, we confirm the general decrease trend of the equivalent widths during the spin-down period. We also report on the detection of a cyclotron line feature centered at approx 37 keV. In spite of the fact that a dramatic increase of the X-ray luminosity (0.5-100 keV) of a factor of approx 3.5 occurred between these two observations, no significant change in the energy of the cyclotron line feature was observed. However, the intensity of the approx 1 keV line complex increased by an overall factor of approx 10.

Camero-Arranz, A.↗
NASA NTRS1994

High-resolution spectroscopy of Balmer-dominated shocks in the Large Magellanic Cloud

We present high-resolution spectra of the four Balmar-dominated supernova remnants (SNRs) in the Large Magellanic Cloud (LMC). These data allow us to measure the width of the narrow component of H alpha emission in the nonradiative filaments present in these SNRs. We find that the widths range from 30 to 50 km/s FWHM, similar to the only previously measured width of a nonradiative shock filament, that of about 30 km/s in the NE Cygnus Loop. The line widths do not appear to scale with shock velocity. These observations severely limit the possible broadening mechanisms. We discuss several possibilities, the most promising of which is a precursor associtated with cosmic rays. Assuming a cosmic-ray precursor, we are able to place constraints on the cosmic-ray diffusion coefficient. Observations such as these may provide the best method currently available to probe cosmic-ray acceleration in SNR shock waves.

Smith, R. Chris↗
NASA NTRS1973

Theoretical emergent Lyman alpha intensities from Mars.

The behavior of the Lyman alpha 1216-A intensity on Mars is presented for a range of atomic hydrogen density distributions below 200 km. Two sets of radiative transfer calculations have been performed. The first is based on spherical geometry and includes the effect of pure absorption of the resonance photons by CO2. The second set is based on the simpler plane parallel geometry and includes the effects of both pure absorption and a varying Doppler width associated with the planetary Lyman alpha line. From the plane parallel solutions, we are able to estimate and account for the effect of a varying Doppler width on our spherical model results. When pure absorption and a varying Doppler width are incorporated in the theory, the maximum change in the Lyman alpha disc intensity is a factor of about 2 over the range of hydrogen density models considered.

Strickland, D. J.↗
NASA NTRS1990

A survey of the profiles of narrow emission lines in Seyfert galaxies

An atlas of the nuclear spectra of 58 Seyfert galaxies and six galaxies with nuclear H II regions is presented. For all but three galaxies, the range of rest wavelengths covered is about 6000-6800 A, with spectral resolution at H-alpha either 45 km/s or 130 km/s. Widths are given for the emission lines forbidden Fe VII 6086 A, forbidden O I 6300 A, H-alpha, forbidden N II 6584, and forbidden S II 6717,6731 A. In all, widths for some 210 lines in 53 galaxies are listed. A comparison is made between the present and previous line width measurements.

Wilson, A. S.↗
NASA NTRS1994

The Role of Crack Formation in Chevron-Notched Four-Point Bend Specimens

The failure sequence following crack formation in a chevron-notched four-point bend 1 specimen is examined in a parametric study using the Bluhm slice synthesis model. Premature failure resulting from crack formation forces which exceed those required to propagate a crack beyond alpha (min) is examined together with the critical crack length and critical crack front length. An energy based approach is used to establish factors which forecast the tendency of such premature failure due to crack formation for any selected chevron-notched geometry. A comparative study reveals that, for constant values of alpha (1) and alpha (0), the dimensionless beam compliance and stress intensity factor are essentially independent of specimen width and thickness. The chevron tip position, alpha (0) has its primary effect on the force required to initiate a sharp crack. Small values for alpha (0) maximize the stable region length, however, the premature failure tendency is also high for smaller alpha (0) values. Improvements in premature failure resistance can be realized for larger values of alpha (0) with only a minor reduction in the stable region length. The stable region length is also maximized for larger chevron based positions, alpha (1) but the chance for premature failure is also raised. Smaller base positions improve the premature failure resistance with only minor decreases in the stable region length. Chevron geometries having a good balance of premature failure resistance, stable region length, and crack front length are 0.20 less than or equal to alpha (0) is less than or equal to 0.30 and 0.70 is less than or equal to alpha (1) is less than or equal to 0.80.

Calomino, Anthony M.↗
NASA NTRS1982

Radial widths, optical depths, and eccentricities of the Uranian rings

Observations of the stellar occultation by the Uranian rings of 15/16 August 1980 are used to estimate radial widths and normal optical depths for segments of rings 6, 5, 4, alpha, beta, eta, gamma, and delta. Synthetic occultation profiles are generated to match the observed light curves. A review of published data confirms the existence of width-radius relations for rings alpha and beta, and indicates that the optical depths of these two rings vary inversely with their radial widths. Masses are obtained for rings alpha and beta, on the assumption that differential precession is prevented by their self-gravity. A quantitative comparison of seven epsilon-ring occultation profiles obtained over a period of 3.4 yr reveals a consistent structure, which may reflect the presence of unresolved gaps and subrings.

Nicholson, P. D.↗
NASA NTRS1979

X-ray evidence for electron-ion equilibrium and ionization nonequilibrium in Young supernova remnants

X-ray emission up to 25 keV from the supernova remnants Cas A and Tycho has been detected with the A-2 spectroscopy experiment on HEAO 1. The spectra must include continuum components with effective temperature of about 10 to the 8th K which could arise from optically thin plasmas in the collisionless shock fronts. This is the first indication of electron-ion temperature equilibrium in the expanding shell of young remnants. The equivalent widths of the K-alpha and K-beta iron line blends in Cas A have also been measured and it is found that their ratio is not compatible with the measured X-ray temperature in the collisional ionization equilibrium model. Finally, an unsuccessful search has been conducted for hard X-ray pulsars in both remnants.

Pravdo, S. H.↗
NASA NTRS1984

VW Hyi - The white dwarf revealed

Nonsimultaneous IUE, optical, and near-IR observations of VW Hyi at quiescence are presented. Using these and UV data from other investigations, a broad feature in the ultraviolet is identified with L-alpha absorption. The presence and width of the line imply that (1) the white dwarf in VW Hyi is directly visible in the UV and (2) the effective temperature of this star is approximately 18,000 + or - 2000 K for log g = 8. The continuum observations, combined with the J and K photometry of Sherrington et al., (1980), can be fit with a combination of this relatively cool white dwarf and a steady-state disk model with an accretion rate of 10 to the -11th solar masses/yr. Additional observations of the hump in the optical light curve can be reasonably fit by a 12,000-K blackbody. Such a source is consistent with the hump being a minor contribution to the system's overall continuum distribution shortward of 2000 A and longward of about 1 micron.

Mateo, M.↗
NASA NTRS1989

Long-slit optical spectroscopy of powerful far-infrared galaxies - The nature of the nuclear energy source

Optical spectroscopic data are presented for a sample of 47 powerful far-IR galaxies chosen for IR spectral shape, and for six other IR-bright galaxies. The stellar absorption lines expected from a population of old stars are generally very weak in the nuclei of the galaxies. Very weak Mg I absorption is found in regions well off the nucleus, implying that the visible spectrum is dominated by young stars and not by an AGN. At least one, and probably five, of the galaxies have detectable WR emission features, providing additional evidence for a young stellar population. About 20 percent of the galaxies have strong Balmer absorption lines, indicating the presence of a substantial intermediate-age stellar population. The equivalent width of the H-alpha emission line can be modeled as arising from a mixture of a large young population and an intermediate-age population of stars.

Armus, Lee↗
NASA NTRS1993

Spectroscopic investigation of a low-power arcjet plume

We report the results of spectroscopic measurements on the exhaust plume from a 1 kW NASA Lewis arcjet operated on simulated ammonia. In particular, we analyze emissions from the Balmer lines of atomic hydrogen and from one of the rotational bands of the NH radical. We find that exit plane temperatures are in the range 2000 to 3500 K, depending on the measurement method, and that the electron density upstream of the exit plane is on the order of 1.5 x 10 exp 14/cu cm as determined by the Stark width of the Balmer-alpha line. Also, we have determined that the average velocity of atomic hydrogen at the exit plane is about 4 km/sec, and that strong acceleration (to 5.5 km/sec) of the flow occurs just beyond the exit plane.

Ruyten, W. M.↗
NASA NTRS1997

Determination of 3D coronal structures from UVCS/SOHO synoptic observations

Daily coronal synoptic observations with the ultraviolet coronagraph spectrometer (UVCS) on SOHO are used to create Carrington maps of line of sight intensities and spectral line widths for H I Lyman alpha and the O 6 1032/1037 doublet. These 2D maps can then be used as inputs to a tomographic inversion routine to produce 3D models of the corona out to the 2.5 solar radius in the polar regions (3.0 solar radius in equatorial regions). The initial results for the determination of O(5+) outflow velocities as a function of heliographic latitude is presented.

Strachan, L.↗
NASA NTRS1999

AKN 564: An Unusual Component in the X-ray Spectra of NLSy1 Galaxies

We present an ASCA observation of the narrow-line Seyfert l (NLSyl) Arakelian 564. The X-ray light curve shows rapid variability, but no evidence for energy-dependence to these variations, within the 0.6 - 10 keV bandpass. A strong (EW approximately 70 eV) spectral feature is observed close to 1 keV. A similar feature has been observed in TON S180, another member of the NLSyl class of objects, but has not been observed in broad-line Seyfert galaxies. The feature energy suggests a large contribution from Fe L-shell lines but its intensity is difficult to explain in terms of emission and/or absorption from photoionized gas. The models which predict most emission at 1 keV are characterized by extreme values of column density, Fe abundance and ionization parameter. Models based on gas in thermal equilibrium with kT approximately l keV provide an alternative parameterization of the soft spectrum. The latter may be interpreted as the hot intercloud medium, undergoing rapid cooling and producing strong Fe L-shell recombination lines. In all cases the physical conditions are rather different from those observed in broad-line Seyferts. The hard X-ray spectrum shows a broad and asymmetric Fe K(alpha) line of large equivalent width (approximately 550 eV) suggestive of significant emission from the inner accretion disk. The profile can be explained by a neutral disk viewed at approximately 60 deg to the line-of-sight, contrary to the hypothesis that NLSyls are viewed pole-on. The large EW of this line, the strong 1 keV emission and the strong optical Fe emission lines all suggest an extreme Fe abundance in this and perhaps other NLSyls.

Turner, T. J.↗
NASA NTRS1999

Near-Simultaneous Spectroscopic and Broadband Polarimetric Observations of Be Stars

Near simultaneous optical spectroscopic (on four nights) and broadband linear continuum (B, V, R, and I bands) polarimetric (on seven nights) observations of 29 Be stars were carried out during 1993 November-December. The program Be stars displayed wavelength dependence of intrinsic polarizations with no frequency dependence of polarimetric position angles. Some of the Be stars displayed long-term polarization variability. The Be and Be-shell stars could not be distinguished from one another solely on the basis of their polarization values. Full widths at half-maximum of the H.alpha profiles and the intrinsic linear continuum polarizations are closely correlated with the projected rotational velocities of the program stars. Photospheric-absorption-corrected equivalent widths of H.alpha profiles [W(alpha)] and the radii of H.alpha-emitting or -absorbing envelopes (R(sub e) or R(sub a)) are nonlinearly correlated with the intrinsic continuum polarizations of these stars. However, W(alpha) and R(sub e) are linearly correlated. With large uncertainties, there is a trend of spectral dependence of polarization. Detailed discussion of these results is presented in this paper.

Ghosh, K.↗
NASA NTRS2006

Comprehensive Analysis of RXTE Data from Cyg X-1. Spectral Index-Quasi-Periodic Oscillation Frequency-Luminosity Correlations

We present timing and spectral analysis of approx. 2.2 Ms of Rossi X-ray Time Explorer (RXTE) archival data from Cyg X-1. Using the generic Comptonization model we reveal that the spectrum of Cyg X-1 consists of three components: a thermal seed photon spectrum, a Comptonized part of the seed photon spectrum and the iron line. We find a strong correlation between 0.1-20 Hz frequencies of quasiperiodic oscillations (QPOs) and the spectral power-law index. Presence of two spectral phases (states) are clearly seen in the data when the spectral indices saturate at low and high values of QPO frequencies. This saturation effect was discovered earlier in a number of black hole candidate (BHC) sources and now we strongly confirm this phenomenon in Cyg X-1. In the soft state this index- QPO frequency correlation shows a saturation of the photon index Gamma approx. 2.1 at high values of the low frequency upsilon(sub L). The saturation level of Gamma approx. 2.1 is the lowest value found yet in BHCs. The bolometric luminosity does not show clear correlation with the index. We also show that Fe K(sub alpha) emission line strength (equivalent width, EW) correlates with the QPO frequency. EW increases from 200 eV in the low/hard state to 1.5 keV in the high/soft state. The revealed observational correlations allow us to propose a scenario for the spectral transition and iron line formation which occur in BHC sources. We also present the spectral state (the power-law index) evolution for eight years of Cyg X-1 observations by RXTE.

Shaposhnikov, Nickolai↗
NASA NTRS1984

Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

Phenomenological fits to the hard X-ray spectrum of AM Hercules have failed to explain the high equivalent width (0.8 + or - 0.1 keV) of Fe K-alpha emission. The scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base are investigated using the Monte Carlo method. It is shown that the Fe emission equivalent width observed in the spectrum of AM Her can be explained without resorting to an overabundance of Fe in the accreting material. For sufficient optical depth across the accretion column, equivalent widths of K-alpha emission even larger than the observed values can be obtained. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values.

Swank, J. H.↗
NASA NTRS1989

A comparison of some spectrograms obtained with a Reticon and by coaddition of photographic plates

High-dispersion 2.4 A/mm spectra with signal-to-noise ratios of order 80 were obtained for three stars by using a Reticon detector and by coadding photographic spectrograms at the Dominion Astrophysical Observatory. Metal lines of equivalent widths 5 to 75 mA in Alpha Dra and Iota CrB show systematic differences of order 4 percent with an uncertainty of order 3 percent and an rms scatter of 2.0 to 3.7 mA about the mean equivalent-width differences.

Adelman, Saul J.↗
NASA NTRS1994

A kinematic search for supernova remnants in giant extragalactic H II regions

We have obtained velocity fields of the Giant H II complexes NGC 5471 in M101, NGC 2363 in NGC 2366, and the largest H II region in NGC 2403 from H-alpha observations using the TAURUS imaging Fabry-Perot interferometer. We have detected five H-alpha sources with velocity profiles which are broad when compared with the surrounding H II region. Region B in NGC 5471 has been previously determined to contain a supernova remnant by the presence of nonthermal radio continuum radiation and enhanced (O I) and (S II) emission (Skillman 1985) and broad H-alpha emission (Chu & Kennicutt 1986). Two broad H-alpha sources in NGC 2363 coincide with regions where strong splitting has been found in the (O III) line (Roy et al. 1991). Two more broad H-alpha sources have been identified in the largest H II region in NGC 2403. Very Large Array (VLA) radio continuum observations with a resolution of 2 sec at lambda(6) and lambda(20) cm of all 3 H II complexes are presented. In addition, high resolution (subarcsecond) VLA images of NGC 5471 were made at lambda(2) and lambda(6) cm. The presence of a nonthermal source in region NGC 5471 B was confirmed while region NGC 5471 A appears to be dominated by thermal emission. The nonthermal spectral index in NGC 2363 A indicates the existence of none or more supernova remnants at the position of a large velocity width source detected in H-alpha emission. No similar nonthermal sources were detected in NGC 2403 #1. Supernovae explosions and stellar winds are considered as causes for these large velocity width sources (LVWS). If the emission from the LVWSs is attributed to single supernova remnants, they are unusually luminous in both nonthermal radio continuum and H-alpha emision. The very large H-alpha luminosities could be a result of high velocity gas being ionized by the neighboring stellar cluster.

Yang, Hui↗