Blue Edge Research Articles

Red Antenna States of PS I of Cyanobacteria: Stark Effect and Interstate Energy Transfer

Previously, Stark hole-burning spectroscopy and effects of pressure at low temperature were used to determine the number of red antenna states of the cyanobacteria Synechococcus elongatus and Synechocystis PCC6803 (Hayes, J. M.; Matsuzaki, S.; Rätsep, M.; Small, G. J. J. Phys. Chem. B 2000 104, 5625. Zazubovich, V.; Matsuzaki, S.; Johnson, T. W.; Hayes, J. M.; Chitnis, P. R.; Small Chem. Phys. 2002, 275, 47). Distinct differences in linear pressure shift rates, the magnitude of the permanent dipole moment change, fΔμ, and electron−phonon coupling strength clearly show that in Synechococcus there are three red states (C708, C715, and C719), whereas in Synechocystis, there are two red states (C708 and C714). In the Stark hole-burning spectra of the lowest states of these two systems, hole splitting was not observed, only hole broadening, for excitation polarization both parallel and perpendicular to the Stark field direction. The theories of Stark hole burning predict that splitting should occur for one of the polarizations unless there is a large, random component to the induced dipole moment change, Δμind, which is not expected to be the case for pigment−protein complexes in which the orientations of pigments relative to the protein matrix are nonrandom. In this paper, Stark hole burning at higher resolution is used to reinvestigate the absence of splitting. However, even at higher resolution, no splitting is detected. This is explained by invoking large variations of the inherent dipole moment change Δμ0 of the dimer (the origin of the red-state absorption) rather than of the induced dipole moment change. These arise from a distribution of the relative orientations and separations between the components of the dimer. This distribution also results in a random component of the polarizability change tensor, Δα. The random components of Δμ0 and Δα not only obscure the Stark splitting but also cause the large inhomogeneous broadening observed for these lowest-energy red states. Temperature-dependent hole widths were also measured for C708 and C714 of Synechocystis. For C714, a T1.3 temperature dependence was observed, consistent with dephasing by the disordered protein matrix. At 708 nm, however, much higher fluences were required to saturate the absorption of the blue edge of the C714 band and then begin to burn C708. The contribution of the C708 component to the broadening was weakly temperature dependent over the range measured, 2 to 14 K. This contribution is due to energy transfer from C708 to C714, and the width measured corresponds to an energy-transfer time of 6 ps. This observation provides further proof of the existence of two red antenna states, C708 and C714.

Physical Characteristics of the RR Lyrae Stars in the Very Metal Poor Globular Cluster NGC 5053

The physical characteristics of the 10 RR Lyrae stars in the very metal-poor globular cluster NGC 5053 are derived from photometry of ∼1000 B and V CCD frames acquired from 1994 to 2002 with the Dominion Astrophysical Observatory 1.8 m Plaskett Telescope. Revised pulsation periods and light curves, mean magnitudes, colors, amplitudes, and Fourier parameters are presented. Periods accurate to ≲10-5 days are now known for all 10 RR Lyrae stars. Using times of maximum light dating back to Baade's original 1923–1927 observations, period change rates, dP/dt, accurate to ≲0.07 days Myr-1, have been derived for the 10 stars. Seven stars have increasing periods, and three have decreasing periods, with the estimated period change rates for V1, V2, V9, and V10 being very close to zero. The mean dP/dt is equal to 0.04 ± 0.04 days Myr-1 and is consistent with Lee's evolutionary model predictions for a cluster with horizontal-branch type ∼0.5. Mean B - V colors range from 0.20 to 0.40 and are more consistent with near-zero reddening than alternative higher estimates. A reddening EB-V = 0.018 ± 0.003 is derived from the 1998 SFD maps. Mean effective temperatures vary from 6040 K (V10) to 7290 K (V6), with 2.6 ≤ log g ≤ 3.1. Visual and bolometric absolute magnitudes, bolometric corrections, and luminosities are derived using Fourier methods and using intensity- and magnitude-averaged mean magnitudes. Mean locations of the stars in the H-R diagram tend to progress from hotter, lower L stars to cooler, higher L stars and are consistent with theoretical blue and red edges of the instability strip. Masses estimated assuming zero reddening and Dorman's oxygen-enhanced models range from 0.68 ⊙ (V6) to 0.78 ⊙ (V10) for the 10 stars. The mean metal abundance for NGC 5053 derived using the Jurcsik-Kovács method lies significantly higher than the range -2.3 to -2.6 dex determined using other, more well established methods. This finding supports recent suggestions that metallicities derived from Fourier-based [Fe/H] calibrations need to be revised downward by at least 0.3 dex for RR Lyrae stars with very low metal abundances.

Imaging spectroscopy for early detection of nitrogen deficiency in grass swards

The potential of an experimental imaging spectroscopy system with high spatial (0.16–0.28 mm 2) and spectral resolution (5–13 nm) was explored for early detection of nitrogen (N) stress. From June through October 2000, a greenhouse experiment was conducted with 15 Lolium perenne L. mini-swards and 5 N treatments. Images were recorded twice a week. With the experimental system, spectra of grass leaves in the canopy can be obtained. Treatment effects on ground cover (GC) and changes in leaf spectral characteristics were studied separately. Leaf pixels with similar reflection intensity were grouped in intensity classes (IC). An index of reflection intensity (IRI) indicates the percentages of strongly reflecting grass pixels. Blue edge, green edge and red edge positions were calculated for each IC. Both GC and IRI increased until harvest, with largest increases for liberal N treatments. The width of the chlorophyll-dominated absorption band around 680 nm (CAW) increased up to a maximum of 133 nm for both liberal and limited N in the first two weeks after harvesting. CAW decreased for limited N in the second half of the growth period in contrast to liberal N. At harvest CAW explained 95% of the variation in relative dry matter (DM) yield between treatments. Principal component analyses showed an intertwined response of the principal components to both DM yield and N content. Edge positions changed strongly with IC. Possible effects of sensor characteristics, canopy geometry, leaf angle and changes in leaf characteristics with canopy position on the observed relation between IC and edge position are discussed.

Testing the Binary Black Hole Paradigm through the Fe K Line Profile: Application to 3C 273

We propose the study of long-term variations in the Fe Kα line profile as a discriminator for binary black hole (BH) systems. The existence of a binary BH in the center of an active galaxy will produce a particular signature in the evolution of the line profile, as a result of disk precession. This signature is a periodic variation of the position of the blue edge of the profile, accompanied by periodic change of its intensity. We show that detection of the former is clearly within the observational capabilities of planned X-ray missions. Detecting a periodic variation of line profiles would provide the first direct evidence for precessing disks in active galactic nuclei, as opposed to the existing evidence supporting only the precession of jets. We apply these ideas to 3C 273.

The Evolutionary Status of M3 RR Lyrae Variable Stars: Breakdown of the Canonical Framework?

In order to test the prevailing paradigm of horizontal-branch (HB) stellar evolution, we use the large databases of measured RR Lyrae parameters for the globular cluster M3 (NGC 5272) recently provided by Bakos et al. and Corwin & Carney. We compare the observed distribution of fundamentalized periods against the predictions of synthetic HBs. The observed distribution shows a sharp peak at Pf ≈ 0.55 days, which is primarily due to the RRab variables, whereas the model predictions instead indicate that the distribution should be more uniform in Pf, with a buildup of variables with shorter periods (Pf < 0.5 days). Detailed statistical tests show, for the first time, that the observed and predicted distributions are incompatible with one another at a high significance level. This indicates either that canonical HB models are inappropriate, or that M3 is a pathological case that cannot be considered representative of the Oosterhoff type I (OoI) class. In this sense, we show that the OoI cluster with the next largest number of RR Lyrae variables, M5 (NGC 5904), presents a similar, although less dramatic, challenge to the models. We show that the sharp peak in the M3 period distribution receives a significant contribution from the Blazhko variables in the cluster. We also show that M15 (NGC 7078) and M68 (NGC 4590) show similar peaks in their Pf distributions, which in spite of being located at a Pf value similar to that of M3, can, however, be primarily ascribed to the RRc variables. Again similar to M3, a demise of RRc variables toward the blue edge of the instability strip is also identified in these two globulars. This is again in sharp contrast to the evolutionary scenario, which also foresees a strong buildup of RRc variables with short periods in OoII globulars. We speculate that in OoI systems RRab variables may somehow get close to the transition line between RRab and RRc pulsators as they evolve to the blue in the H-R diagram, whereas in OoII systems it is the RRc variables that may get similarly trapped instead, as they evolve to the red, before changing their pulsation mode to RRab. Such a scenario is supported by the available CMDs and Bailey diagrams for M3, M15, and M68.

Electron and Hole Intraband Spectroscopy of GaSe Nanoparticles

The electron and hole intraband spectroscopy in GaSe nanoparticles having diameters ranging from 4 to 9 nm is studied by femtosecond transient absorption polarization methods. The results indicate that the transient absorption spectrum in the 500−700 nm region has a size-independent peak at about 600 nm. Polarization results indicate that the absorption anisotropy is small or negative on the blue edge of the spectrum and increases with increasing wavelength. The anisotropy reaches a maximum in the 600 nm region and remains approximately constant out to 700 nm. Smaller particles exhibit smaller (or more negative) anisotropies and a larger wavelength dependence than larger particles. These results are interpreted in terms of a simple effective mass model. Due to the approximately cylindrical symmetry of these two-dimensional particles, the electron and hole states are described by particle-in-a-cylinder wave functions and the optical transitions may be calculated from these wave functions. These calculation...

A Theoretical γ Doradus Instability Strip

In this paper, we present the first theoretical γ Doradus instability strip. We find that our model instability strip agrees very well with the previously established, observationally based, instability strip of Handler & Shobbrook. We stress, as do Guzik et al., that the convection zone depth plays the major role in the determination of our instability strip. Once this depth becomes too deep or too shallow, the convection zone no longer allows for pulsational instability. Our theoretical γ Dor instability strip is bounded by ~6850 and 7360 K at the red and blue edge, respectively, on the zero-age main sequence and by ~6560 and 7000 K at the red and blue edge, respectively, approximately 2 mag more luminous. This theoretical strip, transformed to the observer's color-magnitude diagram, overlays the region where most of the 30 bona fide γ Dor stars are found.

A Comparative Femtosecond Coherence Study of the Unligated Monomeric Hemeproteins Myoglobin and Leghemoglobin

Impulsive optical excitation has been performed on wild type, unligated leghemoglobin for the first time to compare the induced vibrational coherence with that observed in myoglobin. Both proteins were excited at the Soret maxima and probed at red and blue edges of the Soret band. The resulting kinetic traces were modulated by low-frequency vibrations. Leghemoglobin shows a decrease in vibrational amplitude compared with myoglobin. The possible cause for the amplitude differences is discussed in terms of contributions from both ground- and excited-state vibrational coherences and ground-state heterogeneity.

A Confirmation of the Optical Spectroscopy Approach: Discovery of Two More Pulsating DA (ZZ Ceti) White Dwarfs

We first review and rebut the arguments that have been put forward recently against the use of optical spectroscopy in the determinations of the atmospheric parameters of ZZ Ceti and neighboring stars in the log g-Teff diagram. We reiterate instead the conclusion of Bergeron et al. that optical spectroscopy alone, when properly handled and modeled, leads to very accurate and reliable estimates of the surface gravities and effective temperatures of ZZ Ceti pulsators. The optical spectroscopy approach has had a yield of 100% so far in predicting the variability of candidate ZZ Ceti stars, and we present evidence here of its successful application to two more objects. We hence report the detection of multiperiodic luminosity variations in the light curves of two DA white dwarfs, MCT 0145-2211 and HE 0532-5605, selected on the basis of an analysis of their optical spectra. This brings the number of known ZZ Ceti stars to a total of 34. Our study reveals that MCT 0145-2211 has Teff = 11,550 K and log g = 8.14, while HE 0532-5605 has Teff = 11,560 K and log g = 8.49, which places them both inside the empirical instability strip uncovered by Bergeron et al. We find that the amplitudes, periods, and degree of complexity of the light curves are consistent with the positions of the stars rather near the red edge. Using the same homogeneous approach, we have, so far, analyzed high-quality optical spectra for some 103 nonvariable DA white dwarfs and all of the 34 known ZZ Ceti stars. The picture of the empirical instability strip that emerges is that of a pure strip, in which no nonvariable stars are found. It has a trapezoidal shape in the log g-Teff plane, with the blue edge showing a stronger dependence on the surface gravity than the red edge does.

Preparing the COROT space mission: Incidence and characterisation of pulsation in the lower instability strip

By pursuing the goal to find new variables in the COROT field-of-view we characterised a sample of stars located in the lower part of the instability strip. Our sample is composed of stars belonging to the disk population in the solar neigh- bourhood. We found that 23% of the stars display multiperiodic light variability up to a few mmag in amplitude, i.e., easily detectable on a single night of photometry. uvbyβ photometry fixed most of the variables in the middle of the instability strip and high-resolution spectroscopy established that they have v sini > 100 km s −1 . An analysis of the Rodr´ oguez & Breger (2001) sample (δ Sct stars in the whole Galaxy) shows slightly different features, i.e., most δ Sct stars have a 0.05-mag redder (b − y)0 index and lower v sini values. Additional investigation in the open cluster NGC 6633 confirms the same incidence of variabil- ity, i.e., around 20%. The wide variety of pulsational behaviours of δ Sct stars (including unusual objects such as a variable beyond the blue edge or a rapidly rotating high-amplitude pulsator) makes them very powerful asteroseismic tools to be used by COROT. Being quite common among bright stars, δ Sct stars are suitable targets for optical observations from space.

Yield and enrichment studies of C-13 isotope by multi-photon dissociation of Freon-22 at low temperatures

Multi-photon dissociation of Freon-22 (CF2HC1) at low temperatures has been carried out to separate the C-13 isotope using a TEA CO2 laser. Yield and enrichment of C-13 isotope in the product C2F4 are studied at 9P(22) laser line as a function of temperature (−50°C to 30°C). It is observed that at a given fluence when the temperature is lowered the yield decreases and the enrichment factor of C-13 increases.Room temperature irradiation of CF2HC1 towards the blue edge of C-13 absorption (i.e. at 9P(20) laser line) gives low yield of the product (C2F4) at a fluence, which produces the desired enrichment factor of 100. An increase in fluence gives very high yield of C2F4 but the enrichment factor is very low. Irradiating CF2HC1 at a temperature of −10°C enhances the enrichment factor to 100 and the yield obtained is comparable to that towards the red edge of C-13 absorption (i.e. at 9P(26) laser line).At a given enrichment factor higher enrichment efficiency is achieved when CF2HC1 is irradiated at lower temperature.

Vibrational relaxation and spectral evolution following ultrafast OH stretch excitation of water

Ultrafast anti-Stokes Raman measurements of OH stretching excitations (3000–3600 cm −1) in water show an ∼0.4 ps spectral evolution from the red to the blue that is similar to what is seen in the Raman spectrum of water heated to 90 °C. The lifetime of OH stretching excitations T 1=0.7 ps. A small portion of the spectrum on the blue edge of the band decays more slowly with T 1=1.1 ps. A previous measurement of T 1≈0.3 ps for water [J. Chem. Phys. 117 (2002) 1708] is reinterpreted shown to consistent with the present work.

Transit Target Selection Using Reduced Proper Motions

In searches for planetary transits in the field, well over half of the survey stars are typically giants or other stars that are too large to permit straightforward detection of planets. For all-sky searches of bright V<~11 stars, the fraction is ~90%. We show that the great majority of these contaminants can be removed from the sample by analyzing their reduced proper motions (RPMs): giants have much lower RPMs than dwarfs of the same color. We use Hipparcos data to design a RPM selection function that eliminates most evolved stars, while rejecting only 9% of viable transit targets. Our method can be applied using existing or soon-to-be-released all-sky data to stars V<12.5 in the northern hemisphere and V<12 in the south. The method degrades at fainter magnitudes, but does so gracefully. For example, at V=14 it can still be used to eliminate giants redward of V-I~0.95, that is, the blue edge of the red giant clump.

Low-Intensity Pump-Probe Measurements on the B800 Band of Rhodospirillum molischianum

We have measured low-intensity, polarized one-color pump-probe traces in the B800 band of the light-harvesting complex LH2 of Rhodospirillum molischianum at 77 K. The excitation/detection wavelength was tuned through the B800 band. A single-wavelength and a global target analysis of the data were performed with a model that accounts for excitation energy transfer among the B800 molecules and from B800 to B850. By including the anisotropy of the signals into the fitting procedure, both transfer processes could be separated. It was estimated in the global target analysis that the intra-B800 energy transfer, i.e., the hopping of the excitation from one B800 to another B800 molecule, takes ∼0.5 ps at 77 K. This transfer time increases with the excitation/detection wavelength from 0.3 ps on the blue side of the B800 band to ∼0.8 ps on the red side. The residual B800 anisotropy shows a wavelength dependence as expected for energy transfer within an inhomogeneously broadened cluster of weakly coupled pigments. In the global target analysis, the transfer time from B800 to B850 was determined to be ∼1.7 ps at 77 K. In the single-wavelength analysis, a speeding-up of the B800 → B850 energy transfer rate toward the blue edge of the B800 band was found. This nicely correlates with the proposed position of the suggested high-exciton component of the B850 band acting as an additional decay channel for B800 excitations.

Energy Equilibration among the Chlorophylls in the Electron-Transfer System of Photosystem I Reaction Center from Spinach

Excitation-wavelength dependence of the transient absorbance changes of photosystem I reaction center particles with a reduced number of antenna chlorophylls (16 chlorophylls/primary electron donor chlorophyll (P700)) hasbeen studied in an effort to understand the energy equilibration among the chlorophylls in the electron-transfer system. The photobleaching and stimulated-emission signals in the Q y band region of the chlorophylls upon the preferential excitation of chlorophyll spectral forms at the blue edge (662 nm) and red edge (697 nm) of the Q y band are analyzed. In the case of the red-edge excitation, spectral equilibration proceeds with a time constant of 0.34 (′0.07) ps, which is attributable to the energy equilibration between P700 and neighboring chlorophylls absorbing around 686 nm in the electron-transfer system. This equilibration seems to precede the fastest phase of the primary charge separation (apparent time constant of 0.8 ps) reported previously (Kumazaki et al. J. Phys. Chem. B 2001, 105, 1093). A slow decay of the excited states because of the slow phase of the primary charge separation proceeds with a time constant of 7.2 (′0.6) ps. In the case of the blue-edge excitation, vibrational relaxation and downhill energy transfer proceed with a time constant of 0.38 (′0.08) ps, which are followed by a slow downhill energy transfer from residual antenna chlorophylls to the electron-transfer system. Even with the slow energy transfer from the residual antenna chlorophylls to the electron-transfer system, the overall primary charge separation is completed with a time constant of 10 (′0.7) ps. These interpretations are in part supported by control experiments on chlorophyll a in ethanol under equivalent optical conditions. Implications of these results for understanding the primary processes in more intact photosystem I are discussed.

Fluorescence characteristics of protonated form of 6-hydroxyquinoline in Nafion® film

Fluorescence characteristics of 6-hydroxyquinoline (6-HQ) have been studied at room temperature in Nafion® film by steady state and nano-second time-resolved fluorescence spectroscopy. The fluorescence spectrum exhibits single emission band corresponding to the protonated form of 6-HQ in this matrix. However, the decay fits with two or three exponential functions depending on the emission wavelength monitored. At blue edge of the emission, the decay fits to three-exponential function, whereas at longer wavelengths, the decay fits to bi-exponential function. Two tentative mechanisms have been proposed to explain the experimental data, viz. a closely lying charge transfer state (CT) or an excited state proton transfer (ESPT) process. The photophysical parameters appear to be sensitive to the change in microstructure due to swelling of the membrane by the solvents.

Relaxation dynamics in photoexcited GaSe nanoparticles

The photophysics and relaxation dynamics of GaSe nanoparticles have been studied in room temperature solutions, using static and time-resolved emission spectroscopy. Following 400 nm excitation, these particles exhibit a static emission maximum at 480 nm. This emission is polarized and the anisotropy is largest on the blue edge of the emission spectrum. Both the total (unpolarized) emission kinetics and the emission anisotropy kinetics are obtained. Static emission spectra along with wavelength-dependent kinetic results permit the reconstruction of time-dependent spectra. The kinetic results reported here show an 80 ps decay component in the total emission, but not in the anisotropy decay kinetics. There is an ∼270 cm−1 shift in the emission maximum during this decay. This transient is assigned to direct to indirect band edge relaxation. This is followed by a 400 ps decay in both the total emission and the anisotropy kinetics. A very small shift (∼170 cm−1) in the emission maximum occurs during this decay. This transient is assigned to trapping of holes in shallow acceptor levels. Finally, there is a 2.4 ns decay of both the total emission and the emission anisotropy. As this decay occurs, the 480 nm emission is replaced by a much weaker, broad and unpolarized 520 nm emission. This decay is assigned to relaxation of holes into deep traps. The kinetic results are interpreted in terms of a model which is based on the relative energetics of the direct and indirect band edges and the hole trap states in bulk GaSe.

High‐Amplitude δ Scuti and SX Phoenicis Stars: The Effects of Chemical Composition on Pulsations and the Period‐Luminosity Relation

We present a theoretical study of the radially pulsating δ Scuti and SX Phoenicis variables, concentrating on the blue straggler SX Phoenicis variables found in globular clusters. We have evolved a grid of stellar models with the metal abundance of the globular cluster M55, including models with alpha-enhanced metal abundances, and tested these models for radial pulsations observed in the high-amplitude δ Scuti and SX Phoenicis stars. Our grid includes models with globally enriched helium content to simulate the effects of stellar collisions and global mixing possible in blue stragglers. We find that global enrichment of helium strongly affects the temperature and luminosity of a given star, but the location of the instability strip blue edge and the slope of the period-luminosity (PL) relation are unchanged. This suggests that the PL relation is not affected by blue straggler formation if blue stragglers are fully mixed stellar mergers. Our blue edges and PL relations are in agreement with other theoretical determinations and also with the observational PL relation of M55, but they are not in agreement with the PL relation previously derived for high-amplitude δ Scuti stars in the field. Analysis of the double-mode variable, V41, suggests either that the star may not be pulsating in the first and second overtones as claimed or that normal stellar models may not be accurate models of blue straggler stars.

ITAL]Hubble Space Telescope[/ITAL] Spectra of GW Librae: A Hot Pulsating White Dwarf in a Cataclysmic Variable

We have obtained Hubble Space Telescope UV spectra of the white dwarf in GW Lib, the only known nonradially pulsating white dwarf in a cataclysmic variable and the first known DAZQ variable. The UV light curve reveals large-amplitude (10%) pulsations in the UV with the same periods (646, 376, and 237 s) as those seen at optical wavelengths, but the mean spectrum fits with an average white dwarf temperature (14,700 K for a 0.6 M☉ white dwarf) that is too hot to be in the normal instability strip for ZZ Ceti stars. A better fit is achieved with a dual-temperature model (with 63% of the white dwarf surface at a temperature of 13,300 K and 37% at 17,100 K) and a higher mass (0.8 M☉) white dwarf with 0.1 solar metal abundance. Since the blue edge of the instability strip moves to higher temperature with increasing mass, the lower temperature of this model is within the instability strip. However, the presence of accretion likely causes abundance and atmospheric temperature differences in GW Lib compared to all known single white dwarf pulsators, and the current models that have been capable of explaining ZZ Ceti stars may not apply.

MWC 560: An SS 433 type object with a white dwarf

Spectral variations of the peculiar symbiotic object MWC 560 (V694 Mon) have been monitored for 10 years since 1991. The radial velocity of the blue edge of the broad absorption components of H I lines is measured to evaluate the outflow velocity of the jet. The variation of the outflow velocity suggests that there are active and stable stages in this system. The outflow velocity in the stable stage seems to vary according to the long-term light variation with a period of 1930 days. This variation of the outflow velocity could be explained with a model of gas outflow from an accretion disk precessing with a period of 1930 days. If the observed amplitude of the light variation, $\Delta m_{\rm pg} \cong 0.72$ mag, was purely due to the precession, the maximum inclination of the disk to the line of sight should be about 59 degrees. Since the outflow is observed always as absorption, the open angle of the outflow should be larger than 59 degrees. However, the amplitude of the light variation due to the precession of the disk seems to be still rather uncertain. In the active stage the outflow velocity was much higher (in the negative sense) than in the stable stage, and rapid variations of the outflow velocity were observed. During the outburst in 1990, this object was in the active stage, while no significant brightening was observed in the active stages in 1993 and 1999 at least in the V band. The durations of the active stages were several months.