Modelling the Galactic distribution of free electrons

In this paper we test 8 models of the free electron distribution in the Milky Way that have been published previously, and we introduce 4 additional models that explore the parameter space of possible models further. These new models consist of a simple exponential thick disk model, and updated versions of the models by Taylor & Cordes and Cordes & Lazio with more extended thick disks. The final model we introduce uses the observed H-alpha intensity as a proxy for the total electron column density, also known as the dispersion measure (DM). We use the latest available data sets of pulsars with accurate distances (through parallax measurements or association with globular clusters) to optimise the parameters in these models. In the process of fitting a new scale height for the thick disk in the model by Cordes & Lazio we discuss why this thick disk cannot be replaced by the thick disk that Gaensler et al. advocated in a recent paper. In the second part of our paper we test how well the different models can predict the DMs of these pulsars at known distances. Almost all models perform well, in that they predict DMs within a factor of 1.5-2 of the observed DMs for about 75% of the lines of sight. This is somewhat surprising since the models we tested range from very simple models that only contain a single exponential thick disk to very complex models like the model by Cordes & Lazio. We show that the model by Taylor & Cordes that we updated with a more extended thick disk consistently performs better than the other models we tested. Finally, we analyse which sightlines have DMs that prove difficult to predict by most models, which indicates the presence of local features in the ISM between us and the pulsar. (abridged)Comment: 16 pages, 10 figures, 5 tables. Accepted for publication in the Monthly Notices of the RAS by the Royal Astronomical Society and Blackwell Publishin

An approach towards rapid optical measurements of antioxidant activity in blueberry cultivars

Blueberries are well known for their high antioxidant levels. Compared to bilberries (V. myrtillus) with higher antioxidant activity and more intensive blue colour throughout the whole berry, highbush blueberries have the blue pigments concentrated in the skin. Highbush blueberry skin is found to contain a very high content of phenolic compounds. To measure the total antioxidant activity in blueberries, several methods, mostly destructive, including the FRAP assay, have been used. This work is an initial approach towards a simple and rapid method, combining optical and antioxidant activity measurements. Highbush blueberry (V. corymbosum) cultivars ‘Bluecrop’, ‘Hardyblue’, ‘Patriot’, and lowbush cultivars ‘Putte’ (a hybrid originated from V. angustifolium) and ‘Aron’ (V. corymbosum x V. uliginosum) were grown at the Norwegian University of Life Sciences (59º 40’N). Berries were harvested at commercial blue-ripe stage of maturity. Fresh berries were cut horizontally and placed on a scanner in order to examine berry size and skin thickness. Berries were weighed, and analysed for antioxidant activity using the FRAP (Ferric Reducing Ability of Plasma) assay. The FRAP assay is a non-specific method based on absorption changes following a reduction of a ferric- to a ferrous-complex in the presence of antioxidants.Own previous results have shown that antioxidant activity and berry weight varied between cultivars (REMBERG et al., 2003). Small berries had higher antioxidant activity compared to larger berries. In this follow-up project, skin thickness and berry diameter were measured by using an image- processing program. Berry and skin cross-section areas were correlated with the antioxidant activity

Determination of the Far-Infrared Cosmic Background Using COBE/DIRBE and WHAM Data

Determination of the cosmic infrared background (CIB) at far infrared wavelengths using COBE/DIRBE data is limited by the accuracy to which foreground interplanetary and Galactic dust emission can be modeled and subtracted. Previous determinations of the far infrared CIB (e.g., Hauser et al. 1998) were based on the detection of residual isotropic emission in skymaps from which the emission from interplanetary dust and the neutral interstellar medium were removed. In this paper we use the Wisconsin H-alpha Mapper (WHAM) Northern Sky Survey as a tracer of the ionized medium to examine the effect of this foreground component on determination of the CIB. We decompose the DIRBE far infrared data for five high Galactic latitude regions into H I and H-alpha correlated components and a residual component. We find the H-alpha correlated component to be consistent with zero for each region, and we find that addition of an H-alpha correlated component in modeling the foreground emission has negligible effect on derived CIB results. Our CIB detections and 2 sigma upper limits are essentially the same as those derived by Hauser et al. and are given by nu I_nu (nW m-2 sr-1) < 75, < 32, 25 +- 8, and 13 +- 3 at 60, 100, 140, and 240 microns, respectively. Our residuals have not been subjected to a detailed anisotropy test, so our CIB results do not supersede those of Hauser et al. We derive upper limits on the 100 micron emissivity of the ionized medium that are typically about 40% of the 100 micron emissivity of the neutral atomic medium. This low value may be caused in part by a lower dust-to-gas mass ratio in the ionized medium than in the neutral medium, and in part by a shortcoming of using H-alpha intensity as a tracer of far infrared emission.Comment: 38 pages, 8 figures. Accepted for publication in Ap

Multiwavelength observations of the M15 intermediate velocity cloud

We present Westerbork Synthesis Radio Telescope HI images, Lovell Telescope multibeam HI wide-field mapping, Wisconsin H-alpha Mapper facility images, William Herschel Telescope longslit echelle CaII observations, and IRAS ISSA 60 and 100 micron coadded images towards the intermediate velocity cloud located in the general direction of the M15 globular cluster. When combined with previously-published Arecibo data, the HI gas in the IVC is found to be clumpy, with peak HI column density of 1.5x10^(20) cm^(-2), inferred volume density (assuming spherical symmetry) of 24 cm^(-3)/(D kpc), and maximum brightness temperature at a resolution of 81x14 arcsec of 14 K. The HI gas in the cloud is warm, with a minimum FWHM value of 5 km/s, corresponding to a kinetic temperature, in the absence of turbulence, of 540 K. There are indications in the HI data of 2-component velocity structure in the IVC, indicative of cloudlets. This velocity structure is also tentatively seen in the CaK spectra, although the SNR is low. The main IVC condensation is detected by WHAM in H-alpha with intensities uncorrected for Galactic absorption of upto 1.3 Rayleigh, indicating that the cloud is partially ionised. The FWHM of the ionised component, at a resolution of 1 degree, exceeds 30 km/s. The spatial and velocity coincidence of the H-alpha and HI peaks in emission is qualitatively good. Finally, the 100 and 60 micron IRAS images show spatial coincidence over a 0.7 degree field, with low and intermediate-velocity gas, respectively, indicating that the IVC may contain dust.Comment: MNRAS, in pres

Measurement of a Magnetic Field in a Leading Arm High Velocity Cloud

Using a recent catalogue of extragalactic Faraday rotation derived from the NRAO VLA Sky Survey we have found an agreement between Faraday rotation structure and the HI emission structure of a High Velocity Cloud (HVC) associated with the Leading Arm of the Magellanic System. We suggest that this morphological agreement is indicative of Faraday rotation through the HVC. Under this assumption we have used 48 rotation measures through the HVC, together with estimates of the electron column density from H-\alpha\ measurements and QSO absorption lines to estimate a strength for the line-of-sight component of the coherent magnetic field in the HVC of > 6 {\rm \mu G}$. A coherent magnetic field of this strength is more than sufficient to dynamically stabilize the cloud against ram pressure stripping by the Milky Way halo and may also provide thermal insulation for the cold cloud. We estimate an upper limit to the ratio of random to coherent magnetic field of$B_{r}/B_{||} < 0.8$, which suggests that the random field does not dominate over the coherent field as it does in the Magellanic Clouds from which this HVC likely originates.Comment: 17 pages, 3 figure

Constraining Balmer Alpha Fine Structure Excitation Measured in Geocoronal Hydrogen Observations

Cascade contributions to geocoronal Balmer α airglow line profiles are directly proportional to the Balmer β ∕α line ratio and can therefore be determined with near simultaneous Balmer β observations. Due to scattering differences for solar Lyman β and Lyman γ (responsible for the terrestrial Balmer α and Balmer β fluorescence, respectively), there is an expected trend for the cascade emission to become a smaller fraction of the Balmer α intensity at larger shadow altitudes. Near-coincident Balmer α and Balmer β data sets, obtained from the Wisconsin H alpha Mapper Fabry-Perot, are used to determine the cascade contribution to the Balmer α line profile and to show, for the first time, the Balmer β∕α line ratio, as a function of shadow altitude. We show that this result is in agreement with direct cascade determinations from Balmer α line profile fits obtained independently by high-resolution Fabry-Perot at Pine Bluff, WI. We also demonstrate with radiative transport forward modeling that a solar cycle influence on cascade is expected, and that the Balmer β ∕α line ratio poses a tight constraint on retrieved aeronomical parameters (such as hydrogen’s evaporative escape rate and exobase density)

The extragalactic background and its fluctuations in the far-infrared wavelengths

A Cosmic Far-InfraRed Background (CFIRB) has long been predicted that would traces the intial phases of galaxy formation. It has been first detected by Puget et al.(1996) using COBE data and has been later confirmed by several recent studies (Fixsen et al. 1998, Hauser et al. 1998, Lagache et al. 1999). We will present a new determination of the CFIRB that uses for the first time, in addition to COBE data, two independent gas tracers: the HI survey of Leiden/Dwingeloo (hartmann, 1998) and the WHAM H$_{\alpha}$ survey (Reynolds et al 1998). We will see that the CFIRB above 100 micron is now very well constrained. The next step is to see if we can detect its fluctuations. To search for the CFIRB fluctuations, we have used the FIRBACK observations. FIRBACK is a deep cosmological survey conducted at 170 micron with ISOPHOT (Dole et al., 2000). We show that the emission of unresolved extra-galactic sources clearly dominates, at arcminute scales, the background fluctuations in the lowest galactic emission regions. This is the first detection of the CFIRB fluctuations.Comment: To appear in "ISO Surveys of a Dusty Universe", Workshop at Ringberg Castle, November 8 - 12, 199

Geocoronal Hydrogen Observations Spanning Three Solar Minima

The 11-year solar cycle is a dominant source of natural variability in the upper atmosphere, and its effect on atomic hydrogen distributions and emissions must be understood to investigate possible signs of longer-term climatic trends in this region. We present midlatitude geocoronal hydrogen Balmer α observations from solar cycle 23 (1997–2006) and three solar minimum periods, 1985, 1997, and 2006. The 1997 through 2006 observations were taken with the Wisconsin H-αMapper Fabry-Perot (WHAM), a ground-based CCD-annular summing instrument that began observations at the Kitt Peak Observatory in Arizona in 1997. The 1985 observations were made with a similarly designed “pre-WHAM” Fabry-Perot Interferometer utilizing photomultiplier detection and located in Wisconsin. WHAM has consistently observed higher column emission intensities during solar maximum periods than during solar minimum conditions, with the ratio dependent upon the viewing geometry. The observations from three solar minimum periods agree to within 18% uncertainties over most of the shadow altitude range. An analysis of recent Fabry-Perot observations of upper atmospheric hydrogen during solar cycle 23 and during three solar minima (1985, 1997, 2006) established a reference data set of highly precise, consistently calibrated, thermospheric plus exospheric hydrogen column emission observations from northern midlatitudes that can be used to compare with future observations

Geocoronal H-A [Alpha] Intensity Measurements Using the Wisconsin H-A [Alpha] Mapper Fabry-Perot Facility

The Wisconsin H-a [alpha] Mapper (WHAM), a remotely operable, semi-automated Fabry-Perot located at Kitt Peak Observatory, has been making an all-sky survey of interstellar hydrogen Balmer a [alpha] (H-a [alpha]) emissions since 1997. Using the annular summing spectroscopy technique, WHAM has acquired ~[approx.] 37,000 spectra to date, spanning almost 100 nights of observations. Since all of the galactic emission spectral data contain the terrestrial H-a [alpha] (6562.7 Å) emission line, these measurements constitute a rich source of geocoronal data for investigating natural variability in the upper atmosphere. The WHAM observations also serve as a benchmark for comparison with future data. Analysis of the first year of WHAM data shows only small day-to-day variations after shadow altitude variations are taken into account. For example, at shadow altitudes of 2000 and 3000 km, the RMS scatter is within approximately +/- 20%; this variability is expected to be reduced with accurate accounting of the smaller-scale effects of observational slant path, zenith angle, and azimuth on the H-a [alpha] intensity. This result is consistent with past midlatitude Wisconsin data sets but different from observations made by other observers and instruments at the low-latitude Arecibo site. The multiple viewing geometries of the observations provide stringent modeling constraints, useful in testing current modeling capabilities. Modeling of the WHAM data with a global nonisothermal resonance radiation transport code (lyao_rt) indicates that the signal-to-noise of the data is sufficient to determine relative variations in upper atmospheric atomic hydrogen column densities to better than 5%. This paper describes the WHAM aeronomy program and its observational scheme, analysis procedures, and results from data taken in 1997. Case study comparisons are made with past data sets and with predictions from the lyao_rt resonant radiation transport modeling code of Bishop [1999]