Accurate Observational Data Research Articles

A revised rotation curve of the Milky Way with maser astrometry

We reconstruct the rotation curve of the Milky Way using the new trigonometric parallax and proper motion data for masers in 43 high-mass star-forming regions obtained by VLBI, as well as the existing data from the literature, based on a new set of galactic constants (R0, Θ0) = (8.4 kpc, 254 km s−1) measured by Reid et al. The revised rotation curve of the Milky Way is almost flat or slightly rising in the region from about 15 to 6 kpc. The rotation velocities within 5 kpc of the Galactic center, as determined by VLBI, differ from those obtained by measurement of the HI- and CO-line tangent velocities. We fitted the revised rotation curve arising from three mass components: the bulge, disk and dark matter halo. The total mass of the Milky Way is found to be 2.3 × 1011 M⊙ (20 kpc). This is about 10% larger than that from Sofue et al, and is comparable with the mass of M31, 3.4 × 1011 M⊙ (35 kpc), given by Carignan et al. The limited accurate observational data, especially the VLBI data, do not permit a fully satisfactory fit to the rotation curve. The extensive parallax and proper motion data that will be produced by the Bar and Spiral Structure Legacy Survey project in the next few years should lead to considerable progress in understanding the rotation curve and dark matter halo of the Milky Way.

Assessing the accuracy and applied use of satellite-derived precipitation estimates over Nepal

Accurate observational precipitation data supplied at a fine spatial resolution is vital for informing sustainable water resources management in Nepal. Livelihoods in Nepal are acutely impacted by precipitation. The amount of monsoon precipitation determines water available for drinking, hydropower and irrigation. Extreme precipitation events often result in landslides, flash flooding and crop damages. Freely available satellite-derived precipitation data products have the potential to substantially inform water policy. Such products could advocate sustainable use of water resources and enhance the adaptive capacity of rural populations in Nepal to future precipitation changes. In this research, statistical measures were used to assess the accuracy of Tropical Rainfall Measuring Mission satellite-derived precipitation estimates (TRMM 3B42) relative to ground-based precipitation data (APHRODITE), seasonally from 2001 to 2007. In all seasons the majority of satellite precipitation estimates were significantly correlated with ground-based precipitation. However, satellite precipitation estimates consistently overestimated the amount of precipitation, with error greatest in the monsoon season. The satellite precipitation product inaccurately detected extreme precipitation events, 'rainy days' and precipitation intensity in the monsoon season. Results suggest that precipitation estimates derived from this satellite product have limited use in agricultural planning, water resource management and developing mitigation measures to the impacts of extreme events in Nepal. Currently, ground-based precipitation measurements still provide the most accurate information for use in water resources management. Maintaining and developing precipitation gauge networks in Nepal, particularly in regions of high relief, is extremely important for increasing the accuracy of both ground-based and satellite-derived precipitation products.

Detection of gravitational waves through observations of a group of pulsars

We suggest a new approach to the detection of gravitational waves using observations of a group of millisecond pulsars. In contrast to the usual method, based on increasing the accuracy of the arrival times of pulses by excluding possible distorting factors, our method supposes that the additive phase noise that is inevitably present even in the most accurate observational data has various spectral components, which have characteristic amplitudes and begin to appear on different time scales. We use the “Caterpillar” (Singular Spectral Analysis, SSA) method to decompose the signal into its components. Our initial data are the residuals of the pulse arrival times for six millisecond pulsars. We constructed the angular correlation function for components of the decomposition of a given number, whose theoretical form for the case of an isotropic and homogeneous gravitational-wave background is known. The individual decomposition components show a statistically significant agreement with the theoretical expectations (correlation coefficient ρ = 0.92 ± 0.10).

The dynamics of photospheric line-of-sight velocities in emerging active regions

We suggest a new approach to the detection of gravitational waves using observations of a group of millisecond pulsars. In contrast to the usual method, based on increasing the accuracy of the arrival times of pulses by excluding possible distorting factors, our method supposes that the additive phase noise that is inevitably present even in the most accurate observational data has various spectral components, which have characteristic amplitudes and begin to appear on different time scales. We use the "Caterpillar" (Singular Spectral Analysis, SSA) method to decompose the signal into its components. Our initial data are the residuals of the pulse arrival times for six millisecond pulsars. We constructed the angular correlation function for components of the decomposition of a given number, whose theoretical form for the case of an isotropic and homogeneous gravitational-wave background is known. The individual decomposition components show a statistically significant agreement with the theoretical expectations (correlation coefficient $\rho=0.92\pm 0.10$).

Observational tests for oscillating expansion rate of the Universe

We investigate the observational constraints on the oscillating scalar field model using data from type Ia supernovae, cosmic microwave background anisotropies, and baryon acoustic oscillations. According to a Fourier analysis, the galaxy number count $N$ from redshift $z$ data indicates that galaxies have preferred periodic redshift spacings. We fix the mass of the scalar field as ${m}_{\ensuremath{\phi}}=3.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}31}h\text{ }\text{ }\mathrm{eV}$ such that the scalar field model can account for the redshift spacings, and we constrain the other basic parameters by comparing the model with accurate observational data. We obtain the following constraints: ${\ensuremath{\Omega}}_{m,0}=0.28\ifmmode\pm\else\textpm\fi{}0.03$ (95% C.L.), ${\ensuremath{\Omega}}_{\ensuremath{\phi},0}<0.035$ (95% C.L.), and $\ensuremath{\xi}>\ensuremath{-}158$ (95% C.L.) (in the range $\ensuremath{\xi}\ensuremath{\le}0$). The best fit values of the energy density parameter of the scalar field and the coupling constant are ${\ensuremath{\Omega}}_{\ensuremath{\phi},0}=0.01$ and $\ensuremath{\xi}=\ensuremath{-}25$, respectively. The value of ${\ensuremath{\Omega}}_{\ensuremath{\phi},0}$ is close to but not equal to 0. Hence, in the scalar field model, the amplitude of the galaxy number count cannot be large. However, because the best fit values of ${\ensuremath{\Omega}}_{\ensuremath{\phi},0}$ and $\ensuremath{\xi}$ are not 0, the scalar field model has the possibility of accounting for the periodic structure in the $N\mathrm{\text{\ensuremath{-}}}z$ relation of galaxies. The variation of the effective gravitational constant in the scalar field model is not inconsistent with the bound from observation.

Multifluid models for cyclic cosmology

Inspired by the Landau two-fluid model of superfluidity, we consider a similar multifluid description for cosmology where two normal fluids occur for matter and radiation, respectively. For cyclic cosmology, two dark energy superfluid components turn out to be insufficient but three superfluids can lead to a sensible five-fluid model which in a certain limit becomes indistinguishable from a brane-world cyclic model proposed earlier. Distinguishing more general five-fluid models from brane-world models for cyclic cosmology could be feasible with more accurate observational data.

The surface radiation budget over North America: gridded data assessment and evaluation of regional climate models

AbstractWhile surface station observations of downwelling radiation offer accuracy at high temporal resolution, they do not easily allow an evaluation of model surface radiation budgets (SRB) over a wide geographical area. We evaluate three gridded SRB data sets against detailed observations from six surface radiation sites from the US surface radiation (SURFRAD) network. We subsequently use the most accurate surrogate observational data set for evaluation of model‐simulated SRB. The data sets assessed are: ERA40—reanalysis of European Centre for Medium‐Range Weather Forecasts (ECMWF), North American Regional Reanalysis (NARR)—regional reanalysis of National Centres for Environmental Prediction (NCEP) and the surface radiative budget (SRB) from the International Satellite Cloud Climatology Project (ISCCP). Due to varying constraints with respect to temporal coverage of each data set, the evaluation period used in this study is 1996–2001, inclusive.The ERA40 downwelling longwave radiation (DLR) appears the most accurate surrogate observation, while both ERA40 and ISCCP show accurate results when the incoming shortwave radiation (ISR) is considered across the annual cycle. Winter DLR is less accurate in ISCCP with a positive bias and lack of very low (<200 Wm−2) flux values. The NARR SRB shows a large positive bias in the ISR throughout the annual cycle, linked to a significant underestimate of cloud cover.The ERA40 data are subsequently used to evaluate the simulated SRB in three regional climate models across North America. With respect to solar radiation, cloud cover biases are seen to be crucial, while for longwave fluxes both cloud fraction and in‐cloud water content are important to simulate correctly. Inclusion of trace gases beyond H2O, CO2 and O3 appears necessary for an accurate calculation of clear‐sky longwave radiation. Error compensation frequently occurs between the various components contributing to a model total‐sky SRB. This is important to consider when trying to identify the underlying causes of errors in the simulated total SRB. Copyright © 2009 Royal Meteorological Society

ON THE SOLAR NICKEL AND OXYGEN ABUNDANCES

Determinations of the solar oxygen content relying on the neutral forbidden transition at 630 nm depend upon the nickel abundance, due to a Ni I blend. Here we rederive the solar nickel abundance, using the same ab initio 3D hydrodynamic model of the solar photosphere employed in the recent revision of the abundances of C, N, O and other elements. Using 17 weak, unblended lines of Ni I together with the most accurate atomic and observational data available we find log epsilon_Ni = 6.17 +/- 0.02 (statistical) +/- 0.05 (systematic), a downwards shift of 0.06 to 0.08 dex relative to previous 1D-based abundances. We investigate the implications of the new nickel abundance for studies of the solar oxygen abundance based on the [O I] 630 nm line in the quiet Sun. Furthermore, we demonstrate that the oxygen abundance implied by the recent sunspot spectropolarimetric study of Centeno & Socas-Navarro needs to be revised downwards from log epsilon_O = 8.86 +/- 0.07 to 8.71 +/- 0.10. This revision is based on the new nickel abundance, application of the best available gf-value for the 630 nm forbidden oxygen line, and a more transparent treatment of CO formation. Determinations of the solar oxygen content relying on forbidden lines now appear to converge around log epsilon_O = 8.7.

Eclipsing binaries and the mass-luminosity relation

We have compared radii of eclipsing binary components and single stars. We have found a noticeable difference for BOV-GOV components of eclipsing binaries and single stars of the corresponding spectral type. This difference can be confirmed by a re-analysis of results of other published investigations and, in particular, it can explain the disagreement between published scales of bolometric corrections. According to our results, A- and F-type main sequence eclipsing binaries have larger radii and/or higher temperatures than single stars while B-type eclipsing binaries have smaller radii. Possible explanations for these features are proposed. We have concluded that the mass-luminosity relation based on empirical data of eclipsing binary components cannot be used to derive the stellar initial mass function. While our current knowledge of the empirical mass-luminosity relation for masses more than 1.5 m O . is based exclusively on eclipsing binaries data, accurate observational data for a few hundred visual binaries of intermediate and high masses should be collected. Then the initial mass function for this mass range should be revised.

A new inversion scheme for the RPV model

Parametric bi-directional reflectance factor (BRF) models are often inverted against remote sensing data to describe the amplitude and shape of the anisotropy of geophysical media. For a given geophysical situation, this approach hinges on the availability of (1) a suitable inversion procedure delivering the most probable values of the coefficients entering these models, and (2) reliable and accurate observational data acquired under suitable geometries of illumination and observation. The Rahman, Pinty Verstraete (RPV) model one of the parametric BRF models, idealizes the BRF values through a simple non-linear equation requiring the values of three parameters to be estimated from the remote sensing data. One parameter describes the amplitude of the BRF and the other two jointly represent the angular shape of the anisotropy. The computational load and efficiency required to perform the inversion of the RPV model are critical for operational application. Most, if not all, of the suggested inversion procedures apply to linear versions of parametric models, including a linearized version of the RPV model. Although this approach enables fast inversion methods to be implemented, the linearization prevents the model from representing adequately the wide diversity of observed BRF fields. The present paper describes a computationally efficient inversion method that can be used with the original, i.e., non-linear, version of the RPV model. This method can be applied to retrieve the three model parameters of the original RPV model from an analysis of actual BRF data, while offering the opportunity of specifying the desired accuracy. The procedure delivers ranges of parameter values that depend on the user requirements and capitalizes on the performance of this non-linear model. Two applications are made with laboratory measurements and BRF data sets measured using the multi-angle imaging spectroradiometer (MISR) instrument of the Jet Propulsion Laboratory (JPL) on board the NASA EOS Terra platform.

Age and metallicity estimates for moderate-mass stars in eclipsing binaries

We estimate the ages and metallicities for the components of 43 binary systems using a compilation of accurate observational data on eclipsing binaries for which lines of both components are visible in their spectra, together with two independent modern sets of stellar evolution models computed for a wide range of masses and chemical abundances. The uncertainties of the resulting values are computed, and their stability is demonstrated. The ages and metallicity are compared with those derived in other studies using different methods, as well as with independent estimates from photometric observations and observations of clusters. These comparisons con firm the reliability of our age estimates. The resulting metallicities depend significantly on the choice of theoretical model. Comparison with independent estimates favors the estimates based on the evolutionary tracks of the Geneva group.

Dynamical Reference Frame — Current Relevance and Future Prospects

AbstractPlanetary and lunar ephemerides are no longer used for the determination of inertial space. Instead, the new fundamental reference frame, the ICRF, is inherently less susceptible to extraneous, non-inertial rotations than would be a dynamical reference frame determined by the ephemerides. Consequently, the ephemerides are now adjusted onto the ICRF, and they are fit to two modern, accurate observational data types: ranging (radar, lunar laser, spacecraft) and VLBI (of spacecraft near planets).The uncertainties remaining in the inner planet ephemerides are on the order of 1 kilometer, both in relative positions between the bodies and in the orientation of the inner system as a whole. The predictive capabilities of the inner planet ephemerides are limited by the uncertainties in the masses of many asteroids. For this reason, future improvements to the ephemerides must await determinations of many asteroid masses. Until then, it will be necessary to constantly update the ephemerides with a continuous supply of observational data.

Old open clusters: the interesting case of Berkeley 21

ABSTRACT We present CCD BVI photometry of the old open cluster Berkeley 21, one of themost distant clusters in the Galactic anticentre direction, and possibly the lowestmetallicity object in the open clusters sample. Its position and metal abundance makeit very important for the study of the Galactic disc.Using the synthetic Colour - Magnitude Diagram method, we estimate values fordistance modulus (m-M) 0 = 13.4–13.6, reddening E(B−V)= 0.74–0.78 (with possibledifferential absorption), and age = 2.2–2.5 Gyr.Key words: Hertzsprung-Russell (HR) diagram – open clusters and associations:general – open clusters and associations: individual: Berkeley 21 1 INTRODUCTIONOld open clusters cover a large range of distances, metal-licities, and ages (Friel 1995), and that warrants their usein investigations of the chemical and dynamical evolution ofour Galaxy. To study the metallicity and age distribution ofopen clusters with Galactocentric distance, and avoid unnec-essary and dangerous biases, a key requisite is homogenousanalysis of very accurate observational data, as discussed by,e.g, Janes & Phelps (1994, JP94) Carraro & Chiosi (1994,CC94), Friel (1995), Twarog et al. (1997,TAAT97).This is the fifth paper of a series dedicated to the exami-nation of old open clusters of different ages and metallicities,and located at different Galactic radii: for them we measurein a homogenous way distance, age, reddening and metal-licity. These quantities are derived from comparison of theobserved colour-magnitude diagrams (CMDs) to syntheticones generated by a numerical code based on stellar evolu-tion tracks and taking into account theoretical and obser-vational uncertainties (Tosi et al. 1991). These simulationsare much more powerful than the classical isochrone fittingmethod to study the evolutionary status of the analysedregion and have been successfully applied both to nearby ir-regular galaxies (Greggio et al. 1998 and references therein)and to galactic open clusters (NGC2243: Bonifazi et al. 1990;Cr261: Gozzoli et al. 1996; NGC6253: Bragaglia et al. 1997;NGC2506: Marconi et al. 1997).Berkeley 21 (Be21) is located toward the Galactic an-ticentre, at coordinates RA(1950) = 5:48:42, DEC(1950)= 21:46, and l

The effect of diffusion on the red giant luminosity function ‘bump’

This paper investigates the effect of microscopic diffusion of helium and heavy elements on the location of the Red Giant Branch Luminosity Function Bump in Population II stellar models. To this aim updated evolutionary models taking into account diffusion from the Main Sequence until the Zero Age Horizontal Branch have been computed. The observational luminosity difference between the RGB bump and the ZAHB, as collected for a sample of galactic globular clusters, has been compared with the corresponding theoretical values obtained by adopting both canonical and diffusive models. We find that the effect of diffusion, even if slightly improving the agreement between observations and theory, is negligible with respect to the observational uncertainties. In any case the theoretical predictions in models with and without diffusion appear in agreement with the observational results within the estimated errors. Thus canonical models can be still safely adopted, at least until much more accurate observational data will be available.

Big Bang nucleosynthesis

In the first thousand seconds of its evolution the Universe was a primordial nuclear reactor synthesizing the nuclides D, $^3$He, $^4$He and $^7$Li. These messengers from the Big Bang provide a unique window on the early, hot, dense Universe, offering the opportunity for tests of the standard models of particle physics and of cosmology. A new, statistically coherent comparison of the primordial abundances of these nuclides inferred from increasingly accurate observational data with those predicted by the standard model hints at a possible crisis. The case for this emerging crisis is presented and several paths towards ameliorating it are explored.

METAL-RICH GLOBULAR CLUSTERS OF THE GALAXY: MORPHOLOGY OF THE HELIUM-BURNING "CLUMP," AND THE DETERMINATION OF RELATIVE AGES THROUGH THE "DELTA-V" METHOD

ABSTRACT Morphological aspects of the V, B-V diagram of metal-rich globular clusters are analyzed, on the basis of stellar evolution models for horizontal-branch (HB) and red giant branch stars. These have been incorporated into detailed synthetic HB models, the influence of differential reddening upon which is also discussed. The synthetic HB models are found to be very clumpy in the color-magnitude diagram, though more extended structures occasionally result due to the effect of evolution away from the zero-age HB. In particular, "sloped" clumps may be naturally expected for sufficiently high helium abundances. Differential reddening is found to have a smaller influence than evolution itself upon the morphology of the clump. The synthetic HB models are also used to study the age difference between metal-rich clusters on the basis of the "Delta-V" method. We emphasize the importance of knowing in advance the relative abundances of helium and metals in order to estimate this age difference quantitatively. We present chemical evolution models that serve to illustrate the effect, and show that, for two clusters of identical [Fe/H] and Delta-V, the one enriched predominantly by ejecta from supernovae type II explosions will appear younger than the other which also suffered enrichment from supernovae type Ia ejecta. The implied locations of the red giant branch feature known as the "bump" are also discussed on the basis of recent observational and theoretical results. Our corresponding predictions should be checked against accurate observational data obtained with the Hubble Space Telescope.

The Dynamical Reference Frame

Planetary and lunar ephemerides continue to improve in accuracy as they continue to be adjusted to newer and more accurate observational data. An additional improvement will be that of the orientation of the ephemerides; in the future, the ephemerides produced at JPL will be based upon the reference frame of the radio source catalogues. Recent planetary observations have been made directly with respect to the radio reference frame, and these observations have shown a satisfying degree of absolute accuracy and internal consistency; they enable the automatic orientation of the ephemerides onto the radio reference system during the ephemeris adjustment process.

Big bang nucleosynthesis

In the first thousand seconds of its evolution the Universe was a primordial nuclear reactor synthesizing the light nuclides D, 3He, 4He and 7Li. These messengers from the Big Bang provide a unique window in the early, hot, dense Universe, offering the opportunity for tests of the standard models of particle physics and of cosmology. A new, statistically coherent comparison of the primordial abundances of these nuclides inferred from increasingly accurate observational data with those predicted by standard models hints at a possible crisis. The case for this emerging crisis is presented and several paths towards ameliorating it are explored.

Non-uniform extinction in ten young open clusters

It is believed that groups of new stars have their birth places within gravitationally bound molecular clouds. With time ( ~ 107108yr) the gas and dust of the clouds are either used in star formation processes or blown away by radiation pressure of hot stars present in the system. Consequently, a systematic study of nonuniform extinction in young ( ~ 108 yr) open clusters helps in understanding the star formation processes in these clusters. Most of the earlier studies (cf. Blanco & Williams 1959; Reddish 1967; Krelowski & Strobel 1979) on the subject are based either on accurate observational data without reliable cluster members or vice-versa and the importance of the use of both accurate observational data and reliable cluster members in the type of analysis discussed here is shown by Bohannan (1975). Sagar (1987) has noticed the evidence for the presence of non-uniform extinction in 10 out of the analyzed 15 young open clusters on the basis of relaible proper motion members and use of accurate photometricand spectroscopic data. The possible cause of non-uniform extinction in these I0 objects is discussed here. The details of the observational material used in this study are given elsewhere (cf. Sagar 1987).

The secular variantion of longitudes and plate tectonic motion

According to the plate tectonic theory of Le Pichon [1968] we summarized the absolute values of the angular rate of rotation of the Eurasia and America plates determined by astronomical latitude observations. The authors then tried to use the data of longitude observation so far available to emphasize the existence of similar crust movements. The analysis of longitude data has shown the minor homogeneity of these astronomical observations especially as far as the observations obtained by means of PZT are concerned. By using particularly accurate observational data [Torao & Okasahi, 1965, 1969] the data of longitude variations confirm the existence of movements in the earth’s crust, exactly equal to those deduced by the analysis of latitude observations and in agreement with the results of geophysical measurements.