Automated Determination of Stellar Parameters from Simulated Dispersed Images for DIVA

We have assessed how well stellar parameters (T_eff, logg and [Fe/H]) can be retrieved from low-resolution dispersed images to be obtained by the DIVA satellite. Although DIVA is primarily an all-sky astrometric mission, it will also obtain spectrophotometric information for about 13 million stars (operational limiting magnitude V ~ 13.5 mag). Constructional studies foresee a grating system yielding a dispersion of ~200nm/mm on the focal plane (first spectral order). For astrometric reasons there will be no cross dispersion which results in the overlapping of the first to third diffraction orders. The one-dimensional, position related intensity function is called a DISPI (DISPersed Intensity). We simulated DISPIS from synthetic spectra (...) for a limited range of metallicites i.e. our results are for [Fe/H] in the range -0.3 to 1 dex. We show that there is no need to deconvolve these low resolution signals in order to obtain basic stellar parameters. Using neural network methods and by including simulated data of DIVA's UV telescope, we can determine T_eff to an average accuracy of about 2% for DISPIS from stars with 2000 K < T_eff < 20000 K and visual magnitudes of V=13 mag (end of mission data). logg can be determined for all temperatures with an accuracy better than 0.25 dex for magnitudes brighter than V=12 mag. For low temperature stars with 2000 K < T_eff < 5000 K and for metallicities in the range -0.3 to +1 dex a determination of [Fe/H] is possible (to better than 0.2 dex) for these magnitudes. Additionally we examined the effects of extinction E(B-V) on DISPIS and found that it can be determined to better than 0.07 mag for magnitudes brighter than V=14 mag if the UV information is included.Comment: 12 pages, 8 figures, Accepted for publication in A&

The design and performance of the Gaia photometric system

The European Gaia astrometry mission is due for launch in 2011. Gaia will rely on the proven principles of the ESA Hipparcos mission to create an all-sky survey of about one billion stars throughout our Galaxy and beyond, by observing all objects down to 20 mag. Through its massive measurement of stellar distances, motions and multicolour photometry, it will provide fundamental data necessary for unravelling the structure, formation and evolution of the Galaxy. This paper presents the design and performance of the broad- and medium-band set of photometric filters adopted as the baseline for Gaia. The 19 selected passbands (extending from the UV to the far-red), the criteria and the methodology on which this choice has been based are discussed in detail. We analyse the photometric capabilities for characterizing the luminosity, temperature, gravity and chemical composition of stars. We also discuss the automatic determination of these physical parameters for the large number of observations involved, for objects located throughout the entire Hertzsprung-Russell diagram. Finally, the capability of the photometric system (PS) to deal with the main Gaia science case is outline

Horizontal Branch Stars: The Interplay between Observations and Theory, and Insights into the Formation of the Galaxy

We review HB stars in a broad astrophysical context, including both variable and non-variable stars. A reassessment of the Oosterhoff dichotomy is presented, which provides unprecedented detail regarding its origin and systematics. We show that the Oosterhoff dichotomy and the distribution of globular clusters (GCs) in the HB morphology-metallicity plane both exclude, with high statistical significance, the possibility that the Galactic halo may have formed from the accretion of dwarf galaxies resembling present-day Milky Way satellites such as Fornax, Sagittarius, and the LMC. A rediscussion of the second-parameter problem is presented. A technique is proposed to estimate the HB types of extragalactic GCs on the basis of integrated far-UV photometry. The relationship between the absolute V magnitude of the HB at the RR Lyrae level and metallicity, as obtained on the basis of trigonometric parallax measurements for the star RR Lyrae, is also revisited, giving a distance modulus to the LMC of (m-M)_0 = 18.44+/-0.11. RR Lyrae period change rates are studied. Finally, the conductive opacities used in evolutionary calculations of low-mass stars are investigated. [ABRIDGED]Comment: 56 pages, 22 figures. Invited review, to appear in Astrophysics and Space Scienc

Permissive tolerance of the patent ductus arteriosus may increase the risk of Chronic Lung Disease

Joseph W Kaempf,1 Robert Huston,2 YingXing Wu,1 Andrew J Kaempf,1 Lian Wang,1 Gary Grunkemeier,1 Rebecca Mischel,2 Howard Cohen,3 Bret Freitag41Providence St Vincent Medical Center, Portland, OR, 2Randall Children&amp;rsquo;s Hospital at Legacy Emanuel, Portland, OR, 3Salem Hospital, Salem, OR, 4Legacy Salmon Creek Hospital, Vancouver, WA, USAPurpose: Because early closure therapies of the patent ductus arteriosus (PDA) have not been shown to confer benefit to premature infants, the authors&amp;rsquo; four neonatal intensive care units adopted a less aggressive PDA management protocol.Study design: A before&amp;ndash;after investigation in infants with PDAs born 501&amp;ndash;1500 g. Era 1 (January 2005 to December 2007) featured traditional management with indomethacin and/or surgical ligation used early to close PDAs; Era 2 (January 2008 to June 2009) featured fluid restriction and watchful waiting for PDA closure, limiting indomethacin or surgical ligation to only those infants with large PDAs needing significant respiratory support.Results: Era 2 infants (n = 129, mean &amp;plusmn; standard deviation 27 &amp;plusmn; 2 weeks) received less and later indomethacin and less Day 1&amp;ndash;28 total fluids as compared to Era 1 infants (n = 240, mean &amp;plusmn; standard deviation 27 &amp;plusmn; 2 weeks). The Chronic Lung Disease (CLD) rate was higher in Era 2 (48% versus 34%, P &amp;lt; 0.01) as was the combined outcome of Death after Day 7 or CLD (57% versus 42%, P &amp;lt; 0.01). Multiple regression analysis showed Era 2 birth was a predictor of CLD. However, Poisson regression analysis determined the predictors of all seven major Vermont Oxford Network morbidities were earlier gestational age, lower birth weight, and male gender, not the era of birth. Significantly more infants were discharged home with PDAs in Era 2.Conclusion: Permissive tolerance of PDAs may increase the risk of CLD and Death after Day 7 or CLD but is not associated with significant changes in other Vermont Oxford Network morbidities.Keywords: premature infant, indomethacin, surgical ligation, quality improvemen

Analysis of Stellar Parameter Uncertainty Estimates from Bootstrapping Neural Networks

Abstract: The derivation of stellar parameters by automated methods is only meaningful if some measure of confidence for the predicted value can be stated. In this work we introduce one possible method for obtaining standard errors and confidence intervals for stellar parameters Teff, log g, [Fe/H] and extinction AV as predicted by neural networks (NN). We applied the bootstrapping method to a feedforward NN for Blind Testing Cycle 2 medium band 1X and 2F photometry for end of mission magnitudes G=15 and 19 mag. We further tested whether the parametrization results can be improved if multiple noisy versions of a filter flux vector (for a given astrophysical parameter) are used in the training set. The obtained results show that the bootstrap standard errors only change significantly if the overall signal to noise ratio is high.