Far‐Ultraviolet Absolute Flux of α Virginis

Morales, Carmen; Trapero, J.; Gómez, José F.; Giménez, Á.; Orozco, Verónica; Bowyer, Stuart; Edelstein, Jerry; Korpela, E. J.; Lampton, M.; Cobb, Jeff

doi:10.1086/308362

Cited by 12 publications

(12 citation statements)

References 27 publications

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“…It has been widely discussed in the literature that deviations from LTE are to be expected for hot stars and the cores of strong lines in stars of intermediate type (Mihalas 1972). However, it has also been demonstrated that at low resolution the agreement between LTE and NLTE model fluxes is good, and that comparison of far-UV and mid-UV observational data with LTE model fluxes also results in good agreement (Morales et al 2000). At high resolution such a comparison has been anticipated by but not yet quantitatively assessed.…”

Section: Lte Vs Nltementioning

confidence: 99%

UVBLUE: A New High‐Resolution Theoretical Library of Ultraviolet Stellar Spectra

Rodríguez-Merino

Chávez

Bertone

et al. 2005

ApJ

134

131

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We present an extended ultraviolet-blue (850-4700Å) library of theoretical stellar spectral energy distributions (SEDs) computed at high resolution, λ/∆λ= 50 000. The Uvblue grid, as we named the library, is based on LTE calculations carried out with Atlas9 and Synthe codes developed by R. L. Kurucz and consists of nearly 1800 entries that cover a large volume of the parameter space. It spans a range in T eff from 3000 to 50 000 K, the surface gravity ranges from log g= 0.0 to 5.0 with ∆ log g= 0.5 dex, while seven chemical compositions are considered: [M/H]= −2.0, −1.5, −1.0, −0.5, +0.0, +0.3 and +0.5 dex. For its coverage across the H-R diagram, this library is the most comprehensive one ever computed at high resolution in the short-wavelength spectral range, and useful application can be foreseen both for the study of single stars and in population synthesis models of galaxies and other stellar systems.We briefly discuss some relevant issues for a safe application of the theoretical output to ultraviolet observations, and a comparison of our LTE models with the NLTE ones from the Tlusty code is also carried out. NLTE spectra are found, in average, to be slightly "redder" compared to the LTE ones for the same value of T eff , while a larger difference could be detected for weak lines, that are nearly wiped out by the enhanced core emission component in case of NLTE atmospheres. These effects seem to magnify at low metallicity (typically [M/H] −1).A match with a working sample of 111 stars from the IUE atlas, with available atmosphere parameters from the literature, shows that Uvblue models provide an accurate description of the main mid-and low-resolution spectral features for stars along the whole sequence from the B to ∼G5 type. The comparison sensibly degrades for later spectral types, with supergiant stars that are in general more poorly reproduced than dwarfs. As a possible explanation of this overall trend, we could partly invoke the uncertainty in the input atmosphere parameters to compute the theoretical spectra. In addition, one should also consider the important contamination of the IUE stellar sample, where the presence of binary and variable stars certainly works in the sense of artificially worsening the match between theory and observations.

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Section: Lte Vs Nltementioning

confidence: 99%

UVBLUE: A New High‐Resolution Theoretical Library of Ultraviolet Stellar Spectra

Rodríguez-Merino

Chávez

Bertone

et al. 2005

ApJ

134

131

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“…Further information regarding the spacecraft mission and the EURD instrument is provided by Edelstein et al [2001] and Gómez et al [2001]. Absolute calibration is discussed by Morales et al [2000, 2001], with in‐flight calibration in the 911–1100 Å wavelength interval based on α Vir (Spica, HD 116658) and other bright B star spectrum measurements. A preliminary description of the nightside airglow as seen by EURD is given by López‐Moreno et al [1998].…”

Section: March 2000 Measurementsmentioning

confidence: 99%

Data‐model comparison search analysis of coincident PBO Balmer α, EURD Lyman β geocoronal measurements from March 2000

et al. 2004

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[1] Recent Lyman series and Balmer series airglow measurements provide a fresh opportunity to investigate the density distribution and variability of atomic hydrogen in the upper atmosphere. Dedicated nightside Balmer a Fabry-Perot spectrometer measurements at the Pine Bluff Observatory (PBO), University of Wisconsin-Madison, have been acquired since late 1999 taking advantage of several technological advances. Extreme ultraviolet spectral radiance measurements by the Espectrógrafo Ultravioleta extremo para la Radiación Difusa (EURD) instrument on the Spanish MINISAT-1 satellite from October 1997 to December 2001 provide extensive sets of geocoronal Lyman b, Lyman g and He 584 Å emission intensities. In this paper, coincident EURD Lyman b and PBO Balmer a radiance measurements from the early March 2000 new moon period are presented. In addition to serving as examples of the data sets now available, the data volume poses an analysis challenge not faced in prior geocoronal studies. A datamodel comparison search procedure employing resonance radiation transport results for extensive sets of parametric density distribution models is being developed for use in analyses of multiple large data sets; this is described, and example results for the PBO and EURD March 2000 data sets are presented. The tightness of the constraints obtained for the solar line-center Lyman b irradiance and the atomic hydrogen column abundance is somewhat surprising, given the crudeness of the parameter binning in the search procedure and the fact that a small number of recognized corrections remain to be made to each data set.

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“…The model spectral energy distribution (SED) of Spica for i = 116 • is a pretty good match to archival absolute spectrophotometry ( EURD and IUE data for Spica, HD 116658, 13-color spectrophotometry data for Spica, HR 5056 ) as shown in Figure 4, at least longward of 1100 Å. The model SED is systematically lower the Espectrógrafo Ultravioleta extremo para la Radiación Difusa (EURD) spectrum (Morales et al 2000), suggesting perhaps a weaker far-UV extinction than provided by the (Cardelli et al 1989) mean extinction curve, a cooler primary star and/or an absolute calibration issue with the EURD data. We discuss these possibilities further in Section 6.…”

Section: Stellar Atmosphere Models For the Spica Binarymentioning

confidence: 52%

Modeling the H$α$ Emission Surrounding Spica using the Lyman Continuum from a Gravity-darkened Central Star

Aufdenberg,

Hammill

2021

Preprint

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The large, faint Hα emission surrounding the early B-star binary Spica has been used to constrain the total hydrogen recombination rate of the nebula and indirectly probe the Lyman continuum luminosity of the primary star. Early analysis suggested that a stellar atmosphere model, consistent with Spica A's spectral type, has a Lyman continuum luminosity about two times lower than required to account for the measured Hα surface brightness within the nebula. To more consistently model both the stellar and nebular emission, we have used a model atmosphere for Spica A which includes the effects of gravity darkening as input to photoionization models to produce synthetic Hα surface brightness distributions for comparison to data from the Southern Hα Sky Survey Atlas (SHASSA).This paper presents a method for the computation of projected surface brightness profiles from 1D volume emissivity models and constrains both stellar and nebular parameters. A mean effective temperature for Spica A of 24,800 K is sufficient to match both the observed absolute spectrophotometry, from the far-UV to the near-IR, and radial Hα surface brightness distributions. Model hydrogen densities increase with the distance from the star, more steeply and linearly towards the southeast. The northwest matter-bounded portion of the nebula is predicted to leak ∼ 17% of Lyman continuum photons. Model H II region column densities are consistent with archival observations along the line of sight.

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Far‐Ultraviolet Absolute Flux of α Virginis

Cited by 12 publications

References 27 publications

UVBLUE: A New High‐Resolution Theoretical Library of Ultraviolet Stellar Spectra

UVBLUE: A New High‐Resolution Theoretical Library of Ultraviolet Stellar Spectra

Data‐model comparison search analysis of coincident PBO Balmer α, EURD Lyman β geocoronal measurements from March 2000

Modeling the H$α$ Emission Surrounding Spica using the Lyman Continuum from a Gravity-darkened Central Star

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