We have identified 50 T Tauri stars (TTS) and 74 Herbig Ae/Be (HAEBE) stars observed in the IUE short-wavelength bandpass (1150-1980 A). Each low-resolution (R ~ 6 A) spectrum was visually inspected for source contamination and data quality, and then all good spectra were combined to form a single time-averaged spectrum for each star. Use of IUE Final Archive spectra processed with NEWSIPS reduces fixed pattern noise in individual spectra, allowing significant signal-to-noise ratio gains in our co-added spectra. For the TTS observed by IUE, we measured fluxes and uncertainties for 17 spectral features, including two continuum windows and four fluoresced H2 complexes. Thirteen of the 32 accreting TTS observed by IUE have detectable H2 emission, which until now had been reported only for T Tau. Using an empirical correlation between H2 and C IV line flux, we show that lack of sensitivity can account for practically all nondetections, suggesting that H2 fluorescence may be intrinsically strong in all accreting TTS systems. Comparison of IUE and GHRS spectra of T Tau show extended emission primarily, but not exclusively, in lines of H2. We also fit reddened main-sequence templates to 72 HAEBE stars, determining extinction and checking spectral types. Several of the HAEBE stars could not be fitted well or yielded implausibly low extinctions, suggesting the presence of a minority emission component hotter than the stellar photosphere, perhaps caused by white dwarf companions or heating in accretion shocks. We identified broad wavelength intervals in the far-UV that contain circumstellar absorption features ubiquitous in B5-A4 HAEBE stars, declining in prominence for earlier spectral types, perhaps caused by increasing ionization of metal resonance lines. For 61 HAEBE stars, we measured or set upper limits on a depth index that characterizes the strength of circumstellar absorption and compared this depth index with published IR properties.

An IUE Atlas of Pre-Main-Sequence Stars. I. Co-added Final Archive Spectra from the SWP Camera

We have fit synthetic visibilities from three-dimensional ((COBOLD)-B-5+PHOENIX) and one-dimensional (PHOENIX, ATLAS 12) model stellar atmospheres of Procyon (F5 IV) to high-precision interferometric data from the VLT Interferometer (K band) and from the Mark III interferometer (500 and 800 nm). These data sets provide a test of theoretical wavelength-dependent limb-darkening predictions. The work of Allende Prieto et al. has shown that the temperature structure from a spatially and temporally averaged three-dimensional hydrodynamic model produces significantly less limb darkening at 500 nm relative to the temperature structure of a one-dimensional MARCS model atmosphere with a standard mixing-length approximation for convection. Our direct fits to the interferometric data confirm this prediction. A one-dimensional ATLAS 12 model with " approximate overshooting" provides the required temperature gradient. We show, however, that one-dimensional models cannot reproduce the ultraviolet spectrophotometry below 160 nm with effective temperatures in the range constrained by the measured bolometric flux and angular diameter. We find that a good match to the full spectral energy distribution can be obtained with a composite model consisting of a weighted average of 12 one-dimensional model atmospheres based on the surface intensity distribution of a three-dimensional granulation simulation. We emphasize that one-dimensional models with overshooting may realistically represent the mean temperature structure of F-type stars such as Procyon, but the same models will predict redder colors than observed because they lack the multicomponent temperature distribution expected for the surfaces of these stars. (Less)

On the limb darkening, spectral energy distribution, and temperature structure of procyon

This paper analyses the integrated ultraviolet spectra taken with the International Ultraviolet Explorer (IUE) and optical ground-based spectra taken with the William Herschel Telescope (WHT) of the giant H ii region NGC 604. These data are complemented with ultraviolet (WFPC2 through F170W) and Hα (WFPC2 through F656N) images retrieved from the Hubble Space Telescope (HST) archive.



The ultraviolet resonance wind stellar lines, the nebular optical emission lines and the higher order terms of the Balmer series, and He i absorption lines detected in the spectra of NGC 604 are interpreted using evolutionary models optimized for young star-forming regions. The evolutionary state and the massive stellar content of the region are derived in a self-consistent way.



The three techniques applied suggest that the central ionizing cluster in NGC 604 is very young, ≃3 Myr old, and that the stars in the cluster were formed in an instantaneous burst following a Salpeter (α=2.35) or flatter (α=1.5) initial mass function (IMF), having stars more massive that 80 M⊙. The stellar cluster is able to provide most of the ionizing photons needed to photoionize the whole nebula, and the wind power to form the central shell structure where the cluster core is located. The stellar cluster is affected by an extinction similar to the average extinction that affects the ionized gas. The estimated number of massive stars in the cluster is also in agreement with that derived from previous studies based on the detection of individual stars. The results that we present here support the use of these techniques for the interpretation of the integrated light of more distant star-forming regions.

/pdf/the-massive-stellar-content-of-the-h-ii-region-ngc-604-and-20a4106j4c.pdf

The massive stellar content of the H ii region NGC 604 and its evolutionary state

A series of 59 moderate-resolution high signal-to-noise spectra of the pulsating helium star V652 Her covering 1.06 pulsation cycles was obtained with the William Herschel Telescope. These have been supplemented by archival ultraviolet and visual spectrophotometry and used to make a time-dependent study of the properties of V652 Her throughout the pulsation cycle. This study includes the following features: the most precise radial velocity curve for V652 Her measured so far, new software for the automatic measurement of effective temperature, surface gravity and projected rotation velocities from moderate-resolution spectra, self-consistent high-precision measurements of effective temperature and surface gravity around the pulsation cycle, a demonstration of excessive line-broadening at minimum radius and evidence for a pulsation-driven shock front, a new method for the direct measurement of the radius of a pulsating star using radial velocity and surface gravity measurements alone, new software for the automatic measurement of chemical abundances and microturbulent velocity, updated chemical abundances for V652 Her compared with previous work ([CITE]), a reanalysis of the total flux variations (cf. [CITE]) in good agreement with previous work, and revised measurements of the stellar mass and radius which are similar to recent results for another pulsating helium star, BX Cir. Masses measured without reference to the ultraviolet fluxes turn out to be unphysically low (). The best estimate for the dimensions of V652 Her averaged over the pulsation cycle is given by: and (ionization equilibrium), (total flux method), , , and kpc. Two significant problems were encountered. The line-blanketed hydrogen-deficient model atmospheres used yield effective temperatures from the optical spectrum (ionization equilibrium) and visual and UV photometry (bolometric flux) that are inconsistent. Secondly, the IUE spectra are poorly distributed in phase and have low signal-to-noise. These problems may introduce systematic errors of up to .

/pdf/time-resolved-spectral-analysis-of-the-pulsating-helium-star-3184r481c9.pdf

Time-resolved spectral analysis of the pulsating helium star V652 Her

In this paper we apply the reverberation method to determine the mass of the black hole in 3C273 from the Ly a and C iv emission lines using archival IUE observations. Following the standard assumptions of the method, we find a maximum-likelihood estimate of the mass of 6.59 10^9 Mo, with a 1 sigma confidence interval 5.69-8.27 10^9 Mo. This estimate is more than one order of magnitude larger than that obtained in a previous study using Balmer lines. We reanalyze the optical data and show that the method applied to the Ha, Hb, and Hg Balmer lines produce mass estimates lower by a factor 2.5, but already much larger than the previous estimate derived from the same lines. The finding of such a high mass in a face-on object is a strong indication that the gas motion is not confined to the accretion disk. The new mass estimate makes 3C273 accreting with an accretion rate about six times lower than the Eddington rate. We discuss the implications of our result for the broad-line-region size and black-hole mass vs luminosity relationships for the set of objects for which reverberation black-hole masses have been obtained. We find that, while objects with super-Eddington luminosities might theoretically be possible, their existence is not necessarily implied by this sample.

/pdf/the-mass-of-the-black-hole-in-3c-273-3p882x3vrk.pdf

The Mass of the black hole in 3C 273

We present the extraction and processing of the IUE Low Dispersion spectra within the framework of the ESA \IUE Newly Extracted Spectra" (INES) System. Weak points of SWET, the optimal extraction imple- mentation to produce the NEWSIPS output products (extracted spectra) are discussed, and the procedures im- plemented in INES to solve these problems are outlined. The more relevant modications are: 1) the use of a new noise model, 2) a more accurate representation of the spa- tial prole of the spectrum and 3) a more reliable deter- mination of the background. The INES extraction also includes a correction for the contamination by solar light in long wavelength spectra. Examples showing the im- provements obtained in INES with respect to SWET are described. Finally, the linearity and repeatability charac- teristics of INES data are evaluated and the validity of the errors provided in the extraction is discussed.

/pdf/the-iue-ines-system-improved-data-extraction-procedures-for-4c85yipadv.pdf

The IUE INES System: Improved data extraction procedures for IUE

We present the extraction and processing of the IUE Low Dispersion spectra within the framework of the ESA ``IUE Newly Extracted Spectra'' (INES) System. Weak points of SWET, the optimal extraction implementation to produce the NEWSIPS output products (extracted spectra) are discussed, and the procedures implemented in INES to solve these problems are outlined. The more relevant modifications are: 1) the use of a new noise model, 2) a more accurate representation of the spatial profile of the spectrum and 3) a more reliable determination of the background. The INES extraction also includes a correction for the contamination by solar light in long wavelength spectra. Examples showing the improvements obtained in INES with respect to SWET are described. Finally, the linearity and repeatability characteristics of INES data are evaluated and the validity of the errors provided in the extraction is discussed.

Improved data extraction procedures for IUE Low Resolution Spectra: The INES System

In this paper we outline the modifications introduced to the optimal extraction algorithms for IUE Low-Dispersion data under INES. A major modification has been the creation of new noise models for the three cameras, in order to improve the handling of very high and very low FN values. Other changes affect the background estimate, the extraction profile determination and the treatment of flagged pixels. Altogether, the changes do not affect significantly to the vast majority of IUE Low-Dispersion data, but definitely improve the quality for those cases where SWET was known to produce unsatisfactory results.

/pdf/extraction-of-low-dispersion-spectra-for-ines-4gharppk1t.pdf

Norbert Schartel

Papers

The IUE INES System: Improved data extraction procedures for IUE

Improved data extraction procedures for IUE Low Resolution Spectra: The INES System

Extraction of Low Dispersion Spectra for Ines