Intrinsic ultraviolet (912-3200 A) energy distribution of OB stars

Longo, Renata; Stalio, R.; Polidan, R. S.; Rossi, L.

doi:10.1086/167311

Cited by 26 publications

(11 citation statements)

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“…For the power law fit, we specified initial guesses at a normalization, A (the flux at 1000 Å), and the exponent of the power law, α, so that F = A(λ/1000) −α . We also applied a Seaton (1979) galactic extinction law, extropolated to the Lyman limit in a manner that is consistent with Voyager measurements (Longo et al 1989). For the Her X-1 HUT spectrum, we find A = 1.3 ± 0.3 × 10 −13 erg s −1 cm −2 Å−1 , α = 1.33 ± 0.17, and E(B − V ) = 0.09 ± 0.02.…”

Section: Analysis Of the Uv Continuumsupporting

confidence: 70%

Hopkins Ultraviolet Telescope Observations of Hercules X‐1

Boroson

Blair

Davidsen

et al. 1997

ApJ

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We have obtained a far-ultraviolet spectrum of the X-ray binary Hercules X-1/HZ Herculis using the Hopkins Ultraviolet Telescope aboard the Astro-1 space shuttle mission in 1990 December. This is the first spectrum of Her X-1 that extends down to the Lyman limit at 912 Å. We observed emission lines of O VI λλ 1031.9, 1037.6, N V λλ 1238.8, 1242.8, and C IV λλ 1548.2, 1550.8, and the far UV continuum extending to the Lyman limit. We examine the conditions of the emitting gas through line strengths, line ratios, and doublet ratios. The UV flux is lower by about a factor of 2 than expected at the orbital phase of the observation. We model the UV continuum with a simple power-law and with a detailed model of an X-ray-illuminated accretion disk and companion star. The power-law provides a superior fit, as the detailed model predicts too little flux below 1200 Å. We note, however, that there are uncertainties in the interstellar reddening, in the background airglow spectrum, and in the long-term phase of the accretion disk. We have searched the data for UV line and continuum pulsations near the neutron star spin period but found none at a detectable level.

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Section: Analysis Of the Uv Continuumsupporting

confidence: 70%

Hopkins Ultraviolet Telescope Observations of Hercules X‐1

Boroson

Blair

Davidsen

et al. 1997

ApJ

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“…Measurements of extinction curves in the FUV (here 912 − 1216 Å) have been made by Longo et al (1989) and Snow, Allen & Polidan (1990) using Voyager 1 and 2, IUE, and TD-1 data, and by Green et al (1992) with a rocket-borne experiment. Green et al measure the extinction towards ρ Oph, a region which is known to show anomalous dust extinction, attributable to an excess of large dust grains and a deficit of small grains.…”

Section: Introductionmentioning

confidence: 99%

A New Measurement of the Average Far‐Ultraviolet Extinction Curve

Sasseen¹,

Hurwitz²,

Dixon³

et al. 2002

ApJ

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We have measured the extinction curve in the far-ultraviolet wavelength region of (900 -1200Å) using spectra obtained with the Berkeley EUV/FUV spectrometer during the ORFEUS-I and the ORFEUS-II missions in 1993 and 1996. From the complete sample of early-type stars observed during these missions, we have selected pairs of stars with the same spectral type but different reddenings to measure the differential FUV extinction. We model the effects of molecular hydrogen absorption and exclude affected regions of the spectrum to determine the extinction from dust alone. We minimize errors from inaccuracies in the cataloged spectral types of the stars by making our own determinations of spectral types based on their IUE spectra. We find substantial scatter in the curves of individual star pairs and present a detailed examination of the uncertainties and their effects on each extinction curve. We find that, given the potentially large uncertainties inherent in using the pair method at FUV wavelengths, a careful analysis of measurement uncertainties is critical to assessing the true dust extinction. We present a new measurement of the average far-ultraviolet extinction curve to the Lyman limit; our new measurement is consistent with an extrapolation of the standard extinction curve of Savage & Mathis (1979).

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“…1 as well. These spectra are calculated by using simulations for stellar atmospheres performed by Kurucz (Kurucz 1979(Kurucz , 1993Kurucz et al 1974), which gave very realistic results when compared to actual measured spectra (Malagnini 1983;Longo et al 1989). The flux at the top of the Earth's atmosphere is calculated in terms of UBV photometry (Hagen & Boksenberg 1995).…”

Section: Experimental Set-up and Methodsmentioning

confidence: 99%

Feasibility study of an absolute energy calibration of imaging atmospheric Cherenkov telescopes by starlight

Karschnick¹,

Gils²,

Stamm³

2000

Astron. Astrophys. Suppl. Ser.

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Abstract.A new method is presented for an absolute energy calibration of imaging atmospheric Cherenkov telescopes as a whole instrument at all relevant wavelengths. For this study the Cherenkov telescope #1 of the HEGRA 1 experiment was used. The calibration was carried out by detecting the light of different selected stars during one night. From the data a simple linear correlation was derived between the anode current of the Cherenkov camera photomultiplier tubes and the incident photon flux. This result is important for the imaging air Cherenkov technique in several aspects: The method enables to determine the response function of Cherenkov telescopes in the energetic range of Cherenkov light quickly and reliably. Therefore it can be used as an atmospheric calorimeter by measuring the absolute integrated flux of Cherenkov photons. Moreover, the signal of a point run can be predicted and a simulation of the apparatus response can be carried out more reliably.

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Intrinsic ultraviolet (912-3200 A) energy distribution of OB stars

Cited by 26 publications

References 0 publications

Hopkins Ultraviolet Telescope Observations of Hercules X‐1

Hopkins Ultraviolet Telescope Observations of Hercules X‐1

A New Measurement of the Average Far‐Ultraviolet Extinction Curve

Feasibility study of an absolute energy calibration of imaging atmospheric Cherenkov telescopes by starlight

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