SWP Camera Research Articles

The FUV Fluxes of A-type Star Members of the Hyades

The International Ultraviolet Explorer database has been searched for the FUV spectra of the A stars which are members of the Hyades. Eight out of 16 confirmed members of the Hyades have FUV absolute fluxes obtained with the SWP camera through the large aperture. The observed sharp decrease of the FUV fluxes from spectral type A2 to A9 is essentially a temperature effect. The FUV flux of the A7 IV star HD 28310, a δ Scuti star, is clearly variable.

The Far Ultraviolet Light Curve of 78 Vir (A2p SrCrEu)

All IUE spectra obtained shortwards of 2000 Å with the SWP camera are used to construct a far-ultraviolet (FUV) light curve at 1500 Å for 78 Vir over its rotational period. Setting an arbitrary phase 0.00 for the first spectrum recorded on 1987 May 10, the minimum and maximum occur respectively near phases 0.20–0.25 and 0.60–0.70. The Fine Error Sensor counts, which measure the brightness near the V band, vary in phase with the FUV flux, which is the opposite situation to that observed in another cool Ap star, 21 Com.

The Behavior of Bp He-weak Stars in the Far UV—Paper XIV: HD 143699

The analysis of seven spectra of the B6 He-weak star HD 143699 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far ultraviolet spectral energy distribution shortwards of 1600 Å in spectra collected from 1994 April 12 to July 9. These variations do not seem to reflect rotational modulation. They could be caused by pulsation with the recently derived pulsation period close to 4 hr. The resonance line of Si ii at 1526.71 Å clearly shows an interstellar component. There is no evidence of C iv absorption at 1550 Å in any of the spectra.

The Behavior of the Bp Stars in the Far UV—Paper VII: HD 22316

The analysis of seven spectra of the B9 Cr Hg Si star HD 22316 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal any variations of the far ultraviolet spectral energy distribution shortwards of 1800 Å in spectra collected over 2 yr with identical exposure times. The low excitation line at 1363.45 Å and the resonance line of Cl i at 1379.53 Å are most likely present. Several lines of Al ii, Si ii, P ii but none of S i could be found at their expected wavelengths. The synthesis of several Al ii lines consistently yields a clear underabundance of aluminum of about 0.40 times the solar aluminum abundance.

The Behavior of Bp HgMn Stars in the Far UV—Paper 28: HD 110073

The analysis of three spectra of the B8 Mn star HD 110073 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal any variations of the far ultraviolet spectral energy distribution shortwards of 1800 Å in spectra collected over 8 yr with identical exposure times. The Ga ii line at 1414.40 Å is a prominent feature in the mean FUV spectrum of this star. The modeling of the optical line of Ga ii at 6334.07 Å yields an overabundance of 1600 times the solar abundance, much lower than previous determinations. The projected rotational velocity is close to 15 km s−1. The silicon abundance derived from the Si ii line at 6347.10 Å is solar.

The Behavior of Bp He-weak Stars in the Far UV—Paper XIII: HD 161480

The analysis of four spectra of the B7 He-weak star HD 161480 recorded by the SWP camera on board the International Ultraviolet Explorer reveals instances of variations of the far ultraviolet spectral energy distribution shortwards of 1800 Å in spectra collected over 4 consecutive days with identical exposure times. The Si ii doublet near 1530 Å is stronger at phase of FUV minimum. The C iv doublet at 1550 Å is absent. These variations suggest that silicon and other chemical elements are probably distributed in an inhomogeneous manner over the surface of HD 161480. The radial velocity of the Si ii doublet varies over the 4 days observation, reflecting the orbital motion of this SB1 star.

The Behavior of Ap/Fp Stars in the Ultraviolet—Paper I: HD 137949 (33 Lib)

Abstract The analysis of six spectra of the F0Vp EuGdSr star HD 137949 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal any variations of the far-ultraviolet spectral energy distribution shortwards of 1800 Å over slightly more than 2 yr and a half. The five spectra taken consecutively on 1984 February 23 do not show evidence either for rapid variations of the flux over 2 hr and 50 minutes (whereas the main pulsational period is 8.27 minutes for this rapidly oscillating Fp star). This behavior remarkably differs from the 50% flux variability of δ Scuti (F2 III) in the FUV over its 4 hr and 40 minutes period.

The Behavior of Bp He-weak Stars in the far-UV—Paper XI: HD 35456

The analysis of four spectra of the B7 He-weak star HD 35456 recorded by the SWP camera on board the International Ultraviolet Explorer does not reveal any variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å over slightly more than one rotational period. There is no sign of variability in the numerous Si ii, Si iii and Si iv lines present in the far-ultraviolet. The profile of the resonance line of C ii at 1335 Å remains constant too.

The Behavior of Bp He-weak Stars in the Far-UV—Paper XII: HD 175156

The analysis of four spectra of the B5 He-variable star HD 175156 recorded by the SWP camera on board the International Ultraviolet Explorer reveals one possible instance of variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å in spectra separated by 5 yr. Spectra collected over 4 consecutive days with identical exposure times do not vary, which probably rules out the possibility that HD 175156 be a rotational variable. The modeling of the Space Telescope Imaging Spectrograph spectrum reveals the presence of interesting resonance or low lying transitions of C i, N i, S i, P ii and several iron-peak elements, which provide interesting diagnostics of the atmosphere of this evolved sub-giant.

The Behavior of Bp He-weak stars in the far-UV—Paper X: HD 49333

The analysis of four spectra of the B7 He-weak Si star HD 49333 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å over slightly more than 1 day, ie. about 46% of the rotational period. Several Si ii, Si iii and Si iv vary consistently. Silicon must be distributed in a non uniform manner over the surface of HD 49333 so as to modulate the FUV flux over the rotational period. The profile of the resonance line of C ii at 1335 Å does not vary at these two rotational phases.

The Behavior of Bp He-weak Stars in the Far UV—Paper IX: HD 142990

The analysis of eighteen spectra of the B6 He-weak star HD 142990 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å over about 6 hr, ie. about 25% of the rotational period. Several Si ii, Si iii and Si iv vary consistently. Silicon must be distributed in a non uniform manner over the surface of HD 142990 so as to modulate the FUV flux over the rotational period. The low resolution spectra also confirm this variability.

The Behavior of Bp He-weak Stars in the far-UV—Paper VIII: HD 131120

The analysis of four spectra of the B8 He-weak star HD 131120 recorded by the SWP camera on board the International Ultraviolet Explorer reveals low amplitude variations of the far-ultraviolet spectral energy distribution shortwards of 1500 Å over about half its rotational period in 1984. Silicon must be distributed in a non uniform manner over the surface of HD 131120 so as to modulate the FUV flux over the rotational period. This confirms the results of earlier investigations based on phase resolved high resolution optical spectra.

The Behavior of Bp He-weak Stars in the Far UV—Paper VII: HD 144334

The analysis of 14 spectra of the B8 He-weak Si star HD 144334 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution shortwards of 1600 Å over a time interval of about five days in 1994 October. In contrast, the level of the mid-UV flux did not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations.

The Behavior of Bp He-weak Stars in the Far UV—Paper VI: HD 21699

The analysis of spectra of the B8 He-weak Si star HD 21699 recorded by the SWP camera on board the International Ultraviolet Explorer in 1987 reveals large amplitude variations of the far-ultraviolet spectral energy distribution over a time interval of about four days in 1987 October. In contrast, the level of the mid-UV flux did not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The lines of C iv doublet near 1550 Å are stronger and have an extended blue wing at phase of far-UV maximum. The optical brightness recorded by the Fine Error Sensor on board IUE is probably anticorrelated with the FUV flux, reflecting the redistribution of the FUV flux toward longer wavelengths.

The Behavior of Bp Si Stars in the far-UV—Paper VI: HD 215441

The analysis of spectra of the B9 Si star HD 215441 recorded by the SWP camera on board the International Ultraviolet Explorer reveals large amplitude variations of the far-ultraviolet spectral energy distribution over a time interval of about half the rotation period. In contrast, the level of the mid-UV flux does not vary between phases of FUV flux maximum and minimum which suggests that changes of the silicon continuous and line opacity play an important role in the variations. The optical brightness recorded by the Fine Error Sensor on board IUE is anticorrelated with the FUV flux, reflecting the redistribution of the FUV flux towards longer wavelengths.

The Behavior of Bp He-strong Stars in the far UV—Paper I: HD 37776

The analysis of thirty-two spectra of the Bp He-strong variable star HD 37776 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution over a time interval of about 26 hr. Variations are present shortwards of 1450 Å which can be partly attributed to variations of lines and continuum of Si ii. Other lines due to C ii, Si iii and Si iv also contribute to the opacity in this range too. The variations suggest that silicon and possibly carbon are not distributed in a uniform manner over the surface.

The Behavior of Bp Si Stars in the Far UV—Paper V: HD 92664

The analysis of spectra of the B8 Si-rich HD 92664 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution shortwards of 1700 Å over a time interval of about 2 months. In contrast, the mid-UV flux does not vary which suggests that changes of the silicon continuous and line opacity are the cause of the variations. The iron-peak elements, chromium, manganese and iron play a lesser role than silicon in these variations. Phased on previous ephemeris, the FUV minimum occurs at the rotational phase, ϕ = 0.0, which corresponds to maximum light in the V-band and minimum longitudinal magnetic field.

The Behavior of Bp He-weak Stars in the Far-UV—Paper 5: HD 142301

The analysis of eigthteen spectra of the B8 He-weak Si star HD 142301 recorded by the SWP camera on board the International Ultraviolet Explorer reveals large variations of the far-ultraviolet spectral energy distribution over a time interval of 14 yr and 5 months. Variations are present shortwards of 1700 Å which can be partly attributed to variations of lines and continuum of Si ii. Other lines due to C ii and Si iii also contribute to the opacity in this range too. The variations suggest that silicon is not distributed in a uniform manner over the surface and that the horizontal gradients of the silicon abundance are probably large.

The Behavior of Bp He-weak Stars in the Far UV—Paper IV: HD 28843

The analysis of five spectra of the Bp He-weak Si star HD 28843 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution over a time interval of 4 yr and eight months. Variations are present shortwards of 1700 Å which can be partly attributed to variations of lines and continuum of Si ii. Other lines due to C ii and Si iii also contribute to the opacity in this range too. The variations suggest that silicon is not distributed in a uniform manner over the surface and that the horizontal gradients of the silicon abundance are probably quite large.

The Behavior of Bp He-weak Stars in the Far UV—Paper III: HD 175362

The analysis of twelve spectra of the Bp He-weak Si star HD 175362 recorded by the SWP camera on board the International Ultraviolet Explorer reveals variations of the far-ultraviolet spectral energy distribution over a time interval of several years. Variations are present shortwards of 1700 Å which can be partly attributed to variations of lines and continuum of Si ii. Other lines due to C ii, Si iii and Si iv also contribute to the opacity in this range too. The variations suggest that silicon and carbon are not distributed in a uniform manner over the surface.