SWP Camera Research Articles

The Behavior of HgMn stars in the far-UV -Paper 13: HD 182308 and HD 190229

The analysis of low and high resolution spectra of the chemically peculiar stars HD 182308 and HD 190229 recorded by the SWP camera on board the International Ultraviolet Explorer reveals no variations of the far-ultraviolet fluxes of these stars. The far-ultraviolet resonance lines of Ga ii and Ga iii are strong absorbers in the spectrum of HD 182308. A search for successive maxima in the TESS lightcurves of HD 182308 and HD 190229 suggests periods close to 19.11 ± 0.15 days and 9.50 ± 0.15 days respectively which could be the rotational periods.

The Silicon Lines in the Far Ultraviolet Spectrum of HD 172883

The comparison of the mean high resolution spectrum of the chemically peculiar star HD 172883 recorded by the SWP camera on board the International Ultraviolet Explorer with the mean spectrum of HD 38899, a normal late B-type star having similar fundamental parameters, reveals the large flux deficiency of HD 172883 shortwards of 1700 Å. This flux deficiency is due to the strong lines, photoionization edges and autoionization transitions of Si ii. The three strongest autoionization lines of Si ii are present The strong resonance line of Al ii conspicuous in HD 38899 is very ewak in HD 172883 highlighting a strong aluminum deficiency in HD 172883. Conversely, the Hg ii resonance line at 1649.94 Å is much stronger in HD 172883, confirming the large overabundance of mercury in this star.

The Behavior of HgMn Stars in the Far-UV—Paper 12: HD 172883

The analysis of high resolution spectra of the chemically peculiar star HD 172883 recorded by the SWP camera on board the International Ultraviolet Explorer reveals no significant variations of the far-ultraviolet flux of this star. The far-ultraviolet resonance and autoionization lines of Si ii, characteristic of the Bp Si-rich stars, are strong absorbers in the spectrum of HD 172883. The comparison of the mean SWP spectrum of HD 172883 with that of HD 38899, a normal late B-type star having similar fundamental parameters, reveals the presence of a strong resonance line of Hg ii line at 1942.27 Å for the first time. The TESS lightcurve of HD 172883 does not show a clear pattern of variability.

The Behavior of HgMn Stars in the Far UV-Paper 11: HD 53929 and HD 172044

The analysis of low and high resolution spectra of the chemically peculiar stars HD 53929 and HD 172044 recorded by the SWP camera on board the International Ultraviolet Explorer reveals no variations of the far-ultraviolet fluxes of these stars. The far-ultraviolet Ga ii and Ga iii resonance lines are strong absorbers in the spectrum of HD 172044. The TESS lightcurve of HD 172044 suggests a period close to 4.347 ± 0.135 days which could be the rotational period. On SWP 34118 the resonance lines of Si ii and Ga ii are blueshifted compared to SWP 34110 probably reflecting the orbital motion of HD 172044.

The Behavior of HgMn Stars in the Far-UV—Paper 10: HD 174933A and HD 35548A

The analysis of low and high resolution spectra of the chemically peculiar stars HR 7113 and HR 1800 recorded by the SWP camera on board the International Ultraviolet Explorer reveals no variations of the far-ultraviolet flux for spectra separated by 4 months and 3 days for HR 7113 and 1 day apart for HR 1800 respectively. The TESS lightcurve of HR 7113 suggests a period close to 6.46 days which is close to the orbital period previously determined. For HR 1800, a clear period is not seen, time intervals between successive maxima range from 5.53 to 5.82 days.

A Study of the Wavelength Calibration of NEWSIPS High‐Dispersion Spectra

ABSTRACTIn this study we cross‐correlate many IUE echellograms of a variety of well‐observed stars to evaluate systematic error sources in the wavelength zero points (velocities) of all three cameras. We first evaluate differences between the final archived (“NEWSIPS”) and the originally processed (“IUESIPS”) echellograms. These show a marked time dependence in zero point for the SWP camera resulting from several revisions of wavelength calibration coefficients used for IUESIPS. Smaller offsets are present for the LWR camera between the two processings. We also evaluated small‐amplitude fluctuations in the zero points of the NEWSIPS wavelength calibration spectra themselves. In the case of the SWP camera, these variations are too complicated to have been completely removed in the NEWSIPS wavelength calibration. We also examine wavelength zero‐point disparities between data obtained both through the small and large entrance apertures as well as for observations made by different target acquisitions of faint and bright stars. We also find that statistical differences between these alternative observing modes are virtually nil. For large‐aperture observations, the dominant error source is the placement of the target in the aperture. These give rise to non‐Gaussian, extended “tails” in apparent velocity. We also searched for spurious trends. Except for a possible trend for faint objects with SWP camera data, we cannot detect significant dependences with time. Additionally, we discovered a trend with telescope focus for data sets derived from intensive monitoring campaigns of bright stars. These exhibit a repeatable, 1 day “radial velocity variation” with a semiamplitude of nearly 3 km s−1. This pattern appears to be a by‐product of fluctuations in telescope focus caused by operational procedures to maintain the ambient instrument temperature.In the second part of the paper, we measure the mean zero‐point errors of NEWSIPS echellogram data with respect to laboratory results by using the Goddard High Resolution Spectrograph (GHRS) spectral atlas of the O9 V spectral standard 10 Lacertae as an intermediary reference. We find that the derived apparent velocity difference for this star is essentially zero: −1 ± 3.5 km s−1. Several less precise comparisons lead to similar results, including cross‐correlations of (1) spectra of 10 Lac and two stars with similar spectra, HD 93521 and HD 60753; (2) lines in common with the SWP camera and GHRS and STIS atlases of Arcturus and Procyon; and (3) interstellar lines in the GHRS spectrum of the white dwarf G191‐B2B. The zero points of the NEWSIPS‐processed long‐wavelength cameras are evaluated and are also found to be nearly zero (±5 km s−1) relative to the Arcturus and Procyon atlas calibrations and relative to one another. In general, these results do not support the suggestion by González‐Riestra and coworkers that corrections should be introduced to the wavelength scales of various NEWSIPS high‐dispersion data products. Despite our optimistic results, it is obvious that using small IUE data sets from large‐aperture observations of arbitrarily chosen stars can contain velocity errors of at least a few km s−1.

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

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.

A UV Spectrophotometric Technique for Measuring Temperatures of CS Structures over B Stars

Do optical/UV variations of spectra of Be stars arise from pulsations or structures hanging over them? There is a need for a temperature-sensitive discriminator for circumstellar structures above Be stars to determine whether their UV flux variations are due to occulting structures or photospheric pulsations.To address this question, we acquired far-UV (SWP camera) echellograms covering λλ1150–2100 from the IUE final archive. For selected B stars we have selected suitably exposed spectra observed within a short timespan, typically 1–3 days. We summed all the valid net fluxes within each of 60 echelle orders and placed them into an order vs. time array. We identify those times corresponding to high and low fluxes over several reference orders and form the quantity 1 - Fmin(λ)/Fmax(λ), for all echelle orders. The result is a low-resolution spectrum sensitive to absorptions at certain wavelengths, either strong lines such as Lyman α and several UV resonance lines or aggregates of metallic lines. All these are potentially sensitive to temperature variations.

The INES system

In this paper we document the results of the study which led to the ripple correction and absolute calibration algorithms applied to the high resolution spectra processed with the software for the Final Archive of the Project. In this analysis, based on a very large number of spectra, we find that both the K and α parameters (not only the former as previously believed) vary with order number. This fact, together with the finding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in . The internal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute calibration algorithms here described apply also to data processed and distributed with the system.

THE HOT WHITE DWARF COMPANIONS OF HR 1608, HR 8210, AND HD 15638

ABSTRACT We have obtained low-dispersion IUE spectra of the late-type stars HD 15638 (F3 V), HR 1608 (=63 Eri, K0 IV), and HR 8210 (A8m). Each of these stars had been detected as a strong EUV source with the Wide Field Camera (WFC) aboard the ROSAT satellite. The short-wavelength IUE spectrum of each star reveals the presence of a hot white dwarf companion. We have fit the Ly-alpha profile and ultraviolet continuum of each white dwarf using pure hydrogen models. The excellent fit of the data to the models provides confirmation of the Finley and Koester absolute calibration of the SWP camera of IUE. The ultraviolet data alone are insufficient to constrain the model gravity, but an additional constraint is provided by the photometric distance to the late-type primary. We derive Teff = 50,000 K, log g = 8.15 for the white dwarf companion to HD 15638, Teff = 26,000 ± 1500 K, log g = 7.5 ± 0.5 for the companion to HR 1608, and Teff = 35,500 ± 1500 K and log g = 9.0 for the companion to HR 8210. The most interesting of the three white dwarfs is the companion to HR 8210 for which our results imply a mass of 1.15 M. This result is in good agreement with the lower limit on the mass derived from the spectroscopic orbit (M > 1.1 solar mass), provided that the inclination is close to 90 degrees. HR 8210 thus shows similarities to the Sirius system, although with a cooler primary (7700 K vs. 10,000 K), a hotter white dwarf (35,500 K vs. 25,000 K), and a 100 times smaller component separation (3 x 107 km vs. 3 x 109 km). We discuss the importance of future observations of HR 8210 for the study of high mass white dwarfs, and for scenarios of binary star evolution.

Ultraviolet Fe VII absorption and Fe II emission lines of central stars of planetary nebulae

The SWP camera of the IUE satellite was used in the high-dispersion mode to search for Fe VII absorption and Fe II high-excitation emission lines in five additional very hot central stars of planetary nebulae. Some of the Fe VII lines were detected at 1208, 1239, and 1332 A in all the objects of this program, LT 5, NGC 6058, NGC 7094, A43, and Lo 1 (= K1-26), as well as some of the Fe II emission lines at A 1360, 1776, 1869, 1881, 1884, and 1975 A. Two additional objects, NGC 2867 and He 2-131, were obtained from the IUE archive and were evaluated. The present study probably exhausts the list of candidates that are sufficiently bright and hot to be reached with the high-dispersion mode of the IUE.

IUE observations of PG 1115 + 080 - The He I Gunn-Peterson test and a search for the lensing galaxy

Five observations of PG 1115 + 080 taken with the IUE SWP camera have been combined in order to carry out the He I Gunn-Peterson test and to search for a Lyman limit which could determine the redshift of the lens candidate reported by Christian et al. (1987). No Lyman-limit discontinuities are found, implying that the lensing galaxy does not intercept the line of sight or does not contain enough neutral hydrogen to be detected as a Lyman-limit edge. It is estimated that the lens column density for neutral hydrogen is 3 x 10 to the 16th/sq cm or less if it intercepts the line of sight.

FG Sagittae - No hot companion?

The nucleus of the planetary nebula He 1-5 (= PK 60 -7 deg 1), the variable star FG Sge, was observed with the SWP camera of the International Ultraviolet Explorer satellite to detect a hot companion of the star, if such a companion exists. The observation found no evidence for the existance of a hot companion in the 1200-2000 A range of the SWP camera and supported the contention that FG Sge underwent a helium shell flash during the past century, and that the surrounding nebula, He 1-5, is a nebula of fossil ionization. Despite the currently accepted fossil ionization model, constraints posed by the satellite detection limit, the observed H-beta flux, and the adopted radii for white dwarfs still allow the possibility of a putative hot companion photoionizing this nebula.

Ultraviolet observations of the enigmatic bipolar nebula M1-92

IUE observations of the bipolar nebula M1-92 indicate that this object is an evolved object and possibly a preplanetary nebula. Data acquired in the SWP camera clearly show a flat UV continuum indicative of a relatively unobscured O subdwarf. Data acquired in the long wavelength region of the SWP and in the LWP camera reveal an object which mimics the characteristics of an F2 supergiant. These results, combined with other data at visual and infrared wavelengths, strongly favor that the central object of M1-92 is an evolved binary system. The He I 5876 and 6678 A absorption seen in optical spectra is extremely problematic. This, plus the presence of Fe II, Mg II, and Mg I absorption arising from resonance transitions and transitions from low-lying metastable levels, leads to the suggestion that the object resembling an F2 star is actually an early-type subdwarf cloaked in a thick circumstellar nebula. This interpretation and the similarities of the IR flux distribution to Vy 2-2, a preplanetary prototype, is consistent with M1-92 being in the process of forming a planetary nebula. The bipolar flow, the optical Fe II and ultraviolet Mg II emission of M1-92 are also characteristics of T Tauri stars. Although constraints definitely rule out that M1-92 is a pre-main-sequence object, these similarities imply that in many cases it may be difficult to distinguish between T Tauri stars and protoplanetary nebulae.

The ultraviolet calibration of the Hubble Space Telescope. II - A correction for the change in sensitivity of the SWP camera on the IUE

The IUE data on standard stars that will be the basis of UV absolute photometric calibration for the Hubble Space Telescope must be corrected for the changes that are apparent in the low-dispersion spectra of the five standard stars. A set of 895 spectra is presently analyzed in order to determine the change in sensitivity of the SWP camera for the first 8 years of flight operations. Sensitivity loss is noted to be most acute at the shortest (1400-1500 A) wavelengths, as well as beyond 1800 A, where total degradation often exceeds 10 percent. 11 references.

Redshifts of high-temperature emission lines in the far-ultraviolet spectra of late-type stars. II - New, precise measurements of dwarfs and giants

Results are presented from an IUE SWP camera investigation of the occurrence of gasdynamic flows, analogous to the downdrafts of 10 to the 5th K material observed over magnetic active regions of the sun, among stars of late spectral type. The SWP calibration spectra study conducted documents the existence of local, small, persistent distortions of the echelle wavelength scales that are of unknown origin. Attention is given to the enormous widths of the stellar high-excitation emission lines in both the dwarfs and the giants, with respect to the comparatively small, subsonic Doppler shifts; the widths are typically an order of magnitude greater than the redshifts.

SPECTROSCOPIC DETERMINATIONS OF SURFACE GRAVITIES OF GIANT STARS AND ULTRAVIOLET OBSERVATIONS OF RR LYRAE AND X ARIETIS

The surface gravities of four Κ giant stars, including the well-known standard stars Arcturus (a Bootis) and Aldebaran (a Tauri) are determined from an analysis of the molecular dissociation equilibrium of OH. High-resolution FTS spectra of the infrared ground state vibration-rotation lines of the OH Δυ = 1 and Δϋ = 2 sequences were used in the analysis. The oxygen abundances were derived from the [O i] lines at 6300 A and 6363 A. Lifetimes for the OH Δ ν = 2 sequence lines are derived based on the Werner et al. (1983) electric dipole moment function and rotationless Einstein A values. Additionally, the Δυ = 2 sequence OH lines are identified in the solar spectrum using the infrared atlas of Delbouille et al. (1981) and analyzed to establish the accuracy of the calculated lifetimes. Masses for the stars based on the derived gravities, measured parallaxes and angular diameters are also discussed. The results indicated by the OH/[O i] solutions for Arcturus are logg = 1.7 ± 0.2 for an effective temperature of 4375 ± 50 Κ and a mass of 0.8 3ΚΘ. The corresponding results for Aldebaran are log g = 1.0 ± 0.5 using a temperature of 3860 ± 100 Κ and amass of0.73Jio. The surface gravities of five further G and Κ giants were determined from an analysis of the molecular equilibrium of MgH, the magnesium abundances being derived from visible and near-infrared high-excitation potential Mg I lines. The MgH features used, near 5135 A, are from the A-X system (0,0) band. The effects of C2 Swan band blends are included in the MgH analysis. The sensitivity of the derived gravities to the adopted model-atmosphere parameters is described. As a test for non-LTE effects, the MgH/Mg I gravities are compared to surface gravities derived based on an analysis of the ionization equilibrium of iron. Masses derived using these gravities, measured parallaxes, and angular diameters determined from theoretical surface brightness vs. color relationships are given. It is found that the giant star masses are not significantly subsolar. Ultraviolet photometric observations of RR Lyrae obtained with the Astronomical Netherlands Satellite (ANS) are also discussed. These observations are compared with light curves derived using model atmospheres and synthetic spectrum calculations in conjunction with angular diameters determined by Manduca et al. (1981) from photometry at longer wavelengths. A good agreement is found. These results represent an important independent confirmation of the distance and obtained for RR Lyr by Manduca et al. using a theoretically calibrated surface-brightness relation. As an extension of this work, seven low-dispersion spectra of RR Lyr and eleven of X Arietis were obtained with the LWR camera of the International Ultraviolet Explorer (IUE) satellite. RR Lyr was also observed in the low-dispersion mode with the SWP camera (9 spectra) and in the high-dispersion mode with the LWR camera (3 spectra). These observed fluxes are also compared with fluxes calculated using synthetic spectra and the Manduca et al. angular diameters. The IUE fluxes for RR Lyr are found to be significantly fainter than the computed ones. RR Lyr is also found to be 0T4 fainter at 2200 A and 2400 A during minimum light than it was during the previous set of observations made with the ANS satellite. It is suggested that both these differences are due to the combined effect of the secondary cycle of the star (the Blazhko effect) and line blocking not included in the synthetic flux calculations. One of the high-dispersion exposures made near maximum light is deep enough to reveal the cores of the Mg H h and k lines. No emission is observed in this exposure and a strong Mg π interstellar absorption component is present. Emission features are also found to be generally absent from the SWP spectra. An excellent agreement between observed and calculated fluxes is found for X Ari, an extremely metal-poor RR Lyrae star which has no observed secondary cycle. This result for X Ari strongly supports the Manduca et al. distance and .

About the Photometric Calibration of IUE High Resolution Spectra: Quantification of the Order Overlap for the SWP Camera

In order to quantify the errors in the IUE line profiles caused by the order overlap, we have compared line depths in IUE and Copernicus spectra. The excess line depth in IUE spectra suggests that the amount of order overlap is about 32% at 1150Å and decreases to zero at about 1400Å, for spectra extracted with the recent version of IUESISPS (the IUE standard extraction software). The transfer of a spectral feature from one order to the next is below the 5% level.Based on these results, a correction technique is described.

International Ultraviolet Explorer observations of the peculiar variable spectrum of the eclipsing binary R Arae

The eclipsing binary system R Arae = HD 149730 is a relatively bright southern system with an orbital period of about 4.4 days. It is a single-lined spectroscopic binary. The spectral class of the primary component is B9 Vp. The system was included in a study of mass flow and evolution in close binary systems using the International Ultraviolet Explorer satellite (IUE). Four spectra in the wavelength range from 1150 to 1900 A were obtained with the far-ultraviolet SWP camera, and six spectra in the range from 1900 to 3200 range were obtained with the mid-ultraviolet LWR camera. The close binary R Arae exhibits very unusual ultraviolet spectra. It appears that no other close binary system, observed with any of the orbiting satellites, shows outside-eclipse ultraviolet continuum flux variations of this nature.