Fine Error Sensor Research Articles

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.

Is the Far-ultraviolet Flux of 21 Com Anticorrelated to its Optical Brightness?

The comparison of 20 ultraviolet spectra of 21 Com taken over continuous 24 hr to the optical counts collected by the Fine Error Sensor on board IUE reveals that large variations observed shortwards of 1700 Å occur in anti-phase with the optical brightness for part of the observations but not all. In this data, the FUV flux at 1540 Å reaches a minimum at rotational phase 0.32 and increases afterwards while the FES counts continue to increase after this phase. The Fe ii resonance line at 1608.45 Å is Doppler shifted by 0.13 Å at phase 0.00 and −0.13 Å at phase of FUV flux minimum.

The Unexpected Optical and Ultraviolet Variability of the Standard Star α Sex (HD 87887)

The analysis of the available Transiting Exoplanet Survey Satellite (TESS) light curves of α Sex (HD 87887) reveals low-frequency pulsations with a period of about 9.1 hr in this spectroscopic A0 III standard star. The IUE observations in 1992 December reveal large flux variations both in the far-UV and in the mid-UV, which are accompanied by variations of the brightness in the V band recorded by the the Fine Error Sensor on board IUE. The ultraviolet variability could be due to an eclipse by an hitherto undetected companion of smaller radius, possibly 2.5 R ⊙, but this needs confirmation by further monitoring possibly with TESS. An abundance determination yields solar abundances for most elements. Only carbon and strontium are underabundant and titanium, vanadium, and baryum mildly overabundant. Identification is provided for most of the lines absorbing more than 2% in the optical spectrum of α Sex. Stellar evolution modeling shows that α Sex is near the terminal-age main sequence, and its mass, radius, and age are estimated to be M = 2.57 ± 0.32 M ⊙, R = 3.07 ± 0.90 R ⊙, A = 385 ± 77 Myr, respectively.

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 BpSi Stars in the Far UV—Paper II: HD 9996 (HR 465)

The analysis of IUE spectra of the B9 SiCrEu star HD 9996 recorded by the SWP and the LWP camera on board the International Ultraviolet Explorer collected at two phases of its very long rotational period (separated by Δϕ = 0.40), reveals large variations of the far and mid ultraviolet flux. The FUV flux seems to vary in opposition with the optical brightness recorded by the Fine Error Sensor near the V band. At ultraviolet maximum, the lines of Mg ii, Cr ii and Fe ii are definitely stronger than at minimum, which suggests that these elements are distributed in a non uniform manner on the stellar disk with large horizontal gradients. However, the changing aspect of the magnetic field between the two rotational phases observed could also cause part of the ultraviolet variability.

The Ultraviolet Variability of 78 Vir (A2p SrCrEu) throughout the IUE Mission

Abstract Forty-one spectra of 78 Vir (A2p ScrCrEu) obtained through the large apertures of the SWP and LWP/LWR cameras on board International Ultraviolet Explorer (IUE) are compared to look for variations of the absolute flux of 78 Vir over the spectral range 1200–3000 Å. Large variations of the spectral energy distribution occur in the far ultraviolet shortwards of 2000 Å. In contrast, the flux at wavelengths larger than 2000 Å does not vary but several lines are variable between phases of far-UV (FUV) maximum and FUV minimum. The large FUV variability is probably caused by changes in the continuous and line opacity driven by modest horizontal gradients of the abundances of chemical elements over the surface of 78 Vir as the star is probably seen at a low inclination angle. The FUV flux at 1500 Å varies in anticorrelation with the FES counts (optical brightness) recorded before each exposure by the Fine Error Sensor on board IUE.

The Ultraviolet Flux Variations of ρ Puppis as Recorded by IUE

Abstract The archival IUE spectra of the bright δ Scuti star ρ Puppis (HD 67523) reveal large flux variations from 2000 to 3000 Å over an 8 hr observing run. The time separating two successive flux maxima at 2900 Å is 3 hr and 19 minutes which compares well to the period of the radial fundamental mode. At 2900 Å, the flux at maximum is about 1.20 larger than at minimum which is consistent with a 260 K increase of the effective temperature between minimum and maximum. The optical brightness around 5400 Å as recorded by the Fine Error Sensor varied in phase with the ultraviolet flux, corresponding to a decrease in magnitude of −0.11 mag.

Pulsational activity on IK Pegasi

High-time-resolution photometry of millimagnitude precision using the Fine Error Sensor on board the International Ultraviolet Explorer is presented. A few hours of data, when subjected to an optimal (Bayesian) analysis, reveal two pulsational frequencies in the star IK PegA, one of which was not previously known. A fit to the empirical P-L-C relation identifies the modes (almost) unambiguously, and interpolation from stellar evolution models yields fundamental parameters for this star, which are used to refine the dynamic parameters of its binary companion, a massive white dwarf. A study of an archival Hβ spectrum using spectral synthesis techniques demonstrates that IK Peg A is, in all probability, of normal abundances and should not, therefore, be cited as an example of a star exhibiting pulsation and metallism

THE APPLICATION OF ARTIFICIAL NEURAL NETWORKS FOR TELESCOPE GUIDANCE: A FEASIBILITY STUDY FOR LYMAN FUSE

ABSTRACT Since the fine error sensor camera of the Lyman Far Ultraviolet Spectrographic Explorer (FUSE) has significant residual field curvature aberration, the star images over the field of view have a wide variety of shapes. A search for appropriate backup guiding techniques led to the investigation of artificial neural networks (ANN). Such a technique is shown to be capable of learning the image shapes of stars if they are sufficiently differnet. This study investigates the feasibility of using image patterns as positional references for telescope guidance to satisfy redundancy requirements for the mission. For this initial simulation, the ANN was trained to categorize images according to how far they were from the center of the field of view (radius). We found that a non-linear, single hidden layer ANN learned 90 percent of the training patterns, then correctly classified 89 percent of a set of patterns randomly spread over the field of view. This indicates that the network interpolates between training images. Half of the misclassifications are attributed to the image pattern degradation caused by the secondary support structure spider.

Line profile variations in M giants - Clues to mass-loss and chromospheric heating mechanisms

view Abstract Citations (8) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Line Profile Variations in M Giants: Clues to Mass-Loss and Chromospheric Heating Mechanisms Judge, P. G. ; Luttermoser, D. G. ; Neff, D. H. ; Cuntz, M. ; Stencel, R. E. Abstract Analysis is presented of time-series, high dispersion spectra of the Mg II, k, Ca II H, and K lines of the semiregular giants Rho Per (M4 II-III, periodicity of about 50 days), R Lyr (M5 III, period of about 46 days), and g Her (M6 III, period of about 90 days). The fine error sensor on the IUE satellite and ground based UBV photometry was used to relate line profile variations to photospheric variations. The above mentioned stars were selected to study the relative importance of convective motions and global stellar pulsations in determining the structure of the outer atmospheres. Small amplitude changes, but substantial changes in the profiles of Mg II and Ca II lines were detected. It is contended that the observed variability is due to changes in chromospheric conditions and not variations within the circumstellar shell. The picture of a steady state chromosphere, which is modulated on long time scales, is corroborated by these observations. Localized heating is found in g Her. Publication: The Astronomical Journal Pub Date: May 1993 DOI: 10.1086/116573 Bibcode: 1993AJ....105.1973J Keywords: Giant Stars; M Stars; Spectral Line Width; Stellar Mass Ejection; Stellar Motions; Stellar Oscillations; Astronomical Photometry; Atmospheric Heating; Chromosphere; Data Reduction; Iue; Stellar Envelopes; Ubv Spectra; Astrophysics; STARS: GIANTS; STARS: MASS-LOSS; STARS: CHROMOSPHERES full text sources ADS | data products SIMBAD (6) MAST (1) INES (1)

Multiwavelength monitoring of the BL Lacertae object PKS 2155-304. I - The IUE campaign

view Abstract Citations (107) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304. I. The IUE Campaign Urry, C. M. ; Maraschi, L. ; Edelson, R. ; Koratkar, A. ; Krolik, J. ; Madejski, G. ; Pian, E. ; Pike, G. ; Reichert, G. ; Treves, A. ; Wamsteker, W. ; Bohlin, R. ; Bregman, J. ; Brinkmann, W. ; Chiappetti, L. ; Courvoisier, T. ; Filippenko, A. V. ; Fink, H. ; George, I. M. ; Kondo, Y. ; Martin, P. G. ; Miller, H. R. ; O'Brien, P. ; Shull, J. M. ; Sitko, M. ; Szymkowiak, A. E. ; Tagliaferri, G. ; Wagner, S. ; Warwick, R. Abstract Daily monitoring of PKS 2155 - 304 with the IUE satellite throughout 1991 November has revealed dramatic, large-amplitude, rapid variations in the ultraviolet flux of this BL Lac object. Many smaller, rapid flares are superposed on a general doubling of the intensity. During the 5^d^ period when sampling was roughly continuous, the rapid flaring had an apparent quasi-periodic nature, with peaks repeating every ~0.7^d^. The short- and long-wavelength ultraviolet light curves are well correlated with each other, and with the optical light curve deduced from the Fine Error Sensor (FES) on IUE. The formal lag is zero, but the cross- correlation is asymmetric in the sense that the shorter wavelength emission leads the longer. The ultraviolet spectral shape varies a small but significant amount. The correlation between spectral shape and intensity is complicated; an increase in intensity is associated with spectral hardening, but lags behind the spectral change by ~1 day. The sign of the correlation is consistent with the nonthermal acceleration processes expected in relativistic plasmas, so that the present results are consistent with relativistic jet models, which can also account for quasi-periodic flaring. In contrast, currently proposed accretion disk models are strongly ruled out by the simultaneous optical and ultraviolet variability. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172864 arXiv: arXiv:astro-ph/9304003 Bibcode: 1993ApJ...411..614U Keywords: Accretion Disks; Active Galactic Nuclei; Active Galaxies; Bl Lacertae Objects; Iue; Light Curve; Ultraviolet Spectra; Astronomical Models; Blazars; Brightness Temperature; Relativistic Plasmas; Astrophysics; Astrophysics E-Print: 27 pages, plain TeX, STScI Preprint 714 full text sources arXiv | ADS | data products SIMBAD (3) NED (1) MAST (1) INES (1) Related Materials (3) Part 2: 1994A&A...288..433B Part 3: 1995ApJ...438..108C Part 4: 1995ApJ...438..120E

The Blazhko Effect in RR Lyrae

AbstractThe cause of the Blazhko effect, the long-term modulation of the light and radial velocity curves of some RR Lyr stars, is still not understood. The observational characteristics of the Blazhko effect are discussed in §1. Some preliminary results are presented from aomw recent of campaigns to observe RR Lyr, using the International Ultraviolet Explorer along with ground-based spectroscopy and photometry, throughout a pulsation cycle, at a variety of Blazhko phases. A set of ultraviolet light curves have been generated from low dispersion IUE spectra. In addition, the (visual) light curves from IUE's Fine Error Sensor are analyzed using the Fourier decomposition technique. The values of the parameters ϕ21 and R21 at different Blazhko phasas of RR Lyr span the range of values found for non-Blazhko variables of similar period.

Ultraviolet and visible variability of the coma of Comet Levy (1990c)

Short-term variability of the coma Levy (1990c) was detected and monitored with the International Ultraviolet Explorer (IUE) satellite observatory during August and September 1990 including 24 hr of continuous observation on 18 September. The visible lightcurve obtained on this date with the IUE Fine Error Sensor (FES) shows two distinct maxima separated by 17.0 ± 0.1 hr. However, this period cannot properly match in phase the FES data obtained during 8-hr shifts on 11 and 13 September, and suggests a decrease in apparent period of ∼1.3% per day. A similar decrease is derived from a comparison with the period derived from ground-based data taken in late August. The variation in the ultraviolet emissions of OH, CS, and CO 2 +, as well as that of the ultraviolet continuum (λ = 2960 A ̊ ) , was also determined from 18 consecutive long-wavelength IUE spectra taken on 18 September. From these data it is possible to model a production rate source function based on a nucleus whose activity exhibits a hemispherical asymmetry. Moreover, the ratio of gas to dust production rates is found to show a similar asymmetry. It is also found that the dust outflow velocity is about one-fourth the gas velocity. A sharp change in CO 2 + brightness suggests that a subsurface region of volatiles, including CO 2, may be partly responsible for the observed variability, although the origin of the decrease in period remains unexplained. CO was also observed, with a production rate 0.04 ± 0.01 that of H 2O, but the long exposure time required for this measurement precluded any determination of CO variability. IUE observations made postperihelion on 9–10 January 1991 showed no variability.

Asteroid 4 Vesta: Simultaneous visible and ultraviolet IUE observations

On 6–7 October 1990, 16 long-wavelength primary camera (LWP) spectra were recorded with the long-wavelength primary spectrograph of the International Ultraviolet Explorer (IUE) to obtain the resolved UV lightcurve of asteroid 4 Vesta. Simultaneously, the fine error sensor (FES) of the telescope was used to obtain Vesta's near-B lightcurve. Deep LWP and short-wavelength primary camera (SWP) spectra were also collected to establish the reflectivity curve of Vesta in the 1700–3200 Å region. The FES data show that the rotation period is of the order of 5 hr; combined with an old observation obtained in similar geometrical conditions, we derive a new, accurate value of the rotation period, 0.22258840 ± 8 × 10 −8 day. Thus, our observations were obtained during three consecutive revolutions of the asteroid about its axis. The UV and optical lightcurves have one single minimum and one single maximum. The shape of the UV reflectivity curves is constant with rotational phase at the 3–5% level between 2600 and 3000 Å. The UV spectrum is redder than that of the Sun. The asteroid albedo increases linearly with wavelength from 2300 to 3000 Å, and this characteristic probably holds over the entire 2000–3500 Å range; its value near 2700 Å is 7.5% and it does not exceed ≈4% at 2000 Å. The intrinsic amplitude of Vesta's lightcurve is of the order of 10% and does not vary with wavelength from UV to near-IR. The present observations are compared with existing data to develop a self-consistent picture of Vesta's surface properties. No true large-scale and large-amplitude absorptions are observed in the 0.2–2.5 μm range. Small-amplitude colored features are observed at all phases: they seem to be part of a progressive and extended color change that renders one hemisphere slightly bluer than the other.

The ultraviolet variations of Delta Scuti

This paper reports on low resolution observations of the pulsating star Delta Scuti (F2IIIp) obtained with the International Ultraviolet Explorer (IUE) at different phases of the 4 hr and 40 min pulsation cycle. The ultraviolet flux varies in phase with the optical flux measured with the Fine Error Sensor (FES). The amplitude of the ultraviolet variations increases toward shorter wavelengths from 20 percent at 3000 A to 50 percent around 1900 A. Most likely, the ultraviolet variations are caused by the alteration of the effective temperature over the pulsation cycle. A comparison of the spectra of Delta Scuti at maximum and minimum light with low resolution IUE spectra of nonvariable stars indicates that the effective temperature does not vary by more than 400 K over a cycle, in agreement with Trodahl and Sullivan's (1977) result based on optical spectrophotometry. Two high-resolution spectra covering the range 1900-3200 A are also presented. A line identification was presented showing that the mid-UV spectrum of Delta Scuti is crowded with lines of neutral and singly ionized iron-peak elements, in particular those of Fe II, Cr II, Mn II, and Ti II. 18 refs.

Comparison of water production rates from UV spectroscopy and visual magnitudes for some recent comets

The temporal evolution of comets Bradfield (1987 XXIX), P/Tempel 2 (1987g), Wilson (1987 VII), and P/Halley (1986 III), as derived from the ultraviolet and visible coma emissions observed with the International Ultraviolet Explorer (IUE), are compared with the visual lightcurves from magnitudes reported in the IAU circulars. Water production rates derived from visual magnitudes using the method of Newburn agree with OH-derived rates to first order, but are sometimes displaced or fail to show the same pre/postperihelion asymmetry. Some correlation with gas-to-dust ratio is noted. The agreement is best for P/Tempel 2, a relatively dust-free comet. Lightcurves from the IUE fine error sensor (FES) are generally in agreement with the curves based on reported total visual magnitude, despite the simple equation used to extrapolate from the small effective aperture of the FES (∼18″) to an effective total magnitude.

HM Sge still evolving

In their study on C/N/O abundances in red giants, planetary nebulae, novae and symbiotic stars Nussbaumer, Schild, Schmid and Vogel (1988: Astron.Astrophys.198, 179) pointed out that among symbiotic stars HM Sge is quite exceptional, in that its C/N/O abundance ratios rather resemble those of novae and not of symbiotic stars.In 1975 HM Sge brightened within a few months by at least 4m. The object has been observed in radio, visual, X-ray, and since 1978 with IUE. Here we show the changing level of activity in the UV. Figure 1 gives the FES (IUE fine error sensor) counts, representing an integrated flux at visual wavelengths. This flux shows a general decline with a secondary maximum in 1982. – Our mFES is at variance with the visual magnitude estimates given by Munari and Whitelock (1989: Mon.Not.Roy.astr.Soc. 237, 45p). They report high brightness up to at least the end of 1984.

The ultraviolet spectrum of the eclipsing binary IM Aurigae

view Abstract Citations (2) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The ultraviolet spectrum of the eclipsing binary IM Aurigae. Bruhweiler, F. C. ; Feibelman, W. A. ; Kondo, Y. Abstract After recent ground-based photometry of the eclipsing Algol-type system IM Aurigae showed a rapid increase in O-C values of the primary minimum, a spectral search at ultraviolet wavelengths was conducted for evidence of a recent mass-loss "event". Low-dispersion IUE spectra were obtained at primary and secondary minima, as well as a high-dispersion spectrum near maximum. Weak, sharp absorption features are seen at two distinct velocities in the high-dispersion data. These features are attributed to circumbinary gaseous shells and/or gas streams between the stellar components. The time of primary minimum observed utilizing the Fine Error Sensor of the IUE agreed with that predicted by the original ephemeris appropriate to the time prior to the onset of the increased O-C values. The implications of the results are discussed. Publication: The Astronomical Journal Pub Date: August 1986 DOI: 10.1086/114172 Bibcode: 1986AJ.....92..441B Keywords: Absorption Spectra; Eclipsing Binary Stars; Stellar Mass Ejection; Stellar Spectrophotometry; Ultraviolet Spectra; Hot Stars; Iue; Spectral Energy Distribution; Spectrum Analysis; Stellar Envelopes; Stellar Mass Accretion; Astrophysics full text sources ADS | data products SIMBAD (1) MAST (1)

IUE observations of the perplexing bipolar planetary nebula NGC 2346

A preliminary analysis of International Ultraviolet Explorer (IUE) low-dispersion spectrograms of NGC 2346, obtained at various phases of the eclipsing nucleus, shows features typical of a high-excitation planetary nebula. Variations in line profiles, intensities, and stellar continuum are observed as a function of time. An orbital period of 16.0 days was determined from 1.8m(v) variations measured by the IUE Fine Error Sensor (FES) and agrees with the period derived from radial velocity measurements by Mendez.