Space Telescope Imaging Spectrograph Observations Research Articles

Emission profiles of neutral oxygen and sulfur in Io's exospheric corona

Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph (STIS) observations of Io acquired in 1997 [Roesler et al., 1999] provided the first simultaneous spatially resolved measurements of emission from neutral sulfur and oxygen, the dominant atomic species in Io's exospheric corona. Previous measurements of Io's corona relied primarily on sunlight resonantly scattered from sodium, a trace element in Io's atmosphere, and required measurement during mutual satellite eclipses to obtain the necessary spatial resolution. We present here spatial profiles of Io's extended emissions derived from observations spanning the time period from October 1997 to February 2000. The STIS Far Ultraviolet Multi‐Anode Microchannel Array (FUV‐MAMA) detector permits measurement of the emissions with a spatial resolution of ∼0.05 Io radii out to distances of ∼20 Io radii. Useful measurements are limited to ∼10 Io radii owing to the low signal‐to‐noise ratio of the extended emission features. The coronal emission profiles vary considerably in slope and intensity and are generally brighter for Io west (duskside) of Jupiter. Emission profiles obtained near western elongation are relatively symmetric about Io; profiles obtained in other orbital positions display varying degrees of asymmetry, with enhanced emissions and generally steeper slopes in the downstream direction relative to the plasma flow. The downstream‐upstream profile asymmetry is thought to be caused by higher electron densities in Io's plasma wake. While the coverage of the data is limited in both Jovian System III coordinates and geocentric phase, the intensities of emission from regions both near Io and in the extended corona vary with System III longitude in a near‐simultaneous fashion, suggesting local torus electron density as the probable source of this modulation. The observed ratio of oxygen to sulfur emission is relatively constant in time, perhaps reflecting the stoichiometric ratio of the SO2 source molecules. Eclipse and posteclipse observations on February 25, 2000, show a dramatic increase in profile emission brightness and slope, suggesting a dynamic response by a sublimation‐supported component of Io's SO2 atmosphere and associated atomic species.

Spectrophotometric Standards from the Far-Ultraviolet to the Near-Infrared: STIS and NICMOS Fluxes

With photometric repeatability in the 0.2%–0.4% range and wavelength coverage from 1150 to 10,200 A, the Space Telescope Imaging Spectrograph (STIS) low-dispersion spectrophotometry provides excellent absolute flux standards. STIS observations of 19 stars are used to update the database of Hubble Space Telescope standard stars with absolute fluxes that are based on the white dwarf pure hydrogen scale. Uncertainties in the STIS absolute flux calibration range from 4% in the far-UV to 2% at longer wavelengths. The relative and absolute fluxes of our composite standards in the IR are verified by the Near Infrared Camera and Multi-Object Spectrograph (NICMOS) observations and by ground-based IR photometry.

The Diversity of High‐ and Intermediate‐Velocity Clouds: Complex C versus IV Arch

We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope Imaging Spectrograph (STIS) observations of interstellar ultraviolet absorption lines in the Galactic high-velocity cloud Complex C and the Intermediate-Velocity Arch (IV Arch) in the direction of the quasar PG 1259+593 (l = 1206, b = +581). Absorption lines from C II, N I, N II, O I, Al II, Si II, P II, S II, Ar I, Fe II, and Fe III are used to study the atomic abundances in these two halo clouds at VLSR ~ -130 km s-1 (Complex C) and -55 km s-1 (IV Arch). The O I/H I ratio provides the best measure of the overall metallicity in the diffuse interstellar medium because ionization effects do not alter the ratio, and oxygen is at most only lightly depleted from the gas into dust grains. For Complex C, we find an oxygen abundance of 0.093 times solar, consistent with the idea that Complex C represents the infall of low-metallicity gas onto the Milky Way. In contrast, the oxygen abundance in the IV Arch is 0.98 times solar, which indicates a Galactic origin. We report the detection of an intermediate-velocity absorption component at +60 km s-1 that is not seen in H I 21 cm emission. The clouds along the PG 1259+593 sight line have a variety of properties, proving that multiple processes are responsible for the creation and circulation of intermediate and high-velocity gas in the Milky Way halo.

High-Velocity Cloud Complex C: Galactic Fuel or Galactic Waste?

We present HST Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph observations of five quasi stellar objects that probe the prominent high-velocity cloud (HVC) Complex C, covering ~10% of the northern sky. Based upon a single sight-line measurement (Mrk 290), a metallicity [S/H] = -1.05 ? 0.12 has been associated with Complex C by Wakker et al. When coupled with its inferred distance (5 d 30 kpc) and line-of-sight velocity (v ~ -100 to -200 km s-1), Complex C appeared to represent the first direct evidence for infalling low-metallicity gas onto the Milky Way, which could provide the bulk of the fuel for star formation in the Galaxy. We have extended the abundance analysis of Complex C to encompass five sight lines. We detect S II absorption in three targets (Mrk 290, 817, and 279); the resulting [S II/H I] values range from -0.36 (Mrk 279) to -0.48 (Mrk 817) to -1.10 (Mrk 290). Our preliminary O I FUSE analysis of the Mrk 817 sight line also supports the conclusion that metallicities as high as 0.3 times solar are encountered within Complex C. These results complicate an interpretation of Complex C as infalling low-metallicity Galactic fuel. Ionization corrections for H II and S III cannot easily reconcile the higher apparent metallicities along the Mrk 817 and Mrk 279 sight lines with that seen toward Mrk 290, since H? emission measures preclude the existence of sufficient H II. If gas along the other lines of sight has a similar pressure and temperature to that sampled toward Mrk 290, the predicted H? emission measures would be ~900 mR. It may be necessary to reclassify Complex C as mildly enriched Galactic waste from the Milky Way or processed gas torn from a disrupted neighboring dwarf, as opposed to low-metallicity Galactic fuel.

Hubble Space TelescopeSTIS Observations of GRB 000301C: CCD Imaging and Near‐Ultraviolet MAMA Spectroscopy

We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the gamma-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R~=21.50+/-0.15 source with no apparent host galaxy. An 8000 s, 1150 A 18 on the line of sight to the OT. This measured redshift is conservatively a lower limit to the GRB redshift. However, as all other GRBs that have deep Hubble Space Telescope images appear to lie on the stellar field of a host galaxy, and as the large H I column density measured here and in later ground-based observations is unlikely on a random line of sight, we believe we are probably seeing absorption from H I in the host galaxy. In any case, this represents the largest direct redshift determination of a gamma-ray burster to date. Our data are compatible with an OT spectrum represented by a power law with an intrinsic index alpha=1.2 (fnu~nu-alpha) and no extinction in the host galaxy, or with alpha=0.5 and extinction by SMC-like dust in the OT rest frame with AV=0.15. The large NHI and the lack of a detected host are similar to the situation for damped Lyalpha absorbers at z>2. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

S[CLC]r[/CLC] [CSC]ii[/CSC] and [S[CLC]r[/CLC] [CSC]ii[/CSC]] Emission in the Ejecta of η Carinae

We have discovered four extremely surprising emission lines of strontium in ejecta near η Carinae. Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) observations made in 1999 show two narrow features whose wavelengths correspond to the forbidden transitions of Sr II, and we have found no other plausible identification for these lines. The identifications are confirmed by new HST/STIS observations of the same stellar position, in which the Sr II resonance lines are observed. Moreover, [Ti II], [Ni II], [Mn II], and [Co II] lines are unusually strong relative to [Fe II] at the same position.

The Rich Ultraviolet Spectrum of Vibrationally Excited Interstellar H[TINF]2[/TINF] toward HD 37903

Based on recent high-resolution Hubble Space Telescope Space Telescope Imaging Spectrograph observations over the 1160-1360 Å wavelength region, we have discovered that HD 37903 (the illuminating star of the bright reflection nebula NGC 2023 in Orion) exhibits a rich spectrum of vibrationally excited interstellar H2 absorption. We have identified a total of over 500 H2 lines arising from various rotational levels (as high as J = 13) in all 14 excited vibrational states of the ground electronic state. Prior to this study, the only published UV absorption measurements of vibrationally excited interstellar H2 consisted of two weak lines toward the star ζ Ophiuchi. In terms of abundance, the v = 3 J = 1 H2 column density toward HD 37903 is over 200 times greater than that toward ζ Oph. Overall, the populations of the excited H2 rovibrational states toward HD 37903 exhibit a nonthermal distribution that is consistent with the UV fluorescent excitation of dense (nH ≈ 104 cm-3) molecular gas located about 0.5 pc from the B1.5 V star. We contrast these results with those provided by near-IR H2 emission-line studies of NGC 2023 and discuss opportunities for future UV observations of vibrationally excited H2 toward HD 37903 and other sight lines.

Multiwavelength Studies of Hercules X‐1 during Short High and Anomalous Low States: On‐again, Off‐again

We present results from multiwavelength observations of the Hercules X-1 system during a short high state (SHS) and during an anomalous low state (ALS). The magnitude of deviation from spin-up appears to be positively correlated with duration of the ALS. Such a correlation is consistent with an interpreta- tion of the ALS in terms of a change in mass accretion rate that causes the disk to tilt and twist beyond the normal deviations that cause the 35 day cycle. A larger deviation from the average results in a M0 stronger disruption of the disk and causes the disk to take longer to settle back to its ii normal ˇˇ 35 day behavior. Our modelwhich includes X-ray heating of the disk and companion star, shadowing of the X-ray —ux by the disk, and a contribution to the continuum emission from the accretion stream or hot spotcan consistently explain the observed changes in X-ray, ultraviolet (UV), and optical continuum light curves for both the SHS and ALS. The Hubble Space Telescope (HST ) and Space Telescope Imaging Spectrograph (STIS) observations presented here are the —rst UV observations of sufficient spectral and temporal resolution to construct Doppler tomograms of the line emission. Doppler tomo- grams of the UV emission lines during SHS and ALS show the majority of the emission coming from the surface of the companion star rather than from the accretion disk. Tomograms made after separating the N V emission lines into broad and narrow components suggests that while the narrow component is associated with emission from the companion star, the broad component may be associated with emis- sion from a distorted disk. The Doppler maps also show that heating over the inner face of HZ Her is not uniform and imply partial eclipse of the UV line emission by an accretion stream and/or hot spot. Subject headings: accretion, accretion disksbinaries: closepulsars: individual (Hercules X-1) ¨ ultraviolet: starsX-rays: stars On-line material: color —gures

STIS and GHRS Observations of Warm and Hot Gas Overlying the Scutum Supershell (GS 018−04+44)

We present Space Telescope Imaging Spectrograph (STIS) and Goddard High Resolution Spectrograph (GHRS) observations of interstellar UV absorption toward HD 177989, a B0 III star at 4.9 kpc in the direction l = 178, b = -119. The line of sight passes through the high-latitude ejecta of the Scutum supershell (GS 018-06+44), which is ~5° in diameter extending ~7° below the Galactic plane at a kinematic distance of ~3.5 kpc in the Scutum spiral arm. The observations with the STIS E140H and GHRS echelle B gratings provide far- and middle-UV spectra at resolutions (FWHM) of ~3 km s-1 and a signal-to-noise ratio (S/N) of ~20:1 to 50:1. The observations reveal strong and broad absorption in the lines of Si IV and C IV centered on LSR velocities of +18 and +42 km s-1 and weaker absorption from these ions near -50 and -13 km s-1. Weak absorption by N V extends over the full velocity range traced by Si IV and C IV. The +18 km s-1 high-ionization absorption likely occurs in gas ~400 pc below the Sagittarius spiral arm, while the extremely strong +42 km s-1 absorption occurs in highly ionized gas in the Scutum supershell at a distance of ~700 pc below the Galactic plane. The properties of the highly ionized gas associated with the Scutum supershell are similar to the gas found in radio loops I and IV; in both cases there is a strong enhancement in the column density of C IV without a corresponding increase in the column density of N V, which causes N(C IV)/N(N V) to be among the largest measured in the interstellar medium. The low-ionization absorption lines of N I, S II, Si II, and Fe II produce narrow absorption features at +37, +40 km s-1 and +55, +60 km s-1. The strength and kinematic properties of these absorption features bear no resemblance to those expected for the high-latitude neutral cloud seen in the H I 21 cm line. This may be due to the relatively low angular resolution (FWHM ~21') of the 21 cm observations. The kinematic relationships among the high-ionization and low-ionization absorption lines observed in the UV suggest a related origin in a hot-warm gas interface region. We are possibly seeing the warm gas in the swept-up shell surrounding a region where hot gas is being vented into the halo. In the warm gas, N(N I)/N(S II) ~0.01 solar, which implies a similar value for N(H0)/[N(H0) + N(H+)]. The warm neutral and ionized gas in the matter overlying the Scutum supershell has values of Si /S and Fe /S roughly similar to those found in the warm neutral medium of the Galactic disk in the vicinity of the Sun. While there has been grain processing in the ejecta of the Scutum supershell, the processing has not been complete. Based on observations of interstellar C IV and Si IV at high S/N and high resolution toward four very distant stars, we determine that highly ionized gas absorption components occur at a frequency of ~1 component kpc-1. The strongest components are associated with lines of sight that pass over or under spiral arms or that pass though Galactic supershells.

Anticipating High‐Resolution STIS Spectra of Four Multiphase MgiiAbsorbers: A Test of Photoionization Models

In this paper we propose a test of the validity of a photoionization modeling technique that is applicable when a combination of high- and low-resolution spectra are available for various chemical transitions. We apply this technique to the four Mg II systems along the line of sight toward the zem = 1.335 quasar PG 1634+706 to infer the physical conditions in the multiple phases of their absorbing gas. We apply constraints from (1) High Resolution Spectrograph (HIRES/Keck I) profiles (R = 45,000 and FWHM = 6.6 km s-1) of low-ionization species Mg II and Fe II and (2) a Hubble Space Telescope (HST) archival, low-resolution Faint Object Spectrograph (FOS) spectrum (FWHM = 230 km s-1) covering Lyα, Lyβ, Si II, Si III, Si IV, C II, C III, C IV, and N V. For this bright quasar, very high signal-to-noise ratio (S/N) Space Telescope Imaging Spectrograph (STIS) spectra at high resolution (FWHM = 10 km s-1) were recently obtained (1999 May and June), covering 1850-3100 A. However, at the time of this writing, these data are still proprietary in the HST archive, and we deliberately present this paper without knowledge of the spectra. Since, in the near term, it is only plausible to obtain high-resolution UV spectra for a handful of the brightest quasars, it is important to determine, without any after the fact biases, what can be learned from low-resolution FOS data. Photoionization models of the four Mg II systems are constrained by the existing FOS and HIRES absorption profiles. In general, it is possible to constrain the low-ionization Mg II phase and to infer the presence of an additional high-ionization phase, but not to infer the detailed properties of the latter. Using some examples of consistent models, we simulate STIS high-resolution profiles of the key transitions that will be covered by the new observations, at the expected S/N. This study will serve as a fair test of the applicability of the photoionization modeling of a combination of low- and high-resolution profiles and also as an unbiased guide for extracting the detailed gaseous conditions from the forthcoming, high-resolution STIS observations. We find that the four Mg II absorbers along the PG 1634+706 line of sight exhibit a variety of Mg II kinematic structures and higher ionization phases. The z = 0.8182 system is a single-cloud, weak Mg II absorber without detected C IV in the FOS spectrum [Wr(C ) < 0.07 A at 3 σ]. The new STIS observations could detect C IV to a higher sensitivity and distinguish between a broad C IV phase and C IV associated with the narrow Mg II cloud. In contrast, the z = 0.9056 absorber is a weak, single-cloud system with strong C IV absorption in the FOS spectrum; we infer that it must have supersolar metallicity, depletion of Fe relative to Mg, or an α-group-enhanced abundance pattern. In this system, three phases were required to match the FOS profiles: the narrow b ~ 3 km s-1 Mg II cloud phase, a broader b ~ 20 km s-1 phase required to produce the observed C IV, and an effective b ~ 400 km s-1 phase needed to fit the wings of the Lyα line. The z = 0.9902 system is a strong Mg II absorber with five blended components; it has a relatively low metallicity, Z < -1, constrained by a strong Lyman limit break; and it also requires a broad b ~ 40 km s-1 phase to fit the observed C IV. The z = 1.0414 system has four, very weak, blended Mg II clouds and is most unusual in that two components of C IV absorption are apparent, even in the low-resolution FOS spectrum. The redward component is centered on the Mg II, but the stronger component is ~200 km s-1 to the blue of the Mg II clouds and thus requires an offset, broad, high-ionization phase.

Ultraviolet Galaxy Counts from Space Telescope Imaging Spectrograph Observations of the Hubble Deep Fields

We present galaxy counts in the near-ultraviolet (NUV; 2365 A) and far-ultraviolet (FUV; 1595 A) obtained from Space Telescope Imaging Spectrograph observations of portions of the Hubble Deep Field-North (HDF-N), the Hubble Deep Field-South (HDF-S), and a parallel field near the HDF-N. All three fields have deep (AB > 29) optical imaging, and we determine magnitudes by taking the ultraviolet flux detected within the limiting optical isophote. An analysis of the UV-optical colors of detected objects, combined with a visual inspection of the UV images, indicates that there are no detectable objects in the UV images that are not also detected in the optical. We determine our detection area and completeness as a function of magnitude with a simulated distribution of galaxies based on the HDF-N Wide Field Planetary Camera 2 (WFPC2) V + I image. The galaxy counts reach to NUVAB = 29 and FUVAB = 30, which is 1 mag fainter than the HDF-N WFPC2/F300W counts and 7 mag fainter than balloon-based counts. We integrate our measurements in order to present the extragalactic background radiation coming from resolved objects. The NUV galaxy counts show a flattening or turnover beginning at about NUVAB = 26.0, which is not predicted either by no-evolution models based on a local luminosity function with a steep faint-end slope or by a semianalytic model in which starbursts are caused by major mergers. The FUV counts also show a flat slope. We argue that the flat slopes could be caused by a short duty cycle for star formation, additional starbursts triggered by minor mergers, and an extended quiescent phase between starburst episodes.

Oviand Multicomponent HiAbsorption Associated with a Galaxy Group in the Direction of PG 0953+415: Physical Conditions and Baryonic Content

We report the discovery of an O VI absorption system at zabs = 0.14232 in a high-resolution FUV spectrum of PG 0953+415 obtained with the Space Telescope Imaging Spectrograph (STIS). Both lines of the O VI ??1032, 1038 doublet and multicomponent H I Ly? absorption are detected, but the N V doublet and the strong lines of C II and Si III are not apparent. We examine the ionization mechanism of the O VI absorber and find that while theoretical considerations favor collisional ionization, it is difficult to observationally rule out photoionization. If the absorber is collisionally ionized, it may not be in equilibrium due to the rapid cooling of gas in the appropriate temperature range. Nonequilibrium collisionally ionized models are shown to be consistent with the observations. A WIYN survey of galaxy redshifts near the sight line has revealed a galaxy at a projected distance of 395 kpc separated by ~130 km s-1 from this absorber, and three additional galaxies are found within 130 km s-1 of this redshift with projected separations ranging from 1.0 Mpc to 3.0 Mpc. All of these galaxies are luminous (0.6-4.0 L*), and two of them show the [O II] ?3727 emission line indicative of active star formation. The galaxies with [O II] emission are probably normal spirals. Combining the STIS observations of PG 0953+415 with previous high signal-to-noise observations of H1821+643 with the Goddard High Resolution Spectrograph (GHRS), we find two O VI systems with Wr > 60 m? and z 50 m? is 102 ? 16. We use this sample to obtain a first estimate of the cosmological mass density of the O VI systems at z ? 0. If further observations confirm the large dN/dz derived for the O VI systems, then these absorbers trace a significant reservoir of baryonic matter at low redshift.

The Surprising Emission Distribution within the Helix Nebula Cometary Knots

We compare the morphology of the cometary knots in the Helix Nebula in different emission lines using Hubble Space Telescope Wide Field Planetary Camera 2 and Space Telescope Imaging Spectrograph observations. We find that the [N II] 6658 A line emission from the cometary heads is displaced with respect to Hα, peaking at a position that is closer to the central ionizing star. This result seems at first sight to be in conflict with simple photoionization models, which predict that the [N II] emission is closer to the ionization front (IF) because it is confined to a thin H+-He0 layer, a prediction confirmed by calculations with both our own and the CLOUDY programs. However, the ratio of [N II] to Hα is very temperature sensitive, and the observations can be explained if the knots are modeled as photoevaporating globules. In this case, there is a strong temperature gradient across the IF, resulting in the [N II] emission being depressed in the partially neutral zones. We also find a strong correlation between the strength of the [N II] and [O III] emission in individual knots, with both being higher in the knots that are closer to the central star. On the current evidence, it is unclear whether this is due to interknot variations in metal abundances or in gas temperature.

The D/H Ratio in Interstellar Gas toward the Hot, White Dwarf G191-B2B

Space Telescope Imaging Spectrograph (STIS) observations of the D/H ratio in the two velocity components towards G191-B2B are consistent with 1.5 ± 0.1 × 10−5 and do not agree with the values derived using the Goddard High Resolution Spectrograph (GHRS) data. We present some new work on the G191-B2B sightline, and the results we obtain are consistent with those of Sahu et al. (1999).

On the Nuclear Rotation Curve of M31

The currently favored model for the double nucleus of M31 consists of an eccentric disk with an off-center density concentration caused by stars lingering at the apocenters of their orbits about the central black hole. If such a disk is to be in equilibrium, the requirement that it precess uniformly because of self-gravity imposes a characteristic radial structure on the orbits that comprise it, creating an observable feature in the rotation curve. The sequence of closed orbits through the densest part of the disk must follow a steep eccentricity gradient, which reverses the arrangement of pericenter and apocenter with respect to the central mass. Stars making up the inner part of the density concentration are at apocenter, while stars making up the outer part are at pericenter, producing a steep local velocity gradient and a distinctive in the projected rotation curve near the eccentric density peak. This wiggle closely resembles a feature seen near the off-center brightness peak (P1) in the nuclear rotation curve observed by the Hubble Space Telescope Faint Object Camera Spectrograph. If confirmed by upcoming Space Telescope Imaging Spectrograph observations, this feature will lend further strong support to the eccentric disk picture and provide important constraints for more realistic dynamical models.

Space Telescope Imaging Spectrograph Observations of the Interstellar Velocity Structure and Chemical Composition toward the Carina Nebula

We have observed the O-type star CPD -59°2603 in the Carina Nebula with the Space Telescope Imaging Spectrograph near-UV and far-UV high-resolution echelles, at a resolving power of ~110,000 (FWHM) and S/N ~ 30. This sight line has complex velocity and excitation structure in the interstellar absorption lines, corresponding to three distinct regions: very high velocity components formed within the nebula; a warm, expanding H II region; and cool, low-velocity gas near the Sun. The Mg I and Mg II profiles show many components, with velocities extending from -235 to +123 km s-1. We have derived physical conditions in the expanding H II region from the Si IV doublet and the excited fine-structure lines of C I. Heavy elements (O, Ni, Cu, Ga) are present in the low-velocity gas, and their abundances indicate depletions consistent with nearby, cool diffuse clouds.12CO is detected in just one low-velocity component, suggesting different amounts of processing among the clouds near the Sun.

High-Velocity L[CLC]y[/CLC]α Emission from SNR 1987A

The high-velocity Lya emission from SN 1987A observed with the Space Telescope Imaging Spectrograph (STIS) evidently comes from a reverse shock formed where the outer envelope of SN 1987A strikes ionized gas inside the inner circumstellar ring. The observations can be explained by a simple kinematic model, in which the Lya emission comes from hydrogen atoms with radial velocity »15,000 km s 21 crossing a reverse shock in the shape of a slightly prolate ellipsoid with equatorial radius cm or »80% of the distance to the 17 4.8 # 10 inner surface of the inner ring. N v ll1239, 1243 emission, if present, has a net luminosity &30% times that of the Lya emission. Future STIS observations should enable us to predict the time of impact with the inner ring and to determine unambiguously whether or not N v emission is present. These observations will offer a unique opportunity to probe the structure of SN 1987A’s circumstellar environment and the hydrodynamics and kinetics of very fast shocks. Subject heading: circumstellar matter — hydrodynamics — supernovae: individual (SN 1987A) — ultraviolet: ISM