Continuum Slope Research Articles

The far-infrared spectra of Jupiter and Saturn

We present far-infrared, disk-averaged spectra of Jupiter and Saturn that were measured with the Long Wavelength Spectrometer aboard the Infrared Space Observatory. The Long Wavelength Spectrometer covered the wavelength region between 43 and 197μm and achieved in grating mode a resolving power of 150–300.The spectra observed in the far infrared are compared to synthetic spectra calculated from atmospheric radiative transfer models using expected values for the constituent vertical concentration profiles. Rotational transitions of ammonia and phosphine are responsible for the broad absorption features observed: Strong ammonia absorption manifolds are obvious against the background continuum slope, appearing at 63, 72, 84, 101 and 125μm in both Jupiter and Saturn. Also phosphine absorption features are clearly present; we found them at the expected wavelengths of 113 and 141μm in both planets and at 81, 87, 94, 103, 126 and 160μm on Saturn only.Our findings are in good agreement with the results obtained with other instruments, in particular the Short Wavelength Spectrometer of the Infrared Space Observatory. On Jupiter we obtained the best fit to the observations with models having an NH3 mixing ratio of 2×10−4. We fitted Saturn's measured spectrum with models where the ammonia mixing ratio amounted to 10−4. For phosphine we found an abundance of 7−3.5+7×10−6 in the troposphere of this planet.

The hard X-ray spectrum of the Seyfert galaxy IRAS 18325-5926: reflection from an ionized disc and variable iron K emission

We report our analysis of the X-ray spectra of the Seyfert galaxy IRAS 18325-5926 (= Fairall 49) obtained from various X-ray observatories prior to XMM-Newton, including new results from two RXTE and one BeppoSAX observations. A relatively steep continuum slope (Γ ≃ 2.2) in the 2-15 keV band is confirmed. The continuum spectrum observed with the BeppoSAX PDS shows a possible roll-over at energies above 30 keV, indicating a Comptonizing corona cooler than in other Seyfert nuclei. The X-ray spectrum above 2 keV is best explained with a model including reflection from a highly ionized disc with significant relativistic blurring. The iron Ka emission feature is then mainly due to Fe XXV. The seven recent observations show that the iron K emission flux appears to follow the continuum between the observations separated by a few months to years, although some exceptions suggest that the linestrength may be determined in a more complex way.

Near-infrared spectroscopy of PKS 1549-79: a protoquasar revealed?

We present a near-infrared (near-IR) spectrum of the nearby radio galaxy PKS 1549-79 (z = 0.153). These data were taken with the aim of testing the idea that this object contains a quasar nucleus that is moderately extinguished, despite evidence that its radio jet points close to our line of sight. We detect broad Paa emission (FWHM 1745 ′ 40 km s - 1 ), relatively bright continuum emission, and a continuum slope consistent with a reddened quasar spectrum (3.1 < A v < 7.3), all emitted by an unresolved point source. Therefore we conclude that we have, indeed, detected a hidden quasar nucleus in PKS 1549-79. Combined with previous results, these observations are consistent with the idea that PKS 1549-79 is a young radio source in whit the cocoon of debris left over from the triggering events has not yet been swept aside by c rcumnuclear outflows.

The Baldwin Effect and Black Hole Accretion: A Spectral Principal Component Analysis of a Complete Quasar Sample

We have performed a spectral principal component analysis (SPCA) for an essentially complete sample of 22 low-redshift QSOs with spectral data from Lyto H� . SPCA yields a set of independent principal compo- nent spectra, each of which represents a set of relationships among QSO continuum and line properties. We find three significant principal components, which account for � 78% of the total intrinsic variance. The first component, carrying � 41% of the intrinsic variance, represents Baldwin relationships: anticorrelations between equivalent widths of broad emission lines and continuum luminosity. The narrow-line core (FWHM � 2000 km s � 1 ) of the broad emission lines dominate this component. The second component, accounting for � 23% of the intrinsic variance, represents the variations in UV continuum slope, which is probably the result of dust reddening, with possible contributions from starlight. The third principal component is directly related to the Boroson & Green '' eigenvector 1 '' (their first principal component), clearly showing the anti- correlation between strengths of optical Fe ii and (O iii) � 5007, and other relationships previously found in the H� -(O iii) region. This third component shows the expected strong correlation with soft X-ray spectral index. The widths of C iii) � 1909, Mg ii � 2798, and Balmer emission lines are also involved and clearly corre- lated, relating this component to black hole mass or Eddington accretion ratio. We find an inverse correlation between the strengths of the UV and optical Fe ii blends, as suggested by some photoionization models. We also find correlations of the strengths of several low-ionization UV lines with Fe ii(opt), and a strong positive correlation of C iv � 1549 with (O iii) strength. The wide wavelength coverage of our data enables us to see clearly the relationships between the UV and optical spectra of QSOs. The Baldwin effect and Boroson & Green's eigenvector 1 relationship are clearly independent. We demonstrate how Baldwin relationships can be derived using our first principal component, virtually eliminating the scatter caused by the third principal component. This rekindles the hope that the Baldwin relationships can be used for cosmological study. Subject headings: galaxies: active — galaxies: nuclei — quasars: emission lines — ultraviolet: galaxies

XMM–Newtonobservations of the Seyfert 1 galaxy ESO 141–G55

We report on an observation of the Seyfert 1 galaxy ESO 141–G55 performed in October 2001 with the EPIC MOS cameras and Reflection Grating Spectrometers (RGS) on board the XMM – Newton observatory. We find the hard (3–10 keV) continuum slope, including reflection, to be somewhat flatter ($\Gamma = 1.72 \pm 0.06$) than that of a typical broad-line Seyfert 1 galaxy. The spectrum shows a weak emission line at 6.45 ± 0.04 keV with a measured equivalent width of ≈ 40 eV. A broad spectral feature is observed around 7 keV that can be fitted by an absorption edge at 7.6 ± 0.1 keV. The extrapolation of the primary power law continuum to energies lower than 2 keV indicates the presence of a soft excess component contributing to 45 ± 3% of the overall flux in the 0.3-2.0 keV energy range. This soft-excess cannot be explained solely by enhanced reflection from a highly ionized disk.

Calculating iron contents of lunar highland materials surrounding Tycho crater from integrated Clementine UV‐visible and near‐infrared data

Optical properties of lunar surface materials are modified by exposure to the space environment, including bombardment by solar wind particles and micrometeorites. One of the main problems in the interpretation of lunar spectral observations is to separate the effects of exposure (“space weathering”) and those due to the composition of the soils (mainly iron and titanium content). Here we use Clementine near‐infrared (NIR) data to investigate this problem for highland‐type soils in the Tycho crater area. Our approach is based on the methods developed for an analysis of a mare region near Aristarchus Plateau [Le Mouélic et al., 2000]. We show that the systematic relationships between spectral parameters (1‐μm band depth and continuum slope), which were previously observed in a mare area with varying maturity degree, are also valid for highland‐type soils. This technique aimed at evaluating the iron content of the surface materials from Clementine UV‐visible (UVVIS) and near‐infrared data can therefore be applied globally. This approach complements the widely used method of Lucey and coworkers, which relies on the UV‐visible bands only. The proposed method relies mostly on band ratios. The iron map produced from this method is therefore less dependent on topography than the iron estimates obtained with UV‐visible data alone, where brightness is one of the controlling parameters. Therefore the proposed approach should be particularly useful at middle to high latitudes, where local topography generates large variations in brightness and therefore hampers the interpretation of iron maps produced from UV‐visible bands only.

Active Nuclei and Star-forming Objects at [ITAL][CLC]z[/CLC][/ITAL] ] 2: Metallicities, Winds, and Formation Histories

We present near-infrared observations of the active galactic nuclei (AGNs) and star-forming objects in the field of the radio galaxy 53W002 at z = 2.39. The star-forming objects are of special interest as candidate protogalactic objects. The 1.1–2.2 μm passbands sample the emitted-optical range at this redshift, providing new diagnostics of the structure, metal abundance, and age of the members of this grouping originally selected through Lyα emission. The star-forming objects are uniformly very blue in continuum slope, which fits with the strong Lyα emission in indicating metal abundances that are less than half solar; some are as blue as the most metal-poor local objects. They fall in a range of luminosity and metallicity that is not populated by local objects, indicating a shorter star-forming history at this early epoch. The best local analogs, such as Mrk 66 and 357, either have several times lower luminosity at comparable [O/H] or significantly higher [O/H] for comparable luminosity. Spectroscopy from the Near-Infrared Camera and Multi-Object Spectrometer yields detections of [O III] emission for two objects and interesting [O III] and Hβ limits for the rest, augmented by Hα limits from Infrared Telescope Facility imaging. These data are satisfied by model stellar populations that have been forming stars for the last 2–5 × 106 yr before z = 2.39. We do not see evidence for older preexisting stellar populations, either in the broadband colors or as redder halos in which the star-forming regions are imbedded. These results suggest that the compact star-forming objects we see at z = 2.0–2.5 are indeed early stages in the building of galaxies rather than transient star-forming events in larger pre-existing dynamical systems. The results also allow an alternative scheme, in which these are low-mass systems that are blowing winds rather than self-enriching, in which case they should fade rapidly with cosmic epoch. For the three prominent AGNs at z = 2.39, Hα and [O III] emission were measured. Unlike the fainter star-forming objects, their line ratios (specifically Lyα/Hα) show metallicities just as high as in nearby systems. If the AGNs occur in those systems that started with the highest density and began active star formation before the less massive surrounding objects, they will have higher metallicity (as we see in their emitted-ultraviolet line ratios). The "ionization cones" seen prominently in Lyα also appear in [O III] and Hα, with a role for continuum reflection in some cases as well. The contrast between the AGNs and fainter star-forming objects can be broadly accommodated in a hierarchical formation picture, although there are still important unknowns as to the fate of the star-forming objects.

ChandraObservations of the QSO Pair Q2345+007: Binary or Massive Dark Lens?

The components of the wide (73) separation quasar pair Q2345+007A,B (z = 2.15) have the most strikingly similar optical spectra seen to date (Steidel & Sargent) yet no detected lensing mass, making this system the best candidate known for a massive (~1014 M?) dark matter lens system. Here we present results from a 65 ks Chandra observation designed to investigate whether it is a binary quasar or a gravitational lens. We find no X-ray evidence for a lensing cluster to a (0.5-2 keV) flux limit of 2 ? 10-15 ergs cm-2 s-1, which is consistent with lensing only for a reduced baryon fraction. Using the Chandra X-ray observations of the quasars themselves, together with new and published optical measurements, we use the observed emission properties of the quasars for further tests between the lens and binary hypotheses. Assuming similar line-of-sight absorption to the images, we find that their X-ray continuum slopes are inconsistent (?A = 2.30 and ?B = 0.83) as are their X-ray-to-optical flux ratios. The probability that B suffers intrinsic absorption sufficient to account for these spectral differences is negligible. We present new optical evidence that the flux ratio of the pair is variable, so the time delay in a lens scenario could cause some of the discrepancies. However, adequately large variations in overall spectral energy distribution are rare in individual QSOs. All new evidence here weighs strongly toward the binary interpretation. Q2345+007 thus may represent the highest redshift example known of an interaction-triggered but as-yet unmerged luminous active galactic nucleus.

Spatial and Compositional Constraints on Non-ice Components and H 2O on Pluto's Surface

We present four new near-infrared spectra of Pluto, measured separately from its satellite Charon during four HST/NICMOS observations in 1998, timed to sample four evenly spaced longitudes on Pluto. Being free of contamination by telluric absorptions or by Charon light, the new data are particularly valuable for studies of Pluto's continuum absorption. Previous studies of the major volatile species indicate the existence of at least three distinct terrains on Pluto's surface: N 2-rich, CH 4-rich, and volatile-depleted. The new data provide evidence that each of these three terrains has distinct near-infrared continuum absorption features. CH 4-rich regions appear to show reddish continuum absorption through the near-infrared spectral range. N 2-rich regions have very little continuum absorption. Visually dark, volatile-depleted regions exhibit intermediate continuum albedos with a bluish continuum slope. By analogy with Triton, we expected that careful spectral modeling would reveal strong evidence for the existence of H 2O ice on Pluto's surface, but we found only very weak evidence for its existence in the volatile-depleted regions. These data require H 2O ice to play a much less prominent role on Pluto's surface than it does on Triton's.

ITAL]N[/ITAL]-Band Observations of Henize 2-10: Unveiling the Dusty Engine of a Starburst Galaxy

As part of an ongoing program to better understand the early stages of massive star cluster evolution and the physical conditions for their formation, we have obtained J, H, K', and N (10.8 μm) images of the nuclear region of the starburst galaxy He 2-10. The N-band images were obtained with the Gemini North Telescope. In only 10 minutes of on-source integration time with Gemini, we were able to detect four of the five enshrouded clusters, or ultradense H II (UD H II regions) recently discovered in radio maps. None of these sources appears in either the optical Hubble Space Telescope images or the near-infrared (J, H, and K') images. These sources make up about 60% of the total N-band flux from He 2-10 and, we suspect, a similar fraction of the total far-infrared flux measured by IRAS. The inferred spectra of the UD H II regions are strikingly similar to those of Galactic ultracompact H II regions. We have modeled the radio and IR spectra of these UD H II regions under the assumption that they are scaled-up Galactic ultracompact H II regions. From this model, the bolometric luminosity of the brightest cluster alone is estimated to be ~2 × 109 L☉. The total mass of the dust and gas in this UD H II region is Mshell ≈ 107 M☉. We have also used the observed spectra to place constraints on the masses and ages of the stellar clusters enshrouded within the UD H II regions. For the brightest UD H II region, we find that the stellar mass must be Mcluster 2.5 × 106 M☉, and the age must be 4.8 × 106 yr, with the most probable age being 3.6 × 106 yr. If we assume that the region is pressure confined and enforce the requirement that the star formation efficiency must be less than ~90%, we find that the age of this stellar cluster must lie within a very narrow range, 4 × 105 < τ < 5 × 106 yr. All the clusters within the UD H II regions in He 2-10 are estimated to have ages less than about 5 × 106 yr and masses greater than about 5 × 105 M☉. We find that the logarithmic ratio of the radio to far-infrared flux densities, q, for the UD H II regions in He 2-10 is ~4; q ≈ 2.6 for both He 2-10 as a whole and NGC 5253, another nearby starburst known to host UD H II regions. These values of q are significantly larger than the average q = 2.35 found for normal galaxies but are comparable to the values of q found for ultraluminous infrared galaxies. We suggest that large q values for starburst galaxies may indicate that a significant fraction of the far-infrared flux may arise from thermal dust emission from UD H II regions. Finally, the possibility that all the far-infrared flux from He 2-10 and other starburst galaxies may be produced by regions completely obscured at wavelengths as long as K' suggests that the well-known correlation between ultraviolet continuum slope and infrared-to-ultraviolet flux ratio in starbursts cannot be due entirely to reprocessing of ultraviolet radiation by dust in a foreground screen geometry. In fact, the dust that reddens the ultraviolet continuum slope must be largely decoupled from the dust that produces the large infrared fluxes in some starbursts.

NEAR Infrared Spectrometer Photometry of Asteroid 433 Eros

We present near-infrared spectrometer (NIS) observations (0.8 to 2.4 μm) of the S-type asteroid 433 Eros obtained by the NEAR Shoemaker spacecraft and report results of our Hapke photometric model analysis of data obtained at phase angles ranging from 1.2° to 111.0° and at spatial resolutions of 1.25×2.5 to 2.75×5.5 km/spectrum. Our Hapke model fits successfully to the NEAR spectroscopic data for systematic color variations that accompany changing viewing and illumination geometry. Model parameters imply a geometric albedo at 0.946 μm of 0.27±0.04, which corresponds to a geometric albedo at 0.550 μm of 0.25±0.05. We find that Eros exhibits phase reddening of up to 10% across the phase angle range of 0–100°. We observe a 10% increase in the 1-μm band depth at high phase angles. In contrast, we observe only a 5% increase in continuum slope from 1.486 to 2.363 μm and essentially no difference in the 2-μm band depth at higher phase angles. These contrasting phase effects imply that there are phase-dependent differences in the parametric measurements of 1- and 2-μm band areas, and in their ratio. The Hapke model fits suggest that Eros exhibits a weaker opposition surge than either 951 Gaspra or 243 Ida (the only other S-type asteroids for which we possess disk-resolved photometric observations). On average, we find that Eros at 0.946 μm has a higher geometric albedo and a higher single-scatter albedo than Gaspra or Ida at 0.56 μm; however, Eros's single-particle phase function asymmetry and average surface macroscopic roughness parameters are intermediate between Gaspra and Ida. Only two of the five Hapke model parameters exhibit a notable wavelength dependence: (1) The single-scatter albedo mimics the spectrum of Eros, and (2) there is a decrease in angular width of the opposition surge with increasing wavelength from 0.8 to 1.7 μm. Such opposition surge behavior is not adequately modeled with our shadow-hiding Hapke model, consistent with coherent backscattering phenomena near zero phase.

Importance of space weathering simulation products in compositional modeling of asteroids: 349 Dembowska and 446 Aeternitas as examples

Abstract— Based on recent progress in simulating space weathering on asteroids using pulse‐laser irradiation onto olivine and orthopyroxene samples, detailed analyses of two of the A and R type asteroid reflectance spectra have been performed using reflectance spectra of laser‐treated samples. The visible‐near‐infrared spectrum of olivine is more altered than that of pyroxene at the same pulse‐laser energy, suggesting that olivine weathers more rapidly than orthopyroxene in space. The same trend can be detected from reflectance spectra of the asteroids, where the more olivine an asteroid has, the redder its 1 μm band continuum can become. Comparison of the 1 μm band continuum slope and the 2/1 μm band area ratio between the asteroids and olivine and pyroxene samples (including the laser‐treated ones) suggests that asteroids may be limited in the degree of space weathering they can exhibit, possibly due to the short life of their surface regolith. Their pyroxenes may also have a limited chemical composition range. Fitting the visible continuum shape and other parts of the spectra (especially the 2μm part) has been impossible with any combination of common rock‐forming minerals such as silicates and metallic irons. However, this study shows, for the first time, excellent fits of reflectance spectra of an A asteroid (Aeternitas) and an R asteroid (Dembowska), including their visible spectral curves, band depths and shapes, and overall continuum shapes. Our results provide estimates that Aeternitas consists of 2% fresh olivine, 93% space‐weathered olivine, 1% space‐weathered orthopyroxene, and 4% chromite, and that Dembowska consists of 1% fresh olivine, 55% space‐weathered olivine, and 44% space‐weathered orthopyroxene. These results suggest that space weathering effects maybe important to the interpretation of asteroid reflectance spectra, even those with deep silicate absorption bands. Modified Gaussian model deconvolutions of the laser‐irradiated olivine samples show that their identity as olivine remained. The most recent submicroscopic mineralogical analyses have revealed that the laser‐irradiated olivine samples contain nanophase iron particles similar to those in space‐weathered lunar samples.

The Underlying White Dwarf Accretor in the Dwarf Nova UU Aquilae

ABSTRACTWe present a high‐gravity, solar composition model atmosphere and model accretion disk study of the U Gem type dwarf nova UU Aql. We have identified the far‐UV signature of the underlying white dwarf for the first time. Our best‐fit model atmosphere to the observed far‐UV spectrum in quiescence is 27,000 ± 1000 K. The solar abundance high‐gravity photosphere provides a consistent explanation for the sharp absorption lines due to metals in the white dwarf’s atmosphere. This interpretation is also consistent with the predicted 20,000–30,000 K small, hot, far‐UV source (smaller than an accretion disk) proposed by Patterson & Raymond. Model accretion disk fits do not account for the sharp absorption lines and continuum slope. The best‐fit accretion disk corresponds to Mwd = 0.8 M⊙, i = 60°, and M ˙ = 10-9.5 M⊙ yr−1. Optically thick disk models at accretion rates lower than 1 × 10-9.5 M⊙ yr−1 are ruled out because of marked flux deficiency shortward of 1400 Å. Theoretical arguments are presented that rule out accretion rates as high as 1 × 10-9.5 M⊙ yr−1 during dwarf nova quiescence. While we can rule out the quiescent disk as being a significant UV flux contributor, we believe the heated white dwarf accounts for the majority of the far‐UV flux. The white dwarf is only the fifth accretor among U Gem systems with a known surface temperature. The temperatures of all five accretors lie between 25,000 and 35,000 K.

AnXMM‐Newton Observation of the Luminous Seyfert 1 Galaxy Markarian 509

We present the spectral analysis of an early XMM-Newton observation of the luminous Seyfert 1 galaxy Mrk 509. We find the hard (2-10 keV) continuum slope, including reflection, to be somewhat flatter (? = 1.75) than that of a typical broad-line Seyfert 1 galaxy. The most obvious feature in the hard X-ray spectrum is a narrow emission line near 6.4 keV with an equivalent width of ~50 eV. The energy and strength of this line is consistent with fluorescence from neutral iron in the molecular torus, and we note the emerging ubiquity of this feature in XMM-Newton and Chandra observations of Seyfert 1 galaxies over a wide luminosity range. We also find evidence for a second emission line at 6.7-6.9 keV, which we attempt to model by reflection from a highly ionized disk. A soft excess, evident as an upward curvature in the continuum flux below ~1.5 keV, cannot be explained solely by enhanced reflection from the ionized disk. The RGS spectrum shows only weak discrete emission and absorption features in the soft X-ray spectrum, supporting our conclusion that the soft excess emission in Mrk 509 represents the high-energy portion of optically thick, thermal emission from the inner accretion disk.

Plasma and X-UV source characteristics for Al targets heated by 40 ns Nd-laser pulses

The total laser energy (3–32 J), temporal history (40 ns full width at half maximum) and focal energy distribution (3×1013 W/cm2 peak, 1.5×1013 W/cm2 average) for λ=1.06 μm Nd:glass laser interactions with planar Al targets were measured. Laser-produced plasma emissions within the 1–3 keV x-ray range were recorded, with limited measurements in the 10–1000 eV range. Primary emphasis was given to obtaining the dependence of kilovolt x-ray emission on irradiance (varied by altering the energy on target or the lens-target spacing). A maximum efficiency for the conversion of incident laser energy to radiation above 1.5 keV was 0.25% into 2π sr. Integrated x-ray energy radiated over this range of photon energy was found to increase as the 3.2 power of laser energy at best focus. X-ray emission decreased when a prepulse preceded the main pulse by a controlled amount exceeding 0.2 μs but &amp;lt;5 μs, with a minimum emission at 0.5 μs separation. Plasma temperatures were estimated from x-ray line ratios and continuum slopes: a value near 230 eV was obtained from free-bound continuum slope for 3×1013 W/cm2 peak irradiance. Temperatures decreased at lower irradiances, as inferred from x-ray line ratios.

An Ultraviolet through Infrared Look at Star Formation and Super Star Clusters in Two Circumnuclear Starburst Rings

We present broadband (U, V, I, and H) and narrowband (H?+[N II] and Pa?) images of the circumnuclear starburst rings in two nearby spiral galaxies, NGC 1512 and NGC 5248, obtained with the WFPC2 and NICMOS cameras on HST. Combined with previously published ultraviolet (UV) HST images at 2300 ?, these data provide a particularly wide wavelength range with which to study the properties of the stellar populations, the gas, and the dust in the rings. The young star clusters and the line-emitting gas have different spatial distributions, with some large (50 pc scale) line-emitting regions that have little associated continuum emission, but a Pa? equivalent width indicating an embedded stellar population a few megayears old. The observed H?/Pa? intensity ratios suggest the gas is mixed with dust, making it effective at completely obscuring some of the young clusters. We identify the major (about 500 in each galaxy) compact continuum sources (super star clusters and individual stars) and analyze their spectral energy distributions (SEDs) from 0.2 to 1.6 ?m by fitting them with a grid of spectral synthesis models with a range of ages and dust extinction. Most of the visible clusters are only mildly reddened, with AV = 0 to 1 mag, suggesting that the processes that clear out the gas and dust of the stellar birth clouds are efficient and fast. The patchiness of the dust distribution makes it difficult to reliably estimate the star formation rate, based on UV continuum slope or hydrogen emission-line ratios, in starbursts such as these. The cluster SEDs are consistent with a range in ages, from 1 to 300 Myr, but with only a minority older than a few tens of megayears. We point out an age bias, the result of the steep luminosity function of the clusters combined with the fading of clusters as they age, which causes young clusters to be overrepresented at any luminosity. Accounting for this bias, the fraction of old clusters is consistent with continuous star formation in the rings over the past ~300 Myr. Because of the uncertainties in dating the clusters, we cannot rule out episodic, ~20 Myr long bursts of star formation, but the presence of UV-bright rings in about 10% of spiral galaxies argues against this possibility. Although most of the observed SEDs are well fitted by a range of models, some of the brightest young clusters have excess emission in the IR that is not predicted by the models and may be thermal reradiation by circumstellar dust. The cluster mass functions follow a power-law distribution with index -2, similar to that recently derived for the starburst in the merging Antennae galaxies, and extending to ~105 M?. The lack of a mass scale means that subsequent evolution of the mass function is required, if some of the SSCs are to evolve into globular clusters. The clusters are spatially unresolved or marginally resolved, corresponding to V-band Gaussian radii of less than a few parsecs, at an assumed distance of 10 Mpc. In NGC 5248, we report a previously unknown, 60 pc radius, inner emission-line ring, and in NGC 1512, a peculiar compact (01 diameter) source with an H?+[N II] equivalent width of ~7000 ?, which may be a so-called Balmer-dominated supernova remnant.

An XMM-Newton observation of the luminous Seyfert 1 galaxy Markarian 509

We present the spectral analysis of an early XMM-Newton observation of the luminous Seyfert 1 galaxy Mrk 509. We find the hard (2-10 keV) continuum slope, including reflection, to be somewhat flatter (? = 1.75) than that of a typical broad-line Seyfert 1 galaxy. The most obvious feature in the hard X-ray spectrum is a narrow emission line near 6.4 keV with an equivalent width of ~50 eV. The energy and strength of this line is consistent with fluorescence from neutral iron in the molecular torus, and we note the emerging ubiquity of this feature in XMM-Newton and Chandra observations of Seyfert 1 galaxies over a wide luminosity range. We also find evidence for a second emission line at 6.7-6.9 keV, which we attempt to model by reflection from a highly ionized disk. A soft excess, evident as an upward curvature in the continuum flux below ~1.5 keV, cannot be explained solely by enhanced reflection from the ionized disk. The RGS spectrum shows only weak discrete emission and absorption features in the soft X-ray spectrum, supporting our conclusion that the soft excess emission in Mrk 509 represents the high-energy portion of optically thick, thermal emission from the inner accretion disk.

Evidence for Rapid Iron Kα Line Flux Variability in MCG −6‐30‐15

This paper employs direct spectral fitting of individual orbital data in order to measure rapid X-ray iron Kα line and continuum spectral slope variations in Seyfert 1 galaxies with unprecedented temporal resolution. Application of this technique to a long RXTE observation of MCG -6-30-15 indicates that the line flux does vary on short (1 day) timescales, but that these variations are not correlated with changes in the continuum flux or slope. These rapid variations indicate that the line does indeed originate close to the black hole, confirming predictions based on its very broad profile. However, the lack of a correlation with the continuum presents problems for models in which the line variations are driven by those in the continuum, modified only by light-travel time effects. Instead, it may be that the line responds according to a physical process with a different timescale, such as ionization instabilities in the disk, or perhaps that the geometry and physical picture is more complex than implied by the simplest disk-corona models. These data also indicate that the slope of the underlying power-law continuum (Γ) shows strong variability and is tightly correlated with the continuum flux in the sense that the spectrum steepens as the source brightens. All of these results have been checked with extensive simulations, which also indicated that a spurious correlation between Γ and Compton reflection fraction (R) will result if these quantities are measured from the same spectra. This casts serious doubts on previous claims of such a Γ-R correlation.

Variability of Southern T Tauri Stars. I. The Continuum and the Hβ Inverse P Cygni Profile of GQ Lupi

We present time series spectrophotometric observations of GQ Lupi, a typical representative of the YY Orionis subgroup of T Tauri stars that show conspicuous inverse P Cygni profiles. The data set consists of 32 exposures taken over five and eight consecutive nights of 1998 May and July, respectively, and covers the spectral range of 3100 Å < λ < 5100 Å. The region redward and next to the Balmer jump varies significantly on a night-to-night basis, and the amplitude of such variability decreases sharply at λ > 4600 Å. The Balmer continuum slope indicates that the spectral energy distribution is governed by a gas of temperature greater than that of the stellar photosphere. The variability of the Balmer continuum flux has the largest amplitude. Flux increases in the B band are accompanied by concurrent flux increases in the U band. The contrary is not always verified.

Near-infrared reflectance spectroscopy of bulk analog materials for planetary crust

In the present study, the differences in near-infrared (NIR) reflectance spectra of powders and bulk surfaces of basalt and pyroxene samples were examined. Furthermore, the effect of a variation in the roughness of the bulk surfaces on the spectra was investigated. The study revealed significant differences between the spectra of powders and bulk surfaces, as observed previously. The most important differences concern the NIR continuum slope and the band depths of the pyroxene absorption bands I (located close to 1 μm ) and II (located close to 2 μm ). Compared to powders, the spectra of bulk surfaces are characterized by lower band depths and a preference for a blue-sloped continuum. The effects on bulk surface spectra produced by a variation of the roughness are similar to the well-known effects that arise from a variation of the grain size in powder spectra. Detailed chemical and physical analyses of the mineral and rock samples have enabled a better understanding of the spectral properties than in past studies. A simple model of lateral light passage through bulk surfaces is proposed to explain this analogy between roughness and grain size. The results of this study have implications for the spectroscopic laboratory investigation of analog materials as well as for the interpretation of reflectance spectra acquired in remote sensing situations.