Space Telescope Science Institute Research Articles

Multivariate Predictors of Lyman Continuum Escape. I. A Survival Analysis of the Low-redshift Lyman Continuum Survey* * Based on observations made 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. These observations are associated with programs GO-15626, GO-13744,

To understand how galaxies reionized the Universe, we must determine how the escape fraction of Lyman continuum (LyC) photons (f esc) depends on galaxy properties. Using the z ∼ 0.3 Low-redshift Lyman Continuum Survey (LzLCS), we develop and analyze new multivariate predictors of f esc. These predictions use the Cox proportional hazards model, a survival analysis technique that incorporates both detections and upper limits. Our best model predicts the LzLCS f esc detections with an rms scatter of 0.31 dex, better than single-variable correlations. According to ranking techniques, the most important predictors of f esc are the equivalent width (EW) of Lyman-series absorption lines and the UV dust attenuation, which track line-of-sight absorption due to H i and dust. The H i absorption EW is uniquely crucial for predicting f esc for the strongest LyC emitters, which show properties similar to weaker LyC emitters and whose high f esc may therefore result from favorable orientation. In the absence of H i information, star formation rate surface density (ΣSFR) and [O iii]/[O ii] ratio are the most predictive variables and highlight the connection between feedback and f esc. We generate a model suitable for z > 6, which uses only the UV slope, ΣSFR, and [O iii]/[O ii]. We find that ΣSFR is more important in predicting f esc at higher stellar masses, whereas [O iii]/[O ii] plays a greater role at lower masses. We also analyze predictions for other parameters, such as the ionizing-to-nonionizing flux ratio and Lyα escape fraction. These multivariate models represent a promising tool for predicting f esc at high redshift.

Atomic Transition Probabilities for Ultraviolet and Optical Lines of Tm ii * *Based on observations made 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 NAS5-26555 (program GO-15657). This paper also includes data gathered with the 6.5 m Magellan Telescopes

We report new branching fraction measurements for 224 ultraviolet and optical transitions of Tm ii. These transitions range in wavelength (wavenumber) from 2350 to 6417 Å (42,532–15,579 cm−1) and originate in 13 odd-parity and 24 even-parity upper levels. Thirty-five of the 37 levels, accounting for 213 of the 224 transitions, are studied for the first time. Branching fractions are determined for two levels studied previously for comparison to earlier results. The levels studied for the first time are high lying, ranging in energy from 35,753 to 54,989 cm−1. The branching fractions are determined from emission spectra from two different high-resolution spectrometers. These are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5% to 30%. Comparison is made to experimental and theoretical transition probabilities from the literature where such data exist. These new log(gf) values are used to derive an abundance from one previously unused Tm ii line in the UV spectrum of the r-process-enhanced metal-poor star HD 222925, and this abundance is consistent with previous determinations based on other Tm ii lines.

Glimmers in the Cosmic Dawn: A Census of the Youngest Supermassive Black Holes by Photometric Variability* * This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555. These observations are associated with

We report the first results from a deep near-infrared campaign with the Hubble Space Telescope to obtain late-epoch images of the Hubble Ultra Deep Field, 10–15 yr after the first epoch data were obtained. The main objectives are to search for faint active galactic nuclei (AGN) at high redshifts by virtue of their photometric variability and measure (or constrain) the comoving number density of supermassive black holes (SMBHs), n SMBH, at early times. In this Letter, we present an overview of the program and preliminary results concerning eight objects. Three variables are supernovae, two of which are apparently hostless with indeterminable redshifts, although one has previously been recorded as a z ≈ 6 object precisely because of its transient nature. Two further objects are clear AGN at z = 2.0 and 3.2, based on morphology and/or infrared spectroscopy from JWST. Three variable targets are identified at z = 6–7 that are also likely AGN candidates. These sources provide a first measure of n SMBH in the reionization epoch by photometric variability, which places a firm lower limit of 3 × 10−4 cMpc−3. After accounting for variability and luminosity incompleteness, we estimate n SMBH ≳ 8 × 10−3 cMpc−3, which is the largest value so far reported at these redshifts. This SMBH abundance is also strikingly similar to estimates of n SMBH in the local Universe. We discuss how these results test various theories for SMBH formation.

CHAOS. VIII. Far-ultraviolet Spectra of M101 and the Impact of Wolf–Rayet Stars* ∗Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive 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.

We investigate the stellar and nebular properties of nine H ii regions in the spiral galaxy M101 with far-ultraviolet (FUV; ∼900–2000 Å) and optical (∼3200–10,000 Å) spectra. We detect significant C iii] λλ1907,1909 nebular emission in seven regions, but O iii] λ1666 only in the lowest-metallicity region. We produce new analytic functions of the carbon ionization correction factors as a function of metallicity in order to perform a preliminary C/O abundance analysis. The FUV spectra also contain numerous stellar emission and P-Cygni features that we fit with luminosity-weighted combinations of single-burst Starburst99 and BPASS models. We find that the best-fit Starburst99 models closely match the observed very-high-ionization P-Cygni features, requiring very hot, young (≲3 Myr), metal-enriched massive stars. The youngest stellar populations are strongly correlated with broad He ii emission, nitrogen Wolf–Rayet (WR) FUV and optical spectral features, and enhanced N/O gas abundances. Thus, the short-lived WR phase may be driving excess emission in several N P-Cygni wind features (λ955, λ991, λ1720) that bias the stellar continuum fits to higher metallicities relative to the gas-phase metallicities. Accurate characterization of these H ii regions requires additional inclusion of WR stars in the stellar population synthesis models. Our FUV spectra demonstrate that the ∼900–1200 Å FUV can provide a strong test bed for future WR atmosphere and evolution models.

Toward an Auditory Virtual Observatory

The large ecosystem of observations generated by major space telescope missions can be remotely analyzed using interoperable virtual observatory technologies. In this context of astronomical big data analysis, sonification has the potential of adding a complementary dimension to visualization, enhancing the accessibility of the archives, and offering an alternative strategy to be used when overlapping issues are found in purely graphical representations. This article presents a collection of sonification and musification prototypes that explore the case studies of the MILES and STELIB stellar libraries from the Spanish Virtual Observatory and the Kepler and TESS light curve databases from the Space Telescope Science Institute archive. Using automation and deep learning algorithms, it offers a “palette” of resources that could be used in future developments oriented toward an auditory virtual observatory proposal. The work includes a user study with quantitative and qualitative feedback from specialized and nonspecialized users analyzing the use of sine waves and musical instrument mappings for revealing overlapped lines in galaxy transmission spectra, confirming the need for training and prior knowledge for the correct interpretation of accurate sonifications, and providing potential guidelines to inspire future designs of widely accepted auditory representations for outreach purposes.

Boron Abundances in Early B Dwarfs of the Galactic Open Cluster NGC 3293* * Based on observations made 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. These observations are associated with proposal GO-14673.

New boron abundances or upper limits have been determined for eight early B stars in the young Galactic open cluster NGC 3293, using UV spectra obtained by the Hubble Space Telescope Cosmic Origins Spectrograph. With previous observations, there are now 18 early B stars in this cluster with boron measurements. Six of the newly observed stars have projected rotational velocities greater than 200 km s−1, allowing new constraints on rotationally driven mixing in main-sequence stars. When comparing to synthetic model populations, we find that the majority of our sample stars agree well with the predicted trends of stronger boron depletion for larger rotation and for larger mass or luminosity. Based on those, a smaller than the canonical rotational mixing efficiency (f c ≈ 0.0165 versus the more standard value of 0.033) appears to be favored. In addition, the five mostly slowly rotating stars, when considered as a group, tend to show more boron depletion than expected from rotational mixing, and we speculate that most or all of these originate from binary mergers.

Resolving Red Giant Winds with the Hubble Space Telescope* *Based on observations made 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. These observations are associated with programs GO-15903 and GO-15904.

We describe recent spectroscopic observations of red giant stars made by the Space Telescope Imaging Spectrograph (STIS) instrument on board the Hubble Space Telescope, which has provided spatially resolved observations of the warm chromospheric winds that predominate for early K to mid-M giants. The H i Lyα lines of a set of 11 red giants observed with the STIS/E140M echelle grating are first analyzed to ascertain wind H i column densities and total wind mass-loss rates. The M giants have estimated mass-loss rates of Ṁ=(14–86)×10−11 M ⊙ yr−1, while the K giants with detected wind absorption have weaker winds with Ṁ=(1.5–2.8)×10−11 M ⊙ yr−1. We use long-slit spectra of H i Lyα for two particular red giants, α Tau (K5 III) and γ Cru (M3.5 III), to study the spatial extent of the Lyα emission. From these data we estimate limits for the extent of detectable emission, which are r = 193 R * for γ Cru and r = 44 R * for α Tau. The cross-dispersion emission profiles in the STIS echelle spectra of the larger sample of red giants also show evidence for spatial resolution, not only for H i Lyα but for other lines with visible wind absorption, such as Fe ii, Mg ii, Mg i, O i, and C ii. We characterize the nature of these spatial signatures. The spatial extent is far more apparent for the M giants than for the K giants, consistent with the stronger winds found for the M giants from the Lyα analysis.

Gas-dynamical Mass Measurements of the Supermassive Black Holes in the Early-type Galaxies NGC 4786 and NGC 5193 from ALMA and HST Observations* *Based on observations made 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 NAS5-26555. These observations are associated

We present molecular gas-dynamical mass measurements of the central black holes in the giant elliptical galaxies NGC 4786 and NGC 5193, based on CO (2−1) observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope near-infrared imaging. The central region in each galaxy contains a circumnuclear disk that exhibits orderly rotation with projected line-of-sight velocities of ∼270 km s−1. We build gas-dynamical models for the rotating disk in each galaxy and fit them directly to the ALMA data cubes. At 0.″31 resolution, the ALMA observations do not fully resolve the black hole sphere of influence (SOI), and neither galaxy exhibits a central rise in rotation speed, indicating that emission from deep within the SOI is not detected. As a result, our models do not tightly constrain the central black hole mass in either galaxy, but they prefer the presence of a central massive object in both galaxies. We measure the black hole mass to be (MBH/108M⊙)=5.0±0.2[1σstatistical]−1.3+1.4[systematic] in NGC 4786 and (MBH/108M⊙)=1.4±0.03[1σstatistical]−0.1+1.5[systematic] in NGC 5193. The largest component of each measurement’s error budget is from the systematic uncertainty associated with the extinction correction in the host galaxy models. This underscores the importance of assessing the impact of dust attenuation on the inferred M BH.

A JWST Project on 47 Tucanae. Overview, Photometry, and Early Spectroscopic Results of M Dwarfs and Observations of Brown Dwarfs* *The main data set presented in this article was obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/6t82-4360.

James Webb Space Telescope (JWST) observations have been demonstrated to be efficient in detecting multiple stellar populations in globular clusters (GCs) in the low-mass regime of M dwarfs. We present an overview, and first results, of different projects that can be explored by using the JWST observations gathered under program GO2560 for 47 Tucanae, the first program entirely devoted to the investigation of multiple populations in very-low-mass stars, which includes spectroscopic data for the faintest GC stars for which spectra are available. Our color–magnitude diagram (CMD) shows some substructures for ultracool stars, including gaps and breaks in slope. In particular, we observe both a gap and a minimum in the F322W2 luminosity function less than 1 mag apart, and discuss which it could be associated with the H-burning limit. We detect stars fainter than this minimum, very likely brown dwarfs. We corroborate the ubiquity of the multiple populations across different masses, from ∼0.1 M ⊙ up to red giants (∼0.8 M ⊙). The oxygen range inferred for the M dwarfs, both from the CMD and from the spectra of two M dwarfs associated with different populations, is similar to that observed for giants. We have not detected any difference between the fractions of stars in distinct populations across stellar masses ≳ 0.1 M ⊙. This work demonstrates the JWST's capability in uncovering multiple populations within M dwarfs and illustrates the possibility to analyze very-low-mass stars in GCs approaching the H-burning limit and the brown-dwarf sequence.

Aperture and Resolution Effects on Ultraviolet Star-forming Properties: Insights from Local Galaxies and Implications for High-redshift Observations* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive 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.

We present an analysis of the effects of spectral resolution and aperture scale on derived galaxy properties using far-ultraviolet (FUV) spectra of local star-forming galaxies from the International Ultraviolet Explorer (R ∼ 250, field of view (FOV) ∼ 10″ × 20″) and Cosmic Origins Spectrograph on the Hubble Space Telescope (R ∼ 15,000, FOV ∼ 2.″5). Using these spectra, we measured FUV luminosities, spectral slopes, dust attenuation, and equivalent widths. We find that galaxies with one dominant stellar cluster have FUV properties that are independent of aperture size, while galaxies with multiple bright clusters are sensitive to the total light fraction captured by the aperture. Additionally, we find significant correlations between the strength of stellar and interstellar absorption lines and metallicity, indicating metallicity-dependent line-driven stellar winds and interstellar macroscopic gas flows shape stellar and interstellar spectral lines, respectively. The observed line strength versus metallicity relation of stellar-wind lines agrees with the prediction of population synthesis models for young starbursts. In particular, measurements of the strong stellar C iv λλ1548, 1550 line provide an opportunity to determine stellar abundances as a complement to gas-phase abundances. We provide a relation between the equivalent width of the C iv line and the oxygen abundance of the galaxy. We discuss this relation in terms of the stellar-wind properties of massive stars. As the driving lines in stellar winds are mostly ionized iron species, the C iv line may eventually offer a method to probe α-element-to-iron ratios in star-forming galaxies once consistent models with nonsolar abundance ratios are available. These results have important implications for the galaxy-scale, low-resolution observations of high-redshift galaxies from JWST (R ∼ 100–3500).

The Metallicities of Five Small High-velocity Clouds* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program 15887.

High-velocity clouds (HVCs) are multiphase gas structures whose velocities (∣v LSR∣ ≥ 100 km s−1) are too high to be explained by Galactic disk rotation. While large HVCs are well characterized, compact and small HVCs (with H i angular sizes of a few degrees) are poorly understood. Possible origins for such small clouds include Milky Way (MW) halo gas or fragments of the Magellanic System, but neither their origin nor their connection to the MW halo has been confirmed. We use new Hubble Space Telescope/Cosmic Origins Spectrograph UV spectra and Green Bank Telescope H i spectra to measure the metallicities of five small HVCs in the southern Galactic sky projected near the Magellanic System. We build a set of distance-dependent Cloudy photoionization models for each cloud and calculate their ionization-corrected metallicities. All five small HVCs have oxygen metallicities ≤0.17 Z ⊙, indicating they do not originate in the disk of the MW. Two of the five have metallicities of 0.16–0.17 Z ⊙, similar to the Magellanic Stream, suggesting these clouds are fragments of the Magellanic System. The remaining three clouds have much lower metallicities of 0.02–0.04 Z ⊙. While the origin of these low-metallicity clouds is unclear, they could be gaseous minihalos or gas stripped from dwarf galaxies by ram pressure or tidal interactions. These results suggest that small HVCs do not all reside in the inner MW halo or the Magellanic System, but instead can trace more distant structures.

An Algorithm to Mitigate Charge Migration Effects in Data from the Near Infrared Imager and Slitless Spectrograph on the James Webb Space Telescope* *This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association

We present an algorithm that mitigates the effects of charge migration due to the “brighter-fatter effect” (BFE) that occurs for highly illuminated stars in the Teledyne HAWAII-2RG detectors used in the NIRCam, NIRISS, and NIRSpec science instruments aboard the James Webb Space Telescope (JWST). The impact of this effect is most significant for photometry and spectrophotometry of bright stars in data for which the point-spread function (PSF) is undersampled, which is the case for several observing modes of the NIRISS instrument. The main impact of BFE to NIRISS data is incorrect count rate determinations for pixels in the central regions of PSFs of bright stars due to jump detections that are caused by charge migration from peak pixels to surrounding pixels. The effect is especially significant for bright compact sources in resampled, distortion-free images produced by the drizzle algorithm: quantitatively, apparent flux losses of >50% can occur in such images due to BFE. We describe the algorithm of the “charge_migration” mitigation step that has been implemented in version 10.0 of the operational JWST calibration pipeline as of 2023 December 5. We illustrate the impact of this step in terms of the resulting improvements of the precision of imaging photometry of point sources. The algorithm renders the effects of BFE on photometry and surface brightness measurements to stay within 1%.

White Dwarf Photospheric Abundances in Cataclysmic Variables. IV. Deriving the [N/C] Ratio* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of University for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

We present results from our ongoing far-ultraviolet archival analysis of cataclysmic variable white dwarf (WD) abundances for six more systems: four SU UMa dwarf novae (BW Scl, SW UMa, BC UMa, and VW Hyi) together with the dwarf nova RX And, and the novalike DW UMa. To derive a reliable nitrogen abundance, for the four SU UMa systems (with a WD temperature T wd ∼ 14,000 to ∼22,000 K), we use the dominant N i (1492 Å) absorption line; for DW UMa (with T wd possibly as high as 60,000 K), we use the N v (∼1240 Å) doublet; and for RX And (with T wd = 33,800 K), we use the N iii (1183.0 and 1184.6 Å) absorption lines. We find a [N/C] ratio of the order of 1–100 (in solar units). Oxygen, silicon, phosphorus are mostly underabundant while aluminum is mostly overabundant. We also derive magnesium, sulfur, calcium, and iron for a few systems. VW Hyi has a solar composition secondary implying the suprasolar [N/C] ratio very likely originates in the WD itself, e.g., accretion-driven dredge-up, mixing, and convection bringing material from deeper regions to the WD surface. If the donor star in the other five systems is nonevolved, the WD is the origin for the [N/C] ratio in these systems, either directly as in VW Hyi or due to contamination of the donor and accretion disk by the repetitive explosive CNO burning during the common envelope stage of the nova explosions.

Observations of Multiphase, High-velocity, Shocked Gas in the Vela Supernova Remnant* *Based on observations made with the NASA/ESA Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer, obtained from the MAST data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on

We present an analysis of high-resolution far-UV archival spectra obtained with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope of the star HD 75309, which probes high-velocity shocked gas in the Vela supernova remnant (SNR). We examine high-velocity features from intrinsically strong absorption lines of O i, Si ii, Si ii*, C ii, C ii*, and Si iii. We also detect high-velocity components in the N v doublet and compare these features to observations of high-velocity O vi absorption, available from archival Far Ultraviolet Spectroscopic Explorer data. Kinetic temperatures are derived from the observed fractional abundances of the various ions, while gas densities and thermal pressures are obtained from the relative populations in excited fine-structure levels of C ii and Si ii. Our results indicate that the highly ionized species at high velocity probe gas in a region immediately behind a shock driven into an interstellar cloud, while the lower-ionization species trace material further downstream in the cooling region of the postshock flow. Low-velocity N v and O vi absorption may trace gas in a conductive boundary layer between the unshocked portion of the cloud and the hot X-ray-emitting intercloud medium. Temporal variations in high-velocity Ca ii absorption features observed toward HD 75309 further confirm the highly inhomogeneous nature of the interstellar medium interacting with the Vela SNR.

The Metallicity Variations Along the Chromosome Maps: The Globular Cluster 47 Tucanae* *Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 105.20NB, and on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

The “chromosome maps” (ChMs) of globular clusters (GCs) have revealed that these ancient structures are inhomogeneous in metallicity in various ways and in different natures. Type II GCs generally display larger variations, sometimes coupled with slow neutron-capture (s) element enrichments on the ChMs redder sequences, which have been interpreted as due to multiple generations of stars. On the other hand, most GCs have inhomogeneous first populations (1P) in the form of large ranges in the ΔF275W,F814W values, pointing toward a not fully mixed pristine molecular cloud. We analyze the chemical composition of GC 47 Tucanae, which shows both inhomogeneous 1P stars and, although not formally a Type II GC, hosts a small number of stars distributed on the red side of the main stream of ChM stars. Our results suggest that 1P stars are inhomogeneous in the overall metallicity, with variations on the order of ∼0.10 dex in all the chemical species. The anomalous stars distributed on a redder sequence of the ChM are further enriched in metals but have no evidence for a significant enrichment in the s elements. Our three second population stars located on the normal component of the map have metallicities similar to those of the metal-richer 1P oup, suggesting that this population formed from these stars. Although three stars is a too-small sample to draw strong conclusions, the low spread in metals of these objects might point toward formation in a fully mixed medium, possibly after a cooling flow phase.

CLASSY VII Lyα Profiles: The Structure and Kinematics of Neutral Gas and Implications for LyC Escape in Reionization-era Analogs* * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive 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.

Lyα line profiles are a powerful probe of interstellar medium (ISM) structure, outflow speed, and Lyman-continuum escape fraction. In this paper, we present the Lyα line profiles of the Cosmic Origins Spectrograph (COS) Legacy Archive Spectroscopic SurveY, a sample rich in spectroscopic analogs of reionization-era galaxies. A large fraction of the spectra show a complex profile, consisting of a double-peaked Lyα emission profile in the bottom of a damped, Lyα absorption trough. Such profiles reveal an inhomogeneous ISM. We successfully fit the damped Lyα absorption and the Lyα emission profiles separately, but with complementary covering factors, a surprising result because this approach requires no Lyα exchange between high-N H i and low-N H i paths. The combined distribution of column densities is qualitatively similar to the bimodal distributions observed in numerical simulations. We find an inverse relation between Lyα peak separation and the [O iii]/[O ii] flux ratio, confirming that the covering fraction of Lyman-continuum-thin sightlines increases as the Lyα peak separation decreases. We combine measurements of Lyα peak separation and Lyα red peak asymmetry in a diagnostic diagram, which identifies six Lyman-continuum leakers in the COS Legacy Archive Spectrocopy SurveY (CLASSY) sample. We find a strong correlation between the Lyα trough velocity and the outflow velocity measured from interstellar absorption lines. We argue that greater vignetting of the blueshifted Lyα peak, relative to the redshifted peak, is the source of the well-known discrepancy between shell-model parameters and directly measured outflow properties. The CLASSY sample illustrates how scattering of Lyα photons outside the spectroscopic aperture reshapes Lyα profiles because the distances to these compact starbursts span a large range.

Comparing Globular Cluster System Properties with Host Galaxy Environment* * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the Data Archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with programs 14219 and 15265.

We present Hubble Space Telescope photometry in the optical (F475X) and near-infrared (F110W) bands of the globular cluster (GC) systems of the inner halos of a sample of 15 massive elliptical galaxies. The targets are selected from the volume-limited MASSIVE survey, and chosen to sample a range of environments from sparsely populated groups to the brightest cluster galaxies in dense clusters. We also present a quantitative model of the relation between (F475X − F110W) color and cluster metallicity [M/H], using simulated GCs. Because much of the GC population in such galaxies is built up through accretion, the metallicity distribution of the GC systems might be expected to vary with galaxy environment. The photometry is used to create a completeness-corrected metallicity distribution for each galaxy in the sample, and to fit a double Gaussian curve to each histogram in order to model the two standard red and blue subpopulations. Finally, the properties of the GC metallicity distribution are correlated against galaxy environment. We find that almost no GCS properties and host galaxy environmental properties are correlated, with the exception of a weak but consistent correlation between blue fraction and nth-nearest-neighbor surface density. The results suggest that the systemic properties of the GC systems, at least in the inner to midhalo regions, are influenced more strongly by the local environment at early times, rather than by the environmental properties we see today.

X-Ray and Near-Infrared Observations of the Middle-aged Pulsar B1055–52, Its Multiwavelength Spectrum, and Proper Motion* * Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. Based also on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by

Previous observations of the middle-aged γ-ray, X-ray, and radio pulsar B1055–52 indicated some peculiarities, such as a suspected changing of the X-ray flux and spectral parameters, a large excess of the alleged thermal component of the UV spectrum over the Rayleigh–Jeans extension of the X-ray thermal spectrum, and a possible double break in the nonthermal spectral component between the optical and X-ray bands. We observed PSR B1055–52 with the XMM-Newton observatory in X-rays and the Hubble Space Telescope in near-infrared (NIR). The analysis of the XMM-Newton observations does not support the notion of long-term changes in the X-ray flux and broadband X-ray spectrum of the pulsar. Using an observing mode less affected by background noise than the previous XMM-Newton observations, we constrain the power-law (PL) spectral index as (F ν ∝ ν α ) in the energy band 3–10 keV. From the NIR–optical data we obtain a PL slope α O = −0.24 ± 0.10 for the color index E(B − V) = 0.03 mag. The slopes and fluxes of the NIR–optical and X-ray nonthermal spectra suggest that the NIR through X-ray emission can be described by the same PL and is generated by the same mechanism, unlike the pulsar’s γ-ray emission. The excess of the UV thermal component over the extension of the X-ray thermal component became smaller but did not disappear, indicating a nonuniformity of the bulk surface temperature. The NIR data also enable us to measure the proper motion accurately, with values μ α = 47.5 ± 0.7 mas yr−1 and μ δ = −8.7 ± 0.7 mas yr−1.

The Distribution of Metallicities in the Local Galactic Interstellar Medium* *Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the MAST data archive at the Space Telescope Science Institute. The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on data obtained from the

In this investigation, we present an analysis of the metallicity distribution that pertains to neutral gas in the local Galactic interstellar medium (ISM). We derive relative ISM metallicities for a sample of 84 sight lines probing diffuse atomic and molecular gas within 4 kpc of the Sun. Our analysis is based in large part on column density measurements reported in the literature for 22 different elements that are commonly studied in interstellar clouds. We supplement the literature data with new column density determinations for certain key elements and several individual sight lines important to our analysis. Our methodology involves comparing the relative gas-phase abundances of many different elements for a given sight line to simultaneously determine the strength of dust depletion in that direction and the overall metallicity offset. We find that many sight lines probe multiple distinct gas regions with different depletion properties, which complicates the metallicity analysis. Nevertheless, our results provide clear evidence that the dispersion in the metallicities of neutral interstellar clouds in the solar neighborhood is small (∼0.10 dex) and only slightly larger than the typical measurement uncertainties. We find no evidence for the existence of very low metallicity gas (as has recently been reported by De Cia et al.) along any of the 84 sight lines in our sample. Our results are consistent with a local Galactic ISM that is well mixed and chemically homogeneous.

White Dwarf Photospheric Abundances in Cataclysmic Variables. III. Five Dwarf Novae with an Evolved Secondary Donor Star* * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of University for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

In the last two decades infrared spectroscopy has brought mounting evidence, in the form of weak CO features together with enhanced 13C, of the presence of CNO-processed material in the atmosphere of the donor star of some nonmagnetic cataclysmic variables. Some of these donors also exhibit a temperature too high for their binary orbital period, indicating that they evolved off the main sequence before mass transfer began. The ultraviolet spectra of evolved donor systems exhibit strong N v (λ1240) and the almost complete absence of C iv (λ1550) emission lines. We present here an archival Hubble Space Telescope ultraviolet spectral analysis of five systems containing an evolved donor star. We derive their white dwarf masses, effective temperatures, and photospheric chemical abundances. The [N/C] ratio is very large, of the order 102–103 (in solar units) for the short-period systems V485 Cen, GZ Cet, and QZ Ser, and of the order 20 for the longer-period systems HS 0218 and EY Cyg. Silicon ([S/H]) is solar for GZ Cet and QZ Ser, suprasolar for V485 Cen, and subsolar for HS 0218 and EY Cyg. We also derive abundances of O, Mg, Al, Si, P, S, Ca, and Fe, which vary from system to system. The abundances we derived are consistent with the more evolved nature of the donor star (metal enriched, hydrogen depleted). It is impossible to confirm hydrogen deficiency for these systems, since at these wavelengths (1100–2000 Å) white dwarf spectra show little dependency on the [He/H] ratio, unless it is extremely large ([He/H] ≫ 1).