Archival Hubble Space Telescope Data Research Articles

The carbon-rich type Ic supernova 2016adj in the iconic dust lane of Centaurus A: Potential signatures of an interaction with circumstellar hydrogen

We present a comprehensive data set of supernova (SN) 2016adj located within the central dust lane of Centaurus A. SN 2016adj is significantly reddened and after correcting the peak apparent $B$-band magnitude ($m_B = 17.48 for Milky Way reddening and our inferred host-galaxy reddening parameters (i.e. V host and V host we estimated it reached a peak absolute magnitude of $M_B -18$. A detailed inspection of the optical and near-infrared (NIR) spectroscopic time series reveals a carbon-rich SN Ic and not a SN Ib/IIb as previously suggested in the literature. The NIR spectra show prevalent carbon-monoxide formation occurring already by $+$41 days past $B$-band maximum, which is $ 11$ days earlier than previously reported in the literature for this object. Interestingly, around two months past maximum, the NIR spectrum of SN 2016adj begins to exhibit H features, with a $+$97 days medium resolution spectrum revealing both Paschen and Bracket lines with absorption minima of $ 2,000$ km $, full-width-half-maximum emission velocities of $ 1,000$ km $, and emission line ratios consistent with a dense emission region. We speculate that these attributes are due to a circumstellar interaction (CSI) between the rapidly expanding SN ejecta and a H-rich shell of material that formed during the pre-SN phase. A bolometric light curve was constructed and a semi-analytical model fit suggests the SN synthesized 0.5 $M_ sun $ of 56Ni and ejected 4.7 $M_ sun $ of material, though these values should be approached with caution given the large uncertainties associated with the adopted reddening parameters and known light echo emission. Finally, inspection of the Hubble Space Telescope archival data yielded no progenitor detection.

Revisiting the Helium and Hydrogen Accretion Indicators at TWA 27B: Weak Mass Flow at Near-freefall Velocity

TWA 27B (2M1207b) is the first directly imaged planetary-mass (M p ≈ 5 M J) companion and was observed at 0.9–5.3 μm with ​​​JWST/NIRSpec. To understand the accretion properties of TWA 27B, we search for continuum-subtracted near-infrared helium and hydrogen emission lines and measure their widths and luminosities. We detect the He i triplet at 4.3σ and all Paschen-series lines covered by NIRSpec (Paα, Paβ, Paγ, Paδ) at 4σ–5σ. The three brightest Brackett-series lines (Brα, Brβ, Brγ) as well as Pfγ and Pfδ are tentative detections at 2σ–3σ. We provide upper limits on the other hydrogen lines, including on Hα through Hubble Space Telescope archival data. Three lines can be reliably deconvolved to reveal an intrinsic width Δv intrsc = (67 ± 9) km s−1, which is 60% of the surface freefall velocity. The line luminosities seem significantly too high to be due to chromospheric activity. Converting line luminosities to an accretion rate yields Ṁ≈5×10−9MJyr−1 when using scaling relationships for planetary masses, and Ṁ≈0.1×10−9MJyr−1 with extrapolated stellar scalings. Several of these lines represent the first detections at an accretor of such low mass. The weak accretion rate implies that formation is likely over. This analysis shows that JWST can be used to measure low line-emitting mass accretion rates onto planetary-mass objects, motivates deeper searches for the mass reservoir feeding TWA 27B, and hints that other young directly imaged objects might—hitherto unbeknownst—also be accreting.

HH 80/81: Structure and Kinematics of the Fastest Protostellar Outflow

Hubble Space Telescope (HST) images obtained in 2018 are combined with archival HST data taken in 1995 to detect changes and measure proper motions in the HH 80/81 shock complex, which is powered by the fastest known jet driven by a forming star, the massive object IRAS 18162-2048. Some persistent features close to the radio jet axis have proper motions of >1000 km s−1 away from IRAS 18162-2048. About 3–5 pc downstream from the IRAS source and beyond HH 80/81, Hα emission traces the rim of a parsec-scale bubble blown by the jet. Lower speed motions are seen in [S ii] away from the jet axis; these features have a large component of motion at right angles to the jet. We identify new HH objects and H2 shocks in the counterflow opposite HH 80/81. The northeastern counterflow to HH 80/81 exhibits an extended but faint complex of 2.12 μm H2 shocks. The inner portion of the outflow is traced by dim 1.64 μm [Fe ii] emission. The full extent of this outflow is at least 1500″ (∼10 pc in projection at a distance of 1.4 kpc). We speculate about the conditions responsible for the production of the ultrafast jet and the absence of prominent large-scale molecular outflow lobes.

Dynamical masses and ages of Sirius-like systems

ABSTRACT We measure precise orbits and dynamical masses and derive age constraints for six confirmed and one candidate Sirius-like systems, including the Hyades member HD 27483. Our orbital analysis incorporates radial velocities, relative astrometry, and Hipparcos–Gaia astrometric accelerations. We constrain the main-sequence lifetime of a white dwarf’s progenitor from the remnant’s dynamical mass and semi-empirical initial–final mass relations and infer the cooling age from mass and effective temperature. We present new relative astrometry of HD 27483 B from Keck/NIRC2 observations and archival Hubble Space Telescope data, and obtain the first dynamical mass of ${0.798}_{-0.041}^{+0.10}$ M⊙, and an age of ${450}_{-180}^{+570}$ Myr, consistent with previous age estimates of Hyades. We also measure precise dynamical masses for HD 114174 B (0.591 ± 0.011 M⊙) and HD 169889 B (${0.526}_{-0.037}^{+0.039}$ M⊙), but their age precisions are limited by their uncertain temperatures. For HD 27786 B, the unusually small mass of 0.443 ± 0.012 M⊙ suggests a history of rapid mass-loss, possibly due to binary interaction in its progenitor’s asymtotic giant branch phase. The orbits of HD 118475 and HD 136138 from our radial velocity fitting are overall in good agreement with Gaia DR3 astrometric two-body solutions, despite moderate differences in the eccentricity and period of HD 136138. The mass of ${0.580}_{-0.039}^{+0.052}$ M⊙ for HD 118475 B and a speckle imaging non-detection confirms that the companion is a white dwarf. Our analysis shows examples of a rich number of precise WD dynamical mass measurements enabled by Gaia DR3 and later releases, which will improve empirical calibrations of the white dwarf initial–final mass relation.

PHANGS–JWST First Results: A Combined HST and JWST Analysis of the Nuclear Star Cluster in NGC 628

We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (r eff ∼ 5 pc) and ellipticity (ϵ ∼ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared, r eff ∼ 12 pc, ϵ ∼ 0.4, and n ∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of , as derived through B − V, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.

The disappearances of six supernova progenitors

ABSTRACT As part of a larger completed Hubble Space Telescope (HST) Snapshot program, we observed the sites of six nearby core-collapse supernovae (SNe) at high spatial resolution: SN 2012A, SN 2013ej, SN 2016gkg, SN 2017eaw, SN 2018zd, and SN 2018aoq. These observations were all conducted at sufficiently late times in each SN’s evolution to demonstrate that the massive-star progenitor candidate identified in each case in pre-explosion imaging data had indeed vanished and was therefore most likely the actual progenitor. However, we have determined for SN 2016gkg that the progenitor candidate was most likely a blend of two objects: the progenitor, which itself has likely vanished, and another closely neighbouring star. We thus provide a revised estimate of that progenitor’s properties: a binary system with a hydrogen-stripped primary star at explosion with effective temperature ≈6300–7900 K, bolometric luminosity ≈104.65 L⊙, radius ≈118–154 R⊙, and initial mass 9.5–11 M⊙. Utilizing late-time additional archival HST data nearly contemporaneous with our Snapshots, we also show that SN 2017eaw had a luminous ultraviolet excess, which is best explained as a result of ongoing interaction of the SN shock with pre-existing circumstellar matter. We offer the caveat, particularly in the case of SN 2013ej, that obscuration from SN dust may be compromising our conclusions. This sample adds to the growing list of confirmed or likely core-collapse SN progenitors.

Demographics of the M-star Multiple Population in the Orion Nebula Cluster

We present updated results constraining multiplicity demographics for the stellar population of the Orion Nebula Cluster (ONC, a high-mass, high-density star-forming region), across primary masses 0.08–0.7 M ⊙. Our study utilizes archival Hubble Space Telescope data obtained with the Advanced Camera for Surveys using multiple filters (GO-10246). Previous multiplicity surveys in low-mass, low-density associations like Taurus identify an excess of companions to low-mass stars roughly twice that of the Galactic field and find the mass ratio distribution consistent with the field. Previously, we found the companion frequency to low-mass stars in the ONC is consistent with the Galactic field over mass ratios = 0.6–1.0 and projected separations = 30–160 au, without placing constraints on the mass ratio distribution. In this study, we investigate the companion population of the ONC with a double point-spread function (PSF) fitting algorithm sensitive to separations larger than 10 au (0.″025) using empirical PSF models. We identified 44 companions (14 new), and with a Bayesian analysis we estimate the companion frequency to low-mass stars in the ONC = 0.13 and the index of the power-law fit to the mass ratio distribution = 2.08 over all mass ratios and projected separations of 10–200 au. We find the companion frequency in the ONC is consistent with the Galactic field population, likely from states of high transient stellar density, and a probability of 0.002 that it is consistent with that of Taurus. We also find the ONC mass ratio distribution is consistent with the field and Taurus, potentially indicative of its primordial nature, a direct outcome of the star formation process.

Joint lensing–dynamics constraint on the elliptical galaxy mass profile from the largest galaxy–galaxy lens sample

AbstractFrom various lensing and non-lensing observations, the total density profile in elliptical galaxies is well approximated by a power law mass distribution. However, as neither the dark matter nor the baryons individually follow the power law, this observational result has been referred to as the “bulge–halo conspiracy”. We investigate the consistency of this conspiracy with higher precision than previous studies with the largest ever sample of galaxy–galaxy lenses assembled from archival Hubble Space Telescope (HST) data. By performing lens modelling with power law profiles and combining them with stellar dynamics using the mass-sheet transformation, we can constrain the profile’s deviation from the power law model over a redshift range of 0.1 to 0.8. To uniformly model such a large sample of lens models, we use the automated modelling pipeline dolphin. We also investigate the evolutionary trend of the total mass density slope of the lensing galaxies.

Forbidden hugs in pandemic times

We present an observational study of the luminous red nova (LRN) AT 2021biy in the nearby galaxy NGC 4631. The field of the object was routinely imaged during the pre-eruptive stage by synoptic surveys, but the transient was detected only at a few epochs from ∼231 days before maximum brightness. The LRN outburst was monitored with unprecedented cadence both photometrically and spectroscopically. AT 2021biy shows a short-duration blue peak, with a bolometric luminosity of ∼1.6 × 1041 erg s−1, followed by the longest plateau among LRNe to date, with a duration of 210 days. A late-time hump in the light curve was also observed, possibly produced by a shell-shell collision. AT 2021biy exhibits the typical spectral evolution of LRNe. Early-time spectra are characterised by a blue continuum and prominent H emission lines. Then, the continuum becomes redder, resembling that of a K-type star with a forest of metal absorption lines during the plateau phase. Finally, late-time spectra show a very red continuum (TBB ≈ 2050 K) with molecular features (e.g., TiO) resembling those of M-type stars. Spectropolarimetric analysis indicates that AT 2021biy has local dust properties similar to those of V838 Mon in the Milky Way Galaxy. Inspection of archival Hubble Space Telescope data taken on 2003 August 3 reveals a ∼20 M⊙ progenitor candidate with log (L/L⊙) = 5.0 dex and Teff = 5900 K at solar metallicity. The above luminosity and colour match those of a luminous yellow supergiant. Most likely, this source is a close binary, with a 17–24 M⊙ primary component.

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIII. Proper-motion Catalogs and Internal Kinematics

A number of studies based on the data collected by the Hubble Space Telescope (HST) GO-13297 program “HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation” have investigated the photometric properties of a large sample of Galactic globular clusters and revolutionized our understanding of their stellar populations. In this paper, we expand upon previous studies by focusing our attention on the stellar clusters’ internal kinematics. We computed proper motions for stars in 56 globular clusters and one open cluster by combining the GO-13297 images with archival HST data. The astrophotometric catalogs released with this paper represent the most complete and homogeneous collection of proper motions of stars in the cores of stellar clusters to date, and expand the information provided by the current (and future) Gaia data releases to much fainter stars and into the crowded central regions. We also census the general kinematic properties of stellar clusters by computing the velocity dispersion and anisotropy radial profiles of their bright members. We study the dependence on concentration and relaxation time, and derive dynamical distances. Finally, we present an in-depth kinematic analysis of the globular cluster NGC 5904.

Evaluating the feasibility of interpretable machine learning for globular cluster detection

Extragalactic globular clusters (GCs) are important tracers of galaxy formation and evolution because their properties, luminosity functions, and radial distributions hold valuable information about the assembly history of their host galaxies. Obtaining GC catalogues from photometric data involves several steps which will likely become too time-consuming to perform on the large data volumes that are expected from upcoming wide-field imaging projects such as Euclid. In this work, we explore the feasibility of various machine learning methods to aid the search for GCs in extensive databases. We use archivalHubbleSpace Telescope data in theF475WandF850LPbands of 141 early-type galaxies in the Fornax and Virgo galaxy clusters. Using existing GC catalogues to label the data, we obtained an extensive data set of 84929 sources containing 18556 GCs and we trained several machine learning methods both on image and tabular data containing physically relevant features extracted from the images. We find that our evaluated machine learning models are capable of producing catalogues of a similar quality as the existing ones which were constructed from mixture modelling and structural fitting. The best performing methods, ensemble-based models such as random forests, and convolutional neural networks recover ∼90−94% of GCs while producing an acceptable amount of false detections (∼6−8%), with some falsely detected sources being identifiable as GCs which have not been labelled as such in the used catalogues. In the magnitude range 22 < m4_g ≤ 24.5 mag, 98−99% of GCs are recovered. We even find such high performance levels when training on Virgo and evaluating on Fornax data (and vice versa), illustrating that the models are transferable to environments with different conditions, such as different distances than in the used training data. Apart from performance metrics, we demonstrate how interpretable methods can be utilised to better understand model predictions, recovering that magnitudes, colours, and sizes are important properties for identifying GCs. Moreover, comparing colour distributions from our detected sources to the reference distributions from input catalogues finds great agreement and the mean colour is recovered even for systems with fewer than 20 GCs. These are encouraging results, indicating that similar methods trained on an informative sub-sample can be applied for creating GC catalogues for a large number of galaxies, with tools being available for increasing the transparency and reliability of said methods.

A search for ionised gas outflows in an Hα imaging atlas of nearby LINERs

Context. Outflows play a major role in the evolution of galaxies. However, we do not yet have a complete picture of their properties (extension, geometry, orientation, and clumpiness). For low-luminosity active galactic nuclei (AGNs), in particular low-ionisation nuclear emission line regions (LINERs), the rate of outflows and their properties are largely unknown. Aims. The main goal of this work is to create the largest up-to-date atlas of ionised gas outflow candidates in a sample of 70 nearby LINERs. We aim to use narrowband imaging data to analyse the morphological properties of the ionised gas nuclear emission of these galaxies and to identify signatures of extended emission with distinctive outflow morphologies. Methods. We obtained new imaging data from Alhambra Faint Object Spectrograph and Camera (ALFOSC)/Nordic Optical Telescope (NOT) for a total of 32 LINERs, and complemented it with Hubble Space Telescope archival data (HST) for six objects. We extracted the Hα emission of the galaxies and used it to morphologically classify the circumnuclear emission. We combined our results with those from the literature for additional 32 targets. We additionally obtained soft X-ray data from Chandra archive to compare this emission with the ionised gas. Results. The distribution of the ionised gas in these LINER indicates that ∼32% show Bubble emission, ∼28% show Core-halo unresolved emission, and ∼21% of the sample have a Disky distribution. Dust lanes prevent any detailed classification for ∼11% of the sample, which we call Dusty. The soft X-ray emission is in most cases (∼60%) co-spatial with the ionised gas. If we account for the kinematical information which is available for a total of 60 galaxies, we end up with a total of 48% of the LINERs with detected outflows or inflows in the emission lines (50% considering only kinematical information based on Integral Field Spectroscopic data). Conclusions. Our results suggest that the incidence of outflows in LINERs may vary from 41% to 56%, based on both the Hα morphology and the kinematical information from the literature. The ionised gas seems to be correlated with the soft X-ray emission, so that they may have a common origin. We discuss the use of Hα imaging for the pre-selection of candidates likely hosting ionised gas outflows.

The Smallest Scale of Hierarchy Survey (SSH) – II. Extended star formation and bar-like features in the dwarf galaxy NGC 3741: recent merger or ongoing gas accretion?

ABSTRACTUsing Large Binocular Telescope deep imaging data from the Smallest Scale of Hierarchy Survey (SSH) and archival Hubble Space Telescope data, we reveal the presence of two elongated stellar features contiguous to a bar-like stellar structure in the inner regions of the dwarf irregular galaxy NGC 3741. These structures are dominated by stars younger than a few hundred Myr and collectively are about twice as extended as the old stellar component. These properties are very unusual for dwarf galaxies in the nearby Universe and difficult to explain by hydro-dynamical simulations. From the analysis of archival 21-cm observations, we find that the young stellar ‘bar’ coincides with an H i high-density region proposed by previous studies to be a purely gaseous bar; we furthermore confirm radial motions of a few km s−1, compatible with an inflow/outflow, and derive a steeply rising rotation curve and high H i surface density at the centre, indicating a very concentrated mass distribution. We propose that the peculiar properties of the stellar and gaseous components of NGC 3741 may be explained by a recent merger or ongoing gas accretion from the intergalactic medium, which caused gas inflows towards the galaxy centre and triggered star formation a few hundred Myr ago. This event may explain the young and extended stellar features, the bar-like structure, the very extended H i disc and the central H i spiral arms. The high central H i density and the steeply rising rotation curve suggest that NGC 3741 may be the progenitor or the descendant of a starburst dwarf.

Equivalent widths of Lyman α emitters in MUSE-Wide and MUSE-Deep

Context. The hydrogen Lyman α line is often the only measurable feature in optical spectra of high-redshift galaxies. Its shape and strength are influenced by radiative transfer processes and the properties of the underlying stellar population. High equivalent widths of several hundred Å are especially hard to explain by models and could point towards unusual stellar populations, for example with low metallicities, young stellar ages, and a top-heavy initial mass function. Other aspects influencing equivalent widths are the morphology of the galaxy and its gas properties. Aims. The aim of this study is to better understand the connection between the Lyman α rest-frame equivalent width (EW0) and spectral properties as well as ultraviolet (UV) continuum morphology by obtaining reliable EW0 histograms for a statistical sample of galaxies and by assessing the fraction of objects with large equivalent widths. Methods. We used integral field spectroscopy from the Multi Unit Spectroscopic Explorer (MUSE) combined with broad-band data from the Hubble Space Telescope (HST) to measure EW0. We analysed the emission lines of 1920 Lyman α emitters (LAEs) detected in the full MUSE-Wide (one hour exposure time) and MUSE-Deep (ten hour exposure time) surveys and found UV continuum counterparts in archival HST data. We fitted the UV continuum photometric images using the Galfit software to gain morphological information on the rest-UV emission and fitted the spectra obtained from MUSE to determine the double peak fraction, asymmetry, full-width at half maximum, and flux of the Lyman α line. Results. The two surveys show different histograms of Lyman α EW0. In MUSE-Wide, 20% of objects have EW0 > 240 Å, while this fraction is only 11% in MUSE-Deep and ≈16% for the full sample. This includes objects without HST continuum counterparts (one-third of our sample), for which we give lower limits for EW0. The object with the highest securely measured EW0 has EW0 = 589 ± 193 Å (the highest lower limit being EW0 = 4464 Å). We investigate the connection between EW0 and Lyman α spectral or UV continuum morphological properties. Conclusions. The survey depth has to be taken into account when studying EW0 distributions. We find that in general, high EW0 objects can have a wide range of spectral and UV morphological properties, which might reflect that the underlying causes for high EW0 values are equally varied.

ESASky SSOSS: Solar System Object Search Service and the case of Psyche

Context. The store of data collected in public astronomical archives across the world is continuously expanding and, thus, providing a convenient interface for accessing this information is a major concern for ensuring a second life for the data. In this context, Solar System objects (SSOs) are often difficult or even impossible to query, owing to their ever-changing sky coordinates. Aims. Our study is aimed at providing the scientific community with a search service for all potential detections of SSOs among the ESA astronomy archival imaging data, called the Solar System Object Search Service (SSOSS). We illustrate its functionalities using the case of asteroid (16) Psyche, for which no information in the far-IR (70–500 μm) has previously been reported, to derive its thermal properties in preparation for the upcoming NASA Psyche mission. Methods. We performed a geometrical cross-match of the orbital path of each object, as seen by the satellite reference frame, with respect to the public high-level imaging footprints stored in the ESA archives. There are about 800 000 asteroids and 2000 comets included in the SSOSS, available through ESASky, providing both targeted and serendipitous observations. For this first release, three missions were chosen: XMM-Newton, the Hubble Space Telescope (HST), and Herschel. Results. We present a catalog listing all potential detections of asteroids within estimated limiting magnitude or flux limit in Herschel, XMM-Newton, and HST archival imaging data, including 909 serendipitous detections in Herschel images, 985 in XMM-Newton Optical Monitor camera images, and over 32 000 potential serendipitous detections in HST images. We also present a case study: the analysis of the thermal properties of Psyche from four serendipitous Herschel detections, combined with previously published thermal IR measurements. We see strong evidence for an unusual drop in (hemispherical spectral) emissivity, from 0.9 at 100 μm down to about 0.6 at 350 μm, followed by a possible but not well-constrained increase towards 500 μm, comparable to what was found for Vesta. The combined thermal data set puts a strong constraint on Psyche’s thermal inertia (between 20 to 80 J m−2 s−1/2 K−1) and favors an intermediate to low level surface roughness (below 0.4 for the rms of surface slopes). Conclusions. Using the example of Psyche, we show how the SSOSS provides fast access to observations of SSOs from the ESA astronomical archives, regardless of whether the particular object was the actual target. This greatly simplifies the task of searching, identifying and retrieving such data for scientific analysis.

Binary Formation in the Orion Nebula Cluster: Exploring the Substellar Limit

Abstract We present results constraining the multiplicity of the very low mass stars and substellar objects in the Orion Nebula Cluster (ONC). Our sample covers primary masses 0.012–0.1 M ⊙ using archival Hubble Space Telescope data obtained with the Advanced Camera for Surveys using multiple filters. Studying the binary populations of clusters provides valuable constraints of how the birth environment affects binary formation and evolution. Prior surveys have shown that the binary populations of high-mass, high-density star clusters like the ONC may substantially differ from those in low-mass associations. Very low mass stellar and substellar binaries at wide separations, >20 au, are statistically rare in the Galactic field and have been identified in stellar associations like Taurus-Auriga and Ophiuchus. They also may be susceptible to dynamical interactions, and their formation may be suppressed by feedback from ongoing star formation. We implement a double point-spread function (PSF) fitting algorithm using empirical, position-dependent PSF models to search for binary companions at projected separations >10 au (0.″025). With this technique, we identify seven very low mass binaries, five of which are new detections, resulting in a binary frequency of 12 − 3.2 + 6 % over mass ratios of 0.5–1.0 and projected separations of 20–200 au. We find an excess of very low mass binaries in the ONC compared to the Galactic field, with a probability of 10−6 that the populations are statistically consistent. The substellar population of the ONC may require further dynamical processing of the lowest binding energy binaries to resemble the field population.

Fragmenting Active Asteroid 331P/Gibbs

Abstract We describe active asteroid 331P/Gibbs (2012 F5) using archival Hubble Space Telescope (HST) data taken between 2015 and 2018. 331P is an outer main belt active asteroid with a long-lived debris trail that formed in 2011. Embedded in the debris trail we identify 19 fragments with radii between 0.04 and 0.11 km (albedo 0.05 assumed) containing about 1% of the mass of the primary nucleus. The largest shows a photometric range (∼1.5 mag), a V-shaped minimum, and a two-peaked lightcurve period near 9 hr, consistent with a symmetric contact binary. Less convincing explanations are that 331P-A is a monolithic, elongated splinter or that its surface shows hemispheric 4:1 albedo variations. The debris trail is composed of centimeter-sized and larger particles ejected with characteristic 10 cm s−1 speeds following a size distribution with index q = 3.7 ± 0.1 to 4.1 ± 0.2. The HST data show that earlier, ground-based measurements of the nucleus were contaminated by near-nucleus debris, which cleared by 2015. We find that the primary nucleus has effective radius 0.8 ± 0.1 km and is in rapid rotation (3.26 ± 0.01 hr), with a lightcurve range of 0.25 mag and a minimum density of 1600 kg m−3 if strengthless. The properties of 331P are consistent with (1) formation about 1.5 Myr ago by impact shattering of a precursor body, (2) spin-up by radiation torques to critical rotation, (3) ejection of about 1% of the nucleus mass in mid 2011 by rotational instability, and (4) subsequent evolution of the fragments and dispersal of the debris by radiation pressure.

Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES): Data Release I

Abstract We present the first Data Release (DR1) from the Hubble Space Telescope (HST) Ultraviolet Legacy Library of Young Stars as Essential Standards (ULLYSES) program, a Director’s Discretionary program devoting approximately 1000 HST orbits to the production of an ultraviolet spectroscopic library of young high- and low-mass stars in the local universe. The science products in this release are combined from individual, extracted and calibrated spectra obtained with the COS and STIS instruments aboard HST. Products are made using both archival HST data and new HST observations obtained through the ULLYSES program. DR1 acts as the first step toward completing a goal of generating a fully public data set for the purpose of enabling, supporting, and stimulating a broad range of transformative astrophysical research.

Luminosity Models and Density Profiles for Nuclear Star Clusters for a Nearby Volume-limited Sample of 29 Galaxies

Abstract Nuclear star clusters (NSCs) are dense stellar clusters that are found at the centers of a majority of galaxies. In this paper, we study the density profiles for 29 galaxies in a volume-limited survey within 10 Mpc to characterize their NSCs. These galaxies span a 3 × 108–8 × 1010 M ⊙ and a wide range of Hubble types. We use high-resolution Hubble Space Telescope archival data to create luminosity models for the galaxies using Sérsic profiles to parameterize the NSCs. We also provide estimates for photometric masses of NSCs and their host galaxies using color–M/L relationships and examine their correlation. We use the multi-Gaussian expansion to derive the NSC densities and their 3D mass-density profiles. The 3D density profiles characterize the NSC densities on scales as small as ∼1 pc, approaching the likely spheres of influence for BHs in these objects. We find that these densities correlate with galaxy mass, with NSC density profiles becoming both denser and flatter at higher galaxy masses. Most galaxy NSCs are denser than typical globular clusters. We parameterize the 3D NSC density profiles and their scatter and slope as a function of galaxy stellar mass to enable the construction of realistic nuclear mass profiles. Our fitted profiles and the derived relations are useful in predicting the rate of tidal disruption events in galaxies. We will verify the results of this paper in a follow-up paper that presents the dynamical modeling of the same sample of NSCs.

Is NGC 300 a pure exponential disk galaxy?

NGC 300 is a low-mass disk galaxy in the Sculptor group. In the literature, it has been identified as a pure exponential disk galaxy, as its luminosity profile can be well fit with a single exponential law over many disk scale lengths (Type I). We investigate the stellar luminosity distribution of NGC 300 using Hubble Space Telescope archive data, reaching farther and deeper than any other previous studies. Color-magnitude diagrams show a significant population of old red giant branch (RGB) stars in all fields out to R ∼ 19 kpc (32′), as well as younger populations in the inner regions. We construct the density profiles of the young, intermediate-aged, and old stellar populations, and find two clear breaks in the density profiles of the old RGB and intermediate-aged stars: one down bending (Type II) at R ∼ 5.9 kpc, and another up bending (Type III) at R ∼ 8.3 kpc. Moreover, the old RGB stars exhibit a negative radial color gradient with an upward bend at R ∼ 8 kpc, beyond which the stellar populations are uniformly old (>7 Gyr) and metal poor ([Fe/H] = −1.6−0.4+0.2 dex). The outer stellar component at R ⪆ 8 kpc is therefore well separated from the inner disk in terms of stellar density and stellar population. While our results cast doubt on the currently established wisdom that NGC 300 is a pure exponential disk galaxy, a more detailed survey should be carried out to identify the outskirts as either a disk or a stellar halo.