Archival Hubble Space Telescope Research Articles

A Radio Frequency Study of the Accreting Millisecond X-ray Pulsar, IGR J16597–3704, in the Globular Cluster NGC 6256

Abstract We present Karl G. Jansky Very Large Array radio frequency observations of the new accreting millisecond X-ray pulsar (AMXP), IGR J16597−3704, located in the globular cluster NGC 6256. With these data, we detect a radio counterpart to IGR J16597−3704, and determine an improved source position. Pairing our radio observations with quasi-simultaneous Swift/XRT X-ray observations, we place IGR J16597−3704 on the radio–X-ray luminosity plane, where we find that IGR J16597−3704 is one of the more radio-quiet neutron star low-mass X-ray binaries known to date. We discuss the mechanisms that may govern radio luminosity (and in turn jet production and evolution) in AMXPs. Furthermore, we use our derived radio position to search for a counterpart in archival Hubble Space Telescope and Chandra X-ray Observatory data, and estimate an upper limit on the X-ray luminosity of IGR J16597−3704 during quiescence.

HD 104860 and HD 192758: Two Debris Disks Newly Imaged in Scattered Light with the Hubble Space Telescope

Abstract We present the first scattered-light images of two debris disks around the F8 star HD 104860 and the F0V star HD 192758, respectively ∼45 and ∼67 pc away. We detected these systems in the F110W and F160W filters through our reanalysis of archival Hubble Space Telescope (HST) NICMOS data with modern starlight-subtraction techniques. Our image of HD 104860 confirms the morphology previously observed by Herschel in thermal emission with a well-defined ring at a radius of ∼114 au inclined by ∼58°. Although the outer edge profile is consistent with dynamical evolution models, the sharp inner edge suggests sculpting by unseen perturbers. Our images of HD 192758 reveal a disk at radius ∼95 au inclined by ∼59°, never resolved so far. These disks have low scattering albedos of 10% and 13%, respectively, inconsistent with water ice grain compositions. They are reminiscent of several other disks with similar inclination and scattering albedos: Fomalhaut, HD 92945, HD 202628, and HD 207129. They are also very distinct from brighter disks in the same inclination bin, which point to different compositions between these two populations. Varying scattering albedo values can be explained by different grain porosities, chemical compositions, or grain size distributions, which may indicate distinct formation mechanisms or dynamical processes at work in these systems. Finally, these faint disks with large infrared excesses may be representative of an underlying population of systems with low albedo values. Searches with more sensitive instruments on HST or on the James Webb Space Telescope and using state-of-the art starlight-subtraction methods may help discover more of such faint systems.

Non-negative Matrix Factorization: Robust Extraction of Extended Structures

Abstract We apply the vectorized non-negative matrix factorization (NMF) method to the post-processing of the direct imaging data of exoplanetary systems such as circumstellar disks. NMF is an iterative approach, which first creates a nonorthogonal and non-negative basis of components using the given reference images and then models a target with the components. The constructed model is then rescaled with a factor to compensate for the contribution from the disks. We compare NMF with existing methods (classical reference differential imaging method, and the Karhunen–Loève image projection algorithm) using synthetic circumstellar disks and demonstrate the superiority of NMF: with no need of prior selection of references, NMF not only can detect fainter circumstellar disks but also better preserves their morphology and does not require forward modeling. As an application to a well-known disk example, we process the archival Hubble Space Telescope STIS coronagraphic observations of HD 181327 with different methods and compare them, and NMF is able to extract some circumstellar materials inside the primary ring for the first time. In an appendix, we mathematically investigate the stability of NMF components during the iteration and the linearity of NMF modeling.

Multiband counterparts of two eclipsing ultraluminous X-ray sources in M 51

We present the discovery and interpretation of ionized nebulae around two ultraluminous X-ray sources in M 51; both sources share the rare property of showing X-ray eclipses by their companion stars and are therefore prime targets for follow-up studies. Using archival Hubble Space Telescope images, we found an elongated, 100-pc-long emission-line structure associated with one X-ray source (CXOM51 J132940.0+471237; ULX-1 for simplicity), and a more circular, ionized nebula at the location of the second source (CXOM51 J132939.5+471244; ULX-2 for simplicity). We observed both nebulae with the Large Binocular Telescope’s Multi-Object Double Spectrograph. From our analysis of the optical spectra, we argue that the gas in the ULX-1 bubble is shock-ionized, consistent with the effect of a jet with a kinetic power of ≈2 × 1039 erg s−1. Additional X-ray photoionization may also be present, to explain the strength of high-ionization lines such as He ii λ4686 and [Ne v] λ3426. On the other hand, the emission lines from the ULX-2 bubble are typical for photoionization by normal O stars suggesting that the nebula is actually an H ii region not physically related to the ULX but is simply a chance alignment. From archival Very Large Array data, we also detect spatially extended, steep-spectrum radio emission at the location of the ULX-1 bubble (consistent with its jet origin), but no radio counterpart for ULX-2 (consistent with the lack of shock-ionized gas around that source).

Inflows, Outflows, and a Giant Donor in the Remarkable Recurrent Nova M31N 2008-12a?—Hubble Space Telescope Photometry of the 2015 Eruption

Abstract The recurrent nova M31N 2008-12a experiences annual eruptions, contains a near-Chandrasekhar-mass white dwarf, and has the largest mass accretion rate in any nova system. In this paper, we present Hubble Space Telescope (HST) WFC3/UVIS photometry of the late decline of the 2015 eruption. We couple these new data with archival HST observations of the quiescent system and Keck spectroscopy of the 2014 eruption. The late-time photometry reveals a rapid decline to a minimum luminosity state, before a possible recovery/rebrightening in the run up to the next eruption. Comparison with accretion disk models supports the survival of the accretion disk during the eruptions, and uncovers a quiescent disk mass accretion rate of the order of 10 − 6 M ⊙ yr − 1 , which may rise beyond 10 − 5 M ⊙ yr − 1 during the super-soft source phase—both of which could be problematic for a number of well-established nova eruption models. Such large accretion rates, close to the Eddington limit, might be expected to be accompanied by additional mass loss from the disk through a wind and even through collimated outflows. The archival HST observations, combined with the disk modeling, provide the first constraints on the mass donor: L donor = 103 − 11 + 12 L ⊙ , R donor = 14.14 − 0.47 + 0.46 R ⊙ , and T eff , donor = 4890 ± 110 K, which may be consistent with an irradiated M31 red-clump star. Such a donor would require a system orbital period ≳ 5 days. Our updated analysis predicts that the M31N 2008-12a WD could reach the Chandrasekhar mass in < 20 kyr.

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

Abstract We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational-wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked at ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 yr−1, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of Gyr, with a 90% confidence range of . This in turn indicates an initial binary separation of , comparable to the inferred values for Galactic BNS systems. We also use new and archival Hubble Space Telescope images to measure a projected offset of the optical counterpart of 2.1 kpc (0.64r e ) from the center of NGC 4993 and to place a limit of mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of ∼200 km s−1. Future GW–EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of r-process enrichment in the universe.

Interpretation of a Variable Reflection Nebula Associated with HBC 340 and HBC 341 in NGC 1333

Abstract We present multi-epoch, R-band imaging obtained from the Palomar Transient Factory of a small, fan-shaped reflection nebula in NGC 1333 that experiences prominent brightness fluctuations. Photometry of HBC 340 (K7e) and HBC 341 (M5e), a visual pair of late-type, young stellar objects lying near the apex of the nebula, demonstrates that while both are variable, the former has brightened by more than two magnitudes following a deep local minimum in 2014 September. Keck high-dispersion (R ∼ 45,000–66,000), optical spectroscopy of HBC 340 suggests that the protostar is a spectroscopic binary (HBC 340Aa + HBC 340Ab). Both HBC 340 and HBC 341 exhibit strong Hα and forbidden line emission, consistent with accretion and outflow. We conclude that the brightness fluctuations in the reflection nebula represent light echos produced by varying incident radiation emanating from HBC 340. The short-term variability observed in the protostar is attributed to irregular accretion activity, while correlated, dipping behavior on a several hundred day timescale may be due to eclipse-like events caused by orbiting circumstellar material. Archival Hubble Space Telescope imaging of the region reveals a second, faint (F814W ∼ 20.3 mag) companion to HBC 340 that lies 1.″02 (∼235 au) east of the protostar. If associated, this probable substellar mass object (20–50 Jupiter masses), HBC 340B, is likely unrelated to the observed brightness variations. The sustained brightening of HBC 340 since late 2014 can be explained by an EXor-like outburst, the recovery from a long duration eclipse event caused by obscuring circumstellar dust, or by the gradual removal of extincting material from along the line of sight. Our analysis here favors one of the extinction scenarios.

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Abstract The environment around protoplanetary disks (PPDs) regulates processes that drive the chemical and structural evolution of circumstellar material. We perform a detailed empirical survey of warm molecular hydrogen (H2) absorption observed against H i-Lyα (Lyα: λ1215.67) emission profiles for 22 PPDs, using archival Hubble Space Telescope ultraviolet (UV) spectra to identify H2 absorption signatures and quantify the column densities of H2 ground states in each sightline. We compare thermal equilibrium models of H2 to the observed H2 rovibrational level distributions. We find that, for the majority of targets, there is a clear deviation in high-energy states (T exc ≳ 20,000 K) away from thermal equilibrium populations (T(H2) ≳ 3500 K). We create a metric to estimate the total column density of non-thermal H2 (N(H2)nLTE) and find that the total column densities of thermal (N(H2)) and N(H2)nLTE correlate for transition disks and targets with detectable C iv-pumped H2 fluorescence. We compare N(H2) and N(H2)nLTE to circumstellar observables and find that N(H2)nLTE correlates with X-ray and far-UV luminosities, but no correlations are observed with the luminosities of discrete emission features (e.g., Lyα, C iv). Additionally, N(H2) and N(H2)nLTE are too low to account for the H2 fluorescence observed in PPDs, so we speculate that this H2 may instead be associated with a diffuse, hot, atomic halo surrounding the planet-forming disk. We create a simple photon-pumping model for each target to test this hypothesis and find that Lyα efficiently pumps H2 levels with T exc ≥ 10,000 K out of thermal equilibrium.

A Complete Census of Hα Emitters in NGC 6397

Abstract We used a data set of archival Hubble Space Telescope images obtained through the F555W, F814W, and F656N filters to perform a complete search for objects showing emission in the globular cluster NGC 6397. As a photometric diagnostic, we used the color excess in the – color–color diagram. In the analyzed field of view, we identified 53 emitters. In particular, we confirmed the optical counterpart to 20 X-ray sources (7 cataclysmic variables, 2 millisecond pulsars and 11 active binaries) and identified 33 previously unknown sources, thus significantly enlarging the population of known active binaries in this cluster. We report the main characteristics for each class of objects. Photometric estimates of the equivalent width of the emission line were derived from the -excess and, for the first time, compared to the spectroscopic measurements obtained from the analysis of MUSE spectra. The very good agreement between the spectroscopic and photometric measures fully confirmed the reliability of the proposed approach to measure the emission. The search demonstrated the efficiency of this novel approach to pinpoint and measure -emitters, thus offering a powerful tool to conduct a complete census of objects with formations and evolutions that can be strongly affected by dynamical interactions in star clusters.

Discovery of a Rapid, Luminous Nova in NGC 300 by the KMTNet Supernova Program

Abstract We present the discovery of a rapidly evolving transient by the Korean Microlensing Telescope Network Supernova Program (KSP). KSP is a novel high-cadence supernova survey that offers deep (∼21.5 mag in BV I bands), nearly continuous wide-field monitoring for the discovery of early and/or fast optical transients. KSP-OT-201509a, reported here, was discovered on 2015 September 27 during the KSP commissioning run in the direction of the nearby galaxy NGC 300, and stayed above detection limit for ∼22 days. We use our BV I light curves to constrain the ascent rate, −3.7(7) mag day−1 in V, decay timescale, days, and peak absolute magnitude, mag. We also find evidence for a short-lived pre-maximum halt in all bands. The peak luminosity and light-curve evolution make KSP-OT-201509a consistent with a bright, rapidly decaying nova outburst. We discuss constraints on the nature of the progenitor and its environment using archival Hubble Space Telescope (HST)/ACS images and conclude with a broad discussion on the nature of the system.

ALMA Observations of the Gravitational Lens SDP.9

Abstract We present long-baseline ALMA observations of the strong gravitational lens H-ATLAS J090740.0−004200 (SDP.9), which consists of an elliptical galaxy at lensing a background submillimeter galaxy into two extended arcs. The data include Band 6 continuum observations, as well as CO J = 6−5 molecular line observations, from which we measure an updated source redshift of . The image morphology in the ALMA data is different from that of the Hubble Space Telescope (HST) data, indicating a spatial offset between the stellar, gas, and dust component of the source galaxy. We model the lens as an elliptical power law density profile with external shear using a combination of archival HST data and conjugate points identified in the ALMA data. Our best model has an Einstein radius of and a slightly steeper than isothermal mass profile slope. We search for the central image of the lens, which can be used constrain the inner mass distribution of the lens galaxy including the central supermassive black hole, but do not detect it in the integrated CO image at a 3σ rms level of 0.0471 Jy km s−1.

The Lyman Continuum Escape Fraction of Emission Line-selected z ∼ 2.5 Galaxies Is Less Than 15%

Abstract Recent work suggests that strong emission line, star-forming galaxies (SFGs) may be significant Lyman continuum leakers. We combine archival Hubble Space Telescope broadband ultraviolet and optical imaging (F275W and F606W, respectively) with emission line catalogs derived from WFC3 IR G141 grism spectroscopy to search for escaping Lyman continuum (LyC) emission from homogeneously selected z ∼ 2.5 SFGs. We detect no escaping Lyman continuum from SFGs selected on [O ii] nebular emission (N = 208) and, within a narrow redshift range, on [O iii]/[O ii]. We measure 1σ upper limits to the LyC escape fraction relative to the non-ionizing UV continuum from [O ii] emitters, f esc ≲ 5.6%, and strong [O iii]/[O ii] > 5 ELGs, f esc ≲ 14.0%. Our observations are not deep enough to detect f esc ∼ 10% typical of low-redshift Lyman continuum emitters. However, we find that this population represents a small fraction of the star-forming galaxy population at z ∼ 2. Thus, unless the number of extreme emission line galaxies grows substantially to z ≳ 6, such galaxies may be insufficient for reionization. Deeper survey data in the rest-frame ionizing UV will be necessary to determine whether strong line ratios could be useful for pre-selecting LyC leakers at high redshift.

A study of the sensitivity of shape measurements to the input parameters of weak-lensing image simulations

Improvements in the accuracy of shape measurements are essential to exploit the statistical power of planned imaging surveys that aim to constrain cosmological parameters using weak lensing by large-scale structure. Although a range of tests can be performed using the measurements, the performance of the algorithm can only be quantified using simulated images. This yields, however, only meaningful results if the simulated images resemble the real observations sufficiently well. In this paper we explore the sensitivity of the multiplicative bias to the input parameters of Euclid-like image simulations.We find that algorithms will need to account for the local density of sources. In particular the impact of galaxies below the detection limit warrants further study, because magnification changes their number density, resulting in correlations between the lensing signal and multiplicative bias. Although achieving sub-percent accuracy will require further study, we estimate that sufficient archival Hubble Space Telescope data are available to create realistic populations of galaxies.

Discovery of a Satellite of the Large Trans-Neptunian Object (225088) 2007 OR10

Abstract 2007 OR10 is currently the third largest known dwarf planet in the trans-Neptunian region, with an effective radiometric diameter of ∼1535 km. It has a slow rotation period of ∼45 hr that was suspected to be caused by tidal interactions with a satellite undetected at that time. Here, we report on the discovery of a likely moon of 2007 OR10, identified on archival Hubble Space Telescope WFC3/UVIS system images. Although the satellite is detected at two epochs, this does not allow an unambiguous determination of the orbit and the orbital period. A feasible 1.5–5.8 · 1021 kg estimate for the system mass leads to a likely 35–100 day orbital period. The moon is about 4.ͫ2 fainter than 2007 OR10 in HST images that corresponds to a diameter of 237 km assuming equal albedos with the primary. Due to the relatively small size of the moon, the previous size and albedo estimates for the primary remains unchanged. With this discovery all trans-Neptunian objects larger than 1000 km are now known to harbor satellites, an important constraint for moon formation theories in the young solar system.

Supernova progenitors, their variability and the Type IIP Supernova ASASSN-16fq in M66

We identify a pre-explosion counterpart to the nearby Type IIP supernova ASASSN-16fq (SN 2016cok) in archival Hubble Space Telescope (HST) data. The source appears to be a blend of several stars that prevents obtaining accurate photometry. However, with reasonable assumptions about the stellar temperature and extinction, the progenitor almost certainly had an initial mass M<17Msun, and was most likely in the mass range 8-12Msun. Observations once ASASSN-16fq has faded will have no difficulty accurately determining the properties of the progenitor. In 8 years of Large Binocular Telescope (LBT) data, no significant progenitor variability is detected to RMS limits of roughly 0.03 mag. Of the six nearby SN with constraints on low level variability, SN 1987A, SN 1993J, SN 2008cn, SN 2011dh, SN 2013ej and ASASSN-16fq, only the slowly fading progenitor of SN 2011dh showed clear evidence of variability. Excluding SN 1987A, the 90% confidence limit implied by these sources on the number of outbursts over the last decade before the SN that last longer than 0.1 years (FWHM) and are brighter than M_R<-8 mag is approximately N<3. Our continuing LBT monitoring program will steadily improve constraints on pre-SN progenitor variability at amplitudes far lower than achievable by SN surveys.

The Progenitor and Early Evolution of the Type IIb SN 2016gkg

Abstract We report initial observations and analysis on the Type IIb SN 2016gkg in the nearby galaxy NGC 613. SN 2016gkg exhibited a clear double-peaked light curve during its early evolution, as evidenced by our intensive photometric follow-up campaign. SN 2016gkg shows strong similarities with other Type IIb SNe, in particular, with respect to the He i emission features observed in both the optical and near-infrared. SN 2016gkg evolved faster than the prototypical Type IIb SN 1993J, with a decline similar to that of SN 2011dh after the first peak. The analysis of archival Hubble Space Telescope images indicate a pre-explosion source at SN 2016gkg’s position, suggesting a progenitor star with a ∼mid-F spectral type and initial mass M , depending on the distance modulus adopted for NGC 613. Modeling the temperature evolution within of explosion, we obtain a progenitor radius of R , smaller than that obtained from the analysis of the pre-explosion images ( R ).

Masses of the Planetary Nebula Central Stars in the Galactic Globular Cluster System from HST Imaging and Spectroscopy∗

Abstract The globular cluster (GC) system of our Galaxy contains four planetary nebulae (PNe): K 648 (or Ps 1) in M15, IRAS 18333-2357 in M22, JaFu 1 in Pal 6, and JaFu 2 in NGC 6441. Because single-star evolution at the low stellar mass of present-epoch GCs was considered incapable of producing visible PNe, their origin presented a puzzle. We imaged the PN JaFu 1 with the Hubble Space Telescope (HST) to obtain photometry of its central star (CS) and high-resolution morphological information. We imaged IRAS 18333-2357 with better depth and resolution, and we analyzed its archival HST spectra to constrain its CS temperature and luminosity. All PNe in Galactic GCs now have quality HST data, allowing us to improve CS mass estimates. We find reasonably consistent masses between 0.53 and 0.58 M ⊙ for all four objects, though estimates vary when adopting different stellar evolutionary calculations. The CS mass of IRAS 18333-2357, though, depends strongly on its temperature, which remains elusive due to reddening uncertainties. For all four objects, we consider their CS and nebula masses, their morphologies, and other incongruities to assess the likelihood that these objects formed from binary stars. Although generally limited by uncertainties (∼0.02 M ⊙) in post-AGB tracks and core mass versus luminosity relations, the high-mass CS in K 648 indicates a binary origin. The CS of JaFu 1 exhibits compact, bright [O iii] and Hα emission, like EGB 6, suggesting a binary companion or disk. Evidence is weaker for a binary origin of JaFu 2.

The Tip of the Red Giant Branch Distances to Typa Ia Supernova Host Galaxies. V. NGC 3021, NGC 3370, and NGC 1309 and the Value of the Hubble Constant

Abstract We present final results of a program for the determination of the Hubble constant based on the calibration of the Type Ia supernovae (SNe Ia) using the Tip of the Red Giant Branch (TRGB). We report TRGB distances to three SN Ia host galaxies, NGC 3021, NGC 3370, and NGC 1309. We obtain F555W and F814W photometry of resolved stars from the archival Hubble Space Telescope data. Luminosity functions of red giant stars in the outer regions of these galaxies show the TRGB to be at F814W ≈ QT = 28.2 ∼ 28.5 mag. From these TRGB magnitudes and the revised TRGB calibration based on two distance anchors (NGC 4258 and the LMC) in Jang &amp; Lee (2017; Paper IV), we derive the distances: ( m − M ) 0 = 32.178 ± 0.033 for NGC 3021, 32.253 ± 0.041 for NGC 3370, and 32.471 ± 0.040 for NGC 1309. We update our previous results on the TRGB distances to five SN Ia host galaxies using the revised TRGB calibration. By combining the TRGB distance estimates to SN Ia host galaxies in this study with the SN Ia calibration provided by Riess et al. (2011), we obtain a value of the Hubble constant: H 0 = 71.66 ± 1.80(random) ± 1.88(systematic) km s−1 Mpc−1 (a 3.6% uncertainty including systematics) from all eight SNe, and H 0 = 73.72 ± 2.03 ± 1.94 km s−1 Mpc−1 (a 3.8% uncertainty) from six low-reddened SNe. We present our best estimate, H 0 = 71.17 ± 1.66 ± 1.87 km s−1 Mpc−1 (a 3.5% uncertainty) from six low-reddened SNe with the recent SN Ia calibration in Riess et al. (2016). This value is between those from the Cepheid calibrated SNe Ia and those from the Cosmic Microwave Background analysis, lowering the Hubble tension.

Transient X-Ray Sources in the Magellanic-type Galaxy NGC 4449

Abstract We report the identification of seven transient X-ray sources in the nearby Magellanic-type galaxy NGC 4449 using archival multi-epoch X-ray observations conducted with the Chandra, XMM-Newton, and Swift telescopes over the years 2001–2013. Among them, two sources are classified as supersoft X-ray sources (SSSs) because of their soft X-ray color; the rest of the sources are X-ray binaries (XRBs). Transient SSSs’ spectra can be fitted with a blackbody of effective temperature ∼80–105 eV, and luminosities were in 0.3–8 keV. These properties are consistent with the widely accepted model for SSSs, an accreting white dwarf with steady nuclear burning on its surface, and the SSS emission has also been observed in many post-nova systems. Detailed analysis of one sufficiently bright SSS revealed strong short-term variability, possibly showing a 2.3-hr periodic modulation, and long-term variability, detectable over 23 years with different X-ray telescopes before the year 2003. The X-ray properties of four other transients are consistent with neutron star or black hole binaries in their hard state, whereas the remaining source is most likely an XRB with a quasi-soft X-ray spectrum. Analysis of archival Hubble Space Telescope image data was also conducted, and multiple massive stars were found as possible counterparts. We conclude that the X-ray transient properties in NGC 4449 are similar to those in other Magellanic-type galaxies.

First Scattered-light Images of the Gas-rich Debris Disk around 49 Ceti

Abstract We present the first scattered-light images of the debris disk around 49 Ceti, a ∼40 Myr A1 main-sequence star at 59 pc, famous for hosting two massive dust belts as well as large quantities of atomic and molecular gas. The outer disk is revealed in reprocessed archival Hubble Space Telescope NICMOS-F110W images, as well as new coronagraphic H-band images from the Very Large Telescope SPHERE instrument. The disk extends from 1.″1 (65 au) to 4.″6 (250 au) and is seen at an inclination of 73°, which refines previous measurements at lower angular resolution. We also report no companion detection larger than 3 M Jup at projected separations beyond 20 au from the star (0.″34). Comparison between the F110W and H-band images is consistent with a gray color of 49 Ceti’s dust, indicating grains larger than ≳2 μm. Our photometric measurements indicate a scattering efficiency/infrared excess ratio of 0.2–0.4, relatively low compared to other characterized debris disks. We find that 49 Ceti presents morphological and scattering properties very similar to the gas-rich HD 131835 system. From our constraint on the disk inclination we find that the atomic gas previously detected in absorption must extend to the inner disk, and that the latter must be depleted of CO gas. Building on previous studies, we propose a schematic view of the system describing the dust and gas structure around 49 Ceti and hypothetical scenarios for the gas nature and origin.