P. A. M. van Hoof
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View article: Fe XVIII-XXIV K beta Inner-shell Absorption Lines in the X-ray Spectra of Neutron Star and Black Hole Binaries with XRISM
Fe XVIII-XXIV K beta Inner-shell Absorption Lines in the X-ray Spectra of Neutron Star and Black Hole Binaries with XRISM Open
The advent of the X-ray microcalorimeter spectrometer Resolve onboard the XRISM space telescope opened a new era for high-resolution X-ray spectroscopy of astrophysical plasmas. Many spectral features were newly detected, including the K a…
View article: CLOUDY and the High-resolution Microcalorimeter Revolution: Optical, UV, and X-Ray Spectra of One-electron Systems
CLOUDY and the High-resolution Microcalorimeter Revolution: Optical, UV, and X-Ray Spectra of One-electron Systems Open
With the launch of the XRISM microcalorimeter mission, space-based X-ray observations will achieve a record spectral resolving power of R ≡ E /Δ E ∼ 1200. With this resolving power, emission features associated with fine-structure energy l…
View article: The <i>JWST</i>/MIRI view of the planetary nebula NGC 6302 – I. A UV-irradiated torus and a hot bubble triggering PAH formation
The <i>JWST</i>/MIRI view of the planetary nebula NGC 6302 – I. A UV-irradiated torus and a hot bubble triggering PAH formation Open
NGC 6302 is a spectacular bipolar planetary nebula (PN) whose spectrum exhibits fast outflows and highly ionized emission lines, indicating the presence of a very hot central star (${\sim}$220 000 K). Its infrared spectrum reveals a mixed …
View article: <i>JWST</i> observations of the Ring Nebula (NGC 6720) – II. PAH emission
<i>JWST</i> observations of the Ring Nebula (NGC 6720) – II. PAH emission Open
Polycyclic aromatic hydrocarbons (PAHs) and carbonaceous dust have been observed in clumpy circumstellar environments, yet their formation and evolutionary pathways in such environments remain elusive. We aim to characterize the PAH emissi…
View article: JWST Observations of the Ring Nebula (NGC 6720). III. A Dusty Disk around Its Central Star
JWST Observations of the Ring Nebula (NGC 6720). III. A Dusty Disk around Its Central Star Open
The planetary nebula NGC 6720, also known as the “Ring Nebula,” is one of the most iconic examples of nearby planetary nebulae whose morphologies present a challenge to our theoretical understanding of the processes that govern the deaths …
View article: New insights with XRISM and Cloudy: A novel column density diagnostic
New insights with XRISM and Cloudy: A novel column density diagnostic Open
Aims. We present a simple yet powerful column density diagnostic for plasmas enabled by X-ray microcalorimeter observations. Methods. With the recent developments of the spectral simulation code C LOUDY , inspired by the high spectral reso…
View article: Cloudy and the High-Resolution Microcalorimeter Revolution: Optical, UV, and X-ray Spectra of One-electron Systems
Cloudy and the High-Resolution Microcalorimeter Revolution: Optical, UV, and X-ray Spectra of One-electron Systems Open
With the launch of the XRISM microcalorimeter mission, space-based X-ray observations will achieve a record spectral resolving power of $R\equiv E/ΔE\sim$1200. With this resolving power, emission features associated with fine-structure ene…
View article: New Insights with XRISM & Cloudy: A novel Column Density Diagnostic
New Insights with XRISM & Cloudy: A novel Column Density Diagnostic Open
We present a simple, yet powerful column density diagnostic for plasmas enabled by X-ray microcalorimeter observations. With the recent developments of the spectral simulation code Cloudy, inspired by the high spectral resolution of the X-…
View article: Sakurai's object: a [WC] star in a new bipolar nebula after a VLTP
Sakurai's object: a [WC] star in a new bipolar nebula after a VLTP Open
Optical spectra of the Very Late Thermal Pulse (VLTP) object V4334 Sgr have shown a rapidly changing spectrum resulting from shocks in the outflow, which created a new bipolar nebula inside the old nebula. We see C II and C III emission li…
View article: Non-thermal radio emission in Sakurai’s Object
Non-thermal radio emission in Sakurai’s Object Open
Context. The very late thermal pulse (VLTP) affects the evolution of ∼20% of 1–8 M ⊙ stars, repeating the last red giant phases within a few years and leading to the formation of a new, but hydrogen-poor, nebula within the old planetary ne…
View article: <i>JWST</i> observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs
<i>JWST</i> observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs Open
We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6 to 25 $\, \mu$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in H2, with a characterist…
View article: The 23.01 Release of Cloudy
The 23.01 Release of Cloudy Open
We announce the C23.01 update of cloudy . This corrects a simple coding error, present since ∼1990, in one routine that required a conversion from the line-center to the mean normalization of the Ly α optical depth. This affects the destru…
View article: The 23.01 release of Cloudy
The 23.01 release of Cloudy Open
We announce the C23.01 update of Cloudy. This corrects a simple coding error, present since $\sim$ 1990, in one routine that required a conversion from the line-center to the mean normalization of the Ly$α$ optical depth. This affects the …
View article: MELCHIORS: The Mercator Library of High Resolution Stellar Spectroscopy
MELCHIORS: The Mercator Library of High Resolution Stellar Spectroscopy Open
Over the past decades, libraries of stellar spectra have been used in a large variety of science cases, including as sources of reference spectra for a given object or a given spectral type. Despite the existence of large libraries and the…
View article: MELCHIORS
MELCHIORS Open
Aims . Over the past decades, libraries of stellar spectra have been used in a large variety of science cases, including as sources of reference spectra for a given object or a given spectral type. Despite the existence of large libraries …
View article: THE 2023 RELEASE OF Cloudy
THE 2023 RELEASE OF Cloudy Open
We describe the 2023 release of the spectral synthesis code Cloudy. Since the previous major release, migrations of our online services motivated us to adopt git as our version control system. This change alone led us to adopt an annual re…
View article: The heart of Sakurai’s object revealed by ALMA
The heart of Sakurai’s object revealed by ALMA Open
We present high-angular-resolution observations of Sakurai’s object using the Atacama Large Millimeter Array, shedding new light on its morpho-kinematical structure. The millimetre continuum emission observed at an angular resolution of 20…
View article: The heart of Sakurai's Object revealed by ALMA
The heart of Sakurai's Object revealed by ALMA Open
We present high angular-resolution observations of Sakurai's object using the Atacama Large Millimeter Array, shedding new light on its morpho-kinematical structure. The millimetre continuum emission, observed at an angular resolution of 2…
View article: JWST observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs
JWST observations of the Ring Nebula (NGC 6720): I. Imaging of the rings, globules, and arcs Open
We present JWST images of the well-known planetary nebula NGC 6720 (the Ring Nebula), covering wavelengths from 1.6$μ$m to 25 $μ$m. The bright shell is strongly fragmented with some 20 000 dense globules, bright in H$_2$, with a characteri…
View article: The 2023 release of Cloudy
The 2023 release of Cloudy Open
We describe the 2023 release of the spectral synthesis code Cloudy. Since the previous major release, migrations of our online services motivated us to adopt git as our version control system. This change alone led us to adopt an annual re…
View article: Recombination of Hot Ionized Nebulae: The Old Planetary Nebula around V4334 Sgr (Sakurai’s Star)*
Recombination of Hot Ionized Nebulae: The Old Planetary Nebula around V4334 Sgr (Sakurai’s Star)* Open
After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. Recombination cannot normally be observed in isolation, because the ionization foll…
View article: Recombination of hot ionized nebulae: The old planetary nebula around V4334 Sgr (Sakurai's star)
Recombination of hot ionized nebulae: The old planetary nebula around V4334 Sgr (Sakurai's star) Open
After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. The recombination cannot normally be observed in isolation, because the ionization …
View article: First Images of the Molecular Gas around a Born-again Star Revealed by ALMA
First Images of the Molecular Gas around a Born-again Star Revealed by ALMA Open
Born-again stars allow probing stellar evolution in human timescales and provide the most promising path for the formation of hydrogen-deficient post-asymptotic giant branch objects, but their cold and molecular components remain poorly ex…
View article: H, He-like recombination spectra – IV. Clarification and refinement of methodology for <i>l</i>-changing collisions
H, He-like recombination spectra – IV. Clarification and refinement of methodology for <i>l</i>-changing collisions Open
Precise spectral diagnostic modelling of H i and He ii recombination spectra can constrain theoretical models that describe many astrophysical environments. Simple analytic expressions are of interest for collisional l-changing rate coeffi…
View article: Improved Fe ii Emission-line Models for AGNs Using New Atomic Data Sets
Improved Fe ii Emission-line Models for AGNs Using New Atomic Data Sets Open
Understanding the Fe II emission from active galactic nuclei (AGNs) has been a grand challenge for many decades. The rewards from understanding the AGN spectra would be immense, involving both quasar classification schemes such as “Eigenve…
View article: The cooling-down central star of the planetary nebula SwSt 1: a late thermal pulse in a massive post-AGB star?
The cooling-down central star of the planetary nebula SwSt 1: a late thermal pulse in a massive post-AGB star? Open
SwSt 1 (PN G001.5-06.7) is a bright and compact planetary nebula containing a late [WC]-type central star. Previous studies suggested that the nebular and stellar lines are slowly changing with time. We studied new and archival optical and…
View article: The Belgian Repository of Fundamental Atomic Data and Stellar Spectra (BRASS)
The Belgian Repository of Fundamental Atomic Data and Stellar Spectra (BRASS) Open
Background: BRASS (Belgian Repository of Fundamental Atomic Data and Stellar Spectra) is an international networking project for the development of a new public database providing accurate fundamental atomic data of vital importance for st…
View article: A Wind-based Unification Model for NGC 5548: Spectral Holidays, Nondisk Emission, and Implications for Changing-look Quasars
A Wind-based Unification Model for NGC 5548: Spectral Holidays, Nondisk Emission, and Implications for Changing-look Quasars Open
The 180 day Space Telescope and Optical Reverberation Mapping campaign on NGC 5548 discovered an anomalous period, the broad-line region (BLR) holiday, in which the emission lines decorrelated from the continuum variations. This is importa…
View article: Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548
Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548 Open
The Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission-line variations followed chang…
View article: H-, He-like recombination spectra – III. n-changing collisions in highly excited Rydberg states and their impact on the radio, IR, and optical recombination lines
H-, He-like recombination spectra – III. n-changing collisions in highly excited Rydberg states and their impact on the radio, IR, and optical recombination lines Open
At intermediate to high densities, electron (de-)excitation collisions are the dominant process for populating or depopulating high Rydberg states. In particular, the accurate knowledge of the energy changing (n-changing) collisional rates…