arXiv subjects

Andreas Ritter

Publications and source records attributed to Andreas Ritter.

At least 19 recordsLinked to original sources

arXiv2026

Chang'e 7 Lunar Lander Optical Camera-Telescope: Optical Astronomy from the Moon

We report the design and manufacture of a new, lightweight, wide-field, optical camera-telescope on board the Chang'e 7 lunar mission (launched in August 2026 and due for lunar touchdown in late November 2026). The camera is capable of static, panchromatic imagery within a $420-696~nm$ optical wavelength range. The camera was designed and built under the small lunar astronomy observation station program of the Chinese National Space Agency (CNSA) as a collaboration between the International Lunar Observatory Association of Hawaii (ILOA), the Laboratory for Space Research (LSR) of the University of Hong Kong (HKU) and the Beijing Institute of Space Mechanics and Electricity (BISME). The camera has been built to meet science goals of the mission for sustainable astronomical operation over a large range of temperatures from the Moon's south pole. We report on the design and ground based preliminary performance, together with an analysis of the camera's simulated output to indicate the range of astronomical observations possible from the lunar surface given the camera's limited sensitivity and angular resolution given the modest aperture and wide field of view.

astro-ph.IM↗

arXiv2026

One cluster, two clusters, no cluster? -- The curious case of HSC 2686 and Lynga 3

This study was motivated by the search for Planetary Nebulae (PNe) and Open Cluster (OCs) associations. Only 5 PNe are currently in Galactic OCs among the previous $\sim4,800$ OCs known. They are valuable because as cluster members their properties can be linked to their progenitor stars, something not possible for general field PNe. Since the GAIA astrometric satellite first data release, thousands of new OC candidates have been identified. This offers fresh motivation to search them as hosts for known PNe. Statistically we expect 30 OC-PN pairs to be present. We searched these GAIA candidate OCs, found by Hunt \& Reffert (2023), for known central stars of PNe (CSPNe) as a practical proxy for the PNe themselves and one suited to automated searches. We identified 1 potential CSPN (IRAS 15127-5811) of "Likely" PN [GKF2010] MN18 in the HASH database, as a claimed member of the putative cluster HSC~2686. A second cluster (Lynga~3) with similar parameters and in very close angular proximity could also be a potential host. Here we reclassify CSPN IRAS 15127-5811 as a blue supergiant with a surrounding bi-polar nebula. Nevertheless, we collected all available information on proposed member stars for both these clusters. We conclude that neither claimed cluster is real. Our results shed considerable doubt on the veracity of many newly identified OCs that have modest numbers of stellar members.

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arXiv2026

IFU Spectroscopic Study of the Planetary Nebula Abell 30: Mapping the Ionisation and Kinematic Structure of the Inner Complex

This work presents integrated flux and velocity channel maps of the planetary nebula Abell 30 (A30) inner knot system. The observations were taken with the INTEGRAL spectrograph at the William Herschel Telescope (WHT). Our IFU data cube partially covers knots J1, J2, and completely covers knots J3, J4 in the system. Optical Recombination Lines of C II, He I, He II, N III, O II and Collisionally Excited Lines of [Ar IV], [Ar V], [N II], [Ne III], [Ne IV], and [O III] were detected. Our integrated flux maps visualise the ionisation structure and the chemical inhomogeneity in the system previously reported by other groups. We find that ORLs are concentrated in the polar region (J1, J3), whereas the equatorial knots (J2, J4) are dominated by CELs. The flux ratio map of the diagnostic [O III] lambda 5007/4363 Angstrom lines reveals the electron temperature distribution, which shows cold cores of 15,000 K in knots J3 and J4 surrounded by a hot outer layer of above 20,000 K. Our channel maps show positive and negative velocity excursions from the systemic value among the ions. Several ions show variation in their velocity structures from their lower-energy-level counterparts, including [Ar IV] and [Ar V], [Ne III] and [Ne IV], and He I and He II. New recurrent velocity structures are identified in the low-density regions where the ions move much faster compared to their surrounding environments. The velocity dispersion measurements highlight extreme turbulence in some of the ions (sigma_vrad approx 140 km/s), consistent with supersonic/hypersonic motion driven by shocks. The forbidden line species [N II] exhibits lower turbulence (sigma_vrad approx 50-60 km/s), tracing denser, less-turbulent gases. Based on our data, we conclude both the ionisation and kinematic studies hint at shock heating and multiple ejection history in the evolutionary pathway of A30.

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arXiv2024

Diverse Science from VLT imagery and spectroscopy of PNe in the Galactic Bulge

We have undertaken a deep investigation of a well defined sample of 136 PNe located in a 10x10 degree central region of the Galactic Bulge observed with the ESO VLT and supplemented by archival HST imagery. These studies have provided precise morphologies, major axes position angles and the most robust sample of consistently derived chemical abundances available to date. Using these data we have statistically confirmed, at 5-sigma, the precise PNe population that provides the PNe alignment of major axes previously suggested in the Galactic Bulge, revealed a partial solution to the sulfur anomaly and uncovered interesting morphological, abundance and kinematic features. We summarise the most significant findings here with detailed results appearing in a series of related publications.

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arXiv2024

Evaluation of the performance of a CdZnTe-based soft $\gamma$-ray detector for CubeSat payloads

The low-energy $\gamma$-ray (0.1-30 MeV) sky has been relatively unexplored since the decommissioning of the COMPTEL instrument on the Compton Gamma-Ray Observatory (CGRO) satellite in 2000. However, the study of this part of the energy spectrum (the ``MeV gap") is crucial for addressing numerous unresolved questions in high-energy and multi-messenger astrophysics. Although several large MeV $\gamma$-ray missions like AMEGO and e-ASTROGAM are being proposed, they are predominantly in the developmental phase, with launches not anticipated until the next decade at the earliest. In recent times, there has been a surge in proposed CubeSat missions as cost-effective and rapidly implementable ``pathfinder" alternatives. A MeV CubeSat dedicated to $\gamma$-ray astronomy has the potential to serve as a demonstrator for future, larger-scale MeV payloads. This paper presents a $\gamma$-ray payload design featuring a CdZnTe crystal calorimeter module developed by IDEAS. We report the detailed results of simulations to assess the performance of this proposed payload and compare it with those of previous $\gamma$-ray instruments.

astro-ph.HE↗

arXiv2023

From an amateur PN candidate to the Rosetta Stone of SN Iax research

On August 25th 2013 Dana Patchick from the "Deep Sky Hunters" (DSH) amateur astronomer group discovered a diffuse nebulosity in the Wide-field Infrared Survey Explorer (WISE) mid-IR image archive that had no optical counterpart but appeared similar to many Planetary Nebulae (PNe) in WISE. As his 30th discovery he named it Pa 30 and it was added to the HASH PN database as a new PN candidate. Little did he know how important his discovery would become. 10 years later this object is the only known bound remnant of a violent double WD merger accompanied by a rare Type Iax SN, observed and recorded by the ancient Chinese and Japanese in 1181 AD. This makes Pa 30 and its central star IRAS 00500+6713 (WD J005311) the only SN Iax remnant in our Galaxy, the only known bound remnant of any SN, and based on the central star's spectrum the only Wolf-Rayet star known that neither has a massive progenitor nor is the central star of a Planetary Nebula. We cover this story and our key role in it.

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arXiv2023

Performance Evaluation of a silicon-based 6U Cubesat detector for soft $\gamma$-ray astronomy

The observation of the low-energy $\gamma$-ray (0.1-30 MeV) sky has been significantly limited since the COMPTEL instrument was decommissioned aboard the Compton Gamma-ray Observer (CGRO) satellite in 2000. The exploration of $\gamma$-ray photons within this energy band, often referred to as the \say{MeV gap}, is crucial to address numerous unresolved mysteries in high-energy and multi-messenger astrophysics. Although several large MeV $\gamma$-ray missions have been proposed (e.g., e-ASTROGAM, AMEGO, COSI), most of these are in the planning phase, with launches not expected until the next decade, at the earliest. Recently, there has been a surge in proposed CubeSat missions as cost-effective and rapidly implementable \say{pathfinder} alternatives. A MeV CubeSat payload dedicated to $\gamma$-ray astronomy could serve as a valuable demonstrator for large-scale future MeV payloads. This paper proposes a $\gamma$-ray payload design with a Silicon-based tracker and a Ceasium-Iodide-based calorimeter. We report the results of a simulation study to assess the performance of this payload concept and compare the results with those of previous $\gamma$-ray instruments. As part of the performance assessment and comparison, we show that with our proposed payload design, a sensitivity better than IBIS can be achieved for energies between 0.1 and 10 MeV, and for energies up to around 1 MeV, the achieved sensitivity is comparable to COMPTEL, therefore opening up a window towards cost-effective observational astronomy with comparable performance to past missions.

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arXiv2023

When the Stars Align: A 5 {\sigma} Concordance of Planetary Nebulae Major Axes in the Centre of our Galaxy

We report observations of a remarkable major axes alignment nearly parallel to the Galactic plane of 5{\sigma} significance for a subset of bulge "planetary nebulae" (PNe) that host, or are inferred to host, short period binaries. Nearly all are bipolar. It is solely this specific PNe population that accounts for the much weaker statistical alignments previously reported for the more general bulge PNe. It is clear evidence of a persistent, organised process acting on a measurable parameter at the heart of our Galaxy over perhaps cosmologically significant periods of time for this very particular PNe sample. Stable magnetic fields are currently the only plausible mechanism that could affect multiple binary star orbits as revealed by the observed major axes orientations of their eventual PNe. Examples are fed into the current bulge planetary nebulae population at a rate determined by their formation history and mass range of their binary stellar progenitors.

astro-ph.GA↗

arXiv2023

ZTBus: A Large Dataset of Time-Resolved City Bus Driving Missions

This paper presents the Zurich Transit Bus (ZTBus) dataset, which consists of data recorded during driving missions of electric city buses in Zurich, Switzerland. The data was collected over several years on two trolley buses as part of multiple research projects. It involves more than a thousand missions across all seasons, each mission usually covering a full day of operation. The ZTBus dataset contains detailed information on the vehicle's power demand, propulsion system, odometry, global position, ambient temperature, door openings, number of passengers, dispatch patterns within the public transportation network, etc. All signals are synchronized in time and include an absolute timestamp in tabular form. The dataset can be used as a foundation for a variety of studies and analyses. For example, the data can serve as a basis for simulations to estimate the performance of different public transit vehicle types, or to evaluate and optimize control strategies of hybrid electric vehicles. Furthermore, numerous influencing factors on vehicle operation, such as traffic, passenger volume, etc., can be analyzed in detail.

eess.SY↗

arXiv2023

Highly Efficient Year-Round Energy and Comfort Optimization of HVAC Systems in Electric City Buses

In this paper, we present a novel approach to perform highly efficient numerical simulations of the heating, ventilation, and air-conditioning (HVAC) system of an electric city bus. The models for this simulation are based on the assumption of a steady-state operation. We show two approaches to obtain the minimum energy requirement for a certain thermal comfort criterion under specific ambient conditions. Due to the computationally efficient approach developed, we can evaluate the model on a large dataset of 7500 scenarios in various ambient conditions to estimate the year-round performance of the system subject to different comfort requirements. Compared to a heating strategy based on positive temperature coefficient (PTC) elements, we can thus show that a heat pump (HP) can reduce the annual mean power consumption by up to 60%. Ceiling-mounted radiant heating elements complementing a PTC heating system can reduce the annual mean power consumption by up to 10%, while they cannot improve the energy efficiency when used in conjunction with a HP. Finally, a broad sensitivity study reveals the fact that improving the HP's heating-mode coefficient of performance (COP) manifests the largest leverage in terms of mean annual power consumption. Moreover, the annual energy expenditure for cooling are around eight times smaller than those for heating. The case study considered thus reveals that the advantages of improving the COP of the cooling mode are significantly lower.

eess.SY↗

arXiv2022

Morphologies and Central Stars of Planetary Nebulae in the Galactic bulge from VLT, $\textit{HST}$ and Pan-STARRS imaging

This is the first in a series of papers that present sets of different results for 136 compact, known planetary nebulae within a 10 $\times$ 10 degree region of the Galactic bulge. We use a large, previously unpublished sample of our own extensive ESO 8 m VLT deep imaging and spectroscopic data. This is combined with archival deep $\textit{HST}$ imaging where available to provide a detailed morphological classification and study. The influence of angular resolution and sensitivity when assigning a morphology is discussed. A large fraction (68%) of the sample are shown to be bipolars and the implications for this in the context of planetary nebulae progenitors are explored. Four new planetary nebula central stars are also identified which are not in $\textit{Gaia}$. This is based on both VLT and deep archival Pan-STARRS broad-band imagery. Some 11 putative central stars previously reported, based on $\textit{Gaia}$ positions, are also not the true central star. In other cases the $\textit{Gaia}$ central stars reported in the literature are actually based on the overall centroid position of a very compact planetary nebula rather than the actual central star within it. $\textit{Gaia}$ parallax distances and kinematic ages for PNe in this sample are provided where possible based on fresh angular size measures from the new VLT imagery and $\textit{Gaia}$ distances and literature expansion velocities when available. All these results are discussed within the context of the overall characteristics of the Galactic bulge and its planetary nebula population.

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arXiv2022

WHTZ 1: A high excitation Planetary Nebula not a gaseous cocoon from runaway star HD 185806

We present evidence that the nebular cocoon and bow-shock emission nebula putatively and recently reported as deriving from the 9th magnitude "runaway" star HD 185806 is the previously discovered but obscure planetary nebula WHTZ 1 (Ra 7). It has a Gaia DR3 G~16 blue ionizing star at its geometric centre. We present imagery, spectroscopy, other data and arguments to support that this emission source is a high excitation Planetary Nebula not a stellar wind bow shock.

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arXiv2022

A new study on a type Iax stellar remnant and its probable association with SN 1181

We report observations and modeling of the stellar remnant and presumed double-degenerate merger of Type~Iax supernova Pa30, which is the probable remnant of SN~1181~AD. It is the only known bound stellar SN remnant and the only star with Wolf-Rayet features that is neither a planetary nebula central star nor a massive Pop I progenitor. We model the unique emission-line spectrum with broad, strong O~{\sc vi} and O~{\sc viii} lines as a fast stellar wind and shocked, hot gas. Non-LTE wind modeling indicates a mass-loss rate of $\sim 10^{-6}\,\rm M_\odot\,yr^{-1}$ and a terminal velocity of $ \sim$15,000~km\,s$^{-1}$, consistent with earlier results. O~{\sc viii} lines indicate shocked gas temperatures of $T \simeq 4\,$MK. We derive a magnetic field upper limit of $B<2.5\,$MG, below earlier suggestions. The luminosity indicates a remnant mass of 1.0--1.65\,\rm M$_\odot$ with ejecta mass $0.15\pm0.05\,\rm M_\odot$. Archival photometry suggests the stellar remnant has dimmed by $\sim$0.5 magnitudes over 100 years. A low Ne/O$\,<0.15$ argues against a O-Ne white dwarf in the merger. A cold dust shell is only the second detection of dust in a SN Iax and the first of cold dust. Our ejecta mass and kinetic energy estimates of the remnant are consistent with Type Iax extragalactic sources.

astro-ph.SR↗

arXiv2021

The remnant and origin of the historical supernova 1181AD

The guest star of AD 1181 is the only historical supernova of the last millennium that is without a definite counterpart. The previously proposed association with supernova remnant 3C58 is in strong doubt because of the inferred age of this remnant. Here we report a new identification of SN 1181 with our codiscovery of the hottest known Wolf Rayet star of the Oxygen sequence (dubbed Parkers star) and its surrounding nebula Pa 30. Our spectroscopy of the nebula shows a fast shock with extreme velocities of approx. 1,100kms. The derived expansion age of the nebula implies an explosive event approx 1,000 years ago which agrees with the 1181 AD event. The on sky location also fits the historical Chinese and Japanese reports of SN 1181 to 3.5degrees. Pa 30 and Parkers star have previously been proposed to be the result of a double-degenerate merger, leading to a rare Type Iax supernova. The likely historical magnitude and the distance suggest the event was subluminous for normal supernova. This agrees with the proposed Type Iax association which would also be the first of its kind in the Galaxy. Taken together, the age, location, event magnitude and duration elevate Pa 30 to prime position as the counterpart of SN 1181. This source is the only Type Iax supernova where detailed studies of the remnant star and nebula are possible. It provides strong observational support for the double degenerate merger scenario for Type Iax supernovae.

astro-ph.HE↗

arXiv2020

The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- II: Stellar Atmospheric Parameters, Chemical Abundances and Distances

We present part 2 of the 6th and final Data Release (DR6 or FDR) of the Radial Velocity Experiment (RAVE), a magnitude-limited (9<I<12) spectroscopic survey of Galactic stars randomly selected in the southern hemisphere. The RAVE medium-resolution spectra (R~7500) cover the Ca-triplet region (8410-8795A) and span the complete time frame from the start of RAVE observations on 12 April 2003 to their completion on 4 April 2013. In the second of two publications, we present the data products derived from 518387 observations of 451783 unique stars using a suite of advanced reduction pipelines focussing on stellar atmospheric parameters, in particular purely spectroscopically derived stellar atmospheric parameters (Teff, log(g), and the overall metallicity), enhanced stellar atmospheric parameters inferred via a Bayesian pipeline using Gaia DR2 astrometric priors, and asteroseismically calibrated stellar atmospheric parameters for giant stars based on asteroseismic observations for 699 K2 stars. In addition, we provide abundances of the elements Fe, Al, and Ni, as well as an overall [alpha/Fe] ratio obtained using a new pipeline based on the GAUGUIN optimization method that is able to deal with variable signal-to-noise ratios. The RAVE DR6 catalogs are cross matched with relevant astrometric and photometric catalogs, and are complemented by orbital parameters and effective temperatures based on the infrared flux method. The data can be accessed via the RAVE Web site (http://rave-survey.org) or the Vizier database.

astro-ph.SR↗

arXiv2020

The Sixth Data Release of the Radial Velocity Experiment (RAVE) -- I: Survey Description, Spectra and Radial Velocities

The Radial Velocity Experiment (RAVE) is a magnitude-limited (9<I<12) spectroscopic survey of Galactic stars randomly selected in the southern hemisphere. The RAVE medium-resolution spectra (R~7500) cover the Ca-triplet region (8410-8795A). The 6th and final data release (DR6 or FDR) is based on 518387 observations of 451783 unique stars. RAVE observations were taken between 12 April 2003 and 4 April 2013. Here we present the genesis, setup and data reduction of RAVE as well as wavelength-calibrated and flux-normalized spectra and error spectra for all observations in RAVE DR6. Furthermore, we present derived spectral classification and radial velocities for the RAVE targets, complemented by cross matches with Gaia DR2 and other relevant catalogs. A comparison between internal error estimates, variances derived from stars with more than one observing epoch and a comparison with radial velocities of Gaia DR2 reveals consistently that 68% of the objects have a velocity accuracy better than 1.4 km/s, while 95% of the objects have radial velocities better than 4.0 km/s. Stellar atmospheric parameters, abundances and distances are presented in subsequent publication. The data can be accessed via the RAVE Web (http://rave-survey.org) or the Vizier database.

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arXiv2020

A Preferred Orientation Angle for Bipolar Planetary Nebulae

We present preliminary results from measuring Galactic orientation angles of 800 elliptical and bipolar Planetary Nebulae (PNe) in the Hong Kong/Australian Astronomical Observatory/Strasbourg Observatory H-alpha Planetary Nebula (HASH) research platform and database (Parker et al. [1], [2]). For elliptical PNe the distribution of orientation angles is found to be essentially uniform. However, for bipolar PNe there is statistically significant evidence for preferred orientation angles (as tentatively reported before with smaller samples) across the whole Galaxy.

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arXiv2017

The SED Machine: a robotic spectrograph for fast transient classification

Current time domain facilities are finding several hundreds of transient astronomical events a year. The discovery rate is expected to increase in the future as soon as new surveys such as the Zwicky Transient Facility (ZTF) and the Large Synoptic Sky Survey (LSST) come on line. At the present time, the rate at which transients are classified is approximately one order or magnitude lower than the discovery rate, leading to an increasing "follow-up drought". Existing telescopes with moderate aperture can help address this deficit when equipped with spectrographs optimized for spectral classification. Here, we provide an overview of the design, operations and first results of the Spectral Energy Distribution Machine (SEDM), operating on the Palomar 60-inch telescope (P60). The instrument is optimized for classification and high observing efficiency. It combines a low-resolution (R$\sim$100) integral field unit (IFU) spectrograph with "Rainbow Camera" (RC), a multi-band field acquisition camera which also serves as multi-band (ugri) photometer. The SEDM was commissioned during the operation of the intermediate Palomar Transient Factory (iPTF) and has already proved lived up to its promise. The success of the SEDM demonstrates the value of spectrographs optimized to spectral classification. Introduction of similar spectrographs on existing telescopes will help alleviate the follow-up drought and thereby accelerate the rate of discoveries.

astro-ph.IM↗