arXiv subjects

Christoph Ries

Publications and source records attributed to Christoph Ries.

15 recordsLinked to original sources

arXiv2026

Discovery of an extremely narrow trail-like feature crossing the Veil Supernova Remnant in deep amateur observations

We report the discovery of an extremely narrow and highly collimated gaseous trail-like structure crossing the eastern region of the Veil Nebula (Cygnus Loop). The feature was first identified in deep narrow-band H-alpha images obtained by a small telescope and was confirmed in more than a dozen publicly available amateur and professional images in the last two decades, rejecting the possibility of being an artifact (e.g., artificial satellite trail). To characterize its structural and luminosity parameters, we applied a model-fitting code originally developed for the analysis of extragalactic stellar tidal streams. The structure is only detected in H-alpha emission, with no detectable counterpart in [SII] or in visible observations, and shows an almost constant brightness and width along its extension. It exhibits a surface brightness of 22.32+/- 0.13 H-alpha mag arcsec^2. Model fitting yields a median width of 1.63", which corresponds to a physical scale of approximately 1200 UA, assuming it is at the same distance (2400 light-years) as the Veil Nebula remnant. We discuss several potential scenarios for the origin of this feature: a Herbig-Haro-like jet, the trail of a high-velocity object, or a non-radiative shock associated with the supernova remnant. We rule out the Herbig-Haro scenario, given the absence of a driving stellar source and the lack of [S II] emission. A high-velocity-object wake cannot yet be excluded, particularly if the driver is a compact remnant, but the absence of an obvious source or bow-shock apex and the extremely small, nearly constant width of the structure make a normal runaway-star origin unlikely. The current evidence instead favours a Balmer-dominated non-radiative shock associated with the Cygnus Loop, generated as the SNR blast wave encounters a dense material layer or magnetic structure viewed nearly edge-on.

astro-ph.GA↗

arXiv2026

TOI-2147 b and TOI-6019 b: Two eccentric warm Jupiters detected and characterized with TESS and MaHPS

The population of Jupiter-sized exoplanets with orbital periods between 10 and 200 days (WJs) exhibits a broad range of orbital eccentricities and system architectures, suggesting a diversity of formation and migration pathways. In this work, we report the detection and characterization of two new eccentric WJs, TOI-2147 b and TOI-6019 b, initially identified as planet candidates by the Transiting Exoplanet Survey Satellite (TESS). We combined TESS photometry with ground-based follow-up observations, including multiband photometry from LCOGT and MuSCAT2, high-angular-resolution speckle imaging, and high-precision radial velocity measurements from the high-resolution Manfred Hirt Planet Finder Spectrograph (MaHPS). Using these data, we were able to confirm the planetary nature of both candidates. TOI-2147 b has a radius of $10.5 \pm 0.3\,\mathrm{R}_\oplus$ and a mass of $116 \pm 22\,\mathrm{M}_\oplus$. It orbits its slightly metal-poor ($\mathrm{[Fe/H]} = -0.29^{+0.07}_{-0.08}$) G-type host star on an eccentric orbit ($e = 0.29 \pm 0.07$) with a period of 26.2 days. TOI-6019 b has a radius of $12.3 \pm 0.3\,\mathrm{R}_\oplus$ and a mass of $149 \pm 15\,\mathrm{M}_\oplus$. It orbits a slightly evolved, solar-metallicity G-type sub-giant with a period of 14.5 days on a significantly eccentric orbit ($e = 0.48^{+0.05}_{-0.04}$). Both planets have bulk densities below that of Jupiter, indicating mildly inflated radii, with interior structure modeling using GASTLI. This suggests that tidal heating from the nonzero eccentricities likely contributes to this inflation and disfavors large atmospheric metal enrichment. No significant signals from additional companions were detected in the radial velocity time series or transit timing variations. Together with the elevated eccentricities, this is consistent with a high-eccentricity migration origin for both systems.

astro-ph.EP↗

arXiv2026

EP260321a/SN 2026gzf: The Faintest Shock Breakout Associated with a Broad-Lined Supernova

The explosion of a star is first marked by the shock wave breaking out of the stellar surface, producing a burst of ultraviolet and X-ray radiation. These events are observationally rare, despite likely accompanying the majority of supernovae. Here, we report on our multi-wavelength observing campaign of the closest Einstein Probe fast X-ray transient EP260321a at $z=0.0344$. The thermal ($kT=130$ eV) X-ray emission with peak luminosity $1.0\times10^{45}$ erg s$^{-1}$ points to a shock breakout origin. We demonstrate that EP260321a is accompanied by a broad-lined Type Ic supernova, SN 2026gzf. The supernova properties, including its spectral evolution, lightcurve evolution, and expansion velocities, are all typical of the energetic stripped-envelope supernovae associated with gamma-ray bursts. However, deep X-ray upper limits obtained with the \textit{Chandra X-ray Observatory} do not detect an X-ray afterglow, and instead exclude the afterglow of known gamma-ray bursts or fast X-ray transients. If the stellar explosion launched a successful relativistic jet, we require that it had both a low Lorentz factor $\Gamma_0$\,$<$\,$30$ and a kinetic energy $E_\textrm{kin}$\,$<$\,$10^{49}$ erg for a stellar wind density of $A_*$\,$\gtrsim$\,$1$. We propose that EP260321a originated from a mildly relativistic, weak outflow that was choked by the progenitor star. This scenario is capable of naturally explaining its low X-ray luminosity and lack of prompt gamma-ray emission. EP260321a bridges the gap between SN 2008D and low-luminosity GRBs, suggesting a greater diversity in the physical parameters of stripped stars as they undergo terminal collapse.

astro-ph.HE↗

arXiv2026

GRB 260310A/SN 2026fgk: Photometric and Spectroscopic Evolution of a Nearby GRB-Supernova and an Exceptionally Bright Afterglow at z=0.153

The association of broad-lined Type Ic supernovae with long-duration gamma-ray bursts (GRBs) has been known for 28 years. However, only about seventy gamma-ray burst supernovae (GRB-SNe) have been identified, of which only half have spectroscopic classifications. At $z=0.153$, GRB 260310A is the 12th spectroscopically confirmed GRB-SN discovered within 1 Gpc, offering a critical opportunity to follow one of these rare supernovae in detail. We present optical to near-infrared imaging and spectroscopy of GRB 260310A and SN 2026fgk out to 65 d after discovery. The optical afterglow is among the brightest ever observed from a GRB. Spectra obtained more than two weeks after the explosion reveal broad absorption features that securely identify SN 2026fgk as a Type Ic-BL supernova. Modeling of the multi-wavelength ($grizJK_s$) lightcurve shows that the supernova is approximately half the luminosity ($k_\textrm{98bw}=0.4-0.6$) of the canonical GRB-SN 1998bw. We derive a nickel mass of $M_\textrm{Ni}=0.4-0.5$ $M_\odot$ with a total ejected mass of $M_\textrm{ej}\approx4-6 $ $M_\odot$ and kinetic energy $E_\textrm{K}=(3-8)\times10^{51}$ erg. The GRB exploded at an extremely large offset of 15 kpc from its host galaxy. Long-slit spectra reveal a ``bridge'' of nebular emission extending along the galaxy's disk to the GRB location, which has a sub-solar metallicity ($\sim$\,$0.4Z_\odot$), compared to a near solar metallicity for the host galaxy. This indicates that the large offset arises from the galaxy's extended light profile rather than an isolated environment.

astro-ph.HE↗

arXiv2025

Galaxy Luminosity Function of the Coma Cluster from Deep $u'-g'-r'$ Wendelstein Imaging Data

We derive the $g'$ band galaxy luminosity function (GLF) of quenched resolved galaxies in the Coma cluster from a deep-imaging survey with $\approx1.5\,\mathrm{deg^2}$ around the cluster center. The dataset comprises deep $u'$-, $g'$-, and $r'$-band data obtained with the Wendelstein Wide Field Imager on the $2.1\,$m Fraunhofer Wendelstein Telescope reaching median $3\sigma$ surface brightness limits in 10" $\times$ 10" boxes of $\mathrm{ (30.0\,u',\,\,29.6\,g',\,\,28.7\,r')\,mag\,arcsec^{-2}}$. We measure structural parameters across a large dynamic range in galaxy brightness ($-24.5\,g'\,\mathrm{mag} \lessapprox M\lessapprox-11.3\,g'\,\mathrm{mag}$), from the brightest cluster galaxy to low-luminosity dwarfs, including compact dwarf galaxies and ultra-diffuse galaxies. We automatically identify more than 6000 cluster member candidates based on their membership on the quiescent sequence in the $u'-g'$ versus $g'-r'$ color-color diagram. The structural parameters of bright galaxies are obtained via isophotal modeling, and fully automated parametric image fitting for faint ones. Injection-recovery tests and two identically analyzed reference fields provide statistical corrections for completeness and contamination, yielding a representative GLF that reliably probes the faint end and may serve as a benchmark for future studies. We report a best-fit single Schechter $g'$ band GLF with $M^\star=-21.71^{+0.26}_{-0.29}\,g'\,\mathrm{mag}$, $\log_{10}(\phi^\star\,[\mathrm{deg}^{-2}\,\mathrm{mag}^{-1}])=1.355^{+0.076}_{-0.079}$, and a comparatively steep faint-end slope $\alpha=-1.444^{+0.015}_{-0.015}$. A directly matched comparison with the Coma counterpart in SLOW, a constrained cosmological simulation using CDM, shows broad agreement between the GLFs down to the simulation limit of $M = -15.5\,g'\,\mathrm{mag}$, despite a deficit of bright galaxies.

astro-ph.GA↗

arXiv2025

The curious case of EP241021a: Unraveling the mystery of its exceptional rebrightening

Fast X-ray Transients (FXTs) are a rare and poorly understood phenomenon with a variety of possible progenitors. The launch of the Einstein Probe (EP) mission has facilitated a rapid increase in the real-time discovery and follow-up of FXTs. We focus on the recent EP discovered transient EP241021a, which shows a peculiar panchromatic behavior. We obtained optical and near-infrared multi-band imaging and spectroscopy with the Fraunhofer Telescope at Wendelstein Observatory, the Hobby-Eberly Telescope, and the Very Large Telescope over the first 100 days of its evolution. EP241021a was discovered by EP as a soft X-ray trigger, but was not detected at gamma-ray frequencies. The observed soft X-ray prompt emission spectrum is consistent with non-thermal radiation, which requires at least a mildly relativistic outflow with bulk Lorentz factor $Γ\gtrsim 4$. The optical and near-infrared lightcurve has a two component behavior where an initially fading component $\sim t^{-1}$ turns to a rise steeper than $\sim t^{4}$ after a few days before peaking at $M_r\approx -21.8$ mag and quickly returning to the initial decay. The peak absolute magnitude is the most luminous optical emission associated to an FXT, superseding EP240414a. Standard supernova models are unable to reproduce either the absolute magnitude or rapid timescale ($<2$ d) of the rebrightening. The X-ray, optical and near-infrared spectral energy distributions display a red color $r-J\approx 0.8$ mag, and point to a non-thermal origin ($ν^{-1}$) for the broadband emission. By considering a gamma-ray burst as a plausible scenario, we favor a refreshed shock as the cause of the rebrightening. This is consistent with the inference of an at least mildly relativistic outflow based on the prompt trigger. Our results suggest a link between EP discovered FXTs and gamma-ray bursts.

astro-ph.HE↗

arXiv2025

Kilonova constraints for the LIGO/Virgo/KAGRA neutron star merger candidate S250206dm: GW-MMADS observations

Gravitational wave (GW) neutron star mergers with an associated electromagnetic counterpart constitute powerful probes of binary evolution, the production sites of heavy elements, general relativity, and the expansion of the universe. Only a handful of candidate GW binary mergers during the fourth LIGO/Virgo/KAGRA observing run (O4) so far are believed to include a neutron star. We present optical-near infrared follow-up observations of the candidate neutron-star black hole GW merger S250206dm. This is the first high-significance mass gap neutron star-black hole candidate observed by multiple GW detectors (thus having a significantly smaller sky localization than one-detector events), offering the first opportunity to effectively follow up a GW event of this kind. Our GW MultiMessenger Astronomy DECam Survey (GW-MMADS) campaign consisted of a wide-field search using the Dark Energy Camera (DECam) and T80-South (T80S), as well as galaxy-targeted observations using the Southern Astrophysical Research (SOAR) imager and the Wendelstein 2.1m 3-channel camera. No viable kilonova counterpart was found in our observations. We use our observation depths to place competitive constraints on kilonova models similar to or brighter than the GW170817 kilonova AT 2017gfo within our observed fields, ruling out 100\% of such models with SOAR galaxy-targeted observations and $\sim43$\% (48\%) with DECam (DECam and T80S).

astro-ph.HE↗

arXiv2025

Confirmation of four hot Jupiters detected by TESS using follow-up spectroscopy from MaHPS at Wendelstein together with NEID and TRES

We report the confirmation and characterization of four hot Jupiter-type exoplanets initially detected by TESS: TOI-1295 b, TOI-2580 b, TOI-6016 b, and TOI-6130 b. Using observations with the high-resolution echelle spectrograph MaHPS on the 2.1m telescope at Wendelstein Observatory, together with NEID at Kitt Peak National Observatory and TRES at the Fred Lawrence Whipple Observatory, we confirmed the planetary nature of these four planet candidates. We also performed precise mass measurements. All four planets are found to be hot Jupiters with orbital periods between 2.4 and 4.0 days. The sizes of these planets range from 1.29 to 1.64 Jupiter radii, while their masses range from 0.6 to 1.5 Jupiter masses. Additionally, we investigated whether there are signs of other planets in the systems but have found none. Lastly, we compared the radii of our four objects to the results of an empirical study of radius inflation and see that all four demonstrate a good fit with the current models. These four planets belong to the first array of planets confirmed with MaHPS data, supporting the ability of the spectrograph to detect planets around fainter stars as faint as V=12.

astro-ph.EP↗

arXiv2025

TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS and SOPHIE

We report the discovery and characterization of two sub-Saturns from the Transiting Exoplanet Survey Satellite (\textit{TESS}) using high-resolution spectroscopic observations from the MaHPS spectrograph at the Wendelstein Observatory and the SOPHIE spectrograph at the Haute-Provence Observatory. Combining photometry from TESS, KeplerCam, LCOGT, and MuSCAT2 with the radial velocity measurements from MaHPS and SOPHIE we measure precise radii and masses for both planets. TOI-5108 b is a sub-Saturn with a radius of $6.6 \pm 0.1$ $R_\oplus$ and a mass of $32 \pm 5$ $M_\oplus$. TOI-5786 b is similar to Saturn with a radius of $8.54 \pm 0.13$ $R_\oplus$ and a mass of $73 \pm 9$ $M_\oplus$. The host star for TOI-5108 b is a moderately bright (Vmag 9.75) G-type star. TOI-5786 is a slightly dimmer (Vmag 10.2) F-type star. Both planets are close to their host stars with periods of 6.75 days and 12.78 days respectively. This puts TOI-5108 b just inside the bounds of the Neptune desert while TOI-5786 b is right above the upper edge. We estimate hydrogen-helium envelope mass fractions of $38 \%$ for TOI-5108 b and $74 \% $ for TOI-5786 b. However, using a model for the interior structure that includes tidal effects the envelope fraction of TOI-5108 b could be much lower ($\sim 20\,\%$) depending on the obliquity. We estimate mass-loss rates between 1.0 * $10^9$ g/s and 9.8 * $10^9$ g/s for TOI-5108 b and between 3.6 * $10^8$ g/s and 3.5 * $10^9$ g/s for TOI-5786 b. Given their masses, this means that both planets are stable against photoevaporation. We also detect a transit signal for a second planet candidate in the TESS data of TOI-5786 with a period of 6.998 days and a radius of $3.83 \pm 0.16$ $R_\oplus$. Using our RV data and photodynamical modeling, we are able to provide a 3-$σ$ upper limit of 26.5 $M_\oplus$ for the mass of the potential inner companion to TOI-5786 b.

astro-ph.EP↗

arXiv2020

Mt. Wendelstein imaging of comet 41P/Tuttle-Giacobini-Kresak during the 2017 perihelion arc

Comet 41P/Tuttle-Giacobini-Kresak (41P), a Jupiter family comet with three discoveries over about 100 years, is in a short-periodic orbit around the Sun with the perihelion close to the Earth distance. The 2017 apparition of 41P offered a long-lasting visibility of the comet at a close distance to Earth. The four month-long imaging campaign with the 2 m telescope at the Mount Wendelstein Observatory was aimed at characterizing dust activity and nucleus properties of the comet. Using a new analysis method of the inner coma flux, we derived a small mean equivalent radius of about 600 m for the nucleus with an unusual body axes ratio that is higher than two. The nucleus rotation axis was determined from the geometric appearance of coma structures, which were enhanced in the images. A long-lasting coma fan was produced by an extended region at high latitudes on the slowly rotating nucleus, whereas isolated jets originated from narrow, low latitude active regions on the nucleus. The dust activity of 41P, despite being difficult to quantify exactly because of an unknown phase function correction for the comet, indicates a steep radial profile that falls off with an increasing distance from the Sun. Colors and flux profiles provide evidence for dust fragmentation in the inner coma of the comet. A singular outburst event created various dust structures in the coma. The outburst came from an extended region on the nucleus and was due to either a landslide on the nucleus or a sudden material release from a subsurface pocket of volatile ice.

astro-ph.EP↗

arXiv2018

The Wendelstein Weak Lensing (WWL) pathfinder: Accurate weak lensing masses for Planck clusters

We present results from the Wendelstein Weak Lensing (WWL) pathfinder project, in which we have observed three intermediate redshift Planck clusters of galaxies with the new 30'$\times 30$' wide field imager at the 2m Fraunhofer Telescope at Wendelstein Observatory. We investigate the presence of biases in our shear catalogues and estimate their impact on our weak lensing mass estimates. The overall calibration uncertainty depends on the cluster redshift and is below 8.1-15 per cent for $z \approx 0.27-0.77$. It will decrease with improvements on the background sample selection and the multiplicative shear bias calibration. We present the first weak lensing mass estimates for PSZ1 G109.88+27.94 and PSZ1 G139.61+24.20, two SZ-selected cluster candidates. Based on Wendelstein colors and SDSS photometry, we find that the redshift of PSZ1 G109.88+27.94 has to be corrected to $z \approx 0.77$. We investigate the influence of line-of-sight structures on the weak lensing mass estimates and find upper limits for two groups in each of the fields of PSZ1 G109.88+27.94 and PSZ1 G186.98+38.66. We compare our results to SZ and dynamical mass estimates from the literature, and in the case of PSZ1 G186.98+38.66 to previous weak lensing mass estimates. We conclude that our pathfinder project demonstrates that weak lensing cluster masses can be accurately measured with the 2m Fraunhofer Telescope.

astro-ph.CO↗

arXiv2017

Preference-based Teaching

We introduce a new model of teaching named "preference-based teaching" and a corresponding complexity parameter---the preference-based teaching dimension (PBTD)---representing the worst-case number of examples needed to teach any concept in a given concept class. Although the PBTD coincides with the well-known recursive teaching dimension (RTD) on finite classes, it is radically different on infinite ones: the RTD becomes infinite already for trivial infinite classes (such as half-intervals) whereas the PBTD evaluates to reasonably small values for a wide collection of infinite classes including classes consisting of so-called closed sets w.r.t. a given closure operator, including various classes related to linear sets over $\mathbb{N}_0$ (whose RTD had been studied quite recently) and including the class of Euclidean half-spaces. On top of presenting these concrete results, we provide the reader with a theoretical framework (of a combinatorial flavor) which helps to derive bounds on the PBTD.

cs.LG↗

arXiv2016

Mt. Wendelstein Imaging of the Post-Perihelion Dust Coma of 67P/Churyumov-Gerasimenko in 2015/2016

Comet 67P/Churyumov-Gerasimenko (67P) was imaged with the 2m telescope at Mt. Wendelstein Observatory in the Alps. Coma and tail monitoring was performed during 51 nights between 22 August 2015 and 9 May 2016. The images through r and i Sloan Digital Sky Survey (SDSS) filters show the dust distribution around the comet, while images in the SDSS g filter indicate also the presence of coma gas in early September 2015. The dust color of 67P implies intrinsic reddening of 9 %/100nm. After maximum shortly after perihelion passage the dust activity decreased with a heliocentric exponent of 4.1 to 4.2 from late September 2015 until May 2016. The opposition surge during early 2016 can be explained by a linear light scattering phase function (beta ~ 0.04) or an asteroid-like HG-type phase function (G ~ 0.15). The radial brightness profile indicates a 'quasi-steady-state' dust coma from late September to the end of 2015. Dust fragmentation during about a month after perihelion may be responsible for radial coma profiles with slopes below unity, while dust accumulation due to very slow dust expansion velocity may result in steeper than unity profiles during 2016. Three fan-shape dust structures are characterized in the coma of 67P. A short dust ejection event on 22 -23 August 2015 has produced a dust arc-let and jet feature in the coma. In September 2015 the appearance of cometary dust tail is dominated by young dust produced around perihelion. The older dust dominates the tail appearance as of mid November 2015.

astro-ph.EP↗

arXiv2009

Extensive optical and near-infrared observations of the nearby, narrow-lined type Ic SN 2007gr: days 5 to 415

We present photometric and spectroscopic observations at optical and near-infrared wavelengths of the nearby type Ic SN 2007gr. These represent the most extensive data-set to date of any supernova of this sub-type, with frequent coverage from shortly after discovery to more than one year post-explosion. We deduce a rise time to B-band maximum of 11.5 \pm 2.7 days. We find a peak B-band magnitude of M_B=-16.8, and light curves which are remarkably similar to the so-called 'hypernova' SN 2002ap. In contrast, the spectra of SNe 2007gr and 2002ap show marked differences, not least in their respective expansion velocities. We attribute these differences primarily to the density profiles of their progenitor stars at the time of explosion i.e. a more compact star for SN 2007gr compared to SN 2002ap. From the quasi-bolometric light curve of SN 2007gr, we estimate that 0.076 $\pm$ 0.010 Msun of 56Ni was produced in the explosion. Our near-infrared (IR) spectra clearly show the onset and disappearance of the first overtone of carbon monoxide (CO) between ~70 to 175 days relative to B-band maximum. The detection of the CO molecule implies that ionised He was not microscopically mixed within the carbon/oxygen layers. From the optical spectra, near-IR light curves, and colour evolution, we find no evidence for dust condensation in the ejecta out to about 400 days. Given the combination of unprecedented temporal coverage, and high signal-to-noise data, we suggest that SN 2007gr could be used as a template object for supernovae of this sub-class.

astro-ph.SR↗

arXiv2003

WeCAPP - The Wendelstein Calar Alto Pixellensing Project I Tracing Dark and Bright Matter in M31

We present WeCAPP, a long term monitoring project searching for microlensing events towards M 31. Since 1997 the bulge of M 31 was monitored in two different wavebands with the Wendelstein 0.8 m telescope. In 1999 we extended our observations to the Calar Alto 1.23 m telescope. Observing simultaneously at these two sites we obtained a time coverage of 53 % during the observability of M 31. To check thousands of frames for variability of unresolved sources, we used the optimal image subtraction method (OIS) by Alard & Lupton (1998) This enabled us to minimize the residuals in the difference image analysis (DIA) and to detect variable sources with amplitudes at the photon noise level. Thus we can detect microlensing events with corresponding amplifications A > 10 of red clump giants with M_I = 0.

astro-ph↗