arXiv subjects

Kamil Hornoch

Publications and source records attributed to Kamil Hornoch.

At least 19 recordsLinked to original sources

arXiv2026

K 1-6 is a photoionised ISM nebula shaped by a fast-moving hot white dwarf in a triple system

K 1-6 has long been classified as a planetary nebula (PN) hosting a binary central star, yet it has remained poorly studied due to its faintness. The central star exhibits pronounced photometric variability whose origin has so far been unclear. We aim to present a comprehensive characterisation of the K 1-6 system, including the physical properties of its stellar components and the nature of the surrounding nebulosity. We conducted a multi-wavelength analysis combining optical and UV spectroscopy obtained with the Gran Telescopio Canarias, the Telescopio Nazionale Galileo, the Nordic Optical Telescope, and the Hubble Space Telescope. We also present long-term multi-band ground- and space-based photometry, including high-cadence data from the Transiting Exoplanet Survey Satellite, narrow-band imaging, and the latest astrometric constraints from Gaia. Our results show that the nebula is not a remnant PN, but instead consists of interstellar medium photoionised by a hot white dwarf, which is relatively evolved. It has a cooling age of 1-2 Myr, implying that any original PN has long since dissipated. We further find that the central object is a hierarchical triple system, comprising an inner binary with an orbital period likely of the order of thousands of days and a distant tertiary companion on a timescale of tens of thousands of years. The optically dominant cool component of the inner binary is an inflated K-type star displaying extreme magnetic activity, including large-amplitude variability and flaring. Its properties resemble those of BY Dra-type binaries and Abell 35-type systems, and are difficult to reconcile with single-star evolution, pointing instead to a history of binary interaction.

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arXiv2026

TESS light curves and surface activity in two low-mass eclipsing binaries: NSVS 01031772 and 2MASS J04100497+2931023

The VRIC light curves were regularly measured for two eclipsing binaries, NSVS 01031772 and 2MASS J04100497+2931023 as part of our long-term observational project to study low-mass eclipsing binaries with a short orbital period and surface activity. The solution of the TESS light curves in PHOEBE results in a detached configuration. Absolute parameters of all components were improved: for N103: M1 = 0.5475 +/- 0.0035 M\sun, R1 = 0.5297 +/- 0.0035 R\sun, M2 = 0.5038 +/- 0.0040 M\sun, R2 = 0.5217 +/- 0.0035 R\sun, for 2M0410: M1 = 0.639 +/- 0.045 M\sun, R1 = 0.655 +/- 0.035 R\sun, M2 = 0.609 +/- 0.045 M\sun, R2 = 0.631 +/- 0.035 R\sun, where the temperatures of the primary components were adopted according to previous studies. The spectral type of the primary components was confirmed to be M4 and K5, and the mass ratio was derived as q = 0.920 +/- 0.003 or 0.952 +/- 0.010, respectively. We propose the presence of a third body in these systems: in the case of N103, a companion with a minimal mass of 50 MJup, orbiting the eclipsing pair with a period of about 19 years, and in 2M0410 a third body with a minimal mass of about 0.1 M\sun and a short orbital period of about 2.1 years. For N103, the hierarchical structure (2+1)+1 of a possible quadruple system was tested, but its stability was not proven. The characteristics and statistics of the flare events and dark regions on the surface of the components were estimated on the basis of the TESS and our own data. For N103, a mean frequency of flares of one per 40 hours was determined. In the case of 2M0410, practically no flares were detected.

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arXiv2026

Size, shape, density, and atmospheric limit of (50000) Quaoar revealed from 14 years of stellar occultation

We present results from 28 stellar occultations by the large Trans-Neptunian Object (50000) Quaoar registered between 2018 and 2025. By performing a joint analysis of this occultation data-set, along with other 9 published events, we were able to fit an oblate ellipsoid shape, with equatorial semi-axes, a and b of 566.1+2.5-2.2 km, and a polar semi-axis, c, of 511.2+3.6-3.7 km. It provides an equivalent volumetric diameter of 1094.4 +/- 4.6 km and polar oblateness of 0.097 +/- 0.011. Considering an absolute magnitude of H = 2.79 +/- 0.35, we derive a geometric albedo of pV = 0.125 +/- 0.038. We have derived new upper limits to the surface pressure of a CH4 atmosphere of 0.15 nbar (1-sigma) and 0.65 nbar (3-sigma). We also provide a table with the 36 new astrometric positions for Quaoar. Using the new system mass derived from Weywot's orbit around Quaoar, we calculated a density of 1.760 +/- 0.109 g/cm3. Moreover, from the derived size and rotation period (8.8394 +/- 0.0002 hours (Ortiz et al. 2003)), we calculate that, if Quaoar is in Maclaurin hydrostatic equilibrium state, it would have a density of 1.859 +/- 0.200 g/cm3. This result, within the error bars, is compatible with the value we found. Therefore, this work shows that Quaoar can be a Maclaurin object, being eligible as a dwarf planet.

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arXiv2026

The Recurrent Nova Population in M31

The positions of more than 1300 nova eruptions in M31 catalogued through the end of calendar year 2025 have been compared in order to identify recurrent nova candidates. The work extends the study of Shafter et al. (2015) who identified a total of 12 recurrent novae with high confidence (plus four possible recurrent novae) from an analysis of 964 M31 novae observed prior to 2014. During the past 12 years an additional seven recurrent novae have been discovered in M31. In addition, we have confirmed that one of the possible recurrent novae is in fact recurrent (M31N 1990-10a), while another was shown to be a foreground dwarf nova (M31N 1966-08a). At present, there are a total of 79 nova eruptions associated with 20 known recurrent novae in M31, with four additional eruptions from two candidates remaining unconfirmed. A comparison of the spatial distribution of the recurrent novae with that for all novae shows no significant difference between the two. In addition, we find no significant difference between the light curve properties (peak luminosities and rates of decline) between the M31 and Galactic recurrent nova populations. However, the recurrence time distributions appear different, with half of the M31 recurrent novae having recurrence times shorter than U Sco, the Galactic recurrent nova with the shortest known recurrence time, $T_\mathrm{rec}=10.3$ yr. As expected, recurrent novae are found to be both fainter and faster than novae generally, being mostly found in the lower left quadrant of the MMRD plane.

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arXiv2026

Astrometric follow-up of near-Earth asteroid 2024 YR4 during a Torino scale level 3 alert

The discovery of 2024 YR4 presented the planetary defense community with the most significant impact threat in almost two decades, reaching level 3 on the Torino scale. The community, now mature and well-organized, responded with a global observational effort. Astrometric measurements, forming the basis for orbital refinement and impact prediction, were a central component of this response. In this paper, we present the astrometric data collected by the international community, from the time of discovery until the object became too faint for all existing observational assets, including JWST. We also discuss the coordination role played by the International Asteroid Warning Network, and the importance of publicly available image archives to enable precovery searches.

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arXiv2026

Fundamental Properties of Novae in M31

The peak luminosities and rates of decline for a large sample of novae recently published by Clark et al. have been analyzed using the Yaron et al. nova models to estimate fundamental properties of the M31 nova population. The apparent white dwarf (WD) mass distribution is approximately Gaussian with a mean $\langle M_\mathrm{WD} \rangle = 1.16\pm0.14~M_{\odot}$. When corrected for recurrence-time bias, the mean drops to $\langle M_\mathrm{WD} \rangle = 1.07~M_\odot$. The average WD mass of the M31 nova sample is found to be remarkably similar to that found by Shara et al. in their study of 82 Galactic novae, but $\sim0.15~M_\odot$ more massive than the mean recently determined by Schaefer in his comprehensive study of more than 300 systems. As expected, the average WD mass for the recurrent novae included in the M31 sample, $\langle M_\mathrm{WD} \rangle = 1.33\pm0.08~M_{\odot}$, is significantly higher than that for novae generally. Other parameters of interest, such as the accretion rate, velocity of the ejecta, and the predicted recurrence time, are characterized by skewed distributions with large spreads about means of $\langle \log \dot M ~(M_\odot~\mathrm{yr}^{-1}) \rangle \simeq -9.27$, $\langle V_\mathrm{max} \rangle \simeq 1690~\mathrm{km~s}^{-1}$, and $\langle \log P_\mathrm{rec}~\mathrm{(yr)} \rangle \simeq 4.39$, respectively. The role of hibernation in affecting the $\dot M$ and $P_\mathrm{rec}$ distributions is briefly discussed. Finally, the nova properties were studied as a function of apparent position (isophotal radius) in M31, with the preponderance of evidence failing to establish any clear dependence on stellar population.

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arXiv2025

Rapid-response characterization of near-Earth asteroid 2024 YR4 during a Torino Scale 3 alert

On 27 December 2024, near-Earth object (NEO) 2024 YR$_4$ was discovered by the ATLAS survey and identified as a virtual impactor. A few weeks later, it eventually reached level 3 on the Torino Scale and was the first and only asteroid to be ever classified at that level. Here we report an intensive observational campaign combining time-series photometry in the visible, broadband visible and near-infrared colors, and low-resolution visible reflectance spectroscopy to assess its physical properties. Fourier analysis of the lightcurves yields a synodic rotation period of $P = 19.46341 \pm 0.00008$ min, placing 2024 YR$_4$ among the fast rotators, even if such rotation is common for objects of similar $H$ magnitude. Its visible and near-infrared colors and spectra are most consistent with an Sq or K taxonomic classification, though some ambiguity remains. Finally, its phase curve exhibits a notably shallow slope ($G = 0.51 \pm 0.11$), from which we derive an absolute magnitude of $H_\mathrm{R} = 23.82\pm0.09$ mag. After color correction and taking into account other models for the phase function, we report an absolute magnitude of $H_\mathrm{V} = 24.14\pm0.25$ mag. These characterizations, rotation period, taxonomy, and surface properties, would have been crucial for risk assessment and mitigation planning had the initially high impact probability scenario been confirmed, underscoring the importance for planetary defense of a rapid, coordinated international response.

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arXiv2025

Shape and spin state model of contact binary (388188) 2006 DP14 using combined radar and optical observations

Contact binaries are found throughout the solar system. The recent discovery of Selam, the satellite of MBA (152830) Dinkinesh, by the NASA LUCY mission has made it clear that the term `contact binary' covers a variety of different types of bi-modal mass distributions and formation mechanisms. Only by modelling more contact binaries can this population be properly understood. We determined a spin state and shape model for the Apollo group contact binary asteroid (388188) 2006 DP14 using ground-based optical and radar observations collected between 2014 and 2023. Radar delay-Doppler images and continuous wave spectra were collected over two days in February 2014, while 16 lightcurves in the Cousins R and SDSS-r filters were collected in 2014, 2022 and 2023. We modelled the spin state using convex inversion before using the SHAPE modelling software to include the radar observations in modelling concavities and the distinctive neck structure connecting the two lobes. We find a spin state with a period of $(5.7860\pm0.0001)$ hours and pole solution of $λ= (180\pm121)^\circ$ and $β= (-80\pm7)^\circ$ with morphology indicating a 520 m long bi-lobed shape. The model's asymmetrical bi-modal mass distribution resembles other small NEA contact binaries such as (85990) 1999 JV6 or (8567) 1996 HW1, which also feature a smaller `head' attached to a larger `body'. The final model features a crater on the larger lobe, similar to several other modelled contact binaries. The model's resolution is 25 m, comparable to that of the radar images used.

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arXiv2024

Discovery of Two New Eruptions of the Ultrashort Recurrence Time Nova M31N 2017-01e

We report the recent discovery of two new eruptions of the recurrent nova M31N 2017-01e in the Andromeda galaxy. The latest eruption, M31N 2024-08c, reached $R=17.8$ on 2024 August 06.85 UT, $\sim2$ months earlier than predicted. In addition to this recent eruption, a search of archival PTF data has revealed a previously unreported eruption on 2014 June 18.46 UT that reached a peak brightness of $R\sim17.9$ approximately a day later. The addition of these two eruption timings has allowed us to update the mean recurrence time of the nova. We find $\langle T_\mathrm{rec} \rangle = 924.0\pm7.0$ days ($2.53\pm0.02$ yr), which is slightly shorter than our previous determination. Thus, M31N 2017-01e remains the nova with the second shortest recurrence time known, with only M31N 2008-12a being shorter. We also present a low-resolution spectrum of the likely quiescent counterpart of the nova, a $\sim20.5$ mag evolved B star displaying an $\sim14.3$ d photometric modulation.

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arXiv2024

Exploring the MMRD Relation for Novae in M31

The results of a two decade long $R$-band photometric survey of novae in M31 are presented. From these data, $R$-band light curves have been determined for 180 novae with data sufficient for estimating peak brightness and subsequent rate of decline. The data show a weak correlation of peak brightness with fade rate consistent with the well-known Maximum Magnitude versus Rate of Decline (MMRD) relation. As generally appreciated for Galactic novae, the large scatter in the MMRD relation precludes its use in determining distances to individual novae. The novae at maximum light are distributed with standard deviation $σ=0.89$ mag about a mean $R$-band absolute magnitude given by $\langle M_R \rangle=-7.57\pm0.07$. The overall M31 luminosity distribution is in excellent agreement with that found for Galactic novae suggesting that the nova populations in M31 and the Galaxy are quite similar. The notion that all novae can be characterized by a standard luminosity 15 d after maximum light ($M_{15}$) is also explored. Surprisingly, the distribution of $M_{15}$ values is characterized by a standard deviation only slightly smaller than that for novae at maximum light and thus offers little promise for precise extragalactic distance determinations. A dozen faint and fast novae that are likely to be previously unidentified recurrent novae have been identified from their position in the MMRD plot and in the $M_{15}$ distribution.

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arXiv2024

M31N 2013-10c: A Newly Identified Recurrent Nova in M31

The nova M31N 2023-11f (2023yoa) has been recently identified as the second eruption of a previously recognized nova, M31N 2013-10c, establishing the latter object as the 21st recurrent nova system thus far identified in M31. Here we present well sampled $R$-band lightcurves of both the 2013 and 2023 eruptions of this system. The photometric evolution of each eruption was quite similar as expected for the same progenitor system. The 2013 and 2023 eruptions each reached peak magnitudes just brighter than $R\sim16$, with fits to the declining branches of the eruptions yielding times to decline by two magnitudes of $t_2(R)=5.5\pm1.7$ and $t_2(R)=3.4\pm1.5$ days, respectively. M31N 2013-10c has an absolute magnitude at peak, $M_R=-8.8\pm0.2$, making it the most luminous known recurrent nova in M31.

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arXiv2023

Photometry of the Didymos system across the DART impact apparition

On 26 September 2022, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes (Thomas et al. 2023). Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite's orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from July 2022 to February 2023. We focus here on decomposable lightcurves, i.e. those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the post-impact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ~1 day after impact, and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days post-impact. This bulk photometric behavior was not well represented by an HG photometric model. An HG1G2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least March 2023. Its persistence implied ongoing escape of ejecta from the system many months after DART impact.

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arXiv2023

Concerning the Verity of the MMRD Relation for Novae

It has long been claimed that novae reaching the highest luminosity at the peak of their eruptions appear to fade the fastest from maximum light. The relationship between peak brightness and fade rate is known as the Maximum-Magnitude, Rate-of-Decline (MMRD) relation. Lightcurve parameters for the most recent sample of M31 recurrent novae are presented and used to buttress the case that the observed MMRD relation can be explained as a consequence of observational selection effects coupled with expectations from standard nova models.

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arXiv2023

Do the Outburst Properties of M31N 2008-12a Depend on the Time Since the Previous Eruption?

Photometric observations spanning the UV to the near IR during the nine most recent eruptions (2014-2022) of the extragalactic nova M31N 2008-12a are presented and analyzed in order to explore whether the lightcurve properties for a given eruption, specifically the peak magnitudes and fade rates, are correlated with the time interval since the previous eruption. No significant correlation between the pre-eruption interval and the rate of decline was found, however it appears that the brightness at the peak of an outburst may be positively correlated with the time interval since the previous eruption.

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arXiv2023

Implications for the Formation of 2005 UD from a New Convex Shape Model

(155140) 2005 UD has a similar orbit to (3200) Phaethon, an active asteroid in a highly eccentric orbit thought to be the source of the Geminid meteor shower. Evidence points to a genetic relationship between these two objects, but we have yet to fully understand how 2005 UD and Phaethon could have separated into this associated pair. Presented herein are new observations of 2005 UD from five observatories that were carried out during the 2018, 2019, and 2021 apparitions. We implemented light curve inversion using our new data, as well as dense and sparse archival data from epochs in 2005--2021 to better constrain the rotational period and derive a convex shape model of 2005 UD. We discuss two equally well-fitting pole solutions ($λ= 116.6^{\circ}$, $β= -53.6^{\circ}$) and ($λ= 300.3^{\circ}$, $β= -55.4^{\circ}$), the former largely in agreement with previous thermophysical analyses and the latter interesting due to its proximity to Phaethon's pole orientation. We also present a refined sidereal period of $P_{\text{sid}} = 5.234246 \pm 0.000097$ hr. A search for surface color heterogeneity showed no significant rotational variation. An activity search using the deepest stacked image available of 2005 UD near aphelion did not reveal a coma or tail but allowed modeling of an upper limit of 0.04 to 0.37~kg s$^{-1}$ for dust production. We then leveraged our spin solutions to help limit the range of formation scenarios and the link to Phaethon in the context of nongravitational forces and timescales associated with the physical evolution of the system.

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arXiv2023

Orbital Period Change of Dimorphos Due to the DART Kinetic Impact

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 minutes was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement ($β$) was possible. In the years prior to impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be -33.0 +/- 1.0 (3$σ$) minutes. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a significant amount of momentum to the asteroid beyond what the DART spacecraft carried.

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arXiv2022

M31N 2017-01e: Discovery of a Previous Eruption in this Enigmatic Recurrent Nova

We report the discovery of a previously unknown eruption of the recurrent nova M31N 2017-01e that took place on 11 January 2012. The earlier eruption was detected by Pan-STARRS and occurred 1847 days (5.06 yr) prior to the eruption on 31 January 2017 (M31N 2017-01e). The nova has now been seen to have had a total of four recorded eruptions (M31N 2012-01c, 2017-01e, 2019-09d, and 2022-03d) with a mean time between outbursts of just $929.5\pm6.8$ days ($2.545\pm0.019$ yr), the second shortest recurrence time known for any nova. We also show that there is a blue variable source ($\langle V \rangle = 20.56\pm0.17$, $B-V\simeq0.045$), apparently coincident with the position of the nova, that exhibits a 14.3 d periodicity. Possible models of the system are proposed, but none are entirely satisfactory.

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arXiv2022

M31N 1926-07c: A Recurrent Nova in M31 with a 2.8 Year Recurrence Time

The M31 recurrent nova M31N 1926-07c has had five recorded eruptions. Well-sampled light curves of the two most recent outbursts, in January of 2020 (M31N 2020-01b) and September 2022 (M31N 2022-09a), are presented showing that the photometric evolution of the two events were quite similar, with peak magnitudes of $R=17.2\pm0.1$ and $R=17.1\pm0.1$, and $t_2$ times of $9.7\pm0.9$ and $8.1\pm0.5$ days for the 2020 and 2022 eruptions, respectively. After considering the dates of the four most recent eruptions (where the cycle count is believed to be known), a mean recurrence interval of $\langle P_\mathrm{rec}\rangle=2.78\pm0.03$ years is found, establishing that M31N 1926-07c has one of the shortest recurrence times known.

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